Some Like It Hot
DUISBURG, Germany, Jan. 4, 2010 -- Normally, microelectronic chips designed to take pressure readings are very delicate. But a new technology makes them robust enough to continue operating normally at temperatures up to 250 °C (482 °F).
Researchers at Fraunhofer Institute for Microelectronics Circuits and Systems (IMS) developed the sensor for applications such as oil and gas exploration. In those applications, as the drill bit burrows deeper into the earth, working its way through rock, dozens of sensors monitor pressure and evaluate porosity. Because of the extreme conditions they face, the sensors are required to withstand high temperatures and pressures as well as shocks and vibrations as they send data to the surface to help geologists with tasks such as searching for oil deposits.
On average, pressure sensors can withstand temperatures only between 80 and 125 °C, but at great depths, the temperature often is significantly higher. Because of this, Fraunhofer IMS aimed to create a more robust sensor.
The new pressure sensor works at temperatures up to 250 °C (Photo ©Fraunhofer IMS)
"The pressure sensors consist of two components that are located on a microelectronic chip or wafer," said Dr. Hoc Khiem Trieu, department head at IMS. "The first component is the sensor itself, and the other component is the EEPROM (the element that stores all the readings together with the data required for calibration)."
Normally, wafers tend to be made of monocrystalline silicon, but the Fraunhofer researchers chose silicon oxide to enable the chip to function properly even at extremely high temperatures.
"The additional oxide layer provides better electrical insulation," Trieu said. "It prevents the leakage current that typically occurs at very high temperatures, which is the principal reason that conventional sensors fail when they reach a certain temperature."
The oxide layer enabled them to improve the insulation of the memory component by three to four orders of magnitude. In theory, this should enable the pressure sensors to withstand temperatures of up to 350 °C (662 °F), they said. So far, the researchers have provided practical proof of stability up to 250 °C and are planning to conduct further studies at higher temperatures. In addition, they are analyzing the prototypes of the pressure sensors in endurance tests.
There is a broad range of potential applications, with engineers hoping to use the high-temperature pressure sensors not only in the petrochemical environment but in automobile engines and geothermal applications.
For more information, visit: www.fraunhofer.de/en/index.jsp
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