Abstract
A ZnO-Bi2O3 two-layer composite film formed by rf sputtering was studied as a model of a single grain boundary in a ZnO varistor. The current-voltage (I-V) characteristics, capacitance-voltage (C-V) characteristics and thermallystimulated currents (TSC) were measured. The ZnO-Bi203 two-layer films showed highly non-linear conduction. A negative charge and associated potential barrier at the ZnO-Bi2O3 interface controlled the conduction. The breakdown voltage was also affected by the thickness of the Bi2O3 layer. This and TSC experiments showed that space charge was responsible for the thickness dependence. This system can be used as a thin-film varistor and a humidity sensor because of its high non-linearity coefficient (60-100), and high sensitivity and fast response to humidity.
