Electrical properties of crosslinked aliphatic polyurea thin films prepared by vapor deposition polymerization

Vapor deposition polymerization (VDP) is a method for producing high-performance polymeric thin films, such as polyimide, polyamide and polyurea, by co-evaporation of two types of bi-functional monomers on the substrate surface. Polymeric films obtained by VDP have a high dielectric constant and high breakdown voltage and low impurity content due to being solvent-free. In this study, polyurea thin films were prepared by VDP. The relation between the electrical properties and the chemical structures was investigated by IR spectroscopy. The IR spectra of the crosslinked aliphatic polyurea thin films indicated strong intermolecular hydrogen bonds even in the disordered network structure without molecular orientation. In addition, the crosslinking agent gave rise to an increase in the concentration of urea groups. Both effects of the crosslinking agent may have contributed to the simultaneous improvement of the dielectric constant and the dielectric loss, even though they generally have a trade-off relationship.