Overestimation of the field-effect mobility via transconductance measurements and the origin of the output/transfer characteristic discrepancy in organic field-effect transistors

Paramount to the rational design of electronic materials is the accurate characterization of their intrinsic properties. In particular, many applications of conducting and semiconducting soft materials have been driven by the development of materials with high, bias-stable field-effect mobility. Here, we demonstrate the effect of parasitic resistance and bias-dependent mobility on device electrical characteristics. Specifically, we analyze two of the most commonly employed test algorithms-the output and transfer curves-via a closed-form analysis. The analysis exhibits characteristics endemic to those published in literature, such as effective mobilities with maxima with respect to gate voltage that may lead to overstatements of mobility by manyfold. Furthermore, analysis reveals that common overestimation relative to intrinsic and output-estimated mobilities is caused solely by gate-bias-dependent mobility, and parasitic resistance can only lead to an underestimation of the effective mobility. We introduce a method for accurate mobility estimation and a dimensionless variable for evaluating the importance of contact resistance.