On the bipolar resistive-switching characteristics of Al2O3- and HfO2-based memory cells operated in the soft-breakdown regime

In this article, we investigate extensively the bipolar-switching properties of Al2O3- and HfO2-based resistive-switching memory cells operated at low current down to <1μA. We show that the switching characteristics differ considerably from those typically reported for larger current range (>15μA), which we relate as intrinsic to soft-breakdown (SBD) regime. We evidence a larger impact of the used switching-oxide in this current range, due to lower density of oxygen-vacancy (Vo) defects in the SBD regime. In this respect, deep resetting and large memory window may be achieved using the stoichiometric Al2O3 material due to efficient Vo annihilation, although no complete erasure of the conductive-filament (CF) is obtained. We finally emphasize that the conduction may be described by a quantum point-contact (QPC) model down to very low current level where only a few Vo defects compose the QPC constriction. The large switching variability inherent to this latter aspect is mitigated by CF shape tuning through adequate engineering of an Al2O3HfO2 bilayer.