Fabrication of ceria thin films for high performance resistive random access memory applications

Abstract

Resistive random access memories (RRAMs) have attracted much attention because of their unique advantages, such as simpler structure, faster reading and writing speed, smaller bit size and lower power consumption. Metal oxide thin films are potential candidates for RRAMs owing to their tunable physical properties, e.g. oxygen vacancy concentration. In this dissertation, solution processed metal oxide thin films with tunable resistive switching properties have been explored. First, sputtered CeO2 ceria thin films were fabricated by implementing different sputtering (temperatures and powers) conditions. The films deposited at low temperatures were found to have random crystal orientation and dense structure. The effects of deposition conditions on resistive switching characteristics were investigated. Improved and stable resistive switching behaviours were achieved at low deposition temperatures. In addition, the possible switching mechanism was explained on the basis of quantitative analysis. Furthermore, indium doped CeO2 nanocrystalline films were directly grown by a one-step template-free electrochemical deposition process. The Au/In-CeO2 /FTO capacitor exhibits stable bipolar resistive switching behavior, and the resistive switching behavior may be related to the oxygen vacancies, giving rise to the formation of straight and extensible conducting filaments along the electric fields. Superior stability in resistive switching characteristics was also observed, indicating that CeO2 is a potential material for next-generation nonvolatile memory applications. Finally, different elements were doped into CeO2 for investigating doping effects on the resistive switching properties of CeO¬2. The studies in this dissertation demonstrate the great potential of fabricating novel CeO2 based RRAM devices by both physical and chemical approaches. Doping indium or gadolinium into ceria can enhance the performances of the resistive switching behaviour by introducing more oxygen vacancies. This study presents a potential research direction towards developing new approaches to fabricate next generation nanoelectronic devices.