Voltage‐Free Flexoelectric Gating of α‐In ₂ Se ₃ ‐Based Optoelectronic Synapses for Enhanced Visual Memory Applications

ABSTRACT 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 ‐ nanosheets are engineered via substrate patterning to establish lithographically defined flexoelectric fields, enabling the modulation of optoelectronic synaptic behavior. By transferring the ‐ 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 gate bias or a 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.