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344 MEMS and Microstructures in Aerospace Applications

Electrostatic discharge (ESD) or electrical overstress (EOS) occurs when a
device is improperly handled. A human body routinely develops an electric potential
in excess of 1000 V. Upon contact with an electronic device, this build-up will
discharge, creating a large potential difference across the device. The effect is
known to have catastrophic effects in circuits and could have similar effects on
MEMS devices where ESD may cause attractions or shifts. While the deleterious
effects of ESD onMEMS structures arejust beginningto be published, 34,35 one should
assume that certain electrostatically actuated devices will be susceptible to ESD
damage.

15.6 CONCLUSION
For MEMS devices to be properly operated in space, materials and hardware
reliability is essential. MEMS reliability can be achieved by applying conventional
reliability practices for electronics while taking space environmental effects into
consideration. For a space application, reliability practices are validated as require-
ments and reflected in a mission design and review cycle with key milestones such
as preliminary design review (PDR) and critical design review (CDR) which are
covered in the next chapter on quality assurance.
The performance of MEMS devices is strongly affected by environmental
factors and the effect may vary according to specific MEMS applications. The
environmental impact occurs during all mission phases. Generally, the impact is
more severe under the preoperational environments than more benign operational
and maintenance environments. Under the worst scenario, the synergy of environ-
mental factors may cause detrimental effects and render the devices useless.
To warrant a successful mission, MEMS designers need to pay attention to
prevent potential failure mechanisms in space. MEMS devices are susceptible to
corona and high breakdown voltage. Lessons learned from numerous space mission
failures provide important information for future MEMS design. During MEMS
design and operation, additional effort is required to mitigate failure mechanisms
related to materials and structures.
The study of POF, like any other scientific discipline, requires testing to
validate hypotheses and gather data on failure mechanisms. A significant amount
of research can be conducted on the ground, but some amount of space-based
research is likely to be necessary. POF research could make extensive use of low-
cost ‘‘time-in-space’’ facilities, such as Shuttle deployed free-flying spacecraft,
balloon demonstrations and sounding rockets. Inexpensive long-duration missions
might allow data to be gathered on actual performance in space, with components
being returned to Earth for analysis.

REFERENCES
1. IEEE Standard Computer Dictionary: A Compilation of IEEE Standard
Computer Glossaries. Institute of Electrical and Electronics Engineers, New York,
NY, 1990.

© 2006 by Taylor & Francis Group, LLC