Asymmetric Resistive Switching of Bilayer HfOx/AlOy and AlOy/HfOx Memristors: The Oxide Layer Characteristics and Performance Optimization for Digital Set and Analog Reset Switching

Understanding the resistance switching behavior of oxide-based memristive devices is critical for evaluating their usefulness in nonvolatile memory and/or in artificial neural networks. Oxide memristors often employ bi- or multilayered metal oxide thin films for improved performance compared to devices with a single-metal-oxide active layer. However, a clear understanding of the mechanisms that lead to improved performance for specific combinations of oxide thin films is still missing. Herein, we fabricated two types of bilayered heterostructure devices, with HfOx/AlOy and AlOy/HfOx bilayer films sandwiched between Au electrodes. Electrical responses of these bilayer devices reveal a digital set and an analog reset transition process. Single-layer HfOx and AlOy devices are also examined as control samples to validate the switching mechanism. The role of bilayered heterostructures is investigated using both the experimental and simulated results. Our results suggest that synergistic switching performance can be achieved with a proper combination of these materials, optimized structures, and proper test conditions. These results open the avenue for designing more efficient double- or multilayered memristive devices for an analog response.