bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electronic Structure Of (AgSb)xPbn-2xTen
Authors: Bilc Daniel I , Mahanti S.D. , Kanatzidis M.G. 
Published: April 2011

ABSTRACTComplex quaternary chalcogenides (AgSb)xPbn-2xTen (0<x<n/2) are thought to be narrow band-gap semiconductors which are very good candidates for room and high temperature thermoelectric applications. These systems form in the rock-salt structure similar to the well known two component system PbTe (x=0). In these systems Ag and Sb occupy Pb sites randomly although there is some evidence of short-range order. To gain insights into the electronic structure of these compounds, we have performed electronic structure calculations in AgSbTe2 (x=n/2). These calculations were carried out within ab initio density functional theory (DFT) using full potential linearized augmented plane wave (LAPW) method. The generalized gradient approximation (GGA) was used to treat the exchange and correlation potential. Spinorbit interaction (SOI) was incorporated using a second variational procedure. Since it is difficult to treat disorder in ab initio calculations, we have used several ordered structures for AgSbTe2. All these structures show semimetallic behavior with a pseudogap near the Fermi energy. Te and Sb p orbitals, which are close in energy, hybridize rather strongly indicating a covalent interaction between Te and Sb atoms.
Thermoelectric Properties of TiS2 type materials
Authors: Abbott Edward E. , Kolis Joseph W. , Lowhorn Nathan D. , Sams William , Tritt Terry M 
Published: April 2011

ABSTRACTTiS2 belongs to a family of layered compounds that displays promise as a thermoelectric material. At room temperature the thermopower (a) of TiS2 displays an n-type behavior, with a magnitude of ≈ -200 μV/K. The electrical resistivity (ρ), is on the order of 1 mΩ-cm at room temperature and displays a “metallic-like” behavior with dR/dT > 0 from 300 K to 10 K. Thus, these compounds exhibit relatively large power factors (PF = α2/ρ) with a PF ∼30 μW/K2 cm at T = 300 K, which are comparable to the state-of-the art Bi2Te3 type materials, which have a PF ∼40 μW/K2, at T = 330K. These values suggest that further investigations of these systems could be profitable. Thin plate-like crystals of TiS2 are grown by the iodine vapor transport method with planar dimensions of 1 cm and thicknesses of 20 μm or more. In this synthetic approach some dopants can be integrated into the parent compound, effectively providing a route for the tuning of electronic properties. We present here some effects of elemental doping on the electronic properties in these TiS2 based materials.
Thermoelectric performance of textured Bi2Te 3-based sintered materials prepared by spark plasma sintering
Authors: Chen Lidong , Jiang Jun , Shi Xun 
Published: April 2011

ABSTRACTThermoelectric performance of polycrystalline materials is greatly influenced by their microstructures including grain sizes, grain boundaries, grain orientations in anisotropic compounds, etc. The material microstructures are sensitive to the preparation processes and the starting materials. In the present study, n-type and p-type Bi2Te3-based sintered materials with highly preferred grain orientations have been fabricated through a spark plasma sintering (SPS) technique, by controlling the particle sizes of the starting powder and other sintering process parameters. The obtained textured Bi2Te3-based materials show a high mechanical strength as 80MPa in bending strength, which is 7 to 8 times as that of the melted ingot materials, and a significant anisotropy in thermoelectric transport properties. The optimal figure of merit (ZT) of the sintered materials in the direction perpendicular to the pressing direction (with c-axis preferred orientation) is comparable to that of the zone-melted ingots in the same crystallographic orientation.
Thermal and thermoelectric properties of III-nitride and III-oxynitride films prepared by reactive RF sputtering
Authors: Izaki R. , Kaiwa N. , Sugimura S. , Yamaguchi S. , Yamamoto A. 
Published: April 2011

ABSTRACTTowards fabricating a thermoelectric power device using III-nitrides and III-oxynitrides, we studied their thermal and thermoelectric properties and, in particular, we have focused on their thermal conductivity. AInN and AlInON were prepared by reactive radio-frequency sputtering method. We measured the thermal diffusivity and specific heat using the ac calorimetric method, and we estimated values of the thermal conductivity to be 2.2 W/mK (at 773 K) for AlInN and 3.3 W/mK (at 673 K) for AlInON. These values are much smaller than expected considering the large thermal conductivity of nitrides. As for a device composed of 20-pair Chromel-AlInN films, the maximum output power was 0.36 μW at the temperature difference of 180 K, and the open voltage was 0.10 V.
Guided Formation of Nanostructures in Thin Films
Authors: Lu Wei , Kim Dongchoul 
Published: April 2011

ABSTRACTA thin two-component epilayer grown on a solid surface may separate into distinct phases. Sometimes the phases select sizes about 10 nm, and order into an array of stripes or disks. However, the pattern types are limited and the location of the features is not controlled. This paper develops a dynamic model to simulate guided self-assembly. In particular, we look at the effect of surface chemistry on the pattern formation process. The simulations suggest that diverse patterns may be produced by tuning the surface chemistry of a substrate. In addition, the self-assembled features may be anchored at specific locations.
Mechanical Properties and Morphology of Polycrystalline 3C-SiC Films Deposited on Si and SiO2 by LPCVD
Authors: Fu Xiao-an , Dunning Jeremy , Rajgopal Srihari , Zhang Ming , Zorman Christian A. , Mehregany Mehran 
Published: April 2011

ABSTRACTPoly-SiC films were deposited on Si and SiO2 substrates in a high-throughput, low pressure chemical vapor deposition (LPCVD) furnace using dichlorosilane (DCS) and acetylene precursors. The deposition temperature and pressure were fixed at 900°C and 2 Torr, respectively, while the flow rate of DCS was varied between 18 and 54 sccm. Poly-SiC deposition rates on both Si and SiO2 were nearly identical to each other and increased as a function of DCS flow rate. Consistent with both substrate materials, the following observations were made. A slope change of the deposition rate versus DCS flow rate was observed around a DCS flow rate of 35 sccm. Residual stress varied with respect to the deposition rate, with tensile stresses occurring at lower deposition rates and compressive stresses at higher deposition rates. The tensile-to-compressive stress transition corresponded to the slope change of the deposition rate versus DCS flow rate. The surface morphology consisted of pyramidal grains, as observed under an SEM. TEM analysis for poly-SiC films grown on Si substrates showed that microstructural differences exist for poly-SiC films having tensile and compressive stresses.
Measurement of Thin-Film Stress, Stiffness, and Strength Using an Enhanced Membrane Pressure-Bulge Technique
Authors: Chalekian Aaron J. , Engelstad Roxann L. , Lovell Edward G. 
Published: April 2011

ABSTRACTAccurate mechanical properties of thin films are essential for viable design and fabrication of semiconductor devices and microelectromechanical systems. Relevant properties of thin films such as intrinsic stress, biaxial modulus, and fracture strength can be significantly different than their corresponding bulk values, and much more difficult to measure. However, such data can be obtained from the pressure-deflection response of clamped freestanding membranes, i.e., the so-called pressure-bulge test. Experimental challenges include membrane leakage prevention, ensuring proper structural boundary conditions, and accurately measuring applied pressure and transverse displacements simultaneously. In addition to these issues, most previously-developed pressure-bulge instruments rely on vacuum pump loadings. Such tools are limited by the one-atmosphere differential pressure over the membrane, which is inadequate for burst testing of high-strength films. Consequently, an enhanced pressure-bulge tool has been developed and will be described in this paper. It incorporates positive pressure to overcome the one-atmosphere load limitation, improved edge constraints, and the ability to test an array of membrane windows across a single substrate.
A Study on Selective Etching of SiGe Layers in SiGe/Si Systems for Device Applications
Authors: Yamazaki Takashi , Sekikawa Tomohide , Morita Shinya , Hakamada Yoshitaka , Ohri Hiroyuki , Ohmi Shun-ichiro , Sakai Tetsushi 
Published: April 2011

ABSTRACTSelective etching of a SiGe layer for Si/SiGe/Si stacked layers was investigated for device applications. The SiGe layer is selectively and laterally etched by a HF:HNO3:H2O solution after patterning the layers. The selective etching rate of the SiGe layer increased as the Ge ratio increased. The etching rate of a SiGe layer annealed at 800°C did not change from an as-grown sample, and the Ge diffusion into Si was very small. However, the etching rate of a layer annealed at 1000°C was found to have decreased, and Ge diffused into Si in large amounts. This indicates that annealing at less than 800°C is suitable for device applications.
Asymmetry in Multilayer Adhesion: the Zinc Oxide / Silver Interface
Authors: Barthel E. , Nael P. , Kerjan O. , Nadaud N. 
Published: April 2011

ABSTRACTWe have developed a wedge-loaded double-cantilever beam adhesion measurement set-up for thin films deposited on glass by magnetron sputtering. Results on the Glass/ZnO/Ag/ZnO multilayer evidence that the upper Ag/ZnO interface is tougher than the lower ZnO/Ag interface. This asymmetry in the adhesion energy between identical materials is not expected from first principles. It results from different non-equilibrium interfacial structures.
Dislocation Image Stresses at Free Surfaces by the Finite Element Method
Authors: Tang Meijie , Xu Guanshui , Cai Wei , Bulatov Vasily 
Published: April 2011

ABSTRACTThe finite element method has been routinely used to calculate the image stresses of dislocation segments. When these segments intersect with surfaces, the image stresses at the surfaces diverge singularly. At the presence of these singularities, both convergence and accuracy of using the finite element method need to be examined critically. This article addresses these issues with the aim toward the application of dislocation dynamics simulations in thin films.
Understanding adhesion failure in low-k dielectric stack during Chemical-Mechanical Polishing
Authors: Iacopi F. , Degryse D. , Vos I. , Patz M. , Maex K. 
Published: April 2011

ABSTRACTLow-k dielectrics are currently starting to replace SiO2 in advanced on-chip interconnects. Being low surface energy materials, a major concern for the integration of such dielectrics in Cu damascene processes is given by adhesion failure at the interfaces of the low-k films with cap or liner layers during Chemical Mechanical Polishing (CMP). A cross-comparison between interface fracture energies as measured through four-point bending, CMP experiments and stress fields computed by Finite Element Modeling, shows that it is not possible to predict failures by setting a ‘universal’ threshold on adhesion strength.In particular, we report on the critical role of CMP –induced shear stress on the onset of interface debonding, and the way the shear load is transmitted to the critical interfaces. The top-down load transmission depends on the position of the weak interfaces, and on the way the intermediate films in the stack can confine such load through their thickness and mechanical (elastic and plastic) properties.
Effects of Varying Mean Stress and Stress Amplitude on the Fatigue of Polysilicon
Authors: Kahn H. , Ballarini R. , Heuer A. H. 
Published: April 2011

ABSTRACTPolycrystalline silicon (polysilicon) single edge-notched fatigue specimens with micrometer-sized dimensions were macromachined and subjected to cyclic loading using an integrated electrostatic actuator. The effects of fatigue were determined by comparing the monotonic bend strength measured after cyclic loading to the monotonic bend strength of specimens that received no cycling. Both strengthening and weakening were observed, depending on the levels of mean stress and fatigue stress amplitude during the cyclic loading. Monotonic loading with similar stress levels prior to bend strength measurements had no effect on measured bend strength. Possible physical mechanisms responsible for this fatigue behavior are discussed.
In Situ, Real-Time Curvature Imaging During Chemical Vapor Deposition
Authors: Boyd David A. , Tripathi Ashok B. , El-Naggar Mohamed , Goodwin David G. 
Published: April 2011

AbstractCoherent Gradient Sensing (CGS) is a full-field optical technique that produces real-time images of macroscopic wafer curvature, which, for thin films, can be related to stress through Stoney's equation. Here we describe the use of CGS as an in situ diagnostic to observe film stress distributions during chemical vapor deposition. The application of this method to measure oxygen diffusion rates in thin film YBa2Cu3O6+δ(YBCO) and stresses in thin film PbxBa1-xTiO3 (PBT) under chemical vapor deposition (CVD) conditions will be discussed.
Determination of Residual-Stress-Free State and Mapping of Residual Stress Fields Using Speckle Interferometry and Thermal Relaxation
Authors: Kim Dong-Won , Kim Jong-jin , Son Dongil , Lee Nak-Kyu , Na Kyung-Hoan , Kwon Dongil 
Published: April 2011

ABSTRACTWe used an electronic speckle pattern interferometer (ESPI) for nondestructive measurement in-situ displacement fields in microsystems. A four-step phase-shift technique and magnifier with long working distance were adopted to increase displacement resolution to ∼10−2 μm and spatial resolution to ∼2 μm. A thermal vacuum chamber was designed to induce thermal treatments, including annealing. From the identification of the residual-stress-free state, we quantitatively modeled thermal strains/stress fields, relaxation stresses during annealing, and residual stress fields. Thermoelasticity theory was applied to model the relationship between the relaxation stresses and the displacements measured by ESPI during the evolution of the residual-stress-free state. We assessed the surface residual stress fields of indented bulk Cu; a Fe-Ni lead frame of 100 μm width; and 0.5 μm Au film. In the indented Cu, the normal and shear residual stresses around the indented point range from –1.7 GPa to 700 MPa and –800 MPa to 600 MPa, respectively, and the residual stress in the bending area of the Fe-Ni lead frame was estimated at 148 MPa and verified using beam-bending theory. In the Au film, tensile residual stresses are uniformly distributed from 500 MPa to 800 MPa as verified by X-ray diffraction.
Dislocation Nucleation and Segregation in Nano-scale Contact of Stepped Surfaces
Authors: Yu H. H. , Shrotriya P. , Wang J. , Kim K.-S. 
Published: April 2011

ABSTRACTA myriad of engineering applications involve contact between two surfaces, which induces localized plastic deformation near the surface asperities. As a generic problem in studying nanometer scale plastic deformation of solid surfaces, a unit process model of dislocation formation near a surface step under contact loading of a flat rigid surface is considered. The driving force on the dislocation is calculated using conservation integrals. The effect of surface adhesion, step size and lattice resistance on the dislocation driving force are analyzed in a continuum dislocation model, while the nucleation process is simulated atomistically. The driving force formula is used for a dislocation nucleation criterion and to get the equilibrium distance traveled by the dislocation away from the surface step. Results of the unit process model show that under a normal contact load dislocations nucleated in certain slip planes can only stay in a thin layer near the surface, while dislocations nucleated along other slip planes easily move away from the surface into the bulk material. The former dislocation is named anti-load dislocation and the latter dislocation is called pro-load dislocation. Embedded atom method (EAM) is utilized to perform the atomistic simulation of the unit-process model. As predicted by the continuum dislocation model, the atomistic simulations also indicate that surface adhesion plays significant role in dislocation nucleation process. Varying the surface adhesion leads to three different regimes of load-deflection instabilities, namely, just dislocation nucleation instability for no adhesive interaction, two distinct surface adhesion and dislocation nucleation instabilities for weak adhesive interaction and a simultaneous surface adhesion and dislocation nucleation instability for strong adhesive interaction. The atomistic simulations provide additional information on dislocation nucleation and growth near the surface steps. The results of dislocation segregation predict existence of a thin tensile-stress layer near the deformed surface and the results on the adhesion effect provides a cold-welding criterion.
Subcritical Delamination of Dielectric and Metal Films from Low-k Organosilicate Glass (OSG) Thin Films in Buffered pH Solutions
Authors: Lin Y. , Vlassak J. J. , Tsui T. Y. , McKerrow A. J. 
Published: April 2011

ABSTRACTUnderstanding subcritical fracture of low-k dielectric materials and barrier thin films in buffered solutions of different pH value is of both technical and scientific importance. Subcritical delamination of dielectric and metal barrier films from low-k organosilicate glass (OSG) films in pH buffer solutions was studied in this work. Crack path and subcritical fracture behavior of OSG depends on the choice of barrier layers. For the OSG/TaN system, fracture takes place in the OSG layer near the interface, while in OSG/SiNx system, delamination occurs at the interface. Delamination behavior of both systems is well described by a hyperbolic sine model that had been developed previously based on a chemical reaction controlled fracture process at the crack tip. The threshold toughness of both systems decreases linearly with increasing pH value. The slopes of the reaction-controlled regime of the crack velocity curves for both systems are independent of pH as predicted by the model. Near transport-controlled regime behavior was observed in OSG/TaN system.
Tuning the Mechanical Properties of SiO2 Thin Film for MEMS Application
Authors: Su Wang-Shen , Fang Weileun , Tsai Ming-Shih 
Published: April 2011

ABSTRACTThis study reported a novel method for tuning thin film mechanical properties by means of plasma surface modification. In order to demonstrate the feasibility of this approach, various plasma treatments, including O2, H2, NH3 atmospheres, were implemented to tune the Young's modulus and residual stress of SiO2 film. Without plasma treatment, the static tip deflection of 200μm long SiO2 cantilever was 9.01μm. After treatment with H2, O2, and NH3 plasma, the tip deformation of the treated cantilevers became 10.22μm, 8.28μm, and -6.84μm respectively. The Young's modulus of the SiO2 cantilever without plasma treatment was 76.3GPa. After treated with H2, O2, NH3 plasma, the Young's modului of those treated cantilevers became 70.8 GPa, 74.7 GPa, and 71.4 GPa, respectively. Hence, after H2 and NH3 plasma treatment, the equivalent elastic modulus of SiO2 cantilever could be reduced about 7%.
Determination of mechanical parameters for rotating MEMS structures as a function of deposition method
Authors: Soare S. , Bull S. J. , Oila A. , O'Neill A. G. , Wright N. , Horsfall A. , dos Santos J. 
Published: April 2011

ABSTRACTThe dimensions of microelectronic devices are constantly being reduced due to the increasing operational demands imposed such as higher working frequencies, higher component density and lower power consumption. This affects the geometrical dimensions of the metallisation, i.e. its width and thickness. The mechanical properties of very thin films are considerably different from those of bulk materials and, also, the deposition method may influence the mechanical behaviour of the components. In order to obtain reliable metallisation it is therefore important to assess accurately the mechanical parameters of the interconnecting lines. As part of designing, developing and manufacturing of a stress micro-sensor there is a need to extract properties useful for performance prediction such as yield stress or creep relaxation behaviour. Part of the data may be obtained by nanoindentation but to have a more complete view, finite element analysis of the indentation cycle has to be employed. In this study nanoindentation testing was carried out at various depths on sputtered and evaporated aluminium layers with different thicknesses deposited on (100) silicon. The loading curves were then simulated by FEA and the results compared to identify the yield properties of the coating. Modelling data for thicker samples closely follows experimental data but for thinner coatings there is a considerable gradient in properties through the film thickness. By incorporating a peak load hold the creep behaviour of the metallization can also be assessed and modelling parameters developed.
Position Control of Nucleation in Solid-Phase Crystallization of a-Si/SiO2 by Ge Layer Insertion
Authors: Sadoh Taizoh , Nagatomo Kei , Tsunoda Isao , Kenjo Atsushi , Miyao Masanobu 
Published: April 2011

ABSTRACTThe effects of Ge layer insertion on the solid-phase crystallization (SPC) of a-Si on SiO2 have been investigated. Three types of sample structures, i.e., (a) a-Si/a-Ge/a-Si/SiO2, (b) a-Si/a-Ge/SiO2, and (c) SiO2/a-Ge/a-Si/SiO2, were prepared and annealed at 600°C. For the structure (a) with a thin (∼ 5 nm) Ge layer, Ge atoms completely diffused into a-Si, and SPC was not enhanced. On the other hand, for the structure (a) with Ge layers thicker than 10 nm, Ge atoms were localized at the initial position. Such a localization of Ge atoms was remarkable for the structures (b) and (c) even for samples with thin Ge layers. For samples with Ge localization, significant enhancement of SPC of a-Si was observed. These results indicated that crystal nucleation was initiated in the inserted Ge layers, and then propagated into a-Si. The Ge layer insertion can be employed for positioning of crystal nucleation in SPC of a-Si.
High electron mobility in AlGaN/GaN HEMT grown on sapphire: strain modification by means of AlN interlayers.
Authors: Germain Marianne , Leys Maarten , Boeykens Steven , Degroote Stefan , Wang Wenfei , Schreurs Dominique , Ruythooren Wouter , Choi Kang-Hoon , Daele Benny Van , Tendeloo Gustaaf Van , Borghs Gustaaf 
Published: April 2011

ABSTRACTThe performance of AlGaN/GaN High Electron Mobility (HEMT) transistors is directly related to the electrical characteristics of the two-dimensional electron gas formed at the interface thanks to the piezoelectric field. Modification of the Al content or thickness of the AlGaN layer can within a certain limit modify the carrier density and mobility in the 2DEG. However, further reduction of the sheet resistance requires strain engineering of the heterostructure. An effective way to reduce the sheet resistance, as well as to lower the threading dislocation (TD) density, is to perform strain engineering through the use of low temperature AlN interlayers inserted in the GaN buffer layer. From correlation of AFM, TEM and HRXRD mapping of the HEMT layers, the strain modification, as well as the mechanism reducing the TD density, can be explained by the highly defected nature of the AlN interlayer grown at low temperature, as well as its very small thickness. The LT AlN acts as a second nucleation layer for the GaN grown on top. Contrarily, when the AlN interlayer is grown at 1050°C, its high crystalline quality and the possibility to grow pseudomorphic and abrupt interfaces, allows its use at the AlGaN/GaN interface. Optimal combination of the AlGaN and AlN layer thickness leads to record values of the mobility at room temperature of 2050 cm2/Vs, for heterostructures grown on sapphire, which is approaching state-of-the-art for HEMT grown on SiC.