W-Band Graded-Channel GaN HEMTs With Record 45% Power-Added-Efficiency at 94 GHz

We report the
$W$
-band large-signal power and efficiency performance of Ga-polar graded-channel (GC) AlGaN/GaN high-electron-mobility transistors (HEMTs) with a 50-nm gate-length mini-field-plate (FP) T-gate. The pre-matched GC GaN HEMT devices with on-chip pre-matching networks show a peak power-added efficiency (PAE) of 45% at 94 GHz at 2.1 W/mm associated power density. With de-embedding of the metal losses in the matching networks, the peak PAE at the GC GaN HEMT itself was estimated to be 50% at 94 GHz with a 2.2 W/mm power density. These efficiencies are the highest reported at
$W$
-band frequencies among all GaN HEMT technologies, including both Ga-polar and N-polar orientations. The power performance was facilitated by high extrinsic
$f_{T}$
and
$f_{\mathrm {MAX}}$
of 170 and 347 GHz, respectively, with a GC GaN HEMT structure and a mini-FP T-Gate.