Solution-processed oxide semiconductor-based artificial optoelectronic synapse array for spatiotemporal synaptic integration

Optoelectronic neuromorphic systems mimicking the structure and the signal processing of biological neural systems have gained significant interest due to their potential advantages such as high computing speed, high bandwidth, parallel processing, and low power requirements. Here, we demonstrate an optoelectronic synapse array consisting of solution-processed indium-gallium-zinc-oxide (IGZO) synapse devices emulating complex neural functions such as the spatiotemporal synaptic integration for neuromorphic implementation. Particularly, we adopted a vertically stacked metal-insulator-semiconductor-metal structure for IGZO synapse device to enable efficient light-induced conductance update and a low-voltage operation typically below 3 V. Using light as the stimulation, versatile synaptic functions including short-term memory/long-term memory, symmetric spike-timing dependent plasticity, and spike-number dependent plasticity were mimicked. In addition, we obtained a high recognition accuracy of handwritten digit images up to 89.4% by implementing ADAM training algorithm. Furthermore, using a crossbar structure 3 × 3 IGZO synapse array, the emulation of spatiotemporal summation was successfully carried out which is believed to be responsible for the neural encoding and the auditory recognition processes occur in the brain.