Thermal-stress control of microshutter arrays in cryogenic applications for the James Webb Space Telescope

Details Thermal-stress control of microshutter arrays in cryogenic applications for the James Webb Space Telescope Thermal-stress control of microshutter arrays in cryogenic applications for the James Webb Space Telescope

Jul 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005spie.5836..171k&link_type=abstract

Smart Sensors, Actuators, and MEMS II. Edited by Cane, Carles; Chiao, Jung-Chih; Vidal Verdu, Fernando. Proceedings of the SPI

Computer Science

Scientific paper

We 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 384x175 individually addressable shutters which can be magnetically rotated 90° into the plane of the array and electrostatically latched open. Each shutter is a 100x200 μm rectangular membrane suspended by a small neck region and torsion flexure. The primary materials in the shutter are a 5000Å Si3N4 layer for mechanical rigidity, 2000Å Al for opacity and electrostatic latching, and 2200Å Co90Fe10 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 (30K). 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 30K 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.

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