bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Electrochemical Deposition of Copper and Microstructure Evolution in Fine Lines
Authors: Grunow Stephan , Diatezual Deda , Seo Soon-Cheon , Stoner Timothy , Kaloyeros Alain E.
Published: April 2011

As computer chip technologies evolve from aluminum-based metallization schemes to their copper-based counterparts, Electrochemical Deposition (ECD) is emerging as a viable deposition technique for copper (Cu) interconnects. This paper presents the results of a first-pass study to examine the underlying mechanisms that control ECD Cu nucleation, growth kinetics, and post-deposition microstructure evolution (self-annealing), leading to the development and optimization of an ECD Cu process recipe for sub-quarter-micron device generations. The influence of bath composition, current waveform, type and texture of Cu seed layer, and device feature size (scaling effect) on the evolution of film texture, morphology, electrical properties, and fill characteristics was investigated using a manufacturing-worthy ReynoldsTech 8” wafer plating tool. Resulting films were analyzed by X-ray Diffraction (XRD), four-point resistivity probe, Focused-Ion-Beam Scanning Electron Microscopy (FIB-SEM), and Atomic Force Microscopy (AFM). These investigations identified an optimized process window for the complete fill of aggressive device structures with pure Cu with resistivity ∼ 2.0 µΩ-cm and smooth surface morphology.
The Intercorrelation Between Microstructure and Chemicalmechanical Polish of Metal Thin Films
Authors: Tseng Wei-Tsu , Wang Ying-Lang
Published: April 2011

The correlation between microstructures of Al and W metal thin films and their respective CMP performance is investigated. It is found that CMP removal rate decreases with increasing grain size. In both cases, the textures of the metal films are altered and their resistivity increased after CMP. The phenomenon is more pronounced for polish under a greater down force. The table speed, on the other hand, has only minimum effects on microstructure and resistivity. The possible underlying mechanisms leading to this phenomenon are proposed and their potential impacts on metallization reliability is discussed.
Effects on Selective CVD of Titanium Disilicide by Substrate Doping and Selective Silicon Deposition
Authors: Maa Jer-shen , Howard David J.
Published: April 2011

During selective chemical vapor deposition (CVD) of titanium disilicide on silicon, consumption of As implanted silicon substrates is enhanced relative to Si substrates implanted with other species. In this study, a selective epitaxially grown Si (SEG Si) layer has been deposited prior to selective CVD of titanium disilicide on samples with different implanted doses of either As or B. If no SEG Si film is deposited, the selective CVD TiSi2 film properties strongly depended on dopant type (As vs. B) and on dopant dose. Addition of a SEG Si film prior to selective CVD TiSi2 improves process stability as a function of changes in initial ion implanted conditions. Use of a SEG Si film prior to selective CVD TiSi2 results in values of TiSi2 thickness and TiSi2 sheet resistance which are approximately constant as a function of initial ion implant dose, and are approximately equal for both the As and B implanted samples used in this study.
Line-Width Dependence of Void Formation in Ti-Salicided BF2-Doped Polysilicon Lines
Authors: Chua H. N. , Pey K. L. , Siah S. Y. , Lim E. H. , Ho C. S.
Published: April 2011

We report the first observation of voids in sub-quarter micron Ti-salicided BF2-dopedpolycrystalline silicon (polySi) lines. Some of the voids, with sizes ranging from 10 to 100nm, can be clearly seen on the surface of the TiSi2 film whereas others are situated below the TiSi2 surface. The void density and size increase with decreasing polySi line-width, especially for line-widths < 0.24 µm. The voiding phenomenon was also observed to be moresevere for TiSi2 fabricated with enhanced salicidation techniques such as pre-amorphization-implant(PAl) and implant-through-metal (ITM) as compared to the conventional salicidationmethod without amorphization. The origin of the voids is found to coincide with the fluorinepeak at the TiSi2/polySi interface in the SIMS depth-concentration profiles.
Preparation and Characterization of High Porosity Si02 Xerogels for Low k Dielectrics
Authors: Colomer M. T.
Published: April 2011

Due to its low dielectric constant, high porosity SiO2 is a potential intermetal dielectric (IMD) film for sub-half micron devices. High porosity SiO2 xerogels with a low dielectric constant were prepared by a sol-gel method. Basic and mixtures of SiO2 sols (acid/base) aqueous particulate suspensions were employed using TEOS as a precursor.

Porosity values up to 55% could be obtained for the silica xerogels calcined at 250°C. The porosity values were estimated by means of nitrogen adsorption (BET). The dielectric constant was directly measured using an impedance analyzer and also calculated from the nitrogen adsorption measurements. Both techniques were in good agreement and resulted in a dielectric constant value of 2.32 for xerogels having the highest porosity.
A Novel Air-Bridge Type Gate-Data Line Inter-Crossing to Reduce Signal delay for Large size AMLCD
Authors: Park C-M , Kang J-H , Han M-K
Published: April 2011

A new TFT-LCD panel with an air-bridge type gate to data line inter-crossing has been proposed and its characteristics have been measured. The proposed structure has air-gap between gate and data line intercrossing. This air-bridge TFT-LCD panel has very small amount of capacitance between gate and data line. The new panel structure achieves 9 times faster signal delay compared with conventional panel, which enables to have enough design margin of over 20-inch diagonal size UXGA panel. We have examined thermal and mechanical durability of new panel to verify capability for commercial AMLCD application.
Atomic Structure Impacts on Dielectric and Mechanical Properties of Hydrogen-Silsesquioxane During Thermal Processing
Authors: Liu Youfan , Dall Fred
Published: April 2011

Atomic structure impacts on the dielectric and mechanical properties of hydrogen-silsesquioxane (HSQ) were investigated to determine the sensitivity of HSQ to Si-H bond degradation during thermal processing. It was demonstrated that the dielectric properties of HSQ films are not sensitive to Si-H bond degradation up to 50 % if polar silanol or water species are not induced during thermal processing at a temperature of ≤ 450 °C. However, as the Si-H bond density is reduced, the mechanical properties are changed due to the increasingly formed Si-O-Si networks. This provides an opportunity for tuning mechanical properties per application requirements by process optimization.
Newly Developed Low-Density Methylsiloxane Spin-On-Glass Films
Authors: Yamada Noriko , Takahashi Toru
Published: April 2011

Spin-on-glass (SOG) solution has been prepared from methyltriethoxysilane and dimethoxymethyl-3,3,3-trifluoropropylsilane. Trifluoropropyl groups attached to silicon are thermally decomposed by curing at 450°C in nitrogen. Since the overall methylsiloxane network is maintained without a significant shrinkage upon the thermal decomposition of trifluoropropyl groups, vacant spaces whose sizes are comparable to those of trifluoropropyl groups are introduced into the methylsiloxane network, leading to the low-density film with the Brunauer, Emmet and Teller (BET) surface area of 270 m2/g. The film shows the dielectric constant of 2.3, heat stability, low moisture uptake, good planarization property and no corrosion toward aluminum conducting lines.
In Situ Plasma Analysis, Fluorine Incorporation, Thermostability, Stress, and Hardness Comparison of Fluorinated Amorphous Carbon and Hydrogenated Amorphous Carbon Thin Films Deposited on Si by Plasma Enhanced Chemical Vapor Deposition
Authors: Glew A. D. , Cappelli M. A. , Touzelbaev M. N. , Hu Y.
Published: April 2011

In situ observation of the plasma properties during deposition of fluorinated amorphous hydrogenated carbon (FLAC) and unfluorinated amorphous hydrogenated carbon are performed. The relationship between film properties and impinging ion energy and incident ion momentum is discussed within the framework of existing models of diamond-like carbon (DLC) formation. The DLC films are deposited in a low pressure radio frequency discharge operating at 13.57 MHz with methane and carbon tetra-fluoride as the source gases. Thermostability, stress, and mechanical properties are investigated. The films are elevated to 400 degrees C in order to investigate thermostability. Thin film stress and nano-hardness are also studied. The film density is investigated by gravimetric methods. The fluorinated film stoichiometry is explored with x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.
The Use of Electron Channeling Patterns for Process Optimization of Low-Temperature Epitaxial Silicon Using Hot-Wire Chemical Vapor Deposition
Authors: Matson R. , Thiesen J. , Jones K.M. , Crandall R. , Iwaniczko E. , Mahan H.
Published: April 2011

We demonstrate the first reported use of electron channeling patterns (ECPs) as a response for a statistical design of experiments process-optimization for epitaxial silicon. In an effort to fully characterize the new hot-wire chemical vapor deposition (HWCVD) method of epitaxial growth recently discovered at NREL, a large number of parameters with widely varying values needed to be considered. To accomplish this, we used the statistical design of experiments method. This technique allows one to limit the number of sample points necessary to evaluate a given parameter space. In this work we demonstrate how ECPs can effectively be used to optimize the process space as well as to quickly and economically provide the process engineer with absolutely key information.
Epitaxial Lateral Overgrowth of Gallium Arsenide Studied by Synchrotron Topography
Authors: Rantamäki R. , Tuomi T. , Zytkiewicz Z. R. , Dobosz D. , Mcnally P. J. , Danilewsky A. N.
Published: April 2011

Synchrotron x-ray topographs of GaAs epitaxial lateral overgrowth (ELO) samples are made both in transmission and reflection geometries. The topographs show that the bending of the ELO layers is visible in most geometries. A simulation of the topographic images is implemented taking into account only the orientational contrast. Simulated back reflection section topographs are in good agreement with the experimental ones. The shape of the lattice planes in an ELO layer is calculated using the simulation data and compared to the measured surface profile of the same ELO stripe.
The nature of ripples and islands in strained SiGe/Si heteroepitaxy: nucleation vs. instability phenomena
Authors: Christiansen S.H. , Albrecht M. , Becker M. , Strunk H.P. , Wawra H.
Published: April 2011

Using liquid phase epitaxy from Bi solution in the temperature range 550°–700°C at low growth rates we study the formation of ripples and islands and their interdependence. As main results we find from the dependencies on growth time and temperature that ripples are an instability phenomenon and that islands nucleate thermally activated. Island nucleation on a ripple template (that is, as an instability phenomenon, highly ordered) has huge impact on the achievable order of the islands.
Cluster ‘Contact Epitaxy’- Direct Evidence for Novel Particle: Substrate Interactions
Authors: Yeadon M. , Yang J.C. , Ghaly M. , Averback R.S. , Gibson J.M.
Published: April 2011

In this paper we describe observations of novel interactions between clusters of Ag deposited on the clean (001) Cu surface. The experiments are analogous to those performed by Gleiter and co-workers in the 1970's, where grain boundary orientations in particles of Cu and Ag supported on single crystal metal substrates were studied. Upon annealing close to the melting point, these particles (∼10–100μm in diameter) were found to rotate on the surface, forming low-energy grain boundary configurations with the substrate. The particles studied in our experiments are ∼104 times smaller, and show rather different behavior. In the case of Ag nanoparticles we have observed a novel phenomenon, which we call ‘contact epitaxy’, involving the formation of several monolayers of epitaxially oriented Ag at the Cu surface upon contact between this surface and the Ag cluster. The phenomenon may be understood from molecular dynamics simulations of the ‘soft impact’ between the nanoparticle and surface, which indicate that the ordered layers form within picoseconds of contact. We will discuss the mechanisms by which ‘contact epitaxy’ is believed to occur.
Heteroepitaxial Growth of Zinc Oxide Single Crystal Thin Films on (111) Plane YSZ by Pulsed Laser Deposition
Authors: Ohta Hiromichi , Tanji Hiroaki , Orita Masahiro , Hosono Hideo , Kawazoe Hiroshi
Published: April 2011

Heteroepitaxial ZnO films were grown on (111) surface of yttria stabilized zirconia (YSZ) and (0001) surface of sapphire by PLD method, using KrF eximer laser (248nm) in an ultra-high-vacuum chamber. ZnO grown on YSZ (111) at the substrate temperature of 800°C had an epitaxial relationship at the ZnO/YSZ interface of ZnO [1120]//YSZ [110]. Hexagonalshaped grains were observed whose surfaces were atomically flat. The grain size of ZnO increased and the Hall mobility rose toward 1400nm and 75cm2/Vs. respectively as film thickness increased from 10 nm to 800 nm.
The Role of the Lattice Step in Epitaxial Growth
Authors: Fu Tsu-Yi , Tsong Tien T.
Published: April 2011

Solid surfaces have many lattice steps. In epitaxy, aggregation of deposited atoms into islands or clusters during their diffusing can create many additional atomic steps. We study the effects of lattice steps on epitaxial growth in two aspects: 1. Movement of atoms across the step edge: a series of field ion microscope experiments reveal the importance of reflective and trapping properties of steps, and provide quantitative information that helps explain various growth modes observed in homoepitaxial growth. 2. Diffusion along the step edge: a number of field ion microscope experiments are done to determine diffusion parameters of a ledge atom along the step edge, and to derive the potential-energy diagram along different diffusion paths that helps explain the growth morphology. During growth, an atom undergoes a number of elementary atomic processes. Each process is characterized by a few energy parameters in bonding and diffusion. The integrated effect of all of these processes determines the growth process. We provide reliable experimental data and find the temperature ranges where various atomic processes are important
Optical Characterization of SiC Wafers
Authors: Burton J. C. , Pophristic M. , Long F. H. , Ferguson I.
Published: April 2011

Raman spectroscopy has been used to investigate wafers of both 4H-SiC and 6H-SiC. The two-phonon Raman spectra from both 4H- and 6H-SiC have been measured and found to be polytype dependent, consistent with changes in the vibrational density of states. We have observed electronic Raman scattering from nitrogen defect levels in both 4H- and 6H-SiC at room temperature. We have found that electronic Raman scattering from the nitrogen defect levels is significantly enhanced with excitation by red or near IR laser light. These results demonstrate that the laser wavelength is a key parameter in the characterization of SiC by Raman scattering. These results suggest that Raman spectroscopy can be used as a noninvasive, in situ diagnostic for SiC wafer production and substrate evaluation. We also present results on time-resolved photoluminescence spectra of n-type SiC wafers.
Growth and Characterization of 2″ 6H-Silicon Carbide
Authors: Schmitt Erwin , Eckstein Robert , Kölbl Martin , Weber Amd-Dietrich
Published: April 2011

For the growth of 2″ 6H-SiC a sublimation growth process was developed. By different means of characterization crystal quality was evaluated. Higher defect densities, mainly in the periphery of the crystals were found to be correlated to unfavourable process conditions. Improvement of thermal boundary conditions lead to a decreased defect density and better homogeneity over the wafer area.
Epitaxial Growth of GaN Thin Films Using a Hybrid Pulsed Laser Deposition System
Authors: Mérel Philippe , Chaker Mohamed , Pépin Henri , Tabbal Malek
Published: April 2011

A hybrid Pulsed Laser Deposition system was developed to perform epitaxial growth of GaN on sapphire(0001). This system combines the laser ablation of a cooled Ga target with a well-characterized atomic nitrogen source. Taking advantage of the flexibility of this unique deposition system, high quality GaN thin films were deposited by optimizing both the laser intensity and the nitrogen flux. To date, our best GaN films show a FWHM of the GaN(0002) rocking curve peak equal to 480 arcsec. This result has been obtained at a laser intensity of I = 7×107 W/cm2, a substrate temperature of 800°C and under Ga-rich growth conditions.
Photoluminescence between 3.36 eV and 3.41 eV from GaN Epitaxial Layers
Authors: Seitz R. , Gaspar C. , Monteiro T. , Pereira E. , Poisson M. A. , Beaumont B.
Published: April 2011

GaN, its alloys, QWs and MQWs have gained an important place among shortwavelength optical emitters and high temperature electronic devices [1,2]. The performance of such devices is limited by the presence of native and impurity defects. The understanding of the optical properties of the basic material allows us to improve its quality and thus increase the performance of these materials.
Current-Voltage Characteristics of Ungated AlGaN/GaN Heterostructures
Authors: Albrecht J. D. , Rudento P. P. , Binari S. C. , Ikossi-Anastasiou K. , Ancona M. G. , Henry R. L. , Koleske D. D. , Wickenden A. E.
Published: April 2011

Results of a systematic study of the current vs. voltage characteristics of ungated AIGaN/GaN heterostructures grown on sapphire substrates are presented. It is experimentally observed that the saturation current nearly doubles as the source-to-drain channel lengths decrease from 11.8 to 1.7μm. The average electric field at which current saturation occurs is 10 to 30kV/cm, i.e. much less than the electron velocity saturation field. The experimental data is interpreted in the framework of a new model that takes into account the non-uniformity of the electron density in the channel, electron velocity saturation, and thermal effects. The temperature dependent electron transport characteristics of the model are based on Monte Carlo simulations of electron transport in GaN. It is shown that appreciable contact resistance, which leads to partial channel depletion near the source, and significant self-heating of the devices under high drain-to-source bias are the main reasons for the observed current saturation. The effective ambient temperature in the channel of the devices is calculated from a two-dimensional thermal model of heat dissipation through the sapphire substrate. Equilibrium channel carrier concentrations and low-field mobilities are determined from Hall effect data. The ungated structures are demonstrated to provide much useful materials and process characterization data for the development of AIGaN/GaN heterostructure field effect transistors.
Hydrostatic and uniaxial stress dependence and photo induced effects on the channel conductance of n-A1GaN/GaN heterostructures grown on sapphire substrates
Authors: Fung A. K. , Cai C. , Ruden P. P. , Nathan M. I. , Chen M. Y. , McDermott B. T. , Sullivan G. J. , Hove J. M. Van , Boutros K. , Redwing J. , Yange J. W. , Chene Q. , Khane M. A. , Schaff W. , Murphy M.
Published: April 2011

We measure the hydrostatic stress, uniaxial stress, and photo induced dependence of the channel conductance of two-dimensional electron gas AlGaN/GaN heterostructures grown on c-axis sapphire. The structures examined are grown by nitrogen-plasma molecular beam epitaxy and metal organic chemical vapor deposition. Electrical conductance measurements are made with four point probes on Hall bar samples. Both, hydrostatic stress and uniaxial stress result in changes in the conductance. Moreover, these changes in conductance have long settling times after the stress is applied and may be due to deep level defects, the energy levels of which change with stress. Stress coefficients extracted from the samples are partially attributed to deep level defects and to the piezoelectric effect resulting from different piezoelectric coefficients of GaN and AlN. Photo induced changes of the two-dimensional electron gas are also observed. We find that pulsed illumination produces long transient times in the conductance. These transients are reduced by thermal heating in some samples. However, they can still be present at 153°C.
Piezoelectric Scattering in Large-Bandgap Semiconductors and Low-Dimensional Heterostructures
Authors: Ridley B. K. , Zakhleniuk N. A. , Bennett C. R. , Babiker M. , Anderson D. R.
Published: April 2011

We develop a rigorous theory of piezoacoustic phonon limited electron transport in bulk GaN and GaN-based heterostructures. Within the Boltzmann equation approach we derive a new expression for the momentum relaxation rate and show that the Pauli principle restrictions are comparable in importance to a screening effect at temperatures up to 150 K provided that the electron density is large. This is of particular importance for electrons in GaN/AlN-based quantum wells where very high electron densities initiated by the piezoelectric effect have recently been reported. Variations of the piezoacoustic phonon limited electron mobility with the lattice temperature and with the electron density for a zinc-blende and wurtzite GaN are presented.
Correlation of Drain Current Pulsed Response with Microwave Power Output in AlGaN/GaN HEMTs
Authors: Binari S. C. , Ikossi-Anastasiou K. , Kruppa W. , Dietrich H. B. , Kelner G. , Henry R. L. , Koleske D. D. , Wickenden A. E.
Published: April 2011

The drain-current response to short (<1μs) gate pulses has been measured for a series of GaN HEMT wafers that have similar dc and small-signal characteristics. This response has been found to correlate well with the measured microwave power output. For example, for devices where the pulsed drain current is greater than 70% of the dc value, output power densities of up to 2.3 W/mm are attained. This is in contrast with 0.5 W/mm measured for devices with low pulse response (less than 20% of the dc value). These results, which can be explained by the presence of traps in the device structure, provide a convenient test which is predictive of power performance.
High Voltage Schottky Barrier Diodes on P-Type SiC using Metal-Overlap on a Thick Oxide Layer as Edge Termination
Authors: Zhang Q. , Madangarli V. , Soloviev S. , Sudarshan T. S.
Published: April 2011

P-type 6H SiC Schottky barrier diodes with good rectifying characteristics upto breakdown voltage as high as 1000V have been successfully fabricated using metal-overlap over a thick oxide layer (∼ 6000 Å) as edge termination and Al as the barrier metal. The influence of the oxide layer edge termination in improving the reverse breakdown voltage as well as the forward current – voltage characteristics is presented. The terminated Schottky diodes indicate a factor of two higher breakdown voltage and 2–3 times larger forward current densities than those without edge termination. The specific series resistance of the unterminated diodes was ∼228 mΩ-cm2, while that of the terminated diodes was ∼84 mΩ-cm2.
A Study of Semiconductor Quantum Structures by Microwave Modulated Photolumenescence
Authors: Guliamov R. , Lifshitz E. , Cohen E. , Ron A. , Shtrikman H.
Published: April 2011

Mixed types I - type II multiple quantum wells (QW) structures consist of alternating narrow- and wide GaAs wells, separated by AlAs barriers. Transfer of electrons from the narrow- to the wide well results in the formation of a two-dimensional electron gas (2DEG) in the wide wells and a hole gas (2DHG) in the narrow ones. The present study investigated the effect of these gases on the various photoluminescence (PL) bands. The study utilized two modulations techniques: double beam PL and microwave modulated PL (MMPL), offering high-resolution spectroscopy, control of the 2DEG density and effective temperature. The results showed that the formation of a low density 2DEG in the wide wells cause the formation of trions. However, a large density of excess electrons makes mutual collisions with other photo-generated species, causing the dissociation of the trions and excitons. In addition, electrons transfer through the barrier gives rise to barrier-well indirect recombination emission.
Energy Band Offsets at a Ga2O3(Gd2O3)-GaAs Interface
Authors: Lay T. S. , Hong M. , Kwo J. , Mannaerts J. P. , Hung W. H. , Huang D. J.
Published: April 2011

We report the energy band offsets at a Ga2O3(Gd2O3)-GaAs interface. The valence-band offset (ΔEv) is ∼ 2.6 eV, measured by soft x-ray photoemission spectroscopy. Analysis of the current-voltage characteristics of a Pt-Ga2O3(Gd2O3)-GaAs MOS (metal-oxide-semiconductor) structure, which are dominated by Fowler-Nordheim tunneling, reveals a conduction-band offset (ΔEC) ∼ 1.4 eV at the Ga2O3(Gd2O3)-GaAs interface and an electron effective mass (m*) ∼ 0.29 me of the Ga2O3(Gd2O3) film.
Oxidation and Carbon Contamination in GaAs (100) Wet Treatments
Authors: Elbahnasawy R. F. , McInerney J. G. , Hughes G.
Published: April 2011

Oxidation and carbon contamination of n-type GaAs (100) surfaces have been investigated by x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS) for a variety of cleaning and etching pretreatment procedures prior to immersion in either (NH4)2S, Na2S aqueous solutions or S2Cl2 solution in dichloromethane. The study has shown that sulfur passivation removes surface oxide and minimize carbon contamination for surfaces treated in (NH4)2S and S2Cl2 solutions. A significant oxygen and carbon contamination in the anodic passivation of GaAs (100) in (NH4)2Sx aqueous solution have been quantitatively measured. In addition, pretreatment in basic solutions have shown minimal oxygen and carbon level in comparison with the acidic solutions. Surface pretreatment carried out ex-situ has shown a higher risk of surface contamination prior to sulfur passivation.
Wet Oxidation of High-Al-Content III–V Semiconductors: Important Materials Considerations for Device Applications
Authors: Ashby Carol I. H.
Published: April 2011

Wet oxidation of high-Al-content AIGaAs semiconductor layers in vertical cavity surface emitting lasers (VCSELs) has produced devices with record low threshold currents and voltages and with wall-plug efficiencies greater than 50%. Wet oxidation of buried AlGaAs layers has been employed to reduce the problems associated with substrate current leakage in GaAs-on-insulator (GOL) MESFETs. Wet oxidation has also been considered as a route to the long-sought goal of a III-V MIS technology. To continue improving device designs for even higher performance and to establish a truly manufacturable technology based on wet oxidation, the effect of oxidation of a given layer on the properties of the entire device structure must be understood. The oxidation of a given layer can strongly affect the electrical and chemical properties of adjacent layers. Many of these effects are derived from the production of large amounts of elemental As during the oxidation reaction, the resultant generation of point defects, and the diffusion of these defects into adjacent regions. This can modify the chemical and electrical properties of these regions in ways that can impact device design, fabrication, and performance. Current understanding of the problem is discussed here
Surface Passivation of GaAs Power FETs
Authors: Tanaka Tsuyoshi , Furukawa Hidetoshi , Miyatsuji Kazuo , Ueda Daisuke
Published: April 2011

The surface passivation of GaAs power FET has been investigated. Intermodulation distortion of GaAs power FET was found to be affected by frequency dispersion which originates from electron trap at the surface in the vicinity of the gate. There are two ways to suppress the frequency dispersion. One is reducing electron trap itself by using surface passivation, the other is making surface insensitive to the surface trapping effect. We found the FET with undoped InGaP layers on the n-GaAs channel is free from surface trapping effects. The undoped InGaP layer acts as an ideal passivation layer for the channel, since it shows only 2% frequency dispersion of drain current at 1MHz compared to DC condition.
Development of Low Temperature Silicon Nitride and Silicon Dioxide Films by Inductively-Coupled Plasma Chemical Vapor Deposition
Authors: Lee J. W. , Mackenzie K. D. , Johnson D. , Pearton S. J. , Ren F. , Sasserath J. N.
Published: April 2011

High-density plasma technology is becoming increasingly attractive for the deposition of dielectric films such as silicon nitride and silicon dioxide. In particular, inductively-coupled plasma chemical vapor deposition (ICPCVD) offers a great advantage for low temperature processing over plasma-enhanced chemical vapor deposition (PECVD) for a range of devices including compound semiconductors. In this paper, the development of low temperature (< 200°C) silicon nitride and silicon dioxide films utilizing ICP technology will be discussed. The material properties of these films have been investigated as a function of ICP source power, rf chuck power, chamber pressure, gas chemistry, and temperature. The ICPCVD films will be compared to PECVD films in terms of wet etch rate, stress, and other film characteristics. Two different gas chemistries, SiH4/N2/Ar and SiH4/NH3/He, were explored for the deposition of ICPCVD silicon nitride. The ICPCVD silicon dioxide films were prepared from SiH4/O2/Ar. The wet etch rates of both silicon nitride and silicon dioxide films are significantly lower than films prepared by conventional PECVD. This implies that ICPCVD films prepared at these low temperatures are of higher quality. The advanced ICPCVD technology can also be used for efficient void-free filling of high aspect ratio (3:1) sub-micron trenches.
Passivation of Interfaces in High-Efficiency Photovoltaic Devices
Authors: Kurtz Sarah R. , Olson J. M. , Friedman D. J. , Geisz J. F. , Bertness K. A. , Kibbler A. E.
Published: April 2011

Solar cells made from III–V materials have achieved efficiencies greater than 30%. Effectively ideal passivation plays an important role in achieving these high efficiencies. Standard modeling techniques are applied to Ga0.5In0.5P solar cells to show the effects of passivation. Accurate knowledge of the absorption coefficient is essential (see appendix). Although ultralow (<2 cm/s) interface recombination velocities have been reported, in practice, it is difficult to achieve such low recombination velocities in solar cells because the doping levels are high and because of accidental incorporation of impurities and dopant diffusion. Examples are given of how dopant diffusion can both help and hinder interface passivation, and of how incorporation of oxygen or hydrogen can cause problems.
Platinum-Catalyzed Polymer Electrolyte Membrane for Fuel Cells
Authors: Hwang T. Jan , Shao Hong , Richards Neville , Schmitt Jerome , Hunt Andrew , Lin Wen-Yi
Published: April 2011

The objective of this research is to develop the combustion chemical vapor deposition (CCVD) process for low-cost manufacture of catalytic coatings for proton exchange membrane fuel cell (PEMFC) applications. The platinum coatings as well as the fabrication process for membrane-electrode-assemblies (MEAs) were evaluated in a single testing fuel cell using hydrogen/oxygen. It was found that increasing the platinum loading from 0.05 to 0.1 mg/cm2 did not increase the fuel cell performance. The in-house MEA fabrication process needs to be improved to reduce the cell resistance. Significantly higher performance of Pt coating by the CCVD process has been obtained by MCT's fuelcell industry collaborators who are more experienced with MEA fabrication. The results can not be revealed due to confidentiality agreements.
Organic-Inorganic Hybrid Protonic Polymeric Electrolytes Grafted by Sulfonic Acid / Sulfonamide Moieties
Authors: Depre Laurent , Poinsignon Christiane , Popall Michael
Published: April 2011

Thin proton conducting membranes of an organic-inorganic polymer electrolyte bearing sulphonamide and sulfonic groups are prepared by sol-gel process. Polycondensation of alkoxysilanes provides the inorganic silicate backbone whereas the organic network is formed from reactive functional groups R'((-CH2)3-SO3H) and [(-CH2)3-SO2 NH2] of alkoxysilanes of R'Si[OR3] type. Proton conductivity measured in the dry and wet state under controlled Temperature and Relative Humidity increases from 10 -4 S.cm-1 under vacuum to 6 10-2S.cm-1 at 70°C and 96% RH. Conductivity dependence on temperature and associated conduction mechanisms are discussed in both states.
Development of Zirconia Electrolyte Films on Porous Doped Lanthanum Manganite Cathodes by Electrophoretic Deposition
Authors: Basu R. N. , Randall C. A. , Mayo M. J.
Published: April 2011

Electrophoretic deposition (EPD) was explored as an inexpensive route for fabricating the 8mol% yttria stabilized zirconia electrolyte in solid oxide fuel cells (SOFCs). Normally, deposition of particulate ceramic powders onto a sintered porous surface yields a non uniform coating which, after sintering, results in porosity, surface roughness and cracking in the coating. To overcome this problem, the present study used a fugitive graphite interlayer between the porous air electrode supported (AES) cathode tube (doped-LaMnO3) and the deposited zirconia film. By this approach, a fairly dense green coating (˜ 60%) was obtained, which yielded a smooth surface and pore-free microstructure after sintering. Preliminary results on the effect of a fugitive interlayer on the unfired (green) and fired zirconia coatings are discussed.
Modelling Study on the Electrical Behaviour of YSZ-BASED Composites
Authors: Dotelli G. , Casartelli F. , Sora I. Natali , Schmid C. , Mari C. M.
Published: April 2011

Electrical properties of yttria-stabilised zirconia/alumina (YSZ/AI2O3) composites were tentatively foreseen by simulating their complex impedance spectra. A digital image-based model was developed to describe the electrical conduction process in polycrystalline mono- or multi-phase materials. The microstructure of each polycrystalline sample was reconstructed using the Voronoi tessellation technique (in fact, ad hoc modifications with respect to the original algorithm were introduced) and it was then converted into a threedimensional electrical network according to a set of well-defined rules. The network was solved via an iterative procedure for different frequency values and successively the Nyquist plot generated The complex impedance spectra of different composites were simulated considering the alumina content (5,10 and 15 %wt) as a parameter; both the bulk and grain boundary electrical conductivity were calculated and the Arrhenius plots obtained. Experimental and simulated results were compared and discussed.
A Novel Conducting Polymer with O-S-S-O Bonds for Positive Material:Poly(2,2′-Diaminobenzyloxydisulfide)
Authors: Su Y. Z. , Ma W. S. , Gong K. C.
Published: April 2011

Organic disulfide compounds has been proposed as a new class of high-energy storage material. Poly(2,2'-diaminobenzyloxydisulfide), a novel conducting polymer having O-S-S-O bond joined two moieties of anilines, is synthesized both chemically and electrochemically as a new positive storage material. It exhibits conductivity in the region of 10-3 S cm-1 by the fourprobe method and the O-S-S-0 bonds in it are confirmed by Fourie Transform Raman Spectroscopy(FT-RS) and Fourie Transform Infrared Spectroscopy(FT-IR). The poly(2,2'- diaminobenzyloxydisulfide) films are formed by electropolymerization from a AN/THF solution containing 0. IM LiClO4, 0. IM HCl and 0.05 M 2,2'-diaminobenzyloxydisulfide monomer on Pt electrode under continuous cycling between -0.30V and 1.20V vs Ag/AgCl(sat. KCI) at scanning rate 50mv s-1. The cyclic voltammetry shows its electrochemical behaviour is similar to polyaniline. The redox peak current of the cyclic voltammograms increase with increasing of the cyclic numbers.
Performance of Electric Double Layer Capacitors with Polymer Gel Electrolytes
Authors: Ishikawa Masashi , Kishino Takahiro , Katada Naoji , Morita Masayuki
Published: April 2011

Polymer gel electrolytes consisting of poly(vinylidene fluoride) (PVdF), tetraethylammoniumtetrafluoroborate (TEABF4), and propylene carbonate (PC) as a plasticizer have been investigatedfor electric double layer capacitors. The PVdF gel electrolytes showed high ionic conductivity (ca.6 mS cm-1at 298 K). To assemble model capacitors with the PVdF gel electrolytes and activatedcarbon fiber cloth electrodes, a pair of the fixed electrodes was soaked in a precursor solutioncontaining PC, PVdF, and TEABF4, followed by evaporation of the PC solvent in a vacuumoven. The resulting gel electrolytes were in good contact with the electrodes. The modelcapacitors with the PVdF gel electrolytes showed a large value of capacitance and high coulombicefficiency in operation voltage ranges of 1–2 and 1–3 V. It is worth noting that the capacitors withthe PVdF electrolytes showed long voltage retention in a self-discharge test. These goodcharacteristics of our gel capacitors were comparable to those of typical double layer capacitorswith a liquid organic electrolyte containing PC and TEABF4; rather, the voltage retentivity of thePVdF gel capacitors was much superior to that of the capacitors with the organic electrolyte.
Solid State Synthesis and Properties of Doped LiMnO2 Cathode Materials
Authors: Ammundsen B. , Desilvestro J. , Groutso T. , Hassell D. , Metson J. B. , Regan E. , Steiner R. , Pickering P. J.
Published: April 2011

The crystal structures, microstructures and electrochemical properties of Al-doped lithium manganese oxide materials LiAlxMn1−xO2 (0 ≤ x ≤ 0.1) prepared by solid state reactions have been investigated. A1 doping results in increased cation disorder in the orthorhombic polymorph of LiMnO2, and produces layered monoclinic LiMnO2 with an α-NaFeO2 type crystal structure. The formation of monoclinic LiAlxMn1-xO2 confirms earlier observations by Chiang et al. [1,2]. A mechanism is proposed for the orthorhombic-monoclinic transformation, based on Li-Mn inversion in the orthorhombic structure. Al ions substitute in Mn sites in the monoclinic phase and give rise to microstrain in the [2 0 -l] planes. Microstructural analysis by scanning electron microscopy has revealed Al-deficient striations which may represent residual zones of orthorhombic phase. In cycling tests in Li button cells, increasing the amount of Al dopant extends the number of cycles required for the capacity to evolve to its maximum value, but results in increased stability of the capacity at 55 °C. The layered structure of the monoclinic materials is retained on the first cycle, but transforms to a spinel-type structure on extended cycling.
Lithium Ion Diffusion Measurements in High Quality LiCoO2 thin Film Battery Cathodes
Authors: Bahn Christian S. , McGraw Jeanne M. , Perkins John D. , Parilla Phillip A. , Ginley David S.
Published: April 2011

Highly crystalline, textured thin films of LiCoxAl1-xO2 (x=0, 0.5) have been grown by pulsed laser deposition. Films of both stoichiometries were dense and uniaxially textured with Li, Co (or Co, A1) layers parallel to the substrate. It was found that crystal quality depended strongly on oxygen partial pressure, substrate temperature, and substrate material. The deposition of LiCo0.5Al0.5O2 is also highly dependent upon laser fluence, requiring at least 12.8 J/cm2 for high quality films. Chemical diffusion measurements were performed over a wide range of lithium contents using the potentiostatic intermittent titration technique. Maximum and minimum effective for LiCoO2 were 4.0 × 10−11 and 1.2 × 10−2 cm2/s, respectively, and for LiCo0.5A10.5O2, 2.2 × 10−12 and 8.0 × 10−17 cm2/s, respectively.
Synthesis and Electrochemical characterization of LiNi1-yCoyO2 powders obtained by complex sol-gel process
Authors: Croce F. , D'Epifanio A. , Deptula A. , Lada W. , Ciancia A. , Bartolomeo A. Di , Brignocchi A.
Published: April 2011

The layered oxides, among the wide family of intercalation compounds, have received considerable attention as positive electrode materials in high-energy density lithium and lithium ion batteries. Within this frame LiNiO2 and LiCoO2 oxides and their solid solutions have been extensively studied as they (and the LiMn2O4 spinels) are the only known materials able to intercalate reversibly lithium at high cell voltage (3.5-4 V). Recently, solid solutions such as LiNi1-xCoxO2 have attracted the attention as alternative cathodes to the state of art LiCoO2 in commercial rechargeable Li-ion batteries. Here we have used the Complex Sol-Gel Process (CSGP) to prepare LiNi1-xCoxO2 (x= 0, 0.25, 0.5, 0.75, 1). Starting sols were prepared from Li+-(1-x)Ni2+-xCo2+ acetate aqueous solution in two different routes. According to route-A aqueous ammonia was added to a starting solution containing 0.2M ascorbic acid (ASC) on 1 M total Me. According to route B the starting acetate solutions were first alkalized by ammonia and then the ascorbic acid was added. Regular sols were concentrated to 1/3 of their initial volume and dried slowly up to 170°C. Thermal transformation of the gels to solids was studied by XRD and IR. The electrochemical properties of the compound LiNi0.75Co0.25O2 prepared by the Route-A were evaluated and reported.
Controlled Cleavage of Fully-Condensed Silsesquioxane Frameworks: A Revolutionary New Method for Manufacturing Precursors to Hybrid Inorganic/Organic Materials
Authors: Feher Frank J. , Soulivong Daravong
Published: April 2011

The reaction of readily available Cy8Si8O12(3) with triflic acid (TfOH) can produce two different ditriflates derived from controlled cleavage of Si-O-Si linkages. These ditriflates can be subsequently hydrolyzed to four different incompletely condensed silsesquioxanes, which are attractive precursors to hybrid inorganic/organic materials.
Maleimide Functionalized Siloxane Resins
Authors: Shaltout R. M. , Loy D. A. , Wheeler D. R.
Published: April 2011

In-situ filling through hydrolysis and condensation of silicon alkoxides dissolved into polymers has been utilized to generate nanocomposites in which the filler phase can be intimately associated with the polymer on relatively small length scales. One problem of the method has been achieving useful fill volumes without bulk phase separation of the growing inorganic component from the polymer. In this paper, we describe the preparation of a new class of nanocomposite materials in which the inorganic filler phase is pre-assembled before copolymerization with an organic monomer. Maleimide monomers, prepared from alkoxysilylpropyl amines and maleic anhydride, were protected against side reactions by forming the oxonorbornene Diels-Alder adduct with furan. The monomers were then reacted under solgel conditions to form oligomers or polymers making up the filler phase. The material was activated by thermal deprotection of the maleimide and reacted with organic monomers or polymers to form the filled nanocomposite.
Self-Assembled Monolayers Derived from Bidentate Organosulfur Adsorbates
Authors: Shon Young-Seok , Garg Nupur , Colorado Ramon , Villazana Ramon J. , Lee T. Randall
Published: April 2011

The adsorption of a series of 1,2-bis(mercaptomethyl)-4,5-dialkylbenzenes (1), spiroalkanedithiols (2), and aliphatic dithiocarboxylic acids (3) on gold yielded new types of self-assembled monolayers (SAMs). The new SAMs were characterized by optical ellipsometry, contact angle goniometry, and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). These results were compared to those obtained from SAMs derived from normal alkanethiols (4) of analogous chain length. Comparisons of ellipsometric thickness and contact angle wettability showed that the new SAMs were well packed and highly oriented. Comparisons of the PM-IRRAS data showed that the SAMs generated from 1 and 2 exhibited slightly less crystallinity than their alkanethiolate-based analogs, while the SAMs generated from 3 exhibited comparable crystallinity to their alkanethiolate-based analogs. Moreover, the SAMs derived from 1 and 2 showed no “odd-even” wettability or PM-IRRAS effects, while those derived from 3 showed remarkably large “odd-even” effects compared to those derived from normal alkanethiols.
One-Pot Synthesis Of A Cubic Silicate Phase Functionalized With Phenyl Groups
Authors: Goletto V. , Dagry V. , Babonneau F.
Published: April 2011

Organically-modified porous silicates have been prepared according to a one-pot synthetic approach. A mixture of phenyltriethoxysilane and tetraethoxysilane was reacted with an acidic solution of cetyltrimethylammonium bromide (CTAB). Depending on the preparation conditions, not only the hexagonal (2d, p6m) but also a cubic phase has been prepared analogous to the already reported SBA-1 phase, whose X-ray pattern matches the (Pm3n) space group. To our knowledge, it is the first time that this phase is obtained with CTAB as structuring agent, which suggests specific interactions between the phenyl groups and the surfactant polar head group. The surfactant was removed by solvent extraction or calcination at 350°C, without any alteration of the ordering: a cubic porous silicate network functionnalized by phenyl groups was thus obtained. Calcination could even be performed at 600°C to prepare a pure silicate network that still exhibits the same cubic symmetry.
Siliceous Mesostructured Cellular Foams with Uniformly Sized and Shaped Pores
Authors: Schmidt-Winkel P. , Lukens W. W. , Zhao D. , Yang P. , Chmelka B. F. , Stucky G. D.
Published: April 2011

Mesostructured siliceous cellular foams (mesocellular foams, MCFs) with homogeneous ultra-large mesopores are described. MCFs consist of uniform spherical cells 21–36 nm in diameter and possess surface areas up to 900 m2/g. Uniform windows, 7–18 nm in diameter, interconnect the cells to form a continuous 3-D pore system, which makes the MCFs attractive candidates for supports for catalysis and in separation and immobilization involving large molecules. They may be of interest in low-dielectric applications. The size of the cells can be controlled by the concentration of the added organic cosolvent. Adding small amounts of NH4F selectively enlarges the windows. We propose that the MCFs are templated by oil-inwater microemulsion droplets. The large-pore MCF materials resemble aerogels, with the benefit of a facilitated synthesis procedure in combination with well-defined pores and wall structure.
Synthesis and Texture of Mesophase Templated Silica Layers Seeded with Nanoparticles
Authors: Klotz M. , Ayral A. , Van Der Lee A. , Guizard C. , MÉnager C. , Cabuil V.
Published: April 2011

Mesophase templated silica layers seeded with magnetic or non magnetic nanoparticles are prepared. The study of the interactions between the nanoparticles and the others compounds of the synthesis solution is first described to explain the synthesis conditions allowing a homogeneous seeding. X-ray diffraction measurements are then used to study the texture of thick layers seeded with magnetic nanoparticles.
Protonic Conducting Properties of Sol-Gel derived Organic/Inorganic Nanocomposites Membrane doped with Acidic Functional Molecules
Authors: Honma I. , Takeda Y. , Bae J. M.
Published: April 2011

High temperature protonic conducting polymer membranes provide new technological applications in electrochemicaldevices including electrochromic displays, chemicalsensors and fuel cells. Organic/inorganimanocomposite membranes consisting of SiO2 /PEO (Polyethylene Oxides) hybrid are a remarkable family of isotropic, flexible, amorphous polymer materials, which have been synthesized through sol-gel processes. The hybrid membrane doped with acidic moieties such as monododecylphosphate or phosphotungstic acid shows good protonic conductivities at temperatures above 100°C. The protonic conducting membrane was found to be thermally stable at temperatures because of the inorganic SiO2 framework in the nanocomposites matrix.