Bi₂O₂Se-Based Monolithic Floating-Gate Nonvolatile Memory with Enhanced Charge Retention and Switching Performance

The continuous scaling of conventional floating-gate memories faces major challenges due to charge leakage and complex multilayer architectures. Here, we report a monolithic nonvolatile memory (NVM) device constructed using a single 2D material, Bi₂O₂Se, that integrates channel, charge storage, and tunneling functions within the same material system. Upon UV-ozone treatment, semiconducting Bi₂O₂Se (s-BOS) forms a conformal and crystalline β-Bi₂SeO₅ shell. Subsequent thermal annealing introduces selenium vacancies into the core, converting it to metallic Bi₂O₂Se (m-BOS), which serves as a floating-gate capable of efficient charge trapping, while the crystalline BOS oxide shell provides robust tunneling insulation and suppresses leakage. This monolithic structure integrates channel (s-BOS), storage (m-BOS), and tunneling functions (BOS oxide) within a single material system. The devices exhibit a large memory window, a high charge storage density (∼5 × 10¹³ cm^-2), and a current ON/OFF ratio exceeding 10⁸. They also show fast programming/erasing with ±12 V, 100 ms pulses, robust endurance over 2000 cycles, and charge retention exceeding 10⁴ seconds. Compared with other 2D NVMs employing separate materials for each functional layer, this single-material platform enables simplified fabrication and improved scalability in the 2D memory device design.