Improvement Of Bending Strength And Optimization Of Microwave Dielectric Properties Of Li₂MgTi₃O₈ Low Temperature Co-Fired Ceramics

With the approach of the new era of 6 G,electronic components are inclined to the direction of miniature and feature-rich development.Low temperature co-fired ceramics（LTCC）can adapt to complex working environment and withstand external shocks are increasingly valued,and lowε_r microwave dielectric ceramics have the advantage of fast information transmission rate,which meets the characteristics of the future development trend.In recent years,Li₂MgTi₃O₈ ceramics（LMT）with spinel structure have been sought after by many researchers because of their inherent low sintering temperature,lowε_r and high Q×f.Unfortunately,as a potential material for LTCC technology,the bending strength of LMT ceramics is not satisfactory.Therefore,it is an urgent problem to improve the bending strength of the ceramics and make the microwave dielectric properties not be deteriorated seriously.In this paper,LMT ceramics were obtained by the solid state sintering method.When the pre-sintering temperature is 800℃ and the sintering temperature is 1075℃,the LMT ceramic has the best performance of Q×f=65006 GHz,ε_r=24.67,τ_f=-6.54ppm/℃,and the bulk density is 3.374 g/cm³.Based on the high-performance LMT ceramics,the following three studies were carried out:（1）By doping 0.1～0.75 wt%Si₃N₄ into the LMT ceramics,the bending strength of LMT+0.5 wt%Si₃N₄ ceramics sintered at 1050℃ could reach 176.144 MPa,which was 76.97%higher than that of pure LMT ceramics.And the ceramics show good microwave dielectric properties withε_r=23.20,Q×f=49344 GHz,τ_f=-5.90 ppm/℃.We have preliminary experience in improving the bending strength of LMT ceramics.（2）By doping 0.1～0.4 wt%TiN into the LMT ceramics,the LMT+0.2 wt%TiN ceramics have the best overall performances in terms of both microwave dielectric properties and bending strength.When the sintering temperature is 1025℃,the bending strength is 75.52%higher than that of pure phase LMT ceramics,and the microwave dielectric properties of ceramics performed well:Q×f=67275 GHz,τ_f=-6.02 ppm/℃,ε_r=24.53.The LMT+0.3 wt%TiN ceramic has excellent dielectric properties,but the bending strength is not improved significantly.B₂O₃,Bi₂O₃,V₂O₅-ZnO and LiF-MgO were added into LMT+0.3 wt%TiN ceramics to study their effects on the ceramic properties.The sintering temperature was successfully reduced to below950℃ and the bending strength was all greatly improved.In particular,the bending strength of LMT ceramics doped with LiF-MgO sintered at 850℃ reaches a maximum value of 200.98 MPa,which is 101.9%higher than that of pure phase LMT ceramics.It has excellent dielectric properties and does not react with Ag electrode,which is a great breakthrough for our research.（3）The impacts of Al₂O₃ particles and Al₂O₃ whiskers on the performances of LMT ceramics were investigated.The optimal properties of the ceramics doped with Al₂O₃ particles are Q×f=67056 GHz,τ_f=-8.25 ppm/℃,ε_r=24.34.And the bending strength is 152.5 MPa,it is 53.21%higher than the pure LMT ceramics.The optimum properties of ceramics doped with Al₂O₃ whiskers are Q×f=68670 GHz,τ_f=-8.94ppm/℃,ε_r=24.32.And the bending strength is 166.73 MPa,it is 67.52%higher than the pure phase LMT ceramics.