Evaluating Optically Transparent Conductors at RF and Microwave Frequencies: A New Figure of Merit

Abstract

Optically transparent conductors (TCs) have been implemented and adopted into next-generation transmission lines and other RF structures from UHF to millimeter-wave (mmWave) applications. A current method of evaluating the performance of optically TCs uses a figure of merit (FOM) which is frequency agnostic. A new FOM for optically TCs at RF, microwave, and millimeter-wave frequencies is presented and provides distinction to the TC FOM proposed in 1976 where it adds a frequency dependence, by incorporating the skin effect requirement. A detailed analysis of the new FOM for both transparent conducting oxides and mesh conductors is presented and compared using TC literature data analyzed at 24 and 240 GHz where large FOM variation is shown. The manuscript shows the new RF FOM and classical FOM can vary by up to a factor of 10 when the skin depth of the conductor is not considered.