Studies of oxygen-vacancy-based resistive random access memory obtained using atomic layer deposition and electrochemical deposition

Abstract

Resistive random access memory (RRAM) is a promising candidate for next generation non-volatile memory (NVM), because of simple structure (metal-insulator-metal), low power consumption, high stacking density, fast switching, fast fabrication process, high scalability and multistate behavior. Although dramatic progress has been achieved in RRAM research, further research is necessary, including use of RRAM in practical applications such as switching mechanisms, improvement of fabrication methods, and evaluation of device performance. Atomic layer deposition (ALD) and electrochemical deposition (ECD) can be used to fabricate RRAM. Because ALD is based on self-limiting growth, it has many advantages such as large area uniformity, low temperature deposition, thickness control in atomic scale and good conformality. The ECD process has many advantages such as fast process time, simple step, highly uniform layer and low cost fabrication method. Both ALD and ECD process have many advantages and can be used in RRAM fabrication. Because ALD is based on self-limiting growth and ECD process is one of the bottom up process, we can easily control the thickness in atomic scale and deposited material characteristic. We focused on oxygen-vacancy-based resistive random access memory obtained using ALD and ECD. In this study, we use the ECD process to fabricate the Ni/CuOx/Ni flexible RRAM devices and Ni/CuOx/Ni nanowires RRAM because ECD process has many advantages. RRAM devices composed of Ni/CuOx/Ni structure by ECD process is applied in flexible memory and nanowire memory device. We demonstrate the feasibility of using ECD to fabricate Ni/CuOx/Ni flexible RRAM devices. Flexibility of memory devices should be evaluated, because the demand for flexible electronics systems has been increasing due to their light weight, excellent portability, low cost, and user-friendly interfaces compared to usual rigid substrates. Moreover, to understand the mechanism when devices size is decreased, nano-sized RRAM should be investigated. We demonstrate synthesis of Ni/CuOx/Ni nanowires (NW) by bottom up ECD process on anodized aluminum oxide (AAO) membranes. This devices showed bipolar RRAM characteristic and self-compliance behavior. In both experiments, the resistive switching mechanism is associated with migration of oxygen vacancies (Vos) and Joule heating. Furthermore we fabricated resistive random access memory devices composed of Al/AlOx(water)/AlOx(ozone)/Pt structure by ALD. To control the amount of oxygen vacancies, we use the water and ozone oxidizer source. When we use the water oxidizer source, the AlOx contains more oxygen vacancies than AlOx which is fabricated by ozone oxidizer. In case of Al/AlOx(water)/AlOx(ozone)/Pt devices, conductive filament remain stable in the AlOx(water) layer which has more oxygen vacancies, whereas partial dissociation of conductive filaments in the AlOx(Ozone) layer. AlOx(water)/ AlOx(ozone) bilayer RRAM can achieve reliable retention characteristic, uniform distribution of switching voltage and more stable resistance switching properties than single oxide layer.