Researchers at Fraunhofer IZM in Berlin have developed a pressure sensor that operates up to 600°C by using silicon carbide (SiC).
The sensor is initially aimed at fine-tuning the combustion process in jet turbines to reduce the fuel consumption of aircraft and spacecraft.
Today’s silicon sensors operate up to 150°C, with Silicon on Insulator (SOI) devices operating up to 400°C. Using SiC provides advantages at high temperature but the hardness of the material, comparable to diamond, makes it difficult to work with for sensors.
“Silicon carbide is a blessing and a curse. The unique strength and durability of the material make it very promising for electronic components, but the same properties make processing SiC a real headache,” said Piotr Mackowiak, researcher at Fraunhofer IZM.
The challenge was to create a semiconductor manufacturing process to build a tiny, but stable base body on a thin membrane. The team developed a fast double etching process that etches the silicon carbide at four micrometres per minute. This is eight times the conventional speed, and it makes the technology interesting for the high throughput rates in industrial production.
Using a piezoresistive sensing element also allowed the development of an unusual shape that keeps the design stable at high temperatures without any need for external cooling
“Our thinking was to keep the design to the essential basics, to ensure that it is heat resistant, but also so thin that it can bend and work as a piezometer – and we did both with deep etching,” said Mackowiak
Existing sensors use the piezoelectric effect for measurements, which can record dynamic, but not static pressure, and they cannot withstand the very high temperatures they are exposed to for too long. “Our sensors use the piezoresistive effect, which means that they can track both dynamic and static pressure, and that over long periods at even higher temperatures,” he said.
Monitoring the oscillations in temperature and pressure alongside other process parameters right in the jet turbine can provide improved control over the process. The fuel-to-air ratio could then be fine-tuned for more efficient and cleaner combustion, reducing the amount of jet fuel used.
The sensor and the package are now available to future research project partners, who could also get involved in adapting the sensors for other application such as electric cars or deep drilling.
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