Characterization of Threshold Voltage Instability Under OFF-State Drain Stress and Its Impact on p-GaN HEMT Performance

The beta-GaN gate technology is commonly implemented to achieve normally OFF gallium nitride (GaN) devices. Nonetheless, the threshold voltage instability under OFF-state stress remains a concern. In this article, the characterization technique of threshold voltage shift is proposed and the Vth shift's impact on device performance is investigated. Specifically, a fast Vth the measurement circuit is introduced and validated to successfully characterize both the magnitude and the time-constant of the Vth shift. According to the experimental results, the Vth increases by more than 50% within several mu s after the high drain voltage is applied. In contrast, the Vth slowly (tens of seconds) gets back to the static value after the stress is removed. Following the characterization, the threshold voltage instability's impact on the device's static/switching performance is studied experimentally. A knee point shift is observed at low gate voltage, and the static ON-resistance value remains unchanged. Regarding the switching performance, the turn-ON loss increases by >20% after the high drain voltage stress. The change in turn-ON loss can be reduced when the gate resistance is decreased from 20 to 0 Omega. In terms of the turn-OFF loss, the impact of the Vth shift is negligible. It is concluded that time-dependent threshold voltage shift needs to be considered in p-GaN device's modeling, and high gate drive voltage together with low gate resistance is recommended to mitigate the Vth instability's effect on p-GaN high-electron-mobility transistor's performance.

Automated summary

The article presents a technique to characterize threshold voltage shift in normally OFF gallium nitride (GaN) devices using beta-GaN gate technology. Experimental results show that the Vth increases by more than 50% within several microseconds under high drain voltage stress. The impact of the Vth shift on device performance is studied, suggesting that a high gate drive voltage and low gate resistance can mitigate the instability effect on p-GaN high-electron-mobility transistor's performance.