Titanium hydride formation in Ti/Pt/Au-gated InPHEMTs

Ti/Pt metal layers are an integral part of the gate stack of many GaAs PHEMTs and InP HEMTs, These devices are known to be affected by H-2 exposure. In this study, Auger Electron Spectroscopy (AES) measurements of Ti/Pt bilayers are correlated with electrical measurements of InP HEMTs fabricated with Ti/Pt/Au gates. The FET measurements show that H-2 exposure shifts the device threshold voltage through the piezoelectric effect. AES reveals the formation of titanium hydride (TiHx) in Ti/Pt bilayers after identical H-2 exposures. These results indicate that the volume expansion associated with TiHx formation causes compressive stress in Ti/Pt/Au gates, leading to the piezoelectric effect. After a subsequent recovery anneal in N-2, the FET measurements show that V-T recovers. AES measurements confirm that the TiHx in hydrogenated Ti/Pt bilayers also decreases after further annealing in N-2.