Thin film absorbers for visible, near-infrared, and short-wavelength infrared spectra

Two thin film absorbers are presented in this paper: one for the visible (VIS) and the near-infrared (NIR) spectra in the wavelength range of 350…1000 nm, the other for the short-wavelength infrared (SWIR) spectrum in the wavelength range of 1200…2000 nm. First, the refractive indices were determined for Al2O3 films prepared with atomic layer deposition (ALD), and amorphous Mo–Si–N films prepared with reactive sputter deposition. The measurements were made by spectroscopic reflectometry, ellipsometry, gonioreflectometry, and double-beam transfer standard spectrometry. The results were utilised in the design of the absorbers. The absorbers were manufactured as well, and they proved to have high absorption over their whole working spectra varying from 93.4% at the minimum to 99.9% at the maximum. The absorbers are applicable, e.g. to MEMS thermopile detectors.