The effect of gate metal interdiffusion on reliability performance in GaAs PHEMTs

While Ti metal interdiffusion of Ti-Pt-Au gate metal stacks in GaAs pseudomorphic HEMT (PHEMTs) has been explored, the effect of Ti metal interdiffusion on the reliability performance is still lacking. We use a scanning transmission electron microscopy technique to correlate Ti-metal-InGaAs-channel-separation and Ti-sinking-depth with a threshold voltage V_T. It has been found that Ti-sinking-depth is insensitive to V_T. However, Ti metal interdiffusion reduces the separation of the gate metal and InGaAs channel, thus affecting the I_dss degradation rate. Accordingly, we observe the dependence of ΔI_dss on V_T. Devices with less negative V_T exhibit inferior reliability performance to those devices with more negative V_T. The results provide insight into a critical device parameter, V_T, for optimizing reliability performance based on I_dss degradation.