bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanical strain evolution in Cu/low K interconnect lines
Authors: Besser Paul R. , Jiang Qing-Ting 
Published: April 2011

ABSTRACTThe mechanical stresses in Cu interconnect lines arise from thermal expansion (CTE) differences, and the magnitude of the stress can be calculated based on the measured strain. In the current work, the strain (and stress) state of narrow Cu lines fabricated in oxide and porous organic spin-on dielectrics (low K) has been determined with X-Ray diffraction (XRD) during annealing. The room temperature stress along the length (X) and width (Y) of the lines are not dramatically different while the Z component is somewhat smaller with the spin-on ILD. These small perturbations in the magnitude of the Cu stress do not reflect the dramatic differences in the CTE. More insight into the materials system is obtained by studying the strain-temperature behavior, which illustrates the effect of the ILD clearly. The X strain is similar in magnitude and variation with temperature for both ILDs, supporting strain being imposed by the substrate. However, the Z strain is compressive at RT and linearly increases with temperature for Cu in low K, reflecting the lack of constraint by the ILD and the higher CTE of the ILD.
Use of the curvature method to determine the misfit stress of epitaxial semiconducting systems: the case of samples thinned for TEM observation.
Authors: Ponchet A. , Cabié M. , Durand L. , Rivoal M. , Rocher A. 
Published: April 2011

ABSTRACTThe curvature method which allows to measure the stress in epitaxial layers has been adapted to transmission electron microscopy observations. The samples thinned by the substrate side present some particular mechanical characteristics. The ratio between the substrate thickness and the layer thickness should be taken into account. The experimental conditions allowing a reliable determination of the stress have been established. A finite element calculation has been used to show that the dimensions of the area where the measure is performed can not systematically be neglected. This method has been applied to the semiconducting systems Ga1-xInxAs/GaAs and Ga1-xInxAs/InP.
A Theoretical Study on the Indentation of Viscoelastic Materials
Authors: Fu Guanghui 
Published: April 2011

ABSTRACTNanoindentation experiments have been used to investigate mechanical properties of polymeric thin films. In this paper, the problem is modeled as normal indentation of a viscoelastic half-space by a rigid smooth frictionless axisymmetric polynomial indenter. An analytical solution, which relates the indentation load to the penetration depth, is presented. The solution is valid as long as the contact region is simply connected and the indenter is in complete contact with the half-space. It shows that a similar fundamental relation exists in Laplace space.
Thermo-mechanical behavior of Fe thin films
Authors: Chamsoutdinov Nail R. , Böttger Amarante J. , Delhez Rob , Tichelaar Frans D. 
Published: April 2011

ABSTRACTThe thermo-mechanical behavior of magnetron sputtered Fe polycrystalline films of thickness between 50 nm and 400 nm has been investigated. The state of stress has been determined by means of wafer curvature and X-ray diffraction (sin2ψ-method). Both methods are in good agreement for layers of thickness above 200 nm. For specimens of smaller layer thickness, however, the average stresses as measured by X-ray diffraction are systematically higher than those observed by wafer curvature experiments. The results can be interpreted in terms of differences in micro-strain (estimated using X-ray diffraction peak width analysis) and grain size as obtained by transmission and scanning electron microscopy. Thermal cycling experiments were performed between RT and 873 K. The effect of microstructure on thermo-mechanical properties was shown to be crucial.
Characterizing Thin-Film Stress Fields by Resonance of Membrane Arrays
Authors: Engelstad R. , Lovell E. , Chalekian A. , Janowski S. , Cash M. , Eguchi H. 
Published: April 2011

ABSTRACTControlling thin-film stress magnitudes and nonuniformities is a persistent and pervasive challenge for applications ranging from the semiconductor industry to nanotechnology. Consequently, the ability to accurately measure the intensity and spatial distribution of film stress is essential for fabrication process optimization. This paper describes novel extensions of the membrane resonance method to characterize in-plane film stress gradients. Arrays of freestanding membrane windows are fabricated by first depositing thin films over a silicon substrate. Back-etching then creates an array of membrane windows which are sequentially resonated with a compatible drive electrode. The technique was used to determine stress uniformity across electron projection lithography masks, which incorporate membrane window arrays. In addition, a procedure is presented for identifying the two principal stresses in individual membranes.
Residual Stress in Silicon Nitride Thin Films Deposited by ECR-PECVD
Authors: Cianci E. , Foglietti V. 
Published: April 2011

ABSTRACTWe have investigated the influence of process parameters in electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD) of silicon nitride, on the intrinsic stress of thin SiN films and on their composition, in order to obtain SiNx films suitable to micromechanical applications. The silane to nitrogen gas flow ratio, along with addition of helium to gas mixture, was found to be a critical parameter for the tuning of the intrinsic stress in ECR-PECVD SiNx films, from compressive to tensile stress, with a maximum related to the largest Si-N bond density in the film.
Microstructure and Current Transport Properties of YBa2Cu3O7-x/(Ba0.05, Sr0.95)TiO3 Multiple-Layer Thin Films
Authors: Luo Y. , Hughes R. A. , Preston J. S. , Botton G. A. 
Published: April 2011

ABSTRACTYBa2Cu3O7-x (YBCO) films grown by pulsed laser deposition (PLD) on (100) LaAlO3 (LAO) substrates show a strong thickness dependence on the electrical properties. For example, for films in excess of 0.3 μm, the critical current density decreases with increasing thickness. In contrast, nano-composite films consisting of a series of multiple layers of YBa2Cu3O7-x and (Ba0.05, Sr0.95)TiO3 (BSTO) thin films having a total thickness of 5 μm show improved electrical properties. In order to understand this phenomenon, a detailed microstructural characterization has been undertaken. Transmission electron microscopy (TEM) observations show that cracks, stacking faults, c-║ crystals and secondary phase precipitates are present on the single-layer films, while a high-quality microstructure is observed for the nanocomposite multiple-layer films although defects at YBCO/BSTO interface are still present. In addition, nanocomposite films have a reduced surface roughness. In this complex microstructure, the YBCO/BSTO interfaces and the lattice mismatch strain play a crucial role in controlling the nature of the defects and stability of phases. In order to understand the role of the BSTO layer has on the microstructure, the interfacial mismatch strain and defects are analyzed by high-resolution transmission electron microscopy (HRTEM) in combination with the Moiré fringe technique.
DLC/Hydroxyapatite Nanocomposites
Authors: Narayan Roger J. 
Published: April 2011

ABSTRACTStudies of orthopaedic implant failures have shown that mechanical failure of an implant almost exclusively occurs at the biomaterial-tissue interface. Hydroxyapatite (HA) mimics the behavior of natural bone, and provides a strong, long-lasting adhesive interface between a bone replacement implant and the surrounding tissue. Currently, thin film HA is not commonly used because it contains defects, porosity, and cracks. Delamination of the hydroxyapatite film and formation of hydroxyapatite particles may lead to implant wear and loosening. Furthermore, the coating also acts only as a temporary barrier to ion release from the bulk biomaterial. One method to improve the tribological properties of a bioactive coating is to strengthen the microstructure of the coating through the placement of a DLC (hydrogen-free diamondlike carbon) interlayer. DLC coatings possess properties close to diamond in terms of hardness, atomic smoothness, and chemical inertness. We have developed a diamondlike carbon/HA bilayer, in which the bilayer surface (HA) is bioactive and the interlayer (diamondlike carbon) is biocompatible, wear resistant, and corrosion resistant. We have successfully deposited nanocrystalline hydroxyapatite and DLC films by ablating a hydroxyapatite target and a graphite target using a KrF laser. A novel target design was adopted to incorporate alloying atoms into the films during pulsed laser deposition. These alloying elements possess unique biological properties. Surface morphology was studied using SEM, interfacial structure was studied using TEM, and HA phase microstructure was studied using XRD. The DLC/nanocrystalline HA bilayer material is potentially useful for several orthopedic implant designs.
Phase Field Modeling of Surface Instabilities Induced by Stresses
Authors: Seol D. J. , Hu S. Y. , Liu Z. K. , Kim S. G. , Kim W. T. , Oh K. H. , Chen L. Q. 
Published: April 2011

ABSTRACTIn this work, we developed a phase field model describing surface evolution dynamics of a strained solid in contact with gas phase. Elastic solutions are solved with an iteration method for the system in which a solid film, strained by the mismatch strain between the film and substrate, has anisotropic elastic constants and the vapor phase has zero elastic constants. Elastic solutions are incorporated into the phase field evolution equation. The model predicts stable morphology at a given mismatch strain and perturbation wavelength.
Single-crystal and Nano-columnar Growth of Gadolinium-doped Ceria Thin Films on Oxide Substrates Studied Using Electron Microscopy
Authors: Huang D. X. , Chen C. L. , Jacobson A. J. 
Published: April 2011

ABSTRACTGadolinium-doped ceria (GDC) thin films were grown by pulsed laser ablation on various oxide single crystal substrates including MgO, YSZ, LAO, NGO, and STO with different film-substrate lattice mismatch ratios. The film microstructures were characterized mainly by using electron microscopy. A clear influence of the filmsubstrate lattice mismatch on the film crystallinity has been observed. The GDC films usually exhibit columnar grain growth for a large range of film-substrate lattice mismatch ratios. A cube-on-cube growth of GDC film on MgO has been observed with a surprisingly high lattice mismatch ratio of 28%. The highest film crystallinity is obtained on the LAO substrates under a small compressive strain. This single-crystalline GDC film shows no columnar grain growth but presents a novel directionally-aligned precipitated Gd-rich nanoparticle system, which plays a specific role in relaxing various kinds of strain fields induced during the thin film growth to ensure the film crystallinity.
Young's Modulus Variation with Thickness of Thin Films
Authors: Zhou L. G. , Huang Hanchen 
Published: April 2011

ABSTRACTThis paper describes atomistic determinations of the Young's modulus of free standing thin films, or nanoplates. Using a combination of analytical formulation and molecular statics simulations, we show that the Young's modulus of a nanoplate may either increase or decrease with the thickness. It is the competition of bond saturation and bond loss on surfaces that dictates the increase or decrease. Taking Cu as an example, we demonstrate that the Young's modulus is larger than its bulk counterparts for nanoplates having some surfaces and loading directions, and smaller for others.
Internal Oxidation and Mechanical Properties of Pt-IrO2 Thin Films
Authors: Chromik Richard R. , Bannuru Thirumalesh , Vinci Richard P. 
Published: April 2011

ABSTRACTPt-IrO2 films, approximately 200 nm thick, were fabricated by co-sputter deposition of Pt and Ir in an Ar-O2 mixture followed by annealing at 700°C in O2 for 4 hours. X-ray photoelectron spectroscopy and x-ray diffraction measurements indicate the presence of IrO2 throughout the thickness of the films. After a thermal cycle in vacuum to 700°C, the room temperature residual stress is significantly lower in the internally oxidized films than in pure Pt films of similar thickness subjected to identical cycling. Initial analysis of the behavior of the films during thermal cycling indicates that the primary cause for the difference in residual stress level is a decrease in the thermoelastic slope associated with the introduction of IrO2.
Mechanisms controlling the hardness of Si and Ge
Authors: Vandeperre L. J. , Giuliani F. , Lloyd S. J. , Clegg W. J. 
Published: April 2011

ABSTRACTIt is generally accepted that the hardness of silicon and germanium is limited by a phase transformation. Observations of the deformation under indents using transmission electron microscopy indicate that, in addition to the phase transformation, there is also plastic flow both in the transformed and in the untransformed material. These observations are consistent with those made elsewhere and with predictions based on the spherical cavity model for indentation, modified to quantify the effect of a phase transformation on the measured hardness. The analysis predicts that the hardness can only be approximately equal to the transformation pressure provided the yield strength of the transformed material is low, and that there is a region where plastic deformation in the untransformed material can occur in addition to the phase transformation. These predictions are consistent with the experimental observations of substantial plastic deformation of the transformed phase, as well as with estimates of its Peierls stress.
Optimization of Film Stresses Utilized in Composite Piezoelectric Membrane Microgenerators
Authors: Kennedy M. S. , Zosel M. , Richards C. D. , Richards R. F. , Bahr D. F. , Hipps K. W. , Moody N. R. 
Published: April 2011

ABSTRACTTo improve the mechanical compliance of a piezoelectric generator membrane, alterations in PZT processing including variations in crystallization temperature, cooling rates and precursor chemistry were made to reduce the residual stress. In addition to changing the stresses, these treatments also altered the morphology of the PZT and its modulus. Nanoindentation of these films were made to determine the moduli of the PZT films, which varied from 70GPa to 90GPa. The residual stress of 40:60 2-MOE PZT taken by x-ray diffraction were shown to reduce in residual stress from 210 MPa to 154 MPa with annealing. The static pressure-deflection of membranes with these films showed correlating composite effective stresses of 110MPa and 83MPa. Adding PEG to the precursor solution also lowered the stress of the PZT films. Bulge testing showed that decreasing the crystallization temperature from 700°C to 600°C lowered residual stress from 210 MPa to 154 MPa. Raman spectroscopy showed differences in both stress and structure of PZT deposited on thin support structures (2μm) over bulk wafers (350 μm). The compliance of the generators was also increased by etching Pt in highly stressed regions.
Bonding Characterization of Oxidized PDMS Thin Films
Authors: McMahon J. J. , Kwon Y. , Lu J.-Q. , Cale T. S. , Gutmann R. J. 
Published: April 2011

ABSTRACTThis paper reports on the use of poly(dimethylsiloxane) (PDMS) thin films to bond pairs of glass slides, borosilicate glass, and silicon substrates, with an emphasis on application for wafer-level three-dimensional (3D) heterogeneous integration technology platforms. PDMS films were spin-cast and cured, surface modified using low power oxygen plasma, and then bonded to various materials. These bonds were destructively tested using a four point bending technique. The critical adhesion energy obtained using surface modified PDMS to bond glass slides is 3.0 J/m2. Adhesion energies obtained using unmodified PDMS are 2.8, 1.8, and 1.6 J/m2 for bonded silicon, glass slides, and borosilicate glass, respectively. Correlation of these results to material surface and interface properties indicates that although PDMS has process advantages as a bonding material for heterogeneous integration, its adhesion strength is lower than that of other dielectric bonding glues.
Transparent Transistor Development
Authors: Hong D. , Dehuff N. L. , Presley R. E. , Munsee C. L. , Bender J. P. , Park C.-H. , Wager J. F. , Keszler D. A. 
Published: April 2011

ABSTRACTTransparent electronics is an embryonic technology whose objective is the realization of invisible electronic circuits. We have recently reported the fabrication of a novel n-channel transparent thin-film transistor (TTFT). [1] This ZnO-based TTFT is highly transparent and exhibits electrical characteristics that appear to be suitable for implementation as a transparent select-transistor in each pixel of an active-matrix liquid-crystal display. Moreover, the processing technology used to fabricate this device is relatively simple and appears to be compatible with inexpensive glass substrate technology. The objective of the work reported herein is to summarize some of our recent TTFT electrical performance results. Materials, processing, and device structure details related to these devices appear in future publications.
Low Resistivity Boron Doped Amorphous Silicon-Germanium Alloy Films Obtained with a Low Frequency
Authors: Heredia-J Plasma A. , Torres-J A. , De la Hidalga-W F.J. , Jaramillo-N A. , Sanchez-M J. , Zúñiga-I C. , Basurto P M. , Pérez A. 
Published: April 2011

AbstractThe structural and electrical properties of boron doped amorphous silicon-germanium alloy films, obtained using a low frequency plasma enhanced chemical vapor deposition (LF PECVD), are presented in this contribution. These thin films were deposited on a substrate heated at 270°C, and by decomposing a mixture of silane, germane, and diborane gases. The chemical bond structure was studied by Infrared Spectroscopy. Our results show that, for a constant diborane flow, the increase of germane flow enhances the incorporation of boron into the film; the peak at 2540 cm−1 becomes larger as the Ge content increases. Transport of carriers was studied by measuring current-voltage curves as a function of temperature. The conductivity increased from 10−6 to 10 (Ω-cm)−1, while the refraction index increased from 3.312 to 4.4458, for an increasing Ge content; this makes the films suitable for optical waveguide applications. On the other hand, the activation energy varied from 0.668 to 0.220 eV when the sample was doped with boron. The AFM images showed that the surface roughness was improved for an alloy with 50% of Ge.
Effects of Film Interfaces on the Properties of Poly-Si Grown by The Metal-Induced Technique for Solar Cell Applications
Authors: Ji Chunhai , Anderson Wayne A. 
Published: April 2011

ABSTRACTIn the metal-induced growth (MIG) process, the poly-Si layer hetero-epitaxially grows from a thin silicide layer, formed by reaction of a metal seed-layer and sputtered silicon, due to an extremely close lattice match between silicon and the metal silicide. The produced poly-Si has shown a promising device quality for photovoltaic applications. Recent results show that the interface of the silicide and poly-Si has a significant effect on the properties of the poly-Si which works as an active layer for photon absorption. In the study of the MIG process, two metals were used as a seed-layer, i.e. Ni and Co. Although CoSi2has a larger lattice mismatch with Si (1.2%) than does NiSi2(0.4%), the poly-Si growing from Co has a smoother interface between the poly-Si and silicide, while the one for the Ni seed-layer samples is rather rough. Backscattered XSEM shows that the Ni-contained phase extended into the Si layer by forming long spikes. This might cause crystal defects in the Si layer. The Auger depth profile also showed that the Ni atoms diffuse into the Si layer much more than does the Co. This kind of difference in interface structure causes the different properties of the poly-Si layer. X-ray diffraction (XRD) analysis on the Si layer showed that the Co seed-layer sample had a predominant growth orientation of (220) and the FWHM of 0.2°. The Ni seed-layer samples grew mainly in both <111> and <220> direction, with FWHM of 0.3° and 0.4°, respectively. By comparison, the poly-Si from the Co seed-layer had a higher carrier lifetime of 0.458μs compared to 0.305μs from Ni.
High Power 330 nm AlInGaN UV LEDs in the High Injection Regime
Authors: Gherasimova M. , Su J. , Cui G. , Han J. , Peng H. , Makarona E. , He Y. , Song Y.-K. , Nurmikko A. V. 
Published: April 2011

ABSTRACTWe report on the growth and testing of the light emitting diode structures incorporating quaternary AlInGaN active region with an emission wavelength of 330 nm. Small area circular devices were fabricated, yielding the output power of 110 μW measured with a bare-chip configuration in a high current injection regime (8 kA/cm2 for a 20 μm diameter device). Structural properties of the constituent epitaxial layers were evaluated by atomic force microscopy and transmission electron microscopy, resulting in the observation of two-dimensional growth morphologies of AlN and AlGaN, and the estimate of threading dislocation densities in the low 109 cm-2 range in the structures grown on sapphire substrates.
Optical Properties of AlN/AlGa(In)N Short Period Superlattices – Deep UV Light Emitting Diodes
Authors: Holtz M. , Ahmad I. , Kuryatkov V. V. , Borisov B. A. , Kipshidze G. D. , Chandolu A. , Nikishin S. A. , Temkin H. 
Published: April 2011

ABSTRACTWe report optical properties of deep UV light emitting diodes (LEDs). Devices are based on short period superlattices of AlN/AlxGa1-x(In)N (x ∼ 0.08) grown by gas source molecular beam epitaxy with ammonia. Structures consist of a 50-nm thick AlN nucleation/buffer layer deposited on sapphire. This is followed by a 1-micron thick Si-doped buffer layer of AlGaN or AlN/AlGa(In)N designed to be transparent for wavelengths longer than 240 nm. The design thickness of the superlattice well layers is systematically varied from 0.50 nm to 1.25 nm and the thickness of the barrier is varied from 0.75 nm to 2.00 nm. The n- and p-type SPSLs were doped with Si derived from silane and Mg evaporated from an effusion cell, respectively. We investigate device structures as well as superlattices which are nominally undoped, p-type, and n-type. Optical properties are investigated using reflectance, cathodoluminescence, and, in the case of LEDs, using electroluminescence. By controlling the properties of the superlattice, we obtain optical gaps ranging from 4.5 eV (276 nm) and 5.3 eV (234 nm). A systematic shift between the optical gap and the CL peak emission energy is discussed. Electrical properties are studied using I-V, C-V, and Hall effect. LEDs based on these superlattices and operating in the range of 260 to 280 nm exhibit turn-on voltages in the range of 4 to 6 V and support dc current densities in excess of 500 A/cm2 at room temperature. We present results on the electrical and optical properties of our LEDs designed using these studies.
Proposal to Use GaAs(114) Substrates for Improvement of the Optical Transition Probability in Nitride Semiconductor Quantum Wells
Authors: Funato Mitsuru , Kawaguchi Yoshinobu , Fujita Shigeo 
Published: April 2011

ABSTRACTThe dependence of the spontaneous emission lifetime of excitons in InGaN/GaN quantum disks (QDs) on the crystalline orientation is calculated. For 1-nm-thick QDs, it is found that the lifetime in the conventional c-oriented QDs is ten times as long as that in QDs tilted by 30° and 90°, and that the difference is pronounced by increasing the QDs thickness. This is totally due to the presence of the electric field in strained InGaN. Taking into account our preceding study, in which it was revealed that GaN on GaAs(114) was titled by 30°, we propose the use of GaAs(114) as a substrate for nitride light emitting devices to improve the optical transition probability.