Atomic-Scale Investigation of Structural Evolution and Resistive Switching Behaviors in Bismuth Selenium-Based Resistive Random-Access Memory

Recently, the electronic devices have flourishing evolution especially in the memory devices. Various types of non-volatile memories have been discussed, such as magnetic random-access memory (MRAM), ferroelectric random-access memory (FeRAM), phase change random-access memory (PCRAM), and resistive random-access memory (RRAM). Resistive random-access memory is considered the potential candidate for next-generation non-volatile memory owing to its simple structure, fast switching speed, and high storage density. Resistive switching has been found in a variety of oxides, and 2D Bi₂O₂Se has gained attraction worldwide due to its small theoretical bandgap (0.8 eV), good air stability, and high carrier mobility at the ambient temperature. However, Bi₂O₂Se is rarely used as the switching layers in memristors, and the comprehension of the structure transformation during resistive switching is insufficient.
In this work, we utilize the 2D layered material, Bi₂O₂Se (BOS), epitaxially grown on Nb-doped SrTiO₃(Nb-STO) substrate as the switching layer for an RRAM device. Pt metal was deposited as the top electrode to measure its electrical properties. This device have excellent performance including outstanding endurance exceed 2000 cycles, high on/off ratio over 10³, and long retention time up to 10⁴ seconds. Moreover, to investigate the resistive switching behaviors, we used the high-resolution transmission electron microscopy (HRTEM) and the atomic-scale scanning transmission electron microscopy (STEM) to observe the structural transformation and the oxygen-ion migration in Bi₂O₂Se. From the TEM results and the corresponding fast-Fourier-transform diffraction patterns (FFT-DP), after continuously applying voltages sweep cycles, the structure transforms from the tetragonal structure to a hybrid structure of tetragonal Bi₂O₂Se and hexagonal Bi₂O₃, and some of the areas are Bi-rich, which predicted as the conduction region. Additionally, we conduct X-ray photoelectron spectroscopy (XPS) to demonstrate the chemical composition for further study of the microstructural evolution and resistive switching behaviors.
This study not only revealed the structural transformation of Bi₂O₂Se but also proved it to be a promising candidate for RRAM application.