A NEW SELF-ALIGNED AND T-SHAPED GATE TECHNOLOGY FOR GAAS POWER MESFETS

A new self-aligned and T-shaped gate technology suitable for the fabri cation of GaAs power MESFET was demonstrated using optical lithography . The process employed methods to solve the problems of high gate resi stance 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 voltag e of 35 V. The cut-off frequency and the maximum frequency of oscillat ion were measured to be 25 and 90 GHz, respectively. The power perform ance, 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 effici ency (PAE) of 56%. These are the highest PAE and gain in MESFET struct ure 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 goo d electrical performances were due to the new MESFET design incorporat ing an undoped GaAs cap and a thick lightly doped active layers. The M ESFETs developed in the present work are expected to be very useful as a power amplifying device for satellite applications. (C) 1998 Publis hed by Elsevier Science Ltd. All rights reserved.