Engineering the threshold switching response of Nb₂O₅-Based memristors by Ti doping

Two terminal metal-oxide-metal devices based on niobium oxide thin films exhibit a wide range of non-linear electrical characteristics that have applications in hardware-based neuromorphic computing. In this study, we compare the threshold-switching and current-controlled negative differential resistance (NDR) characteristics of cross-point devices fabricated from undoped Nb2O5 and Ti-doped Nb2O5 and show that doping offers an effective means of engineering the device response for particular applications. In particular, doping is shown to improve the device reliability and to provide a means of tuning the threshold and hold voltages, the hysteresis window, and the magnitude of the negative differential resistance. Based on temperature-dependent current-voltage characteristics and lumped-element modelling, these effects are attributed to doping-induced reductions in the device resistance and its rate of change with temperature (i.e., the effective thermal activation energy for conduction). Significantly, these studies also show that a critical activation energy is required for devices to exhibit NDR, with doping providing an effective means of engineering the current-voltage characteristics. These results afford an improved understanding of the physical mechanisms responsible for threshold switching and provide new insights for designing devices for specific applications.