bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of Alkali Durability of Silver-Based Multilayer Coatings for Use in Flat Panel Displays
Authors: Aoshima Yuki , Miyazaki Masami , Sato Kazuo , Akao Yasuhiko , Takaki Satoru , Adachi Kunihiko
Published: October 2002

Silver-based multilayer coatings are well known to be transparent films with low electrical resistivity. In particular, indium and zinc composite oxide (IZO)/silver containing palladium (AgPd) multilayer coatings have good pattering properties and durability. However, the IZO/AgPd multilayer coatings do not have sufficient alkali durability as transparent electrodes of flat panel displays (FPDs). In order to solve this problem, coatings covered with a protective layer of tin-doped indium oxide (ITO) were investigated. Over-coating of an ITO layer degraded the patterning properties of the multilayer coatings because the etching rates of ITO, IZO and AgPd layer were very different. From the viewpoint of controlling the etching rate of each layer independently, the etching solution composed of hydrobromic acid and iron chloride was adjusted, so that the ITO/IZO/AgPd/IZO/AgPd/IZO/substrate multilayer coatings could be fabricated into fine patterns for electrodes. The multilayer coatings thus prepared are more tolerable for alkali detergents used in the production process of FPDs.
Preparation of a Contact System with a Single-Oriented (111)Al Overlayer by Interposing a Thin ZrN/Zr Bilayered Barrier Applicable to Sub-0.25-µm Design Rule
Authors: Hidekazu Miyake Hidekazu Miyake , Hideto Yanagisawa Hideto Yanagisawa , Katsutaka Sasaki Katsutaka Sasaki , Satoko Shinkai Satoko Shinkai , Yoshio Abe Yoshio Abe
Published: October 2002

Sequential single-oriented growth of a (111)Al/(111)ZrN/(002)Zr trilayered film could be realized on (001)Si, when a ZrN(200 Å)/Zr(200 Å) bilayered film was interposed between Al and Si. It was revealed that the system tolerated thermal treatment at 400°C, while maintaining a ZrSi2 region with the lowest contact resistivity at the Si interface and the single-oriented state of (111)Al overlayer. Therefore, it is concluded that the interposition of a ZrN/Zr bilayered film, which is applicable to the sub-0.25-µm design rule, is useful for realizing a highly reliable contact system.
Synchrotron Radiation-Induced Nitrization and Oxidation on Si Surface at Low Temperature
Authors: Kanashima Takeshi , Maida Osamu , Kohma Norinao , Agata Masashi , Yudate Shinji , Ueno Masato , Okuyama Masanori , Ohashi Haruhiko
Published: October 2002

Irradiation effects of soft X-rays on Si wafer in O2 and N2 atmospheres have been studied at SPring-8, the synchrotron radiation (SR) facility in Japan. Si wafers were irradiated in O2 and N2 ambients of 3 ×10-3, 0.2 and 12 Pa. The Si surfaces were analyzed by Auger electron spectroscopy to study the changes on the Si surface. In the case where O2 or N2 gas pressure is the order of 10-3 Pa, etching of the native oxide is observed. On the other hand, a Si (92 eV) L
23
V
V peak shift was observed at a pressure of 12 Pa at low temperatures below 150°C. Nitrization and oxidation of the Si surface can be promoted by direct reaction of silicon with nitrogen and oxygen gases at low temperature by soft X-ray irradiation.
High Voltage Generation from Inductive Pulsed Power Generator Using a Marx Circuit and an Exploding Wire
Authors: Shimomura Naoyuki , Nagata Masayoshi , Akiyama Hidenori
Published: October 2002

High voltage output up to 800 kV with voltage risetimes of 15 to 40 ns is successfully generated by a compact pulsed power generator (60×120×150 cm3) with an inductive energy storage system. This pulsed power generator consists of a Marx circuit, an inductor, and a thin and long exploding copper wire. The circuit parameters including an exploding wire are optimized for a high voltage generation, avoiding a re-strike of the wire. It is shown that the ratio of the energy in a storage inductor at the beginning of wire vaporization on the energy consumed during wire vaporization is essential in the production of a high voltage.
Electrical Circuit Analysis of Coplanar Plasma Display Panels Using a Simple Discharge Model
Authors: Tamida Taichiro , Iwata Akihiko , Nishimae Jun-ichi , Tanaka Masaaki
Published: October 2002

We have developed a simple method of modeling the electrical characteristics of a plasma display panel discharge. We analyze the discharge phenomena of coplanar plasma display panels (PDPs), and the model is sufficiently simple to express the electrical characteristics of the phenomena. Being a combination of primitive electric elements, this model can be calculated using a general-purpose circuit simulator, which enables us to simulate the PDP electrical characteristics easily and promptly. This model can quantitatively predict the discharge current waveform, and its dependence on the power supply condition and electrode geometry within the range of practical conditions. We can state that this model is a very useful tool for the analysis and design of PDP apparatus.
Photo-electrochemical Deposition of Platinum on TiO2 with Resolution of Twenty Nanometers using a Mask Elaborated with Electron-Beam Lithography
Authors: Juodkazis Saulius , Yamaguchi Akira , Ishii Hidekazu , Matsuo Shigeki , Takagi Hitoshi , Misawa Hiroaki
Published: October 2002

We report the patterning of Pt on a TiO2-rutile single crystal (the fundamental absorption band starts at 396 nm) by direct deposition from a water solution of H2PtCl6 (10–20 mmol/dm3) using laser beam writing at 390–396 nm, or by Hg-lamp illumination (i-line at 365 nm). Pt deposition was corroborated by microchemical analysis. A resolution of the Pt patterning down to 20-30 nm was achieved. To create a Pt pattern with resolution of twenty nanometers, we employed a mask elaborated with electron-beam (EB) drawing lithography. The mask was transparent to the writing illumination. The Pt was reduced from the solution by laser beam scanning over resist-covered regions, while the pattern was formed in the openings of the resist. Separation of the growth and illumination regions, typically, by 0.5–2 µm, facilitates the deposition of reproducible, high-aspect-ratio patterns. It is demonstrated that Pt was deposited through a process of diffusion of the light-excited carriers. The possibility of fabrication of a three-dimensional Pt pattern by the overgrowth of the resist is discussed.
Simulation of the van der Pauw Measurement for Electrically Anisotropic Semiconductors Using the Finite-Element Method
Authors: Sato Yuichi , Sato Susumu
Published: October 2002

Semiconductors, which are electrically anisotropic, are often obtained due to their methods of preparation or their own characteristics. Measurement values of such anisotropic semiconductors obtained by the van der Pauw method are simulated using the finite-element method (FEM). It is clarified that the values are quite sensitive to anisotropy of the carrier mobility, and variations in the measurement values can reach about two orders of magnitude even when the anisotropy is small.
Structural Stability of Carbon Nanotube Tips on Nanoindentation of Polycarbonate
Authors: Seiji Akita Seiji Akita , Yoshikazu Nakayama Yoshikazu Nakayama
Published: October 2002

We have investigated conditions for making nanoindents on a polycarbonate using a carbon nanotube tip in terms of structural stability of the nanotube tip. Even under a weak force of ∼ 50 nN acting in the axial direction to the nanotube, the indents with mean depth of 3.91 nm were successfully realized on the polycarbonate in air at room temperature. In this case, there were no structural changes of the nanotube tip after 51 indentation experiments from observations using a transmission electron microscope. This could be achieved by using not only a low-force condition but also by the appropriate shape of the nanotube tip.
Photoluminescence of GaAs Tip Apex Excited by Evanescent Wave
Authors: Satoshi Hattori Satoshi Hattori , Kazuhisa Sueoka Kazuhisa Sueoka , Yasuo Ohdaira Yasuo Ohdaira , Hirokazu Hori Hirokazu Hori , Kōichi Mukasa Kōichi Mukasa
Published: October 2002

To characterize the optical properties of a semiconductor tip apex or semiconductor nanoparticles attached to a tip apex, an experimental setup to detect the photoluminescence (PL) spectra of the specimens excited by the evanescent wave was constructed. The tip-prism surface distance dependency of the PL spectra was observed by means of a prism covered with conducting thin films which were used to define the origin of the separation by detecting the tunneling current. It was demonstrated that the PL intensity exponentially depends upon the separation.
Molecular Ferroelectricity of Vinylidene Fluoride Oligomer Investigated by Atomic Force Microscopy
Authors: Kei Noda Kei Noda , Kenji Ishida Kenji Ishida , Atsushi Kubono Atsushi Kubono , Toshihisa Horiuchi Toshihisa Horiuchi , Hirofumi Yamada Hirofumi Yamada , Kazumi Matsushige Kazumi Matsushige
Published: October 2002

Nanometer-scale electrical properties of local ferroelectric domains formed in thin films of newly synthesized vinylidene fluoride (VDF) oligomer were investigated by atomic force microscopy (AFM). Local poling and observation of the piezoelectric response revealed that the polarized domains were reversibly formed and erased in a nanometer-thick film by applying dc or pulse voltages between the electrically conductive AFM tip and the bottom electrode. The formed domain size depends on the pulse poling conditions and increases when the magnitude and the duration of a pulse voltage are increased. A local domain with a diameter of 65 nm was successfully created. The results in this work are comparable to those of previous studies performed on ferroelectric polymer thin films, suggesting that this material is one of the promising candidates for ferroelectric applications such as high-density data storages, and for molecular controls of ferroelectric properties.
N-Plasma Assisted Molecular Beam Epitaxy of GaN(0001̄) Thin Films on 6H-SiC(0001̄)
Authors: Xue Qi-Zhen , Xue Qi-Kun , Kuwano Satoko , Nakayama Koji , Sakurai Toshio
Published: October 2002

On the atomically flat C-face 6H-SiC surface prepared by ultra high vacuum Si-etching, two-dimensional growth of GaN (0001̄) thin films is observed with an AlN buffer layer using N-plasma assisted molecular beam epitaxy. Scanning tunneling microscopy measurements reveal a series of Ga-stabilized reconstructions, which are consistent with the surface phases reported for the GaN (0001̄) film, but are different from that of the GaN(0001) surface. The result agrees with the polarity assignment of the heteroepitaxial wurtzite GaN films on polar 6H-SiC substrates, that is, a GaN film grown on SiC(0001̄) is <0001̄> oriented (N-face) while that on SiC(0001) is <0001> oriented (Ga-face).
Adsorption and Wetting Structures of Kr on Pt(111) at 8 K and 45 K Studied by Scanning Tunneling Microscopy
Authors: Jun Li Yan , Norimi Futaba Koji Miyake , Masuaki Matsumoto Masuaki Matsumoto , Tatsuo Okano Tatsuo Okano , Hidemi Shigekawa Hidemi Shigekawa
Published: October 2002

Adsorption and wetting structures of Kr on Pt(111) were studied using scanning tunneling microscopy. The characteristics were different from those of Xe/Pt(111) and Xe/Cu(111). At 8 K, Kr atoms adsorbed on terraces and preferential adsorption to step edges was not observed. Kr atoms were imaged with 0.12 nm height and 1.0 nm full width at half maximum. With the additional exposure, adsorption at step edges occurred, with a slight preference for the upper step edges. However, no evidence for the characteristic properties, such as repulsive interaction between adsorbates or modification of the electronic structures at step edges, was observed. With the rise in temperature to 45 K, Kr atoms on the terraces increased in size with hexagonal shape, and wetting of the step edges began. In the wetting process, the lower step edge was more preferential, and the wetting region on both step edges grew with a stripe shape; the edge of the wetting region was not irregular but straight and parallel to the steps. In addition, the height of the Kr images decreased and showed two different values, namely, Kr stripes grown from the lower step edges were observed to have 0.10 nm height, 0.02 nm higher than those with a height of 0.08 nm grown on terraces or at upper step edges. The obtained results indicate the existence of two different structures, which may be attributed to the two structures previously observed by the macroscopic analyses.
Manipulation of Atoms and Molecules with the Low-Temperature Scanning Tunneling Microscope
Authors: Meyer Gerhard , Moresco Francesca , Hla Saw Wai , Repp Jascha , Braun Kai-Felix , Fölsch Stefan , Rieder Karl Heinz
Published: October 2002

The controlled manipulation with a scanning tunneling microscope (STM) down to the scale of small molecules and single atoms allows the buildup of molecular and atomic nanostructures. In the case of the lateral manipulation of adsorbed species, in which only tip/particle forces are used, three different manipulation modes (pushing, pulling, sliding) can be discerned. Vertical manipulation of Xe and CO is demonstrated, leading to the formation of functionalized tips, which can be used for improved imaging and even to perform vibrational spectroscopy on single molecules. Furthermore, we describe how we have reproduced a full chemical reaction with single molecules, whereby all basic steps, namely, preparation of the reactants, diffusion and association, are induced with the STM tip.
Experimental Evaluation of Pencil Beam Algorithm by Measurements of Dose Distributions of Protons Traversing an L-Shaped Phantom
Authors: Ryosuke Kohno Ryosuke Kohno , Yoshihisa Takada Yoshihisa Takada , Takeji Sakae Takeji Sakae , Akihiro Nohtomi Akihiro Nohtomi , Toshiyuki Terunuma Toshiyuki Terunuma , Kiyoshi Yasuoka Kiyoshi Yasuoka
Published: October 2002

A proton dose-calculation method has been developed on the basis of the pencil-beam algorithm (PBA), which is expected to improve the precision of the conventional method based on the broad-beam algorithm (BBA). In order to verify the accuracy of calculation by the PBA, dose distributions formed by a horizontal proton beam traversing a phantom with an L-shaped horizontal cross section were measured using a silicon semiconductor detector (SSD) in a water vessel. The results of the measured dose distributions agree well with the ones calculated using the PBA within an rms error of 2.3%. Therefore, the dose-calculation method by the PBA is useful and applicable to actual treatment planning of the proton therapy.
Photoluminescence Study on InGaN/GaN Quantum Well Structure Grown on (112̄0) Sapphire Substrate
Authors: Bai Jie , Wang Tao , Sakai Shiro
Published: October 2002

An investigation of temperature-dependent photoluminescence is carried out on InGaN/GaN multiple-quantum-well (MQW) structures with 2.5 nm well thickness grown on (0001) and (112̄0) orientation sapphire substrates. Based on a band-tail model, the exciton localization effect is investigated with regard to the substrate orientation. On the (0001) sapphire substrate, the emission energy decreases monotonically with increasing temperature from 10 K to room temperature. However, on the (112̄0) sapphire substrate, the emission energy shows a temperature-induced blue shift at temperatures above 70 K, which is a typical characteristic of the occurrence of the exciton localization effect in an InGaN/GaN quantum well structure. Therefore, our result indicates that the exciton localization effect can be enhanced by growing InGaN/GaN MQW structures on (112̄0) sapphire substrates. Since the exciton localization effect is generally accepted to be advantageous for enhancing the emission quantum efficiency of the InGaN/GaN MQW, the results presented in this paper should be seriously considered.
Structural Features of Σ=3 and 9, [110] GaAs Tilt Grain Boundaries
Authors: Cho Nam-Hee , Carter C. B.
Published: October 2002

The planar density of coincidence sites appears to be high along the observed boundary planes for the Σ=3 and 9, [110] GaAs tilt grain boundaries. The polarity in each grain on either side of the tilt grain boundaries has been confirmed by direct or indirect methods. The result indicates that a lower number of anti-site type bonds occur along the boundaries compared to when the polarity of one grain is reversed. Based on high-resolution transmission electron microscopy (HRTEM) analysis of several different symmetric and asymmetric Σ=3 and 9, [110] tilt grain boundaries in GaAs, models for the atomic structures of these boundaries have been made for the first time; particular atomic arrangements form the structural units of these boundaries.
A New Sample Structure for Position-Controlled Giant-Grain Growth of Silicon using Phase-Modulated Excimer-Laser Annealing
Authors: Yoshimoto Satoshi , Oh Chang-Ho , Matsumura Masakiyo
Published: October 2002

A new sample structure has been proposed for position-controlled growth of giant Si grains by a phase-modulated excimer-laser annealing method. The sample consists of a layered structure with an organic silica underlayer at the bottom for reducing the heat removal rate from the Si layer placed on it, and a thick silica capping-layer on the top, for enlarging the amount of excess stored heat. These layers effectively elongated the grain growth time, resulting in the long lateral grain growth to 24 µm. In addition, a sample having a buried silica island array in the Si layer has also been proposed for achieving two-dimensional position control, where the island determines the starting position of the lateral grain growth. By combining these technologies, we have grown single crystals of Si grains as large as 12 µm at pre-designated positions by single-shot irradiation.
Si Nanocrystal Memory Cell with Room-Temperature Single Electron Effects
Authors: Kim Ilgweon , Han Sangyeon , Han Kwangseok , Lee Jongho , Shin Hyungcheol
Published: October 2002

A metal oxide semiconductor (MOS) memory based on Si nanocrystals has been fabricated. We have developed a repeatable process for forming uniform, small and high-density Si nanocrystals by low pressure chemical vapor deposition (LPCVD). Spherical nanocrystals with a 4.5 nm average diameter and a density of 5×1011/cm2 were obtained. A single transistor memory-cell structure, with a change in threshold voltage of about 0.48 V, corresponding to single electron storage in individual nanocrystals and having the capability of long-term charge storage is fabricated and characterized. For the first time, the single electron effect at room temperature, which shows a saturation of threshold voltage in a range of gate voltages with a periodicity of ΔV
GS≈1.7 V, corresponding to single and multiple electron storage is reported. These finding prove the feasibility of a practical nanocrystal memory with potential for significantly high density, low power, and fast reading properties.
Transport Characteristics of the Cross Junction of Atomic Chains
Authors: Shimizu Tomo , Kenji Natori Kenji Natori , Nobuyuki Sano Nobuyuki Sano
Published: October 2002

The electronic transport through the cross junction of atomic chain wires is investigated considering the subband coupling. The transmission and the reflection probabilities are analyzed using the tight-binding model for the one-row, two-row, three-row and five-row chain crosses. Due to mirror symmetry of the system, the number of forward-transmitted responses is limited by parity conservation, but the side-turning transmission suffers no such restriction. The forward transmission prevails when the incident wave energy is near the band edge. However, a considerable amount of flux is directed sideways toward the midband, and eventually, the side-turning transmission shows a great lead over the forward transmission around the midband, which is characteristic of the discrete atomic chain cross junction. The bound state at the cross point is also investigated.
Selective Excitation of a Symmetric Interference Plasmon Mode in Two Close Planar SiO2/Si Interfaces Observed by Electron Energy-Loss Spectroscopy
Authors: Komoda Hirotaka , Watada Atsuyuki , Ishida Kazutaka , Sasakawa Kaoru , Okano Tomoki , Tsubokawa Yoshiyuki , Terauchi Masami
Published: October 2002

We have studied the effects of the SiO2/Si interface parallel to an electron beam on transmission electron energy-loss spectra of a SiO2 area for poly-Si/SiO2/Si samples. The dependence of the energy-loss spectra on the distance from the interface to the probe position and on the distance between two interfaces was investigated. Spectra obtained from the center of the thick (150 nm) SiO2 layer had no peak in the energy region of 4–10 eV. However, a peak at about 7 eV was observed in the spectra obtained at a position of 7.5 nm from the SiO2/Si interface for the same specimen. This peak was assigned to a SiO2/Si interface plasmon excitation. For the thin (15 nm) oxide poly-Si/SiO2/Si sample, on the other hand, the peak appeared at 8.7 eV. Furthermore, this peak shifts to higher energies as the oxide thickness decreases. This peak was assigned to an excitation of a symmetric interference plasmon mode in two close planar SiO2/Si interfaces.
Crystallinity of GaN Thin Films Directly Grown on Metal Foils by the Reactive Evaporation Method
Authors: Sato Yuichi , Hishinuma Toshifumi , Sato Susumu
Published: October 2002

GaN thin films are grown on several metal foils of 50 µm thickness and their crystallinity is compared with that of films on a quartz glass substrate. X-ray diffraction peaks other than the GaN c-face appear when the metal foils are used, while highly c-axis-oriented GaN thin films are obtained on the quartz glass substrate under the same growth conditions. The reasons for the difference in their crystallinity are discussed from the viewpoints of surface roughness, diffusion property and crystallinity of the metal foils used.
Characterization of Internal Capacitors Based on Glass-Added Barium Titanate
Authors: Chen Lih-Shan , Fu Shen-Li , Lin Wen-Kuan , Huang Kwan-Dar
Published: October 2002

Barium–calcium–aluminum–borosilicate glass is added as a sintering promoter to reduce the sintering temperature of barium titanate. The dielectric properties of the glass-added barium titanate-based internal capacitors are investigated. The dielectric constants of the composites were found to increase with sintering temperature. A capacitance of about 2.3 nF/cm2 with the dissipation factor of 2.9% is obtained for a 20 wt% glass-added BaTiO3 internal capacitor after being cofired with low dielectric constant ceramic substrate at 950°C. The percent change of capacitance is confined within ±10% and the dissipation factor is stable in the measured temperature range.
Calculation Principle of Stored Energy and Effective Power in Piezoelectric Transducer using Infinite Series of a Complex Dynamical Variable and Its Finite Difference
Authors: Michio Ohki Michio Ohki , Kohji Toda Kohji Toda
Published: October 2002

Both effective power and stored energy in a piezoelectric transducer can be calculated by a simple mathematical method using infinite geometric series of a complex dynamical variable η instead of solving an ordinary or partial differential equation; this differs from the conventional methods which deal with the concept of complex power based on the theory of alternating-current phenomenon. The stored energy can be obtained by a superposition of η, in which the method of superposition reflects the electrical and mechanical boundary conditions in the transducer. By considering the finite difference of η, the effective power can also be evaluated using a method of superposition and the uncertainty principle. This method can deal with the system having an infinite number of degrees of freedom along with dissipative process, simply and easily, and is consistent with the second law of thermodynamics.
Realization of Cu(111) Single-Oriented State on SiO2 by Annealing Cu–Zr Film and the Thermal Stability of Cu–Zr/ZrN/Zr/Si Contact System
Authors: Katsutaka Sasaki Katsutaka Sasaki , Hidekazu Miyake Hidekazu Miyake , Satoko Shinkai Satoko Shinkai , Yoshio Abe Yoshio Abe , Hideto Yanagisawa Hideto Yanagisawa
Published: October 2002

We investigated whether the Cu(111) single-oriented state having excellent electromigration resistance could be realized on SiO2/Si and Si wafers by annealing Cu–Zr alloy films in vacuum. It was revealed that the Cu(111) single-oriented state could be realized on both substrates of SiO2/Si and 7059 glass, when Cu–Zr films were annealed at 500°C for 5 min. The obtained resistivities of the Cu–Zr films after annealing above 400°C were lower than those (3–3.5 µΩcm) of Al alloy systems. Next, we examined the thermal stability of the Cu–Zr/ZrN/Zr/Si contact system, and compared it with that of the Cu/ZrN/Zr/Si system. As a result, although the thermal stability of the former was somewhat inferior to that of the latter, the system was sufficiently stable up to 550°C, maintaining the single-oriented state of the Cu(111) overlayer and the ZrSi2 region with the lowest contact resistivity at the Si interface.
Numerical Study of Population Inversion between Excited States of Ar i in a Recombining Ar Plasma by He Contact Cooling
Authors: Kano Katsuhiro , Akatsuka Hiroshi
Published: October 2002

In the present paper we report on the numerical simulation of He contact cooling of electrons for generation of population inversion in a recombining Ar plasma. It is shown that the electron temperature of Ar plasma is significantly decreased by the gas-contact cooling, so that population inversion is created between excited states of Ar i. The mechanism leading to the population inversion in Ar plasma has also been investigated. It has been shown that the electron density should be controlled to obtain a large overpopulation density.
Effect of Gas Composition on TiN Thin-Film Fabrication in N2/H2/Ar/TiCl4Inductively Coupled Plasma-Enhanced Chemical Vapor Deposition System
Authors: Jang Seong-Soo , Lee Won-Jong
Published: October 2002

TiN films were deposited in a N2/H2/Ar/TiCl4rf inductively coupled plasma and the effect of gas composition on the properties of the TiN films were analyzed through investigation of the plasmas with a Langmuir single probe and a mass spectrometer. The quality of TiN films depended critically on the concentration of H and N radicals. H2had the effect of removing Cl from the TiCl4and reducing N radicals in the plasma although the plasma density and electron temperature were not significantly affected. Accordingly, high-quality TiN films with low Cl content and good electric properties were obtained with 10∼20% of H2. With the addition of Ar, the plasma density increased and the dissociation of the precursors was enhanced; as a result, the production of N and H radicals was enhanced and the quality of TiN films was improved.
Increased Thermal Stability of W/Ta2O5 Gate Structure Using Effective Diffusion Barrier of Denuded Tungsten Nitride
Authors: Cho Ihl Hyun , Park Ji-Soo , Sohn Dong Kyun , Ha Jae Hee
Published: October 2002

We investigated the effect of TiN and WN
x
diffusion barrier on the thermal stability and electrical properties of W/Ta2O5 gate structure. For TiN/Ta2O5 system annealed at 950°C, both tantalum and oxygen in Ta2O5 films significantly migrated to TiN layer, resulting in the partial oxidation of TiN and the formation of voids in the Ta2O5 layers and increasing the roughness at the TiN/Ta2O5 interface. However, for the WN
x
/Ta2O5 system annealed even at 950°C, no outdiffusion of tantalum and oxygen from Ta2O5 into annealed-WN
x
layer was observed. A nitrogen-rich barrier with Ta–O–N bonding formed on Ta2O5 surface during denudation of WN
x
caused the high thermal stability of WN
x
/Ta2O5. The electrical characteristics of W/WN
x
/Ta2O5 system was found to be more superior than that of W/TiN/Ta2O5 in the respect of leakage current and breakdown voltage, thus it can be one of promising metal gate structures with high-dielectric in sub-100 nm metal-oxide semiconductor (MOS) devices.
Evolution of Magnetotransport Properties and Spin-Glass Behavior of the La0.7-xNdxPb0.3MnO3 System
Authors: Young S. L. , Chen H. Z. , Horng Lance , Shi J. B. , Chen Y. C.
Published: October 2002

The effect of neodymium substitution on the lanthanum site in La0.7-x
Nd
x
Pb0.3MnO3 perovskite polycrystalline has been systematically studied. The substitution of neodymium for lanthanum causes structure change from rhombohedral to orthorhombic. Ferromagnetism is suppressed as neodymium content increases. The magnetic order changes from a ferromagnetic long-range order with x=0.0 to a spin-glass nature with x=0.7. Besides, the ferromagnetic-paramagnetic transition temperature values are lower for the neodymium phases than for the lanthanum ones. Therefore, the introduction of neodymium degrades symmetry of the structure, diminishes the spin-coupling exchange interaction, and results in changes of magnetic properties. This fact is in good agreement with increasing the B value in Bloch's T
3/2 law and decreasing the spin-wave stiffness parameter D in quadratic dispersion relation.
Dielectric Properties of BaTiO3 Codoped with Er2O3 and MgO
Authors: Hwang Jin Hyun , Choi Sang Keun , Han Young Ho
Published: October 2002

The effect of Er2O3 and MgO addition on the dielectric properties of BaTiO3 ceramics was studied in a reduced atmosphere. MgO effectively prevented the material from being reduced and suppressed grain growth. An X7R material with moderate temperature dependence was developed by the addition of MgO with higher than 2.0 mol% Er2O3 to BaTiO3, which is ascribed to the decrease in grain size and the grain core-grain shell structure. In the presence of equimolar amount of B-site metal ions, there was no evidence to support the incorporation of Er ions into the octahedral and dodecahedral cation sites.
Low-Loss Dielectrics in Pb(Mg1/3Nb2/3)O3–SrTiO3 System
Authors: Chen Xiang Ming , Hu Xing , Hu Guo Long
Published: October 2002

Pb(Mg1/3Nb2/3)O3 dielectrics modified by SrTiO3 were prepared by a solid-state reaction method, and microstructure analyses were performed together with the dielectric characterization. The solid solutions with a cubic perovskite structure were obtained for all the compositions in the present system, except that a small amount of pyrochlore secondary phase was observed for x=0.1. The dielectric loss and temperature coefficient could be markedly reduced by incorporating SrTiO3 into Pb(Mg1/3Nb2/3)O3. Low-loss dielectrics (tan
δ=0.0003–0.0007 at 1 MHz) with a very high dielectric constant (289–2022) and a reduced temperature coefficient (τc∼-2746 to -5299 ppm/°C) were obtained in the present system.
Synthesis of C-Axis-Oriented Aluminum Nitride Films by Reactive RF Magnetron Sputtering for Surface Acoustic Wave
Authors: Kao Kuo-Sheng , Cheng Chien-Chuan , Chen Ying-Chung
Published: October 2002

C-axis-oriented aluminum nitride (AlN) films were deposited on SiO2-coated Si substrates by reactive rf magnetron sputtering. The crystallization of the AlN films, identified by X-ray diffraction (XRD) , was dependent on the deposition conditions. Highly c-axis-oriented AlN films, for fabricating AlN/SiO2/Si-based surface acoustic wave (SAW) devices, were obtained under an rf power of 300 W, substrate temperature of 350°C, sputtering pressure of 7.5 mTorr and N2 concentration of 75%. A dense pebblelike surface texture of the c-axis-oriented AlN films with an average grain size of about 100 nm was observed by scanning electron microscopy (SEM). The phase velocity showed a tendency to decrease with increasing k
h, where k=2π/λ is the wavenumber and h is the AlN film thickness. In partucular, the phase velocity and the electromechanical coupling coefficient of the sample at k
h=0.4 were calculated to be about 6080 m/s and 1.1%, respectively.
Enhanced Retention Characteristics of Pb(Zr, Ti)O3 Capacitors by Ozone Treatment
Authors: Lee Kyu-Mann , An Hyeong-Geun , Lee June-Key , Lee Yong-Tak , Lee Sang-Woo , Joo Suk-Ho , Nam Sang-Don , Park Kun-Sang , Lee Moon-Sook , Park Soon-Oh , Kang Ho-Kyu , Moon Joo-Tae
Published: October 2002

Effects of ozone treatment and charged defects on retention characteristics of Ir/IrO2/Pb(Zr, Ti)O3 (PZT)/Pt/IrO2/Ir capacitors were systematically investigated. For these purposes, PZT thin films were exposed to ozone environment to promote enhanced surface oxidation. After baking the Ir/IrO2/PZT/Pt/IrO2/Ir capacitors at 125°C for 500 h, degradation of Q
nv (non-volatile charge) value of the ozone-treated capacitors was approximately 17.6%, that is less than one fifth of that of the untreated capacitors. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) studies showed that the amount of oxygen-vacancies near the PZT surface was dramatically decreased by the ozone treatment. The Schottky barrier height of the ozone-treated capacitors increased when compared to that of the untreated capacitors (the Schottky barrier height of the untreated and the ozone-treated capacitor was 0.29 eV and 0.43 eV, respectively). Therefore, one can conclude that the retention characteristics seem to be closely associated with oxygen related defects near the ferroelectric/electrode interface and the control of the interface properties of PZT thin film is a key technology to pursue reliable function characteristics of ferroelectric random access memory (FRAM) devices.
Mechanical String Model for Liquid Crystal Ensemble: A Comprehensive Model for Polymorphism
Authors: Toriyama Kazuhisa , Kimura Hatsuo , Onnagawa Hiroyoshi
Published: October 2002

A mechanical string model is proposed for liquid crystal phase behaviour to comprehensively interpret the polymorphism phenomenon. In the proposed mechanical string model, the strings consist of many molecules existing among many layers in a smectic phase stretched perpendicular to the layers. The string itself induces self-excitation, a resonance between the string's vibrational mode and local molecular vibration or rotational motion, which in turn induces a phase transition from one phase to another phase at these resonance points. We propose a possible procedure for extracting and assigning a set of two parameters that represent the string's eigenvalue (energy term) and freedom of motion (entropy term) from the existing experimental data. The set of parameters or the code is a representation of the phase sequence or polymorphism of each liquid crystal. It is directed that such a code assignment of the ratios with rational numbers be originated in the mechanics of the string. The characteristic representations of the rational number sets for various liquid crystals are correlated to the molecular structures and their mechanical and dynamical characteristics.
Subtransition of Multilamellar L-α, Dibehenoyl (Cn=22) Phosphatidylcholine
Authors: Utoh Shigenori , Okubo Nobuaki
Published: October 2002

In multilamellar phospholipids in which the number of carbons per hydrocarbon chain (C
n
) is equal to or less than 18, e.g., L-α, Dipalmitoyl phosphatidylcholine (DPPC) for C
n
=16 and L-α, Distearoyl phosphatidylcholine (DSPC) for C
n
=18, the subtransition appears only during the heating process under atmospheric pressure after the phospholipids satisfy some special conditions such as the long-term cooling storage around 0°C for more than 72 h. However, the subtransition of multilamellar L-α, Dibehenoyl phosphatidylcholine with C
n
=22 (abbreviated as DBPC) appears not only during heating, but also in the subsequent cooling run without any special conditions under atmospheric pressure, and it is confirmed that the subtransition of multilamellar DBPC is composed of two phenomena. X-ray scattering analyses indicated changes of hydrocarbon chain packing as the subtransition by the following two-step process; orthorhombic symmetry \rightleftarrowsquasi-orthorhombic symmetry \rightleftarrowsquasi-hexagonal symmetry. These experimental results closely correspond to the phenomena under high pressure, which are obtained from multilamellar DPPC and DSPC conditioned by high-pressure melting above 250 MPa.
Interface and Surface Characterization of Lead Zirconate Titanate Thin Films Grown by Sol–Gel Method
Authors: Zhang Qi , Ren Tianling , Zhang Lintao , Zhu Jing , Li Zhijian
Published: October 2002

The ferroelectric Pb(Zr, Ti)O3 (PZT) thin films have been directly synthesized on silicon substrates by sol–gel method. X-ray diffraction (XRD) analysis reveals that besides the rhombohedral structure, the random oriented tetragonal perovskite PZT is formed with the lattice parameters of a=3.97 Å and c=4.10 Å. Energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) results indicate that the chemical composition of the PZT thin film is stoichiometric just as designed. High resolution electron microscopy (HREM) results show that amorphous SiO
x
(x=1–2) layer and nanometer lead grains are formed at the interface between the silicon substrate and PZT thin film.
Electron Tunneling through SiO2/Si Structures in Scanning Tunneling Microscopy
Authors: Iwasaki Hiroshi , Gotoh Masahide , Sudoh Koichi
Published: October 2002

We study electron tunneling through SiO2/Si(001) structures in scanning tunneling microscopy (STM), where the oxide thickness ranges from 0.6 to 2.7 nm. Electron tunneling probabilities through the structures are calculated by employing an exactly solvable one-dimensional model. The calculation reproduces the measured I–V characteristics very well. It is shown by experiment and calculation that a region covered by SiO2 is seen as a higher patch than the Si bare surface in a STM topography (constant current mode measurement). The apparent SiO2 “thickness” in STM topography is comparable to the calculated one for the 0.6 nm SiO2 but appears to be much thinner than the calculated one for the 2.7 nm SiO2. Origin of the discrepancy is discussed in terms of the electron scattering at the interfaces and in the bulk of SiO2 films.
Serially Grafted Waveguide Fabrication of Organic Crystal and Transparent Polymer
Authors: Takayama Kazuya , Komatsu Kyoji , Kaino Toshikuni
Published: October 2002

We have successfully fabricated a serially grafted waveguide combining a type of organic nonlinear optical (NLO) crystal, 4-(p-dimethylaminostyryl)-1-methylpyridinium tosylate (DAST), and a transparent polymer. To utilize the large electrooptic coefficient of the DAST effectively, a waveguide structure is desirable. Since organic crystals with large NLO effects show large optical losses, a major part of this serially grafted waveguide was composed of the transparent polymer. The input/output optical beam has been effectively coupled to the DAST crystal waveguide through the transparent polymer waveguide. This serially grafted structure is a potential candidate for fabricating many types of practical devices with optical nonlinearity such as the Mach-Zehnder interferometer(MZI).
Experimental Study on the Propagation of Electromagnetic Waves and the Spatial Distribution of Electric Potential
Authors: Hideo Sato Hideo Sato , Chihiro Yamanaka Chihiro Yamanaka , Motoji Ikeya Motoji Ikeya
Published: October 2002

A scaling model experiment on the propagation of electromagnetic (EM) waves, which satisfies the attenuation with distance, has been proposed theoretically and carried out experimentally. A model consisting of parallel plate waveguides representing the earth and ionosphere, ocean and conductive layer in the crust is constructed using a solution of NaCl as the model crust and aluminum foils as the ocean both with resistivities, ρ, which are 10-6 times lower than those of the real ones. The frequency of the EM waves, f was 106 times higher than the real value so that the wavelength and the skin depth, d=√2 πf/ρ were scaled down to 10-6 in concordance with the scaling factor. A method using the electrolytic tank was used to determine the distribution of DC potential. The profiles of the EM waves and the DC potential were influenced by the presence of the ocean and faults of the Tokai area, taken as an example. A scaling-up experiment was suggested for the mezoscopic and nanosized optical and EM devices.
Infrared Study of SiH4-Adsorbed Si(100) Surfaces: Observation and Mode Assignment of New Peaks
Authors: Yoshikazu Tsukidate Yoshikazu Tsukidate , Maki Suemitsu Maki Suemitsu
Published: October 2002

SiHn adspecies on Si(100)-2 ×1 surfaces adsorbed with SiH4 have been studied using multiple-internal-reflection infrared spectroscopy. In addition to the stretching modes of SiH, SiH2, and SiH3 known to be present on H-terminated Si surfaces, three new peaks were observed at 2036, 2060–2064, and 2077 cm-1. By observing the change of the peak intensities before and after the 300°C annealing as well as the effects of polarized radiation, the stretching modes at 2060–2064 cm-1 were concluded to be related to step-edge monohydrides, while the one at 2077 cm-1 was considered to be related to the monohydride at a dimer whose counterpart is –SiH3. Moreover, the SiH2 vibration is assigned to the bridging dihydrides between dimers, which is different from the one on HF-treated Si(100) known to be formed by breakage of the dimer bonds. These stretching modes are closely related to the presence of Si adatoms on the surface, providing new convenient probes for studying surface chemistry during epitaxy using SiH4 or Si2H6.
Characterization of InGaP/GaAs Heterojunction Bipolar Transistors with a Heavily Doped Base
Authors: Oka Tohru , Ouchi Kiyoshi , Mochizuki Kazuhiro
Published: October 2002

Characteristics of InGaP/GaAs heterojunction bipolar transistors (HBTs) with a heavily doped base are examined at the base doping level N
B ranging from 5×1019 to 5×1020 cm-3. At N
B of less than 3×1020 cm-3, the current gain is mainly determined by Auger recombination in the intrinsic base region and is inversely proportional to the square of N
B. In contrast, the current gain at N
B above 3×1020 cm-3 is significantly decreased. We evaluated the effective barrier height of holes between the emitter and the base by measuring temperature dependence of current gain, and found that the effective hole barrier is reduced as N
B increases. This result is explained by the large energy shift of the Fermi level inside the valence band due to heavy doping, causing the increase in the back injection of holes into the emitter, and thus reducing the current gain.
Extraction of Trap States at the Oxide-Silicon Interface and Grain Boundary for Polycrystalline Silicon Thin-Film Transistors
Authors: Kimura Mutsumi , Nozawa Ryoichi , Inoue Satoshi , Shimoda Tatsuya , Lui Basil On-Kit , Tam Simon Wing-Bun , Migliorato Piero
Published: October 2002

A technique to extract trap states at the oxide-silicon interface and grain boundary has been developed for polycrystalline silicon thin-film transistors with large grains. From the capacitance–voltage characteristic, the oxide-silicon interface traps can be extracted. Potential and carrier density are also extracted. From the potential, carrier density, and current–voltage characteristic, the grain boundary traps can be extracted by considering the potential barrier at the grain boundary. Since these trap states are sequentially extracted, any shape of energy distribution of the trap states can be extracted. The correctness of this extraction technique is confirmed by comparison with two-dimensional device simulation.
Device Simulation of Carrier Transport through Grain Boundaries in Lightly Doped Polysilicon Films and Dependence on Dopant Density
Authors: Kimura Mutsumi , Inoue Satoshi , Shimoda Tatsuya , Sameshima Toshiyuki
Published: October 2002

Carrier transport through grain boundaries in lightly doped polysilicon films has been analyzed using device simulation. Grain boundary defects not only trap and reduce free carriers, but also form potential barriers and interfere with carrier movement. The dependence of the energy band, carrier density, potential barrier and electric conductivity on the dopant density has been closely investigated. The carrier density increases monotonically as the dopant density increases. The potential barrier height reaches its maximum value when the dopant density is roughly equal to the defect density. The electric conductivity dramatically increases around the specific dopant density that is sensitive to the defect density. The actual defect density can be extracted by comparing the experimental electric conductivity with the simulated one. The device simulation is more reliable than analytical methods, since it can accurately handle phenomena such as the energy distribution and partial occupation of the grain boundary defects, partial ionization of the dopants, gradual depletion and so forth, which are neglected or approximated in the analytical methods.
Spectroscopic Ellipsometry Studies of Cd1-xMnxTe Films Grown on GaAs
Authors: Hwang Younghun , Kim Hyekyeong , Chung Moonsung , Um Youngho , Park Hyoyeol , Yoo Pyoungkil
Published: October 2002

Spectroscopic ellipsometry measurements of the complex dielectric function of a series of Cd1-x
MnxTe (0 ≤x ≤0.7) films grown on (100) GaAs by hot wall epitaxy have been performed in the 1.5–5.5 eV photon energy range at room temperature. The measured data were analyzed by fitting the second-derivative spectra (d
2ε/dω2) with a theoretical model, namely, the standard critical-point (SCP) line shapes. It was found that the SCP model explains the measured derivative spectra successfully. The composition dependence of the critical-point (CP) energies and Lorentzian broadening (Γ) was determined.
A Latch-up Immunized Lateral Trench Insulated Gate Bipolar Transistor with a p+ Diverter Structure for Smart Power Integrated Circuit
Authors: Goo Kang Ey , Hyun Moon Seung , Young Sung Man
Published: October 2002

A new lateral trench insulated gate bipolar transistor (LTIGBT) with a p+ diverter was proposed to improve the characteristics of the conventional LTIGBT. The p+ diverter layer was placed between the anode electrode and the cathode electrode. As the conventional LTIGBT has a p+ divert region, the forward blocking voltage was decreased significantly because the n-drift layer corresponding to the punch-through region was reduced. However, the forward blocking voltage of the proposed LTIGBT with a p+ diverter was about 140 V. That of the conventional LTIGBT of the same size was 105 V. Because the p+ diverter region of the proposed device was enclosed in a trench oxide layer, the electric field moved toward the trench-oxide layer, and punch-through breakdown of LTIGBT with p+ diverter occurred late. Therefore, the p+ diverter of the proposed LTIGBT had no effect on the breakdown voltage unlike the conventional LTIGBT. The latch-up current densities of the conventional LTIGBT and LTIGBT with a p+ diverter were 540 A/cm2, and 1453 A/cm2, respectively. The enhanced latch-up capability of the proposed LTIGBT with a p+ diverter was obtained due to the holes in the current directly reaching the cathode via the p+ divert region and p+ cathode layer beneath the n+ cathode layer.
A Highly Selective Photoresist Ashing Process for Silicon Nitride Films by Addition of Trifluoromethane
Authors: Saito Makoto , Eto Hideo , Makino Nobuaki , Omiya Kayoko , Homma Tetsuya , Nagatomo Takao
Published: October 2002

A highly selective photoresist ashing process was developed for the fabrication of thin-film transistor liquid-crystal displays (TFT-LCDs). This ashing process utilizes downflow plasma consisting of a carbon trifluoromethane/oxygen (CHF3/O2) gas mixture at a low temperature. The etching selectivity of photoresist films to silicon nitride (SiN) film increased when using the CHF3/O2 gas mixture plasma, as compared to that when using the carbon tetrafluoride/oxygen (CF4/O2) gas mixture plasma. At the CHF3 gas flow rate of 30 sccm, a high etching selectivity ratio of about 1080 for the photoresist films to the SiN films was achieved at room temperature. On the basis of surface analysis results for SiN films and plasma analysis results for the CHF3/O2 gas mixture, a mechanism for the high etching selectivity of the photoresist films was proposed. Reaction products that were formed on SiN films by the CHF3/O2 gas mixture plasma obstructed the etching of SiN films by fluorine (F) radicals, resulting in the high selectivity. It was found that the CHF3/O2 gas mixture plasma reacted with SiN, resulting in the formation of a protective reaction product that is considered to be an ammonium salt such as (NH4)2SiF6.