Polymer field-effect transistors fabricated by the sequential gravure printing of polythiophene, two insulator layers, and a metal ink gate

The mass production technique of gravure contact printing is used to fabricate state-of-the art polymer field-effect transistors (FETs). Using plastic substrates with prepatterned indium tin oxide source and drain contacts as required for display applications, four different layers are sequentially gravureprinted; the semiconductor poly(3-hexylthiophene-2,S-diyl) (P3HT), two insulator layers, and an Ag gate. A Crosslin kable insulator and an Ag ink are developed which are both printable and highly robust Printing in ambient and using this bottom-contact/top-gate geometry, an on/off ratio of >10 ⁴ and a mobility of 0.04 cm² V^-1 s^-1 are achieved. This rivals the best top-gate polymer FETs fabricated with these materials. Printing using low concentration, low viscosity ink formulations, and different P3HT molecular weights is demonstrated. The printing speed of 40 m min^-1 on a flexible polymer substrate demonstrates that very high-volume, reel-to-reel production of organic electronic devices is possible.