Synthesis of zinc oxide varistors with a breakdown voltage of three volts using an intergranular glass phase in the bismuth–boron–oxide system

Zinc oxide (ZnO) crystals joined by using an intergranular glass phase were investigated in order to develop surge filters for low-voltage applications and to clarify the current transport mechanism through the junction. The junctions having a ZnO/glass/ZnO sandwich structure were synthesized by using an interfacial glass phase of the Bi–B–O system. A highly nonlinear current–voltage curve was obtained for the ZnO/glass/ZnO junction with Co-doped ZnO single crystals, and the current through the junction at the breakdown voltage was proportional to the 30th power of the bias voltage. Dielectric measurements revealed that a double-sided depletion layer was formed at the interface, and the observed high nonlinearity was ascribed to the corresponding potential barrier formed at the interface.