Fabrication of 128 x 128 MEMS tunable F-P cavity optical filter array with surface micromachining

In this paper, a tunable Fabry-Perot (F-P) cavity filter with a large 128 x 128 array is successfully fabricated for an infrared (IR) hyperspectral imager via surface micromachining technology. A low-temperature (less than 200 degrees C) surface micromachining process is developed for manufacturing F-P tunable filter arrays, which has satisfactory compatibility. A suspended micro-bridge structure is created with a polyimide sacrificial layer. To obtain a large tuning range, long support arm structures are studied. The structure also has a compact array of folding arms. The filter can be tuned via an electrostatic force. The filter, which has an initial cavity length of 2.3 mu m, has a displacement of 1.5 mu m at an applied bias voltage of 8 V. The tuning wavelength of the filter is from 4.7 mu m to 2.8 mu m with an actuation voltage of less than 2 V. At the centre wavelength of 4 mu m, the spectral transmittance of the filter is 73%. The technology for the fabrication of microelectro mechanical systems (MEMS) filter arrays as dispersive elements has potential applications in hyperspectral imaging.