bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Power, Continuous-wave and Blue Light Generation by Intracavity Frequency Doubling of a Cr:LiSrAlF6 Laser
Authors: Makio Satoshi , Sato Masayoshi , Sasaki Takatomo
Published: October 2002

Thermal quenching phenomena in a Cr doped LiSrAlF6 (Cr:LiSAF) laser pumped by a laser diode (LD) was studied to improve the second harmonic generation (SHG). The second harmonic to obtain blue light was generated by an intracavity frequency doubled solid state laser where LiB3O5 (LBO) crystal was inserted in the cavity. A circular pumping beam profile was essential to suppress thermal quenching, which was realized by the arrangement of horizontal and vertical two LD pumping or bundled fiber pumping. In particular for the latter case, blue light of 120 mW was obtained with pump power of 1200 mW.
Enhancement of the Bandwidth of p-i-n Photodiodes by Utilizing Tandem Structures
Authors: Kakinuma Hiroaki
Published: October 2002

We propose a new method of increasing the maximum 3dB-bandwidth of InGaAs/InP p-i-n photodiodes for optical communication applications. It is demonstrated by calculation that employing tandem structures (p-i-n)
N
(N≧2) enhances the maximum 3dB-bandwidth by a factor of √N after optimizing the i-layer thickness for the side illumination case, although the photosensitivity decreases by a factor of N. Conditions imposed on the i-layer thickness for complete carrier recombination in the intermediate n-p junctions are derived.
Optical Anisotropy in InAs Quantum Dots Formed on GaAs Pyramids
Authors: An Haiyan , Motohisa Junichi , Fukui Takashi
Published: October 2002

In this paper, we present the results of polarization-dependent micro-photoluminescence (µ-PL) measurements of InAs quantum dots (QDs) selectively formed on GaAs pyramidal structures by selective area metalorganic vapor phase epitaxy. Under nonresonant excitation, strong optical anisotropy is observed in the PL spectra of the InAs QDs. Under near-resonant excitation, where the excitation energy is close to the wetting layer luminescence, the linear polarization degree of InAs QD is larger than that observed under nonresonant excitation. When excited and detected lights have the same polarization along two <110> directions, the PL is intense. However, in the cross polarization configurations, the PL intensities are very weak. The observed strong optical anisotropy in InAs QDs formed on GaAs pyramids under nonresonant excitation can be attributed mainly to the asymmetry of the QD potential which results from the anisotropic strain relaxation and shape of QDs, while that under the near-resonant excitation is explained by the hot photoluminescence effect.
Thermoluminescence of Photodarkened CdS-Doped Glasses
Authors: Miyoshi Tadaki , Sera Hiroki , Matsuo Naoto , Kaneda Teruhisa
Published: October 2002

Thermoluminescence of photodarkened CdS-doped glasses has been measured to investigate traps in glasses, which are responsible for photodarkening. Glow peaks are observed at 150–350°C in glow curves of luminescence. The location of the traps is evaluated from the glow curves.
Depressed DC Breakdown Phenomena near Curie Temperature of BaTiO3-Based Ceramic Capacitors
Authors: Zhou Yuanxiang , Yan Ping , Yoshimura Noboru , Cheng Zixia , Liang Xidong , Guan Zhicheng
Published: October 2002

In this paper, temperature-dependent dc breakdown in BaTiO3-based multilayer ceramic capacitors (MLCs) is studied. We measured dc breakdown fields (BDFs) at temperatures ranging from room temperature to 250°C. According to the change in the breakdown characteristics with temperature, the breakdown process can be regarded as consisting of three regions: room, Curie and high temperature regions. An abnormal depressed BDF was observed in the Curie temperature region. After analyzing the dc prestressing effect on the dc BDF, it was found that the homo effect of space charges plays an important role during dc breakdown in the room and Curie temperature regions. In the high temperature region, the thermal breakdown tends to dominate the breakdown process of MLCs. In addition, based on a structure controlled Schottky conduction process, we combined the thermionic emission process with the influence of barrier height on space charge accumulation. By relating the combined result with the experimental results, it was concluded that the abnormal depression in the dc breakdown is consistent with the change in barrier height caused by the phase transition of the BaTiO3-based ceramic insulator near its Curie temperature.
Shock-Induced Electromotive Force in Aqueous Solution of Potassium Fluoride
Authors: Ogura Toshiyuki , Hironaka Yoichiro , Nicol Malcolm F. , Nakamura Kazutaka G. , Kondo Ken-ichi
Published: October 2002

Shock-induced electromotive forces (emf) were measured in water and water-potassium fluoride solutions with concentrations of KF ranging from 2×10-7 to 2×10-2 mole fraction. The emf was positive and increased with increasing shock pressure and concentration of potassium fluoride for concentrations below 2×10-4. The increment of shock-induced polarization was proportional to cube root of concentration. For the dense solutions above 2×10-3, on the contrary, the polarity of the emf changed to negative.
Axial and Polar Orientational Changes by Rubbing/Photoalignment Processes in a Liquid Crystal Alignment Layer Studied by Optical Second-Harmonic Generation
Authors: Shioda Tatsutoshi , Chung Doo-Han , Takanishi Yoichi , Ishikawa Ken , Park Byoungchoo , Takezoe Hideo
Published: October 2002

Molecular reorientation by rubbing and photoalignment processes in polymer alignment layer for liquid crystals has been studied by linear optical absorption and surface optical second-harmonic generation. It was found that rubbing produces polar and axial orders in the photoisomerizable polyamic acid (PAA) containing azobenzene groups in the main chain, while photoalignment after rubbing destroys the polar order but is capable of reorienting the PAA main chain without creating further polar order.
Characterization of Tantalum Nitride Thin Films Fabricated by Pulsed Nd:YAG Laser Deposition Method
Authors: Hiroharu Kawasaki Hiroharu Kawasaki , Kazuya Doi Kazuya Doi , Jun Namba Jun Namba , Yoshiaki Suda Yoshiaki Suda , Tamiko Ohshima Tamiko Ohshima , Kenji Ebihara Kenji Ebihara
Published: October 2002

Growth mechanisms of crystalline tantalum nitride (TaN) films have been studied on silicon substrates using a pulsed Nd:YAG laser deposition method. Experimental results show that the properties of the TaN films strongly depend on the substrate temperatures and nitrogen gas pressures. This suggests that both the phase reaction in the plasma plume and the surface reaction on the substrate are important for preparing crystalline TaN films.
Pressure Dependence of Effective Pair Potentials in AgBr Determined by Extended X-Ray Absorption Fine Structure
Authors: Yoshiasa Akira , Murai Kei-ichiro , Nagai Takaya , Katayama Yoshinori
Published: October 2002

The pressure dependence of extended X-ray absorption fine structure (EXAFS) Debye-Waller factors in AgBr has been investigated using the cumulant expansion method. The Br K-edge EXAFS spectra were measured in the transmission mode under high pressure (≤9.1 GPa) at room temperature using a cubic anvil type apparatus (MAX90) and synchrotron radiation from the Photon Factory, Tsukuba. The effective pair potentials, V(u)=a
u
2/2+b
u
3/3!, were evaluated and the potential coefficient a at 2.1, 4.2 and 6.1 GPa are 1.59(4), 1.75(4) and 1.91(4) eV/Å-2, respectively. The energies of the third-order anharmonic potential coefficient b maintain nearly constant values with pressure though the third-order cumulant σ3 decreases with increasing in pressure.
Leakage Current and Fatigue Properties of Pb(Zr, Ti)O3 Ferroelectric Films Prepared by RF-Magnetron Sputtering on Textured LaNiO3 Electrode
Authors: Chao Gwo-Chin , Wu Jenn-Ming
Published: October 2002

The leakage current and the fatigue properties of Pb(Zr, Ti)O3 (PZT) films prepared by rf-magnetron sputtering on (100)-textured LaNiO3 electrode were investigated. Sputtering parameters such as excess PbO content in the target, sputtering power, Ar/O2 ratio, and working pressure were studied. PZT films of the perovskite phase with (100)-preferred orientation can be easily obtained under our sputtering conditions. The optimal sputtering conditions are: 30% excess PbO, sputtering power 40 W, working pressure 5 mTorr, and Ar/O2=95/5. The effect of these sputtering parameters on leakage current and fatigue properties can be explained by the variation of the concentrations of lead vacancies and holes produced by the sputtering conditions. PZT films deposited under these optimal conditions can endure fatigue up to more than 1011 cycles and possess a low leakage current density (10-8–10-7 A/cm2) at an electric field strength lower than 100 kV/cm. The conduction mechanism of the leakage is proposed to be a Schottky thermionic emission.
Homogeneous and Multilayered Shields for Neutrons and Gamma-Rays
Authors: El-Sayed Abdo A. , Megahid R. M.
Published: October 2002

Measurements were carried-out to compare the attenuation properties of homogeneous shields and shields of two layers and three layers for fast neutrons and total gamma rays. These were performed by measuring the fast neutron and total gamma-ray spectra behind homogeneous shields of magnetite–limonite, ilmenite–ilmenite and magnetite–magnetite concretes. The two layers assembly consists of iron and one of the above mentioned concretes, while the three layers shield consists of water, iron and one of the previously mentioned concretes. All measurements were carried-out using a neutron-gamma spectrometer with stilbene scintillator coupled to a fast photomultiplier tube. Separation between pulses of recoil protons and recoil electrons was achieved by a pulse shape discrimination technique. The obtained data are presented in the form of neutron and gamma spectra measured behind homogeneous shields and shields of two layers and three layers. The spectra measured behind homogeneous shields were used to derive the total macroscopic cross-sections for neutrons and the total attenuation coefficients for total gamma rays.
Observation of Longitudinal Quadrupole-mode Oscillations of a Bunch which were Induced by RF Phase Modulation in the Electron Storage Ring
Authors: Shogo Sakanaka Shogo Sakanaka , Takashi Obina Takashi Obina
Published: October 2002

It has been reported that the beam lifetime in electron storage rings can be improved by applying a small phase modulation on the rf accelerating voltage at a frequency of two-times the synchrotron oscillation frequency. This effect can be explained as being due to the improved Touschek lifetime that is caused by an excited bunch-shape oscillation in the stored bunches. In order to understand this phenomenon further, we investigated the induced bunch-shape oscillation in the 2.5-GeV Photon Factory storage ring at High Energy Accelerator Research Organization (KEK). Using both a streak camera and a spectrum analyzer, we observed the quadrupole-mode oscillations of a stored single bunch very clearly. It showed a splitting of a single bunch into three or two bunchlets, which depended on the modulation frequency. We report on these experimental results, and discuss them using computer simulations and an analytical formalism.
Numerical Simulation of Neutral Beam Injection in the GAMMA10 Anchor Cell
Authors: Ito Toru , Katanuma Isao , Nakashima Yousuke , Yatsu Kiyoshi
Published: October 2002

The GAMMA10 tandem mirror contains neutral beam injectors at the anchor mirror cells to increase the number of high-energy ions there for magnetohydrodynamic stability. We calculate the population of high-energy ions by using the bounce-averaged Fokker-Planck code for various background neutral densities and electron temperatures. We compare the simulation results with results of a point model and make clear the validity of the point model.
Production of Low-Electron-Temperature Electron Cyclotron Resonance Plasma Using Nitrogen Gas in the Mirror Magnetic Field
Authors: Itagaki Naho , Ueda Yoko , Ishii Nobuo , Kawai Yoshinobu
Published: October 2002

An electron cyclotron resonance (ECR) plasma with a low electron temperature (< 2 eV) and high electron density (∼1012 cm-3) was realized in a mirror magnetic field for Ar/N2 or N2 gas. It was found based on the particle and power balance that the decrease in the electron temperature was due to the magnetic-mirror confinement depending on the collision cross section between electrons and neutral particles. The experimental and numerical results suggest that diluting with N2 gas, whose excitation cross section peaks at a low electron energy of about 2 eV, in the mirror magnetic field enables us to reduce the electron temperature efficiently in an ECR plasma.
Driving Duty Ratio Dependence of Lifetime of Tris(8-hydroxy-quinolinate)aluminum-Based Organic Light-Emitting Diodes
Authors: Tsujioka Tsuyoshi , Fujii Hiroyuki , Hamada Yuji , Takahashi Hisakazu
Published: October 2002

The driving duty ratio dependence of the luminance lifetime of various tris(8-hydroxy-quinolinate)aluminum-based organic light-emitting devices (OLEDs) was investigated. High-duty-ratio driven devices with low mean operational voltage had a long lifetime in comparison to DC-driven devices. This indicates voltage-mode degradation was suppressed by high-duty-ratio driving. The long lifetime effected by high-duty-ratio driving became increasingly small in the range of large operational mean current because of accelerated current-mode degradation. The development of high-efficiency OLEDs, therefore, is of prime importance not only to achieve low power consumption but also to obtain long-lifetime OLEDs by high-duty-ratio driving.
Spot Scanning Using Radioactive11C Beams for Heavy-Ion Radiotherapy
Authors: Urakabe Eriko , Kanai Tatsuaki , Kanazawa Mitsutaka , Kitagawa Atsushi , Noda Koji , Tomitani Takehiro , Suda Mitsuru , Iseki Yasushi , Hanawa Katsushi , Sato Kohsuke , Shimbo Munefumi , Mizuno Hideyuki , Hirata Yoichi , Futami Yasuyuki , Iwashita Yoshihisa , Noda Akira
Published: October 2002

A scheme for spot scanning using11C beams has been developed in order to form and verify a three-dimensionally conformal irradiation field for cancer radiotherapy. By selecting the momentum spread of a11C beam, we could considerably decrease the distal falloff of the irradiation field, thus conserving the beam quality. To estimate and optimize the dose distribution in the irradiation field, it is essential to evaluate the precise dose distribution of spot beams. The coupling of the lateral dose and depth-dose distributions originating from a wide momentum spread should be taken into account to calculate the dose distribution of11C beams. The reconstructed dose distribution of the irradiation field was in good agreement with the experimental results, i.e., within ±0.2%. An irradiation field of 35×35×43 mm3was optimized and spot scanning using11C beams was carried out. The flatness was within ±2.3% with an error of 1% in the detector resolution.
Surface Channel Metal Gate Complementary MOS with Light Counter Doping and Single Work Function Gate Electrode
Authors: Nishinohara Kazumi T. , Akasaka Yasushi , Saito Tomohiro , Yagishita Atsushi , Murakoshi Atsushi , Suguro Kyoichi , Arikado Tsunetoshi
Published: October 2002

We propose a channel engineering guideline for the low threshold voltage (V
th) metal oxide silicon field effect transistor (MOSFET) with metal gate, which is promising for highly miniaturized MOSFETs. For lowering V
th of metal gate MOSFET, counter doping is useful. However, a buried channel with heavy counter doping has several disadvantages, such as the degradation of subthreshold swing. In this work, using a design with light counter doping, a surface channel complementary metal oxide silicon (CMOS) of low V
th with a single work function gate electrode was successfully fabricated showing superior characteristics. Device simulation was used to investigate the impacts of the channel profile of such a device. It was found that using counter doping with low concentration to an optimized depth results in better subthreshold characteristics than that using shallow counter doping with high concentration. A lower counter dopant concentration also suppresses V
th deviations. The damascene gate process was used in the fabrication.
Bandgap and Strain Engineering in SiGeC Heterojunction Bipolar Transistors
Authors: Yuki Koichiro , Toyoda Kenji , Takagi Takeshi , Kanzawa Yoshihiko , Nozawa Katsuya , Saitoh Toru , Kubo Minoru
Published: October 2002

The incorporation of C into Si1-x
Ge
x
alloys contributes to enlarging the critical layer thickness and to improving the thermal budget. It also realizes a narrower bandgap with compensated strain. These effects would introduce good performance at high frequency in the devices. We fabricate heterojunction bipolar transistors (HBTs) with an Si1-x-y
Ge
x
C
y
base layer using ultrahigh-vacuum chemical vapor deposition (UHV-CVD) technology. The bandgaps of Si1-x-y
Ge
x
C
y
base layers are measured by the evaluation of the collector current dependence on temperature. The strain of the pseudomorphic Si1-x-y
Ge
x
C
y
layer is also extracted by an analysis of the X-ray diffraction spectra. Good flexibility of Si1-x-y
Ge
x
C
y
alloy is shown for the bandgap and strain engineering. The devices using the excellent characteristics of Si1-x-y
Ge
x
C
y
alloy have numerous applications for wireless telecommunications.
Reducing of ROn in Vertical Power-MOSFETs due to Local Channel Doping
Authors: Fink Christoph , Schulze Jörg , Eisele Ignaz , Hansch Walter , Werner Wolfgang , Kanert Werner
Published: October 2002

In this work we present a new approach for solving the tradeoff between breakdown capability and on state resistance for Power-metal-oxid-semiconductor field effect transistor (MOSFET) devices. Therefore we use a vertical transistor on an epitaxial layer. This concept allows the adjustment of the breakdown voltage due to the thickness of the epi-layer separately from the on-state resistance, which is defined by the vertical transistor. The transistor was fabricated by means of molecular beam epitaxy (MBE), which allows very small channel length and doping control on atomistic scale. Devices with breakdown voltages between 12 V and 40 V were produced. It is also shown that the usage of local channel doping instead of homogenous doping in the switching transistor reduces the on state resistance of the device significantly.
Atomic-Scale Characterization of Nitridation Processes on Si(100)-2×1 Surfaces by Radical Nitrogen
Authors: Matsushita Daisuke , Ikeda Hiroya , Sakai Akira , Zaima Shigeaki , Yasuda Yukio
Published: October 2002

We have investigated the initial nitridation process of Si(100)-2×1 surfaces by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The nitridation was performed by radical nitrogen at a high temperature of 850°C. After the radical-nitrogen exposure of about 1 Langmuir, linear defects perpendicular to dimer rows were formed. Furthermore, doublet dark lines were frequently observed in the STM image. STS analysis of the dark-line regions clarified that the initial nitridation reaction occurs preferentially at the backbonds of surface Si atoms. Then, the nitridation proceeds via lateral growth of two-dimensional nitride-islands. These islands grow preferentially along the <011> direction perpendicular to the Si dimer rows. STS spectra obtained from the 0.5-nm-thick nitride islands distinctly showed a bandgap of about 4.0 eV that is very close to the bandgap of bulk Si3N4.
Advanced Co Salicide Technology for Sub-0.20 µm Fully-Depleted SOI Devices
Authors: Ichimori Takashi , Hirashita Norio
Published: October 2002

The mechanism of buried oxide (BOX) breakdown in fully-depleted silicon-on-insulator (FD SOI) devices is investigated by cross-sectional transmission electron microscopy (XTEM), and pinhole formation in the BOX at the bottom of a contact hole is found to be the predominant reason for this breakdown. Since this it is attributed to nonuniform silicidation of thin SOI films, improvement of silicide surface flatness is strongly required. In this paper, we present the significant effect of our new salicide on the silicide surface structure, which has enabled volume production of 0.20 µm FD SOI devices. Using this contact-hole-etching-prior-to-the-second-annealing (CHEPSA) cobalt salicide, perfect BOX yield is obtained down to 25-nm-thick SOI on commercially available separation-by-implanted-oxygen (SIMOX) substrates, which falls in the 0.13–0.10 µm range technology node.
Formation Process of High-Field Domain in Superlattices Observed by Photoluminescence Spectra Branch
Authors: Makoto Hosoda Makoto Hosoda , Naoki Ohtani Naoki Ohtani , Chiaki Domoto Chiaki Domoto , Tahito Aida Tahito Aida
Published: October 2002

We report photoluminescence Stark-shift behaviors under various optical excitation intensity for a GaAs/AlAs superlattice. The study clarifies the formation process of the high-field domain by analyzing photoluminescence (PL) spectra. We observed changes in splitting feature of the PL spectra, by varying excitation carrier density near resonance voltages between the Γ states. This clarifies how the inner electric field in superlattices varies by increasing carrier density.
Effects of a Low-Melting-Point Underlayer on Excimer-Laser-Induced Lateral Crystallization of Si Thin-Films
Authors: Yeh Wen-Chang , Masakiyo Matsumura Masakiyo Matsumura
Published: October 2002

The effects of an ultrathin metallic underlayer on excimer-laser crystallization of Si thin-films have been investigated experimentally. For a Si/Cr/SiO2 structure, the grain size became 1.3 times larger than that for the simple Si/SiO2 structure. This enlargement resulted from the formation of an ultrathin liquid layer of Cr-Si eutectic alloy, which suppresses heterogeneous nucleation at the Si/SiO2 interface. The Si layer mixes only partly with the ultrathin Cr layer, resulting in the formation of a large-grain-Si/CrSix bilayer structure.
Long-term Ion Transport in Nematic Liquid Crystal Displays
Authors: Vleeschouwer Herbert De , Asselt Alwin Verschueren , Els Alexander Els Alexander , Stefaan Vermael Stefaan Vermael , Kristiaan Neyts Kristiaan Neyts , Herman Pauwels Herman Pauwels
Published: October 2002

Leakage current measurements are performed on prototype cells revealing an S-shaped current versus voltage curve. This result indicates the presence of ion generation and recombination in the liquid crystal bulk. The compensation of the electrical field and the saturation current are related to the alignment layer thickness and to the temperature. The slope of the I–V curve corresponds with Onsager's dependency of the ion generation. The time dependency of the current is modelled by an empirical fitting of the generation constant. A complete theoretical model is thus presented. The simulation fits with the measurements and gives a profound insight in the long term ion transport in nematic liquid crystal displays.
Characteristics of Very-High-Frequency-Excited SiH4 Plasmas using a Ladder-Shaped Electrode
Authors: Takeuchi Yoshiaki , Mashima Hiroshi , Murata Masayoshi , Uchino Satoshi , Kawai Yoshinobu
Published: October 2002

A very-high-frequency (VHF) -excited SiH4 plasma was generated using a ladder-shaped electrode where the discharge frequency ranged up to 100 MHz and the plasma parameters were measured using a heated Langmuir probe. In the SiH4 plasma as well as in the H2 plasma, it was confirmed that when the discharge frequency is increased, the electron density increases while the electron temperature decreases. The electron density obtained at 100 MHz was 1.7×1010 cm-3, which is sevenfold that at 13.56 MHz. It was also found that the electron temperature tends to increase with increasing gas pressure in the SiH4 plasma at a very high frequency of 100 MHz.
Gas Residence Time Effects on Plasma Parameters: Comparison between Ar and C4F8
Authors: Doh Hyun-Ho , Horiike Yasuhiro
Published: October 2002

The effects of gas residence time on the plasma parameters such as the ion current density (ICD) and hot-electron population have been studied in an inductively coupled plasma (ICP) system employing Ar and C4F8, separately. The fluorocarbon ionic and radical compositions with respect to the residence time have also been studied in the case of C4F8 ICP. The ion current density with the gas residence time shows a totally opposite behavior in Ar and C4F8 discharge. To elucidate this phenomenon, the hot-electron population with the gas residence time was investigated. The measurement of hot electron population reveals that the energetic electrons are generated much more in Ar discharge but they become less in the case of C4F8 with the decrease of the residence time. Moreover, hot electron population is 3–6 times higher in Ar discharge than in C4F8. In the C4F8 ICP system, the number of all CF
x
(x=1–3) radicals increases but the intensity of the fluorocarbon ionic species [CF
x

+ (x=1–3)] except for the high-order molecular ions decreases with the decrease of the residence time. All of the diagnostic results show that the effects of the gas residence time must be considered by the characteristics of the plasma parameters as well as the effect of the adsorption and the desorption rate in the etch process.
Empirical Model of Flicker in Silicon Light Valves
Authors: Huang Ho-Chi , Cheng Po-Wing
Published: October 2002

We have performed systematic characterizations of flicker in silicon light valves. It was found that temperature was the most important factor associated with flicker. Temperature could assist conduction mechanisms in silicon light valves and enhance the flicker accordingly. The major conduction mechanisms of flicker in silicon light valves were residual DC charge on the silicon surface, the voltage holding capability of a liquid crystal cell, the voltage holding capability of a silicon panel, light leakage and parasitic capacitor coupling. Major causes of these flicker mechanisms were identified through systematic characterizations. An empirical model of flicker was proposed with quantitative experimental data and theories. Among these conduction mechanisms, temperature could boost the voltage holding capabilities of a silicon panel to become the most dominant cause of flicker when the temperature was above 40°C. At temperatures below 30°C, the other four conduction mechanisms contributed to the flicker in different ways. Minimization of flicker could be achieved through materials and device optimization.
Integration of Terraced Laser Diode and Garnet Crystals by Wafer Direct Bonding
Authors: Yokoi Hideki , Waniishi Takashi , Mizumoto Tetsuya , Shimizu Masafumi , Sakurai Kazumasa , Futakuchi Naoki , Nakano Yoshiaki
Published: October 2002

Integration of a semiconductor laser diode and an optical isolator was studied using the wafer direct bonding technique. A terraced laser diode was fabricated by reactive ion etching using CH4/H2/O2 gas. A smooth and vertical mirror facet was obtained by adjusting the flow rate of the etchant gas. Room-temperature pulsed laser operation was achieved in the laser diode with one cleaved facet and the second facet formed by reactive ion etching. The terraced laser diode was integrated with garnet crystals by wafer direct bonding. Room-temperature pulsed laser operation was confirmed after the bonding process.
Femtosecond Laser Micromachining of Si-on-SiO2 for Photonic Band Gap Crystal Fabrication
Authors: Li Ming , Liu Xinbing
Published: October 2002

Femtosecond laser pulses at 387 nm were used to machine Si-on-SiO2 substrates for photonic band gap crystals. With 387 nm ultrashort near-UV pulses, we obtained holes as small as 160 nm, which is smaller than one half of the laser wavelength with only conventional optics. Moreover, a pitch size of 420 nm is also obtained in Si-on-SiO2, which meets the spacing requirement for today's telecommunication frequency -1550 nm. Ultrafast laser micromachining is fast and versatile, thus it is a powerful tool for in-situ microstructure operations such as nanostructuring, repairing, and production industrial applications.
Micro Bubble and Sonoluminescence
Authors: Hideto Mitome Hideto Mitome
Published: October 2002

The author reviews the interaction of micro bubbles with ultrasound. First, the action of acoustic radiation pressure on bubbles is discussed in contrast with that on small particles noting the concept of Bjerknes force, resonant bubbles and nonlinear oscillation of bubbles. In the past decade, sonoluminescence, light emission from a single oscillating bubble, attracted attention of researchers because of its strange characteristics. A short history of sonoluminescence and its characteristics are summarized based on bubble motion in a sound field. Lastly, industrial and medical applications of extreme environment generated by collapsing micro bubbles are discussed as promising technology in the new century.
Near-Infrared Photoluminescence and Electroluminescence of Neodymium(III), Erbium(III), and Ytterbium(III) Complexes
Authors: Kawamura Yuichiro , Wada Yuji , Yanagida Shozo
Published: October 2002

Tris(dibenzoylmethanato)(monobathophenanthroline)lanthanide(III) complex [Ln(DBM)3 bath (Ln: Nd, Er and Yb)] both in solutions and thin films at room temperature showed narrow band photoluminescence (PL) due to the f–f transitions in the near-IR region: 890, 1070 and 1350 nm for Nd(III), 980 and 1540 nm for Er(III), and 985 nm for Yb(III). The PL efficiencies in solution were determined [φPL=3.3×10-3 for Nd(III), 7.0×10-5 for Er(III), and 1.4×10-2 for Yb(III)]. Organic electroluminescent (EL) devices having the structure of glass substrate/indium-tin oxide/N,N
′-diphenyl-N,N
′-di(m-tolyl)benzidine/Ln(DBM)3bath(Ln: Nd, Er and Yb)/bathocuproine/Mg:Ag/Ag were fabricated, giving the EL bands around 900–1600 nm at room temperature. The external near-IR EL efficiencies at low current density were estimated by comparing with that of the Eu(III) device having the same structure. The saturation of near-IR EL intensity observed at the high current density suggested that the near-IR EL should suffer the T–T annihilation.
Equivalent Representation of Mode Coupling in Two-Dimensional Bulk Waves Using Unitary Matrix with 4 ×4 Elements
Authors: Michio Ohki Michio Ohki , Kohji Toda Kohji Toda
Published: October 2002

Mode coupling in two-dimensional bulk waves confined in a two-dimensional rectangular resonator is discussed using a 4 ×4 unitary matrix and Neumann series; this differs from the conventional methods which involve a coupling between N resonance systems solved as an eigenvalue problem of an N ×N matrix, which becomes complicated when the loss phenomenon is included or when the value of N increases. The coupling is dealt with by considering the energy distribution between the two modes with unitarity or energy conservation. The 4 ×4 unitary matrix is adopted to distinguish between self-coupling and mutual coupling, and the confinement of wave energy due to the multiple reflection is represented by the Neumann series. Simple and unified matrix algebra gives the resonance characteristics when the mode coupling occurs in an infinite number of degrees of freedom.
Viscosity Measurement of Nematic Liquid Crystal Using Shear Horizontal Wave Propagation in Liquid Crystal Cell
Authors: Masaru Inoue Masaru Inoue , Katsumi Yoshino Katsumi Yoshino , Hiroshi Moritake Hiroshi Moritake , Kohji Toda Kohji Toda
Published: October 2002

Propagation characteristics of a shear horizontal (SH) wave in a cell structure containing a nematic liquid crystal layer are described on the basis of numerical analysis and experimental results. The SH wave propagation is described by the numerical analysis result for the nematic liquid crystal as an anisotropic liquid, considering the director angle of the liquid crystal. The temperature dependence of effective viscosities of a typical nematic liquid crystal N-(p-methoxybenzylidene)-p'butylaniline)] (MBBA) is evaluated from the measurement of the phase velocity change of the SH wave in the liquid crystal cell.
Step-Down Piezoelectric Transformer for AC-DC Converters
Authors: Mitsuru Yamamoto Mitsuru Yamamoto , Yasuhiro Sasaki Yasuhiro Sasaki , Atsushi Ochi Atsushi Ochi , Takeshi Inoue Takeshi Inoue , Sunao Hamamura Sunao Hamamura
Published: October 2002

In this paper, a new piezoelectric transformer for AC-DC converters is presented. This piezoelectric transformer, with a multilayered construction in the thickness direction, operates in a fundamental contour-extensional vibration mode. Output impedance is designed to be low, approximately several tens of ohms. First, we simulated the design of the transformer using equivalent circuit method and finite element method (FEM) analyses. We calculated that the transformer could work with an eficiency higher than 95% and a gain of 0.4 at a resonant frequency of 140 kHz. Second, we fabricated a transformer of 14 mm length, 14 mm width and 5.8 mm thickness and examined it. It was found that the transformer exhibited a 0.4 gain and 96.3% efficiency at 135 kHz, when the temperature increase was 30°C. We applied the transformer to the fabrication of an AC-DC converter using a half-bridge zero voltage switching circuit, and examined the converter. It was found to achieve good line and load regulation, and the highest efficiency of 90% was obtained for V
in=80–120 Vac, V
out=13 Vdc, and I
out= 0.8–1.5 A.
Modal Analysis of Hollow Cylindrical Guided Waves and Applications
Authors: Nishino Hideo , Takashina Sunao , Uchida Fukutoshi , Takemoto Mikio , Ono Kanji
Published: October 2002

Dispersion behavior of guided waves in hollow cylinders (cylindrical waves) was evaluated theoretically and experimentally. Observed dispersion behavior suggests an assignment, different from the traditional one, of longitudinal (L-), flexural (F-) and torsional (T-) modes which are consistent with Lamb waves and shear-horizontal (SH) mode waves. The L- and F-modes of the cylindrical waves have characteristics which are asymptotic to Lamb waves and to waves in a solid cylinder. Experimentally, wide-band cylindrical waves in aluminum pipes were generated using a laser-ultrasonic method. Wavelet transform of the cylindrical wave signals was utilized for time-frequency analysis in order to compare them with the theoretical dispersion curves. For the L(0, 1), F(1, 1), F(2, 1), L(0, 2), F(1, 2) and F(2, 2) modes of the cylindrical waves, which were efficiently excited, theoretical and experimental dispersion curves agree with each other.
Design of the Double Ultrasonic Transducer for Nonlinearity Measurement of Acoustic Waves
Authors: Kim Jung-Ho , Kim Chun-Duck , Kim Moo-Joon , Ha Kang-Lyeol , Chubachi Noriyoshi
Published: October 2002

In this paper, we propose and design a new ultrasonic probe that can effectively measure both the fundamental and the second-harmonic waves simultaneously. The transducer consists of two bonded Pb(Zr, Ti)O3 (PZT) disks with the same properties and the same polarization, and a variable capacitor is connected to the electric terminals of one of the PZT disks for the simulation and experiment. It is shown that the second harmonic as well as the fundamental component can be efficiently received by controlling the capacitance. The result of the nonlinearity parameter B/A for ethanol measured using the double ultrasonic transducer shows good agreement with the reference value, and the B/A value for soybean is obtained.
Equivalent Circuit Representation of a Flexurally Vibrating Bar with Axial Force
Authors: Sugawara Sumio , Masuda Kazutoshi , Tomikawa Yoshiro
Published: October 2002

The equivalent circuit for a flexurally vibrating thick bar with axial force is represented by impedance analogy. The effect of axial force is not represented as terminal pairs on the circuit, but is included in its matrix elements. It is shown that the resonant frequency equations under various end conditions can be easily obtained from the circuit. As an example, the resonant frequency change of the slender bar with both clamped ends by axial force was analyzed, and confirmed experimentally. The relationship between the change rate of the resonant frequency and axial force is linear. The value of the change rate for the first mode is larger than that for the second mode, and decreases as the thickness and width become larger. Moreover, the value increases with the length. These results will be utilized for the development and design of a force sensor based on the principle of the resonant frequency change by axial force.
Monitoring of Si Molecular-Beam Epitaxial Growth by an Ellipsometric Method
Authors: Yoshioka Yoshifumi , Ikuta Tetsuya , Taji Toshiya , Mizobata Kouzou , Shimura Takayoshi , Umeno Masataka
Published: October 2002

Ellipsometric measurements were applied to investigate Si homoepitaxial growth by molecular-beam epitaxy on a Si(111) substrate, and the changes in film thickness and optical parameters were monitored. The reflection high-energy electron diffraction (RHEED) intensity oscillation monitoring method was also employed for comparison. In the epitaxial growth mode, Ψ and Δ values showed only a small spiral variation and the analyzed optical constants were nearly the same as those of single-crystal Si. The film thickness obtained by the ellipsometric method exhibited good agreement with that obtained by RHEED oscillation as well as by a quartz crystal monitor. Thus, it was shown that the film thickness monitoring by ellipsometry is useful even for the Si/Si homoepitaxial growth with a step flow mechanism, where the RHEED oscillation monitoring method is not available.
Ultrasonic Joining of Silicon Nitride Plates Without an Adhesive Material Using a 19 kHz Vibration System
Authors: Iijima Mitsuo , Watanabe Yuji
Published: October 2002

In recent years, we have attempted ultrasonic ceramic joining for the purpose of extending the application field of ultrasonic joining. By devising a vibration system, the authors have attempted ceramic ultrasonic joining by which a metal becomes an intermediate material. In this method, however, the high temperature resistance and strength of the joint are dependent on the melting point and strength of the metallic material. Therefore, in this study, we attempted ultrasonic joining of silicon nitride (Si3N4) plates without using any intermediate material. The experimental result showed that ultrasonic joining was possible without using the intermediate material. The maximum joint strength was 33 MPa and the joining time required was about 10 s.
Near-Field Distribution of Radial Line Slot Antenna for Surface-Wave-Coupled Plasma Generation
Authors: Yamamoto Tetsuya , Ono Mitsuhiro , Ando Makoto , Goto Naohisa , Ishii Nobuo , Yasaka Yasuyoshi
Published: October 2002

In plasma processing systems for large-size wafers, quick evacuation of reaction gas by making the process space narrow is urgently required to realize higher productivity and better quality for microelectronic devices. Wafers must be placed close to the antenna aperture in this case. A radial line slot antenna (RLSA) for surface-wave-coupled plasma (SWP) is a promising candidate to this end. A novel slot arrangement in the aperture, consisting of densely arrayed transverse slots, was fabricated and tested. A uniform, high-density (3×1011 cm-3) and large-area plasma at low electron temperature has already been realized in previous experiments. It dispenses with the DC magnetic fields required in ECR systems. For further development of the slot design, as well as the mechanism determination of plasma generation, in this paper we evaluate the electromagnetic near fields of SWP-RLSAs. As the first step, antennas in free space without the plasma as well as a glass vacuum window, are analyzed using a periodic array model. The predicted near-field distribution is compared with those of previous experiments and a reasonable agreement is reported.
Three-Dimensional Imaging Using Spherical Ultrasound Wave Generated by Laser-Induced Breakdown
Authors: Yoshihiro Yasumuro Yoshihiro Yasumuro , Atsunori Machida Atsunori Machida , Motonori Doi Motonori Doi , Osamu Oshiro Osamu Oshiro , Kunihiro Chihara Kunihiro Chihara , Daisuke Ueda Daisuke Ueda , Tadao Sugiura Tadao Sugiura , Satoshi Kawada Satoshi Kawada
Published: October 2002

In this paper, we propose a new framework of ultrasonic (US) three-dimensional (3D) imaging, introducing laser-induced breakdown (LIB) as an acoustic source. LIB is a phenomenon in which a substance is transformed to a plasma by a pulsed laser beam. LIB explosively emits a variety of energies such as heat, light and sound which also includes pulsed ultrasound. Emitted US waves have suitable characteristics for US 3D imaging in terms of low directivity, enabling a wide view and sharply pulsed waves. Utilizing these characteristics, we attempt to apply the synthetic aperture method for frontal 3D imaging in a real-time process. Experimental results show that even sparsely arrayed sensors allow a wider frontal view than that allowed in the case using existing transducers.
Development of a New Diagnostic System for Human Liver Diseases Based on Conventional Ultrasonic Diagnostic Equipment
Authors: Kikuchi Tsuneo , Nakazawa Toshihiro , Harada Akimitsu , Sato Hiroaki , Maruyama Yukio , Sato Sojun
Published: October 2002

In this paper, the authors present the experimental results of using a quantitative ultrasonic diagnosis technique for human liver diseases using the fractal dimension (FD) of the shape of the power spectra (PS) of RF signals. We have developed an experimental system based on a conventional ultrasonic diagnostic system. As a result, we show that normal livers, fatty livers and liver cirrhosis can be identified using the FD values.
Transmission-Type Ultrasonic Inverse Scattering Computed Tomography Using Observation Data on Circular Arc Points
Authors: Akira Yamada Akira Yamada , Katsuhiko Kurita Katsuhiko Kurita
Published: October 2002

Transmission-type inverse scattering computed tomography for reconstructing both sound speed and attenuation images using the observation data along circular arc points was explored. To date, there has been difficulty in reconstructing the attenuation image, but not the sound speed image, since the attenuation contrast of tissue is very low compared to that of sound speed. Hence, a high-precision data observation, being tolerant to measurement noise and avoidable of spurious edge wave interference, is inevitable to realize stable attenuation image reconstruction. To this end, the present study revealed that circular arc observation method was highly superior to the conventional straight line observation. The optimum determination of circular-observation distance and angular-observation aperture was investigated through numerical examination of the attenuation image. Furthermore, an experimental phantom examination assuming actual parameters in tissues was performed. As a result, the validity of the present method was demonstrated.
High-Power 1.5 µm InGaAsP/InP Strained Quantum Wells Integrated Superluminescent Light Source with Tilted Structure
Authors: Liu Yang , Song Junfeng , Zeng Yuping , Wu Bin , Zhang Yuantao , Qian Ying , Sun Yingzhi , Du Guotong
Published: October 2002

Based on our original idea about monolithic integration of the superluminescent diode (SLD) with a semiconductor optical amplifier (SOA), the axis of the current injection area was tilted. High superluminescent power (more than 200 mW) at 1.5 µm was obtained by optimizing the tilted device structure. No lasing mode was discovered within the range of measurement. In addition, it was discovered that the tilted integrated device had the function of lasing suppression, to some extent.
Nitrogen Profile in SiOxNy Prepared by Thermal Nitridation of Ozone Oxide
Authors: Kaoru Nakajima Kaoru Nakajima , Kenji Kimura Kenji Kimura , Akira Kurokawa Akira Kurokawa , Shingo Ichimura Shingo Ichimura , Hisashi Fukuda Hisashi Fukuda
Published: October 2002

Ultrathin silicon oxynitride films are prepared by ozone and thermal oxidation of Si(001) followed by rapid thermal nitridation. The nitrogen depth profiles in these films are measured by high-resolution Rutherford backscattering spectroscopy. The observed nitrogen profiles are essentially similar, having a peak at the SiO2/Si interface, although the interface strain in the ozone oxide is known to be much smaller than that of the thermal oxide. This indicates that the interface strain relaxation due to the nitrogen incorporation is not responsible for the nitrogen accumulation at the interface.
Fully Integrated Spiral-type Microtransformers on a Silicon Substrate
Authors: Park Jae Y. , Bu Jong U.
Published: October 2002

Surface micromachining techniques have been utilized to realize microtransformers on a silicon substrate for being integrated with a multi-chip package, allowing compact integration with chips, complementary metal-oxide-semiconductor (CMOS) circuits, sensors, and other components. Two different microtransformers comprised of two-layer vertically stacked spiral-type copper conductor lines and permalloy magnetic cores have been designed, fabricated, and characterized. Low temperature processes have been chosen for fabricating these microtransformers. The fabricated microtransformers have been tested and compared for finding out better geometries for integrated microtransformers. Electroplated thick permalloy cores and copper coils have been utilized for obtaining better performance characteristics in the intermediate frequency range. The fabricated microtransformers have a turn ratio of 1, coupling coefficient of 0.85, dc resistance of 3.3 Ω, and gain characteristics of -5 dB, respectively. Since these devices have also high current carrying capability (up to 2A steady DC current), they are suitable for integrated power converter applications.
Electroluminescence of β-FeSi2 Light Emitting Devices
Authors: Lourenço M. A. , Butler T. M. , Kewell A. K. , Gwilliam R. M. , Kirkby K. J. , Homewood K. P.
Published: October 2002

Ion beam synthesised β-FeSi2 light emitting devices have been fabricated by ion implantation of iron into pre-grown abrupt silicon p–n junctions. Several samples were fabricated by varying the implant conditions and the junction characteristics (layer thickness and doping concentration). Light emission at ∼1.5 µm was obtained from all devices but the intensity decreased with increasing temperature. The electroluminescence quenching was found to depend on both the iron implant conditions and the characteristics of the p–n junction.
Direct-Gap Reduction and Valence-Band Splitting of Ordered Indirect-Gap AlInP2 Studied by Polarized Piezoreflectance
Authors: Yeh Wen-Chun , Lin Chi-Jen , Huang Ying-Sheng , Chang Chih-Song , Tiong Kwong-Kau
Published: October 2002

The order-dependent direct-gap reduction and valence-band splitting in spontaneously ordered indirect-gap AlInP2 are determined by polarized piezoreflectance spectroscopy at room temperature. The experimentally deduced values of the ratio of band-gap reduction to crystal field splitting for the perfectly ordered alloys, ζ=-ΔE
g
(1)/ΔCF
(1)=1.15, and the ratio of band-gap reduction to the ordering change of spin-orbit splitting between the perfectly ordered and random alloys, ξ=-ΔE
g
(1)/[ΔSO
(1)-ΔSO
(0)]=8.24, are in good agreement with the recent theoretically calculated value of 1.13 and 13.5, respectively, by [S. H. Wei and A. Zunger. Phys. Rev. B 57, (1998) 8983] but are much larger than those of the previous report by [M. Schubert et al..: Phys. Rev. B 54 (1996) 17616] using dark-field spectroscopy.