Bipolar Switching Behavior of ZnO _x Thin Films Deposited by Metalorganic Chemical Vapor Deposition at Various Growth Temperatures

The bipolar resistive switching behaviors of ZnO films grown at various temperatures by metalorganic chemical vapor deposition have been investigated. The ZnO films were grown on Pt/Ti/SiO₂/Si(100) substrate, and the ZnO growth temperature was varied from 300°C to 500°C in steps of 100°C. Rutherford backscattering spectroscopy analysis results showed that the chemical compositions of the ZnO films were oxygen-poor Zn₁O_0.9 at 300°C, stoichiometric Zn₁O₁ at 400°C, and oxygen-rich Zn₁O_1.3 at 500°C. Resistive switching properties were observed in the ZnO films grown at 300°C and 400°C. In contrast, high current, without switching properties, was found in the ZnO film grown at 500°C. The ZnO film grown at 500°C had higher concentration of both nonlattice oxygen (4.95%) and oxygen vacancy (3.23%) than those grown at 300°C or 400°C. The resistive switching behaviors of ZnO films are related to the ZnO growth temperature via the relative amount of oxygen vacancies in the film. Pt/ZnO/Pt devices showed asymmetric resistive switching with narrow dispersion of switching voltage.