Enhancing Synaptic Memory through an Ion Reservoir Layer in Carbon Nanotube Synaptic Transistors

Organic electrochemical synaptic transistors (OESTs) for neuromorphic computing are gaining attention as a promising platform for mimicking biological synaptic plasticity based on a mixed ion-electron conduction mechanism. Carbon nanotubes (CNTs) are widely studied as channel materials due to their high charge mobility and compatibility with solution-based processes; however, they have the limitation that their memory retention properties are restricted by the rapid back-diffusion of ions after stimulus offset. To overcome this, this study introduced poly(allylamine hydrochloride) (PAH), a cationic polyelectrolyte, as an ion reservoir layer. The protonated amine groups of PAH temporarily trap ions through electrostatic interactions with electrolyte anions, enabling their gradual release into the channel and inducing a gradual relaxation of the doping state. As a result, improved EPSC retention characteristics and a transition from short-term to long-term synaptic plasticity were achieved. We propose that the polyelectrolyte-based ion storage layer represents a novel material design strategy for effectively controlling the synaptic dynamics of CNT-OESTs.