On the investigation of gate metal interdiffusion in GaAs HEMTs

Ti interdiffusion of Ti/Pt/Au gate metal stacks in 0.15 /spl mu/m GaAs HEMTs subjected to high-temperature lifetest has been physically identified using STEM technique. Further EDX analysis substantiates the intermetallic formation of Ti-AlGaAs and Ti sinking into the AlGaAs Schottky barrier layer. Ti interdiffusion reduces the separation of the gate metal and InGaAs channel, thus leading to the evolution of a slight Gm increase, positive shift of pinchoff voltage, and S21 increase during the initial stage of lifetest. The STEM was further used to correlate Ti-InGaAs-channel-separation and Ti-sinking depth with a device parameter, Vgs - an indicator of Ti-InGaAs-channel-separation. It has been discovered that Ti-sinking-depth is insensitive to Vgs. However, as Ti interdiffuses, the separation of, the gate metal and InGaAs channel is decreased, therefore affecting the Idss degradation rate. As a result, we observe the dependence of /spl Delta/Idss on Vgs. The results provide insight into a critical parameter, Vgs, for optimizing reliability performance based on /spl Delta/ldss.