Fabrication Conditions of Diopside for Millimeterwave Dielectrics

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Recent developments in wireless communications have been expanded to millimeter waves for the high speed and the high rate transmission. Dielectrics with an ultrahigh quality factor Q and low dielectric constant \varepsilon_{\text{r}} are desired. Silicates are good candidates for millimeter wave dielectrics because of their low \varepsilon_{\text{r}}. Diopside (CaMgSi2O6) is one of the silicates with a chain SiO4 structure and a low \varepsilon_{\text{r}}. In this study, we focused on the fabrication conditions of diopside by the means of solid state reactions. The best ceramic of diopside with dielectric properties of \varepsilon_{\text{r}} = 7.6, Q \cdot f = 121{,}381 GHz and \mathit{TCf}= -66 ppm/°C was obtained by means of sintering a fine powder fabricated under the following conditions. Fine calcined grain powders were fabricated using fine raw materials with more than 99.9% purity, milling well for 24 h using ZrO2 balls with ca. 5 mm\phi, and calcining at 1200 °C for 3 h. The powder was a fine isolated powder without necking with ca. 0.3 μm size, as observed by scanning electron microscopy (SEM), and the specific surface area was ca. 3 m2/g, corresponding to ca. 0.66 μm grain sizes, as determined by the Brunauer--Emmett--Teller (BET) method. The relative density of sintered ceramics with mainly diopside composition formed by sintering the high-density green pellet applied cold isostatic pressing (CIP) at 1300 °C for 3 h was ca. 97%. The necking at 1250 °C was formed by a eutectic liquid on the SiO2--MgO binary system, which is formed by residual SiO2 in the core of low SiO2 materials.
2012-09-25

Fabrication Conditions of Diopside for Millimeterwave Dielectrics

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