  A new statistical approach has been developed to analyze Resistive Random
Access Memory (RRAM) variability. The stochastic nature of the physical
processes behind the operation of resistive memories makes variability one of
the key issues to solve from the industrial viewpoint of these new devices. The
statistical features of variability have been usually studied making use of
Weibull distribution. However, this probability distribution does not work
correctly for some resistive memories, in particular for those based on the
Ni/HfO2/Si structure that has been employed in this work. A completely new
approach based on phase-type modeling is proposed in this paper to characterize
the randomness of resistive memories operation. An in-depth comparison with
experimental results shows that the fitted phase-type distribution works better
than the Weibull distribution and also helps to understand the physics of the
resistive memories.
