bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical mode conversion by magnetostatic surface waves in multilayered waveguides
Authors: Hasegawa Kazuo , Miyazaki Yasumitsu
Published: July 2007

Conventional optical functional elements which utilize the magnetooptical effect induced by magnetostatic surface waves have been those of a thick film structure for a waveguide to excite a magnetostatic surface wave. Therefore, they can offer a single‐mode waveguide, leading therefore to a degradation of performance due to a coupling between higher‐order modes in the waveguide. Such a waveguide which can propagate only a single fundamental mode without lowering the interaction cross section can be fabricated by constructing a magnetic double‐layer film with two different refractive indices.

This paper considers the case where the magnetostatic potential of the magnetostatic surface wave varies significantly near the surface. This structure provides further improvement in mode conversion efficiency and characteristics by adjusting the saturation magnetization of the film. A model for elements is proposed by which one can shorten an interaction length, and the calculated results are discussed.
A Thin‐Film Waveguide Polarizer with SiN Clad
Authors: Kato Isamu , Mori Kazutomi , Sato Koki
Published: July 2007

A discussion on a complex refractive index (n = nc″ ‐ jnc″) for a clad film of a thin‐film waveguide polarizer is presented. A guided light of a wavelength 0.5145 μm is chosen. Based on simulation result using a slab approximation, experimental results are discussed for SiN clad films. SiN films are fabricated onto a three‐dimensional waveguide as clad films with a waveguide width 20 μm. Five SiN films with different nc″ (= 0.02, 0.07, 0.12, 0.16, 0.23) are examined for the performance characteristics. As a result, nc″ = 0.16 is found to be best for a TE mode transmission polarizer with an extinction ratio 27 dB and an insertion loss 6 dB. Also, for a TM mode transmission polarizer, nc″ = 0.07 is found to be most suitable where an extinction ratio is 26 dB and an insertion loss is 2 dB.
Stabilization of Voltage Limiter Circuit for High‐Density DRAMs Using Miller Compensation
Authors: Tanaka Hitoshi , Aoki Masakazu , Etoh Jun , Horiguchi Masashi , Itoh Kiyoo , Kajigaya Kazuhiko , Matsumoto Tetsurou
Published: July 2007

The feasibility is examined of using the Miller phase‐compensation circuit to ensure the stability of the voltage limiter circuit in high‐density CMOS DRAMs. First, analytical expressions are obtained for the condition of stabilization to support the comprehensive circuit design and it is shown that both load capacity and load current affect the stability significantly. Second, by using the analytical expressions, parameters for the voltage limiter and the phase compensation circuit are calculated. By computer simulation and experiment voltage variations within the chip are evaluated when the internal circuit operates and external power supply voltage is changed. Results show that the voltage variation caused by the operation of the internal circuit is within 10 percent, resulting in no problem in practice.

The voltage variation caused by the change in the external power supply voltage is 3 percent in the case of low‐frequency noise (tr,tf= 1μs) and is as large as 20 percent in the case of high‐frequency noise (tr,tf= 10 ns) and attention must be paid to the latter case in the circuit design.
A Two‐Wire Silicon Capacitive Accelerometer
Authors: Shirai Toshihito , Esashi Masayoshi , Ura Noritake
Published: July 2007

Differential capacitive accelerometers have been fabricated using silicon micromachining, and a capacitance‐detection circuit and hybrid two‐wire sensing system have been realized.

The features of the differential capacitive accelerometer are the small influence of both acceleration at other axes and temperature and in restrained parasitic capacitance due to the concentration of efforts on the structural design of the sensor. The sensitivity of the sensor depends on the residual stress in beams supporting the weight.

By careful design of the capacitance‐detection circuit, the effect of both power supply voltage and temperature is small while the output signal of the sensor can be obtained from the current flowing in the two wires for power supply.
High‐density recording characteristics of perpendicular magnetic recording with sliding‐contact hard disk system
Authors: Muraoka Hiroaki , Nakamura Yoshihisa
Published: July 2007

High linear recording density by combining a single‐pole magnetic head and Co‐Cr/Ni‐Fe double‐layer medium in a perpendicular magnetic recording hard disk drive is discussed. The present perpendicular magnetic recording system adopts a sliding contact head‐disk interface suitable for high‐density recording. A spacing as small as 30 nm between a head and a medium is obtained, measured by an optical interference method. Attaining such a small spacing promises superiority of the sliding contact head.

An attempt is made to fabricate a composite head (= separate configuration of read/write head) to realize high resolution. This composite head is designed to maintain an important feature of saturation recording in the perpendicular magnetic recording scheme.

A computer simulation analysis of the head‐disk interaction shows that a stronger interaction gives rise to a better resolution for a single‐pole head. In view of those results, heads and media with various Co‐Cr thicknesses are fabricated. A high D50 value of 170 kFRPI and a good overwrite performance better than ‐30 dB are demonstrated.
An optical neural network using a feature‐extracting optical neuron device
Authors: Kuratomi Yasunori , Takimoto Akio , Akiyama Koji , Ogawa Hisahito
Published: July 2007

A method for feature extraction and an optical neural network model which can easily be implemented in optics have been proposed. In the method, the vector feature which denotes direction, existing position, and length of the line segments included in the pattern is extracted without any negative synaptic weights. It has been shown analytically that the vector feature is superior to the conventional mesh feature for handwritten character recognition.

The model using the method is featured as follows: (1) high recognition ability to recognize handwritten characters by extracting vector feature; (2) fast learning convergence; and (3) possibility of all‐optical implementation. By applying a newly developed feature‐extracting optical neuron device to the model, an optical neural network for handwritten character recognition has been constructed. It has also been confirmed that the feature‐extracting optical neuron device can extract four kinds of line segment in parallel processing. Due to the optical parallelism, the device is substantially useful for implementation of massive systems.
Fabrication of stretched gold island films with large optical anisotropy
Authors: Katsu Jun‐Ichiro , Baba Kazutaka , Miyagi Mitsunobu
Published: July 2007

As materials for a polarizer with a large aperture and short length, stretched gold island films with large optical anisotropy have been fabricated and their optical properties have been investigated experimentally. By embedding an island film into a glass medium and stretching the embedded film with large tension, large optical anisotropy can be achieved. When a 90‐Å thick gold island film deposited on a soda‐glass substrate and embedded in a 0.35‐μm thick pyrex glass was stretched five times with a tension of 0.23 kg/mm2 at 650°C, the resonance wavelength of the film changed from 0.54 to 0.95 μm in light polarized in the stretching direction.

In light polarized in the direction perpendicular to the stretching direction, the resonance wavelength showed almost no change and was 0.53 μm. The multilayer consisting of the anisotropic island films can be used for a thin optical polarizer with a large aperture.
Resonance characteristics of whispering gallery modes on a dielectric disk
Authors: Tomabechi Yoshiro , Matsumura Kazuhito
Published: July 2007

Resonance and loss characteristics of whispering gallery modes in a dielectric disk resonator are discussed three‐dimensionally by using an approximate variable separation method. A radius of the disk is sufficiently large compared to a wavelength. A cylindrical function with a complex order and argument whose absolute values are much larger than unity is included in an eigenvalue equation.

In this paper, the eigenvalue equation is solved analytically by using a newly developed calculation method of the cylindrical function. As a result, resonance and loss characteristics of the dielectric disk resonator in a wide frequency ranging from a microwave to optical wave are understood. The present method can be applied to a whispering gallery mode resonator made of lossy dielectric materials. Therefore, one can obtain a radiation loss separately from a dielectric loss based on a loss tangent of the materials.
Analysis of 1 × 3 coupled‐waveguide optical power dividers by the implicit finite‐difference method
Authors: Yamauchi Junji , Ando Takashi , Nakano Hisamatsu
Published: July 2007

Optical 1 × 3 power dividers composed of coupled waveguides are analyzed using the implicit finite‐difference method and the low‐loss configuration with reduced size is investigated. First, to check the accuracy of the method, the mismatching loss of the eigenmode of a straight waveguide is evaluated and it is verified that the error does not accumulate with the propagation distance.

Next, the characteristics of 1 × 3 power dividers using coupled waveguides inclined with respect to each other are investigated and the range of the tilt angle and the effects of the angular error upon power distribution are clarified. To widen the tilt angle, which results in reduced‐size dividers, the corner bends with modified refractive‐index distribution are introduced. As a result, the loss of a 3‐degree tilt angle divider is found to be reduced by more than 1.5 dB due to the introduction of the corner bend with modified refractive‐index distribution.
Hairpin‐shaped stripline split‐ring resonators and their applications
Authors: Yabuki Hiroyuki , Endo Haruyoshi , Sagawa Morikazu , Makimoto Mitsuo
Published: July 2007

The split‐ring resonator made of an open‐ended ring‐shaped stripline connected at its ends with a lumped element capacitance has already been used in practice as a resonator element for an oscillator. If this lumped element capacitance is replaced with a distributed capacitance, the structure can be modified to a hairpin‐shaped resonator with a distributed coupling circuit.

This paper studies such fundamental characteristics as the resonant condition of this resonator. In addition, by using its characteristics, applications are proposed for multiple‐stage filters and push‐push oscillators. The design data are organized and a trial fabrication is carried out for verification. The experiment is carried out in the L band. From the results, it is found that the resonator of this configuration is small in size and has high degrees of freedom. The structure can be applied to MIC or MMIC at much higher frequencies.
Finite‐element analysis of planar electron waveguides
Authors: Kaji Ryosaku , Hayata Kazuya , Koshiba Masanori
Published: July 2007

As a method for guided mode analysis of a planar electron waveguide with an arbitrarily shaped potential profile and an arbitrary effective mass profile, an analysis method based on the finite element method is proposed. The methods for computation are presented for the phase constant, mode confinement factor, and group velocity of the guided mode. Specifically, the present method is applied to rectangular and parabolic electron waveguides so that the validity and effectiveness of the method are presented.
Synthesis of symmetrical double‐barrier structures and analysis of their resonant tunneling characteristics
Authors: Kato Fumio , Iwasaki Hideo
Published: July 2007

As a first step toward establishing a methodology for a quantum effect device design, the resonant characteristics in a symmetrical double‐barrier structure were studied and its synthesis problem was investigated. It was found that the resonance levels are not always dependent on the barrier width and the well width. Some are dependent on only one of them or on neither of them. By deriving an equation explicitly expressing each resonance level or its upper and lower bounds, the profile was found. In the synthesis problem, with the barrier width and the well width as variable parameters, the realization of one level given arbitrarily was discussed and the methodology was presented. It was shown that higher‐order resonances of second and third orders can be realized. A synthesis method is presented.
Analysis of ferrite slab waveguides with resistive strip gratings
Authors: Ozaki Akira , Asai Masamitsu , Yamakita Jiro , Sawa Shinnosuke
Published: July 2007

An analysis and numerical calculation of a leaky wave propagating in a magnetic waveguide with a resistive strip grating are presented. The analysis is formulated by a matrix. A characteristic equation of the waveguide is derived by applying the Galerkin method to a resistive boundary condition expressed by a Green function in a spectrum region for a magnetic material and also by a surface current density which is expanded in terms of functions.

A numerical calculation is made for a leaky region where the effect of a surface resistance and magnetic loss are considered. A step function and a function with a singularity are used in expanding a surface current density. The validity of limiting expansion terms and the convergence of solutions are discussed for not only a propagation constant but also a root mean square error of the resistive boundary condition and a surface current density.
Chemical beam epitaxy growth of gainasp/inp and application to surface‐emitting lasers
Authors: Uchida Takashi , Yokouchi Noriyuki , Miyamoto Tomoyuki , Koyama Fumio , Iga Kenichi
Published: July 2007

This paper discusses the doping characteristics and the crystalline quality of GaInAsP/InP grown by a chemical beam epitaxy method important for realizing surface‐emitting lasers of long wavelengths. A good controllability of Be doping and very little degradation examined by photoluminescence are found in GaInAsP and InP for a wide range of Be dopants. The crystalline quality of a double heterostructure is improved by optimizing a growth condition. As a result, a minimum threshold current density of 5 kA/cm2is obtained for edge‐emitting lasers at a 1‐μm thick active layer.

Under the optimized condition, a circular mesa‐cap surface‐emitter laser is fabricated. The minimum threshold current of 2.7 mA and the threshold current density 450 A/cm2are obtained at 77 K under the CW operation. A pulsed operation of an SE laser with GaInAsP/InP multilayer reflector is confirmed near room temperature. The applicability of the chemical beam epitaxy method for growing an SE laser is described.
A study on partial response system in digital magnetic recording
Authors: Okamoto Yoshihiro , Osawa Hisashi , Takigawa Kiyoshi , Ono Kazuo
Published: July 2007

The partial response (PR) system is believed to be an important scheme for signal processing in high‐density digital magnetic recording. This paper discusses the improvement in performance of the PR(1, 0m ‐ 1, ‐1) system, which is one of the PR systems. With increasing recording density, a high‐frequency noise due to the compensation for a high‐frequency attenuation increases significantly and accordingly a signal‐to‐noise ratio (SNR) becomes lower, which is also tied to the inherent high‐frequency boost characteristics of PR(1, 0m ‐ 1, ‐1).

Also proposed is a new PR system and a signal‐detection method by which one can expect to improve the characteristics by using an intersymbol interference for a signal detection caused by suppressing a high‐frequency noise through a bandwidth limitation in PR(1, 0m ‐ 1, ‐1). For the proposed system and the conventional PR(1, 0m ‐ 1, ‐1) system, the SNR required to achieve a bit error rate of 10−8 is obtained. It is confirmed that the proposed system provides a better performance than the conventional system.
Composition analysis of anodic SiO2/Si interface region using the XPS method
Authors: Nanjo Junji , Kawahara Tadashi , Mostafa Kamal Abu Hena , Nomura Shigeru , Kitamura Naoko
Published: July 2007

Silicon oxide film, which has been used as a protective and active layer in Si devices, has been fabricated electrochemically at room temperature. The fabrication method is anodization combining a constant current and constant voltage mode. Ethylene glycol was used as an electrolyte. To improve the characteristics of silicon oxide film and also the interfacial property of the film with an Si substrate, the oxide film was annealed under hydrogen atmosphere. The depth profile of an atomic concentration was measured by X‐ray photoelectron spectrum (XPS). The thickness of the oxide film was varied by etching with p‐etchant. The as‐grown film is composed of nonstoichiometric silicon oxide of sub‐oxides, SiO2, SiO, and Si2O3, which are nonuniformly present near the Si‐oxide interface up to 40 Å from the Si surface. The remainder of the oxide is stoichiometric amorphous SiO2. After annealing, the amount of sub‐oxides decreases.
New integral equations for designing dielectric waveguide bend circuits: Guided‐mode extracted integral equations
Authors: Tanaka Kazuo
Published: July 2007

For the new integral equation proposed previously by the author for the discontinuity problem in a dielectric waveguide, the nature of the numerical solution based on the moment method (boundary element method) is studied in detail by applying the method to a bend of a dielectric slab waveguide with an arbitrary shape. The necessary discretization range for the desired results, the location of the virtual boundary and the effect of the convergence of the field on the results are studied in detail by comparison with rigorous solutions. Further, dielectric bends of various shapes for reducing the radiation loss are analyzed. It is shown that an optimum shape can be obtained by means of the new integral equation.
Analysis of obliquely propagating waves along dielectric grating waveguide with square corrugation
Authors: Matsumoto Keiji , Rokushima Katsu , Yamakita Jiro
Published: July 2007

In a slab waveguide with a rectangular dielectric grating, the analysis of an optical wave propagating at an arbitrary angle with respect to the grating vector is formulated by means of the spatial harmonic expansion method. For this guided‐wave problem, a hypothetical excitation condition is introduced for determination of the direction making the attenuation of the propagation wave maximum and the phase velocity direction.

Hence, the complex propagation constant to be derived is determined as the singular solution to the three‐dimensional guided‐wave problem dependent on three directional relationships on the grating vector, maximum attenuation, and phase velocity. In the analysis, the solution can be made more accurate by increasing the orders to truncate the permittivity profile and the spatial harmonics, since no approximations other than these truncations exist.

In the numerical examples, the accuracy of the solution is shown for the waveguide for which the grating vector direction and the maximum attenuation direction coincide. In addition, it is pointed out that there exists a peculiar stopband due to the coupling between the TE and TM waves as well as a radiation region of the leaky wave caused by the oblique propagation. Further, the radiation is considered in the case where a leaky wave is generated and the numerical results are presented for the radiation efficiency.
Long‐term aging effect on led circuit with fe‐based amorphous current transformer
Authors: Fukuhara Minoru , Kakehashi Hidenori , Ohta Yukihiko , Fukunaga Hirotoshi , Ninomiya Tamotsu
Published: July 2007

The current transformer used in a conduction detector switch circuit for lighting up an light emitting diode (LED) for detection of load current in distribution lines has to be small and of low excitation current. Since field‐annealed Fe‐based amorphous cores have high saturation magnetization and the squareness ratio of a hysteresis loop and low coercive force, current transformers that are superior to ferrite cores can be designed. Furthermore, in cases where reliability is required over long periods such as in LED lighting circuits, for the purpose of design, it is necessary to predict what influence is exerted on the circuit characteristics by the aging variations of the amorphous magnetic characteristics [1, 2]. Therefore, recently, based on a prediction method of dc coercive force researched by the present authors [3], aging variation prediction was carried out on ac (60 Hz) coercive force.

Next, the ac magnetic characteristics of Fe‐based amorphous cores were approximated by Potter's model [4], LED circuit analysis was carried out by application in a Spice program, and good agreement with experimental results was confirmed. In addition, using the prediction values of aging variation of the cores, on deducing the effect of influence on circuit characteristics it was found that the degradation of LED circuit characteristics at 100°C and 106 hours of elapse was minimal, and it is possible to predict the maintenance of excellent characteristics better than in the case of ferrite cores.
Construction of electromagnetic scattered fields from smooth dielectric cylindrical objects with relative‐refractive‐index less than 1 by using the extended ray theory
Authors: Ohmori Toshiyuki , Ikuno Hiroyoshi , Nishimoto Masahiko
Published: July 2007

The problem of scattering by a cylindrical dielectric having a relative index of refraction smaller than unity with a smooth boundary is analyzed by the extended ray theory (ERT). According to the ERT, the scattering process of the electromagnetic wave can be analyzed systematically if the scattered field is analyzed with the six elementary processes described in regard to the geometrical optics phenomena and the diffraction phenomena. Hence, for each elementary process, the scattering center was derived and the amplitude and phase of the ray are evaluated. The amplitude is computed as the product of the scattering coefficient of the canonical problem and the amplitude derived geometrically from the energy conservation law.

The phase is determined from the optical path length of the ray and the propagation coefficient of the canonical problem. Then the scattered field can be constructed by superposition of the rays of the scattering processes obtained from each elementary process and their combinations. In this problem, the diffraction effect generally is weak. Hence, the scattered field is constructed from the geometrical optics rays. As a typical example, the transient scattering responses by a circular dielectric cylinder and a dielectric cylinder with a concave‐convex boundary were constructed by the ERT. The results agree well with the reference solutions. It is demonstrated that the electromagnetic scattered field in this problem can be analyzed by the real and complex geometrical optics rays.
Optimization of disk array subsystem using small disks
Authors: Sakurai Norihiko , Kishigami Junichi
Published: July 2007

One of the recent trends in the development of magnetic disk devices is the advent of small disks. The small disk has a great influence on the performance of the magnetic disk subsystem.

This paper assumes that the small‐sized magnetic disk subsystem will be introduced around 1995 and formulates the relation between the disk size and the performance/cost. The disk array subsystem architecture using small disks is considered, and the evaluation is made based on the number of disks for the parallel synchronous transfer.

As to the file performance, code and image information are considered and the condition for the subsystem with the best cost/performance ratio for each kind of information is shown. It is shown that small disks of 1 to 2.5 inches are being developed rapidly at present aiming at the application to the portable equipment and will experience the widest area of application. The requirement for the magnetic disk device, e.g., the relation between the rotation for each size and the number of parallel synchronous transfer in the best configuration, is discussed.
Differential output type microflow sensor
Authors: Esashi Masayoshi , Kawai Hiroshi , Yoshimi Kenichi
Published: July 2007

To realize a flow sensor sensitive to a flow rate lower than 0.1 cc/min, a differential output‐type mass‐flow sensor with a pair of heaters was fabricated using the micromachining technique. In a conventional sensor with a single heater, sensitivity degradation occurs because of the natural convection around the heater. On the other hand, in the sensor in this study, the influence of the convection was eliminated by utilizing the differential outputs between the pair of heaters which were located closely together. As a result, the nonlinearity of the sensor was less than 2 percent even when the flow was lower than 0.1 cc/min.
Autostereoscopic 3‐D television
Authors: Isono Haruo , Yasuda Minoru , Takemori Daisuke , Kanayama Hideyuki , Yamada Chihiko , Chiba Kazuo
Published: July 2007

This paper describes a diagonal autostereoscopic three‐dimensional (3‐D) television system with a liquid‐crystal video projector, the picture of which could be observed without the need to use special glasses. As the representation method of 3‐D images of this system, the pixels from four television cameras are composed electronically to make stripe images which are projected onto the rear surface of a lenticular screen by a high‐quality HDTV liquid‐crystal video projector. In this way, clear full‐color diagonal stereoscopic 50‐inch television pictures could be displayed.

Besides the lack of obligation to use special glasses, the advantages of this system are: the observation range is broadened, compared to the previous stereoscopic 3‐D television; and the pictures are more natural and easier to observe. The newly realized diagonal autostereoscopic 3‐D television system, the lenticular screen, the diagonal autostereoscopic 3‐D cameras, the recording equipment of 3‐D pictures, etc., are discussed in this paper.
Effect of Ag2O on fishing effect of bipbsrcacuo superconductor
Authors: Lee Sangheon , Akiba Yukio , Kurosu Tateki , Iida Masamori
Published: July 2007

In this study, the fishing effect observed in a Bi‐based BiPbSrCaCuO (BPSCCO) superconductor was investigated. The electromagnetic properties of a silver‐oxide (Ag2O) doped BPSCCO superconductor and an undoped superconductor were evaluated to investigate the contribution of the pinning centers to the fishing effect.

It was confirmed experimentally that a large amount of magnetic flux was trapped in the Ag2O doped sample than that in the undoped one, indicating that the pinning centers of magnetic flux are related closely to the occurrence mechanism of the fishing effect.

It is considered that by adding Ag2O, the area where normal conduction takes place increases and the magnetic flux penetrating through the sample increases. It also is considered that Ag2O acts to increase pinning centers of magnetic flux, contributing to the occurrence of the fishing effect. The occurrence mechanism of the fishing effect can be explained by a qualitative model based on the relationship between the pinning centers and the distribution of the lines of magnetic force caused by a toroidal permanent magnet.
Properties of bridge‐type weak‐link device with YBCO thin film
Authors: Park Chan‐Hoon , Kobayashi Tadayuki , Goto Toshinari
Published: July 2007

Thin films of YBaCuO were deposited onto polished MgO(100) substrates by a dc hollow cathode sputtering with stoichiometric YBa2Cu3Oz targets. The films of Tc zero with a good c‐axis orientation were fabricated successfully under the condition of a sputtering gas Ar + 5% o2, sputter‐pressure 820 m torr, and substrate temperature during deposition 700°C. The present study aims to realize a variable thickness bridge (VTB) device with thin bridge portions.

VTB devices were fabricated by using photolithography, oblique incident evaporation of Al, and fine fabrication of 85 to 410 nm by low‐energy ion‐beam etching. Measurements were made for a frequency from microwave (9.67 GHz) to millimeter wave (94 GHz). Those devices were found to respond properly to a millimeter wave.
Switched branch line pin diode phase shifter
Authors: Matsunaga Makoto , Katagi Takashi , Hashimoto Tsutomu , Nakahara Shintaro
Published: July 2007

As a small phase shifter with a phase shift of 180 degrees from two PIN diodes, a switched branch‐line phase shifter is proposed and its characteristics, design method, and experimental results are presented. In the present phase shifter, the ratio of the characteristic impedances of the main line and the branch line is made to be 1 : 2. It is found that by this ratio the matching is always possible regardless of the impedance value of the diodes. The relationship is shown between the diode parameters and the circuit to obtain a phase shift of 180 degrees. In addition, the magnitude of the diode loss inherent to the present phase shifter is expressed in terms of the switching cutoff frequency which is a figure of merit of the diode. Also, the relationship is obtained between the input power and the voltage applied to the diode so that the maximum power capability determined from the breakdown voltage of the diode is obtained. Further, a phase shifter is fabricated atLband so that the effectiveness of the design method is confirmed.

The performance of the phase shifter fabricated for experiment has a phase‐shift error of 7°MAX, an insertion loss of 0.5 dBMAX, VSWR of 1.4MAX, and maximum peak power of about 3 W in the PIN diode with a breakdown voltage of 60 V. These results agree well with the design values. The present phase shifter does not require hybrid couplers used in a reflection type and which occupy a large area. In addition, this phase shifter is useful for size reduction and cost reduction since only two diodes are needed.
A numerical analysis of plane‐wave diffraction from a multicoated grating
Authors: Matsuda Toyonori , Okuno Yoichi
Published: July 2007

In this paper, a numerical analysis algorithm has been derived for the analysis of the problem of plane wave diffraction by a multilayered grating. This algorithm is based on the Yasuura method with the smoothing procedure and can be applied to the problems of arbitrary multilayered dielectric (or metallic) grating with smoothly shaped grooves. The convergence of the approximate solution obtained by the present algorithm has been investigated numerically. It was demonstrated that a highly accurate approximate solution can be computed by the introduction of the smoothing procedure.

The present algorithm is applicable to problems of a multilayered grating over the range from infrared to visible. As a numerical example, the diffraction efficiency of the multilayered diffraction grating made of alternate lamination of the high‐index and low‐index dielectric layers deposited on a metal grating is calculated by the algorithm in this paper.

The following items are confirmed: (1) by coating dielectric films, the power absorption of the incident light by the metal grating is reduced in a specific wavelength region; and (2) in a multilayered grating, anomalous resonant absorption occurs by the coupling of the guided mode excited by the dielectric thin film and the diffracted wave.
Preparation and properties of tantalum oxide films by sol‐gel method
Authors: Ōishi Tomoji , Nakazawa Tetsuo , Katou Akira
Published: July 2007

The preparation of tantalum oxide thin film by the sol‐gel method is discussed. The conditions of the film growth are investigated carefully to avoid pinholes and cracks. In particular, the effect of hydrochloric acid added to the sol solution is clarified.

The spectral and electrical properties of the thin film are investigated. The as‐grown film was amorphous and became crystallized at 720°C. The relative dielectric constant increases with an increase of the heat‐treatment temperature and the breakdown voltage decreased rapidly when the heat‐treatment temperature exceeded 600°. The optimum heat‐treatment temperature to achieve both high relative dielectric constant and high breakdown voltage was 400°C.

It was found by TEM observation that the rapid degradation of the breakdown voltage was due to pinholes created during crystallization process.
Low‐temperature formation of gate‐sio2 films for poly‐si tfts by o2‐ar sputtering
Authors: Suyama Shiro , Okamoto Akio , Shirai Seiiti , Serikawa Tadashi
Published: July 2007

High‐quality gate‐oxide films for poly‐Si TFTs are obtained successfully by oxygen‐argon sputter deposition at low temperature (200°C). SiO2 films deposited in an oxygen‐argon mixture on poly‐Si have higher resistivities and breakdown fields than those deposited only in argon and thermal oxides grown on poly‐Si, resulting in the same film characteristics as thermal oxides grown on single‐Si. Moreover, poly‐Si TFT mobilities are improved considerably by mixing oxygen, resulting in very high mobility of 383 cm2/V · s. This high mobility is caused by reduction in SiO2/Si interface states and in barrier heights at the poly‐Si grain boundaries in addition to the improvement of poly‐Si films.

These characteristic improvements result from migration enhancement of sputtering particles on film surface and the reduction of plasma damage by oxygen mixture. These results confirm the usefulness of gate‐oxide films sputter‐deposited in an oxygen‐argon mixture for low‐temperature fabrication of high‐quality poly‐Si TFTs.
Characterization of interfaces of sio2and thin gaas active layers for gaas ics
Authors: Miyazaki Masaru , Imamura Yoshinori , Oda Hiroto , Saitoh Tadashi
Published: July 2007

To improve the controllability of threshold voltage of FETs for high‐performance GaAs ICs, it is necessary to establish a processing method of fabricating a surface‐protective SiO2layer without changing the thin active‐layer thickness.

In this paper, a new method is proposed for evaluating the thickness of a removed GaAs active layer. This technique involves sheet resistance measurement of FET devices after surface treatment. Using this method, about a 5‐nm thick GaAs layer was found to be removed by the HF etching process for an SiO2film deposited by thermal CVD. This phenomenon is due to the formation of an intermediate layer between SiO2and GaAs interfaces. This intermediate layer consists of GaAs oxides and excess As.

Spectroscopic ellipsometry has been applied to evaluate the thickness of the intermediate layer. Using this method, it was found that no intermediate layer is formed in the case of SiO2films fabricated by photo‐CVD, which is advantageous for low‐temperature processing. Furthermore, no removal of the GaAs active layer was found after HF etching of the SiO2films. SiO2films made by the photo‐CVD method are most suitable as protective layers for thin GaAs active layers of GaAs ICs.
Light coupling characteristics of a planar microlens
Authors: Oikawa Masahiro , Imanishi Hideki , Kishimoto Takashi
Published: July 2007

The two‐dimensional (2‐D) integrated planar microlens (PML) is expected to be used in connection with various 2‐D devices in parallel optical fiber communication systems. In this paper, we demonstrate recent progresses made for PML and its light coupling characteristics. The coupling characteristics between (1) LD and single‐mode fiber, (2) LED and GI‐50 fiber, (3) single‐mode fiber and single‐mode fiber, and (4) single‐mode fiber and detector were evaluated. In this paper, we evaluate coupling characteristics corresponding to single lens in an array.
Use of a modified mode‐matching method to analyze microstrip lines with thick strip conductors
Authors: Nakai Takashi , Tsuji Mikio , Shigesawa Hiroshi
Published: July 2007

This paper proposes an analytical method for microstrip lines with finite metallization thickness of the strip. The reliability of solution for such lines depends greatly on the treatment of the behavior of electromagnetic fields near the conductor edges of the strip. For example, when the conventional mode‐matching method is used for the analysis, considerable modal functions are required to represent the field behavior near the conductor edge, making it difficult to obtain accurate results.

An alternative method is presented for microstrip lines with finite metallization thickness of the strip. This method is based on the mode‐matching method already presented by the authors where singularities of the electromagnetic field at the conductor edges are taken into account. The effectiveness of the present method is verified by investigating the convergence of solution and the edge effect in detail and also by comparing the results with others reported in the literature.
Advanced analyses for reduction of contamination in ulsi manufacturing line
Authors: Mizogami Yasuo , Ajioka Tsuneo
Published: July 2007

Analytical methods applied for clean ULSI manufacturing lines are discussed. Traced metals of such transition metals as Fe and light elements such as Al and Na, which influence device performance, can be detected with high sensitivity and reproducibility through a combination of both total reflection X‐ray fluorescence (TRXRF) and polysilicon encapsulation secondary ion mass spectroscopy (PC‐SIMS) methods. High‐resolution analytical electron microscopy (AEM), together with Auger electron spectroscopy (AES) and electron probe microanalysis (EPMA), is powerful for analyzing a nanoscale microscopic region (where a diffusion and re‐excitation of secondary electrons cannot be neglected). A method of chemical analysis for ULSI manufacturing process line is proposed, that is, TRXRF with TRXRF + HF condensation and PC‐SIMS for traced metallic contamination and wafer EPMA with AES and AEM for particles and device defects. The metallic contamination in almost all processes has been evaluated, and it was found that those analytical techniques are very effective and useful.
Observation of magnetic domains of magnetic recording medium
Authors: Sakurai Tomoaki , Shimada Yutaka , Sueyoshi Toshinobu , Okuwaki Toyoji
Published: July 2007

Using the colloid‐SEM technique for observing minute magnetic domains, combined with the gas evaporation method where high resolution was needed, an attempt was made to observe the magnetization profile through a magnetically recorded S‐VHS tape in order to analyze the recording magnetization pattern produced by the application of an external magnetic field.

From this, simultaneously with the first observation of the magnetization pattern of a dual wavelength superimposed recording, it was found that, with the short wavelength of the recorded magnetization, the observed magnetization decreases and, moreover, it became clear that, with respect to the short wavelength region, it is of the same magnitude as the recorded wavelength.
The effects of post‐hydrogenation on amorphous‐silicon thin‐film transistors
Authors: Ahn Byung‐Chul , Usami Koh‐Ichi , Kanoh Hiroshi , Sugiura Osamu , Matsumura Masakiyo
Published: July 2007

The characteristics of amorphous silicon thin‐film transistors fabricated by chemical vapor deposition method is discussed in detail in conjunction with posthydrogenation. As the hydrogenation around an active interface starts, the transistor performance is abruptly improved and then does not change with further hydrogenation. A critical condition for hydrogenation for such an abrupt improvement may be accounted for based on a simple formula using a transit time of hydrogen atoms. A desirable thickness of amorphous silicon films for high performance TFT is thicker than 100 nm. In addition, it is recommended that hydrogenation is to be made at a temperature as low as possible as long as it can be possible.
Dynamic characteristics of leakage current in amorphous silicon thin‐film transistors
Authors: Motai Tomonobu , Suzuki Kouhei , Suzuki Kouji
Published: July 2007

The transient off‐currents of thin‐film transistors (TFTs) have been characterized. The authors connected the TFT to a capacitor equivalent to an actual pixel capacitance and made accurate measurements of the voltage at the capacitor under a drive condition actually used for the TFT‐LCDs. The currents were calculated from the measured voltages. Inverted staggered‐type TFTs were used with the gate on‐voltageVgs= 20 V and the drain voltageVsig=Vsigc± 5 V (Vsigc= 4 ± 10 V). It has been found that the off‐current shows an increase or decrease with a time delay of a few milliseconds. The change in the off‐current has been characterized as a relation between the gate bias voltageVgsand the off‐currentIds. Comparing the results with the dc characteristics, it has been found that theIdsvs.Vgscurves approach the dc curves from the positive side ofVgs'i.e., the transient current curves shift from their dc curves in the positive direction ofVgs. The authors have verified that this behavior of the off‐current with time delay can be explained by introducing a trap level inside the TFT.
High‐performance polycrystalline silicon tfts using self‐aligned grain boundary control technique
Authors: Shinohara Toshiro , Tarui Yasuo
Published: July 2007

To improve the reproducibility of the properties of thin‐film transistors (TFTs) formed by using solid‐phase grown polycrystalline silicon, a self‐aligned grain boundary control technique was developed. In this technique, the gate electrode of a coplanar TFT serves as a mark for ion implantation to the source and drain regions. At the same time, it limits amorphization of polycrystalline silicon only to the channel region. The channel region becomes amorphized by a high‐energy silicon ion beam through the gate electrode and oxide. However, since the silicon ions penetrate through the source and drain regions, crystalline seeds remain in the regions. Then the solid‐phase growth is carried out in the regions from the source and drain regions to the center of the channel before the crystalline nuclei are formed in the channel region.

By this process, the presence of the grain boundary is limited to the center of the channel. When this technique is used, the mobility is improved by 60 percent and the scattering of the mobility value is reduced to half.
Application and study of the wiener‐hopf technique from filtering viewpoint
Authors: Uchida Kazunori , Noda Takeaki , Matsunaga Toshiaki
Published: July 2007

This paper introduces a filtering operation in the spectral domain which extracts the spectrum corresponding to semiinfinite or finite range in the original space. Its application to electromagnetic problems also is considered.

First, it is demonstrated that for a semiinfinite boundary value problem, the rigorous Wiener‐Hopf solution can be obtained in terms of algebraic filtering operations.

Second, it is shown that for finite boundary value problems, the rigorous solutions cannot, in general, be obtained only through algebraic filtering operations. Three approximate methods also are proposed for the latter problems: a direct numerical method; an approximation based on the formal solutions; and an iterative method. As an application of the iterative method, the electromagnetic wave scattering by a conducting strip is considered and an analytic expression is derived for surface currents which holds in the high‐frequency region. Numerical examples also are given for the surface current distributions.
History and Trend of Giant Microelectronics
Authors: Morozumi Shinji
Published: July 2007

Giant microelectronics is defined as technology which forms electronic devices with fine structures on a large‐area substrate such as a glass. They are applied to image input/output (I/O) devices of active‐matrix liquid‐crystal displays, printer heads, and image sensors. The thin‐film transistor (TFT) is the typical device formed on such a large‐area substrate. It has been developed since the 1960s, realized for practical applications in the 1980s, and will be used widely in the 1990s.

For active‐matrix liquid‐crystal displays, amorphous Si TFTs which are formed at low temperature by plasma CVD have been used. Recently, these displays have begun to be used for personal computers. However, the cost reduction of these displays must be achieved by increasing the size of the substrate and throughput of the products. At the same time, the integration of the driver circuits using the low‐temperature polycrystalline Si TFT must be carried out.

Japan is a leader in the production of giant electronics devices. However, to establish this technology, international cooperation will be important.
Layered structure devices with a‐Axis‐Oriented YBa2Cu3O7 ‐ x films
Authors: Fujimaki Akira , Terai Hirotaka , Hayakawa Hisao
Published: July 2007

To clarify the characteristic of contact between a‐axis‐oriented YBa2Cu3O7 ‐ x (YBCO) and normal conduction material, two types of SNS junctions were formed. In the YBCO/Au/Nb junction, the Josephson coupling was confirmed from the magnetic field characteristic. In addition, the London penetration depth in a‐axis‐oriented YBCO was calculated to be around 800 nm. It was found that this large penetration depth causes an increase in kinetic inductance, resulting in the influence on the current flow distribution in the junction.

The current density and IcRn product were estimated to be two orders of magnitude larger than those in the c‐axis‐oriented junction (1.0 × 109 A/cm2 and 100 μ V, respectively) and anisotropic electrical conduction in YBCO was confirmed. It was found also that the order parameter of YBCO attenuated drastically at the YBCO/Au interface. In the PrBa2Cu3O7 ‐ x (PBCO)/Au/Nb junction, a Josephson junction with a good junction planar uniformity was formed when PBCO was less than 20‐nm thick.

The coherence length of PBCO was estimated to be 4 nm from the PBCO thickness dependence of the IcRn product. Even when the PBCO film was as thick as 300 nm, the abnormal decrease of the junction resistance due to the superconductivity of YBCO was observed. The mechanism of the forementioned symptoms must be clarified in the future.
Fabrication and properties of high Tc superconductor tunnel junctions using organic film as a barrier
Authors: Okabe Hiroshi , Moriya Masataka , Usami Koichi , Kobayashi Tadayuki , Goto Toshinari
Published: July 2007

Using hexamethyldisilane (HMDS), high Tc super‐conductor/HMDS/metal superconductor junctions were fabricated. First, a YBa2Cu3O7 ‐ x YBCO film was made by dc hollow cathode sputtering or rf off‐axis sputtering. Then HMDS was absorbed in the film. In this case, one molecular layer (about 1 nm) was formed; Pb (Tc = 7.2 K) was deposited as a counterelectrode. Measurements of current‐voltage characteristics were made for this tunnel junction thus obtained. As a result, an energy gap and Josephson current were observed. Also, a microwave response and a magnetic field dependence of Josephson current were investigated.
A superconducting‐base transistor using Ba1‐xKx BiO3 Superconductor
Authors: Usuki Tatsuro , Suzuki Seiji , Iyori Masahiro , Yamano Kouji , Suzuki Hiroshi , Yamamoto Tetsuya , Yoshisato Yorinobu
Published: July 2007

An analysis of the performance of a superconducting‐base transistor using Ba1‐xKxBiO3 (BKBO) has been made. Also, an Au/natural barrier/BKBO/SrTiO3 (Nb‐doped) superconducting‐base transistor has been fabricated and its performance has been examined.

The analysis of a quasi‐particle transmission in an interface of base/collector or superconductor/semiconductor, which is the most important factor for its device characteristics, has been carried out. When the interface barrier is of Schottky type, the transmission probability depends significantly on the barrier height (U0). If U0 · Δ (superconducting energy gap), a transmission of more than 0.9 can be obtained even for low‐energy quasiparticles of about 3Δ.

It was confirmed experimentally that about 2 percent of low‐energy quasi‐particles can reach a collector and they are injected through a tunnel junction (common‐base current gain α = 0.02). Experimental results of common‐base characteristics are well founded based on the assumption that a barrier height of a BKBO/SrTiO3 (Nb‐doped) is U0 = 280 me V and that a collector is a superconductor degenerated at about 30 me V.