Optimization of long-term potentiation procedure through electropolymerization on the gate electrode in solid electrolyte OECT for control applications

Driven by the growing demand for biocompatible technologies, recent advances in electronic architecture are increasingly focused on neuromorphic functionalities, aiming to emulate synaptic behavior and enhance the efficiency of data processing. On one hand, neuromorphic devices already have the ability of storing information through conductivity variations, mimicking mostly short-term plasticity that relates to an induced strengthening/weakening of the synaptic weight that is dissipated after a characteristic time constant.1 However, long-term plasticity requires stable modifications on the device structure, in order to obtain permanent data storage. This contribution demonstrates the induction of long-term potentiation through electropolymerization of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) on the gate electrode of an organic electrochemical transistor (OECT), achieved via a sequence of training pulses.2 The induced modifications allow an increase in the gate capacitance, thus boosting the gating ability and defining long-term potentiation. Similarly, depotentiation was investigated by applying a different set of training pulses, overoxidizing the electropolymerized PEDOT. The enhanced Id modulation can then be restored by training again the gate electrode. This procedure, however, requires the presence of an aqueous electrolyte, that appears challenging for the aspiring integration of said device in an electronic system. Consequently, an agarose hydrogel-based solid electrolyte was implemented. EDOT:ClO4 was electropolymerized directly onto the gate electrode, to obtain an encapsulated biocompatible OECT-based device with enhanced transconductance and potentiation durability. The final device conductivity is preserved for about three months, surpassing traditional aqueous OECT systems. Moreover, aiming at the control of an external device, the possibility of modulating Vd was investigated. A similar modulation can be applied at a Vd signal, by imposing a constant Id at the channel and thus inducing PEDOT electropolymerization. The resulting data highlights an ohmic behavior for positive values applied Id, that are opposed to a non-ohmic yet enhanced Vd modulation for negative Id. 1. Gkoupidenis, P.; Schaefer, N.; Strakosas, X.; Fairfield, J. A.; Malliaras, G. G. Synaptic Plasticity Functions in an Organic Electrochemical Transistor. Applied Physics Letters 2015, 107 (26), 263302.. 2. Mariani, F.; Decataldo, F.; Bonafè, F.; Tessarolo, M.; Cramer, T.; Gualandi, I.; Fraboni, B.; Scavetta, E. High-Endurance Long-Term Potentiation in Neuromorphic Organic Electrochemical Transistors by PEDOT:PSS Electrochemical Polymerization on the Gate Electrode. ACS Appl. Mater. Interfaces 2023, acsami.3c10576.