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1

TDDB characteristic and breakdown mechanism of ultra-thin SiO2/HfO2 bilayer gate dielectrics  

NASA Astrophysics Data System (ADS)

The characteristics of TDDB (time-dependent dielectric breakdown) and SILC (stress-induced leakage current) for an ultra-thin SiO2/HfO2 gate dielectric stack are studied. The EOT (equivalent-oxide-thickness) of the gate stack (Si/SiO2/HfO2/TiN/TiAl/TiN/W) is 0.91 nm. The field acceleration factor extracted in TDDB experiments is 1.59 s·cm/MV, and the maximum voltage is 1.06 V when the devices operate at 125 °C for ten years. A detailed study on the defect generation mechanism induced by SILC is presented to deeply understand the breakdown behavior. The trap energy levels can be calculated by the SILC peaks: one SILC peak is most likely to be caused by the neutral oxygen vacancy in the HfO2 bulk layer at 0.51 eV below the Si conduction band minimum; another SILC peak is induced by the interface traps, which are aligned with the silicon conduction band edge. Furthermore, the great difference between the two SILC peaks demonstrates that the degeneration of the high-k layer dominates the breakdown behavior of the extremely thin gate dielectric.

Fenfen, Tao; Hong, Yang; Bo, Tang; Zhaoyun, Tang; Yefeng, Xu; Jing, Xu; Qingpu, Wang; Jiang, Yan

2014-06-01

2

Characteristics of ultrathin HfO2 gate dielectrics on strained-Si0.74Ge0.26 layers  

NASA Astrophysics Data System (ADS)

The structural and electrical characteristics of HfO2 gate dielectrics along with the interfacial layers formed on strained-Si0.74Ge0.26 films have been investigated. The polycrystalline HfO2 film with a physical thickness of ˜4.0 nm and an amorphous Hf-silicate interfacial layer with a physical thickness of ˜4.5 nm have been observed by high-resolution transmission electron microscopy and time-of-flight secondary ion mass spectroscopy. The electrical properties have been studied using metal-oxide-semiconductor (MOS) structures. A dielectric constant of 26 for HfO2 film and 8.0 for Hf-silicate interfacial layer have been calculated from the accumulation capacitances of the capacitors. These dielectrics show an equivalent oxide thickness as low as 0.6 nm for HfO2 and 2.2 nm for the Hf-silicate layers. The fabricated SiGe MOS capacitors show a low leakage current density of ˜6.5×10-7 A/cm2 at a gate voltage of -1.0 V, breakdown field of 6.5 MV/cm, and moderately low interface state density of 5.5×1011 cm-2 eV-1.

Lee, Je-Hun; Maikap, S.; Kim, Doh-Y.; Mahapatra, R.; Ray, S. K.; No, Y. S.; Choi, Won-Kook

2003-07-01

3

Characteristics of sandwich-structured Al 2O 3/HfO 2/Al 2O 3 gate dielectric films on ultra-thin silicon-on-insulator substrates  

NASA Astrophysics Data System (ADS)

Sandwich-structure Al 2O 3/HfO 2/Al 2O 3 gate dielectric films were grown on ultra-thin silicon-on-insulator (SOI) substrates by vacuum electron beam evaporation (EB-PVD) method. AFM and TEM observations showed that the films remained amorphous even after post-annealing treatment at 950 °C with smooth surface and clean silicon interface. EDX- and XPS-analysis results revealed no silicate or silicide at the silicon interface. The equivalent oxide thickness was 3 nm and the dielectric constant was around 7.2, as determined by electrical measurements. A fixed charge density of 3 × 10 10 cm -2 and a leakage current of 5 × 10 -7A/cm 2 at 2 V gate bias were achieved for Au/gate stack /Si/SiO 2/Si/Au MIS capacitors. Post-annealing treatment was found to effectively reduce trap density, but increase in annealing temperature did not made any significant difference in the electrical performance.

Cheng, Xinhong; Song, Zhaorui; Jiang, Jun; Yu, Yuehui

2005-12-01

4

Effects of interfacial NH 3/N 2O-plasma treatment on the structural and electrical properties of ultra-thin HfO 2 gate dielectrics on p-Si substrates  

NASA Astrophysics Data System (ADS)

The interfacial characteristics of high- ? HfO 2 on NH 3- and N 2O-plasma treated p-Si substrates have been investigated using high-resolution transmission electron microscopy (HRTEM), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and auger electron spectroscopy (AES). NH 3- and N 2O-plasma treated films show the formation of a nitrogen-rich Hf-silicate interfacial layer between the deposited HfO 2 and Si substrates. The electrical characteristics have been studied using metal-oxide-semiconductor (MOS) structures. Interfacial nitrogen increases the capacitances by ˜33% for NH 3 and ˜47% for N 2O-treated Si as compared to the untreated surface. A dielectric constant of ˜26 for HfO 2 film, ˜6.0 for Hf-silicate, ˜9.0 for NH 3- and ˜11.0 for N 2O-treated interfacial layers have been calculated from the accumulation capacitances of the MOS capacitors. The relatively higher dielectric constant, lower capacitance equivalent thickness (CET), lower leakage current and higher breakdown voltage for N 2O-plasma treated film makes it attractive for scaled Si MOSFET applications.

Maikap, S.; Lee, Je-Hun; Mahapatra, R.; Pal, Samik; No, Y. S.; Choi, Won-Kook; Ray, S. K.; Kim, Doh-Y.

2005-04-01

5

Effect of plasma N2 and thermal NH3 nitridation in HfO2 for ultrathin equivalent oxide thickness  

NASA Astrophysics Data System (ADS)

Two methods of HfO2 nitridation including plasma N2 nitridation and thermal NH3 anneal were studied for ultrathin HfO2 gate dielectrics with <1 nm equivalent oxide thickness (EOT). The detailed nitridation mechanism, nitrogen depth profile, and nitrogen behavior during the anneal process were thoroughly investigated by XPS and SIMS analysis for the two types of nitridation processes at different process conditions. Intermediate metastable nitrogen was observed and found to be important during the plasma nitridation process. For thermal NH3 nitridation, pressure was found to be most critical to control the nitrogen profile while process time and temperature produced second order effects. The physical analyses on the impacts of various process conditions are well correlated to the electrical properties of the films, such as leakage current, EOT, mobility, and transistor bias temperature instability.

Dai, Min; Wang, Yanfeng; Shepard, Joseph; Liu, Jinping; Brodsky, Maryjane; Siddiqui, Shahab; Ronsheim, Paul; Ioannou, Dimitris P.; Reddy, Chandra; Henson, William; Krishnan, Siddarth; Narayanan, Vijay; Chudzik, Michael P.

2013-01-01

6

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

7

Electrical characteristics of highly reliable ultrathin hafnium oxide gate dielectric  

Microsoft Academic Search

Electrical and reliability properties of ultrathin HfO2 have been investigated. Pt electroded MOS capacitors with HfO2 gate dielectric (physical thickness ~45-135 Å and equivalent oxide thickness ~13.5-25 Å) were fabricated. HfO2 was deposited using reactive sputtering of a Hf target with O2 modulation technique. The leakage current of the 45 Å HfO2 sample was about 1×10-4 A\\/cm 2 at +1.0

Laegu Kang; Byoung Hun Lee; Wen-Jie Qi; Yongjoo Jeon; Renee Nieh; Sundar Gopalan; Katsunori Onishi; Jack C. Lee

2000-01-01

8

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

9

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

10

Interface studies of GaAs metal-oxide-semiconductor structures using atomic-layer-deposited HfO2/Al2O3 nanolaminate gate dielectric  

E-print Network

-layer-deposited HfO2/Al2O3 nanolaminates as gate dielectrics. A HfO2/Al2O3 nanolaminate gate dielectric improves Gd2O3 and ex situ atomic-layer-deposited ALD Al2O3 show promising results,1­6 a direct ALD HfO2 on ALD HfO2/Al2O3 nanolaminate gate dielectric on n- and p-type GaAs MOS devices, which combines

Ye, Peide "Peter"

11

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

12

Effect of hydrogen participation on the improvement in electrical characteristics of HfO2 gate dielectrics by post-deposition remote N2, N2/H2, and NH3 plasma treatments  

NASA Astrophysics Data System (ADS)

The structural and electrical characteristics of hafnium oxide (HfO2) gate dielectrics treated by a variety of post-deposition nitridation processes, including remote N2, N2/H2 and NH3 plasma, are presented by the x-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy and electrical measurements. The XPS measurement reveals that the nitrogen content in the HfO2 thin film treated by remote nitrogen and hydrogen plasma is higher than that treated only by remote nitrogen plasma, suggesting that the hydrogen has the capability to facilitate nitrogen dissociation. An ultra-thin interfacial layer (IL) thickness (˜0.3 nm), a high dielectric constant (20), an acceptable gate leakage current density (˜9 × 10-6 A cm-2), and a low capacitance equivalent thickness (1.9 nm) of the HfO2 gate dielectric were achieved by the post-deposition remote NH3 plasma nitridation treatment. However, an IL layer as thick as 1.5 nm was observed in the sample treated only by remote N2 plasma. The results indicate that the participation of hydrogen in the nitridation process is a promising way to improve the electrical properties of HfO2 gate dielectrics.

Huang, Li-Tien; Chang, Ming-Lun; Huang, Jhih-Jie; Kuo, Chin-Lung; Lin, Hsin-Chih; Liao, Ming-Han; Lee, Min-Hung; Chen, Miin-Jang

2013-02-01

13

First-Principles Studies of the Electronic and Dielectric Properties of Si/SiO2/HfO2 Interfaces  

NASA Astrophysics Data System (ADS)

In an effort to link first-principles electronic structure information with device-level modeling and simulations, first-principles calculations were performed to model Si/SiO2/HfO2 gate stacks, and models of their interfaces were developed. The electronic and dielectric properties, including the band edge and the local dielectric constant profiles, were investigated and found to display non-abrupt transitions at the hetero-material boundaries. The first-principles equivalent oxide thickness (EOT) parameter was introduced to represent the overall dielectric characteristics of the gate stack. The role of defects in the oxides was investigated by performing first-principles calculations of a Si/SiO2/HfO2 slab model with an oxygen vacancy near the SiO2/HfO2 interface. The oxygen vacancy was found to reduce the EOT.

Park, Yongjin; Kong, Ki-jeong; Chang, Hyunju; Shin, Mincheol

2013-04-01

14

High-performance p-channel LTPS-TFT using HfO2 gate dielectric and nitrogen ion implantation  

NASA Astrophysics Data System (ADS)

In this communication, a high-performance p-channel low-temperature poly-Si thin-film transistor with HfO2 gate dielectric and nitrogen ion implantation is demonstrated for the first time. A low threshold voltage VTH = -0.8 V, excellent subthreshold swing S.S. = 0.123 V/decade, high field effect mobility ?FE = 64.14 cm2 V-1 s-1 and high driving current IDsat = 9.14 µA µm-1 @ 3 V operation voltage of the p-channel LTPS-TFT can be achieved. The high performance characteristics are attributed to the very low effective oxide thickness EOT = 8.4 nm provided by the HfO2 gate dielectric and the passivation of effective interface states and grain boundary traps by the nitrogen ion implantation treatment. It would be very suitable for the application of a high-speed and low-power pixel-driving device in flat-panel displays.

Ma, Ming-Wen; Chiang, Tsung-Yu; Chao, Tien-Sheng; Lei, Tan-Fu

2009-07-01

15

HfO2 dielectrics engineering using low power SF6 plasma on InP and In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistors  

NASA Astrophysics Data System (ADS)

In this work, we demonstrate that device characteristics could be significantly improved by incorporating more fluorine (F) into HfO2 dielectrics layer using low power SF6 plasma treatment at different positions of gate oxide. Fluorine was incorporated in three ways: 4 min treatment from the top of 6 nm HfO2, 4 min treatment in the middle of 6 nm HfO2, or 2 min treatment each in the middle and from the top of HfO2 layer. Drive current (Id) and effective channel mobility could be improved by 70% and 51%, respectively, for devices with treatment both in the middle and from the top of HfO2 high ? layer compared to those of devices without SF6 treatment. The impact of SF6 plasma treatment on devices with HfO2/In0.53Ga0.47As stack is also presented.

Wang, Yanzhen; Chen, Yen-Ting; Xue, Fei; Zhou, Fei; Lee, Jack C.

2012-06-01

16

Effects of plasma nitridation of Al2O3 interlayer on thermal stability, fixed charge density, and interfacial trap states of HfO2 gate dielectric  

E-print Network

Effects of plasma nitridation of Al2O3 interlayer on thermal stability, fixed charge density 151-742, Korea Received 7 February 2003; accepted 19 May 2003 HfO2 /Al2O3 gate dielectric thin-film stacks were deposited on Si wafers using an atomic-layer-deposition technique. A 2.3-nm-thick Al2O3

Oh, Se-Jung

17

Composite HfO2/Al2O3-dielectric AlGaAs/InGaAs MOS-HEMTs by using RF sputtering/ozone water oxidation  

NASA Astrophysics Data System (ADS)

Composite HfO2/Al2O3-dielectric In0.2Ga0.8As/Al0.24Ga0.76As metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) by using RF sputtering/ozone water oxidization, respectively, are investigated. In comparison with a conventional Schottky-gate device on the same epitaxial structure, an Al2O3 liner was chemically formed for the present MOS-HEMT to improve interfacial quality and decrease gate leakages. Moreover, a high-k HfO2 layer was further deposited on the Al2O3 liner to enhance the gate modulation capability. The present MOS-HEMT with the devised HfO2/Al2O3 dielectric stack has demonstrated excellent switching characteristics, including superior subthreshold slope (S.S.) of 70 mV/dec and high drain-source current (IDS) on-off ratio of up to 6 orders. Improved direct-current (DC), radio-frequency (RF), and high-temperature device performances of the present design are also comprehensively studied in this work.

Lee, Ching-Sung; Liao, Yu-Hao; Chou, Bo-Yi; Liu, Han-Yin; Hsu, Wei-Chou

2014-08-01

18

Interfacial oxide determination and chemical/electrical structures of HfO 2/SiO x/Si gate dielectrics  

NASA Astrophysics Data System (ADS)

An expression that can be used to determine the thickness of an interfacial oxide layer between a high-K dielectric and Si substrate has been derived using the photoelectron intensity ratio of high resolution X-ray photoelectron spectroscopy (HRXPS). Experimental results show the interfacial silicon oxide thickness obtained with the expression fits very well with Ellipsometer measurements. We also studied the formation of an interfacial layer between a high-k HfO 2 film and a Si substrate as well as its thermal stability. The results have revealed that: (i) the interfacial oxide formation requires the existence of thermally energized oxygen in an environment to break the H-Si bonds first for hydrogen terminated Si surface and (ii) the thermodynamic stability of the oxide interfacial layer depends on its initial formation process. The valence band structures of Si, SiO 2, and HfO 2 have been analyzed using HRXPS and an energy band diagram of HfO 2/SiO 2/Si has been constructed.

Xie, L.; Zhao, Y.; White, M. H.

2004-11-01

19

HfO 2\\/spacer-interface breakdown in HfO 2 high- ?\\/poly-silicon gate stacks  

Microsoft Academic Search

The gate dielectric breakdown induced microstructral changes in HfO2 high-? gate stacks are analyzed using high resolution transmission electron microscopy. A new failure mechanism along the interface of HfO2\\/spacer has been observed in HfO2 high-? gate stacks. This breakdown which is more common in accumulation mode stressing conditions in HfO2 high-? \\/poly-Si gate stacks has not been observed in oxynitride

R. Ranjan; K. L. Pey; C. H. Tung; L. J. Tang; B. Elattari; T. Kauerauf; G. Groeseneken; R. Degraeve; D. S. Ang; L. K. Bera

2005-01-01

20

Influence of O2 flow rate on HfO2 gate dielectrics for back-gated graphene transistors  

NASA Astrophysics Data System (ADS)

HfO2 thin films deposited on Si substrate using electron beam evaporation, are evaluated for back-gated graphene transistors. The amount of O2 flow rate, during evaporation is optimized for 35 nm thick HfO2 films, to achieve the best optical, chemical and electrical properties. It has been observed that with increasing oxygen flow rate, thickness of the films increased and refractive index decreased due to increase in porosity resulting from the scattering of the evaporant. The films deposited at low O2 flow rates (1 and 3 SCCM) show better optical and compositional properties. The effects of post-deposition annealing and post-metallization annealing in forming gas ambience (FGA) on the optical and electrical properties of the films have been analyzed. The film deposited at 3 SCCM O2 flow rate shows the best properties as measured on MOS capacitors. To evaluate the performance of device properties, back-gated bilayer graphene transistors on HfO2 films deposited at two O2 flow rates of 3 and 20 SCCM have been fabricated and characterized. The transistor with HfO2 film deposited at 3 SCCM O2 flow rate shows better electrical properties consistent with the observations on MOS capacitor structures. This suggests that an optimum oxygen pressure is necessary to get good quality films for high performance devices.

Lakshmi Ganapathi, Kolla; Bhat, Navakanta; Mohan, Sangeneni

2014-05-01

21

Nucleation and growth study of atomic layer deposited HfO2 gate dielectrics resulting in improved scaling and electron mobility  

NASA Astrophysics Data System (ADS)

HfO2 films have been grown with two atomic layer deposition (ALD) chemistries: (a) tetrakis(ethylmethylamino)hafnium (TEMAHf)+O3 and (b) HfCl4+H2O. The resulting films were studied as a function of ALD cycle number on Si(100) surfaces prepared with chemical oxide, HF last, and NH3 annealing. TEMAHf+O3 growth is independent of surface preparation, while HfCl4+H2O shows a surface dependence. Rutherford backscattering shows that HfCl4+H2O coverage per cycle is l3% of a monolayer on chemical oxide while TEMAHf+O3 coverage per cycle is 23% of a monolayer independent of surface. Low energy ion scattering, x-ray reflectivity, and x-ray photoelectron spectroscopy were used to understand film continuity, density, and chemical bonding. TEMAHf+O3 ALD shows continuous films, density >9 g/cm3, and bulk Hf-O bonding after 15 cycles [physical thickness (Tphys)=1.2+/-0.2 nm] even on H-terminated Si(100). Conversely, on H-terminated Si(100), HfCl4+H2O requires 50 cycles (Tphys~3 nm) for continuous films and bulk Hf-O bonding. TEMAHf+O3 ALD was implemented in HfO2/TiN transistor gate stacks, over the range 1.2 nm<=Tphys<=3.3 nm. Electrical results are consistent with material analysis suggesting that at Tphys=1.2 nm HfO2 properties begin to deviate from thick film properties. At Tphys=1.2 nm, electrical thickness scaling slows, gate current density begins to deviate from scaling trendlines, and no hard dielectric breakdown occurs. Most importantly, n-channel transistors show improvement in peak and high field electron mobility as Tphys scales from 3.3 to 1.2 nm. This improvement may be attributed to reduced charge trapping and Coulomb scattering in thinner films. Scaled HfO2 enables 1 nm equivalent oxide thickness and 82% of universal SiO2 mobility.

Kirsch, P. D.; Quevedo-Lopez, M. A.; Li, H.-J.; Senzaki, Y.; Peterson, J. J.; Song, S. C.; Krishnan, S. A.; Moumen, N.; Barnett, J.; Bersuker, G.; Hung, P. Y.; Lee, B. H.; Lafford, T.; Wang, Q.; Gay, D.; Ekerdt, J. G.

2006-01-01

22

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

23

Atomic layer deposition of Y2O3 and yttrium-doped HfO2 using a newly synthesized Y(iPrCp)2(N-iPr-amd) precursor for a high permittivity gate dielectric  

NASA Astrophysics Data System (ADS)

We systematically investigated the effects of Y doping in HfO2 dielectric layer, focusing on structural phase transformation and the dielectric properties of the resultant films. Y doping was carried out using atomic layer deposition (ALD) with a novel Y(iPrCp)2(N-iPr-amd) precursor, which exhibits good thermal stability without any decomposition and clean evaporation. As a result, the ALD process of the Y2O3 films showed well-saturated and linear growth characteristics of ˜0.45 Å/cycle without significant incubation delays and produced pure Y2O3 films. Then, yttrium-doped HfO2 films with various Y/(Y + Hf) compositions (yttrium content: 0.6- 4.8 mol%) were prepared by alternating Y2O3 and HfO2 growth cycles. Structural and electrical characterization revealed that the addition of yttrium to HfO2 induced phase transformations from the monoclinic to the cubic or tetragonal phases, even at low post-annealing temperatures of 600 °C, and improved leakage current densities by inducing oxygen vacancy-related complex defects. A maximum relative dielectric constant of ˜33.4 was obtained for films with a yttrium content of ˜1.2 mol%. Excellent EOT scalability was observed down to ˜1 nm without dielectric constant degradation.

Lee, Jae-Seung; Kim, Woo-Hee; Oh, Il-Kwon; Kim, Min-Kyu; Lee, Gyeongho; Lee, Chang-Wan; Park, Jusang; Lansalot-Matras, Clement; Noh, Wontae; Kim, Hyungjun

2014-04-01

24

Quasi-breakdowns in ultrathin dielectrics  

NASA Astrophysics Data System (ADS)

In this paper, the quasi-breakdown is demonstrated to be a dominant failure mechanism in ultra-thin dielectrics with thicknesses less than 50 angstrom and should be considered as a reliability issue to avoid overestimation of dielectric breakdown. Under high stress current density (-Vg), the charge to catastrophic breakdown decreases with decreasing the oxide thickness because of dielectric breakdown in the structural transition layer existing SiO2/Si interface. But the Qbd rapidly increases again with decreasing the oxide thickness below 50 angstroms under low stress current density due to the difficulty in building up electric field to cause catastrophic breakdown through the localized conduction path induced by the quasi-breakdown prior to catastrophic breakdown. The quasi-breakdown was suppressed in NO-annealed oxide.

Min, Byoung W.; Kwong, Dim-Lee

1997-08-01

25

Controllable nitrogen incorporation in HfO2 films by modulating capacitively-combined inductively-coupled plasmas  

NASA Astrophysics Data System (ADS)

Capacitively-combined inductively-coupled nitrogen (N) plasma discharges were investigated to nitridize ultrathin HfO2 films (5 nm) for leakage improvement. The result of x-ray photoelectron spectroscopy analysis shows N incorporation into the HfO2 films. In terms of the plasma chemical and surface processes, nitridation samples show great improvements in surface structure and the leakage current property (it decreases from 4.6 × 10-4 to 2.1 × 10-7 A cm-2), while the leakage current is independent of the morphology. The radical concentration of N atoms increases with inductively-coupled plasma (ICP) power. This kind of capacitively-coupled plasma (CCP) combined with ICP modes is capable of modulating the electron energy probability functions (EEPFs) based on the power levels of ICP and can facilitate tuning of the N2 discharge dissociation characteristics. By modulating the EEPFs depending on the power levels of CCP and ICP, the radical concentration of the N atom increases by the electron-neutrals collision dependence on the high-energy electron, resulting in more N atoms incorporated in HfO2 films. The lower effective electron temperature and ion energy were obtained with ICP power, causing less film surface damage. Therefore, N atoms possess intrinsic effects that drastically reduce the electron leakage current through HfO2 dielectrics by deactivating the oxygen vacancy related gap states.

Jin, C. G.; Yang, Y.; Zhang, H. Y.; Huang, T. Y.; Wu, M. Z.; Zhuge, L. J.; Wu, X. M.; Ye, C.

2013-12-01

26

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

27

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

28

Low interfacial trap density and sub-nm equivalent oxide thickness in In0.53Ga0.47As (001) metal-oxide-semiconductor devices using molecular beam deposited HfO2/Al2O3 as gate dielectrics  

NASA Astrophysics Data System (ADS)

We investigated the passivation of In0.53Ga0.47As (001) surface by molecular beam epitaxy techniques. After growth of strained In0.53Ga0.47As on InP (001) substrate, HfO2/Al2O3 high-? oxide stacks have been deposited in-situ after surface reconstruction engineering. Excellent capacitance-voltage characteristics have been demonstrated along with low gate leakage currents. The interfacial density of states (Dit) of the Al2O3/In0.53Ga0.47As interface have been revealed by conductance measurement, indicating a downward Dit profile from the energy close to the valence band (medium 1012 cm-2eV-1) towards that close to the conduction band (1011 cm-2eV-1). The low Dit's are in good agreement with the high Fermi-level movement efficiency of greater than 80%. Moreover, excellent scalability of the HfO2 has been demonstrated as evidenced by the good dependence of capacitance oxide thickness on the HfO2 thickness (dielectric constant of HfO2 ˜20) and the remained low Dit's due to the thin Al2O3 passivation layer. The sample with HfO2 (3.4 nm)/Al2O3 (1.2 nm) as the gate dielectrics has exhibited an equivalent oxide thickness of ˜0.93 nm.

Chu, L. K.; Merckling, C.; Alian, A.; Dekoster, J.; Kwo, J.; Hong, M.; Caymax, M.; Heyns, M.

2011-07-01

29

Performance enhancement of metal-oxide-semiconductor tunneling temperature sensors with nanoscale oxides by employing ultrathin Al2O3 high-k dielectrics.  

PubMed

We demonstrated a promising route for enhancing temperature sensitivity, improving saturation voltage, and reducing power consumption of the MOS(p) tunneling temperature sensors by introducing ultrathin Al2O3 into the dielectric stacks. Detailed illustrations of the working mechanism and device concept are given in this work. Three kinds of MOS(p) tunneling temperature sensors with nanoscale SiO2, HfO2, and Al2O3 dielectrics were compared comprehensively. For Al2O3 MOS(p) devices with an equivalent oxide thickness of 2 nm, the sensing performance was effectively improved and the temperature-sensitive current-voltage characteristics are reliable and reproducible. The low-temperature processing Al2O3 MOS(p) tunneling temperature sensors are potential candidates for temperature monitoring sensors on chips or biomedical systems under low thermal budget processing consideration. PMID:23881221

Lin, Chien-Chih; Hwu, Jenn-Gwo

2013-09-01

30

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

31

Ultrathin hafnium oxide with low leakage and excellent reliability for alternative gate dielectric application  

Microsoft Academic Search

Physical, electrical and reliability characteristics of ultra thin HfO2 as an alternative gate dielectric were studied for the first time. Crucial process parameters of oxygen modulated dc magnetron sputtering were optimized to achieve an equivalent oxide thickness (EOT) of 11.5 Å without deducting the quantum mechanical effect. Leakage current was 3×10-2 A\\/cm2 at +1 V. Excellent dielectric properties such as

Byoung Hun Lee; Laegu Kang; Wen-Jie Qi; Renee Nieh; Yongjoo Jeon; Katsunori Onishi; J. C. Lee

1999-01-01

32

Thermal stability of HfO2 nanotube arrays  

SciTech Connect

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

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

2010-01-01

33

Impact of electrical stress on the electrical characteristics of 2 MeV electron irradiated metal-oxide-silicon capacitors with atomic layer deposited Al2O3, HfO2 and nanolaminated dielectrics  

NASA Astrophysics Data System (ADS)

In this work, the impact of electrical stress on the electrical characteristics of 2 MeV electron irradiated metal-oxide-silicon capacitors with atomic layer deposited (ALD) high permittivity (high-k) dielectric layers of Al2O3, HfO2 and a nanolaminate of them is evaluated. The aim is to investigate the susceptibility to electrical stress of the radiation effects created in irradiated MOS structures, paying especial attention to any possible interaction between the radiation-induced damage and the subsequent electrical stress degradation. For this study, MOS capacitors with a nominal dielectric physical thickness of 10 nm (equivalent oxide thickness (EOT) between 3 nm and 7 nm) on different p-type and n-type silicon substrates were investigated. An exponentially increasing stress current was forced to flow in accumulation through the different dielectric layers, registering the evolution of gate voltage versus stress time until dielectric breakdown occurred. Capacitance-voltage characteristics of the different irradiated and non-irradiated structures are analyzed as a function of electrical stress. Different charge trapping behaviors and significant polarity dependence in interface state generation are observed for the dielectric layers subjected to substrate and gate injections. No clear interaction between radiation and electrical stress damages is noticed under substrate injection (n-type samples). However, higher negative charge trapping near the metal/dielectric interface is registered for the irradiated Al2O3 and nanolaminate layers subjected to gate injection and, in the case of the most irradiated samples, the radiation-induced interface states damage is found to dominate against the damage generated in early stages of the electrical stress.

Rafí, J. M.; González, M. B.; Takakura, K.; Tsunoda, I.; Yoneoka, M.; Beldarrain, O.; Zabala, M.; Campabadal, F.

2013-11-01

34

Noise characterization of ALD HfO2 MOS capacitors with different metal (Au, Pd and Pt) gates  

NASA Astrophysics Data System (ADS)

Ultra-thin HfO2 high-k gate dielectric has been deposited directly on strained Si0.81Ge0.19 by atomic layer deposition (ALD). The effects of metal gate electrodes (Au, Pd and Pt) on dielectric properties and charge trapping behavior of metal-insulator-semiconductor (MIS) capacitors are investigated. Grazing incidence X-ray diffraction (GIXRD) analysis shows that the conversion from amorphous to crystalline phase start to appear in the HfO2 films when annealed between 400-500°C. The measured ?Vfband hysteresis in high frequency C-V characteristics are used to study the pre-existing traps in the dielectric. Low-frequency noise characteristics have been measured using MIS capacitors with contact area ~ 2×10-3 cm2. The power spectral densities (PSD) of the MIS capacitors with metal gate electrodes are compared and their bias dependencies are reported. While a two level random telegraph signal (RTS) is observed at low voltage, multilevel RTS is observed at higher bias voltages.

Mallik, S.; Mukherjee, C.; Mahata, C.; Dalapati, G. K.; Chi, D. Z.; Maiti, C. K.

2012-10-01

35

Thermal stability of HfO2-on-GaAs nanopatterns.  

PubMed

We have evaluated the effect of thermal annealing on the morphology, crystalline phase and elemental composition of high-k dielectric HfO(2)-on-GaAs nanopatterns at 500-620 °C by using atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS). While the HfO(2)-GaAs interface continues to be atomically abrupt at 620 °C, we have found a gradual shrinkage in the pattern linewidth and period with increasing temperature. Facet formation triggered by a nanoscale-modulated sequence of tensile and compressive stresses on the GaAs substrate, observed at 620 °C, has been attributed to a volumetric expansion of the HfO(2) nanostructures, caused by the tetragonal/cubic to monoclinic HfO(2) phase transformation and, to a lesser extent, by solid-state diffusion of As into HfO(2). PMID:22610587

Galiana, Beatriz; Benedicto, Marcos; Vázquez, Luis; Molina-Aldareguia, Jon M; Tejedor, Paloma

2012-06-21

36

Two-step annealing effects on ultrathin EOT higher-k (k = 40) ALD-HfO2 gate stacks  

NASA Astrophysics Data System (ADS)

Ultrathin HfO2 gate stacks with very high permittivity were fabricated by atomic layer deposition (ALD) and a novel two-step post-deposition annealing (PDA) technique. First, a no-cap pre-crystallization anneal degasses residual contaminations in the ALD layer, and second, a Ti-cap anneal enhances the permittivity of HfO2 by generating a cubic crystal phase. The Ti-cap layer simultaneously suppresses growth of interfacial SiO2 during annealing by absorbing residual oxygen released from HfO2. Using these techniques, the dielectric constant of the ALD-HfO2 could be enhanced to 40 for 2.4-4.0 nm HfO2 thickness.

Morita, Yukinori; Migita, Shinji; Mizubayashi, Wataru; Masahara, Meishoku; Ota, Hiroyuki

2013-06-01

37

Radiation Induced Charge Trapping in Ultrathin Based MOSFETs  

Microsoft Academic Search

Radiation induced charge trapping in ultrathin HfO2 -based n-channel MOSFETs is characterized as a function of dielectric thickness and irradiation bias following exposure to 10 keV X-rays and\\/or constant voltage stress. Positive and negative oxide-trap charges are observed, depending on irradiation and bias stress conditions. No significant interface-trap buildup is found in these devices under these irradiation and stress conditions.

Sriram K. Dixit; Xing J. Zhou; Ronald D. Schrimpf; Daniel M. Fleetwood; Sokrates T. Pantelides; Rino Choi; Gennadi Bersuker; Leonard C. Feldman

2007-01-01

38

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

39

Electron Trap Energy Distribution in HfO2 by the Discharge-Based Pulse I–V Technique  

NASA Astrophysics Data System (ADS)

The electron traps in HfO2 are a major concern of the reliability of metal-oxide-semiconductor field effect transistors (MOSFETs) beyond the 30 nm technology generation. In this work, the principle of the discharge-based pulse I–V technique is demonstrated in detail. By using this technique, the thorough energy distribution of electron traps across the 4 nm HfO2 layer is identified, which overcomes the shortcomings of the current techniques. It is observed that there are two peaks in HfO2. The large peak is at around 1.0 eV below the HfO2 conduction band bottom. The small peak is at about 1.43 eV below the HfO2 conduction band bottom. The results provide valuable information for theoretical modeling establishment, fast material assessment and process optimization for MOSFETs with high-k gate dielectrics.

Zheng, Xue-Feng; Fan, Shuang; Kang, Di; Zhang, Jian-Kun; Cao, Yan-Rong; Ma, Xiao-Hua; Hao, Yue

2014-12-01

40

Role of oxygen vacancies in HfO2-based gate stack breakdown  

NASA Astrophysics Data System (ADS)

We study the influence of multiple oxygen vacancy traps in the percolated dielectric on the postbreakdown random telegraph noise (RTN) digital fluctuations in HfO2-based metal-oxide-semiconductor transistors. Our electrical characterization results indicate that these digital fluctuations are triggered only beyond a certain gate stress voltage. First-principles calculations suggest the oxygen vacancies to be responsible for the formation of a subband in the forbidden band gap region, which affects the triggering voltage (VTRIG) for the RTN fluctuations and leads to a shrinkage of the HfO2 band gap.

Wu, X.; Migas, D. B.; Li, X.; Bosman, M.; Raghavan, N.; Borisenko, V. E.; Pey, K. L.

2010-04-01

41

Nucleation and growth of HfO2 layers on graphene by chemical vapor deposition  

NASA Astrophysics Data System (ADS)

We investigate a seed layer-free growth of HfO2 on commercially available chemical vapor deposited (CVD) graphene from various suppliers. It is revealed that the samples of monolayer graphene transferred from Cu to SiO2/Si substrates have different coverage with bi- and multi-layer graphene islands. We find that the distribution and number of such islands impact the nucleation and growth of HfO2 by CVD. In particular, we show that the edges and surface of densely distributed bi-layer graphene islands provide good nucleation sites for conformal CVD HfO2 layers. Dielectric constant of 16 is extracted from measurements on graphene-HfO2-TiN capacitors.

Lupina, Grzegorz; Lukosius, Mindaugas; Kitzmann, Julia; Dabrowski, Jarek; Wolff, Andre; Mehr, Wolfgang

2013-10-01

42

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

43

Improved thermal stability and device performance of ultra-thin (EOT<10 Å) gate dielectric MOSFETs by using hafnium oxynitride (HfOxNy)  

Microsoft Academic Search

Hafnium oxynitride (HfOxNy) film was prepared and characterized for gate dielectrics application with EOT<10 Å for the first time. Thermal stability and crystallization during the subsequent thermal process were improved significantly by using HfOxNy over HfO2. Furthermore, excellent transistor characteristics were obtained for both p and nMOSFETs.

Chang Seok Kang; H.-J. Cho; K. Onishi; R. Choi; R. Nieh; S. Goplan; S. Krishnan; J. C. Lee

2002-01-01

44

Annealing behavior of atomic layer deposited HfO2 films studied by synchrotron x-ray reflectivity and grazing incidence small angle scattering  

NASA Astrophysics Data System (ADS)

New results are presented for the annealing behavior of ultrathin complementary-metal-oxide-semiconductor (CMOS) gate dielectric HfO2 films grown by atomic layer deposition (ALD). A series of ALD HfO2 dielectric films has been studied by a combination of x-ray reflectivity (XRR) and grazing-incidence small-angle x-ray scattering (GISAXS) measurements. By using these techniques together, we have shown that the surface, interfaces, and internal structure of thin ALD films can be characterized with unprecedented sensitivity. Changes in film thickness, film roughness, or diffuseness of the film/substrate interface as measured by XRR are correlated with the corresponding changes in the internal film nanostructure, as measured by GISAXS. Although the films are dense, an internal film structure is shown to exist, attributed primarily to ?2 nm "missing island" porosity features close to the substrate; these are most likely associated with coalescence defects as a result of initial ALD growth, as they are not observed in the upper regions of the film. Some 8-9 nm heterogeneities are also present, which may indicate a widespread modulation in the film density pervading the entire film volume, and which likely also give rise to surface roughness. Comparison of the data between different scattering geometries and among a carefully designed sequence of samples has enabled important insights to be derived for the annealing behavior of the ALD HfO2 films. The main effects of single, brief, high temperature excursions to above 900 °C are to anneal out some of the fine voids and reduce the mean roughness and interfacial diffuseness of the film. These changes are indicative of densification. However, depending on the film thickness, the annealing behavior at temperatures between 650 and 800 °C is quite different for single excursion and cyclic anneals. Particularly for thin, just-coalesced films, XRR indicates marked increases in the film thickness and in the mean roughness/diffuseness dimension for cyclic anneals. GISAXS also shows an increase, rather than a reduction, in the void microstructure under these conditions. These changes in the film microstructure appear sufficient to overcome the expected film densification at elevated temperatures with implications for the gate dielectric performance of the films after extended high temperature exposure and cycling, as may occur during gate dielectric fabrication.

Green, M. L.; Allen, A. J.; Jordan-Sweet, J. L.; Ilavsky, J.

2009-05-01

45

Low standby power CMOS with HfO2 gate oxide for 100-nm generation  

Microsoft Academic Search

We have fabricated 55-nm poly-Si gated n- and p-MOSFETs with HfO2 gate dielectric of 3-nm physical thickness deposited by atomic layer deposition (ALD). A conventional CMOS process was used with high-temperature S\\/D anneal of ?1000°C, cobalt-silicide and pocket implants. The devices showed very promising characteristics for low standby power applications due to drastic reduction of gate leakage current.

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

2002-01-01

46

X-ray reflection spectroscopy of the HfO2/SiO2/Si system in the region of the O-K absorption edge  

E-print Network

1 X-ray reflection spectroscopy of the HfO2/SiO2/Si system in the region of the O-K absorption edge Keywords : 405 Reflection spec.; 541 X-ray absorption; 96 Dielectrics; 354 Oxides PACS : Reflection spectra, 78.40.nq; X-ray reflectometry, 61.10.Kw; Dielectric materials, 77.84.ns; Dielectric properties

Boyer, Edmond

47

Computational investigation of the phase stability and the electronic properties for Gd-doped HfO2  

NASA Astrophysics Data System (ADS)

Rare earth doping is an important approach to improve the desired properties of high-k gate dielectric oxides. We have carried out a comprehensive theoretical investigation on the phase stability, band gap, formation of oxygen vacancies, and dielectric properties for the Gd-doped HfO2. Our calculated results indicate that the tetragonal phase is more stable than the monoclinic phase when the Gd doping concentration is greater than 15.5%, which is in a good agreement with the experimental observations. The dopant's geometric effect is mainly responsible for the phase stability. The Gd doping enlarges the band gap of the material. The dielectric constant for the Gd-doped HfO2 is in the range of 20-30 that is suitable for high-k dielectric applications. The neutral oxygen vacancy formation energy is 3.2 eV lower in the doped material than in pure HfO2. We explain the experimental observation on the decrease of photoluminescence intensities in the Gd-doped HfO2 according to forming the dopant-oxygen vacancy complexes.

Wang, L. G.; Xiong, Y.; Xiao, W.; Cheng, L.; Du, J.; Tu, H.; van de Walle, A.

2014-05-01

48

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

E-print Network

and electron barriers.1 Recently, HfO2 received much attention among gate-dielectric materi- als of metal films are thermally stable and remain amorphous up to 900 °C.3­5 Charge trapping, a common phenomenon layer and/or its interfaces with silicon.6 Therefore, the related defects have been the subject

Gong, Xingao

49

Reduction of thermal damage in ultrathin gate oxides after intrinsic dielectric breakdown  

Microsoft Academic Search

We have compared the thermal damage in ultrathin gate SiO2 layers of 5.6 and 3 nm thickness after intrinsic dielectric breakdown due to constant voltage Fowler-Nordheim stress. The power dissipated through the metal-oxide-semiconductor capacitor during the breakdown transient, measured with high time resolution, strongly decreases with oxide thickness. This is reflected in a noticeable reduction of the thermal damage found

S. Lombardo; A. La Magna; I. Crupi; C. Gerardi; F. Crupi

2001-01-01

50

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

51

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

52

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

53

Autonomic self-healing lipid monolayer: a new class of ultrathin dielectric.  

PubMed

The electrical performance of stabilized lipid monolayers on H-terminated silicon is reported for the first time. We show that these 2.7 nm thick only ultrathin layers present extremely low current leakage at high electric field and high breakdown voltage that both compare favorably with the best data reported on organic thin film dielectrics. We demonstrate a very unique property of autonomic self-healing of the layer at room temperature with the total recovery of its performance after electrical breakdown. The mechanisms involved in breakdown and self-healing are described. PMID:21967619

Dumas, Carine; El Zein, Racha; Dallaporta, Hervé; Charrier, Anne M

2011-11-15

54

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

55

Thermal stability and structural characteristics of HfO2 films on Si (100) grown by atomic-layer deposition  

NASA Astrophysics Data System (ADS)

The thermal stability and structural characteristics for gate stack structure of HfO2 dielectrics deposited by atomic-layer deposition (ALD) were investigated. The structural characteristics and chemical state of the HfO2 films in relation to the film thickness and postannealing temperature were examined by x-ray diffraction and x-ray photoelectron spectroscopy. An interfacial layer of hafnium silicate with an amorphous structure was grown on the oxidized Si substrate at an initial growth stage. The structural characteristics of the HfO2 films are closely affected by the interfacial layer and are depended on the thickness of the films. The 45 A thick HfO2 film with an amorphous structure was changed into a polycrystalline structure after rapid temperature annealing of 750 degC for 5 min, while thicker films were grown into a polycrystalline structure of monoclinic or tetragonal crystal structure. The silicate layer grown at the interfacial region is not stable even at 700 degC under ultrahigh vacuum condition and changes into the silicide layers.

Cho, M.-H.; Roh, Y. S.; Whang, C. N.; Jeong, K.; Nahm, S. W.; Ko, D.-H.; Lee, J. H.; Lee, N. I.; Fujihara, K.

2002-07-01

56

Characteristics of Pentacene Organic Field-Effect Transistors with Self-Assembled-Monolayer-Treated HfO2 Gate Oxide  

NASA Astrophysics Data System (ADS)

In this study, the dependence of the crystal structure and dislocation distribution of pentacene on high-dielectric-constant hafnium oxide (HfO2) after surface modification is investigated. In addition to the analysis of pentacene layer such as crystal structure and grain size, the electrical characteristics of devices depending on surface modification are also investigated. As a surface modification of the HfO2 gate oxide, octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) are used. OTS monolayers with hydrophobic functional groups react stably on HfO2 film. They play an important role in decreasing the surface energy of HfO2 film to below about 45 mN/m. In addition, they significantly affect the crystal structure, dislocation distribution, and alignment of pentacene. As a result of OTS SAMs treatment, the mobility of pentacene devices was improved by the presence of a single thin-film phase that led to through the high ordering of pentacene molecules alignment and the lower scattering at the surface and dislocation.

Lee, Sunwoo; Lee, Sang Seol; Park, Jung Ho; Park, In-Sung; Ahn, Jinho

2009-06-01

57

A physically based compact gate CV model for ultrathin (EOT ?1 nm and below) gate dielectric MOS devices  

Microsoft Academic Search

A computationally efficient and accurate physically based gate capacitance model of MOS devices with advanced ultrathin equivalent oxide thickness (EOT) oxides (down to 0.5 nm explicitly considered here) is introduced for the current and near future integrated circuit technology nodes. In such a thin gate dielectric regime, the modeling of quantum-mechanical (QM) effects simply with the assumption of an infinite

Fei Li; Sivakumar Mudanai; Leonard Franklin Register; Sanjay K. Banerjee

2005-01-01

58

478 IEEE ELECTRON DEVICE LETTERS, VOL. 30, NO. 5, MAY 2009 HfO2III-Nitride RF Switch With  

E-print Network

dielectric and sur- face passivation layer. The new insulating-gate RF switch has a lower leakage current-power, reliable, and robust replacement of MEMS-based, pin-diode, and GaAs HEMT RF switches [1]­ [3478 IEEE ELECTRON DEVICE LETTERS, VOL. 30, NO. 5, MAY 2009 HfO2­III-Nitride RF Switch

Pala, Nezih

59

Low-voltage organic transistors and inverters with ultrathin fluoropolymer gate dielectric  

NASA Astrophysics Data System (ADS)

We report on the simple fabrication of hysteresis-free and electrically stable organic field-effect transistors (OFETs) and inverters operating at voltages <1-2 V, enabled by the almost trap-free interface between the organic semiconductor and an ultrathin (<20 nm) and highly insulating single-layer fluoropolymer gate dielectric (Cytop). OFETs with PTCDI-C13 (N,N'-ditridecylperylene-3,4,9,10-tetracarboxylicdiimide) as semiconductor exhibit outstanding transistor characteristics; very low threshold voltage (0.2 V), onset at 0 V, steep subthreshold swing (0.1-0.2 V/decade), no hysteresis, and excellent stability against gate bias stress. It is gratifying to notice that such small OFET operating voltages can be achieved with the relatively simple processing techniques employed in this study.

Walser, M. P.; Kalb, W. L.; Mathis, T.; Batlogg, B.

2009-12-01

60

Reduction of thermal damage in ultrathin gate oxides after intrinsic dielectric breakdown  

NASA Astrophysics Data System (ADS)

We have compared the thermal damage in ultrathin gate SiO2 layers of 5.6 and 3 nm thickness after intrinsic dielectric breakdown due to constant voltage Fowler-Nordheim stress. The power dissipated through the metal-oxide-semiconductor capacitor during the breakdown transient, measured with high time resolution, strongly decreases with oxide thickness. This is reflected in a noticeable reduction of the thermal damage found in the structure after breakdown. The effect can be explained as the consequence of the lower amount of defects present in the oxide at the breakdown instant and of the occurrence of a softer breakdown in the initial spot. The present data allow us to estimate the power threshold at the boundary between soft and hard breakdown, and they are compared to numerical simulations of heat flow.

Lombardo, S.; La Magna, A.; Crupi, I.; Gerardi, C.; Crupi, F.

2001-09-01

61

Breakdown voltage of ultrathin dielectric film subject to electrostatic discharge stress  

NASA Astrophysics Data System (ADS)

Ultrathin silicon oxide film for nano-electromechanical system (NEMS) applications is investigated under electrostatic discharge (ESD) stress using a transmission line pulse (TLP) tester. The measured breakdown voltage and transient response are analyzed. The results show that the voltage stress time has a significant effect on the breakdown voltage. By shortening the stress time, the breakdown voltage increases by 2-3 times. With the area shrinking breakdown voltage increases, and there is a critical value, below which the breakdown voltage increases dramatically with decreasing area. It is possible to enhance the ESD robustness by using a multiple small-area dielectric layer structure. Shorten ESD pulse rise-time induces a higher overshoot current and then accelerates oxide failure, resulting in a lower breakdown voltage for a faster pulse.

Jin, Hao; Dong, Shurong; Miao, Meng; Jei Liou, Juin; Yang, Cary Y.

2011-09-01

62

Room Temperature Growth of Cu on HfON and HfO2  

Microsoft Academic Search

The room temperature growth and annealing of ultrathin copper films on hafnium dioxide and hafnium oxinitride dielectric films was studied using Scanning Tunneling Microscopy (STM). The dielectric films were specially prepared on Si(100) substrates. Thermal annealing was done at 300 C and 500 C. We report on the initial nucleation of copper, and the effects of annealing on the surface

I. A. Akwani; J. Lozano; K. R. Kimberlin; K. R. Roos

2003-01-01

63

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

64

Transport properties of HfO2 top-gated bilayer graphene field effect transistors  

NASA Astrophysics Data System (ADS)

We present the fabrication and electrical transport studies of SiO2/HfO2 double-gated bilayer graphene field effect transistors (FETs). The top gate dielectric layer is formed by depositing 30nm HfO2 onto graphene FETs fabricated on conventional SiO2/doped Si substrates, using low temperature atomic layer deposition without the use of an adhesion layer. The top gate has an excellent gating efficiency of ˜2.8x10^12/cm^2V, which is 40 times larger than that of the Si backgate and can reach carrier density 1.4x10^ 13/cm^2. We observe electron mobility up to 6,000 cm^2 /Vs in double-gated bilayers. Pristine bilayer graphene on SiO2, on the other hand, exhibits ? = 12,000 cm^2 /Vs. We report and discuss the temperature-dependent conductivity in double and single-gated bilayer graphene at different densities and bias electric fields.

Zou, K.; Zhu, J.

2010-03-01

65

Structural and surface potential characterization of annealed HfO2 and (HfO2)x(SiO2)1-x films  

NASA Astrophysics Data System (ADS)

The evolution of the microscopic electrical properties of hafnium oxide and hafnium silicate films with high temperature anneals and their relationship to morphological changes is reported. The as-grown, amorphous 3nm thick HfO2 and 2.2nm thick Hf0.78Si0.22O2 layers were deposited ex situ on Si (100) by atomic layer deposition and metal organic vapor deposition, respectively, and annealed in situ in ultra high vacuum. A noncontact atomic force microscope operating in the electrostatic force mode was used to image the topography, contact potential difference (CPD), and differential capacitance. The as-grown and annealed films essentially retained their smoothness even after undergoing crystallization; rms roughness of ˜0.13nm for HfO2 and 0.077nm for the 900°C annealed Hf0.78Si0.22O2 layer were measured. These values compare favorably with state-of-the-art rapid thermal oxidation and nitrided SiO2 gate oxides. CPD or surface potential fluctuations of up to 0.3-0.4V were observed in images of area 200×200nm2; values that did not change appreciably with annealing. A lack of correlation between topographic and CPD image features for the as-grown amorphous samples changed dramatically once the films crystallized, with higher CPD values associated with grain boundaries for both oxide and silicate layers. CPD variations were about a factor of 2 larger than for SiO2 gate oxides. Differential capacitance images reflected mainly topographic surface features, as the high ? inhibits image contrast in the images for small to moderate changes in ?. Nevertheless, for the Hf0.78Si0.22O2 sample annealed at 900°C, which exhibited the lowest roughness, increase in differential capacitance could be attributed to microstructures of high-? material, most likely HfO2, which phase separated during the anneal. Because of screening, the high ? dielectric also tends to suppress contributions of isolated charges to the CPD image. A spherical tip model is presented that supports these observations.

Ludeke, R.; Gusev, E.

2004-08-01

66

Materials characterization of ZrO2-SiO2 and HfO2-SiO2 binary oxides deposited by chemical solution deposition  

NASA Astrophysics Data System (ADS)

The thermal stability, microstructure, and electrical properties of xZrO2?(100-x)SiO2 (ZSO) and xHfO2?(100-x)SiO2 (HSO) (x=15%, 25%, 50%, and 75%) binary oxides were evaluated to help assess their suitability as a replacement for silicon dioxide gate dielectrics in complementary metal-oxide-semiconductor transistors. The films were prepared by chemical solution deposition using a solution prepared from a mixture of zirconium, hafnium, and silicon butoxyethoxides dissolved in butoxyethanol. The films were spun onto SiOxNy coated Si wafers and furnace annealed at temperatures from 500 to 1200 °C in oxygen for 30-60 min. The microstructure and electrical properties of ZSO and HSO films were examined as a function of the Zr/Si and Hf/Si ratio and annealing temperature. The films were characterized by x-ray diffraction, mid- and far-Fourier transform infrared (FTIR), Rutherford backscattering spectroscopy, and Auger electron spectroscopy. At ZrO2 or HfO2 concentrations ?50%, phase separation and crystallization of tetragonal ZrO2 or HfO2 were observed at 800 °C. At ZrO2 or HfO2 concentrations ? 25%, phase separation and crystallization of tetragonal ZrO2 or HfO2 were observed at 1000 °C. As the annealing temperature increased, a progressive change in microstructure was observed in the FTIR spectra. Additionally, the FTIR spectra suggest that HfO2 is far more disruptive of the silica network than ZrO2 even at HfO2 concentrations ?25%. The dielectric constants of the 25%, 50%, and 75% ZSO films were measured and were observed to be less than the linear combination of ZrO2 and SiO2 dielectric constants. The dielectric constant was also observed to increase with increasing ZrO2 content. The dielectric constant was also observed to be annealing temperature dependent with larger dielectric constants observed in nonphase separated films. The Clausius-Mossoti equation and a simple capacitor model for a phase separated system were observed to fit the data with the prediction that to achieve a dielectric constant larger than 10 doping concentrations of ZrO2 would have to be greater than 70%.

Neumayer, D. A.; Cartier, E.

2001-08-01

67

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

68

The effect of a HfO2 insulator on the improvement of breakdown voltage in field-plated GaN-based HEMT  

NASA Astrophysics Data System (ADS)

A GaN/Al0.3Ga0.7N/AlN/GaN high-electron mobility transistor utilizing a field plate (with a 0.3 ?m overhang towards the drain and a 0.2 ?m overhang towards the source) over a 165-nm sputtered HfO2 insulator (HfO2-FP-HEMT) is fabricated on a sapphire substrate. Compared with the conventional field-plated HEMT, which has the same geometric structure but uses a 60-nm SiN insulator beneath the field plate (SiN-FP-HEMT), the HfO2-FP-HEMT exhibits a significant improvement of the breakdown voltage (up to 181 V) as well as a record field-plate efficiency (up to 276 V/?m). This is because the HfO2 insulator can further improve the modulation of the field plate on the electric field distribution in the device channel, which is proved by the numerical simulation results. Based on the simulation results, a novel approach named the proportional design is proposed to predict the optimal dielectric thickness beneath the field plate. It can simplify the field-plated HEMT design significantly.

Mao, Wei; Yang, Cui; Hao, Yue; Ma, Xiao-Hua; Wang, Chong; Zhang, Jin-Cheng; Liu, Hong-Xia; Bi, Zhi-Wei; Xu, Sheng-Rui; Yang, Lin-An; Yang, Ling; Zhang, Kai; Zhang, Nai-Qian; Pei, Yi

2011-09-01

69

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

70

Flat band voltage (VFB) modulation by controlling compositional depth profile in La2O3/HfO2 nanolaminate gate oxide  

NASA Astrophysics Data System (ADS)

We investigated the flat band voltage (VFB) modulation by insertion of lanthanum oxide (La2O3) into hafnium oxide (HfO2) gate dielectrics. The properties of La2O3/HfO2 nanolaminates were precisely modulated by controlling the position of La2O3 layer at bottom, middle, or top using atomic layer deposition. When the La2O3 layer was positioned closer to the interface (bottom), the reduction in VFB shift was more effective than the other two cases (middle and top). From our experimental results, we propose that the main mechanism of VFB modulation using La2O3 layer is dipole moment formation at an interfacial layer between high k gate dielectric and Si substrate.

Maeng, W. J.; Kim, Woo-Hee; Kim, Hyungjun

2010-04-01

71

Electrical properties of HfO2 deposited via atomic layer deposition using Hf(NO3)4 and H2O  

NASA Astrophysics Data System (ADS)

We report on the electrical properties of HfO2 deposited via atomic layer deposition using Hf(NO3)4 precursor for metal/oxide/semiconductor gate dielectric applications. Thin films, with less than 1% variation in accumulation capacitance over a 150 mm wafer, have been deposited directly on hydrogen-terminated Si wafers. The effective dielectric constant of thin (<10 nm) films was in the range of ?eff=10-12, the breakdown voltage was about 6-9 MV/cm, and the leakage current was between 3-6 orders of magnitude lower than that of SiO2. The relative benefit of lower leakage current of HfO2 over SiO2 decreased with decreasing effective thickness. Electron trapping was observed under constant voltage stressing.

Conley, J. F.; Ono, Y.; Solanki, R.; Stecker, G.; Zhuang, W.

2003-05-01

72

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

73

Modification of electronic properties of top-gated graphene devices by ultrathin yttrium-oxide dielectric layers  

NASA Astrophysics Data System (ADS)

We report the structure characterization and electronic property modification of single layer graphene (SLG) field-effect transistor (FET) devices top-gated using ultrathin Y2O3 as dielectric layers. Based on the Boltzmann transport theory within variant screening, Coulomb scattering is confirmed quantitatively to be dominant in Y2O3-covered SLG and a very few short-range impurities have been introduced by Y2O3. Both DC transport and AC capacitance measurements carried out at cryogenic temperatures demonstrate that the broadening of Landau levels is mainly due to the additional charged impurities and inhomogeneity of carriers induced by Y2O3 layers.

Wang, Lin; Chen, Xiaolong; Wang, Yang; Wu, Zefei; Li, Wei; Han, Yu; Zhang, Mingwei; He, Yuheng; Zhu, Chao; Fung, Kwok Kwong; Wang, Ning

2013-01-01

74

Modification of electronic properties of top-gated graphene devices by ultrathin yttrium-oxide dielectric layers.  

PubMed

We report the structure characterization and electronic property modification of single layer graphene (SLG) field-effect transistor (FET) devices top-gated using ultrathin Y(2)O(3) as dielectric layers. Based on the Boltzmann transport theory within variant screening, Coulomb scattering is confirmed quantitatively to be dominant in Y(2)O(3)-covered SLG and a very few short-range impurities have been introduced by Y(2)O(3). Both DC transport and AC capacitance measurements carried out at cryogenic temperatures demonstrate that the broadening of Landau levels is mainly due to the additional charged impurities and inhomogeneity of carriers induced by Y(2)O(3) layers. PMID:23263255

Wang, Lin; Chen, Xiaolong; Wang, Yang; Wu, Zefei; Li, Wei; Han, Yu; Zhang, Mingwei; He, Yuheng; Zhu, Chao; Fung, Kwok Kwong; Wang, Ning

2013-02-01

75

Semiconducting ZnO effect on Maxwell–Wagner relaxation in HfO2/ZnO nanolaminates fabricated by atomic layer deposition  

NASA Astrophysics Data System (ADS)

Amorphous nanolaminates (NLs) consisting of alternate HfO2 and ZnO oxide sublayers were prepared using an atomic layer deposition method. Cross-sectional transmission electron microscopy observations reveal the existence of high-quality interfaces in the NLs. Dielectric properties are shown to depend more strongly on the ZnO sublayer thickness with respect to the number of interfaces. With increasing the ZnO thickness in the (1.7?nm) HfO2/ZnO NLs, the enhanced permittivity is clearly observed despite the same or an even lower number of interfaces, and the large permittivity persists up to 105–106?Hz, followed by a step-like decrease at the higher frequency. Frequency dependence of dielectric loss is combined with a complex impedance analysis to understand the physical origin underlying the enhancement of permittivity and the effect of the ZnO sublayer thickness. It suggests that the enhancement be attributed to the presence of numerous charge carriers in the ZnO semiconducting sublayer, which results in a large accumulation of the charges at the HfO2/ZnO interfaces through Maxwell–Wagner relaxation. The present work proves an effective way for improving dielectric properties by increasing the electrical conductivity of one of the sublayers in laminating systems.

Zhang, Qiannan; Li, Jin; Bi, Xiaofang

2014-12-01

76

Intrinsic versus extrinsic ferromagnetism in HfO2 -x and Ni: HfO 2 -x thin films  

NASA Astrophysics Data System (ADS)

We have investigated the possible evolution of an intrinsic stable ferromagnetic moment in oxygen deficient undoped and magnetically doped HfO2 -x thin films grown by reactive molecular beam epitaxy. Neither oxygen vacancies nor substituted Ni in combination with such vacancies results in an observable magnetic moment for a broad range of oxygen vacancy concentrations. By combining integral and element specific magnetization measurements, we show that a fluctuating deposition rate of the magnetic dopant induces extrinsic ferromagnetism by promoting the formation of metallic clusters. We suggest the element specific measurement of an induced magnetic moment at the nonmagnetic site as a proof of intrinsic ferromagnetism in diluted magnetic semiconductors.

Hildebrandt, Erwin; Yazdi, Mehrdad Baghaie; Kurian, Jose; Sharath, S. U.; Wilhelm, Fabrice; Rogalev, Andrei; Alff, Lambert

2014-10-01

77

Rare-earth-doped HfO2 nanoparticles embedded in SiO2-HfO2 planar waveguides: preparation and optical, structural, and spectroscopic characterization  

NASA Astrophysics Data System (ADS)

In this work we present result on the preparation of planar waveguides based on HfO2 and HfO2-SiO$2). Stable sols containing europium and erbium doped HfO2 nanoparticles have been prepared and characterized. The nanosized sol was either deposited on quartz substrates or embedded in (3-glycidoxipropil)trimethoxisilane used as a hybrid host for posterior deposition. The refractive index dispersion and luminescence characteristics were determined for the resulting HfO2 films. The optical parameters of the waveguides such as refractive index, thickness and propagation losses were measured for the hybrid composite. The planar waveguides present thickness of a few micra and support well confined propagating modes.

Ribeiro, Sidney J. L.; Goncalves, Rogeria R.; Messaddeq, Younes; Aegerter, Michel A.; Montagna, Maurizio; Duverger, Claire; Ferrari, Maurizio

2000-05-01

78

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

79

XPS and cathodoluminescence studies of HfO2, Sc2O3 and (HfO2)1-x(Sc2O3)x films  

NASA Astrophysics Data System (ADS)

X-ray photoelectron spectroscopy (XPS) and cathodoluminescence (CL) method have been employed to study the chemical composition and the oxygen vacancy concentration of HfO2, Sc2 O3 and (HfO2)1-x(Sc2O3)x films. It was found that the increase of Sc content led to monotonic decreasing the Hf4f7/2 and Sc2p3/2 binding energies indicating to form solid solution (HfO2)1-x(Sc2O3)x. All the samples characterized by the intensive CL spectra with maximum around 3 eV which originated due to some radiative recombination emission caused by oxygen deficiency. The concentration of oxygen vacancy in the Sc-doped HfO2 is sensitive to the Sc content and as a result the intensity of CL spectra of (HfO2)1-x(Sc2O3)x is lower that those of pure HfO2 and Sc2O3.

Kaichev, Vasily V.; Ivanova, Ekaterina V.; Zamoryanskaya, Maria V.; Smirnova, Tamara P.; Yakovkina, Lubov V.; Gritsenko, Vladimir A.

2013-10-01

80

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

81

Current conduction mechanisms in atomic-layer-deposited HfO2/nitrided SiO2 stacked gate on 4H silicon carbide  

NASA Astrophysics Data System (ADS)

In this paper, current conduction mechanisms of an atomic-layer-deposited HfO2 gate stacked on different thicknesses of thermally nitrided SiO2 based on n-type 4H SiC have been investigated and analyzed. Current-voltage and high-frequency capacitance-voltage measurements conducted at various temperatures (25-140 °C) were performed in metal-oxide-semiconductor test structures with 13 nm thick HfO2 stacked on 0-, 2-, 4-, or 6 nm thick nitrided SiO2. Various conduction mechanisms, such as Schottky emission, Fowler-Nordheim tunneling, Poole-Frenkel emission, and space-charge-limited conduction, have been systematically evaluated. The mechanisms of the current conducted through the oxides were affected by the thickness of the nitrided oxide and the electric field applied. Finally, current conduction mechanisms that contributed to hard and soft dielectric breakdown have been proposed.

Cheong, Kuan Yew; Moon, Jeong Hyun; Kim, Hyeong Joon; Bahng, Wook; Kim, Nam-Kyun

2008-04-01

82

Ultra-thin film and interface analysis of high-k dielectric materials employing Time-Of-Flight Medium Energy Ion Scattering (TOF-MEIS)  

NASA Astrophysics Data System (ADS)

We explore the potential of Time-Of-Flight Medium Energy Ion Scattering (TOF-MEIS) for thin film analysis and analyze possible difficulties in evaluation of experimental spectra. As a model system high-k material stacks made from ultra-thin films of HfO2 grown on a p-type Si (1 0 0) substrate with a 0.5 nm SiO2 interface layer have been investigated. By comparison of experimental spectra and computer simulations TOF-MEIS was employed to establish a depth profile of the films and thus obtaining information on stoichiometry and film quality. Nominal film thicknesses were in the range from 1.8 to 12.2 nm. A comparison of the results with those from other MEIS approaches is made. Issues regarding different combinations of composition and stopping power as well as the influence of channeling are discussed. As a supporting method Rutherford-Backscattering spectrometry (RBS) was employed to obtain the areal density of Hf atoms in the films.

Primetzhofer, D.; Dentoni Litta, E.; Hallén, A.; Linnarsson, M. K.; Possnert, G.

2014-08-01

83

Acoustic spectroscopy and electrical characterization of Si/NAOS-SiO2/HfO2 structures  

NASA Astrophysics Data System (ADS)

The MOS structure prepared on n-type Si substrate with SiO2/HfO2 gate dielectric layers was formed by 5 nm HfO2 oxide deposited by atomic layer deposition on 0.6 nm SiO2 oxide film prepared with nitric acid oxidation of Si (NAOS) in ˜100% HNO3 vapor. The set of this MOS structure was annealed in N2 atmosphere at 200, 300 and 400 °C for 10 min to stabilize the structure, to decrease the interface states density and leakage current density. The both acoustic deep level transient spectroscopy (A-DLTS) and acoustoelectric response signal versus gate voltage dependence (Uac-Ug characteristics) were used to characterize the interface states and the role of annealing treatment, except ordinary electrical investigation represented by current-voltage and capacitance-voltage measurements. The main interface deep centers with activation energies ˜0.30 eV typical for dangling-bond type defects were observed as well as a particular influence of annealing treatment on the interface states. The obtained results are analyzed and discussed.

Bury, Peter; Matsumoto, Taketoshi; Bellan, Ivan; Janek, Marián; Kobayashi, Hikaru

2013-03-01

84

A strong analogy between the dielectric breakdown of high-K gate stacks and the progressive breakdown of ultrathin oxides  

NASA Astrophysics Data System (ADS)

The breakdown of high-K (HK) stack gate dielectrics is shown to be analogous to the failure of ultrathin SiO2-based oxides showing progressive breakdown. The breakdown of a HK stack is shown to occur in two phases. First, one or several percolation paths are formed in the SiO2-based interfacial layer. Then, these partial breakdowns propagate into the HK through defect generation in this layer. This propagation phase is equivalent to the progressive breakdown local degradation phenomenon. As a consequence of this analogy, the reliability assessment tools developed for ultrathin single-layer oxides can also be used without significant changes to assess the reliability of HK stacks. This analogy is so strong that the experimental distinction between HK propagation and conventional progressive breakdown appears to be rather difficult. However, the residual time distribution from first breakdown to final oxide failure is shown to be significantly different for both processes at low failure percentiles. This has allowed us to obtain experimental evidence of HK propagation (as opposed to conventional progressive breakdown effects) in relatively thick Hf-based gate stacks where the detection of first BD appears to be feasible.

Tous, Santi; Wu, Ernest Y.; Miranda, Enrique; Suñé, Jordi

2011-06-01

85

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

NASA Astrophysics Data System (ADS)

Fermi level pinning at metal/n-InP interface and effective Schottky barrier height (?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 ?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; Chen, Lin; Zhou, Peng; Wang, Peng-Fei; Wei Zhang, David; Xiao, Fei

2013-12-01

86

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

87

Interface and plasma damage analysis of PEALD TaCN deposited on HfO2 for advanced CMOS studied by angle resolved XPS and C-V  

NASA Astrophysics Data System (ADS)

Plasma enhanced atomic layer deposition (PEALD) TaCN deposited on HfO2 was studied by X-ray photoelectron spectroscopy (XPS) to understand the reactions taking place at the interface and connect them with C-V electrical characteristics of MOS devices. Moreover, angular resolved XPS (AR-XPS) was used for composition depth profiling of TaCN/HfO2/SiO2/Si stacks. Clear oxidation of the metal electrode through Tasbnd O bonding formation and migration of N in the dielectric with Hfsbnd N are shown. These modifications of chemical bonding give an insight on the electrical results. Low equivalent oxide thicknesses (EOT), as low as 0.89 nm and current leakage improvement by more than 5 decades, are observed for deposition with low plasma power and can be related to HfN content in HfO2 layer. The increase of plasma power used for TaCN deposition results in densification of the layer and promotes the creation of TaC in TaCN material. However H2 plasma has an impact on HfO2 with a reduction and scattering of the measured current leak gain. TaCN/HfO2 interface is also impacted with further creation of TaOx, leading to an increase of EOT when plasma power is increased. Based on these findings, reaction mechanisms with the corresponding Gibbs free energy are proposed.

Piallat, Fabien; Beugin, Virginie; Gassilloud, Remy; Dussault, Laurent; Pelissier, Bernard; Leroux, Charles; Caubet, Pierre; Vallée, Christophe

2014-06-01

88

Interfacial reaction between chemically vapor-deposited HfO2 thin films and a HF-cleaned Si substrate during film growth and postannealing  

NASA Astrophysics Data System (ADS)

Interfacial reactions between HfO2 thin films and a Si substrate during thin-film growth and postannealing under a N2 atmosphere were investigated by high-resolution transmission electron microscopy, Auger electron spectroscopy, and electrical measurements of metal-insulator-semiconductor capacitors. HfO2 thin films were deposited on HF-cleaned Si wafers by a chemical-vapor-deposition technique at a wafer temperature of 200 °C using a carbon-free precursor [Hf(NO3)4]. The film thicknesses ranged from 1.5 to 5.6 nm. During the initial stage of film growth, the Si surface oxidized to form a Si-rich hafnium silicate film. With increasing deposition time, Hf-rich hafnium silicate films grew. Postannealing resulted in a double-layered film structure with upper and interfacial layers having dielectric constants of approximately 9.3 and 5.6, respectively. The results were compared with the results from HfO2 films grown on SiO2-passivated Si wafers.

Park, Byoung Keon; Park, Jaehoo; Cho, Moonju; Hwang, Cheol Seong; Oh, Kiyoung; Han, Youngki; Yang, Doo Young

2002-04-01

89

Formation of the dopant-oxygen vacancy complexes and its influence on the photoluminescence emissions in Gd-doped HfO2  

NASA Astrophysics Data System (ADS)

Rare earth doping is widely used to improve the desired properties of high-k dielectric oxides. However, whether rare earth doping can suppress the formation of oxygen vacancies is still debated. By using the first-principles calculations with the generalized gradient approximation and more advanced hybrid functional, we have investigated the structural and electronic properties of the dopant-oxygen vacancy complexes in Gd-doped HfO2. Our calculations indicate that the Gd dopants interacting with oxygen vacancies can substantially shift up the VO energy states towards the conduction band edge. This together with other effects, such as capturing the localized electrons at the oxygen vacancy by Gd dopants and suppressing the randomicity of oxygen vacancy formation, improves the reliability of the devices made from Gd-doped HfO2. Based on our calculated results, we have presented an explanation for the experimentally observed decrease of the VO-related photoluminescence intensities upon Gd doping in HfO2.

Wang, L. G.; Tu, H. L.; Xiong, Y. H.; Xiao, W.; Du, J.; Wang, J. W.; Huang, G. J.

2014-09-01

90

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

91

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

PubMed

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 cm(2) 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

2013-11-01

92

Influence of bulk bias on negative bias temperature instability of p-channel metal-oxide-semiconductor field-effect transistors with ultrathin SiON gate dielectrics  

Microsoft Academic Search

Bulk (well) bias effects (grounded, positively biased, and floating) on both static and dynamic negative bias temperature instability of p-channel metal-oxide-semiconductor field-effect transistors with ultrathin SiON gate dielectrics were systematically investigated. The device degradation under both static and dynamic negative bias temperature (NBT) stresses with relatively large gate voltage (Vg) is significantly enhanced by a positive bulk bias (Vb). Moreover,

Shiyang Zhu; Anri Nakajima; Takuo Ohashi; Hideharu Miyake

2006-01-01

93

In-Line Compositional and Thickness Metrology Using XPS for Ultra-Thin Dielectric Films  

SciTech Connect

65 nm and 45 nm silicon devices will utilize compositionally critical processes for gate dielectrics, capacitor dielectrics, gate and capacitor electrodes, and ultra shallow junction layers. For example, small changes in nitrogen composition have been correlated with unacceptable shifts in electrical properties of devices with SiOxNy gate dielectrics. Present optically-based metrology technologies for such applications are reaching limits for precise thickness measurements and do not provide direct and adequately precise compositional information. As a result, mature analytical techniques, such as x-ray photoelectron spectroscopy (XPS), are now being transitioned to in-line production metrology usage.We discuss the application of XPS optimized for 200/300 mm production to compositional and thickness metrology of SiOxNy and high k gate dielectrics, high k capacitor dielectrics, and new electrode materials. The development of optimized hardware, robust data analysis algorithms and high throughput, fully automated operation has led to production implementation of XPS in advanced logic applications. The precise correlation of plasma nitridation metrology data with electrical device parameters has proven valuable in detecting process drifts early in the process flow, without the need to prepare devices through the first metal layer for testing. High density maps of film thickness and composition have enabled optimization of oxidation, nitridation and post-nitridation anneal processes for SiOxNy film production for 90 nm, 65 nm and below. High precision compositional and thickness metrology data for high-k gate and capacitor dielectrics is also presented.

Truman, J. Kelly; Gurer, Emir; Larson, C. Thomas; Reed, David [ReVera, Inc., 810 Kifer Road, Sunnyvale, CA 94086 (United States)

2005-09-09

94

Thermal stability of TiO2, ZrO2, or HfO2 on Si(100) by photoelectron emission microscopy  

NASA Astrophysics Data System (ADS)

The thermal stability of thin films (3 nm) of transition-metal (TM) oxides (TiO2, ZrO2, and HfO2) grown on ultrathin (~0.5 nm) SiO2 buffer layers on Si(100) surfaces was investigated with ultraviolet photoelectron emission microscopy (UV-PEEM). The decomposition of the TM oxides was observed in the PEEM during ultrahigh-vacuum annealing at temperatures of ~870, ~900, and ~1000 °C for the TiO2, ZrO2, and HfO2, respectively. Following the decomposition reaction, atomic force microscopy measurements of the annealed surfaces revealed a high density of islands in the decomposed regions. The degradation of the TM oxide films is attributed to a reaction occurring at defects at the TM oxide/SiO2/Si interfaces, which forms SiO species. Once a portion of the interfacial SiO2 layer is desorbed as a result of this reaction, Si from the substrate can diffuse into contact with the TM oxide layer, resulting in the formation of a TM silicide and the evolution of SiO. This process continues until the entire TM oxide layer is consumed and only silicide islands remain.

Zeman, M. C.; Fulton, C. C.; Lucovsky, G.; Nemanich, R. J.; Yang, W.-C.

2006-01-01

95

Molecular dynamics simulation of amorphous HfO2 for resistive RAM applications  

NASA Astrophysics Data System (ADS)

HfO2 is widely investigated as the favoured material for resistive RAM device implementation. The structural features of HfO2 play a fundamental role in the switching mechanisms governing resistive RAM operations, and a comprehensive understanding of the relation between the atomistic properties and final device behaviour is still missing. In addition, despite the fact that ultra-scaled 10 nm resistive RAM will probably be made of amorphous HfO2, a deeper investigation of the structure is necessary. In this paper, the classical molecular dynamics technique was used to investigate the disordered atomic configuration of amorphous HfO2. The influence of density on both the atomistic structure and the diffusion of O species was carefully analysed. The results achieved show that the atomistic structure of an amorphous HfO2 system is strongly affected by the density, and the amorphous system is rearranged in an atomic configuration similar to the crystalline configuration at similar densities. The diffusion of oxygen atoms increases with the decrease of the density, consistent with a less-packed atomic structure which allows for easier movement of this species.

Broglia, G.; Ori, G.; Larcher, L.; Montorsi, M.

2014-09-01

96

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

97

Maximizing performance for higher K gate dielectrics  

NASA Astrophysics Data System (ADS)

Further scaling of complementary metal oxide semiconductor gate stacks will require gate dielectrics with a higher dielectric constant (K) than HfO2. We point out that this will require strategies to minimize the overall effective oxide thickness of the gate stack, and not just maximizing the dielectric constant, so that the channel mobility is not impaired and there is still control of the flatband voltages. This may require retention of a SiO2-based interfacial layer, and attention should be paid to the flatband voltages of lanthanide oxides. Phase control of HfO2 and ZrO2 by addition of group IV elements offers simpler advances.

Robertson, John

2008-12-01

98

Crystallization of HfO2 in InAs/HfO2 core-shell nanowires  

NASA Astrophysics Data System (ADS)

We report the impact of deposition parameters on the structure of HfO2 covering InAs nanowires (NWs) being potential candidates for future field-effect transistors (FETs). Molecular beam epitaxial-grown Au-free InAs NWs were covered with HfO2 deposited by atomic-layer deposition. The impact of the film thickness as well as the deposition temperature on the occurrence and amount of crystalline HfO2 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 HfO2 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 HfO2 films, they contain monoclinic as well as orthorhombic HfO2 nanocrystals. Combining HfO2 and Al2O3 into a laminate structure is capable of suppressing the formation of crystalline HfO2 grains.

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

2014-10-01

99

Energy band alignment of atomic layer deposited HfO2 on epitaxial (110)Ge grown by molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

The band alignment properties of atomic layer HfO2 film deposited on epitaxial (110)Ge, grown by molecular beam epitaxy, was investigated using x-ray photoelectron spectroscopy. The cross-sectional transmission electron microscopy exhibited a sharp interface between the (110)Ge epilayer and the HfO2 film. The measured valence band offset value of HfO2 relative to (110)Ge was 2.28 ± 0.05 eV. The extracted conduction band offset value was 2.66 ± 0.1 eV using the bandgaps of HfO2 of 5.61 eV and Ge bandgap of 0.67 eV. These band offset parameters and the interface chemical properties of HfO2/(110)Ge system are of tremendous importance for the design of future high hole mobility and low-power Ge-based metal-oxide transistor devices.

Hudait, M. K.; Zhu, Y.; Maurya, D.; Priya, S.

2013-03-01

100

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

101

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

102

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

103

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

104

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

2014-01-01

105

Resistive switching properties of HfO2-based ReRAM with implanted Si/Al ions  

NASA Astrophysics Data System (ADS)

The effects of Si and Al ion implantation on the resistive switching properties of a HfO2-based resistive random access memory (RRAM) device are investigated. Testing results demonstrate that Si or Al implantation into HfO2 films results in reduced electroforming voltages and improves reproducibility of resistive switching over 1,000 cycles as measured by a DC voltage sweeping method. Furthermore, the Si or Al implantation into HfO2 resistive switching memory devices was found to improve device yields, reduce operating voltages and their variability, expand on/off resistance ratio (>103 for Al-doped, > 500 for Si-doped), and increase retention times (>3 × 105 s at room temperature). Doping by Si or Al ion is suggested to improve the formation of conducting filaments in HfO2 matrix and thus improve the performances of the Pt/Ti/HfO2/Pt device.

Xie, Hongwei; Wang, Ming; Kurunczi, Peter; Erokhin, Yuri; Liu, Qi; Lv, Hangbing; Li, Yingtao; Long, Shibing; Liu, Su; Liu, Ming

2012-11-01

106

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

PubMed

Mesoporous-graphitic-carbon-supported HfO2 (HfO2 -MGC) nanohybrids were synthesized by using a soft-template route. Characterization and a systematic investigation of the catalytic properties, stability, and catalytic mechanism were performed for HfO2 -MGC counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The new HfO2 -MGC as a CE in DSSCs showed a surprisingly high efficiency of 7.75 % for the triiodide/iodide redox couple and 3.69 % for the disulfide/thiolate redox couple, greater than the Pt electrode in the corresponding electrolyte system, which opens up a possibility for its practical application. PMID:24399514

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

2014-02-01

107

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

108

Influence of phosphorous precursors on spectroscopic properties of Er3+-activated SiO2-HfO2-P2O5 planar waveguides  

NASA Astrophysics Data System (ADS)

(70-x)SiO2-30HfO2 -xP2O5 (x= 5, 10 mol %) glass planar waveguides activated by 0.5 mol% Er3+ ions were prepared by sol-gel route. Several phosphorous precursors have been investigated for the synthesis of a dielectric stable sol useful for the realization of planar waveguides. The waveguides were investigated by different diagnostic techniques. The optical properties such as refractive index, thickness, number of propagating modes and attenuation coefficient were measured at 632.8 and 543.5 nm by prism coupling technique. Transmission measurements were carried out in order to assess the transparency of the deposited films. Photoluminescence measurements and lifetime decay curves of the Er3+ transition (4I13/2 ? 4I15/2) were performed in order to investigate the role of P2O5.

Vasilchenko, I.; Carpentiero, A.; Chiappini, A.; Chiasera, A.; Vaccari, A.; Lukowiak, A.; Righini, G. C.; Vereshagin, V.; Ferrari, M.

2014-12-01

109

Effect of atomic layer deposition growth temperature on the interfacial characteristics of HfO2/p-GaAs metal-oxide-semiconductor capacitors  

NASA Astrophysics Data System (ADS)

The effect of atomic layer deposition (ALD) growth temperature on the interfacial characteristics of p-GaAs MOS capacitors with ALD HfO2 high-k dielectric using tetrakis(ethylmethyl)amino halfnium precursor is investigated in this study. Using the combination of capacitance-voltage (C-V) and X-ray photoelectron spectroscopy (XPS) measurements, ALD growth temperature is found to play a large role in controlling the reaction between interfacial oxides and precursor and ultimately determining the interface properties. The reduction of surface oxides is observed to be insignificant for ALD at 200 °C, while markedly pronounced for growth at 300 °C. The corresponding C-V characteristics are also shown to be ALD temperature dependent and match well with the XPS results. Thus, proper ALD process is crucial in optimizing the interface quality.

Liu, C.; Zhang, Y. M.; Zhang, Y. M.; Lv, H. L.

2014-12-01

110

Local structure around Er3+ in SiO2-HfO2 glassy waveguides using EXAFS  

NASA Astrophysics Data System (ADS)

Er3+ -doped SiO2-HfO2 glassy waveguides with HfO2 concentrations ranging from 10to50mol% were prepared using the sol-gel route and deposited on v-SiO2 substrates using the dip-coating technique. The local environment around Er3+ ions was determined from Er L3 -edge extended x-ray-absorption fine-structure (EXAFS) measurements. The first coordination shell around Er3+ ions is composed of oxygen atoms. Hafnium is the main constituent of the second coordination shell of Er3+ , differing from the cases of pure SiO2 and SiO2-TiO2 glassy hosts, in which silicon is the main atomic species. The local structure around Er3+ ions has been found to be independent on HfO2 concentration within the studied composition range. This fact implies that Er3+ ions are preferentially dispersed in HfO2 -rich regions of the glassy waveguide, even at the lowest HfO2 concentration. For all samples, no Er3+-Er3+ coordination shell has been detected by EXAFS. The presented structural results allow us to understand some spectroscopic properties typical of Er3+ -doped SiO2 glassy waveguides co-doped with HfO2 .

Afify, N. D.; Dalba, G.; Armellini, C.; Ferrari, M.; Rocca, F.; Kuzmin, A.

2007-07-01

111

High quality atomic-layer-deposited ultrathin Si-nitride gate dielectrics with low density of interface and bulk traps  

NASA Astrophysics Data System (ADS)

Interface trap and bulk trap densities of atomic-layer-deposited (ALD) Si-nitride dielectrics have been evaluated by bipolar-voltage-pulse-induced current and electrical-stress-induced leakage-current measurements, respectively. In comparison with the conventional SiO2 dielectrics, significantly lower (˜1/3) interface trap density near the conduction band edge is observed in the ALD Si-nitride dielectrics. Moreover, the observed lower interface and bulk trap generations consistently explain the soft-breakdown-free phenomena observed in capacitors with the ALD Si-nitride gate dielectrics. Enhanced dielectric reliability and several other significant features have made the ALD Si-nitride gate dielectrics a front line candidate for extremely thin (equivalent oxide thickness ˜1 nm) gate dielectrics of sub-100-nm technology nodes.

Nakajima, Anri; Khosru, Quazi D. M.; Yoshimoto, Takashi; Kasai, Tetsurou; Yokoyama, Shin

2003-07-01

112

Effects of Flat HfO2 Films Derived from Diethanolamine Solution on Structure and Properties of Metal/Ferroelectrics/Insulator/Semiconductor  

NASA Astrophysics Data System (ADS)

HfO2 films were prepared using precursor solutions with and without diethanolamine. The microstructure of HfO2 films changed with the presence of diethanolamine. This result is thought to be due to the difference in the progress of organic decomposition and the behavior of nucleation and grain growth. The microstructure of HfO2 films affected the crystallization and microstructure of Y0.5Yb0.5MnO3 films on these HfO2 films. The flatness of HfO2 and Y0.5Yb0.5MnO3 films was improved by the modification of HfO2 precursor solutions with diethanolamine.

Suzuki, Kazuyuki; Tanaka, Kiyotaka; Kato, Kazumi

2008-09-01

113

XRD and EXAFS studies on the structure of Er3+-doped SiO2-HfO2 glass-ceramic waveguides: Er3+-activated HfO2 nanocrystals  

NASA Astrophysics Data System (ADS)

This paper describes the structure of Er3+-doped SiO2-HfO2 waveguides containing nanocrystals of HfO2. Pure and 1 mol% Er3+-doped 70SiO2-30HfO2 films were deposited by the sol-gel method on amorphous SiO2 substrates using the dip-coating technique. Each waveguide has experienced a single thermal treatment at temperatures ranging from 900 to 1200 °C, for either short (30 min) or long (24 h) durations. Crystallization and microstructure were studied by x-ray diffraction (XRD). The local environments of hafnium and erbium ions were determined, respectively, from Hf and Er L3-edges extended x-ray absorption fine structure (EXAFS) experiments. Both XRD and EXAFS results demonstrate the substitution of Hf4+ by Er3+ ions in the crystalline structure. XRD shows the nucleation of tetragonal HfO2 nanocrystals after heat treatment at 1000 °C for 30 min in the pure waveguide, and at 900 °C for 24 h in the waveguide doped with Er3+. In both series, partial transformation from tetragonal to monoclinic HfO2 nanocrystals starts after heat treatment at 1100 °C for 24 h. The average crystallite size and size distribution can be controlled by thermal annealing temperature and duration, respectively, with brief treatment yielding a more homogeneous nanocrystal size.

Afify, N. D.; Dalba, G.; Rocca, F.

2009-06-01

114

High Performance ALD HfO2-Al2O3 Laminate MIM Capacitors for RF and Mixed Signal IC Applications  

E-print Network

High Performance ALD HfO2-Al2O3 Laminate MIM Capacitors for RF and Mixed Signal IC Applications ALD HfO2-Al2O3 laminate metal-insulator-metal (MIM) capacitor is demonstrated for the first time electrical properties and reliability suggest that the ALD HfO2-Al2O3 laminate is a very promising material

Fu, Li Ming

115

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

116

First-principles study of structural, vibrational, and lattice dielectric properties of hafnium oxide  

Microsoft Academic Search

Crystalline structures, zone-center phonon modes, and the related dielectric response of the three low-pressure phases of HfO2 have been investigated in density-functional theory using ultrasoft pseudopotentials and a plane-wave basis. The structures of low-pressure HfO2 polymorphs are carefully studied with both the local-density approximation (LDA) and the generalized gradient approximation. The fully relaxed structures obtained with either exchange-correlation scheme agree

Xinyuan Zhao; David Vanderbilt

2002-01-01

117

A study on structural, optical and hydrophobic properties of oblique angle sputter deposited HfO2 films  

NASA Astrophysics Data System (ADS)

HfO2 thin films have been synthesized by oblique angle reactive DC magnetron sputtering technique. Present study reports the effect of deposition angle on the hydrophobic, structural, surface morphological and optical properties of HfO2 thin films. All the films were deposited at room temperature. HfO2 thin films were found to possess monoclinic crystal structure. Significant changes in topography of the films, with change in deposition angle, have been observed. Surface roughness increases with decrease in deposition angle as observed from AFM image analysis. UV-vis spectroscopy has been used to study the optical properties of the films. Small changes in transmission and refractive index have been observed. The films are hydrophobic in nature and the contact angle is strongly influenced by deposition angle due to change in its surface roughness. Contact angle of 106.3° has been achieved for deposition angle of 30° which is highest so far for HfO2 thin films prepared by magnetron sputtering. The results of this study reflect that contact angle of the films can be tuned by deposition angle. Good optical transmission along with hydrophobic character make HfO2 thin films of great use as optical coatings for lenses, windshields and optoelectronic devices.

Jain, Ravish K.; Gautam, Yogendra K.; Dave, Vikramaditya; Chawla, Amit K.; Chandra, Ramesh

2013-10-01

118

Chemical vapor deposition of anisotropic ultrathin gold films on optical fibers: real-time sensing by tilted fiber Bragg gratings and use of a dielectric pre-coating  

NASA Astrophysics Data System (ADS)

Tilted fiber Bragg gratings (TFBGs) are refractometry-based sensor platforms that have been employed herein as devices for the real-time monitoring of chemical vapour deposition (CVD) in the near-infrared range (NIR). The coreguided light launched within the TFBG core is back-reflected off a gold mirror sputtered onto the fiber-end and is scattered out into the cladding where it can interact with a nucleating thin film. Evanescent fields of the growing gold nanostructures behave differently depending on the polarization state of the core-guided light interrogating the growing film, therefore the resulting spectral profile is typically decomposed into two separate peak families for the orthogonal S- and P-polarizations. Wavelength shifts and attenuation profiles generated from gold films in the thickness regime of 5-100 nm are typically degenerate for deposition directly onto the TFBG. However, a polarization-dependence can be imposed by adding a thin dielectric pre-coating onto the TFBG prior to using the device for CVD monitoring of the ultrathin gold films. It is found that addition of the pre-coating enhances the sensitivity of the P-polarized peak family to the deposition of ultrathin gold films and renders the films optically anisotropic. It is shown herein that addition of the metal oxide coating can increase the peak-to-peak wavelength separation between orthogonal polarization modes as well as allow for easy resonance tracking during deposition. This is also the first reporting of anisotropic gold films generated from this particular gold precursor and CVD process. Using an ensemble of x-ray techniques, the local fine structure of the gold films deposited directly on the TFBG is compared to gold films of similar thicknesses deposited on the Al2O3 pre-coated TFBG and witness slides.

Mandia, David J.; Zhou, Wenjun; Ward, Matthew J.; Joress, Howie; Giorgi, Javier B.; Gordon, Peter; Albert, Jacques; Barry, Seán. T.

2014-09-01

119

A chemical mechanism for nitrogen incorporation into HfO 2 ALD films using ammonia and alkylamide as precursors  

NASA Astrophysics Data System (ADS)

An atomistic mechanism for the incorporation of nitrogen into HfO 2 ALD films grown using Hf[N(CH 3) 2] 4 and NH 3 was investigated using density functional theory. We find a ligand-exchange mechanism similar to those thought to occur in the ALD of other metal oxide films. Both half-reactions form intermediates that are more stable than the products, have larger barriers than for reaction between H 2O and Hf[N(CH3)2]x? and will thus be significantly slower at ALD temperatures. Therefore water must be purged from the chamber when depositing Hf nitrides or incorporating N into HfO 2 using this chemistry. These results indicate that NH 3 and Hf[N(CH 3) 2] 4 can be used to either incorporate N into HfO 2 ALD films or grow hafnium nitride.

Xu, Ye; Musgrave, Charles B.

2005-10-01

120

Low temperature atomic layer deposited HfO2 film for high performance charge trapping flash memory application  

NASA Astrophysics Data System (ADS)

The impact of key process parameters on the electrical characteristics of atomic layer deposited HfO2 films has been systematically studied with MHOS devices via capacitance-voltage (C-V) measurement. C-V hysteresis curves revealed that charge storage capacity is significantly enhanced with decreasing substrate temperature from 350 down to 150 °C and/or increasing purge time of the inert gas. The developed HfO2 trapping layer was also demonstrated by a MAHOS memory device. Improved memory window, fast program speed and good retention characteristics have been obtained. The study provides a reference for memory performance improvement of HfO2-based charge trap flash memory.

Chen, Guoxing; Huo, Zongliang; Jin, Lei; Zhang, Dong; Zhao, Shengjie; Han, Yulong; Liu, Su; Liu, Ming

2014-04-01

121

Characterization of high-k HfO2 films prepared using chemically modified alkoxy-derived solutions  

NASA Astrophysics Data System (ADS)

The HfO2 films were prepared using alkoxy-derived precursor solutions. The effects of the chemical composition of precursor solutions on the microstructure development and electrical properties were investigated. The flatness and refractive index of the HfO2 films were improved by using diethanolamine-added solution. This result is considered to be due to the difference in the progress of organic decomposition and the behavior of nucleation and grain growth. The difference in the chemical composition affected the electrical properties such as leakage current and capacitance-voltage characteristics, which are related to the defects in the film and interface state.

Suzuki, Kazuyuki; Kato, Kazumi

2009-03-01

122

Investigation of interaction between graphene and dielectrics  

Microsoft Academic Search

The properties of micromechanically exfoliated graphene on different oxide dielectrics— SiO2, Al2O3, and HfO2—are investigated by Raman spectroscopy and AFM measurement. The pristine graphene has stronger adhesion and a higher hole concentration when the dielectric constant of the underlying oxide is higher. It is found that annealing under a high vacuum significantly enhances the adhesion between graphene and the oxides

Seung Min Song; Byung Jin Cho

2010-01-01

123

Investigation of interaction between graphene and dielectrics  

Microsoft Academic Search

The properties of micromechanically exfoliated graphene on different oxide dielectrics--- SiO2, Al2O3, and HfO2---are investigated by Raman spectroscopy and AFM measurement. The pristine graphene has stronger adhesion and a higher hole concentration when the dielectric constant of the underlying oxide is higher. It is found that annealing under a high vacuum significantly enhances the adhesion between graphene and the oxides

Seung Min Song; Byung Jin Cho

2010-01-01

124

The effect of aluminum doping on crystallinity, non-lattice oxygen, and resistance switching of Al-doped HfO2 films deposited by reactive sputtering  

NASA Astrophysics Data System (ADS)

In this work, the resistance switching characteristics of Al-doped HfO2 thin films were investigated with by systematically varying the Al concentration and analyzing of the microstructure and the chemical bonding states. TiN/Al-doped HfO2/Pt metal-insulator-metal stacks were fabricated with various Al concentrations of up to 16.8% by using reactive DC magnetron co-sputtering. X-ray diffraction and transmission electron microscopy measurement showed that HfO2 doped with more than 10.4% Al had an amorphous structure, while HfO2 doped with Al of less than 5.6% had a crystalline structure. X-ray photoelectron spectroscopy (XPS) showed that the concentration of non-lattice oxygen in Aldoped HfO2 films increased with increasing Al up to 5.6% and was saturated for Al concentrations above 5.6%. TiN/Al-doped HfO2/Pt stacks showed typical bipolar resistance switching characteristics. HfO2 doped with Al = 5.6% showed the smallest grains and the smallest uniformity in the forming electric field and the SET/RESET resistance distribution. We conclude that the grain boundaries play a more important role than point defects such as non-lattice oxygen in the resistance switching.

Lee, Kyumin; Na, Heedo; Sohn, Hyunchul; Kim, Jonggi

2014-09-01

125

Structure and Electrical Properties of Al-Doped HfO2 and ZrO2 Films Grown via Atomic Layer Deposition on Mo Electrodes.  

PubMed

The effects of Al doping in atomic-layer-deposited HfO2 (AHO) and ZrO2 (AZO) films on the evolutions of their crystallographic phases, grain sizes, and electric properties, such as their dielectric constants and leakage current densities, were examined for their applications in high-voltage devices. The film thickness and Al-doping concentration were varied in the ranges of 60-75 nm and 0.5-9.7%, respectively, for AHO and 55-90 nm and 1.0-10.3%, respectively, for AZO. The top and bottom electrodes were sputtered Mo films. The detailed structural and electrical property variations were examined as functions of the Al concentration and film thickness. The AHO films showed a transition from the monoclinic phase (Al concentration up to 1.4%) to the tetragonal/cubic phase (Al concentration 2.0-3.5%), and finally, to the amorphous phase (Al concentration >4.7%), whereas the AZO films remained in the tetragonal/cubic phase up to the Al concentration of 6.4%. For both the AHO and AZO films, the monoclinic and amorphous phases had dielectric constants of 20-25, and the tetragonal/cubic phases had dielectric constants of 30-35. The highest electrical performance levels for the application to the high-voltage charge storage capacitors in flat panel displays were achieved with the 4.7-9.7% Al-doped AHO films and the 2.6% Al-doped AZO films. PMID:25423483

Yoo, Yeon Woo; Jeon, Woojin; Lee, Woongkyu; An, Cheol Hyun; Kim, Seong Keun; Hwang, Cheol Seong

2014-12-24

126

Improvement of carrier mobility of top-gated SiC epitaxial graphene transistors using a PVA dielectric buffer layer  

NASA Astrophysics Data System (ADS)

The effects of treatment with polyvinyl alcohol (PVA) and a dielectric film of HfO2 on the properties of SiC based epitaxial graphene have been explored and analyzed. We have characterized the carrier mobility of graphene on Si-face and C-face SiC with a layer of HfO2, with or without an initial PVA treatment on the device active layer. Epitaxial graphene grown on the C-face displays a higher mobility than a film grown on the silicon face. Also, the mobility in the presence of the PVA treatment with HfO2 dielectric layer has been improved, compared with the mobility after deposition of only gate dielectric: ˜20% in C-face graphene and ˜90% in Si-face graphene. This is a major improvement over the degradation normally observed with dielectric/graphene systems.

Kim, Moonkyung; Hwang, Jeonghyun; Lepak, Lori A.; Lee, Jo-won; Spencer, Michael G.; Tiwari, Sandip

2012-08-01

127

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

PubMed

Fourier transform ion cyclotron resonance mass spectrometry was used to characterize the gas-phase reactivity of Hf dipositive ions, Hf(2+)and HfO(2+), toward several oxidants: thermodynamically facile O-atom donor N(2)O, ineffective donor CO, and intermediate donors O(2), CO(2), NO, and CH(2)O. The Hf(2+) ion exhibited electron transfer with N(2)O, O(2), NO, and CH(2)O, reflecting the high ionization energy of Hf(+). The HfO(2+) ion was produced by O-atom transfer to Hf(2+) from N(2)O, O(2), and CO(2), and the HfO(2)(2+) ion by O-atom transfer to HfO(2+) from N(2)O; these reactions were fairly efficient. Density functional theory revealed the structure of HfO(2)(2+) as a peroxide. The HfO(2)(2+) ion reacted by electron transfer with N(2)O, CO(2), and CO to give HfO(2)(+). Estimates were made for the second ionization energies of Hf (14.5 ± 0.5 eV), HfO (14.3 ± 0.5 eV), and HfO(2) (16.2 ± 0.5 eV), and also for the bond dissociation energies, D[Hf(2+)-O] = 686 ± 69 kJ mol(-1) and D[OHf(2+)-O] = 186 ± 98 kJ mol(-1). The computed bond dissociation energies, 751 and 270 kJ mol(-1), respectively, are within these experimental ranges. Additionally, it was found that HfO(2)(2+) oxidized CO to CO(2) and is thus a catalyst in the oxidation of CO by N(2)O and that Hf(2+) activates methane to produce a carbene, HfCH(2)(2+). PMID:23186013

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

2012-12-27

128

Mise en evidence et etude de la phase ordonnée Y2Hf7O17 dans le système HfO2-Y2O3  

Microsoft Academic Search

Le système HfO2-Y2O3 présente une phase ordonnée par rapport à la phase métastable type fluorite, correspondant au composé défini Y2Hf7O17. La transformation ordre --> désordre a étéétudiée par différentes méthodes. Les résultats obtenus permettent de tracer le diagramme de phase du système HfO2-Y2O3 dans la zone riche en dioxyde de hafnium. The HfO2-Y2O3 system shows an ordered phase, compared with

Michel Duclot; Jean Vicat; Charles Deportes

1970-01-01

129

Growth and properties of hafnicone and HfO(2)/hafnicone nanolaminate and alloy films using molecular layer deposition techniques.  

PubMed

Molecular layer deposition (MLD) of the hafnium alkoxide polymer known as "hafnicone" was grown using sequential exposures of tetrakis(dimethylamido) hafnium (TDMAH) and ethylene glycol (EG) as the reactants. In situ quartz crystal microbalance (QCM) experiments demonstrated self-limiting reactions and linear growth versus the number of TDMAH/EG reaction cycles. Ex situ X-ray reflectivity (XRR) analysis confirmed linear growth and measured the density of the hafnicone films. The hafnicone growth rates were temperature-dependent and decreased from 1.2 Å per cycle at 105 °C to 0.4 Å per cycle at 205 °C. The measured density was ?3.0 g/cm(3) for the hafnicone films at all temperatures. Transmission electron microscopy images revealed very uniform and conformal hafnicone films. The XRR studies also showed that the hafnicone films were very stable with time. Nanoindentation measurements determined that the elastic modulus and hardness of the hafnicone films were 47 ± 2 and 2.6 ± 0.2 GPa, respectively. HfO2/hafnicone nanolaminate films also were fabricated using HfO2 atomic layer deposition (ALD) and hafnicone MLD at 145 °C. The in situ QCM measurements revealed that HfO2 ALD nucleation on the hafnicone MLD surface required at least 18 TDMAH/H2O cycles. Hafnicone alloys were also fabricated by combining HfO2 ALD and hafnicone MLD at 145 °C. The composition of the hafnicone alloy was varied by adjusting the relative number of TDMAH/H2O ALD cycles and TDMAH/EG MLD cycles in the reaction sequence. The electron density changed continuously from 8.2 × 10(23) e(-)/cm(3) for pure hafnicone MLD films to 2.4 × 10(24) e(-)/cm(3) for pure HfO2 ALD films. These hafnicone films and the HfO2/hafnicone nanolaminates and alloys may be useful for flexible thin-film devices. PMID:25203487

Lee, Byoung H; Anderson, Virginia R; George, Steven M

2014-10-01

130

Behavior of hydrogen in high dielectric constant oxide gate insulators  

NASA Astrophysics Data System (ADS)

Interstitial hydrogen is calculated to act as a shallow donor in the candidate high dielectric constant (k) gate oxides ZrO2, HfO2, La2O3, Y2O3, TiO2, SrTiO3, and LaAlO3 but is deep in the oxides SiO2, Al2O3, ZrSiO4, HfSiO4, and SrZrO3. This may account for the change of sign of fixed charge in oxides, from negative in Al2O3 to positive in HfO2.

Peacock, P. W.; Robertson, J.

2003-09-01

131

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

132

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

133

Memory characteristics of cobalt-silicide nanocrystals embedded in HfO2 gate oxide for nonvolatile nanocrystal flash devices  

Microsoft Academic Search

Cobalt-silicide (CoSi2) nanocrystals (NCs) were investigated for use in charge storage for metal oxide semiconductor (MOS) devices with thin HfO2 tunneling and control oxide layers. CoSi2 NCs were synthesized by exposure of Co\\/Si\\/HfO2 tunneling oxide\\/Si stacks to an external UV laser. Observations from transmission electron microscopy and x-ray photoelectron spectroscopy clearly confirm the formation of CoSi2 NCs and the values

Joohyung Kim; Jungyup Yang; Junseok Lee; Jinpyo Hong

2008-01-01

134

SiC, , composite materials, HfO2, ZrO2 Pyrolytic graphite (PG/002)  

E-print Network

#12;#12;SiC, , composite materials, HfO2, ZrO2 #12;#12;Ge Pyrolytic graphite (PG/002) Ge Pyrolytic graphite (PG/002) #12; ° ° ° ° #12;, µ µ µ Diffraction 10 20 30 40 50 60 70 80 90 100 110 -1300Ti-Cu-Aggraphite Graphite/filler interface 012 34 56 7 8 6 9 BE ¡¢ £A C ¢ ¤ X I H #12;

135

Feature Modeling of HfO2 Atomic Layer Deposition Using HfCl4/H2O  

NASA Astrophysics Data System (ADS)

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

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

2003-03-01

136

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

137

Characteristics of TaN gate MOSFET with ultrathin hafnium oxide (8 Å-12 Å)  

Microsoft Academic Search

MOSFET's with equivalent oxide thickness of 8-12 Å have been demonstrated by using high-K gate dielectric thin films (HfO2) and TaN gate electrode. Both self-aligned (higher thermal budget process) and non-self-aligned process (low thermal budget as in the replacement gate process) were used and compared. Excellent electrical characteristics (e.g. S~68 mV\\/dec) and reliability characteristics (e.g. high EBD, low charge trapping

Byoung Hun Lee; R. Choi; L. Kang; S. Gopalan; R. Nieh; K. Onishi; Y. Jeon; Wen-Jie Qi; C. Kang; J. C. Lee

2000-01-01

138

Indium diffusion through high-k dielectrics in high-k/InP stacks  

NASA Astrophysics Data System (ADS)

Evidence of indium diffusion through high-k dielectric (Al2O3 and HfO2) films grown on InP (100) by atomic layer deposition is observed by angle resolved X-ray photoelectron spectroscopy and low energy ion scattering spectroscopy. The analysis establishes that In-out diffusion occurs and results in the formation of a POx rich interface.

Dong, H.; Cabrera, W.; Galatage, R. V.; Santosh KC, Brennan, B.; Qin, X.; McDonnell, S.; Zhernokletov, D.; Hinkle, C. L.; Cho, K.; Chabal, Y. J.; Wallace, R. M.

2013-08-01

139

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

140

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

141

Capacitance-voltage and retention characteristics of Pt/SrBi2Ta2O9/HfO2/Si structures with various buffer layer thickness  

NASA Astrophysics Data System (ADS)

The metal-ferroelectric-insulator-semiconductor (MFIS) structure diodes with SrBi2Ta2O9 (SBT) as ferroelectric thin film and HfO2 as insulating buffer layer were fabricated. The electrical properties of MFIS structure were investigated for different HfO2 buffer layer thickness. The experimental results show that the memory window extended significantly as the HfO2 layer thickness increased from 6 to 10 nm. It is also observed that the leakage current was reduced to about 10-10 A at applied voltage of 4 V, and the high and low capacitances remained distinguishable for over 8 h even if we extrapolate the measured data to 10 years.

Tang, M. H.; Sun, Z. H.; Zhou, Y. C.; Sugiyama, Y.; Ishiwara, H.

2009-05-01

142

Formation of hafnium-aluminum-oxide gate dielectric using single cocktail liquid source in MOCVD process  

Microsoft Academic Search

We demonstrate that a high quality metal organic chemical vapor deposition (MOCVD) HfAlxOy (hereafter HfAlO) dielectric film can successfully be deposited with a wide range of composition controllability between HfO2 and Al2O3 in HfAlO using a single cocktail liquid source HfAl(MMP)2(OiPr)5. A composition ratio between 45 to 90% of HfO2 in HfAlO is achieved by controlling deposition process parameters. The

Moon Sig Joo; Byung Jin Cho; Chia Ching Yeo; Daniel Siu Hung Chan; Sung Jin Whoang; S. Mathew; L. Kanta Bera; N. Balasubramanian; Dim-Lee Kwong

2003-01-01

143

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

SciTech Connect

Hafnium oxide (HfO?) thin films have been made by radio-frequency (rf) magnetron-sputtering onto Si(100) substrates under varying growth temperature (Ts). HfO? ceramic target has been employed for sputtering while varying the Ts from room temperature to 500?C during deposition. The effect of Ts on the growth and microstructure of deposited HfO? films has been studied using grazing incidence x-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), and high-resolution scanning electron microscopy (HR-SEM) coupled with energy dispersive x-ray spectrometry (EDS). The results indicate that the effect of Ts is significant on the growth, surface and interface structure, morphology and chemical composition of the HfO? films. Structural characterization indicates that the HfO? films grown at Ts<200 ?C are amorphous while films grown at Ts>200 ?C are nanocrystalline. An amorphous-to-crystalline transition occurs at Ts=200 ?C. Nanocrystalline HfO? films crystallized in a monoclinic structure with a (-111) orientation. XPS measurements indicated the high surface-chemical quality and stoichiometric nature of the grown HfO? films. An interface layer (IL) formation occurs due to reaction at the HfO?-Si interface for HfO? films deposited at Ts>200 ?C. The thickness of IL increases with increasing Ts. XPS and EDS at the HfO?-Si cross-section indicate the IL is a (Hf, Si)-O compound. The electrical characterization using capacitance-voltage measurements indicate that the dielectric constant decreases from 25 to 16 with increasing Ts.

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

2011-01-01

144

X-ray photoelectron spectroscopy of Er3+-activated SiO2-HfO2 glass-ceramic waveguides  

NASA Astrophysics Data System (ADS)

xHfO2-(100 - x) SiO2 (x = 10, 20, 30 mol%) glass-ceramic planar waveguides doped with 0.3 mol% Er3+ ions, prepared by the sol-gel route and heat treated at 1000 °C to nucleate HfO2 crystals, were analysed by x-ray photoelectron spectroscopy, x-ray diffraction, high resolution transmission electron microscopy and photoluminescence spectroscopy. Formation of tetragonal HfO2 nanocrystals has been evidenced in all the samples. Spectroscopic parameters concerning the 4I13/2 metastable state of Er3+ion are revisited as a function of XPS analysis.

Minati, L.; Speranza, G.; Micheli, V.; Ferrari, M.; Jestin, Y.

2009-01-01

145

Ultra-thin multilayer capacitors  

Microsoft Academic Search

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

Timothy Jerome Renk; Todd C. Monson

2009-01-01

146

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

147

Ion beam studies of Hafnium based alternate high-k dielectric films deposited on silicon  

NASA Astrophysics Data System (ADS)

Hafnium based high dielectric constant materials are critical for the state-of-the-art integrated circuit technology. As the size of the transistor decreases, the thickness of the gate dielectric (SiO2) should be reduced to maintain device capacitance at a desired level. This thickness reduction results in high OFF-state leakage current due to quantum tunneling. Recently alternate high-k materials, like HfO2, have been introduced as gate dielectrics. However deposition of these high-k materials on Si wafers results in high concentration of interface defects due to their thermodynamic instability on Si. Introduction of thin inter layer of Silicon oxide/nitrides between Si and HfO2 is expected to improve interface quality. Hence it is important to study the composition, thickness and intermixing effects to optimize the fabrication of Hafnium based Metal-Oxide-Semiconductor (MOS) devices. Here, we have performed High Resolution Rutherford Backscattering Spectrometry (HRBS) and X-ray Reflectivity (XRR) measurements to characterize HfO2/SiO2/Si samples. These samples were further irradiated by 80 MeV Ni ions to study ion induced inter-diffusion of Hf and Si across HfO2/Si interface as a function of ion fluence.

Manikanthababu, N.; Chan, T. K.; Pathak, A. P.; Devaraju, G.; Srinivasa Rao, N.; Yang, P.; Breese, M. B. H.; Osipowicz, T.; Nageswara Rao, S. V. S.

2014-08-01

148

Charge storage characteristics of Au nanocrystal memory improved by the oxygen vacancy-reduced HfO2 blocking layer  

PubMed Central

This study characterizes the charge storage characteristics of metal/HfO2/Au nanocrystals (NCs)/SiO2/Si and significantly improves memory performance and retention time by annealing the HfO2 blocking layer in O2 ambient at 400°C. Experimental evidence shows that the underlying mechanism can be effectively applied to reduce oxygen vacancy and suppress unwanted electron trap-assisted tunneling. A memory window of 1 V at an applied sweeping voltage of ±2 V is also shown. The low program/erase voltage (±2 V) and the promising retention performances indicate the potential application of NCs in low-voltage, non-volatile memory devices. PMID:23984794

2013-01-01

149

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

150

Atomic Layer Deposition of HfO2 Thin Films on Si and GaAs Substrates Justin C Hackley1  

E-print Network

that have shown efficient growth of HfO2 films on Si-H at 100°C using amide precursors and heavy water.4 Hf were deposited using a home built hot-wall flow type reactor that is computer-controlled via a Labview

Gougousi, Theodosia

151

A study of some optical properties of hafnium dioxide (HfO2) thin films and their applications  

NASA Astrophysics Data System (ADS)

By use of evaporation conditions adjusted for the deposition of hafnium dioxide (HfO2), a series of films ranging in thickness from 50 to 10000 nm was prepared by using an electron beam gun inside an evacuated coating chamber of pressure 1×10-5 mbar. The films were obtained on optical glass substrate by using oxygen with a backfill pressure of 2.4×10-4 mbar during the deposition processes. The optical constants of the films were computed in the spectral wavelength region (350-2000 nm) from the transmission, reflection and thickness measurements. A computer program was created to determine two optical parameters n and k of the films, and this was achieved by entering the practical results into the computer program, which solved a series of equations for each wavelength. The effects created by changing various evaporation conditions (thickness, substrate temperature and evaporation rate) were studied in the spectral wavelength range, and the optimum values of the various conditions were obtained while achieving the best optical performance. According to the investigations of the HfO2 material, two applications of the anti-reflection (AR) multi-layer coatings were achieved in two different spectral wavelength ranges. The first application was measured in the visible and near infra-red (VIS/NIR) range from 500 nm to 850 nm deposited on the glass substrate. The second application was measured in the infrared (IR) range from 7500 nm to 11500 nm deposited on germanium substrate. Computer modelling for designing the optical multi-layer system has been presented. The theoretical formulation and experimental results with the same specification were achieved. The correlation between the theoretical and the experimental results reveals a close agreement that offers a convenient method for predicting and controlling the multi-layer coating. By continuous measurement of the optical and mechanical (durability) performances of the coating process, high-quality films were produced in the manufacture of various optical devices.

Fadel, M.; Azim M., O. A.; Omer, O. A.; Basily, R. R.

152

The electrical and material characterization of hafnium oxynitride gate dielectrics with TaN-gate electrode  

Microsoft Academic Search

Electrical and material characteristics of hafnium oxynitride (HfON) gate dielectrics have been studied in comparison with HfO2. HfON was prepared by a deposition of HfN followed by post-deposition-anneal (PDA). By secondary ion mass spectroscopy (SIMS), incorporated nitrogen in the HfON was found to pile up at the dielectric\\/Si interface layer. Based on the SIMS profile, the interfacial layer (IL) composition

Chang Seok Kang; Hag-Ju Cho; Rino Choi; Young-Hee Kim; Chang Yong Kang; Se Jong Rhee; Changhwan Choi; M. S. Akbar; J. C. Lee

2004-01-01

153

Suppressed crystallization of Hf-based gate dielectrics by controlled addition of Al2O3 using atomic layer deposition  

E-print Network

Suppressed crystallization of Hf-based gate dielectrics by controlled addition of Al2O3 using the controlled addition of Al2O3 . The (HfO2)x(Al2O3)1 x films, deposited using atomic layer deposition, exhibit-ray diffraction, we show that (HfO2)x(Al2O3)1 x films with Hf:Al 3:1 25% Al remain amorphous up to 900 °C, while

Gustafsson, Torgny

154

Electrical properties of ALD HfO2 (EOT 0.47 nm)  

NASA Astrophysics Data System (ADS)

The electric properties of the dielectric stack based hafnium were characterized by C-V and I-V curves before and after annealing. The lowest equivalent oxide thickness (EOT) was obtained after PMA and equals to 0.47 nm. The leakage current for this sample at 1V gate voltage was about 10 A/cm2. Charge density in the volume of high-k was extremely high (1.61·1018 cm-3). Obtained density of interface charge is equal to moderate value 1.03·1012 cm-2.

Molchanova, A.; Rogozhin, A.

2014-12-01

155

A quantum mechanical model of gate leakage current for scaled NMOS transistors with ultra-thin High-K dielectrics and metal gate electrodes  

Microsoft Academic Search

This paper develops a quantum mechanical model for gate leakage current in scaled high-K metal-gate,NMOS transistors by considering both DT and TAT in low gate voltage regions,which can also be applied to other dual dielectric layer systems. The tunneling current is very sensitive to the low dielectric constant layer thickness. The proper control of the interfacial layer is important to

Yanli Zhang; Zhian Jin; Gan Wang; L. S. Liyanage; M. H. White

2007-01-01

156

High-performance polycrystalline silicon thin-film transistors integrating sputtered aluminum-oxide gate dielectric with bridged-grain active channel  

E-print Network

(TFTs) integrating sputtered Al2O3 gate dielectric with bridged-grain active channel are demonstrated­7], such as Al2O3 [4], HfO2 [5], Pr2O3 [6] and Y2O3 [7], are applied into the poly-Si TFTs to improve device dielectrics [4­12]. In this work, poly-Si TFTs integrating a high-k Al2O3 gate dielectric with bridged

157

Charging phenomena in dielectric/semiconductor heterostructures during x-ray photoelectron spectroscopy measurements  

NASA Astrophysics Data System (ADS)

The determination of the valence band offset (VBO) by x-ray photoelectron spectroscopy (XPS) is commonly performed using the so-called Kraut's method that was developed for VBO determination in semiconductor/semiconductor heterojunctions. Although the physical model, which is the basis of the method, can be safely extended to dielectric/semiconductor (D/S) heterojunctions, in these systems a careful evaluation of the experimental results is necessary due to the differential charging phenomena originating at D/S interface during x-ray bombardment. As a consequence, precise determination of the VBO requires an accurate calibration of the energy scale in order to remove artifacts induced by the progressive charging of the oxide during the XPS measurement. In this work a detailed analysis of the band alignment between e-beam evaporated amorphous HfO2 films and Si substrates is reported. The HfO2/Si heterojunction was selected as a prototype for this study since HfO2 based dielectrics have already been implemented as gate dielectrics in real devices and have been the subject of a wide number of publications providing controversial results in terms of VBO values. A clear dependence of the binding energy of the Hf 4f and O 1s core lines on the thickness of the HfO2 film is identified. The time evolution of these signals indicates that different steady states are reached after prolonged x-ray bombardment depending on the thickness of the HfO2 films. On the basis of the original work of Iwata et al. [J. App. Phys. 79, 6653 (1996)], a rigorous method to remove these artifacts and empirically determine the real band offsets in D/S heterojunctions is proposed and validated by comparison with internal photoemission and photoconductivity data obtained on the same set of samples.

Perego, M.; Seguini, G.

2011-09-01

158

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

159

Nitrogen engineering of ultrathin oxynitrides by a thermal NO/O2/NO E. P. Gusev,a)  

E-print Network

Nitrogen engineering of ultrathin oxynitrides by a thermal NO/O2/NO process E. P. Gusev,a) H. C. Lu discusses nitrogen engineering of ultrathin ( 5 nm oxynitride gate dielectrics. The dielectric film that we have aimed for has two nitrogen enhanced layers: one at the SiO2/polysilicon interface to retard boron

Gustafsson, Torgny

160

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

161

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

162

Exciton polaritons in a CuBr microcavity with HfO2/SiO2 distributed Bragg reflectors  

NASA Astrophysics Data System (ADS)

We have investigated the characteristics of exciton-photon strong coupling in a CuBr bulk microcavity that consists of a CuBr active layer with an effective thickness of ?/2 and HfO2/SiO2 distributed Bragg reflectors: ? corresponds to an effective resonant wavelength of the lowest-lying exciton. The CuBr crystal has three excitons labeled Zf, Z1,2, and Z3 at the ? point, where the Zf exciton originates from a triplet state, which is peculiar to CuBr. Angle-resolved reflectance spectra measured at 10 K demonstrate the strong coupling behavior of the Zf, Z1,2, and Z3 excitons and cavity photon, resulting in the formation of four cavity-polariton branches. Analyzing the cavity-polariton dispersion relations based on a phenomenological Hamiltonian for the strong coupling, we evaluated the vacuum Rabi-splitting energies of the Zf, Z1,2, and Z3 excitons to be 31, 108, and 84 meV, respectively. These Rabi-splitting energies reflect the magnitudes of the oscillator strengths of the relevant excitons. Furthermore, we precisely measured angle-resolved photoluminescence (PL) spectra of the lower polariton branch under a weak excitation condition. In the bottleneck region, the population of the cavity polaritons is negligible, and the PL intensity at k = 0 is the highest. These facts suggest that the relaxation process of the cavity polaritons is not affected by a bottleneck effect.

Nakayama, M.; Kanatanai, Y.; Kawase, T.; Kim, D.

2012-05-01

163

Influence of Si/SiO 2 interface properties on electrical performance and breakdown characteristics of ultrathin stacked oxide/nitride dielectric films  

NASA Astrophysics Data System (ADS)

In this work, the influence of Si/SiO 2 interface properties, interface nitridation and remote-plasma-assisted oxidation (RPAO) thickness (<1 nm), on electrical performance and TDDB characteristics of sub-2 nm stacked oxide/nitride gate dielectrics has been investigated using a constant voltage stress (CVS). It is demonstrated that interfacial plasma nitridation improves the breakdown and electrical characteristics. In the case of PMOSFETs stressed in accumulation, interface nitridation suppresses the hole traps at the Si/SiO 2 interface evidenced by less negative Vt shifts. Interface nitridation also retards hole tunneling between the gate and drain, resulting in reduced off-state drain leakage. In addition, the RPAO thickness of stacked gate dielectrics shows a profound effect in device performance and TDDB reliability. Also, it is demonstrated that TDDB characteristics are improved for both PMOS and NMOS devices with the 0.6 nm-RPAO layer using Weibull analysis. The maximum operating voltage is projected to be improved by 0.3 V difference for a 10-year lifetime. However, physical breakdown mechanism and effective defect radius during stress appear to be independent of RPAO thickness from the observation of the Weibull slopes. A correlation between trap generation and dielectric thickness changes based on the C- V distortion and oxide thinning model is presented to clarify the trapping behavior in the RPAO and bulk nitride layer during CVS stress.

Lee, Yi-Mu; Wu, Yider

2008-05-01

164

Atomic scale characterization of HfO2/Al2O3 thin films grown on nitrided and oxidized Si substrates  

NASA Astrophysics Data System (ADS)

One and three bilayers of HfO2(9Å )/Al2O3(3Å) thin films were grown by atomic layer chemical-vapor deposition on Si(001) substrates whose surfaces were nitrided or oxidized. The films as-grown and postannealed in an ultrahigh vacuum were analyzed by atomic force microscopy, photoelectron spectroscopy, and medium energy ion scattering. For the one- and three-bilayer films grown on the nitrided Si substrates, the HfO2 and Al2O3 layers are mixed to form Hf aluminates at temperatures above 600°C. The mixed Hf aluminate layer is partly decomposed into HfO2 and Al2O3 grains and Al2O3 segregates to the surface by postannealing at 900°C. Complete decomposition takes place at 1000°C and the surface is covered with Al2O3. The surfaces are uniform and almost flat up to 900°C but are considerably roughened at 1000°C due to the complete decomposition of the Hf aluminate layer. In contrast, for one- bilayer films stacked on the oxidized Si substrates, Hf silicate layers, including Hf aluminate, are formed by annealing at 600-800°C. At temperatures above 900°C, HfSi2 grows and Al oxide escapes from the surface.

Nishimura, T.; Okazawa, T.; Hoshino, Y.; Kido, Y.; Iwamoto, K.; Tominaga, K.; Nabatame, T.; Yasuda, T.; Toriumi, A.

2004-12-01

165

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

166

Optical and Structural Properties of Ultra-thin Gold Films  

E-print Network

Realizing laterally continuous ultra-thin gold films on transparent substrates is a challenge of significant technological importance. In the present work, formation of ultra-thin gold films on fused silica is studied, demonstrating how suppression of island formation and reduction of plasmonic absorption can be achieved by treating substrates with (3-mercaptopropyl) trimethoxysilane prior to deposition. Void-free fi lms with deposition thickness as low as 5.4 nm are realized and remain structurally stable at room temperature. Based on detailed structural analysis of the fi lms by specular and diffuse X-ray reflectivity measurements, it is shown that optical transmission properties of continuous ultra-thin films can be accounted for using the bulk dielectric function of gold. However, it is important to take into account the non-abrupt transition zone between the metal and the surrounding dielectrics, which extends through several lattice constants for the laterally continuous ultra-thin films (film thickness...

Kossoy, Anna; Simakov, Denis; Leosson, Kristjan; Kéna-Cohen, Stéphane; Maier, Stefan A

2014-01-01

167

Thickness mapping of high-κ dielectrics at the nanoscale  

NASA Astrophysics Data System (ADS)

Contact potential difference measurements by Kelvin probe force microscopy (KPFM) together with corona charging was applied for contactless equivalent oxide thickness (EOT) mapping with nanometer range lateral resolution. Characterization was performed under ambient conditions and compared to a conventional macroscale method based on Kelvin probe measurements. The presented method is directly applicable for dielectrics with homogeneous thicknesses. For other dielectric layers, the implemented laboratory setup suffers from imprecise KPFM sample positioning. If such samples have microscopically non-flat surfaces a proposed data evaluation procedure overcomes that issue which is demonstrated for nanoscale EOT maps of HfO2 and HfSixOy samples.

Trapnauskas, J.; Rommel, M.; Bauer, A. J.; Frey, L.

2014-02-01

168

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

169

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

SciTech Connect

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

Ren, H.; Shohet, J. L. [Department of Electrical and Computer Engineering, Plasma Processing and Technology Laboratory, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Cheng, S. L.; Nishi, Y. [Stanford University, Stanford, California 94305 (United States)

2010-05-10

170

Electrical transport properties of ultrathin disordered films  

Microsoft Academic Search

We report an experimental study of quench condensed (2K?T?15K) disordered ultrathin films of Bi where localization effects and superconductivity compete. Experiments are done with different substrates and\\/or different underlayers. Quasi-free-standing films of Bi, prepared by quenching Bi vapours onto solid Xe, are also studied. The results show a dependence of the transport properties both on the dielectric constant of the

G. Sambandamurthy; K. Das Gupta; N. Chandrasekhar

2000-01-01

171

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

172

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

173

X-ray photoelectron spectroscopy of SiO2-HfO2 amorphous and glass-ceramic waveguides: a comparative study  

NASA Astrophysics Data System (ADS)

X-ray photoelectron spectroscopy (XPS) was used to characterize xHfO2 - (100-x) SiO2 (x = 10, 20, 30, 40 mol%) amorphous waveguides and xHfO2 - (100-x) SiO2 (x = 10, 20, 30 mol%) glass-ceramic waveguides, doped with 0.3 mol% Er3+ ions, and prepared by the sol-gel route. The XPS analysis provided a detailed description of the mechanisms underlying the structural properties of the two different silica-hafnia systems. In particular the effect of the Hf concentration and of the annealing protocol on the material structure were worked out by studying the oxygen, silicon and hafnium core lines. In the case of SiO2-HfO2 amorphous waveguides with hafnia concentration <= 30 mol%, core lines show the formation of hafnium silicate homogeneously dispersed in the silica matrix. For higher hafnia concentrations the material undergoes a spinodal decomposition with generation of HfO2 rich domains. In the glass-ceramics the thermal treatments lead to the growth of crystallites also at Hf concentration as low as 10%. Optical, structural and spectroscopic properties of the amorphous and glass-ceramic waveguides are compared and discussed on the basis of the XPS results, allowing us to understand the chemical-physics of the fabricated waveguides, which are characterized by low-losses and by efficient luminescence @ 1.5 ?m.

Minati, L.; Speranza, G.; Torrengo, S.; Alombert-Goget, G.; Ferrari, M.; Jestin, Y.; Righini, G. C.

2009-05-01

174

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

PubMed

The nano-precursors in the subsurface of Nd:YLF crystal were limiting factor that decreased the laser-induced damage threshold (LIDT) of HfO(2)/SiO(2) high reflection (HR) coatings irradiated from crystal-film interface. To investigate the contribution of electric-field (E-field) to laser damage originating from nano-precursors and then to probe the distribution of vulnerable nano-precursors in the direction of subsurface depth, two 1064 nm HfO(2)/SiO(2) HR coatings having different standing-wave (SW) E-field distributions in subsurface of Nd:YLF c5424181043036123rystal were designed and prepared. Artificial gold nano-particles were implanted into the crystal-film interface prior to deposition of HR coatings to study the damage behaviors in a more reliable way. The damage test results revealed that the SW E-field rather than the travelling-wave (TW) E-field contributed to laser damage. By comparing the SW E-field distributions and LIDTs of two HR coating designs, the most vulnerable nano-precursors were determined to be concentrated in a thin redeposition layer that is within 100 nm from the crystal-film interface. PMID:23787674

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

2013-06-17

175

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

176

On the bipolar resistive-switching characteristics of Al2O3- and HfO2-based memory cells operated in the soft-breakdown regime  

NASA Astrophysics Data System (ADS)

In this article, we investigate extensively the bipolar-switching properties of Al2O3- and HfO2-based resistive-switching memory cells operated at low current down to <1 ?A. We show that the switching characteristics differ considerably from those typically reported for larger current range (>15 ?A), which we relate as intrinsic to soft-breakdown (SBD) regime. We evidence a larger impact of the used switching-oxide in this current range, due to lower density of oxygen-vacancy (Vo) defects in the SBD regime. In this respect, deep resetting and large memory window may be achieved using the stoichiometric Al2O3 material due to efficient Vo annihilation, although no complete erasure of the conductive-filament (CF) is obtained. We finally emphasize that the conduction may be described by a quantum point-contact (QPC) model down to very low current level where only a few Vo defects compose the QPC constriction. The large switching variability inherent to this latter aspect is mitigated by CF shape tuning through adequate engineering of an Al2O3HfO2 bilayer.

Goux, L.; Raghavan, N.; Fantini, A.; Nigon, R.; Strangio, S.; Degraeve, R.; Kar, G.; Chen, Y. Y.; De Stefano, F.; Afanas'ev, V. V.; Jurczak, M.

2014-10-01

177

Comparative studies of AlGaN/GaN MOS-HEMTs with stacked gate dielectrics by the mixed thin film growth method  

NASA Astrophysics Data System (ADS)

This paper reports Al0.27Ga0.73N/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) with stacked Al2O3/HfO2 gate dielectrics by using hydrogen peroxideoxidation/sputtering techniques. The Al2O3 employed as a gate dielectric and surface passivation layer effectively suppresses the gate leakage current, improves RF drain current collapse and exhibits good thermal stability. Moreover, by stacking the good insulating high-k HfO2 dielectric further suppresses the gate leakage, enhances the dielectric breakdown field and power-added efficiency, and decreases the equivalent oxide thickness. The present MOS-HEMT design has demonstrated superior improvements of 10.1% (16.4%) in the maximum drain-source current (IDS, max), 11.4% (22.5%) in the gate voltage swing and 12.5%/14.4% (21.9%/22.3%) in the two-terminal gate-drain breakdown/turn-on voltages (BVGD/VON), and the present design also demonstrates the lowest gate leakage current and best thermal stability characteristics as compared to two reference MOS-HEMTs with a single Al2O3/(HfO2) dielectric layer of the same physical thickness.

Chou, Bo-Yi; Hsu, Wei-Chou; Lee, Ching-Sung; Liu, Han-Yin; Ho, Chiu-Sheng

2013-07-01

178

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

179

Improved growth behavior of atomic-layer-deposited high-k dielectrics on multilayer MoS2 by oxygen plasma pretreatment.  

PubMed

We report on the effect of oxygen plasma treatment of two-dimensional multilayer MoS2 crystals on the subsequent growth of Al2O3 and HfO2 films, which were formed by atomic layer deposition (ALD) using trimethylaluminum and tetrakis-(ethylmethylamino)hafnium metal precursors, respectively, with water oxidant. Due to the formation of an ultrathin Mo-oxide layer on the MoS2 surface, the surface coverage of Al2O3 and HfO2 films was significantly improved compared to those on pristine MoS2, even at a high ALD temperature. These results indicate that the surface modification of MoS2 by oxygen plasma treatment can have a major impact on the subsequent deposition of high-k thin films, with important implications on their integration in thin film transistors. PMID:23683268

Yang, Jaehyun; Kim, Sunkook; Choi, Woong; Park, Sang Han; Jung, Youngkwon; Cho, Mann-Ho; Kim, Hyoungsub

2013-06-12

180

Performance analysis of silicon nanowire transistors considering effective oxide thickness of high-k gate dielectric  

NASA Astrophysics Data System (ADS)

We have analyzed the effective oxide thickness (EOT) of the dielectric material for which we have optimum performance and the output characteristics of the silicon nanowire transistors by replacing the traditional SiO2 gate insulator with a material that has a much higher dielectric constant (high-k) gate, materials like Si3N4, Al2O3, Y2O3 and HfO2. We have also analyzed the channel conductance, the effect of a change in thickness, the average velocity of the charge carrier and the conductance efficiency in order to study the performance of silicon nanowire transistors in the nanometer region. The analysis was performed using the Fettoy, a numerical simulator for ballistic nanowire transistors using a simple top of the barrier (Natori) approach, which is composed of several matlab scripts. Our results show that hafnium oxide (HfO2) gate insulator material provides good thermal stability, a high recrystallization temperature and better interface qualities when compared with other gate insulator materials; also the effective oxide thickness of HfO2 is found to be 0.4 nm.

Chandra, S. Theodore; Balamurugan, N. B.

2014-04-01

181

Leakage current in high dielectric oxides: Role of defect-induced energies  

NASA Astrophysics Data System (ADS)

Model evaluations of field-dependent leakage currents in the high-k dielectric oxides HfO2 and ZrO2 are presented. The treatment includes a number of competing transport processes on an equal footing. Our simulation results show that trap-assisted-tunneling, though important, is not the most significant contributor. The combined Poole-Frenkel mechanism with modifications from inelastic trap-related processes dominates at electric fields above 1.5 MV/cm. Our model predictions compare very favorably against the reported experimental data for both HfO2 and ZrO2. Finally, results obtained from the density functional theory based castep simulator are suggestive of dynamic changes in the net energy levels and the possible formation of a mini-band due to oxygen vacancies.

Maleeswaran, P.; Nagulapally, D.; Joshi, R. P.; Pradhan, A. K.

2013-05-01

182

Thickness and post-annealing effects of the sputtered La-capping layer inserted between the TiN gate and Hf-based dielectrics.  

PubMed

We investigated effects of the sputtered La-capping layer inserted between TiN and Hf-based dielectrics, HfO2 and HfSiO4/HfO2, mainly focusing on effective work function (EWF) and equivalent oxide thickness (EOT) changes by modulation of its thickness and post-metal annealing (PMA). The use of thin La capping up to 5 Å showed a linear flatband voltage (V(FB)) shift of -60 mV/Å, regardless of gate dielectrics. However, with the increase of the La thickness, a slight increase in EOT was observed for HfO2, whereas a negligible change in EOT was shown for the HfSiO4/HfO2 bilayer. It might be ascribed to the facile La oxidation, which acts as an additional oxide layer on both of the gate dielectrics. Meanwhile, high-temperature PMA exhibited slight reduction in V(FB) as well as an EOT increase for both of the Hf-based dielectrics. On the basis of X-ray photoelectron spectroscopy (XPS) results, the reason for the slightly decreased EWF resulted from two competing dipoles formed by movements of oxygen vacancies (V(O)) and La atoms during the PMA. Additionally, oxygen affinity and diffusion of the La-capping layer on both of the gate dielectrics are further discussed in conjunction with thermodynamic analyses, and thereby, schematic energy band diagrams were proposed by taking into account competing dipole layers by VO movement and La diffusion. PMID:24641256

Kim, Woo-Hee; Lee, Nae-In; Lee, Jong-Ho; Kim, Kug-Hwan

2014-04-01

183

Statistics of electrical breakdown field in HfO2 and SiO2 films from millimeter to nanometer length scales  

NASA Astrophysics Data System (ADS)

The statistics of electrical breakdown field (Ebd) of HfO2 and SiO2 thin films has been evaluated over multiple length scales using macroscopic testing of standardized metal-oxide-semiconductor (TiN /SiO2/Si) and metal-insulator-metal (TiN/HfO2/TiN) capacitors (10-2mm2-10?m2 area) on a full 200mm wafer along with conductive-atomic-force microscopy. It is shown that Ebd follows the same Weibull distribution when the data are scaled using the testing area. This overall scaling suggests that the defect density is ˜1015cm-2 and Ebd is ˜40MV/cm for nanometer-length scales; as such, breakdown in these materials is most likely initiated by bond breaking rather than punctual defects.

Sire, Cédric; Blonkowski, Serge; Gordon, Michael J.; Baron, Thierry

2007-12-01

184

Sol-gel Er-doped SiO2-HfO2 planar waveguides: A viable system for 1.5 mum application  

NASA Astrophysics Data System (ADS)

70SiO2-30HfO2 planar waveguides, doped with Er3+ concentrations ranging from 0.3 to 1 mol %, were prepared by sol-gel route, using dip-coating deposition on silica glass substrates. The waveguides show high densification degree, effective intermingling of the two components of the film, and uniform surface morphology. Propagation losses of about 1 dB/cm were measured at 632.8 nm. When pumped with 987 or 514.5 nm continuous-wave laser light, the waveguides show the 4I13/2[right arrow]4I15/2 emission band with a bandwidth of 48 nm. The spectral features are found independent both on erbium content and excitation wavelength. The 4I13/2 level decay curves presented a single-exponential profile, with a lifetime between 2.9 and 5.0 ms, depending on the erbium concentration.

Goncalves, R. R.; Carturan, G.; Zampedri, L.; Ferrari, M.; Montagna, M.; Chiasera, A.; Righini, G. C.; Pelli, S.; Ribeiro, S. J. L.; Messaddeq, Y.

2002-07-01

185

Influence of Ti substitution on the electrical properties of metal-ferroelectric (BiFeO3)-insulator (HfO2)-silicon structures for nonvolatile memory applications  

NASA Astrophysics Data System (ADS)

Metal-ferroelectric (Ti-substituted BiFeO3)-insulator (HfO2)-semiconductor structures have been fabricated via the cosputtering technique. Ti4+ substitution at the Fe site was investigated through x-ray photoelectron spectra and x-ray diffraction patterns at postannealing temperatures of 500 to 700 °C. The capacitance-voltage memory windows as functions of the insulator film thickness and the dc power for Ti were measured and compared. A memory window of 3.1 V was obtained at a sweep voltage of 8 V under O2-rich conditions. The leakage current and the charge injection effect, especially gate injection, can be greatly improved by Ti substitution. The effects of the postannealing temperature and the substitution amount on the leakage current can be well explained by the defect reaction model.

Pi-Chun Juan, Trevor; Liu, Yu-Wei

2011-05-01

186

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

187

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

E-print Network

their fabrication. We have studied hafnium oxide and aluminum oxide grown on gallium arsenide by atomic layer oxide is removed during the ALD pro- cess. ALD-grown Al2O3 also results in good gate stack properties; published online 4 April 2005 High-performance metal-oxide-semiconductor field effect transistors MOSFETs

Garfunkel, Eric

188

An ultrathin directional carpet cloak based on generalized Snell's law  

NASA Astrophysics Data System (ADS)

Based on generalized Snell's law, we propose an ultrathin directional carpet cloak operating in the reflection geometry. The cloak is constructed by two identical ultrathin metal-backed dielectric slabs with metallic "H" patterns on the other sides to form a triangular region. When put on an infinite ground plane and illuminated by electromagnetic waves from overhead, it can manipulate the reflected wavefronts to mimic the infinite ground plane. We fabricate a microwave sample and perform near-field scanning experiments to verify the cloaking effect. The measurement results are in good agreement with full-wave simulations and theoretical analysis.

Zhang, Jing; Lei Mei, Zhong; Ru Zhang, Wan; Yang, Fan; Jun Cui, Tie

2013-10-01

189

Interfaces of high- k dielectrics on GaAs: Their common features and the relationship with Fermi level pinning (Invited Paper)  

Microsoft Academic Search

Numerous metal oxides have been studied worldwide as possible high-k gate dielectric candidates for MOS devices on alternative semiconductor materials (Ge, III\\/V compounds). We will discuss thermal and plasma-enhanced atomic layer deposition (ALD) of a few materials, HfO2 and Al2O3. We will spend some attention to characteristic features of the growth process and specific growth precursors as this is known

Matty Caymax; Guy Brammertz; Annelies Delabie; Sonja Sioncke; Dennis Lin; Marco Scarrozza; Geoffrey Pourtois; Wei-E Wang; Marc Meuris; Marc Heyns

2009-01-01

190

Leakage current and breakdown electric-field studies on ultrathin atomic-layer-deposited Al2O3 on GaAs  

E-print Network

Leakage current and breakdown electric-field studies on ultrathin atomic-layer-deposited Al2O3-field characteristics of ultrathin Al2O3 dielectrics on GaAs grown by ALD. The leakage current in ultrathin Al2O3 on Ga properties for Al2O3. A Fowler-Nordheim tunneling analysis on the GaAs/Al2O3 barrier height is also presented

Ye, Peide "Peter"

191

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

192

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

193

Local Dielectric Spectroscopy of Nanocomposite Materials Interfaces  

E-print Network

Local dielectric spectroscopy is performed to study how relaxation dynamics of a poly-vinyl-acetate ultra-thin film is influenced by inorganic nano-inclusions of a layered silicate (montmorillonite). Dielectric loss spectra are measured by electrostatic force microscopy in the frequency-modulation mode in ambient air. Spectral changes in both shape and relaxation time are evidenced across the boundary between pure polymer and montmorillonite sheets. Dielectric loss imaging is also performed, evidencing spatial variations of dielectric properties near to nanostructures with nanometer scale resolution.

Massimiliano Labardi; Daniele Prevosto; Kim Hung Nguyen; Simone Capaccioli; Mauro Lucchesi; Pierangelo Rolla

2009-11-09

194

Control of Rabi Splitting Energies in CuCl Microcavities with HfO2/SiO2 Distributed Bragg Reflectors  

NASA Astrophysics Data System (ADS)

The exciton-photon interaction in CuCl microcavities with HfO2/SiO2 distributed Bragg reflectors has been investigated from the viewpoint of the active-layer-thickness dependence of the interaction energy, the so-called vacuum Rabi splitting energy. The active layer thickness was changed from A/32 to A/5, where A corresponds to an effective resonant wavelength of the lowest-lying Z3 exciton. We performed angle-resolved reflectance measurements, and clearly detected three cavity-polariton modes originating from the lower, middle, and upper polariton branches in a strong coupling regime of the Z3 and Z1,2 excitons, and cavity photon. The incidence-angle dependence of the cavity-polariton energies was analyzed with a phenomenological Hamiltonian for the strong coupling. The vacuum Rabi splitting energies are systematically controlled from 22 (37) to 68 (122) meV for the Z3 (Z1,2) exciton with an increase in the active layer thickness. The active-layer-thickness dependence of the Rabi splitting energy is quantitatively explained using a simple model for quantum-well microcavities.

Nakayama, M.; Miyazaki, K.; Kawase, T.; Kim, D.

195

Near-field nano-ellipsometer for ultrathin film characterization.  

PubMed

We describe a near-field ellipsometer for accurate characterization of ultrathin dielectric films. Optical tunnelling mimics the absorption in metallic films, enabling accurate measurement of the refractive index of ultrathin dielectric film. A regression model shows that a refractive index resolution of 0.001 for films as thin as 1 nm is possible. A solid-immersion nano-ellipsometer that incorporates this near-field ellipsometric technique with a solid-immersion lens is constructed to demonstrate the viability of this technique. Such a nano-ellipsometer can accurately characterize thin films ranging in thickness from subnanometre to micrometres with potential transverse resolution of the order of 100 nm. PMID:12787087

Zhan, Q; Leger, J R

2003-06-01

196

A comparative study of depth profiling of interface states using charge pumping and low frequency noise measurement in SiO 2\\/HfO 2 gate stack nMOSFETs  

Microsoft Academic Search

Charge pumping and low frequency noise measurements for depth profiling have been studied systematically using a set of gate stacks with various combinations of IL and HfO2 thicknesses. The distribution of generated traps after HCI and PBTI stress was also investigated. The drain-current power spectral density made up all of the traps of IL in 0

Kyong Taek Lee; Chang Yong Kang; Hyun-Sik Choi; Seung-Ho Hong; Gil-Bok Choi; Jae Chul Kim; Seung-Hyun Song; Rock-Hyun Baek; Min-Sang Park; Hyun Chul Sagong; Byoung Hun Lee; Gennadi Bersuker; Hsing-Huang Tseng; Raj Jammy; Yoon-Ha Jeong

2009-01-01

197

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

198

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

199

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

200

Determination of energy barrier profiles for high-k dielectric materials utilizing bias-dependent internal photoemission  

NASA Astrophysics Data System (ADS)

We utilize bias-dependent internal photoemission spectroscopy to determine the metal/dielectric/silicon energy barrier profiles for Au /HfO2/Si and Au /Al2O3/Si structures. The results indicate that the applied voltage plays a large role in determining the effective barrier height and we attribute much of the variation in this case to image potential barrier lowering in measurements of single layers. By measuring current at both positive and negative voltages, we are able to measure the band offsets from Si and also to determine the flatband voltage and the barrier asymmetry at 0V. Our SiO2 calibration sample yielded a conduction band offset value of 3.03±0.1eV. Measurements on HfO2 give a conduction band offset value of 2.7±0.2eV (at 1.0V) and Al2O3 gives an offset of 3.3±0.1 (at 1.0V). We believe that interfacial SiO2 layers may dominate the electron transport from silicon for these films. The Au /HfO2 barrier height was found to be 3.6±0.1eV while the Au /Al2O3 barrier is 3.5±0.1eV.

Brewer, Julie Casperson; Walters, Robert J.; Bell, L. Douglas; Farmer, Damon B.; Gordon, Roy G.; Atwater, Harry A.

2004-11-01

201

Remote Phonon Scattering in Si and Ge with SiO2 and HfO2 Insulators: Does the Electron Mobility Determine Short Channel Performance?  

Microsoft Academic Search

We have computed the low-field electron mobility in inversion layers for single-gate metal-oxide-semiconductor-field-effect-transistor (MOSFET) structures with Si and Ge substrates and high-kappa gate dielectrics. Scattering with bulk phonons, surface roughness, and surface optical phonons has been included. The mobility has been studied as a function of electron sheet density, gate dielectric, temperature, equivalent dielectric thickness and for polycrystalline Si and

Terrance O'Regan; Massimo Fischetti

2007-01-01

202

Memory window widening of Pt/SrBi2Ta2O9/HfO2/Si ferroelectric-gate field-effect transistors by nitriding Si  

NASA Astrophysics Data System (ADS)

The optimum temperature of rapid thermal nitridation (RTN) of Si substrates was investigated for minimizing an equivalent oxide thickness (EOT) of an interfacial layer (IL) which was grown between HfO2 and Si of Pt/SrBi2Ta2O9(SBT)/HfO2/Si ferroelectric-gate field-effect transistors (FeFETs) during a post-annealing process. The RTN was performed in NH3 gas at various temperatures ranging from 800 °C to 1190 °C. As the RTN temperature was raised from 800 °C to 1080 °C, memory windows of drain current-gate voltage curves became wider. Large memory windows were obtained at the range from 1020 °C to 1130 °C. The maximum was 1.36 V obtained at 1080 °C. It was 10% larger than the typical values of Pt/SBT/HfO2/Si FeFETs without the RTN. At higher RTN temperatures than 1080 °C, the memory windows tended to decrease. At 800 °C and 1190 °C, all layer boundaries among SBT-HfO2-IL-Si seemed unclear in scanning transmission electron microscopic views probably due to material diffusions. The optimum RTN temperature for minimizing the EOT of the IL and maximizing the memory window of the Pt/SBT/HfO2/SiNx/Si FeFET was 1080 °C. The FeFET using the Si processed by the RTN at 1080 °C also showed good retentions without significant degradations over two days.

Horiuchi, Takeshi; Takahashi, Mitsue; Ohhashi, Kentaro; Sakai, Shigeki

2009-10-01

203

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

204

Effects of interfacial nitrogen on the structural and electrical properties of ultrathin ZrO2 gate dielectrics on partially strain-compensated SiGeC/Si heterolayers  

NASA Astrophysics Data System (ADS)

The interfacial characteristics of high-? ZrO2 on O2 and N2O-plasma-treated Si0.69Ge0.3C0.01 surfaces have been investigated using secondary ion mass spectroscopy and x-ray photoelectron spectroscopy. N2O-plasma-treated films show the formation of a nitrogen-rich Zr-germano-silicate interfacial layer between the deposited ZrO2 and SiGeC films. The N-treated film has a higher accumulation capacitance (˜1200 pF), lower leakage current density (7×10-9 A/cm2@-1 V), higher breakdown field (˜11 MV/cm), and higher interfacial layer dielectric constant (˜10) than that of the non-nitrogen-treated films. Relatively lower positive trap charge generated by a constant current stressing in N-incorporated dielectric films makes it attractive for scaled metal-oxide-semiconductor field-effect transistor applications.

Mahapatra, R.; Maikap, S.; Lee, Je-Hun; Kar, G. S.; Dhar, A.; Hwang, Nong-M.; Kim, Doh-Y.; Mathur, B. K.; Ray, S. K.

2003-06-01

205

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

206

In situ auger electron spectroscopy study of atomic layer deposition: growth initiation and interface formation reactions during ruthenium ALD on Si-H, SiO2, and HfO2 surfaces.  

PubMed

Growth initiation and film nucleation in atomic layer deposition (ALD) is important for controlling interface composition and achieving atomic-scale films with well-defined composition. Ruthenium ALD is studied here using ruthenocene and oxygen as reactants, and growth initiation and nucleation are characterized on several different growth surfaces, including SiO2, HfO2, and hydrogen terminated silicon, using on-line Auger electron spectroscopy and ex-situ X-ray photoelectron spectroscopy. The time needed to reach the full growth rate (typically approximately 1 A per deposition cycle) is found to increase as the surface energy of the starting surface (determined from contact angle measurements) decreased. Growth starts more readily on HfO2 than on SiO2 or Si-H surfaces, and Auger analysis indicates distinct differences in surface reactions on the various surfaces during film nucleation. Specifically, surface oxygen is consumed during ruthenocene exposure, so the nucleation rate will depend on the availability of oxygen and the energetics of surface oxygen bonding on the starting substrate surface. PMID:17461600

Park, Kie Jin; Terry, David B; Stewart, S Michael; Parsons, Gregory N

2007-05-22

207

Ultra-thin quadri-band metamaterial absorber based on spiral structure  

NASA Astrophysics Data System (ADS)

We introduce a design of the metamaterial absorber (MA) consisting of spiral artificial inclusions printed on an ultra-thin dielectric layer backed by a metal plate. Both simulations and experiments show that the MA can achieve absorptions up to 96.49, 94.25, 98.94 and 92.04 % at 6.69, 8.70, 11.90 and 15.14 GHz, respectively. The surface current and power loss density of each absorption frequency were discussed to reveal the physical mechanism. Moreover, the proposed quadri-band MA possesses the advantages of being ultra-thin and polarization-insensitive and thus may find potential applications.

Wang, Wenjie; Yan, Mingbao; Pang, Yongqiang; Wang, Jiafu; Ma, Hua; Qua, Shaobo; Chen, Hongya; Xu, Cuilian; Feng, Mingde

2015-02-01

208

Interface Electronic State Characterization of Plasma Enhanced Atomic Layer Deposited Dielectrics on GaN  

NASA Astrophysics Data System (ADS)

In this dissertation, the interface chemistry and electronic structure of plasma-enhanced atomic layer deposited (PEALD) dielectrics on GaN are investigated with x-ray and ultraviolet photoemission spectroscopy (XPS and UPS). Three interrelated issues are discussed in this study: (1) PEALD dielectric growth process optimization, (2) interface electronic structure of comparative PEALD dielectrics on GaN, and (3) interface electronic structure of PEALD dielectrics on Ga- and N-face GaN. The first study involved an in-depth case study of PEALD Al2O3 growth using dimethylaluminum isopropoxide, with a special focus on oxygen plasma effects. Saturated and self-limiting growth of Al2O3 films were obtained with an enhanced growth rate within the PEALD temperature window (25--220 °C). The properties of Al2O3 deposited at various temperatures were characterized to better understand the relation between the growth parameters and film properties. In the second study, the interface electronic structures of PEALD dielectrics on Ga-face GaN films were measured. Five promising dielectrics (Al2O3, HfO2, SiO2, La2O 3, and ZnO) with a range of band gap energies were chosen. Prior to dielectric growth, a combined wet chemical and in-situ H 2/N2 plasma clean process was employed to remove the carbon contamination and prepare the surface for dielectric deposition. The surface band bending and band offsets were measured by XPS and UPS for dielectrics on GaN. The trends of the experimental band offsets on GaN were related to the dielectric band gap energies. In addition, the experimental band offsets were near the calculated values based on the charge neutrality level model. The third study focused on the effect of the polarization bound charge of the Ga- and N-face GaN on interface electronic structures. A surface pretreatment process consisting of a NH4OH wet chemical and an in-situ NH3 plasma treatment was applied to remove carbon contamination, retain monolayer oxygen coverage, and potentially passivate N-vacancy related defects. The surface band bending and polarization charge compensation of Ga- and N-face GaN were investigated. The surface band bending and band offsets were determined for Al2O3, HfO2, and SiO 2 on Ga- and N-face GaN. Different dielectric thicknesses and post deposition processing were investigated to understand process related defect formation and/or reduction.

Yang, Jialing

209

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride  

NASA Astrophysics Data System (ADS)

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride (h-BN) on gold-coated mica was investigated using conductive atomic force microscopy. Low-bias direct tunneling was observed in mono-, bi-, and tri-layer h-BN. For all thicknesses, Fowler-Nordheim tunneling (FNT) occurred at high bias, showing an increase 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.

Lee, Gwan-Hyoung; Yu, Young-Jun; Lee, Changgu; Dean, Cory; Shepard, Kenneth L.; Kim, Philip; Hone, James

2011-12-01

210

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

211

Structural, electronic, vibrational and dielectric properties of selected high-shape K semiconductor oxides  

NASA Astrophysics Data System (ADS)

The semiconductor oxides SnO2, HfO2, ZrO2, TiO2 and SrTiO3 are interesting materials for applications as high-K dielectric gate materials in silicon-based devices and spintronics, among others. Here we review our theoretical work about the structural, electronic and vibrational properties of these oxides in their most stable structural phases, including dielectric properties as derived from the electronic structure taking into account the lattice contribution. Finally, we address the recent role played by the presence of transition metal atoms in semiconductor oxides, considering in particular SnO2 as an example in forming diluted magnetic alloys.

Scolfaro, L. M. R.; Leite Alves, H. W.; Borges, P. D.; Garcia, J. C.; da Silva, E. F., Jr.

2014-10-01

212

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

213

Global optimization of omnidirectional wavelength selective emitters/absorbers based on dielectric-filled anti-reflection coated two-dimensional metallic photonic crystals.  

PubMed

We report the design of dielectric-filled anti-reflection coated (ARC) two-dimensional (2D) metallic photonic crystals (MPhCs) capable of omnidirectional, polarization insensitive, wavelength selective emission/absorption. Using non-linear global optimization methods, optimized hafnium oxide (HfO2)-filled ARC 2D Tantalum (Ta) PhC designs exhibiting up to 26% improvement in emittance/absorptance at wavelengths ? below a cutoff wavelength ?c over the unfilled 2D TaPhCs are demonstrated. The optimized designs possess high hemispherically average emittance/absorptance ?H of 0.86 at ? < ?c and low ?H of 0.12 at ? > ?c. PMID:25321547

Yeng, Yi Xiang; Chou, Jeffrey B; Rinnerbauer, Veronika; Shen, Yichen; Kim, Sang-Gook; Joannopoulos, John D; Soljacic, Marin; Celanovi?, Ivan

2014-09-01

214

Dielectric function of warm dense gold  

SciTech Connect

Single-state measurements of the broadband (450-800 nm) dielectric function of gold using a supercontinuum probe are reviewed. These measurements have demonstrated the first evidence of the existence of band structure in ultrathin gold foils isochorically heated by a femtosecond laser pulse to energy densities of 10{sup 6}-10{sup 7} J/kg. The Drude component of the dielectric function increases with energy density while the interband component shows both enhancement and redshift. Ab initio molecular-dynamics calculations based on thermalized electrons cannot reproduce the experimental results, suggesting a non-Fermi distribution of excited electrons.

Ping, Y.; Ogitsu, T.; Schwegler, E.; Collins, G. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Hanson, D.; Koslow, I. [Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia (Canada); Prendergast, D. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Ng, A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia (Canada)

2008-05-15

215

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

216

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

217

Investigation of an anomalous hump in gate current after negative-bias temperature-instability in HfO2/metal gate p-channel metal-oxide-semiconductor field-effect transistors  

NASA Astrophysics Data System (ADS)

This Letter investigates a hump in gate current after negative-bias temperature-instability (NBTI) in HfO2/metal gate p-channel metal-oxide-semiconductor field-effect transistors. Measuring gate current at initial through body floating and source/drain floating shows that hole current flows from source/drain. The fitting of gate current (Ig)-gate voltage (Vg) characteristic curves demonstrates that the Frenkel-Poole mechanism dominates the conduction. Next, by fitting the gate current after NBTI, in the order of Frenkel-Poole then tunneling, the Frenkel-Poole mechanism can be confirmed. These phenomena can be attributed to hole trapping in high-k bulk and the electric field formula Ehigh-k ?high-k = Q + Esio2?sio2.

Ho, Szu-Han; Chang, Ting-Chang; Wu, Chi-Wei; Lo, Wen-Hung; Chen, Ching-En; Tsai, Jyun-Yu; Liu, Guan-Ru; Chen, Hua-Mao; Lu, Ying-Shin; Wang, Bin-Wei; Tseng, Tseung-Yuen; Cheng, Osbert; Huang, Cheng-Tung; Sze, Simon M.

2013-01-01

218

Theoretical views on activation of methane catalyzed by Hf2+ and oxidation of CO (x(1)?(+)) by N2O (x(1)?(+)) Catalyzed by HfO2+ and TaO2+.  

PubMed

The mechanisms of activation of CH4 catalyzed by (1/3)Hf(2+) and oxidation of CO by N2O catalyzed by (1/3)HfO(2+) or (2/4)TaO(2+) have been investigated using the B3LYP level of theory. For the activation of methane, the TSR (two-state reactivity) mechanism has been certified through the spin-orbit coupling (SOC) calculation and the Landau-Zener-type model. In the vicinity of the minimum energy crossing point (MECP), SOC equals 900.23 cm(-1) and the probability of intersystem crossing is approximately 0.62. Spin inversion makes the activation barrier decline from 1.63 to 0.57 eV. NBO analysis demonstrates that empty 6s and 5d orbitals of the Hf atom play the major role for the activation of C-H bonds. Finally, CH4 dehydrogenates to produce Hf-CH2(2+). For oxidation of CO by N2O catalyzed by HfO(2+) or TaO(2+), the covalent bonds between transition metal atoms and the oxygen atom restrict the freedom of valence electrons. Therefore, they are all SSR (single-state reactivity). The oxygen atom is directly extracted during the course of oxygen transfer, and its microscopic essence has been discussed. The detailed kinetic information of two catalytic cycles has been calculated by referencing the "energetic span (?E)" model. Finally, TOF(HfO(2+))/TOF(TaO(2+)) = 2.7 at 298.15 K, which has a good consistency with the experimental result. PMID:23947756

Nian, Jingyan; Tie, Lu; Wang, Ben; Guo, Zhiguang

2013-09-12

219

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

220

Ultrathin Planar Graphene Supercapacitors  

SciTech Connect

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

Huang, Jingsong [ORNL; Meunier, Vincent [ORNL; Sumpter, Bobby G [ORNL; Ajayan, Pullikel M [Rice University; Yoo, Jung Joon [KAIST, Daejeon, Republic of Korea; Balakrishnan, Kaushik [Rice University; Srivastava, Anchal [Rice University; Conway, Michelle [Rice University; Reddy, Arava Leela Mohan [Rice University; Yu, Jin [Rice University; Vajtai, Robert [Rice University

2011-01-01

221

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

222

Leakage compensated charge method for determining static CV characteristics of ultra-thin MOS capacitors  

Microsoft Academic Search

We describe a charge measurement method to determine static capacitance versus voltage characteristics of ultra-thin silicon oxide dielectric (<~3.5 nm), metal-oxide-silicon device structures in which significant leakage current is present. The leakage is accounted for using current compensation circuitry in combination with elementary charge integration electronics. For the thinnest oxides where direct tunneling is significant (<~2.5 nm), the circuit is

Hui Song; Edwin Dons; Xi Qing Sun; K. R. Farmer

1998-01-01

223

An Ultra-Thin Decoupling Capacitor with SrTiO3thin film on polyimide  

Microsoft Academic Search

An ultra-thin decoupling capacitor device has been developed, and its thickness and volume are one-seventh and one-third of those of conventional ceramics capacitors, respectively. Low temperature deposition of high dielectric constant SrTiO3thin film and flexible polyimide film as a base material make the capacitor smaller drastically. Mn impurity doping into SrTiO3improves the capacitor reliability and Mo-based electrode successfully prevents the

S. Yamamichi; A. Shibuya

2005-01-01

224

Leakage compensated charge method for determining static CV characteristics of ultra-thin MOS capacitors  

Microsoft Academic Search

We describe a charge measurement method to determine static capacitance versus voltage characteristics of ultra-thin silicon oxide dielectric (

Hui Song; Edwin Dons; Xi Qing Sun; K. R. Farmer

1998-01-01

225

Graphene field effect transistors with mica as gate dielectric layers.  

PubMed

Chemical vapor deposited monolayer graphene is transferred onto atomically flat and ultra-thin muscovite mica to study the transport characteristics of graphene with a test structure of mica-based graphene field effect transistor (GFET). The transfer curve of the 24 nm mica-based GFET shows an effective carrier mobility of 2748 cm(2)/Vs and a transconductance of 3.36 ?S, a factor of 2 and 7 larger than those values obtained from 40 nm SiO2 based GFET, respectively. The results demonstrate that mica is an excellent gate dielectric material due to its high dielectric constant, high dielectric strength, and atomically flat surface. PMID:25044452

Low, Chong Guan; Zhang, Qing; Hao, Yufeng; Ruoff, Rodney S

2014-10-29

226

Spatial fluctuation of dielectric properties in Hf-based high-k gate films studied by scanning capacitance microscopy  

NASA Astrophysics Data System (ADS)

Scanning capacitance microscopy using a self-sensing probe has been applied to the quantification of local dielectric properties in Hf-based high-k films grown by an atomic layer deposition method. Local capacitance spectroscopy revealed distinctive contrasts in dC /dV and dC /dZ images originating from the spatial distribution of fixed charges in the films. We also found that the HfSiON film shows better performance than HfSiO and HfO2, in terms of flat-band voltage (VFB) shift and spatial fluctuation. In every sample, the spatial fluctuations of gate capacitance (COX) are less than 3%. Considering VFB shift and COX fluctuations, HfSiON was found to be a promising candidate for gate dielectric applications.

Naitou, Y.; Ando, A.; Ogiso, H.; Kamiyama, S.; Nara, Y.; Nakamura, K.; Watanabe, H.; Yasutake, K.

2005-12-01

227

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

228

Dielectric siphons.  

NASA Technical Reports Server (NTRS)

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

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

1971-01-01

229

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

230

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

NASA Astrophysics Data System (ADS)

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

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

1995-01-01

231

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

NASA Astrophysics Data System (ADS)

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

Zhou, Xing

232

Electrostatic doping of graphene through ultrathin hexagonal boron nitride films.  

PubMed

When combined with graphene, hexagonal boron nitride (h-BN) is an ideal substrate and gate dielectric with which to build metal|h-BN|graphene field-effect devices. We use first-principles density functional theory (DFT) calculations for Cu|h-BN|graphene stacks to study how the graphene doping depends on the thickness of the h-BN layer and on a potential difference applied between Cu and graphene. We develop an analytical model that describes the doping very well, allowing us to identify the key parameters that govern the device behavior. A predicted intrinsic doping of graphene is particularly prominent for ultrathin h-BN layers and should be observable in experiment. It is dominated by novel interface terms that we evaluate from DFT calculations for the individual materials and for interfaces between h-BN and Cu or graphene. PMID:21936569

Bokdam, Menno; Khomyakov, Petr A; Brocks, Geert; Zhong, Zhicheng; Kelly, Paul J

2011-11-01

233

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

234

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

235

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

236

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

237

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

238

Effect of Cr additions on the electrical properties of Ni–BaTiO 3 ultra-thin multilayer capacitors  

Microsoft Academic Search

Multilayer ceramic capacitors based on BaTiO3 dielectric compositions and Ni inner electrodes have complex interfacial reactions that impact the continuity of the inner\\u000a electrode microstructure. Previously we demonstrated that through the addition of Cr to Ni, a significant improvement in the\\u000a continuity of ultra-thin Ni electrodes in Ni–BaTiO3 multilayer capacitors could be achieved. Here, the effect of the Cr addition

Anton V. Polotai; Tae-Hee Jeong; Gai-Ying Yang; Elizabeth C. Dickey; Clive A. Randall; Pascal Pinceloup; Abhijit S. Gurav

2009-01-01

239

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

240

Wrinkling of Ultrathin Polymer Films  

E-print Network

This paper presents a bilayer model to account for surface effects on the wrinkling of ultrathin polymer films. Assuming a surface layer of finite thickness, effects of surface properties on the critical strain, the equilibrium wavelength, and the wrinkle amplitude are discussed in comparison with conventional analysis. Experimental measurements of wrinkling in polymer films with thickness ranging from 200 nm to 5 nm are conducted. The bilayer model provides a consistent understanding of the experiments that deviate from conventional analysis for thickness less than 30 nm. A set of empirical surface properties is deduced from the experimental data.

Rui Huang; Christopher M. Stafford; Bryan D. Vogt

241

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

242

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

PubMed

Cr(3+), ZrO(2+), HfO(2+) and UO(2)(2+) complexes of oxalohydrazide (H(2)L(1)) and oxalyl bis(diacetylmonoxime hydrazone) [its IUPAC name is oxalyl bis(3-hydroxyimino)butan-2-ylidene)oxalohydrazide] (H(4)L(2)) have been synthesized and characterized by partial elemental analysis, spectral (IR; electronic), thermal and magnetic measurements. [Cr(L(1))(H(2)O)(3)(Cl)].H(2)O, [ZrO(HL(1))(2)].C(2)H(5)OH, [UO(2)(L(1))(H(2)O)(2)] [ZrO(H(3)L(2))(Cl)](2).2H(2)O, [HfO(H(3)L(2))(Cl)](2).2H(2)O and [UO(2)(H(2)L(2))].2H(2)O have been suggested. H(2)L(1) behaves as a monobasic or dibasic bidentate ligand while H(4)L(2) acts as a tetrabasic octadentate with the two metal centers. The molecular modeling of the two ligands have been drawn and their molecular parameters were calculated. Examination of the DNA degradation of H(2)L(1) and H(4)L(2) as well as their complexes revealed that direct contact of [ZrO(H(3)L(2))(Cl)](2).2H(2)O or [HfO(H(3)L(2))(Cl)](2).2H(2)O degrading the DNA of Eukaryotic subject. The ligands and their metal complexes were tested against Gram's positive Bacillus thuringiensis (BT) and Gram's negative (Escherichia coli) bacteria. All compounds have small inhibitory effects. PMID:20451440

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

2010-09-01

243

Leakage current and breakdown electric-field studies on ultrathin atomic-layer-deposited Al2O3 on GaAs  

NASA Astrophysics Data System (ADS)

Atomic-layer deposition (ALD) provides a unique opportunity to integrate high-quality gate dielectrics on III-V compound semiconductors. We report detailed leakage current and breakdown electric-field characteristics of ultrathin Al2O3 dielectrics on GaAs grown by ALD. The leakage current in ultrathin Al2O3 on GaAs is comparable to or even lower than that of state-of-the-art SiO2 on Si, not counting the high-k dielectric properties for Al2O3. A Fowler-Nordheim tunneling analysis on the GaAs /Al2O3 barrier height is also presented. The breakdown electric field of Al2O3 is measured as high as 10MV/cm as a bulk property. A significant enhancement on breakdown electric field up to 30MV/cm is observed as the film thickness approaches to 1nm.

Lin, H. C.; Ye, P. D.; Wilk, G. D.

2005-10-01

244

Ultrathin, flexible organic-inorganic hybrid solar cells based on silicon nanowires and PEDOT:PSS.  

PubMed

Recently, free-standing, ultrathin, single-crystal silicon (c-Si) membranes have attracted considerable attention as a suitable material for low-cost, mechanically flexible electronics. In this paper, we report a promising ultrathin, flexible, hybrid solar cell based on silicon nanowire (SiNW) arrays and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The free-standing, ultrathin c-Si membranes of different thicknesses were produced by KOH etching of double-side-polished silicon wafers for various etching times. The processed free-standing silicon membranes were observed to be mechanically flexible, and in spite of their relatively small thickness, the samples tolerated the different steps of solar cell fabrication, including surface nanotexturization, spin-casting, dielectric film deposition, and metallization. However, in terms of the optical performance, ultrathin c-Si membranes suffer from noticeable transmission losses, especially in the long-wavelength region. We describe the experimental performance of a promising light-trapping scheme in the aforementioned ultrathin c-Si membranes of thicknesses as small as 5.7 ?m employing front-surface random SiNW texturization in combination with a back-surface distribution of silver (Ag) nanoparticles (NPs). We report the enhancement of both the short-circuit current density (JSC) and the open-circuit voltage (VOC) that has been achieved in the described devices. Such enhancement is attributable to the plasmonic backscattering effect of the back-surface Ag NPs, which led to an overall 10% increase in the power conversion efficiency (PCE) of the devices compared to similar structures without Ag NPs. A PCE in excess of 6.62% has been achieved in the described devices having a c-Si membrane of thickness 8.6 ?m. The described device technology could prove crucial in achieving an efficient, low-cost, mechanically flexible photovoltaic device in the near future. PMID:24568116

Sharma, Manisha; Pudasaini, Pushpa Raj; Ruiz-Zepeda, Francisco; Elam, David; Ayon, Arturo A

2014-03-26

245

Atomic Layer Deposition of High-k Dielectrics Using Supercritical CO2  

NASA Astrophysics Data System (ADS)

Atomic layer deposition (ALD) of high-?dielectric was performed in supercritical CO2 (SCCO2), using a two-step reaction sequence. In step one, tetraethoxy silane (TEOS) precursor was injected in SCCO2 at 80-100 C and 50 MPa pressure to obtain a chemisorbed surface monolayer, which was then oxidized into SiO2 using peroxide entrained in SCCO2. ALD process was controlled by estimating precursor solubility and its mass transport with respect to the density of SCCO2, and correlating these parameters with precursor injection volume. In the ALD process, 7 pulses of precursor were used anticipating deposition of one atomic layer in each of the pulses. The thickness of the SiO2 atomic layers deposited using SCCO2 was measured by variable angle spectroscopic ellipsometry (VASE), and the C-V measurements were also performed. The result obtained using VASE indicates that there were 7 monolayers of SiO2 with total thickness of 35 å, and the dielectric constant of the deposited layers was 4.0±0.1. Our initial findings clearly demonstrate that SCCO2 is capable of atomic layer deposition of high quality dielectric films at very low process temperatures preventing interface reaction. More research is in progress to achieve ALD of HfO2 and TiO2 in SCCO2.

Shende, Rajesh

2005-03-01

246

Local study of ultrathin silicon dioxide/silicon for nanoelectronics by scanning probe microscopy  

NASA Astrophysics Data System (ADS)

Systematical local studies of ultrathin SiO2/Si properties are carried out by scanning probe microscopy (SPM) with nanometer resolution. By exploiting the advantages of scanning tunneling spectroscopy (STS) studies with the exactly same tip and same sample, monolayer-resolved local electronic properties of ultrathin SiO2 are scrutinized. It shows that an electronically transitional instead of abrupt region (3 monolayers) existed near silicon oxide/silicon interface and silicon oxide band gap increased gradually with thickness in this region. Furthermore, in an oxide thinner than three monolayers, oxide gap state can be discerned due to silicon substrate states penetration into the oxide, determining the intrinsic ultrathin limit of usable Si oxide thickness to be 3 monolayers. Electron resonant tunneling (ERT) phenomena between a metal tip and ultrathin SiO2/Si are investigated for the first time in STM setup experimentally and theoretically. A one-dimensional transport model is adopted to simulate the spectra based on accurate numerical solution of Schrodinger equation by transfer matrix method. Electron confinement and quantum interference are found to be the guided mechanism. Local oxide electric fields are evaluated from the ERT spectra to be 1-2 x 107V/cm, higher than dielectric strength of bulk SiO2. Electrical stability of ultrathin SiO2 is studied by electrical stressing. In nanometer scale, we find that Weibull statistics of the defect generation still hold valid. Differences in soft breakdown behaviors under dynamic and DC stressing show that threshold energy exists for soft breakdown to be triggered. Thermal stability of ultrathin SiO2 is scrutinized by in-situ observation of the decomposition processes by UHV thermal annealing. Morphology effects to decomposition are studied for the first time. We show that the lateral reaction boundary roughness and vertical distance played an important role, which gives insights for fully understanding of decomposition mechanism. In the end, nanometer-scale artificial structures on ultrathin SiO 2/Si are fabricated and characterized by STM. Tungsten nanodots are fabricated by a novel method via field induced tip elongation and nanocontact. The ultra small feature size and nanometer scale localization ability make which promising for future nano electronics application.

Xue, Kun

247

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

248

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

249

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

250

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

251

Effect of Al 2 O 3 concentration on zirconolite (Ca(Zr,Hf)Ti 2 O 7 ) crystallization in (TiO 2 ,ZrO 2 ,HfO 2 )-rich SiO 2 –Al 2 O 3 –CaO–Na 2 O glasses  

Microsoft Academic Search

Glass-ceramic matrices containing zirconolite (nominally Ca(Zr,Hf)Ti2O7) crystals in their bulk that would incorporate high proportions of minor actinides (Np, Am, Cm) or plutonium could be envisaged\\u000a for their immobilization. Zirconolite-based glass-ceramics can be prepared by controlled crystallization of zirconolite in\\u000a glasses belonging to SiO2–Al2O3–CaO–Na2O–TiO2–ZrO2–HfO2 system. In this study, neodymium was used as trivalent actinides surrogate. Increasing Al2O3 concentration in glass

Daniel Caurant; Pascal Loiseau; Isabelle Bardez; Christel Gervais

2007-01-01

252

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride  

E-print Network

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride Gwan-Hyoung Lee://apl.aip.org/about/rights_and_permissions #12;Electron tunneling through atomically flat and ultrathin hexagonal boron nitride Gwan-Hyoung Lee,1 atomically flat and ultrathin hexagonal boron nitride (h-BN) on gold-coated mica was investigated using

Hone, James

253

Advancing quasi-freestanding epitaxial graphene electronics through integration of wafer scale hexagonal boron nitride dielectrics  

NASA Astrophysics Data System (ADS)

A key limitation to graphene based electronics is graphene's interaction with dielectric interfaces. SiO2 and various high-k gate dielectrics can introduce scattering from charged surface states, impurities, and surface optical phonons; degrading the transport properties of graphene. Hexagonal boron nitride (h-BN) exhibits an atomically smooth surface that is expected to be free of dangling bonds, leading to an interface that is relatively free of surface charge traps and adsorbed impurities. Additionally, the decreased surface optical phonon interaction from h-BN is expected to further reduce scattering. While h-BN gated graphene FETs have been demonstrated on a small scale utilizing CVD grown or exfoliated graphene, integrating quasi-freestanding epitaxial graphene (QFEG) with h-BN gate dielectrics on a wafer scale has not been explored. We present results from the first large scale CVD growth of h-BN and its subsequent transfer to a 75mm QFEG wafer. The effects of growth conditions on the thickness and quality of the h-BN film and its potential and limitations as a gate dielectric to QFEG are discussed. The introduction of charged impurities during the transfer process resulted in an average degradation in mobility of only 9%. Despite the slight degradation, we show that h-BN is highly beneficial compared to high-k dielectrics when the charged impurity concentration of QFEG is below 5x1012cm-2. Here we show improvements in mobility of >3x and intrinsic cutoff frequency of >2x compared to HfO2.

Bresnehan, Michael S.; Hollander, Matthew J.; Marucci, Rebecca L.; LaBella, Michael; Trumbull, Kathleen A.; Cavalero, Randal; Snyder, David W.; Robinson, Joshua A.

2012-09-01

254

Chemically Tunable Ultrathin Silsesquiazane Interlayer for n-Type and p-Type Organic Transistors on Flexible Plastic.  

PubMed

In organic field-effect transistors (OFETs), surface modification of the gate-dielectric is a critical technique for enhancing the electrical properties of the device. Here, we report a simple and versatile method for fabricating an ultrathin cross-linked interlayer (thickness ?3 nm) on an oxide gate dielectric by using polymeric silsesquiazane (SSQZ). The fabricated siloxane film exhibited an ultrasmooth surface with minimal hydroxyl groups; the properties of the surface were chemically tuned by introducing phenyl and phenyl/fluorine pendent groups into the SSQZ. The growth characteristics of two semiconductors-pentacene (p-type) and N,N'-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C13, n-type)-on this ultrathin film were systematically investigated according to the type of pendent groups in the SSQZ-treated gate dielectric. Pentacene films on phenyl/fluorine groups exhibited large grains and excellent crystalline homogeneity. By contrast, PTCDI-C13 films exhibited greater crystalline order and perfectness when deposited on phenyl groups rather than on phenyl/fluorine groups. These microstructural characteristics of the organic semiconductors, as well as the dipole moment of the pendent groups, determined the electrical properties of FETs based on pentacene or PTCDI-C13. Importantly, compared to FETs in which the gate dielectric was treated with a silane-coupling agent (a commonly used surface treatment), the FETs fabricated using the tunable SSQZ treatment showed much higher field-effect mobilities. Finally, surface treatment with an ultrathin SSQZ layer was also utilized to fabricate flexible OFETs on a plastic substrate. This was facilitated by the facile SSQZ deposition process and the compatibility of SSQZ with the plastic substrate. PMID:25459690

Lee, Wi Hyoung; Lee, Seung Goo; Kwark, Young-Je; Lee, Dong Ryeol; Lee, Shichoon; Cho, Jeong Ho

2014-12-24

255

Ultrathin core-sheath fibers for liposome stabilization.  

PubMed

Ultrathin core-sheath fibers with small unilamellar vesicles (SUVs) in the core were prepared by coaxial electrospinning. SUVs/sodium hyaluranate (HA-Na)/water and polyvinylpyrrolidone (PVP)/ethanol solutions were used as core and sheath fluid in electrospinning, respectively. The ultrathin fibers were characterized by scanning and transmission electron microscopy (SEM and TEM) and laser scanning confocal microscopy (LSCM). The SUVs were successfully encapsulated in the core HA-Na matrix of the ultrathin fibers and are in the elliptic shape. The SUVs encapsulated in the core matrix of the ultrathin fibers have an excellent stability. The SUVs embedded in the ultrathin fibers are stable. When the ultrathin fibers were re-dissolved in water after one-month storage at room temperature, the rehydrated SUVs have the similar size and size distribution as the as-prepared SUVs. The liposome-loaded ultrathin fiber mats have the promising applications in wound healing materials. PMID:25130418

Li, Zhuang; Kang, Hongliang; Li, Qinmei; Che, Ning; Liu, Zhijing; Li, Pingping; Zhang, Chao; Liu, Ruigang; Huang, Yong

2014-10-01

256

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

257

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.

Christian, Wolfgang; Belloni, Mario

2007-01-26

258

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

259

Quantum chemistry study of dielectric materials deposition  

NASA Astrophysics Data System (ADS)

The drive to continually decrease the device dimensions of integrated circuits in the microelectronics industry requires that deposited films approach subnanometer thicknesses. Hence, a fundamental understanding of the physics and chemistry of film deposition is important to obtain better control of the properties of the deposited film. We use ab initio quantum chemistry calculations to explore chemical reactions at the atomic level. Important thermodynamic and kinetic parameters are then obtained, which can then be used as inputs in constructing first-principles based reactor models. Studies of new systems for which data are not available can be conducted as well. In this dissertation, we use quantum chemistry simulations to study the deposition of gate dielectrics for metal-oxide-semiconductor (MOS) devices. The focus of this study is on heterogeneous reactions between gaseous precursors and solid surfaces. Adsorbate-surface interactions introduce additional degrees of complexity compared to the corresponding gas-phase or solid-state reactions. The applicability and accuracy of cluster approximations to represent solid surfaces are first investigated. The majority of our results are obtained using B3LYP density functional theory (DFT). The structures of reactants, products, and transition states are obtained, followed by calculations of thermochemical and kinetic properties. Whenever experimental data are available, qualitative and/or quantitative comparisons are drawn. Atomistic mechanisms and the energetics of several reactions leading to the deposition of SiO2, Si3N4, and potential new high-kappa materials such as ZrO2, HfO2, and Al 2O3 have been explored in this dissertation. Competing reaction pathways are explored for each of the deposition reactions studied. For example, the potential energy surface (PES) for ZrO2 ALD shows that the reactions proceed through a trapping-mediated mechanism, which results in a competition between desorption and decomposition of the gaseous reactants, i.e. ZrCl4 and H2O, on the ZrO2 surface. This competition results in relatively low saturation coverage, which consequently leads to a slow growth rate and possibly affects the thickness uniformity and conformality. The insights gained are then used to systematically improve deposition reactions. For instance, from the ZrO2 ALD PES, we are able to suggest the use of high temperature and pressure to obtain higher surface coverage.

Widjaja, Yuniarto

260

High-k Al2O3 gate dielectrics prepared by oxidation of aluminum film in nitric acid followed by high-temperature annealing  

Microsoft Academic Search

A simple, cost-effective, and room temperature process was proposed to prepare high-k gate dielectrics. An aluminum oxide (Al2O3) gate dielectric was prepared by oxidation of ultrathin Al film in nitric acid (HNO3) at room temperature then followed by high-temperature annealing in O2 or N2. The substrate injection current behavior and interface trap-induced capacitance were introduced to investigate the interfacial property

Chih-Sheng Kuo; Jui-Feng Hsu; Szu-Wei Huang; Lurng-Shehng Lee; Ming-Jinn Tsai; Jenn-Gwo Hwu

2004-01-01

261

Growth, strain relaxation properties and high-? dielectric integration of mixed-anion GaAs1-ySby metamorphic materials  

NASA Astrophysics Data System (ADS)

Mixed-anion, GaAs1-ySby metamorphic materials with a wide range of antimony (Sb) compositions extending from 15% to 62%, were grown by solid source molecular beam epitaxy (MBE) on GaAs substrates. The impact of different growth parameters on the Sb composition in GaAs1-ySby materials was systemically investigated. The Sb composition was well-controlled by carefully optimizing the As/Ga ratio, the Sb/Ga ratio, and the substrate temperature during the MBE growth process. High-resolution x-ray diffraction demonstrated a quasi-complete strain relaxation within each composition of GaAs1-ySby. Atomic force microscopy exhibited smooth surface morphologies across the wide range of Sb compositions in the GaAs1-ySby structures. Selected high-? dielectric materials, Al2O3, HfO2, and Ta2O5 were deposited using atomic layer deposition on the GaAs0.38Sb0.62 material, and their respective band alignment properties were investigated by x-ray photoelectron spectroscopy (XPS). Detailed XPS analysis revealed a valence band offset of >2 eV for all three dielectric materials on GaAs0.38Sb0.62, indicating the potential of utilizing these dielectrics on GaAs0.38Sb0.62 for p-type metal-oxide-semiconductor (MOS) applications. Moreover, both Al2O3 and HfO2 showed a conduction band offset of >2 eV on GaAs0.38Sb0.62, suggesting these two dielectrics can also be used for n-type MOS applications. The well-controlled Sb composition in several GaAs1-ySby material systems and the detailed band alignment analysis of multiple high-? dielectric materials on a fixed Sb composition, GaAs0.38Sb0.62, provides a pathway to utilize GaAs1-ySby materials in future microelectronic and optoelectronic applications.

Zhu, Y.; Clavel, M.; Goley, P.; Hudait, M. K.

2014-10-01

262

An improved procedure for immunoelectron microscopy: ultrathin plastic embedding of immunolabeled ultrathin frozen sections.  

PubMed Central

Ultrathin frozen sections are ideal substrates with which to carry out immunolabeling experiments in electron microscopy. However, the ultrastructural delineation in positively stained frozen sections has not been as detailed as in conventionally osmium-stained and plastic-embedded sections. We now describe a simple technique in which immunolabeled ultrathin frozen sections are subsequently treated with osmium tetroxide, dehydrated, and then embedded in plastic by impregnation with a monomer to the thickness of the section, followed by polymerization of the monomer. By this technique ultrastructural definition as good as that of conventional plastic sections is achieved, while the high density and specificity of immunolabeling characteristic of ultrathin frozen sections are retained. Images PMID:6435119

Keller, G A; Tokuyasu, K T; Dutton, A H; Singer, S J

1984-01-01

263

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

264

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

265

Super Dielectric Materials  

NASA Astrophysics Data System (ADS)

Evidence is provided that a class of materials with dielectric constants greater than 100,000, herein called super dielectric materials (SDM), can be generated readily from common, inexpensive materials.

Fromille, Samuel; Phillips, Jonathan

2014-12-01

266

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

267

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

268

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

269

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride  

E-print Network

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride Gwan-Hyoung Lee,1 atomically flat and ultrathin hexagonal boron nitride (h-BN) on gold-coated mica was investigated using and long term stability of MOSFETs.5,6 Recently, hexagonal boron nitride (h-BN), which is an iso- morph

Kim, Philip

270

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.

271

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

272

Multi-technique Approach for the Evaluation of the Crystalline Phase of Ultrathin High-k Gate Oxide Films  

NASA Astrophysics Data System (ADS)

In order to continue scaling metal oxide semiconductor field effect transistors (MOSFETs) with HfO2 gate oxides, efforts are being made to further improve the deposited high-k film properties. Recently, a process whereby an HfO2 film is deposited through a series of depositions and anneals (so-called DADA process) has been shown to result in films that give rise to MOS capacitors (MOSCAPs) which are electrically scaled compared to MOSCAPs with HfO2 films that only received post deposition anneals (PDA) or no anneals. We have measured as-deposited, DADA and PDA HfO2 films using four measurement techniques, all of which are non-destructive and capable of being used for in-line processing, to evaluate their crystallinity and crystalline phases. Grazing incidence in-plane X-ray diffraction was used to determine the crystalline phases of the HfO2 films. We observed the crystalline phases of these films to be process dependent. Additionally, X-ray and UV photoelectron spectroscopy were used to show the presence of crystallinity in the films. As a fourth technique, spectroscopic ellipsometry was used to determine if the crystalline phases were monoclinic. The combination of techniques was useful in that XPS and UPS were able to confirm the amorphous nature of a 30 cycle DADA film, as measured by GIIXRD, and GIIXRD was able to help us interpret the SE data as being an indication of the monoclinic phase of HfO2.

Bersch, E.; LaRose, J. D.; Wells, I.; Consiglio, S.; Clark, R. D.; Leusink, G. J.; Matyi, R. J.; Diebold, A. C.

2011-11-01

273

Ultrathin self-assembled polyelectrolyte multilayer membranes  

NASA Astrophysics Data System (ADS)

The paper is concerned with ultrathin membranes prepared upon alternating layer-by-layer adsorption of cationic and anionic polyelectrolytes on a porous substructure. The formation of the polyelectrolyte multilayer membranes is characterised and the transport of gases, liquid mixtures and ions across the membranes is studied. In particular, the use of the membranes for alcohol/water separation under pervaporation conditions, and for the separation of mono- and divalent ions is described. It is demonstrated that upon a suitable choice of polyelectrolytes and substructures, and a careful optimisation of preparation and operation conditions, membranes can be tailored exhibiting an excellent separation capability.

Tieke, B.; van Ackern, F.; Krasemann, L.; Toutianoush, A.

274

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

275

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

276

Flexible low-voltage organic complementary circuits: finding the optimum combination of semiconductors and monolayer gate dielectrics.  

PubMed

Low-voltage p-channel and n-channel organic transistors with channel lengths down to 0.5 ?m using four small-molecule semiconductors and ultra-thin dielectrics based on two different phosphonic acid monolayers are fabricated on plastic substrates and studied in terms of effective mobility, intrinsic mobility and contact resistance. For the optimum materials combination, flexible complementary circuits have signal delays of 3.1 ?s at 5 V. PMID:25330764

Kraft, Ulrike; Sejfi?, Mirsada; Kang, Myeong Jin; Takimiya, Kazuo; Zaki, Tarek; Letzkus, Florian; Burghartz, Joachim N; Weber, Edwin; Klauk, Hagen

2015-01-01

277

Resonant dielectric metamaterials  

DOEpatents

A resonant dielectric metamaterial comprises a first and a second set of dielectric scattering particles (e.g., spheres) having different permittivities arranged in a cubic array. The array can be an ordered or randomized array of particles. The resonant dielectric metamaterials are low-loss 3D isotropic materials with negative permittivity and permeability. Such isotropic double negative materials offer polarization and direction independent electromagnetic wave propagation.

Loui, Hung; Carroll, James; Clem, Paul G; Sinclair, Michael B

2014-12-02

278

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

279

Optical properties of ultrafine line and space polymeric nanogratings coated with metal and metal-dielectric-metal thin films  

NASA Astrophysics Data System (ADS)

Noble metal and metal-dielectric-metal ultrathin films were deposited on the surfaces of ultrafine polymeric nanogratings, which were fabricated using nanoimprint lithography. Experimental results showed dramatic differences of the surface morphologies for single metal and triple metal-dielectric-metal films deposited on flat and corrugated polymeric surfaces. The effect of the surface morphology on the optical properties was hence investigated and analyzed under linearly polarized light. The surface plasmon resonances of single metal and triple metal-dielectric-metal films deposited on polymeric nanograting surfaces were also characterized based on the Kretschmann prism-coupling method. The single metal and triple metal-dielectric-metal films deposited on polymeric nanograting surfaces are important for the study of photon-plasmon interactions (i.e. couplings and conversions) at the interfaces between a nanograting and metal films.

Leong, Eunice Sok Ping; Wu, Siji; Zhang, Nan; Loh, Wei Wei; Huat Khoo, Eng; Si, Guang Yuan; Dai, Hai Tao; Liu, Yan Jun

2014-02-01

280

Optical properties of ultrafine line and space polymeric nanogratings coated with metal and metal-dielectric-metal thin films.  

PubMed

Noble metal and metal-dielectric-metal ultrathin films were deposited on the surfaces of ultrafine polymeric nanogratings, which were fabricated using nanoimprint lithography. Experimental results showed dramatic differences of the surface morphologies for single metal and triple metal-dielectric-metal films deposited on flat and corrugated polymeric surfaces. The effect of the surface morphology on the optical properties was hence investigated and analyzed under linearly polarized light. The surface plasmon resonances of single metal and triple metal-dielectric-metal films deposited on polymeric nanograting surfaces were also characterized based on the Kretschmann prism-coupling method. The single metal and triple metal-dielectric-metal films deposited on polymeric nanograting surfaces are important for the study of photon-plasmon interactions (i.e. couplings and conversions) at the interfaces between a nanograting and metal films. PMID:24406796

Leong, Eunice Sok Ping; Wu, Siji; Zhang, Nan; Loh, Wei Wei; Khoo, Eng Huat; Si, Guang Yuan; Dai, Hai Tao; Liu, Yan Jun

2014-02-01

281

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

282

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

283

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

284

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

285

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

286

"Perfect" Electrochemical Molecular Sieving by Thin and Ultrathin Metallopolymeric Films  

E-print Network

molecular structure with the observed electrochemical reactivity. Molecular sieving behavior is discussed"Perfect" Electrochemical Molecular Sieving by Thin and Ultrathin Metallopolymeric Films Suzanne Be by formation of nonelectroactive films, which are electronically insulating at least over the electrochemical

287

Direct glassed and ultrathin GaAs cells  

Microsoft Academic Search

Solar cells can be attached to their protective cover-glass without any flexible adhesive. The devices then potentially have the advantages of higher ruggedness, lower mass and increased radiation hardness in high radiation environments. This paper describes the development of direct glassed (DG) GaAs solar cells, ultrathin cells (UTCs), and direct glassed ultrathin cells (DG-UTCs), for first in-orbit testing on the

C. Hardingham; A. Hayward; T. A. Cross; C. Goodbody

1994-01-01

288

From ultrathin networks to microcapsules: Structure, properties and theoretical description  

Microsoft Academic Search

Surfactants tend to form spontaneously ultra-thin films at oil-water interfaces. Besides the two-dimensionally analo- gous states of the gas, liquid or solid phase one can also observe network formation. These ultra-thin structures are characterized by complex rheological properties. The flow behavior of these membranes are reminescent to gels, and the coherent structures lead to an enhanced stabiliza- tion of fluid

Heinz Rehage; Martin Husmann; Anja Walter

289

Analysis of an Ultrathin Graphite-Based Compact Heat Exchanger  

Microsoft Academic Search

The emerging production of ultrathin graphite material is applied to thermal management in a numerical comparison of aluminum and graphite-based plate-fin heat exchangers. Considering anisotropic thermal conductivity in which out-of-plane transport is about two orders of magnitude lower than in-plane values, the ultrathin graphite-based solution outperforms aluminum by rejecting up to twenty percent more heat on a volumetric basis. Thermal

Alex Heltzel; Columbia Mishra; Rodney S. Ruoff; Andrew Fleming

2012-01-01

290

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

291

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

292

Hot electron effect in ultrathin photovoltaic devices  

NASA Astrophysics Data System (ADS)

The focus of the research work described in the following thesis is increasing the efficiency of photovoltaic devices by reducing hot carrier thermalization losses. In principle this can be achieved by reducing the size of the absorber down to lengths comparable to the thermalization length for hot carriers. With the use of ultrathin absorbers hot carrier can be collected before they have reached thermal equilibrium with the lattice. The theoretical work on the subject is comprised of improving the empirical relationship developed in the most recent publication on the topic by. By making the assumption that the energy loss rate fits the exponential decay model, an expression for the energy as a function of absorber thickness was developed. The experimental work consist of fabricating devices with different absorber thicknesses and testing their ability to show change in performance due to collection of hot electrons.

Mihaylov, Deyan Ivov

293

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

294

Nitric acid compensated aluminum oxide dielectrics with improved negative bias reliability and positive bias temperature response  

NASA Astrophysics Data System (ADS)

The room-temperature nitric acid (HNO3) compensation method is introduced to effectively improve the dielectric quality of ultrathin aluminum oxide (Al2O3) gate dielectrics under low thermal budget consideration. The physical properties, electrical characteristics, and temperature response of Al2O3 metal-oxide-semiconductor (MOS) devices without and with HNO3 compensation are compared. The surface roughness and interface trap density are obviously decreased by utilizing HNO3 compensation. Under negative gate bias, the leakage current, hard breakdown characteristics, and temperature-dependent reliability of the Al2O3 MOS(p) capacitors are clearly improved by HNO3 compensation. Under positive gate bias, the highly temperature-dependent current is principally dominated by generation-recombination mechanism. However, the diodes without HNO3 compensation show irregular temperature response especially at temperature above 70 °C. From Frenkel-Poole emission analysis, the oxide traps in Al2O3 without HNO3 compensation are responsible to this abnormal temperature response. These results suggest that the quality of ultrathin Al2O3 gate dielectrics can be cost-effectively improved by HNO3 compensation.

Lin, Chien-Chih; Hwu, Jenn-Gwo

2013-02-01

295

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.

Christian, Wolfgang; Belloni, Mario

2006-01-19

296

Improved Dielectric Films For Capacitors  

NASA Technical Reports Server (NTRS)

Dielectric films made from blends of some commercially available high-dielectric-constant cyanoresins with each other and with cellulose triacetate (CTA) have both high dielectric constants and high breakdown strengths. Dielectric constants as high as 16.2. Films used to produce high-energy-density capacitors.

Yen, Shiao-Ping S.; Lewis, Carol R.; Cygan, Peter J.; Jow, T. Richard

1994-01-01

297

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

298

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 is demonstrated and the thermal stability of these films is investigated. Ultrathin ( 13 nm) strained silicon

299

Metal-dielectric interactions  

NASA Technical Reports Server (NTRS)

There is a wide variety of situations wherein metals are in solid state contact with dielectric materials. The paper reviews some of the factors that influence solid state interactions for metals in contact with dielectric surfaces. Since surfaces play an important part in these reactions, the use of analytical tools in characterizing surfaces is discussed. Adhesion, friction, and wear are utilized as indicators of the nature of interfacial bonding between metals and dielectrics can be effectively determined with adhesion and friction force measurements. Films present on the surface, such as oxygen or water vapor, markedly alter adhesive bond strength which in turn affects friction force and interfacial fracture when attempts are made to separate the contact regions. Analytical surface tools such as the field ion microscope, Auger emission spectroscopy, and X-ray photoelectron spectroscopy are very effective in providing insight into the effect of contact on the surfaces of metals and dielectrics.

Buckley, D. H.

1979-01-01

300

Interfacial diffusion behavior in Ni-BaTiO 3 MLCCs with ultra-thin active layers  

NASA Astrophysics Data System (ADS)

The interfacial structure and diffusion behavior between the dielectric layers (BaTiO3) and internal electrode layers (Ni) in X5R-type multilayer ceramic capacitors (MLCCs, from -55°C to 85°C, at a temperature capacitance coefficient within ±15%) with ultra-thin active layers ( T = 1-3 µm) have been investigated by several microstructural techniques (SEM/TEM/HRTEM) with energy-dispersive x-ray spectroscopy (EDS). In the MLCC samples with different active layer thicknesses (1-3 µm), weak interfacial diffusion was observed between BaTiO3 and Ni. It was also found that the diffusion capability of Ni into the BaTiO3 layer was stronger than that of BaTiO3 to the Ni electrode, which indicated that the diffusion of Ni was the dominant factor for the interfacial diffusion behavior in the ultra-thin layered MLCCs. The mechanism of Ni diffusion is discussed in this study as well.

Gong, Huiling; Wang, Xiaohui; Tian, Zhibin; Zhang, Hui; Li, Longtu

2014-03-01

301

Pattern formation in dielectric barrier discharges with different dielectric materials  

SciTech Connect

The influence of dielectric material on the bifurcation and spatiotemporal dynamics of the patterns in dielectric barrier discharge in argon/air at atmospheric pressure is studied. It is found that pattern bifurcation sequences are different with different dielectric materials. The spatiotemporal dynamics of the hexagonal pattern in dielectric barrier discharge depends on the dielectric material. The hexagon pattern with glass dielectric is an interleaving of two rectangular sublattices appearing at different moments. The hexagon pattern with quartz dielectric is composed of one set of hexagonal lattice discharging twice in one half cycle of the applied voltage, one is at the rising edge and the other at the falling edge. It results in that the accumulation of wall charges in individual microdischarges in a hexagon pattern with quartz dielectric is greater than that with glass dielectric, which is in agreement with the electron density measurement by Stark broadening of Ar I 696.54 nm.

Dong, L. F.; Fan, W. L.; Wang, S.; Ji, Y. F. [College of Physics Science and Technology, Hebei University, Baoding 071002 (China); Liu, Z. W.; Chen, Q. [Laboratory of Plasma Physics and Materials, Beijing Institute of Graphic Communication, Daxing 102600, Beijing (China)

2011-03-15

302

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.

2015-01-01

303

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

304

Resilience of ultra-thin oxynitride films to percolative wear-out and reliability implications for high-? stacks at low voltage stress  

NASA Astrophysics Data System (ADS)

Localized progressive wear-out and degradation of ultra-thin dielectrics around the oxygen vacancy percolation path formed during accelerated time dependent dielectric breakdown tests is a well-known phenomenon documented for silicon oxynitride (SiON) based gate stacks in metal oxide semiconductor field effect transistors. This progressive or post breakdown stage involves an initial phase characterized by "digital" random telegraph noise fluctuations followed by the wear-out of the percolation path, which results in an "analog" increase in the leakage current, culminating in a thermal runaway and hard breakdown. The relative contribution of the digital and analog phases of degradation at very low voltage stress in ultra-thin SiON (16 Å´) is yet to be fully investigated, which represents the core of this study. We investigate the wear-out process by combining electrical and physical analysis evidences with modeling and simulation results using Kinetic Monte Carlo defect generation and multi-phonon trap assisted tunneling (PTAT) models. We show that the transition from the digital to the analog regime is governed by a critical voltage (VCRIT), which determines the reliability margin in the post breakdown phase. Our results have a significant impact on the post-breakdown operational reliability of SiON and advanced high-?-SiOx interfacial layer gate stacks, wherein the SiOx layer seems to be the weakest link for percolation event.

Raghavan, Nagarajan; Padovani, Andrea; Li, Xiang; Wu, Xing; Lip Lo, Vui; Bosman, Michel; Larcher, Luca; Leong Pey, Kin

2013-09-01

305

Versatile ultrathin nanoporous silicon nitride membranes  

SciTech Connect

Single- and multiple-nanopore membranes are both highly interesting for biosensing and separation processes, as well as their ability to mimic biological membranes. The density of pores, their shape, and their surface chemistry are the key factors that determine membrane transport and separation capabilities. Here, we report silicon nitride (SiN) membranes with fully controlled porosity, pore geometry, and pore surface chemistry. An ultrathin freestanding SiN platform is described with conical or double-conical nanopores of diameters as small as several nanometers, prepared by the track-etching technique. This technique allows the membrane porosity to be tuned from one to billions of pores per square centimeter. We demonstrate the separation capabilities of these membranes by discrimination of dye and protein molecules based on their charge and size. This separation process is based on an electrostatic mechanism and operates in physiological electrolyte conditions. As we have also shown, the separation capabilities can be tuned by chemically modifying the pore walls. Compared with typical membranes with cylindrical pores, the conical and double-conical pores reported here allow for higher fluxes, a critical advantage in separation applications. In addition, the conical pore shape results in a shorter effective length, which gives advantages for single biomolecule detection applications such as nanopore-based DNA analysis.

Vlassiouk, Ivan V [ORNL

2009-01-01

306

Dynamics of Nanowalls In Ferroelectric Ultrathin Films  

NASA Astrophysics Data System (ADS)

Nanoscale ferroelectric films can exhibit nanostripes that are nanoscopic regions of ``up'' and ``down'' polarizations, hence forming domain walls which separate nanodomains with different polarization directions. The dynamical properties of domain walls are of technological importance since they are at the heart of ultradense ferroelectric memory technology and may play an important role in nanoscale ferroelectric sensors, actuators, and others. Here [1] we take advantage of accurate first-principle-based simulations to reveal the intrinsic dynamics of nanodomains in ultra-thin PbTi0.6Zr0.4O3 films with thickness ranging from 2 to 20 nm. We first demonstrate that the nanodomain walls oscillate under driving AC-field of sub-switching amplitude. Secondly, we reveal that nanowalls can exhibit two types of intrinsic dynamics (resonance and relaxation) at the same frequencies. Thirdly, we prove that at nanoscale the dynamics is determined by the domain size which manifests itself via a unique size-driven transition from relaxational to resonance dynamics.[4pt] [1] Q. Zhang et al, Phys. Rev. Lett. 107, 177601 (2011).

Zhang, Qingteng; Herchig, Ryan; Ponomareva, Inna

2012-02-01

307

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

308

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

309

Large Ultrathin Shelled Drops Produced via Non-Confined Microfluidics.  

PubMed

We present a facile approach for producing large and monodisperse core-shell drops with ultrathin shells using a single-step process. A biphasic compound jet is introduced into a quiescent third (outer) phase that ruptures to form core-shell drops. Ultrathin shelled drops could only be produced within a certain range of surfactant concentrations and flow rates, highlighting the effect of interfacial tension in engulfing the core in a thin shell. An increase in surfactant concentrations initially resulted in drops with thinner shells. However, the drops with thinnest shells were obtained at an optimum surfactant concentration, and a further increase in the surfactant concentrations increased the shell thickness. Highly monodisperse (coefficient of variation smaller than 3?%) core-shell drops with diameter of ?200 ?m-2 mm with shell thickness as small as ?2 ?m were produced. The resulting drops were stable enough to undergo polymerisation and produce ultrathin shelled capsules. PMID:25382308

Chaurasia, Ankur S; Josephides, Dimitris N; Sajjadi, Shahriar

2015-02-01

310

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

311

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

E-print Network

. Masuduzzaman, A.E. Islam, and M.A. Alam Dept. of ECE, Purdue University West Lafayette, IN-47907, USA *Phone, it is thus extremely impor- tant to know the locations (both in energy and position) of the initial process

Alam, Muhammad A.

312

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

313

Method for laser welding ultra-thin metal foils  

DOEpatents

A method for simultaneously cutting and welding ultra-thin foils having a thickness of less than 0.002 inches wherein two ultra-thin films are stacked and clamped together. A pulsed laser such as of the Neodymium: YAG type is provided and the beam of the laser is directed onto the stacked films to cut a channel through the films. The laser is moved relative to the stacked foils to cut the stacked foils at successive locations and to form a plurality of connected weld beads to form a continuous weld. 5 figs.

Pernicka, J.C.; Benson, D.K.; Tracy, C.E.

1996-03-26

314

Method for laser welding ultra-thin metal foils  

DOEpatents

A method for simultaneously cutting and welding ultra-thin foils having a thickness of less than 0.002 inches wherein two ultra-thin films are stacked and clamped together. A pulsed laser such as of the Neodymium: YAG type is provided and the beam of the laser is directed onto the stacked films to cut a channel through the films. The laser is moved relative to the stacked foils to cut the stacked foils at successive locations and to form a plurality of connected weld beads to form a continuous weld.

Pernicka, John C. (Fort Collins, CO); Benson, David K. (Golden, CO); Tracy, C. Edwin (Golden, CO)

1996-01-01

315

All-dielectric nanoantennas  

NASA Astrophysics Data System (ADS)

The study of optical nanoantennas is a rapidly developing area of optics and nanophotonics. Nowdays, the most popular type of nanoantennas is a plasmonic one made of metallic elements. However, plasmonic nanoantennas have large dissipative losses. Here we present an overview of the recent results of a newly emerged field of all-dielectric optical nanoantennas. These optical nanoantennas are made of high-permittivity low-loss dielectric particles. Moreover, in addition to the electric resonances such nanoscale particles exhibit very strong magnetic response in the visible range. We introduce and study a highly efficient Huygens element and Yagi-Uda type nanoantennas based on dielectric nanoparticles. We also introduce a novel concept of all-dielectric superdirective nanoantennas based on the generation of higher-order optically-induced magnetic multipole modes. For such superdirective dielectric nanoantennas, we predict the effect of beam steering at the nanoscale characterized by a subwavelength sensitivity of the beam radiation direction to the source position. Based on all these new properties, optical nanoantennas offer unique opportunities for applications such as optical communications, photovoltaics, non-classical light emission, and sensing.

Krasnok, Alexander E.; Miroshnichenko, Andrey E.; Belov, Pavel A.; Kivshar, Yuri S.

2013-09-01

316

Nonlinear dielectric composites  

NASA Astrophysics Data System (ADS)

Polymer composites with high dielectric constant are widely used as shielding and field grading materials. An improvement of the refractive grading can be expected for a dielectric constant being a nonlinear function of the electric field or the temperature, as it is known for nonlinear resistive field grading. An increase of the dielectric constant in those areas, where the highest electrical fields occur, will result in a homogenization of the field distribution. Such composite materials can be considered as having the smart functions of sensing and actuating. The influence of nonlinear properties of filler material on the resulting dielectric properties have been studied both theoretically and experimentally. Calculations using effective medium theory show how much of the non-linearity of the filler is transferred to the composite. They are compared with experiments on composites containing ferroelectric, semiconducting and varistor-type filler material in a thermoset or thermoplastic matrix. Depending on the filler type, the dielectric constant increases by a factor of up to three, for example, by raising the temperature from 30 degree(s)C to 150 degree(s)C. Such an enhancement can be sufficient to rearrange the field distribution in stressed insulating parts.

Struempler, Ralf G.; Rhyner, Jakob; Greuter, Felix; Kluge-Weiss, Petra

1995-05-01

317

Dielectrically actuated liquid lens  

NASA Astrophysics Data System (ADS)

A packaged liquid lens driven by the dielectric force was demonstrated. The liquid lens consisted of a low dielectric constant droplet and a high dielectric constant sealing liquid. The two non-conductive liquids were sealed in a chamber under the condition of iso-density. Focal length of a liquid lens with an aperture of 3mm changed from 34mm to 12mm in the range of 0-200V. Hysteresis was observed in the liquid lens, with a maximum value measured of 12.5° at 120 volts in terms of droplet's contact angle. The focal spot size measured approximately 80?m. Rise and fall times were 650ms and 300ms, respectively. The lens consumed 1mW of power when applying a 200 volt, 1 kHz signal. The longitudinal and transverse spherical aberrations were estimated to be nearly invariant when the focal length exceeded 20mm.

Cheng, Chih-Cheng; Yeh, J. Andrew

2007-06-01

318

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

319

Dielectric resonator antenna (DRA) for wireless application  

Microsoft Academic Search

This paper describes a simple design on dielectric resonator antenna using disk shape. The dielectric resonator antenna (DRA) consists of high dielectric constant materials, high quality factors and mounted on a grounded dielectric substrate of lower permittivity. The selected dielectric disk is operating at frequency of 2.4 GHz with dielectric constant of 34.73. The miscrostrip transmission line has been used

M. S. M. Aras; M. K. A. Rahim; A. Asrokin; M. Z. A. A. Aziz

2008-01-01

320

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

321

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

322

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

323

Silicon-ion-implanted PMMA with nanostructured ultrathin layers for plastic electronics  

NASA Astrophysics Data System (ADS)

Being of interest for plastic electronics, ion-beam produced nanostructure, namely silicon ion (Si+) implanted polymethyl-methacrylate (PMMA) with ultrathin nanostructured dielectric (NSD) top layer and nanocomposite (NC) buried layer, is examined by electric measurements. In the proposed field-effect organic nanomaterial structure produced within the PMMA network by ion implantation with low energy (50 keV) Si+ at the fluence of 3.2 × 1016 cm?2 the gate NSD is ion-nanotracks-modified low-conductive surface layer, and the channel NC consists of carbon nanoclusters. In the studied ion-modified PMMA field-effect configuration, the gate NSD and the buried NC are formed as planar layers both with a thickness of about 80 nm. The NC channel of nano-clustered amorphous carbon (that is an organic semiconductor) provides a huge increase in the electrical conduction of the material in the subsurface region, but also modulates the electric field distribution in the drift region. The field effect via the gate NSD is analyzed. The most important performance parameters, such as the charge carrier field-effect mobility and amplification of this particular type of PMMA- based transconductance device with NC n-type channel and gate NSD top layer, are determined.

Hadjichristov, G. B.; Ivanov, Tz E.; Marinov, Y. G.

2014-12-01

324

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

325

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

326

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

327

Ultrathin Thermoelectric Devices for On-Chip Peltier Cooling  

Microsoft Academic Search

The efficient usage of thermoelectric (TE) devices for microelectronics cooling application requires investigation and remedy of various obstacles such as integration of these devices with electronic package, parasitic contact resistances, and utilization of appropriate current pulses. We develop a computational model to investigate the effect of steady state and transient mode of operation of ultrathin thermoelectric cooler (TEC) devices on

Man Prakash Gupta; Min-Hee Sayer; Saibal Mukhopadhyay; Satish Kumar

2011-01-01

328

Conversion of multilayer graphene into continuous ultrathin sp3  

E-print Network

, and the production of large-area crystals has been a long term goal. The conventional synthetic methods employed for the production of artificial diamond usually require extremely high pressure and temperature1,2 , or plasma on metal surfaces. Our computation results suggest a method of preparing an ultrathin `diamond' layer over

329

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.

330

Dielectric disk radiating elements  

NASA Astrophysics Data System (ADS)

A new class of antennas, consisting of dielectric resonant cylinders located on a conducting plane, is investigated numerically and experimentally. The numerical formulation is applied to the problem of a dielectric body of revolution in the presence of an electrically thin wire, or in the presence of a slot aperture. The formulation enables one to compute the input impedance of practical dielectric-cylinder antennas, which are fed either by a probe at the end of a coaxial cable, or by a slot in the ground plane of a microstrip transmission line. Such computations were heretofore unavailable in the published literature. Experiments were performed to verify the impedance behavior as a function of frequency. The agreement with the numerical results is excellent for the wire-fed antennas but, for the slot-fed antennas, the measured values are strongly influenced by the details of the feeding arrangement. The slot-fed dielectric antennas will require further investigation before the influence of the aperture details is fully understood, and a satisfactory agreement between the theory and experiment is obtained.

Junker, G. P.; Kishk, A. A.; Glisson, A. W.; Kajfez, D.

1995-08-01

331

Bandwidth-enhanced dual-band dual-layer polarization-independent ultra-thin metamaterial absorber  

NASA Astrophysics Data System (ADS)

In this paper, a polarization-independent metamaterial absorber with enhanced bandwidth at two separate frequency bands is proposed over wide angle of incidence. The proposed structure consists of two layers of dielectric substrate. The unit cell is designed on the top surfaces of both the layers of the dielectric by parametric optimization in such a way that bandwidth-enhanced absorptions occur in C and X bands. The proposed structure is fabricated, and experimental results are in good agreement with the simulated responses. This bandwidth-enhanced dual-band absorption nature is maintained for any angle of polarization under normal incidence, thus making the absorber polarization independent in nature. The structure also shows bandwidth-enhanced dual-band absorptions over wide angle of incidence up to 45° under TE polarization and 30° under TM polarization. Moreover, the proposed structure is ultra-thin, having total thickness of 3.2 mm, ~ ?/14 and ?/10 with respect to the center frequencies of two absorption bands.

Bhattacharyya, Somak; Ghosh, Saptarshi; Chaurasiya, Devkinandan; Srivastava, Kumar Vaibhav

2015-01-01

332

Bandwidth-enhanced dual-band dual-layer polarization-independent ultra-thin metamaterial absorber  

NASA Astrophysics Data System (ADS)

In this paper, a polarization-independent metamaterial absorber with enhanced bandwidth at two separate frequency bands is proposed over wide angle of incidence. The proposed structure consists of two layers of dielectric substrate. The unit cell is designed on the top surfaces of both the layers of the dielectric by parametric optimization in such a way that bandwidth-enhanced absorptions occur in C and X bands. The proposed structure is fabricated, and experimental results are in good agreement with the simulated responses. This bandwidth-enhanced dual-band absorption nature is maintained for any angle of polarization under normal incidence, thus making the absorber polarization independent in nature. The structure also shows bandwidth-enhanced dual-band absorptions over wide angle of incidence up to 45° under TE polarization and 30° under TM polarization. Moreover, the proposed structure is ultra-thin, having total thickness of 3.2 mm, ~?/14 and ?/10 with respect to the center frequencies of two absorption bands.

Bhattacharyya, Somak; Ghosh, Saptarshi; Chaurasiya, Devkinandan; Srivastava, Kumar Vaibhav

2014-11-01

333

Self-assembly of large-scale and ultrathin silver nanoplate films with tunable plasmon resonance properties.  

PubMed

We describe a rapid, simple, room-temperature technique for the production of large-scale metallic thin films with tunable plasmonic properties assembled from size-selected silver nanoplates (SNPs). We outline the properties of a series of ultrathin monolayer metallic films (8-20 nm) self-assembled on glass substrates in which the localized surface plasmon resonance can be tuned over a range from 500 to 800 nm. It is found that the resonance peaks of the films are strongly dependent on the size of the nanoplates and the refractive index of the surrounding dielectric. It is also shown that the bandwidth and the resonance peak of the plasmon resonance spectrum of the metallic films can be engineered by simply controlling aggregation of the SNP. A three-dimensional finite element method was used to investigate the plasmon resonance properties for individual SNPs in different dielectrics and plasmon coupling in SNP aggregates. A 5-17 times enhancement of scattering from these SNP films has been observed experimentally. Our experimental results, together with numerical simulations, indicate that this self-assembly method shows great promise in the production of nanoscale metallic films with enormous electric-field enhancements at visible and near-infrared wavelengths. These may be utilized in biochemical sensing, solar photovoltaic, and optical processing applications. PMID:21955107

Zhang, Xiao-Yang; Hu, Anming; Zhang, Tong; Lei, Wei; Xue, Xiao-Jun; Zhou, Yunhong; Duley, Walt W

2011-11-22

334

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

335

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

336

Gate Last Indium-Gallium-Arsenide MOSFETs with Regrown Source-Drain Regions and ALD Dielectrics  

NASA Astrophysics Data System (ADS)

III-V-based MOSFETs have the potential to exceed the performance of silicon-based MOSFETs due to the semiconductor's small electron effective mass. Modern silicon-based MOSFETs with 22 nm gate lengths utilize high-k gate insulators and non-planar device geometries to optimize device performance. III-V HEMT technology has achieved similar gate lengths, but large source-drain access resistances and the lack of high-quality gate insulators prevent further device performance scaling. Sub-22 nm gate length III-V MOSFETs require metal-semiconductor contact resistivity to be less than 1 ohm-micron squared, gate insulators with less than 1 nm effective oxide thickness, and semiconductor-insulator interface trap densities less than 2E12 per square centimeter per electron volt. This dissertation presents InGaAs-based III-V MOSFET process flows and device results to assess their use in VLSI circuits. Previous III-V MOSFET results focused on long (>100 nm) gate lengths and ion implantation for source-drain region formation. Scaling III-V MOSFETs to shorter gate lengths requires source-drain regions that have low sheet resistance, high mobile charge densities, and low metal-semiconductor contact resistance. MBE- and MOCVD-based raised epitaxial source-drain regrowth meet these requirements. MBE InAs source-drain regrowth samples have shown 0.5 to 2 ohm-micron squared metal semiconductor contact resistivities. MOCVD InGaAs source-drain regrowth samples have shown < 100 ohm-micron single-sided access resistance to InGaAs MOSFETs. Gate insulators on III-V materials require large conduction band offsets to the channel, high dielectric permittivities, and low semiconductor-insulator interface trap densities. An in-situ hydrogen plasma / trimethylaluminum treatment has been developed to lower the gate semiconductor-insulator interface trap density. This treatment, done immediately before gate insulator deposition, has been shown to lower MOS capacitor interface trap densities by more than a factor of two. Devices using gate-first MBE regrowth, gate-last MBE regrowth, and gate-last MOCVD regrowth were fabricated and resulting devices characterized. 65 nm gate length gate-first MBE regrowth devices employing a 2.2 nm EOT Al 2O3 gate insulator show peak transconductances of 0.3 mS/micron at 1 V Vds. Gate-first FET performance scaling is limited by processed-induced damage and ungated access regions. 64 nm gate length gate-last MBE regrowth devices employing a 1.21 nm EOT Al2O 3 / HfO2 bi-layer gate insulator show peak transconductances of 1.4 mS/micron at 0.5 V Vds. Other gate-last MBE samples had long channel subthreshold swings as low as 117 mV/dec. 48 nm gate length gate-last MOCVD MOSFETs employing a 0.8 nm EOT HfO2 gate insulator and digital channel etching show peak transconductances of 2 mS/micron at 0.5 V Vds, with long channel devices having 97 mV/dec subthreshold swing.

Carter, Andrew Daniel

337

Dielectric loaded aperture antennas.  

NASA Technical Reports Server (NTRS)

This paper describes a primarily experimental study of the effect of placing dielectric obstacles having various geometries directly upon the aperture of circular and rectangular waveguide antennas. It is found that plexiglas spheres, and in some cases plexiglas cubes, one to four wavelengths in dimension, produce directive patterns with low sidelobes. The measured gain in some cases is 6 dB greater than the gain of an optimum horn having an equal aperture size.

Croswell, W. F.; Chatterjee, J. S.

1972-01-01

338

The dielectric breakdown limit of silicone dielectric elastomer actuators  

NASA Astrophysics Data System (ADS)

Soft silicone elastomers are used in a generation of dielectric elastomer actuators (DEAs) with improved actuation speed and durability compared to the commonly used, highly viscoelastic polyacrylate 3M VHB™ films. The maximum voltage-induced stretch of DEAs is ultimately limited by their dielectric breakdown field strength. We measure the dependence of dielectric breakdown field strength on thickness and stretch for a silicone elastomer, when voltage-induced deformation is prevented. The experimental results are combined with an analytic model of equi-biaxial actuation to show that accounting for variable dielectric field strength results in different values of optimal pre-stretch and thickness that maximize the DEA actuation.

Gatti, Davide; Haus, Henry; Matysek, Marc; Frohnapfel, Bettina; Tropea, Cameron; Schlaak, Helmut F.

2014-02-01

339

New silicone dielectric elastomers with a high dielectric constant  

NASA Astrophysics Data System (ADS)

Dielectric elastomers (Des) are a type of EAPs with unique electrical properties and mechanical properties: high actuation strains and stresses, fast response times, high efficiency, stability, reliability and durability. The excellent figures of merit possessed by dielectric elastomers make them the most performing materials which can be applied in many domains: biomimetics, aerospace, mechanics, medicals, etc. In this paper, we present a kind of electroactive polymer composites based on silicone Dielectric elastomers with a high dielectric constant. Novel high DEs could be realized by means of a composite approach. By filling an ordinary elastomer (e.g. silicone) with a component of functional ceramic filler having a greater dielectric permittivity, it is possible to obtain a resulting composite showing the fruitful combination of the matrix's advantageous elasticity and the filler's high permittivity. Here we add the ferroelectric relaxor ceramics (mainly BaTiO3) which has high dielectric constant (>3000) to the conventional silicone Dielectric elastomers, to get the dielectric elastomer which can exhibit high elastic energy densities induced by an electric field of about 15 MV/m. Tests of the physical and chemical properties of the dielectric elastomers are conducted, which verify our supposes and offer the experimental data supporting further researches.

Zhang, Zhen; Liu, Liwu; Fan, Jiumin; Yu, Kai; Liu, Yanju; Shi, Liang; Leng, Jinsong

2008-03-01

340

Zirconium-doped tantalum oxide high-k gate dielectric films  

NASA Astrophysics Data System (ADS)

A new high-k dielectric material, i.e., zirconium-doped tantalum oxide (Zr-doped TaOx), in the form of a sputter-deposited thin film with a thickness range of 5--100 nm, has been studied. Important applications of this new dielectric material include the gate dielectric layer for the next generation metal-oxide-semiconductor field effect transistor (MOSFET). Due to the aggressive device scaling in ultra-large-scale integrated circuitry (ULSI), the ultra-thin conventional gate oxide (SiO2) is unacceptable for many practical reasons. By replacing the SiO2 layer with a high dielectric constant material (high-k), many of the problems can be solved. In this study, a novel high-k dielectric thin film, i.e., TaO x doped with Zr, was deposited and studied. The film's electrical, chemical, and structural properties were investigated experimentally. The Zr dopant concentration and the thermal treatment condition were studied with respect to gas composition, pressure, temperature, and annealing time. Interface layer formation and properties were studied with or without an inserted thin tantalum nitride (TaNx) layer. The gate electrode material influence on the dielectric properties was also investigated. Four types of gate materials, i.e., aluminum (Al), molybdenum (Mo), molybdenum nitride (MoN), and tungsten nitride (WN), were used in this study. The films were analyzed with ESCA, XRD, SIMS, and TEM. Films were made into MOS capacitors and characterized using I-V and C-V curves. Many promising results were obtained using this kind of high-k film. It is potentially applicable to future MOS devices.

Tewg, Jun-Yen

341

Dielectric phantoms for electromagnetic radiation  

Microsoft Academic Search

The report describes the design and performance of a synthetic material that has the same dielectric-heating characteristics as living muscle in the 1-1000 MHz frequency range. The dielectric phantom is a combination of four components: (1) a 50\\/50 solution of ethylene carbonate and propylene carbonate chosen to have the same dielectric constant as water, (2) an organic salt to provide

M. G. Broadhurst; C. K. Chiang; G. T. Davis

1986-01-01

342

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

343

Direct glassed and ultrathin GaAs cells  

SciTech Connect

Solar cells can be attached to their protective cover-glass without any flexible adhesive. The devices then potentially have the advantages of higher ruggedness, lower mass and increased radiation hardness in high radiation environments. This paper describes the development of direct glassed (DG) GaAs solar cells, ultrathin cells (UTCs), and direct glassed ultrathin cells (DG-UTCs), for first in-orbit testing on the STRV solar cell flight experiment. To date, 4 cm{sup 2} UTCs bonded with conventional DC93-500 have been demonstrated with 1 sun AM0 (25 C) efficiencies of up to 19.7%. Thick (280 {micro}m) DG cells with efficiencies up to 16.3%, and 10 {micro}m DG-UTCs of up to 17.8% have been realized. The trials have indicated several approaches to improve UTCs to avoid any performance penalty, at a moderate increase in cost over conventional unthinned cells.

Hardingham, C.; Hayward, A.; Cross, T.A. [EEV Ltd., Chelmsford (United Kingdom); Goodbody, C. [Defence Research Agency, Farnborough (United Kingdom)

1994-12-31

344

Magnetic excitations in ultrathin magnetic films: Temperature effects  

NASA Astrophysics Data System (ADS)

The idea of investigating large wave-vector magnetic excitations in ultrathin films by spin-polarized electron spectroscopy is briefly reviewed. The historical background of the paper is based on the personal experience of the authors who collaborated and discussed with Douglas Mills regarding this subject. Douglas Mills' impact on the understanding of fundamental mechanisms involved in the excitation process and the development of the theory of magnetic excitations is outlined. In addition, the temperature effects on the large wave-vector magnetic excitations in ultrathin Fe films are addressed. The experimental results of magnon excitations in the pseudomorphic Fe monolayer on W(110) are presented. The temperature dependence of the magnon dispersion relation is discussed.

Zakeri, Kh.; Prokop, J.; Zhang, Y.; Kirschner, J.

2014-12-01

345

Structure-dependent mechanical properties of ultrathin zinc oxide nanowires  

PubMed Central

Mechanical properties of ultrathin zinc oxide (ZnO) nanowires of about 0.7-1.1 nm width and in the unbuckled wurtzite (WZ) phase have been carried out by molecular dynamics simulation. As the width of the nanowire decreases, Young's modulus, stress-strain behavior, and yielding stress all increase. In addition, the yielding strength and Young's modulus of Type III are much lower than the other two types, because Type I and II have prominent edges on the cross-section of the nanowire. Due to the flexibility of the Zn-O bond, the phase transformation from an unbuckled WZ phase to a buckled WZ is observed under the tensile process, and this behavior is reversible. Moreover, one- and two-atom-wide chains can be observed before the ZnO nanowires rupture. These results indicate that the ultrathin nanowire possesses very high malleability. PMID:21711876

2011-01-01

346

Ultrathin and lightweight organic solar cells with high flexibility.  

PubMed

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

347

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

348

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

349

Thermal stress and glass transition of ultrathin polystyrene films  

NASA Astrophysics Data System (ADS)

The thermal stress of thin and ultrathin polystyrene (PS) films on Si substrate has been studied and the glass transition temperature (Tg) is determined from the thermal stress data. Tg of PS turned out to be thickness independent for thick films but decreases when the film thickness is comparable to the end-to-end distance of the polymer chains (<100 nm). The thermal stress level and the slope of the stress temperature curve of the film also decrease as the film thickness decreases. The slope reduction indicates that the product of the biaxial modulus E/(1-?) and the coefficient of thermal expansion (CTE) of the film decreases with film thickness. Assuming that the CTE increases for ultrathin films, the modulus is found to decrease significantly with respect to the bulk value.

Zhao, Jie-Hua; Kiene, Michael; Hu, Chuan; Ho, Paul S.

2000-10-01

350

Ultrathin GaAs solar cells using germanium substrates  

NASA Astrophysics Data System (ADS)

An approach is presented for etch thinning to produce ultrathin (less than 6 micron GaAs thickness) devices utilizing cheaper Ge substrates to attack the problems of high cost and mass. The use of a double heterostructure GaAs cell design and a total-loss etch process to produce devices of only 6-micron GaAs thickness is discussed. The benefits of this process in comparison with alternative ultrathin GaAs cell techniques are outlined. The mass specific power of this class of device using a 100-micron coverglass can exceed 670 W/kg at the connector integrated cell level, compared with less than 330 W/kg for 100-micron silicon cells.

Huggins, C. R.; Cross, T. A.; Hardingham, C. M.

351

Ultrathin and lightweight organic solar cells with high flexibility  

NASA Astrophysics Data System (ADS)

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.

Kaltenbrunner, Martin; White, Matthew S.; G?owacki, Eric D.; Sekitani, Tsuyoshi; Someya, Takao; Sariciftci, Niyazi Serdar; Bauer, Siegfried

2012-04-01

352

Ultrathin aluminum sample cans for single crystal inelastic neutron scattering  

NASA Astrophysics Data System (ADS)

Single crystal inelastic neutron scattering measurements are often performed using a sample environment for controlling sample temperature. One difficulty associated with this is establishing appropriate thermal coupling from the sample to the temperature controlled portion of the sample environment. This is usually accomplished via a sample can which thermally couples the sample environment to the sample can and the sample can to the sample via an exchange gas. Unfortunately, this can will contribute additional background signal to one's measurement. We present here the design of an ultrathin aluminum sample can based upon established technology for producing aluminum beverage cans. This design minimizes parasitic sample can scattering. Neutron scattering measurements comparing a machined sample can to our beverage can design clearly indicate a large reduction in scattering intensity and texture when using the ultrathin sample can design. We also examine the possibility of using standard commercial beverage cans as sample cans.

Stone, M. B.; Loguillo, M. J.; Abernathy, D. L.

2011-05-01

353

Colossal spin Hall effect in ultrathin metallic films  

NASA Astrophysics Data System (ADS)

We predict spin Hall angles up to 80% for ultrathin noble-metal films with substitutional Bi impurities. The colossal spin Hall effect is caused by enhancement of the spin Hall conductivity in reduced sample dimension and a strong reduction of the charge conductivity by resonant impurity scattering. These findings can be exploited to create materials with high efficiency of charge to spin current conversion by strain engineering.

Herschbach, Christian; Fedorov, Dmitry V.; Gradhand, Martin; Mertig, Ingrid

2014-11-01

354

Giant room-temperature elastocaloric effect in ferroelectric ultrathin films.  

PubMed

Environmentally friendly ultrathin BaTiO3 capacitors can exhibit a giant stress-induced elastocaloric effect without hysteresis loss or Joule heating. By combining this novel elastocaloric effect with the intrinsic electrocaloric effect, an ideal refrigeration cycle with high performance (temperature change over 10 K with a wide working-temperature window of 60 K) at room temperature is proposed for future cooling applications. PMID:25042767

Liu, Yang; Infante, Ingrid C; Lou, Xiaojie; Bellaiche, Laurent; Scott, James F; Dkhil, Brahim

2014-09-17

355

High-mobility ultrathin semiconducting films prepared by spin coating  

Microsoft Academic Search

The ability to deposit and tailor reliable semiconducting films (with a particular recent emphasis on ultrathin systems) is indispensable for contemporary solid-state electronics. The search for thin-film semiconductors that provide simultaneously high carrier mobility and convenient solution-based deposition is also an important research direction, with the resulting expectations of new technologies (such as flexible or wearable computers, large-area high-resolution displays

David B. Mitzi; Laura L. Kosbar; Conal E. Murray; Matthew Copel; Ali Afzali

2004-01-01

356

Nanotemplate with Holes: Ultrathin Alumina on Ni3Al(111)  

Microsoft Academic Search

We have determined the structure of the ultrathin (67×67)R12.2° aluminum oxide on Ni3Al(111) by a combination of scanning tunneling microscopy and density functional theory. In addition to other local defects, the main structural feature of the unit cell is a 0.4-nm-diameter hole reaching down to the metal substrate. Understanding the structure and metal growth on this oxide allows us to

M. Schmid; G. Kresse; A. Buchsbaum; E. Napetschnig; S. Gritschneder; M. Reichling; P. Varga

2007-01-01

357

All-dielectric optical nanoantennas  

NASA Astrophysics Data System (ADS)

We study a novel type of optical nanoantennas made of high-permittivity low-loss dielectric particles. In addition to the electric resonances, the dielectric particles exhibit very strong magnetic resonances at the nanoscale. As result, single dielectric nanoparticle can have the properties of a Huygens element in the optical wavelength range. A highly efficient Yagi-Uda nanoantenna based on dielectric nano-particles is studied analytically, numerically and experimentally. Optical nanoantennas allow for enhancing and manipulating light on the scale much smaller than wavelength of light. Based on this ability, optical nanoantennas offer unique opportunities regarding key applications such as optical communications, photovoltaics, non-classical light emission, and sensing.

Krasnok, Alexander E.; Miroshnichenko, Andrey E.; Belov, Pavel A.; Kivshar, Yuri S.

2012-09-01

358

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

359

Development of Electrolytic-Capacitor-Less Ultra-Thin Flyback Converter Shintaro Takagi*, Toshihiko Noguchi (Nagaoka University of Technology),  

E-print Network

SPC-08-07 16 Development of Electrolytic-Capacitor-Less Ultra-Thin Flyback Converter Shintaro, flyback converter, electrolytic capacitor, ultra-thin transformer) 1 EL CCFL LED DC/DC 2 Co., Ltd.) Abstract This paper describes two novel approaches to develop an ultra-thin switching

Fujimoto, Hiroshi

360

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

361

Very high dielectric strength for dielectric elastomer actuators in liquid dielectric immersion  

NASA Astrophysics Data System (ADS)

This letter reported that a dielectric elastomer actuator (3M VHB), which is immersed in a liquid dielectric bath, is enhanced tremendously in dielectric strength up to 800 MV/m, as compared to 450 MV/m for the actuator operated in air. The bath consists of silicone oil (Dow Corning Fluid 200 50cSt), which is 6.5 times more thermally conductive than air, and it is found able to maintain the actuator at a stable temperature. As a result, the oil-immersed dielectric elastomer actuator is prevented from local thermal runaway, which causes loss of electrical insulation, and consequently avoids the damage by electromechanical instability.

La, Thanh-Giang; Lau, Gih-Keong

2013-05-01

362

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

363

An extremely high dielectric constant in bismuth-based pyrochlore multilayer film capacitors combined with percolative structure  

SciTech Connect

The percolative film capacitor structure of Pt/Bi{sub 2}Mg{sub 2/3}Nb{sub 4/3}O{sub 7}[BMN(Ar) films deposited at pure argon atmosphere]/Pt was addressed for achievement of a high dielectric constant in the films deposited at room temperature by radio frequency magnetron sputtering. The deterioration of the leakage current characteristics in the percolative capacitor was mitigated using the multilayer films of BMN(O)/BMN(Ar)/BMN(O), where ultrathin BMN(O) films were deposited at a mixed atmosphere of argon and oxygen. An extremely high dielectric constant of 120 and a low leakage current density of 6x10{sup -6} A/cm{sup 2} at 3 V were observed in percolative BMN multilayer films as-deposited at room temperature.

Cuong, Nguyen Duy; Ahn, Jun-Ku; Park, Kyung-Woo; Seong, Nak-Jin; Yoon, Soon-Gil [School of Nano Science and Technology, Chungnam National University, Daeduk Science Town, 305-764, Daejeon (Korea, Republic of)

2008-11-24

364

Heterogeneous ultrathin films fabricated by alternate assembly of exfoliated layered double hydroxides and polyanionw  

E-print Network

Heterogeneous ultrathin films fabricated by alternate assembly of exfoliated layered double September 2008 DOI: 10.1039/b807479h Transparent heterogeneous ultrathin films of exfoliated layered double. Layered double hydroxides (LDHs), also well-known as hydro- talcite-like compounds or anionic clays

Wang, Zhong L.

365

Ultrathin, high-efficiency, broad-band, omni-acceptance, organic solar cells enhanced by  

E-print Network

-pass active layer absorptance; leading to (3) a 4.4% power conversion efficiency (PCE) at standard-solarUltrathin, high-efficiency, broad-band, omni- acceptance, organic solar cells enhanced by plasmonic and demonstration of a new ultra-thin high- efficiency organic solar cell (SC), termed "plasmonic cavity

366

POWERING A CLEANER FUTURE R&D on an Ultra-Thin Composite  

E-print Network

POWERING A CLEANER FUTURE R&D on an Ultra-Thin Composite Membrane for High-Temperature Operation High-Temperature Composite Membrane/MEA Porous Support Solid Superacid NAFION Proton Conductor Cathode- Membrane Interface Cathode Ionic Conductivity GOAL: ULTRA-THIN, DURABLE, >100°C HIGH- TEMPERATURE COMPOSITE

367

Design and fabrication of photonic crystals in epitaxial free silicon for ultrathin solar cells  

E-print Network

Design and fabrication of photonic crystals in epitaxial free silicon for ultrathin solar cells the epitaxial free c-Si [6] as a 1D and 2D PC. The global design of the ultra-thin film solar cell, which has photovoltaic solar cell. Optical simulations performed on a complete solar cell revealed that patterning

Paris-Sud XI, Université de

368

Ultrathin Oxide Films by Atomic Layer Deposition on Graphene Jonathan J. Travis,  

E-print Network

Ultrathin Oxide Films by Atomic Layer Deposition on Graphene Luda Wang, Jonathan J. Travis, Andrew with controlled, nanometer-scale thickness using atomic layer deposition (ALD) on graphene. Aluminum oxide films is presented to create and characterize mechanically robust, free-standing, ultrathin, oxide films

Bunch, Scott

369

Structural optimization for broadband scattering in several ultra-thin white beetle scales  

E-print Network

Structural 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 of the white beetle Cyphochilus. It was suggested that its brilliant whiteness and brightness were due

Exeter, University of

370

A self-assembled ultrathin crystalline polymer film for high performance phototransistors.  

PubMed

The ?-conjugated polymer, PQBOC8, can be easily assembled into a large-area crystalline ultrathin film at the CHCl3/water interface. A phototransistor based on this ultrathin film showed a large photoresponsivity of 970 A W(-1), and a photocurrent/dark current ratio of 1.36 × 10(4) under a very low white light irradiation. PMID:25096751

Li, Hui; Wu, Yishi; Wang, Xuedong; Kong, Qinghua; Fu, Hongbing

2014-09-28

371

Slow DNA transport through nanopores in hafnium oxide membranes.  

PubMed

We present a study of double- and single-stranded DNA transport through nanopores fabricated in ultrathin (2-7 nm thick) freestanding hafnium oxide (HfO2) membranes. The high chemical stability of ultrathin HfO2 enables long-lived experiments with <2 nm diameter pores that last several hours, in which we observe >50 000 DNA translocations with no detectable pore expansion. Mean DNA velocities are slower than velocities through comparable silicon nitride pores, providing evidence that HfO2 nanopores have favorable physicochemical interactions with nucleic acids that can be leveraged to slow down DNA in a nanopore. PMID:24083444

Larkin, Joseph; Henley, Robert; Bell, David C; Cohen-Karni, Tzahi; Rosenstein, Jacob K; Wanunu, Meni

2013-11-26

372

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...

373

Semileaky waves in dielectric chirowaveguides.  

PubMed

The occurrence of semileaky waves in dielectric chirowaveguides is investigated. It is shown that a thinfilm dielectric chiroslabguide with an achiral superstrate and in which both the film and substrate are chiral can support semileaky modes radiating energy into the substrate, provided that the chirality parameters are properly chosen. PMID:19798279

Paiva, C R; Topa, A L; Barbosa, A M

1992-12-01

374

Extruded dielectric dc cable development  

Microsoft Academic Search

An extruded 100 kilovolt (kV), direct-current (dc) cable insulated with mineral filled polymeric dielectrics was developed. The analysis of the factors controlling the rated stress and load limits indicated that capabilities of an extruded dc cable could be improved by reducing the dependency of electrical resistivity on temperature and the thermal resistivity of the dielectrics. It was experimentally determined that

S. E. Kiersztyn; B. T. MacKenzie

1980-01-01

375

Electric fields in irradiated dielectrics  

NASA Technical Reports Server (NTRS)

An existing model for quantitatively predicting electric field build-up in dielectrics is used to demonstrate the importance of material parameters. Results indicate that electron irradiation will produce 10 to the 6th power V/cm in important materials. Parameters which can alter this build-up are discussed. Comparison to known irradiation induced dielectric charging experiments is discussed.

Frederickson, A. R.

1979-01-01

376

Microwave Propagation in Dielectric Fluids.  

ERIC Educational Resources Information Center

Describes an undergraduate experiment designed to verify quantitatively the effect of a dielectric fluid's dielectric constant on the observed wavelength of microwave radiation propagating through the fluid. The fluid used is castor oil, and results agree with the expected behavior within 5 percent. (Author/CS)

Lonc, W. P.

1980-01-01

377

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

378

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

379

Low dielectric polyimide fibers  

NASA Technical Reports Server (NTRS)

A high temperature resistant polyimide fiber that has a dielectric constant of less than 3 is presented. The fiber was prepared by first reacting 2,2-bis (4-(4aminophenoxy)phenyl) hexafluoropropane with 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride in an aprotic solvent to form a polyamic acid resin solution. The polyamic acid resin solution is then extruded into a coagulation medium to form polyamic acid fibers. The fibers are thermally cured to their polyimide form. Alternatively, 2,2-bis(4-(4-aminophenoxy)phenyl) hexafluoropropane is reacted with 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride to form a polyamic acid, and the polyamic acid is chemically converted to its polyimide form. The polyimide is then dissolved in a solvent to form a polyimide resin solution, and the polyimide resin is extruded into a coagulation medium to form a polyimide wet gel filament. In order to obtain polyimide fibers of increased tensile properties, the polyimide wet gel filaments are stretched at elevated temperatures. The tensile properties of the fibers were measured and found to be in the range of standard textile fibers. Polyimide fibers obtained by either method will have a dielectric constant similar to that of the corresponding polymer, viz., less than 3 at 10 GHz.

Dorogy, William E., Jr. (inventor); St.clair, Anne K. (inventor)

1994-01-01

380

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

381

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

382

Charge Trapping at Deep States in HfSilicate Based High-Gate Dielectrics  

E-print Network

under negative bias conditions, which confirms that O-vacancy-induced deep defects determine the potential to be the ultimate limiting factor for the long-term reliability of Hf-based high- gate threshold instability, and lower mobility degradation compared to HfO2.3,4 In addition, silicates form

Misra, Durgamadhab "Durga"

383

Multilayer optical dielectric coating  

DOEpatents

A highly damage resistant, multilayer, optical reflective coating includes alternating layers of doped and undoped dielectric material. The doping levels are low enough that there are no distinct interfaces between the doped and undoped layers so that the coating has properties nearly identical to the undoped material. The coating is fabricated at high temperature with plasma-assisted chemical vapor deposition techniques to eliminate defects, reduce energy-absorption sites, and maintain proper chemical stoichiometry. A number of differently-doped layer pairs, each layer having a thickness equal to one-quarter of a predetermined wavelength in the material are combined to form a narrowband reflective coating for a predetermined wavelength. Broadband reflectors are made by using a number of narrowband reflectors, each covering a portion of the broadband.

Emmett, John L. (Pleasanton, CA)

1990-01-01

384

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

385

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

386

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

387

Chemical surface deposition of ultra-thin semiconductors  

DOEpatents

A chemical surface deposition process for forming an ultra-thin semiconducting film of Group IIB-VIA compounds onto a substrate. This process eliminates particulates formed by homogeneous reactions in bath, dramatically increases the utilization of Group IIB species, and results in the formation of a dense, adherent film for thin film solar cells. The process involves applying a pre-mixed liquid coating composition containing Group IIB and Group VIA ionic species onto a preheated substrate. Heat from the substrate causes a heterogeneous reaction between the Group IIB and VIA ionic species of the liquid coating composition, thus forming a solid reaction product film on the substrate surface.

McCandless, Brian E. (243 W. Main St., Elkton, MD 21921); Shafarman, William N. (1905 N. Van Buren St., Wilmington, DE 19802)

2003-03-25

388

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

389

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

390

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

391

Slowing Down of Accelerated Structural Relaxation in Ultrathin Polymer Films  

NASA Astrophysics Data System (ADS)

We demonstrate with molecular simulation that the acceleration of structural relaxation, also known as physical aging, commonly experimentally observed in thin polymer films slows down at extremely small thicknesses. This phenomenon can be attributed to an inversed free volume diffusion process caused by the sliding motion of chain molecules. Our findings provide direct evidence of the relationship between the sliding motion of short chain fragments and the structural relaxation of ultrathin polymer films, and also verify the existence of a new confinement effect at the nanoscale.

Tang, Qiyun; Hu, Wenbing; Napolitano, Simone

2014-04-01

392

Plasmonic multilayer structure for ultrathin amorphous silicon film photovoltaic cell  

NASA Astrophysics Data System (ADS)

A plasmonic multilayer structure (PMS) is proposed for photovoltaic cells with an ultrathin active layer that is 30 nm amorphous Si ( ?-Si). The optical properties of the PMS are analyzed by rigorous coupled-wave analysis (RCWA) and finite-difference time-domain (FDTD) method. Using the PMS, the incident light can be trapped into localized surface plasmon (LSP) and then the localized surface plasmon induces the surface plasmon (SP) that propagates transversely within the ?-Si layer. Compared with the indium tin oxide (ITO)/ ?-Si/Ag structure, the photon number absorbed by PMS increase 28.7% while a normal incident transverse magnetic (TM) polarization wave is applied.

Chao, Chien-Chang; Wang, Chih-Ming; Chang, Yia-Chung; Chang, Jenq-Yang

2009-05-01

393

Piezoelectric ultrathin BaTiO3 films  

NASA Astrophysics Data System (ADS)

Ultrathin (about 3 nm thick) BaTiO3 films were deposited by rf sputtering on a Si(100) substrate. LaNiO3 thin films were used as bottom and top conductive electrodes. The BaTiO3 films show piezoelectric behavior characterized by a coefficient d31=-1.8pC/N. The BaTiO3 films have an extremely high resistance to electrical breakdown up to a field of about 200 MV/cm.

Drezner, Y.; Nitzani, M.; Berger, S.

2005-01-01

394

Optical visualization of ultrathin mica flakes on semitransparent gold substrates  

PubMed Central

We show that optical visualization of ultrathin mica flakes on metallic substrates is viable using semitransparent gold as substrates. This enables to easily localize mica flakes and rapidly estimate their thickness directly on gold substrates by conventional optical reflection microscopy. We experimentally demonstrate it by comparing optical images with atomic force microscopy images of mica flakes on semitransparent gold. Present results open the possibility for simple and rapid characterization of thin mica flakes as well as other thin sheets directly on metallic substrates. PMID:23819688

2013-01-01

395

Thermal properties of ultra-thin copper nanobridges  

NASA Astrophysics Data System (ADS)

We have investigated several ultra-thin copper nanobridges between supporting layers using a classical molecular dynamics simulation and a many-body potential function of the second-moment approximation of the tight-binding scheme. When the nanobridge has a well-defined structure, the resonance frequency of the nanobridge is defined and the resonance phenomenon is in common with classical oscillation systems. The caloric curve and the diffusivity of the nanobridge have shown information on the melting and the breaking of the nanobridge. The supporting layers of the nanobridge play an important role in the dynamics and thermal properties of nanobridges.

Kang, Jeong Won; Hwang, Ho Jung

2002-08-01

396

Ultrathin conformal coating for complex magneto-photonic structures.  

PubMed

We report on an extremely fast and versatile synthetic approach, based on microwave assisted sol-gel chemistry, that allows a conformal nanometric coating of intricate three-dimensional structures. Using this methodology, we have achieved a conformal coverage of large areas of three-dimensional opals with a superparamagnetic manganese ferrite layer, yielding magneto-photonic crystals with excellent quality. The use of a ternary oxide for the ultrathin coating demonstrates the potential of this methodology to realize three-dimensional structures with complex materials that may find applications beyond photonics, such as energy, sensing or catalysis. PMID:21987109

Pascu, Oana; Caicedo, José Manuel; López-García, Martín; Canalejas, Víctor; Blanco, Álvaro; López, Cefe; Arbiol, Jordi; Fontcuberta, Josep; Roig, Anna; Herranz, Gervasi

2011-11-01

397

Nanotemplate with holes: ultrathin alumina on Ni3Al(111).  

PubMed

We have determined the structure of the ultrathin (sqrt[67] x sqrt[67])R12.2 degrees aluminum oxide on Ni3Al(111) by a combination of scanning tunneling microscopy and density functional theory. In addition to other local defects, the main structural feature of the unit cell is a 0.4-nm-diameter hole reaching down to the metal substrate. Understanding the structure and metal growth on this oxide allows us to use it as a template for growing highly regular arrays of nanoparticles. PMID:18233088

Schmid, M; Kresse, G; Buchsbaum, A; Napetschnig, E; Gritschneder, S; Reichling, M; Varga, P

2007-11-01

398

Low-threshold optical bistabilities in ultrathin nonlinear metamaterials.  

PubMed

Optical bistability typically occurs only when the optical thickness in the device or the input light power is unfavorably large. Here we show that, for a class of plasmonic metamaterials consisting of ultrathin holey metallic plates filled with nonlinear materials, the optical bistability can occur with an ultralow excitation power. We present a realistic design working at 0.2 THz and perform full-wave simulations to quantitatively study its optical bistability properties. An analytical model is developed to explain the inherent physics and provides a general design guideline for future development. PMID:24876015

Tang, Shiwei; Zhu, Baocheng; Xiao, Shiyi; Shen, Jung-Tsung; Zhou, Lei

2014-06-01

399

Thermal Casimir effect between random layered dielectrics  

NASA Astrophysics Data System (ADS)

We study the thermal Casimir effect between two thick slabs composed of plane-parallel layers of random dielectric materials interacting across an intervening homogeneous dielectric. It is found that the effective interaction at long distances is self-averaging and is given by a description in terms of effective dielectric functions. The behavior at short distances becomes random (sample dependent) and is dominated by the local values of the dielectric function proximal to each other across the dielectrically homogeneous slab.

Dean, David S.; Horgan, R. R.; Naji, Ali; Podgornik, R.

2009-04-01

400

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

401

Growth and performance of yttrium oxide as an ideal high-kappa gate dielectric for carbon-based electronics.  

PubMed

High-quality yttrium oxide (Y(2)O(3)) is investigated as an ideal high-kappa gate dielectric for carbon-based electronics through a simple and cheap process. Utilizing the excellent wetting behavior of yttrium on sp(2) carbon framework, ultrathin (about few nm) and uniform Y(2)O(3) layers have been directly grown on the surfaces of carbon nanotube (CNT) and graphene without using noncovalent functionalization layers or introducing large structural distortion and damage. A top-gate CNT field-effect transistor (FET) adopting 5 nm Y(2)O(3) layer as its top-gate dielectric shows excellent device characteristics, including an ideal subthreshold swing of 60 mV/decade (up to the theoretical limit of an ideal FET at room temperature). The high electrical quality Y(2)O(3) dielectric layer has also been integrated into a graphene FET as its top-gate dielectric with a capacitance of up to 1200 nF/cm(2), showing an improvement on the gate efficiency and on state transconductance of over 100 times when compared with that of its back-gate counterpart. PMID:20455575

Wang, Zhenxing; Xu, Huilong; Zhang, Zhiyong; Wang, Sheng; Ding, Li; Zeng, Qingsheng; Yang, Leijing; Pei, Tian; Liang, Xuelei; Gao, Min; Peng, Lian-Mao

2010-06-01

402

Thickness dependence of elastic modulus and hardness of on-wafer low-k ultrathin polytetrafluoroethylene films  

SciTech Connect

Elastic modulus and hardness of on-wafer low-k dielectric polytetrafluoroethylene films in the thickness range of 48.1 to 1,141 nm have been investigated using the dynamic contact module (DCM) in a frequency-specific depth-sensing indentation. It was observed that, when the film thickness is less than 500 nm, both the modulus and hardness of the films decrease sharply as the thickness of the film increases. However, when the films are thicker than 500 nm, the modulus and hardness are practically independent of the film thickness, and equal to approximately 2.3 Pa and 58 MPa, respectively. These values are about 5 times of the values obtained from the corresponding bulk sample. The significant increase in mechanical strength is probably resulted from a molecular reorganization in thin/ultrathin polymer films, often observed in polymeric materials. The present findings suggest that the chemical-mechanical polishing (CMP) characteristics of polytetrafluoroethylene films are thickness dependent.

Wang, J.; Shi, F.G.; Nieh, T.G.; Zhao, B.; Brongo, M.R.; Qu, S.; Rosenmayer, T.

2000-03-17

403

Dielectric phantoms for electromagnetic radiation  

SciTech Connect

The report describes the design and performance of a synthetic material that has the same dielectric-heating characteristics as living muscle in the 1-1000 MHz frequency range. The dielectric phantom is a combination of four components: (1) a 50/50 solution of ethylene carbonate and propylene carbonate chosen to have the same dielectric constant as water, (2) an organic salt to provide the same conductivity as biological electrolytes, (3) flakes of polyethylene terephthalate to provide the interfacial polarization that occurs at cell walls in biological tissue and (4) an inorganic and a polymeric gelling agents to provide mechanical rigidity. The resulting composite material is more stable to biological attack and drying than are existing aqueous-based phantom materials, and its dielectric properties are more closely matched to those of natural tissues over most of the frequency range of interest.

Broadhurst, M.G.; Chiang, C.K.; Davis, G.T.

1986-03-01

404

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

405

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

406

High dielectrics in microwave cavities  

Microsoft Academic Search

This paper identifies three distinct types of losses associated with high dielectric materials in a rf electric field, specifically in a rectangular TE102 microwave cavity. Various orientations of high dielectric structures relative to the electric field polarization have been studied using ansoft high frequency structure simulator (HFSS) (version 9.0, Pittsburgh, PA) and Computer Simulation Technology (CST) Microwave Studio (version 5.0,

Jason W. Sidabras; Richard R. Mett; James S Hyde

2004-01-01

407

Deswelling of ultrathin molecular layer-by-layer polyamide water desalination membranes.  

PubMed

The selective layer of pressure-induced water desalination membranes is an ultrathin and highly crosslinked aromatic polyamide (PA) film that separates salt from water based on differences in permeability, which is a product of diffusivity and solubility. Characterizing the transport properties of the selective layer is necessary in understanding its permselective performance. However, measuring transport of ultrathin films in general is nontrivial. Here, Poroelastic Relaxation Indentation (PRI) is employed as a simple deswelling technique for measuring the transport properties of these ultrathin selective layers. PMID:24658339

Chan, Edwin P

2014-05-01

408

Curie temperature of ultrathin ferromagnetic layer with Dzyaloshinskii-Moriya interaction  

NASA Astrophysics Data System (ADS)

We investigate the effect of the Dzyaloshinskii-Moriya interaction (DMI) on the Curie temperature of the ultrathin ferromagnetic layers. It has been known that the Curie temperature of the ferromagnet depends on spin wave excitation energies, and they are affected by DMI. Therefore, the ferromagnetic transition temperature of the ultrathin ferromagnetic layer must be sensitive on the DMI. We find that the Curie temperature depends on the DMI by using the double time Green's function method. Since the DMI is arisen by the inversion symmetry breaking structure, the DMI is always important in the inversion symmetry breaking ultrathin ferromagnetic layers.

You, Chun-Yeol

2014-08-01

409

Spatial confinement effects on ultrathin semiconducting polymer heterojunction thin films  

SciTech Connect

Thin and ultrathin films of electroactive and photoactive polymers are of growing interest for applications in electronic and optoelectronic devices such as thin film transistors, light emitting diodes, solar cells, and xerographic photoreceptors. Although spatial confinement effects on the electronic, optical, optoelectronic, magnetic, and mechanical properties of inorganic semiconductors, metals, oxides, and ceramics are well known and understood, very little is currently known about nanoscale size effects in electroactive and photoactive polymers. Therefore, we recently initiated studies aimed at the understanding of spatial confinement effects on electroactive and photoactive nanostructured polymers and related thin film devices. We have extensively investigated layered nanoscale semiconducting polymer heterojunctions by applying several experimental techniques including photoluminescence, optical absorption, transient absorption, electroluminescence, cyclic voltammetry, and current-voltage measurements. Our findings reveal clear evidence of spatial confinement effects, including: dramatic enhancement of photoconductivity in ultrathin films; enhancement of electroluminescence efficiency and performance characteristics in nanoscale heterojunction devices; observation of novel phenomena in nanoscale devices. These spatial confinement effects in nanostructured semiconducting polymers can be understood in terms of classical charge transport and interfacial processes without invoking quantum size effects.

Xuejun Zhang; Jenekhe, S.A. [Univ. of Rochester, NY (United States)

1996-12-31

410

Ultra-thin, light-trapping silicon solar cells  

NASA Technical Reports Server (NTRS)

Design concepts for ultra-thin (2 to 10 microns) high efficiency single-crystal silicon cells are discussed. Light trapping allows more light to be absorbed at a given thickness, or allows thinner cells of a given Jsc. Extremely thin cells require low surface recombination velocity at both surfaces, including the ohmic contacts. Reduction of surface recombination by growth of heterojunctions of ZnS and GaP on Si has been demonstrated. The effects of these improvements on AM0 efficiency is shown. The peak efficiency increases, and the optimum thickness decreases. Cells under 10 microns thickness can retain almost optimum power. The increase of absorptance due to light trapping is considered. This is not a problem if the light-trapping cells are sufficiently thin. Ultra-thin cells have high radiation tolerance. A 2 microns thick light-trapping cell remains over 18 percent efficient after the equivalent of 20 years in geosynchronous orbit. Including a 50 microns thick coverglass, the thin cells had specific power after irradiation over ten times higher than the baseline design.

Landis, Geoffrey A.

1989-01-01

411

Processing and characterization of Ultrathin carbon coatings on glass  

SciTech Connect

Ultrathin carbon layers, on the order of 3-6 nm in thickness, were formed on glass substrates by spin coating and pyrolysis of polymer precursors. The organic precursors used were poly(furfuryl alcohol), coal tar pitch, and a photoresist. The carbon coatings were characterized by ellipsometry, optical profilometry, water contact angle, confocal Raman spectroscopy, UV-vis spectroscopy, and atomic force microscopy. We also report the transparency, hydrophobicity, friction, weathering resistance, and electrical conductivity of the carbon-coated glass. The results reveal that up to 97% transparent, ultrathin carbon films could be formed on glass substrates with a root-mean-square roughness of less than about to 0.3 nm. This carbon layer modified the otherwise hydrophilic surface of the glass to yield a water contact angle of 85{sup o}. The coatings were also found to provide a water barrier against weathering under hot and humid conditions. A 4.5-nm-thick carbon film on glass had a sheet resistance of 55.6 k {Omega} m and a conductivity of 40 S/cm.

Lee, H.; Rajagopalan, R.; Robinson, J.; Pantano, C.G. [Penn State University, University Park, PA (United States)

2009-04-15

412

The Calorimetric Glass Transition of Polystyrene Ultrathin Films  

NASA Astrophysics Data System (ADS)

The glass transition temperature (Tg) for nanoconfined materials have been widely studied since the early 1990s. For supported polystyrene ultrathin films, Tg differs from bulk value. Recent work has attributed nanoconstrained Tg effects to artifact. In this study, we attempted to resolve this controversy and measure Tg for single polystyrene ultrathin films using Flash DSC. Films have been prepared in two ways: spincast films placed on a layer of inert oil or grease and films directly spincast on the back of the calorimetric chip. For the films on oil or on grease, the 160 nm thick films show no Tg depression. On the other hand, thinner films on oil and on grease show a Tg depression which decreases with increasing cooling rate. The depression reverts to the bulk values over the course of a day at 160 ^oC due to dewetting and thickening. For directly spincast films, no Tg depression is observed, consistent with results from other nanocalorimetry work. Our results are consistent with literature results that Tg decreases with decreasing substrate surface energy, and they also demonstrate that the Tg depression observed is not due to degradation or to plasticization effects.

Gao, Siyang; Koh, Yung P.; Simon, Sindee S.

2013-03-01

413

Ultrathin Films of TiO2 Nanoparticles at Interfaces.  

PubMed

The properties of a material change remarkably as a result of the scaling dimensions. The Langmuir-Blodgett (LB) film deposition technique is known to offer precise control over the film thickness and the interparticle separation. To form a well-ordered LB film, it is essential to form a stable Langmuir film at the air-water interface. Here, we report our studies on ultrathin films of TiO2 nanoparticles at air-water and air-solid interfaces. The Langmuir film of TiO2 nanoparticles at the air-water interface was found to be very stable, and it exhibits loose-packing and close-packing phases. The LB films were transferred onto solid substrates for characterization and application. The surface morphology of the LB film was obtained by a field emission scanning electron microscope. The optical and electronic properties of the LB films of TiO2 nanoparticles were studied using UV-vis spectroscopy and current-voltage measurements, respectively. The LB film of TiO2 nanoparticles was employed for ethanol gas sensing, and the sensing performance was compared to that of bulk material. Because of the enormous gain in the surface to volume ratio and the increase in crystalline defect density in the ultrathin LB film of TiO2 nanoparticles, the LB film is found to be a potential functional layer for ethanol sensing as compared to the bulk material. PMID:25557246

Choudhary, Keerti; Manjuladevi, V; Gupta, R K; Bhattacharyya, P; Hazra, A; Kumar, S

2015-02-01

414

Domain wall magnetoresistance in strained manganite ultrathin films  

NASA Astrophysics Data System (ADS)

We have recently reported unusually large low-field magnetoresistance (LFMR) in compressive-strained epitaxial manganite ultrathin films and suggested the domain wall (DW) scattering could be responsible for the anomalous LFMR.^1 Due to the strain anisotropy energy, the easy axis is perpendicular to the film plane in these films. In order to study the contribution of the DW to the LFMR, we have measured the resistance of the compressive-strained manganite thin films in several different demagnetized states: 1), A magnetic field was initially applied parallel to the film plane and then reduced to zero using oscillation mode, resulting in a "maze domain" pattern.^2 2), The field was applied parallel to the film plane and then removed using linear mode, which is believed to create domain stripes due to competition between the magnetic anisotropy and the exchange energies. Resistance measurements from the two states were compared with that of the demagnetized state which induces a single perpendicular domain. The results show that the DW-related resistance can be very large (300 % at 40 K) in the ultrathin films, indicating that the large LFMR we observed is related to the domain structure and movement. 1. H. S. Wang and Qi Li, Appl. Phys. Lett. 73, 2360 (1998). 2. Yan Wu, ibid. 75, 2295 (1999).

Wang, H. S.; Hu, Y. F.; Wertz, E.; Li, Qi

2000-03-01

415

Hanoi Tower-like Multilayered Ultrathin Palladium Nanosheets.  

PubMed

This paper describes the synthesis, formation mechanism, and mechanical property of multilayered ultrathin Pd nanosheets. An anisotropic, Hanoi Tower-like assembly of Pd nanosheets was identified by transmission electron microscopy and atomic force microscopy (AFM). These nanosheets may contain ultrathin Pd layers, down to single unit cell thickness. Selected area electron diffraction and scanning transmission electron microscopy data show the interconnected atomically thick layers stacking vertically with rotational mismatches, resulting in unique diffractions and Moiré patterns. Density functional theory (DFT) calculation with van der Waals correction (DFT+vdW) shows the adsorption of Pd4(CO)4(OAc)4 on Pd(110) surface (Ead = -5.68 eV) is much stronger than that on Pd(100) (Ead = -4.72 eV) or on Pd(111) (Ead = -3.80 eV). The adsorption strength of this Pd complex is significantly stronger than that of CO on the same Pd surfaces. The DFT+vdW calculation results suggest a new mechanism for the observed anisotropic growth of nanosheets with unusually high aspect ratio, in which the competitive adsorptions between Pd4(CO)4(OAc)4 complex and CO on various surfaces result in a favored growth along the ?110? directions and inhibition along ?111? directions. The mechanical property of these multilayered Pd nanosheets was studied using AFM and nanoindentation techniques, which indicate multilayered nanosheets show more plastic deformation than the bulk in response to an applied force. PMID:25369350

Yin, Xi; Liu, Xinhong; Pan, Yung-Tin; Walsh, Kathleen A; Yang, Hong

2014-12-10

416

Ultrathin nickel oxide nanosheets for enhanced sodium and lithium storage  

NASA Astrophysics Data System (ADS)

Outstanding sodium and lithium storage capability is successfully demonstrated in ultrathin NiO nanosheets (4-5 nm in thickness) synthesized via a facile solvothermal process followed by annealing in air. For sodium storage, the NiO nanosheets deliver a high reversible specific capacity of 299 mA h g-1 at a current density of 1 A g-1, and the capacity still remains up to 154 mA h g-1 at 10 A g-1. Upon charge/discharge cycling, the specific capacity maintains to be as high as 266 mA h g-1 during the 100th cycle at 1 A g-1. Such sodium storage capability of NiO nanosheets is by far one of the best reported for transition metal oxides. For lithium storage, the cell achieves a high reversible specific capacity of 1242 and 250 mA h g-1 at 0.2 and 15 A g-1, respectively. The capacity for lithium storage maintains to be 851 mA h g-1 during the 170th cycle at 2 A g-1. The present results demonstrate that ultrathin NiO nanosheets are highly attractive for fast sodium/lithium diffusion with high-rate capability for rechargeable sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs).

Sun, Wenping; Rui, Xianhong; Zhu, Jixin; Yu, Linghui; Zhang, Yu; Xu, Zhichuan; Madhavi, Srinivasan; Yan, Qingyu

2015-01-01

417

Ultrathin conformal coating for complex magneto-photonic structures  

NASA Astrophysics Data System (ADS)

We report on an extremely fast and versatile synthetic approach, based on microwave assisted sol-gel chemistry, that allows a conformal nanometric coating of intricate three-dimensional structures. Using this methodology, we have achieved a conformal coverage of large areas of three-dimensional opals with a superparamagnetic manganese ferrite layer, yielding magneto-photonic crystals with excellent quality. The use of a ternary oxide for the ultrathin coating demonstrates the potential of this methodology to realize three-dimensional structures with complex materials that may find applications beyond photonics, such as energy, sensing or catalysis.We report on an extremely fast and versatile synthetic approach, based on microwave assisted sol-gel chemistry, that allows a conformal nanometric coating of intricate three-dimensional structures. Using this methodology, we have achieved a conformal coverage of large areas of three-dimensional opals with a superparamagnetic manganese ferrite layer, yielding magneto-photonic crystals with excellent quality. The use of a ternary oxide for the ultrathin coating demonstrates the potential of this methodology to realize three-dimensional structures with complex materials that may find applications beyond photonics, such as energy, sensing or catalysis. Electronic supplementary information (ESI) available. See DOI: 10.1039/c1nr10959f

Pascu, Oana; Caicedo, José Manuel; López-García, Martín; Canalejas, Víctor; Blanco, Álvaro; López, Cefe; Arbiol, Jordi; Fontcuberta, Josep; Roig, Anna; Herranz, Gervasi

2011-11-01

418

Supersonically blown ultrathin thorny devil nanofibers for efficient air cooling.  

PubMed

The effect of the supersonically blown below-74 nm nanofibers on cooling of high-temperature surfaces is studied experimentally and theoretically. The ultrathin supersonically blown nanofibers were deposited and then copper-plated, while their surfaces resembled those of the thorny-devil nanofibers. Here, we study for the first time the enhancement of surface cooling in gas in the cases of the forced and natural convection with the help of ultrathin thorny-devil nanofibers. These polymer core-metal shell nanofibers in nanometric scale possess a relatively high thickness of the metal shell and a high effective thermal conductivity, which facilitates heat transfer. The additional surface temperature reduction close to 5 °C in the case of the forced convection in the impinging air jet and close to 17 °C in the case of the natural convection was achieved. Correspondingly, an increase in the value of the heat transfer coefficient of about 41% in the forced convection, and about 20% in the natural convection was achieved due to the presence of the thorny devil electrospun and/or supersonically blown nanofibers. PMID:25017392

An, Seongpil; Lee, Changmin; Liou, Minho; Jo, Hong Seok; Park, Jung-Jae; Yarin, Alexander L; Yoon, Sam S

2014-08-27

419

Metal-dielectric interactions  

NASA Technical Reports Server (NTRS)

Metal direlectric surface interactions and dielectric films on metal substrates were investigated. Since interfacial interaction depends so heavily on the nature of the surfaces, analytical surface tools such as Auger emission spectroscopy, X-ray photoelectron spectroscopy and field ion microscopy were used to assist in surface and interfacial characterization. The results indicate that with metals contacting certain glasses in the clean state interfacial, bonding produces fractures in the glasses while when a film such as water is present, fractures occur in the metal near the interface. Friction forces were used to measure the interfacial bond strengths. Studies with metals contacting polymers using field ion microscopy revealed that strong bonding forces could develop being between a metal and polymer surface with polymer transferring to the metal surface in various ways depending upon the forces applied to the surface in contact. With the deposition of refractory carbides, silicides and borides onto metal and alloy substrates the presence of oxides at the interface or active gases in the deposition plasma were shown to alter interfacial properties and chemistry. Auger ion depth profile analysis indicated the chemical composition at the interface and this could be related to the mechanical, friction, and wear behavior of the coating.

Buckley, D. H.

1979-01-01

420

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

421

Unified theory for perfect absorption in ultrathin absorptive films with constant tangential electric or magnetic fields  

NASA Astrophysics Data System (ADS)

The maximal absorption rate of ultrathin films is 50% under the condition that the tangential electric (or magnetic) field is almost constant across the film in a symmetrical environment. However, with certain reflectors, the absorption rate can be greatly increased, even to perfect absorption (100%). In this paper, we explicitly derive the general conditions of the ultrathin absorptive film parameters to achieve perfect absorption with general types of reflectors under the condition that the tangential electric (or magnetic) field is almost constant across the film. We find that the parameters of the film can be classified into three groups, exhibiting (1) a large permittivity (permeability), (2) a near-zero permeability (permittivity), or (3) a suitable combination of permittivity and permeability, respectively. Interestingly, the latter two cases demonstrate extraordinary absorption in ultrathin films with almost vanishing losses. Our paper serves as a guide for designing ultrathin perfect absorbers with general types of reflectors.

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

2014-10-01

422

Effect of Changes in Relative Humidity and Temperature on Ultrathin Chitosan Films  

E-print Network

Effect of Changes in Relative Humidity and Temperature on Ultrathin Chitosan Films Christopher A; Revised Manuscript Received July 4, 2006 We have prepared uniform films of chitosan with thicknesses 20 nm chitosan dissolved in dilute acetic acid onto silicon

Dutcher, John

423

Near-Infrared Surface Plasmon Resonance Measurements of Ultrathin Films. 1. Angle Shift  

E-print Network

Near-Infrared Surface Plasmon Resonance Measurements of Ultrathin Films. 1. Angle Shift and SPR be followed with SPR imaging experiments (e.g., the assay of antibodies with antigen arrays, the sequence

424

Dielectric behaviors and high energy storage density of nanocomposites with core-shell BaTiO3@TiO2 in poly(vinylidene fluoride-hexafluoropropylene).  

PubMed

Nanocomposites comprising a P(VDF-HFP) polymer matrix and core-shell structured nanoparticle fillers were prepared, in which a crystalline, ultrathin TiO2 shell layer encapsulates BaTiO3 nanoparticles. A large dielectric constant (>110) was obtained, which was unexpectedly more than 3 times higher than that of the nanocomposite without the TiO2 shell layer. The significant improvement in electric polarization is attributed to the highly interactive interfaces among the multiple dielectric materials with the introduction of the intermediate TiO2 layer, which also improves the breakdown field (>340 MV m(-1)). Thus a resulting dielectric energy density of 12.2 J cm(-3) is achieved, among the highest energy densities for polymer-ceramic composites. PMID:23999532

Rahimabady, Mojtaba; Mirshekarloo, Meysam Sharifzadeh; Yao, Kui; Lu, Li

2013-10-14

425

Simplified analytic formula for magneto-optical Kerr effects in ultrathin magnetic films.  

SciTech Connect

Expressions are presented for various magneto-optical Kerr effects in the ultrathin film limit with arbitrary magnetization direction by considering the multiple reflections within an optically thin film. The Kerr effect of p- and s-polarization consists of products of two factors: the prefactor, dependent only on the optical parameters of the system, and the main factor of the polar Kerr effect for normal incidence in the ultrathin limit.

You, C.-Y.

1998-06-10

426

Reliability characterizations and failure mechanism of ultra-thin oxides for MOS devices  

Microsoft Academic Search

The aggressive scaling of smaller\\/faster logic and memory devices demands accurate reliability characterization and knowledge of the failure mechanisms of ultra-thin (<30 A) silicon dioxide (SiO 2) layers in the gates of metal-oxide semiconductor (MOS) structures. The increased occurrence of soft breakdown in ultra-thin oxide films necessitates the development of more sophisticated techniques to detect breakdown. One such technique is

Bin Wang

2001-01-01

427

Structural advantage for the EOT scaling and improved electron channel mobility by incorporating dysprosium oxide (Dy\\/sub 2\\/O\\/sub 3\\/) into HfO\\/sub 2\\/ n-MOSFETs  

Microsoft Academic Search

A structural approach of fabricating laminated Dy2O3-incorporated HfO2 multimetal oxide dielectric has been developed for high-performance CMOS applications. Top Dy2O3 laminated HfO2 bilayer structure shows the thinnest equivalent oxide thickness (EOT) with a reduced leakage current compared to HfO2. This structure shows a great advantage for the EOT scaling CMOS technology. Excellent electrical performances of the Dy2O3\\/HfO 2 multimetal stack

Tackhwi Lee; Se Jong Rhee; Chang Yong Kang; Feng Zhu; Hyoung-sub Kim; Changhwan Choi; Manhong Zhang; S. Krishnan; G. Thareja; J. C. Lee

2006-01-01

428

Tailoring magnetic skyrmions in ultra-thin transition metal films.  

PubMed

Skyrmions in magnetic materials offer attractive perspectives for future spintronic applications since they are topologically stabilized spin structures on the nanometre scale, which can be manipulated with electric current densities that are by orders of magnitude lower than those required for moving domain walls. So far, they were restricted to bulk magnets with a particular chiral crystal symmetry greatly limiting the number of available systems and the adjustability of their properties. Recently, it has been experimentally discovered that magnetic skyrmion phases can also occur in ultra-thin transition metal films at surfaces. Here we present an understanding of skyrmions in such systems based on first-principles electronic structure theory. We demonstrate that the properties of magnetic skyrmions at transition metal interfaces such as their diameter and their stability can be tuned by the structure and composition of the interface and that a description beyond a micromagnetic model is required in such systems. PMID:24893652

Dupé, Bertrand; Hoffmann, Markus; Paillard, Charles; Heinze, Stefan

2014-01-01

429

Iodide sensing via electrochemical etching of ultrathin gold films.  

PubMed

Iodide is an essential element for humans and animals and insufficient intake is still a major problem. Affordable and accurate methods are required to quantify iodide concentrations in biological and environmental fluids. A simple and low cost sensing device is presented which is based on iodide induced electrochemical etching of ultrathin gold films. The sensitivity of resistance measurements to film thickness changes is increased by using films with a thickness smaller than the electron mean free path. The underlying mechanism is demonstrated by simultaneous cyclic voltammetry experiments and resistance change measurements in a buffer solution. Iodide sensing is conducted in buffer solutions as well as in lake water with limits of detection in the range of 1 ?M (127 ?g L(-1)) and 2 ?M (254 ?g L(-1)), respectively. In addition, nanoholes embedded in the thin films are tested for suitability of optical iodide sensing based on localized surface plasmon resonance. PMID:25513753

Dielacher, Bernd; Tiefenauer, Raphael F; Junesch, Juliane; Vörös, János

2015-01-16

430

Reflected wavefront manipulation based on ultrathin planar acoustic metasurfaces  

PubMed Central

The introduction of metasurfaces has renewed the Snell's law and opened up new degrees of freedom to tailor the optical wavefront at will. Here, we theoretically demonstrate that the generalized Snell's law can be achieved for reflected acoustic waves based on ultrathin planar acoustic metasurfaces. The metasurfaces are constructed with eight units of a solid structure to provide discrete phase shifts covering the full 2? span with steps of ?/4 by coiling up the space. By careful selection of the phase profiles in the transverse direction of the metasurfaces, some fascinating wavefront engineering phenomena are demonstrated, such as anomalous reflections, conversion of propagating waves into surface waves, planar aberration-free lens and nondiffracting Bessel beam generated by planar acoustic axicon. Our results could open up a new avenue for acoustic wavefront engineering and manipulations. PMID:23986034

Li, Yong; Liang, Bin; Gu, Zhong-ming; Zou, Xin-ye; Cheng, Jian-chun

2013-01-01

431

Long-living terahertz magnons in ultrathin metallic ferromagnets.  

PubMed

The main idea behind magnonics is to use the elementary magnetic excitations (magnons) for information transfer and processing. One of the main challenges, hindering the application of ultrafast terahertz magnons in magnonics, has been the short lifetime of these excitations in metallic ferromagnets. Here, we demonstrate that the engineering of the electronic structure of a ferromagnetic metal, by reducing its dimensionality and changing its chemical composition, opens a possibility to strongly suppress the relaxation channels of terahertz magnons and thereby enhance the magnons' lifetime. For the first time, we report on the long-lived terahertz magnons excited in ultrathin metallic alloy films. On the basis of the first-principles calculations, we explain the microscopic nature of the long lifetime being a consequence of the peculiar electronic hybridizations of the species. We further demonstrate a way of tailoring magnon energies (frequencies) by varying the chemical composition of the film. PMID:25625857

Qin, H J; Zakeri, Kh; Ernst, A; Sandratskii, L M; Buczek, P; Marmodoro, A; Chuang, T-H; Zhang, Y; Kirschner, J

2015-01-01

432

Swelling and surface modification of ultrathin chitosan films  

NASA Astrophysics Data System (ADS)

Chitosan is a biodegradable polysaccharide derived from seashell waste products. The high water absorbency and biocompatibility of chitosan have enabled its use as a hydrogel in specialty biomedical applications. We present the results of several experiments focused on characterizing properties of ultrathin films of chitosan critical to their use in techniques such as wound dressings, medical implants and drug delivery systems. Uniform thin films with thicknesses of 15 to 600 nm and rms roughness of the order of 1 nm were prepared using techniques previously developed in our research group. The swelling of these films in the presence of high humidity has been characterized using reflection ellipsometry, atomic force microscopy and quartz crystal microbalance techniques. The effects of exposure to elevated temperature and UV/ozone (a common surface modification technique) on the surface properties such as hydrophobicity are described.

Murray, Chris

2005-03-01

433

Pattern-Directed Dewetting of Ultrathin Polymer Films  

NSDL National Science Digital Library

We utilize chemically patterned substrates with arrays of progressively narrower stripes (1-15 mm) to investigate the influence of pattern size on the morphology of ultrathin dewetting polystyrene films. The scale and orientation of the spinodal-like height fluctuations of the dewetting patterns are coupled to the imposed substrate chemical frequency, providing a powerful means of morphological control. Dewetting patterns are correlated to the substrate pattern period leading to the formation of droplet arrays. The measurements confirm recent numerical simulations by Kargupta and Sharma of the existence of upper and lower cutoff scales for pattern recognition of a dewetting fluid. For pattern dimensions less than the characteristic scale on nonpatterned substrates, the droplets become anisotropic as they coarsen to a scale comparable to the stripe width, and then undergo a morphological transition to circular droplets that cross multiple stripes. This leads to quantization of droplet size and contact angles, as indicated by theory.

Sehgal, Amit

2002-03-09

434

Exotic magnetic structures in ultrathin helimagnetic holmium films  

NASA Astrophysics Data System (ADS)

The problem of spin arrangement in ultrathin films of materials with competing medium-range interactions has been investigated by classical Monte Carlo simulations, assuming the model pertinent to bulk holmium. We find that in addition to distorted helical configurations at low temperature, unusual blocked phases—with some inner disordered planes intercalating ordered blocks and with the inner planes undergoing a Kosterlitz-Thouless phase transition as the temperature rises—may appear at intermediate temperature. The blocked phases turn out to be much more structured than those predicted by mean-field calculations, and their contribution to the static structure factor appear substantially indistinguishable from that corresponding to helical order thus constituting a challenge for their experimental probing by conventional elastic scattering techniques.

Cinti, F.; Cuccoli, A.; Rettori, A.

2008-07-01

435

Ultrathin single-channel fiberscopes for biomedical imaging.  

PubMed

Ultrathin flexible fiberscopes typically have separate illumination and imaging channels and are available in diameters ranging from 0.5 to 2.5 mm. Diameters can potentially be reduced by combining the illumination and imaging paths into a single fiberoptic channel. Single-channel fiberscopes must incorporate a system to minimize Fresnel reflections from air-glass interfaces within the common illumination and detection path. The Fresnel reflection at the proximal surface of the fiber bundle is particularly problematic. This paper describes and compares methods to reduce the background signal from the proximal surface of the fiber bundle. Three techniques are evaluated: (1) antireflective (AR)-coating the proximal face of the fiber, (2) incorporating crossed polarizers into the light path, and (3) a novel technique called numerical aperture sharing, whereby a portion of the image numerical aperture is devoted to illumination and a portion to detection. PMID:23334688

Kano, Angelique; Rouse, Andrew R; Gmitro, Arthur F

2013-01-01

436

Advanced Materials and Detection Methods in Ultrathin-Layer Chromatography  

NASA Astrophysics Data System (ADS)

The performance of highly anisotropic, nanostructured, thin-film ultrathin-layer chromatography (UTLC) media with porosity and architecture engineered using the glancing-angle deposition (GLAD) process is investigated. Anisotropic structures resembling nanoblades are fabricated on the plates, producing channel-like features that partially decouple analyte migration from development direction, and offering new separation behaviours. These GLAD UTLC plates provide channel features that reduce transverse spot broadening while providing the wide pores required for rapid migration and high separation performance with plate numbers approaching 800. The rapid separations typical of these miniaturized plates call for new alternative detection techniques. I have designed, implemented and characterized a measurement system which records UTLC separations in full colour with 32 µm spatial resolution and 33 ms temporal resolution. My code analyzes multiple tracks per plate, filters analyte spots by colour, and automatically generates time-resolved figures of merit. Both absorption and transmission detection modes are examined, each of which offers their own advantages.

Oko, Anthony James

2013-01-01

437

Iodide sensing via electrochemical etching of ultrathin gold films  

NASA Astrophysics Data System (ADS)

Iodide is an essential element for humans and animals and insufficient intake is still a major problem. Affordable and accurate methods are required to quantify iodide concentrations in biological and environmental fluids. A simple and low cost sensing device is presented which is based on iodide induced electrochemical etching of ultrathin gold films. The sensitivity of resistance measurements to film thickness changes is increased by using films with a thickness smaller than the electron mean free path. The underlying mechanism is demonstrated by simultaneous cyclic voltammetry experiments and resistance change measurements in a buffer solution. Iodide sensing is conducted in buffer solutions as well as in lake water with limits of detection in the range of 1 ?M (127 ?g L?1) and 2 ?M (254 ?g L?1), respectively. In addition, nanoholes embedded in the thin films are tested for suitability of optical iodide sensing based on localized surface plasmon resonance.

Dielacher, Bernd; Tiefenauer, Raphael F.; Junesch, Juliane; Vörös, János

2015-01-01

438

Asymmetric Orbital-Lattice Interactions in Ultrathin Correlated Oxide Films  

NASA Astrophysics Data System (ADS)

Epitaxial control of strongly correlated electrons offers opportunities to push beyond the bulk phase diagram and access new ground states. Using resonant x-ray spectroscopies combined with density functional calculations, we report the discovery of an asymmetric biaxial strain-induced 3d-orbital response in ultrathin films of the correlated metal LaNiO3 that are not accessible in the bulk [J. Chakhalian et al., PRL, 107, 116805 (2011)]. Compressive strain results in an orbital polarization due to structural induced changes in the crystal field, but tensile strain shows no orbital response. This is accompanied by a strong change in the oxygen hole states due a systematic change of the charge transfer energy as a function of strain. We suggest that knowledge of this asymmetric orbital-lattice interaction is fundamental to the rational design of quantum materials with exotic correlated phases and enhanced critical temperatures.

Chakhalian, Jak

2012-02-01

439

Reflected wavefront manipulation based on ultrathin planar acoustic metasurfaces  

NASA Astrophysics Data System (ADS)

The introduction of metasurfaces has renewed the Snell's law and opened up new degrees of freedom to tailor the optical wavefront at will. Here, we theoretically demonstrate that the generalized Snell's law can be achieved for reflected acoustic waves based on ultrathin planar acoustic metasurfaces. The metasurfaces are constructed with eight units of a solid structure to provide discrete phase shifts covering the full 2? span with steps of ?/4 by coiling up the space. By careful selection of the phase profiles in the transverse direction of the metasurfaces, some fascinating wavefront engineering phenomena are demonstrated, such as anomalous reflections, conversion of propagating waves into surface waves, planar aberration-free lens and nondiffracting Bessel beam generated by planar acoustic axicon. Our results could open up a new avenue for acoustic wavefront engineering and manipulations.

Li, Yong; Liang, Bin; Gu, Zhong-Ming; Zou, Xin-Ye; Cheng, Jian-Chun

2013-08-01

440

Dendrimer-mediated hydrothermal synthesis of ultrathin gold nanowires  

PubMed Central

We report the use of poly(amidoamine) dendrimers as stabilizers to synthesize ultrathin Au nanowires (NWs) with a diameter of 1.3?nm via a hydrothermal approach. The formation of uniform Au NWs was optimized by varying the Au/Ag salt molar ratio, dendrimer stabilizers, and reaction solvent, temperature, and time. A novel growth mechanism involving a synergic facet-dependent deposition/reduction of Ag(I) and oriented migration of Au atoms is proposed based on density functional theory calculations and the experimental results. This work can significantly expand the scope of dendrimers as stabilizers to generate metal NWs in aqueous solution that may be further functionalized for different applications. PMID:24212329

Liu, Hui; Cao, Xiaoming; Yang, Jianmao; Gong, Xue-Qing; Shi, Xiangyang

2013-01-01

441

Ultrathin porous carbon films as amperometric transducers for biocatalytic sensors  

SciTech Connect

Novel ultrathin (0.4 [mu]m) porous carbon films are employed as transducers for amperometric biosensors. Such foamlike nanoscopic films couple the advantages of high enzyme loadings (within the micropore hosts) and large microscopic area with a small geometric area. Both electropolymerization and metalization are used to entrap the enzyme within the micropores. Scanning electron microscopy sheds useful insights into the unique morphology of the growing enzyme layer. The greatly enhanced sensitivity is coupled with a fast and stable response. Factors influencing the performance of porous-film-based biosensors are examined and discussed. The improved performance is illustrated in connection with glucose and phenol sensors. The latter offers a remarkably low detection limit of 2.5 x 10[sup [minus]8] M. The new nanoscopic foams should prove useful for many other electroanalytical applications. 11 refs., 7 figs.

Wang, J.; Chen, Q. (New Mexico State Univ., Las Cruces, NM (United States)); Renschler, C.L.; White, C. (Sandia National Lab., Albuquerque, NM (United States))

1994-07-01

442

Unidirectional phase singularity in ultrathin metamaterials at exceptional points  

NASA Astrophysics Data System (ADS)

Scattering properties of light in metamaterials are similar to those in open quantum systems. Here we propose an ultrathin tailored metamaterial designed to show that one-way zero reflection yielding to topologically stable phase dislocation is responsible for the exceptional point, one of the most important degeneracies in the non-Hermitian Hamiltonian. In order to bridge the exotic macroscopic optical phenomenon occurring in metamaterials, a phenomenological model under microscopic view is developed and good agreement with the full-blown numerical simulation is found. Our investigation uncovers the capabilities of metamaterials to exhibit extreme optical properties and to provide us with many potential applications such as the suppression of undesired scattering signals in the spectral band ranging from microwaves to visible light.

Kang, Ming; Cui, Hai-Xu; Li, Teng-Fei; Chen, Jing; Zhu, Weiren; Premaratne, Malin

2014-06-01

443

Microwave dielectric method for moisture sensing almonds  

Technology Transfer Automated Retrieval System (TEKTRAN)

A dielectric –based method was developed for rapid and nondestructive determination of moisture content in almond kernels independent of bulk density from measurement of their dielectric properties at a single microwave frequency. Calibration equations for moisture determination with temperature com...

444

Light propagation in dielectric materials  

E-print Network

We present a pedagogic derivation of the electromagnetic field established in a dielectric material by an impinging external field. We consider the problem from the point of view of the physical mechanism involved at the microscopic level. The internal field emerges when the material is thought of as an assembly of atoms in vacuum, each of them being polarized by the external incident field and by the re-radiated fields of all the other polarized atoms of the material. In this way, each atom becomes itself a source of secondary radiation that adds and interferes with all the other internal fields (including the internal extension of the externally impinging field), contributing to build up the total internal field within the dielectric material as well as the externally scattered field. This picture naturally leads to a connection between the microscopic properties of the material and its index of refraction, that describes the dielectric response to the applied electromagnetic field. Calculations also show t...

Stefanini, Ledo

2015-01-01

445

Efficiency enhancement of a dielectric barrier plasma discharge by dielectric barrier optimization  

SciTech Connect

The characteristic feature of a dielectric barrier discharge (DBD) is the dielectric barrier placed between the electrodes. In the present work, the influence of the dielectric barrier to the properties of a DBD in air was investigated. Spectroscopic characterization of the DBD and electrical measurements were carried out. It was shown that the efficiency of a DBD can be considerably improved by optimizing the dielectric barrier. The dielectric material should possess an appropriate relative permittivity and thickness. For thin dielectric barriers, a high secondary emission coefficient becomes important. Additionally, the use of only one dielectric barrier is advantageous.

Meiners, Annette; Leck, Michael [Department of Science and Technology, University of Applied Science and Arts, Von-Ossietzky-Str. 99, 37085 Goettingen (Germany); Abel, Bernd [Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry, University Leipzig, Linnestr. 2, 04103 Leipzig (Germany)

2010-11-15

446

CVD Diamond Dielectric Accelerating Structures  

SciTech Connect

The electrical and mechanical properties of diamond make it an ideal candidate material for use in dielectric accelerating structures: high RF breakdown field, extremely low dielectric losses and the highest available thermoconductive coefficient. Using chemical vapor deposition (CVD) cylindrical diamond structures have been manufactured with dimensions corresponding to fundamental TM{sub 01} mode frequencies in the GHz to THz range. Surface treatments are being developed to reduce the secondary electron emission (SEE) coefficient below unity to reduce the possibility of multipactor. The diamond CVD cylindrical waveguide technology developed here can be applied to a variety of other high frequency, large-signal applications.

Schoessow, P.; Kanareykin, A. [Euclid Techlabs, 1375 Piccard Dr Rockville MD 20850 (United States); Gat, R. [CTS Inc., Boston MA (United States)

2009-01-22

447

Flat dielectric grating reflectors with focusing abilities  

E-print Network

mirrors have been used to replace the top dielectric stacks in vertical-cavity surface-emitting lasersFlat dielectric grating reflectors with focusing abilities David Fattal*, Jingjing Li, Zhen Peng laser cavities to CD/DVD read/write heads. Resonant effects in dielectric gratings were first clearly

Li, Jingjing

448

Dielectric response of the human tooth dentine  

Microsoft Academic Search

Dielectric properties of tooth dentine can be well described by the model which was developed for the dielectric response to hydrating porous cement paste. It is shown that the normalized dielectric constant and the normalized specific conductivity are proportional to the model parameters ?v0 and ?v, indicating the deposition of AgCl in the dentine tubules during the duration of the

J. Leskovec; C. Filipic; A. Levstik

2005-01-01

449

Propagation of transients in dispersive dielectric media  

Microsoft Academic Search

The propagation of transient electromagnetic fields in dispersive dielectric media is studied. The dielectric medium is assumed to be linear, isotropic, and homogeneous, and is described by the Debye model. Incident fields are assumed to be transverse electromagnetic plane wave pulses. The dielectric body can assume the form of infinite half space or an infinite circular cylinder, either of which

Man D. Bui; Stanislaw S. Stuchly; George I. Costache

1991-01-01

450

Cellulose Triacetate Dielectric Films For Capacitors  

NASA Technical Reports Server (NTRS)

Cellulose triacetate investigated for use as dielectric material in high-energy-density capacitors for pulsed-electrical-power systems. Films of cellulose triacetate metalized on one or both sides for use as substrates for electrodes and/or as dielectrics between electrodes in capacitors. Used without metalization as simple dielectric films. Advantages include high breakdown strength and self-healing capability.

Yen, Shiao-Ping S.; Jow, T. Richard

1994-01-01

451

Dielectric properties of agricultural products and applications  

Technology Transfer Automated Retrieval System (TEKTRAN)

The use of dielectric properties of agricultural products for sensing moisture in grain and seed and their application in radio-frequency and microwave dielectric heating is discussed briefly. Values for the dielectric properties of a number of products, including grain and seed, fruits and vegetab...

452

Applications for Dielectric Properties of Agricultural Products  

Technology Transfer Automated Retrieval System (TEKTRAN)

The use of dielectric properties of agricultural products for sensing moisture in grain and seed and their application in radio-frequency and microwave dielectric heating are discussed briefly. Values for the dielectric properties of a number of products, including grain, fruit, and poultry products...

453

DIELECTRIC SPECTROSCOPY OF FRESH FRUITS AND VEGETABLES  

Technology Transfer Automated Retrieval System (TEKTRAN)

Dielectric properties of agricultural products are of interest for several reasons. These include the sensing of moisture content through its correlation with the dielectric properties, or permittivities, of cereal grain and oilseed crops, the influence of permittivity on the dielectric heating of p...

454

Microwave dielectrics under high temperature conditions  

Microsoft Academic Search

The work reviews methods and equipment for the high-temperature testing of microwave dielectrics and for the simulation of such operational conditions as the aerodynamic heating of aircraft radomes. Consideration is given to waveguide, optical and resonator methods for measuring the temperature dependence of dielectrics, and the study of dielectrics in free space is discussed. Techniques for achieving high temperatures under

E. A. Vorobev; V. F. Mikhailov; A. A. Kharitonov

1977-01-01

455

Dielectric Scanning Locates Voids in Glass Foam  

NASA Technical Reports Server (NTRS)

Capacitive probes succeed where X-ray and ultrasonic equipment do not. Crossbar switching of pairs of conductors enables detection of dielectric inhomogeneities in selected small volume elements of slab of material. Large void in sample detected as low capacitance reading for volume element containing void. Applicable in nondestructive testing of other dielectric objects for internal defects that exhibit dielectric inhomogeneities.

Gammell, P. M.

1983-01-01

456

Energy Storage via Polyvinylidene Fluoride Dielectric on the Counterelectrode of Dye-Sensitized Solar Cells.  

PubMed

To study the fundamental energy storage mechanism of photovoltaically self-charging cells (PSCs) without involving light-responsive semiconductor materials such as Si powder and ZnO nanowires, we fabricate a two-electrode PSC with the dual functions of photocurrent output and energy storage by introducing a PVDF film dielectric on the counterelectrode of a dye-sensitized solar cell. A layer of ultrathin Au film used as a quasi-electrode establishes a shared interface for the I(-)/I3 (-) redox reaction and for the contact between the electrolyte and the dielectric for the energy storage, and prohibits recombination during the discharging period because of its discontinuity. PSCs with a 10-nm-thick PVDF provide a steady photocurrent output and achieve a light-to-electricity conversion efficiency (?) of 3.38%, and simultaneously offer energy storage with a charge density of 1.67 C g(-1). Using this quasi-electrode design, optimized energy storage structures may be used in PSCs for high energy storage density. PMID:24327797

Huang, Xuezhen; Zhang, Xi; Jiang, Hongrui

2014-02-15

457

Energy Storage via Polyvinylidene Fluoride Dielectric on the Counterelectrode of Dye-Sensitized Solar Cells  

PubMed Central

To study the fundamental energy storage mechanism of photovoltaically self-charging cells (PSCs) without involving light-responsive semiconductor materials such as Si powder and ZnO nanowires, we fabricate a two-electrode PSC with the dual functions of photocurrent output and energy storage by introducing a PVDF film dielectric on the counterelectrode of a dye-sensitized solar cell. A layer of ultrathin Au film used as a quasi-electrode establishes a shared interface for the I?/I3? redox reaction and for the contact between the electrolyte and the dielectric for the energy storage, and prohibits recombination during the discharging period because of its discontinuity. PSCs with a 10-nm-thick PVDF provide a steady photocurrent output and achieve a light-to-electricity conversion efficiency (?) of 3.38%, and simultaneously offer energy storage with a charge density of 1.67 C g?1. Using this quasi-electrode design, optimized energy storage structures may be used in PSCs for high energy storage density. PMID:24327797

Huang, Xuezhen; Zhang, Xi

2013-01-01

458

Dielectric nanocomposites with insulating properties  

Microsoft Academic Search

Polymer nanocomposites possess promising high performances as engineering materials, if they are prepared and fabricated properly. Some work has been recently done on such polymer nanocomposites as dielectrics and electrical insulation. This was reviewed in 2004 based on the literatures published up to 2003. New significant findings have been added since then. Furthermore, a multi-core model with the far-distance effect,

Toshikatsu Tanaka

2005-01-01

459

Dielectric-loaded horn antenna  

Microsoft Academic Search

A wide-band dual-mode horn, which has a rotationally symmetric beam and extremely low sidelobe levels, can be obtained by loading a dielectric band inside the horn antenna. Measured radiation characteristics of such antennas, including the so-called shaped-beam antenna, are shown.

TOSHIO SATOH

1972-01-01

460

Polarization of Dielectrics by Acceleration  

E-print Network

We argue that acceleration induces electric polarization in usual dielectrics. Both accelerations in superfluid participate in the medium polarization. Excitations contribution to the polarization is calculated at low temperatures. Estimates of the effect show order of magnitude agreement with recent experimental results on electric effect of superflow.

L. A. Melnikovsky

2005-05-04

461

Dynamic response of dielectric elastomers  

Microsoft Academic Search

Dielectric elastomers have received a great deal of attention recently for effectively transforming electrical energy to mechanical work. Their large strains and conformability make them enticing materials for many new types of actuators. Unfortunately, their non-linear material behavior and large deformations make actual devices difficult to model. However, the reason for this difficulty can also be used to design actuators

Eric M. Mockensturm; Nakhiah Goulbourne

2006-01-01

462

Charge generation on dielectric surfaces  

Microsoft Academic Search

Measurements have been made of the charge density produced on dielectric surfaces by contact with metals of known difference in work function in vacuo. The injected charge density is dependent on the metal work function and, therefore, described by electron transfer for all the materials examined. Values of work function are presented for PVC, 4·85 ev; polyimide, 4·36 ev; PTFE,

D K Davies

1969-01-01

463

Dielectric THz waveguides  

NASA Astrophysics Data System (ADS)

In this thesis we have explored a wide variety of dielectric waveguides that rely on many different waveguiding mechanisms to guide THz (far-infrared) radiation. We have explored both theoretically and experimentally a large number of waveguide designs with the aim of reducing propagation and bending losses. The different waveguides can be classified into two fundamentally different strategies for reducing the propagation loss: small-core single-mode evanescent-field fibers or large hollow-core multi-mode tubes. Our focus was first set on exploring the small-core evanescent-field fiber strategy for reducing propagation losses. Following initial theoretical work in our group, much effort was spent on the fabrication and measurement of evanescent porous subwavelength diameter plastic fibers, in an attempt to further reduce the propagation losses. The fabrication of such fibers is a challenge and many novel techniques were devised to enable fiber drawing without hole collapse. The first method sealed the holes of an assembly of polymer tubes and lead to fibers of relatively low porosity (˜25% air within the core) due to reduction in hole size during fiber drawing. The second method was a novel sacrificial polymer technique whereby drawing a completely solid fiber prevented any hole collapse and the subsequent dissolution of the sacrificial polymer revealed the holes in the fiber. The third method was a combination of preform casting using glass molds and drawing with pressurized air within the holes. This led to fibers of record porosity (86% air). The measurement of these porous fibers began with a collaboration with a group from the university of Sherbrooke. At the time, the only available detector was a frequency integrating liquid-helium-cooled bolometer (powermeter). A novel directional coupler method for measuring the losses of subwavelength fibers was developed whereby an evanescent coupler is formed by bringing a probe fiber in proximity to the sample fiber. By translating the coupling probe fiber along the length of the sample the propagation loss could be estimated in a non-destructive way. Because of the low-pass frequency filtering of the probe fiber and the frequency integration of the detector, the results required careful interpretation and spectral information was limited to the vicinity of 0.2 THz. Subsequent transmission experiments using the adjustable THz-TDS setup enabled the measurement of the full loss spectrum and confirmed the very low propagation loss (< 0.02 cm-1) of the porous subwavelength fibers, among some of the lowest reported losses to date. These measurements further demonstrated that the addition of porosity blue-shifted absorption losses, by virtue of increasing the fraction of power guided in air, thus enabling transmission at higher frequencies and with a wider transmission peak than non-porous subwavelength fibers. Much effort was also spent on exploring the hollow-core waveguide strategy with the development of large hollow-core Bragg fibers. Owing to the similarities in the refractive indices of polymers in the THz regime, two different methods were proposed and implemented for increasing the refractive index contrast between the layers of the Bragg reflector. The first method consisted of co-rolling a polymer film with powder particles in order to create air layers. The second method consisted in rolling a bi-layer of a TiO2 doped polyethylene film and a pure polyethylene film. Despite the increased index contrast between the doped and undoped layers, the overall propagation loss was larger than that of the air-polymer Bragg fiber due to the high absorption loss of the TiO2 doped film. Although much prior work had been done by others on planar THz Bragg reflectors this is the first implementation of a THz Bragg fiber. Unfortunately, in their current implementation the fibers are either too lossy or mechanically unstable. (Abstract shortened by UMI.)

Dupuis, Alexandre

464

Dielectric behaviour in Ni-Zn ferrites  

NASA Astrophysics Data System (ADS)

The dielectric properties were studied as a function of temperature, frequency and composition for a series of Ni 1- xZn xFe 2O 4 ferrite samples prepared by the usual ceramic technique. The real dielectric constant ?' and dielectric loss factor tan ? were found to decrease as the frequency increases. Each of ?' and tan ? increase on increasing the temperature. Abnormal dielectric behaviour (peaks) were observed for tan ? curves at relatively high temperatures. The relaxation frequency fD shifts to higher values on increasing the temperature. Both ?' and tan ? increase whereas the activation energy for dielectric relaxation ED decreases as the Zn 2+ ion substitution increases.

Abdeen, A. M.

1999-02-01

465

Two-phase mixed media dielectric with macro dielectric beads for enhancing resistivity and breakdown strength  

SciTech Connect

A two-phase mixed media insulator having a dielectric fluid filling the interstices between macro-sized dielectric beads packed into a confined volume, so that the packed dielectric beads inhibit electro-hydrodynamically driven current flows of the dielectric liquid and thereby increase the resistivity and breakdown strength of the two-phase insulator over the dielectric liquid alone. In addition, an electrical apparatus incorporates the two-phase mixed media insulator to insulate between electrical components of different electrical potentials. And a method of electrically insulating between electrical components of different electrical potentials fills a confined volume between the electrical components with the two-phase dielectric composite, so that the macro dielectric beads are packed in the confined volume and interstices formed between the macro dielectric beads are filled with the dielectric liquid.

Falabella, Steven; Meyer, Glenn A; Tang, Vincent; Guethlein, Gary

2014-06-10

466

Ultra-thin Titanium Oxide Films on Accession #s 00936, 00937,00938 Mo(112), Measured by XPS Technique: XPS  

E-print Network

Ultra-thin Titanium Oxide Films on Accession #s 00936, 00937,00938 Mo(112), Measured by XPS preparation methods were employed to grow a well-ordered ultra-thin titanium oxide film on Mo(J (2), The tirst: photoemission; titanium oxide; tllin film PACS: 81.15.Gh. 79,60.Dp SPECIMEN DESCRIPTION (Accession #00936) Host

Goodman, Wayne

467

Hot Electrons in Ultrathin Photovoltaic Junctions In solar cells, captured light generates free electrons in energy states distributed throughout the  

E-print Network

Hot Electrons in Ultrathin Photovoltaic Junctions In solar cells, captured light generates free a mechanism to extract hot electrons before they cool, by using ultrathin solar cells. As shown at right, when in a solar cell, and offers a route to ultrahigh efficiency solar power. Applied Physics Letters, Vol. 95