Tricorder Tech: Exploring Europe with Silicon-Germanium Transistor Technology

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Europa is more than just one of Jupiter’s many moons — it’s also one of the most promising places in the solar system to search for extraterrestrial life.

Beneath 10 kilometers of ice lies an ocean of liquid water that could support life.

But with surface temperatures of -180 degrees Celsius and extreme radiation levels, 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.

Professor John D. Cressler of Regents 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 like Europa.

“Because of the way they are manufactured, these devices survive these extreme conditions without any changes to the underlying technology itself,” said Cressler, who is the project’s investigator. “You can build it for whatever 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 under the NASA Concepts for Ocean Worlds Life Detection Technology (COLDTech) program to design the electronic infrastructure for the upcoming Europa surface missions. NASA plans to launch the Europa Clipper in 2024, an orbiting spacecraft that will map Europe’s oceans, then possibly send a landing vehicle, Europa Lander, to break through the ice and explore its ocean. But it all starts with electronics capable of operating in Europe’s extreme environment.

Cressler and his students, along with researchers from NASA Jet Propulsion Lab (JPL) and the University of Tennessee (UT), demonstrated the capabilities of SiGe HBTs for this harsh environment in a paper presented at the IEEE Nuclear and Space conference. Radiation Effects in July.

Europe’s challenge

Like Earth, Jupiter also has a core of liquid metal that generates a magnetic field, producing high-energy proton and electron radiation belts from the incident solar wind. Unfortunately, as Jupiter’s moon, Europa sits squarely within these radiation belts. Indeed, any technology designed for the surface of Europa should not only be able to survive the cold temperatures but also the worst radiation encountered in the solar system.

Fortunately, SiGe HBTs are ideal for this harsh 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 economy of scale and low cost of traditional silicon transistors. SiGe HBTs have the unique ability to maintain their performance under extreme radiation exposure, and their properties naturally improve at colder temperatures. Such a unique combination makes them ideal candidates for exploring Europe.

“It’s not just about doing basic science and proving that SiGe works,” Cressler said. “It’s actually about developing electronics for NASA to use on Europa. We know that SiGe can survive high levels of radiation. And we know it stays functional in cold temperatures. What we didn’t know was if it could do both at the same time, which is necessary for Europa surface missions.

Test transistors

To answer this question, the WG researchers used JPL’s Dynamitron, a machine that shoots high-flux electrons at very low temperatures to test SiGe in Europa-like environments. They exposed SiGe HBTs to one million Volt electrons at a radiation dose of five million rads of radiation (200-400 rads are lethal to humans), at 300, 200 and 115 Kelvins (-160 Celsius).

“What had never been done was to use electronics like we did in this experiment,” Cressler said. “So we literally worked for the first year to get the results contained in this paper, which is essentially definitive proof that what we’re claiming is, in fact, true – that SiGe survives the surface conditions of Europe.”

Over the next two years, GT and UT researchers will develop real circuits from SiGe that could be used on Europa, such as radios and microcontrollers. More importantly, these devices could then be used seamlessly in almost any space environment, including the Moon and Mars.

“If Europa is the worst environment in the solar system and you can build them to work on Europa, they will work anywhere,” Cressler said. “This research bridges previous research that we have done in my team here at Georgia Tech for a long time and shows some really interesting and novel applications of these technologies. We are proud to use our research to innovate and thus enable new applications. »

Astrobiology

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