The Investigation On Preparation And Dielectric Properties Of LTCC Materials Based On Ba₅Nb₄O₁₅

In the context of the rapid progress of microwave communication technology,the trend of device miniaturization,multi-functionalization and high integration has promoted the development of new materials,and has also accelerated the progress of LTCC technology.The sintering temperature of LTCC material is usually lower than 960℃,and the material has a dielectric constant that matches the application scenario,a higher quality factor,and a nearly zero frequency temperature coefficient.Exploring dielectric materials with excellent performance under low-temperature sintering conditions has become an urgent topic.The research of this paper is mainly focused on the following two directions:（1）exploring low-temperature co-fired ceramics with medium dielectric constant（20≤ε_r≤80）;（2）exploring low-temperature co-fired ceramics with frequency temperature coefficient（τ_f）close to zero.This article takes Ba₅Nb₄O₁₅ ceramics as the research object,and successfully reduces the porcelain-forming temperature（≤950℃）of the ceramic system through doping and compounding methods.And on the basis of the ceramic-glass system,the frequency temperature coefficient of the system is adjusted to nearly zero,and the performance to meet the requirements of microwave integrated circuits（ε_r～40,Q×f≥8000GHz,τ_f～±5ppm/℃）is achieved.The details of the study are as follows:1.Ba₅Nb₄O₁₅ ceramics were prepared by solid-phase sintering method.The Ba₅Nb₄O₁₅ powders sintered at different prefiring temperatures for 4h were analyzed by XRD,and no second phase was generated at 800℃～1100℃.Subsequently,the optimal prefiring temperature of Ba₅Nb₄O₁₅ ceramics was determined to be 900℃ by comparison with the standard peak of Ba₅Nb₄O₁₅ and the comparison of peak intensities.Then sintered at 1340℃～1400℃,combined with the analysis of microscopic morphology and dielectric properties,the Ba₅Nb₄O₁₅ ceramic captured by sintering at 1380℃for 3h shows the best microwave dielectric properties:ε_r=40.2,Q×f=29418GHz,τ_f=79.8 ppm/℃.2.In order to reduce the sintering temperature of Ba₅Nb₄O₁₅ ceramics,this paper proposes to use a variety of homemade glasses Li₂O-B₂O₃-SiO₂-Al₂O₃-Ca O（G1）,MgO-Al₂O₃-B₂O₃-SiO₂-TiO₂（G2）,BaO-ZnO-B₂O₃（G3）,CaO-B₂O₃-SiO₂（G4）,B₂O₃-SiO₂（BS）as sintering additives.The principle is that the low melting point glass forms a liquid phase to fill the grain gap during the sintering process,so that the ceramics form a dense structure and enhance their dielectric properties.The results show that the addition of G1～G4 glasses can reduce the sintering temperature of Ba₅Nb₄O₁₅ ceramics to about 950℃.However,the quality factor of Ba₅Nb₄O₁₅ceramics is drastically reduced due to the engagement of glass performance loss,which limits its further application.With the help of BS glass,the sintering temperature of Ba₅Nb₄O₁₅ ceramics was reduced from 1380℃ to 925℃.The ceramic structure was dense and no second phase was formed.Excellent properties of Ba₅Nb₄O₁₅ ceramics doped with 0.6 wt.%BS were obtained by sintering at 925℃ for 4 h:ε_r=41.2,Q×f=22238 GHz,τ_f=53.1 ppm/℃3.In this chapter,based on the low-temperature sintered ceramic system Ba₅Nb₄O₁₅-0.6 wt.%BS obtained in the previous chapter,compound-glass composite doping was added on purpose of improving the capability of the system.The added compounds were 2wt.% WO₃,CaCO₃,B₂O₃,and CuO.The results showed that doping with B₂O₃ would enhance the performance,and a quality factor of 29756 GHz was obtained by sintering at 950℃ for 3h.CaCO₃ would decompose and produce gas during the sintering process,forming more pores inside the ceramics and preventing the ceramics from forming a dense structure.The copper ions in CuO enter the lattice during the sintering process,and the defects in the ceramics increase,and the best performance is obtained at 925℃:ε_r=38.6,Q×f=25734 GHz.4.In this chapter,LiNb₃O₈ with negativeτ_f is added to adjust the frequency temperature coefficient of the ceramic system Ba₅Nb₄O₁₅-0.6 wt.%BS.It is found experimentally that LiNb₃O₈ can effectively adjust the frequency-temperature coefficient of this system,and the results are in accordance with the logarithmic law.However,LiNb₃O₈ introduces the heterogeneous phase LiBa₄Nb₃O₁₂,which makes the quality factor of the ceramics seriously deteriorate.Excessive additions can lead to ceramics that are not porcelain-forming and have poor densities.When 40% LiNb₃O₈is added,0.6 Ba₅Nb₄O₁₅+0.4 LiNb₃O₈+0.6 wt.%BS ceramic system can be sintered at 950℃ for 3h to obtain the desired dielectric properties:ε_r=35.4,Q×f=8637 GHz,τ_f=4.3 ppm/℃.