Fabrication of AlGaN/GaN Fin-Type HEMT Using a Novel T-Gate Process for Improved Radio-Frequency Performance

To increase the radio-frequency (RF) performance of AlGaN/GaN-based fin-type high electron mobility transistors (HEMTs), a novel T-gate process was developed and applied to fabricate a device with high RF performance. In a single lithography process, the applied T-gate process shows a technique for forming a T-gate using the reactivity difference of several photoresists. The fabricated device has a steep fin width (W
_fin
) of 130 nm, a fin height (H
_fin
) of 250 nm, and a gate length (L
_G
) of 190 nm. The device exhibits a low leakage current (I
_off
) of 6.6 × 10
^-10
A/mm and a high I
_on
/I
_off
current ratio of 4.7 × 10
⁸
. Moreover, the fabricated device achieved a high cut-off frequency (f
_T
) of 9.7 GHz and a very high maximum oscillation frequency (f
_max
) of 27.8 GHz. The f
_max
value of the proposed device is 138% higher than that of GaN-based fin-type HEMTs without T-gate.