Multilevel programming in Cu/NiOy/NiOx/Pt unipolar resistive switching devices

The application of a NiOy/NiOx bilayer in resistive switching (RS) devices with x > y was studied for its ability to achieve reliable multilevel cell (MLC) characteristics. A sharp change in resistance brought about by sweeping the voltage, along with an improved on/off ratio (> 103) and endurance (104) were achieved in the bilayer structure as compared to the single NiOx layer devices. Moreover, it was found that nonvolatile and stable resistance levels, especially the multiple low-resistance states of Cu/NiOy/NiOx/Pt memory devices, could be controlled by varying the compliance current. All the multilevel resistance states of the Cu/NiOy/NiOx/Pt bilayer devices were stable for up to 500 consecutive dc switching cycles, as compared to the Cu/NiOx/Pt single layer devices. The temperature-dependent variation of the high and low resistance states of both the bilayer and single layer devices was further investigated to elucidate the charge conduction mechanism. Finally, based on a detailed analysis of the experimental results, comparisons of the possible models for RS in bilayer and single layer memory devices have also been discussed.