Optimized Method for Low-Energy and Highly Reliable Multibit Operation in a HfO₂-Based Resistive Switching Device

Here, an optimized method for energy-efficient and highly reliable multibit operation in a Au/Al₂O₃/HfO₂/TiN resistive switching (RS) device is investigated. A thin Al₂O₃ layer inserted between the top electrode and the HfO₂ RS layer in a capacitor-like RS device plays the role of an electrical resistor and modulates the external bias-dependent resistance variation behavior of the RS device. Compared to the case where a single HfO₂ layer is used, the device with a Al₂O₃/HfO₂ stacked layer shows slow and nonvolatile resistance state variation with a stepwise increase of the applied voltage, which can significantly reduce the occurrence frequency of the abnormal cases during the incremental-step-pulse-programming (ISPP) and error-check-and-correction (ECC) processes. This phenomenon reduces the number of ISPP/ECC sequences, which is advantageous for achieving energy-efficient programming in the multibit operation of an RS device. To clarify the role of the Al₂O₃ thin film layer, a comparative study is performed with an Au/HfO₂/TiN stacked device and a serially connected external load resistor. The observed behavior is consistent with that of the device with an Al₂O₃ layer. This study demonstrates that the simple insertion of an insulating layer in an RS device can facilitate reliable and energy-efficient multibit operation for future nonvolatile memory applications.