Analysis of MOCVD SiNx Passivated N-Polar GaN MIS-HEMTs on Sapphire With High $f_{max}\cdot V_{DS,Q}$

This letter presents an analysis of N-polar metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with a 40 nm MOCVD SiN
_x
passivation and a trench-gate design. A device with a 50 nm gate-length (
L
_g
) demonstrates a 313 GHz power gain cutoff frequency (
f
_max
) at a quiescent drain bias (
V
$_{{DS,Q}}$
) of 26 V. The high
$f_{max}\cdot V_{DS,Q}$
of 8.1 THz
$\cdot$
V exhibits great potential of the device in high-frequency power applications. Investigation on small-signal parameters shows that
f
_max
improves with
V
$_{{DS,Q}}$
due to a reduction of gate-drain capacitance (
c
_gd
) and an increase of output resistance (
r_ds
). When comparing with the previously reported planar HEMT design, the shorter
L
_g
enabled by the trench-gate design enhances the intrinsic current gain cutoff frequency (
f
$_{{T,int}}$
) leading to a higher peak
f
_max
at a higher
V
$_{{DS,Q}}$
.