  We report on the optical, mechanical and structural characterization of the
sputtered coating materials of Advanced LIGO, Advanced Virgo and KAGRA
gravitational-waves detectors. We present the latest results of our research
program aiming at decreasing coating thermal noise through doping, optimization
of deposition parameters and post-deposition annealing. Finally, we propose
sputtered Si3N4 as a candidate material for the mirrors of future detectors.
