A synaptic device based on the optoelectronic properties of ZnO thin film transistors

Optoelectronic synapses are devices that use electromagnetic radiation to mimic synaptic plasticity and its related functions. Such devices are considered key elements for the implementation of neuromorphic computing systems, that is, based on the functioning of the brain, with sensing, memory and learning properties. This work demonstrates an optoelectronic device with synaptic properties based on a thin-film transistor (TFT) configuration, with the semiconductor channel consisting by a zinc oxide (ZnO) film deposited by RF magnetron sputtering. The synaptic properties take advantage of the phenomenon of persistent photoconductivity presented by the ZnO film. The incidence of light in the channel increases the electrical current intensity measured between the drain and source electrodes (IDS)—for a given potential applied to the gate electrode (VGS). With this, the synaptic functions of sensing, short- and long-term memory, learning and relearning, and paired pulse facilitation, are verified in the ZnO TFT. The variations in IDS caused by lighting with ultraviolet (UV) radiation can reach up to 108 A, which demonstrates the high sensitivity of the device, a crucial aspect for its effectiveness in terms of recognizing and discriminating the light stimulus.