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Proceedings Paper

Film stress of microshutter arrays for the James Webb Space Telescope
Author(s): Yun Zheng; Shu-Fan Cheng; Rainer K. Fettig; Mary J. Li; Brent Mott; Harvey S. Moseley
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Paper Abstract

The James Webb Space Telescope (JWST), formally Next Generation Space Telescope (NGST), is one of NASA’s challenging projects for advancing the exploration of space. The NGST will be equipped with a Multi-Object-Spectrometer (MOS) that covers the wavelength ranging from 0.6 to 5 micron. To selectively direct light rays from different regions of space into the spectrometer, one approach is to use microshutter arrays serving as the slit mask for the spectrometer. A large format (2Kx1K) individually addressable microshutter array with a lateral pixel size of 100μm x 200μm is being developed and fabricated using MEMS technologies. The microshutter arrays are close-packed silicon nitride membrane cantilevers. A ferromagnetic Co90Fe10 film is deposited on the membranes to magnetically actuate the microshutters. During deposition a Co90Fe10 film is susceptible to develop large tensile stress that can distort the nitride membranes and affect the contrast of the MOS, especially at cryogenic temperatures. In this paper, we discuss how to minimize the film stress. Stress-test cantilevers are micro machined and used in conjunction with Stoney’s formula to determine film stresses. The effects of deposition pressure and power on the Co90Fe10 film, aluminum film and multiple-layer film stress are discussed. It is found that sputter-deposition of Co90Fe10 at low pressure and power results in favor of low tensile stresses in films.

Paper Details

Date Published: 14 November 2002
PDF: 8 pages
Proc. SPIE 4935, Smart Structures, Devices, and Systems, (14 November 2002); doi: 10.1117/12.476118
Show Author Affiliations
Yun Zheng, NASA Goddard Space Flight Ctr. (United States)
QSS Group, Inc. (United States)
Shu-Fan Cheng, Naval Research Lab. (United States)
Rainer K. Fettig, NASA Goddard Space Flight Ctr. (United States)
Raytheon Corp. (United States)
Mary J. Li, NASA Goddard Space Flight Ctr. (United States)
Brent Mott, NASA Goddard Space Flight Ctr. (United States)
Harvey S. Moseley, NASA Goddard Space Flight Ctr. (United States)

Published in SPIE Proceedings Vol. 4935:
Smart Structures, Devices, and Systems
Erol C. Harvey; Derek Abbott; Vijay K. Varadan, Editor(s)

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