Modeling of Capacitance Characteristics of Printed p-Type Organic Thin-Film Transistors

We studied the capacitance characteristics of printed p-type organic thin-film transistors (OTFTs) under various frequencies and dc bias conditions. The experimental results show that the device capacitance is largely influenced by parasitic capacitances, related to the large gate-active layer overlap areas required by the printing processes. We developed a nonquasistatic small-signal capacitance model that adopts a transmission line approach and considers the specific layout of the OTFTs, taking into account for the parasitic capacitances and, hence, is particularly well suited for printed devices. In addition, the model included parasitic impedance at the metal-organic semiconductor contacts, related to the nonohmic behavior of source-drain contacts. The model has been shown to nicely reproduce the experimental capacitance characteristics in all their features. It should be pointed out that the proposed model allows the reproducing of any device layout and could be implemented in device simulator to analyze small-signal dynamic characteristics.