Impact of ultrathin Al₂O₃ interlayers on resistive switching in TiO_x thin films deposited by atomic layer deposition

TiO_x and TiO_x/Al₂O₃/TiO_x sandwiched thin films were fabricated by using atomic layer deposition at 250 °C. As compared to single-layered TiO_x, TiO_x/Al₂O₃/TiO_x sandwiched thin films exhibit stable resistive switching with a substantially improved OFF/ON ratio and elongated endurance. Essentially, the embedded ultrathin Al₂O₃ interlayer will suppress the crystallization of amorphous TiO_x and thus reduce the channels for current leakage. As a result, the resistive switching properties are substantially enhanced. The TiO_x/Al₂O₃/TiO_x sandwiched thin films with the Al₂O₃ thickness of more than 2 nm show stable unipolar resistive switching, and the rupture and reformation of conductive filaments mainly occur at the top interface between Al₂O₃ and TiO_x layers. A physical model is proposed to understand the resistive switching behaviors.