How do we build electronic materials that can survive radiation?
When engineers created the device you’re reading this story on, they did so with certain expectations in mind: that you’d be using it in within a normal earthly temperature range, and inside an atmosphere that filters out most of the damaging radiation emitted by our sun.
But what about the gadgets we send into space? These critical sensors and control circuits are based on the same silicon chips found in consumer electronics — only in space these components get bombarded by protons, electrons, X-rays, gamma rays and other forms of cosmic radiation. They may also experience rapid temperature swings — from heat that could melt metals to a chill that slows atomic motion to a crawl. Despite how sturdy silicon chips seem on Earth, decades of space exploration have shown that exposure to extremes of radiation or heat can disrupt normal data processing. In some cases, radioactive particles can zip right through silicon chips, disrupting the careful balance of electrons inside the gadget. Eventually, if enough of these defects accumulate, the device stops behaving the way it was intended, and the electronics fail.
“There’s a whole cocktail of radiation churning through space,” says Debbie Senesky, an assistant professor of aeronautics and astronautics and director of the EXtreme Environment Microsystems Laboratory (XLab).
In recent years, her XLab has developed electronics that can shrug off the temperature swings of space. Now, Senesky is studying whether these same heat-resistant materials can also withstand bombardment by the cocktail of extraterrestrial radiation.
Historically, to protect traditional electronics from radiation, engineers have relied on shielding, redundancy and hope, said Thomas Heuser, a doctoral student in the XLab.
Covering devices with lead or aluminum can shield them from some forms of radiation. Another radiation-defense strategy involves putting several copies of a critical component onto a satellite so that if one fails, the others can pick up the slack. Then engineers hope for the best.
Such strategies have worked, although many missions have had to overcome component failures. Voyager 2, launched in 1977, made it safely beyond the edge of our solar system. But space missions are becoming more complex. Scientists want to pack the next generation of satellites and spacecraft with more intelligent sensors and instrumentation. Given that it costs $10,000 to launch every pound of payload into space, it becomes imperative to find electronic materials that can resist radiation without the heavy shielding and redundancy needed to protect silicon.
With this in mind, XLab researchers have been experimenting with chips made of gallium nitride and zinc oxide. Unlike silicon, which has comparatively fragile atomic bonds, these two semiconductor materials have powerful bonds that make them intrinsically more resistant to radiation damage. With gallium nitride and zinc oxide, unlike with weakly bonded silicon, radiation particles can’t as easily bump atoms out of place. If energetic radiation does shift electrons out of place, these materials have such strong bonds that their atomic lattices exert a self-healing force that guides atoms back to their proper locations.
To prove the point, Heuser has been using the particle accelerator at the Los Alamos Ion Beam Materials Laboratory in New Mexico to blast sensors made from zinc oxide — the same compound in sunscreen and cosmetics — with proton particles, one of the most common forms of radiation in space. XLab is also preparing to test its technology in space. In mid-November, the researchers launched their sensors aboard Assistant Professor Zachary Manchester’s KickSat-2 — a satellite about the size of a shoebox, capable of deploying over 100 micro-satellites the size of postage stamps.
The team’s radiation research builds on their prior work on heat. Rapid shifts from hot to cold can disrupt the relatively fragile atomic lattice upon which silicon chips depend. Senesky’s team has previously explored how the robust bonds and electrical properties that allow gallium nitride and zinc oxide to shrug off radiation exposure also give these materials thermal stability.
XLab graduate student Max Holliday said NASA already has the propulsion and spacecraft technology needed to explore the solar system. What’s lacking is electronics that can withstand the radiation and temperature extremes of space. XLab hopes its work will factor into future missions like the possible exploration of Europa. This cold, radiation-rich moon of Jupiter could harbor evidence of life. Sensors made from gallium nitride and zinc oxide could plausibly survive the voyage to Europa and aid in its exploration.
“Developing tiny but tough electronics will help enable the next era of space exploration,” Senesky said.
