LOW-FIRE BISMUTH-BASED DIELECTRIC CERAMICS FOR MICROWAVE USE

We have investigated dielectric properties of several bismuth-based ceramics at microwave frequencies. BiNbO4 ceramics containing CuO and V2O5, had a high Q value of Q=4260 (at 4.3 GHz), epsilon = 43, and tau(f)=+38 ppm/degrees-C. In the Bi2O3-CaO-Nb2O5 system, Bi18Ca8Nb12O65 composition had a high dielectric constant of epsilon = 59, Q=610 (at 3.7 GHz), and tau(f)=+24 ppm/degrees-C. The crystal structure of this composition is considered to be an ordered structure based on the body center tetragonal cell (a = 0.377, c = 0.542 nm). Furthermore, by substituting Zn for Ca, epsilon increased and tau(f) changed to negative values. In the composition of 45.75BiO3/2-21.75(Ca0.725Zn0.275)O-32.5NbO5/2, excellent properties of epsilon=79, Q=360 (at 3.3 GHz), and tau(f)=+1 ppm/degrees-C were obtained. As all the above ceramics can be sintered below 950-degrees-C, they are applicable to multilayer microwave devices with Ag inner conductors.