Extremely High-Frequency Flexible Graphene Thin-Film Transistors

We have achieved 140-nm channel length graphene thin-film transistors (TFTs) on flexible glass with a 95-GHz intrinsic cutoff frequency and greater than 30-GHz intrinsic power frequency after standard de-embedding. The flexible glass substrate offers subnanometer surface smoothness as well as high thermal conductivity, 1 W/m . K, which can prevent thermomechanical failure, which is a limitation of plastic and rubber substrates. In addition, we developed a flexible 60-nm polyimide thin film as gate dielectric with low surface roughness less than 0.35 nm for optimal carrier transport and facilitate edge-injection contacts for low contact resistance. The maximum electron (hole) mobility is 4540 (1100) cm(2)/V . s, and the extracted contact resistance in the electron (hole) branch is 1140 (720) Omega . mu m. The intrinsic cutoff frequency is 196% higher than our previous results on polymeric substrates. Importantly, the experimental saturation velocity of the graphene TFT is the highest for any flexible transistor on any material system reported so far.