All-polymer thin film transistors fabricated by inkjet printing

All-polymer thin film transistors and circuits have been fabricated by inkjet printing. Source, drain and gate electrodes were printed with a solution of conducting conjugated polymer, poly-ethylenedioxythiophene (PEDOT), and semiconductor and gate dielectric were spin-coated from solutions of conjugated polymer and insulator polymer, respectively. The transistors printed in air show comparable performances to the reference samples with gold electrodes. In order to overcome the resolution limit of inkjet printing, water-based PEDOT solution has been deposited onto a pre-patterned substrate which defines a channel by wettability contrast between hydrophilic and hydrophobic surface regions. Polymer transistors with a channel length of 5 microns have been achieved by this approach. In order to improve carrier mobility, main chains of the polymer semiconductor were self-aligned along the channel direction, and a mobility of 0.02 cm2/V+s has been achieved in the printed transistor. We demonstrate simple printed circuits (inverters) with via-holes and load resistors formed by inkjet technology.