Near-Infrared-Sensing Flexible Organic Synaptic Transistors with Water-Processable Charge-Trapping Polymers for Potential Neuromorphic Computing/Skin Applications

Abstract

Neuromorphic devices, which can mimic the human body's neural system, are rising as an essential technology for artificial intelligence. Here, two types of organic synaptic transistors (OSTRs), OSTR-A and OSTR-B, are fabricated on either glass or polymer film using water-processable charge-trapping gate-insulating layers that are prepared by reacting ethylenediamine (EDA) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA). OSTR-A is designed to function as a basic artificial synapse by gate pulse stimulation only, while OSTR-B has additional near-infrared (NIR)-absorbing conjugated polymer layers for further sensing of NIR light upon gate voltage stimulations. The PAMPSA:EDA films are found to contain permanent charge bridges (ion pairs of –SO3− +NH3-) that play a charge-trapping role in OSTRs. Both devices with the PAMPSA:EDA layers exhibit clear postsynaptic current (PSC) signals upon gate voltage pulses, leading to long-term potentiation/depression characteristics. The flexible OSTR-B devices can sense the NIR light (905 nm) upon gate pulse stimulation and their PSC signals are well maintained even after bending (>5000 times). Artificial neural network simulations disclose that the flexible OSTR-B devices can stably perform synaptic operations under the NIR light with high accuracy (>90%) even after repeated bending (5000 times), indicative of potential use in artificial neuromorphic skin applications.