30-nm-Gate AlGaN/GaN Heterostructure Field-Effect Transistors with a Current-Gain Cutoff Frequency of 181 GHz

We fabricated Al 0.4 Ga 0.6 N(8 nm)/GaN heterostructure field-effect transistors (HFETs) with a gate length ( L G ) of 30 nm on a sapphire substrate. The AlGaN/GaN HFETs, which had a 2-nm-thick SiN passivation and gate-insulating layer formed by catalytic chemical vapor deposition, showed a maximum drain current density of 1.49 A/mm, a peak extrinsic transconductance of 402 mS/mm, a current-gain cutoff frequency ( f T ) of 181 GHz, and a maximum oscillation frequency of 186 GHz. From a delay time analysis of f T for the HFETs with L G =30–150 nm, the electron velocity overshoot was not observed even when L G was decreased to 30 nm.