ALD-Deposited Nanometer Scale Metal Oxide Films as Adhesion Promoters for Sputtered Metal and Ceramic Coatings on PMMA

摘要

Magnetron sputtered metal and ceramic films have poor adhesion to certain polymer structures especially poly-methylmethacrylate (PMMA) because of ion bombardment and short wavelength vacuum ultraviolet (VUV) radiation from the plasma. The PMMA surface suffers scission of the molecule's side chain by degradation of the ester group, consequently weakening the mechanical properties of the polymer. Nanometer-scale metal oxide Al_2O_3 and TiO_2 films deposited by atom ic layer deposition (ALD) were deposited on PMMA plates prior to magnetron sputtered Ti and TiC films. They proved to have a multifunctional role in enhancing the adhesion of the sputtered layer. The adhesion significantly improved with increasing ALD film thickness up to -40 nm thickness at which point the adhesion strength reached the cohesive strength of the substrate material itself. Using infra-red spectroscopy (ATR-FTIR) to monitor changes in the bonding in the surface layers, it is shown that the ALD layers act both as a shield against ion bombardment and also against the effects of VUV radiation from the plasma and so prevents the structural changes in the PMMA which otherwise cause degradation of adhesion.