220GHz fT and 400GHz fmax in 40-nm GaN DH-HEMTs with re-grown ohmic

We report record RF performance in 40nm-gate GaN-HEMT technology. Through vertical scaling in an AlN/GaN/AlGaN double heterojunction (DH) HEMT structure and reduction of access resistance using MBE re-growth of n
⁺
-GaN ohmic contacts, fully-passivated 40-nm devices exhibited excellent DC characteristics, such as an R
_on
of 0.81Ω·mm, an I
_dmax
of 1.61A/mm, a BV
_off
of 42V, and a peak extrinsic g
_m
of 723mS/mm, resulting in a peak f
_T
of 220GHz and a peak f
_max
of 400GHz. The measured f
_T
and f
_max
are the highest ever reported in a GaN-HEMT technology. Small signal model and delay time analysis showed that the parasitic charging time was only 10% of total delay time and the gate transit time scaled with the gate length (L
_g
) down to 40nm, demonstrating high scalability of the new technology.