<\/a><\/p>\nFigure 1: RF performance of unpassivated 60-nm gate length HEMT showing fT<\/sub> = 70 GHz and fmax<\/sub> = 300 GHz. The fT<\/sub> and fmax<\/sub> values are extrapolated following a -20 dB\/dec ideal decrease with frequency.<\/p>\n<\/div>\nGaN-based high-electron-mobility transistors (HEMTs) have become one of the prime candidates for solid-state power amplifiers at frequencies above 30 GHz. To maximize the performance of GaN HEMTs at millimeter-wave frequencies (30-300 GHz), one of the key challenges is to increase the power-gain cut-off frequency (fmax<\/sub>). In this project, we have obtained state-of-the-art fmax<\/sub> in GaN HEMTs by combining low-damage gate recess technology, scaled device geometry, and recessed source\/drain ohmic contacts to simultaneously enable minimum short-channel effects (i.e., high output resistance, Rds<\/sub>) and very low parasitic resistances. A 60-nm gate-length HEMT with recessed AlGaN barrier exhibited excellent Rds<\/sub> of 95.7 \u03a9\u00b7mm, Ron<\/sub> of 1.1~1.2 \u03a9\u00b7mm, and fmax<\/sub> of 300 GHz (Figure 1) with a breakdown voltage of ~20 V [