A cavity structure was obtained under the gate-head by depositing thick SiN dielectric after fabrication of the T-shaped gate in the trench.

T-shaped gate with gate length of 0.1 μm was fabricated by using a bi-layer e-beam resist.

Air cavity structure brings in low parasitic gate capacitance, which increases the f_T from 60 to 84 GHz and f_max from 93 to 104 GHz at the cost of slightly lower gate breakdown voltage.

Model parameters of the devices were extracted by using cold-FET extraction method.