Low-Fire Bismuth-Based Dielectric Ceramics for Microwave Use

Abstract

We have investigated dielectric properties of several bismuth-based ceramics at microwave frequencies. BiNbO 4 ceramics containing CuO and V 2 O 5 , had a high Q value of Q =4260 (at 4.3 GHz), ε=43, and τ f =+38 ppm/°C. In the Bi 2 O 3 -CaO-Nb 2 O 5 system, Bi 18 Ca 8 Nb 12 O 65 composition had a high dielectric constant of ε=59, Q =610 (at 3.7 GHz), and τ f =+24 ppm/°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, ε increased and τ f changed to negative values. In the composition of 45.75BiO 3/2 -21.75(Ca 0.725 Zn 0.275 )O-32.5NbO 5/2 , excellent properties of ε=79, Q =360 (at 3.3 GHz), and τ f =+1 ppm/°C were obtained. As all the above ceramics can be sintered below 950°C, they are applicable to multilayer microwave devices with Ag inner conductors.