The path to low temperature crack-free high refractive index inorganic thin films

Abstract

In optics, inorganic coatings such as TiO2, ZrO2, HfO2, La2O3, and Ta2O5 surpass their organic or hybrid counterparts in terms of performance. They have the highest refractive index and remain unaffected by environmental degradation issues like yellowing. However, existing methods for creating inorganic coatings are limited to two approaches. The first involves costly and time-consuming techniques like physical vapor deposition (PVD) or chemical vapor deposition (CVD). The second approach, sol-gel synthesis, necessitates high temperatures that are incompatible with many substrates, resulting in rough surfaces and cracked samples. Phosio has introduced a platform technology for producing inorganic coatings with tunable refractive indices (ranging from n=1.30 to n=2.35). These coatings possess atomic smoothness and require minimal processing temperatures as low as 150°C. Furthermore, these materials can be cured with UV light and are compatible with nanoimprint lithography, all while maintaining environmental stability. In this manuscript, we share our journey to the process of achieving increased film thickness while ensuring the absence of cracks.