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132 MEMS and Microstructures in Aerospace Applications

does not provide a direct path for light or high energy charged particles to pass and
be detected. 10 The mask elements were fabricated using deep reactive ion-etching
(DRIE) and anisotropic wet-etch techniques. Processing was performed on silicon-
on-insulator (SOI) wafers taking advantage of the 1-mm thick buried oxide layer in
providing electrical isolation of the electrostatic analyzer region from the rest of the
device. A highly anisotropic plasma etch of the handle-side of the SOI die gener-
ating 400-mm wide and 300-mm deep slits was followed by a device-side wet-etch
to generate 20-mm wide and 50-mm deep slits. This, and oxide removal in only the
aperture areas resulted in entrance and exit aperture mask elements for each pixel.
With the geometry specified above, the energy resolution is about 5%. The elec-
trostatic analyzer is almost identical to the collimator, made from copper beryllium
using EDM machining at different angles in each of the detectors.
1
The final two elements of the FlaPS instrument head (excluding the control
electronics) are the microchannel plates for signal amplification and the anode for
detection. A Chevron assembled MCP with channels of 10 mm diameter is used in
this instrument. On the anode, one anode per pixel is patterned on a single ceramic
substrate with Cr, Cu, Ni, or Au conductors and plated through vias for bonding to
each of the five preamplifier discriminator circuits located on the amplifier array
electronics board mounted below. An appealing extension of the basic FlaPS design
is to distribute an array of analyzers around a satellite or onto a spinning satellite,
with a common high-voltage supply and microchannel plate holder, allowing wide
ranges of directions to be measured.

7.2.2 MAGNETOMETERS AND ELECTRIC FIELD DETECTORS

The determination of planetary electric and magnetic fields and their interactions
with the solar wind and other charged particles have been an important focus for
past space missions and future mission planning. Magnetic measurements, such as
those carried out by MagSat and Oersted, are essential for the maps used in satellite
orientation and navigation, as well as for geophysical mapping of Earth’s field. In
addition, magnetometers are used for navigation and attitude control, which will be
discussed in Chapter 10. For the Oersted mission, the fluxgate magnetometer’s
noise level was in the order of about 100 pT at 1 Hz; for deep space mission,
sensitivities below these levels are desirable. Most instruments are fluxgates, which
are the most suitable vector magnetic field sensors besides SQUIDs in this
range. 11,12 Initial attempts to micromachine fluxgates have resulted in sensitivities
of the order of around 100 nT. 13–17 Disadvantages of fluxgate sensors are offset due
to the magnetic cores, limited dynamic range, and relatively low frequency ranges.
Other miniature magnetometers are based on magnetoresistance, 18 or giant magne-
toresistance, 19 which can achieve about 10 nT sensitivities at very high frequencies
and relatively low noise levels. Two types of magnetometers have been successfully
micromachined, one based on the torque 20–22 or magnetostriction 23,24 created by a
ferromagnetic material, and the other based on the Lorentz force. 2,24 The disadvan-
tages of the first type are the integration of ferromagnetic materials into the
fabrication process. This may interfere with the promise of batch production at

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