Study On Low-temperature Sintering And Properties Of BaWO₄ Microwave Ceramics

In the 5G communication market,microwave dielectric ceramics play an indispensable role.In order to achieve the purpose of small signal transmission delay and low loss,low-dielectric and low-loss ceramic materials have attracted more attention.With the development of IC technology following Moore’s Law,the size of electronic products is getting smaller,resulting the multi-layer and integration of devices has become the mainstream technology.Low-temperature co-firing ceramics（LTCC）technology provides a solution for the development of miniaturized devices.The melting points of Ag and Cu are around 960～1000℃.In order to achieve co-firing with electrodes such as Ag and Cu to satisfy the requirements of LTCC technology,the sintering temperature of ceramic materials is lower than 950℃.At the same time,the high Q×f value and the near-zeroτ_f value are another advantage of LTCC ceramic materials.With a dielectric constant of 8 and a quality factor of 57,500 GHz,BaWO₄ has a very broad application prospect.Therefore,based on BaWO₄ ceramics,this thesis used different glass to reduce sintering temperature,TiO₂ was added to adjustτ_fvalue,and then the phase structure and microwave dielectric properties were analyzed through different testing methods.Finally,the ceramic of BaWO₄ doped with LBBC glass was used as dielectric material to prepare microstrip patch antenna.The detailed research contents were introduced as follows:1.The different contents of LBS glass was firstly doped to BaWO₄ ceramics to reduce the sintering temperature,then the dielectric properties of ceramics were measured.Combined with DSC curve and image sintering analysis,LBS glass had a melting point of 693.1℃.XRD and SEM results proved that the doped phase was still BaWO₄ phase.As the temperature increased from 800℃ to 950℃,the dielectric properties of ceramics dramatically decreased.Comprehensive performance analysis showed that when the LBS glass content was 2 wt.%,the best microwave dielectric properties can be got at 800℃ for 4h:ε_r=8.11,Q×f=37,375 GHz,τ_f=-61.2 ppm/℃.2.Researched on the effect of BaWO₄ ceramics with different dosages of LBBC glass.Combined with DSC curve and image sintering analysis,it can be determined that the softening point of the glass was around 742.8℃.XRD and SEM results proved that it was still BaWO₄ crystal phase.As the temperature increased from 850℃ to 900℃,the dielectric properties of ceramics showed a decreasing trend.Experiments showed that BaWO₄-1 wt.%LBBC ceramic had the optimal microwave dielectric properties:Q×f=58,855 GHz,ε_r=8.33 andτ_f=-61.43 ppm/℃ when sintered at 850℃.3.TiO₂ was selected to adjust theτ_f value of BaWO₄-1 wt.%LBBC.TiO₂ has a large positiveτ_fvalue（+450 ppm/℃）,which can compensate for the negative one.By adding a certain amount of TiO₂,theτ_f can be adjusted to zero.Through XRD and SEM analysis,it can be seen that with the addition of TiO₂,the second phase of TiO₂ gradually appeared.The BaWO₄ and the TiO₂ crystal phase coexisted.But due to the second phase,the dielectric constant of the composite ceramic system had a certain increase,while the Q×f value had a certain degree of reduction.Combine temperature serialization and content serialization analysis,when the sintering temperature was 950℃,BaWO₄-1 wt.%LBBC-9 wt.%TiO₂ had excellent performance:ε_r=12.05,Q×f=17,488 GHz andτ_f=-1.2ppm/℃.4.The sintering kinetics of BaWO₄ ceramic systems doped with LBS glass and LBBC glass was studied here.A thermal dilatometer was used to measure the thermal shrinkage curve of the green embryo samples,and several groups of constant heating rates were set.Based on the Arrhenius equation model,the sintering activation energy（E_a）of the two groups of samples was fitted and calculated.The E_a of ceramic doped LBS glass was 300.22 k J mol^-1,the E_a of ceramic doped LBBC glass was 345.81 k J mol^-1.5.BaWO₄-1 wt.%LBBC ceramic material was select to design a microstrip patch antenna.The results of HFSS simulation and experiments measured showed that the radiation efficiency of the antenna was about 80% and the gain was about 3d B.