Unipolar Resistive Switching Effects Based on Al/ZnO/P⁺⁺-Si Diodes for Nonvolatile Memory Applications

Al/ZnO/P⁺⁺-Si diodes exhibit typical unipolar resistive switching behaviors. The electroforming-free characteristics are observed after annealing the ZnO thin film at 400°C in air. The ON/OFF ratios of the resistance are in the range of 10⁴–10⁵ at a very low operation voltage of 0.1 V, and the devices show good endurance characteristics of over 400 cycles with negligible reduction. Finally, the memory mechanisms of the diodes are proposed on the basis of the current-voltage and resistance-voltage results. These results indicate that Al/ZnO/P⁺⁺-Si devices have potential applications in nonvolatile memory devices.