Research On Modification And Application Of Low Loss ZnTiNb₂O₈ Microwave Dielectric Ceramic Materials

With the continuous development of modern information and communication technology,the promotion and wide application of 5G communications,IoT,smart wearable devices,and smart medical electronic equipment,various terminal devices are gradually developing toward miniaturization,high-density integration,and high stability.The demand for high-performance microwave devices keeps ratcheting up.Higher requirements including miniaturization,higher integration and multi-functionalization are required for electronic components.Low Temperature Co-fired Ceramic（LTCC）technology,as one of the mainstream passive integration technology,provides an effective way to achieve the miniaturization and higher integration of devices.Higher requirements are put forward for LTCC materials,at the same time,not only suitable dielectric constant,higher quality factor and near-zero resonance temperature coefficient,but also lower sintering temperature（usually≤950℃）,and good chemical compatibility when co-fired with the electrode material.In this thesis the niobate microwave dielectric ceramic with medium dielectric constant—ZnTiNb₂O₈—was chosen as the research object,aiming at two major obstacles to applying in the LTCC field:the temperature coefficient of resonance frequency with larger negative value,and a relatively high sintering temperature.Methods like ion substitution,addition of sintering aids and combination of two phases,were adopted in the modification researches.All ceramic samples were fabricated by the traditional solid-state reaction method.Based on relavant theories and research reports,analysis and characterization methods like X-ray diffraction,scanning electron microscopy and Rietveld refinement,etc.were taken to investigate correlations between phase composition,crystal structure,microscopic morphology and microwave dielectric properties of the modified ZnTiNb₂O₈ ceramics.The main research content is divided into four parts:Firstly,Zn²⁺ in ZnTiNb₂O₈ was substituted by Mn²⁺,due to thier similar ion radius.Substituting appropriate amount of Mn²⁺formed a stable（Zn,Mn）Ti Nb₂O₈ solid solution.Excessive substitution will generate the secondary phase MnTiNb₂O₈ and affect the microscopic morphology and crystal structure,which will deteriorate the microwave dielectric properties of the ceramic.Theε_r value is mainly affected by the relative density,the Q×f value is determined by the packing fraction,and theτ_f value is closely related to the[Zn/Ti/Nb O₆]octahedral distortion.The microwave dielectric properties of the Zn₁-_xMn_xTi Nb₂O₈（x=0.05）ceramic sample sintered at 1100℃ are:ε_r=35.91,Q×f=63,672 GHz,τ_f=-68.68 ppm/℃.Then,two kinds of low-melting glass LMZBS and LBBS were used as the sintering aids.The addition of these two glasses can effectively reduce the sintering temperature of ZnTiNb₂O₈ from 1250℃ to 950℃.In addition,the microwave dielectric properties are improved to different degrees compared with ZnTiNb₂O₈sintered at high temperature.The ZnTiNb₂O₈-1.0wt.%LMZBS ceramics sintered at950℃ show excellent microwave dielectric properties:ε_r=33.512,Q×f=65,272 GHz,τ_f=-52.64 ppm/℃.The microwave dielectric properties of the ZnTiNb₂O₈-0.25 wt.%LBBS ceramic sintered at 950℃ are:ε_r=35.513,Q×f=52,932 GHz,τ_f=-58.17ppm/℃.After that,the temperature coefficient of the resonance frequency of ZnTiNb₂O₈-1.5wt.%LMZBS ceramic were adjusted by adding CaTiO₃.With the increase of the doping amount of CaTiO₃,the content of the Ca Nb₂O₆ andTiO₂ phases with positive temperature coefficients produced by the reaction gradually increased,so that the resonance temperature coefficient of the composite ceramics continuously moved in the positive direction.When x=0.35,the temperature coefficient was adjusted to near±10 ppm/℃,0.65 ZnTiNb₂O₈-0.35CaTiO₃-1.5wt.%LMZBS composite ceramics sintered at 925℃ show good microwave dielectric properties:ε_r=26.456,Q×f=12,726 GHz,τ_f=12.28ppm/℃.Finally,basing on the developed LTCC material withε_r=26.456,a probe-fed rectangular microstrip patch antenna with center frequency of 3.57 GHz was designed.The input impedance bandwidth of the antenna is about 47.5MHz,the return loss S₁₁ is around-29 d B,and the maximum gain is 4.38 d Bi,and the size of the microstrip antenna is 11.54 mm×21.6 mm×5 mm,which meets the requiements of relavant performance parameters.Realized the miniaturization of the antenna,and the practicability of the new matrix is verified.