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With the increasing requirements of infrared detectors for high sensitivity, fast response, low cost and other performance parameters, the new uncooled microbolometer has attracted great attention and interest. In this paper, a micro-radiometric thermopile unit structure with a bilayer umbrella-shaped hollow absorption layer was designed, and the performances of different structures was analysed by simulation. The effects of the thickness and area of the absorber layer on the infrared absorption rate, thermal time constant and voltage response rate were investigated. The results show that the infrared absorption rate of the absorbing layer of the bilayer umbrella structure with a thickness of 70 nm exceeds 82. 5%. The response time of the optimized design model with an absorbing layer area of 106. 4 αm² and a thickness of 70 nm, with a response time of 0. 54 ms, demonstrating fast response and high stability. Electrical simulation results show that the structure possesses an effective thermal conductivity of 7. 384×10-8 W/K and a response rate of 2. 461×105 V/W under a bias current of 2 μA, which is suitable for preparing high-performance fast-response uncooled infrared focal-plane detectors and provides a good solution for the preparation and circuit design of uncooled infrared detectors. This provides feasible theoretical guidance for the preparation and circuit design of uncooled infrared detectors. [ABSTRACT FROM AUTHOR]

Uncooled and shutterless microbolometer cameras are good candidates for infrared imaging systems installed on small satellites or small unmanned aerial vehicles: they are light and passive since no cooling system or mechanical shutter is required and they can be operated at ambient temperatures. However, the radiometric compensation has to be carefully performed to make the system compatible with applications where the radiometric accuracy of the images is mandatory. In this paper, we study the impact of the camera environment to the radiometric accuracy of the images. We propose and test hardware and software solutions to improve this accuracy and the quality of the radiometric images. We show that the radiometric calibration of the camera with our model is valid over a long time period— about 3 years—using in-door experiments. [ABSTRACT FROM AUTHOR]

This work evaluates the electrical, optical and thermal properties of Sn-doped GexSi1-xOy thin films for use as microbolometer sensing materials. The films were prepared using a combination of a radio frequency (RF) magnetron and direct current (DC) sputtering using a Kurt J Leskar Proline PVD-75 series sputtering machine. Thin films were deposited in an O2+Ar environment at a chamber pressure of 4 mTorr. The thicknesses of the thin films were varied between 300 nm–1.2 µm by varying the deposition time. The morphology and microstructure of thin films were investigated by atomic force microscope (AFM) imaging and X-ray diffraction (XRD), while the atomic composition was determined using the energy dispersive spectroscopy (EDS) function of a scanning electron microscope. The thin film with an atomic composition of Ge0.45Si0.05Sn0.15O0.35 was found to be amorphous. We used the Arrhenius relationship to determine the activation energy as well as temperature coefficient of resistance of the thin films, which were found to be 0.2529 eV and −3.26%/K, respectively. The noise voltage power spectral density (PSD) of the film was analyzed using a Primarius—9812DX noise analyzer using frequencies ranging from 2 Hz to 10 kHz. The noise voltage PSD of the film was found to be 1.76 × 10−11 V2/Hz and 2.78 × 10−14 V2/Hz at 2 Hz and 1 K H z frequencies, respectively. The optical constants were determined using the ellipsometry reflection data of samples using an RC2 and infrared (IR) VASE Mark-II ellipsometer from J A Woollam. Absorption, transmission and reflection data for a wavelength range of 900 nm–5000 nm were also determined. We also determined the optical constant values such as the real and imaginary parts of refractive index (n and k, respectively) and real and imaginary part of permittivity ( ε 1 and ε 2 , respectively) for wavelength ranges between 193 nm to 35 µm. An optical band gap of 1.03 eV was determined from absorption data and using Tauc's equation. In addition, the thermal conductivity of the film was analyzed using a Linseis thin film analyzer employing the 3ω method. The thermal conductivity of a 780 nm thick film was found to be 0.38 Wm−1K−1 at 300 K. From the data, the Ge-Si-Sn-O alloy was found to be a promising material for use as a sensing material for microbolometers. [ABSTRACT FROM AUTHOR]

The Europa Thermal Emission Imaging System (E-THEMIS) on the Europa Clipper spacecraft will investigate the temperature and physical properties of Europa using thermal infrared (TIR) images in three wavelength bands centered from 7-14 μm, 14-28 μm and 28-80 μm. E-THEMIS will map >80% of the surface Europa at multiple times of day at a resolution of 8-km per pixel, ∼32% percent of the surface at ≤1 km/pixel resolution, and ∼6% percent at ≤100 m/pixel resolution. The specific objectives of the investigation are to 1) understand the formation of surface features, including sites of recent or current geologic activity, in order to understand regional and global processes and evolution and 2) to identify safe sites for future landed missions. E-THEMIS uses an uncooled microbolometer detector array for the IR focal plane. The E-THEMIS focal plane has 920 cross-track pixels (896 active) and 140 along-track pixels in each of the three spectral bands. The image data are collected at 14-bits per pixel at a frame rate of 60 Hz. The instrument can operate in framing mode, where full frame images are collected, and optionally co-added in time, in each band, or in time-delay-integration (TDI) mode where consecutive rows from each band are offset spatially to remove the spacecraft motion and then summed. In addition, the data in each band can be spatially aggregated from 2 × 2 to 5 × 5 pixels. These modes will be varied throughout each Europa flyby to optimize the data precision while fitting within the E-THEMIS data allocation. The expected temperature precision, measured as the noise equivalent spectral radiance, is 1.2 K at scene temperatures ≥90 K for a TDI of 16 with 4 × 4 pixel coaggregation in Band 2. The absolute accuracy at 90 K is 2−3 K in Band 2. E-THEMIS is an all-reflective, three-mirror anastigmat telescope with a 6.45-cm effective aperture and a speed of f/1.34 cross-track and 1.92 along-track. The mass of instrument Sensor Assembly, mounted on the spacecraft nadir deck, is 11.4 kg, the vault electronics are 1.8 kg, and the two are connected through a 3.1 kg harness. The Sensor volume is 23.7 cm x 31.8 cm x 29.8 cm. E-THEMIS consumes an average operation power of 34.8 W at 28 V. E-THEMIS was developed by Arizona State University with Raytheon Vision Systems developing the microbolometer focal plane assembly and Ball Aerospace developing the electronics. E-THEMIS was integrated, tested, and radiometrically calibrated on the Arizona State University campus in Tempe, AZ. [ABSTRACT FROM AUTHOR]

Microbolometer arrays, i.e., arrays of micro-scale pixels sensing temperature via resistance changes, have proven to be an effective basis for real-time imaging instrumentation in infrared as well as terahertz frequencies. In previous work, a design of THz and IR absorbing nano-laminates of dielectric and metal layers was studied. It was shown via numerical modeling that absorption may be maximized by appropriate choices of thickness, permittivity and conductivity. In this work, an analytical approach to the problem is formulated based on the standard recursive multiple reflection formulas for multi-layered planar structures. The results fully confirm and extend previous numerical work. A previous relationship between wavelength and silicon thickness for maximum absorption, derived numerically for specific parameter combinations, is now generalized in a parametric closed form. The method can be extended to include multiple lossy dielectric layers and may serve as a tool for optimizing the absorption characteristics of more complex layered absorbing structures. This could enhance the sensitivity of the detection scheme of interest, providing benefits in terms of cost, efficiency, precision, and adjustability. [ABSTRACT FROM AUTHOR]

Determination of optical, mechanical and electrical characteristics is one of the decisive factors in the design of instrumentation structures of thermal uncooled bolometer-type detectors (microbolometers). The paper presents the results of optimization calculations by means of computer simulation of absorption, transmittance and reflection spectra of device structures of microbolometers based on thermosensitive vanadium oxide film by finite-difference time-domain method (FDTD). The characteristics of the investigated microbolometer structure were checked for compliance with mechanical and electrical requirements for this class of devices.

Uncooled and shutterless microbolometer cameras are good candidates for infrared imaging systems installed on small satellites or small unmanned aerial vehicles: they are light and passive since no cooling system or mechanical shutter is required and they can be operated at ambient temperatures. However, the radiometric compensation has to be carefully performed to make the system compatible with applications where the radiometric accuracy of the images is mandatory. In this paper, we study the impact of the camera environment to the radiometric accuracy of the images. We propose and test hardware and software solutions to improve this accuracy and the quality of the radiometric images. We show that the radiometric calibration of the camera with our model is valid over a long time period— about 3 years—using in-door experiments.

This study demonstrates the conversion of metallic titanium (Ti) to titanium oxide just by conducting electrical current through Ti thin film in vacuum and increasing the temperature by Joule heating. This led to the improvement of electrical and thermal properties of a microbolometer. A microbolometer with an integrated Ti thermistor and heater width of 2.7 µm and a length of 50 µm was fabricated for the current study. Constant-voltage stresses were applied to the thermistor wire to observe the effect of the Joule heating on its properties. Thermistor resistance ~14 times the initial resistance was observed owing to the heating. A negative large temperature coefficient of resistance (TCR) of −0.32%/K was also observed owing to the treatment, leading to an improved responsivity of ~4.5 times from devices with untreated Ti thermistors. However, this does not improve the noise equivalent power (NEP), due to the increased flicker noise. Microstructural analyses with transmission electron microscopy (TEM), transmission electron diffraction (TED) and energy dispersive X-ray (EDX) confirm the formation of a titanium oxide (TiOx) semiconducting phase on the Ti phase (~85% purity) deposited initially, further to the heating. Formation of TiOx during annealing could minimize the narrow width effect, which we reported previously in thin metal wires, leading to enhancement of responsivity. [ABSTRACT FROM AUTHOR]

Plasmonic metamaterial absorbers (PMAs) designed for multispectral imaging in the infrared (IR) with uncooled microbolometers are investigated. The study presents Fourier transform infrared spectroscopy (FTIR) measurements of PMAs consisting of metal-insulator-metal-stacks (MIM) with square-shaped micropatches as top metal layers. The measurements reveal high absorptances of 82% to 99% for distinct wavelengths within a range from 2 μm to 9.2 μm. The spectra are evaluated with respect to the lateral dimensions of the patches and to the refractive indices of the used dielectrics SiO2, Al2O3 and Ta2O5. Numerical simulations and analytical calculations of the TM010-mode using the transmission line model (TLM) for microstrip antennas show good qualitative agreement with the measurement results. Additionally, bispectral PMAs were fabricated consisting of fields of PMAs with two different patch sizes arranged in a chessboard pattern. The individual fields of this pattern correspond to microbolometers with 12 μm pitch in shape and size. Two distinct absorption maxima can be seen in the spectra measured by FTIR. The choice of materials, deposition methods and patterning processes is suitable for the integration into the existing Fraunhofer IMS's nanotube microbolometer technology to realize multispectral infrared imaging. The fabrication process is CMOS-compatible and carried out on 8-in. wafers.

The increased interest in utilizing uncooled thermal bolometer-type detectors (microbolometers) within the infrared or terahertz detection field is justified by their operational and technological characteristics, in particular: relatively low manufacturing cost, high detection efficiency, compatibility with silicon CMOS technology, and operation at room temperature. The performance of such detectors depends on optimizing critical parameters, which are dictated by both the geometrical design and the electrical, optical, and thermal properties of the materials used. The determination of optical parameters stands as a decisive factor in the design of microbolometer structures. This article delves into the examination of optical parameters of thin films of structural materials of microbolometer based on thermosensitive vanadium oxide film manufactured at JSC “INTEGRAL”. The investigation showcases the results of determining optical constants (refractive indexes n and absorption coefficients k) of thin films from the transmission curve by applying the reflection-transmission method. Furthermore, a comparison is carried out between the results of computer modeling of the transmission, reflection and absorption spectra – taking into account the obtained values of the coefficients n and k – and the empirical data from the in-situ experiment.

Analytical relations for temperature response of the bolometer to periodic radiation pulses are obtained. It is theoretically shown and experimentally confirmed by the example of infrared bolometers that when detecting short radiation pulses, in contrast to the case of constant radiation, increasing the thermal conductivity of the bolometer and, accordingly, decreasing its thermal relaxation time, it is possible to significantly increase the response rate of the receiver, practically without reducing its sensitivity. The possibility of effective registration of pulsed terahertz radiation by microbolometers with a resistively coupled, thermally non-isolated antenna is considered. It is shown that such bolometers, which have increased thermal conductivity and, accordingly, reduced sensitivity to continuous-wave radiation, can be highly effective when detecting pulsed radiation with a duration shorter than the thermal relaxation time of the bolometer. On their basis, uncooled matrix detectors of pulsed terahertz radiation, characterized by a minimum detectable energy of less than 1 × 10–12 J and a frame rate of up to 1000 Hz, can be developed. [ABSTRACT FROM AUTHOR]

Microbolometer arrays, i.e., arrays of micro-scale pixels sensing temperature via resistance changes, have proven to be an effective basis for real-time imaging instrumentation in infrared as well as terahertz frequencies. In previous work, a design of THz and IR absorbing nano-laminates of dielectric and metal layers was studied. It was shown via numerical modeling that absorption may be maximized by appropriate choices of thickness, permittivity and conductivity. In this work, an analytical approach to the problem is formulated based on the standard recursive multiple reflection formulas for multi-layered planar structures. The results fully confirm and extend previous numerical work. A previous relationship between wavelength and silicon thickness for maximum absorption, derived numerically for specific parameter combinations, is now generalized in a parametric closed form. The method can be extended to include multiple lossy dielectric layers and may serve as a tool for optimizing the absorption characteristics of more complex layered absorbing structures. This could enhance the sensitivity of the detection scheme of interest, providing benefits in terms of cost, efficiency, precision, and adjustability.

The paper reports the art of recording a real-time imaging of concealed metallic objects, paracetamol drug, wood and TNT explosive using 0.11 Terahertz(THz) IMPATT diode laser source of 60 mW power and a 320 × 260 pixels plane focal array (PFA) uncooled microbolometer-based camera coupled with indigenously designed Teflon lenses and metallic mirrors. The noise equivalent power (NEP) and noise equivalent temperature difference (NETD) of microbolometer were ascertained of the order of 0.9pW/ Hz and 1004.5 mK, respectively. The image of the object was recorded using a X–Y motorized stage. The microbolometer camera with each pixel size of 150 µm combined with FLIR software for the recording the raw imaging data of the metallic sample. In the next step, raw data were transferred to python software for generating terahertz images. Finally, the quality of images is compared with the terahertz pulsed imaging system in reflection mode, which consist of an optical fiber-coupled femtosecond laser of 60 fs pulse width and repetition rate of 100 MHz for the generation and detection of THz radiation. [ABSTRACT FROM AUTHOR]

A comparative analysis of the characteristics of the main types of bolometers is indicated in the article. The constructive solution of an uncooled thermal detector of the bolometric type, formed using the technology of microelectromechanical systems, is studied. By means of computer simulation in modern computer-aided design systems in microelectronics, a static mechanical analysis was performed to assess the effect of mechanical stresses arising in structural materials during their formation on the magnitude of deformation. It has been established that to ensure the normal functioning of the microbolometer (to reduce the maximum deviation value of the film from the nominal value), it is necessary to reduce the internal mechanical stresses in the NiCr film. For the Si3N4 films, on the contrary, this value should be increased.

In this study, an experimental investigation was conducted to explore Ge1–xPbxOy as a candidate material for temperature-sensing layers in uncooled microbolometers. RF and DC sputtering techniques were used to deposit Ge1–xPbxOy thin films with various oxygen concentrations on silicon substrates at room temperature. The composition of the samples was experimentally analyzed using energy dispersive X-ray spectroscopy (EDX) that showed various oxygen concentrations. Atomic force microscopy (AFM) analysis showed excellent average surface roughness ranging from 0.6995 to 0.8660 nm. Increasing the concentration of oxygen up to 31% improved the thermoelectric and optical characteristics of the prepared Ge1–xPbxOy thin films. The highest temperature coefficient of resistance (TCR) of the fabricated samples was −3.85%/K for the Ge0.94Pb0.06O0.31 thin film. By using Essential McLeod software, optical simulation of the thin film samples was performed to assess the highest absorptance of the cavity microbolometer structure, which was 81.88% for the Ge0.94Pb0.06O0.31 thin film.

The resistive microbolometer fabricated by using CMOS technology can be monolithically integrated with the readout circuit but usually performs poorly in responsivity and detectivity. In this paper, the salicide poly-Si microbolometer with Al grating structure is demonstrated in the standard CMOS process. The simulation results show that not only are surface plasmon polaritons generated at the interface of the Al grating and SiO2, Al grating also provides the infrared resonant cavity required for the absorber, which improves the responsivity of the microbolometer. According to the experimental results, the maximum detectivity of the microbolometer with the grating structure reaches up to 2.26 × 109 cmHz1/2/W at 10 μm, which means an increase by 27.8% compared to the one without the Al grating. Moreover, the average detectivity of the microbolometer is also improved when the wavelength ranges from 7 μm to 13 μm. It is effortless to implement the proposed high-performance microbolometer in a unit structure based on CMOS technology, which is favorable to high-density array integration.

Thermal vision-based devices are nowadays used in a number of industries, ranging from the automotive industry, surveillance, navigation, fire detection, and rescue missions to precision agriculture. This work describes the development of a low-cost imaging device based on thermographic technology. The proposed device uses a miniature microbolometer module, a 32-bit ARM microcontroller, and a high-accuracy ambient temperature sensor. The developed device is capable of enhancing RAW high dynamic thermal readings obtained from the sensor using a computationally efficient image enhancement algorithm and presenting its visual result on the integrated OLED display. The choice of microcontroller, rather than the alternative System on Chip (SoC), offers almost instantaneous power uptime and extremely low power consumption while providing real-time imaging of an environment. The implemented image enhancement algorithm employs the modified histogram equalization, where the ambient temperature sensor helps the algorithm enhance both background objects near ambient temperature and foreground objects (humans, animals, and other heat sources) that actively emit heat. The proposed imaging device was evaluated on a number of environmental scenarios using standard no-reference image quality measures and comparisons against the existing state-of-the-art enhancement algorithms. Qualitative results obtained from the survey of 11 subjects are also provided. The quantitative evaluations show that, on average, images acquired by the developed camera provide better perception quality in 75% of tested cases. According to qualitative evaluations, images acquired by the developed camera provide better perception quality in 69% of tested cases. The obtained results verify the usability of the developed low-cost device for a range of applications where thermal imaging is needed. [ABSTRACT FROM AUTHOR]

The rapid expansion of the applications of infrared (IR) sensing in the commercial market has driven the need to develop new materials and detector designs for enhanced performance. In this work, we describe the design of a microbolometer that uses two cavities to suspend two layers (sensing and absorber). Here, we implemented the finite element method (FEM) from COMSOL Multiphysics to design the microbolometer. We varied the layout, thickness, and dimensions (width and length) of different layers one at a time to study the heat transfer effect for obtaining the maximum figure of merit. This work reports the design, simulation, and performance analysis of the figure of merit of a microbolometer that uses GexSiySnzOr thin films as the sensing layer. From our design, we obtained an effective thermal conductance of 1.0135 × 10 − 7   W / K , a time constant of 11   m s , responsivity of 5.040 × 10 5   V / W , and detectivity of 9.357 × 10 7   c m − H z 1 / 2 / W considering a 2   μ A bias current. [ABSTRACT FROM AUTHOR]

The utilization of amorphous germanium-tin (Ge1-xSnx) semiconducting thin films as temperature-sensing layers in microbolometers was recently presented and patented. The work in this paper was performed as an extension of the latest study to acquire better Sn concentrations % for microbolometer applications. In this work, Ge1-xSnx thin films with various Sn concentrations %, x, where 0.31 ≤ x ≤ 0.48, were sputter-deposited. The elemental composition of each film was evaluated using energy-dispersive X-ray (EDX) spectroscopy, and the surface morphology was evaluated using atomic force microscopy (AFM), showing average roughness values between ~ 0.2 and 0.8 nm. Measurements of the sheet resistance versus temperature were performed and analyzed, revealing temperature coefficients of resistance, TCRs, ranging from –3.11%/K to –2.52%/K for x ranging from 0.31 to 0.40 above which the Ge1-xSnx thin film was found to exhibit metallic behavior at 0.40 < x ≤ 0.48. Empirical relationships relating the resistivity, TCR, and Sn concentration % of the amorphous Ge1-xSnx thin films were derived. One of the films with a 31% Sn concentration (Ge0.69Sn0.31) was used to fabricate 10×10 μm2 microbolometer prototypes using electron-beam lithography and lift-off techniques, and the microbolometer was fabricated on top of oxidized silicon substrates with no air gap between them. The noise behavior and the maximum detected signal of the fabricated microbolometer were measured. The signal-to-noise ratio, voltage responsivity, and noise equivalent power values of the prototypes were calculated. Finally, the expected performance of a proposed air-bridge microbolometer configuration was calculated. [ABSTRACT FROM AUTHOR]

This study demonstrates the conversion of metallic titanium (Ti) to titanium oxide just by conducting electrical current through Ti thin film in vacuum and increasing the temperature by Joule heating. This led to the improvement of electrical and thermal properties of a microbolometer. A microbolometer with an integrated Ti thermistor and heater width of 2.7 µm and a length of 50 µm was fabricated for the current study. Constant-voltage stresses were applied to the thermistor wire to observe the effect of the Joule heating on its properties. Thermistor resistance ~14 times the initial resistance was observed owing to the heating. A negative large temperature coefficient of resistance (TCR) of −0.32%/K was also observed owing to the treatment, leading to an improved responsivity of ~4.5 times from devices with untreated Ti thermistors. However, this does not improve the noise equivalent power (NEP), due to the increased flicker noise. Microstructural analyses with transmission electron microscopy (TEM), transmission electron diffraction (TED) and energy dispersive X-ray (EDX) confirm the formation of a titanium oxide (TiOx) semiconducting phase on the Ti phase (~85% purity) deposited initially, further to the heating. Formation of TiOx during annealing could minimize the narrow width effect, which we reported previously in thin metal wires, leading to enhancement of responsivity.

The microbolometer is an important device that has a variety of civilian, industrial, and military applications, especially in remote sensing and night vision. Microbolometers are sensor elements in uncooled infrared sensors, which makes the uncooled infrared sensors have the advantage of being smaller in size, light in weight and less expensive compared with cooled infrared sensors. If the microbolometers are arranged in a two-dimensional array, a thermo-graph of the object can be determined using a microbolometer based uncooled infrared sensor. Building the electro-thermal modeling over the microbolometer pixel is essential to determine the uncooled infrared sensor's performance, optimize the sensor's design structure and monitor its condition. Due to the fact that the knowledge for the complex semiconductor-material-based microbolometers over various kinds of design structures with the adjustable thermal conductance is limited so far, this work focuses on the thermal distribution first by considering factors of the radiation absorption, thermal conductance, convection feature and joule heating on varied geometry design structures using Finite Element Analysis (FEA) methods. Then the change of thermal conductance is depicted when the simulated voltage is applied quantitatively between the microplate and electrode through the dynamic interaction of the electro force and the structure deformation via the electro particles redistribution balance by utilizing the Microeletromechanical system (MEMS). In addition, a more accurate contact voltage is derived through the numerical simulation compared with the previous theoretical value and is also verified by the experiment.

To make the mid-infrared (MIR) dispersive spectrograph a practical tool in industrial food processing lines, we designed a dispersive spectrograph system with an uncooled microbolometer focal plane array (FPA) detector for MIR spectral acquisition. To precisely regulate the angle of a rotatable grating to acquire the MIR spectrum, the spectral resolution and spatial resolution of the system were rigorously controlled to improve system performance. In the reflectance operation mode of the MIR dispersive spectrograph, the uncooled microbolometer FPA detector offered a maximum spectral resolution of 12 nm for the MIR, when a 300 grooves/mm blazed grating was used. Utilizing an optical parametric oscillator (OPO) pulse laser source, the wavelengths of the first-order diffraction were validated, and the system's spectral resolution limit was determined. As a line-scanning source, a Globar broadband source was installed, and the USAF 1951 Resolution Calculator was used to establish the spatial resolution of the imaging spectrograph. Using NI LabView, the logical operational technique for controlling the MIR dispersive spectrograph was encoded into system firmware. The GUI and test results are thoroughly described. [ABSTRACT FROM AUTHOR]

Most microsensors are composed of devices and covers. Due to the complicated structure of the cover and various other requirements, it difficult to use wafer-level packaging with such microsensors. In particular, for monolithic microsensors combined with read-out ICs, the available process margins are further reduced due to the thermal and mechanical effects applied to IC wafers during the packaging process. This research proposes a low-temperature, wafer-level vacuum packaging technology based on Cu-Sn bonding and nano-multilayer getter materials for use with microbolometers. In Cu-Sn bonding, the Cu/Cu3Sn/Cu microstructure required to ensure reliability can be obtained by optimizing the bonding temperature, pressure, and time. The Zr-Ti-Ru based nanomultilayer getter coating inside the cap wafer with high step height has been improved by self-aligned shadow masking. The device pad, composed of bonded wafer, was opened by wafer grinding, and the thermoelectrical properties were evaluated at the wafer-level. The bonding strength and vacuum level were characterized by a shear test and thermoelectrical test using microbolometer test pixels. The vacuum level of the packaged samples showed very narrow distribution near 50 mTorr. This wafer-level packaging platform could be very useful for sensor development whereby high reliability and excellent mechanical/optical performance are both required. Due to its reliability and the low material cost and bonding temperature, this wafer-based packaging approach is suitable for commercial applications. [ABSTRACT FROM AUTHOR]

A key challenge in further improving infrared (IR) sensor capabilities is the development of efficient data pre-processing algorithms. This paper addresses this challenge by providing a mathematical model and synthetic data generation framework for an uncooled IR sensor. The developed model is capable of generating synthetic data for the design of data pre-processing algorithms of uncooled IR sensors. The mathematical model accounts for the physical characteristics of the focal plane array, bolometer readout, optics and the environment. The framework permits the sensor simulation with a range of sensor configurations, pixel defectiveness, non-uniformity and noise parameters. [ABSTRACT FROM AUTHOR]

TUBIN is a microsatellite mission tasked with the demonstration of microbolometer technology for the detection of high-temperature events. To this end, the spacecraft employs a set of two microbolometers sensitive in the thermal range of the electromagnetic spectrum as well as a complementary CMOS-based imager for the visible spectrum. Additionally, the mission serves to demonstrate the upgraded capabilities of the TUBiX20 microsatellite platform after its initial implementation within the TechnoSat mission, launched in 2017. Here, the platform was upgraded with star trackers for enhanced attitude determination to enable the pointing accuracy required by the mission. Launched in June 2021, TUBIN has already successfully detected wildfires and volcanic activity in different biomes across the globe. Additionally, the sensor suite of the TUBIN mission was applied to examine its capabilities in the assessment of light-pollution in dedicated night time imaging campaigns. In this paper, we present and analyze data sets captured in the first six months of operation to illustrate capabilities, accomplishments, and challenges regarding payload operation, calibration, and data analysis for the TUBIN mission. Finally, the plans for the second half of TUBIN's nominal lifetime are outlined, including an on-orbit calibration campaign and increased automation in payload operations. • Wildfire detection with a small satellite platform in the 20 kg range using uncooled microbolometer technology. • We introduce updates to the highly modular satellite platform. • Initial orbit results are presented to showcase the performance of the payload. • More than a thousand images were taken to demonstrate detection of high-temperature events, calibration routine and other applications. [ABSTRACT FROM AUTHOR]

The advent of packaged infrared (IR) bolometers has led to thermography-based techniques becoming popular for non-destructive evaluation of aerospace structures. In this work, a real-time monitoring system for in situ crack detection has been presented which uses an original equipment manufacturer microbolometer. The system costs one-tenth the price of a packaged bolometer and has the potential to transform the use of IR imaging for condition and structural health monitoring in the aerospace industry and elsewhere. A computer, consisting of a single circuit board with dimensions comparable to a credit card, has been integrated into the system for real-time, on-board data processing. Crack detection has been performed based on the principles of thermoelastic stress analysis (TSA). Proof-of-concept laboratory tests were performed on open-hole aluminium specimens to compare the performance of the proposed system against a state-of-the-art cooled IR photovoltaic effect detector. It was demonstrated that cracks as small as 1 mm in length can be detected with loading frequencies as low as 0.3 Hz. This represents a significant advance in the viability of TSA-based crack detection in large-scale structural tests where loading frequencies are usually lower than 1 Hz. [ABSTRACT FROM AUTHOR]

This paper describes a new readout integrated circuit and non-uniformity correction (NUC) method that ensures that the bolometer array has low non-uniformity over a wide operating temperature range without a thermoelectric cooler (TEC). The proposed NUC minimizes the circuit and memory required for signal processing, making it suitable for compact and power-efficient portable infrared cameras. It corrects the aging phenomenon through start-up calibration and corrects non-uniformities without a TEC through calibration during operation mode. It minimizes the calibration process during operation mode and uses a pixel-level analog-to-digital converter to enable real-time NUC. A 0.18 μm standard CMOS process is applied to the proposed NUC. The frame rate for calibration during the operation mode is approximately 14.3 Hz. The proposed NUC demonstrates excellent uniformity with a non-uniformity of less than 0.12% over a wide operating temperature range (−20 to 50 °C). [ABSTRACT FROM AUTHOR]

A low-cost 80×60 microbolometer CMOS (complementary metal-oxide-semiconductor) thermal imager is presented. The imager system integrated with a proposed 12-b biasing digital-to-analog converter (DAC) has 100 ms start-up time, which is 300× faster than commercial products, while ensuring comparable 100 mK noise-equivalent temperature difference. The low-noise biasing DAC adopts a current-mode divider-stacking structure and a bit-inversion technique, leading to mismatch-insensitive operation. The 12-b biasing DAC in a 0.18 μm CMOS imager IC has a low noise of 1.89 μVrms and INL (integral non-linearity)/DNL (differential non-linearity) of 0.14/0.09 LSB, respectively. [ABSTRACT FROM AUTHOR]

The processes of reactive magnetron sputtering of a V target in Ar/O2 gas mixture are investigated. It was found that when using a pulsed current for sputtering and a pressure in the chamber less than 0.06 Pa, the intensities of the emission lines of vanadium at 437.922 nm, argon at 750.386 nm, and oxygen at 777.417 nm with a change in the oxygen concentration in Ar/O2 gas mixtures (ГO2) have no hysteresis and unambiguously depend on the parameters of the sputtering process, which makes it possible to stabilize the process without using feedback systems. By monitoring the sputtering process by optical emission spectroscopy and depositing films on a rotating substrate of diameter 100 mm, vanadium oxide (VOx) films with nonuniformity thickness less than ±2.4 % and surface resistance less than ±2.5 % were obtained. Studies by transmission line method of the influence of the parameters of the reactive magnetron sputtering and subsequent annealing at O2 pressure of 0.04 Pa on the characteristics of thermoresistive structures based on VOx films showed that when the contacts are deposited without ion cleaning, the current-voltage characteristics (IV) and the dependence of the resistance on the length of resistors R(L) are nonlinear, which indicates the presence of a potential barrier in the contacts. Preliminary ion cleaning can significantly improve the linearity of the IV characteristic. The most linear IV characteristics were obtained for Ti contacts. However, the specific contact resistance of the VOx/Ti contact increases with an increase in the oxidation state of the VOx films and reaches ρc = 0.1 Ohm·m2 at the specific resistance of vanadium oxide ρ = 0.1 Ohm·m. The analysis of the dependences of the temperature coefficient of resistance (TCR) and ρ of VOx films on the annealing temperature showed that, upon annealing, ρ and TCR slightly decrease, i. e. there occurs a partial deoxidation of the films. However, unlike annealing at atmospheric pressure, there are no temperature regions at which a sharp decrease in the resistivity and TCR occurs.

The aim of this work was to study the effect of the parameters of deposition process and subsequent annealing on the properties of vanadium oxide VOx films deposited by the pulsed reactive magnetron sputtering of a V target in an Ar/O2 gas mixture. The dependences of the structure, phase, temperature coefficient of resistance (TCR), resistivity p, band gap Egof the films on the oxygen concentration in Ar/O2 gas mixture during the deposition ГO2, and the temperature of annealing in an O2 atmosphere were obtained. The films were found to have an amorphous structure after deposition. Crystallization processes are observed at temperatures above 275 °C. In this case, depending on the temperature, polycrystalline films with a monoclinic, cubic or mixed crystal lattice are formed and a transition occurs from the intermediate oxide V4O9 to the mixed phase VO2/VOx/V2O5 and then to the higher oxide V2O5. The character of changes in p, TCR and Egof films coming from the change in the annealing temperature is complex and largely determined by ГO2. It was established that with the view of using VOx films as thermosensitive layers, the following conditions of deposition and annealing would be preferable: films deposited at the oxygen concentration 25 % in Ar/O2 gas mixture and annealed at a temperature of 250–275 °C in an O2 atmosphere for 10 min. Under these conditions VOx films with the following properties were obtained: p= (1.0 – 3.0).10-2 Ohm.m, TCR = 2.05 %/°C, and Eg= 3.76–3.78 eV.

Thermal vision-based devices are nowadays used in a number of industries, ranging from the automotive industry, surveillance, navigation, fire detection, and rescue missions to precision agriculture. This work describes the development of a low-cost imaging device based on thermographic technology. The proposed device uses a miniature microbolometer module, a 32-bit ARM microcontroller, and a high-accuracy ambient temperature sensor. The developed device is capable of enhancing RAW high dynamic thermal readings obtained from the sensor using a computationally efficient image enhancement algorithm and presenting its visual result on the integrated OLED display. The choice of microcontroller, rather than the alternative System on Chip (SoC), offers almost instantaneous power uptime and extremely low power consumption while providing real-time imaging of an environment. The implemented image enhancement algorithm employs the modified histogram equalization, where the ambient temperature sensor helps the algorithm enhance both background objects near ambient temperature and foreground objects (humans, animals, and other heat sources) that actively emit heat. The proposed imaging device was evaluated on a number of environmental scenarios using standard no-reference image quality measures and comparisons against the existing state-of-the-art enhancement algorithms. Qualitative results obtained from the survey of 11 subjects are also provided. The quantitative evaluations show that, on average, images acquired by the developed camera provide better perception quality in 75% of tested cases. According to qualitative evaluations, images acquired by the developed camera provide better perception quality in 69% of tested cases. The obtained results verify the usability of the developed low-cost device for a range of applications where thermal imaging is needed.

The rapid expansion of the applications of infrared (IR) sensing in the commercial market has driven the need to develop new materials and detector designs for enhanced performance. In this work, we describe the design of a microbolometer that uses two cavities to suspend two layers (sensing and absorber). Here, we implemented the finite element method (FEM) from COMSOL Multiphysics to design the microbolometer. We varied the layout, thickness, and dimensions (width and length) of different layers one at a time to study the heat transfer effect for obtaining the maximum figure of merit. This work reports the design, simulation, and performance analysis of the figure of merit of a microbolometer that uses GexSiySnzOr thin films as the sensing layer. From our design, we obtained an effective thermal conductance of 1.0135×10−7 W/K, a time constant of 11 ms, responsivity of 5.040×105 V/W, and detectivity of 9.357×107 cm−Hz1/2/W considering a 2 μA bias current.

This study describes a new method to compensate bias heating effects for microbolometer readout circuits using a finely adjustable CMOS resistance as a reference. The proposed self calibrated cooler-less structure dynamically modifies CMOS resistance during integration time. This compensation structure also includes a feedback loop, which forces the oscillators to work in the linear region. The proposed self calibration circuit is designed and simulated using a 65-nm process node, and achieves 40 mK NETD (Noise Equivalent Temperature Difference) value for one percent resistance non-uniformity of pixel resistance values across one row. The layout area of this circuit occupies approximately one third of the layout area used by classical readout circuits. The circuit dissipates one third of power compared with classical microbolometer readout approaches. • Automatic Self-Heating Calibration Method. • Row-based Self-heating calibration to eliminate substrate temperature drift of classical microbolometer readout. • Low Supply Voltage and Low Area Microbolometer Readout Architecture. • VCO-based microbolometer Readout Circuit. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a periodic structure based on metallic split-ring resonators is integrated into micro-bridge structures of THz microbolometer array to achieve high THz wave absorption in a wide frequency range. With a small unit size of 35 μm × 35 μm, the effect of split-ring structure on THz wave absorption characteristics of the multilayer structure array is studied to manipulate the resonance absorption frequencies. The absorption bandwidth is effectively increased by integrating a combined structure of split-ring and metallic disk. Broadband THz absorption is formed by coupling the absorption peaks of different structures. The periodic structure of dual-ring combined with a metallic disk provides a broadband THz wave absorption in the range of 4–7 THz. The highest absorption in the band reaches 90% and the lowest absorption is higher than 40%. The designed structure is process-compatible and easy to implement for small-pixel THz microbolometers with high absorption in a wide spectrum range. The research provides a scheme for broadband THz sensing and real-time imaging at room temperature.

The aim of this work was to study the effect of the gas composition during sputtering on the electrophysical properties of vanadium oxide films deposited by pulsed reactive magnetron sputtering of a vanadium target in an Ar/O2 medium of working gases.The dependences of the magnetron discharge voltage, deposition rate, resistivity, temperature coefficient of resistance (TCR), and the band gap of vanadium oxide films on the oxygen concentration in the gas mixture are obtained. It was found that amorphous films of vanadium oxide are formed during reactive magnetron sputtering. It is shown that the properties of the deposited vanadium oxide films have a strong dependence on the oxygen concentration in the Ar/O2 gas mixture, which is associated with the formation of a mixture of various intermediate vanadium oxides in the film. It was found that from the point of view of using vanadium oxide films as thermosensitive layers of microbolometers, the films must be deposited at oxygen concentrations in the gas mixture of 17 to 25 %. At the given oxygen concentrations without heating the substrates, vanadium oxide films with a resistivity (0.6–4.0)·10-2 Ohm·m, TCR 2.2–2.3%/°C and a band gap for direct transitions of 3.7–3.78 eV. The obtained characteristics make it possible to use these films as thermosensitive layers of microbolometers.

Most microsensors are composed of devices and covers. Due to the complicated structure of the cover and various other requirements, it difficult to use wafer-level packaging with such microsensors. In particular, for monolithic microsensors combined with read-out ICs, the available process margins are further reduced due to the thermal and mechanical effects applied to IC wafers during the packaging process. This research proposes a low-temperature, wafer-level vacuum packaging technology based on Cu-Sn bonding and nano-multilayer getter materials for use with microbolometers. In Cu-Sn bonding, the Cu/Cu3Sn/Cu microstructure required to ensure reliability can be obtained by optimizing the bonding temperature, pressure, and time. The Zr-Ti-Ru based nanomultilayer getter coating inside the cap wafer with high step height has been improved by self-aligned shadow masking. The device pad, composed of bonded wafer, was opened by wafer grinding, and the thermoelectrical properties were evaluated at the wafer-level. The bonding strength and vacuum level were characterized by a shear test and thermoelectrical test using microbolometer test pixels. The vacuum level of the packaged samples showed very narrow distribution near 50 mTorr. This wafer-level packaging platform could be very useful for sensor development whereby high reliability and excellent mechanical/optical performance are both required. Due to its reliability and the low material cost and bonding temperature, this wafer-based packaging approach is suitable for commercial applications.

To make the mid-infrared (MIR) dispersive spectrograph a practical tool in industrial food processing lines, we designed a dispersive spectrograph system with an uncooled microbolometer focal plane array (FPA) detector for MIR spectral acquisition. To precisely regulate the angle of a rotatable grating to acquire the MIR spectrum, the spectral resolution and spatial resolution of the system were rigorously controlled to improve system performance. In the reflectance operation mode of the MIR dispersive spectrograph, the uncooled microbolometer FPA detector offered a maximum spectral resolution of 12 nm for the MIR, when a 300 grooves/mm blazed grating was used. Utilizing an optical parametric oscillator (OPO) pulse laser source, the wavelengths of the first-order diffraction were validated, and the system’s spectral resolution limit was determined. As a line-scanning source, a Globar broadband source was installed, and the USAF 1951 Resolution Calculator was used to establish the spatial resolution of the imaging spectrograph. Using NI LabView, the logical operational technique for controlling the MIR dispersive spectrograph was encoded into system firmware. The GUI and test results are thoroughly described.

Uncooled thermal cameras have been employed as common UAV payloads for aerial temperature surveillance in recent years. Due to the lack of internal cooling systems, such cameras often suffer from thermal-drift-induced nonuniformity or vignetting despite having built-in mechanisms to minimize the noise. The current study examined a UAV-based uncooled thermal camera vignetting regarding camera warmup time, ambient temperature, and wind speed and direction, and proposed a simple calibration-based vignetting migration method. The experiments suggested that the camera needed to undergo a warmup period to achieve stabilized performance. The required warmup duration ranged from 20 to 40 min depending on ambient temperature. Camera vignetting severity increased with camera warmup time, decreasing ambient temperature, and wind presence, while wind speed and direction did not make a difference to camera vignetting during the experiments. Utilizing a single image of a customized calibration target, we were able to mitigate vignetting of outdoor images captured in a 30 min duration by approximately 70% to 80% in terms of the intra-image pixel standard deviation (IISD) and 75% in terms of the pixel-wise mean (PWMN) range. The results indicated that outdoor environmental conditions such as air temperature and wind speed during short UAV flights might only minimally influence the thermal camera vignetting severity and pattern. Nonetheless, frequent external shutter-based corrections and considering the camera nonlinear temperature response in future studies have the potential to further improve vignetting correction efficacy for large scene temperature ranges.

A key challenge in further improving infrared (IR) sensor capabilities is the development of efficient data pre-processing algorithms. This paper addresses this challenge by providing a mathematical model and synthetic data generation framework for an uncooled IR sensor. The developed model is capable of generating synthetic data for the design of data pre-processing algorithms of uncooled IR sensors. The mathematical model accounts for the physical characteristics of the focal plane array, bolometer readout, optics and the environment. The framework permits the sensor simulation with a range of sensor configurations, pixel defectiveness, non-uniformity and noise parameters.

The theoretical relations optimizing the design of the microbolometric element of the focal plane arrays (FPAs) and ensuring the improvement of its performance characteristics are considered. The requirements for the parameters of the elements and the materials used for their manufacture are formulated, which provide a fundamental opportunity to minimize the thermal relaxation time constant of the bolometric sensor in order to increase the frame frequency of the matrices. The results of their modeling are presented, which make it possible to optimize the design and its implementation using modern technological processes for the formation of microbolometric elements with high operating speed, taking into account the requirements of specific applications. [ABSTRACT FROM AUTHOR]

Hermetic sealing microelectronic devices in package become more and more of a challenge for manufacturers due to the complexity of thermal management, getter integration, and material selection and interactions. Such complexity drives the original equipment manufacturer (OEM) to deliver the equipment and technology to meet manufacturers’ requirements. This study has successfully demonstrated that a vacuum reflow technology is able to deliver packages with an excellent hermetic seal. The measured leak rates of these two package types are about two orders of magnitude better than the requirement by Mil-Std 883 method 1014 specification. The result is clear that optimization of the force applied to the lid and package during seal process is essential and the force density of 5 kPa is able to produce a great hermeticity for the two packages under study. A good solder joint strength is essential to deliver a package with hermeticity but is not enough, while a weak joint strength is not possible to achieve hermeticity. [ABSTRACT FROM AUTHOR]