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We describe abnormal dual bipolar resistive switching events in simple Pt/Ta2O5-x/TiOxNy and Pt/Ta2O5-x/TiN matrices in which the typical switching directions (SD) are initially clockwise (CW). The negative difference region in a high resistance state before reaching the typical 'CW set' process enables the SD transition to a counterclockwise direction. It thereby emphasizes the occurrence of a highly stable secondary bipolar resistive switching curve. The origin of two different switching modes is described by adapting a bias-dependent oxygen ion accumulation and depletion process at TiOxNy and TiN electrode interfaces and by performing various structural analyses. [ABSTRACT FROM AUTHOR]

We examine multilevel (ML) resistance switching properties in a Pt/Ta2O5-x/TiOxNy/TiN/Ta2O5-x/Pt matrix, in which two bipolar resistive switching elements Pt/Ta2O5-x/TiOxNy and TiN/Ta2O5-x/Pt are anti-serially and electrically connected. The ML features for the three assigned, distinguishable resistance states are clearly identified by using an I-V device operation scheme, indicating that the middle TiN and TiOxNy electrodes are crucial for adjusting ML resistance states. Experimental observations suggest that the ML switching events rely on electrically induced oxygen ion drifts at interfaces between the top/bottom Ta2O5-x and middle TiN/TiOxNy layers. [ABSTRACT FROM AUTHOR]