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 (Pr6O11) layer was formed on the ZnO layer by the RF sputtering with Pr6O11 target at room temperature, Ar pressure of 5 Pa and RF power of 80 W. The upper Au electrode was formed on the Pr6O11 layer by vacuum evaporation. The conduction mechanism of the ZnO/Pr6O11 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, if was found that a depletion region was formed in the ZnO layer close to the interface between ZnO and Pr6O11 layers. (C) 1998 Elsevier Science Ltd. AII rights reserved.