bluuebunny/crossref_metadata_2025 huggingface dataset:
SiH3CH3+F: A Potential Reaction System for Preparing Uniform SiC Film Predicted by Using an Ab Initio Molecular Orbital Method
Authors: Sato Kota , Yano Daisuke , Iwabuchi Susumu , Hirano Tsuneo , Koinuma Hideomi
Published: October 2002

Abstraction reactions and substitution reactions on SiH3CH3 by an F atom were studied on the basis of an ab initio molecular orbital method. The structures and the total energies of the reactants, the transition states, and the products were obtained at a third order Møller Plesset (MP3)/D95**//Har-tree Fock (HF)/D95** and an MP3/6-21+G//HF/6-21+G level. The activation energies for hydrogen abstractions from Si and C were -5.20 kcal/mol and 1.65 kcal/mol, respectively, while those for substitution reactions caused by Si attack and C attack were 20.96 kcal/mol and 25.58 kcal/mol, respectively. The activation energies for hydrogen abstraction reactions which retained an Si–C bond were much lower than those for substitution reactions by which an Si–C bond was cleaved. Thus, the SiH3CH3+F system was proven to be promising for preparing a uniform SiC film at relatively low temperatures.
Spectroscopic Characterization of Low-Temperature Grown GaAs Epitaxial Films
Authors: Tani Masahiko , Sakai Kiyomi , Abe Hajime , Nakashima Shin-ichi , Harima Hiroshi , Hangyo Masanori , Tokuda Yasunori , Kanamoto Kyozo , Abe Yuji , Tsukada Noriaki
Published: October 2002

Femtosecond time-resolved reflectance and Raman scattering studies have been made on GaAs epitaxial layers grown at temperatures between 200 and 300° C and subsequently annealed. A subpicosecond carrier lifetime (∼0.25 ps) has been measured for a sample grown at 250° C and annealed at 600° C. Raman measurements using a back scattering geometry show a strong TO phonon band for samples grown at 200° C and 250° C, while it is absent for samples grown at 275 and 300° C. The band width of the LO band increases with decreasing growth temperature. A phonon band corresponding to As precipitates is also observed at 200 cm-1 for samples grown at 200 and 250° C. A strong correlation is found between the measured carrier lifetime and Raman profile.
Effects of Surface Orientation and Molar Ratio of (SrxCay)F2 Films on Electrical Characteristics of Metal/Fluoride/GaAs Structures
Authors: Yamamoto Masahiko , Negishi Tohru , Jotaro Igarashi Jotaro Igarashi , Hideaki Ikoma Hideaki Ikoma
Published: October 2002

The (Sr

x

Ca

y

)F2 (x:y=3:7, 1:1 and 7:3)/GaAs (100), (111)A and (111)B metal-insulator-semiconductor (MIS) structures were investigated by the capacitance-voltage (C-V) measurements and the X-ray photoelectron spectroscopy (XPS) to study the effects of the surface orientation of GaAs and the mol ratio (x:y) of the fluoride films on the quality of the interface between these fluoride films and GaAs. The fluoride films were deposited on the GaAs substrates by co-evaporating SrF2 and CaF2 powders in a vacuum of 1–2×10-6 Torr. The C-V measurements indicated that the best result was obtained for the (SrCa)F2(Sr:Ca=1:1 in molar ratio)/GaAs (100) surface and the next, for the (Sr0.3Ca0.7)F2/GaAs (111)B surface. Very poor C-V characteristics were obtained for the GaAs (111)A surface for all the molar ratios of Sr and Ca studied here. It is concluded that the lattice matching between the fluoride film and GaAs plays an important role in the formation of a good-quality interface for the GaAs (100)-oriented surface, while the presence of a large amount of stable Ca–As bonds is more effective for GaAs (111)-oriented surfaces. The XPS data indicated that the native oxide of GaAs, which is mainly composed of As2O3 and Ga2O3, was removed upon evaporation of the fluoride films. Sr is considered to reduce the native oxide and was oxidized itself. Sharp peaks of the XPS data were observed and the binding energies of these peaks varied nearly linearly with the molar ratio of Sr and Ca. These indicate that stoichiometric (Sr

x

Ca

y

)F2 films were formed even by the conventional vacuum-evaporation technique. Elemental Sr and/or Ca was observed to exist at the interface with GaAs.
High-Mobility Inverted Modulation-Doped GaAs/AlGaAs Heterostructures
Authors: Saku Tadashi , Yoshiji Horikoshi Yoshiji Horikoshi , Seigo Tarucha Seigo Tarucha
Published: October 2002

High-quality inverted GaAs/AlGaAs modulation-doped heterostructures have been grown by MBE. An AlAs/GaAs superlattice buffer layer is grown below the AlGaAs spacer layer to improve the morphology at the inverted heterointerface. An atomic layer doping and a thick spacer layer are adopted to alleviate the scattering by ionized donors. The observed electron mobility at 1.5 K is 4.3×106cm2/ Vs at a 2D electron density of 2.8×1011/ cm2. Two 2D electron channels; one formed at the inverted interface and the other at the normal interface are found to be operative in the observed characteristic. The electron mobility in the inverted channel is estimated to be as high as 4.9× 106cm2/ Vs at an electron density of 2.2×1011/ cm2, while, in the normal channel, it is 2.1×106cm2/ Vs at a density of 6×1010/ cm2.
Effect of Ionized Impurities at Heterointerface on Concentration and Mobility of Two-Dimensional Electrons in Selectively Doped Heterojunction Structures
Authors: Kadoya Yutaka , Noge Hiroshi , Sakaki Hiroyuki
Published: October 2002

The concentration N
S and the low-temperature mobility µ of two-dimensional electron gas in GaAs/AlGaAs selectively doped heterojunctions have been studied theoretically and experimentally for the case where ionized impurities are present at heterointerfaces. It is found that N
S scarcely changes when the concentration N
IF of interfacial impurities is below 1×1011 cm-2, but it rapidly disappears at higher values of N
IF if the impurities are of the acceptor type. In contrast, the mobility is found to decrease substantially even when N
IF is as low as 109 cm-2. Based on these results, a quantitative guideline is drawn on the acceptable level of contamination in ultrahigh-vacuum wafer processings including molecular beam epitaxial regrowth.
Effects of Vacancies on the Electrical Characteristics of Metal/GaAs Schottky Contacts “A Quantitative Model”
Authors: Jyi-Jhy Sze Jyi-Jhy Sze , Huang-Chung Cheng Huang-Chung Cheng
Published: October 2002

An analytical method, proceeding by solving the Poisson equations both in the metal and in the GaAs substrate, is proposed to study the effects of the vacancies on the electrical characteristics of metal/GaAs contacts. A quantitative model used to calculate the effective charges contributed by the vacancies is developed here for the first time. From this analysis, it is found that the phenomenon of the Fermi level pinning in metal/GaAs contacts can be explained by the existence of vacancies at the metal/GaAs interface. Because of the amphoteric property of the vacancies in GaAs, the Fermi level is pinned at a level, called the “neutral level” of the vacancy, at which the effective charge introduced by the vacancies is zero. The change of the Fermi level pinning positions observed in previous experimental results for p and n GaAs can be ascribed to the change of vacancy types due to the nonstoichiometry in the GaAs substrate.
Coulomb Blockade of Two Quantum Dots in Series
Authors: Sakamoto Toshitsugu , Hwang Sungwoo , Nihey Fumiyuki , Yasunobu Nakamura Yasunobu Nakamura , Kazuo Nakamura Kazuo Nakamura
Published: October 2002

A Coulomb blockade of two quantum dots in series has been investigated. Despite the two dots being connected by tunneling barrier, no electrostatic interaction is observed in the conductance. This result is consistent with numerical calculations performed by using experimental parameters. The interaction is reduced in a system where the ratio of inter-dot capacitance and the total capacitance is small.
Effects of Heat Treatment on Bonding Properties in InP-to-Si Direct Wafer Bonding
Authors: Hiroshi Wada Hiroshi Wada , Takeshi Kamijoh Takeshi Kamijoh
Published: October 2002

Effects of heat treatment on bonding properties, which include bonding strength, photoluminescence intensity, and electrical conduction through the interface, have been investigated in InP-to-Si direct wafer bonding for the first time. Bonding strength and electrical conduction were found to be improved by heat treatment. On the other hand, a degradation of photoluminescence intensity was observed with high-temperature treatment.
Influence of Preparation Conditions on Decay of Second-Harmonic Generation in Polyurea Thin Films Prepared by Vapor Deposition Polymerization
Authors: Segi Takeshi , Hikita Masayuki , Yasuo Suzuoki Yasuo Suzuoki , Teruyoshi Mizutani Teruyoshi Mizutani
Published: October 2002

Aromatic polyurea (PU) films were fabricated by vapor deposition polymerization using 4,4′-diphenylmethane diisocyanate and 4,4′-diaminodiphenylmethane. To investigate the influence of preparation conditions upon decay of optical second harmonic generation (SHG) after poling, two kinds of films were deposited: PU(No. 1) involving less residual isocyanate groups and PU(No. 2) with a smaller molecular weight and more residual isocyanate groups. PU(No. 2) showed significant decay, while PU(No. 1) did not. The results of IR spectrometry and differential scanning calorimetry indicated that the formation of urea bonds during poling of as-deposited films was due to reaction of the isocyanate groups with amino groups in PU(No. 1) and with water in PU(No. 2). We ascribed the SHG decay in PU(No. 2) to free volume formation by elimination of or plasticizing by CO2 generated during the above reaction, and/or to the smaller molecular weight.
Tunable Dye Laser with Variable Pulse Width for Investigation of Nonlinear Optical Effect
Authors: Shigetaka Yoshikawa Shigetaka Yoshikawa , Totaro Imasaka Totaro Imasaka
Published: October 2002

A quenching cavity is constructed for pulse shortening in a conventional grazing-incidence dye laser. The quenching beam is further introduced into two succeeding preamplifiers to suppress amplification of spontaneous emission from the oscillator. The pulse width (14 ns) obtained without a quenching cavity is reduced to 1.8 ns by quenching the oscillating beam. In this system, the pulse width can be switched instantly by interrupting the beam path of the quenching cavity. The laser system is applied to generation of multicolor laser emission based on the two-color stimulated Raman effect. The efficiency is substantially improved by increasing the peak power, due to the nonlinear behavior of this effect.
Mechanical-Stress Induced Nd:YAG Active Quarter-Wave Plate
Authors: Ohmi Masato , Akatsuka Masanori , Ishikawa Koji , Naito Kenta , Yonezawa Yoshiyuki , Yamanaka Masanobu , Yasukazu Izawa Yasukazu Izawa , Sadao Nakai Sadao Nakai
Published: October 2002

A quarter-wave retardation was obtained by mechanically induced stress in a Nd:YAG laser rod and a laser gain of 1.15 at 1064 nm was obtained by pumping with a quasi-CW 300 W laser-diode array at 808 nm. The laser rod was held in a brass heatsink in which the mechanical stress was induced horizontally by means of screws. The effective quarter-wave area was measured to be 1 mm (vertical)×2 mm (horizontal) in the center of the 4 mm-diameter Nd:YAG rod by means of a newly constructed polarimeter.
Effect of Impact Ionization on Photoluminescence in Single- and Polycrystalline InP
Authors: Yoshimura Satoshi , Fujii Ken-ichi , Ohyama Tyuji , Otsuka Eizo , Yanagimachi Satoshi , Sakai Hiroyuki , Kobayashi Toshiki , Igaki Kenzo
Published: October 2002

Impact ionizations in single- and polycrystalline InP have been investigated by means of photoluminescence measurement with external electric and magnetic fields. From a line-shape analysis of photoluminescence spectra, electron distribution can be determined as a function of electric field. In both single- and polycrystalline InP, each onset point of a rapid increase of electron temperature shows a good agreement with each threshold electric field of impact ionization. In single-crystalline InP, the suppression of electron temperature due to two transverse acoustic phonon emissions is observed between 6 V/cm and 11 V/cm, in spite of no observation of similar structures in DC measurement. In polycrystalline InP, on the contrary, such a suppression of electron temperature is not be observed. This indicates that photoluminescence originates from grain boundary regions.
Characteristics of Right- and Left-Handed Polymer-Dispersed Cholesteric Liquid Crystals
Authors: Kato Kinya , Tanaka Keiji , Shinji Tsuru Shinji Tsuru , Shigenobu Sakai Shigenobu Sakai
Published: October 2002

The characteristics of right- and left-handed polymer-dispersed cholesteric (chiral nematic) liquid crystals (PDCLCs), which were fabricated using an enantiomeric pair of dopants, are confirmed to be basically the same. These have a memory effect that stably maintains both selectively reflective and transparent states. A stack of right-handed PDCLC cell and left-handed one with enantiomeric selective-reflection characteristics increases the reflectivity of a PDCLC reflective-color display. Furthermore, the observed selective reflection in the transparent state suggests that the operation of the PDCLC is based on a rearrangement of helical axes produced by the applied electric field.
Physics and Electronic Model of Deformed Helix Ferroelectric Liquid Crystal Displays
Authors: Jürg Fünfschilling Jürg Fünfschilling , Martin Schadt Martin Schadt
Published: October 2002

An electronic equivalent circuit is shown to completely describe both the electrical as well as the electrooptical properties of deformed helix ferroelectric (DHF) liquid crystal displays (LCDs). The static and the dynamic performance of DHF-LCDs are modeled using an equivalent circuit. The agreement between modeled gray-scale performance of DHF-LCDs and experiments is excellent. Several driving schemes derived from the equivalent circuit provide the full gray scale and render DHF-LCDs video-compatible at voltages below 13 V. Moreover, dc-free and thus ghost-image-free operation of DHF-LCDs is shown to be feasible with minimal loss of brightness. Capacitive coupling is shown to decrease the switching time of DHF-LCDs from 30 µs to 6 µs.
Anisotropic Thermal Diffusivity and Conductivity of YBCO(123) and YBCO(211) Mixed Crystals. I
Authors: Fujishiro Hiroyuki , Ikebe Manabu , Naito Tomoyuki , Noto Koshichi , Kohayashi Shuichi , Yoshizawa Shuji
Published: October 2002

The anisotropic thermal diffusivity α of the highly c-axis-oriented Y–Ba–Cu–O bulk superconducting crystals has been measured quasi-simultaneously with the thermal conductivity κ. The estimated values of the specific heat C by use of α and κ values parallel and perpendicular to the c-direction agreed with each other. In these crystals prepared by the modified melt texture growth (MMTG) method, fine Y2BaCuO5 particles are dispersed in the YBa2Cu3O7-
x

superconducting matrix phase. Based on a simple model, the thermal diffusivity and the specific heat of the YBa2Cu3O7-
x

matrix phase are separated using independently measured data of a Y2BaCuO5 polycrystal. The influence of Y2BaCuO5 particles on the thermal properties of the mixed crystals is discussed.
Phenomenological Interpretation of Excimer Laser Ablation of Single-Crystal Oxides (MgO, SrTiO3 and LaAlO3)
Authors: Hiroshige Ishibashi Hiroshige Ishibashi , Syuji Arisaka Syuji Arisaka , Kazuya Kinoshita Kazuya Kinoshita , Takeshi Kobayashi Takeshi Kobayashi
Published: October 2002

ArF excimer laser ablation of single-crystal oxide surfaces was investigated experimentally and theoretically. All specimens (MgO, SrTiO3 and LaAlO3) showed the presence of the threshold laser fluence for the ablation, possibly suggesting a thermal process. With increase in the fluence, etching rate increased sublinearly (downward bowing), and with further increase in the fluence, it increased almost linearly. To interpret the ablation mechanism and this nonlinearity, we proposed the ablation model, imposing two factors (effects of laser recoil pressure and optical reflection by the surface molten layer) to a previous dynamical model. Our proposed model explained the results well, and it was found that surface reflection by the molten layer is mainly responsible for the nonlinearity.
Optimization of Fabrication Parameters for Ge-Based Laminated Polarizer
Authors: Takahashi Hiroki , Hirotoshi Nagata Hirotoshi Nagata , Haruki Kataoka Haruki Kataoka
Published: October 2002

Ge laminated polarizers (Ge-LAMIPOLs) consist of Ge/SiO2 multilayers which are designed to absorb the TE mode of the light wave at 850 nm wavelength. Such Ge-LAMIPOLs facilitate the miniaturization of optical components, but they usually break during the fabrication processes because of their low mechanical strength. This problem is solved by insertion of Si binding layers at Ge and SiO2 interfaces. Further improvement is also achieved by reduction of the internal stresses in SiO2 layers, using the hydrogenation technique. The optical properties of the Ge-LAMIPOLs can be optimized by adjustment of the film deposition parameters. As the result, 250-µm-thick Ge/Si-LAMIPOLs with 54.0 dB extinction ratio and 0.37 dB insertion loss are successfully fabricated.
Structural and Electrical Properties of BaTiO3 Thin Films on Si(100) Substrate by Hydrothermal Synthesis
Authors: Cho Chae-Ryong , Shi Erwei , Jang Min-Su , Kim Se-Young Jeong
Published: October 2002

Crack-free, dense, polycrystalline BaTiO3 thin films have been synthesized on the Ti-deposited Si(100) substrates with various alkaline solutions of barium salts in the temperature range from 150° C to 280° C by hydrothermal method. The fabricated BaTiO3 thin films were found to have good adhesion on the substrate. The structural properties of thin films were investigated by X-ray diffraction (XRD) measurements. It was discussed about the crystallinity, surface morphology and interfaces of the resultant films depending on the reaction conditions such as time, temperature and solution. The thickness of the films increased with increasing temperature and time of reaction. The dielectric constants and the loss factor of thin film were measured in the frequency range from 100 Hz to 1 MHz at room temperature.
Multiplate Microwave Launcher for Producing High-Density Electron Cyclotron Resonance Plasmas
Authors: Masayoshi Tanaka Masayoshi Tanaka , Keisuke Nagao Keisuke Nagao , Hiroaki Shoyama Hiroaki Shoyama , Masaya Sugimoto Masaya Sugimoto , Yoshinobu Kawai Yoshinobu Kawai
Published: October 2002

A multiplate microwave launcher is developed to produce high-density electron cyclotron resonance plasmas. An electron cyclotron wave is successfully excited in the plasma, and the plasma production performance of the new launcher is comparable to that without shielding plates. This launcher allows high-power operations, and a density of 0.9 ×1013 cm-3 is obtained with a 2.45 GHz microwave at 5 kW input.
Electron Cyclotron Resonance Plasma in Multicusp Magnets with a Checkered Pattern
Authors: Mitsuru Maeda Mitsuru Maeda , Hiroshi Amemiya Hiroshi Amemiya
Published: October 2002

Electron cyclotron resonance (ECR) plasmas are generated by microwaves of 2.45 GHz in the pressure range of 0.1 to 0.01 Pa in a multicusp magnetic field by arranging SmCo magnets in a checkered pattern. Observations were made on the discharge property and the sustaining power. The plasma density and the electron energy distribution are measured by a Langmuir probe, and the ion spectra are measured by using a deflecting magnet. The characteristics are compared with those in the case of linear multicusp configuration and a discussion on the effects of the pattern of magnet arrangement is presented.
In Situ Chamber Cleaning Using Halogenated–Gas Plasmas Evaluated by Plasma-Parameter Extraction
Authors: Ino Kazuhide , Natori Iwao , Ichikawa Akihiro , Ohmi Tadahiro
Published: October 2002

We have demonstrated that high-efficiencyin situchamber cleaning with high gas flow rate is possible for SiO2reactive-ion-etching chambers by use of NF3plasma. The plasma of NF3gas, which has a low bond energy, can generate a high density of ions and radicals with low kinetic energy. The cleaning efficiency of several halogenated-gas plasmas has been evaluated based on extracted-plasma-parameter analysis. In this analysis important plasma parameters, such as ion energy and ion flux density, could be extracted from a simple rf waveform analysis at the excitation electrode. The accuracy of this technique has been confirmed with a newly developed rf-plasma direct probing method. Furthermore, the waveform of the rf-excited plasma potential has been directly measured by the rf-plasma probing method, which has clarified the relationship between the plasma potential and the rf electrode voltage.
Fabrication of Dye-Dispersed Optical-Quality Polymer Films by Coprecipitation of Cyanine Dye with Polymers
Authors: Takashi Hiraga Takashi Hiraga , Shigeru Takarada Shigeru Takarada , Norio Tanaka Norio Tanaka , Kikuko Hayamizu Kikuko Hayamizu , Tetsuo Moriya Tetsuo Moriya
Published: October 2002

3,3'-Diethyloxadicarbocyanine iodide (DODCI)-dissolved polymer powders were formed by coprecipitation of DODCI with polymers [poly(methyl methacrylate) (PMMA), poly(2-hydroxypropyl methacrylate) (PHPMA), etc.]. An acetone solution of DODCI in which a purified polymer was also dissolved was injected into a large amount of n-hexane. The precipitated powder in n-hexane was filtered and then dried under ultrahigh vacuum (UHV), and formed into a thin film by a hot-press method [Hiraga et al.: Chem. Lett. (1990) 2255]. Another method for preparing a powder by coprecipitation has successfully been developed using a vacuum process. The acetone solution of DODCI and polymer was directly injected into UHV from the liquid phase through a modified needle valve. Deposits were formed on a heat-controlled substrate through quick evaporation of a carrier solvent and they were hot-pressed to produce a thin transparent film. Condensed states of DODCI associates in these films have been analyzed by optical absorption and emission, small-angle X-ray scattering (SAXS), and NMR spectroscopy. A new technique to control the arrangement of dye associates in three-dimensional space has been proposed.
Temperature Dependence of Resonance Frequency of Shape-Memory Alloy Vibrated Photothermally
Authors: Inaba Seiki , Kumazaki Hironori , Horibe Masahiro , Hane Kazuhiro
Published: October 2002

The temperature dependence of the resonance frequency for a cantilever of a shape-memory alloy vibrated photothermally is described. The temperature coefficient of the resonance frequency of the alloy with memory for shape recovery was positive (2.0×10-2/° C) at a temperature near the martensitic transformation, in contrast with it being negative (-2.2×10-3/° C) for the alloy without memory. The technique of using one laser for both excitation and detection was adopted for determining the resonance frequency of the photothermal vibration.
Symmetric Magnetic Doublet Optics with Dynamically Compensated Field Aberration for Reducing Image Projection System
Authors: Nakasuji Mamoru , Hiroyasu Shimizu Hiroyasu Shimizu , Teruaki Okino Teruaki Okino
Published: October 2002

Aberrations calculated from the electron trajectories are compared with those estimated from the third-order aberration coefficients. Field curvature and radial and azimuthal distortions are consistent with each other for moderate radial value R. In order to optimize lens positions, a method is adopted which makes the lens condition under which the principal ray trajectory from the largest objective radius R
o crosses the optical axis at its normal position equal to that under which the trajectories diverging from the same R
o focus on the image. For the 50 cm object-to-image distance optics, residual aberrations are calculated through the trajectory calculation after the corrections of lens current, crossover and beam position. When the main and subfield sizes are 20 mm and 0.25 mm square, the residual field curvature, astigmatism, and radial and azimuthal distortions are 13.1 nm, 6.4 nm, 19 nm, and 8.35 nm, respectively, when the beam semiangle is 0.1 mrad, and the beam energy is 100 keV.
Stability of an Intense Pulsed Ion Beam during Successive Operation
Authors: Yoshiyuki Hashimoto Yoshiyuki Hashimoto , Mitsuyasu Yatsuzuka Mitsuyasu Yatsuzuka , Sadao Nobuhara Sadao Nobuhara
Published: October 2002

Stability of an intense pulsed ion beam during successive operation was studied experimentally with an inverse pinch ion diode. When an anode of metals or plastics is used for an ion source, the diode impedance and ion beam current were changed with every shot of operation. In the case of a copper anode, the ion current at 10 shots was reduced to one-half or one-third that at the first shot. Using a soda-lime glass ( Na2O·CaO·5SiO2), on the surface of which vacuum oil or Aquadag was coated as the ion source, the diode impedance and the ion current remained constant for 20–30 shots. With the vacuum oil ion source, the most dominant species of the ion beam was C3+, which has energy in the range of 150–200 keV. The current density of the ion beam at 120 mm behind the anode was about 100 A/cm2.
Effect of Starting Oxide Preparation on Electrical Properties of Reoxidized Nitrided and N2O-Annealed Gate Oxides
Authors: You-Lin Wu You-Lin Wu , Jenn-Gwo Hwu Jenn-Gwo Hwu
Published: October 2002

In this work, the effect of the starting oxides with and without postoxidation annealing on the reoxidized nitrided gate oxides (RNO) and N2O-annealed oxides (NAO) of metal-oxide-semiconductor (MOS) structures is discussed. It is found that both the radiation hardness and the constant-current stress resisitance can be improved if the starting oxides of the RNO and NAO are prepared without postoxidation annealing (i.e., fast pull-out from the furnace after the oxidation is completed). The improvements are related to the excess oxygen existing in the fast-pull-out oxides, which results in higher nitrogen incorporation in the oxide and reduces the strain gradient near the oxide interface.
Effect of Extinction on Neutron Diffraction Intensity of Silicon Single Crystals
Authors: Soejima Yuji , Aomine Nobutaka , Yamada Hiroshi , Tadanori Koga Tadanori Koga , Atsushi Okazaki Atsushi Okazaki
Published: October 2002

Anomalous temperature dependence previously observed in the neutron diffraction intensity of silicon single crystals has been re-examined. Single-crystal specimens in a special form are used in order to separate intensity contributions from two regions, with and without stresses. It is found that a stressed crystal shows an intensity increase with a broad peak around 200 K, while a stress-free one shows no anomaly.
Effects of O3 on Growth and Electrical Properties of Pb(Zr, Ti)O3 Thin Films by Photoenhanced Metalorganic Chemical Vapor Deposition
Authors: Shimizu Masaru , Fujisawa Hironori , Masataka Sugiyama Masataka Sugiyama , Tadashi Shiosaki Tadashi Shiosaki
Published: October 2002

Effects of O3 on the growth and electrical properties of Pb(Zr, Ti)O3 (PZT) thin films grown by photoenhanced metalorganic chemical vapor deposition (MOCVD) were investigated. Ferroelectric PZT films were obtained by both MOCVD and photoenhanced MOCVD using O3 at substrate temperatures ranging from 560° C to 625° C. The crystalline orientation, growth rate and growth temperature were not appreciably influenced by the use of O3 and photoirradiation. However, in the leakage current characteristics, an improvement in breakdown voltage by the use of O3 and photoirradiation was observed. From scanning electron microscope (SEM) observations, it was found that this improvement may be caused by the microscopic change in film structure.
Dislocation-Free Silicon on Sapphire by Wafer Bonding
Authors: Abe Takao , Ohki Konomu , Uchiyama Atsuo , Nakazawa Kazushi , Nakazato Yasuyuki
Published: October 2002

A 300 µm thick silicon wafer with oxide of 200 A in thickness which prevents void formation is sticked with a sapphire wafer at room temperature. To avoid the crack generation of a silicon wafer, a sticked wafer is heated up to 270C for 2 h and then a silicon layer is removed by grinding from 525 µm to 10 µm. To remove grinding damage and to further thin the silicon layer to 3 µm, KOH etching at 80C is used. Finally, to obtain the silicon layer having the thickness range of 0∼3 µm, polishing is employed. Although the high density of dislocations is observed in the 2.2 µm thick specimen annealed at 900C for 2 h, however, when the specimen is thinned down to 0.2 µm, silicon layer becomes dislocation-free, as confirmed by double crystal X-ray topography and transmission electron microscope (TEM). The thin oxide between silicon and sapphire plays an important role in the prevention of diffusion of boron as a contaminant at the bonded interface.
Uniform Ultra-Thin Pb(Zr,Ti)O3 Films Formed by Metal-Organic Chemical Vapor Deposition and Their Electrical Characteristics
Authors: Hiroshi Miki Hiroshi Miki , Yuzuru Ohji Yuzuru Ohji
Published: October 2002

Lead zirconate titanate ( Pb(Zr,Ti)O3) thin films were deposited on Pt films sputtered on thermally oxidized silicon wafers by metal-organic chemical vapor deposition (MOCVD). The films were less than 100 nm thick (typically 80 nm), thin enough for use in LSI semiconductor memories. The films were characterized by inductive coupling plasma mass spectroscopy and X-ray diffraction. Electrical measurements revealed that the films had good ferroelectric characteristics, with a low coercive voltage of 0.7 V. In addition, the non-switching dielectric characteristics for application to dynamic random access memory (DRAM) were equivalent to those of 0.4 nm of SiO2 with small leakage current.
Preparation of Pb(Zr,Ti)O3 Thin Films by Sol-Gel Technique
Authors: Tomoyasu Takusagawa Tomoyasu Takusagawa , Noriaki Yamada Noriaki Yamada , Terumasa Kato Terumasa Kato , Hajime Hattori Hajime Hattori , Teruyuki Matsui Teruyuki Matsui
Published: October 2002

In the preparation of P
b(Z
r,T
i)O
3 thin films by the sol-gel technique, the following procedures are involved: evaporation of solvents, thermal decomposition of organometallic compounds and crystallization. In this study, a thermodynamic approach was employed for the sol-gel technique, and the processing conditions were determined. For the processes of evaporation and thermal decomposition, the processing conditions were determined by applying Ozawa's method [Bull. Chem. Soc. Jpn. 38 (1965) 1881]. By means of both the X-ray diffraction technique and scanning electron microscope technique, crystal structure and surface morphology were evaluated. It was observed that the perovskite phase began to form at 500° C and was completed at 600° C. Moreover, a dense Pb(Zr,Ti)O3 thin film was also formed by annealing at 700° C for 120 min.
Dielectric Properties of (111) and (100) Lead-Zirconate-Titanate Films Prepared by Sol-Gel Technique
Authors: Aoki Katsuhiro , Fukuda Yukio , Ken Numata Ken Numata , Akitoshi Nishimura Akitoshi Nishimura
Published: October 2002

Dielectric properties of <111>- and <100>-preferred lead-zirconate-titanate (PZT) films with thickness of 400 nm prepared by the sol-gel deposition technique have been investigated from ferroelectric random-access memory (FRAM) and dynamic random-access memory (DRAM) application standpoints. Remanent polarization of <111>-preferred film is 23.5 µ C/cm2, which is somewhat higher than that of the <100>-preferred one. In contrast, the dielectric constant of <100>-preferred film is 730 which is larger than that of the <111>-preferred one. Thus, dielectric properties of PZT films are strongly dependent on their crystalline orientations. The <111>-preferred PZT film is appropriate for FRAM application and the <100>-preferred one is better for DRAM.
Influence of Buffer Layers on Microstructural and Ferroelectric Characteristics of Sol-Gel Derived PbZrxTi1-xO3 Thin Films
Authors: Doi Hidekazu , Atsuki Tsutomu , Soyama Nobuyuki , Sasaki Go , Yonezawa Tadashi , Ogi Katsumi
Published: October 2002

Pb(Zr, Ti)O3 (PZT) films with very thin PbTiO3 (PT) and ( Ba0.5Sr0.5)TiO3 (BST) buffer layers inserted between the film and Pt/Ti/ SiO2/Si substrate were synthesized by the sol-gel technique, and effects of variation in thickness upon microstructural and ferroelectric characteristics were investigated. Insertion of buffer layers was found to exert marked effects. PT buffer layers with thicknesses as thin as 2–4 nm yield PZT films with dense, homogeneous microstructure and good ferroelectric properties such as large remanent polarization, small coercive field and low leakage current densities. On the other hand, use of (2–4)-nm-thick BST buffer layers yields PZT films with dense microstructure and good dielectric properties such as increased permittivity, small coercive field and good leakage current characteristics. However, fatigue behavior of PZT films was not improved through insertion of PT or BST buffer layer.
Interaction of PbTiO3 Films with Si Substrate
Authors: Shichi Yushi , Tanimoto Satoshi , Goto Takaaki , Kuroiwa Koichi , Tarui Yasuo
Published: October 2002

An investigation was made of the reasons why ferroelectric PbTiO3 films are hard to grow on single-crystal Si substrates. PbTiO3 films were formed on Si(100) and MgO(100) single-crystal substrates, and X-ray photoelectron spectroscopy (XPS) was used to analyze the composition, chemical structure and oxidation state at the interface between the substrate and the film. It was found that lead, oxygen and silicon diffused markedly at the interface and that the PbTiO3 film experienced both a lead deficiency and Si diffusion. These phenomena are thought to be the reasons why it is difficult to form good PbTiO3 films on silicon substrates by chemical vapor deposition (CVD). It was observed that the addition of TiO2 and ZrO2 films at the interface with the silicon substrate reduced the diffusion of Si to the PbTiO3 film.
Electrical Properties of Ferroelectric BaMgF4 Films on Si Substrates
Authors: Koji Aizawa Koji Aizawa , Hiroshi Ishiwara Hiroshi Ishiwara
Published: October 2002

Electrical properties of (120)-oriented BaMgF4 films grown on n-Si(111) substrates have been investigated. It has been found that capacitance-voltage (C-V) characteristics of Al/ BaMgF4(120)/n-Si(111) structures show hysteresis loops with counterclockwise traces and that the memory window (the loop width) is proportional to the magnitude of the voltage applied to the film. It is speculated from these phenomena that the hysteresis loop is caused by remanent polarization of the BaMgF4 film. The value of the surface charge density, which was estimated from the memory window, was about 0.1 µ C/cm2 in a 330-nm-thick BaMgF4 film. It has also been found from C-V and current-voltage characteristics that typical dielectric constant and average resistivity of BaMgF4 films are 9.4 at 5 kHz and 3.6×1011 Ω· cm at a current density of 1 µ A/cm2, respectively.
Dielectric Properties of (BaxSr1-x)TiO3 Thin Films Prepared by RF Sputtering for Dynamic Random Access Memory Application
Authors: Kuroiwa Takeharu , Tsunemine Yoshikazu , Horikawa Tsuyoshi , Makita Tetsuro , Tanimura Jyunji , Noboru Mikami Noboru Mikami , Kazunao Sato Kazunao Sato
Published: October 2002

Dielectric properties of (Ba0.5Sr0.5)TiO3 and (Ba0.75Sr0.25)TiO3 thin films have been investigated, focusing on the effects of film structure and Ba/Sr compositions on the dielectric properties. Dielectric constant of the films increased with increasing grain size and with improvement in film crystallinity. For the 50-nm-thick films deposited at 660° C, the dielectric constant of 400 for the (Ba0.5Sr0.5)TiO3 film is larger than that of 320 for the (Ba0.75Sr0.25)TiO3 film. This indicated that dielectric constant is affected by the ratio of Ba/Sr composition. Leakage current density of less than 1×10-7 A/cm2 at 1 V and SiO2 equivalent thickness of 0.38 nm are measured at 120° C for 660° C-deposited (Ba0.5Sr0.5)TiO3 film of 30 nm in thickness. The (Ba0.5Sr0.5)TiO3 film has the possibility for application to generations beyond 256 Mbit dynamic random access memories.
Partial Switching Kinetics of Ferroelectric PbZrxTi1-xO3 Thin Films Prepared by Sol-Gel Technique
Authors: Tokumitsu Eisuke , Noriaki Tanisake Noriaki Tanisake , Hiroshi Ishiwara Hiroshi Ishiwara
Published: October 2002

Switching characteristics of ferroelectric PbZr

x

Ti1-
x

O3 thin films prepared by the sol-gel technique have been studied for “adaptive learning” metal-ferroelectric-semiconductor field effect transistor (MFSFET) applications. It is demonstrated that by applying positive short pulses to the metal-ferroelectric-metal (MFM) capacitors, the polarization of PZT films can be gradually reversed. We have also measured the switching characteristics by applying various input voltages. Experimentally measured current responses and polarization changes can be well fitted by the Kolmogorov-Avrami theory by taking into account the voltage dependence of the reversed polarization.
Preparation of Pb(Zr,Ti)O3 Thin Films on Ir and IrO2 Electrodes
Authors: Takashi Nakamura Takashi Nakamura , Yuichi Nakao Yuichi Nakao , Akira Kamisawa Akira Kamisawa , Hidemi Takasu Hidemi Takasu
Published: October 2002

Pb(Zr

x

Ti1-
x

)O3 (PZT) thin films were prepared on Ir and IrO2 electrodes. Ir has very similar properties to Pt, and IrO2 is a conductive oxide. Perovskite single-phase PZT thin films were obtained on their electrodes. PZT thin films were grown by the conventional sol-gel method with rapid thermal annealing (RTA) at 700° C. When Pt thin films were deposited directly on poly-Si, PtSi layers were formed, and PZT thin films on the Pt had very poor crystallinity. When an IrO2 layer was formed between PZT and poly-Si, a high-quality PZT thin film was obtained. Moreover, when electrodes including the IrO2 layer were used, fatigue properties of PZT thin films were drastically improved.
Effects of Oxygen Concentration on Growth of Bi4Ti3O12 Thin Films by Metalorganic Chemical Vapor Deposition
Authors: Muhammet Rusul , Nakamura Takashi , Shimizu Masaru , Shiosaki Tadashi
Published: October 2002

The effects of oxygen concentration on the growth of Bi4Ti3O12 thin films by metalorganic chemical vapor deposition (MOCVD) were investigated, using Bi(C6H5)3 and Ti( i-OC3H7)4 precursors, c-axis-oriented Bi4Ti3O12 thin films were obtained at an oxygen gas flow rate of 200 sccm and a substrate temperature of 600° C on Pt(111)/ SiO2/Si(100) substrates without Bi2Ti2O7 buffer layers. This film shows remanent polarization of 1.3 µ C/cm2, coercive field of 25 kV/cm, dielectric constant of 130 and leakage current density as low as 10-8–10-7 A/cm2.
Control of Grain Structure of Laser-Deposited (Ba, Sr)TiO3 Films to Reduce Leakage Current
Authors: Bhattacharya Pijush , Kyung-ho Park Kyung-ho Park , Yasushiro Nishioka Yasushiro Nishioka
Published: October 2002

A new technique to realize a low leakage current of (Ba, Sr)TiO3 (BSTO) thin films by controlling the grain structure of BSTO has been proposed. This includes the deposition of amorphous BSTO at 500° C and annealing of the amorphous films at 650° C in O2 for crystallization. The leakage current of the film produced from the amorphous one was significantly lower than that of BSTO films deposited directly at the substrate temperature of 650° C. The crystalline structure of the film produced from the amorphous one was found to be circular. In contrast, as-grown crystalline film showed columnar grain structures. The reduction of the leakage current may be attributed to the differences in the grain structures.
Preparation of Pb(Zr, Ti)O3 Thin Films by Multitarget Sputtering
Authors: Hase Takashi , Hirata Kazuo , Amanuma Kazushi , Hosokawa Naokichi , Yoichi Miyasaka Yoichi Miyasaka
Published: October 2002

Thin lead zirconate titanate [PZT] (Zr/Ti=50/50) films (230–430 nm) were deposited by multitarget sputtering with three stoichiometric PZT targets and one PbO target. To control Pb content in film, the rf power for the PbO target was varied. The rf power for each PZT target was also varied to control the deposition rate. PZT films with single perovskite phase or dominant perovskite phase were obtained only when the film composition was self-controlled. Low deposition rate resulted in a wider range of PbO input power in which Pb/(Zr+Ti) ratio was almost constant. Therefore low deposition rate would enhance the self composition control (SCC) mechanism. A 240-nm-thick PZT film deposited under the SCC mechanism and low deposition rate showed remanent polarization of 21.5 µ C/cm2, dielectric constant of 600 and leakage current of 7.0×10-8 A/cm2.
Dielectric Property of Epitaxial Films of BaTiO3 Synthesized by Laser Ablation
Authors: Takashi Nose Takashi Nose , Hyun-Tak Kim Hyun-Tak Kim , Hiromoto Uwe Hiromoto Uwe
Published: October 2002

Epitaxial BaTiO3 films have been synthesized on (100)SrTiO3 at the substrate temperature of 700° C and 100 mTorr of oxygen by the method of laser ablation. The surface of the film is found to be flat with a surface roughness of about 7 nm. For the film with the thickness of 2000 Å, the relative dielectric constant, ε r, exhibits a broad peak at about 150° C; on the other hand, the ε r exhibits a sharp peak at the tetragonal to orthorhombic transition.
Study on Pb-Based Ferroelectric Thin Films Prepared by Sol-Gel Method for Memory Application
Authors: Yuichi Nakao Yuichi Nakao , Takashi Nakamura Takashi Nakamura , Akira Kamisawa Akira Kamisawa , Hidemi Takasu Hidemi Takasu , Nobuyuki Soyama Nobuyuki Soyama , Tsutomu Atsuki Tsutomu Atsuki , Katsumi Ogi Katsumi Ogi
Published: October 2002

Pb(Zr,Ti)O3 (PZT), PbTiO3 (PT), and (Pb,La)TiO3 (PLT) thin films were deposited by sol-gel method on Pt/IrO2 electrodes. Deposited films were annealed at 625–700° C by rapid thermal annealing (RTA). These prepared films were examined as to whether they were suitable for ferroelectric nonvolatile memory using a metal-ferroelectric-metal-insulator-semiconductor (MFMIS) structure. In the application to a MFMIS structure, widely used PZT films have some problems such as the cracking on SiO2 and too high a dielectric constant. In this study, we examined the ferroelectric thin films to solve these problems.
Preparation of Dielectric Thin Films from Photosensitive Sol-Gel Solution
Authors: Soyama Nobuyuki , Sasaki Go , Atsuki Tsutomu , Tadashi Yonezawa Tadashi Yonezawa , Katsumi Ogi Katsumi Ogi
Published: October 2002

Fine-patterned Ba

x

Sr1-
x

TiO3 (BST) thin films were successfully fabricated from a photosensitive sol-gel solution by means of UV irradiation. This solution was prepared from barium acetate, strontium acetate, and titanium isopropoxide. BST gel films on substrates formed from the solution by spin-coating were irradiated with UV rays through a mask pattern and developed with a mixture of ethanol and water. The obtained patterns were a negative of the mask. The films were finally annealed for crystallization. The obtained films had perovskite structure and good properties.
Fabrication of Ferroelectric Bi4Ti3O12 Thin Films by Dipping Pyrolysis of Metal Naphthenates and Micropatterns by an Electron Beam
Authors: Kakimi Atsushi , Okamura Soichiro , Yagi Yukie , Mori Katsumi , Takeyo Tsukamoto Takeyo Tsukamoto
Published: October 2002

Fabrication of ferroelectric Bi4Ti3O12 thin films was carried out by dipping pyrolysis of metal naphthenates. Single-phase Bi4Ti3O12 thin films with c-axis orientation perpendicular to the substrate surface were fabricated on Pt plates. They exhibited good ferroelectric properties: coercive field of 7.7 kV/cm and remanent polarization of 8.2 µ C/cm2. For the films fabricated on Pt/Ti/ SiO2/Si substrates, however, the Bi2Ti2O7 phase mainly grew because of Ti diffusion into the bismuth titanate layer during the heat treatment. Fine micropatterns with linewidth of less than 1 µ m in precursors of Bi4Ti3O12 were formed by spin-coating, irradiation with an electron beam and development. They were crystallized into the Bi4Ti3O12 phase by successive pyrolysis and annealing. The reaction between the metal naphthenate films and energized electrons was studied by IR spectroscopic analysis.
Analysis of Interfacial Phase between Substrates and Lead Zirconate Titanate Thin Films Synthesized by Hydrothermal Method
Authors: Ohba Yoko , Arita Koji , Takaaki Tsurumi Takaaki Tsurumi , Masaki Daimon Masaki Daimon
Published: October 2002

Hydrothermal synthesis of lead zirconate titanate (PZT) films was achieved using two sequential processes. The first step is the reaction of the substrate with a solution, which is called the “nucleation process”, and the second step is the “crystal growth process”. Variation in the morphology of final products was produced by changing the duration of the nucleation process. At least 12 h of the nucleation process was required to obtain a PZT film. A duration over 12 h in the nucleation process resulted in thicker PZT film and larger displacement of the bending actuator fabricated using such a film. These findings can be explained by assuming the existence of an interfacial phase between the Ti substrate and PZT film, the piezoelectric constant of which would be lower than that of the PZT film. Energy dispersive X-ray spectrometry (EDX) analyses provide evidence to support the assumption that the interfacial phase is Ti-rich PZT.
Recrystallization and Microstructure in Electrophoretically Deposited Ferroelectric BaTiO3 Films under CO2-Laser Irradiation
Authors: Kakemoto Hirofumi , Okutomi Mamoru , Tsukamoto Koichi , Okamura Soichiro , Koura Nobuyuki , Takeyo Tsukamoto Takeyo Tsukamoto
Published: October 2002

Recrystallization of BaTiO3 films deposited electrophoretically on Pt plates was investigated under the irradiation of a CO2-laser beam. Laser irradiation of the films caused significant growth of platelike crystals and strip grains on the surface. Considerable recrystallization occurred in a wide temperature gradient region around the laser-irradiated portions. The laser scanning process is suited for the growth of large grains with preferred orientation. The recrystallized phase of film was the tetragonal one of BaTiO3. Remanent polarization of 4.8 µ C/cm2 and coercive field of 3.2 kV/cm were obtained in the film with 4 µ m thickness.
Effects of dc Electric Field on Mechanical Properties of Piezoelectric Ceramics
Authors: Hiroaki Makino Hiroaki Makino , Nobuo Kamiya Nobuo Kamiya
Published: October 2002

The effects of dc electric field on mechanical properties such as hardness, fracture toughness, flexural strength and flexural fatigue strength of piezoelectric ceramics were investigated. Hardness and fracture toughness were not influenced by the dc electric field, where as the flexural strength and the fatigue strength degraded with the absolute value of the electric field. The degradation of the flexural strength and the acceleration of fatigue were greater under an electric field whose direction was opposite to the poling direction than an electric field whose direction was the same as the poling direction. The main cause of strength degradation and fatigue acceleration in piezoelectric ceramics is estimated to be the microscopic internal stress which is generated at the grain boundary by the piezoelectric and domain switching deformations.
Electric Properties of Pb(Sb1/2Nb1/2)O3–PbTiO3–PbZrO3 Ceramics
Authors: Yasushi Kawamura Yasushi Kawamura , Hiromu Ohuchi Hiromu Ohuchi
Published: October 2002

Solid-solution ceramics of ternary system xPb(Sb1/2Nb1/2)O3– yPbTiO3– zPbZrO3 were prepared by the solid-state reaction of powder materials. Ceramic, electric, dielectric and piezoelectric properties and crystal structures of the system were studied. Sintering of the system xPb(Sb1/2Nb1/2)O3– yPbTiO3– zPbZrO3 is much easier than that of each end composition, and well-sintered high-density ceramics were obtained for the compositions near the morphotropic transformation. Piezoelectric ceramics with high relative dielectric constants, high radial coupling coefficient and low resonant resistance were obtained for the composition near the morphotropic transformation. The composition Pb(Sb1/2Nb1/2)0.075Ti0.45Zr0.475O3 showed the highest dielectric constant (ε
r=1690), and the composition Pb(Sb1/2Nb1/2)0.05Ti0.45Zr0.5O3 showed the highest radial coupling coefficient (kp=64%).