bluuebunny/crossref_metadata_2025_split huggingface dataset:
Indentation of Piezoelectric Ceramics: Theory, Experiments and Applications
Authors: Suresh Subra , Giannakopoulos Antonios E. , Sridhar S. , Ramamurty U. 
Published: April 2011

AbstractA new method is proposed for the characterization of properties of piezoelectric materials using depth-sensing indentation involving both mechanical and electrical measurements. First, a rigorous general theory is presented for axisymmetric indentation of piezoelectric solids with anisotropic properties. The theoretical results facilitate the prediction of the indentation load versus the depth of penetration of indenter into the substrate, as well as some transient electrical effects for different electrical boundary conditions. Used in conjunction with instrumented indentation experiments at the nanoscopic, microscopic or macroscopic size scales, these results lead to the prediction of some of the elastic, dielectric and piezoelectric constants as well as the activation energy for depolarization. The predictions of the theory as well as the validity of the approach have been substantiated further with detailed indentation experiments on PZT-4 and barium titanate using either a conducting indenter or an insulated indenter. The theoretical predictions of the coupled electrical-mechanical indentation of piezoelectric solids have also been checked with finite element analyses. The implications of the proposed method for the design and characterization of piezoelectric materials and for quality control in commercial production are also addressed.
New Concept for Resonant Longitudinal-Shear Ultrasonic Motor
Authors: Bouchilloux P. , Koc B. , Uchino K. 
Published: April 2011

AbstractThis paper presents an original linear piezoelectric motor for applications in space and robotics. The originality of this motor consists in the combination of longitudinal and shear modes of vibration of the stator. These two modes are mixed to produce an elliptical vibration of the surface of the stator in contact with a slider. The motion of the linear slider is obtained through friction forces that develop at the interface between the stator and the slider.This motor is being developed for applications in active truss members of variable geometry structures, such as those used in space. Currently, these structures employ stepper motors. It is expected that replacing these electromagnetic devices with ultrasonic motors will offer the following advantages: position-locking without power supply, compactness, nonmagnetic operation, and lower power consumption.This paper details the design of this motor and emphasizes the novel concept that was developed to combine the longitudinal and shear modes of vibration.
Characterization of NiTi Materials Using a Novel Aces Methodology
Authors: Mizar S. P. , Pech-Canul M. I. , Pryputniewicz R J. 
Published: April 2011

AbstractEffective use of Shape Memory Alloys (SMAs) depends upon detailed knowledge of their thermiomechanical behavior. In this paper, thermomechanical behavior of SMAs is studied using a novel ACES methodology. More specifically, variation of modulus of elasticity of equiatomic NiTi is studied, as a function of temperature. The results show that the modulus of elasticity of the NiTi studied herein varies from 38 GPa to 72 GPa as the temperature changes from –15 °C to 190°C, corresponding to phase transition from martensite to austenite. Comparison of Analytical, Computational, and Experimental Solutions (ACES) results showed good correlation.
Suppression of Stiction in MEMS
Authors: Mastrangelo C. H. 
Published: April 2011

AbstractStiction failures in microelectromechanical systems (MEMS) occur when suspended elastic members are unexpectedly pinned to their substrates. This type of device failure develops both in fabrication and during device operation, being a dominant source of yield loss in MEMS. Stiction failures require first a collapse force that brings the elastic member contact with the substrate followed by an intersolid adhesion sufficiently large to overcome the elastic restoring force. Stiction failure mechanisms have been studied extensively elsewhere [1]. This paper briefly summarizes these mechanisms in a the practical way. Over the last decade, stiction failure rates in MEMS have been minimized using a wide variety of processing, surface treatment, and physical schemes. An update of these methods is provided.
Selective W for Coating and Releasing MEMS Devices
Authors: Mani S. S. , Fleming J. G. , Sniegowski J. J. , Boer M. P. de , Irwin L. W. , Walraven J. A. , Tanner D. M. , Van D. A. La 
Published: April 2011

AbstractTwo major problems associated with Si-based MEMS (MicroElectroMechanical Systems) devices are stiction and wear. Surface modifications are needed to reduce both adhesion and friction in micromechanical structures to solve these problems. In this paper, we will present a CVD (Chemical Vapor Deposition) process that selectively coats MEMS devices with tungsten and significantly enhances device durability. Tungsten CVD is used in the integrated-circuit industry, which makes this approach manufacturable. This selective deposition process results in a very conformal coating and can potentially address both stiction and wear problems confronting MEMS processing. The selective deposition of tungsten is accomplished through the silicon reduction of WF6. The self-limiting nature of this selective W deposition process ensures the consistency necessary for process control. The tungsten is deposited after the removal of the sacrificial oxides to minimize stress and process integration problems. Tungsten coating adheres well and is hard and conducting, requirements for device performance. Furthermore, since the deposited tungsten infiltrates under adhered silicon parts and the volume of W deposited is less than the amount of Si consumed, it appears to be possible to release stuck parts that are contacted over small areas such as dimples. The wear resistance of selectively coated W parts has been shown to be significantly improved on microengine test structures.
Testing of Critical Features of Polysilicon MEMS
Authors: Lavan D. A. , Buchheit T. E. 
Published: April 2011

AbstractThe behavior of MEMS devices is limited by the strength of critical features such as thin ligaments, oxide cuts joining layers, pin joints and hinges. Devices fabricated at Sandia's Microelectronic Development Laboratory have been successfully tested to investigate these features. A series of measurements were performed on samples with gage lengths of 15 to 1000 microns, using conventional and tungsten coated samples as well as samples that include the critical features of standard components in the test section. Specimens have a freely moving pin joint on one end that anchors the sample to the silicon die to allow rotation to reduce effects of bending. Each sample is loaded in uniaxial tension by pulling laterally with a flat tipped diamond in a computer-controlled Nanoindenter. Load is calculated by resolving the measured lateral and normal forces into the applied tensile force and frictional losses. The specimen cross section and gage length dimensions were verified by measuring against a standard in the SEM. Multiple tests can be programmed at one time and performed without operator assistance allowing the collection of significant populations of data.
Micromachined Polysilicon Resonating Xylophone Bar Magnetometer: Resonance Characteristics
Authors: Lamb J. L. , Wickenden D. K. , Champion J. L. , Givens R. B. , Osiander R. , Kistenmacher T. J. 
Published: April 2011

AbstractA miniaturized, polysilicon version of a xylophone bar magnetometer (with dimensions on the order of microns) has been fabricated by microelectromechanical systems (MEMS) processing techniques. All devices tested to date have performed extremely well in static magnetic fields and exhibit mechanical quality factors, Q, of up to 30,000 at reduced pressures. The resonance frequency of the fundamental flexural mode of vibration of these polysilicon xylophone bars has been found to be a sensitive function of the torsional stiffness of the support arms, in quantitative accord with an analytical model based on Bernoulli-Euler beam theory.
Molecular Beam Mass Spectrometry Studies of the Thermal Decomposition of Tetrakis(dimethylamino)Titanium
Authors: Amato-Wierda Carmela C. , Norton Edward T. , Wierda Derk A. 
Published: April 2011

AbstractTetrakis(dimethylamino)titanium (TDMAT) is an important precursor for TiN, TiCN, and TiSiN thin films in chemical vapor deposition. In order to better understand how the gas phase chemistry influences the formation of these films, the decomposition of TDMAT has been studied in a high-temperature flow reactor (HTFR) by molecular beam mass spectrometry (MBMS). Two kinetic regimes have been observed as a function of temperature. Rate expressions and mechanistic implications will be presented. Further studies are in progress to identify the gas phase species relevant to the decomposition mechanism of TDMAT.
Sol-Gel Synthesis of BaTiO3 Based Films for Photonic Applications
Authors: Fuflyigin V. , Jiang H. , Wang F. , Yip P. , Vakhutinsky P. , hao J. 
Published: April 2011

AbstractHigh quality barium titanate films were grown on (001)LaAlO3 and r-Al2O3 in a wide thickness range of 0.5-10 µtm by sol-gel technique. Significant improvement of the films' crystallinity and optical quality was observed if acetate precursors are used vs. alkoxide precursors, and in the presence of lead oxide. The material is transparent at 350-2000 nm, indicating the possibility of its application in light controlling devices at wavelengths used in optical communication: 1300 and 1500 nm. Maximum field induced relative phase shift of 0.22 radian was measured in the film with composition of Ba0.9Pb0.1TiO3 under a field strength of 3.106 V/cm.
β-Acetoxyethyl Silsesquioxanes: Chloride-Free Precursors for SiO2 Films Via Staged Hydrolysis
Authors: Ezbiansky Karin A. , Arkles Barry , Composto Russell J. , Berry Donald H. 
Published: April 2011

AbstractSilsesquioxanes containing β-acetoxyethyl (BAE) groups are processible resins that can be employed as spin-on-glass precursors to dielectric silica films. Thermal treatment >250 °C results in extrusion of ethylene from the CH2CH2OCOCH3 moiety with formation of Si- OCOCH3 groups, which undergo facile hydrolysis to a silica network. A minor pathway involving extrusion of acetic acid leaves some silicon vinyl groups, leading to residual organic carbon in the material. However, addition of a fluoride ion catalyst greatly accelerates the major reaction, resulting in lower conversion temperatures (<200 °C), quantitative extrusion of ethylene, and essentially pure silica. Alternatively, BAESSQs can be processed photochemically (λ <200 nm) to cleanly yield silica at ambient temperature.
High Density Plasma Etching of Ta2O5-Selectivity to Si and Effect of UV Light Enhancement
Authors: Lee K.P , Cho H. , Singh R. K. , Pearton S. J. , Hobbs C. , Tobin P. 
Published: April 2011

AbstractEtch rates up to 1200 Åmin−1 for Ta2O5 were achieved in both SF6/Ar and Cl2/Ar discharges under Inductively Coupled Plasma conditions. The etch rates with N2/Ar or CH4/H2/Ar chemistries were an order of magnitude lower. There was no effect of post deposition annealing on the Ta2O5 etch rates, at least up to 800 °C. Selectivities to Si of ∼1 were achieved at low source powers, but at higher powers the Si typically etched 4-7 times faster than Ta 20 5. UV illumination during ICP etching in both SF6/Ar and Cl2/Ar produced significant enhancements (up to a factor of 2) in etch rates due to photo-assisted desorption of the TaFx products. The UV illumination is an alternative to employing elevated sample temperatures during etching to increase the volatility of the etch products and may find application where the thermal budget should be minimized during processing.
High-Power Mid-IR Interband Cascade Lasers Based on Type-II Heterostructures
Authors: Yang Rui Q. , Bruno J. D. , Bradshaw J. L. , Pham J. T. , Wortman D. E. 
Published: April 2011

AbstractThe interband cascade lasers (IC) represent a new class of mid-IR light sources, which take advantage of the broken-gap alignment in type-II quantum wells to reuse electrons for sequential photon emissions from serially connected active regions. Here, we describe recent progress in InAs/GaInSb type-II IC lasers at emission wavelengths of 3.8-4 µm; these semiconductor lasers have exhibited significantly higher differential quantum efficiencies and peak powers than previously reported. Also, these lasers were able to operate at temperatures up to 217 K, which is higher than the previous record (182 K) for an IC laser at this wavelength. We observed from several devices at temperatures above 80 K a slope efficiency of ∼800 mW/A per facet, corresponding to a differential external quantum efficiency of /500%. A peak optical output power exceeding 4 W/facet and peak power efficiency of /7% were observed from a device at 80 K. Also, we report the first cw operation of IC lasers.
Type-II InAs/InGaSb Superlattices on Compliant GaAs Substrates
Authors: Brown G. J. , Mahalingam K. , Saxler A. , Linville R. , Szmulowicz F. , Seaford M. L. , Tomich D. H. , Lin Chih-Hsiang , Kuo C. H. , Hwang W. Y. 
Published: April 2011

AbstractType-II InAs/GaInSb superlattices of different designs have been grown by molecular beam epitaxy on wafer bonded InGaAs on GaAs, and on standard GaSb substrates. The extremely thin (∼100Å) InGaAs layer is loosely bonded to the GaAs substrate and serves as a compliant layer for subsequent epitaxy of a larger lattice constant material. The effects of these substrates on the optical, electrical, and structural properties of the superlattice were studied. The superlattices grown on bonded substrates were found to have uniform layers, with broader x-ray linewidths than superlattices grown on GaSb. The photoresponse results for the superlattices on the bonded 2 inch diameter substrates, with the InGaAs compliant layer, were not as favorable as early work on similar, smaller area, bonded substrates. However, refinements to the wafer bonding process to eliminate microvoids between the bonded layers will provide higher quality superlattices.
Pseudopotential Methods for Superlattices: Applications to Mid-Infrared Semiconductor Lasers
Authors: Dente G. C. , Tilton M. L. 
Published: April 2011

AbstractCalculations of optoelectronic properties for superlattice materials require accurate subband energies, wavefunctions and radiative matrix elements. We have recently begun using a solution method based on the Empirical Pseudopotential Method, or EPM. This method shows particular strength in analyzing structures with short periods or thin layers, for which the standard method, based on k,p perturbation theory and the envelope function approximation, may be problematical. We will describe the EPM applied to bulk solids and then demonstrate our direct generalization of the method for applications to superlattice structures. Finally, we will apply the EPM method to several type II superlattice samples and compare the predictions to absorbance spectroscopy data.
Progress in Monolithic Photonic Integration Using Quantum Well Shape Modification Enhanced by Ion Implantation
Authors: Koteles Emil S. 
Published: April 2011

AbstractProgress in the development of ion implantation enhanced quantum well shape modification as a technique for monolithically integrating optoelectronic devices of varying functionalities is reviewed. Fundamental issues related to the physics of the technique, both material issues and device issues, are considered and the performance of both discrete and integrated devices is discussed. The main conclusion of this review is that there are no inherent drawbacks to the utilization of this technique and some serendipitous advantages but that more work on reproducibility and reliability is required to ensure commercial viability.
AlGaAs/GaAs Distributed Feedback Quantum Cascade Lasers
Authors: Schrenk W. , Finger N. , Gianordoli S. , Strasser G. , Gornik E. 
Published: April 2011

AbstractWe report on the realization of distributed feedback quantum cascade lasers in the GaAs/AIGaAs material system. The use of a metallized surface relief grating for feedback allows a fabrication process without regrowth. A feature of this laser is that either single mode or double mode emission at λ ≍ 10 µm is achieved, which is typical for index coupled lasers. The coupling coefficient is measured from the mode spacing for double mode emission of a strong overcoupled laser to be κ ≍ 24 cm"−1. The emission wavenumber can be continuously tuned with the temperature at a rate of dv / dT ≍ 0.048 cm−1/K, which is in close agreement to the temperature dependence of the refractive index of GaAs.
Low Frequency Noise and Random Telegraph Signal in a Multiple Quantum Well Infrared Photodetector
Authors: Kore L. , Bosman G. 
Published: April 2011

AbstractCurrent-voltage, voltage-time, and noise measurements were taken on a three well, twenty period, InGaAs/A1GaAs quantum well infrared photodetector at low temperature and low constant current bias. Data from the voltage-time measurements exhibited random telegraph signal (RTS) which is a manifestation of a single electron capture/emission event. It thus contributes to generation-recombination noise of the device. A model is proposed that allows extraction of number of mobile carriers, continuum state electron mobility, electron emission times and trap activation energy from the RTS data. These parameters may then be utilized to predict the excess noise spectrum. Data from the noise spectral density measurements show 1/f like noise at frequencies below I kHz. It can be shown to be a sum of Lorenztian curves with various electron emission times.The model proposed predicts that the local number of mobile charge carriers in any barrier section is less than 5 (total in the device around 300), there is nearly ballistic electron transport (mobility values around 3×105cm2/Vs), and the traps causing the RTS are in the barriers of the device and there are two of them in the device tested. The model applies to the linear mode of operation and assumes that the well regions are electron reservoirs, i.e. contacts, for the resistive barrier regions. The device is thus divided into a number of resistive portions in series. Each resistive portion is statistically independent from the others at low temperatures since the time the electrons spend in the wells is long compared to intra-well scattering times. This allows the electrons to fully thermalize and lose any statistical information from their previous continuum state trajectory.
Electronic Structures of Shallow Acceptors Confined in Si/SiGe Quantum Well Structures
Authors: Zhao Q.X. , Willander M. 
Published: April 2011

AbstractEnergy levels of the shallow acceptor states have been calculated for center-doped Si/Si1−xGex/Si quantum wells (QWs). The impurity states were calculated using an effective-mass theory that accounts for valence-band mixing as well as the mismatch of band parameters and dielectric constants between well and barrier materials. Acceptor binding energies and splitting between the acceptor 1S3/2(Γ7) and 1S3/2(Γ6) ground states were studied at various Ge concentrations and well widths. The results are discussed in comparison with the recent experimental data from the lateral transport measurements in boron-doped Si/SiGe quantum wells.
Effect of Fast Electron Irradiation on Electrical and Optical Properties of CdGeAs2 and ZnGep2
Authors: Zwieback I. , Maffetone J. , Perlov D. , Harper J. , Ruderman W. , Bachmann K. , Dietz N. 
Published: April 2011

AbstractWe report on the effects of fast electron irradiation on the optical absorption (α) of CdGeAs2and ZnGeP2 and on the electrical properties of CdGeAs2. In p-CdGeAs2 irradiation led to the reduction in α and an increase in the electrical resistivity. The lowest values of α (about 0.1 cm' at 5µm<λ<10µm) were obtained on irradiated crystals of p-type with the highest degree of compensation. Further accumulation of the electron dose caused conversion to n-type and deterioration of the optical transmission. In ZnGeP2 irradiation caused a decrease in a at λ>0.85 λm and increase in α at λ<0.85 μm. At λ=2.05 μm, α for the o-ray could be reduced to less than 0.08 cm−1. At higher doses, saturation in α was observed. The effects of irradiation are discussed in connection with possible mechanisms of optical absorption in CdGeAs2 and ZnGeP2.
Optical Diagnostics of Microstructures Fabricated Using Quantum Well Intermixing
Authors: Saher Helmy A. , Bryce A.C. , Ironside C.N. , Aitchison J.S. , Marsh J.H. , Ayling S.G. 
Published: April 2011

AbstractIn this paper we shall discuss techniques for accurate, non-destructive, optical characterisation of structures fabricated using quantum well intermixing (QWI). Spatially resolved photoluminescence and Raman spectroscopy were used to characterise the lateral bandgap profiles produced by impurity free vacancy disordering (IFVD) technology. Different features were used to examine the spatial resolution of the intermixing process. Features include 1:1 gratings as well as isolated stripes. From the measurements, the spatial selectivity of IFVD could be identified, and was found to be ∼4.5 μm, in contrast with the spatial resolution of the process of sputtering induced intermixing, which was found to be ∼2.5 μm. In addition, PL measurements on 1:1 gratings fabricated using IFVD show almost complete suppression of intermixing dielectric cap gratings with periods less than 10 microns. Finally, some insight into the limitations and merits of PL and Raman for the precision characterisation of QWI will be presented.
X-RAY Photoemission Spectroscopic Study of Light-Induced Structural Changes in Amorphous Silicon
Authors: Sheng Shuran , Sacher Edward , Yelon Arthur 
Published: April 2011

ABSTRACTLight- and annealing-induced structural changes in undoped hydrogenated amorphous silicon (a-Si:H), pure amorphous silicon (a-Si) and crystalline silicon (c-Si) have been investigated in detail by X-ray photoemission spectroscopy (XPS). Both the Si2s and Si2p peaks in a-Si:H films were found to shift simultaneously to lower binding energies by the same amount with illumination time, and nearly reach saturation at about 0.06 eV after one hour of light-soaking at the intensity used. In contrast to the metastable changes in electronic properties [Staebler-Wronski effect (SWE)], the light-induced shifts in both peaks are unstable even at room temperature and can be reversed by annealing with a lower activation energy than that for the SWE. The absence of metastable XPS changes in pure a-Si and c-Si suggests that hydrogen is actively involved in the light-induced structural changes. Furthermore, visible light exposure produces XPS changes in a-Si:H less effectively than X-ray irradiation, despite its much higher incident intensity, indicating a high-energy photon irradiation effect. Our present results suggest that essentially the whole Si network structure is affected by light-soaking or X-ray irradiation, and becomes more stable after repeated irradiation-annealing training. These structural changes may be an independent metastable phenomenon or a precursor process of the SWE.
Improved Resolution in A P-I-N Image Sensor by Changing the Structure of the Doped Layers
Authors: Vieira M. , Fernandes M. , Martins J. , Louro P. , Maçarico A. , Schwarz R. , Schubert M. 
Published: April 2011

ABSTRACTAn amorphous ZnO/p-i-n/Al imager that uses a small-signal scanning beam to read out the short circuit current signal is presented. An analysis of the image geometric distortion, restoration, and enhancement is performed. A simple image-processing algorithm is used to recover main features of projected images. Modifications of the transducer structure are proposed for improving the sensor performance.The effect of the doped layers and image intensity on the sensor output characteristics are analysed. Results show that a trade-off between the sensor structure and contact geometry is needed for a correct read-out. Algorithms and tools are proposed for image analysis.