Preparation of zinc oxide/metal oxide multilayered thin films for low-voltage varistors

Zinc oxide/metal oxide multilayered composite thin film varistors have been fabricated by the radio-frequency (RF, 13.56 MHz) sputtering method and the electrical properties of the films were investigated. After the Au electrode was formed on a quartz substrate by vacuum evaporation, zinc oxide (ZnO) layer was deposited by the RF sputtering with ZnO target at room temperature, Ar partial pressure of 2.5 Pa, O 2 partial pressure of 2.5 Pa and RF power of 50 W. Praseodymium oxide (Pr 6 O 11 ) layer was formed on the ZnO layer by the RF sputtering with Pr 6 O 11 target at room temperature, Ar pressure of 5 Pa and RF power of 80 W. The upper Au electrode was formed on the Pr 6 O 11 layer by vacuum evaporation. The conduction mechanism of the ZnO/Pr 6 O 11 double-layered thin film varistor was discussed on the basis of the measurements of voltage-current ( V - I ) and capacitance-voltage ( C - V ) characteristics and thermally stimulated current (TSC). From the results of V - I and C - V measurements, it was found that a depletion region was formed in the ZnO layer close to the interface between ZnO and Pr 6 O 11 layers.