Microwave dielectric properties of Mg4Nb2O9–3.0 wt.% LiF ceramics prepared with CaTiO3 additions

A family of low-temperature co-fired ceramics (LTCC) based on mixtures of Mg4Nb2O9–3.0 wt.% LiF (MNLF) and CaTiO3 ceramics has been investigated for microwave applications. In this study, it was found that, when increasing amounts of CaTiO3 additions from 0 to 10 wt.%, the temperature coefficient of resonant frequency (τf) extremely varied from −71.5 to 39.9 ppm/°C. The dielectric constants (ɛr) increased from 12.3 to 18.3 and the quality factor (Q·f) drastically decreased from 118,989 to 11,119 GHz. From these results, the MNLF–6 wt.% CaTiO3 ceramic sintered at 950 °C for 10 h was shown to be the appropriate dielectric properties: ɛr = 15.7, Q·f = 22,098 GHz, and τf = −3.3 ppm/°C. As for the chemical compatibility of MNLF–6 wt.% CaTiO3 ceramic with Ag, any secondary phase was not recognized from the XRPD profile of the samples heat-treated at 920 °C for 10 h. Thus, it was considered that the MNLF–x wt.% CaTiO3 ceramics are applicable to the multilayer devices with silver.