Degradation of performance in MESFETs and HEMTs: simulation and measurement of reliability

Abstract

Low noise GaAs based metal semiconductor field effect transistors (MESFETs) and high electron mobility field effect transistors (HEMTs) are subjected to temperature accelerated testing in order to study the degradation mechanism of the tested devices as a function of temperature and time. The major failure modes are found to consist of a decrease in the zero-bias drain-to-source saturation current ( I DSS ) and pinch-off voltage ( V p ), and an increase in series resistance of ohmic contact. A degradation model based on the “gate sinking” and degradation of ohmic contact is proposed to simulate the degradation of I–V characteristics. The proposed model includes the effects of a decrease in effective channel thickness, reduction of free carrier mobility, and compensation of free carrier due to the gate metal penetration into the active channel layer, which results in good agreement between the calculated and experimental results.