Fig. 2
Current-density-decomposition as a precursor to electroforming in memristors. a An i-sweep (blue) on a previously un-operated crosspoint tantalum oxide memristor clearly showing reversible current-controlled NDR. A v-sweep (red) following the i-sweep on the same device, revealing non-volatile switching. Positive v-sweep was applied first, with the abrupt non-volatile switching occurring at a voltage value of VS. Inferred stable (iH and iL) and unstable (iU) current levels are marked on the experimental data. iH was extrapolated from the total electrode resistance since this is the only internal current compliance capable of arresting transient current overshoots. (a, inset) schematic of the crosspoint device structure. b Lateral oxygen concentration (CO) map of a different but nominally identical device to that shown in a after several non-volatile switching events, obtained by transmission synchrotron x-ray spectromicroscopy. The ring-like feature (indicated by a black arrow) is caused by a radial oxygen concentration gradient. Dashed lines mark the edges of the electrodes. c A simulated temperature (T) profile for a decomposed current density calculated from the measured current/voltage levels during operation, with a common scale displayed in c. The common scale bar in b is 2 µm. Additional analysis shown in Supplementary Fig. 6
