Cycle-to-Cycle Intrinsic RESET Statistics in HfO₂-Based Unipolar RRAM Devices

The statistics of the RESET voltage (VRESET) and the RESET current (IRESET) of Pt/HfO2/Pt resistive random access memory (RRAM) devices operated under unipolar mode are analyzed. The experimental results show that both the distributions ofIRESETandVRESETare strongly influenced by the distribution of initial resistance in the ON state (RON), which is related to the size of the conductive filament (CF) before RESET. By screening the statistical data into different resistance ranges, both the distributions ofIRESETandVRESETare shown to be compatible with a Weibull model. Contrary to previous reports for NiO-based RRAM, the Weibull slopes of theIRESETandVRESETare demonstrated to be independent ofRON. This is an indication that the RESET point, defined in this letter as the point of maximum current, corresponds to the initial phase of CF dissolution. On the other hand, given that the scale factor of theVRESETdistribution (VRESET63%) is roughly independent ofRON, the scale factor of theIRESET(IRESET63%) is inversely proportional toRON. This is analogous to what was found in NiO-based RRAM and it is consistent with the thermal dissolution model of RESET. Our results highlight the intrinsic link between the SET and RESET statistics and the need for controlling the variation of ON-state resistance to reduce the variability of the RESET voltage and current.