Voltage-Free Flexoelectric Gating of α-In₂Se₃-Based Optoelectronic Synapses for Enhanced Visual Memory Applications

Flexoelectricity refers to the generation of electric polarization by strain gradients, enabling voltage-free modulation of material properties. This effect is particularly pronounced in two-dimensional (2D) materials due to their atomic-scale thickness and mechanical flexibility. Here, suspended (Formula presented.) - (Formula presented.) nanosheets are engineered via substrate patterning to establish lithographically defined flexoelectric fields, enabling the modulation of optoelectronic synaptic behavior. By transferring the (Formula presented.) - (Formula presented.) nano-structures onto pre-patterned substrates, suspended structures with geometries designed to introduce localized bending are constructed, leading to strain-gradient-induced polarization with well-defined spatial distribution. Compared to flat counterparts, suspended devices exhibit enhanced conductivity and a remarkable transition from long-term potentiation (LTP) to long-term depression (LTD) under optical stimulation, outperforming the effects induced by applying a (Formula presented.) gate bias or a (Formula presented.) gate-pulse-driven ferroelectric polarization. Flexoelectric gating thus enables voltage-free control of synaptic plasticity, offering long-term retention and geometry-defined tunability. Furthermore, spatial integration of LTP and LTD supports contrast-enhanced memory functions, mimicking sharpening mechanisms in biological visual systems. The present work establishes a programmable neuromorphic optoelectronic platform for energy-efficient implementation of 2D synaptic networks.