| Summary: | 碩士 === 國立中山大學 === 電機工程學系研究所 === 90 === Microwave dielectric resonators (DRs) are being widely used in microwave telecommunication devices owing to their excellent characteristics of suitable dielectric constant, good temperature stability, and low dielectric loss. In this study, the crystalline phase and the microwave dielectric properties of the (1-x)Al2O3 - xTiO2 (x=0.08, 0.12, 0.16) compositions with 2wt%, 4wt%, 6wt%, and 8wt% MgO-CaO-Al2O3-SiO2 (MCAS) glass addition have been investigated. By combining the material Al2O3 with negative temperature coefficient of the resonant frequency (τf = -55 ppm/℃) and the material TiO2 with positive τf value (τf = +450 ppm/℃), it is desired to produce the ceramics with τf ~0 ppm/℃. The MCAS is used as liquid-phase sintering aid to lower down the sintering temperature.
In the MCAS-doped (1-x)Al2O3 - xTiO2 system, the Al2TiO5 phase starts to appear at about 1250℃, and then the crystalline intensity of Al2TiO5 phase increases with the increase of sintering temperatures and MCAS glass content, until the temperatures that TiO2 is consumed. As the sintering temperature increases, the maximum dielectric constants and Q×f values can be obtained at 1250℃, and the τf values shift from positive to negative. The optimum τf value of —0.6 ppm/℃ exists in the 88mol%Al2O3 - 12mol%TiO2 composition with 2wt% MCAS addition and sintering temperature of 1300℃. The MCAS content, TiO2 content, and sintering temperature will result in the variation of microwave dielectric properties. In this study, MCAS-doped (1-x)Al2O3 - xTiO2 system exhibits the microwave dielectric properties of： εr=7~9.5, Q×f=6500~11000, and τf = -60 to +40ppm/℃. By adjusting the MCAS content, TiO2 content, and sintering temperatures, ceramics with good microwave properties can be obtained in the MCAS-doped (1-x)Al2O3 - xTiO2 system.
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