The effect of chip-mounting attachment on the thermal resistance of GaAs power field effect transistor (FET) modules has been experimentally investigated. The thermal resistance was evaluated for different GaAs chip thickness of 150 and 250 m through an electrical method utilizing temperature dependence of Schottky-barrier in the GaAs metal semiconductor FET's (MESFET's). The thermal resistance of low-cost epoxy-mounted GaAs chips, suitable for uniplanar monolithic microwave IC's (MMIC's), was found not to increase even up to a chip thickness of 250 m, while that of AuSn-mounted GaAs chips increased as was conventionally expected. Numerical simulation has also been presented for the similar case of GaAs power MMIC's. The result of simulation suggests that lower thermal conductivity of attachment material, such as epoxy attachment, leads to larger optimum chip thickness that minimizes the total thermal resistance.

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Abs t raclhave developed a GaAs direct-conversion 1/4n QPSK modulator IC equipped with variable attenuators for controlling the output power level of the 1.9 GHz Personal Handy Phone system (PHS). The IC was successfully demonstrated showing state-of-the-art performance with the image rejection ratio of more than 36 d3 at a low input power of -10 dl3m in the 1.9 GHz fi-equency range. By using the "Gate Current Control method by Pull-down FET's" (GCCPF), the equipped attenuators vary the output power from 0 d3 to -28 d3 by 4 d3 step. The IC operates at a 2.7 V supply with the power dissipation of 259 mW. The 2.6 x 4.6 mm2 chip with about 400 elements was fabricated by a 0.5 pm WNx-gate BPLDD GaAs MESFET process.

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Drift mobility profiles in self-aligned WNX-undoped AlGaAs/n-GaAs/undoped AlGaAs doped-channel hetero MISFETs (DMT) with different gate lengths are evaluated (L G=1, 2, 4, 9 µm). The mobility profiles peak between 1400 and 1600 cm2/Vs in the accumulation mode of operation. The drift mobility maximum is shifted to higher gate voltages with decreasing the gate length.