Epitaxial-Graphene RF Field-Effect Transistors on Si-Face 6H-SiC Substrates

We report dc and the first-ever measured small-signal radio-frequency (RF) performance of epitaxial-graphene RF field-effect transistors (FETs), where the epitaxial-graphene layer is formed by graphitization of 2-in-diameter Si-face semi-insulating 6H-SiC (0001) substrates. The gate is processed with a metal gate on top of a high-k Al2O3 gate dielectric deposited via an atomic-layer-deposition method. With a gate length (L-g) of 2 mu m and an extrinsic transconductance of 148 mS/mm, the extrinsic current-gain cutoff frequency (f(T)) is measured as 4.4 GHz, yielding an extrinsic f(T) . L-g of 8.8 GHz . mu m. This is comparable to that of Si NMOS. With graphene FETs fabricated in a layout similar to those of Si n-MOSFETs, ON-state current density increases dramatically to as high as 1.18 A/mm at Vds = 1 V and 3 A/mm at Vds = 5 V. The current drive level is the highest ever observed in any semiconductor FETs.