2010 Volume 18 Pages 103-107
Metal oxides have recently renewed the interests due to the resistive memory switching phenomena based on the electrically stimulated change of the resistance of a metal-insulator-metal (MIM) memory cell, frequently called resistive switching RAM (ReRAM). The ReRAM devices are expected to be future nonvolatile memory devices used as alternatives to the current flash memory technology. The nonvolatile memory characteristics have been intensively investigated using the thin film forms, and excellent memory characteristics have been demonstrated. However, to achieve high-density memory and improve the performance of the devices, it is crucial to reduce the size of the cells beyond the limitation of current lithographic length scales. In addition, details of resistive memory switching mechanisms, including the switching types (bipolar and/or unipolar), have not been well understood. Thus the scaling down of the cell structures is strongly desired not only for understanding the underlying memory mechanisms within a confined nanoscale but also for improving the device characteristics of ReRAM. The bottom-up approach using self-assembled nanowires is a promising solution for scaling down the size of memory devices. Thus, single crystalline oxide nanowires formed via a self-assembling fashion would be a candidate for overcoming the above issues. However difficulties in both fabricating nanowires composed of metal oxides and evaluating electrically the insulative oxide nanowires have impeded investigation of the resistive memory switching events in oxide nanowires. Here we have demonstrated nonvolatile bipolar resistive memory switching in heterostructured oxide nanowires. The self-assembled oxide nanowires are expected to open up opportunities to explore not only the detailed nanoscale mechanisms in resistive memory switching but also next-generation nanoscale nonvolatile memory devices with the potential for high-density device integration and improved memory characteristics.