  We have measured the transition process from the high to low resistivity
states, i.e., the reset process of resistive switching based memristors based
on Ni/HfO2/Si-n+ structures, and have also developed an analytical model for
their electrical characteristics. When the characteristic curves are plotted in
the current-voltage (I-V) domain a high variability is observed. In spite of
that, when the same curves are plotted in the charge-flux domain (Q-f), they
can be described by a simple model containing only three parameters: the charge
(Qrst) and the flux (frst) at the reset point, and an exponent, n, relating the
charge and the flux before the reset transition. The three parameters can be
easily extracted from the Q-f plots. There is a strong correlation between
these three parameters, the origin of which is still under study.
