Resistive switching characteristics of a spinel ZnAl2O4 thin film prepared by radio frequency sputtering

In this study, ZnAl2O4 (ZAO) films having a thickness of 20.1 nm, which serve as the resistive switching layer in random access memory (RRAM) devices based on a Pt/ZAO/Pt structure, were prepared using radio frequency magnetron sputtering. The as-deposited film appeared to be amorphous with distributed nano-crystalline ZnAl2O4 particles, while the ZAO film annealed at 450 degrees C was composed of cubic ZnAl2O4 spinel crystallites. The chemical formula of the former was (Zn0.340Al0.66)O-0.69 square(0.64) while that of the latter was (Zn0.91Al0.09)Al2O3.73 0.27, as calculated from energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) results, indicating that both these films consisted of oxygen vacancies. Pt/ZAO/Pt devices containing the as-deposited ZAO film exhibited excellent unipolar switching behavior marked with a resistance ratio larger than an order of magnitude, good endurance, and a long retention time. The conduction mechanisms for the low resistive state and high resistive state were dominated by the Ohmic conduction and trap-controlled space charge limited current mechanisms, respectively. The resistive switching behavior in the Pt/ZAO/Pt device was attributed to the formation and rupture of the conduction filaments formed by the oxygen vacancies. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.