Alternative lithography strategies for flexible electronics

Main aim of the research has been the development of alternative lithography strategies for the fabrication of complex, flexible electronic devices. Flexible bottom-contact, bottom-gate thin-film transistors were solely patterned with UV nanoimprint lithography on poly(ethylene naphthalate) foil. Patterning and process strategies had to be developed for thermal and UV nanoimprint lithography to control the residual layer thickness and its complete removal on the temperature sensitive, mechanically and in-plane instable foils. The foil was temporarily bonded to a supporting carrier (foil-on-carrier) to reduce the bending radius and in-plane waviness of the foil, and to provide a mechanically stable platform for proper processing. Foil-on-carriers were thermally flat imprinted with nanoimprint lithography, or a flat plateau was created on the foil-on-carrier by UV nanoimprint lithography-based step-and-repeat planarization. Thin-film transistors with a channel length from 5 μm down to 250 nm were obtained and characterized. Palladium nanoparticles and self-sintering silver nanoparticles were studied as a solution-based route for fast, low-cost and room temperature patterning of metallic wires in open microchannels on flexible foils. The ease of patterning thin but very conductive silver wires from a long-term stable aqueous solution allows integration in a roll-two-roll line to pattern the metallic contacts of a flexible electronic device. The here studied fabrication methods can be potentially integrated in low-cost, high-throughput roll-to-roll fabrication lines and represent in combination with a self-aligned device layout a strategy for future generations of flexible electronic devices.