Stability Improvement of GaN Power HEMT by a Multifunctional Monolithic Protection Circuit

This work presents a gate electrostatic discharge (ESD) protection circuit monolithically integrated with the GaN power high-electron-mobility-transistor (HEMT). In addition to enhancing the gate robustness against the ESD event, this multifunctional circuit also improves the stability of on-resistance (R_ON) and threshold voltage (V_TH) when power HEMT is under normal switching operations. Such improvement is enabled by clamping the HEMT's negative gate bias (V_G) at the off state, which is a critical cause of the R_ON and V_TH instabilities in power p-gate GaN HEMTs. A circuit setup is deployed for the in situ monitoring of the dynamic R_ON and its evolution from the first switching cycle to the steady state. Under the off-state stress with negative V_G and high drain bias (V_D), the GaN HEMT without ESD circuit shows a drastic dynamic R_ON increase in the first tens of switching cycles. Such a phenomenon is fully suppressed by the ESD protection circuit. In addition, the longer-term stability of R_ON and V_TH is tested under the prolonged stresses of V_G and V_D, in which the device with an ESD circuit shows superior stability. Physics-based technology-aided computer design simulation unveils the critical physics accounting for such stability improvement. These results reveal a new pathway to address the p-gate GaN HEMTs' inherent instability while simultaneously boosting their gate robustness.