VIS Fabry-Pérot-Interferometer with (HL)4 PE-Si3N4/PE-SiO2 reflectors on freestanding LP-Si3N4 membranes for surface enhanced Raman spectroscopy

Abstract

Profound developments of miniaturized spectrometry systems enable new breakthrough applications such as online monitoring systems for specific molecules by Surface Enhanced Raman Spectroscopy (SERS). The spectrometry system is based on SERS active surfaces in-situ generating nanoparticles and miniaturized detectors with tunable Fabry-Pérot- Interferometers (FPI) with very sharp transmission peaks and a FWHM bandwidth below 2 nm. The key part of this online monitoring system is a tunable FPI, which is fabricated with MEMS technology. This contribution presents a 7.5 x 7.5 mm² chip size FPI, consisting of a moveable reflector on a 210 nm thin and up to 5.5 mm in diameter Si3N4 membrane on a silicon carrier, and a fixed reflector on glass. The optical resonator with an aperture of 2 mm diameter is designed for the central wavelength of 570 nm and realized by adhesive SU-8 bonding of the silicon on glass substrate. The moveable Si3N4 membrane is fabricated by combined wet and dry etching of silicon. The dielectric (HL)4 Si3N4/ SiO2 reflector stack with a reflectance of 93 % is deposited by PE-CVD on the LP-CVD-Si3N4 and structured by dry etching on the membrane and the glass. The measured peak transmittance is between 52 % and 74 % with a FWHM bandwidth between 1.3 nm and 2.0 nm. It was shown, that the FPIs are tunable over the spectral range from 555 nm to 585 nm which is relevant for this SERS application with a tuning voltage of 25 V.