Fabrication and Characterization of Gate-Last Self-Aligned AlN/GaN MISHEMTs With In Situ SiNx Gate Dielectric

This paper reports on the fabrication and characterization of gate-last self-alignedin situSiNx/AlN/GaN MISHEMTs. The devices featuredin situgrown SiNxby metal–organic chemical vapor deposition as a gate dielectric and for surface passivation. Selective source/drain regrowth was incorporated to reduce contact resistance. SiNxsidewall spacers and low-κbenzocyclobutene polymer (κ =2.65) supporting layers were employed under the gate head to minimize the parasitic capacitance for high-frequency operation. The device with a gate length (LG)of0.23~μ mexhibited a maximum drain current density (IDS)exceeding 1600 mA/mm with a high ON/OFF ratio (I_ ON/I_ OFF)of over10⁷. The current gain cutoff frequency (fT)and maximum oscillation frequency (fₘₐₓ)were 55 and 86 GHz, respectively. In addition, the effect of temperature, from room temperature up to 550 K, on the dc and RF performances of the gate-last self-aligned MISHEMTs was studied.