VIS Fabry-Pérot Interferometer with structured (TiO2/PE-SiO2)³ Bragg-reflectors on 5 mm large LP-Si3N4 membranes

Miniaturized spectrometry systems are achievable e.g. by the use of MEMS based tunable Fabry-Perot Interferometers (FPI) as wavelength selective filter elements. Main part of a FPI is the reflector which is usually realized as a stack of alternating dielectric layers with high and low refractive index. To achieve high reflectance layer stacks with larger number of layers and/or layers with a higher refractive index contrast are needed. Both have to be integrated within the manufacturing processes chain which in practice proves to be a difficult process. We present a FPI with a (TiO2/SiO2)3 reflector stack with a reflectance of 97 % and TiO2 as high refractive index layer for the use in the VIS-range of 555 nm to 585 nm. Main achievements of TiO2 instead of Si3N4 are a higher reflectance and a minimized reflector complexity. Furthermore, we introduce a dry etch process which is compatible and integrated in the manufacturing process chain of the MEMS FPI. Manufacturing of the 7.5 mm x 7.5 mm chip size FPI is done on 6 wafers consisting of a moveable reflector on a 210 nm thin and 5 mm in diameter LP-Si3N4 membrane and a fixed reflector with an aperture of 2 mm in diameter. The measured peak transmittance is between 28 % and 37 % with a FWHM bandwidth between 1.5 nm and 1.8 nm. It could be shown that the FPIs are tunable over the spectral range from 555 nm to 585 nm with a maximum control voltage of 45 V using the 18th interference order.