Growth and properties of high index Ta2O5 optical coatings prepared by HiPIMS and other methods

In the present work, we investigate amorphous Ta2O5 films prepared using different magnetron sputtering techniques at a constant average power but under various power delivery conditions in the context of their application as high index material in optical coatings. We used a broad range of pulse frequencies and pulse durations, discharge voltage and current levels. This allowed us to systematically assess the effect of the specific deposition conditions on the growth characteristics, surface morphology, as well as on the optical and mechanical properties. In particular, we show that the HiPIMS-deposited films exhibit enhanced properties such as low surface roughness (∼ 0.2 nm), low residual stress (∼ − 50 MPa), high refractive index (n550 ∼ 2.22) and high hardness (∼ 7.8 GPa). Some of these properties are found to be comparable with the values reported for fully dense thermally-grown films. The presented observations are discussed in terms of energetic conditions at the substrate level.