N-Polar GaN MIS-HEMTs on Sapphire With High Combination of Power Gain Cutoff Frequency and Three-Terminal Breakdown Voltage

Nitrogen polar SiN
_x
/AlGaN/GaN/AlGaN metal– insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) with 28.6-nm equivalent GaN channel thickness grown by metal–organic chemical vapor deposition on sapphire substrate with a high combination of current/power gain cutoff frequencies (
$f_{T}/f_{\max }$
) and three-terminal breakdown voltage (BV
_DS
) are demonstrated.
$f_{T}$
/BV
_DS
of 103 GHz/114 V and
$f_{\max }$
/BV
_DS
of 248 GHz/114 V were achieved in devices with the gate widths of
$2 \times 50\mu \text{m}$
and
$2 \times 25\mu \text{m}$
, respectively, comparing well with recent reports of fully passivated and vertically scaled Ga-polar GaN HEMTs. Devices with a gate width of
$2 \times 75 \mu \text{m}$
showed the peak output power densities of 5.74 W/mm at 4 GHz and 6.29 W/mm at 10 GHz obtained by load-pull measurements.