Comparison of Single-Step and Two-Step EBL T-Gates Fabrication Techniques for In P-Based HEMT

T-Gate fabrication processes for In P-based High electron mobility transistors（HEMTs） are described using PMMA/Al/UVIII. The single-step and two-step Electron beam lithography（EBL） methods are proposed contrastively without dielectric support layer. The optimal gate-foot length is 196 nm for 50 nm geometry path by single-step EBL technique. Since the gate-foot and gate-head are defined independently, the two-step EBL process minimizes forward scattering and enables smaller gate-foot length, which improves to be 141 nm for 50 nm geometry path and also 88 nm for 30 nm geometry path.Both EBL methods have been incorporated into In Pbased HEMTs fabrication. With the gate-foot length decreases from 196 nm to 141 nm, the current-gain cutoff frequency（fT） is improved from 125 GHz to 164 GHz, and also the maximum oscillation frequency（fmax） increases from305 GHz to 375 GHz.