Accuracy issues in microwave characterization of graphene transmission lines

In this paper, we compare several calibration methods available for on-wafer microwave measurements conducted on transmission lines made of graphene. Multi-layered graphene films were grown on Si wafers coated with SiO₂ and Ni using chemical vapor deposition. In order to facilitate high frequency characterization, and to replicate their function as radio frequency integrated circuits (RFIC) interconnects, the graphene films were constructed in the form of co-planar transmission lines using electron beam lithography. The transmission lines are in the form of co-planar waveguide (CPW) so that it they are compatible with the RF probes used to measure the properties of this material. In order to compare the accuracy, three on-wafer calibration techniques were considered, namely the popular Short-Open-Load-Thru (SOLT) method, and the new Line-Reflect-Match (LRM) and Thru-Reflect-Line (TRL) methods. This study aims to improve the accuracy of graphene measurement so that the behaviors of this material will be better understood.