氧化鋅積層變阻器的微結構與電性間之關係研究

Abstract

The performances of ceramics depend strongly on their microstructures. Recently, ZnO-based multilayer varistors (MLVs) have become available. In the present study, AgPd inner electrodes are used in the multilayered ZnO-based varistors. The microstructure of ZnO-based MLV is affected by sintering temperature, dwell time, layer thickness, additives and so on. The relationships between microstructures and electrical properties of the ZnO-based multilayer varistors are therefore investigated. The results indicate that the breakdown voltage (VB) and nonlinear coefficient (α) are directly controlled by the layer thickness after sintering at 1000°C for 60 min. Although the average size of ZnO grains within MLVs increases with the increasing sintering temperature and time, the effects of secondary phases and discontinuity of AgPd electrodes also affect the electrical properties profoundly. A pyrochlore phase is formed due to the interaction between Bi-rich liquid and spinel phase during heating and cooling stages. The Bi2O3–rich liquid phase can penetrate into the inner electrode and reacts with AgPd to form PdBi2O4. Discontinuity of AgPd electrodes induces the increase of the breakdown voltage and decrease of nonlinear properties. The optimum microstructure and nonlinear ohmic characteristic of the ZnO-based MLV with layer thickness of 10 μm can be obtained by sintering at 1000°C for 60 min.