Contactless impedance measurement of large-area high-quality graphene

We present experimental work on the contactless measurement of graphene sheet impedance at frequencies up to 110 GHz in different waveguide geometries. Low-loss coplanar waveguides in series and shunt configuration have been demonstrated. A new coaxial waveguide coupled Corbino disk geometry with facile fabrication is introduced. Critical to the success of these measurements is a low contact impedance at high-frequencies, wherein the dc contact resistance is shunted by a contact capacitance that ultimately enables contactless measurement. The quasi-optic nature of waveguide measurements minimizes the effect of inevitable cracks in the graphene sheet, in contrast with typical transport measurements. We have applied our technique to the characterization of the sheet impedance and contact impedance of large-area, high-quality graphene grown by chemical vapour deposition.