Amorphous silicon oxide, silicon oxynitride and silicon nitride films were deposited in a PECVD reactor using silane (SiH4),ammonia (NH3) and nitrous oxide (N2O) as precursor gases. The N2O/NH3 flow ratio was varied in order to obtain different oxynitride compositions. The films were characterized by spectroscopic ellipsometry, XPS and FTIR spectroscopy. The compositions and infrared optical absorption properties of the three different types of films were investigated and compared. Special attention was paid to analyze the Si-O/Si-N bond stretching absorption including the absorption band intensity. It was found that the silicon oxynitride films show a dominant infrared stretching band due to the Si-O/Si-N bond , with the infrared absorption peak located between 860cm-1(11.6μm) for Si-N bond in silicon nitride and 1063cm-1(9.4μm) for Si-O bond in silicon oxide. The position of peak also shifts to a shorter wavelength when increasing the N2O/NH3 flow ratio. The infrared optical absorption properties of the silicon oxynitride films make them well suited for the absorber of uncooled microbolometer detectors© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.