Study On Low-temperature Sintering Of Ca_O-Li₂OSm_2O3TiO₂ Ceramics With Multiple Sintering Additives

With the rapid progress in mobile telecommunication and wireless local area network, it has been strongly required that the related components become small-sized, usable at higher frequency range, integration, and low cost. In order to meet these requirements, design and fabrication of multilayer chip microwave components using low temperature co-fired ceramics technology has attracted many attentions. From the view points of cost cutting and environment protection, the dielectric materials with excellent dielectric properties and good compatibility with inner electrode such as Ag and Cu in co-firing were required for LTCC applications.High K CaO-Li₂O-Ln₂O₃-TiO₂ system ceramics exhibit low dielectric loss and adjustable and near zero temperature coefficients of resonant frequency, which enable it one of the promising materials for the fabrication of small-sized component in microwave communications. So 16CaO-9Li₂O-12Sm₂O₃-63TiO₂ (CLST) and ceramics with excellent dielectric properties among CaO-Li₂O-Ln₂O₃-TiO₂ system were selected as the research objects in this dissertation. The effects of BaCu(B₂O₅)-ZnO, Bi₂ZnB₂O₇(BZB)on the sintering behavior, microstructure and dielectric properties of CLST ceramics were investigated. The sintering mechanism and densification process of low temperature fired CLST ceramics were also studied by SEM, TEM and HRTEM. The tape-casting properties of CLST with BCB slurry are studied. The main research results are as follows:In CLST ceramics, adding both BCB and ZnO together as sintering additives results in lower sintering temperature. And the excellent dielectric properties can be kept as well. Such asεr=69.53,tanδ=0.0259,Ï„f = 8ppm /°C. Using the newly synthetized multiple oxide Bi₂ZnB₂O₇ as sintering additives can also reduce the sintering temperature, and keep the good dielectric properties of ceramics. Such asεr=78.11,tanδ=0.006,Ï„f = 12.36ppm /℃.In the process of study on low teperature sintering mechanism, the densification mechanism of low temperature sintered CLST ceramics was discovered through the combination of SEM, TEM, HRTEM and XRD analysis methods. It is that the low temperature sintering mechanism of CLST ceramics with ZnO, BaCu(B₂O₅) and Bi₂ZnB₂O₇ is a kind of active liquid sintering. In the densified CLST ceramics with 4wt% of BaCu(B₂O₅)-1% of ZnO or 6 wt% of Bi₂ZnB₂O₇ ,a 1.5-2.0nm thickness of amorphous phase formed by solidification of the liquid of sintering additives between lattices and some sintering additives existing as amorphous object in trigeminal grains or along the boundary between grains can be seen intuitively through TEM and HRTEM. Actually, the above-mentioned fusant can promote the densification of CLST ceramics in sintering.As for the study on tape casting of BCB-CLST ceramic, we got the better composition of the tape casting slurry through NDJ-79 rotational viscometer and other analysis methods. It is that slurry with a combination solvent of EtOH and DMAC(1:3 by volume), a 0.8wt% concentration of dispersant, binder 8wt%, R(the ratio of plasticizer to binder) 0.6 and solid content 50wt% shows better flowing properties and is easier to be tape cast.