| The rapid progress of high-frequency wireless communication technology, increasingly high demand for the miniaturization, integration and high-performance of electronic components, also put forward higher requirements for the electronic packaging technology. LTCC technology provided the realization of the miniaturization and high-density packaging of the components, which is the most promising technology to achieve the integration of electronic components and the substrate in the field of high frequency applications. With the in-depth research and development of low-temperature sintering of LTCC ceramic and electrode paste, the LTCC substrate is increasingly widespread application in the electronic packaging. To accelerate the study of LTCC substrate and antenna materials not only socially, but also thought to improve the design and development of electronic components in the future a better platform to bring economic benefits,In this thesis, the microwave dielectric properties of the silicate material system applied to the LTCC substrate were studied, and improved their microwave dielectric properties and sintering temperature, prepared excellent LTCC substrate and microwave antenna ceramics; discuss the effects of intrinsic loss related to the crystal structure and extrinsic loss due to the preparation process on the microwave dielectric properties of the silicate ceramic; analysed the low-temperature sintering mechanism of liquid-phase sintering, and explored the compatibility of the system with Ag; explore the dielectric loss characteristics of silicate base microwave ceramic material and the silicate base microwave ceramic material modification theory, discussed the modification theory of the dielectric constant and dielectric loss, and compared with the experimental data analysis.Silicate ceramics is a important part of inorganic non-metallic materials, their microwave dielectric properties are extremely good, applied extremely extensive in microwave dielectric ceramics domain, such as:MgSiO4and Zn2SiO4have the extremely prominent high quality factor in all the microwave ceramic material have been reported. But their extremely high sintering temperature and poor thermal stability severely limit them as LTCC substrate materials in the practical application. According to the Lichnetecker rule, in this paper we select CaTiO3with positive temperature coefficient τf=+859ppm/℃as a compensation function material to get adjustable τf value. When the addition amount of CaTiO3increase from6.0to10.0mol%, the τf values of the (1-x)Mg2SiO4-xCaTiO3composite ceramic increase to14.2from-27.1ppm/℃. When x=0.08and0.09, the (1-x)Mg2SiO4-xCaTiO3ceramic samples have close to zero τf values-3.0and6.8ppm/℃. Compared with the Q×fvalues of Mg2SiO4-CaTiO3ceramics, the Q×f values and changing trends of Zn2SiO4-CaTiO3ceramics are the same. When the addition amount of CaTiO3from0increases to7.0mol%, the τf values of (1-x)Zn2SiO4-xCaTiO3composite ceramic increase to28.6from-61.0ppm/℃. When x=0.05, the (1-x)Zn2SiO4-xCaTiO3has close to zero τf value is0.8ppm/℃. And in the process of the analysis of experimental results, we find the addition of CaTiO3has certain effect of low sintering temperature.According to the restriction condition the silicate ceramic sintering temperature are higher than the LTCC ceramic sintering temperature of950℃, first use of Li+alternative Zn2+to reduce the sintering temperature, and research the microwave dielectric properties of the ceramic after ion substitution, to explore the feasibility of the ways to reduce the sintering temperature and research the τf through doping CaTiO3. Studies have found that after Li+alternative Zn2+, the Q×f values of Li2yZn(2-y)Si04(y=0.5,0.8,1) and sintering temperatures are fall, especially when y=1. When x=0.17,(1-x)Li2ZnSiO4-xCaTi03ceramic samples has close to zero τf value-1.3ppm/℃. But the sintering temperatures are more than950℃. At last, we successfully reduced the sintering temperature of three composite ceramics by means of adding low melting point mixed oxide Bi2O3-Li2CO3-H3BO3(BLB), Li2CO3-H3BO3and zinc boron (ZB) glass as low temperature sintering additives to950℃below, meeting the basic requirements of the application of LTCC, and a deep research on the relations of sintering additives addition and microwave dielectric properties:When the addition amount of ZB glass is25.0wt.%, the microwave dielectric properties of the0.75Li2ZnSiO4-0.25CaTiO3ceramic samples are εr=9.5, Q×f=11,800GHz, τf=-5.2ppm/℃; when the addition amount of BLB is12.0wt.%, the microwave dielectric properties of the0.91Mg2SiO4-0.09CaTiO3ceramic samples are εr=7.7, Qxf=11,300GHz, τf=-5.0ppm/℃; when the L12CO3-H3BO3quantity added to4.0wt.%, the microwave dielectric properties of the0.95Zn2SiO4-0.05CaTiO3ceramic samples are εr=7.1, Q×f=26,300GHz, τf=-4.5ppm/℃. We also found that0.95Zn2SiO4-0.05CaTiO3composite ceramic and Ag electrode have good chemical compatibility, can be co-fired, they can be used as the LTCC materials in the microwave antenna and substrate. The paper studied the modified theory of the silicate base microwave ceramic materials, discussed the modification theory of relative dielectric constant, dielectric loss and resonance frequency temperature coefficient, and compared with the experimental data analysis. From the positive valence cations replace, doping new phase, add sintering additives and change the sintering temperature four aspects made a thorough research to microwave ceramic material modification theory, obtained some research achievements. Finally, powder sintering principle are discussed. The results show that the unit volume inside ion electricity price is higher, more dipoles, the microwave ceramic relative dielectric constant is bigger, high ion replacement low state ion, the craft on the grain growth fully, density as far as possible to achieve saturation, and improve the material density is effective methods of relative dielectric constant improvement. For polycrystalline ceramics, attenuation constant y related to the loss caused by grain boundary, void, dislocation, periodic defect, impurity atom and vacancy. Lichnetecker rule is an important formula for microwave dielectric properties of multiphase coexistence composite microwave dielectric ceramics, has the guidance meaning to the dielectric property modification mechanism of composite ceramic. Sintering mechanism of the sintering process has automatic happen trend, from the view of thermodynamics point, powder sintering is the reducing process of system free energy, the reducing of free and lattice variable energy is the main driving force of sintering. The distribution of liquid phase under the sintering temperature will play a decisive role to material sintering densification. In different sintering period, reasonable choice sintering process can make the grain size reasonable proportion, uniform, reduce porosity, be helpful for the material dielectric performance optimization of microwave ceramic. |
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