Atomic Layer Deposition of Vanadium Oxide and Tantalum Oxide Thin Films for Resistive Switching Applications

Redox-based resistive switching random access memory (ReRAM) cells have emerged as a promising candidate for the next generation nonvolatile storage devices because of their high performance, energy efficiency, scalability and economic potential. They possess simple metal-insulator-metal (MIM) structure and register the resistance change of the insulating layer (i.e. metal oxide thin film) as response to the electrical stimuli to store the information. However, ReRAM devices demands precise thin film fabrication technology. In recent decades, atomic layer deposition (ALD) has been a subject of intensive research by both academic researchers and industrial partners because of its potential to grow ultrathin (= 10 nm) metal oxide films. Inspired by the steadily growing ReRAM research, the present thesis focuses on ALD of two transition metal oxides, namely vanadium oxides (e.g. V2O5 and VO2) and tantalum oxide (Ta2O5). In the first part of this work, vanadium oxide thin films were deposited by ALD from vanadyl tri-isopropoxide (VO(OiPr)3, VTIP) and water. Post growth annealing processes were carried out under various temperatures (from 350 to 500 °C) and time durations (from 30 to 300 min). Based on the results from the post-growth annealing studies, a 15 nm as-grown amorphous VOx film was fabricate into the Pt/VOx/Ti/Pt crossbar structures with the size of 1 µm2. The second part of this work focuses on the ALD grown Ta2O5 films by tantalum isopropoxide ([Ta(OiPr)5]2) and water as metal and oxide precursors, respectively. The resistive switching behaviors of the amorphous Ta2O5 based ReRAM devices were tested with respect to different thickness of integrated Ta layer (5, 10 and 15 nm) and cell dimensions (2x2 µm2 and 10x10 µm2). The thickness of the Ta layer influences the electroforming process. Electroforming-free and reliable resistive switching was observed on devices with larger Ta thickness (10 nm and 15 nm).