Reliability of Improved Power GaAs Field-Effect Transistors

Some 270 6-mm power GaAs FETs with aluminum gates and silicon-nitride passivation have been aged at elevated channel temperatures under dc-bias with or without rf-drive. One catastrophic burnout and extremely slow degradation have been observed for 2-million device-hours. Tentatively estimated failure rates for burnout and for gradual degradation at a maximum channel temperature in normal operation of 110°C are both well below 100 FITs. This represents an improvement of at least one order of magnitude over previous devices whose reliability is presented in a companion paper1. In the improved model no deterioration in gates and ohmic contacts has been observed. Gradual degradation has been caused by deterioration in the channel material. However, this has been an extremely slow process, giving rise to practically no problem. There has been no difference in gradual degradation between devices aged with and without rf-drive for 6,000 hours at 250°C channel temperature. The present study has already. demonstrated that the power GaAs FETs used as the samples are very reliable.