A ZnO micro/nanowire-based photonic synapse with piezo-phototronic modulation

Neuromorphic computing systems that emulate the working principle of the biological brain is capable of overcoming the von Neumann bottleneck. Artificial synapses are critical information processing units in the neuromorphic computing systems. Because of the fast speed, large bandwidth, and high reliability, light or photonic interaction controlled artificial synapses (i.e., photonic synapses) are receiving great attention in recent years. Applying an additional stimuli to the photonic synapse will lead to a multi-level adjustment of synaptic plasticity behavior, which is useful for developing a multi-sensory neuromorphic system. In this work, we present a transparent and flexible photonic synapse based on a single ZnO micro/nanowire with modulation by piezo-phototronic effect, which is coupling by strain-induced piezoelectric effect and photoexcitation. The synaptic functions including paired-pulse facilitation, short-term plasticity, and long-term plasticity are demonstrated with pulsed UV illumination. Furthermore, the synaptic weight change can be effectively modulated by applying compressive strains due to the piezo-phototronic effect induced in the ZnO micro/nanowire. Specifically, the weight change can be reduced from 1437.5% to 191.4% with a compressive strain change from −0.00% to −0.28% under a UV light pulse of 4.2 mW cm⁻². A mechanism is proposed to explain the observed phenomenon of the photonic synapse under compressive strains. In addition, the relaxation of long-term plasticity can be modulated by controlling the transport of photo-generated carriers through the Schottky contact via the piezo-phototronic effect. This work demonstrates an effective approach to developing photonic synapses with tunable functions for multi-sensory neuromorphic computing systems.