Sensors withstand extreme temperatures

So believe engineers at the Fraunhofer Institute for Microelectronic Circuits and Systems (IMS) in Duisburg, where the pressure system has been developed.

The pressure system is viewed as something that could be particularly helpful for geologists with work such as searching for oil deposits. In these cases, drill bits will gradually burrow deeper into the earth, working through rock.

Meanwhile, dozens of sensors must engage in tasks such as taking pressure readings and evaluating porosity. The conditions they face are extreme, with the sensors being required to withstand high temperatures and pressures as well as shocks and vibrations. The sensors then send the data they collect to the surface.

One hurdle for these sensors, however, is on average they can only withstand temperatures of between 80^oC and 125^oC, but at great depths the temperature is often significantly higher.

In order to combat this problem, the Fraunhofer engineers developed new pressure sensors. These consist of two components that are located on a microelectronic chip or wafer.

Hoc Khiem Trieu, department head at IMS, explained the first component is the sensor itself, and the other component is the EEPROM.

‘This is the element that stores all the readings, together with the data required for calibration,’ he said.

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.

He added: ‘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.’

It is claimed the oxide layer enabled the researchers to improve the insulation of the memory component by three to four orders of magnitude. It is believed this should enable the pressure sensors to withstand temperatures of up to 350^oC.

While the researchers have only yet provided practical proof of stability up to 250^oC, they are planning to conduct further studies at higher temperatures. In addition, the researchers are analysing the prototypes of the pressure sensors in endurance tests.

The team believes there is a broad range of potential applications for the high-temperature pressure sensors, ranging from the petrochemical environment to automobile engines and geothermal applications.