Vertical Growth of Ultrathin Bi₂WO₆ Nanosheets for Visual Optoelectronic Neuromorphic Devices

Planar-grown 2D Bi₂WO₆ is promising for ferroelectric and opto-synaptic applications, but the fabrication of the device relies on organic solvents, which introduce residues. As a result, the devices show short opto-synaptic memory and non-electrically erasable behavior, limiting their suitability for neuromorphic applications. Therefore, developing stable preparation methods for vertical 2D Bi₂WO₆ samples and exploring their applications in low-power neuromorphic devices are of significant importance. Here, ultrathin Bi₂WO₆ nanosheets with tunable vertical and planar morphologies are synthesized via controlled one-step chemical vapor deposition (CVD), where vertically aligned configurations enable residue-free transfer. Building on this, simple two-terminal Bi₂WO₆ optoelectronic synaptic devices that exhibit an ultralow dark current (∼0.1 pA), a high I_ph/I_dark ratio (>10⁵), and long memory retention (∼25 000 s) are fabricated. These devices successfully emulate key synaptic functions, including excitatory postsynaptic currents (EPSC), paired-pulse facilitation (PPF), and short-to-long-term plasticity (STP-to-LTP) transitions under optical stimuli. Critically, optically programmed long-term potentiation (LTP) and electrically erased long-term depression (LTD) are achieved with ultra-low energy consumption below 1 pJ per operation. The Bi₂WO₆ devices, through their optically programmable plasticity and energy-efficient neuromorphic operation, demonstrate significant potential for next-generation artificial vision systems, sensing-memory-computing integrated architectures, and high-fidelity neuromorphic hardware.