Reverse DC bias stress shifts in organic thin-film transistors with gate dielectrics using parylene-C

We have systematically investigated the reliability of organic thin-film transistors (TFTs) using polychloro-p-xylylene (parylene-C) as a gate dielectric material. The fabricated organic TFT devices exhibited positive bias shifts with negative DC gate-source voltages; however, no hysteresis was observed in the transfer characteristics for the tested TFT devices. Moreover, this tendency was enhanced with increasing annealing temperatures, whereby X-ray diffraction (XRD) results revealed that the crystallinity of the parylene-C layers increased with thermal annealing. As a result the total dipole moments normal to the surface of the parylene-C layers grew, which caused reverse bias shifts in the TFT devices. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim