Influence of annealing on the resistive switching properties of YBa2Cu3O7−x/Nb:SrTiO3 heterostructures

YBa2Cu3O7−x (YBCO) films are deposited on Nb:SrTiO3 (NSTO) single-crystal substrates via pulsed laser deposition to fabricate YBCO/NSTO heterostructures. Various annealing processes are utilized to modulate the electrical properties and oxygen vacancy (Vo) concentration of the YBCO films. At high voltages, the heterostructure exhibits a pronounced counterclockwise bipolar resistive switching (RS) effect, characterized by abrupt resistance transitions that confirm the conductive filament mechanism. The RS behavior is attributed to a nonsuperconducting interfacial layer formed at the YBCO/NSTO interface due to lattice distortion or interface defect. Within this layer, Vo-based conductive filaments are formed and subsequently ruptured under an applied bias. As YBCO superconductivity degrades (correlating with increased Vo concentration), the heterostructure consequently requires higher Set/Reset voltages and shows reduced current. Notably, in samples with severely degraded superconductivity (high Vo concentration), low-voltage bias triggers Vo migration to the interface, inducing a severe insulator phase transition in the interfacial YBCO layer (or aggravating the thickness of the nonsuperconducting layer) and resulting in a unconventional clockwise bipolar RS effect. These findings provide insights into RS mechanisms, oxide-based memory applications, and multilevel storage technologies.