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1

Improved electrical properties of Ge metal-oxide-semiconductor devices with HfO2 gate dielectrics using an ultrathin GeSnOx film as the surface passivation layer  

NASA Astrophysics Data System (ADS)

A surface passivation method for improving the interface quality of HfO2 gate dielectric on Ge substrate by using an ultrathin GeSnOx layer is reported. The GeSnOx layer is fabricated using a unique method. A GeSn layer is formed by sputtering Sn on Ge substrate and then removing the top Sn layer with diluted HCl solution. The ultrathin GeSn layer translates into the GeSnOx layer during thermal oxidation in an oxygen atmosphere. It is found that the electrical properties can be improved significantly for Ge/HfO2 devices with the introduction of a GeSnOx layer, including low midgap interface trap density and extremely low leakage current density of the gate stack.

Zhao, Mei; Liang, Renrong; Wang, Jing; Xu, Jun

2013-04-01

2

The mechanism for the suppression of leakage current in high dielectric TiO2 thin films by adopting ultra-thin HfO2 films for memory application  

NASA Astrophysics Data System (ADS)

The electrical leakage current of thin rutile structured TiO2 films deposited by atomic layer deposition on a Ru electrode was enormously reduced by depositing an extremely thin HfO2 (< 1 nm) on top. The sacrifice of the capacitance density by the HfO2 was minimized. The leakage mechanism analysis on the Pt/TiO2/Ru and Pt/HfO2/TiO2/Ru structures revealed that the improvement in leakage current was attributed to the reduction of defect (trap) density in the TiO2 film. The interfacial potential barrier height for electron transport in thinner (˜ 10 nm) TiO2 films was lower than that of thicker (˜ 20 nm) TiO2 films, which resulted in a higher leakage current in these films. The capping of ultra-thin (˜ 0.7 nm) HfO2 films effectively increased the potential barrier height, and the leakage current was decreased accordingly. The leakage current behavior was systematically analyzed from quantum mechanical transport simulations.

Seo, Minha; Ho Rha, Sang; Keun Kim, Seong; Hwan Han, Jeong; Lee, Woongkyu; Han, Sora; Seong Hwang, Cheol

2011-07-01

3

Multilayer HfO2/TiO2 gate dielectric engineering of graphene field effect transistors  

NASA Astrophysics Data System (ADS)

Graphene field effect transistors and capacitors that employ ultra-thin atomic layer deposited high-? TiO2 dielectrics are demonstrated. Of the three TiO2 gate insulation schemes employed, the sequentially deposited HfO2:TiO2 gate insulator stack enabled the reduction of equivalent oxide thickness while simultaneously providing an ultra-thin gate insulation layer that minimized gate leakage current. The multilayer gate insulation scheme demonstrates a means for advanced device scaling in graphene-based devices.

Deen, David A.; Champlain, James G.; Koester, Steven J.

2013-08-01

4

Compatibility of polycrystalline silicon gate deposition with HfO2 and Al2O3/HfO2 gate dielectrics  

NASA Astrophysics Data System (ADS)

Polycrystalline-silicon (poly-Si) gate compatibility issues with HfO2 and Al2O3 capped HfO2 gate dielectrics are reported. It can be generally stated that chemical vapor deposition (CVD) silicon gates using silane deposited directly onto HfO2 results in electrical properties much worse compared to similar HfO2 films using platinum metal gates. However, depositing CVD silicon gates directly onto Al2O3 capped HfO2 showed greater than a 104 times reduction in gate leakage compared to the poly-Si/HfO2 and poly-Si/SiO2 controls of similar electrical thickness.

Gilmer, D. C.; Hegde, R.; Cotton, R.; Garcia, R.; Dhandapani, V.; Triyoso, D.; Roan, D.; Franke, A.; Rai, R.; Prabhu, L.

2002-08-01

5

Characterization and comparison of the charge trapping in HfSiON and HfO2 gate dielectrics  

Microsoft Academic Search

Charge trapping in HfSiON and HfO2 gate dielectrics was studied using both DC and pulsed ID-VG characterization techniques. The data shows a significant amount of hysteresis in HfO2 but negligible instability in HfSiON. Constant voltage stress measurements of HfO2 and HfSiON films show that the threshold voltage shift in HfO2 films is as much as 10 times higher than that

A. Shanware; M. R. Visokay; J. J. Chambers; A. L. P. Rotondaro; J. McPherson; L. Colombo

2003-01-01

6

Evaluation of NBTI in HfO2 gate-dielectric stacks with tungsten gates  

Microsoft Academic Search

Negative-bias temperature instability (NBTI) of the threshold voltage in ultrathin HfO2 p-type field-effect transistors (pFET) with tungsten gates is reported. The dependence of threshold voltage, transconductance peak, and interface trap density on stress time is investigated for various negative stress voltages and temperatures. The measurements show that the threshold voltage shifts with a concomitant decrease in transconductance peak and increase

Sufi Zafar; Byoung H. Lee; James Stathis

2004-01-01

7

80 nm poly-Si gate CMOS with HfO2 gate dielectric  

Microsoft Academic Search

We report here for the first time the formation of an amorphous oxide layer between the polysilicon gate and hafnium oxide (HfO2 ) gate dielectric due to a lateral oxidation mechanism at the gate edge. Using a polySi reoxidation-free CMOS process, well behaved 80 nm MOSFETs were fabricated with no evidence of lateral oxidation. A CETinv of 25 Å with

C. Hobbs; H. Tseng; K. Reid; B. Taylor; L. Dip; L. Hebert; R. Garcia; R. Hegde; J. Grant; D. Gilmer; A. Franke; V. Dhandapani; M. Azrak; L. Prabhu; R. Rai; S. Bagchi; J. Conner; S. Backer; F. Dumbuya; B. Nguyen; P. Tobin

2001-01-01

8

Structural and dielectric properties of amorphous ZrO2 and HfO2 Davide Ceresoli* and David Vanderbilt  

E-print Network

Structural and dielectric properties of amorphous ZrO2 and HfO2 Davide Ceresoli* and David September 2006 Zirconia ZrO2 and hafnia HfO2 are leading candidates for replacing SiO2 as the gate insulator in comple- mentary metal-oxide semiconductor technology. Amorphous versions of these materials a-ZrO2 and a

Vanderbilt, David

9

A physics-based model of the dielectric breakdown in HfO2 for statistical reliability prediction  

Microsoft Academic Search

We present a quantitative physical model describing the current evolution due to the formation of a conductive filament responsible for the HfO2 dielectric breakdown. By linking the microscopic properties of the stress-generated electrical defects to the local power dissipation and to the corresponding temperature increase along the conductive path the model reproduces the rapid current increase observed during the breakdown.

Luca Vandelli; Andrea Padovani; Luca Larcher; Gennadi Bersuker; Jung Yum; Paolo Pavan

2011-01-01

10

Rotating compensator spectroscopic ellipsometry (RCSE) and its application to high-k dielectric film HfO2  

NASA Astrophysics Data System (ADS)

High-k gate dielectric films with equivalent oxide thickness (EOT) of 3 nm or less are becoming the main theme of research and development in ultra-large-scale integrated circuits industry with device dimensions scaled down to less than 130 nm. Among the high-k gate dielectric materials hafnium dioxide (HfO2) is very promising with its high dielectric constant (approximately 30) and stability in contact with Si. The samples were prepared with a DC magnetron-reactive sputtering method and subsequently annealed in the furnace with a temperature range of 500- 850 degree(s)C. The thickness of the HfO2 varied from 3.5- 18nm with a hafnium silicate interface layer of approximately 1 nm. The electrical measurement showed that the breakdown voltage is inversely proportional to the physical thickness, suggesting the breakdown process occur at the HfO2 thin film rather than in the interface layer. To measure the physical thickness of hafnium dioxide and hafnium silicate interface simultaneously, a research grade bench top rotating compensator spectroscopic ellipsometry (RCSE) in the wavelength range of 195-915 nm was used. The dispersion of HfO2 film was characterized with a two-peak critical point (CP) model and the dispersion of the interface layer of hafnium silicate was characterized with a five-peak CP model. An interface layer thickness of 0.7-2 nm was found for all hafnium dioxide films on Si, depending on the process conditions such as annealing temperature and oxygen flow rate. The same wafers measured by RCSE were later studied by transmission electron microscopy (TEM). The thickness of hafnium dioxide and hafnium silicate determined by TEM is in good agreement with the noninvasive RCSE method.

Leng, JingMin; Li, Shifang; Opsal, Jon L.; Aspnes, David E.; Lee, Byoung H.; Lee, Jack C.

2000-11-01

11

Amorphous stability of HfO 2 based ternary and binary composition spread oxide films as alternative gate dielectrics  

NASA Astrophysics Data System (ADS)

A ternary alloyed thin film library of HfO 2-Y 2O 3-Al 2O 3 was grown on a Si(1 0 0) substrate in a few hours by a new pulsed laser deposition (PLD) system installed with a masking and substrate rotating scheme. This specially designed combinatorial ternary composition spread method enabled us to fabricate continuous ternary and binary composition spread film libraries. It is noteworthy that the library made by this system is addressable; each film composition covers the full range (from 0 to 100%) and can be directly correlated with the film location in the ternary and binary phase diagram. Rapid permittivity measurement on the film libraries was carried out by a scanning microwave microscope, while the crystal structure was by a combinatorial X-ray diffractometer (XRD). The (HfO 2) 6(Y 2O 3) 1(Al 2O 3) 3 ternary composition area in an amorphous phase was found to have a dielectric constant higher than HfO 2-Y 2O 3 binary area. This ternary oxide is promising as amorphous gate dielectric material.

Hasegawa, K.; Ahmet, P.; Okazaki, N.; Hasegawa, T.; Fujimoto, K.; Watanabe, M.; Chikyow, T.; Koinuma, H.

2004-02-01

12

ToF-SIMS depth profiling of Hf and Al composition variations in ultrathin mixed HfO 2\\/Al 2O 3 oxides  

Microsoft Academic Search

Ultrathin (a few nm) mixed HfO2\\/Al2O3 oxides deposited by ALCVD on Si substrates were analyzed with low energy (250eV) Cs+ and Xe+ ions by ToF-SIMS in the dual beam mode. The analysis beam was 15keV Ga+. Several layers were measured, with different metal ratios (Hf:Al) and different number of deposition cycles. We observed a significant enhancement of the Al (and

L. Houssiau; R. G. Vitchev; T. Conard; W. Vandervorst; H. Bender

2004-01-01

13

Effect of Nitridation on Low-Frequency (1/f) Noise in n-and p-MOSFETS with HFO2 Gate Dielectrics  

E-print Network

Effect of Nitridation on Low-Frequency (1/f) Noise in n- and p-MOSFETS with HFO2 Gate Dielectrics P in metallorganic chemical vapor deposited HfO2 n- and p-metal oxide semiconductor field effect transistors MOSFETs to be the origin of the 1/f fluctuations for most n-MOSFET process splits. For p-MOSFETs, no significant impact

Misra, Durgamadhab "Durga"

14

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

PubMed

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. PMID:21430314

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

2011-05-13

15

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

NASA Astrophysics Data System (ADS)

The thermal decomposition of ultrathin HfO2 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 HfO2 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.

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

2011-05-01

16

HfO2 and Al2O3 gate dielectrics on GaAs grown by atomic layer deposition Martin M. Franka  

E-print Network

HfO2 and Al2O3 gate dielectrics on GaAs grown by atomic layer deposition Martin M. Franka IBM on III­V semiconductors have long proven elusive. High-permittivity high- gate dielectrics may enable states.2 Excess inter- facial As occupying AsGa antisite defects causes gap states as well.2

Garfunkel, Eric

17

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

18

Thermodynamic Stability of High-K Dielectric Metal Oxides ZrO2 and HfO2 in Contact with Si and SiO2  

SciTech Connect

We present theoretical and experimental results regarding the thermodynamic stability of the high-k dielectrics MO2 (M= Zr and Hf) in contact with Si and SiO2. The HfO2/Si interface is found to be stable with respect to formation of silicides whereas the ZrO2/Si interface is not. The MO2/SiO2 interface is marginally unstable with respect to formation of silicates. Cross-sectional transmission electron micrographs expose formation of nodules, identified as silicides, across the polysilicon/ZrO2/Si interfaces but not for the interfaces with HfO2. For both ZrO2 and HfO2, the X-ray photoemission spectra illustrate formation of silicate-like compounds in the MO2/SiO2 interface.

Gutowski, Maciej S.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Jaffe, John E.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Lui, Chun-Li (Motorola, Austin, TX) [Motorola, Austin, TX; Stoker, Matt (Motorola, Austin TX) [Motorola, Austin TX; Hegde, Rama I.(Motorola, Austin, TX) [Motorola, Austin, TX; Rai, Raghaw S.(Motorola, Austin, TX) [Motorola, Austin, TX; Tobin, Philip J.(Motorola, Austin, TX) [Motorola, Austin, TX

2002-03-18

19

A quantum mechanical mobility model for scaled NMOS transistors with ultra-thin high- K dielectrics and metal gate electrodes  

Microsoft Academic Search

A quantum mechanical model of electron mobility for scaled NMOS transistors with ultra-thin SiO2\\/HfO2 dielectrics (effective oxide thickness is less than 1nm) and metal gate electrode is presented in this paper. The inversion layer carrier density is calculated quantum mechanically due to the consideration of high transverse electric field created in the transistor channel. The mobility model includes: (1) Coulomb

Yanli Zhang; Marvin H. White

2008-01-01

20

Conventional n-channel MOSFET devices using single layer HfO2 and ZrO2 as high-k gate dielectrics with polysilicon gate electrode  

Microsoft Academic Search

Conventional self-aligned MOSFET transistors with poly-silicon gate-electrode were successfully fabricated using Hf-oxide and Zr-oxide as high-k gate-dielectrics. The gate-stack consisting of poly-silicon on Hf-oxide exhibited promising transistor characteristics with a S\\/D RTA temperature of 1000°C, demonstrating feasibility of integrating high-k gate-dielectrics into conventional CMOS process technology. Effects of S\\/D RTA temperatures on the HfO2\\/poly-Si transistor characteristics were discussed. A gate-dimension

Yudong Kim; Gabriel Gebara; Michael Freiler; Joel Barnett; Deborah Riley; Jerry Chen; Kenneth Torres; JaeEun Lim; Brendan Foran; Fred Shaapur; Avinash Agarwal; Patrick Lysaght; George A. Brown; Chadwin Young; Swarnal Borthakur; Hong-Jyh Li; Billy Nguyen; Peter Zeitzoff; Gennadi Bersuker; David Derro; Renate Bergmann; Robert W. Murto; Alex Hou; Howard R. Huff; Eric Shero; Christophe Pomarede; Michael Givens; M. Mazanez; Chris Werkhoven

2001-01-01

21

Ultra-thin (Teff inv = 1.7 nm) poly-Si-gated SiN\\/HfO2\\/SiON high-k stack dielectrics with high thermal stability (1050°C)  

Microsoft Academic Search

Demonstrated the high-performance and high-reliability of ultra-thin poly-Si-gated SiN\\/HfO2\\/SiON high-k stack dielectrics. A SiN layer deposited on HfO2 is shown to be indispensable to the suppression of the reaction of poly-Si and HfO2, resulting in high thermal stability (1050°C). This thermally stable SiN\\/HfO2\\/SiON structure can achieve an ultrathin oxide thickness of Teffinv (effective oxide thickness measured in strong inversion region)

Y. Morisaki; T. Aoyama; Y. Sugita; K. Irino; T. Sugii; T. Nakamura

2002-01-01

22

Experimental study on the oxide trap coupling effect in metal oxide semiconductor field effect transistors with HfO2 gate dielectrics  

NASA Astrophysics Data System (ADS)

In this Letter, the coupling effect between multi-traps in HfO2 gate dielectrics is experimentally studied in scaled high-?/metal-gate metal oxide semiconductor field effect transistors (MOSFETs). Deviated from conventional understanding, mechanism that affects trap coupling is found, which is originated from local carrier density perturbation due to random dopant fluctuation (RDF) in the channel. The competition of conventional Coulomb repulsion effect and RDF induced local carrier density perturbation effect results in the nonmonotonic voltage dependence of trap coupling intensity.

Ren, Pengpeng; Wang, Runsheng; Jiang, Xiaobo; Qiu, Yingxin; Liu, Changze; Huang, Ru

2014-06-01

23

Interfacial Transition Regions at Germanium/Hf Oxide Based Dielectric Interfaces: Qualitative Differences Between Non-Crystalline Hf Si Oxynitride and Nanocrystalline HfO2 Gate Stacks  

SciTech Connect

The contribution from a relatively low-K SiON (K {approx} 6) interfacial transition region (ITR) between Si and transition metal high-K gate dielectrics such as nanocrystalline HfO2 (K {approx} 20), and non-crystalline Hf Si oxynitride (K {approx} 10-12) places a significant limitation on equivalent oxide thickness (EOT) scaling. This limitation is equally significant for metal-oxide-semiconductor capacitors and field effect transistors, MOSCAPs and MOSFETs, respectively, fabricated on Ge substrates. This article uses a novel remote plasma processing approach to remove native Ge ITRs and bond transition metal gate dielectrics directly onto crystalline Ge substrates. Proceeding in this way we identify (i) the source of significant electron trapping at interfaces between Ge and Ge native oxide, nitride and oxynitride ITRs, and (ii) a methodology for eliminating native oxide, or nitride IRTs on Ge, and achieving direct contact between nanocrystalline HfO2 and non-crystalline high Si3N4 content Hf Si oxynitride alloys, and crystalline Ge substrates. We then combine spectroscopic studies, theory and modeling with electrical measurements to demonstrate the relative performance of qualitatively different nanocrystalline and non-crystalline gate dielectrics for MOS Ge test devices.

Lucovsky, G.; Lee, S; Long, J; Seo, H; Luning, J

2009-01-01

24

Composition, structure, and electrical characteristics of HfO2 gate dielectrics grown using the remote- and direct-plasma atomic layer deposition methods  

NASA Astrophysics Data System (ADS)

Hafnium oxide thin films were deposited using both the remote-plasma atomic layer deposition (RPALD) and direct-plasma atomic layer deposition (DPALD) methods. Metal-oxide semiconductor (MOS) capacitors and transistors were fabricated with HfO2 gate dielectric to examine their electrical characteristics. The as-deposited RPALD HfO2 layer exhibited an amorphous structure, while the DPALD HfO2 layer exhibited a polycrystalline structure. Medium-energy ion scattering measurement data indicate that the interfacial layer consisted of interfacial SiO2-x and silicate layers. This suggests that the change in stoichiometry with depth could be related to the energetic plasma beam used in the plasma ALD process, resulting in damage to the Si surface and an interaction between Hf and SiO2-x. The as-deposited RPALD HfO2 films had better interfacial layer characteristics, such as an effective fixed oxide charge density (Qf,eff) and interfacial roughness than the DPALD HfO2 films did. A MOS capacitor fabricated using the RPALD method exhibited an equivalent oxide thickness (EOT) of 1.8 nm with a Qf,eff=-4.2×1011 q/cm2 (where q is the elementary charge, 1.6022×10-19 C), whereas a MOS capacitor fabricated using the DPALD method had an EOT=2.0 nm and a Qf,eff=-1.2×1013 q/cm2. At a power=0.6 MV/cm, the RPALD n-type metal-oxide semiconductor field-effect transistor (nMOSFET) showed ?eff=168 cm2/V s, which was 50% greater than the value of the DPALD nMOSFET (?eff=111 cm2/V s). In the region where Vg-Vt=2.0 V, the RPALD MOSFET drain current was about 30% higher than the DPALD MOSFET drain current. These improvements are believed to be due to the lower effective fixed charge density, and they minimize problems arising from plasma charging damage.

Kim, Jinwoo; Kim, Seokhoon; Kang, Hyunseok; Choi, Jihoon; Jeon, Hyeongtag; Cho, Mannho; Chung, Kwunbum; Back, Sungkwun; Yoo, Kyungdong; Bae, Choelhwyi

2005-11-01

25

Influence of the oxygen concentration of atomic-layer-deposited HfO2 films on the dielectric property and interface trap density  

NASA Astrophysics Data System (ADS)

The influence of the ozone concentration (160-370g/m3) during atomic layer deposition of HfO2-gate dielectrics on the dielectric performance of the films grown on Si was studied. Although ozone was effective in reducing the impurity concentration in the film compared to H2O, the higher concentration slightly deteriorated the dielectric performance. More importantly, the degradation in the interface trap property with increasing post-annealing temperature became more serious as the ozone concentration increased. Investigation of the interface states using x-ray photoelectron spectroscopy revealed that the excessive oxygen incorporated during the film growth made the interfacial sub-oxide species (SiO, Si2O3, and silicate) and SiO2 coordinate more with oxygen. This increased the interface trap density and degraded the interface properties.

Park, Jaehoo; Cho, Moonju; Kim, Seong Keun; Park, Tae Joo; Lee, Suk Woo; Hong, Sug Hun; Hwang, Cheol Seong

2005-03-01

26

A study of nitrogen behavior in the formation of Ta/TaN and Ti/TaN alloyed metal electrodes on SiO2 and HfO2 dielectrics  

NASA Astrophysics Data System (ADS)

We studied Ta, TaN, and sub-stoichiometric TaNx electrodes (obtained by nitrogen redistribution in Ta/TaN or Ti/TaN bilayers) deposited on thermal SiO2 and HfO2/IL (0.8 nm SiO2 IL, i.e., interlayer) stacks. Effective work-functions (WF) were extracted on MOS capacitor structures on SiO2 bevelled insulator of 4.2 eV for pure Ta, 4.6 eV for TaN, and 4.3 eV for sub-stoichiometric TaNx. This intermediate WF value is explained by TaN nitrogen redistribution with reactive Ta or Ti elements shifting the gate work-function toward the Si conduction band. The same electrodes deposited on an HfO2/IL dielectric showed different behavior: First, the Ta/HfO2/IL stack shows a +200 meV WF increase (towards the Si valence band) compared to the SiO2 dielectric stack. This increase is explained by the well-known HfO2/IL dipole formation. Second, in contrast to electrodes deposited on SiO2, sub-stoichiometric TaNx/HfO2 is found to have a lower WF (4.3 eV), than pure Ta on HfO2 (4.4 eV). This inversion in work-function behavior measured on SiO2 vs. HfO2 is explained by the nitrogen redistribution in Ta/TaN bilayer together with diffusion of nitrogen through the HfO2 layer, leading to Si-N formation which prevents dipole formation at the HfO2/IL interface.

Gassilloud, R.; Maunoury, C.; Leroux, C.; Piallat, F.; Saidi, B.; Martin, F.; Maitrejean, S.

2014-04-01

27

Sub-250 nm low-threshold deep-ultraviolet AlGaN-based heterostructure laser employing HfO2/SiO2 dielectric mirrors  

NASA Astrophysics Data System (ADS)

We report a sub-250-nm, optically pumped, deep-ultraviolet laser using an AlxGa1-xN-based multi-quantum-well structure grown on a bulk Al-polar c-plane AlN substrate. TE-polarization-dominant lasing action was observed at room temperature with a threshold pumping power density of 250 kW/cm2. After employing high-reflectivity SiO2/HfO2 dielectric mirrors on both facets, the threshold pumping power density was further reduced to 180 kW/cm2. The internal loss and threshold modal gain can be calculated as 2 cm-1 and 10.9 cm-1, respectively.

Kao, Tsung-Ting; Liu, Yuh-Shiuan; Mahbub Satter, Md.; Li, Xiao-Hang; Lochner, Zachary; Douglas Yoder, P.; Detchprohm, Theeradetch; Dupuis, Russell D.; Shen, Shyh-Chiang; Ryou, Jae-Hyun; Fischer, Alec M.; Wei, Yong; Xie, Hongen; Ponce, Fernando A.

2013-11-01

28

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

NASA Astrophysics Data System (ADS)

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).

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

29

Nanoscale electrical characterization of HfO2\\/SiO2 MOS gate stacks with enhanced-CAFM  

Microsoft Academic Search

The conduction and dielectric breakdown (BD) of an ultra-thin HfO2\\/SiO2 gate stack is studied at the nanoscale. With this purpose, an enhanced conductive atomic force microscope (a CAFM with extended electrical performance) has been developed. Using this new set up, different conduction modes have been observed before BD, which can be masked during standard tests. The study of the BD

M. Nafria; X. Blasco; M. Porti; L. Aguilera; X. Aymerich; J. Petry; W. Vandervorst

2005-01-01

30

A quantum mechanical mobility model for scaled NMOS transistors with ultra-thin high- K dielectrics and metal gate electrodes  

NASA Astrophysics Data System (ADS)

A quantum mechanical model of electron mobility for scaled NMOS transistors with ultra-thin SiO 2/HfO 2 dielectrics (effective oxide thickness is less than 1 nm) and metal gate electrode is presented in this paper. The inversion layer carrier density is calculated quantum mechanically due to the consideration of high transverse electric field created in the transistor channel. The mobility model includes: (1) Coulomb scattering effect arising from the scattering centers at the semiconductor-dielectric interface, fixed charges in the high- K film and bulk impurities, and (2) surface roughness effect associated with the semiconductor-dielectric interface. The model predicts the electron mobility in MOS transistors will increase with continuous dielectric layer scaling and a fixed volume trap density assumption in high- K film. The Coulomb scattering mobility dependence on the interface trap density, fixed charges in the high- K film, interfacial oxide layer thickness and high- K film thickness is demonstrated in the paper.

Zhang, Yanli; White, Marvin H.

2008-11-01

31

Structural, electronic, and dielectric properties of ultrathin zirconia films on silicon  

E-print Network

rigorously pursued. We and others have shown that crystal structure of ZrO2 films have considerable effects dielectrics with higher permittivity ones such as HfO2 and ZrO2.2 The dielectric constant values in the litera- ture vary from 16 to 453­7 for HfO2 and 18 to 358­10 for ZrO2. Similarly, the reported band gap values

Garfunkel, Eric

32

Epitaxial strained germanium p-MOSFETs with HfO2 gate dielectric and TaN gate electrode  

Microsoft Academic Search

Germanium p-MOSFETs with a thin high-k dielectric (EOT?1.6 nm) were fabricated on bulk Ge and epitaxial germanium-on-silicon substrates. These devices exhibited sub-90 mV\\/decade subthreshold swing and low gate leakage. The IV and CV characteristics achieved in this work allow for accurate extraction of important device parameters such as transconductance (Gm) and low-field mobility. Results from n-MOSFETs fabricated on bulk Ge

A. Ritenour; S. Yu; M. L. Lee; N. Lu; W. Bai; A. Pitera; E. A. Fitzgerald; D. L. Kwong; D. A. Antoniadis

2003-01-01

33

Dielectric properties of ultrathin SiO2 slabs  

NASA Astrophysics Data System (ADS)

First-principles total energy calculations have been performed to determine the extent to which surfaces impact the dielectric properties of ultrathin dielectric materials. SiO2 (0001) slabs in ?-quartz phase with various thicknesses were considered in this study, using a new method that allows for the partitioning of the surface and bulk contributions to the total field-induced polarization. It was found that the bulk polarization and the dielectric constant can be determined even from ultrathin films terminated with Si atoms, and that surface effects do not significantly impact the dielectric properties of (0001) ?-quartz slabs.

Shi, N.; Ramprasad, R.

2005-12-01

34

Energetics and electronic structure of aluminum point defects in HfO2: A first-principles study  

E-print Network

Energetics and electronic structure of aluminum point defects in HfO2: A first-principles study Z and substitutional point defect of dopant aluminum in monoclinic HfO2. Our results show that the doped Al atom.1063/1.3109206 I. INTRODUCTION Hafnia HfO2 is a wide-band-gap oxide with a relatively high dielectric constant

Gong, Xingao

35

Ultrathin high-K metal oxides on silicon: processing, characterization and integration issues  

Microsoft Academic Search

An overview of our recent work on ultrathin (<100 Å) films of metal oxides deposited on silicon for advanced gate dielectrics applications will be presented. Data on ultrathin Al2O3, ZrO2, HfO2, and Y2O3 will be shown to illustrate the complex processing, integration and device-related issues for high dielectric constant (‘high-K’) materials. Both physical and electrical properties, as well as the

E. P Gusev; E Cartier; D. A Buchanan; M Gribelyuk; M Copel; H Okorn-Schmidt; C D’Emic

2001-01-01

36

Effects of ALD HfO 2 thickness on charge trapping and mobility  

Microsoft Academic Search

The effects of HfO2 thickness on charge trapping and mobility were investigated. The impact of fast transient electron trapping on DC measurements results in underestimating channel carrier mobility. Scaling the physical thickness of the HfO2 dielectric causes less charge trapping and higher mobility. A HfO2 -based high-k solution requires fine-tuning the thickness of the high-k film to maintain a balance

J. H. Sim; S. C. Song; P. D. Kirsch; C. D. Young; R. Choi; D. L. Kwong; B. H. Lee; G. Bersuker

2005-01-01

37

arXiv:cond-mat/0301016v12Jan2003 First-principles Study of Electronic and Dielectric Properties of ZrO2 and HfO2  

E-print Network

of ZrO2 and HfO2 Xinyuan Zhao and David Vanderbilt Department of Physics and Astronomy, Rutgers, tetragonal, and monoclinic) phases of ZrO2 and HfO2, in order to elucidate phonon modes, Born effective (or even increasing) the gate capacitance. ZrO2, HfO2 and their structure-modified derivatives (e

Vanderbilt, David

38

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

PubMed Central

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

2011-01-01

39

Percolation path and dielectric-breakdown-induced-epitaxy evolution during ultrathin gate dielectric breakdown transient  

Microsoft Academic Search

A physical model has been developed which complies with the experimental observation on the failure mechanism of ultrathin gate oxide breakdown during constant voltage stress. Dynamic equilibrium needs to be established between the percolation conductive path and the dielectric breakdown induced epitaxy (DBIE) formation during gate dielectric breakdown transient. The model is capable of linking the percolation model, soft breakdown,

Chih Hang Tung; Kin Leong Pey; Lei Jun Tang; M. K. Radhakrishnan; Wen He Lin; Felix Palumbo; Salvatore Lombardo

2003-01-01

40

Characterization of ultrathin gate dielectrics and multilayer charge injection barriers  

NASA Astrophysics Data System (ADS)

Since the invention of the first integrated circuit, the semiconductor industry has distinguished itself by a phenomenally rapid pace of improvements in device performance. This trend of ever smaller and faster devices is a result of the ability to exponentially reduce feature sizes of integrated circuits, a trend commonly known as "scaling". A reduction of overall feature sizes requires a simultaneous reduction in the thickness of the gate dielectric, SiO2, of a MOSFET. Gate oxides in the ultrathin regime (<35 A) feature a large direct tunneling leakage current. The presence of this leakage current requires a reevaluation of standard characterization techniques as well as a reevaluation of the continued usefulness of SiO 2 as the gate dielectric of choice for future applications. On the other hand, a thorough understanding of the dynamics of ultrathin oxides opens up a range of future device applications that were not possible with thicker oxides. Capacitance-voltage characterization has been the standard technique to study the electrical properties and interface quality of MOS devices. However, the presence of a large leakage current in ultrathin oxides distorts standard C-V measurements, rendering this technique no longer useful. In this work, a leakage compensated charge measurement is developed to overcome this difficulty. This technique produces static C-V curves, even for oxides as thin as 24 A, thereby permitting C-V characterization well into the direct tunneling regime. As an extension of this leakage problem, the usefulness of SiO2 as the gate dielectric of choice for future CMOS devices has been called into question. One solution---but not the only---calls for a new dielectric to replace SiO2 for future gate applications. This research presents some of the earliest results ever on the electrical properties of MOCVD and ALCVD hafnium oxides as a potential candidate. Electrical characterization revealed that the devices have characteristics such as large leakage currents, dielectric charging under stress, hysteresis and a large flatband voltage shift that is commonly found in materials such as the one that was investigated in this work. As one example of future device applications that become possible due to the scaling of ultrathin oxides, silicon-based multilayer charge injection barriers have been investigated. These barriers consist of alternating layers of ultrathin SiO2 and Si. The electrical properties of these structures were studied in detail and revealed that they can be used as an active tunnel dielectric in nonvolatile memory devices.

Dons, Edwin M.

41

Dielectric and pyroelectric properties of ultrathin, monocrystalline lithium tantalate  

NASA Astrophysics Data System (ADS)

Ultrathin, self-supporting lithium tantalate (LiTaO3) wafers have been fabricated out of a single crystal with a minimum thickness of about 0.4 ?m using ion-beam milling. The most decisive parameters (pyroelectric coefficient, relative permittivity, and dielectric loss factor) for their use in pyroelectric radiation detectors were studied in dependence on film thickness and temperature. The potential performance of pyroelectric materials was evaluated using appropriate figures of merit. In addition, the dielectric and pyroelectric properties of stoichiometric LiTaO3 were investigated and compared to congruent LiTaO3 bulk material conventionally used for pyroelectric detectors.

Schossig, Marco; Norkus, Volkmar; Gerlach, Gerald

2014-03-01

42

HfO2 Gate Dielectric on (NH4)2S Passivated (100) GaAs Grown by Atomic Layer Deposition  

SciTech Connect

The interface between hafnium oxide grown by atomic layer deposition and (100) GaAs treated with HCl cleaning and (NH{sub 4}){sub 2}S passivation has been characterized. Synchrotron radiation photoemission core level spectra indicated successful removal of the native oxides and formation of passivating sulfides on the GaAs surface. Layer-by-layer removal of the hafnia film revealed a small amount of As{sub 2}O{sub 3} formed at the interface during the dielectric deposition. Traces of arsenic and sulfur out-diffusion into the hafnia film were observed after a 450 C post-deposition anneal, and may be the origins for the electrically active defects. Transmission electron microscopy cross section images showed thicker HfO{sub 2} films for a given precursor exposure on S-treated GaAs versus the non-treated sample. In addition, the valence-band and the conduction-band offsets at the HfO{sub 2}/GaAs interface were deduced to be 3.18 eV and a range of 0.87-0.97 eV, respectively. It appears that HCl+(NH{sub 4})2{sub S} treatments provide a superior chemical passivation for GaAs and initial surface for ALD deposition.

Chen, P.T.; /Stanford U., Materials Sci. Dept.; Sun, Y.; /SLAC, SSRL; Kim, E.; McIntyre, P.C.; /Stanford U., Materials Sci. Dept.; Tsai, W.; Garner, M.; /Intel, Santa Clara; Pianetta, P.; /SLAC, SSRL; Nishi, Y.; /Stanford U., Elect. Eng. Dept.; Chui, C.O.; /UCLA

2007-09-28

43

A multi-probe correlated bulk defect characterization scheme for ultra-thin high-dielectric  

E-print Network

A multi-probe correlated bulk defect characterization scheme for ultra-thin high- dielectric *M dielectrics in modern CMOS transistors suffer from process-induced defects and are prone to defect formation-induced leakage current (SILC) etc. are being used to identify the trap location within the dielectric. However

Alam, Muhammad A.

44

Density functional theory study of first-layer adsorption of ZrO2 and HfO2 on Ge(100)  

E-print Network

Density functional theory study of first-layer adsorption of ZrO2 and HfO2 on Ge(100) T.J. Grassman a survey of transition metal oxide (MO2 = ZrO2, HfO2) ordered molecular adsor- bate bonding configurations, gate dielectric materials are the transition metal dioxides ZrO2 and HfO2 (denoted as MO2

Kummel, Andrew C.

45

Characterization of Interfaces between HfO2 Thin Film and Metal Electrode with Pre-Post Treatments  

NASA Astrophysics Data System (ADS)

We investigated the effects of post O3 feeding treatment and pre-post O2 plasma treatment on HfO2 dielectric films in the metal/insulator/metal (MIM) structure TiN/HfO2/TiN. The carbon contents of the HfO2 films decreases with increasing O3 feeding time, which leads to the improvement in leakage current. The O2 plasma and O3 feeding treatments produce Hf-Hf bonds in the bulk HfO2 film and a Ti oxide layer at the film/bottom electrode and HfO2/TiN interface, which prevent the out diffusion of nitrogen into the HfO2 layer. In addition, these treatments also create the local crystallization of HfO2 at the interface. In the case of rapid thermal annealing of an actual dynamic random access memory (DRAM) structure, TiN/HfO2/Al2O3/HfO2/TiN, a local crystallization is also observed in the HfO2 layer, which enhances leakage current.

Kim, Young-Nam

2012-04-01

46

Kelvin probe study on formation of electric dipole at direct-contact HfO2/Si interfaces  

NASA Astrophysics Data System (ADS)

Although the direct-contact HfO2/Si structure has been demonstrated to have advantages on an equivalent oxide thickness scaling of <1 nm, characteristic electric charges have been reported to be formed at the HfO2/Si interface. A Kelvin probe method was used to examine the electric charges in HfO2/Si structures. We first describe the basic principles behind the Kelvin probe measurements of electric charges in an oxide/Si structure, and then point out what effect the surface adsorbates have on the measured contact-potential-difference voltage (VCPD). A large VCPD difference (>0.5 V) was observed between the direct-contact HfO2/Si and HfO2/SiO2/Si stack surfaces, which suggests the existence of a strong interface dipole. This result is consistent with previous reports using electrical measurements of metal-oxide-semiconductor capacitances. We also found that the dipole completely disappeared after ultrahigh vacuum annealing at 700 °C, and appeared again after exposure to O2 at room temperature. The formation of a dipole by exposure to O2 had a correlation with the formation of Si-O bonds at the HfO2/Si interface. We propose that interface Si-O-Hf bonding naturally produces a strong interface dipole from simple electrostatic potential analysis mainly due to the effect of the large dielectric constant of HfO2.

Miyata, Noriyuki; Yasuda, Tetsuji; Abe, Yasuhiro

2011-10-01

47

High quality HfO2/p-GaSb(001) metal-oxide-semiconductor capacitors with 0.8 nm equivalent oxide thickness  

NASA Astrophysics Data System (ADS)

We investigate in-situ cleaning of GaSb surfaces and its effect on the electrical performance of p-type GaSb metal-oxide-semiconductor capacitor (MOSCAP) using a remote hydrogen plasma. Ultrathin HfO2 films grown by atomic layer deposition were used as a high permittivity gate dielectric. Compared to conventional ex-situ chemical cleaning methods, the in-situ GaSb surface treatment resulted in a drastic improvement in the impedance characteristics of the MOSCAPs, directly evidencing a much lower interface trap density and enhanced Fermi level movement efficiency. We demonstrate that by using a combination of ex-situ and in-situ surface cleaning steps, aggressively scaled HfO2/p-GaSb MOSCAP structures with a low equivalent oxide thickness of 0.8 nm and efficient gate modulation of the surface potential are achieved, allowing to push the Fermi level far away from the valence band edge high up into the band gap of GaSb.

Barth, Michael; Bruce Rayner, G.; McDonnell, Stephen; Wallace, Robert M.; Bennett, Brian R.; Engel-Herbert, Roman; Datta, Suman

2014-12-01

48

Structural, electronic, optical, elastic properties and Born effective charges of monoclinic HfO2 from first-principles calculations  

NASA Astrophysics Data System (ADS)

First-principles calculations of structural, electronic, optical, elastic, mechanical properties, and Born effective charges of monoclinic HfO2 are performed with the plane-wave pseudopotential technique based on the density-functional theory. The calculated structural properties are consistent with the previous theoretical and experimental results. The electronic structure reveals that monoclinic HfO2 has an indirect band gap. The analyses of density of states and Mulliken charges show mainly covalent nature in Hf-O bonds. Optical properties, including the dielectric function, refractive index, extinction coefficient, reflectivity, absorption coefficient, loss function, and optical conductivity each as a function of photon energy are calculated and show an optical anisotropy. Moreover, the independent elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, compressibility, Lamé constant, sound velocity, Debye temperature, and Born effective charges of monoclinic HfO2 are obtained, which may help to understand monoclinic HfO2 for future work.

Liu, Qi-Jun; Zhang, Ning-Chao; Liu, Fu-Sheng; Liu, Zheng-Tang

2014-04-01

49

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

NASA Astrophysics Data System (ADS)

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.

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

2005-03-01

50

Direct tunneling gate leakage current in transistors with ultrathin silicon nitride gate dielectric  

Microsoft Academic Search

We present a study on the characterization and modeling of direct tunneling gate leakage current in both N- and P-type MOSFETs with ultrathin silicon nitride (Si3N4) gate dielectric formed by the jet-vapor deposition (JVD) technique. The tunneling mechanisms in the N- and PMOSFETs were clarified. The electron and hole tunneling masses and barrier potentials for the different tunneling mechanisms mere

Yee Chia Yeo; Qiang Lu; Wen Chin Lee; Tsu-Jae King; Chenming Hu; Xiewen Wang; Xin Guo; T. P. Ma

2000-01-01

51

Electrical properties of high-quality ultrathin nitride\\/oxide stack dielectrics  

Microsoft Academic Search

The electrical properties of ultrathin nitride\\/oxide (N\\/O) stack dielectrics (2-4 nm), produced by in-situ jet vapor deposition (JVD), have been studied in some detail. Both theoretical calculation and experimental data show that the leakage current in the N\\/O stack is substantially lower than that in the single oxide layer of the same equivalent oxide thickness (EOT). When compared to the

Ying Shi; Xiewen Wang; Tso-Ping Ma

1999-01-01

52

Modeling ultrathin dielectric breakdown on correlation of charge trap-generation to charge-to-breakdown  

Microsoft Academic Search

Degradation in ultrathin dielectric films due to high-field stress is a critical concern in ULSI technology. We investigate here the link between trap-generation and breakdown as a function of five technologically relevant parameters, namely stress-current density (10\\/sup -3\\/-10\\/sup 1\\/ A\\/cm\\/sup 2\\/), oxide thickness (70-250 A), stress temperature (25-100 \\/spl deg\\/C), charge-injection polarity (gate vs substrate), and nitridation of pure oxide

Pushkar P. Apte; Krishna C. Saraswat

1994-01-01

53

Germanium MOS capacitors incorporating ultrathin high-? gate dielectric  

Microsoft Academic Search

For the first time, we have successfully demonstrated the feasibility of integrating a high-permittivity (?) gate dielectric material zirconium oxide into the MOS capacitors fabricated on pure germanium substrates. The entire fabrication process was essentially performed at room temperature with the exception of a 410°C forming gas anneal. After processing steps intended to remove the germanium native oxide interlayer between

Chi On Chui; S. Ramanathan; B. B. Triplett; P. C. McIntyre; K. C. Saraswat

2002-01-01

54

Dielectric property and conduction mechanism of ultrathin zirconium oxide films  

NASA Astrophysics Data System (ADS)

Stoichiometric, uniform, amorphous ZrO2 films with an equivalent oxide thickness of ˜1.5 nm and a dielectric constant of ˜18 were deposited by an atomic layer controlled deposition process on silicon for potential applications in metal-oxide-semiconductor (MOS) devices. The conduction mechanism is identified as Schottky emission at low electric fields and as Poole-Frenkel emission at high electric fields. The MOS devices showed low leakage current, small hysteresis (<50 mV), and low interface state density (˜2×1011cm-2 eV-1). Microdiffraction and high-resolution transmission electron microscopy showed a localized monoclinic phase of ?-ZrO2 and an amorphous interfacial ZrSixOy layer which has a corresponding dielectric constant of 11.

Chang, J. P.; Lin, Y.-S.

2001-11-01

55

Dielectric properties of cobalt ferrite nanoparticles in ultrathin nanocomposite films.  

PubMed

Multilayered nanocomposite films (thickness 50-90 nm) of cobalt ferrite nanoparticles (np-CoFe2O4, 18 nm) were deposited on top of interdigitated microelectrodes by the layer-by-layer technique in order to study their dielectric properties. For that purpose, two different types of nanocomposite films were prepared by assembling np-CoFe2O4 either with poly(3,4-ethylenedioxy thiophene):poly(styrene sulfonic acid) or with polyaniline and sulfonated lignin. Despite the different film architectures, the morphology of both was dominated by densely-packed layers of nanoparticles surrounded by polyelectrolytes. The dominant effect of np-CoFe2O4 was also observed after impedance spectroscopy measurements, which revealed that dielectric behavior of the nanocomposites was largely influenced by the charge transport across nanoparticle-polyelectrolyte interfaces. For example, nanocomposites containing np-CoFe2O4 exhibited a single low-frequency relaxation process, with time constants exceeding 15 ms. At 1 kHz, the dielectric constant and the dissipation factor (tan ?) of these nanocomposites were 15 and 0.15, respectively. These values are substantially inferior to those reported for pressed pellets made exclusively of similar nanoparticles. Impedance data were further fitted with equivalent circuit models from which individual contributions of particle's bulk and interfaces to the charge transport within the nanocomposites could be evaluated. The present study evidences that such nanocomposites display a dielectric behavior dissimilar from that exhibited by their individual counterparts much likely due to enlarged nanoparticle-polyelectrolyte interfaces. PMID:24145704

Alcantara, Gustavo B; Paterno, Leonardo G; Fonseca, Fernando J; Pereira-da-Silva, Marcelo A; Morais, Paulo C; Soler, Maria A G

2013-12-01

56

Effect of Si substrate on interfacial SiO2 scavenging in HfO2/SiO2/Si stacks  

NASA Astrophysics Data System (ADS)

The scavenging kinetics of an ultra-thin SiO2 interface layer (SiO2-IL) in an HfO2/SiO2/Si stack is discussed by focusing on the substrate effect in addition to oxygen diffusion. 18O tracing experiments demonstrate that the O-atom moves from the SiO2-IL to the HfO2 layer during scavenging. SiO2-IL scavenging with various substrates (Si, SiC, and sapphire) has been found to be significantly different, which suggests that the Si in the substrate is also necessary to continuously cause the scavenging. Based on these findings and thermodynamic considerations, a kinetic model where oxygen vacancy (VO) transferred from the HfO2 reacts with the SiO2, which is in contact with the Si-substrate, is proposed for the SiO2-IL scavenging.

Li, Xiuyan; Yajima, Takeaki; Nishimura, Tomonori; Nagashio, Kosuke; Toriumi, Akira

2014-11-01

57

Development of Nitrous Oxide-Based Ultrathin Gate and Tunnel Dielectrics for MOS Devices.  

NASA Astrophysics Data System (ADS)

The use of ultrathin dielectric in the ULSI (Ultra -Large Scale Itegration) era is curcial for device functionality and reliability. However, it is well known that conventional thermally grown pure oxides in the ultra-thin regime (40 -60A) do not provide adequate electrical and reliability characteristics. The use of N_2O gas in oxidation produces oxides (oxynitrides) with better dielectric integrity, lower defect density, less boron penetration and better process control, etc.. The N _2O oxide is thus a better candidate for ultrathin oxide application. Pre-oxidation surface preparation by conventional RCA clean increases surface microroughness and provides no passivation to the wafer surface. A new cleaning method based on methanol/HF has been developed and show improvement in the dielectric integrity of both oxides and oxynitrides. A microscopic model is also proposed. The thickness dependent of stress-induced leakage current (SILC) was studied for pure oxides and N _2O oxides. A "turn around" effect was observed such that for thickness going down from ~ 50A, SILC actually decreases. This effect is modeled by the two-step trap-assisted tunneling model where trap generation rate and tunneling time constants are the determining factors for the SILC. Effects of oxide exposure, photoresist and gate dopant activation on the plasma damage immunity of ultrathin oxides were studied. It was found that not only charging damage and radiation damage are present during plasma exposure, photo-annealing by low energy UV light is competing with the damaging processes. The actual extent of damage depends on the plasma operating condition. It implies that using fully-covered MOSCAP structures is not an accurate indicator of the actual damage in integrated circuits. It was also found that photoresist quality affect plasma damage and patterning gate before ion implantation can reduce charging problem. Damage recovery effect of various RTA annealing processes is also studied. The effects of different gate dopant species, concentration and microstructure on the electrical and reliability characteristics of ultrathin oxides and N _2O oxynitrides are studied. Optimization of the gate doping level is based on poly depletion, charge -to-breakdown, and stress-induced leakage current. The optimization conditions for N+ and P+ gate are found to be very different.

Lai, Ka-Fai

58

Effects of Metal Gates and Back-End-of-Line Materials on X-Ray Dose in ${\\\\rm HfO}_{2}$ Gate Oxide  

Microsoft Academic Search

The effects of 10-keV and 400-keV endpoint-energy bremsstrahlung x-rays have been studied using the Monte Carlo simulator, MRED, for MOS capacitors with ${\\\\rm HfO}_{2}$ gate dielectrics and TiN and TaN metal gates. We compute the reduction in dose that occurs for 10-keV x-ray irradiation of thin ${\\\\rm HfO}_{2}$ gate dielectrics sandwiched between the metal gate and the Si substrate. We

Aritra Dasgupta; Daniel M. Fleetwood; Robert A. Reed; Robert A. Weller; Marcus H. Mendenhall

2011-01-01

59

Interaction of highly charged ions with ultrathin dielectric films  

NASA Astrophysics Data System (ADS)

The excitations occurring at a solid surface due to slow highly charged ion (HCI) impacts are interesting from the perspective of fundamental processes in atomic collisions and materials science. This thesis focuses on two questions: (1) How much HCI potential energy deposition is required to form permanent surface modifications?, (2) How does the presence of a thin dielectric surface film change the classical over-the-barrier picture for neutralization above a clean metal? I describe a measurement of craters in thin dielectric films formed by XeQ+ (26 ? Q ? 44) projectiles. Tunnel junction devices with ion-irradiated barriers were used to amplify the effect of charge-dependent cratering through the exponential dependence of tunneling conductance on barrier thickness. Electrical conductance of a crater sigmac(Q) increased by four orders of magnitude (7.9 x 10 -4 muS to 6.1 muS) as Q increased, corresponding to crater depths ranging from 2 A to 11 A. According to a heated spike model, the energy required to produce the craters spans from 8 keV to 25 keV over the investigated charge states. Considering energy from pre-equilibrium nuclear and electronic stopping as well as neutralization, we find that at least (27 +/- 2) % of available projectile neutralization energy is deposited into the thin film during impact. Additionally, an extension of the classical over-barrier model for HCI neutralization above dielectric covered metal surfaces is presented. The model is used to obtain the critical distance for the onset of neutralization above C60/Au(111), Al2O3/ Co, and LiF/Au(111) targets. The model predicts that for thin films with low electrical permittivity and positive electron affinity, the onset of neutralization can begin with the electrons in the metal, and at further ion-surface distances than for clean metals. The model describes three distinct over-the-barrier regimes of "vacuum limited" capture from the metal, "thin film" limited capture from the metal, and capture from the insulator. These regimes are detailed in terms of charge state, target material parameters and film thickness.

Lake, Russell E.

60

Leakage current limit of time domain reflectometry in ultrathin dielectric characterization  

NASA Astrophysics Data System (ADS)

The accurate characterization of highly leaky dielectrics has been a serious challenge in MOSFET and capacitor studies. We have shown that time domain reflectometry (TDR) can be used to measure the capacitance of ultrathin SiO2 MOS capacitors even at a leakage current density as high as ˜3000 A/cm2, which is approximately 103 times higher than the limit of a conventional impedance analyzer. The extremely short interaction time of the TDR C-V method makes the TDR capacitance measurement more immune to the leakage current. Since the TDR C-V method does not require special high-frequency test structures other than a ground-signal pad pattern, the TDR C-V method is a promising capacitance measurement method for leaky dielectrics.

Kim, Yonghun; Baek, Seung-heon Chris; Jeon, Changhoon; Lee, Young Gon; Kim, Jin Ju; Jung, Ukjin; Kang, Soo Cheol; Park, Woojin; Lee, Seok Hee; Lee, Byoung Hun

2014-08-01

61

Monte Carlo study of remote Coulomb and remote surface roughness scattering in nanoscale Ge PMOSFETs with ultrathin high- ? dielectrics  

Microsoft Academic Search

In this work we perform full-band Monte Carlo simulations of nanoscale Ge bulk PMOSFETs with ultrathin (<2nm) effective oxide thickness high-? dielectrics and investigate the importance of remote Coulomb and remote surface roughness scattering in these devices. In addition to these remote scattering mechanisms, transport is considered in the presence of phonon, ionized impurity, surface roughness scattering and impact ionization.

Bahniman Ghosh; Jer-Hueih Chen; Xiao-Feng Fan; Leonard F. Register; Sanjay K. Banerjee

2006-01-01

62

Optical Properties of Ultrathin Films: Evidence for a Dielectric Anomaly at the Insulator-to-Metal Transition  

E-print Network

The insulator-to-metal (I=M) and insulator-to- superconductor (I=S) transitions are fundamental issues in modernOptical Properties of Ultrathin Films: Evidence for a Dielectric Anomaly at the Insulator-to-Metal Transition J. J. Tu,* C. C. Homes, and M. Strongin Department of Physics, Brookhaven National Laboratory

Lombardi, John R.

63

Broadband absorption enhancement in ultrathin-film solar cells by combining dielectric nanogratings and metallic nanoribbons  

NASA Astrophysics Data System (ADS)

Optical absorption improvement and cost reduction of thin-film solar cells have been long-time issues. These two aims are achieved simultaneously by combining metallic nanoribbons and dielectric gratings at the front side of ultrathin-film amorphous silicon solar cells. Surface-plasmon-polariton waves excited by the nanoribbons at the long wavelength co-operates with Uller-Zenneck waves and cavity resonances excited by the gratings at the short wavelength with little cross-effect, leading to a complementary absorption enhancement of 31% when compared to planar structure. In addition, this design exhibits wide-angle absorption as well as a high fabrication tolerance. Compared to the previous work combining different mechanisms, this design provides fewer fabrication steps and an easier approach. Moreover, the nanoribbons can be used as a transparent conducting electrode for a low-cost alternative to expensive indium tin oxide thin-film.

Gou, Fangwang; Li, Xian; Chen, Ji; Su, Guangyao; Liu, Chuanhong; Zhang, Zhaoyu

2015-01-01

64

Effective work function tunability and interfacial reactions with underlying HfO2 layer of plasma-enhanced atomic layer deposited TaCxNy films  

NASA Astrophysics Data System (ADS)

This study examined the interfacial reaction of plasma-enhanced atomic layer deposited TaCxNy films with underlying SiO2 and HfO2 layers, as well as their effective work functions (EWFs). The adoption of Ar /H2 plasma as a reducing agent suppressed the interfacial reactions resulting in a lower electrical thickness. However, it increased the interface state density due to the massive Ar+ plasma damage on the dielectric films. The interfacial reactions were suppressed in TaCxNy on HfO2 compared with that on SiO2. The EWF of TaCxNy with the H2 plasma and Ar /H2 plasma on HfO2 was ˜4.9-5.2 and ˜4.6eV, respectively.

Park, Tae Joo; Kim, Jeong Hwan; Jang, Jae Hyuck; Na, Kwang Duk; Hwang, Cheol Seong; Kim, Gee-Man; Choi, Kang Jun; Jeong, Jae Hak

2008-05-01

65

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

PubMed

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 ?F 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

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

2015-02-01

66

In-situ MBE and ALD deposited HfO2 on In0.53Ga0.47As  

NASA Astrophysics Data System (ADS)

The semiconductor industry is calling for innovative devices offering high performance with low power consumption. High-? dielectrics/metal gates on high carrier mobility channels are now strong contenders in the post Si CMOS application. Hafnium-based oxide has been employed as the gate dielectric in Si CMOS since 45 nm node and InGaAs is a leading candidate for channel materials. However, reports of HfO2 on InGaAs are scant, and surface treatments using H2S or trimethylaluminum are claimed to be required for achieving high quality HfO2(high-?)/InGaAs interface. In this work, HfO2 has been in-situ deposited on n- and p-In0.53Ga0.47As using both molecular-beam-epitaxy (MBE) and atomic-layer- deposition (ALD), without using any interfacial passivation layer or surface treatments. The HfO2/In0.53Ga0.47As metal-oxide-semiconductor capacitors (MOSCAPs) all exhibit outstanding thermal stabilities (> 800^oC), low leakage currents (˜ 10-8 A/cm^2 at 1 MV/cm), and good CV characteristics. Moreover, the MOSCAPs have shown spectra of interfacial trap densities (Dit's) with no discernible peaks at mid-gap, confirmed by temperature-dependent conductance method.

Lee, W. C.; Lin, C. A.; Huang, M. L.; Kwo, J.; Chang, Y. H.; Chang, P.; Lin, T. D.; Hong, M.

2012-02-01

67

The simulated vibrational spectra of HfO2 polymorphs  

NASA Astrophysics Data System (ADS)

The Raman and infrared (IR) spectra of HfO2 polymorphs are simulated within the framework of density functional perturbation theory. The joint lattice-dynamical model treatment of the monoclinic, orthorhombic-I, orthorhombic-II and tetragonal-polymorphs of HfO2 is conducted with an emphasis on the evolution of their vibrational spectra. Our method is based upon the local density approximation with Hartwigsen-Goedecker-Hutter-type pseudopotentials and it gives a precise description of the phonon energies in these polymorphs with small deviations relative to the available experimental data. The simulated Raman spectra of the orthorhombic-I and II HfO2 are consistent with the data from high-pressure experiments, which indicates that these samples are well crystallized and randomly oriented. Rigid assignments of all the Raman peaks of these four polymorphs are obtained. Further, the simulated IR spectra of these four polymorphs are firstly presented, and the characteristics of these spectra are obtained, which provide potential ways to identify these phases in production environments.

Zhou, B.; Shi, H.; Zhang, X. D.; Su, Q.; Jiang, Z. Y.

2014-03-01

68

Low-temperature molecular vapor deposition of ultrathin metal oxide dielectric for low-voltage vertical organic field effect transistors.  

PubMed

We demonstrate a low-temperature layer-by-layer formation of a metal-oxide-only (AlOx) gate dielectric to attain low-voltage operation of a self-assembly based vertical organic field effect transistor (VOFET). The AlOx deposition method results in uniform films characterized by high quality dielectric properties. Pin-hole free ultrathin layers with thicknesses ranging between 1.2 and 24 nm feature bulk dielectric permittivity, ?AlOx, of 8.2, high breakdownfield (>8 MV cm(-1)), low leakage currents (<10(-7) A cm(-2) at 3MV cm(-1)), and high capacitance (up to 1 ?F cm(-2)). We show the benefits of the tunable surface properties of the oxide-only dielectric utilized here, in facilitating the subsequent nanostructuring steps required to realize the VOFET patterned source electrode. Optimal wetting properties enable the directional block-copolymer based self-assembly patterning, as well as the formation of robust and continuous ultrathin metallic films. Supported by computer modeling, the vertical architecture and the methods demonstrated here offer a simple, low-cost, and free of expensive lithography route for the realization of low-voltage (VGS/DS?3 V), low-power, and potentially high-frequency large-area electronics. PMID:23484807

Ben-Sasson, Ariel J; Ankonina, Guy; Greenman, Michael; Grimes, Michael T; Tessler, Nir

2013-04-10

69

HfO2/GeOxNy/Ge gate stacks with sub-nanometer capacitance equivalent thickness and low interface trap density by in situ NH3 plasma pretreatment  

NASA Astrophysics Data System (ADS)

The native oxides on Ge substrates can be transformed into GeOxNy by in situ NH3 plasma pretreatment. The interfacial and electrical properties of HfO2 caps gate stacks on Ge with and without ultrathin GeOxNy barrier layers have been investigated thoroughly. HfO2/GeOxNy/Ge stacking structure shows a sharp and flat interface between HfO2 and Ge substrates without recognized interfacial layer. In situ NH3 plasma pretreatment effectively improves the electrical properties such as higher accumulation capacitance, smaller frequency dispersion, and lower interface trap density (Dit) than without NH3 plasma pretreatment. It is ascribed to that fact that the GeOxNy barrier layer between HfO2 and Ge substrates shows better thermal stability and suppresses the Ge outdiffusion. The 3-nm-thick HfO2 gate stacks on Ge with 60 s NH3 plasma pretreatment exhibit a capacitance equivalent thickness of 0.96 nm and a leakage current density of 1.12 mA/cm2 at +1 V gate bias with acceptable Dit value of 3.42 × 1012 eV-1 cm-2. These results indicate that the surface nitridation by in situ NH3 plasma pretreatment may be a promising approach for the realization of high quality Ge-based transistor devices.

Cao, Yan-Qiang; Chen, Jun; Liu, Xiao-Jie; Li, Xin; Cao, Zheng-Yi; Ma, Yuan-Jie; Wu, Di; Li, Ai-Dong

2015-01-01

70

Functionalized graphene as an ultrathin seed layer for the atomic layer deposition of conformal high-k dielectrics on graphene.  

PubMed

Ultrathin functionalized graphene (FG) is demonstrated to work as an effective seed layer for the atomic layer deposition (ALD) of high-k dielectrics on graphene that is synthesized via chemical vapor deposition (CVD). The FG layer is prepared using a low-density oxygen plasma treatment on CVD graphene and is characterized using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). While the ALD deposition on graphene results in a patchy and rough dielectric deposition, the abundant oxygen species provided by the FG seed layer enable conformal and pinhole-free dielectric film deposition over the entire area of the graphene channel. The metal-insulator-graphene (MIG) capacitors fabricated with the FG-seeded Al2O3 exhibit superior scaling capabilities with low leakage currents when compared with the co-processed capacitors with Al seed layers. PMID:24171487

Shin, Woo Cheol; Bong, Jae Hoon; Choi, Sung-Yool; Cho, Byung Jin

2013-11-27

71

Topology dependent electronic and dielectric properties of free standing alloyed ultrathin nanowires of noble metals  

NASA Astrophysics Data System (ADS)

Structural, electronic and dielectric properties of free standing ultrathin alloyed nanowires of noble metals (AgAu, AgCu, AgPt, AuCu, AuPt and CuPt) in various topologies (linear, ladder and double zigzag) have been studied by using ab initio density functional theory. Among the different topologies of alloyed ultrathin nanowires of noble metals, double zigzag (DZZ) topology has been found to be most stable and the linear topology the least stable. Also the binding energy of alloyed nanowires of AgAu and AuCu for all the studied topologies is found to be larger than the average binding energy of the corresponding pristine nanowires, indicating a strong alloying effect for these topologies. Among electronic properties, the alloyed nanowires of different topologies containing Pt (AgPt, AuPt and AuCu) are found to be ferromagnetic in nature, a result of d charge depletion in Ag, Au and Cu sites and d charge gain at Pt sites. On the other hand, all the topologies (except ladder topology) of alloyed nanowires viz. AgAu, AgCu and AuCu are found to be semiconducting in nature. The optical properties of the studied alloyed nanowires have been found to be different from their corresponding pristine nanowires due to change in the band structure on alloying. The linear topology of AgAu, AgCu and AuCu and DZZ topologies (DZZ1, DZZ2 and DZZ3) of Ag, Au, Cu, AgAu, AgCu and AuCu are semiconducting in nature with band gap lying in the infrared region, causing absorption of photons from a visible spectrum leading to blackish appearance. Whereas, remaining topologies are found to be metallic in nature, with plasmon frequency lying in the energy range of 0.35 eV to 1.62 eV, which is in the infrared region and hence these nanowires shall appear to be transparent to the visible region.

Kumar, Arun; Kumar, Ashok; Ahluwalia, P. K.

2014-08-01

72

Quantitatively enhanced reliability and uniformity of high-? dielectrics on graphene enabled by self-assembled seeding layers.  

PubMed

The full potential of graphene in integrated circuits can only be realized with a reliable ultrathin high-? top-gate dielectric. Here, we report the first statistical analysis of the breakdown characteristics of dielectrics on graphene, which allows the simultaneous optimization of gate capacitance and the key parameters that describe large-area uniformity and dielectric strength. In particular, vertically heterogeneous and laterally homogeneous Al2O3 and HfO2 stacks grown via atomic-layer deposition and seeded by a molecularly thin perylene-3,4,9,10-tetracarboxylic dianhydride organic monolayer exhibit high uniformities (Weibull shape parameter ? > 25) and large breakdown strengths (Weibull scale parameter, E(BD) > 7 MV/cm) that are comparable to control dielectrics grown on Si substrates. PMID:23387502

Sangwan, Vinod K; Jariwala, Deep; Filippone, Stephen A; Karmel, Hunter J; Johns, James E; Alaboson, Justice M P; Marks, Tobin J; Lauhon, Lincoln J; Hersam, Mark C

2013-03-13

73

Band alignment of HfO2 on SiO2/Si structure  

NASA Astrophysics Data System (ADS)

Band alignment of HfO2 with various thicknesses on SiO2/Si structure is investigated by x-ray photoelectron spectroscopy (XPS). Band bending of HfO2/SiO2/Si system is found to vary with HfO2 thickness. Band alignment of entire HfO2/SiO2/Si is demonstrated using concepts of interfacial or surface gap states and charge neutrality level (CNL). The XPS results are interpreted and attributed to lower CNL of HfO2 than SiO2/Si which induces electron transfer from SiO2/Si to HfO2, resulting in band bending upward for SiO2/Si. These further confirm feasibility of gap state based theory in investigating band alignments of oxide/semiconductor and oxide/oxide interfaces.

Wang, Xiaolei; Han, Kai; Wang, Wenwu; Xiang, Jinjuan; Yang, Hong; Zhang, Jing; Ma, Xueli; Zhao, Chao; Chen, Dapeng; Ye, Tianchun

2012-03-01

74

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

SciTech Connect

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.

Grandfond, A.; Gautier, B.; Militaru, L.; Albertini, D.; Descamps-Mandine, A. [Institut des Nanotechnologies de Lyon (INL), UMR CNRS 5270, INSA de Lyon, 7 Avenue Jean Capelle, 69621 Villeurbanne CEDEX (France)

2014-04-07

75

Multiple spectrum analysis and evaluation for optical constants of HfO2 thin films  

NASA Astrophysics Data System (ADS)

HfO2 thin films were deposited on ZS1 silica by Ion Beam Sputtering (IBS) technique. Optical constants of HfO2 thin films were obtained by multiple spectrum analysis method, which combined the transmittance spectrum and ellipsometry spectrum of the film. The refractive index and extinction coiefficient of HfO2 thin films were evaluated by etching experiments of the film. The analysis spectral range was between 250nm and 850nm.

Liu, Dandan; Liu, Huasong; Jiang, Chenghui; Jiang, Yugang; Wang, Lishuan; Zhao, Zhihong; Ji, Yiqin

2014-08-01

76

Ab initio calculation of relative permittivity of La-doped HfO2  

NASA Astrophysics Data System (ADS)

First principles calculations of HfO2 and La-doped HfO2 structures were carried out to investigate the effect of La doping on the relative permittivity of HfO2 films. In this study 6.25% of La was incorporated into HfO2. Upon examination, we found out that La addition increased the value of the relative permittivity from 19 to 26 and this was because the La-induced distortion increased the range of frequencies that contribute to the IR-active modes.

Ong, T. M.; Xu, S.

2014-12-01

77

Electron beam induced local crystallization of HfO2 nanopores for biosensing applications  

PubMed Central

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

Shim, Jiwook; Rivera, Jose; Bashir, Rashid

2013-01-01

78

Impact of the crystal structure of HfO2 on the transport properties of model HfO2/Si/HfO2 silicon-on-insulator field-effect transistors: A combined DFT-scattering theory approach  

NASA Astrophysics Data System (ADS)

Motivated by the polycrystalline structure of the high permittivity dielectric HfO2 in contact with Si, we report calculations of carrier transport in nanometer-thin atomistic silicon-on-insulator field-effect transistor models. To qualitatively understand the impact of different crystalline phases of the dielectric on the transport characteristics of the channel, we have investigated two polymorphs of HfO2 interfacing with Si, namely, the well-known tetragonal (t-HfO2) and the theoretically proposed anatase (a-HfO2) phases. For the transport calculations we have employed tetragonal- (t-HfO2/Si/t-HfO2) and anatase-based (a-HfO2/Si/a-HfO2) NSOI films. Our calculations reveal that transport is more efficient for the anatase polymorph since its good lattice match to Si does not create interface states in the Si band gap. The tetragonal polymorph creates scattering states in the Si band valence-band edge through the presence of stretched Si-Si bonds at the interface, resulting in degraded transport characteristics. Our study suggests that different bonding arrangements along the channel length create regions of increased carrier scattering even in the absence of other scattering processes such as phonons, trapped charges, or interface roughness.

Giorgi, G.; Fonseca, L. R. C.; Korkin, A.; Yamashita, K.

2009-06-01

79

Monte Carlo study of remote Coulomb and remote surface roughness scattering in nanoscale Ge PMOSFETs with ultrathin high- ? dielectrics  

NASA Astrophysics Data System (ADS)

In this work we perform full-band Monte Carlo simulations of nanoscale Ge bulk PMOSFETs with ultrathin (<2 nm) effective oxide thickness high- ? dielectrics and investigate the importance of remote Coulomb and remote surface roughness scattering in these devices. In addition to these remote scattering mechanisms, transport is considered in the presence of phonon, ionized impurity, surface roughness scattering and impact ionization. Quantum confinement in the inversion layer is taken into account in the form of a modified potential. We show that the experimentally observed data on the dependence of mobility on the thickness of the high- ? dielectric can be accurately modeled via scattering by remote surface roughness at the gate-dielectric interface and remote Coulomb scattering due to fixed charges in the dielectric. The parameters in the remote scattering mechanisms are fitted by matching Monte Carlo data with those obtained from experiments on the dependence of mobility on the thickness of the dielectric. For a gate overdrive, ( Vg - Vt), of 1.0 V, remote scattering mechanisms seem to decrease the saturation current by as much as 15% in these devices. We also show that at the high vertical fields (˜1 MV/cm) in these experimental devices, remote scattering mechanisms can substantially reduce the mobility for oxide thicknesses below 5 nm.

Ghosh, Bahniman; Chen, Jer-Hueih; Fan, Xiao-Feng; Register, Leonard F.; Banerjee, Sanjay K.

2006-02-01

80

Investigation of SiO 2/HfO 2 gate stacks for application to non-volatile memory devices  

NASA Astrophysics Data System (ADS)

Engineering of the tunnel barrier of non-volatile memories is addressed in this paper. The strong potential of multilayer stacks for reducing the programming times of these devices, without altering their retention characteristics, is studied. To this aim, experimental results showing the improved field sensitivity of the gate current of MOS devices with SiO 2/HfO 2 gate stacks compared to SiO 2 of identical electrical thickness (EOT) are presented. Simulations of the corresponding tunnelling currents are also reported. Our electrical measurements suggest that it is of great interest to investigate the use of SiO 2/HfO 2 stacks as tunnel barriers for NVMs. These experimental results on double-layer stacks allow to confirm experimentally a conduction principal that could be used in symmetrical triple-layer SiO 2/high- k/SiO 2 tunnel barriers, thus allowing an advantageous behaviour in both conduction directions. Further simulations are presented in order to evaluate the best parameters that the high- k layer should have in order to lead to better performance than a SiO 2 tunnel barrier. They suggest that if the high- k has 1.5-2.0 eV conduction band offset compared to Si its relative effective mass and dielectric constant should meet the constraint: ?·?{m}?5 ( mhigh- k, relative electron mass; ?high- k, relative dielectric constant).

Buckley, J.; Salvo, B. De; Ghibaudo, G.; Gely, M.; Damlencourt, J. F.; Martin, F.; Nicotra, G.; Deleonibus, S.

2005-11-01

81

Seeding atomic layer deposition of high-k dielectric on graphene with ultrathin poly(4-vinylphenol) layer for enhanced device performance and reliability  

NASA Astrophysics Data System (ADS)

We demonstrate that ultrathin poly(4-vinylphenol) (PVP) acts as an effective organic seeding layer for atomic layer deposition (ALD) of high-k dielectric on large-scale graphene fabricated by chemical vapor deposition (CVD). While identical ALD conditions result in incomplete and rough dielectric deposition on CVD graphene, the reactive groups provided by the PVP seeding layer yield conformal and pinhole-free dielectric films throughout the large-scale graphene. Top-gate graphene field effect transistors fabricated with the high quality, PVP-seeded Al2O3 gate dielectric show superior carrier mobility and enhanced reliability performance, which are desirable for graphene nanoelectronics.

Cheol Shin, Woo; Yong Kim, Taek; Sul, Onejae; Jin Cho, Byung

2012-07-01

82

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)

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.

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

1990-01-01

83

Correlation between Stress-Induced Leakage Current (SILC) and the HfO2 bulk trap density in a SiO2\\/HfO2 stack  

Microsoft Academic Search

Both trap generation and Stress-Induced Leakage Current (SILC) are measured as a function of the stress voltage on a 1nm\\/4nm SiO2\\/HfO2 stack. The SILC firstly rises proportionally with the bulk trap density in the HfO2 but close to breakdown this relation becomes quadratic, indicating that first single-trap conduction paths are causing the SILC, later followed by two-trap conduction paths. At

F. Crupi; R. Degraeve; A. Kerber; D. H. Kwak; G. Groeseneken

2004-01-01

84

Ge MOS Capacitors with Thermally Evaporated HfO2 as Gate * D. Misra,a,  

E-print Network

surface carrier mobility degradation has been observed in metal oxide semiconductor MOS devices using HfO2 to surface carrier mobility degradation as Ge has higher carrier mobility in comparison to Si. Devices using by thermal evaporation. Oxygen was added at constant partial pressure during the deposition to form HfO2

Misra, Durgamadhab "Durga"

85

Effect of Al addition on the microstructure and electronic structure of HfO2 film  

E-print Network

Effect of Al addition on the microstructure and electronic structure of HfO2 film X. F. Wang investigated the microstructures and electronic structures of a series of hafnium aluminate HfAlO films with Al concentration ranging from 0% to 100%. When the films evolve from pure HfO2 to pure Al2O3 by increasing

Gong, Xingao

86

Plasma-nitrided silicon-rich oxide as an extension to ultrathin nitrided oxide gate dielectrics  

SciTech Connect

We have investigated the mechanism of N incorporation, during plasma nitridation, in thermally grown ultrathin (<2 nm) SiO{sub 2} films and deposited silicon-rich oxide films. X-ray photoelectron spectroscopy analysis indicates that N atoms exchange mainly with O to bond with Si atoms in ultrathin plasma-nitrided oxides. Based on this understanding, we were able to increase the amount of N that can be incorporated in plasma-nitrided silicon oxides by increasing the silicon content in these films. This was achieved by depositing ultrathin substoichiometric silicon-rich oxide films. We demonstrate an increase of almost twice as much N in these ultrathin plasma-nitrided silicon-rich oxide films yielding lower gate leakage current for a given thickness.

Cubaynes, F.N.; Venezia, V.C.; Marel, C. van der; Snijders, J.H.M.; Everaert, J.L.; Shi, X.; Rothschild, A.; Schaekers, M. [Philips Research Leuven, Kapeldreef 75, 3001 Leuven (Belgium); Philips Research Eindhoven, Prof. Holstlaan 4, 5656 AA, Eindhoven (Netherlands); Imec, Kapeldreef 75, 3001 Leuven (Belgium)

2005-04-25

87

Critical thickness for extrinsic contributions to the dielectric and piezoelectric response in lead zirconate titanate ultrathin films  

NASA Astrophysics Data System (ADS)

Highly (100)-textured Pb(Zr0.53Ti0.47)O3 films (Lotgering factors ?90%) with thicknesses ranging from 20 to 260 nm were grown on platinized Si substrates using sol-gel deposition. Ferroelectric hysteresis, low field dielectric permittivity, and nonlinear dielectric response as well as converse longitudinal piezoelectric response (d33,f) of the ultrathin films were studied at 1 kHz. The measurements revealed the existence of a critical film thickness, ˜50 nm, below which the extrinsic contributions to the dielectric response are almost completely suppressed. Piezoelectric response of the films also showed a significant (˜50%) drop at the same critical thickness. Due to the columnar microstructure of these films the critical dimension of the ferroelectric is represented by the thickness rather than the lateral grain size, where the latter is invariant across the samples. The critical thickness led also to a deviation of the thickness dependence of the dielectric permittivity from the in-series capacitors model frequently representing "interfacial dead layers." The critical size is attributed to significant reduction in domain wall population and/or mobility in films thinner than ˜50 nm.

Bastani, Yaser; Schmitz-Kempen, Thorsten; Roelofs, Andreas; Bassiri-Gharb, Nazanin

2011-01-01

88

Study of potential high-k dielectric for UTB SOI MOSFETs using analytical modeling of the gate tunneling leakage  

NASA Astrophysics Data System (ADS)

In this paper, we use analytical models of the direct tunneling gate leakage current to determine the high-k dielectric suitable for the nanoscale ultra-thin body SOI MOSFET structure with the predicted equivalent oxide thickness (EOT) and the maximum value of gate leakage current according to the requirements of the latest ITRS roadmap for three technological nodes. The most important criteria for selecting alternative dielectrics (maximum gate leakage current, EOT, electron effective mass, dielectric constant k-value, barrier height and SiO2 thickness as an interfacial layer) were taken into account to determine the suitability of the gate oxide materials. In the ideal case without an interfacial layer, HfO2 and Lu2O3 were found to be the best gate oxide materials for the 17, 15 and 14 nm technological node requirements.

Darbandy, Ghader; Lime, François; Cerdeira, Antonio; Estrada, Magali; Garduño, Ivan; Iñiguez, Benjamin

2011-11-01

89

HfO2/SiO2 enhanced diamond turned aluminum mirrors for IR laser optics  

NASA Astrophysics Data System (ADS)

HfO2/SiO2 multilayers were deposited on single point diamond turned aluminum substrates via modified reactive plasma ion assisted deposition to form a laser durable and environmentally stable dielectric enhanced IR mirror at a wavelength of 1064nm. The effect of the surface quality of the diamond turned aluminum on the optical performance of the dielectric enhanced mirror was assessed. A laser-induced damage threshold up to 11 J/cm2 was obtained from the enhanced aluminum mirror tested in pulse mode at 1064nm with a pulse length of 20ns and a repetition rate of 20Hz. Laser damage morphology was revealed by a scanning electron microscopy. The damage mechanism was attributed to nodule defects generated by particle embedded on the aluminum substrate surface.

Wang, Jue; Davis, Ronald W.; Wang, Angela Q.; Schreiber, Horst; Wilkinson, Scott J.; Crifasi, Joseph C.; Felock, Robert D.

2011-12-01

90

Effect of post-deposition annealing temperature on RF-sputtered HfO2 thin film for advanced CMOS technology  

NASA Astrophysics Data System (ADS)

Structural and electrical properties of HfO2 gate-dielectric metal-oxide-semiconductor (MOS) capacitors deposited by sputtering are investigated. The HfO2 high-k thin films have been deposited on p-type <100> silicon wafer using RF-Magnetron sputtering technique. The Ellipsometric, FTIR and AFM characterizations have been done. The thickness of the as deposited film is measured to be 35.38 nm. Post deposition annealing in N2 ambient is carried out at 350, 550, 750 °C. The chemical bonding and surface morphology of the film is verified using FTIR and AFM respectively. The structural characterization confirmed that the thin film was free of physical defects and root mean square surface roughness decreased as the annealing temperature increased. The smooth surface HfO2 thin films were used for Al/HfO2/p-Si MOS structures fabrication. The fabricated Al/HfO2/p-Si structure had been used for extracting electrical properties such as dielectric constant, EOT, interface trap density and leakage current density through capacitance voltage and current voltage measurements. The interface state density extracted from the G-V measurement using Hill Coleman method. Sample annealed at 750 °C showed the lowest interface trap density (3.48 × 1011 eV-1 cm-2), effective oxide charge (1.33 × 1012 cm-2) and low leakage current density (3.39 × 10-9 A cm-2) at 1.5 V.

Khairnar, A. G.; Mahajan, A. M.

2013-01-01

91

Optical characteristics of H2O-based and O3-based HfO2 films deposited by ALD using spectroscopy ellipsometry  

NASA Astrophysics Data System (ADS)

Optical properties of thin atomic layer-deposited HfO2 films grown by H2O and O3 are analyzed by variable angle spectroscopic ellipsometry. By investigating the dielectric constant, it is found that a higher real part of the dielectric constant (? 1) value is observed for H2O-based film due to less silicate component in the film. Careful examination of the log scale of imaginary part of the dielectric constant (? 2) leads to the conclusion that the absorption features in the energy range of 3.2-5.35 eV originate from the interface layer between the silicon substrate and the native oxide. In particular, O3-based gate stacks have less sub-band gap defect states besides the silicon's critical features. Moreover, a larger high-frequency dielectric constant, direct and indirect band gap values are obtained for O3-based film. Meanwhile, suitable valence band offsets (3.38 and 3.55 eV) and conduction band offsets (1.58 and 1.47 eV) are obtained for H2O- and O3-based HfO2 gate stacks, respectively, indicating both type of dielectric films can provide sufficient tunneling barriers for both electrons and holes.

Fan, Xiaojiao; Liu, Hongxia; Zhong, Bo; Fei, Chenxi; Wang, Xing; Wang, Qianqiong

2015-02-01

92

Temperature dependent structural, optical and hydrophobic properties of sputtered deposited HfO2 films  

NASA Astrophysics Data System (ADS)

Hafnium oxide being high-k dielectric has been successfully utilized in electronic and optical applications. Being thermodynamically stable and having good mechanical strength, it can be used as a protective coating for outdoor HV insulators which are suffering from surface flashover problem due to contamination. In this paper, we are investigating the effect of substrate temperature on structural, optical and hydrophobic properties of hafnium oxide coating deposited over glass insulators by DC magnetron sputtering. X-ray diffraction is applied to determine the crystalline phase and crystallite size of the film. The morphology of the samples is examined using atomic force microscopy. The optical properties are studied using UV-vis-NIR spectrophotometer. The wettability of the film is investigated using contact angle meter. The thickness is measured using surface profilometer and verified through optical data. The relationship between substrate temperature with grain size, roughness, refractive index, and hydrophobicity is manifested. The maximum contact angle for HfO2 film was found to be 106° at 400°C.

Dave, V.; Dubey, P.; Gupta, H. O.; Chandra, R.

2014-01-01

93

Phase diagrams, dielectric response, and piezoelectric properties of epitaxial ultrathin (001) lead zirconate titanate films under anisotropic misfit strains  

NASA Astrophysics Data System (ADS)

We develop a nonlinear thermodynamic model to predict the phase stability of ultrathin epitaxial (001)-oriented ferroelectric PbZr1-xTixO3 (PZT) films with x =1.0, 0.9, 0.8, and 0.7 on substrates which induce anisotropic in-plane strains. The theoretical formalism incorporates the relaxation by misfit dislocations at the film deposition temperature, the possibility of formation of ferroelectric polydomain structures, and the effect of the internal electric field that is generated due to incomplete charge screening at the film-electrode interfaces and the termination of the ferroelectric layer. This analysis allows the development of misfit strain phase diagrams that provide the regions of stability of monodomain and polydomain structures at a given temperature, film thickness, and composition. It is shown that the range of stability for rotational monodomain phase is markedly increased in comparison to the same ferroelectric films on isotropic substrates. Furthermore, the model finds a strong similarity between ultrathin PbTiO3 and relatively thicker PZT films in terms of phase stability. The combinations of the in-plane misfit strains that yield a phase transition sequence that results in a polarization rotation from the c-phase (polarization parallel to the [001] direction in the film) to the r-phase, and eventually to an in-plane polarization parallel to the [110] direction (the aa-phase) is determined to be the path with the most attractive dielectric and piezoelectric coefficients resulting in enhancements of 10 to 100 times in the dielectric permittivity and piezoresponse compared to bulk tetragonal ferroelectrics of the same PZT composition.

Qiu, Q. Y.; Alpay, S. P.; Nagarajan, V.

2010-06-01

94

Chemical structures and electrical properties of atomic layer deposited HfO2 thin films grown at an extremely low temperature (?100 °C) using O3 as an oxygen source  

NASA Astrophysics Data System (ADS)

The properties of atomic layer deposited (ALD) HfO2 films grown at low temperatures (?100 °C) were examined for potential applications in flexible display and bioelectronics. A saturated ALD growth behavior was observed even at an extremely low temperature (30 °C) due to the strong oxidizing potential of O3. However, HfO2 films grown at low temperatures showed a low film density and high impurity concentration, because the thermal energy during film growth was insufficient to remove ligands completely from Hf ions in precursor molecule. This resulted in low dielectric constant and high leakage current density of the films. Nevertheless, HfO2 film grown at 100 °C using O3 gas with a high concentration (390 g/Nm3) showed a tolerable impurity concentration with the dielectric constant of ?16 and breakdown field of ?4 MV/cm, which are approximately two-thirds of those of HfO2 film grown at 250 °C.

Kim, Jeong Hwan; Park, Tae Joo; Kim, Seong Keun; Cho, Deok-Yong; Jung, Hyung-Suk; Lee, Sang Young; Hwang, Cheol Seong

2014-02-01

95

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

SciTech Connect

Fermi level pinning at metal/n-InP interface and effective Schottky barrier height (?{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 ?{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.

Zheng, Shan; Yang, Wen; Sun, Qing-Qing, E-mail: qqsun@fudan.edu.cn, E-mail: linchen@fudan.edu.cn; Zhou, Peng; Wang, Peng-Fei; Wei Zhang, David [State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433 (China)] [State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433 (China); Chen, Lin; Xiao, Fei [Department of Materials Science, Fudan University, Shanghai 200433 (China)] [Department of Materials Science, Fudan University, Shanghai 200433 (China)

2013-12-23

96

Incubation effect of laser-induced surface damage of HfO2/SiO2 HR coating in the femto-nanosecond region  

NASA Astrophysics Data System (ADS)

This paper is devoted to a long-term investigation into the nature of incubation effect of multilayer dielectric HR mirror coatings. Accumulated damage behaviors of HfO2/SiO2 mirrors for 800nm, 1053nm, and 1064nm, both fabricated by conventional electron beam evaporation (EBE), were investigated by ultra-short pulse (800nm/~100fs), short pulse (1053nm/~1ps), and long pulse (1064nm/~10ns) lasers, respectively. Incubation effect was found to be a universal phenomenon for HfO2/SiO2 mirrors irradiating by the femto-nanosecond lasers. And when the shot number was about 100, the multi-pulse damage threshold of samples decreased to the level of 60~70% of the single-pulse threshold. Typical damage morphologies and depths information of HR samples were characterized by optical microscope and surface profiler. The results revealed that the electric field distribution within the mirrors had significant influence on the initial damage onset of the mirrors. In addition, theoretical simulation was carried out to describe the incubation behaviors of HfO2/SiO2 mirrors in the femto- and nano-second regions. It seemed reasonable that incubation effect was attributed to the accumulation of native or laser-induced electronic trapping states.

Chen, Shunli; Zhao, Yuanan; Kong, Fanyu; Li, Dawei; He, Hongbo; Shao, Jianda

2011-11-01

97

Incubation effect of laser-induced surface damage of HfO2/SiO2 HR coating in the femto-nanosecond region  

NASA Astrophysics Data System (ADS)

This paper is devoted to a long-term investigation into the nature of incubation effect of multilayer dielectric HR mirror coatings. Accumulated damage behaviors of HfO2/SiO2 mirrors for 800nm, 1053nm, and 1064nm, both fabricated by conventional electron beam evaporation (EBE), were investigated by ultra-short pulse (800nm/~100fs), short pulse (1053nm/~1ps), and long pulse (1064nm/~10ns) lasers, respectively. Incubation effect was found to be a universal phenomenon for HfO2/SiO2 mirrors irradiating by the femto-nanosecond lasers. And when the shot number was about 100, the multi-pulse damage threshold of samples decreased to the level of 60~70% of the single-pulse threshold. Typical damage morphologies and depths information of HR samples were characterized by optical microscope and surface profiler. The results revealed that the electric field distribution within the mirrors had significant influence on the initial damage onset of the mirrors. In addition, theoretical simulation was carried out to describe the incubation behaviors of HfO2/SiO2 mirrors in the femto- and nano-second regions. It seemed reasonable that incubation effect was attributed to the accumulation of native or laser-induced electronic trapping states.

Chen, Shunli; Zhao, Yuanan; Kong, Fanyu; Li, Dawei; He, Hongbo; Shao, Jianda

2012-01-01

98

III-Nitride grating grown on freestanding HfO2 gratings  

PubMed Central

We report here the epitaxial growth of III-nitride material on freestanding HfO2 gratings by molecular beam epitaxy. Freestanding HfO2 gratings are fabricated by combining film evaporation, electron beam lithography, and fast atom beam etching of an HfO2 film by a front-side silicon process. The 60-?m long HfO2 grating beam can sustain the stress change during the epitaxial growth of a III-nitride material. Grating structures locally change the growth condition and vary indium composition in the InGaN/GaN quantum wells and thus, the photoluminescence spectra of epitaxial III-nitride grating are tuned. Guided mode resonances are experimentally demonstrated in fabricated III-nitride gratings, opening the possibility to achieve the interaction between the excited light and the grating structure through guided mode resonance. PACS: 78.55.Cr; 81.65.Cf; 81.15.Hi. PMID:21849084

2011-01-01

99

Electronic Structure Differences in ZrO2 vs. HfO2  

SciTech Connect

While ZrO2 and HfO2 are, for the most part, quite similar chemically, subtle differences in their electronic structures appear to be responsible for differing MO2/Si (M = Zr, Hf) interface stabilities. In order to shed light on the electronic structure differences between ZrO2 and HfO2, we have conducted joint experimental/theoretical studies. Since electron affinities are a sensitive probe of electronic structure, we have measured them by conducting photoelectron spectroscopic experiments on ZrO2- and HfO2-. The electron affinity of HfO2 was determined to be 2.14? 0.03 eV, while that of ZrO2 was determined to be 1.64 ? 0.03 eV. Concurrently, electronic structure calculations were conducted to determine electron affinities, vibrational frequencies, and geometries of these systems. The calculated electron affinities of HfO2 and ZrO2 were found to be 2.05 and 1.62 eV, respectively. The molecular results confirm earlier predictions from solid phases that HfO2 is more ionic than ZrO2. The excess electron in MO2- occupies an sd-type hybrid orbital localized on the M atom (M=Zr, Hf). The structural parameters of ZrO2 and HfO2 were found to be very similar. The difference in geometries between the neutral and the anion is along the symmetrical stretching and bending modes. Together, these studies unveil significant differences in the electronic structures of ZrO2 and HfO2.

Zheng, Weijun; Bowen Jr., K.H.; Li, Jun; Dabkowska, Iwona; Gutowski, Maciej S.

2005-12-22

100

Charge trapping in ultrathin hafnium oxide  

Microsoft Academic Search

The charge trapping properties of ultrathin HfO2 in MOS capacitors during constant voltage stress have been investigated. The effects of stress voltage, substrate type, annealing temperature, and gate electrode are presented in this letter. It is shown that the generation of interface-trap density under constant-voltage stress is much more significant for samples with Pt gate electrodes than that with Al

W. J. Zhu; T. P. Ma; S. Zafar; T. Tamagawa

2002-01-01

101

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

PubMed Central

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 (? = 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

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

2013-01-01

102

DC and RF characteristics of advanced MIM capacitors for MMIC's using ultra-thin remote-PECVD Si3N4 dielectric layers  

Microsoft Academic Search

We have fabricated advanced metal-insulator-metal (MIM) capacitors with ultra-thin (200 Å) remote-PECVD Si3N4 dielectric layers having excellent electrical properties. The breakdown field strength of MIM capacitors with 200-Å-thick Si3N 4 was larger than 3.5 MV\\/cm, which indicates the excellent quality of the deposited Si3N4 film. The main capacitance per unit area extracted by radio frequency (RF) measurements was as high

Jae-Hak Lee; Dae-Hyun Kim; Yong-Soon Park; Myoung-Kyu Sohn; Kwang-Seok Seo

1999-01-01

103

Monte Carlo study of remote Coulomb and remote surface roughness scattering in nanoscale Ge PMOSFETs with ultrathin high-k dielectrics  

Microsoft Academic Search

In this work we perform full-band Monte Carlo simulations of nanoscale Ge bulk PMOSFETs with ultrathin (<2 nm ) effective oxide thickness high-kappa dielectrics and investigate the importance of remote Coulomb and remote surface roughness scattering in these devices. For a gate overdrive, (Vg-Vt), of 1.0 V, remote scattering mechanisms seem to decrease the saturation current by as much as

B. Ghosh; X.-F. Fan; L. F. Register; S. K. Banerjee

2006-01-01

104

Structural, electronic, and dielectric properties of amorphous ZrO2 from ab initio molecular dynamics  

E-print Network

Structural, electronic, and dielectric properties of amorphous ZrO2 from ab initio molecular October 2004; published 9 February 2005 Realistic models of amorphous ZrO2 are generated in a "melt semiconductor technology, and may also have implications for HfO2 and for silicates of ZrO2 and HfO2. DOI: 10

Vanderbilt, David

105

Residual stress and interface effect on dielectric mechanisms in poled ultrathin relaxor ferroelectric single crystals  

NASA Astrophysics Data System (ADS)

We have investigated the dielectric performances and mechanism of super-thin Mn-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals, exhibiting significantly different dielectric behaviors compared with thick wafer. Dramatic decrease by 5 times and large frequency dispersion of permittivity, changed diffuse degree of phase transition, dielectric loss anomaly with frequency and dielectric performances with direct-current electric field for thin wafers are observed, proving the existence of large surface residual stress and interface effects. Additionally, a theoretical model of low-permittivity and low-ferroelectric surface damage layers is concurrently proposed. These observations have important implications for actual performances of thin wafers applied in practical devices.

Li, Long; Zhao, Xiangyong; Li, Xiaobing; Xu, Qing; Yang, Linrong; Wang, Sheng; Luo, Haosu

2014-05-01

106

Fabrication and characterization of ultrathin double dielectric mirror GaN microcavities  

NASA Astrophysics Data System (ADS)

The optical properties and fabrication of ultrathin GaN-based microcavities grown on silicon substrates are described. The epitaxial part of the optical cavities, consisting of a ?/2 GaN layer above a 3-period epitaxial Bragg mirror, is sandwiched between two silica/zirconia mirrors. At a suitable point in the fabrication process the silicon substrate was selectively removed using via holes. The cavity mode and excitonic resonance are observed by reflectivity at low and room temperature, demonstrating a quality factor of ~125. The dispersion of the modes and their linewidth is measured using angle-resolved reflectivity and successfully modelled using transfer matrix simulations.

Bejtka, K.; Edwards, P. R.; Martin, R. W.; Reveret, F.; Vasson, A.; Leymarie, J.; Sellers, I. R.; Leroux, M.; Semond, F.

2008-04-01

107

Hafnium zirconate gate dielectric for advanced gate stack applications  

Microsoft Academic Search

We report on the development of a hafnium zirconate (HfZrO4) alloy gate dielectric for advanced gate stack applications. The HfZrO4 and hafnium dioxide (HfO2) films were formed by atomic layer deposition using metal halides and heavy water as precursors. The HfZrO4 material properties were examined and compared with those of HfO2 by a wide variety of analytical methods. The dielectric

R. I. Hegde; D. H. Triyoso; S. B. Samavedam; B. E. White

2007-01-01

108

Effect of thermal annealing and oxygen partial pressure on the swelling of HfO2/SiO2/Si metal-oxide-semiconductor structure grown by rf sputtering: A synchrotron x-ray reflectivity study  

NASA Astrophysics Data System (ADS)

As-grown and rapid thermal annealed thin HfO2 films, deposited on Si(100) substrate by reactive rf sputtering at various partial pressures of O2 and Ar, are studied by synchrotron x-ray reflectivity. The growth of interfacial layer (IL) of SiO2 is more or less linear with the decrease in oxygen partial pressure (pO2) in the O2/Ar mixture. The thickest oxide is found to be grown at the minimum oxygen partial pressure (pO2). It is observed that the IL swells upon annealing at higher temperature, and swelling is maximum for the sample grown in minimum pO2. The surface roughness and thickness of the HfO2 films decrease upon annealing indicating a denser film. The HfO2/Si interface roughness is also decreased upon annealing. Therefore, lower annealing temperature and higher pO2 is to be set to reduce the IL thickness and for higher dielectric constant and larger oxide capacitance. High frequency capacitance-voltage (C-V) measurement on the devices, annealed at higher temperature, further shows the necessity for optimization of pO2 during the deposition of HfO2 film to minimize the fixed oxide charge density of metal-oxide-semiconductor devices.

Biswas, Debaleen; Md Faruque, Sk Abdul Kader; Sinha, Anil Kumar; Upadhyay, Anuj; Chakraborty, Supratic

2014-09-01

109

Substrate-assisted nucleation of ultra-thin dielectric layers on graphene by atomic layer deposition  

E-print Network

,15). Indeed, the surface of a defect-free, clean graphene sheet is inert under the soft chemical ALD process.7,8,14,16,17 Increasing the wetting of ALD dielectrics on graphene would thus allow a seed layer to be avoided. In this direction, Shin et al.18... proposed to increase the surface energy of graphene by an O2 plasma, which improves wettability, but at a cost of inducing defects in the graphene lattice. In this paper, we demonstrate an alternative method to enhance wetting of ALD dielectric films...

Dlubak, Bruno; Kidambi, Piran R.; Weatherup, Robert S.; Hofmann, Stephan; Robertson, John

2012-04-26

110

Metal dopants in HfO2-based RRAM: first principle study  

NASA Astrophysics Data System (ADS)

Based on density-functional theory (DFT), the effects of metal dopants in HfO2-based RRAM are studied by the Vienna ab initio simulation package (VASP). Metal dopants are classified into two types (interstitial and substitutional) according to the formation energy when they exist in HfO2 cell. Several conductive channels are observed through the isosurface plots of the partial charge density for HfO2 doped with interstitial metals, while this phenomenon cannot be found in HfO2 doped with substitutional metals. The electron density of states (DOS) and the projected electron density of states (PDOS) are calculated and analyzed; it is found that the conduction filament in HfO2 is directly formed by the interstitial metals and further, that the substitutional metals cannot directly generate conduction filament. However, all the metal dopants contribute to the formation of the oxygen vacancy (VO) filament. The formation energy of the VO and the interaction between metal dopants and VO are calculated; it is revealed that the P-type substitutional metal dopants have a strong enhanced effect on the VO filament, the interstitial metal dopants have a minor assistant effect, while Hf-like and N-type substitutional metal dopants have the weakest assistant effect.

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

2014-04-01

111

Strong light-matter coupling in ultrathin double dielectric mirror GaN microcavities  

SciTech Connect

Strong light-matter coupling is demonstrated at low temperature in an ultrathin GaN microcavity fabricated using two silica/zirconia Bragg mirrors, in addition to a three-period epitaxial (Al,Ga)N mirror serving as an etch stop and assuring good quality of the overgrown GaN. The {lambda}/2 cavity is grown by molecular beam epitaxy on a Si substrate. Analysis of angle-resolved data reveal key features of the strong coupling regime in both reflectivity and transmission spectra at 5 K: anticrossing with a normal mode splitting of 43{+-}2 meV and 56{+-}2 meV for reflectivity and transmission, respectively, and narrowing of the lower polariton linewidth near resonance.

Bejtka, K.; Martin, R. W. [Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG (United Kingdom); CRHEA-CNRS, Rue Bernard Gregory, Parc Sophia Antipolis, 06560 Valbonne (France); Reveret, F.; Vasson, A.; Leymarie, J. [LASMEA, UMR 6602 UBP/CNRS, 24 Avenue des Landais, F-63177 Aubiere Cedex (France); Edwards, P. R. [Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Sellers, I. R.; Duboz, J. Y.; Leroux, M.; Semond, F. [CRHEA-CNRS, Rue Bernard Gregory, Parc Sophia Antipolis, 06560 Valbonne (France)

2008-06-16

112

Facile preparation of sol-gel-derived ultrathin and high-dielectric zirconia films for capacitor devices  

NASA Astrophysics Data System (ADS)

This study successfully prepared zirconia ultrathin films from the sol-gel solution with dispersion of zirconium halide in 1-octanol solvent. The film was subjected to annealing treatments after sol-gel spin-coating, and the films of interest were evaluated. The amorphous morphology of the zirconia film was identified using high-resolution transmission electron microscopy and X-ray diffractometry. The plot of the current density with respect to the electric field demonstrates that the as-deposited film at 500 °C annealing exhibited an inferior leakage current, whereas 600 °C annealing stabilized the film with a satisfactory leakage current of 10-8 to 10-9 A/cm2. The out-gassing behavior of the sol-gel-derived thin film was evaluated using a thermal desorption system, that is, atmospheric pressure ionization mass spectrometry. The dielectric constant of the film was dependent on the retention effect of the preparation solvents. The low residual solvent for the preparation of the thin film with 1-octanol solvent and 600 °C annealing contributed to the superior high-k property.

You, Hsin-Chiang; Chang, Chun-Ming; Liu, Tzeng-Feng; Cheng, Chih-Chia; Chang, Feng-Chih; Ko, Fu-Hsiang

2012-10-01

113

Microwave and power characteristics of AlGaN/GaN/Si high-electron mobility transistors with HfO2 and TiO2 passivation  

NASA Astrophysics Data System (ADS)

This work presents AlGaN/GaN high-electron mobility transistors (HEMTs) that are grown on silicon. Various passivation layers are deposited on AlGaN/GaN HEMTs. AlGaN/GaN HEMTs were fabricated with TiO2 dielectrics, and their performance was compared with that of unpassivated and that of HfO2-passivated HEMTs. The TiO2-passivated HEMT with a gate length of 1 ?m exhibits a maximum extrinsic transconductance of 134.4 mS mm?1, a current-gain cutoff frequency of 10.62 GHz, and a maximum frequency of oscillation of 16.37 GHz. Capping with any of the dielectric materials used herein improves the device performance over that of the unpassivated HEMTs. Additionally, experimental data demonstrate that the use of TiO2 is a favorable alternative to HfO2 passivation. This work is the first to present the microwave power of TiO2-passivated AlGaN/GaN HEMTs.

Lin, Yu-Shyan; Lin, Shin-Fu; Hsu, Wei-Chou

2015-01-01

114

Quantum size effect on dielectric function of ultrathin metal film: a first-principles study of Al(1?1?1)  

NASA Astrophysics Data System (ADS)

Using first-principles calculations, we show manifestations of the quantum size effect in the dielectric function ?2 of free-standing Al(1?1?1) ultrathin films of 1 monolayer to 20 monolayers, taking into account size dependent contributions from both interband and intraband electronic transitions. Overall the in-plane components (interband transition) of ?2 increase with film thickness at all frequencies, converging towards a constant value. However, the out-of-plane components of ?2 show a more complex behavior, and, only at frequencies less than 0.75 eV, increase with film thickness without convergence. This suggests that ultrathin films can possibly be used for low-loss plasmonics devices in the visible and ultraviolet range. Our findings may shed light on searching for low-loss plasmonic materials via quantum size effect.

Ming, Wenmei; Blair, Steve; Liu, Feng

2014-12-01

115

Crystallization of HfO2 in InAs/HfO2 core-shell nanowires.  

PubMed

We report the impact of deposition parameters on the structure of HfO(2) covering InAs nanowires (NWs) being potential candidates for future field-effect transistors (FETs). Molecular beam epitaxial-grown Au-free InAs NWs were covered with HfO(2) deposited by atomic-layer deposition. The impact of the film thickness as well as the deposition temperature on the occurrence and amount of crystalline HfO(2) regions was investigated by high-resolution transmission electron microscopy (TEM) and x-ray diffraction. Compared to the deposition on planar Si substrates, the formation probability of crystalline HfO(2) on InAs NWs is significantly enhanced. Here, even 3 nm thick films deposited at 250 °C are partly crystalline. Similarly, a low deposition temperature of 125 °C does not result in completely amorphous 10 nm thick HfO(2) films, they contain monoclinic as well as orthorhombic HfO(2) nanocrystals. Combining HfO(2) and Al(2)O(3) into a laminate structure is capable of suppressing the formation of crystalline HfO2 grains. PMID:25211286

Rieger, T; Jörres, T; Vogel, J; Biermanns, A; Pietsch, U; Grützmacher, D; Lepsa, M I

2014-10-10

116

Seeding atomic layer deposition of high-k dielectrics on epitaxial graphene with organic self-assembled monolayers.  

PubMed

The development of high-performance graphene-based nanoelectronics requires the integration of ultrathin and pinhole-free high-k dielectric films with graphene at the wafer scale. Here, we demonstrate that self-assembled monolayers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) act as effective organic seeding layers for atomic layer deposition (ALD) of HfO(2) and Al(2)O(3) on epitaxial graphene on SiC(0001). The PTCDA is deposited via sublimation in ultrahigh vacuum and shown to be highly ordered with low defect density by molecular-resolution scanning tunneling microscopy. Whereas identical ALD conditions lead to incomplete and rough dielectric deposition on bare graphene, the chemical functionality provided by the PTCDA seeding layer yields highly uniform and conformal films. The morphology and chemistry of the dielectric films are characterized by atomic force microscopy, ellipsometry, cross-sectional scanning electron microscopy, and X-ray photoelectron spectroscopy, while high-resolution X-ray reflectivity measurements indicate that the underlying graphene remains intact following ALD. Using the PTCDA seeding layer, metal-oxide-graphene capacitors fabricated with a 3 nm Al(2)O(3) and 10 nm HfO(2) dielectric stack show high capacitance values of ?700 nF/cm(2) and low leakage currents of ?5 × 10(-9) A/cm(2) at 1 V applied bias. These results demonstrate the viability of sublimated organic self-assembled monolayers as seeding layers for high-k dielectric films in graphene-based nanoelectronics. PMID:21553842

Alaboson, Justice M P; Wang, Qing Hua; Emery, Jonathan D; Lipson, Albert L; Bedzyk, Michael J; Elam, Jeffrey W; Pellin, Michael J; Hersam, Mark C

2011-06-28

117

Effects of surface pretreatments on interface structure during formation of ultra-thin yttrium silicate dielectric films on silicon  

E-print Network

1 Effects of surface pretreatments on interface structure during formation of ultra-thin yttrium of ultra-thin films of mixed yttrium, silicon, and oxygen, formed by oxidation of metal on clean and pre-treated silicon. XPS and MEIS analyses indicate that oxidation of yttrium on bare silicon results in a fully

Garfunkel, Eric

118

Femtosecond laser desorption of ultrathin polymer films from a dielectric surface  

NASA Astrophysics Data System (ADS)

By focusing femtosecond pulses on the front and rear surface of a fused silica coverslip, we desorb 8-nm thick polymer films at submicron scale. To determine the role of the substrate in the desorption process, we measure the threshold for nonlinear absorption in fused silica and compare it to the threshold for desorption, taking into account the enhancement of the field at the dielectric-air interface. The results indicate that absorption of energy only occurs in the film. We then measure the beam radius in situ by the knife-edge technique and characterize the desorption by atomic force microscopy. The radius of the laser desorbed area is determined by the desorption threshold intensity and can be a factor of 5 smaller than the beam waist.

Mercadier, Laurent; Peng, Jiahui; Sultan, Yasir; Davis, Thomas A.; Rayner, David M.; Corkum, Paul B.

2013-08-01

119

Ferroelectricity in Si-doped HfO2 revealed: a binary lead-free ferroelectric.  

PubMed

Static domain structures and polarization dynamics of silicon doped HfO2 are explored. The evolution of ferroelectricity as a function of Si-doping level driving the transition from paraelectricity via ferroelectricity to antiferroelectricity is investigated. Ferroelectric and antiferroelectric properties can be observed locally on the pristine, poled and electroded surfaces, providing conclusive evidence to intrinsic ferroic behavior. PMID:25352107

Martin, Dominik; Müller, Johannes; Schenk, Tony; Arruda, Thomas M; Kumar, Amit; Strelcov, Evgheni; Yurchuk, Ekaterina; Müller, Stefan; Pohl, Darius; Schröder, Uwe; Kalinin, Sergei V; Mikolajick, Thomas

2014-12-23

120

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

121

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

122

Band offsets of ultrathin high-oxide films with Si Eric Bersch, Sylvie Rangan, and Robert Allen Bartynski  

E-print Network

of electrically active defects and thus allows high channel mobility. However, as the required thickness of SiO2 these problems is to replace the SiO2 gate oxide with an alternative dielectric that has a high dielectric, most high- dielectrics, such as HfO2, ZrO2, and their silicates, have much smaller band gaps than those

Garfunkel, Eric

123

Experimental and theoretical studies of the energy-loss straggling of H and He ion beams in HfO2 films  

NASA Astrophysics Data System (ADS)

We report an experimental-theoretical study of the energy-loss straggling of protons and alpha particles in HfO{2} films. In the case of H ions the experiments were performed in the energy range 40-1750 keV. For the lower energy interval (40-250 keV) we have used the medium energy ion scattering (MEIS) technique with a resolution of ? E/E˜ 4×10-3, while for the higher energies the Rutherford backscattering technique (RBS) was employed with an overall resolution of 7 keV. Concerning the He ions the straggling study has covered an energy range between 250 and 3000 keV by using RBS measurements, which in this case had a resolution better than 10 keV. The theoretical calculations were done in the framework of the dielectric formalism using the MELF-GOS model to obtain a proper description of the energy loss function (ELF) of the HfO{2} target. It is shown that for both projectiles the experimental data and the theoretical predictions for the energy-loss straggling display a very good agreement.

Abril, I.; Behar, M.; Garcia-Molina, R.; Fadanelli, R. C.; Nagamine, L. C. C. M.; Grande, P. L.; Schünemann, L.; Denton, C. D.; Arista, N. R.; Saitovitch, E. B.

2009-07-01

124

Inelastic electron tunneling spectroscopy study of metal-oxide-semiconductor diodes based on high-? gate dielectrics  

NASA Astrophysics Data System (ADS)

Inelastic electron tunneling spectroscopy (IETS) was applied to characterize the microstructure, interface, and trap-related states in silicon metal-oxide-semiconductor devices consisting of high-? gate dielectrics HfO2, Y2O3, and stacked HfO2/Y2O3 bilayer by molecular beam epitaxy and atomic layer deposition under various heat treatments. Reproducible vibrational modes of monoclinic HfO2 and cubic Y2O3 were identified from IETS spectra, along with phonon modes related to interfacial structures for a given metal-oxide-semiconductor fabrication process. A simple modeling was employed to analyze the trap related features in IETS spectra of stacked HfO2/Y2O3 bilayers, and showed that most traps are located near the HfO2/Y2O3 interface due to dissimilar charge distributions of two ionic oxides of different cation valences, and the presence of interfacial strains of dissimilar structures.

You, S. L.; Huang, C. C.; Wang, C. J.; Ho, H. C.; Kwo, J.; Lee, W. C.; Lee, K. Y.; Wu, Y. D.; Lee, Y. J.; Hong, M.

2008-01-01

125

Local elastic modulus of RF sputtered HfO2 thin film by atomic force acoustic microscopy  

NASA Astrophysics Data System (ADS)

Atomic force acoustic microscopy (AFAM) is a useful nondestructive technique for measurement of local elastic modulus of materials at nano-scale spatial resolution by measuring the contact resonance spectra for higher order modes of the AFM cantilever. The elastic modulus of RF sputtered HfO2 thin film has been measured quantitatively, using reference approach in which measurements are performed on the test and reference samples. Using AFAM, the measured elastic modulus of the HfO2 thin film is 223±27 GPa, which is in agreement with the literature value of 220±40 GPa for atomic layer deposited HfO2 thin film using nanoindentation technique.

Jena, S.; Tokas, R. B.; Sarkar, P.; Misal, J. S.; Rao, K. D.; Thakur, S.; Sahoo, N. K.

2014-04-01

126

Femtosecond laser-induced damage of HfO2/SiO2 mirror with different stack structure.  

PubMed

Laser-induced damage of the "standard" (?/4 stack structure) and "modified" (reduced standing-wave field) HfO(2)/SiO(2) mirrors were investigated by a commercial 800 nm Ti:sapphire laser system. Three kinds of pulse duration of 50 fs, 105 fs, and 135 fs were chosen. The results show that the single-shot damage threshold of the "modified" mirror was about 14%-23% higher compared to that of the "standard" mirror. A model based on the rate equation for free electron generation was adopted to explain the threshold results. It took in account the transient changes in the dielectric function of material during the laser pulse. The simulated threshold agreed with the experimental very well. Besides, for two kinds of mirror, typical breakdown craters for both the single-shots and multi-shots damage tests reveal striking distinct characteristics. Interestingly, the multi-shots damage crater with zigzag-like edge was observed only on the "standard" mirror. These phenomena were illustrated reasonably by the distribution features of the electric field intensity within the mirrors. PMID:22945167

Chen, Shunli; Zhao, Yuan'an; Yu, Zhenkun; Fang, Zhou; Li, Dawei; He, Hongbo; Shao, Jianda

2012-09-01

127

Photoluminescent characteristics of hafnium oxide layers activated with trivalent terbium (HfO2:Tb+3)  

NASA Astrophysics Data System (ADS)

Hafnium oxide layers doped with trivalent terbium ions have been synthesized using the ultrasonic spray pyrolysis technique. Photoluminescence properties were studied as a function of growth parameters such as the substrate temperature and the terbium concentration. The films were grown starting 6rom aqueous solution of Hafnium and Terbium chlorides. The results show that crystalline structure of HfO2:Tb+3 films depends on the temperature. Emission and excitation spectra were obtained for the HfO2:Tb+3 films using 262 nm as the excitation wavelength. All emission spectra show bands centered at 488, 542, 584 and 621 nm, which correspond to the electronic transitions: 5D4?7Fj (jD3, .., 6) characteristic of trivalent terbium ion. The dominant emission intensity corresponds to the green color, which depend on the terbium concentration incorporated inside the host matrix.

Guzm&Án-Mendoza, J.; Albarr&Án-Arreguín, D.; Alvarez-Fragoso, O.; Alvarez-Perez, M. A.; Falcony, C.; García-Hipólito, M.

128

Grain boundary mediated leakage current in polycrystalline HfO2 films  

SciTech Connect

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.

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

2011-07-01

129

HfO2 on UV–O3 exposed transition metal dichalcogenides: interfacial reactions study  

NASA Astrophysics Data System (ADS)

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.

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

130

Design and Fabrication of Interdigital Nanocapacitors Coated with HfO2.  

PubMed

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

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

2015-01-01

131

Laser damage testing of SiO2 and HfO2 thin films  

Microsoft Academic Search

SiO2 and HfO2 thin films have been deposited on polished fused silica substrates by the ion assisted electron beam evaporation technique in different deposition conditions. The role of the assisting ion beam parameters either on the otpical and structural film properties and the film damage threshold at 308 nm has been investigated. Laser damage thresholds have been determined by the

M. di Giulio; Marco Alvisi; Maria R. Perrone; Maria L. Protopapa; Antonio Valentini; Lorenzo Vasanelli

1999-01-01

132

Growth and phase stabilization of HfO 2 thin films by ALD using novel precursors  

NASA Astrophysics Data System (ADS)

HfO 2 thin films were grown at temperatures between 250 and 400 °C by atomic layer deposition using novel cyclopentadienyl-alkylamido precursors, namely CpHf(NMe 2) 3 and (CpMe)Hf(NMe 2) 3 (Cp, cyclopentadienyl=C 5H 5). Ozone was used as the oxygen source. The self-limiting growth mode was verified at 300 °C with a growth rate of 0.7-0.8 Å/cycle, depending on the precursor. Thermal decomposition started to have an effect on the growth mechanism at temperatures near 350 °C. As compared to the widely applied Hf(NEtMe) 4 precursor, these novel precursors with higher thermal stability resulted in HfO 2 films with lower impurity contents. The carbon and hydrogen contents below 0.5 and 1.0 at.%, respectively, were characterized for films deposited at 300 °C from both novel precursors. The 50-nm-thick HfO 2 films deposited at 300 °C or above were crystallized in mixture of monoclinic and cubic or tetragonal phases. Doping with low amounts of yttrium and subsequent annealing of 7-nm-thick film on TiN stabilized the preferred high-permittivity cubic or tetragonal phases, resulting in low capacitance equivalent thickness and leakage current density.

Niinistö, Jaakko; Mäntymäki, Miia; Kukli, Kaupo; Costelle, Leila; Puukilainen, Esa; Ritala, Mikko; Leskelä, Markku

2010-01-01

133

Scanning transmission electron microscopy investigations of interfacial layers in HfO2 gate stacks  

NASA Astrophysics Data System (ADS)

Electron energy-loss spectroscopy combined with high-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy was used to investigate the chemistry of interfacial layers in HfO2 gate stacks capped with polycrystalline Si gate electrodes. To interpret the energy-loss near-edge fine structure (ELNES) obtained from the interfacial layers, reference spectra were obtained from single crystal hafnium silicate (HfSiO4), monoclinic HfO2 powder, and amorphous SiO2. No bulk-like silicate bonding could be detected in the ELNES of Si L2,3 and O K edges recorded from layers at the Si substrate interface. Compared to bulk SiO2, the interfacial ELNES showed additional features that were caused by overlap of signals from Si, HfO2, and SiO2, despite a relatively small electron probe size of ˜3Å. HAADF showed that interfacial roughness caused the projected thickness of nominally pure SiO2 (within the detection limit of the method) to be as small as ˜5Å in many locations.

Agustin, Melody P.; Bersuker, Gennadi; Foran, Brendan; Boatner, Lynn A.; Stemmer, Susanne

2006-07-01

134

Thermoluminescent characterization of HfO2:Tb3+ synthesized by hydrothermal route.  

PubMed

Thermo and photoluminescent properties of nanoparticles (NPs) of hafnium oxide (HfO2), both intrinsic and doped with terbium (Tb(3+)) are reported. The NPs of HfO2 were synthesized by hydrothermal route, using hafnium tetrachloride (HfCl4) and terbium chloride hexahydrated (TbCl3?6H2O) as precursors and sodium hydroxide (NaOH) to adjust the pH. Deionized water was used as solvent in all cases. The synthesis was carried out at different dopant concentrations from 0 to 20 at% of terbium with respect to the amount of hafnium in the precursor solution. The temperature of hydrothermal treatment was 200 °C and 80 min of reaction time. X-ray diffraction results show that at terbium concentrations higher than 15 at% the HfO2 nanoparticles have a crystalline structure corresponding to the tetragonal phase. Thermoluminescent (TL) characterization was performed after 5 min irradiation of the samples with ultraviolet light of 200 nm wavelength. The highest TL emission was observed on samples with 7 at% of Tb, with the TL peak centered at 128 °C. Thermoluminescence analysis shows behavior associated with second-order kinetics with activation energy of 0.49 eV. Photoluminescent spectrum present the characteristics (5)D4?(7)FJ (J=3-6) terbium ion electronic transitions lines centered on 489 nm, 543 nm, 584 nm and 622 nm. PMID:23948482

Montes, E; Cerón, P; Rivera Montalvo, T; Guzmán, J; García-Hipólito, M; Soto-Guzmán, A B; García-Salcedo, R; Falcony, C

2014-01-01

135

Ferroelectricity and Antiferroelectricity of Doped Thin HfO2 -Based Films.  

PubMed

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 SrBi2 Ta2 O9 , 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 ?C 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. PMID:25677113

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

2015-03-01

136

Resistive switching of HfO 2-based metal-insulator-metal diodes: Impact of the top electrode material  

Microsoft Academic Search

This paper deals with the impact of the top metal electrode on the resistive switching properties of HfO2-based Metal\\/Insulator\\/Metal diodes. By screening five different metals as top electrode, Al-Cu-Hf-Pt-Ti, we have demonstrated the feasibility of the resistive switching effect on HfO2. Metals with a low enthalpy of formation of oxides ?Hf0 (Pt and Cu) lead to unipolar switching whereas easily

T. Bertaud; D. Walczyk; Ch. Walczyk; S. Kubotsch; M. Sowinska; T. Schroeder; Ch. Wenger; C. Vallée; P. Gonon; C. Mannequin; V. Jousseaume; H. Grampeix

137

Vortex polarization, strain induced phase transitions and dielectric response in ultra-thin PbTiO3 nanowires from first principles  

NASA Astrophysics Data System (ADS)

Nature of ferroelectricity in nanostructures and the resulting dielectric response are of both fundamental and applied interest. Here, using density functional theory (DFT) based computations, we investigate polarization configurations as a function of axial strain in ultra-thin PbTiO3 [001] nanowires. Our computations involved relaxed and axially strained free-standing nanowires with varying sidewall terminations and diameters. While stress-free nanowires with their sidewalls terminated by PbO surfaces displayed purely rectilinear axial polarization at all sizes, the TiO2-terminated nanowires, at a critical diameter of 16 å, display a non-rectilinear vortex polarization transverse to the nanowire axis. We discuss the origins of such behavior. We also predict the existence of novel stress-induced phase transitions between the mutually exclusive vortex and the axial polarization states in both the PbO- and TiO2-terminated nanowires. Normal mode vibrational frequency analysis of these nanowires further confirms these results. Furthermore, by employing density functional perturbation theory in combination with effective medium dielectric theory we calculate dielectric permittivity of the ferroelectric nanowires and compare it with the corresponding bulk results.

Pilania, Ghanshyam; Ramprasad, R.

2012-02-01

138

Study of electrical and microstructure properties of high dielectric hafnium oxide thin film for MOS devices  

Microsoft Academic Search

Hafnium oxide (HfO2) has emerged as the most promising highkdielectric for MOS devices. As-deposited sputtered HfO2 thin films have large number of defects resulting in increased oxide charge and leakage current. In this paper the effect\\u000a of sputtering voltage, bias sputtering and post deposition thermal annealing is investigated. The I–V and C–V characteristics of the dielectric film are studied employing

R. K. Nahar; Vikram Singh; Aparna Sharma

2007-01-01

139

Characterization of nanostructured HfO 2 films using RBS and PAC  

NASA Astrophysics Data System (ADS)

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,?) 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.

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

140

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

NASA Astrophysics Data System (ADS)

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, ?)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.

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

141

Fully solution-processed low-voltage aqueous In2O3 thin-film transistors using an ultrathin ZrO(x) dielectric.  

PubMed

We reported here "aqueous-route" fabrication of In2O3 thin-film transistors (TFTs) using an ultrathin solution-processed ZrOx dielectric thin film. The formation and properties of In2O3 thin films under various annealing temperatures were intensively examined by thermogravimetric analysis, Fourier transform infrared spectroscopy, and atomic force microscopy. The solution-processed ZrOx thin film followed by sequential UV/ozone treatment and low-temperature thermal-annealing processes showed an amorphous structure, a low leakage-current density (?1 × 10(-9) A/cm(2) at 2 MV/cm), and a high breakdown electric field (?7.2 MV/cm). On the basis of its implementation as the gate insulator, the In2O3 TFTs based on ZrOx annealed at 250 °C exhibit an on/off current ratio larger than 10(7), a field-effect mobility of 23.6 cm(2)/V·s, a subthreshold swing of 90 mV/decade, a threshold voltage of 0.13 V, and high stability. These promising properties were obtained at a low operating voltage of 1.5 V. These results suggest that "aqueous-route" In2O3 TFTs based on a solution-processed ZrOx dielectric could potentially be used for low-cost, low-temperature-processing, high-performance, and flexible devices. PMID:25285983

Liu, Ao; Liu, Guo Xia; Zhu, Hui Hui; Xu, Feng; Fortunato, Elvira; Martins, Rodrigo; Shan, Fu Kai

2014-10-22

142

Oxygen passivation of vacancy defects in metal-nitride gated HfO2/SiO2/Si devices  

NASA Astrophysics Data System (ADS)

We show that oxygen can be diffused through thin TiN layers to correct flatband voltage offsets in HfO2/SiO2/Si structures, achieving nearly band-edge capacitance voltage characteristics without undue growth of parasitic SiO2. Photoemission reveals that the TiN remains conductive despite mild oxidation, although over-oxidation results in insulating layers. Secondary ionization mass spectroscopy of samples treated with isotopically labeled O18 was used to assess how much oxygen is required to fully passivate the defects caused by thermal processing of metallized HfO2/SiO2/Si devices.

Cartier, E.; Hopstaken, M.; Copel, M.

2009-07-01

143

High-magnetic field annealing effect on room-temperature ferromagnetism enhancement of un-doped HfO2 thin films  

NASA Astrophysics Data System (ADS)

Monoclinic HfO2 thin films with intrinsic defects were prepared by annealing in flowing argon. The behavior of the HfO2 films could be manipulated by applying an external magnetic field during annealing processing. Room-temperature ferromagnetism and visible photoluminescence were observed in these un-doped HfO2 films due to the involvement of oxygen vacancies. The results demonstrated that the density of oxygen vacancies in HfO2 films could be controlled by varying the intensity of the magnetic field. This study could facilitate understanding of ferromagnetism origin in un-doped oxides, also suggests an effective way to alter the intrinsic defects in HfO2 to improve its performance.

Xie, Qian; Wang, Weipeng; Xie, Zheng; Ning, Shuai; Li, Zhengcao; Zhang, Zhengjun

2015-03-01

144

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

Microsoft Academic Search

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,

Bo Ling; Hongbo He; Jianda Shao

2007-01-01

145

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

146

Hafnium zirconate gate dielectric for advanced gate stack applications  

NASA Astrophysics Data System (ADS)

We report on the development of a hafnium zirconate (HfZrO4) alloy gate dielectric for advanced gate stack applications. The HfZrO4 and hafnium dioxide (HfO2) films were formed by atomic layer deposition using metal halides and heavy water as precursors. The HfZrO4 material properties were examined and compared with those of HfO2 by a wide variety of analytical methods. The dielectric properties, device performance, and reliability of HfZrO4 were investigated by fabricating HfZrO4/tantalum carbide (TaxCy) metal-oxide-semiconductor field effect transistor. The HfZrO4 dielectric film has smaller band gap, smaller and more uniform grains, less charge traps, and more uniform film quality than HfO2. The HfZrO4 dielectric films exhibited good thermal stability with silicon. Compared to HfO2, the HfZrO4 gate dielectric showed lower capacitance equivalent thickness value, higher transconductance, less charge trapping, higher drive current, lower threshold voltage (Vt), reduced capacitance-voltage (C-V ) hysteresis, lower interface state density, superior wafer level thickness uniformity, and longer positive bias temperature instability lifetime. Incorporation of zirconium dioxide (ZrO2) into HfO2 enhances the dielectric constant (k ) of the resulting HfZrO4 which is associated with structural phase transformation from mainly monoclinic to tetragonal. The tetragonal phase increases the k value of HfZrO4 dielectric to a large value as predicted. The improved device characteristics are attributed to less oxygen vacancy in the fine grained microstructure of HfZrO4 films.

Hegde, R. I.; Triyoso, D. H.; Samavedam, S. B.; White, B. E.

2007-04-01

147

REVIEWS OF TOPICAL PROBLEMS: Application and electronic structure of high-permittivity dielectrics  

NASA Astrophysics Data System (ADS)

Major applications of high-permittivity dielectric materials in silicon devices are reviewed. The basics and software implementations of the electron density functional method are considered. Results of first-principle calculations of the electronic structure are analyzed for the three most important and promising high-permittivity dielectrics, Al2O3, HfO2, and TiO2.

Perevalov, Timofei V.; Gritsenko, Vladimir A.

2010-09-01

148

Solid-Solution Nanoparticles: Use of a Nonhydrolytic Sol-Gel Synthesis To Prepare HfO2 and HfxZr1-xO2  

E-print Network

. for the synthesis of ZrO2 nanocrystals (J. Am. Chem. Soc. 2003, 125, 6553-6557) was used to synthesize highly nanocrystals, i.e., HfO2-ZrO2, ZrO2- TiO2, and HfO2-TiO2. Efforts to prepare nanocrystals of HfxZr1-xO2 over to include binary solid solutions of chemically similar oxides. HfO2 and ZrO2 are called twin oxides

149

Phase Change Memory Based on (Sb2Te3)0.85--(HfO2)0.15 Composite Film  

Microsoft Academic Search

The phase change characteristics of an (Sb2Te3)0.85--(HfO2)0.15 composite film were investigated by X-ray diffraction patterns, X-ray photoelectron spectroscopy, and resistance measurements. It is shown that the incorporation of HfO2 could improve the archival life stability of amorphous Sb2Te3 film, as evidenced by the increased crystallization temperature ranging from 200 to 250 °C. The required dissipated energy of (Sb2Te3)0.85--(HfO2)0.15-based device was

Yegang Lu; Sannian Song; Zhitang Song; Dongning Yao; Wei Xi; Weijun Yin; Hao Zheng; Songlin Feng

2010-01-01

150

Reliability of Strained SiGe Channel p-Channel MetalOxideSemiconductor Field-Effect Transistors with Ultra-Thin (EOT=3.1 nm) N2O-Annealed SiN Gate Dielectric  

Microsoft Academic Search

The p-channel metal-oxide-semiconductor field-effect transistor (pMOSFET) with 50-nm-thick Si0.85Ge0.15 channel and ultra-thin (EOT=3.1 nm) N2O-annealed SiN gate dielectric has been shown to have well-performing on\\/off and output characteristics. Several methodologies for the device reliability characterization, such as stress-induced-leakage-current (SILC), drain-avalanche-hot-carrier (DAHC) injection, channel hot-carrier (CHC) injection and negative-bias-temperature-instability (NBTI), have been used and the results were compared. In terms of

Ching-Wei Chen; Chao-Hsin Chien; Yi-Cheng Chen; Shih-Lu Hsu; Chun-Yen Chang

2005-01-01

151

High-field study of muonium states in HfO2 and ZrO2  

NASA Astrophysics Data System (ADS)

We present high-transverse field measurements, as a function of temperature, in monoclinic ZrO2 and HfO2. In monoclinic zirconia and hafnia, a diamagnetic component had been previously reported in low-transverse-fields, but a significant fraction of the total muon polarization was missing in these experiments. We now characterize this missing fraction using the high-field capabilities at TRIUMF: a high relaxation component (above 100 ?s?1 in monoclinic ZrO2, about 10 ?s?1 in HfO2) is observed, which we relate to the formation of compact muonium in these materials. A model for the formation of muonium in these materials is presented.

Vieira, R. B. L.; Vilão, R. C.; Alberto, H. V.; Gil, J. M.; Weidinger, A.; Baker, B. B.; Mengyan, P. W.; Lichti, R. L.

2014-12-01

152

First-principles calculations of electronic and optical properties of F, C-codoped cubic HfO2  

NASA Astrophysics Data System (ADS)

First-principles calculations based on DFT+U were performed on electronic and optical properties of F, C-codoped cubic HfO2. The calculations show that strong 2p-2p/5d admixtures result in half-metallic ferromagnetism behaviors of F, C-codoped cubic HfO2. Both the direct 2p-2p interaction and the indirect 2p-5d/2p-2p coupling interactions can be expected to contribute to the long-range magnetic coupling. Meanwhile, F and C codoping induces obvious increase of refractive index and new steep absorption peaks at lower energy region ?2.8 eV, which can be used for photoabsorption applications.

Zhang, Yu-Fen; Ren, Hao; Hou, Zhi-Tao

2015-02-01

153

Low-temperature Polymorphs of ZrO2 and HfO2. A Density Functional Theory Study  

SciTech Connect

We present density functional calculations of the total energies and equations of state of the monoclinic, tetragonal, cubic, orthorhombic-I (Pbca) and orthorhombic-II (cotunnite)-structure phases of zirconia and hafnia in the local density (LDA) and generalized-gradient (GGA) approximations. The accuracy of the LDA approximation is not sufficient and GGA corrections are critical to obtain low-temperature phase transitions under pressure that are consistent with experiment, i.e., (monoclinic‡ orthorhombic-I ‡ cotunnite). The GGA values of the bulk modulus of the cotunnite phase were found to be 251 and 259 GPa for ZrO2 and HfO2, respectively. We developed a new population analysis scheme in which atomic radii are adapted to the actual charge distribution in the material. The results indicate that the effective atomic radius of Hf is smaller than that of Zr, which is a drastic manifestation of the relativistic lanthanide contraction. The population analysis results demonstrate that ionicity: (i) increases from the monoclinic to the cotunnite phase, and (ii) is larger for HfO2 than for ZrO2. This variable ionicity may be the reason why LDA fails to describe the relative stability of different polymorphs. The bandgap and heat of formation are also larger for monoclinic HfO2 than for ZrO2 by 0.6 eV and 0.60 eV/formula unit, respectively. The tetragonal phase, which often exists as a metastable phase at ambient conditions, has a bandgap larger than the monoclinic phase by 0.35 and 0.65 eV for ZrO2 and HfO2, respectively.

Jaffe, John E.; Bachorz, Rafal A.; Gutowski, Maciej S.

2005-10-20

154

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

NASA Astrophysics Data System (ADS)

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.

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

2008-04-01

155

Damage thresholds of HfO2/SiO2 and ZrO2/SiO2 high reflectors at 1.064 microns deposited by reactive DC magnetron sputtering  

NASA Astrophysics Data System (ADS)

HfO2/SiO2 and ZrO2/SiO2 high reflectors at 1.064 microns were deposited by pulsed reactive DC magnetron sputtering. These dielectric thin film high reflectors were deposited with and without the use of an electron source. The electron source greatly decreased arcing of the magnetrons during the deposition process resulting in thin films with fewer defects. The high reflectors were laser damage tested at 1.064 microns. The optical properties of the thin film coatings were characterized prior to laser damage testing. Optical characterization techniques included angle resolved scatter (BRDF), total integrated scatter (TIS), and adiabatic calorimetry. The dependence of the laser damage threshold and optical properties on deposition conditions is reported.

Reicher, David; Navarro, Martha; Sydenstricker, Robin; Oberling, Jason; Marquez, Micheal; Villafuert, Julio; Ogloza, Albert A.; Pentony, Joni; Langston, Peter; O'Conner, David; Marrs, Denton

2005-02-01

156

Electronic properties of defects in polycrystalline dielectric materials  

Microsoft Academic Search

Grain boundaries have been implicated in current leakage and dielectric breakdown of CMOS devices. We calculate the electronic properties of oxygen vacancy defects near grain boundaries in the dielectric insulators MgO and HfO2 using first principles methods. In both materials we find that oxygen vacancies favourably segregate to grain boundaries, in various charge states. Their electronic properties are different from

K. P. McKenna; A. L. Shluger

2009-01-01

157

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

NASA Astrophysics Data System (ADS)

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-oxides into device structures. The novel process involving the TiOx buffer layer for TiO2 and the POLD process of HfO2 have been developed as new processing methods for high dielectric applications.

Yoon, Meeyoung

158

Simulation study of HEMT structures with HfO2 cap layer for mitigating inverse piezoelectric effect related device failures  

NASA Astrophysics Data System (ADS)

The Inverse Piezoelectric Effect (IPE) is thought to contribute to possible device failure of GaN High Electron Mobility Transistors (HEMTs). Here we focus on a simulation study to probe the possible mitigation of the IPE by reducing the internal electric fields and related elastic energy through the use of high-k materials. Inclusion of a HfO2 "cap layer" above the AlGaN barrier particularly with a partial mesa structure is shown to have potential advantages. Simulations reveal even greater reductions in the internal electric fields by using "field plates" in concert with high-k oxides.

Nagulapally, Deepthi; Joshi, Ravi P.; Pradhan, Aswini

2015-01-01

159

Synthesis and electrical characterization of a MOS memory containing Si nanoparticles embedded in high-k HfO2 thin film  

NASA Astrophysics Data System (ADS)

The size-controlled, non-agglomerated, 5nm Si nanoparticles were fabricated in the middle of HfO2 layers using a pulsed laser ablation (PLA) system at a relatively low pressure and formed trilayer structure (HfO2/Si-nps/HfO2) on n-type Si. These high density nanoparticles (>1x1011 cm-2) were imaged with SEM. The crystallinity of HfO2 and Si nanoparticles were characterized by HRTEM. The memory effect of a Si nanoparticles floating gate memory structure consisting of HfO2 tunneling and control oxides have been investigated by means of high-frequency (1 MHz) capacitance-voltage (C-V) measurements. HRTEM study revealed that the Si nanoparticles are single crystals with average size of about 5 nm in diameter and are well distributed within the amorphous HfO2 matrix. The memory effect was observed by the hysteresis loop in the C-V curves and a high storage charge density of about 5×1011cm-2 and a large flat-band voltage shift of 4.8V have been achieved due to charging and discharging to the nanoparticles.

Wang, Lei; Ji, Mei; Zhu, Shiwei; Tu, Hailin; Du, Jun

2009-03-01

160

Inorganic–organic membranes based on Nafion, [(ZrO 2)·(HfO 2) 0.25] and [(SiO 2)·(HfO 2) 0.28]. Part I: Synthesis, thermal stability and performance in a single PEMFC  

Microsoft Academic Search

This work reports the preparation, characterization and test in a single fuel cell of two families of hybrid inorganic-organic proton-conducting membranes, each based on Nafion and a different “core-shell” nanofiller. Nanofillers, based on either a ZrO2 “core” covered with a HfO2 “shell” (ZrHf) or a HfO2 “core” solvated by a “shell” of SiO2 nanoparticles (SiHf), are considered. The two families

Vito Di Noto; Nicola Boaretto; Enrico Negro; Guinevere A. Giffin; Sandra Lavina; Stefano Polizzi

161

High damage threshold HfO2/SiO2 multilayer mirrors deposited by novel remote plasma sputtering  

NASA Astrophysics Data System (ADS)

Sputtering deposition coatings offer significant advantages on electron beam (EB) deposition, including high packing density, environmental stability and extremely low losses. But the inherent high compressive stress affects its application in high power laser system. This paper describes the technical feasibility of high damage threshold laser mirrors deposited by a novel remote plasma sputtering technique. This technique is based on generating intensive plasma remotely from the target and then magnetically steering the plasma to the target to realize the full uniform sputtering. The pseudo-independence between target voltage and target current provides us very flexible parameters tuning, especially for the films stress control. Deposition conditions are optimized to yield fully oxidized and low compressive stress single layer HfO2 and SiO2. The high damage threshold of 43.8 J/cm2 for HfO2/SiO2 laser mirrors at 1064 nm is obtained. For the first time the remote plasma sputtering is successfully applied in depositing laser mirrors with high performance.

Xu, Ying; Chen, Nan; Bu, Yi-Kun

2011-11-01

162

Interplay between gadolinium dopants and oxygen vacancies in HfO2: A density functional theory plus Hubbard U investigation  

NASA Astrophysics Data System (ADS)

The influence of gadolinium (Gd) doping on the oxygen vacancy (VO) in monoclinic HfO2 have been studied by the first-principles calculations within the spin-polarized generalized gradient approximation plus Hubbard U approach. It is found that the Gd dopant and VO show strong attractive interaction, resulting in a cooperative effect that the substitution of Gd for Hf (GdHf) would increase the probability of oxygen vacancies generation and vice versa. The GdHf is more energetically favorable to be next to the vacancy site of a three-coordinated oxygen (O3), forming a complex defect GdHf + VO. A single GdHf acts a hole donor and passivates the defect states of VO. Our results suggest that the decrease of the VO-related defect states observed in the photoluminescence spectra of Gd-HfO2 is because Gd doping passivates the defect states of VO, rather than caused by decrease of VO concentration. Our findings would clarify the debate about the influence of Gd doping on the oxygen vacancies in HfO2.

Zhang, Wei; Hou, Z. F.

2014-03-01

163

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

PubMed

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

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

164

Field-effect modulation of conductance in VO2 nanobeam transistors with HfO2 as the gate dielectric  

E-print Network

. (The nanobeams are embedded in a 1.1 lm thick layer of SiO2 grown on Si wafers.) Two and four probe beam as a function of temperature (data from device 1). Stress builds up in the sys- tem device to another (380- 400 K) and is dictated by the stress induced due to adhesion to the substrate

Deshmukh, Mandar M.

165

Analysis of thermal stresses in HfO2/SiO2 high reflective optical coatings for high power laser applications  

NASA Astrophysics Data System (ADS)

HfO2/SiO2 high reflective optical coatings are widely used in high power laser applications because of their high laser damage resistance and appropriate spectral performance. The residual stresses strongly influence the performance and longevity of the optical coatings. Thermal stresses are the primary components of the residual stresses. In the present work, the distribution of thermal stresses in HfO2/SiO2 high reflective optical coatings was investigated using two different computational methods: finite element method (FEM) and an analytical method based on force and moment balances and classical beam bending theory. The results by these two methods were compared and found to be in agreement with each other, demonstrating that these two methods are effective and accurate ways to predict the thermal stresses in HfO2/SiO2 optical coatings. In addition, these two methods were also used to obtain the thermal stresses in HfO2/SiO2 optical coatings with different layer number to investigate the effect of the layer number on the thermal stresses of the HfO2/SiO2 optical coatings. The results show that with the increase of the layer number, the stresses in the substrate increase, while the stresses in the respective SiO2 and HfO2 layers decrease. Besides, it was also found that the radius of curvature of the coating system decreases as the layer number increases, leading to larger bending curvature in the system.

Gao, Chunxue; Zhao, Zhiwei; Zhu, Zhuoya; Li, Shuang; Mi, Changwen

2015-02-01

166

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

PubMed

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. PMID:21369234

Jiao, Hongfei; Ding, Tao; Zhang, Qian

2011-02-28

167

Performance improvement of phase-change memory cell with Ge 2 Sb 2 Te 5 HfO 2 composite films  

Microsoft Academic Search

The phase-change characteristics of Ge2Sb2Te5 (GST) films for phase-change random access memory (PCM) devices were improved by incorporating HfO2 into GST film using cosputtering at room temperature. Phase separation (GST-rich nanocrystals were surrounded by HfO2-rich amorphous phase) has been observed in annealed GST-HfO2 composite films and the segregated domains exhibited a relatively uniform size. The reduced reset voltage of GST-HfO2

Sannian Song; Zhitang Song; Bo Liu; Liangcai Wu; Songlin Feng

2010-01-01

168

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

PubMed

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. PMID:22905534

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

2012-06-01

169

On the origin of the mobility reduction in bulk-Si, UTBOX-FDSOI and SiGe devices with ultrathin-EOT dielectrics  

Microsoft Academic Search

The effects of ultrathin EOT on the carrier mobility in bulk-Si, UTBOX-FDSOI and SiGe-QW pFET devices were compared. The mobility is found to decrease dramatically with the EOT (Tinv) as a result of stronger charge and surface roughness scattering at thinner SiOx interface layers irrespective of the device technology. UTBOXFDSOI and bulk-Si nFETs have identical mobility values (190 cm 2

L.-A. Ragnarsson; J. Mitard; T. Kauerauf; A. De Keersgieter; T. Schram; E. Rohr; N. Collaert; M. Jurczak; S.-H. Hong; J. Tseng; W.-E. Wang; L. Trojman; K. K. Bourdelle; B.-Y. Nguyen; P. Absil; T. Y. Hoffmann

2011-01-01

170

High-Performance Poly-Si TFTs Using Ultrathin Gate Dielectric for Monolithic Three-Dimensional Integrated Circuits and System on Glass Applications  

Microsoft Academic Search

High-performance poly-Si thin-film transistors (TFTs) using an ultrathin high- ? metal gate stack with a subthreshold swing (SS) of 193 mV\\/dec when operating at room temperature and maximum thermal budget of 700°C are readily compatible with monolithic 3-D integrated circuits (3D-ICs) and silicon-on-glass (SOG) applications. The SS is reduced to 31 mV\\/dec, and the on\\/off current ratio is increased to

M. H. Lee; S. L. Wu; M.-J. Yang; K.-J. Chen; G.-L. Luo; L.-S. Lee; M.-J. Kao

2010-01-01

171

High Mobility and Excellent Electrical Stability of MOSFETs Using a Novel HfTaO Gate Dielectric  

E-print Network

-based gate dielectric for MOSFETs with TaN metal gate. By incorporating Ta into HfO2 films, significant) electron peak mobility is enhanced by more than two times; (4) charge trapping and threshold voltage shift. After gate patterning, phosphorus was implanted at 50 KeV with a dose of 5x1015 cm-2 . Dopant activation

Fu, Li Ming

172

Germanium nanowire field-effect transistors with SiO2 and high-HfO2 gate dielectrics  

E-print Network

Germanium nanowire field-effect transistors with SiO2 and high- HfO2 gate dielectrics Dunwei Wang­6 Currently, for further device scaling and miniatur- ization, germanium is of renewed interest characteristics are obtained with these de- vices. GeNWs were synthesized by CVD of germanium at 275 °C on Au

Javey, Ali

173

Voltage and Power-Controlled Regimes in the Progressive Unipolar RESET Transition of HfO2-Based RRAM  

PubMed Central

Resistive switching (RS) based on the formation and rupture of conductive filament (CF) is promising in novel memory and logic device applications. Understanding the physics of RS and the nature of CF is of utmost importance to control the performance, variability and reliability of resistive switching memory (RRAM). Here, the RESET switching of HfO2-based RRAM was statistically investigated in terms of the CF conductance evolution. The RESET usually combines an abrupt conductance drop with a progressive phase ending with the complete CF rupture. RESET1 and RESET2 events, corresponding to the initial and final phase of RESET, are found to be controlled by the voltage and power in the CF, respectively. A Monte Carlo simulator based on the thermal dissolution model of unipolar RESET reproduces all of the experimental observations. The results contribute to an improved physics-based understanding on the switching mechanisms and provide additional support to the thermal dissolution model. PMID:24121547

Long, Shibing; Perniola, Luca; Cagli, Carlo; Buckley, Julien; Lian, Xiaojuan; Miranda, Enrique; Pan, Feng; Liu, Ming; Suñé, Jordi

2013-01-01

174

Characterization of HfO2-SiO2 rugate multilayers deposited by ion beam sputtering  

NASA Astrophysics Data System (ADS)

Ion beam sputtering (IBS) is a deposition technique being well known for resulting in very dense and damage resistant coatings due to high kinetic energies of the sputtered atoms. While different layers are deposited homogeneously, abrupt interfaces between the materials are the most susceptible part of the stack. Therefore we aim for an improvement of the laser damage threshold by sputtering material mixtures. Using a target with high- and low-index material next to each other, arbitrary refractive indices can be realized by adjusting the target axis. Our material system of choice is HfO2- SiO2, already yielding good results with non-rugate coatings. A comparison in terms of laser damage threshold between these designs and varying refractive index coatings will be shown.

Rauhut, R.; Nehls, K.; Mechold, L.

2014-10-01

175

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

NASA Technical Reports Server (NTRS)

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.

Zhu, Dongming; Harder, Bryan James

2014-01-01

176

Giant magneto-optical Kerr effect in HfO2/Co/HfO2/Al/silicon structure  

NASA Astrophysics Data System (ADS)

An extraordinary enhancement of magneto-optical Kerr effect was demonstrated in HfO2/Co/HfO2/Al/substrate composite structure by experimental measurements as well as theoretical calculations. Giant polar Kerr rotation was observed within a broad spectral region, and especially a peak of -7.92° was found at wavelength of 496 nm, which is nearly forty times as large as that of a single Co film. In addition, a Kerr rotation reversal was also observed in short wavelength region in the longitudinal geometry. We proposed that the multiple reflections and optical interference in the optical cavities lead to the enormous enhancement and modulation of the Kerr rotation.

Zhang, S. Y.; Gao, J. L.; Xia, W. B.; Luo, X. J.; Tang, S. L.; Du, Y. W.

2013-08-01

177

One step synthesis of pure cubic and monoclinic HfO2 nanoparticles: Correlating the structure to the electronic properties of the two polymorphs  

NASA Astrophysics Data System (ADS)

Hafnium dioxide is a wide band-gap, high-? material, and Hafnium based compounds have already been integrated into micro-electronic devices. The pure cubic HfO2 phase is promising as it presents a higher permittivity (? > 25), but needs to be stabilized by addition of divalent or trivalent dopants, which in turn modify the electronic properties of HfO2. Here, we employ a one-pot synthesis approach to produce undoped cubic and monoclinic HfO2 nanoparticles by choice of solvent alone. The average size of these nanoparticles from transmission electron microscopy studies was estimated to be around 2.6 nm. We present a study of the morphology and microstructure and also demonstrate the presence of a strong visible photoluminescence linked to the nanosize of the particles. Furthermore, the synthesis in equivalent conditions of these two phases of HfO2 provides means for direct comparison of the chemical composition and electronic structures of the two polymorphs. This has therefore allowed us to experimentally elucidate similarities and differences in the valence band, band gap states, and conduction band of these pure phases seconded by first principles calculations within the density functional theory.

Rauwel, P.; Rauwel, E.; Persson, C.; Sunding, M. F.; Galeckas, A.

2012-11-01

178

The Impact of Dielectric Material and Temperature on Dielectric Charging in RF MEMS Capacitive Switches  

Microsoft Academic Search

\\u000a The present work attempts to provide a better insight on the dielectric charging in RF-MEMS capacitive switches that constitutes\\u000a a key issue limiting parameter of their commercialization. The dependence of the charging process on the nature of dielectric\\u000a materials widely used in these devices, such as SiO2, Si3N4, AlN, Al2O3, Ta2O5, HfO2, which consist of covalent or ionic bonds and

George Papaioannou

2010-01-01

179

Tailoring the interface quality between HfO2 and GaAs via in situ ZnO passivation using atomic layer deposition.  

PubMed

We investigated ZnO surface passivation of a GaAs (100) substrate using an atomic layer deposition (ALD) process to prepare an ultrathin ZnO layer prior to ALD-HfO2 gate dielectric deposition. Significant suppression of both Ga-O bond formation near the interface and As segregation at the interface was achieved. In addition, this method effectively suppressed the trapping of carriers in oxide defects with energies near the valence band edge of GaAs. According to electrical analyses of the interface state response on p- and n-type GaAs substrates, the interface states in the bottom half of the GaAs band gap were largely removed. However, the interface trap response in the top half of the band gap increased somewhat for the ZnO-passivated surface. PMID:24911531

Byun, Young-Chul; Choi, Sungho; An, Youngseo; McIntyre, Paul C; Kim, Hyoungsub

2014-07-01

180

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

NASA Astrophysics Data System (ADS)

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.

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

2011-02-01

181

Effects of Support Composition and Pretreatment Conditions on the Structure of Vanadia Dispersed on SiO2, Al2O3, TiO2, ZrO2, and HfO2  

E-print Network

on SiO2, Al2O3, TiO2, ZrO2, and HfO2 Bryan Olthof, Andrei Khodakov, Alexis T. Bell,*, and Enrique on the structure of dispersed VOx for vanadia supported on SiO2, Al2O3, TiO2, ZrO2, and HfO2 prepared with VOx supports, with the extent of these species decreasing in the order HfO2 > Al2O3 > ZrO2 > TiO2 > SiO2

Iglesia, Enrique

182

Charge trapping characteristics of atomic-layer-deposited HfO2 films with Al2O3 as a blocking oxide for high-density non-volatile memory device applications  

Microsoft Academic Search

Charge trapping characteristics of high-relative permittivity (high-?) HfO2 films with Al2O3 as a blocking oxide in p-Si\\/SiO2\\/HfO2\\/Al2O3\\/metal memory structures have been investigated. All high-? films have been grown by atomic layer deposition. A transmission electron microscope image shows that the HfO2 film is polycrystalline, while the Al2O3 film is partially crystalline after a high temperature annealing treatment at 1000 °C

S Maikap; H Y Lee; T-Y Wang; P-J Tzeng; C C Wang; L S Lee; K C Liu; J-R Yang; M-J Tsai

2007-01-01

183

High-performance self-aligned inversion-channel In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistors by in-situ atomic-layer-deposited HfO2  

NASA Astrophysics Data System (ADS)

Self-aligned inversion-channel In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistors (MOSFETs) have been fabricated using the gate dielectrics of in-situ directly atomic-layer-deposited (ALD) HfO2 followed by ALD-Al2O3. There were no surface pretreatments and no interfacial passivation/barrier layers prior to the ALD. TiN/Al2O3 (4 nm)/HfO2 (1 nm)/In0.53Ga0.47As/InP MOS capacitors exhibited well-behaved capacitance-voltage characteristics with true inversion behavior, low leakage current densities of ˜10-8 A/cm2 at ±1 MV/cm, and thermodynamic stability at high temperatures. Al2O3 (3 nm)/HfO2 (1 nm)/In0.53Ga0.47As MOSFETs of 1 ?m gate length, with 700 °C-800 °C rapid thermal annealing in source/drain activation, have exhibited high extrinsic drain current (ID) of 1.5 mA/?m, transconductance (Gm) of 0.84 mS/?m, ION/IOFF of ˜104, low sub-threshold swing of 103 mV/decade, and field-effect electron mobility of 1100 cm2/V . s. The devices have also achieved very high intrinsic ID and Gm of 2 mA/?m and 1.2 mS/?m, respectively.

Lin, T. D.; Chang, W. H.; Chu, R. L.; Chang, Y. C.; Chang, Y. H.; Lee, M. Y.; Hong, P. F.; Chen, Min-Cheng; Kwo, J.; Hong, M.

2013-12-01

184

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)

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.

Ye, Liwang; Gougousi, Theodosia

2014-09-01

185

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

NASA Astrophysics Data System (ADS)

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.

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

2008-03-01

186

Oblique angle deposition of HfO2 thin films: quantitative assessment of indentation modulus and micro structural properties  

NASA Astrophysics Data System (ADS)

Oblique angle deposition of oxides is used routinely for fabricating inhomogeneous thin films with proven correlation between refractive index and the angle of deposition. Inhomogeneous layers play a key role in the development of rugate interference devices for photo-physical applications. Such obliquely deposited thin films show high porosity which is a critical issue related to their density, mechanical and environmental stability. Hence, it is important to investigate elastic properties of such film in addition to optical properties. Using atomic force acoustic microscopy, we report indentation modulus of HfO2 thin films deposited at angles 80, 68, 57, 40 and 0 degree with normal to substrate plane on Si (100) substrate. Such films were measured to have indentation modulus of 42 GPa for extreme obliquely deposited film and indentation modulus increases with decrease in angle to become highest with a value of 221 GPa for normally deposited films. We also report microstructural properties and density of films measured by FESEM and grazing angle x-ray reflectometer, respectively. Both indentation modulus and density depict a nonlinearly decreasing behavior with angle of deposition. Variation of density is again confirmed from FESEM cross-sectional morphology.

Tokas, R. B.; Jena, S.; Sarkar, P.; Polaki, S. R.; Thakur, S.; Basu, S.; Sahoo, N. K.

2015-03-01

187

Addition of HfO2 interface layer for improved synaptic performance of phase change memory (PCM) devices  

NASA Astrophysics Data System (ADS)

In this work, we will focus on the use of phase change memory (PCM) to emulate synaptic behavior in emerging neuromorphic system-architectures. In particular, we will show that the performance and energy-efficiency of large scale neuromorphic systems can be improved by engineering individual PCM devices used as synapses. This is obtained by adding a thin HfO2 interface layer to standard GST PCM devices, allowing for the lowering of the Set/Reset currents and the increase of the number of intermediate resistance states (or synaptic weights) in the synaptic potentiation characteristics. The experimentally obtained potentiation characteristics of such PCM devices are used to simulate a 2-layer ultra-dense spiking neural network (SNN) and to perform a complex visual pattern extraction from a test case based on real world data (i.e. cars passing on a 6-lane freeway). The total power dissipated in the learning mode, for the pattern extraction experiment is estimated to be as low as 60 ?W. Average detection rate of cars is found to be greater than 90%.

Suri, M.; Bichler, O.; Hubert, Q.; Perniola, L.; Sousa, V.; Jahan, C.; Vuillaume, D.; Gamrat, C.; DeSalvo, B.

2013-01-01

188

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

NASA Astrophysics Data System (ADS)

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.

Winkowski, P.; Marsza?ek, Konstanty W.

2013-07-01

189

A high-pressure high-temperature X ray study of phase relations and polymorphism of HfO2  

NASA Astrophysics Data System (ADS)

X ray diffraction experiments have been carried out to study the two pressure-induced phase transitions in HfO2. Angle-dispersive experiments were performed at room temperature in a diamond anvil cell using synchrotron radiation and imaging plates. Experiments at high temperature were performed with a multianvil device using the energy dispersive technique and a rotating-anode generator with a solid state detector. It was found that the monoclinic-orthorhombic I (ortho I) transition occurred around 5 GPa with a volume reduction of 3.4% and the ortho I - ortho II transition occurred at 26 GPa with a volume reduction of 9.4%. The phase boundary between the ortho I and ortho II phases above 400°C is expressed approximately by a linear equation, T(°C)=4720-300P(GPa). The kinetic limit curves gradually towards the higher pressure side at lower temperatures because of the sluggishness of the transition. The ortho II phase was identified as the cotunnite-type structure for both at high pressure and quenched samples.

Tang, J.; Kai, M.; Kobayashi, Y.; Endo, S.; Shimomura, O.; Kikegawa, T.; Ashida, T.

190

Physicochemical and electrical characterizations of atomic layer deposition grown HfO2 on TiN and Pt for metal-insulator-metal application  

E-print Network

N and Pt for metal-insulator-metal application C. Jorel,a C. Vallée,b E. Gourvest, B. Pelissier, M. Kahn, M; published 9 February 2009 This work reports on the study of two HfO2 metal-insulator-metal structures using.1116/1.3021036 I. INTRODUCTION Meta-insulator-metal MIM capacitors are key compo- nents of electronic circuits

Boyer, Edmond

191

Electrical characterization of high K dielectrics and metals, modeling of dielectric response, and modification of metal work function  

NASA Astrophysics Data System (ADS)

During the deposition of HfO2 gate oxide by atomic layer deposition (ALD) and post deposition annealing, it is observed that SiOx growth on Si, interdiffusion of Hf, Si, and O species, formation of Hf-O-Si bond linkages and amorphous Hf silicates through reactions at internal interfaces, and nucleation and growth of HfO2 occurs. Due to this intermixing, an intermediate layer with graded composition and dielectric permittivity (K) is formed, and which must be taken into account to model the total equivalent oxide thickness (EOTtot) of the stack. Therefore, quantum corrected EOTtot of this stack was estimated from C-V measurements, and using a three-layer capacitance model, that reflects the spatial dependence of composition (and K) in the dielectric sub-layers, the respective contributions to EOT tot and the K of the interfacial layer are determined. Since the interlayer contribution to the EOTtot is about 50%, nitridation of the interface is carried out to reduce its effect. Additionally, ALD silicates are used to control the nanostructure evolution and thermal stability of the HfO 2 layer, for these Hf-Si-O films with various HfO2 content (40, 60, and 75 mol%) are electrically characterized. The properties of as-deposited and forming gas annealed (FGA) Ta 2O5 thin-film capacitors deposited by ALD and plasma-enhanced ALD (PEALD) on native oxide surface (SiOx/Si) are examined and qualitatively compared using cross-sectional high resolution transmission electron microscopy (HRTEM), high angle annular dark field scanning TEM (HAADF-STEM) equipped with parallel electron energy loss spectrometer (PEELS), capacitance-voltage (C-V) and leakage current-voltage (JL-V) techniques, and oxide breakdown statistics. The effective metal work function (?M,eff) for Ru, Re, Pt and Pd on ALD HfO2, which are different from the vacuum work function and important for device threshold voltage control, are measured by the C-V method, and the extracted charge neutrality level (? CNL,HK) and screening parameter (S) are correlated with the stoichiometry and permittivity of the HfO2 film. Finally, a novel method is used to change the ?Ti,eff using self-assembled monolayer (SAM) of dipolar molecules, aminopropyl triethoxy silane or APTES molecules; a chance attributed to the change in the electric potential at the Ti/SAM interface.

Gu, Diefeng

2006-04-01

192

Effect of current compliance and voltage sweep rate on the resistive switching of HfO2/ITO/Invar structure as measured by conductive atomic force microscopy  

NASA Astrophysics Data System (ADS)

The electrical characterization of HfO2/ITO/Invar resistive switching memory structure was studied using conductive atomic force microscopy (AFM) with a semiconductor parameter analyzer, Agilent 4156C. The metal alloy Invar was used as the metal substrate to ensure good ohmic contact with the substrate holder of the AFM. A conductive Pt/Ir AFM tip was placed in direct contact with the HfO2 surface, such that it acted as the top electrode. Nanoscale current-voltage (I-V) characteristics of the HfO2/ITO/Invar structure were measured by applying a ramp voltage through the conductive AFM tip at various current compliances and ramp voltage sweep rates. It was found that the resistance of the low resistance state (RLRS) decreased with increasing current compliance value, but resistance of high resistance state (RHRS) barely changed. However, both the RHRS and RLRS decreased as the voltage sweep rate increased. The reasons for this dependency on current compliance and voltage sweep rate are discussed.

Wu, You-Lin; Liao, Chun-Wei; Ling, Jing-Jenn

2014-06-01

193

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

PubMed

Use of high-? 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. PMID:25474786

Xu, Toby; Tekes, Coskun; Degertekin, F

2014-12-01

194

Application of zero-temperature-gradient zero-bias thermally stimulated current spectroscopy to ultrathin high-dielectric-constant insulator film characterization  

NASA Astrophysics Data System (ADS)

Previously, we have reported our application of the zero-bias thermally stimulated current (ZBTSC) spectroscopy technique to study defect states in high-dielectric-constant insulator films such as tantalum oxide with much less parasitic current which can be a serious limitation for the conventional thermally stimulated current method. However, a parasitic current can still be observed for ZBTSC because of a small parasitic temperature gradient across the sample. The thermal design of the ZBTSC system can be improved, resulting in zero-temperature-gradient ZBTSC which can be used to detect deeper traps than those by ZBTSC.

Lau, W. S.; Wong, K. F.; Han, Taejoon; Sandler, Nathan P.

2006-04-01

195

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

NASA Astrophysics Data System (ADS)

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.

Marsza?ek, Konstanty; Winkowski, Pawe?; Jaglarz, Janusz

2014-01-01

196

Pulse-induced low-power resistive switching in HfO2 metal-insulator-metal diodes for nonvolatile memory applications  

Microsoft Academic Search

The conduction process as well as the unipolar resistive switching behavior of Au\\/HfO2\\/TiN metal-insulator-metal structures were investigated for future nonvolatile memory applications. With current-voltage measurements performed at different temperatures (200-400 K), the Poole-Frenkel effect as conduction process was identified. In particular, we extracted a trap energy level at phit=0.35+\\/-0.05 eV below the HfO2 conduction band to which a microscopic origin

Ch. Walczyk; Ch. Wenger; R. Sohal; M. Lukosius; A. Fox; J. daBrowski; D. Wolansky; B. Tillack; H.-J. Müssig; T. Schroeder

2009-01-01

197

Interface absorption versus film absorption in HfO2 SiO2 thin-film pairs in the near-ultraviolet and the relation to pulsed-laser damage  

NASA Astrophysics Data System (ADS)

Near-ultraviolet absorption in hafnium oxide and silica oxide thin-film pairs in a configuration strongly departing from the regular quarter-wave-thickness approach has been studied with the goal of separating film and interfacial contributions to absorption and pulsed laser damage. For this purpose, we manufactured a model HfO2 SiO2 thin-film coating containing seven HfO2 layers separated by narrow SiO2 layers and a single-layer HfO2 film in one coating run. The two coatings were characterized by a one-wave total optical thickness for the HfO2 material and similar E-field peak intensity inside the film. Absorption in the electron-beam-deposited films was measured using photothermal heterodyne imaging. By comparing absorption for the seven-layer and single-layer films, one can estimate the partial HfO2 SiO2 interface contribution. Relevance of obtained data to the thin-film pulsed-laser damage was verified by conducting 351-nm, nanosecond-laser-damage measurements and damage-morphology characterization using atomic force microscopy.

Papernov, S.; Kozlov, A. A.; Oliver, J. B.

2014-10-01

198

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

PubMed

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 ~10(6)?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

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

2015-01-01

199

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

200

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

PubMed Central

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

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

2015-01-01

201

Enhanced ultraviolet electroluminescence and spectral narrowing from ZnO quantum dots/GaN heterojunction diodes by using high-k HfO2 electron blocking layer  

NASA Astrophysics Data System (ADS)

We demonstrated the capability of realizing enhanced ZnO-related UV emissions by using the low-cost and solution-processable ZnO quantum dots (QDs) with the help of a high-k HfO2 electron blocking layer (EBL) for the ZnO QDs/p-GaN light-emitting diodes (LEDs). Full-width at half maximum of the LED devices was greatly decreased from ˜110 to ˜54 nm, and recombinations related to nonradiative centers were significantly suppressed with inserting HfO2 EBL. The electroluminescence of the ZnO QDs/HfO2/p-GaN LEDs demonstrated an interesting spectral narrowing effect with increasing HfO2 thickness. The Gaussian fitting revealed that the great enhancement of the Zni-related emission at ˜414 nm whereas the deep suppression of the interfacial recombination at ˜477 nm should be the main reason for the spectral narrowing effect.

Mo, Xiaoming; Long, Hao; Wang, Haoning; Li, Songzhan; Chen, Zhao; Wan, Jiawei; Feng, Yamin; Liu, Yuping; Ouyang, Yifang; Fang, Guojia

2014-08-01

202

Improvements on surface carrier mobility and electrical stability of MOSFETs using HfTaO gate dielectric  

Microsoft Academic Search

Physical and electrical characteristics of HfTaO gate dielectric have been systematically investigated for the first time. Based on the X-ray diffraction spectra and high-resolution transmission electron microscope pictures, the crystallization temperature of HfO2 film is significantly increased with incorporating Ta, and the HfTaO with 43% Ta film remains amorphous after annealing at 950°C for 30 s. X-ray photoelectron spectroscopy results

Xiongfei Yu; Chunxiang Zhu; Mingbin Yu; Dim-Lee Kwong

2004-01-01

203

Laser-damage susceptibility of nodular defects in dielectric mirror coatings: AFM measurements and electric-field modeling  

Microsoft Academic Search

Atomic force microscopy (AFM) and electromagnetic field modeling were used to study the influence of nodular coating defects on laser-induced damage of multilayer dielectric coatings. In studies of HfO2\\/SiO2 mirrors with 1.06 ?m illumination, AFM results showed that nodular defects with high dome heights (?0.6 ?m) were most susceptible to laser damage. Crater defects, formed by nodules ejected from the

M. R. Kozlowski; J. F. DeFord; M. C. Staggs

1993-01-01

204

A study on HfO2 RRAM in HRS based on I-V and RTN analysis  

NASA Astrophysics Data System (ADS)

This paper presents a statistical characterization of random telegraph noise (RTN) in hafnium-oxide-based resistive random access memories (RRAMs) in high resistive state (HRS). Complex RTN signals are analyzed exploiting a Factorial Hidden Markov Model (FHMM) approach, which allows to derive the statistical properties of the RTN signals, directly related to the physical properties of the traps responsible for the multi-level RTN measured in these devices. Noise characteristics in different reset conditions are explored through consecutive switching cycles. Noise spectral analysis is also performed to fully support the investigation. An RRAM compact model is also exploited to estimate the physical properties of the conductive filament and of the dielectric barrier from simple I-V data. These tools are combined together to prove the existence of a direct statistical relation between the reset conditions, the volume of the dielectric barrier created during the reset operation and the average number of active traps contributing to the RTN.

Puglisi, Francesco M.; Pavan, Paolo; Padovani, Andrea; Larcher, Luca

2014-12-01

205

Influence of charged particle bombardment and sputtering parameters on the properties of HfO 2 films prepared by dc reactive magnetron sputtering  

NASA Astrophysics Data System (ADS)

HfO 2 films prepared on glass substrates by dc reactive magnetron sputtering in an Ar + O 2 atmosphere are investigated. The films are polycrystallized with a pure monoclinic phase, and the crystallization strongly relates to the technology environment. Charged particle bombardment mainly caused by negative oxygen ions during sputtering on the films results in rougher surface morphology and worse crystalline property. Influence of sputtering pressure, substrate temperature and Ar:O 2 flow ratio is studied. The main orientations of the films are (-1 1 1) and (1 1 1). The (-1 1 1) orientation is stable, but (1 1 1) orientation is very sensitive to the sputtering condition, and it can be suppressed effectively by introducing charged particle bombardment, lowing sputtering pressure and increasing oxygen concentration.

Liu, Xin; Li, Dejie

2006-12-01

206

Ultrathin Dielectric Oxide Films On Silicon  

DOEpatents

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.

Klemperer, Walter G. (Champaign, IL); Lee, Jason (Liverpool, GB); Mikalsen, Erik A. (Urbana, IL); Payne, David A. (Champaign, IL)

2004-09-21

207

Charge injection in high-? gate dielectrics of single-walled carbon nanotube thin-film transistors.  

PubMed

We investigate charge injection into the gate dielectric of single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) having Al(2)O(3) and HfO(2) gate dielectrics. We demonstrate the use of electric field gradient microscopy (EFM) to identify the sign and approximate the magnitude of the injected charge carriers. Charge injection rates and saturation levels are found to differ between electrons and holes and also vary according to gate dielectric material. Electrically, Al(2)O(3) gated devices demonstrate smaller average hysteresis and notably higher average on-state current and p-type mobility than those gated by HfO(2). These differences in transfer characteristics are attributed to the charge injection, observed via EFM, and correlate well with differences in tunneling barrier height for electrons and holes formed in the conduction and valence at the SWCNT/dielectric interface, respectively. This work emphasizes the need to understand the SWCNT/dielectric interface to overcome charge injection that occurs in the focused field region adjacent to SWCNTs and indicates that large barrier heights are key to minimizing the effect. PMID:22545966

McMorrow, Julian J; Cress, Cory D; Affouda, Chaffra A

2012-06-26

208

Impedance spectroscopic analysis on effects of partial oxidation of TiN bottom electrode and microstructure of amorphous and crystalline HfO2 thin films on their bipolar resistive switching  

NASA Astrophysics Data System (ADS)

The electrical resistance switching (RS) properties of amorphous HfO2 (a-HfO2) and crystalline HfO2 (c-HfO2) thin films grown on a TiN substrate via atomic layer deposition were examined using DC current-voltage (I-V) sweep and AC impedance spectroscopic (IS) analyses. The rapid thermal annealing of the a-HfO2 film at 500 °C under a N2 atmosphere for 5 min crystallized the HfO2 film and induced an interfacial TiON barrier layer. The a-HfO2 sample showed fluent bipolar RS performance with a high on/off ratio (~500), whereas the c-HfO2 sample showed a much lower on/off ratio (<~10), but its switching uniformity was better than that of a-HfO2. Such critical differences can be mainly attributed to the absence and presence of the TiON barrier layer in the a-HfO2 and c-HfO2 samples, respectively. The AC IS especially enabled the resistance states of the HfO2/Pt interface and the HfO2/TiN interface to be separately examined during one complete switching cycle of each sample. Although the Pt/c-HfO2 interface has a Schottky barrier in the pristine state, it disappeared once the c-HfO2 was electroformed and was not recovered even after the reset step. In contrast, the Pt/a-HfO2 interface partly recovered the Schottky barrier after the reset.

Yoon, Ji-Wook; Yoon, Jung Ho; Lee, Jong-Heun; Hwang, Cheol Seong

2014-05-01

209

Impedance spectroscopic analysis on effects of partial oxidation of TiN bottom electrode and microstructure of amorphous and crystalline HfO2 thin films on their bipolar resistive switching.  

PubMed

The electrical resistance switching (RS) properties of amorphous HfO2 (a-HfO2) and crystalline HfO2 (c-HfO2) thin films grown on a TiN substrate via atomic layer deposition were examined using DC current-voltage (I-V) sweep and AC impedance spectroscopic (IS) analyses. The rapid thermal annealing of the a-HfO2 film at 500 °C under a N2 atmosphere for 5 min crystallized the HfO2 film and induced an interfacial TiON barrier layer. The a-HfO2 sample showed fluent bipolar RS performance with a high on/off ratio (? 500), whereas the c-HfO2 sample showed a much lower on/off ratio (

Yoon, Ji-Wook; Yoon, Jung Ho; Lee, Jong-Heun; Hwang, Cheol Seong

2014-06-21

210

Manufacturable embedded CMOS 6T-SRAM technology with high-k gate dielectric device for system-on-chip applications  

Microsoft Academic Search

Manufacturable embedded CMOS 6T-SRAM with the HfO2-Al2O3 dielectric for system-on-chip (SoC) applications is successfully demonstrated for the first time in the semiconductor industry. The possibility of the high-k gate dielectric in low power SoC applications is suggested. 0.11?m NFET and PFET devices with thin high-k gate dielectric have 470 and 150?A\\/?m at Ioff=0.1nA\\/um and Vdd=1.2V, respectively. Inversion thickness of NFET

C. B. Oh; H. S. Kang; H. J. Ryu; M. H. Oh; H. S. Jung; Y. S. Kim; J. H. He; N. I. Lee; K. H. Cho; D. H. Lee; T. H. Yang; I. S. Cho; H. K. Kang; Y. W. Kim; K. P. Suh

2002-01-01

211

Dielectric response of sputtered transition metal oxides  

NASA Astrophysics Data System (ADS)

We have investigated the dielectric properties of thin layers of five oxides of transition metals (Ta2O5, HfO2, ZrO2, (ZrO2)0.91(Y2O3)0.09, and Sn0.2Zr0.2Ti0.6O2) sputtered from ceramic targets at different pressures. We find that layers deposited at low pressure behave as expected from literature, whereas layers deposited at high pressure all exhibit an anomalous dielectric response similar to that reported for the so-called "colossal" dielectric constant materials. The characterization of the thickness, frequency, and temperature dependence of the capacitance, as well as the comparison of film properties before and after annealing show that the anomalous dielectric response is due to quenched-in vacancies that act as dopants and cause the insulating layers to behave as semiconductors. An increase in quenched-in vacancies concentration with sputtering pressure results in a transition from normal to anomalous dielectric response and gradual increase in layer conductivity. In contrast, the refractive index does not depend on sputtering pressure. This observation indicates the possible application of these materials as transparent coatings with a tunable electrical conductivity.

Iosad, N. N.; Ruis, G. J.; Morks, E. V.; Morpurgo, A. F.; van der Pers, N. M.; Alkemade, P. F. A.; Sivel, V. G. M.

2004-06-01

212

Interaction of oxygen vacancies and lanthanum in Hf-based high-k dielectrics: an ab initio investigation.  

PubMed

The interaction between oxygen vacancies and La atoms in the La doped HfO(2) dielectric were studied using first principles total energy calculations. La dopants in the vicinity of a neutral oxygen vacancy (V(O)) show lower formation energy compared to the La defects far from V(O) centres. La doping in HfO(2) leads to the shift of the defect states of oxygen vacancies towards the conduction band edge. A statistical average of this shift over several possible configurations of La atoms and V(O) shows that the incorporation of La effectively passivates the V(O) induced defect states leading to the reduction of the gate leakage current and improvement of the device reliability. PMID:21865638

Nadimi, Ebrahim; Ottking, Rolf; Plänitz, Philipp; Trentzsch, Martin; Kelwing, Torben; Carter, Rick; Schreiber, Michael; Radehaus, Christian

2011-09-14

213

Reduced intermolecular interaction in organic ultrathin films  

NASA Astrophysics Data System (ADS)

Submonolayer sensitivity was achieved using in situ ellipsometry to monitor the evolution of the dielectric function of tris(8-hydroxyquinoline)-aluminum(III) (Alq3) layers from submonolayer coverage to thick bulklike layers. The Alq3 layers were deposited under ultrahigh vacuum conditions onto hydrogen passivated silicon. The characteristic vacuum-ultraviolet (VUV) absorption lines of Alq3 were detected using synchrotron radiation as light source. In such ultrathin films the absorption lines corresponding to molecular transitions of the Alq3 are found to be spectrally blueshifted with respect to bulklike layers. We attribute the shift to the effect of reduced intermolecular interaction in the submonolayer regime.

Gordan, O. D.; Himcinschi, C.; Zahn, D. R. T.; Cobet, C.; Esser, N.; Braun, W.

2006-04-01

214

Investigation of etching properties of HfO based high-K dielectrics using inductively coupled plasma  

NASA Astrophysics Data System (ADS)

The etching properties of HfO based high dielectric constant (K) films, HfO2, HfON, HfSiO, and HfAlO, were investigated using inductively coupled plasma of Cl2/HBr/CHF3/CF4/O2. The etch rates varied depending on the chemical components in the films. Among HfO2, HfON, HfSiO, and HfAlO, the etch rates of HfSiO increased most significantly with increasing radio frequency bias power. This may be attributed to the ternary network of Hf-Si-O that is different from the binary network of other films of Hf-O, Hf-N, Si-O, and Al-O. The etch rates of HfON were higher than those of HfO2 due to the effect of the high Hf-N etch rates compared to the Hf-O etch rates, whereas the HfAlO etch rates were lower than those of HfO2 due to the effect of the low Al-O etch rates. Etch residues and chemical compositions of HfO based dielectrics were analyzed by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. A significant amount of fluorides existed on the surface after CF4/CHF3 etching whereas only a small amount of chloride and bromide existed after Cl2/HBr etching. The high temperature post-treatment step was effective in reducing the amount of residues. .

Chen, Jinghao; Yoo, Won Jong; Tan, Zerlinda Yl; Wang, Yingqian; Chan, Daniel S. H.

2004-07-01

215

High-k dielectrics on n-Al0.25Ga0.75N via atomic layer deposition  

NASA Astrophysics Data System (ADS)

AlGaN/GaN and AlInN/GaN high-electron-mobility transistors (HEMTs) are promising devices for high-temperature and high-power electronics applications. A key issue with these devices is the high gate leakage current, particularly for enhancement-mode HEMTs. There has been an increased interest in developing high quality gate insulators to reduce gate leakage current. Al2O3 and HfO2 layers (21nm thick)were deposited via atomic layer deposition on n-Al0.25Ga0.75N pretreated with one of two different surface preparations, H2O2:H2SO4 (1:5) (piranha) or HF:H2O (1:3). Dielectrics were characterized using spectroscopic ellipsometry, X-ray photoelectron spectroscopy, atomic force microscopy (AFM), and capacitance-voltage (C-V) measurements. AFM shows that Al2O3 and HfO2 layers are continuous and uniform in thickness on both HF and piranha pretreated surfaces. However, C-V measurement shows smaller (15%) hysteresis for HF pretreated samples. The estimated dielectric constants (?) are 9 and 18 for Al2O3 and HfO2 on HF pretreated surfaces, respectively, in general agreement with theoretical values of 9 and 25. Al2O3 layers on Al0.25Ga0.75N exhibited a lower leakage (7x10-8 A/cm^2 at 5 V) current and higher forward breakdown voltage of 7.5 MV/cm compared to that of HfO2 layer. The higher breakdown voltage and lower leakage current for Al2O3 is due to larger conduction band offset with Al0.25Ga0.75N.

Nepal, N.; Garces, N. Y.; Meyer, D.; Anderson, T. J.; Hite, J. K.; Mastro, M. A.; Eddy, C. R., Jr.

2012-02-01

216

Calculation of the electron mobility in III-V inversion layers with high-? dielectrics  

NASA Astrophysics Data System (ADS)

We calculate the electron mobility for a metal-oxide-semiconductor system with a metallic gate, high-? dielectric layer, and III-V substrate, including scattering with longitudinal-optical (LO) polar-phonons of the III-V substrate and with the interfacial excitations resulting from the coupling of insulator and substrate optical modes among themselves and with substrate plasmons. In treating scattering with the substrate LO-modes, multisubband dynamic screening is included and compared to the dielectric screening in the static limit and with the commonly used screening model obtained by defining an effective screening wave vector. The electron mobility components limited by substrate LO phonons and interfacial modes are calculated for In0.53Ga0.47As and GaAs substrates with SiO2 and HfO2 gate dielectrics. The mobility components limited by the LO-modes and interfacial phonons are also investigated as a function of temperature. Scattering with surface roughness, fixed interface charge, and nonpolar-phonons is also included to judge the relative impact of each scattering mechanism in the total mobility for In0.53Ga0.47As with HfO2 gate dielectric. We show that InGaAs is affected by interfacial-phonon scattering to an extent larger than Si, lowering the expected performance, but probably not enough to question the technological relevance of InGaAs.

O'Regan, T. P.; Fischetti, M. V.; Sorée, B.; Jin, S.; Magnus, W.; Meuris, M.

2010-11-01

217

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

PubMed

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. PMID:24508952

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

218

Effect of CO2 laser irradiation on the performances of sol-gel-derived Er3+-activated SiO2 - ZrO2 and SiO2 - HfO2 planar waveguides  

Microsoft Academic Search

Erbium activated SiO2-ZrO2 and SiO2-HfO2 planar waveguides doped with Er3+ ranging from 0.5 to 5 mol% were prepared by sol-gel route using dip-coating deposition on silica glass substrates. All the planar waveguides were optimized in order to confine one propagating mode at 1550 nm. The aim of this work is to present an alternative method for planar optical waveguides processing

C. Goyes; M. Ferrari; C. Armellini; A. Chiasera; Y. Jestin; G. C. Righini; A. Casas; C. Meacock; E. Solarte

2007-01-01

219

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

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

220

Effects of layer sequence and postdeposition annealing temperature on performance of La2O3 and HfO2 multilayer composite oxides on In0.53Ga0.47As for MOS capacitor application  

NASA Astrophysics Data System (ADS)

In this paper, we report on high-k composite oxides that are formed by depositing multiple layers of HfO2 and La2O3 on In0.53Ga0.47As for MOS device application. Both multilayer HfO2 (0.8 nm)/La2O3 (0.8 nm)/In0.53Ga0.47As and La2O3 (0.8 nm)/HfO2 (0.8 nm)/In0.53Ga0.47As MOS structures were investigated. The effects of oxide thickness and postdeposition annealing (PDA) temperature on the interface properties of the composite oxide MOS capacitors were studied. It was found that a low CET of 1.41 nm at 1 kHz was achieved using three-layer composite oxides. On the other hand, a small frequency dispersion of 2.8% and an excellent Dit of 7.0 × 1011 cm-2·eV-1 can be achieved using multiple layers of La2O3 (0.8 nm) and HfO2 (0.8 nm) on the In0.53Ga0.47As MOS capacitor with optimum thermal treatment and layer thickness.

Wu, Wen-Hao; Lin, Yueh-Chin; Chuang, Ting-Wei; Chen, Yu-Chen; Hou, Tzu-Ching; Yao, Jing-Neng; Chang, Po-Chun; Iwai, Hiroshi; Kakushima, Kuniyuki; Chang, Edward Yi

2014-03-01

221

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

NASA Astrophysics Data System (ADS)

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.

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

222

Ultra-thin multilayer capacitors.  

SciTech Connect

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.

Renk, Timothy Jerome; Monson, Todd C.

2009-06-01

223

Ab initio study of the elastic properties of single and polycrystal TiO2, ZrO2 and HfO2 in the cotunnite structure  

NASA Astrophysics Data System (ADS)

In this work, we study theoretically the elastic properties of the orthorhombic (Pnma) high-pressure phase of IV-B group oxides: titania, zirconia and hafnia. By means of the self-consistent SIESTA code, pseudopotentials, density functional theory in the LDA and GGA approximations, the total energies, hydrostatic pressures and stress tensor components are calculated. From the stress-strain relationships, in the linear regime, the elastic constants Cij are determined. Derived elastic constants, such as bulk, Young's and shear modulus, Poisson coefficient and brittle/ductile behavior are estimated with the polycrystalline approach, using Voigt-Reuss-Hill theories. We have found that C11, C22 and C33 elastic constants of hafnia and zirconia show increased strength with respect to the experimental values of the normal phase, P 21/c. A similar situation applies to titania if these constants are compared with its normal phase, rutile. However, shear elastic constants C44, C55 and C66 are similar to the values found in the normal phase. This fact increases the compound anisotropy as well as its ductile behavior. The dependence of unit-cell volumes under hydrostatic pressures is also analyzed. P-V data, fitted to third-order Birch-Murnaghan equations of state, provide the bulk modulus B0 and its pressure derivatives B'0. In this case, LDA estimations show good agreement with respect to recent measured bulk moduli of ZrO2 and HfO2. Thermo-acoustic properties, e.g. the propagation speed of transverse, longitudinal elastic waves together with associated Debye temperatures, are also estimated.

Caravaca, M. A.; Miño, J. C.; Pérez, V. J.; Casali, R. A.; Ponce, C. A.

2009-01-01

224

Ab initio study of the elastic properties of single and polycrystal TiO(2), ZrO(2) and HfO(2) in the cotunnite structure.  

PubMed

In this work, we study theoretically the elastic properties of the orthorhombic (Pnma) high-pressure phase of IV-B group oxides: titania, zirconia and hafnia. By means of the self-consistent SIESTA code, pseudopotentials, density functional theory in the LDA and GGA approximations, the total energies, hydrostatic pressures and stress tensor components are calculated. From the stress-strain relationships, in the linear regime, the elastic constants C(ij) are determined. Derived elastic constants, such as bulk, Young's and shear modulus, Poisson coefficient and brittle/ductile behavior are estimated with the polycrystalline approach, using Voigt-Reuss-Hill theories. We have found that C(11), C(22) and C(33) elastic constants of hafnia and zirconia show increased strength with respect to the experimental values of the normal phase, P 2(1)/c. A similar situation applies to titania if these constants are compared with its normal phase, rutile. However, shear elastic constants C(44), C(55) and C(66) are similar to the values found in the normal phase. This fact increases the compound anisotropy as well as its ductile behavior. The dependence of unit-cell volumes under hydrostatic pressures is also analyzed. P-V data, fitted to third-order Birch-Murnaghan equations of state, provide the bulk modulus B(0) and its pressure derivatives B'(0). In this case, LDA estimations show good agreement with respect to recent measured bulk moduli of ZrO(2) and HfO(2). Thermo-acoustic properties, e.g. the propagation speed of transverse, longitudinal elastic waves together with associated Debye temperatures, are also estimated. PMID:21817222

Caravaca, M A; Miño, J C; Pérez, V J; Casali, R A; Ponce, C A

2009-01-01

225

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

226

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

227

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

PubMed

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

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

2015-03-23

228

Low voltage stress-induced-leakage-current in ultrathin gate oxides  

Microsoft Academic Search

Stress-induced-leakage-current (SILC) is an important concern in ultrathin gate oxides because it may impose constraints on dielectric thickness scaling. We show that for oxides less than ~3.5 nm thick, interfacial traps generated from direct tunneling stress result in a sense voltage dependent SILC mechanism that can dominate the gate leakage current at low operating voltages

Paul E. Nicollian; Mark Rodder; Douglas T. Grider; Peijun Chen; Robert M. Wallace; Sunil V. Hattangady

1999-01-01

229

Effect of surface preparation on the radiation hardness of high-dielectric constant gate dielectric  

NASA Astrophysics Data System (ADS)

Effect of surface preparation on the radiation hardness of MOS devices with high dielectric constant gate dielectric of HfO2 and metal gate of TiN is studied using extreme ultra-violet (EUV) light as the radiation source. Three kinds of surface treatment including HF-last, chemical-oxidation, and rapid-thermal-oxidation were evaluated. Among them, chemical-oxidation exhibits the best radiation hardiness in terms of interface traps and border traps. The state-of-the-art MOSFET with a thin high-k dielectric and a high quality chemical oxide interfacial layer shows that the degradation of subthreshold swing is more severe than degradation of threshold voltage. However, the overall degradation is less than 6% even after EUV irradiation to a total dose of 580 mJ/cm2. Off-state current degradation is observed due to the generation of oxide traps and interface traps at the isolation region. This phenomenon does not occur in the conventional optical lithography process but should be considered if EUV lithography is used.

Tsui, Bing-Yue; Su, Ting-Ting; Shew, Bor-Yuan; Huang, Yang-Tung

2013-03-01

230

STM characterization of ultrathin Si oxynitride layers  

NASA Astrophysics Data System (ADS)

Minor defects in thin gate dielectric films play dominant roles in both the performance and reliability of metal-oxide-semiconductor devices. In this work, we used STM and STS to examine the local electric properties of ultrathin Si oxynitride layers. The oxynitride layers were thermally grown on clean Si(001)-2x1 surfaces under 2x10-6 Torr NO pressure at 650^circC. Under these growth conditions, one or two atomic layers of Si on the Si surface react with NO [1]. STM images of the oxynitrided Si surface showed atomic-scale spots (0.3-2 nm in diameter) at a density of about 1x10^14 cm-2. From most of these spots, normal I-V curves explained by electron transport from the tip to the sample were observed. From a few spots, negative differential resistance (NDR) and plateau curves were observed in the positive sample bias region. These electric properties indicated atomic-scale localization on the spots. We considered that the NDR and plateau features were caused by defect states below or near the SiON conduction band edge. We found that the defect density in the oxynitride layer increased with the NO exposure time and was larger than that of the ultrathin Si oxide layer. [1] N. Miyata, H. Watanabe, and M. Ichikawa, Appl. Phys. Lett. 76, 3561 (2000). This work was partly supported by NEDO.

Miyata, Noriyuki; Ichikawa, Masakazu

2001-03-01

231

Electrical characteristics of SiGe MOSFETs integrated with Tantalum or Titanium oxynitride higher-k gate dielectrics  

Microsoft Academic Search

Metal oxide semiconductor field effect transistors (MOSFET) with SiGe channel and higher-k gate dielectric are studied in this work. Samples with TaON\\/HfO2 or TiON\\/HfO2 stacks show larger drain current, transconductance, and smaller subthreshold swing than that with single HfO2 layer. In addition, the reliability of SiGe MOSFET device is clearly improved with TaON\\/HfO2 stacks in terms of degradation of Gm

Chen-Chien Li; Kuei-Shu Chang-Liao; Chung-Hao Fu; Te-Hsuen Tzeng; Tien-Ko Wang; Wen-Fa Tsai; Chi-Fong Ai

2011-01-01

232

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

PubMed

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. PMID:23668386

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

2013-06-25

233

Growth and electrical properties of spin coated ultrathin ZrO2 films on silicon  

NASA Astrophysics Data System (ADS)

Ultrathin (<50 nm) zirconium oxide (ZrO2) films are being intensively studied as high-k dielectrics for future metal-oxide-semiconductor (MOS) technology. In this paper, ultrathin ZrO2 films are deposited on silicon substrates by spin on deposition technique and annealed at 700 °C for different duration. The phase formation and morphological study have been performed by x-ray diffraction and scanning electron microscopy, respectively. Electrical properties of the films are investigated. The threshold voltages of the MOS structure were found to vary from -1.5 V to -2.5 V as the annealing time increases. The dielectric constants of the films are found to be 7.2-7.67 at 1 KHz. Leakage current of the films is found to increase with the annealing time. The dielectric breakdown field of the film is found to be 6.29-8.15 MV/cm.

Dutta, Shankar; Pandey, Akhilesh; Yadav, Isha; Thakur, O. P.; Kumar, A.; Pal, Ramjay; Chatterjee, Ratnamala

2013-07-01

234

All-dielectric diffraction grating for multi-petawatt laser systems  

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

235

Guided Bloch surface waves on ultrathin polymeric ridges.  

PubMed

We present a direct evidence of Bloch surface waves (BSWs) waveguiding on ultrathin polymeric ridges, supported by near-field measurements. It is demonstrated that near-infrared BSWs sustained by a silicon-based multilayer can be locally coupled and guided through dielectric ridges of nanometric thickness with low propagation losses. Using a conventional prism-based configuration, we demonstrate a wavelength-selective BSW coupling inside and outside the ridge. Such a result can open interesting opportunities in surface wave-mediated sensing applications, where light could be selectively coupled in specific regions defined by nanometric reliefs. PMID:20446750

Descrovi, Emiliano; Sfez, Tristan; Quaglio, Marzia; Brunazzo, Daniele; Dominici, Lorenzo; Michelotti, Francesco; Herzig, Hans Peter; Martin, Olivier J F; Giorgis, Fabrizio

2010-06-01

236

Refractive-index sensing with ultra-thin plasmonic nanotubes  

E-print Network

We study the refractive-index sensing properties of plasmonic nanotubes with a dielectric core and ultra-thin metal shell. The few-nm thin metal shell is described by both the usual Drude model and the nonlocal hydrodynamic model to investigate the effects of nonlocality. We derive an analytical expression for the extinction cross section and show how sensing of the refractive index of the surrounding medium and the figure-of-merit are affected by the shape and size of the nanotubes. Comparison with other localized surface plasmon resonance sensors reveals that the nanotube exhibits superior sensitivity and comparable figure-of-merit.

Raza, S; Jauho, A -P; Mortensen, N A; Wubs, M

2012-01-01

237

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)

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.

Zhu, Dongming

2014-01-01

238

Investigation of metal oxide dielectrics for non-volatile floating gate and resistance switching memory applications  

NASA Astrophysics Data System (ADS)

Floating gate transistor based flash memories have seen more than a decade of continuous growth as the prominent non-volatile memory technology. However, the recent trends indicate that the scaling of flash memory is expected to saturate in the near future. Several alternative technologies are being considered for the replacement of flash in the near future. The basic motivation for this work is to investigate the material properties of metal oxide based high-k dielectrics for potential applications in floating gate and resistance switching memory applications. This dissertation can be divided into two main sections. In the first section, the tunneling characteristics of the SiO2/HfO 2 stacks were investigated. Previous theoretical studies for thin SiO 2/ thick high-k stacks predict an increase in tunneling current in the high-bias regime (better programming) and a decrease in the low-bias regime (better retention) in comparison to pure SiO2 of same equivalent oxide thickness (EOT). However, our studies indicated that the performance improvement in SiO2/HfO2 stacks with thick HfO2 layer is difficult due to significant amount of charge traps in thick HfO2 layers. Oxygen anneal on the stacks did not improve the programming current and retention. X-ray photoelectron spectroscopy (XPS) studies indicated that this was due to formation of an interfacial oxide layer. The second part of the dissertation deals with the investigation of resistive switching in metal oxides. Although promising, practical applications of resistive random access memories (RRAM) require addressing several issues including high forming voltage, large operating currents and reliability. We first investigated resistive switching in HfTiOx nanolaminate with conventional TiN electrodes. The forming-free switching observed in the structures could be described by the quantum point contact model. The modelling results indicated that the forming-free characteristics can be due to a higher number of filaments in comparison to a device that requires forming. Forming-free resistive switching with low current operation in graphene-insulator-graphene structures was also investigated. Electrical as well as Raman and XPS analysis indicated that low current operation is due to the migration and subsequent physisorption of oxygen ions on the graphene surface during the set operation. A statistical model was also developed for quantitative prediction of the effect of noise on RRAM characteristics.

Chakrabarti, Bhaswar

239

Ultrathin and broadband high impedance surface absorbers based on metamaterial substrates.  

PubMed

An ultrathin and simultaneously broadband high impedance surface absorber based on a metamaterial (MM) substrate is presented at microwave frequencies. The MM substrate is designed using metallic split ring resonators (SRRs) vertically embedded into a dielectric slab. Both the simulated and experimental results display two absorption peaks and an expanded absorption bandwidth of less than -10 dB compared to conventional ultrathin absorbers. By analyzing the field distributions and the substrate impedance characteristics, it is found that this feature is mainly related to the LC resonance of the substrate caused by the embedded SRRs. Our results demonstrate the great feasibility of broadening the absorption bandwidth of the ultrathin high impedance surface absorbers by the MMs incorporation. PMID:22714239

Pang, Yongqiang; Cheng, Haifeng; Zhou, Yongjiang; Li, Zenggnag; Wang, Jun

2012-05-21

240

Conformal surface plasmons propagating on ultrathin and flexible films  

PubMed Central

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

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

2013-01-01

241

Ultra-thin titanium oxide  

NASA Astrophysics Data System (ADS)

We demonstrate the fabrication of ultra-thin titanium oxide films by plasma-induced surface oxidation. Ellipsometry measurements indicate an oxide thickness of about 2 nm. Electrical characterization was performed on microscale and nanoscale metal-insulator-metal tunneling diodes. Electrical fields up to 22 MV/cm were applied without destroying the titanium oxide films. The current-voltage-characteristic of the diodes are found to be asymmetric with respect to zero bias when employing electrodes with different work functions. The permittivity of the ultra-thin titanium oxide was determined to be less than 6, which is the smallest permittivity that has been reported for titanium oxide.

Bareiß, M.; Kälblein, D.; Jirauschek, C.; Exner, A.; Pavlichenko, I.; Lotsch, B.; Zschieschang, U.; Klauk, H.; Scarpa, G.; Fabel, B.; Porod, W.; Lugli, P.

2012-08-01

242

Light emission from conductive paths in nanocrystalline CdSe embedded Zr-doped HfO2 high-k stack  

NASA Astrophysics Data System (ADS)

Electrical and optical properties of the solid state incandescent light emitting devices made of zirconium doped hafnium oxide high-k films with and without an embedded nanocrystalline CdSe layer on the p-type Si wafer have been studied. The broad band white light was emitted from nano sized conductive paths through the thermal excitation mechanism. Conductive paths formed from the dielectric breakdown have been confirmed from scanning electron microscopic and atomic force microscopic images and the secondary ion mass spectrometric elemental profiles. Si was diffused from the wafer to the device surface through the conductive path during the high temperature light emission process. There are many potential applications of this type of device.

Lin, Chi-Chou; Kuo, Yue

2015-03-01

243

Spectroscopic Studies of Electronically Active Defects in Transition Metal Oxides for Advanced Si Devices  

SciTech Connect

Based on spectroscopic studies, and guided by ab initio theory, the electron and hole traps in HfO2 and other transition metal elemental oxides e.g., TiO2, are assigned to O-atom divacancies, clustered at internal grain boundaries. Engineering solutions for defect reduction are identified: (i) deposition of ultra-thin, < 2 nm HfO2 and phase separated Hf silicate dielectrics, in which grain boundary formation is suppressed by effectively eliminating inter-primitive unit cell {pi}-bonding interactions, and (ii) non-crystalline Zr/Hf Si oxynitrides without nanocrystalline grain boundaries.

Lucovsky, G.; Luning, J.

2009-06-04

244

Wave manipulation with designer dielectric metasurfaces.  

PubMed

The concept of an ultra-thin metasurface made of single layer of only-dielectric disks for successful phase control over a full range is demonstrated. Conduction loss is avoided compared to its plasmonic counterpart. The interaction of the Mie resonances of the first two modes of the dielectric particles, magnetic and electric dipoles, is tailored by the dimensions of the disks, providing required phase shift for the transmitted beam from 0° to 360°, together with high transmission efficiency. The successful performance of a beam-tilting array and a large-scale lens functioning at 195 THz demonstrates the ability of the dielectric metasurface that is thin and has also high efficiency of more than 80%. Such configurations can serve as outstanding alternatives for plasmonic metasurfaces especially that it can be a scalable design. PMID:25361335

Cheng, Jierong; Ansari-Oghol-Beig, Davood; Mosallaei, Hossein

2014-11-01

245

Dielectric constants by multifrequency non-contact atomic force microscopy  

NASA Astrophysics Data System (ADS)

We present a method to obtain capacitive forces and dielectric constants of ultra-thin films on metallic substrates using multifrequency non-contact atomic force microscopy with amplitude feedback in air. Capacitive forces are measured via cantilever oscillations induced at the second bending mode and dielectric constants are calculated by fitting an analytic expression for the capacitance (Casuso et al 2007 Appl. Phys. Lett. 91 063111) to the experimental data. Dielectric constants for self-assembled monolayers of thiol molecules on gold (2.0 ± 0.1) and sputtered SiO2 (3.6 ± 0.07) were obtained under dry conditions, in good agreement with previous measurements. The high Q-factor of the second bending mode of the cantilever increases the accuracy of the capacitive measurements while the low applied potentials minimize the likelihood of variation of the dielectric constants at high field strength and of damage from dielectric breakdown of air.

Kumar, Bharat; Bonvallet, Joseph C.; Crittenden, Scott R.

2012-01-01

246

Dielectric constants by multifrequency non-contact atomic force microscopy.  

PubMed

We present a method to obtain capacitive forces and dielectric constants of ultra-thin films on metallic substrates using multifrequency non-contact atomic force microscopy with amplitude feedback in air. Capacitive forces are measured via cantilever oscillations induced at the second bending mode and dielectric constants are calculated by fitting an analytic expression for the capacitance (Casuso et al 2007 Appl. Phys. Lett. 91 063111) to the experimental data. Dielectric constants for self-assembled monolayers of thiol molecules on gold (2.0±0.1) and sputtered SiO2 (3.6±0.07) were obtained under dry conditions, in good agreement with previous measurements. The high Q-factor of the second bending mode of the cantilever increases the accuracy of the capacitive measurements while the low applied potentials minimize the likelihood of variation of the dielectric constants at high field strength and of damage from dielectric breakdown of air. PMID:22166734

Kumar, Bharat; Bonvallet, Joseph C; Crittenden, Scott R

2012-01-20

247

Low operation voltage and high thermal stability of a WSi2 nanocrystal memory device using an Al2O3/HfO2/Al2O3 tunnel layer  

NASA Astrophysics Data System (ADS)

A WSi2 nanocrystal nonvolatile memory device was fabricated with an Al2O3/HfO2/Al2O3 (AHA) tunnel layer and its electrical characteristics were evaluated at 25, 50, 70, 100, and 125 °C. The program/erase (P/E) speed at 125 °C was approximately 500 ?s under threshold voltage shifts of 1 V during voltage sweeping of 8 V/-8 V. When the applied pulse voltage was ±9 V for 1 s for the P/E conditions, the memory window at 125 °C was approximately 1.25 V after 105 s. The activation energies for the charge losses of 5%, 10%, 15%, 20%, 25%, 30%, and 35% were approximately 0.05, 0.11, 0.17, 0.21, 0.23, 0.23, and 0.23 eV, respectively. The charge loss mechanisms were direct tunneling and Pool-Frenkel emission between the WSi2 nanocrystals and the AHA barrier engineered tunneling layer. The WSi2 nanocrystal memory device with multi-stacked high-K tunnel layers showed strong potential for applications in nonvolatile memory devices.

Uk Lee, Dong; Jun Lee, Hyo; Kyu Kim, Eun; You, Hee-Wook; Cho, Won-Ju

2012-02-01

248

High-k dielectric stack-ellipsometry and electron diffraction measurements of interfacial oxides  

NASA Astrophysics Data System (ADS)

With the silicon interface becoming increasingly scrutinized in high dielectric constant materials for SiO2 replacement, fine distinctions in the quality of silicon cleaning can have a large impact on MOS parameters. One of the cleaning schemes that have potential to replace the industry standard RCA clean with HF/H2O etch is a modified version of the Shiraki clean. The evolution of Si (100) surface cleaned by the modified Shiraki method has been investigated by a conventional, single-wave length ellipsometer. Using Low Energy Electron Diffraction (LEED), we have calibrated the ellipsometric measurement for the as-cleaned silicon surface. It was found that a lower baseline of 0.7˜0.9 nm from ellipsometric measurements could be established as equivalent to a clean, hydrogen passivated surface. To verify the effect of the interfacial oxide thickness on the dielectric constant of the high-k gate stack, thickness of the thin-oxide grown under high vacuum condition was measured and correlated with the dielectric constant of the HfO2 gate dielectric layer.

Choi, Kisik; Harris, Harlan R.; Nikishin, Sergey; Gangopadhyay, Shubhra; Temkin, Henryk

2003-09-01

249

Dielectric gradient metasurface optical elements.  

PubMed

Gradient metasurfaces are two-dimensional optical elements capable of manipulating light by imparting local, space-variant phase changes on an incident electromagnetic wave. These surfaces have thus far been constructed from nanometallic optical antennas, and high diffraction efficiencies have been limited to operation in reflection mode. We describe the experimental realization and operation of dielectric gradient metasurface optical elements capable of also achieving high efficiencies in transmission mode in the visible spectrum. Ultrathin gratings, lenses, and axicons have been realized by patterning a 100-nanometer-thick Si layer into a dense arrangement of Si nanobeam antennas. The use of semiconductors can broaden the general applicability of gradient metasurfaces, as they offer facile integration with electronics and can be realized by mature semiconductor fabrication technologies. PMID:25035488

Lin, Dianmin; Fan, Pengyu; Hasman, Erez; Brongersma, Mark L

2014-07-18

250

Size oscillations of the work function of a metal film on a dielectric substrate  

NASA Astrophysics Data System (ADS)

Analytical expressions for the size dependence of the Fermi electronic energy of ultrathin metal films on a dielectric substrate have been derived in the model of free electrons and finite-depth asymmetric potential well. The work functions have been calculated for Al films on SiO2 and Al2O3. It has been shown that the presence of a dielectric leads to a shift in the work function, while retaining the general character of the size dependences.

Korotun, A. V.

2015-02-01

251

Electron tunneling through ultrathin boron nitride crystalline barriers.  

PubMed

We investigate the electronic properties of ultrathin hexagonal boron nitride (h-BN) crystalline layers with different conducting materials (graphite, graphene, and gold) on either side of the barrier layer. The tunnel current depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field. It offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel. PMID:22380756

Britnell, Liam; Gorbachev, Roman V; Jalil, Rashid; Belle, Branson D; Schedin, Fred; Katsnelson, Mikhail I; Eaves, Laurence; Morozov, Sergey V; Mayorov, Alexander S; Peres, Nuno M R; Neto, Antonio H Castro; Leist, Jon; Geim, Andre K; Ponomarenko, Leonid A; Novoselov, Kostya S

2012-03-14

252

Negative differential resistance in ultrathin Ge-on-insulator FETs  

NASA Astrophysics Data System (ADS)

In this paper we report on the fabrication of all-epitaxial ultrathin germanium-on-crystalline lanthanum-yttrium-oxide field effect transistors. The oxide is lattice matched to Si (1 1 1) and has a dielectric constant of ~18. The transistors show ambipolar behaviour, both N- and P-channel operations on the same device at any temperature. The transistor characteristics have an ON/OFF ratio of 102 at room temperature, while at cryogenic temperatures negative differential resistance (NDR) is observed in the channel. The NDR effect, which is stronger for lower temperatures, can be attributed to a number of reasons from intervalley or intersubband electron transfer to a heavy transport effective mass (low mobility) band or to charge trapping. A germanium-on-insulator technology, provided the material (Ge and oxide) quality improves, may be useful for building circuits that combine conventional FETs with unconventional ambipolar or NDR devices all on the same substrate.

Kazazis, D.; Zaslavsky, A.; Tutuc, E.; Bojarczuk, N. A.; Guha, S.

2007-01-01

253

Making silicon nitride film a viable gate dielectric  

Microsoft Academic Search

To extend the scaling limit of thermal SiO2 in the ultrathin regime when the direct tunneling current becomes significant, members of this author's research team at Yale University, in collaboration with the Jet Process Corporation, embarked on a program to explore the potential of silicon nitride as an alternative gate dielectric. In this paper, high-quality silicon nitride (or oxynitride) films

T. P. Ma

1998-01-01

254

Microwave-Assisted and Gram-Scale Synthesis of Ultrathin SnO2 Nanosheets with Enhanced Lithium Storage Properties.  

PubMed

The rational design and fabrication of SnO2-based anode materials could offer a powerful way of effectively alleviating their large volume variation and guaranteeing excellent reaction kinetics for electrochemical lithium storage. Herein, we present an ultrarapid, low-cost, and simple microwave-assisted synthesis of ultrathin SnO2 nanosheets at the gram-scale. The two-dimensional (2D) anisotropic growth depends on microwave dielectric irradiation coupled with surfactant structural direction, and is conducted under low-temperature atmospheric conditions. The ultrathin 2D nanostructure holds a great surface tin atom percentage with high activity, where the electrochemical reaction processes could be facilitated that highly dependent on the surface. Compared with 1D SnO2 nanorods, the ultrathin SnO2 nanosheets exhibit remarkably improved electrochemical lithium storage properties with a high reversible capacity of 757.6 mAh g(-1) at a current density of 200 mA g(-1) up to 40 cycles as well as excellent rate capability and cycling stability. Specifically, the ultrathin 2D nanosheet could significantly reduce ion diffusion paths, thus allowing faster phase transitions, while the sufficient external surface interspace and interior porous configuration could successfully accommodate the huge volume changes. Even more importantly, we develop a promising strategy to produce ultrathin SnO2 nanosheets to tackle their intrinsic problems for commercial applications. PMID:25594865

Zhu, Youqi; Guo, Huizi; Zhai, Huazhang; Cao, Chuanbao

2015-02-01

255

Broadband polarization-independent resonant light absorption using ultrathin plasmonic super absorbers.  

PubMed

Resonant plasmonic and metamaterial structures allow for control of fundamental optical processes such as absorption, emission and refraction at the nanoscale. Considerable recent research has focused on energy absorption processes, and plasmonic nanostructures have been shown to enhance the performance of photovoltaic and thermophotovoltaic cells. Although reducing metallic losses is a widely sought goal in nanophotonics, the design of nanostructured 'black' super absorbers from materials comprising only lossless dielectric materials and highly reflective noble metals represents a new research direction. Here we demonstrate an ultrathin (260 nm) plasmonic super absorber consisting of a metal-insulator-metal stack with a nanostructured top silver film composed of crossed trapezoidal arrays. Our super absorber yields broadband and polarization-independent resonant light absorption over the entire visible spectrum (400-700 nm) with an average measured absorption of 0.71 and simulated absorption of 0.85. Proposed nanostructured absorbers open a path to realize ultrathin black metamaterials based on resonant absorption. PMID:22044996

Aydin, Koray; Ferry, Vivian E; Briggs, Ryan M; Atwater, Harry A

2011-01-01

256

Low-temperature deposition of ultrathin SiO2 films on Si substrates  

NASA Astrophysics Data System (ADS)

We present a detailed investigation of the properties of silicon dioxide deposited at a low temperature. The advantages of this process include its low thermal requirements (about 200 °C), the absence of corrosive by-products and the lack of need of vacuum equipment. Sol solutions were prepared for the deposition of ultrathin SiO2 films by spin-coating at the low annealing temperature of 200 °C. The layers' thickness was 24 nm and 5 nm. We describe in detail the material properties of this novel low-temperature SiO2 layers obtained by extensive characterization using Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), XPS spectroscopy, capacitance-voltage (C-V) and current-voltage (I-V) measurements. The ultrathin oxide layers on Si substrates show good dielectric properties.

Vitanov, P.; Harizanova, A.; Ivanova, T.; Dikov, H.

2014-05-01

257

Broadband polarization-independent resonant light absorption using ultrathin plasmonic super absorbers  

NASA Astrophysics Data System (ADS)

Resonant plasmonic and metamaterial structures allow for control of fundamental optical processes such as absorption, emission and refraction at the nanoscale. Considerable recent research has focused on energy absorption processes, and plasmonic nanostructures have been shown to enhance the performance of photovoltaic and thermophotovoltaic cells. Although reducing metallic losses is a widely sought goal in nanophotonics, the design of nanostructured 'black' super absorbers from materials comprising only lossless dielectric materials and highly reflective noble metals represents a new research direction. Here we demonstrate an ultrathin (260 nm) plasmonic super absorber consisting of a metal-insulator-metal stack with a nanostructured top silver film composed of crossed trapezoidal arrays. Our super absorber yields broadband and polarization-independent resonant light absorption over the entire visible spectrum (400-700 nm) with an average measured absorption of 0.71 and simulated absorption of 0.85. Proposed nanostructured absorbers open a path to realize ultrathin black metamaterials based on resonant absorption.

Aydin, Koray; Ferry, Vivian E.; Briggs, Ryan M.; Atwater, Harry A.

2011-11-01

258

Electric Dipole at High-k/SiO2 Interface and Physical Origin by Dielectric Contact Induced Gap States  

NASA Astrophysics Data System (ADS)

The characteristic of electric dipole at high-k/SiO2 interface is quantitatively analyzed. The dipoles of HfO2/SiO2 and HfGdOx/SiO2 systems are experimentally estimated to be about -0.38 and -1.03 V, respectively. The dipole formation is explained by the dielectric contact induced gap states (DCIGS). The charge neutrality level (CNL) of the DCIGS is for the first time utilized to study the dipole moment. The charge transfer due to different CNLs of high-k and SiO2 is considered to be the dominant origin of dipole formation. The prediction by this model is in good agreement with the experimental data.

Wang, Xiaolei; Han, Kai; Wang, Wenwu; Ma, Xueli; Xiang, Jinjuan; Chen, Dapeng; Zhang, Jing

2011-10-01

259

Fundamental Limits of Ultrathin Metasurfaces  

E-print Network

We present universal theoretical limits on the operation and performance of non-magnetic passive ultrathin metasurfaces. In particular, we prove that their local transmission, reflection, and polarization conversion coefficients are confined to limited regions of the complex plane. As a result, full control over the phase of the light transmitted through such metasurfaces cannot be achieved if the polarization of the light is not to be affected at the same time. We also establish fundamental limits on the maximum polarization conversion efficiency of these metasurfaces, and show that they cannot achieve more than 25% polarization conversion efficiency in transmission.

Arbabi, Amir

2014-01-01

260

Broadband trapeziform multilayer dielectric grating for femtosecond pulse compressor: design, fabrication, and analysis  

NASA Astrophysics Data System (ADS)

Rectangular HfO2 grating fabrication is difficult, so a trapeziform multilayer dielectric pulse compression grating (PCG) has been designed using a genetic algorithm and the Fourier mode method. Simulation results show that a greater than 120 nm wavelength range multilayer dielectric grating (MDG) is obtained with a minus-first-order diffraction efficiency (DE) exceeding 95%. The bandwidth is 136 nm with the minus-first-order DE exceeding 90%. The trapeziform structure shows good tolerances for grating fabrication. The multilayer dielectric is deposited by e-beam evaporation, then the MDG is fabricated by reactive ion beam etching. A 128 nm bandwidth of the MDG for the transverse electric polarization with an efficiency exceeding 90% is obtained, and the maximum DE can reach up to 98.3%. The trapeziform MDG is an ideal PCG for chirped pulse amplification systems with high DE, broad bandwidth and good fabrication tolerances. Laser-induced damage thresholds of 0.53 J cm?2 under 40 fs pulses are experimentally reached with very high and uniform efficiency.

Guan, Heyuan; Jin, Yunxia; Liu, Shijie; Kong, Fanyu; Du, Ying; He, Kai; Yi, Kui; Shao, Jianda

2013-11-01

261

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

PubMed

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. PMID:22695179

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

2012-07-24

262

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

PubMed Central

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

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

2012-01-01

263

Hybrid gate dielectric materials for unconventional electronic circuitry.  

PubMed

Recent advances in semiconductor performance made possible by organic ?-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 ?-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 importance of gate dielectric materials in thin-film transistor (TFT) operation. Next, we describe the design, fabrication, properties, and applications of solution-deposited multilayer organic-inorganic hybrid gate dielectrics, using self-assembly techniques, which provide bonding between the organic and inorganic layers. Finally, we discuss approaches for preparing analogous hybrid multilayers by vapor-phase growth and discuss the properties of these materials. PMID:24428627

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

2014-04-15

264

Ultrathin BaTiO3 templates for multiferroic nanostructures  

NASA Astrophysics Data System (ADS)

The structural, electronic and dielectric properties of high-quality ultrathin BaTiO3 films were investigated. The films, which were grown by ozone-assisted molecular beam epitaxy on Nb-doped SrTiO3(001) substrates and have thicknesses as low as 8 unit cells (u.c.) (3.2 nm), are unreconstructed and atomically smooth with large crystalline terraces. A strain-driven transition to three-dimensional (3D) island formation is observed for films of 13 u.c. thickness (5.2 nm). The high structural quality of the surfaces, together with dielectric properties similar to bulk BaTiO3 and dominantly TiO2 surface termination, makes these films suitable templates for the synthesis of high-quality metal-oxide multiferroic heterostructures for the fundamental study and exploitation of magneto-electric effects, such as a recently proposed interface effect in Fe/BaTiO3 heterostructures based on Fe-Ti interface bonds.

Chen, Xumin; Yang, Seolun; Kim, Ji-Hyun; Kim, Hyung-Do; Kim, Jae-Sung; Rojas, Geoffrey; Skomski, Ralph; Lu, Haidong; Bhattacharya, Anand; Santos, Tiffany; Guisinger, Nathan; Bode, Matthias; Gruverman, Alexei; Enders, Axel

2011-08-01

265

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

NASA Astrophysics Data System (ADS)

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 starts with the ligand-mediated attachment of the precursor (through a N atom), followed by dissociation of a metal-ligand bond. In addition, the C-H bond is broken, possibly forming Si-C bonds and causing carbon incorporation. This model is found to be rather robust and to adequately describe other types of metalorganic precursors. It allows establishing a generalized model able to explain the success or failure of a metalorganic precursor chemistry for film deposition. Finally, amine-functionalized silicon surfaces are considered as prototypical systems where the spatial distribution of adsorbates and the control over the reactivity of surface sites can be investigated. The spatial distribution of molecules is investigated at the atomic level by considering the saturation of a Si(100) surface with NH3. It is found that the distribution of (Si)NH2 species can be controlled thermally and, more importantly, that during thermal decomposition N inserts into the substrate in manners that minimize the arising strain. When the surface is covered with NH 3 or with organic amines, its chemical behavior is determined by the basicity of the molecule functionalizing the surface. The precise tuning of the reactivity (basicity) of surface sites opens the doors for highly controllable, selective reactions. Although these results are obtained from rather fundamental grounds, their interpretation is often translated into manners in which technological applications can be improved. Further directions worth exploring emanated from this work are outlined and discussed. Ultimately, this work intends to highlight the current importance of surface physical chemistry in the continuous development of modern society through the improvement of its technology.

Rodriguez-Reyes, Juan Carlos F.

266

Dielectric Ceramics  

NASA Astrophysics Data System (ADS)

The structural and microwave properties of (Mg,Zn/Co)TiO3 dielectric ceramics have been investigated. The grown samples have been characterized by means of x-ray diffraction, Rietveld refinement, scanning electron microscopy, and energy dispersive x-ray spectroscopy analysis. The microwave dielectric properties of grown samples have been measured using the Hakki-Coleman resonator method and found to depend on the ionic polarizability, electronic polarizability, and Mg-site substitutions. The Mg0.95Zn0.05TiO3 compound shows a maximum Q × f value of 210,000 GHz (at 10 GHz), ?r of 16.31, and ?f value of -62.43.

Rajput, Shailendra Singh; Keshri, Sunita

2014-06-01

267

Physicochemically functional ultrathin films by interfacial polymerization  

DOEpatents

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.

Lonsdale, Harold K. (Bend, OR); Babcock, Walter C. (Bend, OR); Friensen, Dwayne T. (Bend, OR); Smith, Kelly L. (Bend, OR); Johnson, Bruce M. (Bend, OR); Wamser, Carl C. (West Linn, OR)

1990-01-01

268

Physicochemically functional ultrathin films by interfacial polymerization  

DOEpatents

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.

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

1990-08-14

269

Ultrathinning Dental Porcelain for Transmitted Light Microscopy  

Microsoft Academic Search

A technique for ultrathinning brittle materials, originally developed at Battelle Pacific Northwest Labs for examination of lunar materials, has been successfully adapted for the preparation of dental porcelain specimens. A commercial dental porcelain and \\

J. R. Mackert; M. B. Butts; G. M. Beaudreau; C. W. Fairhurst; R. H. Beauchamp

1985-01-01

270

Solid-state dewetting of ultra-thin Au films on SiO? and HfO?.  

PubMed

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 10(12) 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 10(11) 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. PMID:25410136

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

2014-12-12

271

Ultra-Thin, Flexible Electronics  

NASA Technical Reports Server (NTRS)

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.

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

2008-01-01

272

Ultrathin fiberscope for stereoscopic vision  

NASA Astrophysics Data System (ADS)

Endoscope for stereoscopic vision is in great demand for medical field to diagnose and treat disease parts of patients more precisely. The authors are convinced that the silica based imagefiber is suitable for making a thinner fiberscope for stereoscopic vision. The structure of the fiberscope and the quality of transmitted image have been investigated. It has been found that stereognosis depends on the magnification of eyepiece, distance between left and right objective lenses and the image quality between two transmitting systems. On the basis of these results, the ultrathin fiberscope with silica based imagefibers for stereoscopic vision have been developed. The diameter of fiberscope is only 2 mm with two transmitting systems that consist of two imagefibers with 10000 pixels and lightguide for illumination and objective lenses. This fiberscope for stereoscopic vision can be used for the micro surgery, such as the laparoscopic surgery and the thoracoscopic surgery required for the thin diameter.

Kaneda, Keiji; Ohashi, T.; Tsumanuma, Takashi; Sanada, Kazuo

1993-05-01

273

Charge trapping in high k gate dielectric stacks  

Microsoft Academic Search

Charge trapping in Al2O3 and HfO2 nFETs is studied. The dependence of threshold voltage, subthreshold slope and gate leakage currents are investigated as a function of stressing time, voltage and temperature. Based on the experimental data, a model is developed for predicting threshold voltage shifts as a function stressing time. The model is compatible with both Al2O3 and HfO2 data.

S. Zafar; A. Callegari; E. Gusev; M. V. Fischetti

2002-01-01

274

Correlation of trap generation to charge-to-breakdown (Qbd ): a physical-damage model of dielectric breakdown  

Microsoft Academic Search

Ultrathin gate and tunnel oxides in MOS devices are subjected to high-field stress during device operation, which degrades the oxide and eventually causes dielectric breakdown. Oxide reliability, therefore, is a key concern in technology scaling for ultra-large scale integration (ULSI). Here we provide critical new insight into oxide degradation (and consequently, reliability) by a systematic study of five technologically relevant

Pushkar P. Apte; Krishna C. Saraswat

1994-01-01

275

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

NASA Astrophysics Data System (ADS)

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 charge centers. Upon forming gas annealing (FGA) and PDA, these charge centers became hydrogen-passivated. Using remote plasma nitridation of an ALD Hf-O film on chemical oxide IL/Si, the Hf-O layer remained amorphous even at 1000°C and exhibited a reduced tendency towards Hf-O-Si bond formation and interlayer growth when nitrogen incorporation was ˜1.7 at % of surface Hf atoms. However, the positive fixed charge density increased and oxide trapped charge density decreased with nitrogen incorporation. Finally, upon PDA in nitrogen at 1000°C for 10 seconds of ALD Hf-Si-O films with 60 and 75 mol % HfO2, the amorphous films transformed to t-HfO2 nano-crystallites embedded in a silica-rich amorphous matrix. However, amorphous Hf-Si-O films with 40 mol% HfO2 (i.e., silica-rich) when subjected to the same PDA, phase segregated into predominantly two amorphous phases.

Das, Anirban

276

Atomic layer deposited Al2O3 for gate dielectric and passivation layer of single-walled carbon nanotube transistors  

E-print Network

- ited ALD 8­20 nm thick high-k zirconium oxide ZrO2 Ref. 4 and hafnium oxide HfO2 .5 Among the above tech- niques, utilizing high-k ALD ZrO2 and HfO2 as gate dielec- tric is very promising and has of these techniques are that high-k materials such as ZrO2 and HfO2 are difficult to grow and difficult to re- move

Ye, Peide "Peter"

277

Terahertz Spectroscopy as a non contact estimation technique of defect states in high dielectric constant materials  

NASA Astrophysics Data System (ADS)

A large number of gate dielectric materials have been examined during the past few years to replace Silicon dioxide in the MOSFET industry to reduce gate leakage currents for microfabrication of devices. Among them, Hafnium based materials have become a very promising candidate. In the reported work, the effect of Hafnium dioxide films on p-type silicon substrates has been investigated and compared with conventional dielectric material, Silicon dioxide, using CW visible pump/THz probe spectroscopy. Drude analysis of the experimentally obtained differential transmission spectra evaluates the electric permittivity of the interfacial layer and the calculated defect density is found to be higher for HfO2 than for SiO2 which agrees with Hall measurements. Additional measurements on Silicon Nitride deposition and photoresist coated p+ Silicon on p-type silicon wafers without any oxide gave an interfacial defect density 50 times higher than that of SiO2/p+ interface. Results indicate that the mobility of the layer underneath Hafnium is less than that of Silicon. Hence the present study emphasizes the advantage of THz spectroscopy as a non-contact tool for semiconductor metrological applications.

Sengupta, Amartya; Bandyopadhyay, Aparajita; Altan, Hakan; Federici, John; Grebel, Haim

2006-03-01

278

Gate Stack Dielectric Degradation of Rare-Earth Oxides Grown on High Mobility Ge Substrates  

E-print Network

We report on the dielectric degradation of Rare-Earth Oxides (REOs), when used as interfacial buffer layers together with HfO2 high-k films (REOs/HfO2) on high mobility Ge substrates. Metal-Oxide-Semiconductor (MOS) devices with these stacks,show dissimilar charge trapping phenomena under varying levels of Constant- Voltage-Stress (CVS) conditions, which also influences the measured densities of the interface (Nit) and border (NBT) traps. In the present study we also report on C-Vg hysteresis curves related to Nit and NBT. We also propose a new model based on Maxwell-Wagner instabilities mechanism that explains the dielectric degradations (current decay transient behavior) of the gate stack devices grown on high mobility substrates under CVS bias from low to higher fields, and which is unlike to those used for other MOS devices. Finally, the time dependent degradation of the corresponding devices revealed an initial current decay due to relaxation, followed by charge trapping and generation of stress-induced ...

Rahman, Md Shahinur; Konofaos, Nikos; Dimoulas, A

2012-01-01

279

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

NASA Astrophysics Data System (ADS)

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.

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

280

Scalable synthesis of uniform few-layer hexagonal boron nitride dielectric films.  

PubMed

Two-dimensional or ultrathin layered materials are attracting broad interest in both fundamental science and applications. While exfoliation can provide high-quality single- and few-layer flakes with nanometer to micrometer size, the development of wafer-scale synthesis methods is important for realizing the full potential of ultrathin layered materials. Here we demonstrate the growth of high quality few-layer boron nitride (BN) films with controlled thickness by magnetron sputtering of B in N(2)/Ar, a scalable process using only benign, nontoxic reagents. BN films up to two atomic layers are synthesized by reactive deposition at high substrate temperatures. Thicker monocrystalline BN films with an arbitrary number of atomic layers are achieved in a two-step process comprising cycles of alternating room temperature deposition and annealing. Tunneling transport across these BN films shows pinhole-free insulating behavior on ?m(2) scales, demonstrating the realization of high quality ultrathin dielectrics. PMID:23244762

Sutter, P; Lahiri, J; Zahl, P; Wang, B; Sutter, E

2013-01-01

281

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)

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.

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

2014-09-01

282

Capacitor with Movable Dielectric  

NSDL National Science Digital Library

Click-drag the dielectric block into the capacitor (charge given in mC and position given in centimeters). Observe how the electric field and the charge on the capacitor and the dielectric change when you move the dielectric. The light red and light blue circles represent the position of the charge on the dielectric.

Wolfgang Christian

283

Low field leakage current and soft breakdown in ultra-thin gate oxides after heavy ions, electron or X-ray irradiation  

Microsoft Academic Search

The excess leakage current across ultra-thin dielectrics has been studied for different ionizing radiation sources. X-rays, 8 MeV electrons, and three ion beams with different LETs values have been used on large area MOS capacitors with 4-nm thick oxides. Small oxide fields were applied during irradiation, reaching 3 MV\\/cm at most. For ionizing radiation with relatively low LET (<10 MeV

M. Ceschia; A. Paccagnella; S. Sandrin; G. Ghidini; J. Wyss; M. Lavale; O. Flament

2000-01-01

284

A study on the evolution of dielectric function of ZnO thin films with decreasing film thickness  

SciTech Connect

Dielectric function, band gap, and exciton binding energies of ultrathin ZnO films as a function of film thickness have been obtained with spectroscopic ellipsometry. As the film thickness decreases, both real (?{sub 1}) and imaginary (?{sub 2}) parts of the dielectric function decrease significantly, and ?{sub 2} shows a blue shift. The film thickness dependence of the dielectric function is shown related to the changes in the interband absorption, discrete-exciton absorption, and continuum-exciton absorption, which can be attributed to the quantum confinement effect on both the band gap and exciton binding energies.

Li, X. D.; Chen, T. P., E-mail: echentp@ntu.edu.sg; Liu, P. [School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 Singapore (Singapore); Liu, Y. [State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology, Chengdu 610054 (China); Liu, Z. [School of Materials and Energy, Guangdong University of Technology, Guangzhou 510006 (China); Leong, K. C. [GLOBALFOUNDRIES Singapore Pte Ltd, 738406 Singapore (Singapore)

2014-03-14

285

Impact of ultrathin Al2O3 diffusion barriers on defects in high-k LaLuO3 on Si  

E-print Network

and relative densities in metal/high- dielectric LaLuO3/Si stacks, defects produced by LaLuO3­Si interdiffusion/high- dielectric LaLuO3/Si stacks, the new defects produced by LaLuO3­Si 100 interdiffusion, and suppres- sionImpact of ultrathin Al2O3 diffusion barriers on defects in high-k LaLuO3 on Si S. Shen,1,a Y. Liu,2

286

The structure, optical behavior, and thermal stability of sputter-deposited hafnium dioxide single layer and hafnium dioxide-aluminum oxide nanolaminate thin-films  

Microsoft Academic Search

Hafnium dioxide (HfO2, hafnia) is a refractory material that has gained importance in thin films for wide band gap and optical coating applications. The goal of this work is to examine the crystallization behavior, optical absorption, and thermal stability of single layer HfO2 and nanolaminate HfO2-Al2O3 films, and to investigate the nucleation behavior of nanocrystalline HfO2 in ultrathin layers. Films

Elizabeth Ellen Hoppe

2009-01-01

287

Universit de Grenoble Structure of ultrathin antiferromagnetic  

E-print Network

.2. Theoretical models 5 a) Domain walls close to uncompensated interface b) "Spin-flop" c) Random field model dUniversité de Grenoble Structure of ultrathin antiferromagnetic films for exchange coupling systems) Domain state model e) Coercivity enhancement 2. Surface X-ray diffraction 9 2.1. X-ray diffraction from

Paris-Sud XI, Université de

288

Dielectric breakdown and reliability of MOS microstructures: Traditional characterization and low-frequency noise measurements  

Microsoft Academic Search

Four different types of ultra-thin oxide MOS structures have been analyzed to investigate the dielectric breakdown, by using a combination of techniques: time-zero breakdown, time-dependent breakdown and low-frequency noise measurements. The experiments have shown that different devices presenting lifetime values depending on the fabrication technology are all affected, before breakdown, by sharp fluctuations of the current tunnelling through the oxide

B. Neri; P. Olivo; R. Saletti; M. Signoretta

1995-01-01

289

Charge trapping and degradation in high-permittivity TiO2 dielectric films  

Microsoft Academic Search

Suitable replacement materials for ultrathin SiO2 in deeply scaled MOSFETs such as lattice polarizable films, which have much higher permittivities than SiO2, have bandgaps of only 3.0 to 4.0 eV. Due to these small bandgaps, the reliability of these films as a gate insulator is a serious concern. Ramped voltage, time dependent dielectric breakdown (TDDB), and capacitance-voltage (C-V) measurements were

Hyeon-Seag Kim; S. A. Campbell; C. Gilmer

1997-01-01

290

Dielectric and complex impedance properties of tetravalent hafnium (HF 4+) integrated cobalt ferrite  

NASA Astrophysics Data System (ADS)

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 responses in impedance formalism are attributed to the grain and grain-boundary effects, respectively, which also accounts for the observed two dielectric-relaxations. The results demonstrate that the dielectric phenomena in CFO-Hf can be tailored by tuning Hf-concentration.

Sanchez, Luis

291

Ultrathin silver nanowires produced by amyloid biotemplating.  

PubMed

By using a self-assembled amyloid from lysozyme as biotemplate we produced an ultrathin silver wire of 1 nm diameter and up to 2 mum in length, which is at the limit attainable in nanobiotechnological manufacturing. We showed that 2,2,2-trifluoroethanol produces a dual effect: it reduces ionic silver to colloidal nanoparticles with a regular size, depending on the length of incubation, and induces fibrillar assembly into the amyloid scaffold, forming the hollow channel filled with silver. PMID:19194928

Malisauskas, Mantas; Meskys, Rolandas; Morozova-Roche, Ludmilla A

2008-01-01

292

Monte Carlo Simulations of Ultrathin Magnetic Dots  

E-print Network

In this work we study the thermodynamic properties of ultrathin ferromagnetic dots using Monte Carlo simulations. We investigate the vortex density as a function of the temperature and the vortex structure in monolayer dots with perpendicular anisotropy and long-range dipole interaction. The interplay between these two terms in the hamiltonian leads to an interesting behavior of the thermodynamic quantities as well as the vortex density.

M. Rapini; R. A. Dias; D. P. Landau; B. V. Costa

2006-04-10

293

Photoresponsive properties of ultrathin silicon nanowires  

NASA Astrophysics Data System (ADS)

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 × 104 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.

Tran, Duy P.; Macdonald, Thomas J.; Wolfrum, Bernhard; Stockmann, Regina; Nann, Thomas; Offenhäusser, Andreas; Thierry, Benjamin

2014-12-01

294

Microwave absorptions of ultrathin conductive films and designs of frequency-independent ultrathin absorbers  

SciTech Connect

We study the absorption properties of ultrathin conductive films in the microwave regime, and find a moderate absorption effect which gives rise to maximal absorbance 50% if the sheet (square) resistance of the film meets an impedance matching condition. The maximal absorption exhibits a frequency-independent feature and takes place on an extremely subwavelength scale, the film thickness. As a realistic instance, ?5 nm thick Au film is predicted to achieve the optimal absorption. In addition, a methodology based on metallic mesh structure is proposed to design the frequency-independent ultrathin absorbers. We perform a design of such absorbers with 50% absorption, which is verified by numerical simulations.

Li, Sucheng; Anwar, Shahzad; Lu, Weixin; Hang, Zhi Hong; Hou, Bo, E-mail: houbo@suda.edu.cn, E-mail: phyhoubo@gmail.com; Shen, Mingrong [School of Physical Science and Technology, Soochow University, 1 Shizi Street, Suzhou 215006 (China)] [School of Physical Science and Technology, Soochow University, 1 Shizi Street, Suzhou 215006 (China); Wang, Chin-Hua [Institute of Modern Optical Technologies and Collaborative Innovation Center of Suzhou Nano Science and Technology, Jiangsu Key Lab of Advanced Optical Manufacturing Technologies, Soochow University, 1 Shizi Street, Suzhou 215006 (China)] [Institute of Modern Optical Technologies and Collaborative Innovation Center of Suzhou Nano Science and Technology, Jiangsu Key Lab of Advanced Optical Manufacturing Technologies, Soochow University, 1 Shizi Street, Suzhou 215006 (China)

2014-01-15

295

Broadband Frequency-Selective Spoof Surface Plasmon Polaritons on Ultrathin Metallic Structure  

NASA Astrophysics Data System (ADS)

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.

Yin, Jia Yuan; Ren, Jian; Zhang, Hao Chi; Pan, Bai Cao; Cui, Tie Jun

2015-02-01

296

Broadband frequency-selective spoof surface plasmon polaritons on ultrathin metallic structure.  

PubMed

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

Yin, Jia Yuan; Ren, Jian; Zhang, Hao Chi; Pan, Bai Cao; Cui, Tie Jun

2015-01-01

297

Ultrathin compound semiconductor on insulator layers for high-performance nanoscale transistors.  

PubMed

Over the past several years, the inherent scaling limitations of silicon (Si) electron devices have fuelled the exploration of alternative semiconductors, with high carrier mobility, to further enhance device performance. In particular, compound semiconductors heterogeneously integrated on Si substrates have been actively studied: such devices combine the high mobility of III-V semiconductors and the well established, low-cost processing of Si technology. This integration, however, presents significant challenges. Conventionally, heteroepitaxial growth of complex multilayers on Si has been explored-but besides complexity, high defect densities and junction leakage currents present limitations in this approach. Motivated by this challenge, here we use an epitaxial transfer method for the integration of ultrathin layers of single-crystal InAs on Si/SiO(2) substrates. As a parallel with silicon-on-insulator (SOI) technology, we use 'XOI' to represent our compound semiconductor-on-insulator platform. Through experiments and simulation, the electrical properties of InAs XOI transistors are explored, elucidating the critical role of quantum confinement in the transport properties of ultrathin XOI layers. Importantly, a high-quality InAs/dielectric interface is obtained by the use of a novel thermally grown interfacial InAsO(x) layer (~1 nm thick). The fabricated field-effect transistors exhibit a peak transconductance of ~1.6 mS µm(-1) at a drain-source voltage of 0.5 V, with an on/off current ratio of greater than 10,000. PMID:21068839

Ko, Hyunhyub; Takei, Kuniharu; Kapadia, Rehan; Chuang, Steven; Fang, Hui; Leu, Paul W; Ganapathi, Kartik; Plis, Elena; Kim, Ha Sul; Chen, Szu-Ying; Madsen, Morten; Ford, Alexandra C; Chueh, Yu-Lun; Krishna, Sanjay; Salahuddin, Sayeef; Javey, Ali

2010-11-11

298

Broadband Frequency-Selective Spoof Surface Plasmon Polaritons on Ultrathin Metallic Structure  

PubMed Central

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

Yin, Jia Yuan; Ren, Jian; Zhang, Hao Chi; Pan, Bai Cao; Cui, Tie Jun

2015-01-01

299

An ultrathin and broadband metamaterial absorber using multi-layer structures  

NASA Astrophysics Data System (ADS)

An ultrathin and broadband absorber is investigated in this paper. The metamaterial absorber is composed of a periodic array of loop-dielectric multilayered structure. By tuning the scale factor of the loop and the height of every layer, a desirable refractive index dispersion spectrum is realized, which is the reason to realize a successive anti-reflection in a wide frequency range. The interference mechanism and resonance absorption are identified through analytical derivation and numerical simulations. Numerical results show that the absorption at normal incidence is above 90% in the frequency range of 8.37-21 GHz. Moreover, the structure has a thickness of 3.65 mm (only 0.10? to 0.26? at the lowest and highest frequencies, respectively). The explanation to the physical mechanism of the metamaterial absorber is presented and verified.

Xiong, Han; Hong, Jin-Song; Luo, Chao-Ming; Zhong, Lin-Lin

2013-08-01

300

Ultrathin silicon-on-insulator vertical tunneling transistor A. Zaslavskya)  

E-print Network

Ultrathin silicon-on-insulator vertical tunneling transistor A. Zaslavskya) and C. Aydin Division silicon-on-insulator SOI transistors with an ultrathin Si channel of 5 nm, tunneling gate oxide of 1 nm on the electrode biasing. © 2003 American Institute of Physics. DOI: 10.1063/1.1600832 Silicon-on-insulator SOI

Luryi, Serge

301

Charge trapping\\/detrapping and dielectric breakdown in SiO\\/sub 2\\/\\/Si\\/sub 3\\/N\\/sub 4\\/\\/SiO\\/sub 2\\/ stacked layers on rugged poly-Si under dynamic stress  

Microsoft Academic Search

The authors report a study on charge trapping\\/detrapping and dielectric breakdown of ultrathin reoxidized Si\\/sub 3\\/N\\/sub 4\\/ stacked layers on rugged poly-Si under dynamic stress. It was found that the dielectric time-to-breakdown (t\\/sub BD\\/) in capacitors with rugged poly-Si under dynamic stress increases with increasing frequency, whereas t\\/sub BD\\/ in capacitors with smooth poly-Si decreases with frequency. Charge trapping\\/detrapping has

G. Q. Lo; S. Ito; D. L. Kwong; V. K. Mathews; P. C. Fazan; A. Ditali

1992-01-01

302

Semitransparent ultrathin CdTe solar cells Semitransparent ultrathin CdTe solar cells and durabilityand durability  

E-print Network

: · Window area >> rooftop space · PV windows produce power and reduce Solar Heat Gain (SHG). Generate power bl d ) (very poor aesthetics) (good efficiency but venetian blind appearance, expensive) Solar RoofSemitransparent ultrathin CdTe solar cells Semitransparent ultrathin CdTe solar cells

Rollins, Andrew M.

303

Infrared Dielectric Resonator Metamaterial  

E-print Network

We demonstrate, for the first time, an all-dielectric metamaterial resonator in the mid-wave infrared based on high-index tellurium cubic inclusions. Dielectric resonators are desirable compared to conventional metallo-dielectric metamaterials at optical frequencies as they are largely angular invariant, free of ohmic loss, and easily integrated into three-dimensional volumes. With these low-loss, isotropic elements, disruptive optical metamaterial designs, such as wide-angle lenses and cloaks, can be more easily realized.

Ginn, James C; Peters, David W; Wendt, Joel R; Stevens, Jeffrey O; Hines, Paul F; Basilio, Lorena I; Warne, Larry K; Ihlefeld, Jon F; Clem, Paul G; Sinclair, Michael B

2011-01-01

304

Design and Fabrication of Ultrathin Plasmonic Nanostructures for Photovoltaics, Color Filtering and Biosensing  

NASA Astrophysics Data System (ADS)

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 with record-high transmission efficiency and other unique properties; (3) rapid and highly-sensitive plasmonic bio-sensors employing ultrathin nanogratings. The successful development of these new plasmonic platforms have far-reaching impact on green energy technologies, next-generation displays and imagers, and label-free bio-sensing for point-of-care diagnostics.

Zeng, Beibei

305

On the structural development during ultrathin amorphous Al2O3 film growth on Al(111) and Al(100) surfaces by thermal oxidation  

NASA Astrophysics Data System (ADS)

The structural developments during growth of ultrathin amorphous Al2O3 film on bare Al(100) and Al(111) surfaces, by dry thermal oxidation in the oxygen partial pressure range of 1 × 10- 5-1.0 Pa at 300 K, were investigated as function of the oxide-film thickness by (local) chemical state analysis using angle-resolved X-ray photoelectron spectroscopy in combination with low electron energy diffraction and cross-sectional high resolution transmission electron microscopy. The effect of the dielectric discontinuity, at the interfaces of the surficial Al2O3 film has been determined quantitatively and has been subtracted from the observed chemical shifts of the core level photoelectron binding energies as well as from the observed Auger transition kinetic energies. It is revealed that ultrathin amorphous Al2O3 films on the Al(111) and Al(100) surfaces experience remarkably different structural developments upon growth.

Flötotto, D.; Wang, Z. M.; Mittemeijer, E. J.

2015-03-01

306

AGRICULTURAL APPLICATIONS OF DIELECTRIC MEASUREMENTS  

Technology Transfer Automated Retrieval System (TEKTRAN)

A brief historical perspective on dielectric properties of agricultural products is presented, including their use for rapid measurement of moisture content in grain and in considering potential dielectric heating applications. General principles are discussed as they relate to dielectric propertie...

307

Dielectric Theory of the Vacuum  

E-print Network

The vacuum is proposed to be a dielectric medium constituted of neutral but polarizable vacuuons based on overall experimental observations in separate publications. In the present paper I formally develop the dielectric theory for this dielectric vacuum.

J. X. Zheng-Johansson

2006-12-11

308

Band Edge Traps at Spectroscopically-Detected O-Atom Vacancies in Nanocrystalline Zro (2) And Hfo (2) : An Engineering Solution for Elimination of O-Atom Vacancy Defects in Non-Crystalline Ternary Silicate Alloys  

SciTech Connect

Spectroscopic studies, supported by theory indicate that neutral and negatively charged O-atom vacancies are the most important intrinsic defects in nanocrystalline thin films of Hf(Zr)O2. O-atom vacancy defects are identified in this paper by different spectroscopic technique: vacuum ultra-violet spectroscopic ellipsometry, near edge x-ray absorption spectroscopy, and cathodo-luminescence spectroscopy. O-vacancy defects are active as (1) interface traps for Si substrate injection of holes, and (2) bulk film traps for Si substrate injection of electrons. The markedly different electron and hole trapping properties are a potentially serious problem for threshold voltage control and stability in CMOS inverter FETs using nanocrystalline Hf(Zr)O2 dielectrics. O-vacancy defects are not observed spectroscopically in thermally and chemically stable Zr Si oxynitride alloy films, (SiO2)x(Si3N4)y(ZrO2)z, that have been annealed at 1100 C in Ar. Si3N4 concentrations in these alloys must be controlled within narrow limits, {approx}0.36 to 0.4, with equal SiO2 and ZrO2 concentrations of approximately 0.32 to 0.3.

Lucovsky, G.; Luning, J.; Stoute, N.A.; Seo, H.; Hinkle, C.L.; Ju, B.

2007-08-24

309

Magnetoresistance of disordered ultrathin Pt wires  

Microsoft Academic Search

We have measured the transverse magnetoresistance of heavily disordered ultrathin drawn Pt wires which show an unusually large low-temperature resistance increase in zero magnetic field deltaR (T)R~10-3-10-2 at 1.5 K. An anomalous positive magnetoresistance deltaR (H)R~10-4-10-3 is observed at moderate fields H50 muOmega cm) wires. The magnitude of deltaR (H)R increases with resistivity, opposite to Kohler's rule, and increases at

A. C. Sacharoff; R. M. Westervelt; J. Bevk

1984-01-01

310

Elementary spin excitations in ultrathin itinerant magnets  

NASA Astrophysics Data System (ADS)

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 in complex low-dimensional ferromagnetic oxide nanostructures is discussed. The influence of the relativistic spin-orbit coupling on high-energy magnons is addressed. It is shown how the spin-orbit coupling breaks the energy degeneracy of the magnons excited in an ultrathin ferromagnet, and how it influences their lifetime, amplitude, group and phase velocity. A potential application of these new effects in modern spintronics is outlined. It is illustrated how one can take advantage of collective nature of magnons and use these quasi-particles for probing the magnetic exchange interaction at buried interfaces.

Zakeri, Khalil

2014-12-01

311

Ultrathin, epitaxial cerium dioxide on silicon  

SciTech Connect

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.

Flege, Jan Ingo, E-mail: flege@ifp.uni-bremen.de; Kaemena, Björn; Höcker, Jan; Schmidt, Thomas; Falta, Jens [Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen (Germany); Bertram, Florian [Photon Science, Deutsches Elektronensynchrotron (DESY), Notkestraße 85, 22607 Hamburg (Germany); Wollschläger, Joachim [Department of Physics, University of Osnabrück, Barbarastraße 7, 49069 Osnabrück (Germany)

2014-03-31

312

Characterizing stress in ultrathin silicon wafers  

NASA Astrophysics Data System (ADS)

The aim of this letter is to calculate the mechanical grinding induced bow and stress in ultrathin silicon wafers. The reverse leakage current of a p-n junction diode fabricated on a 4in. silicon wafer was measured for wafers thinned to various thicknesses. A correlation with the residual stress was obtained through band gap narrowing effect. The analytical results were compared with experimental bow measurements using a laser profiler. The bow in 50?m thick wafer was found to be less than 2mm using the current grinding process.

Paul, Indrajit; Majeed, Bivragh; Razeeb, Kafil M.; Barton, John

2006-08-01

313

Arrays of ultrathin silicon solar microcells  

DOEpatents

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.

Rogers, John A; Rockett, Angus A; Nuzzo, Ralph; Yoon, Jongseung; Baca, Alfred

2014-03-25

314

On dielectric breakdown statistics  

Microsoft Academic Search

In this paper, we investigate the dielectric breakdown data of some insulating materials and focus on the applicability of the two- and three-parameter Weibull distributions. A new distribution function is also proposed. In order to assess the model distribution's trustworthiness, we employ the Monte Carlo technique and, randomly selecting data-subsets from the whole dielectric breakdown data, determine whether the selected

Enis Tuncer; D Randy James; Isidor Sauers; Alvin R Ellis; Marshall O Pace

2006-01-01

315

Dielectric waveguide antenna  

Microsoft Academic Search

Investigations have continued into developing design criteria for a dielectric waveguide line source antenna. The Marcatili analysis has proven to be a reliable guide for the transmission line design. There is, however, no practical design information available permitting the synthesis of a symmetrical amplitude taper along a grooved dielectric waveguide antenna. This investigation presents a measurement procedure that will permit

J. Borowick; W. Bayha; R. A. Stern; R. W. Babbitt

1982-01-01

316

Electronic band structure of zirconia and hafnia polymorphs from the GW perspective Hong Jiang,1,* Ricardo I. Gomez-Abal,1 Patrick Rinke,1,2 and Matthias Scheffler1,2  

E-print Network

13 January 2010; published 24 February 2010 The electronic structure of crystalline ZrO2 and HfO2 . ZrO2 and HfO2 are found to have very similar quasi- particle band structures. Small differences but capacitively equivalent gate dielectrics.1 Hafnia HfO2 and zirconia ZrO2 are currently among the most

317

Effect of PVD process parameters on the quality and reliability of thin (10-30 nm) Al2O3 dielectrics  

NASA Astrophysics Data System (ADS)

Over the last decade, dielectric scaling in non-volatile memories (NVM) and CMOS logic applications has reached a point where better innovations will be required to meet the reliability and performance requirements of future products. For both these applications, high k materials are being explored as possible candidates to replace the traditional SiO2 and oxide/nitride/oxide-based films used today. While there are several attractive candidates to replace these materials, HfO2 and Al2O3 are considered as the most promising ones. Although there has been a lot of work on CVD-based Al2O3, there has not been much reported for PVD-based Al2O3 for NVM applications, especially in the thickness regime of 10-30 nm. This paper discusses the effects of process parameters such a plasma power and annealing conditions on the quality of Al2O3 dielectrics. It was observed that a post deposition anneal in O2 ambient at 700°C for 15 s is essential to obtain a fully oxidized film with high density. While higher power (1,500 W) results in thicker films with better k values, they also lead to more substrate damage and poorer reliability. Annealing done at temperatures greater than 700°C for 60 s or more results in failure of the film possibly due to diffusion of silicon into Al2O3 and its subsequent reaction.

Dutta, Shibesh; Ramesh, Sivaramakrishnan; Shankar, Balakrishnan; Gopalan, Sundar

2012-03-01

318

Super absorption of ultra-thin organic photovoltaic films  

NASA Astrophysics Data System (ADS)

This article summarized our recent progress in theoretical designs for achieving super absorption in ultra-thin organic photovoltaic (OPV) films based on various planar OPV-on-metal and metal-OPV-metal structures. Three different structures were numerically simulated to demonstrate strongly enhanced optical absorption in ultra-thin OPV layers, which is polarization-independent and occurs over a wide range of incident angles in visible regime. Physical mechanisms associated with these super absorptive ultra-thin layers are analyzed and validated using numerical and analytical modeling.

Liu, Kai; Zeng, Beibei; Song, Haoming; Gan, Qiaoqiang; Bartoli, Filbert J.; Kafafi, Zakya H.

2014-03-01

319

Flexible, Ultra-Thin, Embedded Die Packaging  

NASA Astrophysics Data System (ADS)

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.

McPherson, Ryan J.

320

Ultrathin Optical Panel And A Method Of Making An Ultrathin Optical Panel.  

DOEpatents

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.

Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchoque, NY); DeSanto, Leonard (Patchoque, NY); Veligdan, James T. (Manorville, NY)

2005-02-15

321

Ultrathin optical panel and a method of making an ultrathin optical panel  

DOEpatents

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.

Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchogue, NY); DeSanto, Leonard (Patchogue, NY); Veligdan, James T. (Manorville, NY)

2001-10-09

322

Ultrathin Optical Panel And A Method Of Making An Ultrathin Optical Panel.  

DOEpatents

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.

Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchogue, NY); DeSanto, Leonard (Patchogue, NY); Veligdan, James T. (Manorville, NY)

2005-05-17

323

Ultrathin optical panel and a method of making an ultrathin optical panel  

DOEpatents

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.

Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchogue, NY); DeSanto, Leonard (Patchogue, NY); Veligdan, James T. (Manorville, NY)

2003-02-11

324

Ultrathin optical panel and a method of making an ultrathin optical panel  

DOEpatents

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.

Biscardi, Cyrus (Bellport, NY); Brewster, Calvin (North Patchogue, NY); DeSanto, Leonard (Patchogue, NY); Veligdan, James T. (Manorville, NY)

2002-01-01

325

Multi-frequency amplitude modulated non-contact atomic force microscopy for nanoscale dielectric measurements  

NASA Astrophysics Data System (ADS)

Multi-frequency non-contact atomic force microscopy with amplitude feedback in air was used to obtain the dielectric constant of ultra-thin films on metallic substrates. The cantilever was excited at its second bending mode by applying an AC electric field between the substrate and cantilever. The capacitance gradient between the cantilever tip and sample substrate was obtained by measuring the capacitive force driving the cantilever at its second bending mode. An analytic expression relating capacitance and dielectric constant of thin film was then used to fit the experimental data and the dielectric constant was obtained from the fit parameters. The method was validated by obtaining the dielectric constants of self-assembled monolayers of thiol molecules (2.0 ±0.1) on gold substrate, and sputtered SiO2 (3.6 ±0.07) thin film. The high Q-factor of the second bending mode of the cantilever increases the accuracy of capacitive measurements while the low applied potentials minimize the likelihood of variation of dielectric constants at high field strength and of damage from dielectric breakdown of air.

Kumar, Bharat; Bonvallet, Joseph; Crittenden, Scott

2012-02-01

326

Study of HfSiO film prepared by electron beam evaporation for high- k gate dielectric applications  

NASA Astrophysics Data System (ADS)

The purpose of this paper is to report some experimental results with HfSiO films formed on silicon substrates by electron beam evaporation (EB-PVD) and annealed at different temperatures. The images of atomic force microscope (AFM) indicated that HfSiO film annealed at 900 °C was still amorphous, with a surface roughness of 0.173 nm. X-ray photoelectron spectroscopy (XPS) analysis revealed that the chemical composition of the film was (HfO 2) 3(SiO 2) and Hf-Si-O bonds existed in the annealed film. Electrical measurements showed that the equivalent oxide thickness (EOT) was 4 nm, the dielectric constant was around 6, the breakdown voltage was 10 MV/cm, the fixed charge density was -1.2 × 10 12 cm -2, and the leakage current was 0.4 ?A/cm 2 at the gate bias of 2 V for 6 nm HfSiO film. The annealing after deposition effectively reduced trapping density and the leakage current, and eliminated hysteresis in the C- V curves. Annealing also induced SiO 2 growth at the interface.

Cheng, Xinhong; Song, Zhaorui; Jiang, Jun; Yu, Yuehui; Yang, Wenwei; Shen, Dashen

2006-09-01

327

Advanced Physics: Capacitors and Dielectrics  

NSDL National Science Digital Library

Click-drag the dielectric blocks, dielectric constants k1= 2.4 and k2, respectively, into the capacitor (charge given in mC and position given in centimeters). Observe how the electric field and the charge on the capacitor and the dielectric change when you move the dielectric.

Wolfgang Christian

328

Nanopyramid structure for ultrathin c-Si tandem solar cells.  

PubMed

Recently, ultrathin crystalline silicon solar cells have gained tremendous interest because they are deemed to dramatically reduce material usage. However, the resulting conversion efficiency is still limited by the incomplete light absorption in such ultrathin devices. In this letter, we propose ultrathin a-Si/c-Si tandem solar cells with an efficient light trapping design, where a nanopyramid structure is introduced between the top and bottom cells. The superior light harvesting results in a 48% and 35% remarkable improvement of the short-circuit current density for the top and bottom cells, respectively. Meanwhile, the use of SiOx mixed-phase nanomaterial helps to provide the maximum light trapping without paying the price of reduced electrical performance, and conversion efficiencies of up to 13.3% have been achieved for the ultrathin tandem cell employing only 8 ?m of silicon, which is 29% higher than the result obtained for the planar cell. PMID:24730470

Li, Guijun; Li, He; Ho, Jacob Y L; Wong, Man; Kwok, Hoi Sing

2014-05-14

329

Dual-layer ultrathin film optics: I. Theory and analysis  

NASA Astrophysics Data System (ADS)

This paper revisits dual-layer ultrathin film optics, which can be used for functional graded refractive index thin film stack. We present the detailed derivation including s-polarized and p-polarized light under arbitrary incidence angle showing the equivalence between the dual-layer ultrathin films and a negative birefringent thin film and also the approximations made during the derivation. Analysis of the approximations shows the influence of thickness of dual-layer thin films, the incidence angle and desired refractive index of the birefringent film. Numerical comparison between the titanium dioxide/aluminum oxide based dual-layer ultrathin film stack and the equivalent birefringent film verifies the theoretical analysis. The detailed theoretical study and numerical comparison provide a physical insight and design guidelines for dual-layer ultrathin film based optical devices.

Wang, Qian; Lim, Kim Peng

2015-03-01

330

GaS and GaSe ultrathin layer transistors.  

PubMed

Room-temperature, bottom-gate, field-effect transistor characteristics of 2D ultrathin layer GaS and GaSe prepared from the bulk crystals using a micromechanical cleavage technique are reported. The transistors based on active GaS and GaSe ultrathin layers demonstrate typical n-and p-type conductance transistor operation along with a good ON/OFF ratio and electron differential mobility. PMID:22678832

Late, Dattatray J; Liu, Bin; Luo, Jiajun; Yan, Aiming; Matte, H S S Ramakrishna; Grayson, Matthew; Rao, C N R; Dravid, Vinayak P

2012-07-10

331

Medium energy ion scattering for the high depth resolution characterisation of high-k dielectric layers of nanometer thickness  

NASA Astrophysics Data System (ADS)

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 device dimensions continue to be scaled down.

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

332

Broadband Liquid Dielectric Spectrometer  

NASA Astrophysics Data System (ADS)

A dielectric spectrometer was built to measure the dielectric relaxation of proteins in solution. The dielectric cell consisted of two parallel stainless-steel electrodes (separation of 8.5 mm) embedded in PTFE. To provide temperature stability, thermally regulated water flowed through both electrodes. The cell was connected to a 4294A Precision Impedance Analyzer, providing impedance measurements from 40Hz to 110 MHz. Due to electrode polarization and high frequency parasitics, useful measurements were obtained for frequencies ranging from 10 kHz to 10 MHz. Calibration was performed using air, iso-propanol and deionized water. Experiments were also conducted on buffers and salt solutions. The dielectric relaxation of the protein beta-lactoglobulin was measured at mg/ml concentrations.

Chandra, Satyan; Arellano, Jesus; Mazzeo, Brian

2009-10-01

333

Electric field effect in ultrathin black phosphorus  

NASA Astrophysics Data System (ADS)

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/SiO2 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 cm2/Vs and drain current modulation of over 103. At low temperatures, the on-off ratio exceeds 105, 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.

Koenig, Steven P.; Doganov, Rostislav A.; Schmidt, Hennrik; Castro Neto, A. H.; Özyilmaz, Barbaros

2014-03-01

334

Ultra-thin microporous/hybrid materials  

DOEpatents

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.

Jiang, Ying-Bing (Albuquerque, NM); Cecchi, Joseph L. (Albuquerque, NM); Brinker, C. Jeffrey (Albuquerque, NM)

2012-05-29

335

Electric field effect in ultrathin black phosphorus  

SciTech Connect

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.

Koenig, Steven P.; Schmidt, Hennrik [Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546 (Singapore); Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore); Doganov, Rostislav A.; Castro Neto, A. H.; Özyilmaz, Barbaros [Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546 (Singapore); Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore); Graduate School for Integrative Sciences and Engineering (NGS), National University of Singapore, 28 Medical Drive, Singapore 117456 (Singapore)

2014-03-10

336

Self-Organized Ultrathin Oxide Nanocrystals  

SciTech Connect

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.

Huo, Ziyang; Tsung, Chia-kuang; Huang, Wenyu; Fardy, Melissa; Yan, Ruoxue; Li, Yadong; Yang, Piedong; Zhang, Xiaofeng

2009-01-08

337

Dielectric properties of aerogels  

Microsoft Academic Search

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

L. W. Hrubesh; L. E. Keene; V. R. Latorre

1993-01-01

338

High dielectric constant oxides  

Microsoft Academic Search

The scaling of complementary metal oxide semiconductor (CMOS) transistors has led to the silicon dioxide layer used as a gate dielectric becoming so thin (1.4 nm) that its leakage current is too large. It is necessary to replace the SiO{2} with a physically thicker layer of oxides of higher dielectric constant (kappa) or `high K' gate oxides such as hafnium

J. Robertson

2004-01-01

339

Dielectric behavior of polychloroprene  

Microsoft Academic Search

Summary  The dielectric measurement of polychloroprene (PCP) over the range of 1 c\\/s ? 1 Mc\\/s and ?100 °C ? 20 °C gave high temperature\\u000a absorption (?aabsorption) and low temperature absorption (?\\u000a \\u000a a\\u000a -absorption). In order to clarify the relationship between the dielectric behavior and the chemical structure, the result\\u000a of PCP was compared with that of polyvinylchloride (PVC). The apparent

Masato Matsuo; Y?ichi Ishida; Kaoru Yamafuji; Motowo Takayanagi; Fujio Irie

1965-01-01

340

Aperture excited dielectric antennas  

NASA Technical Reports Server (NTRS)

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.

Crosswell, W. F.; Chatterjee, J. S.; Mason, V. B.; Tai, C. T.

1974-01-01

341

All-nanosheet ultrathin capacitors assembled layer-by-layer via solution-based processes.  

PubMed

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 ?m ?) 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 ?F 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. PMID:24548057

Wang, Chengxiang; Osada, Minoru; Ebina, Yasuo; Li, Bao-Wen; Akatsuka, Kosho; Fukuda, Katsutoshi; Sugimoto, Wataru; Ma, Renzhi; Sasaki, Takayoshi

2014-03-25

342

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

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.

Powell, C.J. [Surface and Microanalysis Science Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8370 (United States); Smekal, W.; Werner, W.S.M. [Institut fuer Allgemeine Physik, Vienna University of Technology, Wiedner Hauptstrasse 8-10, A-1040 Vienna (Austria)

2005-09-09

343

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)

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 ( ?) = 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 ( ? 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.

Maheswari, D.; Venkatachalam, P.

2015-03-01

344

High performance organic field-effect transistors with ultra-thin HfO{sub 2} gate insulator deposited directly onto the organic semiconductor  

SciTech Connect

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.

Ono, S., E-mail: shimpei@criepi.denken.or.jp [Central Research Institute of Electric Power Industry, Komae, Tokyo 201-8511 (Japan); Häusermann, R. [Central Research Institute of Electric Power Industry, Komae, Tokyo 201-8511 (Japan) [Central Research Institute of Electric Power Industry, Komae, Tokyo 201-8511 (Japan); Laboratory for Solid State Physics, ETH Zurich, Zurich 8093 (Switzerland); Chiba, D. [Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan) [Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 322-0012 (Japan); Department of Applied Physics, University of Tokyo, Tokyo 113-8656 (Japan); Shimamura, K.; Ono, T. [Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan)] [Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Batlogg, B. [Laboratory for Solid State Physics, ETH Zurich, Zurich 8093 (Switzerland)] [Laboratory for Solid State Physics, ETH Zurich, Zurich 8093 (Switzerland)

2014-01-06

345

Ge nanocrystals embedded in Hf-aluminate high-k gate dielectric for floating gate memory application  

NASA Astrophysics Data System (ADS)

Recently, many efforts have been made to improve the device performance of nanocrystal memory by replacing the SiO2 with various high dielectric constant (high-k) materials, especially embedded with Ge nanocrystals. This paper demonstrates the floating gate memory effect by embedding nanometer-sized Ge nanocrystals in hafnium aluminate (HfAlO) high-k gate dielectric. A 5 nm-thick amorphous thin film of HfAlO was first deposited on (100) p-Si substrates as a tunneling gate oxide layer by laser molecular beam epitaxy deposition using a HfO2 and Al2O3 composite target. Well-defined (~10 nm in diameter) nanometer-sized Ge dots were subsequently deposited on this thin tunneling gate oxide followed by a 30 nm-thick top control gate oxide of HfAlO. Transmission electron microscopy has been carried out for a detailed study of structural properties of the Ge nanocrystals embedded in the HfAlO films, and their relationships to electrical properties. Electrical properties have been characterized by means of high-frequency capacitance-voltage (C-V) and current-voltage (I-V) measurements on the metal-oxide-semiconductor capacitors. A counter-clockwise hysteresis C-V loop has been obtained and a threshold voltage shift of 1.0 V has been achieved indicating stored electrons (up to a density of 2x1012 cm-2) in the Ge-nanodots floating gate and thus the memory effect. Time-dependent I-V measurement also showed low leakage current of floating gate system. These results suggest that the Ge nanocrystals embedded in HfAlO are promising for floating gate memory device application.

Lee, Pui F.; Liu, Wei L.; Song, Zhi T.; Dai, Ji Y.

2005-02-01

346

Achieving wide-band linear-to-circular polarization conversion using ultra-thin bi-layered metasurfaces  

NASA Astrophysics Data System (ADS)

In this paper, we propose to achieve wideband linear-to-circular (LTC) polarization conversion by ultra-thin bi-layered metasurfaces. As an example, an LTC polarization conversion metasurface operating in 11.4-14.3 GHz is designed and fabricated, which is composed of two layers of metallic pattern arrays separated by a 1.5 mm-thick dielectric spacer. When linearly polarized waves impinge on the bi-layered metasurface, LTC polarization conversion transmission is greater than 90% over a wide frequency range from 11.0 GHz to 18.3 GHz. Meanwhile, the axis ratio is lower than 3 dB in 9.8-18.3 GHz. This wide-band and highly efficient LTC polarization conversion transmission is analyzed theoretically. The measured LTC polarization conversion transmissions are well consistent with the simulated results.

Li, Yongfeng; Zhang, Jieqiu; Qu, Shaobo; Wang, Jiafu; Zheng, Lin; Pang, Yongqiang; Xu, Zhuo; Zhang, Anxue

2015-01-01

347

Effect of a dielectric substrate with a subwavelength thickness on light diffraction by rectangular hole arrays on metallic film  

NASA Astrophysics Data System (ADS)

A theoretical study of the effect of ultrathin dielectric substrate in THz wave diffraction phenomena on a subwavelength nanostructured system is conducted. The proposed system is composed of a dielectric substrate with a thickness of ˜ ?/1000 and a subwavelength-scaled rectangular hole array on a metal thin film in THz wavelength region. A modified Rayleigh diffraction theory has been developed to take into account the contribution of reflection at the air-substrate interface. A calculation of the terahertz transmission while varying the thickness shows that the effect of a thin dielectric substrate starts to vanish when the thickness becomes ˜1/100 of the incident light's wavelength. Theoretically, the results are well explained because most electric fields are confined near the rectangular aperture, which results in the dominant existence of the field inside the thin substrate. Additionally, the effect of a thin dispersive substrate is discussed.

Park, D. J.; Jeong, M. S.; Choi, S. B.

2014-11-01

348

Controlling birefringence in dielectrics  

NASA Astrophysics Data System (ADS)

Birefringence, from the very essence of the word itself, refers to the splitting of light rays into two parts. In natural birefringent materials, this splitting is a beautiful phenomenon, resulting in the perception of a double image. In optical metamaterials, birefringence is often an unwanted side effect of forcing a device designed through transformation optics to operate in dielectrics. One polarization is usually implemented in dielectrics, and the other is sacrificed. Here we show, with techniques beyond transformation optics, that this need not be the case, that both polarizations can be controlled to perform useful tasks in dielectrics, and that rays, at all incident angles, can even follow different trajectories through a device and emerge together as if the birefringence did not exist at all. A number of examples are shown, including a combination Maxwell fisheye/Luneburg lens that performs a useful task and is achievable with current fabrication materials.

Danner, Aaron J.; Tyc, Tomáš; Leonhardt, Ulf

2011-06-01

349

PREFACE: Dielectrics 2013  

NASA Astrophysics Data System (ADS)

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 pleased to express our thanks to the Conference Department of the Institute of Physics for their invaluable support in organizing this event. We are especially grateful to Dawn Stewart for her responsive and day-to-day handling of this conference, as well as Claire Garland for help in planning and managing this international event. We would also like to thank Dr Steve Welch, Director at ESP Central Ltd, representing the interest of the Electronics, Sensors, Photonics Knowledge Transfer Network, as well as Paul Naylor and Susan Matos for their contribution towards the KTN session of the Conference. Finally, we would like to thank Solartron Analytical, Ametek and Princeton Applied Research for demonstrating precision electrochemical impedance spectroscopy measurement techniques at the conference. We hope that the wider Dielectrics community will find these proceedings of interest and will use them as reference text in their future work. Programme committee R Pethig, University of Edinburgh J Blackburn, National Physical Laboratory J Swingler, Heriot Watt University S Hadjiloucas, University of Reading A West, University of Sheffiled M Hughes, University of Surrey S Dodd, University of Leicester D Almond, University of Bath M Cain, National Physical Laboratory D J Swaffield, University of Southampton N Green, University of Southampton A Vaughan, University of Southampton Sillas Hadjiloucas and John Blackburn (Summer 2013)

Hadjiloucas, Sillas; Blackburn, John

2013-11-01

350

Fabrication of artificially stacked ultrathin ZnS/MgF2 multilayer dielectric optical filters.  

PubMed

We report a design and fabrication strategy for creating an artificially stacked multilayered optical filters using a thermal evaporation technique. We have selectively chosen a zinc sulphide (ZnS) lattice for the high refractive index (n = 2.35) layer and a magnesium fluoride (MgF2) lattice as the low refractive index (n = 1.38) layer. Furthermore, the microstructures of the ZnS/MgF2 multilayer films are also investigated through TEM and HRTEM imaging. The fabricated filters consist of high and low refractive 7 and 13 alternating layers, which exhibit a reflectance of 89.60% and 99%, respectively. The optical microcavity achieved an average transmittance of 85.13% within the visible range. The obtained results suggest that these filters could be an exceptional choice for next-generation antireflection coatings, high-reflection mirrors, and polarized interference filters. PMID:23716485

Kedawat, Garima; Srivastava, Subodh; Jain, Vipin Kumar; Kumar, Pawan; Kataria, Vanjula; Agrawal, Yogyata; Gupta, Bipin Kumar; Vijay, Yogesh K

2013-06-12

351

MoS{sub 2} functionalization for ultra-thin atomic layer deposited dielectrics  

SciTech Connect

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.

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., E-mail: rmwallace@utdallas.edu [Department of Materials Science and Engineering, The University of Texas at Dallas, 800 West Campbell Road, Richardson, Texas 75080 (United States); Mordi, Greg I. [Department of Electrical Engineering, The University of Texas at Dallas, 800 West Campbell Road, Richardson, Texas 75080 (United States); Kim, Jiyoung [Department of Materials Science and Engineering, The University of Texas at Dallas, 800 West Campbell Road, Richardson, Texas 75080 (United States); Department of Electrical Engineering, The University of Texas at Dallas, 800 West Campbell Road, Richardson, Texas 75080 (United States)

2014-03-17

352

Ultrathin, Ultrasmooth Gold Layer on Dielectrics without the Use of Additional Metallic Adhesion Layers.  

PubMed

With advances in the plasmonics and metamaterials research field, it has become more and more important to fabricate thin and smooth Au metal films in a reliable way. Here, by thin films we mean that their average height is below 10 nm and their average roughness is below 5% of the total thickness. In this article, we investigated the use of amino- and mercaptosilanes to increase the adhesion of Au on Si wafers, thus obtaining a smooth and thin layer. This method does not include the use of other metals to improve the adhesion of gold, like Ti or Cr, since they would reduce the optical characteristics of the structure. Our results show that layers having 6 nm thickness and below 0.3 nm roughness can be reproducibly obtained using aminosilanes. Layers having a nominal thickness of 5 nm have a yield of 58%; thus, this thickness is the limit for the process that we investigated. PMID:25723253

Leandro, Lorenzo; Malureanu, Radu; Rozlosnik, Noemi; Lavrinenko, Andrei

2015-03-18

353

Thermally switchable dielectrics  

DOEpatents

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.

Dirk, Shawn M.; Johnson, Ross S.

2013-04-30

354

Circular dielectric liquid iris.  

PubMed

We demonstrate a liquid iris diaphragm using dielectric force, enabling its aperture to vary from 4 mm at the resting state to 1.5 mm at 160 V(rms). The liquid iris is a packaged optical component comprised of transparent oil, opaque ink, and a set of driving electrodes on a glass substrate. The iris aperture shrinks with the dielectric force, which is exerted on the interface between the two nonconductive liquids. The transmittance was measured to exceed 85% with no antireflection coatings over the spectrum of visible light. The maximum electric power consumed is measured to be 5.7 mW. PMID:20634871

Tsai, C Gary; Yeh, J Andrew

2010-07-15

355

Multilayer dielectric diffraction gratings  

DOEpatents

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.

Perry, Michael D. (Livermore, CA); Britten, Jerald A. (Oakley, CA); Nguyen, Hoang T. (Livermore, CA); Boyd, Robert (Livermore, CA); Shore, Bruce W. (Livermore, CA)

1999-01-01

356

Multilayer dielectric diffraction gratings  

DOEpatents

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.

Perry, M.D.; Britten, J.A.; Nguyen, H.T.; Boyd, R.; Shore, B.W.

1999-05-25

357

Dielectric Optical Cloak  

E-print Network

Invisibility or cloaking has captured human's imagination for many years. With the recent advancement of metamaterials, several theoretical proposals show cloaking of objects is possible, however, so far there is a lack of an experimental demonstration at optical frequencies. Here, we report the first experimental realization of a dielectric optical cloak. The cloak is designed using quasi-conformal mapping to conceal an object that is placed under a curved reflecting surface which imitates the reflection of a flat surface. Our cloak consists only of isotropic dielectric materials which enables broadband and low-loss invisibility at a wavelength range of 1400-1800 nm.

Valentine, Jason; Zentgraf, Thomas; Bartal, Guy; Zhang, Xiang

2009-01-01

358

Metal-gate-induced reduction of the interfacial layer in Hf oxide gate stacks L. V. Goncharova,a  

E-print Network

following dielectric deposition. We report here results from medium energy ion scattering and x is likely to be related to defects in crystalline HfO2 films, such as grain boundaries. HighON dielectrics need to be replaced with a higher dielectric constant material, such as HfO2 and the metallic gate

Gustafsson, Torgny

359

Cellulose as biodegradable high-k dielectric layer in organic complementary inverters  

NASA Astrophysics Data System (ADS)

We report on the natural source based and biodegradable material cellulose on Al2O3 as ultrathin hybrid high-k dielectric layer for applications in green electronics. Dielectric films of 16 nm cellulose (? ? 8.4) and 8 nm Al2O3 (? ? 9) exhibit low leakage currents up to electric fields of 1.5 MV/cm. Pentacene and C60 based organic thin film transistors show a well-balanced performance with operation voltages around 2 V. They are implemented in complementary inverters with excellent switching behavior, a small-signal gain up to 60 and with exceptionally high and balanced noise margin values of 82% at ultralow operation voltage (VDD = 2.5 V).

Petritz, A.; Wolfberger, A.; Fian, A.; Irimia-Vladu, M.; Haase, A.; Gold, H.; Rothländer, T.; Griesser, T.; Stadlober, B.

2013-10-01

360

DIELECTRICS-BEYOND WATER CONTENT  

Technology Transfer Automated Retrieval System (TEKTRAN)

To properly understand capacitance probes and time domain reflectometry (TDR), and the effect of operating frequency, it is necessary to study dielectrics as a function of frequency (dielectric spectroscopy). The objectives of this study are to see if dielectric spectroscopy can help interpret diel...

361

On coherent radiation by relativistic electrons in ultrathin crystals  

NASA Astrophysics Data System (ADS)

A quantitative theory of the radiation process by ultrarelativistic electrons in ultrathin crystals is proposed. The theory is based upon the factorization theorem of the radiation cross-section and upon the description of the scattering process on the basis of the eikonal approximation of quantum electrodynamics. The conditions are obtained, under which the effect of radiation suppression in ultrathin crystals must take place. It is shown that these conditions may be fulfilled at the interaction of electrons with the energy accessible on CERN accelerator with ultrathin silicon crystals. Since the last years one can produce such crystals for the experiments in high energy physics. This opens new possibilities in study of interaction of high energy particles with matter.

Shul'ga, N. F.; Shul'ga, S. N.

2014-08-01

362

Engineering curvature in graphene ribbons using ultrathin polymer films.  

PubMed

We propose a method to induce curvature in graphene nanoribbons in a controlled manner using an ultrathin thermoset polymer in a bimaterial strip setup and test it via molecular dynamics (MD) simulations. Continuum mechanics shows that curvature develops to release the residual stress caused by the chemical and thermal shrinkage of the polymer during processing and that this curvature increases with decreasing film thickness; however, significant deformation is only achieved for ultrathin polymer films. Quite surprisingly, explicit MD simulations of the curing and annealing processes show that the predicted trend not just continues down to film thicknesses of 1-2 nm but that the curvature development is enhanced significantly in such ultrathin films due to surface tension effects. This combination of effects leads to very large curvatures of over 0.14 nm(-1) that can be tuned via film thickness. This provides a new avenue to engineer curvature and, thus, electromagnetic properties of graphene. PMID:25375290

Li, Chunyu; Koslowski, Marisol; Strachan, Alejandro

2014-12-10

363

Dispersion characteristic of ultrathin terahertz planar lenses based on metasurface  

NASA Astrophysics Data System (ADS)

Terahertz (THz) radiation has attached a lot of attention due to its potential applications. The smart optical components will greatly boost the application of the THz technology. Ultrathin planar lenses which can greatly reduce the thickness of the components are designed and fabricated in the THz region based on the metasurface. The dispersion characteristic of this kind of ultrathin planar lenses is systematically investigated. It is demonstrated that the focal lengths of the proposed lenses become shorter with the wavelength of the illuminating light increasing. Moreover, the ultrathin planar lenses perform a good focusing characteristic over a broad wavelength range. The results help us to further understand the optical properties of the lenses based on the metasurface and provide a considerable important reference for its future applications in miniaturization and integration of the THz system.

Hu, Dan; Moreno, Gabriel; Wang, Xinke; He, Jingwen; Chahadih, Abdallah; Xie, Zhenwei; Wang, Bo; Akalin, Tahsin; Zhang, Yan

2014-07-01

364

Nonlinear characteristics in fracture strength test of ultrathin silicon die  

NASA Astrophysics Data System (ADS)

The precise evaluation of fracture strength of ultrathin (<50 ?m thick) silicon chips/ribbons plays a critical role in design of deformability and lifetime of flexible/stretchable electronics. In its three-point bending test, however, the classical linear theory used to convert the experimental fracture load into fracture strength value fails to match the emerged geometrically nonlinear characteristics for such an ultrathin silicon die. Here, we consider the geometric large deformation and present its nonlinear solution to more reliably evaluate the fracture stress of ultrathin specimen by virtue of the obtained experimental fracture load. A quite good agreement on experiments shows that the nonlinear analytical predictions allow a more comprehensive understanding for the effects of the silicon samples’ thickness on the transformation from linear relation to nonlinearity. The comparisons indicate that the fracture strength values are lower from linear evaluations, and to this the corresponding correction factor is defined to enhance the estimate precision.

Liu, Zunxu; Huang, YongAn; Xiao, Lin; Tang, Pengpeng; Yin, Zhouping

2015-04-01

365

Swelling of ultrathin crosslinked polyamide water purification membranes  

NASA Astrophysics Data System (ADS)

Polyamide (PA) ultrathin films represent the state-of-the-art nanofiltration and reverse osmosis membranes used in water desalination. The performance of these materials, such as permselectivity, is intimately linked with extent of swelling of the PA network. Thus, quantifying their swelling behavior would be a useful and simple route to understanding the specific network structural parameters that control membrane performance. In this work, we measure the swelling behavior of PA ultrathin films using X-ray reflectivity as a function of water hydration. By applying the Flory-Rehner theory used to describe the swelling behavior of polymer networks, we quantify the PA network properties including Flory interaction parameter and the monomer units between crosslinks. Finally, we demonstrate application of this measurement approach for characterizing the network properties of different types of PA ultrathin films relevant to water purification and discuss the relationship between network and transport properties.

Chan, Edwin; Stafford, Christopher

2013-03-01

366

Lunar permafrost - Dielectric identification.  

NASA Technical Reports Server (NTRS)

A simulator of lunar permafrost at 100 K exhibits a dielectric relaxation centered at approximately 300 hertz. If permafrost exists in the moon between 100 and 213 K, it should present a relaxation peak at approximately 300 hertz. For temperatures up to 263 K it may go up to 20 kilohertz.

Alvarez, R.

1973-01-01

367

Generalized dielectric breakdown model  

Microsoft Academic Search

We propose a generalized version of the dielectric breakdown model (DBM) for generic breakdown processes. It interpolates between the standard DBM and its analog with quenched disorder (QDBM), as a temperaturelike parameter is varied. The physics of other well-known fractal growth phenomena such as invasion percolation and the Eden model are also recovered for some particular parameter values. Competition between

R. Cafiero; A. Gabrielli; M. Marsili; M. A. Muñoz; L. Pietronero

1999-01-01

368

Molds for cable dielectrics  

DOEpatents

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.

Roose, Lars D. (Albuquerque, NM)

1996-01-01

369

Molds for cable dielectrics  

DOEpatents

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.

Roose, L.D.

1996-12-10

370

Dielectric Optical Cloak  

Microsoft Academic Search

Invisibility or cloaking has captured human's imagination for many years. With the recent advancement of metamaterials, several theoretical proposals show cloaking of objects is possible, however, so far there is a lack of an experimental demonstration at optical frequencies. Here, we report the first experimental realization of a dielectric optical cloak. The cloak is designed using quasi-conformal mapping to conceal

Jason Valentine; Jensen Li; Thomas Zentgraf; Guy Bartal; Xiang Zhang

2009-01-01

371

Enhanced charge storage of ultrathin polythiophene films within porous nanostructures.  

PubMed

In a single step polymerization and coating, oxidative chemical vapor deposition (oCVD) has been used to synthesize unsubstituted polythiophene. Coatings have been conformally coated within porous nanostructures of anodized aluminum oxide, titanium dioxide, and activated carbon. Significant enhancement in charge capacity has been found with ultrathin polythiophene coatings that preserve the surface area and pore space of the nanostructures. Pseudocapacitors consisting of ultrathin polythiophene coated within activated carbon yielded increases of 50 and 250% in specific and volumetric capacitance compared with bare activated carbon. Devices were stable up to the 5000 cycles tested with only a 10% decrease in capacitance. PMID:24840296

Nejati, Siamak; Minford, Thomas E; Smolin, Yuriy Y; Lau, Kenneth K S

2014-06-24

372

Ultrathin metals and nano-structuring for photonic applications  

NASA Astrophysics Data System (ADS)

Ultrathin materials and nano-structuring are becoming essential for the functionalization of optical surfaces. In the talk we will show how ultrathin metals can be exploited to create competitive transparent electrodes. At the same time they can be used to create nanostructured surfaces through mass scalable dewetting and etching techniques. After presenting the techniques, we will focus on the applications made possible by these materials and technologies, including self-cleaning or easy-to-clean display screens, efficient indium-free light emitting diodes and solar cells, antireflective structures for the laser industry and super-wetting surfaces for biology.

Formica, Nadia; Carrilero, Albert; Chen, Tong Lai; Ghosh, Dhriti S.; Mazumder, Prantik; Pruneri, Valerio

2014-03-01

373

Surface-sensitive UHV dielectric studies of nanoscale organic thin films: Adsorption, crystallization, and sublimation  

NASA Astrophysics Data System (ADS)

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.

Underwood, Jason M.

374

Characterization of dielectric breakdown behavior by in situ transmission electron microscopy  

NASA Astrophysics Data System (ADS)

Dielectric breakdown (BD) is the loss of capacitance upheld by an insulating material through defect formation and charge trapping. Dielectric BD is well-studied in the framework of reliability physics for semiconductor applications, and presents itself as a viable mechanism during materials processing by electric field assisted sintering (EFAS). So far a mechanistic understanding of dielectric BD is incomplete due to the limitations in nanoscale defect characterization techniques. The recent development of novel in situ transmission electron microscopy (TEM) capabilities enables the atomic-scale characterization of dielectric BD mechanisms, which was the subject of this dissertation. As the technology of semiconductor devices moves toward the sub-25 nm technology the electronic properties of gate oxide layers are affected eventually leading to device failure by dielectric BD. This study aimed to provide a systematic approach of simultaneous imaging and local application of electrical stress using in situ TEM by contacting an electrically biased Scanning Tunnelling Microscopy (STM) probe directly to the TEM sample. This experimental setup therefore allows a correlation of electrical signatures with defect structure evolution. In situ TEM experiments carried out with a single SiO2-based field effect transistor resulted to catastrophic failure of the dielectric layer consistent with descriptions of soft dielectric breakdown (SBD) and hard dielectric breakdown (HBD). A variety of in situ TEM techniques was further utilized to investigate whether electric field induced dielectric breakdown may contribute to densification of metallic powder particles during EFAS. In situ heating and STM-TEM experiments were systematically applied to separately study thermal and athermal effects during densification, respectively. Nanometric metal powders used for sintering typically possess surface oxides that affect the thermodynamics and kinetics of neck formation during the initial stage of sintering. The thermal effects were found to be driven by reduction-oxidation reactions of nickel oxide with carbon. The presence of carbon promotes the removal of surface oxides at lower temperatures and, therefore, can accelerate densification. By the controlled application of electrical bias, EFAS conditions were reproduced during in situ TEM and revealed reduction of ultra-thin nickel oxide surface layers by electric field-induced dielectric breakdown. The results provide evidence for previously suggested effects of local electric field amplification at inter-particle contact areas, which, hence, triggers surface cleaning through electric field-induced dielectric breakdown.

Bonifacio, Cecile Semana

375

Antenna with Dielectric Having Geometric Patterns  

NASA Technical Reports Server (NTRS)

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.

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

376

Structures of ultrathin copper nanowires encapsulated in carbon nanotubes  

Microsoft Academic Search

We have investigated the structures of copper nanowires encapsulated in carbon nanotubes using a structural optimization process applied to the steepest descent method. The results showed that the stable morphology of the cylindrical ultrathin copper nanowires in carbon nanotubes is multishell packs consisting of coaxial cylindrical shells. As the diameter of carbon nanotubes increased, the encapsulated copper nanowires have the

Won Young Choi; Jeong Won Kang; Ho Jung Hwang

2003-01-01

377

Aging and coarsening in an ultra-thin film model  

Microsoft Academic Search

In this work we study the nonequilibrium dynamical properties of an ultra-thin magnetic film model. Previous works on this system revealed the presence of novel dynamical properties that were difficult to interpret within a single physical scenario: on one hand the analysis of the aging properties suggested a glassy behavior. On the other, the study of the violation of the

Pablo M. Gleiser; Marcelo A. Montemurro

2006-01-01

378

Acoustic scattering cancellation via ultrathin pseudo-surface  

Microsoft Academic Search

We propose the use of an ultrathin cloak made of an acoustic surface impedance that leads to invisibility for acoustic waves. Unlike current acoustic cloaks that require volumetric metamaterials and a significant shell thickness, the mantle cloak presented here is based on a patterned acoustic metasurface that produces similar effects in a thinner geometry. We show that by covering a

Pai-Yen Chen; Mohamed Farhat; Se´bastien Guenneau; Stefan Enoch

2011-01-01

379

Dynamic response of ultrathin highly dense ZIF-8 nanofilms.  

PubMed

Ultrathin ZIF-8 nanofilms are prepared by facile step-by-step dip coating. A critical withdrawal speed allows for films with a very uniform minimum thickness. The high refractive index of the films denotes the absence of mesopores. The dynamic response of the films to CO2 exposure resembles behaviour observed for non-equilibrium organic polymers. PMID:25142780

Cookney, Joanna; Ogieglo, Wojciech; Hrabanek, Pavel; Vankelecom, Ivo; Fila, Vlastimil; Benes, Nieck E

2014-10-11

380

Ultrathin fluorinated diamondlike carbon coating for nanoimprint lithography imprinters  

E-print Network

Ultrathin fluorinated diamondlike carbon coating for nanoimprint lithography imprinters Ryan W of the imprinter. Previous work on thick 100 nm diamondlike carbon DLC layers indicates that fluorinated DLC F interest is the plasma deposition of a layer of fluorinated diamondlike car- bon F-DLC . Diamondlike carbon

Krchnavek, Robert R.

381

Micromagnetic model of magnetization reversal of magnetically hard ultrathin dots  

E-print Network

Micromagnetic model of magnetization reversal of magnetically hard ultrathin dots and stripes M, France Abstract We propose improvements and extensions to an analytical model of magnetization reversal of nucleation volumes in hard magnetic materials, we use the concept of edge demagnetizing torque, where all

Boyer, Edmond

382

Electronic and magnetic properties of ultrathin rhodium nanowires  

Microsoft Academic Search

The structures of ultrathin rhodium nanowires are studied using empirical molecular dynamics simulations with a genetic algorithm. Helical multishell cylindrical and pentagonal packing structures are found. The electronic and magnetic properties of the rhodium nanowires are calculated using an spd tight-binding Hamiltonian in the unrestricted Hartree-Fock approximation. The average magnetic moment and electronic density of states are obtained. Our results

Baolin Wang; Guanghou Wang; Yun Ren; Houqian Sun; Xiaoshuang Chen; Jijun Zhao

2003-01-01

383

Conversion of multilayer graphene into continuous ultrathin sp3  

E-print Network

- enhanced chemical vapor deposition (CVD)3­5 . Advances in the growth of large-area graphene6,7 and bilayer even very large area by conversion of appropriate multilayer graphene on metal surfaces. The resulting suggest a route to experimental realization of large-area ultrathin sp3 -bonded carbon films on metal

384

An ultra-thin isotropic metamaterial thermal radiator  

Microsoft Academic Search

We design an ultra-thin infrared metamaterial thermal radiator which has nearly isotropic emission pattern for a wide range of angles. Our design is achieved by overlapping both the electric and magnetic resonances in the spectral domain and is insensitive to both TE and TM polarizations. The thermal emission of the metamaterial is nearly isotropic in which the deviation in the

Y. Zhou; T. Feng; Z. Liang; J. Li; D. Liu

2011-01-01

385

Synthesis and Characterization of Zirconium Tungstate Ultra-Thin Fibers  

SciTech Connect

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.

Zhang, Lifeng [South Dakota School of Mines and Technology; Howe, Jane Y [ORNL; Fong, Hao [South Dakota School of Mines and Technology; Zhang, Yan [Anhui Normal University, People's Republic of China

2009-01-01

386

Surface Structure of Ultrathin Fe Films on Cu(001) Revisited  

Microsoft Academic Search

The structure and magnetism of ultrathin Fe films epitaxially grown on a Cu(001) surface are investigated by grazing scattering of fast H and He atoms or ions. By making use of a new variant of ion beam triangulation based on the detection of the number of emitted electrons, we obtain direct information on the structure of the film surface. We

T. Bernhard; M. Baron; M. Gruyters; H. Winter

2005-01-01

387

Dielectric fluid motors  

SciTech Connect

On the application of high electric fields to a dielectric fluid, a convective motion of the fluid is induced. By controlling the fluid motion in nonuniform dc fields, a new type of fluid motor is developed. An angular velocity of more than 15s{sup {minus}1} (150 rpm) can be achieved at a dc voltage of 5 kV for a motor with a rotor radius of 10 mm. The efficiency of energy transformation from electric to kinetic energy is about 4{percent}. Since magnetic fields and switching circuits are not required, the advantage of the fluid motor will be enhanced by size reduction. The dielectric fluid motor is attractive as a source of mechanical energy in a micromachine. {copyright} {ital 1997 American Institute of Physics.}

Otsubo, Y. [Center of Cooperative Research, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba-shi 263 (Japan)] [Center of Cooperative Research, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba-shi 263 (Japan); Edamura, K. [New Technology Management Co., Higashi-Shinkoiwa 2-9-1-306, Katsushika-ku, Tokyo 124 (Japan)] [New Technology Management Co., Higashi-Shinkoiwa 2-9-1-306, Katsushika-ku, Tokyo 124 (Japan)

1997-07-01

388

Temperature switchable polymer dielectrics.  

SciTech Connect

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).

Johnson, Ross Stefan

2010-08-01

389

Dielectric breakdown in continuous models of metal-loaded dielectrics  

Microsoft Academic Search

We develop two- and three-dimensional models for breakdown of metal-loaded dielectrics based on the breakdown of random arrays of perfectly conducting cylinders and spheres embedded in a uniform dielectric and placed in a uniform external electric field. We determine the breakdown field, breakdown-path geometry, and dielectric constant as a function of metal packing fraction. The computer solution of Laplace's equation

Mark F. Gyure; Paul D. Beale

1992-01-01

390

Anisotropic effective permittivity of an ultrathin gold coating on optical fiber in air, water and saline solutions.  

PubMed

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

Zhou, Wenjun; Mandia, David J; Barry, Seán T; Albert, Jacques

2014-12-29

391

Accurate model for computing dielectric constant of dielectric nanocomposites  

NASA Astrophysics Data System (ADS)

In this paper, an accurate model for computing dielectric constant of dielectric nanocomposites is presented. The effect of interaction zone between the nanofiller and the resin material is calculated and taken into consideration in the developed model for polymer and ceramic resins. Also, the effect of filler volume fraction, filler dielectric constant and particle shape is studied through the proposed model. Finally, the validity of the proposed model for evaluating the dielectric constant of a uniform composite system of discrete particles dispersed within a matrix is achieved by comparison with experimental results. The proposed model shows simplicity and gives accurate results as compared to the other theoretical models.

Ezzat, M.; Sabiha, N. A.; Izzularab, M.

2014-03-01

392

Atomic layer deposition of hafnium oxide on germanium substrates  

NASA Astrophysics Data System (ADS)

Germanium combined with high-? dielectrics has recently been put forth by the semiconductor industry as potential replacement for planar silicon transistors, which are unlikely to accommodate the severe scaling requirements for sub-45-nm generations. Therefore, we have studied the atomic layer deposition (ALD) of HfO2 high-? dielectric layers on HF-cleaned Ge substrates. In this contribution, we describe the HfO2 growth characteristics, HfO2 bulk properties, and Ge interface. Substrate-enhanced HfO2 growth occurs: the growth per cycle is larger in the first reaction cycles than the steady growth per cycle of 0.04nm. The enhanced growth goes together with island growth, indicating that more than a monolayer coverage of HfO2 is required for a closed film. A closed HfO2 layer is achieved after depositing 4-5HfO2 monolayers, corresponding to about 25 ALD reaction cycles. Cross-sectional transmission electron microscopy images show that HfO2 layers thinner than 3nm are amorphous as deposited, while local epitaxial crystallization has occurred in thicker HfO2 films. Other HfO2 bulk properties are similar for Ge and Si substrates. According to this physical characterization study, HfO2 can be used in Ge-based devices as a gate oxide with physical thickness scaled down to 1.6nm.

Delabie, Annelies; Puurunen, Riikka L.; Brijs, Bert; Caymax, Matty; Conard, Thierry; Onsia, Bart; Richard, Olivier; Vandervorst, Wilfried; Zhao, Chao; Heyns, Marc M.; Meuris, Marc; Viitanen, Minna M.; Brongersma, Hidde H.; de Ridder, Marco; Goncharova, Lyudmila V.; Garfunkel, Eric; Gustafsson, Torgny; Tsai, Wilman

2005-03-01

393

Low-voltage zinc oxide thin-film transistors with solution-processed channel and dielectric layers below 150 °C  

NASA Astrophysics Data System (ADS)

In this letter, solution processed low voltage (<3 V) zinc oxide (ZnO) thin-film transistors with the maximum process temperature not exceeding 150 °C were achieved. In the devices, an ultra-thin zirconium oxide layer was formed as the gate dielectric via ultraviolet irradiation assisted sol-gel processes, and the ZnO channel was processed from an aqueous precursor of ammine-hydroxo zinc complex. The devices can be operated under a voltage of 3 V, and show decent device performance with the field effect mobility of 0.45 cm2/V . s and an ON/OFF current ratio of 105.

Xu, Xiaoli; Cui, Qingyu; Jin, Yizheng; Guo, Xiaojun

2012-11-01

394

Ultra-Thin Coatings Beautify Art  

NASA Technical Reports Server (NTRS)

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.

2013-01-01

395

Additive manufacturing of graded dielectrics  

NASA Astrophysics Data System (ADS)

A method for the fabrication of graded dielectrics within a structural composite is presented. This system employs an ultrasonic powder deposition head to print high dielectric powders onto a woven fabric composite substrate. It is shown how this system can integrate 3D variations of dielectric properties at millimeter resolution within a mechanically rugged substrate. To conclude, the system’s practical application is demonstrated with experimental results from a graded index lens.

Roper, David A.; Good, Brandon L.; McCauley, Raymond; Yarlagadda, Shridhar; Smith, Jared; Good, Austin; Pa, Peter; Mirotznik, Mark S.

2014-04-01

396

Morphology and structure of polymers in ultrathin films and constrained geometries  

NASA Astrophysics Data System (ADS)

We have explored the organization of polycaprolactone (PCL) constrained in ultrathin films and nanometer-scale domains. Specifically, PCL functionalized with triethoxysilane functional groups was used to create tethered ultrathin films on silicon (100) substrates through silanization, and a sol-gel reaction was used to produce PCL/silsesquioxane composites with nanoscale phase-separated domains. In the first case, analysis by AFM and ellipsometry showed the existence of an amorphous sublayer up to 4 nm thick. Above this, physisorbed PCL formed heterogeneous surface features, up to 7 nm thick, with the morphology dependent on the polymer solution concentration during the deposition process. Low PCL solution concentration produced amorphous globular domains, while higher polymer concentrations allowed the growth of dendritic crystalline features. We report the results of in situ thermal analysis of grafted PCL by AFM, which show the melting of the surface structures at the film surface as well as growth of new dendritic structures upon recrystallization. High tapping forces applied by the AFM tip revealed the presence of crystalline lamellae buried below an amorphous layer in the dendritic structures, as well as in the PCL sublayer when the film was cooled below room temperature. PCL phase separation behavior and morphology in sol-gel organic/inorganic nanocomposites with methylsilsesquioxane (MSSQ) or phenylsilsesquioxane (PSSQ) was probed using TEM, FTIR, and fluorescence spectroscopy of dansyl and pyrene-labeled PCL. Star-like and linear PCL were used to study the effects of molecular weight, endgroup functionality, and polymer geometry on the phase separation behavior in these materials. PCL crystallinity, as detected through FTIR, served to detect the presence of macroscopic phase separation, as well as the critical PCL loading amount at which this occurs, for a given PCL/SSQ system. Fluorescence spectroscopy of dansyl-labeled PCL detected the presence of an immobilized interfacial layer for PCL domains in MSSQ composites. While most PCL molecules proved to be highly compatible with PSSQ, linear PCL/MSSQ composites exhibited nanoscale phase separation only with low polymer content and low molecular weight. By contrast, star-like PCL/MSSQ nanocomposites possessed nanoscale domains with significant polymer loading, and hold the most promise for potential applications in the area of low-k dielectric insulators.

Gullerud, Steven Olaf

397

Technology and design aspects of ultra-thin silicon chips for bendable electronics  

Microsoft Academic Search

Plastic electronics, thin-film-transistors on foil and ultra-thin chips on foil are technologies currently pursued to support the strongly emerging market for flexible electronics. Ultra-thin CMOS chips in such systems will provide solutions whenever high circuit performance and\\/or complexity are required. Ultra-thin Si chips (6 to 20 mum) are fabricated by using a recently introduced technology based on the pre\\/post-process modules

Harald Richter; Horst D. Rempp; Mahadi-Ul Hassan; Christine Harendt; Nicoleta Wacker; M. Zimmermann; J. N. Burghartz

2009-01-01

398

Chemical crosslinking and biophysical properties of electrospun hyaluronic acid based ultra-thin fibrous membranes  

Microsoft Academic Search

Hyaluronic acid (HA) ultra-thin fibrous membranes by electrospinning technology had been fabricated successfully by our group. However, these HA fibrous membranes dissolve and decompose rapidly in water. In this study, chemical crosslinking of HA and HA based ultra-thin fibrous membranes was studied in detail. It was found that the chemically crosslinked pure HA ultra-thin fibrous membranes with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride

Shanshan Xu; Junxing Li; Aihua He; Wenwen Liu; Xingyu Jiang; Jianfen Zheng; Charles C. Han; Benjamin S. Hsiao; Benjamin Chu; Dufei Fang

2009-01-01

399

Dielectric waveguide lasers  

NASA Astrophysics Data System (ADS)

Our recent results on planar and channel waveguide fabrication and lasers in the dielectric oxide materials Ti:sapphire and rare-earth-ion-doped potassium yttrium double tungstate (KYW) are reviewed. We have employed waveguide fabrication methods such as liquid phase epitaxy and reactive ion etching as well as ion beam implantation and femtosecond laser writing. We have obtained surface and buried channel waveguide lasers in Ti:sapphire near 800 nm and planar waveguide lasers in KYW:Yb near 1 ?m and KYW:Tm near 2 ?m.

Pollnau, Markus

2007-06-01

400

Low Dielectric Polymers  

NASA Technical Reports Server (NTRS)

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.

Cassidy, Patrick E.

2002-01-01

401

The strip dielectric breakdown model  

Microsoft Academic Search

This paper reports on the analysis of the strip dielectric breakdown (DB) model for an electrically impermeable crack in a piezoelectric medium based on the general linear constitutive equations. The DB model assumes that the electric field in a strip ahead of the crack tip is equal to the dielectric breakdown strength, which is in analogy with the classical Dugdale

TONG-YI ZHANG; MING-HAO ZHAO; CUN-FA GAO

2005-01-01

402

Material dependent dielectric breakdown model  

Microsoft Academic Search

Dielectric breakdown in ceramics and composites has previously been determined by the dielectric breakdown model, dependent only on the electric field strength at a certain point and intermolecular distance in a lattice. This does not take into account quantum aspects of the lattice structure into account. The present model takes into account quantum variations of particles in conjunction with different

Khalil Arshak; Ivor Guiney; Edward Forde

2008-01-01

403

DIELECTRIC SPECTROSCOPY APPLICATIONS IN AGRICULTURE  

Technology Transfer Automated Retrieval System (TEKTRAN)

Permittivities, or dielectric properties, of agricultural products are of interest for sensing qualities of products, such as moisture content in cereal grain and oilseed crops. These properties are also necessary in studies on radio-frequency or microwave dielectric heating for processing or condi...

404

Voltage sensor and dielectric material  

DOEpatents

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.

Yakymyshyn, Christopher Paul; Yakymyshyn, Pamela Jane; Brubaker, Michael Allen

2006-10-17

405

DIELECTRIC-BASED MULTIPARAMETER SENSOR  

Technology Transfer Automated Retrieval System (TEKTRAN)

In the last few decades, microwave dielectric-based sensors were mainly developed for sensing moisture in different materials. The fact that these sensors rely on measurement of dielectric properties, which are also dependent on other physical properties of the material, make them potentially multi...

406

Dielectric Composites for Naval Applications  

NASA Astrophysics Data System (ADS)

As an integral part of the U.S. Navy's all-electric ship effort, the Naval Research Laboratory (NRL) has been developing advanced dielectrics to provide viable solutions for high energy density capacitors as well as high-dielectric-constant (K) filter capacitors. Our group at NRL has focused on ceramic and ceramic-based composite dielectrics, which are characterized by the high dielectric constant (from 200 to 4000) relative to polymer materials (typically <5) and high breakdown strengths (>200 kV/cm). This article details three approaches to creating high energy density and high-K-filter capacitor materials. These approaches use different processing routes to produce ceramic-based composite dielectrics and include freeze-casting, glass-ceramic, and nanocomposite technologies.

Gorzkowski, E. P.; Pan, M.-J.

2013-12-01

407

Dielectric laser accelerators  

NASA Astrophysics Data System (ADS)

The use of infrared lasers to power optical-scale lithographically fabricated particle accelerators is a developing area of research that has garnered increasing interest in recent years. The physics and technology of this approach is reviewed, which is referred to as dielectric laser acceleration (DLA). In the DLA scheme operating at typical laser pulse lengths of 0.1 to 1 ps, the laser damage fluences for robust dielectric materials correspond to peak surface electric fields in the GV /m regime. The corresponding accelerating field enhancement represents a potential reduction in active length of the accelerator between 1 and 2 orders of magnitude. Power sources for DLA-based accelerators (lasers) are less costly than microwave sources (klystrons) for equivalent average power levels due to wider availability and private sector investment. Because of the high laser-to-particle coupling efficiency, required pulse energies are consistent with tabletop microJoule class lasers. Combined with the very high (MHz) repetition rates these lasers can provide, the DLA approach appears promising for a variety of applications, including future high-energy physics colliders, compact light sources, and portable medical scanners and radiative therapy machines.

England, R. Joel; Noble, Robert J.; Bane, Karl; Dowell, David H.; Ng, Cho-Kuen; Spencer, James E.; Tantawi, Sami; Wu, Ziran; Byer, Robert L.; Peralta, Edgar; Soong, Ken; Chang, Chia-Ming; Montazeri, Behnam; Wolf, Stephen J.; Cowan, Benjamin; Dawson, Jay; Gai, Wei; Hommelhoff, Peter; Huang, Yen-Chieh; Jing, Chunguang; McGuinness, Christopher; Palmer, Robert B.; Naranjo, Brian; Rosenzweig, James; Travish, Gil; Mizrahi, Amit; Schachter, Levi; Sears, Christopher; Werner, Gregory R.; Yoder, Rodney B.

2014-10-01

408

Folded dielectric elastomer actuators  

NASA Astrophysics Data System (ADS)

Polymer-based linear actuators with contractile ability are currently demanded for several types of applications. Within the class of dielectric elastomer actuators, two basic configurations are available today for such a purpose: the multi-layer stack and the helical structure. The first consists of several layers of elementary planar actuators stacked in series mechanically and parallel electrically. The second configuration relies on a couple of helical compliant electrodes alternated with a couple of helical dielectrics. The fabrication of both these configurations presents some specific drawbacks today, arising from the peculiarity of each structure. Accordingly, the availability of simpler solutions may boost the short-term use of contractile actuators in practical applications. For this purpose, a new configuration is here described. It consists of a monolithic structure made of an electroded sheet, which is folded up and compacted. The resulting device is functionally equivalent to a multi-layer stack with interdigitated electrodes. However, with respect to a stack the new configuration is advantageously not discontinuous and can be manufactured in one single phase, avoiding layer-by-layer multi-step procedures. The development and preliminary testing of prototype samples of this new actuator made of a silicone elastomer are presented here.

Carpi, Federico; Salaris, Claudio; DeRossi, Danilo

2007-04-01

409

Magnetoelectric transport and quantum interference effect in ultrathin manganite films  

SciTech Connect

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.

Wang, Cong; Jin, Kui-juan, E-mail: kjjin@iphy.ac.cn; Gu, Lin; Lu, Hui-bin; Li, Shan-ming; Zhou, Wen-jia; Zhao, Rui-qiang; Guo, Hai-zhong; He, Meng; Yang, Guo-zhen [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

2014-04-21

410

Tunable ultrathin mantle cloak via varactor-diode-loaded metasurface.  

PubMed

We propose a tunable strategy for the ultrathin mantle cloak via metasurface. The tunable cloak is implemented by loading varactor diodes between two neighboring horizontal metallic strips which constitute the metasurface. We demonstrate that the varactor diodes enable the capacitive reactance of the metasurface to be tunable from -157 ? to -3 ? when the DC bias voltage is properly changed. The active metasurface is then explored to cloak conformally a conducting cylinder. Both numerical and experiment results show that the cloaking frequency can be continuously controlled from 2.3 GHz to 3.7 GHz by appropriately adjusting the bias voltage. The flexible tunability and good cloaking performance are further examined by the measured field distributions. The advanced features of tunability, low profile, and conformal ability of the ultrathin cloak pave the way for practical applications of cloaking devices. PMID:24921534

Liu, Shuo; Xu, He-Xiu; Zhang, Hao Chi; Cui, Tie Jun

2014-06-01

411

Effect of interfacial octahedral behavior in ultrathin manganite films.  

PubMed

We investigate structural coupling of the MnO6 octahedra across a film/substrate interface and the resultant changes of the physical properties of ultrathin La2/3Sr1/3MnO3 (LSMO) films. In order to isolate the effect of interfacial MnO6 octahedral behavior from that of epitaxial strain, LSMO films are grown on substrates with different symmetry and similar lattice parameters. Ultrathin LSMO films show an increased magnetization and electrical conductivity on cubic (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) compared to those grown on orthorhombic NdGaO3 (NGO) substrates, an effect that subsides as the thickness of the films is increased. This study demonstrates that interfacial structural coupling can play a critical role in the functional properties of oxide heterostructures. PMID:24697503

Moon, E J; Balachandran, P V; Kirby, B J; Keavney, D J; Sichel-Tissot, R J; Schlepütz, C M; Karapetrova, E; Cheng, X M; Rondinelli, J M; May, S J

2014-05-14

412

Ultrathin and lightweight organic solar cells with high flexibility  

PubMed Central

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??m 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

Kaltenbrunner, Martin; White, Matthew S.; G?owacki, Eric D.; Sekitani, Tsuyoshi; Someya, Takao; Sariciftci, Niyazi Serdar; Bauer, Siegfried

2012-01-01

413

Polarization switching kinetics in ultrathin ferroelectric barium titanate film  

NASA Astrophysics Data System (ADS)

The investigation of polarization switching kinetics in an ultrathin barium titanate film reveals true threshold switching at a large coercive electric field, evidence that switching is of intrinsic thermodynamic nature, rather than of extrinsic nature initiated by thermal nucleation, which has no true threshold field. The switching speed of a 7 nm thick epitaxial film exhibits a critical slowing as the threshold is approached from above, a key characteristic of intrinsic switching. In contrast, a bulk crystal exhibits nucleation-initiated switching, which has no threshold, and proceeds even at fields well below the nominal coercive field, which was determined independently from the polarization-electric field hysteresis loop. Previously, this phenomenon was only reported for ultrathin ferroelectric polymer Langmuir-Blodgett films. Since both the thermodynamic coercive field and the intrinsic switching kinetics are derived from the mean field theory of ferroelectricity, we expect that these phenomena will be found in other ferroelectric films at the nanoscale.

Gaynutdinov, R.; Minnekaev, M.; Mitko, S.; Tolstikhina, A.; Zenkevich, A.; Ducharme, S.; Fridkin, V.

2013-09-01

414

Ultrathin septuple layered PbBi2Se4 nanosheets.  

PubMed

Layered lead bismuth selenide, PbBi2Se4, an intergrowth compound of PbSe (rocksalt) and Bi2Se3 (hexagonal), is a topological insulator in the bulk phase. We present a simple solution based synthesis of two dimensional (2D) few seven atomic (septuple) layered PbBi2Se4 nanosheets (4-7 nm thick) for the first time. The excellent electrical transport in ultrathin PbBi2Se4 is attributed to the presence of dominant surface states that offer high electrical mobility (?153 cm(2) V(-1) s(-1)) and scattering resistant carriers. Ultrathin 3-5 SLs PbBi2Se4 shows an n-type semiconducting behaviour with a band gap of ?0.6 eV, which is confirmed by optical spectroscopy and thermopower measurements. PMID:24916418

Chatterjee, Arindom; Guin, Satya N; Biswas, Kanishka

2014-07-28

415

Dielectric Actuation of Polymers  

NASA Astrophysics Data System (ADS)

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 in tactile display is investigated by the prototyping of a large scale refreshable Braille display device. Braille is a critical way for the vision impaired community to learn literacy and improve life quality. Current piezoelectrics-based refreshable Braille display technologies are limited to up to 1 line of Braille text, due to the bulky size of bimorph actuators. Based on the unique actuation feature of BSEP, refreshable Braille display devices up to smartphone-size have been demonstrated by polymer sheet laminates. Dots in the devices can be individually controlled via incorporated field-driven BSEP actuators and Joule heater units. A composite material consisting of silver nanowires (AgNW) embedded in a polymer substrate is brought up as a compliant electrode candidate for BSEP application. The AgNW composite is highly conductive (Rs: 10 ?/sq) and remains conductive at strains as high as 140% (Rs: <10 3 ?/sq). The baseline conductivity has only small changes up to 90% strain, which makes it low enough for both field driving and stretchable Joule heating. An out-of-plane bistable area strain up to 68% under Joule heating is achieved.

Niu, Xiaofan

416

Anisotropic magnetoconductance in quench-condensed ultrathin beryllium films  

Microsoft Academic Search

Near the superconductor-insulator (S-I) transition, quench-condensed ultrathin Be films show a large magnetoconductance which is highly anisotropic in the direction of the applied field. Film conductance can drop as much as seven orders of magnitude in a weak perpendicular field (<=1 T), but is insensitive to a parallel field in the same field range. We believe that this negative magnetoconductance

E. Bielejec; Jinhao Ruan

2001-01-01

417

Ultra-thin flexible 100 V Chipfilm™ N-LDMOS  

Microsoft Academic Search

The cross-sectional structure of the fabricated ultra-thin NLDMOS transistor is shown in Fig.1. It comprises drain, source, and gate contacts as well as channel and drift regions and gate field-plate as the characteristic features. The n-drift region is rather deep (5 µm), considering the small chip thickness, in order to reduce the number of CMOS process steps by combining n-well

Ali Asif; Harald Richter; Christoph Comtesse; Joachim N. Burghartz

2011-01-01

418

DEFLECTIONS MEASURED ON EXPERIMENTAL ULTRA-THIN WHITETOPPING PAVEMENTS  

Microsoft Academic Search

In the spring of 1998, the Federal Highway Administration (FHWA) and the American Concrete Pavement Association (ACPA) jointly constructed eight full-scale lanes of ultra-thin whitetopping (UTW) over existing hot mix asphalt (HMA) pavements. These sections were placed at the FHWA's Pavement Test Facility, located at the Turner-Fairbank Highway Research Center in McLean, Virginia. The experiment employed various combinations of thickness,

Xicheng Qi; James A. Sherwood; FHWA Terry Mitchell

419

Intrinsic mechanical properties of ultra-thin amorphous carbon layers  

Microsoft Academic Search

In this work, we extracted the film's hardness (HF) of ultra-thin diamond-like carbon layers by simultaneously taking into account the tip blunting and the substrate effect. As compared to previous approaches, which did not consider tip blunting, this resulted in marked differences (30–100%) for the HF value of the thinner carbon coatings. We find that the nature of the substrate

P. Lemoine; J. P. Quinn; P. D. Maguire; J. F. Zhao; J. A. McLaughlin

2007-01-01

420

Ultra-thin film nanostructured gallium arsenide solar cells  

NASA Astrophysics Data System (ADS)

State-of-the-art III-V cells have reached the highest energy conversion efficiency among all types of solar cells. However, these cells are not applicable to widespread terrestrial solar energy system yet due to the high cost of epitaxial growth. Ultra-thin film absorbers with advanced light management is one of the most promising solutions to drive down the cost. In this paper, we present an ultra-thin film nano-window gallium arsenide (GaAs) solar cell design. This ultrathin cell consists of a nano-structured Al0.8Ga0.2As window layer on the front side to reduce the reflection and to trap the light, and a metal reflector on the back side to further increase the light path. The 300 nm thick GaAs cell with Al0.8Ga0.2As nano-window shows a broad band absorption enhancement from visible to near infrared (NIR), achieving a spectrally averaged absorption of 94% under normal incidence. In addition, this cell shows excellent angular absorption properties, achieving over 85% spectral averaged absorption at up to 60 degree off normal incidence. Meanwhile, this structure with planar junction and nano-window has solved the issue of low fill factor and low open-circuit voltage in nano-structured GaAs solar cell. A nano-window cell with a 3 ?m thick GaAs junction demonstrated an open circuit voltage of 0.9V.

Kang, Yangsen; Chen, Yusi; Huo, Yijie; Zhao, Li; Jia, Jieyang; Deng, Huiyang; Harris, James S.

2014-11-01

421

Magnetism and surface structure of atomically controlled ultrathin metal films.  

SciTech Connect

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.

Shiratsuchi, Yu.; Yamamoto, M.; Bader, S. D.; Materials Science Division; Osaka Univ.

2007-01-01

422

Simple and rapid synthesis of ultrathin gold nanowires, their self-assembly and application in surface-enhanced Raman scatteringw  

E-print Network

Simple and rapid synthesis of ultrathin gold nanowires, their self-assembly and application.1039/b822507a A simple and one-step method to rapidly synthesize single crystalline ultrathin gold nanowires at room temperature within a few hours has been developed, and the self-assembled ultrathin gold

Xing, Bengang

423

High Sensitivity Attenuated Total Reflection Fourier Transform Infrared Spectroscopy Study of Ultrathin ZrO2 Films: A Study of Phase Change  

SciTech Connect

Attenuated total reflection fourier transform infrared spectroscopy (FTIR ATR) was performed on ultrathin ZrO2 films as thin as {approx}3.0 nm deposited on silicon. An observed vibrational mode near 710 cm-1 undergoes a very pronounced absorption line shape change, corresponding to a structural phase change, as a function of film thickness and thermal processing. This absorption, attributed to the Eu(LO2) and A2u(LO) modes of tetragonal ZrO2, marks the first experimental measurement and verification of vibrational modes for tetragonal ZrO2 in this spectral range. The FTIR-ATR method shows promise as an extremely sensitive and nondestructive tool for high-kappa dielectric film characterization.

Sayan,S.; Chandler-Horowitz, D.; Nguyen, N.; Ehrstein, J.

2008-01-01

424

An electrode-free method of characterizing the microwave dielectric properties of high-permittivity thin films  

NASA Astrophysics Data System (ADS)

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 TE01? 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 ?'?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.

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

425

Dielectric elastomer cantilever beam sensor  

NASA Astrophysics Data System (ADS)

Dielectric elastomer sensors are a recent type of mechanical sensors utilized to detect forces, pressures and deformations. The sensors have several advantages compared with traditional sensors including high elasticity, capacitive sensing and inexpensive fabrication. In this paper, a new sensing device for measuring small concentrated force is proposed. The device deploys the dielectric membrane on the surface of cantilever beam of constant strength. The dielectric membrane is a capacitance sensor built with dielectric polymer coated with soft electrodes. The change in strain arising from the cantilever beam with concentrated force at free end can be quickly transferred to the dielectric membrane. The strain variation of the dielectric membrane induces the change in the capacitance of the membrane. Tests on the device show that the concentrated force at the free end of the cantilever beam is approximately proportional to the change in the capacitance. According to the relation, the unknown concentrated force can be obtained accurately by measuring the change in the capacitance of the dielectric membrane. The new device is capable of monitoring small concentrated force with prominent sensitivity.

Ni, Na; Zhang, Ling; Zhou, Jinxiong; Wang, Yin; Liu, Fan

2014-03-01

426

Ultrathin oxide films as templates for magnetic nanostructures  

NASA Astrophysics Data System (ADS)

The study of ultrathin oxide film as templates for magnetic nanostructures is presented. The ultrathin oxide thin films are investigated for the surface morphology, electronic properties, surface terminations, and ferroelectric properties by the combination of various local and non-local surface science techniques. Ultrathin oxide films, only a few unit cells in thickness, have significant advantages over bulk oxides, such as atomically defined, unreconstructed and stoichiometric surfaces. The high structural quality makes them suitable templates for the fabrication of metal-oxide heterostructures with unprecedented interface quality. This is expected to enable the studies of fundamental interactions between the oxide and metallic adsorbates, such as the theoretically predicted magnetoelectric coupling based on interfacial Fe-Ti bonds. Two kinds of oxide films, BaTiO3 and Cr2O3, are discussed. Scanning tunneling microscopy is utilized to investigate their structure and electronic properties. Firstly, studies of magnetism of Fe nanoclusters deposited on BaTiO3 by X-ray absorption and photoelectron spectroscopy demonstrate that the oxidization of Fe is largely suppressed by the molecular beam epitaxy growth at low temperature so that even isolated Fe atoms on the BaTiO 3 have significant magnetic moments. As a second example, the growth and characterization of ultrathin chromia film are discussed. The thin chromia films exhibit highly ordered and atomically smooth surfaces. The electronic structure is locally explored with scanning tunneling spectroscopy, to resolve surface termination and polarization. The presented studies on the ultrathin oxide films are expected to advance the fundamental understanding of interface effects in multiferroics and may help improving magneto-electric effects. In a third example, the formation of magnetic Co nanoclusters on boron nitride nanotemplates is analyzed. The analytic models and Monte-Carlo simulations for the analysis of the coverage of Co clusters show that interactions between particles are the determining factor in template-assisted cluster deposition experiments. Growth models are discussed that include inter-cluster interaction to describe the layer formation and predict layer filling.

Chen, Xumin

427

THE DIELECTRIC WALL ACCELERATOR  

SciTech Connect

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.

Caporaso, G J; Chen, Y; Sampayan, S E

2009-08-17

428

Lead Titanate Based Ferroelectric Superlattices with Conventional and Novel Dielectric Components  

NASA Astrophysics Data System (ADS)

Within the family of oxide materials which have a perovskite structure there are many different types of materials: ferroelectrics, metals, ferromagnets and antiferromagnets, superconductors, and dielectric insulators. Ferroelectric materials are those with a switchable, spontaneous electric polarization and by combining them with other perovskite oxides in a superlattice structure, the properties of the system can be tailored by exploiting competition between the interacting properties of the constituent materials. In ferroelectric/dielectric superlattices important structural and functional properties of the system can be tailored by the relative thicknesses of the ferroelectric and non-ferroelectric layers. In PbTiO3/SrTiO 3 superlattice SrTiO3, an insulator, plays the role of a conventional dielectric. Ferroelectric stripe domains in this system were investigated and it was found that the domain periodicity as a function of PbTiO3 layer thickness displays a scaling relation which raises interesting questions about the Kittel Scaling law as applied to ferroelectric superlattices. In addition to the static properties of the domains the evolution of domain structure under electric field was studied by time-resolved x-ray studies at the APS. A second system, PbTiO3/SrRuO3, uses SrRuO 3, which is normally metallic in bulk but displays insulating behavior in the ultrathin limit, as a novel dielectric component to create superlattices that display an out-of-plane ferroelectric polarization. The incorporation of SrRuO3 also breaks inversion symmetry at the interface between the two materials, which affects the ferroelectric double-well energy potential and the system's dielectric properties. The transport properties of this system are also of interest, with anisotropic conductivity and resonant tunneling between layers. This was investigated by electrical measurements and photoemission studies performed at NSLS U13.

Callori, Sara Jane

429

Physical and dielectric properties of pharmaceutical powders  

Microsoft Academic Search

The limited availability of published physical and dielectric property data for pharmaceutical powders hinders the design of processing systems, particularly dryers. In this study, the physical properties (solubility and boiling point) and dielectric properties, in terms of temperature rise, dielectric constant, and dielectric loss factor, of selected pharmaceutical powders were measured. The pharmaceutical actives, paracetamol and aspirin, and selected common

C. M McLoughlin; W. A. M McMinn; T. R. A Magee

2003-01-01

430

Effect of rapid thermal annealing on strain in ultrathin strained silicon on insulator layers  

E-print Network

Effect of rapid thermal annealing on strain in ultrathin strained silicon on insulator layers T. S March 2003; accepted 4 June 2003 The fabrication of ultrathin strained silicon directly on insulator on insulator layers were fabricated by epitaxial growth of strained silicon on relaxed SiGe, wafer bonding

431

Structural optimization for broadband scattering in several ultra-thin white beetle scales  

E-print Network

work, the scarab beetle Cyphochilus was reported to display brilliant whiteness from a layer of scalesStructural optimization for broadband scattering in several ultra-thin white beetle scales Stephen optimization for broadband scattering in several ultra-thin white beetle scales Stephen M. Luke,1, * Benny T

Exeter, University of

432

Noninvasive picosecond ultrasonic detection of ultrathin interfacial layers: CFx at the AVSi interface  

E-print Network

Noninvasive picosecond ultrasonic detection of ultrathin interfacial layers: CFx at the AVSi ultrasonics technique has been used to detect interfacial fluorocarbon (CF,) layers as thin as 0.5 nm between techniqueld based on pulsed picosecond ultrasonics which is sensitive to ultrathin interfacial layers

Rubloff, Gary W.

433

Transmission properties of terahertz pulses through an ultrathin subwavelength silicon hole array  

E-print Network

Transmission properties of terahertz pulses through an ultrathin subwavelength silicon hole array 30 March 2005 We demonstrate extraordinary THz transmission of an array of subwavelength apertures patterned on ultrathin highly doped silicon by reactive ion etching. The zero-order transmission spectra

434

CONCRETE REQUIREMENTS FOR ULTRA-THIN CONCRETE OVERLAYS (WHITETOPPING) FOR FLEXIBLE PAVEMENTS  

Microsoft Academic Search

SUMMARY Whitetopping solutions for old flexible asphalt pavement overlays have been a challange for highway agencies and designers in the recent past years, with special regards to ultra-thin concrete overlays, also called by ultra-thin whitetopping (UTW). Considering the needs of full bond between the UTW and the old asphalt concrete (AC) layer it is clear the impossibility of applying conventional

José T. Balbo; Marcos P. Rodolfo

435

The ultra-thin solar cells that could generate power through windows  

E-print Network

The ultra-thin solar cells that could generate power through windows By Claire Bates Last updated, generating enough electricity to power the GPS or air conditioning. Solar cells, which convert solar energy into tinted windows Page 1 of 3The ultra-thin solar cells that could generate power through windows | Mail

Rogers, John A.

436

White Organic Light-Emitting Diodes with fine chromaticity tuning via ultrathin layer position shifting  

E-print Network

White Organic Light-Emitting Diodes with fine chromaticity tuning via ultrathin layer position : Non-doped white organic light-emitting diodes using an ultrathin yellow-emitting layer of rubrene (5 via a bright white (WOLED) with CIE coordinates (x= 0.33, y= 0.32), a ext of 1.9%, and a color

Paris-Sud XI, Université de

437

A high-performance hydrogen gas sensor using ultrathin polypyrrole-coated CNT nanohybrids.  

PubMed

A novel strategy for designing ultrathin polypyrrole skin-coated carbon nanotube (CNT) nanohybrids is demonstrated by vapor deposition polymerization (VDP). The ultrathin skin technology provides a stable immobilization of the mono-disperse Pd nanoparticles (NPs) on the CP-CNT nanohybrid surface, leading to a high-performance hydrogen gas sensor at room temperature. PMID:23586080

Park, Seon Joo; Kwon, Oh Seok; Jang, Jyongsik

2013-05-21

438

Reliability of ultra-thin insulation coatings for long-term electrophysiological recordings  

NASA Astrophysics Data System (ADS)

Improved measurement of neural signals is needed for research into Alzheimer's, Parkinson's, epilepsy, strokes, and spinal cord injuries. At the heart of such instruments are microelectrodes that measure electrical signals in the body. Such electrodes must be small, stable, biocompatible, and robust. However, it is also important that they be easily implanted without causing substantial damage to surrounding tissue. Tissue damage can lead to the generation of immune responses that can interfere with the electrical measurement, preventing long-term recording. Recent advances in microfabrication and nanotechnology afford the opportunity to dramatically reduce the physical dimensions of recording electrodes, thereby minimizing insertion damage. However, one potential cause for concern is the reliability of the insulating coatings, applied to these ultra-fine-diameter wires to precisely control impedance. Such coatings are often polymeric and are applied everywhere but the sharpened tips of the wires, resulting in nominal impedances between 0.5 MOhms and 2.0 MOhms. However, during operation, the polymer degrades, changing the exposed area and the impedance. In this work, ultra-thin ceramic coatings were deposited as an alternative to polymer coatings. Processing conditions were varied to determine the effect of microstructure on measurement stability during two-electrode measurements in a standard buffer solution. Coatings were applied to seven different metals to determine any differences in performance due to the surface characteristics of the underlying wire. Sintering temperature and wire type had significant effects on coating degradation. Dielectric breakdown was also observed at relatively low voltages, indicating that test conditions must be carefully controlled to maximize reliability.

Hooker, S. A.

2006-03-01

439

Dielectric microscopy with submillimeter resolution  

E-print Network

In analogy with optical near-field scanning methods, we use tapered dielectric waveguides as probes for a millimeter wave vector network analyzer. By scanning thin samples between two such probes we are able to map the spatially varying dielectric properties of materials with sub-wavelength resolution; using a 150 GHz probe in transmision mode we see spatial resolution of around 500 microns. We have applied this method to a variety of highly heterogeneous materials. Here we show dielectric maps of granite and oil shale.

Nathan S. Greeney; John A. Scales

2007-06-20

440

Maxwell stress on a small dielectric sphere in a dielectric  

NASA Astrophysics Data System (ADS)

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.

Datsyuk, Vitaly V.; Pavlyniuk, Oleg R.

2015-02-01

441

Classical over-the-barrier model for neutralization of highly charged ions above thin dielectric films  

NASA Astrophysics Data System (ADS)

We apply the classical over-the-barrier (COB) model to charge transfer between highly charged ions (HCIs) and targets consisting of thin dielectric films on metals. Distances for the onset of classically allowed above-surface electron capture are obtained as a function of HCI charge state, film thickness, film permittivity, and film-metal electron binding energies. The model describes the crossover between the previously existing COB model for bulk metals and bulk dielectrics as the thickness of a dielectric film on a metal substrate increases through three distinct regimes. For ultrathin films with low permittivity and positive electron affinity, over-the-barrier charge transfer initiates from the metal electrons behind the film and critical distances are greater than those from bare metal targets. This result is consistent and compared with the recent observation of potential emission enhancement above thin C60 films on Au(111) with increasing film thickness [Bodewits, Hoekstra, Kowarik, Dobes, and Aumayr, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.84.042901 84, 042901 (2011)].

Lake, R. E.; Sosolik, C. E.; Pomeroy, J. M.

2013-06-01

442

Towards all-dielectric metamaterials and nanophotonics  

E-print Network

We review a new, rapidly developing field of all-dielectric nanophotonics which allows to control both magnetic and electric response of structured matter by engineering the Mie resonances in high-index dielectric nanoparticles. We discuss optical properties of such dielectric nanoparticles, methods of their fabrication, and also recent advances in all-dielectric metadevices including couple-resonator dielectric waveguides, nanoantennas, and metasurfaces.

Krasnok, Alexander; Petrov, Mikhail; Savelev, Roman; Belov, Pavel; Kivshar, Yuri

2015-01-01

443

Fractal Dimension of Dielectric Breakdown  

Microsoft Academic Search

It is shown that the simplest nontrivial stochastic model for dielectric breakdown naturally leads to fractal structures for the discharge pattern. Planar discharges are studied in detail and the results are compared with properly designed experiments.

L. Niemeyer; L. Pietronero; H. J. Wiesmann

1984-01-01

444

Linear dielectric-breakdown electrostatics  

NASA Astrophysics Data System (ADS)

The dielectric breakdown of solids is a problem of great practical and theoretical interest. It is the electrical analog of the fracture of solids under applied loads. In the case of fracture, the reigning theory for linear elastic materials is linear elastic fracture mechanics. This paper develops the analogous theory, linear dielectric-breakdown electrostatics, based on a Griffith-like energy-balance calculation applied to a single conducting crack in an isotropic dielectric medium. Results include the development of the critical field-intensity factor, Kec, and the introduction of a contour-independent line integral, Je, which is analogous to the J integral of linear and nonlinear elastic fracture mechanics. Some discussion of the relation between these results and recent lattice models of dielectric breakdown is given.

Garboczi, E. J.

1988-11-01

445

Infrared cubic dielectric resonator metamaterial.  

SciTech Connect

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.

Sinclair, Michael B.; Brener, Igal; Peters, David William; Ginn, James Cleveland, III; Ten Eyck, Gregory A.

2010-06-01

446

Conflicting theories of dielectric relaxation  

Microsoft Academic Search

Differences in theories of dielectric relaxation in polar liquids are shown, by thermodynamic analysis, to arise from artificial internal surface states associated with physical discontinuities in cavity model calculations.

S. H. Glarum

1972-01-01

447

Generalized dielectric permittivity of ice  

NASA Astrophysics Data System (ADS)

The generalized dielectric permittivity describes the electric response of both bound charges (normal dielectric constant) and free charges (conductivity). The generalized dielectric permittivity of ice (water) has been calculated within the model of classical quasiparticles as a function of the wave vector and frequency ?( q, ?). At zero wave vector and nonzero frequency, this function describes the response to a uniform alternating electric field, whereas at nonzero wave vector and zero frequency, it describes the screening of a static electric field. At simultaneously nonzero wave vector and frequency, it can be used to study electromagnetic waves in ice. In addition, the generalized dielectric permittivity allows the calculation of the dynamic correlation function of the electric polarization in terms of the fluctuation-dissipation theorem.

Klyuev, A. V.; Ryzhkin, I. A.; Ryzhkin, M. I.

2015-01-01

448

Linear dielectric-breakdown electrostatics  

Microsoft Academic Search

The dielectric breakdown of solids is a problem of great practical and theoretical interest. It is the electrical analog of the fracture of solids under applied loads. In the case of fracture, the reigning theory for linear elastic materials is linear elastic fracture mechanics. This paper develops the analogous theory, linear dielectric-breakdown electrostatics, based on a Griffith-like energy-balance calculation applied

E. J. Garboczi

1988-01-01

449

Graphene-graphite oxide field-effect transistors.  

PubMed

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, ? ? 4.3. PMID:22380722

Standley, Brian; Mendez, Anthony; Schmidgall, Emma; Bockrath, Marc

2012-03-14

450

Parity-time symmetry from stacking purely dielectric and magnetic slabs  

E-print Network

We show that Parity-time symmetry in matching electric permittivity to magnetic permeability can be established by considering an effective Parity operator involving both mirror symmetry and coupling between electric and magnetic fields. This approach extends the discussion of Parity-time symmetry to the situation with more than one material potential. We show that the band structure of a one-dimensional photonic crystal with alternating purely dielectric and purely magnetic slabs can undergo a phase transition between propagation modes and evanescent modes when the balanced gain/loss parameter is varied. The cross-matching between different material potentials also allows exceptional points of the constitutive matrix to appear in the long wavelength limit where they can be used to construct ultrathin metamaterials with unidirectional reflection.

Gear, James; Chu, S T; Rotter, Stefan; Li, Jensen

2015-01-01

451

Enhanced Performance Using an SU-8 Dielectric Interlayer in a Bulk Heterojunction Organic Solar Cell.  

PubMed

The effect of inserting an SU-8 dielectric interlayer into inverted bulk heterojunction (BHJ) organic solar cells (OSCs) was studied. Insertion of an ultrathin layer of SU-8 between the zinc oxide (ZnO) electron transport layer and the photoactive layer resulted in a smoother interface and a 14% enhancement in power conversion efficiency. The properties of devices with and without an SU-8 interlayer were investigated using transient photovoltage (TPV) and double injection (DoI) techniques, and it was found that devices with SU-8 show longer carrier lifetimes and greater mobility-lifetime (?-?) products than those without. Devices with SU-8 were also found to have improved stability. The results indicate that the insertion of an SU-8 interlayer reduces the recombination rate for photogenerated carriers without affecting the charge transport properties, improving overall performance and stability. PMID:25658649

Pang, Christina; Chellappan, Vijila; Yim, Jong Hyuk; Tan, Mein Jin; Goh, Glen Tai Wei; Lee, Soonil; Zhang, Jie; de Mello, John

2015-03-11

452

Parity-time symmetry from stacking purely dielectric and magnetic slabs  

NASA Astrophysics Data System (ADS)

We show that parity-time symmetry in matching electric permittivity to magnetic permeability can be established by considering an effective parity operator involving both mirror symmetry and coupling between electric and magnetic fields. This approach extends the discussion of parity-time symmetry to the situation with more than one material potential. We show that the band structure of a one-dimensional photonic crystal with alternating purely dielectric and purely magnetic slabs can undergo a phase transition between propagation modes and evanescent modes when the balanced gain or loss parameter is varied. The cross matching between different material potentials also allows exceptional points of the constitutive matrix to appear in the long-wavelength limit where they can be used to construct ultrathin metamaterials with unidirectional reflection.

Gear, James; Liu, Fu; Chu, S. T.; Rotter, Stefan; Li, Jensen

2015-03-01

453

Nonvolatile memory characteristics of WSi2 nanocrystals embedded in SiO2 dielectrics.  

PubMed

A nano-floating gate capacitor with WSi2 nanocrystals embedded in SiO2 dielectrics was fabricated. The WSi2 nanocrystals were created from ultrathin WSi2 film during rapid thermal annealing process and their average size and density were about 2.5 nm and 3.59 x 10(12) cm(-2), respectively. The flat-band voltage shift due to the carrier charging effect of WSi2 nanocrystals were measured up to 5.9 V when the gate voltage sweep in the range of +/- 9 V. The memory window was decreased from 3.7 V to 1.9 V after 1 h and remained about 3.7 V after 10(5) programming/erasing cycles. These results show that there is a possibility for the WSi2 nanocrystals to be applied to nonvolatile memory devices. PMID:21446472

Seo, Ki Bong; Lee, Dong Uk; Han, Seung Jong; Kim, Seon Pil; Kim, Eun Kyu

2011-01-01

454

One-way absorption of terahertz waves in rod-type and multilayer structures containing polar dielectrics  

NASA Astrophysics Data System (ADS)

One-way absorption can be obtained at terahertz frequencies in low-profile rod-type and multilayer dielectric structures with broken spatial inversion symmetry, which contain either a rod layer or an ultrathin homogeneous layer made of a polar dielectric. Perfect absorption for one of the two opposite incidence directions and perfect reflection for the other one are observed at the edge of the polaritonic gap in a wide range of the incident angle variation, when the thickness of the entire structure is of the order of the incident wavelength. Moreover, this regime appears in a wide frequency range, in which the forward-to-backward absorption contrast is strong. The exploited mechanism is connected with the parameter adjustment that enables the location of the polaritonic gap of the polar dielectric, of which the lossy part of the structure is made, inside the stop band arising due to the periodicity of the lossless part of the structure that is made of a nondispersive dielectric. It also exploits absorption enhancement in the lossy part by backing it with the highly reflecting lossless part, which has alternating stop and pass bands.

Serebryannikov, Andriy E.; Nojima, Shunji; Ozbay, Ekmel

2014-12-01

455

Conduction band states of transition metal (TM) high-k gate dielectrics as determined from X-ray absorption spectra  

E-print Network

V for ZrO2. Finally, the experimental spin­orbit splittings are 5.6 eV ± 0.3 eV for the Ti 2p states, 13 strengths for the d* and s* features in the p state spectra for TiO2, ZrO2 and HfO2 are markedly different for the ZrO2 M3 and M2 spectra, and are stronger for the HfO2 N2,3 spectra. 0026-2714/$ - see front matter Ó

456

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride  

E-print Network

of breakdown voltage with thickness. Based on the FNT model, the barrier height for tunneling (3.07 eV) and dielectric strength (7.94 MV/cm) of h-BN are obtained; these values are comparable to those of SiO2. VC 2011­3 These materials require ultra- flat and low-disorder dielectric layers for device fabrication. However, charged

Kim, Philip

457

Open dielectric branes  

NASA Astrophysics Data System (ADS)

We derive leading terms in the effective actions describing the coupling of bulk supergravity fields to systems of arbitrary numbers of Dp-branes and D(p+4)-branes in type-IIA/IIB string theory. We use these actions to investigate the physics of Dp-D(p+4) systems in the presence of weak background fields. In particular, we construct various solutions describing collections of Dp-branes blown up into open D(p+2)-branes ending on D(p+4)- branes. The configurations are stabilized by the presence of background fields and represent an open-brane analogue of the Myers dielectric effect. To deduce the D-brane actions, we use supersymmetry to derive operators corresponding to moments of various conserved currents in the Berkooz-Douglas matrix model of M-theory in the presence of longitudinal M5-branes and then use dualities to relate these operators to the worldvolume operators appearing in the Dp-D(p+4)-brane effective actions.

Van Raamsdonk, Mark

2002-02-01

458

Dielectric and permeability  

NASA Technical Reports Server (NTRS)

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.

Cole, K. D.

1982-01-01

459

Dielectric coated ion thruster  

SciTech Connect

This paper describes an ion accelerator apparatus. It comprises: a source of free electrons; a chamber connected to the source of free electrons; means for accelerating the free electrons within the chamber; means for introducing a flow of a gas comprising atoms having a neutral charge into the chamber, the accelerated free electrons colliding with the atoms of the gas causing valence shell electrons to be lost by the atoms, producing therefrom a plasma of positively charged ions; and a metallic grid plate comprising one wall of the chamber and provided with spaced apart perforations extending therethrough, the grid plate being coated on both its inner and outer sides with a layer of an insulating material having a much higher dielectric constant that the metallic grid plate, the grid plate being connected to an electric potential substantially more negative than the positively charged ions so that ions drifting into the vicinity of the metallic grid plate are accelerated toward it, passing out of the chamber through the perforations. The surface of the layer of insulating material on the inner side of the metallic grid plate has an electric potential approximately equal to that of the plasma and thus acting as a screen grid, both layers of insulating material protecting the metallic grid plate from erosion by charged ions and insulating the chamber against thermal and electrical losses.

Grim, D.; Lichon, P.G.

1990-06-26

460

Real-Time Deposition Monitor for Ultrathin Conductive Films  

NASA Technical Reports Server (NTRS)

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 continuous, real-time monitoring of film deposition. For use with different films, the device would need to be calibrated to provide an understanding of how film thickness is related to film conductivity, as the device is responding primarily to conductivity effects (and not to mass loading effects) in this ultrathin film regime.

Hines, Jacqueline

2011-01-01

461

An ultra-thin isotropic metamaterial thermal radiator  

NASA Astrophysics Data System (ADS)

We design an ultra-thin infrared metamaterial thermal radiator which has nearly isotropic emission pattern for a wide range of angles. Our design is achieved by overlapping both the electric and magnetic resonances in the spectral domain and is insensitive to both TE and TM polarizations. The thermal emission of the metamaterial is nearly isotropic in which the deviation in the angular emissivity is within 10% up to an angle of 75 degrees at the resonating wavelength of 2.86 ?m. Moreover, our metamaterial can be easily scaled to have different resonating wavelengths for efficient radiative cooling or thermal emission at different temperatures.

Zhou, Y.; Feng, T.; Liang, Z.; Li, J.; Liu, D.

2011-10-01

462

1% solar cells derived from ultrathin carbon nanotube photoabsorbing films  

NASA Astrophysics Data System (ADS)

Using a carbon nanotube photoabsorbing film <5 nm in thickness, we demonstrate a 1% solar cell. Specifically, polymer wrapped, highly monochiral (7, 5) nanotubes are implemented in a bilayered heterojunction with acceptor C60. The nanotubes drive 63% of the conversion, several times stronger than previously demonstrated. Peak external quantum efficiency (QE) of 43% at the nanotube bandgap (1055 nm) and power conversion efficiency of 0.95% and 1.02% at 1.0 and 1.5 suns, respectively, are achieved. The high internal QE from the ultrathin layers suggests that nanostructured or multijunction cells exploiting multiple nanotube layers will be many times more efficient.

Shea, Matthew J.; Arnold, Michael S.

2013-06-01

463

Ultrathin ?-FeOOH and ?-Fe2O3 nanowires  

NASA Astrophysics Data System (ADS)

We report the facile synthesis of ultrathin ?-FeOOH and ?-Fe2O3 nanowires with diameter of 2-3 nm. The ?-FeOOH nanowires show the unique optical properties attributed to the size- and shape-related quantum confinement effect. Upon heat treatment, they are transformed into ?-Fe2O3 nanowires, which exhibit the different magnetic properties compared with the previously reported ?-Fe2O3 nanostructures synthesized in silica matrices. The ?-Fe2O3 nanowires also exhibit high catalytic efficiency and hold potential for environmental-remediation applications.

Li, Shaozhou; Gan, Chee Lip

2014-11-01

464

Low thermal conductivity in ultrathin carbon nanotube (2, 1)  

PubMed Central

Molecular dynamic simulations reveal that the ultrathin carbon nanotube (CNT) (2, 1) with a reconstructed structure exhibits a surprisingly low thermal conductivity, which is only ~16–30% of those in regular CNTs, e.g. CNT (2, 2) and (5, 5). Detailed lattice dynamic calculations suggest that the acoustic phonon modes greatly soften in CNT (2, 1) as compared to regular CNTs. Moreover, both phonon group velocities and phonon lifetimes strikingly decrease in CNT (2, 1), which result in the remarkable reduction of thermal conductivity. Besides, isotope doping and chemical functionalization enable the further reduction of thermal conductivity in CNT (2, 1). PMID:24815003

Zhu, Liyan; Li, Baowen

2014-01-01

465

Interface defects of ultrathin rapid-thermal oxide on silicon  

NASA Astrophysics Data System (ADS)

We have used capacitance-voltage and electron paramagnetic resonance to measure interface defects in ultrathin (30 Å) SiO2 prepared by rapid-thermal oxidation. We observe a very narrow interface state peak in the upper portion of the Si band gap, as well as both Pb0 and Pb1 defects in the as-oxidized film. Forming-gas annealing removes the interface state and most of the Pb centers. However, from the energy level and charge state of the interface state peak, we argue that it cannot be reliably ascribed to either Pb0 or Pb1.

Stathis, J. H.; Buchanan, D. A.; Quinlan, D. L.; Parsons, A. H.; Kotecki, D. E.

1993-05-01

466

Design of an ultra-thin dual band infrared system  

NASA Astrophysics Data System (ADS)

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 3~12?m.

Du, Ke; Cheng, Xuemin; Lv, Qichao; Hu, YiFei

2014-11-01

467

Electronic and magnetic properties of ultrathin rhodium nanowires  

NASA Astrophysics Data System (ADS)

The structures of ultrathin rhodium nanowires are studied using empirical molecular dynamics simulations with a genetic algorithm. Helical multishell cylindrical and pentagonal packing structures are found. The electronic and magnetic properties of the rhodium nanowires are calculated using an spd tight-binding Hamiltonian in the unrestricted Hartree-Fock approximation. The average magnetic moment and electronic density of states are obtained. Our results indicate that the electronic and magnetic properties of the rhodium nanowires depend not only on the size of the wire but also on the atomic structure. In particular, centred pentagonal and hexagonal structures can be unusually ferromagnetic.

Wang, Baolin; Wang, Guanghou; Ren, Yun; Sun, Houqian; Chen, Xiaoshuang; Zhao, Jijun

2003-04-01

468

Asymmetric Orbital-Lattice Interactions in Ultrathin Correlated Oxide Films  

NASA Astrophysics Data System (ADS)

Using resonant x-ray spectroscopies combined with density functional calculations, we find an asymmetric biaxial strain-induced d-orbital response in ultrathin films of the correlated metal LaNiO3 which are not accessible in the bulk. The sign of the misfit strain governs the stability of an octahedral “breathing” distortion, which, in turn, produces an emergent charge-ordered ground state with an altered ligand-hole density and bond covalency. Control of this new mechanism opens a pathway to rational orbital engineering, providing a platform for artificially designed Mott materials.

Chakhalian, J.; Rondinelli, J. M.; Liu, Jian; Gray, B. A.; Kareev, M.; Moon, E. J.; Prasai, N.; Cohn, J. L.; Varela, M.; Tung, I. C.; Bedzyk, M. J.; Altendorf, S. G.; Strigari, F.; Dabrowski, B.; Tjeng, L. H.; Ryan, P. J.; Freeland, J. W.

2011-09-01

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