▎ 摘　　要

We present the characterization of ballistic graphene field-effect transistors (GFETs) with an effective oxide thickness of 3.5 nm. Graphene channels are fully encapsulated within hexagonal boron nitride, and self-aligned contacts are formed to the edge of the single-layer graphene. Devices of channel lengths (L-G) down to 67 nm are fabricated, and a virtual-source transport model is used to model the resulting current-voltage characteristics. The mobility and sourceinjection velocity as a function of L-G yields a mean-free-path, ballistic velocity, and effective mobility of 850 nm, 9.3x10(7) cm/s, and 13 700 cm(2)/Vs, respectively, which are among the highest velocities and mobilities reported for GFETs. Despite these best-in-class attributes, these devices achieve transconductance (g(m)) and output conductance (g(ds)) of only 600 and 300 mu S/mu m, respectively, due to the fundamental limitations of graphene's quantum capacitance and zero-bandgap. gm values, which are less than those of comparable ballistic silicon devices, benefit from the high ballistic velocity in graphene but are degraded by an effective gate capacitance reduced by the quantum capacitance. The gds values, which limit the effective power gain achievable in these devices, are significantly worse than comparable silicon devices due to the properties of the zero-bandgap graphene channel.