Robust sensor for harsh environmental conditions

Sensors that function reliably even at extremely high temperatures or in corrosive environments are in demand, for example, for use in energy technology, such as geothermal or turbine applications, or in chemical engineering. In a joint project, eight Fraunhofer institutes have developed a technology platform for the realization of suitable robust sensor systems. The Fraunhofer Institute for Microstructure of Materials and Systems IMWS in Halle (Saale) contributed its expertise in materials analysis and developed new possibilities for material characterization in the high-temperature range.

© Fraunhofer IMS
Demonstrator for turbine applications developed in the project.
© Fraunhofer IMWS
X-ray CT analysis for tightness evaluation of the joined sensor components.

Powerful sensors are just as important for the efficient operation of processes and plants as they are for early fault detection and quality assurance. They monitor condition parameters such as temperatures and pressures during operation and thus enable energy-efficient control of process management or detect unusual operating conditions that may indicate faults.

As essential as their importance already is to many industrial sectors, the challenge for reliable applications is even greater in extremely harsh environments, such as the interior of power plant or aircraft turbines or geothermal wells, where high temperatures and pressures prevail and aggressive gases and liquids as well as dirt can clog the sensors. Conventional components and materials are not suitable for use in such areas. Eight Fraunhofer institutes have therefore pooled their expertise to develop particularly robust sensors using new technology concepts for extremely harsh environments. The result was two demonstrators - one for use in engines/turbines and one for boreholes for geothermal energy.

The Fraunhofer IMWS was responsible in the project for evaluating the materials used, such as particularly heat-resistant ceramics or specially adapted electronic materials. In order to test their applicability, reliability properties such as critical thermo-mechanical loads, wear resistance, susceptibility to cracking or corrosion were investigated, in each case at very high temperatures or pressure loads. Another focus was parameter determination under these conditions for reliability assessment using simulation models or for understanding potential failure mechanisms using high-resolution failure analytics.

"To make this possible, we adapted numerous diagnostic methods to the relevant material systems and also developed new test methods and experimental setups," says Falk Naumann, who led the subproject at Fraunhofer IMWS. The institute is now making the findings from the project available to its customers for similar issues for the high-temperature material characterization of electronic components and other material systems.

These include micromechanical testing methods up to 500°C (tensile, compression and flexure tests) as well as the temperature-dependent characterization of thin films with penetrant testing methods using nano-indentation, non-destructive in-situ X-ray analysis for 2D and 3D imaging or adapted solutions for the sample preparation required for this in each case, for example using ion- and laser-based routines for high-resolution defect analysis in the transmission electron microscope.

In the project, the Fraunhofer IMWS thus provided support in the selection and identification of suitable materials for the use of sensors in harsh environments and in reliability simulation by providing the necessary material and damage characteristics for selected materials. "Overall, we were able to gain a deeper understanding of the failure mechanisms on the ceramic circuit carriers as well as interconnect and package materials, which can now be used in a variety of ways, such as for design optimization or stress testing of service life in the development of new electronic components," says Naumann.

The research team from Halle (Saale) was thus able to contribute to the success of the overall project. The sensor elements developed as demonstrators for pressure or temperature measurements in turbines or geothermal applications combine both sensor and evaluation electronics. This ensures greater stability and lower susceptibility to interference of the sensor signals as well as improved integration of the sensor elements. Thanks to a defined matching of the properties of the housing materials, the connection and sensor elements, the ceramic sensors can be used at temperatures of 500°C and a pressure of up to 200 bar. The electronic inner workings are designed for around 300°C.