Resistive Switching and Neuromorphic Computing in Metal/Nb:SrTiO$_3$: Mechanisms, Interface Physics, and Charge Transport

Abstract: Resistive switching (RS) in Nb-doped SrTiO$_3$ (Nb:STO) based memristive devices has attracted sustained interest in information processing and novel computing because of its forming-free operation, large on/off ratio, and gradual conductance modulation. Metal/Nb:STO Schottky junctions have emerged as a prototypical system for understanding RS mechanisms. Despite more than two decades of research, the physical origin of RS remains controversial, with proposed mechanisms including charge trapping and detrapping, oxygen vacancy migration, tunneling, interfacial redox reactions, and conductive filament formation. In this review, we examine these seemingly competing mechanisms and show that many experimental observations can be understood within a unified framework centered on the formation and evolution of an extrinsic interfacial layer at the metal/Nb:STO interface. We discuss how interface quality and defect-mediated processes, including proton incorporation, oxygen vacancy dynamics, and tunneling, govern Schottky barrier modulation and RS behavior. We further summarize how fabrication conditions, measurement protocols, and aging influence the interface formation and switching characteristics. This review establishes an integrated picture of M/Nb:STO heterojunctions and provides design principles for reliable oxide memristive devices through interface and defect engineering in M/Nb:STO and M/oxide/Nb:STO systems.