bluuebunny/crossref_metadata_2025 huggingface dataset:
Polyimide Optical Waveguide with Multi-Fan-Out for Multi-Chip Module Application
Authors: Takuji Matsumoto Takuji Matsumoto , Yutaka Noguchi Yutaka Noguchi , Yoshiharu Kudoh Yoshiharu Kudoh , Mitsumasa Koyanagi Mitsumasa Koyanagi
Published: October 2002

We developed a polyimide optical waveguide with multi-fan-out which can be used as an optical interconnection between the many LSI chips in a multichip module system. The propagation direction of the signal light is changed from horizontal to vertical and from vertical to horizontal using aluminum micromirrors in this waveguide. We then introduced a signal light into this waveguide, the propagation direction of which was bent by an aluminum micromirror. It impinged on the photodiode to induce a significant increase in the photodiode current.
Excitation Power Dependent Photoluminescence Behavior in Etched Quantum Wires having Silicon Interlayer-Based Edge Passivation and Its Interpretation
Authors: Fujikura Hajime , Masahiro Kubo Masahiro Kubo , Hideki Hasegawa Hideki Hasegawa
Published: October 2002

A novel Si interface control layer (ICL)-based passivation technique is applied to the edge passivation of etched In0.53Ga0.47As wires and the effect of the passivation is characterized in terms of the photoluminescence (PL) properties of the wires. The observed PL behavior is found to be strongly excitation power-dependent and inexplicable by the conventionally used PL model assuming a constant surface recombination velocity and an optically “dead layer” having a constant width at the wire edges. A novel one-dimensional computer simulation of wire PL is developed. The result of the simulation indicates that the surface recombination velocity and the surface depletion layer width are excitation power-dependent, providing an explanation for the observed excitation power-dependent PL behavior. The theory and experiments show that the Si ICL edge passivation significantly reduces the surface state density at the edge and improves the PL properties.
Metalorganic Vapor Phase Epitaxy Growth of a High-Quality GaN/InGaN Single Quantum Well Structure Using a Misoriented SiC Substrate
Authors: Ishibashi Akihiko , Takeishi Hidemi , Uemura Nobuyuki , Kume Masahiro , Yabuuchi Yasufumi , Yuzaburoh Ban Yuzaburoh Ban
Published: October 2002

A high-quality GaN/InGaN single quantum well (SQW) structure has been successfully grown using a misoriented 6H–SiC substrate, the face of which is tilted from (0001) toward [1120] by 3.5°, by low pressure metalorganic vapor phase epitaxy (MOVPE). A sharp emission, whose full-width at half maximum (FWHM) was 24.3 meV, from the GaN/InGaN SQW structure was observed at 385 nm in the 77 K photoluminescence spectrum. From the transmission electron microscopy (TEM) analysis, the dislocations in the GaN film grown on the misoriented substrate were bent from the c-direction, and the threading dislocations to the InGaN film on the GaN film were decreased. For the InGaN film grown on the misoriented substrate, only the sharp band edge emission, whose FWHM was 92.3 meV, was observed at 385 nm in the PL spectrum at 77 K. The dislocation density, which was estimated from TEM photographs, in the InGaN film on the GaN film grown on the misoriented substrate was about 5×108 cm-2, which was nearly half of that grown on the (0001) substrate.
Exciton Spectra of Cubic and Hexagonal GaN Epitaxial Films
Authors: Chichibu Shigefusa , Okumura Hajime , Nakamura Shuji , Feuillet Guy , Azuhata Takashi , Sota Takayuki , Yoshida Sadafumi
Published: October 2002

Fundamental exciton structures in both cubic (c) and hexagonal (h) polytypes of GaN epitaxial films were compared. The photoreflectance (PR) spectra of both polytypes exhibited excitonic transitions up to room temperature (RT). The lowest exciton resonance energy of c-GaN (3.267 eV at 10 K) was confirmed to be smaller by 0.21 eV than that of h-GaN. The low-temperature photoluminescence (PL) spectra of both polytypes were dominated by excitonic emissions; h-GaN exhibited well-resolved bound and free exciton peaks and c-GaN exhibited a broadened excitonic emission, which was dominated by bound and free excitons below and above 80 K, respectively. The PL spectra at RT of h-GaN exhibited predominant A and B free exciton emissions. The E2phonon replicas of excitons were found in the PL spectra of h-GaN, indicating the coupling of excitons with nonpolar phonons through the deformation potential.
Vibration and Rotation of Hydrogen Molecule in Silicon
Authors: Kazutaka G. Nakamura Kazutaka G. Nakamura , Masahiro Kitajima Masahiro Kitajima
Published: October 2002

Ab initio Hartree-Fock calculations have been performed on hydrogen molecules in silicon using cluster models. A tetrahedral site for the hydrogen molecule is a stable trapping site, and the calculated vibrational frequency of the hydrogen molecule is 4500±45 cm-1, which is in reasonable agreement with the experimentally reported frequency of H2 in the silicon crystal. The hydrogen molecule is belived to rotate at the tetrahedral site at room temperature.
Plasma Passivation Effects on Polycrystalline Silicon Thin-Film Transistors Utilizing Nitrous Oxide Plasma
Authors: Wang Fang-Shing , Chun-Yao Huang Chun-Yao Huang , Huang-Chung Cheng Huang-Chung Cheng
Published: October 2002

A novel defect passivation process in polycrystalline silicon (poly-Si) thin-film transistors (TFTs) utilizing nitrous oxide ( N2O) plasma has been performed to significantly improve the electrical characteristics of poly-Si TFTs. For example, the on/off current ratio increased to 6.58×106; the threshold voltage decreased to 0.55 V, and the field effect mobility increased to 48.2 cm2/ Vs. The distribution of N incorporated in this oxide and these poly-Si films was examined by means of secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES). It is believed that the nitrogen radicals which dissociated from the N2O gas as well as the hydrogen radicals which dissociated from the residual H2O can both diffuse into the active poly-Si layer to passivate the grain-boundary defect states and accumulate at the gate SiO2/poly-Si interface to reduce the interface state density. Thus, the hot-carrier reliability of TFTs was also enhanced after the N2O plasma treatments.
Ni Electroless Plating Process for Solder Bump Chip on Glass Technology
Authors: Jeong In Han Jeong In Han , Sung Jei Hong Sung Jei Hong
Published: October 2002

In the solder bump chip on glass process, for the connection of the driver chip to Al pad on the glass substrate, the process of the electroless plating was developed to coat Ni on Al/photoresist system. It is necessary to pretreat Al surface to remove the oxide layer before the plating. In order to find the pretreatment process which does not damage photoresist or the substrate glass, the alkaline and fluoridic zincate processes have been investigated. Because the photoresist and Al thin film could be easily dissolved in the alkaline solution, it was considered that the fluoridic zincate process was a suitable one. After immersion in the zincate solution containing 1.5 g/ l NH4HF2 and 100 g/ l ZnSO4, electroless Ni plating was performed well. The additives in the zincate solution and thiourea in the plating solution enhanced the flatness of deposited surface. Acid dip improved the uniformity of the surface.
The Effects of Substrate Temperature and Lead Precursor Flow Rate on the Fabrication of (Pb,La)(Zr,Ti)O 3 Thin Films by Electron Cyclotron Resonance Plasma-Enhanced Chemical Vapor Deposition
Authors: Joong-Shik Shin Joong-Shik Shin , Soung-Soon Chun Soung-Soon Chun , Won-Jong Lee Won-Jong Lee
Published: October 2002

La-doped lead zirconate titanate (PLZT) thin films were fabricated on Pt/Ti/SiO2/Si substrates by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) method. The composition and the electrical properties of the films were investigated as a function of deposition temperature and Pb-source flow rate. Stoichiometric film with pure perovskite structure was fabricated at a deposition temperature as low as 450°C. As the deposition temperature was increased, the vapor pressure of lead oxide molecules increased and thus the PLZT film tended to be Pb-deficient, resulting in the formation of a non-perovskite phase and the degradation of electrical properties. This problem could be relieved by increasing the Pb-source flow rate. Rapid thermal annealing (RTA) greatly enhanced the electrical properties of the PLZT film as long as the as-deposited film had stoichiometric composition and pure perovskite structure. The rapid thermal annealed PLZT film (74 nm thick) had an effective charge density of 150 fF/µm2, dielectric constant of 1216 and SiO2 equivalent thickness of 0.24 nm.
Scanning Force Microscopy Studies of Domain Structure in BaTiO3 Single Crystals
Authors: Gruverman Alexei L. , Hatano Jun , Hiroshi Tokumoto Hiroshi Tokumoto
Published: October 2002

Domain structure of barium titanate single crystals has been studied by scanning force microscopy (SFM). In the SFM topography mode, a–c-domain contrast was observed due to surface deformation as a result of lattice distortion on the domain wall separating a- and c-domains. The variety of configurations in which a- and c-domains are arranged results in complex topography of the crystal surface. Antiparallel c-domains of submicron size were produced by applying a voltage bias to the SFM tip and subsequently imaged in the SFM piezoresponse mode with a resolution of less than 20 nm.
Analysis of Thermally Dielectric Relaxation Phenomena in Organic Monolayer Films by Debye Brownian Motion Equation
Authors: Chen-Xu Wu Chen-Xu Wu , Yoshinobu Mizutani Yoshinobu Mizutani , Mitsumasa Iwamoto Mitsumasa Iwamoto
Published: October 2002

The thermally dielectric relaxation phenomena in organic monolayer films on a material surface have been analyzed on the basis of the rotational Debye Brownian motion equation. The orientational disordering of monolayers polarized with biasing is discussed with respect to two phases, i.e., the liquid phase and the liquid-crystalline phase, with consideration of the dielectric relaxation time τ and the friction constant ξ of monolayers. The interface effect and the intermolecular interaction are taken into consideration in the analysis.
Elastic Wave Propagation Characteristics at Chiral Interfaces
Authors: Ruyen Ro Ruyen Ro
Published: October 2002

Propagation characteristics of elastic waves in isotropic, noncentrosymmetric (chiral) media are described herein by the displacement field and an independent rotation vector. Six different wavenumbers are eigenvalues for elastic waves propagating in chiral (acoustically active) media. Two corresponding eigenfunctions are longitudinally polarized and the remaining four represent circularly polarized waves. Reflection and transmission characteristics of elastic waves normally impinging upon chiral-chiral interfaces are of primary concern in this study. Results illustrate that appropriate boundary conditions for achiral-chiral interfaces can be found theoretically and, hence, scattering characteristics at achiral-chiral interfaces can be determined uniquely. Based on results obtained, it will be possible to obtain reflection and transmission characteristics of chiral slabs and to tailor acoustically active materials in the near future.
Preparation of WNx Films and Their Diffusion Barrier Properties in Cu/Si Contact Systems
Authors: Mayumi Takeyama Mayumi Takeyama , Atsushi Noya Atsushi Noya
Published: October 2002

We prepared thin WN

x

films with various compositions by reactive sputtering and examined their characterizations and barrier properties applied to Cu/WN

x

/Si contact systems. The results indicate that the W65N35 barrier, which is in the W2N phase with preferred orientation in the (111) plane, shows excellent barrier properties for Cu metallization. The obtained Cu/W2N/Si system is fairly stable without diffusion and/or reaction even after annealing at 800° C for 1 h. This system stability is speculated to originate from the thermal stability of the W2N film itself, which is chemically inert and scarcely changes in structure due to annealing.
Applications of Pulsed Excimer Laser Deposition with a Frozen Nitrogen Target to Deposition of NbN and BN Films
Authors: Hiroshima Yasushi , Ishiguro Takashi , Esaki Kotaro
Published: October 2002

NbN and/or BN films were deposited by pulsed laser deposition (PLD) with a frozen nitrogen target. This novel method makes it possible to prepare active nitrogen species such as atomic nitrogen and it is expected to be useful for synthesis of nitride films. The usefulness of this method is confirmed by comparison with films formed by conventional ambient-controlled PLD. The deposited films were characterized by X-ray diffraction measurements, X-ray photoelectron spectroscopy (XPS) and Fourier transform infra-red (FT-IR) absorption spectroscopy. It was confirmed that the concentration of nitrogen in the films fabricated by PLD with a frozen nitrogen target increases and the nitriding process is enhanced.
Characteristics of Epitaxial ZnO Films on Sapphire Substrates Deposited using RF-Magnetron Sputtering
Authors: Young-Jin Kim Young-Jin Kim , Ki-Wan Kim Ki-Wan Kim
Published: October 2002

We have grown ZnO epitaxial films on the (01overline12)\) plane of sapphire using rf-magnetron sputtering and studied the properties of films sputtered at different rf powers. A surface of (11\overline20) ZnO film was produced on a (01\overline12) plane of sapphire. The (11\overline20) films of ZnO have smooth enough surfaces for use as surface acoustic wave (SAW) filters. The surface acoustic wave properties were measured by propagation along the c axis of ZnO films on the (01\overline12) plane of sapphire substrates. An observation of the SAW filter was carried out under untuned conditions. Center frequencies of the 0th and 1st modes were observed at 300 MHz and 400 MHz, respectively.
Kinetic Study on Oxidation of Si(111) Surfaces using H 2O
Authors: Seiichi Takami Seiichi Takami , Yasuyuki Egashira Yasuyuki Egashira , Hiroshi Komiyama Hiroshi Komiyama
Published: October 2002

Using X-ray photoelectron spectroscopy, we investigated the temperature dependence of the reaction rates at which oxidation of a hydrogen-terminated Si (Si–H) surface proceeds using H2O vapor. The rates of oxidation at temperatures lower than 250°C are not sensitive to the oxidation temperature or the number of impinging H2O molecules. This result indicates that the rate of oxidation of Si–H at lower temperatures are controlled by generation of activated Si–Si back bonds on Si substrates. On the other hand, the rates of oxidation at temperatures higher than 450°C are controlled by the rate at which hydrogen desorbs from the Si–H surface.
Main Cause of Surface Waveguides Formed under LiNbO3 Crystal Surface during Thermal Treatment
Authors: Koide Akira , Hajime Shimizu Hajime Shimizu , Toshihiko Saito Toshihiko Saito
Published: October 2002

The formation of a surface waveguide on LiNbO3 crystals at about 1000°C was examined by systematic experimentation with respect to the content of H2O vapor in the heating atmosphere and OH- ions contained in the crystals before heating. The thermal diffusion of OH- ions led to the formation of inhomogeneous layers which had a refractive-index fluctuation around n
S. We concluded that the main cause of the surface waveguide formation was OH- ions. The formation of a surface waveguide and its prevention by H2O vapor are concluded to be regarded as the same mechanism.
Negative Ion Extraction from Pulsed Discharges
Authors: Overzet Lawrence J. , Smith Brian A. , Jennifer Kleber Jennifer Kleber , Sivananda K. Kanakasabapathy Sivananda K. Kanakasabapathy
Published: October 2002

Time-resolved measurements of pulsed discharges can provide information on how negative ions can be used for surface processing. Negative ions are ordinarily trapped inside the plasma volume, but pulsed plasmas allow for efficient negative ion extraction during the afterglow period because the negative ion to electron concentration ratio can increase dramatically. In addition, high-density sources can facilitate negative ion extraction because of their thin sheaths and remote position with respect to the processing wafer. In either case, the first negative ions to reach a processing surface are likely to have crossed the bulk of the sheath region as electrons and attached near the surface.
Characteristics of Very High-Aspect-Ratio Contact Hole Etching
Authors: Ikegami Naokatsu , Yabata Atsushi , Matsui Takayuki , Horiike Jun Kanamori
Published: October 2002

An ultrahigh-aspect-ratio, 0.06-µ m-diameter, 2-µ m-deep contact hole pattern of SiO2 was successfully fabricated using a poly-Si mask and a magnetically enhanced reactive-ion-etching (RIE) system in a mixture of CHF3/CO gas. In this dimensional area, processing for vertical profiles is extremely difficult, and problems in the form of bowing at the sidewalls of the holes can occur. Furthermore, it is possible that ion flux and energy are significantly reduced when ions pass through the poly-Si mask, rather than through the SiO2 hole. The bowing is associated with bending of the incident ion trajectories, where the first stage of the trajectory change occurs at the mask, and subsequent multiple scattering of ions at the sidewall of the hole can occur. Other factors include sidewall protection by redeposited Si sputtered from the poly-Si mask and/or the deposited fluorocarbon polymers, and the effects of ion energy and flux bombarding these deposited materials.
Mechanisms for Microscopic Nonuniformity in Low-Pressure, High-Density Plasma Etching of Poly-Si in Cl2 and Cl2/O2 Mixtures
Authors: Mutumi Tuda Mutumi Tuda , Kouichi Ono Kouichi Ono
Published: October 2002

Etch anisotropy and microscopic uniformity have been investigated in low-pressure, high-density plasma etching environments. Polycrystalline Si films masked with a photoresist pattern of lines and spaces were etched in electron cyclotron resonance (ECR) Cl2 and Cl2/O2 plasmas with additional rf biasing. Experiments were performed by varying the gas pressure, substrate temperature, and percentage of O2 added. Moreover, the profile evolution during etching was simulated taking into account the transport of neutral and ionic species in microstructures and the following surface reactions: adsorption of neutral reactants, ion-stimulated desorption of reaction products, surface oxidation, and redeposition of etch products. The etched profiles obtained in ECR Cl2 and Cl2/O2 plasmas were compared with simulated results, and interpreted in terms of the deposition of etch products and the surface oxidation that occur competitively during etching. Etch products desorbed from the surface in microstructures have a sticking coefficient S
p\lesssim0.1, while etch products arriving from the plasma have a much larger coefficient S
p\gtrsim0.5. It was also shown that the competitive surface oxidation by incoming oxygen atoms plays a more important role in achieving aspect-ratio-independent etching than the deposition of etch products: the increased deposition of etch products resulted in enhanced sidewall tapering with little change in vertical etch rate; the surface oxidation resulted in inverse reactive-ion-etching lag without significant change in sidewall tapering.
Decoupled Plasma Source Technology: Process Region Choices For Silicide Etching
Authors: Pan Shaoher , Songlin Xu Songlin Xu , Dragan Podlesnik Dragan Podlesnik
Published: October 2002

We have developed a decoupled plasma source (DPS) etcher for polysilicon and polycide etching. A series of experiments has been carried out to study polycide gate etching in the DPS etcher. By combining conventional techniques of process evaluation with in situ monitoring of ions and radical chemistry and with real-time ion flux density distribution measurements, we quantitatively determined trends in polycide processing and etching with simple Cl2 and He/O2 chemistry. Performance parameters, such as etch rate, etch rate microloading, etch rate uniformity, profile, profile microloading and profile uniformity on WSi

x

, oxide, polysilicon and photoresist, were measured at 24 points on the surface matrix. These results were correlated with the physical and chemical parameters of the decoupled plasma, such as ion flux distribution, DC-bias potential across the wafer, plasma ion composition and concentration of neutrals. A vertical profile can be obtained with highly selective polycide etch in a single step main etch with Cl2 and He/O2 using a decoupled plasma silicon etch reactor.
Roles of the Higher Order Anisotropic Terms in Successive Structural Phase Transitions: The Method of Determination of Phenomenological Parameters
Authors: Ishibashi Kazuhiko Fujita
Published: October 2002

A simple and general method for choosing appropriate coefficients of the higher order invariants in the free energy function to reproduce successive phase transitions is presented. It is found, when applied to perovskite structure-based systems, that the phase sequences such as cubic-rhombohedral-orthorhombic-tetragonal, cubic-tetragonal-rhombohedral, cubic-rhombohedral-orthorhombic and cubic-rhombohedral-tetragonal are reproducible in the phase diagram as a result of appropriate choice of model parameters as shown using the present method.
A Mass Spectrometric Study of Reaction Mechanisms in Chemical Vapor Deposition of (Ba, Sr)TiO3 Films
Authors: Yamamuka Mikio , Kawahara Takaaki , Tsuyoshi Horikawa Tsuyoshi Horikawa , Kouichi Ono Kouichi Ono
Published: October 2002

Reaction mechanisms in chemical vapor deposition (CVD) of SrTiO3 films have been studied using dipivaloylmethanato (DPM) complexes as sources, to gain insight into the complicated mechanisms for the CVD of (Ba, Sr)TiO3 films. Thermal decomposition processes were investigated for Sr(DPM)2 and TiO(DPM)2 using quadruple mass spectrometry (QMS), and the sticking probabilities of film precursors were estimated from trench coverages of SrO, TiO2 and SrTiO3 films. Intense signals at m/e=126 and 110 were observed in the decomposition spectra from Sr(DPM)2 and TiO(DPM)2, respectively, and their intensities increased substantially during the initial stages of reaction. This indicates that the m/e=126 and 110 peaks are attributable to products derived directly from Sr(DPM)2 and TiO(DPM)2, respectively. In the mixture of Sr(DPM)2 and TiO(DPM)2, the rate of increase of the intensity of the m/e=126 peak was reduced, while the peak at m/e=110 continued to increase with time. This implies that the decomposition rate for Sr(DPM)2 was reduced, and different products were produced in the mixture. The sticking probabilities for SrO, TiO2 and SrTiO3 film precursors were estimated to be 0.5, 0.03 and 0.05, respectively; the sticking probability for SrTiO3 was found to be much lower than the average of those for SrO and TiO2. Based on these results, we conclude that different film precursors are produced in the mixture of Sr(DPM)2 and TiO(DPM)2 during SrTiO3 film deposition.
Room-Temperature Operation of GaInNAs/GaInP Double-Heterostructure Laser Diodes Grown by Metalorganic Chemical Vapor Deposition
Authors: Sato Shun-ichi , Yasuhiro Osawa Yasuhiro Osawa , Tetsuro Saitoh Tetsuro Saitoh
Published: October 2002

We have achieved the growth of a GaInNAs lattice matched to GaAs by metalorganic chemical vapor deposition using dimethylhydrazine (DMHy) as a nitrogen source for the first time. We demonstrate the room-temperature operation of GaInNAs/GaInP double-heterostructure laser diodes. Lasing operation can be achieved at a wavelength of 1.26 µ m under pulsed operation. The threshold current characteristic temperature of 1.17 µ m laser diodes is found to be 96 K (at ambient temperatures between 10 and 50° C) and 69 K (at ambient temperatures between 50 and 70° C). Light emission for light-emitting diodes (LEDs) grown on a GaAs substrate is also demonstrated at a wavelength range from 1.2 to 1.45 µ m. A wavelength of 1.45 µ m is the longest reported to date for a GaInNAs lattice matched to GaAs. These results indicate the potential of GaInNAs for application to laser diodes without thermal cooling because they are more stable at ambient temperatures than conventional GaInPAs laser diodes at wavelengths from 1.3 to 1.55 µ m.
Absorption of CO2 Laser Beam in Relation to Laser Cutting Process
Authors: Yilbas Bekir S. , Kahraman Mehmet Sunar
Published: October 2002

The absorption of incident laser beam is important when the quality of the laser machining is concerned, since the surface plasma acts as a medium between the workpiece and a laser beam. In the present study, the measurement of electron number density and temperature is carried out using a Langmuir probe. Effective absorption coefficients due to electron-ion and electron-neutral collisions as well as photoionization processes are dealt with analytically using the Maxwell's equations. The validity of classical treatment for the electron-neutral collision in relation to absorption is introduced and discussed. Consequently, the absorption coefficients due to these processes are computed within the frame of the data obtained from the present work. The study is extended to include the transmittance of He–Ne laser beam through the surface plasma generated during laser beam-workpiece interaction. It is found that the electron-ion collision is the dominant mechanism in the absorption process. The present data indicates that about 85% of the reference He–Ne is absorbed at the location close to the irradiated spot center in the plasma, therefore, the attenuation, scattering and deflection of the reference beam is mainly due to vapor atoms than the charged particles.
Transform-Limited 30-fs Pulse Generation from a Diode-Pumped Kerr-Lens Mode-Locked Cr:LiSAF Laser
Authors: Shin-ichiro Aoshima Shin-ichiro Aoshima , Haruyasu Itoh Haruyasu Itoh , Yutaka Tsuchiya Yutaka Tsuchiya
Published: October 2002

The generation of transform-limited 30-fs pulses from a laser-diode pumped, Kerr-lens mode-locked Cr:LiSAF laser is reported. Good mode-locking was achieved by use of a simple cavity configuration with a laser diode pumping source which had a separate section of a laser diode amplifier. The 30-fs optical pulse width was confirmed by use of an autocorrelator having little internal dispersion due to its composition of only reflecting mirror optics. A time-bandwidth product of 0.318 was obtained for the laser output pulse by assumption of a sech2 waveform.
Improved Switching Performance of Multiple Quantum Well Asymmetric Fabry-Perot Ultrafast All-Optical Switch by Coupled-Cavity Configuration
Authors: Akiyama Tomoyuki , Masahiro Tsuchiya Masahiro Tsuchiya , Takeshi Kamiya Takeshi Kamiya
Published: October 2002

We show theoretically that mode splitting of a vertical coupled-cavity is very effective for realizing high contrast and lossless operation in asymmetric Fabry-Perot all-optical ultrafast time-division switches having a multiple quantum well saturable absorber. The merit of the coupled-cavity is mode splitting, which makes pump and signal pulse frequencies independently adjustable without lengthening of cavity; the short cavity feature is indispensable for fast response with high sensitivity. With 7.7 fJ/µ m2, a 0.2 dB internal loss is achieved for a coupled-cavity, while a conventional single cavity has a loss of 17 dB. The maximum extinction ratio for a coupled-cavity reaches 32 dB, while that for a single cavity saturates at around 22 dB.
Second Harmonic Generation Studies of Polymer-Stabilized Cholesteric Texture Films
Authors: Fuh Andy Ying-Guey , Chi-Yen Huang Chi-Yen Huang , Cheuk-Wah Lau Cheuk-Wah Lau
Published: October 2002

Using a mode-locking Nd:YAG laser, we measured the second harmonic generation (SHG) of polymer-stabilized cholesteric texture (PSCT) films. The SHG observed in these samples is due to the dielectric gradient which arises from the interfaces between the cholesteric liquid crystal/polymer and those between the adjacent cholesteric focal conic domains having a different helical axis. Both the SHG intensities and the electro-optical characteristics of PSCT films were measured as a function of the polymer concentration. In addition, polymer network structures formed in PSCT films were investigated. Good correlations among the SHG measurements, electro-optical characteristics, and the polymer network morphologies were found. This means that SHG measurements could provide us with another qualitative, nondestructive method to analyze the PSCT films.
Maxwell Displacement Current Across Monolayers with Dielectric Anisotropy due to Biaxiality on a Water Surface
Authors: Wu Chen-Xu , Shin-ichi Kuragasaki Shin-ichi Kuragasaki , Mitsumasa Iwamoto Mitsumasa Iwamoto
Published: October 2002

Maxwell displacement currents (MDCs) across mesogenic liquid crystal monolayers of 4-cyano-4'-n-alkyl-biphenyl (nCB) with positive anisotropy, a mixture of 4-alkoxyphenyl 4-alkyl-cyclohexanecarboxylates of k-17-N-73-I (DON103) with negative dielectric anisotropy, and LVI-035L without dielectric anisotropy on a water surface were measured by compression of the monolayer film in the range of immeasurably low surface pressures by means of a MDC-measuring technique. It is shown that the MDCs generated in the Langm\ddot uir films in the range just after the phase transition from the planar surface alignment isotropic phase to the polar orientational alignment phase mainly depend on the orientational change of the long-axis-orienting dipole moment of organic molecules. A novel theoretical explanation was introduced for study of this dependence. That is, a biaxial molecule model expressible with two order parameters S
∥ and S
⊥ was developed for the first time, and applied to the analysis of the aforementioned experimental results. Here S
∥ and S
⊥ are the orientational order parameter in the direction parallel and perpendicular to the molecular long-axis, respectively. It is found that the monolayer films of LVI-035L without dielectric anisotropy exhibit no MDC generation as the Langmüir films are compressed, and the extent of MDC generation in monolayers with positive dielectric anisotropy is much larger than that in monolayers with negative dielectric anisotropy. We concluded that the developed mathematical expressions based on the biaxial molecule model are useful for the analysis of the MDC generation across biaxial monolayers.
Improved Heat Treatment for Wafer Direct Bonding between Semiconductors and Magnetic Garnets
Authors: Yokoi Hideki , Mizumoto Tetsuya , Koichi Maru Koichi Maru , Yoshiyuki Naito Yoshiyuki Naito
Published: October 2002

The optical propagation loss of rib waveguides fabricated on magnetic garnet films increased upon annealing in H2 ambient during wafer direct bonding. The heat treatment in wafer direct bonding between InP and Gd3Ga5O12 was investigated with the aim of circumventing the loss increase. The bonding was achieved by heat treatment in H2 ambient at temperatures of ≦330° C or in N2 ambient.
Origin of SiC Precipitation during the Micro-Pulling-Down Processing of Si–Ge Fibers
Authors: Epelbaum Boris M. , Gurjiyants Pavel A. , Inaba Katsuhiko , Shimamura Kiyoshi , Uda Satoshi , Junichi Kon Junichi Kon , Tsuguo Fukuda Tsuguo Fukuda
Published: October 2002

The problem of SiC precipitation during micro-pulling-down growth of Si–Ge mixed crystals has been analyzed as an important constraint of the technique. Three mechanisms of SiC microcrystal formation have been discussed. The solute transport in the melt and the dependence of the rate of Si–Ge melt evaporation on melt composition have been investigated. The troublesome influence of CO on SiC formation has been reduced by modification of the micro-pulling-down (µ-PD) growth assembly with optimization of argon flow. As a result the effective lifespan of the crucible was increased at least fivefold.
Optical In Situ Observation of Electron Beam Induced Surface Modification of Epitaxial Fluoride Films
Authors: Koji Kawasaki Koji Kawasaki , Manabu Tomisaka Manabu Tomisaka , Kazuo Tsutsui Kazuo Tsutsui
Published: October 2002

An in situ optical observation method for investigations of fluoride surface modification induced by electron irradiation was developed for the purpose of improving the heteroepitaxy of semiconductors on fluorides. Spectra of reflected light after the electron irradiation and continuous intensity change of reflected light at a fixed wavelength during the electron irradiation were observed. It was found that a Ca colloidal absorption band at around 580 nm due to aggregation of Ca atoms appeared as the electron dose to the CaF2 surface was increased. Progressive P atom adsorption during the electron irradiation was also observed in the case of use of a probing light of 400 nm wavelength. The amount of adsorbed P atoms increased as the electron dose increased and saturated at approximately one atomic monolayer on the CaF2 surface. Effects of the acceleration energy of electrons on the surface modification were also investigated and it was found that the efficiency of P adsorption increased as the electron energy increased, while that of Ca aggregation decreased. A possible mechanism of this phenomenon is discussed.
One-Dimensional Growth of Phenylene Oligomer Single Crystals on Friction-Transferred Poly(p-phenylene) Film
Authors: Han Kiyoshi Yase , Yamamoto Kaoru , Yoshida Yuji , Noriyuki Takada Noriyuki Takada , Nobutaka Tanigaki Nobutaka Tanigaki
Published: October 2002

One-dimensionally oriented thin crystals of a phenylene oligomer, p-sexiphenylene (6P), are grown on the poly( p-phenylene) (PPP) film prepared by the friction-transfer method. The 6P molecules tend to grow epitaxially on the (001) planes of alkali halides and the molecular axis is parallel to the <110> directions of alkali halides. The needle crystals orient along two directions. On the other hand, 6P stands on quartz plates with random orientations. The slender crystals of 6P formed on the friction-transferred PPP on alkali halides and quartz plates confirm that the uniaxial orientation has anisotropic optical properties.
Evaluation of Body Motion by Optical Flow Analysis
Authors: Nakajima Kazuki , Osa Atsushi , Maekawa Tsuyoshi , Hidetoshi Miike Hidetoshi Miike
Published: October 2002

For quantitative evaluation of body motion, a fully noncontact and unconstraining monitoring method was developed by introducing image sequence analysis. A spatiotemporal local optimization method was applied to determine optical flow in the image sequence. The optical flow visualized the apparent velocity field of the entire body motion, including both breast movement of respiration and posture changes in a bed. The experiment was carried out under regulated posture changes and under a sleeping condition by measuring heart rate, respiration and digitized image sequences using a video camera. A temporal increase in heart rate reflected the magnitude of physical activities. We proposed two candidate parameters for evaluation of respiratory and physical activities based on comparison among experimental results. The average of squared motion velocities reflected the magnitude of physical activities. The representative field-averaged component showed a waveform with periodic fluctuation corresponding to that of respiration obtained with a nasal thermistor.
Ultrasound Bioeffects and Clinical Diagnostic Relevance
Authors: Floyd Dunn Floyd Dunn
Published: October 2002

During the approximately one-third century that diagnostic ultrasound has been employed, there have been no verified reports of adverse effects. Ultrasound, at sufficient amplitudes, can produce irreversible biological effects by thermal and nonthermal mechanisms. Thermal effects result from the absorption of ultrasound by tissues. Laboratory studies have documented the response of biological systems to temperature elevation. This has led to the conclusion that expected temperature increases of less than 2° C can be considered innocuous. However, for an expected temperature increase greater than 2° C, the duration of exposure time should be considered. The nonthermal mechanism of cavitation is known to produce tissue disruption during gas body collapse. Laboratory studies and safety considerations have led to a mechanical index ( MI)=p/√f. For MI less than 1, the likelihood of cavitation occurring is very low, whereas for MI greater than 1, the examination should be considered to pose a risk (though none has ever been reported). Implementation of on-screen displays of estimates of temperature elevation and cavitation likelihood provides the physician the necessary information for conducting low risk examination.
Effects of Heat Treatment on Ultrasonic Attenuation in Mn-Ferrites
Authors: Yoriyoshi Kawai Yoriyoshi Kawai
Published: October 2002

Acoustic losses in single crystals of Mn-ferrite were studied in the temperature range of 180–650 K. Loss peaks were observed at 232 and 537 K with activation energies of 0.3 and 0.8 eV, respectively. The 232 K peak arises from the relaxation of electrons between cations on octahedral sites. The 537 K peak is ascribed to the exchange of cations and their vacancies on octahedral sites. A small peak was observed at around 290 K after a heat treatment in reducing atmosphere. Heat treatments at 300 and 600° C affect the oxygen stoichiometry and the distribution of cations between octahedral and tetrahedral sites.
Dynamical Properties of the FR(LT)-FR(HT) Phase Transition in Zr-Rich Lead Zirconate Titanate Ceramics
Authors: Xianlin Dong Xianlin Dong , Seiji Kojima Seiji Kojima
Published: October 2002

The dielectric, elastic and piezoelectric properties of the F R(LT)-F R(HT) phase transition were investigated on Nb-doped lead zirconate titanate (PZT) Pb(Zr1-x
Tix)O3 ceramics (x=0.05 and 0.25). Dielectric anomaly and thermal hysteresis are observed through the F R(LT)-F R(HT) phase transition in PZT(Nb)95/5, but no anomaly appears in PZT(Nb)75/25. Two compositions show pronounced dielectric dispersions in the rhombohedral ferroelectric phases. The temperature dependences of resonance frequency (f
r), elastic constant (s
11
E) and Poisson's ratio(σ) show remarkable anomalies around the F R(LT)-F R(HT) phase transition in both compositions. However, the temperature range of the anomaly of PZT(Nb)75/25 is much broader than that of PZT(Nb)95/5. The electromechanical coupling factor (K
p) decreases abruptly in PZT(Nb)95/5, while, in contrast, it increases gradually in PZT(Nb)75/25. These results are discussed on the basis of the coupling of M-type and R-type oxygen octahedral tilts to polarization and strain.
Low-Loss Surface Acoustic Wave Filter on Natural-Single Phase Unidirectional Transducter Orientations of a Li 2B 4O 7 Substrate
Authors: Masao Takeuchi Masao Takeuchi , Hiroyuki Odagawa Hiroyuki Odagawa , Mitsuhiro Tanaka Mitsuhiro Tanaka , Kazuhiko Yamanouchi Kazuhiko Yamanouchi
Published: October 2002

Natural-single phase unidirectional transducers (NSPUDT) have attracted much attention for the implementation of low-loss surface acoustic wave (SAW) devices. In this paper, we describe a low-loss SAW filter using NSPUDT orientations of a Li2B4O7 substrate previously reported by the authors. Since the unidirectionality of NSPUDT is inherent to the substrate orientation, it is necessary to make the receiving transducer unidirectional in the opposite direction in order to obtain a low-loss filter using two transducers with reverse directivity. A new transducer configuration to reverse the directivity of an NSPUDT substrate is proposed, which utilizes reflector banks within the ladder transducer. The configuration has the advantage that it can be fabricated through a single level and a single metallization with minimum electrode width of λ/4. The principle of the operation of a reversal of directivity transducer is described. A 200-MHz-band low-loss SAW transversal filter with minimum insertion loss below 3 dB and low passband ripple are demonstrated with a theoretical filter response using coupling-of-modes theory.
The Power Durability of 900 MHz Band Double-Mode-Type Surface Acoustic Wave Filters and Improvement in Power Durability of Al–Cu Thin Film Electrodes by Cu Atom Segregation
Authors: Kimura Noritoshi , Nakano Masahiro , Michiyuki Nakazawa Michiyuki Nakazawa , Katsuo Sato Katsuo Sato
Published: October 2002

The power durability of double-mode-type surface acoustic wave filters, which have recently seen wide use in cellular phones, is investigated. It was found that the lifetime of double-mode-type surface acoustic wave filters is reduced considerably when high input power is applied, due to non-linear behavior. Moreover, the authors demonstrate that the power durability of an Al–Cu thin film electrode is greatly improved by Cu atom segregation in the grain boundaries.
Electrical Equivalent Circuit of Loaded Thick Langevin Flexural Transducer
Authors: Yoshikazu Koike Yoshikazu Koike , Takeshi Tamura Takeshi Tamura , Sadayuki Ueha Sadayuki Ueha
Published: October 2002

In this paper, an electrical equivalent circuit of a loaded thick Langevin flexural transducer is proposed. As there are two vibration components at the mechanical output terminal of a thick flexural transducer, that is, lateral and rotational components. A load, corresponding to each vibration component, applied to the transducer must also be considered separately. When it is assumed that the load is fluid and that the mechanical output port is the end surface of the flexural transducer, the rotary motion of the end surface only contributes to sound radiation into fluid. An analytical solution of Timoshenko's beam theory given by Miklowitz and the piezoelectric equation are applied to calculate the free vibration mode and the electrical equivalent components of transducer. Using this derived equivalent circuit, the behavior of the loaded flexural transducer is experimentally studied to prove the validity of the proposed circuit.
Study on Estimation of Metal Film Thickness by Attenuated Total Reflection
Authors: Tokunaga Yoshiaki , Watanabe Hirofumi , Minamide Akiyuki , Minamikawa Toshiharu
Published: October 2002

The estimation of thin film thickness by attenuated total reflection (ATR) was proposed. This technique is caused by be fitted curve evaluated from Fresnel's formula to experimental values of reflectivity in the resonance dip due to surface plasmon. The equation for the thickness, d
spr, estimated from ATR and the minimum, R
min, of the resonance dip in reflectivity due to surface plasmon resonance is represented by d
spr=D+√E(R
min-F). The values obtained by this method were compared with those obtained by the surface roughness tester made by the Rank Tayler Hobson Company. From this comparison, the experimental formula d
srt=G
d
spr+H was proposed, and G and H were obtained as 0.69 and 6.7 respectively for an Ag film, 0.86 and -1.45 respectively for an Au film, and 0.67 and 8.98 respectively for a Cu film, all ranging from about 30 nm to 70 nm in thickness.
Measurement of Temperature Distribution in Space Using Ultrasound Computerized Tomography
Authors: Koichi Mizutani Koichi Mizutani , Kenta Nishizaki Kenta Nishizaki , Keinosuke Nagai Keinosuke Nagai , Kennichi Harakawa Kennichi Harakawa
Published: October 2002

We propose a method for measuring the temperature distribution in space using ultrasound computerized tomography (CT). We verified by simulations and experiments that reconstruction of the air temperature distribution is possible using a time of flight profile. Good experimental results were obtained in the reconstruction of a point heat source 30° hotter than room temperature in an area of 100 mm × 100 mm using ultrasound with a frequency of 40 kHz.
Stress Sensitivity Distribution Measurement Using a Low-Frequency Sound Wave and Its Application to Quartz Crystal Microbalances
Authors: Goka Shigeyoshi , Yasuaki Watanabe Yasuaki Watanabe , Hitoshi Sekimoto Hitoshi Sekimoto
Published: October 2002

A new method for measuring the stress sensitivity distribution on a resonator surface, including a region without electrodes, using a low-frequency sound wave is described. The experimental results for an AT-cut quartz crystal resonator obtained using the proposed method and the current pulsed-laser method are shown. Additionally, we applied this method to the design of quartz crystal microbalances using multiple resonance modes.
Weak Scattering Acoustic Wave Field Analysis Using Backward Propagation Rytov Transform
Authors: Akira Yamada Akira Yamada
Published: October 2002

A novel linearization method for the scattering acoustic wave equation based on the holographic backward propagation prior to the Rytov approximation transform is described. The technique is applied to approximate scattered acoustic wave field analysis for arbitrary weak scattering inhomogeneous objects based on the superposition principle. As a simulation test examination, wave fields scattered from a concentric double cylinder are calculated based on the summation of the backward propagation Rytov data for the outer and inner element cylinders. Compared with the results calculated by the rigorous analytical formula for the concentric double cylinder, the effectiveness of the present technique is verified to be satisfactory.
Effect of Pressure in Blood Vessel Model on Ultrasound Scattered Power from Microbubbles
Authors: Kawan Soetanto Kawan Soetanto , Tomohiro Saito Tomohiro Saito , Motoyoshi Okujima Motoyoshi Okujima
Published: October 2002

To obtain a clearer ultrasonic diagnostic image using a microbubble contrast agent, investigation of power scattering from microbubbles is indispensable. The scattered power from the microbubbles should be as large as possible, and, since it depends largely on the elasticity of the microbubble shells, it is desirable to have as large an elasticity as possible. However, microbubbles with weak shells are easily broken under high pressure. Although hard-shell microbubbles are effective under high pressure, these microbubbles do not consistently produce scattered power. Thus, it is very important to fabricate microbubbles that can be used as ultrasound contrast agents. In this study, the effect of pressure on the scattered power and longevity of microbubbles in a blood vessel model was investigated using a blood vessel model system. Microbubbles coated with sodium laurate were compared with hollow silicone microcapsules (Grandoll) which have a different shell type. The effect of the pressure in the blood vessel model on these microbubbles was investigated by ultrasound scattered power measurement. According to the results, the scattered power from the sodium laurate microbubbles decreases when the pressure increases because of the disappearance of microbubbles. In contrast, the effect of pressure on scattered power from hard-shell microbubbles is negligible.
Properties of a-Si:H Film Deposited by Amplitude-Modulated RF Plasma Chemical Vapour Deposition for Thin Film Transistor
Authors: Nakahigashi Takahiro , Hayashi Tsukasa , Izumi Yoshihiro , Kobayashi Masanao , Hajime Kuwahara Hajime Kuwahara , Masahiro Nakabayashi Masahiro Nakabayashi
Published: October 2002

The method of amplitude-modulated RF plasma enhanced chemical vapour deposition (p-CVD) has been used to deposit the a-Si:H film. Various properties of the deposited a-Si:H film such as uniformity of thickness, stress of film and hydrogen concentration in the film are studied. These film properties are improved in the case of amplitude-modulated RF p-CVD compared with the CW case, particularly at the high deposition rate. Further investigation has been carried out by constructing a bottom gate thin film transistor (TFT) device without an etch stop layer. The measured electron mobility and threshold voltage, are also improved up to the deposition rate of 32 nm/min by the method of amplitude modulated RF p-CVD at the modulation frequency of 68 kHz.