Degradation mechanism of GaAs PHEMT power amplifiers under elevated temperature lifetest with RF-overdrive

The degradation mechanism of 0.15 /spl mu/m GaAs PHEMTs subjected to three-temperature elevated lifetest (T/sub 1/=185/spl deg/C, T/sub 2/=200/spl deg/C, and T/sub 3/=215/spl deg/C ambient temperatures in N/sub 2/ atmosphere and stressed at Vds=5V/Ids=250 mA/mm) under RF-overdrive at 20 GHz was investigated. The results show that Pout degradation is due to Ids degradation induced by Ti gate metal interdiffusion into the AlGaAs Schottky barrier layer. However, /spl Delta/Imax, /spl Delta/Gmp, and Ti interdiffusion depth depend on the RF-drive levels. Accordingly, a distinct difference of reliability performance between DC (no RF-overdrive) and RF-overdrive lifetests was demonstrated. It has been found that both DC and RF-overdrive lifetests exhibit similar activation energy, which is approximately 1.65 eV. However, the mean-time-to-failure (MTTF) of RF-overdrive lifetest is inferior to that of DC lifetest. The difference is attributed to the higher electric field present in the RF-overdriven lifetest.