Bulk micromachined tunable Fabry-Perot micro-interferometer for the visible spectral range

The design, fabrication and measured characteristics of a bulk-micromachined tunable Fabry-Perot MicroInterferometer (FPMI) for the visible spectral range are presented. The FPMI is formed by two parallel 40 nm thick silver mirrors supported by a 300 nm low-tensile stress silicon nitride membrane with a square aperture (side length of 2 mm) and initial cavity gap of 1.2 µm. One of the mirrors is fixed, the other is under tension on a movable Si frame, which is electrostatically deflected, using several dis-tributed electrodes, to control cavity spacing and mirror parallelism. Performance achieved is: high flatness of the mirrors (λ/10 for the visible part of the spectrum), low control voltages (<21 V for 450 nm deflection) and simple fabrication. Keywords: interferometer, Fabry-Perot, spectrometer, FWHM, finesse