Effect of Bilayer CeO 2−x /ZnO and ZnO/CeO 2−x Heterostructures and Electroforming Polarity on Switching Properties of Non-volatile Memory

Memory devices with bilayer CeO2−x/ZnO and ZnO/CeO2−x heterostructures sandwiched between Ti top and Pt bottom electrodes were fabricated by RF-magnetron sputtering at room temperature. N-type semiconductor materials were used in both device heterostructures, but interestingly, change in heterostructure and electroforming polarity caused significant variations in resistive switching (RS) properties. Results have revealed that the electroforming polarity has great influence on both CeO2−x/ZnO and ZnO/CeO2−x heterostructure performance such as electroforming voltage, good switching cycle-to-cycle endurance (~ 102), and ON/OFF ratio. A device with CeO2−x/ZnO heterostructure reveals good RS performance due to the formation of Schottky barrier at top and bottom interfaces. Dominant conduction mechanism of high resistance state (HRS) was Schottky emission in high field region. Nature of the temperature dependence of low resistance state and HRS confirmed that RS is caused by the formation and rupture of conductive filaments composed of oxygen vacancies.