| The development of high frequency technology has become the inevitable trend of the development of wireless communication technology. Microwave dielectric ceramics play an important role in this process.Dielectric antennas,dielectric substrates,filters,diplexers and other components fabricated by microwave dielectric ceramics are widely used in the communication field.However,with the further development of device miniaturization,high performance and multi-function,it also poses a challenge to the development of new high performance ceramic systems.Based on this point,new Al2Mo3O12-based microwave dielectric ceramic system was studied in this paper.The relationship between the process parameters and the phase composition,microstructure and microwave dielectric properties of ceramics was systematically studied by using the traditional solid-state reaction sintering method,and the preparation process of the new ceramic system was explored.Furthermore,Al2Mo3O12-based composites for low temperature co-firing ceramic technology and high performance microwave substrate were developed combined with the characteristics of Al2Mo3O12-based ceramics.The achievements are listed as follows:(1)The optimal process route of preparing Al2Mo3O12 ceramic by solid-state reaction sintering was determined.Firstly,pure Al2Mo3O12 powder was obtained by controlling the calcination temperature.In addition,Al2Mo3O12 ceramic with stable phase composition,compact microstructure and uniform grain size distribution was then obtained by controlling sintering temperature and sintering time respectively.Finally,after calcined at 750℃ and sintered at 790℃ for 12 h,Al2Mo3O12 microwave dielectric ceramics with the highest density were obtained for the first time.The dielectric constant is 5.69,the quality factor is 73900 GHz and the temperature coefficient of resonant frequency is-32.3 ppm/℃.(2)By adding TiO2 to adjust temperature coefficient of resonant frequency of Al2Mo3O12 to zero,novel temperature-stable Al2Mo3O12 composite ceramic suitable for low temperature co-firing ceramic technology was obtained.It was revealed that the rutile TiO2 could co-exist with monoclinic Al2Mo3O12 in the samples.With increasing addition of TiO2 from 0 mol to 0.4 mol,the εr value of the obtained ceramics increased from 5.69 to 6.85,the value of Q ×f decreased from 73900 GHz to 45700 GHz,and τf varied from-32.3 to+9.2 ppm/℃.Finally,0.7 Al2Mo3O12-0.3 TiO2 microwave dielectric ceramics with near zero frequency temperature coefficient were obtained.Such high-performance microwave dielectric ceramics can be sintered at low temperature with high density and has outstanding properties among other similar systems.(3)An Al2Mo3O12-based microwave dielectric ceramic system which can be co-fired with Al electrode at ultra-low temperature was obtained.By adding Bi2O3 to the Al2No3O12 matrix,Bi2O3 could react with the matrix to form Bi2Mo3O12 phase with ultra-low melting point,which effectively reduces the sintering temperature of the composite ceramics to below 660℃.With 4 wt.%Bi2O3 addition,the composite ceramic sintered at 650℃ for 12 h presents good microwave dielectric properties of:εr=5.91,Q×f=49600 GHz and τf=-41.2 ppm/℃,and excellent chemical stability cofiring with the electrode metal Al,indicating that it is a promising candidate for ULTCC applications.(4)Novel microwave dielectric composites of PTFE filled with Al2Mo3O12 ceramic were developed.By modifying the ceramic surface with coupling agent,the dispersion of Al2Mo3O12 ceramic powder in PTFE was effectively improved,thus improving the performance of the composites,especially in microwave dielectric properties,thermal and mechanical properties.This composite shows its value as high performance microwave substrate.(5)A 24 GHz substrate integrated waveguide bandpass filter based on the Al2Mo3O12-PTFE composite substrate was carried out.In order to verify the reliability of the substrate,CST software was used to simulate the multi-physical field of the filter.Firstly,based on the microwave dielectric properties of Al2Mo3O12-PTFE composite,the filter satisfying the index was designed.Then,the mechanical and thermal properties of Al2Mo3O12-PTFE composite substrate were measured.Through multiphysic simulation,the temperature distribution and mechanical displacements of the filter were analyzed.It is revealed that the filter presents high stability on the performance caused by self-heating and dimension deformation due to the good microwave dielectric,thermal and mechanical properties of the substrate.These results indicate that the Al2Mo3O12-PTFE composite would be a promising candidate for high-performance microwave dielectric substrates as well as providing a reference for the development of other high performance materials. |
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