Faculté des sciences

MEMS-based mirror array for astronomical instrumentation

Waldis, Severin ; Rooij, Nico de (Dir.) ; Herzig, Hans Peter (Codir.) ; Noell, W. (Codir.) ; Shea, H. (Codir.) ; Zamkostian, F. (Codir.)

Thèse de doctorat : Université de Neuchâtel, 2010.

The NASA’s and ESA’s James Webb Space telescope program, the development of the European Extremly Large Telescope (E-ELT) and the European Cosmic Vision program bring into fashion what astronomy always wanted to do, explaining where we are coming from by studying the formation of the galaxies and their evolution. Two requirements become a necessity: multiplexing and high spatial resolution... More

Add to personal list
    Summary
    The NASA’s and ESA’s James Webb Space telescope program, the development of the European Extremly Large Telescope (E-ELT) and the European Cosmic Vision program bring into fashion what astronomy always wanted to do, explaining where we are coming from by studying the formation of the galaxies and their evolution. Two requirements become a necessity: multiplexing and high spatial resolution capabilities. Thanks to its multiplexing capabilities, Multi-Object Spectroscopy (MOS) is becoming the central method to study large numbers of objects by recording simultaneously hundreds of spectra and utilizing a target selection mechanism in the field of view. Micro-electromechanical systems (MEMS) where identified by the major global astronomical and space societies as high-potential candidates for the use as reconfigurable target selection masks in future MOS: they are lightweight, remote-configurable, versatile and have the potential to be operated in cryogenic environment. Within the scope of this thesis the corner stones for a new class of MEMS mirror arrays (MMA) for the use in future MOS has been laid. The main requirements are: large tilt-angles of ≥ 20◦, feed-forward tilt-angle uniformity, large micromirrors of 100 × 200μm2 with a surface quality better than λ/20 and operation in cryogenic environment. The device concept, conceived to tackle these challenges, include a twochip architecture required to accommodate the large tilt-angle and mirror size. The micromirrors are made from 10μm-thick bulk single crystalline silicon to provide maximum flatness. The micromirrors are suspended with polysilicon cantilever beams located on the mirror backside. A system of landing and stopper beams has been implemented, which, together with intermediate supporting beams for uniform spacing between mirror and electrode, aimed to provide feed-forward tilt-angle uniformity over large arrays. The individual chips were fabricated utilizing a combination of bulk- and surface micromachining. An assembly scheme for mirror and electrode chip, allowing passive alignment with an accuracy of ±5μm, has been developed and demonstrated. The mirrors of fabricated 5×5 arrays showed to have an excellent surface quality, with a peak-to-valley deformation of 35nm for gold-coated mirrors at room temperature and 50nm for gold-coated mirrors at cryogenic temperatures (100K). Electromechanical characterization showed micromirrors yielding a tilt-angle of 20◦ at an actuation voltage below 90V. The tiltangle in ON-state was stable within 3arcmin over a voltage range of more than 10V, demonstrating the stopper and landing beam concept. Successful operation of the micromirror array in vacuo and cryogenic environment at temperatures below 100K has been showed and a preliminary demonstration of the object selection capabilities of the fabricated micromirrors has been carried out.