Transfer printing as a method for fabricating hybrid devices on flexible substrates

Abstract

Printing methods are becoming important in the fabrication of flexible electronics. A transfer printing method has been developed for the fabrication of organic thin-film transistors (OTFT), capacitors, resistors and inductors onto plastic substrates. The method relies primarily on differential adhesion for the transfer of a printable layer from a transfer substrate to a device substrate. A range of materials applications is illustrated, including metals, organic semiconductors, organic dielectrics, nanotube and nanowire mats, a patterned inorganic semiconductor and graphene. Transfer printing can be used to create complex structures including many disparate materials sequentially printed onto the flexible substrate, with no mixed processing steps performed on the device substrate. Specifically, the fabrication and performance of model OTFT devices consisting of a polyethylene terephthalate (PET) substrate, gold (Au) gate and source/drain electrodes, a poly(methyl methacrylate) (PMMA) dielectric layer and either a pentacene (Pn) or a poly(3- hexylthiophene) (P3HT) organic semiconductor layer will be presented. These transfer printed OTFTs on plastic outperform non-printed devices on a Si substrate with a SiO₂ dielectric layer (SiO₂/Si). Transfer printed Pn OTFTs on a plastic substrate have exhibited mobilities of 0.237 cm²/Vs, compared to non-printed Pn OTFTs on a SiO₂/Si substrate with mobilities of 0.1 cm²/Vs. Transfer printed P3HT TFTs on a plastic substrate have exhibited mobilites of 0.04 cm²/Vs, compared to non-printed P3HT TFTs on a SiO₂/Si substrate with mobilities of 0.007 cm²/Vs.