Study On Co-firing Process And Electromagnetic Properties Of Mg MgTiO₃-CaTiO₃/YIG Circular Composite Substrate

In this paper,considering the practical application of the circulator from multi-frequency doubling,miniaturization and intermodulation problems,the Mg Ti O₃-Ca Ti O₃/Y₃Fe₅O₁₂(MCT/YIG)base microwave dielectric ceramics-yttrium iron garnet ferrite circular composite substrates were prepared by using the integrated co-firing technology.In order to obtain a circular composite substrate,with seamless and good performance,which was used for 5G communication base station circulator.Two kinds of ferrites Bi_0.3Y_2.3Ca_0.4Fe_4.6Zr_0.4O₁₂(B-YIG)and Y_1.6Ca_1.4Fe_3.8V_0.6Zr_0.4Zn_0.2O₁₂(V-YIG),and microwave dielectric ceramic 0.95Mg Ti O₃-0.05Ca Ti O₃(MCT)were prepared by solid reaction method,and their crystal structures,electromagnetic properties and co-firing of matching properties were analyzed.The saturation magnetization of the prepared B-YIG is28.7 emu/g,the coercivity is about 5 Oe,and the process stability of magnetic properties is good.With the increase in co-firing temperature,the saturation magnetization of V-YIG increases from 23.46 emu/g to 37.4 emu/g,and the coercive force increases from 28 Oe to the highest 64 Oe,indicating its poor process stability.Therefore,V-YIG is not suitable for solid-phase preparation.Exploring the shrinkage of B-YIG,V-YIG and MCT of different pre-sintering temperatures,it was found that the sintering shrinkage of the prepared V-YIG was greater than that MCT of different pre-sintering temperatures,which was not in line with the principle of co-firing matching.The sintering shrinkage of B-YIG is slightly smaller than that MCT of different pre-sintering temperatures,which is in line with the principle of co-firing matching.The factors that affect the co-firing matching of the MCT/B-YIG circular composite substrate are as follows:decreasing the cooling rate can reduce the residual stress inside the circular composite substrate and the gap between MCT and B-YIG in the circular composite substrate,increase the shear strength of the MCT/B-YIG circular composite substrates.Moreover,the pre-sintering temperature will affect the sintering shrinkage of ceramics and the ion diffusion of the MCT/B-YIG circular composite substrate interface,thereby affecting the shear strength of the MCT/B-YIG circular composite substrate.Furthermore,with the increase in sintering temperature,the shear strength of the MCT/B-YIG circular composite substrate increases.However,the difference of ion diffusion coefficient increases at the higher sintering temperature,which leads to the increase of Kirkendall pores and thermal defects,leading to the reduced shear strength of the composite substrate,finally.During the co-firing process,a MCT/B-YIG ion diffusion couple will be formed at the interface of MCT and B-YIG,leading to the formation of Mg Fe₂O₄ and Y₂Ti₂O₇ crystal phases,which are the main reason for the increase in shear strength of sintered circular composite substrates.When the cooling rate is2°C/min,the pre-sintering temperature is 1050°C,and the sintering temperature is 1280°C,the obtained MCT/B-YIG circular composite substrate has a shear strength of up to 63 MPa and a dielectric loss of 6×10^-4.After co-firing,the B-YIG shows a magnetization of 0.73emu/g and a coercive force of 6.13 Oe.Therefore,the prepared MCT/B-YIG circular composite substrate has excellent comprehensive performance and can be used as the circulator of 5G communication base station.The research on the co-firing technology of MCT/B-YIG has practical guiding significance for the preparation of ferrite-microwave dielectric ceramic annular composite substrates.