Advanced gate technologies for state-of-the-art fT in AlGaN/GaN HEMTs

In this paper, the lower-than-expected frequency performance observed in many AlGaN/GaN high electron mobility transistors (HEMTs) has been attributed to a significant drop of the intrinsic small-signal transconductance (g
m
) with respect to the intrinsic DC g
m
. To reduce this g
m
-collapse and improve high frequency performance, we have developed a new technology based on a combination of vertical gate-recess, oxygen plasma treatment, and lateral gate-etch which has allowed us to fabricate AlGaN/GaN HEMTs with a record current-gain cutoff frequency (f
T
) of 225 GHz for a gate length (L
g
) of 55 nm, and 162 GHz for an L
g
of 110 nm.