Low emission sputtered coatings for smart glazing

Optically selective low-emissive (low-E) filters, constituted of different ultrathin layers and suitable to an effective employment in glazing technology for low energy consumption buildings have been designed and fabricated on glass by means of sputtering technique. Sputtering process parameters, layers sequence of the stacked structure and thicknesses of the layers have been selected by means of a semi-empirical approach. Once defined optical requirements of high visible transmittance and low emissivity (< 5%), proper materials have been selected as metals and ceramics to create the optical filter. In particular, silver as highly IR reflecting metal and aluminium nitride as transparent insulating material, have been alternated in a very simple and highly effective coating formulation. However, preliminary optical simulation of optimized low-E coating did not take into account critical technological aspects such as the difficulty in producing high metallic quality ultrathin Ag layers and the undesired photo-emissive metal-nitrogen complexes formation at the Ag/AlN interfaces. The goal of obtaining Ag ultrathin compact layers has been reached with the aid of a proper aluminium nitride as adaptive layer. At the same time the chemical reactivity at the metal/ceramic interface (with consequent photo-emissive defects formation) has been prevented working in transition regime during AlN reactive sputtering process. In conclusion, a very simple low cost sputtering process is proposed for fabricating highly effective low-E coatings on large area glasses.