From: Georgia Institute of Technology
September
30, 2022 -- Europa is more than just one of Jupiter's many moons -- it's also
one of most promising places in the solar system to look for extraterrestrial
life. Under 10 kilometers of ice is a liquid water ocean that could sustain
life. But with surface temperatures at -180 Celsius and with extreme levels of
radiation, it's also one of the most inhospitable places in the solar system.
Exploring Europa could be possible in the coming years thanks to new
applications for silicon-germanium transistor technology research at Georgia
Tech.
Regents'
Professor John D. Cressler in the School of Electrical and Computer Engineering
(ECE) and his students have been working with silicon-germanium heterojunction
bipolar transistors (SiGe HBTs) for decades and have found them to have unique
advantages in extreme environments like Europa.
"Due
to the way that they're made, these devices actually survive those extreme
conditions without any changes made to the underlying technology itself,"
said Cressler, who is the project investigator. "You can build it for what
you want it to do on Earth, and you then can use it in space."
The
researchers are in year one of a three-year grant in the NASA Concepts for
Ocean Worlds Life Detection Technology (COLDTech) program to design the
electronics infrastructure for upcoming Europa surface missions. NASA plans to
launch the Europa Clipper in 2024, an orbiting spacecraft that will map the
oceans of Europa, and then eventually send a landing vehicle, Europa Lander, to
drill through the ice and explore its ocean. But it all starts with electronics
that can function in Europa's extreme environment.
Cressler
and his students, together with researchers from NASA Jet Propulsion Lab (JPL)
and the University of Tennessee (UT), demonstrated the capabilities of SiGe
HBTs for this hostile environment in a paper presented at the IEEE
Nuclear and Space Radiation Effects Conferencein July.
Europa's
Challenge
Like
Earth, Jupiter also has a liquid metal core that generates a magnetic field,
producing radiation belts of high-energy protons and electrons from the
impinging solar wind. Unfortunately, as a moon of Jupiter, Europa sits squarely
in those radiation belts. In effect, any technology designed for Europa's
surface would not only need to be able to survive the cold temperatures but
also the worst radiation encountered in the solar system.
Fortunately,
SiGe HBTs are ideal for this hostile environment. The SiGe HBT introduces a
nanoscale Si-Ge alloy inside a typical bipolar transistor to nano-engineer its
properties, effectively producing a much faster transistor while maintaining
the economy-of-scale and low cost of traditional silicon transistors. SiGe HBTs
have the unique ability to maintain performance under extreme radiation
exposure, and their properties naturally improve at colder temperatures. Such a
unique combination makes them ideal candidates for Europa exploration.
"It's
not just doing the basic science and proving that SiGe works," Cressler
said. "It's actually developing electronics for NASA to use on Europa. We
know SiGe can survive high levels of radiation. And we know it's remains
functional at cold temperatures. What we did not know is if it could do both at
the same time, which is needed for Europa surface missions."
Testing
the Transistors
To
answer this question, the GT researchers used JPL's Dynamitron, a machine that
shoots high-flux electrons at very low temperatures to test SiGe in Europa-type
environments. They exposed SiGe HBTs to one million Volt electrons to a
radiation dose of five million rads of radiation (200-400 rads is lethal to
humans), at 300, 200, and 115 Kelvins (-160 Celsius).
"What
had never been done was to use electronics like we did in that
experiment," Cressler said. "So, we worked literally for the first
year to get the results that are in that paper, which is in essence definitive
proof that what we claimed is, in fact, true -- that SiGe does survive Europa
surface conditions."
In
the next two years, the GT and UT researchers will develop actual circuits from
SiGe that could be used on Europa, such as radios and microcontrollers. Yet
more importantly, these devices could then be seamlessly used in almost any
space environment, including on the moon and Mars.
"If
Europa is the worst-case environment in the solar system, and you can build
these to work on Europa, then they will work anywhere," Cressler said.
"This research ties together past research that we have done in my team
here at Georgia Tech for a long time and shows really interesting and novel
applications of these technologies. We pride ourselves on using our research to
break new innovative ground and thereby enable novel applications."
https://www.sciencedaily.com/releases/2022/09/220930163205.htm
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