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 fT and fMAX of 82 and 197 GHz, respectively, were obtained for LG = 112 nm, and that of 95 and 204 GHz, respectively, were obtained for LG = 75 nm. Large signal measurements for LG = 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 Pout and power-added efficiency have been also discussed.