We present a state-of-the-art overview of microthermomechanical infrared sensor technology. The working principle of this sensor is based on a bi-material actuated micromechanical deflection, generated by an induced temperature rise due to incident infrared radiation absorption. In order to generate a thermal image the thermomechanical deflections of the freestanding microstructures are read by either capacitive, piezoresistive or optical means. Research and development activities in this field began in the early 1990s. The development of this technology within the last 20 years has resulted in innovations such as uncooled multiband infrared detection, high-speed infrared sensing and uncooled THz imaging. This paper outlines representative milestones of this technology and analyses important results of notable groups. Significant activities on capacitive and optical readout techniques of thermomechanical infrared arrays are presented. Furthermore the advantages of microthermomechanical infrared sensors over current well-established uncooled infrared technologies are summarized. In conclusion the latest developments of this technology offer a highly potential solution for a variety of important energy-saving, safety and security applications.
Zusammenfassung: Wir berichten über die Entwicklung eines Wärmebildgeräts, das auf einem neuartigen, patentierten Sensor basiert. Der Sensor besteht aus einer Matrix aus Mikro-Spiegeln für deren Betreib keine Energiezufuhr in Form von Strom oder Spannung und darüber hinaus keine Kühlung notwendig ist. Die Mikro-Spiegel verbiegen sich proportional zur aufgenommen Wärme-strahlung (Infrarot-Intensität), vergleichbar mit einem biMetall-Thermometer. Die Verbiegung des einzelnen MikroSpiegels wird durch Auslenkung eines, an dem Spiegel reflektierten Kaltlichtstrahles von einem konventionellen CCD-Sensor erfasst und in Echtzeit-Wärmebilder umgewandelt. Das System besteht aus optischen Standardkomponenten. Durch Dünnschichttechnologien und CMOSKompatibilität des Sensors besitzt diese Innovation klare Kostenvorteile gegenüber aktuellen Infrarotdetektoren. Schlüsselwörter: Wärmestrahlung, Mikrospiegelmatrix, Wärmebildgerät, CCD-Sensor.Abstract: The development of a thermal imaging system with a novel-type of infrared micro-sensor is presented. The sensor consists of a bi-material actuated micro-mirror focal plane array and does not require cooling for its operation. In addition the sensor does not require any electrical power for its operation, hence is completely passive. Its working principle is thermo-mechanical actuation. Due to a temperature rise of the free standing micro-structure generated by absorbed incident infrared flux, the structure experiences a mechanical deflection due to the mismatch of coefficients of thermal expansion of two different materials. The deflection is proportional to incident infrared intensity and is captured by an optical readout. The readout includes a visual light source (LED), standard optical components and a CCD-imager. The micro-mechanical movements are captured by the conventional CCD-sensor and directly presented as a real-time thermal image. Due to the novel sensor-design and the optimized straightforward, thin-film technology and CMOS-compatible micromachining process this patented innovation has a clear competitive advantage over current infrared technologies.
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