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Sample records for ultrathin hfo2 dielectric

  1. Microstructure and thermal stability of HfO2 gate dielectric deposited on Ge (100)

    NASA Astrophysics Data System (ADS)

    Gusev, E. P.; Shang, H.; Copel, M.; Gribelyuk, M.; D'Emic, C.; Kozlowski, P.; Zabel, T.

    2004-09-01

    We report on physical and electrical characterization of ultrathin (3-10nm) high-κHfO2 gate stacks deposited on Ge (100) by atomic-layer deposition. It is observed that uniform films of HfO2 can be deposited on Ge without significant interfacial growth. The lack of an interlayer enables quasiepitaxial growth of HfO2 on the Ge surface after wet chemical treatment whereas a nitrided interface (grown by thermal oxynitridation in ammonia) results in an amorphous HfO2. The stacks exhibit surprisingly good thermal stability, up to temperatures only 150°C below the melting point of Ge. In terms of electrical properties, HfO2 on Ge shows significantly reduced (up to 4 decades) gate leakage currents in the ultrathin regime of equivalent electrical thickness down to ˜1.4nm due to the high-dielectric constant of ˜23. Nitrided interface is observed to be important for good insulating properties of the stack.

  2. Reliability assessment of ultra-thin HfO2 films deposited on silicon wafer

    NASA Astrophysics Data System (ADS)

    Fu, Wei-En; Chang, Chia-Wei; Chang, Yong-Qing; Yao, Chih-Kai; Liao, Jiunn-Der

    2012-09-01

    Ultra-thin hafnium dioxide (HfO2) is used to replace silicon dioxide to meet the required transistor feature size in advanced semiconductor industry. The process integration compatibility and long-term reliability for the transistors depend on the mechanical performance of ultra-thin HfO2 films. The criteria of reliability including wear resistance, thermal fatigue, and stress-driven failure rely on film adhesion significantly. The adhesion and variations in mechanical properties induced by thermal annealing of the ultra-thin HfO2 films deposited on silicon wafers (HfO2/SiO2/Si) are not fully understood. In this work, the mechanical properties of an atomic layer deposited HfO2 (nominal thickness ≈10 nm) on a silicon wafer were characterized by the diamond-coated tip of an atomic force microscope and compared with those of annealed samples. The results indicate that the annealing process leads to the formation of crystallized HfO2 phases for the atomic layer deposited HfO2. The HfSixOy complex formed at the interface between HfO2 and SiO2/Si, where the thermal diffusion of Hf, Si, and O atoms occurred. The annealing process increases the surface hardness of crystallized HfO2 film and therefore the resistance to nano-scratches. In addition, the annealing process significantly decreases the harmonic contact stiffness (or thereafter eliminate the stress at the interface) and increases the nano-hardness, as measured by vertically sensitive nano-indentation. Quality assessments on as-deposited and annealed HfO2 films can be thereafter used to estimate the mechanical properties and adhesion of ultra-thin HfO2 films on SiO2/Si substrates.

  3. High performance organic field-effect transistors with ultra-thin HfO2 gate insulator deposited directly onto the organic semiconductor

    NASA Astrophysics Data System (ADS)

    Ono, S.; Häusermann, R.; Chiba, D.; Shimamura, K.; Ono, T.; Batlogg, B.

    2014-01-01

    We have produced stable organic field-effect transistors (OFETs) with an ultra-thin HfO2 gate insulator deposited directly on top of rubrene single crystals by atomic layer deposition (ALD). We find that ALD is a gentle deposition process to grow thin films without damaging rubrene single crystals, as results these devices have a negligibly small threshold voltage and are very stable against gate-bias-stress, and the mobility exceeds 1 cm2/V s. Moreover, the devices show very little degradation even when kept in air for more than 2 months. These results demonstrate thin HfO2 layers deposited by ALD to be well suited as high capacitance gate dielectrics in OFETs operating at small gate voltage. In addition, the dielectric layer acts as an effective passivation layer to protect the organic semiconductor.

  4. HfO2 dielectric thickness dependence of electrical properties in graphene field effect transistors with double conductance minima

    NASA Astrophysics Data System (ADS)

    Zhang, Cheng; Xie, Dan; Xu, Jian-Long; Li, Xin-Ming; Sun, Yi-Lin; Dai, Rui-Xuan; Li, Xian; Zhu, Hong-Wei

    2015-10-01

    We investigate the electrical properties in back-gated graphene field effect transistors (GFETs) with SiO2 dielectric and different thickness of high-k HfO2 dielectric. The results show that transform characteristic (Ids-Vgs) curves of GFETs are uniquely W-shaped with two charge neutrality point (left and right) in both SiO2 and HfO2 dielectric (SiO2-GFETs and HfO2-GFETs). The gate voltage reduces drastically in HfO2-GFETs compared with that in SiO2-GFETs, and it becomes much smaller with the decline of HfO2 thickness. The left charge neutrality point in Id-Vg curves of all HfO2-GFETs is negative, compared to the positive ones in SiO2-GFETs, which means that there exists n-doping in graphene with HfO2 as bottom dielectric. We speculate that this n-doping comes from the HfO2 layer, which brings fixed charged impurities in close proximity to graphene. The carrier mobility is also researched, demonstrating a decreasing trend of hole mobility in HfO2-GFETs contrast to that in SiO2-GFETs. In a series of HfO2-GFETs with different HfO2 dielectric thickness, the hole mobility shows a tendency of rise when the thickness decreases to 7 nm. The possible reason might be due to the introduced impurities into HfO2 film from atomic layer deposition process, the concentration of which varies from the thickness of HfO2 layer.

  5. Atomic layer deposition HfO2 capping layer effect on porous low dielectric constant materials

    NASA Astrophysics Data System (ADS)

    Cheng, Yi-Lung; Kao, Kai-Chieh; Huang, Chi-Jia; Chen, Giin-Shan; Fang, Jau-Shiung

    2015-11-01

    Low dielectric constant (low-k) materials are used as inter-level insulators between copper (Cu) conductors to improve the characteristics of integrated circuits. This work proposes a new method for improving the characteristics of porous low-k dielectric film by capping it with an HfO2 film by atomic layer deposition (ALD). Experimental results revealed that capping a porous low-k dielectric film with a ∼1.0 nm-thick HfO2 film increases its dielectric constant from 2.56 to 2.65 because the pores in the surface of the film are sealed by Hf precursors. The leakage current density and reliability of the porous low-k dielectrics are greatly improved. The HfO2 capping film also increased resistances against Cu diffusion and damage by oxygen plasma. Therefore, this ALD-deposited HfO2 capping film can be used as a pore-sealing layer and a Cu barrier layer for the porous low-k dielectric film in the future advanced technologies.

  6. Interface and electrical properties of ultra-thin HfO2 film grown by radio frequency sputtering

    NASA Astrophysics Data System (ADS)

    Nath, Madhuchhanda; Roy, Asim

    2016-02-01

    Interfacial composition and electrical properties of ultra-thin hafnium oxide (HfO2) films on p-type <100> Si substrate are reported. Hafnium oxide (HfO2) thin films are prepared using radio-frequency sputtering method and subsequently annealed at different temperature. The effect of post-deposition annealing on the interfacial and chemical state of HfO2/Si gate stack has been characterised by means of X-ray reflectivity and X-ray photoelectron spectroscopy studies. Peaks of X-ray photoelectron spectroscopy spectra at 530.50 and 532.25 eV originate from Hf-O-Si bond illustrated the creation of Hf-silicate based interfacial layer at the high-k/Si interface. X-ray reflectivity fitting result also corroborated the formation of Hf silicate interfacial layer. Capacitance-voltage measurements revealed insignificant hysteresis in case of film annealed at 600 °C. Interface trap density has been extracted using Terman method and is found to be 3.18×10-11 cm-2 eV-1 at -1.0 V. Minimum equivalent oxide thickness (EOT) of 1.3 nm was obtained for the film annealed at 600° C. The gate leakage current density of the HfO2 film annealed at 600 °C is 1.5×10-5 A/cm2 at a bias voltage of -2 V.

  7. Study of strained-Si p-channel MOSFETs with HfO2 gate dielectric

    NASA Astrophysics Data System (ADS)

    Pradhan, Diana; Das, Sanghamitra; Dash, Tara Prasanna

    2016-10-01

    In this work, the transconductance of strained-Si p-MOSFETs with high-K dielectric (HfO2) as gate oxide, has been presented through simulation using the TCAD tool Silvaco-ATLAS. The results have been compared with a SiO2/strained-Si p-MOSFET device. Peak transconductance enhancement factors of 2.97 and 2.73 has been obtained for strained-Si p-MOSFETs in comparison to bulk Si channel p-MOSFETs with SiO2 and high-K dielectric respectively. This behavior is in good agreement with the reported experimental results. The transconductance of the strained-Si device at low temperatures has also been simulated. As expected, the mobility and hence the transconductance increases at lower temperatures due to reduced phonon scattering. However, the enhancements with high-K gate dielectric is less as compared to that with SiO2.

  8. The impact of ultrathin Al2O3 films on the electrical response of p-Ge/Al2O3/HfO2/Au MOS structures

    NASA Astrophysics Data System (ADS)

    Botzakaki, M. A.; Skoulatakis, G.; Kennou, S.; Ladas, S.; Tsamis, C.; Georga, S. N.; Krontiras, C. A.

    2016-09-01

    It is well known that the most critical issue in Ge CMOS technology is the successful growth of high-k gate dielectrics on Ge substrates. The high interface quality of Ge/high-k dielectric is connected with advanced electrical responses of Ge based MOS devices. Following this trend, atomic layer deposition deposited ultrathin Al2O3 and HfO2 films were grown on p-Ge. Al2O3 acts as a passivation layer between p-Ge and high-k HfO2 films. An extensive set of p-Ge/Al2O3/HfO2 structures were fabricated with Al2O3 thickness ranging from 0.5 nm to 1.5 nm and HfO2 thickness varying from 2.0 nm to 3.0 nm. All structures were characterized by x-ray photoelectron spectroscopy (XPS) and AFM. XPS analysis revealed the stoichiometric growth of both films in the absence of Ge sub-oxides between p-Ge and Al2O3 films. AFM analysis revealed the growth of smooth and cohesive films, which exhibited minimal roughness (~0.2 nm) comparable to that of clean bare p-Ge surfaces. The electrical response of all structures was analyzed by C-V, G-V, C-f, G-f and J-V characteristics, from 80 K to 300 K. It is found that the incorporation of ultrathin Al2O3 passivation layers between p-Ge and HfO2 films leads to superior electrical responses of the structures. All structures exhibit well defined C-V curves with parasitic effects, gradually diminishing and becoming absent below 170 K. D it values were calculated at each temperature, using both Hill-Coleman and Conductance methods. Structures of p-Ge/0.5 nm Al2O3/2.0 nm HfO2/Au, with an equivalent oxide thickness (EOT) equal to 1.3 nm, exhibit D it values as low as ~7.4  ×  1010 eV-1 cm-2. To our knowledge, these values are among the lowest reported. J-V measurements reveal leakage currents in the order of 10-1 A cm-2, which are comparable to previously published results for structures with the same EOT. A complete mapping of the energy distribution of D its into the energy bandgap of p-Ge, from the valence band

  9. The impact of ultrathin Al2O3 films on the electrical response of p-Ge/Al2O3/HfO2/Au MOS structures

    NASA Astrophysics Data System (ADS)

    Botzakaki, M. A.; Skoulatakis, G.; Kennou, S.; Ladas, S.; Tsamis, C.; Georga, S. N.; Krontiras, C. A.

    2016-09-01

    It is well known that the most critical issue in Ge CMOS technology is the successful growth of high-k gate dielectrics on Ge substrates. The high interface quality of Ge/high-k dielectric is connected with advanced electrical responses of Ge based MOS devices. Following this trend, atomic layer deposition deposited ultrathin Al2O3 and HfO2 films were grown on p-Ge. Al2O3 acts as a passivation layer between p-Ge and high-k HfO2 films. An extensive set of p-Ge/Al2O3/HfO2 structures were fabricated with Al2O3 thickness ranging from 0.5 nm to 1.5 nm and HfO2 thickness varying from 2.0 nm to 3.0 nm. All structures were characterized by x-ray photoelectron spectroscopy (XPS) and AFM. XPS analysis revealed the stoichiometric growth of both films in the absence of Ge sub-oxides between p-Ge and Al2O3 films. AFM analysis revealed the growth of smooth and cohesive films, which exhibited minimal roughness (~0.2 nm) comparable to that of clean bare p-Ge surfaces. The electrical response of all structures was analyzed by C–V, G–V, C–f, G–f and J–V characteristics, from 80 K to 300 K. It is found that the incorporation of ultrathin Al2O3 passivation layers between p-Ge and HfO2 films leads to superior electrical responses of the structures. All structures exhibit well defined C–V curves with parasitic effects, gradually diminishing and becoming absent below 170 K. D it values were calculated at each temperature, using both Hill–Coleman and Conductance methods. Structures of p-Ge/0.5 nm Al2O3/2.0 nm HfO2/Au, with an equivalent oxide thickness (EOT) equal to 1.3 nm, exhibit D it values as low as ~7.4  ×  1010 eV‑1 cm‑2. To our knowledge, these values are among the lowest reported. J–V measurements reveal leakage currents in the order of 10–1 A cm‑2, which are comparable to previously published results for structures with the same EOT. A complete mapping of the energy distribution of D its into the energy bandgap of p-Ge, from

  10. Internal dielectric interface: SiO2- HfO2

    NASA Astrophysics Data System (ADS)

    Sharia, Onise; Demkov, Alex; Bersuker, Genadi; Lee, Byoung Hun

    2006-03-01

    Hafnia is the leading candidate to replace silica as the gate dielectric in CMOS technology. Typically, hafnia films are deposited by atomic layer deposition (ALD) on the oxidized surface of a silicon wafer. The oxide could be native or thermally grown. Therefore, the high-k dielectric film is not in direct contact with Si, but rather with silicon dioxide. We investigate theoretically the atomic structure of the SiO2-HfO2 interface, its energretics, and thermodynamic stability with respect to oxygen exchange across the interface. We have examined the electronic properties of the interface including the band discontinuity using density functional theory. To model the interface we build a supercell structure by connecting β-crystobalite (crystalline silica polymorph) and cubic hafnia. This model, while being obviously rather simplistic allows for systematic study of the dielectric thickness effects, and consistent placement of defects with respect to the interface. The striking atomic feature of the calculated interface structure is three-fold coordinated interfacial oxygen atoms connected to one Si and two Hf neighbors. The Si-O and Hf-O bond lengths are 1.62 and 2.1 å, respectively. The energy of the interface is estimated to be in the range of 900-4000 erg/cm^2 depending on the oxygen chemical potential. The structure has no states in the gap, and the estimated valence band offset agrees well with the MIGS theory. We discuss the effect of vacancies on the band alignment, and possible implications of our results to Si-SiO2-HfO2-Metal stacks.

  11. The effect of ultraviolet irradiation on the ultra-thin HfO2 based CO gas sensor

    NASA Astrophysics Data System (ADS)

    Karaduman, Irmak; Barin, Ã.-zlem; Yıldız, Dilber Esra; Acar, Selim

    2015-11-01

    In this work, an effort has been made to fabricate ultrathin HfO2/Al2O3 sample by atomic layer deposition method for the fast detection of CO gas at room temperature. The effect of the operating temperature and the UV light on the gas sensing characteristics has been studied. We investigated the optimum operating temperature for the sample by sensing 25 ppm CO and CO2 gases from room temperature to 150 °C for 10 °C steps. The maximum response was obtained at 150 °C for both gases in the measurement temperature range. Also, the photoresponse measurements clearly show the effect of UV light on the sample. At room temperature, sensor showed superior response (14%) for 5 ppm CO gas. The response time of sensor is 6 s to 5 ppm CO gas concentration. The ultrathin HfO2 based sample shows acceptable gas sensitivity for 5 ppm CO gas at room temperature under UV light irradiation.

  12. The thickness measurement of ultrathin films from new high-k material HfO2 by grazing incidence x-ray reflectivity

    NASA Astrophysics Data System (ADS)

    Jia, Yabin; Gao, Huifang; Li, Xu; Yao, Yaxuan; Wang, Meiling; Tao, Xingfu; Tian, Rongrong; Ren, Lingling; Qin, Lin

    2016-06-01

    The thickness of HfO2 ultrathin films was determined by grazing incidence x-ray reflectivity (GIXRR) with simulation. Two samples were prepared by atomic layer deposition, and the Si substrate of one sample was treated by HF acid (1:20) to erase the native oxide layer, while the other was not. According to the GIXRR, the films consisted of two contamination layers, an interface layer, a HfO2 layer and a native oxide layer (except for the acid-treated sample) from top to bottom. As a result, the HfO2 thickness of the two samples was 1.23 nm and 1.25 nm respectively, and the thicknesses of the interface layers between the HfO2 and the Si substrate were 0.1 nm and 0.95 nm respectively. The chemical states of the film were investigated by ultrasonification and x-ray photoemission spectroscopy (XPS), and the thickness was verified by transmission electron microscopy (TEM). All these phenomena proved that GIXRR is a powerful and effective piece of technology for characterizing HfO2 ultrathin film.

  13. Effects of adding HfO2 on the microstructure and dielectric properties of giant dielectric constant ceramic CaCu3Ti4O12

    NASA Astrophysics Data System (ADS)

    Yuan, W. X.; Hark, S. K.

    2010-03-01

    CaCu3Ti4O12 (CCTO), an unusual perovskite-like ceramic, is known for its extraordinarily high (˜10^4) and relatively frequency independent dielectric constant. It has drawn a lot of attention recently because of its potential applications in microelectronics and microwave devices. In this investigation, HfO2 powder was added to a pre-reacted CCTO powder, which was synthesized by a conventional solid-state reaction, at different concentrations from 1 to 70 wt% and the mixture was sintered into disc-shaped ceramic samples. The effects of adding HfO2 on the microstructure and dielectric properties of CCTO ceramics were investigated. In general, we found that the dielectric constant tends to increase with HfO2 addition up to 8 wt% and then decrease with further addition. Moreover, the dielectric loss was also influenced by the addition of HfO2, and a low loss tangent of ˜0.035 was obtained. The ac conductivity, impedance, complex dielectric permittivity and electric modulus graphs were used to analyze the data. These observations were explained on the basis of the internal-barrier-layer capacitor model with Maxwell-Wagner relaxations.

  14. Solid-state dewetting of ultra-thin Au films on SiO2 and HfO2

    NASA Astrophysics Data System (ADS)

    Seguini, G.; Llamoja Curi, J.; Spiga, S.; Tallarida, G.; Wiemer, C.; Perego, M.

    2014-12-01

    Ultra-thin Au films with thickness (h) ranging from 0.5 to 6.0 nm were deposited at room temperature (RT) by means of e-beam evaporation on SiO2 and HfO2. Due to the natural solid-state dewetting (SSD) of the as-deposited films, Au nanoparticles (NPs) were formed on the substrates. By properly adjusting the h value, the size and the density of the Au NPs can be finely tuned. For h = 0.5 nm, spherical-like Au NPs with diameter below 5 nm and density in the order of 1012 Au NPs cm-2 were obtained without any additional thermal treatment independently from the substrate. The dependence of the Au NPs characteristics on the substrate starts to be effective for h ≥ 1.0 nm where the Au NPs diameter is in the 5-10 nm range and the density is around 1011 Au NPs cm-2. The effect of a subsequent high temperature (400-800 °C) annealing in N2 atmosphere on the Au NPs was investigated as well. For h ≤ 1.0 nm, the Au NPs characteristics evidenced an excellent thermal stability. Whereas the thermal treatment affects the cristallinity of the Au NPs. For the thicker films (2.0 ≤ h ≤ 6.0 nm), the thermal treatment becomes effective to induce the SSD. The proposed methodology can be exploited for the synthesis of Au NPs with diameter below 10 nm on different substrates at RT.

  15. Probing the thermal decomposition behaviors of ultrathin HfO2 films by an in situ high temperature scanning tunneling microscope.

    PubMed

    Xue, Kun; Wang, Lei; An, Jin; Xu, Jianbin

    2011-05-13

    The thermal decomposition of ultrathin HfO(2) films (∼0.6-1.2 nm) on Si by ultrahigh vacuum annealing (25-800 °C) is investigated in situ in real time by scanning tunneling microscopy. Two distinct thickness-dependent decomposition behaviors are observed. When the HfO(2) thickness is ∼ 0.6 nm, no discernible morphological changes are found below ∼ 700 °C. Then an abrupt reaction occurs at 750 °C with crystalline hafnium silicide nanostructures formed instantaneously. However, when the thickness is about 1.2 nm, the decomposition proceeds gradually with the creation and growth of two-dimensional voids at 800 °C. The observed thickness-dependent behavior is closely related to the SiO desorption, which is believed to be the rate-limiting step of the decomposition process.

  16. Ultrathin ZnS and ZnO Interfacial Passivation Layers for Atomic-Layer-Deposited HfO2 Films on InP Substrates.

    PubMed

    Kim, Seung Hyun; Joo, So Yeong; Jin, Hyun Soo; Kim, Woo-Byoung; Park, Tae Joo

    2016-08-17

    Ultrathin ZnS and ZnO films grown by atomic layer deposition (ALD) were employed as interfacial passivation layers (IPLs) for HfO2 films on InP substrates. The interfacial layer growth during the ALD of the HfO2 film was effectively suppressed by the IPLs, resulting in the decrease of electrical thickness, hysteresis, and interface state density. Compared with the ZnO IPL, the ZnS IPL was more effective in reducing the interface state density near the valence band edge. The leakage current density through the film was considerably lowered by the IPLs because the film crystallization was suppressed. Especially for the film with the ZnS IPL, the leakage current density in the low-voltage region was significantly lower than that observed for the film with the ZnO IPL, because the direct tunneling current was suppressed by the higher conduction band offset of ZnS with the InP substrate. PMID:27467383

  17. Effects of annealing on electrical performance of multilayer MoS2 transistors with atomic layer deposited HfO2 gate dielectric

    NASA Astrophysics Data System (ADS)

    Wen, Ming; Xu, Jingping; Liu, Lu; Lai, Pui-To; Tang, Wing-Man

    2016-09-01

    Atomic layer deposited HfO2 annealed in different ambients (N2, O2, and NH3) is used to replace SiO2 as a gate dielectric for fabricating back-gated multilayer MoS2 transistors. Excellent electrical properties such as a mobility of 15.1 cm2/(V·s), an on/off ratio exceeding 107, and a hysteresis of 0.133 V are achieved for samples annealed in NH3 at 400 °C for 10 min. This is caused by the NH3 annealing passivation effects that reduce defective states in the HfO2 dielectric and the interface. The capacitance equivalent thickness is only 7.85 nm, which is quite small for a back-gated MoS2 transistor and is conducive to the scaling down of the device.

  18. A tunneling current density model for ultra thin HfO2 high-k dielectric material based MOS devices

    NASA Astrophysics Data System (ADS)

    Maity, Niladri Pratap; Maity, Reshmi; Thapa, R. K.; Baishya, Srimanta

    2016-07-01

    In this paper, an analytical model for evaluation of tunneling current density of ultra thin MOS devices is presented. The impacts of the promising high-k dielectric material, HfO2 on the current density model have been carried out. In this work, improvement in the results is brought in by taking into account the barrier height lowering due to the image force effect. The considered voltage range is from 0 to ψ1/e i.e., 0 < V < ψ1/e, where ψ1 is the barrier height at the interface of metal and the oxide. Initially we are neglecting the image force effect for a MOS device consisting asymmetric barrier. Later, image force effect of ultra thin oxide layer has been introduced for practical potential barrier by superimposing the potential barrier on the trapezoidal barrier. Theoretical predictions are compared with the results obtained by the 2-D numerical device simulator ATLAS and published experimental results. Excellent agreements among the three are observed.

  19. Competitive effects of oxygen vacancy formation and interfacial oxidation on an ultra-thin HfO2-based resistive switching memory: beyond filament and charge hopping models.

    PubMed

    Nakamura, Hisao; Asai, Yoshihiro

    2016-04-01

    We studied the quantum transport mechanism of an ultra-thin HfO2-based resistive random access memory (ReRAM) cell with TiN electrodes and proposed the design of a sub-10 nm scale device. It is believed that formation and rupture of the conduction path in the local filament causes the switching between high and low resistive states. However, the validity of this simple filament model is not obvious in the sub-10 nm scale device because the redox processes occur mainly in a few nm range at the interface. Furthermore, the intrinsic transport mechanism of the device, in particular, quantum coherence, depends on device materials and length-scale. The relationship between the redox states and the transport mechanism like ballistic or hopping is still under debate when the device length scale is less than 10 nm. In the present study, we performed first-principles calculations of the non-equilibrium Green's function including electron-phonon interactions. We examined several characteristic structures of the HfO(x) wire (nano-scale conduction path) and the interfaces between the resistive switching layer and electrodes. We found that the metal buffer layer induced a change in the oxygen-reduction site from the interface of HfO(x)/TiN to the buffer layer. Even when the inserted buffer layer is a few atomic layers, this effect plays an important role in the enhancement of the performance of ON/OFF resistive switching and in the reduction of the inelastic electric current by electron-phonon scattering. The latter suppresses the hopping mechanism, which makes the ballistic conduction the dominant mechanism. We evaluated the activation energy in the high temperature limit by using the first-principles results of inelastic current. Our theoretical model explains the observed crossover of the temperature dependence of ReRAM cells and gives a new insight into the principle of operation on a sub-10 nm scale ReRAM device. PMID:26975565

  20. Energy-band alignment of atomic layer deposited (HfO2)x(Al2O3)1 - x gate dielectrics on 4H-SiC

    NASA Astrophysics Data System (ADS)

    Jia, Ren-Xu; Dong, Lin-Peng; Niu, Ying-Xi; Li, Cheng-Zhan; Song, Qing-Wen; Tang, Xiao-Yan; Yang, Fei; Zhang, Yu-Ming

    2015-03-01

    We study a series of (HfO2)x(Al2O3)1 - x /4H-SiC MOS capacitors. It is shown that the conduction band offset of HfO2 is 0.5 eV and the conduction band offset of HfAlO is 1.11-1.72 eV. The conduction band offsets of (HfO2)x(Al2O3)1 - x are increased with the increase of the Al composition, and the (HfO2)x(Al2O3)1 - x offer acceptable barrier heights (> 1 eV) for both electrons and holes. With a higher conduction band offset, (HfO2)x(Al2O3)1 - x/4H-SiC MOS capacitors result in a ˜ 3 orders of magnitude lower gate leakage current at an effective electric field of 15 MV/cm and roughly the same effective breakdown field of ˜ 25 MV/cm compared to HfO2. Considering the tradeoff among the band gap, the band offset, and the dielectric constant, we conclude that the optimum Al2O3 concentration is about 30% for an alternative gate dielectric in 4H-SiC power MOS-based transistors. Project supported by the National Natural Science Foundation of China (Grant Nos. 51272202 and 61234006) and the Science Project of State Grid, China (Grant No. SGRI-WD-71-14-004).

  1. Effect of pre-deposition annealing on the performance of MIS capacitor formed using atomic layer deposition of ultrathin HfO2

    NASA Astrophysics Data System (ADS)

    Maurya, Savita; Singh, B. R.; Radhakrishna, M.

    2013-06-01

    In this work, we report the effect of pre-deposition annealing on electrical characteristics of metal-insulator-semiconductor (MIS) capacitors, with HfO2 as high-k insulator. HfO2 has been deposited via atomic layer deposition (ALD) using Tetrakis [Ethyl Methyl Amino] Hafnium, Hf[N(CH3)(C2H5(]4 (TEMAHf) as metal oxide precursor and water (H2O) as oxidizing precursor. The results obtained have shown that the pre-and post deposition annealing have profound effect on electrical characteristic of MIS Capacitors. This led us to hypothesize that the preparation of Silicon substrate with pre-deposition temperature treatment forms an interfacial layer between hafnium dioxide & substrate and that will have influence on the ALD deposition and consequentially on the electrical characteristic of the device formed through ALD. By controlling the post deposition conditions, the electrical characteristic behavior is ascribed to the predeposition treatment. The promising hypothesis of such a behavior, supported with some preliminary experimental data has been presented in this short communication.

  2. A comparison between HfO2/Al2O3 nano-laminates and ternary HfxAlyO compound as the dielectric material in InGaAs based metal-oxide-semiconductor (MOS) capacitors

    NASA Astrophysics Data System (ADS)

    Krylov, Igor; Pokroy, Boaz; Eizenberg, Moshe; Ritter, Dan

    2016-09-01

    We compare the electrical properties of HfO2/Al2O3 nano-laminates with those of the ternary HfxAlyO compound in metal oxide semiconductor (MOS) capacitors. The dielectrics were deposited by atomic layer deposition on InGaAs. Water, ozone, and oxygen plasma were tested as oxygen precursors, and best results were obtained using water. The total dielectric thickness was kept constant in our experiments. It was found that the effective dielectric constant increased and the leakage current decreased with the number of periods. Best results were obtained for the ternary compound. The effect of the sublayer thicknesses on the electrical properties of the interface was carefully investigated, as well as the role of post-metallization annealing. Possible explanations for the observed trends are provided. We conclude that the ternary HfxAlyO compound is more favorable than the nano-laminates approach for InGaAs based MOS transistor applications.

  3. In0.53Ga0.47As FinFETs with self-aligned molybdenum contacts and HfO2/Al2O3 gate dielectric

    NASA Astrophysics Data System (ADS)

    Zhang, Xingui; Guo, Hua Xin; Zhu, Zhu; Gong, Xiao; Yeo, Yee-Chia

    2013-06-01

    InGaAs channel FinFETs with self-aligned molybdenum (Mo) contacts was demonstrated using a gate-last process. By realizing Mo contacts on in situ doped n++ InGaAs source and drain and self-aligned to channel, the FinFETs achieved series resistance of ˜250 Ω μm, which is the lowest value reported-to-date for InGaAs non-planar n-MOSFETs. A FinFET with channel length of 500 nm and equivalent oxide thickness (EOT) of 3 nm has an on-state/off-state current ratio of ˜105 and peak extrinsic transconductance of 255 μS/μm at drain voltage of 0.5 V. To further reduce EOT, atomic-layer-deposited HfO2/Al2O3 high-k dielectric was integrated in InGaAs FinFETs. Good interface quality and small EOT of ˜1 nm were achieved. Forming gas annealing (FGA) was used for drive current enhancement. A 300 °C 30 min FGA leads to ˜48% increase in drive current as well as significant reduction of subthreshold swing, probably due to an improvement of the HfO2/Al2O3/InGaAs interface quality.

  4. Fabrication of HfO2 patterns by laser interference nanolithography and selective dry etching for III-V CMOS application

    PubMed Central

    2011-01-01

    Nanostructuring of ultrathin HfO2 films deposited on GaAs (001) substrates by high-resolution Lloyd's mirror laser interference nanolithography is described. Pattern transfer to the HfO2 film was carried out by reactive ion beam etching using CF4 and O2 plasmas. A combination of atomic force microscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis was used to characterise the various etching steps of the process and the resulting HfO2/GaAs pattern morphology, structure, and chemical composition. We show that the patterning process can be applied to fabricate uniform arrays of HfO2 mesa stripes with tapered sidewalls and linewidths of 100 nm. The exposed GaAs trenches were found to be residue-free and atomically smooth with a root-mean-square line roughness of 0.18 nm after plasma etching. PACS: Dielectric oxides 77.84.Bw, Nanoscale pattern formation 81.16.Rf, Plasma etching 52.77.Bn, Fabrication of III-V semiconductors 81.05.Ea PMID:21711946

  5. Thermal stability of HfO2 nanotube arrays

    SciTech Connect

    Qiu, Xiaofeng; Howe, Jane Y; Meyer III, Harry M; Tuncer, Enis; Paranthaman, Mariappan Parans

    2010-01-01

    Thermal stability of highly ordered hafnium oxide (HfO2) nanotube arrays prepared through an electrochemical anodization method in the presence of ammonium fluoride is investigated in a temperature range of room temperature to 900 C in flowing argon atmosphere. The formation of the HfO2 nanotube arrays was monitored by current density transient characteristics during anodization of hafnium metal foil. Morphologies of the as-grown and post-annealed HfO2 nanotube arrays were analyzed by powder Xray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Although monoclinic HfO2 is thermally stable up to 2000K in bulk, the morphology of HfO2 nanotube arrays degraded at 900 C. A detailed X-ray photoelectron spectroscopy (XPS) study revealed that the thermal treatment significantly impacted the composition and the chemical environment of the core elements (Hf and O), as well as F content coming from the electrolyte. Possible reasons for the degradation of the nanotube at high temperature were discussed based on XPS study and possible future improvements have also been suggested. Moreover, dielectric measurements were carried out on both the as-grown amorphous film and 500 C post-annealed crystalline film. This study will help us to understand the temperature impact on the morphology of nanotube arrays, which is important to its further applications at elevated temperatures.

  6. Crossbar Nanoscale HfO2-Based Electronic Synapses

    NASA Astrophysics Data System (ADS)

    Matveyev, Yury; Kirtaev, Roman; Fetisova, Alena; Zakharchenko, Sergey; Negrov, Dmitry; Zenkevich, Andrey

    2016-03-01

    Crossbar resistive switching devices down to 40 × 40 nm2 in size comprising 3-nm-thick HfO2 layers are forming-free and exhibit up to 105 switching cycles. Four-nanometer-thick devices display the ability of gradual switching in both directions, thus emulating long-term potentiation/depression properties akin to biological synapses. Both forming-free and gradual switching properties are modeled in terms of oxygen vacancy generation in an ultrathin HfO2 layer. By applying the voltage pulses to the opposite electrodes of nanodevices with the shape emulating spikes in biological neurons, spike-timing-dependent plasticity functionality is demonstrated. Thus, the fabricated memristors in crossbar geometry are promising candidates for hardware implementation of hybrid CMOS-neuron/memristor-synapse neural networks.

  7. Effect of native defects and Co doping on ferromagnetism in HfO2: first-principles calculations.

    PubMed

    Han, Chong; Yan, Shi-Shen; Lin, Xue-Ling; Hu, Shu-Jun; Zhao, Ming-Wen; Yao, Xin-Xin; Chen, Yan-Xue; Liu, Guo-Lei; Mei, Liang-Mo

    2011-05-01

    First-principles calculations of undoped HfO(2) and cobalt-doped HfO(2) have been carried out to study the magnetic properties of the dielectric material. In contrast to previous reports, it was found that the native defects in HfO(2) could not induce strong ferromagnetism. However, the cobalt substituting hafnium is the most stable defect under oxidation condition, and the ferromagnetic (FM) coupling between the cobalt substitutions is favorable in various configurations. We found that the FM coupling is mediated by the threefold-coordinated oxygen atoms in monoclinic HfO(2) and could be further enhanced in electron-rich condition.

  8. High reflectance dielectric distributed Bragg reflectors for near ultra-violet planar microcavities: SiO2/HfO2 versus SiO2/SiNx

    NASA Astrophysics Data System (ADS)

    Réveret, F.; Bignet, L.; Zhigang, W.; Lafosse, X.; Patriarche, G.; Disseix, P.; Médard, F.; Mihailovic, M.; Leymarie, J.; Zúñiga-Pérez, J.; Bouchoule, S.

    2016-09-01

    SiO2/SiNx and SiO2/HfO2 distributed Bragg reflectors for the ultra-violet (λ = 360 nm-380 nm) are compared through their structural and optical properties. The SiO2/HfO2 system exhibits a lower interface roughness, higher reflectance, larger stop band, and lower penetration depth than SiO2/SiNx. A cavity quality factor of 3700 at about 360 nm is measured on a passive SiO2/HfO2-based planar microcavity. Compared with values obtained in the literature for the near UV range, the latter is rather large. Micro-reflectance measurements have been performed on a series of passive microcavities with increasing cavity thickness to determine the residual absorption in the SiO2 and HfO2 layers. Absorption coefficients of 30 (k = 0.86 × 10-4) and 160 cm-1 (k = 4.59 × 10-4) near λ ˜ 360 nm have been extracted for SiO2 and HfO2, respectively. Transfer-matrix simulations taking into account the residual absorption show that microcavity quality factors up to 8000 can be expected at 360-380 nm with this material system. Such values are well-suited for the fabrication of UV-vertical cavity surface emitting lasers or microcavity polariton lasers operating at room temperature.

  9. Interface and bulk properties of HfO2 films

    NASA Astrophysics Data System (ADS)

    Biswas, Nivedita; Harris, Harlan; Choi, Kisik; Temkin, Henryk; Gangopadhyay, Shubhra

    2003-03-01

    HfO2 films of varying thickness were deposited on silicon and titanium by reactive electron beam evaporation. Metal gates of Titanium were deposited to form MIS and MIM structures. Capacitance-voltage and conductance-voltage measurements were performed to analyze the HfO2/Si interface and HfO2 bulk. For samples having thickness between 30 and 300 Å the C-V curves of the as-deposited samples were marked by charge leakage, huge hysteresis and frequency dispersion. However, annealing the sample in H2 ambient reduced charge leakage, hysteresis and the frequency dispersion of the C-V curves. A dielectric constant of the annealed films was calculated to be 17. The interface state density as calculated using the method of Nicollian and Brews was 2-3E10 cm-2eV-1 close to the midgap. To study the bulk properties, HfO2 films of thickness 2100 Å with platinum electrodes were deposited on silicon and titanium nitride. The C-V and G-V curves of both as-deposited and annealed samples were measured. Interface state density was found to be comparable to that of the thin samples. Thus the passivation of bulk and interface states with hydrogen annealing is independent of thickness. The gap state densities were found compatible with the observed hysteresis of the as-deposited ( 1E16-1E17 eV-1cm-3) and annealed sample (1E14-1E15eV-1cm-3).

  10. Physisorbed-precursor-assisted atomic layer deposition of reliable ultrathin dielectric films on inert graphene surfaces for low-power electronics

    NASA Astrophysics Data System (ADS)

    Jeong, Seong-Jun; Kim, Hyo Won; Heo, Jinseong; Lee, Min-Hyun; Song, Hyun Jae; Ku, JiYeon; Lee, Yunseong; Cho, Yeonchoo; Jeon, Woojin; Suh, Hwansoo; Hwang, Sungwoo; Park, Seongjun

    2016-09-01

    Among the most fundamental challenges encountered in the successful incorporation of graphene in silicon-based electronics is the conformal growth of ultrathin dielectric films, especially those with thicknesses lower than 5 nm, on chemically inert graphene surfaces. Here, we present physisorbed-precursor-assisted atomic layer deposition (pALD) as an extremely robust method for fabricating such films. Using atomic-scale characterisation, it is confirmed that conformal and intact ultrathin Al2O3 films can be synthesised on graphene by pALD. The mechanism underlying the pALD process is identified through first-principles calculations based on density functional theory. Further, this novel deposition technique is used to fabricate two types of wafer-scale devices. It is found that the incorporation of a 5 nm-thick pALD Al2O3 gate dielectric film improves the performance of metal-oxide-graphene field-effect transistors to a greater extent than does the incorporation of a conventional ALD Al2O3 film. We also employ a 5 nm-thick pALD HfO2 film as a highly scalable dielectric layer with a capacitance equivalent oxide thickness of 1 nm in graphene-based tunnelling field-effect transistors fabricated on a glass wafer and achieve a subthreshold swing of 30 mV/dec. This significant improvement in switching allows for the low-voltage operation of an inverter within 0.5 V of both the drain and the gate voltages, thus paving the way for low-power electronics.

  11. Interface Engineering for the Enhancement of Carrier Transport in Black Phosphorus Transistor with Ultra-Thin High-k Gate Dielectric.

    PubMed

    Ling, Zhi-Peng; Zhu, Jun-Tao; Liu, Xinke; Ang, Kah-Wee

    2016-01-01

    Black phosphorus (BP) is the most stable allotrope of phosphorus which exhibits strong in-plane anisotropic charge transport. Discovering its interface properties between BP and high-k gate dielectric is fundamentally important for enhancing the carrier mobility and electrostatics control. Here, we investigate the impact of interface engineering on the transport properties of BP transistors with an ultra-thin hafnium-dioxide (HfO2) gate dielectric of ~3.4 nm. A high hole mobility of ~536 cm(2)V(-1)s(-1) coupled with a near ideal subthreshold swing (SS) of ~66 mV/dec were simultaneously achieved at room temperature by improving the BP/HfO2 interface quality through thermal treatment. This is attributed to the passivation of phosphorus dangling bonds by hafnium (Hf) adatoms which produces a more chemically stable interface, as evidenced by the significant reduction in interface states density. Additionally, we found that an excessively high thermal treatment temperature (beyond 200 °C) could detrimentally modify the BP crystal structure, which results in channel resistance and mobility degradation due to charge-impurities scattering and lattice displacement. This study contributes to an insight for the development of high performance BP-based transistors through interface engineering. PMID:27222074

  12. Interface Engineering for the Enhancement of Carrier Transport in Black Phosphorus Transistor with Ultra-Thin High-k Gate Dielectric

    PubMed Central

    Ling, Zhi-Peng; Zhu, Jun-Tao; Liu, Xinke; Ang, Kah-Wee

    2016-01-01

    Black phosphorus (BP) is the most stable allotrope of phosphorus which exhibits strong in-plane anisotropic charge transport. Discovering its interface properties between BP and high-k gate dielectric is fundamentally important for enhancing the carrier mobility and electrostatics control. Here, we investigate the impact of interface engineering on the transport properties of BP transistors with an ultra-thin hafnium-dioxide (HfO2) gate dielectric of ~3.4 nm. A high hole mobility of ~536 cm2V−1s−1 coupled with a near ideal subthreshold swing (SS) of ~66 mV/dec were simultaneously achieved at room temperature by improving the BP/HfO2 interface quality through thermal treatment. This is attributed to the passivation of phosphorus dangling bonds by hafnium (Hf) adatoms which produces a more chemically stable interface, as evidenced by the significant reduction in interface states density. Additionally, we found that an excessively high thermal treatment temperature (beyond 200 °C) could detrimentally modify the BP crystal structure, which results in channel resistance and mobility degradation due to charge-impurities scattering and lattice displacement. This study contributes to an insight for the development of high performance BP-based transistors through interface engineering. PMID:27222074

  13. Interface Engineering for the Enhancement of Carrier Transport in Black Phosphorus Transistor with Ultra-Thin High-k Gate Dielectric

    NASA Astrophysics Data System (ADS)

    Ling, Zhi-Peng; Zhu, Jun-Tao; Liu, Xinke; Ang, Kah-Wee

    2016-05-01

    Black phosphorus (BP) is the most stable allotrope of phosphorus which exhibits strong in-plane anisotropic charge transport. Discovering its interface properties between BP and high-k gate dielectric is fundamentally important for enhancing the carrier mobility and electrostatics control. Here, we investigate the impact of interface engineering on the transport properties of BP transistors with an ultra-thin hafnium-dioxide (HfO2) gate dielectric of ~3.4 nm. A high hole mobility of ~536 cm2V‑1s‑1 coupled with a near ideal subthreshold swing (SS) of ~66 mV/dec were simultaneously achieved at room temperature by improving the BP/HfO2 interface quality through thermal treatment. This is attributed to the passivation of phosphorus dangling bonds by hafnium (Hf) adatoms which produces a more chemically stable interface, as evidenced by the significant reduction in interface states density. Additionally, we found that an excessively high thermal treatment temperature (beyond 200 °C) could detrimentally modify the BP crystal structure, which results in channel resistance and mobility degradation due to charge-impurities scattering and lattice displacement. This study contributes to an insight for the development of high performance BP-based transistors through interface engineering.

  14. Surface-tension-tailored aqueous ink for low-temperature deposition of high-k HfO2 thin film

    NASA Astrophysics Data System (ADS)

    Han, Sun Woong; Lee, Keun Ho; Yoo, Young Bum; Park, Jee Ho; Song, Kie Moon; Baik, Hong Koo

    2016-08-01

    In this paper, solution-based deposition of HfO2 thin film at low temperature was demonstrated. By using aqueous HfCl4 solution, the precursor was effectively decomposed with low annealing temperature of 150 °C. Thus it is preferable to use this solution for dielectric coating on flexible substrates. To achieve conformal coating on substrate, formic acid as a cosolvent was added to aqueous ink solution to reduce surface tension of the solution. Due to improved coating quality of HfO2 thin film, the fabricated HfO2 gate dielectric shows reliable breakdown characteristics and low leakage current.

  15. Tailoring the Electrical Properties of HfO2 MOS-Devices by Aluminum Doping.

    PubMed

    Paskaleva, Albena; Rommel, Mathias; Hutzler, Andreas; Spassov, Dencho; Bauer, Anton J

    2015-08-12

    In this work dielectric and electrical properties of Al-doped HfO2 layers deposited by plasma-enhanced atomic layer deposition in dependence on the thickness and the added Al amount in the films have been investigated. Special attention is dedicated to C-V and I-V hysteresis analysis as a measure for trapping phenomena in the films. A detailed study of conduction mechanisms in dependence on the composition of the layers has also been performed. The densities and spatial and energy positions of traps have been examined. It is found that only a small amount of Al-doping decreases the trapping which is assigned to a reduction of oxygen vacancy-related traps in HfO2. On the contrary, higher amounts of Al introduced in HfO2 films increase the trapping ability of the stacks which is due to the introduction of deeper Al2O3-related traps. The results imply that by adding a proper amount of Al into HfO2 it is possible to tailor dielectric and electrical properties of high-k layers toward meeting the criteria for particular applications. PMID:26196163

  16. Correlation of nanochemistry and electrical properties in HfO2 films grown by metalorganic molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Moon, Tae-Hyoung; Ham, Moon-Ho; Myoung, Jae-Min

    2005-03-01

    We present the annealing effects on nanochemistry and electrical properties in HfO2 dielectrics grown by metalorganic molecular-beam epitaxy. After the postannealing treatment of HfO2 films in the temperature range of 600-800°C, the thicknesses and chemical states of the films were examined by high-resolution transmission electron microscopy and angle-resolved x-ray photoelectron spectroscopy. By comparing the line shapes of core-level spectra for the samples with different annealing temperatures, the concentrations of SiO and Hf-silicate with high dielectric constant are found to be highest for HfO2 film annealed at 700°C. This result supports that the accumulation capacitance of the sample annealed at 700°C is not deteriorated in spite of a steep increase in interfacial layer thickness compared with that of the sample annealed at 600°C.

  17. Epitaxial Thin Films of Y doped HfO2

    NASA Astrophysics Data System (ADS)

    Serrao, Claudy; Khan, Asif; Ramamoorthy, Ramesh; Salahuddin, Sayeef

    Hafnium oxide (HfO2) is one of a few metal oxides that is thermodynamically stable on silicon and silicon oxide. There has been renewed interest in HfO2 due to the recent discovery of ferroelectricity and antiferroelectricity in doped HfO2. Typical ferroelectrics - such as strontium bismuth tantalate (SBT) and lead zirconium titanate (PZT) - contain elements that easily react with silicon and silicon oxide at elevated temperatures; therefore, such ferroelectrics are not suited for device applications. Meanwhile, ferroelectric HfO2 offers promise regarding integration with silicon. The stable phase of HfO2 at room temperature is monoclinic, but HfO2 can be stabilized in the tetragonal, orthorhombic or even cubic phase by suitable doping. We stabilized Y-doped HfO2 thin films using pulsed laser deposition. The strain state can be controlled using various perovskite substrates and controlled growth conditions. We report on Y-doped HfO2 domain structures from piezo-response force microscopy (PFM) and structural parameters via X-ray reciprocal space maps (RSM). We hope this work spurs further interest in strain-tuned ferroelectricity in doped HfO2.

  18. Mechanistic Insight into the Stability of HfO2 -Coated MoS2 Nanosheet Anodes for Sodium Ion Batteries.

    PubMed

    Ahmed, Bilal; Anjum, Dalaver H; Hedhili, Mohamed N; Alshareef, Husam N

    2015-09-01

    It is demonstrated for the first time that surface passivation of 2D nanosheets of MoS2 by an ultrathin and uniform layer of HfO2 can significantly improve the cyclic performance of sodium ion batteries. After 50 charge/discharge cycles, bare MoS2 and HfO2 coated MoS2 electrodes deliver the specific capacity of 435 and 636 mAh g(-1) , respectively, at current density of 100 mA g(-1) . These results imply that batteries using HfO2 coated MoS2 anodes retain 91% of the initial capacity; in contrast, bare MoS2 anodes retain only 63%. Also, HfO2 coated MoS2 anodes show one of the highest reported capacity values for MoS2 . Cyclic voltammetry and X-ray photoelectron spectroscopy results suggest that HfO2 does not take part in electrochemical reaction. The mechanism of capacity retention with HfO2 coating is explained by ex situ transmission electron microscope imaging and electrical impedance spectroscopy. It is illustrated that HfO2 acts as a passivation layer at the anode/electrolyte interface and prevents structural degradation during charge/discharge process. Moreover, the amorphous nature of HfO2 allows facile diffusion of Na ions. These results clearly show the potential of HfO2 coated MoS2 anodes, which performance is significantly higher than previous reports where bulk MoS2 or composites of MoS2 with carbonaceous materials are used.

  19. Structural evolution and the control of defects in atomic layer deposited HfO2-Al2O3 stacked films on GaAs.

    PubMed

    Kang, Yu-Seon; Kim, Dae-Kyoung; Jeong, Kwang-Sik; Cho, Mann-Ho; Kim, Chung Yi; Chung, Kwun-Bum; Kim, Hyoungsub; Kim, Dong-Chan

    2013-03-01

    The structural characteristics and interfacial reactions of bilayered dielectric stacks of 3 nm HfO2/2 nm Al2O3 and 3 nm Al2O3/2 nm HfO2 on GaAs, prepared by atomic layer deposition (ALD), were examined during film growth and the postannealing process. During the postdeposition annealing (PDA) of the Al2O3/HfO2/GaAs structures at 700 °C, large amounts of Ga oxides were generated between the Al2O3 and HfO2 films as the result of interfacial reactions between interdiffused oxygen impurities and out-diffused atomic Ga. However, in the case of the HfO2/Al2O3/GaAs structures, the presence of an Al2O3 buffer layer effectively blocked the out-diffusion of atomic Ga, thus suppressing the formation of Ga oxide. Microstructural analyses showed that HfO2 films that were deposited on Al2O3/GaAs had completely crystallized during the PDA process, even at 700 °C, because of the Al2O3 diffusion barrier. Capacitance-voltage measurements showed a relatively large frequency dispersion of the Al2O3/HfO2/GaAs structure in accumulation capacitance compared to the HfO2/Al2O3/GaAs structure due to a higher interface state density. Conductance results revealed that the Al2O3 buffer layer on GaAs resulted in a significant reduction in gap states in GaAs. The induced gap state in the Al2O3/HfO2/GaAs structure originated from the out-diffusion of atomic Ga into the HfO2 film. Density functional theory calculations supported this conclusion.

  20. X-ray reflectivity studies of ultra-thin gate dielectrics

    NASA Astrophysics Data System (ADS)

    Park, Changyong; Ji, Sung-Dae; Lee, Ki-Bong; Youn, Sang-Bae; Park, J.-C.; Choi, H. M.; Wang, Jun

    2000-03-01

    X-ray reflectivity curves were measured using synchrotron radiation to characterize nanometer-thick dielectric thin films such as silicon-oxynitrides and Ta2O5. Penetrating x-rays enabled us to probe oxide layers buried under poly-silicon electrodes. Changes in x-ray reflectivity curves of the dielectrics due to nitridation and annealing processes were clearly observed. Depth-profiles of densities in the ultra-thin dielectics were estimated from analysis on these curves, and the results will be presented.

  1. Partially hollowed ultra-thin dielectric meta-surface for transmission manipulation.

    PubMed

    Liu, Guiqiang; Fu, Guolan; Liu, Zhengqi; Huang, Zhenping; Chen, Jian

    2016-09-01

    Impressive optical properties are numerically demonstrated in the partially hollowed dielectric meta-surface (p-HDMS), which consists of an air cavity array intercalated in an ultra-thin (~λ/6) high-index dielectric film. Multispectral transmission band-stop response with near-perfect spectral modulation depth is achieved. The spectral slop is up to 80%/nm, indicating the sharp and narrowband transmission behavior. Classical Malus law is confirmed by this sub-wavelength platform. Moreover, the multispectral light propagation manipulation can be perfectly reproduced by using the actual dielectric with absorption loss. In this all-dielectric meta-surface, conduction loss is avoided compared to its metallic plasmonic counterpart. Such configurations can therefore serve as excellent alternatives for plasmonic meta-surfaces and constitute an important step in nanophotonics. PMID:27607661

  2. Atomic layer deposition of HfO2 on graphene through controlled ion beam treatment

    NASA Astrophysics Data System (ADS)

    Kim, Ki Seok; Oh, Il-Kwon; Jung, Hanearl; Kim, Hyungjun; Yeom, Geun Young; Kim, Kyong Nam

    2016-05-01

    The polymer residue generated during the graphene transfer process to the substrate tends to cause problems (e.g., a decrease in electron mobility, unwanted doping, and non-uniform deposition of the dielectric material). In this study, by using a controllable low-energy Ar+ ion beam, we cleaned the polymer residue without damaging the graphene network. HfO2 grown by atomic layer deposition on graphene cleaned using an Ar+ ion beam showed a dense uniform structure, whereas that grown on the transferred graphene (before Ar+ ion cleaning) showed a non-uniform structure. A graphene-HfO2-metal capacitor fabricated by growing 20-nm thick HfO2 on graphene exhibited a very low leakage current (<10-11 A/cm2) for Ar+ ion-cleaned graphene, whereas a similar capacitor grown using the transferred graphene showed high leakage current.

  3. Thickness scaling of atomic-layer-deposited HfO2 films and their application to wafer-scale graphene tunnelling transistors

    PubMed Central

    Jeong, Seong-Jun; Gu, Yeahyun; Heo, Jinseong; Yang, Jaehyun; Lee, Chang-Seok; Lee, Min-Hyun; Lee, Yunseong; Kim, Hyoungsub; Park, Seongjun; Hwang, Sungwoo

    2016-01-01

    The downscaling of the capacitance equivalent oxide thickness (CET) of a gate dielectric film with a high dielectric constant, such as atomic layer deposited (ALD) HfO2, is a fundamental challenge in achieving high-performance graphene-based transistors with a low gate leakage current. Here, we assess the application of various surface modification methods on monolayer graphene sheets grown by chemical vapour deposition to obtain a uniform and pinhole-free ALD HfO2 film with a substantially small CET at a wafer scale. The effects of various surface modifications, such as N-methyl-2-pyrrolidone treatment and introduction of sputtered ZnO and e-beam-evaporated Hf seed layers on monolayer graphene, and the subsequent HfO2 film formation under identical ALD process parameters were systematically evaluated. The nucleation layer provided by the Hf seed layer (which transforms to the HfO2 layer during ALD) resulted in the uniform and conformal deposition of the HfO2 film without damaging the graphene, which is suitable for downscaling the CET. After verifying the feasibility of scaling down the HfO2 thickness to achieve a CET of ~1.5 nm from an array of top-gated metal-oxide-graphene field-effect transistors, we fabricated graphene heterojunction tunnelling transistors with a record-low subthreshold swing value of <60 mV/dec on an 8″ glass wafer. PMID:26861833

  4. Cross linking molecular systems to form ultrathin dielectric layers

    NASA Astrophysics Data System (ADS)

    Feng, Danqin

    Dehydrogenation leads to cross linking of polymer or polymer like formation in very different systems: self-assembled monolayers and in closo -carboranes leading to the formation of semiconducting and dielectric boron carbide. We find evidence of intermolecular interactions for a self-assembled monolayer (SAM) formed from a large molecular adsorbate, [1,1';4',1"-terphenyl]-4,4"-dimethanethiol, from the dispersion of the molecular orbitals with changing the wave vector k and from the changes with temperature. With the formation self assembled molecular (SAM) layer, the molecular orbitals hybridize to electronic bands, with indications of significant band dispersion of the unoccupied molecular orbitals. Although organic adsorbates and thin films are generally regarded as "soft" materials, the effective Debye temperature, indicative of the dynamic motion of the lattice normal to the surface, can be very high, e.g. in the multilayer film formed from [1,1'-biphenyl]-4,4'-dimethanethiol (BPDMT). Depending on molecular orientation, the effective Debye temperature can be comparable to that of graphite due to the 'stiffness' of the benzene rings, but follows the expected Debye-Waller behavior for the core level photoemission intensities with temperature. This is not always the case. We find that a monomolecular film formed from [1,1';4',1"-terphenyl]-4,4"-dimethanethiol deviates from Debye-Waller temperature behavior and is likely caused by temperature dependent changes in molecular orientation. We also find evidence for the increase in dielectric character with polymerization (cross-linking) in spite of the decrease in the HOMO-LUMO gap upon irradiation of TPDMT. The changes in the HOMO-LUMO gap, with cross-linking, are roughly consistent with the band dispersion. The decomposition and cross-linking processes are also accompanied by changes in molecular orientation. The energetics of the three isomeric carborane cage compounds [ closo-1,2-orthocarborane, closo-1

  5. Effect of growth rate on crystallization of HfO2 thin films deposited by RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Dhanunjaya, M.; Manikanthababu, N.; Pathak, A. P.; Rao, S. V. S. Nageswara

    2016-05-01

    Hafnium oxide (HfO2) is the potentially useful dielectric material in both; electronics to replace the conventional SiO2 as gate dielectric and in Optics as anti-reflection coating material. In this present work we have synthesized polycrystalline HfO2 thin films by RF magnetron sputtering deposition technique with varying target to substrate distance. The deposited films were characterized by X-ray Diffraction, Rutherford Backscattering Spectrometry (RBS) and transmission and Reflection (T&R) measurements to study the growth behavior, microstructure and optical properties. XRD measurement shows that the samples having mixed phase of monoclinic, cubic and tetragonal crystal structure. RBS measurements suggest the formation of Inter Layer (IL) in between Substrate and film

  6. A small shoulder of optical absorption in polycrystalline HfO2 by LDA+U approach

    NASA Astrophysics Data System (ADS)

    Qin, Liyuan; Li, Jinping; Meng, Songhe; Lu, Hantao; Tohyama, Takami

    2016-10-01

    The dielectric function of the wide-gap optical material HfO2 is investigated by the local density approximation (LDA)+U approach. We focus on the origin of the shoulder-like structure near the edge of the band gap in the imaginary part of the dielectric function, which has been observed on the thin films of monoclinic HfO2. A comparison study on the three polymorphs of hafnia shows that regardless of the underlying crystal structure, the existence of the shoulder is mainly controlled by the value of the shortest length of Hf-O bonds. The proposition is further supported by the numerical simulations of isostatic pressing. A possible implication in high-pressure measurements is suggested accordingly.

  7. SHI induced effects on the electrical and optical properties of HfO2 thin films deposited by RF sputtering

    NASA Astrophysics Data System (ADS)

    Manikanthababu, N.; Dhanunjaya, M.; Nageswara Rao, S. V. S.; Pathak, A. P.

    2016-07-01

    The continuous downscaling of Metal Oxide Semiconductor (MOS) devices has reached a limit with SiO2 as a gate dielectric material. Introducing high-k dielectric materials as a replacement for the conservative SiO2 is the only alternative to reduce the leakage current. HfO2 is a reliable and an impending material for the wide usage as a gate dielectric in semiconductor industry. HfO2 thin films were synthesized by RF sputtering technique. Here, we present a study of Swift Heavy Ion (SHI) irradiation with100 MeV Ag ions for studying the optical properties as well as 80 MeV Ni ions for studying the electrical properties of HfO2/Si thin films. Rutherford Backscattering Spectrometry (RBS), Field Emission Scanning Electron Microscope (FESEM), energy-dispersive X-ray spectroscopy (EDS), profilometer and I-V (leakage current) measurements have been employed to study the SHI induced effects on both the structural, electrical and optical properties.

  8. Dielectric inspired scaling of polarization conversion subwavelength resonances in open ultrathin chiral structures

    NASA Astrophysics Data System (ADS)

    Serebryannikov, Andriy E.; Mutlu, Mehmet; Ozbay, E.

    2015-11-01

    It is shown that the scaling of subwavelength resonances in open ultrathin chiral structures can be obtained by varying only the permittivity of dielectric spacers, while multiband one-way polarization conversion and related asymmetric transmission remain possible. These features are quite general and obtainable in a wide range of parameter variation. Surprisingly, the difference in the power of ɛ for the classical ɛ-1/2 scaling rule and the empirical rules obtained in the present letter does not exceed 22%, giving an important entry point for future theoretical studies and design strategies. Both spectral scaling and conservation of the polarization characteristics can be achieved by using either tunneling or real-index impedance matching. The scaled structures with strong polarization and directional selectivity may have thickness of λ/100 and smaller.

  9. Instability investigation of In0.7Ga0.3As quantum-well MOSFETs with Al2O3 and Al2O3/HfO2

    NASA Astrophysics Data System (ADS)

    Kwon, Hyuk-Min; Kim, Do-Kywn; Lim, Sung-Kyu; Hwang, Hae-Chul; Son, Seung Woo; Park, Jung Ho; Park, Won-Sang; Kim, Jin Su; Shin, Chan-Soo; Park, Won-Kyu; Lee, Jung Hee; Kim, Taewoo; Kim, Dae-Hyun

    2016-07-01

    We present an instability investigation of In0.7Ga0.3As quantum-well (QW) metal-oxide-semiconductor field-effect-transistors (MOSFETs) on InP substrate with Al2O3 and Al2O3/HfO2 gate stacks. The device with bi-layer Al2O3/HfO2 gate stack exhibits larger shift in threshold-voltage (ΔVT) under a constant-voltage-stress condition (CVS), than one with single Al2O3 gate stack. At cryogenic temperature, the device with bi-layer Al2O3/HfO2 gate stack also induces worse hysteresis behavior than one with single Al2O3 gate stack. These are mainly attributed to more traps inside the HfO2 material, yielding a charge build-up inside the HfO2 gate dielectric. This strongly calls for a follow-up process to minimize those traps within the high-k dielectric layer and eventually to improve the reliability of InGaAs MOSFETs with HfO2-based high-k gate dielectric.

  10. Synthesis of freestanding HfO2 nanostructures

    PubMed Central

    2011-01-01

    Two new methods for synthesizing nanostructured HfO2 have been developed. The first method entails exposing HfTe2 powders to air. This simple process resulted in the formation of nanometer scale crystallites of HfO2. The second method involved a two-step heating process by which macroscopic, freestanding nanosheets of HfO2 were formed as a byproduct during the synthesis of HfTe2. These highly two-dimensional sheets had side lengths measuring up to several millimeters and were stable enough to be manipulated with tweezers and other instruments. The thickness of the sheets ranged from a few to a few hundred nanometers. The thinnest sheets appeared transparent when viewed in a scanning electron microscope. It was found that the presence of Mn enhanced the formation of HfO2 by exposure to ambient conditions and was necessary for the formation of the large scale nanosheets. These results present new routes to create freestanding nanostructured hafnium dioxide. PACS: 81.07.-b, 61.46.Hk, 68.37.Hk. PMID:21711786

  11. Chlorine mobility during annealing in N2 in ZrO2 and HfO2 films grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Ferrari, S.; Scarel, G.; Wiemer, C.; Fanciulli, M.

    2002-12-01

    Atomic layer deposition (ALD) growth of high-κ dielectric films (ZrO2 and HfO2) was performed using ZrCl4, HfCl4, and H2O as precursors. In this work, we use time of flight secondary ion mass spectrometry to investigate the chlorine distribution in ALD grown ZrO2 and HfO2 films, and its evolution during rapid thermal processes in nitrogen atmosphere. Chlorine outdiffusion is found to depend strongly upon annealing temperature and weakly upon the annealing time. While in ZrO2 chlorine concentration is significantly decreased already at 900 °C, in HfO2 it is extremely stable, even at temperatures as high as 1050 °C.

  12. Controlled direct growth of Al2O3-doped HfO2 films on graphene by H2O-based atomic layer deposition.

    PubMed

    Zheng, Li; Cheng, Xinhong; Yu, Yuehui; Xie, Yahong; Li, Xiaolong; Wang, Zhongjian

    2015-02-01

    Graphene has been drawing worldwide attention since its discovery in 2004. In order to realize graphene-based devices, thin, uniform-coverage and pinhole-free dielectric films with high permittivity on top of graphene are required. Here we report the direct growth of Al2O3-doped HfO2 films onto graphene by H2O-based atom layer deposition (ALD). Al2O3-onto-HfO2 stacks benefited the doping of Al2O3 into HfO2 matrices more than HfO2-onto-Al2O3 stacks did due to the micro-molecular property of Al2O3 and the high chemical activity of trimethylaluminum (TMA). Al2O3 acted as a network modifier, maintained the amorphous structure of the film even to 800 °C, and made the film smooth with a root mean square (RMS) roughness of 0.8 nm, comparable to the surface of pristine graphene. The capacitance and the relative permittivity of Al2O3-onto-HfO2 stacks were up to 1.18 μF cm(-2) and 12, respectively, indicating the high quality of Al2O3-doped HfO2 films on graphene. Moreover, the growth process of Al2O3-doped HfO2 films introduced no detective defects into graphene confirmed by Raman measurements. PMID:25519447

  13. Comparison of HfO2 films grown by atomic layer deposition using HfCl4 and H2O or O3 as the oxidant

    NASA Astrophysics Data System (ADS)

    Park, Hong Bae; Cho, Moonju; Park, Jaehoo; Lee, Suk Woo; Hwang, Cheol Seong; Kim, Jong-Pyo; Lee, Jong-Ho; Lee, Nae-In; Kang, Ho-Kyu; Lee, Jong-Cheol; Oh, Se-Jung

    2003-09-01

    HfO2 gate dielectric thin-films were deposited on Si wafers using an atomic-layer deposition (ALD) technique with HfCl4 and either H2O or O3 as the precursor and oxidant, respectively. Although the ALD reactions using either H2O or O3 were successfully confirmed at a deposition temperature of 300 °C, the structural and electrical properties of the HfO2 films grown using the two oxidants were quite different. The stronger oxidation power of the O3 compared to H2O increased the oxygen concentration in the HfO2 film and the rate of interfacial SiO2 formation even at the as-deposited state. Because of the larger oxygen concentration, the decrease in the capacitance density of the film grown with O3 after rapid thermal annealing at 750 °C under N2 atmosphere was slightly larger than that of the HfO2 film grown with H2O. Apart from this weakness, all the other electrical properties, including the fixed charge density, the interface trap density, the leakage current density and the hysteresis in the capacitance-voltage plot of the film grown with O3 were superior to those of the film grown with H2O. Therefore, O3 appears to be a better oxidant for the HfO2 film growth using the ALD method.

  14. A high performance, visible to mid-infrared photodetector based on graphene nanoribbons passivated with HfO2.

    PubMed

    Yu, Xuechao; Dong, Zhaogang; Liu, Yanping; Liu, Tao; Tao, Jin; Zeng, Yongquan; Yang, Joel K W; Wang, Qi Jie

    2016-01-01

    Graphene has drawn tremendous attention as a promising candidate for electronic and optoelectronic applications owing to its extraordinary properties, such as broadband absorption and ultrahigh mobility. Nevertheless, the absence of a bandgap makes graphene unfavorable for digital electronic or photonic applications. Although patterning graphene into nanostructures with the quantum confinement effect is able to open a bandgap, devices based on these graphene nanostructures generally suffer from low carrier mobility and scattering losses. In this paper, we demonstrated that encapsulation of an atomic layer deposited high-quality HfO2 film will greatly enhance the carrier mobility and decrease the scattering losses of graphene nanoribbons, because this high-k dielectric layer weakens carrier coulombic interactions. In addition, a photodetector based on HfO2 layer capped graphene nanoribbons can cover broadband wavelengths from visible to mid-infrared at room temperature, exhibiting ∼10 times higher responsivity than the one without a HfO2 layer in the visible regime and ∼8 times higher responsivity in the mid-infrared regime. The method employed here could be potentially used as a general approach to improve the performance of graphene nanostructures for electronic and optoelectronic applications. PMID:26610363

  15. Spurious phenomena occurring during current measurement on ultra-thin dielectric layers: From electro-thermal effects to surface damage

    SciTech Connect

    Grandfond, A.; Gautier, B.; Militaru, L.; Albertini, D.; Descamps-Mandine, A.

    2014-04-07

    In this paper, the conduction properties of dielectric ultra-thin layers are studied using atomic force microscopy. Especially, the conductive-atomic force microscope allows to measure the leakage current at the nanoscale and to study the degradation mechanisms locally. Nonetheless, the dielectric layer seems to be damaged by a technique's specific phenomenon: hillocks appear when a positive tip bias is applied on different dielectrics. In this paper, the formation of these hillocks is studied. Contrary to what is observed during the dielectric breakdown, the conductivity is reduced after hillocks formation which occurs after the dielectric breakdown. Moreover, we have observed the formation of cavities in the silicon substrate linked to the formation of hillocks, which is not compatible with a swelling process (as dielectric breakdown induced epitaxy). We propose that these results may be explained by an electro-thermal effect due to the large dissipated energy, maybe combined with the oxidation of the substrate. Finally, the interdependence of measurements is demonstrated during serial acquisition.

  16. Ferroelectric HfO2 for Emerging Ferroelectric Semiconductor Devices

    NASA Astrophysics Data System (ADS)

    Florent, Karine

    The spontaneous polarization in ferroelectrics (FE) makes them particularly attractive for non-volatile memory and logic applications. Non-volatile FRAM memories using perovskite structure materials, such as Lead Zirconate Titanate (PZT) and Strontium Bismuth Tantalate (SBT) have been studied for many years. However, because of their scaling limit and incompatibility with CMOS beyond 130 nm node, floating gate Flash memory technology has been preferred for manufacturing. The recent discovery of ferroelectricity in doped HfO2 in 2011 has opened the door for new ferroelectric based devices compatible with CMOS technology, such as Ferroelectric Field Effect Transistor (FeFET) and Ferroelectric Tunnel Junctions (FTJ). This work began with developing ferroelectric hysteresis characterization capabilities at RIT. Initially reactively sputtered aluminum doped HfO 2 films were investigated. It was observed that the composition control using co-sputtering was not achievable within the existing capabilities. During the course of this study, collaboration was established with the NaMLab group in Germany to investigate Si doped HfO2 deposited by Atomic Layer Deposition (ALD). Metal Ferroelectric Metal (MFM) devices were fabricated using TiN as the top and bottom electrode with Si:HfO2 thickness ranging from 6.4 nm to 22.9 nm. The devices were electrically tested for P-E, C-V and I-V characteristics. Structural characterizations included TEM, EELS, XRR, XRD and XPS/Auger spectroscopy. Higher remanant polarization (Pr) was observed for films of 9.3 nm and 13.1 nm thickness. Thicker film (22.9 nm) showed smaller Pr. Devices with 6.4 nm thick films exhibit tunneling behavior showing a memristor like I-V characteristics. The tunnel current and ferroelectricity showed decrease with cycling indicating a possible change in either the structure or the domain configurations. Theoretical simulations using the improved FE model were carried out to model the ferroelectric behavior of different stacks of films.

  17. Solid-State Densification of Spun-Cast Self-Assembled Monolayers for Use in Ultra-Thin Hybrid Dielectrics

    PubMed Central

    Hutchins, Daniel O.; Acton, Orb; Weidner, Tobias; Cernetic, Nathan; Baio, Joe E.; Castner, David G.; Ma, Hong; Jen, Alex K.-Y.

    2013-01-01

    Ultra-thin self-assembled monolayer (SAM)-oxide hybrid dielectrics have gained significant interest for their application in low-voltage organic thin film transistors (OTFTs). A [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) SAM on ultrathin AlOx (2.5 nm) has been developed to significantly enhance the dielectric performance of inorganic oxides through reduction of leakage current while maintaining similar capacitance to the underlying oxide structure. Rapid processing of this SAM in ambient conditions is achieved by spin coating, however, as-cast monolayer density is not sufficient for dielectric applications. Thermal annealing of a bulk spun-cast PhO-19-PA molecular film is explored as a mechanism for SAM densification. SAM density, or surface coverage, and order are examined as a function of annealing temperature. These SAM characteristics are probed through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure spectroscopy (NEXAFS). It is found that at temperatures sufficient to melt the as-cast bulk molecular film, SAM densification is achieved; leading to a rapid processing technique for high performance SAM-oxide hybrid dielectric systems utilizing a single wet processing step. To demonstrate low-voltage devices based on this hybrid dielectric (with leakage current density of 7.7×10−8 A cm−2 and capacitance density of 0.62 µF cm−2 at 3 V), pentacene thin-film transistors (OTFTs) are fabricated and yield sub 2 V operation and charge carrier mobilites of up to 1.1 cm2 V−1 s−1. PMID:24288423

  18. Electron beam induced local crystallization of HfO2 nanopores for biosensing applications

    PubMed Central

    Shim, Jiwook; Rivera, Jose; Bashir, Rashid

    2013-01-01

    We report the development of single, locally crystallized nanopores in HfO2 membranes for biosensing applications. HfO2 is chosen for its isoelectric point of 7.0, mechanical and chemical stability in solution, and for its potential as a high-k material for nanopore ionic field effect transistor applications. The HfO2 membrane is deposited on a graphene layer suspended over a 300 nm FIB hole, where graphene is used as the mechanical support. Exposure of the membrane to a focused electron beam causes crystallization in the vicinity of the nanopore during pore formation. We investigate the effects of crystallization on the electrical and surface properties of HfO2 films. Our surface analysis of HfO2 reveals improved hydrophilicity of crystallized HfO2, a notable advantage over the hydrophobicity of as-deposited HfO2. We also demonstrate detection of dsDNA translocation through HfO2 nanopores under various applied bias levels. In addition, our device architecture also presents a promising first step toward the realization of high-k HfO2 nanopore transistors. PMID:23945603

  19. Electron beam induced local crystallization of HfO2 nanopores for biosensing applications.

    PubMed

    Shim, Jiwook; Rivera, Jose A; Bashir, Rashid

    2013-11-21

    We report the development of single, locally crystallized nanopores in HfO2 membranes for biosensing applications. HfO2 is chosen for its isoelectric point of 7.0, mechanical and chemical stability in solution, and for its potential as a high-k material for nanopore ionic field effect transistor applications. The HfO2 membrane is deposited on a graphene layer suspended over a 300 nm FIB hole, where graphene is used as the mechanical support. Exposure of the membrane to a focused electron beam causes crystallization in the vicinity of the nanopore during pore formation. We investigate the effects of crystallization on the electrical and surface properties of HfO2 films. Our surface analysis of HfO2 reveals improved hydrophilicity of crystallized HfO2, a notable advantage over the hydrophobicity of as-deposited HfO2. We also demonstrate detection of dsDNA translocation through HfO2 nanopores under various applied bias levels. In addition, our device architecture also presents a promising first step toward the realization of high-k HfO2 nanopore transistors.

  20. Effects of ozone post deposition treatment on interfacial and electrical characteristics of atomic-layer-deposited Al2O3 and HfO2 films on GaSb substrates

    NASA Astrophysics Data System (ADS)

    Zhao, Lianfeng; Tan, Zhen; Wang, Jing; Xu, Jun

    2014-01-01

    Atomic-layer-deposited Al2O3 and HfO2 films on GaSb substrates were treated by in-situ ozone post deposition treatment (PDT). The effects of ozone PDT on the interfacial and electrical properties of Al2O3 and HfO2 gate dielectric films on GaSb substrates were investigated carefully. It is found that the dielectric quality and the interfacial properties of the Al2O3 and HfO2 films are improved by ozone PDT. After in-situ ozone PDT for 5 min, the Al2O3 and HfO2 films on GaSb substrates exhibit improved electrical and interfacial properties, such as reduced frequency dispersion, gate leakage current, border traps and interface traps. Interface trap density is reduced by ∼24% for the Al2O3/GaSb stacks and ∼27% for the HfO2/GaSb stacks. In-situ ozone PDT is proved to be a promising technique in improving the quality of high-k gate stacks on GaSb substrates.

  1. Vacuum ultraviolet thin films. I - Optical constants of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 thin films. II - Vacuum ultraviolet all-dielectric narrowband filters

    NASA Technical Reports Server (NTRS)

    Zukic, Muamer; Torr, Douglas G.; Spann, James F.; Torr, Marsha R.

    1990-01-01

    An iteration process matching calculated and measured reflectance and transmittance values in the 120-230 nm VUV region is presently used to ascertain the optical constants of bulk MgF2, as well as films of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 deposited on MgF2 substrates. In the second part of this work, a design concept is demonstrated for two filters, employing rapidly changing extinction coefficients, centered at 135 nm for BaF2 and 141 nm for SiO2. These filters are shown to yield excellent narrowband spectral performance in combination with narrowband reflection filters.

  2. Electron mobility in ultra-thin InGaAs channels: Impact of surface orientation and different gate oxide materials

    NASA Astrophysics Data System (ADS)

    Krivec, Sabina; Poljak, Mirko; Suligoj, Tomislav

    2016-01-01

    Electron mobility is investigated in sub-20 nm-thick InGaAs channels, sandwiched between different gate oxides (SiO2, Al2O3, HfO2) and InP as substrate, using physics-based numerical modeling. Effects of body thickness downscaling to 2 nm, different gate oxides, and surface orientation [(1 0 0) and (1 1 1)] are examined by including all electron valleys and all relevant scattering mechanisms. We report that ultra-thin (1 1 1) Al2O3-InGaAs-InP devices offer greater electron mobility than (1 0 0) devices even in the extremely-thin channels. Furthermore, ultra-thin (1 0 0) InGaAs devices outperform SOI in terms of electron mobility for body thicknesses above ∼4 nm, while (1 1 1) InGaAs channels are superior to SOI for all body thickness values above ∼3 nm. The study of different gate oxides indicates that HfO2 is the optimum gate dielectric regardless of device orientation, offering a mobility improvement of up to 124% for (1 1 1) and 149% for (1 0 0) surface orientation, when compared to the initial Al2O3-InGaAs-InP structure. The (1 1 1) orientation offers improvement over (1 0 0) device irrespective of the body thickness and gate oxide material, with the highest difference reported for SiO2, followed by Al2O3 and HfO2.

  3. Optimizing HiPIMS pressure for deposition of high-k (k = 18.3) amorphous HfO2

    NASA Astrophysics Data System (ADS)

    Ganesan, R.; Murdoch, B. J.; Partridge, J. G.; Bathgate, S.; Treverrow, B.; Dong, X.; Ross, A. E.; McCulloch, D. G.; McKenzie, D. R.; Bilek, M. M. M.

    2016-03-01

    Stoichiometric amorphous HfO2 films have been deposited by reactive High Power Impulse Magnetron Sputtering (HiPIMS) from a Hf target in a 1:1 Ar:O2 atmosphere at pressures 2-4.5 mTorr. An optimum pressure was found for depositing smooth, high refractive index and amorphous films. Stress and refractive index reached a maximum as deposition pressure was increased to 3.5 mTorr. At 3.5 mTorr, HfO2 films were deposited with a refractive index of 2.15 at 500 nm, low leakage currents, moderate fixed charge density and a high dielectric constant of ∼18.3. The intensification of energetic ion bombardment upon the film with increase in HiPIMS pressure plays a dominant role in film properties. Increase in pressure above the optimum relieved the stress in the films and degraded the optical and electrical properties. HiPIMS pressure enables to gain indirect control of ion flux and energy in the plasma and can be used to modify the properties of depositing films.

  4. Photocurrent generation in carbon nanotube/cubic-phase HfO2 nanoparticle hybrid nanocomposites.

    PubMed

    Rauwel, Protima; Galeckas, Augustinas; Salumaa, Martin; Ducroquet, Frédérique; Rauwel, Erwan

    2016-01-01

    A hybrid material consisting of nonfunctionalized multiwall carbon nanotubes (MWCNTs) and cubic-phase HfO2 nanoparticles (NPs) with an average diameter of 2.6 nm has been synthesized. Free standing HfO2 NPs present unusual optical properties and a strong photoluminescence emission in the visible region, originating from surface defects. Transmission electron microscopy studies show that these NPs decorate the MWCNTs on topological defect sites. The electronic structure of the C K-edge in the nanocomposites was probed by electron energy loss spectroscopy, highlighting the key role of the MWCNT growth defects in anchoring HfO2 NPs. A combined optical emission and absorption spectroscopy approach illustrated that, in contrast to HfO2 NPs, the metallic MWCNTs do not emit light but instead expose their discrete electronic structure in the absorption spectra. The hybrid material manifests characteristic absorption features with a gradual merger of the MWCNT π-plasmon resonance band with the intrinsic defect band and fundamental edge of HfO2. The photoluminescence of the nanocomposites indicates features attributed to combined effects of charge desaturation of HfO2 surface states and charge transfer to the MWCNTs with an overall reduction of radiative recombination. Finally, photocurrent generation under UV-vis illumination suggests that a HfO2 NP/MWCNT hybrid system can be used as a flexible nanodevice for light harvesting applications. PMID:27547626

  5. Photocurrent generation in carbon nanotube/cubic-phase HfO2 nanoparticle hybrid nanocomposites

    PubMed Central

    Galeckas, Augustinas; Salumaa, Martin; Ducroquet, Frédérique; Rauwel, Erwan

    2016-01-01

    Summary A hybrid material consisting of nonfunctionalized multiwall carbon nanotubes (MWCNTs) and cubic-phase HfO2 nanoparticles (NPs) with an average diameter of 2.6 nm has been synthesized. Free standing HfO2 NPs present unusual optical properties and a strong photoluminescence emission in the visible region, originating from surface defects. Transmission electron microscopy studies show that these NPs decorate the MWCNTs on topological defect sites. The electronic structure of the C K-edge in the nanocomposites was probed by electron energy loss spectroscopy, highlighting the key role of the MWCNT growth defects in anchoring HfO2 NPs. A combined optical emission and absorption spectroscopy approach illustrated that, in contrast to HfO2 NPs, the metallic MWCNTs do not emit light but instead expose their discrete electronic structure in the absorption spectra. The hybrid material manifests characteristic absorption features with a gradual merger of the MWCNT π-plasmon resonance band with the intrinsic defect band and fundamental edge of HfO2. The photoluminescence of the nanocomposites indicates features attributed to combined effects of charge desaturation of HfO2 surface states and charge transfer to the MWCNTs with an overall reduction of radiative recombination. Finally, photocurrent generation under UV–vis illumination suggests that a HfO2 NP/MWCNT hybrid system can be used as a flexible nanodevice for light harvesting applications. PMID:27547626

  6. Accurate prediction of band gaps and optical properties of HfO2

    NASA Astrophysics Data System (ADS)

    Ondračka, Pavel; Holec, David; Nečas, David; Zajíčková, Lenka

    2016-10-01

    We report on optical properties of various polymorphs of hafnia predicted within the framework of density functional theory. The full potential linearised augmented plane wave method was employed together with the Tran-Blaha modified Becke-Johnson potential (TB-mBJ) for exchange and local density approximation for correlation. Unit cells of monoclinic, cubic and tetragonal crystalline, and a simulated annealing-based model of amorphous hafnia were fully relaxed with respect to internal positions and lattice parameters. Electronic structures and band gaps for monoclinic, cubic, tetragonal and amorphous hafnia were calculated using three different TB-mBJ parametrisations and the results were critically compared with the available experimental and theoretical reports. Conceptual differences between a straightforward comparison of experimental measurements to a calculated band gap on the one hand and to a whole electronic structure (density of electronic states) on the other hand, were pointed out, suggesting the latter should be used whenever possible. Finally, dielectric functions were calculated at two levels, using the random phase approximation without local field effects and with a more accurate Bethe-Salpether equation (BSE) to account for excitonic effects. We conclude that a satisfactory agreement with experimental data for HfO2 was obtained only in the latter case.

  7. Ferroelectric phase stabilization of HfO2 by nitrogen doping

    NASA Astrophysics Data System (ADS)

    Xu, Lun; Nishimura, Tomonori; Shibayama, Shigehisa; Yajima, Takeaki; Migita, Shinji; Toriumi, Akira

    2016-09-01

    We report that nitrogen (N) doping can drive the ferroelectricity of HfO2. It was found that N doping can cause the transition from a monoclinic phase to a highly symmetric phase. The role of N doping is discussed from the viewpoints of charge balance and bond-constraining effects. The former is responsible for the structural transformation from a paraelectric phase to a ferroelectric phase by forming an oxygen vacancy. In addition, Hf-N and N-O bonds with covalent characteristics have strong effects on HfO2 structural and electrical properties, and thus contribute to a marked HfO2 para-/ferroelectric transition.

  8. Schottky barrier height reduction for metal/n-InP by inserting ultra-thin atomic layer deposited high-k dielectrics

    SciTech Connect

    Zheng, Shan; Yang, Wen; Sun, Qing-Qing E-mail: linchen@fudan.edu.cn; Zhou, Peng; Wang, Peng-Fei; Wei Zhang, David; Chen, Lin; Xiao, Fei

    2013-12-23

    Fermi level pinning at metal/n-InP interface and effective Schottky barrier height (Φ{sub B,eff}) were optimized by inserting ultrathin dielectrics in this work. Comparing the inserted monolayer and bilayer high-k dielectrics, we demonstrated that the introduction of bilayer dielectrics can further reduce Φ{sub B,eff} (from 0.49 eV to 0.22 eV) than the monolayer dielectric (from 0.49 eV to 0.32 eV) even though the overall dielectric thickness was thicker. The additional dipole formed at high-k/high-k interfaces could be used to expound the mechanism. This work proposed an effective solution to reduce resistance contacts for InP based transistors and Schottky barrier transistors.

  9. Mechanical properties of low- and high-k dielectric thin films: A surface Brillouin light scattering study

    NASA Astrophysics Data System (ADS)

    Zizka, J.; King, S.; Every, A. G.; Sooryakumar, R.

    2016-04-01

    Surface Brillouin light scattering measurements are used to determine the elastic constants of nano-porous low-k SiOC:H (165 nm) and high-k HfO2 (25 nm) as well as BN:H (100 nm) films grown on Si substrates. In addition, the study investigates the mechanical properties of ultra-thin (25 nm) blanket TiN cap layers often used as hard masks for patterning, and their effects on the underlying low-k dielectrics that support a high level of interconnected porosity. Depending on the relative material properties of individual component layers, the acoustic modes manifest as confined, propagating, or damped resonances in the light scattering spectra, thereby enabling the mechanical properties of the ultra-thin films to be determined.

  10. Microstructure dependent filament forming kinetics in HfO2 programmable metallization cells

    NASA Astrophysics Data System (ADS)

    Clarke, Heidi; Brown, Timothy; Hu, Jianjun; Ganguli, Raj; Reed, Amber; Voevodin, Andrey; Shamberger, Patrick J.

    2016-10-01

    Variability remains the principal concern for commercialization of HfO2 based resistance switching devices. Here, we investigate the role of thermal processing conditions on internal structure of atomic layer deposited HfO2 thin films, and the impact of that structure on filament forming kinetics of p+ Si/HfO2/Cu and TiN/HfO2/Cu devices. Regardless of bias polarity or electrode metal, filament formation times are at least one order of magnitude shorter in polycrystalline than in amorphous films, which we attribute to the presence of fast ion migration along grain boundaries. Within polycrystalline films, filament formation times are correlated with degree of crystalline orientation. Inter-device variability in forming time is roughly equivalent across HfO2 film processing conditions. The kinetics of filament forming are shown to be highly dependent on HfO2 microstructure, with possible implications for the inter-device variability of subsequent switching cycles.

  11. Microstructure dependent filament forming kinetics in HfO2 programmable metallization cells.

    PubMed

    Clarke, Heidi; Brown, Timothy; Hu, Jianjun; Ganguli, Raj; Reed, Amber; Voevodin, Andrey; Shamberger, Patrick J

    2016-10-21

    Variability remains the principal concern for commercialization of HfO2 based resistance switching devices. Here, we investigate the role of thermal processing conditions on internal structure of atomic layer deposited HfO2 thin films, and the impact of that structure on filament forming kinetics of p+ Si/HfO2/Cu and TiN/HfO2/Cu devices. Regardless of bias polarity or electrode metal, filament formation times are at least one order of magnitude shorter in polycrystalline than in amorphous films, which we attribute to the presence of fast ion migration along grain boundaries. Within polycrystalline films, filament formation times are correlated with degree of crystalline orientation. Inter-device variability in forming time is roughly equivalent across HfO2 film processing conditions. The kinetics of filament forming are shown to be highly dependent on HfO2 microstructure, with possible implications for the inter-device variability of subsequent switching cycles.

  12. Materials and electrical characterization of molecular beam deposited CeO2 and CeO2/HfO2 bilayers on germanium

    NASA Astrophysics Data System (ADS)

    Brunco, D. P.; Dimoulas, A.; Boukos, N.; Houssa, M.; Conard, T.; Martens, K.; Zhao, C.; Bellenger, F.; Caymax, M.; Meuris, M.; Heyns, M. M.

    2007-07-01

    Properties of CeO2 and CeO2/HfO2 bilayers grown by molecular beam deposition on in situ prepared, oxide-free Ge(100) surfaces are reported here. Deposition is achieved by a simultaneous flux of electron-beam evaporated metal (Ce or Hf) and of remote plasma generated atomic oxygen. These conditions result in an interfacial layer (IL) between the cubic CeO2 and Ge substrate. Electron energy loss spectroscopy shows that this IL is comprised of Ge and O and a small amount of Ce, and x-ray photoelectron spectroscopy suggests that the Ge is in a mix of 2+ and 3+ oxidation states. A comparison of capacitance, conductance, and leakage data shows a higher quality dielectric for 225 °C deposition than for room temperature. However, CeO2-only deposition results in an unacceptably high leakage current due to the small CeO2 band gap, which is remedied by the use of CeO2/HfO2 bilayers. Using the Nicollian-Goetzberger method, interface trap densities in the mid 1011 eV-1 cm-2 are obtained for CeO2/HfO2 gate stacks on both n- and p-Ge.

  13. Large-Scale Precise Printing of Ultrathin Sol-Gel Oxide Dielectrics for Directly Patterned Solution-Processed Metal Oxide Transistor Arrays.

    PubMed

    Lee, Won-June; Park, Won-Tae; Park, Sungjun; Sung, Sujin; Noh, Yong-Young; Yoon, Myung-Han

    2015-09-01

    Ultrathin and dense metal oxide gate di-electric layers are reported by a simple printing of AlOx and HfOx sol-gel precursors. Large-area printed indium gallium zinc oxide (IGZO) thin-film transistor arrays, which exhibit mobilities >5 cm(2) V(-1) s(-1) and gate leakage current of 10(-9) A cm(-2) at a very low operation voltage of 2 V, are demonstrated by continuous simple bar-coated processes. PMID:26222338

  14. High Performance Ultrathin GaAs Solar Cells Enabled with Heterogeneously Integrated Dielectric Periodic Nanostructures.

    PubMed

    Lee, Sung-Min; Kwong, Anthony; Jung, Daehwan; Faucher, Joseph; Biswas, Roshni; Shen, Lang; Kang, Dongseok; Lee, Minjoo Larry; Yoon, Jongseung

    2015-10-27

    Due to their favorable materials properties including direct bandgap and high electron mobilities, epitaxially grown III-V compound semiconductors such as gallium arsenide (GaAs) provide unmatched performance over silicon in solar energy harvesting. Nonetheless, their large-scale deployment in terrestrial photovoltaics remains challenging mainly due to the high cost of growing device quality epitaxial materials. In this regard, reducing the thickness of constituent active materials under appropriate light management schemes is a conceptually viable option to lower the cost of GaAs solar cells. Here, we present a type of high efficiency, ultrathin GaAs solar cell that incorporates bifacial photon management enabled by techniques of transfer printing to maximize the absorption and photovoltaic performance without compromising the optimized electronic configuration of planar devices. Nanoimprint lithography and dry etching of titanium dioxide (TiO2) deposited directly on the window layer of GaAs solar cells formed hexagonal arrays of nanoscale posts that serve as lossless photonic nanostructures for antireflection, diffraction, and light trapping in conjunction with a co-integrated rear-surface reflector. Systematic studies on optical and electrical properties and photovoltaic performance in experiments, as well as numerical modeling, quantitatively describe the optimal design rules for ultrathin, nanostructured GaAs solar cells and their integrated modules.

  15. High performance p-type organic thin film transistors with an intrinsically photopatternable, ultrathin polymer dielectric layer☆

    PubMed Central

    Petritz, Andreas; Wolfberger, Archim; Fian, Alexander; Krenn, Joachim R.; Griesser, Thomas; Stadlober, Barbara

    2013-01-01

    A high-performing bottom-gate top-contact pentacene-based oTFT technology with an ultrathin (25–48 nm) and electrically dense photopatternable polymeric gate dielectric layer is reported. The photosensitive polymer poly((±)endo,exo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, diphenylester) (PNDPE) is patterned directly by UV-exposure (λ = 254 nm) at a dose typical for conventionally used negative photoresists without the need for any additional photoinitiator. The polymer itself undergoes a photo-Fries rearrangement reaction under UV illumination, which is accompanied by a selective cross-linking of the macromolecules, leading to a change in solubility in organic solvents. This crosslinking reaction and the negative photoresist behavior are investigated by means of sol–gel analysis. The resulting transistors show a field-effect mobility up to 0.8 cm2 V−1 s−1 at an operation voltage as low as −4.5 V. The ultra-low subthreshold swing in the order of 0.1 V dec−1 as well as the completely hysteresis-free transistor characteristics are indicating a very low interface trap density. It can be shown that the device performance is completely stable upon UV-irradiation and development according to a very robust chemical rearrangement. The excellent interface properties, the high stability and the small thickness make the PNDPE gate dielectric a promising candidate for fast organic electronic circuits. PMID:24748853

  16. Mixed Al and Si doping in ferroelectric HfO2 thin films

    NASA Astrophysics Data System (ADS)

    Lomenzo, Patrick D.; Takmeel, Qanit; Zhou, Chuanzhen; Chung, Ching-Chang; Moghaddam, Saeed; Jones, Jacob L.; Nishida, Toshikazu

    2015-12-01

    Ferroelectric HfO2 thin films 10 nm thick are simultaneously doped with Al and Si. The arrangement of the Al and Si dopant layers within the HfO2 greatly influences the resulting ferroelectric properties of the polycrystalline thin films. Optimizing the order of the Si and Al dopant layers led to a remanent polarization of ˜20 μC/cm2 and a coercive field strength of ˜1.2 MV/cm. Post-metallization anneal temperatures from 700 °C to 900 °C were used to crystallize the Al and Si doped HfO2 thin films. Grazing incidence x-ray diffraction detected differences in peak broadening between the mixed Al and Si doped HfO2 thin films, indicating that strain may influence the formation of the ferroelectric phase with variations in the dopant layering. Endurance characteristics show that the mixed Al and Si doped HfO2 thin films exhibit a remanent polarization greater than 15 μC/cm2 up to 108 cycles.

  17. UV-assisted room-temperature gas sensing by HfO2 thin films

    NASA Astrophysics Data System (ADS)

    Karaduman, Irmak; Barin, Özlem; Acar, Selim

    2016-06-01

    This research paper presents a detailed study of the influence of annealing temperature and UV irradiation on the sensitivity to NO2 of HfO2 thin films that can be used for the development of metal-oxide gas sensors. The HfO2 thin films were grown with a 3.3-nm thickness by using atomic layer deposition (ALD) and were annealed at different temperatures. The HfO2 thin films were characterized by using an atomic force microscope (AFM). The roughnesses of thin films were seen to have been affected by the annealing treatment. The effects of annealing temperature, as well as the operating temperature, on the response and the recovery characteristics of the HfO2 film were investigated. The results showed that both the annealing temperature and the operating temperature had significant effects on the sensing characteristics. Also, at room-temperature operation, the sensitivity of HfO2 thin films to 5 ppm of NO2 gas in air was investigated under UV irradiation. UV irradiation not only increased the response but also reduced the response and the recovery times during the gas-sensing measurements.

  18. Logic circuits composed of flexible carbon nanotube thin-film transistor and ultra-thin polymer gate dielectric.

    PubMed

    Lee, Dongil; Yoon, Jinsu; Lee, Juhee; Lee, Byung-Hyun; Seol, Myeong-Lok; Bae, Hagyoul; Jeon, Seung-Bae; Seong, Hyejeong; Im, Sung Gap; Choi, Sung-Jin; Choi, Yang-Kyu

    2016-01-01

    Printing electronics has become increasingly prominent in the field of electronic engineering because this method is highly efficient at producing flexible, low-cost and large-scale thin-film transistors. However, TFTs are typically constructed with rigid insulating layers consisting of oxides and nitrides that are brittle and require high processing temperatures, which can cause a number of problems when used in printed flexible TFTs. In this study, we address these issues and demonstrate a method of producing inkjet-printed TFTs that include an ultra-thin polymeric dielectric layer produced by initiated chemical vapor deposition (iCVD) at room temperature and highly purified 99.9% semiconducting carbon nanotubes. Our integrated approach enables the production of flexible logic circuits consisting of CNT-TFTs on a polyethersulfone (PES) substrate that have a high mobility (up to 9.76 cm(2) V(-1) sec(-)1), a low operating voltage (less than 4 V), a high current on/off ratio (3 × 10(4)), and a total device yield of 90%. Thus, it should be emphasized that this study delineates a guideline for the feasibility of producing flexible CNT-TFT logic circuits with high performance based on a low-cost and simple fabrication process. PMID:27184121

  19. Light Coupling and Trapping in Ultrathin Cu(In,Ga)Se2 Solar Cells Using Dielectric Scattering Patterns.

    PubMed

    van Lare, Claire; Yin, Guanchao; Polman, Albert; Schmid, Martina

    2015-10-27

    We experimentally demonstrate photocurrent enhancement in ultrathin Cu(In,Ga)Se2 (CIGSe) solar cells with absorber layers of 460 nm by nanoscale dielectric light scattering patterns printed by substrate conformal imprint lithography. We show that patterning the front side of the device with TiO2 nanoparticle arrays results in a small photocurrent enhancement in almost the entire 400-1200 nm spectral range due to enhanced light coupling into the cell. Three-dimensional finite-difference time-domain simulations are in good agreement with external quantum efficiency measurements. Patterning the Mo/CIGSe back interface using SiO2 nanoparticles leads to strongly enhanced light trapping, increasing the efficiency from 11.1% for a flat to 12.3% for a patterned cell. Simulations show that optimizing the array geometry could further improve light trapping. Including nanoparticles at the Mo/CIGSe interface leads to substantially reduced parasitic absorption in the Mo back contact. Parasitic absorption in the back contact can be further reduced by fabricating CIGSe cells on top of a SiO2-patterned In2O3:Sn (ITO) back contact. Simulations show that these semitransparent cells have similar spectrally averaged reflection and absorption in the CIGSe active layer as a Mo-based patterned cell, demonstrating that the absorption losses in the Mo can be partially turned into transmission through the semitransparent geometry.

  20. Logic circuits composed of flexible carbon nanotube thin-film transistor and ultra-thin polymer gate dielectric

    PubMed Central

    Lee, Dongil; Yoon, Jinsu; Lee, Juhee; Lee, Byung-Hyun; Seol, Myeong-Lok; Bae, Hagyoul; Jeon, Seung-Bae; Seong, Hyejeong; Im, Sung Gap; Choi, Sung-Jin; Choi, Yang-Kyu

    2016-01-01

    Printing electronics has become increasingly prominent in the field of electronic engineering because this method is highly efficient at producing flexible, low-cost and large-scale thin-film transistors. However, TFTs are typically constructed with rigid insulating layers consisting of oxides and nitrides that are brittle and require high processing temperatures, which can cause a number of problems when used in printed flexible TFTs. In this study, we address these issues and demonstrate a method of producing inkjet-printed TFTs that include an ultra-thin polymeric dielectric layer produced by initiated chemical vapor deposition (iCVD) at room temperature and highly purified 99.9% semiconducting carbon nanotubes. Our integrated approach enables the production of flexible logic circuits consisting of CNT-TFTs on a polyethersulfone (PES) substrate that have a high mobility (up to 9.76 cm2 V−1 sec−1), a low operating voltage (less than 4 V), a high current on/off ratio (3 × 104), and a total device yield of 90%. Thus, it should be emphasized that this study delineates a guideline for the feasibility of producing flexible CNT-TFT logic circuits with high performance based on a low-cost and simple fabrication process. PMID:27184121

  1. Logic circuits composed of flexible carbon nanotube thin-film transistor and ultra-thin polymer gate dielectric

    NASA Astrophysics Data System (ADS)

    Lee, Dongil; Yoon, Jinsu; Lee, Juhee; Lee, Byung-Hyun; Seol, Myeong-Lok; Bae, Hagyoul; Jeon, Seung-Bae; Seong, Hyejeong; Im, Sung Gap; Choi, Sung-Jin; Choi, Yang-Kyu

    2016-05-01

    Printing electronics has become increasingly prominent in the field of electronic engineering because this method is highly efficient at producing flexible, low-cost and large-scale thin-film transistors. However, TFTs are typically constructed with rigid insulating layers consisting of oxides and nitrides that are brittle and require high processing temperatures, which can cause a number of problems when used in printed flexible TFTs. In this study, we address these issues and demonstrate a method of producing inkjet-printed TFTs that include an ultra-thin polymeric dielectric layer produced by initiated chemical vapor deposition (iCVD) at room temperature and highly purified 99.9% semiconducting carbon nanotubes. Our integrated approach enables the production of flexible logic circuits consisting of CNT-TFTs on a polyethersulfone (PES) substrate that have a high mobility (up to 9.76 cm2 V‑1 sec‑1), a low operating voltage (less than 4 V), a high current on/off ratio (3 × 104), and a total device yield of 90%. Thus, it should be emphasized that this study delineates a guideline for the feasibility of producing flexible CNT-TFT logic circuits with high performance based on a low-cost and simple fabrication process.

  2. Enhanced performance of supported HfO2 counter electrodes for redox couples used in dye-sensitized solar cells.

    PubMed

    Yun, Sining; Pu, Haihui; Chen, Junhong; Hagfeldt, Anders; Ma, Tingli

    2014-02-01

    Mesoporous-graphitic-carbon-supported HfO2 (HfO2 -MGC) nanohybrids were synthesized by using a soft-template route. Characterization and a systematic investigation of the catalytic properties, stability, and catalytic mechanism were performed for HfO2 -MGC counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The new HfO2 -MGC as a CE in DSSCs showed a surprisingly high efficiency of 7.75 % for the triiodide/iodide redox couple and 3.69 % for the disulfide/thiolate redox couple, greater than the Pt electrode in the corresponding electrolyte system, which opens up a possibility for its practical application.

  3. Memristor and selector devices fabricated from HfO2-xNx

    NASA Astrophysics Data System (ADS)

    Murdoch, B. J.; McCulloch, D. G.; Ganesan, R.; McKenzie, D. R.; Bilek, M. M. M.; Partridge, J. G.

    2016-04-01

    Monoclinic HfO2-xNx has been incorporated into two-terminal devices exhibiting either memristor or selector operation depending on the controlled inclusion/suppression of mobile oxygen vacancies. In HfO2 memristors containing oxygen vacancies, gradual conductance modulation, short-term plasticity, and long-term potentiation were observed using appropriate voltage-spike stimulation, suggesting suitability for artificial neural networks. Passivation of oxygen vacancies, confirmed by X-ray absorption spectroscopy, was achieved in HfO2-xNx films by the addition of nitrogen during growth. Selector devices formed on these films exhibited threshold switching and current controlled negative differential resistance consistent with thermally driven insulator to metal transitions.

  4. Laser conditioning on HfO2 film monitored by calorimeter.

    PubMed

    Hao, Liu; Songlin, Chen; Yaowei, Wei; Zhe, Zhang; Jin, Luo; Nan, Zheng; Ping, Ma

    2012-01-01

    Conditioning effect on HfO2 single-layer film by quasi-cw laser was investigated. The conditioning process was monitored with laser calorimeter. Experimental results revealed that the HfO2 film absorption decreased as a function of the irradiation dose. Higher laser power accelerated the conditioning process. The conditioning effect could not be explained by water annihilation. AFM pictures of the film surface showed that the structural information in the conditioned region was different from the unconditioned region. Monitoring the in situ absorption, laser calorimeter is a promising tool to investigate the laser conditioning process.

  5. Probing the mechanical properties of high-k dielectric nano-films by Brillouin light scattering study

    NASA Astrophysics Data System (ADS)

    Zizka, Jonathan; Bielefeld, Jeffrey; King, Sean; Sooryakumar, R.

    2014-03-01

    As microelectronic transistors scale to smaller dimensions, device functionality suffers from current leakage. This problem can be overcome by using thicker gate materials with a high dielectric constant. SiO2 has been the material of choice, but becomes unsuitable due to its relatively low dielectric constant (k = 3.9). Alternate materials, such as BN:H (k = 5.7) and HfO2 (k = 25) are promising choices to replace SiO2 to achieve the desired performance while preserving ultra-thin thickness (<10 nm). Despite these promising features, one concern of including these materials, are their mechanical and thermal properties that could degrade device functionality. There is thus a growing need for non-destructive techniques to evaluate the mechanical properties of such laminar structures since traditional methods like nano-indentation are not effective at these dimensions. We report on Brillioun light scattering studies to determine the individual elastic constants and, thus the mechanical properties of BN:H and HfO2 high-k films with thicknesses as low as 24 nm. Young's modulus (E) and Poisson's ratio (ν) were determined by measuring the frequency dispersion of confined and traveling transverse and longitudinal acoustic waves as well as their associated light scattering intensities.

  6. Single vacancy defect spectroscopy on HfO2 using random telegraph noise signals from scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Thamankar, R.; Raghavan, N.; Molina, J.; Puglisi, F. M.; O'Shea, S. J.; Shubhakar, K.; Larcher, L.; Pavan, P.; Padovani, A.; Pey, K. L.

    2016-02-01

    Random telegraph noise (RTN) measurements are typically carried out at the device level using standard probe station based electrical characterization setup, where the measured current represents a cumulative effect of the simultaneous response of electron capture/emission events at multiple oxygen vacancy defect (trap) sites. To better characterize the individual defects in the high-κ dielectric thin film, we propose and demonstrate here the measurement and analysis of RTN at the nanoscale using a room temperature scanning tunneling microscope setup, with an effective area of interaction of the probe tip that is as small as 10 nm in diameter. Two-level and multi-level RTN signals due to single and multiple defect locations (possibly dispersed in space and energy) are observed on 4 nm HfO2 thin films deposited on n-Si (100) substrate. The RTN signals are statistically analyzed using the Factorial Hidden Markov Model technique to decode the noise contribution of more than one defect (if any) and estimate the statistical parameters of each RTN signal (i.e., amplitude of fluctuation, capture and emission time constants). Observation of RTN at the nanoscale presents a new opportunity for studies on defect chemistry, single-defect kinetics and their stochastics in thin film dielectric materials. This method allows us to characterize the fast traps with time constants ranging in the millisecond to tens of seconds range.

  7. Ferroelectricity of nondoped thin HfO2 films in TiN/HfO2/TiN stacks

    NASA Astrophysics Data System (ADS)

    Nishimura, Tomonori; Xu, Lun; Shibayama, Shigehisa; Yajima, Takeaki; Migita, Shinji; Toriumi, Akira

    2016-08-01

    We report on the impact of TiN interfaces on the ferroelectricity of nondoped HfO2. Ferroelectric properties of nondoped HfO2 in TiN/HfO2/TiN stacks are shown in capacitance–voltage and polarization–voltage characteristics. The Curie temperature is also estimated to be around 500 °C. The ferroelectricity of nondoped HfO2 clearly appears by thinning HfO2 film down to ∼35 nm. We directly revealed in thermal treatments that the ferroelectric HfO2 film on TiN was maintained by covering the top surface of HfO2 with TiN, while it was followed by a phase transition to the paraelectric phase in the case of the open surface of HfO2. Thus, it is concluded that the ferroelectricity in nondoped HfO2 in this study was mainly driven by both of top and bottom TiN interfaces.

  8. Monolayer-level controlled incorporation of nitrogen in ultra-thin gate dielectrics using remote plasma processing

    NASA Astrophysics Data System (ADS)

    Niimi, Hiroaki

    A low thermal budget approach to monolayer-level controlled incorporation of nitrogen in ultra-thin gate dielectrics using remote plasma processing is discussed. Incorporation of nitrogen at the Si-SiO2 interface, 'N-O' structure, is achieved by 300°C O2/He remote plasma assisted oxidation of the Si surface followed by N2/He remote plasma nitridation at 0.3 Torr. Secondary ion mass spectroscopy (SIMS) showed that the interfacial nitrogen concentration was linearly proportional to the N2/He plasma exposure time. One monolayer of nitrogen, ˜ 7 x 1014 cm-2, at the Si-SiO 2 interface was achieved by the 90-second N2/He plasma nitridation. This monolayer of nitrogen at the interface reduced leakage currents in Fowler-Nordheim (F-N) and direct tunneling regimes. Core-level photoemission spectroscopy (PES) revealed that the post-oxidation nitridation reduced sub-oxide densities at the interface. This interfacial 'modification' contributed to the reduction of tunneling currents. Incorporation of nitrogen on the top surface of oxide, 'O-N' structure, is achieved by 300°C N2/He remote plasma nitridation of the bulk oxide at 0.1 Torr. SIMS data showed the nitrogen was confined only at the top surface of oxide. This top surface 'nitrided' layer suppressed boron diffusion from boron doped p+ poly-Si gate-electrodes. Thus, combining interfacial and top surface nitridation processes, ' N-O-N' structure, reduced leakage currents and prevented boron diffusion, so that this combination is applicable for advanced symmetric complementary metal-oxide-semiconductor (CMOS) technology.

  9. Enhancement of the blue photoluminescence intensity for the porous silicon with HfO2 filling into microcavities

    PubMed Central

    Jiang, Ran; Du, Xianghao; Sun, Weideng; Han, Zuyin; Wu, Zhengran

    2015-01-01

    With HfO2 filled into the microcavities of the porous single-crystal silicon, the blue photoluminescence was greatly enhanced at room temperature. On one hand, HfO2 contributes to the light emission with the transitions of the defect levels for oxygen vacancy. On the other hand, the special filling-into-microcavities structure of HfO2 leads to the presence of ferroelectricity, which greatly enhances the blue emission from porous silicon. Since both HfO2 and Si are highly compatible with Si-based electronic industry, combined the low-cost and convenient process, the HfO2-filled porous Si shows a promising application prospect. PMID:26503804

  10. Growth and thermal annealing of Cu on HfO 2

    NASA Astrophysics Data System (ADS)

    Park, H. J.; Sun, Y.-M.; Troiani, H.; Santiago, P.; Yacaman, M. J.; White, J. M.

    2002-12-01

    The interface between Cu and HfO 2 synthesized using physical vapor deposition at 300 K has been examined with in situ low-energy ion scattering (LEIS), in situ X-ray photoelectron spectroscopy (XPS) and ex situ scanning transmission electron microscopy (STEM). Cu deposited on HfO 2 at 300 K readily forms three-dimensional clusters. LEIS and XPS data show that the Cu is not oxidized at the Cu-HfO 2 interface. A proposed model allows simulation of the coverage of Cu as a function of Cu dosing time before and after thermal annealing. At 300 K, the model fits the data when two-dimensional islands cover no more than 90% of the HfO 2 surface. After thermal annealing at 673 K for 10 min under vacuum (1×10 -8 Torr), large Cu clusters are formed from smaller ones, but there is no evident diffusion into the HfO 2. For this annealed sample, STEM shows a narrow cluster diameter distribution (10-12 nm). Strain fields at the hafnia-copper interface may help limit the cluster size distribution.

  11. Growth of epitaxial orthorhombic YO1.5-substituted HfO2 thin film

    NASA Astrophysics Data System (ADS)

    Shimizu, Takao; Katayama, Kiliha; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Funakubo, Hiroshi

    2015-07-01

    YO1.5-substituted HfO2 thin films with various substitution amounts were grown on (100) YSZ substrates by the pulsed laser deposition method directly from the vapor phase. The epitaxial growth of film with different YO1.5 amounts was confirmed by the X-ray diffraction method. Wide-area reciprocal lattice mapping measurements were performed to clarify the crystal symmetry of films. The formed phases changed from low-symmetry monoclinic baddeleyite to high-symmetry tetragonal/cubic fluorite phases through an orthorhombic phase as the YO1.5 amount increased from 0 to 0.15. The additional annular bright-field scanning transmission electron microscopy indicates that the orthorhombic phase has polar structure. This means that the direct growth by vapor is of polar orthorhombic HfO2-based film. Moreover, high-temperature X-ray diffraction measurements showed that the film with a YO1.5 amount of 0.07 with orthorhombic structure at room temperature only exhibited a structural phase transition to tetragonal phase above 450 °C. This temperature is much higher than the reported maximum temperature of 200 °C to obtain ferroelectricity as well as the expected temperature for real device application. The growth of epitaxial orthorhombic HfO2-based film helps clarify the nature of ferroelectricity in HfO2-based films (186 words/200 words).

  12. Microstructure dependent filament forming kinetics in HfO2 programmable metallization cells.

    PubMed

    Clarke, Heidi; Brown, Timothy; Hu, Jianjun; Ganguli, Raj; Reed, Amber; Voevodin, Andrey; Shamberger, Patrick J

    2016-10-21

    Variability remains the principal concern for commercialization of HfO2 based resistance switching devices. Here, we investigate the role of thermal processing conditions on internal structure of atomic layer deposited HfO2 thin films, and the impact of that structure on filament forming kinetics of p+ Si/HfO2/Cu and TiN/HfO2/Cu devices. Regardless of bias polarity or electrode metal, filament formation times are at least one order of magnitude shorter in polycrystalline than in amorphous films, which we attribute to the presence of fast ion migration along grain boundaries. Within polycrystalline films, filament formation times are correlated with degree of crystalline orientation. Inter-device variability in forming time is roughly equivalent across HfO2 film processing conditions. The kinetics of filament forming are shown to be highly dependent on HfO2 microstructure, with possible implications for the inter-device variability of subsequent switching cycles. PMID:27632249

  13. Thermal Conductivity and Water Vapor Stability of Ceramic HfO2-Based Coating Materials

    NASA Technical Reports Server (NTRS)

    Zhu, Dong-Ming; Fox, Dennis S.; Bansal, Narottam P.; Miller, Robert A.

    2004-01-01

    HfO2-Y2O3 and La2Zr2O7 are candidate thermal/environmental barrier coating materials for gas turbine ceramic matrix composite (CMC) combustor liner applications because of their relatively low thermal conductivity and high temperature capability. In this paper, thermal conductivity and high temperature phase stability of plasma-sprayed coatings and/or hot-pressed HfO2-5mol%Y2O3, HfO2-15mol%Y2O3 and La2Zr2O7 were evaluated at temperatures up to 1700 C using a steady-state laser heat-flux technique. Sintering behavior of the plasma-sprayed coatings was determined by monitoring the thermal conductivity increases during a 20-hour test period at various temperatures. Durability and failure mechanisms of the HfO2-Y2O3 and La2Zr2O7 coatings on mullite/SiC Hexoloy or CMC substrates were investigated at 1650 C under thermal gradient cyclic conditions. Coating design and testing issues for the 1650 C thermal/environmental barrier coating applications will also be discussed.

  14. Thermal Conductivity and Water Vapor Stability of HfO2-based Ceramic Coating Materials

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Fox, Dennis S.; Bansal, Narottam P.; Miller, Robert A.

    2004-01-01

    HfO2-Y2O3 and La2Zr2O7 are candidate thermal/environmental barrier coating materials for gas turbine ceramic matrix composite (CMC) combustor liner applications because of their relatively low thermal conductivity and high temperature capability. In this paper, thermal conductivity and high temperature phase stability of plasma-sprayed coatings and/or hot-pressed HfO2-5mol%Y2O3, HfO2- 15mol%Y2O3 and La2Zr2O7 were evaluated at temperatures up to 1700 C using a steady-state laser heat-flux technique. Sintering behavior of the plasma-sprayed coatings was determined by monitoring the thermal conductivity increases during a 20-hour test period at various temperatures. Durability and failure mechanisms of the HfO2-Y2O3 and La2Zr2O7 coatings on mullite/SiC Hexoloy or CMC substrates were investigated at 1650 C under thermal gradient cyclic conditions. Coating design and testing issues for the 1650 C thermaVenvironmenta1 barrier coating applications will also be discussed.

  15. Flexible FETs using ultrathin Si microwires embedded in solution processed dielectric and metal layers

    NASA Astrophysics Data System (ADS)

    Khan, S.; Yogeswaran, N.; Taube, W.; Lorenzelli, L.; Dahiya, R.

    2015-12-01

    This work presents a novel manufacturing route for obtaining high performance bendable field effect transistors (FET) by embedding silicon (Si) microwires (2.5 μm thick) in layers of solution-processed dielectric and metallic layers. The objective of this study is to explore heterogeneous integration of Si with polymers and to exploit the benefits of both microelectronics and printing technologies. Arrays of Si microwires are developed on silicon on insulator (SOI) wafers and transfer printed to polyimide (PI) substrate through a polydimethylsiloxane (PDMS) carrier stamp. Following the transfer printing of Si microwires, two different processing steps were developed to obtain top gate top contact and back gate top contact FETs. Electrical characterizations indicate devices having mobility as high as 117.5 cm2 V-1 s-1. The fabricated devices were also modeled using SILVACO Atlas. Simulation results show a trend in the electrical response similar to that of experimental results. In addition, a cyclic test was performed to demonstrate the reliability and mechanical robustness of the Si μ-wires on flexible substrates.

  16. Mesostructured HfxAlyO2 Thin Films as Reliable and Robust Gate Dielectrics with Tunable Dielectric Constants for High-Performance Graphene-Based Transistors.

    PubMed

    Lee, Yunseong; Jeon, Woojin; Cho, Yeonchoo; Lee, Min-Hyun; Jeong, Seong-Jun; Park, Jongsun; Park, Seongjun

    2016-07-26

    We introduce a reliable and robust gate dielectric material with tunable dielectric constants based on a mesostructured HfxAlyO2 film. The ultrathin mesostructured HfxAlyO2 film is deposited on graphene via a physisorbed-precursor-assisted atomic layer deposition process and consists of an intermediate state with small crystallized parts in an amorphous matrix. Crystal phase engineering using Al dopant is employed to achieve HfO2 phase transitions, which produce the crystallized part of the mesostructured HfxAlyO2 film. The effects of various Al doping concentrations are examined, and an enhanced dielectric constant of ∼25 is obtained. Further, the leakage current is suppressed (∼10(-8) A/cm(2)) and the dielectric breakdown properties are enhanced (breakdown field: ∼7 MV/cm) by the partially remaining amorphous matrix. We believe that this contribution is theoretically and practically relevant because excellent gate dielectric performance is obtained. In addition, an array of top-gated metal-insulator-graphene field-effect transistors is fabricated on a 6 in. wafer, yielding a capacitance equivalent oxide thickness of less than 1 nm (0.78 nm). This low capacitance equivalent oxide thickness has important implications for the incorporation of graphene into high-performance silicon-based nanoelectronics. PMID:27355098

  17. Post-Cleaning Effect on a HfO2 Gate Stack Using a NF3/NH3 Plasma.

    PubMed

    Lee, Min-Seon; Oh, Hoon-Jung; Lee, Joo-Hee; Lee, In-Geun; Shin, Woo-Gon; Kim, Kyu-Dong; Park, Jin-Gu; Ko, Dae-Hong

    2016-05-01

    The effects of dry cleaning of a HfO2 gate stack using NF3 only and a NF3/NH3 gas mixture plasma were investigated. The plasma dry cleaning process was carried out after HfO2 deposition using an indirect down-flow capacitively coupled plasma (CCP) system. An analysis of the chemical composition of the HfO2 gate stacks by XPS indicated that fluorine was incorporated into the HfO2 films during the plasma dry cleaning. Significant changes in the HfO2 chemical composition were observed as a result of the NF3 dry cleaning, while they were not observed in this case of NF3/NH3 dry cleaning. TEM results showed that the interfacial layer (IL) between the HfO2 and Si thickness was increased by the plasma dry cleaning. However, in the case of NF3/NH3 dry cleaning using 150 W, the IL thickness was suppressed significantly compared to the sample that had not been dry cleaned. Its electrical properties were also improved, including the low gate leakage currents, and reduced EOT. Finally, the finding show that the IL thickness of the HfO2 gate stack can be controlled by using the novel NF3/NH3 dry cleaning process technique without any the significant changes in chemical composition and metal-oxide-semiconductor (MOS) capacitor characteristics. PMID:27483826

  18. Thermodynamic mixing properties of the UO2-HfO2 solid solution: Density functional theory and Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Yuan, Ke; Ewing, Rodney C.; Becker, Udo

    2015-03-01

    HfO2 is a neutron absorber and has been mechanically mixed with UO2 in nuclear fuel in order to control the core power distribution. During nuclear fission, the temperature at the center of the fuel pellet can reach above 1300 K, where hafnium may substitute uranium and form the binary solid solution of UO2-HfO2. UO2 adopts the cubic fluorite structure, but HfO2 can occur in monoclinic, tetragonal, and cubic structures. The distribution of Hf and U ions in the UO2-HfO2 binary and its atomic structure influence the thermal conductivity and melting point of the fuel. However, experimental data on the UO2-HfO2 binary are limited. Therefore, the enthalpies of mixing of the UO2-HfO2 binary with three different structures were calculated in this study using density functional theory and subsequent Monte Carlo simulations. The free energy of mixing was obtained from thermodynamic integration of the enthalpy of mixing over temperature. From the ΔG of mixing, a phase diagram of the binary was obtained. The calculated UO2-HfO2 binary forms extensive solid solution across the entire compositional range, but there are a variety of possible exsolution phenomena associated with the different HfO2 polymorphs. As the structure of the HfO2 end member adopts lower symmetry and becomes less similar to cubic UO2, the miscibility gap of the phase diagram expands, accompanied by an increase in cell volume by 7-10% as the structure transforms from cubic to monoclinic. Close to the UO2 end member, which is relevant to the nuclear fuel, the isometric uranium-rich solid solutions exsolve as the fuel cools, and there is a tendency to form the monoclinic hafnium-rich phase in the matrix of the isometric, uranium-rich solid solution phase.

  19. HfO2 on UV-O3 exposed transition metal dichalcogenides: interfacial reactions study

    NASA Astrophysics Data System (ADS)

    Azcatl, Angelica; KC, Santosh; Peng, Xin; Lu, Ning; McDonnell, Stephen; Qin, Xiaoye; de Dios, Francis; Addou, Rafik; Kim, Jiyoung; Kim, Moon J.; Cho, Kyeongjae; Wallace, Robert M.

    2015-03-01

    The surface chemistry of MoS2, WSe2 and MoSe2 upon ultraviolet (UV)-O3 exposure was studied in situ by x-ray photoelectron spectroscopy (XPS). Differences in reactivity of these transition metal dichalcogenides (TMDs) towards oxidation during UV-O3 were observed and correlated with density functional theory calculations. Also, sequential HfO2 depositions were performed by atomic layer deposition (ALD) while the interfacial reactions were monitored by XPS. It is found that the surface oxides generated on MoSe2 and WSe2 during UV-O3 exposure were reduced by the ALD process (‘self-cleaning effect’). The effectiveness of the oxide reduction on these TMDs is discussed and correlated with the HfO2 film uniformity.

  20. Grain boundary mediated leakage current in polycrystalline HfO2 films

    SciTech Connect

    Mckenna, Keith P.; Shluger, AL; Iglesias, V.; Porti, M.; Nafria, M.; Lanza, M.; Bersuker, G.

    2011-07-01

    In this work, we combine conductive atomic force microscopy (CAFM) and first principles calculations to investigate leakage current in thin polycrystalline HfO2 films. A clear correlation between the presence of grain boundaries and increased leakage current through the film is demonstrated. The effect is a result of a number of related factors, including local reduction in the oxide film thickness near grain boundaries, the intrinsic electronic properties of grain boundaries which enhance direct tunnelling relative to the bulk, and segregation of oxygen vacancy defects which increase trap assisted tunnelling currents. These results highlight the important role of grain boundaries in determining the electrical properties of polycrystalline HfO2 films with relevance to applications in advanced logic and memory devices.

  1. Silicon surface passivation using thin HfO2 films by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Gope, Jhuma; Vandana; Batra, Neha; Panigrahi, Jagannath; Singh, Rajbir; Maurya, K. K.; Srivastava, Ritu; Singh, P. K.

    2015-12-01

    Hafnium oxide (HfO2) is a potential material for equivalent oxide thickness (EOT) scaling in microelectronics; however, its surface passivation properties particularly on silicon are not well explored. This paper reports investigation on passivation properties of thermally deposited thin HfO2 films by atomic layer deposition system (ALD) on silicon surface. As-deposited pristine film (∼8 nm) shows better passivation with <100 cm/s surface recombination velocity (SRV) vis-à-vis thicker films. Further improvement in passivation quality is achieved with annealing at 400 °C for 10 min where the SRV reduces to ∼20 cm/s. Conductance measurements show that the interface defect density (Dit) increases with film thickness whereas its value decreases after annealing. XRR data corroborate with the observations made by FTIR and SRV data.

  2. Effect of calcination temperature on phase transformation of HfO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Tripathi, S. K.; Kaur, Charanpreet; Kaur, Ramneek; Kaur, Jagdish

    2015-08-01

    Oxides nanomaterials exhibit unique physical, chemical and structural properties and motivated a big research that focus in the integration of these materials for various optoelectronic device applications. In present work, hafnium oxide (HfO2) nanoparticles (NPs) have been synthesized using precipitation method. Hafnium tetrachloride and sodium hydroxide has been used as starting precursors. Prepared oxide material has been characterized by X-Ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR) and UV-Vis spectroscopy. The phase transformation from amorphous to monoclinic is observed with the increase in calcination temperature from 500 °C and 800 °C. In FTIR spectra, the characteristic bands at ν ˜ 758.53 and 509.57 cm-1 reveals the monoclinic phase of prepared HfO2 NPs. UV-Vis spectroscopy shows an absorption peak at 204 nm and the bandgap calculated is 6.07 eV.

  3. Design and Fabrication of Interdigital Nanocapacitors Coated with HfO2

    PubMed Central

    González, Gabriel; Kolosovas-Machuca, Eleazar Samuel; López-Luna, Edgar; Hernández-Arriaga, Heber; González, Francisco Javier

    2015-01-01

    In this article nickel interdigital capacitors were fabricated on top of silicon substrates. The capacitance of the interdigital capacitor was optimized by coating the electrodes with a 60 nm layer of HfO2. An analytical solution of the capacitance was compared to electromagnetic simulations using COMSOL and with experimental measurements. Results show that modeling interdigital capacitors using Finite Element Method software such as COMSOL is effective in the design and electrical characterization of these transducers. PMID:25602271

  4. Design and Fabrication of Interdigital Nanocapacitors Coated with HfO2.

    PubMed

    González, Gabriel; Kolosovas-Machuca, Eleazar Samuel; López-Luna, Edgar; Hernández-Arriaga, Heber; González, Francisco Javier

    2015-01-01

    In this article nickel interdigital capacitors were fabricated on top of silicon substrates. The capacitance of the interdigital capacitor was optimized by coating the electrodes with a 60 nm layer of HfO2. An analytical solution of the capacitance was compared to electromagnetic simulations using COMSOL and with experimental measurements. Results show that modeling interdigital capacitors using Finite Element Method software such as COMSOL is effective in the design and electrical characterization of these transducers.

  5. Design and Fabrication of Interdigital Nanocapacitors Coated with HfO2.

    PubMed

    González, Gabriel; Kolosovas-Machuca, Eleazar Samuel; López-Luna, Edgar; Hernández-Arriaga, Heber; González, Francisco Javier

    2015-01-01

    In this article nickel interdigital capacitors were fabricated on top of silicon substrates. The capacitance of the interdigital capacitor was optimized by coating the electrodes with a 60 nm layer of HfO2. An analytical solution of the capacitance was compared to electromagnetic simulations using COMSOL and with experimental measurements. Results show that modeling interdigital capacitors using Finite Element Method software such as COMSOL is effective in the design and electrical characterization of these transducers. PMID:25602271

  6. Oxygen vacancy effects in HfO2-based resistive switching memory: First principle study

    NASA Astrophysics Data System (ADS)

    Dai, Yuehua; Pan, Zhiyong; Wang, Feifei; Li, Xiaofeng

    2016-08-01

    The work investigated the shape and orientation of oxygen vacancy clusters in HfO2-base resistive random access memory (ReRAM) by using the first-principle method based on the density functional theory. Firstly, the formation energy of different local Vo clusters was calculated in four established orientation systems. Then, the optimized orientation and charger conductor shape were identified by comparing the isosurface plots of partial charge density, formation energy, and the highest isosurface value of oxygen vacancy. The calculated results revealed that the [010] orientation was the optimal migration path of Vo, and the shape of system D4 was the best charge conductor in HfO2, which effectively influenced the SET voltage, formation voltage and the ON/OFF ratio of the device. Afterwards, the PDOS of Hf near Vo and total density of states of the system D4_010 were obtained, revealing the composition of charge conductor was oxygen vacancy instead of metal Hf. Furthermore, the migration barriers of the Vo hopping between neighboring unit cells were calculated along four different orientations. The motion was proved along [010] orientation. The optimal circulation path for Vo migration in the HfO2 super-cell was obtained.

  7. Distribution of electron traps in SiO2/HfO2 nMOSFET

    NASA Astrophysics Data System (ADS)

    Xiao-Hui, Hou; Xue-Feng, Zheng; Ao-Chen, Wang; Ying-Zhe, Wang; Hao-Yu, Wen; Zhi-Jing, Liu; Xiao-Wei, Li; Yin-He, Wu

    2016-05-01

    In this paper, the principle of discharge-based pulsed I-V technique is introduced. By using it, the energy and spatial distributions of electron traps within the 4-nm HfO2 layer have been extracted. Two peaks are observed, which are located at ΔE ˜ -1.0 eV and -1.43 eV, respectively. It is found that the former one is close to the SiO2/HfO2 interface and the latter one is close to the gate electrode. It is also observed that the maximum discharge time has little effect on the energy distribution. Finally, the impact of electrical stress on the HfO2 layer is also studied. During stress, no new electron traps and interface states are generated. Meanwhile, the electrical stress also has no impact on the energy and spatial distribution of as-grown traps. The results provide valuable information for theoretical modeling establishment, material assessment, and reliability improvement for advanced semiconductor devices. Project supported by the National Natural Science Foundation of China (Grant Nos. 61334002, 61106106, and 61474091), the New Experiment Development Funds for Xidian University, China (Grant No. SY1434), and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry, China (Grant No. JY0600132501).

  8. Ferroelectricity and antiferroelectricity of doped thin HfO2-based films.

    PubMed

    Park, Min Hyuk; Lee, Young Hwan; Kim, Han Joon; Kim, Yu Jin; Moon, Taehwan; Kim, Keum Do; Müller, Johannes; Kersch, Alfred; Schroeder, Uwe; Mikolajick, Thomas; Hwang, Cheol Seong

    2015-03-18

    The recent progress in ferroelectricity and antiferroelectricity in HfO2-based thin films is reported. Most ferroelectric thin film research focuses on perovskite structure materials, such as Pb(Zr,Ti)O3, BaTiO3, and SrBi2Ta2O9, which are considered to be feasible candidate materials for non-volatile semiconductor memory devices. However, these conventional ferroelectrics suffer from various problems including poor Si-compatibility, environmental issues related to Pb, large physical thickness, low resistance to hydrogen, and small bandgap. In 2011, ferroelectricity in Si-doped HfO2 thin films was first reported. Various dopants, such as Si, Zr, Al, Y, Gd, Sr, and La can induce ferro-electricity or antiferroelectricity in thin HfO2 films. They have large remanent polarization of up to 45 μC cm(-2), and their coercive field (≈1-2 MV cm(-1)) is larger than conventional ferroelectric films by approximately one order of magnitude. Furthermore, they can be extremely thin (<10 nm) and have a large bandgap (>5 eV). These differences are believed to overcome the barriers of conventional ferroelectrics in memory applications, including ferroelectric field-effect-transistors and three-dimensional capacitors. Moreover, the coupling of electric and thermal properties of the antiferroelectric thin films is expected to be useful for various applications, including energy harvesting/storage, solid-state-cooling, and infrared sensors.

  9. Study on the formation of self-assembled monolayers on sol-gel processed hafnium oxide as dielectric layers.

    PubMed

    Ting, Guy G; Acton, Orb; Ma, Hong; Ka, Jae Won; Jen, Alex K-Y

    2009-02-17

    High dielectric constant (k) metal oxides such as hafnium oxide (HfO2) have gained significant interest due to their applications in microelectronics. In order to study and control the surface properties of hafnium oxide, self-assembled monolayers (SAMs) of four different long aliphatic molecules with binding groups of phosphonic acid, carboxylic acid, and catechol were formed and characterized. Surface modification was performed to improve the interface between metal oxide and top deposited materials as well as to create suitable dielectric properties, that is, leakage current and capacitance densities, which are important in organic thin film transistors. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, contact angle goniometry, atomic force microscopy (AFM), and simple metal-HfO2-SAM-metal devices were used to characterize the surfaces before and after SAM modification on sol-gel processed hafnium oxide. The alkylphosphonic acid provided the best monolayer formation on sol-gel processed hafnium oxide to generate a well-packed, ultrathin dielectric exhibiting a low leakage current density of 2x10(-8) A/cm2 at an applied voltage of -2.0 V and high capacitance density of 0.55 microF/cm2 at 10 kHz. Dialkylcatechol showed similar characteristics and the potential for using the catechol SAMs to modify HfO2 surfaces. In addition, the integration of this alkylphosphonic acid SAM/hafnium oxide hybrid dielectric into pentacene-based thin film transistors yields low-voltage operation within 1.5 V and improved performance over bare hafnium oxide.

  10. Series resistance effect on time zero dielectrics breakdown characteristics of MOSCAP with ultra-thin EOT high-k/metal gate stacks

    NASA Astrophysics Data System (ADS)

    Hao, Xu; Hong, Yang; Yanrong, Wang; Wenwu, Wang; Guangxing, Wan; Shangqing, Ren; Weichun, Luo; Luwei, Qi; Chao, Zhao; Dapeng, Chen; Xinyu, Liu; Tianchun, Ye

    2016-05-01

    The time zero dielectric breakdown characteristics of MOSCAP with ultra-thin EOT high-k metal gate stacks are studied. The TZDB results show an abnormal area dependence due to the series resistance effect. The series resistance components extracted from the Fowler–Nordheim tunneling relation are attributed to the spreading resistance due to the asymmetry electrodes. Based on a series model to eliminate the series resistance effect, an area acceleration dependence is obtained by correcting the TZDB results. The area dependence follows Poisson area scaling rules, which indicates that the mechanism of TZDB is the same as TDDB and could be considered as a trap generation process. Project supported by the National High Technology Research and Development Program (863 Program) of China (No. SS2015AA010601), the National Natural Science Foundation of China (Nos. 61176091, 61306129), and the Opening Project of the Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences.

  11. Effects of the ratio of O2/Ar pressure on wettability and optical properties of HfO2 films before and after doping with Al

    NASA Astrophysics Data System (ADS)

    Lin, Su-Shia; Liao, Chung-Sheng

    2016-09-01

    HfO2 films were doped with Al (HfO2:Al) by simultaneous RF magnetron sputtering of HfO2 and DC magnetron sputtering of Al. This method is characterized by its ability to independently control the Al content. According to XRD and XPS analyses, the HfO2:Al film had a structure similar to that of HfO2 film, and most of the Al atoms were not in the HfO2 crystalline. A small amount of Al3+ dopant could transform the hydrophobicity of HfO2 films into hydrophilicity. Moreover, the hydrophilicity of the HfO2:Al films improved as the ratio of O2/Ar pressure increased. The nonlinear refractive indices of HfO2 and HfO2:Al films deposited in a pure Ar or a mixed Ar-O2 atmosphere were measured by Moiré deflectometry, and were of the order of 10-8 cm2 W-1. A lower surface roughness, higher optical transmission in the UV-vis-NIR region, and higher linear refractive index were obtained at a higher ratio of O2/Ar pressure.

  12. HfO 2 -based ferroelectric modulator of terahertz waves with graphene metamaterial

    NASA Astrophysics Data System (ADS)

    Jiang, Ran; Wu, Zheng-Ran; Han, Zu-Yin; Jung, Hyung-Suk

    2016-10-01

    Tunable modulations of terahertz waves in a graphene/ferroelectric-layer/silicon hybrid structure are demonstrated at low bias voltages. The modulation is due to the creation/elimination of an extra barrier in Si layer in response to the polarization in the ferroelectric Si:HfO2 layer. Considering the good compatibility of HfO2 with the Si-based semiconductor process, the highly tunable characteristics of the graphene metamaterial device under ferroelectric effect open up new avenues for graphene-based high performance integrated active photonic devices compatible with the silicon technology. Project supported by the National Natural Science Foundation of China (Grant No. 11374182).

  13. Characterization of nanostructured HfO 2 films using RBS and PAC

    NASA Astrophysics Data System (ADS)

    Cavalcante, F. H. M.; Gomes, M. R.; Carbonari, A. W.; Pereira, L. F. D.; Rossetto, D. A.; Costa, M. S.; Alves, E.; Barradas, N. P.; Franco, N.; Redondo, L. M.; Lopes, A. M. L.; Soares, J. C.

    2012-02-01

    The hyperfine field at 181Ta lattice sites in a nanostructured HfO 2 thin film doped with Fe was studied using Rutherford Backscattering Spectrometry and Perturbed Angular Correlation techniques. The 409 nm Hf film was deposited by Electron Beam Evaporation on a silicon substrate. The radioactive 181Hf ions were produced by neutron activation of the nanofilm in the Brazilian Research Reactor (IPEN IEA-R1) by the reaction 180Hf(n,γ) 181Hf. These studies provided an excellent opportunity to obtain unique information regarding local arrangement of the grains, structure, phase transformations of nanoparticles and interfaces of nanostructured materials and the thin film.

  14. Characterization of nanostructured HfO2 films using Perturbed Angular Correlation (PAC) technique

    NASA Astrophysics Data System (ADS)

    Cavalcante, F. H. M.; Gomes, M. R.; Carbonari, A. W.; Pereira, L. F. D.; Rossetto, D. A.; Costa, M. S.; Redondo, L. M.; Mestnik-Filho, J.; Saxena, R. N.; Soares, J. C.

    2010-06-01

    The hyperfine field at 181Ta lattice sites in nanostructured HfO2 thin films was studied by the Perturbed Angular Correlation (PAC) technique. Thin oxide films were deposited by Electron Beam Evaporation on a silicon substrate. The thickness of the films was ~100 nm and ~250 nm. Radioactive 181Hf nuclei were produced by neutron activation of the film samples in the Brazilian Research Reactor (IPEN IEA-R1) by the reaction 180Hf(n, γ)181Hf. PAC measurements were carried out after annealing at 1473 K. The PAC technique allows the determination of the electric field gradient (EFG) at the probe sites.

  15. Effects of different dopants on switching behavior of HfO2-based resistive random access memory

    NASA Astrophysics Data System (ADS)

    Deng, Ning; Pang, Hua; Wu, Wei

    2014-10-01

    In this study the effects of doping atoms (Al, Cu, and N) with different electro-negativities and ionic radii on resistive switching of HfO2-based resistive random access memory (RRAM) are systematically investigated. The results show that forming voltages and set voltages of Al/Cu-doped devices are reduced. Among all devices, Cu-doped device shows the narrowest device-to-device distributions of set voltage and low resistance. The effects of different dopants on switching behavior are explained with deferent types of CFs formed in HfO2 depending on dopants: oxygen vacancy (Vo) filaments for Al-doped HfO2 devices, hybrid filaments composed of oxygen vacancies and Cu atoms for Cu-doped HfO2 devices, and nitrogen/oxygen vacancy filaments for N-doped HfO2 devices. The results suggest that a metal dopant with a larger electro-negativity than host metal atom offers the best comprehensive performance.

  16. Theoretical prediction of ion conductivity in solid state HfO2

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Chen, Wen-Zhou; Sun, Jiu-Yu; Jiang, Zhen-Yi

    2013-01-01

    A theoretical prediction of ion conductivity for solid state HfO2 is carried out in analogy to ZrO2 based on the density functional calculation. Geometric and electronic structures of pure bulks exhibit similarity for the two materials. Negative formation enthalpy and negative vacancy formation energy are found for YSH (yttria-stabilized hafnia) and YSZ (yttria-stabilized zirconia), suggesting the stability of both materials. Low activation energies (below 0.7 eV) of diffusion are found in both materials, and YSH's is a little higher than that of YSZ. In addition, for both HfO2 and ZrO2, the supercells with native oxygen vacancies are also studied. The so-called defect states are observed in the supercells with neutral and +1 charge native vacancy but not in the +2 charge one. It can give an explanation to the relatively lower activation energies of yttria-doped oxides and +2 charge vacancy supercells. A brief discussion is presented to explain the different YSH ion conductivities in the experiment and obtained by us, and we attribute this to the different ion vibrations at different temperatures.

  17. Thickness dependent wetting properties and surface free energy of HfO2 thin films

    NASA Astrophysics Data System (ADS)

    Zenkin, Sergei; Belosludtsev, Alexandr; Kos, Šimon; Čerstvý, Radomír; Haviar, Stanislav; Netrvalová, Marie

    2016-06-01

    We show here that intrinsic hydrophobicity of HfO2 thin films can be easily tuned by the variation of film thickness. We used the reactive high-power impulse magnetron sputtering for preparation of high-quality HfO2 films with smooth topography and well-controlled thickness. Results show a strong dependence of wetting properties on the thickness of the film in the range of 50-250 nm due to the dominance of the electrostatic Lifshitz-van der Waals component of the surface free energy. We have found the water droplet contact angle ranging from ≈120° for the thickness of 50 nm to ≈100° for the thickness of 2300 nm. At the same time the surface free energy grows from ≈25 mJ/m2 for the thickness of 50 nm to ≈33 mJ/m2 for the thickness of 2300 nm. We propose two explanations for the observed thickness dependence of the wetting properties: influence of the non-dominant texture and/or non-monotonic size dependence of the particle surface energy.

  18. The demonstration of significant ferroelectricity in epitaxial Y-doped HfO2 film.

    PubMed

    Shimizu, Takao; Katayama, Kiliha; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J; Sakata, Osami; Funakubo, Hiroshi

    2016-01-01

    Ferroelectricity and Curie temperature are demonstrated for epitaxial Y-doped HfO2 film grown on (110) yttrium oxide-stabilized zirconium oxide (YSZ) single crystal using Sn-doped In2O3 (ITO) as bottom electrodes. The XRD measurements for epitaxial film enabled us to investigate its detailed crystal structure including orientations of the film. The ferroelectricity was confirmed by electric displacement filed - electric filed hysteresis measurement, which revealed saturated polarization of 16 μC/cm(2). Estimated spontaneous polarization based on the obtained saturation polarization and the crystal structure analysis was 45 μC/cm(2). This value is the first experimental estimations of the spontaneous polarization and is in good agreement with the theoretical value from first principle calculation. Curie temperature was also estimated to be about 450 °C. This study strongly suggests that the HfO2-based materials are promising for various ferroelectric applications because of their comparable ferroelectric properties including polarization and Curie temperature to conventional ferroelectric materials together with the reported excellent scalability in thickness and compatibility with practical manufacturing processes. PMID:27608815

  19. Morphology and Photoluminescence of HfO2Obtained by Microwave-Hydrothermal

    PubMed Central

    2009-01-01

    In this letter, we report on the obtention of hafnium oxide (HfO2) nanostructures by the microwave-hydrothermal method. These nanostructures were analyzed by X-ray diffraction (XRD), field-emission gum scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDXS), ultraviolet–visible (UV–vis) spectroscopy, and photoluminescence (PL) measurements. XRD patterns confirmed that this material crystallizes in a monoclinic structure. FEG-SEM and TEM micrographs indicated that the rice-like morphologies were formed due to an increase in the effective collisions between the nanoparticles during the MH processing. The EDXS spectrum was used to verify the chemical compositional of this oxide. UV–vis spectrum revealed that this material have an indirect optical band gap. When excited with 488 nm wavelength at room temperature, the HfO2nanostructures exhibited only one broad PL band with a maximum at around 548 nm (green emission). PMID:20628455

  20. The demonstration of significant ferroelectricity in epitaxial Y-doped HfO2 film

    PubMed Central

    Shimizu, Takao; Katayama, Kiliha; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Sakata, Osami; Funakubo, Hiroshi

    2016-01-01

    Ferroelectricity and Curie temperature are demonstrated for epitaxial Y-doped HfO2 film grown on (110) yttrium oxide-stabilized zirconium oxide (YSZ) single crystal using Sn-doped In2O3 (ITO) as bottom electrodes. The XRD measurements for epitaxial film enabled us to investigate its detailed crystal structure including orientations of the film. The ferroelectricity was confirmed by electric displacement filed – electric filed hysteresis measurement, which revealed saturated polarization of 16 μC/cm2. Estimated spontaneous polarization based on the obtained saturation polarization and the crystal structure analysis was 45 μC/cm2. This value is the first experimental estimations of the spontaneous polarization and is in good agreement with the theoretical value from first principle calculation. Curie temperature was also estimated to be about 450 °C. This study strongly suggests that the HfO2-based materials are promising for various ferroelectric applications because of their comparable ferroelectric properties including polarization and Curie temperature to conventional ferroelectric materials together with the reported excellent scalability in thickness and compatibility with practical manufacturing processes. PMID:27608815

  1. The demonstration of significant ferroelectricity in epitaxial Y-doped HfO2 film

    NASA Astrophysics Data System (ADS)

    Shimizu, Takao; Katayama, Kiliha; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Sakata, Osami; Funakubo, Hiroshi

    2016-09-01

    Ferroelectricity and Curie temperature are demonstrated for epitaxial Y-doped HfO2 film grown on (110) yttrium oxide-stabilized zirconium oxide (YSZ) single crystal using Sn-doped In2O3 (ITO) as bottom electrodes. The XRD measurements for epitaxial film enabled us to investigate its detailed crystal structure including orientations of the film. The ferroelectricity was confirmed by electric displacement filed – electric filed hysteresis measurement, which revealed saturated polarization of 16 μC/cm2. Estimated spontaneous polarization based on the obtained saturation polarization and the crystal structure analysis was 45 μC/cm2. This value is the first experimental estimations of the spontaneous polarization and is in good agreement with the theoretical value from first principle calculation. Curie temperature was also estimated to be about 450 °C. This study strongly suggests that the HfO2-based materials are promising for various ferroelectric applications because of their comparable ferroelectric properties including polarization and Curie temperature to conventional ferroelectric materials together with the reported excellent scalability in thickness and compatibility with practical manufacturing processes.

  2. HfO2/Al2O3 multilayer for RRAM arrays: a technique to improve tail-bit retention.

    PubMed

    Huang, Xueyao; Wu, Huaqiang; Bin Gao; Sekar, Deepak C; Dai, Lingjun; Kellam, Mark; Bronner, Gary; Deng, Ning; Qian, He

    2016-09-30

    In this work, the HfO2/Al2O3 multilayer structure is applied for RRAM arrays. Compared to HfO2 RRAM, the data retention failure of tail bits is suppressed significantly, especially for the high resistance state (HRS). The retention of tail bits is studied in detail by temperature simulation and crystallization analysis. We attribute the improvement of tail-bit retention to the decreased oxygen ion diffusivity caused by the Al2O3 layer. Furthermore, the HfO2/Al2O3 multilayer structure exhibits higher crystallization temperature, thus leading to fewer grain boundaries around the filament during the operations. With fewer grain boundaries, oxygen ion diffusion is suppressed, leading to fewer tail bits and better retention. PMID:27537613

  3. Resistance change in memory structures integrating CuTCNQ nanowires grown on dedicated HfO 2 switching layer

    NASA Astrophysics Data System (ADS)

    Muller, Ch.; Deleruyelle, D.; Müller, R.; Thomas, M.; Demolliens, A.; Turquat, Ch.; Spiga, S.

    2011-02-01

    The present paper deals with the bipolar resistive switching of memory elements based on metal-organic complex CuTCNQ (copper-7,7',8,8'-tetracyanoquinodimethane) nanowires grown on a dedicated HfO2 oxide switching layer. Switching characteristics are explored either at millimeter scale on pad-size devices or at nanoscale by using conductive atomic force microscopy. Whatever the investigation scales, the basic memory characteristics appear to be controlled by copper ionic transport within a switching layer. This latter corresponds to either HfO2 layer in pad-size devices or nanogap formed at nanoscale between the atomic force microscopy conductive tip and CuTCNQ surface. Depending upon the observation scale, the switching layer (either HfO2 oxide or nanogap) acts as a matrix in which copper conductive bridges are formed and dissolved thanks to redox processes controlled in alternating applied bias voltages.

  4. HfO2/Al2O3 multilayer for RRAM arrays: a technique to improve tail-bit retention

    NASA Astrophysics Data System (ADS)

    Huang, Xueyao; Wu, Huaqiang; Gao, Bin; Sekar, Deepak C.; Dai, Lingjun; Kellam, Mark; Bronner, Gary; Deng, Ning; Qian, He

    2016-09-01

    In this work, the HfO2/Al2O3 multilayer structure is applied for RRAM arrays. Compared to HfO2 RRAM, the data retention failure of tail bits is suppressed significantly, especially for the high resistance state (HRS). The retention of tail bits is studied in detail by temperature simulation and crystallization analysis. We attribute the improvement of tail-bit retention to the decreased oxygen ion diffusivity caused by the Al2O3 layer. Furthermore, the HfO2/Al2O3 multilayer structure exhibits higher crystallization temperature, thus leading to fewer grain boundaries around the filament during the operations. With fewer grain boundaries, oxygen ion diffusion is suppressed, leading to fewer tail bits and better retention.

  5. RF Micro-Electro-Mechanical Systems Capacitive Switches Using Ultra Thin Hafnium Oxide Dielectric

    NASA Astrophysics Data System (ADS)

    Zhang, Yi; Onodera, Kazumasa; Maeda, Ryutaro

    2006-01-01

    A π-type RF capacitive switch using about 45-nm-thick HfO2 dielectric layer was fabricated. High isolation performance was obtained in wide-band range when the switch was down-state. The isolation was better than -40 dB at the frequency range of 4-35 GHz. Particularly, the isolation was better than -50 dB in the frequency range of 8-12 GHz, i.e., X band. HfO2 showed excellent process compatibility with conventional microfabrication procedure. The 45-nm-thick HfO2 film was prepared using sputtering at room temperature so that it was feasible to be integrated into RF switch and other microwave circuits. The results of constant bias stressing showed that the ultra thin HfO2 had excellent reliability. The electric breakdown of HfO2 was observed, which had no apparent negative effects on the reliability of the dielectric. HfO2 dielectrics were attractive in the application of RF micro-electro-mechanical systems (MEMS) switch for new generation of low-loss high-linearity microwave circuits.

  6. Improved Reliability of InGaN-Based Light-Emitting Diodes by HfO2 Passivation Layer.

    PubMed

    Park, Seung Hyun; Kim, Yoon Seok; Kim, Tae Hoon; Ryu, Sang Wan

    2016-02-01

    We utilized a passivation layer to improve the leakage current and reliability characteristics of GaN-based light-emitting diodes. The electrical and optical characteristics of the fabricated LEDs were characterized by current-voltage and optical power measurements. The HfO2 passivation layer showed no optical power degradation and suppressed leakage current. The low deposition temper- ature of sputtered HfO2 is responsible for the improved reliability of the LEDs because it suppresses the diffusion of hydrogen plasma into GaN to form harmful Mg-H complexes. PMID:27433667

  7. Self-compliance multilevel storage characteristic in HfO2-based device

    NASA Astrophysics Data System (ADS)

    Gao, Xiao-Ping; Fu, Li-Ping; Chen, Chuan-Bing; Yuan, Peng; Li, Ying-Tao

    2016-10-01

    In this paper, the self-compliance bipolar resistive switching characteristic of an HfO2-based memory device with Ag/HfO2/Au structure for multilevel storage is investigated. By applying a positive voltage, the dual-step set processes corresponding to three stable resistance states are observed in the device. The multilevel switching characteristics can still be observed after 48 hours. In addition, the resistance values of all the three states show negligible degradation over 104 s, which may be useful for the applications in nonvolatile multilevel storage. Project supported by the National Natural Science Foundation of China (Grant Nos. 61664001, 61574070, and 61306148) and the Application Research and Development Plan of Gansu Academy of Sciences, China (Grant Nos. 2015JK-11 and 2015JK-01).

  8. Perturbed angular correlation study of a nanostructured HfO2 film

    NASA Astrophysics Data System (ADS)

    Pasquevich, A. F.; Cavalcante, F. H. M.; Soares, J. C.

    2007-09-01

    The hyperfine field at 181Ta lattice sites in a nanostructured HfO2 thin film was studied by the perturbed angular correlation (PAC) technique. The thin oxide film was deposited by pulsed laser ablation on a silicon substrate kept at 673 K. The thickness was about 25 nm. The radioactive 181Hf ions were produced by neutron activation of the very thin film in the Portuguese research reactor by the reaction 180Hf(n, γ)181Hf. PAC measurements were carried out at room temperature after annealing at different temperatures up to 1,473 K in air. The PAC technique allows determining the electric field gradient at the 181Ta probe sites. The 181Ta isotopes appear in the sample as disintegration product of 181Hf.

  9. Statistical analysis of random telegraph noise in HfO2-based RRAM devices in LRS

    NASA Astrophysics Data System (ADS)

    Puglisi, Francesco Maria; Pavan, Paolo; Larcher, Luca; Padovani, Andrea

    2015-11-01

    In this work, we present a thorough statistical characterization of Random Telegraph Noise (RTN) in HfO2-based Resistive Random Access Memory (RRAM) cells in Low Resistive State (LRS). Devices are tested under a variety of operational conditions. A Factorial Hidden Markov Model (FHMM) analysis is exploited to extrapolate the properties of the traps causing multi-level RTN in LRS. The trapping and de-trapping of charge carriers into/out of defects located in the proximity of the conductive filament results in a shielding effect on a portion of the conductive filament, leading to the observed RTN current fluctuations. It is found that both oxygen vacancies and oxygen ions defects may be responsible for the observed RTN. The variations of the current observed at subsequent set/reset cycles are instead attributed to the stochastic variations in the filament due to oxidation/reduction processes during reset and set operations, respectively.

  10. First principle simulations on the effects of oxygen vacancy in HfO2-based RRAM

    NASA Astrophysics Data System (ADS)

    Dai, Yuehua; Zhao, Yuanyang; Wang, Jiayu; Xu, Jianbin; Yang, Fei

    2015-01-01

    HfO2-based resistive random access memory (RRAM) takes advantage of oxygen vacancy (V o) defects in its principle of operation. Since the change in resistivity of the material is controlled by the level of oxygen deficiency in the material, it is significantly important to study the performance of oxygen vacancies in formation of conductive filament. Excluding effects of the applied voltage, the Vienna ab initio simulation package (VASP) is used to investigate the orientation and concentration mechanism of the oxygen vacancies based on the first principle. The optimal value of crystal orientation [010] is identified by means of the calculated isosurface plots of partial charge density, formation energy, highest isosurface value, migration barrier, and energy band of oxygen vacancy in ten established orientation systems. It will effectively influence the SET voltage, forming voltage, and the ON/OFF ratio of the device. Based on the results of orientation dependence, different concentration models are established along crystal orientation [010]. The performance of proposed concentration models is evaluated and analyzed in this paper. The film is weakly conductive for the samples deposited in a mixture with less than 4.167at.% of V o contents, and the resistive switching (RS) phenomenon cannot be observed in this case. The RS behavior improves with an increase in the V o contents from 4.167at.% to 6.25at.%; nonetheless, it is found difficult to switch to a stable state. However, a higher V o concentration shows a more favorable uniformity and stability for HfO2-based RRAM.

  11. Thermal stability of the HfO2/SiO2 interface for sub-0.1 μm complementary metal-oxide-semiconductor gate oxide stacks: A valence band and quantitative core-level study by soft x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Barrett, N.; Renault, O.; Damlencourt, J.-F.; Martin, F.

    2004-12-01

    Synchrotron-radiation photoelectron spectroscopy is used to study the valence-band structure and the core-level photoemission spectra of HfO2 ultrathin films grown onto SiO2/Si substrates by atomic layer deposition (ALD). We determine the band offsets (valence and conduction) of HfO2 to Si as a function of postdeposition annealing treatments (under an inert N2 atmosphere or in situ in ultrahigh vacuum) and find a significant evolution, the conduction-band offset remaining larger than 1.5eV. The Si2p and the Hf4f core-level spectra give detailed information on the composition and the spatial extent of the interfacial Hf silicate layer formed between the SiO2 bottom oxide and the HfO2 ALD thin film. By a quantitative treatment of the Si2p core-level intensities, we examine the thermal stability of the interface silicate after postdeposition annealing under N2 and in situ annealing in ultrahigh vacuum (UHV), both at 800°C. The as-deposited layer gives rise to a HfO2/Hf0.35Si0.65O2/SiO2 stack with corresponding thicknesses of 0.74/0.51/0.73nm. After postdeposition annealing at 800°C in a N2 atmosphere, this becomes a HfO2/Hf0.31Si0.69O2/SiO2 stack with corresponding thicknesses of 0.71:0.58:0.91nm. In situ annealing in UHV, on the other hand, gives a HfO2/Hf0.35Si0.65O2/SiO2 stack with corresponding thicknesses of 0.65:0.70:0.76nm. The former favors an extension of both the silicate and the SiO2 interface layers, whereas the latter develops only the silicate layer.

  12. High-performance fully amorphous bilayer metal-oxide thin film transistors using ultra-thin solution-processed ZrOx dielectric

    NASA Astrophysics Data System (ADS)

    Liu, G. X.; Liu, A.; Shan, F. K.; Meng, Y.; Shin, B. C.; Fortunato, E.; Martins, R.

    2014-09-01

    In this study, we report high-performance amorphous In2O3/InZnO bilayer metal-oxide (BMO) thin-film transistor (TFT) using an ultra-thin solution-processed amorphous ZrOx dielectric. A thin layer of In2O3 offers a higher carrier concentration, thereby maximizing the charge accumulation and yielding high carrier mobility. A thick amorphous layer of InZnO controls the charge conductance resulting in low off-state current and suitable threshold voltage. As a consequence, the BMO TFT showed higher filed-effect mobility (37.9 cm2/V s) than single-layer InZnO TFT (7.6 cm2/V s). Apart from that we obtain an on/off current ratio of 109, a subthreshold swing voltage of 120 mV/decade, and a voltage shift ≤ 0.4 V under positive bias stress for 2.5 h, for a gate voltage of 3 V and drain voltage of 1 V. These data demonstrate that the BMO TFT has great potential for a broad range of applications as switching low-power transistors.

  13. Enhanced resistive switching performance for bilayer HfO2/TiO2 resistive random access memory

    NASA Astrophysics Data System (ADS)

    Ye, Cong; Deng, Tengfei; Zhang, Junchi; Shen, Liangping; He, Pin; Wei, Wei; Wang, Hao

    2016-10-01

    We prepared bilayer HfO2/TiO2 resistive random accessory memory (RRAM) using magnetron sputtering on an ITO/PEN flexible substrate. The switching voltages (V SET and V RESET) were smaller for the Pt/HfO2/TiO2/ITO device than for a Pt/HfO2/ITO memory device. The insertion of a TiO2 layer in the switching layer was inferred to act as an oxygen reservoir to reduce the switching voltages. In addition, greatly improved uniformity was achieved, which showed the coefficient of the variations of V SET and V RESET to be 9.90% and 6.35% for the bilayer structure RRAM. We deduced that occurrence of conductive filament connection/rupture at the interface of the HfO2 and TiO2, in combination with the HfO2 acting as a virtual cathode, led to the improved uniformity. A multilevel storage capability can be obtained by varying the stop voltage in the RESET process for bilayer HfO2/TiO2 RRAM. By analyzing the current conduction mechanism, we demonstrated that the multilevel high resistance state (HRS) was attributable to the increased barrier height when the stop voltage was increased.

  14. Hafnia (HfO2) nanoparticles as an X-ray contrast agent and mid-infrared biosensor

    NASA Astrophysics Data System (ADS)

    McGinnity, Tracie L.; Dominguez, Owen; Curtis, Tyler E.; Nallathamby, Prakash D.; Hoffman, Anthony J.; Roeder, Ryan K.

    2016-07-01

    The interaction of hafnium oxide (HfO2) nanoparticles (NPs) with X-ray and mid-infrared radiation was investigated to assess the potential as a multifunctional diagnostic probe for X-ray computed tomography (CT) and/or mid-infrared biosensing. HfO2 NPs of controlled size were prepared by a sol-gel process and surface functionalized with polyvinylpyrrolidone, resulting in relatively spherical and monodispersed NPs with a tunable mean diameter in the range of ~7-31 nm. The X-ray attenuation of HfO2 NPs was measured over 0.5-50 mM concentration and compared with Au NPs and iodine, which are the most prominent X-ray contrast agents currently used in research and clinical diagnostic imaging, respectively. At clinical CT tube potentials >80 kVp, HfO2 NPs exhibited superior or similar X-ray contrast compared to Au NPs, while both exhibited significantly greater X-ray contrast compared to iodine, due to the favorable location of the k-shell absorption edge for hafnium and gold. Moreover, energy-dependent differences in X-ray attenuation enabled simultaneous quantitative molecular imaging of each agent using photon-counting spectral (multi-energy) CT. HfO2 NPs also exhibited a strong mid-infrared absorption in the Reststrahlen band from ~250-800 cm-1 and negative permittivity below 695 cm-1, which can enable development of mid-infrared biosensors and contrast agents, leveraging surface enhanced mid-infrared and/or phonon polariton absorption.

  15. Hafnia (HfO2) nanoparticles as an X-ray contrast agent and mid-infrared biosensor.

    PubMed

    McGinnity, Tracie L; Dominguez, Owen; Curtis, Tyler E; Nallathamby, Prakash D; Hoffman, Anthony J; Roeder, Ryan K

    2016-07-14

    The interaction of hafnium oxide (HfO2) nanoparticles (NPs) with X-ray and mid-infrared radiation was investigated to assess the potential as a multifunctional diagnostic probe for X-ray computed tomography (CT) and/or mid-infrared biosensing. HfO2 NPs of controlled size were prepared by a sol-gel process and surface functionalized with polyvinylpyrrolidone, resulting in relatively spherical and monodispersed NPs with a tunable mean diameter in the range of ∼7-31 nm. The X-ray attenuation of HfO2 NPs was measured over 0.5-50 mM concentration and compared with Au NPs and iodine, which are the most prominent X-ray contrast agents currently used in research and clinical diagnostic imaging, respectively. At clinical CT tube potentials >80 kVp, HfO2 NPs exhibited superior or similar X-ray contrast compared to Au NPs, while both exhibited significantly greater X-ray contrast compared to iodine, due to the favorable location of the k-shell absorption edge for hafnium and gold. Moreover, energy-dependent differences in X-ray attenuation enabled simultaneous quantitative molecular imaging of each agent using photon-counting spectral (multi-energy) CT. HfO2 NPs also exhibited a strong mid-infrared absorption in the Reststrahlen band from ∼250-800 cm(-1) and negative permittivity below 695 cm(-1), which can enable development of mid-infrared biosensors and contrast agents, leveraging surface enhanced mid-infrared and/or phonon polariton absorption. PMID:27364973

  16. Hafnia (HfO2) nanoparticles as an X-ray contrast agent and mid-infrared biosensor.

    PubMed

    McGinnity, Tracie L; Dominguez, Owen; Curtis, Tyler E; Nallathamby, Prakash D; Hoffman, Anthony J; Roeder, Ryan K

    2016-07-14

    The interaction of hafnium oxide (HfO2) nanoparticles (NPs) with X-ray and mid-infrared radiation was investigated to assess the potential as a multifunctional diagnostic probe for X-ray computed tomography (CT) and/or mid-infrared biosensing. HfO2 NPs of controlled size were prepared by a sol-gel process and surface functionalized with polyvinylpyrrolidone, resulting in relatively spherical and monodispersed NPs with a tunable mean diameter in the range of ∼7-31 nm. The X-ray attenuation of HfO2 NPs was measured over 0.5-50 mM concentration and compared with Au NPs and iodine, which are the most prominent X-ray contrast agents currently used in research and clinical diagnostic imaging, respectively. At clinical CT tube potentials >80 kVp, HfO2 NPs exhibited superior or similar X-ray contrast compared to Au NPs, while both exhibited significantly greater X-ray contrast compared to iodine, due to the favorable location of the k-shell absorption edge for hafnium and gold. Moreover, energy-dependent differences in X-ray attenuation enabled simultaneous quantitative molecular imaging of each agent using photon-counting spectral (multi-energy) CT. HfO2 NPs also exhibited a strong mid-infrared absorption in the Reststrahlen band from ∼250-800 cm(-1) and negative permittivity below 695 cm(-1), which can enable development of mid-infrared biosensors and contrast agents, leveraging surface enhanced mid-infrared and/or phonon polariton absorption.

  17. GaN MOS-HEMT Using Ultra-Thin Al2O3 Dielectric Grown by Atomic Layer Deposition

    NASA Astrophysics Data System (ADS)

    Yue, Yuan-Zheng; Hao, Yue; Feng, Qian; Zhang, Jin-Cheng; Ma, Xiao-Hua; Ni, Jin-Yu

    2007-08-01

    We report a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) with atomic layer deposited (ALD) Al2O3 gate dielectric. Based on the previous work [Appl. Phys. Lett. 86 (2005) 063501] of Ye et al. by decreasing the thickness of the gate oxide to 3.5 nm and optimizing the device fabrication process, the device with maximum transconductance of 150 mS/mm is produced and discussed in comparison with the result of 100 mS/mm of Ye et al. The corresponding drain current density in the 0.8-μm-gate-length MOS-HEMT is 800 mA/mm at the gate bias of 3.0 V. The gate leakage is two orders of magnitude lower than that of the conventional AlGaN/GaN HEMT. The excellent characteristics of this novel MOS-HEMT device structure with ALD Al2O3 gate dielectric are presented.

  18. HfO2-based InP n-channel metal-oxide-semiconductor field-effect transistors and metal-oxide-semiconductor capacitors using a germanium interfacial passivation layer

    NASA Astrophysics Data System (ADS)

    Kim, Hyoung-Sub; Ok, I.; Zhang, M.; Zhu, F.; Park, S.; Yum, J.; Zhao, H.; Lee, Jack C.; Majhi, Prashant

    2008-09-01

    In this letter, we present our experimental results of HfO2-based n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) and metal-oxide-semiconductor capacitors (MOSCAPs) on indium phosphide (InP) substrates using a thin germanium (Ge) interfacial passivation layer (IPL). We found that MOSCAPs on n-InP substrates showed good C-V characteristics such as a small capacitance equivalent thickness (14Å ), a small frequency dispersion (<10% and <200mV), and a low dielectric leakage current (˜5×10-4A/cm2 at Vg=1.5V), whereas MOSCAPs on p-InP exhibited poor characteristics, implying severe Fermi level pinning. It was also found that InP was more vulnerable to a high temperature process such that C-V curves showed a characteristic "bump" and inversion capacitance at relatively high frequencies. From n-channel MOSFETs on a semi-insulating InP substrate using Ge IPL, HfO2, and TaN gate electrodes, excellent electrical characteristics such as a large transconductance (9.3mS /mm) and large drain currents (12.3mA/mm at Vd=2V and Vg=Vth+2V) were achieved, which are comparable to other works.

  19. Broadband and wide-angle light harvesting by ultra-thin silicon solar cells with partially embedded dielectric spheres.

    PubMed

    Yang, Zhenhai; Shang, Aixue; Qin, Linling; Zhan, Yaohui; Zhang, Cheng; Gao, Pingqi; Ye, Jichun; Li, Xiaofeng

    2016-04-01

    We propose a design of crystalline silicon thin-film solar cells (c-Si TFSCs, 2 μm-thick) configured with partially embedded dielectric spheres on the light-injecting side. The intrinsic light trapping and photoconversion are simulated by the complete optoelectronic simulation. It shows that the embedding depth of the spheres provides an effective way to modulate and significantly enhance the optical absorption. Compared to the conventional planar and front sphere systems, the optimized partially embedded sphere design enables a broadband, wide-angle, and strong optical absorption and efficient carrier transportation. Optoelectronic simulation predicts that a 2 μm-thick c-Si TFSC with half-embedded spheres shows an increment of more than 10  mA/cm2 in short-circuit current density and an enhancement ratio of more than 56% in light-conversion efficiency, compared to the conventional planar counterparts.

  20. Gas-phase reaction studies of dipositive hafnium and hafnium oxide ions: generation of the peroxide HfO2(2+).

    PubMed

    Lourenço, Célia; Michelini, Maria del Carmen; Marçalo, Joaquim; Gibson, John K; Oliveira, Maria Conceição

    2012-12-27

    Fourier transform ion cyclotron resonance mass spectrometry was used to characterize the gas-phase reactivity of Hf dipositive ions, Hf(2+)and HfO(2+), toward several oxidants: thermodynamically facile O-atom donor N(2)O, ineffective donor CO, and intermediate donors O(2), CO(2), NO, and CH(2)O. The Hf(2+) ion exhibited electron transfer with N(2)O, O(2), NO, and CH(2)O, reflecting the high ionization energy of Hf(+). The HfO(2+) ion was produced by O-atom transfer to Hf(2+) from N(2)O, O(2), and CO(2), and the HfO(2)(2+) ion by O-atom transfer to HfO(2+) from N(2)O; these reactions were fairly efficient. Density functional theory revealed the structure of HfO(2)(2+) as a peroxide. The HfO(2)(2+) ion reacted by electron transfer with N(2)O, CO(2), and CO to give HfO(2)(+). Estimates were made for the second ionization energies of Hf (14.5 ± 0.5 eV), HfO (14.3 ± 0.5 eV), and HfO(2) (16.2 ± 0.5 eV), and also for the bond dissociation energies, D[Hf(2+)-O] = 686 ± 69 kJ mol(-1) and D[OHf(2+)-O] = 186 ± 98 kJ mol(-1). The computed bond dissociation energies, 751 and 270 kJ mol(-1), respectively, are within these experimental ranges. Additionally, it was found that HfO(2)(2+) oxidized CO to CO(2) and is thus a catalyst in the oxidation of CO by N(2)O and that Hf(2+) activates methane to produce a carbene, HfCH(2)(2+).

  1. Damage evaluation in graphene underlying atomic layer deposition dielectrics

    PubMed Central

    Tang, Xiaohui; Reckinger, Nicolas; Poncelet, Olivier; Louette, Pierre; Ureña, Ferran; Idrissi, Hosni; Turner, Stuart; Cabosart, Damien; Colomer, Jean-François; Raskin, Jean-Pierre; Hackens, Benoit; Francis, Laurent A.

    2015-01-01

    Based on micro-Raman spectroscopy (μRS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, μRS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors. PMID:26311131

  2. Damage evaluation in graphene underlying atomic layer deposition dielectrics.

    PubMed

    Tang, Xiaohui; Reckinger, Nicolas; Poncelet, Olivier; Louette, Pierre; Ureña, Ferran; Idrissi, Hosni; Turner, Stuart; Cabosart, Damien; Colomer, Jean-François; Raskin, Jean-Pierre; Hackens, Benoit; Francis, Laurent A

    2015-08-27

    Based on micro-Raman spectroscopy (μRS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, μRS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors.

  3. Sub-10 nm Ta Channel Responsible for Superior Performance of a HfO2 Memristor

    NASA Astrophysics Data System (ADS)

    Jiang, Hao; Han, Lili; Lin, Peng; Wang, Zhongrui; Jang, Moon Hyung; Wu, Qing; Barnell, Mark; Yang, J. Joshua; Xin, Huolin L.; Xia, Qiangfei

    2016-06-01

    Memristive devices are promising candidates for the next generation non-volatile memory and neuromorphic computing. It has been widely accepted that the motion of oxygen anions leads to the resistance changes for valence-change-memory (VCM) type of materials. Only very recently it was speculated that metal cations could also play an important role, but no direct physical characterizations have been reported yet. Here we report a Ta/HfO2/Pt memristor with fast switching speed, record high endurance (120 billion cycles) and reliable retention. We programmed the device to 24 discrete resistance levels, and also demonstrated over a million (220) epochs of potentiation and depression, suggesting that our devices can be used for both multi-level non-volatile memory and neuromorphic computing applications. More importantly, we directly observed a sub-10 nm Ta-rich and O-deficient conduction channel within the HfO2 layer that is responsible for the switching. This work deepens our understanding of the resistance switching mechanism behind oxide-based memristive devices and paves the way for further device performance optimization for a broad spectrum of applications.

  4. Sub-10 nm Ta Channel Responsible for Superior Performance of a HfO2 Memristor

    PubMed Central

    Jiang, Hao; Han, Lili; Lin, Peng; Wang, Zhongrui; Jang, Moon Hyung; Wu, Qing; Barnell, Mark; Yang, J. Joshua; Xin, Huolin L.; Xia, Qiangfei

    2016-01-01

    Memristive devices are promising candidates for the next generation non-volatile memory and neuromorphic computing. It has been widely accepted that the motion of oxygen anions leads to the resistance changes for valence-change-memory (VCM) type of materials. Only very recently it was speculated that metal cations could also play an important role, but no direct physical characterizations have been reported yet. Here we report a Ta/HfO2/Pt memristor with fast switching speed, record high endurance (120 billion cycles) and reliable retention. We programmed the device to 24 discrete resistance levels, and also demonstrated over a million (220) epochs of potentiation and depression, suggesting that our devices can be used for both multi-level non-volatile memory and neuromorphic computing applications. More importantly, we directly observed a sub-10 nm Ta-rich and O-deficient conduction channel within the HfO2 layer that is responsible for the switching. This work deepens our understanding of the resistance switching mechanism behind oxide-based memristive devices and paves the way for further device performance optimization for a broad spectrum of applications. PMID:27334443

  5. Interface engineered HfO2-based 3D vertical ReRAM

    NASA Astrophysics Data System (ADS)

    Hudec, Boris; Wang, I.-Ting; Lai, Wei-Li; Chang, Che-Chia; Jančovič, Peter; Fröhlich, Karol; Mičušík, Matej; Omastová, Mária; Hou, Tuo-Hung

    2016-06-01

    We demonstrate a double-layer 3D vertical resistive random access memory (ReRAM) stack implementing a Pt/HfO2/TiN memory cell. The HfO2 switching layer is grown by atomic layer deposition on the sidewall of a SiO2/TiN/SiO2/TiN/SiO2 multilayer pillar. A steep vertical profile was achieved using CMOS-compatible TiN dry etching. We employ in situ TiN bottom interface engineering by ozone, which results in (a) significant forming voltage reduction which allows for forming-free operation in AC pulsed mode, and (b) non-linearity tuning of low resistance state by current compliance during Set operation. The vertical ReRAM shows excellent read and write disturb immunity between vertically stacked cells, retention over 104 s and excellent switching stability at 400 K. Endurance of 107 write cycles was achieved using 100 ns wide AC pulses while fast switching speed using pulses of only 10 ns width is also demonstrated. The active switching region was evaluated to be located closer to the bottom interface which allows for the observed high endurance.

  6. Sub-10 nm Ta Channel Responsible for Superior Performance of a HfO2 Memristor.

    PubMed

    Jiang, Hao; Han, Lili; Lin, Peng; Wang, Zhongrui; Jang, Moon Hyung; Wu, Qing; Barnell, Mark; Yang, J Joshua; Xin, Huolin L; Xia, Qiangfei

    2016-06-23

    Memristive devices are promising candidates for the next generation non-volatile memory and neuromorphic computing. It has been widely accepted that the motion of oxygen anions leads to the resistance changes for valence-change-memory (VCM) type of materials. Only very recently it was speculated that metal cations could also play an important role, but no direct physical characterizations have been reported yet. Here we report a Ta/HfO2/Pt memristor with fast switching speed, record high endurance (120 billion cycles) and reliable retention. We programmed the device to 24 discrete resistance levels, and also demonstrated over a million (2(20)) epochs of potentiation and depression, suggesting that our devices can be used for both multi-level non-volatile memory and neuromorphic computing applications. More importantly, we directly observed a sub-10 nm Ta-rich and O-deficient conduction channel within the HfO2 layer that is responsible for the switching. This work deepens our understanding of the resistance switching mechanism behind oxide-based memristive devices and paves the way for further device performance optimization for a broad spectrum of applications.

  7. Ferroelectricity-modulated resistive switching in Pt/Si:HfO2/HfO2-x /Pt memory

    NASA Astrophysics Data System (ADS)

    Ran, Jiang; Xianghao, Du; Zuyin, Han

    2016-08-01

    It is investigated for the effect of a ferroelectric Si:HfO2 thin film on the resistive switching in a stacked Pt/Si:HfO2/highly-oxygen-deficient HfO2-x /Pt structure. Improved resistance performance was observed. It was concluded that the observed resistive switching behavior was related to the modulation of the width and height of a depletion barrier in the HfO2-x layer, which was caused by the Si:HfO2 ferroelectric polarization field effect. Reliable switching reproducibility and long data retention were observed in these memory cells, suggesting their great potential in non-volatile memories applications with full compatibility and simplicity. Project supported by the National Natural Science Foundation of China (No. 11374182), the Natural Science Foundation of Shandong Province (No. ZR2012FQ012), and the Jinan Independent Innovation Projects of Universities (No. 201303019).

  8. Resistive switching phenomena of HfO2 films grown by MOCVD for resistive switching memory devices

    NASA Astrophysics Data System (ADS)

    Kim, Hee-Dong; Yun, Min Ju; Kim, Sungho

    2016-08-01

    The resistive switching phenomena of HfO2 films grown by using metal organic chemical vapor deposition (MOCVD) was studied for the application of resistive random access memory (ReRAM) devices. In the fabricated Pt/HfO2/TiN memory cells, bipolar resistive switching characteristics were observed, and the set and reset states were measured to be as low as 7 μA and 4 μA, respectively, at V READ = 1 V. Regarding the resistive switching performance, stable resistive switching (RS) performance was observed under 40 repetitive dc cycles with small variations of set/reset voltages and the currents and good retention characteristics of over 105 s in both the low-resistance state (LRS) and the high-resistance state (HRS). These results show the possibility of using MOCVDgrown HfO2 films as a promising resistive switching materials for ReRAM applications.

  9. Orientation control and domain structure analysis of {100}-oriented epitaxial ferroelectric orthorhombic HfO2-based thin films

    NASA Astrophysics Data System (ADS)

    Katayama, Kiliha; Shimizu, Takao; Sakata, Osami; Shiraishi, Takahisa; Nakamura, Shogo; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Uchida, Hiroshi; Funakubo, Hiroshi

    2016-04-01

    Orientation control of {100}-oriented epitaxial orthorhombic 0.07YO1.5-0.93HfO2 films grown by pulsed laser deposition was investigated. To achieve in-plane lattice matching, indium tin oxide (ITO) and yttria-stabilized zirconia (YSZ) were selected as underlying layers. We obtained (100)- and (001)/(010)-oriented films on ITO and YSZ, respectively. Ferroelastic domain formation was confirmed for both films by X-ray diffraction using the superlattice diffraction that appeared only for the orthorhombic symmetry. The formation of ferroelastic domains is believed to be induced by the tetragonal-orthorhombic phase transition upon cooling the films after deposition. The present results demonstrate that the orientation of HfO2-based ferroelectric films can be controlled in the same manner as that of ferroelectric films composed of conventional perovskite-type material such as Pb(Zr, Ti)O3 and BiFeO3.

  10. Feature Modeling of HfO2 Atomic Layer Deposition Using HfCl4/H2O

    NASA Astrophysics Data System (ADS)

    Stout, Phillip J.; Adams, Vance; Ventzek, Peter L. G.

    2003-03-01

    A Monte Carlo based feature scale model (Papaya) has been applied to atomic layer deposition (ALD) of HfO2 using HfCl_4/H_20. The model includes physical effects of transport to surface, specular and diffusive reflection within feature, adsorption, surface diffusion, deposition and etching. Discussed will be the 3D feature modeling of HfO2 deposition in assorted features (vias and trenches). The effect of feature aspect ratios, pulse times, cycle number, and temperature on film thickness, feature coverage, and film Cl fraction (surface/bulk) will be discussed. Differences between HfO2 ALD on blanket wafers and in features will be highlighted. For instance, the minimum pulse times sufficient for surface reaction saturation on blanket wafers needs to be increased when depositing on features. Also, HCl products created during the HfCl4 and H_20 pulses are more likely to react within a feature than at the field, reducing OH coverage within the feature (vs blanket wafer) thus limiting the maximum coverage attainable for a pulse over a feature.

  11. Ion-radical synergy in HfO2 etching studied with a XeF2/Ar+ beam setup

    NASA Astrophysics Data System (ADS)

    Gevers, P. M.; Beijerinck, H. C. W.; van de Sanden, M. C. M.; Kessels, W. M. M.

    2008-04-01

    To gain more insight into fundamental aspects of the etching behavior of Hf-based high-k materials in plasma etch reactors, HfO2 films were etched in a multiple-beam setup consisting of a low energy Ar+ ion beam and a XeF2 radical beam. The etch rate and etch products were monitored by real-time ellipsometry and mass spectrometry, respectively. Although etching of HfO2 in XeF2/Ar+ chemistry is mainly a physical effect, an unambiguous proof of the ion-radical synergistic effect for the etching of HfO2 is presented. The etch yield for 400 eV Ar+ ions at a substrate temperature of 300 °C was 0.3 atoms/ion for Ar+ sputtering and increased to 2 atoms/ion when XeF2 was also supplied. The etch yield proved to follow the common square root of ion energy dependence both for pure sputtering and radical enhanced etching, with a threshold energy at room temperature of 69±17 eV for Ar+ ions and 54±14 eV for Ar+ ions with XeF2.

  12. HfO2/SiO2 multilayer based reflective and transmissive optics from the IR to the UV

    NASA Astrophysics Data System (ADS)

    Wang, Jue; Hart, Gary A.; Oudard, Jean Francois; Wamboldt, Leonard; Roy, Brian P.

    2016-05-01

    HfO2/SiO2 multilayer based reflective optics enable threat detection in the short-wave/middle-wave infrared and high power laser targeting capability in the near infrared. On the other hand, HfO2/SiO2 multilayer based transmissive optics empower early missile warning by taking advantage of the extremely low noise light detection in the deep-ultraviolet region where solar irradiation is strongly absorbed by the ozone layer of the earth's atmosphere. The former requires high laser damage resistance, whereas the latter needs a solar-blind property, i.e., high transmission of the radiation below 290 nm and strong suppression of the solar background from 300 nm above. The technical challenges in both cases are revealed. The spectral limits associated with the HfO2 and SiO2 films are discussed and design concepts are schematically illustrated. Spectral performances are realized for potential A and D and commercial applications.

  13. Role of HfO2/SiO2 thin-film interfaces in near-ultraviolet absorption and pulsed laser damage

    DOE PAGES

    Papernov, Semyon; Kozlov, Alexei A.; Oliver, James B.; Smith, Chris; Jensen, Lars; Guenster, Stefan; Maedebach, Heinrich; Ristau, Detlev

    2016-07-15

    Here, the role of thin-film interfaces in the near-ultraviolet (near-UV) absorption and pulsed laser-induced damage was studied for ion-beam-sputtered and electron-beam-evaporated coatings comprised from HfO2 and SiO2 thin-film pairs. To separate contributions from the bulk of the film and from interfacial areas, absorption and damage threshold measurements were performed for a one-wave (355-nm wavelength) thick, HfO2 single-layer film and for a film containing seven narrow HfO2 layers separated by SiO2 layers. The seven-layer film was designed to have a total optical thickness of HfO2 layers, equal to one wave at 355 nm and an E-field peak and average intensity similarmore » to a single-layer HfO2 film. Absorption in both types of films was measured using laser calorimetry and photothermal heterodyne imaging. The results showed a small contribution to total absorption from thin-film interfaces as compared to HfO2 film material. The relevance of obtained absorption data to coating near-UV, nanosecond-pulse laser damage was verified by measuring the damage threshold and characterizing damage morphology. The results of this study revealed a higher damage resistance in the seven-layer coating as compared to the single-layer HfO2 film in both sputtered and evaporated coatings. The results are explained through the similarity of interfacial film structure with structure formed during the codeposition of HfO2 and SiO2 materials.« less

  14. SnO2 anode surface passivation by atomic layer deposited HfO2 improves Li-ion battery performance.

    PubMed

    Yesibolati, Nulati; Shahid, Muhammad; Chen, Wei; Hedhili, M N; Reuter, M C; Ross, F M; Alshareef, H N

    2014-07-23

    For the first time, it is demonstrated that nanoscale HfO2 surface passivation layers formed by atomic layer deposition (ALD) significantly improve the performance of Li ion batteries with SnO2 -based anodes. Specifically, the measured battery capacity at a current density of 150 mAg(-1) after 100 cycles is 548 and 853 mAhg(-1) for the uncoated and HfO2 -coated anodes, respectively. Material analysis reveals that the HfO2 layers are amorphous in nature and conformably coat the SnO2 -based anodes. In addition, the analysis reveals that ALD HfO2 not only protects the SnO2 -based anodes from irreversible reactions with the electrolyte and buffers its volume change, but also chemically interacts with the SnO2 anodes to increase battery capacity, despite the fact that HfO2 is itself electrochemically inactive. The amorphous nature of HfO2 is an important factor in explaining its behavior, as it still allows sufficient Li diffusion for an efficient anode lithiation/delithiation process to occur, leading to higher battery capacity.

  15. Hafnium carbamates and ureates: new class of precursors for low-temperature growth of HfO2 thin films.

    PubMed

    Pothiraja, Ramasamy; Milanov, Andrian P; Barreca, Davide; Gasparotto, Alberto; Becker, Hans-Werner; Winter, Manuela; Fischer, Roland A; Devi, Anjana

    2009-04-21

    Novel volatile compounds of hafnium, namely tetrakis-N,O-dialkylcarbamato hafnium(iv) [Hf((i)PrNC(O)O(i)Pr)(4)] () and tetrakis-N,N,N'-trialkylureato hafnium(iv) [Hf((i)PrNC(O)N-(Me)Et)(4)] (), have been synthesized through the simple insertion reaction of isopropyl isocyanate into hafnium isopropoxide and hafnium ethylmethylamide, respectively; based on the promising thermal properties, compound has been evaluated as a precursor for metalorganic chemical vapor deposition (MOCVD) of HfO(2) thin films, which resulted in the growth of stoichiometric and crystalline layers with a uniform morphology at temperature as low as 250 degrees C.

  16. Gamma irradiation-induced effects on the electrical properties of HfO2-based MOS devices

    NASA Astrophysics Data System (ADS)

    Manikanthababu, N.; Arun, N.; Dhanunjaya, M.; Nageswara Rao, S. V. S.; Pathak, A. P.

    2016-02-01

    Hafnium Oxide (HfO2) thin films were synthesized by e-beam evaporation and Radio frequency magnetron sputtering techniques. Au/HfO2/Si-structured Metal Oxide Semiconductor capacitors have been fabricated to study the effects of gamma irradiation on the electrical properties, leakage current versus voltage (I-V) and capacitance versus voltage (C-V) characteristics, as a function of irradiation dose. Systematic increase in leakage current as well as accumulation capacitance has been observed with increase in the irradiation dose. The influence of gamma irradiation and pre-existing defects on the evolution of oxide and interface traps have been studied in detail.

  17. Deposition and characterization of titanium dioxide and hafnium dioxide thin films for high dielectric applications

    NASA Astrophysics Data System (ADS)

    Yoon, Meeyoung

    The industry's demand for higher integrated circuit density and performance has forced the gate dielectric layer thickness to decrease rapidly. The use of conventional SiO2 films as gate oxide is reaching its limit due to the rapid increase in tunneling current. Therefore, a need for a high dielectric material to produce large oxide capacitance and low leakage current has emerged. Metal-oxides such as titanium dioxide (TiO2) and hafnium dioxide (HfO2) are attractive candidates for gate dielectrics due to their electrical and physical properties suitable for high dielectric applications. MOCVD of TiO2 using titanium isopropoxide (TTIP) precursor on p-type Si(100) has been studied. Insertion of a TiO x buffer layer, formed by depositing metallic Ti followed by oxidation, at the TiO2/Si interface has reduced the carbon contamination in the TiO2 film. Elemental Ti films, analyzed by in-situ AES, were found to grow according to Stranski-Krastanov mode on Si(100). Carbon-free, stoichiometric TiO2 films were successfully produced on Si(100) without any parasitic SiO2 layers at the TiO 2/Si interface. Electron-beam deposition of HfO2 films on Si(100) has also been investigated in this work. HfO2 films are formed by depositing elemental Hf on Si(100) and then oxidizing it either in O2 or O 3. XPS results reveal that with oxidation Hf(4f) peak shifts +3.45eV with 02 and +3.65eV with O3 oxidation. LEED and AFM studies show that the initially ordered crystalline Hf becomes disordered after oxidation. The thermodynamic stability of HfO2 films on Si has been studied using a unique test-bed structure of Hf/O3/Si. Post-Oxidation of Layer Deposition (POLD) has been employed to produce HfO2 films with a desired thickness. XPS results indicate that stoichiometric HfO 2 films were successfully produced using the POLD process. The investigation of the growth and thin film properties of TiO 2 and HfO2 using oxygen and ozone has laid a foundation for the application of these metal

  18. Effective passivation of In0.2Ga0.8As by HfO2 surpassing Al2O3 via in-situ atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Chang, Y. H.; Lin, C. A.; Liu, Y. T.; Chiang, T. H.; Lin, H. Y.; Huang, M. L.; Lin, T. D.; Pi, T. W.; Kwo, J.; Hong, M.

    2012-10-01

    High κ gate dielectrics of HfO2 and Al2O3 were deposited on molecular beam epitaxy-grown In0.2Ga0.8As pristine surface using in-situ atomic-layer-deposition (ALD) without any surface treatment or passivation layer. The ALD-HfO2/p-In0.2Ga0.8As interface showed notable reduction in the interfacial density of states (Dit), deduced from quasi-static capacitance-voltage and conductance-voltage (G-V) at room temperature and 100 °C. More significantly, the midgap peak commonly observed in the Dit(E) of ALD-oxides/In0.2Ga0.8As is now greatly diminished. The midgap Dit value decreases from ≥15 × 1012 eV-1 cm-2 for ALD-Al2O3 to ˜2-4 × 1012 eV-1 cm-2 for ALD-HfO2. Further, thermal stability at 850 °C was achieved in the HfO2/In0.2Ga0.8As, whereas C-V characteristics of Al2O3/p-In0.2Ga0.8As degraded after the high temperature annealing. From in-situ x-ray photoelectron spectra, the AsOx, which is not the oxidized state from the native oxide, but is an induced state from adsorption of trimethylaluminum and H2O, was found at the ALD-Al2O3/In0.2Ga0.8As interface, while that was not detected at the ALD-HfO2/In0.2Ga0.8As interface.

  19. Growth, microstructure and electrical properties of sputter-deposited hafnium oxide (HfO2) thin films grown using HfO2 ceramic target

    SciTech Connect

    Aguirre, B.; Vemuri, R. S.; Zubia, David; Engelhard, Mark H.; Shutthanandan, V.; Kamala Bharathi, K.; Ramana, Chintalapalle V.

    2011-01-01

    Hafnium oxide (HfO₂) thin films have been made by radio-frequency (rf) magnetron-sputtering onto Si(100) substrates under varying growth temperature (Ts). HfO₂ ceramic target has been employed for sputtering while varying the Ts from room temperature to 500⁰C during deposition. The effect of Ts on the growth and microstructure of deposited HfO₂ films has been studied using grazing incidence x-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), and high-resolution scanning electron microscopy (HR-SEM) coupled with energy dispersive x-ray spectrometry (EDS). The results indicate that the effect of Ts is significant on the growth, surface and interface structure, morphology and chemical composition of the HfO₂ films. Structural characterization indicates that the HfO₂ films grown at Ts<200 ⁰C are amorphous while films grown at Ts>200 ⁰C are nanocrystalline. An amorphous-to-crystalline transition occurs at Ts=200 ⁰C. Nanocrystalline HfO₂ films crystallized in a monoclinic structure with a (-111) orientation. XPS measurements indicated the high surface-chemical quality and stoichiometric nature of the grown HfO₂ films. An interface layer (IL) formation occurs due to reaction at the HfO₂-Si interface for HfO₂ films deposited at Ts>200 ⁰C. The thickness of IL increases with increasing Ts. XPS and EDS at the HfO₂-Si cross-section indicate the IL is a (Hf, Si)-O compound. The electrical characterization using capacitance-voltage measurements indicate that the dielectric constant decreases from 25 to 16 with increasing Ts.

  20. Photo-, cathodo- and thermoluminescent properties of dysprosium-doped HfO2 films deposited by ultrasonic spray pyrolysis.

    PubMed

    Manríquez, R Reynoso; Góngora, J A I Díaz; Guzmán-Mendoza, J; Montalvo, T Rivera; Olguín, J C Guzmán; Ramírez, P V Cerón; García-Hipólito, M; Falcony, C

    2014-09-01

    In this work, the photoluminescent (PL), cathodoluminescent (CL) and thermoluminescent (TL) properties of hafnium oxide films doped with trivalent dysprosium ions are reported. The films were deposited on glass substrates at temperatures ranging from 300 to 600°C, using chlorides as precursor reagents. The surface morphology of films showed a veins shaped microstructure at low deposition temperatures, while at higher temperatures the formation of spherical particles was observed on the surface. X-ray diffraction showed the presence of HfO2 monoclinic phase in the films deposited at temperatures greater than 400°C. The PL and CL spectra of the doped films showed the highest emission band centered at 575nm corresponding to the transitions (4)F9/2→(6)H13/2, which is a characteristic transition of Dy(3+) ion. The greatest emission intensities were observed in samples doped with 1 atomic percent (at%) of DyCl3 in the precursor solution. Regarding the TL behavior, the glow curve of HfO2:Dy(+3) films exhibited spectrum with one broad band centered at about 150°C. The highest intensity TL response was observed on the films deposited at 500°C. PMID:25016246

  1. Geometric conductive filament confinement by nanotips for resistive switching of HfO2-RRAM devices with high performance

    PubMed Central

    Niu, Gang; Calka, Pauline; Auf der Maur, Matthias; Santoni, Francesco; Guha, Subhajit; Fraschke, Mirko; Hamoumou, Philippe; Gautier, Brice; Perez, Eduardo; Walczyk, Christian; Wenger, Christian; Di Carlo, Aldo; Alff, Lambert; Schroeder, Thomas

    2016-01-01

    Filament-type HfO2-based RRAM has been considered as one of the most promising candidates for future non-volatile memories. Further improvement of the stability, particularly at the “OFF” state, of such devices is mainly hindered by resistance variation induced by the uncontrolled oxygen vacancies distribution and filament growth in HfO2 films. We report highly stable endurance of TiN/Ti/HfO2/Si-tip RRAM devices using a CMOS compatible nanotip method. Simulations indicate that the nanotip bottom electrode provides a local confinement for the electrical field and ionic current density; thus a nano-confinement for the oxygen vacancy distribution and nano-filament location is created by this approach. Conductive atomic force microscopy measurements confirm that the filaments form only on the nanotip region. Resistance switching by using pulses shows highly stable endurance for both ON and OFF modes, thanks to the geometric confinement of the conductive path and filament only above the nanotip. This nano-engineering approach opens a new pathway to realize forming-free RRAM devices with improved stability and reliability. PMID:27181525

  2. Low-Concentration NO2 Gas Sensor Based on HfO2 Thin Films Irradiated by Ultraviolet Light

    NASA Astrophysics Data System (ADS)

    Karaduman, Irmak; Barin, Özlem; Özer, Metin; Acar, Selim

    2016-08-01

    In this work, we investigate the gas-sensing properties of HfO2 thin films enhanced by ultraviolet (UV) light irradiation. The films were deposited on silicon substrate by atomic layer deposition (ALD) and annealed at 800°C. X-ray diffraction (XRD) and atomic force microscopy (AFM) were used for characterization of the samples, which revealed that the degree of crystallinity and electrical properties of the HfO2 thin films were affected by the annealing temperature. Different film thicknesses (20 nm and 10 nm) were used for gas-sensing measurements. The gas-sensing properties of the films were affected by the UV irradiation time, with improvements in sensor properties observed for samples with more than 30 min of irradiation. The maximum response was found for the 10-nm sensor annealed at 800°C. Moreover, a linear dependence on NO2 concentration was observed for the response, suggesting that the sensing layer is highly suitable for detecting NO2 gas concentrations as low as 1 ppm.

  3. Comparative study of Laser induce damage of HfO2/SiO2 and TiO2/SiO2 mirrors at 1064 nm.

    PubMed

    Jiao, Hongfei; Ding, Tao; Zhang, Qian

    2011-02-28

    A comparative study of laser induced damage of HfO2/SiO2 and TiO2/SiO2 mirrors at 1064 nm has been carried out. One TiO2/SiO2 mirror with absorption of 300 ppm and two HfO2/SiO2 mirrors with absorption of 40 and 4.5 ppm were fabricated using electron beam evaporation method. For r-on-1 test, all HfO2/SiO2 mirrors with low average absorption are above 150 J/cm2 at 10 ns. However, the TiO2/SiO2 mirrors with high average absorption are just 9.5 J/cm2, which are probably due to the rather high absorption and rather low band gap energy. Meanwhile, all the samples were irradiated from front and back side respectively using the raster scan test mode. In case of front side irradiation, it is found that: for TiO2/SiO2 high reflectors, the representative damage morphologies are shallow pits that were probably caused by absorbing centers. However, for HfO2/SiO2 high reflectors, the dominant damage morphologies are micrometer-sized nodules ejected pits and the delamination initiating from the pits. The absorption of HfO2/SiO2 coatings is low enough to have minor influence on the laser damage resistance. In case of backside irradiation, the morphology of TiO2/SiO2 mirrors is mainly center melted pits that are thermal melting induced damage. Meanwhile, HfO2/SiO2 mirrors with isometrical fracture rings damage morphology are thermal induced stress damage.

  4. O-vacancies in (i) nano-crystalline HfO2 and (i) non-crystalline SiO2 and Si3N4 studied by X-ray absorption spectroscopy.

    PubMed

    Lucovsky, Gerald; Miotti, Leonardo; Bastos, Karen Paz

    2012-06-01

    Performance and reliability in semiconductor devices are limited by electronically active defects, primarily O-atom and N-atom vacancies. Synchrotron X-ray spectroscopy results, interpreted in the context of two-electron multiplet theories, have been used to analyze conduction band edge, and O-vacancy defect states in nano-crystalline transition metal oxides, e.g., HfO2, and the noncrystalline dielectrics, SiO2, Si3N4 and Si-oxynitride alloys. Two-electron multiplet theory been used to develop a high-spin state equivalent d2 model for O-vacancy allowed transitions and negative ion states as detected by X-ray absorption spectroscopy in the O K pre-edge regime. Comparisons between theory and experiment have used Tanabe-Sugano energy level diagrams for determining the symmetries and relative energies of intra-d-state transitions for an equivalent d2 ground state occupancy. Trap-assisted-tunneling, Poole-Frenkel hopping transport, and the negative bias temperature instability have been explained in terms of injection and/or trapping into O-atom and N-atom vacancy sites, and applied to gate dielectric, and metal-insulator-metal structures.

  5. Elucidation of Cu Diffusion Surface and Path in Monoclinic HfO2 Conducting-Bridge Memory

    NASA Astrophysics Data System (ADS)

    Yura, S.; Yamasaki, T.; Nakada, K.; Ishii, A.; Kishida, S.; Kinoshita, K.

    It is important to specify the Cu diffusion path in the oxide layer of a Cu/oxide/Pt-structured conducting-bridge random access memory (CB-RAM), in terms of both elucidation of resistive switching mechanism and optimization of memory performance. The first-principles calculation is effective in specifying the Cu diffusion path with atomic resolution. However, reported results of first-principles calculations are based on too simplified model to depict the actual system of CB-RAM. In this paper, a periodic slab model for first-principles calculation of Cu diffusion process in HfO2-CB-RAM was proposed based on experimental results. Both Cu diffusion surface and Cu diffusion path were suggested by the first-principles calculations based on the model.

  6. Temperature dependence of the electric field gradient at 181Ta in nanostructured HfO2 film

    NASA Astrophysics Data System (ADS)

    Cavalcante, F. H. C.; Carbonari, A. W.; Soares, J. C.

    2010-11-01

    The hyperfine field at metal lattice sites in a nanostructured HfO2 thin film was studied by the Perturbed Angular Correlation (PAC) technique using 181Ta as probe nuclei. The thin oxide film was deposited by pulsed laser ablation on a silicon substrate kept at 673 K. The resulting film thickness was about 25 nm. The 181Ta isotopes are formed in Hf sites of the sample as disintegration product of radioactive 181Hf, which were produced by neutron activation of the very thin film by the reaction 180Hf(n,γ)181Hf.. PAC measurements of the electric field gradient at the 181Ta probe sites .were performed with the thin film in the temperature range 295 - 1273 K in vacuum. Results showed that the film has a single crystalline structure and two different quadrupole frequencies could be observed corresponding to 181Ta at monoclinic structure and with oxygen vacancy in its neighborhood.

  7. The role of pulse length in target poisoning during reactive HiPIMS: application to amorphous HfO2

    NASA Astrophysics Data System (ADS)

    Ganesan, R.; Murdoch, B. J.; Treverrow, B.; Ross, A. E.; Falconer, I. S.; Kondyurin, A.; McCulloch, D. G.; Partridge, J. G.; McKenzie, D. R.; Bilek, M. M. M.

    2015-06-01

    In conventional reactive magnetron sputtering, target poisoning frequently leads to an instability that requires the reactive gas flow rate to be actively regulated to maintain a constant composition of the deposited layers. Here we demonstrate that the pulse length in high power impulse magnetron sputtering (HiPIMS) is important for determining the surface conditions on the target that lead to poisoning. By increasing the pulse length, a smooth transition can be achieved from a poisoned target condition (short pulses) to a quasi-metallic target condition (long pulses). Appropriate selection of pulse length eliminates the need for active regulation, enabling stable reactive magnetron sputter deposition of stoichiometric amorphous hafnium oxide (HfO2) from a Hf target. A model is presented for the reactive HiPIMS process in which the target operates in a partially poisoned mode with a distribution of oxide on its surface that depends on the pulse length.

  8. Observation of room temperature ferromagnetic behavior in cluster-free, Co doped HfO2 films

    NASA Astrophysics Data System (ADS)

    Chang, Y. H.; Soo, Y. L.; Lee, W. C.; Huang, M. L.; Lee, Y. J.; Weng, S. C.; Sun, W. H.; Hong, M.; Kwo, J.; Lee, S. F.; Ablett, J. M.; Kao, C.-C.

    2007-08-01

    Extensive structural and magnetic analyses of Hf1-xCoxO2 thin films grown by molecular beam epitaxy are reported. Nearly cobalt cluster-free film with x =0.04-0.1 was obtained via 100°C growth, and Co ions are inferred to be located at interstitial site. Ferromagnetic behavior was observed up to 300K in both magnetization curves and temperature dependence of the moment. Via post-oxygen-annealing studies, a qualitative correlation between saturation magnetization and oxygen vacancy concentration is established, consistent with the impurity-band exchange model, and that the occurrence of ferromagnetic insulator behavior in the Co doped HfO2 is more probable than Co doped ZnO, TiO2, and SnO2 systems for doping concentrations under cation percolation threshold.

  9. An in-depth study of thermal effects in reset transitions in HfO2 based RRAMs

    NASA Astrophysics Data System (ADS)

    Villena, M. A.; González, M. B.; Roldán, J. B.; Campabadal, F.; Jiménez-Molinos, F.; Gómez-Campos, F. M.; Suñé, J.

    2015-09-01

    Reset transitions in HfO2 based RRAMs operated at different temperatures have been studied. Ni/HfO2/Si-n+ devices were fabricated and measured at temperatures ranging from 233 K to 473 K to characterize their reset features. In addition, a simulator including several coupled conductive filaments, series resistance and quantum effects was employed to analyze the same devices. The experimental results were correctly reproduced. It was found that the reset voltage and current show slight temperature dependence. To explain this fact, the roles of the out-diffusion of metallic species from the conductive filament and its conductance temperature dependence have been studied by simulation. The different conductive filament resistance components are also analyzed in the temperature range employed in our study. Finally, the thermal change in the energy barrier linked to quantum effects in the transport properties in the filament is modeled.

  10. The Development of HfO2-Rare Earth Based Oxide Materials and Barrier Coatings for Thermal Protection Systems

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Harder, Bryan James

    2014-01-01

    Advanced hafnia-rare earth oxides, rare earth aluminates and silicates have been developed for thermal environmental barrier systems for aerospace propulsion engine and thermal protection applications. The high temperature stability, low thermal conductivity, excellent oxidation resistance and mechanical properties of these oxide material systems make them attractive and potentially viable for thermal protection systems. This paper will focus on the development of the high performance and high temperature capable ZrO2HfO2-rare earth based alloy and compound oxide materials, processed as protective coating systems using state-or-the-art processing techniques. The emphasis has been in particular placed on assessing their temperature capability, stability and suitability for advanced space vehicle entry thermal protection systems. Fundamental thermophysical and thermomechanical properties of the material systems have been investigated at high temperatures. Laser high-heat-flux testing has also been developed to validate the material systems, and demonstrating durability under space entry high heat flux conditions.

  11. Laser damage study of nodules in electron-beam-evaporated HfO2/SiO2 high reflectors.

    PubMed

    Cheng, Xinbin; Shen, Zhengxiang; Jiao, Hongfei; Zhang, Jinlong; Ma, Bin; Ding, Tao; Lu, Jiangtao; Wang, Xiaodong; Wang, Zhanshan

    2011-03-20

    A reactive electron beam evaporation process was used to fabricate 1.064 μm HfO2/SiO2 high reflectors. The deposition process was optimized to reduce the nodular density. Cross-sectioning of nodular defects by a focused ion-beam milling instrument showed that the nodule seeds were the residual particles on the substrate and the particulates from the silica source "splitting." After optimizing the substrate preparation procedure and the evaporation process, a low nodular density of 2.7/mm2 was achieved. The laser damage test revealed that the ejection fluences and damage growth behaviors of nodules created from deep or shallow seeds were totally different. A mechanism based on directional plasma scald was proposed to interpret observed damage growth phenomenon.

  12. Dual bipolar resistive switching in the sub-forming regime of HfO2 resistive switching devices

    NASA Astrophysics Data System (ADS)

    Recher, Shani; Yalon, Eilam; Ritter, Dan; Riess, Ilan; Salzman, Joseph

    2015-09-01

    Resistive switching in HfO2 in the sub-forming regime (before an electroforming step had been fully performed) is studied by electrical measurements using a very low current compliance of 1 μA. Electroforming under low current limitation results in reduced self-heating and partial filament formation. Following the reset process in this sub-forming regime, the device fully recovers its pristine resistive state. Furthermore, a dual bipolar resistive switching (DBRS) effect is observed, which we model as two antiparallel bipolar resistive switches. We attribute this phenomenon to intermittent formation and rupture of filaments originating from opposite electrodes. Following the rupture of a filament, originating from one of the electrodes, another filament originating from the opposite electrode is formed.

  13. Effects of water vapor in high vacuum chamber on the properties of HfO2 films

    NASA Astrophysics Data System (ADS)

    Ling, Bo; He, Hongbo; Shao, Jianda

    2007-08-01

    The influence of water vapor content in high vacuum chamber during the coating process on physical properties of HfO2 films was investigated. Coatings were deposited on BK7 substrates by electron beam evaporation and photoelectric maximum control method. An in situ residual gas analyzer (RGA) was used to monitor the residual gas composition in the vacuum chamber. The optical properties, microstructure, absorption and laser-induced damage threshold (LIDT) of the samples were characterized by Lambda 900 spectrophotometer, X-ray diffraction (XRD), surface thermal lensing (STL) technique and 1064-nm Q-switched pulsed laser at a pulse duration of 12 ns respectively. It was found that a cold trap is an effective equipment to suppress water vapor in the vacuum chamber during the pumping process, and the coatings deposited in the vacuum atmosphere with relatively low water vapor composition show higher refractive index and smaller grain size. Meanwhile, the higher LIDT value is corresponding to lower absorbance.

  14. Electrical active defects in HfO2 based metal/oxide/metal devices

    NASA Astrophysics Data System (ADS)

    El Kamel, F.

    2016-01-01

    Dielectric as well as thermally stimulated current measurements were performed on metal/HfO2/Pt capacitors in order to study the electrical active defects in hafnia thin films. Two thermally activated relaxation processes have been carried out from both measurements. At low temperatures, the relaxation process can be ascribed to the shallow traps level localized at 0.65 eV and generally evidenced by the second ionization of oxygen vacancies. At high temperatures, the relaxation process arises from the diffusion of positively charged oxygen vacancies by overcoming an energetic barrier of about 1 eV.

  15. Improvement of performances HfO2-based RRAM from elementary cell to 16 kb demonstrator by introduction of thin layer of Al2O3

    NASA Astrophysics Data System (ADS)

    Azzaz, M.; Benoist, A.; Vianello, E.; Garbin, D.; Jalaguier, E.; Cagli, C.; Charpin, C.; Bernasconi, S.; Jeannot, S.; Dewolf, T.; Audoit, G.; Guedj, C.; Denorme, S.; Candelier, P.; Fenouillet-Beranger, C.; Perniola, L.

    2016-11-01

    In this article, the reliability of HfO2-based RRAM devices integrated in an advanced 28 nm CMOS 16 kbit demonstrator is presented. In order to improve the memory performance, a thin Al2O3 layer is inserted in the HfO2-based memory stack (TiN/Ti/HfO2/Al2O3/TiN). Thanks to extensive electrical characterizations on both single layer HfO2 and bilayer HfO2/Al2O3 memory stacks at device and array levels, the potential of the bilayer is put forward. From the experimental results, the thin Al2O3 layer has allowed to improve the endurance (memory window of about one decade after 1 M cycles) and data retention (both the low and the high resistance states are stable after 6 h at 200 °C). Finally, thanks to our 3D model based on calculation of the Conductive Filament resistance using trap assisted tunneling (TAT) the role of Al2O3 as series resistance is highlighted.

  16. Electron trapping properties at HfO2/SiO2 interface, studied by Kelvin probe force microscopy and theoretical analysis

    NASA Astrophysics Data System (ADS)

    Zhang, Man-Hong

    2016-08-01

    Electron trapping properties at the HfO2/SiO2 interface have been measured through Kelvin Probe force microscopy, between room temperature and 90 °C. The electron diffusion in HfO2 shows a multiple-step process. After injection, electrons diffuse quickly toward the HfO2/SiO2 interface and then diffuse laterally near the interface in two sub-steps: The first is a fast diffusion through shallow trap centers and the second is a slow diffusion through deep trap centers. Evolution of contact potential difference profile in the fast lateral diffusion sub-step was simulated by solving a diffusion equation with a term describing the charge loss. In this way, the diffusion coefficient and the average life time at different temperatures were extracted. A value of 0.57 eV was calculated for the activation energy of the shallow trap centers in HfO2. Project supported by the National Natural Science Foundation of China (Grant No. 61176080).

  17. Implementation of nanoscale circuits using dual metal gate engineered nanowire MOSFET with high-k dielectrics for low power applications

    NASA Astrophysics Data System (ADS)

    Charles Pravin, J.; Nirmal, D.; Prajoon, P.; Ajayan, J.

    2016-09-01

    This work covers the impact of dual metal gate engineered Junctionless MOSFET with various high-k dielectric in Nanoscale circuits for low power applications. Due to gate engineering in junctionless MOSFET, graded potential is obtained and results in higher electron velocity of about 31% for HfO2 than SiO2 in the channel region, which in turn improves the carrier transport efficiency. The simulation is done using sentaurus TCAD, ON current, OFF current, ION/IOFF ratio, DIBL, gain, transconductance and transconductance generation factor parameters are analysed. When using HfO2, DIBL shows a reduction of 61.5% over SiO2. The transconductance and transconductance generation factor shows an improvement of 44% and 35% respectively. The gain and output resistance also shows considerable improvement with high-k dielectrics. Using this device, inverter circuit is implemented with different high-k dielectric material and delay have been decreased by 4% with HfO2 when compared to SiO2. In addition, a significant reduction in power dissipation of the inverter circuit is obtained with high-k dielectric Dual Metal Surround Gate Junctionless Transistor than SiO2 based device. From the analysis, it is found that HfO2 will be a better alternative for the future nanoscale device.

  18. Fabrication of BaTiO3-Based Dielectrics for Ultrathin-Layer Multilayer Ceramic Capacitor Application by a Modified Coating Approach

    NASA Astrophysics Data System (ADS)

    Tian, Zhibin; Wang, Xiaohui; Zhang, Yichi; Song, Tae-Ho; Hur, Kang Heon; Li, Longtu

    2011-02-01

    The development of multilayer ceramic capacitor (MLCC) with base metal electrode (BME) requires precise controlling of the microstructure in a very thin dielectric layer (<1 µm). In this paper, a modified coating approach for high coverage of BaTiO3 powder for further MLCC application has been developed. The well dispersed and coated BaTiO3 powders are prepared and the relative mechanism has been discussed. Furthermore, the ultrafine grained X7R dielectric ceramics were produced by both conventional mixing and modified coating methods. Compared with the conventional mixing method, the ceramics prepared by the coating approach exhibited better TCC (the temperature coefficient of capacitance) performance, with dielectric constant over 2000 and grain size below 150 nm. In addition, it is found through the coating method the content of additives can be reduced to a relatively smaller amount than that required in conventional mixing method.

  19. Performance and carrier transport analysis of In0.7Ga0.3As quantum-well MOSFETs with Al2O3/HfO2 gate stack

    NASA Astrophysics Data System (ADS)

    Son, Seung-Woo; Park, Jung-Ho; Baek, Ji-Min; Kim, Jin Su; Kim, Do-Kywn; Shin, Seung Heon; Banerjee, S. K.; Lee, Jung-Hee; Kim, Tae-Woo; Kim, Dae-Hyun

    2016-09-01

    In this paper, we have fabricated and characterized In0.7Ga0.3As quantum-well (QW) metal-oxide-semiconductor field-effect-transistors (MOSFETs). We have employed the gate dielectric of the Al2O3/HfO2 (0.6/2 nm) bi-layer stack by ALD. The fabricated device with Lg = 4 μm exhibits a record maximum transconductance (gm_max) in excess of 520 μS/μm at >1 μm region, and reasonably good electrostatic integrity, such as SS = 110 mV/decade and DIBL = 43 mV/V. Also, we have investigated the gate length scaling behavior in terms of output, transconductance, and transfer characteristics. In particular, our devices feature very uniform values of the electrostatic integrity, such as SS = 100-110 mV/decade, VT = -0.25 V to -0.2 V and DIBL = 40-50 mV/V, as Lg decreases from 10 μm to 4 μm. Furthermore, we have explored the impact of source resistance (RS) onto the device characteristics of the InGaAs QW MOSFETs. In doing so, we have modeled both measured extrinsic transconductance (gm_ext) and intrinsic transconductance (gm_int) as a function of Lg.

  20. Study on influences of TiN capping layer on time-dependent dielectric breakdown characteristic of ultra-thin EOT high-k metal gate NMOSFET with kMC TDDB simulations

    NASA Astrophysics Data System (ADS)

    Xu, Hao; Yang, Hong; Luo, Wei-Chun; Xu, Ye-Feng; Wang, Yan-Rong; Tang, Bo; Wang, Wen-Wu; Qi, Lu-Wei; Li, Jun-Feng; Yan, Jiang; Zhu, Hui-Long; Zhao, Chao; Chen, Da-Peng; Ye, Tian-Chun

    2016-08-01

    The thickness effect of the TiN capping layer on the time dependent dielectric breakdown (TDDB) characteristic of ultra-thin EOT high-k metal gate NMOSFET is investigated in this paper. Based on experimental results, it is found that the device with a thicker TiN layer has a more promising reliability characteristic than that with a thinner TiN layer. From the charge pumping measurement and secondary ion mass spectroscopy (SIMS) analysis, it is indicated that the sample with the thicker TiN layer introduces more Cl passivation at the IL/Si interface and exhibits a lower interface trap density. In addition, the influences of interface and bulk trap density ratio N it/N ot are studied by TDDB simulations through combining percolation theory and the kinetic Monte Carlo (kMC) method. The lifetime reduction and Weibull slope lowering are explained by interface trap effects for TiN capping layers with different thicknesses. Project supported by the National High Technology Research and Development Program of China (Grant No. SS2015AA010601), the National Natural Science Foundation of China (Grant Nos. 61176091 and 61306129), and the Opening Project of Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of MicroElectronics of Chinese Academy of Sciences.

  1. Study on influences of TiN capping layer on time-dependent dielectric breakdown characteristic of ultra-thin EOT high-k metal gate NMOSFET with kMC TDDB simulations

    NASA Astrophysics Data System (ADS)

    Xu, Hao; Yang, Hong; Luo, Wei-Chun; Xu, Ye-Feng; Wang, Yan-Rong; Tang, Bo; Wang, Wen-Wu; Qi, Lu-Wei; Li, Jun-Feng; Yan, Jiang; Zhu, Hui-Long; Zhao, Chao; Chen, Da-Peng; Ye, Tian-Chun

    2016-08-01

    The thickness effect of the TiN capping layer on the time dependent dielectric breakdown (TDDB) characteristic of ultra-thin EOT high-k metal gate NMOSFET is investigated in this paper. Based on experimental results, it is found that the device with a thicker TiN layer has a more promising reliability characteristic than that with a thinner TiN layer. From the charge pumping measurement and secondary ion mass spectroscopy (SIMS) analysis, it is indicated that the sample with the thicker TiN layer introduces more Cl passivation at the IL/Si interface and exhibits a lower interface trap density. In addition, the influences of interface and bulk trap density ratio N it/N ot are studied by TDDB simulations through combining percolation theory and the kinetic Monte Carlo (kMC) method. The lifetime reduction and Weibull slope lowering are explained by interface trap effects for TiN capping layers with different thicknesses. Project supported by the National High Technology Research and Development Program of China (Grant No. SS2015AA010601), the National Natural Science Foundation of China (Grant Nos. 61176091 and 61306129), and the Opening Project of Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of MicroElectronics of Chinese Academy of Sciences.

  2. Wide band antireflective coatings Al2O3 / HfO2 / MgF2 for UV region

    NASA Astrophysics Data System (ADS)

    Winkowski, P.; Marszałek, Konstanty W.

    2013-07-01

    Deposition technology of the three layers antireflective coatings consists of hafnium compound are presented in this paper. Oxide films were deposited by means of e-gun evaporation in vacuum of 5x10-5 mbar in presence of oxygen and fluoride films by thermal evaporation. Substrate temperature was 250°C. Coatings were deposited onto optical lenses made from quartz glass (Corning HPFS). Thickness and deposition rate were controlled by thickness measuring system Inficon XTC/2. Simulations leading to optimization of thickness and experimental results of optical measurements carried during and after deposition process were presented. Physical thickness measurements were made during deposition process and were equal to 43 nm/74 nm/51 nm for Al2O3 / HfO2 / MgF2 respectively. Optimization was carried out for ultraviolet region from 230nm to the beginning of visible region 400 nm. In this region the average reflectance of the antireflective coating was less than 0.5% in the whole range of application.

  3. H-shuttling within a Hf-defect complex in Si/SiO2/HfO2 structures

    NASA Astrophysics Data System (ADS)

    Marinopoulos, A. G.; Batyrev, I.; Zhou, X.; Schrimpf, R.; Fleetwood, D.; Pantelides, S. T.

    2008-03-01

    It was recently shown that, following irradiation of Si-SiO2/HfO2 structures by X-rays or constant-voltage stress, both oxide- and interface-trap densities exhibit oscillations with switch-bias annealing that are much larger than those previously observed in Si/SiO2 devices. Here we describe a particular defect complex that can account for the observations. The complex comprises a suboxide Hf-Si bond and an interfacial dangling bond (Pb center). With the aid of first-principles calculations we show that this defect possesses a symmetric double-well minimum and can provide trapping sites for H atoms near the interface. In the first site, the H atom passivates the dangling bond; in the second site the H atom resides near the center of the Hf-Si bond. A moderate intervening barrier (1.2 eV) suggests a relatively easy hopping of H atoms between these two energy minima, aided by the applied field and temperature. This shuttling mechanism can explain the observed oscillations in the interface trap densities during switched-bias conditions. This work was supported in part by the AFOSR and the DOE.

  4. Growth of (111)-oriented epitaxial and textured ferroelectric Y-doped HfO2 films for downscaled devices

    NASA Astrophysics Data System (ADS)

    Katayama, Kiliha; Shimizu, Takao; Sakata, Osami; Shiraishi, Takahisa; Nakamura, Syogo; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Uchida, Hiroshi; Funakubo, Hiroshi

    2016-09-01

    In this study, the growth of (111)-oriented epitaxial and textured YO1.5-HfO2 (0.07:0.93 ratio) films using the pulsed laser deposition method is presented. Epitaxial films were prepared on ITO//(111)yttria-stabilized zirconia (YSZ) substrates (ITO: Sn-doped In2O3; YSZ: yttria-stabilized zirconia), while textured films were prepared on (111)Pt/TiOx/SiO2//Si substrates with and without an ITO buffer layer via the grain on grain coherent growth. Inserting an ITO layer increased the volume fraction of the ferroelectric orthorhombic phase. Both the epitaxial and uniaxially textured films exhibited similar ferroelectricity with a remanent polarization of around 10 μC/cm2 and a coercive field of 1.9 to 2.0 MV/cm. These results present us with a way of obtaining stable and uniform ferroelectric properties for each grain and device cells consisting of a small number of grains. This opens the door for ultimately miniaturized ferroelectric devices, such as ferroelectric field effect transistors with small gate length and resistive random access memory using ferroelectric tunnel junctions.

  5. In situ infrared spectroscopy study of the interface self-cleaning during the atomic layer deposition of HfO2 on GaAs(100) surfaces

    NASA Astrophysics Data System (ADS)

    Ye, Liwang; Gougousi, Theodosia

    2014-09-01

    In situ attenuated total reflectance Fourier transform infrared spectroscopy was utilized to study the interface evolution during the atomic layer deposition (ALD) of HfO2 on GaAs surfaces using of tetrakis (dimethylamino) hafnium and H2O. The experiments were performed on chemical oxide and hydrogen fluoride etched GaAs(100) starting surfaces. For the deposition of HfO2 on chemical oxide GaAs surfaces at 275 °C, which corresponds to the optimal ALD process temperature, continuous arsenic oxide removal was observed for the first 20 ALD cycles. The oxide removal was more pronounced at the initial 1-2 cycles but nonetheless persisted, at a reduced rate, up to the 20th cycle. The substrate temperature was confirmed to affect the arsenic oxide removal; the rate was significant at temperatures above 250 °C while negligible below 200 °C.

  6. Dielectric Engineering of a Boron Nitride/Hafnium Oxide Heterostructure for High-Performance 2D Field Effect Transistors.

    PubMed

    Zou, Xuming; Huang, Chun-Wei; Wang, Lifeng; Yin, Long-Jing; Li, Wenqing; Wang, Jingli; Wu, Bin; Liu, Yunqi; Yao, Qian; Jiang, Changzhong; Wu, Wen-Wei; He, Lin; Chen, Shanshan; Ho, Johnny C; Liao, Lei

    2016-03-01

    A unique design of a hexagonal boron nitride (h-BN)/HfO2 dielectric heterostructure stack is demonstrated, with few-layer h-BN to alleviate the surface optical phonon scattering, followed by high-κ HfO2 deposition to suppress Coulombic impurity scattering so that high-performance top-gated two-dimensional semiconductor transistors are achieved. Furthermore, this dielectric stack can also be extended to GaN-based transistors to enhance their performance.

  7. Low toxicity of HfO2, SiO2, Al2O3 and CeO2 nanoparticles to the yeast, Saccharomyces cerevisiae.

    PubMed

    García-Saucedo, Citlali; Field, James A; Otero-Gonzalez, Lila; Sierra-Álvarez, Reyes

    2011-09-15

    Increasing use of nanomaterials necessitates an improved understanding of their potential impact on environment health. This study evaluated the cytotoxicity of nanosized HfO(2), SiO(2), Al(2)O(3) and CeO(2) towards the eukaryotic model organism Saccharomyces cerevisiae, and characterized their state of dispersion in bioassay medium. Nanotoxicity was assessed by monitoring oxygen consumption in batch cultures and by analysis of cell membrane integrity. CeO(2), Al(2)O(3), and HfO(2) nanoparticles were highly unstable in yeast medium and formed micron-sized, settleable agglomerates. A non-toxic polyacrylate dispersant (Dispex A40) was used to improve nanoparticle stability and determine the impact of enhanced dispersion on toxicity. None of the NPs tested without dispersant inhibited O(2) uptake by yeast at concentrations as high as 1000 mg/L. Dispersant supplementation only enhanced the toxicity of CeO(2) (47% at 1000 mg/L). Dispersed SiO(2) and Al(2)O(3) (1000 mg/L) caused cell membrane damage, whereas dispersed HfO(2) and CeO(2) did not cause significant disruption of membrane integrity at the same concentration. These results suggest that the O(2) uptake inhibition observed with dispersed CeO(2) NPs was not due to reduced cell viability. This is the first study evaluating toxicity of nanoscale HfO(2), SiO(2), Al(2)O(3) and CeO(2) to S. cerevisiae. Overall the results obtained demonstrate that these nanomaterials display low or no toxicity to yeast.

  8. Novel integration of ultrathin Al2O3 with low-k dielectric as bilayer liner for capacitance optimization and stress mitigation in Cu through-silicon-via

    NASA Astrophysics Data System (ADS)

    Zhang, Lin; Li, Hong Yu; Shang, Yang; Yoo, Woosik; Yu, Hao; Tan, Chuan Seng

    2016-04-01

    Through-silicon-via (TSV) used in three-dimensional (3D) stacked dies must present small electrical parasitic, such as capacitance, to allow for low latency signal transmission. Stable TSV capacitance is desired to overcome the spatial circuit performance variation caused by non-uniform hot-spot heating. In this work, a novel combination of low-k with ultrathin Al2O3 bilayer liner is successfully integrated in the TSV. The TSV capacitance is reduced by ˜26% as compared to plasma-enhanced tetrahydrothosilicate (PETEOS) oxide liner. Stable TSV capacitance within the operating voltage of interest (˜0-5 V) is achieved by operating the TSV in a stable accumulation capacitance region. The positive shift in the flat-band voltage (ΔV FB = +19 V) is achieved by utilizing Al2O3-induced negative fixed charge (|Q f| = 1.3 × 1012 cm-2) at the Si/low-k interface. Leakage current density of the bilayer liner is improved to a level comparable with the PETEOS oxide liner post annealing [forming gas (N2/H2) at 350 °C for 2 h or 400 °C for 0.5 h]. Low-k material with a smaller elastic modulus improves the thermo-mechanical stress exerted on the surrounding Si substrate compared with PETEOS oxide.

  9. The role of film interfaces in near-ultraviolet absorption and pulsed-laser damage in ion-beam-sputtered coatings based on HfO2/SiO2 thin-film pairs

    DOE PAGES

    Ristau, Detlev; Papernov, S.; Kozlov, A. A.; Oliver, J. B.; Smith, C.; Jensen, L.; Gunster, S.; Madebach, H.

    2015-11-23

    The role of thin-film interfaces in the near-ultraviolet absorption and pulsed-laser–induced damage was studied for ion-beam–sputtered and electron-beam–evaporated coatings comprised from HfO2 and SiO2 thin-film pairs. To separate contributions from the bulk of the film and from interfacial areas, absorption and damage-threshold measurements were performed for a one-wave (355-nm wavelength) thick, HfO2 single-layer film and for a film containing seven narrow HfO2 layers separated by SiO2 layers. The seven-layer film was designed to have a total optical thickness of HfO2 layers, equal to one wave at 355 nm and an E-field peak and average intensity similar to a single-layer HfO2more » film. Absorption in both types of films was measured using laser calorimetry and photothermal heterodyne imaging. The results showed a small contribution to total absorption from thin-film interfaces, as compared to HfO2 film material. The relevance of obtained absorption data to coating near-ultraviolet, nanosecond-pulse laser damage was verified by measuring the damage threshold and characterizing damage morphology. The results of this study revealed a higher damage resistance in the seven-layer coating as compared to the single-layer HfO2 film in both sputtered and evaporated coatings. Here, the results are explained through the similarity of interfacial film structure with structure formed during the co-deposition of HfO2 and SiO2 materials.« less

  10. Positive-bias gate-controlled metal-insulator transition in ultrathin VO2 channels with TiO2 gate dielectrics

    NASA Astrophysics Data System (ADS)

    Yajima, Takeaki; Nishimura, Tomonori; Toriumi, Akira

    2015-12-01

    The next generation of electronics is likely to incorporate various functional materials, including those exhibiting ferroelectricity, ferromagnetism and metal-insulator transitions. Metal-insulator transitions can be controlled by electron doping, and so incorporating such a material in transistor channels will enable us to significantly modulate transistor current. However, such gate-controlled metal-insulator transitions have been challenging because of the limited number of electrons accumulated by gate dielectrics, or possible electrochemical reaction in ionic liquid gate. Here we achieve a positive-bias gate-controlled metal-insulator transition near the transition temperature. A significant number of electrons were accumulated via a high-permittivity TiO2 gate dielectric with subnanometre equivalent oxide thickness in the inverse-Schottky-gate geometry. An abrupt transition in the VO2 channel is further exploited, leading to a significant current modulation far beyond the capacitive coupling. This solid-state operation enables us to discuss the electrostatic mechanism as well as the collective nature of gate-controlled metal-insulator transitions, paving the pathway for developing functional field effect transistors.

  11. Positive-bias gate-controlled metal–insulator transition in ultrathin VO2 channels with TiO2 gate dielectrics

    PubMed Central

    Yajima, Takeaki; Nishimura, Tomonori; Toriumi, Akira

    2015-01-01

    The next generation of electronics is likely to incorporate various functional materials, including those exhibiting ferroelectricity, ferromagnetism and metal–insulator transitions. Metal–insulator transitions can be controlled by electron doping, and so incorporating such a material in transistor channels will enable us to significantly modulate transistor current. However, such gate-controlled metal–insulator transitions have been challenging because of the limited number of electrons accumulated by gate dielectrics, or possible electrochemical reaction in ionic liquid gate. Here we achieve a positive-bias gate-controlled metal–insulator transition near the transition temperature. A significant number of electrons were accumulated via a high-permittivity TiO2 gate dielectric with subnanometre equivalent oxide thickness in the inverse-Schottky-gate geometry. An abrupt transition in the VO2 channel is further exploited, leading to a significant current modulation far beyond the capacitive coupling. This solid-state operation enables us to discuss the electrostatic mechanism as well as the collective nature of gate-controlled metal–insulator transitions, paving the pathway for developing functional field effect transistors. PMID:26657761

  12. Formation of (111) orientation-controlled ferroelectric orthorhombic HfO2 thin films from solid phase via annealing

    NASA Astrophysics Data System (ADS)

    Mimura, Takanori; Katayama, Kiliha; Shimizu, Takao; Uchida, Hiroshi; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Sakata, Osami; Funakubo, Hiroshi

    2016-08-01

    0.07YO1.5-0.93HfO2 (YHO7) films were prepared on various substrates by pulse laser deposition at room temperature and subsequent heat treatment to enable a solid phase reaction. (111)-oriented 10 wt. % Sn-doped In2O3(ITO)//(111) yttria-stabilized zirconia, (111)Pt/TiOx/SiO2/(001)Si substrates, and (111)ITO/(111)Pt/TiOx/SiO2/(001)Si substrates were employed for film growth. In this study, X-ray diffraction measurements including θ-2θ measurements, reciprocal space mappings, and pole figure measurements were used to study the films. The film on (111)ITO//(111)yttria-stabilized zirconia was an (111)-orientated epitaxial film with ferroelectric orthorhombic phase; the film on (111)ITO/(111)Pt/TiOx/SiO2/(001)Si was an (111)-oriented uniaxial textured film with ferroelectric orthorhombic phase; and no preferred orientation was observed for the film on the (111)Pt/TiOx/SiO2/(001)Si substrate, which does not contain ITO. Polarization-hysteresis measurements confirmed that the films on ITO covered substrates had saturated ferroelectric hysteresis loops. A remanent polarization (Pr) of 9.6 and 10.8 μC/cm2 and coercive fields (Ec) of 1.9 and 2.0 MV/cm were obtained for the (111)-oriented epitaxial and uniaxial textured YHO7 films, respectively. These results demonstrate that the (111)-oriented ITO bottom electrodes play a key role in controlling the orientation and ferroelectricity of the phase formation of the solid films deposited at room temperature.

  13. Effects of vacuum ultraviolet and ultraviolet irradiation on ultrathin hafnium-oxide dielectric layers on (100)Si as measured with electron-spin resonance

    SciTech Connect

    Ren, H.; Shohet, J. L.; Cheng, S. L.; Nishi, Y.

    2010-05-10

    The effects of vacuum ultraviolet (VUV) (7.2 eV) and UV (4.9 eV) irradiation on hafnium-oxide dielectric layers were studied with electron-spin resonance to detect defect states. Silicon dangling-bond defects (P{sub b} centers) and positively charged oxygen vacancies (E{sup '} centers) were detected with g-factor fitting. VUV irradiation increases the level of P{sub b} states, while UV decreases the level of P{sub b} states but increases the level of E{sup '} states significantly. Rapid thermal annealing appears to mitigate these effects. Absolute values of the defect-state concentrations are presented.

  14. CMUTs with high-K atomic layer deposition dielectric material insulation layer.

    PubMed

    Xu, Toby; Tekes, Coskun; Degertekin, F

    2014-12-01

    Use of high-κ dielectric, atomic layer deposition (ALD) materials as an insulation layer material for capacitive micromachined ultrasonic transducers (CMUTs) is investigated. The effect of insulation layer material and thickness on CMUT performance is evaluated using a simple parallel plate model. The model shows that both high dielectric constant and the electrical breakdown strength are important for the dielectric material, and significant performance improvement can be achieved, especially as the vacuum gap thickness is reduced. In particular, ALD hafnium oxide (HfO2) is evaluated and used as an improvement over plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (Six)Ny)) for CMUTs fabricated by a low-temperature, complementary metal oxide semiconductor transistor-compatible, sacrificial release method. Relevant properties of ALD HfO2) such as dielectric constant and breakdown strength are characterized to further guide CMUT design. Experiments are performed on parallel fabricated test CMUTs with 50-nm gap and 16.5-MHz center frequency to measure and compare pressure output and receive sensitivity for 200-nm PECVD Six)Ny) and 100-nm HfO2) insulation layers. Results for this particular design show a 6-dB improvement in receiver output with the collapse voltage reduced by one-half; while in transmit mode, half the input voltage is needed to achieve the same maximum output pressure.

  15. CMUTs with High-K Atomic Layer Deposition Dielectric Material Insulation Layer

    PubMed Central

    Xu, Toby; Tekes, Coskun; Degertekin, F. Levent

    2014-01-01

    Use of high-κ dielectric, atomic layer deposition (ALD) materials as an insulation layer material for capacitive micromachined ultrasonic transducers (CMUTs) is investigated. The effect of insulation layer material and thickness on CMUT performance is evaluated using a simple parallel plate model. The model shows that both high dielectric constant and the electrical breakdown strength are important for the dielectric material, and significant performance improvement can be achieved, especially as the vacuum gap thickness is reduced. In particular, ALD hafnium oxide (HfO2) is evaluated and used as an improvement over plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SixNy) for CMUTs fabricated by a low-temperature, complementary metal oxide semiconductor transistor-compatible, sacrificial release method. Relevant properties of ALD HfO2 such as dielectric constant and breakdown strength are characterized to further guide CMUT design. Experiments are performed on parallel fabricated test CMUTs with 50-nm gap and 16.5-MHz center frequency to measure and compare pressure output and receive sensitivity for 200-nm PECVD SixNy and 100-nm HfO2 insulation layers. Results for this particular design show a 6-dB improvement in receiver output with the collapse voltage reduced by one-half; while in transmit mode, half the input voltage is needed to achieve the same maximum output pressure. PMID:25474786

  16. Atomic-layer-deposited Al2O3 and HfO2 on InAlAs: A comparative study of interfacial and electrical characteristics

    NASA Astrophysics Data System (ADS)

    Wu, Li-Fan; Zhang, Yu-Ming; Lv, Hong-Liang; Zhang, Yi-Men

    2016-10-01

    Al2O3 and HfO2 thin films are separately deposited on n-type InAlAs epitaxial layers by using atomic layer deposition (ALD). The interfacial properties are revealed by angle-resolved x-ray photoelectron spectroscopy (AR-XPS). It is demonstrated that the Al2O3 layer can reduce interfacial oxidation and trap charge formation. The gate leakage current densities are 1.37 × 10-6 A/cm2 and 3.22 × 10-6 A/cm2 at +1 V for the Al2O3/InAlAs and HfO2/InAlAs MOS capacitors respectively. Compared with the HfO2/InAlAs metal-oxide-semiconductor (MOS) capacitor, the Al2O3/InAlAs MOS capacitor exhibits good electrical properties in reducing gate leakage current, narrowing down the hysteresis loop, shrinking stretch-out of the C-V characteristics, and significantly reducing the oxide trapped charge (Q ot) value and the interface state density (D it). Project supported by the National Basic Research Program of China (Grant No. 2010CB327505), the Advanced Research Foundation of China (Grant No. 914xxx803-051xxx111), the National Defense Advance Research Project, China (Grant No. 513xxxxx306), the National Natural Science Foundation of China (Grant No. 51302215), the Scientific Research Program Funded by Shaanxi Provincial Education Department, China (Grant No. 14JK1656), and the Science and Technology Project of Shaanxi Province, China (Grant No. 2016KRM029).

  17. Optical properties of the Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings

    NASA Astrophysics Data System (ADS)

    Marszałek, Konstanty; Winkowski, Paweł; Jaglarz, Janusz

    2014-01-01

    Investigations of bilayer and trilayer Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings are presented in this paper. The oxide films were deposited on a heated quartz glass by e-gun evaporation in a vacuum of 5 × 10-3 [Pa] in the presence of oxygen. Depositions were performed at three different temperatures of the substrates: 100 °C, 200 °C and 300 °C. The coatings were deposited onto optical quartz glass (Corning HPFS). The thickness and deposition rate were controlled with Inficon XTC/2 thickness measuring system. Deposition rate was equal to 0.6 nm/s for Al2O3, 0.6 nm - 0.8 nm/s for HfO2 and 0.6 nm/s for SiO2. Simulations leading to optimization of the thin film thickness and the experimental results of optical measurements, which were carried out during and after the deposition process, have been presented. The optical thickness values, obtained from the measurements performed during the deposition process were as follows: 78 nm/78 nm for Al2O3/SiO2 and 78 nm/156 nm/78 nm for Al2O3/HfO2/SiO2. The results were then checked by ellipsometric technique. Reflectance of the films depended on the substrate temperature during the deposition process. Starting from 240 nm to the beginning of visible region, the average reflectance of the trilayer system was below 1 % and for the bilayer, minima of the reflectance were equal to 1.6 %, 1.15 % and 0.8 % for deposition temperatures of 100 °C, 200 °C and 300 °C, respectively.

  18. On the mechanisms of cation injection in conducting bridge memories: The case of HfO2 in contact with noble metal anodes (Au, Cu, Ag)

    NASA Astrophysics Data System (ADS)

    Saadi, M.; Gonon, P.; Vallée, C.; Mannequin, C.; Grampeix, H.; Jalaguier, E.; Jomni, F.; Bsiesy, A.

    2016-03-01

    Resistance switching is studied in HfO2 as a function of the anode metal (Au, Cu, and Ag) in view of its application to resistive memories (resistive random access memories, RRAM). Current-voltage (I-V) and current-time (I-t) characteristics are presented. For Au anodes, resistance transition is controlled by oxygen vacancies (oxygen-based resistive random access memory, OxRRAM). For Ag anodes, resistance switching is governed by cation injection (Conducting Bridge random access memory, CBRAM). Cu anodes lead to an intermediate case. I-t experiments are shown to be a valuable tool to distinguish between OxRRAM and CBRAM behaviors. A model is proposed to explain the high-to-low resistance transition in CBRAMs. The model is based on the theory of low-temperature oxidation of metals (Cabrera-Mott theory). Upon electron injection, oxygen vacancies and oxygen ions are generated in the oxide. Oxygen ions are drifted to the anode, and an interfacial oxide is formed at the HfO2/anode interface. If oxygen ion mobility is low in the interfacial oxide, a negative space charge builds-up at the HfO2/oxide interface. This negative space charge is the source of a strong electric field across the interfacial oxide thickness, which pulls out cations from the anode (CBRAM case). Inversely, if oxygen ions migration through the interfacial oxide is important (or if the anode does not oxidize such as Au), bulk oxygen vacancies govern resistance transition (OxRRAM case).

  19. Insights into thermal diffusion of germanium and oxygen atoms in HfO2/GeO2/Ge gate stacks and their suppressed reaction with atomically thin AlOx interlayers

    NASA Astrophysics Data System (ADS)

    Ogawa, Shingo; Asahara, Ryohei; Minoura, Yuya; Sako, Hideki; Kawasaki, Naohiko; Yamada, Ichiko; Miyamoto, Takashi; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2015-12-01

    The thermal diffusion of germanium and oxygen atoms in HfO2/GeO2/Ge gate stacks was comprehensively evaluated by x-ray photoelectron spectroscopy and secondary ion mass spectrometry combined with an isotopic labeling technique. It was found that 18O-tracers composing the GeO2 underlayers diffuse within the HfO2 overlayers based on Fick's law with the low activation energy of about 0.5 eV. Although out-diffusion of the germanium atoms through HfO2 also proceeded at the low temperatures of around 200 °C, the diffusing germanium atoms preferentially segregated on the HfO2 surfaces, and the reaction was further enhanced at high temperatures with the assistance of GeO desorption. A technique to insert atomically thin AlOx interlayers between the HfO2 and GeO2 layers was proven to effectively suppress both of these independent germanium and oxygen intermixing reactions in the gate stacks.

  20. High-dose neutron irradiation performance of dielectric mirrors

    DOE PAGES

    Nimishakavi Anantha Phani Kiran Kumar; Leonard, Keith J.; Jellison, Jr., Gerald Earle; Snead, Lance Lewis

    2015-05-01

    The study presents the high-dose behavior of dielectric mirrors specifically engineered for radiation-tolerance: alternating layers of Al2O3/SiO2 and HfO2/SiO2 were grown on sapphire substrates and exposed to neutron doses of 1 and 4 dpa at 458 10K in the High Flux Isotope Reactor (HFIR). In comparison to previously reported results, these higher doses of 1 and 4 dpa results in a drastic drop in optical reflectance, caused by a failure of the multilayer coating. HfO2/SiO2 mirrors failed completely when exposed to 1 dpa, whereas the reflectance of Al2O3/SiO2 mirrors reduced to 44%, eventually failing at 4 dpa. Transmission electron microscopymore » (TEM) observation of the Al2O3/SiO2 specimens showed SiO2 layer defects which increases size with irradiation dose. The typical size of each defect was 8 nm in 1 dpa and 42 nm in 4 dpa specimens. Buckling type delamination of the interface between the substrate and first layer was typically observed in both 1 and 4 dpa HfO2/SiO2 specimens. Composition changes across the layers were measured in high resolution scanning-TEM mode using energy dispersive spectroscopy. A significant interdiffusion between the film layers was observed in Al2O3/SiO2 mirror, though less evident in HfO2/SiO2 system. Lastly, the ultimate goal of this work is the provide insight into the radiation-induced failure mechanisms of these mirrors.« less

  1. Material insights of HfO2-based integrated 1-transistor-1-resistor resistive random access memory devices processed by batch atomic layer deposition

    PubMed Central

    Niu, Gang; Kim, Hee-Dong; Roelofs, Robin; Perez, Eduardo; Schubert, Markus Andreas; Zaumseil, Peter; Costina, Ioan; Wenger, Christian

    2016-01-01

    With the continuous scaling of resistive random access memory (RRAM) devices, in-depth understanding of the physical mechanism and the material issues, particularly by directly studying integrated cells, become more and more important to further improve the device performances. In this work, HfO2-based integrated 1-transistor-1-resistor (1T1R) RRAM devices were processed in a standard 0.25 μm complementary-metal-oxide-semiconductor (CMOS) process line, using a batch atomic layer deposition (ALD) tool, which is particularly designed for mass production. We demonstrate a systematic study on TiN/Ti/HfO2/TiN/Si RRAM devices to correlate key material factors (nano-crystallites and carbon impurities) with the filament type resistive switching (RS) behaviours. The augmentation of the nano-crystallites density in the film increases the forming voltage of devices and its variation. Carbon residues in HfO2 films turn out to be an even more significant factor strongly impacting the RS behaviour. A relatively higher deposition temperature of 300 °C dramatically reduces the residual carbon concentration, thus leading to enhanced RS performances of devices, including lower power consumption, better endurance and higher reliability. Such thorough understanding on physical mechanism of RS and the correlation between material and device performances will facilitate the realization of high density and reliable embedded RRAM devices with low power consumption. PMID:27312225

  2. Nanosecond pulsed laser damage characteristics of HfO2/SiO2 high reflection coatings irradiated from crystal-film interface.

    PubMed

    Cheng, Xinbin; Jiao, Hongfei; Lu, Jiangtao; Ma, Bin; Wang, Zhanshan

    2013-06-17

    The nano-precursors in the subsurface of Nd:YLF crystal were limiting factor that decreased the laser-induced damage threshold (LIDT) of HfO(2)/SiO(2) high reflection (HR) coatings irradiated from crystal-film interface. To investigate the contribution of electric-field (E-field) to laser damage originating from nano-precursors and then to probe the distribution of vulnerable nano-precursors in the direction of subsurface depth, two 1064 nm HfO(2)/SiO(2) HR coatings having different standing-wave (SW) E-field distributions in subsurface of Nd:YLF c5424181043036123rystal were designed and prepared. Artificial gold nano-particles were implanted into the crystal-film interface prior to deposition of HR coatings to study the damage behaviors in a more reliable way. The damage test results revealed that the SW E-field rather than the travelling-wave (TW) E-field contributed to laser damage. By comparing the SW E-field distributions and LIDTs of two HR coating designs, the most vulnerable nano-precursors were determined to be concentrated in a thin redeposition layer that is within 100 nm from the crystal-film interface.

  3. Integration of lead-free ferroelectric on HfO2/Si (100) for high performance non-volatile memory applications

    PubMed Central

    Kundu, Souvik; Maurya, Deepam; Clavel, Michael; Zhou, Yuan; Halder, Nripendra N.; Hudait, Mantu K.; Banerji, Pallab; Priya, Shashank

    2015-01-01

    We introduce a novel lead-free ferroelectric thin film (1-x)BaTiO3-xBa(Cu1/3Nb2/3)O3 (x = 0.025) (BT-BCN) integrated on to HfO2 buffered Si for non-volatile memory (NVM) applications. Piezoelectric force microscopy (PFM), x-ray diffraction, and high resolution transmission electron microscopy were employed to establish the ferroelectricity in BT-BCN thin films. PFM study reveals that the domains reversal occurs with 180° phase change by applying external voltage, demonstrating its effectiveness for NVM device applications. X-ray photoelectron microscopy was used to investigate the band alignments between atomic layer deposited HfO2 and pulsed laser deposited BT-BCN films. Programming and erasing operations were explained on the basis of band-alignments. The structure offers large memory window, low leakage current, and high and low capacitance values that were easily distinguishable even after ~106 s, indicating strong charge storage potential. This study explains a new approach towards the realization of ferroelectric based memory devices integrated on Si platform and also opens up a new possibility to embed the system within current complementary metal-oxide-semiconductor processing technology. PMID:25683062

  4. Material insights of HfO2-based integrated 1-transistor-1-resistor resistive random access memory devices processed by batch atomic layer deposition.

    PubMed

    Niu, Gang; Kim, Hee-Dong; Roelofs, Robin; Perez, Eduardo; Schubert, Markus Andreas; Zaumseil, Peter; Costina, Ioan; Wenger, Christian

    2016-01-01

    With the continuous scaling of resistive random access memory (RRAM) devices, in-depth understanding of the physical mechanism and the material issues, particularly by directly studying integrated cells, become more and more important to further improve the device performances. In this work, HfO2-based integrated 1-transistor-1-resistor (1T1R) RRAM devices were processed in a standard 0.25 μm complementary-metal-oxide-semiconductor (CMOS) process line, using a batch atomic layer deposition (ALD) tool, which is particularly designed for mass production. We demonstrate a systematic study on TiN/Ti/HfO2/TiN/Si RRAM devices to correlate key material factors (nano-crystallites and carbon impurities) with the filament type resistive switching (RS) behaviours. The augmentation of the nano-crystallites density in the film increases the forming voltage of devices and its variation. Carbon residues in HfO2 films turn out to be an even more significant factor strongly impacting the RS behaviour. A relatively higher deposition temperature of 300 °C dramatically reduces the residual carbon concentration, thus leading to enhanced RS performances of devices, including lower power consumption, better endurance and higher reliability. Such thorough understanding on physical mechanism of RS and the correlation between material and device performances will facilitate the realization of high density and reliable embedded RRAM devices with low power consumption. PMID:27312225

  5. Material insights of HfO2-based integrated 1-transistor-1-resistor resistive random access memory devices processed by batch atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Niu, Gang; Kim, Hee-Dong; Roelofs, Robin; Perez, Eduardo; Schubert, Markus Andreas; Zaumseil, Peter; Costina, Ioan; Wenger, Christian

    2016-06-01

    With the continuous scaling of resistive random access memory (RRAM) devices, in-depth understanding of the physical mechanism and the material issues, particularly by directly studying integrated cells, become more and more important to further improve the device performances. In this work, HfO2-based integrated 1-transistor-1-resistor (1T1R) RRAM devices were processed in a standard 0.25 μm complementary-metal-oxide-semiconductor (CMOS) process line, using a batch atomic layer deposition (ALD) tool, which is particularly designed for mass production. We demonstrate a systematic study on TiN/Ti/HfO2/TiN/Si RRAM devices to correlate key material factors (nano-crystallites and carbon impurities) with the filament type resistive switching (RS) behaviours. The augmentation of the nano-crystallites density in the film increases the forming voltage of devices and its variation. Carbon residues in HfO2 films turn out to be an even more significant factor strongly impacting the RS behaviour. A relatively higher deposition temperature of 300 °C dramatically reduces the residual carbon concentration, thus leading to enhanced RS performances of devices, including lower power consumption, better endurance and higher reliability. Such thorough understanding on physical mechanism of RS and the correlation between material and device performances will facilitate the realization of high density and reliable embedded RRAM devices with low power consumption.

  6. Lateral GaN nanowire prepared by using two-step TMAH wet etching and HfO2 sidewall spacer

    NASA Astrophysics Data System (ADS)

    Im, Ki-Sik; Won, Chul-Ho; Vodapally, Sindhuri; Son, Dong-Hyeok; Jo, Young-Woo; Park, YoHan; Lee, Jae-Hoon; Lee, Jung-Hee

    2016-05-01

    The initially dry-etched GaN layer with trapezoidal cross-section was laterally etched along the <11 2 bar0> direction in the tetramethyl ammonium hydroxide (TMAH) solution to form a sidewall normal to the direction, which is corresponding to the (11 2 bar0) plane. On the other hand, the etched sidewall still maintains the trapezoidal shape with angle of 58.4° when etched along the <1 1 bar00> direction, which is corresponding to the (1 1 bar01) plane. The GaN lateral nanowires with two different types of cross-sections, Ω-shape which is connected to underlying thick buffer layer through very narrow neck region and rectangle shape which is completely separated from underlying buffer layer, were realized with second lateral TMAH wet etching along the <11 2 bar0> direction and by using the atomic layer deposited (ALD) HfO2 layer as a sidewall spacer. The shape is dependent on both the height of the second dry-etched GaN sidewall below the HfO2 spacer and the second wet etching time in TMAH solution. It was found that the dangling bond density at the surface of the crystal plane is responsible for the strong lateral anisotropic etching property of the GaN layer in TMAH solution.

  7. The role of microstructure on the optical performance of neutron irradiated dielectric mirrors

    NASA Astrophysics Data System (ADS)

    Leonard, Keith J.; Jellison, Gerald E.; Kumar, N. A. P. Kiran; Snead, Lance L.

    2014-02-01

    Dielectric mirrors of HfO2/SiO2 and Al2O3/SiO2 designed for optimum reflectivity at 248 nm with 11 and 30 bi-layer coatings, respectively, survived irradiation to 0.1 dpa at 448 K without film cracking or delamination from their sapphire substrates. Subsequent annealing of the irradiated samples resulted in a loss of reflectivity in the HfO2/SiO2 mirror, while the Al2O3/SiO2 type remained unaffected. Microstructural changes that correlate to optical property changes of the mirror are investigated. The amorphous layers of the Al2O3/SiO2 mirror provide greater stability despite increased Al and Si interdiffusion across the film interfaces with increasing dose and post-irradiation annealing temperature. This interdiffusion may have limited the densification of SiO2 in the Al2O3/SiO2 mirror, but no interdiffusion was observed for the HfO2/SiO2 mirror. The thickness changes in the SiO2 layers of the HfO2/SiO2 mirror resulted in a shifting of the peak reflectivity to lower wavelengths. The formation of an amorphous Al-O layer within the substrate is observed in the 0.1 dpa irradiated HfO2/SiO2 mirror, which on further annealing at 573 and 673 K resulted in a buckling-type delamination failures in the mirrors producing a loss in reflectivity.

  8. Loss/gain-induced ultrathin antireflection coatings.

    PubMed

    Luo, Jie; Li, Sucheng; Hou, Bo; Lai, Yun

    2016-01-01

    Tradional antireflection coatings composed of dielectric layers usually require the thickness to be larger than quarter wavelength. Here, we demonstrate that materials with permittivity or permeability dominated by imaginary parts, i.e. lossy or gain media, can realize non-resonant antireflection coatings in deep sub-wavelength scale. Interestingly, while the reflected waves are eliminated as in traditional dielectric antireflection coatings, the transmitted waves can be enhanced or reduced, depending on whether gain or lossy media are applied, respectively. We provide a unified theory for the design of such ultrathin antireflection coatings, showing that under different polarizations and incident angles, different types of ultrathin coatings should be applied. Especially, under transverse magnetic polarization, the requirement shows a switch between gain and lossy media at Brewster angle. As a proof of principle, by using conductive films as a special type of lossy antireflection coatings, we experimentally demonstrate the suppression of Fabry-Pérot resonances in a broad frequency range for microwaves. This valuable functionality can be applied to remove undesired resonant effects, such as the frequency-dependent side lobes induced by resonances in dielectric coverings of antennas. Our work provides a guide for the design of ultrathin antireflection coatings as well as their applications in broadband reflectionless devices. PMID:27349750

  9. Loss/gain-induced ultrathin antireflection coatings

    PubMed Central

    Luo, Jie; Li, Sucheng; Hou, Bo; Lai, Yun

    2016-01-01

    Tradional antireflection coatings composed of dielectric layers usually require the thickness to be larger than quarter wavelength. Here, we demonstrate that materials with permittivity or permeability dominated by imaginary parts, i.e. lossy or gain media, can realize non-resonant antireflection coatings in deep sub-wavelength scale. Interestingly, while the reflected waves are eliminated as in traditional dielectric antireflection coatings, the transmitted waves can be enhanced or reduced, depending on whether gain or lossy media are applied, respectively. We provide a unified theory for the design of such ultrathin antireflection coatings, showing that under different polarizations and incident angles, different types of ultrathin coatings should be applied. Especially, under transverse magnetic polarization, the requirement shows a switch between gain and lossy media at Brewster angle. As a proof of principle, by using conductive films as a special type of lossy antireflection coatings, we experimentally demonstrate the suppression of Fabry-Pérot resonances in a broad frequency range for microwaves. This valuable functionality can be applied to remove undesired resonant effects, such as the frequency-dependent side lobes induced by resonances in dielectric coverings of antennas. Our work provides a guide for the design of ultrathin antireflection coatings as well as their applications in broadband reflectionless devices. PMID:27349750

  10. Effects of dual-spacer dielectrics on low-power and high-speed performance of sub-10 nm tunneling field-effect transistors

    NASA Astrophysics Data System (ADS)

    Yoon, Young Jun; Seo, Jae Hwa; Cho, Seongjae; Kwon, Hyuck-In; Lee, Jung-Hee; Kang, In Man

    2016-06-01

    In this paper, we propose and investigate a dual-spacer dielectric structure for realizing a sub-10 nm tunneling field-effect transistors (TFET) with excellent low-power (LP) and switching performance. The effects of the dual-spacer dielectric were assessed by analyzing the direct current (DC) and radio frequency (RF) performance of the GaAs0.5Sb0.5/In0.53Ga0.47As heterojunction-based short channel TFETs. The dual-spacer dielectric that consists of hafnium oxide (HfO2) and silicon dioxide (SiO2) raises an energy-band on drain-side because of the fringe field induced by the high-k spacer dielectric HfO2. The raised energy-band suppresses direct band-to-band tunneling (BBT) through the channel region and drain-induced barrier thinning (DIBT) phenomenon with improvement in the off-state current (I off) and subthreshold swing (S). The dual-spacer dielectric also influences total gate capacitance (C gg) because the HfO2 in the dual-spacer dielectric increases out-fringe capacitance (C of) in gate-to-drain capacitance (C gd). Although the proposed TFET has a high C gd, the optimized TFET with the HfO2 length (L dual-spacer) of 30 nm achieves a lower intrinsic delay time (τ), a higher cut-off frequency (f T), and a higher maximum oscillation frequency (f max) owing to higher current performance and smaller gate-to-source capacitance (C gs).

  11. Impact of carbon and nitrogen on gate dielectrics in metal-oxide-semiconductor devices

    NASA Astrophysics Data System (ADS)

    Choi, Minseok; Lyons, John; Janotti, Anderson; van de Walle, Chris

    2013-03-01

    Al2O3 and HfO2 are used as alternative gate oxides in CMOS technology. Promising results have been achieved with Al2O3/III-V and HfO2/Si MOS structures, which exhibit relatively low densities of interface states. However, the presence of charge traps and fixed-charge centers near the oxide/semiconductor interface still poses serious limitations in device performance. Native point defects are usually proposed as an explanation; unintentional incorporation of impurities in the gate dielectric during the deposition process has so far received less attention. Using first-principles calculations based on hybrid functionals we investigate the effects of carbon and nitrogen impurities in Al2O3 and HfO2. By analyzing the position of the impurity levels with respect to the III-V and Si band edges, we determine if these impurities can act as charge traps or sources of fixed charge. Our results show that carbon can act as a charge trap and lead to leakage current through the gate dielectric. Nitrogen can act as a source of negative fixed charge, but may be effective in alleviating the problem of charge traps and fixed charges associated with Al, Hf, and O vacancies. This work was supported by the ONR DEFINE MURI program.

  12. Ultrathin Dielectric Oxide Films On Silicon

    DOEpatents

    Klemperer, Walter G.; Lee, Jason; Mikalsen, Erik A.; Payne, David A.

    2004-09-21

    A method of making a semiconductor structure includes contacting a surface of a semiconductor with a liquid including Zr.sub.4 (OPr.sup.n).sub.16 to form a modified surface, activating the modified surface, and repeating the contacting and activating to form a layer of zirconia on the semiconductor surface.

  13. Near-ultraviolet absorption and nanosecond-pulse-laser damage in HfO2 monolayers studied by submicrometer-resolution photothermal heterodyne imaging and atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Papernov, S.; Tait, A.; Bittle, W.; Schmid, A. W.; Oliver, J. B.; Kupinski, P.

    2011-06-01

    Localized absorption in hafnium dioxide used as a high-index component in multilayer coatings for near-ultraviolet, nanosecond-pulse-laser applications is directly linked to laser-induced damage. The nature of the absorbing species and their physical properties remains unknown because of their extremely small sizes. Previous experimental evidence provided by the atomic force microscopy mapping of damage morphology points to a few-nanometer scale of these absorbers. This work demonstrates the submicrometer-resolution mapping of 355-nm absorption in HfO2 monolayers using a recently developed photothermal heterodyne imaging technique. The comparison of absorption maps with the atomic force microscopy investigation of pulsed-laser-induced damage morphology allows one to better estimate the spatial distribution of nanoscale absorbing defects in hafnia thin films. Possible defect-formation mechanisms are discussed.

  14. In situ reaction mechanism studies on ozone-based atomic layer deposition of Al(2)O(3) and HfO(2).

    PubMed

    Rose, Martin; Niinistö, Jaakko; Endler, Ingolf; Bartha, Johann W; Kücher, Peter; Ritala, Mikko

    2010-02-01

    The mechanisms of technologically important atomic layer deposition (ALD) processes, trimethylaluminium (TMA)/ozone and tetrakis(ethylmethylamino)hafnium (TEMAH)/ozone, for the growth of Al(2)O(3) and HfO(2) thin films are studied in situ by a quadrupole mass spectrometer coupled with a 300 mm ALD reactor. In addition to released CH(4) and CO(2), water was detected as one of the reaction byproduct in the TMA/O(3) process. In the TEMAH/O(3) process, the surface after the ozone pulse consisted of chemisorpted active oxygen and -OH groups, leading to the release of H(2)O, CO(2), and HNEtMe during the metal precursor pulse.

  15. The effect of a Ta oxygen scavenger layer on HfO2-based resistive switching behavior: thermodynamic stability, electronic structure, and low-bias transport.

    PubMed

    Zhong, Xiaoliang; Rungger, Ivan; Zapol, Peter; Nakamura, Hisao; Asai, Yoshihiro; Heinonen, Olle

    2016-03-14

    Reversible resistive switching between high-resistance and low-resistance states in metal-oxide-metal heterostructures makes them very interesting for applications in random access memories. While recent experimental work has shown that inserting a metallic "oxygen scavenger layer" between the positive electrode and oxide improves device performance, the fundamental understanding of how the scavenger layer modifies the heterostructure properties is lacking. We use density functional theory to calculate thermodynamic properties and conductance of TiN/HfO2/TiN heterostructures with and without a Ta scavenger layer. First, we show that Ta insertion lowers the formation energy of low-resistance states. Second, while the Ta scavenger layer reduces the Schottky barrier height in the high-resistance state by modifying the interface charge at the oxide-electrode interface, the heterostructure maintains a high resistance ratio between high- and low-resistance states. Finally, we show that the low-bias conductance of device on-states becomes much less sensitive to the spatial distribution of oxygen removed from the HfO2 in the presence of the Ta layer. By providing a fundamental understanding of the observed improvements with scavenger layers, we open a path to engineer interfaces with oxygen scavenger layers to control and enhance device performance. In turn, this may enable the realization of a non-volatile low-power memory technology with concomitant reduction in energy consumption by consumer electronics and offering significant benefits to society.

  16. Atomic layer deposition for fabrication of HfO2/Al2O3 thin films with high laser-induced damage thresholds.

    PubMed

    Wei, Yaowei; Pan, Feng; Zhang, Qinghua; Ma, Ping

    2015-01-01

    Previous research on the laser damage resistance of thin films deposited by atomic layer deposition (ALD) is rare. In this work, the ALD process for thin film generation was investigated using different process parameters such as various precursor types and pulse duration. The laser-induced damage threshold (LIDT) was measured as a key property for thin films used as laser system components. Reasons for film damaged were also investigated. The LIDTs for thin films deposited by improved process parameters reached a higher level than previously measured. Specifically, the LIDT of the Al2O3 thin film reached 40 J/cm(2). The LIDT of the HfO2/Al2O3 anti-reflector film reached 18 J/cm(2), the highest value reported for ALD single and anti-reflect films. In addition, it was shown that the LIDT could be improved by further altering the process parameters. All results show that ALD is an effective film deposition technique for fabrication of thin film components for high-power laser systems.

  17. The effect of a Ta oxygen scavenger layer on HfO2-based resistive switching behavior: thermodynamic stability, electronic structure, and low-bias transport.

    PubMed

    Zhong, Xiaoliang; Rungger, Ivan; Zapol, Peter; Nakamura, Hisao; Asai, Yoshihiro; Heinonen, Olle

    2016-03-14

    Reversible resistive switching between high-resistance and low-resistance states in metal-oxide-metal heterostructures makes them very interesting for applications in random access memories. While recent experimental work has shown that inserting a metallic "oxygen scavenger layer" between the positive electrode and oxide improves device performance, the fundamental understanding of how the scavenger layer modifies the heterostructure properties is lacking. We use density functional theory to calculate thermodynamic properties and conductance of TiN/HfO2/TiN heterostructures with and without a Ta scavenger layer. First, we show that Ta insertion lowers the formation energy of low-resistance states. Second, while the Ta scavenger layer reduces the Schottky barrier height in the high-resistance state by modifying the interface charge at the oxide-electrode interface, the heterostructure maintains a high resistance ratio between high- and low-resistance states. Finally, we show that the low-bias conductance of device on-states becomes much less sensitive to the spatial distribution of oxygen removed from the HfO2 in the presence of the Ta layer. By providing a fundamental understanding of the observed improvements with scavenger layers, we open a path to engineer interfaces with oxygen scavenger layers to control and enhance device performance. In turn, this may enable the realization of a non-volatile low-power memory technology with concomitant reduction in energy consumption by consumer electronics and offering significant benefits to society. PMID:26902598

  18. How reduced vacuum pumping capability in a coating chamber affects the laser damage resistance of HfO2/SiO2 antireflection and high reflection coatings.

    DOE PAGES

    Field, Ella Suzanne; Bellum, John Curtis; Kletecka, Damon E.

    2016-06-01

    Optical coatings with the highest laser damage thresholds rely on clean conditions in the vacuum chamber during the coating deposition process. A low base pressure in the coating chamber, as well as the ability of the vacuum system to maintain the required pressure during deposition, are important aspects of limiting the amount of defects in an optical coating that could induce laser damage. Our large optics coating chamber at Sandia National Laboratories normally relies on three cryo pumps to maintain low pressures for e-beam coating processes. However, on occasion, one or more of the cryo pumps have been out ofmore » commission. In light of this circumstance, we explored how deposition under compromised vacuum conditions resulting from the use of only one or two cryo pumps affects the laser-induced damage thresholds of optical coatings. Finally, the coatings of this study consist of HfO2 and SiO2 layer materials and include antireflection coatings for 527 nm at normal incidence, and high reflection coatings for 527 nm, 45⁰ angle of incidence (AOI), in P-polarization (P-pol).« less

  19. The effect of Ta ``oxygen scavenger layer'' on HfO2-based resistive switching behavior: termodynamic stability, electronic structure, and low-bias transport

    NASA Astrophysics Data System (ADS)

    Zhong, Xiaoliang; Rungger, Ivan; Zapol, Peter; Nakamura, Hisao; Asai, Yoshihiro; Heinonen, Olle

    Metal-oxide-metal heterostructures are promising candidates for next-generation random access memories, which exhibit reversible resistive switching between high- and low-conductance states. Recent experimental work showed that inserting a metallic `oxygen scavenger layer' between TiN electrode and HfO2 significantly improves device switching performance. We show, using atomistic modeling within the GGA +U scheme of Density Functional Theory, that a Ta oxygen scavenger layer significantly enhances the thermodynamic stability of depleting oxygen from the oxide. Furthermore, the presence of a Ta layer reduces the dependence of the Schottky barrier heights on the location of the oxygen removed from the oxide matrix. Finally, the Schottky barrier height has a very small effect on the on-state low-bias conductance; this is more sensitive to the location of the depleted oxygen. We gratefully acknowledge the computing resources provided on Blues, a high-performance computing cluster operated by the Laboratory Computing Resource Center at Argonne National Laboratory. Work at Argonne was supported by U. S. DOE, Office of Science under Contract No. DE-AC02-06CH11357.

  20. Study on the laser-induced damage performance of HfO2, Sc2O3, Y2O3, Al2O3 and SiO2 monolayer coatings

    NASA Astrophysics Data System (ADS)

    Zhu, Meiping; Yi, Kui; Li, Dawei; Qi, Hongji; Zhao, Yuanan; Liu, Jie; Liu, Xiaofeng; Hu, Guohang; Shao, Jianda

    2013-11-01

    The laser induced damage threshold (LIDT) and damage morphology of the monolayer coating are easily influenced by the finish condition of the substrate, which makes it difficult to compare the LIDT of different coating materials. In order to eliminate the influence of defect and sub-defect on the substrate, HfO2, Sc2O3, Y2O3, Al2O3 and SiO2 monolayer coatings were prepared on 1064 nm HfO2/SiO2 high reflection coatings, using conventional e-beam deposition. The LIDT, as well as the damage morphology after laser irradiation at wavelength of 1064 nm, was measured and compared with that of the monolayer coating deposited on BK7 glass substrate.

  1. On device design for steep-slope negative-capacitance field-effect-transistor operating at sub-0.2V supply voltage with ferroelectric HfO2 thin film

    NASA Astrophysics Data System (ADS)

    Kobayashi, Masaharu; Hiramoto, Toshiro

    2016-02-01

    Internet-of-Things (IoT) technologies require a new energy-efficient transistor which operates at ultralow voltage and ultralow power for sensor node devices employing energy-harvesting techniques as power supply. In this paper, a practical device design guideline for low voltage operation of steep-slope negative-capacitance field-effect-transistors (NCFETs) operating at sub-0.2V supply voltage is investigated regarding operation speed, material requirement and energy efficiency in the case of ferroelectric HfO2 gate insulator, which is the material fully compatible to Complementary Metal-Oxide-Semiconductor (CMOS) process technologies. A physics-based numerical simulator was built to design NCFETs with the use of experimental HfO2 material parameters by modeling the ferroelectric gate insulator and FET channel simultaneously. The simulator revealed that NCFETs with ferroelectric HfO2 gate insulator enable hysteresis-free operation by setting appropriate operation point with a few nm thick gate insulator. It also revealed that, if the finite response time of spontaneous polarization of the ferroelectric gate insulator is 10-100psec, 1-10MHz operation speed can be achieved with negligible hysteresis. Finally, by optimizing material parameters and tuning negative capacitance, 2.5 times higher energy efficiency can be achieved by NCFET than by conventional MOSFETs. Thus, NCFET is expected to be a new CMOS technology platform for ultralow power IoT.

  2. Thermal Conductivity and Stability of HfO2-Y2O3 and La2Zr2O7 Evaluated for 1650 Deg C Thermal/Environmental Barrier Coating Applications

    NASA Technical Reports Server (NTRS)

    Zhu, Dong-Ming; Bansal, Narottam P.; Miller, Robert A.

    2003-01-01

    HfO2-Y2O3 and La2Zr2O7 are candidate thermal and environmental barrier coating (T/EBC) materials for gas turbine ceramic matrix composite (CMC) combustor applications because of their relatively low thermal conductivity and high temperature capability. In this paper, thermal conductivity and high temperature stability of hot-pressed and plasma sprayed specimens with representative partially-stabilized and fully-cubic HfO2-Y2O3 compositions and La2Zr2O7 were evaluated at temperatures up to 1700 C using a steady-state laser heat-flux technique. Sintering behavior of the plasmasprayed coatings was determined by monitoring the thermal conductivity increases during a 20-hour test period at various temperatures. Durability and failure mechanisms of the HfO2-Y2O3 and La2Zr2O7 coatings on mullite/SiC hexoloy or SiC/SiC CMC substrates were investigated at 1650 C under thermal gradient cyclic conditions. Coating design and testing issues for the 1650 C thermal/environmental barrier coating applications are also discussed.

  3. CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Growth Related Carrier Mobility Enhancement of Pentacene Thin-Film Transistors with High-k Oxide Gate Dielectric

    NASA Astrophysics Data System (ADS)

    Yu, Ai-Fang; Qi, Qiong; Jiang, Peng; Jiang, Chao

    2009-07-01

    Carrier mobility enhancement from 0.09 to 0.59 cm2/Vs is achieved for pentacene-based thin-film transistors (TFTs) by modifying the HfO2 gate dielectric with a polystyrene (PS) thin film. The improvement of the transistor's performance is found to be strongly related to the initial film morphologies of pentacene on the dielectrics. In contrast to the three-dimensional island-like growth mode on the HfO2 surface, the Stranski-Krastanov growth mode on the smooth and nonpolar PS/HfO2 surface is believed to be the origin of the excellent carrier mobility of the TFTs. A large well-connected first monolayer with fewer boundaries is formed via the Stranski-Krastanov growth mode, which facilitates a charge transport parallel to the substrate and promotes higher carrier mobility.

  4. Evolutionary search for new high-k dielectric materials: methodology and applications to hafnia-based oxides.

    PubMed

    Zeng, Qingfeng; Oganov, Artem R; Lyakhov, Andriy O; Xie, Congwei; Zhang, Xiaodong; Zhang, Jin; Zhu, Qiang; Wei, Bingqing; Grigorenko, Ilya; Zhang, Litong; Cheng, Laifei

    2014-02-01

    High-k dielectric materials are important as gate oxides in microelectronics and as potential dielectrics for capacitors. In order to enable computational discovery of novel high-k dielectric materials, we propose a fitness model (energy storage density) that includes the dielectric constant, bandgap, and intrinsic breakdown field. This model, used as a fitness function in conjunction with first-principles calculations and the global optimization evolutionary algorithm USPEX, efficiently leads to practically important results. We found a number of high-fitness structures of SiO2 and HfO2, some of which correspond to known phases and some of which are new. The results allow us to propose characteristics (genes) common to high-fitness structures--these are the coordination polyhedra and their degree of distortion. Our variable-composition searches in the HfO2-SiO2 system uncovered several high-fitness states. This hybrid algorithm opens up a new avenue for discovering novel high-k dielectrics with both fixed and variable compositions, and will speed up the process of materials discovery.

  5. Deposition, stabilization and characterization of zirconium oxide and hafnium oxide thin films for high k gate dielectrics

    NASA Astrophysics Data System (ADS)

    Gao, Yong

    As the MOS devices continue to scale down in feature size, the gate oxide thickness is approaching the nanometer node. High leakage current densities caused by tunneling is becoming a serious problem. Replacing silicon oxide with a high kappa material as the gate dielectrics is becoming very critical. In recent years, research has been focused on a few promising candidates, such as ZrO2, HfO2, Al2O3, Ta 2O5, and some silicates. However, unary metal oxides tend to crystallize at relatively low temperatures (less than 700°C). Crystallized films usually have a very small grain size and high leakage current due to the grain boundaries. The alternatives are high kappa oxides which are single crystal or amorphous. Silicates remain amorphous at high temperatures, but have some problems such as phase separation, interface reaction, and lower kappa value. In this work, we addressed the crystallization problems of zirconium oxide and hafnium oxide thin films. Both of these two thin films were deposited by DC reactive magnetron sputtering so that very dense films were deposited with little damage. A specially designed system was set up in order to have good control of the deposition process. The crystallization behavior of as-deposited amorphous ZrO2 and HfO2 films was studied. It was found that the films tended to have higher crystallization temperature when the films were thinner than a critical thickness of approximately 5 nm. However, it was still well below 900°C. The crystallization temperature was significantly increased by sandwiching the high kappa oxide layer between two silica layers. Ultra thin HfO2 films of 5nm thickness remained amorphous up to 900°C. This is the highest crystallization temperature which has been reported. The mechanisms for this effect are proposed. Electrical properties of these high kappa dielectric films were also studied. It was found that ultra thin amorphous HfO2 and ZrO 2 films had superior electrical properties to crystalline films

  6. Pulsed external magnetic fields increase the deposition rate in reactive HiPIMS while preserving stoichiometry: An application to amorphous HfO2

    NASA Astrophysics Data System (ADS)

    Ganesan, R.; Treverrow, B.; Denniss, P.; McCulloch, D. G.; McKenzie, D. R.; Bilek, M. M. M.

    2016-09-01

    We compare the use of externally applied pulsed and steady magnetic fields for the enhancement of deposition rate in reactive High Power Impulse Magnetron Sputtering (HiPIMS), using the deposition of amorphous hafnium oxide (a-HfO2) on Si as an example. The external magnetic fields were applied by a solenoidal coil, placed above the magnetron target. In the case of a steady magnetic field, a higher voltage was required to initiate the HiPIMS discharge, a longer delay time was observed for current onset, and the films became substoichiometric. For the pulsed magnetic field, film stoichiometry was maintained under all applied external magnetic field strengths. Varying the duration and delay times of the magnetic field after the application of HiPIMS voltage pulse revealed that the afterglow of the plasma between HiPIMS pulses was actively quenched by the presence of the magnetic field. Therefore, the optimum operation with the highest plasma density was obtained by applying the external magnetic field only when the plasma was established and removing it at the end of the HiPIMS pulse. A model to explain the findings is presented in which the target poisoning by oxide formation is determined by the conditions in the afterglow. We describe an approach to achieve maximum deposition rate while maintaining film stoichiometry and high film quality. Amorphous HfO2 films with leakage current through the film of less than 5 × 10-5 A/cm2 at 0.1 MV/cm were obtained at the maximum deposition rate. The refractive index, at a wavelength of 500 nm, of the film prepared with pulsed magnetic field was 2.05 with a very low extinction coefficient of 8 × 10-5.

  7. The influence of surface preparation on low temperature HfO2 ALD on InGaAs (001) and (110) surfaces

    NASA Astrophysics Data System (ADS)

    Kent, Tyler; Tang, Kechao; Chobpattana, Varistha; Negara, Muhammad Adi; Edmonds, Mary; Mitchell, William; Sahu, Bhagawan; Galatage, Rohit; Droopad, Ravi; McIntyre, Paul; Kummel, Andrew C.

    2015-10-01

    Current logic devices rely on 3D architectures, such as the tri-gate field effect transistor (finFET), which utilize the (001) and (110) crystal faces simultaneously thus requiring passivation methods for the (110) face in order to ensure a pristine 3D surface prior to further processing. Scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and correlated electrical measurement on MOSCAPs were utilized to compare the effects of a previously developed in situ pre-atomic layer deposition (ALD) surface clean on the InGaAs (001) and (110) surfaces. Ex situ wet cleans are very effective on the (001) surface but not the (110) surface. Capacitance voltage indicated the (001) surface with no buffered oxide etch had a higher Cmax hypothesized to be a result of poor nucleation of HfO2 on the native oxide. An in situ pre-ALD surface clean employing both atomic H and trimethylaluminum (TMA) pre-pulsing, developed by Chobpattana et al. and Carter et al. for the (001) surface, was demonstrated to be effective on the (110) surface for producing low Dit high Cox MOSCAPs. Including TMA in the pre-ALD surface clean resulted in reduction of the magnitude of the interface state capacitance. The XPS studies show the role of atomic H pre-pulsing is to remove both carbon and oxygen while STM shows the role of TMA pre-pulsing is to eliminate H induced etching. Devices fabricated at 120 °C and 300 °C were compared.

  8. The influence of surface preparation on low temperature HfO2 ALD on InGaAs (001) and (110) surfaces.

    PubMed

    Kent, Tyler; Tang, Kechao; Chobpattana, Varistha; Negara, Muhammad Adi; Edmonds, Mary; Mitchell, William; Sahu, Bhagawan; Galatage, Rohit; Droopad, Ravi; McIntyre, Paul; Kummel, Andrew C

    2015-10-28

    Current logic devices rely on 3D architectures, such as the tri-gate field effect transistor (finFET), which utilize the (001) and (110) crystal faces simultaneously thus requiring passivation methods for the (110) face in order to ensure a pristine 3D surface prior to further processing. Scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and correlated electrical measurement on MOSCAPs were utilized to compare the effects of a previously developed in situ pre-atomic layer deposition (ALD) surface clean on the InGaAs (001) and (110) surfaces. Ex situ wet cleans are very effective on the (001) surface but not the (110) surface. Capacitance voltage indicated the (001) surface with no buffered oxide etch had a higher C(max) hypothesized to be a result of poor nucleation of HfO2 on the native oxide. An in situ pre-ALD surface clean employing both atomic H and trimethylaluminum (TMA) pre-pulsing, developed by Chobpattana et al. and Carter et al. for the (001) surface, was demonstrated to be effective on the (110) surface for producing low D(it) high C(ox) MOSCAPs. Including TMA in the pre-ALD surface clean resulted in reduction of the magnitude of the interface state capacitance. The XPS studies show the role of atomic H pre-pulsing is to remove both carbon and oxygen while STM shows the role of TMA pre-pulsing is to eliminate H induced etching. Devices fabricated at 120 °C and 300 °C were compared.

  9. Thermal response of Ru electrodes in contact with SiO2 and Hf-based high-k gate dielectrics

    NASA Astrophysics Data System (ADS)

    Wen, H.-C.; Lysaght, P.; Alshareef, H. N.; Huffman, C.; Harris, H. R.; Choi, K.; Senzaki, Y.; Luan, H.; Majhi, P.; Lee, B. H.; Campin, M. J.; Foran, B.; Lian, G. D.; Kwong, D.-L.

    2005-08-01

    A systematic experimental evaluation of the thermal stability of Ru metal gate electrodes in direct contact with SiO2 and Hf-based dielectric layers was performed and correlated with electrical device measurements. The distinctly different interfacial reactions in the Ru /SiO2, Ru /HfO2, and Ru /HfSiOx film systems were observed through cross-sectional high-resolution transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy with electron-energy-loss spectra, and energy dispersive x-ray spectra analysis. Ru interacted with SiO2, but remained stable on HfO2 at 1000°C. The onset of Ru /SiO2 interfacial interactions is identified via silicon substrate pitting possibly from Ru diffusion into the dielectric in samples exposed to a 900°C/10-s anneal. The dependence of capacitor device degradation with decreasing SiO2 thickness suggests Ru diffuses through SiO2, followed by an abrupt, rapid, nonuniform interaction of ruthenium silicide as Ru contacts the Si substrate. Local interdiffusion detected on Ru /HfSiOx samples may be due to phase separation of HfSiOx into HfO2 grains within a SiO2 matrix, suggesting that SiO2 provides a diffusion pathway for Ru. Detailed evidence consistent with a dual reaction mechanism for the Ru /SiO2 system at 1000°C is presented.

  10. Effects of Elevated Source/Drain and Side Spacer Dielectric on the Drivability Optimization of Non-abrupt Ultra Shallow Junction Gate Underlap DG MOSFETs

    NASA Astrophysics Data System (ADS)

    Singh, Kunal; Kumar, Sanjay; Goel, Ekta; Singh, Balraj; Dubey, Sarvesh; Jit, Satyabrata

    2016-09-01

    The effects of drain/source elevation height (h SD) and side spacer dielectric between the gate and source/drain regions on the drivability performance of the non-abrupt ultra-shallow-junction gate underlap double gate metal oxide field effect transistor of 18 nm gate length has been investigated in terms of the on-state (I on), off-state (I off) drain currents, and I on/I off ratio. Among the Air, SiO2, Si3N4, and HfO2 used as spacer dielectrics, while both I on and I on/I off are increased with the elevation height (h SD) and permittivity of the spacer dielectric, interestingly, an inverse relation between the I on and I off for all h SD below ˜32.5 nm is observed only for the SiO2 spacer dielectric. Another new observation is the increase in I off with the h SD and permittivity of the spacer dielectric due to the enhancement of gate-induced drain leakage current owing to the increased vertical electric field at the drain side. For the most commonly used dielectrics SiO2 and HfO2 in the spacer region, the I on/I off ratio is increased by ˜277% (at h SD = 32.5 nm) and ˜516% (at h SD = 9.5 nm) with respect to their corresponding values at zero elevation, respectively.

  11. Design of a recessed-gate GaN-based MOSFET using a dual gate dielectric for high-power applications

    NASA Astrophysics Data System (ADS)

    Yoon, Young Jun; Kang, Hee-Sung; Seo, Jae Hwa; Kim, Young-Jo; Bae, Jin-Hyuk; Lee, Jung-Hee; Kang, In Man; Cho, Seongjae; Cho, Eou-Sik

    2014-11-01

    We have investigated gallium-nitride (GaN)-based metal-oxide-semiconductor field-effect transistors (MOSFETs) having a recessed-gate structure for high-power applications. Recessed-gate GaN-based MOSFETs have been designed with a dual high- k dielectric structure to overcome low current drivability. Compared to recessed-gate GaN-based MOSFETs having a single gate dielectric with the same oxide thickness, recessed-gate GaN-based MOSFETs having a dual high- k dielectric composed of Al2O3 and HfO2 have achieved a high drain current ( I D ) and transconductance ( g m ) due to the high dielectric constant of HfO2. Also, because the dual high- k dielectric forms a high electron density in the channel layer with outstanding gate control capability, low channel resistances ( R ch ) have obtained. In addition, we have studied the effect of the length between the gate and the drain ( L gd ) on the on-resistance ( R on ) to minimize the R on that is associated with power consumption and switching performance. Also, the electric field distribution of a device having a dual high- k dielectric has been examined with a field plate structure for high drive voltage. The proposed device was confirmed to be a remarkable candidate for switching devices in high-power applications.

  12. Ultra-thin multilayer capacitors.

    SciTech Connect

    Renk, Timothy Jerome; Monson, Todd C.

    2009-06-01

    The fabrication of ultra-thin lanthanum-doped lead zirconium titanate (PLZT) multilayer ceramic capacitors (MLCCs) using a high-power pulsed ion beam was studied. The deposition experiments were conducted on the RHEPP-1 facility at Sandia National Laboratories. The goal of this work was to increase the energy density of ceramic capacitors through the formation of a multilayer device with excellent materials properties, dielectric constant, and standoff voltage. For successful device construction, there are a number of challenging requirements including achieving correct stoichiometric and crystallographic composition of the deposited PLZT, as well as the creation of a defect free homogenous film. This report details some success in satisfying these requirements, although 900 C temperatures were necessary for PLZT perovskite phase formation. These temperatures were applied to a previously deposited multi-layer film which was then post-annealed to this temperature. The film exhibited mechanical distress attributable to differences in the coefficient of thermal expansion (CTE) of the various layers. This caused significant defects in the deposited films that led to shorts across devices. A follow-on single layer deposition without post-anneal produced smooth layers with good interface behavior, but without the perovskite phase formation. These issues will need to be addressed in order for ion beam deposited MLCCs to become a viable technology. It is possible that future in-situ heating during deposition may address both the CTE issue, and result in lowered processing temperatures, which in turn could raise the probability of successful MLCC formation.

  13. Improved n-channel Ge gate stack performance using HfAlO high-k dielectric for various Al concentrations

    NASA Astrophysics Data System (ADS)

    Kothari, Shraddha; Joishi, Chandan; Ghosh, Sayantan; Biswas, Dipankar; Vaidya, Dhirendra; Ganguly, Swaroop; Lodha, Saurabh

    2016-07-01

    We demonstrate improved Ge n-channel gate stack performance versus HfO2 using HfAlO high-k dielectric for a wide (1.5–33%) range of Al% and post-high-k-deposition annealing (PDA) at 400 °C. Addition of Al to HfO2 is shown to mitigate degradation of the GeO2/Ge interface during PDA. HfAlO stacks with an equivalent oxide thickness (EOT) of 8 nm and large Al% exhibit improved transistor mobility (1.8 times higher) and midgap D it (2 times lower), whereas thin (1.9 nm) EOT HfAlO stacks show reduced gate leakage J g (by 10 times) and D it (by 1.5 times) and 1.6 times higher mobility for Al% as low as 1.5% at matched EOT.

  14. Integration of atomic layer deposited high-k dielectrics on GaSb via hydrogen plasma exposure

    NASA Astrophysics Data System (ADS)

    Ruppalt, Laura B.; Cleveland, Erin R.; Champlain, James G.; Bennett, Brian R.; Prokes, Sharka M.

    2014-12-01

    In this letter we report the efficacy of a hydrogen plasma pretreatment for integrating atomic layer deposited (ALD) high-k dielectric stacks with device-quality p-type GaSb(001) epitaxial layers. Molecular beam eptiaxy-grown GaSb surfaces were subjected to a 30 minute H2/Ar plasma treatment and subsequently removed to air. High-k HfO2 and Al2O3/HfO2 bilayer insulating films were then deposited via ALD and samples were processed into standard metal-oxide-semiconductor (MOS) capacitors. The quality of the semiconductor/dielectric interface was probed by current-voltage and variable-frequency admittance measurements. Measurement results indicate that the H2-plamsa pretreatment leads to a low density of interface states nearly independent of the deposited dielectric material, suggesting that pre-deposition H2-plasma exposure, coupled with ALD of high-k dielectrics, may provide an effective means for achieving high-quality GaSb MOS structures for advanced Sb-based digital and analog electronics.

  15. Effect of thin gate dielectrics and gate materials on simulated device characteristics of 3D double gate JNT

    NASA Astrophysics Data System (ADS)

    Baidya, A.; Krishnan, V.; Baishya, S.; Lenka, T. R.

    2015-01-01

    In this paper a novel Silicon based three dimensional (3D) double-gate Junctionless Nanowire Transistor (JNT) of 20 nm gate length is proposed. The device characteristics such as gate characteristics and drain characteristics are studied with the help of Sentaurus TCAD by using different gate materials such as Al, Ti, n+ Polysilicon, Au and using different ultra thin gate dielectrics such as SiO2, Si3N4 and HfO2. The effect of various work functions and dielectrics on the threshold voltage of the JNT is also analysed. From the TCAD simulation results it is observed that high-K material (HfO2) as gate dielectric shows better drain characteristics with respect to others. The JNT with Al as gate material gives better current characteristics with respect to others. It is also analysed that under flat-band condition the driving of drain current does not directly depend on the gate-oxide capacitance but depends upon the channel doping concentrations. Thus by choosing the proper gate material and gate dielectric combinations, the desired device characteristics could be obtained for JNT.

  16. Band structures and band offsets of high K dielectrics on Si

    NASA Astrophysics Data System (ADS)

    Robertson, J.

    2002-05-01

    Various high dielectric constant oxides will be used as insulator in ferroelectric memories, dynamic random access memories, and as the gate dielectric material in future complementary metal oxide semiconductor (CMOS) technology. These oxides which have moderately wide bandgaps provide a good test of our understanding of Schottky barrier heights and band offsets at semiconductor interfaces. Metal induced gap states (MIGS) are found to give a good description of these interfaces. The electronic structure and band offsets of these oxides are calculated. It is found that Ta 2O 5 and SrTiO 3 have small or vanishing conduction band offsets on Si. La 2O 3, Y 2O 3, ZrO 2, HfO 2, Al 2O 3 and silicates like ZrSiO 4 have offsets over 1.4 eV for both electrons and holes, making them better gate dielectrics.

  17. Reduced impurities and improved electrical properties of atomic-layer-deposited HfO2 film grown at a low temperature (100 °C) by Al2O3 incorporation

    NASA Astrophysics Data System (ADS)

    Park, Tae Joo; Byun, Youngchol; Wallace, Robert M.; Kim, Jiyoung

    2016-05-01

    The HfO2 films grown by atomic layer deposition (ALD) at a low temperature (100 °C) necessarily has a large amount of residual impurities due to lack of thermal energy for stable ALD reactions such as ligand removal and oxidation, which degrades various properties. However, Al2O3 incorporation into the film significantly decreased the residual impurities despite of a low growth temperature. The decrease in C impurity is attributed to the reduced oxygen vacancies by the incorporated Al2O3 phase or the high reactivity of Al precursor. Consequently, the electronic band structure of the film, and thereby the electrical properties were improved significantly.

  18. Trapping surface plasmon polaritons on ultrathin corrugated metallic strips in microwave frequencies.

    PubMed

    Yang, Yan; Shen, Xiaopeng; Zhao, Pei; Zhang, Hao Chi; Cui, Tie Jun

    2015-03-23

    It has been demonstrated that an ultrathin uniformly corrugated metallic strip is a good plasmonic waveguide in microwave and terahertz frequencies to propagate spoof surface plasmon polaritons (SPPs) with well confinement and small loss (Shen et al., PNAS 110, 40-45, 2013). Here, we propose a simple method to trap SPP waves on the ultrathin corrugated metallic strips in broad band in the microwave frequencies. By properly designing non-uniform corrugations with gradient-depth grooves, we show that the SPP waves are slowed down gradually and then reflected at pre-designed positions along the ultrathin metallic strip when the frequency varies. We design and fabricate the ultrathin gradient-corrugation metallic strip on a thin dielectric film. Both numerical simulation and measurement results validate the efficient trapping of SPP waves in broadband from 9 to 14 GHz. This proposal is a promising candidate for slow-wave devices in both microwave and terahertz regimes. PMID:25837047

  19. Deviation from bulk behaviour in the cold crystallization kinetics of ultrathin films of poly(3-hydroxybutyrate)

    NASA Astrophysics Data System (ADS)

    Napolitano, S.; Wübbenhorst, M.

    2007-05-01

    The cold crystallization kinetics of ultrathin films of poly(3-hydroxybutyrate) (PHB) have been investigated by dielectric spectroscopy. Upon reduction of the film thickness, a lowering of the Avrami exponent accompanied by an increase of the crystallization time was observed. The experimental results are analysed in terms of reduction of the total number of nuclei involved in the crystallization process.

  20. Nanoscale electrochemistry using dielectric thin films as solid electrolytes

    NASA Astrophysics Data System (ADS)

    Valov, Ilia; Lu, Wei D.

    2016-07-01

    It is now well known that at the nanoscale matters behave differently compared to bulk phases. Increased reactivity, deviations in structural, thermodynamic and kinetic properties make nanoscale materials and processes attractive for both fundamental research and applications. Here we show that nanometer thin films of materials with dielectric properties at the macroscopic level such as SiO2, Ta2O5 and HfO2 behave as solid electrolytes and exhibit evident ionic transport and electrochemical redox reactions. Experimental studies demonstrate that classical electrochemical potentiodynamic and steady state methods can be used to study the mass and charge transport at the nanoscale. We believe these reported properties of nanomatter open new opportunities for fundamental research and applications.

  1. Improved interface properties of atomic-layer-deposited HfO2 film on InP using interface sulfur passivation with H2S pre-deposition annealing

    NASA Astrophysics Data System (ADS)

    Jin, Hyun Soo; Cho, Young Jin; Seok, Tae Jun; Kim, Dae Hyun; Kim, Dae Woong; Lee, Sang-Moon; Park, Jong-Bong; Yun, Dong-Jin; Kim, Seong Keun; Hwang, Cheol Seong; Park, Tae Joo

    2015-12-01

    Surface sulfur (S) passivation on InP substrate was performed using a dry process - rapid thermal annealing under H2S atmosphere for III-V compound-semiconductor-based devices. The electrical properties of metal-oxide-semiconductor capacitor fabricated with atomic-layer-deposited HfO2 film as a gate insulator were examined, and were compared with the similar devices with S passivation using a wet process - (NH4)2S solution treatment. The H2S annealing provided solid S passivation with the strong resistance against oxidation compared with the (NH4)2S solution treatment, although S profiles at the interface of HfO2/InP were similar. The decrease in electrical thickness of the gate insulator by S passivation was similar for both methods. However, the H2S annealing was more effective to suppress interface state density near the valence band edge, because thermal energy during the annealing resulted in stronger S bonding and InP surface reconstruction. Moreover, the flatband voltage shift by constant voltage stress was lower for the device with H2S annealing.

  2. High dielectric constant materials: a band line-up problem

    NASA Astrophysics Data System (ADS)

    Fonseca, L.; Tomfohr, J.; Chagarov, E.; Sankey, O. F.; Demkov, A. A.

    2003-03-01

    To insure continuous downscaling of CMOS technology the semiconductor industry must make a transition from the Si-SiO_2-poly-Si triad to a much more complex Si-dielectric-metal system. The dielectric constant of the new gate dielectric is expected to be higher than that of silicon dioxide (4). This will allow maintaining the gate capacitance and therefore the drain-source saturation current without the thickness reduction of the oxide, and thus will cut down the tunneling component of the parasitic gate leakage. The integration of this new stack into the current CMOS flow is one of the most urgent tasks of today's electronics. The oxide's gate action, among other factors, depends on the barrier height (same as band discontinuity) at the oxide-semiconductor and oxide-metal interfaces. The band alignment is often estimated within the so-called metal-induced gap states (MIGS) model. The MIGS model describes both Bardeen and Schottky limits and interpolates between the two in a linear fashion, provided that electron affinities, charge neutralities and the pinning factor are known. We use the complex band structure of several prospective gate dielectrics (SiO_2, SrTiO_3, HfO_2, and Al_2O_3) to calculate their charge neutrality level, and estimate the band offset to Si, Pt, and several other metals. Results of these model calculations are then compared to those obtained with direct electronic structure methods.

  3. Ultrathin metallized PBI paper

    NASA Technical Reports Server (NTRS)

    Chenevey, E. C.

    1978-01-01

    A study to determine the feasibility of preparing ultrathin papers with a target weight of 3.5 g/m squared from polybenzimidazole (PBI) fibrids was undertaken. Small hand sheets of target weight were fabricated. They were light brown, low density materials with sufficient strength to be readily handleable. Characterization of these sheets included strength, fold endurance, thermal gravimetric analysis in air and nitrogen and photomicrographs. Two different batches of PBI fibrids were studied and differences in fabrication performance were noted. In neither case could target weight papers be prepared using conventional paper making techniques.

  4. High-performance, highly bendable MoS2 transistors with high-k dielectrics for flexible low-power systems.

    PubMed

    Chang, Hsiao-Yu; Yang, Shixuan; Lee, Jongho; Tao, Li; Hwang, Wan-Sik; Jena, Debdeep; Lu, Nanshu; Akinwande, Deji

    2013-06-25

    While there has been increasing studies of MoS2 and other two-dimensional (2D) semiconducting dichalcogenides on hard conventional substrates, experimental or analytical studies on flexible substrates has been very limited so far, even though these 2D crystals are understood to have greater prospects for flexible smart systems. In this article, we report detailed studies of MoS2 transistors on industrial plastic sheets. Transistor characteristics afford more than 100x improvement in the ON/OFF current ratio and 4x enhancement in mobility compared to previous flexible MoS2 devices. Mechanical studies reveal robust electronic properties down to a bending radius of 1 mm which is comparable to previous reports for flexible graphene transistors. Experimental investigation identifies that crack formation in the dielectric is the responsible failure mechanism demonstrating that the mechanical properties of the dielectric layer is critical for realizing flexible electronics that can accommodate high strain. Our uniaxial tensile tests have revealed that atomic-layer-deposited HfO2 and Al2O3 films have very similar crack onset strain. However, crack propagation is slower in HfO2 dielectric compared to Al2O3 dielectric, suggesting a subcritical fracture mechanism in the thin oxide films. Rigorous mechanics modeling provides guidance for achieving flexible MoS2 transistors that are reliable at sub-mm bending radius.

  5. Breakdown and defect generation in ultrathin gate oxide

    NASA Astrophysics Data System (ADS)

    Depas, M.; Vermeire, B.; Heyns, M. M.

    1996-07-01

    In this work the dielectric reliability of thermally grown ultrathin 3 nm SiO2 layers in poly-Si/SiO2/Si structures is examined. This is compared with a study of the defect generation in the 3 nm gate oxide during tunnel injection of electrons. In these ultrathin SiO2 layers, direct tunneling of electrons becomes very important. An increase of the direct tunnel and Fowler-Nordheim tunnel current during high-field stressing was observed and is explained by the creation of a positive charge in the oxide associated with slow interface traps. It is demonstrated that a higher current instability corresponds with a lower charge to breakdown value (QBD) of the oxide. From these results we conclude that the creation of slow interface traps is an important precursor effect for the 3 nm gate oxide breakdown.

  6. All-dielectric diffraction grating for multi-petawatt laser systems

    NASA Astrophysics Data System (ADS)

    Vyhlidka, Stepan; Kalinchenko, Galina; Kramer, Daniel; Lerer, Alexander; Rus, Bedrich

    2015-01-01

    All-dielectric grating with more than 98% efficiency over the reflective band of 40 nm with the central wavelength at 1053 nm is simulated for the angle of incidence 72 degrees. For the grating design we used the fact that chirped mirrors give wider reflective band than usual quarter-wavelength dielectric mirrors. Grating grooves and the very first layer under the grooves in our model is made of fused silica; underneath of the top layer we placed a chirped stack of 13 HfO2/SiO2 layers. Tolerances for groove depth and angle of incidence are estimated, optimal duty-cycle parameter is found out. Electric field distribution inside of the grating is also numerically studied. The model is simulated by two methods: numerical Fourier Modal Method in LightTrans Virtual Lab and semi-analytical Volume Integral Equation Method. The results obtained by both methods show excellent agreement.

  7. Ultrathin microwave absorber based on metamaterial

    NASA Astrophysics Data System (ADS)

    Kim, Y. J.; Yoo, Y. J.; Hwang, J. S.; Lee, Y. P.

    2016-11-01

    We suggest that ultrathin broadband metamaterial is a perfect absorber in the microwave regime by utilizing the properties of a resistive sheet and metamaterial. Meta-atoms are composed of four-leaf clover-shape metallic patterns and a metal plane separated by three intermediate resistive sheet layers between four dielectric layers. We interpret the absorption mechanism of the broadband by using the distribution of surface currents at specific frequencies. The simulated absorption was over 99% in 1.8–4.2 GHz. The corresponding experimental absorption was also over 99% in 2.62–4.2 GHz; however, the absorption was slightly lower than 99% in 1.8–2.62 GHz because of the sheet resistance and the changed values for the dielectric constant. Furthermore, it is independent of incident angle. The results of this research indicate the possibility of applications, due to the suppression of noxious exposure, in cell phones, computers and microwave equipments.

  8. Ultrathin flexible dual band terahertz absorber

    NASA Astrophysics Data System (ADS)

    Shan, Yan; Chen, Lin; Shi, Cheng; Cheng, Zhaoxiang; Zang, Xiaofei; Xu, Boqing; Zhu, Yiming

    2015-09-01

    We propose an ultrathin and flexible dual band absorber operated at terahertz frequencies based on metamaterial. The metamaterial structure consists of periodical split ring resonators with two asymmetric gaps and a metallic ground plane, separated by a thin-flexible dielectric spacer. Particularly, the dielectric spacer is a free-standing polyimide film with thickness of 25 μm, resulting in highly flexible for our absorber and making it promising for non-planar applications such as micro-bolometers and stealth aircraft. Experimental results show that the absorber has two resonant absorption frequencies (0.41 THz and 0.75 THz) with absorption rates 92.2% and 97.4%, respectively. The resonances at the absorption frequencies come from normal dipole resonance and high-order dipole resonance which is inaccessible in the symmetrical structure. Multiple reflection interference theory is used to analyze the mechanism of the absorber and the results are in good agreement with simulated and experimental results. Furthermore, the absorption properties are studied under various spacer thicknesses. This kind of metamaterial absorber is insensitive to polarization, has high absorption rates (over 90%) with wide incident angles range from 0° to 45° and the absorption rates are also above 90% when wrapping it to a curved surface.

  9. Ultrathin Hf0.5Zr0.5O2 Ferroelectric Films on Si.

    PubMed

    Chernikova, Anna; Kozodaev, Maksim; Markeev, Andrei; Negrov, Dmitrii; Spiridonov, Maksim; Zarubin, Sergei; Bak, Ohheum; Buragohain, Pratyush; Lu, Haidong; Suvorova, Elena; Gruverman, Alexei; Zenkevich, Andrei

    2016-03-23

    Because of their immense scalability and manufacturability potential, the HfO2-based ferroelectric films attract significant attention as strong candidates for application in ferroelectric memories and related electronic devices. Here, we report the ferroelectric behavior of ultrathin Hf0.5Zr0.5O2 films, with the thickness of just 2.5 nm, which makes them suitable for use in ferroelectric tunnel junctions, thereby further expanding the area of their practical application. Transmission electron microscopy and electron diffraction analysis of the films grown on highly doped Si substrates confirms formation of the fully crystalline non-centrosymmetric orthorhombic phase responsible for ferroelectricity in Hf0.5Zr0.5O2. Piezoresponse force microscopy and pulsed switching testing performed on the deposited top TiN electrodes provide further evidence of the ferroelectric behavior of the Hf0.5Zr0.5O2 films. The electronic band lineup at the top TiN/Hf0.5Zr0.5O2 interface and band bending at the adjacent n(+)-Si bottom layer attributed to the polarization charges in Hf0.5Zr0.5O2 have been determined using in situ X-ray photoelectron spectroscopy analysis. The obtained results represent a significant step toward the experimental implementation of Si-based ferroelectric tunnel junctions.

  10. All-dielectric metamaterials.

    PubMed

    Jahani, Saman; Jacob, Zubin

    2016-01-01

    The ideal material for nanophotonic applications will have a large refractive index at optical frequencies, respond to both the electric and magnetic fields of light, support large optical chirality and anisotropy, confine and guide light at the nanoscale, and be able to modify the phase and amplitude of incoming radiation in a fraction of a wavelength. Artificial electromagnetic media, or metamaterials, based on metallic or polar dielectric nanostructures can provide many of these properties by coupling light to free electrons (plasmons) or phonons (phonon polaritons), respectively, but at the inevitable cost of significant energy dissipation and reduced device efficiency. Recently, however, there has been a shift in the approach to nanophotonics. Low-loss electromagnetic responses covering all four quadrants of possible permittivities and permeabilities have been achieved using completely transparent and high-refractive-index dielectric building blocks. Moreover, an emerging class of all-dielectric metamaterials consisting of anisotropic crystals has been shown to support large refractive index contrast between orthogonal polarizations of light. These advances have revived the exciting prospect of integrating exotic electromagnetic effects in practical photonic devices, to achieve, for example, ultrathin and efficient optical elements, and realize the long-standing goal of subdiffraction confinement and guiding of light without metals. In this Review, we present a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index metamaterials and anisotropic metamaterials. Finally, we discuss current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics, as well as biomimetic metasurfaces.

  11. All-dielectric metamaterials

    NASA Astrophysics Data System (ADS)

    Jahani, Saman; Jacob, Zubin

    2016-01-01

    The ideal material for nanophotonic applications will have a large refractive index at optical frequencies, respond to both the electric and magnetic fields of light, support large optical chirality and anisotropy, confine and guide light at the nanoscale, and be able to modify the phase and amplitude of incoming radiation in a fraction of a wavelength. Artificial electromagnetic media, or metamaterials, based on metallic or polar dielectric nanostructures can provide many of these properties by coupling light to free electrons (plasmons) or phonons (phonon polaritons), respectively, but at the inevitable cost of significant energy dissipation and reduced device efficiency. Recently, however, there has been a shift in the approach to nanophotonics. Low-loss electromagnetic responses covering all four quadrants of possible permittivities and permeabilities have been achieved using completely transparent and high-refractive-index dielectric building blocks. Moreover, an emerging class of all-dielectric metamaterials consisting of anisotropic crystals has been shown to support large refractive index contrast between orthogonal polarizations of light. These advances have revived the exciting prospect of integrating exotic electromagnetic effects in practical photonic devices, to achieve, for example, ultrathin and efficient optical elements, and realize the long-standing goal of subdiffraction confinement and guiding of light without metals. In this Review, we present a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index metamaterials and anisotropic metamaterials. Finally, we discuss current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics, as well as biomimetic metasurfaces.

  12. All-dielectric metamaterials.

    PubMed

    Jahani, Saman; Jacob, Zubin

    2016-01-01

    The ideal material for nanophotonic applications will have a large refractive index at optical frequencies, respond to both the electric and magnetic fields of light, support large optical chirality and anisotropy, confine and guide light at the nanoscale, and be able to modify the phase and amplitude of incoming radiation in a fraction of a wavelength. Artificial electromagnetic media, or metamaterials, based on metallic or polar dielectric nanostructures can provide many of these properties by coupling light to free electrons (plasmons) or phonons (phonon polaritons), respectively, but at the inevitable cost of significant energy dissipation and reduced device efficiency. Recently, however, there has been a shift in the approach to nanophotonics. Low-loss electromagnetic responses covering all four quadrants of possible permittivities and permeabilities have been achieved using completely transparent and high-refractive-index dielectric building blocks. Moreover, an emerging class of all-dielectric metamaterials consisting of anisotropic crystals has been shown to support large refractive index contrast between orthogonal polarizations of light. These advances have revived the exciting prospect of integrating exotic electromagnetic effects in practical photonic devices, to achieve, for example, ultrathin and efficient optical elements, and realize the long-standing goal of subdiffraction confinement and guiding of light without metals. In this Review, we present a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index metamaterials and anisotropic metamaterials. Finally, we discuss current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics, as well as biomimetic metasurfaces. PMID:26740041

  13. Development and Performance Evaluations of HfO2-Si and Rare Earth-Si Based Environmental Barrier Bond Coat Systems for SiC/SiC Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming

    2014-01-01

    Ceramic environmental barrier coatings (EBC) and SiCSiC ceramic matrix composites (CMCs) will play a crucial role in future aircraft propulsion systems because of their ability to significantly increase engine operating temperatures, improve component durability, reduce engine weight and cooling requirements. Advanced EBC systems for SiCSiC CMC turbine and combustor hot section components are currently being developed to meet future turbine engine emission and performance goals. One of the significant material development challenges for the high temperature CMC components is to develop prime-reliant, high strength and high temperature capable environmental barrier coating bond coat systems, since the current silicon bond coat cannot meet the advanced EBC-CMC temperature and stability requirements. In this paper, advanced NASA HfO2-Si based EBC bond coat systems for SiCSiC CMC combustor and turbine airfoil applications are investigated. The coating design approach and stability requirements are specifically emphasized, with the development and implementation focusing on Plasma Sprayed (PS) and Electron Beam-Physic Vapor Deposited (EB-PVD) coating systems and the composition optimizations. High temperature properties of the HfO2-Si based bond coat systems, including the strength, fracture toughness, creep resistance, and oxidation resistance were evaluated in the temperature range of 1200 to 1500 C. Thermal gradient heat flux low cycle fatigue and furnace cyclic oxidation durability tests were also performed at temperatures up to 1500 C. The coating strength improvements, degradation and failure modes of the environmental barrier coating bond coat systems on SiCSiC CMCs tested in simulated stress-environment interactions are briefly discussed and supported by modeling. The performance enhancements of the HfO2-Si bond coat systems with rare earth element dopants and rare earth-silicon based bond coats are also highlighted. The advanced bond coat systems, when integrated with advanced EBC top coats, showed promise to achieve 1500 C temperature capability, helping enable next generation turbine engines with significantly improved engine component temperature capability and long-term durability.

  14. Effect of (HfO2) X (Al2O3)1- X /SiO2 double-layered blocking oxide on program and erase speed in charge trapping memory devices

    NASA Astrophysics Data System (ADS)

    Oh, Jinho; Ko, Eun Jung; Na, Heedo; Ko, Dae-Hong; Sohn, Hyunchul

    2016-03-01

    In this work, the effect of hole injection into the charge trap layers from channel prior to program operation is investigated in charge trapping (CT) memory with stacked blocking oxide (BO). For efficient hole injection, a (HfO2) X (Al2O3)1 - X /SiO2 stacked BO structure is used. The CT memory device with stacked BO shows faster programming and erasing speed compared with single-layered SiO2 BO. The enhanced programming speed is attributed to the enhanced electric field introduced by excess holes injected into SiN charge trap layer. In addition, efficient hole injection from channel produced the widened memory window in CT memory.

  15. Comparison of HfCl4, HfI4, TEMA-Hf, and TDMA-Hf as precursors in early growing stages of HfO2 films deposited by ALD: A DFT study

    NASA Astrophysics Data System (ADS)

    Cortez-Valadez, M.; Fierro, C.; Farias-Mancilla, J. R.; Vargas-Ortiz, A.; Flores-Acosta, M.; Ramírez-Bon, R.; Enriquez-Carrejo, J. L.; Soubervielle-Montalvo, C.; Mani-Gonzalez, P. G.

    2016-06-01

    The final structure of HfO2 films grown by atomic layer deposition (ALD) after reaction with OH- ions has been analyzed by DFT (density functional theory). The interaction of the precursors: HfCl4 (hafnium tetrachloride), HfI4 (hafnium tetraiodide), TEMA-Hf (tetrakis-ethylmethylamino hafnium), and TDMA-Hf (tetrakis-dimethylamino hafnium) with HO-H was studied employing the B3LYP (Becke 3-parameter, Lee-Yang-Parr) hybrid functional and the PBE (Perdew-Burke-Ernzerhof) generalized gradient functional. The structural evolution at the Si(100) surface has been analyzed by LDA (local density approximation). The structural parameters: bond length and bond angle, and the vibrational parameters for the optimized structures are also reported. The presence of hafnium silicate at the interface was detected. The infrared spectra and structural parameters obtained in this work agree with previously reported experimental results.

  16. Comparisons between intrinsic bonding defects in d 0 transition metal oxide such as HfO 2, and impurity atom defects in d 0 complex oxides such as GdScO 3

    NASA Astrophysics Data System (ADS)

    Lucovsky, Gerald; Chung, Kwun-Bum; Miotti, Leonardi; Bastos, Karen Pas; Amado, Carolina; Schlom, Darrell

    2009-12-01

    This article addresses O-atom vacancy defects in the d 0 transition metal (TM) oxides HfO 2 and TiO 2, and Ti substitutions for Sc in the d 0 complex oxide GdScO 3. In each instance this results in occupied TM atoms with d 1 state representations. These are important for different aspects of the ultimate scaling limits for performance and functionality in nano-scale Si devices. The occupancy of d 1 states is cast in terms of many-electron theory in order to determine the effects of correlation on device performance and functionality. The first section of this article identifies equivalent d-state representations using on an ionic model for the effective valence states of Ti and Hf atoms bordering on O-atom vacancy defects. Removal of an O atom to create a neutral vacancy; this is equivalent to the bonding of two electrons to each vacancy site. This give rise to two coupled d 1 states for a mono-vacancy defect. Transitions from these occupied states generate spectroscopic features in the (i) pre-edge shake-up, and (ii) virtual bound state (VBS) shake-off energy regimes in O K edge XAS spectra. The number of states confirm that these are mono-vacancy defects. The second section addresses incorporation of Ti tetravalent impurities into trivalent GdScO 3, forcing Ti into a Ti 3+ state and generating a d 1 electronic structure. Vacancy defect concentrations in HfO 2 are generally <10 19 cm -3. However, the Ti solubility in GdScO 3 is higher, and relative concentrations in excess of 16-17% lead to an insulator to metal transition with a ferri-magnetic electronic structure.

  17. HfO_2and ZrO2 : Comparison of Structures and Thermodynamic and Electronic Properties Based on Ab Initio Calculations and Experiment

    NASA Astrophysics Data System (ADS)

    Demkov, Alexander A.; Navrotsky, Alexandra

    2001-03-01

    The International Technology Roadmap for Semiconductors (ITRS) predicts that the strategy of scaling complementary metal-oxide-semiconductor (CMOS) devices will come to an abrupt end around the year 2012. The main reason for this will be the unacceptably high leakage current through the silicon dioxide gate with a thickness below 20 ÅFinding a gate insulator alternative to SiO2 has proven to be far from trivial. Hafnium and zirconium dioxides and silicates have been recently considered as gate dielectrics with intermediate dielectric constants. Hafnia and ziconia are important ceramic materials as well, and their phase relations are rather well studied. There is also interest in hafnia as a constituent of ceramic waste forms for plutonium, based on its refractory nature and high neutron absorption cross section. We use a combination of the ab-initio calculations and calorimetry to investigate thermodynamic and electronic properties of hafnia and zirconia. We describe the cubic to tetragonal phase transition in the fluorite structure by computing the total energy surface for zone-edge distortions correct to fourth order in the soft-mode displacement with the strain coupling renormalization included. We compare the two materials using some simple chemical concepts.

  18. Dielectric siphons.

    NASA Technical Reports Server (NTRS)

    Jones, T. B.; Perry, M. P.; Melcher, J. R.

    1971-01-01

    The normally weak polarization force density, exerted on insulating dielectric liquids by a nonuniform electric field, is enhanced if high pressures are used. The nonuniform electric field acts as an elastic ?wall' to contain and guide the dielectric fluid. A general theory for these electrohydrodynamic (EHD) conduits has been developed. An illustrative example of the EHD conduits is the dielectric siphon consisting of two U-shaped electrodes held adjacent to each other by insulating nylon screws.

  19. Conformal surface plasmons propagating on ultrathin and flexible films

    PubMed Central

    Shen, Xiaopeng; Cui, Tie Jun; Martin-Cano, Diego; Garcia-Vidal, Francisco J.

    2013-01-01

    Surface plasmon polaritons (SPPs) are localized surface electromagnetic waves that propagate along the interface between a metal and a dielectric. Owing to their inherent subwavelength confinement, SPPs have a strong potential to become building blocks of a type of photonic circuitry built up on 2D metal surfaces; however, SPPs are difficult to control on curved surfaces conformably and flexibly to produce advanced functional devices. Here we propose the concept of conformal surface plasmons (CSPs), surface plasmon waves that can propagate on ultrathin and flexible films to long distances in a wide broadband range from microwave to mid-infrared frequencies. We present the experimental realization of these CSPs in the microwave regime on paper-like dielectric films with a thickness 600-fold smaller than the operating wavelength. The flexible paper-like films can be bent, folded, and even twisted to mold the flow of CSPs. PMID:23248311

  20. Ultrathin Planar Graphene Supercapacitors

    SciTech Connect

    Huang, Jingsong; Meunier, Vincent; Sumpter, Bobby G; Ajayan, Pullikel M; Yoo, Jung Joon; Balakrishnan, Kaushik; Srivastava, Anchal; Conway, Michelle; Reddy, Arava Leela Mohan; Yu, Jin; Vajtai, Robert

    2011-01-01

    With the advent of atomically thin and flat layers of conducting materials such as graphene, new designs for thin film energy storage devices with good performance have become possible. Here, we report an in-plane fabrication approach for ultrathin supercapacitors based on electrodes comprised of pristine graphene and multi-layer reduced graphene oxide. The in-plane design is straightforward to implement and exploits efficiently the surface of each graphene layer for energy storage. The open architecture and the effect of graphene edges enable even the thinnest of devices, made from as grown 1-2 graphene layers, to reach specific capacities up to 80 Fcm-2. While, much higher (394 Fcm-2) specific capacities are observed in case of multi-layered graphene oxide electrodes, owing to the better utilization of the available electrochemical surface area. The performances of devices with pristine as well as thicker graphene based structures are examined using a combination of experiments and model calculations. The demonstrated all solid-state supercapacitors provide a prototype for a broad range of thin-film based energy storage devices.

  1. InAs/GaAs quantum-dot intermixing: comparison of various dielectric encapsulants

    NASA Astrophysics Data System (ADS)

    Alhashim, Hala H.; Khan, Mohammed Zahed Mustafa; Majid, Mohammed A.; Ng, Tien K.; Ooi, Boon S.

    2015-10-01

    We report on the impurity-free vacancy-disordering effect in InAs/GaAs quantum-dot (QD) laser structure based on seven dielectric capping layers. Compared to the typical SiO2 and Si3N4 films, HfO2 and SrTiO3 dielectric layers showed superior enhancement and suppression of intermixing up to 725°C, respectively. A QD peak ground-state differential blue shift of >175 nm (>148 meV) is obtained for HfO2 capped sample. Likewise, investigation of TiO2, Al2O3, and ZnO capping films showed unusual characteristics, such as intermixing-control caps at low annealing temperature (650°C) and interdiffusion-promoting caps at high temperatures (≥675°C). We qualitatively compared the degree of intermixing induced by these films by extracting the rate of intermixing and the temperature for ground-state and excited-state convergences. Based on our systematic characterization, we established reference intermixing processes based on seven different dielectric encapsulation materials. The tailored wavelength emission of ˜1060-1200 nm at room temperature and improved optical quality exhibited from intermixed QDs would serve as key materials for eventual realization of low-cost, compact, and agile lasers. Applications include solid-state laser pumping, optical communications, gas sensing, biomedical imaging, green-yellow-orange coherent light generation, as well as addressing photonic integration via area-selective, and postgrowth bandgap engineering.

  2. Properties of ferroelectric ultrathin films from first principles

    NASA Astrophysics Data System (ADS)

    Bin-Omran, Saad

    First-principles-based methods are used to determine the response of polarization to epitaxial strain in films made of BaTiO3 (BT) and Pb(Zr0.5Ti0.5)O3 (PZT). Unlike in BT films, the strength of this response as well as its sign dramatically depend on the film's thickness and electrical boundary conditions in PZT films. A phenomenological model provides a rationale for these findings. Moreover, we reveal the effect of the depolarizing field on the paraelectric-to-ferroelectric phase transition in BaTiO3 and PZT ultrathin films. We found that with decreasing the beta screening parameter (i.e., when increasing the depolarizing field) (i) the Curie temperature, Tc, linearly decreases; (ii) the dielectric maximum epsilonmax increases; (iii) the phase transition becomes less diffuse. Furthermore, we investigate the effect of mechanical boundary conditions on the paraelectric-to-ferroelectric phase transition in BaTiO3 and PZT ultrathin films. It is predicted that (i) the phase transition temperature (Tc) increases due to the applied compressive strain; (ii) the epitaxial strain decreases the dielectric maximum epsilon max at any given value of the screening parameter beta; (iii) the diffusive character of the transition is larger in compressive films than in freestanding systems at a fixed beta. Also, we reveal that the nature of all paraelectric-to-ferroelectric phase transitions in the BaTiO3 and PZT ultrathin films (that are under different electric and mechanical boundary conditions) is of second-order.

  3. Intercalative poly(carbazole) precursor electropolymerization within hybrid nanostructured titanium oxide ultrathin films.

    PubMed

    Frau, Antonio F; Estillore, Nicel C; Fulghum, Timothy M; Advincula, Rigoberto C

    2010-12-01

    A protocol for nanostructuring and electropolymerization of a hybrid semiconductor polycarbazole-titanium oxide ultrathin film is described. Ultrathin (<100 nm) films based on polycarbazole precursor polyelectrolytes and titanium oxide (TiOx) have been fabricated by combining the layer-by-layer (LbL) and surface sol-gel layering techniques. Film growth was followed and confirmed through UV-vis spectroscopy, ellipsometry and quartz crystal microbalance with dissipation (QCM-D). Subsequent anodic electrochemical oxidation of the carbazole pendant units afforded a conjugated polymer network (CPN) film within intercalating TiOx layers of cross-linked and π-conjugated carbazole units. Cyclic voltammetry (CV), UV-vis, and fluorescence spectroscopy measurements confirmed this process. The LbL-driven polyelectrolyte deposition process resulted in a quantified electrochemical response, proportional to the number of layers, while the TiOx acted as a dielectric spacer limiting electron transfer kinetics and attenuating energy transfer in fluorescence. Electro-optical properties were compared with other polycarbazole thin film materials with respect to bandgap energy (Eg). The straightforward protocol in film nanostructuring and barrier/dielectric properties of the inorganic oxide slab (denoted here as, TiOx) should enable applications in organic light-emitting diodes (OLEDs), dielectric mirrors, planar waveguides, and photovoltaic devices for these hybrid ultrathin films.

  4. Topographic measurements of supersmooth dielectric films made with a mechanical profiler and a scanning force microscope

    NASA Astrophysics Data System (ADS)

    Bennett, Jean M.; Tehrani, Mohammad M.; Jahanmir, Jay; Podlesny, John C.; Balter, Tami L.

    1995-01-01

    The roughnesses of five supersmooth dielectric films of Si3N4, TiO2 , HfO2, Ta2O5 , and Al2O3 prepared by an ion-beam-sputtering technique were measured with a commercial Talystep mechanical profiler and a sensitive Leica WYKO SPM30 scanning force microscope (SFM) to determine how much roughness the films added to the approximately 1-A-rms roughness fused-silica substrates on which they were deposited. In all cases the increase in roughness for the three-quarter-wave optical thickness films was a small fraction of an angstrom. SFM measurements showed that the topography of the Ta2O5 and Al2O3 films was less random than that of the other film materials and the substrates.

  5. Uniform Self-rectifying Resistive Switching Behavior via Preformed Conducting Paths in a Vertical-type Ta2O5/HfO2-x Structure with a Sub-μm(2) Cell Area.

    PubMed

    Yoon, Jung Ho; Yoo, Sijung; Song, Seul Ji; Yoon, Kyung Jean; Kwon, Dae Eun; Kwon, Young Jae; Park, Tae Hyung; Kim, Hye Jin; Shao, Xing Long; Kim, Yumin; Hwang, Cheol Seong

    2016-07-20

    To replace or succeed the present NAND flash memory, resistive switching random access memory (ReRAM) should be implemented in the vertical-type crossbar array configuration. The ReRAM cell must have a highly reproducible resistive switching (RS) performance and an electroforming-free, self-rectifying, low-power-consumption, multilevel-switching, and easy fabrication process with a deep sub-μm(2) cell area. In this work, a Pt/Ta2O5/HfO2-x/TiN RS memory cell fabricated in the form of a vertical-type structure was presented as a feasible contender to meet the above requirements. While the fundamental RS characteristics of this material based on the electron trapping/detrapping mechanisms have been reported elsewhere, the influence of the cell scaling size to 0.34 μm(2) on the RS performance by adopting the vertical integration scheme was carefully examined in this work. The smaller cell area provided much better switching uniformity while all the other benefits of this specific material system were preserved. Using the overstressing technique, the nature of RS through the localized conducting path was further examined, which elucidated the fundamental difference between the present material system and the general ionic-motion-related bipolar RS mechanism.

  6. Effectiveness of ion cleaning to improve the laser damage threshold of HfO2/SiO2 optical coatings for high reflection and antireflection at 527 nm and 1054 nm

    NASA Astrophysics Data System (ADS)

    Field, Ella S.; Bellum, John C.; Kletecka, Damon E.

    2016-07-01

    Preventing contamination is vital to achieving high laser-induced damage thresholds in optical coatings. The importance of removing contamination from optical substrates has led to the development of many specialized cleaning processes, including the application of solvents, acids, mild detergents, and abrasives. To further enhance contamination removal, the substrate may be treated with ion cleaning just prior to depositing the optical coating. Ion cleaning is attractive thanks to the convenience of providing in-situ treatment to optical substrates, and also avoiding the hassle of managing hazardous chemicals or applying mechanical force to scrub off detergents and other cleaning agents. In this study, we compare the effectiveness of ion cleaning for increasing the laser-induced damage thresholds of high reflection (527 nm and 1054 nm) and antireflection (527 nm) coatings. Ion cleaning was performed using a radio frequency ion source with argon and oxygen. The coatings investigated were deposited with layers of HfO2 and SiO2 in an e-beam evaporation system, and are designed to withstand nanosecond pulses from a kJ-class laser.

  7. Uniform Self-rectifying Resistive Switching Behavior via Preformed Conducting Paths in a Vertical-type Ta2O5/HfO2-x Structure with a Sub-μm(2) Cell Area.

    PubMed

    Yoon, Jung Ho; Yoo, Sijung; Song, Seul Ji; Yoon, Kyung Jean; Kwon, Dae Eun; Kwon, Young Jae; Park, Tae Hyung; Kim, Hye Jin; Shao, Xing Long; Kim, Yumin; Hwang, Cheol Seong

    2016-07-20

    To replace or succeed the present NAND flash memory, resistive switching random access memory (ReRAM) should be implemented in the vertical-type crossbar array configuration. The ReRAM cell must have a highly reproducible resistive switching (RS) performance and an electroforming-free, self-rectifying, low-power-consumption, multilevel-switching, and easy fabrication process with a deep sub-μm(2) cell area. In this work, a Pt/Ta2O5/HfO2-x/TiN RS memory cell fabricated in the form of a vertical-type structure was presented as a feasible contender to meet the above requirements. While the fundamental RS characteristics of this material based on the electron trapping/detrapping mechanisms have been reported elsewhere, the influence of the cell scaling size to 0.34 μm(2) on the RS performance by adopting the vertical integration scheme was carefully examined in this work. The smaller cell area provided much better switching uniformity while all the other benefits of this specific material system were preserved. Using the overstressing technique, the nature of RS through the localized conducting path was further examined, which elucidated the fundamental difference between the present material system and the general ionic-motion-related bipolar RS mechanism. PMID:27347693

  8. Charge trapping properties of alternative high-kappa dielectrics in MOS devices

    NASA Astrophysics Data System (ADS)

    Zhou, Xing

    High-kappa dielectrics are promising candidates to replace SiO 2 in advanced integrated circuits in future space systems. Studies of the effects of ionizing radiation and bias-temperature stress (BTS) on high-kappa dielectrics were performed. Trapped charge densities are evaluated as functions of temperature and stress time. Prior radiation exposure enhances BTS-induced degradation in these devices. Worst-case responses in combined effects are positive (or zero) bias irradiation followed by NBTS for HfO2-based devices. Degradation due to oxide or interface trap-charge changes in magnitude with the bias polarity during switched-bias annealing either after irradiation or constant voltage stress (CVS). This demonstrates that metastable electron trapping (dominant during post-rad annealing) and hydrogen transport and reactions (dominant during post-CVS annealing) in the near-interfacial dielectric layers play significant roles in the defect formation process. Additional defect growth with time was observed as a result of additional charge injection through the gate stacks during the annealing process. These results provide insights into fundamental trapping properties of high-kappa dielectrics and can be used to help predict long-term reliability of these devices.

  9. Electrical perturbations of ultrathin bilayers: role of ionic conductive layer.

    PubMed

    Nazaripoor, Hadi; Koch, Charles R; Bhattacharjee, Subir

    2014-12-16

    The effect of electrostatic force on the dynamics, morphological evolution, and drainage time of ultrathin liquid bilayers (<100 nm) are investigated for perfect dielectric-perfect dielectric (PD-PD) and ionic liquid-perfect dielectric (IL-PD) bilayers. The weakly nonlinear "thin film" equation is solved numerically to obtain spatiotemporal evolution of the liquid-liquid interface responses to transverse electric field. In order to predict the electrostatic component of conjoining/disjoining pressure acting on the interface for IL-PD bilayers, an analytical model is developed using the nonlinear Poisson-Boltzmann equation. It is found that IL-PD bilayers with electric permittivity ratio of layers (lower to top), εr, greater than one remain stable under an applied electric field. An extensive numerical study is carried out to generate a map based on εr and the initial mean thickness of the lower layer. This map is used to predict the formation of various structures on PD-PD bilayer interface and provides a baseline for unstable IL-PD bilayers. The use of an ionic liquid (IL) layer is found to reduce the size of the structures, but results in polydispersed and disordered pillars spread over the domain. The numerical predictions follow similar trend of experimental observation of Lau and Russel. (Lau, C. Y.; Russel, W. B. Fundamental Limitations on Ordered Electrohydrodynamic Patterning; Macromolecules 2011, 44, 7746-7751). PMID:25419880

  10. [Ultra-thin transnasal esophagogastroduodenoscopy].

    PubMed

    Kawai, Takashi; Yamamoto, Kei; Fukuzawa, Mari; Sakai, Yoshihiro; Moriyasu, Fuminori

    2010-07-01

    It is reported that ultra-thin transnasal esophagogastroduodenoscopy (TN-EGD) reduces pharyngeal discomfort and is more tolerable for the patients. Ultra-thin transnasal endoscopy has been reported as inferior to transoral conventional EGD (TO-EGD) in terms of image quality, suction, air insufflation and lens washing, due to the smaller endoscope caliber. TN-EGD should be conducted slowly, with short distance observation, and also with image-enhanced endoscopy. With reference to image-enhanced endoscopy, chromoendoscopy method (indigocarmine) is suitable for gastric neoplasm, on the other hand optical digital method (NBI) and digital method (i-scan, FICE) is suitable for esophageal neoplasm. TN-EGD is applied in various gastrointestinal (GI) procedures such as percutaneous endoscopic gastrostomy, nasoenteric feeding tube placement, endoscopic retrograde cholangiopancreaticography with nasobiliary drainage, long intestinal tube placement in small bowel obstruction, esophageal manometry. PMID:20662204

  11. Synthesis, characterization and biological study on Cr 3+, ZrO 2+, HfO 2+ and UO 22+ complexes of oxalohydrazide and bis(3-hydroxyimino)butan-2-ylidene)-oxalohydrazide

    NASA Astrophysics Data System (ADS)

    El-Asmy, A. A.; El-Gammal, O. A.; Radwan, H. A.

    2010-09-01

    Cr 3+, ZrO 2+, HfO 2+ and UO 22+ complexes of oxalohydrazide (H 2L 1) and oxalyl bis(diacetylmonoxime hydrazone) [its IUPAC name is oxalyl bis(3-hydroxyimino)butan-2-ylidene)oxalohydrazide] (H 4L 2) have been synthesized and characterized by partial elemental analysis, spectral (IR; electronic), thermal and magnetic measurements. [Cr(L 1)(H 2O) 3(Cl)]·H 2O, [ZrO(HL 1) 2]·C 2H 5OH, [UO 2(L 1)(H 2O) 2] [ZrO(H 3L 2)(Cl)] 2·2H 2O, [HfO(H 3L 2)(Cl)] 2·2H 2O and [UO 2(H 2L 2)]·2H 2O have been suggested. H 2L 1 behaves as a monobasic or dibasic bidentate ligand while H 4L 2 acts as a tetrabasic octadentate with the two metal centers. The molecular modeling of the two ligands have been drawn and their molecular parameters were calculated. Examination of the DNA degradation of H 2L 1 and H 4L 2 as well as their complexes revealed that direct contact of [ZrO(H 3L 2)(Cl)] 2·2H 2O or [HfO(H 3L 2)(Cl)] 2·2H 2O degrading the DNA of Eukaryotic subject. The ligands and their metal complexes were tested against Gram's positive Bacillus thuringiensis (BT) and Gram's negative ( Escherichia coli) bacteria. All compounds have small inhibitory effects.

  12. Synthesis, characterization and biological study on Cr(3+), ZrO(2+), HfO(2+) and UO(2)(2+) complexes of oxalohydrazide and bis(3-hydroxyimino)butan-2-ylidene)-oxalohydrazide.

    PubMed

    El-Asmy, A A; El-Gammal, O A; Radwan, H A

    2010-09-01

    Cr(3+), ZrO(2+), HfO(2+) and UO(2)(2+) complexes of oxalohydrazide (H(2)L(1)) and oxalyl bis(diacetylmonoxime hydrazone) [its IUPAC name is oxalyl bis(3-hydroxyimino)butan-2-ylidene)oxalohydrazide] (H(4)L(2)) have been synthesized and characterized by partial elemental analysis, spectral (IR; electronic), thermal and magnetic measurements. [Cr(L(1))(H(2)O)(3)(Cl)].H(2)O, [ZrO(HL(1))(2)].C(2)H(5)OH, [UO(2)(L(1))(H(2)O)(2)] [ZrO(H(3)L(2))(Cl)](2).2H(2)O, [HfO(H(3)L(2))(Cl)](2).2H(2)O and [UO(2)(H(2)L(2))].2H(2)O have been suggested. H(2)L(1) behaves as a monobasic or dibasic bidentate ligand while H(4)L(2) acts as a tetrabasic octadentate with the two metal centers. The molecular modeling of the two ligands have been drawn and their molecular parameters were calculated. Examination of the DNA degradation of H(2)L(1) and H(4)L(2) as well as their complexes revealed that direct contact of [ZrO(H(3)L(2))(Cl)](2).2H(2)O or [HfO(H(3)L(2))(Cl)](2).2H(2)O degrading the DNA of Eukaryotic subject. The ligands and their metal complexes were tested against Gram's positive Bacillus thuringiensis (BT) and Gram's negative (Escherichia coli) bacteria. All compounds have small inhibitory effects.

  13. Partitioning behavior and stabilization of hydrophobically coated HfO2, ZrO2 and Hfx Zr 1-x O2 nanoparticles with natural organic matter reveal differences dependent on crystal structure.

    PubMed

    Navarro, Divina A; Depner, Sean W; Watson, David F; Aga, Diana S; Banerjee, Sarbajit

    2011-11-30

    The interactions of engineered nanomaterials with natural organic matter (NOM) exert a profound influence on the mobilities of the former in the environment. However, the influence of specific nanomaterial structural characteristics on the partitioning and colloidal stabilization of engineered nanomaterials in various ecological compartments remains underexplored. Herein, we present a systematic study of the interactions of humic acid (HA, as a model for NOM) with monodisperse, well-characterized, ligand-passivated HfO(2), ZrO(2), and solid-solution Hf(x)Zr(1-x)O(2) nanoparticles (NPs). We note that mixing with HA induces the almost complete phase transfer of hydrophobically coated monoclinic metal oxide (MO) NPs from hexane to water. Furthermore, HA is seen to impart appreciable colloidal stabilization to the NPs in the aqueous phase. In contrast, phase transfer and aqueous-phase colloidal stabilization has not been observed for tetragonal MO-NPs. A mechanistic model for the phase transfer and aqueous dispersal of MO-NPs is proposed on the basis of evidence from transmission electron microscopy, ζ-potential measurements, dynamic light scattering, Raman and infrared spectroscopies, elemental analysis, and systematic experiments on a closely related set of MO-NPs with varying composition and crystal structure. The data indicate the synergistic role of over-coating (micellar), ligand substitution (coordinative), and electrostatic processes wherein HA acts both as an amphiphilic molecule and a charged chelating ligand. The strong observed preference for the phase transfer of monoclinic instead of tetragonal NPs indicates the importance of the preferential binding of HA to specific crystallographic facets and suggests the possibility of being able to design NPs to minimize their mobilities in the aquatic environment.

  14. Surface cleaning effects on reliability for devices with ultrathin oxides or oxynitrides

    NASA Astrophysics Data System (ADS)

    Lai, Kafai; Hao, Ming-Yin; Chen, Wei-Ming; Lee, Jack C.

    1994-09-01

    A new wafer cleaning procedure has been developed for ultra-thin thermal oxidation process (Ultrathin thermal oxides (48 angstrom) and oxynitrides grown in N2O (42 angstrom) were prepared using this new cleaning and other commonly used cleaning methods to investigate the effects of surface preparation on dielectric integrity. It has been found that this two-dip method produces dielectrics with reduced leakage current and stress-induced leakage current, which are believed to be the critical parameters for ultrathin oxides. Furthermore, this new cleaning procedure improves both intrinsic and defect-related breakdown as well as the uniformity of the current- voltage characteristics across a 4-inch wafer. The methanol/HF dip time has also been optimized. The improvement is believed to be due to enhanced silicon surface passivation by hydrogen, the reduced surface micro-roughness and the absence of native oxide.

  15. Ultrathin plasmonic chiral phase plate.

    PubMed

    Gorodetski, Yuri; Genet, Cyriaque; Ebbesen, Thomas W

    2016-09-15

    A thin free-standing gold membrane with complex plasmonic structures engraved on both sides is shown to perform as an ultrathin phase plate. Specifically, we demonstrate the generation of a far-field vortex beam propagating at a desired angle. The angular momentum of the beam is generated by the groove helicity, together with the geometric phase arising from a plasmonic spin-orbit interaction. The radial chirp of the back-side structure is used to modify the emission angle via a specific momentum matching condition. PMID:27628405

  16. UV protection filters by dielectric multilayer thin films on Glass BK-7 and Infrasil 301

    NASA Astrophysics Data System (ADS)

    Abdel-Aziz, M. M.; Azim, Osama A.; Abdel-Wahab, L. A.; Seddik, Mohamed M.

    2006-10-01

    The increasing use of Ultraviolet (UV) light in medicine, industrial environments, for cosmetic use, and even in consumer products necessitates that greater attention be paid to the potential hazards of this type of electromagnetic radiation. To avoid any adverse effects of exposure to this type of radiation, four suitable protection filters were produced to block three UV bands (UVA, UVB, and UVC). The design structure of the required dielectric multilayer filters was done by optical thin film technology using the absorbing property of UV radiation for the substrates and dielectric materials. The computer analyses of the multilayer filter formulas were prepared using Macleod Software for the production processes. The deposition technique was achieved on optical substrates (Glass BK-7 and Infrasil 301) by dielectric material combinations including Titanium dioxide (Ti 2O 3), Hafnium dioxide (HfO 2), and Lima (mixture of oxides SiO 2/Al 2O 3); deposition being achieved using an electron beam gun. The output results of the theoretical and experimental transmittance values for spectral band from 200 nm to 800 nm were discussed in four processes. To analyze the suitability for use in 'real world' applications, the test pieces were subjected to the durability tests (adhesion, abrasion resistance, and humidity) according to Military Standard MIL-C-675C and MIL-C-48497A.

  17. Hybrid gate dielectric materials for unconventional electronic circuitry.

    PubMed

    Ha, Young-Geun; Everaerts, Ken; Hersam, Mark C; Marks, Tobin J

    2014-04-15

    Recent advances in semiconductor performance made possible by organic π-electron molecules, carbon-based nanomaterials, and metal oxides have been a central scientific and technological research focus over the past decade in the quest for flexible and transparent electronic products. However, advances in semiconductor materials require corresponding advances in compatible gate dielectric materials, which must exhibit excellent electrical properties such as large capacitance, high breakdown strength, low leakage current density, and mechanical flexibility on arbitrary substrates. Historically, conventional silicon dioxide (SiO2) has dominated electronics as the preferred gate dielectric material in complementary metal oxide semiconductor (CMOS) integrated transistor circuitry. However, it does not satisfy many of the performance requirements for the aforementioned semiconductors due to its relatively low dielectric constant and intransigent processability. High-k inorganics such as hafnium dioxide (HfO2) or zirconium dioxide (ZrO2) offer some increases in performance, but scientists have great difficulty depositing these materials as smooth films at temperatures compatible with flexible plastic substrates. While various organic polymers are accessible via chemical synthesis and readily form films from solution, they typically exhibit low capacitances, and the corresponding transistors operate at unacceptably high voltages. More recently, researchers have combined the favorable properties of high-k metal oxides and π-electron organics to form processable, structurally well-defined, and robust self-assembled multilayer nanodielectrics, which enable high-performance transistors with a wide variety of unconventional semiconductors. In this Account, we review recent advances in organic-inorganic hybrid gate dielectrics, fabricated by multilayer self-assembly, and their remarkable synergy with unconventional semiconductors. We first discuss the principals and functional

  18. Lithography-free transmission filters at ultraviolet frequencies using ultra-thin aluminum films

    NASA Astrophysics Data System (ADS)

    Li, Zhongyang; Butun, Serkan; Aydin, Koray

    2016-06-01

    Aluminum allows for significant plasmon responses in ultraviolet (UV) regime of spectrum, where conventional plasmonic materials such as silver and gold lack plasmonic behavior due to their inherent dissipative limitation from lower plasmon frequency and inter-band transition. Such UV plasmonic resonance based on aluminum nanostructures could be challenging due to the smaller feature size of nanoscale resonator and remarkable sensitivity to oxidization. Here we theoretically and experimentally demonstrate lithography-free transmission filters using triple layers of continuous ultra-thin Al and dielectric films. Our proposed transmission filter is a triple-layer Fabry-Perot cavity and operates from 2.5 to 5.5 eV with bandwidth down to 0.5 eV and transmission amplitude up to 50%. Such flat Al ultra-thin film coatings suggest the use of aluminum as low-cost UV filters and UV optoelectronics as well as structural coloring applications.

  19. Silicon Nanowires with High-k Hafnium Oxide Dielectrics for Sensitive Detection of Small Nucleic Acid Oligomers

    PubMed Central

    Dorvel, Brian R.; Reddy, Bobby; Go, Jonghyun; Guevara, Carlos Duarte; Salm, Eric; Alam, Muhammad Ashraful; Bashir, Rashid

    2012-01-01

    Nanobiosensors based on silicon nanowire field effect transistors offer advantages of low cost, label-free detection, and potential for massive parallelization. As a result, these sensors have often been suggested as an attractive option for applications in Point-of-care (POC) medical diagnostics. Unfortunately, a number of performance issues such as gate leakage and current instability due to fluid contact, have prevented widespread adoption of the technology for routine use. High-k dielectrics, such as hafnium oxide (HfO2), have the known ability to address these challenges by passivating the exposed surfaces against destabilizing concerns of ion transport. With these fundamental stability issues addressed, a promising target for POC diagnostics and SiNWFET’s has been small oligonucleotides, more specifically microRNA (miRNA). MicroRNA’s are small RNA oligonucleotides which bind to messenger RNA’s, causing translational repression of proteins, gene silencing, and expressions are typically altered in several forms of cancer. In this paper, we describe a process for fabricating stable HfO2 dielectric based silicon nanowires for biosensing applications. Here we demonstrate sensing of single stranded DNA analogues to their microRNA cousins using miR-10b and miR-21 as templates, both known to be upregulated in breast cancer. We characterize the effect of surface functionalization on device performance using the miR-10b DNA analogue as the target sequence and different molecular weight poly-l-lysine as the functionalization layer. By optimizing the surface functionalization and fabrication protocol, we were able to achieve <100fM detection levels of miR-10b DNA analogue, with a theoretical limit of detection of 1fM. Moreover, the non-complementary DNA target strand, based on miR-21, showed very little response, indicating a highly sensitive and highly selective biosensing platform. PMID:22695179

  20. Silicon nanowires with high-k hafnium oxide dielectrics for sensitive detection of small nucleic acid oligomers.

    PubMed

    Dorvel, Brian R; Reddy, Bobby; Go, Jonghyun; Duarte Guevara, Carlos; Salm, Eric; Alam, Muhammad Ashraful; Bashir, Rashid

    2012-07-24

    Nanobiosensors based on silicon nanowire field effect transistors offer advantages of low cost, label-free detection, and potential for massive parallelization. As a result, these sensors have often been suggested as an attractive option for applications in point-of-care (POC) medical diagnostics. Unfortunately, a number of performance issues, such as gate leakage and current instability due to fluid contact, have prevented widespread adoption of the technology for routine use. High-k dielectrics, such as hafnium oxide (HfO(2)), have the known ability to address these challenges by passivating the exposed surfaces against destabilizing concerns of ion transport. With these fundamental stability issues addressed, a promising target for POC diagnostics and SiNWFETs has been small oligonucleotides, more specifically, microRNA (miRNA). MicroRNAs are small RNA oligonucleotides which bind to mRNAs, causing translational repression of proteins, gene silencing, and expressions are typically altered in several forms of cancer. In this paper, we describe a process for fabricating stable HfO(2) dielectric-based silicon nanowires for biosensing applications. Here we demonstrate sensing of single-stranded DNA analogues to their microRNA cousins using miR-10b and miR-21 as templates, both known to be upregulated in breast cancer. We characterize the effect of surface functionalization on device performance using the miR-10b DNA analogue as the target sequence and different molecular weight poly-l-lysine as the functionalization layer. By optimizing the surface functionalization and fabrication protocol, we were able to achieve <100 fM detection levels of the miR-10b DNA analogue, with a theoretical limit of detection of 1 fM. Moreover, the noncomplementary DNA target strand, based on miR-21, showed very little response, indicating a highly sensitive and highly selective biosensing platform.

  1. Physicochemically functional ultrathin films by interfacial polymerization

    DOEpatents

    Lonsdale, H.K.; Babcock, W.C.; Friensen, D.T.; Smith, K.L.; Johnson, B.M.; Wamser, C.C.

    1990-08-14

    Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclosed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers. 3 figs.

  2. Physicochemically functional ultrathin films by interfacial polymerization

    DOEpatents

    Lonsdale, Harold K.; Babcock, Walter C.; Friensen, Dwayne T.; Smith, Kelly L.; Johnson, Bruce M.; Wamser, Carl C.

    1990-01-01

    Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclsoed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers.

  3. Ultra-Thin, Flexible Electronics

    NASA Technical Reports Server (NTRS)

    Holland, Brian; McPherson, Ryan; Zhang, Tan; Hou, Zhenwei; Dean, Robert; Johnson, R. Wayne; DelCastillo, Linda; Moussessian, Alina

    2008-01-01

    Thinned die can be used to realize ultra-thin flexible electronics for applications such as conformal and wearable electronics. Three techniques have been developed to achieve this goal using thinned die: die flip chip bonded onto flexible substrates, die laminated onto LCP films, and die embedded in polyimide. A key to achieving each of these techniques is the thinning of die to a thickness of 50 microns or thinner. Conventional CMP processing can be used to thin to 50 microns. At 50 microns, the active die become flexible and must be handled by temporarily bonding them to a holder die, for further processing. Once bonded face down to the holder die, the active die can be further thinned by DRIE etching the exposed backside. The thinned die can then been packaged in or on the flexible substrate.

  4. Chemical control over the formation and reactivity of ultra-thin films and amino-terminated layers on silicon

    NASA Astrophysics Data System (ADS)

    Rodriguez-Reyes, Juan Carlos F.

    The physical-chemical properties of several interfacial systems of technological relevance are investigated, having as a common goal the elucidation of strategies towards their atomic- and molecular-level control. Such systems can be classified in three groups: (i) ultra-thin films deposited using metalorganic precursors, (ii) metalorganic monolayers on silicon, and (iii) amine-functionalized silicon surfaces. Experimental, theoretical and chemometric methods are conveniently combined to gain a solid understanding of these systems. The ultra-thin films under investigation are titanium carbonitride (TiNC) and hafnium oxide (HfO2). Since these films may serve as substrates for deposition of other materials in circuit components, their surface chemistry needs to be understood and controlled in order to facilitate further deposition steps. The surface of a TiCN film is transformed to titanium nitride (TiN) through nitridation with ammonia; this compositional change can be reversed by the partial decomposition of ethylene molecules on the surface. The surface reactivity is observed to depend on the film composition, and therefore the method described above serves to reversibly tune the reactivity of Ti-based films. As for HfO2 films, it is found that the deposition temperature affects the degree of crystallinity of the films, which in turn affects their surface chemistry. Thus, together with a control of the composition, it is found that the reactivity of a film can be controlled precisely by controlling the crystallinity. The investigation of metalorganic monolayers on silicon surfaces was motivated by the need for understanding the first steps of metalorganic-based deposition of films, which is usually characterized by a heavy presence of contaminants that degrade the film properties. Through a combination of vibrational (infrared) spectroscopy and theoretical methods, a feasible pathway for the adsorption and decomposition of Ti[N(CH3)2]4 is found. This pathway

  5. Dielectric metasurfaces

    NASA Astrophysics Data System (ADS)

    Valentine, Jason

    While plasmonics metasurfaces have seen much development over the past several years, they still face throughput limitations due to ohmic losses. On the other hand, dielectric resonators and associated metasurfaces can eliminate the issue of ohmic loss while still providing the freedom to engineer the optical properties of the composite. In this talk, I will present our recent efforts to harness this freedom using metasurfaces formed from silicon and fabricated using CMOS-compatible techniques. Operating in the telecommunications band, I will discuss how we have used this platform to realize a number of novel functionalities including wavefront control, near-perfect reflection, and high quality factor resonances. In many cases the optical performance of these silicon-based metasurfaces can surpass their plasmonic counterparts. Furthermore, for some cases the surfaces are more amenable to large-area fabrication techniques.

  6. High k dielectrics on silicon: Effects of processing on nanostructure and properties

    NASA Astrophysics Data System (ADS)

    Das, Anirban

    High permittivity hafnia, HfO2, and hafnium silicate, HfSiO 4, are the most promising candidates to replace oxide (SiOx) or oxynitride (SiOxNy) based gate dielectrics in future generation CMOS devices. In this thesis, the effects of processing (deposition techniques, post deposition annealing, nitridation) on nanostructure evolution (crystallization, phase segregation, interlayer growth), changes in nanochemistry (impurity content, interfacial reaction, interdiffusion, oxygen diffusion, paramagnetic charge centers) and properties (EOT, oxide charges) of atomic layer deposited (ALD) Hf-O/Hf-Si-O films on Si, with different interlayers (IL), were studied. A variety of analytical techniques including XRD, RBS, XPS, SIMS, AFM, HRTEM, STEM-EELS and EPR were used. In general, PEALD Hf-O films deposited using metal-organic precursors showed a higher C and H and lower Cl content compared to thermal ALD films using halide based precursors. Also, as-deposited ALD films (Hf-O/IL/Si) showed the formation of Hf-O-Si bonds at the Hf-O/IL interface, with increasing tendency in the presence of a chemical oxide interlayer and upon oxygen annealing. Upon post deposition annealing (PDA) of ALD Hf-O films up to 1000°C, m-HfO2 was the stable crystalline phase. It was observed that the chemical oxide interlayer grew significantly during PDA in oxygen, the rate of which was a f (t, T) due to oxygen diffusion. Additionally, an annealed Hf-O stack (i.e., target Hf-O thickness of 4.0 nm/1.2 nm nitrided chemical oxide interlayer/Si) showed a chemically diffused HfSiOx region (2 nm) in between pure HfO2 (2 nm) and the interlayer (1.2 nm) as a result of interdiffusion and interfacial reactions. Therefore, a three-layer capacitor model was used to determine the respective contributions to the total EOT. Moreover, to correlate the presence of defects with density of interfacial states, as-deposited ALD Hf-O/chemical oxide IL/Si stacks were shown to be EPR active at 8K, due to Pb0, Pb1 type

  7. Measurement of optical anisotropy in ultrathin films using surface plasmon resonance

    NASA Astrophysics Data System (ADS)

    Devanarayanan, V. P.; Manjuladevi, V.; Poonia, Monika; Gupta, R. K.; Gupta, Sanjeev K.; Akhtar, Jamil

    2016-01-01

    The optical phenomenon, surface plasmon resonance (SPR) is employed for the measurement of optical anisotropy in the ultrathin films fabricated through Langmuir-Blodgett (LB) and self-assembled monolayer (SAM) techniques onto 50 nm gold film supported on BK7 glass substrates. The resonance angle (RA) is measured using a home built setup in Kretschmann configuration. The LB films and SAM can provide a single layer of highly ordered and organized molecules on the two dimensional surface. If the film forming molecules are anisotropic, their organization in the LB films and SAM can yield an anisotropic film due to tilt of the molecules with respect to the surface normal. The SPR spectra are recorded for the two orthogonal directions of the film with respect to the plane of incidence. The spectra are simulated by modeling the Fresnel's reflection from 4-layers viz., prism, gold, ultrathin films and air; and the real and imaginary parts of refractive index are estimated. Our study shows the metallic and dielectric nature of the LB films of bundles of single walled carbon nanotubes (SWCNTs) when the long axis of SWCNTs are aligned parallel and perpendicular to plane of incidence, respectively. The optical anisotropy was estimated from the change in real part of refractive index (Δnr) of the ultrathin films measured in the orthogonal directions. In addition, we have also studied such optical anisotropy in the LB film of cadmium-stearate and self-assembled monolayer of octadecanethiol.

  8. Polarization-insensitive ultra-thin quasi-metasurface based on the spoof surface plasmon polaritons

    NASA Astrophysics Data System (ADS)

    Li, Si-Jia; Cao, Xiang-Yu; Gao, Jun; Han, Jiang-Feng; Zhang, Zhao; Huang, Fa; Zhang, Chen; Liu, Xiao

    2016-09-01

    We theoretically and experimentally propose a novel polarization-insensitive ultra-thin quasi-metasurface composed of the twelve gradually increasing two-sided metallic grooves, an ultra-thin flexible dielectric film, and a circular copper surface to induce the spoof surface plasmon polaritons in the microwave frequency. The evolution of dispersion characteristic is systematically analyzed in simulation, and we interestingly reveal that the quasi-metasurface provides a way to convert spatial propagating waves to the spoof surface plasmon polariton waves not only for transverse magnetic incidence but also for transverse electric waves. Hence, the proposed quasi-metasurface converts the scattering direction from incident wave direction to the spoof surface plasmon polaritons wave direction and the far-field scattering patterns can be controlled due to the conversion and transmission. A quasi-metasurface device is easily implemented using the common printed circuit board method for demonstration. Both numerical simulations and experimental results verify the polarization-insensitive ultra-thin quasi-metasurface.

  9. Perfluorodecyltrichlorosilane-based seed-layer for improved chemical vapour deposition of ultrathin hafnium dioxide films on graphene.

    PubMed

    Kitzmann, Julia; Göritz, Alexander; Fraschke, Mirko; Lukosius, Mindaugas; Wenger, Christian; Wolff, Andre; Lupina, Grzegorz

    2016-07-06

    We investigate the use of perfluorodecyltrichlorosilane-based self-assembled monolayer as seeding layer for chemical vapour deposition of HfO2 on large area CVD graphene. The deposition and evolution of the FDTS-based seed layer is investigated by X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy. Crystalline quality of graphene transferred from Cu is monitored during formation of the seed layer as well as the HfO2 growth using Raman spectroscopy. We demonstrate that FDTS-based seed layer significantly improves nucleation of HfO2 layers so that graphene can be coated in a conformal way with HfO2 layers as thin as 10 nm. Proof-of-concept experiments on 200 mm wafers presented here validate applicability of the proposed approach to wafer scale graphene device fabrication.

  10. Perfluorodecyltrichlorosilane-based seed-layer for improved chemical vapour deposition of ultrathin hafnium dioxide films on graphene

    PubMed Central

    Kitzmann, Julia; Göritz, Alexander; Fraschke, Mirko; Lukosius, Mindaugas; Wenger, Christian; Wolff, Andre; Lupina, Grzegorz

    2016-01-01

    We investigate the use of perfluorodecyltrichlorosilane-based self-assembled monolayer as seeding layer for chemical vapour deposition of HfO2 on large area CVD graphene. The deposition and evolution of the FDTS-based seed layer is investigated by X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy. Crystalline quality of graphene transferred from Cu is monitored during formation of the seed layer as well as the HfO2 growth using Raman spectroscopy. We demonstrate that FDTS-based seed layer significantly improves nucleation of HfO2 layers so that graphene can be coated in a conformal way with HfO2 layers as thin as 10 nm. Proof-of-concept experiments on 200 mm wafers presented here validate applicability of the proposed approach to wafer scale graphene device fabrication. PMID:27381715

  11. Perfluorodecyltrichlorosilane-based seed-layer for improved chemical vapour deposition of ultrathin hafnium dioxide films on graphene

    NASA Astrophysics Data System (ADS)

    Kitzmann, Julia; Göritz, Alexander; Fraschke, Mirko; Lukosius, Mindaugas; Wenger, Christian; Wolff, Andre; Lupina, Grzegorz

    2016-07-01

    We investigate the use of perfluorodecyltrichlorosilane-based self-assembled monolayer as seeding layer for chemical vapour deposition of HfO2 on large area CVD graphene. The deposition and evolution of the FDTS-based seed layer is investigated by X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy. Crystalline quality of graphene transferred from Cu is monitored during formation of the seed layer as well as the HfO2 growth using Raman spectroscopy. We demonstrate that FDTS-based seed layer significantly improves nucleation of HfO2 layers so that graphene can be coated in a conformal way with HfO2 layers as thin as 10 nm. Proof-of-concept experiments on 200 mm wafers presented here validate applicability of the proposed approach to wafer scale graphene device fabrication.

  12. Perfluorodecyltrichlorosilane-based seed-layer for improved chemical vapour deposition of ultrathin hafnium dioxide films on graphene.

    PubMed

    Kitzmann, Julia; Göritz, Alexander; Fraschke, Mirko; Lukosius, Mindaugas; Wenger, Christian; Wolff, Andre; Lupina, Grzegorz

    2016-01-01

    We investigate the use of perfluorodecyltrichlorosilane-based self-assembled monolayer as seeding layer for chemical vapour deposition of HfO2 on large area CVD graphene. The deposition and evolution of the FDTS-based seed layer is investigated by X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy. Crystalline quality of graphene transferred from Cu is monitored during formation of the seed layer as well as the HfO2 growth using Raman spectroscopy. We demonstrate that FDTS-based seed layer significantly improves nucleation of HfO2 layers so that graphene can be coated in a conformal way with HfO2 layers as thin as 10 nm. Proof-of-concept experiments on 200 mm wafers presented here validate applicability of the proposed approach to wafer scale graphene device fabrication. PMID:27381715

  13. Surface band bending and band alignment of plasma enhanced atomic layer deposited dielectrics on Ga- and N-face gallium nitride

    NASA Astrophysics Data System (ADS)

    Yang, Jialing; Eller, Brianna S.; Nemanich, Robert J.

    2014-09-01

    The effects of surface pretreatment, dielectric growth, and post deposition annealing on interface electronic structure and polarization charge compensation of Ga- and N-face bulk GaN were investigated. The cleaning process consisted of an ex-situ wet chemical NH4OH treatment and an in-situ elevated temperature NH3 plasma process to remove carbon contamination, reduce oxygen coverage, and potentially passivate N-vacancy related defects. After the cleaning process, carbon contamination decreased below the x-ray photoemission spectroscopy detection limit, and the oxygen coverage stabilized at ˜1 monolayer on both Ga- and N-face GaN. In addition, Ga- and N-face GaN had an upward band bending of 0.8 ± 0.1 eV and 0.6 ± 0.1 eV, respectively, which suggested the net charge of the surface states and polarization bound charge was similar on Ga- and N-face GaN. Furthermore, three dielectrics (HfO2, Al2O3, and SiO2) were prepared by plasma-enhanced atomic layer deposition on Ga- or N-face GaN and annealed in N2 ambient to investigate the effect of the polarization charge on the interface electronic structure and band offsets. The respective valence band offsets of HfO2, Al2O3, and SiO2 with respect to Ga- and N-face GaN were 1.4 ± 0.1, 2.0 ± 0.1, and 3.2 ± 0.1 eV, regardless of dielectric thickness. The corresponding conduction band offsets were 1.0 ± 0.1, 1.3 ± 0.1, and 2.3 ± 0.1 eV, respectively. Experimental band offset results were consistent with theoretical calculations based on the charge neutrality level model. The trend of band offsets for dielectric/GaN interfaces was related to the band gap and/or the electronic part of the dielectric constant. The effect of polarization charge on band offset was apparently screened by the dielectric-GaN interface states.

  14. Characterization of ALD Beryllium Oxide as a Potential High- k Gate Dielectric for Low-Leakage AlGaN/GaN MOSHEMTs

    NASA Astrophysics Data System (ADS)

    Johnson, Derek W.; Yum, Jung Hwan; Hudnall, Todd W.; Mushinski, Ryan M.; Bielawski, Christopher W.; Roberts, John C.; Wang, Wei-E.; Banerjee, Sanjay K.; Harris, H. Rusty

    2014-01-01

    The chemical and electrical characteristics of atomic layer deposited (ALD) beryllium oxide (BeO) on GaN were studied via x-ray photoelectron spectroscopy, current-voltage, and capacitance-voltage measurements and compared with those of ALD Al2O3 and HfO2 on GaN. Radiofrequency (RF) and power electronics based on AlGaN/GaN high-electron-mobility transistors are maturing rapidly, but leakage current reduction and interface defect ( D it) minimization remain heavily researched. BeO has received recent attention as a high- k gate dielectric due to its large band gap (10.6 eV) and thermal stability on InGaAs and Si, but little is known about its performance on GaN. Unintentionally doped GaN was cleaned in dilute aqueous HCl immediately prior to BeO deposition (using diethylberyllium and H2O precursors). Formation of an interfacial layer was observed in as-deposited samples, similar to the layer formed during ALD HfO2 deposition on GaN. Postdeposition anneal (PDA) at 700°C and 900°C had little effect on the observed BeO binding state, confirming the strength of the bond, but led to increased Ga oxide formation, indicating the presence of unincorporated oxygen in the dielectric. Despite the interfacial layer, gate leakage current of 1.1 × 10-7 A/cm2 was realized, confirming the potential of ALD BeO for use in low-leakage AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors.

  15. Lithography-Free Broadband Ultrathin-Film Absorbers with Gap-Plasmon Resonance for Organic Photovoltaics.

    PubMed

    Choi, Minjung; Kang, Gumin; Shin, Dongheok; Barange, Nilesh; Lee, Chang-Won; Ko, Doo-Hyun; Kim, Kyoungsik

    2016-05-25

    Strategies to confine electromagnetic field within ultrathin film emerge as essential technologies for applications from thin-film solar cells to imaging and sensing devices. We demonstrate a lithography-free, low-cost, large-scale method to realize broadband ultrathi-film metal-dielectric-metal (MDM) absorbers, by exploiting gap-plasmon resonances for strongly confined electromagnetic field. A two-steps method, first organizing Au nanoparticles via thermal dewetting and then transferring the nanoparticles to a spacer-reflector substrate, is used to achieve broader absorption bandwidth by manipulating geometric shapes of the top metallic layer into hemiellipsoids. A fast-deposited nominal Au film, instead of a conventional slow one, is employed in the Ostwald ripening process to attain hemiellipsoidal nanoparticles. A polymer supported transferring step allows a wider range of dewetting temperature to manipulate the nanoparticles' shape. By incorporating circularity with ImageJ software, the geometries of hemiellipsoidal nanoparticles are quantitatively characterized. Controlling the top geometry of MDM structure from hemisphere to hemiellipsoid increases the average absorption at 500-900 nm from 23.1% to 43.5% in the ultrathin film and full width at half-maximum of 132-324 nm, which is consistently explained by finite-difference time-domain simulation. The structural advantages of our scheme are easily applicable to thin-film photovoltaic devices because metal electrodes can act as metal reflectors and semiconductor layers as dielectric spacers. PMID:27160410

  16. Lithography-Free Broadband Ultrathin-Film Absorbers with Gap-Plasmon Resonance for Organic Photovoltaics.

    PubMed

    Choi, Minjung; Kang, Gumin; Shin, Dongheok; Barange, Nilesh; Lee, Chang-Won; Ko, Doo-Hyun; Kim, Kyoungsik

    2016-05-25

    Strategies to confine electromagnetic field within ultrathin film emerge as essential technologies for applications from thin-film solar cells to imaging and sensing devices. We demonstrate a lithography-free, low-cost, large-scale method to realize broadband ultrathi-film metal-dielectric-metal (MDM) absorbers, by exploiting gap-plasmon resonances for strongly confined electromagnetic field. A two-steps method, first organizing Au nanoparticles via thermal dewetting and then transferring the nanoparticles to a spacer-reflector substrate, is used to achieve broader absorption bandwidth by manipulating geometric shapes of the top metallic layer into hemiellipsoids. A fast-deposited nominal Au film, instead of a conventional slow one, is employed in the Ostwald ripening process to attain hemiellipsoidal nanoparticles. A polymer supported transferring step allows a wider range of dewetting temperature to manipulate the nanoparticles' shape. By incorporating circularity with ImageJ software, the geometries of hemiellipsoidal nanoparticles are quantitatively characterized. Controlling the top geometry of MDM structure from hemisphere to hemiellipsoid increases the average absorption at 500-900 nm from 23.1% to 43.5% in the ultrathin film and full width at half-maximum of 132-324 nm, which is consistently explained by finite-difference time-domain simulation. The structural advantages of our scheme are easily applicable to thin-film photovoltaic devices because metal electrodes can act as metal reflectors and semiconductor layers as dielectric spacers.

  17. Quantum chemistry study of dielectric materials deposition

    NASA Astrophysics Data System (ADS)

    Widjaja, Yuniarto

    The drive to continually decrease the device dimensions of integrated circuits in the microelectronics industry requires that deposited films approach subnanometer thicknesses. Hence, a fundamental understanding of the physics and chemistry of film deposition is important to obtain better control of the properties of the deposited film. We use ab initio quantum chemistry calculations to explore chemical reactions at the atomic level. Important thermodynamic and kinetic parameters are then obtained, which can then be used as inputs in constructing first-principles based reactor models. Studies of new systems for which data are not available can be conducted as well. In this dissertation, we use quantum chemistry simulations to study the deposition of gate dielectrics for metal-oxide-semiconductor (MOS) devices. The focus of this study is on heterogeneous reactions between gaseous precursors and solid surfaces. Adsorbate-surface interactions introduce additional degrees of complexity compared to the corresponding gas-phase or solid-state reactions. The applicability and accuracy of cluster approximations to represent solid surfaces are first investigated. The majority of our results are obtained using B3LYP density functional theory (DFT). The structures of reactants, products, and transition states are obtained, followed by calculations of thermochemical and kinetic properties. Whenever experimental data are available, qualitative and/or quantitative comparisons are drawn. Atomistic mechanisms and the energetics of several reactions leading to the deposition of SiO2, Si3N4, and potential new high-kappa materials such as ZrO2, HfO2, and Al 2O3 have been explored in this dissertation. Competing reaction pathways are explored for each of the deposition reactions studied. For example, the potential energy surface (PES) for ZrO2 ALD shows that the reactions proceed through a trapping-mediated mechanism, which results in a competition between desorption and decomposition

  18. The jump-into-contact effect in biased AFM probes on dielectric films and its application to quantify the dielectric permittivity of thin layers

    NASA Astrophysics Data System (ADS)

    Revilla, Reynier I.

    2016-07-01

    The jump-into-contact (JIC) phenomenon in biased atomic force microscopy (AFM) probes on dielectric films is studied. The influence of the film thickness on the position at which the AFM tip collapses irreversibly into the sample surface was theoretically analyzed using a widely accepted analytical expression of the probe-sample electrostatic interaction force. It was demonstrated that for relatively high values of voltage (V > 10-20 V) applied between the probe and the substrate the cantilever deflection at the JIC is independent of the dielectric film thickness for thin-ultrathin layers (h < 10-50 nm). Under the same conditions the z-piezo distance at the JIC follows approximately a linear behavior with the film thickness. Based on this effect an empirical model was formulated to estimate the dielectric permittivity of thin/ultrathin dielectric films using the jump-into-contact distance. The procedure was successfully applied on thin PVD-SiO2 films, obtaining good agreement with a dielectric constant value previously reported for the same material.

  19. The jump-into-contact effect in biased AFM probes on dielectric films and its application to quantify the dielectric permittivity of thin layers.

    PubMed

    Revilla, Reynier I

    2016-07-01

    The jump-into-contact (JIC) phenomenon in biased atomic force microscopy (AFM) probes on dielectric films is studied. The influence of the film thickness on the position at which the AFM tip collapses irreversibly into the sample surface was theoretically analyzed using a widely accepted analytical expression of the probe-sample electrostatic interaction force. It was demonstrated that for relatively high values of voltage (V > 10-20 V) applied between the probe and the substrate the cantilever deflection at the JIC is independent of the dielectric film thickness for thin-ultrathin layers (h < 10-50 nm). Under the same conditions the z-piezo distance at the JIC follows approximately a linear behavior with the film thickness. Based on this effect an empirical model was formulated to estimate the dielectric permittivity of thin/ultrathin dielectric films using the jump-into-contact distance. The procedure was successfully applied on thin PVD-SiO2 films, obtaining good agreement with a dielectric constant value previously reported for the same material.

  20. The jump-into-contact effect in biased AFM probes on dielectric films and its application to quantify the dielectric permittivity of thin layers

    NASA Astrophysics Data System (ADS)

    Revilla, Reynier I.

    2016-07-01

    The jump-into-contact (JIC) phenomenon in biased atomic force microscopy (AFM) probes on dielectric films is studied. The influence of the film thickness on the position at which the AFM tip collapses irreversibly into the sample surface was theoretically analyzed using a widely accepted analytical expression of the probe–sample electrostatic interaction force. It was demonstrated that for relatively high values of voltage (V > 10–20 V) applied between the probe and the substrate the cantilever deflection at the JIC is independent of the dielectric film thickness for thin–ultrathin layers (h < 10–50 nm). Under the same conditions the z–piezo distance at the JIC follows approximately a linear behavior with the film thickness. Based on this effect an empirical model was formulated to estimate the dielectric permittivity of thin/ultrathin dielectric films using the jump-into-contact distance. The procedure was successfully applied on thin PVD–SiO2 films, obtaining good agreement with a dielectric constant value previously reported for the same material.

  1. The jump-into-contact effect in biased AFM probes on dielectric films and its application to quantify the dielectric permittivity of thin layers.

    PubMed

    Revilla, Reynier I

    2016-07-01

    The jump-into-contact (JIC) phenomenon in biased atomic force microscopy (AFM) probes on dielectric films is studied. The influence of the film thickness on the position at which the AFM tip collapses irreversibly into the sample surface was theoretically analyzed using a widely accepted analytical expression of the probe-sample electrostatic interaction force. It was demonstrated that for relatively high values of voltage (V > 10-20 V) applied between the probe and the substrate the cantilever deflection at the JIC is independent of the dielectric film thickness for thin-ultrathin layers (h < 10-50 nm). Under the same conditions the z-piezo distance at the JIC follows approximately a linear behavior with the film thickness. Based on this effect an empirical model was formulated to estimate the dielectric permittivity of thin/ultrathin dielectric films using the jump-into-contact distance. The procedure was successfully applied on thin PVD-SiO2 films, obtaining good agreement with a dielectric constant value previously reported for the same material. PMID:27199351

  2. Ultrathin core-sheath fibers for liposome stabilization.

    PubMed

    Li, Zhuang; Kang, Hongliang; Li, Qinmei; Che, Ning; Liu, Zhijing; Li, Pingping; Zhang, Chao; Liu, Ruigang; Huang, Yong

    2014-10-01

    Ultrathin core-sheath fibers with small unilamellar vesicles (SUVs) in the core were prepared by coaxial electrospinning. SUVs/sodium hyaluranate (HA-Na)/water and polyvinylpyrrolidone (PVP)/ethanol solutions were used as core and sheath fluid in electrospinning, respectively. The ultrathin fibers were characterized by scanning and transmission electron microscopy (SEM and TEM) and laser scanning confocal microscopy (LSCM). The SUVs were successfully encapsulated in the core HA-Na matrix of the ultrathin fibers and are in the elliptic shape. The SUVs encapsulated in the core matrix of the ultrathin fibers have an excellent stability. The SUVs embedded in the ultrathin fibers are stable. When the ultrathin fibers were re-dissolved in water after one-month storage at room temperature, the rehydrated SUVs have the similar size and size distribution as the as-prepared SUVs. The liposome-loaded ultrathin fiber mats have the promising applications in wound healing materials.

  3. Condition for unity absorption in an ultrathin and highly lossy film in a Gires-Tournois interferometer configuration.

    PubMed

    Park, Junghyun; Kim, Soo Jin; Brongersma, Mark L

    2015-05-01

    We present a condition for unity absorption for a Gires-Tournois interferometer configuration constructed from an ultrathin and highly lossy film on top of metallic mirror. From the impedance matching condition in the transmission line theory, we identify a solution space for the required complex refractive index of the lossy film in various film thickness and dielectric constants of the metallic mirror. It is shown that strong absorption requires the imaginary part of the refractive index of the ultrathin lossy film be larger than 0.64, and the physical origin of this condition is elucidated. The proposed method is useful in identifying candidate semiconductor materials that can be used as the lossy film in a unity-absorption Gires-Tournois interferometer configuration and designing the thickness of this film to maximize absorption.

  4. Spatially and momentum resolved energy electron loss spectra from an ultra-thin PrNiO{sub 3} layer

    SciTech Connect

    Kinyanjui, M. K. Kaiser, U.; Benner, G.; Pavia, G.; Boucher, F.; Habermeier, H.-U.; Keimer, B.

    2015-05-18

    We present an experimental approach which allows for the acquisition of spectra from ultra-thin films at high spatial, momentum, and energy resolutions. Spatially and momentum (q) resolved electron energy loss spectra have been obtained from a 12 nm ultra-thin PrNiO{sub 3} layer using a nano-beam electron diffraction based approach which enabled the acquisition of momentum resolved spectra from individual, differently oriented nano-domains and at different positions of the PrNiO{sub 3} thin layer. The spatial and wavelength dependence of the spectral excitations are obtained and characterized after the analysis of the experimental spectra using calculated dielectric and energy loss functions. The presented approach makes a contribution towards obtaining momentum-resolved spectra from nanostructures, thin film, heterostructures, surfaces, and interfaces.

  5. Optical absorption enhancement in 40 nm ultrathin film silicon solar cells assisted by photonic and plasmonic modes

    NASA Astrophysics Data System (ADS)

    Saravanan, S.; Dubey, R. S.

    2016-10-01

    Presently, energy problems and environmental issues have attracted the scientific community for the development of cost-effective and high-performance solar cells. Thin film solar cells are cheaper but weak light absorption in longer wavelength has demanded an efficient light trapping scheme for the better harvesting of solar radiation to a maximum possibility. In this paper, we numerically explore the design efforts of an ultrathin film silicon solar cell, integrated with top dielectric and bottom metal gratings. The proposed design is influenced by the localized surface plasmon modes, surface plasmon polariton and optical resonances which leads to the optimal harvesting of sunlight within 40 nm thick absorbing layer. The optimized design of solar cell shows enhanced light absorption with cell efficiency ∼25% at normal transverse magnetic polarization condition. Our design approach assisted by photonic and plasmonic modes is promising for the realization of new generation, low-cost ultrathin film solar cells.

  6. Atomic Structure of Ultrathin Gold Nanowires.

    PubMed

    Yu, Yi; Cui, Fan; Sun, Jianwei; Yang, Peidong

    2016-05-11

    Understanding of the atomic structure and stability of nanowires (NWs) is critical for their applications in nanotechnology, especially when the diameter of NWs reduces to ultrathin scale (1-2 nm). Here, using aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM), we report a detailed atomic structure study of the ultrathin Au NWs, which are synthesized using a silane-mediated approach. The NWs contain large amounts of generalized stacking fault defects. These defects evolve upon sustained electron exposure, and simultaneously the NWs undergo necking and breaking. Quantitative strain analysis reveals the key role of strain in the breakdown process. Besides, ligand-like morphology is observed at the surface of the NWs, indicating the possibility of using AC-HRTEM for surface ligand imaging. Moreover, the coalescence dynamic of ultrathin Au NWs is demonstrated by in situ observations. This work provides a comprehensive understanding of the structure of ultrathin metal NWs at atomic-scale and could have important implications for their applications.

  7. Atomic Structure of Ultrathin Gold Nanowires.

    PubMed

    Yu, Yi; Cui, Fan; Sun, Jianwei; Yang, Peidong

    2016-05-11

    Understanding of the atomic structure and stability of nanowires (NWs) is critical for their applications in nanotechnology, especially when the diameter of NWs reduces to ultrathin scale (1-2 nm). Here, using aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM), we report a detailed atomic structure study of the ultrathin Au NWs, which are synthesized using a silane-mediated approach. The NWs contain large amounts of generalized stacking fault defects. These defects evolve upon sustained electron exposure, and simultaneously the NWs undergo necking and breaking. Quantitative strain analysis reveals the key role of strain in the breakdown process. Besides, ligand-like morphology is observed at the surface of the NWs, indicating the possibility of using AC-HRTEM for surface ligand imaging. Moreover, the coalescence dynamic of ultrathin Au NWs is demonstrated by in situ observations. This work provides a comprehensive understanding of the structure of ultrathin metal NWs at atomic-scale and could have important implications for their applications. PMID:27071038

  8. Dielectric and complex impedance properties of tetravalent hafnium (HF 4+) integrated cobalt ferrite

    NASA Astrophysics Data System (ADS)

    Sanchez, Luis

    The work presented in this thesis was carried out to understand the effects of tetravalent hafnium (Hf4+) ion on the crystal structure and phase, surface morphology, electrical, dielectric and complex impedance properties of cobalt ferrite (CoFe2O4; CFO). Hafnium incorporated cobalt ferrite, CoFe2-xHfxO4, with x = 0.00, 0.05, 0.075, 0.10, 0.15 and 0.20 were prepared by the standard solid state ceramic synthesis method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterizations were performed to determine the structural properties. Most important aspect of this study is to explore the dielectric and complex impedance properties as a function of variable temperature (T=300-1000 K) and frequency (f=20 Hz -1 MHz). Room temperature and the temperature dependence of dielectric constant, loss factor, complex impedance, and the ac resistivity measurements enabled us to understand the effect of temperature and frequency on the electrical and dielectric properties on CoFe2-xHfxO4 and, thus, to derive structure-property relation. X-ray diffraction (XRD) patterns for Hf-incorporated CFO confirm the formation of majority of CFO spinel [with space group Fd3m (227)] phase, in addition to the small amount of HfO2 monoclinic [space group, P1 21/c (14)] phase leading to formation of CFO-Hf composites. The lattice constant values derived from XRD for CFO-Hf were found to increase from 8.374 A (x = 0.000) to 8.391 A (x = 0.200). The lattice expansion is significant at the very first step of Hf-incorporation and then slows down with progressive Hf-incorporation. SEM imaging analysis indicates that Hf resides at the grain boundaries for CFO-Hf. The dielectric constant (epsilon') of CFO-Hf is T-independent at T<450 K, at which point increasing trend prevails. A grain bulk-boundary based two-layer model, where semiconducting-grains separated by insulating-grain boundaries, satisfactorily accounts for epsilon- T (>450 K) variation. Correspondingly, electrical

  9. Reflectance properties of one-dimensional metal-dielectric ternary photonic crystal

    NASA Astrophysics Data System (ADS)

    Pandey, G. N.; Kumar, Narendra; Thapa, Khem B.; Ojha, S. P.

    2016-05-01

    Metallic photonic crystal has a very important application in absorption enhancement in solar cells. It has been found that an ultra-thin metallic layer becomes transparent due to internal scattering of light through the each interface of the dielectric and metal surfaces. The metal has absorption due to their surface plasmon and the plasmon has important parameters for changing optical properties of the metal. We consider ternary metallic-dielectric photonic crystal (MDPC) for having large probabilities to change the optical properties of the MDPC and the photonic crystals may be changed by changing dimensionality, symmetry, lattice parameters, Filling fraction and effective refractive index refractive index contrast. In this present communication, we try to show that the photonic band gap in ternary metal-dielectric photonic crystal can be significantly enlarged when air dielectric constant is considered. All the theoretical analyses are made based on the transfer matrix method together with the Drude model of metal.

  10. Thickness and electric-field-dependent polarizability and dielectric constant in phosphorene

    NASA Astrophysics Data System (ADS)

    Kumar, Piyush; Bhadoria, B. S.; Kumar, Sanjay; Bhowmick, Somnath; Chauhan, Yogesh Singh; Agarwal, Amit

    2016-05-01

    Based on extensive first-principles calculations, we explore the thickness-dependent effective dielectric constant and slab polarizability of few-layer black phosphorene. We find that the dielectric constant in ultrathin phosphorene is thickness-dependent and it can be further tuned by applying an out-of-plane electric field. The decreasing dielectric constant with reducing number of layers of phosphorene is a direct consequence of the lower permittivity of the outer layers and the increasing surface-to-volume ratio. We also show that the slab polarizability depends linearly on the number of layers, implying a nearly constant polarizability per phosphorus atom. Our calculation of the thickness- and electric-field-dependent dielectric properties will be useful for designing and interpreting transport experiments in gated phosphorene devices, wherever electrostatic effects such as capacitance and charge screening are important.

  11. Chemical Treatment of Low-k Dielectric Surfaces for Patterning of Thin Solid Films in Microelectronic Applications.

    PubMed

    Guo, Lei; Qin, Xiangdong; Zaera, Francisco

    2016-03-01

    A protocol has been developed to selectively process low-k SiCOH dielectric substrates in order to activate or deactivate them toward the deposition of thin solid films by chemical (CVD or ALD) means. The original SiCOH surfaces are hydrophobic, an indication that they are alkyl- rather than silanol-terminated and that, consequently, they are fairly unreactive. However, the chemical-mechanical polishing (CMP) sometimes done during microelectronics fabrication renders them hydrophilic and reactive. It was shown here that silylation of the CMP-treated surfaces with any of a number of well-known silylation agents such as HMDS, ODTS, or OTS caps the reactive silanol surface groups and turns them back to being hydrophilic and unreactive. Further exposure of any of the passivated surfaces to a combination of ozone and UV radiation reinstates their hydrophilicity and chemical activity. Importantly, it was also demonstrated that all these changes could be induced without altering the original mechanical, optical, or electrical properties of the samples: atomic force microscopy (AFM) images show no increase in roughness, ellipsometry measurements yield the same values for the index of refraction and dielectric constant, and infrared absorption spectroscopy attests to the preservation of the organic fragments present in the original SiCOH samples. The chemical selectivity of the resulting surfaces was tested for the atomic layer deposition (ALD) of HfO2 films, which could be grown only on the UV/O3 treated substrates. PMID:26956428

  12. Chemical Treatment of Low-k Dielectric Surfaces for Patterning of Thin Solid Films in Microelectronic Applications.

    PubMed

    Guo, Lei; Qin, Xiangdong; Zaera, Francisco

    2016-03-01

    A protocol has been developed to selectively process low-k SiCOH dielectric substrates in order to activate or deactivate them toward the deposition of thin solid films by chemical (CVD or ALD) means. The original SiCOH surfaces are hydrophobic, an indication that they are alkyl- rather than silanol-terminated and that, consequently, they are fairly unreactive. However, the chemical-mechanical polishing (CMP) sometimes done during microelectronics fabrication renders them hydrophilic and reactive. It was shown here that silylation of the CMP-treated surfaces with any of a number of well-known silylation agents such as HMDS, ODTS, or OTS caps the reactive silanol surface groups and turns them back to being hydrophilic and unreactive. Further exposure of any of the passivated surfaces to a combination of ozone and UV radiation reinstates their hydrophilicity and chemical activity. Importantly, it was also demonstrated that all these changes could be induced without altering the original mechanical, optical, or electrical properties of the samples: atomic force microscopy (AFM) images show no increase in roughness, ellipsometry measurements yield the same values for the index of refraction and dielectric constant, and infrared absorption spectroscopy attests to the preservation of the organic fragments present in the original SiCOH samples. The chemical selectivity of the resulting surfaces was tested for the atomic layer deposition (ALD) of HfO2 films, which could be grown only on the UV/O3 treated substrates.

  13. Physical understanding of trends in current collapse with atomic layer deposited dielectrics in AlGaN/GaN MOS heterojunction FETs

    NASA Astrophysics Data System (ADS)

    Ramanan, Narayanan; Lee, Bongmook; Misra, Veena

    2016-03-01

    Many passivation dielectrics are pursued for suppressing current collapse due to trapping/detrapping of access-region surface traps in AlGaN/GaN based metal oxide semiconductor heterojuction field effect transistors (MOS-HFETs). The suppression of current collapse can potentially be achieved either by reducing the interaction of surface traps with the gate via surface leakage current reduction, or by eliminating surface traps that can interact with the gate. But, the latter is undesirable since a high density of surface donor traps is required to sustain a high 2D electron gas density at the AlGaN/GaN heterointerface and provide a low ON-resistance. This presents a practical trade-off wherein a passivation dielectric with the optimal surface trap characteristics and minimal surface leakage is to be chosen. In this work, we compare MOS-HFETs fabricated with popular ALD gate/passivation dielectrics like SiO2, Al2O3, HfO2 and HfAlO along with an additional thick plasma-enhanced chemical vapor deposition SiO2 passivation. It is found that after annealing in N2 at 700 °C, the stack containing ALD HfAlO provides a combination of low surface leakage and a high density of shallow donor traps. Physics-based TCAD simulations confirm that this combination of properties helps quick de-trapping and minimal current collapse along with a low ON resistance.

  14. Improved linearity and reliability in GaN metal-oxide-semiconductor high-electron-mobility transistors using nanolaminate La2O3/SiO2 gate dielectric

    NASA Astrophysics Data System (ADS)

    Hsu, Ching-Hsiang; Shih, Wang-Cheng; Lin, Yueh-Chin; Hsu, Heng-Tung; Hsu, Hisang-Hua; Huang, Yu-Xiang; Lin, Tai-Wei; Wu, Chia-Hsun; Wu, Wen-Hao; Maa, Jer-Shen; Iwai, Hiroshi; Kakushima, Kuniyuki; Chang, Edward Yi

    2016-04-01

    Improved device performance to enable high-linearity power applications has been discussed in this study. We have compared the La2O3/SiO2 AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) with other La2O3-based (La2O3/HfO2, La2O3/CeO2 and single La2O3) MOS-HEMTs. It was found that forming lanthanum silicate films can not only improve the dielectric quality but also can improve the device characteristics. The improved gate insulation, reliability, and linearity of the 8 nm La2O3/SiO2 MOS-HEMT were demonstrated.

  15. Resonant dielectric metamaterials

    DOEpatents

    Loui, Hung; Carroll, James; Clem, Paul G; Sinclair, Michael B

    2014-12-02

    A resonant dielectric metamaterial comprises a first and a second set of dielectric scattering particles (e.g., spheres) having different permittivities arranged in a cubic array. The array can be an ordered or randomized array of particles. The resonant dielectric metamaterials are low-loss 3D isotropic materials with negative permittivity and permeability. Such isotropic double negative materials offer polarization and direction independent electromagnetic wave propagation.

  16. Structure and Electronic Properties of Polycrystalline Dielectrics

    SciTech Connect

    Mckenna, Keith P.; Shluger, AL

    2013-07-07

    We present an overview of the theoretical approaches that can be employed to model polycrystalline oxides along with a discussion of their limitations and associated challenges. We then present results for two metal oxide materials, MgO and HfO2, where theory and experiment have come together to provide insight into the structure and electronic properties of grain boundaries. Finally, we conclude with a discussion and outlook.

  17. Defects and metrology of ultrathin resist films

    NASA Astrophysics Data System (ADS)

    Okoroanyanwu, Uzodinma; Cobb, Jonathan L.; Dentinger, Paul M.; Henderson, Craig C.; Rao, Veena; Monahan, Kevin M.; Luo, David; Pike, Christopher

    2000-06-01

    Defectivity in spin-coated, but unpatterned ultrathin resist (UTR) films (ultrathin resists. Four resist samples formulated from the same Shipley UV6 polymer batch and having the same polymer molecular weight properties but different viscosities, were spin-coated at spin speeds ranging from 1000 to 5000 RPM on a production-grade track in a Class 1 pilot line facility. Defect inspection was carried out with KLA SP1/TBI tool, while defect review was carried out with JEOL 7515 SEM tool and KLA Ultrapointe Confocal Review Station (CRS) Microscope. The results obtained are related to the physical properties of the resist polymers, as well as to spin coating parameters. Also, the results of the defect inspection, review, characterization, and pareto are compared to those obtained on baseline thick resists (>= 3500 Angstrom) processed under similar condition as the ultra-thin resists. The results show that for a well-optimized coating process and within the thickness range explored (800 - 4200 Angstrom), there is no discernible dependence of defectivity on film thickness of the particular resists studied and on spin speed. Also assessed is the capability of the current metrology toolset for inspecting, reviewing, and classifying the various types of defects in UTR films.

  18. Photoresponsive properties of ultrathin silicon nanowires

    SciTech Connect

    Tran, Duy P.; Macdonald, Thomas J.; Nann, Thomas; Thierry, Benjamin E-mail: benjamin.thierry@unisa.edu.au; Wolfrum, Bernhard; Stockmann, Regina; Offenhäusser, Andreas E-mail: benjamin.thierry@unisa.edu.au

    2014-12-08

    Functional silicon nanowires (SiNWs) are promising building blocks in the design of highly sensitive photodetectors and bio-chemical sensors. We systematically investigate the photoresponse properties of ultrathin SiNWs (20 nm) fabricated using a size-reduction method based on e-beam lithography and tetramethylammonium hydroxide wet-etching. The high-quality SiNWs were able to detect light from the UV to the visible range with excellent sensitivity (∼1 pW/array), good time response, and high photoresponsivity (R ∼ 2.5 × 10{sup 4 }A/W). Improvement of the ultrathin SiNWs' photoresponse has been observed in comparison to 40 nm counter-part nanowires. These properties are attributable to the predominance surface-effect due to the high surface-to-volume ratio of ultrathin SiNWs. Long-term measurements at different temperatures in both the forward and reverse bias directions demonstrated the stability and reliability of the fabricated device. By sensitizing the fabricated SiNW arrays with cadmium telluride quantum dots (QDs), hybrid QD SiNW devices displayed an improvement in photocurrent response under UV light, while preserving their performance in the visible light range. The fast, stable, and high photoresponse of these hybrid nanostructures is promising towards the development of optoelectronic and photovoltaic devices.

  19. High-Magnetization FeCo Nanochains with Ultrathin Interfacial Gaps for Broadband Electromagnetic Wave Absorption at Gigahertz.

    PubMed

    Zhang, Xuefeng; Li, Yixing; Liu, Rongge; Rao, Yi; Rong, Huawei; Qin, Gaowu

    2016-02-10

    Superparamagnetic FeCo nanochains consisting of assembled ∼25 nm nanoparticles and ∼1 nm gaps are synthesized by facial wet-chemical route and exhibit significant electromagnetic absorption at gigahertz. Both the dielectric and magnetic loss factors present dual-resonance behaviors at 2-18 GHz frequencies, originated from the asymmetric architecture of the cubic FeCo particles that assembled in a one-dimensional chain structure. Theoretical analyses uncover that the origins of the enhancement of electromagnetic losses are ascribed to the high magnetization (228 emu/g) and the ultrathin gaps (∼1 nm), which enhances the Snoek limit and induces anisotropic dielectric polarizations, consequently constructing a proper electromagnetic match.

  20. High-Magnetization FeCo Nanochains with Ultrathin Interfacial Gaps for Broadband Electromagnetic Wave Absorption at Gigahertz.

    PubMed

    Zhang, Xuefeng; Li, Yixing; Liu, Rongge; Rao, Yi; Rong, Huawei; Qin, Gaowu

    2016-02-10

    Superparamagnetic FeCo nanochains consisting of assembled ∼25 nm nanoparticles and ∼1 nm gaps are synthesized by facial wet-chemical route and exhibit significant electromagnetic absorption at gigahertz. Both the dielectric and magnetic loss factors present dual-resonance behaviors at 2-18 GHz frequencies, originated from the asymmetric architecture of the cubic FeCo particles that assembled in a one-dimensional chain structure. Theoretical analyses uncover that the origins of the enhancement of electromagnetic losses are ascribed to the high magnetization (228 emu/g) and the ultrathin gaps (∼1 nm), which enhances the Snoek limit and induces anisotropic dielectric polarizations, consequently constructing a proper electromagnetic match. PMID:26775668

  1. Ultrathin niobium nanofilms on fiber optical tapers – a new route towards low-loss hybrid plasmonic modes

    PubMed Central

    Wieduwilt, Torsten; Tuniz, Alessandro; Linzen, Sven; Goerke, Sebastian; Dellith, Jan; Hübner, Uwe; Schmidt, Markus A.

    2015-01-01

    Due to the ongoing improvement in nanostructuring technology, ultrathin metallic nanofilms have recently gained substantial attention in plasmonics, e.g. as building blocks of metasurfaces. Typically, noble metals such as silver or gold are the materials of choice, due to their excellent optical properties, however they also possess some intrinsic disadvantages. Here, we introduce niobium nanofilms (~10 nm thickness) as an alternate plasmonic platform. We demonstrate functionality by depositing a niobium nanofilm on a plasmonic fiber taper, and observe a dielectric-loaded niobium surface-plasmon excitation for the first time, with a modal attenuation of only 3–4 dB/mm in aqueous environment and a refractive index sensitivity up to 15 μm/RIU if the analyte index exceeds 1.42. We show that the niobium nanofilm possesses bulk optical properties, is continuous, homogenous, and inert against any environmental influence, thus possessing several superior properties compared to noble metal nanofilms. These results demonstrate that ultrathin niobium nanofilms can serve as a new platform for biomedical diagnostics, superconducting photonics, ultrathin metasurfaces or new types of optoelectronic devices. PMID:26593209

  2. Ultrathin niobium nanofilms on fiber optical tapers--a new route towards low-loss hybrid plasmonic modes.

    PubMed

    Wieduwilt, Torsten; Tuniz, Alessandro; Linzen, Sven; Goerke, Sebastian; Dellith, Jan; Hübner, Uwe; Schmidt, Markus A

    2015-01-01

    Due to the ongoing improvement in nanostructuring technology, ultrathin metallic nanofilms have recently gained substantial attention in plasmonics, e.g. as building blocks of metasurfaces. Typically, noble metals such as silver or gold are the materials of choice, due to their excellent optical properties, however they also possess some intrinsic disadvantages. Here, we introduce niobium nanofilms (~10 nm thickness) as an alternate plasmonic platform. We demonstrate functionality by depositing a niobium nanofilm on a plasmonic fiber taper, and observe a dielectric-loaded niobium surface-plasmon excitation for the first time, with a modal attenuation of only 3-4 dB/mm in aqueous environment and a refractive index sensitivity up to 15 μm/RIU if the analyte index exceeds 1.42. We show that the niobium nanofilm possesses bulk optical properties, is continuous, homogenous, and inert against any environmental influence, thus possessing several superior properties compared to noble metal nanofilms. These results demonstrate that ultrathin niobium nanofilms can serve as a new platform for biomedical diagnostics, superconducting photonics, ultrathin metasurfaces or new types of optoelectronic devices. PMID:26593209

  3. Analysis of laser energy deposition leading to damage and ablation of HfO2 and Nb2O5 single layers submitted to 500 fs pulses at 1030 and 343 nm

    NASA Astrophysics Data System (ADS)

    Douti, Dam-Bé; Bégou, Thomas; Lemarchand, Fabien; Lumeau, Julien; Commandré, Mireille; Gallais, Laurent

    2016-07-01

    Laser- induced damage thresholds and morphologies of laser ablated sites on dielectric thin films are studied based on experiments and simulations. The films are single layers of hafnia and niobia deposited on fused silica substrates with a magnetron sputtering technique. Laser experiments are conducted with 500 fs pulses at 1030 and 343 nm, and the irradiated sites are characterized with optical profilometry and scanning electron microscopy. The results, i.e., LIDT and damage morphologies, are compared to simulations of energy deposition in the films based on the single rate equation for electron excitation, taking into account transient optical properties of the films during the pulse. The results suggest that a critical absorbed energy as a damage criterion gives consistent results both with the measured LIDT and the observed damage morphologies at fluences close to the damage threshold. Based on the numerical and experimental results, the determined LIDT evolution with the wavelength is described as nearly constant in the near-infrared region, and as rapidly decreasing with laser wavelength in the visible and near-ultraviolet regions.

  4. Ultrathin triple-band polarization-insensitive wide-angle compact metamaterial absorber

    NASA Astrophysics Data System (ADS)

    Shang, Shuai; Yang, Shizhong; Tao, Lu; Yang, Lisheng; Cao, Hailin

    2016-07-01

    In this study, the design, realization, and characterization of an ultrathin triple-band polarization-insensitive wide-angle metamaterial absorber are reported. The metamaterial absorber comprises a periodic array of modified six-fold symmetric snowflake-shaped resonators with strip spiral line load, which is printed on a dielectric substrate backed by a metal ground plane. It is shown that the absorber exhibits three distinct near-unity absorption peaks, which are distributed across C, X, Ku bands, respectively. Owing to the six-fold symmetry, the absorber is insensitive to the polarization of the incident radiation. In addition, the absorber shows excellent absorption performance over wide oblique incident angles for both transverse electric and transverse magnetic polarizations. Simulated surface current and field distributions at the three absorption peaks are demonstrated to understand the absorption mechanism. Particularly, the absorption modes come from the fundamental and high-order dipole resonances. Furthermore, the experimental verification of the designed absorber is conducted, and the measured results are in reasonable agreement with the simulated ones. The proposed ultrathin (˜0.018λ0, λ0 corresponding to the lowest peak absorption frequency) compact (0.168λ0×0.168λ0 corresponding to the area of a unit cell) absorber enables potential applications such as stealth technology, electromagnetic interference and spectrum identification.

  5. Broadband frequency-selective spoof surface plasmon polaritons on ultrathin metallic structure.

    PubMed

    Yin, Jia Yuan; Ren, Jian; Zhang, Hao Chi; Pan, Bai Cao; Cui, Tie Jun

    2015-01-01

    We propose an ultrathin metallic structure to produce frequency-selective spoof surface plasmon polaritons (SPPs) in the microwave and terahertz frequencies. Designed on a thin dielectric substrate, the ultrathin metallic structure is composed of two oppositely oriented single-side corrugated strips, which are coupled to two double-side corrugated strips. The structure is fed by a traditional coplanar waveguide (CPW). To make a smooth conversion between the spatial modes in CPW and SPP modes, two transition sections are also designed. We fabricate and measure the frequency-selective spoof SPP structure in microwave frequencies. The measurement results show that the reflection coefficient is less than -10 dB with the transmission loss around 1.5 dB in the selective frequency band from 7 to 10 GHz, which are in good agreements with numerical simulations. The proposed structure can be used as an SPP filter with good performance of low loss, high transmission, and wide bandwidth in the selective frequency band. PMID:25641730

  6. Broadband Frequency-Selective Spoof Surface Plasmon Polaritons on Ultrathin Metallic Structure

    NASA Astrophysics Data System (ADS)

    Yin, Jia Yuan; Ren, Jian; Zhang, Hao Chi; Pan, Bai Cao; Cui, Tie Jun

    2015-02-01

    We propose an ultrathin metallic structure to produce frequency-selective spoof surface plasmon polaritons (SPPs) in the microwave and terahertz frequencies. Designed on a thin dielectric substrate, the ultrathin metallic structure is composed of two oppositely oriented single-side corrugated strips, which are coupled to two double-side corrugated strips. The structure is fed by a traditional coplanar waveguide (CPW). To make a smooth conversion between the spatial modes in CPW and SPP modes, two transition sections are also designed. We fabricate and measure the frequency-selective spoof SPP structure in microwave frequencies. The measurement results show that the reflection coefficient is less than -10 dB with the transmission loss around 1.5 dB in the selective frequency band from 7 to 10 GHz, which are in good agreements with numerical simulations. The proposed structure can be used as an SPP filter with good performance of low loss, high transmission, and wide bandwidth in the selective frequency band.

  7. Confinement effects in ultrathin ZnO polymorph films: Electronic and optical properties

    NASA Astrophysics Data System (ADS)

    Sponza, Lorenzo; Goniakowski, Jacek; Noguera, Claudine

    2016-05-01

    Relying on generalized-gradient and hybrid first-principles simulations, this work provides a complete characterization of the electronic properties of ZnO ultrathin films, cut along the body-centered-tetragonal(010), cubane(100), hexagonal boron nitride(0001), zinc-blende(110), and wurtzite (10 1 ¯0 ) and (0001) orientations. The characteristics of the local densities of states are analyzed in terms of the reduction of the Madelung potential on undercoordinated atoms and surface states/resonances appearing at the top of the valence band and bottom of the conduction band. The gap width in the films is found to be larger than in the corresponding bulks, which is assigned to quantum confinement effects. The components of the high-frequency dielectric constant are determined and the absorption spectra of the films are computed. They display specific features just above the absorption threshold due to transitions from or to the surface resonances. This study provides a first understanding of finite-size effects on the electronic properties of ZnO thin films and a benchmark which is expected to foster experimental characterization of ultrathin films via spectroscopic techniques.

  8. Broadband Frequency-Selective Spoof Surface Plasmon Polaritons on Ultrathin Metallic Structure

    PubMed Central

    Yin, Jia Yuan; Ren, Jian; Zhang, Hao Chi; Pan, Bai Cao; Cui, Tie Jun

    2015-01-01

    We propose an ultrathin metallic structure to produce frequency-selective spoof surface plasmon polaritons (SPPs) in the microwave and terahertz frequencies. Designed on a thin dielectric substrate, the ultrathin metallic structure is composed of two oppositely oriented single-side corrugated strips, which are coupled to two double-side corrugated strips. The structure is fed by a traditional coplanar waveguide (CPW). To make a smooth conversion between the spatial modes in CPW and SPP modes, two transition sections are also designed. We fabricate and measure the frequency-selective spoof SPP structure in microwave frequencies. The measurement results show that the reflection coefficient is less than -10 dB with the transmission loss around 1.5 dB in the selective frequency band from 7 to 10 GHz, which are in good agreements with numerical simulations. The proposed structure can be used as an SPP filter with good performance of low loss, high transmission, and wide bandwidth in the selective frequency band. PMID:25641730

  9. Spoof localized surface plasmons on ultrathin textured MIM ring resonator with enhanced resonances

    PubMed Central

    Zhou, Yong Jin; Xiao, Qian Xun; Jia Yang, Bao

    2015-01-01

    We numerically demonstrate that spoof localized surface plasmons (LSPs) resonant modes can be enhanced based on ultrathin corrugated metal-insulator-metal (MIM) ring resonator. Further enhancement of the LSPs modes has been achieved by incorporating an efficient and ease-of-integration exciting method. Quality factors of resonance peaks have become much larger and multipolar resonances modes can be easily observed on the textured MIM ring resonator excited by a microstrip line. Experimental results validate the high-efficiency excitation and resonance enhancements of spoof LSPs modes on the MIM ring resonator in the microwave frequencies. We have shown that the fabricated resonator is sensitive to the variation of both the dielectric constant and the thickness of surrounding materials under test. The spoof plasmonic resonator can be used as key elements to provide many important device functionalities such as optical communications, signal processing, and spectral engineering in the plasmonic integration platform. PMID:26420668

  10. Terahertz Artificial Dielectric Lens

    NASA Astrophysics Data System (ADS)

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M.

    2016-03-01

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices.

  11. Dielectric properties of aerogels

    SciTech Connect

    Hrubesh, L.W.; Keene, L.E.; Latorre, V.R. )

    1993-07-01

    We have measured the real (dielectric constant) and imaginary (loss factor) components of the complex relative permittivity at 298 [degree]K using microwave frequencies (2, 10, and 18--40 GHz), for bulk SiO[sub 2]-aerogels and for two types of organic aerogels, resorcinol-formaldehyde (RF) and melamine-formaldehyde (MF). Measured dielectric constants are found to vary linearly between values of 1.0 and 2.0 for aerogel densities from 10 to 500 kg/m[sup 3]. For the same range of densities, the measured loss tangents vary linearly between values of 2[times]10[sup [minus]4] and 7[times]10[sup [minus]2]. The observed linearity of the dielectric properties with density in aerogels at microwave frequencies shows that their dielectric behavior is more gas-like than solid-like. The dielectric properties of aerogels are shown to be significantly affected by the adsorbed water internal to the bulk material. For example, water accounts for 7% of the dielectric constant and 70% of the loss at microwave frequencies for silica aerogels. Because of their very high porosity, even with the water content, the aerogels are among the few materials exhibiting such low dielectric properties. Our measurements show that aerogels with greater than 99% porosity have dielectric constants less than 1.03; these are the lowest values ever reported for a bulk solid material.

  12. Terahertz Artificial Dielectric Lens.

    PubMed

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M

    2016-01-01

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices. PMID:26973294

  13. Terahertz Artificial Dielectric Lens.

    PubMed

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M

    2016-03-14

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices.

  14. Terahertz Artificial Dielectric Lens

    PubMed Central

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M.

    2016-01-01

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices. PMID:26973294

  15. Non-contact C-V measurements of ultra thin dielectrics

    NASA Astrophysics Data System (ADS)

    Edelman, P.; Savtchouk, A.; Wilson, M.; D'Amico, J.; Kochey, J. N.; Marinskiy, D.; Lagowski, J.

    2004-07-01

    In this paper, we present a non-contact C-V technique for ultra-thin dielectrics on silicon. The technique uses incremental corona charging of dielectric and a measurement of the surface potential with a vibrating capacitive electrode. A differential quasistatic C-V curve is generated using time-resolved measurements. The technique incorporates transconductance corrections that enable corresponding ultra-low electrical oxide thickness (EOT) determination down to the sub-nanometer range. It also provides a means for monitoring the flat band voltage, V{FB}, the interface trap spectrum, D{IT}, and the total dielectric charge, Q{TOT}. This technique is seen as a replacement for not only MOS C-V measurements but also for mercury-probe C-V. In addition, EOT measurement by the corona C-V has a major advantage over optical thickness methods because it is not affected by water adsorption and molecular airborne contamination, MAC. These effects have been a problem for optical metrology of ultra-thin dielectrics.

  16. Nanoscale electric polarizability of ultrathin biolayers on insulating substrates by electrostatic force microscopy

    NASA Astrophysics Data System (ADS)

    Dols-Perez, A.; Gramse, G.; Calò, A.; Gomila, G.; Fumagalli, L.

    2015-10-01

    We measured and quantified the local electric polarization properties of ultrathin (~5 nm) biolayers on mm-thick mica substrates. We achieved it by scanning a sharp conductive tip (<10 nm radius) of an electrostatic force microscope over the biolayers and quantifying sub-picoNewton electric polarization forces with a sharp-tip model implemented using finite-element numerical calculations. We obtained relative dielectric constants εr = 3.3, 2.4 and 1.9 for bacteriorhodopsin, dioleoylphosphatidylcholine (DOPC) and cholesterol layers, chosen as representative of the main cell membrane components, with an error below 10% and a spatial resolution down to ~50 nm. The ability of using insulating substrates common in biophysics research, such as mica or glass, instead of metallic substrates, offers both a general platform to determine the dielectric properties of biolayers and a wider compatibility with other characterization techniques, such as optical microscopy. This opens up new possibilities for biolayer research at the nanoscale, including nanoscale label-free composition mapping.We measured and quantified the local electric polarization properties of ultrathin (~5 nm) biolayers on mm-thick mica substrates. We achieved it by scanning a sharp conductive tip (<10 nm radius) of an electrostatic force microscope over the biolayers and quantifying sub-picoNewton electric polarization forces with a sharp-tip model implemented using finite-element numerical calculations. We obtained relative dielectric constants εr = 3.3, 2.4 and 1.9 for bacteriorhodopsin, dioleoylphosphatidylcholine (DOPC) and cholesterol layers, chosen as representative of the main cell membrane components, with an error below 10% and a spatial resolution down to ~50 nm. The ability of using insulating substrates common in biophysics research, such as mica or glass, instead of metallic substrates, offers both a general platform to determine the dielectric properties of biolayers and a wider

  17. Effect of film properties for non-linear DPL model in a nanoscale MOSFET with high-k material: ZrO2/HfO2/La2O3

    NASA Astrophysics Data System (ADS)

    Shomali, Zahra; Ghazanfarian, Jafar; Abbassi, Abbas

    2015-07-01

    Numerical simulation of non-linear non-Fourier heat conduction within a nano-scale metal-oxide-semiconductor field-effect transistor (MOSFET) is presented under the framework of Dual-Phase-Lag model including the boundary phonon scattering. The MOSFET is modeled in four cases of: (I) thin silicon slab, (II) including uniform heat generation, (III) double-layered buried oxide MOSFET with uniform heat generation in silicon-dioxide layer, and (IV) high-k/metal gate transistor. First, four cases are studied under four conditions of (a) constant bulk and (b) constant film thermal properties, (c) temperature-dependent properties of bulk silicon, and (d) temperature-dependent thermal properties of film silicon. The heat source and boundary conditions are similar to what existed in a real MOSFET. It is concluded that in all cases, considering the film properties lowers the temperature jump due to the reduction of the Knudsen number. Furthermore, the speed of heat flux penetration for film properties is less than that of the cases concerning bulk properties. Also, considering the temperature-dependent properties drastically changes the temperature and heat flux distributions within the transistor, which increases the diffusion speed and more, decreases the steady state time. Calculations for case (III) presents that all previous studies have underestimated the value of the peak temperature rise by considering the constant bulk properties of silicon. Also, it is found that among the high-k dielectrics investigated in case (IV), zirconium dioxide shows the least peak temperature rise. This presents that zirconium dioxide is a good candidate as far as the thermal issues are concerned.

  18. Multi-technique Approach for the Evaluation of the Crystalline Phase of Ultrathin High-k Gate Oxide Films

    NASA Astrophysics Data System (ADS)

    Bersch, E.; LaRose, J. D.; Wells, I.; Consiglio, S.; Clark, R. D.; Leusink, G. J.; Matyi, R. J.; Diebold, A. C.

    2011-11-01

    In order to continue scaling metal oxide semiconductor field effect transistors (MOSFETs) with HfO2 gate oxides, efforts are being made to further improve the deposited high-k film properties. Recently, a process whereby an HfO2 film is deposited through a series of depositions and anneals (so-called DADA process) has been shown to result in films that give rise to MOS capacitors (MOSCAPs) which are electrically scaled compared to MOSCAPs with HfO2 films that only received post deposition anneals (PDA) or no anneals. We have measured as-deposited, DADA and PDA HfO2 films using four measurement techniques, all of which are non-destructive and capable of being used for in-line processing, to evaluate their crystallinity and crystalline phases. Grazing incidence in-plane X-ray diffraction was used to determine the crystalline phases of the HfO2 films. We observed the crystalline phases of these films to be process dependent. Additionally, X-ray and UV photoelectron spectroscopy were used to show the presence of crystallinity in the films. As a fourth technique, spectroscopic ellipsometry was used to determine if the crystalline phases were monoclinic. The combination of techniques was useful in that XPS and UPS were able to confirm the amorphous nature of a 30 cycle DADA film, as measured by GIIXRD, and GIIXRD was able to help us interpret the SE data as being an indication of the monoclinic phase of HfO2.

  19. Design and Fabrication of Ultrathin Plasmonic Nanostructures for Photovoltaics, Color Filtering and Biosensing

    NASA Astrophysics Data System (ADS)

    Zeng, Beibei

    Since the first report of the extraordinary optical transmission (EOT) phenomenon through periodic subwavelength hole arrays milled in optically-thick metal film, plasmonics have generated considerable interest because they enable new fundamental science and application technologies. Central to this phenomenon is the role of surface plasmon polaritons (SPPs), which are essentially electromagnetic waves trapped at the interface between a metal and a dielectric medium through their interactions with free electrons at the metal surface. The resonant interaction between the incident light and surface charge oscillations enables the concentration and manipulation of light at deep subwavelength scales, opening up exciting application opportunities ranging from subwavelength optics and optoelectronics to bio/chemical sensing. Furthermore, additional phenomena arise as the thickness of metal film decreases to be comparable to its skin depth (optically-thin), and the single-interface SPPs on the top and bottom metal surfaces combine to form two coupled SPPs, the long-range and short-range SPPs. Until now, much less work has focused on the study of surface plasmon resonances (SPRs) in ultrathin nanostructured metals. This dissertation seeks to elucidate underlying physical mechanisms of SPRs in ultrathin nanostructured metals and tailor them for practical applications. Inspired by state-of-the-art advances on plasmonics in optically-thick nanostructured metals, one- (1D) and two-dimensional (2D) ultrathin plasmonic nanostructures are exploited for particular applications in three essential areas: photovoltaics, color filters and biosensors, achieving superior performances compared with their optically-thick counterparts. More specifically, this thesis is focused on systematic investigations on: (1) plasmonic transparent electrodes for organic photovoltaics and polarization-insensitive optical absorption enhancement in the active layer; (2) plasmonic subtractive color filters

  20. Ultrathin, epitaxial cerium dioxide on silicon

    NASA Astrophysics Data System (ADS)

    Flege, Jan Ingo; Kaemena, Björn; Höcker, Jan; Bertram, Florian; Wollschläger, Joachim; Schmidt, Thomas; Falta, Jens

    2014-03-01

    It is shown that ultrathin, highly ordered, continuous films of cerium dioxide may be prepared on silicon following substrate prepassivation using an atomic layer of chlorine. The as-deposited, few-nanometer-thin Ce2O3 film may very effectively be converted at room temperature to almost fully oxidized CeO2 by simple exposure to air, as demonstrated by hard X-ray photoemission spectroscopy and X-ray diffraction. This post-oxidation process essentially results in a negligible loss in film crystallinity and interface abruptness.

  1. Arrays of ultrathin silicon solar microcells

    SciTech Connect

    Rogers, John A.; Rockett, Angus A.; Nuzzo, Ralph; Yoon, Jongseung; Baca, Alfred

    2015-08-11

    Provided are solar cells, photovoltaics and related methods for making solar cells, wherein the solar cell is made of ultrathin solar grade or low quality silicon. In an aspect, the invention is a method of making a solar cell by providing a solar cell substrate having a receiving surface and assembling a printable semiconductor element on the receiving surface of the substrate via contact printing. The semiconductor element has a thickness that is less than or equal to 100 .mu.m and, for example, is made from low grade Si.

  2. Ultrathin, epitaxial cerium dioxide on silicon

    SciTech Connect

    Flege, Jan Ingo Kaemena, Björn; Höcker, Jan; Schmidt, Thomas; Falta, Jens; Bertram, Florian; Wollschläger, Joachim

    2014-03-31

    It is shown that ultrathin, highly ordered, continuous films of cerium dioxide may be prepared on silicon following substrate prepassivation using an atomic layer of chlorine. The as-deposited, few-nanometer-thin Ce{sub 2}O{sub 3} film may very effectively be converted at room temperature to almost fully oxidized CeO{sub 2} by simple exposure to air, as demonstrated by hard X-ray photoemission spectroscopy and X-ray diffraction. This post-oxidation process essentially results in a negligible loss in film crystallinity and interface abruptness.

  3. Elementary spin excitations in ultrathin itinerant magnets

    NASA Astrophysics Data System (ADS)

    Zakeri, Khalil

    2014-12-01

    Elementary spin excitations (magnons) play a fundamental role in condensed matter physics, since many phenomena e.g. magnetic ordering, electrical (as well as heat) transport properties, ultrafast magnetization processes, and most importantly electron/spin dynamics can only be understood when these quasi-particles are taken into consideration. In addition to their fundamental importance, magnons may also be used for information processing in modern spintronics. Here the concept of spin excitations in ultrathin itinerant magnets is discussed and reviewed. Starting with a historical introduction, different classes of magnons are introduced. Different theoretical treatments of spin excitations in solids are outlined. Interaction of spin-polarized electrons with a magnetic surface is discussed. It is shown that, based on the quantum mechanical conservation rules, a magnon can only be excited when a minority electron is injected into the system. While the magnon creation process is forbidden by majority electrons, the magnon annihilation process is allowed instead. These fundamental quantum mechanical selection rules, together with the strong interaction of electrons with matter, make the spin-polarized electron spectroscopies as appropriate tools to excite and probe the elementary spin excitations in low-dimensional magnets e.g ultrathin films and nanostructures. The focus is put on the experimental results obtained by spin-polarized electron energy loss spectroscopy and spin-polarized inelastic tunneling spectroscopy. The magnon dispersion relation, lifetime, group and phase velocity measured using these approaches in various ultrathin magnets are discussed in detail. The differences and similarities with respect to the bulk excitations are addressed. The role of the temperature, atomic structure, number of atomic layers, lattice strain, electronic complexes and hybridization at the interfaces are outlined. A possibility of simultaneous probing of magnons and phonons

  4. Arrays of ultrathin silicon solar microcells

    DOEpatents

    Rogers, John A; Rockett, Angus A; Nuzzo, Ralph; Yoon, Jongseung; Baca, Alfred

    2014-03-25

    Provided are solar cells, photovoltaics and related methods for making solar cells, wherein the solar cell is made of ultrathin solar grade or low quality silicon. In an aspect, the invention is a method of making a solar cell by providing a solar cell substrate having a receiving surface and assembling a printable semiconductor element on the receiving surface of the substrate via contact printing. The semiconductor element has a thickness that is less than or equal to 100 .mu.m and, for example, is made from low grade Si.

  5. Cast dielectric composite linear accelerator

    DOEpatents

    Sanders, David M.; Sampayan, Stephen; Slenes, Kirk; Stoller, H. M.

    2009-11-10

    A linear accelerator having cast dielectric composite layers integrally formed with conductor electrodes in a solventless fabrication process, with the cast dielectric composite preferably having a nanoparticle filler in an organic polymer such as a thermosetting resin. By incorporating this cast dielectric composite the dielectric constant of critical insulating layers of the transmission lines of the accelerator are increased while simultaneously maintaining high dielectric strengths for the accelerator.

  6. Alternate film dielectric materials

    SciTech Connect

    Foster, J.C. . Neutron Devices Dept.); Harris, J.O.; Martinez, J.I. )

    1990-01-01

    This paper presents data on polymeric dielectric films evaluated to support the design of high-energy-density capacitors. Evaluated materials include polycarbonate (two sources), polyphenylene sulfide, polyvinylidene fluoride, polyethermide (three sources), polyimide (four sources), polyethersulfone, and polyetherether ketone. A polyester was evaluated as the control material since many of our prior designs utilized this dielectric. The film evaluations were based on dielectric constant and dissipation factor variation as a function of temperature from {minus}55{degree}C to 300{degree}C, as well as dielectric breakdown strength. Additionally, film/foil capacitors in a dry, wrap-and-fill configuration were fabricated and tested to determine insulation resistance, breakdown voltage, and radiation hardness. Results will be presented for all the evaluations based on the several criteria. 7 refs., 4 figs., 4 tabs.

  7. Ultrathin inorganic molecular nanowire based on polyoxometalates

    PubMed Central

    Zhang, Zhenxin; Murayama, Toru; Sadakane, Masahiro; Ariga, Hiroko; Yasuda, Nobuhiro; Sakaguchi, Norihito; Asakura, Kiyotaka; Ueda, Wataru

    2015-01-01

    The development of metal oxide-based molecular wires is important for fundamental research and potential practical applications. However, examples of these materials are rare. Here we report an all-inorganic transition metal oxide molecular wire prepared by disassembly of larger crystals. The wires are comprised of molybdenum(VI) with either tellurium(IV) or selenium(IV): {(NH4)2[XMo6O21]}n (X=tellurium(IV) or selenium(IV)). The ultrathin molecular nanowires with widths of 1.2 nm grow to micrometre-scale crystals and are characterized by single-crystal X-ray analysis, Rietveld analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, thermal analysis and elemental analysis. The crystals can be disassembled into individual molecular wires through cation exchange and subsequent ultrasound treatment, as visualized by atomic force microscopy and transmission electron microscopy. The ultrathin molecular wire-based material exhibits high activity as an acid catalyst, and the band gap of the molecular wire-based crystal is tunable by heat treatment. PMID:26139011

  8. Flexible, Ultra-Thin, Embedded Die Packaging

    NASA Astrophysics Data System (ADS)

    McPherson, Ryan J.

    As thin, flexible electronics solutions become more robust, their integration into everyday life becomes more likely. With possible applications in wearable electronics, biomedical sensors, or 'peel and stick' sensors, the reliability of these ultra-thin packages becomes paramount. Likewise, the density achievable with stacked packages benefits greatly from thinner die stacks. To this end, techniques previously developed have demonstrated packages with die thinned to approximately 20mum. Covered in this work are methods for thinning and packaging silicon die, as well as information on common materials used in these processes. The author's contribution is a fabrication process for embedding ultra-thin (approximately 10mum) silicon die in polyimide substrates. This method is fully illustrated in Chapter 3 and enumerated in the Appendix as a quick reference. Additionally, thermal cycle testing of passive daisy chain assemblies has shown promising reliability data. Packages were mounted in three alignments: flat, concave, and convex, and placed into thermal shock testing. Finally, the author discusses possible applications for this fabrication process, including the fabrication of multi-chip-modules.

  9. Dielectric cavity relativistic magnetron

    NASA Astrophysics Data System (ADS)

    Hashemi, S. M. A.

    2010-02-01

    An alteration in the structure of the A6 relativistic magnetron is proposed, which introduces an extra degree of freedom to its design and enhances many of its quality factors. This modification involves the partial filling of the cavities of the device with a low-loss dielectric material. The operation of a dielectric-filled A6 is simulated; the results indicate single-mode operation at the desired π mode and a substantially cleaner rf spectrum.

  10. Dielectric spectroscopy in agrophysics

    NASA Astrophysics Data System (ADS)

    Skierucha, W.; Wilczek, A.; Szypłowska, A.

    2012-04-01

    The paper presents scientific foundation and some examples of agrophysical applications of dielectric spectroscopy techniques. The aim of agrophysics is to apply physical methods and techniques for studies of materials and processes which occur in agriculture. Dielectric spectroscopy, which describes the dielectric properties of a sample as a function of frequency, may be successfully used for examinations of properties of various materials. Possible test materials may include agrophysical objects such as soil, fruit, vegetables, intermediate and final products of the food industry, grain, oils, etc. Dielectric spectroscopy techniques enable non-destructive and non-invasive measurements of the agricultural materials, therefore providing tools for rapid evaluation of their water content and quality. There is a limited number of research in the field of dielectric spectroscopy of agricultural objects, which is caused by the relatively high cost of the respective measurement equipment. With the fast development of modern technology, especially in high frequency applications, dielectric spectroscopy has great potential of expansion in agrophysics, both in cognitive and utilitarian aspects.

  11. Aperture excited dielectric antennas

    NASA Technical Reports Server (NTRS)

    Crosswell, W. F.; Chatterjee, J. S.; Mason, V. B.; Tai, C. T.

    1974-01-01

    The results of a comprehensive experimental and theoretical study of the effect of placing dielectric objects over the aperture of waveguide antennas are presented. Experimental measurements of the radiation patterns, gain, impedance, near-field amplitude, and pattern and impedance coupling between pairs of antennas are given for various Plexiglas shapes, including the sphere and the cube, excited by rectangular, circular, and square waveguide feed apertures. The waveguide excitation of a dielectric sphere is modeled using the Huygens' source, and expressions for the resulting electric fields, directivity, and efficiency are derived. Calculations using this model show good overall agreement with experimental patterns and directivity measurements. The waveguide under an infinite dielectric slab is used as an impedance model. Calculations using this model agree qualitatively with the measured impedance data. It is concluded that dielectric loaded antennas such as the waveguide excited sphere, cube, or sphere-cylinder can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of 2 wavelengths or less. It is also shown that for certain configurations coupling between two antennas of this type is less than that for the same antennas without dielectric loading.

  12. High-k Dielectric Nanosheets for Two-Dimensional material Electronics

    NASA Astrophysics Data System (ADS)

    Hao, Yufeng; Cui, Xu; Yin, Jun; Lee, Gwan-Hyoung; Arefe, Ghidewon; Osada, Minoru; Sasaki, Takayoshi; Hone, James

    2015-03-01

    Two-dimensional (2D) materials, such as graphene, hexagonal boron nitride (hBN), transition metal dichalcogenides, have shown great potential in nano-electronics because of their unique and superior physical properties. Among them, hBN has been known as an alternative dielectric that is atomically flat and free of trapped charges, which drastically enhance the mobility of graphene or MoS2. However, low dielectric constant (k ~ 3.5) of hBN limits its use in transistors as gate lengths are scaled down to tens of nanometers. Here we demonstrate high performance graphene and MoS2 field effect transistors by using ultrathin Ca2NaNb4O13 nanosheet as a dielectric and mechanically stacking 2D materials. We developed a facile transfer strategy to build 2D materials devices based on the Ca2NaNb4O13 nanosheets. We measured and found that the oxide nanosheet has high dielectric strength, along with high dielectric constant at thickness of a few tens of nanometer. Therefore, multiple-stacked heterostructure of 2D materials shows high mobility at small operating voltage. This study shows possibility of high-k dielectric nanosheets for 2D electronics.

  13. Solution-Processed Dielectrics Based on Thickness-Sorted Two-Dimensional Hexagonal Boron Nitride Nanosheets.

    PubMed

    Zhu, Jian; Kang, Joohoon; Kang, Junmo; Jariwala, Deep; Wood, Joshua D; Seo, Jung-Woo T; Chen, Kan-Sheng; Marks, Tobin J; Hersam, Mark C

    2015-10-14

    Gate dielectrics directly affect the mobility, hysteresis, power consumption, and other critical device metrics in high-performance nanoelectronics. With atomically flat and dangling bond-free surfaces, hexagonal boron nitride (h-BN) has emerged as an ideal dielectric for graphene and related two-dimensional semiconductors. While high-quality, atomically thin h-BN has been realized via micromechanical cleavage and chemical vapor deposition, existing liquid exfoliation methods lack sufficient control over h-BN thickness and large-area film quality, thus limiting its use in solution-processed electronics. Here, we employ isopycnic density gradient ultracentrifugation for the preparation of monodisperse, thickness-sorted h-BN inks, which are subsequently layer-by-layer assembled into ultrathin dielectrics with low leakage currents of 3 × 10(-9) A/cm(2) at 2 MV/cm and high capacitances of 245 nF/cm(2). The resulting solution-processed h-BN dielectric films enable the fabrication of graphene field-effect transistors with negligible hysteresis and high mobilities up to 7100 cm(2) V(-1) s(-1) at room temperature. These h-BN inks can also be used as coatings on conventional dielectrics to minimize the effects of underlying traps, resulting in improvements in overall device performance. Overall, this approach for producing and assembling h-BN dielectric inks holds significant promise for translating the superlative performance of two-dimensional heterostructure devices to large-area, solution-processed nanoelectronics. PMID:26348822

  14. Broadband terahertz absorption enabled by coating an ultrathin antireflection film on doped semiconductor.

    PubMed

    Wu, Hongxing; Shi, Fenghua; Chen, Yihang

    2016-09-01

    We show that perfect absorption of terahertz wave can be achieved in a compact system where an ultrathin film of lossless dielectric is coated on a doped semiconductor substrate. Due to the nontrivial reflection phase shift at the interface between the two media, strong resonant behavior and the concomitant antireflection occur at wavelengths that are much larger than the thickness of the dielectric film, resulting in strong absorption of the incident wave in a wide frequency range. Using this mechanism, we design a broadband terahertz absorber by coating a Ge film on a highly doped GaAs substrate. We show that such a system not only has a perfect absorption peak, but also exhibits high absorptance (over 0.9) within a fractional bandwidth of over 20%. By varying the free carrier density in the GaAs substrate, the central frequency of the absorption band can be tuned from 1.79 to 2.69 THz. In addition, the absorption performance of the proposed system is shown to be insensitive to both incident angle and polarization. Our results offer a low-cost way for the design of absorption-based THz devices. PMID:27607670

  15. Reversible optical switching of highly confined phonon-polaritons with an ultrathin phase-change material

    NASA Astrophysics Data System (ADS)

    Li, Peining; Yang, Xiaosheng; Maß, Tobias W. W.; Hanss, Julian; Lewin, Martin; Michel, Ann-Katrin U.; Wuttig, Matthias; Taubner, Thomas

    2016-08-01

    Surface phonon-polaritons (SPhPs), collective excitations of photons coupled with phonons in polar crystals, enable strong light-matter interaction and numerous infrared nanophotonic applications. However, as the lattice vibrations are determined by the crystal structure, the dynamical control of SPhPs remains challenging. Here, we realize the all-optical, non-volatile, and reversible switching of SPhPs by controlling the structural phase of a phase-change material (PCM) employed as a switchable dielectric environment. We experimentally demonstrate optical switching of an ultrathin PCM film (down to 7 nm, <λ/1,200) with single laser pulses and detect ultra-confined SPhPs (polariton wavevector kp > 70k0, k0 = 2π/λ) in quartz. Our proof of concept allows the preparation of all-dielectric, rewritable SPhP resonators without the need for complex fabrication methods. With optimized materials and parallelized optical addressing we foresee application potential for switchable infrared nanophotonic elements, for example, imaging elements such as superlenses and hyperlenses, as well as reconfigurable metasurfaces and sensors.

  16. Ultrathin phase-change coatings on metals for electrothermally tunable colors

    NASA Astrophysics Data System (ADS)

    Bakan, Gokhan; Ayas, Sencer; Saidzoda, Tohir; Celebi, Kemal; Dana, Aykutlu

    2016-08-01

    Metal surfaces coated with ultrathin lossy dielectrics enable color generation through strong interferences in the visible spectrum. Using a phase-change thin film as the coating layer offers tuning the generated color by crystallization or re-amorphization. Here, we study the optical response of surfaces consisting of thin (5-40 nm) phase-changing Ge2Sb2Te5 (GST) films on metal, primarily Al, layers. A color scale ranging from yellow to red to blue that is obtained using different thicknesses of as-deposited amorphous GST layers turns dim gray upon annealing-induced crystallization of the GST. Moreover, when a relatively thick (>100 nm) and lossless dielectric film is introduced between the GST and Al layers, optical cavity modes are observed, offering a rich color gamut at the expense of the angle independent optical response. Finally, a color pixel structure is proposed for ultrahigh resolution (pixel size: 5 × 5 μm2), non-volatile displays, where the metal layer acting like a mirror is used as a heater element. The electrothermal simulations of such a pixel structure suggest that crystallization and re-amorphization of the GST layer using electrical pulses are possible for electrothermal color tuning.

  17. Nanoscale electric polarizability of ultrathin biolayers on insulating substrates by electrostatic force microscopy.

    PubMed

    Dols-Perez, A; Gramse, G; Calò, A; Gomila, G; Fumagalli, L

    2015-11-21

    We measured and quantified the local electric polarization properties of ultrathin (∼5 nm) biolayers on mm-thick mica substrates. We achieved it by scanning a sharp conductive tip (<10 nm radius) of an electrostatic force microscope over the biolayers and quantifying sub-picoNewton electric polarization forces with a sharp-tip model implemented using finite-element numerical calculations. We obtained relative dielectric constants εr = 3.3, 2.4 and 1.9 for bacteriorhodopsin, dioleoylphosphatidylcholine (DOPC) and cholesterol layers, chosen as representative of the main cell membrane components, with an error below 10% and a spatial resolution down to ∼50 nm. The ability of using insulating substrates common in biophysics research, such as mica or glass, instead of metallic substrates, offers both a general platform to determine the dielectric properties of biolayers and a wider compatibility with other characterization techniques, such as optical microscopy. This opens up new possibilities for biolayer research at the nanoscale, including nanoscale label-free composition mapping.

  18. Ultrathin optical panel and a method of making an ultrathin optical panel

    DOEpatents

    Biscardi, Cyrus; Brewster, Calvin; DeSanto, Leonard; Veligdan, James T.

    2001-10-09

    An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated with a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

  19. Ultrathin Optical Panel And A Method Of Making An Ultrathin Optical Panel.

    DOEpatents

    Biscardi, Cyrus; Brewster, Calvin; DeSanto, Leonard; Veligdan, James T.

    2005-02-15

    An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated with a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

  20. Ultrathin optical panel and a method of making an ultrathin optical panel

    DOEpatents

    Biscardi, Cyrus; Brewster, Calvin; DeSanto, Leonard; Veligdan, James T.

    2002-01-01

    An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated With a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

  1. Ultrathin optical panel and a method of making an ultrathin optical panel

    DOEpatents

    Biscardi, Cyrus; Brewster, Calvin; DeSanto, Leonard; Veligdan, James T.

    2003-02-11

    An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated with a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

  2. Ultrathin Optical Panel And A Method Of Making An Ultrathin Optical Panel.

    DOEpatents

    Biscardi, Cyrus; Brewster, Calvin; DeSanto, Leonard; Veligdan, James T.

    2005-05-17

    An ultrathin optical panel, and a method of producing an ultrathin optical panel, are disclosed, including stacking a plurality of glass sheets, which sheets may be coated with a transparent cladding substance or may be uncoated, fastening together the plurality of stacked coated glass sheets using an epoxy or ultraviolet adhesive, applying uniform pressure to the stack, curing the stack, sawing the stack to form an inlet face on a side of the stack and an outlet face on an opposed side of the stack, bonding a coupler to the inlet face of the stack, and fastening the stack, having the coupler bonded thereto, within a rectangular housing having an open front which is aligned with the outlet face, the rectangular housing having therein a light generator which is optically aligned with the coupler. The light generator is preferably placed parallel to and proximate with the inlet face, thereby allowing for a reduction in the depth of the housing.

  3. Electrical stability of metal/low dielectric constant material systems

    NASA Astrophysics Data System (ADS)

    Mallikarjunan, Anupama

    In order to boost the performance of future generation silicon integrated circuits, new materials with lower dielectric constant (kappa) are under evaluation to replace traditional SiO2 as on-chip inter-layer dielectrics (ILDs). The goal of this thesis has been to investigate the intrinsic electrical stability and metal penetration resistance of a variety of low kappa materials: fluorinated silica glass (FSG), polyparaxylylene-N (parylene-N), polyarylether (PAE) and hybrid organosiloxane polymer (HOSP). Emphasis was placed on fundamental understanding of the factors controlling the electrical properties of different metal/low kappa dielectric systems. Traditionally, metal ion penetration is studied using Bias Temperature Stressing (BTS) with Capacitance-Voltage (C-V) measurement. In this work, an alternative technique, Triangular Voltage Sweep (TVS), was also adopted to provide insight into metal penetration behavior. Surprisingly, aluminum ion penetration into oxygen containing polymers such as PAE and HOSP was detected, and was in contrast to the stability of the Al/SiO2 system. Platinum was demonstrated as a viable control for metal drift studies in such polymers, as no platinum ion penetration was detected. Among the blanket dielectrics, the number of copper ions detected was lowest in HOSP, demonstrating its promise for ILD applications. Experimentation with a variety of metals led to the result that ion penetration behavior in HOSP showed the trend Pt < Cu < Ta < Al. This trend indicated that metal penetration increases with metal ionization and oxidation tendency. Plasma modification of HOSP by converting its surface to a thin intrinsic dielectric barrier resembling SiO2 dramatically reduced aluminum ion penetration in HOSP. Surface modification is therefore a powerful strategy to realize the future requirement of ultra-thin barriers. The impact of on-chip integration on electrical stability was also studied. Copper ions were detected along fast diffusion

  4. Medium energy ion scattering for the high depth resolution characterisation of high-k dielectric layers of nanometer thickness

    NASA Astrophysics Data System (ADS)

    van den Berg, J. A.; Reading, M. A.; Bailey, P.; Noakes, T. Q. C.; Adelmann, C.; Popovici, M.; Tielens, H.; Conard, T.; de Gendt, S.; van Elshocht, S.

    2013-09-01

    Medium energy ion scattering (MEIS) using, typically, 100-200 keV H+ or He+ ions derives it ability to characterise nanolayers from the fact that the energy after backscattering depends (i) on the elastic energy loss suffered in a single collision with a target atom and (ii) on the inelastic energy losses on its incoming and outgoing trajectories. From the former the mass of the atom can be determined and from the latter its depth. Thus MEIS yields depth dependent compositional and structural information, with high depth resolution (sub-nm near the surface) and good sensitivity for all but the lighter masses. It is particularly well suited for the depth analysis of high-k multilayers of nanometer thickness. Accurate quantification of the depth distributions of atomic species can be obtained using suitable spectrum simulation. In the present paper, important aspects of MEIS including quantification, depth resolution and spectrum simulation are briefly discussed. The capabilities of the technique in terms of the high depth resolution layer compositional and structural information it yields, is illustrated with reference to the detailed characterisation of a range of high-k nanolayer and multilayer structures for current microelectronic devices or those still under development: (i) HfO2 and HfSiOx for gate dielectric applications, including a TiN/Al2O3/HfO2/SiO2/Si structure, (ii) TiN/SrTiO3/TiN and (iii) TiO2/Ru/TiN multilayer structures for metal-insulator-metal capacitors (MIMcaps) in DRAM applications. The unique information provided by the technique is highlighted by its clear capability to accurately quantify the composition profiles and thickness of nanolayers and complex multilayers as grown, and to identify the nature and extent of atom redistribution (e.g. intermixing, segregation) during layer deposition, annealing and plasma processing. The ability makes it a valuable tool in the development of the nanostructures that will become increasingly important as

  5. Self-Organized Ultrathin Oxide Nanocrystals

    SciTech Connect

    Huo, Ziyang; Tsung, Chia-kuang; Huang, Wenyu; Fardy, Melissa; Yan, Ruoxue; Li, Yadong; Yang, Piedong; Zhang, Xiaofeng

    2009-01-08

    Sub-2-nm (down to one-unit cell) uniform oxide nanocrystals and highly ordered superstructures were obtained in one step using oleylamine and oleic acid as capping and structure directing agents. The cooperative nature of the nanocrystal growth and assembly resulted in mesoscopic one-dimensional ribbon-like superstructures made of these ultrathin nanocrystals. The process reported here is general and can be readily extended to the production of many other transition metal (TiO2, ZnO, Nb2O5) and rare earth oxide (Eu2O3, Sm2O3, Er2O3, Y2O3, Tb2O3, and Yb2O3) systems.

  6. Electric field effect in ultrathin black phosphorus

    SciTech Connect

    Koenig, Steven P.; Schmidt, Hennrik; Doganov, Rostislav A.; Castro Neto, A. H.; Özyilmaz, Barbaros

    2014-03-10

    Black phosphorus exhibits a layered structure similar to graphene, allowing mechanical exfoliation of ultrathin single crystals. Here, we demonstrate few-layer black phosphorus field effect devices on Si/SiO{sub 2} and measure charge carrier mobility in a four-probe configuration as well as drain current modulation in a two-point configuration. We find room-temperature mobilities of up to 300 cm{sup 2}/Vs and drain current modulation of over 10{sup 3}. At low temperatures, the on-off ratio exceeds 10{sup 5}, and the device exhibits both electron and hole conduction. Using atomic force microscopy, we observe significant surface roughening of thin black phosphorus crystals over the course of 1 h after exfoliation.

  7. Ultra-thin microporous/hybrid materials

    DOEpatents

    Jiang, Ying-Bing; Cecchi, Joseph L.; Brinker, C. Jeffrey

    2012-05-29

    Ultra-thin hybrid and/or microporous materials and methods for their fabrication are provided. In one embodiment, the exemplary hybrid membranes can be formed including successive surface activation and reaction steps on a porous support that is patterned or non-patterned. The surface activation can be performed using remote plasma exposure to locally activate the exterior surfaces of porous support. Organic/inorganic hybrid precursors such as organometallic silane precursors can be condensed on the locally activated exterior surfaces, whereby ALD reactions can then take place between the condensed hybrid precursors and a reactant. Various embodiments can also include an intermittent replacement of ALD precursors during the membrane formation so as to enhance the hybrid molecular network of the membranes.

  8. Fracture and fatigue of ultrathin nanoporous polymer films

    NASA Astrophysics Data System (ADS)

    Kearney, Andrew V.

    Nanoporous polymer layers are being considered for a range of emerging nanoscale applications, from low permittivity materials for interlayer dielectrics in microelectronics and anti-reflective coatings in optical technologies, to biosensors and size-selective membranes for biological applications. Polymer thin films have inherently low elastic modulus, strength and hardness, but exhibit fracture properties that are higher than those reported for glass, ceramic, and even some metal layers. However, constraint of a ductile polymer between two elastic layers is expected to affect the local plasticity ahead of a crack tip and its contribution to the film adhesion with films below a micron in thickness. Additionally, nanoporosity would be expected to have a deleterious effect on mechanical properties, producing materials and layers that are structurally weaker than fully dense versions they replace. Therefore, the integration of these nanoporous polymer layer at nanometer thicknesses would present significantly processing and mechanical reliability challenges. In this dissertation, surprising evidence is presented that nanoporous polymer films exhibit increasing fracture energy with increasing porosity. Such behavior is in stark contrast to a wide range of reported behavior for porous solids. A ductile nano-void growth and coalescence fracture mechanics-based model is presented to rationalize the increase in fracture toughness of the voided polymer film. The model is shown to explain the behavior in terms of a specific scaling of the size of the pores with pore volume fraction. It is demonstrated that the pore size must increase with close to a linear dependence on the volume fraction in order to increase rather than decrease the fracture energy. Independent characterization of the pore size as a function of volume fraction is shown to confirm predictions made by the model. The fracture behavior of these constrained polymer films are also examined with film thickness

  9. Improved Performance of Dye-Sensitized Solar Cells Fabricated from a Coumarin NKX-2700 Dye-Sensitized TiO2/MgO Core-Shell Photoanode with an HfO2 Blocking Layer and a Quasi-Solid-State Electrolyte

    NASA Astrophysics Data System (ADS)

    Maheswari, D.; Venkatachalam, P.

    2015-03-01

    Dye sensitized solar cells (DSSC) were fabricated from a coumarin NKX-2700 dye-sensitized core-shell photoanode and a quasi-solid-state electrolyte, sandwiched together, with a cobalt sulfide-coated counter electrode. The core-shell photoanode consisted of a composite mixture of 90% TiO2 nanoparticles and 10% TiO2 nanowires (TNPW) as core layer and MgO nanoparticles (MNP) as shell layer. Hafnium oxide (HfO2) was applied to the core-shell photoanode film as a blocking layer. TiO2 nanoparticles, TiO2 nanowires, and TNPW/MNP were characterized by x-ray diffractometry, scanning electron microscopy, and transmission electron microscopy. It was apparent from the UV-visible spectrum of the sensitizing dye coumarin NKX-2700 that its absorption was maximum at 525 nm. Power conversion efficiency (PCE) was greater for DSSC-1, fabricated with a core-shell TNPW/MNP/HfO2 photoanode, than for the other DSSC; its photovoltaic properties were: short circuit photocurrent J sc = 19 mA/cm2, open circuit voltage ( V oc) = 720 mV, fill factor ( FF) = 66%, and PCE ( η) = 9.02%. The charge-transport and charge-recombination behavior of the DSSC were investigated by electrochemical impedance spectroscopy; the results showed that the composite core-shell film resulted in the lowest charge-transfer resistance ( R CE) and the longest electron lifetime ( τ eff). Hence, the improved performance of DSSC-1 could be ascribed to the core-shell photoanode with blocking layer, which increased electron transport and suppressed recombination of charge carriers at the photoanode/dye/electrolyte interface.

  10. A New NIST Database for the Simulation of Electron Spectra for Surface Analysis (SESSA): Application to Angle-Resolved X-ray Photoelectron Spectroscopy of HfO2, ZrO2, HfSiO4, and ZrSiO4 Films on Silicon

    SciTech Connect

    Powell, C.J.; Smekal, W.; Werner, W.S.M.

    2005-09-09

    We describe a new NIST database for the Simulation of Electron Spectra for Surface Analysis (SESSA). This database provides data for the many parameters needed in quantitative Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). In addition, AES and XPS spectra can be simulated for layered samples. The simulated spectra, for layer compositions and thicknesses specified by the user, can be compared with measured spectra. The layer compositions and thicknesses can then be adjusted to find maximum consistency between simulated and measured spectra. In this way, AES and XPS can provide more detailed characterization of multilayer thin-film materials. We report on the use of SESSA for determining the thicknesses of HfO2, ZrO2, HfSiO4, and ZrSiO4 films on Si by angle-resolved XPS. Practical effective attenuation lengths (EALs) have been computed from SESSA as a function of film thickness and photoelectron emission angle (i.e., to simulate the effects of tilting the sample). These EALs have been compared with similar values obtained from the NIST Electron Effective-Attenuation-Length Database (SRD 82). Generally good agreement was found between corresponding EAL values, but there were differences for film thicknesses less than the inelastic mean free path of the photoelectrons in the overlayer film. These differences are due to a simplifying approximation in the algorithm used to compute EALs in SRD 82. SESSA, with realistic cross sections for elastic and inelastic scattering in the film and substrate materials, is believed to provide more accurate EALs than SRD 82 for thin-film thickness measurements, particularly in applications where the film and substrate have different electron-scattering properties.

  11. A New NIST Database for the Simulation of Electron Spectra for Surface Analysis (SESSA): Application to Angle-Resolved X-ray Photoelectron Spectroscopy of HfO2, ZrO2, HfSiO4, and ZrSiO4 Films on Silicon

    NASA Astrophysics Data System (ADS)

    Powell, C. J.; Smekal, W.; Werner, W. S. M.

    2005-09-01

    We describe a new NIST database for the Simulation of Electron Spectra for Surface Analysis (SESSA). This database provides data for the many parameters needed in quantitative Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). In addition, AES and XPS spectra can be simulated for layered samples. The simulated spectra, for layer compositions and thicknesses specified by the user, can be compared with measured spectra. The layer compositions and thicknesses can then be adjusted to find maximum consistency between simulated and measured spectra. In this way, AES and XPS can provide more detailed characterization of multilayer thin-film materials. We report on the use of SESSA for determining the thicknesses of HfO2, ZrO2, HfSiO4, and ZrSiO4 films on Si by angle-resolved XPS. Practical effective attenuation lengths (EALs) have been computed from SESSA as a function of film thickness and photoelectron emission angle (i.e., to simulate the effects of tilting the sample). These EALs have been compared with similar values obtained from the NIST Electron Effective-Attenuation-Length Database (SRD 82). Generally good agreement was found between corresponding EAL values, but there were differences for film thicknesses less than the inelastic mean free path of the photoelectrons in the overlayer film. These differences are due to a simplifying approximation in the algorithm used to compute EALs in SRD 82. SESSA, with realistic cross sections for elastic and inelastic scattering in the film and substrate materials, is believed to provide more accurate EALs than SRD 82 for thin-film thickness measurements, particularly in applications where the film and substrate have different electron-scattering properties.

  12. Superdirective dielectric nanoantennas

    NASA Astrophysics Data System (ADS)

    Krasnok, Alexander E.; Simovski, Constantin R.; Belov, Pavel A.; Kivshar, Yuri S.

    2014-06-01

    We introduce the novel concept of superdirective nanoantennas based on the excitation of higher-order magnetic multipole moments in subwavelength dielectric nanoparticles. Our superdirective nanoantenna is a small Si nanosphere containing a notch, and is excited by a dipole located within the notch. In addition to extraordinary directivity, this nanoantenna demonstrates efficient radiation steering at the nanoscale, resulting from the subwavelength sensitivity of the beam radiation direction to variation of the source position inside the notch. We compare our dielectric nanoantenna with a plasmonic nanoantenna of similar geometry, and reveal that the nanoantenna's high directivity in the regime of transmission is not associated with strong localization of near fields in the regime of reception. Likewise, the absence of hot spots inside the nanoantenna leads to low dissipation in the radiation regime, so that our dielectric nanoantenna has significantly smaller losses and high radiation efficiency of up to 70%.

  13. Dielectric assist accelerating structure

    NASA Astrophysics Data System (ADS)

    Satoh, D.; Yoshida, M.; Hayashizaki, N.

    2016-01-01

    A higher-order TM02 n mode accelerating structure is proposed based on a novel concept of dielectric loaded rf cavities. This accelerating structure consists of ultralow-loss dielectric cylinders and disks with irises which are periodically arranged in a metallic enclosure. Unlike conventional dielectric loaded accelerating structures, most of the rf power is stored in the vacuum space near the beam axis, leading to a significant reduction of the wall loss, much lower than that of conventional normal-conducting linac structures. This allows us to realize an extremely high quality factor and a very high shunt impedance at room temperature. A simulation of a 5 cell prototype design with an existing alumina ceramic indicates an unloaded quality factor of the accelerating mode over 120 000 and a shunt impedance exceeding 650 M Ω /m at room temperature.

  14. PREFACE: Dielectrics 2013

    NASA Astrophysics Data System (ADS)

    Hadjiloucas, Sillas; Blackburn, John

    2013-11-01

    This volume records the 42nd Dielectrics Group Proceedings of the Dielectrics Conference that took place at the University of Reading UK from 10-12 April 2013. The meeting is part of the biennial Dielectrics series of the Dielectrics Group, and formerly Dielectrics Society, and is organised by the Institute of Physics. The conference proceedings showcase some of the diversity and activity of the Dielectrics community worldwide, and bring together contributions from academics and industrial researchers with a diverse background and experiences from the Physics, Chemistry and Engineering communities. It is interesting to note some continuing themes such as Insulation/HV Materials, Dielectric Spectroscopy, Dielectric Measurement Techniques and Ferroelectric materials have a growing importance across a range of technologically important areas from the Energy sector to Materials research, Semiconductor and Electronics industries, and Metrology. We would like to thank all of our colleagues and friends in the Dielectrics community who have supported this event by contributing manuscripts and participating in the event. The conference has provided excellent networking opportunities for all delegates. Our thanks go also to our theme chairs: Dr Stephen Dodd (University of Leicester) on Insulation/HV Materials, Professor Darryl Almond (University of Bath) on Dielectric Spectroscopy, Dr John Blackburn (NPL) on Dielectric Measurement Techniques and Professor Anthony R West (University of Sheffield) on Ferroelectric Materials. We would also like to thank the other members of the Technical Programme Committee for their support, and refereeing the submitted manuscripts. Our community would also like to wish a full recovery to our plenary speaker Prof John Fothergill (City University London) who was unexpectedly unable to give his talk as well as thank Professor Alun Vaughan for stepping in and giving an excellent plenary lecture in his place at such very short notice. We are also

  15. Dielectric Monitoring of Curing Composites

    NASA Technical Reports Server (NTRS)

    Goldberg, Benjamin E.; Semmel, Marie L.

    1987-01-01

    Report describes preliminary attempts at dielectric monitoring of curing of graphite/epoxy and carbon/phenolic composites. Objective is to develop dielectric monitoring for optimizing curing process and reduce incidence of failures of produced composite structures.

  16. Thermally switchable dielectrics

    DOEpatents

    Dirk, Shawn M.; Johnson, Ross S.

    2013-04-30

    Precursor polymers to conjugated polymers, such as poly(phenylene vinylene), poly(poly(thiophene vinylene), poly(aniline vinylene), and poly(pyrrole vinylene), can be used as thermally switchable capacitor dielectrics that fail at a specific temperature due to the non-conjugated precursor polymer irreversibly switching from an insulator to the conjugated polymer, which serves as a bleed resistor. The precursor polymer is a good dielectric until it reaches a specific temperature determined by the stability of the leaving groups. Conjugation of the polymer backbone at high temperature effectively disables the capacitor, providing a `built-in` safety mechanism for electronic devices.

  17. Multilayer dielectric diffraction gratings

    DOEpatents

    Perry, Michael D.; Britten, Jerald A.; Nguyen, Hoang T.; Boyd, Robert; Shore, Bruce W.

    1999-01-01

    The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described.

  18. Multilayer dielectric diffraction gratings

    DOEpatents

    Perry, M.D.; Britten, J.A.; Nguyen, H.T.; Boyd, R.; Shore, B.W.

    1999-05-25

    The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described. 7 figs.

  19. AFM, ellipsometry, XPS and TEM on ultra-thin oxide/polymer nanocomposite layers in organic thin film transistors.

    PubMed

    Fian, A; Haase, A; Stadlober, B; Jakopic, G; Matsko, N B; Grogger, W; Leising, G

    2008-03-01

    Here we report on the fabrication and characterization of ultra-thin nanocomposite layers used as gate dielectric in low-voltage and high-performance flexible organic thin film transistors (oTFTs). Reactive sputtered zirconia layers were deposited with low thermal exposure of the substrate and the resulting porous oxide films with high leakage currents were spin-coated with an additional layer of poly-alpha-methylstyrene (P alphaMS). After this treatment a strong improvement of the oTFT performance could be observed; leakage currents could be eliminated almost completely. In ellipsometric studies a higher refractive index of the ZrO(2)/P alphaMS layers compared to the "as sputtered" zirconia films could be detected without a significant enhancement of the film thickness. Atomic force microscopy (AFM) measurements of the surface topography clearly showed a surface smoothing after the P alphaMS coating. Further studies with X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) also indicated that the polymer definitely did not form an extra layer. The polymer chains rather (self-)assemble in the nano-scaled interspaces of the porous oxide film giving an oxide-polymer "nanocomposite" with a high oxide filling grade resulting in high dielectric constants larger than 15. The dielectric strength of more than 1 MV cm(-1) is in good accordance with the polymer-filled interspaces. PMID:17952415

  20. Dielectric spectroscopy of monatomic alcohols

    NASA Astrophysics Data System (ADS)

    Baida, A. A.; Rudakov, A. V.; Agaev, S. G.

    2013-04-01

    The frequency dependences of permittivity ɛ( f) and dielectric loss tanδ( f) of monatomic alcohols are measured in range of frequencies f from 0.025 to 1000 kHz. Dielectric relaxation is observed in the investigated frequency range. Empirical correlation equations describing the relationships between the dielectric characteristics and physicochemical properties of monatomic alcohols are obtained.

  1. Probing the ultrathin limit of hyperbolic metamaterial: nonlocality induced topological transitions (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Chen, Long; Zhang, Cheng; Zhou, Jing; Guo, L. Jay

    2015-09-01

    An ideal hyperbolic metamaterial (HMM), which has a perfect hyperbolic dispersion curve, theoretically can support modes with indefinite wavenumbers, leading to large photon local density of states (LDOS) and many applications such as enhancing light-matter interactions, spontaneous emission and thermal radiation. Here in this presentation, HMMs based on ultrathin metal-dielectric multilayers have been studied by considering the nonlocal response of electrons in metal. Based on the hydrodynamic model of the nonlocal response, we investigate the effect of nonlocality on the performance (dispersion relation, ray refraction, LDOS and spontaneous emission) of HMMs when gradually approaching the ultrathin limit of the unit cell. We show that nonlocality will induce topological transitions of the iso-frequency surfaces and limit the wavenumber as well as LDOS for both type I and type II HMMs. Under nonlocal treatment, the iso-frequency surface of type II HMM transforms from a hyperbola to a bullet shape, while for type I HMM, the surface splits into two branches: a cylindrical-like branch at high k region and an elliptical branch at the low k region. In the high k region, the nonlocality set a cut-off k for the allowed wavenumbers in both type I and type II HMMs. This cut-off k which is defined by the electron Fermi velocity of the metal intrinsically limits the LDOS and light-matter interactions. These results indicate that in the aim of achieving high performance HMMs, merely thinning the constituent films according to the local theories is no longer valid.

  2. Resonance behavior of single ultrathin slot antennas on finite dielectric substrates in terahertz regime

    NASA Astrophysics Data System (ADS)

    Park, H. R.; Koo, S. M.; Suwal, O. K.; Park, Y. M.; Kyoung, J. S.; Seo, M. A.; Choi, S. S.; Park, N. K.; Kim, D. S.; Ahn, K. J.

    2010-05-01

    We investigate resonance behaviors of optically thin metallic slot antennas on finite substrates in terahertz frequency regime. By carefully analyzing theoretical and experimental results, we observe that slot antennas fabricated in a gold film with a thickness below the skin depth of gold show blueshifted resonance frequencies for the increasing slot width, while the opposite resonance behaviors appear when the slot antennas are perforated in perfectly electric conductor. In addition, we find that for slot antenna sustained by a finite substrate its thickness and the slot width are additional crucial factors determining the resonance frequency of slot antennas.

  3. MoS{sub 2} functionalization for ultra-thin atomic layer deposited dielectrics

    SciTech Connect

    Azcatl, Angelica; McDonnell, Stephen; Santosh, K.C.; Peng, Xin; Dong, Hong; Qin, Xiaoye; Addou, Rafik; Lu, Ning; Kim, Moon J.; Cho, Kyeongjae; Wallace, Robert M.; Mordi, Greg I.; Kim, Jiyoung

    2014-03-17

    The effect of room temperature ultraviolet-ozone (UV-O{sub 3}) exposure of MoS{sub 2} on the uniformity of subsequent atomic layer deposition of Al{sub 2}O{sub 3} is investigated. It is found that a UV-O{sub 3} pre-treatment removes adsorbed carbon contamination from the MoS{sub 2} surface and also functionalizes the MoS{sub 2} surface through the formation of a weak sulfur-oxygen bond without any evidence of molybdenum-sulfur bond disruption. This is supported by first principles density functional theory calculations which show that oxygen bonded to a surface sulfur atom while the sulfur is simultaneously back-bonded to three molybdenum atoms is a thermodynamically favorable configuration. The adsorbed oxygen increases the reactivity of MoS{sub 2} surface and provides nucleation sites for atomic layer deposition of Al{sub 2}O{sub 3}. The enhanced nucleation is found to be dependent on the thin film deposition temperature.

  4. Molds for cable dielectrics

    DOEpatents

    Roose, L.D.

    1996-12-10

    Molds for use in making end moldings for high-voltage cables are described wherein the dielectric insulator of a cable is heated and molded to conform to a desired shape. As a consequence, high quality substantially bubble-free cable connectors suitable for mating to premanufactured fittings are made. 5 figs.

  5. Molds for cable dielectrics

    DOEpatents

    Roose, Lars D.

    1996-01-01

    Molds for use in making end moldings for high-voltage cables are described wherein the dielectric insulator of a cable is heated and molded to conform to a desired shape. As a consequence, high quality substantially bubble-free cable connectors suitable for mating to premanufactured fittings are made.

  6. Interfaces: nanometric dielectrics

    NASA Astrophysics Data System (ADS)

    Lewis, T. J.

    2005-01-01

    The incorporation of nanometric size particles in a matrix to form dielectric composites shows promise of materials (nanodielectrics) with new and improved properties. It is argued that the properties of the interfaces between the particles and the matrix, which will themselves be of nanometric dimensions, will have an increasingly dominant role in determining dielectric performance as the particle size decreases. The forces that determine the electrical and dielectric properties of interfaces are considered, with emphasis on the way in which they might influence composite behaviour. A number of examples are given in which interfaces at the nanometric level exercise both passive and active control over dielectric, optical and conductive properties. Electromechanical properties are also considered, and it is shown that interfaces have important electrostrictive and piezoelectric characteristics. It is demonstrated that the process of poling, namely subjecting macroscopic composite materials to electrical stress and raised temperatures to create piezoelectric materials, can be explained in terms of optimizing the collective response of the nanometric interfaces involved. If the electrical and electromechanical features are coupled to the long-established electrochemical properties, interfaces represent highly versatile active elements with considerable potential in nanotechnology.

  7. Dielectric elastomer memory

    NASA Astrophysics Data System (ADS)

    O'Brien, Benjamin M.; McKay, Thomas G.; Xie, Sheng Q.; Calius, Emilio P.; Anderson, Iain A.

    2011-04-01

    Life shows us that the distribution of intelligence throughout flexible muscular networks is a highly successful solution to a wide range of challenges, for example: human hearts, octopi, or even starfish. Recreating this success in engineered systems requires soft actuator technologies with embedded sensing and intelligence. Dielectric Elastomer Actuator(s) (DEA) are promising due to their large stresses and strains, as well as quiet flexible multimodal operation. Recently dielectric elastomer devices were presented with built in sensor, driver, and logic capability enabled by a new concept called the Dielectric Elastomer Switch(es) (DES). DES use electrode piezoresistivity to control the charge on DEA and enable the distribution of intelligence throughout a DEA device. In this paper we advance the capabilities of DES further to form volatile memory elements. A set reset flip-flop with inverted reset line was developed based on DES and DEA. With a 3200V supply the flip-flop behaved appropriately and demonstrated the creation of dielectric elastomer memory capable of changing state in response to 1 second long set and reset pulses. This memory opens up applications such as oscillator, de-bounce, timing, and sequential logic circuits; all of which could be distributed throughout biomimetic actuator arrays. Future work will include miniaturisation to improve response speed, implementation into more complex circuits, and investigation of longer lasting and more sensitive switching materials.

  8. Atomic layer deposition of dielectrics on graphene using reversibly physisorbed ozone.

    PubMed

    Jandhyala, Srikar; Mordi, Greg; Lee, Bongki; Lee, Geunsik; Floresca, Carlo; Cha, Pil-Ryung; Ahn, Jinho; Wallace, Robert M; Chabal, Yves J; Kim, Moon J; Colombo, Luigi; Cho, Kyeongjae; Kim, Jiyoung

    2012-03-27

    Integration of graphene field-effect transistors (GFETs) requires the ability to grow or deposit high-quality, ultrathin dielectric insulators on graphene to modulate the channel potential. Here, we study a novel and facile approach based on atomic layer deposition through ozone functionalization to deposit high-κ dielectrics (such as Al(2)O(3)) without breaking vacuum. The underlying mechanisms of functionalization have been studied theoretically using ab initio calculations and experimentally using in situ monitoring of transport properties. It is found that ozone molecules are physisorbed on the surface of graphene, which act as nucleation sites for dielectric deposition. The physisorbed ozone molecules eventually react with the metal precursor, trimethylaluminum to form Al(2)O(3). Additionally, we successfully demonstrate the performance of dual-gated GFETs with Al(2)O(3) of sub-5 nm physical thickness as a gate dielectric. Back-gated GFETs with mobilities of ~19,000 cm(2)/(V·s) are also achieved after Al(2)O(3) deposition. These results indicate that ozone functionalization is a promising pathway to achieve scaled gate dielectrics on graphene without leaving a residual nucleation layer.

  9. High performance organic field-effect transistors with ultra-thin HfO{sub 2} gate insulator deposited directly onto the organic semiconductor

    SciTech Connect

    Ono, S.; Häusermann, R.; Chiba, D.; Shimamura, K.; Ono, T.; Batlogg, B.

    2014-01-06

    We have produced stable organic field-effect transistors (OFETs) with an ultra-thin HfO{sub 2} gate insulator deposited directly on top of rubrene single crystals by atomic layer deposition (ALD). We find that ALD is a gentle deposition process to grow thin films without damaging rubrene single crystals, as results these devices have a negligibly small threshold voltage and are very stable against gate-bias-stress, and the mobility exceeds 1 cm{sup 2}/V s. Moreover, the devices show very little degradation even when kept in air for more than 2 months. These results demonstrate thin HfO{sub 2} layers deposited by ALD to be well suited as high capacitance gate dielectrics in OFETs operating at small gate voltage. In addition, the dielectric layer acts as an effective passivation layer to protect the organic semiconductor.

  10. Effects of the dielectric properties of the ceramic-solvent interface on the binding of proteins to oxide ceramics: a non-local electrostatic approach

    NASA Astrophysics Data System (ADS)

    Rubinstein, Alexander I.; Sabirianov, Renat F.; Namavar, Fereydoon

    2016-10-01

    The rapid development of nanoscience and nanotechnology has raised many fundamental questions that significantly impede progress in these fields. In particular, understanding the physicochemical processes at the interface in aqueous solvents requires the development and application of efficient and accurate methods. In the present work we evaluate the electrostatic contribution to the energy of model protein-ceramic complex formation in an aqueous solvent. We apply a non-local (NL) electrostatic approach that accounts for the effects of the short-range structure of the solvent on the electrostatic interactions of the interfacial systems. In this approach the aqueous solvent is considered as a non-ionic liquid, with the rigid and strongly correlated dipoles of the water molecules. We have found that an ordered interfacial aqueous solvent layer at the protein- and ceramic-solvent interfaces reduces the charging energy of both the ceramic and the protein in the solvent, and significantly increases the electrostatic contribution to their association into a complex. This contribution in the presented NL approach was found to be significantly shifted with respect to the classical model at any dielectric constant value of the ceramics. This implies a significant increase of the adsorption energy in the protein-ceramic complex formation for any ceramic material. We show that for several biocompatible ceramics (for example HfO2, ZrO2, and Ta2O5) the above effect predicts electrostatically induced protein-ceramic complex formation. However, in the framework of the classical continuum electrostatic model (the aqueous solvent as a uniform dielectric medium with a high dielectric constant ˜80) the above ceramics cannot be considered as suitable for electrostatically induced complex formation. Our results also show that the protein-ceramic electrostatic interactions can be strong enough to compensate for the unfavorable desolvation effect in the process of protein

  11. Effects of the dielectric properties of the ceramic-solvent interface on the binding of proteins to oxide ceramics: a non-local electrostatic approach.

    PubMed

    Rubinstein, Alexander I; Sabirianov, Renat F; Namavar, Fereydoon

    2016-10-14

    The rapid development of nanoscience and nanotechnology has raised many fundamental questions that significantly impede progress in these fields. In particular, understanding the physicochemical processes at the interface in aqueous solvents requires the development and application of efficient and accurate methods. In the present work we evaluate the electrostatic contribution to the energy of model protein-ceramic complex formation in an aqueous solvent. We apply a non-local (NL) electrostatic approach that accounts for the effects of the short-range structure of the solvent on the electrostatic interactions of the interfacial systems. In this approach the aqueous solvent is considered as a non-ionic liquid, with the rigid and strongly correlated dipoles of the water molecules. We have found that an ordered interfacial aqueous solvent layer at the protein- and ceramic-solvent interfaces reduces the charging energy of both the ceramic and the protein in the solvent, and significantly increases the electrostatic contribution to their association into a complex. This contribution in the presented NL approach was found to be significantly shifted with respect to the classical model at any dielectric constant value of the ceramics. This implies a significant increase of the adsorption energy in the protein-ceramic complex formation for any ceramic material. We show that for several biocompatible ceramics (for example HfO2, ZrO2, and Ta2O5) the above effect predicts electrostatically induced protein-ceramic complex formation. However, in the framework of the classical continuum electrostatic model (the aqueous solvent as a uniform dielectric medium with a high dielectric constant ∼80) the above ceramics cannot be considered as suitable for electrostatically induced complex formation. Our results also show that the protein-ceramic electrostatic interactions can be strong enough to compensate for the unfavorable desolvation effect in the process of protein

  12. Effects of the dielectric properties of the ceramic-solvent interface on the binding of proteins to oxide ceramics: a non-local electrostatic approach.

    PubMed

    Rubinstein, Alexander I; Sabirianov, Renat F; Namavar, Fereydoon

    2016-10-14

    The rapid development of nanoscience and nanotechnology has raised many fundamental questions that significantly impede progress in these fields. In particular, understanding the physicochemical processes at the interface in aqueous solvents requires the development and application of efficient and accurate methods. In the present work we evaluate the electrostatic contribution to the energy of model protein-ceramic complex formation in an aqueous solvent. We apply a non-local (NL) electrostatic approach that accounts for the effects of the short-range structure of the solvent on the electrostatic interactions of the interfacial systems. In this approach the aqueous solvent is considered as a non-ionic liquid, with the rigid and strongly correlated dipoles of the water molecules. We have found that an ordered interfacial aqueous solvent layer at the protein- and ceramic-solvent interfaces reduces the charging energy of both the ceramic and the protein in the solvent, and significantly increases the electrostatic contribution to their association into a complex. This contribution in the presented NL approach was found to be significantly shifted with respect to the classical model at any dielectric constant value of the ceramics. This implies a significant increase of the adsorption energy in the protein-ceramic complex formation for any ceramic material. We show that for several biocompatible ceramics (for example HfO2, ZrO2, and Ta2O5) the above effect predicts electrostatically induced protein-ceramic complex formation. However, in the framework of the classical continuum electrostatic model (the aqueous solvent as a uniform dielectric medium with a high dielectric constant ∼80) the above ceramics cannot be considered as suitable for electrostatically induced complex formation. Our results also show that the protein-ceramic electrostatic interactions can be strong enough to compensate for the unfavorable desolvation effect in the process of protein

  13. Optimized actuators for ultrathin deformable primary mirrors.

    PubMed

    Laslandes, Marie; Patterson, Keith; Pellegrino, Sergio

    2015-05-20

    A novel design and selection scheme for surface-parallel actuators for ultrathin, lightweight mirrors is presented. The actuation system consists of electrodes printed on a continuous layer of piezoelectric material bonded to an optical-quality substrate. The electrodes provide almost full coverage of the piezoelectric layer, in order to maximize the amount of active material that is available for actuation, and their shape is optimized to maximize the correctability and stroke of the mirror for a chosen number of independent actuators and for a dominant imperfection mode. The starting point for the design of the electrodes is the observation that the correction of a figure error that has at least two planes of mirror symmetry is optimally done with twin actuators that have the same optimized shape but are rotated through a suitable angle. Additional sets of optimized twin actuators are defined by considering the intersection between the twin actuators, and hence an arbitrarily fine actuation pattern can be generated. It is shown that this approach leads to actuator systems with better performance than simple, geometrically based actuators. Several actuator patterns to correct third-order astigmatism aberrations are presented, and an experimental demonstration of a 41-actuator mirror is also presented. PMID:26192533

  14. Inducing electric polarization in ultrathin insulating layers

    NASA Astrophysics Data System (ADS)

    Martinez-Castro, Jose; Piantek, Marten; Persson, Mats; Serrate, David; Hirjibehedin, Cyrus F.

    Studies of ultrathin polar oxide films have attracted the interest of researchers for a long time due to their different properties compared to bulk materials. However they present several challenges such as the difficulty in the stabilization of the polar surfaces and the limited success in tailoring their properties. Moreover, recently developed Van der Waals materials have shown that the stacking of 2D-layers trigger new collective states thanks to the interaction between layers. Similarly, interface phenomena emerge in polar oxides, like induced ferroelectricity. This represents a promising way for the creation of new materials with customized properties that differ from those of the isolated layers. Here we present a new approach for the fabrication and study of atomically thin insulating films. We show that the properties of insulating polar layers of sodium chloride (NaCl) can be engineered when they are placed on top of a charge modulated template of copper nitride (Cu2N). STM studies carried out in ultra-high vacuum and at low temperatures over NaCl/Cu2N/Cu(001) show that we are able to build up and stabilize interfaces of polar surface at the limit of one atomic layer showing new properties not present before at the atomic scale.

  15. Antenna with Dielectric Having Geometric Patterns

    NASA Technical Reports Server (NTRS)

    Dudley, Kenneth L. (Inventor); Elliott, Holly A. (Inventor); Cravey, Robin L. (Inventor); Connell, John W. (Inventor); Ghose, Sayata (Inventor); Watson, Kent A. (Inventor); Smith, Jr., Joseph G. (Inventor)

    2013-01-01

    An antenna includes a ground plane, a dielectric disposed on the ground plane, and an electrically-conductive radiator disposed on the dielectric. The dielectric includes at least one layer of a first dielectric material and a second dielectric material that collectively define a dielectric geometric pattern, which may comprise a fractal geometry. The radiator defines a radiator geometric pattern, and the dielectric geometric pattern is geometrically identical, or substantially geometrically identical, to the radiator geometric pattern.

  16. Solution-processed Al2O3 gate dielectrics for graphene field-effect transistors

    NASA Astrophysics Data System (ADS)

    Park, Goon-Ho; Kim, Kwan-Soo; Fukidome, Hirokazu; Suemitsu, Tetsuya; Otsuji, Taiichi; Cho, Won-Ju; Suemitsu, Maki

    2016-09-01

    The performance of actual graphene FETs suffers significant degradation from that expected for pristine graphene, which can be partly attributed to the onset of defects and the doping of the graphene induced during the fabrication of gate dielectric layers. These effects are mainly due to high-temperature processes such as postdeposition annealing. Here, we propose a novel low-temperature method for the fabrication of gate dielectrics, which consists of the natural oxidation of an ultrathin Al layer and a sol–gel process with oxygen plasma treatment to form an Al2O3 layer. The method results in a significant reduction of defects and doping in graphene, and devices fabricated by this method show an intrinsic carrier mobility as high as 9100 cm2 V‑1 s‑1.

  17. Temperature switchable polymer dielectrics.

    SciTech Connect

    Johnson, Ross Stefan

    2010-08-01

    Materials with switchable states are desirable in many areas of science and technology. The ability to thermally transform a dielectric material to a conductive state should allow for the creation of electronics with built-in safety features. Specifically, the non-desirable build-up and discharge of electricity in the event of a fire or over-heating would be averted by utilizing thermo-switchable dielectrics in the capacitors of electrical devices (preventing the capacitors from charging at elevated temperatures). We have designed a series of polymers that effectively switch from a non-conductive to a conductive state. The thermal transition is governed by the stability of the leaving group after it leaves as a free entity. Here, we present the synthesis and characterization of a series of precursor polymers that eliminate to form poly(p-phenylene vinylene) (PPV's).

  18. Temperature switchable polymer dielectrics.

    SciTech Connect

    Kholwadwala, Fenil Manish; Johnson, Ross Stefan; Dirk, Shawn M.

    2010-06-01

    Materials with switchable states are desirable in many areas of science and technology. The ability to thermally transform a dielectric material to a conductive state should allow for the creation of electronics with built-in safety features. Specifically, the non-desirable build-up and discharge of electricity in the event of a fire or over-heating would be averted by utilizing thermo-switchable dielectrics in the capacitors of electrical devices (preventing the capacitors from charging at elevated temperatures). We have designed a series of polymers that effectively switch from a non-conductive to a conductive state. The thermal transition is governed by the stability of the leaving group after it leaves as a free entity. Here, we present the synthesis and characterization of a series of precursor polymers that eliminate to form poly(p-phenylene vinylene) (PPV's).

  19. Large ultrathin shelled drops produced via non-confined microfluidics.

    PubMed

    Chaurasia, Ankur S; Josephides, Dimitris N; Sajjadi, Shahriar

    2015-02-01

    We present a facile approach for producing large and monodisperse core-shell drops with ultrathin shells using a single-step process. A biphasic compound jet is introduced into a quiescent third (outer) phase that ruptures to form core-shell drops. Ultrathin shelled drops could only be produced within a certain range of surfactant concentrations and flow rates, highlighting the effect of interfacial tension in engulfing the core in a thin shell. An increase in surfactant concentrations initially resulted in drops with thinner shells. However, the drops with thinnest shells were obtained at an optimum surfactant concentration, and a further increase in the surfactant concentrations increased the shell thickness. Highly monodisperse (coefficient of variation smaller than 3 %) core-shell drops with diameter of ∼200 μm-2 mm with shell thickness as small as ∼2 μm were produced. The resulting drops were stable enough to undergo polymerisation and produce ultrathin shelled capsules.

  20. Printable Ultrathin Metal Oxide Semiconductor-Based Conformal Biosensors.

    PubMed

    Rim, You Seung; Bae, Sang-Hoon; Chen, Huajun; Yang, Jonathan L; Kim, Jaemyung; Andrews, Anne M; Weiss, Paul S; Yang, Yang; Tseng, Hsian-Rong

    2015-12-22

    Conformal bioelectronics enable wearable, noninvasive, and health-monitoring platforms. We demonstrate a simple and straightforward method for producing thin, sensitive In2O3-based conformal biosensors based on field-effect transistors using facile solution-based processing. One-step coating via aqueous In2O3 solution resulted in ultrathin (3.5 nm), high-density, uniform films over large areas. Conformal In2O3-based biosensors on ultrathin polyimide films displayed good device performance, low mechanical stress, and highly conformal contact determined using polydimethylsiloxane artificial skin having complex curvilinear surfaces or an artificial eye. Immobilized In2O3 field-effect transistors with self-assembled monolayers of NH2-terminated silanes functioned as pH sensors. Functionalization with glucose oxidase enabled d-glucose detection at physiologically relevant levels. The conformal ultrathin field-effect transistor biosensors developed here offer new opportunities for future wearable human technologies. PMID:26498319

  1. In situ electrical transport measurementof superconductive ultrathin films

    NASA Astrophysics Data System (ADS)

    Liu, Can-Hua; Jia, Jin-Feng

    2015-11-01

    The discovery of an extraordinarily superconductive large energy gap in SrTiO3 supported single-layer FeSe films has recently initiated a great deal of research interests in surface-enhanced superconductivity and superconductive ultrathin films fabricated on crystal surfaces. On account of the instability of ultra-thin films in air, it is desirable to perform electrical transport measurement in ultra-high vaccum (UHV). Here we review the experimental techniques of in situ electrical transport measurement and their applications on superconductive ultrathin films. The work in SJTU was supported by the National Basic Research Program of China (Grant Nos. 2013CB921902 and 2011CB922200) and the National Natural Science Foundation of China (Grant Nos. 11227404, 11274228, 11521404, 11174199, and 11134008).

  2. Ultra-thin Graphitic Film: Synthesis and Physical Properties

    NASA Astrophysics Data System (ADS)

    Kaplas, Tommi; Kuzhir, Polina

    2016-02-01

    A scalable technique of chemical vapor deposition (CVD) growth of ultra-thin graphitic film is proposed. Ultra-thin graphitic films grown by a one-step CVD process on catalytic copper substrate have higher crystallinity than pyrolytic carbon grown on a non-catalytic surface and appear to be more robust than a graphene monolayer. The obtained graphitic material, not thicker than 8 nm, survives during the transfer process from a Cu substrate without a template polymer layer, typically used in the graphene transfer process to protect graphene. This makes the transfer process much more simple and cost-effective. Having electrical and optical properties compatible with what was observed for a few layers of CVD graphene, the proposed ultra-thin graphitic film offers new avenues for implementing 2D materials in real-world devices.

  3. Printable Ultrathin Metal Oxide Semiconductor-Based Conformal Biosensors.

    PubMed

    Rim, You Seung; Bae, Sang-Hoon; Chen, Huajun; Yang, Jonathan L; Kim, Jaemyung; Andrews, Anne M; Weiss, Paul S; Yang, Yang; Tseng, Hsian-Rong

    2015-12-22

    Conformal bioelectronics enable wearable, noninvasive, and health-monitoring platforms. We demonstrate a simple and straightforward method for producing thin, sensitive In2O3-based conformal biosensors based on field-effect transistors using facile solution-based processing. One-step coating via aqueous In2O3 solution resulted in ultrathin (3.5 nm), high-density, uniform films over large areas. Conformal In2O3-based biosensors on ultrathin polyimide films displayed good device performance, low mechanical stress, and highly conformal contact determined using polydimethylsiloxane artificial skin having complex curvilinear surfaces or an artificial eye. Immobilized In2O3 field-effect transistors with self-assembled monolayers of NH2-terminated silanes functioned as pH sensors. Functionalization with glucose oxidase enabled d-glucose detection at physiologically relevant levels. The conformal ultrathin field-effect transistor biosensors developed here offer new opportunities for future wearable human technologies.

  4. Properties of two-dimensional insulators: A DFT study of bimetallic oxide CrW2O9 clusters adsorption on MgO ultrathin films

    NASA Astrophysics Data System (ADS)

    Zhu, Jia; Zhang, Hui; Zhao, Ling; Xiong, Wei; Huang, Xin; Wang, Bin; Zhang, Yongfan

    2016-08-01

    Periodic density functional theory calculations have been performed to study the electronic properties of bimetallic oxide CrW2O9 clusters adsorbed on MgO/Ag(001) ultrathin films (<1 nm). Our results show that after deposition completely different structures, electronic properties and chemical reactivity of dispersed CrW2O9 clusters on ultrathin films are observed compared with that on the thick MgO surface. On the thick MgO(001) surface, adsorbed CrW2O9 clusters are distorted significantly and just a little electron transfer occurs from oxide surface to clusters, which originates from the formation of adsorption dative bonds at interface. Whereas on the MgO/Ag(001) ultrathin films, the resulting CrW2O9 clusters keep the cyclic structures and the geometries are similar to that of gas-phase [CrW2O9]-. Interestingly, we predicted the occurrence of a net transfer of one electron by direct electron tunneling from the MgO/Ag(001) films to CrW2O9 clusters through the thin MgO dielectric barrier. Furthermore, our work reveals a progressive Lewis acid site where spin density preferentially localizes around the Cr atom not the W atoms for CrW2O9/MgO/Ag(001) system, indicating a potentially good bimetallic oxide for better catalytic activities with respect to that of pure W3O9 clusters. As a consequence, present results reveal that the adsorption of bimetallic oxide CrW2O9 clusters on the MgO/Ag(001) ultrathin films provide a new perspective to tune and modify the properties and chemical reactivity of bimetallic oxide adsorbates as a function of the thickness of the oxide films.

  5. Low-k Dielectrics

    NASA Astrophysics Data System (ADS)

    Hayashi, Yoshihiro

    As CMOS transistors were scaled, interconnects to link them are also shrunk to reduce the line pitches [1-10]. As shown in Fig. 22.1, the interconnect pitches have been shrunk from 180 nm, 140 nm, and 100 nm for 65 [4], 45 [32], and 32 nm nodes [10] LSIs, respectively. To eliminate the interconnect parasitic capacitance, low-k dielectric films which have lower permittivity than the conventional silica (SiO2) dielectrics have been introduced. Figure 22.2 shows the technology trend of the k-value and the deposition process, in which the low-k films are deposited by spin-on-dielectric (SOD) method or plasma-enhanced CVD. In the case of SOD, precursor solution is poured on a rotated wafer, and the precursor film is heated to vaporize the solvent followed by reaction and densification to make a low-k film. In the case of PECVD [36, 42], on the other hand, precursor solution is vaporized with inert carrier gas such as He, and the precursor gas is introduced into PECVD chamber with RF power. The vaporized precursor gas is exited from plasma, depositing a low-k film on a wafer heated in high vacuum. The SOD method is advantageous to decrease the k-value, while PECVD method is superior in the adhesion strength due to the possibility of in-suite plasma surface treatment in vacuum just before the low-k deposition.

  6. Tunable Dielectric Properties of Ferrite-Dielectric Based Metamaterial

    PubMed Central

    Bi, K.; Huang, K.; Zeng, L. Y.; Zhou, M. H.; Wang, Q. M.; Wang, Y. G.; Lei, M.

    2015-01-01

    A ferrite-dielectric metamaterial composed of dielectric and ferrite cuboids has been investigated by experiments and simulations. By interacting with the electromagnetic wave, the Mie resonance can take place in the dielectric cuboids and the ferromagnetic precession will appear in the ferrite cuboids. The magnetic field distributions show the electric Mie resonance of the dielectric cuboids can be influenced by the ferromagnetic precession of ferrite cuboids when a certain magnetic field is applied. The effective permittivity of the metamaterial can be tuned by modifying the applied magnetic field. A good agreement between experimental and simulated results is demonstrated, which confirms that these metamaterials can be used for tunable microwave devices. PMID:25993433

  7. New silicone dielectric elastomers with a high dielectric constant

    NASA Astrophysics Data System (ADS)

    Zhang, Zhen; Liu, Liwu; Fan, Jiumin; Yu, Kai; Liu, Yanju; Shi, Liang; Leng, Jinsong

    2008-03-01

    Dielectric elastomers (Des) are a type of EAPs with unique electrical properties and mechanical properties: high actuation strains and stresses, fast response times, high efficiency, stability, reliability and durability. The excellent figures of merit possessed by dielectric elastomers make them the most performing materials which can be applied in many domains: biomimetics, aerospace, mechanics, medicals, etc. In this paper, we present a kind of electroactive polymer composites based on silicone Dielectric elastomers with a high dielectric constant. Novel high DEs could be realized by means of a composite approach. By filling an ordinary elastomer (e.g. silicone) with a component of functional ceramic filler having a greater dielectric permittivity, it is possible to obtain a resulting composite showing the fruitful combination of the matrix's advantageous elasticity and the filler's high permittivity. Here we add the ferroelectric relaxor ceramics (mainly BaTiO3) which has high dielectric constant (>3000) to the conventional silicone Dielectric elastomers, to get the dielectric elastomer which can exhibit high elastic energy densities induced by an electric field of about 15 MV/m. Tests of the physical and chemical properties of the dielectric elastomers are conducted, which verify our supposes and offer the experimental data supporting further researches.

  8. Method for laser welding ultra-thin metal foils

    DOEpatents

    Pernicka, J.C.; Benson, D.K.; Tracy, C.E.

    1996-03-26

    A method for simultaneously cutting and welding ultra-thin foils having a thickness of less than 0.002 inches wherein two ultra-thin films are stacked and clamped together. A pulsed laser such as of the Neodymium: YAG type is provided and the beam of the laser is directed onto the stacked films to cut a channel through the films. The laser is moved relative to the stacked foils to cut the stacked foils at successive locations and to form a plurality of connected weld beads to form a continuous weld. 5 figs.

  9. Method for laser welding ultra-thin metal foils

    DOEpatents

    Pernicka, John C.; Benson, David K.; Tracy, C. Edwin

    1996-01-01

    A method for simultaneously cutting and welding ultra-thin foils having a thickness of less than 0.002 inches wherein two ultra-thin films are stacked and clamped together. A pulsed laser such as of the Neodymium: YAG type is provided and the beam of the laser is directed onto the stacked films to cut a channel through the films. The laser is moved relative to the stacked foils to cut the stacked foils at successive locations and to form a plurality of connected weld beads to form a continuous weld.

  10. Phase Formation Behavior in Ultrathin Iron Oxide.

    PubMed

    Jõgi, Indrek; Jacobsson, T Jesper; Fondell, Mattis; Wätjen, Timo; Carlsson, Jan-Otto; Boman, Mats; Edvinsson, Tomas

    2015-11-17

    Nanostructured iron oxides, and especially hematite, are interesting for a wide range of applications ranging from gas sensors to renewable solar hydrogen production. A promising method for deposition of low-dimensional films is atomic layer deposition (ALD). Although a potent technique, ALD of ultrathin films is critically sensitive to the substrate and temperature conditions where initial formation of islands and crystallites influences the properties of the films. In this work, deposition at the border of the ALD window forming a hybrid ALD/pulsed CVD (pCVD) deposition is utilized to obtain a deposition less sensitive to the substrate. A thorough analysis of iron oxide phases formation on two different substrates, Si(100) and SiO2, was performed. Films between 3 and 50 nm were deposited and analyzed with diffraction techniques, high-resolution Raman spectroscopy, and optical spectroscopy. Below 10 nm nominal film thickness, island formation and phase dependent particle crystallization impose constraints for deposition of phase pure iron oxides on non-lattice-matching substrates. Films between 10 and 20 nm thickness on SiO2 could effectively be recrystallized into hematite whereas for the corresponding films on Si(100), no recrystallization occurred. For films thicker than 20 nm, phase pure hematite can be formed directly with ALD/pCVD with very low influence of the substrate on either Si or SiO2. For more lattice matched substrates such as SnO2:F, Raman spectroscopy indicated formation of the hematite phase already for films with 3 nm nominal thickness and clearly for 6 nm films. Analysis of the optical properties corroborated the analysis and showed a quantum confined blue-shift of the absorption edge for the thinnest films. PMID:26506091

  11. Semiconductor/dielectric interface engineering and characterization

    NASA Astrophysics Data System (ADS)

    Lucero, Antonio T.

    The focus of this dissertation is the application and characterization of several, novel interface passivation techniques for III-V semiconductors, and the development of an in-situ electrical characterization. Two different interface passivation techniques were evaluated. The first is interface nitridation using a nitrogen radical plasma source. The nitrogen radical plasma generator is a unique system which is capable of producing a large flux of N-radicals free of energetic ions. This was applied to Si and the surface was studied using x-ray photoelectron spectroscopy (XPS). Ultra-thin nitride layers could be formed from 200-400° C. Metal-oxide-semiconductor capacitors (MOSCAPs) were fabricated using this passivation technique. Interface nitridation was able to reduce leakage current and improve the equivalent oxide thickness of the devices. The second passivation technique studied is the atomic layer deposition (ALD) diethylzinc (DEZ)/water treatment of sulfur treated InGaAs and GaSb. On InGaAs this passivation technique is able to chemically reduce higher oxidation states on the surface, and the process results in the deposition of a ZnS/ZnO interface passivation layer, as determined by XPS. Capacitance-voltage (C-V) measurements of MOSCAPs made on p-InGaAs reveal a large reduction in accumulation dispersion and a reduction in the density of interfacial traps. The same technique was applied to GaSb and the process was studied in an in-situ half-cycle XPS experiment. DEZ/H2O is able to remove all Sb-S from the surface, forming a stable ZnS passivation layer. This passivation layer is resistant to further reoxidation during dielectric deposition. The final part of this dissertation is the design and construction of an ultra-high vacuum cluster tool for in-situ electrical characterization. The system consists of three deposition chambers coupled to an electrical probe station. With this setup, devices can be processed and subsequently electrically characterized

  12. Surface-sensitive UHV dielectric studies of nanoscale organic thin films: Adsorption, crystallization, and sublimation

    NASA Astrophysics Data System (ADS)

    Underwood, Jason M.

    Nanoscale systems are small collections of atoms or molecules, which as a result of their limited extent, show measurable thermodynamic deviations from bulk samples of the same species. The deviations may result from purely finite-size effects, or may be due to an increased significance of the interaction between the nanoscale system and its container. Ultra-thin (<100 nm) films of organic molecules adsorbed on surfaces afford unique opportunities to study the interplay of forces relevant to nanoscale physics. This thesis describes the development of a novel ultra-high vacuum apparatus to study the behavior of adsorbed polar molecules via dielectric spectroscopy (UHV-DS). Ultra-thin films are grown and characterized in-situ. The use of interdigitated electrode capacitors and a ratio-transformer bridge technique yields resolutions of ˜1 aF and ˜10-5 ppm in the capacitance and loss tangent, respectively. Typical sensitivity is 10 aF per monolayer at 80 K. Results are given for studies on water, methanol, and Cp* (a synthetic molecular rotor). The desorption event in the dielectric spectra is correlated with thermal desorption spectroscopy. During growth of methanol films, we observe partial crystallization for temperatures above ≳ 100 K. Crystallization is also observed upon heating glassy films grown at 80 K. Finally, we discuss UHV-DS as a probe for solid thin-film vapor pressure measurements, and show that our data on methanol compare favorably with those in the literature.

  13. Ultra-thin anisotropic metasurface for polarized beam splitting and reflected beam steering applications

    NASA Astrophysics Data System (ADS)

    Guo, Wenlong; Wang, Guangming; Li, Tangjing; Li, Haipeng; Zhuang, Yaqiang; Hou, Haisheng

    2016-10-01

    In this paper, we propose a polarization beam splitter utilizing an ultra-thin anisotropic metasurface. The proposed anisotropic element is composed of triple-layered rectangular patches spaced with double-layered dielectric isolators. By tailoring the metallic patches, the cell is capable of transmitting x-polarized waves efficiently and reflecting y-polarized beams with almost 100% efficiency at 15 GHz. In addition to this, the reflected phases can be modulated by adjusting the size of the element, which contributes to beam steering in reflection mode. By assigning gradient phases on the metasurface, the constructed sample has the ability to refract x-polarized waves normally and reflect y-polarized beams anomalously. For verification, a sample with a size of 240 × 240 mm2 is fabricated and measured. Consistent numerical and experimental results have both validated the efficiently anomalous reflection for y-polarized waves and normal refraction for x-polarized beams operating from 14.6-15.4 GHz. Furthermore, the proposed sample has a thickness of 0.1λ at 15 GHz, which provides a promising approach for steering and splitting beams in a compact size.

  14. Tri-gate InGaAs-OI junctionless FETs with PE-ALD Al2O3 gate dielectric and H2/Ar anneal

    NASA Astrophysics Data System (ADS)

    Djara, Vladimir; Czornomaz, Lukas; Deshpande, Veeresh; Daix, Nicolas; Uccelli, Emanuele; Caimi, Daniele; Sousa, Marilyne; Fompeyrine, Jean

    2016-01-01

    We present a tri-gate In0.53Ga0.47As-on-insulator (InGaAs-OI) junctionless field-effect transistor (JLFET) architecture. The fabricated devices feature a 20-nm-thick n-In0.53Ga0.47As channel doped to 1018/cm3 obtained by metal organic chemical vapor phase deposition and direct wafer bonding along with a 3.5-nm-thick Al2O3 gate dielectric deposited by plasma-enhanced atomic layer deposition (PE-ALD). The PE-ALD Al2O3 presents a bandgap of 7.0 eV, a k-value of 8.1 and a breakdown field of 8-10.5 MV/cm. A post-fabrication H2/Ar anneal applied to the PE-ALD Al2O3/In0.53Ga0.47As-OI gate stack yielded a low density of interface traps (Dit) of 7 × 1011/cm2 eV at Ec - E = -0.1 eV along with lower border trap density values than recently reported PE-ALD bi-layer Al2O3/HfO2 and thermal ALD HfO2 gate stacks deposited on In0.53Ga0.47As. The H2/Ar anneal also improved the subthreshold performance of the tri-gate InGaAs-OI JLFETs. After H2/Ar anneal, the long-channel (10 μm) device featured a threshold voltage (VT) of 0.25 V, a subthreshold swing (SS) of 88 mV/dec and a drain-induced barrier lowering (DIBL) of 65 mV/V, while the short-channel (160 nm) device exhibited a VT of 0.1 V, a SS of 127 mV/dec and a DIBL of 218 mV/V. Overall, the tri-gate InGaAs-OI JLFETs showed the best compromise in terms of VT, SS and DIBL compared to the other III-V JLFET architectures reported to date. However, a 15× increase in access resistance was observed after H2/Ar anneal, significantly degrading the maximum drain current of the tri-gate InGaAs-OI JLFETs.

  15. Utilizing self-assembled-monolayer-based gate dielectrics to fabricate molybdenum disulfide field-effect transistors

    NASA Astrophysics Data System (ADS)

    Kawanago, Takamasa; Oda, Shunri

    2016-01-01

    In this study, we apply self-assembled-monolayer (SAM)-based gate dielectrics to the fabrication of molybdenum disulfide (MoS2) field-effect transistors. A simple fabrication process involving the selective formation of a SAM on metal oxides in conjunction with the dry transfer of MoS2 flakes was established. A subthreshold slope (SS) of 69 mV/dec and no hysteresis were demonstrated with the ultrathin SAM-based gate dielectrics accompanied by a low gate leakage current. The small SS and no hysteresis indicate the superior interfacial properties of the MoS2/SAM structure. Cross-sectional transmission electron microscopy revealed a sharp and abrupt interface of the MoS2/SAM structure. The SAM-based gate dielectrics are found to be applicable to the fabrication of low-voltage MoS2 field-effect transistors and can also be extended to various layered semiconductor materials. This study opens up intriguing possibilities of SAM-based gate dielectrics in functional electronic devices.

  16. Square dielectric THz waveguides.

    PubMed

    Aflakian, N; Yang, N; LaFave, T; Henderson, R M; O, K K; MacFarlane, D L

    2016-06-27

    A holey cladding dielectric waveguide with square cross section is designed, simulated, fabricated and characterized. The TOPAS waveguide is designed to be single mode across the broad frequency range of 180 GHz to 360 GHz as shown by finite-difference time domain simulation and to robustly support simultaneous TE and TM mode propagation. The square fiber geometry is realized by pulling through a heat distribution made square by appropriate furnace design. The transmitted mode profile is imaged using a vector network analyzer with a pinhole at the receiver module. Good agreement between the measured mode distribution and the calculated mode distribution is demonstrated. PMID:27410645

  17. Low Dielectric Polymers

    NASA Technical Reports Server (NTRS)

    Cassidy, Patrick E.

    2002-01-01

    This report summarizes results obtained through our current research effort entitled 'Low Dielectric Polymers'. Results are reported in four areas: (1) Development of an alkyne containing a crosslinking agent for 12F-PEK and its analogues; (2) Preparation and evaluation of new silicon- and/or fluorine-containing polymers for low temperature applications; (3) Polymers derived from a new highly fluorinated monomer; and (4) Continued evaluation of the scale-up of the preparation of 6FC11- and 6FC17-PEKs.

  18. Low Dielectric Polymers

    NASA Technical Reports Server (NTRS)

    Venumbaka, Sreenivasulu R.; Cassidy, Patrick E.

    2002-01-01

    This report summarizes results obtained from research funded through Research Cooperative Agreement No. NCC-1-01033-"Low Dielectric Polymers" (from 5/10/01 through 5/09/02). Results are reported in three of the proposed research areas (Tasks 1-3 in the original proposal): (1) Repeat and confirm the preparation and properties of the new alkyl-substituted PEK, 6HC17-PEK, (2) Prepare and evaluate polymers derived from a highly fluorinated monomer, and (3) Prepare and evaluate new silicon and/or fluorine-containing polymers expected to retain useful properties at low temperature.

  19. Dielectric Properties Of Nanoferrites

    SciTech Connect

    Jankov, Stevan B.; Cvejic, Zeljka N.; Rakic, Srdjan; Srdic, Vladimir

    2007-04-23

    Dielectric properties: permittivity, loss factor, tan delta and ionic conductivity of nanostructured ferrites have been measured. Samples used were nickel, zinc and yttrium doped ferrites mixed in various ratios. The synthesis has been performed using precipitation method and obtained powders were pressed in pellets under varying pressure. X-ray diffractography approach for the refinement of structure and microstructural analysis has been performed. All parameters have been measured in 1 Hz to 100 kHz frequency range and 30 deg. C to 80 deg. C temperature range. Significant improvements in permittivity, loss factor and ionic conductivity comparing to bulk samples have been observed.

  20. Synthesis and Characterization of Zirconium Tungstate Ultra-Thin Fibers

    SciTech Connect

    Zhang, Lifeng; Howe, Jane Y; Fong, Hao; Zhang, Yan

    2009-01-01

    This study reports an innovative method of electrospinning followed by pyrolysis to synthesize zirconium tungstate (ZrW2O8), a material with negative coefficient of thermal expansion (CTE), in ultra-thin fiber form. Morphologies and microstructures of the as-electrospun precursor fibers, the heat-treated intermediate fibers, and the final ZrW2O8 ultra-thin fibers were characterized by SEM, XRD, and TEM. The ZrW2O8 ultra-thin fibers had diameters in the sub-micrometer range with aspect ratios larger than 100; these fibers were polycrystalline, and consisted of single crystalline ZrW2O8 crystallites with sizes of 30-50 nm and surface roughness of several nanometers. The ZrW2O8 ultra-thin fibers are expected to outperform spherically, cylindrically, and/or irregularly shaped polycrystalline ZrW2O8 particles for the development of composites with precisely controlled CTEs. Additionally, this reported method could be utilized as a general approach to convert nano-scaled inorganic particles into fibers.

  1. Ultra-Thin Coatings Beautify Art

    NASA Technical Reports Server (NTRS)

    2013-01-01

    The craftsmen in the Roman Empire who constructed the Lycurgus Cup 17 centuries ago probably didn't think their artifact would survive for nearly 2,000 years as a prized possession. And they certainly couldn't have known that the technology they used to make it would eventually become an important part of space exploration. Carved from one solid mass, the cup is one of the few complete glass objects from that period, and the only one made from dichroic glass. Meaning "two-colored" in Greek, dichroic glass was originally created by adding trace amounts of gold and silver to a large volume of glass melt. The resulting medium partially reflects the light passing through it, causing an observer to see different colors depending on the direction of the light source. The Lycurgus Cup, for example, is famous for appearing green in daylight and red when lit at night, symbolic of the ripening grapes used to fill it with wine. NASA revitalized the production of dichroic glass in the 1950s and 1960s as a means of protecting its astronauts. Ordinary clear substances cannot protect human vision from the harsh rays of unfiltered sunlight, and everything from the human body to spacecraft sensors and computers are at risk if left unprotected from the radiation that permeates space. The microscopic amounts of metal present in dichroic glass make it an effective barrier against such harmful radiation. While the ancient manufacturing technique called for adding metals to glass melt, NASA developed a process in which metals are vaporized by electron beams in a vacuum chamber and then applied directly to surfaces in an ultra-thin film. The vapor condenses in the form of crystal structures, and the process is repeated for up to several dozen coatings. The resulting material, still only about 30 millionths of an inch thick, is sufficient to reflect radiation even while the glass, or polycarbonate, as in the case of space suit helmets, remains transparent to the human eye.

  2. Anisotropic effective permittivity of an ultrathin gold coating on optical fiber in air, water and saline solutions.

    PubMed

    Zhou, Wenjun; Mandia, David J; Barry, Seán T; Albert, Jacques

    2014-12-29

    The optical properties of an ultrathin discontinuous gold film in different dielectric surroundings are investigated experimentally by measuring the polarization-dependent wavelength shifts and amplitudes of the cladding mode resonances of a tilted fiber Bragg grating. The gold film was prepared by electron-beam evaporation and had an average thickness of 5.5 nm ( ± 1 nm). Scanning electron imaging was used to determine that the film is actually formed of individual particles with average lateral dimensions of 28 nm ( ± 8 nm). The complex refractive indices of the equivalent uniform film in air at a wavelength of 1570 nm were calculated from the measurements to be 4.84-i0.74 and 3.97-i0.85 for TM and TE polarizations respectively (compared to the value for bulk gold: 0.54-i10.9). Additionally, changes in the birefringence and dichroism of the films were measured as a function of the surrounding medium, in air, water and a saturated NaCl (salt) solution. These results show that the film has stronger dielectric behavior for TM light than for TE, a trend that increases with increasing surrounding index. Finally, the experimental results are compared to predictions from two widely used effective medium approximations, the generalized Maxwell-Garnett and Bruggeman theories for gold particles in a surrounding matrix. It is found that both of these methods fail to predict the observed behavior for the film considered. PMID:25607137

  3. Reversible optical switching of highly confined phonon-polaritons with an ultrathin phase-change material.

    PubMed

    Li, Peining; Yang, Xiaosheng; Maß, Tobias W W; Hanss, Julian; Lewin, Martin; Michel, Ann-Katrin U; Wuttig, Matthias; Taubner, Thomas

    2016-08-01

    Surface phonon-polaritons (SPhPs), collective excitations of photons coupled with phonons in polar crystals, enable strong light-matter interaction and numerous infrared nanophotonic applications. However, as the lattice vibrations are determined by the crystal structure, the dynamical control of SPhPs remains challenging. Here, we realize the all-optical, non-volatile, and reversible switching of SPhPs by controlling the structural phase of a phase-change material (PCM) employed as a switchable dielectric environment. We experimentally demonstrate optical switching of an ultrathin PCM film (down to 7 nm, <λ/1,200) with single laser pulses and detect ultra-confined SPhPs (polariton wavevector kp > 70k0, k0 = 2π/λ) in quartz. Our proof of concept allows the preparation of all-dielectric, rewritable SPhP resonators without the need for complex fabrication methods. With optimized materials and parallelized optical addressing we foresee application potential for switchable infrared nanophotonic elements, for example, imaging elements such as superlenses and hyperlenses, as well as reconfigurable metasurfaces and sensors. PMID:27213955

  4. Voltage sensor and dielectric material

    DOEpatents

    Yakymyshyn, Christopher Paul; Yakymyshyn, Pamela Jane; Brubaker, Michael Allen

    2006-10-17

    A voltage sensor is described that consists of an arrangement of impedance elements. The sensor is optimized to provide an output ratio that is substantially immune to changes in voltage, temperature variations or aging. Also disclosed is a material with a large and stable dielectric constant. The dielectric constant can be tailored to vary with position or direction in the material.

  5. Microwave Propagation in Dielectric Fluids.

    ERIC Educational Resources Information Center

    Lonc, W. P.

    1980-01-01

    Describes an undergraduate experiment designed to verify quantitatively the effect of a dielectric fluid's dielectric constant on the observed wavelength of microwave radiation propagating through the fluid. The fluid used is castor oil, and results agree with the expected behavior within 5 percent. (Author/CS)

  6. Ferroelectric-dielectric tunable composites

    NASA Astrophysics Data System (ADS)

    Sherman, Vladimir O.; Tagantsev, Alexander K.; Setter, Nava; Iddles, David; Price, Tim

    2006-04-01

    The dielectric response of ferroelectric-dielectric composites is theoretically addressed. Dielectric permittivity, tunability (relative change of the permittivity driven by dc electric field), and loss tangent are evaluated for various composite models. The analytical results for small dielectric concentration and relative tunability are obtained in terms of the traditional electrostatic consideration. The results for large tunability are obtained numerically. A method is proposed for the evaluation of the tunability and loss at large concentrations of the dielectric. The basic idea of the method is to reformulate the effective medium approach in terms of electrical energies stored and dissipated in the composite. The important practical conclusion of the paper is that, for random ferroelectric-dielectric composite, the addition of small amounts of a linear dielectric into the tunable ferroelectric results in an increase of the tunability of the mixture. The loss tangent of such composites is shown to be virtually unaffected by the addition of moderate amounts of the low-loss dielectric. The experimental data for (Ba,Sr)TiO3 based composites are analyzed in terms of the theory developed and shown to be in a reasonable agreement with the theoretical results.

  7. Low dielectric polyimide fibers

    NASA Technical Reports Server (NTRS)

    Dorogy, William E., Jr. (Inventor); St.clair, Anne K. (Inventor)

    1994-01-01

    A high temperature resistant polyimide fiber that has a dielectric constant of less than 3 is presented. The fiber was prepared by first reacting 2,2-bis (4-(4aminophenoxy)phenyl) hexafluoropropane with 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride in an aprotic solvent to form a polyamic acid resin solution. The polyamic acid resin solution is then extruded into a coagulation medium to form polyamic acid fibers. The fibers are thermally cured to their polyimide form. Alternatively, 2,2-bis(4-(4-aminophenoxy)phenyl) hexafluoropropane is reacted with 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride to form a polyamic acid, and the polyamic acid is chemically converted to its polyimide form. The polyimide is then dissolved in a solvent to form a polyimide resin solution, and the polyimide resin is extruded into a coagulation medium to form a polyimide wet gel filament. In order to obtain polyimide fibers of increased tensile properties, the polyimide wet gel filaments are stretched at elevated temperatures. The tensile properties of the fibers were measured and found to be in the range of standard textile fibers. Polyimide fibers obtained by either method will have a dielectric constant similar to that of the corresponding polymer, viz., less than 3 at 10 GHz.

  8. Plasmonics without negative dielectrics

    NASA Astrophysics Data System (ADS)

    Della Giovampaola, Cristian; Engheta, Nader

    2016-05-01

    Plasmonic phenomena are exhibited in light-matter interaction involving materials whose real parts of permittivity functions attain negative values at operating wavelengths. However, such materials usually suffer from dissipative losses, thus limiting the performance of plasmon-based optical devices. Here, we utilize an alternative methodology that mimics a variety of plasmonic phenomena by exploiting the well-known structural dispersion of electromagnetic modes in bounded guided-wave structures filled with only materials with positive permittivity. A key issue in the design of such structures is prevention of mode coupling, which can be achieved by implementing thin metallic wires at proper interfaces. This method, which is more suitable for lower frequencies, allows designers to employ conventional dielectrics and highly conductive metals for which the loss is low at these frequencies, while achieving plasmonic features. We demonstrate, numerically and analytically, that this platform can provide surface plasmon polaritons, local plasmonic resonance, plasmonic cloaking, and epsilon-near-zero-based tunneling using conventional positive-dielectric materials.

  9. Dielectric Actuation of Polymers

    NASA Astrophysics Data System (ADS)

    Niu, Xiaofan

    Dielectric polymers are widely used in a plurality of applications, such as electrical insulation, dielectric capacitors, and electromechanical actuators. Dielectric polymers with large strain deformations under an electric field are named dielectric elastomers (DE), because of their relative low modulus, high elongation at break, and outstanding resilience. Dielectric elastomer actuators (DEA) are superior to traditional transducers as a muscle-like technology: large strains, high energy densities, high coupling efficiency, quiet operation, and light weight. One focus of this dissertation is on the design of DE materials with high performance and easy processing. UV radiation curing of reactive species is studied as a generic synthesis methodology to provide a platform for material scientists to customize their own DE materials. Oligomers/monomers, crosslinkers, and other additives are mixed and cured at appropriate ratios to control the stress-strain response, suppress electromechanical instability of the resulting polymers, and provide stable actuation strains larger than 100% and energy densities higher than 1 J/g. The processing is largely simplified in the new material system by removal of the prestretching step. Multilayer stack actuators with 11% linear strain are demonstrated in a procedure fully compatible with industrial production. A multifunctional DE derivative material, bistable electroactive polymer (BSEP), is invented enabling repeatable rigid-to-rigid deformation without bulky external structures. Bistable actuation allows the polymer actuator to have two distinct states that can support external load without device failure. Plasticizers are used to lower the glass transition temperature to 45 °C. Interpenetrating polymer network structure is established inside the BSEP to suppress electromechanical instability, providing a breakdown field of 194 MV/m and a stable bistable strain as large as 228% with a 97% strain fixity. The application of BSEP

  10. Fabrication of air-stable n-type carbon nanotube thin-film transistors on flexible substrates using bilayer dielectrics

    NASA Astrophysics Data System (ADS)

    Li, Guanhong; Li, Qunqing; Jin, Yuanhao; Zhao, Yudan; Xiao, Xiaoyang; Jiang, Kaili; Wang, Jiaping; Fan, Shoushan

    2015-10-01

    Single-walled carbon nanotube (SWNT) thin-film transistors hold great potential for flexible electronics. However, fabrication of air-stable n-type devices by methods compatible with standard photolithography on flexible substrates is challenging. Here, we demonstrated that by using a bilayer dielectric structure of MgO and atomic layer deposited (ALD) Al2O3 or HfO2, air-stable n-type devices can be obtained. The mechanism for conduction type conversion was elucidated and attributed to the hole depletion in SWNT, the decrease of the trap state density by MgO assimilating adsorbed water molecules in the vicinity of SWNT, and the energy band bending because of the positive fixed charges in the ALD layer. The key advantage of the method is the relatively low temperature (120 or 90 °C) required here for the ALD process because we need not employ this step to totally remove the absorbates on the SWNTs. This advantage facilitates the integration of both p-type and n-type transistors through a simple lift off process and compact CMOS inverters were demonstrated. We also demonstrated that the doping of SWNTs in the channel plays a more important role than the Schottky barriers at the metal contacts in carbon nanotube thin-film transistors, unlike the situation in individual SWNT-based transistors.Single-walled carbon nanotube (SWNT) thin-film transistors hold great potential for flexible electronics. However, fabrication of air-stable n-type devices by methods compatible with standard photolithography on flexible substrates is challenging. Here, we demonstrated that by using a bilayer dielectric structure of MgO and atomic layer deposited (ALD) Al2O3 or HfO2, air-stable n-type devices can be obtained. The mechanism for conduction type conversion was elucidated and attributed to the hole depletion in SWNT, the decrease of the trap state density by MgO assimilating adsorbed water molecules in the vicinity of SWNT, and the energy band bending because of the positive fixed

  11. All-nanosheet ultrathin capacitors assembled layer-by-layer via solution-based processes.

    PubMed

    Wang, Chengxiang; Osada, Minoru; Ebina, Yasuo; Li, Bao-Wen; Akatsuka, Kosho; Fukuda, Katsutoshi; Sugimoto, Wataru; Ma, Renzhi; Sasaki, Takayoshi

    2014-03-25

    All-nanosheet ultrathin capacitors of Ru0.95O20.2-/Ca2Nb3O10-/Ru0.95O20.2- were successfully assembled through facile room-temperature solution-based processes. As a bottom electrode, conductive Ru0.95O20.2- nanosheets were first assembled on a quartz glass substrate through a sequential adsorption process with polycations. On top of the Ru0.95O20.2- nanosheet film, Ca2Nb3O10- nanosheets were deposited by the Langmuir-Blodgett technique to serve as a dielectric layer. Deposition parameters were optimized for each process to construct a densely packed multilayer structure. The multilayer buildup process was monitored by various characterizations such as atomic force microscopy (AFM), ultraviolet-visible absorption spectra, and X-ray diffraction data, which provided compelling evidence for regular growth of Ru0.95O20.2- and Ca2Nb3O10- nanosheet films with the designed multilayer structures. Finally, an array of circular films (50 μm ϕ) of Ru0.95O20.2- nanosheets was fabricated as top electrodes on the as-deposited nanosheet films by combining the standard photolithography and sequential adsorption processes. Microscopic observations by AFM and cross-sectional transmission electron microscopy, as well as nanoscopic elemental analysis, visualized the sandwich metal-insulator-metal structure of Ru0.95O20.2-/Ca2Nb3O10-/Ru0.95O20.2- with a total thickness less than 30 nm. Electrical measurements indicate that the system really works as an ultrathin capacitor, achieving a capacitance density of ∼27.5 μF cm(-2), which is far superior to currently available commercial capacitor devices. This work demonstrates the great potential of functional oxide nanosheets as components for nanoelectronics, thus contributing to the development of next-generation high-performance electronic devices.

  12. The Dielectric Wall Accelerator

    SciTech Connect

    Caporaso, George J.; Chen, Yu-Jiuan; Sampayan, Stephen E.

    2009-01-01

    The Dielectric Wall Accelerator (DWA), a class of induction accelerators, employs a novel insulating beam tube to impress a longitudinal electric field on a bunch of charged particles. The surface flashover characteristics of this tube may permit the attainment of accelerating gradients on the order of 100 MV/m for accelerating pulses on the order of a nanosecond in duration. A virtual traveling wave of excitation along the tube is produced at any desired speed by controlling the timing of pulse generating modules that supply a tangential electric field to the tube wall. Because of the ability to control the speed of this virtual wave, the accelerator is capable of handling any charge to mass ratio particle; hence it can be used for electrons, protons and any ion. The accelerator architectures, key technologies and development challenges will be described.

  13. Multilayer optical dielectric coating

    DOEpatents

    Emmett, John L.

    1990-01-01

    A highly damage resistant, multilayer, optical reflective coating includes alternating layers of doped and undoped dielectric material. The doping levels are low enough that there are no distinct interfaces between the doped and undoped layers so that the coating has properties nearly identical to the undoped material. The coating is fabricated at high temperature with plasma-assisted chemical vapor deposition techniques to eliminate defects, reduce energy-absorption sites, and maintain proper chemical stoichiometry. A number of differently-doped layer pairs, each layer having a thickness equal to one-quarter of a predetermined wavelength in the material are combined to form a narrowband reflective coating for a predetermined wavelength. Broadband reflectors are made by using a number of narrowband reflectors, each covering a portion of the broadband.

  14. Maxwell stress on a small dielectric sphere in a dielectric

    NASA Astrophysics Data System (ADS)

    Datsyuk, Vitaly V.; Pavlyniuk, Oleg R.

    2015-02-01

    Electrically induced normal pressure and tangential stress at the surface of a small dielectric sphere (or cavity) in a dielectric are calculated using the Minkowski, Einstein-Laub, Abraham, and Lorentz forms of the Maxwell stress tensor. Only the Lorentz tensor is in agreement with the following observations: (1) A spherical cavity in a dielectric transforms into a sharp-edge plate perpendicular to the electric field; (2) a liquid drop placed in a medium with a slightly lower refractive index is stretched along the electric field; and (3) there is a torque on a small birefringent sphere. These phenomena cannot be explained by the conventional theory using the Minkowski stress tensor. For example, the Minkowski stress tensor predicts lateral compression of a spherical cavity in a dielectric.

  15. Structural, Dielectric, and Interface Properties of Crystalline Barium Silicate Films on Si(100): A Robust High-κ Material

    NASA Astrophysics Data System (ADS)

    Islam, S.; Hofmann, K. R.; Feldhoff, A.; Pfnür, H.

    2016-05-01

    The quality and crystallinity of ultrathin dielectric layers depend crucially on the details of interface formation and chemical stability. Using a combination of photoelectron (XPS) and electron-energy-loss spectroscopy, low-energy electron-diffraction, and transmission electron microscopy (TEM), we show that crystalline epitaxial layers of Ba2 SiO4 can be grown on Si(100) substrates from evaporated Ba in oxygen background atmosphere at 650 °C . Since the silicate is chemically by far more stable than the oxides of Si and Ba, an atomically sharp interface with no interface oxide is formed, as confirmed by XPS and TEM. However, the interface is rough on the atomic scale. dc and frequency-dependent electrical measurements reveal a relative dielectric constant of 22.8, low hysteresis in C V measurements, and low leakage currents but still fairly high interface trap densities.

  16. Structure-dependent mechanical properties of ultrathin zinc oxide nanowires

    PubMed Central

    2011-01-01

    Mechanical properties of ultrathin zinc oxide (ZnO) nanowires of about 0.7-1.1 nm width and in the unbuckled wurtzite (WZ) phase have been carried out by molecular dynamics simulation. As the width of the nanowire decreases, Young's modulus, stress-strain behavior, and yielding stress all increase. In addition, the yielding strength and Young's modulus of Type III are much lower than the other two types, because Type I and II have prominent edges on the cross-section of the nanowire. Due to the flexibility of the Zn-O bond, the phase transformation from an unbuckled WZ phase to a buckled WZ is observed under the tensile process, and this behavior is reversible. Moreover, one- and two-atom-wide chains can be observed before the ZnO nanowires rupture. These results indicate that the ultrathin nanowire possesses very high malleability. PMID:21711876

  17. Ultrathin flexible memory devices based on organic ferroelectric transistors

    NASA Astrophysics Data System (ADS)

    Sugano, Ryo; Hirai, Yoshinori; Tashiro, Tomoya; Sekine, Tomohito; Fukuda, Kenjiro; Kumaki, Daisuke; Domingues dos Santos, Fabrice; Miyabo, Atsushi; Tokito, Shizuo

    2016-10-01

    Here, we demonstrate ultrathin, flexible nonvolatile memory devices with excellent durability under compressive strain. Ferroelectric-gate field-effect transistors (FeFETs) employing organic semiconductor and polymer ferroelectric layers are fabricated on a 1-µm-thick plastic film substrate. The FeFETs are characterized by measuring their transfer characteristics, programming time, and data retention time. The data retention time is almost unchanged even when a 50% compressive strain is applied to the devices. To clarify the origin of the excellent durability of the devices against compressive strain, an intermediate plane is calculated. From the calculation result, the intermediate plane is placed close to the channel region of the FeFETs. The high flexibility of the ferroelectric polymer and ultrathin device structure contributes to achieving a bending radius of 0.8 µm without the degradation of memory characteristics.

  18. The development of the ultra-thin lithium battery

    NASA Astrophysics Data System (ADS)

    Suzuki, S.; Fujita, H.; Asami, Y.; Homma, F.; Sato, Y.

    An ultrathin (0.5 mm) lithium battery has been developed. The battery has a voltage of 3 V and uses manganese dioxide for the cathode material and metallic lithium for the anode material. The cathode is composed of manganese dioxide as an active material mixed with graphite conductor and polytetrafluoroethylene binder. The mixture is coated using printing technology, with a stainless steel plate serving as both the positive internal current collector and the external terminal. The dimensions of the battery are shown in a line drawing. Its shape is rectangular, 16.5 mm x 34.5 mm which permits a high degree of freedom in the design of electronic equipment. Some of the potential applications of ultrathin lithium batteries include: power sources for IC cards; CMOS SRAM; and bank credit cards.

  19. Magnetoelectric transport and quantum interference effect in ultrathin manganite films

    SciTech Connect

    Wang, Cong; Jin, Kui-juan Gu, Lin; Lu, Hui-bin; Li, Shan-ming; Zhou, Wen-jia; Zhao, Rui-qiang; Guo, Hai-zhong; He, Meng; Yang, Guo-zhen

    2014-04-21

    The magnetoelectric transport behavior with respect to the thicknesses of ultrathin La{sub 0.9}Sr{sub 0.1}MnO{sub 3} films is investigated in detail. The metal-insulator phase transition, which has never been observed in bulk La{sub 0.9}Sr{sub 0.1}MnO{sub 3}, is found in ultrathin films with thicknesses larger than 6 unit cells. Low-temperature resistivity minima appeared in films with thicknesses less than 10 unit cells. This is attributed to the presence of quantum interference effects. These data suggest that the influence of the weak localization becomes much pronounced as the film thickness decreases from 16 to 8 unit cells.

  20. Ultrathin aluminum sample cans for single crystal inelastic neutron scattering

    SciTech Connect

    Stone, Matthew B; Loguillo, Mark; Abernathy, Douglas L

    2011-01-01

    Single crystal inelastic neutron scattering measurements are often performed using a sample environment for controlling sample temperature. One difficulty associated with this is establishing appropriate thermal coupling from the sample to the temperature controlled portion of the sample environment. This is usually accomplished via a sample can which thermally couples the sample environment to the sample can and the sample can to the sample via an exchange gas. Unfortunately, this can will contribute additional background signal to ones measurement. We present here the design of an ultrathin aluminum sample can based upon established technology for producing aluminum beverage cans. This design minimizes parasitic sample can scattering. Neutron scattering measurements comparing a machined sample can to our beverage can design clearly indicate a large reduction in scattering intensity and texture when using the ultrathin sample can design. We also examine the possibility of using standard commercial beverage cans as sample cans.

  1. Ultrathin aluminum sample cans for single crystal inelastic neutron scattering

    NASA Astrophysics Data System (ADS)

    Stone, M. B.; Loguillo, M. J.; Abernathy, D. L.

    2011-05-01

    Single crystal inelastic neutron scattering measurements are often performed using a sample environment for controlling sample temperature. One difficulty associated with this is establishing appropriate thermal coupling from the sample to the temperature controlled portion of the sample environment. This is usually accomplished via a sample can which thermally couples the sample environment to the sample can and the sample can to the sample via an exchange gas. Unfortunately, this can will contribute additional background signal to one's measurement. We present here the design of an ultrathin aluminum sample can based upon established technology for producing aluminum beverage cans. This design minimizes parasitic sample can scattering. Neutron scattering measurements comparing a machined sample can to our beverage can design clearly indicate a large reduction in scattering intensity and texture when using the ultrathin sample can design. We also examine the possibility of using standard commercial beverage cans as sample cans.

  2. A broadband terahertz ultrathin multi-focus lens

    PubMed Central

    He, Jingwen; Ye, Jiasheng; Wang, Xinke; Kan, Qiang; Zhang, Yan

    2016-01-01

    Ultrathin transmission metasurface devices are designed on the basis of the Yang-Gu amplitude-phase retrieval algorithm for focusing the terahertz (THz) radiation into four or nine spots with focal spacing of 2 or 3 mm at a frequency of 0.8 THz. The focal properties are experimentally investigated in detail, and the results agree well with the theoretical expectations. The designed THz multi-focus lens (TMFL) demonstrates a good focusing function over a broad frequency range from 0.3 to 1.1 THz. As a transmission-type device based on metasurface, the diffraction efficiency of the TMFL can be as high as 33.92% at the designed frequency. The imaging function of the TMFL is also demonstrated experimentally and clear images are obtained. The proposed method produces an ultrathin, low-cost, and broadband multi-focus lens for THz-band application PMID:27346430

  3. A broadband terahertz ultrathin multi-focus lens

    NASA Astrophysics Data System (ADS)

    He, Jingwen; Ye, Jiasheng; Wang, Xinke; Kan, Qiang; Zhang, Yan

    2016-06-01

    Ultrathin transmission metasurface devices are designed on the basis of the Yang-Gu amplitude-phase retrieval algorithm for focusing the terahertz (THz) radiation into four or nine spots with focal spacing of 2 or 3 mm at a frequency of 0.8 THz. The focal properties are experimentally investigated in detail, and the results agree well with the theoretical expectations. The designed THz multi-focus lens (TMFL) demonstrates a good focusing function over a broad frequency range from 0.3 to 1.1 THz. As a transmission-type device based on metasurface, the diffraction efficiency of the TMFL can be as high as 33.92% at the designed frequency. The imaging function of the TMFL is also demonstrated experimentally and clear images are obtained. The proposed method produces an ultrathin, low-cost, and broadband multi-focus lens for THz-band application

  4. A broadband terahertz ultrathin multi-focus lens.

    PubMed

    He, Jingwen; Ye, Jiasheng; Wang, Xinke; Kan, Qiang; Zhang, Yan

    2016-01-01

    Ultrathin transmission metasurface devices are designed on the basis of the Yang-Gu amplitude-phase retrieval algorithm for focusing the terahertz (THz) radiation into four or nine spots with focal spacing of 2 or 3 mm at a frequency of 0.8 THz. The focal properties are experimentally investigated in detail, and the results agree well with the theoretical expectations. The designed THz multi-focus lens (TMFL) demonstrates a good focusing function over a broad frequency range from 0.3 to 1.1 THz. As a transmission-type device based on metasurface, the diffraction efficiency of the TMFL can be as high as 33.92% at the designed frequency. The imaging function of the TMFL is also demonstrated experimentally and clear images are obtained. The proposed method produces an ultrathin, low-cost, and broadband multi-focus lens for THz-band application. PMID:27346430

  5. Ultrathin and lightweight organic solar cells with high flexibility

    PubMed Central

    Kaltenbrunner, Martin; White, Matthew S.; Głowacki, Eric D.; Sekitani, Tsuyoshi; Someya, Takao; Sariciftci, Niyazi Serdar; Bauer, Siegfried

    2012-01-01

    Application-specific requirements for future lighting, displays and photovoltaics will include large-area, low-weight and mechanical resilience for dual-purpose uses such as electronic skin, textiles and surface conforming foils. Here we demonstrate polymer-based photovoltaic devices on plastic foil substrates less than 2 μm thick, with equal power conversion efficiency to their glass-based counterparts. They can reversibly withstand extreme mechanical deformation and have unprecedented solar cell-specific weight. Instead of a single bend, we form a random network of folds within the device area. The processing methods are standard, so the same weight and flexibility should be achievable in light emitting diodes, capacitors and transistors to fully realize ultrathin organic electronics. These ultrathin organic solar cells are over ten times thinner, lighter and more flexible than any other solar cell of any technology to date. PMID:22473014

  6. Low temperature CVD growth of ultrathin carbon films

    NASA Astrophysics Data System (ADS)

    Yang, Chao; Wu, Peng; Gan, Wei; Habib, Muhammad; Xu, Weiyu; Fang, Qi; Song, Li

    2016-05-01

    We demonstrate the low temperature, large area growth of ultrathin carbon films by chemical vapor deposition under atmospheric pressure on various substrates. In particularly, uniform and continuous carbon films with the thickness of 2-5 nm were successfully grown at a temperature as low as 500 oC on copper foils, as well as glass substrates coated with a 100 nm thick copper layer. The characterizations revealed that the low-temperature-grown carbon films consist on few short, curved graphene layers and thin amorphous carbon films. Particularly, the low-temperature grown samples exhibited over 90% transmittance at a wavelength range of 400-750 nm and comparable sheet resistance in contrast with the 1000oC-grown one. This low-temperature growth method may offer a facile way to directly prepare visible ultrathin carbon films on various substrate surfaces that are compatible with temperatures (500-600oC) used in several device processing technologies.

  7. Strain-induced water dissociation on supported ultrathin oxide films

    PubMed Central

    Song, Zhenjun; Fan, Jing; Xu, Hu

    2016-01-01

    Controlling the dissociation of single water molecule on an insulating surface plays a crucial role in many catalytic reactions. In this work, we have identified the enhanced chemical reactivity of ultrathin MgO(100) films deposited on Mo(100) substrate that causes water dissociation. We reveal that the ability to split water on insulating surface closely depends on the lattice mismatch between ultrathin films and the underlying substrate, and substrate-induced in-plane tensile strain dramatically results in water dissociation on MgO(100). Three dissociative adsorption configurations of water with lower energy are predicted, and the structural transition going from molecular form to dissociative form is almost barrierless. Our results provide an effective avenue to achieve water dissociation at the single-molecule level and shed light on how to tune the chemical reactions of insulating surfaces by choosing the suitable substrates. PMID:26953105

  8. Room-temperature chiral magnetic skyrmions in ultrathin magnetic nanostructures

    NASA Astrophysics Data System (ADS)

    Boulle, Olivier; Vogel, Jan; Yang, Hongxin; Pizzini, Stefania; de Souza Chaves, Dayane; Locatelli, Andrea; Menteş, Tevfik Onur; Sala, Alessandro; Buda-Prejbeanu, Liliana D.; Klein, Olivier; Belmeguenai, Mohamed; Roussigné, Yves; Stashkevich, Andrey; Chérif, Salim Mourad; Aballe, Lucia; Foerster, Michael; Chshiev, Mairbek; Auffret, Stéphane; Miron, Ioan Mihai; Gaudin, Gilles

    2016-05-01

    Magnetic skyrmions are chiral spin structures with a whirling configuration. Their topological properties, nanometre size and the fact that they can be moved by small current densities have opened a new paradigm for the manipulation of magnetization at the nanoscale. Chiral skyrmion structures have so far been experimentally demonstrated only in bulk materials and in epitaxial ultrathin films, and under an external magnetic field or at low temperature. Here, we report on the observation of stable skyrmions in sputtered ultrathin Pt/Co/MgO nanostructures at room temperature and zero external magnetic field. We use high lateral resolution X-ray magnetic circular dichroism microscopy to image their chiral Néel internal structure, which we explain as due to the large strength of the Dzyaloshinskii–Moriya interaction as revealed by spin wave spectroscopy measurements. Our results are substantiated by micromagnetic simulations and numerical models, which allow the identification of the physical mechanisms governing the size and stability of the skyrmions.

  9. Competing weak localization and weak antilocalization in ultrathin topological insulators.

    PubMed

    Lang, Murong; He, Liang; Kou, Xufeng; Upadhyaya, Pramey; Fan, Yabin; Chu, Hao; Jiang, Ying; Bardarson, Jens H; Jiang, Wanjun; Choi, Eun Sang; Wang, Yong; Yeh, Nai-Chang; Moore, Joel; Wang, Kang L

    2013-01-01

    We demonstrate evidence of a surface gap opening in topological insulator (TI) thin films of (Bi(0.57)Sb(0.43))(2)Te(3) below six quintuple layers through transport and scanning tunneling spectroscopy measurements. By effective tuning the Fermi level via gate-voltage control, we unveil a striking competition between weak localization and weak antilocalization at low magnetic fields in nonmagnetic ultrathin films, possibly owing to the change of the net Berry phase. Furthermore, when the Fermi level is swept into the surface gap of ultrathin samples, the overall unitary behaviors are revealed at higher magnetic fields, which are in contrast to the pure WAL signals obtained in thicker films. Our findings show an exotic phenomenon characterizing the gapped TI surface states and point to the future realization of quantum spin Hall effect and dissipationless TI-based applications.

  10. Electrolytes near structured dielectric interfaces

    NASA Astrophysics Data System (ADS)

    Wu, Huanxin; Jing, Yufei; Solis, Francisco; Olvera de La Cruz, Monica; Luijten, Erik

    2015-03-01

    The ion distribution in an electrolyte near a dielectric interface has important consequences for numerous applications. To date, most studies have focused on planar interfaces, where, e.g., simulations can take advantage of the image-charge method. However, for surfaces that display structure on the nanoscale, dielectric effects may be significantly different. Here, we investigate such interfaces via a combination of computer simulations and Poisson-Boltzmann theory. We demonstrate how, even for systems with piecewise uniform dielectric constant, surface structure affects the induced polarization charge as well as the ion distribution near the interface, in particular for asymmetric salts. We explore the role of ion concentration, dielectric mismatch and characteristic length scale of the surface structure.

  11. Infrared cubic dielectric resonator metamaterial.

    SciTech Connect

    Sinclair, Michael B.; Brener, Igal; Peters, David William; Ginn, James Cleveland, III; Ten Eyck, Gregory A.

    2010-06-01

    Dielectric resonators are an effective means to realize isotropic, low-loss optical metamaterials. As proof of this concept, a cubic resonator is analytically designed and then tested in the long-wave infrared.

  12. Thermo-switchable polymer dielectrics.

    SciTech Connect

    Kholwadwala, Fenil Manish; Johnson, Ross Stefan; Dirk, Shawn M.

    2010-11-01

    We are interested in utilizing the thermo-switchable properties of precursor poly(p-phenylene vinylene) (PPV) polymers to develop capacitor dielectrics that will fail at specific temperatures due to the material irreversibly switching from an insulator to a conducting polymer. By utilizing different leaving groups on the polymer main chain, the temperature at which the polymer transforms into a conductor can be varied over a range of temperatures. Electrical characterization of thin-film capacitors prepared from several precursor PPV polymers indicates that these materials have good dielectric properties until they reach elevated temperatures, at which point conjugation of the polymer backbone effectively disables the device. Here, we present the synthesis, dielectric processing, and electrical characterization of a new thermo-switchable polymer dielectric.

  13. Giant room-temperature elastocaloric effect in ferroelectric ultrathin films.

    PubMed

    Liu, Yang; Infante, Ingrid C; Lou, Xiaojie; Bellaiche, Laurent; Scott, James F; Dkhil, Brahim

    2014-09-17

    Environmentally friendly ultrathin BaTiO3 capacitors can exhibit a giant stress-induced elastocaloric effect without hysteresis loss or Joule heating. By combining this novel elastocaloric effect with the intrinsic electrocaloric effect, an ideal refrigeration cycle with high performance (temperature change over 10 K with a wide working-temperature window of 60 K) at room temperature is proposed for future cooling applications. PMID:25042767

  14. The aftereffect in ultrathin ferromagnetic films with easy perpendicular direction

    NASA Astrophysics Data System (ADS)

    Schmidt, W.

    1992-08-01

    We consider a model of the aftereffect where the walls are detached from pin defects by vibrations. Dependence is obtained between the activation energy on the external field which is used to estimate the distance between defects, the radius of pin cavity and the stability time in a real film. The calculation is restricted to limp domain walls and ultrathin films with easy perpendicular direction. The model is tested to compare experimental data of the coercive force with a calculated value.

  15. Magnetism and surface structure of atomically controlled ultrathin metal films.

    SciTech Connect

    Shiratsuchi, Yu.; Yamamoto, M.; Bader, S. D.; Materials Science Division; Osaka Univ.

    2007-01-01

    We review the correlation of magnetism and surface structure in ultrathin metal films, including the tailoring of novel magnetic properties using atomic scale control of the nanostructure. We provide an overview of modern fabrication and characterization techniques used to create and explore these fascinating materials, and highlight important phenomena of interest. We also discuss techniques that control and characterize both the magnetic and structural properties on an atomic scale. Recent advances in the development and applications of these techniques allow nanomagnetism to be investigated in an unprecedented manner. A system cannot necessarily retain a two-dimensional structure as it enters the ultrathin region, but it can transform into a three-dimensional, discontinuous structure due to the Volmer-Weber growth mechanism. This structural transformation can give rise to superparamagnetism. During this evolution, competing factors such as interparticle interactions and the effective magnetic anisotropy govern the magnetic state. These magnetic parameters are influenced by the nanostructure of the film. In particular, controlling the magnetic anisotropy is critical for determining the magnetic properties. Surface effects play especially important roles in influencing both the magnitude and direction of the magnetic anisotropy in ultrathin films. By properly altering the surface structure, the strength and direction of the magnetic anisotropy are controlled via spin-orbit and/or dipole interactions.

  16. Mechanically Tunable Hollow Silica Ultrathin Nanoshells for Ultrasound Contrast Agents

    PubMed Central

    Liberman, A.; Wang, J.; Lu, N.; Viveros, R.D.; Allen, C. A.; Mattrey, R.F.; Blair, S.L.; Trogler, W.C.; Kim, M. J.; Kummel, A.C.

    2015-01-01

    Perfluoropentane (PFP) gas filled biodegradable iron-doped silica nanoshells have been demonstrated as long-lived ultrasound contrast agents. Nanoshells are synthesized by a sol-gel process with tetramethyl orthosilicate (TMOS) and iron ethoxide. Substituting a fraction of the TMOS with R-substituted trialkoxysilanes produces ultrathin nanoshells with varying shell thicknesses and morphologies composed of fused nanoflakes. The ultrathin nanoshells had continuous ultrasound Doppler imaging lifetimes exceeding 3 hours, were twice as bright using contrast specific imaging, and had decreased pressure thresholds compared to control nanoshells synthesized with just TMOS. Transmission electron microscopy (TEM) showed that the R-group substituted trialkoxysilanes could reduce the mechanically critical nanoshell layer to 1.4 nm. These ultrathin nanoshells have the mechanical behavior of weakly linked nanoflakes but the chemical stability of silica. The synthesis can be adapted for general fabrication of three-dimensional nanostructures composed of nanoflakes, which have thicknesses from 1.4–3.8 nm and diameters from 2–23 nm. PMID:26955300

  17. Extraordinary optical transmission in nanopatterned ultrathin metal films without holes

    DOE PAGES

    Peer, Akshit; Biswas, Rana

    2016-02-01

    In this study, we experimentally and theoretically demonstrate that a continuous gold film on a periodically textured substrate exhibits extraordinary optical transmission, even though no holes were etched in the film. Our film synthesis started by nanoimprinting a periodic array of nanocups with a period of ~750 nm on a polystyrene film over a glass substrate. A thin non-conformal gold film was sputter-deposited on the polystyrene by angle-directed deposition. The gold film was continuous with spatial thickness variation, the film being thinnest at the bottom of the nanocup. Measurements revealed an extraordinary transmission peak at a wavelength just smaller thanmore » the period, with an enhancement of ~2.5 compared to the classically expected value. Scattering matrix simulations model well the transmission and reflectance measurements when an ultrathin gold layer (~5 nm), smaller than the skin depth is retained at the bottom of the nanocups. Electric field intensities are enhanced by >100 within the nanocup, and ~40 in the ultrathin gold layer causing transmission through it. We show a wavelength red-shift of ~30 nm in the extraordinary transmission peak when the nanocups are coated with a thin film of a few nanometers, which can be utilized for biosensing. The continuous corrugated metal films are far simpler structures to observe extraordinary transmission, circumventing the difficult process of etching the metal film. Such continuous metal films with ultrathin regions are simple platforms for non-linear optics, plasmonics, and biological and chemical sensing.« less

  18. Ultrathin Free-Standing Bombyx mori Silk Nanofibril Membranes.

    PubMed

    Ling, Shengjie; Jin, Kai; Kaplan, David L; Buehler, Markus J

    2016-06-01

    We report a new ultrathin filtration membrane prepared from silk nanofibrils (SNFs), directly exfoliated from natural Bombyx mori silk fibers to retain structure and physical properties. These membranes can be prepared with a thickness down to 40 nm with a narrow distribution of pore sizes ranging from 8 to 12 nm. Typically, 40 nm thick membranes prepared from SNFs have pure water fluxes of 13 000 L h(-1) m(-2) bar(-1), more than 1000 times higher than most commercial ultrathin filtration membranes and comparable with the highest water flux reported previously. The commercial membranes are commonly prepared from polysulfone, poly(ether sulfone), and polyamide. The SNF-based ultrathin membranes exhibit efficient separation for dyes, proteins, and colloids of nanoparticles with at least a 64% rejection of Rhodamine B. This broad-spectrum filtration membrane would have potential utility in applications such as wastewater treatment, nanotechnology, food industry, and life sciences in part due to the protein-based membrane polymer (silk), combined with the robust mechanical and separation performance features. PMID:27076389

  19. Features of transport in ultrathin gold nanowire structures.

    PubMed

    Pud, Sergii; Kisner, Alexandre; Heggen, Marc; Belaineh, Dagmawi; Temirov, Ruslan; Simon, Ulrich; Offenhäusser, Andreas; Mourzina, Yulia; Vitusevich, Svetlana

    2013-03-25

    The origin of the interface formation appearing due to the realization of contacts to ultrathin gold nanowire devices is revealed. Such interfaces play an important role in transport mechanisms in nanowire structures and can determine the electrical and operating parameters of a nanodevice. Based on experimental results, the specific electrical properties of bundles of ultrathin gold nanowires fabricated by wet chemical synthesis and subsequently assembled and contacted with gold electrodes are reported. It is demonstrated that these properties are strongly affected by the monolayers of organic molecules inevitably present on the surface of the nanowires due to synthetic conditions. In particular, such layers form a potential barrier to tunneling of the electrons from contacts to the nanowires. The electric transport behavior of the investigated nanowire structures in the temperature range from 500 mK to 300 K obeys the model of thermal fluctuation-induced tunneling conduction through the nanowire-metal electrode molecular junction. Application of this model allows calculation of the parameters of the molecular potential barrier. The formation of such a molecular barrier is verified by scanning tunneling microscope (STM) and transmission electron microscope (TEM) measurements performed using a supporting graphene layer. These findings are important for designing novel nanodevices for molecular electronics on the basis of ultrathin nanowires.

  20. Thermal characterization and modeling of ultra-thin silicon chips

    NASA Astrophysics Data System (ADS)

    Alshahed, Muhammad; Yu, Zili; Rempp, Horst; Richter, Harald; Harendt, Christine; Burghartz, Joachim N.

    2015-11-01

    Manufacturing ultra-thin chip is an emerging field in semiconductor technology that is driven by 3-D integrated circuits and flexible electronics. Unlike bulk silicon (Si) chips with thickness greater than 400 μm, the thermal management of ultra-thin Si chips with thickness smaller than 20 μm is challenging due to the increased lateral thermal resistance implying stringent cooling requirements. Therefore, a reasonable prediction of temperature gradients in such chips is necessary. In this work, a thermal chip is implemented in an ultra-thin 0.5 μm CMOS technology to be employed in surface steady-state and transient temperature measurement. Test chips are either packaged in a Pin Grid Array (PGA) ceramic package or attached to a flexible polyimide substrate. The experimental results show an on-chip temperature gradient of ∼15 °C for a dissipated power of 0.4 W in the case of the PGA package and ∼30 °C for the polyimide substrate. The time constants are ∼50 s and ∼1 s for the PGA and the polyimide packages respectively. The measurements are complemented by FEM simulations using ANSYS 14.5 workbench and spice simulations using an equivalent lumped-component thermal circuit model. The lumped-element thermal circuit model is then used for the surface temperature prediction, which is compared to measurement results.

  1. An electrode-free method of characterizing the microwave dielectric properties of high-permittivity thin films

    NASA Astrophysics Data System (ADS)

    Bovtun, V.; Pashkov, V.; Kempa, M.; Kamba, S.; Eremenko, A.; Molchanov, V.; Poplavko, Y.; Yakymenko, Y.; Lee, J. H.; Schlom, D. G.

    2011-01-01

    A thin dielectric resonator consisting of a dielectric substrate and the thin film deposited upon it is shown to suffice for microwave characterization and dielectric parameter measurement of high-permittivity thin films without electrodes. The TE01δ resonance mode was excited and measured in thin (down to 0.1 mm) rectangular- or disk-shaped low-loss dielectric substrates (D ˜10 mm) with permittivity ɛ'≥10 inserted into a cylindrical shielding cavity or rectangular waveguide. The in-plane dielectric permittivity and losses of alumina, DyScO3, SmScO3, and (LaAlO3)0.29(SrAl1/2Ta1/2O3)0.71 (LSAT) substrates were measured from 10 to 18 GHz. The substrate thickness optimal for characterization of the overlying thin film was determined as a function of the substrate permittivity. The high sensitivity and efficiency of the method, i.e., of a thin dielectric resonator to the dielectric parameters of an overlying film, was demonstrated by characterizing ultrathin strained EuTiO3 films. A 22 nm thick EuTiO3 film grown on a (100) LSAT substrate and strained in biaxial compression by 0.9% exhibited an increase in microwave permittivity at low temperatures consistent with it being an incipient ferroelectric; no strain-induced ferroelectric phase transition was seen. In contrast, a 100 nm thick EuTiO3 film grown on a (110) DyScO3 substrate and strained in biaxial tension by 1% showed two peaks as a function of temperature in microwave permittivity and loss. These peaks correspond to a strain-induced ferroelectric phase transition near 250 K and to domain wall motion.

  2. Interconnect Between a Waveguide and a Dielectric Waveguide Comprising an Impedance Matched Dielectric Lens

    NASA Technical Reports Server (NTRS)

    Decrossas, Emmanuel (Inventor); Chattopadhyay, Goutam (Inventor); Chahat, Nacer (Inventor); Tang, Adrian J. (Inventor)

    2016-01-01

    A lens for interconnecting a metallic waveguide with a dielectric waveguide is provided. The lens may be coupled a metallic waveguide and a dielectric waveguide, and minimize a signal loss between the metallic waveguide and the dielectric waveguide.

  3. Dielectric properties of marsh vegetation

    NASA Astrophysics Data System (ADS)

    Kochetkova, Tatiana D.; Suslyaev, Valentin I.; Shcheglova, Anna S.

    2015-10-01

    The present work is devoted to the measurement of the dielectric properties of mosses and lichens in the frequency range from 500 MHz to 18 GHz. Subjects of this research were three species of march vegetation - moss (Dicranum polysetum Michx), groundcedar (Diphasiastrum complanatum (L.) Holub) and lichen (Cladonia stellaris). Samples of vegetation were collected in Tomsk region, Western Siberia, Russia. Complex dielectric permittivity was measured in coaxial section by Agilent Technologies vector network analyzer E8363B. Green samples was measured for some moisture contents from 100% to 3-5 % during a natural drying. The measurements were performed at room temperature, which remained within 21 ÷ 23 ° C. The frequency dependence of the dielectric constant for the three species of marsh vegetation differ markedly. Different parts of the complex permittivity dependency on moisture were fitted by line for all frequency points. Two break point were observed corresponding to the transition of water in the vegetation in various phase states. The complex permittivity spectra of water in the vegetation allow determining the most likely corresponding dielectric model of water in the vegetation by the method of hypothesis testing. It is the Debye's model. Parameters of Debye's model were obtained by numerical methods for all of three states of water. This enables to calculate the dielectric constant of water at any frequency range from 500 MHz to 18 GHz and to find the parameters of the dielectric model of the vegetation.

  4. Dielectric and permeability

    NASA Technical Reports Server (NTRS)

    Cole, K. D.

    1982-01-01

    Using the unabridged Maxwell equations (including vectors D, E and H) new effects in collisionless plasmas are uncovered. In a steady state, it is found that spatially varying energy density of the electric field (E perpendicular) orthogonal to B produces electric current leading, under certain conditions, to the relationship P perpendicular+B(2)/8 pi-epsilon E perpendicular(2)/8 pi = constant, where epsilon is the dielectric constant of the plasma for fields orthogonal to B. In steady state quasi-two-dimensional flows in plasmas, a general relationship between the components of electric field parallel and perpendicular to B is found. These effects are significant in goephysical and astrophysical plasmas. The general conditions for a steady state in collisionless plasma are deduced. With time variations in a plasma, slow compared to ion-gyroperiod, there is a general current, (j*), which includes the well-known polarisation current, given by J*=d/dt (ExM)+(PxB)xB B(-2) where M and P are the magnetization and polarization vectors respectively.

  5. Metal-dielectric interactions

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1979-01-01

    Metal direlectric surface interactions and dielectric films on metal substrates were investigated. Since interfacial interaction depends so heavily on the nature of the surfaces, analytical surface tools such as Auger emission spectroscopy, X-ray photoelectron spectroscopy and field ion microscopy were used to assist in surface and interfacial characterization. The results indicate that with metals contacting certain glasses in the clean state interfacial, bonding produces fractures in the glasses while when a film such as water is present, fractures occur in the metal near the interface. Friction forces were used to measure the interfacial bond strengths. Studies with metals contacting polymers using field ion microscopy revealed that strong bonding forces could develop being between a metal and polymer surface with polymer transferring to the metal surface in various ways depending upon the forces applied to the surface in contact. With the deposition of refractory carbides, silicides and borides onto metal and alloy substrates the presence of oxides at the interface or active gases in the deposition plasma were shown to alter interfacial properties and chemistry. Auger ion depth profile analysis indicated the chemical composition at the interface and this could be related to the mechanical, friction, and wear behavior of the coating.

  6. Dielectric optical invisibility cloaks

    NASA Astrophysics Data System (ADS)

    Blair, J.; Tamma, V. A.; Park, W.; Summers, C. J.

    2010-08-01

    Recently, metamaterial cloaks for the microwave frequency range have been designed using transformative optics design techniques and experimentally demonstrated. The design of these structures requires extreme values of permittivity and permeability within the device, which has been accomplished by the use of resonating metal elements. However, these elements severely limit the operating frequency range of the cloak due to their non-ideal dispersion properties at optical frequencies. In this paper we present designs to implement a simpler demonstration of cloaking, the carpet cloak, in which a curved reflective surface is compressed into a flat reflective surface, effectively shielding objects behind the curve from view with respect to the incoming radiation source. This approach eliminates the need for metallic resonant elements. These structures can now be fabricated using only high index dielectric materials by the use of electron beam lithography and standard cleanroom technologies. The design method, simulation analysis, device fabrication, and near field optical microscopy (NSOM) characterization results are presented for devices designed to operate in the 1400-1600nm wavelength range. Improvements to device performance by the deposition/infiltration of linear, and potentially non-linear optical materials, were investigated.

  7. Studying tantalum-based high-κ dielectrics in terms of capacitance measurements

    NASA Astrophysics Data System (ADS)

    Stojanovska-Georgievska, L.

    2016-08-01

    The trend of rapid development of microelectronics towards nano-miniaturization dictates the inevitable introduction of dielectrics with high permittivity (high-κ dielectrics), as alternative material for replacing SiO2. Therefore, studying these materials in terms of their characteristics, especially in terms of reliability, is of great importance for proper design and manufacture of devices. In this paper, alteration of capacitance in different frequency regimes is used, in order to determine the overall behavior of the material. Samples investigated here are MOS structures containing nanoscale tantalum based dielectrics. Layers of pure Ta2O5, but also Hf and Ti doped tantalum pentoxide, i.e. Ta2O5:Hf and Ta2O5:Ti are studied here. All samples are considered as ultrathin oxide layers with thicknesses less than 15 nm, obtained by radio frequent sputtering on p-type silicon substrate. Measuring capacitive characteristics enables determination of several specific parameters of the structures. The obtained results for capacitance in accumulation, the thickness and time evolution of the interfacial SiO2 layer, values of flatband and threshold voltage, density of oxide charges, interfacial and border states, and reliability properties favor the possibilities for more intensive use of studied materials in new nanoelectronic technologies.

  8. Strain-induced phase variation and dielectric constant enhancement of epitaxial Gd2O3

    NASA Astrophysics Data System (ADS)

    Shekhter, P.; Schwendt, D.; Amouyal, Y.; Wietler, T. F.; Osten, H. J.; Eizenberg, M.

    2016-07-01

    One of the approaches for realizing advanced high k insulators for metal oxide semiconductor field effect transistors based devices is the use of rare earth oxides. When these oxides are deposited as epitaxial thin films, they demonstrate dielectric properties that differ greatly from those that are known for bulk oxides. Using structural and spectroscopic techniques, as well as first-principles calculations, Gd2O3 films deposited on Si (111) and Ge (111) were characterized. It was seen that the same 4 nm thick film, grown simultaneously on Ge and Si, presents an unstrained lattice on Ge while showing a metastable phase on Si. This change from the cubic lattice to the distorted metastable phase is characterized by an increase in the dielectric constant of more than 30% and a change in band gap. The case in study shows that extreme structural changes can occur in ultra-thin epitaxial rare earth oxide films and modify their dielectric properties when the underlying substrate is altered.

  9. Influence of localized surface plasmon resonance and free electrons on the optical properties of ultrathin Au films: a study of the aggregation effect.

    PubMed

    Li, X D; Chen, T P; Liu, Y; Leong, K C

    2014-03-10

    The contributions of localized surface plasmon resonance (LSPR) and Drude (free electrons) absorption to the complex dielectric function of ultrathin Au films were investigated with spectroscopic ellipsometry. When the Au film thickness is thinner than ~10 nm, Au nanoparticles (NPs) are formed as a result of the discontinuity in the films, leading to the emergence of LSPR of Au NPs; and the LSPR exhibits a splitting when the films thinner than ~8 nm, which could be attributed to the near-field coupling of the Au NPs and/or the inhomogeneous polarizations of the Au NPs. On the other hand, the delocalization of electrons in Au NPs due to the aggregation of Au NPs in a thicker film leads to an increase in the free-electron absorption and a suppression of the LSPR. PMID:24663852

  10. Fully printed 3 microns thick dielectric elastomer actuator

    NASA Astrophysics Data System (ADS)

    Poulin, A.; Rosset, S.; Shea, H.

    2016-04-01

    In this work we present a new fabrication technique to print thin dielectric elastomer actuators (DEAs), reducing the driving voltage below 300 V while keeping good actuation performance. With operation voltages in the kV-range, standard DEAs are limited in terms of potential applications. Using thinner membranes is one of the few existing methods to achieve lower operation voltages. Typical DEAs have membranes in the 20-100 μm range, values below which membrane fabrication becomes challenging and the membrane quality and uniformity degrade. Using pad printing we produced thin silicone elastomer membranes, on which we pad-printed compliant electrodes. We then fabricated DEAs by assembling two membranes back to back. We obtain an actuation strain of 7.5% at only 245 V on a 3 μm thick DEA. In order to investigate the stiffening impact of the electrodes we developed a simple DEA model that includes their mechanical properties. We also developed a strain-mapping algorithm based on optical correlation. The simulation results and the strain-mapping measurements confirm that the stiffening impact of the electrodes increases for thinner membranes. Electrodes are an important element that cannot be neglected in the design and optimization of ultra-thin DEAs.

  11. Alternate capacitor dielectric film materials

    SciTech Connect

    Foster, J.C.

    1990-08-01

    New high-temperature, high-energy density, and high-radiation tolerant capacitor applications require the evaluation of alternate dielectric materials. Evaluation work was performed at GE Neutron Devices (GEND) and Sandia National Laboratories (SNL), Albuquerque. US Department of Energy (DOE) requirements for capacitor function and environments are unique, and the representations included in this report do not constitute an endorsement of any material or manufacturer. This report presents data on polymeric dielectric films evaluated to support the design of new high-energy density capacitors. Materials which were evaluated include polycarbonate (two sources), polyphenylene sulfide, polyvinylidene fluoride, polyetherimide (three sources), polyimide (four sources), polyethersulfone, and polyetherether ketone. A polyester was evaluated as the control material since many prior designs utilized this dielectric. The film evaluations were based on dielectric constant and dissipation factor variation as a function of temperature ({minus}55{degree}C to 300{degree}C) as well as dielectric breakdown strength. Additionally, film/foil capacitors in a dry wrap-and-fill configuration were fabricated and tested to determine insulation resistance, breakdown voltage, and radiation hardness. Results are given for all evaluations. 7 refs., 4 figs., 4 tabs.

  12. Crystal and multiple melting behaviors of PCL lamellae in ultrathin films

    NASA Astrophysics Data System (ADS)

    Yu, Xiang; Wang, Na; Lv, Shanshan

    2016-03-01

    In this paper, isothermal crystallization at different temperatures and multiple melting of four molecular weights (MW) PCL ultrathin films were investigated by using Atomic Force Microscopy (AFM). The results showed that: two different crystal structures, Flat-on and Edge-on lamellae, were simultaneously formed in PCL ultrathin films when the Tc lower than 30 °C. During the heating process, Edge-on lamellae was melted firstly. This demonstrated that the multiple melting behavior of PCL in ultrathin films was caused by the two different lamellar structures. With the increase of MW, or with the decrease of Tc, PCL chains in ultrathin films changed from Flat-on to Edge-on, and the controlled factors of growth process in ultrathin films transformed from surface nucleation-limited (NL) to melt diffusion-limited (DL).

  13. High efficiency double-wavelength dielectric metasurface lenses with dichroic birefringent meta-atoms.

    PubMed

    Arbabi, Ehsan; Arbabi, Amir; Kamali, Seyedeh Mahsa; Horie, Yu; Faraon, Andrei

    2016-08-01

    Metasurfaces are ultrathin optical structures that manipulate optical wavefronts. Most metasurface devices which deflect light are designed for operation at a single wavelength, and their function changes as the wavelength is varied. Here we propose and demonstrate a double-wavelength metasurface based on polarization dependent dielectric meta-atoms that control the phases of two orthogonal polarizations independently. Using this platform, we design lenses that focus light at 915 and 780 nm with perpendicular linear polarizations to the same focal distance. Lenses with numerical apertures up to 0.7 and efficiencies from 65% to above 90% are demonstrated. In addition to the high efficiency and numerical aperture, an important feature of this technique is that the two operation wavelengths can be chosen to be arbitrarily close. These characteristics make these lenses especially attractive for fluorescence microscopy applications. PMID:27505810

  14. Mid-infrared hyperbolic metamaterial based on graphene-dielectric multilayers

    NASA Astrophysics Data System (ADS)

    Chang, You-Chia; Kildishev, Alexander V.; Narimanov, Evgenii E.; Liu, Che-Hung; Liu, Chang-Hua; Zhang, Siyuan; Marder, Seth R.; Zhong, Zhaohui; Norris, Theodore B.

    2015-09-01

    Graphene-based hyperbolic metamaterials (HMMs) enable new possibilities that are not attainable with conventional metal-based HMMs, such as tunability of optical properties and the ability to combine with graphene-based photodetection. A graphene HMM is made of alternating graphene-dielectric multilayers, whose properties can be understood with the effective-medium approximation (EMA). The initial experimental realization of this novel metamaterial has been demonstrated with a far-field measurement, and in this paper we investigate the light coupling from free space into a graphene HMM slab with a metallic grating using numerical simulations. We show that light can be efficiently coupled into the high-k guided modes in the HMM slab and be absorbed by the graphene layers, which can be applied to create ultrathin super absorbers.

  15. Capacitive Cells for Dielectric Constant Measurement

    ERIC Educational Resources Information Center

    Aguilar, Horacio Munguía; Maldonado, Rigoberto Franco

    2015-01-01

    A simple capacitive cell for dielectric constant measurement in liquids is presented. As an illustrative application, the cell is used for measuring the degradation of overheated edible oil through the evaluation of their dielectric constant.

  16. USDA/ARS and dielectric properties research

    Technology Transfer Automated Retrieval System (TEKTRAN)

    An overview of the research is presented, including RF dielectric heating for seed treatment, insect control, product conditioning, and moisture and quality sensing applications, equipment used, dielectric properties measurement techniques, broad- frequency- range data obtained, and research results...

  17. Slow DNA transport through nanopores in hafnium oxide membranes.

    PubMed

    Larkin, Joseph; Henley, Robert; Bell, David C; Cohen-Karni, Tzahi; Rosenstein, Jacob K; Wanunu, Meni

    2013-11-26

    We present a study of double- and single-stranded DNA transport through nanopores fabricated in ultrathin (2-7 nm thick) freestanding hafnium oxide (HfO2) membranes. The high chemical stability of ultrathin HfO2 enables long-lived experiments with <2 nm diameter pores that last several hours, in which we observe >50 000 DNA translocations with no detectable pore expansion. Mean DNA velocities are slower than velocities through comparable silicon nitride pores, providing evidence that HfO2 nanopores have favorable physicochemical interactions with nucleic acids that can be leveraged to slow down DNA in a nanopore.

  18. Slow DNA Transport through Nanopores in Hafnium Oxide Membranes

    PubMed Central

    Bell, David C.; Cohen-Karni, Tzahi; Rosenstein, Jacob K.; Wanunu, Meni

    2016-01-01

    We present a study of double- and single-stranded DNA transport through nanopores fabricated in ultrathin (2–7 nm thick) free-standing hafnium oxide (HfO2) membranes. The high chemical stability of ultrathin HfO2 enables long-lived experiments with <2 nm diameter pores that last several hours, in which we observe >50 000 DNA translocations with no detectable pore expansion. Mean DNA velocities are slower than velocities through comparable silicon nitride pores, providing evidence that HfO2 nanopores have favorable physicochemical interactions with nucleic acids that can be leveraged to slow down DNA in a nanopore. PMID:24083444

  19. Ultra-thin Materials from Atomic Layer Deposition for Microbolometers

    NASA Astrophysics Data System (ADS)

    Eigenfeld, Nathan Thomas

    This research focuses on the incorporation of atomic layer deposition (ALD) materials into microbolometer devices for infrared (IR) imaging. Microbolometers are suspended micro-electromechanical (MEMS) devices, which respond electrically to absorbed IR radiation. By minimizing the heat capacity (thermal mass) of these devices, their performance may be substantially improved. Thus, implementing ultra-thin freestanding ALD materials into microbolometer devices will offer a substantial reduction in the overall heat capacity of the device. A novel nanofabrication method is developed to produce robust ultra-thin suspended structures from ALD generated materials including W, Ru and Al2O 3. Unique aspects of ALD such as high conformality offer the ability to create 3-dimensional structures with mechanical reinforcement. Additionally, the ability to tune residual stresses via atomically precise thickness control enables the fabrication of flat suspended structures. Since microbolometer elements are electro-thermally active, the electro-thermal properties of ultra-thin ALD W, Ru and Al2O3 are investigated. Several distinct deviations from bulk electro-thermal properties of resistivity, temperature coefficient of resistance, thermal conductivity and specific heat capacity are identified and interpreted with traditional nanoscale transport modeling and theory. For example, for ALD W, the electrical resistivity is increased by up to 99%, thermal conductivity is reduced by up to 91% and specific heat capacity increased 70% from bulk. Finally, the developed ALD nano-fabrication process and measured ALD material properties are combined to fabricate an industrial level, state-of-the-art microbolometer pixel structure with 1.4X performance improvement. Further microbolomter performance enhancements based on the developed nanofabrication methods and electro-thermal measurements are discussed.

  20. CVD Diamond Dielectric Accelerating Structures

    SciTech Connect

    Schoessow, P.; Kanareykin, A.; Gat, R.

    2009-01-22

    The electrical and mechanical properties of diamond make it an ideal candidate material for use in dielectric accelerating structures: high RF breakdown field, extremely low dielectric losses and the highest available thermoconductive coefficient. Using chemical vapor deposition (CVD) cylindrical diamond structures have been manufactured with dimensions corresponding to fundamental TM{sub 01} mode frequencies in the GHz to THz range. Surface treatments are being developed to reduce the secondary electron emission (SEE) coefficient below unity to reduce the possibility of multipactor. The diamond CVD cylindrical waveguide technology developed here can be applied to a variety of other high frequency, large-signal applications.

  1. Dielectric Properties of Piezoelectric Polyimides

    NASA Technical Reports Server (NTRS)

    Ounaies, Z.; Young, J. A.; Simpson, J. O.; Farmer, B. L.

    1997-01-01

    Molecular modeling and dielectric measurements are being used to identify mechanisms governing piezoelectric behavior in polyimides such as dipole orientation during poling, as well as degree of piezoelectricity achievable. Molecular modeling on polyimides containing pendant, polar nitrile (CN) groups has been completed to determine their remanent polarization. Experimental investigation of their dielectric properties evaluated as a function of temperature and frequency has substantiated numerical predictions. With this information in hand, we are then able to suggest changes in the molecular structures, which will then improve upon the piezoelectric response.

  2. Analysis of rib dielectric waveguides

    NASA Astrophysics Data System (ADS)

    Dagli, N.; Fonstad, C. G.

    1985-04-01

    It is noted in the present analysis of rib dielectric waveguides on the basis of a mode-matching technique that, when the constituent slab guides support only one guided mode, the cutoff condition for the higher-order modes is the same as the result yielded by the effective dielectric constant method. When the rib region is thick enough to support two guided slab modes, however, the cutoff conditions are significantly different. Universal design curves are obtained for this case, and the results obtained are compared with the Marcatili (1974) theory for such structures.

  3. Microwave dielectric properties of biopolymers

    NASA Astrophysics Data System (ADS)

    Bartsch, Carrie M.; Subramanyam, Guru; Grote, James G.; Hopkins, F. Kenneth; Brott, Lawrence L.; Naik, Rajesh R.

    2006-09-01

    A new capacitive test structure is used to characterize biopolymers at microwave frequencies. The new test structure is comprised of a parallel plate capacitor, combined with coplanar waveguide-based input and output feed lines. This allows microwave measurements to be taken easily under an applied DC electric field. The microwave dielectric properties are characterized for two biopolymer thin films: a deoxyribonucleic acid (DNA)-based film and a bovine serum albumin (BSA)-based film. These bio-dielectric thin-films are compared with a standard commercial polymer thin film, poly[Bisphenol A carbonate-co-4,4'(3,3,5-trimethyl cyclohexylidene) diphenol], or amorphous polycarbonate (APC).

  4. Ultra-Thin Veneers Without Tooth Preparation in Extensive Oligodontia.

    PubMed

    Savi, Andrea; Crescini, Aldo; Tinti, Carlo; Manfredi, Maddalena

    2015-01-01

    Dental agenesis is the most commonly encountered dental anomaly in humans. Oligodontia, however, is a rare condition that involves the congenital absence of six or more teeth, excluding the third molars. Treatment of oligodontia requires an interdisciplinary approach. The prosthetic treatment plan should carefully consider esthetic and functional rehabilitation but should take a conservative approach. Adhesive techniques, combined with the new ceramic materials, permit functional and esthetic prosthetic restorations that are more conservative in comparison to those used in the past. Ultrathin occlusal veneers without tooth preparations may represent a good esthetic and conservative approach for oral rehabilitation of patients affected by severe hypodontia.

  5. Ultrathin conformal coating for complex magneto-photonic structures.

    PubMed

    Pascu, Oana; Caicedo, José Manuel; López-García, Martín; Canalejas, Víctor; Blanco, Álvaro; López, Cefe; Arbiol, Jordi; Fontcuberta, Josep; Roig, Anna; Herranz, Gervasi

    2011-11-01

    We report on an extremely fast and versatile synthetic approach, based on microwave assisted sol-gel chemistry, that allows a conformal nanometric coating of intricate three-dimensional structures. Using this methodology, we have achieved a conformal coverage of large areas of three-dimensional opals with a superparamagnetic manganese ferrite layer, yielding magneto-photonic crystals with excellent quality. The use of a ternary oxide for the ultrathin coating demonstrates the potential of this methodology to realize three-dimensional structures with complex materials that may find applications beyond photonics, such as energy, sensing or catalysis. PMID:21987109

  6. Design of an ultra-thin dual band infrared system

    NASA Astrophysics Data System (ADS)

    Du, Ke; Cheng, Xuemin; Lv, Qichao; Hu, YiFei

    2014-11-01

    The ultra-thin imaging system using reflective multiple-fold structure has smaller volume and less weight while maintaining high resolution compared with conventional optical systems. The multi-folded approach can significantly extend focal distance within wide spectral range without incurring chromatic aberrations. In this paper, we present a dual infrared imaging system of four-folded reflection with two air-spaced concentric reflective surfaces. The dual brand IR system has 107mm effective focal length, 0.7NA, +/-4° FOV, and 50mm effective aperture with 80mm outer diameter into a 25mm total thickness, which spectral response is 3~12μm.

  7. Helical Growth of Ultrathin Gold-Copper Nanowires.

    PubMed

    Mendoza-Cruz, Rubén; Bazán-Díaz, Lourdes; Velázquez-Salazar, J Jesús; Plascencia-Villa, Germán; Bahena-Uribe, Daniel; Reyes-Gasga, José; Romeu, David; Guisbiers, Grégory; Herrera-Becerra, Raúl; José-Yacamán, Miguel

    2016-03-01

    In this work, we report the synthesis and detailed structural characterization of novel helical gold-copper nanowires. The nanowires possess the Boerdijk-Coxeter-Bernal structure, based on the pile up of octahedral, icosahedral, and/or decahedral seeds. They are self-assembled into a coiled manner as individual wires or into a parallel-ordering way as groups of wires. The helical nanowires are ultrathin with a diameter of less than 10 nm and variable length of several micrometers, presenting a high density of twin boundaries and stacking faults. To the best of our knowledge, such gold-copper nanowires have never been reported previously. PMID:26849249

  8. Real-Time Deposition Monitor for Ultrathin Conductive Films

    NASA Technical Reports Server (NTRS)

    Hines, Jacqueline

    2011-01-01

    A device has been developed that can be used for the real-time monitoring of ultrathin (2 or more) conductive films. The device responds in less than two microseconds, and can be used to monitor film depositions up to about 60 thick. Actual thickness monitoring capability will vary based on properties of the film being deposited. This is a single-use device, which, due to the very low device cost, can be disposable. Conventional quartz/crystal microbalance devices have proven inadequate to monitor the thickness of Pd films during deposition of ultrathin films for hydrogen sensor devices. When the deposited film is less than 100 , the QCM measurements are inadequate to allow monitoring of the ultrathin films being developed. Thus, an improved, high-sensitivity, real-time deposition monitor was needed to continue Pd film deposition development. The new deposition monitor utilizes a surface acoustic wave (SAW) device in a differential delay-line configuration to produce both a reference response and a response for the portion of the device on which the film is being deposited. Both responses are monitored simultaneously during deposition. The reference response remains unchanged, while the attenuation of the sensing path (where the film is being deposited) varies as the film thickness increases. This device utilizes the fact that on high-coupling piezoelectric substrates, the attenuation of an SAW undergoes a transition from low to very high, and back to low as the conductivity of a film on the device surface goes from nonconductive to highly conductive. Thus, the sensing path response starts with a low insertion loss, and as a conductive film is deposited, the film conductivity increases, causing the device insertion loss to increase dramatically (by up to 80 dB or more), and then with continued film thickness increases (and the corresponding conductivity increases), the device insertion loss goes back down to the low level at which it started. This provides a

  9. Multicolor 4D Fluorescence Microscopy using Ultrathin Bessel Light Sheets.

    PubMed

    Zhao, Teng; Lau, Sze Cheung; Wang, Ying; Su, Yumian; Wang, Hao; Cheng, Aifang; Herrup, Karl; Ip, Nancy Y; Du, Shengwang; Loy, M M T

    2016-01-01

    We demonstrate a simple and efficient method for producing ultrathin Bessel ('non-diffracting') light sheets of any color using a line-shaped beam and an annulus filter. With this robust and cost-effective technology, we obtained two-color, 3D images of biological samples with lateral/axial resolution of 250 nm/400 nm, and high-speed, 4D volume imaging of 20 μm sized live sample at 1 Hz temporal resolution. PMID:27189786

  10. Metal Adatoms and Clusters on Ultrathin Zirconia Films

    PubMed Central

    2016-01-01

    Nucleation and growth of transition metals on zirconia has been studied by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. Since STM requires electrical conductivity, ultrathin ZrO2 films grown by oxidation of Pt3Zr(0001) and Pd3Zr(0001) were used as model systems. DFT studies were performed for single metal adatoms on supported ZrO2 films as well as the (1̅11) surface of monoclinic ZrO2. STM shows decreasing cluster size, indicative of increasing metal–oxide interaction, in the sequence Ag < Pd ≈ Au < Ni ≈ Fe. Ag and Pd nucleate mostly at steps and domain boundaries of ZrO2/Pt3Zr(0001) and form three-dimensional clusters. Deposition of low coverages of Ni and Fe at room temperature leads to a high density of few-atom clusters on the oxide terraces. Weak bonding of Ag to the oxide is demonstrated by removing Ag clusters with the STM tip. DFT calculations for single adatoms show that the metal–oxide interaction strength increases in the sequence Ag < Au < Pd < Ni on monoclinic ZrO2, and Ag ≈ Au < Pd < Ni on the supported ultrathin ZrO2 film. With the exception of Au, metal nucleation and growth on ultrathin zirconia films follow the usual rules: More reactive (more electropositive) metals result in a higher cluster density and wet the surface more strongly than more noble metals. These bind mainly to the oxygen anions of the oxide. Au is an exception because it can bind strongly to the Zr cations. Au diffusion may be impeded by changing its charge state between −1 and +1. We discuss differences between the supported ultrathin zirconia films and the surfaces of bulk ZrO2, such as the possibility of charge transfer to the substrate of the films. Due to their large in-plane lattice constant and the variety of adsorption sites, ZrO2{111} surfaces are more reactive than many other oxygen-terminated oxide surfaces. PMID:27213024

  11. Multicolor 4D Fluorescence Microscopy using Ultrathin Bessel Light Sheets

    PubMed Central

    Zhao, Teng; Lau, Sze Cheung; Wang, Ying; Su, Yumian; Wang, Hao; Cheng, Aifang; Herrup, Karl; Ip, Nancy Y.; Du, Shengwang; Loy, M. M. T.

    2016-01-01

    We demonstrate a simple and efficient method for producing ultrathin Bessel (‘non-diffracting’) light sheets of any color using a line-shaped beam and an annulus filter. With this robust and cost-effective technology, we obtained two-color, 3D images of biological samples with lateral/axial resolution of 250 nm/400 nm, and high-speed, 4D volume imaging of 20 μm sized live sample at 1 Hz temporal resolution. PMID:27189786

  12. Ultra-Thin Veneers Without Tooth Preparation in Extensive Oligodontia.

    PubMed

    Savi, Andrea; Crescini, Aldo; Tinti, Carlo; Manfredi, Maddalena

    2015-01-01

    Dental agenesis is the most commonly encountered dental anomaly in humans. Oligodontia, however, is a rare condition that involves the congenital absence of six or more teeth, excluding the third molars. Treatment of oligodontia requires an interdisciplinary approach. The prosthetic treatment plan should carefully consider esthetic and functional rehabilitation but should take a conservative approach. Adhesive techniques, combined with the new ceramic materials, permit functional and esthetic prosthetic restorations that are more conservative in comparison to those used in the past. Ultrathin occlusal veneers without tooth preparations may represent a good esthetic and conservative approach for oral rehabilitation of patients affected by severe hypodontia. PMID:26509995

  13. Hand Allograft Saved by an Ultrathin Groin Flap

    PubMed Central

    Château, Joseph; Gazarian, Aram; Boucher, Fabien; Badet, Lionel; Braye, Fabienne; Saint-Cyr, Michel

    2016-01-01

    Summary: We report a case of a young double-hand allotransplant patient who presented with a full-thickness skin necrosis of the dorsum of the left hand after vascular compromise of the allotransplantation. Considering the lack of viable dorsal tissue overlying the extensor tendons and the need for early hand rehabilitation, an ultrathin pedicled groin flap was used for the coverage. This procedure resulted in salvaging the allotransplantation, and the patient was able to successfully return to work after his surgery. To our knowledge, this is the only case of an upper extremity allotransplant salvaged by a pedicled flap. PMID:27757334

  14. Dielectric barrier discharges applied for optical spectrometry

    NASA Astrophysics Data System (ADS)

    Brandt, S.; Schütz, A.; Klute, F. D.; Kratzer, J.; Franzke, J.

    2016-09-01

    The present review reflects the importance of dielectric barrier discharges for optical spectrometric detection in analytical chemistry. In contrast to usual discharges with a direct current the electrodes are separated by at least one dielectric barrier. There are two main features of the dielectric barrier discharges: they can serve as dissociation and excitation devices as well as ionization sources, respectively. This article portrays various application fields of dielectric barrier discharges in analytical chemistry used for elemental and molecular detection with optical spectrometry.

  15. Dielectric material degradation monitoring of dielectric barrier discharge plasma actuators

    NASA Astrophysics Data System (ADS)

    Hanson, Ronald E.; Houser, Nicole M.; Lavoie, Philippe

    2014-01-01

    It is a known phenomenon that some dielectric materials used to construct plasma actuators degrade during operation. However, the rate at which this process occurs, to what extent, as well as a method to monitor is yet to be established. In this experimental study, it is shown that electrical measurements can be used to monitor changes in the material of the plasma actuators. The procedure we introduce for monitoring the actuators follows from the work of Kriegseis, Grundmann, and Tropea [Kriegseis et al., J. Appl. Phys. 110, 013305 (2011)], who used Lissajous figures to measure actuator power consumption and capacitance. In the present study, we quantify changes in both the power consumption and capacitance of the actuators over long operating durations. It is shown that the increase in the effective capacitance of the actuator is related to degradation (thinning) of the dielectric layer, which is accompanied by an increase in actuator power consumption. For actuators constructed from layers of Kapton® polyimide tape, these changes are self-limiting. Although the polyimide film degrades relatively quickly, the underlying adhesive layer appears to remain intact. Over time, the effective capacitance was found to increase by up to 36%, 25%, and 11% for actuators constructed with 2, 3, and 4 layers of Kapton tape, respectively. A method is presented to prevent erosion of the Kapton dielectric layer using a coating of Polydimethylsiloxane oil. It is shown the application of this treatment can delay the onset of degradation of the Kapton dielectric material.

  16. Cellulose Triacetate Dielectric Films For Capacitors

    NASA Technical Reports Server (NTRS)

    Yen, Shiao-Ping S.; Jow, T. Richard

    1994-01-01

    Cellulose triacetate investigated for use as dielectric material in high-energy-density capacitors for pulsed-electrical-power systems. Films of cellulose triacetate metalized on one or both sides for use as substrates for electrodes and/or as dielectrics between electrodes in capacitors. Used without metalization as simple dielectric films. Advantages include high breakdown strength and self-healing capability.

  17. Flexible metamaterial narrow-band-pass filter based on magnetic resonance coupling between ultra-thin bilayer frequency selective surfaces

    NASA Astrophysics Data System (ADS)

    Bai, Zhengyuan; Zhang, Qing; Ju, Yongfeng; Tao, Guiju; Jiang, Xiongwei; Kang, Ning; Liu, Chengpu; Zhang, Long

    2016-02-01

    A novel flexible metamaterial narrow-band-pass filter is designed and proved to be reliable by both numerical simulations and experimental measurements. The unit cell of the designed structure consists of circle ring resonators on top of a thin dielectric layer backed by a metallic mesh. The investigations on the distribution of the surface current and magnetic field as well as the analysis of the equivalent circuit model reveal that the magnetic resonance response between layers induced by the reverse surface current contributes to the high quality factor band-pass property. Importantly, it is a flexible design with a tunable resonance frequency by just changing the radius of the circle rings and can also be easily extended to have the multi-band-pass property. Moreover, this simplified structure with low duty cycle and ultra-thin thickness is also a symmetric design which is insensitive to the polarization and incident angles. Therefore, such a metamaterial narrow-band-pass filter is of great importance in the practical applications such as filtering and radar stealth, and especially for the conformal structure applications in the infrared and optical window area.

  18. Quantitative resonant soft x-ray reflectivity of ultrathin anisotropic organic layers: Simulation and experiment of PTCDA on Au

    NASA Astrophysics Data System (ADS)

    Capelli, R.; Mahne, N.; Koshmak, K.; Giglia, A.; Doyle, B. P.; Mukherjee, S.; Nannarone, S.; Pasquali, L.

    2016-07-01

    Resonant soft X-ray reflectivity at the carbon K edge, with linearly polarized light, was used to derive quantitative information of film morphology, molecular arrangement, and electronic orbital anisotropies of an ultrathin 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) film on Au(111). The experimental spectra were simulated by computing the propagation of the electromagnetic field in a trilayer system (vacuum/PTCDA/Au), where the organic film was treated as an anisotropic medium. Optical constants were derived from the calculated (through density functional theory) absorption cross sections of the single molecule along the three principal molecular axes. These were used to construct the dielectric tensor of the film, assuming the molecules to be lying flat with respect to the substrate and with a herringbone arrangement parallel to the substrate plane. Resonant soft X-ray reflectivity proved to be extremely sensitive to film thickness, down to the single molecular layer. The best agreement between simulation and experiment was found for a film of 1.6 nm, with flat laying configuration of the molecules. The high sensitivity to experimental geometries in terms of beam incidence and light polarization was also clarified through simulations. The optical anisotropies of the organic film were experimentally determined and through the comparison with calculations, it was possible to relate them to the orbital symmetry of the empty electronic states.

  19. Quantitative resonant soft x-ray reflectivity of ultrathin anisotropic organic layers: Simulation and experiment of PTCDA on Au.

    PubMed

    Capelli, R; Mahne, N; Koshmak, K; Giglia, A; Doyle, B P; Mukherjee, S; Nannarone, S; Pasquali, L

    2016-07-14

    Resonant soft X-ray reflectivity at the carbon K edge, with linearly polarized light, was used to derive quantitative information of film morphology, molecular arrangement, and electronic orbital anisotropies of an ultrathin 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) film on Au(111). The experimental spectra were simulated by computing the propagation of the electromagnetic field in a trilayer system (vacuum/PTCDA/Au), where the organic film was treated as an anisotropic medium. Optical constants were derived from the calculated (through density functional theory) absorption cross sections of the single molecule along the three principal molecular axes. These were used to construct the dielectric tensor of the film, assuming the molecules to be lying flat with respect to the substrate and with a herringbone arrangement parallel to the substrate plane. Resonant soft X-ray reflectivity proved to be extremely sensitive to film thickness, down to the single molecular layer. The best agreement between simulation and experiment was found for a film of 1.6 nm, with flat laying configuration of the molecules. The high sensitivity to experimental geometries in terms of beam incidence and light polarization was also clarified through simulations. The optical anisotropies of the organic film were experimentally determined and through the comparison with calculations, it was possible to relate them to the orbital symmetry of the empty electronic states. PMID:27421398

  20. Graphene-graphite oxide field-effect transistors.

    PubMed

    Standley, Brian; Mendez, Anthony; Schmidgall, Emma; Bockrath, Marc

    2012-03-14

    Graphene's high mobility and two-dimensional nature make it an attractive material for field-effect transistors. Previous efforts in this area have used bulk gate dielectric materials such as SiO(2) or HfO(2). In contrast, we have studied the use of an ultrathin layered material, graphene's insulating analogue, graphite oxide. We have fabricated transistors comprising single or bilayer graphene channels, graphite oxide gate insulators, and metal top-gates. The graphite oxide layers show relatively minimal leakage at room temperature. The breakdown electric field of graphite oxide was found to be comparable to SiO(2), typically ~1-3 × 10(8) V/m, while its dielectric constant is slightly higher, κ ≈ 4.3.