Sodium molybdate-hexagonal boron nitride composites enabled by cold sintering for microwave dielectric substrates

To fulfill the demands of more bandwidth in 5G and 6G communication technology, new dielectric substrates that can be co-fired into packages and devices that have low dielectric loss and improved thermal conductivity are desired. The motivation for this study is to design composites with low dielectric loss (tan delta) and high thermal conductivity (kappa), while still limiting the electrical conductivity, for microwave applications involving high power and high frequency. This work describes the fabrication of high-density electroceramic composites with a model dielectric material for cold sintering, namely sodium molybdate (Na2Mo2O7), and fillers with higher thermal conductivity such as hexagonal boron nitride. The physical properties of the composites were characterized as a function of filler vol.%, temperature, and frequency. Understanding the variation in measured properties is achieved through analyzing the respective transport mechanisms.