Gate-Stress-Induced Threshold Voltage Instabilites, a Comparison of Ohmic and Schottky p-Gate GaN HEMTs

In this study, we investigate the threshold voltage (V_th) instability of p-gate GaN HEMTs due to off-state gate stress by means of experimental results. For this purpose, two commercially available devices with an ohmic-gate and a Schottkygate are compared. The V_th instability is shown to be a temporal phenomenon including short time constants, which is why a custom pulse setup is used here. With it, we observed a temporal deviation of the drain current in saturation, which is based on a temporal V_th shift. The ohmic-gate device exhibits a negative V_th instability, while the Schottky-gate device tends to a positive one. Both devices show a noticeable V_th instability at their recommended on-state gate voltage $V_{GS,nom}$. The impact on the Schottky-gate device is up to 10 times higher, compared to the ohmic-gate device.