Sputtering technique was applied to fabricate nearly perfect double Schottky barrier as a model of a single grain boundary in a ceramic varistor. Donor density of ZnO and interface states were controlled in the ZnO(Al)/ZnO(Co)/PrCoO_x/ZnO(Co)/ZnO(Al) structure. In this multilayered thin-film varistor, the symmetric voltage-current (V-I) characteristics (breakdown-voltage-6V, α=31) in bias directions were obtained. From the deep-level transient spectroscopy (DLTS) measurements, the interface state of 0.61eV was detected.