bluuebunny/crossref_metadata_2025 huggingface dataset:
A Phase Field Model for Grain Refinement in Deeply Undercooled Metallic Melts
Authors: Mullis A.M. , Cochrane R.F.
Published: April 2011

We present the results of phase field simulations of dendritic growth into pure undercooled melts, at growth velocities up to 35 m s−1. We find that, at low growth velocities, dendrite morphologies are broadly self-similar with increasing growth velocity. However, above ≈ 15 m s−1 the initiation of side-branching moves closer to the dendrite tip with increasing growth velocity. This appears to be related to the level of kinetic undercooling at the tip. Once side- branch initiation begins to occur within 1-2 radii of the tip, profound morphological changes occur, leading to severe thinning of the dendrite trunk and ultimately repeated multiple tip- splitting. This process can be invoked to explain many of the observed features of spontaneous grain refinement in deeply undercooled metallic melts.
Molecular Modeling of the Dielectric Saturation in Proton Exchange Membranes
Authors: Paul Reginald , Paddison Stephen J.
Published: April 2011

A molecular statistical mechanical method is employed to compute the field dependant permittivity of water contained in the hydrophilic pores of hydrated proton exchange membranes. The anionic (-SO-3) groups in proximity to the pore walls generate spatially varying fields resulting in dielectric saturation, the effects of which are investigated.
Effects of Nanostructure on Bulk Mechanical Properties of Nacre - 3D Finite Element Modeling of the Segmented/Layered Biocomposite
Authors: Katti Dinesh R. , Katti Kalpana S , Tang Jingpeng , Sopp Jeffrey M. , Sarikaya Mehmet
Published: April 2011

Nacre is a segmented layered composite containing both nanoscale-thick organic and sub- micrometer thick scale inorganic phases. In addition to controlling the formation of the intricate architecture, the organic plays a significant role in the mechanical properties of the biocomposite. In our previous work, three dimensional finite element models of nacre were constructed to design “brick and mortar” micro-architecture to study effects of nonlinear response of the organic component. Recently, nanomechanical properties such as hardness and elastic moduli of the individual components of nacre have been determined using nanoindentation techniques. In this work, we used these actual properties of the components to perform mesoscale finite element models to quantitatively evaluate nanoscale effects. Specifically, we studied the effect of the solid contacts between the platelets through the organic layer on bulk properties under tensile and compressive loading. In the new 3D finite element model, we also incorporated the pseudo-hexagonal platelet morphology to more accurately represent the nacre microstructure. The multiscale approach in our study involves incorporation of experimentally obtained nanoscale parameters into meso-macroscale numerical models. Our simulations imply that mineral contacts in the aragonitic platelets have marginal impact both on bulk elastic behavior of nacre and yielding. Stress concentration in contact regions were high enough for the contacts to break long before yield started in nacre. These results have important implications in the design of biomimetic segmented-layered composites for improved mechanical properties.
Novel Solid State Hybrid QM/MM Embedding Investigation into Methanol Synthesis over Cu Supported on ZnO Catalysts
Authors: French Samuel A. , Bromley S. T. , Sokol A. A. , Catlow C. R. A. , Kendrick J. , Rogers S. , Sherwood P.
Published: April 2011

A new solid-state embedding approach has been developed which focuses on modelling the surfaces of polar materials. The method is applied to investigate the chemisorption of pre- methanol species on the polar (000-1) surface of zincite (a major phase of zinc oxide having the wurtzite structure). Initial results include the geometries of active sites and adsorbates in different charge states.
Multiscale Modeling of Stress-Mediated Diffusion in Silicon - Volume Tensors
Authors: Windl W. , Daw M. S. , Carlson N. N. , Laudon M.
Published: April 2011

In a previous paper, we presented a general theoretical treatment of the effect of stress on defect diffusion in Si (M. S. Daw, W. Windl, N. N. Carlson, M. Laudon, and M. P. Masquelier, to be published in Phys. Rev. B). In this paper, we discuss the calculation of the parameters governing the stress dependence of the diffusivity, which are volume quantities, and present the fully anisotropic volume tensor for vacancy formation in Si.
Stress Distribution and Tomographic Profiling with Energy Dispersive X-Ray Scattering
Authors: Croft Mark , Zakharchenko Igor , Zhong Zhong , Tsakalakos Thomas , Gulak Yuriy , Kalman Zwi. , Hastings Jerome , Hu Jingzhu , Holtz Ronald , Sadananda Kuntimaddi
Published: April 2011

Two novel and potentially powerful, x-ray scattering techniques for tomographic profiling of composite materials and for profiling residual strain variation, versus depth, in a specimen are presented. The techniques utilize a high intensity/energy “white” beam synchrotron source and monitor the energy dispersive scattering from a fixed micro-volume as the specimen is scanned through it. The tomographic profiles based on the net scattered intensity and exploiting absorption coefficient/scattering-power variations, can be contrast enhanced by selectively monitoring scattering from specific crystal structures in a composite material. The strain profiling technique is shown to chronicle the detailed internal the stress variation over several mm's of steel. The initial state residual stresses, the effect of a cantilever spring imposed external stress, and their interplay in elastic/plastic deformation are discussed.
Synchrotron X-ray Diffraction Measurement of Reinforcement Strains in Uniaxially Stressed Bulk Metallic Glass Composites
Authors: Balch Dorian K. , Üstündag Ersan , Dunand David C.
Published: April 2011

High-energy synchrotron x-rays were used to measure internal reinforcement strains in bulk metallic glass composites containing tungsten or tantalum particles during in-situ uniaxial tensile loading. Load transfer from the matrix to the stiffer but weaker particles was characterized in both their elastic and plastic regimes and compared to theoretical predictions.
Grazing incidence small-angle x-ray scattering applied to the characterization of nanocomposite thin films
Authors: Babonneau David , Suárez-García Amelia , Gonzalo José , Videnovic Ivan R. , Garnier Michael G. , Oelhafen Peter , Jaouen Michel , Naudon André
Published: April 2011

Grazing incidence small-angle x-ray scattering (GISAXS) allows to investigate precisely the microstructure of nanocomposite thin films containing metal nanocrystals produced using different synthesis techniques. We present results on the size, size distribution, shape, and correlation length of metallic nanoparticles embedded in different matrices fabricated by sequential pulsed laser deposition, magnetron sputtering, and ion-beam sputtering co-deposition. The morphology of the nanoparticles is discussed in terms of the different growth process that takes place in each case.
Analysis of Residual Stress Gradients Below the Surface of a Material Using a Multi-Energy Method
Authors: Xiao Yanan , Graber Tim , Lee Myungae , Wittmer Dale E. , Mini Susan M.
Published: April 2011

The residual-stress-gradient distribution just below the surface of a material is an important factor to consider during the engineering and design of a component. With the availability of an intense energy-tunable synchrotron x-ray source, it becomes easier to analyze the stress gradient below the surface, using a multi-energy x-ray diffraction method. A program was developed to efficiently determine possible experimental parameters using a sample with a known stress gradient distribution. In addition, this program can also calculate the stress gradient distribution below the surface taking into account experimental results. It also includes a subroutine for calculating the x-ray absorption coefficients of all of the elements, generalizing it for use with any material. As an example, in the present study, the relationship between x-ray energy and the residual stress gradient is discussed according to the calculated result for a silicon nitride composition.
Investigations of Buried Interfaces Using High Energy X-Ray Reflectivity
Authors: Rieutord F. , Eymery J. , Plantevin O. , Bataillou B. , Buttard D. , Fournel F.
Published: April 2011

X-ray reflectivity using high-energy X-rays allows one to characterize interfaces between thick materials at nanometer scale. The technique combines the high penetration of X-rays allowing the crossing of the radiation through large thicknesses of material with the interface sensitivity of grazing angle techniques. In the case of a buried interface between two thick materials, the beam enters the sample through the side of one material and contributions of external surfaces are suppressed. Then, the technique is sensitive to the interface structure only. Examples are given using wafer bonding interfaces, both in the hydrophilic case (as used e.g. in Silicon-On-Insulator substrate fabrication) and in the hydrophobic case (Silicon/Silicon bonding).
Analysis of the Use of Molecular Resonant Tunneling Diodes for Local Refresh of Dynamic Random Access Memory Cells
Authors: Berg Jonas , Bengtsson Stefan , Lundgren Per
Published: April 2011

Simulations have been made to analyze the use of molecular resonant tunneling diodes for local refresh of DRAM (Dynamic Random Access Memory) cells. Local refresh can be provided by a latch consisting of a pair of resonant tunneling diodes connected to the storage capacitor of the cell. Such a solution would significantly reduce the standby power consumption of the DRAM cell. We have compared the requirements on the resonant tunneling diodes for proper refresh operation with the electrical properties of published molecules with resonant IV-curves. The simulations show that no molecules with resonant electrical properties published so far in the literature have properties making them useful for this particular application. This is true also for low temperature operation. The issues of maximum tolerable series resistance and of maximum tolerable fluctuations in the number of attached molecules have also been addressed. Our results show that the focus for development of molecules with resonant electrical properties should be to find molecules with resonance for lower applied voltages and lower current levels than the molecules published so far. If the synthesis of new molecules with attractive properties is successful the merging of silicon technology and molecular electronics, for instance for new generations of DRAM cells, is a realistic future path of microelectronics.
Supramolecular Ultrathin Film Strategies for DNA Assemblies: Substrates for Optobioelectronics, Gene Therapy, and Microarrays
Authors: Advincula Rigoberto C. , Wang Yingfan , Park Mi-Kyoung , Bhatia Gautam , Stepleton Seth , Monroe Cara , Shelton Iman , Blanton Wally , Fan Xiaowu
Published: April 2011

We describe our strategies and results in the preparation of supramolecularly ordered ultrathin films of DNA assemblies using the layer-by-layer (LbL) alternate polyelectrolyte adsorption technique. The properties of DNA are intimately associated with their polyelectrolyte behavior in solution. Deposition at interfaces is governed by conformation, orientation, and charge density of these biomolecules in relation to the physisorption phenomena in oppositely charged surfaces. Thus, controlling the nature of surfaces (polymer charge density, ionic strength, other non-covalent interactions, etc.) is important in modifying the adsorption phenomena. In this work, differences in adsorption and incorporation of DNA with dyes, linear polymers and dendrimers are highlighted. A number of surface sensitive spectroscopic and microscopic techniques were used to probe the adsorption and multilayer assembly phenomena, e.g. surface plasmon resonance spectroscopy (SPS), AFM, quartz crystal microbalance (QCM) and ellipsometry. These studies are important for future applications such as the use of polycations as non-viral gene transfection vectors for drug-delivery and DNA adsorption on microarray surfaces. By combining with the alternate assembly of azobenzene and phthalocyanine dyes, we have been able to prepare optobiolelectronic substrates where the phenomena of irradiation and electrochemistry can be used to probe the ordering and response of these films.
Modeling of a Breakdown Voltage in GaN Rectifiers and SiC Rectifiers
Authors: Lee You-Sang , Han Min-Koo , Choi Yearn-Ik
Published: April 2011

The breakdown voltage of wurtzite and zinc-blende GaN rectifiers as function of a doping concentration and the width of epitaxial layer were successfully modeled in the reach-through case. The breakdown voltage was derived by the impact ionization integral employing the effective impact ionization coefficient and an accurate approximation. Our model shows that the breakdown voltage of wurtzite GaN rectifier was larger than those of zinc-blende GaN rectifier and SiC rectifiers including 4H-SiC and 6H-SiC in the condition that both the thickness and doping concentration of epitaxial layer are identical.
X-band Silicon Carbide IMPATT Oscillator
Authors: Vassilevski Konstantin V. , Zorenko Alexandr V. , Zekentes Konstantinos
Published: April 2011

Pulsed X-band (8.2 - 12.4 GHz) IMPATT oscillators have been fabricated and characterized. They utilized 4H-SiC diodes with single drift p+-n-n+ structures and avalanche breakdown voltages of about 290 V. The microwave oscillations appeared at a threshold current of 0.3 A. The maximum measured output power was about 300 mW at input pulse current of 0.35 A and pulse duration of 40 ns.
High Spatial Resolution Thermal Conductivity investigation of SiC Wafers
Authors: Florescu D.I. , Pollak Fred H. , Brande G.R. , Landini B.E. , Salant A.D.
Published: April 2011

Silicon carbide (SiC) is a material with very attractive properties for high power/high temperature electronic devices. Its mechanical strength, high thermal conductivity ( κ), large bandgap, and extreme chemical inertness are a few of the characteristics making SiC interesting for semiconductor electronics. Due to the significant head load generated over large areas in high power devices, it is desirable forthe thermal properties of the substrate to be uniform and optimal. Scanning thermal microscopy (SThM), which provides nondestructive, absolute measurements of the thermal conductivity with a spatial/depth resolution in the 2-3 μm range, was used to examine the room temperature κ as a function of position of four 2” diameter SiC wafers. Wafers of 4H and 6H polytype were fabricated with carrier concentrations in the(1-3)×1018 cm−3 and (6-9)×1017 cm−3 ranges, respectively. A radial distribution of the thermal conductivity was determined for all the investigated samples. For a radius r < r1 (r1 ∼ 0.3”) and r > r2 (r2 ∼ 0.7”) highest thermal conductivity values were measured in the range of (3.8-3.9) W/cm-K, comparable to the highest κ reported for this material [D. Morelli et al., Inst. Phys. Conf. Ser. 137, 313 (1993); E.A. Burgemeister,.et al., J. Appl. Phys. 50, 5790 (1979)]. For r1 < r < r2 the thermal conductivity drops to about (2.85-3.25) W/cm-κinterval. Atomic force microscopy (AFM) investigation revealsthat the influence of surface roughness effects on κ is negligible. The κ dip may arise from a higher basal plane defect density in this region that could be associated with the presence of super screw dislocations, or “micropipes” [M. Dudley et al., J. Phys. D: Appl. Phys. 28, A63 (1995)]. The implications of these findings for device applications and design are considered.
Single-Crystal Aluminum Nitride Substrate Preparation from Bulk Crystals
Authors: Rojo J. Carlos , Schowalter Leo J. , Morgan Kenneth , Florescu Doru I. , Pollak Fred H. , Raghothamachar Balaji , Dudley Michael
Published: April 2011

Large (15mm diameter) single-crystal AlN boules have been prepared using sublimationrecondensation growth. X-ray topography shows that the dislocation density averages less than 103 cm2 in some of the substrates but also that the dislocations are not uniformly distributed. Also, strain due to the differential expansion with the crucible walls seems to cause severe cracking in the periphery of the crystal and high-strain regions. Thermal analysis using the Scanning Thermal Microscopy (SThM) reveals a thermal conductivity of 3.4 ± 0.2 W/K-cm, which is the largest value ever reported for AlN.
Influence of growth parameters on the nitrogen incorporation in 4H- and 6H-SiC epilayers grown by hot-wall chemical vapour deposition
Authors: Forsberg U. , Henry A. , Danielsson Ö. , Linnarsson M.K. , Janzén E.
Published: April 2011

We have investigated the nitrogen incorporation dependency on temperature, pressure, C/Si ratio and growth rate in a horizontal hot-wall CVD reactor. The incorporation mechanism for 4H- and 6H-SiC both for Si- and C-face material is presented. A comparison with previously published results in a cold-wall reactor is also made.
Frequency Response of Trap States in an AlxGa1−xN/GaN Heterostructure Field-Effect Transistor Measured at the Nanoscale by dC/dV Spectroscopy
Authors: Schaadt Daniel M. , Yu Edward T.
Published: April 2011

Scanning capacitance spectroscopy has been used to characterize, at the nanoscale, the frequency-dependent response of surface charge and of charge in the two-dimensional electron gas of an AlxGa1−xN/GaN heterostructure field-effect transistor structure. dC/dV spectra were measured in a scanning capacitance microscope with a voltage signal consisting of a triangle wave at frequencies of 1 – 50 Hz applied to the sample. The spectra were obtained in the dark (except for 600 nm laser light from the scanning capacitance apparatus) and under illumination. Measurements were performed in the vicinity of and away from charged threading dislocations visible in scanning capacitance images. In the absence of illumination, the dC/dV data indicate that electrons are trapped at or near the AlxGa1−xN surface, consistent with suggestions in the literature that a high density of surface states exists on the free AlxGa1−xN surface. Frequency-dependent measurements show that emission times for these traps can be as long as several hundred ms. In the presence of illumination, reduced electron trapping is observed. The nature and behavior of trap states in the vicinity of threading dislocations is found to differ significantly from that in regions between dislocations for measurements in the dark, and suggest that the electrostatic potential due to the charged threading dislocation is negligible at the surface.
Effects of Beam Current Density on Ion Beam Synthesis OF SiC
Authors: Chen D.H. , Wong S.P. , Lindner J.K.N.
Published: April 2011

Thin SiC layers were synthesized by high dose C implantation into silicon using a metal vapor vacuum arc ion source at various conditions. Characterization of the ion beam synthesized SiC layers was performed using various techniques including x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) absorption, and Raman spectroscopy. The XPS results showed that for samples with over-stoichiometric implant doses, if the implant beam current density was not high enough, even after prolonged thermal annealing at high temperatures, the as-implanted gaussian-like carbon depth profile remained unchanged. However, if the implant beam current density was sufficiently high, there was significant carbon redistribution during annealing, so that a thicker stoichiometric SiC layer can be formed after annealing. The XPS and Raman results also showed that there were carbon clusters formed in the as-implanted layers for the low beam current density implanted samples, while the formation of such carbon clusters was minimal in the high beam current density as-implanted samples. The effect of beam current density on the fraction of different bonding states of the implanted carbon atoms was studied.
Carrier-Density Fluctuation Noise and the Interface Trap Density in GaN/AlGaN HFETs
Authors: Kotchetkov Dmitri , Balandin Alexander A.
Published: April 2011

The interface trap density NT is extracted from the experimental low-frequency noise data for GaN/AlGaN heterostructure field-effect transistors (HFETs). The trap density is determined based on the carrier-density fluctuation formalism. We show that the value of NT approximately defines the noise response of different GaN/AlGaN HFETs fabricated on the same wafer and it weakly depends on the gate bias. The dependence is due to the non-uniformity of the trap distribution. A model for computer simulation of the low-frequency noise in GaN devices is proposed.
Photo EPR Study of Trapping and Recombination Processes in Semi-Insulating 4H-SiC Crystals as Function of Temperature
Authors: Kalabukhova E.N. , Lukin S.N. , Saxler A. , Mitchel W.C. , Smith S R. , Solomon J.S. , Evwaraye A.O.
Published: April 2011

Photo-Electron Paramagnetic Resonance (photo-EPR) measurements of semi-insulating (s.-i.) 4H SiC have been made at 37 GHz including photo excitation and photo quenching techniques in the temperature interval from 77 K to 50 K. At T = 77 K in the dark the EPR spectrum consists of a low intensity line due to boron on the cubic lattice site and a single line with isotropic g∥ = g⊥ = 2.0025 due to a carbon-related surface defect. During illumination with ultraviolet light the EPR lines of hexagonal boron and cubic nitrogen appear in the EPR spectrum and persist after the illumination is removed. Subsequent illumination of the sample with sub-band gap, visible, light resulted in the quenching of the EPR lines from nitrogen and appearance of the IP1EPR line with g∥ = 2.0048, g⊥ = 2.0030 caused by direct transfer of electrons from nitrogen donor to the P1 center. The lifetime of the photo-generated carriers trapped by the P1 centers is found to be more than 15- 20 hours after the photo-excitation was turned off. The deep donor P1 local center is suggested to be the as yet unidentified deep level located at EC – 1.1 eV which pins the Fermi level in this sample at this energy in the dark. As the temperature is lowered from 77K and the quasi Fermi level positions reach shallow donor and acceptor states, an additional EPR line, ID, with g∥ = 2.0063, g⊥ = 2.0006, appears at 50 K in the excitation EPR spectrum and is attributed to the antisite defect Si−c with an energy level shallower than nitrogen. At the same time the ratio of the photo-excited EPR line intensities responsible for boron on the cubic and hexagonal sites, IkB:IhB, returns to the value observed at 77 K and becomes equal to 0.4 at 50 K, showing that the concentration of boron in the hexagonal site is higher than on the cubic site.
Raman scattering spectra in C-implanted GaN epilayers
Authors: Sun W. H. , Chua S. J. , Zhang J. , Wang L. S. , Hao M. S. , Chen K. M. , Qin G.G.
Published: April 2011

We have investigated the Raman scattering spectra in C-implanted GaN epilayers. (a) In as-implanted GaN, new Raman bands at 293, 376, 669, 1027, 1094 and 1053 cm−1 appeared. From phonon-dispersion curves for hexagonal GaN, the 293 cm−1 and 669 cm−1 bands were tentatively assigned to the highest acoustic-phonon branch and the optical-phonon branch at the Brillouin zone boundaries, respectively; the 1027 and 1094 cm−1 peaks might be caused by two-phonon scattering involving the 376 and 669 cm−1 phonons, and the 376 cm−1and A1(LO) phonons respectively. (b) Two sharp bands at ∼1350 and ∼1600 cm−1 were observed in the Raman spectra of carbon- implanted GaN after post-implantation annealing treatments. The intensities of these two bands increased while their full widths at half maximum decreased with increasing annealing temperature. We assigned them, respectively, to the D and G bands of small graphite crystallites arising from C implantation and post-implantation annealing. The observation of these two bands indicates the formation of small graphite crystallites in C-implanted GaN.
Underfill Encapsulant Flow Measured using Capacitance Measurement Techniques
Authors: Driscoll T. E. , Lehmann G. L. , Cotts E. J.
Published: April 2011

Capillary flows of dense, model suspensions and industrial underfill encapsulants are investigated. Flow behavior is characterized by measuring the infiltration rate of an encapsulant or model suspension into a channel formed by parallel surfaces. A capacitance measurement technique is used to track the advancement of the front. Significantly this technique allows the channel surfaces to be formed from opaque materials such as those that found in the principal industrial application of electronics packaging. A scaling law to describe the functional dependence of the front position on channel spacing, surface tension and viscosity is presented.
Simultaneous Measurements of Electrical Resistivity and Raman Scattering from Conductive Die Attach Adhesives
Authors: Miragliotta Joseph , Benson Richard C. , Phillips Terry E. , Emerson John A.
Published: April 2011

The development of electrical conductivity in silver (Ag)-filled conductive polymer adhesives is dependent on the thermal profile of the curing process. Previous studies of polymer adhesive systems have shown that chemical reactions at the interface of the micronsized Ag filler are a key factor in determining the subsequent performance of the conductive system. In an attempt to correlate the behavior of electrical conductivity with the chemical nature of the Ag particle interface, we have simultaneously performed electrical resistivity and surface enhanced Raman scattering (SERS) measurements on a commercial conductive adhesive. At room temperature in the low conductance state (∼10−9 ohms−1), the SERS spectrum from the uncured adhesive exhibited peaks that were identified with a molecular species bound to Ag surface via the carboxylate functionality of the adsorbate. During the thermal cure processing, the SERS data showed a partial decomposition of the carboxylate species and the formation of an amorphous carbon layer at the Ag surface. A comparison of the simultaneously recorded electrical resistance and SERS data showed a strong correlation between the development of high conductance (∼ 1 ohm−1) in the adhesive and the formation of the amorphous carbon layer.
Mechanical Properties and Fracture Behavior of the Cu and Cu6Sn5–Dispersed Sn-Pb Solder Bumps Processed by Screen Printing
Authors: Cha Ho-Seob , Lee Kwang-Eung , Choi Jin-Won , Oh Tae-Sung
Published: April 2011

The mechanical properties of the 1-9 vol % Cu and Cu6Sn5-dispersed 63Sn-37Pb solder alloys were characterized with tensile test. Also, the Cu and Cu6Sn5-dispersed 63Sn-37Pb solder bumps of 760 μm size were fabricated on the Au(5 μm)/Ni(5 μm)/Cu(27 μm) BGA substrates by screen printing process, and their shear strength were characterized with variations of the dwell time at the reflow peak temperature(220°C) and aging time at 150°C. The yield strength and ultimate tensile strength of the 63Sn-37Pb solder alloy increased with dispersion of 1-9 vol % Cu and Cu6Sn5. In general, however, the Cu and Cu6Sn5-dispersed solder bumps exhibited lower shear strengths than those of the 63Sn-37Pb solder bumps The failure surface of the solder bumps after ball shear test could be divided into two regions of slow crack propagation and critical crack propagation, and the shear strength of solder bumps was inversely proportional to the slow crack propagation length.
New Stepped Process and Materials for Chip Bonding Technology on Non-rigid and Flexible Substrates
Authors: Park Sung Kyu , Han Jeong In , Kim Won Keun , Kwak Min Gi
Published: April 2011

A reliable interconnection of electrodes to the flexible polymer substrate with anisotropic conductive film (ACF) of which the conductive particles were similar in elasticity to the substrates was accomplished. The contact resistance value was maintained even while the junction was stressed under sudden changes in temperature and pressure. We found that the conduction failure is caused by the action of a complex mechanism on the changes of a joint structure. The major driving factor seems likely to be defects in the transparent electrodes due to the thermal strain of the substrate and penetration of conductive particles into the substrate. The materials of substrate and conductive particle are polycarbonate (PC) with a gas barrier layer and poly-divinylbenzene (DVB) whose hardness is similar to that of the polymer substrate, respectively. In this paper, several experiments were performed with an emphasis on the properties of polymer substrates. Furthermore, the electrical and mechanical performance of the joint structure was studied by evaluating contact resistance and scanning electron microscope (SEM) observations. Moreover, for the experiments, we fabricated test IC with Au bumps through photolithography and electro-plating process. Conductive particle with elasticity similar to that of the polymer substrates did little damage to the transparent electrodes on the substrates, and low temperature and pressure under a stepped process did not bring about their deformation either. Consequently, we adopted the results on the fabrication of plastic based flat panel display module and thus could obtain a highly reliable interconnect with a low contact resistance ( 20-25ω ).
Implementation of a low temperature wafer bonding process for acceleration sensors
Authors: Wiemer Maik , Otto Thomas , Gessner Thomas , Hiller Karla , Kapser Konrad , Seidel Helmut , Bagdahn Joerg , Petzold Matthias
Published: April 2011

The paper describes a low temperature bond process based on an oxygen plasma pretreatment followed by 200°C and 400°C annealing which was to be integrated in our technological process flow to produce micromechanical devices in bulk and surface micromachining like acceleration sensors, gyroscopes and mirror arrays [1]. The results of infrared transmission and the measured bond strengths of the prepared test wafers will be presented in dependence on various pre-treatments and annealing times as well as temperatures. First die separation tests as well as additional detailed investigations showed that the bonding process has the potential to replace an anodic bonding process. During the development of the low temperature bond process it was shown that it is possible to reach a bond strength between 1.5 J/m2 and 2.8 J/m2 depending on the annealing conditions. To optimize the necessary size of the bond frame and to quantify the bond strength limits of the process a test pattern was designed with different arrangements of sensor structures like bond frames, spaces and chevron notch structures. The investigation showed the achieved bond yield in dependence on different sensor structures and bond conditions.
Nano-lamellar Structures in a Rolled Cu-Ag Alloy
Authors: Lyttle Mark T. , Hughes D.A.
Published: April 2011

The microstructural evolution and texture development in a Cu-Ag eutectic during rolling are systematically investigated. A directionally solidified Cu-Ag alloy with a single dominant texture is deformed to several rolling reductions. At each of these strains, the microstructure and texture are characterized. Rapid divergence of local crystal orientations leads to the early development of high-angle Cu-Ag boundary/interface orientations, while less misorientation accumulation occurs within the individual copper and silver layers. With increasing deformation, orientations of the copper and silver phases in a single region are observed to diverge to two distinct textures, and within each of the single phases, there is a greater spread of orientations of individual cells while still retaining an identifiable preferred orientation.
Macroscopic Shear Banding in an Aluminum-Based Alloy During Equal-Channel Angular Pressing
Authors: Wang Jingtao , Xu Yuzhong , Wang Lizhong , Zhao Xicheng , Wang Haibo
Published: April 2011

Equal-channel angular pressing is now recognized as an effective technique for fabricating materials with ultrafine structures. It is generally considered that the strain is homogeneously distributed in the materials after ECA pressing. The present investigation shows, however, that severe macroscopic shear band, which extends from bottom to top surface and slants to the longitudinal axis of specimen at an angle of about 45°, develops at regular intervals, with a high shear strain accommodation of about 3.7 within the band. Different families of macroscopic shear bands may cut across each other, and the total volume fraction of macroscopic shear bands may well surpass 50%.
Evaluation of Dislocation Storage by Means of Crystal Plasticity Analysis
Authors: Ohashi Tetsuya , Asakawa Kazuhisa
Published: April 2011

A numerical model of two phase metal microstructure of f.c.c. type crystal is made where a harder inclusion of a spherical shape is embedded in softer matrix. The model is subjected to a tensile load and its deformation is analyzed by a finite element crystal plasticity code. Under the tensile load, plastic slip deformation on {111}<110> slip systems take place in the matrix and the density distribution of the geometrically necessary dislocations is evaluated from the gradient of plastic shear strain on slip systems. Obtained results show not only a simple loop structure around the inclusion but also kink wall structure and some smaller loops. Details of the strucuture are discussed.
Beyond the Classroom: Educating Undergraduates in Materials Science Research and Careers via the CPIMA SURE Program
Authors: Goldman Marni , Wade Charles G. , Waller Brenda E. , Frank Curtis W.
Published: April 2011

The Center on Polymer Interfaces and Macromolecular Assemblies (CPIMA), an NSF MRSEC and joint partnership among Stanford University, IBM Almaden, and University of California at Davis, established the Summer Undergraduate Research Experience (SURE) Program in 1995. Its mission is twofold: to expose undergraduate students to cutting-edge research and to help students with their ultimate career decisions. Approximately twenty-five students each summer are assigned a research project under the direction of a mentor. Students are exposed to a variety of research environments including universities, industry, and laboratories overseas. Regardless of site, students participate in research group meetings and learn the research process –a valuable experience that is often not obtained during a student's undergraduate years. To complete the research experience, SURE students attend a CPIMA Forum where they present posters on their research and interact with members of both academia and industry. While undergraduates are exposed to academia, they are often not exposed to industry or alternative careers. SURE students learn about industrial research by visiting IBM and getting a tour of the Almaden Research Center. A Career Day is held during the Program where students are given workshops on applying to graduate school as well as talks from people in different scientific careers, both traditional and nontraditional. Assessment surveys show that after their exposure to a number of experiences and ideas over 10 weeks, the SURE students have learned important lessons that a traditional classroom does not afford. To date, over 150 students have participated.
Scientists as Mentors to Science Teachers
Authors: Goodchild Fiona , Johnston Carol
Published: April 2011

This study of teacher researchers and mentor scientists at the Materials Research Laboratory at UCSB takes a socio-cultural perspective, assuming group norms in terms of language and practice associated with being a science teacher and a research scientist. The paper will report on data gathered from individual interviews with 6 science teachers and their mentor scientists, before and after the RET six week session in summer 2000. The interviews reveal some of the expectations and benefits expressed by teachers and scientists as well as some of the contrasts in the cultures of science teaching and research science. These factors need to be accommodated in RET project design.
Evaluating Science Research Experience For Teachers Programs and Their Effects on Student Interest and Academic Performance: A Preliminary Report of an Ongoing Collaborative Study by Eight Programs
Authors: Dubner Jay , Silverstein Samuel C. , Carey Nancy , Frechtling Joy , Busch-Johnsen Tamra , Han Jeannie , Ordway George , Hutchison Nancy , Lanza Janet , Winter Jim , Miller Jon , Ohme Paul , Rayford James , Weisbaum Kathryn Sloane , Storm Kaye , Zounar Elda
Published: April 2011

Formal programs that provide research experiences for teachers (RET) have been in existence for more than 20 years. Currently there are more than 70 formalized Scientific Work Experiences Programs for Teachers (SWEPTs) nationwide. The underlying assumption of most RETs is that these intensive summer work immersion experiences, coupled with appropriate follow-up activities during the school year, expand teachers' professional skills and networks, and thereby improve the performance of their students. Many SWEPTs have collected anecdotal evidence indicating their program's positive impact on teachers. Missing from all SWEPT evaluations is quantitative evidence that teacher participation in these programs affects student interest and performance in the subject taught by the SWEPT teacher. As professional evaluators attest, it is difficult to differentiate the roles of teachers and teaching practices in changing student academic interest and performance from other factors (e.g., curriculum, school administration, non-random assignment of students, etc.).

This study controls for many of these factors by comparing interest and achievement of students in classes of SWEPT teachers with students in classes of comparison teachers in the same school and teaching the same subject. The study's longitudinal design is commensurate with the philosophy and practices of the participating SWEPTs.
Imprint in Ferroelectric Thin Films Caused by Screening of an Electric Field in a Thin Surface Layer
Authors: Grossmann Michael , Lohse Oliver , Bolten Dierk , Boettger Ulrich , Waser Rainer
Published: April 2011

Imprint describes an aging effect in ferroelectric thin films which manifests itself by a shift of the P-V hysteresis loop on the voltage axis. In this paper a mechanism is described which attributes imprint to the screening of a large electric field within a thin surface layer by electronic charges. The field at the surface arises due to the existence of a thin surface layer in which the spontaneous ferroelectric polarization is suppressed. In the course of aging this field is gradually screened by electronic charges which are generated by a Frenkel-Poole effect and then become trapped near the electrode-thin-film interface causing the shift of the hysteresis loop. A numerical simulation based on this model allows a quantitative description of the imprint effect as a function of various experimental parameters.
Ferroelectric-Gate Structures and Field-Effect Transistors Using (Bi,La)4Ti3O12 Films
Authors: Tokumitsu Eisuke , Suzuki Takuya , Sugita Naoki
Published: April 2011

We have fabricated and characterized metal-ferroelectric-metal-insulator-semiconductor (MFMIS) diodes and field-effect-transistors (FETs) using (Bi,La)4Ti3O12 (BLT) films. 9-nm-thick SiO2 is used as an “I” layer. It is shown that the memory window in the capacitance-voltage (C-V) characteristics of the MFMIS structures is as large as 3V for a voltage sweep of 5V, when the area ratio of the MIS region (SI) to the ferroelectric capacitor region (SF), SI/SF, is 15. It is also demonstrated that the MFMIS-FETs using Pt/BLT(150nm)/Pt/SiO2(9nm)/Si structures have hysteresis loops due to the ferroelectric BLT film in the drain current-gate voltage (ID-VG) characteristics. Observed threshold voltage shift is 3V and excellent data retention characteristics are demonstrated for the device with an area ratio SI/SF of 15.
Investigation of the Role of Carbonylchemistry to Pattern Platinum Electrodes
Authors: Schneider St. , Kohlstedt H. , Waser R.
Published: April 2011

Noble metals like platinum or irdium are used as electrode materials in DRAM or FRAM devices. Their etch process is a challenge as conventional, sputter driven etch processes either result in redeposition problems (fences) or in a severe sloping (loss of dimension control) and are not acceptable for high density integration architectures. The high temperature etch regime offers a solution by increasing the chemical etch component and thus the volatility of the etch products.

As previously reported, the platinum etch rate increases exponentially for a chlorine etch process with increasing wafer temperature. In this study we investigate the particular role of carbon monoxide in a Cl2/CO etch process. We find that carbon monoxide additions to a chlorine process boost the chemical component of the platinum etch rate very significantly, exceeding the effects in the chlorine only process regime by far. Additionally we compare these results with a Cl2/O2 and a Cl2/CO2 process chemistry, which are not found to be particularly beneficial.

To better understand the etch process we use an energy dispersive quadrupole mass spectrometer for in situ monitoring, attached to the chamber at two different locations. We are able to position the probe orifice at the place of the wafer electrode, to record ion energy and ion mass spectra of species impinging on the wafer plane. A second off axis position allows for etch product monitoring.
Analysis of Alternating Current Conduction and Impedance Spectroscopy Study of BaBi2Nb2O9 Thin Films
Authors: Laha Apurba , Saha S. , Krupanidhi S. B.
Published: April 2011

Alternating current conduction in BaBi2Nb2O9 (BBN) thin films has been studied over a wide range of temperatures and frequencies. A power law relation was used to explain the frequency dependence of ac conductivity. In the higher frequency region, ac conductivity of the BBN thin films was temperature independent. The activation energy calculated from the Arrhenius plot of ac conductivity was found to be around 0.25 eV. It was attributed to shallow trap controlled space charge conduction in the bulk of the sample. The impedance analysis of the BBN thin films was also performed to gain insight into the microstructure of the films, including the characteristics of the grains, grain boundaries, and film-electrode interface. The response of a single RC combination has been observed for our case. The effect of other components, such as the grain boundary interface and electrode/film interface was negligible. The imaginary component of impedance (Z”) exhibited different peak maxima at different temperatures. A Debye mechanism was found to be appropriate to explain the polarization relaxation in BBN thin films.
Impact of Template Layers on Dielectric and Electrical Properties of Pulsed-Laser Ablated Pb(Mg1/3 Nb2/3)O3 - PbTiO3 Thin Films
Authors: Laha Apurba , Saha S. , Krupanidhi S. B.
Published: April 2011

A study was done on pulsed laser deposited relaxor ferroelectric thin films of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) deposited on platinized silicon substrates with template layers to observe the influence of the template layers on physical and electrical properties. Initial results, showed that perovskite phase (80% by volume) was obtained through proper selection of the processing conditions on Pt/Ti/SiO2/Si substrates. The films were grown at 300°C and then annealed in a rapid thermal annealing furnace in the temperature range of 750-850°C to induce crystallization. Comparison of the films annealed at different temperatures revealed a change in crystallinity, perovskite phase formation and grain size. These results were further used to improve the quality of the perovskite PMN-PT phase by inserting thin layers of TiO2 on the Pt substrate. These resulted in an increase in perovskite phase in the films even at lower annealing temperatures. Dielectric studies on the PMN-PT films show very high values of dielectric constant (1300) at room temperature, which further improved with the insertion of the template seed layer. The relaxor properties of the PMN-PT were correlated with Vogel-Fulcher theory to determine the actual nature of the relaxation process.
Microstructural and Dielectrical Properties for Ceramics and Thin Films of the xPbTiO3-(1−x)SrTiO3 Solid Solution
Authors: Martínez E. , Fundora A. , Blanco O. , García S. , Heredia E. , Siqueiros J. M.
Published: April 2011

SrTiO3 and PbTiO3 perovskites are combined to form the xPbTiO3-(1−x)SrTiO3 (PST) solid solution. The effect of the PbTiO3 content on the microstructural and dielectric properties is studied for different compositions (x=0.1,0.3,0.5,0.7, and 0.9). Microstructural features of the PST system are studied by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques. Electrical properties are studied by the thermoelectric analysis technique at both fixed frequency and varying frequency to study the behavior of the dielectric constant and dielectric loss.Films of 0.5PbTiO3-0.5SrTiO3 (PST50) have been obtained by RF ion sputtering on different substrates. We investigate the relation between the crystalline structure and the dielectric properties of PST50 films deposited on different metallic films. Scanning Electron Microscopy (SEM) and X-Ray Diffraction were used for the structural analysis of the PST50/TiN/Si and PST50/RuO2/TiN /Si systems. The dielectric properties of the PST50 films were measured for TiN/PST50/TiN/Si, and RuO2/PST50/RuO2/TiN/Si capacitors and the results were correlated to the structure and composition. The charge storage capabilities of the PST50 films are evaluated for possible application in integrated circuit technology.
Interdigital Ag(Ta,Nb)O3 thin Film Capacitors on Sapphire
Authors: Koh Jung-Hyuk , Grishin Alex , Shibuya Akira , Okuyama Masanori
Published: April 2011

Polycrystalline 0.4 μm thick films of Ag(Ta,Nb)O3 (ATN) were grown on sapphire (Al2O3-0112, r-plane) wafers by pulsed laser deposition technique. 2 and 4 μm gap interdigital capacitors were defined by photolithography on the top of Au/Cr/ATN(0.4μm)/Al2O3 film structures. They exhibit high dielectric performance. In the frequency range of 1 kHz to 1 MHz dielectric permittivity shows frequency dispersion as low as 3.5 %, loss tangent ∼ 0.0035 @ 1 MHz, Kfactor = tunability/tan δ is about 20.2 @ 200 kV/cm, and resistivity as high as 1.8 × 1011 ×cm @ 100 kV/cm. C-V and I-V characteristics recorded in time domain revealed slow Curie-von Schweidler-type relaxation of the polarization. Low frequency dispersion and loss, high tunability and low noise in the biased state promise thin ATN film capacitors for microwave applications.
RF-Magnetron Sputtered Au/(Na,K)NbO3/SiO2/Si MFIS-diode Structures
Authors: Shibuya Akira , Koh Jung-Hyuk , Grishin Alex , Kugler Veronika , Music Denis , Helmersson Ulf , Okuyama Masanori
Published: April 2011

Recently we proposed ferroelectric sodium potassium niobate (Na0.5K0.5NbO3, NKN) thin films to be a candidate for applications in nonvolatile memories and electrically tunable devices [1-5]. In this paper we report on processing and characterization of metal-ferroelectric-insulatorsemiconductor (MFIS) diode structures based on RF-magnetron sputtered NKN films. 0.7 μm thick NKN films have been deposited at 650 °C on the thermally grown 47 nm thick SiO2 layer on Si(001) wafers. Stoichiometric Na0.5K0.5NbO3 ceramic target was sputtered in an O2-Ar atmosphere with a total pressure of 5 mTorr. Grown films were analyzed as deposited as well as after an oxygen annealing at 600 °C for 30 minutes. The NKN films exhibit a strong (001) preferential orientation, which was appreciably improved after the oxygen annealing. A leakage current density of 2.3 nA/cm2 at an electric field of 400 kV/cm, and a memory window of 7.2 V was measured for Au/NKN/SiO2(47nm)/Si(001) diode structures at the programmable voltage of 40 V. I-V measurements were performed in the time domain to distinguish between the relaxation of polarization, “true” leakage current, and the degradation of the resistance in ferroelectric NKN film.