Consistent and reliable MESFET parasitic capacitance extraction method

Abstract

An improved model is proposed to evaluate the parasitic capacitances of GaAs MESFET transistors from the cold-FET S-parameter. Inherent in most conventional parasitic de-embedding methods, the extraction result for Cpd varies drastically with Vgs under cold-FET measurement, and this is in great contradiction with the normally adopted bias-independent Cpd assumption in active device modelling. An improved model is proposed to tackle this problem. Model parameters can thus be uniquely determined by using only two sets of cold-FET S-parameters under different Vgs biasing conditions. The resulting capacitance value, Cpd, is found to be independent of Vgs when Vgs<Vp.