Complementary integrated circuits on plastic foil using inkjet printed n- and p-type organic semiconductors: Fabrication, characterization, and circuit analysis

Complementary thin-film transistor circuits composed of 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-PEN) and a rylene carboxylic diimide derivative for p-and n-channel thin-film transistors (TFTs) were fabricated on flexible foils. The so-called staggered TFT configuration is used, meaning that the semiconductors layers are deposited last. The work-function of the injecting gold electrodes were modified using several self-assembled monolayers (SAMs). For optimized contacts the mobility of the n- and p-channel TFTs was 0.5 cm(2)/Vs and 0.2 cm(2)/Vs, respectively. Strongly degraded performance is obtained when the n-channel material was printed on contacts optimized for the p-channel TFT, and vice versa. This illustrates that for CMOS circuits we need careful work-function engineering to allow proper injection for both electrons and holes. We show for the first time that by using a bimolecular mixture for the SAM we can systematically vary the work function, and demonstrate how this affects the performance of discrete n-type and p-type transistors, as well as CMOS inverters and ring oscillators. Under optimal processing conditions we realized complementary 19-stage ring oscillators with 10 mu s stage delay operating at 20 V. (C) 2012 Elsevier B.V. All rights reserved.