Performance Adjustment And Mechanism Investigation In The Low-loss Microwave Dielectric Ceramics With Medium Permittivity

With the advent of 5G era,the new generation of microwave communication technology puts higher demands on the power consumption of RF circuits.The power consumption of passive components in the RF front-end is an important component of the energy consumption in microwave communication.Taking the communication base station as an example,the energy consumption of the passive components accounts for more than 40%of the system.Dielectric ceramics are the basis of microwave passive components.Therefore,exploring the physical mechanism and revealing the influence of different factors on dielectric loss can provide theoretical guidance for the development of ultra-low loss dielectric materials and devices.At present,researches on dielectric ceramics were limited to the microwave performance,while the internal and external factors affecting the dielectric properties were inadequate.Here,works were carried out on it.At first,Ba₃Zn Nb₂O₉,Li Zn Nb O₄,Li₂Zn Ti₃O₈ and Zn₃Nb₂O₈ system were prepared and the dielectric properties were improved by optimizing the preparing process,phase compositions and microstructure.Then,the effects of intrinsic and extrinsic factors on dielectric loss were studied by Raman scattering,SEM,EPR,THz time domain spectroscopy,impedance spectroscopy,Materials Studio and HFSS.Finally,theoretical methods based on crystal structure and phase compositions were proposed to reduce the loss of dielectric ceramics.Firstly,Ba₃Zn Nb₂O₉ ceramics were prepared and the intrinsic correlation between 1:2 order and microwave dielectric loss was explored:（a）Appropriate content of Mo⁶⁺and annealing process were applied to improve the 1:2 order and reduce the intrinsic loss of Ba₃Zn(Nb_2-xMo_x)O_9+x/2 ceramics;（b）The ordered structure of Ba₃Zn(Nb_2-xMo_x)O_9+x/2 was analyzed,and the intrinsic relationship between order degree and quality factor was elucidated based on the bond energy of Nb-O;（c）Due to the influence of coordination field,the Shannon rules was no longer applicable.And,chemical bond ionic was introduced to predict theoretical dielectric constant,which was highly consistent with the measured value;（d）Ba₃Zn(Nb_1.992Mo_0.008)O_9.004ceramics withε_r=38.9,Qf=102,931 GHz,τ_f=-19.1 ppm/^oC were obtained,which was expected to meet the application requirements of ultra-low loss microwave communication.Secondly,Li Zn Nb O₄ ceramics were prepared,the effects of Co²⁺/Ni²⁺ions on lattice vibration/oxygen vacancies and microwave dielectric loss were studied:（a）Appropriate content of Co²⁺/Ni²⁺entered Li Zn Nb O₄ system would increase the atomic bulk density and improve the quality factor;（b）Based on the group theory and first-principles calculation,Raman modes of Li Zn Nb O₄ system were confirmed.And,Co²⁺/Ni²⁺occupations in Li Zn Nb O₄ were explored according to the change of Raman modes;（c）The dielectric loss frequency characteristics of Li Zn_1-xM_xNb O₄ were measured and fitted with the modified Q v.s.f relation.By this way,the effect of Co²⁺/Ni²⁺on the lattice vibration and oxygen vacancy and its contribution to the microwave dielectric loss were systematically investigated;（d）Li Zn_0.98M_0.02Nb O₄ceramics withε_r=～15,Qf>100,000 GHz,τ_f=-60 ppm/^oC,T_s=995-1010^oC was prepared and expected to used in the LTCC devices.Thirdly,Li₂Zn Ti₃O₈ ceramics were prepared,the effects of acceptor/donor ions on lattice vibration/oxygen vacancies and microwave dielectric loss were investigated:（a）Different donor and acceptor ions were selected,and the doping method was optimized to regulate the lattice vibration and oxygen vacancies in Li₂Zn Ti₃O₈ceramics.As a result,the quality factor of the system was greatly improved;（b）The influency of different doping ions on crystal structure of Li₂Zn Ti_3-xM_xO₈ system was analysized according to XRD refinement,Electron paramagnetic resonance and Raman spectroscopy;（c）AC impedance spectrum and THz time-domain spectrum were collected and fitted,then the frequency response curves of lattice vibration and oxygen vacancy were calculated.Then,it can be concluded that lattice vibration contributed 80%of the dielectric loss,and the conduction loss contributed the remaining parts（20%）.Moreover,（1-x）（3Zn O-Nb₂O₅）-x Ge O₂ ceramics were investigated with regard to the preparation,phase composition and microwave dielectric properties:（a）Appropriate content of Ge O₂ could modify the phase composition and improve the microwave dielectric properties of the systems;（b）The phase transition mechanism of（1-x）（3Zn O-Nb₂O₅）-x Ge O₂ ceramics were systematically studied based on the coordination environment and ternary phase diagram;（c）The factors affecting microwave dielectric properties of（1-x）（3Zn O-Nb₂O₅）-x Ge O₂ ceramics were analyzed by random distribution model and the intrinsic correlation between phase composition and microwave dielectric properties was clarified.At last,a novel sandwich Zn₃Nb₂O₈-Ti O₂-Zn₃Nb₂O₈ ceramics was prepared and the effects of phase distribution on microwave dielectric loss were studied:（a）Compared with samples with random phase distribution,the Ti O₂ content required to achieve the near-zero temperature coefficient of the resonant frequency in sandwich Zn₃Nb₂O₈-Ti O₂-Zn₃Nb₂O₈ceramics was greatly reduced.As a result,the quality factor was improved by 8 times;（b）The electromagnetic fields in sandwich Zn₃Nb₂O₈-Ti O₂-Zn₃Nb₂O₈ ceramics were simulated by HFSS;（c）The microwave dielectric properties were theoretically simulated and the anomalous phenomena in dielectric constant and loss were investigated from the perspective of electromagnetic field distribution.