Bottom up Approach: An Efficient Fabrication of CeO2 Thin Films for High Performance Resistive Random Access Memories

Abstract

Resistive random access memories (RRAMs) based on metal oxide thin films have unique advantages over conventional non-volatile memories. In particular, RRAM exhibits two resistances states that can be switched by an external bias and this process is referred as resistive switching process. The resistive switching processes in metal oxides are usually limited to a small region near the interfaces, therefore the understanding of the interfaces and growth of nanometre scale oxide films are extremely desirable. Meanwhile, there is a barrier that the current top-down approaches for making nanoscale features are prohibitively costly and complicated. Therefore, this dissertation will focus on the development of bottom up approaches for improved resistive switching performances via materials design, defect and interface engineering. In this dissertation, cerium oxide (CeO2) has been selected as the resistive switching material and solution processed thin film deposition technologies have been deployed for controlling the morphology and tuning the resistive switching properties. For instance, CeO2-ZnO nanocomposite exhibited an increment of 100 times in RON/ROFF ratio as compared to electrodeposited CeO2 polycrystalline thin films. Additionally, high RON/ROFF ratio (>104) with excellent uniformity was achieved by using interface engineered CeO2 nanocubes based thin films. The degree of self-assembly was also proven to be critical to improve the resistive switching behavior of CeO2 nanocubes in terms of shorter switching response time with high uniformity in switching characteristics. Furthermore, doping effects on the resistive switching properties has been studied via estimation of switching probabilities at low biasing conditions. Finally, a stepwise quantized conductance behavior was observed in the CeO2 based nanocomposite (SnO2-CeO2) films which later on were attributed to the formation and disruption of atomic scale conducting filaments. This dissertation demonstrated the great potential of bottom up technology to fabricate novel RRAM devices. Also, the performance of the resistive switching devices reported in these studies were comparable to those fabricated by high cost, complex and sophisticated top-down techniques. This approach may also provide a new research direction towards developing multifunctional novel nanoelectronics