Growth and defect engineering of two-dimensional materials for memristor improvement

The non-volatile resistive switching phenomenon has been widely observed recently in the Two-dimensional (2D) materials down to monolayer, with promising memristor applications. However, many fundamental challenges for 2D memristors remain towards industrialization, including large-scale growth of 2D thin films and device reliability. This dissertation presents a feasible method for wafer-scale synthesis of MoS₂ and WS₂ films and multiple strategies to improve the reliability of 2D memristor. In Chapter 2, a significant improvement in yield and endurance has been demonstrated with defect engineering. The E-beam irradiation effect on MoS₂ is detailed studied with material characterization and Montre Carlo simulations. Chapter 3 presents a simple one-step low-temperature sulfurization process to synthesize wafer-scale few-layer MoS₂ and WS₂. The sulfurized film-based memristors show stable non-volatile switching and a satisfactory on/off current ratio. The impact of sulfurization parameters on film quality has been systematically studied to guide device optimization. The performance of memristors based on MoS₂ grown with sulfurization parameters is evaluated and compared. A qualitative model is proposed to provide more insight on reliability improvement with sulfurization parameters adjustment. In Chapter 5, MoS₂ memristors under fabrication configurations are comprehensively compared. Considerable reliability (yield and endurance) improvements are achieved by reducing top electrode deposition rate and increasing MoS₂ thickness. The statistical analysis further reveals an intriguing convergence of switching metrics, despite the reliability difference. The reliability improvements and independence switching metrics can be understood with a proposed general-purpose “active layer” model. Monte Carlo simulations have been performed to provide a more intuitive understanding of endurance failure mode associated with the formation of clusters in the active layer.