T-gate technology for N-polar GaN-based self-aligned MIS-HEMTs with state-of-the-art fMAX of 127 GHz: Pathway towards scaling to 30nm GaN HEMTs

N-polar GaN/AlGaN HEMTs have been of interest to the nitride community recently due to their several advantages over Ga-polar GaN-based HEMTs such as lower contact resistance [1], better electron confinement [2], and enhancement mode operation. For very high frequency performance, it is necessary to scale the parasitic elements in the device along with the gate length. First reports on scaled self-aligned HEMTs on N-face with regrown access regions [3] demonstrated minimization of access resistances which resulted in linear scaling of total delay up to 120 nm gate length (Fig. 1). However, even though excellent fT.Lg products of 16.8 GHz-µm were achieved, very low fMAX of 17 GHz was achieved due to high resistivity of the W-gates in the gate-first process.