A new self-aligned and T-shaped gate technology for GaAs power mesfets

Abstract

A new self-aligned and T-shaped gate technology suitable for the fabrication of GaAs power MESFET was demonstrated using optical lithography. The process employed methods to solve the problems of high gate resistance and low breakdown voltage inherent in power MESFET. The devices with 0,5 mu m T-shaped gate, fabricated on a high-low doped epitaxial layer, showed an uniform transconductance of 150 mS/mm at gate biases ranged from -0.8 to +0.8 V and a high gate-to-drain break down voltage of 35 V. The cut-off frequency and the maximum frequency of oscillation were measured to be 25 and 90 GHz, respectively. The power performance, measured at a drain bias of 8 V and an operation frequency of 12 GHz, displayed an associated gain of 10.0 dB and a power-added efficiency (PAE) of 56%. These are the highest PAE and gain in MESFET structure ever reported at Ku-band frequencies. The mean time to failure of the MESFET at 125 degrees C was evaluated to be 2 x 10(8) h. These good electrical performances were due to the new MESFET design incorporating an undoped GaAs cap and a thick lightly doped active layers. The MESFETs developed in the present work are expected to be very useful as a power amplifying device for satellite applications. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.