Phase/Interfacial-Engineered Two-Dimensional-Layered WSe 2 Films by a Plasma-Assisted Selenization Process: Modulation of Oxygen Vacancies in Resistive Random-Access Memory.

Here, we propose phase and interfacial engineering by inserting a functional WO 3 layer and selenized it to achieve a 2D-layered WSe 2 /WO 3 heterolayer structure by a plasma-assisted selenization process. The 2D-layered WSe 2 /WO 3 heterolayer was coupled with an Al 2 O 3 film as a resistive switching (RS) layer to form a hybrid structure, with which Pt and W films were used as the top and bottom electrodes, respectively. The device with good uniformity in SET/RESET voltage and high low-/high-resistance window can be obtained by controlling a conversion ratio from a WO 3 film to a 2D-layered WSe 2 thin film. The Pt/Al 2 O 3 /(2D-layered WSe 2 /WO 3 )/W structure shows remarkable improvement to the pristine Pt/Al 2 O 3 /W and Pt/Al 2 O 3 /2D-layered WO 3 /W in terms of low SET/RESET voltage variability (-20/20)%, multilevel characteristics (uniform LRS/HRS distribution), high on/off ratio (10 4 -10 5 ), and retention (∼10 5 s). The thickness of the obtained WSe 2 was tuned at different gas ratios to optimize different 2D-layered WSe 2 /WO 3 (%) ratios, showing a distinctive trend of reduced and uniform SET/RESET voltage variability as 2D-layered WSe 2 /WO 3 (%) changes from 90/10 (%) to 45/55 (%), respectively. The electrical measurements confirm the superior ability of the metallic 1T phase of the 2D-layered WSe 2 over the semiconducting 2H phase. Through systemic studies of RS behaviors on the effect of 1T/2H phases and 2D-layered WSe 2 /WO 3 ratios, the low-temperature plasma-assisted selenization offers compatibility with the temperature-limited 3D integration process and also provides much better thickness control over a large area.