Fully Passivated AlInN/GaN HEMTs With $f_{\rm T}/f_{\rm MAX}$ of 205/220 GHz

We report the fabrication and characterization of 30-nm-gate fully passivated AlInN/GaN high-electron mobility transistors (HEMTs) with cutoff frequencies
f
_T
and
f
_MAX
simultaneously exceeding 200 GHz at a given bias point. The current gain cutoff frequency does not vary significantly for 2.5 <;
V
_DS
<; 10 V, while
f
_MAX
reaches a maximum value of
f
_MAX
= 230 GHz at
V
_DS
= 6 V. This is the first realization of fully passivated AlInN/GaN HEMTs with
f
_T
/
f
_MAX
≥ 205 GHz, a performance enabled by the careful shaping of the gate electrode profile and the use of a thin 60-nm SiN encapsulation film.