Low-voltage flexible pentacene thin film transistors with a solution-processed dielectric and modified copper source-drain electrodes

Low-voltage, flexibility and low-cost are essential prerequisites for large scale application of organic thin film transistors (OTFTs) in future low-end electronics. Here, we demonstrate a low-voltage flexible OTFT by using a low-temperature, solution-processed gate dielectric. Such a dielectric can be well integrated with an Au coated polyimide film, and exhibits a low leakage current density of less than 10(-6) A cm(-2) and a high capacitance density of 180 nF cm(-2). Pentacene films deposited onto the solution-processed dielectric show a highly ordered "thin film phase". The source-drain (S/D) electrodes are made of in situ modified Cu encapsulated by Au (Au/M-Cu). The obtained flexible OTFT exhibits outstanding electrical characteristics under a gate voltage of only -2 V, which include an on/off ratio of 2 x 10(4), a mobility (mu) of 1.5 cm(2) V-1 s(-1), a threshold voltage (V-T) of -0.3 V and a subthreshold slope (SS) of 161 mV dec(-1). The obtained mobility value is among the highest achieved in flexible pentacene OTFTs. The mechanical flexibility and reliability of the OTFTs are also studied and discussed in detail, and the observed degradation of the device performance under strains is attributed to the damage induced in the electrodes giving rise to increased contact resistance and the phase transition from the thin film phase to bulk phase of the pentacene films.