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Low Dielectric Loss Ceramics in the ZnAl2O4–TiO2 System as a τf Compensator

Authors

  • Cheng-Liang Huang,

    Corresponding author
    1. Department of Electrical Engineering, National Cheng Kung University, Tainan, Taiwan
      †Author to whom correspondence should be addressed. e-mail: huangcl@mail.ncku.edu.tw
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    • *Member, The American Ceramic Society.

  • Tung-Jung Yang,

    1. Department of Electrical Engineering, National Cheng Kung University, Tainan, Taiwan
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  • Chung-Chia Huang

    1. Department of Electrical Engineering, National Cheng Kung University, Tainan, Taiwan
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  • X. M. Chen—contributing editor

  • This work was financially supported by the National Science Council of Taiwan under Grant No. NSC 96-2221-E-006-117.

†Author to whom correspondence should be addressed. e-mail: huangcl@mail.ncku.edu.tw

Abstract

The microstructure and microwave dielectric properties of a (1−x)ZnAl2O4xTiO2 ceramic system prepared by the mixed oxide route have been investigated. The phases of ZnAl2O4 and TiO2 co-exist with each other and form a two-phase system, which is confirmed by the X-ray diffraction patterns and the energy dispersive X-ray spectrometer analysis. The microwave dielectric properties of the specimens are strongly related to the sintering temperature, the density, and the mole ratio of ZnAl2O4/TiO2. The sintering temperature of the specimen can be effectively lowered by increasing the TiO2 content. The Qu×f values of the ceramics can be significantly boosted by adding an appropriate amount of TiO2 and by sintering at a suitable temperature. Consequently, a very high Qu×f of 277 000 GHz associated with an ɛr of 25.2 and a large resonant frequency (τf) of 177 ppm/°C are obtained using 0.5ZnAl2O4–0.5TiO2 ceramics at 1390°C/4 h. These unique properties can be utilized as a τf compensator for dielectrics that would require extremely low loss. The MgTiO3 and Mg4Nb2O9 having negative τf were mixed with 0.5ZnAl2O4–0.5TiO2 ceramics to achieve dielectrics with a low ɛr, a high Qu×f, and a nearly-zero τf. In addition, a circle dual-mode microstrip bandpass filter is designed and fabricated using the proposed dielectric to study its performance.

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