New technology helps sensors endure extreme temperatures

In rugged applications, pressure sensors are limited in that they can only withstand temperatures of between 80 and 125 ^°C. However, at great depths the temperature is often significantly higher. The Fraunhofer Institute for Microelectronic Circuits and Systems IMS in Duisburg says it has addressed this problem and has developed a pressure sensor system that continues to function normally even at 250^°C. Dr Hoc Khiem Trieu, department head at IMS explained that the pressure sensors consist of two components that are located on a microelectronic chip or wafer. The first component is the sensor itself, and the other component is the EEPROM - an element that stores all the readings together with the data required for calibration. To enable the pressure sensor to function properly even at extremely high temperatures, the developers modified the wafer. While normal wafers tend to be made of monocrystalline silicon, the researchers chose silicon oxide for this application. Dr Trieu said: "The additional oxide layer provides better electrical insulation. 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." According to Trieu, the oxide layer enabled the researchers 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. The researchers claim to have provided practical proof of stability up to 250^°C and are planning to conduct further studies at higher temperatures. In addition, the researchers are analysing the prototypes of the pressure sensors in endurance tests. Potential applications for high temperature pressure sensors include petrochemical, automotive and geothermal sectors.