Chemical defect-dependent resistive switching characterization in CeO2 thin films

Abstract

The aim of this study was to characterize the resistive memory switching mechanism of cerium dioxide (CeO2) thin insulating films for different dopants. Three chemical elements (Gd, Zr, and Ca) were used for the doping of 60 nm CeO2 thin films in Pt/CeO2/Pt memory devices. The switching mechanism exhibited unipolar behavior. The results of the electrical measurements for the Gd- and Zr-doping of the Pt/CeO2/Pt device showed a high-resistance ratio of approximately 104, good data retention, which was stable and maintained at approximately 104 s at 25 °C, and reliable endurance over 1500 cycles. However, Ca-doping had the opposite effects. The results suggested that the chemical defects and oxygen vacancies in metallic Gd and Zr were more effective than those of Ca in the CeO2 films. The X-ray photoelectron spectroscopy (XPS) results indicated the important role of oxygen in the doped film composition to generate conductive filaments, which lead to component resistance conversion in the insulating layer. Furthermore, the bond energy analysis of XPS showed that, compared to the undoped components, the Gd- and Zr-doped components had a lower CeO2 bond energy, resulting in a stable configuration conversion, while the Ca-doped components had a higher CeO2 bond energy, resulting in an unstable configuration conversion.