Uncooled Infrared Focal Plane Array Research Articles

Optimal design of optomechanical uncooled infrared focal plane array with integrated metalens

Optomechanical uncooled infrared (IR) detectors based on the thermal deformation of bi-material micro-cantilever have proved of significant potential in the IR imaging fields. However, compared to other uncooled infrared detectors, the optomechanical type relies on the mechanical deformation of the thermomechanical cantilevers, which compete for space with the absorbers and isolation beams, resulting in limited sensitivity. By integrating a designed metalens, large deformation, high thermal isolation, and high effective fill factor can be achieved simultaneously. Several pixel designs of optomechanical uncooled IR focal plane array (FPA) with designed integrated metalens are evaluated and optimized through numerical simulation. High thermal conversion efficiency and thermomechanical sensitivity μm K−1 are simultaneously achieved with an inherent noise-equivalent temperature difference(NETD) value of mK at the preset × pixels. Using Figure of Merit(FOM) as a comprehensive evaluation of NETD and response time, the optimized structure can be improved by up to 40% over the original structure.

Fixed-pattern noise model for filters in uncooled infrared focal plane array imaging optical paths

In recent years, uncooled infrared focal plane arrays (IRFPAs) have gained importance in the field of industrial gas leak detection; however, their applications often require the inclusion of narrow-band filters in the infrared objective lenses to limit the range of incident radiation, which, in turn, produces fixed-pattern noise that affects imaging quality. To this end, this study investigates the fixed-pattern noise model of uncooled IRFPA imaging considering the influence of filters and adopts the theory of the radiation conversion angle coefficient to establish a model of the fixed-pattern noise distribution formed by the filter’s, reflected, and stray radiations from the optical path environment on the IRFPA surface. Theoretical analysis and test results demonstrate that both results are basically consistent. Notably, the results of this study have a guiding meaning for the gas leak uncooled infrared imaging detection system for targeted non-uniformity correction, and have application value for improving the detection efficiency of the detection system.

A Time-Efficient Self-Test Method for Evaluating Thermal Parameters of Uncooled Infrared Detectors

Uncooled infrared (IR) detectors are widely used in industry and civil imaging fields. Moreover, thermal parameters have a strong impact on detectors’ performance, especially under the trend towards higher spatial resolution. Therefore, evaluating them is important for detectors improvement. In this work, inspired by the traditional optical frequency-domain concept, a self-test method for evaluating thermal parameters of an uncooled IR focal plane array (FPA) is proposed. Utilizing a frequency-adjustable pulsed Joule heating power stimulus, the relationship between the Joule heating power, pixels’ thermal parameters, and pixels’ response voltage was firstly analyzed and established. This method was validated experimentally using a 3 × 3 format diode-based detector. For comparison, an experiment applying the steady-state method was also conducted. The results of all experiments were in good mutual agreement, demonstrating the reliability of the proposed method. For a 1280 × 1024 format FPA, the steady-state method needs approximately 90 h to finish measurements, while the proposed method requires only 5 min, illustrating that the proposed self-test method could considerably reduce the thermal parameter testing time for large-scale uncooled IR FPA.

Uncooled infrared focal plane arrays

After a long incubation period, commercialization of uncooled infrared focal plane arrays (IRFPAs) is progressing rapidly. In the high‐end field, pixel pitch reduction is approaching the diffraction limit of optics, and full high‐definition IRFPAs have been reported. On the other hand, low‐cost infrared array sensors (IRASs), which are small‐format IRFPAs for non‐imaging applications, are finding new applications in areas such as home appliances. This paper reviews the basics of and advances in uncooled IRFPAs, including IRASs. Some emerging trends in business and applications are also discussed.

Uncooled Focal Plane Array for Multiband IR Imaging Using Optical-Readout Bimaterial Cantilevers

This paper presents the design, fabrication, and performance of a 256 × 256 multiband infrared (IR) focal plane array (FPA) using microbimaterial cantilever as the sensitive pixel. Different from traditional uncooled IR FPA that works only at long wavelength IR, the working bandwidth of the presented FPA is extended to full band IR, covering the three IR atmospheric windows of 1-2.5 μm, 3-5 μm and 8-14 μm simultaneously. The multiband performance is attributed to the elaborately designed multiband absorber consisting of a stacked layer of silicon nitride, chromium nanofilm, and gold mirror. The absorbing mechanism of the stacked layer is discussed in detail and testified by experimental results. Images of short-wavelength, middle-wavelength, and long-wavelength IR were captured successfully with the single FPA. The measured sensitivity and noise equivalent temperature difference of the FPA are 0.18 μm/K and 194.7 mK, respectively.

A High Resolution Single Slope ADC with Low Operation Speed for Uncooled Infrared Focal Plane Array

Due to the advantages of the uncooled infrared focal plane array (UIFPA), it is widely used in various fields. To achieve more vivid image, the dimensions of infrared focal plane array need to be enlarged. Hence the high speed analog to digital converter (ADC) integrated on-chip needs to obtain the digital infrared imaging signal. We propose a new single slope ADC with half-period counter and two ramp generators to realize the high resolution digitizing, which can operate at much lower speed. The operation speed of this proposed single slope ADC can be decreased to the 25% of the conventional structure while the static characteristics are still good.

Uncooled infrared detectors toward smaller pixel pitch with newly proposed pixel structure

An uncooled infrared (IR) focal plane array (FPA) with 23.5 μm pixel pitch has been successfully demonstrated and has found wide commercial applications in the areas of thermography, security cameras, and other applications. One of the key issues for uncooled IRFPA technology is to shrink the pixel pitch because the size of the pixel pitch determines the overall size of the FPA, which, in turn, determines the cost of the IR camera products. This paper proposes an innovative pixel structure with a diaphragm and beams placed in different levels to realize an uncooled IRFPA with smaller pixel pitch (≦17 μm ). The upper level consists of a diaphragm with VO x bolometer and IR absorber layers, while the lower level consists of the two beams, which are designed to be placed on the adjacent pixels. The test devices of this pixel design with 12, 15, and 17 μm pitch have been fabricated on the Si read-out integrated circuit (ROIC) of quarter video graphics array (QVGA) (320×240 ) with 23.5 μm pitch. Their performances are nearly equal to those of the IRFPA with 23.5 μm pitch. For example, a noise equivalent temperature difference of 12 μm pixel is 63.1 mK for F/1 optics with the thermal time constant of 14.5 ms. Then, the proposed structure is shown to be effective for the existing IRFPA with 23.5 μm pitch because of the improvements in IR sensitivity. Furthermore, the advanced pixel structure that has the beams composed of two levels are demonstrated to be realizable.

Adaptive bias voltage driving technique of uncooled infrared focal plane array

In order to have the ability of detecting the infrared scene with different temperature range, the bias voltage of uncooled infrared focal plane array (IRFPA) is usually fixed. While, under this condition two situations may occur. One is that the dynamic range of the scene is far bigger than IRFPA, and then the response of IRFPA is not the real scene gray. The response of IRFPA at some scene temperature may be cut off. The other is that the dynamic range of the scene is far smaller than IRFPA, and then most response dynamic range is wasted which reduces the ability of distinguishing details. In order to solve this problem, we brought forward the adaptive bias voltage driving technique of uncooled IRFPA in this manuscript. We computed the real scene temperature range according to the response of IRFPA and current bias voltage, set the adjustable threshold of bias voltage and computed the matching bias voltage. Adopting the technique, we can guarantee that the response dynamic range is accordant with the real scene continuously. The theory derivation and experiment demonstrate that the technique is effective in making the scene temperature dynamic rang and response dynamic range of IRFPA be consistent. And the technique can increase the IR image detai1 resolution by a big margin.

Design and analysis of a high fill-factor SOI diode uncooled infrared focal plane array

A new concept for uncooled infrared (IR) imaging with a high fill-factor SOI diode structure has been proposed. This approach has the potential of reaching a noise equivalent temperature difference (NETD) in the milli-Kelvin range. This detector makes the IR absorbing structure cover almost the entire pixel area, in which the fill factor can reach 80%. Using the multilever structure, thermal isolation can be independently optimized without sacrificing the IR absorption area. The analysis shows that this high fill-factor SOI diode uncooled IR focal plane array can be made without failure of structure breakdown or buckling. The design shows that the sensitivity is of 7.75 × 10−3 V K−1, and the NETD is of 42 mK (f/1.0, 30Hz) which can be achieved in a 35 µm × 35 µm micromachined structure.

Design, Fabrication, and Characterization of a 240 $ \times$ 240 MEMS Uncooled Infrared Focal Plane Array With 42-$\mu \hbox{m}$ Pitch Pixels

We report a significant step in the design, fabrication, and performance evaluation of a 240 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\times$</tex></formula> 240 microelectromechanical system uncooled infrared (IR) focal plane array (FPA) with 42- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> pitch pixels. An improved analytical model has been developed to optimize the design. The optimal key parameters have been verified through experiments, including thermal transmission efficiency, thermomechanical sensitivity, thermal sensitivity, and response time. Compared with our previous work, the number of the fabricated FPA's pixels is increased by 125% and the corresponding pixel's area is decreased by 51%. Furthermore, our FPA has a good sensitivity with a noise equivalent temperature difference of about 373 mK, thus providing an extension of state-of-the-art IR FPA and practical information for future applications. <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hfill$</tex></formula> [2012-0226]

Stripe nonuniformity correction based on registration for infrared-focal plane arrays

Stripe nonuniformity is a very typical fixed pattern noise in line infrared focal plane arrays(IR-FPA) and uncooled staring IR-FPA.Its origination was analyzed.A stripe nonuniformity correction algorithm based on brightness constancy assumption and registration was proposed.Brightness mean-square error function was obtained according to adjacent frames.Nonuniformity correction parameters could be derived through the unique global optimum by minimizing the function.Experimental results indicate that the proposed algorithm could achieve a great convergence in several frames with low computational complexity and enhance the effective of stripe nonuniformity correction.

Deposition and Characterization of Pyroelectric PMN-PT Thin Films for Uncooled Infrared Focal Plane Arrays

Modern uncooled infrared focal plane arrays (UFPA) development is oriented toward silicon microstructure monolithic arrays by employing pyroelectric thin films with continuing trends in high performance and miniaturization. In order to exploit high performance pyroelectric thin films, (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3(PMN-PT) thin films withx= 0.26 were deposited on LaNiO3/Si substrates by the radio-frequency magnetron sputtering technique. (110) preferred orientation thin films with pure perovskite structures were obtained at a substrate temperature of 500°C. The ferroelectric, dielectric and pyroelectric properties of the films were investigated. The films show a typical polarization – electric filed hysteresis loop with a large remnant polarization of 17.2 μC/cm2. At room temperature, the high pyroelectric coefficient of 3.1 × 10-4C/m2K together with low dielectric constant of 470 and loss tangent of 0.04 render the film promising for uncooled infrared device applications. The origin of the differences in electrical properties between the films and bulk materials has also been discussed.

Theoretical analysis and experimental application of CDS CMOS integrated circuit for uncooled infrared focal plane arrays

In this paper, a typical correlated double sampling (CDS) complementary metal oxide semiconductor (CMOS) circuit for uncooled infrared focal plane array (IRFPA) is theoretically analyzed, the key factor of CDS CMOS integrated circuit is pointed out, and a new CDS integrated circuit which is high correlative for low-frequency noise is applied in an experimental readout chip for uncooled IRFPA. Theoretical analysis indicates that the sample transfer function of a noise source acted on by CDS processing is related to noise frequency and sampling time interval and the key factor of CDS circuit for reducing or eliminating noise in readout integrated circuit is the sampling time interval. The experimental readout chip with high noise-correlative CDS integrated circuit is fabricated to verify the theoretical analysis, which can be applied to uncooled IRFPAs.

Correction method for stripe nonuniformity

Stripe nonuniformity is very typical in line infrared focal plane arrays (IR-FPA) and uncooled staring IR-FPA. In this paper, the mechanism of the stripe nonuniformity is analyzed, and the gray-scale co-occurrence matrix theory and optimization theory are studied. Through these efforts, the stripe nonuniformity correction problem is translated into the optimization problem. The goal of the optimization is to find the minimal energy of the image's line gradient. After solving the constrained nonlinear optimization equation, the parameters of the stripe nonuniformity correction are obtained and the stripe nonuniformity correction is achieved. The experiments indicate that this algorithm is effective and efficient.

Low temperature growth and laser-induced phase transformation of perovskite oxide films for uncooled IR detector applications

AbstractPyroelectric infrared (IR) detectors based on perovskite oxides are of interest in part because of their lack of need for cooling, which makes them relatively more affordable and operationally simpler than cooled photon detector systems. We are investigating two methods for low-cost growth of perovskite oxide thin films, namely, a bio-inspired, low-temperature synthesis method and a modified industry-standard metalorganic solution deposition (MOSD) method. Subsequent to film synthesis, we utilize direct-write laser phase conversion and micro-electro-mechanical systems (MEMS) fabrication for development of an uncooled IR focal plane array (FPA). Film growth, crystallization and MEMS processes are compatible with monolithic integration of the detector pixels directly onto Si readout integrated circuits (ROICs).

APPLICATION OF ELECTROLESS Ni PLATING IN INFRARED FPA FABRICATION

Electroless nickel plating(ENP) is introduced to realize interconnection for a photosensitive array and CMOS read-out circuit(ROIC) in uncooled infrared focal plane array(UIRFPA) fabrication process.It has advantages of selective deposition and no requirement for external current source supply.The effective interconnection pencent can be over 85% by using this technology for 32×32 UIRFPA fabrication process.The method is certified as a simple,low cost and reliable method for interconnection between IRFPA and ROIC.

FABRICATION AND CHARACTERISTICS OF Pb DOPED BST FERROELECTRIC THIN FILMS FOR UNCOOLED INFRARED FOCAL PLANE ARRAYS

ABSTRACT (Ba1-xSrx)TiO3 (BST) ferroelectric thin films with Pb doped from 1 to 10 mol % were fabricated on Pt/Ti/SiO2/Si substrates by sol-gel technique in order to improve the crystallographic properties and decrease the ferroelectric relaxation and the diffuse phase transition. The microstructures, surface morphology, dielectric properties, and ferroelectric properties of BST thin films were studied. The Pb doping increased the BST grain size, lowered the diffusion phase transition, and narrowed the diffuse phase region of BST thin films. We found that 5 mol% Pb doped (Ba0.8Sr0.2)TiO3 thin films show a strong preferential orientation of crystallites in (110), excellent ferroelectric properties, the better crystallographic properties, and low loss tangent, which is basically suitable for the detecting materials of uncooled infrared focal plane arrays (UFPAs). The 5 mol% Pb doped BST thin films with dielectric constant of 402, loss tangent of 0.011, remanent polarization of 3.8 μCcm−2, a coercive field of 45 kVcm−1 have been fabricated by using sol-gel process.

Failure analysis of uncooled infrared focal plane array under a high-g inertial load

This paper describes the failure analysis of an uncooled infrared focal plane array (IRFPA) under a high-g inertial load system using finite element simulation and experimental validation methods. The uncooled IRFPA, responding to a source of infrared (IR) radiation with spectral range from 8 µm to 14 µm, is a cantilever array, which consists of two materials with mismatched thermal expansion coefficients. The radiance distribution of the IR source could be obtained by measuring the thermal–mechanical rotation angle distribution of every pixel in the cantilever array using a visible optical readout method. Based on this principle, room-temperature infrared imaging was developed under a static gravity environment, as described in our previous paper (Li C et al 2006 Meas. Sci. Technol. 17 1981–6). But under a dynamic inertial load, the rotation angle of every pixel includes not only the thermal–mechanical part but also a part induced by the inertial load. In the elastic deformation range, with a linearly increasing acceleration, the deformation angle induced by the inertial load increases linearly, which is validated by finite element simulation. This linear change in deformation, which can be subtracted from the total rotation angle in the optical readout using certain arithmetic, will not influence the imaging result. It is noteworthy that failure stress will occur when the deformation angle induced by the inertial load moves into the plastic deformation range, and the optical readout cannot image the IR object. Through finite element simulation the critical load resulting in IRFPA failure is 2715g, and this can be validated through impact using a Hopkinson bar after the IRFPA is placed in vacuum. By finite element simulation, the initial IRFPA surface profile without IR radiance after the 2715g load showed a conicoid characteristic. Simulation of the failure analysis of the uncooled IRFPA under 2715g acceleration predicts the military application of IRFPAs for an uncooled infrared imaging system in the high-g tactical range.

New thermally isolated pixel structure for high-resolution &lt;inline-formula&gt;&lt;math altimg="none" display="inline" overflow="scroll"&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mn&gt;640&lt;/mn&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;mn&gt;480&lt;/mn&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/inline-formula&gt; uncooled infrared focal plane arrays

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.

Crystallization behavior and ferroelectric properties of PbTiO3/Ba0.85Sr0.15TiO3/PbTiO3 sandwich thin film on Pt/Ti/SiO2/Si substrates

A PbTiO3/Ba0.85Sr0.15TiO3/PbTiO3 (PT/BST15/PT) sandwich thin film has been prepared on Pt/Ti/SiO2/Si substrates by an improved sol-gel technique. It is found that such films under rapid thermal annealing at 700°C crystallize more favorably with the addition of a PbTiO3 layer. They possess a pure, perovskite-phase structure with a random orientation. The polarization-electric field (P-E) hysteresis loop and current-voltage (I-V) characteristic curves reveal that a PT/BST15/PT film exhibits good ferroelectricity at room temperature. However, no sharp peak, only a weak maximum, is observed in the curves of the dielectric constant versus temperature. The dielectric constant, loss tangent, leakage current density at 20 kV/cm, remnant polarization, and coercive field of the PT/BST15/PT film are 438, 0.025, 1.3 × 10−6 Acm−2, 2.46 µCcm−2, and 41 kVcm−1, respectively, at 25°C and 10 kHz. The PT/BST15/PT film is a candidate material for high sensitivity elements for uncooled, infrared, focal plane arrays (UFPAs) to be used at near ambient temperature.