ELECTRICAL-PROPERTIES OF ZNO/BI2O3 2-LAYER COMPOSITES - EFFECTS OF THICKNESS OF BI2O3 LAYER

A ZnO/Bi2O3 two-layer composite formed by rf sputtering was studied as a model of a single-grain boundary in a ceramic ZnO varistor to clarify the mechanisms of degradation and nonlinear conduction and also to realize a thin film varistor. The current-voltage characteristics and the thermally stimulated currents (TSC) were measured. The composite under a reverse bias showed highly nonlinear conduction comparable to that in an actual ceramic varistor. The breakdown voltage of ZnO/Bi2O3 two-layer specimens increased with the thickness of the Bi2O3 layer and, thus can be controlled by changing it. This can be explained in terms of enhancement of the electric field at the ZnO/Bi2O3 interface by space charge accumulation in the Bi2O3 layer and at the interface. TSC for reverse-bias poling voltage flowed in the direction of depolarization at temperatures < 120°C, but it flowed in the direction of polarization at temperatures > 120°C. This can also be explained by the space charge accumulation in the Bi2O3 bulk and at the interface, and supports the above model. © 1990 IEEE