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1

Crystallization kinetics and microstructure-dependent leakage current behavior of ultrathin HfO2 dielectrics: In situ annealing studies  

NASA Astrophysics Data System (ADS)

The crystallization kinetics of ~3 nm HfO2 films grown by atomic layer deposition (ALD) on SiO2-passivated Si (100) wafers were investigated using an in situ transmission electron microscope (TEM) with heating capability. Through gray-scale analysis of dark-field TEM images, it was found that a two-dimensional nucleation and growth mechanism with a decreasing of nucleation rate could account for the observed transformation rate behavior. The effects of crystalline defects (e.g., grain boundaries) on the leakage current were studied using a reduced pressure in situ postdeposition anneal in the ALD system to avoid interfacial SiO2 growth. The leakage current magnitude and temperature dependence were found to be essentially independent of the microstructural changes that accompany crystallization of the HfO2 films.

Kim, Hyoungsub; Marshall, Ann; McIntyre, Paul C.; Saraswat, Krishna C.

2004-03-01

2

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

3

The dielectric properties enhancement due to Yb incorporation into HfO2  

NASA Astrophysics Data System (ADS)

The effects of Yb concentration and annealing temperature on the dielectric constant change of Yb-doped HfO2 thin film were investigated. The results show that the dielectric constant of Yb-doped HfO2 increased when doping with Yb after annealing. Compared with the undoped HfO2, the dielectric constant enhancement may result from the crystallographic change from monoclinic phase to the cubic phase. The Yb-doped HfO2 exhibited a lower leakage current than that of undoped HfO2 thin film. The electrical characteristics of Yb-doped HfO2 thin film illustrated that it is a promising gate dielectric layer for future high dielectric constant (high-k) gate dielectric applications.

Chen, Shuai; Liu, Zhengtang; Feng, Liping; Che, Xingsen; Zhao, Xiaoru

2013-09-01

4

Electrical properties of HfO2/La2O3 gate dielectrics on Ge with ultrathin nitride interfacial layer formed by in situ N2/H2/Ar radical pretreatment  

NASA Astrophysics Data System (ADS)

In situ N2/H2/Ar radical pretreatment on p-type Ge (100) with HfO2/La2O3 high-? gate oxide was investigated by remote rf plasma on radical-assisted atomic layer deposition. The interfacial LaGeOxNy formation and Ge outdiffusion were also investigated by x-ray photoelectron spectroscopy and transmission electron microscopy. The high-? MOS device with an ultrathin LaGeOxNy interfacial layer shows good electrical characteristics, including larger ? value, smaller equivalent oxide thickness, lower leakage current density, smaller C-V hysteresis, and lower interface-state density. The involved mechanism lies in that the LaGeOxNy interfacial layer can effectively block Ge outdiffusion, thus improving the high-? films/Ge interface quality.

Lin, Ming-Ho; Lan, Chun-Kai; Chen, Chih-Chiao; Wu, Jyun-Yi

2011-10-01

5

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

6

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

7

Nanostructuring of ultra-thin HfO2 layers for high-k/III-V device application.  

PubMed

We report on the nanopatterning by electron beam lithography (EBL) and reactive ion etching (RIE) in a SF6/Ar+ plasma of ultra-thin HfO2 films deposited on GaAs (001) substrates for gate oxide application in next generation III-V metal-oxide-semiconductor field effect transistors (MOSFETs). Characterization of the HfO2/GaAs nanostructured samples by atomic force microscopy (AFM), high-resolution scanning electron microscopy (HRSEM), energy-dispersive X-ray spectroscopy microanalysis (EDX) and transmission electron microscopy (TEM) has shown the formation of well defined HfO2 patterns with nanometre-scale linewidth control and anisotropic profiles. In addition, atomically smooth, stoichiometric and residue-free bottom GaAs etched lines with a lateral dimension of approximately 50 nm have been demonstrated. PMID:22400270

Benedicto, M; Anguita, J; Alvaro, R; Galiana, B; Molina-Aldereguia, J M; Tejedor, P

2011-10-01

8

Electrical stress in CdS thin film transistors using HfO2 gate dielectric  

NASA Astrophysics Data System (ADS)

During thin film transistor (TFT) operation, gate dielectric is under a bias stress condition. In this work, bias stress effect for CdS TFT using HfO2 as gate dielectric is analyzed. Threshold voltage, Ion/Ioff ratio, and subthreshold slope were studied in order to understand changes produced at the dielectric semiconductor interface. We observed that threshold voltage shift is related with negative charge trapping in the dielectric/semiconductor interface and for this phenomenon we propose a trapping charge model. Finally, the TFT output characteristic was modeled considering a shift in the threshold voltage for each gate voltage curve.

García, R.; Mejia, I.; Molinar-Solis, J. E.; Salas-Villasenor, A. L.; Morales, A.; García, B.; Quevedo-Lopez, M. A.; Alemán, M.

2013-05-01

9

A first-principles study of enhanced dielectric responses in Ti and Ce doped HfO2  

NASA Astrophysics Data System (ADS)

In this letter, the dielectric response in Ti and Ce doped hafnia (HfO2) has been investigated by density functional theory calculations based on pseudopotentials, plane wave basis, and local density approximation. It is found that Ti doped samples give greater dielectric response than Ce doped HfO2, with Hf0.5Ti0.5O2 having the highest response. The Born effective charges on atoms and infrared-active phonon modes have been studied; soft phonon modes cause enhancement in the responses. The materials remain insulating upon doping of HfO2 and are of potential importance for applications as gate oxide.

Dutta, Gargi

2009-01-01

10

Vacuum-Ultraviolet Reflectometry of Ultra-thin HfO2 Films  

NASA Astrophysics Data System (ADS)

Blanket HfO2 layers, deposited with 2 to 40 ALD cycles, were measured using VUV-SR. The measured HfO2 thickness was compared to both XRR and process conditions. A linear correlation coefficient, R2, of 0.9977 to the number of ALD HfO2 cycles demonstrated sensitivity for the thickness range studied, 1.5 to 37 A?, while the mean repeatability for thickness measurements (1-?) was 0.05 A?.

Hurst, Jeffrey; Vartanian, Victor

2009-09-01

11

Effect of Al inclusion in HfO2 on the physical and electrical properties of the dielectrics  

Microsoft Academic Search

This authors present the effect of Al inclusion in HfO2 on the crystallization temperature, leakage current, band gap, dielectric constant, and border traps. It has been found that the crystallization temperature is significantly increased by adding Al into the HfO2 film. With an addition of 31.7% Al, the crystallization temperature is about 400-500°C higher than that without Al. This additional

W. J. Zhu; T. Tamagawa; M. Gibson; T. Furukawa; T. P. Ma

2002-01-01

12

A comprehensive model for breakdown mechanism in HfO2 high-k gate stacks  

Microsoft Academic Search

Based on physical analysis results, a model describing the breakdown (BD) mechanism of HfO2\\/polysilicon gate stack is proposed. Due to the high mechanical strength and the polycrystalline nature of annealed HfO2 dielectrics, and a very complicated BD induced thermo-chemical reaction and self-healing process, the BD mechanism and transient evolution in HfO2 gate stacks are different from that of ultrathin SiOxNy.

R. Ranjan; K. L. Pey; C. H. Tung; L. J. Tang; G. Groeseneken; L. K. Bera; S. De Gendt

2004-01-01

13

HfO2 high-? gate dielectrics on Ge (100) by atomic oxygen beam deposition  

NASA Astrophysics Data System (ADS)

Thin insulator films of the high-? dielectric HfO2 are deposited on Ge(100) substrates by evaporating Hf in atomic oxygen beams after in situ thermal desorption of the native oxide in ultrahigh vacuum and subsequent treatment of the clean Ge surface in oxygen and nitrogen. It is shown that HfO2 forms atomically sharp interfaces with Ge and behaves as an excellent insulator with dielectric permittivity ?~25, which is close to the expected bulk value. Very low equivalent oxide thickness of 0.75 (+/-0.1) nm with a low gate leakage current of ~4.5×10-4 A/cm2 at 1 V in accumulation is achieved. Strong frequency dispersion of the inversion capacitance and low frequency behavior of the high frequency capacitance-voltage curves is observed. This is attributed to a combined effect of a high generation rate of minority carriers due to impurity traps and the high intrinsic carrier concentration in Ge, which result in a short minority carrier response time.

Dimoulas, A.; Mavrou, G.; Vellianitis, G.; Evangelou, E.; Boukos, N.; Houssa, M.; Caymax, M.

2005-01-01

14

Impact of High-k HfO2 Dielectric on the Low-Frequency Noise Behaviors in Amorphous InGaZnO Thin Film Transistors  

Microsoft Academic Search

We have investigated the impact of high-k HfO2 gate dielectric on the low-frequency noise (LFN) behaviors of amorphous indium-gallium-zinc oxide thin-film transistors by comparing the LFNs of devices with SiO2 and HfO2 dielectrics. Measured LFNs are nearly 1\\/ f type for both devices, but the normalized noise for the HfO2 device is around one order of magnitude higher than that

Jae Chul Park; Sun Il Kim; Chang Jung Kim; Sungchul Kim; Dae Hwan Kim; In-Tak Cho; Hyuck-In Kwon

2010-01-01

15

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

16

Dielectric property and thermal stability of HfO2 on silicon  

NASA Astrophysics Data System (ADS)

A stoichiometric, uniform, and amorphous hafnium oxide thin film is deposited by an atomic layer deposition process. The as-deposited hafnium oxide films showed superior electrical properties compared to zirconium oxides, including a dielectric constant of 23, a flatband voltage shift of +0.3 V, a hysteresis of 25 mV, an interfacial trap density of 1.8 x1011 cm-2 eV-1, and a leakage current density several orders of magnitude lower than SiO2 at an equivalent oxide thickness of 9.3 A, suitable for metal-oxide-semiconductor device applications. The thermal stability of hafnium oxide on silicon was determined to be better than that of zirconium oxide. Post-deposition annealing in oxygen and ammonia further improved the thermal stability of HfO2 to 1000 and 1100 degC, respectively.

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

2002-09-01

17

Impact of High-k HfO2 Dielectric on the Low-Frequency Noise Behaviors in Amorphous InGaZnO Thin Film Transistors  

NASA Astrophysics Data System (ADS)

We have investigated the impact of high-k HfO2 gate dielectric on the low-frequency noise (LFN) behaviors of amorphous indium-gallium-zinc oxide thin-film transistors by comparing the LFNs of devices with SiO2 and HfO2 dielectrics. Measured LFNs are nearly 1/ f type for both devices, but the normalized noise for the HfO2 device is around one order of magnitude higher than that for the SiO2 device. The bulk mobility fluctuation is considered as the dominant LFN mechanism in both devices, and the increased LFN in the HfO2 device is attributed to the enhanced mobility fluctuation by the remote phonon scattering from the HfO2.

Park, Jae Chul; Kim, Sun Il; Kim, Chang Jung; Kim, Sungchul; Kim, Dae Hwan; Cho, In-Tak; Kwon, Hyuck-In

2010-10-01

18

Effective control of flat-band voltage in HfO2 gate dielectric with La2O3 incorporation  

Microsoft Academic Search

The origin of negative flat-band shift using La2O3 incorporation in HfO2 dielectrics has been extensively examined. From careful extraction of effective work function of gate electrode and fixed charges at each interface, it has been revealed that La2O3 at high-k\\/Si substrate or high-k\\/SiO2 interface has either large amount of positive fixed charges or an additional dipole of 0.36 V compared

K. Okamoto; M. Adachi; K. Kakushima; P. Ahmet; N. Sugii; K. Tsutsui; T. Hattori; H. Iwai

2007-01-01

19

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

20

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

PubMed

The thermal decomposition of ultrathin HfO(2) films (?0.6-1.2 nm) on Si by ultrahigh vacuum annealing (25-800?°C) is investigated in situ in real time by scanning tunneling microscopy. Two distinct thickness-dependent decomposition behaviors are observed. When the HfO(2) thickness is ? 0.6 nm, no discernible morphological changes are found below ? 700?°C. Then an abrupt reaction occurs at 750?°C with crystalline hafnium silicide nanostructures formed instantaneously. However, when the thickness is about 1.2 nm, the decomposition proceeds gradually with the creation and growth of two-dimensional voids at 800?°C. The observed thickness-dependent behavior is closely related to the SiO desorption, which is believed to be the rate-limiting step of the decomposition process. PMID:21430314

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

2011-03-23

21

Electrical Properties of Atomic Layer Deposited HfO2 Gate Dielectric Film Using D2O as Oxidant for Improved Reliability  

NASA Astrophysics Data System (ADS)

The initial performance and reliability characteristics of metal-oxide-semiconductor (MOS) capacitors with HfO2 films deposited with H2O or D2O as an oxidant and Hf[N(C2H5)(CH3)]4 as a metal precursor using atomic layer deposition (ALD) were investigated. From secondary ion mass spectroscopy (SIMS) analysis, we observed that deuterium was homogeneously incorporated into the HfO2 film using D2O during ALD. Compared with H2O-processed devices, D2O-processed devices exhibit less charge trapping, less interface trap density generation, and longer time-dependent dielectric breakdown (TDDB) under electrical stress. This improvement of reliability characteristics can be explained by the deuterium isotope effect, which leads to a larger bonding strength of deuterium in the HfO2 film and at the HfO2/Si interface.

Lee, Taeho; Ko, Han-Kyoung; Ahn, Jinho; Park, In-Sung; Sim, Hyunjun; Park, Hokyung; Hwang, Hyunsang

2006-09-01

22

Impact of interfacial layer control using Gd2O3 in HfO2 gate dielectric on GaAs  

NASA Astrophysics Data System (ADS)

Structural and electrical properties of HfO2 and HfO2/Gd2O3 gate stacks on p-GaAs substrates have been investigated. It has been demonstrated that the presence of thin layer of Gd2O3 between HfO2 and GaAs improves metal-oxide-semiconductor device characteristics such as interface state density, accumulation capacitance, frequency dispersion, and leakage current. It is also found that HfO2/Gd2O3 stack can reduce the interfacial GaAs-oxide formation, thus reduce the outdiffusion of elemental Ga and As during post-thermal annealing process. Such suppression of outdiffusion significantly improves the electrical properties of the dielectric stacks.

Dalapati, Goutam Kumar; Tong, Yi; Loh, Wei Yip; Mun, Hoe Keat; Cho, Byung Jin

2007-04-01

23

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

NASA Astrophysics Data System (ADS)

A systematic capacitance-voltage study has been performed on GaAs metal-oxide-semiconductor (MOS) structures with atomic-layer-deposited HfO2/Al2O3 nanolaminates as gate dielectrics. A HfO2/Al2O3 nanolaminate gate dielectric improves the GaAs MOS characteristics such as dielectric constant, breakdown voltage, and frequency dispersion. A possible origin for the widely observed larger frequency dispersion on n-type GaAs than p-type GaAs is discussed. Further experiments show that the observed hysteresis is mainly from the mobile changes and traps induced by HfO2 in bulk oxide instead of those at oxide/GaAs interface.

Yang, T.; Xuan, Y.; Zemlyanov, D.; Shen, T.; Wu, Y. Q.; Woodall, J. M.; Ye, P. D.; Aguirre-Tostado, F. S.; Milojevic, M.; McDonnell, S.; Wallace, R. M.

2007-10-01

24

Interfacial reaction and electrical properties of HfO2 film gate dielectric prepared by pulsed laser deposition in nitrogen: role of rapid thermal annealing and gate electrode.  

PubMed

The high-k dielectric HfO(2) thin films were deposited by pulsed laser deposition in nitrogen atmosphere. Rapid thermal annealing effect on film surface roughness, structure and electrical properties of HfO(2) film was investigated. The mechanism of interfacial reaction and the annealing atmosphere effect on the interfacial layer thickness were discussed. The sample annealed in nitrogen shows an amorphous dominated structure and the lowest leakage current density. Capacitors with high-k HfO(2) film as gate dielectric were fabricated, using Pt, Au, and Ti as the top gate electrode whereas Pt constitutes the bottom side electrode. At the gate injection case, the Pt- and Au-gated metal oxide semiconductor devices present a lower leakage current than that of the Ti-gated device, as well as similar leakage current conduction mechanism and interfacial properties at the metal/HfO(2) interface, because of their close work function and chemical properties. PMID:21910462

Wang, Yi; Wang, Hao; Ye, Cong; Zhang, Jun; Wang, Hanbin; Jiang, Yong

2011-09-27

25

In situ photoemission spectroscopy study on formation of HfO2 dielectrics on epitaxial graphene on SiC substrate  

NASA Astrophysics Data System (ADS)

High quality HfO2 dielectrics have been grown on epitaxial graphene on 4H-SiC substrates and have been studied by using in situ x-ray photoemission spectroscopy. The in situ thermal treatment shows that the HfO2/graphene/4H-SiC heterojunctions have good thermal stability up to 650 °C. A shift of core-level spectra from graphene layer implies that charge transfer takes place at the interface. The high thermal stability and sufficient barrier heights between HfO2 and graphene indicate that high-k dielectric grown on graphene is very promising for the development of graphene-based electronic devices.

Chen, Q.; Huang, H.; Chen, W.; Wee, A. T. S.; Feng, Y. P.; Chai, J. W.; Zhang, Z.; Pan, J. S.; Wang, S. J.

2010-02-01

26

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

SciTech Connect

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

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

2002-03-18

27

Low-temperature method for enhancing sputter-deposited HfO2 films with complete oxidization  

NASA Astrophysics Data System (ADS)

A low-temperature method, supercritical CO2 fluid (SCF) technology, is proposed to improve the dielectric properties of ultrathin hafnium oxide (HfO2) film at 150 °C without significant formation of parasitic oxide at the interface between HfO2 and Si substrate. In this research, the HfO2 films were deposited by dc sputter at room temperature and post-treated by SCF which is mixed with 5 vol % propyl alcohol and 5 vol % H2O. From high-resolution transmission electron microscopy image, the interfacial oxide of SCF-treated HfO2 film is only 5 A? thick. Additionally, the enhancements in the qualities of sputter-deposited HfO2 film after SCF process are exhibited by x-ray photoelectron spectroscopy and capacitance-voltage (C-V) measurement.

Tsai, Chih-Tsung; Chang, Ting-Chang; Liu, Po-Tsun; Yang, Po-Yu; Kuo, Yu-Chieh; Kin, Kon-Tsu; Chang, Pei-Lin; Huang, Fon-Shan

2007-07-01

28

Etching of High-k Dielectric HfO2 Films in BCl3-Containing Plasmas Enhanced with O2 Addition  

NASA Astrophysics Data System (ADS)

Etching characteristics of high dielectric constant HfO2 films have been studied in high-density BCl3-containing plasmas without rf biasing. Emphasis was placed on plasma conditions and etch chemistries to achieve a high selectivity over Si and SiO2 and to enhance the etch rates. The HfO2 etch rate was ˜5 nm/min at a pressure P0=10 mTorr in a BCl3 plasma, giving a selectivity of >10 over Si and SiO2. At lower P0 ? 6 mTorr in BCl3, the deposition of boron-chlorine compounds BxCly was observed on all sample surfaces of HfO2, Si, and SiO2 to inhibit etching. The addition of O2 to BCl3 was found to suppress the deposition and significantly enhance the HfO2 etch rate, which was ˜50 nm/min at P0=5 mTorr in a BCl3/30%-O2 plasma; at higher O2 addition ?40%, the heavy deposition of boron-oxygen compounds BxOy occurred on surfaces to inhibit etching. The mechanisms underlying the phenomena observed are discussed based on plasma and surface diagnostics.

Kitagawa, Tomohiro; Nakamura, Keisuke; Osari, Kazushi; Takahashi, Kazuo; Ono, Kouichi; Oosawa, Masanori; Hasaka, Satoshi; Inoue, Minoru

2006-03-01

29

Thermal stability and electrical characteristics of ultrathin hafnium oxide gate dielectric reoxidized with rapid thermal annealing  

NASA Astrophysics Data System (ADS)

Dielectric properties of ultrathin hafnium oxide reoxidized with rapid thermal annealing (RTA) have been investigated. Capacitance equivalent oxide thickness (CET) of 45 Å hafnium oxide was scaled down to ~10 Å with a leakage current less than 3×10-2 A/cm2 at -1.5 V (i.e., ~2 V below VFB). Leakage current increase due to crystallization was not observed even after 900 °C rapid thermal annealing (RTA), but CET did increase after high temperature RTA due to the interfacial layer growth and possible silicate formation in the HfO2 film.

Lee, Byoung Hun; Kang, Laegu; Nieh, Renee; Qi, Wen-Jie; Lee, Jack C.

2000-04-01

30

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

Microsoft Academic Search

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

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

2001-01-01

31

Top-gated graphene nanoribbon transistors with ultrathin high-k dielectrics.  

PubMed

The integration ultrathin high dielectric constant (high-k) materials with graphene nanoribbons (GNRs) for top-gated transistors can push their performance limit for nanoscale electronics. Here we report the assembly of Si/HfO(2) core/shell nanowires on top of individual GNRs as the top-gates for GNR field-effect transistors with ultrathin high-k dielectrics. The Si/HfO(2) core/shell nanowires are synthesized by atomic layer deposition of the HfO(2) shell on highly doped silicon nanowires with a precise control of the dielectric thickness down to 1-2 nm. Using the core/shell nanowires as the top-gates, high-performance GNR transistors have been achieved with transconductance reaching 3.2 mS microm(-1), the highest value for GNR transistors reported to date. This method, for the first time, demonstrates the effective integration of ultrathin high-k dielectrics with graphene with precisely controlled thickness and quality, representing an important step toward high-performance graphene electronics. PMID:20380441

Liao, Lei; Bai, Jingwei; Cheng, Rui; Lin, Yung-Chen; Jiang, Shan; Huang, Yu; Duan, Xiangfeng

2010-05-12

32

Transient phenomena in the dielectric breakdown of HfO2 optical films probed by ultrafast laser pulse pairs  

NASA Astrophysics Data System (ADS)

The laser induced breakdown threshold of HfO2 films is studied with single pairs of pulses of variable delay and 50 fs and 1 ps pulse duration. Two distinct transient regimes are observed that can be related to the relaxation of the electron density from the conduction band via an intermediate state to the valence band. The experimental results are in good agreement with a theoretical model that assumes occupation of mid gap states after the first pulse on a time scale of several tens of picoseconds and subsequent decay of this population via recombination with holes in the valence band on a time scale of several tens of milliseconds.

Nguyen, Duy N.; Emmert, Luke A.; Patel, Dinesh; Menoni, Carmen S.; Rudolph, Wolfgang

2010-11-01

33

Formation of Reliable HfO2/HfSixOy Gate-Dielectric for Metal-Oxide-Semiconductor Devices  

NASA Astrophysics Data System (ADS)

The HfO2/HfSixOy thin film for gate oxides in the metal-oxide-semiconductor (MOS) device is obtained by a simple method which involves the oxidation of sputtered Hf metal films on Si followed by N2 annealing. Based on the transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses, we found that a high-quality HfO2/HfSixOy stack layer is formed by the oxidation of the thin Hf film on Si. The hysteresis window of the Pd-HfO2/HfSixOy-Si MOS capacitors was negligible (i.e., less than 10 mV). The equivalent oxide thickness (EOT) and leakage current density were 1.2 nm and 2× 10-3 A/cm2 at 1.5 V (after compensating the flatband voltage of 1.5 V), respectively. We suggested that the low leakage current characteristics were obtained due to the presence of the amorphous HfSixOy buffer layer. The conduction mechanism of the Pd-HfO2/HfSixOy-Si MOS capacitors is identified as Poole-Frenkel emission and as Fowler-Nordheim tunneling in low and high electric field regions, respectively.

Quan, Yong Chun; Lee, Jang Eun; Kang, Hyeoksu; Roh, Yonghan; Jung, Donggeun; Yang, Cheol-Woong

2002-11-01

34

Improved interface properties of an HfO2 gate dielectric GaAs MOS device by using SiNx as an interfacial passivation layer  

NASA Astrophysics Data System (ADS)

A GaAs metal-oxide-semiconductor (MOS) capacitor with HfO2 as gate dielectric and silicon nitride (SiNx) as the interlayer (IL) is fabricated. Experimental results show that the sample with the SiNx IL has an improved capacitance—voltage characteristic, lower leakage current density (0.785 × 10-6 A/cm2 at Vfb + 1 V) and lower interface-state density (2.9 × 1012 eV-1 cm-2) compared with other samples with N2- or NH3—plasma pretreatment. The influences of post-deposition annealing temperature on electrical properties are also investigated for the samples with SiNx IL. The sample annealed at 600°C exhibits better electrical properties than that annealed at 500°C, which is attributed to the suppression of native oxides, as confirmed by XPS analyses.

Zhu, Shu-Yan; Xu, Jing-Ping; Wang, Li-Sheng; Huang, Yuan

2013-09-01

35

Depletion-mode GaAs metal-oxide-semiconductor field-effect transistor with HfO2 dielectric and germanium interfacial passivation layer  

NASA Astrophysics Data System (ADS)

The authors present depletion-mode n-channel GaAs metal-oxide-semiconductor field-effect transistor (MOSFET) with a TaN gate electrode, a thin HfO2 gate dielectric, and a thin germanium (Ge) interfacial passivation layer (IPL). Depletion-mode MOSFET on the molecular-beam epitaxy-grown n-type GaAs layer with an equivalent oxide thickness of 17 A? exhibits excellent transistor output characteristics such as a maximum transconductance of 176 mS/mm and a maximum effective electron mobility of 970 cm2/V s. MOSFET shows a surface accumulation channel conduction above flatband condition, indicating that a high quality interface can be achieved using a Ge IPL on GaAs substrate.

Kim, Hyoung-Sub; Ok, Injo; Zhang, Manhong; Lee, T.; Zhu, F.; Yu, L.; Lee, Jack C.; Koveshnikov, S.; Tsai, W.; Tokranov, V.; Yakimov, M.; Oktyabrsky, S.

2006-11-01

36

Characterization of HfO2/Al2O3 gate dielectric nanometer-stacks grown by atomic layer deposition on Ge substrates  

NASA Astrophysics Data System (ADS)

We report the characteristics of HfO2/Al2O3 gate dielectric nanometer-stacks deposited on Ge substrates at 250 °C by atomic layer deposition using Hf[N(CH3)(C2H5)]4 and Al(CH3)3 as the precursors. The annealing effect on the interface and electrical properties of stack films was investigated by X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and electrical measurements. It is demonstrated that the regrowth of GeOx during annealing is suppressed by Al2O3 layer. And the annealed samples exhibit better electrical properties with reduction hysteresis, high capacitance value and improved leakage current density.

Li, Xue-Fei; Li, Ai-Dong; Qian, Xu; Fu, Ying-Ying; Wu, Di

2012-09-01

37

Effects of dielectric structure of HfO2 on carrier generation rate in Si substrate and channel mobility  

NASA Astrophysics Data System (ADS)

This letter presents the effects of surface preparation for hafnium-based dielectrics on the bulk carrier generation rates and the carrier mobility. Different surface preparations result in different interfacial layers. Nitrogen-incorporated layers effectively block impurity penetration from hafnium oxide, and lead to the increase of bulk carrier generation lifetime. However, nitrogen-incorporated interface layers increase interface state density and degrade channel mobility, even though bulk carrier generation lifetime is increased. Thus, mobility degradation is preliminarily caused by fixed charge and interface states of the high-k dielectrics.

Kang, Chang Yong; Cho, Hag-Ju; Choi, Rino; Kang, Chang Seok; Kim, Young Hee; Rhee, Se Jong; Choi, Chang Hwan; Akbar, Shahriar M.; Lee, Jack C.

2004-03-01

38

Dielectric relaxation in hafnium oxide: A study of transient currents and admittance spectroscopy in HfO2 metal-insulator-metal devices  

NASA Astrophysics Data System (ADS)

Dielectric relaxation is studied in 10 nm HfO2 thin films which are deposited by atomic layer deposition on TiN and Pt electrodes. Transient currents are recorded from 10-3 s to 10 s, as a function of bias (0.1 V to 1 V) and temperature (20 °C to 180 °C). A Curie-von Schweidler law is observed, I = Q0/t?. The power law exponent ? is constant with bias and strongly depends on the temperature (varying in the 0.65-1.05 range, with a peak at 75 °C). The amplitude Q0 is described by a relation of the form Q0 = C0V?, where the factor C0 is weakly activated and the exponent ? varies with temperature (in the 0.9-1.5 range as T varies). Transient currents are discussed along with tunneling based models from the literature. To complement transient current experiments, admittance spectroscopy (conductance G and capacitance C) is performed at low frequencies, from 0.01 Hz to 10 kHz. The dispersion law of the conductance is of the form G ~ ?s. The capacitance is the sum of two terms, a non-dispersive term (C?) and a low-frequency dispersive term, CLF ~ ?-n. The critical exponents s and n verify s ~ ? and n ~ 1-?. At room temperature, the dielectric constant is expressed as ?' = ?\\eh' f-n + \\eh'?, where \\eh'? = 11.1, n ~ 0.2/0.3 (Pt/TiN), and ?\\eh' ~ 1.5/0.7 (Pt/TiN).

Mannequin, C.; Gonon, P.; Vallée, C.; Bsiesy, A.; Grampeix, H.; Jousseaume, V.

2011-11-01

39

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

40

Organic thin film transistors with HfO2 high-k gate dielectric grown by anodic oxidation or deposited by sol-gel  

Microsoft Academic Search

We report here on pentacene based organic field effect transistors (OFETs) with a high-k HfO2 gate oxide. HfO2 layers were prepared by two different methods: anodic oxidation and sol–gel. A comparison of the two processes on the electrical properties of OFETs is given. Ultra thin nanoporous (20nm) sol–gel deposited oxide films were obtained following an annealing at 450°C. They lead

J. Tardy; M. Erouel; A. L. Deman; A. Gagnaire; V. Teodorescu; M. G. Blanchin; B. Canut; A. Barau; M. Zaharescu

2007-01-01

41

Structure and dielectric properties of amorphous high-? oxides: HfO2, ZrO2, and their alloys  

NASA Astrophysics Data System (ADS)

High-? metal oxides are a class of materials playing an increasingly important role in modern device physics and technology. Here we report theoretical investigations of the properties of structural and lattice dielectric constants of bulk amorphous metal oxides by a combined approach of classical molecular dynamics (MD), for structure evolution, and quantum mechanical first-principles density function theory (DFT), for electronic structure analysis. Using classical MD based on the Born-Mayer-Buckingham potential function within a melt and quench scheme, amorphous structures of high-? metal oxides Hf1-xZrxO2 with different values of the concentration x are generated. The coordination numbers and the radial distribution functions of the structures are in good agreement with the corresponding experimental data. We then calculate the lattice dielectric constants of the materials from quantum mechanical first principles, and the values averaged over an ensemble of samples agree well with the available experimental data and are very close to the dielectric constants of their cubic form.

Wang, Yin; Zahid, Ferdows; Wang, Jian; Guo, Hong

2012-06-01

42

Freestanding HfO2 grating fabricated by fast atom beam etching  

PubMed Central

We report here the fabrication of freestanding HfO2 grating by combining fast atom beam etching (FAB) of HfO2 film with dry etching of silicon substrate. HfO2 film is deposited onto silicon substrate by electron beam evaporator. The grating patterns are then defined by electron beam lithography and transferred to HfO2 film by FAB etching. The silicon substrate beneath the HfO2 grating region is removed to make the HfO2 grating suspend in space. Period- and polarization-dependent optical responses of fabricated HfO2 gratings are experimentally characterized in the reflectance measurements. The simple process is feasible for fabricating freestanding HfO2 grating that is a potential candidate for single layer dielectric reflector. PACS: 73.40.Ty; 42.70.Qs; 81.65.Cf.

2011-01-01

43

Impact of elemental arsenic on electrical characteristics of metal-oxide-semiconductor capacitors on GaAs using atomic-layer deposited HfO2 gate dielectric  

NASA Astrophysics Data System (ADS)

The interface between HfO2 and sulfur-passivated GaAs was analyzed after atomic-layer deposition (ALD) and postdeposition annealing (PDA) using x-ray photoelectron spectroscopy. The HfO2 ALD process resulted in elemental arsenic buildup at the interface. Electrical measurements confirmed that the elemental arsenic caused anomalously large values for equivalent oxide thickness (EOT), hysteresis, and frequency dispersion in accumulation. Arsenic outdiffusion after PDA lowered the EOT but increased the gate leakage. Annealing the (NH4)2S-treated GaAs prior to ALD yielded an EOT of 1.85 nm and leakage of 6.6×10-4 A/cm2 at Vg=Vfb-1 V. This modified passivation scheme looks promising for achieving a high-quality HfO2/GaAs interface.

Suri, Rahul; Lichtenwalner, Daniel J.; Misra, Veena

2008-06-01

44

Post-Deposition Annealing Analysis for HfO2 Thin Films Using GIXRR/GIXRD  

NASA Astrophysics Data System (ADS)

High-k materials, such as HfO2, Al2O3, and many others, have been employed to replace the SiO2 insulator in the gate dielectric device in order to offer significant gate leakage reduction. In this study, the physical properties of hafnium dioxide (HfO2) thin films were analyzed and characterized in the cases of `as-deposited' and `post-deposition annealing' (PDA). Ultra-thin hafnium dioxide films of thickness 2.5, 5 and 10 nm were deposited on Si (100) substrates using atomic layer deposition (ALD) at temperature of 300° C. After deposition, the films were annealed using furnace in Ar ambient for 10 minutes at 450° C, 550° C, 650° C and 750° C. The thickness, density, roughness and the crystalline evolution of the HfO2 films were investigated by Grazing Incidence X-Ray Reflectometry (GIXRR) and Grazing Incidence X-Ray Diffraction (GIXRD) for both as-deposited and post-annealing conditions. Transmission Electron Microscope (TEM) was used to provide image verification of the two-layer model applied in XRR fitting analysis. Furthermore, the grain sizes were evaluated by X-ray diffraction peak-broadening (full width at half maximum, FWHM) calculation according to the Scherrer method. The experimental results showed that the annealing temperatures had significant impact on the thickness, density and roughness of the HfO2 and SiO2 layers. In addition, the experimental results demonstrated the grain sizes depend on not only the thickness of the film, but also the annealing temperatures in the crystallization process.

Fu, Wei-En; Chang, Yong-Qing; Chen, Yi-Ching

2009-09-01

45

MIM HfO2 low leakage capacitors for eDRAM integration at interconnect levels  

Microsoft Academic Search

An innovative 6 nm HfO2 MIM capacitor was integrated in interconnect levels for eDRAM functions. HfO2 layers or Al2O3-HfO2 stacks were deposited by ALCVD®. Using damascene process with TiN electrodes, this method is fully compatible with copper interconnects technology. No high temperature annealing is required to obtain dielectric performances satisfying eDRAM needs: 30 fF per cell, low leakages and high

Pascale Mazoyer; Serge Blonkowski; FranGois Mondon; A. Farcy; J. Torres; G. Reimbold; F. Martin; J.-F. Damlencourt; Y. Morand; N. Bicais; S. Descombes

2003-01-01

46

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

47

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

NASA Astrophysics Data System (ADS)

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

Benedicto, Marcos; Galiana, Beatriz; Molina-Aldareguia, Jon M.; Monaghan, Scott; Hurley, Paul K.; Cherkaoui, Karim; Vazquez, Luis; Tejedor, Paloma

2011-05-01

48

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

PubMed

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

Benedicto, Marcos; Galiana, Beatriz; Molina-Aldareguia, Jon M; Monaghan, Scott; Hurley, Paul K; Cherkaoui, Karim; Vazquez, Luis; Tejedor, Paloma

2011-05-31

49

Electrical characteristics of hydrogen-terminated diamond metal-oxide-semiconductor with atomic layer deposited HfO2 as gate dielectric  

NASA Astrophysics Data System (ADS)

HfO2 films have been deposited on hydrogen-terminated diamond (H-diamond) by an atomic layer deposition (ALD) technique at 120 °C. Effect of rapid thermal annealing treatment on electrical properties of Au/Ti/Pd/ALD-HfO2/H-diamond metal-oxide-semiconductor (MOS) diodes has been investigated. The leakage current density of the MOS diode after annealing at 300 °C is as small as 10-8 A/cm2 at gate biases from -5.0 to 4.0 V. The capacitance-voltage curve in the depletion mode of the MOS diode after annealing is much sharper than that of the MOS diode before annealing and close to the theoretical dependence, which indicates the small interface state density. The annealed MOS diode is concluded to be more suitable for the fabrication of field effect transistors.

Liu, J. W.; Liao, M. Y.; Imura, M.; Oosato, H.; Watanabe, E.; Koide, Y.

2013-03-01

50

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

51

Electronic excited states at ultrathin dielectric-metal interfaces  

NASA Astrophysics Data System (ADS)

Electronic excited states at a bcc(110) lithium surface, both bare and covered by ionic ultrathin (1–2 monolayers) LiF epitaxial films, are investigated via many-body perturbation theory calculations achieving an atomistic level of detail. The full self-consistent solution of the GW equations is used to account for correlation effects and to properly describe the screened potential in the vacuum. In addition to the correct prediction of image-potential states, we find that the mixing between resonances and image states and the charge compression due to the dielectric ultrathin overlayer give rise to excitations with a hybrid localized but low-lying character whose accurate description cannot intrinsically be achieved via simple models or low-level calculations, but which are expected to play a crucial role in determining the electronic response and transport properties of these systems.

Sementa, L.; Marini, A.; Barcaro, G.; Negreiros, F. R.; Fortunelli, A.

2013-09-01

52

Thermal stability of HfO2-on-GaAs nanopatterns  

NASA Astrophysics Data System (ADS)

We have evaluated the effect of thermal annealing on the morphology, crystalline phase and elemental composition of high-k dielectric HfO2-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 HfO2-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 HfO2 nanostructures, caused by the tetragonal/cubic to monoclinic HfO2 phase transformation and, to a lesser extent, by solid-state diffusion of As into HfO2.

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

2012-05-01

53

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

2012-05-21

54

Uncorrelated multiple conductive filament nucleation and rupture in ultra-thin high-? dielectric based resistive random access memory  

NASA Astrophysics Data System (ADS)

Resistive switching in transition metal oxides could form the basis for next-generation non-volatile memory (NVM). It has been reported that the current in the high-conductivity state of several technologically relevant oxide materials flows through localized filaments, but these filaments have been characterized only individually, limiting our understanding of the possibility of multiple conductive filaments nucleation and rupture and the correlation kinetics of their evolution. In this study, direct visualization of uncorrelated multiple conductive filaments in ultra-thin HfO2-based high-? dielectric resistive random access memory (RRAM) device has been achieved by high-resolution transmission electron microscopy (HRTEM), along with electron energy loss spectroscopy (EELS), for nanoscale chemical analysis. The locations of these multiple filaments are found to be spatially uncorrelated. The evolution of these microstructural changes and chemical properties of these filaments will provide a fundamental understanding of the switching mechanism for RRAM in thin oxide films and pave way for the investigation into improving the stability and scalability of switching memory devices.

Wu, Xing; Li, Kun; Raghavan, Nagarajan; Bosman, Michel; Wang, Qing-Xiao; Cha, Dongkyu; Zhang, Xi-Xiang; Pey, Kin-Leong

2011-08-01

55

Ab initio study of phase transition and dielectric constants of high-? HfO2 as a function of Ge alloying  

NASA Astrophysics Data System (ADS)

I present an ab initio study of the phase stability and dielectric constant (?0) of Hf1-xGexO2 alloy as a function of Ge concentration in the range 0?x?0.25. I determine the critical concentration xc at which the monoclinic structure (the stable phase at low x and at low temperatures) has a phase transition into the high-?0 fluorite structure. I found that, at xc, the fluorite phase presents a dielectric constant that is more than 50% higher than the orientationally averaged dielectric constant of undoped bulk monoclinic phase. I studied the effect of temperature on this phase transition. I identified the microscopic mechanisms which influence the dielectric properties of the fluorite phase finding that the decrease of the Born effective charge of Ge with respect to that of Hf is locally compensated by a variation of the Born effective charge of the O atoms which are neighbors of the Ge. I predict that the bulk modulus of this superhard oxide increases as a function of doping. My results are relevant to improve, by Ge alloying, the dielectric and mechanical properties of hafnia in advanced technological applications.

Debernardi, A.

2012-01-01

56

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

PubMed

First-principles calculations of undoped HfO(2) and cobalt-doped HfO(2) have been carried out to study the magnetic properties of the dielectric material. In contrast to previous reports, it was found that the native defects in HfO(2) could not induce strong ferromagnetism. However, the cobalt substituting hafnium is the most stable defect under oxidation condition, and the ferromagnetic (FM) coupling between the cobalt substitutions is favorable in various configurations. We found that the FM coupling is mediated by the threefold-coordinated oxygen atoms in monoclinic HfO(2) and could be further enhanced in electron-rich condition. PMID:21425287

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

2010-12-16

57

Permittivity increase of yttrium-doped HfO2 through structural phase transformation  

Microsoft Academic Search

An approach to control the dielectric properties of hafnium-based oxide films with an intentional structural phase transformation was proposed and demonstrated. Yttrium serves effectively as a dopant to induce a phase transformation from the monoclinic to the cubic phase even at 600 °C. The yttrium-doped HfO2 films show higher permittivity than undoped HfO2, and the permittivity as high as 27

Koji Kita; Kentaro Kyuno; Akira Toriumi

2005-01-01

58

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

59

Novel hysteresis effect in ultrathin epitaxial Gd2O3 high-k dielectric  

Microsoft Academic Search

Charge trapping in ultrathin high-k Gd2O3 dielectric leading to appearance of hysteresis in C-V curves is studied by capacitance-voltage, conductance-frequency and current-voltage techniques at different temperatures. It was shown that the large leakage current at a negative gate voltage causes the reversible trapping of the positive charge in the dielectric layer, without electrical degradation of the dielectric and dielectric- semiconductor

A. N. Nazarov; Y. V. Gomeniuk; Y. Y. Gomeniuk; V. S. Lysenko; H. D. B. Gottlob; M. Schmidt; M. Czernohorsky; H. J. Osten

60

Extraction of parameters of high permittivity ultrathin (0.5-2.0 nm) gate dielectrics  

Microsoft Academic Search

A new capacitance technique is proposed for the extraction of important parameters of MOS nano-transistors with high permittivity ultrathin (equivalent oxide thickness (EOT)=0.5 to 2.0 nm) gate dielectrics. These parameters include the gate dielectric capacitance, the flat-band voltage, the surface potential versus bias relation, the dielectric potential, the quantization indices for the accumulation and the strong inversion layer, the doping

S. Kar

2004-01-01

61

Ultra-thin TiO2 dielectric film for high capacitance capacitor  

Microsoft Academic Search

This research activity attempts to develop an ultra-thin capacitor using TiO2 as a dielectric film for high-temperature microelectronics in commerical or military applications. There has been an increasing demand for a high dielectric constant insulator for the replacement of SiO2. TiO2 film is promising because it has a high dielectric constant with a sufficiently high breakdown voltage. In spite of

Band-Hung Tsao; Sandra Fries Carr; Joseph A. Weimer

1995-01-01

62

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

63

Design of microfluidic channels separated by an ultra-thin free-standing dielectric membrane  

Microsoft Academic Search

A microfluidic (MF) surface plasmon polariton sensor featuring a gold Mach–Zehnder interferometer on an ultra-thin (20–35 nm)\\u000a dielectric membrane is described. While the presence of the membrane is required to maintain a near mirror symmetry of the\\u000a dielectric properties of the medium on either side of the interferometer, it is a source of unique challenges in the MF system\\u000a design. The

Michal Tencer; Pierre Berini

2009-01-01

64

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

65

Interaction of molecular contaminants with high-k dielectric surfaces  

NASA Astrophysics Data System (ADS)

As the device feature size shrinks, films of silicon oxide (SiO 2) will become unsuitable for MOSFET gate dielectric applications and have to be replaced by thicker films of a high-k dielectric material. Among the high-k materials, hafnium oxide (HfO2) and zirconium oxide (ZrO2) are the most promising candidates. Molecular contamination can affect the quality of the new gate dielectric films in a manner similar to ultrathin SiO2 films. Therefore, characterization of contaminant adsorption behavior of these high-k films should assist in deciding their potential for successful integration in silicon MOS technology. The interactions of moisture and organic (in particular IPA) contamination with ALCVD(TM) deposited 5-nm HfO2 and ZrO2 films were investigated using mass spectrometry. HfO2 and ZrO2 were found to have similar moisture adsorption loadings, but significantly higher than that of SiO2. The new high-k materials also retained a higher portion of the adsorbed moisture after an isothermal nitrogen purge. Almost all the adsorbed moisture could be removed from SiO2 and HfO2 after a 300°C bake under nitrogen purge, whereas ZrO 2 surfaces retained significant amounts of the adsorbed moisture. Experiments with ppb-levels of IPA showed that the adsorption loading on the three surfaces had the following order: ZrO2 > HfO2 > SiO2. The relatively slow desorption kinetics of H2O and IPA highlighted the difficulty in removal of these contaminants from HfO2 and ZrO 2 surfaces. Presence of pre-adsorbed moisture increased IPA adsorption on SiO2, but reduced adsorption on HfO2 and ZrO 2. Isotope labeling studies with D2O showed that IPA reacted with surface hydroxyl groups to form a chemisorbed alkoxy species on all oxides. A multilayer model for adsorption of water and IPA was developed to understand the mechanism of interactions of contaminants with these surfaces. Results indicated that ZrO2 formed the strongest surface-hydroxyl bond and also physisorbed IPA stronger than HfO2 and SiO2. The practical application of the adsorption model is also demonstrated. The results of this work should aid in the selection of the most appropriate dielectric film and design of process/equipment so that it can be more readily integrated into silicon technology.

Raghu, Prashant

66

Control of the interfacial reaction in HfO2 on Si-passivated GaAs  

NASA Astrophysics Data System (ADS)

The physical and electrical effects caused by interfacial reactions of HfO2 on Si-passivated GaAs were investigated by various methods. The results showed that the Si layer decreases the diffusion and formation of GaO. Moreover, post-nitridation in HfO2/Si/GaAs significantly reduced the formation of AsO and GaO. The depth profiling data showed that two separated layered structures were formed with HfO2 and a mixture of HfO2 and SiO2 after the annealing process. The crystalline structure and formation of GaO in the film affect the band offsets between GaAs and the high-k HfO2 dielectric. Moreover, the Si passivation effectively suppressed the interfacial defects caused by GaO diffusion during the annealing treatment. The nitridation cause As diffusion to oxygen vacancy of HfO2 result in the increase of the interfacial defect.

Park, Sang Han; Kang, Yu Seon; Chae, Jimin; Kim, Hyo Jin; Cho, Mann-Ho; Ko, Dae-Hong; Byun, Young-Chul; Kim, Hyoungsub; Cho, Sang Wan; Kim, Chung Yi; Seo, Jung-Hye

2013-10-01

67

Device performance of sub-50 nm CMOS with ultra-thin plasma nitrided gate dielectrics  

Microsoft Academic Search

In this paper, the physical and electrical characteristics of ultra-thin plasma nitrided gate dielectrics are reported, aiming for sub-50 nm gate length CMOS applications. The impact of plasma nitridation conditions on DC characteristics was investigated extensively by changing nitrogen plasma pressure, plasma immersion time, or plasma generation power. NBTI has been also investigated and the lifetime at 105°C and 0.85

S. Inaba; T. Shimizu; S. Mori; K. Sekine; K. Saki; H. Suto; H. Fukui; M. Nagamine; M. Fujiwara; T. Yamamoto; M. Takayanagi; I. Mizushima; K. Okano; S. Matsuda; H. Oyamatsu; Y. Tsunashima; S. Yamada; Y. Toyoshima; H. Ishiuchi

2002-01-01

68

Depth profiling of ultra-thin oxynitride gate dielectrics by using MCs 2 + technique  

Microsoft Academic Search

Ultra-thin silicon oxynitride (SiOxNy) is the leading candidate to replace pure silicon oxide (SiO2) before high k dielectrics come into place because oxynitrides demonstrate several properties superior to those of the conventional gate oxides. The performance of the transistor was reported to depend on the N dose and its distribution in the gate oxide. Therefore, accurate characterization of SiOxNy is

D. Gui; Z. Q. Mo; Z. X. Xing; Y. H. Huang; Y. N. Hua; S. P. Zhao; L. Z. Cha

2008-01-01

69

First-principles model of the dielectric response of ultrathin perovskite films  

NASA Astrophysics Data System (ADS)

Using a recently developed first-principles model [1] for the structural energetics of ultrathin PbTiO3 films, we investigate the thickness dependence of the dielectric response of perfect single-crystal films. The dependence on field direction and on the mechanical and electrical boundary conditions are examined, and the effects of surface relaxations discussed. 1. Ph. Ghosez and K. M. Rabe, Appl. Phys. Lett. 76, 2767 (2000).

Rabe, Karin; Ghosez, Philippe

2001-03-01

70

Gate quality ultrathin (2.5 nm) PECVD deposited oxynitride and nitrided oxide dielectrics  

Microsoft Academic Search

Ultrathin oxynitride using plasma assisted deposition was evaluated against thermal oxide and nitrided thermal oxide as an alternative direct tunneling gate dielectric to thermal oxide in the 2.5-nm regime. The oxynitride showed an enhanced high field effective mobility relative to the thermal oxide although the low field mobility was slightly depressed. The N2O nitrided oxide showed an enhanced high field

Effiong Ibok; Khaled Ahmed; Ming-Yin Hao; Bob Ogle; Jimmie J. Wortman; John R. Hauser

1999-01-01

71

Terahertz surface plasmons excitation by nonlinear mixing of lasers in over ultrathin metal film coated dielectric  

NASA Astrophysics Data System (ADS)

An ultrathin metal film deposited on dielectric plate supports low loss THz surface plasma wave (SPW). The SPW field falls off away from the metal film both inside the dielectric as well as in free space. Two lasers normally incident, from free space on the planar structure, exert a difference frequency ponderomotive force on the free electrons of the film and resonantly excite THz SPW. The ratio of SPW amplitude to lasers is 10-3 at laser intensity of 3 × 1012 W/cm2 at 1 ? m wavelength. The growth rate falls monotonically because at higher frequency the coupling of SPW is weak.

Kumar, Pawan; Tripathi, V. K.

2013-08-01

72

Atomic - vapour - deposited HfO 2 and Sr 4Ta 2O 9 layers for metal-insulator-metal applications  

Microsoft Academic Search

Sr4Ta2O9 and HfO2 films were prepared on 200 mm TiN\\/Si(100) substrates by Atomic Vapour Deposition (AVD). Depositions were carried out within a thermal budget of CMOS back end of line. Electrical properties have been investigated in metal-insulator-metal capacitors after sputter deposition of Au top electrodes. Both Sr4Ta2O9 and HfO2 dielectrics show excellent electrical performances. Oxides possess high capacitance densities of

M. Lukosius; Ch. Wenger; T. Schroeder; J. Dabrowski; R. Sorge; I. Costina; H.-J. Müssig; S. Pasko; Ch. Lohe

2007-01-01

73

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

74

Cross linking molecular systems to form ultrathin dielectric layers  

Microsoft Academic Search

Dehydrogenation leads to cross linking of polymer or polymer like formation in very different systems: self-assembled monolayers and in closo -carboranes leading to the formation of semiconducting and dielectric boron carbide. We find evidence of intermolecular interactions for a self-assembled monolayer (SAM) formed from a large molecular adsorbate, [1,1';4',1\\

Danqin Feng

2007-01-01

75

High-pressure reactively sputtered HfO2: Composition, morphology, and optical properties  

NASA Astrophysics Data System (ADS)

Hafnium oxide films were deposited by high pressure reactive sputtering using different deposition pressures and times. The composition, morphology, and optical properties of the films, together with the sputtering process growth kinetics were investigated using heavy ion elastic recoil detection analysis, Fourier transform infrared spectroscopy, ultraviolet-visible-near infrared spectroscopy, x-ray diffraction, and transmission electron microscopy. The films showed a monoclinic polycrystalline structure, with a grain size depending on the deposition pressure. All films were slightly oxygen rich with respect to stoichiometric HfO2 and presented a significant amount of hydrogen (up to 6 at. %), which is attributed to the high affinity for moisture of the HfO2 films. The absorption coefficient was fitted to the Tauc law, obtaining a band gap value of 5.54 eV. It was found that the growth rate of the HfO2 films depends on the deposition pressure (P) as P-1.75. This dependence is explained by a diffusion model of the thermalized atoms in high-pressure sputtering. Additionally, the formation of an interfacial silicon oxide layer when the films were grown on silicon was observed, with a minimum thickness for deposition pressures around 1.2 mbars. This interfacial layer was formed mainly during the initial stages of the deposition process, with only a slight increase in thickness afterwards. These results are explained by the oxidizing action of the oxygen plasma and the diffusion of oxygen radicals and hydroxyl groups through the polycrystalline HfO2 film. Finally, the dielectric properties of the HfO2/SiO2 stacks were studied by means of conductance and capacitance measurements on Al/HfO2/SiO2/Si devices as a function of gate voltage and ac frequency signal.

Toledano-Luque, M.; San Andrés, E.; Del Prado, A.; Mártil, I.; Lucía, M. L.; González-Díaz, G.; Martínez, F. L.; Bohne, W.; Röhrich, J.; Strub, E.

2007-08-01

76

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

2013-10-22

77

Thermal behavior of hafnium-based ultrathin films on silicon  

NASA Astrophysics Data System (ADS)

We report here on the thermodynamical stability of ultrathin, hafnium-based dielectric films, namely hafnium oxide (HfO2), silicate (HfSixOy), and aluminum silicate (AlHfxSiyOz), deposited on silicon. These materials are promising candidates to replace the well established silicon oxide and oxynitride as gate dielectric materials in advanced Si-based complementary metal-oxide-semiconductor technology. Since there are mandatory requirements on the gate dielectric material, hafnium oxide is currently being modified, by adding silicon and aluminum into the matrix, increasing its thermal stability, and improving its electrical properties. Diffusion-reaction during thermal processing was investigated using isotopic substitution together with ion beam techniques such as Rutherford backscattering spectrometry, narrow nuclear resonance profiling, and nuclear reaction analysis. The chemical changes in the films were accessed by x-ray photoelectron spectroscopy.

Pezzi, R. P.; Morais, J.; Dahmen, S. R.; Bastos, K. P.; Miotti, L.; Soares, G. V.; Baumvol, I. J. R.; Freire, F. L.

2003-07-01

78

Electrical, structural, and chemical properties of HfO2 films formed by electron beam evaporation  

NASA Astrophysics Data System (ADS)

High dielectric constant hafnium oxide films were formed by electron beam (e-beam) evaporation on HF last terminated silicon (100) wafers. We report on the influence of low energy argon plasma (~70 eV) and oxygen flow rate on the electrical, chemical, and structural properties of metal-insulator-silicon structures incorporating these e-beam deposited HfO2 films. The use of the film-densifying low energy argon plasma during the deposition results in an increase in the equivalent oxide thickness (EOT) values. We employ high resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and medium energy ion scattering experiments to investigate and understand the mechanisms leading to the EOT increase. We demonstrate very good agreement between the interfacial silicon oxide thicknesses derived independently from XPS and HRTEM measurements. We find that the e-beam evaporation technique enabled us to control the SiOx interfacial layer thickness down to ~6 A?. Very low leakage current density (<10-4 A/cm2) is measured at flatband voltage +1 V into accumulation for an estimated EOT of 10.9+/-0.1 A?. Based on a combined HRTEM and capacitance-voltage (CV) analysis, employing a quantum-mechanical CV fitting procedure, we determine the dielectric constant (k) of HfO2 films, and associated interfacial SiOx layers, formed under various processing conditions. The k values are found to be 21.2 for HfO2 and 6.3 for the thinnest (~6 A?) SiOx interfacial layer. The cross-wafer variations in the physical and electrical properties of the HfO2 films are presented.

Cherkaoui, K.; Monaghan, S.; Negara, M. A.; Modreanu, M.; Hurley, P. K.; O'Connell, D.; McDonnell, S.; Hughes, G.; Wright, S.; Barklie, R. C.; Bailey, P.; Noakes, T. C. Q.

2008-09-01

79

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

2011-10-17

80

Distortion of electronic structure in HfO2 induced by the out-diffused As from GaAs substrate  

NASA Astrophysics Data System (ADS)

The out diffusion of As is considered as one of the key issues of GaAs-based devices. We performed first-principles calculation to study the electronic structure distortion of HfO2 induced by out-diffused As. As diffused into oxygen vacancy of HfO2 results in several gap states ranging from 1.38 eV to 2.33 eV above HfO2 valence band maximum through As 4p and Hf 5d interaction; on the other hand, interstitial As not only introduces two gap states but also donates one electron to the conduction band of HfO2. These findings provide an interpretation for the degraded electrical performance of dielectrics on GaAs.

He, Jing-Lan; Sun, Qing-Qing; Lu, Hong-Liang; Wang, Peng-Fei; Ding, Shi-Jin; Wei Zhang, David

2013-05-01

81

The chemical analysis about post annealing effect of HfO2 on Si-passivated GaAs  

NASA Astrophysics Data System (ADS)

In order to develop a high performance MOS device, 3-5 based semiconductors as a high carrier transport semiconductors have been seriously considered. Especially, GaAs with HfO2 as gate dielectric material attract as a candidate for future MOS FET device. Since, larger trap density at HfO2/GaAs interface than for HfO2/Si interface degrade device performance, Si interfacial layer was introduced to reduce interfacial trap. Moreover, Si reduces intrinsic defects at GaAs surface by reconstruct Ga or As homo bonds. In this study, we focused on changes in the chemical and structural characteristics of HfO2/Si/GaAs film as a function of post annealing temperature. The interfacial reactions induced by post annealing were investigated by XPS, REELS, and XAS. The results show that Si layer decrease the diffusion and oxide formation of Ga and As. Also, the post nitridation significantly improve the diffusion barrier by forming the Ga-N layer. XAS result also consists with the fact that the post nitridation suppress Ga diffusion. The band offsets between GaAs and high-k gate dielectric were aligned using XPS and REELS.

Park, Sang Han; Kim, Hyo Jin; Kim, Dae-Kyong; Cho, Mann-Ho; Kim, Chung Yi; Kim, Hyoungsub

2012-02-01

82

Nonvolatile memories using deep traps formed in HfO2 by Nb ion implantation  

NASA Astrophysics Data System (ADS)

We report nonvolatile memories (NVMs) based on deep-energy trap levels formed in HfO2 by metal ion implantation. A comparison of Nb- and Ta-implanted samples shows that suitable charge-trapping centers are formed in Nb-implanted samples, but not in Ta-implanted samples. This is consistent with density-functional theory calculations which predict that only Nb will form deep-energy levels in the bandgap of HfO2. Photocurrent spectroscopy exhibits characteristics consistent with one of the trap levels predicted in these calculations. Nb-implanted samples showing memory windows in capacitance-voltage (V) curves always exhibit current (I) peaks in I-V curves, indicating that NVM effects result from deep traps in HfO2. In contrast, Ta-implanted samples show dielectric breakdowns during the I-V sweeps between 5 and 11 V, consistent with the fact that no trap levels are present. For a sample implanted with a fluence of 1013 Nb cm-2, the charge losses after 104 s are ~9.8 and ~25.5% at room temperature (RT) and 85°C, respectively, and the expected charge loss after 10 years is ~34% at RT, very promising for commercial NVMs.

Choul Kim, Min; Oh Kim, Chang; Taek Oh, Houng; Choi, Suk-Ho; Belay, K.; Elliman, R. G.; Russo, S. P.

2011-03-01

83

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

84

Improved interfacial and electrical properties of atomic layer deposition HfO2 films on Ge with La2O3 passivation  

NASA Astrophysics Data System (ADS)

We report the characteristics of HfO2 films deposited on Ge substrates with and without La2O3 passivation at 250 °C by atomic layer deposition (ALD) using La[N(SiMe3)2]3 and Hf[N(CH3)(C2H5)]4 as the precursors. The HfO2 is observed to form defective HfGeOx at its interface during 500 °C postdeposition annealing. The insertion of an ultrathin La2O3 interfacial passivation layer effectively prevents the Ge outdiffusion and improves interfacial and electrical properties. Capacitance equivalent thickness (CET) of 1.35 nm with leakage current density JA of 8.3 × 10?4 A/cm2 at Vg = 1 V is achieved for the HfO2/La2O3 gate stacks on Ge substrates.

Li, Xue-Fei; Liu, Xiao-Jie; Cao, Yan-Qiang; Li, Ai-Dong; Li, Hui; Wu, Di

2013-01-01

85

Hafnium oxide films for application as gate dielectrics  

NASA Astrophysics Data System (ADS)

The deposition and characterization of HfO2 films for potential application as a high-kappa gate dielectric in MOS devices has been investigated. DC magnetron reactive sputtering was utilized to prepare the HfO2 films. Structural, chemical, and electrical analyses were performed to characterize the various physical, chemical and electrical properties of the sputtered HfO2 films. The sputtered HfO2 films were annealed to simulate the dopant activation process used in semiconductor processing, and to study the thermal stability of the high-kappa, films. The changes in the film properties due to the annealing are also discussed in this work. Glancing angle XRD was used to analyse the atomic scale structure of the films. The as deposited films exhibit an amorphous, regardless of the film thickness. During post-deposition annealing, the thicker films crystallized at lower temperature (< 600°C), and ultra-thin (5.8 nm) film crystallized at higher temperature (600--720°C). The crystalline phase which formed depended on the thickness of the films. The low temperature phase (monoclinic) formed in the 10--20 nm annealed films, and high temperature phase (tetragonal) formed in the ultra-thin annealed HfO2 film. TEM cross-section studies of as deposited samples show that an interfacial layer (< 1nm) exists between HfO2/Si for all film thicknesses. The interfacial layer grows thicker during heat treatment, and grows more rapidly when grain boundaries are present. XPS surface analysis shows the as deposited films are fully oxidized with an excess of oxygen. Interfacial chemistry analysis indicated that the interfacial layer is a silicon-rich silicate layer, which tends to transform to silica-like layer during heat treatment. I-V measurements show the leakage current density of the Al/as deposited-HfO 2/Si MOS diode is of the order of 10-3 A/cm 2, two orders of magnitude lower than that of a ZrO2 film with similar physical thickness. Carrier transport is dominated by Schottky emission at lower electric fields, and by Frenkel-Poole emission in the higher electric field region. After annealing, the leakage current density decreases significantly as the structure remains amorphous structure. It is suggested that this decrease is assorted with the densification and defect healing which accures when the porous as-deposited amorphous structure is annealed. The leakage current density increases of the HfO2 layer crystallizes on annealing, which is attributed to the presence of grain boundaries. C-V measurements of the as deposited film shows typical C-V characteristics, with negligible hystersis, a small flat band voltage shift, but great frequency dispersion. The relative permittivity of HfO2/interfacial layer stack obtained from the capacitance at accumulation is 15, which corresponds to an EOT (equivalent oxide thickness) = 1.66 nm. After annealing, the frequency dispersion is greatly enhanced, and the C-V curve is shifted toward the negative voltage. Reliability tests show that the HfO2 films which remain amorphous after annealing possess superior resistance to constant voltage stress and ambient aging. This study concluded that the sputtered HfO 2 films exhibit an amorphous as deposited. Postdeposition annealing alters the crystallinity, interfacial properties, and electrical characteristics. The HfO2 films which remain amorphous structure after annealing possess the best electrical properties.

Hsu, Shuo-Lin

86

Competitive Si and La effect in HfO2 phase stabilization in multi-layer (La2O3)0.08(HfO2) films  

NASA Astrophysics Data System (ADS)

The effect of Si diffusion in HfO2 and the presence of La on phase transformation were investigated. Tetragonal HfO2 structures exhibited high permittivity, and the addition of exotic atoms to HfO2 facilitated tetragonal phase transformation. In multi-layer (La2O3)0.08(HfO2) films, the top HfO2 layer was transformed into a perfect tetragonal structure, and the bottom HfO2 layer near the interfacial layer was of a cubic structure, after annealing at 800 °C. The permittivity reached 50-60. Si diffusion into the HfO2 film stabilized the tetragonal structure, and La incorporation into HfO2 facilitated the transition of the cubic structure.

Cao, Duo; Cheng, Xinhong; Yu, Yuehui; Li, Xiaolong; Liu, Chunze; Shen, Dashen; Mändl, Stephan

2013-08-01

87

Ultra-thin filaments revealed by the dielectric response across the metal-insulator transition in VO2  

NASA Astrophysics Data System (ADS)

Temperature dependent dielectric spectroscopy measurements on vanadium dioxide thin films allow us to distinguish between the resistive, capacitive, and inductive contributions to the impedance across the metal-insulator transition (MIT). We developed a single, universal, equivalent circuit model to describe the dielectric behavior above and below the MIT. Our model takes account of phase-coexistence of metallic and insulating regions. We find evidence for the existence at low temperature of ultra-thin threads as described by a resistor-inductor element. A conventional resistor-capacitor element connected in parallel accounts for the insulating phase and the dielectric relaxation.

Ramírez, J.-G.; Schmidt, Rainer; Sharoni, A.; Gómez, M. E.; Schuller, Ivan K.; Patiño, Edgar J.

2013-02-01

88

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

89

Differences Between Charge Trapping States in Irradiated NanoCrystalline HfO2 and Non-Crystalline Hf Silicates  

Microsoft Academic Search

This paper provides an explanation for qualitative differences between radiation-induced charge trapping states in nano-crystalline HfO 2 and non-crystalline Hf silicate alloys in high-kappa gate stacks by combining electrical measurements with spectroscopic studies and theory. Differences in the observed electrical response to X-ray and gamma-ray irradiation are consistent with fundamental differences in electronic structures between high-kappa dielectrics that are nano-crystalline

G. Lucovsky; D. M. Fleetwood; S. Lee; H. Seo; R. D. Schrimpf; J. A. Felix; J. Lning; L. B. Fleming; M. Ulrich; D. E. Aspnes

2006-01-01

90

Interface plasmonic properties of silver coated by ultrathin metal oxides  

NASA Astrophysics Data System (ADS)

Many fields of high technology take advantage of conductor-dielectric interface properties. Deeper knowledge of physical processes that determine the optical response of the structures containing metal-dielectric interfaces is important for improving the performance of thin film devices containing such materials. Here we present a study on optical properties of several ultrathin metal oxides deposited over thin silver layers. Some widely used materials (Al2O3, SiO2, Y2O3, HfO2) were selected for deposition by r.f. sputtering, and the created metal-dielectric structures with two of them, alumina and silica, were investigated in this work using attenuated total reflectance (ATR) technique and by variable-angle spectroscopic ellipsometry (VASE). VASE was performed with a help of a commercial ellipsometer at various incident angles and in a wide spectral range. A home-made sample holder manufactured for WVASE ellipsometer and operational in Otto configuration has been implemented for angle-resolved and spectral ATR measurements. Simultaneous analysis of data obtained by these two independent techniques allows elaboration of a representative model for plasmonic-related phenomena at metal-dielectric interface. The optical constants of the interface layers formed between metal and ultrathin oxide layers are investigated. A series of oxides chosen for this study allows a comparative analysis aimed for selection of the most appropriate materials for different applications.

Sytchkova, A.; Zola, D.; Grilli, M. L.; Piegari, A.; Fang, M.; He, H.; Shao, J.

2011-09-01

91

Metal-oxide-semiconductor field-effect-transistors on indium phosphide using HfO2 and silicon passivation layer with equivalent oxide thickness of 18 A?  

NASA Astrophysics Data System (ADS)

In this letter, we demonstrate the electrical properties of metal-oxide-semiconductor capacitors and metal-oxide-semiconductor field-effect transistors (MOSFETs) on InP using atomic layer deposited HfO2 gate dielectric and a thin silicon interface passivation layer (Si IPL). Compared with single HfO2, the use of Si IPL results in better interface quality with InP substrate, as illustrated by smaller frequency dispersion and reduced hysteresis. MOSFETs with Si IPL show much higher drive current and transconductance, improved subthreshold swing, interface-trap density and gate leakage current with equivalent oxide thickness scaling down to 18 A?.

Chen, Yen-Ting; Zhao, Han; Yum, Jung Hwan; Wang, Yanzhen; Lee, Jack C.

2009-05-01

92

Experimental evidence of the quantum point contact theory in the conduction mechanism of bipolar HfO2-based resistive random access memories  

NASA Astrophysics Data System (ADS)

The quantum point contact (QPC) model for dielectric breakdown is used to explain the electron transport mechanism in HfO2-based resistive random access memories (ReRAM) with TiN(30 nm)\\HfO2(5 nm)\\Hf(10 nm)\\TiN(30 nm) stacks. Based on experimental I-V characteristics of bipolar HfO2-based ReRAM, we extracted QPC model parameters related to the conduction mechanism in several devices in order to make a statistical study. In addition, we investigated the temperature effect on the conduction mechanism and compared it with the QPC model. Based on these experimental results, we show that the QPC model agrees well with the conduction behavior of HfO2-based ReRAM memory cells.

Prócel, L. M.; Trojman, L.; Moreno, J.; Crupi, F.; Maccaronio, V.; Degraeve, R.; Goux, L.; Simoen, E.

2013-08-01

93

Design and fabrication of a novel high damage threshold HfO2/TiO2/SiO2 multilayer laser mirror  

NASA Astrophysics Data System (ADS)

This paper describes a new method to design a laser mirror with high reflectivity, wide reflection bandwidth and high laserinduced damage threshold. The mirror is constructed by three materials of HfO2/TiO2/SiO2 based on electric field and temperature field distribution characteristics of all-dielectric laser high reflector. TiO2/SiO2 stacks act as the high reflector (HR) and broaden the reflection bandwidth, while HfO2/SiO2 stacks are used for increasing the laser resistance. The HfO2/TiO2/SiO2 laser mirror with 34 layers is fabricated by a novel remote plasma sputtering deposition. The damage threshold of zero damage probability for the new mirror is up to 39.6 J/cm2 (1064 nm, 12 ns). The possible laser damage mechanism of the mirror is discussed.

Meng, Zeng-you; Huang, Sha-ling; Liu, Zhe; Zeng, Cheng-hang; Bu, Yi-kun

2012-05-01

94

Characterization of HfO2 films deposited on 4H-SiC by atomic layer deposition  

NASA Astrophysics Data System (ADS)

Hafnium oxide films with a measured relative dielectric constant of 15.4 were deposited at room temperature on Si and 4H-SiC substrates, as well as on 4H-SiC p-i-n diodes. An 8 nm thick SiO2 interfacial layer on SiC increased the breakdown field of the HfO2/SiO2 stack by 6%, while a 13 nm thick SiO2 layer reduced it by 35%. The evidence of different current conduction mechanisms in SiO2 is shown to be related to the oxide thickness. For the diodes, the breakdown voltage was extended by at least 20%, compared to nonpassivated devices. Annealing at 400 °C in a forming gas changed the crystallinity and increased the relative dielectric constant of the HfO2 layers. There is an indication of reaction between HfO2 and SiO2 in the stacked films after annealing.

Wolborski, Maciej; Rooth, Ma?Rten; Bakowski, Mietek; Hallén, Anders

2007-06-01

95

Synthesis of freestanding HfO2 nanostructures  

NASA Astrophysics Data System (ADS)

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

Kidd, Timothy; O'Shea, Aaron; Boyle, Kayla; Wallace, Jeff; Strauss, Laura

2011-12-01

96

Synthesis of freestanding HfO2 nanostructures.  

PubMed

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

Kidd, Timothy; O'Shea, Aaron; Boyle, Kayla; Wallace, Jeff; Strauss, Laura

2011-04-05

97

Synthesis of freestanding HfO2 nanostructures  

PubMed Central

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

2011-01-01

98

Optical properties of monoclinic HfO2 studied by first-principles local density approximation + U approach  

NASA Astrophysics Data System (ADS)

The band structures and optical properties of monoclinic HfO2 are investigated by the local density approximation + U approach. With the on-site Coulomb interaction being introduced to 5d orbitals of Hf atom and 2p orbitals of O atom, the experimental band gap is reproduced. The imaginary part of the complex dielectric function shows a small shoulder at the edge of the band gap, coinciding with the experiments. This intrinsic property of crystallized monoclinic HfO2, which is absent in both the tetragonal phase and cubic phase, can be understood as a consequence of the reconstruction of the electronic states near the band edge following the adjustment of the crystal structure. The existence of a similar shoulder-like-structure in the monoclinic phase of ZrO2 is predicted.

Li, Jinping; Han, Jiecai; Meng, Songhe; Lu, Hantao; Tohyama, Takami

2013-08-01

99

Photoemission Studies of Pulsed-RF Plasma Nitrided Ultra-thin SiON Dielectric Layers  

SciTech Connect

Results are presented of a photoemission study of the electronic structure of SiON layers formed by a pulsed-RF decoupled plasma nitration (DPN) of ultra-thin SiO{sub 2} grown base layers approximately 1.0 nm thick. The optical thickness of these device grade nitrided dielectric layers was in the range 1.4-1.6 nm. X-ray photoelectron spectroscopy (XPS) studies indicate that the nitrogen is incorporated in a single chemical environment at concentration levels in the range 15-17%. Angle resolved XPS measurements show that the nitrogen is distributed through the layer, with the binding energy of the N 1s peak at 398.3 eV which is indicative of a Si{sub 3}N{sub 4}-like chemical species in an oxide environment. High resolution core level photoemission studies of the spin orbit stripped Si 2p{sup 4+} peak revealed full width half maximum values in the range 1.4-1.55 eV, which are significantly larger than the 1.15 eV value reported for SiO{sub 2} layers. Synchrotron radiation photoemission studies of the valence band spectra enable the valence band off-set at the Si/SON interface to be evaluated as 2.3 eV and to infer a conduction band off-set of 2.1 eV.

O'Connor,R.; McDonnell, S.; Hughes, G.; Smith, K.

2006-01-01

100

Preparation and characterization of HfO{2} thin films by photo-assisted MOCVD  

NASA Astrophysics Data System (ADS)

High-k dielectric HfO{2} thin films have been prepared by photo-assisted metal-organic chemical vapor deposition (MOCVD). Vacuum ultraviolet (VUV) light is used for enhancement of chemical reaction of the source materials of (Hf(O-t-C{4}H{9})4) (HTB) and H{2}O. The absorption spectrum of HTB has been calculated with molecular orbital method. The calculated infrared absorption of HTB is found in VUV region (around 150 nm), and HfO{2} thin films were deposited under the irradiation with VUV light of a D{2} lamp including the HTB absorption band. These prepared films are characterized by FT-IR measurement to estimate the concentration of organic impurities. It shows that C-H peak drastically decreases less in the photo-assisted MOCVD film than the MOCVD. Moreover, C-V characteristics show that accumulation capacitance is increased in the film deposited under VUV irradiation. The accumulation capacitance is much increased by rapid thermal annealing (RTA) in the case of photo-assisted MOCVD. AFM observation results show that very smooth surface is obtained in the photo-assisted MOCVD films.

Kanashima, T.; Tada, T.; Okuyama, M.

2006-03-01

101

Electronic properties of oxygen vacancy in HfO2 within GW calculations  

NASA Astrophysics Data System (ADS)

Hafnia (HfO2) has attracted much attention as a high-k dielectric material, which substitutes for silicon gate oxide in nanoscale metal-oxide-semiconductor (MOS) devices. However, there remain several problems to be resolved in hafnia-based devices, such as flat band shift and threshold voltage instability. Oxygen vacancy, as the most common intrinsic defect, is regarded as a major cause of these problems. As previous calculations mostly rely on the local-density-functional approximation (LDA), the defect levels of oxygen vacancy are not accurately determined because of the LDA band gap problem. Here we perform GW calculations for the defect levels of oxygen vacancy in monoclinic HfO2. Our calculations show that the Fermi level pinning of p+ poly Si gate electrode is due to the charge transfer from oxygen vacancy to the electrode. In addition, the charge trap of oxygen vacancy can lead to the threshold voltage instability in both nMOS and pMOS devices. Finally, we suggest that oxygen vacancy may be a cause of the gate leakage current by the Poole-Frenkel conduction.

Choi, Eun-Ae; Chang, Kee Joo

2009-03-01

102

Epitaxial growth and electrical properties of ultrathin La2Hf2O7 high-k gate dielectric films  

NASA Astrophysics Data System (ADS)

Ultrathin La2Hf2O7 (LHO) high-k gate dielectric films (˜3.4 nm) have been epitaxially grown on Si (0 0 1) substrates through a pulsed laser deposition system. The epitaxial growth characteristics, composition, interface with Si, optical band gap, and electrical properties of the ultrathin LHO films have been investigated by in situ reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) and transmittance spectroscopy, as well as semiconductor characterization analysis. Results show that ultrathin LHO film grown at 800 °C shows a good crystallinity and no obvious interfacial layer forms. La is deficient and oxygen is slightly excessive in LHO film. The epitaxial LHO film has a band gap of ˜5.7 eV. The gate leakage current density Jg of the ultrathin epitaxial LHO film follows the space-charge limited conduction mechanism and Jg is ˜0.3 A/cm2 at a gate voltage of 1 V. Additionally, a suitable permittivity ˜ 16.7, a small hysteresis ˜ 30 mV and a low capacitance equivalent thickness ˜ 0.79 nm have been obtained.

Xiong, Yu-Hua; Tu, Hai-Ling; Du, Jun; Wei, Feng; Zhang, Xin-Qiang; Yang, Meng-Meng; Zhao, Hong-Bin; Chen, Da-Peng; Wang, Wen-Wu

2013-10-01

103

Reduction of interfacial SiO2 at HfO2/Si interface with Ta2O5 cap  

NASA Astrophysics Data System (ADS)

We investigated SiO2 interfacial layer (IL-SiO2) reduction with a Ta2O5 cap to realize the direct contact formation of HfO2 on a Si substrate for the equivalent oxide thickness scaling of Hf-based high-k gate dielectrics. X-ray reflectivity and x-ray photoelectron spectroscopy measurements revealed that the Ta2O5 cap was effective in taking oxygen from the IL-SiO2 and caused SiO2 reduction, which resulted from Ta diffusion into the HfO2 layer from the Ta2O5. With this technique, the Ta2O5 cap deposited on the HfO2/SiO2/Si reduced the IL-SiO2 by 0.2 nm without any thermal treatment. Rapid thermal annealing at 300 °C enhanced the IL-SiO2 reduction. This result reveals that our method is a promising approach to achieve direct contact between the high-k layer and the Si substrate. Therefore, Ta2O5 has good potential as a cap for SiO2 interfacial layer reduction.

Kobashi, Kazuyoshi; Nagata, Takahiro; Ogura, Atsushi; Nabatame, Toshihide; Chikyow, Toyohiro

2013-07-01

104

Anti-reflection resonance in distributed Bragg reflectors-based ultrathin highly absorbing dielectric and its application in solar cells  

NASA Astrophysics Data System (ADS)

We present a design of anti-reflection resonance in distributed Bragg reflectors (DBRs) based ultrathin highly absorbing dielectric. In such structure, anti-reflection resonance can be supported at wavelengths much longer than those achieved by the previous metal-based structure due to the appropriate reflection phase from the DBRs surface. The proposed anti-reflection resonance can find applications in thin-film organic solar cells for light trappings. By replacing partial metal electrode with DBRs to provide the desired reflection phase, the overall absorptivity can be greatly increased by ~31% due to the good matching between anti-reflection resonance and high-absorption range of the active layers.

Zhang, Xu-Lin; Song, Jun-Feng; Li, Xian-Bin; Feng, Jing; Sun, Hong-Bo

2013-03-01

105

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

2012-12-21

106

Leakage current comparison between ultra-thin Ta2O5 films and conventional gate dielectrics  

Microsoft Academic Search

Capacitors with ultra-thin (6.0-12.0 nm) CVD Ta2O5 film were fabricated on lightly doped Si substrates and their leakage current (Ig-Vg) and capacitance (C-V) characteristics were studied. For the first time, samples with stack equivalent oxide thickness around 2.0 nm were compared with ultra-thin silicon dioxide and silicon oxynitride. The Ta2O5 samples showed remarkably lower leakage current, which not only verified

Qiang Lu; A. Kalnitsky; C. Chang; Chia-Cheng Cheng; Sing Pin Tay; Tsu-Jae King; Chenming Hu

1998-01-01

107

Broadband light-trapping enhancement in an ultrathin film a-Si absorber using whispering gallery modes and guided wave modes with dielectric surface-textured structures.  

PubMed

An embedded nanosphere dielectric structure on an a-Si ultrathin film improves weighted absorption from 23.8% to 39.9%. The PMMA embedding layer offers a guided wave mode as well as mechanical robustness, in addition to the resonant whispering gallery modes coupling. Broadband light-trapping enhancements are observed by dielectric surface textured structures of hemispheres, nanocones, nanospheres, or embedded nanospheres. PMID:23529900

Kang, Gumin; Park, Haesung; Shin, Dongheok; Baek, Seunghwa; Choi, Minjung; Yu, Dai-Hyuk; Kim, Kyoungsik; Padilla, Willie J

2013-03-26

108

Improvement of gate dielectric reliability for p+poly MOS devices using remote PECVD top nitride deposition on ultra-thin (2.4–6 nm) gate oxides  

Microsoft Academic Search

Dual layer dielectrics have been formed by remote PECVD deposition of ultra-thin (0.4–1.2nm) nitrides onto thin thermal oxides grown on n-type Si(100) substrates. Activation of boron-implanted p+ polycrystalline silicon gate electrodes was accomplished by a high temperature anneal, 1–4min at 1000°C. Boron penetration through the dielectric film to the n-type substrate was investigated by performing a quasi-static C–V analysis and

Y Wu; G Lucovsky

1999-01-01

109

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

110

GaN-Based Metal--Insulator--Semiconductor Ultraviolet Photodetectors with HfO2 Insulators  

NASA Astrophysics Data System (ADS)

Nitride-based metal--insulator--semiconductor (MIS) ultraviolet (UV) photodetectors (PDs) with a hafnium oxide (HfO2) insulating layer was fabricated for the first time and characterized successfully. It was found that we can achieve a small dark current and a large photocurrent to dark current contrast ratio using the proposed device with the HfO2 insulating layer. Furthermore, the noise equivalent power was substantially reduced, and detectivity was increased using HfO2 insulators.

Chen, Chin-Hsiang

2013-08-01

111

Elastic and vibrational properties of monoclinic HfO2 from first-principles study  

Microsoft Academic Search

The elastic and vibrational properties of crystalline monoclinic HfO2 have been investigated using density functional perturbation theory. Using the Voigt and Reuss theory, we estimate the bulk, shear and Young's modulus for polycrystalline HfO2, which agree very well with the available experimental and theoretical data. Additionally, we present a systematic analysis of the elastic properties of HfO2 polymorphs and find

Rui Wu; Bo Zhou; Qian Li; ZhenYi Jiang; WenBo Wang; WenYan Ma; XiaoDong Zhang

2012-01-01

112

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

PubMed

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

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

2013-08-15

113

Energy band alignment of HfO2 on Ge  

NASA Astrophysics Data System (ADS)

The band alignment of hafnium oxide films grown on Ge (100) by atomic layer deposition has been investigated by x-ray photoelectron spectroscopy (XPS) and internal photoemission (IPE) spectroscopy. HfO2 films have been grown using HfCl4 as hafnium precursor while O3 or H2O have been used as oxygen precursors. The valence-band offset (VBO) values, determined by XPS, are 3.0+/-0.1 eV and 3.1+/-0.1 eV for the samples grown using O3 and H2O, respectively. A conduction-band offset (CBO) value of 2.0+/-0.1 eV has been obtained by IPE for all the samples. Considering a band gap of 5.6+/-0.1 eV, as obtained by photoconductivity measurements, XPS and IPE results have been found to be in excellent agreement. The CBO and VBO values are the same in all the samples within the experimental error. The presence of a thick GeOx interfacial layer in the samples grown using O3 is not affecting the band alignment of the HfO2/Ge heterojunction.

Perego, M.; Seguini, G.; Fanciulli, M.

2006-11-01

114

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

115

Inversion-type enhancement-mode HfO2-based GaAs metal-oxide-semiconductor field effect transistors with a thin Ge layer  

NASA Astrophysics Data System (ADS)

Using a thin germanium (Ge) interfacial passivation layer (IPL), GaAs HfO2-based inversion-type enhancement-mode metal-oxide-semiconductor field effect transistors (MOSFETs) are realized. The n-channel MOSFETs on semi-insulating GaAs substrate clearly show surface modulation and excellent current control by gate bias. The threshold voltage of ~0.5 V, the transconductance of ~0.25 mS/mm, the subthreshold swing of ~130 mV/decade, and the drain current of ~162 ?A/mm (normalized to the gate length of 1 ?m) at Vd=2 V and Vg=Vth+2 V are obtained. In comparison with previous reports, the dc characteristics of the inversion-type GaAs MOSFETs with a Ge IPL and HfO2 dielectric demonstrate much similar results.

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

2008-01-01

116

Optimization of pH sensing using silicon nanowire field effect transistors with HfO2 as the sensing surface  

NASA Astrophysics Data System (ADS)

Silicon nanowire field effect transistor sensors with SiO2/HfO2 as the gate dielectric sensing surface are fabricated using a top down approach. These sensors are optimized for pH sensing with two key characteristics. First, the pH sensitivity is shown to be independent of buffer concentration. Second, the observed pH sensitivity is enhanced and is equal to the Nernst maximum sensitivity limit of 59 mV/pH with a corresponding subthreshold drain current change of ~ 650%/pH. These two enhanced pH sensing characteristics are attributed to the use of HfO2 as the sensing surface and an optimized fabrication process compatible with silicon processing technology.

Zafar, Sufi; D'Emic, Christopher; Afzali, Ali; Fletcher, Benjamin; Zhu, Y.; Ning, Tak

2011-10-01

117

Localized breakdown in dielectrics and macroscopic charge transport through the whole gate stack: A comparative study  

NASA Astrophysics Data System (ADS)

Au-HfO2-SiOx-Si structures with 4 nm HfO2 and 1.5 nm SiOx interfacial layer (IL) have been electrically stressed by ballistic electron emission spectroscopy (BEES). The continuous BEES stressing at the same location induced gradual degradations and finally led to breakdowns in the IL. The degradation and breakdown cannot be observed using macroscopic conventional current-voltage (IV) measurements over the same area just before and after the BEES stressing process. The localized degradation and breakdown in the dielectric is masked by the macroscopic gate area. Tunneling calculations can estimate the critical area required for a macroscopic device to be able to measure such microscopic breakdown, a problem that becomes increasingly important for characterizing ultrathin gate dielectrics.

Zheng, Yi; Wee, Andrew T. S.; Ong, Yi Ching; Pey, K. L.; Troadec, Cedric; O'Shea, Sean J.; Chandrasekhar, N.

2008-01-01

118

Bias-temperature stability of ultrathin parylene-capped dielectrics: influence of surface oxygen on copper ion diffusion  

NASA Astrophysics Data System (ADS)

The effect of interfacial oxygen on copper ion penetration was investigated with metal-insulator-semiconductor capacitor (MISCAP) structures with and without an ultrathin (50 Å) polymer-capping layer. The amount of interfacial oxygen and hence the degree of copper ion penetration could be affected by the thermal annealing of the MISCAPs at 150 and 250 °C and in inert and reducing environments. The bias-temperature stressing (BTS) of a Cu/50 Å parylene-N/3000 Å plasma-enhanced tetraethoxysilane (PETEOS)/200 Å thermal SiO2/Si MISCAP at 150 °C and 1 MV/cm and previously annealed at 250 °C in Ar-3%H2 resulted in no flatband voltage shift from as-annealed to 180 min of BTS. The lack of flatband voltage shift is indicative of no copper ion penetration and a stable dielectric. Under higher electric fields (1.5-2 MV/cm) and at 150 °C, the polymer-capped PETEOS dielectric hindered copper ion penetration, but did not prevent it.

Senkevich, Jay J.; Wang, Pei-I.; Wiegand, Chris J.; Lu, T.-M.

2004-04-01

119

Properties of Ultrathin Al2O3-TiO2 Nanolaminate Films for Gate Dielectric Applications Deposited by Plasma-Assisted Atomic Layer Deposition  

NASA Astrophysics Data System (ADS)

High permittivity dielectrics such as Al2O3, HfO2, Ta2O5, TiO2, etc., are an essential component of aggressively-scaled III-V and graphene field effect transistors (FETs) where insulators are necessary to reduce gate leakage current while maintaining high gate capacitance and charge control of the channel. Atomic layer deposition (ALD) has the capability to deposit hybrid films, or nanolaminates, of two or more dielectrics that have unique properties. Thin [Al2O3+TiO2] nanolaminates with varying TiO2 and Al2O3 content were deposited on n-Si substrates at ˜225-300 C using ALD. A nanolaminate is composed of bilayers, defined as the sum of (x)Al2O3 and (y)TiO2, where x, and y indicate the number of times a component monolayer is repeated. While the overall thickness of the dielectric was held at ˜ 17-20 nm, the relative ratio of Al2O3 to TiO2 in the bilayer stack was varied to evaluate changes in the material properties and electrical performance of the oxides. C-V and I-V measurements on various [(x)TiO2+(y)Al2O3] MOS capacitors were taken. The high-TiO2-content films show limited evidence of oxide charge trapping and relatively large dielectric constants (?˜15), whereas the high-Al2O3-content films offer a larger optical bandgap and improved suppression of leakage current. We will discuss the properties of very thin nanolaminates and their possible use as gate oxides. Morphological, electrical, and XPS composition assessments will be presented.

Garces, Nelson; Meyer, David; Nepal, Neeraj; Wheeler, Virginia; Eddy, Charles

2012-02-01

120

Modeling Effects of Interface Trap States on the Gate CV Characteristics of MOS Devices with Ultrathin High-K Gate Dielectrics  

Microsoft Academic Search

A physically based, quantum mechanical model is presented for C-V characteristics of MOS devices with ultrathin high-K gate dielectrics including interface trap and wave function penetration effects. Numerical results show that C-V curves are rather sensitive to the details of the interface trap distributions. The proposed model may be used for accurately extracting profiles of interface trap states from low

M. M. Satter; M. A. Haque

2007-01-01

121

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

Microsoft Academic Search

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

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

1999-01-01

122

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

123

High quality ultra-thin (1.5 nm) TiO2Si3N 4 gate dielectric for deep sub-micron CMOS technology  

Microsoft Academic Search

This paper presents the physical and electrical properties of ultra-thin (~1.5 nm EOT) TiO2\\/Si3N4 gate dielectrics fabricated by the jet-vapor deposition (JVD) process for both n- and p-channel field-effect transistors. It will be shown that the use of TiO2\\/Si3N4 to replace SiO2 as gate dielectric can reduce the gate leakage current by several orders of magnitude while maintaining excellent interface

Xin Guo; Xiewen Wang; Zhijiong Luo; T. P. Ma; T. Tamagawa

1999-01-01

124

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

125

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

NASA Astrophysics Data System (ADS)

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

2005-09-01

126

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

127

Physical and Electrical Characterization of HfO2, HfSiO4, and ZrSiO4 Memristors Based on Sol-Gel Synthesis  

NASA Astrophysics Data System (ADS)

To date, most memristive devices have been fabricated by using TiO2 or TaOx dielectric films. In order to explore the possible advantages of other high-? dielectrics in memristive devices, memristors were fabricated with HfO2, HfSiO4, and ZrSiO4 layers synthesized from sol-gels. X-ray photoelectron spectroscopy measurements are consistent with reported spectra of HfO2, HfSiO4, and ZrSiO4 films, but contain significant amounts of carbon. The films also have low densities and are flat, as measured by vacuum ultraviolet spectroscopic ellipsometry and optical profilometry measurements, respectively. This flat morphology is different from previous solution-processed dielectric films that exhibited rough surfaces [1]. Transmission electron microscopy measurements were also used to characterize these dielectric films. Current-voltage measurements indicate that, despite the contamination, the memristors exhibit nonvolatile bipolar resistive switching. The retention times measured for these memristors are ˜10^6 s. Capacitance and conductance measurements of these memristors indicate differences between the ON and OFF states, which will be discussed further. [1] J.L. Tedesco, et al., ECS Trans. 35, 111 (2011).

Tedesco, J. L.; Zheng, Walter; Pookpanratana, S.; Herzing, A. A.; Kavuri, P. P.; Kirillov, O. A.; Nguyen, N. V.; Richter, C. A.

2012-02-01

128

Preparation of HfO2 Thin Films Using Flashing Spray CVD Method  

NASA Astrophysics Data System (ADS)

The authors proposed the novel evaporation supply method, flashing spray chemical vapor deposition (FS-CVD). In the experiment, tetrakisethylmethylamidohafnium (TEMAH) was used as the precursor and n-pentane was used as the low boiling point organic solvent. The critical consolute temperature of TEMAH and n-pentane mixed material solution was 276K. The vapor pressure of the mixed material solution was ten times higher than that of TEMAH by formation of two-phase region. HfO2 film was deposited on Si wafer by using TEMAH and n-pentane with FS-CVD. As the result, the uniformity of HfO2 film was +/-5% and film thickness was 133.6nm. The uniformity of HfO2 film of refractive index was +/-5% and refractive index was 1.63. It is found that the precursor was evaporated by flash boiling and HfO2 film was deposited by decomposition.

Ohshima, Motohiro; Kimura, Daiichiro; Tsuchida, Tomoya; Senda, Jiro

129

III-Nitride grating grown on freestanding HfO2 gratings  

PubMed Central

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

2011-01-01

130

Effect of Gate Electrodes on Structure and Electrical Properties of Sputtered HfO2 Thin Films  

NASA Astrophysics Data System (ADS)

High dielectric hafnium oxide films were grown by magnetron sputtering and post heat treatment in nitrogen atmosphere at 500°C for 30 min using vacuum annealing furnace. The film keeps amorphous at 500°C and has better interface quality as revealed by X-ray diffraction and transmission electron microscopy. The influence of TiN and Pt electrodes on the electrical property of the film was compared. For the annealed films, TiN electrode was presented as the optimal one. For the conduction mechanism of Pt/HfO2/p-Si MOS capacitors under gate electron injection, the dominant conduction mechanism at low electric field is Schottky emission. At high electric field, the conversion of current transport mechanism from Schottky emission to trap-assisted tunneling for the annealed HfO2 film occurs at 0.64 MV/cm.

Dong, Ming; Wang, Hao; Shen, Liangping; Ye, Cong; Wei, Qinxiang

2012-10-01

131

Leakage current through the poly-crystalline HfO2: Trap densities at grains and grain boundaries  

NASA Astrophysics Data System (ADS)

We investigate the role of grains and grain boundaries (GBs) in the electron transport through poly-crystalline HfO2 by means of conductive atomic force microscopy (CAFM) measurements and trap-assisted tunneling simulations. CAFM experiments demonstrate that the leakage current through a thin dielectric film preferentially flows via the GBs. The current I-V characteristics measured on both types of sites, grains, and GBs are successfully simulated by utilizing the multiphonon trap-assisted tunneling model, which accounts for the inelastic charge transport via the electron traps. The extracted density of electrically active traps, whose energy parameters match those of the positively charged oxygen vacancies in hafnia, is ~3 × 1019 cm-3 at the grains, whereas a much higher value of (0.9÷2.1) × 1021 cm-3 is required to reproduce the leakage current through the GBs.

Pirrotta, Onofrio; Larcher, Luca; Lanza, Mario; Padovani, Andrea; Porti, Marc; Nafría, Montserrat; Bersuker, Gennadi

2013-10-01

132

Electronic Structure Differences in ZrO2 vs. HfO2  

SciTech Connect

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

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

2005-12-22

133

Phase equilibria and ordering in the system HfO 2 Yb 2 O 3  

Microsoft Academic Search

The system HfO2-Yb2O3 was investigated in the 0 to 100 mol % Yb2O3 range using X-ray diffraction analysis, linear thermal expansion measurements and melting point studies. At high temperatures, the system is dominated by wide regions of solid solutions based on HfO2 and Yb2O3 separated by a two-phase field which appears to extend to the solidus. The extent of the

P. Duran; C. Pascual

1984-01-01

134

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

Microsoft Academic Search

HfO2\\/SiO2 and ZrO2\\/SiO2 high reflectors at 1.064 microns were deposited by pulsed reactive DC magnetron sputtering. These dielectric thin film high reflectors were deposited with and without the use of an electron source. The electron source greatly decreased arcing of the magnetrons during the deposition process resulting in thin films with fewer defects. The high reflectors were laser damage tested

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

2005-01-01

135

Phase diagrams and dielectric response of epitaxial (BaxSr1-x)TiO3 ultrathin films: A first-principles study  

NASA Astrophysics Data System (ADS)

A method based on first-principles calculations was used to construct temperature versus misfit strain phase diagrams for epitaxial (BaxSr1-x)TiO3 ultrathin films over the entire composition range from x=0 to x=1. The predicated phase diagrams show “topologies” that are similar to those calculated by Shirokov et al. (Phy. Rev. B. 79 (2009) 144118), but with quantitative differences that are examined and explained. The dependence of the dielectric permittivity on the misfit strain and the film composition at room temperature are also investigated and compared with available theoretical predications and experimental measurements.

Bin-Omran, S.

2012-09-01

136

Optical properties of a HfO2/Si stack with a trace amount of nitrogen incorporation  

NASA Astrophysics Data System (ADS)

HfO2 films were deposited by atomic layer deposition through alternating pulsing of Hf[N(C2H5)(CH3)]4 and H2O2. A trace amount of nitrogen was incorporated into the HfO2 through ammonia annealing. The composition, the interface stability of the HfO2/Si stack and the optical properties of the annealed films were analyzed to investigate the property evolution of HfO2 during thermal treatment. With a nitrogen concentration increase from 1.41 to 7.45%, the bandgap of the films decreased from 5.82 to 4.94 eV.

Ye, Li; Tingting, Jiang; Qingqing, Sun; Pengfei, Wang; Shijin, Ding; Wei, Zhang

2012-03-01

137

HfOxNy gate dielectric on p-GaAs  

NASA Astrophysics Data System (ADS)

Plasma nitridation method is used for nitrogen incorporation in HfO2 based gate dielectrics for future GaAs-based devices. The nitrided HfO2 (HfOxNy) films on p-GaAs improve metal-oxide-semiconductor device characteristics such as interface state density, accumulation capacitance, hysteresis, and leakage current. An equivalent oxide thickness of 3.6 nm and a leakage current density of 10-6 A cm-2 have been achieved at VFB-1 V for nitrided HfO2 films. A nitride interfacial layer (GaAsO:N) was observed at HfO2-GaAs interface, which can reduce the outdiffusion of elemental Ga and As during post-thermal annealing process. Such suppression of outdiffusion led to a substantial enhancement in the overall dielectric properties of the HfO2 film.

Dalapati, G. K.; Sridhara, A.; Wong, A. S. W.; Chia, C. K.; Chi, D. Z.

2009-02-01

138

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

139

Damage Behavior of HfO2 Monolayer Film Containing Gold Nanoparticles as Artificial Absorbing Defects  

SciTech Connect

Hafnia is one of the most utilized high-index materials in thin-film multilayer coatings for high-power lasers. It is well established that in the HfO2/SiO2 multilayers for 351 nm, nanosecond-pulse applications the damage is driven by the nanoscale absorbers localized in the hafnia layers. In this work, damage-crater formation thresholds and morphology are investigated for the undoped HfO2 monolayer films and films containing isolated gold nanoparticles of 2- and 5-nm average diameter.

Paperov, S.; Schmid, A.W.; Rigatti, A.L.; Oliver, J.B.; Howe, J.D.

2006-03-01

140

Laser conditioning on HfO2 film monitored by calorimeter.  

PubMed

Conditioning effect on HfO2 single-layer film by quasi-cw laser was investigated. The conditioning process was monitored with laser calorimeter. Experimental results revealed that the HfO2 film absorption decreased as a function of the irradiation dose. Higher laser power accelerated the conditioning process. The conditioning effect could not be explained by water annihilation. AFM pictures of the film surface showed that the structural information in the conditioned region was different from the unconditioned region. Monitoring the in situ absorption, laser calorimeter is a promising tool to investigate the laser conditioning process. PMID:22274394

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

2012-01-01

141

Electrical and physical properties of HfO2 films prepared by remote plasma oxidation of Hf metal  

NASA Astrophysics Data System (ADS)

The electrical and physical properties of thin hafnium oxide (HfO2) films fabricated by a remote plasma oxidation of a hafnium metal were investigated. The HfO2 capacitors with TiN electrodes exhibited excellent electrical characteristics such as equivalent oxide thickness (EOT) of 0.65 nm with leakage current density of 2.7 A/cm2 at the gate bias of Vfb-1 (V). The HfO2 thickness dependence of the EOT demonstrated that the permittivity of 19 for HfO2 layer and the interfacial layer thickness of 0.36 nm. X-ray photoelectron spectroscopy study revealed that the oxygen radicals oxidize the Hf metal selectively than Si substrate, leading to an increase of permittivity of HfO2 with reduced interfacial layer growth.

Yamamoto, Kazuhiko; Hayashi, Shigenori; Niwa, Masaaki; Asai, Masayuki; Horii, Sadayoshi; Miya, Hironobu

2003-09-01

142

Graphene on amorphous HfO2 surface: An ab initio investigation  

NASA Astrophysics Data System (ADS)

The energetic stability, electronic, and structural properties of graphene adsorbed on the amorphous HfO2 surface (G/HfO2) have been examined through ab initio theoretical investigations. We have considered the graphene adsorption on (i) defect-free (pristine) and defective HfO2 surfaces, (ii) oxygen vacancy, and (iii) interstitial oxygen atoms. We find that the formation of G/HfO2 is an exothermic process, ruled by van der Waals interactions. In (i) and (iii) there is no net charge transfer between the graphene and the HfO2 surface. In contrast, upon the presence of oxygen vacancy, the adsorbed graphene sheet becomes n-type doped, due to a donor level lying above the Dirac point of the graphene. The absence of G-HfO2 chemical bonds has been maintained, however, the graphene adsorption energy increases when compared with (i) and (iii). Finally, in (ii) we find that HfO2 surface potential becomes more inhomogeneous, strengthening the formation of electron- and hole-rich regions on the graphene sheet.

Scopel, W. L.; Fazzio, A.; Miwa, R. H.; Schmidt, T. M.

2013-04-01

143

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

National Technical Information Service (NTIS)

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 ...

D. M. Zhu D. S. Fox N. P. Bansal R. A. Miller

2004-01-01

144

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

NASA Astrophysics Data System (ADS)

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

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

2009-07-01

145

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

NASA Astrophysics Data System (ADS)

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

Pilania, Ghanshyam; Ramprasad, R.

2012-02-01

146

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

147

Design and control of Ge-based metal-oxide-semiconductor interfaces for high-mobility field-effect transistors with ultrathin oxynitride gate dielectrics  

NASA Astrophysics Data System (ADS)

High-quality Ge-based metal-oxide-semiconductor (MOS) stacks were achieved with ultrathin oxynitride (GeON) gate dielectrics. An in situ process based on plasma nitridation of the base germanium oxide (GeO2) surface and subsequent metal electrode deposition was proven to be effective for suppressing electrical deterioration induced by the reaction at the metal/insulator interface. The electrical properties of the bottom GeON/Ge interface were further improved by both low-temperature oxidation for base GeO2 formation and high-temperature in situ vacuum annealing after plasma nitridation of the base oxide. Based on the optimized in situ gate stack fabrication process, very high inversion carrier mobility (?hole: 445 cm2/Vs, ?electron: 1114 cm2/Vs) was demonstrated for p- and n-channel Ge MOSFETs with Al/GeON/Ge gate stacks at scaled equivalent oxide thickness down to 1.4 nm.

Minoura, Yuya; Kasuya, Atsushi; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

2013-07-01

148

First principles calculation of dopant solution energy in HfO2 polymorphs  

NASA Astrophysics Data System (ADS)

The solution behavior of dopants, Si, La, and N, in HfO2 polymorphs, monoclinic, tetragonal, and cubic was investigated by using a first principles calculation based on density functional theory within the local density approximation. It was found that the Si and La solutions are more preferable under oxidization atmosphere than reduction atmosphere, and the most efficient nitridation condition for the HfO2 is NO/NO2 atmosphere. By comparing the energy difference between the monoclinic and the tetragonal phases, it was found that the energy difference is decreased by the Si or La doping, whereas influence of the N doping is small, indicating that the phase transition from the monoclinic to tetragonal phase would be enhanced by the Si or La doping.

Saitoh, M.; Mizoguchi, T.; Tohei, T.; Ikuhara, Y.

2012-10-01

149

Electrical, Structural and Interfacial Characterization of HfO2 Films on Si Substrates  

NASA Astrophysics Data System (ADS)

Hafnium oxide films are deposited on Si (100) substrates by means of rf magnetron sputtering. The interfacial structure is studied using high-resolution transmission electron microscopy (HRTEM) and x-ray photoelectron spectroscopy (XPS), and the electrical properties of the Au/HfO2/Si stack are analyzed by frequency-dependent capacitance-voltage (C—V—f) measurements. The amorphous interfacial layer between HfO2 and the Si substrate is observed by the HRTEM method. From the results of XPS, the interfacial layer comprises hafnium silicate and silicon oxide. For C—V—f measurements, the C—V plots show a peak at a low frequency and the change in frequency has effects on the intensity of the peak. As expected, rapid thermal annealing can passivate the interface states of the HfO2/Si stack.

Tan, Ting-Ting; Liu, Zheng-Tang; Li, Yan-Yan

2011-08-01

150

Ferromagnetism in HfO2 induced by hole doping: First-principles calculations  

NASA Astrophysics Data System (ADS)

According to recent reports of the unexpected magnetism discovered in thin films of HfO2 , a set of first-principles calculations is carried out on the hole-doped HfO2 system with nonmagnetic ions. It is found that the holes are doped into the p bands of the oxygen atoms near the dopant, which form a nearly planar trigonal structure with their nearby three Hf atoms surrounding them. The doped holes will make the p bands spin split. In addition, the total number of Bohr magneton in the supercell is equal to the number of doped holes by keeping the system in high spin state. Our results show that ferromagnetism in the oxygen p orbital induced by hole doping is quite possible and is a general phenomenon in ionic oxides, which would be a possible way to find new ferromagnetic materials or half-metals in nonmagnetic d0 composites.

Weng, Hongming; Dong, Jinming

2006-04-01

151

Phase transition in sputtered HfO2 thin films: A qualitative Raman study  

NASA Astrophysics Data System (ADS)

In this work the results of Linear Raman Spectroscopy experiments on hafnium dioxide (HfO2) thin films deposited by magnetron sputtering using different deposition conditions and post-deposition annealing are reported. Raman bands were identified considering the active symmetry modes expected from a tetragonal or monoclinic phase. The as-deposited HfOx films sputtered from an Hf target exhibit a tetragonal phase, which may be due to a crystallite size effect. However, the as-deposited HfOx films from the HfO2 target is found to be amorphous. As these films are annealed, these films remain or begin to become amorphous. However, at 600 °C they both begin to crystallize into a stable monoclinic phase.

Belo, G. S.; Nakagomi, F.; Minko, A.; da Silva, S. W.; Morais, P. C.; Buchanan, D. A.

2012-11-01

152

Change in band alignment of HfO2 films with annealing treatments  

NASA Astrophysics Data System (ADS)

Energy band alignment of a nitrided HfO2 film and dependence of the band gap (Eg) on annealing treatments with nitrogen plasma and ambient gases (N2 and O2) were studied by reflection electron energy loss spectra and x-ray photoelectron spectroscopy. We also investigated the nitrogen content in the film and its influence on the band alignment using medium energy ion scattering. The nitrogen incorporated into the HfO2 film by directed nitrogen plasma treatment significantly decreased the band gap and band offsets, i.e., the incorporated N in the film decreased both conduction and valance band offsets. The nitrogen content in depth direction was dependent on the postannealing conditions using O2 or N2.

Yim, C. J.; Ko, D.-H.; Jang, M. H.; Chung, K. B.; Cho, M.-H.; Jeon, H. T.

2008-01-01

153

Rare-earth substituted HfO 2 thin films grown by metalorganic chemical vapor deposition  

Microsoft Academic Search

Thin films of HfGdOx and HfDyOx were deposited by metalorganic chemical vapor deposition (MOCVD) utilizing guanidinate precursors for Hf, Gd and Dy. The close match in the thermal properties of the precursors enabled the MOCVD of rare-earth (RE) substituted HfO2 over a wide temperature window. Film deposition was carried out in the temperature range 300–700°C in the presence of oxygen

Anjana Devi; Stefan Cwik; Ke Xu; Andrian P. Milanov; Heshmat Noei; Yuemin Wang; Davide Barreca; Jan Maijer; Detlef Rogalla; Divine Kahn; Richard Cross; Shashi Paul; Harish Parala

154

Electrical characterization of HfO2 films obtained by UV assisted injection MOCVD  

Microsoft Academic Search

HfO2 films were deposited at low temperature (?400°C) by UV assisted injection metal-organic chemical vapor deposition (UVI-MOCVD). A three-step process was used for this study, consisting of (A) Pre-deposition anneal for nitridation; (B) Deposition step; (C) Post-deposition annealing in oxygen. Special attention was paid to the effect of UV exposure during these steps. Films were characterized by physical, optical and

J. M. Decams; H. Guillon; C. Jiménez; M. Audier; J. P. Sénateur; C. Dubourdieu; O. Cadix; B. J. O’Sullivan; M. Modreanu; P. K. Hurley; S. Rusworth; T. J. Leedham; H. Davies; Q. Fang; I. Boyd

2005-01-01

155

Infrared Reflectivity Studies On Composite HfO2/SiO2 Thin Films  

NASA Astrophysics Data System (ADS)

The HfO2-SiO2 composite films were prepared by reactive electron beam co-deposition process with various pre-determined mixing compositions. The films have been characterized by FTIR spectroscopy. IR reflectivity data shows a regular trend with the increase of silica concentration. For low silica concentrations, refractive index shows anomalously hardened value, whereas for low hafnia concentrations, abosorption spectra show the formation of hafnium silicate.

Bhatt, Himal; Deo, M. N.; Sahoo, N. K.; Kamble, N. M.; Tokas, R. B.; Thakur, S.

2010-12-01

156

Ion irradiation temperature effect on HfO2/MgO multi-layer structures  

NASA Astrophysics Data System (ADS)

Properties of nuclear materials may be improved by employing composite materials. However, these properties usually degrade during the operation in a nuclear reactor environment due to radiation damage accumulation. For this study we fabricated a multi-layer structure composed of MgO and HfO2 thin films on a sapphire substrate. This multi-layer structure was designed to mimic a CERCER (ceramic-ceramic) composite fuel form. The goal of this study was to investigate features of radiation damage evolution cause by ion beam irradiation in a wide temperature range. We observed phase transformation in HfO2 from monoclinic to the tetragonal polymorph and no changes in MgO. Formation of thin amorphous regions adjacent to the MgO/HfO2 and HfO2/sapphire substrate interfaces was identified in both cases. Phase and microstructural changes demonstrated pronounced dependence on irradiation temperature, which we attributed to either enhanced annihilation of irradiation induced point defects or intermixing between the components of our multi-layered structure.

Usov, I. O.; Valdez, J. A.; Won, J.; Devlin, D. J.

2012-01-01

157

Phase diagram up to 105 GPa and mechanical strength of HfO2  

NASA Astrophysics Data System (ADS)

Using high-resolution synchrotron powder x-ray diffraction, we have investigated the stability and equation of state (EOS) of hafnia HfO2 phases under high pressures before and after laser heating to high temperatures. We observe three phases with increasing pressure: baddeleyite (monoclinic, MI), orthorhombic I (OI), and cotunnite (orthorhombic, OII). The OII phase is stable up to a pressure of at least 105 GPa before and after laser heating to ˜1800 (±200)K . We provide experimental EOSs for the observed phases. The present results for MI-HfO2 EOS are distinct from previous measurements yielding an ambient-pressure volume (V0) of 34.50 (±0.04)Å3/f.u. and an ambient-pressure bulk modulus K0 of 185 (±23)GPa , assuming K0'=4 . In contrast, the experimental EOSs of OI and OII are in good agreement with previous studies. The measured EOSs are consistent with our density-functional theory calculations. The large volume decrease across the OI?OII phase transition as obtained from both our experiments and calculations is ˜9% . Despite the large increase in density and high bulk modulus of OII-HfO2 , we find, using scaling relations, that all HfO2 phases show similar mechanical hardness (H) of ˜10-12GPa , too low for HfO2 to be considered a superhard material.

Al-Khatatbeh, Yahya; Lee, Kanani K. M.; Kiefer, Boris

2010-10-01

158

Normally-off HfO2-gated diamond field effect transistors  

NASA Astrophysics Data System (ADS)

A normally-off hydrogenated-diamond (H-diamond) field effect transistor (FET) using a HfO2 gate oxide is demonstrated. The HfO2 gate oxide has a bilayer structure which is fabricated by a sputter-deposition (SD) technique on a thin buffer layer prepared by an atomic layer deposition (ALD) technique. The role of the ALD-HfO2 is found to prevent deterioration of the H-diamond surface by the SD process. The leakage current density of the SD-HfO2/ALD-HfO2/H-diamond structure is smaller than 1.1 × 10-4 A cm-2 at gate voltages from -9.0 to 2.0 V. The capacitance-voltage characteristic shows that fixed and trapped charge densities are low enough to operate the FET. The HfO2-gated FET has p-type channel and complete normally-off characteristics. The drain-source current maximum, threshold voltage, extrinsic transconductance maximum, and effective mobility of the FET with gate length of 4 ?m are -37.6 mA mm-1, -1.3 +/- 0.1 V, 11.2 +/- 0.1 mS mm-1, and 38.7 +/- 0.5 cm2 V-1 s-1, respectively.

Liu, J. W.; Liao, M. Y.; Imura, M.; Koide, Y.

2013-08-01

159

Influence of plasma-based in-situ surface cleaning procedures on HfO2/In0.53Ga0.47As gate stack properties  

NASA Astrophysics Data System (ADS)

We report on the influence of variations in the process parameters of an in-situ surface cleaning procedure, consisting of alternating cycles of nitrogen plasma and trimethylaluminum dosing, on the interface trap density of highly scaled HfO2 gate dielectrics deposited on n-In0.53Ga0.47As by atomic layer deposition. We discuss the interface chemistry of stacks resulting from the pre-deposition exposure to nitrogen plasma/trimethylaluminum cycles. Measurements of interface trap densities, interface chemistry, and surface morphology show that variations in the cleaning process have a large effect on nucleation and surface coverage, which in turn are crucial for achieving low interface state densities.

Chobpattana, Varistha; Mates, Thomas E.; Mitchell, William J.; Zhang, Jack Y.; Stemmer, Susanne

2013-10-01

160

Suppression of near-edge optical absorption band in sputter deposited HfO2-Al2O3 nanolaminates containing nonmonoclinic HfO2  

NASA Astrophysics Data System (ADS)

Nanolaminates of polycrystalline (tetragonal+orthorhombic) HfO2 and amorphous Al2O3 are sputter deposited on unheated fused SiO2, air annealed at 573-1273 K, and analyzed by x-ray diffraction and spectrophometry. Significant O 2p-->Hf 5d interband absorption occurs in all films at energy E>=6.2 eV. For E<6.2 eV, films annealed below 1273 K retain a featureless optical absorption edge despite further crystallization. A band with a 5.65 eV onset concurrently develops with m-HfO2 crystallization after a 1273 K anneal, indicating this phase and not nanocrystallinity per se is responsible for increased absorption.

Hoppe, E. E.; Aita, C. R.

2008-04-01

161

First-principles investigation of H2O on HfO2 (1 1 0) surface  

NASA Astrophysics Data System (ADS)

As the water to be an important precursor mater in atomic layer deposition (ALD) of preparation of HfO2 thin film, water-gas shift (WGS) reaction and heterogeneous catalysis, surface hydroxyl groups played a vital role as the reactive species that remain on the surface. First-principle calculation based on density functional (DFT) approach and generalized gradient approximation (GGA) have been utilized to investigate the molecular and dissociative adsorption of water molecule on the stoichiometric cubic HfO2 (1 1 0) surface with different sites at different coverages. The calculation employed slab geometry and periodic boundary condition with partial relaxation of atom position. Adsorption geometries, Mulliken population charges and density of states for HfO2H2O, HfO2OH, HfO2O and HfO2H at the coverage of 0.5 ML were also calculated. It was found that the adsorption energies varied a little as coverages increased, and the most favorable configuration of H2O on HfO2 surface was corresponding to the coordination of H2O via its oxygen with the surface (surface Hf atom). It was also confirmed that the coordination interaction and hydrogen bonding were the main contributions in dissociative adsorption process. For both molecular and dissociative adsorption, it has been elucidated that the surface hafnium played a key role as the active site. For dissociation reaction H2O (ads) ? H (ads) + OH (ads), the barrier energy calculated to be 17.3 kJ/mol, whereas, the second step dehydrogenation reaction OH (ads) + H (ads) ? O (ads) + 2H (ads), hardly occurred on this surface because of the high barrier energy 208.3 kJ/mol.

Li, Lu; Huang, Xin; Zhang, Yong-Fan; Guo, Xin; Chen, Wen-Kai

2013-01-01

162

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

163

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

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

164

Preparation of HfO2 Thin Films using Flashing Spray CVD Method  

NASA Astrophysics Data System (ADS)

The authors proposed a novel chemical vapor deposition system, a new evaporation supply method by using flash boiling spray, to improve several kinds of problems such as the decomposition of the precursor at supply line and evaporator. In this paper, the relation between film surface condition and injection quantity was investigated. Tetraethyl methyl amino hafnium and n-pentane were used as the mixed solution, and HfO2 film was deposited on Si substrate by using this method. As a result, the film surface roughness and grain size are increased as increasing injection quantity.

Oshima, Motohiro; Senda, Jiro; Tominaga, Koji; Shimizu, Tetsuo; Ishida, Kozo

165

Search for ferromagnetism in transition metal doped monoclinic HfO2  

NASA Astrophysics Data System (ADS)

Electronic and structural properties of the bulk monoclinic (m) phase of HfO2 are calculated using density functional theory as implemented in SIESTA code. We have considered substitutional doping of transition metals (TM) V and Cr in m-hafnia and studied electronic and magnetic properties of the resulting system. We found that TM doped systems are ferromagnetic. Also Cr doped m-hafnia exhibit half-metallic characteristics and posses Curie temperature above room temperature. Therefore TM doped m-hafnia offers the possibility of integration of CMOS with spintronic technology.

Seema, K.; Kumar, Ranjan

2013-02-01

166

The conductive path in HfO2: first principles study  

NASA Astrophysics Data System (ADS)

The conductive path formed by the interstitial Ag or substitutional Ag in HfO2 was investigated by using the Vienna ab initio simulation package based on the DFT theory. The calculated results indicated that the ordering of interstitial Ag ions at special positions can form a conductive path, and it cannot form at other positions. The orientation dependence of this conductive path was then investigated. Various types of super cells are also built to study the rupture of the path, which corresponds to some possible “off" states.

Maoxiu, Zhou; Qiang, Zhao; Wei, Zhang; Qi, Liu; Yuehua, Dai

2012-07-01

167

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

168

Structural and electrical properties of metal ferroelectric insulator semiconductor structure of Al/SrBi2Ta2O9/HfO2/Si using HfO2 as buffer layer  

NASA Astrophysics Data System (ADS)

Ferroelectric SrBi2Ta2O9 (SBT) thin films have been deposited by the radio-frequency magnetron sputtering technique on bare p-Si as well as on HfO2 insulating buffer p-Si. XRD patterns revealed the formation of a well-crystallized SBT perovskite thin film on the HfO2 buffer layer. The electrical properties of the metal-ferroelectric-insulator-semiconductor (MFIS) structure were characterized by varying thicknesses of the HfO2 layer. The MFIS structure exhibits a maximum clockwise C-V memory window of 1.60 V when the thickness of the HfO2 layer was 12 nm with a lower leakage current density of 6.20 × 10-7 A cm-2 at a positive applied voltage of 7 V. However, the memory window reaches a maximum value of 0.7 V at a bias voltage of ±5 and then decreases due to charge injection in the case of the insulating buffer layer thickness of 3 nm. The density of oxide trapped charges at/near the buffer layer-ferroelectric interface is studied by the voltage stress method. Capacitance-voltage (C-V) and leakage current density (J-V) characteristics of the Al/SBT/HfO2/Si(1 0 0) capacitor indicate that the introduction of the HfO2 buffer layer prevents interfacial diffusion between the SBT thin film and the Si substrate effectively and improves the interface quality. Furthermore, the Al/SBT/HfO2/Si structures exhibit excellent retention characteristics, the high and low capacitance values clearly distinguishable for over 1 h and 30 min. This shows that the proposed Al/SrBi2Ta2O9/HfO2/Si structure is ideally suitable for high performance ferroelectric memories.

Roy, A.; Dhar, A.; Bhattacharya, D.; Ray, S. K.

2008-05-01

169

Theoretical prediction of ion conductivity in solid state HfO2  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

170

HfO2:X (X = Eu(3+), Ce(3+), Y(3+)) sol gel powders for ultradense scintillating materials.  

PubMed

Hafnium dioxide (HfO 2) presents a high crystalline density which makes it attractive for host lattice activated by rare earths for applications as scintillating materials. HfO 2 powders doped with Eu (3+) or Ce (3+) luminescent ions are prepared by sol gel process. The annealing temperature and the concentration of doping ions are optimized to provide the powder presenting the best scintillation yield. The powders are crystallized in monoclinic phase whatever annealing temperature above 800 degrees C. The emission spectra are characterized by a white broadband between 400 and 600 nm. After optimization, the most efficient composition, namely HfO 2:2.5% Eu 1% Y (molar percent) exhibits a scintillation yield about 31,000 photons/MeV, which is about 3.8 times that of the standard Bi 3Ge 5O 12 (BGO) commercial powder. PMID:18811128

LeLuyer, C; Villanueva-Ibañez, M; Pillonnet, A; Dujardin, C

2008-09-24

171

Investigation of high-quality ultra-thin LaAlO3 films as high-k gate dielectrics  

Microsoft Academic Search

We have studied the formation of a high-quality LaAlO3 (LAO) film directly on silicon substrates by the pulsed laser deposition method as a novel high-k gate dielectric. The LAO films can remain amorphous at temperatures up to 850°C. An atomic force microscopy study indicated a very smooth surface of the deposited films with a rms of 0.14 nm for an

X. B. Lu; Z. G. Liu; X. Zhang; R. Huang; H. W. Zhou; X. P. Wang; Bich-Yen Nguyen

2003-01-01

172

Hafnium dioxide gate dielectrics, metal gate electrodes, and phenomena occurring at their interfaces  

NASA Astrophysics Data System (ADS)

As metal-oxide-semiconductor field-effect transistor (MOSFET) gate lengths scale down below 45 nm, the gate oxide thickness approaches 1 nm equivalent oxide thickness. At this thickness, conventional silicon dioxide (SiO 2) gate dielectrics suffer from excessive gate leakage. Higher permittivity dielectrics are required to counter the increase in gate leakage. Hafnium dioxide (HfO2) has emerged as a promising dielectric candidate. HfO2 films deposited using metal organic chemical vapor deposition are being studied to determine the impact of process and annealing conditions on the physical and electrical properties of the gate dielectric. This study indicates that deposition and annealing temperatures influence the microstructure, density, impurity concentration, chemical environment of the impurities, and band-gap of the HfO2 dielectric. Correlations of the electrical and physical properties of the films indicate that impurities in the form of segregated carbon clusters, and low HfO2 density are detrimental to the leakage properties of the gate dielectric. Additionally, as the HfO2 thickness scales, the additional series capacitance due to poly-silicon depletion plays a larger roll in reducing the total gate capacitance. To solve this problem, high performance bulk MOSFETs will require dual metal gate electrodes possessing work functions near the silicon band edges for optimized drive current. This investigation evaluates TiN, Ta-Si-N, Ti-Al-N, WN, TaN, TaSi, Ir and IrO2 electrodes as candidate electrodes on HfO2 dielectrics. The metal-dielectric compatibility was studied by annealing the gate stacks at different temperatures. The physical stability and effective work functions of metal electrodes on HfO2 are discussed. Finally, Fermi level pinning of the metal is a barrier to identifying materials with appropriate threshold voltages. The contributions to the Fermi level pinning of platinum electrodes on HfO2 gate dielectrics are investigated by examining the impact of oxygen and forming gas anneals on the effective work function of platinum-HfO2-silicon capacitors. Oxygen anneals result in higher effective work functions for platinum on HfO 2 than forming gas anneals. The presence of interfacial oxygen vacancies or Pt-Hf bonds is believed to be responsible for a degree of pinning that is stronger than predicted from the metal induced gap states model alone.

Schaeffer, James Kenyon, III

173

Investigation of the structure of thin HfO(2) films by soft x-ray reflectometry techniques.  

PubMed

HfO(2) thin films of different thicknesses and deposited by two methods (ALD and MOCVD) were studied. The microstructure of films was characterized by reflection spectroscopy, x-ray diffraction (XRD), and soft x-ray reflectometry. It was established that the HfO(2) film microstructure is closely dependent on film thickness. The 5 nm thick film synthesized by ALD shows an amorphous phase while the film prepared by MOCVD was inhomogeneous in depth and showed signs of crystalline structure. First results on the reconstruction of the depth distribution of chemical elements based on the analysis of reflectivity curves are discussed. PMID:21825458

Filatova, E O; Sokolov, A A; Kozhevnikov, I V; Taracheva, E Yu; Grunsky, O S; Schaefers, F; Braun, W

2009-03-31

174

Comparison of n-type Gd2O3 and Gd-doped HfO2  

Microsoft Academic Search

Gd2O3 and Gd-doped HfO2 films were deposited on p-type silicon substrates in a reducing atmosphere. Gd 4f photoexcitation peaks at roughly 7 and 5 eV below the valence band maximum have been identified using the resonant photoemission of Gd2O3 and Gd-doped HfO2 films, respectively. In the case of Gd2O3, strong hybridization with the O 2p band is demonstrated, and there

Ya B. Losovyj; David Wooten; Juan Colon Santana; Joonhee Michael An; K. D. Belashchenko; N. Lozova; J. Petrosky; A. Sokolov; Jinke Tang; Wendong Wang; Navamoney Arulsamy; P. A. Dowben

2009-01-01

175

The effect of high/low permittivity in bilayer HfO2/BN resistance random access memory  

NASA Astrophysics Data System (ADS)

This letter investigated the electrical characteristics of resistance random access memory (RRAM) with HfO2/BN bilayer structures. By adopting the high/low permittivity structure, we obtained the excellent device characteristics such as uniform distribution of switching voltage and more stable resistance switching properties of RRAM. The current conduction mechanism of low resistance state in the HfO2/BN device was transferred to space-charge-limited current conduction from Ohmic conduction owing to space electric effect concentrated by the high/low permittivity bilayer structures. The electric field in the bilayer can be verified by comsol simulation software.

Huang, Jen-Wei; Zhang, Rui; Chang, Ting-Chang; Tsai, Tsung-Ming; Chang, Kuan-Chang; Lou, J. C.; Young, Tai-Fa; Chen, Jung-Hui; Chen, Hsin-Lu; Pan, Yin-Chih; Huang, Xuan; Zhang, Fengyan; Syu, Yong-En; Sze, Simon M.

2013-05-01

176

Soft breakdown of ultra-thin gate oxide layers  

Microsoft Academic Search

The dielectric breakdown of ultra-thin 3 nm and 4 nm SiO2 layers used as a gate dielectric in poly-Si gate capacitors is investigated. The ultra-thin gate oxide reliability was determined using tunnel current injection stressing measurements. A soft breakdown mechanism is demonstrated for these ultra-thin gate oxide layers. The soft breakdown phenomenon corresponds with an anomalous increase of the stress

Michel Depas; Tanya Nigam; Marc M. Heyns

1996-01-01

177

Perturbed angular correlation study of a nanostructured HfO2 film  

NASA Astrophysics Data System (ADS)

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

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

2007-09-01

178

Chemical and electrical characterization of the HfO2/InAlAs interface  

NASA Astrophysics Data System (ADS)

InAlAs has the potential to be used as a barrier layer in buried channel quantum well field effect transistor devices due to favorable lattice-matching and carrier confinement properties with InGaAs. Field effect device structures of this nature may also require a high-k oxide deposited on the InAlAs surface to reduce leakage current. This study investigates the impact of surface preparations and atomic layer deposition of HfO2 on these surfaces using x-ray photoelectron spectroscopy to analyse the chemical interactions taking place, as well as the electrical performance of associated capacitor devices. A large concentration of As related surface features is observed at the InAlAs surface, and is attributed to a large Dit response in electrical measurements.

Brennan, B.; Galatage, R. V.; Thomas, K.; Pelucchi, E.; Hurley, P. K.; Kim, J.; Hinkle, C. L.; Vogel, E. M.; Wallace, R. M.

2013-09-01

179

Frequency converter layers based on terbium and ytterbium activated HfO2 glass-ceramics  

NASA Astrophysics Data System (ADS)

One of the ways in which the cell efficiency of solar cells may be improved by better exploitation of the solar spectrum makes use of the down-conversion mechanism, where one high energy photon is cut into two low energy photons. When energy transfer between rare earth ions is used to activate this process, high emission and absorption cross sections as well as low cutoff phonon energy are mandatory. Glass-ceramics can be a viable system to fulfill these requirements. The main advantage of the glass-ceramic is to combine the mechanical and optical properties of the glass with a crystallike environment for the rare-earth ions, where higher cross-sections of the rare earth ion can be exploited. In the case of silica-hafnia system the glass ceramic is constituted by nanocrystals of HfO2, containing the rare earth ion, imbedded in the silica-hafnia host. Hafnia nanocrystals are characterized by a cutoff frequency of about 700 cm-1, so that nonradiative transition rates are strongly reduced, thus increasing the luminescent quantum yield of the rare-earth ions. In this work we investigated the Tb3+/Yb3+ energy transfer efficiency in a 70SiO2-30HfO2 glass-ceramic waveguide in order to convert absorbed photons at 488 nm in photons at 980 nm. The energy transfer efficiency was estimated as a function of the Tb3+/Yb3+ molar ratio as well as of the total amount of rare earth ions. A transfer efficiency of 38% was obtained for Tb3+/Yb3+ = 0.25 mol and a rare earth content [Tb+Yb]/[Si+Hf] = 5% mol.

Alombert Goget, G.; Armellini, C.; Chiappini, A.; Chiasera, A.; Ferrari, M.; Berneschi, S.; Brenci, M.; Pelli, S.; Righini, G. C.; Bregoli, M.; Maglione, A.; Pucker, G.; Speranza, G.

2010-04-01

180

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

Microsoft Academic Search

The influence of water vapor content in high vacuum chamber during the coating process on physical properties of HfO2 films was investigated. Coatings were deposited on BK7 substrates by electron beam evaporation and photoelectric maximum control method. An in situ residual gas analyzer (RGA) was used to monitor the residual gas composition in the vacuum chamber. The optical properties, microstructure,

Bo Ling; Hongbo He; Jianda Shao

2007-01-01

181

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

NASA Astrophysics Data System (ADS)

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

Perevalov, Timofei V.; Gritsenko, Vladimir A.

2010-09-01

182

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

183

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

NASA Astrophysics Data System (ADS)

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

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

2008-09-01

184

Achieving 1 nm capacitive effective thickness in atomic layer deposited HfO2 on In0.53Ga0.47As  

NASA Astrophysics Data System (ADS)

A capacitive effective thickness (CET) value of 1.0 nm has been achieved in atomic layer deposited (ALD) high ? dielectrics HfO2 on In0.53Ga0.47As/InP. The key is a short air exposure under 10 min between removal of the freshly grown semiconductor epilayers and loading to the ALD reactor. This has led to minimal formation of the interfacial layer thickness, as confirmed using x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. The measured electrical characteristics of metal-oxide-semiconductor diodes of Au/Ti/HfO2(4.5 nm)/In0.53Ga0.47As showed a low leakage current density of 3.8×10-4 A/cm2 at VFB+1 V, which is about eight orders of magnitudes lower than that of SiO2 with the same CET. The capacitance-voltage curves show an overall ? value of 17-18, a nearly zero flatband shift, and an interfacial density of states Dit of 2×1012 cm-2 eV-1.

Lee, K. Y.; Lee, Y. J.; Chang, P.; Huang, M. L.; Chang, Y. C.; Hong, M.; Kwo, J.

2008-06-01

185

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

Microsoft Academic Search

The size-controlled, non-agglomerated, 5nm Si nanoparticles were fabricated in the middle of HfO2 layers using a pulsed laser ablation (PLA) system at a relatively low pressure and formed trilayer structure (HfO2\\/Si-nps\\/HfO2) on n-type Si. These high density nanoparticles (>1x1011 cm-2) were imaged with SEM. The crystallinity of HfO2 and Si nanoparticles were characterized by HRTEM. The memory effect of a

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

2009-01-01

186

Optical constants of crystalline HfO2 for energy range 140-930 eV  

SciTech Connect

We calculated the optical constants of the monoclinic phase of a HfO2 film from reflection spectra measured using synchrotron radiation in the spectral region from 143 eV to 927 eV, which includes the HfN4,5{sup -}, HfN2,3{sup -}, and OK absorption edges. The calculations were carried out using the Kramers-Kronig relations. It could be shown that the relation R(E){approx}E{sup -4} can be used for extrapolation of the experimental reflection spectrum of HfO2 (and probably of other heavy elements) for energies such that {theta}/{theta}c>3.7.

Filatova, Elena; Sokolov, Andrey; Andre, Jean-Michel; Schaefers, Franz; Braun, Walter

2010-05-10

187

Band alignment at the SiO2/HfO2 interface: Group IIIA versus group IIIB metal dopants  

NASA Astrophysics Data System (ADS)

Using density functional theory (DFT) we examine the effect of Al and La incorporation on the electronic properties of the interface in the SiO2/HfO2 high-k gate stacks recently introduced into the advanced modern field effect transistors (FETs). We show that La and Al doping have opposite effects on the band alignment at the SiO2/HfO2 interface: while the Al ions, which substitute preferentially for Si in the SiO2 layer, promote higher effective work function (EWF) values, the substitution of La for Hf decreases EWF. The analysis of the electronic structure of the doped interface suggests a simple relation between the electronegativity of the doping metal, screening properties of the interfacial layer, and the band offset, which allows predicting qualitatively the effect of the high-k gate stack doping with a variety of metals on its EWF.

Luo, Xuhui; Bersuker, Gennadi; Demkov, Alexander A.

2011-11-01

188

Stress-induced leakage current and trap generation in HfO2 thin films  

NASA Astrophysics Data System (ADS)

Stress-induced leakage current (SILC) is studied in 10 nm HfO2 metal-insulator-metal capacitors. Three regimes are observed in the current-time characteristics, namely, (1) an absorption current, (2) a quasi linear increase of current with time (SILC), and (3) thermal breakdown. Magnitude of SILC is strongly correlated to the nature of the cathode (being large for TiN and weak for Pt and Au), showing that SILC is governed by electron injection. Recovery is observed when short-circuiting the samples, pointing out that SILC is a reversible phenomenon. Desorption current and SILC are not correlated, which indicates that different defects control the absorption current and SILC. SILC is ascribed to the generation of oxygen vacancies upon hot electron injection, while recovery is ascribed to the recombination of oxygen ions with vacancies. In the SILC regime, the current varies as Ktn (n = 1.15 at room temperature). Bias and temperature dependence of K and n are studied. The dependence of K on bias can be described either by a Fowler-Nordheim law or by an exponential law, while the exponent n is almost independent of bias. When temperature is increased, K increases according to an Arrhenius law and n decreases. SILC is modeled by considering the generation of oxygen vacancies by hot electron impact and subsequent electron trapping at vacancies (hopping conduction). An analytical expression for SILC growth is obtained from first order kinetics.

Mannequin, C.; Gonon, P.; Vallée, C.; Latu-Romain, L.; Bsiesy, A.; Grampeix, H.; Salaün, A.; Jousseaume, V.

2012-10-01

189

Theoretical prediction of intrinsic self-trapping of electrons and holes in monoclinic HfO2.  

PubMed

We predict, by means of ab initio calculations, stable electron and hole polaron states in perfect monoclinic HfO2. Hole polarons are localized on oxygen atoms in the two oxygen sublattices. An electron polaron is localized on hafnium atoms. Small barriers for polaron hopping suggest relatively high mobility of trapped charges. The one-electron energy levels in the gap, optical transition energies and ESR g-tensor components are calculated. PMID:17995181

Muñoz Ramo, D; Shluger, A L; Gavartin, J L; Bersuker, G

2007-10-12

190

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

SciTech Connect

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

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

2005-10-20

191

Thermal stability of high-k Si-rich HfO(2) layers grown by RF magnetron sputtering.  

PubMed

The microstructure and optical properties of HfSiO films fabricated by RF magnetron sputtering were studied by means of x-ray diffraction, transmission electron microscopy, spectroscopic ellipsometry and attenuated total reflection infrared spectroscopy versus annealing treatment. It was shown that silicon incorporation in the HfO(2) matrix plays an important role in the structure stability of the layers. Thus, the increase of the annealing temperature up to 1000 degrees C did not lead to the crystallization of the films. The evolution of the chemical composition as well as a decrease of the density of the films was attributed to the phase separation of HfSiO on HfO(2) and SiO(2) phases in the film. An annealing at 1000-1100 degrees C results in the formation of the multilayer Si-rich/Hf-rich structure and was explained by a surface-directed spinodal decomposition. The formation of the stable tetragonal structure of HfO(2) phase was shown upon annealing treatment at 1100 degrees C. PMID:20585152

Khomenkova, L; Portier, X; Cardin, J; Gourbilleau, F

2010-06-28

192

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

193

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

NASA Astrophysics Data System (ADS)

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

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

2005-02-01

194

High mobility HfO2-based In0.53Ga0.47As n-channel metal-oxide-semiconductor field effect transistors using a germanium interfacial passivation layer  

NASA Astrophysics Data System (ADS)

The electrical characteristics of HfO2-based n-channel metal-oxide-semiconductor field effect transistors (MOSFETs) and metal-oxide-semiconductor capacitors (MOSCAPs) on high indium content In0.53Ga0.47As channel layers are presented. N-channel MOSFETs with a germanium (Ge) interfacial passivation layer (IPL) show maximum mobility 3186 cm2/V s from split capacitance-voltage (C-V) method and the normalized drain current (to the channel length of 1 ?m) of 753 mA/mm at Vg=Vth+2 V and Vd=2 V. On the contrary, MOSFETs without a Ge IPL or with high temperature post-metal annealing (PMA) exhibit inferior characteristics. MOSCAPs on n-type In0.53Ga0.47As layers demonstrate excellent C-V characteristics including low C-V frequency dispersion and low dielectric leakage current.

Kim, Hyoung-Sub; Ok, Injo; Zhu, Feng; Zhang, M.; Park, S.; Yum, J.; Zhao, H.; Majhi, Prashant; Garcia-Gutierrez, Domingo I.; Goel, Niti; Tsai, W.; Gaspe, C. K.; Santos, M. B.; Lee, Jack C.

2008-09-01

195

Differential Light Addressable Potentiometric Sensor with Poly(vinyl chloride) and HfO2 Membranes for pH Sensors  

Microsoft Academic Search

In this paper, a differential measurement setup for the light addressable potentiometric sensor (LAPS) is proposed. The LAPS with a HfO2 layer as the sensing membrane was used, and different weight percentages of DNP\\/(PVC+DNP) [DNP: dinonylphtalate, PVC: poly(vinyl chloride)] membrane were cast on the surface of HfO2-LAPS. The pH sensitivity can be decreased from 58.6 to 24.5 mV\\/pH by using

Cheng-En Lue; Chao-Sung Lai; Jer-Chyi Wang; Ching-Mie Wu; Chia-Ming Yang

2010-01-01

196

Fabrication of transparent ceramics through melt solidification of near eutectic compositions in HfO 2–Al 2O 3–GdAlO 3 system  

Microsoft Academic Search

Solidification of eutectic melts in multiple oxide systems can produce directionally solidified eutectic composites by slow cooling, while rapid cooling would give the formation of amorphous phases as super cooled liquids. We have successfully fabricated an amorphous bulk ceramics in the ternary system HfO2–Al2O3–GdAlO3 for the first time. It has the near eutectic composition of HfO2 (14mol%), Al2O3 (63mol%) and

Shunji Araki; Masahiro Yoshimura

2005-01-01

197

Fabrication of transparent ceramics through melt solidification of near eutectic compositions in HfO 2–Al 2O 3–GdAlO 3 system  

Microsoft Academic Search

Solidification of eutectic melts in multiple oxide systems can produce directionally solidified eutectic composites by slow cooling, while rapid cooling would give the formation of amorphous phases as super cooled liquids. We have successfully fabricated an amorphous bulk ceramics in the ternary system HfO2–Al2O3–GdAlO3 for the first time. It has the near eutectic composition of HfO2 (14mol%), Al2O3 (63mol%) and

Shunji Araki; Masahiro Yoshimura

2006-01-01

198

Improved speed and data retention characteristics in flash memory using a stacked HfO2/Ta2O5 charge-trapping layer  

NASA Astrophysics Data System (ADS)

This paper reports the simultaneous improvements in erase speed and data retention characteristics in flash memory using a stacked HfO2/Ta2O5 charge-trapping layer. In comparison to a memory capacitor with a single HfO2 trapping layer, the erase speed of a memory capacitor with a stacked HfO2/Ta2O5 charge-trapping layer is 100 times faster and its memory window is enlarged from 2.7 to 4.8 V for the same ±16 V sweeping voltage range. With the same initial window of ?VFB = 4 V, the device with a stacked HfO2/Ta2O5 charge-trapping layer has a 3.5 V extrapolated 10-year retention window, while the control device with a single HfO2 trapping layer has only 2.5 V for the extrapolated 10-year window. The present results demonstrate that the device with the stacked HfO2/Ta2O5 charge-trapping layer has a strong potential for future high-performance nonvolatile memory application.

Zheng, Zhiwei; Huo, Zongliang; Zhang, Manhong; Zhu, Chenxin; Liu, Jing; Liu, Ming

2011-10-01

199

Structural phase transformation of Y2O3 doped HfO2 films grown on Si using atomic layer deposition  

NASA Astrophysics Data System (ADS)

HfO2 and Y2O3 films, along with Y2O3-doped HfO2 composite films, have been deposited on Si by means of atomic layer deposition (ALD) using tetrakis(diethylamino)hafnium and tris(ethylcyclopentadienyl)yttrium with water vapor as the oxidizer. The growth rate and structural properties of these films have been investigated by spectral ellipsometry, grazing incidence x-ray diffraction, and x-ray photoelectron spectroscopy (XPS). The film growth temperature dependence of both HfO2 and Y2O3 films indicate overlapping ALD windows in the 250-285 °C region, which is critical for ALD of Y2O3-doped HfO2 films. The composition of such films is controlled by altering precursor cycle ratios, and XPS analyses of the resulting films indicate strong correlation between the precursor cycle ratio and the film composition. From structural analyses, the as-deposited HfO2 was found to be amorphous but after annealing at 600 °C or higher, it became monoclinic. In contrast, all Y2O3 films whether annealed or not had evidence of cubic crystallinity. Having a cycle ratio of at least 2.5% in a Y2O3-doped HfO2 composite film is observed to induce cubic phase crystallinity in the film after postdeposition annealing at 600 °C or greater.

Majumder, Prodyut; Jursich, Gregory; Takoudis, Christos

2009-05-01

200

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

NASA Astrophysics Data System (ADS)

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 reasonably well with experiment, although LDA yields better overall agreement. After calculating the Born effective charge tensors and the force-constant matrices by finite-difference methods, the lattice dielectric susceptibility tensors for the three HfO2 phases are computed by decomposing the tensors into the contributions from individual infrared-active phonon modes.

Zhao, Xinyuan; Vanderbilt, David

2002-06-01

201

The use of angle resolved XPS to measure the fractional coverage of high-k dielectric materials on silicon and silicon dioxide surfaces  

NASA Astrophysics Data System (ADS)

Angle resolved XPS (ARXPS) is a powerful tool for the determination of the thickness of ultra-thin films. In the case of high-k dielectric layers, the technique is capable of measuring the thickness of both the high-k layer and intermediate layers of silicon dioxide or metal silicate. The values for layer thickness are in close agreement with those generated by a variety of other techniques. As well as knowing the thickness of these layers, it is important to determine whether the layers are continuous or whether the coverage of the high-k layer is only partial. Using ARXPS, a method has been developed to determine whether the coverage of the high-k material is continuous and, if not, to calculate the fraction of the surface that is covered. The method is described with reference to the layers of Al2O3 grown on SiO2 using atomic layer deposition (ALD). The method is then applied to HfO2 layers produced using ALD on silicon wafers whose surfaces had received three different types of surface treatment. The way in which the layers grow and the nature of the resulting layer were found to depend upon the pre-treatment method. For example, growth on a thermal silicon dioxide surface resulted in complete coverage of HfO2 after fewer ALD cycles than layers grown on an H-terminated surface. The results from ARXPS are compared with those obtained from ToF SIMS that have been shown earlier to be a valuable alternative to the LEIS analysis [1].

Mack, P.; White, R. G.; Wolstenholme, J.; Conard, T.

2006-09-01

202

Local Dielectric Property of Hafnium and Lanthanum Atoms in HfLaOx  

NASA Astrophysics Data System (ADS)

In this work, we investigate the electronic contribution to local dielectric property of La2O3 and HfO2 using cluster models. The relation between the coordinate number of metal atoms and their bonding energy shows a hint that hafnia takes the cubic structure by the incorporation of La2O3 in HfO2. The local properties of polarizability and dielectric constant of La2O3 and HfO2 are closely similar to each other. It is considered to be one of the reasons why the incorporation of lanthanum atoms does not lower the permittivity of HfO2. We confirm this by the study of the local dielectric property of the HfLaOx cluster model. We compare the dielectric properties around an oxygen atom and that between the oxygen atom and a next metal atom. Our results show that the contribution to the dielectric response from the bond regions is not so large.

Fukushima, Akinori; Sugino, Shinya; Tsuchida, Yasushi; Senami, Masato; Tachibana, Akitomo

2010-12-01

203

An ultrathin Zr(Ge) alloy film as an exhaustion interlayer combined with Cu(Zr) seed layer for the Cu/porous SiOC:H dielectric integration  

SciTech Connect

A highly reliable interface of an ultrathin Zr(Ge) exhaustion interlayer between Cu(Zr) film and porous SiOC:H (p-SiOC:H) dielectric has been developed in the present work. After being processed at a moderate elevated temperature (say, 450 deg. C), a self-formed nanomultilayer of CuGe{sub x}/ZrO{sub x}(ZrSi{sub y}O{sub x}) was produced at the interface of Cu(Zr)/p-SiOC:H film stacks, which showed strong ability to effectively hinder Cu atoms diffusion into p-SiOC:H film and free Si atoms diffusion into Cu film. The mechanism involving the thermal stability of the films system is analyzed based on detailed characterization studies.

Liu, B.; Song, Z. X.; Li, Y. H.; Xu, K. W. [State-key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049 (China)

2008-10-27

204

Solvothermal and surfactant-free synthesis of crystalline Nb(2)O(5), Ta(2)O(5), HfO(2), and Co-doped HfO(2) nanoparticles.  

PubMed

A simple route to niobium, hafnium and tantalum oxide nanocrystals using a nonaqueous sol-gel route based on the solvothermal reaction of the corresponding metal chlorides with benzyl alcohol is presented. This approach can easily be extended to the preparation of high quality Co-doped HfO(2) nanoparticles of uniform size and shape and with a homogenous distribution of the magnetic ions. The structural characterization of all these nanomaterials as well as the magnetic properties of pure and doped hafnia, with special attention to the doping efficiency, are discussed. The obtained Co-doped hafnia exhibits paramagnetic properties with very weak antiferromagnetic interactions between Co ions moments. PMID:20976360

Buha, Jelena; Ar?on, Denis; Niederberger, Markus; Djerdj, Igor

2010-10-26

205

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

206

Space charge effect in ultrathin ferroelectric films  

NASA Astrophysics Data System (ADS)

Space charge influence on the depolarization field becomes pronounced in nano-scale ferroelectric films in static state. We have studied theoretically the ferroelectric, dielectric, and piezoelectric properties of ultrathin ferroelectric films with the consideration of influence from space charges, surface, incomplete screening, and misfit strain. It is found that space charges accumulated near the surface of the film can modify the depolarization field, which results an enhancement of the polarization in ultrathin films and a persisting polarization even below the critical thickness. The singularities of the dielectric constant and piezoelectric coefficient were all being rounded near the critical thickness.

Lu, Xiaoyan; Cao, Wenwu; Li, Hui

2012-04-01

207

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.

2013-01-01

208

Hydroxo and Chloro Complexes/Ion-Interactions of Hf4+ and the Solubility Product of HfO2(am)  

SciTech Connect

SUMMARY-The solubility of HfO2(am) was determined at different equilibration periods from the over- and undersaturation directions, in very acidic to basic solutions (0.1 m HCl to 3.2 m NaOH), and in NaCl solutions ranging in concentrations from very dilute to as high as 5.59 m and in a pCH+ range from 1 to 4 to obtain reliable thermodynamic data for the Hf4+-Cl- -Na+-H+-OH- -H2O system...

Rai, Dhanpat; Xia, Yuanxian; Hess, Nancy J.; Strachan, Denis M.; McGrail, B. Peter

2001-11-11

209

Low-temperature conductance measurements of surface states in HfO 2–Si structures with different gate materials  

Microsoft Academic Search

Metal-oxide-semiconductor capacitors based on HfO2 gate stack with different metal and metal compound gates (Al, TiN, NiSi and NiAlN) are compared to study the effect of the gate electrode material on the trap density at the insulator–semiconductor interface.C–V and G–? measurements were made in the frequency range from 1kHz to 1MHz in the temperature range 180–300K. From the maximum of

Y. Gomeniuk; A. Nazarov; Ya. Vovk; Yi Lu; O. Buiu; S. Hall; J. K. Efavi; M. C. Lemme

2006-01-01

210

Interfacial layer growth condition dependent carrier transport mechanisms in HfO2/SiO2 gate stacks  

NASA Astrophysics Data System (ADS)

The temperature and field dependent leakage current in HfO2/SiO2 gate stack for in situ steam grown and chemical interfacial layers (ILs) are studied in the temperature range of 20 °C to 105 °C. Poole-Frenkel mechanism in high field whereas Ohmic conduction in low field region are dominant for both devices. Leakage current decreases whereas both trap energy level (?t) and activation energy (Ea) increase for chemically grown IL devices. The trap level energy, (?t) ~ 0.2 eV, indicates that doubly charged oxygen vacancies (V2-) are the active electron traps which contribute to the leakage current in these gate stacks.

Sahoo, S. K.; Misra, D.

2012-06-01

211

Physical properties and band structure of reactive molecular beam epitaxy grown oxygen engineered HfO2+/-x  

NASA Astrophysics Data System (ADS)

We have conducted a detailed thin film growth structure of oxygen engineered monoclinic HfO2+/-x grown by reactive molecular beam epitaxy. The oxidation conditions induce a switching between (111) and (002) texture of hafnium oxide. The band gap of oxygen deficient hafnia decreases with increasing amount of oxygen vacancies by more than 1 eV. For high oxygen vacancy concentrations, defect bands form inside the band gap that induce optical transitions and p-type conductivity. The resistivity changes by several orders of magnitude as a function of oxidation conditions. Oxygen vacancies do not give rise to ferromagnetic behavior.

Hildebrandt, Erwin; Kurian, Jose; Alff, Lambert

2012-12-01

212

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

NASA Astrophysics Data System (ADS)

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.

Tang, Ruifan; Huang, Kai; Lai, Hongkai; Li, Cheng; Wu, Zhiming; Kang, Junyong

2013-08-01

213

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

214

Role of high-frequency power in C4F8 dual-frequency capacitively coupled plasmas treating high-k HfO2 films  

NASA Astrophysics Data System (ADS)

Plasma treatment of HfO2 films by octafluorocyclobutane (C4F8) 60 MHz(HF)/2 MHz(LF) dual-frequency capacitively coupled plasmas (DF-CCPs) was investigated. It is found that the fluorine atoms were incorporated into the HfO2 films by C4F8 DF-CCP treatment, but the C?:?F films were formed on the surface of the HfO2/Si gate stacks. The results also show that both the plasma treatment and the process of post-deposition annealing play major roles in stabilizing the tetragonal structure, leading to a large band gap and good electrical properties. The formation of t-HfO2 is related to oxygen vacancy generation and Si diffusion into the HfO2 films. The capacitance-voltage measurement showed that the smallest ?Vfb and the lowest interface trap density were obtained at the HF power of 120 W and the LF power of 30 W. Therefore, the C4F8 DF-CCP is a suitable method to improve the electrical characteristics of HfO2/Si gate stacks.

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

2013-10-01

215

Gate oxide scaling down in HfO2-GaAs metal-oxide-semiconductor capacitor using germanium interfacial passivation layer  

NASA Astrophysics Data System (ADS)

The primary goal of this work is to investigate the capability of gate oxide scaling down in HfO2-based GaAs metal-oxide-semiconductor capacitor (MOSCAP) using a thin germanium (Ge) interfacial passivation layer (IPL). With HfO2 of 45-50 A?, an equivalent oxide thickness (EOT) of 8.7 A? was achieved with a low gate oxide leakage current density (Jg) of (2-4)×10-3 A/cm2 at VG-VFB=1.0 V. This is the thinnest EOT thickness ever reported for high-k III-V MOSCAPs. On the other hand, with thicker HfO2 of 100-110 A?, an EOT of 20-22 A? with Jg of (2-4)×10-6 A/cm2 at VG-VFB=1.0 V was attained. In addition, breakdown voltages of gate oxide and hysteresis characteristics according to different thicknesses of HfO2 were studied. The results indicate that a Ge IPL and thin HfO2 enable excellent gate oxide scaling down in GaAs system.

Kim, Hyoung-Sub; Ok, Injo; Zhang, Manhong; Zhu, F.; Park, S.; Yum, J.; Zhao, Han; Lee, Jack C.

2007-07-01

216

Study of the surface modification with oleic acid of nanosized HfO2 synthesized by the polymerized complex derived sol-gel method  

NASA Astrophysics Data System (ADS)

The synthesis of nanosized hafnium oxide by the polymerized complex derived sol-gel method is reported. The structural and morphological characterization of the HfO2 was carried out by X-ray diffraction and scanning electron microscopy. The surface of hafnium oxide nanoparticles was modified by capping with oleic acid. The nanoparticle surface area was measured by the gas adsorption technique in order to determine the minimal amount of oleic acid needed to obtain a uniform coverage of the hafnium oxide. The existence of organic layer can be confirmed by Fourier transform spectroscopy, solid state nuclear magnetic resonance spectroscopy, thermal gravimetric analysis and transmission electron microscopy. The FTIR and solid state NMR results reveal that oleic acid is chemisorbed as a carboxylate onto the HfO2 nanoparticle surface and confirm the formation of a monomolecular layer of oleic acid surrounding the HfO2. The cover density of oleic acid on the HfO2 increases with the amount of oleic acid used to modify the nanoparticles and the surface properties of HfO2 nanoparticles modified with oleic acid change from hydrophilic to hydrophobic.

Ramos-González, R.; García-Cerda, L. A.; Quevedo-López, M. A.

2012-06-01

217

Synthesis, integration, and characterization of metal oxide films as alternative gate dielectric materials  

Microsoft Academic Search

ZrO2 and HfO2 were investigated in this study to replace SiO2 as the potential gate dielectric materials in metal-oxide-semiconductor field effect transistors. ZrO2 and HfO2 films were deposited on p-type Si (100) wafers by an atomic layer chemical vapor deposition (ALCVD) process using zirconium (IV) t-butoxide and hafnium (IV) t-butoxide as the metal precursors, respectively. Oxygen was used alternatively with

You-Sheng Lin

2003-01-01

218

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

219

Atomic layer deposition grown composite dielectric oxides and ZnO for transparent electronic applications  

Microsoft Academic Search

In this paper, we report on transparent transistor obtained using laminar structure of two high-k dielectric oxides (hafnium dioxide, HfO2 and aluminum oxide, Al2O3) and zinc oxide (ZnO) layer grown at low temperature (60°C–100°C) using Atomic Layer Deposition (ALD) technology. Our research was focused on the optimization of technological parameters for composite layers Al2O3\\/HfO2\\/Al2O3 for thin film transistor structures with

S. Gieraltowska; L. Wachnicki; B. S. Witkowski; M. Godlewski; E. Guziewicz

220

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

221

Demonstrating 1 nm-oxide-equivalent-thickness HfO2/InSb structure with unpinning Fermi level and low gate leakage current density  

NASA Astrophysics Data System (ADS)

In this work, the band alignment, interface, and electrical characteristics of HfO2/InSb metal-oxide-semiconductor structure have been investigated. By using x-ray photoelectron spectroscopy analysis, the conduction band offset of 1.78 +/- 0.1 eV and valence band offset of 3.35 +/- 0.1 eV have been extracted. The transmission electron microscopy analysis has shown that HfO2 layer would be a good diffusion barrier for InSb. As a result, 1 nm equivalent-oxide-thickness in the 4 nm HfO2/InSb structure has been demonstrated with unpinning Fermi level and low leakage current of 10-4 A/cm-2. The Dit value of smaller than 1012 eV-1cm-2 has been obtained using conduction method.

Trinh, Hai-Dang; Lin, Yueh-Chin; Nguyen, Minh-Thuy; Nguyen, Hong-Quan; Duong, Quoc-Van; Luc, Quang-Ho; Wang, Shin-Yuan; Nguyen, Manh-Nghia; Yi Chang, Edward

2013-09-01

222

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

223

Mechanism for 355 nm nanosecond-pulse-driven damage in HfO2/SiO2 high reflectivity coating  

NASA Astrophysics Data System (ADS)

The effect of oxygen vacancy on the laser-induced damage behaviors of HfO2/SiO2 high reflective coating was investigated by single 355nm-8ns laser. The oxygen vacancy was tuned by controlling the oxygenation of the outmost HfO2 layer during the deposition procedure. The reflectivity of the coating with higher oxygen vacancy drops by 0.2% and the damage threshold drops by 60%, compared with the normal coating. Damage morphologies of samples were obtained by optical microscope, AFM, SEM and FIB technology. Typical morphologies of these coatings show little difference. Average oxygen vacancy of single HfO2 layer prepared on the BK7 substrate measured by XPS is about 43%. Theoretical analysis with a nonlinear thermodynamics model shows that the damage can be attributed to nonlinear thermal process. Moreover, the size of damage crater can be interpreted by a mechanics model.

Yu, Zhenkun; He, Hongbo; Qi, Hongji; Chen, Shunli; Xiao, Qiling

2013-07-01

224

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

225

Quantum tunneling and scalability of HfO2 and HfAlO gate stacks  

Microsoft Academic Search

We present a physical model for tunneling current through high-? gate stacks including an ultra thin interfacial layer between high-? layers and the Si substrate. The energy band offsets of high-? are determined by XPS. Accurate carrier quantization in the substrate or gate is found to play a more significant role in tunneling through high-? dielectrics than in SiO2. Excellent

Y. T. Hou; M. F. Li; H. Y. Yu; Y. Jin; D.-L. Kwong

2002-01-01

226

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

227

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

228

The effect of thermal treatment induced inter-diffusion at the interfaces on the charge trapping performance of HfO2/Al2O3 nanolaminate-based memory devices  

NASA Astrophysics Data System (ADS)

The charge trapping memory devices based on different HfO2/Al2O3 nanolaminated charge trapping layers were prepared and investigated. The memory device with 6 interfaces HfO2/Al2O3 shows a memory window of 4.7 V in its capacitance-voltage curve and a better retention property. It was suggested that the thermal treatment would reduce the defects inside the bulk HfO2, but cause an inter-diffusion at the interface HfO2/Al2O3, which could create additional defects at HfO2/Al2O3 interface. Increasing the number of the interfaces could enhance the charge trapping capability of the devices. The band alignments were established to explain the variation trend of the memory window and the retention characteristics of the memory devices with different laminated structures.

Lan, Xuexin; Ou, Xin; Cao, Yanqiang; Tang, Shiyu; Gong, Changjie; Xu, Bo; Xia, Yidong; Yin, Jiang; Li, Aidong; Yan, Feng; Liu, Zhiguo

2013-07-01

229

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

230

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

PubMed

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

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

2013-10-14

231

Submicrometer-resolution mapping of ultraweak 355-nm absorption in HfO2 monolayers using photothermal heterodyne imaging  

NASA Astrophysics Data System (ADS)

Nanosecond-pulse UV-laser-damage initiation in multilayer coatings comprised from metal oxide as a high-index component, and silica oxide as a low-index material, is strongly linked to metal oxide. The nature of the absorbing species and their physical properties remain unknown because of extremely small sizes. Previous experimental evidence provided by high-resolution mapping of damage morphology points to a few-nanometer scale of these absorbers. This work demonstrates submicrometer mapping of 355-nm absorption in HfO2 monolayers using a recently developed photothermal heterodyne imaging technique. Comparison of absorption maps with spatial distribution of UV pulsed-laser- induced damage morphology allows one to better estimate the size and densities of nanoscale absorbing defects in hafnia thin films. Possible defect-formation mechanisms are discussed.

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

2010-10-01

232

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

233

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

PubMed Central

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

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

2013-01-01

234

Threshold voltage instabilities in high-? gate dielectric stacks  

Microsoft Academic Search

Over recent years, there has been increasing research and development efforts to replace SiO2 with high dielectric constant (high-?) materials such as HfO2, HfSiO, and Al2O3. An important transistor reliability issue is the threshold voltage stability under prolonged stressing. In these materials, threshold voltage is observed to shift with stressing time and conditions, thereby giving rise to threshold voltage instabilities.

Sufi Zafar; Arvind Kumar; Evgeni Gusev; E. Cartier

2005-01-01

235

Special features of the sintering of composite laminates based on HfO 2 and W. I. Effect of the sintering temperature on shrinkage and porosity  

Microsoft Academic Search

The investigation of the special features of sintering composite laminates based on HfO2 and W permits a number of conclusions. Firstly, shrinkage and porosity of a CL depend strongly on the matching of the sintering characteristics of its components. If composites with high density are to be obtained, it is necessary to use components with the nearest possible values of

S. M. Kats; T. S. Basalaeva; V. N. Bogin; S. S. Ordan'yan; K. P. Akimova

1988-01-01

236

Impact of atomic layer deposition temperature on HfO2/InGaAs metal-oxide-semiconductor interface properties  

NASA Astrophysics Data System (ADS)

We have studied the impact of atomic-layer-deposition (ALD) temperature on the HfO2/InGaAs metal-oxide-semiconductor (MOS) interface with a comparison to the Al2O3/InGaAs interface. It is found that the interface properties such as the C-V characteristics and the interface trap density (Dit) and the interface structure of HfO2/InGaAs have strong dependence on the ALD temperature, while the Al2O3/InGaAs interfaces hardly depend on it. As a result, we have achieved the HfO2/InGaAs interfaces with low Dit comparable to that in the Al2O3/InGaAs interface by lowering the ALD temperature down to 200 °C or less. Also, we have found that As2O3 and Ga2O3 formed at the interface during ALD increase with a decrease in the ALD temperature. Combined with the ALD temperature dependence of the electrical characteristics, the better C-V characteristics and the lower Dit obtained at the lower ALD temperature can be explained by the As2O3 and Ga2O3 passivation of the HfO2/InGaAs interfaces, which is consistent with a reported theoretical result on the effective passivation of III-V MOS interfaces by trivalent oxides.

Suzuki, Rena; Taoka, Noriyuki; Yokoyama, Masafumi; Kim, Sang-Hyeon; Hoshii, Takuya; Maeda, Tatsuro; Yasuda, Tetsuji; Ichikawa, Osamu; Fukuhara, Noboru; Hata, Masahiko; Takenaka, Mitsuru; Takagi, Shinichi

2012-10-01

237

Towards -1 effective index with one-dimensional metal-dielectric metamaterial: a quantitative analysis of the role of absorption losses  

Microsoft Academic Search

We propose a theoretical study of the optimization of one dimensional metal-dielectric metamaterials in order to approach -1 effective optical index. Taking into account actual values of dielectric constants of metal (silver) and dielectrics (HfO2, GaP), and taking advantage of the dispersion relation of Bloch modes, we get a silver\\/HfO2metamaterial with suitable parameters that possesses a near 1 effective optical

Jinlong Zhang; Haitao Jiang; Boris Gralak; Stefan Enoch; Gérard Tayeb; Michel Lequime

2007-01-01

238

Fabrication of BaTiO3Based Dielectrics for Ultrathin-Layer Multilayer Ceramic Capacitor Application by a Modified Coating Approach  

Microsoft Academic Search

The development of multilayer ceramic capacitor (MLCC) with base metal electrode (BME) requires precise controlling of the microstructure in a very thin dielectric layer (<1 mum). In this paper, a modified coating approach for high coverage of BaTiO3 powder for further MLCC application has been developed. The well dispersed and coated BaTiO3 powders are prepared and the relative mechanism has

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

2011-01-01

239

On the Physically Based Compact Gate C –V Model for Ultrathin Gate Dielectric MOS Devices Using the Modified Airy Function Approximation  

Microsoft Academic Search

The exponent of the modified Airy function solution of the quantized energy levels in the MOS potential well, which is used in the physically based quantum-mechanical compact gate C-V model of Li et al., has been found to be dependent on the barrier height at the Si-dielectric interface and the substrate doping density. The physical origins of this dependence are

I. B. Shams; K. M. M. Habib; Q. D. M. Khosru; A. N. M. Zainuddin; A. Haque

2007-01-01

240

Effects of interface traps and oxide traps on gate capacitance of MOS devices with ultrathin (EOT ~ 1 nm) high-? stacked gate dielectrics  

Microsoft Academic Search

A quantum mechanical (QM) self-consistent model is developed for nano-MOS devices for high-? insulator including wave function penetration effect into the gate dielectrics. The effects of different types of interface trap distributions are incorporated. It has been observed that capacitance-voltage (C-V) characteristics are sensitive to the interface trap distribution. Simulated results has been compared with a published result both for

A. T. M. G. Sarwar; Mahmudur Rahman Siddiqui; Radwanul Hasan Siddique; Quazi Deen Mohd Khosru

2009-01-01

241

Flexible and stretchable dielectrics  

Microsoft Academic Search

A brief tour d'horizon is given through recent research on flexible and stretchable dielectrics. Ultrathin dielectrics with low leakage currents and high breakdown strength are essential in flexible electronic devices, illustrated with low voltage field-effect transistors for optothermal sensing and flash memories. Electrets with a permanently stored electrical charge are useful to control the threshold voltage in field-effect devices. Ferroelectrets

Siegfried Bauer

2010-01-01

242

Electron paramagnetic resonance characterization of defects in monoclinic HfO2 and ZrO2 powders  

NASA Astrophysics Data System (ADS)

Electron paramagnetic resonance (EPR) measurements have been made at X-band and room temperature on monoclinic HfO2 and ZrO2 powders from several suppliers. They reveal the presence of eight main paramagnetic centers H1, H2, H3, H4, and Z1, Z2, Z3, and Z4. H1 and Z1 are analogous as H4 and Z4 and H2 and Z2 are similar as H3 and Z3. H1 and Z1 have axial symmetry with g?=300 °C. Their concentration reaches a maximum of order 1017 cm-3 or 1012 cm-2 in the range of 550-750 °C. They are also most likely to be mainly at and/or near the surface and to involve an electron trapped in an oxygen vacancy cluster. The EPR spectra of H2 and Z2 are consistent with those of S=1/2 centers of orthorhombic symmetry with principal g values about equal to or just less than ge suggesting that they are trapped electron centers. The electrons produced by ?-irradiation are trapped at precursors to H2 but are easily detrapped. Z2 centers also appear to be shallow electron traps. Their identity is uncertain; they have some characteristics of electrons trapped in oxygen vacancies and of CO2- radicals. H3 and Z3 are likely to involve holes trapped on oxygen, possibly as O- and O2- type centers, respectively, but their location in not known. Their concentration increases to an upper limit as the ?-ray dose is increased and this shows that their precursors are trapping charge generated by the ?-rays. Like the H2 and Z2 centers, even annealing at 100 °C releases the charge but their precursors, at least in HfO2, are not destroyed. The significance of these centers is discussed.

Wright, Sandra; Barklie, R. C.

2009-11-01

243

Electrical Properties of Low-Temperature-Compatible P-Channel Polycrystalline-Silicon TFTs Using High Gate Dielectrics  

Microsoft Academic Search

In this paper, we describe a systematic study of the electrical properties of low-temperature-compatible p-channel polycrystalline-silicon thin-film transistors (poly-Si TFTs) using HfO2 and HfSiOx, high-k gate dielectrics. Because of their larger gate capacitance density, the TFTs containing the high-k gate dielectrics exhibited superior device performance in terms of higher Ion\\/Ioff current ratios, lower subthreshold swings (SSs), and lower threshold voltages

Ming-Jui Yang; Chao-Hsin Chien; Yi-Hsien Lu; Chih-Yen Shen; Tiao-Yuan Huang

2008-01-01

244

Chemical states and electronic structure of a HfO(-2) / Ge(001) interface  

SciTech Connect

We report the chemical bonding structure and valence band alignment at the HfO{sub 2}/Ge (001) interface by systematically probing various core level spectra as well as valence band spectra using soft x-rays at the Stanford Synchrotron Radiation Laboratory. We investigated the chemical bonding changes as a function of depth through the dielectric stack by taking a series of synchrotron photoemission spectra as we etched through the HfO{sub 2} film using a dilute HF-solution. We found that a very non-stoichiometric GeO{sub x} layer exists at the HfO{sub 2}/Ge interface. The valence band spectra near the Fermi level in each different film structure were carefully analyzed, and as a result, the valence band offset between Ge and GeO{sub x} was determined to be {Delta}E{sub v} (Ge-GeO{sub x}) = 2.2 {+-} 0.15 eV, and that between Ge and HfO{sub 2}, {Delta}E{sub v} (Ge-HfO{sub 2}) = 2.7 {+-} 0.15 eV.

Seo, Kang-ill; McIntyre, Paul C.; /Stanford U., Materials Sci. Dept.; Sun, Shiyu; Lee, Dong-Ick; Pianetta, Piero; /SLAC, SSRL; Saraswat, Krishna C.; /Stanford U., Elect. Eng. Dept.

2005-05-04

245

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

246

In situ study of the role of substrate temperature during atomic layer deposition of HfO2 on InP  

NASA Astrophysics Data System (ADS)

The dependence of the ``self cleaning'' effect of the substrate oxides on substrate temperature during atomic layer deposition (ALD) of HfO2 on various chemically treated and native oxide InP (100) substrates is investigated using in situ X-ray photoelectron spectroscopy. The removal of In-oxide is found to be more efficient at higher ALD temperatures. The P oxidation states on native oxide and acid etched samples are seen to change, with the total P-oxide concentration remaining constant, after 10 cycles of ALD HfO2 at different temperatures. An (NH4)2 S treatment is seen to effectively remove native oxides and passivate the InP surfaces independent of substrate temperature studied (200 °C, 250 °C and 300 °C) before and after the ALD process. Density functional theory modeling provides insight into the mechanism of the changes in the P-oxide chemical states.

Dong, H.; Santosh, K. C.; Qin, X.; Brennan, B.; McDonnell, S.; Zhernokletov, D.; Hinkle, C. L.; Kim, J.; Cho, K.; Wallace, R. M.

2013-10-01

247

Differential Light Addressable Potentiometric Sensor with Poly(vinyl chloride) and HfO2 Membranes for pH Sensors  

NASA Astrophysics Data System (ADS)

In this paper, a differential measurement setup for the light addressable potentiometric sensor (LAPS) is proposed. The LAPS with a HfO2 layer as the sensing membrane was used, and different weight percentages of DNP/(PVC+DNP) [DNP: dinonylphtalate, PVC: poly(vinyl chloride)] membrane were cast on the surface of HfO2-LAPS. The pH sensitivity can be decreased from 58.6 to 24.5 mV/pH by using 60 wt % PVC cocktail. Then, the pH sensitivity measured through a differential circuit was 30.1 mV/pH, showing high potential for replacing the function of a conventional reference electrode as an ion-sensitive field-effect transistor (ISFET)/reference field-effect transistor (REFET) pair. In addition, to confirm the output signal of the two substrate electrodes, a specific measurement setup was used.

Cheng-En Lue,; Chao-Sung Lai,; Jer-Chyi Wang,; Ching-Mie Wu,; Chia-Ming Yang,

2010-04-01

248

Effect of SiO2 overcoat thickness on laser damage morphology of HfO2/SiO2 Brewster's angle polarizers at 1064 nm  

NASA Astrophysics Data System (ADS)

HfO2/SiO2 Brewster's angle polarizers are being developed at Lawrence Livermore National Laboratory for the National Ignition Facility. Damage threshold studies using a 3-ns pulse length 1064-nm laser have revealed a number of different damage morphologies such as nodular ejection pits, plasma scalds, and overcoat delaminations. Of these laser damage morphologies, delaminations have the most negative impact on fusion laser performance. By increasing the thickness of the SiO2 overcoat, the delamination morphology is eliminated without significantly modifying the spectral characteristics of the coating. A model of the thermal mechanical response of the overcoats is presented for various SIO2 overcoat thicknesses. The overcoat thickness influences the electric-field profile resulting in different thermal gradients between the outer SiO2 and HfO2 layers. This modeling effort attempts to understand the relationship between the thermal stress distribution in the overcoat and the occurrence of delamination.

Stolz, Christopher J.; Genin, Francois Y.; Reitter, T. A.; Molau, Nicole E.; Bevis, R. P.; von Gunten, Marc K.; Smith, Douglas J.; Anzellotti, J. F.

1997-05-01

249

Electrode effects on the conduction mechanisms in HfO2-based metal-insulator-metal capacitors  

NASA Astrophysics Data System (ADS)

The impact of top-electrode metal on the conduction mechanisms of HfO2 thin films-based metal-insulator-metal capacitors was investigated at temperature ranging from 25 to 150 °C. Al, Cr, and Au are considered as top electrodes whereas Pt constitutes the commune bottom electrode. It was found for both capacitors that in the high field region, the leakage mechanism is electrode-limited. The leakage current, measured at the Al/HfO2 and Cr/HfO2 interfaces, was largely governed by Fowler-Nordheim tunneling in the whole measured temperature range. The barrier heights, at the Al/HfO2 and the Cr/HfO2 interfaces, were around 0.77 and 0.95 eV, respectively. In the case of Au/HfO2/Pt capacitors, the Au/HfO2 interface acts as a Schottky barrier with a height of 1.06 eV.

El Kamel, F.; Gonon, P.; Vallée, C.; Jorel, C.

2009-09-01

250

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

251

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

252

Bandgap engineering of tunnel oxide with multistacked layers of Al2O3\\/HfO2\\/SiO2 for Au-nanocrystal memory application  

Microsoft Academic Search

Charge storage characteristics of metal-oxide-semiconductor (MOS) structure containing Au nanocrystals on tunnel oxide composed of triply stacked SiO2, HfO2, and Al2O3 layers were studied. Significantly high charge injection and detrapping efficiency for program and erase operations along with a satisfactory long-term charge retention were obtained from the above MOS structure. It is attributed to the bandgap engineering of tunnel oxide

Yun-Shan Lo; Ke-Chih Liu; Jyun-Yi Wu; Cheng-Hao Hou; Tai-Bor Wu

2008-01-01

253

Study of rapid thermal annealing on ultra thin high- k HfO 2 films properties for nano scaled MOSFET technology  

Microsoft Academic Search

The effect of rapid thermal annealing on structural and electrical properties of high-k HfO2 ultra thin films deposited by rf-sputtering system is investigated. The films properties were investigated for optimum rapid thermal annealing temperature in oxygen and nitrogen ambient, respectively to get the best electrical results as a MOS device structure. Detailed studies of temperature induced annealing effects on the

Vikram Singh; Satinder K. Sharma; Dinesh Kumar; R. K. Nahar

254

CMOS compatible Ge\\/Si core\\/shell nanowire gate-all-around pMOSFET integrated with HfO2\\/TaN gate stack  

Microsoft Academic Search

Ge\\/Si core\\/shell gate-all-round nanowire pMOSFET integrated with HfO2\\/TaN gate stack is demonstrated using fully CMOS compatible process. Devices with 100 nm gate length achieved high ION of ~946 ¿A\\/¿m at VG - VT = -0.7 V and VDS = -1 V and on\\/off ratio of 104 with decent subthreshold behavior. Significant improvement in hole mobility and ballistic efficiency is demonstrated

J. W. Peng; N. Singh; G. Q. Lo; D. L. Kwong; S. J. Lee

2009-01-01

255

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

PubMed

Increasing use of nanomaterials necessitates an improved understanding of their potential impact on environment health. This study evaluated the cytotoxicity of nanosized HfO(2), SiO(2), Al(2)O(3) and CeO(2) towards the eukaryotic model organism Saccharomyces cerevisiae, and characterized their state of dispersion in bioassay medium. Nanotoxicity was assessed by monitoring oxygen consumption in batch cultures and by analysis of cell membrane integrity. CeO(2), Al(2)O(3), and HfO(2) nanoparticles were highly unstable in yeast medium and formed micron-sized, settleable agglomerates. A non-toxic polyacrylate dispersant (Dispex A40) was used to improve nanoparticle stability and determine the impact of enhanced dispersion on toxicity. None of the NPs tested without dispersant inhibited O(2) uptake by yeast at concentrations as high as 1000 mg/L. Dispersant supplementation only enhanced the toxicity of CeO(2) (47% at 1000 mg/L). Dispersed SiO(2) and Al(2)O(3) (1000 mg/L) caused cell membrane damage, whereas dispersed HfO(2) and CeO(2) did not cause significant disruption of membrane integrity at the same concentration. These results suggest that the O(2) uptake inhibition observed with dispersed CeO(2) NPs was not due to reduced cell viability. This is the first study evaluating toxicity of nanoscale HfO(2), SiO(2), Al(2)O(3) and CeO(2) to S. cerevisiae. Overall the results obtained demonstrate that these nanomaterials display low or no toxicity to yeast. PMID:21782338

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

2011-07-02

256

Segregation trends of the metal alloys MoRe and Mo-Pt on HfO2: A first-principles study  

Microsoft Academic Search

Using first-principles calculations, we compared the segregation trends at the surface of metal alloys with those at an interface with HfO2. The choice of this oxide was motivated by its significance as a potential replacement for SiO2 in advanced transistors. We considered Mo-Re and Mo-Pt alloys as typical examples of disordered and ordered alloys, respectively. The segregation to the surface\\/interface

A. A. Knizhnik; A. V. Gavrikov; A. A. Safonov; I. M. Iskandarova; A. A. Bagatur'yants; B. V. Potapkin; L. R. C. Fonseca; M. W. Stoker

2006-01-01

257

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

258

Energy band alignment of atomic layer deposited HfO2 oxide film on epitaxial (100)Ge, (110)Ge, and (111)Ge layers  

NASA Astrophysics Data System (ADS)

Crystallographically oriented epitaxial Ge layers were grown on (100), (110), and (111)A GaAs substrates by in situ growth process using two separate molecular beam epitaxy chambers. The band alignment properties of atomic layer hafnium oxide (HfO2) film deposited on crystallographically oriented epitaxial Ge were investigated using x-ray photoelectron spectroscopy (XPS). Valence band offset, ?Ev values of HfO2 relative to (100)Ge, (110)Ge, and (111)Ge orientations were 2.8 eV, 2.28 eV, and 2.5 eV, respectively. Using XPS data, variation in valence band offset, ?EV(100)Ge>?EV(111)Ge>?EV(110)Ge, was obtained related to Ge orientation. Also, the conduction band offset, ?Ec relation, ?Ec(110)Ge>?Ec(111)Ge>?Ec(100)Ge related to Ge orientations was obtained using the measured bandgap of HfO2 on each orientation and with the Ge bandgap of 0.67 eV. These band offset parameters for carrier confinement would offer an important guidance to design Ge-based p- and n-channel metal-oxide field-effect transistor for low-power application.

Hudait, Mantu K.; Zhu, Yan

2013-03-01

259

Correlation between local structure and refractive index of e-beam evaporated (HfO2-SiO2) composite thin films  

NASA Astrophysics Data System (ADS)

In the present work we have reported the results of investigations on local structures of e-beam evaporated (HfO2-SiO2) composite thin films by synchrotron based extended x-ray absorption fine structure measurements. It has been observed that for the composite film with 10% SiO2 content, both Hf-O and Hf-Hf bond lengths are less than their values in pure HfO2 film. However the bond lengths subsequently increase to higher values as the SiO2 content in the composite films is increased further. It has also been observed that at the same composition of 10% SiO2 content, the films have smallest grain sizes (as obtained from atomic force microscopy measurements) and highest refractive index (as obtained from spectroscopic ellipsometry (SE) measurements) which suggests that the e-beam evaporated HfO2-SiO2 composite films with 10% SiO2 content leads to the most compact amorphous thin film structure.

Das, N. C.; Sahoo, N. K.; Bhattacharyya, D.; Thakur, S.; Kamble, N. M.; Nanda, D.; Hazra, S.; Bal, J. K.; Lee, J. F.; Tai, Y. L.; Hsieh, C. A.

2010-07-01

260

Photoelectron spectroscopy of the molecular anions, ZrO-, HfO-, HfHO-, and HfO2H-.  

PubMed

Negative ion photoelectron spectra of ZrO(-), HfO(-), HfHO(-), and HfO(2)H(-) are reported. Even though zirconium- and hafnium-containing molecules typically exhibit similar chemistries, the negative ion photoelectron spectral profiles of ZrO(-) and HfO(-) are dramatically different from one another. By comparing these data with relevant theoretical and experimental studies, as well as by using insights drawn from atomic spectra, spin-orbit interactions, and relativistic effects, the photodetachment transitions in the spectra of ZrO(-) and HfO(-) were assigned. As a result, the electron affinities of ZrO and HfO were determined to be 1.26 ± 0.05 eV and 0.60 ± 0.05 eV, respectively. The anion photoelectron spectra of HfHO(-) and HfO(2)H(-) are similar to one another and their structural connectivities are likely to be H-Hf-O(-) and O-Hf-OH(-), respectively. The electron affinities of HfHO and HfO(2)H are 1.70 ± 0.05 eV and 1.73 ± 0.05 eV, respectively. PMID:22519325

Li, Xiang; Zheng, Weijun; Buonaugurio, Angela; Buytendyk, Allyson; Bowen, Kit; Balasubramanian, Krishnan

2012-04-21

261

Irradiation effects in an HfO2/MgO/HfO2 tri-layer structure induced by 10 MeV Au ions  

NASA Astrophysics Data System (ADS)

In this report, we present radiation damage effects in a thin film, tri-layer structure, HfO2/MgO/HfO2. Irradiations were performed with 10 MeV Au ions in a recently developed medium energy ion irradiation facility at Los Alamos National Laboratory, which is described in this paper. Energy deposition by 10 MeV Au ions corresponds to a mixed regime, wherein electronic and nuclear stopping contribute to radiation damage. In this study, we investigated modifications of both surface and bulk properties in order to assess the structural stability of our oxide tri-layers under the severe irradiation conditions employed here. The most dramatic structural changes were observed to occur on the surfaces of the tri-layer samples. Surface features consisted of large craters and spires. The dimensions of these craters and spires exceed those of the individual ion tracks by almost three orders of magnitude. As for the bulk tri-layer structure, our conclusions are that this structure is stable in terms of: (i) resistance to amorphization; (ii) resistance to compositional mixing and (iii) resistance to pronounced nucleation and growth of extended defects. The main effect observed in the tri-layer structure was the transformation of the first HfO2 layer from a monoclinic to either a tetragonal or cubic form of HfO2.

Usov, I. O.; Valdez, J. A.; Won, J.; Hawley, M.; Devlin, D. J.; Dickerson, R. M.; Uberuaga, B. P.; Wang, Y. Q.; Reichhardt, C. J. Olson; Jarvinen, G. D.; Sickafus, K. E.

2009-06-01

262

Segregation trends of the metal alloys Mo-Re and Mo-Pt on HfO2: A first-principles study  

NASA Astrophysics Data System (ADS)

Using first-principles calculations, we compared the segregation trends at the surface of metal alloys with those at an interface with HfO2. The choice of this oxide was motivated by its significance as a potential replacement for SiO2 in advanced transistors. We considered Mo-Re and Mo-Pt alloys as typical examples of disordered and ordered alloys, respectively. The segregation to the surface/interface was analyzed in terms of metal and oxygen adsorption energies. It is shown that chemical bonding at the metal/oxide interface strongly influences segregation both in Mo-Re and Mo-Pt alloys. In particular, bonding with oxygen atoms at the oxide/Mo-Re alloy interface depletes the Re content of the interfacial layer. In the case of Mo-Pt on HfO2 an oxygen-rich interface promotes the formation of one monolayer (but not two monolayers) of Mo separating PtMox from HfO2, while a stoichiometric interface favors an abrupt PtMox/HfO2 interface. This study also shows that the presence of Mo in the alloy stabilizes Pt which can potentially decrease the tendency of Pt to diffuse into the oxide matrix. The individual constituents of these intermetallic compounds exhibit high vacuum work functions, and therefore these alloys are also likely to have sufficiently high work functions to be considered as promising candidates for p-type gate electrodes in future generations of transistors.

Knizhnik, A. A.; Gavrikov, A. V.; Safonov, A. A.; Iskandarova, I. M.; Bagatur'yants, A. A.; Potapkin, B. V.; Fonseca, L. R. C.; Stoker, M. W.

2006-07-01

263

Ab initio localized basis set study of structural parameters and elastic properties of HfO2 polymorphs  

NASA Astrophysics Data System (ADS)

The SIESTA approach based on pseudopotentials and a localized basis set is used to calculate the electronic, elastic and equilibrium properties of P 21/c, Pbca, Pnma, Fm3m, P42nmc and Pa3 phases of HfO2. Using separable Troullier-Martins norm-conserving pseudopotentials which include partial core corrections for Hf, we tested important physical properties as a function of the basis set size, grid size and cut-off ratio of the pseudo-atomic orbitals (PAOs). We found that calculations in this oxide with the LDA approach and using a minimal basis set (simple zeta, SZ) improve calculated phase transition pressures with respect to the double-zeta basis set and LDA (DZ-LDA), and show similar accuracy to that determined with the PPPW and GGA approach. Still, the equilibrium volumes and structural properties calculated with SZ-LDA compare better with experiments than the GGA approach. The bandgaps and elastic and structural properties calculated with DZ-LDA are accurate in agreement with previous state of the art ab initio calculations and experimental evidence and cannot be improved with a polarized basis set. These calculated properties show low sensitivity to the PAO localization parameter range between 40 and 100 meV. However, this is not true for the relative energy, which improves upon decrease of the mentioned parameter. We found a non-linear behaviour in the lattice parameters with pressure in the P 21/c phase, showing a discontinuity of the derivative of the a lattice parameter with respect to external pressure, as found in experiments. The common enthalpy values calculated with the minimal basis set give pressure transitions of 3.3 and 10.8 GPa for P2_1/c \\rightarrow Pbca and Pbca \\rightarrow Pnma , respectively, in accordance with different high pressure experimental values.

Caravaca, M. A.; Casali, R. A.

2005-09-01

264

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

Microsoft Academic Search

High permittivity hafnia, HfO2, and hafnium silicate, HfSiO 4, are the most promising candidates to replace oxide (SiOx) or oxynitride (SiOxNy) based gate dielectrics in future generation CMOS devices. In this thesis, the effects of processing (deposition techniques, post deposition annealing, nitridation) on nanostructure evolution (crystallization, phase segregation, interlayer growth), changes in nanochemistry (impurity content, interfacial reaction, interdiffusion, oxygen diffusion,

Anirban Das

2005-01-01

265

Band Alignment of Plasma-Enhanced ALD High-k Dielectrics on Gallium Nitride  

NASA Astrophysics Data System (ADS)

GaN-based transistors have shown immense promise because of their high saturation velocity and breakdown field, but their performance is limited by the high gate leakage. This limitation is mitigated with the use of metal/high-k oxide/III-N structures. This experiment investigates three promising high-k dielectrics deposited by plasma enhanced ALD: Al2O3, HfO2, and La2O3. The band gaps of these materials are 6.5eV, 5.8eV, and 4.3eV, while the dielectric constants are 9, 20, and 27, respectively. The large band gap associated with Al2O3 reduces the leakage current; however, the lower dielectric constant increases the equivalent oxide thickness. The band alignment of the high-k oxide/GaN interface plays a critical role in determining the confinement properties of semiconductor carriers and ultimately device performance. In situ photoemission gave valence band offsets for Al2O3, HfO2, and La2O3 with GaN as 1.8eV, 1.3eV, and 0.9eV. The results are described by the charge neutrality level and interface dipole models. We also investigated the use of Al2O3 as an interfacial passivation layer between HfO2 and GaN. This research is supported by the Office of Naval Research.

Yang, Jialing; Eller, Brianna; Zhu, Chiyu; Nemanich, Robert

2012-02-01

266

Ultrathin multiband gigahertz metamaterial absorbers  

NASA Astrophysics Data System (ADS)

We propose ultrathin multiband metamaterial absorbers in the microwave frequencies in which the design, analysis, fabrication, and measurement of the absorbers working in multiple bands are presented. The metamaterial absorbers consist of a periodic arrangement of different scales of electric-field-coupled-LC (ELC) resonators and a metallic background plane, separated by only 1 mm dielectric spacer. By tuning the scale factor of the ELC unit cells, we achieve independently multiple absorptions at different customized frequencies. Experiments demonstrate excellent absorption rates in the designed frequency bands over wide angles of incident waves for both transverse electric and magnetic polarizations. The explanation to the physical mechanism of the multiband metamaterial absorber is presented and verified.

Li, Hui; Yuan, Li Hua; Zhou, Bin; Shen, Xiao Peng; Cheng, Qiang; Cui, Tie Jun

2011-07-01

267

Dielectric response in ferroelectric superlattices.  

SciTech Connect

The dielectric response of a ferroelectric multilayer, having a designed heterogeneity, has been studied near its phase transition range by use of the Landau-Ginzburg theory. The coherent lattice coupling between ultrathin layers can be significantly strong, resulting in a broad phase transition of the superlattice system as a whole. The thickness of layers and their spatial distribution hold the keys for enhancing dielectric properties in a broad temperature range.

Li, S.; Eastman, J. A.; Vetrone, J. M.; Newnham, R. E.; Cross, L. E.; Materials Science Division; Pennsylvania State Univ.

1997-01-01

268

Role of point defects and HfO2/TiN interface stoichiometry on effective work function modulation in ultra-scaled complementary metal-oxide-semiconductor devices  

NASA Astrophysics Data System (ADS)

We investigate the physical properties of a portion of the gate stack of an ultra-scaled complementary metal-oxide-semiconductor (CMOS) device. The effects of point defects, such as oxygen vacancy, oxygen, and aluminum interstitials at the HfO2/TiN interface, on the effective work function of TiN are explored using density functional theory. We compute the diffusion barriers of such point defects in the bulk TiN and across the HfO2/TiN interface. Diffusion of these point defects across the HfO2/TiN interface occurs during the device integration process. This results in variation of the effective work function and hence in the threshold voltage variation in the devices. Further, we simulate the effects of varying the HfO2/TiN interface stoichiometry on the effective work function modulation in these extremely-scaled CMOS devices. Our results show that the interface rich in nitrogen gives higher effective work function, whereas the interface rich in titanium gives lower effective work function, compared to a stoichiometric HfO2/TiN interface. This theoretical prediction is confirmed by the experiment, demonstrating over 700 meV modulation in the effective work function.

Pandey, R. K.; Sathiyanarayanan, Rajesh; Kwon, Unoh; Narayanan, Vijay; Murali, K. V. R. M.

2013-07-01

269

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

270

Effects of Thickness Effect and Rapid Thermal Annealing on pH Sensing Characteristics of Thin HfO2 Films Formed by Atomic Layer Deposition  

NASA Astrophysics Data System (ADS)

In this article, thin hafnium oxide (HfO2) films deposited by atomic layer deposition (ALD) were investigated as a sensing layer on an electrolyte--insulator--semiconductor (EIS) structure for pH sensor applications. Compared with sputtering, ALD provides the possibility of shrinking the thickness of the HfO2 sensing layer down to 3.5 nm with a low drift coefficient (<0.2 mV/h). To increase the pH response, an additional rapid thermal annealing was performed on a 3.5-nm-thick ALD-HfO2 film. After annealing at 900 °C, the pH sensitivity could be effectively increased to that near the Nernstian response (59.6 mV/pH), and the drift coefficient (<1 mV/h) and hysteresis width (4.26 mV) are still sufficient. On the basis of the results of atomic force microscopy (AFM) analysis, the increase in surface roughness is possibly the reason for the increase in pH response after annealing. For compatibility with advanced complementary metal--oxide--semiconductor (CMOS) technology, the thin ALD-HfO2 film is a promising candidate for pH sensor fabrications.

Lu, Tseng-Fu; Chuang, Hao-Chun; Wang, Jer-Chyi; Yang, Chia-Ming; Kuo, Pei-Chun; Lai, Chao-Sung

2011-10-01

271

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

272

Investigation of the initial stage of growth of HfO2 films on Si(100) grown by atomic-layer deposition using in situ medium energy ion scattering  

NASA Astrophysics Data System (ADS)

The initial stage of growth of HfO2 films on p-type Si(100) grown by atomic-layer deposition (ALD) was investigated using in situ medium energy ion scattering (MEIS). The interaction between adsorbed HfCl4 molecules and the oxidized Si surface was examined as a function of growth cycles. The results clearly show that island-like growth occurs during the initial HfO2 growth and the islands are then merged into a continuous atomic layer with an increase in ALD cycles. The morphology of thicker HfO2 films remained essentially unchanged with growth cycles. Interfacial reactions between Hf and Si during the initial growth stage were minimal. As a result, the effect of insufficient nucleation density is a dominant factor in the initial stage of growth of hafnium oxide on the oxidized Si substrate, resulting in nonlinear growth behavior.

Chang, Hyo Sik; Hwang, Hyunsang; Cho, Mann-Ho; Moon, Dae Won

2005-01-01

273

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

274

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

2013-05-30

275

Atomic Layer Deposition of High k Dielectric and Metal Gate Stacks for MOS Devices  

SciTech Connect

High-k gate stack fabrication via atomic layer deposition (ALD) of ultra thin HfO2 and HfxSi1-xO2 films is demonstrated utilizing metal-amide precursors and ozone as an oxidant. High resolution transmission electron microscopy (TEM) shows that films near 2.0 nm are reproducible. X-ray reflectivity (XRR) and Rutherford backscattering (RBS) indicate that this ALD chemistry proceeds similarly on multiple surface preparations including HF last without growth incubation. High field mobility of more than 85% of the universal SiO2 mobility has been achieved at EOT {approx}1nm with a reduction of more than two orders of magnitude in leakage current density as compared with a SiO2/poly Si gate. Various ALD metal nitrides such as TiN, HfN, HfSiN have been deposited on HfO2 and HfSiOx dielectrics which enabled a study of the interfacial reaction between high-k dielectrics and metal electrode materials. The thermal stability of PVD Ru deposited on ALD HfO2 has also been observed.

Senzaki, Yoshihide; Choi, Kisik; Kirsch, Paul D.; Majhi, Prashant; Lee, Byoung Hun [SEMATECH, 2706 Montopolis Drive, Austin, TX 78741 (United States)

2005-09-09

276

An investigation of conductivity, microstructure and stability of HfO 2–ZrO 2–Y 2O 3–Al 2O 3 electrolyte compositions for high-temperature oxygen measurement  

Microsoft Academic Search

In search of better ionically conducting ceramics for high temperature oxygen fuel cells and sensors, the conductivity and microstructure of the HfO2–ZrO2–Y2O3 system with 15 mol% of Y2O3 and the HfO2–ZrO2–Y2O3–Al2O3 system with 50 mol% of Al2O3 have been investigated with X-ray diffractometry (XRD), scanning electron microscopy (SEM) and conductivity measurements as a function of temperature. The stability of electrolyte

Serge Zhuiykov

2000-01-01

277

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

278

Medium Energy Ion Scattering Investigation of Ultra-thin Oxides on Semiconductor Materials*  

NASA Astrophysics Data System (ADS)

A comprehensive understanding of the growth kinetics and thermal stability of alternative dielectric films on Si is still lacking. Our work demonstrates the potential of Medium energy Ion Scattering (MEIS) to quantitatively study the composition, structure and stability of dielectric films on Si with a depth resolution in the sub-nm range. We have investigated films (metal oxides, silicates, aluminates) grown by various deposition techniques, including sputtering, atomic layer chemical vapor deposition and molecular beam epitaxy.^1,2 In particular we found that the formation of an interfacial SiO2 layer can be avoided in an oxygen free process environment. Vacuum annealing of HfO2 and ZrO2 films led to the removal of existing SiO2 layers, without influencing the metal-oxide film. 1. B.W. Busch et al., Appl. Phys. Lett. 79, 2447 (2001). 2. B.W. Busch et al., Phys. Rev. B62 13290 (2000)

Schulte, W.-H.; Starodub, D.; Nishimura, T.; Gustafsson, T.; Garfunkel, E.; Busch, B. W.

2002-03-01

279

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

PubMed

The mechanisms of technologically important atomic layer deposition (ALD) processes, trimethylaluminium (TMA)/ozone and tetrakis(ethylmethylamino)hafnium (TEMAH)/ozone, for the growth of Al(2)O(3) and HfO(2) thin films are studied in situ by a quadrupole mass spectrometer coupled with a 300 mm ALD reactor. In addition to released CH(4) and CO(2), water was detected as one of the reaction byproduct in the TMA/O(3) process. In the TEMAH/O(3) process, the surface after the ozone pulse consisted of chemisorpted active oxygen and -OH groups, leading to the release of H(2)O, CO(2), and HNEtMe during the metal precursor pulse. PMID:20356179

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

2010-02-01

280

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

281

InAs hole inversion and bandgap interface state density of 2 × 1011 cm-2 eV-1 at HfO2/InAs interfaces  

NASA Astrophysics Data System (ADS)

High-k/InAs interfaces have been manufactured using InAs surface oxygen termination and low temperature atomic layer deposition of HfO2. Capacitance-voltage (C-V) curves revert to essentially classical shape revealing mobile carrier response in accumulation and depletion, hole inversion is observed, and predicted minority carrier response frequency in the hundred kHz range is experimentally confirmed; reference samples using conventional techniques show a trap dominated capacitance response. C-V curves have been fitted using advanced models including nonparabolicity and Fermi-Dirac distribution. For an equivalent oxide thickness of 1.3 nm, an interface state density Dit = 2.2 × 1011 cm-2 eV-1 has been obtained throughout the InAs bandgap.

Wang, C. H.; Wang, S. W.; Doornbos, G.; Astromskas, G.; Bhuwalka, K.; Contreras-Guerrero, R.; Edirisooriya, M.; Rojas-Ramirez, J. S.; Vellianitis, G.; Oxland, R.; Holland, M. C.; Hsieh, C. H.; Ramvall, P.; Lind, E.; Hsu, W. C.; Wernersson, L.-E.; Droopad, R.; Passlack, M.; Diaz, C. H.

2013-09-01

282

Effects of CF4 Plasma Treatment on pH and pNa Sensing Properties of Light-Addressable Potentiometric Sensor with a 2-nm-Thick Sensitive HfO2 Layer Grown by Atomic Layer Deposition  

NASA Astrophysics Data System (ADS)

We investigated the effect of the carbon tetrafluoride (CF4) plasma treatment on pH and pNa sensing characteristics of a light-addressable potentiometric sensor (LAPS) with a 2-nm-thick HfO2 film grown by atomic layer deposition (ALD). An inorganic CF4 plasma treatment with different times was performed using plasma enhance chemical vapor deposition (PECVD). For pH detection, the pH sensitivity slightly decreased with increasing CF4 plasma time. For pNa detection, the proposed fluorinated HfO2 film on a LAPS device is sensitive to Na+ ions. The linear relationship between pNa sensitivity and plasma treatment time was observed and the highest pNa sensitivity of 33.9 mV/pNa measured from pNa 1 to pNa 3 was achieved. Compared with that of the same structure without plasma treatment, the sensitivity was improved by twofold. The response mechanism of the fluorinated HfO2 LAPS is discussed according to the chemical states determined by X-ray photoelectron spectroscopy (XPS) analysis. The analysis of F 1s, Hf 4f, and O 1s spectra gives evidence that the enhancement of pNa sensitivity is due to the high concentration of incorporated fluorine in HfO2 films by CF4 plasma surface treatment.

Chin, Chi-Hang; Lu, Tseng-Fu; Wang, Jer-Chyi; Yang, Jung-Hsiang; Lue, Cheng-En; Yang, Chia-Ming; Li, Sheng-Shian; Lai, Chao-Sung

2011-04-01

283

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

National Technical Information Service (NTIS)

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...

D. Zhu N. P. Bansal R. A. Miller

2003-01-01

284

Improvements on Electrical Characteristics of p-Channel Metal-Oxide-Semiconductor Field Effect Transistors with HfO2 Gate Stacks by Post Deposition N2O Plasma Treatment  

NASA Astrophysics Data System (ADS)

In this work, we found that employing a post deposition N2O plasma treatment following the deposition of HfO2 film can effectively improve the electrical characteristics of p-type channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) with a HfO2 gate stack in terms of lower gate leakage current, lower interface state density, superior subthreshold swing, higher normalized transconductance and enhanced driving current even though it had led to a slightly higher equivalent oxide thickness (EOT) value of the HfO2 gate stack by around 0.3 nm. In order to clarify the attributes of the improvements, we used charge pumping (CP) measurement to analyze the densities of interface states and bulk traps in the HfO2 gate stacks. The improvements are then ascribed to the higher interface quality offered by the post deposition N2O plasma treatment. Moreover, we found that to more accurately estimate the bulk traps from the CP measurement, the leakage should be taken into account especially at low frequencies. Finally, it was found that the levels of the bulk traps and interface states can be reduced by the N2O plasma treatment, which also helps significantly eliminate the degradation of the gate stack during the subsequent voltage stress.

Lu, Wen-Tai; Chien, Chao-Hsin; Lan, Wen-Ting; Lee, Tsung-Chieh; Yang, Ming-Jui; Shen, Shih-Wen; Lehnen, Peer; Huang, Tiao-Yuan

2005-11-01

285

Atomic layer deposited TaCy metal gates: Impact on microstructure, electrical properties, and work function on HfO2 high-k dielectrics  

Microsoft Academic Search

TaCy has been reported to have the appropriate work function for negative metal-oxide semiconductor metal in high-k metal-oxide field-effect transistors. As device size continues to shrink, a conformal deposition for metal gate electrodes is needed. In this work, we report on the development and characterization of a novel TaCy process by atomic layer deposition (ALD). Detailed physical properties of TaCy

D. H. Triyoso; R. Gregory; J. K. Schaeffer; D. Werho; D. Li; S. Marcus; G. D. Wilk

2007-01-01

286

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

Microsoft Academic Search

Single-crystal Ge nanowires are synthesized by a low-temperature (275 °C) chemical vapor deposition (CVD) method. Boron doped p-type GeNW field-effect transistors (FETs) with back-gates and thin SiO2 (10 nm) gate insulators are constructed. Hole mobility higher than 600 cm2\\/V s is observed in these devices, suggesting high quality and excellent electrical properties of as-grown Ge wires. In addition, integration of

Dunwei Wang; Qian Wang; Ali Javey; Ryan Tu; Hongjie Dai; Hyoungsub Kim; Paul C. McIntyre; Tejas Krishnamohan; Krishna C. Saraswat

2003-01-01

287

Dielectric response of sputtered transition metal oxides  

NASA Astrophysics Data System (ADS)

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

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

2004-06-01

288

Structure analysis of the system Hafnium\\/Silicon ( 1 0 0 ) by means of X-ray photoelectron spectroscopy and X-ray photoelectron diffraction (XPD)  

Microsoft Academic Search

Due to the ongoing miniaturization of semiconductor devices new gate dielectrics are required for future applications. In this work we investigated hafnium silicide as a pre-system for hafnium oxide, one of the most promising candidates. One of the major problems of HfO2-films on silicon is the formation of hafnium silicide at the HfO2\\/Si interface. Therefore, ultrathin films of the system

C. R. Flüchter; A. de Siervo; D. Weier; M. Schürmann; U. Berges; S. Dreiner; M. F. Carazzolle; R. Landers; G. G. Kleiman; C. Westphal

2006-01-01

289

The effect of sub-1000°C source\\/drain anneal temperature on transistor in conventional SiO2 integration and high-k dielectric integration  

Microsoft Academic Search

The effect of a sub-1000°C source\\/drain anneal on electrical characteristics of transistors with SiO2 and HfO2 gate dielectric was investigated. In the case of lower temperature anneal for the conventional SiO2 transistors, implantation-related defects in the source\\/drain junctions lead to an increase of the off-state current, while gate electrode depletion effect and series resistance degrade transistor performance. For NMOS devices,

Jae Eun Lim; Yudong Kim; Kenneth Torres; Gennadi Bersuker; George Brown; Joe Bennett; Brendan Foran; Larry Larson

2002-01-01

290

Study of electrical and micro-structural properties of nano-scale ultra thin gate dielectric stacks in a MOS Device using Pulse Laser Deposition technique  

Microsoft Academic Search

The electrical properties of La2O3\\\\HfO2 gate dielectric stacks as a MOS structure deposited using Pulse Laser Deposition technique under optimized pressure, substrate temperature and numbers of shots in oxygen ambient gas were investigated. The film thickness and microstructure is examined using Ellipsometer, AFM to see the effect of operating pressure, number of PLD shots and substrate temperature on the film.

A. Srivastava; R. K. Nahar; V. Gupta; C K Sarkar

2011-01-01

291

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

292

Ultrathin harmonic generators  

SciTech Connect

In second-harmonic generation in optical materials with extremely large nonlinearity (about 1,000 that in KDP), efficient conversion may be expected for gain lengths of just a few micrometers. If the gain length is less than the coherence length, the phase-matching condition normally invoked for KDP and other common nonlinear materials may not apply. Devices based on such ultrathin media are potentially insensitive to wavelength, bandwidth, temperature, and poor beam quality. The authors have analyzed harmonic generation in ultrathin media to evaluate their materials requirements. They show that in such devices the conversion efficiency to the second harmonic is necessarily limited to about 25%, because higher harmonics are also necessarily generated with significant efficiencies. Ultrathin devices are therefore subject to large thermal loads, and perhaps optical damage arising from the generation of strong ultraviolet or soft X-ray harmonics. Whereas ultrathin media are not as efficient as conventional phase-matched crystals for second-harmonic generation, they do generate phase-coherent, multiple higher harmonics. As a consequence, they can generate optical square waves electromagnetic shock waves, and may find application as coherent soft X-ray generators.

Eimerl, D. (Lawrence Livermore National Lab., CA (United States). Nonlinear Optical Materials Group)

1991-09-01

293

Surface Control of Bottom Electrode in Ultra-Thin SiN Metal-Insulator-Metal Decoupling Capacitors for High Speed Processors  

Microsoft Academic Search

Highly reliable metal-insulator-metal (MIM) capacitor with ultra-thin SiN dielectrics is developed on the surface-controlled bottom electrode in nanometer-scales. Coverage of the TiN bottom electrode with a Ta thin layer achieves smooth surface. In addition, this electrode structure exhibits excellent etching controllability even for the MIM with the ultra-thin SiN dielectrics. The smooth surface of the Ta\\/TiN stacked electrode improves the

Naoya Inoue; Ippei Kume; Jun Kawahara; Shinobu Saito; Naoya Furutake; Takeshi Toda; Koichiro Matsui; Takayuki Iwaki; Masayuki Furumiya; Toshiki Shinmura; Koichi Ohto; Yoshihiro Hayashi

2007-01-01

294

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

295

Growth of highly oriented HfO2 thin films of monoclinic phase on yttrium-stabilized ZrO2 and Si substrates by pulsed-laser deposition  

NASA Astrophysics Data System (ADS)

We report on the growth of highly oriented HfO2 thin films of monoclinic phase stabilized by 5% Co doping on (001) yttrium-stabilized zirconia (YSZ) using pulsed-laser deposition at 700 °C at an oxygen partial pressure of 10-4 Torr. On the other hand, pure HfO2 of such quality did not grow on YSZ in wide range of growth parameters. Rutherford backscattering-ion channeling in this film showed a 24% minimum yield (?min) indicating highly oriented film growth, while hardly any ion channeling was observed in the undoped sample. High-resolution transmission electron microscopy revealed a sharp interface, and no signature of Co clusters. Electron energy loss spectroscopy showed that Co is in the 2+ state. Attempts were also made to grow films on a (001) Si substrate, and the results showed a very low ion channeling yield (~8%).

Dhar, S.; Ramachandra Rao, M. S.; Ogale, S. B.; Kundaliya, Darshan C.; Shinde, S. R.; Venkatesan, T.; Welz, S. J.; Erni, R.; Browning, N. D.

2005-12-01

296

Atomic layer deposition of HfO 2: Effect of structure development on growth rate, morphology and optical properties of thin films  

NASA Astrophysics Data System (ADS)

HfO 2 films were grown by atomic layer deposition from HfCl 4 and H 2O on Si(1 0 0), Si(1 1 1) and amorphous SiO 2 substrates at 180-750 °C and the effect of deposition temperature and film thickness on the growth rate and optical properties of the film material was studied. Crystallization, texture development and surface roughening were demonstrated to result in a noticeable growth rate increase with increasing film thickness. Highest surface roughness values were determined for the films deposited at 350-450 °C on all substrates used. The density of the film material increased with the concentration of crystalline phase but, within experimental uncertainty, was independent of orientation and sizes of crystallites in polycrystalline films. Refractive index increased with the material density. In addition, the refractive index values that were calculated from the transmission spectra depended on the surface roughness and crystallite sizes because the light scattering, which directly influenced the extinction coefficient, caused also a decrease of the refractive index determined in this way.

Rammula, Raul; Aarik, Jaan; Mändar, Hugo; Ritslaid, Peeter; Sammelselg, Väino

2010-11-01

297

Comparative Analysis of Bandgap-Engineered Pillar Type Flash Memory with HfO2 and S3N4 as Trapping Layer  

NASA Astrophysics Data System (ADS)

In this paper, we fabricated a gate-all-around bandgap- engineered (BE) silicon-oxide-nitride-oxide-silicon (SONOS) and silicon-oxide-high-k-oxide-silicon (SOHOS) flash memory device with a vertical silicon pillar type structure for a potential solution to scaling down. Silicon nitride (Si3N4) and hafnium oxide (HfO2) were used as trapping layers in the SONOS and SOHOS devices, respectively. The BE-SOHOS device has better electrical characteristics such as a lower threshold voltage (VTH) of 0.16V, a higher gm.max of 0.593µA/V and on/off current ratio of 5.76×108, than the BE-SONOS device. The memory characteristics of the BE-SONOS device, such as program/erase speed (P/E speed), endurance, and data retention, were compared with those of the BE-SOHOS device. The measured data show that the BE-SONOS device has good memory characteristics, such as program speed and data retention. Compared with the BE-SONOS device, the erase speed is enhanced about five times in BE-SOHOS, while the program speed and data retention characteristic are slightly worse, which can be explained via the many interface traps between the trapping layer and the tunneling oxide.

Lee, Sang-Youl; Yang, Seung-Dong; Oh, Jae-Sub; Yun, Ho-Jin; Jeong, Kwang-Seok; Kim, Yu-Mi; Lee, Hi-Deok; Lee, Ga-Won

298

Interface studies of high dielectric constant gate stack material  

NASA Astrophysics Data System (ADS)

To extend the minimum feature size beyond the 100 nm node in Ultra-Large Scale Integration, a suitable replacement must be found for silicon dioxide in the gate region of field effect transistors (FET). To reduce the power consumption, the silicon dioxide thickness is typically reduced to decrease the threshold voltage (VT) of the FET. The current thickness of silicon dioxide in production is about 2 nm, but any further reduction in thickness would increase the operating current exponentially due to quantum mechanical tunneling. The solution is to replace the silicon dioxide with a dielectric that has a significantly larger dielectric constant. This would allow a thicker gate dielectric to reduce current and threshold voltage at the same time, since VT is inversely proportional to dielectric constant. Several possible replacements have been identified that form a thermodynamically stable interface with silicon dioxide, the most promising of which are zirconium dioxide (ZrO2) and hafnium dioxide (HfO2). However, the dynamics of the interfacial layer formed with silicon are not very well understood. This dissertation describes the study of the interface using electron diffraction tools, including identification of ultra-clean silicon preparation, deposition of hafnium dioxide using reactive electron beam evaporation, and the subsequent electrical characterization. Also included are the design and implementation of an ultra-high vacuum deposition system with in situ observation of the surface using electron diffraction and the electrical characterization of HfO2 deposited in this chamber, as well as the characterization of subsequent films deposited in ultra-high vacuum.

Harris, Harlan Rusty

299

Effects of CF4 Plasma Treatment on pH and pNa Sensing Properties of Light-Addressable Potentiometric Sensor with a 2-nm-Thick Sensitive HfO2 Layer Grown by Atomic Layer Deposition  

Microsoft Academic Search

We investigated the effect of the carbon tetrafluoride (CF4) plasma treatment on pH and pNa sensing characteristics of a light-addressable potentiometric sensor (LAPS) with a 2-nm-thick HfO2 film grown by atomic layer deposition (ALD). An inorganic CF4 plasma treatment with different times was performed using plasma enhance chemical vapor deposition (PECVD). For pH detection, the pH sensitivity slightly decreased with

Chi-Hang Chin; Tseng-Fu Lu; Jer-Chyi Wang; Jung-Hsiang Yang; Cheng-En Lue; Chia-Ming Yang; Sheng-Shian Li; Chao-Sung Lai

2011-01-01

300

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

NASA Astrophysics Data System (ADS)

As the MOS devices continue to scale down in feature size, the gate oxide thickness is approaching the nanometer node. High leakage current densities caused by tunneling is becoming a serious problem. Replacing silicon oxide with a high kappa material as the gate dielectrics is becoming very critical. In recent years, research has been focused on a few promising candidates, such as ZrO2, HfO2, Al2O3, Ta 2O5, and some silicates. However, unary metal oxides tend to crystallize at relatively low temperatures (less than 700°C). Crystallized films usually have a very small grain size and high leakage current due to the grain boundaries. The alternatives are high kappa oxides which are single crystal or amorphous. Silicates remain amorphous at high temperatures, but have some problems such as phase separation, interface reaction, and lower kappa value. In this work, we addressed the crystallization problems of zirconium oxide and hafnium oxide thin films. Both of these two thin films were deposited by DC reactive magnetron sputtering so that very dense films were deposited with little damage. A specially designed system was set up in order to have good control of the deposition process. The crystallization behavior of as-deposited amorphous ZrO2 and HfO2 films was studied. It was found that the films tended to have higher crystallization temperature when the films were thinner than a critical thickness of approximately 5 nm. However, it was still well below 900°C. The crystallization temperature was significantly increased by sandwiching the high kappa oxide layer between two silica layers. Ultra thin HfO2 films of 5nm thickness remained amorphous up to 900°C. This is the highest crystallization temperature which has been reported. The mechanisms for this effect are proposed. Electrical properties of these high kappa dielectric films were also studied. It was found that ultra thin amorphous HfO2 and ZrO 2 films had superior electrical properties to crystalline films. The leakage current density of ultra thin amorphous films was at least two orders of magnitude lower than that of crystallized films. Amorphous films also showed much less hysteresis in the capacitance-voltage curve than uncapped crystallized films. The mechanisms for the electrical property differences between ultra thin crystalline and amorphous films were studied. Due to successful control of the low dielectric interfacial layer thickness, an effective oxide thickness of 1.2 and 1.4 nm was obtained for HfO2 and ZrO2 films, respectively.

Gao, Yong

301

Metal-gate/high-k dielectric stack engineering by atomic layer deposition: Materials issues and electrical properties  

NASA Astrophysics Data System (ADS)

Scaling of silicon devices beyond the 65nm node requires the replacement of poly-Si/SiO2 gate stack with a metal gate/high-k dielectric stack that can potentially reduce the off-state leakage current without compromising device performance. In this study, we have evaluated HfO2 as the gate dielectric material and TaN as the metal gate electrode deposited using the Atomic Layer Deposition (ALD) technique. ALD provides us with the unique capability of growing high quality thin films with excellent control over the film thickness, stoichiometry and conformality. Nanoscale HfO2 films were deposited by ALD on Si substrates using two different precursor chemistries---HfCl4 and Tetrakis (Diethylamido) Hafnium (TDEAH) with H2O as the oxidant. A systematic study of the physical and electrical properties of the HfO2 films derived using the two different chemistries revealed that the magnitude and sign of the fixed charge in the dielectric varied depending on the precursor used for the deposition. Our results indicate that Cl impurities, left behind by the HfCl4 precursor during deposition, significantly impact the electrical properties of the chloride-HfO 2. Tantalum nitride thin films were deposited by a remote plasma-enhanced ALD (PEALD) method using a novel metal organic precursor---isopropylimino tris(ethylmethylamino) tantalum (IPTEMT). It was identified that the as-deposited tantalum nitride film was the dielectric Ta3N5 phase. High temperature in-situ anneals performed in the TEM column crystallized the ALD tantalum nitride film at 850°C into the stoichiometric cubic TaN phase. The phase transformation from dielectric Ta3N5 to metallic TaN is achieved by out-diffusion of excess nitrogen atoms from the Ta3N5 film during the high temperature anneal. TaN was evaluated as a potential gate electrode material both on SiO2 and HfO2 gate dielectrics. The impact of high temperature anneals on the mobility of hydroxyl and oxygen impurities in the stack and its effect on the thickness of the interfacial layer was studied in detail. A novel low temperature process was identified to engineer the TaN/HfO2 gate stack using a reactive titanium metal overlayer to getter the excess nitrogen from Ta3N5.

Sreenivasan, Raghavasimhan

302

Structure, phase transformations, and defects of HfO2 and ZrO2 nanoparticles studied by Ta181 and Cd111 perturbed angular correlations, H1 magic-angle spinning NMR, XPS, and x-ray and electron diffraction  

Microsoft Academic Search

Structure, phase transformations, grain growth, and defects of bare and alumina-coated nanoparticles of HfO2 and ZrO2 synthesized in a microwave-plasma process have been investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM), and perturbed angular correlation (PAC) spectroscopy. The PAC technique was used to measure the electric quadrupole interactions (QIs) of the nuclear probes Ta181 and Cd111 in nanocrystalline HfO2

M. Forker; P. de La Presa; W. Hoffbauer; S. Schlabach; M. Bruns; D. V. Szabó

2008-01-01

303

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/cm2at-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

304

Growth and structure control of HfO2-x films with cubic and tetragonal structures obtained by ion beam assisted deposition  

NASA Astrophysics Data System (ADS)

Hafnium oxide films were grown by ion beam assisted deposition on water-cooled Si (100) substrates, under conditions of oxygen starvation, using hafnium vapor and an oxygen ion beam. The transport ratio (TR), i.e., the ratio between the arrival rate of hafnium to that of oxygen, was varied between 0.5 and 10, and ion energy was varied between 1 and 20 keV. The films were analyzed using x-ray diffraction and x-ray photoelectron spectroscopy. Films having the CaF2 cubic structure with a lattice parameter of about 0.512 nm were repeatedly obtained. In addition, at 20 keV ion energy and TR values of 4 and above, films with a tetragonal structure were obtained. The latter structure, believed to be a distortion of the cubic structure, has a c/a ratio of 1.01 and its space group is considered to be different from the high temperature tetragonal HfO2 structure. The new tetragonal structure also presents high Knoop hardness, with values between 15 and 25 GPa. Substrate rotation speed was found to affect the structure and the orientation of the films. All films exhibit a stoichiometry in the vicinity of HfO1.6, with the tetragonal films apparently being Hf2O3. These structures are attributed to a very fast cooling rate during film formation. Films deposited without substrate water cooling, or with substrate heating up to 500 °C contain a large component of the monoclinic phase. The new cubic and tetragonal structures are stable at room temperature and upon annealing up to 450 °C in vacuum, but convert to the monoclinic structure upon annealing at 500 °C in air, indicating that their low oxygen content is a key factor for their stability.

Manory, Rafael R.; Mori, Takanori; Shimizu, Ippei; Miyake, Shoji; Kimmel, Giora

2002-03-01

305

Multifunctional role of rare earth doping in optical materials: nonaqueous sol-gel synthesis of stabilized cubic HfO2 luminescent nanoparticles.  

PubMed

In this work a strategy for the control of structure and optical properties of inorganic luminescent oxide-based nanoparticles is presented. The nonaqueous sol-gel route is found to be suitable for the synthesis of hafnia nanoparticles and their doping with rare earths (RE) ions, which gives rise to their luminescence either under UV and X-ray irradiation. Moreover, we have revealed the capability of the technique to achieve the low-temperature stabilization of the cubic phase through the effective incorporation of trivalent RE ions into the crystal lattice. Particular attention has been paid to doping with europium, causing a red luminescence, and with lutetium. Structure and morphology characterization by XRD, TEM/SEM, elemental analysis, and Raman/IR vibrational spectroscopies have confirmed the occurrence of the HfO2 cubic polymorph for dopant concentrations exceeding a threshold value of nominal 5 mol %, for either Lu(3+) or Eu(3+). The optical properties of the nanopowders were investigated by room temperature radio- and photoluminescence experiments. Specific features of Eu(3+) luminescence sensitive to the local crystal field were employed for probing the lattice modifications at the atomic scale. Moreover, we detected an intrinsic blue emission, allowing for a luminescence color switch depending on excitation wavelength in the UV region. We also demonstrate the possibility of changing the emission spectrum by multiple RE doping in minor concentration, while deputing the cubic phase stabilization to a larger concentration of optically inactive Lu(3+) ions. The peculiar properties arising from the solvothermal nonaqueous synthesis here used are described through the comparison with thermally treated powders. PMID:23898781

Lauria, Alessandro; Villa, Irene; Fasoli, Mauro; Niederberger, Markus; Vedda, Anna

2013-08-09

306

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

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

307

Enhancement of absorption and color contrast in ultra-thin highly absorbing optical coatings  

NASA Astrophysics Data System (ADS)

Recently a new class of optical interference coatings was introduced which comprises ultra-thin, highly absorbing dielectric layers on metal substrates. We show that these lossy coatings can be augmented by an additional transparent subwavelength layer. We fabricated a sample comprising a gold substrate, an ultra-thin film of germanium with a thickness gradient, and several alumina films. The experimental reflectivity spectra showed that the additional alumina layer increases the color range that can be obtained, in agreement with calculations. More generally, this transparent layer can be used to enhance optical absorption, protect against erosion, or as a transparent electrode for optoelectronic devices.

Kats, Mikhail A.; Byrnes, Steven J.; Blanchard, Romain; Kolle, Mathias; Genevet, Patrice; Aizenberg, Joanna; Capasso, Federico

2013-09-01

308

Processing and reliability studies on hafnium oxide and hafnium silicate for the advanced gate dielectric application  

NASA Astrophysics Data System (ADS)

As the CMOS integrated circuits reduce to the 100-nanometer regime and beyond, the conventional SiO2 based gate dielectric is facing serious challenges such as high leakage current, impurity diffusion, and dielectric thickness uniformity control across a 300 mm wafer. Consequently, high-k materials, which have higher dielectric constants (k) than SiO2, are expected to replace it as the gate insulator. Amongst all the materials investigated, HfO2 and its silicate appear to be the most promising candidates since they have thermodynamic stability in contact with silicon, reasonable energy bandgap (>5eV), moderate dielectric constant and good thermal expansion matching with Si. In this Ph.D. work, the issues with HfO2 and potential solutions to these problems are discussed. Since scaling of Hf-based high-k dielectrics has been limited due to the interfacial layer formation, NH3 surface nitridation has been investigated to reduce EOT and to improve reliability. Surface nitridation achieved a minimum EOT of 7.1A, better thermal stability and higher breakdown field compared to a sample without surface nitridation. However, the surface nitridation exhibited adverse effects such as high hysteresis, lower interface quality and reduced carrier mobility. High-temperature forming gas (FG) prior to metallization successfully enhanced the carrier mobility of HfO2 gate dielectric MOSFETs with TaN gate electrode by improving HfO2/Si interface quality. Although improvement by high-temperature FG anneal was achieved, hydrogen atoms introduced by forming gas anneal can lead to unavoidable side effects such as poor NBTI and hot carrier degradation. Therefore, an attempt to reduce this degradation by using heavier deuterium atoms was executed. In addition to improved carrier mobility, improved reliability was also observed. Finally, the reliability issues of MOSFETs with hafnium silicate have been researched. A significant charge detrapping has been observed when the constant stress bias was removed. The rates of detrapping depend on the stress bias and time. Considering the fact that the real circuit operates at high frequency and low duty cycle, the reliability of high-k dielectric evaluated using conventional DC stress tests are excessively pessimistic to predict the long-term reliability of high-k gate dielectric. Polarity dependence of bias stress induced degradation was observed on the nMOSFET with HfSiON gate dielectric. Negative bias stress resulted in more significant increase of interface states and, accordingly, degradation of subthreshold swing than positive stress. It is suggested that the drain to gate stress on nMOSFET can damage the area of the high-k gate dielectric near the drain, resulting in asymmetric subthreshold swing degradation. Since this effect is more prominent in short channel MOSFETs, drain to gate stress during the off-state may play a greater role in the scaled devices.

Choi, Rino

309

A novel flash-ion-sensitive field-effect transistor (FISFET) with HfO2\\/Gd2O3(Gd) nano-crystal\\/SiO2 sensing membranes under super nernstian phenomenon for pH and urea detection  

Microsoft Academic Search

An enhanced hydrogen and urea biosensor based on a novel flash-ion-sensitive field-effect transistor (FISFET) with HfO2\\/Gd2O3(Gd) nano-crystal\\/SiO2 sensing membrane is demonstrated experimentally. The super Nernstian phenomenon of hydrogen detection (~80 mV\\/pH) is achieved according to the charge trapping effect. The performance of reliability including long-term stability and endurance are systematic studied. For urea detection, the higher sensitivity is obtained (~20

Tseng-Fu Lua; Jer-Chyi Wanga; Chao-Sung Laia; Chia-Ming Yanga; Min-Hsien Wu; Chuan-Pu Liu; Rong-Shie Huang; Yu-Ching Fang

2009-01-01

310

Tunneling Current through Ultrathin Silicon Dioxide Films under Light Exposure  

NASA Astrophysics Data System (ADS)

Tunneling current through ultrathin silicon dioxide films with a thickness of approximately 3.1 nm, formed on n-Si (100) by controlling preoxide growth during heating, is examined using Al/oxide/n-Si structures. Electron tunneling current through the oxide from n-Si to Al is decreased and the dielectric breakdown voltage is increased by the preoxide growth control. Electron tunneling current from Al to n-Si is increased by light exposure. The increase in electron tunneling current can be explained by the increase in oxide voltage with an inversion layer formed by photoexcitation.

Morita, Satoru; Shinozaki, Akihito; Morita, Yuuki; Nishimura, Kazuo; Okazaki, Tatsuya; Urabe, Shinichi; Morita, Mizuho

2004-11-01

311

Optical Transmission Through Multilayered Ultra-Thin Metal Gratings  

Microsoft Academic Search

Optical transmission properties of multilayered ultra-thin metal gratings are numerically studied. The transmission spectrum\\u000a has a broad stop-band with extremely low transmittance compared to that of a single-layer one for TM polarization. The stop-band\\u000a is shown to be formed by multiple-interference tunneling and various plasmon resonance processes in ultra-thin-metal and dielectric\\u000a multilayers. That is on the transmission background of non-apertured

Zhijun Sun; Xiaoliu Zuo; Jie Li

312

Acceptor deactivation in individual silicon nanowires: From thick to ultrathin  

NASA Astrophysics Data System (ADS)

We investigate the doping behavior in the ultrathin part of individual free standing spicular or conic silicon nanowires (NWs) by measuring the local resistivity of the NWs using scanning spreading resistance microscopy. The NWs are boron-doped and the doping efficiency is found to dramatically decrease as the NW diameter is below 25 nm. Our experimental results reveal the dependence of the acceptor deactivation on the diameter of the NW cross section. The deactivation mechanism is discussed by comparing the experimental data with theoretical models considering the dopant deactivation induced by carrier traps at the Si/SiO2 interface and due to the dielectric mismatch.

Ou, Xin; Geyer, Nadine; Kögler, Reinhard; Werner, Peter; Skorupa, Wolfgang

2011-06-01

313

Tunable magnetic properties in ultrathin Co/garnet heterostructures  

NASA Astrophysics Data System (ADS)

We demonstrate how the magnetic properties of metal/dielectric Co/yttrium iron garnet heterostructures can be engineered by both changing the garnet thickness and adding an ultrathin Co cover layer. The observed magnetization reversal process in the heterostructures is explained by both cubic and perpendicular growth-induced magnetic anisotropy of the garnet films. In particular, the perpendicular magnetic anisotropy can be strongly increased for reduced thickness. A strong influence of a 2 nm Co layer on the domain structure geometry and magnetization processes has been found for 1.8 µm garnet films.

Pashkevich, M.; Stupakiewicz, A.; Kirilyuk, A.; Maziewski, A.; Stognij, A.; Novitskii, N.; Kimel, A.; Rasing, Th.

2012-01-01

314

Double-well model of dielectric relaxation current  

NASA Astrophysics Data System (ADS)

We show that a straightforward account of dielectric relaxation current in glasses follows from a semiclassical treatment of the double-well model [P. W. Anderson, B. I. Halperin, and C. M. Varma, Philos. Mag. 25, 1 (1972) and W. A. Phillips, J. Low Temp. Phys. 7, 351 (1972)] explaining the linear specific heat of glasses at low temperature. The current is obtained from the field-induced tunneling of the glass between the minima of its potential energy surface, and is found to have the experimentally observed linear dependence on field and inverse dependence on time. The effects of temperature and prior biases are briefly discussed, as well as the relation of the model to the theory of charge trapping. No dielectric relaxation is expected in a perfect insulating crystal, raising the important technological question of how perfect high-k dielectrics like HfO2 and ZrO2 must be in order to serve as gate dielectrics in transistors.

Jameson, John R.; Harrison, Walter; Griffin, P. B.; Plummer, J. D.

2004-05-01

315

Conformal surface plasmons propagating on ultrathin and flexible films.  

PubMed

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

2012-12-17

316

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

317

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

318

High-performance CdS:P nanoribbon field-effect transistors constructed with high-kappa dielectric and top-gate geometry  

Microsoft Academic Search

High-performance field-effect transistors (FETs) based on single phosphorus-doped n-type CdS nanoribbon with high-kappa HfO2 dielectric and top-gate geometry were constructed. In contrast to the nano-FETs that were fabricated on SiO2\\/Si substrate with back-gate device configuration, the top-gate FETs exhibit a substantial improvement in performances, i.e., work voltage was reduced to a small value of within +\\/-5 V, the subthreshold swing

Di Wu; Yang Jiang; Li Wang; Shanying Li; Bo Wu; Xinzheng Lan; Yongqiang Yu; Chunyan Wu; Zhuangbing Wang; Jiansheng Jie

2010-01-01

319

Ultra-thin films and multigate devices architectures for future CMOS scaling  

Microsoft Academic Search

The nanoelectronics industry is facing historical challenges to scale down CMOS devices to meet demands for low voltage, low\\u000a power, high performance and increased functionality. Using new materials and devices architectures is necessary. HiK gate\\u000a dielectrics and metal gates have been introduced and have shown their ability to reduce power consumption. Fully depleted\\u000a ultra-thin SOI devices are a good alternative

Simon Deleonibus

2011-01-01

320

Trapping of hydrogen in hafnium-based high kappa dielectric thin films for advanced CMOS applications  

NASA Astrophysics Data System (ADS)

In recent years, advanced high kappa gate dielectrics are under serious consideration to replace SiO2 and SiON in semiconductor industry. Hafnium-based dielectrics such as hafnium oxides, oxynitrides and Hf-based silicates/nitrided silicates are emerging as some of the most promising alternatives to SiO2/SiON gate dielectrics in complementary metal oxide semiconductor (CMOS) devices. Extensive efforts have been taken to understand the effects of hydrogen impurities in semiconductors and its behavior such as incorporation, diffusion, trapping and release with the aim of controlling and using it to optimize the performance of electronic device structures. In this dissertation, a systematic study of hydrogen trapping and the role of carbon impurities in various alternate gate dielectric candidates, HfO2/Si, HfxSi1-xO2/Si, HfON/Si and HfON(C)/Si is presented. It has been shown that processing of high kappa dielectrics may lead to some crystallization issues. Rutherford backscattering spectroscopy (RBS) for measuring oxygen deficiencies, elastic recoil detection analysis (ERDA) for quantifying hydrogen and nuclear reaction analysis (NRA) for quantifying carbon, X-ray diffraction (XRD) for measuring degree of crystallinity and X-ray photoelectron spectroscopy (XPS) were used to characterize these thin dielectric materials. ERDA data are used to characterize the evolution of hydrogen during annealing in hydrogen ambient in combination with preprocessing in oxygen and nitrogen.

Ukirde, Vaishali

321

Textured crystallization of ultrathin hafnium oxide films on silicon substrate  

NASA Astrophysics Data System (ADS)

The effects of rapid thermal annealing are reported here on the structure of 2 nm thick hafnium oxide films grown on silicon (100) substrates. The films grown by atomic layer deposition have a 1 nm SiO2 transition layer between silicon and the HfO2 layer. The amorphous structure of the as-deposited films is retained after annealing at 600 °C. The HfO2 films crystallized into an orthorhombic phase with an out-of-plane texture after annealing at 800 °C or higher. In contrast, films grown on thick amorphous SiO2 substrates crystallize without any texture. The authors attribute the texture of HfO2 on Si (100) to the role of interfacial SiO2 transition layer.

Bohra, Fakhruddin; Jiang, Bin; Zuo, Jian-Min

2007-04-01

322

Ultra-thin Multilayer Capacitors.  

National Technical Information Service (NTIS)

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 Laborat...

T. C. Monson T. J. Renk

2009-01-01

323

Immunochemistry on ultrathin frozen sections  

Microsoft Academic Search

Summary  Ultrathin frozen sections can be cut smoothly from many fixed and appropriately treated specimens. To use such sections for immunochemical localization of intracellular antigens, fixa ion conditions must be selected to optimize at least three variables, namely, preservation of ultrastructure, preservation of antigenicity and retention of accessibility of the antigen to the antibody. Furthermore, staining of the sections must be

K. T. Tokuyasu

1980-01-01

324

Engineering high dielectric constant materials on silicon carbide  

NASA Astrophysics Data System (ADS)

The high dielectric constant (high-kappa) materials of hafnium oxide (HfO2) and aluminum oxide (Al2O3) were grown by atomic layer deposition (ALD) and investigated for integration as gate dielectrics in silicon carbide (SiC) power metal-oxide-semiconductor field-effect transistors (MOSFETs). Smooth HfO2 films were grown on 4H-SiC at temperatures of 200-300°C at a deposition rate of 1-2 A/cycle. A temperature-dependent phase transition from amorphous layer-by-layer growth to polycrystalline three-dimensional island growth was observed by in-situ reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). No interfacial layer formation was observed by in-situ X-ray photoelectron spectroscopy (XPS) and an abrupt interface was confirmed by high-resolution transmission electron microscopy (HRTEM). An asymmetric band alignment at the HfO2/4H-SiC interface was determined by XPS and supported by density functional theory calculations. As a result, a high leakage current density of 10-3 A/cm2 at 3 MV/cm was observed in MOS capacitors. Al2O3 was studied due to its larger bandgap and potential to form a crystalline oxide film. Epitaxial gamma-Al2O 3 thin films were engineered by post-deposition rapid thermal annealing of amorphous Al2O3 films grown by ALD. An epitaxial relationship of gamma-Al2O3 (111) || 4H-SiC (0001) and gamma-Al2O3 (44¯0) || 4H-SiC (112¯0) was determined by selected area electron diffraction and synchrotron X-ray scattering. An abrupt crystalline interface was observed by HRTEM in films up to 200 A thick. The in-plane alignment between the film and the substrate was nearly complete for gamma-Al2O3 films up to 115 A in thickness, but quickly diminished in thicker films. Mixed amorphous and polycrystalline regions were observed in Al2O3 films thicker than 225 A, and negligible crystallization was observed in films thicker than 500 A. Twinning around the [111] axis was observed in all of the films. Larger barrier heights were determined for the Al2O 3/4H-SiC interface compared to the HfO2/4H-SiC interface and as a result, low leakage current of 10-3 A/cm2 was measured for amorphous Al2O3 films up to an electric field of 8 MV/cm. This state-of-the-art electric field strength is promising for the integration of these materials in SiC power MOSFETs. However, higher leakage current was measured for crystalline Al2O3 films due to conduction along the twin boundaries. Further work is proposed to optimize the quality of the epitaxial Al2O3 films for these applications.

Tanner, Carey Marie

325

Remote phonon and impurity screening effect of substrate and gate dielectric on electron dynamics in single layer MoS2  

NASA Astrophysics Data System (ADS)

The effect of both remote phonon originating from and the screening of extrinsic charged impurity by substrate and gate dielectric on the electron dynamics of single layer MoS2 are investigated with Monte Carlo method. The temperature-dependent mobility curve measured by Hall effect is reproduced by taking the two counter roles played by substrate and gate dielectric into consideration. Based on the analysis of remote phonon effect and charged impurity screening, an optimized transistor structure which is composed of single HfO2 gate dielectric with interfacial layer and absence of SiO2 substrate is proposed for the realization of mobility approaching intrinsic value and best device performance.

Zeng, Lang; Xin, Zheng; Chen, Shaowen; Du, Gang; Kang, Jinfeng; Liu, Xiaoyan

2013-09-01

326

Electrical characteristics of high quality La2O3 gate dielectric with equivalent oxide thickness of 5 Å  

Microsoft Academic Search

Electrical and reliability properties of ultrathin La2O 3 gate dielectric have been investigated. The measured capacitance of 33 Å La2O3 gate dielectric is 7.2 ?F\\/cm2 that gives an effective K value of 27 and an equivalent oxide thickness of 4.8 Å. Good dielectric integrity is evidenced from the low leakage current density of 0.06 A\\/cm2 at -1 V, high effective

Y. H. Wu; M. Y. Yang; Albert Chin; W. J. Chen; C. M. Kwei

2000-01-01

327

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

328

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

2011-09-30

329

Ultrathin Polymer Films, Patterned Arrays, and Microwells  

Microsoft Academic Search

The ability to control and tailor the surface and interface properties of materials is important in microelectronics, cell growth control, and lab-on-a-chip devices. Modification of material surfaces with ultrathin polymer films is attractive due to the availability of a variety of polymers either commercially or by synthesis. We have developed two approaches to the attachment of ultrathin polymer films on

Mingdi Yan

2002-01-01

330

Ferroelectric Properties of Ultrathin Perovskite Heterostructures.  

NASA Astrophysics Data System (ADS)

Due to their switchable spontaneous polarization, ferroelectric thin films can be used in non-volatile ferroelectric random access memories (FeRAMs). Recently, 30 Gbit/cm^2 data storage densities have been demonstrated for Pb(Zr_0.2Ti_0.8)O3 films on a metallic oxide electrode (T. Tybell et al.), Phys. Rev. Lett. 89, 097601 (2002). While industry's demands for ultrahigh density information storage imposes a reduction of the cell-sizes and thicknesses of the ferroelectric thin films, fundamental questions concerning thickness dependence of ferroelectricity and related properties becomes crucial. Using a first-principles density-functional-theory approach (J. M. Soler et al.), J. Phys.: Condens. Matter 14, 2745 (2002) we have simulated the behaviour at 0 K of a typical ferroelectric capacitor epitaxially grown on a SrTiO3 substrate and made of an ultrathin film of BaTiO3 in between two SrRuO3 electrodes in short circuit (J. Junquera and Ph. Ghosez, Nature 422), 506 (2003). Both the electrical and the mechanical boundary conditions were properly considered in the calculations. We predict the existence of a critical thickness for ferroelectricity of about six unit cells (26 Ang), and relate it to an incomplete screening of the depolarizing field by real metallic electrodes. Transposing these ideas into a first-principles-based model Hamiltonian, (U. V. Waghmare and K. M. Rabe, Phys. Rev. B 55), 6161 (1997) and using Monte Carlo simulations, we have analyzed the temperature dependence of the thickness evolution of the polarization and tetragonality of the samples, as well as the piezoelectric and dielectric tensors. Our theoretical results show good agreement with very recent experimental measurements.

Junquera, Javier

2004-03-01

331

Dielectric relaxation of 4-cyano-4- n-pentylbiphenyl (5CB) thin layer adsorbed on carbon nanotube – MD simulation  

Microsoft Academic Search

The ultra-thin layer of mesogenous molecules 5CB adsorbed on a single walled carbon nanotube (SWNT) has been studied by molecular dynamics (MD) simulation method. The focus was on the temperature dependence (200Kdielectric loss of ultra-thin mesogene layer covering carbon nanotube has been also studied.

A. Dawid; Z. Gburski

2007-01-01

332

Characterization of defect evolution in ultrathin SiO2 layers under applied electrical stress  

NASA Astrophysics Data System (ADS)

The structural evolution of ultrathin dielectric SiO2 layers within a Co-silicide/poly-Si/SiO2/Si multilayer system was studied by in situ transmission electron microscopy (TEM). The interface structure represents a model system for field effect transistors with a SiO2 dielectric layer. Electrical bias was applied across the interfaces of cross sectional TEM samples using a scanning tunneling microscopy (STM) tip. Atomic structure modifications of the dielectric layer due to the applied electrical field were observed by this in situ STM-TEM technique. Constant bias (+5.0 V) and ramped bias (+3.0 to +10.5 V) stresses applied to the CoSi2 gate electrode resulted in a loss in capacitance of the dielectric layer consistent with descriptions of soft dielectric breakdown (SBD) and hard dielectric breakdown (HBD). It was found that SBD events are characterized by fluctuations within uniform current step increase of 21 nA and increased roughness of the SiO2 film due to oxygen vacancy percolation. HBD, however, was found to be preceded by multiple SBD events between +6.5 V and +10 V, cobalt atom migration into the dielectric layer, partial crystallization of the amorphous gate dielectric (dielectric breakdown induced epitaxy), and significant diffusion of oxygen from the SiO2 layer into the silicon substrate through a reduction-oxidation reaction of the Si/SiO2 interface. Experimental results demonstrate the feasibility of in situ STM-TEM experiments for studying time-dependent dielectric breakdown behaviors to obtain a direct correlation of individual defect structures and their corresponding electrical signatures. Experimental limitations of this new technique are critically discussed.

Bonifacio, Cecile S.; van Benthem, Klaus

2012-11-01

333

Ultrathin fiberscope for stereoscopic vision  

NASA Astrophysics Data System (ADS)

Endoscope for stereoscopic vision is in great demand for medical field to diagnose and treat disease parts of patients more precisely. The authors are convinced that the silica-based imagefiber is suitable for making a thinner fiberscope for stereoscopic vision and have developed an ultrathin fiberscope with silica-based imagefibers for stereoscopic vision. The diameter of fiberscope is only 2 mm with two transmitting systems that consist of two imagefibers with 10000 pixels and lightguide for illumination and objective lenses. This fiberscope for stereoscopic vision can be used for the microsurgery, such as the laparoscopic surgery and the thoracoscopic surgery required for the thin diameter.

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

1993-09-01

334

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

335

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

PubMed

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

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

2011-11-01

336

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

337

Ultrathin Si capping layer suppresses charge trapping in HfOxNy/Ge metal-insulator-semiconductor capacitors  

NASA Astrophysics Data System (ADS)

In this study the authors investigated the Ge outdiffusion characteristics of HfOxNy/Ge metal-insulator-semiconductor capacitors to determine their charge trapping behavior. Capping the Ge substrate with an ultrathin Si layer inhibits the incorporation of Ge into the high-k bulk dielectric in the form of GeOx, thereby diminishing the resultant oxide charge trapping. The thermal stability of the entire capacitor structure was also improved after performing an additional Si passivation process.

Cheng, Chao-Ching; Chien, Chao-Hsin; Luo, Guang-Li; Yang, Chun-Hui; Kuo, Mei-Ling; Lin, Je-Hung; Chang, Chun-Yen

2007-01-01

338

High temperature calorimetric studies of heat of solution of NiO, CuO, La 2O 3, TiO 2, HfO 2 in sodium silicate liquids  

NASA Astrophysics Data System (ADS)

The enthalpies of solution of La 2O 3, TiO 2, HfO 2, NiO and CuO were measured in sodium silicate melts at high temperature. When the heat of fusion was available, we derived the corresponding liquid-liquid enthalpies of mixing. These data, combined with previously published work, provide insight into the speciation reactions in sodium silicate melts. The heat of solution of La 2O 3 in these silicate solvents is strongly exothermic and varies little with La 2O 3 concentration. The variation of heat of solution with composition of the liquid reflects the ability of La(III) to perturb the transient silicate framework and compete with other cations for oxygen. The enthalpy of solution of TiO 2 is temperature-dependent and indicates that the formation of Na-O-Si species is favored over Na-O-Ti at low temperature. The speciation reactions can be interpreted in terms of recent spectroscopic studies of titanium-bearing melts which identify a dual role of Ti 4+ as both a network-former end network-modifier. The heats of solution of oxides of transition elements (Ni and Cu) are endothermic, concentration-dependent and reach a maximum with concentration. These indicate a charge balanced substitution which diminishes the network modifying role of Na + by addition of Ni 2+ or Cu 2+. The transition metal is believed to be in tetrahedral coordination, charge balanced by the sodium cation in the melts.

Linard, Yannick; Wilding, Martin C.; Navrotsky, Alexandra

2008-01-01

339

First-principles study of fission product (Xe, Cs, Sr) incorporation and segregation in alkaline earth metal oxides, HfO2, and the MgO-HfO2 interface  

NASA Astrophysics Data System (ADS)

In order to close the nuclear fuel cycle, advanced concepts for separating out fission products are necessary. One approach is to use a dispersion fuel form in which a fissile core is surrounded by an inert matrix that captures and immobilizes the fission products from the core. If this inert matrix can be easily separated from the fuel, via e.g. solution chemistry, the fission products can be separated from the fissile material. We examine a surrogate dispersion fuel composition, in which hafnia (HfO2) is a surrogate for the fissile core and alkaline earth metal oxides are used as the inert matrix. The questions of fission product incorporation in these oxides and possible segregation behavior at interfaces are considered. Density functional theory based calculations for fission product elements (Xe, Sr, and Cs) in these oxides are carried out. We find smaller incorporation energy in hafnia than in MgO for Cs and Sr, and Xe if variation of charge state is allowed. We also find that this trend is reversed or reduced for alkaline earth metal oxides with large cation sizes. Model interfacial calculations show a strong tendency of segregation from bulk MgO to MgO-HfO2 interfaces.

Liu, Xiang-Yang; Uberuaga, Blas P.; Sickafus, Kurt E.

2009-01-01

340

First-principles study of fission product (Xe, Cs, Sr) incorporation and segregation in alkaline earth metal oxides, HfO(2), and the MgO-HfO(2) interface.  

PubMed

In order to close the nuclear fuel cycle, advanced concepts for separating out fission products are necessary. One approach is to use a dispersion fuel form in which a fissile core is surrounded by an inert matrix that captures and immobilizes the fission products from the core. If this inert matrix can be easily separated from the fuel, via e.g. solution chemistry, the fission products can be separated from the fissile material. We examine a surrogate dispersion fuel composition, in which hafnia (HfO(2)) is a surrogate for the fissile core and alkaline earth metal oxides are used as the inert matrix. The questions of fission product incorporation in these oxides and possible segregation behavior at interfaces are considered. Density functional theory based calculations for fission product elements (Xe, Sr, and Cs) in these oxides are carried out. We find smaller incorporation energy in hafnia than in MgO for Cs and Sr, and Xe if variation of charge state is allowed. We also find that this trend is reversed or reduced for alkaline earth metal oxides with large cation sizes. Model interfacial calculations show a strong tendency of segregation from bulk MgO to MgO-HfO(2) interfaces. PMID:21715804

Liu, Xiang-Yang; Uberuaga, Blas P; Sickafus, Kurt E

2009-01-08

341

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

342

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

343

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

344

Fundamental studies on nano-scale zirconia dielectrics  

NASA Astrophysics Data System (ADS)

High-dielectric-constant metal-oxides are currently being investigated for application as gate dielectric materials to replace SiO2 in future complementary-metal-oxide-semiconductor devices. In particular, zirconia is considered to be a potential candidate owing to its high dielectric constant, relatively large conduction band offset with Si and predicted thermodynamic stability on silicon. It is hence important to develop processing science for growing ultra-thin (2--5 nm) dielectric films with good structural and electrical properties. We have developed a technique to grow ultra-thin metal oxide films by ultraviolet (UV)-ozone oxidation. In this method, a thin metal film (of Zr) deposited on passivated Si surfaces by UHV sputtering is oxidized in-situ by oxygen in presence of UV light. The oxidation kinetics of Zr and Al films has been studied by the method of nuclear reaction analysis. We have performed detailed transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) studies to characterize the dielectric films and their interfaces. Capacitor structures have been fabricated to study the electrical properties of the dielectric films grown on different surfaces and have been directly correlated to their electronic structure using EELS and x-ray absorption spectroscopy. It has been shown that partially-oxidized dielectrics show severe frequency dispersion in the capacitance-voltage characteristics and very high leakage currents while stoichiometric zirconia films do not. Electronic structure studies using both EELS and XAS have shown that oxygen-deficient zirconia dielectrics can be identified by investigation of the oxygen-K absorption near-edge fine structure. The frequency-dependence of the C-V curves has been explained by the Maxwell-Wagner-Sillars interfacial polarization mechanism. We have also studied the electrical properties of zirconia/SiO2 gate stacks grown in-situ by the UV-ozone method. Capacitors with an electrical thickness of ˜1.5 nm, with leakage current of only ˜1.8 x 10-4 A/cm2 at 1 V from flatband, and low hysteresis have been fabricated. Ultra-thin SiO 2 films grown by the UVO method appear to be promising templates for growth of the high-dielectric-constant dielectrics. It is shown that in order to grow gate stacks of good electrical quality, it is important to understand the oxidation kinetics.

Ramanathan, Shriram

345

Ultrathin fiberscope for stereoscopic vision  

NASA Astrophysics Data System (ADS)

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

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

1993-05-01

346

Anisotropic permittivity of ultra-thin crystalline Au films: Impacts on the plasmonic response of metasurfaces  

NASA Astrophysics Data System (ADS)

It has been determined by density functional theory (DFT) simulations that the extracted permittivities of ultra-thin crystalline gold (Au) films exhibit large anisotropies which are not predicted by classical models or previous experimental determinations of the dielectric function. The optical scattering characteristics of a periodic array of Au discs are simulated with the DFT extracted permittivity and contrasted against those obtained with several commonly used Au permittivity models. It is demonstrated that the DFT-based transmittance spectra for these plasmonic metasurfaces lead to significantly redshifted results when compared to those predicted by standard Drude and Johnson-Christy permittivity models.

Campbell, Sawyer D.; Ziolkowski, Richard W.; Cao, Jiangrong; Laref, Slimane; Muralidharan, Krishna; Deymier, Pierre

2013-08-01

347

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

348

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

2010-04-21

349

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

PubMed

The interactions of engineered nanomaterials with natural organic matter (NOM) exert a profound influence on the mobilities of the former in the environment. However, the influence of specific nanomaterial structural characteristics on the partitioning and colloidal stabilization of engineered nanomaterials in various ecological compartments remains underexplored. Herein, we present a systematic study of the interactions of humic acid (HA, as a model for NOM) with monodisperse, well-characterized, ligand-passivated HfO(2), ZrO(2), and solid-solution Hf(x)Zr(1-x)O(2) nanoparticles (NPs). We note that mixing with HA induces the almost complete phase transfer of hydrophobically coated monoclinic metal oxide (MO) NPs from hexane to water. Furthermore, HA is seen to impart appreciable colloidal stabilization to the NPs in the aqueous phase. In contrast, phase transfer and aqueous-phase colloidal stabilization has not been observed for tetragonal MO-NPs. A mechanistic model for the phase transfer and aqueous dispersal of MO-NPs is proposed on the basis of evidence from transmission electron microscopy, ?-potential measurements, dynamic light scattering, Raman and infrared spectroscopies, elemental analysis, and systematic experiments on a closely related set of MO-NPs with varying composition and crystal structure. The data indicate the synergistic role of over-coating (micellar), ligand substitution (coordinative), and electrostatic processes wherein HA acts both as an amphiphilic molecule and a charged chelating ligand. The strong observed preference for the phase transfer of monoclinic instead of tetragonal NPs indicates the importance of the preferential binding of HA to specific crystallographic facets and suggests the possibility of being able to design NPs to minimize their mobilities in the aquatic environment. PMID:21963173

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

2011-09-14

350

Effect of selected atomic layer deposition parameters on the structure and dielectric properties of hafnium oxide films  

NASA Astrophysics Data System (ADS)

HfO2 films were atomic layer deposited from HfCl4 and H2O on Si(100) in the temperature range of 226-750 °C. The films consisted of dominantly the monoclinic polymorph. Elastic recoil detection analysis revealed high residual chlorine and hydrogen contents (2-5 at. %) in the films grown below 300-350 °C. The content of residual hydrogen and chlorine monotonously decreased with increasing growth temperature. The effective permittivity insignificantly depended on the growth temperature and water partial pressure. Capacitance-voltage curves exhibited marked hysteresis especially in the films grown at 400-450 °C, and demonstrated enhanced distortions likely due to the increased trap densities in the films grown at 700-750 °C. Changes in water pressure led to some changes in the extent of crystallization, but did not induce any clear changes in the capacitance of the dielectric layer.

Kukli, Kaupo; Aarik, Jaan; Ritala, Mikko; Uustare, Teet; Sajavaara, Timo; Lu, Jun; Sundqvist, Jonas; Aidla, Aleks; Pung, Lembit; Ha?Rsta, Anders; Leskelä, Markku

2004-11-01

351

Simple method for the fabrication of a high dielectric constant metal-oxide-semiconductor capacitor embedded with Pt nanoparticles  

NASA Astrophysics Data System (ADS)

We present a simple method for the fabrication of Pt nanoparticles embedded in a high-k dielectric. The nanoparticles are formed during the first deposition stages of a thin Pt layer on a 30 A? SiO2 tunneling layer, at room temperature, performed with electron-beam (e-beam) evaporation of metallic Pt. Then, the nanoparticles are covered, in situ, by a thicker HfO2 layer, which forms a control oxide. The fabricated nanoparticles have an average diameter of 4.9 nm, sheet density of 3.2×1012 cm-2 and they present high uniformity in their size. High-frequency capacitance-voltage (C-V) measurements demonstrate that this structure operates as a memory device.

Sargentis, Ch.; Giannakopoulos, K.; Travlos, A.; Boukos, N.; Tsamakis, D.

2006-02-01

352

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

353

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

PubMed

Nanobiosensors based on silicon nanowire field effect transistors offer advantages of low cost, label-free detection, and potential for massive parallelization. As a result, these sensors have often been suggested as an attractive option for applications in point-of-care (POC) medical diagnostics. Unfortunately, a number of performance issues, such as gate leakage and current instability due to fluid contact, have prevented widespread adoption of the technology for routine use. High-k dielectrics, such as hafnium oxide (HfO(2)), have the known ability to address these challenges by passivating the exposed surfaces against destabilizing concerns of ion transport. With these fundamental stability issues addressed, a promising target for POC diagnostics and SiNWFETs has been small oligonucleotides, more specifically, microRNA (miRNA). MicroRNAs are small RNA oligonucleotides which bind to mRNAs, causing translational repression of proteins, gene silencing, and expressions are typically altered in several forms of cancer. In this paper, we describe a process for fabricating stable HfO(2) dielectric-based silicon nanowires for biosensing applications. Here we demonstrate sensing of single-stranded DNA analogues to their microRNA cousins using miR-10b and miR-21 as templates, both known to be upregulated in breast cancer. We characterize the effect of surface functionalization on device performance using the miR-10b DNA analogue as the target sequence and different molecular weight poly-l-lysine as the functionalization layer. By optimizing the surface functionalization and fabrication protocol, we were able to achieve <100 fM detection levels of the miR-10b DNA analogue, with a theoretical limit of detection of 1 fM. Moreover, the noncomplementary DNA target strand, based on miR-21, showed very little response, indicating a highly sensitive and highly selective biosensing platform. PMID:22695179

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

2012-06-22

354

Ion backscattering study of ultra-thin oxides: Al2O3 and AlHfOx films on Si  

NASA Astrophysics Data System (ADS)

Ultra-thin films of aluminum oxide and hafnium oxide are currently being explored as high-k gate dielectrics for next generation CMOS and related devices. Among the many methods to produce such films, atomic layer deposition (ALD) appears very promising as it enables deposition of ultra-thin layers on Si and other substrates with monolayer control. For device applications, it is critical to be able to measure and control the total oxide film thickness, as well as that of the SiO2 which often forms at the high-k/Si interface. In this work we show how Hf, O, Al and Si from ultra-thin oxides can be detected and separated from the Si substrate scattering spectrum. In order to separate the Si substrate signal from the amorphous ultra-thin oxide O, Al and Si signals, ion channeling is applied. While the separation of Al and Si signals from thin oxide layers in typical 2 MeV He RBS is difficult due to the small mass difference, we demonstrate that separating these signals is possible using higher energy scattering, 2.7 MeV. The effects of non-Rutherford scattering cross-sections, including the O(?, ?)O resonance at 3030 keV, will be discussed.

Wielunski, Leszek S.; Chabal, Yves; Paunescu, Margareta; Ho, M.-T.; Brewer, Rhett; Reyes, Johan E.

2005-12-01

355

Electrical properties of SiO 2\\/TiO 2 high- k gate dielectric stack  

Microsoft Academic Search

The trapping\\/detrapping behavior of charge carriers in ultrathin SiO2\\/TiO2 stacked gate dielectric during constant current (CCS) and voltage stressing (CVS) has been investigated. Titanium tetrakis iso-propoxides (TTIP) was used as the organometallic source for the deposition of ultra-thin TiO2 films at low temperature (<200°C) on strained-Si\\/relaxed-Si0.8Ge0.2 heterolayers by plasma-enhanced chemical vapor deposition (PECVD) in a microwave (700W, 2.45GHz) plasma cavity

M. K. Bera; C. K. Maiti

2006-01-01

356

Ultrathin, highly flexible and stretchable PLEDs  

NASA Astrophysics Data System (ADS)

We demonstrate ultrathin (2 µm thick) red and orange polymer light-emitting diodes with unprecedented mechanical properties in terms of their flexibility and ability to be stretched. The devices have a luminance greater than 100 cd m-2, sufficient for a variety of optoelectronic applications including indoor displays. They can be operated as free-standing ultrathin films, allowing for crumpling during device operation. Furthermore, they may be applied to almost any surface whether rigid or elastomeric, and can withstand the associated mechanical deformation. They are shown to be extremely flexible, with radii of curvature under 10 µm, and stretch-compatible to 100% tensile strain. Such ultrathin light-emitting foils constitute an important step towards integration with malleable materials like textiles and artificial skin.

White, Matthew S.; Kaltenbrunner, Martin; G?owacki, Eric D.; Gutnichenko, Kateryna; Kettlgruber, Gerald; Graz, Ingrid; Aazou, Safae; Ulbricht, Christoph; Egbe, Daniel A. M.; Miron, Matei C.; Major, Zoltan; Scharber, Markus C.; Sekitani, Tsuyoshi; Someya, Takao; Bauer, Siegfried; Sariciftci, Niyazi Serdar

2013-10-01

357

Physical effects of ultrathin photovoltaic junctions  

NASA Astrophysics Data System (ADS)

Hot carrier photovoltaic cells have potential to increase conversion efficiency beyond the Shockley-Queisser limit. In addition to implementing selective energy filters into the device in order to extract the hot carriers at elevated energies beyond the band edges, a possible requirement, of particular importance for non-crystalline material, is that the device also be constructed ultrathin in order to extract the hot carriers as usable energy on time scales of less than one picosecond, after which thermalisation sets in. Ultrathin amorphous silicon p-i-n junctions have been shown to extract hot carriers as usable energy at fixed short circuit current density for p- and n- region thicknesses of 5 nm, and i-layer thickness less than 50 nm [Appl. Phys. Lett. 95, 233121 (2009)]. Physical effects on device performance in ultrathin cells, such as optical absorption, scattering, band structure, and transport are discussed.

Kirkpatrick, T.; Kempa, K.; Naughton, M. J.

2011-03-01

358

Photoemission investigation of the electronic properties of gallium-face gallium nitride (0001)-dielectric interfaces  

NASA Astrophysics Data System (ADS)

The characteristics of clean n- and p-type GaN (0001) surfaces and the interface between this surface and SiO2, Si3N4 , and HfO2 have been investigated. Both n- and p-type Ga-face GaN (0001) surfaces have been cleaned via an 860°C anneal in an ammonia atmosphere, and carbon and oxygen contaminants were reduced to below the detection limits. Layers of SiO2, Si3N4, or HfO 2 were carefully deposited to limit the reaction between the plasma and the GaN surface. After stepwise deposition, the electronic states were measured with x-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS). A valence band offset (VBO) of 2.0 +/- 0.2 eV with a conduction band offset (CBO) of 3.6 +/- 0.2 eV was determined for the GaN/SiO2 interface. The large band offsets suggest SiO2 is an excellent candidate for passivation of GaN. For the GaN/Si3N 4 interface, type II band alignment was observed with a VBO of 0.5 +/- 0.2 eV with a CBO of 2.4 +/- 0.2 eV. While Si3N4 should passivate n-type GaN surfaces, it may not be appropriate for p-type GaN surfaces. A VBO of 0.4 +/- 0.2 eV with a CBO of 2.0 +/- 0.2 eV was determined for the GaN/HfO2 interface. An instability was observed in the HfO2 film, with energy bands shifting ˜0.5 eV during a 650°C densification anneal. The electron affinity measurements via UPS were 3.0, 1.1, 1.8, and 2.9 +/- 0.1 eV for GaN, SiO2, Si3N4, and HfO2 surfaces, respectively. Electron affinity measurements, along with band alignment data, allow a deviation from the electron affinity model due to a change of the interface dipole to be observed. Interface dipoles of 1.7, 1.1 and 1.9 +/- 0.2 eV were observed for the GaN/SiO2, GaN/Si3N4, and GaN/HfO 2 interfaces, respectively. The existence of Ga-O bonding at the heterojunction significantly increases the interface dipole, which raises the dielectric bands in relation to the GaN.

Cook, Ted Edwin, Jr.

359

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

NASA Astrophysics Data System (ADS)

High permittivity hafnia, HfO2, and hafnium silicate, HfSiO 4, are the most promising candidates to replace oxide (SiOx) or oxynitride (SiOxNy) based gate dielectrics in future generation CMOS devices. In this thesis, the effects of processing (deposition techniques, post deposition annealing, nitridation) on nanostructure evolution (crystallization, phase segregation, interlayer growth), changes in nanochemistry (impurity content, interfacial reaction, interdiffusion, oxygen diffusion, paramagnetic charge centers) and properties (EOT, oxide charges) of atomic layer deposited (ALD) Hf-O/Hf-Si-O films on Si, with different interlayers (IL), were studied. A variety of analytical techniques including XRD, RBS, XPS, SIMS, AFM, HRTEM, STEM-EELS and EPR were used. In general, PEALD Hf-O films deposited using metal-organic precursors showed a higher C and H and lower Cl content compared to thermal ALD films using halide based precursors. Also, as-deposited ALD films (Hf-O/IL/Si) showed the formation of Hf-O-Si bonds at the Hf-O/IL interface, with increasing tendency in the presence of a chemical oxide interlayer and upon oxygen annealing. Upon post deposition annealing (PDA) of ALD Hf-O films up to 1000°C, m-HfO2 was the stable crystalline phase. It was observed that the chemical oxide interlayer grew significantly during PDA in oxygen, the rate of which was a f (t, T) due to oxygen diffusion. Additionally, an annealed Hf-O stack (i.e., target Hf-O thickness of 4.0 nm/1.2 nm nitrided chemical oxide interlayer/Si) showed a chemically diffused HfSiOx region (2 nm) in between pure HfO2 (2 nm) and the interlayer (1.2 nm) as a result of interdiffusion and interfacial reactions. Therefore, a three-layer capacitor model was used to determine the respective contributions to the total EOT. Moreover, to correlate the presence of defects with density of interfacial states, as-deposited ALD Hf-O/chemical oxide IL/Si stacks were shown to be EPR active at 8K, due to Pb0, Pb1 type charge centers. Upon forming gas annealing (FGA) and PDA, these charge centers became hydrogen-passivated. Using remote plasma nitridation of an ALD Hf-O film on chemical oxide IL/Si, the Hf-O layer remained amorphous even at 1000°C and exhibited a reduced tendency towards Hf-O-Si bond formation and interlayer growth when nitrogen incorporation was ˜1.7 at % of surface Hf atoms. However, the positive fixed charge density increased and oxide trapped charge density decreased with nitrogen incorporation. Finally, upon PDA in nitrogen at 1000°C for 10 seconds of ALD Hf-Si-O films with 60 and 75 mol % HfO2, the amorphous films transformed to t-HfO2 nano-crystallites embedded in a silica-rich amorphous matrix. However, amorphous Hf-Si-O films with 40 mol% HfO2 (i.e., silica-rich) when subjected to the same PDA, phase segregated into predominantly two amorphous phases.

Das, Anirban

360

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

PubMed

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

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

2012-12-20

361

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

362

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

363

Towards -1 effective index with one-dimensional metal-dielectric metamaterial: a quantitative analysis of the role of absorption losses  

NASA Astrophysics Data System (ADS)

We propose a theoretical study of the optimization of one dimensional metal-dielectric metamaterials in order to approach -1 effective optical index. Taking into account actual values of dielectric constants of metal (silver) and dielectrics (HfO2, GaP), and taking advantage of the dispersion relation of Bloch modes, we get a silver/HfO2metamaterial with suitable parameters that possesses a near 1 effective optical index for all angles of incidence at a visible wavelength for H-polarized light (i.e. the magnetic field is parallel to the interfaces). The absorption losses of materials appear to be a crucial factor that affects the effective properties of the metamaterial. We show that the losses not only decrease the transmission of the stack, but also change the negative refraction effect. Then, we propose another silver/GaP structure design that is less sensitive to losses. When considering finite thickness structures, and with adequate thickness for the terminating layers, it is possible to achieve a high transmittance of the structure. A near 1 effective index and high transmittance metal-dielectric metamaterial may pave the way to the realization of negative refraction in the visible or ultraviolet wavelength range.

Zhang, Jinlong; Jiang, Haitao; Gralak, Boris; Enoch, Stefan; Tayeb, Gérard; Lequime, Michel

2007-06-01

364

Towards -1 effective index with one-dimensional metal-dielectric metamaterial: a quantitative analysis of the role of absorption losses.  

PubMed

We propose a theoretical study of the optimization of one dimensional metal-dielectric metamaterials in order to approach -1 effective optical index. Taking into account actual values of dielectric constants of metal (silver) and dielectrics (HfO(2), GaP), and taking advantage of the dispersion relation of Bloch modes, we get a silver/HfO(2)metamaterial with suitable parameters that possesses a near -1 effective optical index for all angles of incidence at a visible wavelength for H-polarized light (i.e. the magnetic field is parallel to the interfaces). The absorption losses of materials appear to be a crucial factor that affects the effective properties of the metamaterial. We show that the losses not only decrease the transmission of the stack, but also change the negative refraction effect. Then, we propose another silver/GaP structure design that is less sensitive to losses. When considering finite thickness structures, and with adequate thickness for the terminating layers, it is possible to achieve a high transmittance of the structure. A near -1 effective index and high transmittance metal-dielectric metamaterial may pave the way to the realization of negative refraction in the visible or ultraviolet wavelength range. PMID:19547101

Zhang, Jinlong; Jiang, Haitao; Gralak, Boris; Enoch, Stefan; Tayeb, Gérard; Lequime, Michel

2007-06-11

365

Improvement of gate dielectric reliability for p\\/sup +\\/ poly MOS devices using remote PECVD top nitride deposition on thin gate oxides  

Microsoft Academic Search

Dual layer dielectrics have been formed by remote PECVD of ultra-thin (0.4\\/spl sim\\/1.2 nm) nitrides on thin thermal oxides grown on n-type Si(100) substrates. Activation of boron-implanted p\\/sup +\\/ polycrystalline silicon gate electrodes was accomplished by a high temperature anneal for 1\\/spl sim\\/4 minutes at 1000\\/spl deg\\/C. Boron penetration through the dielectric film to the n-type substrate was investigated by

Yider Wu; Gerald Lucovsky; H. Z. Massoud

1998-01-01

366

Material, Physical and Electronic Properties of Novel Medium-and High-K Gate Dielectrics  

NASA Astrophysics Data System (ADS)

Silicon dioxide has been used as a gate dielectric for CMOS technology since the 1960's. The aggressive shrinking of the CMOS device dimension to meet demanding speed and density drives the traditional SiO2 gate dielectric towards its thickness-scaling limit. Severe direct tunneling and reliability problems at extremely small thickness will soon set a barrier for this naturally given material. To replace SiO2, many alternative gate dielectrics have been studied. The search for new gate dielectrics has encompassed a wide range of materials from nitrided SiO2 to metal oxides with wide range of dielectric constant, k, such as Ta2O5, TiO2, Al2O3, HfSixOy , ZrSixOy, ZrO2 , HfO2, HfAlO3, ZrAlO3, LaAlO3 and SrTiO3. Alternative dielectric materials with a higher k-value provide a larger physical thickness than SiO2 to reduce the gate leakage. However barrier height and break down decreases with increasing dielectric constant, there is a tradeoff in selecting the high K materials. Morphology, phase stability and impurities incorporation of metal oxide films also play a critical role in controlling leakage, dopant diffusion and charge trapping. In addition, there are numerous challenges involved in the integration of these metal oxides. These integration challenges must be overcome to achieve the desired results of increased gate capacitance, reduced gate leakage and comparable performance and reliability to thermal SiO2 or oxynitride gate dielectrics. We will review the recent progress of the high K material developments including the impact of the deposition technique and chemical sources. The discussion includes formation of a low permittivity oxide at the metal oxide/silicon interface, chemical and thermal stability of various metal oxides in contact with the silicon and gate electrode, the impact of processing condition on material, physical and electrical properties of the metal oxide films.

Nguyen, Bich-Yen

2003-03-01

367

Dielectric properties of rf sputtered Ta2O5 on rapid thermally nitrided Si  

Microsoft Academic Search

Dielectric properties, including leakage currents of stacked structures composed of rf sputtered Ta2O5 and ultrathin SiOxNy grown by rapid thermal nitridation (RTN) in N2O or NH3 ambient, have been investigated. It was previously established that the leakage current in the structures is controlled by both hopping conduction and tunnelling in the SiOxNy layer and Poole-Frenkel emission in Ta2O5. The analysis

N. Novkovski; A. Paskaleva; E. Atanassova

2005-01-01

368

Electrical characteristics of low temperature polysilicon TFT with a novel TEOS\\/oxynitride stack gate dielectric  

Microsoft Academic Search

This investigation is the first to demonstrate a novel tetraethylorthosilicate (TEOS)\\/oxynitride stack gate dielectric for low-temperature poly-Si (LTPS) thin film transistors (TFTs), composed of a plasma-enhanced chemical vapor deposition (PECVD) thick TEOS oxide\\/ultrathin oxynitride grown by PECVD N2O-plasma. The stack oxide shows a very high electrical breakdown field of 8.4 MV\\/cm, which is approximately 3 MV\\/cm larger than traditional PECVD

Kow-Ming Chang; Wen-Chih Yang; Chiu-Pao Tsai

2003-01-01

369

Thickness dependent properties of magnetic ultrathin films  

NASA Astrophysics Data System (ADS)

The dependence of magnetic properties on the thickness of few-layer thin films is investigated at finite temperature using the functional integral method for solving the Heisenberg spin model. The temperature dependence of the ultra-thin film's magnetization and Curie temperature are calculated in terms of the mean field theory and of the Gaussian spin fluctuation approximations. It has been shown that both Curie temperature and temperature interval, where the magnetization is non-zero, are strongly reduced with the thickness reduction by using the spin fluctuation approximations in comparison with the mean field results. Curie temperature dependence on the film thickness calculated numerically well agrees with the experimental data for Ni/Cu(1 0 0) and Ni/Cu(1 1 1) ultrathin films.

Cong, Bach Thanh; Thao, Pham Huong

2013-10-01

370

Giant magnetoresistance in ultra-thin layers  

NASA Astrophysics Data System (ADS)

We consider the transport properties in magnetic ultra-thin multilayers for electronic current in the plane of the surfaces. In the case of ultra-thin films, the conduction electron transport behavior is influenced by the shape and the thickness of a sample. The boundary conditions at the surface and interfaces lead to the electric charge density distribution across a film. We discuss the influence of sample thickness on some electronic properties like the Fermi energy, distribution of electrons and their spin polarisation. We justify some parameters introduced to the model potential whose values for spacer and ferromagnetic metals depend on the layer thickness. In this aspect the present approach constitutes improvement of Hood-Falicov model for the case of very thin layers.

Warda, K.; Wojtczak, L.; Wiatrowski, G.; Baldomir, D.; Pereiro, M.; Arias, J. E.

2002-01-01

371

Ultrathin silver films on Ni(111)  

Microsoft Academic Search

The growth and atomic structure of ultrathin silver films on Ni(111) was investigated by low-energy electron microscopy and diffraction (LEEM\\/LEED) as well as intensity-voltage [I(V)] -LEEM in the growth temperature range between 470 and 850 K. We find that silver grows in a Stranski-Krastanov mode with a two monolayer thin wetting layer which takes on a p(7×7) reconstruction at temperatures

Axel Meyer; J. Ingo Flege; Robert E. Rettew; Sanjaya D. Senanayake; Thomas Schmidt; Faisal M. Alamgir; Jens Falta

2010-01-01

372

Spin Damping in Ultrathin Magnetic Films  

Microsoft Academic Search

This chapter reviews the origin of the damping of spin motions in ultra-thin ferromagnetic films and multilayer structures,\\u000a with focus on the linear response regime probed by ferromagnetic resonance or Brillouin light scattering. We begin with a\\u000a description of the spin response provided by the Landau-Lifshitz equation, which ascribes damping to dissipative processes\\u000a of intrinsic origin. It is noted that

Douglas L. Mills; Sergio M. Rezende

373

Phase transition in ultrathin Bi films  

NASA Astrophysics Data System (ADS)

Dynamical studies of Bi ultrathin films prepared on carbon at 100 K exhibit a phase transition from nanocrystalline to amorphouslike clusters. Evidence for the transition at a thickness of ~8 Å is provided by the form, intensity, and polarization dependence of in situ Raman-scattering measurements in ultrahigh vacuum. A substantial increase in frequency of the opticlike band with decreasing thickness indicates increased covalent interactions. This contrasts with superconducting Bi films, suggesting a semiconducting amorphous state in clusters.

Mitch, M. G.; Chase, S. J.; Fortner, J.; Yu, R. Q.; Lannin, J. S.

1991-08-01

374

Oxygen transport and reaction mechanisms in rhenium gate contacts on hafnium oxide films on Si  

NASA Astrophysics Data System (ADS)

Oxygen transport and incorporation were investigated following postdeposition annealing of metal-oxide-semiconductor structures having ultrathin rhenium films as metal electrode and HfO2 films as dielectric on Si(001). Isotopic tracing, nuclear reaction analysis, narrow resonant nuclear reaction profiling, and x-ray photoelectron spectroscopy were used to pursue this investigation. For annealing temperatures below 400 °C, oxygen from the gas phase incorporates mainly in near-surface regions of the overlying Re cap. Significant oxygen incorporation into the HfO2 films is observed only after annealing at 500 °C. The present results are discussed considering that supplying oxygen to the metal/dielectric interface can cause device threshold voltage shifts.

Pezzi, R. P.; Copel, M.; Gordon, M.; Cartier, E.; Baumvol, I. J. R.

2006-06-01

375

Surface Control of Bottom Electrode in Ultra-Thin SiN Metal-Insulator-Metal Decoupling Capacitors for High Speed Processors  

NASA Astrophysics Data System (ADS)

Highly reliable metal-insulator-metal (MIM) capacitor with ultra-thin SiN dielectrics is developed on the surface-controlled bottom electrode in nanometer-scales. Coverage of the TiN bottom electrode with a Ta thin layer achieves smooth surface. In addition, this electrode structure exhibits excellent etching controllability even for the MIM with the ultra-thin SiN dielectrics. The smooth surface of the Ta/TiN stacked electrode improves the dielectric characteristics such as leakage, breakdown and time-dependent dielectric breakdown (TDDB) reliability in the MIM capacitors, integrated into Cu dual-damascene interconnects (DDIs). As a result, the SiN-MIM with the Ta/TiN bottom electrode achieves high capacitance of 7 fF/?m2 as well as high reliabilities, which are 20% higher breakdown field and 6000 times longer TDDB lifetime than that without Ta-insertion. These values guarantee the high performance operation for more than 10 years under the environment at 85 °C.

Inoue, Naoya; Kume, Ippei; Kawahara, Jun; Saito, Shinobu; Furutake, Naoya; Toda, Takeshi; Matsui, Koichiro; Iwaki, Takayuki; Furumiya, Masayuki; Shinmura, Toshiki; Ohto, Koichi; Hayashi, Yoshihiro

2007-04-01

376

Imaging Electrons in Ultra-thin Nanowires  

NASA Astrophysics Data System (ADS)

Ultra-thin semiconductor nanowires are promising systems in which to explore novel low-dimensional physics and are attractive candidates for future nanoelectronics. Ultra-thin nanowires with diameters of 20 to 30 nm are essentially one-dimensional (ID) for moderate electron number, because only one radial subband is occupied. Low-temperature scanning gate microscopy is especially well suited for improving our understanding of nanowires in order to optimize the construction of nanowire systems. We use a home-built liquid-He cooled scanning gate microscope (SGM) to probe and manipulate electrons beneath the surface of devices. The SGM's conductance images are obtained by scanning the charged SGM tip above the sample and recording the change in conductance through the device as a function of tip position. We present simulations of extracting the amplitude of the 1D electron wavefunction along the length of the quantum dot in an ultra-thin InAs/InP heterostructure nanowire (diameter = 30 nm) using a SGM. A weakly perturbing SGM tip slightly dents the electron wavefunction inside the quantum dot, and we propose measuring the change in energy of the dot due to the perturbation as a function of tip position. By measuring the change in energy of the dot and by knowing the form of the tip potential, the amplitude of the wavefunction can be found. This extraction technique could serve as a powerful tool to improve our understanding of electron behavior in quasi-1 D systems. We have used our SGM to image the conductance through an ultra-thin (diameter ˜ 30 nm) 1nAs nanowire with two InP barriers. Our imaging technique provides detailed information regarding the position and flow of electrons in the nanowire. We demonstrate that the charged SPM tip's position or voltage can be used to control the number of electrons on the quantum dots. We spatially locate three quantum dots in series along the length of the ultra-thin nanowire. Using energy level spectroscopy and the conductance images, we find the length of all three of the dots, and we determine the dots' relative coupling strength.

Boyd, Erin E.

377

Interfacial study and band alignment of ultrathin La2Hf2O7 films on GaAs substrates  

NASA Astrophysics Data System (ADS)

We report ultrathin amorphous La2Hf2O7 (LHO) films grown on p-GaAs (0 0 1) substrates as high-k gate dielectric using the pulsed laser deposition method. Interfacial characterization of the LHO/GaAs has been carried out. It shows that the interfacial layer with a thickness of less than 0.5 nm is composed of Ga2O3. Experimental results show that the 5.7 ± 0.1 eV bandgap of LHO is aligned to the bandgap of GaAs with a valence band offset of 3.15 ± 0.05 eV and a conduction band offset of 1.1 ± 0.1 eV. Capacitance-voltage and current-voltage measurements indicate that LHO could be a promising gate dielectric for GaAs metal-oxide-semiconductor devices.

Wei, F.; Xiong, Y.-H.; Zhang, X.-Q.; Du, J.; Tu, H.-L.

2013-09-01

378

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

PubMed

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

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

2010-11-11

379

An ultrathin and broadband metamaterial absorber using multi-layer structures  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

380

Surface metallic states in ultrathin Bi(001) films studied with terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Dynamical response of surface metallic states in single crystalline ultrathin Bi(001) films on Si(111) 7 × 7 surface was investigated at a spectral range of 0.1-12 THz by broadband terahertz time-domain spectroscopy. The observed transmittance increased with a decrease in the thickness, without showing a gap structure. The measured complex dielectric dispersion was analyzed using a Drude model, and the plasma frequency (?p) and damping constant (?) were found to be inversely proportional to the thickness. The results strongly indicate the existence of surface metallic states, whose carrier density and damping constant are estimated to be 3.08 × 1019 cm-3 and 4.83 × 102 THz, respectively.

Yokota, K.; Takeda, J.; Dang, C.; Han, G.; McCarthy, D. N.; Nagao, T.; Hishita, S.; Kitajima, M.; Katayama, I.

2012-06-01

381

Influence of Confinement and Substrate Interaction on the Crystallization Kinetics of PET Ultrathin Films  

SciTech Connect

The cold crystallization kinetics of ultra-thin polymeric films (thickness: 10 nm divide 0.250 mm) of poly(ethylene terephthalate) (PET) have been investigated by dielectric spectroscopy, X-ray diffraction, infrared spectroscopy (FTIR, ATR, RAIR) and Atomic Force Microscopy (AFM) imaging. The crystallization kinetics, as well as the structural dynamics, departed form the bulk behavior in a region below 100 nm, with a stronger slowing down associated to films deposited on strongly interacting substrates. By means of AFM technique, the crystallization kinetics located at the free surface (air/polymer) were monitored: for thick samples, the kinetics at the free surface were found much faster than within the bulk. Reducing the thickness, as the free surface approached the substrate, the crystallization kinetics probed by AFM technique became slower. This effect was more relevant for strongly interacting substrates, up to prevent crystallization in very thin films.

Capaccioli, S.; Lucchesi, M.; Prevosto, D.; Rolla, P. A. [polyLab, CNR-INFM, Largo B. Pontecorvo 3, I-56127, Pisa (Italy); Dip. Fisica, Universita di Pisa, Largo B. Pontecorvo 3, I-56127, Pisa (Italy); Rotella, C.; Bertoldo, M. [polyLab, CNR-INFM, Largo B. Pontecorvo 3, I-56127, Pisa (Italy); Pingue, P. [NEST, CNR-INFM and Scuola Normale Superiore, I-56100, Pisa (Italy)

2008-07-07

382

Dielectric nonlinearity of ferroelectrics  

Microsoft Academic Search

The ac field dependence of the dielectric constant and first order reversal curves (FORC) distribution were employed to quantify the effect of dielectric thickness, grain size, oxygen vacancy concentration, and microstructural heterogeneity on the dielectric nonlinearity of PbZr0.52Ti0.48O 3 thin films and BaTiO3-based ceramics on a wide electric field range. With the FORC distribution, the dielectric properties were calculated using

Ichiro Fujii

2010-01-01

383

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.

384

Ultrathin epitaxially grown bismuth (111) membranes  

SciTech Connect

An ex situ cleaning and etching technique was applied to NaCl single crystals to prepare atomically flat and clean NaCl surfaces. These were used as substrates for molecular beam epitaxial growth of ultrathin continuous Bi(111) films. The high film quality - as studied with low energy electron diffraction, atomic force microscopy, and transmission electron diffraction - is attributed to the commensurate 10:7 ratio of the lattice constants. Dissolving the NaCl substrates in water allows the fabrication of freestanding 20 nm thin Bi(111) membranes of centimeter size.

Payer, T.; Rajkovic, I.; Ligges, M.; Linde, D. von der [Fachbereich Physik, Universitaet Duisburg-Essen, Lotharstrasse 1, 47057 Duisburg (Germany); Horn-von Hoegen, M.; Meyer zu Heringdorf, F.-J. [Fachbereich Physik, Universitaet Duisburg-Essen, Lotharstrasse 1, 47057 Duisburg (Germany); Center for Nanointegration (CeNIDE), Universitaet Duisburg-Essen, Lotharstrasse 1, 47057 Duisburg (Germany)

2008-09-01

385

Characterization of growth and thermal behaviors of thin films for the advanced gate stack grown by chemical vapor deposition  

NASA Astrophysics Data System (ADS)

Studies have been done on the materials for alternative gate dielectrics (high-k) and a metal gate electrode, which will replace conventional SiO 2 gate dielectric and poly silicon gate electrode, for the sub-100 nm CMOS technologies. Ultrathin HfO2 films prepared by chemical vapor deposition on Si(100) were annealed in high vacuum or N2 ambient at high temperature and their thermal stability was measured. Based on in-situ XPS, annealing HfO2 films grown by CVD on clean Si(100) leads to silicide formation at 950°C for ultrahigh vacuum but not 4 Torr of N 2. For an HfO2 film capped with amorphous Si, silicide does form upon annealing in 4 torr, but not 760 torr, of N2. TEM shows when hafnium silicide forms, it forms discontinuous islands. HfON thin film prepared by chemical vapor deposition on silicon substrate showed superior thermal stability compared to HfO2 thin film. X-ray photoelectron spectroscopy studies shows that HfON thin film is chemically stable in contact with silicon up to 1000°C under high vacuum. Excellent resistance to crystallization of HfON thin film during high temperature process is proven by a glancing angle XRD. MOS devices using HfON dielectric thin film showed better electrical properties than HfO2. CVD TaN film exhibited excellent thermal stability in terms of chemical, structural, and electrical aspects. PMOS compatible work function (˜5.0 eV) and the excellent electrical performance of CVD TaN gate electrode suggest that it is a promising candidate to replace p+ poly silicon for sub-100 nm CMOS technology.

Jeon, Taek Soo

386

Gate stack dielectric degradation of rare-earth oxides grown on high mobility Ge substrates  

NASA Astrophysics Data System (ADS)

We report on the reliability characteristics and their analysis, of rare-earth oxides (REOs) dielectric degradation, when used as interfacial buffer layers together with HfO2 high-k films (REOs/HfO2) on high mobility Ge substrates. Metal-oxide-semiconductor (MOS) devices with these stacks, show dissimilar charge trapping phenomena under varying levels of constant-voltage-stress (CVS) conditions, influencing the measured densities of the interface (Nit) and border (NBT) traps. In the present study, we report on C-Vg hysteresis curves related to both Nit and NBT. We propose a new model based on the Maxwell-Wagner mechanism, and this model explains the current decay transient observed under CVS bias from low to higher fields of MOS gate stack devices grown on Ge substrates. The proposed model is unlike to those used for other MOS devices. Finally, CVS measurements for very long times at moderate fields reveal an initial current decay due to relaxation, followed by charge trapping and generation of stress-induced leakage which eventually lead to hard breakdown.

Shahinur Rahman, Md.; Evangelou, E. K.; Konofaos, N.; Dimoulas, A.

2012-11-01

387

A high-C capacitor (20.4 fF\\/?m2) with ultrathin CVD-Ta2O5 films deposited on rugged poly-Si for high density DRAMs  

Microsoft Academic Search

Storage capacitors integrating ultrathin chemical vapor deposited-Ta2O5 (10 to 15 nm thick) on rapid thermal nitrided rugged polycrystalline silicon electrodes are proposed for 256 Mb stacked dynamic random access memory applications. The unique combination of this high dielectric constant material with a rugged hemispherical grain silicon electrode allows the manufacture of the ultra high capacitance (20.4 fF\\/?m2) stacked structures needed

P. C. Fazan; V. K. Mathews; N. Sandler; G. Q. Lo; D. L. Kwong

1992-01-01

388

Copper Electrodeposition from Ultrathin Layer of Electrolyte  

NASA Astrophysics Data System (ADS)

Electrochemical metallization of copper is used in microelectronics e.g., on-chip interconnection. The need for the fundamental understanding of the copper electrodeposition and the avoiding of ramified deposits, by exploration of especially the influence of the chemical-physical environment on the deposition, becomes more essential for the development of the microelectronic- and other related industries. Contrary to standard electrochemistry the electrodeposition from an ultrathin layer of electrolyte produces much more regular deposits, because of suppressed convection noises within this ultrathin layer. The details of the deposit morphology give information about how the copper deposition develops. It also hints at the influence of the local electric field and the local concentration filed on the morphology and the structure of copper deposits. This unique growth system may have significant implications on the pattern formation of many interfacial growth systems. Besides the use for basic scientific research, there are also perspectives for different applications in the field of parallel micro- and nano-wiring and the creation of periodical nanostructured films.

Zhong, S.; Koch, T.; Wang, M.; Zhang, M.; Schimmel, T.

389

Flexible, Ultra-Thin, Embedded Die Packaging  

NASA Astrophysics Data System (ADS)

As thin, flexible electronics solutions become more robust, their integration into everyday life becomes more likely. With possible applications in wearable electronics, biomedical sensors, or 'peel and stick' sensors, the reliability of these ultra-thin packages becomes paramount. Likewise, the density achievable with stacked packages benefits greatly from thinner die stacks. To this end, techniques previously developed have demonstrated packages with die thinned to approximately 20mum. Covered in this work are methods for thinning and packaging silicon die, as well as information on common materials used in these processes. The author's contribution is a fabrication process for embedding ultra-thin (approximately 10mum) silicon die in polyimide substrates. This method is fully illustrated in Chapter 3 and enumerated in the Appendix as a quick reference. Additionally, thermal cycle testing of passive daisy chain assemblies has shown promising reliability data. Packages were mounted in three alignments: flat, concave, and convex, and placed into thermal shock testing. Finally, the author discusses possible applications for this fabrication process, including the fabrication of multi-chip-modules.

McPherson, Ryan J.

390

An ultrathin but nearly perfect direct current electric cloak  

NASA Astrophysics Data System (ADS)

We propose and experimentally demonstrate an ultrathin but nearly perfect dc electric invisibility cloak. In the dc limit, transformation optics reduces to transformation electrostatics. Based on a special coordinate transformation, we derive a nearly perfect dc electric cloak which is composed of homogeneous and anisotropic conducting material. Due to the homogeneity feature, the dc cloak is realized using an ultrathin dc metamaterial with only one-unit-cell thickness, which is the ultra limit for practical artificial materials. Although ultrathin, our experimental results show that the dc cloak has excellent performance with nearly perfect cloaking behaviour.

Xiang Jiang, Wei; Yang Luo, Chen; Lei Mei, Zhong; Jun Cui, Tie

2013-01-01

391

Surfactant-Free Sub-2 nm Ultrathin Triangular Gold Nanoframes.  

PubMed

Ultrathin triangular gold nanoframes are synthesized in high yield through selective gold deposition on the edges of triangular silver nanoprisms and subsequent silver etching with mild wet etchants. These ultrathin gold nanoframes are surfactant-free with tailorable ridge thickness from 1.8 to 6 nm and exhibit adjustable and distinct surface plasmon resonance bands in the visible and near-IR region. In comparison, etching of the nanoprism template by galvanic replacement can only create frame structures with much thicker ridges, which have much lower catalytic activity for 4-nitrophenol reduction than the ultrathin gold nanoframes. PMID:23447112

Shahjamali, Mohammad Mehdi; Bosman, Michel; Cao, Shaowen; Huang, Xiao; Cao, Xiehong; Zhang, Hua; Pramana, Stevin Snellius; Xue, Can

2013-02-28

392

Abnormal sub-threshold swing degradation under dynamic hot carrier stress in HfO2/TiN n-channel metal-oxide-semiconductor field-effect-transistors  

NASA Astrophysics Data System (ADS)

This work finds abnormal sub-threshold swing (S.S.) degradation under dynamic hot carrier stress (HCS) in n-channel metal-oxide-semiconductor field-effect-transistors with high-k gate dielectric. Results indicate that there is no change in S.S. after dynamic HCS due to band-to-band hot hole injection at the drain side which acts to diminish the stress field. Moreover, the impaired stress field causes the interface states to mainly distribute in shallow states. This results in ON state current and transconductance decreases, whereas S.S. degradation is insignificant after dynamic HCS. The proposed model is confirmed by one-side charge pumping measurement and gate-to-drain capacitance at varying frequencies.

Tsai, Jyun-Yu; Chang, Ting-Chang; Lo, Wen-Hung; Chen, Ching-En; Ho, Szu-Han; Chen, Hua-Mao; Tai, Ya-Hsiang; Cheng, Osbert; Huang, Cheng-Tung

2013-07-01

393

Study of interfacial reactions and phase stabilization of mixed Sc, Dy, Hf high- k oxides by attenuated total reflectance infrared spectroscopy  

NASA Astrophysics Data System (ADS)

Grazing angle attenuated total reflectance Fourier transform infrared spectroscopy is applied to study ultrathin film Hf 4+, Sc 3+ and Dy 3+oxides, due to its high surface sensitivity. The (multi)metal oxides studied, are of interest as high- k dielectrics. Important properties affecting the permittivity, such as the amorphous or crystalline phase and interfacial reactions, are characterized. Dy 2O 3 is prone to silicate formation on SiO 2/Si substrates, which is expressed in DyScO 3 as well, but suppressed in HfDyO x. Sc 2O 3, HfScO x and HfO 2 were found to be stable in contact with SiO 2/Si. Deposition of HfO 2 in between Dy 2O 3 or DyScO 3 and SiO 2, prevents silicate formation, showing a buffer-like behavior for the HfO 2. Doping of HfO 2 with Dy or Sc prevents monoclinic phase crystallization. Instead, a cubic phase is obtained, which allows a higher permittivity of the films. The phase remains stable after anneal at high temperature.

Hardy, A.; Adelmann, C.; Van Elshocht, S.; Van den Rul, H.; Van Bael, M. K.; De Gendt, S.; D'Olieslaeger, M.; Heyns, M.; Kittl, J. A.; Mullens, J.

2009-06-01

394

AGRICULTURAL APPLICATIONS OF DIELECTRIC MEASUREMENTS  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

395

Study on Surface Energy of Ultra-thin Film  

NASA Astrophysics Data System (ADS)

The dependences of surface energy on ultra-thin film thickness are investigated experimentally and theoretically. Langmuir-Blodgett (LB) film and perfluoropolyether (PFPE) lubricant on solid substrates are used as ultra-thin film samples. Surface energies as a function of film thickness are experimentally obtained from contact angle measurements. The theoretical equation of the dispersive component of the surface energy of ultra-thin film is derived from the corrected van der Waals pressure equation for a multilayered system proposed by the authors. The theoretical values are found to agree with the experimental values. The theoretical equation presented in this study is considered to be useful in predicting the surface energy of an ultra-thin film on a solid substrate.

Matsuoka, Hiroshige; Ono, Katsunori; Fukui, Shigehisa

396

Mesostructured assemblies of ultrathin superlong tellurium nanowires and their photoconductivity.  

PubMed

Well-defined periodic mesostructures of hydrophilic ultrathin Te nanowires with aspect ratios of at least 10(4) can be produced by the Langmuir-Blodgett technique without any extra hydrophobic pretreatment or functionalization. Packing the arrayed nanowire monolayers will allow construction of nanomesh-like mesostructures or more complex multilayered structures composed of ultrathin nanowires on a planar substrate. The well-organized monolayer of Te nanowires with periodic mesostructures can be readily used as a stamp to transfer such mesostructured nanopatterns to other substrates or can be embedded within a polymer matrix. The mesostructures of ultrathin Te nanowire films show reversibly switched photoelectric properties between the lower- and higher-conductivity states when the light is off and on, and the photocurrent is influenced by the light intensity and the number of mesostructured nanowire monolayer films. This method can be extended for fabrication of other mesostructured assemblies of ultrathin nanowires or nanotubes. PMID:20545345

Liu, Jian-Wei; Zhu, Jian-Hua; Zhang, Chuan-Ling; Liang, Hai-Wei; Yu, Shu-Hong

2010-07-01

397

Insulating behavior in ultrathin bismuth selenide field effect transistors.  

PubMed

Ultrathin (approximately three quintuple layer) field-effect transistors (FETs) of topological insulator Bi(2)Se(3) are prepared by mechanical exfoliation on 300 nm SiO(2)/Si susbtrates. Temperature- and gate-voltage-dependent conductance measurements show that ultrathin Bi(2)Se(3) FETs are n-type and have a clear OFF state at negative gate voltage, with activated temperature-dependent conductance and energy barriers up to 250 meV. PMID:21486055

Cho, Sungjae; Butch, Nicholas P; Paglione, Johnpierre; Fuhrer, Michael S

2011-04-12

398

Insulating Behavior in Ultrathin Bismuth Selenide Field Effect Transistors  

NASA Astrophysics Data System (ADS)

Ultrathin (~3 quintuple layer) field-effect transistors (FETs) of topological insulator Bi2Se3 are prepared by mechanical exfoliation on 300nm SiO2/Si susbtrates. Temperature- and gate-voltage dependent conductance measurements show that ultrathin Bi2Se3 FETs are n-type, and have a clear OFF state at negative gate voltage, with activated temperature-dependent conductance and energy barriers up to 250 meV.

Cho, Sungjae; Butch, Nicholas P.; Paglione, Johnpierre; Fuhrer, Michael S.

2011-05-01

399

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

400

Temperature?Induced Pattern Transition in Crystallizing Ultrathin Polymer Films  

Microsoft Academic Search

The crystallization patterns of ultrathin poly(ethylene oxide)\\/poly(methyl methacrylate)(PEO\\/PMMA) blend films crystallized at different undercooling were investigated by atomic force microscopy. Dendrite pattern formed as a result of crystalline anisotropy at low undercooling and evolved into seaweed pattern with increasing undercooling. Although the configuration of macromolecules is far different from that of simple small molecules, the crystallization pattern transition in ultrathin

Jun Zhu; Mingtai Wang

2008-01-01

401

Accurate surface profilometry of ultrathin wafers  

NASA Astrophysics Data System (ADS)

Geometric characterization of 50 mm diameter, 50 µm thick single-crystal Si(1 1 1) wafers has been performed using complementary methods: industry-standard capacitance measurements of warp and total thickness variation (TTV), and a technique we term scanned chromatic confocal profilometry (SCCP). We compare the measurements made by the two techniques and demonstrate the limitations of capacitance measurements when applied to ultrathin wafers. The two-dimensional SCCP measurements are shown to enhance the description of wafer thickness variations beyond that generated by the standard test method. We discuss a Fourier transform-based analysis and show it to be useful in wafer quality assessment. Adding a summary of spatial frequencies in a wafer's thickness map to the conventional measures of warp and TTV provides a more complete summary of the salient features of a wafer's geometry.

Weeks, A. E.; Litwin, D.; Galas, J.; Surma, B.; Piatkowski, B.; MacLaren, D. A.; Allison, W.

2007-09-01

402

Self-organized ultrathin oxide nanocrystals.  

PubMed

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. PMID:19206219

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

2009-03-01

403

Ultrathin ferroelectric strontium bismuth tantalate films  

NASA Astrophysics Data System (ADS)

Continuous strontium bismuth tantalate films with an average thickness of ~36 nm have been prepared by spin-coating deposition of solutions onto Pt/TiO2/SiO2/(100)Si substrates and by rapid thermal processing. The films microstructure was formed by rod-shaped grains and fine equiaxed grains. This densely packed microstructure makes the growth of a continuous ultrathin film possible without shorts in the capacitor. The films exhibited values of coercive field of Ec~226+/-40 kV/cm and of remanent polarization of Pr~7.4+/-1.5 ?C/cm2. They retain their Pr up to ~105 s and do not fatigue up to ~1010 cycles.

González, A.; Jiménez, R.; Mendiola, J.; Alemany, C.; Calzada, M. L.

2002-09-01

404

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

405

Structure, phase transformations, and defects of HfO2 and ZrO2 nanoparticles studied by Ta181 and Cd111 perturbed angular correlations, H1 magic-angle spinning NMR, XPS, and x-ray and electron diffraction  

NASA Astrophysics Data System (ADS)

Structure, phase transformations, grain growth, and defects of bare and alumina-coated nanoparticles of HfO2 and ZrO2 synthesized in a microwave-plasma process have been investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM), and perturbed angular correlation (PAC) spectroscopy. The PAC technique was used to measure the electric quadrupole interactions (QIs) of the nuclear probes Ta181 and Cd111 in nanocrystalline HfO2 and ZrO2 as a function of temperature. For comparison, the QI of Ta181 in the bulk oxides was determined in the same temperature range 300K?T?1550K . The oxygen-metal ratio of the as-synthesized particles was determined by x-ray photoelectron spectroscopy to be in the range 1.4?x?1.8 . A hydrate surface layer with a hydrogen content of 5-10wt% , consisting of chemisorbed hydroxyl groups and organic precursor fragments, was detected by H1 magic-angle spinning NMR. XRD and TEM show that bare n-ZrO2 , Al2O3 -coated n-ZrO2 , and Al2O3 -coated n-HfO2 are synthesized in the tetragonal or cubic modification with a particle size d<5nm , whereas bare n-HfO2 is mainly monoclinic. The grain growth activation enthalpy of bare n-ZrO2 is QA=32(5)kJ/mol . Coating with Al2O3 stabilizes the tetragonal over the monoclinic phase, both in hafnia and zirconia nanoparticles. While TEM micrographs of the native nanoparticles reveal a well-ordered cation sublattice, the observation of a broad QI distribution in the PAC spectra suggests a high degree of disorder of the oxygen sublattice. The gradual transformation of the disordered state and the phase evolution were studied by high-temperature QI measurements. Hafnia nanoparticles persist in the monoclinic (m) phase up to T?1400K . In coated n-ZrO2/Al2O3 , the monoclinic and tetragonal (t) phases coexist over a large temperature range, whereas uncoated, initially tetragonal or cubic ( t or c ) n-ZrO2 presents a sharp m?t transition. A “defect” component involving 30%-40% of the probe nuclei appears in the Ta181 PAC spectra of all nanoparticles when these are cooled from high temperatures T?1200K . The temperature dependence of this component can be reproduced by assuming that Ta impurities in hafnia and zirconia may trap electrons at low temperatures. The observation that the defect component appears only in nanoparticles with diameter d<100nm suggests that mobile electrons are available only in the surface region of the oxide particles, either from oxygen vacancies (VO) and/or VO -hydrogen donors at the interface of the nanoparticles and their hydrate layers. This conclusion is supported by the absence of a size effect for Cd111 probes in HfO2 and ZrO2 . The temperature dependence of the Ta181 defect fraction is consistent with a Ta+ impurity level at Ed˜0.9 and 0.6eV below the hafnia and zirconia conduction band, respectively.

Forker, M.; de La Presa, P.; Hoffbauer, W.; Schlabach, S.; Bruns, M.; Szabó, D. V.

2008-02-01

406

Ultrathin SrTiO3 films prepared by chemical vapor deposition on Nb-doped SrTiO3 substrates  

Microsoft Academic Search

The SrTiO3 ultrathin film capacitors were realized on Nb-doped single-crystal SrTiO3 substrates by chemical vapor deposition. The leakage current density of 10.4 nm thick SrTiO3 thin-film capacitor was below 1×10?8 A\\/cm2 in the applied voltage range of ?1.8 to +0.45 V, and its SiO2 equivalent thickness was 0.48 nm. The relative dielectric constant was over 160 for SrTiO3 thickness above

Masahiro Kiyotoshi; Kazuhiro Eguchi

1995-01-01

407

Ultrathin Polymer Films, Patterned Arrays, and Microwells  

NASA Astrophysics Data System (ADS)

The ability to control and tailor the surface and interface properties of materials is important in microelectronics, cell growth control, and lab-on-a-chip devices. Modification of material surfaces with ultrathin polymer films is attractive due to the availability of a variety of polymers either commercially or by synthesis. We have developed two approaches to the attachment of ultrathin polymer films on solid substrates. In the first method, a silane-functionalized perfluorophenyl azide (PFPA-silane) was synthesized and used to covalently immobilize polymer thin films on silicon wafers. Silanization of the wafer surface with the PFPA-silane introduced a monolayer of azido groups which in turn covalently attached the polymer film by way of photochemically initiated insertion reactions. The thickness of the film could be adjusted by the type and the molecular weight of the polymer. The method is versatile due to the general C-H and/or N-H insertion reactions of crosslinker; and therefore, no specific reactive functional groups on the polymers are required. Using this method, a new type of microwell array was fabricated from covalently immobilized polymer thin films on flat substrates. The arrays were characterized with AFM, XPS, and TOF-SIMS. The second method describes the attachment of polymer thin films on solid substrates via UV irradiation. The procedure consisted of spin-coating a polymer film and irradiating the film with UV light. Following solvent extraction, a thin film remained. The thickness of the film, from a few to over a hundred nanometers, was controlled by varying solution concentration and the molecular weight of the polymer.

Yan, Mingdi

2002-05-01

408

Fracture and fatigue of ultrathin nanoporous polymer films  

NASA Astrophysics Data System (ADS)

Nanoporous polymer layers are being considered for a range of emerging nanoscale applications, from low permittivity materials for interlayer dielectrics in microelectronics and anti-reflective coatings in optical technologies, to biosensors and size-selective membranes for biological applications. Polymer thin films have inherently low elastic modulus, strength and hardness, but exhibit fracture properties that are higher than those reported for glass, ceramic, and even some metal layers. However, constraint of a ductile polymer between two elastic layers is expected to affect the local plasticity ahead of a crack tip and its contribution to the film adhesion with films below a micron in thickness. Additionally, nanoporosity would be expected to have a deleterious effect on mechanical properties, producing materials and layers that are structurally weaker than fully dense versions they replace. Therefore, the integration of these nanoporous polymer layer at nanometer thicknesses would present significantly processing and mechanical reliability challenges. In this dissertation, surprising evidence is presented that nanoporous polymer films exhibit increasing fracture energy with increasing porosity. Such behavior is in stark contrast to a wide range of reported behavior for porous solids. A ductile nano-void growth and coalescence fracture mechanics-based model is presented to rationalize the increase in fracture toughness of the voided polymer film. The model is shown to explain the behavior in terms of a specific scaling of the size of the pores with pore volume fraction. It is demonstrated that the pore size must increase with close to a linear dependence on the volume fraction in order to increase rather than decrease the fracture energy. Independent characterization of the pore size as a function of volume fraction is shown to confirm predictions made by the model. The fracture behavior of these constrained polymer films are also examined with film thickness as low as 7.5 nm. Unlike a continuous decrease in adhesion observed in a dense polymer with decreasing film thickness, the adhesion of nanoporous layers is also shown to be insensitive to film thickness down to thickness of ˜50 nm. A sharp transition in fracture behavior is observed below this critical film thickness. Extension of the nano-void growth model can be used to predict this transition point for a nanoporous layer. Finally, subcritical crack growth mechanism like environmentally-assisted crack and fatigue are also considered for these ultrathin polymers films. These crack growth behaviors also have key parameters that are influenced by the level of porosity and thickness of the film.

Kearney, Andrew V.

409

PREFACE: Dielectrics 2011  

Microsoft Academic Search

In 2011, the biennial meeting of the Dielectrics Group of the IOP, Dielectrics 2011, was held for the first time in a number of years at the University of Kent at Canterbury. This conference represents the most recent in a long standing series that can trace its roots back to a two-day meeting that was held in the spring of

Alun Vaughan; Paul Lewin

2011-01-01

410

Theory of dielectric elastomers  

Microsoft Academic Search

In response to a stimulus, a soft material deforms, and the deformation provides a function. We call such a material a soft active material (SAM). This review focuses on one class of soft active materials: dielectric elastomers. When a membrane of a dielectric elastomer is subject to a voltage through its thickness, the membrane reduces thickness and expands area, possibly

Zhigang Suo

2010-01-01

411

Dielectric Waveguide Phase Shifter  

Microsoft Academic Search

Using ferrite waveguide toroids and dielectric ribs (epsilon r = 50), we have demonstrated that a dielectric waveguide (no metal walls) phase shifter (Delta Phi = 600°) can propagate with reasonable insertion loss (?3 dB) and modest cross coupling (? 15 dB). With brass inserts, the cross coupling can be further reduced (> 20 dB) with some sacrifice of insertion

J. J. Green

1982-01-01

412

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

SciTech Connect

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

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

2007-08-24

413

Thermal stability of precursors for atomic layer deposition of TiO2, ZrO2, and HfO2: an ab initio study of alpha-hydrogen abstraction in bis-cyclopentadienyl dimethyl complexes.  

PubMed

Thin film dielectrics based on hafnium and zirconium oxides are being introduced to increase the permittivity of insulating layers in nanoelectronic transistor and memory devices. Atomic layer deposition (ALD) is the process of choice for fabricating these films, and the success of this method depends crucially on the chemical properties of the precursor molecules. Designing new precursors requires molecular engineering and chemical tailoring to obtain specific physical properties and performance capabilities. A successful ALD precursor should be volatile, stable in the gas-phase, but reactive on the substrate and growing surface, leading to inert byproduct. This study is concerned with the thermal stability in the gas phase of Ti, Zr, and Hf precursors that contain cyclopentadienyl (Cp = C(5)H(5-x)R(x)) ligands. We use density functional theory (DFT) to probe the non-ALD decomposition pathway and find a mechanism via intramolecular alpha-H transfer that produces an alkylidene complex. The analysis shows that thermal stabilities of complexes of the type MCp(2)(CH(3))(2) increase down group 4 (M = Ti, Zr, and Hf) due to an increase in the HOMO-LUMO band gap of the reactants, which itself increases with the electrophilicity of the metal. Precursor decomposition via this pathway in the gas phase can therefore be avoided by replacing the alpha-H donor or acceptor ligands or by increasing the electrophilicity of the metal. This illustrates how the ALD process window can be widened by rational molecular design based on mechanistic understanding. PMID:20055493

Zydor, Aleksandra; Elliott, Simon D

2010-02-01

414

Enhanced bias stress stability of a-InGaZnO thin film transistors by inserting an ultra-thin interfacial InGaZnO:N layer  

NASA Astrophysics Data System (ADS)

Amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs) having an ultra-thin nitrogenated a-IGZO (a-IGZO:N) layer sandwiched at the channel/gate dielectric interface are fabricated. It is found that the device shows enhanced bias stress stability with significantly reduced threshold voltage drift under positive gate bias stress. Based on x-ray photoelectron spectroscopy measurement, the concentration of oxygen vacancies within the a-IGZO:N layer is suppressed due to the formation of N-Ga bonds. Meanwhile, low frequency noise analysis indicates that the average trap density near the channel/dielectric interface continuously drops as the nitrogen content within the a-IGZO:N layer increases. The improved interface quality upon nitrogen doping agrees with the enhanced bias stress stability of the a-IGZO TFTs.

Huang, Xiaoming; Wu, Chenfei; Lu, Hai; Ren, Fangfang; Chen, Dunjun; Zhang, Rong; Zheng, Youdou

2013-05-01

415

Valence Electron Energy-loss Spectroscopy of Ultrathin SrTiO3 Films Grown on Silicon (100) Single Crystal  

SciTech Connect

Valence electron energy-loss spectroscopy is used to investigate the plasmon excitations of ultrathin SrTiO{sub 3} sandwiched between amorphous Si and crystalline Si. Two plasmon excitations were observed, one at 15.8 eV and the other at 28.7 eV. Our calculations, based on dielectric-function theory, suggest that the former peak originates from the coupling of the Si layers and is related to the geometry of the structure, and the latter peak results from the SrTiO{sub 3} bulk plasmon after a redshift. Our findings demonstrate the value of valence electron energy-loss spectroscopy in detecting a local change in the effective electron mass.

Su, D.; Yang, B.; Jiang, N.; Sawicki, M.; Broadbridge, C.; Couillard,, M.; Reiner, J.W.; Walker, F.J.; Ahn, C.H.; Zhu, Y.

2010-03-25

416

Switchable Dielectric Waveguide Circulator.  

National Technical Information Service (NTIS)

A switchable dielectric waveguide circulator is provided for millimeter wave frequency applications comprising a ferrite right prism having two polygonal prism bases and at least three lateral prism faces. A control wire is threaded through a number of bo...

R. A. Stern R. W. Babbitt

1987-01-01

417

Ionic Thermocurrents in Dielectrics.  

National Technical Information Service (NTIS)

The ionic thermoconductivity (ITC) method, consisting of the study of the thermally activated release of dielectric polarization, is studied in great detail in alkali halide crystals. The (divalent metal ion, cation vacancy) dipoles give rise to an ITC ba...

G. Guidi C. Bucci R. Fieschi

1966-01-01

418

Scalability of TiN\\/HfAlO\\/TiN MIM DRAM capacitor to 0.7-nm-EOT and beyond  

Microsoft Academic Search

We have proposed guiding principle of material selection of electrode\\/dielectric combination for MIM DRAM capacitors by theoretically taking the tunneling barrier height into account. Accordingly, we found that phase-controlled HfO2 (HfAlO) with TiN electrode is promising. TiN\\/HfAlO\\/TiN MIM capacitors with an ultra-thin Al2O3 on the bottom TiN electrode were fabricated and an EOT of 0.7 nm with a leakage current

N. Mise; O. Tonomura; T. Sekiguchi; S. Horii; H. Itatani; A. Ogawa; T. Saito; M. Sakai; Y. Takebayashi; H. Yamazaki; K. Torii

2009-01-01

419

Tensile-Strained Germanium CMOS Integration on Silicon  

Microsoft Academic Search

Monolithic integration of tensile-strained Si\\/ Germanium (Ge)-channel n-MOS and tensile-strained Ge p-MOS with ultrathin (equivalent oxide thickness ~14 Aring) HfO2 gate dielectric and TaN gate stack on Si substrate is demonstrated. Defect-free Ge layer (279 nm) grown by ultrahigh vacuum chemical-vapor deposition is achieved using a two-step Ge-growth technique coupled with compliant Si\\/SiGe buffer layers. The epi-Ge layer experiences tensile

H. Zang; W. Y. Loh; J. D. Ye; G. Q. Lo; Byung Jin Cho

2007-01-01

420

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

421

Temperature dependence of the dielectric constant of acrylic dielectric elastomer  

NASA Astrophysics Data System (ADS)

The dielectric constant is an essential electrical parameter to the achievable voltage-induced deformation of the dielectric elastomer. This paper primarily focuses on the temperature dependence of the dielectric constant (within the range of 173 K to 373 K) for the most widely used acrylic dielectric elastomer (VHB 4910). First the dielectric constant was investigated experimentally with the broadband dielectric spectrometer (BDS). Results showed that the dielectric constant first increased with temperature up to a peak value and then dropped to a relative small value. Then by analyzing the fitted curves, the Cole-Cole dispersion equation was found better to characterize the rising process before the peak values than the Debye dispersion equation, while the decrease process afterward can be well described by the simple Debye model. Finally, a mathematical model of dielectric constant of VHB 4910 was obtained from the fitted results which can be used to further probe the electromechanical stability of the dielectric elastomers.

Sheng, Junjie; Chen, Hualing; Li, Bo; Chang, Longfei

2013-02-01

422

Ultrathin Silver Films on Ni(111)  

SciTech Connect

The growth and atomic structure of ultrathin silver films on Ni(111) was investigated by low-energy electron microscopy and diffraction (LEEM/LEED) as well as intensity-voltage [I(V)]-LEEM in the growth temperature range between 470 and 850 K. We find that silver grows in a Stranski-Krastanov mode with a two monolayer thin wetting layer which takes on a p(7 x 7) reconstruction at temperatures lower than 700 K and a ({radical}52 x {radical}52)R13.9{sup o} reconstruction at higher temperatures. The occurrence of the two distinct reconstructions is shown to have profound implications for the growth characteristics of films exhibiting thicknesses of one and two monolayers. The nanoscale I(V) characteristics of the films were analyzed by means of multiple-scattering calculations based on dynamical LEED theory. Furthermore, the vertical interatomic spacing at the interface between the Ag film and the Ni substrate was determined to (2.8 {+-} 0.1) {angstrom} for all film thicknesses (<13 ML) while the uppermost silver layer relaxes by about (4 {+-} 1)% toward the crystal.

Meyer, A.; Flege, J; Rettew, R; Senanayake, S; Schmidt, T; Alamgir, F; Falta, J

2010-01-01

423

Ultrathin Silver Films on Ni(111)  

SciTech Connect

The growth and atomic structure of ultrathin silver films on Ni(111) was investigated by low-energy electron microscopy and diffraction (LEEM/LEED) as well as intensity-voltage [I(V)]-LEEM in the growth temperature range between 470 and 850 K. We find that silver grows in a Stranski-Krastanov mode with a two monolayer thin wetting layer which takes on a p(7 x 7) reconstruction at temperatures lower than 700 K and a ({radical}52 x {radical}52)R13.9{sup o} reconstruction at higher temperatures. The occurrence of the two distinct reconstructions is shown to have profound implications for the growth characteristics of films exhibiting thicknesses of one and two monolayers. The nanoscale I(V) characteristics of the films were analyzed by means of multiple-scattering calculations based on dynamical LEED theory. Furthermore, the vertical interatomic spacing at the interface between the Ag film and the Ni substrate was determined to (2.8 {+-} 0.1) {angstrom} for all film thicknesses (<13 ML) while the uppermost silver layer relaxes by about (4 {+-} 1)% toward the crystal.

Flege, J.I.; Senanayake, S.; Meyer, A.; Rettew, R.E.; Schmidt, T.; Alamgir, F.M.; Falta, J.

2010-08-16

424

Quantum suppression of superconductivity in ultrathin nanowires  

PubMed

It is of fundamental importance to establish whether there is a limit to how thin a superconducting wire can be, while retaining its superconducting character--and if there is a limit, to determine what sets it. This issue may also be of practical importance in defining the limit to miniaturization of superconducting electronic circuits. At high temperatures, the resistance of linear superconductors is caused by excitations called thermally activated phase slips. Quantum tunnelling of phase slips is another possible source of resistance that is still being debated. It has been theoretically predicted that such quantum phase slips can destroy superconductivity in very narrow wires. Here we report resistance measurements on ultrathin (< or = 10 nm) nanowires produced by coating carbon nanotubes with a superconducting Mo-Ge alloy. We find that nanowires can be superconducting or insulating depending on the ratio of their normal-state resistance (R(N)) to the quantum resistance for Cooper pairs (Rq). If R(N) < Rq, quantum tunnelling of phase slips is prohibited by strong damping, and so the wires stay superconducting. In contrast, we observe an insulating state for R(N) > Rq, which we explain in terms of proliferation of quantum phase slips and a corresponding localization of Cooper pairs. PMID:10801120

Bezryadin; Lau; Tinkham

2000-04-27

425

Ultrathin hydrogel films for rapid optical biosensing.  

PubMed

Novel biosensors have been designed by reporting an analyte-induced (de)swelling of a stimuli-responsive hydrogel (usually in a form of thin film) with a suitable optical transducer. These simple, inexpensive hydrogel biosensors are highly desirable, however, their practical applications have been hindered, largely because of their slow response. Here we show that quick response hydrogel sensors can be designed from ultrathin hydrogel films. By the adoption of layer-by-layer assembly, a simple but versatile approach, glucose-sensitive hydrogel films with thickness on submicrometer or micrometer scale, which is 2 orders of magnitude thinner than films used in ordinary hydrogel sensors, can be facilely fabricated. The hydrogel films can not only respond to the variation in glucose concentration, but also report the event via the shift of Fabry-Perot fringes using the thin film itself as Fabry-Perot cavity. The response is linear and reversible. More importantly, the response is quite fast, making it possible to be used for continuous glucose monitoring. PMID:22136353

Zhang, Xi; Guan, Ying; Zhang, Yongjun

2011-12-14

426

Dielectric spectroscopy in agrophysics  

NASA Astrophysics Data System (ADS)

The paper presents scientific foundation and some examples of agrophysical applications of dielectric spectroscopy techniques. The aim of agrophysics is to apply physical methods and techniques for studies of materials and processes which occur in agriculture. Dielectric spectroscopy, which describes the dielectric properties of a sample as a function of frequency, may be successfully used for examinations of properties of various materials. Possible test materials may include agrophysical objects such as soil, fruit, vegetables, intermediate and final products of the food industry, grain, oils, etc. Dielectric spectroscopy techniques enable non-destructive and non-invasive measurements of the agricultural materials, therefore providing tools for rapid evaluation of their water content and quality. There is a limited number of research in the field of dielectric spectroscopy of agricultural objects, which is caused by the relatively high cost of the respective measurement equipment. With the fast development of modern technology, especially in high frequency applications, dielectric spectroscopy has great potential of expansion in agrophysics, both in cognitive and utilitarian aspects.

Skierucha, W.; Wilczek, A.; Szyp?owska, A.

2012-04-01

427

Dielectric spectroscopy in agrophysics  

NASA Astrophysics Data System (ADS)

The paper presents scientific foundation and some examples of agrophysical applications of dielectric spectroscopy techniques. The aim of agrophysics is to apply physical methods and techniques for studies of materials and processes which occur in agriculture. Dielectric spectroscopy, which describes the dielectric properties of a sample as a function of frequency, may be successfully used for examinations of properties of various materials. Possible test materials may include agrophysical objects such as soil, fruit, vegetables, intermediate and final products of the food industry, grain, oils, etc. Dielectric spectroscopy techniques enable non-destructive and non-invasive measurements of the agricultural materials, therefore providing tools for rapid evaluation of their water content and quality. There is a limited number of research in the field of dielectric spectroscopy of agricultural objects, which is caused by the relatively high cost of the respective measurement equipment. With the fast development of modern technology, especially in high frequency applications, dielectric spectroscopy has great potential of expansion in agrophysics, both in cognitive and utilitarian aspects.

Skierucha, W.; Wilczek, A.; Szyp?owska, A.

2012-04-01

428

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

NASA Astrophysics Data System (ADS)

Medium energy ion scattering (MEIS) using, typically, 100–200 keV H+ or He+ ions derives it ability to characterise nanolayers from the fact that the energy after backscattering depends (i) on the elastic energy loss suffered in a single collision with a target atom and (ii) on the inelastic energy losses on its incoming and outgoing trajectories. From the former the mass of the atom can be determined and from the latter its depth. Thus MEIS yields depth dependent compositional and structural information, with high depth resolution (sub-nm near the surface) and good sensitivity for all but the lighter masses. It is particularly well suited for the depth analysis of high-k multilayers of nanometer thickness. Accurate quantification of the depth distributions of atomic species can be obtained using suitable spectrum simulation.In the present paper, important aspects of MEIS including quantification, depth resolution and spectrum simulation are briefly discussed. The capabilities of the technique in terms of the high depth resolution layer compositional and structural information it yields, is illustrated with reference to the detailed characterisation of a range of high-k nanolayer and multilayer structures for current microelectronic devices or those still under development: (i) HfO2 and HfSiOx for gate dielectric applications, including a TiN/Al2O3/HfO2/SiO2/Si structure, (ii) TiN/SrTiO3/TiN and (iii) TiO2/Ru/TiN multilayer structures for metal–insulator–metal capacitors (MIMcaps) in DRAM applications.The unique information provided by the technique is highlighted by its clear capability to accurately quantify the composition profiles and thickness of nanolayers and complex multilayers as grown, and to identify the nature and extent of atom redistribution (e.g. intermixing, segregation) during layer deposition, annealing and plasma processing. The ability makes it a valuable tool in the development of the nanostructures that will become increasingly important as device dimensions continue to be scaled down.

van den Berg, J. A.; Reading, M. A.; Bailey, P.; Noakes, T. Q. C.; Adelmann, C.; Popovici, M.; Tielens, H.; Conard, T.; de Gendt, S.; van Elshocht, S.

2013-09-01

429

Organic light-emitting diodes with nanostructured fullerene ultrathin layers  

NASA Astrophysics Data System (ADS)

Organic light-emitting diodes (OLEDs) with nanostructured fullerene (C60) ultrathin layers were fabricated. The luminance and efficiency are decreased due to exciton quenching in the OLEDs with C60 layers at the N,N?-Di (naphth-2-yl)-N, N?-diphenyl-benzidine (NPB)/8-hydroxyquinoline aluminum (Alq3) interface. It is opposite to the results reported by Kato [K. Kato, K. Takahashi, K. Suzuki, T. Sato, K. Shinbo, F. Kaneko et al., Curr. Appl. Phys. 5, 2005, 321]. And C60 ultrathin layers play a role of weak p-type delta-dopant in the NPB layer due to forming of a charge transfer complex C60-:NPB+. The current density and luminance are enhanced in the OLEDs with 0.7 nm C60 ultrathin layers inserted in NPB layer. A suggested explanation is p-type delta-doping effect in the NPB layer which increases the charge mobility of NPB films.

Lü, Zhaoyue; Deng, Zhenbo; Zheng, Jianjie; Yin, Yuehong; Chen, Yanli; Wang, Yongsheng

2010-01-01

430

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

431

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 A?´) 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

432

Molecular dynamics and dielectric loss in 4-cyano-4- n-pentylbiphenyl (5CB) mesogene film surrounding carbon nanotube – Computer simulation  

Microsoft Academic Search

The ultrathin film of mesogenous molecules 5CB surrounding a carbon nanotube has been investigated by molecular dynamics (MD) technique. The dynamical observables of 4-cyano-4-n-pentylbiphenyl (5CB) were calculated for several temperatures: the mean square displacement, diffusion coefficient, translational, angular velocity autocorrelation function, etc. We have also calculated the total dipole moment, autocorrelation function and dielectric loss of 5CB mesogene layer. The

W. Gwizdala; K. Górny; Z. Gburski

2008-01-01

433

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

PubMed

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

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

2013-05-28

434

Ultra-thin gold films on transparent polymers  

NASA Astrophysics Data System (ADS)

Fabrication of continuous ultra-thin gold films (<10 nm) on the surface of optical polymers (CYCLOTENE and ORMOCLEAR) is reported. Using a range of electrical, optical and structural characterization techniques, we show that polymers can be superior to more conventional (inorganic) materials as optical substrates for realizing ultra-thin gold films. Using these transparent polymer substrates, smooth, patternable gold films can be fabricated with conventional deposition techniques at room temperature, without adhesion or seeding layers, facilitating new photonic and plasmonic nanostructures, including transparent electrical contacts, thin film waveguides, metamaterials, biosensors and high-contrast superlenses.

Leosson, Kristjan; Ingason, Arni S.; Agnarsson, Bjorn; Kossoy, Anna; Olafsson, Sveinn; Gather, Malte C.

2013-02-01

435

Experimental and theoretical investigation of the effect of SiO2 content in gate dielectrics on work function shift induced by nanoscale capping layers  

NASA Astrophysics Data System (ADS)

The impact of SiO2 content in ultrathin gate dielectrics on the magnitude of the effective work function (EWF) shift induced by nanoscale capping layers has been investigated experimentally and theoretically. The magnitude of the effective work function shift for four different capping layers (AlN, Al2O3, La2O3, and Gd2O3) is measured as a function of SiO2 content in the gate dielectric. A nearly linear increase of this shift with SiO2 content is observed for all capping layers. The origin of this dependence is explained using density functional theory simulations.

Caraveo-Frescas, J. A.; Wang, H.; Schwingenschlögl, U.; Alshareef, H. N.

2012-09-01

436

Optical transparency and electrical conductivity of nonstoichiometric ultrathin In{sub x}O{sub y} films  

SciTech Connect

The effect of thickness and composition on the electrical conductivity and optical transparency, mainly in the infrared, of ultrathin In{sub x}O{sub y} films was studied. In{sub x}O{sub y} films 35-470 A thick with oxygen atomic fractions of {approx}0.3 and {approx}0.5 were prepared via dc magnetron sputtering. All films were polycrystalline, consisting of only the cubic bixbiyte phase of In{sub 2}O{sub 3}. The average grain size of the films increased from 30 to 95 nm as the film thickness increased. The weak dependence of the electrical conductivity on the frequency and the low activation energies for conduction, a few hundredths of an eV, provided an indication that free band conduction was the primary electrical conduction mechanism in the case of all ultrathin In{sub x}O{sub y} films. It was found that introducing a high degree of nonstoichiometry in the form of oxygen deficiency did not help improve the electrical conductivity, since not all vacancies contributed two free electrons for conduction and due to impurity scattering. The optical nature of these films, studied mainly by ellipsometry, was found to be dependent on the film's composition and thickness. In the infrared, the dielectric function of all In{sub x}O{sub y} films was consistent with the Drude model, inferring that the transparency loss in this region was a result of free charge carriers. In the visible however, In{sub x}O{sub y} films under 170 A, which had an oxygen atomic fraction of {approx}0.5, were modeled by extending the Drude model to the shorter wavelengths. Films over 170 A, with the same composition, were modeled using the Cauchy dispersion model, meaning that no absorption was measured. These results indicate that, optically, under specific compositions, ultrathin In{sub x}O{sub y} films undergo a transition from metalliclike behavior to dielectric behavior with increasing film thickness. Using a figure of merit approach, it was determined that a nonstoichiometric 230 A thick In{sub x}O{sub y} film, with an oxygen atomic fraction of {approx}0.3, had the best combination of conductivity and transparency, namely, absorption of less than 20% in the infrared, about 10% in the visible, and electrical resistance of only 230 {Omega} at 20 kHz. Such a film may be classified as a highly conductive transparent oxide even in the infrared.

Joseph, Shay; Berger, Shlomo [Department of Materials Engineering, Technion, Technion City, Haifa, 32000 (Israel)

2011-07-15

437

Atomic layer deposition of dielectrics on graphene using reversibly physisorbed ozone.  

PubMed

Integration of graphene field-effect transistors (GFETs) requires the ability to grow or deposit high-quality, ultrathin dielectric insulators on graphene to modulate the channel potential. Here, we study a novel and facile approach based on atomic layer deposition through ozone functionalization to deposit high-? dielectrics (such as Al(2)O(3)) without breaking vacuum. The underlying mechanisms of functionalization have been studied theoretically using ab initio calculations and experimentally using in situ monitoring of transport properties. It is found that ozone molecules are physisorbed on the surface of graphene, which act as nucleation sites for dielectric deposition. The physisorbed ozone molecules eventually react with the metal precursor, trimethylaluminum to form Al(2)O(3). Additionally, we successfully demonstrate the performance of dual-gated GFETs with Al(2)O(3) of sub-5 nm physical thickness as a gate dielectric. Back-gated GFETs with mobilities of ~19,000 cm(2)/(V·s) are also achieved after Al(2)O(3) deposition. These results indicate that ozone functionalization is a promising pathway to achieve scaled gate dielectrics on graphene without leaving a residual nucleation layer. PMID:22352388

Jandhyala, Srikar; Mordi, Greg; Lee, Bongki; Lee, Geunsik; Floresca, Carlo; Cha, Pil-Ryung; Ahn, Jinho; Wallace, Robert M; Chabal, Yves J; Kim, Moon J; Colombo, Luigi; Cho, Kyeongjae; Kim, Jiyoung

2012-03-06

438

Polar ultra-thin Langmuir-Blodgett films for nonlinear optical applications  

NASA Astrophysics Data System (ADS)

A series of side chain liquid crystalline copolymers having a different spacer length, copolymer composition, and chromophore type were synthesized and characterized at the gas-water interface. The liquid crystalline properties were identified by differential scanning calorimetry (DSC), optical microscopy, and X-ray diffraction (XRD). Copolymer with a spacer length of 4, 5, 10, and 11 show SA phases with a batonnet texture. The LC phase is stabilized as the spacer is increased. The monolayers and transferred film were investigated. Evidence of nanodomain in copolymer with high NBP content was shown. These were related to anomalous dielectric response around room temperature. The second order nonlinear optical response of an ultra- thin Langmuir-Blodgett (LB) film of a sidechain polysiloxane copolymer was enhanced by replacing the nitrobiphenyl sidechain with a nitrostilbene sidechain. The second order nonlinear optical response of Cop11/50%NSB was improved by 1.7 to 1.8 times over the nitrobiphenyl, Cop11/50%NBP. The dynamics of the polar ultra-thin LB film are revealed through our dielectric study. The effect of the spacer length, copolymer composition, and chromophore type was investigated. The copolymer with long spacer lengths exhibit two relaxation processes, at room temperature and before the crystalline (K) to liquid crystal transition (LC), while the shorter spacer length copolymers exhibits only one relaxation. Increasing of the nitrobiphenyl composition in the copolymer, spacer 11, does not effect the activation energy of the K-LC transition; however, the relaxation for a given frequency is observed at a lower temperature. The monolayer and mixed monolayers of diacetylenic acid containing nitrobiphenyl, DA8/1NBP, and methoxybiphenyl, DA8/1OMe, were investigated. The monolayer DA8/1OMe does not undergo solid state polymerization at the gas-water interface but its Cd2+ and Ba2+ salts do. The coarea of the mixed monolayer is too small which indicates aggregation of the material.

Srikhirin, Toemsak

1998-11-01

439

Dielectric materials for electrowetting-on-dielectric actuation  

Microsoft Academic Search

The fundamental building blocks of typical electrowetting-on-dielectric (EWOD) actuation and their importance in the EWOD\\u000a mechanism are introduced and reviewed, respectively. The emphasis in this experimental study of EWOD is on dielectric materials,\\u000a upon which the performance of EWOD devices is heavily dependent. Dielectric breakdown of several typical polymeric and inorganic\\u000a insulators employed as dielectrics for EWOD has been analytically

Hong Liu; Saman Dharmatilleke; Devendra K. Maurya; Andrew A. O. Tay

2010-01-01

440

Method of fabricating an ultra dielectric constant (K) dielectric layer  

US Patent & Trademark Office Database

A fabrication method of an ultra low-k dielectric layer is provided. A deposition process is performed, under the control of a temperature varying program or a pressure varying program, by reacting a dielectric matrix to form porous low-k dielectric layers with a gradient density on a barrier layer over a substrate.

2012-01-10

441

Dielectric Losses at Radio Frequencies in Liquid Dielectrics  

Microsoft Academic Search

Dielectric losses and dielectric constants at radio frequencies for nitrobenzene, water and xylene.-The method of resistance variation was used to measure the phase difference psi and dielectric constant K for frequencies between 2 × 105 and 14 × 105 cycles\\/sec. Special cells were required. (1) Variation with frequency. The results agree approximately with the equations: For carefully dried nitrobenzene at

A. B. Bryan

1923-01-01

442

A New NIST Database for the Simulation of Electron Spectra for Surface Analysis (SESSA): Application to Angle-Resolved X-ray Photoelectron Spectroscopy of HfO2, ZrO2, HfSiO4, and ZrSiO4 Films on Silicon  

SciTech Connect

We describe a new NIST database for the Simulation of Electron Spectra for Surface Analysis (SESSA). This database provides data for the many parameters needed in quantitative Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). In addition, AES and XPS spectra can be simulated for layered samples. The simulated spectra, for layer compositions and thicknesses specified by the user, can be compared with measured spectra. The layer compositions and thicknesses can then be adjusted to find maximum consistency between simulated and measured spectra. In this way, AES and XPS can provide more detailed characterization of multilayer thin-film materials. We report on the use of SESSA for determining the thicknesses of HfO2, ZrO2, HfSiO4, and ZrSiO4 films on Si by angle-resolved XPS. Practical effective attenuation lengths (EALs) have been computed from SESSA as a function of film thickness and photoelectron emission angle (i.e., to simulate the effects of tilting the sample). These EALs have been compared with similar values obtained from the NIST Electron Effective-Attenuation-Length Database (SRD 82). Generally good agreement was found between corresponding EAL values, but there were differences for film thicknesses less than the inelastic mean free path of the photoelectrons in the overlayer film. These differences are due to a simplifying approximation in the algorithm used to compute EALs in SRD 82. SESSA, with realistic cross sections for elastic and inelastic scattering in the film and substrate materials, is believed to provide more accurate EALs than SRD 82 for thin-film thickness measurements, particularly in applications where the film and substrate have different electron-scattering properties.

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

2005-09-09

443

Fabrication of Polyurethane Dielectric Actuators.  

National Technical Information Service (NTIS)

This paper provides a summary of a 3-year Technology Investment Fund Project entitled 'Dielectric Polymer Actuators for Active/Passive Vibration Isolation,' which was completed in March 2005. The purpose of this project was to investigate dielectric polym...

J. P. Szabo

2005-01-01

444

Microwave Dielectric Resonator-Tuning.  

National Technical Information Service (NTIS)

Dielectric resonators have applications as low-loss compact filters in the microwave region. Tuning characteristics of dielectric resonators that might allow for temperature compensation and frequency variability were investigated both theoretically and e...

U. H. W. Lammers M. R. Stiglitz

1974-01-01

445

Controlling birefringence in dielectrics  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

446

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

447

Determination of Molecular Orientation in Biaxially Oriented Ultrathin Films  

Microsoft Academic Search

Biaxial orientation in ultrathin films is characterized by a preferential orientation of the main molecular axis in the plane of the film in addition to its orientation with respect to the normal of the film. In this paper, analytical expressions allowing the calculation of the molecular orientation in biaxially oriented films from their anisotropic optical constants are presented for the

Isabelle Pelletier; Isabelle Laurin; Thierry Buffeteau; Michel Pezolet

2004-01-01

448

Skyrmion Nucleation in Ultrathin Magnetic Film by Strong Magnetic Tip  

Microsoft Academic Search

We study numerically the dynamics of skyrmion creation in ultrathin metallic ferromagnetic film by vertyically uniformly moving strong magnetic tip. Nucleated magnetic bubble domain gradually transforms into skyrmion after complete removal of the tip. The RKKY interaction between localized spins in ferromagnetic metal mediated by conduction electrons together with fourth order exchange interaction stabilizes skyrmion, which is clearly seen in

Arman Kirakosyan; Valery Pokrovsky

2003-01-01

449

Morphological modification of nanostructured ultrathin-layer chromatography stationary phases  

Microsoft Academic Search

Ultrathin-layer chromatography (UTLC) provides the high sensitivities and rapid separations over short distances desirable in many analytical applications. The dependence of these performance benefits on UTLC layer microstructure motivates continued stationary phase engineering efforts. A new method of modifying the elution behaviours of nanostructured thin film UTLC stationary phases is investigated in this report. Macroporous normal phase silica thin films

S. R. Jim; A. J. Oko; M. T. Taschuk; M. J. Brett

2011-01-01

450

Versatile waveguide polarizer incorporating an ultrathin discontinuous silver film  

Microsoft Academic Search

We demonstrate the first transverse magnetic (TM) pass waveguide polarizer suitable for integrated optic or fiber optic geometries. The polarizing properties of waveguides incorporating an ultrathin discontinuous silver film are due to excitation of a localized surface plasmon mode. The polarizers have a large bandwidth (?100 nm), high extinction ratios, and do not rely on sensitive phase matching conditions. We

Mark J. Bloemer; Joseph W. Haus

1992-01-01

451