Abstract:In order to get high-performance low voltage varistors, Cr₂O₃ doped ZnO ceramic thick films were fabricated by modified sol-gel process. The precursors were fabricated by dispersing doped-ZnO ceramic nano-powders in the sols, which were prepared by dissolving zinc acetate dihydrate into 2-methoxyethanol and stabilized by diethanolamine and glacial acetic acid and doped with a concentrated solution of bismuth nitrate, phenylstibonic acid, cobalt nitrate, manganese acetate and chromium nitrate. The results show that ZnCr₂O₄ phase can form in ZnO based ceramic films doped 1.0% (mole fraction) Cr₂O₃. Three secondary phases, such as Bi₂O₃, Zn₇Sb₂O₁₂, and ZnCr₂O₄ phases, are detected in the thick films. The Raman spectra show that the intensity and the position of Raman bands of Zn₇Sb₂O₁₂ and ZnCr₂O₄ phases change obviously with increasing Cr₂O₃ doping. The nonlinearity coefficient α of ZnO thick films is 7.0, the nonlinear voltage is 6 V, and the leakage current density is 0.7 µA/mm².

Key words: sol-gel processs; thick films; ZnO; secondary phases; low voltage varistors