Engineers print circuitry to withstand extreme conditions
Image credit: Pixabay
Researchers from Michigan State University have developed more heat-resilient circuitry, in a step towards technology capable of tolerating extreme conditions, such as those on other planets.
The researchers are working to enable devices such as next-generation fuel cells, high-temperature semiconductors, and solid-oxide electrolysis cells, which have potential applications across the auto, energy and aerospace industries.
While these types of devices are not commercially available, they are under development and researchers are testing them in a range of different environments. For example, Nasa developed a solid-oxide electrolysis cell that enabled the Perseverance Rover to produce oxygen from gas in the Martian atmosphere on 22 April. Nasa hopes this prototype could eventually lead to equipment which supports human life and creates rocket fuel on Mars.
For these experimental devices to become commercial products, they will need to be capable of maintaining their performance at extreme temperatures over useful periods of time. Professor Jason Nicholas, of Michigan State University’s College of Engineering, was drawn to the field after years of using solid-oxide fuel cells, which generate electricity by oxidising a fuel using a solid-oxide electrolyte.
“Solid-oxide fuel cells work with gases at high temperature,” says Nicholas. “We’re able to electrochemically react those gases to get electricity out and that process is a lot more efficient than exploding fuel like an internal combustion engine does.”
Even without combustion, Nicholas explains, the fuel cells need to continue working under intense conditions.
“These devices commonly operate around 700 to 800°C, and they have to do it for a long time: 40,000 hours over their lifetime. For comparison, that’s […] about double the temperature of a commercial pizza oven. And over that lifetime, you’re thermally cycling it; you’re cooling it down and heating it back up. It’s a very extreme environment. You can have circuit leads pop off.”
One of the major hurdles that stands in the path of commercialising this technology is surprisingly rudimentary: keeping the circuitry, which is often made from silver, stuck to the underlying ceramic components.
Nicholas and his colleagues found that they could improve adhesion by inserting an intermediate layer of porous nickel between the silver and ceramic. They deposited the thin, porous nickel layers on the ceramic in designs of their choice using screen printing, the same simple technique used to decorate t-shirts.
Once the nickel is in place, they put it in contact with molten silver at 1,000°C. The nickel, which has an even higher melting point, distributes the liquified silver uniformly over its features through a process called capillary action (roughly analogous to how plants transport water to its leaves and branches).
Once the silver cools to a solid, the nickel keeps it 'locked' onto the ceramic, even under the extreme temperatures inside a solid-oxide fuel cell or electrolysis cell. The technique is described in a Scripta Materialia paper.
The technique has the potential to help other electronics withstand extreme temperatures in other groups of technologies.
“There are a wide variety of electronic applications that require circuit boards that can withstand high temperatures or high power,” said Jon Debling, who works at the university’s tech transfer office. “These include existing applications in automotive, aerospace, industrial, and military markets, but also newer ones such as solar cells and solar oxide fuel cells.”
“This technology is a significant improvement – in cost and temperature stability – over existing paste and vapour deposition techniques.”
Nicholas adds that he is interested in cutting-edge applications on the horizon and ensuring that they can withstand future applications: “We’re working to improve their reliability here on Earth, and on Mars.”
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