Gigahertz Field-Effect Transistors with CMOS-Compatible TransferFree Graphene

High-quality graphene grown on metal-free substrates
represents a vital milestone that provides an atomic clean interface and a
complementary metal-oxide-semiconductor-compatible manufacturing
process for electronic applications. We report a scalable approach to
fabricate radio frequency field-effect transistors with a graphene channel
grown directly on the sapphire substrate using the technique of remotecatalyzed chemical vapor deposition (CVD). A mushroom-shaped AlOx
top gate is used to allow the self-aligned drain/source contacts, yielding
remarkable increase of device transconductance and reduction of the
associated parasitic resistance. The quality of thus-grown graphene is
reflected in the high extrinsic cutoff frequency and maximum oscillation
frequency of 10.1 and 5.6 GHz for the graphene channel of length 200
nm and width 80 μm, respectively, potentially comparable with those of
transferred CVD graphene at the same channel length and holding promise for applications in high-speed wireless
communications