Long-term potentiation through electrochemical polymerization on the gate electrode for high-endurance plasticity

With an increasing interest in information processing and the development of biocompatible technologies, the opportunities regarding neuromorphic structures have risen. On one hand, neural networks have the ability of storing information through irreversible chemical modifications, obtaining long-term plasticity.1 On the other hand, short-term plasticity, which is defined by the ability of temporarily store information, relates to an induced strengthening/weakening of the synaptic weight that is dissipated after a characteristic time constant.2 Considering organic electrochemical transistors (OECTs) as suitable components for said applications, our research group has recently developed a method that induces long-term plasticity involving direct electropolymerization of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) on the gate electrode, thanks to series of voltage pulses.3 The modifications induced on the gate electrode allow an increase in the gate capacitance, thus boosting the gating ability. The long-term potentiation occurs when the +0.7 V threshold is overcome, in analogy with biological synapses. The correlation between the neuromorphic characteristics and the modifications on the gate electrode is then confirmed by operando AFM measurements, which highlight the direct effects of the polymerization. A following depotentiation is applied through similar train at +3.0 V potential, thus overoxidizing PEDOT on the gate electrode and decreasing the gating ability. 1. Buzsáki, G. & Draguhn, A. Neuronal Oscillations in Cortical Networks. Science 304, 1926–1929 (2004). 2. Gkoupidenis, P., Schaefer, N., Strakosas, X., Fairfield, J. A. & Malliaras, G. G. Synaptic plasticity functions in an organic electrochemical transistor. Applied Physics Letters 107, 263302 (2015). 3. Mariani, F. et al. High-Endurance Long-Term Potentiation in Neuromorphic Organic Electrochemical Transistors by PEDOT:PSS Electrochemical Polymerization on the Gate Electrode. ACS Appl. Mater. Interfaces (2023) ASAP