High Visible‐Light‐Stimulated Plasticity in Optoelectronic Synaptic Transistors for Irradiation History‐Dependent Learning

• Published in: Advanced electronic materials Vol. 6; no. 4
• Main Authors: Wu, Mingze, Shang, Shangyang, Wei, Qi, Liu, Chang, Li, Aidong, Gao, Xu, Wang, Suidong, Yin, Jiang, Xia, Yidong, Liu, Zhiguo
• Format: Journal Article
• Language: English
• Published: Wiley-VCH 01-04-2020
• Subjects: history‐dependent learning; optoelectronics; plasticity; synaptic transistors; synaptic weight modulation
• ISSN: 2199-160X; 2199-160X
• DOI: 10.1002/aelm.201901255

Recent years have witnessed the emergence of visible‐light‐stimulated synaptic transistors, which has potential for the construction of visual cognition and light‐controlled neuromorphic hardware. Efforts are made to improve the visible light‐stimulated plasticity by boosting the synaptic weight after optical neural activities. However, such modulation at the expense of increased initial synaptic weight before the stimuli still results in the limited plasticity. Here, instead of employing those inherent interfacial trap‐induced effects that raise the activated synaptic weight, it is demonstrated that an interfacial modification to inhibit them can greatly reduce the initial synaptic weight. Hence, with the assistance of the charge‐trapping memory effect, the initial and the activated synaptic weight can be modulated, leading to a significantly enhanced plasticity. Such enhancement is accomplished in a type of pentacene‐based synaptic transistors in which a visible‐light‐triggered plasticity above 108% (at 0 V gate voltage and −1 V source–drain voltage) can be achieved under a moderate optoelectronic stimulus. As a demonstration, long‐term potentiation is implemented to showcase synaptic responses with high plasticity after repeated light‐triggered neural activities, suggesting the proposed mechanism and design paradigm would be beneficial for future optical neuromorphic architectures.
Dramatically enhanced visible light‐stimulated plasticity is successfully realized in organic synaptic transistors. An interfacial modification method greatly reduces the initial synaptic weight before stimuli, while the activated synaptic weight is modulated with the assistance of charge‐trapping memory effect, accomplishing an ultrahigh visible light‐triggered plasticity above 108%. This provides a promising mechanism for a variety of future optical neuromorphic architectures.