Fraunhofer Institute for Photonic Microsystems
Fraunhofer Institute for Photonic Microsystems

Pyrosensors

Thermal imaging sensors and thermal infrared sensors

CMOS-compatible pyrosensors and thermopile sensors for industrial, medical, and safety-critical applications

Noncontact detection of thermal radiation is a key technology for numerous industrial, medical, and scientific applications. Thermal infrared sensors enable the precise measurement of surface temperatures and the detection of even the smallest temperature differences without coming into contact with the object being measured. This makes them suitable, among other things, for 

  • Thermal imaging and thermography
  • Industrial process monitoring
  • Gas analysis and environmental monitoring
  • Security applications
  • Mobility applications
  • Medical technology / Ambient Assisted Living
  • Smart buildings and the Internet of Things

Unlike cooled infrared detectors, thermal infrared sensors operate at ambient temperature, thereby enabling compact, energy-efficient, and cost-effective sensor systems. Advances in micro- and nanotechnology are now opening up new possibilities for significantly increasing the performance of uncooled sensors while simultaneously reducing their manufacturing costs.

Fraunhofer IPMS develops CMOS-compatible technologies for uncooled thermal infrared sensors. The focus is on pyroelectric sensors based on ferroelectric hafnium oxide thin films. In addition, Fraunhofer IPMS develops MEMS technologies for thermal infrared sensors, particularly post-CMOS fabrication processes for thermally isolated structures, such as those required for thermopile sensors. By combining MEMS technology, CMOS compatibility, and many years of experience in sensor development, Fraunhofer IPMS supports companies from material development through sensor design to application-specific demonstrators and pilot manufacturing.

Thermopile Sensors

Thermopile sensors consist of several thermocouples connected in series. When infrared radiation strikes the sensor’s absorber, a temperature difference arises between the absorbing membrane and the substrate. This difference is converted directly into an electrical voltage via the Seebeck effect, which is proportional to the incident heat power. Unlike pyroelectric sensors, they also detect time-invariant infrared radiation (DC-capable) and, after compensation for their own reference temperature, can provide a measure of the object’s temperature.

By arranging many sensor elements in an array, temperature distributions can be measured in two dimensions. Such thermopile arrays form the basis of compact, uncooled thermal imaging sensors for industrial, medical, and security-related applications.

Key Research Areas at Fraunhofer IPMS

  • Post-CMOS fabrication processes for thermally isolated structures, such as those required for thermopile sensors. The goal is to further increase the performance and sensitivity of uncooled thermal imaging sensors
  • Use of novel thermoelectric materials such as bismuth telluride and antimony telluride for CMOS-compatible MEMS processes. In combination with vacuum-insulated sensor structures and optimized thermal insulation, this results in compact sensor arrays with high temperature resolution for future thermal imaging systems.

 

Advantages of Thermopile Sensors

  • Non-contact measurement of absolute temperatures
  • No modulation of infrared radiation required
  • Uncooled operation
  • CMOS-compatible MEMS fabrication
  • Compact thermopile arrays for thermal imaging sensors
  • High integration capability for intelligent sensor systems thanks to compact MEMS design
  • Potential for temperature resolutions below 20 mK using novel thermoelectric materials

 

Typical Applications

  • noncontact temperature measurement,
  • industrial process monitoring,
  • building automation,
  • smart home systems,
  • medical technology,
  • thermal imaging

Integrated pyroelectric sensors based on hafnium oxide

Pyroelectric sensors have many applications in the fields of gas analysis, flame sensing, process technology and infrared detection. Many pyroelectric materials used so far are not compatible with modern manufacturing processes or are even toxic. At Fraunhofer IPMS, research is being carried out on sensors based on hafnium oxide, which have many advantages over conventional materials. In particular, the compatibility with semiconductor manufacturing processes (CMOS compatibility) and environmental compatibility (RoHS compatibility) make the material interesting for future integrated sensor applications. Compared to semiconductor detectors, pyroelectric sensors have a broad spectral sensitivity without the need for active cooling.

Hafnium oxide has a long history in semiconductor technology. The pyroelectric properties of the material have only been explored in recent years, opening up new possibilities for the fabrication of highly integrated and miniaturised sensor devices. Pyroelectric thin films based on hafnium oxide show promising properties for a variety of applications. In addition to sensor applications, the recovery of heat loss (so-called "energy harvesting") and electrocaloric cooling are also the subject of active research at Fraunhofer IPMS.

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