Kazuo Miyatsuji

STUDY OF INTERFACE ROUGHNESS DEPENDENCE OF ELECTRON MOBILITY IN SI INVERSION LAYERS USING THE MONTE CARLO METHOD

The electron mobility in the inversion layer of a metal–oxide semiconductor field effect transistor formed on the (100) silicon surface is calculated by using a Monte Carlo approach which takes into account size quantization, acoustic phonon scattering, intervalley phonon scattering and surface roughness scattering. Degeneracy is also considered because it is important at higher normal effective fields (high gate voltages). The main emphasis is placed on the influence of the specific autocovariance function, used to describe the surface roughness, on the electron mobility. Here we compare the mobilities obtained using exponential and Gaussian autocovariance functions. It is found that the electron mobility calculated with roughness scattering rates based on the exponential function shows good agreement with experiments. The effect of the degeneracy and screening on the roughness scattering is also discussed.

Super self-aligned GaAs RF switch IC with 0.25 dB extremely low insertion loss for mobile communication systems

An extremely low loss switch IC has been implemented by using a 0.15 /spl mu/m-gate super self-aligned FET with reduced drain/source area. Both off-state-capacitance and the specific on-resistance of the implemented FET have been dramatically reduced by the novel device structure. The experimentally fabricated switch IC showed the low insertion loss of 0.25 dB at an added power of 35 dBm at a frequency of 0.9 GHz, which is the lowest value ever reported.

A low power GaAs front-end IC with current-reuse configuration using 0.15 /spl mu/m gate MODFETs

We have developed a novel current-reuse configuration of front-end IC, where the current can be reused in the whole circuit blocks such as low noise amplifier, local amplifier and mixer. The power dissipation is reduced by the factor of three. Excellent high frequency performance such as conversion gain of 30 dB and NF of 1.6 dB at 1.5 GHz is attained under the conditions of supply voltage and current of 3.6 V and 3 mA, respectively.

A Proposal of Single Quantum Well Transistor (SQWT) –Self-Consistent Calculations of 2D Electrons in a Quantum Well with External Voltage

New devices are proposed with an operation principle based on the wave function control of two dimensional electron gas in a single quantum well composed of double heterostructures, for example, AlGaAs/GaAs/AlGaAs. Self-consistent calculations indicate that the current channel of the two dimensional electrons can be easily confined in one of the heterojunction surfaces by applying an external voltage. We show that the mechanism has the capability of fabricating high speed logic devices.

A novel GaAs power MESFET with low distortion characteristics employing semi-insulating setback layer under the gate

A low distortion GaAs power MESFET has been developed by employing a semi-insulating setback layer under the gate. The setback region was obtained by diffusing chromium from the Cr/Pt/Au gate metal in self-aligned manner. The novel power FET with the setback layer was found to be insensitive to surface trapping effects. They showed only 5-6 percent frequency dispersion of drain current at 1 MHz compared to DC condition. Because of this small frequency dispersion, the typical measurement FET, which has a surface setback layer, with a gate width of 36 mm exhibited 1.5 dB larger output power at 1 dB gain compression point than that of the FET without the setback layer. Moreover, in the /spl pi//4 shift-QPSK modulation that has been most popular in digital mobile communication system, the FET exhibited 11 dB smaller adjacent channel leakage power than the conventional one at the output power of 31.5 dBm.

Surface Passivation of GaAs Power FETs

The surface passivation of GaAs power FET has been investigated. Intermodulation distortion of GaAs power FET was found to be affected by frequency dispersion which originates from electron trap at the surface in the vicinity of the gate. There are two ways to suppress the frequency dispersion. One is reducing electron trap itself by using surface passivation, the other is making surface insensitive to the surface trapping effect. We found the FET with undoped InGaP layers on the n-GaAs channel is free from surface trapping effects. The undoped InGaP layer acts as an ideal passivation layer for the channel, since it shows only 2% frequency dispersion of drain current at 1MHz compared to DC condition.

High Field Transport of Hot Electrons in Strained Si/SiGe Heterostructure.

Monte Carlo simulation of two-dimensional electron gas in strained Si/SiGe heterostructures has been carried out to investigate the high electric field transport phenomena. In the Monte Carlo simulation we take into account the intervalley scattering due to the f-type phonons between twofold and fourfold valleys of Si well layer split by the tensile strain in addition to the g-phonon scattering. We obtained the electron drift velocity at room temperature of as high as 1×107 cm/s at 10 kV/cm. Calculated results at 4.2 and 77 K show negative differential mobility beyond 10 kV/cm. At 77 K, transient response of the drift velocity shows a marked overshoot reaching about 3×107 cm/s at 0.2 ps and 10 kV/cm. Ohmic mobility calculated using self-consistent wave functions is also demonstrated. Results are given for the strained Si well width of 10 nm. Obtained low field electron mobility at high temperatures shows a good agreement with the experimental results reported so far.

A low-current and low-distortion wideband amplifier using 0.2-/spl mu/m gate MODFET fabricated by using phase-shift lithography

We have developed a wide-band amplifier that can keep a gain over 10 dB at an operation current of 10 mA from 100 MHz to 3 GHz. The fabricated integrated circuit (IC) achieved a high-output third-order intercept point of 30 dBm and low noise figure of 1.6 dB at 800 MHz, respectively. The present IC employs a MODFET with 0.2-/spl mu/m gate fabricated by using a phase-shift lithography technique.

A low-power GaAs front-end IC with current-reuse configuration using 0.15-/spl mu/m-gate MODFETs

We have developed a novel current-reuse configuration of front-end IC, where the current can be reused in the whole circuit blocks such as low noise amplifier, local amplifier and mixer. The power dissipation is reduced by the factor of three. Excellent high frequency performance such as conversion gain of 30 dB and NF of 1.6 dB at 1.5 GHz is attained under the conditions of supply voltage and current of 3.6 V and 3 mA, respectively.

Temperature-independent transconductance in 0.05 μm-gate AlGaAsGaAs MODFET

Abstract Temperature-independent transconductance has been observed in a 0.05 μm-gate AlGaAs GaAs MODFET. The fabricated device has been provided with 0.15 μm-deep and 0.25 μm-wide gate-recess structure where the high electric field more than 1 × 105 V/cm and the short electron transporting time less than 0.15 ps can be attained at the applied drain voltage of 3 V. Using simple short-channel device modeling, the electron velocity of the present device is extracted to be 8.2 × 107 cm/s which is independent of temperature. These results suggest that the electrons are transported without scattering in the present 0.05 μm-gate AlGaAs GaAs MODFET.