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This work investigates the spectral quantum efficiency and inter-pixel crosstalk of a MWIR-LWIR dual band, HgCdTe-based focal plane array (FPA) photodetector (MWIR and LWIR stand for mid- and long-wavelength infrared bands). Pixels are $\text{10}\,\mu$ m-wide with truncated pyramid geometry and separated by deep trenches. Three-dimensional combined full-wave electromagnetic and electrical simulations in the drift-diffusion approximation allowed to describe the complex, standing-wave-like spectral features resulting from the light interference and diffraction due to the pixels and illuminating beam aperture. The inter-pixel crosstalk for the MWIR operation demonstrated to be very sensitive to the trench depth, in contrast to the LWIR electrooptical response, left almost unchanged. The present work also investigates the causes of performance worsening in the two IR bands when pixel pitch is reduced to $\text{5}\,\mu$ m, hence well below typical LWIR wavelengths and close to the diffraction limited operation.

In this paper, an unequal printed structure is proposed to obtain high quality factor (Q-factor) coil antenna in wireless power transmission system. In the resonance method wireless power transmission, the quality factor is one of the important factors that determine the transmission efficiency. Generally, the quality factor is increased by increasing the size of the resonator, but through the structure presented in this paper, the quality factor can be maximized without changing the size. In addition, this method can improve the low quality factor of the "printed antenna", which was pointed out as a disadvantage. The main idea to achieve high quality factor is a pitch and width that is not constant along the width. The line pitch and width of the printed pattern are gradually increased in proportion with outer diameter. By using this design method, the Q-factor is increased about 21.8% in comparison with conventionally designed antenna. In addition, it can be confirmed that the antenna performance is substantially superior to that of a typical coil antenna if the size conditions are the same.

In this article, we define the technical requirements for a light field display to provide effective depth cues such as binocular disparity, motion parallax, and accommodation at a pixel resolution expected by the eye. These requirements are evaluated with respect to existing technologies (e.g.,integral imaging displays) or expected future ones (e.g., micro-light-emitting diode (LED) displays). Simulation of light field displays are proposed for different display sizes (smartphone, desktop, or TV), resolution per view, and pixel pitch. These simulations convey the main impact of the pixel pitch to reach the light field display goal in terms of depth cue requirements. The last part of the paper focusses on data generation issues: how to generate the necessary amount of views at the display side and what the adapted data formats are for such a purpose. The paper is associated with supplementary videos that will illustrate the view generation topic using a dedicated data format that is optimized for current graphics processing unit (GPU) processors. Video capture of early-stage light field displays will also be provided .

An in-tool, on-wafer detectors’ array for monitoring deep ultraviolet (DUV) light is proposed and demonstrated in this work. The proposed electronic layer detectors array (ELDA) features FinFET CMOS compatibility and compact pixel structure. Its minimum pixel pitch can reach 0.7 $\mu \text{m}$ , enabling the realization of high spatial resolution array. Most importantly, the sensing results from DUV exposure can be stored in the in-pixel storage node for days without external power supply, providing offline electrical nondestructive measurement and readout.

This article presents a 64 $\times $ 64 indirect time-of-flight (iToF) image sensor with a depth range of 50 m, integrated into a 1P4M 110-nm CMOS process. The sensor is based on a single-photon avalanche diode (SPAD), the range-dependent phase delay of which is measured by compact analog time-gated pulse counters and then read out by column-parallel single-slope (SS) analog-to-digital converters (ADCs). We present two prototypes of iToF sensors that exploit one- or two-tap counters in the pixel. Compared to the one-tap sensor, the two-tap sensor achieves an improved fill factor of 26.3% with a pixel pitch of 32 $\mu \text {m}$ . This improvement is realized by using a retrograde deep n-well as guard-ring structure and two analog counters whose layout has been optimized. By utilizing two different demodulation frequencies of 1.56 and 50 MHz, the two-tap sensor achieves a large depth range of 50 m with a relative depth uncertainty of 0.22% and a high 3-D frame rate of 65 frames/s. When using an optical bandpass filter and multi-frame accumulation, the sensor shows a tolerance of 120-klx sunlight. Compared with the previous iToF benchmarks, the proposed SPAD-based iToF sensor demonstrates the largest depth range without compromising the relative depth uncertainty.

This paper proposes an organic photodiode (OPD) image sensor based on indium zinc oxide (IZO) thin-film transistors (TFTs). The sensor array has a $256\times256$ pixel format with a $50~\mu \text{m}$ pixel size. The continuous OPD fabricated by the solution process is stacked vertically on the top of the IZO TFT backplane. A measurement system is built based on the readout IC driven by the field programmable gate array (FPGA). It is shown that the optical image can be successfully detected by the sensor array with good clarity and high quality. With a leakage current of the IZO TFT as low as $5\times 10^{\vphantom {D^{l}}-14}$ A and a dark current of OPD as low as $10^{-13}$ A, the total electronic noise is less than 683 e−.

In this letter, we present a small pixel pitch image sensor optimized for high external quantum efficiency in short-wavelength infrared (SWIR). Thin-film photodiodes based on PbS colloidal quantum dot (CQD) absorber allow us to exceed the spectral limitations of silicon’s absorption while maintaining the benefits of CMOS technology. By monolithically integrating PbS CDQ thin films with CMOS readout arrays, high-pixel density SWIR image sensors can be achieved. To overcome the remaining disadvantages of the CQD-based image sensors over their bulk III-V semiconductor counterparts (lower sensitivity and reduced linearity), the thin-film photodiode stack is adapted towards the used readout circuit. A prototype image sensor with a $768\times 512$ resolution of 5- $\mu \text{m}$ pitch pixels is fabricated by using a modified 130 nm CMOS process for readout IC, together with the new CQD thin-film photodiode on top. Thanks to the optimized photodiode stack and co-integration process, the prototype image sensor shows less than 5% linearity error while having 40% external quantum efficiency in SWIR, which enables acquisition of high-quality images.

A monolithic thin film red light emitting diode (LED) active-matrix (AM) micro-display driven by a complementary metal-oxide semiconductor (CMOS) driver is demonstrated. The resolution of the micro-display is $64\times36$ , with a $40\,\,\mu \text{m}\,\,\times 40\,\,\mu \text{m}$ pixel pitch. Starting from AlGaInP epi-layers grown on GaAs substrates, the monolithic red LED array was fabricated and then integrated with the AM driver using Au/In flip-chip bonding technology. After removal of the GaAs substrate, a crack-free thin film micro-display was realized with a high pixel yield. The thin film red LED AM micro-display delivers a luminance of $2.35\times 10^{4}$ cd/m2 at full-load conditions and can render images with 4-bit grayscale. This work not only provides a manufacturing-friendly approach for monolithic thin film red LED micro-displays, but also brings the possibility of hybrid integration with blue/green LEDs to achieve full-color LED micro-displays.

In this study, the feasibility of mini-light-emitting diode (LED) RGB display fabricated by a chip-first fan-out panel-level packaging is investigated. Emphasis is placed on the design, materials, process, fabrication, and reliability of the mini-LED RGB display package on a printed circuit board (PCB). The mini-LEDs under consideration and their sizes are red ( $125 \times 250 \times 100 ~\mu \text{m}$ ), green ( $130 \times 270 \times 100 ~\mu \text{m}$ ), and blue ( $130 \times 270 \times 100 ~\mu \text{m}$ ). The spacing among the RGB mini-LEDs is $80~\mu \text{m}$ , the pixel-to-pixel spacing is also $\sim 80~\mu \text{m}$ , and the pixel pitch is $625~\mu \text{m}$ . The temporary glass panel for making the redistribution layers (RDLs) of the package is $515 \times 510 \times 1.1$ mm in size. To increase the SMT assembly yield on the PCB, the mini-LEDs are grouped into 4( $2 \times 2$ pixels)-in-one surface mount device (SMD), that is, a total of 12 R, B, and G mini-LEDs. A PCB ( $132\,\,mm \times 77$ mm) is designed and fabricated for the drop test of the mini-LED package. Thermal cycling of the mini-LED SMD PCB assembly is also performed by a nonlinear temperature- and time-dependent finite-element simulation.

This article presents a prototype $22.4~\mu \text{m}$ pixel pitch global shutter (GS) wide dynamic range (WDR) soft X-ray CMOS image sensor (sxCMOS). Backside-illuminated (BSI) pinned photodiodes with a 45- $\mu \text{m}$ thick Si substrate were introduced for low noise and high radiation hardness to high energy photons. Two-stage lateral overflow integration capacitor (LOFIC) and voltage domain memory bank with high-density Si trench capacitors were introduced for WDR and for GS. The developed sxCMOS achieved maximum 21.9 Me− full well capacity with a single exposure 129 dB dynamic range by GS operation. Over 70% quantum efficiency (QE) toward soft X-ray was successfully achieved. The developed prototype sxCMOS is a step forward toward a 4 M pixel detector system to be utilized in next-generation synchrotron radiation facilities and X-ray free-electron lasers.

We report on the design and characterization of a monolithic single-photon-counting (SPC) X-ray detector integrating an amorphous semiconductor sensor. Our prototype combines amorphous selenium (a-Se), a well-known photoconductor, with a CMOS readout integrated circuit (ROIC) containing two $26\times196$ arrays of single-energy-threshold pixels. We achieve high spatial resolution for capturing single 60-keV photons by implementing 11.4- $\mu \text{m}$ -pitch pixels and by integrating a 70- $\mu \text{m}$ -thick a-Se sensor on the ROIC. We present experimental SPC results using a mono-energetic 60-keV radioactive source. Our results also suggest that our prototype a-Se/CMOS detector leverages the small-pixel effect (SPE) due to the large ratio of a-Se thickness to pixel pitch. This effect could overcome the slow inherent transient response of a-Se for high count rate X-ray diagnostic applications like mammography.

Currently, we are developing a neutron scintillation detector prototype using silicon photomultipliers (SiPMs) as the photodetector. In order to reconstruct the position of single neutron events to an accuracy better than the pixel pitch of the SiPM, a very accurate photon count is required. Each pixel consists of 3200 microcells, operated in Geiger mode. A cell which is already triggered cannot detect any following photons hitting the cell, until it is recharged. This leads to a nonlinearity in the pixel’s response for a higher photon density impinging across the pixel. Previous studies provided a correction factor to estimate the saturation, by assuming a homogeneous photon distribution density and comparing it to the number of microcells. In our specific application, the photon distribution is not homogeneous, which is why we examined the influence of the homogeneity on the saturation. In this work, we present a case study for difference in nonlinearity effect for an inhomogeneous and homogeneous photon distribution density, given the light intensity is equal. The simulation results suggest that the effect could be higher for an inhomogeneous distribution. Therefore, care must be taken when using the established correction factor for saturation and an analysis of the photon distribution homogeneity is necessary.

CMOS image sensor’s ability to collect light depends, amongst others, on its full well capacity (FWC) which is the capability of a pixel of storing electrons. The FWC can be improved either by expensive and time-consuming process modifications or by increasing the pixel photodiode area. Optimizing the pixel layout is crucial to increase the photodiode area at a given pixel pitch. In this article, we present a novel layout technique that reduces the area occupied by the in-pixel transistors by reorganizing the shared diffusions. Such optimization is demonstrated to increase the area of the photodiode for a given pixel pitch and, hence, the fill factor (FF). Both a mathematical model of the methodology and experimental results of pixels manufactured in a commercially available technology are presented. We prove that the technique is particularly effective for small pixel pitches and can lead to an increase in FF and FWC of at least 20% in a 4-transistor CMOS pixel with 2.4- $\mu \text{m}$ pitch.

The X-ray free-electron lasers that became available during the last decade, like the European XFEL (EuXFEL), place high demands on their instrumentation. Especially at low photon energies below $1\,\text{keV}$, detectors with high sensitivity, and consequently low noise and high quantum efficiency, are required to enable facility users to fully exploit the scientific potential of the photon source. A 1-Megapixel pnCCD detector with a $1024\times 1024$ pixel format has been installed and commissioned for imaging applications at the Nano-Sized Quantum System (NQS) station of the Small Quantum System (SQS) instrument at EuXFEL. The instrument is currently operating in the energy range between $0.5$ and $3\,\text{keV}$ and the NQS station is designed for investigations of the interaction of intense FEL pulses with clusters, nano-particles and small bio-molecules, by combining photo-ion and photo-electron spectroscopy with coherent diffraction imaging techniques. The core of the imaging detector is a pn-type charge coupled device (pnCCD) with a pixel pitch of $75\,\mu\text{m}\times 75\,\mu\text{m}$. Depending on the experimental scenario, the pnCCD enables imaging of single photons thanks to its very low electronic noise of $3$e$^-$ and high quantum efficiency. Here we present an overview on the EuXFEL pnCCD detector and the results from the commissioning and first user operation at the SQS experiment in June 2019. The detailed descriptions of the detector design and capabilities, its implementation at EuXFEL both mechanically and from the controls side as well as important data correction steps aim to provide useful background for users planning and analyzing experiments at EuXFEL and may serve as a benchmark for comparing and planning future endstations at other FELs., Comment: 10 pages, 10 figures, submitted to the Journal of Synchrotron Radiation

We present a monolithic hybrid visible-light imager composed of an amorphous selenium (a-Se) photoconductor thin film integrated on a CMOS active pixel sensor (APS) array readout integrated circuit. We achieve more than 14-dB signal-to-noise ratio under monochromatic light at an illuminance of 0.04 lux in one quadrant of the imager containing $7.8\times 7.8-\mu \,\,\text{m}^{2}$ pixels using a 1.6-s exposure (integration) time without operating the a-Se sensor in avalanche mode. Long integration times are made possible by exploiting the low dark-current of a 20- $\mu \text{m}$ -thick a-Se sensor layer and by implementing dark-current reduction techniques in the APS, such as series stacking reset and protection devices. In addition, use of a relatively thick 20- $\mu \text{m}$ a-Se layer obviates the need for an additional planarization step of the sensing layer as was done with a previously-reported avalanche-mode a-Se/CMOS imager that incorporated a 0.5- $\mu \text{m}$ -thick sensing layer. We also demonstrate an improved APS design, with $7.8\times 8.7-\mu \,\,\text{m}^{2}$ dimensions, containing a programmable in-pixel integration capacitor to provide enhanced full-well capacity (FWC) for a-Se/CMOS imagers. Measured results show that our APS achieves a FWC of approximately 230 ke−, which is comparable to several previously-reported photodiode-based CMOS imagers with extended FWC. Our imager can also resolve an effective object size of approximately $12.5~\mu \text{m}$ , demonstrated through measurement of the modulation transfer function.

This work presents a low noise active pixel sensor. It uses one additional transistor compared to standard 4T pixel to obtain 1/f noise reduction and high conversion gain. 1/f noise is reduced by periodically switching the in-pixel source follower between depletion and inversion. The depletion state is achieved by re-configuring the source follower into a MOS capacitor and depleting the channel by controlling the source-drain terminal. The state change of the in-pixel source follower also enhances the conversion gain. The test chip has a $64 \times 64$ pixel array with a $10~ {\mu }\text{m}$ pixel pitch fabricated in 350 nm AMS process. The measured integrated noise of a pixel in the frequency band 128 Hz to 50 KHz is $728~ {\mu V_{rms}}$ without switching. At a switching frequency of 4 MHz, the integrated noise reduces to $306~ {\mu V_{rms}}$ after switching resulting in a 7.5 dB reduction. The input referred noise is reduced from $26 {e_{rms}^{-}}$ to $7.3 {e_{rms}^{-}}$ after applying switching. When both, switching and conversion gain enhancement are applied, the input referred noise is further reduced to $2.3 {e_{rms}^{-}}$ with an enhanced conversion gain of $398\,\, {\mu V/e^{-}}$ .

Holography is a promising technology for photo-realistic three-dimensional (3D) displays because of its ability to replay the light reflected from an object using a spatial light modulator (SLM). However, the enormous computational requirements for calculating computer-generated holograms (CGHs)—which are displayed on an SLM as a diffraction pattern—are a significant problem for practical uses (e.g., for interactive 3D displays for remote navigation systems). Here, we demonstrate an interactive 3D display system using electro-holography that can operate with a consumer’s CPU. The proposed system integrates an efficient and fast CGH computation algorithm for line-drawn 3D objects with inter-frame differencing, so that the trajectory of a line-drawn object that is handwritten on a drawing tablet can be played back interactively using only the CPU. In this system, we used an SLM with 1,920 $$\times $$ × 1,080 pixels and a pixel pitch of 8 μm × 8 μm, a drawing tablet as an interface, and an Intel Core i9–9900K 3.60 GHz CPU. Numerical and optical experiments using a dataset of handwritten inputs show that the proposed system is capable of reproducing handwritten 3D images in real time with sufficient interactivity and image quality.

Flexible printed circuit boards (FPCB) are widely used in smart devices with high wiring density and light weight. In this paper, the chemical etching process of FPCB with 18 $\mu \text{m}$ line pitch is investigated. A geometric model of the FPCB circuit with the shape of “T” is established and simulated by the finite element method. The time evolution of the etching cavity, concentration field and velocity field of CuCl2 solution are studied, as well as the effects of initial concentrations and inlet velocities on the etching cavity profile. Finally, the FPCB sample with 18 $\mu \text{m}$ line pitch is successfully fabricated by employing process parameters from the etching simulation. The results show that as the increase in the etching cavity, recirculating eddies form at the bottom of the photoresist in the corners of the etching cavity, resulting in more etching on the top sides of sidewalls over time. Higher initial concentration of the etching solution will result in a larger etching cavity profile, but the inlet velocity cannot affect the etching cavity profile significantly. Finally, the effectiveness of the simulation model is verified by comparing the etching cavity profiles with four experiments.

Proximity charge sensing is a novel technique used in the field of radiation detection. This research examines the simulation of a pixelated anode proximity charge-sensing device on CZT semiconductors to evaluate the potential performance of the proximity sensing technique on room-temperature detector materials for imaging purposes. The weighting potentials (WPs), of proximity-sensing and directly deposited electrode pixelated designs, were generated using ANSYS Maxwell, and the best design will be considered for the implementation step in the future. The simulation investigated two features of the proximity design, pixel size and pixel pitch. Three different pixel sizes were used in the simulation designs, 0.5 × 0.5 mm2, 1.0 × 1.0 mm2, and 2.0 × 2.0 mm2. The 0.5 × 0.5 mm2 pixel size had the best WP profile, where the generated signal for one radiation energy did not depend on the interaction location. Pixel pitch was examined using the same pixel size, 1.0 × 1.0 mm2, and varying the pixel pitch from 2.0 mm, 3.0 mm up to 4.0 mm. The results showed that as the pixel pitch increases, the signal crosstalk (charge sharing between pixels) decreases. However, as the pixel pitch increases, the spatial resolution of the imaging system decreases, making it difficult to observe objects smaller in diameter than the pixel pitch. Additionally, proximity charge sensing designs showed better performance in terms of signal crosstalk for the same pixel size and pixel pitch in comparison with directly deposited designs.

Experimental assessment of small pitch cooled infrared focal plane arrays (FPA) modulation transfer function (MTF) is becoming an important issue. Indeed, the pitch approaches the typical carrier diffusion length of minority carriers in the absorber material. Therefore, the MTF is an important figure of merit of those arrays as it may be degraded by lateral diffusion. Moreover, the pitch also approaches the sensed wavelength so direct MTF measurement using optical projections becomes difficult. In this paper, we propose the use of electron beam induced current to experimentally characterize the MTF of small pitch cooled FPAs. Practically, the device is mounted inside a scanning electron microscope onto a cooled sample stage. The diode area is then scanned by the electron beam instead of the optical beam in classical MTF measurement. Because of the very narrow electron beam, the MTF can then be estimated with an excellent precision. First scans of mid-wave 7.5 μm pitch HgCdTe diodes are shown, demonstrating a 55% MTF at the Nyquist frequency, consistent with 3D electro-optical modeling. The relevance of this estimation is also discussed, in comparison with classical projection methods.

We have developed a new certified reference material (CRM) for image sharpness evaluation and magnification calibration for scanning electron microscopy (SEM). Designed to be suitable for the image sharpness evaluation by the derivative method, the CRM has nanoscale tungsten dot-array structure fabricated on silicon substrate, which gives steep contrast transition from the dot to the substrate in SEM image. The pitch of the dot-array was SI-traceably measured as a specified value with relative expanded uncertainty ($k=2$) of ~1.3%, which can be utilized for the magnification calibration of SEM. Since specimens, as one of the image formation parameters, easily affect image sharpness value, our CRM, as a ‘pinned specimen’, will play an important role to achieve robust and stable image sharpness measurement system.

InAs/GaAsSb type-II superlattice (T2SL) materials grown at a higher temperature and lattice-matched to InAs substrates are considered to have significant advantages in long wavelength infrared (LWIR) detection. In this work, an InAs/GaAsSb T2SL LWIR focal plane array (FPA) was fabricated and evaluated. The FPA has a format of $320\times256$ with a pixel pitch of 30 $\mu \text{m}$ and exhibits a 100% cutoff wavelength of 9.5 $\mu \text{m}$ at 80 K. Under a bias of -0.02V, the detectors show a dark current of $1.7\times 10^{-5}$ A/cm2 and a differential resistance-area of $1.5\times 10^{3} \Omega \cdot \text {cm}^{2}$ . The noise equivalent temperature difference and operability of the FPA are 20.7 mK and 99.2% respectively under an integration time of $400~\mu \text{s}$ , a 300 K background and F/2.0 optics. This high-performance FPA further verifies the feasibility of InAs/GaAsSb T2SL in LWIR detection.

This letter presents a device for biasing bolometric infrared imaging sensors to increase the operating temperature range and enhance performance. It addresses the market’s need for uncooled readout circuits that are easier to use. Here, we propose an integrated biasing system capable of managing the bolometric sensor’s high-temperature dependence. We demonstrated that a biasing architecture using thermalized bolometers can automatically offset resistance variations in the active bolometer due to temperature variations of the focal plane array (FPA). Our research concerns a 12- $\mu \text{m}$ pixel pitch QVGA matrix that operates at 50-mK noise equivalent temperature difference (NETD).

This letter presents a CMOS indirect time-of-flight (i-ToF) image sensor, which is based on a single-photon avalanche diode (SPAD) and a compact in-pixel time-gated pulse counter. The proposed SPAD-based i-ToF sensor makes it possible to achieve a time-gated photon counting method at the pixel level and to enlarge a depth range up to 40 m while maintaining the pixel demodulation frequency up to 25 MHz. A prototype sensor is implemented in a 110-nm CMOS process and has a pixel array of $64\times64$ with a pixel pitch of $32~{\mu }\text{m}$ . With a 3-D frame rate of 90 frames/s, the sensor achieves high 3-D image quality with a nonlinearity error below 2.25% and a relative precision error of 0.51% at a maximum distance of 40 m.

The design of photon counting spectral imaging (x-CSI) x-ray detectors involves optimising many parameters including pixel thickness, pitch, and type of charge sharing correction algorithm (CSCA) employed, if any. The optimal value for one parameter depends on the other parameter values, as well as extrinsic variables such as application specific photon fluxes and energies of interest. No analytical approaches currently exist for optimising these parameters simultaneously. This work thus utilised our inhouse simulation framework, combining Monte Carlo and finite element methods to systematically simulate the response of 715 different CdTe based x-CSI detectors, comprising 13 different CSCAs, 5 different pixel thicknesses (1 mm – 3 mm), and 11 different pixel pitches ( $100~\mu \text{m}$ – $600~\mu \text{m}$ ). Detector response to monoenergetic irradiation at 80 keV at 4 different fluxes was assessed using a range of metrics. Due to its complexity, the analysis of this work is divided into several publications, with this one focusing on the effects of pixel pitch and thickness. We were able to identify, and provide mechanistic explanations for, general trends in detector performance with varying pixel geometry that will be of interest to x-CSI detectors designers. Superficially similar spectral metrics were found to vary significantly in their sensitivity to different charge sharing mechanisms, underlining the importance of carefully selecting the evaluation metric for photon counting detectors based on their application. The parameters used here were selected based on our own interests, however this work demonstrates the utility of this framework for optimising x-CSI detector parameters for various spectral applications.

The viewing-angle enlargement of a holographic image is a crucial factor for realizing the holographic display. The numerical aperture (NA) of digital hologram other than a pixel specification has been known to determine the angular field extent of image. Here, we provide a valid foundation for the dependence of viewing angle on the hologram numerical aperture by investigating mathematically the internal structure of the sampled point spread function showing a self-similarity of its modulating curves. The enhanced-NA Fresnel hologram reconstructs the images at a viewing angle larger than a diffraction angle by a hologram pixel pitch where its angle value is expressed in terms of the NA of whole hologram aperture, which is systematically observed by optical hologram imaging. Finally, we found that the aliased replica noises generated in the enhanced-NA Fresnel diffraction regime are effectively suppressed within the diffraction scope by a digitized pixel. This characteristic enables us to overcome the image reduction and to remove the interference of high-order images, which leads to the wide viewing-angle holographic display. Optical experiments are shown to be consistent with the results of numerical simulation., Comment: 29 pages, 10 figures

We have developed and demonstrated an image super-resolution method—XR-UNLOC: X-Ray UNsupervised particle LOCalization—for hard x-rays measured with fast-frame-rate detectors that is an adaptation of the principle of photo-activated localization microscopy (PALM) and stochastic optical reconstruction microscopy (STORM), which enabled biological fluorescence imaging at sub-optical-wavelength scales. We demonstrate the approach on experimental coherent Bragg diffraction data measured with 52 keV x-rays from a nanocrystalline sample. From this sample, we resolve the fine fringe detail of a high-energy x-ray Bragg coherent diffraction pattern to an upsampling factor of 16 of the native pixel pitch of 30 μm of a charge-integrating fastCCD detector. This was accomplished by analysis of individual photon locations in a series of “nearly-dark” instances of the diffraction pattern that each contain only a handful of photons. Central to our approach was the adaptation of the UNLOC photon fitting routine for PALM/STORM to the hard x-ray regime to handle much smaller point spread functions, which required a different statistical test for photon detection and for sub-pixel localization. A comparison to a photon-localization strategy used in the x-ray community (“droplet analysis”) showed that XR-UNLOC provides significant improvement in super-resolution. We also developed a metric by which to estimate the limit of reliable upsampling with XR-UNLOC under a given set of experimental conditions in terms of the signal-to-noise ratio of a photon detection event and the size of the point spread function for guiding future x-ray experiments in many disciplines where detector pixelation limits must be overcome.

Here we report a metal-insulator-metal (MIM) based infrared plasmonic metamaterial absorber consisting of deep subwavelength meander line nanoantennas. High absorption composed of two-hybrid modes from 11 μm to 14 μm is experimentally demonstrated with a pixel pitch of 1.47 μm corresponding to a compression ratio of 8.57. The physical mechanisms responsible for novelty spectral absorption, including the strong coupling between the plasmon resonances and the phonon vibrations, material loss from the dielectric spacer, localized surface plasmon resonance (LSPR), and Berreman mode excited by oblique incidence, have been systematically analyzed by finite-difference time-domain (FDTD) method, Fabry-Perot resonance model and two-coupled damped oscillator model. At oblique incidence, a spectral splitting related to the strong coupling between LSPR mode and Berreman mode is also observed. The distribution of local electromagnetic fields and ohmic loss are numerically investigated. Moreover, we evaluate the absorption performances with finite-sized arrays. We also show that the absorber can maintain its absorption with a 2 × 2 nanoantenna array. Such a miniaturized absorber can adapt to infrared focal plane arrays with a pixel size smaller than 5 μm, and thermal analysis is also performed. Our approach provides an effective way to minimize the antenna footprint without undermining the absorber performances, paving the way towards its integration with small pixels of infrared focal plane arrays for enhanced performances and expanded functionalities.

Event-based cameras (EBCs) are of interest for potential application to space domain awareness (SDA). EBC attributes, including asynchronous response and low latency provide data reduction, break the trade-off between latency and power, and enable consideration of additional algorithms and processing architectures due to individual timestamps for each event. Potential data reduction by a factor of 10 or greater is particularly attractive for SDA from satellite platforms with constraints on system power, processing, and communication bandwidth. Here we report our initial evaluation of Prophesee third-generation commercial-off-the-shelf (COTS) EBCs, including development of, and comparison with, a limiting magnitude model. The analytic model is a function of sky background radiance; EBC parameters including contrast threshold, dark current, pixel pitch, and spectral quantum efficiency; and the optic aperture diameter and focal length. Using an 85 mm f/1.4 lens, the measured detection limits for the half-size video graphics array (HVGA) and video graphics array (VGA)-format EBCs are 6.9 and 9.8 visual magnitudes ( m V ), respectively, at a sky background level of about 20.3 m V per square arcsecond. The empirical sensitivity limit for the VGA differs by 0.1 m V from our analytic prediction of 9.7 (less than 10% difference in flux). The limiting magnitude model assumes slow motion of point objects across the EBC focal plane array. Additional experiments exploring temporal behavior show that no stars are detected while scanning across the night sky faster than 0.5 deg per second using the VGA-EBC mounted to a 200 mm f/2.0 lens. The limited sensitivity of the evaluated COTS EBCs prevents their use as a replacement for typical CCD/CMOS framing sensors, but EBCs show clear promise for small-aperture, large-field persistent SDA in terms of their efficient capture of temporal information.

Besides nowadays challenges in contactless measurement of body temperature, the market for uncooled thermal imager continuously increased in the last years. The size of the camera core is a parameter, that needs to follow the miniaturization of the whole camera body. State-of-the-art value for pixel sizes of microbolometers in uncooled thermal imagers is 10 μm. Pushing the microbolometer size to the optical limit, Fraunhofer IMS provides a manufacturing process for FIR-imagers (uncooled thermal imagers) based on a scalable microbolometer technology. Taking this scalable technology as a basis, we are introducing a fully implemented uncooled thermal imager with 6 μm pixel size. The 6 μm microbolometers are made by Fraunhofer IMS’s manufacturing technology for a thermal MEMS isolation realized by vertical nanotubes. Performance of the 6 μm microbolometers is estimated by a 17 μm digital readout integrated circuit in QVGA resolution. Responsivity and number of electrical defect pixels as well as NETD are determined by an electro-optical characterization based on a test setup with a black body at two different temperatures. NETD of the 6 µm microbolometers is estimated to be at 611 mK. Supporting the quantitative measurements, FIR test images will be presented to demonstrate the microbolometer’s functionality in a fully implemented uncooled thermal imager. In summary, a fully implemented uncooled thermal imager with QVGA resolution based on a 6 μm nanotube-microbolometer detector is presented here. Compared with commercially available uncooled thermal imagers, the highly limited absorption area of our microbolometers with structure sizes below the target wavelength causes an accordingly higher NETD. Nevertheless, it can be stated that 6 μm pixel size still shows the capability of absorbing infrared radiation at wavelengths of approximately 10 μm in an uncooled thermal imager.

In 2019, IRnova launched a full-scale production of a reduced size, weight and power integrated detector dewar cooler assemblies (Oden MW; VGA format with 15 μm pixel pitch) covering the full mid-wavelength infrared spectral domain (3.7 μm – 5.1 μm). Oden MW exhibits excellent performance with operating temperatures up to 110 K at F/5.5 with typical values of temporal and spatial noise equivalent temperature of 22 mK and 7 mK, respectively, and an operability higher than 99.85%. More recently, IRnova developed a new detector design with a cut-off wavelength of 5.3 μm which can potentially allow an operating temperature of the detector up to 150K with excellent performance demonstrated on single pixels with a quantum efficiency as high as 46% at 4 µm without antireflection coating, a turn on bias lower than -100 mV and a dark current density as low as 8 × 10-6 A/cm2, which is a factor of < 5 higher than Rule07. The dark current was also found independent of the device size ranging from 10 μm to 223 μm indicating that surface leakage currents are not limiting the dark current. The achievable operating temperature of an FPA made of this new detector design has been estimated to be

International audience; Infrared cameras could serve automotive applications by delivering breakthrough perception systems for both in-cabin passengers monitoring and car surrounding. However, low-cost and high-throughput manufacturing methods are essential to sustain the growth in thermal imaging markets for automotive applications, and for other close-to-consumer applications which have a fast growth potential. Fast low cost infrared lenses suitable for microbolometers are currently already sold by companies like Umicore, Lightpath, FLIR… They are either made of a single inverse meniscus Chalcogenide glass or of two Silicon optics. In this paper, we explore hybrid systems with a large field of view around 40° combining Chalcogenide and Silicon in order to take advantage of both materials. Both are compatible with wafer-level process. Silicon optics can be manufactured by photolithography process and are expected to be more cost-effective than Chalcogenide ones. However they are constrained in shape and sag height. On the other hand, Chalcogenide optics can be collectively molded and could have more free shapes. They are thus more suitable to reach high-demanding performance. So hybrid designs could be seen as a compromise between cost and performance. In this paper, we show that fast lenses with diameter constraints to few millimeters to make affordable wafer-level process lead to small size detectors. As a consequence, the pixel pitch reduction of microbolometers is a key point to maintain a good resolution. Finally, strategies to improve the production yield of hybrid lenses are explored.

The Quanta Image Sensor (QIS) is a photon-counting image sensor conceptualized in 2004 by Fossum and reduced to practice over the past 8 years at Dartmouth using a CMOS image sensor platform, and now referred to as CIS-QIS. This CIS-QIS device is a photon-number resolving sensor that does not use avalanche multiplication, and has been demonstrated in megapixel format with small pixel pitch. This progress will be reported along with associated progress of the spin-out company Gigajot, and other collaborators. In just the past few years, SPAD devices have also been used to explore the QIS concept. Termed SPAD-QIS, the first megapixel SPAD-QIS was reported just in the past few weeks. A comparison of the advantages of CIS-QIS and SPAD-QIS will be presented. Both represent a paradigm shift in image acquisition and may become important for many quantum photonics applications.

Commercial Infrared and Terahertz imaging systems have a focal plane array made of bolometric elements which form the pixels in the imaging system. Bolometers have the disadvantage of being slow and require a bias voltage to operate, which increases the power required to operate the infrared imaging system. The current trend is to transition to small size, weight, and power (SWaP) imaging systems. Seebeck nanoantennas are resonant elements made of two dissimilar thermoelectric materials tuned at a particular wavelength, when this wavelength is incident on the nanoantenna it induces a current that increases the temperature at the feed of the nanaontenna generating a temperature difference that produces a Seebeck voltage. Due to the small size of the antenna and its low thermal mass it makes Seebeck nanoantennas considerably faster than tradition bolometers. Also, since the thermoelectric elements provide an output voltage no bias is needed for operation, reducing the power required by the FPA. In this work an infrared pixel is designed and optimized for detection in the 8-12μm wavelength range, and its thermoelectric voltage is calculated using numerical simulations for different pixel pitch sizes.

Due to the large pixel pitch and limited size of spatial light modulator (SLM), the field of view (FOV) of current holographic display is greatly restricted. Cylindrical holography can effectively overcome the constraints of FOV. However, the existent algorithms of cylindrical hologram are all based on the wave-optics based approach. In this paper, to the best of our knowledge, we adopt the ray-optics based approach in the generation of cylindrical computer generated hologram (CCGH) for the first time. Information of parallax images captured from three-dimensional (3D) objects using a curved camera array is recorded into a cylindrical hologram. Two different recording specific algorithms are proposed, one is based on the Fast Fourier Transform (FFT) method, and another is based on the pinhole-type integral imaging (PII) method. The simulation results confirm that our proposed methods are able to realize a fast generation of the cylindrical photorealistic hologram.

Pixelated silicon detectors are state-of-the-art technology to achieve precise tracking and vertexing at collider experiments, designed to accurately measure the hit position of incoming particles in high rate and radiation environments. The detector requirements become extremely demanding for operation at the High-Luminosity LHC, where up to 200 interactions will overlap in the same bunch crossing on top of the process of interest. Additionally, fluences up to 2.3 × 1016 cm−2 1 MeV neutron equivalent at 3.0 cm distance from the beam are expected for an integrated luminosity of 3000 fb−1. In the last decades, the pixel pitch has constantly been reduced to cope with the experiments’ needs of achieving higher position resolution and maintaining low pixel occupancy per channel. The spatial resolution improves with a decreased pixel size but it degrades with radiation damage. Therefore, prototype sensor modules for the upgrade of the experiments at the HL-LHC need to be tested after being irradiated. This paper describes position resolution measurements on planar prototype sensors with 100 × 25 µm2 pixels for the CMS Phase-2 Upgrade. It reviews the dependence of the position resolution on the relative inclination angle between the incoming particle trajectory and the sensor, the charge threshold applied by the readout chip and the bias voltage. A precision setup with three parallel planes of sensors has been used to investigate the performance of sensors irradiated to fluences up to ϕ eq = 3 . 6 × 1 0 15 cm−2. The measurements were performed with a 5 GeV electron beam. A spatial resolution of 3 . 2 ± 0.1 µm is found for non-irradiated sensors, at the optimal angle for charge sharing. The resolution is 5 . 0 ± 0.2 µm for a proton-irradiated sensor at ϕ eq = 2 . 1 × 1 0 15 cm−2 and a neutron-irradiated sensor at ϕ eq = 3 . 6 × 1 0 15 cm−2. The extrapolated resolution to infinite beam momentum, where the contribution of multiple scattering can be neglected, has also been evaluated.

Using digital holography in camera-based interferometers, 3D surface topography can be measured extremely quickly and with sub-wavelength precision. Using spatial phase-shifting, a single camera image is sufficient to reconstruct complexvalued wavefronts for multiple wavelengths. Recently, measurements on moving objects were demonstrated using setups with 1× magnification. Increasing the lateral resolution by implementing larger magnification in a microscopic setup would open up new application fields, but the larger numerical apertures (NA) of microscope objectives make the acquisition even more sensitive to motion. In this work, we show the first microscopic setup, measuring objects moving at several mm/s using two-wavelength holography. Despite the large NA of 0.42 of the 10×-objective in our setup, measurements can be acquired at 75 mm/s and beyond. Using two lasers emitting slightly different wavelengths (637.76 nm and 632.87 nm), a maximum height difference of 41.3 μm can be detected unambiguously. One single image covers a lineshaped measurement area of 3.7 mm × 0.2 mm with a lateral pixel pitch of 0.47 μm. In order to inspect larger objects, single frames can be stitched together, permitting an infinite measurement area in the direction of motion. Gap-free stitched measurements are limited to 75 mm/s due to the framerate of the camera. Measurements of the groove depth averaged over several pixels on a groove standard show a repeatability exceeding 10 nm at 35 mm/s and 20 nm at 75 mm/s.

There are currently various near-infrared (NIR) light sources for sensing applications. To expand the application of NIR sensing, we are advancing research and development a self-emissive NIR-OLED microdisplay featuring a compact form factor and active drive as a new sensing light source. In general, in the NIR region having a narrow energy gap, an exciton of organic emitters readily decays non-radiatively to the ground state. Therefore, it is challenging to obtain high-efficiency light emission. To overcome this problem, a TADF (thermally-activated delayed fluorescence) material having a rigid electron-accepting unit exhibiting strong electron-withdrawing properties is used as an assisting dopant for a molecule exhibiting fluorescence in the 900nm band. It thereby realized a near-infrared light-emitting characteristic with a longer wavelength, higher efficiency, and higher durability than a conventional device. Furthermore, in order to actively drive this highly efficient NIR-OLED material on a silicon substrate, a top emission structure is required. To cope with this issue, the optical design was optimized for NIR band emission by the micro-cavity effect. The optimum structure for high-efficiency NIR emission was adopted by examining the structure around the emission layer and the encapsulation process. By integrating this high-efficiency NIR-OLED device with a CMOS-based high-definition backplane formed on a silicon substrate, it’ll have the potential to be realized a high-efficiency NIR-OLED microdisplay with a pixel pitch of 7.8 μm and a maximum external quantum efficiency of approximately 1% and an emission wavelength of over 900 nm. Through this study, it was confirmed that the NIR light emission was possible with high efficiency with fine pixel in principle. It’s expected to contribute to power saving and miniaturization as a new sensing light source to be applicable to new value creation.

We developed a $256\times 32$ -pixel needle-type pH image sensor to visualize ion behavior at the cellular level under in vivo conditions. This sensor has a pixel configuration that can be fabricated via a modified CMOS process technology, and it achieved a pixel size of $5.65\times 4.39\ \mu \mathrm{m}^{2}$ . The proposed image sensor is the highest-definition implantable ion image sensor among other conventional image sensors. For in vivo implantation, the sensor's shape was modified to a needle structure of $9.88\times 1.10\ \text{mm}^{2}$ with a thickness of $100\ \mu \mathrm{m}$ . From the measurement results, we verified that the sensor exhibits a high spatiotemporal resolution with a pH sensitivity, pH resolution, and temporal resolution of 56.4 mV/pH, 0.015 pH, and 14.1 fps, respectively. In addition, we detected pH changes in the brain of the experimented mouse during neural hyperexcitation, and successfully reproduced the measured data as 2-D images in real time.

Teledyne e2v has developed the Capella CIS120 which is a general purpose CMOS image sensor with high quantum efficiency that has been specifically designed for space applications and is planned to be used for different Copernicus programs. We will describe the considerations that led to this CMOS sensor concept and then outline the specifications and design details of this back-illuminated detector. Key features include 2048 × 2048 pixels, 10µm pixel pitch, on-chip ADC giving digital outputs in LVDS, both rolling shutter and global shutter modes are available, 45 ke- or 80 ke- full well capacity, peak QE of 90% at 600 nm and latch-up immune and high SEU threshold by design. We will show how the CIS120 can be used for different modes including multi-linear operation, multi-windowing with independent left and right addressing for startracker applications and full frame operation in global or rolling shutter mode for array imaging applications including hyperspectral imaging. The CIS120 is designed to be highly flexible in format allowing; larger variants for astronomical applications and multi die focal plane arrangement, a range of backthinning process options and larger pixel sizes for x-ray applications. Currently the high pixel full capacity version of the CIS120 with 80 ke- per pixel in being characterised. We will present detailed characterisation results and validation data qualifies CIS120 to TRL6 level. We will also present the three different package types have been designed so far for CIS120; standard ceramic package, three side buttable package and sealed Peltier package. Finally, we will summarise plans for future activities including the design and production of a HiRho variant to give significantly improved NIR sensitivity by applying voltage to back surface to be able to operate in full depletion.

In this study, the feasibility of mini-LED RGB display fabricated by a chip-first fan-out panel-level packaging is investigated. Emphasis is placed on the design, materials, process, fabrication, and reliability of the mini-LED RGB display package on a printed circuit board (PCB). The mini-LEDs under consideration and their sizes are Red ( $125 \times 250 \times 100\mu \mathrm{m}$ ), Green ( $130\times 270\times 100 \mu \mathrm{m}$ ), and Blue ( $130 \times 270\times 100\mu \mathrm{m}$ ). The spacing among the RGB mini-LEDs is $80\mu \mathrm{m}$ , the pixel-to-pixel spacing is also $\sim 80\mu \mathrm{m}$ , and the pixel pitch is $625\mu\mathrm{m}$ . The temporary glass panel for making the RDLs of the package is $515 \times 510\times 1.1\text{mm}$ in size. In order to increase the SMT assembly yield on the PCB, the mini-LEDs are grouped into $4(2\times 2\ \text{pixels})$ in one SMD (surface mount device), i.e., a total of 12 R, B, and G mini-LEDs. A PCB ( $132\text{mm}\times 77\text{mm}$ ) is designed and fabricated for the drop test of the mini-LED package. Thermal cycling of the mini-LED SMD PCB assembly is also performed by a nonlinear temperature- and time-dependent finite-element simulation.

A coded-exposure-pixel image sensor for computational imaging applications is presented. Each frame exposure time is divided into ${N}$ subframes. Within each subframe, each pixel sorts photo-generated charge into two charge taps depending on that pixel’s 1-bit binary code. ${N}$ global updates of arbitrary pixel-wise codes are implemented in each frame to enable ${N}$ short global pixel-specific subexposures within one frame. To make these subexposures global, two latches per pixel are utilized in a pipelined fashion. The code for the next subframe is loaded into latch 1 in a row parallel fashion, while the code for the current subframe is being applied by latch 2 globally for photo-generated charge sorting during the current subexposure. A $280^{H}\times 176^{V}$ image sensor prototype with $11.2{\text{-}}\mu \text{m}$ pixel pitch has been fabricated in a $0.11{\text{-}}\mu \text{m}$ CMOS image sensor (CIS) technology. The image sensor has been demonstrated in two computational photography applications, each using only a single frame of a video: 1) computing both albedo (a measure of reflectivity) and 3-D depth maps by means of structured-light imaging and 2) computing surface normals (3-D orientations) map by means of photometric stereo imaging. These demonstrations experimentally validate some of the unique capabilities of this computational image sensor, such as accurate 3-D visual scene reconstruction using only one camera, while maintaining its native specifications: the full spatial resolution and the maximum frame rate.

The sharing of charge between multiple pixels can significantly degrade the energy resolution of small pixelated compound semiconductor detectors. This paper describes an energy calibration and reconstruction technique to correct for absorbed energy that is split over two neighbouring pixels, defined as bipixel events. Results were obtained with a 1 mm thick CdTe detector with 250 µm pixel pitch and an inter-pixel spacing of 50 µm, using the STFC HEXITEC ASIC. The proportion of charge sharing events was found to be 54% for photons at 59.5 keV when applying a noise threshold of 3 keV. Across the energy range investigated, bipixels were the predominant shared event type and the absolute fraction of shared events was found to be dependent on the noise threshold used. The reconstruction technique described reduces the degradation of energy resolution due to charge sharing in bipixel events compared to simple charge sharing summing techniques. This improved counting efficiency compared to using only isolated events and improved energy resolution compared to pixel addition techniques. When only isolated pixels were included, a FWHM energy resolution of 1.42 keV at 140.5 keV was achievable; inclusion of bipixel events using pixel addition results in an energy resolution of 3.33 keV whereas the reconstruction technique described here results in an energy resolution of 2.14 keV. When bipixel events are combined with single pixel events, the number of counts within the 140.5 keV photopeak of 99mTc increased by over 100%.

This paper presents a low-power $1232\,\,\times \,\, 952$ pixel back side-illuminated CMOS image sensor with a pixel pitch of 2.8 $\mu \text{m}$ . It is implemented in a 90-nm CMOS image sensor technology. We propose a method to reduce the pixel readout energy consumption by computing two digital correlated double-sampling (DCDS) results with three analog–digital (A/D) conversions, thereby using an average of 1.5 A/D conversions per pixel. The conventional DCDS readout requires two A/D conversions per pixel. The DCDS operation uses 27.3 pJ/pixel and achieves a figure-of-merit (FoM) of 0.064 $\,\,\text {nJ}\cdot \text {e}^{-}$ , which is the lowest published to date. A pixel is designed with four gain steps that allow 175 $\mu \text{V}/\text{e}^{-}$ conversion gain and 2.33 e− read noise at the highest pixel gain setting and 33.400 e− full well capacity at the lowest pixel gain setting. The pixel design avoids the need for dedicated capacitors in the pixel and instead uses capacitance already existing in the current readout row and the previous row.

To achieve a resolving power greater than 100 000, we are developing a superconducting nanostrip single photon detector (SSPD) for an ultrahigh-resolution RIXS spectrometer in the Taiwan Photon Source. To achieve the target resolving power, the SSPD, combined with a microstripline (MSL) structure, which acts as a delay line, should have a line pitch of 0.5 μm. This study uses numerical simulations to design SSPD. It consists of a meander of a 50-nm-thick Nb nanostrip and a 45-nm-thick SiO2 underlayer. The width of the line and the gap of the meander are 400 and 100 nm, respectively. The estimated velocity of the transmitted pulses due to X-ray absorption in the Nb nanostrip of the above SSPD is ~5% of the speed of light in free space. A detection area of 16 mm × 5 mm is sufficient to allow a time difference of ~1 ns between neighboring nanostrips to be distinguishable using conventional time to digital converters (TDCs). We fabricated a trial SSPD imager with dimensions of 4 mm × 0.1215 mm, and measured signal pulse characteristics for ions simulating soft X-ray photons. During an experiment, the maximum time difference of 7.5 ns between output pulses from both ends of the nanostrip successfully exhibited the proper imaging operation.

A single-projection based phase retrieval method based on the phase attenuation duality principle (PAD) was used to compare the spatial resolution of the acquired phase sensitive and PAD processed phase retrieved images. An inline phase sensitive prototype was used to acquire the phase sensitive images. The prototype incorporates a micro-focus x-ray source and a flat panel detector with a 50 μm pixel pitch. A phantom composed of a 2 cm thick 50-50 adipose-glandular mimicking slab sandwiched with a 0.82 cm thick slanted PMMA sharp edge was used. Phase sensitive image of the phantom was acquired at 120 kV, 3.35 mAs with a 16 μm tube focal spot size under a geometric magnification (M) of 2.5. The PAD based method was applied to the acquired phase sensitive image for the retrieval of phase values. With necessary data processing, modulation transfer function (MTF) curves were determined for the estimation and comparison of the spatial resolution. The PAD processed phase retrieved values of the phantom were in good agreement with the theoretically calculated values. Phase sensitive images showed higher spatial resolution at all spatial frequencies compared to the phase retrieved images. It was noted that the high-frequency signal components in the retrieved image were suppressed that resulted in lower MTF values. When compared to the phase sensitive image, the cutoff resolution (10% MTF) for phase retrieved image dropped 32% from 15.6 lp/mm (32μm) to 10.6 lp/mm (47μm). The resolution offered by this phase sensitive prototype is radiographically enough to detect breast cancer.