Microwave Dielectric Properties Of Zinc Borate Glass-based Low-temperature Sintered Ceramics

In order to realize further progress in high frequency wireless communication technologies, system solution development and hardware technology development will play the important role in greater multifunctionality, higher performance, and sub-miniaturization of mobile terminal devices. Mobile terminal devices are being equipped with multiple functions, in order to curb the resluting increases in circuit size, it is desirable to build the various high frequency fuctions and passive components into the substrate iself. Low temperature co-fired ceramics are regarded as a promising future technology for the integration of components and substrates for high frequency applications.The low sintering, microstructure and microwave dielectric properties of zinc borate glass-based low temperature sintered ceramics were studied. The phase structures and microstructures of specimens were characterized by X-ray diffraction (XRD), scanning electron microscope and differential thermal analysis. The dielectric properties of specimens were measured by parallel-plate resonator method.The linear shrinkage of 3Z2B glass-Al₂O₃ composites exhibited a typical one-stage densification behavior. XRD patterns showed that a new crystalline phase, ZnAl₂O₄ spinel, formed during densification, indicating that certain chemical reaction took place between the 3Z2B glass matrix and the alumina filler. Meanwhile, several zinc borate phases, including 4ZnO·3B₂O₃, crystallized from the glass matrix. Both of the reaction product phase and crystallization phases played an important role in improving the microwave dielectric properties of composites. The optimal composition sintered at 850-950℃showed excellent microwave dielectric properties:εr = ⁵.0, Q·fo = ⁸000 GHz, andτf = ^-32 ppm/K at ⁷.0 GHz.Zinc borate glass/ceramic composites for low temperature co-fired ceramics (LTCC) were prepared from the mixtures of zinc borate glass, Al₂O₃ and TiO2. The effects of the ratio of TiO2 to Al₂O₃ on the phase evolution and dielectric properties of composites were investigated. The results showed that the content of ZnAl₂O₄ , TiO2 and 4ZnO·3B₂O₃ in the composites increases, decreases,remains essentially unchanged respectively with the decrease of the ratio of TiO₂ to Al₂O₃. The dielectric constant and dielectric loss of these composites increase significantly with the increase of the ratio of TiO₂ to Al₂O₃. A near-zero temperature coefficient of resonant frequency of the composite was obtained when the content of TiO2 was 8 wt%.