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

The degradation mechanism of 0.15 μm GaAs PHEMTs subjected to three-temperature elevated lifetest (T₁=185°C, T₂=200°C, and T₃=215°C ambient temperatures in N₂ 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, ΔImax, ΔGmp, 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.