NiO films grown on Pt and Nb:SrTiO3 (NSTO) substrates display filament-type and interface-type resistance switching (RS), respectively. The resistance retention studies show that these two different RSs also lead to distinct resistance evolutions. For Pt/NiO/Pt, both high and low resistance states have good retention property, demonstrating that the conducting filament is stable once it is formed. However, for Pt/NiO/NSTO/In, all resistance states show time-relaxation, and the relaxation trend depends on the polarity of the write bias. The resistive relaxation and nonvolatile features are attributed to the charge migration and electron trapping scenario, respectively.
