The Study Of Low-temperature Sintering Microwave Dielectric Ceramic Based On Tape-casting Technics

With the rapid development of mobile communication, it is the main trend to realize the further miniaturization of microwave components and devices. The primal method was to use high dielectric constant microwave dielectric ceramics and the method has obvious limit. The design of multilayer structure based on the low temperature cofired ceramics technology(LTCC for short) can reduce the size of components effectively, which was the significant way to realize components' miniaturization, integration, high reliabilties and low costs. The key of LTCC technology was to cofire ceramics with Ag or Cu eletrode, and it has been widely studied all over the world. However, on account of the disjunction among material properties, components design and preparations, most of the material systems, which are hard to prepare slurry because of their sintering aids, are difficult to put into practice.According to the tape casting requirements of LTCC preparation process, the sintering aids were designed and optimized in this paper. Na₂O ZnP ZnO-B₂O₃-SiO₂ (ZBS) PbO-BO₃-SiO₂( PBS)B₂O₃ were used as sintering aids and their influences were systematically studied on the sintering characteristics, phase constitution, microstructure and mcirowave dielectric properties of BiNbO₄ and CaO-B₂O₃-SiO₂ ceramics. The slurry and green sheet characteristics were also studied. The research results are as below:1. Low temperature sintering CaO-B₂O₃-SiO₂ ceramicsZBS, PBS and Na₂O/ZnO, as sintering aids for CaO-B₂O₃-SiO₂, can help to reduce sintering temperature about 100℃ to 300℃ and improve the composition of main phase CaSiO₃. Comparely, the addition of Na₂O/ZnO has more obvious effect on reducing sintering temperature than ZBS and PBS. The ceramics are denser and the grain size is more homogeneous with Na₂O/ZnO addition. ZnO addition can decrease the sintering temperature to 1000℃ and has insignificant effects on ceramics dielectric properties. Na₂O addition, though it can decrease the sintering temperature to 950℃, decreases the Q f value sharply because small radius Na+ is easy to move to damage the CaSiO₃ structure and generate ion conductance at high temperature.The ceramics with 2mol%ZnO substitution of CaO, sintered at 1000 for 2h, can obtain the good microwave dielectric properties. CaO-B₂O₃-SiO₂ ceramic slurry is uniform with low viscidity; and the powder particles of green sheets are evenly distributed with no aggregation appeared.2. Low temperature sintering BiNbO₄ ceramicsZB, ZBS and B₂O₃, as sintering aids for BiNbO₄, all can help to reduce ceramic sintering temperature and the temperature of phase transformation to get α -BiNbO₄ Under the same conditions, ZB wets and packs the solid particles more uniformly than ZBS or B₂O₃, and ceramics with uniform grain size, compact structure and good dielectric properties can thus be obtained. The addition of ZBS and B₂O₃ has a big influence on the dielectric constant and Q value of BiNbC>4. The BiNbO₄ ceramics with lwt%ZB addition sintered at 880°C for 4h obtained properties as: er=42, tg5<1.5x10-3. BiNbO₄ ceramic slurry is uniform with low viscidity, and the powder particles of green sheets are evenly distributed with no aggregattion appeared.In this study, sintering aids were designed and optimized to acquire microwave dielectric ceramics of CaO-B₂O₃-SiO₂ and BiNbO₄ with good dielectric properties. The two kinds of ceramics can be suitable for tape-casting process, therefore, set a foundation on the mass production of the LTCC microwave dielectric ceramic .