InAlN/GaN HEMTs on Sapphire Substrate With 2.9-W/mm Output Power Density at 18 GHz

In this letter, small- and large-signal measurements of an In
_0.15
Al
_0.82
N/AlN/GaN high-electron-mobility transistor (HEMT) grown on a sapphire substrate with a 225-nm T-shaped gate are described. A maximum dc current density of 1.2 A/mm and a peak extrinsic transconductance of 460 mS/mm are obtained. The device exhibits a current gain cutoff frequency (
F
_T
) and a power gain cutoff frequency (
F
_MAX
) of 52 and 120 GHz, respectively. At
V
_DS
= 15 V, a continuous-wave output power density of 2.9 W/mm was achieved at 18 GHz with an associated power-added efficiency of 28% and a power gain of 15 dB. It is the best value ever reported from InAlN/GaN HEMTs grown on a sapphire substrate.