NOSCRATCH · Process and material research for ultra-stable antireflective coatings on glass

Broad band anti-reflective coatings need a low-index material at the top position. Normally SiO2 is used. This layer is in direct contact to the environment. While a number of high- and medium-index layers with a high hardness (up to 30 GPa) have been developed in the past, the hardness of the low-index layer on the top is limited to about 10 GPa. Under hard conditions this layer is then the weak point of the total layer stack. This excludes a number of possible applications.The goal of the project is to develope a new, ultra-stable AR-coating and the relevant deposition processes. Therefore a new optical material based on a Al-Six-Oy-Fz composite will be developed. The hardness of this material should exceed 20 GPa and must have a refractive index of lower than 1.60 (at 550 nm). The deposition process shall be based on magnetron sputtering with a special focus on highly ionized sputtering. This ensures that the process can be upscaled and can be used for high deposition rates.The result is a broad band antireflective coating which shows a significant higher scratch resistance (from about 10 to 1000 cycles Taber-abraser test) and a doubled hardness (> 20 GPa). In addition, the coating must be stable against hydrothermal corrosion (1000 cycles autoklave).The project focusses not only on precision optical products but potentially on all flat glas products such as glasses for instruments, photovoltaic modules, automotive, sensors, displays.