Cryogenic characterization and testing of magnetically-actuated microshutter arrays for the James Webb Space Telescope

Two-dimensional MEMS microshuttor arrays (MSA) have been fabricated at the NASA Goddard Space Flight Center (GSFC) for the James Webb Space Telescope (JWST) to enable cryogenic (-35 K) spectrographic astronomy measurements at near-infrared wavelengths. Functioning as a focal plane object selection device, the MSA is a 2D programmable aperture mask with fine resolution, high efficiency and high contrast. The LISA are close-packed silicon nitride shutters (cell size of 100 y m x 200 mm) patterned with a torsion flexure to allow their opening to 90 DG. A layer of magnetic material is deposited onto each shutter to permit magnetic actuation. Two electrodes are deposited, one onto each shutter and another onto the support structure side-wall, permitting electrostatic latching and 2D addressing. New techniques were developed to test MSA under mission-similar conditions (8 K < T < 300 K). The `magnetic rotisserie' has proven to be an excellent tool for rapid characterization of MSA. Tests conducted with the magnetic rotisserie method include accelerated cryogenic lifetesting of unpackaged 128 x 64 LISA and parallel measurement of the magneto-mechanical stiffness of shutters in pathfinder' test samples containing multiple MSA designs. Lifetest results indicate a logarithmic failure rate out to -106 shutter actuations. These results have increased our understanding of failure mechanisms and provide a means to predict the overall reliability of MSA devices.