Exploring Europe made possible with silicon germanium transistor technology

NEWS — Europa isn’t just one of Jupiter’s many moons — it’s also one of the most promising places in the solar system to search for alien life. Below 10 kilometers of ice is an ocean of liquid water that can support life. But it’s also one of the most inhospitable places in the solar system, thanks to a surface temperature of -180 degrees Celsius and extremely high radiation levels. Exploring Europe in the coming years will be possible thanks to new applications of Georgia Tech’s research on silicon germanium transistor technology.

Regents Professor John D. Cressler and his students in the School of Electrical and Computer Engineering (ECE) have been studying silicon-germanium heterojunction bipolar transistors (SiGe HBTs) for decades and have discovered that they offer unique advantages in extreme environments such as Europe .

“Because of the way they are made, these devices can actually survive those extreme conditions without any changes to the underlying technology itself,” said project investigator Cressler. “You can build it for what it does on Earth, and then you can use it in space.”

The researchers are the first year of a three-year grant for NASA’s Concept of Life Detection Technology (COLDTech) program in NASA’s Ocean World, which aims to design the electronics infrastructure for the upcoming Europa surface mission. In 2024, NASA plans to launch Europa Clipper, an orbiting spacecraft that will map Europa’s oceans before eventually sending the lander Europa Lander to drill through the ice and explore its oceans. But it all started with electronics capable of performing in Europe’s extreme environments.

In their paper, Cressler and his students, along with researchers from NASA’s Jet Propulsion Laboratory (JPL) and the University of Tennessee (UT), demonstrate the capabilities of SiGe HBTs in this harsh environment. IEEE Conference on Radiation Effects in Nuclear and Space in July.

Europe’s challenge

Like Earth, Jupiter also has a liquid metal core that generates a magnetic field that produces radiation belts of energetic protons and electrons from the impacting solar wind. Unfortunately, as a moon of Jupiter, Europa is right in those radiation belts. In fact, any technology designed for Europa’s surface would need to be able to withstand not only frigid temperatures, but also the most severe radiation encountered in the solar system.

Fortunately, SiGe HBTs are well suited for this harsh environment. SiGe HBTs introduce nanoscale Si-Ge alloys in typical bipolar transistors to nanoengineer their properties to efficiently produce faster transistors while maintaining the economies of scale and low cost of traditional silicon transistors. SiGe HBTs have the unique ability to maintain performance under extreme radiation exposure, and their performance naturally improves at cooler temperatures. This unique combination makes them ideal for European exploration.

“It’s not just doing basic science and proving that SiGe works,” Cressler said. “It’s actually developing electronics for NASA for Europe. We know that SiGe can withstand high levels of radiation. And we know it’s still effective in cold temperatures. What we don’t know is whether it can do this at the same time. Two missions, and that’s exactly what Europa’s surface mission requires.”

test transistor

To answer this question, the GT researchers used JPL’s Dynamitron, a machine that emits high-flux electrons at extremely low temperatures, to test SiGe in Europa-type environments. They exposed SiGe HBTs to one million volts of electrons at 300, 200, and 115 Kelvin (-160 degrees Celsius) of 5 million rads of radiation (200-400 rads are lethal to humans).

“What was never done was to use electronics like we did in that experiment,” Kressler said. “So we worked hard to get the results in that paper in the first year, which essentially proved what we claimed was true – that SiGe did survive Europa surface conditions.”

Over the next two years, researchers at GT and UT will develop practical circuits from SiGe, such as radios and microcontrollers, that can be used in Europe. What’s more, these devices can be used seamlessly in almost any space environment, including on the moon and Mars.

“If Europa is the worst environment in the solar system, and you can build these to work on Europa, they’ll work anywhere,” Kressler said. “This study ties together research our team at Georgia Tech has been doing for a long time and demonstrates a truly interesting and novel application of these technologies. We open up new areas of innovation for leveraging our research and thereby enable new proud of the application.”

Citation: JW Teng, GN Tzintzarov, D. Nergui, JP Heimerl, Y. Mensah, JP Moody, DO Thorbourn, L. Del Castillo, L. Scheick, MM Mojarradi, BJ Blalock and JD Cressler, “Cryogenic Total Ionization – 4th- Generation SiGe HBTs using 1-MeV Electrons for Europa-Surface Applications”, IEEE Conference on Radiation Effects in Nuclear and Space, July 2022.


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