Photodetector devices based on PIN and barrier structures of the mid-wave IR range of the spectrum

Multilayer structures based on the antimonide group materials with absorber layers InSb or AlxIn1-XSb, and XBn-structures with AlxIn1-XSb barrier layer (InSb/AlxIn1-XSb/InSb), designed for the manufacture of advanced photosensitive devices detecting radiation in the medium-wave infrared (IR) range (MWIR), have been developed and investigated. Various topology photosensitive elements (PSE) with absorbing layers InSb or AlxIn1-XSb were fabricated on the basis of MBE-grown p–i–n and barrier structures. It is shown that wideband ternary al-loys AlxIn1-XSb are considered as an alternative to the narrowband binary compound InSb, since, due to wide-band material properties, photodiodes based on AlxIn1-XSb have lower dark currents, and, consequently, noise. The average values of detectivity D* and noise-equivalent temperature difference (NETD) have been measured for various topology photodetectors, so D* was more than 1011 cmW-1Hz1/2 in p–i–n-structures, and D* exceed of 1012 cmW-1Hz1/2 in barrier structures.

Mesa-structures and Focal Plane Arrays based on epitaxially grown InSb layers

Aspects of epitaxially grown indium antimonide (InSb) on InSb substrates (InSb-on-InSb) by molecular beam epitaxy (MBE) for the 2D focal plane arrays fabrication process have been described. The epitaxial growth offers possibility for complex structure production, and then such structures suppose more effective control of the thermal generation charge carriers as the detector temperature is raised above 80 K. Investigations of mid-wave infrared (MWIR) 320256 FPAs with 30 μm pitch and 640512 FPAs with 15 μm pitch based on InSb-on-InSb layers have shown high performance: the average detectivity at T = 77 K more than 21011 cmW-1Hz1/2, the average value of noise equivalent temperature difference (NETD) with a cold aperture of 60o at T = 77K was in the range of 10–20 mK. High quality thermal imaging images were obtained in real time mode.

Metrological characterization and calibration of thermographic cameras for quantitative temperature measurement

We present the metrological characterization and calibration of three different types of thermographic cameras for quantitative temperature measurement traceable to the International Temperature Scale (ITS-90). Relevant technical specifications – i.e., the non-uniformity of the pixel-to-pixel responsivity, the inhomogeneity equivalent temperature difference (IETD), the noise equivalent temperature difference (NETD), and the size-of-source effect (SSE) – are determined according to the requirements given in the series of Technical Directives VDI/VDE 5585. The measurements are performed with the camera calibration facility of the Physikalisch-Technische Bundesanstalt. The data reference method is applied for the determination and improvement of the non-uniformity, leading to an improved IETD for all three cameras. Finally, the cameras are calibrated according to the different procedures discussed in the VDI/VDE 5585 series. Results achieved with the different calibration procedures are compared for each type of camera and among the three cameras. An uncertainty budget for the calibration of each camera is given according to GUM (ISO, 1995) and VDI/VDE 5585.

Design, Fabrication, and Performance Evaluation of Portable and Large-Area Blackbody System

In this study, a portable and large-area blackbody system was developed following a series of processes including design, computational analysis, fabrication, and experimental analysis and evaluation. The blackbody system was designed to be lightweight (5 kg), and its temperature could exceed the ambient temperature by up to 15 °C under operation. A carbon-fiber-based heat source was used to achieve a uniform temperature distribution. A heat shield fabricated from an insulation material was embedded at the opposite side of the heating element to minimize heat loss. A prototype of the blackbody system was fabricated based on the design and transient coupled electro-thermal simulation results. The operation performance of this system, such as the thermal response, signal transfer function, and noise equivalent temperature difference, was evaluated by employing an infrared imaging system. In addition, emissivity was measured during operation. The results of this study show that the developed portable and large-area blackbody system can be expected to serve as a reliable reference source for the calibration of aerial infrared images for the application of aerial infrared techniques to remote sensing.

Performance Assessment of Low-Cost Thermal Cameras for Medical Applications

Thermal imaging is a promising technology in the medical field. Recent developments in low-cost infrared (IR) sensors, compatible with smartphones, provide competitive advantages for home-monitoring applications. However, these sensors present reduced capabilities compared to more expensive high-end devices. In this work, the characterization of thermal cameras is described and carried out. This characterization includes non-uniformity (NU) effects and correction as well as the thermal cameras’ dependence on room temperature, noise-equivalent temperature difference (NETD), and response curve stability with temperature. Results show that low-cost thermal cameras offer good performance, especially when used in temperature-controlled environments, providing evidence of the suitability of such sensors for medical applications, particularly in the assessment of diabetic foot ulcers on which we focused this study.

Non-uniformity correction in a Long Wave Infrared Focal Plane Array as a calibration temperature function

Despite of the manufactory process, all detector or pixel in a Focal Plane Array (FPA) has a different responsivity and offset when evaluated. These variations result in a specific kind of noise, called Fixed Pattern Noise (FPN) or spatial noise. During the image processing, those pixels who has a large deviation in responsivity or in their noise are considered bad pixels, and have their influence removed during the exhibition of a scene. Knowing the answer of all those pixels are the first test procedure in an FPA characterization. However, during the Non-uniformity correction and bad pixel replacement it is necessary to choose two reference temperatures, calibration points, and those temperature affects important parameters such as Uniformity, Noise Equivalent Temperature Difference (NETD) and Signal Transfer Function (SiTF). This work will study the calibration temperature influence on the Non-Uniformity Correction (NUC) quality by comparing uniformity, bad pixel number, NETD and SiTF values during characterizations.

Shape memory polymer resonators as highly sensitive uncooled infrared detectors

Uncooled infrared detectors have enabled the rapid growth of thermal imaging applications. These detectors are predominantly bolometers, reading out a pixel’s temperature change due to infrared radiation as a resistance change. Another uncooled sensing method is to transduce the infrared radiation into the frequency shift of a mechanical resonator. We present here highly sensitive resonant infrared sensors, based on thermo-responsive shape memory polymers. By exploiting the phase-change polymer as transduction mechanism, our approach provides 2 orders of magnitude improvement of the temperature coefficient of frequency. Noise equivalent temperature difference of 22 mK in vacuum and 112 mK in air are obtained using f/2 optics. The noise equivalent temperature difference is further improved to 6 mK in vacuum by using high-Q silicon nitride membranes as substrates for the shape memory polymers. This high performance in air eliminates the need for vacuum packaging, paving a path towards flexible non-hermetically sealed infrared sensors.