Research of microwave/millimeterwave dielectrics on the silicate system

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The wireless communications have been tremendously developed in the recent ubiquitous age. The utilizable frequency region has been expanded to millimeterwaves because of shortage of conventional frequency regions. For the ultra high frequencies of millimeterwaves, dielectrics with ultra high quality factor Q and low dielectric constant a are desired. Low Er is necessary to short the delay time of signals and to make devices small in size. Silicates for candidate of millimeterwave materials have low dielectric constant, because of silica-oxygen tetrahedra composed of half covalent bonds.Silicates were classified according to connecting system of SiO_4 tetrahedra. In the neso-silicates composed by isolated SiO_4 tetrahedron, it was clarified at 2005 that forsterite and willemite have high Qf more than 200000GHz. The temperature coefficients of resonant frequency tr were improved to O from -60ppm/℃ by adding rutile with high zr. At 2006, cordierite was improved the Qf adding Ni, Zn and Mn. Especially, according to doping Ni, the Qf was improved from 30000GHz to 60000GHz. The origin of the improvement was clarified by crystal structural analysis using Rietveld method. Degradation of ordering of SiO_4 and A10_4 tetrahedra brings, high Q. The degradation was accompanied with high symmetry by the transformation from cordierite to indierite. In this research period, we clarified the microwave properties of silicate compounds more than 11. The dielectric constants of these compounds have low of 6 to 8 revealing the origin of covalency presented by us. The highest Qf was obtained in the forsterite accompanied by willemite. The temperature coefficients of resonant frequency zr are located around -20 to -70 ppm/0C with relative low values