Performance Adjustment And Application Investigation Of High-Q Microwave Dielectric Ceramics

Since the 1980s,wireless communication has evolved from the first-generation of mobile communication technology（1G）to the fifth-generation of mobile communication technology（5G）,which is commercially available on a large scale today,and will move towards the sixth-generation of mobile communication technology（6G）.The frequency for mobile communication has increased dramatically from MHz to tens of GHz,and the terahertz spectrum in higher frequency bands will likely be used in the 6G era.Along with this,the signal propagation process suffers from large free-space losses as well as atmospheric effects,resulting in a significant reduction in communication distance.This requires a further increase in the number of communication devices and signal transmission power to compensate for this part of the attenuation.In the case of 5G base stations,for example,the proliferation of communication devices and other factors lead to the energy consumption of 5G base stations reaching three times that of 4G base stations,with passive devices accounting for more than 40%of the energy consumption.High-quality factor（Q-value）microwave dielectric ceramics are the basis for low-power microwave communication devices.Comprehensive improvement of microwave dielectric ceramic dielectric properties is the key to solving the problem of 5G power consumption,which has important theoretical significance and application value for the development of next-generation higher frequency band communication.In this paper,based on Li₂TiO₃-based microwave dielectric ceramics,microwave dielectric ceramics with suitable dielectric constant,high Q value and near-zero temperature coefficient of resonant frequency are prepared by stack co-fired and doping processes.The loss mechanism of the system in the microwave and terahertz bands was investigated with the help of XRD,SEM,Raman scattering spectra and terahertz time domain spectra.And based on the modified Li₂TiO₃ ceramic substrate,a low-loss ceramic-based open-loop hairpin bandpass filter for wireless communication is developed.The main research contents and results of this paper are as follows:A stacked-layer co-fired approach was introduced to modulate the integrated dielectric properties of the Li₂Ti_0.98Mg_0.02O_2.96F_0.04-1wt%Nb₂O₅（LTMN）system.The main studies are as follows:（1）The effects of the introduction of Li₃Mg₂NbO₆（LMN）layers on the LTMN matrix were investigated with the help of X-ray diffraction mapping（XRD）and scanning electron microscopy（SEM）to probe the feasibility of the stacked-layer composite approach.（2）Based on the parallel distribution model and HFSS modeling simulation,the influence mechanism of the microwave dielectric properties of the system under the stacked co-fired method was investigated by regulating the component content of LMN layers and the stacked composite method.（3）The stacked-layer sample LMN/LTMN/LMN with excellent comprehensive performance was prepared:ε_r～16.8,Q×f～99,600GHz,τ_f～+1.27ppm/℃,whereτ_f was optimized by nearly 96%.The stacked-layer samples maintain excellent dielectric properties in the terahertz band:low dielectric loss<0.008（@0.55THz）and small absorption coefficient<4cm^-1（@0.6THz）.Furthermore,a doping approach was adopted to study the mechanism of LMN content on the lattice structure and dielectric loss of the LTMN system.（1）The phase composition and microstructure of the composite system were analyzed by Rietveld method crystal structure refinement and SEM test to establish the intrinsic correlation between the dielectric properties of microwave dielectric ceramics and the phase composition.（2）The mechanism of the influence of the intrinsic and non-intrinsic factors on the dielectric loss of the system was investigated by Gauss-Lorentz fitting of the Raman spectra.（3）Finally,excellent microwave dielectric properties were obtained in 0.92LTMN_0.02-0.08LMN samples:ε_r～18.1,Q×f～105,660GHz,τ_f～+1.3ppm/℃,which meet the requirements of low-loss open-loop hairpin bandpass filter substrate applications.It also obtained<40cm^-1（@0.3-1THz）absorption coefficient in terahertz band test,exhibited near-transparent properties,and had low dielectric loss<0.04（@0.4-1THz）,providing a promising candidate for dielectric materials for next-generation communication devices.Finally,A 4th-order open-loop hairpin bandpass filter was prepared based on0.92LTMN_0.02-0.08LMN ceramic substrate with excellent dielectric properties.Based on the high-performance ceramic powder obtained,the preparation process of the ceramic substrate was investigated,and the influence of each performance parameter of the substrate on the S-parameter of the filter was analyzed by using the optimetrics function of HFSS software.After that,the physicalization process of the filter was explored,and the final filter test results were as follows:the center frequency（f₀）of the filter is 4.84GHz,the relative bandwidth（FBW）is about 11%,the in-band insertion loss(|S₂₁|)is 1.4dB,which is better than 2dB.The in-band return loss(|S₁₁|)is greater than 16dB,and the attenuation of|S₂₁|value at 4.1GHz and 5.6GHz is greater than 30dB.The overall size is only 10mm×10mm×0.5mm.