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358 MEMS and Microstructures in Aerospace Applications

MEMS vendor and package the device themselves are more than likely underesti-
mating the difficulty of the quality and reliability challenges involved.
MEMS reliability focuses on mechanical failure modes rather than electrical
ones. One major failure mechanism is stiction, or the tendency of two silicon
surfaces to stick to each other. Another concern is the release process and any
postprocesses where contaminants and moisture may be present.

16.4 REVIEWS
Engineering design reviews and fabrication feasibility reviews should be held on
every program considering the use of MEMS devices. These reviews may be held
often and should include peer reviewers. For fabrication feasibility reviews, the
team should be interdisciplinary and cover every area that will have impact on the
design or build. The first major formal review of the detailed design including
MEMS devices will be at the preliminary design review (PDR), 10 which nominally
will cover the subsystem or the system, or the MEMS device(s). Areas of particular
concern to the MEMS provider and user for the PDR are listed below. Since both
the PDR and the critical design review (CDR) may be at a larger subsystems and
systems level, additional guidance is given in this chapter specific to the incorpor-
ation of MEMS in designs for space programs.
The PDR is the first major review of the detailed design and is normally held
prior to the preparation of formal design drawings, yet after the concept feasibility
has been demonstrated in hardware. A PDR is held when the design is advanced
sufficiently to begin some breadboard testing and/or fabrication of design models.
Detail designs are not expected at this time, but system engineering, resource
allocations, and design analyses are required to demonstrate compliance with
requirements. The identification of single point failure modes needs to be assessed
as well as critical design areas that may be life-limiting.
A PDR should cover the following items with the assurance that MEMS
specific information be included in the highlighted sections:

. Science and technical objectives, requirements, general specifications
. Closure of actions from previous review or changes since the last review
. Performance requirements
. Error budget determination
. Weight, power, data rate, commands, EMI/EMC
. Interface requirements
. Mechanical or structural design, analyses, and life tests
. Electrical, thermal, optical, or radiometric design and analyses
. Software requirements and design
. Ground support equipment design
. System performance budgets
. Design verification, test flow and calibration or test plans
. Mission and ground system operations
. Launch vehicle interfaces and drivers

© 2006 by Taylor & Francis Group, LLC