bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of a finite difference time‐domain method to analyze thin‐film microstrip lines with conductor loss
Authors: Kitamura Toshiaki , Hira Masafumi , Kurazono Sadao
Published: July 2007

Thin‐film microstrip lines have been proposed in which microwave transmission lines and circuit elements are placed between or on the metal and insulating layered films on a GaAs substrate. These configurations are intended for size reduction of microwave circuits, realization of new circuit topologies, and improvement of design capability. On the other hand, the finite difference time‐domain method has attracted attention as one of the general‐purpose analysis methods for three‐dimensional configurations. It has been demonstrated that this method is capable of analyzing substantially complex geometry.

However, in the conventional finite difference time‐domain method, the conductors usually are treated as perfect and infinitely thin metals. Hence, the conventional method cannot be applied to the thin‐film microstrip lines in which the conductor thickness cannot be neglected in comparison with the transmission line dimensions.

In the present study, the conductor thickness is taken into consideration and the formulation is carried out including the conductor loss. In the conductor, the discretization spacing is made sufficiently smaller than the conductor thickness while the discretization step is made larger where the field variation is gradual. In this way, the main storage capacity needed is reduced and the computation time is shortened.

Thin‐film microstrip lines of several shapes are analyzed and the frequency characteristics of the transmission line parameters, the electromagnetic field distributions and the Poynting power distribution are derived. Thus, the validity of the method and its range of applications are shown.
Image reconstruction in optical frequency‐domain reflectometry by means of maximum entropy method—fourier transform combination
Authors: Yoshizawa Akio , Iwasaki Takashi
Published: July 2007

In the optical frequency domain reflectometry (OFDR), if the Fourier transform is used for image reconstruction, degradation such as a spread of width in the image for an isolated reflection point occurs due to the fact that the frequency sweep range is finite and the sampling spacing is disturbed. On the other hand, it is known that the reflection position resolution can be improved in a nonlinear spectral estimation method such as the maximum entropy method, whereas it is difficult to measure the intensity of reflection.

In this paper, a new image reconstruction method is proposed in which the position (distance) resolution is improved by the maximum entropy method while the spectral intensity is determined by the Fourier transform. The method is compared with the image reconstruction by the conventional Fourier transform. If “detection and measurement of several isolated reflection points” are the objective, the image degradation can substantially be alleviated and the location of reflection and reflection intensity can be measured accurately. Also, an optical reflectometer is constructed and experiments of reflection measurement are carried out so that the effectiveness of the proposed “combination method” is confirmed.
Estimation of a phase‐recording characteristic of system for synthesizing a kinoform
Authors: Akahori Hiroshi , Seik Yasuo
Published: July 2007

To satisfy the phase matching condition in the formation of a kinoform, it is necessary to understand the phase‐recording characteristics of the formation system. This paper proposes a method for estimating the phase‐recording characteristics by first recovering the phase actually recorded from the reconstructed image intensity distribution of the kinoform by means of the iterative algorithm by Gerchberg‐Saxton and comparing this with the phase to be recorded. The validity of the solution obtained by this iterative algorithm is investigated and a method is provided for the initial solution which can be converged to a global solution.

A computer simulation for this method is carried out. It is shown that there is possibility of estimating the characteristics even if a Gaussian error with a 20‐percent standard deviation of the true values is contained in the reconstructed image intensity data. Also, from an optical experiment, the phase‐recording characteristics of the kinoform formation system with photographic emulsions actually are estimated.

Next, kinoforms are formed in the cases with and without phase corrections based on the estimated characteristics. By comparison of these reconstructed images, the effectiveness of the phase correction and the validity of the estimated results are evaluated.
Sense junction response in a capacitively coupled josephson memory cell
Authors: Suzuki Hideo , Imamura Takeshi , Hasuo Shinya
Published: July 2007

Previously, a capacitively coupled Josephson memory cell was proposed in which an rf‐SQUID device couples capacitively with a single junction. Binary data stored in an rf‐SQUID device can be read through a flux change which generates a pulse signal to be detected. The pulse has a very narrow width, i.e., an order of picoseconds. The current would be different in the time before and after the pulse is applied, which is superimposed by an oscillating current after the application of a pulse. The bias current margin of the memory cell is determined by the way in which a memory is read by using such a pulse. When a memory cell of Josephson junction devices is used, the bias current margin of a sense junction would govern the overall margin of the memory circuit. This bias current margin must be made large for the present study. Therefore, by assuming the read mode of a capacitively coupled memory cell, the response of a single junction has been studied for a very narrow‐width pulse current which varies with fluxons.

The minimum pulsewidth and amplitude required to switch a junction and a bias current dependence before and after the pulse is applied are calculated analytically on the basis of the coupling energy reported by Dong and Van Duzer [18]. The relation between a minimum pulse‐width and amplitude and a switching time for a sense junction, which cannot be solved analytically, is calculated by computer simulation. Further, the influence of a sinusoidal current superimposed over a bias current also is studied by computer simulation.
A parametric current sensor with feedback loop
Authors: Kutsukake Hiroshi , Tanno Yorimoto , Ichikawa Jun‐Ichi
Published: July 2007

This paper considers a sensor for detecting currents from dc to high frequency without disturbing the circuit current through contact. The current sensor is based on the phenomenon of parametric oscillation and uses the fact that the parametric oscillation voltage is amplitude‐modulated by the magnetic field of the measured current.

An examination is made of the previous current sensor circuit with open‐loop construction, and the new circuit construction is closed‐loop and with feedback circuit. In this way, the current‐detecting characteristics are improved greatly, and it was confirmed that a high‐performance current sensor is obtained.
Low‐temperature preparation of poly‐si tft by ar laser annealing at high scanning speed
Authors: Masumo Kunio , Yuki Masanori
Published: July 2007

In an attempt to fabricate poly‐Si TFT with a field‐effect mobility two orders of magnitude higher than a‐Si TFT which can still be made at an equivalent cost as a‐Si TFT, studies have been made of high‐speed scanning Ar laser annealing. This paper proposes that: ±1 based on the result of spin‐density measurements by ESR, the effect of thermal annealing on the improvement of poly‐Si film quality after a laser annealing is most significant at 400°C. Even at 350°C, high‐quality poly‐Si TFT can be fabricated; and ±2 high‐performance poly‐Si TFT can also be obtained with a‐Si films as starting materials which are made not only by plasma CVD but also by the LPCVD method. Therefore, one can choose a fabrication machine suitable for high yield for amorphous silicon films to be used for high‐speed Ar laser annealing.
An optical neuron device capable of optical parallel operations and all‐optical neural networks
Authors: Takimotoww Akio , Akiyama Koji , Ogawa Hisahito
Published: July 2007

We propose a method for implementing an optical neural network system which utilizes a massively parallel processing architecture and aims to provide performance that approximates that of human mental processes. We describe the configuration, fabrication, and functions of an optical neuron device which is capable of performing both summation and threshold operations in optics. We constructed an all‐optical neural network using these devices, a lenslet array for forming optical interconnections between neurons, and a memory mask representing synaptic weights. This optical neural network has 36 neurons in the input layer and an equal number in the output layer. The network demonstrates an associative memory function for three alphabet letters (O, P, and T). It is capable of recalling perfect patterns against imperfect input patterns through purely optical processing without using electric circuits.
Reduction of amplified spontaneous emission (ase) noise from transmitted soliton signals with a nonlinear amplifying optical loop mirror
Authors: Yamada Eiichi , Suzuki Kazunori , Nakazawa Masataka
Published: July 2007

Since the storage of the amplified spontaneous emission (ASE) noise of an amplifier is a cause for the degradation of the transmission characteristics in a long distance soliton transmission using an optical amplifier, the reduction of the ASE is a key issue to be solved for a soliton transmission. A new method to remove the ASE noise using the threshold characteristics (self switching) of a nonlinear amplification loop mirror (NALM) which utilizes the difference in intensity between the soliton signal and the ASE noise is presented in this paper and its application to a transmission experiment is discussed. First, the transmission characteristics of the NALM for a pulse signal are examined. It is demonstrated that the ASE noise can be successfully removed from the pulse signal of high level. The present method is applied to a soliton signal transmitted over 500 km at 10 Gbit/s. The ratio in intensity between the soliton signal and the ASE noise is improved when the NALM is used as compared to the case without it. Finally, it is shown that the switching of pulse close to the transform limit is possible when the phase difference of a pulse peak propagating in a nonlinear loop with a high gain optical amplifier is less than 0.3 π.
Feasibility of very‐short‐channel mos transistors with double‐gate structure
Authors: Sekigawa Toshihiro , Hayashia Yutaka , Ishii Kenich
Published: July 2007

Conventionally, extremely thin gate oxide and high channel‐doping concentration are used to reduce the short channel effect of an MOS transistor below the submicron region. However, with these methods, there are problems such as the degradation in design freedom with respect to the breakdown voltage, the considerable decrease in the carrier mobility and the remarkable variation in characteristics of devices due to the statistical fluctuation of the impurity doping profile; and they need to be solved. Through the numerical analysis of the threshold voltage performance and the experimental fabrication of various devices with effective channel length range from 0.26 μm to 1.26 μm, it has been made clear in this paper that a double‐gate MOS transistor (XMOS) structure with another insulated gate at the lower part of the channel can reduce the short channel effect without the above‐mentioned problems. The results also show that the gate swing has reached about 60 mV/decade that is close to the theoretical limit; the short channel effect can even be reduced with a much shorter channel length if a thinner active channel layer is used and that reduction is independent of the channel doping concentration; and the limit to a possible shorter channel length may be less than 0.1 μm. It is concluded that the problems with the conventional MOS transistor can be solved by using XMOS structure.
Fabrication of poly‐si tfts using laser annealing technique
Authors: Sameshima Toshiyuki
Published: July 2007

A low‐temperature fabrication process of high‐performance polycrystalline silicon thin‐film transistors (poly‐Si TFTs) is discussed. The performance of TFT is found to depend strongly on crystallization, plasma hydrogenation of poly‐Si, and the fabrication process of the SiO2 insulator. Especially, a key issue in a low‐temperature processing is how to fabricate a gate insulator without serious damage. A method of remote plasma chemical vapor deposition is shown to be very useful for fabrication of high‐quality SiO2/Si interface of a large area at low temperatures.
Preparation of poly‐si by excimer laser annealing with solidification process control
Authors: Noguchi Shigeru , Kuwahara Takashi , Hanafusa Hiroshi , Nakano Shoichi , Kuriyama Hiroyuki , Kiyama Seiichi
Published: July 2007

Polycrystalline silicon (poly‐Si) recrystallized by a conventional excimer laser has a small grain of about a few hundred Å and a mobility of about 100 cm2/Vs at most. It is believed that such small grain size could be due to a fast solidification velocity based on the authors's study of the solidification control of molten Si. A thermal analysis by computer simulation indicates that the solidification velocity can be lowered by heating substrate (400°C) during laser irradiation and thinning an amorphous Si (a‐Si) film (500 Å).

Poly‐Si with a large grain (5000 Å) and high mobility (280 cm2/Vs) has been fabricated by excimer laser annealing in the present study. Nonuniformity of characteristics of poly‐Si in an overlapping region of the laser spot also is examined. An uncompleted melting of a mixed region of fine poly‐Si and a‐Si generated at an excimer laser spot edge is the cause for such nonuniformity. An overlapping region of a laser spot is found to become very uniform by using the present solidification control method. Nonuniformity of mobility is improved from ±20 to ±8 percent in the present study. This method is a very useful low‐temperature processing for fabricating large‐sized poly‐Si films.
Polycrystalline‐silicon tfts fabricated at low temperature using ion doping technique
Authors: Yoshinouchi Atsushi , Oda Akihiro , Itoh Masataka , Morita Tatsuo , Tsuchimoto Shuhei
Published: July 2007

Crystallization phenomenon induced by ion beam irradiation from an RF plasma source using large‐area ion doping without mass selection (ion doping technique) at low temperature less than 350°C has been investigated. Phosphorus ions and protons are implanted simultaneously into a polycrystalline silicon film. When the proton dose exceeds 4 × 1015ion/cm2, the amorphous film is crystallized and the crystalline grain size is about 50 nm. Since the crystallization depends on the proton dose, it is obvious that the proton beam contributes to crystallization.

Using this self‐activation technique, the annealing step to activate the implanted dopant can be eliminated. In the polycrystalline thin‐film transistor (TFT) withL/W= 15 μ/5 μ, the mobilities inndandpchannels are 25 cm2/V.s and 14 cm2/V.s, respectively.
Complex‐valued equivalent circuits which represent the connection of wave functions at the heterointerfaces
Authors: Sanada Hirofumi , Nagai Nobuo , Ohtani Naoki , Miki Nobuhiro , Ohkama Hiroshi
Published: July 2007

For the design of devices using the quantum effect, it is necessary to know the wavefunction of the electrons and holes in the quantum well and multiple barrier structures as well as the characteristic energy levels and resonance levels. It is necessary further to manipulate the potential structures to synthesize a desired phenomenon. to attain these objectives, applications of circuit theory to the analysis and design of quantum effect phenomena have been attempted.

In this paper, it is shown that the 2 × 2 interface matrix representing the continuity of the wavefunction and the boundary condition on the wavefunction accompanied by the T‐X mixing are expressed in terms of the lossless two port and four port, respectively. By means of this procedure, it is now possible to carry out a circuit‐oriented treatment of the behaviors of the electrons and holes in the case of superlattices other than GaAs systems requiring the interface matrix and the case where mixing between the minimum points of the conduction band in GaAs/AlxGal ‐ xAs for which no circuit treatment was previously possible. They can now be analyzed systematically with the circuit functions and circuit matrices of the equivalent circuit without special boundary conditions. Also, by means of the proposed circuit representation, analysis examples are presented for the tunneling phenomena in these potential structures.
Theoretical analysis of optical bistability of a faraday medium
Authors: Hirano Masao
Published: July 2007

An optical bistable device can be useful not only for optical memory but also for optical sensing by using its binary signal process characteristics. In this case, if a nonlinear Faraday medium is used in the optical bistable device, some interesting features can be obtained as already shown by the present author. Those unique characteristics are that, by controlling the polarization direction by an external magnetic field, a multiple interference can also be controlled not only by the phase associated with an optical path variation but also the polarization direction.

This paper describes a theoretical analysis of the fluctuation of transmission and reflection as a function of an absorption in a medium besides the incident intensity reduction and discusses the bistability characteristics and the threshold values against the parameters. It is shown that the control of the bistable function, the realization of a low threshold value, and the increase of a discontinuous power variation ratio (= optical intensity ratio between on and off in the binary signal process) at the threshold value are accomplished as the result of the introduction of the external magnetic field control method. Therefore, it can be concluded that a Faraday medium is very useful for an optical bistable device.
Effect of the phase transition of Ti silicide on the thermal stability of Si‐interface in the Cu/CuTi2/Ti/Si contact system
Authors: Sasaki Takahiro , Kagomi Shinya , Sasaki Katsutaka , Noya Atsushi , Yoshimoto Ken'Ichi
Published: July 2007

In an attempt to realize a stable Cu metallization in Si‐LSI, a Cu/CuTi2/Ti/Si contact system was prepared and its thermal stability was studied. As a result, although the phase transition from the intermediate CuTi2 phase to the CuTi phase was observed with increasing annealing temperature in the contact system, the interface between the metallization layers (Cu and CuTi) and Si in the system suppressed the excess diffusion of Si at temperatures up to 570°C. the reason is that the Ti silicide formed at the Si interface acts as an Si diffusion barrier until its chemical state transforms into TiSi2, which is the final phase of Ti silicide. However, the contact system failed due to a direct chemical reaction between Ti and/or Cu in CuTi and Si which diffused into the upper layer through TiSi2 when Ti silicide at Ti/Si interface formed TiSi2 at 600°C. Then the contact system resulted in the phase‐separated bilayer structure of silicide. It was revealed from these results with the thermal stability of this contact system is related closely to the phase transition of the Ti silicide layer at the Si interface with increasing annealing temperature.
Surface‐emitting lasers of low‐threshold 1.3‐μm GaInAsP/InP circular planar‐buried heterostructure
Authors: Baba Toshihiko , Yogo Yukiaki , Suzuki Katsumasa , Koyama Fumio , Iga Kenichi
Published: July 2007

The GaInAsP/InP circular planar‐buried heterostructure is a promising structure to realize a low‐threshold 1.3‐μm surface‐emitting laser for continuous operation at room temperature. In the conventional regrowth process, pinholes which depend on the crystalline orientation of the circular active region tend to occur, resulting in the increase of nonradiative current. As a result, it has been difficult to achieve room temperature oscillation.

To solve this problem, the planar‐buried structure which could be formed by one liquid‐phase epitaxial step without using a mask was adopted to fabricate mesa‐type surface‐emitting lasers. As a result, the reproducibility in forming the buried structure was improved and the non‐radiative current decreased. the resultant devices showed stable electrical and optical characteristics.

When the laser cavity was formed by using SiO2/Si dielectric multilayer mirrors, continuous oscillation was observed at 77 K and the threshold currents of 15 devices were lower than 15 mA. the lowest threshold current was 2.2 mA.

In the room‐temperature pulse operation, the threshold current was 34 mA, the lowest among the values ever reported. Pulse oscillation was observed at 45°C and continuous operation was observed even at −57°C.

If reflecting mirrors with a high thermal conductivity are introduced, the temperature for continuous operation will increase and it will be possible to realize continuous operation at room temperature.
Analysis of open‐type waveguides by the combination of finite element method and boundary element method
Authors: Ise Tomoyuki , Matsuhara Masanori
Published: July 2007

In principle, the finite element method is an analysis method in which an inhomogeneous waveguide with a closed boundary and a complex geometry. By contrast, the boundary element method is suited for the analysis of an open‐region problem.

In this paper, as a method for analyzing the propagation characteristics of the guided modes in an open waveguide, the finite element method is applied to the electromagnetic field of the interior region while the boundary element method is applied to the field outside the waveguide. the fields of the two regions are then connected at the boundary.

By means of the present method, it is possible to analyze without spurious solutions the guided modes in an open waveguide with a cladding made of a different material and an inhomogeneous interior region with a complex geometry. Also, the coefficient matrix of the matrix equation to be solved becomes square. As practical examples, the dispersion characteristics of the rectangular dielectric waveguides and channel waveguides are analyzed so that the validity of the method is verified.
Filtering in discrete fourier transform and its application
Authors: Uchida Kazunori , Noda Takeaki , Matsunaga Toshiaki
Published: July 2007

To carry out numerical calculations efficiently based on the discrete Fourier transform (DFT), the filtering operator with regard to the discrete spectrum is defined and its applications are described. First, for the simultaneous equations containing discrete convolution operations similar to the Wiener‐Hopf‐type integral equation of the first kind, a study is made to determine if a solution method similar to the Wiener‐Hopf technique in the continuous spectrum can be applied. Since the DFT is based on the periodic functions, it is found that such a method is not possible in general except for special cases.

To derive numerical solutions, three methods are proposed in this paper. In the first method, the simultaneous equations derived by using the inner product on the discrete spectrum are solved directly. the next method is a successive solution by repetition of the filtering operation. the last method is a successive solution by repetition of the filtering operation. the last method uses a conjugate gradient method based on the filtering operation. As an example of application of the numerical method based on the conjugate gradient method which can be applied to a wide range of problems, the problem of scattering of electromagnetic waves by a planar grating is investigated. It is shown that the transmitted power and the surface current distribution can be obtained accurately.
Analysis of the characteristics of planar power magnetics for high‐frequency DC/DC converters
Authors: Sakakibara Kazuhiko
Published: July 2007

Although magnetic components combining planar construction windings and flat cores have begun to be applied to planar‐type dc/dc converters, there are many unclear points regarding action of the leakage magnetic flux when the core is made extremely thin.

In this paper, combining the analysis by finite element method and experiment, the quantization of the influence on excitation inductance and winding loss by the leakage magnetic flux is attempted. Also, the flatter the core is, the more the leakage magnetic flux linking and the winding increase. Also, although there is the advantage that the excitation inductance increases, it was clarified that, on the one hand, it is accompanied by the disadvantage of increase of winding loss by the leakage magnetic flux.

Winding losses in various winding constructions are compared, and it is shown that the sandwich construction is the best from the viewpoint of decrease of loss. the suitability of this result was verified by a 1.2‐MHz, 126‐W prototype voltage resonant dc/dc converter.
Frequency stabilization of a semiconductor laser using the magneto‐optical effect and the saturated absorption optical system
Authors: Nakazawa Takao , Nakano Hiroyuki , Ueno Takashi , Sato Takashi , Shimba Minoru
Published: July 2007

When the oscillation frequency of a laser diode is stabilized by means of the absorption line of atoms and molecules, a general method used was to apply infinitesi mel modulation directly on the bias current of the laser diode. However, this method has some disadvantages such as expanded oscillation spectral width and restriction of the stabilization frequency to the center frequency of the absorption line.

In this paper, the laser light was stabilized by providing modulation indirectly instead of direct modulatin of the oscillation frequency. This is done by modulation of the reference frequency by means of the magneto‐optical effect of the absorption line of the atoms. Further, by comparison of three types of saturated absorption spectroscopy systems, the effect of the magneto‐optical phenomena on the stabilization was examined. As a result, it was found that this method provides a degree of stability comparable to or better than the direct modulation system. Also, the stabilization frequency can be swept and controlled in the range of about 1 GHz without degrading the degree of stability.
A high‐efficiency linear power amplifier using an envelope feedback method
Authors: Kosugi Hiroaki , Matsumoto Takayuki , Uwano Tomoki , Enoki Takashi
Published: July 2007

This paper describes a high‐efficiency linear power amplifier using an envelope feedback method for a digital cellular telephone. Adjacent channel interference due to the amplitude and phase distortions of the amplifier is analyzed for a π/4‐shift QPSK modulation scheme. From the analysis amplitude error compensation circuits are proposed and the limit of phase‐shift variation caused by AM/PM conversion is discussed. the drain power efficiency of 50 percent at the low operation voltage of 5.8 V is achieved experimentally.
Design of a low‐phas noise VCO for an analog cellular portable radio application
Authors: Uwano Tomoki , Ishizaki Toshio , Nakagawa Yoshihiro , Nakamura Toshiaki
Published: July 2007

A voltage‐controlled oscillator (VCO) with a small power consumption and an excellent signal‐to‐noise (C/N) ratio was developed for a portable telephone. In the domestic analog portable cellular portable telephone,C/Nis reguired to be more than 107 dBc/Hz at an offcarrier frequency of 12.5 kHz. to realize this value, the noise behavior was studied for a 900‐MHz oscillator using a small‐signal, high‐frequency silicon transistor.

First, the relationship between the transistor noise and theC/N, the operating voltage and current dependence of theC/Nand the relationship between the collector breakdown voltage and the oscillator output were studied experimentally. A transistor was selected which is most suitable for a low‐noise VCO at a low operating current of 3 to 7 mA.

Next, by using this transistor, the relationship between the unloadedQof the resonant circuit and theC/Nwas studied. It was found thatQof 60 is needed to obtain aC/Nwith a 3‐dB margin. On the other hand, with a view to miniaturizing the resonator, a dielectric coaxial resonator with a material having a relative permittivity of 90 was studied experimentally. AQof 200 was realized with a resonator having a cross‐sectional size of 1.8 × 1.8 mm2. By combining it with a varactor diode, aQof more than 60 was attained. Based on these results, a low‐noise VCO was realized which has dimensions of 10 × 10 × 3 mm and is operated with a power supply voltage of 3 V and a current consumption of 10 mA.
A new n/m code and modified viterbi decoding in magnetooptical recording
Authors: Osawa Hisashi , Yamamoto Nobuya , Okamoto Yoshihiro
Published: July 2007

This paper proposes the (4, 5, 6)/11 code, which is a new n/m code, constrained in that the minimum runlength of symbol “O” in the codeword is 2 and is suited to PR(1, 1) equalization. In PR(1) equalization, a pseudo‐PR(1, 1) characteristic is obtained by shifting the sampling points by Ts/2 (where Ts is the symbol interval). Assuming that the conventional Viterbi decoding is applied to the (4, 5, 6)/11 code, the error‐rate characteristic is examined by simulation, and the result is compared to that of the well‐known 4/11 code. It is shown as a result that the (4, 5, 6)/11 code has an excellent performance. Then a modified Viterbi decoding is considered by utilizing the run‐length constraint, and the performance is evaluated.

The colored noise sequence is approximated by a simple Markov process and another modified Viterbi decoding utilizing the correlation of the noise sequence also is considered. It is shown as a result that the CN ratio is improved compared to the conventional Viterbi decoding by about 1.0 dB in the former and about 2.7 dB in the latter, at the error rate of 10−4.
Elastoplastic creep analysis of thermal stress and strain in aluminum interconnects of LSIs
Authors: Hiraoka Kazunori
Published: July 2007

To study a thermally induced open‐failure mechanism of aluminum interconnects of LSIs, a three‐dimensional (3‐D) simulation using a finite element method was carried out. In this calculation, a creep strain increasing with time in addition to an elastoplastic strain was taken into account. Further, the effect of a manufacturing process on a stress and a strain induced in an aluminum layer was examined using a simulation for a subsequent stacking of oxide‐layer/aluminum film/protective layer on an Si chip.

The condition for a 3‐D plasticity to occur was calculated in which case a strain was represented using the von Mises criteria. As a result, after the manufacturing process is completed, the stress is found to decrease significantly with time, while a plastic strain is kept constant. However, the creep strain responsible for the failure is found to increase. the temperature dependence of the creep strain also was studied. the three different results previously reported, i.e.,the lifetime becomes shorter as the temperature rises, there is no temperature dependence, andthe shortest lifetime is at about150°C are all found to be possible. the calculation was applied to the multilayered interconnects and the creep strain is shown to decrease by more than a few tens percent in an aluminum layer.
Analysis of phase characteristics of a GaAs FET power amplifier for digital cellular portable telephones
Authors: Ishizaki Toshio , Ikeda Hikaru , Yoshikawa Yoshishige , Uwano Tomoki
Published: July 2007

The GaAs FET power amplifier in a Class AB operation used for digital cellular portable telephones must be studied for reduction of the transfer phase variation to attain high performance. However, the load impedance dependence of the phase characteristics, which is of significance, has not been analyzed in detail.

In this paper, for the analysis of phase characteristics, a new π‐type FET equivalent circuit is proposed in which a negative conductance is introduced in place of the current source. By means of this equivalent circuit, an analysis and a simulation are carried out for the load impedance dependence of the phase charac‐ teristics. an increase of the drain‐gate conductance and a decrease in the drain conductance accounts for the inverted V‐shape phase‐shift performance. the dependence on the load impedance also is illustrated. Further, the experimental results confirmed the correctness of the analysis since the phase variation is found to be a function of the drain‐gate current.
High‐speed frequency‐switching synthesizer using fractional N phase‐locked loop
Authors: Adachi Hisashi , Kosugi Hiroaki , Uwano Tomoki , Nakabe Kohji
Published: July 2007

A fractional N phase‐locked loop frequency synthe sizer has been developed for small‐size and low‐power applications. It has fast frequency switching and low‐phase noise. the fractional N‐frequency synthesizer realizes fast switching by the high‐frequency reference signal and by widening the loop bandwidth. However, when the bandwidth was widened, deterioration of phase noise is observed. Then the loop bandwidth which is necessary for fast frequency switching and which gives low‐phase noise performance is determined.

Based on these conditions, loop filter switching was studied which realized fast switching by widening the loop bandwidth and the low‐phase noise performance by making the loop bandwidth narrow after the frequency switching. In the conventional filter switching, VCO control voltage fluctuates at the time of switching and the frequency switching time becomes longer.

A new method is proposed which gives small switching fluctuation and which can shorten the frequency switching time. Finally, the synthesizer circuit in the 900‐MHz band was fabricated and the lock‐up time of 1.3 ms, the phase noise of ‐120 dBc/Hz at 50 kHz offset from carrier and spurious level of ‐83 dBc were obtained.
A method of designing a tapered waveguide‐type delay equalizer with quadratic and cubic delay distortions on a negative inclination
Authors: Kamei Toshihisa , Ishihara Fujio
Published: July 2007

A tapered waveguide‐type delay equalizer which makes use of the reflected wave from a cut‐off tapered waveguide is an attractive circuit with many advantages as an equalizer for millimeter wave communication. However, in the conventional configuration, there are limitations in the realizable delay characteristics. Especially, it was not possible to realize an equalizer for which the linear component of the desired delay characteristics has a negative slope.

This paper reports a new method for designing a tapered waveguide‐type delay equalizer which is realizable regardless of whether the linear delay is positive or negative. First, by means of the approximation method reported previously, a design equation for the taper shape is derived and it is pointed out that a design with substantial flexibility is possible. Next, the characteristics are evaluated rigorously by the electromagnetic field method. an attempt was made to eliminate the residual distortion by unwanted reflection. Tests were made on two types of equalizing tapers with different characteristics and several tapers connected before and after these equalizing tapers. the correctness and practicality of the configuration method are confirmed.
Block‐erasing methods for flash memory
Authors: Shiba Kazuyoshi , Kubota Katsuhiko
Published: July 2007

Methods for dividing flash memory arrays into erasable blocks of flexible size have been studied. Blocks are partitioned along the word lines and the source lines in different blocks are disconnected. A minimum block is formed along one word lines from which blocks different in volume are constituted easily. In this dividing scheme, the data disturb time of unselected blocks becomes longer, resulting in undesirable threshold reduction.

It was found that this data disturb endurance is improved by biasing the source at about 5 V. When the state is “1,” it prevents channel formation so that no hot hole injection into the floating gate takes place. In the case of “0” state, this bias reduces the electric fields between the floating gate and the drain; and hence the F‐N tunneling current is suppressed. By this method, data disturb endurance in unselected blocks was improved to be more than 10, 000 cycles.
Measurement of electrooptic constants in proton‐exchanged LiTaO3 optical waveguides
Authors: Kakio Shoji , Minakata Makoto
Published: July 2007

LiTaO3 is considered resistant to optical damage and it has a small dispersion. Thus, LiTaO3 is expected as a solution to such problems as dc drift and optical damage in an LiNbO3 waveguide.

This paper describes a design method for a singlemode, three‐dimensional optical waveguide by means of proton exchange and annealing on a Z‐cut LiTaO3 substrate. A phase modulator with a different annealing time was designed and r33S was measured by the phase modulation method. It is found that the measured value of 6 pm/V immediately after exchange is recovered to 22 pm/V (about 70 percent of the bulk value) by annealing for more than 30 min at 400°C.

By the resonance method, r33T was measured. the result is larger by 30 percent than the measured r33S. After annealing for 30 min, the value was almost equal to the bulk value. Further, by the SIMS (secondary ionmass spectroscopy) analysis, the change of the concentration profiles of Li and H+ before and after annealing is determined. It is found that Li returns to the surface from the interior of the substrate by annealing and H+ is diffused in the depth direction. This suggests that the crystallography of the proton‐exchanged layer approaches that before exchange so that the degradation of r constants is recovered.
Transparent boundary for finite‐element beam propagation method
Authors: Maruta Akihiro , Arai Yasuyuki , Matsuhara Masanori
Published: July 2007

When the wave propagation in an optical circuit is studied by means of the beam‐propagation method, a problem is the reflection of the radiated wave at the virtual boundary surrounding a finitely large region to be investigated. In this paper, it is assumed that the field near the virtual boundary is an outward propagation wave. A method is proposed for transmitting this radia tion without reflection by using the relationship satisfied by this wave as the boundary condition. the method is then applied to the beam‐propagation method based on the finite‐element method. the amount of increase of the computation effort necessary for including this transparent boundary condition is negligibly small in comparison with the amount of computation needed for the successive analysis of the wave propagation. Hence, the method is very effective.
Finite‐element analysis of three‐dimensional waveguide transfer problem‐application to coaxial line system
Authors: Urano Hiroaki , Maruta Akihiro , Matsuhara Masanori
Published: July 2007

As a numerical solution of the electromagnetic waveguide transfer problem with a three‐dimensional discontinuity, the solution in which the finite‐element method is applied to the electromagnetic field at the discontinuity while the eigenmode expansion method is applied to the field in the waveguide is a powerful one. In such a solution, a method for connecting the electromagnetic fields in the waveguide to those in the discontinuity must be considered.

This paper proposes a method in which the Galerkin method using the waveguide modal functions as the weighting functions is used for connecting the field on the boundary between the waveguide and the discontinuity. Since the connecting boundary can be taken very closely to the discontinuity in this method, the size of the matrix equation to be solved is small so that the amount of computation is small. There is no restriction between the number of expansion basis of the field by the finiteelement method and that of expansion modes in the eigenmode expansion method. Also, the matrix equation to be solved is symmetric. the matrix to represent the scattering at the discontinuity can directly be analyzed numerically.

The method is applied in this paper to the simplest discontinuity problem in an axisymmetric coaxial line system to verify the validity of the method.
Improvement of thermal stability of boron in SiGeB/Si heterostructure by stress compensation
Authors: Sakano Junichi , Furukawa Seijiro
Published: July 2007

The thermal diffusion of boron in the SiGe/Si heterostructure during thermal treatment in inert gas was investigated. It was proved experimentally that in the SiGeB/Si structure where the boron concentration in the SiGe layer was higher than that in the Si underlayer, the redistribution of boron from the SiGe layer to the Si layer was less than that in the Si mono‐layer. Also, the thermal stability of boron improved and thep+n junction was shallower than that in the Si monolayer.

To clarify this symptom and to use it in the device process, the equation for the boron diffusion in the hater ostructure structure was derived using the chemical potential. the theoretical equation indicated that boron diffused from the Si layer to the SiGe layer in such a manner that the crystalline strain due to the introduction of Ge was compensated. the experimental results were supported by this theoretical prediction. In addition, it was clarified that the theoretical equation was justified quantitatively by computer simulation.

A new method of forming a shallow p+n junction using the SiGeB/Si heterostructure was proposed based on a theoretical equation, and the guiding principle for the optimization of the process was clarified.
Numerical analysis of scattering from the edge‐type scatterer in a rectangular waveguide by the yasuura method
Authors: Ogata Ryouko , Itakura Tokuya
Published: July 2007

The Yasuura method (mode matching method) was applied to the problem of electromagnetic wave scattering by an obstacle in a rectangular waveguide to prove the usefulness of this method as a general‐purpose analysis method. In this paper, the scattering problem of an inductive obstacle with edges placed in a rectangular waveguide is analyzed numerically, taking into account the singularity of the solution at the edges. the inductive obstacle is considered to be a perfect conductor with an asymmetrical triangular cross section with an arbitrary apex angle. Each corner of the triangle is treated as a singularity.

The algorithm is presented which takes into consideration the singularity of the solution at the edge, and then the accuracy of the analysis is discussed. As a numerical example, the frequency characteristics of reflection and transmission coefficients versus various parameters are shown including the behaviors of higherorder modes. By taking advantage of the fact that the magnitude of the apex angle can be changed arbitrarily, the effect of the slant angle of the triangle on the incident side exerted on the scattering is discussed. Since the structure can be computed for an apex angle starting from 0°, the solution for an apex angle of 0° or the inductive window is compared with the exact solution by Wiener‐Hopf method so that the analysis error is carried out.
Coupling characteristics of nonparallel dielectric waveguides
Authors: Tomabechi Yoshiro , Matsumura Kazuhito
Published: July 2007

A coupled mode equation for two nonparallel dielectric waveguides is rigorously derived from the Lorentz reciprocity theorem. the waveguides are located close to each other. Two local coordinate systems are introduced to present an intrinsic mode function. A global coordinator system also is employed to solve the coupled mode equation. As a numerical example, a coupling system consisting of two dielectric disks with different radii is analyzed. the coupled mode equation for whispering gallery modes propagating along a circumference of the disks is solved numerically in the global coordinate system. Eigenvalues of the whispering gallery modes are complex numbers because of radiation and dielectric losses. As a result, electric field distribution and the coupling coefficient around the coupling system are obtained quantitatively.
A method of calculating step‐shape characteristic in a rectangular waveguide using a transmission equation
Authors: Suga Takashi , Ishihara Fujio
Published: July 2007

It is demonstrated that the step shapes in a rectangular waveguide can be treated rigorously by a transmission equation. an efficient method for computing the characteristics of the step shapes is proposed based on the transmission equation. It is recognized that the step shape is the one in which the derivatives of the shape change in the axial direction diverges. Then the transmission equation is simplified. It is shown that the frequency dependence can be eliminated from the transmission equation if there is no thermal loss in the step shape and that the scale dependence can also be eliminated if the cross‐sectional shape is similar.

By the foregoing procedure, the computation time and the number of computation of the F matrix which consumes the most time in the transmission equation method can now be reduced substantially. It is found that the computation speed can be accelerated effectively by more than one order of magnitude in comparison to the method in which the F matrix is computed by numerical integration. the results are verified experimentally.
Characteristics of ta2O5 thin film prepared by electron beam heating method
Authors: Sekido Yoshihiro
Published: July 2007

A Ta2O5 film formed by ϵ‐beam evaporation (EB‐Ta2O5) was nonstoichiometric because of oxygen deficiency, resulting in electron trapping. As a result, the dielectric constant was higher than that of bulk material. the trapped fixed‐charge density increased with a decrease of film thickness.

When the film was 300 nm, the trapped fixed Charge density was as high as 1016 cm−3. However, when the film was thicker than 300 nm, it decreased rapidly. the dielectric constant approached the bulk value as the film thickness increased, and the film resistance was low because of oxygen deficiency. When the film was 300 nm, the resistivity p was 107 − 108 ω ‐cm (5 × 105 V/cm). When the electric field reached about 7 × 105 V/cm, only the current density increased in spite of the slight increase of the electrical field.

When the film was thicker than 300 nm, the resis tivity increased and the clamp field became unclear with an increase of thickness. an EL (electroluminescent) device was formed using the EB‐Ta2O5 film sandwiched with SiO2 films as the luminescent film. the luminance of the device was 100 cd/2. the luminescence spectrum had peaks at 380, 430, 475, and 540 nm, indicating that there were energy levels at 3.2, 2.9, 2.6, and 2.3 eV.
Conditions of palladium oxide formation caused by mechanochemical reaction
Authors: Yamamoto Takeshi , Sawa Koichiro
Published: July 2007

Palladium has a strong anticorrosion characteristic and has been used as low‐load contact material. This paper investigates the mechanochemical reaction of palladium, which is believed to cause contact failure due to palladium oxide. As a result, it is found that the formation of palladium oxide did not occur when pressure is lower than a certain value and that critical pressure decreases with a decrease of moisture.

It also is found that water vapor suppresses the formation of palladium oxide due to the mechanochemical reaction. It is proposed that the oxidation of palladium is suppressed by the lubrication effect of water vapor. In addition, experiments are carried out under the ambient without water vapor and organic gas; and it is found that the proposition was valid.