Resistive switching characteristics and mechanism of bilayer HfO2/ZrO2 structure deposited by radio-frequency sputtering for nonvolatile memory

In this study, a bilayer HfO2/ZrO2 thin film structure was deposited by radio frequency sputtering at room temperature (RT) to investigate the resistive switching (RS) characteristics, mechanism as well as their reproducibility. Bilayer HfO2/ZrO2 structured device > 10(3) DC switching cycles at RT, and > 10 ON/OFF ratio. The RS uniformity and mechanism were evaluated by Gaussian data fitting and distributions of oxygen vacancies (V(o)s) in the HfO2 and ZrO2 layers through X-ray photo electron spectroscopy (XPS) analysis, respectively. Because of higher thermal conductivity (2.7 Wm(-1)K(-1)) and lower Gibbs free energy (Delta G degrees = -1100 kJ/mol) of ZrO2 layer as compared to those of HfO2 layer (1.1 Wm(-1)K(-1), Delta G degrees = -1010.8 kJ/mol), an easier reduction and oxidation of filaments took place by exchanging oxygen ions with each other (ZrO2/HfO2). A V(o)s-based fila-mentary model has been proposed to explain RS mechanism. Furthermore, a current transport mechanism is noted be based on Schottky emission in the high field region of the high resistance states (HRS).