Poly(3,4-ethylenedioxythiophene) (PEDOT) is an electrically-conducting conjugated polymer that has very good conductivity and demonstrates biocompatibility. Organic electrochemical transistors (OECT) based on PEDOT:PSS have already been proven to be suitable candidates as transducers for various biosensor applications. The electrical conductivity of PEDOT:PSS is changed by (de)doping due to the incorporation of ions from an electrolyte. In this work the electrical characteristics of OECTs based on PEDOT:PSS have been studied. Transistor test devices were fabricated with heavily doped n++ Si wafers with 200 nm thermally grown SiO2 as gate dielectric. Au source and drain electrodes were defined using conventional photolithography. Ti was used as an adhesion layer. A PDMS structure was glued on the substrate to confine the electrolyte and insulate the contacts from the electrolyte solution (KCl). As gate electrode a Ag wire or Ag/AgCl pellet was immersed in the electrolyte. The transfer and output characteristics of the transistors were obtained as a function of salt concentration and gate electrode and analyzed using a device model developed by Bernards et al.(1) The dependence of the OECT characteristics on salt concentration can be explained by a simultaneous decrease of the conductance and pinch-off voltage with increasing salt concentration.
(1). D.A. Bernards and G.G. Malliaras, Adv. Funct. Mat. 17, 3538 (2007)