Physics-based nonlinear circuit model for coplanar waveguides on silicon substrates

A physics-based nonlinear equivalent circuit model for coplanar waveguides (CPWs) fabricated on Si substrates has been developed and verified experimentally. In contrast to conventional R-L-C-G models, the proposed model replicates dispersive effects due to finite substrate resistivity using only frequency-independent shunt components, and is suitable for both metal-oxide-semiconductor and direct-contact metal-semiconductor lines. The modeled junction capacitances and conductances show excellent scalability with substrate doping concentration and transmission line geometry. Numerical calculation of the CPW capacitance, based on two-dimensional solutions of Poisson's equation, as well as experimental investigations of the dependence of model parameters on substrate doping and line geometry have been performed. Measurements of typical devices show close agreement between the model prediction and measured transmission line S-parameters from 100 MHz to 10 GHz.