bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial Distributions of Individual Traps in a Si/SiO 2 Interface
Authors: Toshitsugu Sakamoto Toshitsugu Sakamoto , Hisao Kawaura Hisao Kawaura , Toshio Baba Toshio Baba
Published: October 2002

We have investigated individual traps in the Si/SiO2 interface by observing random telegraph signals (RTSs). The traps having energy levels within a few k
B
T of the Fermi level can capture or emit single electrons, and become sources of RTSs. We report the first investigation of spatial distributions of single-carrier traps in a MOSFET with a double gate structure. We observe RTSs with changing bias voltages on two lower gates, and show that their variations describe the spatial distributions of the individual traps.
Extended Time Dependent Dielectric Breakdown Model Based on Anomalous Gate Area Dependence of Lifetime in Ultra Thin Silicon Dioxides
Authors: Kenji Okada Kenji Okada
Published: October 2002

The conventional time dependent dielectric breakdown (TDDB) model is extended for ultra thin silicon dioxides on the basis of the four stage dielectric breakdown process model (FSM), in which the dielectric breakdown process consists of two individual processes: the “partial breakdown” and the “complete breakdown”. The lifetime measured under constant voltage stressing shows an anomalous gate area dependence as predicted by the extended TDDB model. This model can be adopted not only for the ultra thin oxides but also for oxides where the partial breakdown takes place. The conventional TDDB model is regarded as a case in which the time to complete breakdown after the partial breakdown is ignored compared to the time to partial breakdown. Furthermore, it is demonstrated that one cannot obtain an accurate lifetime without taking into account the extended TDDB model.
Formation of c-Axis-Oriented Bi4Ti3O12 Films with Extremely Flat Surface by Spin-Coating
Authors: Tani Kouichi , Yamanobe Tomomi , Hideaki Matsuhashi Hideaki Matsuhashi , Satoshi Nishikawa Satoshi Nishikawa
Published: October 2002

The formation of c-axis-oriented Bi4Ti3O12 (BIT) films by spin-coating has been investigated. The crystallinity of BIT films depends on the Bi to Ti molar ratio of the starting BIT solution and on the annealing temperature. The BIT film spin-coated with a 10% Bi-rich solution and annealed at 850° C shows a highly c-axis-oriented crystallinity. In addition, it is found that a BIT layer spin-coated on this c-axis-oriented film becomes highly c-axis-oriented even if the starting solution is not Bi-rich, and that the obtained film has an extremely flat surface when the first BIT layer is thinly applied. The resulting films exhibit good properties for use in metal-ferroelectric-metal-insulator-semiconductor (MFMIS) structural memory devices, such as a low leakage current density of 7×10-7 A/cm2 at 3 V, a remanent polarization of 2.5 µ C/cm2, a coercive field of 8 kV/cm, and a dielectric constant of 120.
“Universal” Dependence of Avalanche Breakdown on Bandstructure: Choosing Materials for High-Power Devices
Authors: Jeremy Allam Jeremy Allam
Published: October 2002

A new simple phenomenological relation between the breakdown voltageVband the bandstructure in semiconductor junctions is presented. For narrow-gap semiconductors,Vbscales with the minimum energy gap (Eg) as has been previously reported. However, for wide-gap materials including GaAs, InP, etc.,Vbis linearly dependent on , a Brillouin-zone-averaged energy gap. Values of  are determined from accurate quasi-particle bandstructures for 25 tetrahedral semiconductors. We discuss the origin of this relation and the role of the ionisation probability and electron-phonon scattering rate. The relation can be used to predict the breakdown voltage in semiconductors and semiconductor alloys.
Layer-by-Layer Etching of Si(111) Surface by Oxygen at Elevated Temperature
Authors: Tadahiro Komeda Tadahiro Komeda , Yasushiro Nishioka Yasushiro Nishioka
Published: October 2002

The kinetics of Si surface etching with gas-phase O2 was examined using scanning tunneling microscopy (STM), which was intended for the application of gas-phase etching by O2 for Si surface flattening. High-temperature STM observation showed the recession of the step edges with the O2 flux of 5×10-8 Torr on Si(111) at an elevated temperature of ∼800° C in real time. The high-resolution image clearly showed that the terrace was disordered during the exposure to O2 gas. The recession of step edges is considered to be the result of the detachment of Si atoms from the step edges to fill the defects created by the desorption of SiO.
Smart-Cut: A New Silicon On Insulator Material Technology Based on Hydrogen Implantation and Wafer Bonding*1
Authors: Bruel Michel , Auberton-Hervé Bernard Aspar
Published: October 2002

An alternative route to existing silicon on insulator (SOI) material technologies such as SIMOX (separation by implanted oxygen) and BESOI (bonded and etch-back SOI) is the new Smart-Cut process, which appears to be a good candidate to achieve ULSI criteria. The Smart-Cut process involves two technologies: wafer bonding and ion implantation associated with a temperature treatment which induces a in-depth splitting of the implanted wafer. The details of the Smart-Cut process, the physical phenomena involved in the different technological steps such as hydrogen implantation related mechanisms and wafer bonding are discussed. The characteristics of the final structure in terms of thickness homogeneity, crystalline defects, surface microroughness, and electrical characterization are presented. Other applications of this process are also highlighted.
Electron Energy-loss Spectroscopy Study of the Metal-insulator Transition in VO 2
Authors: Hiroyuki Abe Hiroyuki Abe , Masami Terauchi Masami Terauchi , Michiyoshi Tanaka Michiyoshi Tanaka , Shik Shin Shik Shin , Yutaka Ueda Yutaka Ueda
Published: October 2002

Electron energy-loss spectra of VO2 have been measured from perfect single crystalline areas of 100–180 nm diameter in the metallic and insulating phases. A sharp peak has been observed at 1.2 eV in the valence electron excitation spectra of the metallic phase but not in those of the insulating phase. We assign the peak to an interband transition or d-d transition by inspecting the dielectric function derived from the present loss function with the help of an energy band diagram already given, although an excitation at about 1 eV already observed by optical measurement was assigned to the excitation of a free-carrier plasmon. The peak due to the O 1s → V 3d(t
2g
) transition in the O 1s excitation spectra decreased in intensity but increased in the full width at half-maximum (FWHM) at the transition from the metallic phase to the insulating phase. These changes are considered to have been due to the fact that the d
\varparallel band splits into the upper unoccupied and lower occupied d
\varparallel bands and the upper d
\varparallel band rises above the π* band in the insulating phase, but that the d
\varparallel band is unsplit and located within the π* band in the metallic phase.
Quantification of Electrical Deactivation by Triply Negative Charged Ga Vacancies in Highly Doped Thin GaAs Layers
Authors: Matsushita Shigeharu , Inoue Daijiro , Matsumura Kohji , Sawai Tetsuro , Taniguchi Kenji , Akira Ibaraki Akira Ibaraki
Published: October 2002

We present for the first time a theoretical approach to electrical deactivation by triply negative charged Ga vacancies (V
Ga
3-) in highly doped thin n-GaAs layers grown by molecular beam epitaxy, and quantify their deactivation under as-grown and annealed conditions. We also show that thinning of n-GaAs epitaxial layers results in low-level electrical deactivation. This effect is apparently caused by the fact that thinning of the doped layers results in lowering of the Fermi energy in the doped layers, and thereby inhibition of the generation of V
Ga
3- acceptors. Furthermore, we deduce from the results of this study the thermal equilibrium concentration of V
Ga
3- in intrinsic GaAs. The resulting expression is [V
Ga
3-(i)]=5.37×1031 exp
(-4.64 eV/k
B
T) cm-3.
Investigation of the Indium Atom Interdiffusion on the Growth of GaN/InGaN Heterostructures
Authors: Tsang Jian-Shihn , Guo Jan-Dar , Chan Shih-Hsiung , Feng Ming-Shiann , Chun-Yen Chang Chun-Yen Chang
Published: October 2002

The influence of the growth procedure on the optical quality of InGaN grown on GaN has been investigated. The photoluminescence spectrum of the sample with a low-temperature-grown GaN cap layer or a graded-temperature-grown GaN cap layer has a shorter peak wavelength than that of the sample grown with a normal-temperature-grown GaN layer. The shift of the peak wavelength increases with the increase of the layer thickness for the sample with the low-temperature-grown GaN. This is because the defects contained in the low-temperature-grown GaN cap layer induce the outdiffusion of In atoms during the temperature-ramped procedure. The narrower linewidths and higher intensities of the PL spectra for InGaN after In outdiffusion may be due to the reduction of the strains, dislocations or defects. The Raman spectra and the Auger electron spectra also indicate that the low-temperature-grown GaN has a lot of defects which reduce the phonon peak intensity and induce the interdiffusion of In atom during the growth of GaN/InGaN heterostructures.
The Effects of Cd-Substitution Site on Sintering Behavior and Electrical Properties in Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 Ceramics
Authors: Cho Jeong-Ho , Park In-Kil , Chung Hoon-Taek , Ho-Gi Kim Ho-Gi Kim
Published: October 2002

The effects of Cd2+ substitution site on sintering behavior and electrical properties were investigated in Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 (PNN–PZ–PT) ceramics. Substituting Cd2+ into both A-site and B-site in PNN–PZ–PT made it possible to determine these effects. Sintering was performed at 1100°C and 1200°C. The substitution site of Cd2+ was identified from X-ray photoelectron spectroscopy spectra. Although Cd2+ was substituted into both A-site and B-site in PNN–PZ–PT, the Cd2+ preferred the A-site over the B-site. The densification mechanism were influenced by substitution site of Cd2+, and A-Specimen and B-Specimen was sintered by liquid phase sintering and solid state sintering, respectively. Whereas Cd2+ thus promoted the densification and grain growth in A-Specimen, it retarded densification and grain growth in B-Specimen. When Cd2+ replaces Pb2+, weight gain is observed during sintering. On the other hand, replacing Cd2+ with Ni2+ caused weight loss. The substitution site of the Cd2+ also influenced the electrical properties significantly. Whereas both of a grain and grain boundary influenced the resistivities in A-Specimen, Only a grain effect on the resistivities was shown in B-Specimen.
Suppression of Fluorine Impurity in Blanket Chemical Vapor Deposited Tungsten Film for Via Fills with A Novel Two-step Deposition Technique
Authors: Chang Kow-Ming , Yeh Ta-Hsun , Lain Kuen-Der , Fu Chao-Ming
Published: October 2002

Blanket chemical vapor deposited tungsten (CVD-W) offers the potential to fabricate reliable contacts for submicron multilevel metallization. In via filling application, various aluminum fluorides were formed by the reduction of WF6 with aluminum underlayer. These compounds will stay at CVD-W/Al interface and act as insulating layers which cause electrical degradation. In addition, impurities like fluorine or oxygen induce the formation of β-W lattices as well as high film resistivity. In this work, a two-step chemical vapor deposition of tungsten was developed to suppress the fluorine impurities in tungsten films and at CVD-W/Al interface for blanket CVD-W application. The first step involves a gas phase nucleation with high SiH4/WF6 flow ratio (i.e., 2.5) to deposit a thin tungsten film as the glue layer. It was found that the probability of the WF6 reduction with underlying aluminum was suppressed because the WF6 was completely consumed by SiH4 before arriving onto aluminum surface. Meanwhile, this gas phase nucleated tungsten exhibits blanket deposition capability and an amorphous structure. The second step includes typical CVD-W process (i.e., SiH4/WF6 flow ratio <1) to grow thick tungsten film. Secondary Ion Mass Spectroscopy (SIMS) measurements indicate that the fluorine impurities in tungsten film and at CVD-W/Al interface are drastically reduced. Also, the gas phase nucleated tungsten can be reproducibly deposited without attacking the aluminum underlayer. Moreover, a lower tungsten resistivity, lower via resistance and longer electromigration lifetime are achieved in the Al/W/Al Kelvin structures produced by two-step deposition technique than those of the typical CVD-W films deposited directly on aluminum.
Decrease in Surface States on GaAs Metal-Semiconductor Field-Effect Transistor by High Temperature Operation
Authors: Sasaki Hajime , Hayashi Kazuo , Fujioka Takashi , Mizuguchi Kiyoshi , Yea Byeongdeok , Osaki Tomoyuki , Sugahara Kazunori , Konishi Ryosuke , Kasada Hirofumi , Ando Koshi
Published: October 2002

The decrease mechanism of plasma-induced surface states in a GaAs metal-semiconductor field-effect transistor (MESFET) during high temperature operation has been studied by means of high temperature operational tests, drain current transient analysis and three-terminal gate current measurements. The energy level of trapped electrons in the surface states distributes widely in the band-gap, and its activation energy does not change after decreasing the density of surface states. In order to decrease the surface states effectively, hot-carriers generated by accelerated channel electrons under high temperature operation are required.
Propagation Characteristics of Surface Acoustic Waves in KNbO3/SrTiO3/Si Layered Structures
Authors: Mu-Shiang Wu Mu-Shiang Wu , Wen-Ching Shih Wen-Ching Shih
Published: October 2002

The propagation characteristics of surface acoustic waves (SAWs) in KNObO3/SrTiO3/Si structures were investigated theoretically. Phase velocities (v
p) decrease when the h
K value of the SrTiO3 buffer layer increases from 0.04 to 0.2 for a specified thickness of the KNbO3 film. The value of the coupling coefficient (K
2) can be as high as 10%. A layered structure with the interdigital transducer (IDT) located on top of the KNbO3 film is a better choice for device fabrication if we select a coupling coefficient of 1% as a reference for comparison. The results could provide useful information for combining optical devices, semiconductor devices and SAW devices on the same Si substrate.
Influence of Deposition Temperatures on Bonding State and Microstructure of Carbon Nitride Thin Films Prepared by Ion-Beam-Assisted Deposition
Authors: Matsumuro Masao Kohzaki , Hayashi Toshiyuki , Mutsuo Muramatsu Mutsuo Muramatsu , Katsumi Yamaguchi Katsumi Yamaguchi
Published: October 2002

The influences of the deposition temperature on bonding states and microstructures of carbon nitride films prepared by ion-beam-assisted deposition are analyzed by Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and transmission electron microscopy (TEM). FT-IR absorption spectra exhibit a peak corresponding to the C≡N bond and its population decreases with the deposition temperature. N 1s peaks in XPS spectra indicate the existence of two different N 1s bonding states, one attributed to nitrogen inserted into the graphitic ring structure, and the other attributed to nitrogen surrounded by three carbons in the C–N network. The increase of the deposition temperature leads to the formation of the C–N cluster similar to the highly disordered turbostratic structure. In C–N film growth, however, the sequential phase transformation from sp2-bonded phases to sp3-bonded phase frequently observed in BN film deposition is not found in TEM analyses.
Energy and Angular Distributions of Kinetic Electrons Emitted from a Solid Surface Due to Grazing Incidence of Protons
Authors: Jun Kawata Jun Kawata , Kaoru Ohya Kaoru Ohya
Published: October 2002

A Monte Carlo simulation is performed to analyze the energy and angular distribution of electrons emitted from a carbon surface under grazing incidence of 10–300 keV protons. The calculated energy distribution has a high-energy tail which does not appear in the case of normal incidence, as well as a large low-energy peak. The angular distribution deviates from the well-known cosine dependence on the emission angle measured from the surface normal.
An Analytical Fluid Theory for the Simultaneous Measurement of Cross-Field Viscosity and Parallel Flow Velocity in Magnetized Plasma
Authors: Kyu-Sun Chung Kyu-Sun Chung
Published: October 2002

A one dimensional fluid model is developed for the deduction of cross-field viscosity and parallel flow velocity in magnetized flowing plasma. Analytic solutions are obtained for a free presheath with Dirichlet and/or Neumann boundary conditions. The Fluid model with mixed boundary conditions produces results closer to those using kinetic analysis. For the bounded presheath, the plasma density and flow velocity are derived using a Dirichlet boundary condition in terms of position along the field line, a flow Mach number (M
∞), normalized shear viscosity (α) and the size of the bounded presheath. α and M
∞ are deduced by comparing the two measured ratio (R
s, R
l) with theoretical ratios of ion saturation current densities. R
s is measured using a small Mach probe (SMP) which generates one bounded and one free presheath, and R
l is measured using a large Mach probe (LMP) generating two free presheaths.
A New Analysis of 4-Rod Radio-Frequency Quadrupole Linac with Intrinsic Field Distortions
Authors: Valeri Kapin Valeri Kapin
Published: October 2002

A new formulation for an electric-field potential function in a radio-frequency quadrupole (RFQ) channel with a 4-rod configuration of the electrodes has been developed for analytical study of the effects of the intrinsic field distortion. The RF field in the resonator is expressed as a superposition of four normal modes, coaxial, quadrupole, and two dipole modes, and then the electric-field potential function is expanded into four corresponding components. With this function, an analytical study of beam dynamics for typical RFQ channels with a free-space wavelength (λ) of 2 m has been performed for the case of a periodical accelerating structure. The dependence of beam oscillations on the length of the resonator period l
p has been analyzed, including distorted fields. At a long period of the resonator (l
p/λ>0.1), resonances of beam oscillations have been found, and their occurrence has been confirmed by numerical simulation. Under the resonance condition with a field distortion of 5%, the beam transmission degrades from 95% to 60%.
Oscillating Chemical Instabilities in Contact Etching Diagnosed by Optical Emission
Authors: Susan C. McNevin Susan C. McNevin
Published: October 2002

This paper reports the observed optical emission during the plasma etching in a surface wave plasma tool (SWP). In these experiments, the gas flow was increased at constant pressure. The optical emission had a characteristic periodic behavior. As the gas flow is increased, the period decreased and the amplitude increased. It will be shown that these optical emission oscillations interfere with endpoint detection for <5% open area wafers. These oscillations are consistent with a mechanism involving two coupled auto-catalytic reactions, known in the literature as a “chemical clock”. The optical emission spectra in the SWP is identical to that observed in a transformer coupled plasma tool (TCP) and a high density plasma tool (HDP). However, similar optical emission oscillations have not been seen in the TCP and the HDP. This difference is attributed to two causes: differing residence times and wall temperature/chemistry. These two differences affect the auto-catalytic process involving SiF

x

products.
WSi2/Polysilicon Gate Etching Using TiN Hard Mask in Conjunction with Photoresist
Authors: Suguru Tabara Suguru Tabara
Published: October 2002

We found that the selectivity between TiN and poly-Si film was high enough in Cl2/O2 plasma to use TiN as an etching mask for poly-Si gate etching. We also discovered that the oxidation of the TiN surface is the reason why TiN serves as an etching mask in poly-Si etching using Cl2/O2 plasma. By using a TiN hard mask in conjunction with a thin photoresist, we were able to reduce electron shading damage. The low aspect ratio of the space of a line-and-space (L&S) pattern is the major reason for the reduction in electron shading damage in this TiN mask process. A portion of the TiN surface on which no charge up occurs is exposed to the plasma during the overetch step because photoresist is eroded by ion bombardment. This is an another reason for the reduced electron shading damage.
Ab initio Molecular Orbital Study of Water Absorption and Hydrolysis of Chemical Vapor Deposited SiOF Films I
Authors: Nakasaki Yasushi , Miyajima Hideshi , Hayasaka Ryota Katsumata
Published: October 2002

We investigated the mechanism of water absorption and hydrolysis of F-doped SiO2 (SiOF) films using the ab initio molecular orbital (MO) method with small SiF

n

(OH)4-
n

(n=0–3) tetrahedral model clusters. We focused on the dependence of the reactivity of these clusters with both OH- and H2O on the number of F atoms bonded with a Si atom. The reactivity of defect sites such as non bridging oxygens (NBOs) and free volumes around Si–F bonding were also investigated. The calculations revealed the following. SiOF films are more reactive with OH- than with H2O. Si atoms linked with multiple F atoms become more reactive with H2O by reducing the activation barrier of the –OH coordination to Si, and with OH- by increasing the stabilization energy of the pentacoordinated-Si formation. Multiple H2O attacks at sparse, i.e., sparsely packed, network sites increase the adsorption energy and reduce the activation barrier. NBO defects also promote successive H2O adsorption.
Annealing Properties of Defects in B+- and F+-Implanted Si Studied Using Monoenergetic Positron Beams
Authors: Uedono Akira , Kitano Tomohisa , Hamada Kouji , Moriya Tsuyoshi , Kawano Takao , Tanigawa Shoichiro , Suzuki Ryoichi , Ohdaira Toshiyuki , Mikado Tomohisa
Published: October 2002

Annealing properties of defects in F+- and B+-implanted Si were studied using monoenergetic positron beams. For F+-implanted specimen with a dose of 2×1013 F/cm2, before annealing treatment, the mean size of the open volume of defects was estimated to be close to the size of divacancies. After rapid thermal annealing (RTA) at 700° C, vacancy-fluorine complexes and vacancy clusters were formed. The mean size of the open volume for the vacancy-fluorine complexes was estimated to be close to the size of monovacancies, and their annealing temperature was determined to be 800° C. For F+-implanted specimen with a dose of 4×1015 F/cm2, complexes between vacancy clusters and fluorine atoms were introduced during solid-phase epitaxial growth of the amorphous region, and they were observed even after RTA at 1100° C. Effects of additional B+ implantation on annealing properties of defects are also discussed.
Plasma Enhanced Chemical Vapor Deposition and Characterization of Fluorine Doped Silicon Dioxide Films
Authors: Yoo Woo Sik , Richard Swope Richard Swope , David Mordo David Mordo
Published: October 2002

Fluorine-doped silicon dioxide films were deposited using a dual frequency (DF) multi-station sequential deposition plasma enhanced chemical vapor deposition (PECVD) reactor. Fluorine-doped silicon dioxide films with various Si–F content were deposited using mixture of vaporized tetraethylorthosilicate (TEOS), O2 and C2F6. The Si–F content, physical properties and gap filling capability of the F-doped films were characterized. The physical properties and gap filling capability were found to be dependent upon wafer temperature, pressure, gas phase reactant concentrations and rf power, but is predominantly dependent on Si–F content. Aspect ratios (AR) up to 1.64:1 with 0.5 µm spacing were filled with no observable seams and voids.
Hole Transport in Hydrazone-Doped Polymer Films
Authors: Fujii Akiteru , Shoda Takayuki , Shinji Aramaki Shinji Aramaki , Tetsuo Murayama Tetsuo Murayama
Published: October 2002

Hole drift mobilities were measured in hydrazone-doped polycarbonate films under various concentrations, temperatures and electric fields. Hydrazone molecules used were 9-ethylcarbazole-3-carbaldehyde diphenylhydrazone (CTM1), 9-ethylcarbazole-3-carbaldehyde methylphenylhydrazone (CTM2), and 1-pyrenecarbaldehyde diphenylhydrazone (CTM3). Charge transport in the films obeyed the nonadiabatic small-polaron hopping formalism with almost the same activation energies at concentrations investigated. CTM2 exhibited a different concentration dependency and relatively small mobility especially at high concentrations. Analysis by disorder formalism indicated that the energetic disorder parameter (σ) is almost the same and the non-energetic disorder parameter (Σ) is different. We found some correlations between the mobilities of the CTMs and molecular overlap and orientation in the single crystalline state of CTMs.
Cesium-induced Reconstruction on Si(113)3 × 2 Surface Studied by Low Energy Electron Diffraction and X-ray Photoelectron Spectroscopy
Authors: Ki-Seok An Ki-Seok An , Chan-Cuk Hwang Chan-Cuk Hwang , Rae-Jun Park Rae-Jun Park , Ju-Bong Lee Ju-Bong Lee , Jeong-Seon Kim Jeong-Seon Kim , Chong-Yun Park Chong-Yun Park , Soon-Bo Lee Soon-Bo Lee , Akio Kimura Akio Kimura , Akito Kakizaki Akito Kakizaki
Published: October 2002

We have investigated Cs-induced reconstruction on the Si(113)3×2 surface using low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). For Cs deposition at room temperature, the (3×1) LEED pattern was observed for a wide Cs coverage range. At high substrate temperatures, the (3×1), (1×5+2×) and (2×2) phases were observed with increasing Cs deposition time. The relative Cs saturation coverages of (3×1)-Cs at RT and (2×2)-Cs at 300°C were measured from Cs 3d/Si 2p core level XPS intensity ratios. The results are summarized in a phase diagram as a function of the Cs deposition time.
Synthesis and Surface Acoustic Wave Properties of AlN Thin Films Fabricated on (001) and (110) Sapphire Substrates Using Chemical Vapor Deposition of AlCl3–NH3 System
Authors: Kaya Kiyoshi , Takahashi Hiroshi , Shibata Yoshihiko , Hirai Yasuhito Kanno
Published: October 2002

Thin films of AlN were prepared on sapphire C- and A-plane by chemical vapor deposition. Crystal orientations, oxygen impurity contents and surface acoustic wave properties (SAW) of the films were investigated. Under optimized conditions, epitaxial AlN films were deposited and the crystal orientation relationships were (001)[110]AlN//(001)[110]Al2O3 and (001)[110]AlN//(110)[110]Al2O3. The crystal orientation of the AlN films decreased as the thickness of the films increased slightly, and the oxygen impurity content was less than 1 atm% for both systems. The dependences of SAW velocity (V
s) and the temperature coefficient of the center frequency (τ f) on the film thickness were measured, and τ f was found to increase as the film thickness increased for all measurment directions; however, zero-temperature coefficient was not achieved.
Brillouin Scattering and Ultrasonic Study on an Epoxy Prepolymer
Authors: Matsukawa Mami , Ohtori Norikazu , Nagai Isao , Bohn Klaus-Peter , Krüger Jan K.
Published: October 2002

The temperature dependence of elastic properties in a common epoxy prepolymer was investigated using Brillouin scattering and ultrasonic pulse spectroscopy. In the GHz region, the Brillouin shift frequency curve showed a sharp kink at about 250 K, which was in good accordance with T
g observed by DSC. The D
90R function calculated from the Brillouin shift frequency showed a clear dispersion at temperatures near 350 K, at which a broad peak of the Brillouin linewidth was observed. In the MHz region, ultrasonic wave attenuation also showed a peak near 285 K. Assuming that these changes result from the α relaxation in the glass transition region, the frequency-temperature behavior of the peaks was discussed in connection with the α relaxation in fully cured epoxy resin.
Raman Scattering Study of Cubic to Tetragonal Phase Transitions of Ti-rich Pb(ZrxTi 1-x)O 3
Authors: Yasuo Ikeuchi Yasuo Ikeuchi , Seiji Kojima Seiji Kojima , Takashi Yamamoto Takashi Yamamoto
Published: October 2002

The temperature dependences of Raman scattering spectra were investigated through the ferroelectric phase transition in Ti-rich Pb(Zr
x
Ti1-x
)O3 (x=0.25–0.40). Low frequency spectra show marked dependences on both composition and temperature. Another lower frequency mode appears below the E symmetry soft mode of PbTiO3 as the x increases. The frequencies of the lowest two modes soften slightly, whereas the damping factor of the two modes increases markedly near T
c. These phenomena suggest that the displacive type at x=0 gradually changes to the order-disorder type as x increases. The internal bands higher than 100 cm-1 are insensitive to both composition and temperature. The intensity of these modes gradually decreases with increasing temperature. Although all optical modes should be Raman inactive above T
c, a quasielastic scattering and a few internal modes are still observed in the spectra. Since the intensities of these modes decrease on further heating, the origin of this intensity cannot be the second order Raman scattering but must be the first order one due to local breakdown of cubic symmetry by some kind of disorder.
An Analysis of Stiffened Vibration for Torsional Crystal Resonators and Its Application to Quartz Crystal
Authors: Hirofumi Kawashima Hirofumi Kawashima , Kenji Sunaga Kenji Sunaga
Published: October 2002

In this paper, stiffened vibration for torsional crystal resonators is discussed, and the obtained results are applied to quartz crystal. A relationship of stress vector T, strain vector S, electric displacement vector D, and electric field vector E is derived using the conditions of a bar, and torsional rigidity C
t is obtained from the electrical condition. In particular, piezoelectric terms of quartz crystal have slight influence upon frequency constant, the first and second order temperature coefficients α, β.
The Resonating Properties of a Crystal Unit of Fundamental Frequency 150 MHz
Authors: Tanaka Masako , Ugajin Takayuki , Araki Nobushige , Oomura Yoshimasa
Published: October 2002

150 MHz rectangular AT-cut quartz crystal units were prepared by means of photolithography. For the elimination of the effect on a frequency response by the mechanically damaged layer, chemical etching on both sides was employed. Gold evaporated films were used as the electrodes for frequency stability during long-term driving. As a result, crystal units which had excellent frequency stability during long-term driving and low crystal impedance were obtained. Furthermore, a Colpitts crystal oscillator was constructed, and some experimental data are presented.
Surface Acoustic Wave Characteristics of a ZnO/Quartz Substrate Structure Having a Large Electromechanical Coupling Factor and a Small Temperature Coefficient
Authors: Michio Kadota Michio Kadota
Published: October 2002

A substrate having a suitable electromechanical coupling factor (k
s) value and a good temperature coefficient of frequency (TCF) is required for an applications of resonator surface acoustic wave (SAW) filters and rudder-type SAW filters requiring a specific bandwidth, because their bandwidth largely depends on the coupling factor of the substrate. Although a quartz substrate for SAW devices provides a good TCF, the electromechanical coupling factor obtained is small. The author speculated that an excellent TCF and an appropriate electromechanical coupling factor could be realized by combination of a quartz substrate having a positive TCF and a ZnO film having a negative TCF. As a result of theoretical and experimental investigations performed using a 29°45' rotated Y and a 42°45' rotated Y 35°X propagating quartz substrate, an excellent TCF (≈0 ppm/°C) and an appropriate coupling factor (k
s=0.1–0.11; k
s
2=0.01–0.0121) were realized with a zero degree power flow angle on the structure of IDT/ZnO/quartz or IDT/ZnO/shorted-plane/quartz for the first time.
High Precision Multifrequency Acoustic Radar with an Unequally Spaced Frequency Array Designed by Simulated Annealing
Authors: Toyokatsu Miyashita Toyokatsu Miyashita
Published: October 2002

Multifrequency cw radar with a frequency array is realized by digital signal processing. However, the resolution is limited to the fundamental sampling spacing determined by the aperture width of the frequency array. Furthermore, it has a periodic structure with a usually used equally spaced frequency array which results in the formation of periodic ghosts of an object. These fundamental problems are shown to be solved by the introduction of an unequally spaced frequency array (USFA) and a linear phase interpolation of the reconstructed impulse response between the fundamental sampling points. An amplitude-weighted USFA, which has minimized grating lobes, is designed by the method of simulated annealing from a previously described uniformly weighted USFA. The original level of the grating lobes is as large as -8.93 dB, and the minimized level is -12.5 dB. The resolution is not degraded by the minimization, and a superresolution of 1/60 to 1/300 of the wavelength is maintained.
Blood Vessel Visualization Using a Micromotor Type Intravascular Ultrasound Endoscope
Authors: Md. Salimuzzaman Md. Salimuzzaman , Ayumu Matani Ayumu Matani , Osamu Oshiro Osamu Oshiro , Kunihiro Chihara Kunihiro Chihara , Masato Asao Masato Asao
Published: October 2002

Intravascular ultrasound (IVUS) endoscope is limited by the inability of current devices to define the blood vessels morphology accurately. We have developed a prototype lateral-viewing IVUS catheter using a micromotor, in which an ultrasound beam is scanned radially by a micromotor instead of a rotation transmitting wire. The rotation of the micromotor is performed and controlled by an external magnetic field. To calibrate our micromotor type IUVS endoscope, 6 phantoms were prepared and reconstructed in a water tub. Finally, we reconstructed the image of 1 human arterial specimen through an in vitro experiment. These preliminary data suggested that a lateral-viewing micromotor type IVUS endoscope is feasible and accurate to evaluate the residual wall. Furthermore, it has sufficient ability to define the blood vessels morphology and to diagnose vascular diseases.
Evaluation of the Elastic Properties of a Cantilever Using Resonant Frequencies
Authors: Nakano Shizuka , Ryutaro Maeda Ryutaro Maeda , Kazushi Yamanaka Kazushi Yamanaka
Published: October 2002

A method to evaluate Young's modulus and Poison's ratio of a micro-cantilever is demonstrated using resonant frequency measurements of deflection and torsional vibrations. Both vibrations of the cantilever were excited by a new cantilever holder, and they were measured separately using an optical lever. Five modes of resonant frequencies for deflection and three modes for torsion were obtained. Young's modulus and Poison's ratio were estimated by fitting the theoretically calculated resonant frequencies to the experimental results.
Attempt to Evaluate the Bond Quality of Thin Soldered Laminate Using the Laser Lamb Wave
Authors: Takashi Futatugi Takashi Futatugi , Mikio Takemoto Mikio Takemoto
Published: October 2002

Noncontact evaluation of the bond quality of a thin soldered laminate was attempted by quantitative analysis of the laser Lamb wave. We developed a computer algorithm for calculation of the velocity dispersion of the Lamb wave for a perfect and slip contact three-layer laminate, and measured the velocity dispersion of soldered copper foil using a laser Lamb system. We propose a method for estimation of the bond quality by comparing the measured velocity dispersion of the A0-Lamb wave with that computed for the model laminate.
Finding Cracks in KAWARA by Detecting Characteristic Vibrations of KAWARA
Authors: Kitaori Masaki , Ohdaira Etuzo , Nobuyoshi Masuzawa Nobuyoshi Masuzawa , Masao Ide Masao Ide
Published: October 2002

Sometimes KAWARA (roofing tile) cracks during baking. The cracks cause leaking when it rains and weaken the kawara. For this reason this study explored NDT (nondestructive testing) to find cracks in kawara by observing characteristic vibrations in tiles when they are subjected to impulse ultrasound. Vibrations of kawara are detected with a transducer and analyzed with a personal computer. It was found that cracks in kawara can be detected and their lengths determined by this method.
Photoacoustic and Photoluminescence Studies of CdSxSe1-x Doped Glasses
Authors: Shen Qing , Yuichiro Kato Yuichiro Kato , Taro Toyoda Taro Toyoda
Published: October 2002

A series of CdS

x

Se1-
x

doped glasses with a mole fraction of sulfur in the range 0.68≦x≦0.91 is studied by photoacoustic (PA) and photoluminescence (PL) methods. Unlike the usual transmitted optical absorption measurement in which the samples have to be thin and have good quality surfaces, the photoacoustic spectroscopy (PAS) measurement yields relatively true optical spectra even if the glasses are quite thick. From the PA spectra, shifts in absorption bands due to the quantum confinement effect are observed in the glasses having larger x values. The quantum confinement effect becomes larger in glasses with larger mole fractions of sulfur. The sizes of the microcrystals are expected to be smaller in the glasses having larger x values. This is also consistent with the PL experimental results.
Nondestructive Evaluation of Magnetic Disk Heads Using a Photoacoustic Microscope
Authors: Tsutomu Hoshimiya Tsutomu Hoshimiya
Published: October 2002

Nondestructive evaluation of magnetic disk heads is achieved using a photoacoustic microscope (PAM). A qualitative evaluation for gap or an isolation area of the heads is performed with photoacoustic amplitude and phase images. Resolution achieved is about 2 micrometer. A crack in a ferrite region and a bubble in a glass filler is observed with the PAM.
Molecular Beam Epitaxial Growth of Bulk AlAs0.16Sb0.84 and AlAs0.16Sb0.84/InAs Superlattices on Lattice-Matched InAs Substrates
Authors: Németh Štefan , Grietens Bob , Hugo Bender Hugo Bender , Gustaaf Borghs Gustaaf Borghs
Published: October 2002

AlAs0.16Sb0.84 ternaries and AlAs0.16Sb0.84/InAs superlattices have been grown by molecular beam epitaxy lattice-matched on InAs substrates. The compositional dependence of AlAs

y

Sb1-
y

on the ratio of Sb4 to As2 fluxes as well as on the substrate temperature has been investigated and can be explained qualitatively. The growth of AlAs0.16Sb0.84/InAs superlattices is described and illustrated by the results of reflection high-energy electron diffraction measurements. The crystalline quality of the superlattices is demonstrated by means of transmission electron microscopy and X-ray diffraction measurements.
A Physics-Based Short-Channel Current-Voltage Model for Lightly-Doped-Drain Metal-Oxide-Semiconductor Field-Effect-Transistors
Authors: Hu Man-Chun , Sheng-Lyang Jang Sheng-Lyang Jang , Chwan-Gwo Chyau Chwan-Gwo Chyau
Published: October 2002

In this paper we present a new analytical physics-based drain current model for fully overlapped and partially overlapped lightly-doped-drain metal-oxide-semiconductor field-effect-transistors (LDD MOSFETs). The model was developed by starting from a two-dimensional Poisson equation, and including the effects of series resistances and velocity saturation. In particular the phenomenon of surface accumulation and depletion in the LDD region is included in the model to describe saturation I–V characteristics. The device is partitioned into the source, intrinsic channel, subdiffusion, and overlapped and non-overlapped lightly-doped drain regions. The device parameters such as local threshold voltage and doping concentration are continuous along the channel. The model can describe the I–V characteristics and can be used to calculate the electric fields in the channel region and in the LDD region for the device operated in both the linear and saturation regions. The accuracy of the presented model has been verified by the simulated data using a fully numerical 2D simulator and the experimental data of LDD devices with various geometries.
Control of Carrier Collection Efficiency in n+p Diode with Retrograde Well and Epitaxial Layers
Authors: Takehisa Kishimoto Takehisa Kishimoto , Mikio Takai Mikio Takai , Yoshikazu Ohno Yoshikazu Ohno , Tadashi Nishimura Tadashi Nishimura , Masahide Inuishi Masahide Inuishi
Published: October 2002

The effect of buried implanted layers against carrier collection has been investigated by ion-beam-induced-current (IBIC) measurement. The IBIC measurement revealed that the retrograde well structure is more effective in suppressing soft errors than are conventional well structures in epitaxial substrates. The collection of charge carriers induced by 1.3 MeV proton microprobe irradiation could be reduced by a buried layer formed at a different boron dose. The carrier collection efficiency of the diode with a twin well (i.e., retrograde well) with a higher dose can be reduced to 50% that of a diode with a twin wells in an epitaxial layer.
Microstructure and Giant Magnetoresistance in Fe–Cu Thin Films Prepared by Cluster-Beam Deposition
Authors: Hihara Takehiko , Xu Yingfan , Konno Toyohiko J. , Sumiyama Kenji , Onodera Hideya , Kimio Wakoh Kimio Wakoh , Kenji Suzuki Kenji Suzuki
Published: October 2002

Giant magnetoresistive FexCu100-xgranular thin films have been prepared by cluster-beam deposition. The magnetoresistance (MR) ratio of the as-deposited films decreases monotonically with increasing Fe content. High resolution transmission electron microscopy of a low Fe content (x=12) sample shows chemically-homogeneous, fine grains having a fcc structure. The film withx=28 exhibits, however, distinct chemical heterogeneity, where bcc Fe clusters are formed in the Cu matrix. The film with a higher Fe content (x=53) consists mostly of the bcc phase with a small amount of the fcc phase. Mössbauer spectroscopy indicated that this MR behavior can be ascribed to the change in the magnetic state of Fe clusters with increasing the Fe content of the films: from cluster-glass to antiferromagnetic, and then to ferromagnetic states. After annealing, phase separation occurs in all specimens, and the grain size increases markedly, resulting in the suppression of the MR ratio in the low Fe content region.
Preparation and Electrical Properties of Conducting Polyaniline-Polycarbonate Composite Films
Authors: Yin Xiao Hong , Yoshino Katsumi , Hashizume Kenichi , Isa Isao
Published: October 2002

Conducting polymer polyaniline and insulating polymer polycarbonate composites have been prepared. Electrical conductivity can be controlled in a wide range (more than 15 orders of magnitude) by a small amount of polyaniline. This characteristic can be explained by a percolation model. That is, at the threshold concentration, the electrodes must be bridged by a conducting channel of polyaniline. The percolation threshold and critical exponent of the conductivity parallel to the film surface are different from those perpendicular to the film surface. This suggests the anisotropy of conductivity in the composite. The conductivity of a high polyaniline concentration composite is found to be stable up to 160° C.
Evolution of Switching Characteristics from Tristable to V-Shaped in an Apparently Antiferroelectric Liquid Crystal
Authors: Seomun San Seong , Takanishi Yoichi , Ishikawa Ken , Hideo Takezoe Hideo Takezoe , Atsuo Fukuda Atsuo Fukuda
Published: October 2002

We have identified three smectic phases, smectic A, ferrielectric and antiferroelectric, in a free-standing film of the first component compound of the mixture which was reported to show the V-shaped switching usable for realizing attractive displays [Inui et al..: J. Mater. Chem. 6 (1996) 671]. The switching in the antiferroelectric phase, observed by applying a triangular waveform electric field to a homogeneous cell, evolves from tristable to V-shaped with increasing temperature and frequency; the V-shaped switching occurs uniformly without accompanying any domain boundary movement. The results have been discussed in terms of thresholdless antiferroelectricity in liquid crystals.
Formation of β-FeSi2Layers on Si(001) Substrates
Authors: Masaya Tanaka Masaya Tanaka , Yoshinao Kumagai Yoshinao Kumagai , Takashi Suemasu Takashi Suemasu , Fumio Hasegawa Fumio Hasegawa
Published: October 2002

The crystal quality of β-FeSi2formed on Si(001) by both the thermal reaction method and reactive deposition epitaxy (RDE) was investigated under various growth conditions. Compared with the thermal reaction method, the crystal quality of β-FeSi2formed by RDE was improved. In the RDE method, the Fe deposition rate as well as the growth temperature influenced the crystal quality of β-FeSi2. Among various growth temperatures and deposition rates of Fe, highly (100)-oriented epitaxial β-FeSi2was formed by RDE at 470°C and 0.1 Å/s, respectively. Measurements of the absorption coefficient at room temperature (RT) indicate that β-FeSi2has a direct band gap of about 0.83 eV.
The Study of Initial Mechanism for Al–Au Solid Phase Diffusion Flip-chip Bonding
Authors: Nakamura Atsuko Iida
Published: October 2002

The authors have been developing a thermo-compression flip-chip bonding technique in which an LSI chip is electrically and mechanically connected to a glass substrate through Au bumps formed on the LSI chip and aluminum (Al) electrodes on the glass substrate. In this interconnection, Au bumps and Al electrodes are connected by aluminum–gold (Al–Au) solid phase diffusion. The Al thin film deposited by sputtering at room temperature has a columnar microcrystal structure. In this paper, the study of initial bonding mechanism of the Au bump to the Al thin film with the columnar microcrystals is presented. Initial diffused states were observed. The bonding mechanism is proposed as follows: the Au bump bonding breaks not only the surface oxide layer of Al thin film but also the Al columnar microcrystals, and a part of the Au bump intrudes into the grain boundary. This enables Au atoms to meet a new Al surface of the deformed columnar grain. Thus, the Al–Au solid phase diffusion occurs immediately in the region whose Al columnar microcrystal is deformed.
Feasibility Study on C 60 Plasma Application to Ion Thruster
Authors: Yoshinori Nakayama Yoshinori Nakayama , Haruki Takegahara Haruki Takegahara
Published: October 2002

The application of C60 to an ion thruster will improve thrust generation without increasing electric power consumption, because this molecule has a lower ionization potential and larger molecular weight than the conventional/typical ion thruster propellant. However, the application requires a sublimation device for the gaseous feed as ion thruster propellant, and control of the discharge for prevention of fragmentation and multi-ionization. Considering the advantages and disadvantages of this molecule, an electron bombardment ion thruster was designed and fabricated. Using this thruster, it was confirmed that the flow rate of the sublimated C60 was 4.9 sccm (2.6 mg/s), which was comparable to that of a typical ion thruster, and the thrust was 4.1 mN, which was the largest obtained in several laboratories. In order to advance this study, however, improvements of the propellant utilization efficiency and ion production cost may be necessary.