Understanding the volatile memristor via direct observation of surface diffusion-regulated Cu-based conductive filaments

Abstract This study develops a bioinspired bilayer volatile memristor with a W/SiO₂/Cu _x (SiO ₂ ) _{100- x} /Cu structure. The morphology and crystalline structure of the conductive filaments were directly observed via cross-sectional transmission electron microscopy. Discrete spherical copper-based grains construct conductive filaments with large internal surfaces, some of which are distorted due to stress interactions with the silicon dioxide matrix. According to the results of x-ray photoelectron spectroscopy, the diffusion of copper and redox reactions (involving the valence state transitions of copper to zero valence, positive monovalence, and positive divalence) are the core mechanisms governing the dynamic evolution of conductive filaments. When the stimulus is subsequently removed, the minimization of the thermodynamic surface energy drives the transformation of nonspherical grains into stable spherical grains, leading to conductive filament rupture and spontaneous recovery of the device to the initial state. By regulating the parameters of pulse signals to achieve precise control over conductive filament dynamics, the device successfully reproduces the behavior of nociceptors. A high accuracy of 93.11% for the handwritten digit recognition task in neurocomputing is achieved, showing the multipurpose function of the memristor.