High-resolution miniature FTIR spectrometer enabled by a large linear travel MEMS pop-up mirror

This paper reports the design, fabrication, and characterization of a millimeter diameter, surface micromachined Micro-Electro-Mechanical-Systems (MEMS) mirror, which is assembled perpendicular to the substrate and can be linearly and repeatedly traversed through 600 μm. The moving mirror, when combined with a fixed mirror and beamsplitter, make up a monolithic MEMS Michelson interferometer; all are made on the same substrate and in the same surface micromachined fabrication process. The beamsplitter has been specifically designed such that the motion of the mirror enables modulation of light over the 2-14 μm spectral region. The rapid scan MEMS Michelson interferometer is the engine behind a miniaturized, Fourier transform infrared (FTIR) absorption spectrometer. The FTIR measures the absorption of infrared (IR) radiation by a target material, which can be used for the detection and identification of gases, liquids, or solids. The fabrication of the mirror with the ability to displace 600 μm along the optical axis enables the miniaturized system to have species identification resolution, while leveraging wafer scale batch fabrication to enable extremely low system cost. The successful fabrication of the millimeter diameter mirrors and beamsplitter with interferometric alignment over the range of travel of the moving mirror promises unprecedented sensitivity relative to the size of the FTIR spectrometer system.