Correlation between set and reset voltages in resistive RAM cells

A positive correlation between set voltage, V_set, and the preceding reset voltage, |V_reset|, has been observed in resistive RRAM memory arrays and explained in terms of mechanisms responsible for forming and rupturing of the conductive Cu filament. This correlation can be reproduced on a single device by generating a spread in V_reset values by varying the linear voltage ramp rate. The dependence of V_reset on voltage ramp rate can be modeled by assuming that critical Joules heat is needed to trigger the rupture of the filament. Mechanisms are proposed to explain why higher |V_reset| necessarily leads to a higher V_set value during a subsequent set operation. The resulting dependence of V_set and V_reset on the voltage ramp rate during the reset operation can be used to tighten V_set and V_reset distributions, by applying low voltage ramp rates to cells with high V_set and high ramp rates to cells with low V_set values.