Radio-Frequency Performance of Epitaxial Graphene Field-Effect Transistors on Sapphire Substrates

We report dc and the first-ever measured small signal rf performance of epitaxial graphene field-effect transistors (GFETs), where the epitaxial graphene is grown by chemical vapor deposition (CVD) on a 2-inch c-plane sapphire substrate. Our epitaxial graphene material has a good flatness and uniformity due to the low carbon concentration during the graphene growth. With a gate length L_g=100 nm, the maximum drain source current I_ds and peak transconductance g_m reach 0.92 A/mm and 0.143 S/mm, respectively, which are the highest results reported for GFETs directly grown on sapphire. The extrinsic cutoff frequency (f_T) and maximum oscillation frequency (f_max) of the device are 12 GHz and 9.5 GHz, and up to 32 GHz and 21.5 GHz after de-embedding, respectively. Our work proves that epitaxial graphene on sapphire substrates is a promising candidate for rf electronics.