Short channel effects in regioregular poly(thiophene) thin film transistors

The effects of the physical channel length on the current-voltage characteristics of thin film transistors (TFTs) made with poly[5,5′-bis(3-dodecyl-2-thienyl)-2,2′-bithiophene] were examined. Coplanar transistors with fully patterned electrodes on insulating substrates and with a common gate structure on thermal oxide were fabricated. The output characteristics of TFTs with channel lengths shorter than 10μm showed the presence of a parasitic contact resistance and the lack of current saturation. The origin of these nonidealities was examined by the application of models that included self-heating effects and breakdown of the channel region at high applied biases. The analysis suggests that carriers can break away from the channel at high bias voltages and flow through a bulk region of the semiconducting film leading to higher currents than otherwise expected.