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MEMS Packaging for Space Applications 281

individual functions are processed on a single piece of silicon. These processes,
generally CMOS technology, are compatible with the MEMS processing technol-
ogy. Most SOAC chips are designed with a microprocessor of some type, some
memory, some signal processing and others. It is very conceivable that a MEMS
device could one day be incorporated on a SOAC.

12.6 EXAMPLE APPLICATIONS OF MEMS FOR SPACE
Many types of MEMS devices have been proposed for application to space
systems, all of which serve to reduce size, weight, cost, and power consumption.
Examples of common sensors and actuators that are considered for space appli-
cations include inertial sensors such as accelerometers, gyroscopes, and magnet-
ometers; remote sensors such as spectrometers, shutters or filters, bolometers,
and optical elements; and subsystems such as propulsion and active mechanical
and thermal control systems. This section will focus on MEMS packaging
technologies incorporated in applications of space-science instruments and sub-
systems.

12.6.1 VARIABLE EMITTANCE COATING INSTRUMENT FOR
SPACE TECHNOLOGY 5
Novel packaging techniques that are needed to place MEMS-based thermal control
devices on the skin of a satellite are addressed in the Variable Emittance Coating
Instrument developed by the Johns Hopkins University Applied Physics Laboratory
(JHU/APL). The instrument consists of two components: the MEMS shutter array
(MSA) radiator and the electronic control unit (ECU). The MSA radiator is located
on the bottom deck of the spin-stabilized Space Technology 5 (ST5) spacecraft,
whereas the ECU is located within the spacecraft.
The instrument consists of an array of 36 dies, each 12.65 13.03 mm, which
consists of arrays of 150-mm long and 6-mm wide shutters driven by electrostatic
comb drives, mounted on a radiator. The gold-coated shutters open and close over
the substrate and change the apparent emittance of the radiator. The device had to
be on the exposed side of the radiator, and any cover had to be infrared transparent
well into the far infrared. An additional requirement was that the substrate be
thermally and electrically coupled to the radiator to allow heat transfer and preven-
tion of electric charging effects.
In order to manage the thermal expansion mismatch between Al and Si for the
survival temperature range, 45 to 658C, an intermediate carrier made from
aluminum nitrate was used. Sets of six dies, with wirebonds connecting all the
common inputs, are attached to the aluminum nitride substrate, shown in Figure
12.7, with conductive epoxy, which themselves are attached to the aluminum
radiator with epoxy. The radiator package contains heaters and is pigtailed to the
connectors for the electronic control unit inside the spacecraft.
A photograph of the entire package is shown in Figure 12.8. In order to
eliminate the concern associated with potential particulates from integration and

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