Fabrication of a planar water gated organic field effect transistor using a hydrophilic polythiophene for improved digital inverter performance

A planar water gated OFET (WG-OFET) structure is fabricated by patterning gate, source and drain electrodes on the same plane at the same time. Transistor output characteristics of this novel structure employing commercial regioregular poly(3-hexylthiophene) (rr-P3HT) as polymer semiconductor and deionized (DI) water as gate dielectric show successful field effect transistor operation with an on-off current ratio of 43 A/A and transconductance of 2.5 mu A/V. These output characteristics are improved using P3HT functionalized with poly(ethylene glycol) (PEG) (P3HT-co-P3PEGT), which is more hydrophilic, leading to on-off ratio of 130 A/A and transconductance of 3.9 mu A/V. Utilization of 100 mM NaCl solution instead of DI water significantly increases the on-off ratio to 141 A/A and transconductance to 7.17 mu A/V for commercial P3HT and to 217 A/A and to 11.9 mu A/V for P3HT-co-P3PEGT. Finally, transistors with improved transconductances are used to build digital inverters with improved characteristics. Gain of the inverters employing P3HT and P3HT-co-P3PEGT are measured as 2.9 V/V and 10.3 V/V, respectively, with 100 mM NaCl solution. (C) 2013 Elsevier B. V. All rights reserved.