Annealing effect of Al₂O₃ tunnel barriers in HfO₂-based ReRAM devices on nonlinear resistive switching characteristics

In this study, we demonstrate the enhancement of the nonlinear resistive switching characteristics of HfO₂-based resistive random access memory (ReRAM) devices by carrying out thermal annealing of Al₂O₃ tunnel barriers. The nonlinearity of ReRAM device with an annealed Al₂O₃ tunnel barrier is determined to be 10.1, which is larger than that of the ReRAM device with an as-deposited Al₂O₃ tunnel barrier. From the electrical characteristics of the ReRAM devices with as-deposited and annealed Al₂O₃ tunnel barriers, it reveals that there is a trade-off relationship between nonlinearity in low-resistance state (LRS) current and the ratio of the high-resistance state (HRS) and the LRS. The enhancement of nonlinearity is attributed to a change in the conduction mechanism in the LRS of the ReRAM after the annealing. While the conduction mechanism before the annealing follows Ohmic conduction, the conduction of the ReRAM after the annealing is controlled by a trap-controlled space charge limited conduction mechanism. Additionally, the annealing of the Al₂O₃ tunnel barriers is also shown to improve the endurance and retention characteristics.