Frequency response analysis of pentacene thin-film transistors with low impedance contact by interface molecular doping

Frequency response measurements were performed on top-contact pentacene organic thin-film transistors (OTFTs). The ac characteristics of OTFTs are strongly limited by the contact interface between a metallic electrode and a pentacene thin film. Local doping of a charge transfer molecule (CTM) into the contact interface efficiently improves the ac characteristics. Metal-insulator-semiconductor capacitance measurements revealed that the interface contains parasitic impedance composed of capacitance and resistance in parallel. The parasitic impedance was suppressed by CTM doping of the interface. The limitation factors for the frequency of operation in such an OTFT are discussed based on the experimental results and an equivalent circuit model.