All-ceramics with ultrahigh thermal conductivity and superior dielectric properties created at ultralow temperatures

Ceramics that are thermally conductive and can be sintered at low temperatures are particularly desired for hybrid integration and co-fired technology in upsurging high-frequency communication applications. However, a seemingly contradictory relation between high thermal conductivity and low sintering temperature remains a critical challenge. Herein, we report that densified and oriented boron nitride (BN)-based ceramic composites that are sintered at ultralow temperatures (e.g., 150°C) exhibit an ultrahigh thermal conductivity (42 W m −1 K −1 ), far outperforming current state-of-the-art low-temperature ceramics. We reveal by experiments and simulations that the high thermal conductivity of the ceramic composites is attributable to a high density and high orientation of BN platelets that were previously unattainable at low temperatures, as further supported by our newly developed theoretical model. Coupled with simultaneously achieved excellent microwave dielectric properties, this work opens up a new avenue to high-thermal-conductivity ceramics that are integrable with high-power devices at low temperatures.