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78 MEMS and Microstructures in Aerospace Applications

digital parts, such as memories and microprocessors, which have a large number of
memory cells and registers. However, recent heavy-ion testing has shown that
N-channel power MOSFETs are also susceptible to burnout caused by a single,
high-energy heavy ion. A heavy ion passing through an insulator can sometimes
result in a catastrophic error due to rupturing of the gate dielectric. This is known as
single event gate rupture (SEGR) and it has been observed in power MOSFETs,
SRAMs and EEPROMs. SEGR is a phenomenon that is presently being closely
investigated by the space community. Microcircuits can be hard with respect to
SED while being soft to the total dose effects, or vice versa.
In zero gravity, a significant reliability concern is posed by loose or floating
particles during the process of manufacturing integrated circuits or discrete semi-
conductor devices, loose conductive particles (e.g., solder balls, weld slag, flakes of
metal plating, semiconductor chips, die attach materials, etc.) prior to sealing the
package. In a zero-gravity environment, these particles may float about within the
package and bridge metallization runs, short bond wires, and otherwise damage
electronic circuitry. A thorough program of particle detection is necessary although
the typical microcircuit programs may not be applicable to MEMS devices. Micro-
circuits use a particle impact noise detection (PIND) Particle detection scheme (e.g.,
PIND screening). MIL-STD-883 and MIL-STD-750 both contain PIND test
methods for testing microcircuits and discrete semiconductors, respectively.
Both methods are required screens for space-level, standard devices in accordance
with MIL-M-38510, MIL-PFR-19500, and MIL-STD-975. For MEMS devices
having released structures such as cantilevers the use of a PIND test would fail
good product, as the released structures would produce ‘‘chatter,’’ negating the
validity of the test. The use of particle capture test through stick tapes and other
getter-type materials is encouraged. The inability to ‘‘blow off’’ particulate with an
inert gas where release structures are present reinforces the need for an effective
contaminant control program.
In space microgravity environments, atmospheres of hot, stagnant masses of gas
can collect around sources of heat. Heat loss by unforced convection cannot occur
without gravity. Heated masses of gas simply expand within the surrounding cooler
and denser gaseous media. Heat sinks and fans can be used to prevent overheating
in areas of anticipated heat generation. Unexpected heat producing events, such as
an arc tracking failure of insulation or increasing power dissipation in a deteriorating
capacitor, can rapidly lead to catastrophic failure by thermal runaway. Uncontrolled
heating conditions can also lead to failure in low-pressure environments as heat loss
by convection is effectively eliminated.
The postlaunch environment is one of near-zero atmospheric pressure. Atmos-
pheric pressure changes as a function of altitude. The external pressure at high
altitudes is minimal, thus the volume of existing and outgassed materials is forced
to increase in accordance with Boyle’s Law. The deep-space vacuum is less than
10 12 torr. Under these conditions, corrosive solids may sublimate and expand to
cover exposed surfaces within the system. The corrosive power of these

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