Cold Sintering Na₂Mo₂O₇ Ceramic with Poly(ether imide) (PEI) Polymer to Realize High-Performance Composites and Integrated Multilayer Circuits

The cold-sintering process is utilized to fabricate ceramic–polymer (Na2Mo2O7-poly(ether imide), PEI) composites and integrated multilayer circuits. The Na2Mo2O7-PEI bulk composites cold-sintered at 120 °C show high densities (>90% theoretical). The permittivity at microwave frequencies decreases with increasing PEI content, following the classical logarithmic mixing law, and Qf values show no deterioration with the addition of PEI. Furthermore, the characteristic dielectric breakdown strength of the ceramic–polymer composite obtained from a Weibull plot increases dramatically from 55.1 to 107.5 MV/m with 10–20 vol % PEI additions. In the case of high PEI content where there is more segregation of the polymer within the ceramic matrix, there is a gradual decrease in the dielectric breakdown strength. Na2Mo2O7-PEI-Ag bulk ring resonators can be obtained by post screen printing, and the mixing laws are used to calculate the permittivity of the ring resonators. As a prototype of integrated multilayer circuits, Na2Mo2O7-PEI-Ag multilayer ring resonators with good microwave dielectric properties can be successfully densified by cold-sintered cofired ceramic-composite technology at 120 °C without delamination or warping, demonstrating the feasibility of cold sintering in the ceramic–polymer composite integrated multilayer circuits.