Abstract
Abstract. 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.
Highlights
zinc oxide (ZnO) varistors are ceramic semiconductor materials that are characterized by a highly nonlinear electrical response
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
Summary
ZnO varistors are ceramic semiconductor materials that are characterized by a highly nonlinear electrical response. Their resistance drops remarkably with increasing voltage. The grain boundary resistances determine varistor currents for voltages in the nonlinear breakdown voltage region of the electrical characteristics as well as in the linear pre-breakdown region. Almost all of the models so far presented in the literature operate in 2-D planar geometry They are based either on a Cartesian mesh representation (Vojta et al, 1996; Wen and Clarke, 1993) or on a Voronoi-type tessellation of the varistor sample (Bartkowiak et al, 1996a; Zhao et al, 2007). We present a simulation example featuring the current filamentation phenomenon using a 3-D modeling approach for a realistic varistor sample
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