Tri-level resistive switching characteristics and conductive mechanism of HfO<sub>2</sub>/NiO<sub>x</sub>/HfO<sub>2</sub>

With the extensive integration of portable computers and smartphones with "Internet Things" technology, further miniaturization, high reading/writing speed big storage capacity are required for new generation non-volatile memory devices. Compared traditional charge magnetoresistive memory, resistive random access memory(RRAM) based on transition metal oxides is one promising candidates due to its low power consumption, small footprint, stack ability, fast switching multi-level capacity.<br>Inspired by excellent characteristics NiO HfO<sub>2</sub>, NiO<sub>x</sub> films were deposited magnetron sputtering Pt<111> layer polycrystalline HfO<sub>2</sub> film, respectively. Their microstructures, conductive mechanisms studied. X-ray diffractometer data shows <111> preferred orientation film but <100> layer. photoelectron depth profile Ni2p core level reveals that mixture oxygen-deficient Ni<sub>2</sub>O<sub>3</sub>. NiO<sub>x</sub>(111) show bipolar switching(RS) a clockwise current-voltage(<i>I-V</i>) loop, ratio resistance resistance(<i>R</i><sub>H</sub>/<i>R</i><sub>L</sub>) only~10, endurance also poor. The NiO<sub>x</sub>(200)/HfO<sub>2</sub> exhibits RS counterclockwise <i>I-V</i> loop. <i>R</i><sub>H</sub>/<i>R</i><sub>L</sub> greater than 10<sup>4</sup>, about 10<sup>4</sup> cycles, retention time exceeds s. In initial stage, HfO<sub>2</sub>/NiO<sub>x</sub>(200)/HfO<sub>2</sub> similar bi-level stack. However, in middle last stages, it's curves gradually evolve into tri-level "two-step Set process" positive voltage region, showing potential applications multilevel nonvolatile devices brain-like neural synapses. Its states follow relationship Ohmic conduction (<i>I</i>∝<i>V</i>), while intermediate state dominated space-charge-limited-current mechanism (<i>I</i>∝<i>V</i><sup>2</sup>). phenomena attributed coexistence oxygen-vacancy filaments NiO<sub>x</sub>(200) space limited current upper film.