All-Metal-Oxide Heterojunction Optoelectronic Synapses with Multilevel Memory for Artificial Visual Perception Applications.

Metal-oxide semiconductor-based optoelectronic synaptic transistors have attracted considerable attention due to their high energy efficiency and stability. This work proposes a novel WO/InWZnO heterojunction optoelectronic synaptic transistor, demonstrating the strong potential for emulating the human visual system. The fabricated heterojunction synaptic transistor achieves an impressive optical responsivity of 58.37 A W when exposed to 650 nm light. Furthermore, it successfully emulates transitions from short-term memory (STM) to long-term memory (LTM) by modulating pulse duration, illumination intensity, and pulse number. The heterojunction transistor also exhibits an optimal paired-pulse facilitation (PPF) index of 176% and post-tetanic potentiation (PTP) index of 890% under 460 nm light illumination. It also demonstrates long-term multilevel storage capability via the photogating effect. A multilayer perceptron (MLP) model, employing synaptic weights modulated by 650, 525, and 460 nm light in the long-term potentiation (LTP) region and by electrical stimuli in the long-term depression (LTD) region, achieves a high recognition accuracy of 87.4% for severely distorted handwritten digits. Finally, the U-Net architecture is adopted to evaluate the image segmentation performance through RGB channels, revealing an optimal accuracy of 74.5%, demonstrating the feasibility of the proposed WO/InWZnO heterojunction synaptic transistor for advanced neuromorphic vision system applications.