Li Based Low Loss Microwave Ceramics And Its Application

With the rapid development of wireless communication and microwave products,LTCC technology that enables devices to meet low loss,miniaturization,light weight,high integration,versatility and high reliability has received increasing attention.Li-based microwave dielectric ceramic materials,which have lower sintering temperature and better peformances,occupy an important position in the development of LTCC materials.This paper studied two kinds of Li-based microwave dielectric ceramic materials.Firstly,the LiAlO₂ ceramic material with low dielectric constant was studied.The sintering temperature of the ceramic was reduced by adding LBBS and LBSCA glass sintered at 850°C,900°C and 950°C.The relative density,phase composition,microstucture and microwave dielectric properties of the ceramics were analyzed.Better microwave dielectric properties could be obtained by doping 3wt%LBSCA glass:900°C,?_r=4.48,Q×f=35,540 GHz,?_f=-53 ppm/°C.950°C,?_r=4.50,Q×f=38,979GHz,?_f=-55 ppm/°C.Secondly,the Li₂TiO₃ ceramic material with lower loss was studied.By adding LBSCA glass and BCB ceramic as sintering aids,the Li₂TiO₃+2wt%LBSCA sample had better performances:900°C,?_r=17,Q×f=58,929 GHz.950°C,?_r=17.2,Q×f=61,956 GHz.The doped BCB ceramics could simultaneously reduce the temperature coefficient of the material.The properties of samples doped with 2.0 wt%BCB sintered at 900°C:?_r=15.19,Q×f=58,084 GHz,?_f=15.23 ppm/°C.As the amount of BCB increasing to 4.0 wt%,the?_f value droped to 9.95 ppm/°C.After that,Li₂TiO₃material with positive?_f value and LiAlO₂ material with negative?_f value were compounded to adjust the temperature coefficient closing to 0.The best experimental effect LBSCA glass was used as sintering aids and LiAlO₂-Li₂TiO₃ sample had better performances:900°C,?_r=15.4,Q×f=52,740 GHz,?_f=1.37 ppm/°C.950°C,?_r=15.5,Q×f=53,906 GHz.Through the compatibility analysis with Ag,it was known that the ceramics doped with LBSCA glass had good compatibility with Ag.Finally,based on the research and development of LiAlO₂-Li₂TiO₃ composite ceramic materials designed a laminated chip LTCC bandpass filter,the center frequency of 2.45 GHz,bandwidth of 100 MHz,a loss of 0.2 dB,the out-of-band rejection less than 22 dB at 1710¹990 MHz and less than 26 dB at 4800-5000 MHz,fully meeting the specifications of project.