Non-destructive patterning of conducting-polymer devices using subtractive photolithography

We demonstrate a non-destructive, high-throughput, and high-resolution lithographic patterning method to fabricate organic-semiconductor devices based on UV lithography with the standard equipment of well-established silicon technology. The method is applied to fabricate poly(3-hexylthiophene) (P3HT)-based organic thin-film transistors (OTFTs) with high yield. Patterns with features down to 2 μm are reproducibly demonstrated. We show that a few modifications in the processing steps are necessary in order to spin-coat photoresist onto P3HT films and to completely remove P3HT residues on the substrates that have been treated with a self-assembled monolayer. Compared with OTFTs whose P3HT channels are not patterned, the on/off ratio of the patterned devices is improved by over four orders of magnitude from about 70 to 106, because of the dramatically reduced gate leakage current. The extracted carrier mobility is not only virtually unchanged after the lithography processes, but also as high as 0.027 cm2/V s. Both the on/off ratio and the mobility are among the best reported values in P3HT-based OTFTs fabricated and measured in ambient conditions. © 2006 Elsevier B.V. All rights reserved.