Properties of Self-Aligned Short-Channel Graphene Field-Effect Transistors Based on Boron-Nitride-Dielectric Encapsulation and Edge Contacts

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 (LG) down to 67 nm are fabricated, and a virtual-source transport model is used to model the resulting current-voltage characteristics. The mobility and source-injection velocity as a function of LG yields a mean-free-path, ballistic velocity, and effective mobility of 850 nm, 9.3×10⁷ cm/s, and 13700 cm²/Vs, respectively, which are among the highest velocities and mobilities reported for GFETs. Despite these bestin-class attributes, these devices achieve transconductance (gm) and output conductance (gds) of only 600 and 300 μS/μm, 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.