Insight into distribution and switching of resistive random-access memory filaments based on analysis of variations in memory characteristics

Abstract

Two hypotheses were formulated to validate a multi-filament model (MFM) as a mechanism for the cycle-to-cycle dispersion of Vset in resistive random-access memory. The first is that the probability of Δ(1/Vset) > 0, P[Δ(1/Vset) > 0], increases with the number of filaments in one memory cell, Nfila, and decreases with increasing switching cycle, n. Here, Δ(1/Vset) is the difference between the inverse of the set voltages after the n-th and (n + 1)-th reset processes [1/Vset(n) − 1/Vset(n + 1)]. Thus, Vset decreases with increasing Nfila and increases with n. The second hypothesis is that the probability of Δ(1/R) > 0, P[Δ(1/R) > 0], agrees with P[Δ(1/Vset) > 0], assuming that vset depends on d in the MFM. Here, Δ(1/R) = 1/Rn − 1/Rn + 1, and Rn, vset, and d represent the resistance in the high-resistance state after the n-th reset process, the set voltage of each filament, and the thickness of a gap between the electrode and the end of the filament, respectively. The validity of these two hypotheses was confirmed by measuring the dependence of P[Δ(1/Vset) > 0], P[Δ(1/R) > 0], and the mean value of Vset on both n and the length of the perimeter for Pt/NiO/Pt structures into which filaments were introduced by etching the NiO layer.