Use of a Dielectric Glass to Join Dielectric Ceramics for Microwave Filters

Joining of ceramics with glasses has been widely used for artificial teeth, solid oxide fuel cells, electrical devices, high temperature ceramic filters, structural ceramic components for aeronautic engineering, nuclear reactors, and other applications. This study aimed to explore the possibility of using a dielectric glass to connect a dielectric ceramic resonator to a dielectric ceramic support, in order to make miniaturized microwave filters characterized by higher temperature and environmental stability and low dielectric loss. A mixed powder having Bi2O3-SiO2-Al2O3-MgO-ZnO-CaO glass as a matrix and SiO2-Al2O3-MgO as a ceramic filler was used to join the dielectric ceramic resonators made of the CaTiO3-NdAlO3-Al2O3 system to the dielectric ceramic supports made of the ZnO-TiO2-Al2O3-MgO system. In spite of the strong interfacial bonding obtained, microcracks were observed in the joined bodies, suggesting that not only the dielectric loss of the bonding layer but also the match of the thermal expansion coefficients of the components to be joined should be carefully considered and tailored.