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

T-Gate fabrication processes for InP-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 opti- mal gate-foot length is 196nm for 50nm 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 141nm for 50nm geometry path and also 88nm for 30nm geometry path. Both EBL methods have been incorporated into InP- based HEMTs fabrication. With the gate-foot length de- creases from 196nm to 141nm, the current-gain cutoff fre- quency (fT) is improved from 125GHz to 164GHz, and also the maximum oscillation frequency (fmax )i ncreases from 305GHz to 375GHz.