Boosting densification and microwave dielectric properties in cold sintered BaF2 ceramics for 5.8 GHz WLAN applications

Abstract BaF2 is a low-firing fluoride with excellent microwave dielectric properties, while the densification of BaF2 ceramics is challenging via conventional sintering. In this work, dense BaF2 ceramics with 95.3~98.5% relative densities have been prepared via the cold sintering (150–600 MPa, 150 °C, 1 h) and following post-annealing at 900 °C. The scanning electron microscope images demonstrate closely packed microstructures, and the chemical compatibility between BaF2 ceramics and Ag electrodes is identified. The optimum Qf (82,320 GHz) is 1.53 times higher than that obtained via conventional sintering (53,654 GHz), with a dielectric permittivity, er = 7.3, and a temperature coefficient of resonant frequency, τf = –107.9 ppm/°C. Furthermore, a BaF2-based microstrip patch antenna is fabricated, which realizes an S11 = –16.5 dB, a high gain of 5.84 dB, and total efficiency of −0.38 dB at 5.78 GHz. The exceptional microwave dielectric properties and antenna performances indicate that BaF2 ceramics are promising candidates for 5.8 GHz wireless local area network applications.