Improvement of the Frequency Characteristics of Graphene Field-Effect Transistors on SiC Substrate

Analog applications attract increasing interest for graphene field-effect transistors (GFETs). GFET with a cutoff frequency of up to 427 GHz has been reported; however, the device suffered from the large parasitic parameters and poor drain current saturation, which made their maximum oscillation frequency lower than the cutoff frequency. In this letter, quasi-free-standing bilayer graphene transistors with a gate length of 60 nm and ultra-thin gate dielectric are fabricated by an improved, self-aligned, process. Good gate coupling is achieved, and parasitic parameters are suppressed to a significant extent. The as-measured extrinsic cutoff frequency reaches 70 GHz and the maximum oscillation frequency reaches 120 GHz, which are the highest extrinsic frequencies reported for graphene transistors to date. Our results show the application potential of graphene RF devices in future high-speed electronic systems.