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328 MEMS and Microstructures in Aerospace Applications

The first two types of failures are emphasized in this chapter, while the latter
two types are emphasized in the next chapter covering quality assurance. The
relationship of microelectromechanical systems (MEMS)-known failure modes
and the uniqueness of the space environment stresses are covered in detail in this
section. As with any emerging technology field, the absence of historical data
reduces the ability to depend on known techniques to assure the reliable insertion
of new systems. Considering that the majority of MEMS devices are silicon-based,
it is natural to look to the integrated circuit domain for the base of all quality
assurance and reliability knowledge. For this reason both the traditional specifica-
tions derived from statistical approaches and the use of the physics of failure (POF)
approach to reliability are discussed.

15.2 STATISTICALLY DERIVED QUALITY CONFORMANCE AND
RELIABILITY SPECIFICATIONS
The impact of increasingly complex and dense integrated circuits upon the
civilian and military space programs easily relate to this current problem. The
emergence of the electronic, electrical, and electromechanical part programs for
NASA during the 1960s and 1970s produced a dependence on the military
specifications and standard programs that have continued to evolve over the
years. Reliance on the military program is understandable due to its dominance,
which minimized civilian space consumption of electronics. The Jet Propulsion
3
Laboratory (JPL) MEMS developers at NASA Goddard Space Flight Center
(GSFC), and staff members of the Johns Hopkins University Applied Physics
Laboratory (JHU/APL) have all used this approach. Where the adoption of
microcircuit testing from highly used military specifications and standards is
appropriate, this technique is endorsed. For example, when a hermetic microcir-
cuit package is used for MEMS packaging, traditional packaging qualification is
appropriate. Today, one sees this relationship more in consumer electronic con-
sumption, which dwarfs military consumption. Anomalies from the military
system may be found in the electrical, electronic, and electromechanical (EEE)
parts program in the requirements for such tests as salt spray, which appears more
appropriate for components in use on a Navy ship than for those in use in a
NASA Aerospace program. NASA in turn supplements the military documents
with its own requirements, adding another layer. The significance of these
additional documents provides increased traceability, rigorous de-rating systems,
and a forced usage of a restricted range of components.
There are no prescribed requirements relative to the quality assurance and
reliability for aerospace applications for MEMS. The argument that these rigid
and risk-avoidant approaches have led to overdesigned, expensive, low-technology
systems, and stymied the use of new (and often better) components has some
legitimacy. What worked extremely well with the emerging integrated circuit
(IC) industry may be entirely inappropriate for the mature microcircuit market of
today. Building the MEMS inspection and qualification plans around the current

© 2006 by Taylor & Francis Group, LLC