Improved Performance of the Al₂O₃-Protected HfO₂–TiO₂ Base Layer with a Self-Assembled CH₃NH₃PbI₃ Heterostructure for Extremely Low Operating Voltage and Stable Filament Formation in Nonvolatile Resistive Switching Memory

Herein, we report intriguing observations of an extremely stable nonvolatile bipolar resistive switching (NVBRS) memory device fabricated using HfO2–TiO2 topologically protected by Al2O3 as a stacked base layer for a CH3NH3PbI3 (MAPI) electrolyte layer sandwiched between Ag and fluorine-doped tin oxide (FTO) electrodes. MAPI has been successfully synthesized by a rapid microwave–solvothermal (MW-ST) method within 10 min at 120 °C without requiring any inert gas atmosphere using low-cost precursors and solvents. Subsequently, MAPI powders are dissolved in aprotic solvents (DMF/DMSO = 8:2), and a spin-coated thin film is allowed to recrystallize upon annealing at 120 °C via a solution-based nanoscale self-assembly process. The fabricated memory device with the Ag/MAPI/Al2O3/TiO2-HfO2/FTO configuration shows an enhanced resistance ratio of 105 for >104 s at an extremely lower operating voltage (SET +0.2 V, RESET −0.2 V) when compared to that of the pristine MAPI device (±1 V, 102, 104 s). We show that the memory device also exhibits a remarkable endurance of ≥3500 cycles due to the Al2O3 robust coating on the HfO2–TiO2 layer, facilitating prompt heterojunction formation. Thus, the adopted innovative strategies to prepare structurally and optically stable (∼1.5 years) MAPI under high-humid conditions could offer enhanced performance of NVBRS memory devices for medical, security, internet of things (IoT), and artificial intelligence (AI) applications.