A High-Resolution Electrostatically Actuated MEMS Tunable Fabry–Pérot Filter for LWIR Imaging and Sensing Applications

The long-wave infrared (LWIR) band lies near the peak of natural thermal emission, enabling stable passive imaging without active illumination, and it also covers characteristic spectral features of many important materials, making it a key spectral region for sensing and identification. However, the development of micro-electromechanical systems Fabry–Pérot tunable filters (MEMS-FPTFs) in this band is limited by strong material absorption, scarce low-loss thin-film options, and the difficulty of fabricating thick, low-stress, high-reflectivity distributed Bragg reflectors (DBRs). This work presents an electrostatically actuated MEMS-FPTF tailored for LWIR operation through an optical–mechanical co-design strategy. A low-loss Ge/ZnS DBR with > 92% reflectivity, combined with a C3-symmetric three-terminal ring suspension and a bulk-micromachining fabrication flow, enables high spectral finesse and stable large-stroke actuation. The device achieves a minimum full width at half maximum (FWHM) of 188 nm, a maximum quality factor (Q) of 63.7, and continuous tuning from 10.3 to 12 μm, representing advanced performance among LWIR MEMS-FPTFs. To further demonstrate application potential, we developed a dual-channel spectral–visual proof-of-concept recognition demonstration based on the MEMS-FPTF. Compared with a vision-only neural-network baseline, the hybrid model exhibits a significant improvement in recognition performance under illumination variations and complex background conditions. The proposed MEMS-FPTF offers a compact, low-power, and high-precision solution for LWIR spectral filtering, with strong promise for mineral identification, autonomous perception, and remote spectral sensing.