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 (S 2 L 8 ) decreased the sintering temperature below 880°C without degrading the microwave dielectric properties of ceramics. Microwave dielectric properties of ceramics, including quality factor Q × f , relative permittivity ε r , and temperature coefficient of resonant frequency τ f , were investigated to find the optimum composition and sintering temperature. In general, MgO–7 wt.% S 2 L 8 ceramic sintered at 860°C exhibits outstanding properties of Q × f = 180 233 GHz, ε r = 9.11, τ f = −40.33 ppm/°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.