Study on the electroforming and resistive switching behaviour of nickel oxide thin films for non-volatile memory applications

Over the past decade, the resistance switching eect has drawn attention within the scientic community as a potential candidate for non-volatile random access memories (RAM) and crossbar logic concepts. The resistance switching memory cells are based on (at least) two well-dened non-volatile resistance states, e. g., high resistance state (HRS) and low resistance state (LRS), that dene two (or more) logic memory states, e. g., 1 or 0. Often these cells have a simple capacitor structure and are therefore easy to fabricate. However, the market launch of RRAMs is hindered by several serious obstacles. For example, the underlying microscopical physical and chemical switching mechanism of RRAM devices is still under debate although various models have been proposed to explain the observed phenomena. By missing a deep understanding of the resistive switching eect on an atomistic scale, a reliable fabrication of predictable and well performing Gbit memory seems to be questionable. This thesis is an attempt to develop and physically understand the nickel oxide (NiO) based resistive switching non-volatile memory devices. Although the underlying microscopical switching mechanism is still under debate, the macroscopic switching mechanism of this material system is often described by the creation and rupture of well-conducting nickel laments embedded within an insulating NiO matrix, the so called fuse-antifuse mechanism. The resistive switching characteristics, essentials for future non-volatile memories, such as low voltage and current operation with high resistance ratio between HRS and LRS, fast switching speed, high retention and endurance are presented. Additionally, the emphasis is layed on the understanding of the so called forming process. It describes the rst resistance transition of the resistive switching device in which the proposed nickel lament is formed. Therefore, it is the key process for understanding the resistive switching phenomena. The statistical distribution of the observed forming process is studied under accelerated constant voltage stress conditions and at varying temperatures within the framework of the Weibull statistics. To understand the physical and chemical nature of the lamentary structure, the in uence of dierent ambient atmospheres and temperatures on the forming process is analyzed electrically as well as chemically by XPS analysis. Combining these results with the results of the potentiostatic breakdown studies, a model for the forming process in Pt/NiO/Pt non-volatile resistive switching memory devices is proposed.