Multiple Switching Modes of NiO_x Memristors for Memory-Driven Multifunctional Device Applications

Multiple building components with a variety of switching capabilities are required to implement memory-driven parallel computing architecture and multifunctional device applications. In this regard, there is a high demand for implementing multiple switching modes based on only one active material in a simple device form. In this study, we demonstrated the ability of a solution-processable two-terminal Ag (or Al)/NiOx/ITO memristor that exhibits triple-switching characteristics depending on the different voltage regimes. Notably, the device exhibits an analog bipolar switching behavior under a low programming voltage (≤1.0 V), enabling essential synaptic functions, as well as a high recognition accuracy of 87.42% in a single-layer neural network. After the electroforming process to form the oxygen vacancy-based conductive filament in the NiOx layer, the device concurrently exhibited digital bipolar switching and unipolar threshold switching behaviors at different voltage regimes without compliance current. These three switching characteristics are related to the transition of dominant switching mechanisms depending on the operating scheme, which is investigated using various material and chemical characterization techniques during switching, including cross-sectional scanning transmission electron microscopy, atomic force microscopy, ultraviolet photoelectron spectroscopy, and X-ray photoelectron spectroscopy.