Printed all-polymer electrochemical transistors on patterned ion conducting membranes Nikolai Kaihovirta a,c, * , Tapio Mäkelä a , Xuehan He b , Carl-Johan Wikman b , Carl-Eric Wilén b , Ronald Österbacka a a Center for Functional Materials and Department of Natural Sciences, Åbo Akademi University, Porthansgatan 3, FI-20500 Åbo, Finland b Center for Functional Materials and Department of Chemical Engineering, Åbo Akademi University, Biskopsgatan 8, FI-20500 Åbo, Finland c Graduate School of Materials Research, Turku Universities, Porthansgatan 3, FI-20500 Åbo, Finland article info Article history: Received 3 March 2010 Received in revised form 20 April 2010 Accepted 24 April 2010 Available online 8 May 2010 Keywords: Electrochemical transistor Organic transistor All-polymer PEDOT/PSS Roll-to-roll WORM abstract We report a simple and roll-to-roll suitable method of manufacturing low-voltage, all- polymer electrochemical transistors (ECTs). The ECTs are built on self-supported and pat- terned ion conducting membranes that are tailor-made by the electron beam irradiation induced grafting technique. The redox-active poly(3,4-ethylene dioxythiophene)/poly(sty- rene sulfonate) (PEDOT/PSS) is then printed by flexography onto the membrane in one fab- rication step. The ECTs are ‘‘normally-on” devices that operate below 2 V. We also utilize overoxidation of PEDOT in order to demonstrate write-once read many times (WORM) memory functionality in the ECT. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction The organic electrochemical transistor (ECT) [1] is a sub- class of organic thin-film transistors, among other sub-clas- ses such as the organic field-effect transistor (OFET) [2] and the electric double-layer capacitance (EDLC) gated OFET [3]. However, while the two latter sub-classes, in principle, rely on a capacitive coupling in order to modulate the cur- rent in an ultrathin (nanometer-sized) section at the semi- conductor interface, the organic ECT is an electrochemical device. The ECT is gated by an electrolyte and the electronic bulk-conductivity is tuned by reduction/oxidation (i.e., re- dox) of the p-conjugated (semi)conducting polymer. There- fore, the ECT is less sensitive to dimensional constrains (especially compared to the OFET) and may adopt microm- eter scaled dimensions. Consequently, the organic ECTs have been introduced in sensing devices [4], logic circuits [5], electrochromic active-matrix displays [6] and in fiber- based electronics [7], to name a few. A concept of utilizing the redox-active poly(3,4-ethyl- ene dioxythiophene)/poly(styrene sulfonate) (PEDOT/PSS) as active material for ECTs demonstrated that high-per- forming ECTs could be fabricated in a lateral device geom- etry on low-cost substrates [5,6,8]. In these reports, the starting material was PEDOT/PSS-sheets that were pat- terned by different subtractive patterning techniques to form the electrodes. Thereafter, the electrolyte was applied either by drop-casting or printing. Three terminal PEDOT/ PSS based ECTs and logic elements have successfully also been fabricated by an ordinary desktop inkjet printer onto photo-paper [9]. However, since the organic ECT can be a lateral structure with a micrometer scale resolution, the whole fabrication procedure should also be possible in a roll-to-roll suitable fashion. 1566-1199/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.orgel.2010.04.025 * Corresponding author at: Center for Functional Materials and Depart- ment of Natural Sciences, Åbo Akademi University, Porthansgatan 3, FI- 20500 Åbo, Finland. Tel.: +358 2 215 4607; fax: +358 2 215 4776. E-mail address: nkaihovi@abo.fi (N. Kaihovirta). Organic Electronics 11 (2010) 1207–1211 Contents lists available at ScienceDirect Organic Electronics journal homepage: www.elsevier.com/locate/orgel