R&D of next generation millimeter-wave dielectrics with low dielectric constant and high Q

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Millimeter-wave dielectrics of glass ceramics are formed from the glass with cordierite composition. Glass ceramics composed by indialite which is a polymorph of cordierite were formed. The glass ceramics with superior properties such as high Qf > 200,000 GHz, low dielectric constant (ε_r) of 4.7, temperature coefficient of resonant frequency (TCf) = -27 ppm/℃. But, the glass ceramics shown an anisotropic feature crystallized from glass surface. Cordierite is well known as low thermal expansion material with minus expansion to c-axis and plus expansion to a-axis. A serious problem of clacks appears at the point met the crystals grew from different glass surface. As large cracks are reduced by slow cooling after sintering, measurement of millimeter-wave properties was possible. But, small clacks affected to the Qf values so as to be random variation. Moreover, rutile powder was added in the glass composition for crystal growth agent so as to crystalize in the volume of grass. Consequently, millimeter-wave dielectrics without the cracks and with good properties were fabricated. The properties are as follows: Qf= 120,000GHz, TCf= 0 ppm/OC, ε_r = 7.