Mechanical response of atomic layer deposition alumina coatings on stiff and compliant substrates

In this study, the mechanical properties of atomic layer deposition (ALD) alumina coatings deposited at a range of temperatures from 80 °C onto substrates with differing stiffness including hard, stiff materials (silicon and glass) and soft, compliant materials (PET) have been investigated by nanoindentation. Approaches necessary to extract coating properties from the coating/substrate composite data have been developed in order to obtain reliable data from 150 nm thick coatings on hard, stiff substrates. This has shown that the elastic modulus of ALD alumina increases with deposition temperature as might be expected from the variation in density. Measurements for the ALD alumina coatings on PET using the same analysis method give lower elastic Modulus and hardness values; this is not due to an intrinsic difference in coating properties but is a consequence of the effect of modulus mismatch between coating and substrate on the measurement method. Reliable data for the coatings on PET are therefore more difficult to obtain but can be determined if a suitable modeling approach is adopted.