Morphology transformations of pentacene on an UV-patternable polymer insulator and their effect on performance of flexible organic thin-film transistors

Abstract

This work presents a low temperature with high resolution capability UV-patternable polymer, i.e. mr-UVCur06, for use as a gate insulator in OTFTs, by investigating the morphology transformation of pentacene deposited on the mr-UVCur06. The device structure is polyethylene terephthalate (PET)/indium-tin oxide (ITO)/mr-UVCur06/pentacene/Au (source/drain). In addition to its solution-processable capability, mr-UVCur06 is directly patterned by UV light in a low-temperature process. UV/ozone post-treatment of the patternable mr-UVCur06 can illuminate organic contaminants from its surface and increases surface energy. Experimental results indicate that a high surface energy existing at the mr-UVCur06 surface has produced in a larger ratio of Ithin film phase/Itriclinic bulk phase in pentacene. Then, the distance of pentacene molecular crystal structure, which is arranged in the thin film phase, is shorter than that in triclinic bulk phase. The performance of pentacene-based OTFTs can be enhanced with few contaminants and a high surface energy on the UV-patternable gate insulator. By performing UV/ozone post-treatment on the mr-UVCur06 insulator surface for 60s, the OTFTs demonstrate a mobility, on/off drain current ratio, and VT of 0.34cm2/Vs, 5.5×104, and 2.5V, respectively. Furthermore, the low-temperature photopatternable polymer dielectric paves the way for a relatively easy and low-cost fabrication of an OTFT array without expensive and complicated photolithography and dry etching.Morphology transformations of pentacene on an UV-patternable polymer insulator and their effect on performance of flexible organic thin-film transistors