Study On Preparation,Structure And Properties Of Low-Temperature Co-Fired Borate Microwave Dielectric Ceramics

In recent years,in order to adapt to the development of wireless communication equipment and meet the requirements of high-performance microwave devices,low temperature co-fired ceramic（LTCC）technology emerged as the times require.It has become a key technology to realize the miniaturization,high integration,multi-function,lightweight,low cost and high performance of microwave devices.LTCC materials have low dielectric constant（?_r<10）,high quality factor（Q×f≥5000 GHz）,a near zero resonance frequency temperature coefficient（τ_f）and low firing temperature（≤950℃）.More recently,ultra-low temperature co-fired ceramic（ULTCC）materials have been developed on the basis of LTCC materials.Compared with traditional LTCC,ULTCC is more energy-saving and environmental friendly,short production cycle,and can integrate with semiconductors,base metals and even plastics.Therefore,the research and development of ultra-low permittivity（?_r）,high quality factor（Q×f）and near zero resonance frequency factor（τ_f）materials for ULTCC is of great scientific significance,strategic significance and application value.In this paper,three kinds of low temperature co fired microwave dielectric ceramics were prepared by solid phase sintering.The sintering characteristics,crystal structure,microstructure and microwave dielectric properties of the materials were tested by DSC,FT-IR,XRD,SEM,EDS and network vector analyzer.The results are as follows:1.Cu O-Zn O-B₂O₃（CZB）ceramic system:the results show that Li₂O can reduce the sintering temperature.The main crystalline phases of the ceramics are Zn（BO₃）₂and Cu B₂O₄.The precipitated Li₂Cu O₂and Li₂B₄O₇phases are directly related to the change of Cu O/Zn O molar ratio.With the changes of Cu O/Zn O molar ratio,the Q×f values increase from 8800 GHz to 38093 GHz,τ_fvalues change from-7.57ppm/℃to-1.24ppm/℃and the obtained ceramics can be co-fired with metal Cu electrode,which meets the performance and application requirements of LTCC materials.2.Cu O-Zn O-B₂O₃-Li₂O（CZBL）glass ceramic system:the results show that with the increase of sintering temperature,Zn B₄O₇,Cu B₄O₇and Li₂Cu B₄O₈crystalline phases are successively precipitated from the matrix glass,but the content of crystalline phase decreases with the further increase of sintering temperature.When the sintering temperature is 620℃,CZBL glass ceramic has the best microwave dielectric properties:?_r=3.33,Q×f=17724 GHz,τ_f≈0 ppm/℃.The co-firing of CZBL glass ceramic with metal Ag and Al electrodes is realized,which meets the requirements of ULTCC materials.3.CZBL glass/ceramic（Al₂O₃,Mg Al₂O₄and Si O₂）composite system:XRD results show that CZBL glass reacts with Al₂O₃ceramic to form Cu₂Al₆B₄O₁₇.With the increase of Al₂O₃mass,the Q×f values are in the range of 7860～38557GHz.After sintered at640℃,the glass/ceramic composite containing 10wt%Al₂O₃possesses the excellent microwave dielectric properties:ε_r=3.79,Q×f=38557GHz,τ_f≈0 ppm/℃.It is found that CZBL glass does not react with Mg Al₂O₄ceramics.When the sintering temperature is660℃,the best microwave dielectric properties ofε_r=4.18,Q×f=24029GHz andτ_f≈-5.22 ppm/℃are obtained for the composite with 10wt%Mg Al₂O₄.For CZBL glass/Si O₂ceramic composites,Si O₂will enter CZBL glass as a network former during the sintering process,and has an impact on the microwave dielectric properties of the composite.When the sintering temperature is 720℃,the CZBL glass/Si O₂ceramic composite with 20wt%Si O₂exhibits the best microwave dielectric properties:ε_r=3.3,Q×f=11642 GHz andτ_f≈-9.7ppm/℃.The above research results display that CZBL glass/ceramic（Al₂O₃,Mg Al₂O₄and Si O₂）composites are expected to be used in the field of low temperature co-fired ceramic.