Recessed 70-nm Gate-Length AlGaN/GaN HEMTs Fabricated Using an $\hbox {Al}_{2}\hbox {O}_{3}/\hbox {SiN}_{x}$ Dielectric Layer

In this letter, a novel process for recessed-gate AlGaN/GaN high-electron-mobility transistors using an Al₂O₃/SiNx dielectric has been developed. The Al₂O₃/SiNx dielectric bilayer was used as a recess etch-mask for short-gate-footprint definition. Recessed-gate devices with a gate length of 70 nm have been fabricated on a molecular-beam-epitaxy-grown layer structure using this process. After the removal of the dielectric layers, excellent dc and small-signal results, a high drain-current density of 1.5 A/mm, a unity gain cutoff frequency of 160 GHz, and a maximum frequency of oscillation of 200 GHz were obtained.