Overvoltage Robustness of p-Gate GaN HEMTs in High Frequency Switching up to Megahertz

This article investigates the ruggedness of the GaN high electron mobility transistor (HEMT), a power device without avalanche capability, in continuous, high-frequency, overvoltage switching. A testbed based on a zero-voltage-switched converter with an active clamping circuit is developed to enable the stable switching with kilovolt overvoltage and megahertz frequency. The overvoltage failure boundaries and mechanisms of four commercial p-gate GaN HEMTs from multiple vendors are explored. Besides the electrical failure at the dynamic breakdown voltage (BVDYN), two new failure mechanisms are observed in some devices. One mechanism features a drastic, nearly unrecoverable on-resistance increase, leading to conduction loss ramp-up and thermal failure. The other mechanism exhibits an increase in drain leakage current and a catastrophic breakdown at lower blocking voltage. Both mechanisms are found to occur only at high frequency (>100 kHz) and decrease the BVDYN by at least 30%, and they can be attributed to the serious carrier trapping in GaN HEMTs under the high-frequency overvoltage switching. Finally, we provide a simple method for device users to filter out devices with these extrinsic failure mechanisms and identify the intrinsic BVDYN of GaN HEMTs, which deploys a simple unclamped inductive switching circuit. These results provide critical reference for the protection and qualification of GaN power HEMTs.