IR Imaging Sensor Research Articles

35‐4: Invited Paper: Next Generation Eye‐tracking Technology for AR/VR Devices

Wearable eye‐tracking technology is an essential component in AR/VR devices. Conventional Pupil‐Corneal Reflection (PCR) eye‐tracking technology often presents challenges due to high costs and bulky designs, particularly for compact AR and smart glasses. To overcome these limitations, our next‐generation eyetracking technology relies on AI image analysis, significantly reducing the number of required IR LEDs and image sensors. This simplification enhances flexibility and lowers production costs while maintaining accuracy. Our breakthrough solution makes eye tracking more accessible for the masses in AR/VR devices in the new era of spatial computing and the metaverse.

Highly Efficient Top‐Emitting Infrared‐to‐Visible Up‐Conversion Device Enabled by Microcavity Effect

AbstractInfrared (IR)‐to‐visible up‐conversion device allows a low‐cost, pixel‐free IR imaging over the conventional expensive compound semiconductor‐based IR image sensors. However, the external quantum efficiency has been low due to the integration of an IR photodetector and a light‐emitting diode (LED). Herein, by inducing a strong micro‐cavity effect, a highly efficient top‐emitting IR‐to‐visible up‐conversion device is demonstrated where PbS quantum dots IR‐absorbing layer is integrated with a phosphorescent organic LED. By optimizing the optical cavity length between indium tin oxide (ITO)/thin Ag/ITO anode and semi‐transparent Mg:Ag top cathode, the up‐conversion device yields 15.7% of photon‐to‐photon conversion efficiency from the top‐emission. The high efficiency can be achieved under a low IR transmission through the semi‐reflective anode. Finally, pixel‐free IR imaging is demonstrated using the up‐conversion device, boosting the effect of micro‐cavity on the brightness and the contrast of an IR image.

Carrier density modulation and photocarrier transportation of graphene/InSb heterojunction middle-wavelength infrared photodetectors

The photoresponse mechanism of graphene/InSb heterojunction middle-wavelength infrared (MWIR) photodetectors was investigated. The devices comprised a graphene/InSb heterojunction as a carrier-injection region and an insulator region of graphene on tetraethyl orthosilicate (TEOS) for photogating. The MWIR photoresponse was significantly amplified with an increase in the graphene/TEOS cross-sectional area by covering the entire detector with graphene. The graphene-channel dependence of the MWIR photoresponse indicated that the graphene carrier density was modulated by photocarrier accumulation at the TEOS/InSb boundary, resulting in photogating. The dark current of the devices was suppressed by a decrease in the graphene/InSb carrier-injection region and the formation of the heterojunction using an n-type InSb substrate. The results indicate that photocarrier transportation was dominated by the formation of a Schottky barrier at the interface of the graphene/InSb heterojunction and a Fermi-level shift under bias application. The high-responsivity and low-dark-current photoresponse mechanism was attributed to the graphene/InSb heterojunction diode behavior and the photogating effect. The devices combining the aforementioned features had a noise equivalent power of 0.43 pW / Hz1/2. The results obtained in our study will contribute to the development of high-performance graphene-based IR image sensors.

Photogating for small high-responsivity graphene middle-wavelength infrared photodetectors

We demonstrated a middle-wavelength infrared (MWIR) graphene photodetector using the photogating effect. This effect was induced by photosensitizers situated around a graphene channel that coupled incident light and generated a large electrical charge. The graphene-based MWIR photodetector consisted of a top graphene channel, source–drain electrodes, an insulator layer, and a photosensitizer, and its photoresponse characteristics were determined by current measurements. Irradiation of the graphene channel of the vacuum cooled device by an MWIR laser generated a clear photoresponse, as evidenced by modulation of the output current during irradiation. The MWIR photoresponse with the photogating effect was 100 times greater than that obtained from conventional graphene photodetectors without the photogating effect. The device maintained its MWIR photoresponse at temperatures up to 150 K. The effect of the graphene channel size on the responsivity was evaluated to assess the feasibility of reducing the photodetector area, and decreasing the channel area from 100 to 25 μm2 improved the responsivity from 61.7 to 321.0 AW − 1. The results obtained in our study will contribute to the development of high-performance graphene-based IR imaging sensors.

Electrical transport properties of sensitized PbSe thin films for IR imaging sensors

Electrical transport properties of sensitized PbSe thin films for IR imaging applications were investigated. PbSe thin films were deposited by Chemical Bath Deposition (CBD) method. To sensitize the film, oxidation at 460 °C and iodization at 350 °C were performed successively. As-grown PbSe thin films showed p-type conduction due to Se-rich condition with carrier concentrations, mobility of and electrical resistivity of PbSe thin film after oxidation, the carrier density, mobility and resistivity values were and However, the carrier type was still p-type after oxidation. After sensitization (oxidation and iodization), PbSe thin film showed p-type behavior with carrier concentration of mobility of and resistivity of Iodine-rich PbI2 phase is formed on the top part of the film after iodization. Therefore, this I-rich PbI2 phase still generates p-type conduction without any carrier inversion. A PbI2/PbSe thin film structure showed pp isotype heterojunction characteristics after sensitization. No photoluminescence (PL) signal was observed from as grown thin films and oxidized PbSe thin film showed a peak at 285 meV. After sensitization, a significantly intense IR fluorescence peak from the band gap at 291 meV was observed. The peak height from sensitized PbSe thin film is 12 times higher than that of oxidized PbSe possibly the recombination of photo-generated electron-hole pairs was effectively suppressed. In addition, dark current as a function of temperature in as-grown, oxidized and sensitized PbSe was investigated and results showed the grain boundary activation energy values of 31 meV, 57 meV and 96 meV respectively, which may act as a sensitizing center for electron trapping. In summary, electrical properties data for as grown, oxidized and sensitized PbSe thin films are presented and temperature dependence studies indicates electron trapping mechanism for photoconductivity.

A Thermal Infrared Face Database With Facial Landmarks and Emotion Labels

Thermal infrared imaging is an emerging modality that has gained increasing interest in recent years, mostly due to technical advances resulting in the availability of affordable microbolometer-based IR imaging sensors. However, while sensors are widely available, algorithms for thermal image processing still lack robustness and accuracy when compared to their RGB counterparts. Current methods developed for RGB data make use of machine learning algorithms that require large amounts of labeled images which are currently not available for the thermal domain. In this paper, we address the question whether providing a large number of labeled images would allow the application of current image processing methods on the example of solving challenging face analysis tasks. We introduce a high-resolution thermal facial image database with extensive manual annotations and explore how it can be used to adapt methods from the visual domain for infrared images. In addition, we extend existing approaches for infrared landmark detection with a head pose estimation for improved robustness and analyze the performance of a deep learning method on this task. An evaluation of algorithm performance shows that learning algorithms either outperform available solutions or allow completely new applications that could previously not be addressed. As a conclusion, we prove that investing the effort into acquiring appropriate training data and adapting competitive algorithms is not only a viable approach in analysing thermal infrared images but can also allow outperforming specific task-designed solutions. The database is freely available for academic use at https://github.com/marcinkopaczka/thermalfaceproject .

The performance analysis of three-dimensional track-before-detect algorithm based on Fisher-Tippett-Gnedenko theorem

The dim moving target tracking from the infrared image sequence in the presence of high clutter and noise has been recently under intensive investigation. The track-before-detect (TBD) algorithm processing the image sequence over a number of frames before decisions on the target track and existence is known to be especially attractive in very low SNR environments (⩽3dB). In this paper, we shortly present a three-dimensional (3-D) TBD with dynamic programming (TBD-DP) algorithm using multiple IR image sensors. Since traditional two-dimensional TBD algorithm cannot track and detect the along the viewing direction, we use 3-D TBD with multiple sensors and also strictly analyze the detection performance (false alarm and detection probabilities) based on Fisher-Tippett-Gnedenko theorem. The 3-D TBD-DP algorithm which does not require a separate image registration step uses the pixel intensity values jointly read off from multiple image frames to compute the merit function required in the DP process. Therefore, we also establish the relationship between the pixel coordinates of image frame and the reference coordinates.

Substrate temperature dependent bolometric properties of TiO2−x films for infrared image sensor applications

In this study, we investigated the substrate temperature (TS) dependent bolometric properties on TiO2−x films for infrared image sensor applications. The film crystallinity was changed from amorphous to rutile phase with increasing the TS. The decrement of resistivity with temperature in TiO2−x test-devices confirms the typical semiconducting property. All the test pattern devices have linear I-V characteristic performance which infers that the ohmic contact was well formed at the interface between the TiO2−x and the Ti electrode. The resistivity, activation energy (Ea) and the temperature coefficient of resistance (TCR) values of the device samples were decreased up to 200°C of TS. The sample deposited at 200°C had a significantly low 1/f noise parameter and a high universal bolometric parameter (β). However, at the substrate temperature of 250°C, the Ea, TCR and the 1/f noise values were increased due to increase of the resistivity. The TCR and the 1/f noise values are proportional to the resistivity of TiO2−x films. As a result, the low resistivity of TiO2−x sample deposited at 200°C is a viable bolometric material for uncooled IR image sensors.

Research on Detection of Transmission Line Porcelain Insulator Based on Infrared Technology

With the continuous development of infrared technology, infrared-based detection and diagnosis technology has become a new modern power equipment detection technology. Based on infrared technology, this paper proposed detection and diagnosis method of the transmission line porcelain insulators, including analysis on detection theory of IR imaging sensor, and infrared imaging map introduction. Through establishing porcelain insulator circuit calculation model, computing heating power of trouble insulators, this paper minutely analyzed the heating causes of trouble insulators. The paper provided a reference to the detection of transmission line porcelain insulators, which made it an important measure to ensure the safety and economic operation of electrical equipment.

고감도 적외선 이미지 센서 적용을 위한 금속-유전체 복합 박막의 광전자 특성

고감도 적외선 이미지 센서에 적용이 가능한 우수한 TCR(temperature coefficient of resistance) 값을 갖고 적외선 파장영역에서 흡수 특성을 갖는 막 형성을 위해, 본 연구에서는 Silica와 Titanium 분말을 혼합비율을 달리하여 준비한 후 열 기상 증착기를 이용하여 상온에서 게르마늄과 유리 기판 위에 각각 <TEX>$(SiO_2)_x-(Ti)_y$</TEX> 막을 제작하였다. 챔버 내에 위치한 혼합분말이 담겨진 텅스텐 보트와 기판 간의 거리는 15.5 cm이며, 사용된 <TEX>$SiO_2$</TEX>와 Ti 분말의 혼합비율 x : y는 각각 90 : 10,80 : 20, 70 : 30, 60 : 40이다. <TEX>$(SiO_2)_x-(Ti)_y$</TEX> 막의 전기적 저항은 273~333 K 영역에서 온도 변화에 따라 측정하였으며, TCR 값은 측정된 막의 저항 값으로부터 계산되었다. 다양한 혼합비율 조건 하에서 형성된 <TEX>$(SiO_2)_x-(Ti)_y$</TEX> 막은 수 <TEX>$k{\Omega}$</TEX>~수백 의 <TEX>$k{\Omega}$</TEX> 저항특성을 보였으며, 이러한 막의 TCR은 <TEX>$-1.4{\sim}-2.6%K^{-1}$</TEX>의 다양한 값을 나타내었다. High sensitivity IR image sensors require materials characteristics with temperature coefficient of resistance (TCR) and IR range absorption. In this study, the metal-dielectric thermo sensitive films (MDTF) based on <TEX>$(SiO_2)_x-(Ti)_y$</TEX> composition were deposited on substrates of germanium and glass by thermal evaporator. The <TEX>$SiO_2$</TEX> : Ti mixture was made from the ratio of 9 : 1, 8 : 2, 7 : 3, 6 : 4, respectively. <TEX>$(SiO_2)_x-(Ti)_y$</TEX> mixture powder was loaded on tungsten boat in evaporator and was 15.5 cm from the substrate. Resistance of <TEX>$(SiO_2)_x-(Ti)_y$</TEX> in the range of 273~333K were measured as a function of temperature. Temperature coefficient of resistance (TCR) was calculated by the resistance variation. Under the various mixture ratios condition, it is possible to obtain <TEX>$SiO_2$</TEX>-Ti layers with resistance from units kilo-ohm to hundreds kilo-ohm. Finally, our results showed that Temperature coefficient of resistance (TCR) of these films varies from -1.4 to <TEX>$-2.6%K^{-1}$</TEX>.

FT-IR Image Processing Algorithms for In-Plane Orientation Function and Azimuth Angle of Uniaxially Drawn Polyethylene Composite Film

The FT-IR imaging method has been applied to acquire thousands of infrared spectra at a spatial resolution near the diffraction limit using an IR image sensor. We propose the mathematical procedure to visualize the degree of molecular orientation and the azimuth angle of the orientation axis using the polarized absorbance images measured with a linear polarizer settled at four different angles. It mathematically synthesizes in-plane orientation function that is independent of the direction of the incident polarization and visualizes the molecular orientation and the azimuth angle using an IR imaging sensor. By introducing the azimuth angle image, a small change of the molecular orientation can be detected visually in the early stage of local deformation of the uniaxially drawn process of the polyethylene composite film.

A New CMOS Read-out IC for Uncooled Microbolometer Infrared Image Sensor

An uncooled microbolometer image sensor, used in an IR image sensor, is made by a micro electro mechanical systems (MEMS) process, so the value of the microbolometer resistor has a process variation. Also, the reference resistor, which is used to connect to the microbolometer, is fabricated by a standard CMOS process, and the difference between the values of the microbolometer resistor and the reference resistor generates an unwanted output signal for the same input from the sensor array. In order to minimize this problem, a new CMOS read-out integrated circuit (ROIC) was designed. Instead of a single input mode, a differential input mode scheme and a simple method to compensate the resistor value are proposed. Using results from a computer simulation, it is observed that the output characteristic of the ROIC was improved and the effect of the process variation was decreased without using complex compensation circuits. Based on the simulation results, a prototype device including an ROIC that was fabricated by a standard 0.25um CMOS process and a microbolometer with a 16 x 16 sensor array was fabricated and characterized.

Solution-Processed Infrared Optoelectronics: Photovoltaics, Sensors, and Sources

The fabrication of optoelectronic devices via spin-coating onto an arbitrary substrate offers ease of integration, low cost, and physical flexibility. Reports of active optoelectronic devices operating in the IR, and made via solution-processing, emerged in the early 2000s. Here, we review progress in IR solar cells, image sensors, and optical sources based on solution-processed materials. The latest solution-processed photovoltaics (PV) now provide 4.2% power conversion efficiencies in the IR, placing them a factor of 3 away from enabling a doubling in overall solar power conversion efficiency of today's best visible-wavelength solution-processed PV. The best solution-processed photodetectors now provide sensitivities in the 1013 Jones D* range, exceeding the sensitivity of the best epitaxially grown short-wavelength infrared photodetectors. Infrared optical sources, both broadband light-emitting diodes and, more recently, lasers, have now also been reported at 1.5 mum. We review the progress and future prospects of this rapidly advancing field.

14.4: Integrating Multi‐Touch Function with a Large‐Sized LCD

AbstractMulti‐touch function is integrated with a 52″ LCM. IR image sensors detect touches around normal panel. A few IR image sensors are placed to detect touches. Triangulation, image processing technology and pattern recognition are used for touch algorithm. Positions of touch points are calculated simultaneously by using IR image sensors, IR light sources and a LCD panel. The number of touches and its area is used to perform multi‐touch functions. Multi‐touch LCD can also detect human gestures. At this work, map searching program is used for touch and gesture recognition. As a result, multi‐touch LCD shows its usefulness and it can replace conventional HCI device (mouse, keyboard).

A Readout IC Design for the FPN Reduction of the Bolometer in an IR Image Sensor

In this paper, we propose and discuss the design using a simple method that reduces the fixed pattern noise(FPN) generated on the amorphous Si(<TEX>$\alpha-Si$</TEX>) bolometer. This method is applicable to an IR image sensor. This method can also minimize the size of the reference resistor in the readout integrated circuit(ROIC) which processes the signal of an IR image sensor. By connecting four bolometer cells in parallel and averaging the resistances of the bolometer cells, the fixed pattern noise generated in the bolometer cell due to process variations is remarkably reduced. Moreover an <TEX>$\alpha-Si$</TEX> bolometer cell, which is made by a MEMS process, has a large resistance value to guarantee an accurate resistance value. This makes the reference resistor be large. In the proposed cell structure, because the bolometer cells connected in parallel have a quarter of the original bolometer's resistance, a reference resistor, which is made by poly-Si in a CMOS process chip, is implemented to be the size of a quarter. We designed a ROIC with the proposed cell structure and implemented the circuit using a 0.35 um CMOS process.

Synthetic aperture radar target acquisition model based on a National Imagery Interpretability Rating Scale to probability of discrimination conversion

Previous efforts have established models that relate IR and visible imaging sensor design and operating parameter values to measures of information extraction performance. The surveillance and reconnaissance community predicts National Imagery Interpretability Rating Scale (NIIRS) values using the general image quality equation (GIQE). The target acquisition community predicts probabilities of discrimination (detection, recognition, identification) using various minimum resolvable contrast/minimum resolvable temperature (MRC/MRT) models, and methods have been developed to link the two sets of predictions. No such models currently exist for the radar domain, although a radar NIIRS has been developed. We provide a basis for initial estimates of synthetic aperture radar (SAR) target acquisition performance. First, a conversion from radar to IR (and visible) NIIRS is provided. The IR NIIRS is then converted to probabilities of discrimination values. The two conversions together provide rough estimates of SAR target acquisition performance as a function of radar NIIRS values.

Passive polarimetric IR target classification

Automatic detection and recognition of targets by means of passive IR sensors suffer from limitations due to lack of sufficient contrast between the targets and, their backgrounds and among the facets of a target. A set of novel algorithms is designed and tested that uses the target and background Stokes parameters for detection, segmentation, and classification of targets, In these algorithms, it is assumed that for each pixel in the image data three of the four Stokes parameters are provided. This assumption is justified because we have developed a custom designed Polarimetric IR (PIR) imaging sensor that generates three of the Stokes parameters at each pixel location, in real-time. The empirical performance of the above algorithms, in terms of the probabilities of detection, false alarm rate, segmentation accuracy, and recognition probabilities are computed. The comparison of these results with the results associated with intensity-only imaging sensor (nonpolarimetric IR sensory data) shows that use of polarimetric information can noticeably improve the performance.

Application of a passive polarimetric infrared sensor in improved detection and classification of targets

Automatic detection and recognition of targets by means of passive IR sensors suffer from limitations due to lack of sufficient contrast between the targets and their background, and among the facets of a target. In this paper the results of a suite of polarization-sensitive automatic target detection and recognition algorithms on sets of simulated and real polarimetric IR imagery are presented. A custom designed Polarimetric IR (PIR) imaging sensor is used for collecting real polarimetric target data-three of the four Stokes parameters under a variety of conditions. Then a set of novel algorithms are designed and tested that uses the target and background Stokes parameters for detection, segmentation and classification of targets. The empirical performance results are obtained in terms of the probabilities of detection, false alarm rate, segmentation accuracy, and recognition probabilities as functions of number of pixels on target, aspect and depression angles and under several background conditions (clutter densities) on the polarimetric and non-polarimetrirc data. These results show that a noticeable improvement over the non-polarimetric ATR can be achieved.

Tolerance analysis versus image quality: a case study for cost-effective space optics

Space optical systems generally require near-theoretical performance in hostile environments within size, weight, and cost constraints. We have addressed the challenge of achieving an optimum image quality through a cost-effective tolerance analysis scheme. Two different space optical systems are considered: the UV imager for the International Solar Terrestrial Physics (ISTP) Mission and an afocal telescope for the Advanced Polarized IR Imaging Sensor (APIRIS). These systems are described along with their required performances and designs. A tolerance study is conducted, and the effect of tolerances on image quality and cost is presented.

Monolithic Schottky-barrier infrared image sensor with 71% fill factor

An improved 512 x 512-element PtSi Schottky-barrier IR image sensor (512 x 512 IRCSD) has been developed using the charge sweep device (CSD) readout architecture and 1.2-[mu]m minimum design rules. Finer pattern process technology enhances the advantage of the CSD readout architecture, enlarging the fill factor without sacrificing the saturation signal level. A large fill factor of 71% is achieved in spite of a small pixel size of 26 x 20 [mu]m[sup 2]. At the Schottky-barrier detector reset voltage of 4 V, the differential temperature response with f/1.2 optics at 300 K and saturation signal level were 3.2 [times] 10[sup 4] electrons/K and 2.9 [times] 10[sup 6] electrons, respectively. The noise equivalent temperature difference was estimated as 0.033 K with f/1.2 optics at 300 K. The improved 512 x 512 IRCSD was designed to be operated either in the field or frame integration interlace modes for versatility.