Redox-Based Multilevel Resistive Switching in AlFeO₃ Thin-Film Heterostructures

Next-generation nonvolatile memory devices require many functionalities such as high-speed processing, low power consumption, lightweight, and a simple structure. The use of heterostructures with resistive switching (RS) capabilities is a promising way to achieve these functionalities. In this work, the RS characteristics of a newly identified heterostructure, composed of AlFeO3 thin films, are reported. These films stabilize in an orthorhombic Pna21 structure when deposited on SrTiO3 substrates and have been studied mainly for their ferrimagnetic and ferroelectric properties. However, their semiconducting-like nature can also lead to voltage-induced RS. The current work shows evidence of RS in a Pt/AlFeO3/Nb-doped SrTiO3(111) heterostructure, and a systematic study is carried out to characterize and understand the switching process. The cell exhibits multilevel resistive states, which is attractive for high-density memory storage. The low forming voltage in the heterostructure is attributed to the columnar crystal domains observed in the film. A resistance switching mechanism is proposed, wherein the switching is attributed to the modulation of the Schottky barrier at the Pt/film interface, caused by a voltage-induced redox reaction of the Fe ions. Along with identification of a heterostructure material with attractive RS properties, the current work also highlights the importance of microstructures to tailor the switching characteristics.