High‐Performance Internal Ion‐Gated Organic Electrochemical Transistors for High‐Frequency Bioimpedance Analysis

Abstract Internal ion‐gated organic electrochemical transistor (IGT) demonstrates volume‐dependent transconductance with the unprecedented advantages of high speed and self‐(de)doping capability among ion‐based transistors. The novel characteristics have albeit rendered IGT a promising platform for integrated bioelectronics, its potential in high‐frequency applications has yet been fully harnessed. Moreover, a study from a material's point of view is especially needed for this recently emerged platform as the necessity of maintaining the internal ion reservoir has posed difficulties in processing hydrated poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulphonate) (PEDOT:PSS) with electronically favorable morphologies. Herein, a comprehensive investigation of the structural and functional properties of ion‐embedded PEDOT:PSS modified by different annealing temperatures is performed and correlated to the IGT performance. A short‐time high‐temperature annealing treatment is found effective in facilitating the formation of compact microstructures without significantly influencing film hydration. The structural improvement enhances the film's conductivity and hole mobility, with the corresponding IGTs exhibiting higher gain, higher conductance, and high cut‐off frequency consistently in a batch. This study also successfully demonstrates the first use of electrochemical transistors like IGTs in high‐frequency applications through proof‐of‐concept experiments simulating fluid estimation in 50 kHz bioimpedance analysis. This work contributes to the development of high‐performance IGTs for extensive biological applications.