Organic electrochemical transistors (OECTs) are promising building blocks for bioelectronic devices such as sensors and neural interfaces. While the majority of OECTs use simple planar geometry, there is interest in exploring how these devices operate with much shorter channels on the submicron scale. Here, we show a practical route toward the minimization of the channel length of the transistor using traditional photolithography, enabling large-scale utilization. We describe the fabrication of such transistors using two types of conducting polymers. First, commercial solution-processed poly(dioxyethylenethiophene):poly(styrene sulfonate), PEDOT:PSS. Next, we also exploit the short channel length to support easy in situ electropolymerization of poly(dioxyethylenethiophene):tetrabutyl ammonium hexafluorophosphate, PEDOT:PF6. Both variants show different promising features, leading the way in terms of transconductance (gm), with the measured peak gm up to 68 mS for relatively thin (280 nm) channel layers on devices with the channel length of 350 nm and with widths of 50, 100, and 200 μm. This result suggests that the use of electropolymerized semiconductors, which can be easily customized, is viable with vertical geometry, as uniform and thin layers can be created. Spin-coated PEDOT:PSS lags behind with the lower values of gm; however, it excels in terms of the speed of the device and also has a comparably lower off current (300 nA), leading to unusually high on/off ratio, with values up to 8.6 × 104. Our approach to vertical gap devices is simple, scalable, and can be extended to other applications where small electrochemical channels are desired.

Bioelectronics Materials and Devices Lab Central European Institute of Technology Brno University of Technology Purkyňova 123 61200 Brno Czech Republic

Czech Metrology Institute 638 00 Brno Czech Republic

Department of Electrical and Electronic Technology Faculty of Electrical Engineering and Communication Brno University of Technology 616 00 Brno Czech Republic

Institute of Scientific Instruments of the CAS Královopolská 147 61264 Brno Czech Republic

Laboratory of Organic Electronics ITN Campus Norrköping Linköping University SE 60174 Norrköping Sweden

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In Situ Electropolymerized Ambipolar Copolymers for Vertical OECTs

Vertical organic electrochemical transistor platforms for efficient electropolymerization of thiophene based oligomers