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136 MEMS and Microstructures in Aerospace Applications

is used to select the light from multiple objects for transmission to the infrared
spectrograph. The array consists of 250,000 individually addressable 100 200 mm
shutters, which are magnetically actuated 908 out of plane and then electrostatically
latched. A deep reactive ion etched (DRIE) silicon frame supports the shutters and
provides interconnects and electrodes for latching individual shutters. Figure 7.7
shows SEM images of the 100 100 mm shutters of the proto type as shown in
Figure 7.8 made from single crystal silicon. For the NIRSpec 100 200 mm
shutters will be used. All shutters are slightly magnetized and are opened by
scanning a permanent magnet over the array. Selected apertures are held open
electrostatically via application of a potential between the shutter and an electrode
on the wall. After the magnet has passed, the resilience of the hinges flips the
remaining shutters close. Light shields fabricated onto the frame prevent light from
passing around the edges. The shutters are fabricated on 4-in. SOI wafers and the
completed dies are flip-chip bonded to a silicon substrate which contains the drive
electronics. Four adjoining substrate assemblies produce a complete flight array,
which must withstand launch conditions and be operated at cryogenic temperatures.
At present the MEMS shutter design is finalized and initial flight prototypes
have been fabricated and tested under operating conditions. 40,41 The final flight

FIGURE 7.7 Scanning electron microscope image of the Si microshutter shutter blade,
which is suspended on a torsion beam that allows for a rotation of 908. The torsion beam is
suspended on a support grid. While actuated with a probe tip in this image, the blades will be
actuated magnetically in the JWST–NIRSpec. (Source: NASA GSFC.)

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