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E. J. Garcia, C. A. Nichols (Sandia National Laboratories)
This paper describes how advanced surface micromachining (SMM) technology is being used to develop prototype cryogenic micromirror arrays for evaluation as an instrument optical component for the NGST. SMM devices use fabrication processes adapted from integrated circuit manufacturing to build microscopic-sized electromechanical devices from polycrystalline silicon. Because these devices can be batch fabricated thousands or even millions of devices can be fabricated on a single wafer at costs many orders of magnitude less than conventionally fabricated devices. When used as a spectrograph reflective slit mask, these arrays can yield a factor of ~1000 reduction in mass and power over, traditional motor-driven slit wheels used on HST instruments. In the case of NGST, a factor of 100 improvement in efficiency relative to traditional instrument designs has been estimated.
Prototype micromirror arrays with 100-micron pixels in formats scalable to 2048 x 2048 assemblies have been successfully fabricated and tested. These mirrors were designed to tilt to an angle of 10 degrees, which is large for this type of design. The use of a novel tilting scheme to attain such a large angle overcomes the original problem of spacer layer thickness used in the fabrication process, which limited the maximum rotation angles that earlier designs could attain. The micromirror, which consists of a top mirror surface, a mirror suspension, and an electrostatic actuation mechanism, was successfully fabricated in our multi-layer polycrystalline silicon MEMS process. Test results demonstrated micromirror actuation at 35 volts. The design and testing of a typical mirror and how the process is used to create the desired structures is described and illustrated.
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.
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The author(s) of this abstract have provided an email address for comments about the abstract: ejgarci@sandia.gov