Reliability of power GaAs field-effect transistors

A preliminary report on a comprehensive study of the reliability of power GaAs FETs is presented, concerning the catastrophic burn-out failure and gradual degradation failure. The samples used are all 6-mm-wide devices with a nominal gate length of 2 micrometers. The life tests have been carried out at elevated channel temperatures of 250°C, 210°C, and 175°C, simultaneously, with samples of 16, 56, and 140, respectively, under dc bias conditions of 14-V drain-source voltage and 0.55-A drain current in all cases. Since the initiation of this program, none of the above 212 devices has burned out for a total of 730,000 device-hours at the time of this writing. Therefore, the failure rate at normal operational temperature can be predicted under various assumptions. An extremely slow degradation in the electrical parameters has been observed with the 250°C and 210°C tests. At the 175°C, no detectable deterioration has taken place so far. Using a new technique the gradual degradation symptom has been analyzed and possible mechanisms are pointed out. In addition, thermally accelerated life tests with a 4-GHz input of 0.63W have shown aging results comparable to those of the dc-bias-only cases.