N-Polar GaN/AlN MIS-HEMT With $f_{\rm MAX}$ of 204 GHz for Ka-Band Applications

In this letter, we demonstrate the state-of-the-art small-signal performance from N-polar GaN-based metal insulator-semiconductor high-electron-mobility transistors by using a double-gate-recess technology. The device consists of an AIN/GaN superlattice as a back barrier to reduce alloy scattering. "Funnel" contacts are employed to achieve a low ohmic con tact resistance of 0.12 Ω · mm. Peak f_T and f_MAX of 82 and 197 GHz, respectively, were obtained for L_G = 112 nm, and that of 95 and 204 GHz, respectively, were obtained for L_G = 75 nm. Large signal measurements for L_G = 112 nm resulted in an excellent linear transducer power gain of 12 dB at 30 GHz. The merits and the challenges of the technology toward high output power P_out and power-added efficiency have been also discussed.