Study On High K Dielectric Ceramic For Microstrip Filter

With the rapid development of modern communication equipment towards miniaturization,high frequency and integration,the requirements for the size and operating frequency of microstrip ceramic filters are increasing.Not only the filter design puts forward higher requirements,but also the required properties of filter media substrate material are getting higher and higher.In order to meet the above requirements,this paper developed several microwave dielectric ceramic material formulations which relative dielectric constant are 25 or so,the resonant frequency temperature coefficient approach 0.Based on 0.85MgTiO₃-0.15Ca_0.6La_0.8/3TiO₃ microwave dielectric ceramic?usually called as 85MLC?,the effect of non-stoichiometric ratio,ZnO doping,Co₂O₃ doping,Nd₂O₃ doping,SnO₂ doping on the phase composition,microstructure and dielectric properties of 85 MLC were investigated.The solid phase reaction method was used to synthesize 85 MLC ceramics,and its phase composition,microstructure and microwave dielectric properties were investigated.XRD shows that the main crystal phase of 85 MLC ceramics is MgTiO₃,the second phase is Ca_0.6La_0.8/3TiO₃,and the best sintering temperature is 1255? with a small amount of MgTi₂O₅.When the sintering temperature is too high,The normal density of the ceramic sample becomes lower,and the density of the ceramic sample becomes lower.The effect of non-stoichiometric ratio on the phase composition,microstructure and dielectric properties of 85 MLC ceramics was revealed.The experimental results show that the loss or excess of titanium has no effect on the main phase composition of85 MLC ceramics.The absence of titanium makes the pores of the ceramic sample appear.When the content of titanium increases,the pores disappear and the ceramics become dense.This indicates that TiO₂ can improve the porosity of the ceramics.However,when the content of titanium in the system was too high,more MgTi₂O₅ phase was detected,which decreased the properties of 85 MLC ceramics.The effects of ZnO doping on the phase composition,microstructure and microwave dielectric properties of 85 MLC ceramics were studied.The results show that ZnO can promote the growth of ceramic grains,thus enhancing the density and slightly increasing the relative dielectric constant of the ceramic samples.However,due to thevolatility of ZnO,the content of TiO₂ in the system is relatively large.With the increase of ZnO doping amount,the content of minor phase in the system increases slightly,and the Q×f value of the ceramic is slightly deteriorated.The effects of Co₂O₃ doping on the phase composition,microstructure and microwave dielectric properties of 85 MLC ceramics were studied.The results show that the addition of Co₂O₃ can inhibit the formation of MgTi₂O₅ in the system,so as to improve the Q×f value of the ceramic material.However,with the amount of Co₂O₃ increasing,a new phase of Mg2TiO4 was detected,deteriorating the properties of ceramic materials.The effects of Nd₂O₃ doping on the crystal structure,microstructure and dielectric properties of 85 MLC ceramics were studied.It is found that the relative dielectric constant of the ceramic system gets lower because the ion polarizability of Nd3+ ions is lower than that of La3+ions.In the meanwhile,the Q×f value of the ceramic samples decreases.However,when x =0.2,the resonant frequency temperature coefficient of the ceramic sample is closest to zero.The influence of SnO₂ doping on the phase composition,microstructure,and dielectric properties of 85 MLC ceramics was studied.The results show that the doping of SnO₂ can effectively improve the sintered density of ceramics.Because SnO₂ is very volatile at high temperature,a large number of pores are formed on the ceramic surface,but the porosity of the ceramic is lower than that of the undoped sampleIn this study,excellent microwave dielectric properties have been obtained for the systems investigated?measured at 6.2GHz?:?1?0.85Mg0.90Zn0.10TiO₃-0.15Ca_0.6La_0.8/3TiO₃:?r=25.04,Q×f=43000GHz.?2?Mg0.85Ca0.09La0.04Ti0.95O₃:?r=23.49,Q×f=56000GHz,?f=-3.28ppm/?.?3?0.85MgTiO₃-0.15Ca0.6La0.6/3Nd0.2/3TiO₃:?r=24.76,Q×f=47500GHz,?f=+0.5ppm/?.?4?0.85MgTiO₃-0.15Ca_0.6La_0.8/3TiO₃-0.010SnO₂:?r=24.96,Q×f=50500GHz.?5?0.85MgTiO₃-0.15Ca_0.6La_0.8/3TiO₃+1wt%Co₂O₃:?r=24.28,Q×f=55000GHz.