In this paper, the resistive switching characteristics in a Cu/HfO(2):Cu/Pt sandwiched structure is investigated for multilevel non-volatile memory applications. The device shows excellent resistive switching performance, including good endurance, long retention time, fast operation speed and a large storage window (R(OFF)/R(ON)>10(7)). Based on the temperature-dependent test results, the formation of Cu conducting filaments is believed to be the reason for the resistance switching from the OFF state to the ON state. By integrating the resistive switching mechanism study and the device fabrication, different resistance values are achieved using different compliance currents in the program process. These resistance values can be easily distinguished in a large temperature range, and can be maintained over 10 years by extrapolating retention data at room temperature. The integrated experiment and mechanism studies set up the foundation for the development of high-performance multilevel RRAM.

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The ZrO2 films with Au nanocrystals embedded (ZrO2:nc-Au) are fabricated by e-beam evaporation, and the self-rectifying effect in the Au/ZrO2:nc-Au/n+ Si sandwich structure is investigated. Self-rectifying resistive switching characteristics are obtained when the resistive memory is switched to low-resistance state (LRS). It is found that the Schottky contact at the Au/ZrO2 interface limits charge injection under reverse bias, while under forward bias the current is limited by space charge, resulting in a rectification of 7×102 under ±0.5 V at LRS, which enables the resistive memory to alleviate the cross-talk effect without additional switching elements in crossbar structure arrays. This self-rectifying resistive switching is believed to occur at a localized region and explained by a proposed model.