T-shape gate process & its application in HFET fabrication

This paper will discuss the process of T-shape gate that has been developed by direct-write electron beam lithography (EBL). The multilayer resist technique and different developing and lift-off are used to obtain a T-shape gate structure. The bottom of the "T" gate is about 100 nm. In order to realize the application of the T-shape gate in device, Heterojunction field effect transistors (HFET) have been fabricated using these T-gate structures. The extrapolated unity current gain frequency (f_t) and transconductance (g_m) of these transistors is 86.77 GHz and 450 ms/mm respectively.