This paper discusses crystal-growth and device-design issues associated with the development of high-performance InP/InGaAs heretostructure bipolar transistors (HBTs). It is shown that a highly Si-doped n+-subcollector in the HBT structure causes anomalous Zn redistribution during metalorganic vapor phase epitaxial (MOVPE) growth. A thermodynamical model of and a useful solution to this big problem are presented. A novel hybrid structure consisting of an abrupt emitter-base heterojunction and a compositionally-graded base is shown to enhance nonequilibrium base transport and thereby increase current gain and cutoff frequency fT. A double-heterostructure bipolar transistor (DHBT) with a step-graded InGaAsP collector can improve collector breakdown behavior without any speed penalty. We also elucidate the effect of emitter size shrinkage on high-frequency performance. Maximum oscillation frequency fmax in excess of 250 GHz is reported.

This letter presents SAM, a multiplexer for ATM's circuit emulation services that can precisely control the cell clumping at the connection-level. Compared with a FIFO (First In First Out) multiplexer, it also improves the connection-level diffusion and CDV (Cell Delay Variation) performance. SAM can therefore significantly increase the number of connections accepted by CAC (Call Admission Control) procedures in the subsequent multiplexer.

The radiation behavior of a parallel-plate-fed slit in a thick conducting screen is examined. The Fourier transform and the mode-matching technique are used to obtain simultaneous equations for the transmitted field inside the thick conducting screen. The simultaneous equations are solved to represent the transmitted and scattered fiels in simple series forms. The numerical computation is performed to illustrate the behavior of the radiation from the parallel-plate-fed slit. A substantial reduction in the reflection coefficient is possible by choosing a thickness of the conducting screen.

This paper describes analytical results of high-Tc superconducting asymmetric coplanar strip lines using the frequency-dependent finite-difference time-domain method. The propagation constants of the YBa2Cu3O7-x asymmetric coplanar strip line fabricated on the LiNbO3 substrate are reported. The effect of the SiO2 buffer layer is also investigated.

This paper describes the imaging method for a human forearm in the microwave transmission CT at 3GHz. To improve the spatial resolution, the correction method of the diffraction effects is adopted and the high directivity antennas are used. A cross-sectional image of the human forearm is obtained in vivo.

We report the first monolithic integration of InGaAs/InAlAs resonant tunneling diode (RTD) and high electron mobility transistor (HEMT) epitaxially grown on an InP substrate. The transconductance for a 1-µm gate HEMT was 430 mS/mm and the peak-to-valley current ratio of the RTD was 5.1. Using the integrated structure, we demonstrate basic digital circuits to show low power characteristics of an RTD-load inverter and a static RAM cell circuit, consisting of a single transistor with two RTDs on the transistor. The memory cell circuit exhibits bistability, based on the RTD's negative differential resistance (NDR), at supply voltages from 0.6 to 1.1 V. The static power consumption was 7.3 µW/gate for the inverter and 3.0 µW for memory cell.

We propose a nonlocal impact ionization model applicable for the drain region where electric field increases exponentially. It is expressed as a function of an electric field and a characteristic length which is determined by a thickness of gate oxide and a source/drain junction depth. An analytical substrate current model for n-MOSFET is also derived from the new nonlocal impact ionization model. The model well explains the reason why the theoretical characteristic length differs from empirical expressions used in a pseudo two-dimensional model for MOSFET's. The nonlocal impact ionization model implemented in a device simulator demonstrates that the new model can predict substrate current correctly in the framework of drift-diffusion model.

On mutually coupling lines, the transmission signal is dispersively propagated by crosstalk coupling between lines and shows complex propagation characteristics caused by reciprocal reflections. Usually, the differential equation and the integral equation have been applied to analyze the solutions of transmission lines. In this paper, we propose a different analytical method of the propagation characteristics of signal and crosstalk noise. By setting up crosstalk coupling line as a sectionally divided digital transmission network and by using the signal flow graph and the difference equation, the propagation characteristics in the frequency domain, the space domain and the time domain on mutually coupling lines can be obtained. To verify the validity of this method and analyze the complex propagation problems, we first study the crosstalk characteristics of a twisted pair cable via the third circuit by unidirectional coupling. Subsequently we will analyze the coupling theory of bidirectional coupling lines.

This paper describes the circuit design and experimental results of a video-rate 10-b analog-to-digital converter (ADC) suitable for consumer video products, such as high-definition TV sets. Triple-stage conversion scheme combined with two new conversion methods, "Dynamic Sliding Reference Method" and "Triangular Interpolation Method," and an internal Bi-CMOS Sample/Hold circuit have been developed. These conversion methods require no adjustment circuit to fit reference voltages between conversion stages and realize small active area. As a result, a maximum conversion frequency of 16 MHz, acceptable SNRs of 56 dB and 48 dB for 10 kHz and 8 MHz input frequency respectively and small DNLE of 0.75 LSB have been achieved. This ADC is fabricated with 1.2 µm Bi-CMOS technology and integrates very small number of bipolar transistors of 2 K on a small active area of 2.52.7 mm2 and consumes 350 mW.

A new polarization splitter at optical frequencies is proposed. The basic structure of the device is a tapered velocity coupler which is composed of a straight and a dimensionally tapered slab waveguide on a LiNbO3 substrate. The numerical results obtained with the finite difference method indicate that extinction ratios of polarization less than 2% for both TE and TM modes are possible of realization under moderate control voltages and that the splitting characteristics are stable over a wide range of frequencies.

This paper describes that a neural network, which consists of neurons with piecewise–linear sigmoid characteristics, is able to approximate any piecewise–linear map with origin symmetry. The neural network can generate "deterministic diffusion" originating from its diffusive trajectory.

A simple numerical method for calculating paths of creeping rays around an arbitrary convex object is presented. The adventage of this method is that the path of creeping ray is iteratively determined from initial values of incident point and incident direction of the creeping ray without solving differential equation of geodesic path. As the numerical examples, the path of creeping ray on the prolate spheroid and the resonance path of natural modes are shown.

Numerical studies of reaction–diffusion systems which consist of chaotic oscillators are carried out. The Rössler oscillators are used, which are arranged two–dimensionally and coupled by diffusion. Pacemakers where the average periods of the oscillators are artificially changed are set to produce target patterns. It is found that target patterns emerge from pacemakers and grow up as if they were in a regular oscillatory medium. The wavelength of the pattern can be varied and controlled by changing the parameters (size and frequency) of the pacemaker. The behavior of the coupled system depends on the size of the system and the strength of the pacemaker. When the system size is large, the Poincar return maps show that the behavior of the coupled system is not simple and the orbit falls into a high–dimensional attractor, while for a small system the attractor is rather simple and a one–dimensional map is obtained. Moreover, for appropriate strength of pacemakers and for certain sizes of the systems the oscillations become periodic. It is also found that the largest and local Lyapunov exponents of the system are positive and these values are uniformly distributed over the pattern. The values of the exponents are smaller than that of the uncoupled Rössler oscillator; this is due to the fact that the diffusion reduces the exponents and modifies the form of the attractor. We conclude that the large scale patterns can stably exist in the chaotic medium.

A MOS VCO which has improved linearity of oscillation frequency versus control voltage and has no 1/2 divider is studied. The improved VCO characteristic has been obtained by the use of only two additional transistors, one of which has a role of a load and another of which has a role of a control current source in a differential type delay cell.

A new type of variable beam splitter at optical frequencies is proposed. The basic structure of the device utilizes a tapered velocity coupler which is composed of a center slab waveguide of constant-thickness, constant-index type and two identical outer slab waveguides of constant-thickness, variable-index type. The coupler is assumed to be fabricated on a LiNbO3 substrate, whith an external electric field applied in parallel with the optical axis. The numerical results obtained with the finite difference method show that a wide range of splitting ratios can be obtained with moderate drive voltages and that the splitting characteristics are stable over a wide range of frequencies.

A new simple formulation of absorbing boundary conditions with higher order approximation is proposed for the solution of Maxwell's equations with the finite-difference time-domain (FD-TD) method. Although this higher order approximation is based on the third order approximation of the one-way wave equations, we have succeeded in reducing it to an equation in a form quite similar to the second order appoximation. Numerical tests exhibit smaller reflection errors than the prevalent second order approximation.

We predict that chemical waves can propagate as a guided mode in a reaction-diffusion system that consists of two regions with different wave speeds. In comparison with electromagnetic waveguides, unique features of the guided chemical waves can be seen in their dispersion characteristics. Conditions for supporting lowest-loss guided waves are discussed.

We have studied in detail the effect of gas flow rates on the film properties of low-temperature (300) polycrystalline silicon (poly-Si) films prepared by conventional plasma enhanced chemical vapor deposition (13.56 MHz) with SiF4/SiH4/H2 gases. The effect of SiH4 flow rate on crystallization is shown to be large. A small amount of SiH4 with high SiF4 and H2 flow rates (50[H2]/[SiH4]1200, 20[SiF4]/[SiH4]150, 1[H2]/[SiF4]16) is important to form poly-Si films. The poly-Si films deposited under such optimized conditions had shown preferential 〈110〉-orientation and the crystalline fraction is estimated to be more than 80%. The deposition rates are in the range of 5-30 nm/min. The conductivity is in the range of 10-8-10-6 S/cm. Further, the electrical conduction indicates an activation type, and the activation energy is in the range of 0.5-0.6 eV.

This paper describes small AlGaAs/GaAs HBT's for low-power and high-speed integrated circuits. The device fabrication is based on a new bridged base electrode technology that permits emitter width to be defined down to 1 µm. The new technology features oxygen-ion implantation for emitter-base junction isolation and zinc diffusion for extrinsic base formation. The oxygen-ion implanted emitter-base junction edge has been shown to provide a periphery recombination current much lower than that for the previous proton implanted edgs, the result being a much higher current gain particularly in small devices. The zinc diffusion offers high device yield and good uniformity in device characteristics even for a very thin (0.04 µm) base structure. An HBT with emitter dimensions of 12.4 µm2 yields an fT of 103 GHz and an fmax of 62 GHz, demonstrating that the new technology has a significant advantage in reducing the parasitic elements of small devices. Fabricated one-by-eight static frequency dividers and one-by-four/one-by-five two-modulus prescalers operate at frequencies over 10 GHz. The emitters of HBT's used in the divider are 12.4 µm2 in size, which is the smallest ever reported for AlGaAs/GaAs HBT IC's. These results indicate that the bridged base electrode technology is promising for developing a variety of high-speed HBT IC's.

Gate-controlled negative differential resistance (NDR) due to interband tunneling has been observed at room temperature in a Surface Tunnel Transistor (STT). The STT consists of a highly degenerate p+-drain, an n+-doped channel with an insulated gate, and an n+-source connected to the channel. To demonstrate application as a functional device, a bistable circuit consisting of only one STT and one load resistor was organized and its operation was confirmed. The obtained valley current in the NDR characteristics of the STT, however, is relatively large and limits the device performance. In order to clarify the origin of the valley current, we fabricated p+-n+ tunnel diodes in which growth interruption was done at the pn junction, and investigated the dependence of the NDR characteristics on both the impurity concentration at the regrown interface and the temperature. These measurements indicate that the valley current is mainly caused by the excess tunneling current through traps formed by the residual oxygen at the regrown interface.