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Thermal-Stress Control of Microshutter Arrays in Cryogenic Applications for the James Webb Space TelescopeWe report on methods to minimize thermally-induced deformation in a MEMS-based reconfigurable aperture. The device is an enabling component of the Near-Infrared Spectrometer, a principle instrument on NASA's James Webb Space Telescope. The Microshutter Array consists of 384 x 175 individually addressable shutters which can be magnetically rotated 90 deg into the plane of the array and electrostatically latched open. Each shutter is a 100 x 200 micron rectangular membrane suspended by a small neck region and torsion flexure. The primary materials in the shutter are a 5000A Si3N4 layer for mechanical rigidity, 2000A Al for opacity and electrostatic latching, and 2800A CoFe for magnetic actuation. This multi-layer stack presents a challenge due to the operating temperatures required for the device: both room temperature (300K) and cryogenic temperature (35K). Thermal expansion of the materials causes the shutters to bow out of plane excessively, which can prevent actuation of the shutters, cause damage to portions of the array, and allow light leakage around closed shutters. Here we present our investigation of several methods to prevent microshutter bowing including deposition of additional materials on the shutters to create a symmetrical layer stack and replacing the current stack with low-coefficient of thermal expansion materials. Using shutter-size suspended cantilever beams as a rapid-development test bed, we have reduced out-of-plane bowing between 300K and 35K to 10% or better. We are currently applying these results to microshutter arrays to develop shutters that remain flat from room temperature to cryogenic temperature while retaining the required mechanical, optical, and magnetic properties.
Document ID
20050157876
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Kelly, Daniel P.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Chuang, Wen-Hsien
(Maryland Univ. College Park, MD, United States)
Hess, Larry
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Hu, Ron
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Jhabvala, Murzy
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
King, Todd
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Li, Mary J.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Loughlin, James
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Moseley, S. Harvey
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Ray, Christopher
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 23, 2013
Publication Date
November 1, 2004
Subject Category
Mechanical Engineering
Meeting Information
Meeting: SPIE International Symposium
Location: Seville
Country: Spain
Start Date: May 9, 2005
End Date: May 11, 2005
Distribution Limits
Public
Copyright
Other

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