Resistive switching and synaptic learning performance of a TiO₂ thin film based device prepared by sol–gel and spin coating techniques

A resistance random access memory device based on TiO₂ thin films was fabricated using a sol–gel spin and coating techniques. The composition, surface morphology, and microstructure of the TiO₂ films were characterized using x-ray diffraction, Raman spectroscopy, scanning electronic microscopy, and transmission electron microscopy, respectively. The fabricated Al/TiO₂ film/fluorine-doped tin oxide device exhibited electroforming-free bipolar resistive switching characteristics with a stable ON/OFF ratio higher than 300. The performance of the endurance cycling was still good after 100 direct sweeping cycles. A retention time of no less than 10⁴ s was confirmed. A switching mechanism is systematically discussed based on the test results, and space-charge-limited current was found to be responsible for the switching behavior. Multilevel memory performance was realized in the as-fabricated devices. The synaptic performance was investigated by applying consecutive positive (0–2 V) and negative (0 to −1.6 V) voltage sweeps. The fabricated devices were found to exhibit 'learning-experience' behavior. (paper)