Low-temperature co-fired ceramics with high thermal expansion and reliability for millimeter-wave antennas

Microwave dielectric ceramics (MWDCs) are essential in low-temperature co-fired ceramic (LTCC) technology, necessitating a low sintering temperature, low dielectric constant (εr), and high quality factor (Qf). On the other hand, the mismatch in the coefficients of thermal expansion (CTEs) between MWDCs and electrodes poses reliability challenges. Here, we report BaF2-LiF ceramics to address the need for low-εr, high-Qf materials with high CTEs. The BaF2-LiF ceramics exhibit improved properties, including a substantial decrease in sintering temperature from 1,025°C to 700°C, enhanced relative density from 90.8% to 97.3%, and optimized Qf values increased by 20%. Moreover, the resulting ceramics demonstrate a high CTE of 20.6 ppm/°C, ensuring compatibility with polymer-based laminates and metal electrodes. Additionally, the BaF2-LiF ceramics serve as a promising dielectric resonator for high-performance millimeter-wave antennas. This study presents a comprehensive approach to optimize BaF2 ceramics, addressing key parameters for high-reliability LTCC electronics and millimeter-wave antenna applications.