Low Temperature Sintering Of CaZrO₃, ZnAl₂O₄and Zn₂SiO₄Microwave Dielectric Ceramics

Microwave dielectric ceramic is a new kind of functional ceramics developedrapidly inrecent years, which used to be microwave components, such as resonators,filters, dielectric antennas, medium guided wave circuits and so on. It is widely used inmobile communications, satellite communications and military radar and other aspects.In recent years, the rapid development of microwave communication technologiesrequiring communication terminal as miniaturization, integration, multi-functional,lowcost. In order to meet these requirements,use the low temperature co-fired ceramicstechnology to design multilayer chip microwave components and make themicrowave dielectric ceramics co-fired with low melting point of metal electrode suchas Ag or Cu become a hotspot.CaZrO3ceramics have a very good practical value as capacitors and dielectricresonator at microwave conditions because of its suitable dielectric constant and lowdielectric loss. However, its sintering temperature is particularly high, which greatlyincreases the cost of production in the practical application. In the lowdielectric ceramic systems, ZnAl2O4and Zn2SiO4microwave dielectric ceramicshave a low dielectric constant and ultra-high quality factor, is widelyused in microwave devices such as circuit packaging and dielectric resonator antennas.But the sintering temperature of ZnAl2O4ceramic is particularly high, and whileZn2SiO4ceramic achieve low-temperature sintering, the microwave dielectricproperties are deteriorated very badly, so the usability of them are too badly. Therefore,CaZrO3, ZnAl2O4and Zn2SiO4microwave dielectric ceramics were selected as theinvestigate objects in this dissertation. The ZnO-B2O3-SiO2(ZBS)glass、Li2O-B2O3-SiO2(LBS)glass were added CaZrO3and ZnAl2O4ceramics by solid phase mixmethod, the CuO was added Zn2SiO4ceramics by liquid coating. The effects ofdifferent sintering aids on phase compositions, sintering characteristics,microstructures and dielectric properties of ceramic were investigated. The sintering mechanism and densification process of low temperature fired Zn2SiO4ceramics werealso studied. The main research results are as follows.1. The good microwave dielectric properties of εr=30, Q×f=15000GHz, τf=-26.5×10-6/℃were obtained in the pure CaZrO3ceramics sintered at1550°C for3h.The sintering temperature of CaZrO3ceramics can be lowered by the addition of ZBSglass and LBS glass.(1) The sintering temperature of CaZrO3ceramics can be lowered from1550oCto1000oC with the addition of ZBS glass. The optimum microwave dielectricproperties of εr=25, Q×f=8584GHz, τf=-45×10-6/℃were obtained in the15wt%ZBS-CaZrO3ceramics sintered at1000°C for3h.(2) The sintering temperature of CaZrO3ceramics can be lowered from1550oCto900oC with the addition of LBS glass. The optimum microwave dielectricproperties of εr=28, Q×f=9359GHz, τf=-10×10-6/℃were obtained in the9wt%LBS-CaZrO3ceramics sintered at900°C for3h.2. The good microwave dielectric properties of εr=8, Q×f=50200GHz, τf=-63×10-6/℃were obtained in the pure ZnAl2O4ceramics sintered at1600°C for4h.The effectsof LBS glass on sintering characteristics and microwave dielectric properties ofZnAl2O4ceramics were investigatived.The sintering temperature of ZnAl2O4ceramics can be lowered from1650oC to1250oC with the addition of LBS glass. The optimum microwave dielectric propertiesof εr=7.6, Q×f=24000GHz, τf=-58×10-6/℃were obtained in the6wt%LBS-ZnAl2O4ceramics sintered at1250°C for3h.3. The excellent microwave dielectric properties of εr=6.3, Q×f=58482GHz, τf=-42×10-6/℃were obtained for the pure Zn2SiO4ceramics sintered at1350°C for3h.The CuO was added Zn2SiO4ceramics by solid phase mix method and liquid coatingmethod. The sintering temperature of Zn2SiO4ceramics can be lowered by the additionof CuO.The sintering temperature of Zn2SiO4ceramics can be lowered from1350oC to1000oC with the addition of CuSO4by liquid coating. The optimum microwavedielectric properties of εr=6.8, Q×f=53803GHz, τf=-47×10-6/℃were obtained for the1.0mol/L CuSO4solution added Zn2SiO4ceramics sintered at1000°C for3h.4. The densification mechanisms of low temperature fired Zn2SiO4ceramics wasstudied according to the results of XRD, SEM and TEM.The result shows that theZn2SiO4ceramics doped by CuO by liquid coating densified through liquid phase sintering.