Analysis of electrostatic effects in enhancement-mode GaN HEMTs under picosecond fast-rise VF-TLP stress

To investigate the failure mechanisms and degradation behavior of gallium nitride (GaN) high electron mobility transistor (HEMT) devices under electrostatic discharge (ESD) stress, this paper systematically studies the breakdown characteristics and underlying mechanisms of enhancement-mode GaN HEMTs subjected to very-fast transmission line pulse (VF-TLP) stress. VF-TLP pulses with a rise time of 80 ps and pulse widths of 1 ns, 2 ns, 5 ns, and 10 ns were applied to the gate-source, source-drain, and gate-drain terminal pairs in both positive and negative polarities. The breakdown behavior of each electrode pair was examined, and two-dimensional device simulations were performed using TCAD software to analyze the failure physics. The results reveal that negative VF-TLP pulses are more prone to cause damage to the gate-source, source-drain, and gate-drain pairs. Among the three terminal combinations, the gate-source pair exhibits the lowest breakdown threshold and is the most susceptible to ESD pulses. Furthermore, it is demonstrated that the magnitude and asymmetric spatial distribution of the impact ionization rate inside the device are the key physical mechanisms governing device failure under picosecond-level electrostatic pulses. These findings provide important guidelines for the ESD protection design of GaN HEMTs in ultra-fast transient overvoltage conditions.