Silver-based reflective coatings for micromachined optical filters

Silver films of 40 nm thickness, evaporated on a 300 nm thick low-stress si licon nitride layer, are used as high-quality mirrors operating in the visi ble and near IR spectral range. Application of a silicon nitride membrane u nder tension, placed within a square Si frame after bulk micromachining, im proves the initial mirror flatness. Two parallel mirrors, each with square aperture of up to 2 x 2 mm(2) and an electrostatically controlled spacing. form a tunable Fabry-Perot optical filter. Investigation of the silver-base d reflective coatings. and mirror characterization, including influence of bulk micromachining, are presented.