Study On Low-temperature Sintering Of 0.95MgTiO₃- 0.05CaTiO₃ Microwave Dielectric Ceramics

As new functional electronic materials, microwave dielectric ceramics were widely used as microwave components in satellites, modern mobile communications and radio-controlled fields, for example, in capacitor, filter and resonators and so on. In recent years, with the development of Electronic and Information technology, integration,miniaturize and low cost of microwave devices is increasingly required. Multilayer co-fired ceramics (MLCC) is a solution to satisfed this requirement. Multilayer co-firing technology requires that ceramics could be co-fired with internal conductors such as Ag or Cu. Even though several types of dielectric materials with good microwave dielectric properties have been reported, most of them could only be well sintered at above 1300°C. Therefore, it is important to lower the sintering temperatures of microwave dielectric materials to co-fire with Ag or Cu and without deteriorating the microwave dielectric properties.MgTiO₃–CaTiO₃ (hereafter referred to as MCT) ceramics is well known as the material for temperature compensating type capacitor and dielectric resonator. Especially, it has been became research focus in today's academic circles because it has advantages such as rich of raw materials and low cost. The material is made of a mixture of magnesium titanate (MgTiO₃:εr～17, Q×f value～160,000 at 7 GHz andÏ„f value～-55ppm/°C) and calcium titanate (CaTiO₃:εr～170, Q×f value～3600 at7GHz andÏ„f value～800ppm/°C).With the ratio Mg:Ca=95:5, 0.95MgTiO₃–0.05CaTiO₃ (hereafter referred to as 95MCT) ceramics givesεr～20, Q×f～56,000 at 7GHz, and a zeroÏ„f value. However, it required sintering temperatures as high as 1450°C. Many researchers made efforts to study the microstructures and the microwave dielectric properties of the 95MCT ceramics by adding various additives or varying the processing.The melting point of BaCu(B₂O₅)(BCB) is 850°C. In recent years, it has been used as sintering additive to lower the sintering temperatures of microwave dielectric ceramics such as BaSm₂Ti₄O₁₂(BST), Ba(Zn_1/3Nb_2/3O₃(BZN) and BaTi4O9, it could not only lower sintering temperature but also keep good properties. However, the influence of BaCu(B₂O₅) additive on the sintering behavior and dielectric properties of 95MCT ceramics has not been reported in our related literatures. This paper reviewed the development and study of microwave dielectric ceramics, based on experiment of low-temperature sintering about other dielectric ceramic, 95MCT ceramic was choosed as research object. In this work, the effects of BiVO4, BCB and BCB+ZnO additive contents on the sintering temperature, microstructure and dielectric properties of 95MCT ceramics were studied.1. Dielectric properties of 95MCT doped with BiVO₄ The results suggested that BiVO₄ addition could lower the sintering temperature but not change phase of 95MCT. The 95MCT ceramics with 5wt% BiVO₄ addition sintered at 1100°C for 3h showed:εr of 18.8, Q value of 186.7273.2. Dielectric properties of 95MCT doping with BCB The sintering temperature of BaCu(B₂O₅)-doped 0.95MgTiO₃–0.05CaTiO₃ ceramics can be lowed to 1100°C and effectively inhibited the formation of second phase MgTi2O5. The microwave dielectric Properties of 0.95MgTiO₃–0.05CaTiO₃ Ceramics with 3wt% BaCu(B₂O₅) additions sintered at 1100°C for 3h showedεr of 22.9, Q·f of 25,000GHz(7GHz),Ï„f of-3.3ppm/°C.2. Dielectric properties of 95MCT doping with BCB and ZnOThe sintering temperature of 95MCT could be reduced from 1450°C to 1050°C and co-fired with Cu. It is also effectively inhibited forming the second phase MgTi2O5 by added ZnO. The dielectric properties of 0.95MgTiO₃–0.05CaTiO₃ ceramics with 3wt% BaCu(B₂O₅) and 1wt%ZnO additions sintered at 1050°C for 3h showedεr of 20.5,Q·f of 21,133GHz(7GHz),Ï„f of-10.1ppm/°C.