Variability Improvement of TiO<sub><i>x</i></sub>/Al<sub>2</sub>O<sub>3</sub> Bilayer Nonvolatile Resistive Switching Devices by Interfacial Band Engineering with an Ultrathin Al<sub>2</sub>O<sub>3</sub> Dielectric Material

Variability control over the resistive switching process is one of the key requirements to improve the performance stability of the resistive random access memory (RRAM) devices. In this study, we show the improvement of the variability of the resistive switching operation in the TiO<sub><i>x</i></sub>/Al<sub>2</sub>O<sub>3</sub> bilayer RRAM devices. The achievement is based on the thickness engineering of the Al<sub>2</sub>O<sub>3</sub> layer. A thick Al<sub>2</sub>O<sub>3</sub> dielectric actively takes part to control the resistive switching behavior; on the contrary, the ultrathin layer of Al<sub>2</sub>O<sub>3</sub> behaves as the tunnel barrier in the structure. At lower voltage, the low resistance state conductions follow the trap-assisted tunneling and Fowler–Nordheim tunneling for the thick and thin Al<sub>2</sub>O<sub>3</sub> RRAMs, respectively. Finally, the variation control in device forming, SET voltage distribution, high resistance state, low resistance state, and resistance ratio is achieved with the TiO<sub><i>x</i></sub>/Al<sub>2</sub>O<sub>3</sub> bilayer RRAM devices by interfacial band engineering with an ultrathin Al<sub>2</sub>O<sub>3</sub> dielectric material.