We propose a simple system to investigate the influence of microstructure on the resistive switching behavior via bi-crystal CuO nanowires. CuO nanowires are prepared by thermally oxidizing transmission electron microscopy copper grids in air. Single-crystal and bi-crystal CuO nanowires can be selectively obtained by adjusting the temperature. The devices made of single-crystal nanowires follow Ohm's law, with a high resistance, within the sweeping voltage range of 0-4 V, whereas those made of bi-crystal nanowires exhibit threshold and memory resistive switching behaviors, which are due to the enrichment of copper ions in the grain boundaries of bi-crystal CuO nanowires providing sources for the formation of conductive filaments. Moreover, the bi-crystal nanowires with higher defect densities in grain boundaries result in lower threshold voltages of switching from high to low resistance states. The threshold resistive switching behavior can be turned into memory resistive switching behavior by increasing the thickness of the device electrodes or reducing the compliance current. The endurance of memory resistive switching through the pre-defined conduction paths in the single grain boundaries of bi-crystal CuO nanowires is at least 1000 cycles without any performance deterioration. This high reliability is ascribed to the single conductive filaments.
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