Vertically moving micromirror for detectors in the mid infrared

This paper presents continuative results on the design, fabrication and measurements of a vertically moving, electrostatically actuated micromirror, first shown at the IEEE MEMS 2007 [N. Quack, I. Züst, S. Blunier, J. Dual, M. Arnold, F. Felder, M. Rahim, H. Zogg, Electrostatically actuated micromirror for resonant cavity enhanced detectors, 20th IEEE Conference on Micro Electro Mechanical Systems, Kobe, Japan, 2007]. The micromirror is being developed for the use in a tunable resonant cavity enhanced detector (RCED) for the mid-infrared [M. Arnold, D. Zimin, H. Zogg, Resonant-cavity-enhanced photodetectors for the mid-infrared, Appl. Phys. Lett. 87 (2005) 141103]. RCEDs make use of a standing wave formed in an optical cavity and are sensitive at the resonances. The wavelengths of the resonances are hereby depending on the distance of the two cavity mirrors [M.S. Unlu, S. Strite, Resonant cavity enhanced photonic devices, J. Appl. Phys. 78 (1995) 608]. Moving one of the mirrors allows thus selecting the wavelengths which the device is sensitive at. The presented micromirror is actuated electrostatically and fabricated in a single crystalline silicon substrate. With actuation voltages below 25 V, displacements of 3 µm of a 300 µm x 300 µm mirror could be achieved. These displacements are expected to result in a tuning range over several microns wavelength in the infrared of the detector system. Such narrowband detector systems are sought after in multispectral infrared (IR) thermography or infrared spectroscopy [C.A. Musca, J. Antoszewski, K.J.Winchester, A.J. Keating, T. Nguyen, K.K.M.B.D. Silva, J.M. Dell, L. Faraone, P. Mitra, J.D. Beck, M.R. Skokan, J.E. Robinson, Monolithic integration of an Infrared Photon Detector with a MEMS-based tunable filter, IEEE Electron Dev. Lett. 26, (December (12)) (2005)].