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We report a novel design for bolometric infrared detector operating at the long-wave infrared (LWIR) range for high-resolution human body temperature sensing and monitoring. We propose to incorporate efficient plasmonic absorber and high-responsivity VO2 nanobeam biased at transition temperature in our design to facilitate improvement in both aspects – thermal resolution and spatial resolution. The integration of plasmonic absorber allows efficient and selective radiation absorption. The use of a transducing nanobeam placed in close proximity to the plasmonic local heaters allows the radiation energy to be electronically readable. The use of nanobeam instead of a film in the detector allows over two-orders of magnitude improvement in responsivity owing to the large length to cross-sectional area ratio. Additionally, the use of nanobeam reduces the thermal mass and improves the bandwidth. Our calculation suggests a responsivity of as high as 700 kV/W at 100 Hz for a detector of only $12\,\,\mu \text{m}\,\,\times 12\,\,\mu \text{m}$ pixel size. Also, the theoretical noise equivalent temperature difference is calculated to be as low as 3.67 mK which is almost an order of improvement than the state-of-the-art bolometric LWIR detectors with larger pixel dimensions.

High operating temperature(HOT) is the key for low size, weight and power(SWaP) detector development and SWaP detector is the key for modern weapon system such as unmanned aerial vehicle(UAV) and man portable system. The low dark current that determines the operating temperature can be achieved by adopting InAs/InAsSb type-II superlattice(T2SL) absorber and nBn structure. In this work, HOT mid-wavelength infrared(MWIR) detector with InAs/InAsSb T2SL absorber and AlAsSb barrier was developed. The AlAsSb barrier shows excellent lattice match with GaSb substrate. Only the dry etch for pixel reticulation was applied to fabricate the device. At 80 K, dark current density is 2e-9 A/cm2 at the bias -0.2 V and, at 130 K, 2e-7 A/cm2 at the bias -0.1 V. The quantum efficiency was measured for both front side illumination and back side illumination. The back side illumination offers higher quantum efficiency than the front side illumination. The average quantum efficiency is about 50 % for front side illumination with 3 μm absorber. The 640 x 512 VGA format focal plane array(FPA) with 15 μm pitch was fabricated to study the temperature dependency of electro-optical characteristics. It was found that mean noise equivalent temperature difference(NETD) below 150 K is 15 mK, which is limited by the well capacitance. As the temperature increases NETD increases proportional to the dark current.

The III-V material system has proven to be a solid base for building infrared detector focal plane arrays (FPAs), enabling well-established designs such as bulk InSb-photodiodes, GaAs-based quantum well infrared photodetectors (QWIP) and GaSb-based type-II superlattices (T2SL). The remarkable advancement in the sensitivity and stability of such FPAs seen in the past decades calls for revision of the merits and the acceptance criteria used for the performance evaluation of infrared imaging arrays. Specifically, the early skepticism toward QWIP has largely been focused on their low quantum efficiency, and consequently low specific detectivity of the FPA pixels, as compared to the counterparts with bulk design. It was later demonstrated that unrivalled spatial uniformity of QWIP arrays (typically with a residual non-uniformity

Joining their technological skills and strengths, SOFRADIR and ULIS merged in a new High Tech Company named LYNRED. This new company will be oriented towards excellence in II-VI, III-V and bolometers technologies, covering all Society’s needs in term of infrared detection. Nowadays one noticeable trend in infrared market sensors is the optimization of two key metrics: sensor range and image quality. These metrics depend mostly on three criteria: modulation transfer function (MTF), Noise Equivalent Temperature Difference (NETD) and Residual Fixed Pattern Noise (RFPN). MTF improvement was previously achieved by reducing pixel pitch to 30μm [1] to 10μm [2]. NETD and RFPN were improving thanks to a better material quality. The improvement of NETD and RFPN can also be used to increase the operating temperature. The Modulation Transfer Function performance is directly linked to the ability to distinguish objects details and sharpness of the imaging system. MTF value determines, with NETD and RFPN, the system range via the so -called Minimum Resolvable Temperature Range (MRTD). We need to keep in mind that not only MTF has to be optimized but also MRTD, which is very challenging in the context of High Operating Temperature (HOT) and pixel pitch reduction. There are many challenges to be addressed for future small pitch, large format and HOT+ (> 160K) detectors. Electrical and optical crosstalks are one of the prime concerns for detectors with sub-10μm pixel pitch. We will compare several existing materials and their optical and electronic transport properties, elementary sensors designs, such as III-V superlattice, II-VI materials, MESA, loophole, planar and depleted photodiodes. This discussion will be based on measurements on improved HgCdTe 10μm and 7.5μm pitch technology completed by simulation using Finite Element Modelization (FEM) coupled with Finite Difference Time Domain (FDTD).

Thermal imaging technology is widely used in various fields, such as security, defense, medicine and spaceborne applications in the Geo-synchronous Earth Orbit. Most thermal imaging systems operate in the long-wave infrared (LWIR) range or the medium-wave infrared (MWIR) range. However, the longer the wavelength is, the more difficult the imaging system is to provide high resolution due to diffraction limit. Compared to MWIR and LWIR imagers, a short-wave infrared (SWIR) imager achieves higher resolution owing to its higher diffraction limit. However, radiation from an object at 300 k in the SWIR band is weaker than that in the MWIR and LWIR bands. Therefore, the sensitivity is low. With the rapid development of detector technology, the sensitivity of SWIR detector is improved by low dark current and noise. It exhibits good performance in thermal imaging applications. In order to validate SWIR thermal imaging key performance, this study analyzes the thermal imaging capability of an SWIR imager compared to MWIR and LWIR. The noise equivalent temperature differences (NETDs) of SWIR, MWIR, and LWIR imagers for thermal imaging applications are calculated. A compact SWIR imager prototype covering a spectral range of 2.0–2.7 μm is designed and implemented. The facial thermal imaging experiment proves that the high-sensitivity SWIR imager can obtain high-quality thermal images with an NETD of 24 mK at a temperature of 310 K. In addition, in the continuous integration and multiple read-out (IMRO) imaging mode, the dynamic range of the system is extended by 20 dB. The theoretical analysis and experiment show that the SWIR imager can provide high sensitivity with long integration time. In addition, SWIR thermal imaging can provide higher resolution than MWIR and LWIR imagers. Therefore, SWIR imager has considerable potential for high-sensitivity thermal imaging applications in Geo-synchronous Earth Orbit.

Semi-Conductor Devices’ long-wave infrared 640 × 512/15-μm pitch type II superlattice detector is based on an XBp design with an InAs/GaSb absorbing layer and an InAs/AlSb barrier layer. The barrier architecture ensures a low, diffusion-limited, dark current and allows stable passivation to all fabrication steps. It is shown that the dark current is about 10 times the Rule 07 value and corresponds to a minority carrier lifetime of about 10 ns, while the quantum efficiency can approach within 10% of the HgCdTe value for realistic detector parameters. Detectors are now being manufactured with a reasonable yield for an operability above 99.5%, and a stable and reproducible noise equivalent temperature difference of

This work presents the simulation results and design rules of a new sensor for IR-detection using the thermoelectric effect. Within the Seebeck-effect, thermopiles generate a voltage based on a temperature gradient inside the structure. State of the art thermopiles are manufactured as two-dimensional structures directly on a substrate. Here, a possible method of 3D integration is shown, where the thermoelectric materials are fabricated as thin tubes using an atomic layer deposition (ALD) process. These tubes are connected to an IR-absorber on top, where the IR-radiation causes a temperature gradient relative to the substrate. This has the advantages to achieve a fill factor of nearly 100%. In comparison to microbolometers, the 3D thermopile is a passive structure, which does not need complex readout and supply circuits. Furthermore, the usage of energy harvesting is possible. Additionally, new array circuitry options are discussed to achieve a better signal-to-noise ratio. An electrical series connection of multiple sensors effects a rising specific detectivity and the noise equivalent temperature difference (NETD) decreases analogously. With this technique, groups of pixels of the detector can be merged to one "super-pixel" for detecting even marginal temperature changes of an object.

XBn or XBp barrier detectors exhibit diffusion-limited dark currents comparable with mercury cadmium telluride Rule-07 and high quantum efficiencies. In 2011, SemiConductor Devices (SCD) introduced “HOT Pelican D”, a 640 × 512/15-μm pitch InAsSb/AlSbAs XBn mid-wave infrared (MWIR) detector with a 4.2-μm cut-off and an operating temperature of ∼150 K. Its low power (∼3 W), high pixel operability (>99.5%) and long mean time to failure make HOT Pelican D a highly reliable integrated detector-cooler product with a low size, weight and power. More recently, “HOT Hercules” was launched with a 1280 × 1024/15-μm format and similar advantages. A 3-megapixel, 10-μm pitch version (“HOT Blackbird”) is currently completing development. For long-wave infrared applications, SCD’s 640 × 512/15-μm pitch “Pelican-D LW” XBp type II superlattice (T2SL) detector has a ∼9.3-μm cut-off wavelength. The detector contains InAs/GaSb and InAs/AlSb T2SLs, and is fabricated into focal plane array (FPA) detectors using standard production processes including hybridization to a digital silicon read-out integrated circuit (ROIC), glue underfill and substrate thinning. The ROIC has been designed so that the complete detector closely follows the interfaces of SCD’s MWIR Pelican-D detector family. The Pelican-D LW FPA has a quantum efficiency of ∼50%, and operates at 77 K with a pixel operability of >99% and noise equivalent temperature difference of 13 mK at 30 Hz and F/2.7.

In order to suppress the noise of thermal infrared imaging spectrometer and improve its detection sensitivity, relationship between noise equivalent temperature difference (NETD) and various noise factors was analyzed. Noise of the thermal infrared imaging spectrometer mainly includes the stray light noise defined as nonimaging light scattered by opto-mechanical components’ surfaces and generated by nonworking orders of the grating, the background radiation noise from the opto-mechanical components, and the detector noise. According to the physical mechanism of NETD, the expression containing noise factors of NETD was deduced, and the noise analysis model of the thermal infrared imaging spectrometer was established. An Offner-type imaging spectrometer was taken as an example, whose spectral range is from 8 to 12.5 μm, F number is 2.7, number or spatial channels is 1024, number of spectral channels is 45. And a HgCdTe detector with a D∗ of 4 × 1010 cm Hz1/2 W−1 is used. Relationship between the NETD of this Offner-type spectrometer and its main influencing factors, including cryogenic temperature and optical properties of inwall surfaces of the spectrometer’s mechanical elements, was analyzed. When these parameters are in different value, the proportion of each noise and the main factor affecting NETD are different. Targeted noise suppression methods were proposed for different noise. Usually, background radiation noise is suppressed by cooling the opto-mechanical components and brighten the inwall surfaces. But stray light noise would increase when the inwall surfaces is brightened. Change of NETD with the cryogenic temperature was compared between the inwall surfaces blackened or brightened. When the cryogenic temperature was 90 K, NETD was 0.88 K in both blackened and brightened inwall surfaces case. When the cryogenic temperature was 70 K, NETD was 0.1 K in blackened inwall surfaces case, and 0.52 K in brightened inwall surfaces case. The conclusions have guiding significance for the determination of cryogenic temperature and the inwall surfaces’ optical properties of thermal infrared imaging spectrometer.

When a space infrared camera has a higher temperature sensitivity , the more tiny temperature information it can record in the imaging data. High sensitive infrared camera takes an important role in observation of urban and sea targets and so on. A new space infrared camera system is designed based on pixel-level digital accumulation technology. The new infrared camera based on this technology realize the analog-to-digital convert of detecting signals into single detector pixel, which can reduce the noise caused by readout of analog signal markedly. This infrared system processes input signal by little capacitor packet digital-counting method，the integral capacitor plays the part of “voltage-to-frequency conversion”, which vary far from the traditional detector. The signal quantization process realized by the capacitor packet digitalcounting, every single charge packet is small, a capacitor of several fF in new system has the equal effect of a capacitor of thousands pF in traditional system, that makes the new infrared system can break the limit of integral capacitor’s physical restriction. So the new camera has the ability of achieving 1mK(0.001K) temperature sensitivity by theory without saturation electrons restriction. This ultra-high temperature sensitivity infrared camera system will break the temperature sensitivity limits of all infrared cameras on hand, and improve infrared system’s ability of distinguishing the tiny temperature a lot. The prototype camera has been manufactured and it has a 5mK NETD (Noise Equivalent Temperature Difference), the engineering feasibility of this camera system is valid. The pixel-level digital accumulation infrared camera will be an important development direction of future high-sensitivity space infrared camera technique.

This paper reports an InAs/InAsSb strained-layer superlattice (SLS) mid-wavelength infrared detector and a focal plane array particularly suited for high-temperature operation. Utilizing the nBn architecture, the detector structure was grown by molecular beam epitaxy and consists of a 5.5 &micro, m thick n-type SLS as the infrared-absorbing element. Through detailed characterization, it was found that the detector exhibits a cut-off wavelength of 5.5 um, a peak external quantum efficiency (without anti-reflection coating) of 56%, and a dark current of 3.4 &times, 10-4 A/cm2, which is a factor of 9 times Rule 07, at 160 K temperature. It was also found that the quantum efficiency increases with temperature and reaches ~56% at 140 K, which is probably due to the diffusion length being shorter than the absorber thickness at temperatures below 140 K. A 320 &times, 256 focal plane array was also fabricated and tested, revealing noise equivalent temperature difference of ~10 mK at 80 K with f/2.3 optics and 3 ms integration time. The overall performance indicates that these SLS detectors have the potential to reach the performance comparable to InSb detectors at temperatures higher than 80 K, enabling high-temperature operation.

Utilizing a thermomechanical transduction scheme, we have developed an uncooled, sensitive, and fast THz bolometer by using a doubly clamped GaAs MEMS beam resonator as a sensitive thermistor. Owing to its ultra-high temperature sensitivity (the noise equivalent temperature difference of ~1 µK/ ✓ Hz), the present bolometer achieves not only a high sensitivity but also an operation bandwidth of several kHz, which is ~100 times faster than other uncooled THz thermal sensors. The MEMS bolometers are fabricated by the standard semiconductor fabrication processes and are well suited for making detector arrays for realizing THz cameras.

This paper discusses the improved capabilities developed for and results from a new generation of infrared blackbody sources. Over time infrared sensors have evolved from detectors to imagers and recently IR imagers have branched into low cost uncooled sensors and high resolution, high performing arrays. As the IR cameras get better, the performance of the test equipment needs to improve to maintain a 10:1 (goal), 4:1 (minimum) performance advantage. Two tests that rely on the stability of the extended area blackbody source are Noise Equivalent Temperature Difference (NETD) and Minimum Resolvable Temperature Difference (MRTD). The current state of the art for NETD for a cooled camera is

Large format high resolution FPAs are the key elements for medium to high performance applications including enhanced vision, thermal sights, and industrial applications. In this work, the characteristics of recently developed 10 μm pitch SXGA InSb detector are presented. To develop the 10 μm pitch SXGA InSb detector, three important technical issues were resolved. At first, physically isolating pixels to reduce the crosstalk was adopted to enhance the Modulation Transfer Function (MTF). It was found that the MTF of fabricated detector tested with slanted edge method was improved largely. The MTF of 10 μm pitch FPAs at the Nyquist frequency showed the same MTF of 15 μm pitch device at the Nyquist frequency. Therefore the zoomed image of 10 μm pitch device will have the same image quality as the 15 μm device. Another important issue is the indium bump fabrication process. To fabricate fine bump with uniform height, electrodeposition technology was developed. With this method, uniform indium bump over the 8' ROIC could be achieved. Finally, to achieve large capacitance, 0.18 μm CMOS technology was adopted. To use 0.18 μm CMOS technology, the ROIC should have to be designed all again. The designed and fabricated ROIC has 2.4 Me- with 3.3 V bias voltage and has 8 output channels with 20 MHz output rate. The developed 10 μm pitch InSb SXGA detector showed median NETD (Noise Equivalent Temperature Difference) of 22.6 mK. To measure the stability of developed 10 _m pitch InSb SXGA detector, system NETD(SNETD) was measured after thermal cycling. The SNETD of 30 mK was measured for more than 200 thermal cycling, which shows that the output of developed FPA is very stable.

According to the requirement of high-definition surveillance of the status of space targets in low illuminance, a high SNR (Signal to Noise Ratio) uncooled long-wave infrared system is designed. Based on the detector of UL04371 with 640 × 480 array, the system scheme, acquisition system and real-time image processing algorithms are realized. On the basis of system implementation, the paper mainly focuses on how to reduce the noises from the aspect of hardware circuits and how to realize the real-time processing in the way of specified infrared image algorithms. Finally, the paper gives the test result which shows that the system has achieved a relatively good SNR characteristic with the average NETD (Noise Equivalent Temperature Difference) value of 220mK under the condition of the integration time of 64us and the radiation of 300K black body.

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., Though resonant infrared (IR) detectors are an attractive thermal imaging technology owing to its high performance potential, realizing devices with high sensitivity remains a challenge. Here, the authors report high-sensitivity resonant IR sensors based on thermo-responsive shape memory polymers.

It is well known that every detector in a Focal Plane Array (FPA) has a different responsivity and offset. These variations result in a specific kind of noise, the Fixed Pattern Noise (FPN) or spatial noise. During the image processing, those pixels who has a large deviation in responsivity are considered a bad pixel, and has its value removed of FPA. Knowing the answer of all those pixels are the first test procedure in a FPA characterization. However, during the bad pixels analysis 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 influence of higher calibration temperature on the NonUniformity Correction (NUC) quality.

Recent advances over the last several years in III-V strained-layer superlattice-based infrared detectors have lead this material system to emerge as a solid alternative to HgCdTe for dual-band focal plane arrays (FPAs). Rapid development of superlattice-based detectors has been realized by capitalizing on mature, III-V foundry-compatible processing. Furthermore, superlattice-based epitaxial wafers exhibit a high degree of lateral uniformity with low macroscopic defect densities (< 50 cm-2) and can achieve dark current levels comparable to HgCdTe detectors. In this paper, we review our recent efforts towards producing HD-format (1280x720, 12 μm pitch) superlattice-based, dual-band MWIR/LWIR FPAs. For a representative FPA, characterization was conducted in a pour-fill dewar at 80K, f/3 and using a blackbody range of 22°C to 32°C. For the MWIR band, the noise equivalent temperature difference (NETD) was 14.9 mK with a 3x median NETD operability of 99.91%. For the LWIR band, the median NETD was 28.1 mK with a 3x median NETD operability of 99.66%. To illustrate the manufacturability of superlattice technology, we will present results on 1280x720, 12 μm pitch MWIR/LWIR FPAs built over the last year at HRL through multiple fabrication lots utilizing 4" epiwafers.

Pixel size reduction in an uncooled infrared detector plays a crucial role in determining significant attributes such as size, weight, and cost. Without a loss in sensitivity, however, it is challenging to develop an uncooled infrared detector that has the pixel pitch of 12 μm and below. Especially, there has been a limitation of an uncooled focal plane array (FPA) with a single-level design, which has to accomplish both functions of absorption and heat conduction in a single layer and thus compromise the sensitivity of FPA. A selective etching process of a resistive material, titanium oxide, on the connecting legs in the microbolometer FPA has been developed to overcome the limitation and increase the sensitivity of the single-level design FPA. Furthermore, structural stress modulation has been applied to ensure the mechanical robustness of the developed FPA. Here, we present a 12 μm single-level design FPA using a titanium oxide as a resistive material of microbolometer FPA. High-resolution detectors with an array size of 640 x 480 pixels (VGA format) and 1024 x 768 pixels (XGA format) have been developed, and the noise equivalent temperature difference (NETD) and time constant for the VGA detector are 40.5 mK and 8.3 msec, respectively. Thermal image obtained by the 12 μm XGA detector shows excellent image quality and fine resolution.

ASELSAN A.S., the largest defense company in Turkey, initiated research activities on developing Mercury Cadmium Telluride (MCT) detectors in 2014. These research activities include bulk crystal growth and surface preparation of Cadmium Zinc Telluride (CZT) substrates, Molecular Beam Epitaxial (MBE) growth of MCT layers, MCT detector fabrication, Read-Out-Integrated-Circuit (ROIC) design and detector-dewar-cooler (DDCA) assembly development. Focal plane arrays with resolutions/pixel pitches of 320x256/30 μm and 640x512/15 μm are fabricated. Noise Equivalent Temperature Difference (NETD) of 320x256 FPA is 11 mK (f#/1.5, 77K) while the operability is 98.2%. 640x512 FPA provides NETD of 32 mK (f#/1.5, 77K) and the operability is 93.2%.

A low-power total power radiometer for passive imaging applications is presented. The radiometer is manufactured in a 130 nm SiGe technology with an ft/fmax of 250/370 GHz. The radiometer achieves a minimum noise equivalent temperature difference (NETD) of 0.21 K at 155 GHz. By optimization of the building blocks and biasing stages, a low-power system with a total power consumption of 64 mW is achieved. Due to its low NEP and low-power consumption, the system enables further integration into high-density sensor arrays for passive radiometry in the D-Band.

Noise equivalent temperature difference (NETD) is the critical parameter for passive imaging detection. A modelling of the sensitivity performance including the f-1-type low flicker noise (1/f-noise) influence is presented, specifically investigated on the 1/f-noise to the sensitivity performance and the trade-offs between the low-noise amplifier (LNA)’s gain and the video frequency bandwidth. Measurement bench is set up, and results confirm that low-frequency modulation to the signal helps in improving the sensitivity performance. Based on the measurement results, it is concluded that signal power influences the 1/f-noise properties in detection diode. The amplifier’s output power is suggested to be lower than −30 dBm at least. This level is much lower than the point of P1dB (1 dB compressed point of the LNA).

A thermo-mechanical MEMS detector with 35-μm pixel pitch is designed, fabricated, and characterized. This fabricated design has one of the smallest pixel sizes among the IR thermo-mechanical MEMS sensors in the literature. The working principle of the MEMS detector is based on the bimaterial effect that creates a deflection when exposed to IR radiation in the 8–12-μm waveband. The nanometer level out of plane mechanical motion is observed in response to IR heating of the pixel, which is detected by a diffraction grating-based optical readout. Performance of MEMS sensor arrays with optical readout have been limited by a large DC bias that accompanies a small AC signal. We developed a novel optical setup to reduce the DC term and the related noise using an AC-coupled detection scheme. Detailed noise characterization of the pixel and the readout system is reported in this paper. The noise equivalent temperature difference of our detector is measured as 216 mK using f /0.86 lens with the AC-coupled optical readout. Finally, we obtained a thermal image using a single MEMS pixel combined with a scanning configuration. Despite the reduced pixel size, the measured noise levels are comparable to the state-of-the-art thermo-mechanical IR sensors.

For reasons associated with size, weight, power consumption, and cost, the future of infrared systems for all spectral bands is being driven towards megapixel formats operating under diffraction- and background-limited conditions with ever-smaller pixel pitches and ever-higher operating temperatures. The performance requirements of such systems with regard to both optical and detector limitations are examined for the materials technologies and device architectures that are in vogue today. At elevated operating temperatures, available noise equivalent temperature difference values for diffraction-limited operation are found to be strongly dependent on the available pixel pitch, optimizing at values ∼λ/4, where λ is the operating wavelength. The possibility for extending the operation of mid- and long-wavelength focal plane arrays to room temperature with diffraction- and background-limited performance is discussed, together with the potential issues that must be addressed in order to achieve this ultimate goal.

A MEMS based novel THz detector structure is designed and realized by micro fabrication. The detector is then characterized to extract its mechanical performance. Operating in 1-5 THz band, the detector has a pixel size of 200μm × 200μm. Bimaterial suspension legs consist of Parylene-C and titanium, the pair of which provides a high mismatch in coefficients of thermal expansion. The pixel is a suspended Parylene-C structure having a 200 nm-thick titanium metallization. Operation principle relies on conversion of absorbed THz radiation into heat energy on the pixel. This increases the temperature of the free-standing microstructure that is thermally isolated from the substrate. The increase in temperature induces mechanical deflection due to bimaterial springs. The detector is designed to deliver a noise equivalent temperature difference (NETD) less than 500 mK and a refresh rate of 30Hz.

This paper introduces an 80x80 microbolometer array with a 35 μm pixel pitch operating in the 8-12 μm wavelength range, where the detector is fabricated with the LWIR-band CMOS infrared technology, shortly named as CIR, which is a novel microbolometer implementation technique developed to reduce the detector cost in order to enable the use of microbolometer type sensors in high volume markets, such as the consumer market and IoT. Unlike the widely used conventional surface micromachined microbolometer approaches, MikroSens’ CIR detector technology does not require the use of special high TCR materials like VOx or a-Si, instead, it allows to implement microbolometers with standard CMOS layers, where the suspended bulk micromachined structure is obtained by only few consecutive selective MEMS etching steps while protecting the wirebond pads with a simple lithograpy step. This approach not only reduces the fabrication cost but also increases the production yield. In addition, needing simple subtractive post-CMOS fabrication steps allows the CIR technology to be carried out in any CMOS and MEMS foundry in a truly fabless fashion, where industrially mature and Au-free wafer level vacuum packaging technologies can also be carried out, leading to cost advantage, simplicity, scalability, and flexibility. The CIR approach is used to implement an 80x80 FPA with 35 μm pixel pitch, namely MS0835A, using a 0.18 μm CMOS process. The fabricated sensor is measured to provide NETD (Noise Equivalent Temperature Difference) value of 163 mK at 17 fps (frames per second) and 71 mK at 4 fps with F/1.0 optics in a dewar environment. The measurement results of the wafer level vacuum packaged sensors with one side AR coating shows an NETD values of 112 mK at 4 fps with F/1.1 optics, i.e., demonstrates a good performance for high volume low-cost applications like advanced presence detection and human counting applications. The CIR approach of MikroSens is scalable and can be used to reduce the pixel pitch even further while increasing the array size if necessary for various other low-cost, high volume applications.

Recent advances in superlattice-based infrared detectors have rendered this material system a solid alternative to HgCdTe for dual-band sensing applications. In particular, superlattices are attractive from a manufacturing perspective as the epitaxial wafers can be grown with a high degree of lateral uniformity, low macroscopic defect densities (< 50 cm-2) and achieve dark current levels comparable to HgCdTe detectors. In this paper, we will describe our recent effort on the VISTA program towards producing HD-format (1280x720, 12 μm pitch) superlattice based, dual-band MWIR/LWIR FPAs. We will report results from several multi-wafer fabrication lots of 1280x720, 12 μm pitch FPAs processed over the last two years. To assess the FPA performance, noise equivalent temperature difference (NETD) measurements were conducted at 80K, f/4.21 and using a blackbody range of 22°C to 32°C. For the MWIR band, the NETD was 27.44 mK with a 3x median NETD operability of 99.40%. For the LWIR band, the median NETD was 27.62 mK with a 3x median operability of 99.09%. Over the course of the VISTA program, HRL fabricated over 30 FPAs with similar NETDs and operabilities in excess of 99% for both bands, demonstrating the manufacturability and high uniformity of III-V superlattices. We will also present additional characterization results including blinkers, spatial stability, modulation transfer function and thermal cycles reliability.

Noise equivalent temperature difference (NETD) is an important figure of merit for infrared detectors. Lower NETD means that the detector can realize smaller temperature resolution and longer range recognition. In this work, we investigate the device performance, especially the NETD characteristics of a long-wavelength infrared (LWIR) photodetector based on InAs/GaSb type-II superlattice (T2SL). To achieve mK-level temperature-sensitivity, the effect of detector's intrinsic and extrinsic factors on NETD performance has been discussed. Through a series of efforts, a NETD value of 7 mK was realized for a T2SL detector with a 100% cutoff wavelength of 11.4 μm at 77 K.

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.

This study compares the stress-measurement sensitivity of several commercially available vanadium-oxide microbolometers to a scientific grade cooled indium antimonide imager. The devices were tested under similar conditions on the same mechanically-loaded subjects; one a uniaxially loaded plate containing a circular hole and the other a representative aircraft wing-skin coupon. The microbolometers are shown to consistently outperform the cooled imager for scan durations of 1500 load cycles or more despite having noise equivalent temperature detectivities (NETD) that were inferior by factors of between approximately 2 and 6. This finding is significant in two respects: it suggests that an NETD specification has only limited value as a sensitivity metric for thermoelastic stress analysis and secondly it confirms that microbolometers are able to furnish high-fidelity stress measurements of a type traditionally associated with cooled infrared imagers which are generally more costly to acquire and more cumbers...

We analyze the performance limit of uncooled thermo-mechanical infra-red imagers with optical readout. We have shown that for large enough frame format thermal noise of load resistance of output electronic cascade of optical readout system determines mainly the noise equivalent temperature difference, NETD, of such systems. For middle frame format they can successfully compete with micro-bolometer infra-red detectors. Higher power low noise light source for optical readout system and more exquisite phase detection enable them to be competitive in large frame format too.

The Visible Infrared Imaging Radiometer Suite (VIIRS) sensor aboard the Suomi National Polar-orbiting Partnership spacecraft has successfully operated since its launch in October 2011. The VIIRS collects data in 22 spectral bands that are calibrated by a set of onboard calibrators (OBC). In addition, lunar observations are made to independently track VIIRS long-term calibration stability for the reflective solar bands (RSB). This paper provides an overview of VIIRS OBC functions as well as its on-orbit operation and calibration activities. It also describes sensor calibration methodologies and demonstrates VIIRS on-orbit performance from launch to present. Results reported in this paper include on-orbit changes in sensor spectral band responses, detector noise characterization, and key calibration parameters. Issues identified and their potential impacts on sensor calibration are also discussed. Since launch, the VIIRS instrument nominal operation temperature has been stable to within ±1.0 K. The cold focal plane temperatures have been well controlled, with variations of less than 20 mK over a period of 1.5 years. In general, changes in thermal emissive bands (TEB) detector responses have been less than 0.5%. Despite large response degradation in several near-infrared and short-wave infrared bands and large SD degradation at short visible wavelengths, the VIIRS sensor and OBC overall performance has been excellent postlaunch. The degradation caused by the telescope mirror coating contamination has been modeled and its impact addressed through the use of modulated relative spectral response in the improved calibration and the current sensor data record data production. Based on current instrument characteristics and performance, it is expected that the VIIRS calibration will continue to meet its design requirements, including RSB detector signal to noise ratio and TEB detector noise equivalent temperature difference, throughout its 7 year design lifetime.

A 2D mechanical scanning setup was constructed, and was used to evaluate the potential of quantum cascade detector (QCD) for IR imaging. The peak responsivity of the studied QCD is 22.3 mA/W at 9.3 μm, and the Noise Equivalent Power (NEP) reaches 6.7 × 10 - 10 W / Hz at temperature of 82 K. The Noise Equivalent Temperature Difference (NETD) for this imaging system is estimated to be 102.6 mK. With this experimental setup, thermal images of an operating electric soldering iron and a projection lamp at about 310 K are obtained. The image of the projection lamp demonstrates the feasibility of human body imaging with this QCD. Our research provides a proof-of-concept demonstration of thermal imaging with QCDs and displays that QCDs are potentially useful for thermal imaging applications.

Terahertz (THz) electromagnetic spectrum draws wide attention for nondestructive and/or biocompatible sensing. In order to be widely applicable to the THz sensing, it is of prime importance to develop THz sensors that can be operated at room temperature and have high sensitivity and fast operation speed. However, conventional room-temperature THz thermal sensors fall short of expectations in these characteristics required in various applications of THz sensing, including THz cameras. Utilizing a thermomechanical transduction scheme, we have developed an uncooled, sensitive, and fast THz bolometer by using a doubly clamped GaAs microelectromechanical system (MEMS) beam resonator as a sensitive thermistor. Owing to its ultrahigh temperature sensitivity (the noise equivalent temperature difference of ∼1 μK/√Hz), the present bolometer achieves not only high sensitivity but also an operation bandwidth of several kHz, which is more than 100 times faster than other uncooled THz thermal sensors. The obtained electrical noise equivalent power is as low as ∼90 pW/√Hz, which is close to the limit set by the thermal fluctuation noise. The MEMS bolometers are fabricated by the standard semiconductor fabrication processes and are well suited for making detector arrays for realizing THz cameras.

Due to continuous improvement of traditional liquid-phase epitaxy n-on-p technology, excellent mid-wavelength infrared HgCdTe (MCT) detectors with 1280 × 1024 pixels and 15 μm pitch size have been produced at AIM. At an operating temperature (TOP) of 80 K, a noise equivalent temperature difference (NETD) of 17.8 mK and an operability of 99.96% have been obtained. At TOP = 130 K, the operability remains high at 99.58%. On the basis of these results, the sensitivity of this detector design has been extended into the long-wavelength infrared (LWIR) region, obtaining a detector with an NETD of 30.4 mK and an operability of 99.81% at TOP = 80 K. In parallel, the growing maturity of molecular-beam epitaxy (MBE) growth of MCT on GaAs substrates has led to an improvement of the performance of the MWIR 640 × 512, 15-μm-pitch detector from an operability of 99.30% in 2011 to 99.83% recently.

The thermal or cold wake of the underwater vehicles will be formed at the sea surface in different region during sailing, then the underwater vehicles will be detected by airborne or space borne infrared detectors easily, which will imperil their security. A model between the detection probability and the Noise Equivalent Temperature Difference (NETD) of the detectors, and the temperature difference between the wake and the sea surface, etc., was established and the evaluation of detection probability in different discrimination levels and other parameters, such as time, location, atmosphere, sea, detector performance, wake temperature, etc., was realized, and a software named Wake Detection of Underwater Vehicle by Infrared (WDPUV-IR) was developed. The results showed that the detection probability to the wake with high detector performance or large temperature difference or short detection distance or low discrimination level was relatively high, but it was difficult to detect targets with small temperature difference and size when the atmospheric transmittance value was low.

An uncooled thermal imager is being developed based on a liquid crystal (LC) transducer. Without any electrical connections, the LC transducer pixels change the long-wavelength infrared (LWIR) scene directly into a visible image as opposed to an electric signal in microbolometers. The objectives are to develop an imager technology scalable to large formats (tens of megapixels) while maintaining or improving the noise equivalent temperature difference (NETD) compared to microbolometers. The present work is demonstrating that the LCs have the required performance (sensitivity, dynamic range, speed, etc.) to enable a more flexible uncooled imager. Utilizing 200-mm wafers, a process has been developed and arrays have been fabricated using aligned LCs confined in 20×20-μm cavities elevated on thermal legs. Detectors have been successfully fabricated on both silicon and fused silica wafers using less than 10 photolithographic mask steps. A breadboard camera system has been assembled to test the imagers. Various sensor configurations are described along with advantages and disadvantages of component arrangements.

This paper reports on a measurement which shows for the very first time that uncooled non-quasi static detectors with wide bandwidth integrated in a 32 × 32 pixel focal plane array in standard 65 nm bulk CMOS silicon technology are able to detect non-amplified black-body radiation. With its integrated readout electronics, this “THz camera” shows a noise equivalent temperature difference (NETD) of 20.86 K in integration mode.

This paper presents a low-noise SiGe radiometer at 136 GHz developed in an IBM 90 nm SiGe BiCMOS technology. The radiometer chip consumes 45 mW and results in a minimum NEP of 1.4 fW/Hz½ with a peak responsivity of 52 MV/W at 136 GHz and a noise equivalent temperature difference (NETD) of 0.25K (τ = 3.125 mS). To the best of our knowledge, this is the lowest temperature resolution in silicon technologies at D-band.

Thermal conductance of microbolometer has a directly impact on Noise Equivalent Temperature Difference (NETD) and thermal time constant which are the key indicators of uncooled IR detector. It is of great significance to calculate and evaluate thermal conductance. A calculate approach of thermal conductance for uncooled microbolometer detectors is introduced in this paper. Accurate three-dimensional modeling of microbolometer is found by using MEMS analysis software Intellisuite. Dynamic thermal analysis of this model is solved and then thermal time constant can be read from thermal time curve of the analysis mentioned above. Combined with the calculation of thermal capacitance, more precisely thermal conductance value can be reached which is more accurate than theoretical calculations result and meaningful for design and fabrication of the device.

Driven by the need for more efficient and cost-effective production of infrared (IR) detectors as well as the demands for novel (third-generation) device concepts, a large amount of effort has been spent on the development of molecular beam epitaxy (MBE) for fabrication of high-quality HgCdTe (MCT) layers on both CdZnTe and alternative substrates. The bulk of recent publications focuses on Si as an alternative substrate material. The intent of this paper is to highlight the potential benefit of using GaAs as an alternative substrate material by presenting MCT material grown by MBE on GaAs at AIM. Mid-wave IR MCT/GaAs material has been processed by AIM’s standard planar n-on-p technique. Focal-plane arrays with 640 × 512 pixels and a 15 μm pitch design show low and homogeneous noise equivalent temperature difference of 18.3 ± 2.0 mK at 99.31% operability. To analyze the feasibility of MBE growth of long-wave IR MCT on GaAs, a layer with 8.8 μm cutoff at 80 K has been fabricated and processed into 640 × 512 pixels, 15-μm-pitch arrays. Initial current–voltage characterization yields promising results and illustrates the potential of MBE growth for LWIR MCT detector production.

In this paper, we considered the issues related to modeling and analysis of uncooled infrared detectors noise analysis utilizing pulse train equalization technique. We first developed a mathematical model appropriate for the noise performance study of the detector and then derive the detectivity and noise equivalent temperature difference (NETD) expressions for the predetection, detection, and postdetection noise sources. Our study of the postdetection noise sources was focused on the capacitive transimpedance amplifier unit cell electronics which provides a tight control over the detector bias current and handles a lower background radiation with a superior noise performance. We developed a parametric tradeoff study which provides a guide for optimizing the bolometer noise performance through the adjustment of detector parameters. We also discussed the use of scanning format and time-delay integration technique for improving the performance of multiple arrays of detectors.

We present an ultracompact infrared cryogenic camera integrated inside a standard Sofradir's detector dewar cooler assembly (DDCA) whose field of view is equal to 120°. The multichannel optical architecture produces four nonredundant images on a single SCORPIO detector with a pixel pitch of 15 μm. This ultraminiaturized optical system brings a very low additional optical and mechanical mass to be cooled in the DDCA: the cool-down time is comparable to an equivalent DDCA without an imagery function. Limiting the number of channels is necessary to keep the highest number of resolved points in the final image. However, optical tolerances lead to irregular shifts between the channels. This paper discusses the limits of multichannel architectures. With an image-processing algorithm, the four images produced by the camera are combined to process a single full-resolution image with an equivalent sampling pitch equal to 7.5 μm. Experimental measurements on the modulation transfer function and noise equivalent temperature difference show that this camera achieves good optical performance.

Third generation thermal imagers with dual/multi-band operation capability are the prominent focus of the current research in the field of infrared detection. Dual band quantum-well infrared photodetector (QWIP) focal plane arrays (FPAs) based on various detection and fabrication approaches have been reported. One of these approaches is the three-contact design allowing simultaneous integration of the signals in both bands. However, this approach requires three In bumps on each pixel leading to a complicated fabrication process and lower fill factor. If the spectral response of a two-stack QWIP structure can effectively be shifted between two spectral bands with the applied bias, dual band sensors can be implemented with the conventional FPA fabrication process requiring only one In bump on each pixel making it possible to fabricate large format dual band FPAs at the cost and yield of single band detectors. While some disadvantages of this technique have been discussed in the literature, the detailed assessment of this approach has not been performed at the FPA level yet. We report the characteristics of a large format (640 × 512) voltage tunable dual-band QWIP FPA constructed through series connection of MWIR AlGaAs–InGaAs and LWIR AlGaAs–GaAs multi-quantum well stacks, and provide a detailed assessment of the potential of this approach at both pixel and FPA levels. The dual band FPA having MWIR and LWIR cut-off wavelengths of 5.1 and 8.9 μm provided noise equivalent temperature differences as low as 14 and 31 mK ( f /1.5) with switching voltages within the limits applicable by commercial read-out integrated circuits. The results demonstrate the promise of the approach for achieving large format low cost dual band FPAs.

Thermo-mechanical detector arrays in the 160 x 120 array format are designed, fabricated, and tested. Detectors are composed of SiNx and TiN as absorbing layer, Al to form bimaterial legs, and integrated diffraction grating interferometer underneath each detector. The detector array is a passive component and the optical readout is performed remotely with a laser and CCD camera. All noise sources are considered in making a detailed noise equivalent temperature difference (NETD) estimation, which revealed 12-bit CCD camera for the readout. (C) 2009 Elsevier B.V. All rights reserved.

Low manufacturing cost and ease of use favor spreading of 2-D bolometric infrared detector arrays over various application domains such as predictive maintenance, medical imaging, automotive industry, and security. The infrared detector's main figure of merit has long been the noise equivalent temperature difference (NETD), which sets the minimum temperature difference distinguishable from background noise at sensor output. However, while nowadays uncooled detectors have achieved sufficient NETD, fixed pattern noise (FPN) is indeed becoming a crucial figure of merit especially when the focal plane array (FPA) is not regulated by a thermoelectric cooler (TEC). In this paper, we study the various sources of dispersion of infrared bolometric detectors and their respective impact on FPN in the resulting image. We propose an analytical model to identify main sources of nonuniformity, and the confrontation of results with actual measurements leads to the ability of a highly accurate on-chip thermal drift compensation.

A substrate-free 160 times 160 focal-plane array (FPA) with a 60-mum times 60-mum pitch has been developed and used for an optical readout uncooled infrared (IR) detector. The supporting frame of the FPA is a temperature-variable one due to its large decreases in both heat capacity and thermal conductance. This thermal characteristic significantly increases the temperature change of the microcantilever, which depends on both the temperature change induced by its absorption of IR radiation and the linear superposition of the temperature prechange induced by other microcantilevers, and therefore improves the performance of the substrate-free FPA. In the proposed IR detector, the fabricated FPA had an average noise equivalent temperature difference (NETD) and a response time of 330 mK and 16 ms, respectively. Its performance increased by about 4.3 times compared with that of the substrate FPA that consists of the same microcantilevers.

An analytical model and supporting measured data are presented for a preamplified W-band radiometer with a zero-bias detector appropriate for commercial millimeter-wave imaging cameras. Basic radiometer parameters, including RF bandwidth, are computed directly from simple low-frequency measurements and compare well with those obtained from RF measurements. A detailed analytical model shows how radiometer performance depends on internal component parameters, such as low-noise amplifier gain, noise factor, reflection coefficient, detector responsivity, etc. The measurements suggest that performance is sufficient for operation without a Dicke switch or mechanical chopping. A measured noise equivalent temperature difference of 0.45 K was obtained, assuming a single sensor is scanned across a focal plane, forming 32 pixels with 3.125-ms integration time per pixel. This sensitivity is considered sufficient by commercial manufacturers to obtain quality images in low-contrast (e.g., indoor) environments.

This paper discusses the implementation of a low-cost 128 times 128 uncooled infrared microbolometer detector array together with its integrated readout circuit (ROC) using a standard 0.35 mum n-well CMOS and post-CMOS MEMS processes. The detector array can be created with simple bulk-micromachining processes after the CMOS fabrication, without the need for any complicated lithography or deposition steps. The array detectors are based on suspended p+-active/n-well diode microbolometers with a pixel size of 40 mum times 40 mum and a fill factor of 44%. The p+-active/n-well diode detector has a measured dc responsivity (R) of 4970 V/W and a thermal time constant of 36 ms at 50 mtorr vacuum level. The total measured rms noise of the diode type detector is 0.69 muV for an 8 kHz bandwidth, resulting in a detectivity (D*) of 9.7 times 108 cm ldr Hz1/2/W. The array is scanned by an integrated 32-channel parallel ROC including low-noise differential preamplifiers with an electrical bandwidth of 8 kHz. The 128 times 128 focal plane array (FPA) has one row of infrared-blind reference detectors that reduces the effect of FPA fixed pattern noise and variations in the operating temperature relaxing the requirements for the temperature stabilization. Including the noise of the reference and array detectors together with the ROC noise, the fabricated 128 times 128 FPA has an expected noise equivalent temperature difference (NETD) value of 1 K for f/1 optics at 30 frames/s (fps) scanning rate. This NETD value can be decreased to 350 mK by improving the post-CMOS fabrication steps and increasing the number of readout channels.

An optical readout uncooled infrared (IR) imaging detector of bimaterial cantilever array using knife-edge filter operation (KEFO) is demonstrated. The angle change of each cantilever in a focal plane array (FPA) can be simultaneously detected with a resolution of 10−5 degree. A deformation magnifying substrate-free micro-cantilever unit with multi-fold interval metallized legs is specially designed and modeled. A FPA with 160 × 160 pixels is fabricated and thermal images with noise equivalent temperature difference (NETD) of 400 mK are obtained by this imaging detector.