Characteristics of Epitaxial Graphene on SiC/Si Substrates in the Radio Frequency Spectrum

Graphene is expected to bring substantial benefits for high-frequency applications, however, most of the studies in this area are based on theory. Here, the properties of epitaxial graphene grown on intrinsic silicon carbide on silicon substrates are investigated for potential radio frequency (RF) applications. Metal coplanar waveguides (CPWs) are fabricated that employ graphene as a shunt between the signal and ground planes. The CPWs are used for characterizing the frequency-dependent behavior of the sheet resistance of the graphene shunt from 10 MHz to 10 GHz. The process involves evaluating the CPW's RLCG transmission line parameters and comparing them to a reference un-shunted CPW to extract the sheet resistance. We find that the quality of the metal contact with graphene is one key parameter to observe adequate current injection in the 2D material in the RF spectrum. A mild argon plasma treatment was applied to reach an adequate contact quality. Furthermore, we observe a monotonic decrease of the sheet resistance of the epitaxial graphene for frequencies roughly above 100 MHz. We attribute this behavior to the progressively smaller influence of small-scale discontinuities, such as grain sizes, at those higher frequencies.