High-resolution spatial control of the threshold voltage of organic transistors by microcontact printing of alkyl and fluoroalkylphosphonic acid self-assembled monolayers

A dense array of 500 organic TFTs with two different threshold voltages arranged in a checkerboard pattern has been fabricated. The threshold voltages were defined by preparing self-assembled monolayers (SAMs) of either an alkyl or a fluoroalkylphosphonic acid on the gate-oxide surface of each TFT, using a combination of microcontact printing from an elastomeric stamp and dipping into a solution. The threshold voltages are -1.01 +/- 0.15 V for the TFTs with the fluoroalkyl SAM and -1.28 +/- 0.23 V for the TFTs with the alkyl SAM. ToF-SIMS analysis shows that the two SAMs can be patterned with a pitch of 10 lmand without significant cross-contamination. Cross-sectional TEM and NEXAFS characterization of the SAMs indicate that the properties of the SAMs prepared by microcontact printing and dipping are essentially identical. (C) 2015 Elsevier B.V. All rights reserved.