bluuebunny/crossref_metadata_2025_split huggingface dataset:
Room and Cryogenic Temperature Operation of 280 nm Deep Ultraviolet Light Emitting Diodes
Authors: Shatalov Maxim , Adivarahan Vinod , Zhang Jian Ping , Chitnis Ashay , Wu Shuai , Pachipulusu Radhika , Mandavilli Vasavi , Asif Khan M. 
Published: April 2011

ABSTRACTWe present a study of the electrical and optical characteristics of 280 nm emission deep ultraviolet light emitting diodes (LED) at room and cryogenic temperatures. At low bias the defect assisted carrier tunneling primarily determines the current conduction. The room-temperature spectral performance and optical power are limited mostly by pronounced deep level defect assisted radiative and non-radiative recombination as well as poor electron confinement in the active region. At temperatures below 100 K the electroluminescence peak intensity increases by more than one order of magnitude due to suppression of non-radiative recombination channels indicating that with a proper device design and improved material quality, milliwatt power 280 nm LED are viable.
Material and Device Issues of AlGaN/GaN HEMTs on Silicon Substrates
Authors: Javorka P. , Alam A. , Marso M. , Wolter M. , Fox A. , Heuken M. , Kordoš P. 
Published: April 2011

ABSTRACTResults on the preparation and properties of AlGaN/GaN HEMTs on silicon substrates are presented and selected issues related to the material structure and device performance devices are discussed. Virtually crack-free AlGaN/GaN heterostructures (xAlN ≅ 0.25), with low surface roughness (rms of 0.64 nm), ns ≅ 1×1013 cm−2 and μ ≅ 1100 cm2/V s at 300 K, were grown by LP-MOVPE on 2-inch (111)Si substrates. HEMT devices with Lg = 0.3–0.7 μm were prepared by conventional device processing steps. Photoionization spectroscopy measurements have shown that a trap level of 1.85 eV, additional to two levels of 2.9 and 3.2 eV found before on GaN-based HEMTs on sapphire, is present in the structures investigated. Self-heating effects were studied by means of temperature dependent dc measurements. The channel temperature of a HEMT on Si increases with dissipated power much slower than for similar devices on sapphire substrate (e.g. reaches 95 and 320 °C on Si and sapphire, respectively, for 6 W/mm power). Prepared AlGaN/GaN/Si HEMTs exhibit saturation currents up to 0.91 A/mm, a good pinch-off, peak extrinsic transconductances up to 150 mS/mm and static heat dissipation capability up to ∼16 W/mm. Unity current gain frequencies fT up to 21 and 32 GHz were obtained on devices with gate length of 0.7 and 0.5 μm, respectively. The saturation current and fT values are comparable to those known for similar devices using sapphire and SiC substrates. Properties of AlGaN/GaN/Si HEMTs investigated show that this technology brings a prospect for commercial application of high power rf devices.
Dynamic growth mechanism and interface structure of crystalline zirconia on silicon
Authors: Wang S J , Huan A C H , Ong C K 
Published: April 2011

ABSTRACTIn present report, we have studied the initial stage of the growth of crystalline yttria-stabilized zirconia (YSZ) films on the natively oxidized Si (100) wafer by pulsed-laser deposition. X-ray photoelectron spectroscopy (XPS) and high-resoluti on transmission electron microscopy (HRTEM) show that, for the first few monolayers of crystalline YSZ deposited on Si (100), the dynamic processes appear to be the decomposition of SiO2 to SiO, the formation of ZrO2, and the desorption of SiO. The native amorphous silicon oxide layer is removed completely with the continued deposition of YSZ and the oxygen in this layer is used as oxygen source for forming stable crystalline oxide film. XPS depth profile and HRTEM investigation showed that the interface of crystalline YSZ film in contact with silicon was found to be atomically sharp and commensurately crystallized without an amorphous layer. The interface structure is suggested to have a sequence of-Si-O-Zr-O-. For the film with electrical equivalent oxide thickness 1.46 nm, the leakage current is about 1.1×10-3 A/cm2 at 1 V bias voltage. The hysteresis and interface state density in this film are measured to be less than 10 mV and 2.0×1011eV-1cm-2.
High Temperature Plasma Etching of PZT Capacitor Stacks for High Density FERAMs
Authors: Egger Ulrich , Tomioka Kazuhiro , Stojakovic George , Taniguchi Yasuyuku , Bruchhaus Rainer , Zhuang Haoren , Kanaya Hiroyuki , Beitel Gerhard , Sugimoto Shigeki 
Published: April 2011

ABSTRACTA 32 Mbit chain FeRAM™ stack with 0.20μm minimum feature size was etched with two subsequent lithography/RIE steps: in mask step 1 the platinum/SRO (strontium ruthenium oxide) top electrode and the PZT (lead zirconate titanate) layer, in mask step 2 the bottom electrode together with the Ir/IrO2 diffusion barrier were etched. The stack was etched with various chlorine based chemistries. High temperature etching processes were applied to suppress residues by the formation of volatile etching byproducts resulting in a highly anisotropic etching profile and low redeposition.Profile angles of 75° for step 1 and 80° for step 2 could be achieved. For the thin SRO-layer a separate etching recipe was developed to avoid surface roughening caused by micromasking. The influence of etching temperature and different gas chemistries on the etching behavior was evaluated. Reliable end point detection and good uniformity of the individual etching processes were obtained, both being crucial for the application of a multi-step recipe. The ferroelectric properties of the capacitor were confirmed by hysteresis measurements. This demonstrates that the ferroelectric properties were conserved during RIE etch processes at high temperature.
Chemical Solution Deposition of PLZT Films on Base Metal Foils
Authors: Kim D.-J. , Kaufman D. Y. , Streiffer S. K. , Lee T. H. , Erck R. , Auciello O. 
Published: April 2011

ABSTRACTIn an effort to develop cost effective, volumetrically efficient, high charge density and high energy density capacitors, Pb(Zr,Ti)O3 and La-doped Pb(Zr,Ti)O3 films were deposited by chemical solution deposition on nickel and alloy foils. PZT films deposited on bare foils exhibited lower permittivity and more electric field hysteresis compared to films deposited on platinized silicon substrates, due to the formation of low capacitance interfacial layers and/or diffusion of foil elements into the PZT. However, an ultimate dielectric breakdown strength of approximately 1.35 MV/cm was obtained for a film thickness of 1.8 μm, corresponding to a withstand voltage of 245 V. A reduced temperature dependence of capacitance was observed with decreasing film thickness. In order to improve the dielectric response, barrier layers of LaNiO3, Ru, or Ir were deposited on top of the metal foils used as substrates. The barrier improved relative permittivity and reduced hysteresis in relative permittivity as a function of dc bias.
Basic Study on High-density Ferroelectric Data Storage Using Scanning Nonlinear Dielectric Microscopy
Authors: Hiranaga Yoshiomi , Fujimoto Kenjiro , Wagatsuma Yasuo , Cho Yasuo , Onoe Atsushi , Terabe Kazuya , Kitamura Kenji 
Published: April 2011

ABSTRACTScanning Nonlinear Dielectric Microscopy (SNDM) is the method for observing ferroelectric polarization distribution, and now, its resolution has become to the sub-nanometer order, which is much higher than other scanning probe microscopy (SPM) methods for the same purpose. Up to now, we have studied high-density ferroelectric data storage using this microscopy. In this study, we have conducted fundamental experiments of nano-sized inverted domain formation in LiTaO3 single, and successfully formed inverted dot array with the density of 1.5 Tbit/inch2.
Dielectric Properties of Pulsed Excimer Laser Ablated BaBi2Nb2O9 Thin Films
Authors: Laha Apurba , Krupanidhi S. B. , Saha S. 
Published: April 2011

ABSTRACTThe dielectric response of BaBi2Nb2O9 (BBN) thin films has been studied as a function of frequency over a wide range of temperatures. Both dielectric constant and loss tangent of BBN thin films showed a ‘power law’ dependence with frequency, which was analyzed using the Jonscher's universal dielectric response model. Theoretical fits were utilized to compare the experimental results and also to estimate the value of temperature dependence parameters such as n(T) and a(T) used in the Jonscher's model. The room temperature dielectric constant (ε') of the BBN thin films was 214 with a loss tangent (tanδ) of 0.04 at a frequency of 100 kHz. The films exhibited the second order dielectric phase transition from ferroelectric to paraelectric state at a temperature of 220 °C. The nature of phase transition was confirmed from the temperature dependence of dielectric constant and sponteneous polarization,respectively. The calculated Currie constant for BBN thin films was 4 × 105°C.
Raman Spectroscopy of Ferroelectric Thin Films
Authors: Katiyar R. S. , Dixit A. , Jain M. , Savvinov A. A. , Dobal P. S. 
Published: April 2011

ABSTRACTDuring a ferroelectric phase transition or domain rearrangement, ions or molecules in a ferroelectric material move in a highly cooperative manner from their initial lattice positions into the final positions they occupy and the collective response results into a “soft” lattice vibrational mode. Moreover, the structural changes are always accompanied by at least a few other changes in the normal mode behavior of the material. In the present work, Raman spectroscopy is conveniently employed to study such vibrational modes and other related phenomena in ferroelectric materials at the sub-microscale levels. We have investigated ferroelectric thin films of various lead and barium based perovskites prepared by sol-gel technique. The effect of processing conditions, A- and B- site substitutions, and size dependence on their Raman spectra were analyzed in terms of the structure-property correlations.
Integration Processes and Properties of One Transistor Memory Devices
Authors: Li Tingkai , Hsu Sheng Teng , Ulrich Bruce , Zhang Fengyan , Evans Dave 
Published: April 2011

ABSTRACTMFMPOS (Metal, Ferroelectrics, Metal, Polysilicon, Oxide, and Silicon) one-transistor (1T) ferroelectric memory devices have been fabricated. However, the yield of 1T-memory devices is lower. We find that the main problems of 1T MFMPOS memory devices are shorts, opens, no memory window, smaller memory windows and blank. In order to solve these problems, we studied the reasons resulted in the problems. Then, the integration processes for one transistor memory device were optimized. Fabrication of nMOSFET 1T memory devices starts with shallow trench isolation (STI) on p-type Si. A gate oxide is thermally grown after p-well implantation. Phosphorus ions were implanted after polysilicon gate definition for the formation of self-aligned source, drain, and n-type floating gate. A damascene process using MOCVD PGO deposition and chemical mechanical polishing (CMP) were used to avoid etching damage. Electrodes for the ferroelectric capacitor, i.e., the floating Ir bottom electrode and Pt top electrode, are deposited by E-Beam evaporation. The area ratio of the top and floating gate electrodes is 1:1. After inter-level dielectric (ILD) deposition, contact etching stops on Pt at gate and on Si at source/drain (S/D) without difficulty because of high etch rate selectively to the Pt. Finally, the high quality 1T memory devices have been made. The one-transistor memory devices showed memory windows around 2 – 3V. The memory windows are almost saturated from operation voltage of 3V. The ratios of “on” state current to the “off” state current are closed to 8 – 9 orders. The one-transistor memory devices also show a very good memory characteristics and retention properties.
X-ray Photoelectron and UV Photoyield Spectroscopic Studies on Structural and Electronic Properties of SrxBiyTa2O9 Films
Authors: Takahashi Mitsue , Noda Minoru , Okuyama Masanori 
Published: April 2011

ABSTRACTPhotoelectron spectra by X-ray photoelectron spectroscopy (XPS) and UV-photoyield spectroscopy (UV-PYS) have been analyzed to study O2-annealing effects on band diagrams of ferroelectric SrxBiyTa 2O9 (SBT) thin films deposited by pulsed laser deposition (PLD) and metalorganic dcecomposition (MOD) methods. XPS studies on the annealed PLD-SBT film has shown a rapid shift in its Bi 4f core peaks from the oxidized to the metallic ones, as the film suffer Ar+ bombardment. Surface of the annealed film has exhibited lower Fermi level than the as-deposited one in UV-PYS. The result suggests O2-annealing can suppress leakage current through PLD-SBT films. The UV-PYS studies on MOD-SBT have shown almost the intrinsic Fermi levels before and after the additional annealing. The XPS studies have shown that the additional annealing is not effective to improve stabilities of (Bi2O2)2+ layers, once the film is baked and crystallized.
Acoustic Emission Monitoring of Nanoindentation-Induced Slip and Twinning in Sapphire
Authors: Tymiak Natalia I. , Daugela Antanas , Wyrobek Thomas J. , Warren Oden L. 
Published: April 2011

ABSTRACTMonitoring with an Acoustic Emission (AE) sensor integrated into an indenter tip was utilized for the evaluation of the earliest stages of indentation-induced plasticity in sapphire single crystal. The evaluated surfaces included basal (C), rhombohedral (R) and two different prismatic orientations (A and M). The differences between the mechanisms of the initial stages of plasticity for the various crystallographic orientations were reflected in the following aspects of AE activity: detection of a specific type of AE waveform that correlated to the presence of linear surface features near the indentation impressions; AE signal associated with the yield point, consisting either of one or two distinct waveforms; and presence or absence of AE signals after the yield point. Moreover, analysis of AE activity revealed loading rate effects on the yield point mechanism for the M plane. The possibility of plasticity onset mechanisms involving both slip and twinning is discussed.
Characterization and Tribological Properties of Nanostructured Copper/Carbon Composite Films Prepared by Microwave Plasma-Assisted Dual Deposition Processes
Authors: Thiery François , Pauleau Yves , Pelletier Jacques 
Published: April 2011

ABSTRACTNanocrystalline copper/hydrogenated amorphous carbon films have been deposited on Si substrates at the floating potential using a distributed electron cyclotron resonance microwave plasma reactor. In this deposition technique, the microwave plasma-enhanced chemical vapor deposition process of carbon from argon-methane or argon-acetylene mixtures of various compositions was associated with the sputter deposition of copper from a copper target. The total pressure was fixed at 0.13 Pa. For deposition, the substrates mounted on a water-cooled substrate holder were maintained at ambient temperature. The composition of films determined by Rutherford backscattering spectroscopy, energy recoil detection analyses and nuclear reaction analyses was investigated as a function of the gas phase composition. The structure of films was identified by X-ray diffraction (XRD) techniques and the size of copper crystallites incorporated in the amorphous carbon matrix was deduced from XRD data. The magnitude of residual stresses developed in these films was calculated from the radius of curvature of film/substrate samples determined by profilometry. The residual stress values were found to be nearly independent on the composition of films and deposition parameters.
In situ Fracture and Adhesion Failure of Al-Cu-Fe Quasicrystalline Films
Authors: Daniels M. J. , French B. L. , King David , Bilello J. C. 
Published: April 2011

ABSTRACTQuasicrystalline precursor coatings were deposited on single crystal silicon and sapphire wafers by RF sputtering from an AlCuFe powder composite target. Synchrotron white beam radiography/topography and stress analysis were performed in situ on the wafers during heating to 495 or 585°C, and subsequent cooling. A plateau region of constant stress was present throughout most of the 1 hour anneals before a large tensile stress developed in the film during cooling due to coefficient of thermal expansion mismatch. Cracking was observed for films on both substrates at an average film stress of approximately 930 MPa. Distinct differences in the fracture behavior were observed for the two different substrates. X-ray diffraction performed on films after annealing suggested that texturing took place during the transition to a fully developed quasicrystalline structure.
A Novel Technique for Mixed-mode Thin Film Adhesion Measurement
Authors: Wang Junlan , Sottos Nancy R. , Weaver Richard L. 
Published: April 2011

ABSTRACTGuided by recent parametric studies of laser-induced tensile spallation, we successfully developed a new test method for studying mixed-mode interfacial failure of thin films. By allowing an initial longitudinal wave to mode convert at an oblique surface, a high amplitude shear wave is generated in a fused silica substrate and propagated toward the thin film surface. A shear wave was generated with amplitude large enough to fail an Al film/fused silica interface and the corresponding shear stress was calculated from high-speed interferometric displacement measurements. Examination of the interfaces failed under mixed-mode conditions revealed significant wrinkling and tearing of the film, in great contrast to blister patterns observed in similar Al films failed under tensile loading. Slightly higher interfacial strength was measured for the same Al film/fused silica substrate under mixed-mode loading than under tensile loading. The mixed-mode loading experiment developed in the current work provides a new tool to explore a range of thin film interfacial failure modes as well as the role of extrinsic effects such as residual stress, surface roughness, and imperfections.
Ion Energy/Momentum Effects During Ion Assisted Growth of NbXNY Films
Authors: Klingenberg M. L. , Demaree J. D. , Hirvonen J. K. , Messier R. 
Published: April 2011

ABSTRACTIn a previous paper, it was shown that the tribological properties of NbxNy thin films produced by ion beam assisted deposition (IBAD) depend strongly on the beam energy and the ion-to-atom (R) ratio. This study was designed to separate ion energy vs. ion momentum effects on film stress, crystalline phase, grain size, morphology, and composition, all of which influence the tribological properties of the films. Inert ion beams (Kr, Ar, and Ne) were used in conjunction with a nitrogen gas backfill to independently control ion energy and ion momentum transfer to NbxNy films. The ion species, energies, and R ratios were chosen to create a matrix of coatings that exhibited the same total energy deposition with different momentum transfer or the same momentum transfer but different total energy deposition. The resultant films were characterized using Rutherford Backscattering Spectroscopy (RBS), x-ray diffraction (XRD), atomic force microscopy (AFM), and residual stress analysis. Crystalline phases and texture, as well as residual stress, were more closely correlated with ion momentum transfer to the coating atoms than with overall ion energy input.
Investigations of Multifunctional Graded Zirconium Carbide PVD-Coatings for the Application on Machine Parts
Authors: Lugscheider E. , Knotek O. , Bobzin K. , Maes M. , Arntz K. 
Published: April 2011

ABSTRACTAn efficient way to reduce energy consumption and costs of machines is to reduce the friction in tribological systems such as gear wheels, spindle bearings and regular ball bearings. Tribological PVD (Physical Vapour Deposition)-coatings have thus been developed at the Materials Science Institute in the context of the special research project SFB 442 named “Environmentally Compatible Tribosystems”. The main challenge facing PVD applications is the complex geometry of machine parts as well as the low deposition temperature. Therefore, the use of Magnetron Sputtering Ion Plating (MSIP-PVD) offers the advantage of producing coatings with a much wider range of properties. A superstoichiometric coating with an over saturated amount of carbon is adjusted by PVD parameters. This creates a shear-weak top coating with a low friction coefficient and a self smoothing surface. The coatings were analysed in standard tests such as the calo-test, scratch-test and HRC-test. Furthermore, the nanoindentation and SEM observations proved a clear correlation between chemical composition and physical properties.
Photochemical Lamination of Low Refractive Index Transparent SiO2 Film at Room Temperature for Antireflection Coating
Authors: Ogawa Y. , Murahara M. 
Published: April 2011

ABSTRACTA transparent low refractive index SiO2 film laminated on a glass substrate at room temperature by photochemical reactions with the Xe2* excimer lamp (172nm). This SiO2 film grown on the fused silica glass was proved to avoid reflection of light.A refractive index of the SiO2 film was 1.36. After annealing the film for one hour at 200 degrees centigrade, the refractive index increased to 1.42. The refractive index increased as the F atom density in the SiO 2 film decreased.
Material Mechanical Properties Influence on the Ratio of Drilling Thrust to Hardness
Authors: Mauvoisin G. , Bartier O. , El Abdi R. , Nayebi A. 
Published: April 2011

ABSTRACTA new approach using an experimental hole drilling technique has been developed to determine the hardness profile of superficially heat-treated steels. This method was based on the proportionality between the hardness of the material tested and the cutting thrust measured during the drilling test. Although it was observed that, overall, the increase in the cutting thrust was linear with hardness, locally the variation of thrust was not necessarily regular and linear in particular for iron-carbon alloys. In fact, other parameters related to the material, other than hardness, can modify the cutting thrust level. We report here on the influence of parameters, such as the type of microstructure and the ductility or the work hardening of material, on drilling thrust. The cutting thrust obtained for various brittle or ductile materials will be discussed using results obtained from hardness tests, micrographic observations and microhardness of the chips obtained by drilling test.
Nanoindentation of Vacuum Ultraviolet Light-Irradiated Poly(methylmethacrylate) Substrates
Authors: Hozumi Atsushi , Yokogawa Yoshiyuki , Kameyama Tetsuya , Wu Yunying , Sugimura Hiroyuki , Takai Osamu 
Published: April 2011

ABSTRACTSurface modification of poly(methylmethacrylate) (PMMA) substrates has been demonstrated using an excimer lamp radiating vacuum ultraviolet (VUV) light of 172 nm in wavelength. In this study, we have particularly focused on the effects of atmospheric pressure during VUV irradiation. Each of the substrates was photoirradiated with VUV light under a pressure of 10, 103 or 105 Pa. Changes in nanomechanical properties of the VUV-irradiated sample surfaces were studied based on a scratching test using a nanoindenter. The wear-depth of the PMMA sample treated at 105 Pa was about 137.0 nm, which was much larger than the wear-depth of an untreated PMMA substrate (63.3 nm). On the contrary, when samples were prepared with VUV irradiation conducted at 10 and 103 Pa, their wear-depths markedly decreased down to about 2.2 and 12.5 nm, respectively. The sample treated at 10 Pa was particularly wear-resistant. This high wear-resistance was attributable to the formation of new carbon-carbon bonds such as C=C bonds on the PMMA surfaces.