| The rapid development of microwave communication technology,especially the rapid iteration of mobile communication technology represented by 5G technology,promotes the development of microwave devices in the direction of miniaturization,integration and multi-function,which puts forward higher requirements for microwave dielectric materials.Low Temperature Co-fired Ceramic（LTCC）technology has received extensive attention as an advanced passive integration technology.In general,high dielectric constant is beneficial to the miniaturization of microwave devices.The development of medium and high dielectric LTCC materials with high quality factor（Q×f）and near-zero temperature coefficient of resonance frequency（τf）is important for the miniaturization and integration of microwave devices.In this thesis,focusing on mid-to-high εr ceramic materials,Li1.0Nb0.6Ti0.5O3 ceramics with low sintering temperature（1100℃）were selected as the research object,and the methods of low temperature sintering and ion substitution were used to obtain LTCC materials with midto-high εr,higher Q×f values and near-zero τf values.The details are as follows.（1）The effects of two sintering aids,LBSCA glass and BaCu（B2O5）on Li1.0Nb0.6Ti0.5O3 ceramics at low temperature,were investigated.The sintering temperature of Li1.0Nb0.6Ti0.5O3 were reduced to 925℃ with the addition of 0.4 wt.%LBSCA,and its microwave dielectric properties were:εr=62.9,Q × f=7561 GHz,τf=12.56 ppm/℃.The doping of 0.4 wt.%BaCu（B2O5）could promote the grain growth and the densification of the ceramic,the optimum sintering temperature was 950℃,and the microwave dielectric properties were:εr=61.4,Q×f=6423 GHz,τf=27.5 ppm/℃.In addition,both ceramics prepared above had good chemical compatibility with Ag.（2）The effect of（Ti1/2W1/2）5+substitution on Li1.0Nb0.6-x（Ti1/2W1/2）×Ti0.5O3 ceramics was investigated.The second phase Li2WO4 and excess Ti introduced by the substitution of（Ti1/2W1/2）5+ had an effect on the crystal structure of the main phase.Li1.0Nb0.52（Ti1/2W1/2）0.08Ti0.5O3 ceramic sintered at 1050℃ possessed the lowest dielectric loss,and the microwave dielectric properties were:εr=53.8,Q×f=7482GHz,τf=43.4 ppm/℃.On this basis,the materials above were sintered at low temperature with LBSCA doping,and the Li1.0Nb0.52（Ti1/2W1/2）0.08Ti0.5O3-1.2wt.%LBSCA ceramics sintered at 900℃ obtained the best microwave dielectric properties:εr=49.4,Q × f=8149 GHz,τf=12.0 ppm/℃.（3）The effect of Co2+ substitution on Li1.0-2xCoxNb0.6Ti0.5O3 low temperature sintered ceramics was studied by doping with LBSCA glass which possessed the best sintering performance as sintering aid.Co2+ could be solid-dissolved into the main crystal phase,but would reduce the content of Ti in the main crystal phase and precipitated in the form of TiO2,resulting in the degradation of the overall structure from M phase to LiNbO3.Li0.96Co0.02Nb0.6Ti0.5O3+0.4 wt.%LBSCA ceramic sintered at 950℃ possessed the best comprehensive microwave dielectric properties with a near-zero τf value:Q×f=6255 GHz,εr=62,τf=0.97 ppm/℃.（4）Li0.96Co0.02Nb0.6Ti0.5O3+0.4 wt.%LBSCA ceramic was adopted as the dielectric layer,a 2.7 GHz three-layer SIW bandpass filter based on LTCC was designed,with a relative bandwidth of 5.9%and the minimum insertion loss is-1.086 dB,the return loss is greater than 20dB,which meets the design requirements. |
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