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.