MgF2-based microwave dielectric ceramics with ultra-low sintering temperature and high thermal expansion coefficient

Abstract

Ultralow-temperature co-fired ceramic (ULTCC) materials with low permittivity and dielectric loss are considered promising materials for 5 G communication applications. Herein, a novel multiphase xMgF2-(1x)LiF (x = 0.20, 0.35, 0.50, 0.65) microwave dielectric ceramic was prepared via a conventional solid-state method for ULTCC applications. The ceramic achieves densification at a sintering temperature of 625 °C. The xMgF2-(1-x)LiF ceramics exhibit tunable permittivity ranging from 5.21 to 7.30, Q×f from 39400 to 52800 GHz, and τf from − 61 to − 98 ppm °C−1. Analysis of the crystal structure and microstructure revealed that the volatilisation of fluoride ions in the ceramics led to an increase in defect concentration, contributing to an unfavourable decrease in dielectric loss. The 0.35MgF2-0.65LiF ceramic shows comprehensive properties with the highest Q×f value (52800 GHz) and low permittivity (6.40). Furthermore, the thermal expansion coefficient is an important performance parameter in ceramic packaging with the 0.35 MgF2-0.65 LiF ceramic exhibiting a colossal thermal expansion coefficient of 28.69 ppm °C−1, thus enabling excellent compatibility with printed circuit board (PCB) substrates. Moreover, these high thermal expansion coefficient ceramics are excellent candidates for packaging.