Cordierite-based dielectric thick films on an oxidized copper layer: microstructural evidence of copper diffusion

Cordierite-based dielectric thick films deposited by screen-printing on a Cu₂O-Cu-96% alumina substrate were investigated with regard to microstructural characteristics, densification, and crystallization. Compared to direct deposition of the cordierite layer on metal Cu, the use of the Cu₂O layer as a diffusion barrier caused the cordierite thick film to become more stable without any significant interaction layer at the film interface after firing at 920°C for 30 min in a N₂ atmosphere. On the other hand, microstructural observation of the cordierite thick films on the Cu₂O revealed some evidence of Cu diffusion into the cordierite thick films, i.e., incorporation of Cu into the cordierite and remaining glass, and as Cu precipitates. Additionally, the diffused Cu was found to significantly affect densification and crystallization of the thick films, resulting in lower densification and crystallization temperatures. An XRD analysis supported the Cu incorporation from the Cu₂O layer into the cordierite by showing the disappearance of Cu₂O phase at 700°C, which is below densification temperature.