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-aligned in situ SiN_x/AlN/GaN MISHEMTs. The devices featured in situ grown SiN_x by metal-organic chemical vapor deposition as a gate dielectric and for surface passivation. Selective source/drain regrowth was incorporated to reduce contact resistance. SiNx sidewall spacers and low-κ benzocyclobutene 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 (L_G) of 0.23 μm exhibited a maximum drain current density (I_DS) exceeding 1600 mA/mm with a high ON/OFF ratio (I_ON/I_OFF) of over 107. The current gain cutoff frequency (f_T) and maximum oscillation frequency (f_max) 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.