Research On Mechanism Of Low Temperature Sintering Of Middle-k Dielectric BaO-TiO₂ Composition Ceramics

With the rapidly developing of wireless communication and electronic technologies,microwave dielectric ceramics had been widely used as the new electronic functional materials at microwave communication system.Microwave dielectric ceramics must have a serial of dielectric constant??_r?,low dielectric loss?tand,or highQ×f value,Q?28?1/tand?and small temperature coefficient of resonance frequency??_f?.Low temperature co-fired ceramic?LTCC?technology plays an important role in modern microwave circuits due to the necessity for low cost and miniaturization of microwave devices.The microwave circuit usually uses high conductivity Ag as the circuit wiring material.It is necessary to lower the sintering temperature of microwave dielectric material with excellent properties below 950°? to cofire with Ag.The ceramic samples in this paper were prepared by the traditional solid state reaction.and the influences of sintering aids on the phase composition,microstructure,microwave dielectric properties and the mechanism of the sintering kinetic of BaO-0.15ZnO-4TiO₂?BaZn₂Ti₄O₁₁and BaTi₅O₁₁ ceramics sintered at low temperature were investigated in detail.?.The effects of Li₂O-B₂O₃-SiO₂?LBS?glass on the sintering temperature,phase development,microstructure and microwave dielectric properties of BaO-0.15ZnO-4TiO₂?BZT?ceramics have been investigated in detail.The addition of LBS glass obviously lowers the sintering temperature of the BZT ceramics below950°?.The liquid phase caused by LBS glass reacts with BZT ceramic to form BaTi₅O₁₁ and BaTi?BO₃?₂,which lead to abnormal grain growth.The sintering process of the BZT ceramics significantly accelerated at a low temperature even with a higher activation energy,due to the reaction of BZT ceramics and LBS glass caused by the existence of liquid phase,which provides extra energy at the early stage of sintering,called reactive liquid-phase sintering.Appropriate amount of LBS glass promotes the densification of BZT ceramic and improves the dielectric properties.However,excessive LBS addition leads to the abnormal grain growth,which deteriorates the dielectric properties of the BZT ceramic.The BZT ceramics with 5wt.%LBS glass sintered at 900°? shows excellent microwave dielectric properties:?_r=27.88,Q×f=14795GHz,?_f=5.15 ppm/°?.Li₂O-B₂O₃-SiO₂?LBS?synthesized via a solid-state reaction process was chosen as a novel sintering aid for BZT ceramics and has the similar results to LBS glass.?.To further improve the densification and properties of BZT ceramics,the synergistic effect of LBS glass and LaBO₃?LaB?addition on the wetting behavior,activation energy,phase composition,microstructure and microwave dielectric properties of BZT ceramic has been investigated to understand the low temperature mechanism of the sintering kinetic.The co-doping with LBS glass and La B decreases the activation energy and therefore accelerates the sintering process of the BZT ceramics due to the liquid phase formed at a low sintering temperature.Moreover,the co-doping of LBS glass and La B restrains the appearance of Ba Ti?BO₃?₂ caused by the reaction of BZT ceramics and LBS glass,which has a deleterious effect on the densification and microwave dielectric properties of BZT ceramics.With LBS and LaB co-doped,the sintering temperature of BZT ceramics significantly dropped to850⁸75°? and remained excellent microwave dielectric properties:?_r=30.75,Q×f=14279GHz,?_f=2.07 ppm/°?.?.The sintering temperature of Ba Zn₂T_i4O₁₁ ceramic dropped below 950°? in the presence of a liquid phase containing Li₂O and B₂O₃,and the ceramic remained excellent dielectric microwave properties.The liquid phase caused by LB glass reacts with BaZn₂T_i4O₁₁ ceramic to form Zn₂Ti₃O₈ and BaTi?BO₃?₂,which lead to abnormal grain growth.The sintering mechanism of BaZn₂Ti₄O₁₁ ceramics is similar to that of BZT ceramics.However,the products of Ba Zn₂Ti₄O₁₁ ceramics and LB glass are different from the BZT ceramics and LBS glass.Appropriate amount of LB glass promotes the densification of BaZn₂T_i4O₁₁ ceramic and improves the dielectric properties.However,excessive LB glass addition leads to the abnormal grain growth,which deteriorate the dielectric properties of BaZn₂T_i4O₁₁ ceramic.The Ba Zn₂T_i4O₁₁ceramics with 6wt.%LB glass and 10wt.%Ti O₂ sintered at 875°? shows excellent microwave dielectric properties:_r^e=25.6,Q×f=31508GHz,?_f=1.95 ppm/°?.?.The BaTi₅O₁₁?BT5?ceramics were prepared by the traditional solid state reaction with CuO.The effects of BaO-ZnO-B₂O₃?BZB?glass on the sintering temperature,phase development,microstructure and microwave dielectric properties of BT5 ceramics have been investigated in detail.The addition of BZB glass obviously lowers the sintering temperature of the BT5 ceramics below 950°?.The liquid phase caused by BZB glass accelerates the sintering process and promotes the densification of BT5 ceramic.The liquid phase caused by BZB glass will not react with BT5ceramics and lead to the phase change of BT5 ceramics when sintered at low temperature.The sintering process is liquid-phase sintering and the lower activation energy could be obtain because of the presence of a liquid phase.The BT5 ceramics with 4wt.%BZB glass sintered at 900°? shows excellent microwave dielectric properties:?_r=38.87,Q×f=29163GHz,?_f=33.7ppm/°?.