Millimeter-Wave Dielectric Properties of Cordierite/Indialite Glass Ceramics

Millimeter-wave wireless communications with high data transfer and radar system for Pre-Crash Safety System have been developed recently. Cordierite (Mg 2 Al 4 Si 5 O 18 ) is one of the silicates with good millimeter-wave dielectric properties. Cordierite has two polymorphs: cordierite and indialite. Cordierite is of low symmetry form with ordered structure, and indialite is of high symmetry form with disordered structure. In this study, indialite/cordierite glass ceramics are fabricated with good millimeter-wave properties. The $\mathit{Qf}$ values are dependent on the amount of indialite phase and crystallization conditions. Indialite with high symmetry showed higher $\mathit{Qf}$ values than cordierite with low symmetry. This result clearly shows that high symmetry results in high $\mathit{Qf}$ when the samples are prepared under the same crystallization conditions. However, these glass ceramics are very difficult to make under the same conditions because of non-uniform crystallization. These dielectric glass ceramics show high $\mathit{Qf}$ values of ${>}200{,}000$ GHz, low dielectric constant $\varepsilon_{\text{r}} = 4.7$, and $\mathit{TCf}= -27$ ppm/°C.