Optical characterization of two-dimensional array of 2048 tilting micromirrors for astronomical spectroscopy

Michael David Canonica, Nico de Rooij, Wilfried Noell
Optical Society of America, 2013
Journal paper

A micromirror array composed of 2048 silicon micromirrors measuring 200 x 100 mu m(2) and tilting by 25 degrees was developed as a reconfigurable slit mask for multi-object spectroscopy (MOS) in astronomy. The fill factor, contrast, and mirror deformation at both room and cryogenic temperatures were investigated. Contrast was measured using an optical setup that mimics a MOS instrument, and mirror deformation was characterized using a Twyman-Green interferometer. The results indicate that the array exhibited a fill factor of 82%, a contrast ratio of 1000:1, and surface mirror deformations of 8 nm and 27 nm for mirrors tilted at 298 K and 162 K, respectively. (c) 2013 Optical Society of America

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Michael David Canonica, Nico de Rooij, Wilfried Noell
Optical Society of America, 2013
Journal paper

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https://infoscience.epfl.ch/record/189746?ln=en

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Michael David Canonica, Nico de Rooij, Wilfried Noell

Next-generation infra-red astronomical instrumentation for space and ground-based telescopes requires MOEMS-based programmable slit masks for multi-object spectroscopy (MOS) which has to work in cryogenic environment. A first prototype of micromirror arrays (MMA) of 5 x 5 single-crystal silicon micromirrors was successfully designed, fabricated and tested. 100 x 200 mu m(2) micromirrors can be tilted by electrostatic actuation yielding 20 degrees mechanical tilt-angle. The MMA were successfully actuated before, during and after cryogenic cooling, below 100 K. A MMA is composed of two different chips fabricated on silicon on insulator (SOI) wafers: the mirror chip and the electrode chip. The array was obtained by assembling these two chips. For the assembly step of large array (100 x 200 micromirrors) we needed high precision alignment as well as the suppression of manual handling. Therefore we developed a technique of assembly for such devices and we designed and fabricated a dedicated XYZ tip/tilt stage. This stage allows aligning the electrodes towards the micromirrors with a micrometer precision. Large MMA of 100 x 200 micromirrors, measuring 22 mm x 25 mm, for large field of view were microfabricated and assembled using the above setup. No additional deformations were observed due to the assembly step. The peak to valley (PTV) deformation of the micromirrors was found to be 14 nm PTV. The first actuation tests were carried out.

Spie-Int Soc Optical Engineering, Po Box 10, Bellingham, Wa 98227-0010 Usa2009

Large micromirror array for generating programmable slit masks for Multi-Object Spectroscopy

Michael David Canonica, Nico de Rooij, Wilfried Noell

Multi-object spectroscopy (MOS) is a powerful tool for space and ground-based telescopes for the study of the formation and evolution of galaxies. This technique requires a programmable slit mask for astronomical object selection. We are engaged in a European development of micromirror arrays (MMA) for generating reflective slit masks in future MOS, called MIRA. The 100 x 200 mu m(2) micromirrors are electrostatically tilted providing a precise angle. The main requirements are cryogenic environment capabilities, precise and uniform tilt angle over the whole device, uniformity of the mirror voltage-tilt hysteresis and a low mirror deformation. A first M MA with single-crystal silicon micromirrors was successfully designed, fabricated and tested. A new generation of micromirror arrays composed of 2048 micromirrors (32 x 64) and modelled for individual addressing were fabricated using fusion and eutectic wafer-level bonding. These micromirrors without coating show a peak-to-valley deformation less than 10 nm, a tilt angle of 24 degrees for an actuation voltage of 130 V Individual addressing capability of each mirror has been demonstrated using a line-column algorithm based on an optimized voltage-tilt hysteresis. Devices are currently packaged, wire-bonded and integrated to a dedicated electronics to demonstrate the individual actuation of all micromirrors on an array. An operational test of this large array with gold coated mirrors has been done at cryogenic temperature (162 K): the micromirrors were actuated successfully before, during and after the cryogenic experiment. The micromirror surface deformation was measured at cryo and is below 30 nm peak-to-valley.

Spie-Int Soc Optical Engineering2012