Tunable optical filters based on silicon nitride high contrast gratings

We report the use of a 500-nm-thick silicon nitride membrane as a high-reflectivity mirror in the orange-red spectral range. High contrast gratings based on semiconductors have already been used as high-reflectivity mirrors in the near-IR spectral range, but their use in the visible, which is essential for many types of biosensors, is much less explored. Our membrane is patterned with a high contrast grating of 560-nm period and forms part of a tunable Fabry-Pérot cavity. The cavity is tuned electrostatically and functions as a tunable optical filter. Three different designs of the membrane suspension are investigated to establish the effect of the arm geometry on the surface stress and the displacement of the membrane. By applying 9 V to the device, we observe a 13-nm wavelength shift of the spectral peak centered at 630 nm.