Low Temperature Sintering Of Low Dielectric Constant Li₂(Mg_1-xZn_x)SiO₄ Ceramic Materials And Its Properties

With the expansion of communication frequency to high frequency,microwave dielectric ceramic materials with low dielectric constant and high quality factor have been widely used.Low temperature co-fired ceramic（LTCC）is an important way to realize the miniaturization,integration and multi-functionalization of microwave components.Therefore,it is of great significance to develop microwave dielectric ceramic materials with low dielectric constant and high quality factor,and reduce sintering temperature simultaneously.Li₂MgSiO₄ microwave dielectric ceramics have a dielectric constant of 5⁶,a quality factor Q as high as 15000 GHZ,and being co-fired with Ag metal.However,due to its high sintering temperature,its sintering temperature must be reduced to below 960℃in order to play its performance advantages in LTCC.In this paper,the effects of Zn²⁺ion substitution on Mg²⁺ion on the composition,microstructure and dielectric properties of the Li₂MgSiO₄ ceramics were studied at first.Then,on the basis of the best formula,the effects of self-made glass A,LMZBS glass and LiF-Bi₂O₃ composite additives on the low-temperature sintering properties of Li₂(Mg_0.8Zn_0.2)SiO₄ ceramic were studied,and based on this,the effects of Co²⁺ion substitution for Mg²⁺ion on material properties were investigated.Finally,TiO₂ was selected to adjust the resonant frequency temperature coefficient of the Li₂(Mg_0.8Zn_0.2)SiO₄ ceramics.The main results are as follows:（1）The effects of Zn²⁺ion substitution for Mg²⁺ion on the composition,microstructure and dielectric properties of Li₂MgSiO₄ ceramics were studied.The results showed that when Zn²⁺substitution was 0.2,the ceramic sample contained only Li₂MgSiO₄ phase.The comprehensive dielectric properties of Li₂(Mg_0.8Zn_0.2)SiO₄ceramic sintered at 1200℃for 2h were best and they were as follows:ε_r=5.8,Q×f=49607GHz,τ_f=-148ppm/℃.（2）The effects of glass A,LMZBS glass,LiF-Bi₂O₃ composite additives and Co²⁺substitution on the sintering properties of Li₂(Mg_0.8Zn_0.2)SiO₄ ceramic were studied.The results showed that when adding glass A or LMZBS or Li F-Bi₂O₃ can reduce the sintering temperature of Li₂(Mg_0.8Zn_0.2)SiO₄ ceramic to 900℃without introducing of impure phase.And the comprehensive dielectric properties of 1.5wt%glass A+Li₂(Mg_0.8Zn_0.2)SiO₄ ceramic were best and they were as follows:ε_r=6.1,Q×f=43594GHz,τ_f=-129ppm/℃.Thedielectricpropertiesof5wt%LMZBS+Li₂(Mg_0.8Zn_0.2)SiO₄ ceramic were as follows:ε_r=5.9,Q×f=25660GHz,τ_f=-204ppm/℃.The dielectric properties of 3wt%LiF+3wt%Bi₂O₃+Li₂(Mg_0.8Zn_0.2)SiO₄ceramic were as follows:ε_r=6.4,Q×f=23868GHz,τ_f=-125ppm/℃..Then based on the additive of 3wt%LiF+3wt%Bi₂O₃,the Mg²⁺ion was substituted by Co²⁺ion,and the results showed that no impure phase was introduced though,the quality factor decreased.The dielectric properties of Li2(Zn_0.2Mg_0.78Co_0.02)SiO₄ ceramic sintering at 900℃for 2h were as follows:ε_r=6.2,Q×f=13514GHz,τ_f=-120ppm/℃.（3）The effects of TiO₂ on the resonant frequency temperature coefficient of Li₂(Mg_0.8Zn_0.2)SiO₄ ceramics with glass A additive were studied.The results showed that TiO₂ additive can obviously improve the resonant frequency temperature coefficient of Li₂(Mg_0.8Zn_0.2)SiO₄ ceramic with glass A additive,but Li₂（TiO）（SiO₄）phase and Li₂Ti₂O₄phase were introduced and the dielectric constant increased with the addition of TiO₂,the Q×f also decreased.And the best dielectric properties of Li₂(Mg_0.8Zn_0.2)SiO₄ ceramic sintering at 950℃for 2h with 35wt%of TiO₂ were obtained:ε_r=10.2,Q×f=22073GHz,τ_f=1.7ppm/℃.