Research And Application Of ZnZr/TiNb₂O₈ Low Loss Microwave Dielectric Ceramics

Based on the increased demand for the high-performance devices used in 5G communication technology,intelligent terminals,aerospace and the internet of things fields,electronic components,as the cornerstone to support the development of information industry,have been developed to meet the goal of integration,high frequency and multi-function.Low temperature co-fired ceramic（LTCC）technology has become the mainstream passive device integration technology due to its advantages of high integration degree,high reliability,design flexibility,and high compatibility.However,this technology needs substrate materials with much higher qualification.In addition to the basic excellent microwave dielectric properties,microwave ceramics should be able to be sintered at a lower temperature（generally≤950℃）.In this paper Zn Zn Nb₂O₈ and ZnTiNb₂O₈ with the medium dielectric constant and low loss niobate ceramics have been studied.For the following problem:the sintering temperature is too high and the temperature stability is poor,which hinders the practical application of those two kinds of ceramics.LBSCA glass with low melting point was used to reduce the sintering temperature and CaTiO₃ ceramic with positive temperature coefficient was used to adjust the temperature coefficient.In addition,the microwave dielectric properties of ZnZrNb₂O₈ matrix ceramics were improved by replacing Zr⁴⁺ with Ti⁴⁺ as a preliminary experiment of reducing the firing and adjust the temperature coefficient.Test analysis including:X-ray diffraction（XRD）,Raman spectroscopy,scanning electron microscopy（SEM）,etc.Combined with the theoretical basis and regularity summary of the existing experiments,the correlation between phase composition of ceramics,crystal structure and microwave dielectric property were deeply analyzed and explored.The specific works are as follows:Using Ti⁴⁺ with similar ion radius to replace Zr⁴⁺ in ZnZrNb₂O₈.Substituted with appropriate amount of Ti⁴⁺（x<0.4）,Ti⁴⁺would be solid solution into the Zr lattice,causing changes in the octahedral structure and bond length of NbO₆,which has a positive effect on the microwave dielectric properties of ceramics.In general,ZnZr_0.8Ti_0.2Nb₂O₈ceramics sintered at 1150℃ has the best microwave dielectric properties（ε_r=29.75,Q×f=107303 GHz,τ_f=-24.41 ppm/℃）.Then,LBSCA glass was added into ZnZr_0.8Ti_0.2Nb₂O₈ ceramics to do the sintering reduction experiment.The addition of LBSCA glass facilitated the ceramic reaction at low temperatures and successfully reduced the sintering temperature to 950℃.It has good performance at x=0.6wt%（ε_r=26.58,Q×f=66097 GHz,τ_f=-68.11 ppm/℃）.On this basis,CaTiO₃ ceramics were added into adjust the temperature coefficient,however,second phase CaNb₂O₆ with a small positive temperature coefficient would appear.In this case,the temperature coefficient of ceramics was not well regulated,and the microwave dielectric properties were deteriorated.For ZnTiNb₂O₈ ceramics,LBSCA glass was used as sintering aid.Compared with pure ZnTiNb₂O₈ ceramics sintered at a high temperature,the microwave dielectric properties wereε_r=33.826,Q×f=49143 GHz,τ_f=-57.59 ppm/℃ at 950℃.When ZnTiNb₂O₈-0.6wt%LBSCA ceramic and CaTiO₃ were combined,two kinds of ceramic phases with positive temperature coefficient could be formed,namely,CaNb₂O₆ and TiO₂.The temperature coefficient of ZnTiNb₂O₈-0.6wt%LBSCA ceramic was adjusted to about±10 ppm/℃.Specifically,the properties of 0.7ZnTiNb₂O₈-0.3CaTiO₃-0.6wt%LBSCA ceramic sintered at 925℃ were as follows:ε_r=26.2135,Q×f=14619 GHz,τ_f=-12.53ppm/℃.Finally,a 2.5 GHz LTCC band-pass filter was designed and simulated based on the above ceramic material with a temperature coefficient of-12.53 ppm/℃.The bandwidth of the filter is 160MHz,the maximum insertion loss and return loss are about-1.0824dB and-17.015dB.Morever,the maximum standing wave ratio is about 1.3283,which further enhances the practicability of the material itself.