Bulk-micromachined tunable Fabry-Perot microinterferometer 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 mu m. One of the mirrors is fixed, the other is under tension on a movable Si frame, wh ch is electrostatically deflected, using several distributed electrodes, to control cavity spacing and mirror parallelism. Performance achieved is: high flatness of the mir-ors, low control voltages (<21 V for 450 nm deflection) and simple fabrication.