Improved resistive and synaptic switching performances in bilayer ZrOx/HfOx devices

In this study, we investigated the resistive switching (RS) characteristics of ZrOx/HfOx bilayer-based resistive random-access memory (RRAM) devices. A 1.5-nm-thick HfOx layer was deposited by atomic layer deposition (ALD) between the ZrOx layer and TiN electrode to enhance the RS. Compared to the ZrOx single-layer device, the bilayer device exhibited a lower high resistance state (HRS) current, which improved endurance and reduced energy consumption due to the insulating HfOx layer. In addition, a DC endurance of 300 cycles and strong retention characteristics (10,000 s) were achieved in the bilayer device. Furthermore, the multi-level cell (MLC), potentiation, and depression characteristics were evaluated to demonstrate the suitability of the Ti/ZrOx/HfOx/TiN device for use as a neuromorphic device. With regard to potentiation and depression, various pulse schemes were employed to improve the asymmetric conductance changes for neuromorphic system applications.