Role of the Electrode Material on the RESET Limitation in Oxide ReRAM Devices

Metal-oxide-based bipolar resistive switching (BRS) redox-based resistive switching memory (ReRAM) shows many outstanding properties making it of interest as an emerging nonvolatile memory. However, it often suffers from a low R-OFF/R-ON ratio, while a large ratio is desired to compensate for read margin loss due to the intrinsic variability of the ReRAM cells. Understanding of the physical processes responsible for limitations of the R-OFF and R-ON in ReRAM cells is therefore of high importance. In this paper a study on the RESET process in BRS Ta2O5-based ReRAM cells is presented. The R-OFF is found to be limited by a secondary volatile resistive switching mode that shows an opposite polarity compared to the main BRS mode. Based on results of switching kinetics measurements a physical model is proposed. It involves an oxygen exchange reaction at the metal-oxide/active electrode interface combined with a drift-diffusion induced migration of the resulting oxygen vacancy defects within the metal-oxide. Incorporation of a thin oxygen-blocking layer at the active interface allows for a suppression of the secondary switching mechanism. The improved RESET characteristic results in a strongly increased maximum R-OFF. These results provide new insights into the role of the electrode material on the RESET process in BRS ReRAM cells.