bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiation effects in SiO2/Si structures
Authors: Watanabe Kikuo , Kato Masataka , Nagata Minoru , Okabe Takahiro
Published: July 2007

Radiation effects in SiO2/Si structures are studied by capacitance‐voltage characteristics of MOS diodes. As a radiation, X‐ray is used mainly because it can be shielded easier than γ‐ray from Co 60. Although the two radiations have different photon energy, it is found that they cause the same effects in device characteristics. Therefore, X‐ray is thought to be suitable for irradiation tests of devices. Both the positive fixed charge in the SiO2 film and the SiO2/Si interface states caused by X‐ray irradiation are strongly dependent on the polarity of a bias voltage applied to a metal gate of an MOS diode during irradiation. When the polarity is positive, the radiation effects are several times stronger than those when the polarity is negative. These results are considered to indicate that both the positive fixed charges and the interface states are not generated directly by X‐ray photons, but generated by mobile positive charges created in the SiO2 film due to the irradiation. In addition, dependence of the radiation effects on device fabrication processes is studied. For example, it is found that when thermal oxidation is carried out in ambient‐containing impurities such as chlorine and nitrogen, the radiation effects in the SiO2/Si structures become more severe. These results indicate that the suitable selection of device fabrication processes will lead to a better radiation hardness of the device.
Simulation analysis of semiconductor laser operation
Authors: Kume Masahiro , Takeshima Masumi , Shimizu Hirokazu , Sugino Takashi , Itoh Kunio , Kano Gota
Published: July 2007

Use of the best‐designed structure parameters obtained from a simulation analysis is an efficient means to develop semiconductor lasers. From this viewpoint we have developed a simulation program which is of practical use. The characteristic aspect of the program is to find physical parameters mainly from theoretical calculations without recourse to experimental data, and to take into account the Auger recombination and the intervalence‐band absorption. This makes the program useful for arbitrary materials. To attain high‐speed simulation, we have used some simplifying models for calculations which would otherwise be complicated inherently in the inner stripe geometry. It is found that despite various simplifications, calculated results offer a satisfactory quantitative description of experimental results on laser operations in GaAlAs lasers such as the threshold current and the differential quantum efficiency.
Technique for determining the refractive indices and oscillator strengths with the angle phase‐matching conditions in optical four‐wave sum‐mixing
Authors: Koyanagi Kojiro , Mishima Teruhito , Sakuraba Ichiro
Published: July 2007

A new method is proposed for measurement of the index of refraction of gas and oscillator strength. In four‐wave sum‐mixing in such nonlinear media as metal vapor or rare gas using the third‐order nonlinear optical effect, the refractive index of a nonlinear medium at the sum frequency in the vacuum ultraviolet range is found from the angle phase‐matching condition for the maximum conversion efficiency, and the oscillator strength is determined from the measurement of refractive index by the phase matching in terms of the sum frequency. The present method in which the refractive index and the oscillator strength are determined from the incident angle of each wave satisfying the angle phase‐matching has the advantage of fewer measurement parameters compared to the conventional methods in which a phase‐matching is accomplished with a mixture of gases with ordinary and extraordinary dispersions. This is because no buffer gas is mixed. In addition, the measurement accuracy is found theoretically to improve in the region with a higher atomic density.
Fabrication and characteristics of GalnAsP/InP surface‐emitting laser with circular buried heterostructure
Authors: Yamakawa Hideaki , Watanabe Isao , Uchiyama Seiji , Koyama Fumio , Iga Kenichi
Published: July 2007

In a GaInAsP/InP surface‐emitting laser, there is no current‐confining structure, resulting in the current spreading and a restriction in the electrode area causing a high ohmic resistance. These problems cause a high threshold current and obstruct a laser operation at room temperature. In this study, to effectively inject current into the active region, the buried‐heterostructure with a reverse biased p‐n junction layer is introduced. At the same time, the diameter of the active region is reduced to 15 μm. The threshold current of this laser at 77°K is as low as 19 mA.
Technology of cable transfer system for error‐free digital transmission
Authors: Komatsu Naohisa , Tsuchiya Yuzo
Published: July 2007

At present the transfer or exchange of subscriber cable in the telecommunication network is performed by temporarily cutting off the circuit with the customer's consent. For a communication circuit requiring 24‐hr real‐time service, such as data transmission, however, a cable transfer method must be developed which can handle a live circuit and prevent an error in the information during transmission. From such a viewpoint, this paper considers the cable transfer technique which improves the traditional cable transfer process, and presents the design condition in relation to the transmission quality of the communication circuit. First, a cable transfer method is proposed which can be applied to a live circuit without affecting the telecommunication, such as the interruption or the noise due to transfer. In this method, resistors are inserted into existing and new circuits at two working points for the cable transfer, and the resistances are varied in a pair. The method can be applied to the code transmission circuit in ISDN, in the cable transfer for the subscriber line. Second, an identification method is proposed, which can be applied to the unbalanced circuit, such as the security alarm circuit. The method utilizes the transmission signal at each working point, and compares the measured values. The idea can be applied to the general balanced lines to identify the line with a high speed.
Influence of low‐frequency‐spectrum elimination on reproduced waveforms in MFM and ZM coding methods
Authors: Tanaka Hideo
Published: July 2007

One method to improve the signal‐to‐noise ratio in a magnetic recording is to use a filter to narrow the frequency bandwidth. This paper presents a theoretical analysis of the influence of a low‐frequency spectrum on reproduced waveforms in the MFM and ZM coding methods, together with the evaluation of possible narrowing of the bandwidth. In this method, a reproduced waveform is constructed by superimposing solitary waveforms according to the code‐words of the MFM or ZM modulation methods. Then low‐frequency spectra were eliminated from the Fourier spectrum of the reproduced waveform, and another waveform is obtained by reconstructing the remaining spectra.

The results show the waveform distortions, a change of the amplitude, and peak‐shifts. These are all due to the elimination of low‐frequency spectra. The influance on the design parameters of a disk‐head system (e.g., the length of a gap in its film) was found.
Switched‐capacitor sequential‐flash data converters
Authors: Watanabe Kenzo , Matsumoto Hiroki
Published: July 2007

Sequential‐flash data converters using switched‐capacitor circuits are developed for realizing a given conversion speed with a minimum number of components. Repeating n‐bit flash conversion m times, each converter accomplishes (m x n)‐bit digital‐to‐analog or analog‐to‐digital conversion in m cycles of a clock frequency. An accurate conversion is also possible because each converter is configured such that the offset voltages of op‐amps and parasitic capacitances have no effect on the conversion process. Error analysis shows that a conversion accuracy higher than 8 bits can be expected from each converter if integrated using present MOS technologies. Prototype converters built using discrete components are also given to confirm the principles of operation.
Design of microwave combiner with waveguide ports
Authors: Matsumura Hajime , Mizuno Haruhiko
Published: July 2007

A microwave power combiner with waveguide ports is proposed and its design method is described. It can combine a large number of inputs at the same time and its voltage tolerance is high. On the side wall of a circular TM0m0 (m = 2, 3, 4,…) mode resonator, rectangular waveguides are connected as the input terminal while a circular waveguide is connected at the bottom surface of the resonator as the output port. The output is transformed into a rectangular waveguide via a TM‐TE mode transformer.

Slits on the side of the output circular waveguide prevent propagation of the modes that do not contribute to the power combining. In the design method, the Y parameters are computed from the equivalent circuit seen from the output side. Thus, the matching condition is obtained from the image parameters. Actual dimensions of the iris for adjustment of the coupling between the input and output waveguides and the resonator can be found from this procedure. The insertion loss of a 14‐GHz four‐way combiner with a TM020 mode resonator was 0.25 dB.
Influence of DC bias on nonlinear distortion of contacts
Authors: Minowa Isao
Published: July 2007

When the nonlinear distortion generated at the metal contact is measured by the two‐frequency method, spectroscopic measured results ranging from the second‐ to sixth‐order distortions can be obtained. Depending on the type of contact and the contact condition, the characteristics of these distortion spectra are different. It was reported previously, together with the measurement technique, that this measurement can be used as a measure for finding the physical phenomena on the contact surface. In the present study, the second‐ and third‐order distortions are considered to be representatives of the even‐ and odd‐order distortions for the purpose of finding the cause of the distortion. A dc bias is applied to the contact and the bias dependence of the distortion voltage is studied. As a result, it is found in most contacts that the second‐order distortion voltage is affected strongly and becomes a minimum at a certain bias point. This indicates that at this bias point the diode characteristics which are the cause of the even‐order distortion vanish and the nonlinearity is almost perfectly symmetric for the currents in both directions. Especially, in this measurement, the bias dependence is observed even if glossy metals are contacted. Hence, this is a method for finding the surface phenomena for a thin‐film thickness from the electrical characteristics.
Photocoupler systems using laser diode
Authors: Matsushita Kenji , Shimizu Eiji , Kitamura Hiroaki
Published: July 2007

Due to recent progress in semiconductor lasers, small‐sized optical sources with good coherency characteristics are easily obtainable. Using semiconductor lasers instead of previously employed light‐emitting diodes, it is believed that construction of new photocoupler systems is possible. In this paper, using the coherent light, the basic behavior of photocouplers is discussed and parallel and serial photocoupler systems with new functions are proposed.
Bidirectional characteristics and applications of temperature‐sensitive magnetic semiconductor
Authors: Seki Kyoshiro , Osada Hiroshi , Shida Jun‐Ichi , Murakami Koichi
Published: July 2007

The magnetic and conduction properties of certain ferrites (referred to as temperature‐sensitive magnetic semiconductors (TMS)) exhibit marked temperature dependence. The temperature dependence of the resistance of a TMS is similar to that of a semiconductor thermistor at low voltage. At higher voltages, three regions are observed in the symmetric, bidirectional characteristics. These are a cutoff state, a negative resistance state and an “on” state.

Therefore, a TMS can act as a multifunction magnetic semiconductor device which can be used to satisfy thermistor and bidirectional diode characteristics. Application of TMS diodes for their ability to handle overvoltage and overheating is discussed.
Principles for modal waves in guided wave optics
Authors: Hashimoto Masahiro
Published: July 2007

The geometrical optics theory of modal waves propagating along optical waveguides is described. The theory is general and thus applicable to the general classes of inhomogeneous waveguides including aniso‐tropic media. This paper points out that the light ray, which is the fundamental concept in geometrical optics, is to be definable as the energy ray and the wave‐normal ray. The variational principles valid for these two definitions are explained. The energy ray is the well‐known ray that shows the path of energy transport. The wave‐normal ray is defined to be the locus of the wave‐normal vectors perpendicular to the wavefronts. The variational principles that describe these two rays are different, and therefore the ray equations for both rays are different in anisotropic media. The former is known as Hamiltonian optics, but the latter is not yet established as geometrical optics. It is pointed out that the latter should be used to describe the geometrical behaviors of guided modes and the propagation of modal waves without any logical contradiction. Optics describing guided modes in terms of the wave‐normal rays is called guided wave optics, and some differences from Hamiltonian optics are discussed using several examples.
Fabrication of polycrystalline silicon thin‐film transistors by ion shower doping technique
Authors: Hirano Ryuuma , Setsune Kentaro , Yoshida Akihisa , Hirao Takashi
Published: July 2007

In the fabrications of polycrystalline silicon thin‐film transistors (TFTs), doping of impurities is often carried out by ion implantation. In this study, dopings of phosphorus and boron were carried out by an ion shower doping technique, where the rf plasma of H2‐diluted PH3 or H2‐diluted B2H6 gas with a magnetic field was used for the ion source. To form the source‐drain regions using this technique, the doping characteristics such as sheet resistivity and impurity profiles in polycrystalline Si were investigated. Using the conditions obtained experimentally, n and p channel Si gate polycrystalline Si TFTs were fabricated on a fused silica substrate by using a CMOS process. It was also confirmed that the conventional photoresist can be used for this process. For the n‐channel transistor, field‐effect mobility μ = 3 cm2/V·s, threshold voltage Vth = 5 V, and on‐off current ratio ION (VD = 6 V, VG = 10 V)/IOFF (VD = 6 V, VG = 0 V) ≌ 106 were obtained for W/L = 12 μm/6 μm. In the p‐channel transistor, the characteristics were similar to those obtained by ion implantation. The ion shower doping technique made it possible to fabricate polycrystalline Si TFTs with a CMOS structure, using a simple apparatus. By using this technique, a large area process will be possible.
Finite‐element analysis of plane wave diffraction from metallic gratings with arbitrary complex permittivity
Authors: Nakata Yasunori , Koshiba Masanori
Published: July 2007

A method of analysis based on the finite‐element method is presented for the problem of plane wave diffraction from metallic gratings with arbitrary complex permittivity. First, the problem of diffraction of a plane wave from the metallic reflected‐type grating is analyzed rigorously as a two‐media boundary value problem by the finite‐element method. Next, a new method is proposed in which an approximate boundary condition using the surface impedance is incorporated into the discretized equations by the finite‐element method. Especially, in the method of using the surface impedance approximation, the region to be analyzed is reduced substantially from the one for the two‐media boundary value problem, and the computational effort is expected to be reduced significantly. The diffraction characteristics of grooved gratings with sinusoidal, triangular and rectangular profiles are actually calculated and the results are compared with those by other methods and experiments. In the case of the TE wave incidence, it is found that the results by the two‐media boundary value problem and those by the surface impedance approximation agree well. On the other hand, in the case of the TM wave incidence, the results are substantially different depending on the grating profile. By comparison of the results with those based on the assumption of a perfect conductor, it is found that the loss in the metal must be considered at a longer wavelength in the case of the TM wave incidence than in the case of the TE wave incidence.
Document image compressing and expanding LSI processor
Authors: Nakamura Koozoo , Kojima Yasuyuki , Hamada Nagaharu , Suemori Noboru
Published: July 2007

A single‐chip LSI processor (FCP: Facsimile Codec Processor) is developed which executes the encoding and decoding of binary images using the MH and MR codes. The developed FCP has the following special features: (1) high‐speed changing pixels detection and decoded pixels generation by means of processing 16‐bit pixels in parallel using a 16‐bit video bus operated independently of the MPU bus; (2) use of 2‐μm CMOS technology with about 64,000 transistors; (3) encoding or decoding an A4 size document (standard letter size) in approximately one second.
Uniform asymptotic solution of guided modes in inhomogeneous slab waveguides with an even polynomial refractive index profile
Authors: Yata Akira , Ikuno Hiroyoshi
Published: July 2007

Uniform asymptotic solutions are obtained for the propagation constants and field distributions for guided modes inside slab waveguides with inhomogeneous profiles of refractive index. Uniform asymptotic solutions are formed with an arbitrary order by a recursive algorithm for a related equation method. Through a quantum condition the propagation constant is determined. The parabolic cylinder functions describe the field distributions. By the expansion coefficients of polynomials which approximately represent the refractive index profiles, the asymptotic solutions can be represented analytically. This paper examines the analytic solution for a squared hyperbolic tangent profile, and for a Gaussian profile, it was analyzed numerically. The effectiveness of the uniform asymptotic solutions was verified.
Optical scanning image sensor
Authors: Yamada Satoru , Sakai Syunji , Iguchi Yasuo , Sakamoto Masaaki
Published: July 2007

As an image input device such as a facsimile and an image scanner, various image sensors have been studied. This paper describes an optical scanning contact image sensor as a form of contact image sensor. In the optical scanning type, the dots of the LED array used as a light source are activated one by one and a text is illuminated via a rod lens. The reflected light is converted to electrical signals by one photo‐detector. This system has the advantage of an extremely small power consumption. In the present trial fabrication, an a‐Si photodetector (with a pin structure) with one long element of 128 × 0.5 mm and reading width of the text 122 mm is employed. As a result, the power consumption of the present image sensor is 0.25 W (power supply voltage of 5 V) including the illumination.
Finite‐element formulation in terms of the magnetic‐field vector for axially symmetrical graded‐core optical fibers
Authors: Kumagami Hiroshi , Hayata Kazuya , Koshiba Masanori
Published: July 2007

A finite‐element method for the analysis of axially symmetrical graded‐core optical fibers is formulated in terms of all three components of the magnetic field. By considering the axial symmetry of optical fibers, the inhomogeneous core region to which the finite‐element method is applied is divided into axially symmetrical ring elements and the homogeneous cladding region is treated analytically. Therefore, very accurate results can be obtained even for near cutoff. Also, for elimination of spurious solutions, the penalty method, the transverse magnetic‐field method, and the Kobelansky‐Webb method, which have been developed for the finite‐element analysis of axially nonsymmetrical waveguides, are introduced. Then the accuracy of finite‐element solutions is investigated in detail from the viewpoint of the order of elements and the treatment of refractive index distribution within each element. To check the validity and usefulness of the method proposed herein, a step‐core optical fiber and a graded‐core optical fiber are analyzed, and the results obtained are compared with the exact solutions and the results of the power series expansion method.
Reflection and transmission characteristics of rectangular dielectric waveguide junction with transverse displacement
Authors: Tomabechi Yoshiro , Matsumura Kazuhito
Published: July 2007

In the case where rectangular dielectric waveguides with identical cross sections and relative permittivity are connected with a lateral offset, the reflection and transmission coefficients of the guided mode in this portion are calculated and the radiation power is obtained. First, the boundary condition to be satisfied by the electromagnetic field in the junction plane (perpendicular to the direction of propagation) at the offset junction is determined. Next, a double Fourier transform is applied to this boundary condition and the latter is solved in the spectral domain. The reflection and transmission coefficients thus obtained are used as the first‐order approximation and the parameters corresponding to the phase constants introduced separately in the spectral domain are corrected successively. By means of this approach, the reflection and transmission coefficients of the guided mode can be converged to constant values. The reflection and transmission coefficients obtained in this manner are used for calculation of the radiated power generated at the offset discontinuity. It is confirmed that the energy conservation law holds almost at this offset junction. Hence, the numerical accuracy is believed sufficient. A portion of the results was compared with the experimental data and good agreement was found. The present analysis method is believed to be useful for such integrated circuit design as calculation of the allowable offset values in an optical communication system in which rectangular dielectric waveguides are connected with offset.
Ridge‐shaped narrow‐wall directional coupler. Tight coupling and high‐power handling capability
Authors: Tanaka Toshiaki , Aikawa Masayoshi
Published: July 2007

A new ridge‐shaped narrow‐wall directional coupler is proposed which can realize a tight coupling and a high‐power handling capability. In the proposed coupler, the right‐angled corners of the coupling slot of the conventional ridge‐shaped directional coupler are rounded off so that a tight coupling characteristic can be obtained in a broad frequency range. The new structure preserves the features of the conventional ridge‐shaped coupler, that is: (1) flexibility of the spatial arrangement of the two coupling waveguides, and (2) the possibility as a variable power divider. The boundary element method has been used for the electromagnetic analysis.

The obtained performances are such that the coupling is 1.5±0.5 dB, the return loss is more than 20 dB, and the isolation is more than 20 dB in the frequency range of 27 to 33 GHz. The measured coupling characteristics agree well with the computed results.
Properties of optical retardation plates by easily prepared birefringent bulk plastics
Authors: Muto Shinzo , Ichikawa Akio , Okuda Ken‐Ichi , Kawai Masato , Ito Hiroshi
Published: July 2007

When a dc electric field is applied to molten polystyrene and α‐methylstyrene, the molecules are aligned in the direction of the electric field. Since this state is maintained even in a solid state, birefringent bulk plastics are easily obtained. The merit of this technique is that the magnitude of birefringence is contained by controlling the dc electric field. Since there is no size limitation, λ/4 and λ/2 plates were obtained easily at low cost. Furthermore, these optical retardation plates can be used for a wide range of wavelengths. It was found that the temperature dependence of the optical properties does not cause problems at normal usage temperatures.
Insertion force reduction in multipin connectors with various tip shapes
Authors: Yasuda Kei‐Ichi , Nakano Kenichi , Kanai Tsuneo , Ando Yasuhiro
Published: July 2007

To decrease the insertion force of multipin electrical connectors in communication equipment, the tip shape of the male connector was analyzed theoretically, and a model experiment of contact insertion was carried out. From comparison of the theoretical and experimental results, the following results were obtained: (1) if the friction between contacts in connector insertion is not taken into account, a root curve shape is the optimum tip shape; and (2) the insertion experiment using a model for a male connector tip agrees with the theoretical result. As a result, it was shown that the friction between the contacts has an important role, and that to reduce the insertion force, the shape of the tip must be designed with friction taken into account.

From the foregoing results, the connector tip was designed to make the insertion force constant regardless of friction. By investigating the force reduction using a multipin connector of about 200 pins, the evaluation based on the tip shape was found to be valid.
Slot—coupled directional couplers on a both—sided substrate MIC and their applications
Authors: Tanaka Toshiaki , Tsunoda Kikuo , Aikawa Masayoshi
Published: July 2007

A slot‐coupled directional coupler is proposed and analyzed. In the slot‐coupled directional coupler, microstrip lines set on both sides of a common ground plane are coupled through a slot in the common ground plane. This coupler can easily realize a tight coupling such as 3 dB with a small physical size. This paper shows that it is possible to form a planar multiport directional coupler with 2n (n: integer) input or output ports without line crossings by combining slot‐coupled directional couplers. Using such a planar multiport slot‐coupled directional coupler, a multiport power amplifier and a BMN (Butler matrix network) can easily be formed in a small physical size.

The 3‐dB slot‐coupled directional coupler fabricated for trial has a coupling of 3.2 ± 0.2 dB, a return loss of more than 25 dB, and an isolation of more than 28 dB in the frequency range of fO ±20 percent (fO = 1.5 GHz). These measured values agreed well with computed data.
Vectorial finite—element formalism for electromagnetic waveguiding structures with loss and/or gain
Authors: Hayata Kazuya , Miura Kazunori , Koshiba Masanori
Published: July 2007

To carry out a vectorial wave analysis of the eigenmode in an electromagnetic wave‐guiding structure with loss or gain, an efficient vector finite‐element expression is derived based on the finite‐element method in terms of the transverse magnetic field component. Since the eigenvalue of the final matrix equation corresponds to the propagation constant, it is possible to obtain the propagation constant for a given frequency. Hence, it is possible to avoid inefficient iterative calculations on a complex plane which have been used in a conventional method in which the frequency is used as an eigenvalue. Also, the present method can be applied to a dispersive medium in which the medium constant is dependent on frequency and to a structure containing a conductive material in which the loss tangent varies in proportion to the inverse of frequency. From these properties, the present method is believed to be a practical numerical method for the vectorial analysis of guided wave structures containing loss or gain. To confirm the validity of the method, some analytical results are presented for a rectangular waveguide loaded with a lossy dielectric material. Convergence of the solution is checked and the result is compared with the exact solution. Next, as a more interesting example, guided mode analyses are performed for buried heterostructure semiconductor lasers and lossy coupled dielectric waveguides and the results obtained are discussed.
Two—dimensional ray tracing for wavefronts, wave—normal rays and geometrical optics fields
Authors: Hashimoto Masahiro , Komiyama Akira
Published: July 2007

A method is described for constructing geometrically the two‐dimensional electromagnetic wave in an inhomogeneous anisotropic medium. An example of application is also shown. Since the basic theory has already been reported, an application algorithm is described here in detail. Especially, the geometrical optics field at an arbitrary time is traced numerically after the initial shape of the wavefront and the initial intensity profile of the electromagnetic field are given. In the example, a uniaxial anisotropic medium with a weak inhomogeneity is assumed and the initial intensity profile of the geometrical optics field is taken Gaussian.
Transient analysis of three—dimensional electromagnetic field in through—holes
Authors: Masuzuka Naoki , Yoshida Norinobu , Fukai Ichiro
Published: July 2007

Through‐holes are attached to numerous structures in mutual connections of electronic devices, printed circuit boards which provide supporting functions, multilayer wires of LSI, and external connections of IC packages. With the recent uses in superhigh‐frequency waves in superminiaturized circuits, the influences of through‐holes on the propagation characteristics are becoming increasingly nonnegligible. To understand the characteristics of the total system, analyses of through‐holes have become indispensable. However, through‐holes generate complicated distributions of electromagnetic fields due to their three‐dimensional structures. Thus, it is necessary to perform rigorous vectorial analyses for three‐dimensional fields using all field components, boundary conditions, and properties of the medium.

Hence, for analysis of through‐holes, we applied the method of spatial networks. These networks have many features for analyses of electromagnetic fields in obtaining time responses of the three‐dimensional fields. We simulated their basic field behaviors, and obtained transmitted output waves which provide an important influence of a through‐hole on characteristics of high‐speed pulse operations and reflected wave shapes toward the input terminals. We determined the frequency characteristics of those wave shapes by fast Fourier transforms, and clarified the effectiveness of the application of the present analysis method.
Analysis of a bending dielectric slab waveguide by integral equation formulation
Authors: Matsuhara Masanori , Toyoda Ichihiko , Shirae Hisazumi
Published: July 2007

The waveguide bend is an indispensable circuit element in realizing optical integrated circuits. In this paper, the bend in a dielectric slab waveguide is analyzed numerically by means of the integral equation formulation. When a numerical solution of an integral equation is attempted by the boundary‐element method, two problems exist: 1) how one can connect the field distributions expressed by the boundary‐element method with those by the eigenmodes of the waveguide. In this paper, instead of representing the field at the input/output boundary of the bend in the slab waveguide in terms of the boundary‐element method, a new method is proposed in which the field distributions expressed in terms of the eigenmodes are substituted directly into the integral equation; and 2) the treatment of the radiation mode. In this paper, a discretization method based on the sampling theorem is used. As an example, numerical calculations have been carried out for a conventional bend and a reflection bend in a dielectric slab waveguide. It is confirmed that the results agree well with data obtained by other methods. It is pointed out that good results can be obtained for such cases as a structure with large difference in index of refraction between the core and cladding and the one with a large bend angle, which were difficult to analyze by the conventional methods. Further, it is shown that the bending loss of the reflection bend is substantially smaller than that of the conventional bend.
Three‐dimensional analysis of electromagnetic fields for NRD guide with air gap and finite‐metal plane width
Authors: Terashima Kouji , Yoshida Norinobu , Fukai Ichiro
Published: July 2007

Active researches have been conducted recently on NRD lines which have low loss properties in millimeter wavebands and are suitable for integrated circuits. As an example for them, an asymmetrical structure has been proposed for an NRD guide which may be used for a leaky wave antenna. This paper analyzed such a guide for its three‐dimensional spatial‐time responses based on the Bergeron method. We made vectorial analyses on the instantaneous waveforms for all components of the electromagnetic fields and applied Fourier transform on the instantaneous waveforms in the spatial domain. From the wave number spectra thus obtained, we identified the existence of two leaky waveforms for individual modes. We obtained the propagation constant for each mode. Based on characteristic variations of the propagation constant for the dominant leaky mode as a function of the width of a longitudinal conducting plate and on the Poynting vectors, we showed that an NRD guide of such geometry becomes a leaky wave antenna.
Analysis of transmission characteristics of image fiber‐dependence on higher modes and wavelength
Authors: Yamaguchi Shoji , Shimojima Akira , Hosono Toshio
Published: July 2007

In transmission by image fiber, the image is blurred by mode coupling due to the crosstalk cores, which impairs the resolution. The analysis of such crosstalk phenomena by geometrical optics is very difficult, and wave theory must be employed. There are infinite modes excited in each element fiber of the image fiber. In case of low resolution, that is, when the period of spatial harmonics of the image is small compared with the size of element fiber, higher modes are excited in the fiber.

In this paper, the effects of higher modes upon image transmission characteristics of one‐dimensional image fiber are analyzed using vector wave theory. Since the crosstalk characteristics vary widely with wavelength, and various wavelength components are involved in the input image, the analysis of wavelength dependency of the crosstalk is important. By the numerical method, various characteristics are analyzed, and improvement methods are also discussed.
Study of contact phenomena in the vaporized organic gas atmosphere
Authors: Yoshida Kazuhisa , Motoyama Akira , Isagawa Mitsuo , Miyazaki Youichi
Published: July 2007

In the vaporized organic gas atmosphere, the bridge duration and the switching characteristics of a communication relay under the bridge load (DC10 V, 10 mA) were evaluated. As a result, it was found that the bridge voltage waveform pattern changes because of a carbonized product, the bridge voltage (2 ∼ 4 V), which is higher than the boiling voltage of the contact metal (0.9 V), appears, and the actual bridge duration is about 10 times longer than the bridge duration of the contact metal (1 ∼ 5 μs). When the minimum bridge duration is longer than 10 μs, the probability that the contact resistance is higher than 100 mω is over 75 percent.

The timing of the bridge duration increase depends on the kind of organic gas used. When the organic gas has a high degree of polymerization, the bridge duration should be used as an evaluation parameter because the timing of the increase in the bridge duration and contact resistance are accelerated. Using these concepts, the contact phenomena and degradation mechanism of a relay in the bridge load region in an atmosphere of volatile organic gas has been clarified.
GaAs‐ALGaAs double‐heterostructure coupled‐waveguide optical modulators and their high‐frequency modulation characteristics
Authors: Tada Kunio , Hayashi Hideki , Kawanishi Satoki
Published: July 2007

In this paper, a GaAs‐AlGaAs double‐heterostructure (DH) coupled‐waveguide optical modulator, which is important as a multifunction optical component and for possible monolithic integration, has been studied in detail. A DH device with pn‐junction structure, which is expected to have the lowest switching voltage, has been fabricated and the optical modulation characteristics have been measured at 1.06 μm wavelength. At a reverse bias of 13 V, an extinction ratio of 11 dB has been obtained. However, the cutoff frequency has been limited to about 250 MHz, which was lower than the calculated value of 1.1 GHz obtained using a simple lumped‐element circuit analysis. Therefore, the optical modulation characteristics have been analyzed assuming the device as a distributed‐element circuit line, and also taking into account the external parasitic impedancees. Thus it has been concluded that a reduction of the top‐electrode resistance and an increase of the conductance across the device cross‐section are necessary to improve the high‐frequency optical modulation characteristics.

To verify these results, a DH Schottky contact structure, which essentially possesses no ohmic contact resistance with a thick topelectrode, has been fabricated on a MBE‐grown wafer. At a reverse bias of 16 V, an extinction ratio of 12 dB and a cut‐off frequency of 1.5 GHz have been obtained successfully. It has also been concluded that an even thicker top‐electrode and an improved mounting method which minimizes the external parasitic elements are necessary for further improvement of the optical modulation frequency characteristics.
Automatic measurement for investigation on the contact surface using nonlinear characteristics
Authors: Minowa Isao , Kanno Makoto
Published: July 2007

To improve the reliability of an electrical signal transmission through a contact, not only the contact resistance, but also the nonlinear characteristic must be evaluated, especially in the presence of a surface film. This method is effective in the separation of the film resistance and the constriction resistance, and the measurement of film thickness. To investigate the distribution of the oxide film thickness, the system was fully automated to measure the film thickness at various points on a sample surface. The measured properties were the contact resistance and the dc current which is one of the nonlinear components and is needed to cancel the rectification characteristic. To form a contact, copper, platinum and nickel wires were used. This paper demonstrates three‐dimen‐sionally and statistically the characteristics at various spots on a plane.
Boundary‐element analysis of plane‐wave diffraction from metallic gratings with arbitrary complex permittivity
Authors: Nakata Yasunori , Koshiba Masanori
Published: July 2007

For the problem of plane‐wave diffraction from metallic gratings with arbitrary complex permittivity, a new analysis method based on the boundary‐element method is proposed. First, this diffraction problem is analyzed by the boundary‐element method as a two‐media boundary value problem taking into consideration the metallic loss. Further, a simple method is proposed in which an approximate boundary condition using the surface impedance is incorporated into the discretized equation by the boundary‐element method. Especially, in the method using the surface impedance approximation, the region to be analyzed is reduced to only the incident side so that efficiency of both the formulation and the numerical calculation can be improved significantly. The diffraction characteristics of the sinusoidal grating and the Fourier grating were actually computed. The results were compared with those by other methods and by experiments so that the validity and usefulness of the present method are confirmed.
Fabrication of a micropump for integrated chemical analyzing systems
Authors: Shoji Shuichi , Esashi Masayoshi
Published: July 2007

Utilizing micromachining based on the semiconductor device fabrication technique, a miniature pump (micropump) was fabricated on a silicon substrate. The purpose of this study is to integrate a conventional chemical analyzing system on an Si substrate by using microchemical sensors such as ISFET's and microvalves. The micropump was the diaphragm type. The pump was composed of an inlet and outlet having a one‐way microvalve, a pressure chamber formed on an Si substrate and a miniature piezoactuator. The size of the pump was 8 mm x 10 mm x 10 mm and the flow rate on the order of μl/min could easily be controlled by the voltage signal applied to the actuator. To monitor the flow of the pump, a differential pressure sensor which could be formed on the Si substrate was developed. The sensor was composed of a oneway valve and a piezoresistive diaphragm‐type pressure sensor, and had a high sensitivity to small flow.
Influence of heat and compression treatment on magnetic and demagnetization properties of CoCr perpendicular magnetic recording media
Authors: Honda Yukio , Futamoto Masaaki , Yoshida Kazuetsu
Published: July 2007

CoCr alloy thin films considered useful for perpendicular magnetic recording media and films deposited by vacuum evaporation and sputtering have been evaluated. In this study, a CoCr was vacuum‐deposited on Ge underlayers to prepare preferentially oriented films in the c‐axis direction. The influences of the thermal and pressure treatments on the magnetic properties were investigated. The influences of thermal and pressure treatments on the remanence magnetization where the magnetization was carried out in one direction normal to the film surface and the perpendicular magnetic recording were also investigated. As a result, it was found that the thermal treatment at a temperature higher than the deposition temperature reduced the saturation magnetization and increased the perpendicular coercivity and perpendicular magnetic aniso‐tropy. The amount of these changes was greater for the films deposited at lower substrate temperature which had smaller coercivity values. The changes in the magnetic properties were thought to be due to the Cr diffusion during heat treatment. On the other hand, during the pressure treatment, no change in the magnetic properties was observed. The decrease of magnetization due to the thermal treatment was smaller when a film was recorded perpendicularly magnetic than when it was magnetized in one direction perpendicular to the film surface. The decrease of the magnetization was smaller as the recording density increased. In the pressure treatment, the remanence magnetization where magnetization occurred in one direction decreased monotonically as the applied pressure increased. On the other hand, when the perpendicular magnetic recording was carried out on films, less decrease in magnetization was observed.
Effect of Mn‐codeposition on electroless Co alloy magnetic recording films
Authors: Matsuda Hitoshi , Takano Osamu , Furusawa Satoshi
Published: July 2007

This paper describes the fabrication technique of a longitudinal magnetic recording film by the electroless plating method. When 1 percent Mn is codeposited in Co‐P film, coercivity of 12.0 × 104 A/m (1500 Oe) could be achieved if the film is thicker than 0.05 μm. Furthermore, this high coercivity is also observed in a film as thick as 10 μm. The high coercivity is thought to be due to Mn(OH) formed in the deposition bath and which segregates at the grain boundaries of the film. Moreover, not only does it magnetically isolate each grain but also inhibits the lateral growth of grains during film growth.
Light‐induced degradation characteristics of MIS junction using hydrogenated amorphous silicon
Authors: Kawai Shintaro , Hatanaka Yoshinori
Published: July 2007

In an MIS device composed of a transparent electrode, amorphous silicon nitride insulator, and hydrogenated amorphous silicon, optically induced degradation in the optical current characteristic was observed after optical irradiation at an intensity of 2000 1x. This degradation was strongly dependent on the material used for the transparent electrode. The highest degradation was observed when ITO was used. However, when a Pt electrode was used, no degradation was observed even after optical irradiation for 100 hr. The degradation was lowered by coating the surface of the ITO electrode with a thin Pt film.

A change in the optical current due to the difference in the optical bandgap of the silicon nitride used as a thin insulating layer was not observed. However, as the optical bandgap of the silicon nitride increased, the threshold voltage for the I‐V characteristic under illumination tended to shift to the higher voltage.

It was concluded from the experimental result that the characteristics of an MIS device are strongly dependent on the transparent electrode. Therefore, special care must be taken in the fabrication of the transparent electrode, and coating the electrode with a thin Pt film is an effective way to stabilize the device. The amorphous silicon nitride film should be of high quality and as thin as possible to minimize the optically induced degradation.
Self‐injection locked gunn oscillator using nonradiative dielectric waveguide
Authors: Takada Masayuki , Yoneyama Tsukasa
Published: July 2007

A Gunn oscillator is developed using a nonradiative dielectric waveguide which is employed in millimeter‐wave integrated circuits. First, the structure and operation mechanism of the oscillator are described. The test of the oscillating properties shows the possibility of determining its frequency, and the maximum output power can be compared to that of the waveguide oscillators. Then a self‐injection locked Gunn oscillator using a dielectric resonator is developed for frequency stability and noise reduction. It is found that a TEQ2δ mode high‐dielectric ceramic resonator gives the best results when installed, and the oscillator was proved to be practical by measured performances which show the pushing figure and temperature coefficient as 1 MHz/V and ‐5 ppm/°C, respectively.
Finite element analysis of discontiuities in nonradiative dielectric waveguide
Authors: Endo Yoshinori , Yoneyama Tsukasa
Published: July 2007

Discontinuity problems in the nonradiative dielectric waveguide are treated by the finite element technique. Both computing time and memory can be reduced significantly by introducing infinite elements which take into account the evanescent nature of the fields outside the dielectric strip. The hybrid nature of the fields is also taken into account to improve numerical accuracy when the analysis expression for the far fields and the FEM solution for the near fields of discontinuities are matched. Various structures, such as gaps, high‐permittivity dielectric sheet inserts, bandpass filters and even T‐junctions have been analyzed. Some results are confirmed by experimental value.
The law of total reflection in geometrical optics based on wave normals
Authors: Hashimoto Masahiro
Published: July 2007

A geometrical law describing the reflection of wavefronts and wave normals of non‐spherical waves at interfaces is presented. Generally speaking, the angle of incidence and the angle of reflection are different, and the difference is a function of the configuration of the wavefront of the incident wave. With regard to plane wave reflection, the present results are in agreement with conventional laws.
Properties of a‐Si1‐xCx:H protective surface‐layer for electrophotographic photoreceptor
Authors: Ohno Toshiyuki , Ishikawa Fuminori , Tamahashi Kunihiro
Published: July 2007

For an application for electrophotographic photoreceptors, a‐Si1‐xCx:H film was prepared by a plasma CVD method with C2H4 or CH4 as a carbon source, and the dependence of water wettability on the source gas and carbon concentration as well as the dependence of the contact angle with water on the corona exposure has been examined. Surface reactants formed after the corona exposure have also been examined. As a result, it was found that the wettability of the a‐Si1‐xCx:H film decreases with the carbon concentration independent of the source gas. However, corona exposure for one hour increased the water wettability. This trend was found to be independent of the carbon concentration in the film. As a result of the infrared absorption spectrum, this was attributed to the formation of Si‐Ox bond (x = 1.7 ‐ 2.0) by corona exposure.