| Microwave dielectric ceramics is popular in the study of the dielectric materials, which include many types. With different dielectric constant, microwave dielectric ceramics play important roles in different fields. With the development of mobile communication, the microwave dielectric ceramics with low dielectric constant and high quality is the research focus in the low temperature cofiring ceramic (LTCC) technology. Many researchers devoted a great deal of effort to improve the sintering properties and dielectric properties of such materials which generally has excellent microwave dielectric properties and higher sintering temperature, in order to realize this kind of materials widely used in many areas and meet the demand of technology development.Magnesium silicate (Mg2SiO4) ceramic is a kind of typical low dielectric constant materials with microwave dielectric properties of εr=6～7, Qx f= 240000 GHz, (?)f=-60ppm/℃, however, sintering temperature of Mg2SiO4 ceramic is high and the preparation of it is difficult to be well-densified, the formation of MgSiO3 is difficult to eliminate. These characteristics limit the the performance and the use of this material in the field of LTCC technology. According to the characteristics and problems of Mg2SiO4 ceramic, a large number of related documents had been referenced, the experiment scheme was set to research the sintering properties and dielectric properties of Mg2SiO4 ceramic and used different methods to improve its properties. The main research includes:(1) Mg2SiO4 powders were synthesized by chemical method and prepared the ceramics. The good contact with inter-molecular of raw materials could be achieved by controlling the gelation process. The MgzSiO4 powers were synthesized at lower calcining temperature of 890℃, then the sintering range of Mg2SiO4 ceramic was explored. The advantages and disadvantages of this method were known by analyzing X-ray phase and microwave dielectric properties of ceramic samples. As sintered at 1475℃, the Mg2SiO4 ceramic showed good microwave dielectric properties of εr=634, Q×f=128000GHz, (?)f=-46ppm/℃(2)Based on the experiment of the preparation of non-stoichiometric Mg2SiO4 did by Chen Xiangming, the similar experiment of the preparing non-stoichiometric Mg2SiO4 (Mg/Si=2、2.025、2.04、2.05) was done in our laboratory by conventional solid-reaction method. The samples were detected by X-ray diffraction, and the pure Mg2SiO4 powers were synthesized. The influence of the phase composition on Mg2SiO4 ceramics was researched by the comparison of the properties of the samples. The results indicates that the Mg2SiO4 ceramics with Mg/Si=2.05 sintered at 1350℃ had better microwave dielectric properties of:εr= 5.67, Q× f= 64800GHz, (?)f= -40ppm/℃(3)The Mg2SiO4+xwt%LiF ceramics were prepared by conventional solid-state route. The effect of LiF addition on the sinterability, crystal structure, microstructures and microwave dielectric properties of Mg2SiO4 ceramics were investigated. The sintering temperature of the Mg2SiO4 ceramics was reduced to 940 ℃ from 1350℃ with an amount of LiF addition, which is possible due to the crystal defect as well as eutectic liquid phase. The behaviors of the εr and Q×f of Mg2SiO4 ceramics were associated with the sintering temperature and the amount of LiF. As a result, when sintered at 940 ℃, well-densified structure with excellent microwave dielectric properties of εr= 6.58, Qxf= 132900GHz, (?)f=-57ppm/℃ was obtained by addition of 4wt% LiF in Mg2SiO4 ceramics. The Mg2SiO4+4wt%LiF ceramics could cofired with Ag at 950℃.(4) The temperature coefficient of the resonant frequency ((?)f) of Mg2SiO4 ceremics was negative in a range-60ppm/℃ to-70ppm/℃, to adjust it to zero we added TiO2(rutile) with positive (?)f. Based on the repored of related articles,4wt%LiF and 24wt%TiO2 were added to the Mg2SiO4 powders in the same time and the sample contained complex phases as a result of the chemical reaction among the LiF、TiO2 and Mg2SiO4 during sintering. At the range of sintering temperature at 950℃-970℃, Mg2SiO4 ceremics doped with 4wt% LiF and 24wt% TiO2 showed stable and good microwave dielectric properties of εr= 7.2～7.6, (?)f=-0.2 ～0.6ppm/℃. |
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