Enhancement-Mode N-Polar GaN MOS-HFET With 5-nm GaN Channel, 510-mS/mm $g_{m}$, and 0.66-$\Omega\cdot \hbox{mm}$ $R_{\rm on}$

We report enhanced dc and small-signal RF performance of enhancement-mode (E-mode) metal-oxide-semiconductor heterojunction field-effect transistors (MOS-HFETs) in N-polar GaN technology with an ultrathin 5-nm GaN channel and graded AlGaN back-barrier structure with a record on-resistance (
R
_on
) of 0.66 Ω·mm. The device has a maximum drain current (
Id
) of 1.15 A/mm, a peak transconductance (
gm
) of 510 mS/mm, and a peak current-gain cutoff frequency (
ft
) of 122 GHz, with a positive threshold voltage (
V
_th
) of 1.6 V. The device shows improved saturation and pinchoff characteristics compared to the previously reported N-polar E-mode HFETs with a maximum
I
_on
/
I
_off
ratio of 2.2 × 10
⁵
.