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The demands of operating in a space environment bring unique challenges and unforgiving reliability requirements. Outside the protective cover of the Earth’s atmosphere, the solar system is filled with radiation. Space radiation can damage electronic devices, with potential effects ranging from performance degradation to a complete functional failure.
Due to the lower cost of low-Earth-orbit (LEO) launches, the space industry is now experiencing a rush to deploy small satellite constellations. These lightweight devices—up to a few hundred kilograms—typically operate at altitudes from 400 to 2,000 kilometers. They’re designed for objectives such as internet access and Earth observation missions. In the end, LEO apps will result in more products under development that were previously financially unfeasible to bring to market.
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LEO satellites are exposed to lower levels of radiation than traditional satellites launched into higher orbits. In addition, they’re built for shorter lifetimes. The expected lifetime for satellites in LEO is about five years, significantly lower than the 10- to 20-year requirements of a geostationary-orbit satellite. Thus, the required level of radiation immunity is lower.
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Rad Hardening
In space, ionizing radiation primarily takes the form of charged particles and x-ray radiation. In LEO, the dominant forms of radiation are heavy atomic nuclei, protons, alpha and beta particles, and high-energy photons from solar events. With ionizing radiation, the radiation energy of particles passes through the semiconductor material used to produce electronic components. This energy ruptures the chemical bonds, which in turn introduces changes in electronic component characteristics and can even damage the components.
Radiation-hardening is a process used by IC manufacturers to protect chips from the radiation sources that it may encounter. ICs can be hardened by fabricating them on an insulating substrate in place of the usual semiconductor base. Instead of conventional CMOS semiconductor wafers, silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) are typical bases.
Space-grade SOI and SOS chips can survive radiation exposure levels between 1,000 and 3,000 Grays (100 and 300 krad). A Gray (Gy) is the international system of units—one Gray is equal to the absorption of 1 joule of radiation energy by one kilogram of matter (1 joule/kg). Use of a wide-bandgap substrate like silicon carbide or gallium nitride is helpful in hardening some devices.
In the space environment, designers must be concerned with two main causes of radiation. Single-event effects (SEEs) are random instantaneous cosmic rays and high-energy disruptions triggered by the passage of a single particle or photon. Proton-induced SEEs are the main concern for low Earth orbits and the major component from solar particle events.
Cumulative effects can be subcategorized into total ionizing dose (TID) and displacement damage dose (DDD) (Fig. 1). Total ionizing dose is basically chronic exposure to radiation. TID is a long-term failure mechanism, while SEE is an instantaneous failure mechanism. On that front, Texas Instruments has developed devices that are typically supported with TID and SEE test reports to address potential product degradation in a space environment.
