Jupiter’s moon Europa is one of the most promising locations for searching for extraterrestrial life.
Europa is more than just one of Jupiter’s many moons; it’s also one of the solar system’s most promising locations for searching for extraterrestrial life. There is an ocean of liquid water under 10 kilometers of ice that could support life. However, it is one of the most inhospitable places in the solar system, with surface temperatures of -180 degrees Celsius and extreme radiation levels. Exploring Europe may become possible in the coming years thanks to Georgia Tech’s research into silicon-germanium transistor technology.
Professor John D. Cressler of the Regents’ 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 discovered that they have unique advantages in extreme environments such as Europe.
“The way they’re made allows these devices to survive these extreme conditions without any modification to the underlying technology itself,” said Cressler, the project researcher. “You can build it for what you want it to do on Earth, and you can then use it in space.”
The scientists are in the first year of a three-year NASA Concepts for Ocean Worlds Life Detection Technology (COLDTech) fellowship to design the electronics infrastructure for future European surface missions. NASA plans to launch the Europa Clipper in 2024, an orbiting spacecraft that will map Europa’s oceans, then send a landing vehicle, the Europa Lander, to drill through the ice and explore the ocean. But it all starts with electronics that can work in the harsh environment of Europe.
In a paper presented at the IEEE Nuclear and Space Radiation Effects Conference in July, Cressler and his students, along with researchers from NASA Jet Propulsion Lab (JPL) and the University of Tennessee (UT), demonstrated the potential of SiGe HBTs for these hostile surroundings.
Jupiter, like Earth, has a liquid metallic core that generates a magnetic field, resulting in radiation belts of high-energy protons and electrons from the solar wind. Unfortunately, as Jupiter’s moon, Europa is directly in the path of those radiation belts. In fact, any technology designed for the surface of Europa should be able to withstand not only the cold temperatures, but also the worst radiation from the solar system.
Fortunately, SiGe HBTs are ideal for this harsh environment. The SiGe HBT integrates a nanoscale Si-Ge alloy into a standard bipolar transistor to nanoengineer its properties, resulting in a much faster transistor while maintaining the economies of scale and low cost of traditional silicon transistors. SiGe HBTs have the unique ability to maintain performance even when exposed to high levels of radiation, and their properties naturally improve at lower temperatures. This unique combination makes them ideal candidates for European exploration.
“It’s not just doing the basic science and proving that SiGe works,” Cressler said. “It’s developing electronics for NASA to use on Europa. We know that SiGe can survive high levels of radiation. And we know that it remains functional in cold temperatures. What we didn’t know is whether it could do both at the same time, which is necessary for surface missions.” in Europe.”
Testing the Transistors
The GT researchers used JPL’s Dynamitron, a machine that shoots high-flux electrons at extremely low temperatures, to test SiGe in Europe-like environments. At 300, 200 and 115 Kelvin, they exposed SiGe HBTs to one million Volt electrons and a radiation dose of five million rad (200-400 rad is fatal to humans) (-160 Celsius).
“What had never been done before was to use electronics like we did in that experiment,” Cressler said. “So we literally worked the first year to get the results that are in that document, which is essentially definitive proof that what we claimed is really true — that SiGe survives the surface conditions of Europa.”
Over the next two years, the researchers from GT and UT will develop real SiGe circuits that can be used on Europe, such as radios and microcontrollers. More importantly, these devices could then be used in almost any space environment, including on Mars and the Moon.
“If Europa is the worst environment in the solar system, and you can build these to work on Europa, they will work everywhere,” Cressler said. “This research connects previous research that we have done in my team here at Georgia Tech for a very long time and shows really interesting and new applications of these technologies. We are proud to use our research to break new innovative paths and thereby enabling new applications.”