Overvoltage Robustness of p-Gate GaN HEMTs in High Frequency Switching up to Megahertz
Ruizhe Zhang, Qihao Song, Qiang Li, Yuhao Zhang
Abstract
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 (BV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DYN</sub> ), two new failure mechanisms are observed in some devices. One mechanism features a drastic, nearly unrecoverable <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on-</small> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BV</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DYN</sub> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BV</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DYN</sub> 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.