Scaled Self-Aligned N-Polar GaN/AlGaN MIS-HEMTs With $f_{T}$ of 275 GHz

In this letter, we demonstrate state-of-the-art performance from N-polar GaN/AlGaN metal-insulator-semiconductor high-electron-mobility transistors. Self-aligned gate-first process was used for the fabrication of transistors. Graded InGaN and InN contact layers were used to achieve low ohmic contact resistance. The GaN channel thickness was scaled to 7 nm from previous generation of N-polar GaN devices to improve the aspect ratio and hence achieve better small-signal performance. The devices reported f_T of 210 GHz for L_G = 30 nm. To further improve the device performance, SiN sidewall spacers were etched and replaced with air gaps resulting in further boost in f_T to a state-of-the-art value of 275 GHz.