Switching characteristics of W/Zr/HfO₂/TiN ReRAM devices for multi-level cell non-volatile memory applications

In this paper, we report multi-level cell (MLC) switching characteristics of resistive random access memory devices with a W/Zr/HfO₂/TiN stack. A multi-step forming technique was implemented in this work which efficiently suppressed the forming current overshoot and allowed device switching at a low set/reset voltage and current. Four distinct resistance states, achieved by controlling the reset stop voltages, showed excellent endurance. Write/read/erase energy values for different states were also calculated. Amongst four MLC states, it was found that the lowest resistance state of three distinct high-resistance states was prone to failing over time under constant voltage stress. (paper)