Reliability Characterization of Gallium Nitride MIS-HEMT Based Cascode Devices for Power Electronic Applications

We present a detailed study of dynamic switching instability and static reliability of a Gallium Nitride (GaN) Metal-Insulator-Semiconductor High-Electron-Mobility-Transistor (MIS-HEMT) based cascode switch under off-state (negative bias) Gate bias stress (V-GS,V- OFF). We have investigated drain channel current (I-DS,I- Max) collapse/degradation and turn-on and rise-time (t(R)) delay, on-state resistance (RDS-ON) and maximum transconductance (G(m, max)) degradation and threshold voltage (V-TH) shift for pulsed and prolonged off-state gate bias stress V-GS,V- OFF. We have found that as stress voltage magnitude and stress duration increases, similarly I-DS,I- Max and RDS-ON degradation, V-TH shift and turn-on/rise time (t(R)) delay, and G(m, max) degradation increases. In a pulsed off-state V-GS,V- OFF stress experiment, the device instabilities and degradation with electron trapping effects are studied through two regimes of stress voltages. Under low stress, V-TH shift, I-DS collapse, RDS-ON degradation has very minimal changes, which is a result of a recoverable surface state trapping effect. For high-stress voltages, there is an increased and permanent V-TH shift and high I-DS,I- Max and RDS-ON degradation in pulsed V-GS,V- Stress and increased rise-time and turn-on delay. In addition to this, a positive V-TH shift and G(m, max) degradation were observed in prolonged stress experiments for selected high-stress voltages, which is consistent with interface state generation. These findings provide a path to understand the failure mechanisms under room temperature and also to accelerate the developments of emerging GaN cascode technologies.