ULTCC-Compatible LiPO ₃ Ceramic with Ultralow Permittivity for 5G High-Gain Antenna Array Applications

In contemporary radio frequency (RF) systems, organic substrate materials are extensively utilized due to their low permittivity. However, their low thermal conductivity (κ ≈ 0.25 W/(m·K)) can lead to catastrophic thermal management issues in RF systems. This work proposes a LiPO 3 ceramic substrate, which demonstrates ultralow permittivity (ε r ≈ 4) and exceptional quality factors (tan δ at the 10 –4 level). However, the temperature coefficient of resonant frequency for the LiPO 3 ceramic is a large negative value (TCF ≈ −110 ppm/°C), which requires further adjustment. The ε r of LiPO 3 is comparable to that of organic laminates, which helps reduce signal delay, and its high quality factor gives it excellent frequency selectivity. The low ionic polarizability of Li + and P 5+ in combination with the unique (PO 3 ) n chain structure of the phosphate groups in LiPO 3 is intrinsically responsible for its low permittivity. In addition, the κ of LiPO 3 exceeding 2 W/(m·K) contributes to extending the lifespan of the RF components. Furthermore, LiPO 3 has a sintering temperature of only 630 °C and does not undergo chemical reactions or physical penetration with aluminum. This suggests its potential in the ultralow temperature cofired ceramics (ULTCC) field. The potential of LiPO 3 was validated through an antenna array application in the 5G network. This work effectively resolves the conflict between signal delay and thermal management in high-integration RF systems.