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 ( ε r ), 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 BaF 2 -LiF ceramics to address the need for low- ε r , high- Qf materials with high CTEs. The BaF 2 -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 BaF 2 -LiF ceramics serve as a promising dielectric resonator for high-performance millimeter-wave antennas. This study presents a comprehensive approach to optimize BaF 2 ceramics, addressing key parameters for high-reliability LTCC electronics and millimeter-wave antenna applications.