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/sub T/. It has been found that Ti-sinking-depth is insensitive to V/sub T/. However, Ti metal interdiffusion reduces the separation of the gate metal and InGaAs channel, thus affecting the I/sub dss/ degradation rate. Accordingly, we observe the dependence of /spl Delta/I/sub dss/ on V/sub T/. Devices with less negative V/sub T/ exhibit inferior reliability performance to those devices with more negative V/sub T/. The results provide insight into a critical device parameter, V/sub T/, for optimizing reliability performance based on I/sub dss/ degradation.