Abstract

A transfer printing method for fabricating organic electronics onto flexible substrates has been developed. The method relies primarily on differential adhesion for the transfer of a printable layer from a transfer substrate to a device substrate. The works of adhesion and cohesion for successful printing are discussed and developed for a model organic thin-film transistor device consisting of a polyethylene terephthalate (PET) substrate, gold (Au) gate and source/drain electrodes, a polymethylmethacrylate (PMMA) [or poly(4-vinylphenol)] dielectric layer, and a pentacene (Pn) organic semiconductor layer. The device components are sequentially printed onto the PET device substrate with no mixed processing steps performed on the device substrate. Optimum printing conditions for the Pn layer were determined to be 600psi and 120°C for 3min. A set of devices with a PMMA dielectric layer was measured as a function of channel length and exhibited a contact resistance corrected mobility of 0.237^cm2/Vs. This is larger than the mobility measured for a control device consisting of Pn thermally deposited onto the thermally oxidized surface of a silicon substrate (SiO₂/Si) with e-beam deposited Au top source/drain contacts. The structure of transfer printed Pn films was also investigated using x-ray diffraction. The basal spacing correlation length for a 50nm Pn film printed at 600psi and 120°C for 3min onto a PMMA surface showed a 35% increase as compared to an unprinted film on a thermally oxidized silicon substrate. The crystalline size was seen to correlate with the mobility as a function of printing conditions.