Organic Electrochemical Synaptic Transistors with Improved Retention for Logic and Biosignal Processing

Organic electrochemical synaptic transistors (OESTs) based on organic mixed ionic-electronic conductors (OMIECs) present a promising platform for bio-inspired neuromorphic computing and bioelectronics. However, achieving long-term memory retention and precise conductance modulation under ambient conditions remains a key challenge. Here, a solid-state OEST gated by a semi-solid ionic liquid gel, in which thermal annealing significantly enhances memory characteristics and operation reliability by tuning the thin film microstructure and ion-polymer interactions, is reported. The optimized devices exhibit stable multilevel conductance with 82% retention over 1000 s across five distinct states, and negligible drift over 20000 operation cycles under ambient conditions. These devices are integrated into non-volatile logic gates (NOT, NAND, NOR) and applied in high-fidelity recording and storage of electrocardiogram (ECG) signals for up to 1200 s, with reusability over 7 days. They are also used for neuromorphic computing of photoplethysmography (PPG) signals for activity classification. This work advances the development of reliable, high-performance bio-inspired neuromorphic devices, offering a route toward in-sensory processing and logic-in-memory architectures for bioelectronic applications.