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

Abstract 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.