Investigation of Resistive Switching Mechanism in High-Performance High Entropy Oxide-Based RRAM

The application of high entropy oxide (HEO) attracts great attention in recent years, due to its unique structural characteristics such as excellent electrochemical properties and long-term cycling stability possibilities that HEO has been used as an anode active material in Lithium-ion batteries. Furthermore, transition metal (TM) oxides have been used as dielectric materials of resistive random access memory (RRAM) owing to the stable structure and variable oxidation state of transition metals. However, the switching mechanism of TM-HEO-based RRAM has not been fully investigated to date.<br/>In this work, We grew the high entropy oxide (Cr, Mn, Fe, Co, Ni)₃O₄ on Nb: STO conductive substrate epitaxially, and deposited the Pt metal as the top electrode. The structure of the pristine dielectric layer is spinel. After cycled, we observed that some regions of spinel structure will transform into rock-salt structure by using advanced transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) characterization, and the result data of X-ray photoelectron spectroscopy (XPS) and Electron Energy Loss Spectroscopy (EELS) support this perspective. Only specific elements will change their valence state, which resulted in excellent resistive-switching properties with a high on/off ratio on the order of 10⁴ times, and excellent endurance in the order of 10³cycles at room temperature.