Correlating gate sinking and electrical performance of pseudomorphic high electron mobility transistors

Ti interdiffusion from the Ti/Pt/Au gate into the AlGaAs Schottky barrier layer (SBL) of 0.25-μm GaAs Pseudomorphic High Electron Mobility Transistors (PHEMTs) has been studied using the accelerated life testing technique. Based on measurements and modeling, analytical expressions for quantitative correlation between the positive pinch-off voltage (VP) shift as well as the saturation drain current (IDsat) decrease and the physical damage occurring during gate sinking has been developed. It is suggested that the main cause for device failure is the growth of the TiAs phase leading to the decrease in the SBL thickness. Additionally, it is suggested that VP may be used as a better indicator for device degradation than IDsat since it is linearly proportional to the degrading physical characteristic – the Schottky barrier layer thickness.