FIG. 3C illustrates a series of IV curves of embodiments of a memory device including a programmable metallization cell, such as previously illustrated and described in FIG. 1. These IV curves reflect varying numbers of set and reset operations being carried out on the programmable metallization cell. In the set and reset operations, for example, a voltage is applied across the bottom electrode 106 and the metal layer 112, and the amount of current over the metallization cell varies as a function of the applied voltage, which dictates to what extent a conductive bridge 304 is present. Thus, in the set operation, the applied (e.g., positive) voltage induces formation of the conductive bridge 304 in the dielectric layer 110, whereas in the reset operation, the applied (e.g., negative) voltage removes at least a portion of the conductive bridge 304 from the dielectric layer 110 (or vice versa). Thus, the programmable metallization cells show typical bi-stable I-V curves demonstrating bipolar switching for the cells.