PROCESSING-INDUCED RESISTIVE BARRIERS IN ZNO VARISTOR MATERIAL

Evidence is presented for the origin of high-resistivity barriers at c ertain interfaces in high-field varistor materials. The barriers give rise to terrace contrast which can be observed using remote electron b eam induced current imaging in the SEM. It is proposed that these inte rfaces, which are often associated with a thick intergranular layer of a compositionally distinct bismuth rich oxide, are relicts of the pow der structure and correspond to agglomerate surfaces. It is suggested that the presence of these resistive surfaces ultimately limits the cu rrent that can flow at breakdown.