Achieving Microstructure‐Controlled Synaptic Plasticity and Long‐Term Retention in Ion‐Gel‐Gated Organic Synaptic Transistors

• Published in: Advanced intelligent systems Vol. 2; no. 11
• Main Authors: Go, Gyeong-Tak, Lee, Yeongjun, Seo, Dae-Gyo, Pei, Mingyuan, Lee, Wanhee, Yang, Hoichang, Lee, Tae-Woo
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01.11.2020; Wiley
• Subjects: artificial synapses; Crystallinity; Electrodes; Energy consumption; Handwriting recognition; ion-gel-gated organic transistors; Ions; Microstructure; Moisture absorption; Neuromorphic computing; neuromorphic electronics; Organic semiconductors; organic synaptic transistors; Polymers; Retention; Self-assembled monolayers; Self-assembly; Semiconductors; Synapses; Transistors
• ISSN: 2640-4567; 2640-4567
• DOI: 10.1002/aisy.202000012

Organic synaptic transistors using intrinsic (i.e., non‐doped) organic semiconductors have demonstrated various synaptic functions to mimic biological synapses, but the devices show limited long‐term retention behaviors although long‐term memory is essential for neuromorphic computing. To achieve long‐term retention time, correlating the synaptic responses with the microstructures of polymer semiconductor is an imperative step. It is shown that synaptic plasticity in ion‐gel‐gated organic synaptic transistors (IGOSTs) can be modulated by controlling the microstructure of organic semiconductors and that long‐term memory retention can be significantly prolonged by increasing their crystallinity. The crystallinity of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) films that are spun‐cast on bare and self‐assembled monolayer is systematically controlled, before and after thermal treatments. Long‐term retention tends to extend, as the crystallinity increases. To evaluate synaptic current decay behaviors, it is suggested that the relaxation is a result of de‐doping of the polymer semiconductor over time. The recognition of handwritten digits is simulated and a high classification accuracy (>92%) is achieved with IGOSTs including high crystalline P3HT film. The study provides fundamental information about the effects of polymer microstructure on synaptic plasticity of IGOSTs, which may be applicable in neuromorphic electronics. Long‐term memory retention in poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) ion‐gel‐gated organic synaptic transistors (IGOSTs) is prolonged by modulation of microstructure. Modulation of ordered structure of the organic semiconductor is a new strategy that affects ion spreading and trapping inside the organic semiconductor in an IGOST to achieve reliable long‐term memory retention of synaptic transistors for neuromorphic computing.