Research On The Microwave Dielectric Performance Regulation And 5G Communication Applications Of Tantalate Ceramics

With the emergence and development of advanced radio communication technologies such as 5G communication,NFC and the pre-researched 6G communication etc.,higher requirements are placed on the transmission rate and communication capacity of radio.Dielectric ceramics,as the basic material in radio transmission circuits,is one of the fundamental R&D focuses of modern communication technologies.Emerging telecommunication communications are driving the development of electronic components towards high frequency,integration and functionalization.Exploration and development of high-quality dielectric ceramics with independent intellectual property rights is one of the focus of research work nowadays and an effective way to break the monopoly of science and technology.Therefore,understanding the intrinsic mechanism of microwave dielectric ceramic materials and developing high performance dielectric ceramics are of practical and strategic importance.The present work focuses on MgTa2O6 dielectric ceramics with medium dielectric constant and low dielectric loss.Different ions are used for substitution to systematically study the effects of ion substitution at different crystal sites on the microstructure and macrowave dielectric properties.With the help of XRD,Raman,SEM and other characterization methods,the crystal changes before and after ion substitution are investigated;the mechanism of ion substitution and the tight bonding between microscopic crystal structure and dielectric properties are explored by using chemical bonding theory and first principles calculations.Secondly,the sintering temperature of MgTa2O6 ceramics is effectively reduced and its temperature stability is regulated by adding LBBS glass;a bandpass filter for miniature 5G is designed and fabricated by integrating MgTa2O6-LBBS dielectric ceramic and LTCC technology.The main research contents are as follows.First,the effects of equivalent ion substitution at the Mg site on the crystal structure and microwave dielectric properties of MgTa2O6 ceramics were investigated.To begin with,Ni²⁺was introduced into the Mg site by using the solid-phase reaction method to synthesize substitutional solid solutions and induce cell shrinkage.Ni²⁺substitution reduced the bond ionicity of the entire crystal,thus lowering the dielectric constant of the sample.In addition,Ni²⁺substitution increased the atomic stacking rate and lattice energy of the crystals,which improved the quality factor.However,the introduction of Ni²⁺did not significantly improve the resonant frequency temperature coefficient of MgTa2O6ceramics.By 6%Ni²⁺substitution,the sintering properties of the pristine ceramics were effectively improved and obtaining the best microwave dielectric properties at 1325°C:εr～27,Q×f～173,000 GHz andτf～35 ppm/°C.Second,the Mg sites in the crystal were partially replaced by using Mn²⁺.By the introduction of Mn-O bond,the ionicity of Mg-O and Ta-O bonds in the crystal were reduced,causing a decrease in the dielectric constant.Moreover,the introduction of Mn²⁺causes the lattice energy of the crystal to decrease and the stability of the crystal lattice to become weaker,resulting in a lower Q×f value.Meanwhile,the introduced Mn-O bond can effectively improve the thermal stability of the system.However,when the substitution amount over 10%,the excess Mn²⁺leads to the expansion of Mg O6 octahedra,which affects the lattice stability.In conclusion,a moderate amount of Mn²⁺substitution can improve the microwave dielectric properties of MgTa2O6 ceramics:εr～28,Q×f～10×10⁴ GHz,andτf values can also be reduced to 20 ppm/°C.However,an excess of Mn²⁺can deteriorate the microwave dielectric properties and thermal stability of this type of ceramics.Second,the the effect of equivalent ion substitution at Ta sites on MgTa2O6 dielectric ceramics were studied.Introduction of Sb-O bonds with lower bond dissociation entropy to replace Ta-O bonds in MgTa2O6 crystals partially reduced the sintering temperature of MgTa2O6 ceramics.The Sb⁵⁺ions in the crystal provide more electrons for the adjacent oxygen ions,resulting in a decrease in the ionicity of the Ta-O and Mg-O bonds and causing a decrease in the dielectric constant.In addition,the introduction of Sb⁵⁺leads to a decrease in the crystallinity of the crystal and a slight decrease in the quality factor.However,the Sb ion substitution improves the stability of the Ta O6 polyhedra and enhances the thermal stability.In particular,the optimual microwave dielectric properties were found at 10%Sb⁵⁺substitution and sintering temperature of 1350°C:εr～27,Q×f～106,000 GHz andτf～15 ppm/°C.Then,Nb⁵⁺was utilized as the Ta substitution ion.Due to the synthesis temperature of Mg Nb2O6 is significantly lower than that of MgTa2O6,resulting in the formation of the Mg Nb2O6 phase in the sample,and when the amount introduced exceeds 12%,the MgTa2O6 phase is not detectable in the sample.The appearance of the second phase maintained the original quality factor to some extent and improved the temperature coefficient of the ceramics to near zero,but deteriorated the dielectric constant.Although the literature shows that Ta⁵⁺can replace the Nb site in niobate,Nb⁵⁺is experimentally found to be unable to act as a replacement ion for Ta.In conclusion,the introduction of Nb⁵⁺into MgTa₂O₆ ceramics can modulateτ_f to near zero,with excellent microwave dielectric properties at 12%Nb⁵⁺introduction at 1375°C:εr～23,Q×f～71,000 GHz.Further,the effect of ionic substitution at the O site on the crystal structure and microwave dielectric properties of MgTa2O6 dielectric ceramics was investigated.The MgTa2O6-x F2x fluoro-oxides were synthesized by F-ions doping.F^-can successfully enter into the lattice to occupy the O sites causing cell shrinkage,and the proper amount of F^-will enhance the grain size and improve the microscopic morphology of the samples,while the excessive amount of F^-will lead to the decrease of the crystallinity of the samples.In addition,a suitable amount of F^-substitution improves the crystallinity of the sample,increases the stacking ratio of atoms,and improves the Q×f value.However,when the substitution amount x exceeds 0.4,the densities and crystallinity of the samples deteriorate,leading to a decrease in the Q×f values of the samples.The MgTa2O5.6F0.8fluoro-oxides exhibited excellent microwave dielectric properties at 1425°C:εr～27.8,Q×f～179,000 GHz andτf～43 ppm/°C.In addition,LBBS glass was added to reduce the sintering temperature of the MgTa2O6 dielectric ceramics.The addition of LBBS glass above 7.5 wt.%to Mg0.94Ni0.06Ta2O6 ceramic powder can reduce the sintering temperature to below 950°C,but the appearance of Li Ta O3 leads to a significant deterioration of the microwave dielectric properties.The presence of impurity and glass phases in the samples substantially improves the temperature coefficients to within 10ppm/°C,meeting the requirements for their application in LTCC technology.Finally,a miniaturized bandpass filter for 5G communication was designed,simulated and fabricated based on the developed Mg0.94Ni0.06Ta2O6-7.5 wt.%LBBS composite ceramic.The package size of the filter is only 2.0×1.2×1.0 mm with a center frequency of 4.8 GHz,and the ceramic material is processed into a filter relying on the advanced LTCC packaging technology.The filter’s return loss|S11|is found to deviate from the simulation results,but the performance demonstrated by the filter verifies the practical feasibility of the dielectric material in this study.