Major Areas of Opportunity - Implications of Emerging Micro-and Nanotechnologies - page 35

interesting for MEMS space applications because of its inherent radiation toler-
ance and its built-in etch stop for bulk silicon etching.
Can commercial electronics be used on-orbit with appropriate radiation
shielding? Figure 3-2 shows the yearly total radiation dose in silicon electronics
as a function of aluminum shield thickness for an 800-kilometer altitude Sun-
synchronous orbit. Contributions due to trapped protons and electrons are shown;
contributions due to solar protons and bremsstrahlung were not plotted for clar-
ity. This graph was generated using data supplied by the on-line Space Environ-
ment Information System (SPENVIS). 43 Figure 3-2 indicates that commercial
CMOS devices should have at least several millimeters of shielding to survive a
year in LEO orbit.
Figure 3-3 shows radiation dose rate dependence as a function of circular
equatorial orbit altitude for aluminum shielding with thicknesses of 0.18 and 1.1
centimeters (densities of 0.5 g/cm 2 and 3.0 g/cm 2 , respectively). Note the rapid
rise in dose rate with altitude above about 2,000 kilometers and below 20,000
kilometers. The hard-to-shield proton belt peaks at ~4,000 kilometers, and the
easier-to-shield electron belt peaks at ~20,000 kilometers. At geostationary Earth
orbit (GEO; 35,786 kilometers altitude and 0 degrees inclination) with a maxi-
mum dose of 3,000 rads, 0.5 g/cm 2 (0.22-centimeter silicon) and 3.0 g/cm 2 (1.3-
Aluminum Shield Thickness (mm)
FIGURE 3-2 Yearly radiation dose in silicon. Adapted from data at European Space
Agency, Space Environment Information System. Available online at <http://www.spen
vis.oma.be/spenvis/> [April 24, 2002].