Modeling of electrical transport in Zinc Oxide varistors

The electrical transport in zinc oxide (ZnO) varistors is analyzed using microstructural material modeling. The fully three dimensional current distribution is computed by means of a nonlinear equivalent circuit model representing the assembly of current carrying grains and grain boundaries of the material. The investigation focuses on the phenomenon of current filamentation due to inhomogeneities of the varistor microstructure. Numerical results highlight the importance of 3-D percolation effects in the modeling of varistor currents as well as that of the grain bulk resistivity which so far has been neglected in previous studies.