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316 MEMS and Microstructures in Aerospace Applications

amount of oxygen that impinges on the spacecraft is dependent upon attitude,
altitude, exposure time, and solar activity.
AO does not always lead to erosion. It reacts with certain materials to form a
stable oxide that in turn protects the surface from further corrosion. Silicon and
aluminum will form SiO 2 and Al 2 O 3 , respectively. These coatings along with
indium tin oxide (ITO) are often sputter coated onto other materials as protection
from AO.
Table 14.5 shows the reaction efficiencies for various materials. Most metals do
not show macroscopic effects from atomic oxygen. Silver and osmium react
rapidly, however, and are generally considered unacceptable for use in uncoated
applications. Ion bombardment effects from atomic oxygen can be neglected as the
energies are two orders of magnitude lower than those in a conventional reactive
ion-etching machine. Microscopic changes have been observed, however, and
should be investigated further for devices in which surface properties are critical.

14.5.5 RADIATION
Radiation can damage MEMS devices by causing failure in:

. analog and digital electronic components of MEMS device
. the transduction mechanism of the actuator or sensor
. the mechanical structures
. optical properties (absorptance and refractive index)

TABLE 14.5
Reaction Efficiencies of Materials with
Atomic Oxygen
3
30
Material R c (m /atom 3 10 )
Kapton 3
Mylar 3.4
Tedlar 3.2
Polyethylene 3.7
Teflon <0.1
Carbon 1.2
Polystyrene 1.7
Polyimide 3.3
Platinum 0
0
SiO 2
Indium tin oxide 0
0
Al 2 O 3
Copper 0.05

© 2006 by Taylor & Francis Group, LLC