Enhancement-mode N-polar GaN metal-insulator-semiconductor field effect transistors with current gain cutoff frequency of 120GHz

We report the small-signal high-frequency performance of novel enhancement-mode N-polar GaN metal-insulator-semiconductor field effect transistors with a peak short-circuit current gain cutoff frequency (ft) of 120 GHz for a 70-nm gate length device. The device has an 8-nm GaN channel with AlN back barrier and a 5-nm SiN_x gate dielectric. These devices show a peak drain current of 0.74A/mm and peak transconductance of 260mS/mm at a drain bias of 3.0 V. This is the first demonstration of high-frequency operation of N-polar enhancementmode GaN devices.