Epitaxial Bi₂O₂Se/Bi₂O₅Se Thin Films: Revealing Electric-Field-Driven Oxidation and Resistive Switching Dynamics for...

Resistive random-access memory (RRAM) is a promising technology for nonvolatile applications and neuromorphic computing. 2D bismuth oxyselenide (Bi₂O₂Se) exhibits high air stability, carrier mobility, and process compatibility. Moreover, Bi₂O₂Se naturally oxidizes into a high-κ insulating oxide, Bi₂O₅Se, making it an ideal candidate for fabricating a dielectric layer in RRAM devices with tunable resistive properties. In this study, RRAM devices based on Bi₂O₂Se/Bi₂O₅Se bilayer dielectric thin films were epitaxially grown on (001) Nb-doped SrTiO₃ substrates. The devices exhibited an exceptional nonvolatile performance, including an endurance of 3 × 10⁶ pulse cycles, retention exceeding 10⁴ s, and stable multilevel resistance states. Additionally, the synaptic-like behavior was explored by applying pulses to the devices. High-resolution in situ transmission electron microscopy and aberration-corrected scanning transmission electron microscopy were used to examine the bilayer structural evolution before and after electric-field application. The electric-field-driven oxidation of Bi₂O₂Se was demonstrated, and a new oxygen-deficient phase was explored during switching. These results established a resistance-switching mechanism in the Bi₂O₂Se/Bi₂O₅Se platform for fast and reliable RRAM and neuromorphic operations.