High rate deposition of thick oxide layers on plastic substrates
Plastic materials have optical clarity and the processing benefits of a thermoplastic, but lack abrasion resistance. Al2O3 as well as SiOx layers perform very well as clear abrasion resistant layers. The typical layer thickness ranges from 1 mu m to 6 mu m. High deposition rates at an appreciate layer quality can be reached by application of the hollow cathode activated deposition (HAD) process. The HAD process is based on the reactive evaporation of oxide or metal with high rates in combination with a hollow cathode plasma activation. The hollow cathode plasma source generates an arc discharge plasma with very high plasma densities in the order of 1012 cm-3. For insulating substrates a high self bias potential of about 15 V is obtained. The typical deposition rates are: 100-150 nm/s for Al2O3 and 300-600 nm/s for SiOx. The deposited layers show a dense, amorphous structure and the microhardness (measured by nanoindentation) amounts to 6 GPa for Al2O3 layers respectively 3 GPa for SiOx . Regardless of the different hardnesses the abrasion resistance performs very well for both oxides.