Reliability of Ku-Band GaAs Power FETs Under Highly Stressed RF Operation

Abstract

Accelerated life tests under rf drive have been performed on power FETs with sub-micron aluminum gates and plated via-hole source connections designed for operation up to Ku-band. The tests were performed on a nine channel X-band test station under typical operating bias of Vds = 10 V. The rf level was set to drive the devices well into gain compression with I mA net DC gate current. Two failure modes were observed depending on channel temperature. At 228°C a gradual reduction in gain was observed, accompanied by a slow drop in Ids. MTTF according to a failure criterion of 1 dB gain degradation was 2,100 hours. No gate degradation was observed even after 3,300 hours on test. The only observable effects were drain migration and a slightly reduced Idss. At 280°C the failure mode was catastrophic with an MTTF of 120 hours indicating that such high temperatures do not realistically accelerate the normal operating failure mode. Preliminary results are presented for a third long-term test at 218°C.