Marco Schossig

Infrared Responsivity of Pyroelectric Detectors With Nanostructured NiCr Thin-Film Absorber

This letter reports on the performance of LiTaO3- based pyroelectric single-element detectors coated with a nanostructured thin-film absorber consisting of the same material as the sensor electrodes (NiCr). The fabrication of the absorber structure is achieved with a thermal evaporation technique in high vacuum. A major benefit is the one-step deposition and the functional integration of the sensors top electrode and the absorption layer enabled by a technologically simple deposition technique. The NiCr absorber shows a very high absorption efficiency comparable to that of metal-black coatings but with considerably higher mechanical robustness. The relative spectral responsivity of the detectors was evaluated in the 1-15 μm wavelength range showing good uniformity for a film thickness of about 1 μm.

Optical Absorption Layers for Infrared Radiation

Optical functional layers with high absorption have a large number of applications. Beside their use in infrared radiation (IR) detection, they can be applied to radiation cooling because good radiation absorbers are also good emitters. Another application is the thermography of electronic devices. Here, a thin black layer deposited on a heated device gives a defined emittance of the surface. In this way, the thermal profile is calibrated absolutely in temperature. However, the most noticeable application is their use in thermal infrared detectors to transform radiation into heat. Thereby, infrared absorbing layers have to meet the following demands: (i) high and spectrally homogeneous radiation absorption, (ii) very low thermal mass, (iii) high heat conductivity, (iv) good long-term stability and reproducibility of the properties and (v) their fabrication must be compatible with the detector manufacturing technology. In the past IR absorption technology had focussed on thin films whereby several solutions of optical absorption layers for infrared radiation have been proposed. The most important are: (i) ultrathin metal films, (ii) quarter-wavelength structures, (iii) highly porous metal-black coatings, and (iv) particulate-filled polymer coatings, respectively. In recent years, new opportunities for ultrathin infrared absorption layers are offered due to recent advances in nanotechnology and plasmonics research. This chapter gives an insight into established principles of infrared radiation absorption and presents two new approaches dealing with nano-structured surfaces and plasmon resonance in nanoparticles.

New pyroelectric detectors for pyrometry and security technique

The paper describes the newest layouts and the basic properties of pyroelectric single-element detectors which are built on the basis of lithium tantalate. The research aimed to develop detectors with a signal-to-noise ratio that is high as possible thereby ensuring optimum adjustment of the detectors to their planned application. Typical applications for the two new detector designs can be found in pyrometry and security technique.

Pyroelektrische Infrarotsensoren mit hoher Detektivität

Zusammenfassung Pyroelektrische Infrarotsensoren gehören zur Gruppe der thermischen Strahlungssensoren. Sie werden in sehr großen Stückzahlen in passiven Infrarot-Bewegungsmeldern, Gasanalysegeräten und Geräten zur berührungslosen Temperaturmessung eingesetzt. Der Artikel beschreibt Möglichkeiten der Detektivitätssteigerung und der Anpassung an Sensoranwendungen und gibt damit einen Überblick zum Stand der Sensorentwicklungen am Institut für Festkörperelektronik der TU Dresden. Die Arbeiten wurden in enger Zusammenarbeit mit der DIAS Infrared GmbH durchgeführt.

Absorptionsschichten für thermische Infrarotsensoren

Zusammenfassung Damit thermische Infrarotsensoren, wie z. B. Bolometer, Thermosäulen und pyroelektrische Detektoren, eine maximale Sensorleistung erreichen, muss die einfallende Infrarotstrahlung möglichst vollständig absorbiert werden. Dieser Artikel gibt einen Überblick zu kommerziell eingesetzten Absorptionsschichten sowie Neuentwicklungen, die durch Fortschritte in der Nanotechnologie und auf dem Gebiet der Plasmonik ermöglicht wurden.

A 256-pixel pyroelectric linear array with new black coating

This paper gives a survey of both the design and essential properties of newly developed pyroelectric linear arrays made on the basis of lithium tantalate (LiTaO3). There are up to 256 pixels with a minimum pitch of 50 μm. The detector is a hybrid arrangement of pyroelectric detector chip and 0.8 μm CMOS read-out circuit in a hermetic metal housing. Thanks to the development of a new black coating technology the thermal resolution and the homogeneity of the spectral responsivity have been permanently improved. The absorption layer consists of a columnar NiCr thin film. It is deposited using a special GLAD technology in high vacuum. The band absorption coefficient in the wavelength range 1...15 μm is about 0.9 for a layer with a thickness of about 1 μm. The NiCr absorption layer has very low thermal mass and high temperature stability. It can be patterned by lift-off technology. The measurement results demonstrate the excellent homogeneity of the spectral responsivity and the improvement of the signal-to-noise ratio of the linear arrays.

Microstructured Surfaces on LiTaO

Reflections of the incident radiation from the sensor surface are a major problem in enhancing the performance of pyroelectric infrared detectors. This paper reports on the approach to reduce these reflections by patterning the sensor surface of lithium tantalate (LiTaO3)-based infrared detectors with subwavelength structures. These structures provide a better refractive index matching from air to sensitive material and, therefore, minimize reflections from the sensor surface. First of all, a multi-layer model is considered to describe the optical behavior of LiTaO3 surfaces with subwavelength structures. As a result, design criteria for the structure dimensions are derived allowing elimination of a significant portion of surface reflections. The validity of the model could be proofed experimentally. The fabrication of microstructured LiTaO3 surfaces is done by either a simple lapping process or standard contact lithography with subsequent ion beam milling. As a result, it was possible to enhance the responsivity of LiTaO3-based infrared detectors up to 15%.

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Zusammenfassung Eine in den letzten Jahren entwickelte flexible Herstellungstechnologie für pyroelektrische Infrarotsensoren auf der Basis von Lithiumtantalat (LiTaO3) ermöglicht es, Sensoren zu entwerfen und zu fertigen, die einen hohen Signal-Rausch-Abstand besitzen und der geplanten Anwendung optimal angepasst sind. So wurden ultradünne, freitragende LiTaO3-Schichten mit einer Dicke von weniger als 1 μm hergestellt, mit denen die Sensoren eine spezifische Detektivität D* von über 5×109 cm Hz1/2W-1 erreichen. Abstract In recent years, a flexible technology has been developed for the manufacturing of pyroelectric infrared detectors based on lithium tantalate (LiTaO3) allowing the fabrication of detectors with very high signal-to-noise ratios and their customization for particular applications. In this way, ultrathin self-supporting LiTaO3 layers with film thicknesses of less than 1 μm have been manufactured for high-performance detectors with a maximum specific detectivity D* of more than 5×109 cm Hz1/2 W-1.

-Based Pyroelectric Infrared Detectors

We report a new approach for very thin infrared absorption layers consisting of gold nanorods. By using a modified seeding growth process we were able to prepare gold nanorods with an aspect ratio of up to 50. These nanorods have a typical length of 1,154 plusmn 111 nm and an average diameter of 26 plusmn 4 nm. They showed a longitudinal surface plasmon resonance absorption band at about 4,634 nm which is situated in the mid-wave infrared (MWIR) range. According to this, an enhancement in the responsivity of pyroelectric single element detectors could be observed verifying the functionality of the gold nanorods absorption layer. The position of the absorbance maximum can be easily controlled by the aspect ratio of the gold nanorods.