Research On Microwave Dielectric Properties Of BMN-based Layered Dielectric Ceramics

With the arrival of the 5G commercial era,emerging industries,for instance,artificial intelligence,Industrial Internet,Internet of Things,Internet of Vehicles and et al have put forward new technical requirements for microwave dielectric ceramics and devices such as low loss,high integration,high consistency,and easy processing and so on.For a long time,Ba(Mg_1/3Nb_2/3)O₃（BMN）-based ceramics have been extensively studied due to their low cost and good microwave dielectric properties.Recently,layered dielectric ceramics have unique and excellent performance in dielectric properties,which are worthy of further study.This article mainly studies BMN composite ceramics and BMN-based layered dielectric ceramics.Firstly,BMN was modified in complex phase,and then the BMN composite ceramic was used as a layered component to be co-fired with materials which have negative temperature coefficient of resonate frequency.The BMN-based dielectric ceramic with layered structure was prepared and studied for the first time.First,Ba(Mg_1/3Nb_2/3)O₃-Mg₄Nb₂O₉（BMN-M4N2）composite ceramics were prepared and studied.M4N2 can coexist with BMN,which improves the sintering performance of BMN,reduces the sintering temperature of the system,and increases Q×f values.In particular,a small amount of solid solution is formed between M4N2 and BMN and improves the ordering of BMN structure,thereby obtaining the highest Q×f values of 125 000 GHz;too much M4N2reduces the high temperature stability and the ordering of BMN structure,resulting in a reduction in values of Q×f and difficulty in adjustingτ_f to near zero.When the two-phase composite ratio is 0.875BMN-0.125M4N2,the best microwave dielectric properties can be obtained by sintering at 1320℃for 4 hours:ε_r=26.6,Q×f=111 000 GHz,τ_f=5 ppm/℃.In order to solve the problem that the Q×f value of BMN-M4N2 composite ceramics decreases whenτ_fis adjusted to near zero,A_BMN/B_M4N2/A_BMN and B_M4N2/A_BMN/B_M4N2 type BMN-based layered dielectric ceramics were prepared and studied on the basis of the composite modification to improve the co-firing compatibility of BMN-based ceramics and negative temperature coefficient ceramics M4N2 in this paper.Studies have shown that in addition to the mass fractions of M4N2,the layered structure,composition and residual stress will also have a significant impact on the microwave dielectric properties of the layered dielectric ceramics.Compared with composite modification,increasing the content of BMN layers can significantly reduce theε_r andτ_f of A_BMN/B_M4N2/A_BMN type layered ceramics.In addition,the layered structure can reduce the influence of extrinsic factors such as solid solution or phase segregation on Q×f,so thatτ_f can be adjusted to near zero at a higher Q×f value.In order to reduce the influence of stress on layered ceramics,this paper further optimizes the co-firing compatibility of BMN-based ceramics between M4N2 ceramics by replacing the composition of the A layer.When the A layer is 0.875BMN-0.125M4N2 and the B layer is 10 wt%0.98M4N2-0.02BMN,the A_BMN/B_M4N2/A_BMN type layered ceramic achieves the optimized microwave dielectric properties,whereε_r=22,Q×f=110 000 GHz,τ_f=0.965 ppm/℃.This paper also uses HFSS software to simulate the dielectric properties and electric field distribution of BMN-based layered dielectric ceramics in TE_01δmode,and visually reveals the relationship between the layered structure,composition,and electric field intensity distribution,and proves the difference of electric field intensity distribution is the root cause of the different dielectric properties of the layered dielectric ceramics.Moreover,the intrinsic Q×f values of layered dielectric ceramics can be predicted and designed by HFSS software,which may have guiding significance for the composition and structure design of layered dielectrics in the future.Similarly,this paper found that Mg₂Si O₄（M2S）ceramics with high Q×f value and negativeτ_f can coexist with BMN to form Ba(Mg_1/3Nb_2/3)O₃-Mg₂Si O₄（BMN-M2S）composite ceramics.A proper amount of M2S phase can promote BMN sintering and increase the overall Q×f value.However,when the content of M2S phase is increased in order to further adjustτ_f to near zero,M2S is easy to phase segregation,thereby reducing the sintering density and Q×f value of the system.When the composite ratio is 0.6BMN-0.4M2S,the optimized microwave dielectric properties can be obtained by sintering at 1420℃for 4 hours:ε_r=18.9,Q×f=91 000 GHz andτ_f=2.6 ppm/℃.In order to reduceτ_f on the basis of high Q×f value,in this paper,the layered modification of BMN-M2S ceramics was carried out,and A_BMN/B_M2S/A_BMN type and B_M2S/A_BMN/B_M2S type layered dielectric ceramics were prepared and studied.When the A_BMNlayer is 0.8BMN-0.2M2S and the B_M2S layer is 14 wt%M2S,the A_BMN/B_M2S/A_BMN type layered ceramic achieves the optimum performance:ε_r=18.2,Q×f=75 000 GHz andτ_f=3.9 ppm/℃.