bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractIn 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

AbstractTo 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

AbstractAlthough 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

AbstractWhen 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

AbstractThis 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

AbstractA 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

AbstractThis 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

AbstractTo 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

AbstractThe 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

AbstractA 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

AbstractA 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

AbstractMethods 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

AbstractLiTaO3 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

AbstractWhen 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

AbstractAs 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

AbstractThe 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

AbstractThe 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.