  In recent years, resistive RAM often referred to as memristor is actively
pursued as a replacement for nonvolatile-flash memory due to its superior
characteristics such as high density, scalability, low power operation, high
endurance, and fast operating speed. However, one of the challenges that need
to be overcome is the loss of retention for both ON- and OFF-states; the
retention loss. While various models are proposed to explain the retention loss
in memristors consisting of a switching layer, in this paper, we propose that
the nucleation of clusters made of electrical charges, charge-clusters, in the
switching layer acts as a potential root cause for the retention loss. The
nucleation results from localized electric-field produced intermittently during
cyclic switching operations. We use the phase-field method to illustrate how
the nucleation of charge-clusters gives rise to the retention loss. Our results
suggest that the degree at which the retention loss arises is linked to the
number of cyclic switching operations since the probability at which nucleation
centers form increases with the number of cycle switching operations, which is
consistent with a range of experimental findings previously reported.
