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 <i>Qf</i> 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