Synthesis and Microwave Dielectric Properties of La2O3–$x$B2O3-Based Melt Mixtures for Low-Temperature Cofired Ceramics

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La2O3–$x$B2O3-based melts were fabricated. Two kinds of melts, crystalline at $x=2$ and amorphous at $x=3$ with ZnO additions, were obtained. The microwave dielectric properties and microstructure of the ceramics prepared from the melts and calcined La2O3–B2O3 were investigated. Several mixtures of 50 wt % melts and 50 wt % calcined powder were fireable around 900°C, which was a low firing temperature for cofiring with a low-loss conductor. Among them, the dielectric properties for a fired mixture of 50 wt % La2O3–2B2O3–0.5ZnO melt and 50 wt % calcined powder showed an fQ value of about 30000 GHz and $\varepsilon_{\text{r}}=9--10$ at 13 GHz. 5 wt % crystalline additives fired at 925°C, which have the same composition as the host ceramic material, increased fQ to 63000 GHz. The mixtures of 20–80 wt % crystalline melt and 80–20 wt % amorphous melt were also sinterable below 900°C. The best dielectric properties, $\textit{fQ}=72000$ GHz and $\varepsilon_{\text{r}}=8$ at 13 GHz, with low firing temperatures were exhibited when the mixing ratio was 20 wt % crystalline melt and 80 wt % amorphous melt. The green sheet, which contained two kinds of melts, could be cofired with Ag at 900°C.
2005-09-15