bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis Method for Ocean Acoustic Tomography Data Using Kalman Filter –Evaluation by Identical Twin Experiment–
Authors: Shinke Tomio , Yoshikawa Yasushi , Kamoshida Takashi , Mitsudera Humio
Published: October 2002

A data assimilation scheme for ocean acoustic tomography (OAT) data is developed and evaluated by an identical twin experiment to understand the dynamical processes and the evolution of flow pattern in the Kuroshio extension region. The scheme consists of three components, i.e., the two-layer quasi-geostrophic (QG) oceanic numerical model, the travel time data obtained from OAT, and the data assimilation technique which consists of the Kalman filter and observation equations relating the model variables (stream function and interface displacement) to the OAT-derived reciprocal travel time. The identical twin experiment using two different model fields made from the same model demonstrates both the stability and the availability of the scheme developed in the present study.
A Capacitance Ratio Method Used for Leff Extraction of an Advanced Metal-Oxide-Semiconductor Device with Halo Implant
Authors: Huang Heng-Sheng , Lin Shyh-Jye , Chen Ying-Jyh , Chen I-Kai , Lee Ryan , Chou J. W. , Hong Gary
Published: October 2002

The effective channel length of a metal-oxide-semiconductor (MOS) transistor is usually extracted using current–voltage (I–V) methods. In a current MOS transistor, local surface channel mobility degradation due to halo implants used for obtaining better short channel performance in deep-quarter micron devices degrades the extraction accuracy of the value of effective channel length (L
eff). This paper describes an experimental wafer split under varying halo implant conditions implemented to determine the accuracy of the L
eff values extracted using various methods based on the advanced 0.15 µm complementary metal-oxide-semiconductor (CMOS) technology. The integrated systems engineering technology computer-aided design (ISE TCAD) two-dimensional (2D) simulation tool and a modified capacitance–voltage (C–V) method were adopted to help determine the metallurgical channel-length L
met for each transistor under various halo implant conditions. The relationships between L
met and L
eff values extracted using various methods (including I–V and C–V methods) were also compared. In using the proposed modified C–V method [capacitance–ratio (C–R) method], more consistent and reasonable L
eff data can be obtained even when a heavy halo implant dose is used.
Electron-Beam Focusing and Deflection Properties for Misaligned Dual Gate Field Emitters
Authors: Nicolaescu Dan , Filip Valeriu , Itoh Junji
Published: October 2002

Field emitters are used as distributed electron sources in applications such as field emission displays (FEDs) and electron guns. The focusing and deflection of an electron beam may be achieved using dual gate structures. The fabrication process for such emitters involves self-aligning steps with certain tolerances and also non-self-aligning steps. In this article, the effects of emitter structure misalignments on the device focusing properties are studied. The simulation results have been obtained using the Simion 3D 7.0 software package. The electron trajectories are very sensitive to the relative position of the field emitter within the structure. An optimal position of the focusing gate has been shown to exist even when this electrode is misaligned with respect to the emitter.
Very High Hydrogen Dilution Induced Novel Phenomena of Electronic Transport Properties in Hydrogenated Microcrystalline Silicon-Germanium Thin Films Prepared by Plasma Enhanced Chemical Vapor Deposition Method
Authors: Huang Shaoyun , Chen Kunji , Shi Jianjun , Huang Xinfan , Xu Jun , Ganguly Gautam , Matsuda Akihisa
Published: October 2002

With very high hydrogen diluted silane and germane plasma (R: [H2]/([SiH4]+[GeH4])=100–500 sccm), undoped high-quality alloys (µc-SiGe:H) were prepared in plasma enhanced chemical vapor deposition (PECVD) system with various hydrogen dilutions and substrate temperatures. The microstructures of samples were characterized by X-ray diffraction and micro-Raman scattering spectroscopy. Traveling wave (TW) method was used to investigate the transport properties of these thin films. We found that crystallinity and grain size exerted a big influence on the transport mechanism. Especially with very high hydrogen dilution (R \succ300), both of conductivity and mobility came to decrease and the electronic transport properties degraded, which were different from that of normal µc-SiGe:H films. These novel phenomena were discussed by strong scattering of the potential barriers between the crystallites.
Chrome and Zinc Contaminants Removal from Silicon (100) Surfaces by Remote Plasma Cleaning Techniques
Authors: Lee Seungwook , Lee Jaegab , Lee Chongmu
Published: October 2002

Removal of Cr and Zn impurities on Si surfaces using remote plasma H2 was investigated. Si surfaces were contaminated intentionally with low-purity acetone. To determine the optimum process conditions, remote plasma H2 cleaning was conducted for various rf powers and plasma exposure times. After remote plasma H2 cleaning, Si surfaces were analyzed by total X-ray reflection fluorescence (TXRF), surface photovoltage (SPV) and atomic force microscopy (AFM). The concentrations of Cr and Zn impurities were reduced by more than a factor of 2 and the minority carrier lifetime increased. Also the root-mean-square (RMS) roughness decreased by more than 30% after the remote plasma H2 cleaning. TXRF analysis results show that remote plasma H2 cleaning is effective in eliminating Cr and Zn impurities from the Si surface only if it is performed under optimum process conditions. AFM analysis results also show that remote plasma H2 cleaning causes no damage to the Si surface. Cr and Zn impurities on the Si substrate are considered to be contaminated as forms of hydroxides, silioxides and oxides on chemical oxides formed during intentional chemical contamination. The removal mechanism of Cr and Zn impurities using remote plasma H2 treatments is proposed for the lift-off during the removal of underlying chemical oxides.
Deeply Etched Semiconductor/Benzocyclobutene Distributed Bragg Reflector Laser Combined with Multiple Cavities for 1.5-µm-Wavelength Single-Mode Operation
Authors: Madhan Raj Jörg Wiedmann , Koji Ebihara Koji Ebihara , Kensuke Matsui Kensuke Matsui , Shigeo Tamura Shigeo Tamura , Shigehisa Arai Shigehisa Arai
Published: October 2002

Single-mode GaInAsP lasers at a wavelength of 1.5 µm, fabricated using deep dry-etching technology are presented. In the novel design, the high reflectivity of a fifteen-element distributed Bragg reflector (DBR) is combined with the spectral selectivity of multiple cavities (MC) to achieve single-mode operation with high output efficiency. The etched structure was buried with polymer benzocyclobutene (BCB) in order to reduce the diffraction loss between coupled cavities, to passivate the sidewalls of the waveguide and to protect the structure from damage due to process handling. MC lasers with different numbers of cavities were analyzed by the transfer matrix method (TMM) including groove losses and the results of analysis are compared with experimental results of fabricated devices. For a coupled cavity (CC) laser, which has only two cavities, a threshold current of 11 mA and a submode suppression ratio (SMSR) of 36 dB at a bias current of 1.8 times the threshold were obtained for 5-µm-wide mesa stripe geometry.
Cathodoluminescence Change of YNbO4:Bi Phosphor after Acid Treatment
Authors: Shin Sang Hoon , Jeon Duk Young , Suh Kyung Soo , Kim Jong Min
Published: October 2002

The reason for the cathodoluminescence (CL) change of YNbO4:Bi after acid treatment is determined. It is observed that after acid treatment, the CL intensity of YNbO4:Bi decreased to a value below that of the untreated one at excitation energies lower than 1 keV. However, YNbO4:Bi was brighter than the untreated one at an excitation energy of 1 keV or higher. Meanwhile, ZnGa2O4 was compared with YNbO4:Bi in terms of luminescence properties. After acid treatment, ZnGa2O4 showed the same trend as YNbO4:Bi at excitation energies lower than 1 keV. However, the luminescence intensity of ZnGa2O4 did not increase at an excitation energy of 1 keV or higher. It was found that surface modification using an acid increases the luminescence efficiency of YNbO4:Bi by realizing stoichiometric composition at the phosphor surface.
Theoretical Study for Thermal/Electric Field Poling of Fused Silica
Authors: Liu Xue-Ming , Zhang Ming-De
Published: October 2002

Using the multiple-carrier model, the process of thermal/electric-field poling in fused silica is analyzed in this study for the first time. The depletion region may be composed of a positively charged layer, an ionosphere layer and a negative depletion layer, and the charge density distribution in the depletion region is derived and obtained. The calculation results show that the distribution of the charge density in the entire depletion region has a quasi-step profile, and both the positively charged region and the negative depletion layer have an approximately uniform distribution. Expressions for the depletion width and the electric field distribution in the depletion region are obtained. Theoretical results show that the peak electric field is located in the interior of the depletion region, and the internal electric field is about 109 V/m, up to two orders of magnitude higher than the applied initial poling field.
Reactively Sputtered Amorphous TaSixNy Films Serving as Barrier Layer Against Copper Diffusion
Authors: Lin Cheng-Li , Ku Shaw-Ru , Chen Mao-Chieh
Published: October 2002

Reactively sputtered amorphous TaSi
x
N
y
(x=1.4, y=2.5) films of different thicknesses (5 to 40 nm) serving as diffusion barriers were studied for Cu metallization. The Cu/TaSi
x
N
y
/p+n junction diodes with 5-nm-thick TaSi
x
N
y
barriers were able to sustain a 30 min thermal annealing at temperatures up to 400°C without degradation of the electrical characteristics. With thicker barriers of 10-, 20- and 40-nm-thick TaSi
x
N
y
layers, the thermal stability temperatures of the Cu/TaSi
x
N
y
/p+n junction diodes were increased to 500, 550 and 650°C, respectively. The amorphism of TaSi
x
N
y
films on Si substrates remains unchanged at temperatures up to 800°C, whereas the presence of a Cu overlayer on the surface of the TaSi
x
N
y
/Si structure accelerates the formation of Ta-silicide. Failure of the amorphous TaSi
x
N
y
diffusion barrier is presumably due to Cu diffusion through the barrier layer by way of localized defects.
Molecular Alignment in Monolayer of n-Alkyloxy-Cyanobiphenyl and Clear Evidence of the Odd–Even Effect
Authors: Seiji Taki Seiji Taki , Shoichi Kai Shoichi Kai
Published: October 2002

Systematic observations are carried out to determine molecular alignments of monolayers of homologous series in n-alkyloxy-cyanobiphenyl (nOCB) liquid crystals in the range of n=7 to 10 on both molybdenum disulfide (MoS2) and highly oriented pyroritic graphite (HOPG) substrates using a scanning tunneling microscope. Our observations determined the following. For odd n of carbon atoms in alkylchains such as 7OCB and 9OCB, the molecular alignments on both substrates (MoS2 and HOPG) are mainly due to the interaction between alkylchains and substrates. For even n, on the other hand, the alignments are basically due to the dipole-dipole interaction between liquid crystal molecules on the substrates. These differences occur due to the situation of the end-carbon in an alkylchain. However, 10OCB on HOPG shows an exceptional alignment resulting from the alkylchain-length effect. Excluding this case, all other seven combinations clearly indicate the odd–even effect. The validity of our previous model for molecular alignments of nCB monolayers has been confirmed for nOCB.
Temperature Dependence of Field-Emission Characteristics from a p-Type Si Single Emitter with Real Surface
Authors: Yoshimoto Tomomi , Iwata Tatsuo , Kikuchi Satoru , Yokogawa Naohiro
Published: October 2002

The temperature dependence of field-emission current from a p-type Si single emitter with a real surface was investigated. The field emission pattern of the emitter did not show any symmetry which indicates a clean crystal structure of the surface; however, the highly nonlinear characteristics in log
(I/V
2) vs 1/V plots (F-N plots) commonly observed from a clean p-type Si emitter are obtained. The emission current at the gentle slope region of F-N plots (I
sat) shows strong temperature dependence at a fixed applied voltage. The slope of log
I
sat vs 1/T plots gives an activation energy of 0.58 eV. The most probable conclusion is that the Fermi level is pinned at the middle of the band gap of the surface and electrons generated from the surface state to the conduction band are emitted.
Formation of Two Dimensional Network Structure of DNA Molecules on Highly Ordered Pyrolytic Graphite Surface
Authors: Tanaka Shin-ichi , Maeda Yasushi , Cai Lin-Tao , Tabata Hitoshi , Kawai Tomoji
Published: October 2002

Unique DNA network structures have been constructed, when DNA solutions (concentration range from 50 µg/ml to 500 µg/ml) are spread on mica and highly ordered pyrolytic graphite (HOPG) surfaces. The DNA network structures depend on the fixation time, solution concentration and substrate adhesion force. A novel structure having a hexagonal symmetry has been found on the HOPG surface for the first time. HOPG is one of the promising substrates for photoemission analysis without any charge up problem. Clear C (1s), N (1s), O (1s) and P (2p) peaks corresponding to DNA molecules can be detected.
Short-Pulse X-Ray Generation via Thomson Scattering in 0° and 90° Interactions
Authors: Yorozu Masafumi , Yang Jinfeng , Okada Yasuhiro , Yanagida Tatsuya , Sakai Fumio , Endo Akira
Published: October 2002

Short-pulse X-ray generation was demonstrated in a scattering experiment between a 4 ps electron beam and a 10 ps Nd:YLF laser beam. The beams interacted at 0° and 90°. The X-ray signal was measured using a microchannel plate. Maximum X-ray energy was analytically estimated to be 3.55 keV in the 0° interaction and 1.77 keV in the 90° interaction with a pulse duration of 4 ps for both interactions. Measured X-ray intensities exhibited good linearity with the incident laser light pulse energy for both scattering configurations. The measured X-ray intensity was compared with the intensity analyzed from the beam sizes and energies of both beams. The intensities matched and were of the order of 104 photons in the 0° interaction.
Nanocluster Formation within the Vapor Plume, Produced by Nanosecond-Laser Ablation: Effect of Initial Density and Pressure Distributions
Authors: Masahiro Kuwata Masahiro Kuwata , Boris Luk'yanchuk Boris Luk'yanchuk , Takashi Yabe Takashi Yabe
Published: October 2002

The condensation of vapor in the expanding plume produced by ns-laser ablation is discussed within the framework of the Zeldovich and Raizer theory of condensation. The spherical plume expansion is described by a numerical solution of the hydrodynamic equations by the cubic interpolated pseudo-particle (CIP) method. This permits us to analyze the role of initial distributions of density and pressure on the size distribution function of nanoclusters. For parabolic distributions (for the plume expansion into vacuum), calculations reproduce the same results as those obtained by particular solutions of gas-dynamic equations. When initial distributions deviate from the parabolic distributions, the size distribution function varies. For the rectangular plume, the size distribution function of nanoclusters demonstrates two maximums. A similar effect is observed due to the ambient gas influence.
Composition of Quantum Ratchets with Chaotic Dots
Authors: Hiromu Ishio Hiromu Ishio
Published: October 2002

We present a proposal for a new type of quantum ratchets in application of weak-localization (WL) effect in mesoscopic chaotic dots. Coherent electrons transport through the dots under an applied ac voltage and a synchronized pulsating magnetic field. In the first half cycle of the voltage alternation with no magnetic field, the WL effect reduces the electron transmission on average, while the applied magnetic field breaks the time-reversal symmetry in the latter half cycle, suppressing the WL effect. As a result, nonvanishing amount of net electric current in one direction can be measured. We exactly calculate the net electric current which is found accessible in experiments. It is also suggested that the observation of this rectified current is a good quantitative measure of the WL effect in mesoscopic chaotic dots, in contrast with the WL lineshape measurement.
TiO2 (110) Surface Preparation by UV Light Irradiation for Scanning Tunneling Microscopy Observations
Authors: Yin Donghong , Komiyama Masaharu
Published: October 2002

A new procedure to prepare a clean surface of TiO2 (110) by UV light irradiation in air at room temperature was investigated by scanning tunneling microscopy (STM). A clean (1×1) surface consisting of atomically flat terraces was obtained when the surface was irradiated with UV light and subsequently annealed at 970 K. A (1×2) reconstruction on large flat terraces was also observed with increasing annealing temperature. Compared to the UV light irradiation, Ar+ ion bombardment left the surface rough and disordered. Surface damage with holes about 6–9 Å deep caused by cycles of Ar+ ion sputtering was not easily recovered even after annealing at high temperatures. Ar+ ion bombardment readily induced surface reconstruction compared to UV light irradiation. A (1×3) reconstruction was formed by Ar+ ion sputtering and annealing at high temperatures.
Various Phases on Natural Stilbite (010) Surface Observed by Atomic Force Microscopy under Aqueous Conditions
Authors: Ning Gu Ning Gu , Masaharu Komiyama Masaharu Komiyama
Published: October 2002

Various phases on a natural stilbite (010) surface were observed by atomic force microscopy (AFM) under aqueous conditions. In a wide-area observation, oriented protrusions observed on the surface differed from the “sheaflike” structure which has been found in stilbite in an aqueous NaOH solution. Narrow-area observations showed surfaces consisting of an island structure, or a structure of alternating ridges and trenches. The latter is similar to the one reported previously under ambient conditions. Defects such as dislocations and grain boundaries at the atomic level were also observed.
Characterization of Silicon Nitride Thin Films on Si and Overlayer Growth of Si and Ge
Authors: Wang Xue-Sen , Li Zongquan , Wang Lei , Hu Yanfang , Zhai Guangjie , Yang Jianshu , Wang Yuqi , Fung Kwok-Kwong , Tang Jing-Chang , Wang Xun , Cue Nelson
Published: October 2002

Crystalline silicon nitride (SiN
x
) thin films on Si(111) and amorphous SiN
x
films on Si(001) have been obtained after NH3 or NO exposure at T≈1175 K. The crystallinity of the film on Si(111) has been verified with high-resolution cross-sectional transmission electron microscopy (TEM) and scanning tunneling microscopy. The thickness of the SiN
x
film is 3–6 atomic layers. When compared with the known phases of Si3N4, our SiN
x
film is relatively close to β-Si3N4, but it could be a new phase of silicon nitride. Si or Ge forms 3D islands initially when deposited on both crystalline and amorphous SiN
x
films, and most of the islands are not aligned with the Si substrates. However, on SiN
x
/Si(111), the islands aligned with the Si substrate grow faster than other islands, so that the overlayer gradually grows into a (111)-oriented columnar film. On SiN
x
/Si(001), the overlayer films remain polycrystalline in later stages of growth.
Oscillatory Forces in Liquid Atomic Force Microscopy
Authors: O'Shea Sean J.
Published: October 2002

By analysing oscillatory type solvation forces acting at the tip-surface interface in atomic force microscopy (AFM) in liquids it is possible to study interactions arising from purely physical effects. The observation of oscillatory forces with sharp tips indicates a high geometric symmetry of the tip-liquid-surface system. As such, liquid mediated forces may prove general for high resolution non-contact imaging in liquids. The effective viscosity (damping) increases markedly as the tip apex samples the liquid solvation layers closest to the surface and this suggests that strong damping effects (low Q) may always be present in non-contact imaging in liquids. The magnitude of solvation effects (both interfacial stiffness and viscosity) is less than that observed using the surface force apparatus (SFA) and this is probably related to tip roughness (asymmetry) or to the more limited volume over which liquid is confined in AFM.
Improvement in Aspect Ratio of P-GaAs Oxide Fabricated by Atomic Force Microscope (AFM)-Based Nanolithography Using Pulsed Voltage
Authors: Yuichi Matsuzaki Yuichi Matsuzaki , Shigeki Hasui Shigeki Hasui , Shin-ya Kamada Shin-ya Kamada , Akira Yamada Akira Yamada , Makoto Konagai Makoto Konagai
Published: October 2002

An atomic force microscope (AFM)-based surface nanooxidation method was used to fabricate nanoscale p-GaAs oxide. We were able to realize an increase in the aspect ratio by a factor of 2 for oxide dots using a voltage modulation technique. The aspect ratios of oxide dots reached the maximum at a frequency of about 1000 Hz. Moreover, from a duty ratio dependence of aspect ratios of oxide dots, it was considered that optimization of an anodizing time per cycle of a pulsed voltage was necessary. The oxide could be etched by water. By adjusting both oxidation and etching process conditions, a groove with a 40 nm width and 6 nm depth was successfully fabricated. From these results, it was clear that the aspect ratio of p-GaAs oxide could be improved using a pulsed voltage, and optimization of process conditions, particularly the frequency and duty ratio of a pulsed voltage, was necessary to obtain p-GaAs oxide with a high aspect ratio.
Atom-Resolved Structures of TiO2(001) Surface by Scanning Tunneling Microscopy
Authors: Fukui Ken-ichi , Tero Ryugo , Iwasawa Yasuhiro
Published: October 2002

Surface structures of a TiO2(001) surface are examined in atomic scale by scanning tunneling microscopy (STM). Among two ordered phases which depend on annealing temperature as reported from a low energy electron diffraction (LEED) study, an atomic-scale image of the higher temperature phase, which shows a unique surface reactivity, was successfully visualized. The surface consisted of crossed rows along the [110] direction and the [110] direction. Each row had a bleacher-like structure which formed stairs at both sides with an average slope identical to the {114} face. An atom-resolved STM image showed that each narrow terrace of the stairs is covered with a unit of three bright spots which are ordered in line perpendicular to the step and arranged with a constant separation of 0.65 nm. It was revealed that the STM image is not consistent with the previously proposed {114}-faceted model.
A Step Toward Making and Wiring Up Molecular-Scale Devices
Authors: Wolkow Robert A.
Published: October 2002

For over two decades scientists have been exploring ideas for creating “molecular electronic” devices. The aim has been to make functional units consisting of a very small number of molecules, perhaps only one molecule, that are capable of switching a current. Many such elements could then be combined to create computers and other electronic circuits. The hope has been that this approach will lead to the ultimate miniaturization of devices as well as to optimal operating efficiency and the lowest cost. While this scenario remains little more than a dream, some key steps have recently been made. Here, I outline some background information, and as well, briefly review some recent developments from our lab.
Effects of Rapid Thermal Annealing on the Electrical Properties of Cobalt Contact to p-GaN
Authors: Won Kim Je , Tae Kim Seong-Il Kim , Young Sung Sangsig Kim , In-Hoon Choi In-Hoon Choi
Published: October 2002

The effects of rapid thermal annealing (RTA) on Co/p-GaN contacts in an O2/N2 atmosphere without intermediate metal were investigated. It was observed that the contact resistance (ρc) decreased with increasing RTA temperature and that the resistance was reduced by a factor of about 30 after RTA at 600°C in the O2/N2 atmosphere. The specific minimum contact resistance was in the 10-2 Ω·cm2 range. Comparison of the R
0 and ρc values revealed that the rapid thermal annealing in the O2/N2 was more effective for reducing the contact resistance than conventional furnace annealing. The reason for the reduction of resistance was expected to be the increase of hole concentration due to the highly reactivated removal of hydrogen atoms in the p-GaN by RTA in the O2/N2 atmosphere.
Photoresist Ashing Process Using Carbon Tetrafluoride Gas Plasma with Ammonia Gas Addition
Authors: Saito Makoto , Eto Hideo , Omiya Kayoko , Homma Tetsuya , Nagatomo Takao
Published: October 2002

A low-damage photoresist ashing process was developed for the fabrication of thin-film transistor liquid-crystal displays (TFT-LCDs). This process utilizes a downflow plasma using a carbon tetrafluoride/oxygen (CF4/O2) gas mixture at room temperature. Although this process simultaneously achieves a high ashing rate and a low etching rate for an underlying amorphous silicon (a-Si:H) film containing hydrogen (H), contact resistance increases. We achieved contact resistances of less than 2 kΩ by the addition of ammonia (NH3) gas into the CF4/O2 gas mixture plasma. The ratio of reactive fluorine radicals (F) to argon atoms (Ar) decreased with increasing NH3 gas flow rate and became less than 0.7 at the NH3 gas flow rate higher than 15 sccm. Reaction products formed on a-Si:H films by the addition of NH3 gas to the CF4/O2 gas mixture plasma obstructed the etching of the a-Si:H films by F. On the basis of plasma analysis results for the CF4/O2/NH3 gas mixture, a possible mechanism for low damage to a-Si:H films was proposed.
Quantum-Dot Logic Circuits Based on the Shared Binary-Decision Diagram
Authors: Amemiya Takashi Yamada
Published: October 2002

We propose a method of constructing quantum-dot logic circuits that can be used to develop large digital systems with ultralow power consumption. These dot circuits consist of dot arrays fabricated using a wrap-gate structure, and they perform logic operations on the basis of the binary decision diagram. Sample dot circuits such as elementary logic gates and adder subsystems are designed. The operation of the designed circuits is confirmed by computer simulation.
A Simple Random Noise Generator Employing Metal-Oxide-Semiconductor-Field-Effect-Transistor Channel kT/C Noise and Low-Capacitance Loading Buffer
Authors: Wee Keng Hoong , Shibata Tadashi , Ohmi Tadahiro
Published: October 2002

An eight-transistor random noise generator employing a new circuit architecture has been developed. A compact two-transistor thermal noise source comprising a complementary metal-oxide-semiconductor (CMOS) inverter is proposed as a viable alternative to the area consuming conventional resistive noise source. The total extracted noise power is increased by reducing the effective capacitance at the output of the thermal noise source through the use of a unity-gain low-capacitance loading buffer. A wide-bandwidth high-noise-power random noise generator comprising the CMOS inverter noise source, a CMOS source follower as a low-capacitance loading buffer and a cascode amplifier as a high-gain stage, was fabricated and its noise generation capability experimentally verified. It has a very simple circuit configuration and is fully compatible with current VLSI technology, thus making it a promising candidate for integration of multiple random noise generators on a chip.
Second-Harmonic Generation of Ferroelectric Potassium Lithium Niobate Crystals
Authors: Xu Xue-Wu , Chong Tow-Chong , Zhang Guang-Yu , Kumagai Hirohiko
Published: October 2002

The second-harmonic generation (SHG) properties of a potassium lithium niobate (KLN) crystal with the size of 8×20×43 mm3 were studied in detail. The KLN crystal was grown from a melt consisting of 32 mol% K2O, 24 mol% Li2O and 44 mol% Nb2O5 (denoted as the melt 32:24:44) by the top-seeded solution growth (TSSG) method. The ferroelectricity of the KLN crystal was revealed by the marked dielectric anomaly at the Curie temperature. The full-widths at half maximum (FWHMs) of the wavelength- and temperature-tuning curves of a 4-mm-long KLN crystal sample were found to be 0.6 nm and 2°C, respectively. The SHG conversion efficiency of this crystal was studied and estimated to be 0.03%/W for an input power of 748 mW. The CW tunable blue laser covering the range of 431.1–437.6 nm was achieved by tuning the crystal temperature in the range of 24–80°C. The crystal studied in this paper is more inhomogeneous and has lower SHG efficiency than the KLN crystal grown from the melt 31:26:43, which has higher Li2O content.
Current Reversal of Photon-assisted Tunneling in a Quantum Dot Connected to Superconducting Leads
Authors: Cho Sam Young , Kang Kicheon , Ryu Chang-Mo , Kim Chul Koo
Published: October 2002

We study the current reversal of the photon-assisted electron transport in a single level quantum dot connected to two superconductors. It is found that the direction of photon-assisted tunneling (PAT) current sensitively changes depending on the external frequency and on the electron energy level of the quantum dot. The frequency region for the reversal of the PAT current is determined by a small applied dc-bias or the energy gap difference between the two connecting leads.
Fabrication of High-Performance Lead Zirconate Titanate Actuators Using the Microwave and Hot-Press Hybrid Sintering Processes
Authors: Takahashi Hirofumi , Kato Kazuaki , Qiu Jinhao , Tani Junji , Nagata Kunihiro
Published: October 2002

It has been shown in our previous work that the 28 GHz microwave sintering process can improve the performances of piezoelectric actuators. The improved performances include larger output force, higher strength and a larger electromechanical coupling factor. The improvement in performances is attributed to the repression of grain growth due to rapid heating and improvement of the microstructure because of internal heating. The sintering time was reduced to 1/10 the time needed for the conventional technology due to the larger power and uniform heating in the microwave sintering process. In this study, the microwave sintering process was combined with the hot-press sintering process for further improvement of the performances of lead zirconate titanate (PZT) actuators and the sintering conditions of the hybrid process were investigated. It was confirmed that the combination of microwave and hot-press sintering processes can improve the performances of sintered PZT. In particular, it was found that the piezoelectric constant d
31 could be improved by as much as 30%.
Fabrication of Defect-Free Ferroelectric Liquid Crystal Displays Using Photoalignment and Their Electrooptic Performance
Authors: Kurihara Ryuji , Furue Hirokazu , Takahashi Taiju , Yamashita Tomo-o , Xu Jun , Kobayashi Shunsuke
Published: October 2002

A photoalignment technique has been utilized for fabricating zigzag-defect-free ferroelectric liquid crystal displays (FLCDs) using polyimide RN-1199, -1286, -1266 (Nissan Chem. Ind.) and adopting oblique irradiation of unpolarized UV light. A rubbing technique was also utilized for comparison. It is shown that among these polyimide materials, RN-1199 is the best for fabricating defect-free cells with C-1 uniform states, but RN-1286 requires low energy to produce a photoaligned FLC phase. We have conducted an analytical investigation to clarify the conditions for obtaining zigzag-defect-free C-1 states, and it is theoretically shown that zigzag-defect-free C-1 state is obtained using a low azimuthal anchoring energy at a low pretilt angle, while a zigzag-defect-free C-2 state is obtained by increasing azimuthal anchoring energy above a critical value, also at a low pretilt angle. The estimated critical value of the azimuthal anchoring energy at which a transition from the C-1 state to the C-2 state occurs is 3×10-6J/m2for the FLC material FELIX M4654/100 (Clariant) used in this research; this value is shown to fall in a favorable range which is measured in an independent experiment.
Microdeflection Liquid Crystal Display Modes Using Eight-Division Electrodes
Authors: Ishimaru Masashi , Okada Hiroyuki , Onnagawa Hiroyoshi
Published: October 2002

Microdeflection liquid crystal display modes that use eight-division electrodes are investigated. According to the multidomain formation of the eight-division structure, a wider viewing angle and gentler decay of transmittance versus voltage characteristics are expected. Under He–Ne laser irradiation, the threshold voltage of the transmittance versus voltage characteristics depends on the polarization direction of the incident light in a manner similar to that of previously reported microdeflection liquid crystal display modes. This threshold voltage change is explained by molecular motion and domain formation. The contrast ratio obtained is 354:1. Under white light illumination and crossed polarizer configuration, the contrast ratio is 43:1.
High-Temperature Thermoelectric Properties of NaxCoO2-δ Single Crystals
Authors: Fujita Kenjiro , Mochida Tadashi , Nakamura Kazuo
Published: October 2002

We measure the high-temperature thermoelectric properties of the Na
x
CoO2-δ single crystal for the first time. The Na
x
CoO2-δ single crystals are prepared by a flux technique, and the resulting flaky single crystals are very thin on the c-axis. The in-plane electrical resistivity (ρ), the thermoelectric power (S) and the in-plane thermal conductivity (κ) are measured in the range of 300 K to 800 K. The estimated power factor (PF=S
2·ρ-1) and the figure-of-merit (Z=S
2·ρ-1κ-1) are about 2.4 mW m-1 K-2 and 0.12 mK-1 at 300 K, respectively. These factors increase with temperature, and reach the value of PF=7.7 mW m-1 K-2 and Z=1.5 mK-1 at 800 K, and the dimensionless value of Z
T exceeds the criterion of 1. The PF and Z exceed the values of typical “high-temperature thermoelectric materials”, such as p-type FeSi2 and Si0.7Ge0.3. These results suggest that Na
x
CoO2-δ could be a very promising material for use in high-temperature thermoelectric power generation devices.
Emission Band Shift of the Cathodoluminescence of Y2SiO5:Ce Phosphor Affected by Its Activator Concentration
Authors: Shin Sang Hoon , Jeon Duk Young , Suh Kyung Soo
Published: October 2002

The high-temperature phase (X2-phase) and the low-temperature phase (X1 phase) of a potential low-voltage blue phosphor Y2SiO5:Ce have been studied. It is observed that as the concentration of Ce increased, the emission band of the X2 phase was shifted to the longer wavelength, toward the emission band of the X1 phase, when the phosphor synthesis was performed under reduction atmosphere. This phenomenon seems to be related to a preferential site of Ce in Y2SiO5 as the Ce concentration is increased. It appears that when the number of a large-size ions, Ce3+, is increased under reduction atmosphere, their coordination number is affected. One of the cation sites (B1 site) in its high-temperature phase (X2 phase) is preferentially occupied, and shows emission similiar to that of the low-temperature phase (X1 phase).
AC Calorimetric Thermal Diffusivity Measurement in Relatively Thick Samples by a Distance-Variation Method
Authors: Takahashi Fumiaki , Mori Takatoshi , Hamada Yukihiro , Hatta Ichiro
Published: October 2002

In our previous papers [I. Hatta, K. Fujii, A. Sakakibara, F. Takahashi, Y. Hamada and Y. Kaneda: Jpn. J. Appl. Phys. 38 (1999) 2988 and F. Takahashi, Y. Hamada and I. Hatta: Jpn. J. Appl. Phys. 38 (1999) 5278], we proposed the conditions required for precise ac calorimetric thermal diffusivity measurement along the surface of a plate-like sample by a distance-variation method. It was concluded that the method could be applied even to relatively thick samples although it had been originally developed for the thermal diffusivity measurement of thin samples. To confirm the above facts, we performed the thermal diffusivity measurement for thick samples of ceramics and glass, with thicknesses in the range of 50 to 750 µm. The results of the obtained thermal diffusivities for these samples are considered to be satisfactory for such thick samples.
Chemical Vapor Deposition of Copper Thin Film Using a Novel Precursor of Allyloxytrimethylsilyl Hexafluoroacetylacetonate Copper(I)
Authors: Zhang Minjuan , Sekiguchi Atsushi , Okada Osamu , Itsuki Atsushi , Ogi Katsumi
Published: October 2002

A new volatile liquid copper precursor of allyloxytrimethylsilyl hexafluoroacetylacetonate copper (I) [Cu(hfac)(aotms)], termed Cypron was studied for the chemical vapor deposition of copper (Cu-CVD) thin films. This precursor has higher vapor pressure and more suitable thermal stability than the previously known trimethylvinylsilyl hexafluoroacetylacetonate copper (I) [Cu(hfac)(tmvs)]. In the presence of water vapor, smooth copper films were obtained with a high deposition rate of about 90 nm/min at a low temperature of 190°C. The resistivity of the films was as low as 1.9µΩ·cm. The step coverage and filling property of this novel precursor were excellent.
Study of a Dielectric Constant Due to Electronic Polarization Using a Semiempirical Molecular Orbital Method I
Authors: Yamada Kotaro , Saiki Atsushi , Sakaue Hiroyuki , Shingubara Shoso , Takayuki Takahagi Takayuki Takahagi
Published: October 2002

We studied a method for estimating a dielectric constant due to electronic polarization ε
(e) using a semiempirical molecular orbital method. Using Clausius–Mosotti's relation, ε
(e) values of 350 organic compounds were calculated using electronic polarizability which was calculated using the modified neglect of diatomic overlap (MNDO) method and experimental density. The calculated dielectric constants ε
(e)
calc were compared with experimental data ε
exp, which were equal to the square of the refractive index, and we found a linear relationship represented by ε
exp=0.92 ε
(e)
calc+0.14. We estimated the dielectric constant using the above relationship for several polymer materials and found a close agreement with the experimental data. It is concluded that this relationship is useful in estimating the experimental dielectric constant due to electronic polarization.
Macropore Formation in Anodized p-Type Silicon
Authors: Harada Hiroshi , Shirahashi Takuma , Nakamura Mitsuhiro , Ohwada Takafumi , Sasaki Yoshifuru , Okuda Soichiro , Hosono Akihiko
Published: October 2002

The morphology of anodized p-type Si with the native oxide formed between the back surface of Si and the back metal was studied. Anodization of p-type Si having a 4.2 Å native oxide layer resulted in the formation of approximately rectangular parallelepiped macropores with pore size of 1–3 µm followed by needlelike structures with diameter of 1.7 µm and finally the mirror surface, with an increase of the current density.
Preparation of BiSrCaCuO Multilayers by Use of Slower Q-switched 266 nm YAG Laser
Authors: Satoru Kaneko Satoru Kaneko , Yoshitada Shimizu Yoshitada Shimizu , Seishiro Ohya Seishiro Ohya
Published: October 2002

Multilayers of Bi2Sr2Ca1Cu2O
x
/Bi2Sr2Cu1O
x
were prepared by pulsed laser deposition (PLD) using the fourth harmonic 266 nm YAG. Compared to an excimer laser, YAG PLD required the higher oxygen atmosphere. The higher oxygen pressure together with the lower energy generated by YAG laser collapsed the region of plume emission. In order to produce the same energy density as an excimer, only Q-switch was modulated by 2 Hz while the flash lamp kept the original repetition rate of 10 Hz. With the rate of 2 Hz, we obtained the higher energy density per pulse, and more stable laser output of the fourth harmonics, 266 nm. To characterize the multilayers, reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) were employed, and indicative of epitaxial layers with limited in-plane order. The resistivities of multilayers were measured by the Van der Pauw method, and showed the temperatures of superconducting transition, T
c0 (R=0), around 65 K on the multilayers.
Growth and Dielectric Properties of 0.48 Pb(Fe1/2Nb1/2)O3–0.52 PbTiO3 Single Crystal
Authors: Gao Yuqi , Xu Haiqing , Wu Yongjun , He Tianhou , Xu Guisheng , Luo Haosu
Published: October 2002

Large ferroelectric single crystals of 0.48 Pb(Fe1/2Nb1/2)O3–0.52 PbTiO3 solid solution system were first successfully grown using a modified Bridgman technique and their properties were investigated. The obtained crystals were about 25 mm in diameter, 100 mm in length and black in color. The crystal exhibited abnormal dielectric properties that the dielectric constant was as high as 30000 and the dielectric loss factor was about 0.5 at room temperature. The mechanism of this phenomenon was discussed.
Novel Mesogenic Polymer Stabilized Ferroelectric Liquid Crystal Display Device Exhibiting V-Shaped Electrooptic Characteristics
Authors: Shikada Masahiro , Tanaka Yoshiki , Xu Jun , Furuichi Keiji , Hasebe Hiroshi , Takatsu Haruyoshi , Kobayashi Shunsuke
Published: October 2002

By using a conventional commercially available ferroelectric liquid crystal (FLC), FELIX M4851/100 (Clariant Japan), which is doped with newly developed photocurable mesogenic liquid crystal monomers, 2A363 (DIC), a new FLC device exhibiting V-shaped electrooptic performance is successfully fabricated. In the fabrication process, the photocure is carried out in the smectic A phase without applying an external voltage and the mesogenic monomers may form a polymer network.
Photolithography and Selective Etching of an Array of Quartz Tuning Fork Resonators with Improved Impact Resistance Characteristics
Authors: Lee Sungkyu
Published: October 2002

Quartz tuning fork blanks with improved impact-resistant characteristics for use in Qualcomm mobile station modem (MSM)-3000 central processing unit (CPU) chips for code division multiple access (CDMA), personal communication system (PCS), and global system for mobile communication (GSM) systems were designed using finite element method (FEM) analysis and suitable processing conditions were determined for the reproducible precision etching of a Z-cut quartz wafer into an array of tuning forks. Negative photoresist photolithography for the additive process was used in preference to positive photoresist photolithography for the subtractive process to etch the array of quartz tuning forks. The tuning fork pattern was transferred via a conventional photolithographical chromium/quartz glass template using a standard single-sided aligner and subsequent negative photoresist development. A tightly adhering and pinhole-free 600/2000 Å chromium/gold mask was coated over the developed photoresist pattern which was subsequently stripped in acetone. This procedure was repeated on the back surface of the wafer. With the protective metallization area of the tuning fork geometry thus formed, etching through the quartz wafer was performed at 80°C in a ±1.5°C controlled bath containing a concentrated solution of ammonium bifluoride to remove the unwanted areas of the quartz wafer. The quality of the quartz wafer surface finish after quartz etching depended primarily on the surface finish of the quartz wafer prior to etching and the quality of quartz crystals used. Selective etching of a 100 µm quartz wafer could be achieved within 90 min at 80°C. A selective etching procedure with reproducible precision has thus been established and enables the photolithographic mass production of miniature tuning fork resonators.
The Property of Ta2O5 on Chemical Vapor Deposited Ru Film Fabricated using Tris(2,4-octanedionato)ruthenium for Application to Dynamic Random Access Memory Capacitor
Authors: Lee Joo Wan , Kim Kyong-Min , Song Han-Sang , Jeong Kyung-Cheol , Lee Jong Min , Roh Jae Sung
Published: October 2002

Chemical vapor deposited (CVD) Ru was adopted as a bottom electrode of Ta2O5 capacitor for application to gigabit scale dynamic random access memory (DRAM). Ru film was deposited with the precursor of tris(2,4-octanedionato)ruthenium, Ru(od)3, at 260°C in O2 ambient. We obtained Ru film with 44 µΩ·cm of electric resistivity after annealing at 700°C. The root mean square (RMS) surface roughness of the film was 3.3 nm on SiO2 and 7.4 nm on TiN. We also obtained a leakage current of 4.45×10-9 A/cm2 at 1 V with a SiO2 equivalent thickness of 1.12 nm in the TiN/Ta2O5/Ru capacitor. Double plasma treatment on Ta2O5 was more effective than single plasma treatment for obtaining low leakage current. The TiN layer under Ru was oxidized into TiO
x
during the rapid thermal process (RTP) annealing of the Ru film at 600°C in N2 ambient. The remaining oxygen in the Ru film is believed to be an oxygen source for the oxidation of TiN.
Optimization of Short Channel Effect with Arsenic Halo Implant through Polysilicon Gate
Authors: Chen Coming , Chang Chun-Yen , Chou Jih-Wen , Cheng Yao-Chin
Published: October 2002

Excellent p-type metal oxide semiconductor (PMOS) short channel effect is achieved by using a high-energy, large tilt angle arsenic implant as a P-channel halo. For the first time, it was found that the dopant profile of Halo was implanted through the poly-silicon gate. The channel concentration is modulated not only laterally from the gate edge but also vertically from the top of the polysilicon gate and this resulted in very flat short channel behavior. The effect of the arsenic halo implant was comprehensively studied and well characterized to explain this specific phenomenon. The gate-oxide integrity was examined by charge to break down (Q
BD). Excellent performance of 0.12 µm PMOSFET is also demonstrated in this work.
GaInAsP Microcylinder (Microdisk) Injection Laser with AlInAs(Ox) Claddings
Authors: Masayuki Fujita Masayuki Fujita , Reona Ushigome Reona Ushigome , Toshihiko Baba Toshihiko Baba , Akihiro Matsutani Akihiro Matsutani , Fumio Koyama Fumio Koyama , Kenichi Iga Kenichi Iga
Published: October 2002

We propose and demonstrate a 1.5-µm-GaInAsP/AlInAs microcylinder laser which improves the fragility of the microdisk laser. The threshold current density was comparable to that reported for the 0.98-µm-GaInAs microcylinder laser. The selective oxidation of the AlInAs claddings will further reduce the threshold by strong optical confinement in the disk like structure and will simplify the large-scale integration of this type of device.
Relation between Electron-Spin-Resonance and Constant-Photocurrent-Method Defect Densities in Hydrogenated Amorphous Silicon
Authors: Shimizu Tatsuo , Shimada Masaki , Sugiyama Hidekazu , Kumeda Minoru
Published: October 2002

The cause of a large discrepancy between the defect densities evaluated by electron spin resonance (ESR) and the constant photocurrent method (CPM) in a-Si:H was investigated. a-Si:H films of various thicknesses were light-soaked with both white light and red light to increase the defect density. The defect densities for these light-soaked films were evaluated both by ESR and CPM. The results were reproduced fairly well by a computer simulation by taking into account the inhomogeneous defect distribution across the film thickness caused by a penetration depth of the light smaller than the film thickness. The presence of negatively charged dangling-bonds was found to also contribute to the discrepancy between the defect densities evaluated by ESR and CPM for the thin film light-soaked with the red light in addition to the inhomogeneous distribution of defects.