Understanding and Modeling Quasi-Static Capacitance-Voltage Characteristics of Organic Thin-Film Transistors

C. Ucurum, H. Goebel
Helmut Schmidt University - University of the Federal Armed Forces Hamburg, DE

Keywords: modeling, quasi-static capacitance-voltage characteristics, organic thin-film transistors, hysteresis


We have investigated the quasi-static capacitance-voltage (C-V) characteristics of pentacene-based organic thin-film transistors (OTFTs). Beside the hysteresis which is in accordance with previously reported I-V characteristics of OTFTs, the measured C-V characteristics include a plateau unlike the C-V characteristics of the well-known metal-oxide-semiconductor (MOS) capacitor. In order to explain this phenomenon, the measured structure is investigated as a combination of three parts, each with particular C-V characteristics: i) Cox is the oxide capacitance due to the Au electrode deposited on the gate oxide, ii) CMOS is the MOS capacitance of the sandwich structure made of Si++, gate oxide, pentacene and Au electrode, iii) Cperi is the capacitance of the peripheral pentacene film. We speculate that the observed plateau stems from surface charges with a density of 2.87 x 10e12 cm-2. Using this conception we developed a behavioral circuit model in PSpice which can be dimensioned according to the actual geometry of the device. The model is improved with an RC network in order to take into account the dynamic behavior as well as hysteresis effects. Simulation results obtained with this model are in very good accordance with the measurements.