Low permittivity MgF2-LiF ceramics with ultra-low dielectric loss for ULTCC applications

In this work, MgF2–xwt%LiF (x = 0.5, 1.0, 2.5, 4.0, 5.0) ceramics have been prepared through the standard solid-state reaction method. X-ray diffraction patterns and scanning electron micrographs revealed the successful preparation of dense MgF2–LiF composite ceramics at an exceptionally low sintering temperature range of 525–600°C. The optimal microwave dielectric properties (εr = 5.09 ± 0.03, Qf = 100,733 ± 1646 GHz, τf = −67.4 ± 3.3 ppm/oC) were achieved in MgF2–0.5 wt%LiF ceramics after sintering at 550 oC for 3 h. The present ceramics exhibited an outstanding combination of low-εr, high Qf, and an ultra-low sintering temperature, surpassing the performance of most low-temperature-fired dielectric materials. Moreover, the theoretical Qf value, extrapolated from the fitting of infrared reflectivity spectra, was calculated to be 326,583 GHz, indicating significant potential for further Qf improvement. Additionally, the chemical compatibility with Al electrodes was confirmed, suggesting promising potential for ultra-low temperature co-fired ceramic (ULTCC) applications.