Research On Properties Of Microwave Dielectric Ceramics For The LTCC Technology

Microwave dielectric ceramics is a kind of functional material in the field of information and communication.It have been widely used in dielectric resonators,filters,antennas,etc.In the Low Temperature Co-fired Ceramics?LTCC?technology,microwave dielectric ceramics with low sintered temperature is also used as substrates.Today's rapid advances in wireless telecommunication further drive the searching for microwave dielectric ceramics with high performance.In this dissertation,BiZn₂VO₆,MCa₂Mg₂V₃O₁₂,Li₂NiCoGe₃O₈,Li_4?1+x?WO₅?0?x?0.08?ceramics with low temperature were prepared by the conventional solid-state method.Their structure and microwave dielectric properties were studied.Appropriate substituting and doping were used to adjust their properties.1.A kind of low-firing microwave dielectric ceramics BiZn₂VO₆ was prepared by the conventional solid-state method.The BiZn₂VO₆ ceramic could be well densified at relatively low temperature 780 ^oC.exhibited promising microwave dielectric properties with?_r=15,Q×f=20,640 GHz,?_f=-88 ppm/^oC.Compared with BiMg₂VO₆??_r=13.4,Q×f=15,610 GHz,?_f=-87.2 ppm/^oC?,it has better microwave dielectric properties.And it is compatible with Ag electrodes.2.For ACa₂Mg₂V₃O₁₂?A=K,Li?ceramics sintered at 900 ^oC and 940 ^oC had a relative permittivity??_r?¹0,a quality factor?Q×f?³0,330 GHz,a?_f⁺190.9ppm/^oC and?_r⁹.8,Q×f²4,900 GHz?at 11.0 GHz?,?_f⁺259.2 ppm/^oC respectively.They all have a large positive?_f.And it is found that the large negative?_f value is a common feature for vanadate garnets.So we prepared0.16LiCa₂Mg₂V₃O₁₂-0.84NaCa₂Mg₂V₃O₁₂2 ceramic to tune its microwave dielectric properties.The ceramics with a near-zero?_f=+2 ppm/^oC,?_r=9.9,Q×f=45,500 GHz was obtained at 945 ^oC for 4 h.3.Li₂NiGe₃O₈ ceramic sintered at 940 ^oC with a relative permittivity??_r?⁸.6,a quality factor?Q×f?⁴2,200 GHz?at 12.2 GHz?,a temperature coefficient of resonance frequency?_f^-78.2 ppm/^oC.For Li₂CoGe₃O₈,the ceramic sintered at 950^oC had a?_r of 9.0,a Q×f of 40,500 GHz?at 12.6 GHz?and a?_f of-42 ppm/^o C.The low sintered temperature and high Q×f value indicate these ceramics may be candidates for LTCC technology.The negative?_f values could be tuned by forming composite ceramics with rutile TiO₂.Chemical compatibility measurement indicates that both ceramics did not react with silver.4.Li₄WO₅ belongs to the family of rock salt,and it has good microwave dielectric properties.It is reported that the lithium volatilization will produce porous microstructure and it was detrimental for the microwave dielectric properties.Thus Li_4?1+x?WO₅?x=0.02,0.04,0.06,0.08?ceramics were prepared and the sample with x=0.04 sintered at 950 ^o C obtained good microwave dielectric properties with?_r⁹.5,Q×f⁵0,200 GHz?at 12.2 GHz?,?_f^-3.2 ppm/^o C.It has higher Q×f value than that of Li₄WO₅.