| Indialite Glass Ceramic Substrates for Millimeterwave Applications |
| Hitoshi OHSATO |
| Nagoya Industrial Science Research Institute |
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Millimeterwave dielectric substrates for wireless communications are expected to be developed on the higher quality factor Q, low dielectric constant r and temperature coefficient of resonant frequency TCf. Indialite glass ceramics have been developed for candidate of millimeterwave dielectrics, which have high Qf of more than 200,000 GHz and low r of 4.7, and TCf of -27 ppm/oC[1]. But, there are big problems of cracking of the ceramics, as the crystal growth of indialite from glass occurs as oriented c-axis crystals from the surface [2]. When the crystals with different orientation meet, the cracking occurs.
In this paper, for avoid the cracking of glass ceramics, volume crystallizations on the glass with cordierite composition are applied adding TiO2 as nucleation material [3]. TiO2 10 and 20 wt% doped glasses crystallized at 1200, 1250, 1300 and 1350 oC for 20 h were identified as indialite with rutile. Although 0 wt% added one has cracks, and 10 and 20 wt% doped ones have no cracks.
Fig. 1(a), 1(b) and 1(c) show r, Qf and TCf, respectively, as a function of adding TiO2 wt%. The r increase 4.67 to 7.66. Qf decreased from 176,000 to 52,700 GHz. And TCf increased from -25.8 to +39.4 ppm/oC. TCf with near zero ppm/oC ceramics might be obtained among 10 to 20 wt% TiO2 addition.
Direct casting method for glass ceramics will be presented in the seminal. The glass ceramics fabricated by the direct casting method might be reduced the price because of the short fabricating steps.
Fig. 1 Millimeterwave dielectric properties of r (a), Qf (b) and TCf (c) as a function of TiO2 addition.
References:
[1] H. Ohsato, J-S. Kim, A-Y. Kim, C-Il Cheon, and K-W. Chae, Jpn. J. Applied Physics, 50, (2011) 09NF01-1-5.
[2] H. Ohsato, J-S. Kim, C.-Il Cheon, I. Kagomiya, J. Ceram. Soc. Japn, 121, 649 (2013).
[3] K. Kagomiya and H. Ohsato, Patent application 2014-164285, (2014,08,12).
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| Acknowledgements : The authors thanks to Dr. Chunting Lee and Professors Ken'ichi Kakimoto, Chae-Il Cheon, and Hirotaka Ogawa. A part of this work was supported by a Grant-in Aid for Science Research (C) and Adaptable & Seamless Technology Transfer Program (A-step) by MEXT Japan. |
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