Resistive Switching Behaviors of Transition Metal Oxides Fabricated by Atomic Layer Deposition and Solution Processing

Abstract

With fast development of semiconductor non-volatile memory devices, conventional charge-based memories are approaching to their scaling limit. Among the emerging memory devices, resistive random access memory (RRAM) is one of the most promising candidates for future applications. In this study, we focused on HfOX and AlOX as promising resistive switching candidates, and we applied ALD and spin coating in fabrication of RRAM devices. In chapter 1, we briefly explained general concepts and mechanisms, as well as motivation of this study. In chapter 2, resistive switching behaviors of AlOX/HfOX bilayer structures were investigated. Metal oxides were deposited by atomic layer deposition. Based on preliminary optimization experiments, water as the oxidizer and 300 oC as the deposition temperature were selected. Al and Pt were used as top and bottom electrodes, respectively. Compared with AlOX and HfOX monolayer structures, the bilayer structure showed lower set/reset voltages and more-uniform resistive switching properties. It also exhibited good data retention and endurance. The Al top electrode may gather oxygen ions from the oxide layer underneath and thereby create oxygen vacancies in the oxide layer. The uniform electrical property of the bilayer structure is attributed to confined formation/rupture of conductive filaments in the HfOX layer, whereas undissociated filaments in the AlOX layer nucleate rapid regeneration of filaments. In chapter 3, we investigated the effect of Ni and Ta doping on resistive switching behavior of solution processed HfOX RRAM devices. The observations are discussed in terms of oxygen vacancy concentration. Doping changed the initial resistance and forming voltage due to reduction of formation energy of oxygen vacancy, whereby higher concentration of dopant results in lower forming voltage. Since Ni dopant has a significant effect on concentration of oxygen vacancies, 10% Ni doping can lead to achieve forming free behavior.