Uncooled Microbolometer Array Research Articles

Microbolometer with a salicided polysilicon thermistor in CMOS technology.

The metal-type microbolometers in CMOS technology normally suffer low resistivity and high thermal conductivity, limiting their performance and application areas. In this paper, we demonstrate a polysilicon microbolometer fabricated in 0.18 µm CMOS and post-CMOS processes. The detector is composed of a SiO2 absorber coupled with a salicided poly-Si thermistor that has a high resistivity of 1.37×10-4 Ω·cm and low thermal conductivity of 18 W/m·K. It is experimentally shown that the microbolometer with a 40 µm × 40 µm pixel size has a maximum responsibility and detectivity of 2.13×104 V/W and 2.33×109 cmHz1/2/W, respectively. The results are superior to the reported metal-type and diode-type microbolometers in the CMOS process and provide good potential for a low-cost, high-performance, uncooled microbolometer array for infrared imaging applications.

Tunable graphene nanopatch antenna design for on-chip integrated terahertz detector arrays with potential application in cancer imaging.

Aim: Further to our reports on chip-integrable uncooled terahertz microbolometer arrays, compatible with medium-scale semiconductor device fabrication processes, the possibility of the development of chip-integrable medical device is proposed here. Methods: The concept of graphene-based nanopatch antennas with design optimization by the finite element method (FEM) is explored. The high-frequency structure simulator (HFSS) utilized fine FEM solver for analyzing empirical mode decomposition preprocessing and for modeling and simulating graphene antennas. Results: Graphene nanopatch antennas exhibited tunable features with varying patch dimensions and dependence on substrate material permittivity. Conclusion: This work implements reconfigurable graphene nanopatch antenna compatible with terahertz microbolometer arrays. This design concept further developson-chip medical devices for possible screening of cancer cell with terahertz image processing.

A low-cost chopping system and uncooled microbolometer array for ground-based astronomy

Mid-Infrared imaging is vital for the study of a wide variety of astronomical phenomena, including evolved stars, exoplanets, and dust enshrouded processes such as star formation in galaxies. However, infrared detectors have traditionally been expensive and it is difficult to achieve the sensitivity needed to see beyond the overwhelming mid-infrared background. Here we describe the upgrade and commissioning of a simple prototype, low-cost 10 μ m imaging instrument. The system was built using commercially available components including an uncooled microbolometer focal plane array and chopping system. The system was deployed for a week on the 1.52 m Carlos Sanchez Telescope and used to observe several very bright mid-infrared sources with catalogue fluxes down to sim 600 Jy. We report a sensitivity improvement of sim 4 mag over our previous unchopped observations, in line with our earlier predictions.

Overview of the research work of Dr. Fukuhara in thermal infrared cameras across Hyabusa2, Akatsuki, Wildfire Monitoring and Lunar Flares

A technology that has only been recently introduced into astronomy and space exploration is infrared thermography (IRT) using uncooled microbolometer arrays (UMBA) to capture images. Assistant Professor Tetsuya Fukuhara, from the Department of Physics at Rikkyo University, Tokyo, Japan has been pioneering its use and over the last decade he has proved that UMBA IRT can uncover novel astronomical phenomena, help guide space travel and potentially allow satellites to stay precisely and accurately on orbit.

Uncooled microbolometer arrays for ground-based astronomy

ABSTRACT We describe the design and commissioning of a simple prototype, low-cost 10 μm imaging instrument. The system is built using commercially available components including an uncooled microbolometer array as a detector. The incorporation of adjustable germanium reimaging optics rescale the image to the appropriate plate scale for the 2 m diameter Liverpool Telescope. From observations of bright Solar system and stellar sources, we demonstrate a plate scale of 0.75 arcsec per pixel and confirm the optical design allows diffraction limited imaging. We record a ∼10 $\, {\rm per\, cent}$ photometric stability due to sky variability. We measure a 3σ sensitivity of 7 × 103 Jy for a single, ∼0.11 s exposure. This corresponds to a sensitivity limit of 3 × 102 Jy for a 60 s total integration. We present an example science case from observations of the 2019 January total lunar eclipse and show that the system can detect and measure the anomalous cooling rate associated with the features Bellot and Langrenus during eclipse.

Hyperspectral imager for the mid-infrared spectral range using a single-mirror interferometer and a windowing method

In this paper, we present a static imaging Fourier transform spectrometer (sIFTS) for the mid-infrared spectral range. The system employs imaging optics, a single-mirror interferometer, and an uncooled broadband microbolometer array. As the hyperspectral data cube is acquired using a windowing method, a comparatively high light throughput in a spectral range from 2600 cm−1 to 800 cm−1, respectively 3.8 µm to 13 µm is achieved. The spectral resolution is 12 cm−1, and the spatial resolution amounts to 16 lp/mm, corresponding to a resolution of 62.5 µm at a design wavelength of 10.6 µm. As the employed spectrometer, in contrast to scanning Fourier transform infrared (FTIR) spectrometers, contains no moving parts, the measurement rate is mainly limited by the detector read-out and is currently 25 Hz. After an evaluation of the spatial resolution by both simulations and experimental results, the spatially resolved transmission spectra of a sample containing different polymer films are recorded and compared to a laboratory FTIR spectrometer. Thereby, the acquired spectra show good agreement. As the system combines both a spectrometer with low internal light loss and a windowing technique allowing high etendue, the presented hyperspectral imager shows significant potential especially for the mid-infrared.

Commercial Uncooled Microbolometer Camera Applied to 50-kg Class Satellite

The commercial thermal infrared camera mounting the uncooled microbolometer array (UMBA), which detects thermal wavelengths from 8 to $14~\mu \text{m}$ , was modified for space use and applied to the small earth-observing satellite called Rising-2. The satellite was launched in 2014, and the camera successfully took 17 of the cloud top and 3 of the land images from the sun-synchronous orbit. Observed brightness temperatures based on the reference data acquired in the laboratory before the launch have been compared with verified products derived from the Japanese meteorological satellite called MTSAT-2, and we confirmed that the UMBA could sense brightness temperature distribution of the target. The demonstration of the commercial thermal infrared camera in orbit would innovate in the development of space instruments as a new approach.

Performance improvement of on-chip integrable terahertz microbolometer arrays using nanoscale meander titanium thermistor

In this study, uncooled antenna-coupled microbolometer arrays were fabricated to detect terahertz waves by using nanoscale meander-shaped Ti thermistors with design widths of DW = 0.1 and 0.2 μm, respectively, on SiO2 and SiNx substrates. Each unit device with a thermistor with DW = 0.1 μm yielded double the electrical responsivity (787 V/W) of unit devices with thermistors with DW = 0.2 μm (386 V/W) at the maximum allowable bias current (Ib = 50 for DW = 0.1 μm and 100 μA for DW = 0.2 μm, respectively). However, the calculated noise-equivalent power (NEP) of unit devices with thermistors with DW = 0.1 μm was 1.85×10−10W/Hz at Ib = 50 μA and 1.58×10−10W/Hz at Ib = 100 μA for unit devices with thermistors with DW = 0.2 μm. Hence, the reduction in DW did not lead to an improvement in NEP. This study validates our previous investigation into the effect of width on such device parameters such as the temperature coefficient of resistance (TCR) and resistivity in the context of device miniaturization. The smaller grain size in thinner metal interconnects (thermistors) can be linked to the lower TCR and increased resistivity of the devices. Thus, the enhancement in responsivity in the design was largely due to the nanoscale meander design that, however, was detrimental to the noise response of the devices. These devices with nanoscale Ti meander thermistors deliver high responsivity in unit devices with scope for further miniaturization and have significant potential for application as on-chip integrable detector arrays.

Broadband static Fourier transform mid-infrared spectrometer

For applications where only moderate spectral resolution is required, static Fourier transform infrared spectrometers (sFTS) offer a comparatively cost-effective alternative to classical scanning instruments. In this paper, we present an sFTS based on a single-mirror interferometer using only standard optical components and an uncooled microbolometer array. Because the instrument features concave mirrors rather than lenses, dispersion effects can be minimized. This enables broadband operation in the mid-infrared range from 2800 cm-1 to 600 cm-1 at a spectral resolution of 12 cm-1. In addition, the design guarantees comparatively high light throughput and can potentially be designed for increased temperature stability. Alongside a simulation of the temperature- and wavenumber-dependent behavior of the system, we provide a proof of principle of the proposed design by means of experimental results.

The Industrial Temperature Measurement System Based on the Uncooled IRFPA Detector

Most of the non-contact temperature measuring devices in the market are mainly based on dot infrared thermometers. The single machine operated instruments can only meet the requirements of temperature measurement for local temperature points, and can not feedback the temperature information and temperature direction of the whole temperature field in real time. Under the condition of low temperature, for the Commonly non-contact temperature measurement system, the reaction is not sensitive, can not keep up with the temperature change, Continuous calibration and debugging are needed in the case of changing ambient temperature, resulting in a great waste of personnel and time. In the aspect of infrared detector, the operating wavelength of the traditional infrared CCD is 0.4-1.1μm, affected by the cut-off wavelength, the error of infrared CCD is very large in industrial low temperature measurement. The operating wavelength of uncooled focal plane array infrared camera is generally between 8-14μm, which temperature measurement accuracy can reach 0.01°C under the optimum working environment. The UL01011 is most commonly used as the core photo detector in the uncooled focal plane uncooled micro-bolometer array infrared camera, we used it as the experimental photoelectric detector, Experiments showed that this method could achieve better results in practice.

Optimization of narrow width effect on titanium thermistor in uncooled antenna-coupled terahertz microbolometer

Uncooled antenna-coupled terahertz microbolometer arrays are fabricated with a meander-type Ti thermistor, and design widths (DW) = 0.1 and 0.2 µm, considering the design requirement to miniaturize detectors. Each unit device with DW = 0.1 µm of the thermistor has about 4.7 time higher electrical responsivity (132 V/W) than that with DW = 0.2 µm (28.2 V/W) at 10 µA bias current. For DW = 0.2 µm, the calculated noise equivalent power (NEP) was 2.29 × 10−9 W/, whereas the minimum NEP of 4.43 × 10−10 W/ was obtained for DW = 0.1 µm devices, both at 10 µA bias current. The bulk value of temperature coefficient of resistance (TCR) of the Ti thermistor is markedly compromised in low dimensional devices, still in terms of responsivity and NEP, unit devices with Ti thermistor with the lower DW shows better performance. This is because the narrow width effect is minimized owing to higher resistivity for DW = 0.1 than that for DW = 0.2 µm. In this current report, we highlights the optimization of the narrow width effect on TCR of metal interconnects in nanometer dimensions, which to the best of our knowledge is not available at present.

Detection of Small Wildfire by Thermal Infrared Camera With the Uncooled Microbolometer Array for 50-kg Class Satellite

The thermal infrared camera with the uncooled microbolometer array based on commercial products has been developed in a laboratory of a Japanese university and mounted to a 50-kg class small satellite specialized for discovering wildfire. It has been launched in 2014 and successfully detected considerable hotspots not only wildfire but also volcanoes. Brightness temperature derived from observation has been verified, and the scale of observed wildfire has been provisionally presumed; the smallest wildfire ever detected has a flame zone less than $\sim 300~\text{m}^{\mathrm {\mathbf {2}}}$ and the fire radiative power = ~35.4 mW. It is 1/30th the size of the initial requirement estimated in the design process. Our thermal infrared camera developed in a short time with low cost has attained enough ability to discover small wildfire which is suppressive at initial attack.

Characterization of a low-cost, commercially available, vanadium oxide microbolometer array for spectroscopic imaging

Many long-wave infrared spectroscopic imaging applications are limited by the portability and cost of detector arrays. We present a characterization of a newly available, low-cost, uncooled vanadium oxide microbolometer array, the Seek Compact, in accordance with common infrared detector specifications: noise-equivalent differential temperature (NEDT), optical responsivity spectra, and Allan variance. The Compact’s imaging array consists of 156×206 pixels with a 12-μm pixel pitch, 93% of the pixels yield useful temperature readings. Characterization results show optical response between λ=7.4 and 12 μm with an NEDT of 148 mK (at ≈7 fps). Comparing these results to a research-grade camera, the Seek Compact exhibits a 4× and 48× reduction in weight (2.0/0.5 lbs) and cost ($12,000/$250) but takes 93× longer to achieve the same NEDT (1.55 s/16.6 ms for 45 mK). Additionally, a proof-of-concept spectral imaging experiment of SiN thin films is conducted. Leveraging this price reduction and spectroscopic imaging capability, the Seek Compact has potential in enabling field-deployable and distributed active midinfrared spectroscopic imaging, where cost and portability are the dominate inhibitors and high frame rates are not required.

High-Sensitivity and Broadband, Real-Time Terahertz Camera Incorporating a Micro-Bolometer ArrayWith Resonant Cavity Structure

Terahertz (THz) cameras comprising an uncooled micro-bolometer array have been developed for simple THz imaging, and the improvement of their sensitivity is one of the important issues. We fabricated a new micro-bolometer array with a resonant cavity structure for a real-time THz camera, alongside a new method for evaluating the sensitivity across a wide range of the THz frequency region. The frequency dependence of the sensitivity of the THz camera is measured in the 0.5–2.0-THz frequency range taking the polarization dependence into account. It was found that the resonant cavity structure effectively increased the sensitivity of the THz camera, and, actually, the improvement by one order of magnitude was achieved in the frequency range below 1 THz. The THz camera with much enhanced sensitivity will expand the frontiers of real-time THz imaging such as molecular imaging and nondestructive inspection.

Pair-Wise Serial ROIC for Uncooled Microbolometer Array

This work presents modelling and simulation of a readout integrated circuit (ROIC) design considering pair-wise serial configuration along with thermal modeling of an uncooled microbolometer array. A fully differential approach is used at the input stage in order to reduce fixed pattern noise due to the process variation and self-heating?related issues. Each pair of microbolometers is pulse-biased such that they both fall under the same self-heating point along the self-heating trend line. A ±10% process variation is considered. The proposed design is simulated with a reference input image consisting of an array of 127x92 pixels. This configuration uses only one unity gain differential amplifier along with a single 14-bit analog-to-digital converter in order to minimize the dynamic range requirement of the ROIC

Experimental study of an uncooled microbolometer array for thermal mapping and spectroscopy of asteroids

We report on the experimental study of the imaging and spectroscopic capabilities of an uncooled microbolometer array for space missions to small bodies in the inner solar system. The selected Nano640E T M device manufactured by the ULIS company (Grenoble, France) has a format of 640x480 pixels and can measure temperatures down to at least 255 K, the lower limit reached in our tests. It has a Noise Equivalent Temperature Difference (NETD) of 40.9 ±4.5 mK (300 K, F/0.86) and the capability to produce excellent, radiometrically calibrated images with an error of the order of 1 to 5 K depending upon the number of calibration sources. Using a set of neutral density filters, we determined the signal-to-noise ratio (SNR) of a spectrum acquired by the detector, as a function of the scene temperature, wavelength and spectral resolution. Considering an asteroid at 1 AU from the Sun, an optical system at F/0.86, a spectral resolution of 0.3 μm and a scene temperature of >350 K, the resulting spectrum has sufficient SNR to properly identify the main mineralogical emission features. Our results show that uncooled microbolometer arrays are very promising to acquire calibrated thermal images and mid-infrared (8–14 μm) spectra of the surface of small bodies in the inner solar system.

Terahertz holography for imaging amplitude and phase objects

A non-monochromatic THz Quantum Cascade Laser and an uncooled micro-bolometer array detector with VGA resolution are used in a beam-splitter free holographic set-up to measure amplitude and phase objects in transmission. Phase maps of the diffraction pattern are retrieved using the Fourier transform carrier fringe method; while a Fresnel-Kirchhoff back propagation algorithm is used to reconstruct the complex object image. A lateral resolution of 280 µm and a relative phase sensitivity of about 0.5 rad are estimated from reconstructed images of a metallic Siemens star and a polypropylene test structure, respectively. Simulations corroborate the experimental results.

Uncooled Microbolometer Arrays With High Responsivity Using Meshed Leg Structure

In this letter, a meshed leg structure is proposed for the first time to control the thermal conductivity in the uncooled microbolometer arrays without changing the fill factor. An amorphous silicon-based microbolometer was fabricated with 64 × 64 arrays with a 35 μm pixel pitch to verify the proposed design. The hole in the meshed leg was 0.7 × 0.7 μm2. The uniformity of the pixel resistance within the 64 × 64 arrays was below 2%. Self-heating and responsivity under infrared (IR) irradiation were investigated in three leg types: 1) type 1-normal leg structure; 2) type 2-meshed leg structure; and 3) type 3-metal extended leg structure. Comparison of the IR irradiation current showed the responsivity of the proposed structure (type 2) that was improved by four times over type 3. For the thermal noise equivalent temperature difference value, type 2 is 194 mK, which is much better than 384 mK of type 3.

Mobile speckle interferometer in the long-wave infrared for aeronautical nondestructive testing in field conditions

We present the development of a speckle interferometer based on a CO 2 laser and using a thermal infrared camera based on an uncooled microbolometer array. It is intended to be used for monitoring deformations as well as detecting flaws in aeronautical composites, with a smaller sensitivity to displacement compared to an equivalent system using visible (VIS) lasers. Moreover the long wavelength allows working with such interferometers outside the laboratory. A mobile system has been developed on the basis of previous laboratory developments. Then it is validated in a variety of industrial nondestructive testing applications in field working conditions.

Heterogeneous 3D integration of 17 μm pitch Si/SiGe quantum well bolometer arrays for infrared imaging systems

This paper reports on the realization of 17 μm × 17 μm pitch bolometer arrays for uncooled infrared imagers. Microbolometer arrays have been available in primarily defense applications since the mid-1980s and are typically based on deposited thin films on top of CMOS wafers that are surface-machined into sensor pixels. This paper instead focuses on the heterogeneous integration of monocrystalline Si/SiGe quantum-well-based thermistor material in a CMOS-compliant process using adhesive wafer bonding. The high-quality monocrystalline thermistor material opens up for potentially lower noise compared to commercially available uncooled microbolometer arrays together with a competitive temperature coefficient of resistance (TCR). Characterized bolometers had a TCR of −2.9% K−1 in vacuum, measured thermal conductances around 5 × 10−8 W K−1 and thermal time constants between 4.9 and 8.5 ms, depending on the design. Complications in the fabrication of stress-free bolometer legs and low-noise contacts are discussed and analyzed.