Multi-level resistive write-once-read-many memory device based on CdSe/ZnS quantum dots and ZnO nanoparticles

Multi-level three-state resistive memory devices were fabricated using CdSe/ZnS quantum dots (QDs) and ZnO nanoparticles (NPs). Poly-vinyl carbazole (PVK) was added to the synthesized CdSe/ZnS QDs with a core/shell structure to form a stronger charge storage layer in the QDs. The use of PVK enables the design-stage control of the state current and write voltage, along with improvement of the on/off ratio. All thin films were fabricated by the solution spin coating method. Additional quantum wells can be produced using ZnO NPs, which enables the multistate functionality. We optimized the process conditions with respect to PVK and ZnO NPs, and confirmed that the PVK concentration was optimized at 2.5 wt%. In addition, the optimized memory device had an on/off ratio of 1.43 × 10⁶ at 0.5 V, the write voltages were 2.2 V and 3.5 V, and the current values in the 0, 1 and 2 states were 4.7 × 10⁻⁹ mA, 2.1 × 10⁻⁵ mA, 1.0 × 10⁻¹ mA, respectively. The fabricated device demonstrated high stability and reliability through 20 repeat cycles, and displayed a retention time of 80 h.