▎ 摘　　要

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 remote-catalyzed 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 mu m, respectively, potentially comparable with those of transferred CVD graphene at the same channel length and holding promise for applications in high-speed wireless communications.