Low-temperature-sintered MgO-based microwave dielectric ceramics with ultralow loss and high thermal conductivity

With the development of 5G/6G communication, the requirements of portable devices for miniaturization and multifunction make low-temperature co-fired ceramic (LTCC) more and more important. In the area of high-frequency high-density passive integration, microwave dielectric ceramics with a low dielectric loss and high thermal conductivity are urgently needed to ensure the effective signals transmission and system reliability. However, most microwave dielectric ceramics with a low dielectric loss were not applicable for the LTCC technology due to the high sintering temperature. In this work, a series of MgO-based ceramics [(100 - x) wt.% MgO-x wt.% (0.2SrF(2)-0.8LiF) (x = 5,7,10)] were prepared by solid-state reaction method. The addition of sintering aid 0.2SrF(2)-0.8LiF (S2L8) decreased the sintering temperature below 880 degrees C without degrading the microwave dielectric properties of ceramics. Microwave dielectric properties of ceramics, including quality factor Q x f, relative permittivity epsilon(r), and temperature coefficient of resonant frequency tau(f), were investigated to find the optimum composition and sintering temperature. In general, MgO-7 wt.% S2L8 ceramic sintered at 860 degrees C exhibits outstanding properties of Q x f = 180 233 GHz, epsilon(r) = 9.11, tau(f) = -40.33 ppm/degrees C, and a high thermal conductivity of 24.02 W/(m K). This series of ceramics are suitable to be co-fired with Ag electrodes. With all those great properties, this series of MgO-based ceramics are expected to be the candidates for LTCC applications in 5G/6G technology.