Reliability of power GaAs field-effect transistors

The first report on a comprehensive study of the reliability of power GaAs FET's with aluminum gates and silicon-nitride passivation is presented. A total of 265 standard 6-mm-wide devices has been aged under dc-bias conditions with and without RF drive at channel temperatures of 250, 210, and 175°C. One-million device-hours have been accumulated with no catastrophic failure. A very conservative estimate predicts that the failure rate for burnout at a maximum channel temperature in normal operation of 110°C would be below 100 FIT's. Degradation in the electrical parameters has been very slow even at 250°C channel temperature. It is estimated that the failure rate for gradual degradation at 110°C would be well below 100 FIT's and most likely lower than 10 FIT's. No deterioration in the properties of gates and ohmic contacts have been observed. Diagnostic characterization has revealed that gradual degradation in the sample devices is caused by deterioration in the channel material. There has been no noticeable difference in gradual degradation between devices aged with and without RF drive at the same channel temperature for more than 3000 h. The present study has already demonstrated that the power GaAs FET's used as the samples are very reliable.