Power GaAs MESFET: Reliability aspects and failure mechanisms

In this paper we analyse and discuss some failure analyses performed on power GaAs MESFET. The pieces came both from accelerated tests and from the field. More than one half of the examined devices revealed catastrophic failures with all terminals short circuited due to burn-out occurring in the active area of the FET. In a smaller number of cases devices came from circuits whose power output was decreased and showed parametric degradations such as: an increase in drain to source resistance, a remarkable effect of nonsaturation, a reduction of pinch-off voltage, an increase in the forward gate current. Auger analysis performed on failed transistors clearly reveals an interdiffusion of Au through the Ti and W layers in the gate metallizations, thus reaching the gate active region. Despite the unavailability of test patterns, prepared for the particular purpose, some possible explanations of the electrical characteristics of the parametrically failed devices are presented.