Europa is more than one of Jupiter’s many moons; it is also one of the most promising places in the solar system to look for extraterrestrial life. Less than 10 kilometers of ice is an ocean of liquid water that could support life. But with surface temperatures of -180 degrees Celsius and extreme levels of radiation, it’s also one of the most inhospitable places in the solar system. Exploring Europe 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 HBT) for decades and have found that they have unique advantages in extreme environments such as Europe. .
“Because of the way they’re made, these devices actually survive these extreme conditions without any changes to the underlying technology,” said Cressler, who is the project’s principal investigator. “You can build it for what you want it to do on Earth, and then you can use it in space.”
The researchers are in the first year of a three-year grant from NASA’s Concepts for Ocean Worlds Life Detection Technology (COLDTech) program to design the electronics infrastructure for upcoming missions to Europa’s surface. NASA plans to launch the Europa Clipper in 2024, an orbiting spacecraft that will map Europa’s oceans and eventually send a lander, the Europa Lander, to drill through the ice and explore its ocean. But it all starts with electronics that can work in Europe’s extreme environment.
Cressler and his students, along with researchers from NASA’s 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 Impact Conference of IEEE Nuclear and Space Radiation in July. .
The challenge of Europe
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 lies directly in these radiation belts. Indeed, any technology designed for Europa’s surface would not only need to be able to survive the cold temperatures, but also the worst radiation found in the solar system.
Fortunately, SiGe HBTs are ideal for this hostile environment. The SiGe HBT introduces a nanoscale Si-Ge alloy into a typical bipolar transistor by nano-engineering 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 cooler temperatures. This unique combination makes them ideal candidates for exploring Europe.
“It’s not just about doing the basic science and proving that SiGe works,” Cressler said. “He’s actually developing electronics for NASA to use in Europa. We know that SiGe can survive high levels of radiation. And we know that it remains functional at cold temperatures. What we didn’t know is whether it could do both at the same time , which is needed for missions to Europa’s surface.”
Test the transistors
To answer this question, GT researchers used JPL’s Dynamitron, a machine that fires high-flux electrons at very low temperatures to test SiGe in Europa-type environments. They exposed SiGe HBTs to one million electron volts at a radiation dose of five million rads of radiation (200-400 rads are lethal to humans), at 300, 200, and 115 Kelvin (-160 Celsius).
“What had never been done before was using electronics like we did in that experiment,” Cressler said. “So we literally worked for the first year to get the results that are in this paper, which is essentially definitive proof that what we claimed is, in fact, true: that SiGe survives surface conditions of Europe”.
In the next two years, GT and UT researchers will develop real SiGe circuits that could be used in Europe, such as radios and microcontrollers. But more importantly, these devices could be used without problems in almost any space environment, even on the Moon and Mars.
“If Europa is the worst environment in the solar system, and you can build them to work on Europa, they’ll work anywhere,” Cressler said. “This research ties together previous research that my team here at Georgia Tech has been doing for a long time and shows really interesting and new applications of these technologies. We’re proud to use our research to break new ground and therefore enable new applications”.
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