Single step electron-beam lithography archiving lift-off for T-gate in high electron mobility transistor fabrication

Abstract

In this paper, a new method of electron-beam lithography was proposed to directly obtain a floating T-shaped gate. In the method, only one step of exposure and one step of development were operated on a three-layer photoresist of PMMA/P(MMA-MAA)/ P(MMA-MAA) to form an obvious undercut structure which is very benefit for subsequent lift-off process of gate metal. A high electron mobility transistor (HEMT) with an 80 nm floating T-shaped gate was fabricated on a SiC substrate which has a 10 nm InAlN barrier. Finally, the obtained device by above process has a fT/fmax of 90/200 GHz.