Impact of graphene interface quality on contact resistance and RF device performance

This letter demonstrates the importance of the graphene/metal interface on the ohmic contacts of high-frequency graphene transistors grown by chemical vapor deposition (CVD) on copper. Using an Al sacrificial layer during ohmic lithography, the graphene surface roughness underneath the ohmic contacts is reduced by fourfold, resulting in an improvement in the contact resistance from 2.0 to 0.2-0.5 kΩ.μm. Using this technology, top-gated CVD graphene transistors achieved direct-current transconductances of 200 mS/mm, maximum on current densities in excess of 1000 mA/mm, and hole mobilities ∼ 1500-3000 cm^-2Vs on silicon substrates. Radio-frequency device performance yielded an extrinsic current-gain cutoff frequency f_T of 12 GHz after pad capacitance de-embedding resulting in an f_T-L_G product of 24 GHzμm.