Preparation And Properties Of Ge-based Microwave Dielectric Ceramics With Low Permittivity

With the rapid development of the Internet of Things,big data and 5G networks,the microwave communication technology has been promoted to the direction of high frequency and frequency tunability.The requirements with low cost,miniaturization,integration and modularization are getting higher.The synthesis and preparation of new microwave dielectric ceramics with low dielectric constant,high quality factor and near-zero temperature coefficient of resonance frequency have become the focus of scientific research.In order to explore new microwave dielectric ceramics,a series of low-permittivity materials in the melilite M'₂M"Ge₂O₇?M'=Ba,Sr;M"=Mg,Zn?and willemite system were synthesized by the conventional solid-state method.The effects of phase composition,crystal structure,microstructure,and density on microwave dielectric properties were investigated in terms of X-ray diffraction,electron microscopy and spectroscopic analysis.The main results in this paper are as follows:?1?Both Ba₂M"Ge₂O₇?M"=Mg,Zn?belong to the tetragonal structure,and the space group is P-421m.At the optimal sintering temperature,Ba₂MgGe₂O₇ is monophasic,while Ba₂ZnGe₂O₇ has a second phase of BaZnGeO₄.The existence of the second phase can be proved through the refinement results,SEM,and Raman spectra.Ba₂MgGe₂O₇ sintered at 1280 ^oC has the optimum microwave dielectric properties:e_r?7.76,Q?f?20700 GHz,t_f?-55 ppm/?.The best microwave dielectric properties of Ba₂ZnGe₂O₇ sintered at 1180?ise_r?9.0,Q?f?13950 GHz,t_f?-75ppm/?.?2?Similar to their Ba counterparts,Sr₂M"Ge₂O₇?M"=Mg,Zn?ceramics have the same structure with Ba₂M"Ge₂O₇.Both ceramics were pure phase in their respective sintering temperature range.Optimum microwave dielectric properties with relative permittivity??_r?of 8.56,quality factor?Q×f?of 28,800 GHz,and temperature coefficient of resonance frequency??_f?of-70.5 ppm/°C were obtained in Sr₂MgGe₂O₇sintered at 1330°C.Sr₂ZnGe₂O₇ possessed?_r of 8.81,Q×f of 35,700 GHz,and?_f of-84.4 ppm/°C when sintered at 1290°C.And both ceramics can form composite ceramics with CaTiO₃ to adjust thet_f to near zero.?3?A series of willemite based ceramics Zn₂Ge_1+xO_4+2x with-0.1?x?0.2 were prepared by the solid-state reaction method.Influences of Ge nonstoichiometry on the crystal structure,densification,and microwave dielectric properties were evaluated in terms of X-ray diffraction,SEM,dielectric measurements and Far-infrared spectra.Ge excess favored the formation of single-phase willemite but a high level of excess induced appearance of GeO₂.In contrast,nominal composition and those with Ge deficiency comprised of ZnO and the willemite phase.Ge excess was found to be beneficial to the densification and dielectric properties optimization of Zn₂Ge_1+x+x O_4+2x.A composition with x=0.1(Zn₂Ge_1.1O_4.2)exhibited the optimum microwave dielectric properties with a relative permittivity?_r?7.09,a quality factor Q×f?112,700GHz?at 14.48 GHz?,and a temperature coefficient of resonance frequencyt_f?-51ppm/^oC.The far-infrared reflectance spectrum shows that the theoretical quality factor of Zn₂GeO₄ is 215234 GHz,which indicates the existence of external factors such as pores,second phase,and density,and thus leads to deterioration in the dielectric properties of the Zn₂GeO₄ sample.The effects of external factors on the dielectric properties can be reduced by optimizing the preparation process,and the microwave dielectric properties of Zn₂GeO₄ can be further improved.