Gate Robustness and Reliability of P-Gate GaN HEMT Evaluated by a Circuit Method

The small gate overvoltage margin is a key reliability concern of the GaN Schottky-type p-gate high electron mobility transistor (GaN SP-HEMT). Current evaluation of gate reliability in GaN SP-HEMTs relies on either the dc bias stress or pulse I-V method, neither of which resembles the gate voltage (V-GS) overshoot waveform in practical converters. This article develops a new circuit method to characterize the gate robustness and reliability in GaN SP-HEMTs, which features a resonance-like V-GS ringing with pulse width down to 20 ns and an inductive switching concurrently in the drain-source loop. Using this method, the gate's single-pulse failure boundary, i.e., dynamic gate breakdown voltage (BVDYN), is first obtained under the hard switching (HSW) and drain-source grounded (DSG) conditions. The gate's switching lifetime is then tested under the repetitive V-GS ringing, and the number of switching cycles to failure (SCTF#) is fitted by Weibull or Lognormal distributions. The SCTF# shows a power law relation with the V-GS peak value and little dependence on the switching frequency. More interestingly, the gate's BVDYN and lifetime are both higher in HSW than those in DSG, as well as at higher temperatures. Such findings, as well as the gate degradation behaviors in a prolonged overvoltage stress test, can be explained by the time-dependent Schottky breakdown mechanism. The gate leakage current is found to be the major precursor of gate degradation. At 125 degrees C and 100 kHz, the V-GS limits for a 10-year lifetime are projected to be similar to 6 V and similar to 10 V under the DSG and HSW conditions, respectively. These results provide a new qualification method and reveal new physical insights for gate reliability and robustness in p-gate GaN HEMTs.