Modification And Co-firing With Copper Electrode Of BiNbO₄ And ZnTiO₃ Microwave Dielectric Ceramic

With the development of mobile communication, it is necessary to make the devices made of microwave dielectric ceramics more subminiature and convenient, and LTCC (Low Temperature Co-fired Ceramic) technique makes it possible. In order to satisfy the need of LTCC, microwave dielectric ceramics are developing to low sintering temperature and high frequency. For the sake of lower cost, Copper (Cu) is being used as electrode materials to replace expensive metals such as Pt,Pd,Au,Ag and so on. However, Cu is easy to be oxidized under ambient atmosphere, so it's necessary to be co-fired with ceramics in protective atmosphere.BiNbO4 system ceramic is a kind of dielectric material at low temperature and could be used in kinds of chip components because of its excellent microwave properties. ZnTiO3 ceramic has excellent dielectric properties and can be sintered at 1100℃. In this paper, BiNbO4 and ZnTiO3 were prepared by solid reaction method and their properties were studied in this paper. The effect of sintering aids and atmosphere on phase composition, sintering properties, microstructure and dielectric properties of microwave ceramics was investigated, and the relationship among the parameters was also explained. And so was the co-firing of the optimized ceramic and copper electrode.It is hard for BiNbO4 ceramics to be sintered with high density and BiNbO4 could be slightly reduced under low oxygen partial pressure atmosphere, forming oxygen vacancies and other defects in the lattices. CuO was added into BiNbO4 ceramics to lower sintering temperature; and MnO2 was added to restrain the decomposition of BiNbO4 under N2 atmosphere because Mn element can replace Nb in lattice and form oxygen vacancies to reduce the ones produced by atmosphere. The results show that BiNbO4 ceramics can be sintered at a low temperature which is 920℃with the aid of CuO and also have better microwave properties sintered under N2 atmosphere:εr=43.65, Q×f=3463GHz. At the same time, the reduction reaction of BiNbO4 can be restrained by the addition of MnO2. BiNbO4 ceramic modified by combined additives with 0.2wt% CuO and 0.5wt% MnO2 was co-fired with copper electrode under N2 atmosphere. A new phase was discovered at the interface and the ceramic was reduced into metal bismuth (Bi), which concentrated in the electrode area. Though BiNbO4 ceramic is an excellent dielectric properties material, it couldn't be used in multi-layer microwave equipments. There are some defects in ZnTiO3 ceramic, such as the relatively high sintering temperature, poor thermal stability in narrow temperature range. In this work, sintering temperature was lowered by adding of Zn-B-Si glass. Thermal stability was improved by the addition of MnO2 because the radius of Mn2+ and Zn2+ is close and can form (Zn, Mn)TiO3 solution. The results show that with proper ratio of these additives (2wt% Zn-B-Si glass and 0.2wt%MnO2), the ceramic can be sintered at 870℃with dielectric constant value 27-29 and quality factor value 22000GHz. There was no new phase and element confusion didn't occur at the interface when the ceramic was co-fired with copper electrode.