Mikromechanisches durchstimmbares Fabry-Perot-Filter für die IR-Gasanalytik

This contribution deals with design, fabrication and test of a micro-machined first order Fabry-Perot interferometer (FPI) intended for use as a tunable infrared (IR) filter in the (3-5) mum band. The technical approach minimizes mirror curvature by using 300 mum thick silicon (Si) mirror carriers for the coplanar fixed and movable mirrors of the FPI. Dielectric quarter-wave reflectance stacks consisting of alternating layers of silicon dioxide (SiO2) and polycrystalline silicon are used as mirrors. The moveable mirror consists of two parts to form a parallel spring suspension which provides the necessary vertical movement and minimizes any tilting of the movable mirror carrier. The cavity spacing is electrostatically driven and controlled. Tunable filters with a centre wavelength (CWL) of (4.5... 3.0) mum and a spectral bandwith (FWHM) of about 60 nm were tested and showed a peak transmittance of about 50%.