The Research Of Structure And Properties Of Low-Firing Microwave Dielectric Ceramics With Low Permittivity

Microwave dielectric ceramic should have proper relative permittivity（ε_r）,high quality factor（Q×f）and small temperature coefficient of the resonant frequency（τ_f）.And in order to meeting the demands of LTCC（low temperature co-firing ceramic）technology,making smaller size and higher integration of components,the microwave dielectric ceramic also should be co-fired with low-melting point conductors（Ag et.）.In this work,BCB ceramics were prepared by using the deionized water and alcohol as the medium.Furthermore,series of novellow-temperatures cofired microwave dielectric ceramics with the composition of Li₂MgSiO₄-BCB、Mg₃B₂O₆-BCB were obtained.（1）The effects of different ball grinding media（anhydrous ethanol and deionized water）on thephase transformation,microstructure,bulkdensity and microwave dielectric properties of BaCu（B₂O₅）ceramic werestudied.The results showed that all BaCu（B₂O₅）ceramics prepared in the temperature range of 800°C to 840°C with ball milling medium--anhydrous ethanol and deionized water arethesingle phase.And the optimizedsintering temperature of BaCu（B₂O₅）ceramic skept stable with different ball grinding media.In general,BaCu（B₂O₅）ceramics prepared by ball mill medium of anhydrous ethanol and deionized water can be well sintered at 830°C and 820°C,which exhibited optimal microwave dielectric properties withε_r=6.8,Q×f=15827.5GHz,τ_f=-60.2 ppm/°C andε_r=6.8,Q×f=16650.0GHz,τ_f=-58.4 ppm/°C,respectively.（2）The Li₂MgSiO₄ microwave dielectric ceramic with low relative permittivity was prepared by the solid-state reaction route.After sinteredat 1225°C,the ceramics shown optimal microwave dielectric properties withε_r=5.9,Q×f=21884.9GHz,τ_f=-180ppm/°C.Small anount of BCB was added to reduce the sintering temperature of Li₂MgSiO₄ ceramics.In addition,the phase transformation,microstructure,bulk density and microwave dielectric properties of ceramics were also investigated.All samples of Li₂MgSiO₄+xwt%BCB（x=1,2,3,4）ceramics are Li₂MgSiO₄ single phase,no second phase was detected.Li₂MgSiO₄ ceramic added 3wt%BCB sintered at 925°C demonstrated optimal microwave dielectric properties with Q×f=30069.9GHz,ε_r=5.99 andτ_f=-179ppm/°C.（3）Mg₂B₂O₅ ceramic samples was prepared by the solid-state reaction route using the stoichiometric ratio of MgO:H₃BO₃=1:2.And the phase structure,microstructure,atoms occupation,sintering characteristics and microwave dielectric properties of the ceramics were investigated.All ceramics are single Mg₂B₂O₅ phase.The ceramics sintered at 1100°C exhibited good microwave dielectric properties of Q×f=41,930GHz,ε_r=5.83 andτ_f=-62ppm/°C.（4）Mg₃B₂O₆ ceramic samples was prepared by the solid-state reaction route using the stoichiometric ratio of MgO:H₃BO₃=1:1.The ceramics sintered at 1250°C exhibited good microwave dielectric properties ofε_r=7.64,Q×f=116,450 GHz andτ_f=-56ppm/°C.Small amount of BCB was added to reduce the sintering temperatures of Mg₃B₂O₆ ceramic.Furthermore,the phase structure,microstructure,sintering characteristics and microwave dielectric properties of the ceramics were investigated.With adding BCB,all samples exhibited a mix phases with Mg₃B₂O₆ and Mg₂B₂O₅.The temperature coefficient of resonate frequency for ceramics were adjusted by adding CaTiO₃.The ceramics added 10wt%BCB and a certain amount of CaTiO₃ could be densified at 900°C and had optimized comprehensive performance with Q×f=16596.97 GHz,ε_r=7.432 andτ_f=-30 ppm/°C.（5）The device application of BaCu（B₂O₅）low permittivity LTCC material was investigated and the filters was prepared.Low bending strength and high loss of devices restricted it further application,next work is to improve the bending strength of ceramics.