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We have extended our investigation of corrugated quantum well infrared photodetector focal plane arrays (FPAs) into the far infrared regime. Specifically, we are developing the detectors for the thermal infrared sensor (TIRS) used in the Landsat Data Continuity Mission. To maintain a low dark current, we adopted a low doping density of 0.6×1018 cm−3 and a bound-to-bound state detector. The internal absorption quantum efficiency (QE) is calculated to be 25.4%. With a pixel fill factor of 80% and a substrate transmission of 70.9%, the external QE is 14.4%. To yield the theoretical conversion efficiency (CE), the photoconductive gain was measured and is 0.25 at 5 V, from which CE is predicted to be 3.6%. This value is in agreement with the 3.5% from the FPA measurement. Meanwhile, the dark current is measured to be 2.1×10−6 A/cm2 at 43 K. For regular infrared imaging above 8 μm, the FPA will have an noise equivalent temperature difference (NETD) of 16 mK at 2 ms integration time in the presence of 260 read noise electrons. The highest operability of the tested FPAs is 99.967%. With the CE agreement, we project the FPA performance in the far infrared regime up to 30 μm cutoff.

Application requirements driving present IR technology development activities are improved capability to detect and identify a threat as well as the need to reduce size weight and power consumption (SWaP) of thermal sights. In addition to the development of 3rd Gen IR modules providing dual-band or dual-color capability, AIM is focused on IR FPAs with reduced pitch and high operating temperature for SWaP reduction. State-of-the-art MCT technology allows AIM the production of mid-wave infrared (MWIR) detectors operating at temperatures exceeding 120 K without any need to sacrifice the 5-μm cut-off wavelength. These FPAs allow manufacturing of low cost IR modules with minimum size, weight, and power for state-of-the-art high performance IR systems. AIM has realized full TV format MCT 640×512 mid-wave and long-wave IR detection modules with a 15-μm pitch to meet the requirements of critical military applications like thermal weapon sights or thermal imagers in unmanned aerial vehicles applications. In typical configurations like an F/4.6 cold shield for the 640×512 MWIR module an noise equivalent temperature difference (NETD) 20000, e.g., for warning sensors in 24/7 operation. The modules are available with optional image processing electronics providing nonuniformity correction and further image processing for a complete IR imaging solution. The latest results and performance of those modules and their applications are presented.

We demonstrate the suppression of the bulk generation- recombination current in nBn devices based on an InAsSb active layer (AL) and a AlSbAs barrier layer (BL). This leads to much lower dark cur- rents than in conventional InAsSb photodiodes operating at the same temperature. When the BL is p-type, very high doping must be used in the AL (nBpn + ). This results in a significant shortening of the device cut- off wavelength due to the Moss-Burstein effect. For an n-type BL, low AL doping can be used (nBnn), yielding a cutoff wavelength of ∼4.1 μm and a dark current close to ∼3 × 10 −7 A/cm 2 at 150 K. Such a device with a4 -μm-thick AL will exhibit a quantum efficiency (QE) of 70% and background-limited performance operation up to 160 K at f/3. We have madenBnnfocalplane arraydetectors(FPAs)with a 320 ×256 formatand a 1.3-μm-thick AL. These FPAs have a 35% QE and a noise equivalent temperature difference of 16 mK at 150 K and f/3. The high performance of our nBnn detectors is closely related to the high quality of the molecular beam epitaxy grown InAsSb AL material. On the basis of the temperature dependence of the diffusion limited dark current, we estimate a minority carrier lifetime of ∼670 ns. C 2011 Society of Photo-Optical Instrumentation Engineers

The dominant dark current mechanisms are identified and suppressed to improve the performance of midwave infrared InAs/GaSb type-II superlattice photodiodes at high temperatures. The optimized heterojunction photodiode exhibits a quantum efficiency of 50% for 2 μm thick active region without any bias dependence. At 150 K, R0A of 5100 Ω cm2 and specific detectivity of 1.05×1012 cm Hz0.5/W are demonstrated for a 50% cutoff wavelength of 4.2μm. Assuming 300 K background temperature and 2π field of view, the performance of the detector is background limited up to 180 K, which is improved by 25 °C compared to the homojunction photodiode. Infrared imaging using f/2.3 optics and an integration time of 10.02 ms demonstrates a noise equivalent temperature difference of 11 mK at operating temperatures below 120 K.

A low cost MWIR thermal imaging line scanner based on a multiplexed PbSe FPA has been developed. It was designed to be mounted on the underside of UAVs to remotely map battlefields. It also has many dual-use commercial applications. The first unit has been tested in the laboratory and in roof-top imaging demonstrations. It has produced excellent imagery. The noise equivalent temperature difference has been measured to be 0.55 C in preliminary tests. An improved FPA will be installed soon in the unit which will significantly reduce the NET.

The HgCdTe (MCT) 64 X 64 focal plane array (FPA) for long wavelength infrared (LWIR) detection was developed, using MCT epilayers grown by molecular beam epitaxy (MBE). The n-on-p photodiode array has a cutoff wavelength of 10.7 micrometers . The readout circuit, with off focal plane integration capacitance, was designed for 77 K operation. These components were fabricated independently and were hybridized. The 97.8% operability was obtained. Photodiode characteristics for each pixel were measured directly. Mean R$o)A value of 1.9 (Omega) (DOT) cm 2 and quantum efficiency of 0.3 were obtained. Using an infrared camera system with nonuniformity correction function, the infrared image was successfully demonstrated. An NETD (noise equivalent temperature difference) value of 0.117 K was attained with an F/2.5 optical lens under the 300 K background condition.

We have developed a `1M-IRCSD imager' for thermal imaging in the 3 to 5 micrometers band. The device of this imager is a 1040 X 1040 monolithic PtSi Schottky-barrier (SB) array using the charge sweep device (CSD) readout architecture. In this imager system, four video signals are read out from four independent channels on the chip. The processing of these four outputs, such as sample and hold (S/H), offset control and image correction, is performed in parallel, after which these outputs are combined to produce High Definition TV (HDTV; 1125 lines, 30 Hz) format thermal image in real time. The noise equivalent temperature difference (NETD) with F1.2 optics at 27 degree(s)C background is 0.13 degree(s)C at the HDTV output stage.

We have developed a hybrid HgCdTe focal plane array (FPA) for wavelengths from 8 to 11 micrometers . We describe how we fabricated our back illuminated 64 X 64-element photodiode array on a liquid phase epitaxial (LPE) HgCdTe wafer, and a Si CCD multiplexer with line address readout. We optimized carrier concentration in the p-type HgCdTe layer to maximize charge injection efficiency to the Si CCD readout circuit to more than 99.3%. We achieved excellent uniformity of characteristics of the photodiode array, which is very important for an IRFPA, by using LPE HgCdTe grown with a tipping method, and passivating the photodiode array with an anodic sulfide of HgCdTe. We obtained an average product of zero-bias resistance and area (RoA) of 9.1 (Omega) cm 2 with a cutoff wavelength of 10.6 micrometers at 77 K. We used line address readout to give a large charge storage capacity of 4 X 10 7 electrons. We estimated a noise equivalent temperature difference (NETD) of 0.08 K with F/2.5 optics, including fixed pattern noise. We tried some preliminary experiments to reduce the crosstalk from photogenerated carriers which spread laterally into the epitaxial layer. We improved the modulation transfer function (MTF) at Nyquist spatial frequency from the conventional 35% to 60% by using a crosswise drain structure around each photosensitive n + on p diode.

A high performance 640 X 480 focal plane array has been developed for the 1 - 5 micron band with excellent sensitivity at temperatures below 120 K. The detectors are processed on 2' or 3' diameter PACE-I (producible alternative to CdTe for epitaxy) HgCdTe material. The multiplexer is a direct injection input, switched-FET device with four independent quadrants. The detector is hybridized to the multiplexer through indium columns and is characterized. A mean camera NE(Delta) T (noise equivalent temperature difference) of 13 mK has been achieved for temperatures

The noise equivalent temperature difference (NETD) of forward looking infrared (FLIR) systems is a widely used performance parameter that characterizes the sensitivity of thermal imaging sensors. Although this parameter has been used for many years, there has always been some confusion and misunderstanding about how to measure it. Differences in opinion on how this measurement should be made can cause substantial variations in reported values of NETD measurements. It is the intent of this paper to clearly describe the measurement technique used at Night Vision and Electronic Sensors Directorate (NVESD).

A radiometric math model (RMM) has been developed for use as an analytical tool to establish design requirements and to model performance of the moderate resolution imaging spectroradiometer (MODIS) instrument design. The MODIS instrument is scheduled for flight on the first earth observing system (EOS) AM spacecraft in mid-1998. The model represents a significant advancement in the state of the art in radiometric simulation techniques. Characteristics of the MODIS optical design, focal plane assembly (FPA), scanning and electrical parameters, and the on-board calibrators are input to the model as predicted, estimated, or measured. Primary outputs of the model are radiometric sensitivity [signal- to-noise ratio (SNR) and noise equivalent temperature (NE(Delta) T)] and radiometric accuracy. This paper describes the theory of the model, the input and output parameters, and the major program modules, and presents predictions for the current MODIS design.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A model is presented for analytically predicting the performance of IR staring rays sensitive in the 3-5 and 8-12 micrometer spectral bands. The performance measure will include video SNR, dynamic range, noise equivalent temperature difference, and minimum resolvable temperature difference. The comparative advantages of various arrays such as platinum-silicide, indium-antimonide, and mercury-cadmium-telluride arrays, when viewing terrestrial scenes at various ambient temperatures and through differing atmospheric conditions, are discussed. The analytical approach differs from most others in that signal levels and noise are described in terms of currents which can be readily measured rather than quantized units such as electrons/pixel. Sample calculations are presented, including the effects of optics, cold shields, spectral responsivities, modulation transfer functions, and displays.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Often the need arises for calibration of infrared systems in the environment of intended use, or field environment. The development of a field calibration platform for performance testing of infrared (IR) imaging and spectral analysis instrumentation is discussed. The calibration hardware is required to provide precise and traceable standards over a range of tests including minimum resolvable temperature difference (MRTD), noise equivalent temperature difference (NETD), minimum detectable temperature difference (MDTD), and modulation transfer function (MTF) for imaging systems, and known spectral content output for Fourier transform infrared radiometers (FTIR) and other spectral analysis instruments. The equipment package must consist of non-development components, and be portable, reliable, and repeatable under field conditions.

We present the results of stability testing of a terahertz radiometer based on a superconducting receiver with a SIS tunnel junction as the mixer and a flux-flow oscillator as the local oscillator. In the continuum mode, the receiver with a noise temperature of 95 K at 510 GHz measured over the intermediate frequency (IF) passband of 4–8 GHz offered a noise equivalent temperature difference of 10 ± 1 mK at an integration time of 1 s. We offer a method to significantly increase the integration time without the use of complex measurement equipment. The receiver observed a strong signal over a final detection bandwidth of 4 GHz and offered an Allan time of 5 s.

A large format 1k×1k focal plane array (FPA) is realized using type-II superlattice photodiodes for long wavelength infrared detection. Material growth on a 3 in. GaSb substrate exhibits a 50% cutoff wavelength of 11 μm across the entire wafer. The FPA shows excellent imaging. Noise equivalent temperature differences of 23.6 mK at 81 K and 22.5 mK at 68 K are achieved with an integration time of 0.13 ms, a 300 K background and f/4 optics. We report a dark current density of 3.3×10−4 A cm−2 and differential resistance-area product at zero bias R0A of 166 Ω cm2 at 81 K, and 5.1×10−5 A cm−2 and 1286 Ω cm2, respectively, at 68 K. The quantum efficiency obtained is 78%.

A monolithic infrared focal plane array where photo-diodes and field effect transistors are integrated is presented. The photodiode is connected directly to the integrating capacitor while the transistor controls the integrated signal-charge transfer to the video line. The operating modes of such array are discussed and especially the pseudo-staring mode. Such arrays were produced and their system performance were investigated. The detectors average specific detectivity D * (lambda )(f/no equals 1, (lambda) equals 3.83 micrometers ) was equal to 1.3 X 10 11 [cm-Hz 1/2 /W] and was used to calculate the Noise Equivalent Temperature Difference (NETD) as a function of the number of detectors and vectors. The NETD was estimated to be of 0.039 K for an optimal 5 vectors array.

A long wavelength infrared imaging system is under development at Loral Infrared & Imaging Systems. The imager features a solid state pyroelectric focal plane array sensitive to 8 - 14 micrometers radiation operating at ambient temperature; it needs no cooling or temperature control to obtain performance comparable to conventional cooled FLIR systems. The focal plane array is fabricated as a hybrid structure with a fully reticulated lithium tantalate detector array bump mounted to a CMOS multiplexer. The optical, thermal, and electrical design of the focal plane array is described in detail. The prototype imaging system uses a focal plane array of 192 X 128 pixels on 50 micrometers centers. The next version will use a focal plane with approximately 330 X 240 pixels for full NTSC (U.S. standard television) compatibility. The design of the prototype imaging system is described. The predicted noise equivalent temperature difference (NETD) for these systems is less than 0.1 degree(s)C with f/1 optics at a 30 Hz display rate.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper describes a resolution improvement for a mercury cadmium telluride (MCT) infrared charge-coupled device (IRCCD) using a new microscanner. To keep the microscanner compact, the scanner prism is placed between the lens and the IRCCD, and driven by a bimorph piezoelectric actuator. By compensating the drive pulse and optimizing the prism thickness, the microscanner gives a fast and stable response with low distortion. The medium wavelength imager developed for the microscanner gives a 128 X 128 pixel thermal image in the 3 to 5 micrometers band using a 64 X 64 element IRCCD. The Nyquist frequency was increased from 10 to 20 cycles/mm to reduce aliasing without decreasing the S/N ratio. The noise equivalent temperature difference (NETD) was measured at 0.06 K with an f-1.7 lens. The modulation transfer function (MTF) was estimated by considering the scan distortion and the pixel aperture profile. By optimizing the aperture profile of the photodiode, the MTF at the Nyquist frequency was increased from 0 to 20%.

We have improved the performance of a 512 X 512 element PtSi Schottky-barrier infrared image sensor (512 X 512 IRCSD) by increasing the fill factor and saturation signal level. The sensor consists of 26 micrometers X 20 micrometers pixels in a 512 X 512 array format and has a large fill factor of 71% obtained with 1.2 micrometers minimum design rules and the charge sweep device (CSD) readout architecture. The improved 512 X 512 IRCSD was designed to be operated in either a field or frame integration interlace mode. The saturation signal level of the CSD imager is determined by the storage capacity of the Schottky-barrier detector (SBD). We optimized the structure and impurity concentration of the isolation region of the SBD in order to increase the large storage capacity. For an SBD reset voltage of 4 V, a saturation signal level and differential temperature response at 300 K were 2.9 X 106 electrons and 3.2 X 104 electrons/K, respectively. The noise equivalent temperature difference (NETD) at 300 K is estimated as 0.033 K with an f/1.2 cold shield.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Staring 128 X 128 hybrid HgCdTe FPAs have been demonstrated with very good sensitivity and operability at temperatures compatible with thermoelectric cooling (> 160 K). The FPAs consist of HgCdTe/sapphire (PACE-I; producible alternative to CdTe for epitaxy) detector arrays hybridized to a CMOS readout having a gate modulation input circuit. FPAs with SWIR (2.5 micrometers at 78 K) and MWIR (4.56 micrometers at 180 K) cutoff wavelengths ((lambda) co) were made and evaluated. The SWIR arrays were ZnS passivated; the MWIR arrays were CdTe-passivated. Though the (lambda) co of the MWIR devices was not specifically optimized for terrestrial imaging at TE-cooled temperatures in the preferred 3.4 to 4.1 micrometers band, very good sensitivity was achieved, particularly relative to other technologies at temperatures >= 120 K. Mean laboratory noise equivalent temperature differences (NE(Delta) T) at 120 K, 170 K, and 180 K were 0.0048 K, 0.053 K, and 0.061 K respectively, for the MWIR device. While the NE(Delta) T was measured without a spectral filter, the sensitivity for 3.4 to 4.1 micrometers bandpass extrapolates to camera NE(Delta) T

Noise equivalent temperature difference (NE(Delta) T) values in a PtSi Schottky-barrier (SB) infrared CCD image sensor are calculated with variations in spectral response, device operating temperature, and internal radiation intensity generated from a lens barrel, using measured values from a recently developed 648 X 487 pixel SB infrared CCD image sensor. The barrier height is allowed to vary, whereas it was fixed before. NE(Delta) T values were calculated as a function of barrier height and were found to have a minimum. The optimum barrier height depends on quantum efficiency coefficient, device operating temperature, and internal radiation intensity.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper reviews the progress in the development of infrared image sensors with Schottky- barrier detectors (SBDs). Schottky-barrier focal plane arrays (FPAs) are infrared imagers that are fabricated by a well established silicon VLSI process, therefore, at the present time they represent the most advanced technology for large-area high-density focal plane arrays for many SWIR (1 to 3 micrometers ) and MWIR (3 to 5 micrometers ) applications. SBD line sensing arrays with up to 4096 X 4 elements and 2048 X 16-TDI elements were developed and SBD staring (area) arrays with up to 1040 X 1040 elements have been reported. PtSi SBDs represent the most established SBD technology for applications in the SWIR and MWIR bands. At an operating temperature of 77 K, the dark current density of PtSi SBDs is in the range of 1.0 to 4.0 nA/cm2. Pd2Si SBDs were developed for operation with passive cooling at 120 K in the SWIR band. IrSi SBDs have also been investigated to extend the application of Schottky-barrier focal plane arrays (FPAs) into the LWIR (8 to 10 micrometers ) spectral range. Because of very low readout noise, the IR-CCD imagers with PtSi SBDs which have quantum efficiency of .5% to 1% at 4.0 micrometers are capable of 300 K thermal imaging with a noise equivalent temperature (NE(Delta) T) from 0.033 to 0.15 K for operation at 30 frames/s and f/1.0 to f/2.8 optics.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have developed a series of Schottky-barrier infrared image sensors with a novel readout architecture called the charge sweep device (CSD). Compared with the conventional interline transfer CCD image sensor, the CSD image sensor has a larger charge handling capacity and is suitable for thermal imaging where we have to detect a small signal in a large background. This paper describes the design and performance of the CSD image sensors. The devices described here include a 512x512 element IRCSD, a small size 256x256 element IRCSD, a 256x256 element IRCSD which has the lowest noise equivalent temperature difference of 0.036K (f/1.2), and a 1040x1040 element IRCSD which is the highest resolution device among infrared image sensors.

Demonstrated detectivity of uncooled infrared focal plane arrays is better than O.1°K noise equivalent temperature difference, Uncooled performance levels are now suitable for military and commercial applications. The manufacturing science of this technology lags that for mercury cadmium tellurium based cooled focal planes. The manufacturing issues and approaches for ferroelectric material based uncooled detectors are discussed. The recommended approach is to address producibility issues based on pareto analysis of the process flow and to address the most highly leveraged process steps in terms of time and labor input. Detailed modeling of the process flow has been undertaken as a part of this analysis. Processes addressed in detail are lap and polish of the detector, photolithography, metallization, etches, hybridization, and test. Several approaches are shown to yield comparable cost focal planes, but a process technology leveraging silicon process technologies is shown to minimize space and equipment.

A long wavelength infrared focal plane array based on type-II InAs/GaSb superlattices was fabricated and characterized at 80 K. The noise equivalent temperature difference in the array was measured as low as 23 mK for an integration time of 0.129 ms. The noise behavior of the detectors was properly described by a model based on thermal, shot, read out integrated circuit, and photon noises. The noise of the imager was dominated by photon noise for photon fluxes higher than 1.8×1015 ph s−1 cm−2. At lower irradiance, the imager was limited by the shot noise generated by the dark current or the noise of the testing system. The superlattice detector did not create 1/f noise for frequencies above 4 mHz. As a result, the focal plane array did not require frequent calibrations.

In an optomechanical infrared (IR) detection system, the optical detection sensitivity, a key factor that affects the noise equivalent temperature difference (NETD), is influenced by the length and bend of micro-cantilever reflector of a focus plane array (FPA). The influence on optical detection sensitivity by such a bend due to the bulk micromachining techniques is discussed based on Fourier optics. In this study, the reflectors of the fabricated FPAs with pixel sizes 200 µm, 120 µm and 60 µm have the curvature radii of 23 mm, 11 mm and 8 mm, respectively. Theoretical analysis and experiments show that the sensitivities are degraded by the undesired bend of the micro-cantilever reflector. Moreover, the study demonstrates that the sensitivity reaches the maximum value when the reflector length L and the curvature radius R of the micro-cantilever reflector satisfy the relation: L2/R = λ (λ is the wavelength of illumination light) and this result provides an approach for optimizing the optical sensitivity as the diminishing of the pixel size of FPA. Finally, the methods of optimizing the sensitivity are discussed.

We describe the concept of the submonolayer quantum dot infrared photodetector (SML QDIP) and report experimental device results on long-wavelength infrared detection. An SML QDIP structure was fabricated into megapixel focal plane arrays, which produced clear infrared images up to 80 K. Detectors in the focal plane showed a responsivity peak at 7.8 μm and noise equivalent temperature difference of 33 mK at 70 K.

This note presents an optimized substrate-free focal plane array (FPA), which is implemented in an optical readout uncooled infrared (IR) detector. The supporting frame of such FPA is a temperature-variable one due to the large decreases in both the heat capacity and the thermal conductance. This brings a unique thermal characteristic: the supporting frame functions as a “thermal isolation” frame which reduces the thermal conductance and therefore increases the temperature change and also functions as a “thermal diffusion” frame which certainly results in the temperature prechange in the ones not absorbing IR radiation. This characterization could significantly increase the temperature change of microcantilevers and therefore improve the performance of the substrate-free FPA. In the proposed IR detector, the fabricated 160×160 FPA has an average noise equivalent temperature difference (NETD) and a response time of 330 mK and 16 ms, respectively. The performance of the IR detector theoretically increases b...

Kamakura, Kanagawa, 247, JapanABSTRACTA 256x256 element platinum silicide monolithic image sensor with a large fill factor has been developed as a highsensitivity infrared image sensor. It is essential to increase the maximum signal charge of the staring infrared image sensor toobtain higher sensitivity. We used the Charge Sweep Device readout architecture and improved operations of the floatingdiffusion amplifier to increase the maximum signal charge. A 52x40 pixel using a minimum feature size of 2 jim has a fillfactor of 66%. Evaluating the performance of the device, we confirmed the effectiveness of the improved technologie& Themeasured saturation level is 2.8x1O electrons which is determined by the storage capacity of the detector. We estimated froma measurement point at low background temperature that the noise equivalent temperature difference with a f/1.2 optics is0.036K at 300K background.1. INTRODUCTIONThe progress in the spatial resolution of the Schottky-barrier infrared image sensor for the 3-5pin infrared band isconstant, and several infrared image sensors with video quality have been successfully developed'23. Schottky-barrier infra-red TV cameras with noise equivalent temperature difference from 0.1 to 0.2K are now in production. The state-of-the-artperformance of the Schottky-barrier infrared image sensor is sufficient for almost all civil applications. However, furtherimprovement in the sensitivity is required for detecting very faint objects or detecting objects in a hard environment (such aslow background temperature).The sensitivity can be improved by increasing the quantum efficiency of the detector and/or enlarging the fill factor(the ratio of the effective detector area to the pixel size). Noise reduction technologies such as high conversion gain on-chipamplifier also improve the signal-to-noise ratio of the image sensor. In visible imaging, these improved technologies havebeen successfully applied to high resolution image sensors with small pixels. Unlike visible imaging, the infrared imaging ishigh background imaging with low contrasL The difficulty in the infrared imaging is that any improvement in the sensitivityhas the desired effect of increasing the significant signal and the detrimental effect of increasing the background signal.Therefore it is essenthl to increase the maximum charge of the staring infrared image sensor to obtain higher sensitivity. Thelimitation in the maximum charge becomes a serious problem in high density infrared image sensors even if a Schottky-batherdetector with relatively low quantum efficiency is used56.238

The noise equivalent temperature difference (NETD) is one of the most convenient measures used in describing performance of infrared systems as thermographs and radiometers. The NETD expression is also contained as a kernel within any minimum resolvable temperature difference (MRT) and minimum detectable temperature difference (MDT), so the conclusions to be reached relative to NETD apply to MRT and MDT as well. For reasons of convenience, some assumptions have been made in defining (measuring and deriving relation for) the NETD. However, for a variety of practical purposes in the field, these assumptions are not satisfied. Consequently the conventional laboratory NETD is applicable under certain favorable laboratory conditions. Therefore the typical, laboratory NETD expressions found in the literature cannot be simply applied for infrared systems under field conditions. In this paper the practical, field NETD expression is derived. It incorporates none of the assumptions which have been used in defining and deriving the laboratory NETD expression. Therefore, the given expression can be applied to assessment of infrared systems capabilities under field conditions.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Various companies are now producing 2-dimensional CMT-Si hybrid focal plane arrays. These are complex devices and at present the accepted figures of merit describing the arrays vary significantly between devices of the same type. In infrared imager applications the spatial uniformity of the detector array, particularly with regards to parameters such as noise equivalent temperature difference (NETD) rather than the quality of individual pixels may determine the overall system performance. A small number of unresponsive elements can be effectively masked by correction algorithms in the imager electronics. Assessment apparatus capable of storing the output of all the photodiodes in a focal plane array up to 128 X 128 pixels in size has been used to determine the optimum operating point for three co-ordinate addressed devices, giving rise to a methodology for setting up this type of detector.

We describe the design, fabrication, and characterization of arrays of uncooled infrared and terahertz micromechanical detectors that utilize SiO2 as a main structural material. Materials with highly dissimilar coefficients of thermal expansion, namely, Al and SiO2, were used to form folded bimaterial regions. This approach improved the detector sensitivity by 12 times compared to SiNx-based detectors of similar shape and size. Two types of structural SiO2 layers were investigated: thermally grown and plasma-enhanced chemical-vapor-deposited SiO2. Fabrication of the detector arrays relied on a straightforward process flow that involved three photolithography steps and no wet etching. The noise equivalent temperature difference intrinsic to the detectors fabricated during this work can reach 3.8 mK when excluding any contribution from the optical readout used to interrogate the arrays.

The AlInAs/InGaAs material system is promising for mid-wavelength infrared (MWIR) and multi-band quantum well infrared photodetectors (QWIPs) as a lattice-matched alternative to the strained AlGaAs/InGaAs system. In this paper, we report a large format (640 × 512) AlInAs/InGaAs QWIP focal plane array (FPA) with 4.9 µm cut-off wavelength and assess the performance of this material system for MWIR QWIP applications at both pixel and large format FPA level. We also experimentally demonstrate that the cut-off wavelength of AlInAs/InGaAs QWIPs can be tuned in a sufficiently large range in the MWIR atmospheric window by changing only the quantum well (QW) width at the lattice-matched composition. The cut-off wavelength is shifted from 4.15 to 4.9 µm when the QW width is decreased from 30 to 23 A, in which case a very broad spectral response (Δλ/λp = 32%) with a reasonably high peak detectivity (5.5 × 1010 cm Hz1/2 W−1, f/1.5) is achievable. The AlInAs/InGaAs QWIP FPA yielded excellent sensitivity with a noise equivalent temperature difference as low as 22 mK and a background limited performance (BLIP) temperature as high as 115 K with f/1.5 aperture and 300 K background. The results clearly demonstrate the potential of this material system for completely lattice-matched dual- or multi-band QWIP FPAs for third-generation thermal imagers.

Real-time imaging in the terahertz (THz) spectral range was achieved using a milliwatt-scale, 2.8 THz quantum cascade laser and an uncooled, 160 x 120 pixel microbolometer camera modified with Picarin optics. Noise equivalent temperature difference of the camera in the 1-5 THz frequency range was estimated to be at least 3 K, confirming the need for external THz illumination when imaging in this frequency regime. Despite the appearance of fringe patterns produced by multiple diffraction effects, single-frame and extended video imaging of obscured objects show high-contrast differentiation between metallic and plastic materials, supporting the viability of this imaging approach for use in future security screening applications.

A pixelwise readout circuit for application in microbolometer focal plane arrays (FPAs) is studied. A current mirroring injection input circuit that is suitable for a pixelwise architecture and has high responsivity is proposed. The noise equivalent temperature difference can be improved to 31 mK.

Thermal Imaging Systems are characterized by various tests such as Minimum Resolvable Temperature (MRT), System Intensity Transfer Function (SITF) and Noise Equivalent Temperature Differential (NETD). Numerous sources of errors can effect these test giving misleading results. These error sources are analyzed and a new correction methodology is presented.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Two Geophysical Environmental Research Corp. (GER) scanners are discussed in this paper. The GER 63 channel airborne imaging spectrometer covers 0.4-2.5 micrometer. There are 24 channels from 500-1000 nm, 7 channels from 1-1.8 micrometer and 32 channels from 2-2.5 micrometer. The thermal scanner has one channel in 0.4-1.1 micrometer, one channel in 3-5 micrometer, 3 channels with 1 micrometer bandwidth in 8-12 micrometer, 6 channels with half micrometer bandwidth in 8-12 micrometer and one channel in 8-12 micrometer. The GER thermal scanner was first flown in January 1990. The initial results indicate that this type of scanner gives the lowest noise equivalent temperature available.

The requirements, design, fabrication, and test results are presented for a high-density hybrid FPA based on platinum silicide IR detector technology. The hybrid Schottky FPA is intended to optimize detector and readout design and processing, achieve optimal fill factors, and reduce cell size. Schottky barrier detectors are employed in arrays of 24 micron pixel spacings, in a 244 by 400 array format. The readout and detector structure are detailed, as well as the fast-settling circuitry, and a fill factor of 84 percent is shown. The modeling used to predict optical performance is set forth, indicating detector response and noise level for specified conditions. The preamplified output of each detector was sampled in a performance test consisting of irradiation by an extended blackbody IR source. Results are presented for responsivity, RMS noise, dc uniformity and noise equivalent temperature distance. Sensitivity levels in low background conditions are shown to be suitable. The design permits low-cost readout fabrication and extension to larger arrays.

The Thermal Infrared Profiling Spectrometer (TIPS) is an airborne /spaceborne sensor concept devel- oped at DLR- Institute for Optoelectronics for scientific observations in remote sensing of the earth surface. The patented spectrometer design is based on a fast scanning Fourier spectrometer (FSM) using arotating retroreflector to achieve the appropriate path alteration thus avoiding the usual linear move- ment of one of the mirrors in an conventional Michelson interferometer. The spectral band covers the3 - 13 pm band with a spectral resolution of 5 cm ' (50 nm at. 10 pm).The measured signal is an interferogramm, derived quantities are spectral emissivity, spectral radianceand surface temperature.The optical system consists of an aperture filling plane tilting mirror to provide off -nadir observationand calibration mode. The collecting mirror focal length and the detector area yields an instantaneousfield of view (ifov) of 1.2 mrad, noise equivalent temperature resolution of 0.04K (300K), and a noiseequivalent change in emissivity AE of 6 x 10-4.Calibration is performed by two aperture filling area blackbodies at two different temperatures.An extensive simulation of signal /noise performance of the TIPS has been evaluated by means of thesimulation prograrnm SENSAT9, developed by DI,R. This simulation comprises the sensor perform-ance, typical variations of atmospheric conditions and selected spectra from ground surfaces.Results of this simulation are discussed and a description of the sensor is presented.2. SCIENTIFIS OBJECTIVESScientific objectives are related to improved spectral analysis of surface materials, minerals, soils androcks due to the strong spectral features particularly the silicates and carbonates in the 8 - 23 pm band.Vegetation shows subtle changes in emissivity (1 - 2 %) in the thermal IR connected with water stress.Soil moisture and surface temperature is an important quantity to a variety of remote sensing applica-tions.The proposed TIPS instrument is an earth observation sensor (spectrometer ) complementary to mod-erate and high spatial and spectral resolution imaging sensors, like MODIS -N, MERIS, IIIRIS.

The authors report on a novel substrate-free cantilever-based focal plane array (FPA) fabricated by a deep reactive ion etching technique and discuss its performance as an uncooled infrared imager. A visible optical readout was designed to simultaneously measure the deflections of all the cantilevers in the FPA. The noise equivalent temperature difference (NETD) of our FPA can be reduced by 60% compared to the one fabricated by sacrificial layer technique and some cantilevers exhibited NETD of 375mK, approaching the theoretical prediction of 89.7mK. The FPA has a bending response to temperature of 86nm∕K and a response time of 21ms.

This letter reports a 320×256 middle-wavelength infrared focal plane array operating at temperatures up to 200K based on an InAs quantum dot/InGaAs quantum well/InAlAs barrier detector grown on InP substrate by low pressure metal organic chemical vapor deposition. The device’s low dark current density and the persistence of the photocurrent up to room temperature enabled the high temperature imaging. The focal plane array had a peak detection wavelength of 4μm, a responsivity of 34mA∕W, a conversion efficiency of 1.1%, and a noise equivalent temperature difference of 344mK at an operating temperature of 120K.

The authors demonstrated a microfabricated tuning fork temperature/infrared sensor with noise equivalent temperature difference (NETD) of 0.5mK at 20°C and with a thermal limited noise level of 5μ°C. The sensor raw material can cost less than 10 cents each and has a time constant of approximately 50ms. The sensitivity of infrared signal can potentially be further improved and optimized by selecting polymer materials with a proper thermal response.

We report on fabrication and characterization of arrays of bimaterial microcantilevers and discuss their performance as uncooled infrared imagers. An optical readout was used to simultaneously measure deflections of all microcantilevers in the array. The fabricated arrays had an average noise equivalent temperature difference (NETD) and a response time of 1.5K and 6ms, respectively. Some microcantilevers in the array exhibited NETD values below 500mK, approaching our theoretical prediction of 151mK. A unique and valuable feature of the implemented approach is its straightforward scalability to higher resolution arrays, without progressively growing complexity and cost.

The temperature dependence of noise equivalent temperature change (NEΔT) in Kelvin was obtained for Pt∕Si∕p-Si planar Schottky diodes for temperatures from 50 to 150K. Over this range NEΔT is 0.2K at 120K, remaining below 1K up to about 130K assuming a typical quantum efficiency of 1%, due essentially to the large leakage current from the metal into the semiconductor. A calculation assuming recently measured values of the transport properties for a Pt∕Si∕p-Si composite system shows that a NEΔT of less than 0.2K is attainable at 300K for a film thickness of 0.5μm, with PtSi particle sizes of 3nm with a 15% volume fraction and a 1% quantum efficiency. The leakage here is determined by charge transfer between the metallic grains. At higher efficiencies it is possible to produce a wider range of particle sizes and volume fractions with NEΔT's smaller than 0.5K.

We report measurements of the temperature coefficient of the resistance (TCR) and the low-frequency noise of epitaxial La0.7Sr0.3MnO3 (LSMO) thin films deposited on SrTiO3 (STO) and (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates. An x-ray-diffraction study showed that the films were (001) oriented. A normalized Hooge parameter of 9×10−31m3 was measured at 300K in the case of a 10‐μm-wide, 575‐μm-long line patterned in the 200‐nm-thick film grown on STO substrate. This value is among the lowest reported values for manganites and close to values measured in standard metals and semiconductors. The corresponding noise equivalent temperature (NET) was constant in the 300–340K range and equal to 6×10−7KHz−1∕2 at 10Hz and 150μA for a 10‐μm-wide, 575‐μm-long line patterned in a 200‐nm-thick LSMO film. This very low NET value is comparable to the best published results for manganites and was even found to be lower than the NET of other uncooled thermometers such as amorphous semiconductors, vanadium oxides, or semiconductin...

A new pixel structure with twice-bent beams and eaves structure, suitable for high-resolution uncooled infrared (IR) focal plane arrays (FPAs), is proposed. In comparison with previous results (FPA of 37-µm pixel pitch), the thermal conductance of the test device with the proposed pixel structure of 23.5-µm pitch is reduced about 2.5 times. The eaves structure, which is adopted to increase the fill factor of pixels, improves the responsivity by a factor of 1.3. A 640×480 bolometer-type uncooled IRFPA is demonstrated by utilizing the new pixel structure, with supplementary modification to improve thermal conductance and thermal time constant. It shows a noise equivalent temperature difference (NETD) of 50 mK for F/1.0 optics at 30 frames/sec, a thermal conductance of 0.03 µW/K, and a thermal time constant of 16 msec.

We demonstrate high bandwidth and low-noise readout of a superconductor–insulator–normal metal–insulator–superconductor hot-electron bolometer element. We measure a noise equivalent temperature of better than 0.6μK∕Hz1∕2 and infer an electrical noise equivalent power of 7×10−17W∕Hz1∕2 for a normal-metal volume of 4.5μm3 at an operating temperature of 270mK. Using a pulsed bias technique we measure a thermal time constant of 1.2μs at 270mK. The microwave readout method we employ is compatible with large-format arrays of 103–105pixels required by future far-infrared space and ground-based observatories.

Differential absorption radiometers (DARs) using uncooled detectors are introduced as a simple method for low-cost remote sensing of chemical vapors for domestic security. A DAR consisting of a pair of uncooled LiTaO3 pyroelectric detectors integrated with bandpass filters selected to detect methanol, a simulant of many hazardous vapors, was demonstrated. At a signal-to-noise ratio (SNR) 5, the measured detection limit for methanol was 0.014 atm cm. This corresponds to a detection limit of 5.70×10–4 atm cm (31.5 mg m–2) for dimethyl methylphosphonate (DMMP). For comparison, a DAR consisting of a pair of cryogenically cooled HgCdTe (MCT) detectors was also tested. The detector-limited noise equivalent temperature differential (NETD) of the MCT detectors was measured to be 0.38 mK, whereas for the pyroelectric detector it was 115 mK. Despite the much lower detector noise, the MCT-based DAR provided a detection limit of only 0.005 atm cm for methanol, corresponding to 2.04×10–4 atm cm (11.25 mg m–2) for DMMP. The relatively poor sensitivity of the MCT-based DAR was shown to be limited by small temperature gradients of 15 mK across the noncoincident fields of view of the detectors in the DAR and by environmental fluctuations, which contributed a total NETD = 37 mK.

We explain the technologies used for high-performance long linear arrays based on HgCdTe/CMOS hybrid multiplexers with bidirectional time delay and integration (TDI) functions and describe the development of the first high-resolution IR imaging system with a superextended graphics array (SXGA) format. Long-wavelength IR photodiode arrays are fabricated using liquid-phase epitaxially grown HgCdTe on a CdZnTe substrate. Each photodiode array consists of 480x8 element n+/n-on-p diodes formed by B+ implantation. Diodes with a 10.3-μm cutoff wavelength have a typical zero-bias resistance of 10 MΩ and a shunt resistance of 1 GΩ. Four CMOS readout integrated circuits (ROICs) are used for bidirectional TDI and multiplex operations, where each ROIC sums up and multiplexes eight signals from 120 channels. The ROIC also includes pixel deselection and gain control circuits along with the corresponding memory and writing means. The IR focal plane arrays (IRFPAs) have a typical noise equivalent temperature difference (NETD) of 18 mK after TDI with F/1.55 optics and 10-μs integration. The IR imaging system adopts an interlace scan using the 480x8 element IRFPA to demonstrate a high spatial resolution of 1280 horizontal lines by 960 vertical lines (SXGA format) and an NETD of less than 30 mK. The unique algorithm for image enhancement is successfully confirmed to be efficient.

International audience; We present a new video sensor for multimeasurements in an aircraft cargo compartment called a video sensor unit (VSU). This sensor, based on CCD technology, operates in the near IR (NIR) spectral band to measure temperatures due to overheating and fire events. After a characterization of the measurement chain, a radiometric model is applied to the VSU, enabling the measurement of temperatures ranging from 350 to 900 degreesC with a noise equivalent temperature difference (NETD) lower than +/- 8 degreesC. In the same spectral band (NIR), the VSU can also detect smoke and 3-D load displacements. The geometric model of the VSU is described and the associated calibration procedure is presented.