Study On LTCC Microwave Ceramic Materials And Application Of Niobate Of Middle Permittivity

The rapid popularization of digital information in the world is inseparable from the high-speed transmission of data,which also promotes the development of microwave communication technology.In order to meet the requirements of miniaturization and integration of microwave devices,low temperature co-fired ceramic（LTCC）technology came into being.High-performance microwave dielectric ceramics provide more options for LTCC substrate materials in the high-frequency region.Therefore,the study of ceramic materials is necessary.In this thesis,ZnTiNb2O8 ceramics are taken as the research object to improve its microwave dielectric properties by introducing sintering aids,ion substitution and compounding.By means of various characterization methods and related theories,the changes of microwave dielectric properties of ceramic samples after modulation were systematically investigated.The specific research work is as follows.Firstly,Li₂WO₄ with low melting point is used as a sintering aid to composite with Li₂WO₄ ceramics.Although an appropriate amount of ZnTiNb2O8 can promote the growth of grains and improve the dielectric loss to a certain extent,the effect of reducing sintering is not obvious.The results show that the dielectric properties of 0.98ZnTiNb2O8-0.02Li₂WO₄ at 975℃ ceramic samples are relatively good:εr=31.71,Q × f=24940 GHz,τf=-49 ppm/℃.Then,based on LBSCA glass as a sintering aid,the influence of single ion（Cu2+,Co2+,Ni2+and Sn4+）substitution on microwave dielectric properties of ZnTiNb2O8 ceramics at low temperature.Appropriate amount of substitution can improve the density of the samples,but excessive amount will lead to abnormal grain growth and deteriorate the dielectric loss of the samples.The theoretical analysis of B-site bond valence of main phase（ZnTiNb2O8）can be used to explain for the change of sample temperature coefficient.The experimental results show that the optimum temperature of the substituted samples is 950℃.The dielectric properties of Zn0.96Ni0.04TiNb2O8+0.8 wt%LBSCA samples are as follows:εr=31.89,Q×f=42232 GHz,τf=-47.56 ppm/℃.Better dielectric properties were obtained when the substitution amount of Ni2+and Cu2,is 0.02 mol%:εr=30.91,Q×f=42138 GHz,τf=-48.79 ppm/℃and εr=34.17,Q × f=46526 GHz,τf=-48.36 ppm/℃.Compared with them,the dielectric properties of Zn0.94Co0.06TiNb2O8+0.6 wt%LBSCA ceramics are the best:εr=32.61,Q×f=49200 GHz,τf=-50.71 ppm/℃.In addition,the change of temperature coefficient of（1-x）ZnTiNb2O8xCuTiNb2O8-0.4 wt%LBSCA composite ceramics was investigated.When the addition of CuTiNb2O8 ceramics exceeded a certain amount（x>0.3）,CuTiNb2O8 and Ti3O5 phases appeared in the samples,which was the main reason to increase the temperature coefficient of the samples,but also deteriorated the dielectric loss of the samples.The temperature coefficient of sintered ceramic sample x=0.375 is the best at 875℃（εr=35.01,Q × f=19449 GHz,τf=-0.3ppm/℃）,while the sample with x=0.02 has the best Q×f value（～38711 GHz）.Finally,based on the material with the improved temperature coefficient,a LTCC bandpass filter with a center frequency of 1.5 GHz is designed and simulated.It meets the design requirements and verifies the practicability of the material.