Epitaxial Strain Tuning of Ferroelectricity in 2D Bi₂O₂Se for Nonvolatile Memories

Bi₂O₂Se has emerged as a promising channel material for the development of electronic devices. Efforts have been directed toward exploring ferroelectricity in 2D Bi₂O₂Se to harness its diverse functionalities. In this study, the epitaxial growth of 2D Bi₂O₂Se is engineered to achieve lattice strain at varying levels on different substrates. Atomic displacements and polarization directions under various strain conditions are observed by using scanning transmission electron microscopy (STEM), revealing that tensile strain plays a pivotal role in inducing spontaneous polarization. Additionally, second-harmonic generation (SHG) and piezoresponse force microscopy (PFM) are employed to confirm the non-centrosymmetric structure and the presence of ferroelectricity under tensile strain. The potential application of in-plane 2D Bi₂O₂Se-based ferroelectric tunnel junctions (FTJs) in nonvolatile memory devices is further demonstrated, with switching ratios reaching up to 10⁵ at room temperature. These findings underscore the significant potential of 2D Bi₂O₂Se for nonvolatile ferroelectric memory applications.