Low permittivity SrF2–xwt%LiF ceramics with low dielectric loss for high-reliability LTCC applications

SrF 2 is a promising low-permittivity fluoride with excellent microwave dielectric properties. Nevertheless, realizing densification in SrF 2 ceramics remains challenging due to their low surface energy. In this work, a series of SrF 2 – x wt%LiF ( x  = 0.5–20) ceramics were synthesized using the conventional solid-state reaction method. The incorporation of LiF effectively lowered the sintering temperature from 1050 °C to 775 °C and improved the relative density from 91% to 97.1%. Outstanding microwave dielectric properties ( ɛ r  = 6.39, Qf  = 71,024 GHz at 20 GHz and τ f  = −85.1 ppm/°C) were achieved at x  = 1.0, demonstrating great potential in millimeter-wave communication applications. In addition, the present ceramics demonstrated good chemical compatibility and a well-matched coefficient of thermal expansion with silver electrodes. Finite element simulations further revealed significantly reduced thermal stress when employing the present ceramics as substrates, highlighting the strong potential for high-reliability low temperature co-fired ceramic (LTCC) applications.