Fabrication of ultrashort T gates using a PMMA/LOR/UVIII resist stack

Abstract

In this article, we report a procedure for the fabrication of ultrashort T gates using high resolution electron beam lithography and a PMMA/LOR/UVIII resist stack. The intermediate lift-off resist (LOR) layer improves the quality of gate lithography, and consequently, device yields. It is unaffected by wet chemical gate recessing procedures and we report the application of the procedure to the fabrication of pseudomorphic and metamorphic high electron mobility transistors (pHEMTs) with 50 nm T gates. Fabricated pHEMTs had a gm of 600 mS/mm and ft of 200 GHz. Metamorphic HEMTs had a gm of 1500 mS/mm and ft of 350 GHz. We believe these are the fastest transistors of their kind in the world.