DC and RF Performance of Gate-Last AlN/GaN MOSHEMTs on Si With Regrown Source/Drain

This paper presents the fabrication and characteristics of self-aligned gate-last AlN/GaN metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs) featuring regrown source/drain for low ON-state resistance (R
_ON
). Previously, we demonstrated conventional enhancement-mode AlN/GaN MOSHEMTs on Si substrate with excellent DC performance but limited RF characteristics by large parasitic gate-to-source/drain overlap capacitance. In this paper, the self-aligned gate-last process was developed to minimize the parasitic capacitance. SiN
_x
sidewall and supporting layer were inserted to separate the gate head and source/drain. In the gate-last devices, f
_T
has been improved to be ~40 GHz with a channel length (L
_g
) of 210 nm. Delay time analysis showed that drain delay was relatively small compared with gate transit and parasitic charging time because of the self-aligned structure.