Yasoo Harada

Magnetic wire and box arrays (invited)

Ferromagnetic wire and box arrays with widths and spacings in the range of 2–0.6 μm were successfully fabricated utilizing high‐resolution electron‐beam lithography and lift‐off techniques. The box arrays possessed a unique magnetic switching mechanism. As the magnetic field decreased, the magnetic coherency between the boxes which are in a row first disappeared. Domain wall motion in each box occurred in the next step. The demagnetizing fields observed in the wire arrays with short spacings were different from those calculated by a model, in which the wires are isolated from each other. Ferromagnetic resonance measurement implied the appearance of interwire dipole‐dipole interaction. Multilayered wire arrays were also prepared to study the magnetoresistive characteristics.

High-performance GaAs switch IC's fabricated using MESFET's with two kinds of pinch-off voltages and a symmetrical pattern configuration

GaAs MESFET switch ICs operating at low control voltages of 0/-3 V and +3/0 V have been developed for use in Personal Handy Phones using the 1.9 GHz band. The switch ICs have excellent RF characteristics, and have no need for external circuit installation. The unique points of these ICs are the use of GaAs MESFETs with two kinds of pinch-off voltages and a symmetrical source and drain pattern configuration with respect to the gate. The 0/-3 V IC had low insertion loss of 0.55 dB and 0.65 dB, and high isolation of 31 dB and 24 dB at receiving and transmitting operations, respectively. The +3/0 V IC also had excellent characteristics such as insertion loss of 0.73 dB and 0.95 dB, and isolation of 27 dB and 23 dB, respectively. Both ICs had an output power at 1 dB gain compression point of 25.4 dBm and 3rd order intercept point of more than 46 dBm. >

High-performance GaAs switch ICs fabricated using MESFETs with two kinds of pinch-off voltages [for handy phone]

GaAs MESFET switch ICs operating at low control voltages of 0V/-3V and +3V/0V have been developed for use in the personal handy phone using 1.9 GHz band. The switch ICs have excellent RF characteristics, and have no need for external circuit installation. The unique points of these ICs are the use of GaAs MESFETs with two kinds of pinch-off voltages and a symmetrical source and drain pattern configuration with respect to the gate. The 0V/-3V IC had a low insertion loss of 0.55 dB and 0.65 dB, and high isolation of 31 dB and 24 dB at receiving and transmitting operation, respectively. The +3V/0V IC also had excellent characteristics such as insertion loss of 0.73 dB and 0.95 dB, and isolation of 27 dB and 23 dB, respectively. Both ICs had an output power at 1 dB gain compression point of 25.4 dBm and third-order intercept point of more than 46 dBm.<<ETX>>

A high power-added efficiency GaAs power MESFET operating at a very low drain bias for use in L-band medium-power amplifiers

A power MESFET offering a high eta /sub add/ operating at a very low V/sub DD/ has been developed. The MESFET has a buried p-layer and an improved LDD (lightly doped drain) n+ self-aligned structure which include highly electrically activated ion-implanted regions due to rapid thermal-cap annealing using double-layered SiN films deposited by ECR plasma chemical vapor deposition. The device geometries and implantation conditions were optimized to achieve a high V/sub (BR)GDO/ of more than 10 V and a low V/sub K/ of less than 0.5 V, and to minimize the bias dependence of S-parameters. This produced excellent electrical characteristics such as P/sub 0(1dB/)=177 mW (173 mW), eta /sub add/=38.8% (32.6%) at V/sub DD/=3 V (2 V), and I/sub DS/=0.16 A ( approximately 0.4I/sub DSS/) (0.24 A ( approximately 0.6I/sub DSS/)) at 1.9 GHz.<<ETX>>

MILLIMETER-WAVE TWO-DIMENSIONAL IMAGING ARRAY FOR THE GAMMA 10 TANDEM MIRROR

A millimeter-wave two-dimensional imaging array has been fabricated in order to diagnose the plug-cell plasma of the GAMMA 10 tandem mirror. The heterodyne system with two separate sources enables the measurement of density and electron cyclotron emission (ECE) in one plasma shot. The interferometer successfully measures the time evolution of the axial and radial line-density profiles with phase resolution less than 1/200 fringe and spatial resolution of 16 mm in the vertical direction and 5 mm in the horizontal one. It is shown that the Abel-inverted density profiles are changed due to the injection of electron-cyclotron-resonance heating at the plug/barrier cells and central cell. The axial and radial dependence of the second-harmonic ECE emitted from hot electrons produced in barrier region is observed simultaneously. The fluctuation spectra of the ECE signals are compared with those obtained from the far-forward scattering diagnostic system.

Diffusion and doping of Si into GaAs from undoped SiOx/SiN film

The diffusion and n‐type doping of Si into GaAs from a novel diffusion source consisting of an undoped SiOx/SiN double‐layered film were achieved by rapid thermal annealing at 860–940 °C. The film properties of the double‐layered films employed as Si diffusion sources are experimentally presented. The characteristics of the Si diffused layers were investigated by secondary ion mass spectrometry, capacitance‐voltage measurement, and the Hall method. The carrier profiles exceeded 2×1018 cm−3 and featured an abrupt diffusion front, while a maximum electron concentration of 6×1018 cm−3 was obtained at 940 °C. The diffused Si profiles were consistent with the SiGa+−VGa− pair diffusion model.

A New High Electron Mobility Transistor (HEMT) Structure with a Narrow Quantum Well Formed by Inserting a Few Monolayers in the Channel

A new HEMT wafer has been developed whose channel layer has a narrow bandgap semiconductor with a few monolayers inserted at an optimum position in the channel, namely, the point where the probability density of electrons is maximum in the lowest subband and negligible in the first excited subband. The Al0.22Ga0.78As/In0.15Ga0.85As pseudomorphic HEMT wafer with one InAs monolayer inserted at the optimum position has provided Hall electron mobility increments nearly 15% higher at 300 K and 20% higher at 77 K than those of conventional pseudomorphic HEMT wafers.

A low-power digital matched filter for spread-spectrum systems

A Digital Matched Filter (DMF) is an essential device for Direct-Sequence Spread-Spectrum (DS-SS) communication systems. Reducing the power consumption of a DMF is especially critical for battery-powered terminals. The reception registers and the correlation-calculating unit dissipate the majority of the power in a DMF. In this paper we discuss this problem and propose a low-power architectural approach to a DMF. The total switching activity factor and the switched capacitance are reduced. As a result of power analysis at the gate level, the implementation of the proposed architecture in a standard 0.18-μm CMOS technology achieved a reduction in the power consumption of more than 70%.

A new two-mode channel FET (TMT) for super-low-noise and high-power applications

A super-low-noise two-mode channel FET (TMT) with high- and plateau-shaped transconductance (g/sub m/) characteristics has been developed. It has two electron transport modes against the applied gate voltage (V/sub gs/). That is, the electrons mainly drift in a highly doped channel region at a shallow V/sub gs/. A plateau g/sub m/ region and the maximum g/sub m/ were achieved at a V/sub gs/ range of -0.25 approximately +0.5 V and 535 mS/mm, respectively. The minimum noise figure and associated gain for the TMT were superior in the low-drain-current (I/sub ds/) region and nearly equal in the middle and high I/sub ds/ region to those of an AlGaAs/InGaAs pseudomorphic HEMT fabricated using the same wafer process and device geometry.<<ETX>>

One-chip 15 frame/s mega-pixel real-time image processor

A-one-chip 15 frame/s mega-pixel real time image processor, for mobile multimedia applications is presented. It contains mega-pixel CCD signal processing, a motion-JPEG/MPEG2 image compression/decompression engine, a RISC-CPU, an NTSC encoder, a SDRAM controller and peripheral interfaces.