Design and experiments for tunable optical sensor fabrication using (1 1 1)-oriented silicon micromachining

Abstract

The paper presents the design and the experiments performed for integration of a micromechanical voltage tunable Fabry–Perot interferometer structure with a silicon p–n photodiode in order to obtain a tunable optical sensor. The Fabry–Perot interferometer can be used as a voltage tunable filter for the input radiation or as a voltage controlled attenuator to regulate the light from a monochromatic source. In our approach, the top mirror of the Fabry–Perot cavity is an Au/SiO 2 movable membrane, formed by anisotropic etching of (1 1 1)-oriented Si wafers. The Au layer provides a good reflectivity of the upper mirror. The air–silicon surface acts as the lower mirror, as the anisotropic etching of (1 1 1)-oriented Si wafers provides very smooth surfaces. The upper movable mirror can be electrostatically actuated. This Fabry–Perot interferometer was realized on the top of a p–n photodiode.