Pixel Pitch Research Articles

Programmable broadband ultrathin micropolarizer based on photoalignment technology

A method for creating broadband ultrathin azo dye micropolarizers is introduced, utilizing photoalignment technology and liquid crystal polymers to organize azo dyes into a long-range ordered structure. Achievements include a 3.63 μm thick polarizer with an extinction ratio over 140 and polarization efficiency over 99.3% across 400–650 nm, 5 μm × 5 μm pixel pitch flexible ultrathin checkerboard arrays and 6 μm pixel pitch flexible ultrathin one-dimensional grating with a 0.45 duty ratio through mask exposure technology. After a substrate-transfer technique, the bending cycle test demonstrates the mechanical stability and durability of the broadband ultrathin flexible polarizers, highlighting their potential for widespread use in integrated flexible optoelectronic systems.

Process optimization of preparing CMOS backplane for ultrahigh pixel density red Micro-LED display

Abstract In this paper, an AlGaInP-based red Micro-LED display measured 17.78 mm (0.7 in), with a resolution of 1920 × 1080, a light-emitting mesa size of 6 μm, a pixel pitch of 8 μm and a pixel density of 3175 PPI was designed and fabricated with a CMOS driver backplane. The metal bump preparation technology of the complementary metal-oxide semiconductor driver backplane was optimized to enhance the bonding yield and create an optimal display effect. Improper sizing of the etched window in the SiO2 insulation and passivation layer can have a detrimental impact on the metal bump preparation and subsequent bonding process. By optimizing the settings of lithography and dry etching, the appropriate size of the etched aperture in the passivation layer was achieved. The high density, small size, and large aspect ratio of the photoresist openings for the bump fabrication made it challenging to remove the photoresist following the metal evaporation. To successfully remove the photoresist, it is important to carefully choose suitable experimental conditions for the removal. Afterwards, an 8 μm AlGaInP-based red Micro-LED display was effectively integrated with complementary metal-oxide semiconductor using flip-chip bonding technology. This work may be of reference value to those who work on ultrahigh density red Micro-LEDs that is challenging but crucial for future full color micro displays.

Exploiting incoherent synthetic apertures in integral imaging for optical super-resolution.

Integral imaging (InIm) working with a pixelated device (e.g., a display panel) and a microlens array (MLA) suffers from low spatial resolution because of a significant trade-off between the spatial and angular resolution. The system bandwidth is presumed to be limited by the Nyquist frequency set by the pixel pitch. This study demonstrates that InIm intrinsically works in an incoherent synthetic aperture (ISA) manner with unexploited resolution capabilities. The sampling shifts between lenslets can be controlled and utilized to construct "computational galvos" to introduce varying aliasing; as a result, the Nyquist frequency is broken for optical super-resolution (SR). In particular, an InIm system can be configured for an N-fold oversampling rate with N lenslets. Furthermore, in an InIm display, the fill factor of a pixel's emitting area is always lower than 100%, so the bandwidth limit set by the pixel shape, i.e., two times the Nyquist frequency, is loosened. An InIm display prototype was built with an oversampling rate of four and a pixel fill factor of 75%. In the experiment, the proposed SR method achieved a 2.12 times resolution without dynamic devices or time-multiplexing.

Beyond transfer learning: Leveraging ancillary images in automated classification of plankton

AbstractWe assess whether a supervised machine learning algorithm, specifically a convolutional neural network (CNN), achieves higher accuracy on planktonic image classification when including non‐plankton and ancillary plankton during the training procedure. We focus on the case of optimizing the CNN for a single planktonic image source, while considering ancillary images to be plankton images from other instruments. We conducted two sets of experiments with three different types of plankton images (from a Zooglider, Underwater Vision Profiler 5, and Zooscan), and our results held across all three image types. First, we considered whether single‐stage transfer learning using non‐plankton images was beneficial. For this assessment, we used ImageNet images and the 2015 ImageNet contest‐winning model, ResNet‐152. We found increased accuracy using a ResNet‐152 model pretrained on ImageNet, provided the entire network was retrained rather than retraining only the fully connected layers. Next, we combined all three plankton image types into a single dataset with 3.3 million images (despite their differences in contrast, resolution, and pixel pitch) and conducted a multistage transfer learning assessment. We executed a transfer learning stage from ImageNet to the merged ancillary plankton dataset, then a second transfer learning stage from that merged plankton model to a single instrument dataset. We found that multistage transfer learning resulted in additional accuracy gains. These results should have generality for other image classification tasks.

Characterization of analogue Monolithic Active Pixel Sensor test structures implemented in a 65 nm CMOS imaging process

Analogue test structures were fabricated using the Tower Partners Semiconductor Co. CMOS 65 nm ISC process. The purpose was to characterize and qualify this process and to optimize the sensor for the next generation of Monolithic Active Pixels Sensors for high-energy physics. The technology was explored in several variants which differed by: doping levels, pixel geometries and pixel pitches (10–25 μm). These variants have been tested following exposure to varying levels of irradiation up to 3 MGy and 1016 1 MeV neq cm−2. Here the results from prototypes that feature direct analogue output of a 4 × 4 pixel matrix are reported, allowing the systematic and detailed study of charge collection properties. Measurements were taken both using 55Fe X-ray sources and in beam tests using minimum ionizing particles. The results not only demonstrate the feasibility of using this technology for particle detection but also serve as a reference for future applications and optimizations.

Viewpoint-dependent lighting on polygonal holograms using bump mapping.

Holograms can be observed from different viewpoints, because light waves can be encoded to propagate in multiple directions. Thus, accurate holograms for 3D display should model viewpoint-dependent light reflections. We proposed a new, to the best of our knowledge, hologram generation method for objects represented by polygonal meshes, whose lighting changes as the viewer moves, all while rendering smooth shading using low-poly objects. The proposed method leverages bump mapping and converts it into a bump-phase map encoding the propagation frequency and then spreads the reflected light wave so that only a specific viewpoint can receive them. Simulation experiments with small pixel pitches confirm the method's high computational performance.

Characterisation of analogue MAPS fabricated in 65 nm technology for the ALICE ITS3

The ALICE ITS3 project foresees the use of ultra-light MAPS, developed in the 65 nm imaging process, for the vertex detector in the ALICE experiment at the LHC to drastically improve the vertexing performance. This new development, initiated by an international consortium of the ALICE ITS3 collaboration and the CERN EP R&D project, enhances the overall MAPS performance.Small-scale prototypes are designed to study the analogue properties of the TPSCo 65 nm technology and compare the charge collection performance in different processes, pitches, pixel geometries, and irradiation levels. Recent results from lab and test-beam characterisation detailing the efficiency and the spatial resolution of the APTS with different pixel geometries and pitches satisfy the ALICE ITS3 requirements. A quantitative evolution of the charge collection and sharing among pixels is evident in the CE-65 with different in-pixel readouts. Attaining a spatial resolution better than 3μm with a 10μm pitch and over 99% efficiency in the moderate irradiation environment of ALICE also supports the viability of using 65 nm MAPS for FCC-ee vertex detectors.

Performance Characterization of an Illumination-Based Low-Cost Multispectral Camera.

Spectral imaging has many applications, from methane detection using satellites to disease detection on crops. However, spectral cameras remain a costly solution ranging from 10 thousand to 100 thousand euros for the hardware alone. Here, we present a low-cost multispectral camera (LC-MSC) with 64 LEDs in eight different colors and a monochrome camera with a hardware cost of 340 euros. Our prototype reproduces spectra accurately when compared to a reference spectrometer to within the spectral width of the LEDs used and the ±1σ variation over the surface of ceramic reference tiles. The mean absolute difference in reflectance is an overestimate of 0.03 for the LC-MSC as compared to a spectrometer, due to the spectral shape of the tiles. In environmental light levels of 0.5 W m-2 (bright artificial indoor lighting) our approach shows an increase in noise, but still faithfully reproduces discrete reflectance spectra over 400 nm-1000 nm. Our approach is limited in its application by LED bandwidth and availability of specific LED wavelengths. However, unlike with conventional spectral cameras, the pixel pitch of the camera itself is not limited, providing higher image resolution than typical high-end multi- and hyperspectral cameras. For sample conditions where LED illumination bands provide suitable spectral information, our LC-MSC is an interesting low-cost alternative approach to spectral imaging.

To Reconstruct or Discard: A Comparison of Additive and Subtractive Charge Sharing Correction Algorithms at High and Low X-ray Fluxes.

Effective X-ray photon-counting spectral imaging (x-CSI) detector design involves the optimisation of a wide range of parameters both regarding the sensor (e.g., material, thickness and pixel pitch) and electronics (e.g., signal-processing chain and count-triggering scheme). Our previous publications have looked at the role of pixel pitch, sensor thickness and a range of additive charge sharing correction algorithms (CSCAs), and in this work, we compare additive and subtractive CSCAs to identify the advantages and disadvantages. These CSCAs differ in their approach to dealing with charge sharing: additive approaches attempt to reconstruct the original event, whilst subtractive approaches discard the shared events. Each approach was simulated on data from a wide range of x-CSI detector designs (pixel pitches 100-600 µm, sensor thickness 1.5 mm) and X-ray fluxes (106-109 photons mm-2 s-1), and their performance was characterised in terms of absolute detection efficiency (ADE), absolute photopeak efficiency (APE), relative coincidence counts (RCC) and binned spectral efficiency (BSE). Differences between the two approaches were explained mechanistically in terms of the CSCA's effect on both charge sharing and pule pileup. At low X-ray fluxes, the two approaches perform similarly, but at higher fluxes, they differ in complex ways. Generally, additive CSCAs perform better on absolute metrics (ADE and APE), and subtractive CSCAs perform better on relative metrics (RCC and BSE). Which approach to use will, thus, depend on the expected operating flux and whether dose efficiency or spectral efficiency is more important for the application in mind.

A versatile and fast pixel matrix read-out architecture for MAPS

A digital asynchronous logic is proposed as a generic matrix readout for Monolithic active pixel sensors. The architecture is implemented for pixel pitch ranging from 18 to 30µm. Post-layout simulations with realistic hit shapes and rates up to 200MHz/cm2 show that time stamping at the 20ns level can be achieved for a digital power cost below 10mW/cm2.

In-silico study of the impact of system design parameters on microcalcification detection in wide-angle digital breast tomosynthesis.

Accurate detection of microcalcifications ( ) is crucial for the early detection of breast cancer. Some clinical studies have indicated that digital breast tomosynthesis (DBT) systems with a wide angular range have inferior detectability compared with those with a narrow angular range. This study aims to (1)provide guidance for optimizing wide-angle (WA) DBT for improving detectability and (2)prioritize key optimization factors. An in-silico DBT pipeline was constructed to evaluate detectability of a WA DBT system under various imaging conditions: focal spot motion (FSM), angular dose distribution (ADS), detector pixel pitch, and detector electronic noise (EN). Images were simulated using a digital anthropomorphic breast phantom inserted with clusters. Evaluation metrics included the signal-to-noise ratio (SNR) of the filtered channel observer and the area under the receiver operator curve (AUC) of multiple-reader multiple-case analysis. Results showed that FSM degraded sharpness and decreased the SNR and AUC by 5.2% and 1.8%, respectively. Non-uniform ADS increased the SNR by 62.8% and the AUC by 10.2% for filtered backprojection reconstruction with a typical clinical filter setting. When EN decreased from 2000 to 200 electrons, the SNR and AUC increased by 21.6% and 5.0%, respectively. Decreasing the detector pixel pitch from 85 to improved the SNR and AUC by 55.6% and 7.5%, respectively. The combined improvement of a pixel pitch and EN200 was 89.2% in the SNR and 12.8% in the AUC. Based on the magnitude of impact, the priority for enhancing detectability in WA DBT is as follows: (1)utilizing detectors with a small pixel pitch and low EN level, (2)allocating a higher dose to central projections, and (3)reducing FSM. The results from this study can potentially provide guidance for DBT system optimization in the future.

Soft X-ray performance of an optimised charge-coupled device for astronomy

For the upcoming European Space agency (ESA)/Chinese Academy of Sciences (CAS) SMILE mission, launching in 2025, large-format soft X-ray optimised CCDs have been manufactured by Teledyne e2v, named the CCD370. The CCDs are approximately 8 cm × 8 cm and are comprised of 4510 × 4510 18 μm pitch pixels, with a store shield covering approximately 1/7th of the active imaging area to facilitate frame-transfer operation mode. To optimise quantum efficiency within the soft X-ray energy band, the device is 16 μm thick, back illuminated, and has an additional back surface passivation process. The focal plane of the soft X-ray imager (SXI) on the SMILE spacecraft will be comprised of 2 CCD370s, operating with 6 × 6 on-chip binning to mitigate against CTI-induced charge transfer losses and charge spreading throughout the 3-year mission lifetime.As part of the pre-flight testing and calibration, a CCD370 was characterised at the PTB beamline at the BESSY 2 synchrotron in Berlin, and key metrics such as quantum efficiency and energy resolution in the 0.2–1.8 keV energy band were assessed. The quantum efficiency measurements show expected performance within specification for the instrument, and also match a transmission-layer QE model. The energy resolution is 68 ± 2 eV FWHM @ 1.2 keV, which is an improvement over the current generation of X-ray telescopes such as XMM-Newton, Chandra, and the Swift X-ray Telescope. Although competing technologies such as DEPFETs and scientific CMOS image sensors now have similar performance to CCDs, the performance shown here can still easily satisfy requirements for novel X-ray instruments, and can still be useful in future astronomy missions given the rich heritage, high technology-readiness-level, and maturity of the technology.

Use of Electron Beam-Induced Current Technique to Characterize Transport Properties of Narrow-Gap-Energy Materials for IR Detection

The electron beam-induced current technique (EBIC) developed at CEA-Leti has been a valuable tool for studying the transport properties of minority carriers in HdCdTe. Indeed, previous work has demonstrated the use of this technique for estimating diffusion length from the exponential decay of EBIC as a function of junction distance, as well as direct measurement of the modulation transfer function (MTF) of small pixel pitch diodes. In this work, a modulated electron beam and a lock-in amplifier are used to measure the variation in current and phase shift with the scan distance to the junction. This work is focused on the estimation of the minority carrier lifetime from the linear evolution of the phase shift as a function of junction distance.

Contrast-based notch-to-crack transfer function for digital radiography

To simulate cracks, a series of slits with depths ranging from 17.2% to 40% of 301 stainless steel (SS) plate thickness are fabricated for this study. The examination includes a microfocus X-ray tube and a digital detector array (DDA) with 75 ??m pixel pitch. The basis of this study is to determine the effect of detector scintillator blur, noise and pixelation on the contrast of the resultant radiographic image and, ultimately, on the detectability of a crack. Many crack detectability studies are performed on notched plates rather than true cracks. As the notch width becomes smaller than a pixel, the grey value of the image it generates will be averaged over the entire footprint of the pixel. Therefore, the contrast with neighbouring (no notch) pixels is reduced. This study develops a relationship between the material property, detector parameters, notch geometry and expected contrast that would result from the radiograph image. This relationship can be used as a transfer function towards evaluating the resultant contrast from a notch and extrapolating the results towards a hairline crack.

Rapid calculation of computer-generated holograms for line-drawn 3D objects with varying thicknesses

Accelerating the calculation of computer-generated holograms (CGHs) is an important requirement for three-dimensional (3D) electro-holography display systems. Among the several sophisticated algorithms for CGH acceleration, the CG-line method for projecting 3D wire-frame objects is highly promising due to its high acceleration capability. However, conventional algorithms cannot account for line thickness, and only lines with a constant thickness corresponding to the pixel pitch of the spatial light modulator can be drawn. This restricts the expressiveness and visibility of 3D images, particularly for high-resolution holograms. Therefore, we propose a method for widening the line thickness of the CG-line method. We successfully generated a 3D object comprising bold lines of different thicknesses without sacrificing speed.

Red and green inverted top-emitting quantum dot light-emitting diodes using CMOS-based electrodes for microdisplay applications

Silicon (Si) substrates and complementary metal-oxide-semiconductor (CMOS) technology are being used in microdisplays in augmented reality/virtual reality devices owing to higher pixel resolution. Quantum-dot light-emitting diodes (QLEDs) incorporating colloidal quantum dots have emerged as promising devices for display applications owing to their exceptional color, high luminance, and solution processibility. However, studies on QLEDs on Si, particularly for microdisplay applications, remain limited. This study investigated the device characteristics of inverted top-emitting QLEDs using Si substrates and various CMOS process-based electrode materials (aluminum (Al), Al/titanium nitride (TiN), titanium, cobalt, and tungsten) for microdisplay applications. Devices incorporating a thin TiN layer on an Al electrode exhibited the highest efficiency and luminance compared to those with other electrodes. We successfully fabricated red and green inverted top-emitting QLEDs using microdisplay pixel-structured Al/TiN electrodes, with pixel pitch and fill factor of 10.8 μm × 3.6 μm and 72.5 %, respectively. Further, the device efficiency was optimized by changing hole and electron transport layer thicknesses, resulting in different efficiencies and electroluminescence spectra owing to the microcavity effect. Optical simulations demonstrated consistency with the measured values. Thus, the selection of the bottom electrode and a suitable design that considers the microcavity effect are crucial for high-performance QLED-based microdisplays.

Optical, electrical, and mechanical reliability of 1700 PPI Micro-LED device

With the Micro-LED display device being widely used in the advanced display fields, the high reliability of device had become one of the key issues for applications of Micro-LED in many display fields such as VR/AR, portable displays, and flexible displays. The 512 × 384 green Micro-LEDs 0.39 in. array with 1700 PPI featuring a pixel pitch of 15 μm was integrated with the substrate by the AuIn flip-chip bonding. The average brightness, electroluminescence (EL) spectra, and I-V characteristics of the Micro-LED device aged at 85 °C/85 % RH for different time were measured to evaluate the optical and electrical reliability of the Micro-LED device. The mechanical reliability of the Micro-LED device after 336 h of aging was evaluated by shear test. The average brightness of the Micro-LED device decreased from 2.08 × 104 nit to 1.64 × 104 nit and the on-resistance of the Micro-LED device increased from 2.30 Ω to 2.82 Ω with the aging time increased to 336 h. The Micro-LED device was broken up with the shear strength value of 12.06 MPa, and the shear strength was only reduced by 8.25 % compared with that measured before aging.

25‐1: Invited Paper: Technical Roadmap to Realize Reflective Full‐Color Video Displays for Street Furniture

Outdoor displays become rapidly digital in our digital world. These digital displays are typically emissive, implying a very high‐power consumption to be seen in the daylight, and light pollution in nighttime. Last year Etulipa announced and demonstrated a full colour reflective display based on Electro Wetting Display technology with 10mm pixel pitch. The vertically stacked Cyan Magenta Yellow architecture yields very bright colours. The high switching speed of electrowetting cells enable displaying of video content. The power consumption is 7 W/m 2 implying that the displays can run on solar systems without any need for charging from the grid. The market feedback consists of several exciting applications which are reviewed. Street furniture is expected to be a very early application. Because the typical viewing distance for street furniture applications will be in the order of meters, the pixel pitch should be in the order of millimeters. This requirement defines a technical roadmap for development of the existing electrowetting architecture.

P‐122: Dependence of Aerial image quality on Display parameters in aerial Display system

In this paper, we report the relationship between the imaging spatial resolution and display parameters of the AIRR (aerial imaging by retro‐reflection) system, which we constructed using displays of different brightness, luminance spatial distribution and pixel pitch, respectively, and a line‐pair MTF‐based measurement method is applied to the system. The MTF measurement results show that the spatial resolution depends on the display pixel period size, luminance intensity and luminance spatial distribution.

36‐4: CQD‐Based Sensors for Large Format SWIR Imaging

Quantum dots have been rapidly developed in the display field, especially as photoluminescent color conversion layers. At the same time, quantum dots have also made increasing research progress in the detection field. We reported a short‐wave infrared sensor based on colloidal quantum dot technology. The photosensitive layer of the sensor uses HgTe colloidal quantum dot material. The detection band is 0.9~1.7um, the resolution is 1280*1024, and the pixel pitch is 15um. Colloidal quantum dot short‐wave infrared sensors get rid of the limitations of the indium pillar flip‐chip bonding process of traditional indium gallium arsenide CMOS short‐wave infrared focal plane sensors. The preparation process is simple, the yield is higher, and the cost is low. Based on the colloidal quantum dot shortwave infrared sensor, we implemented a shortwave infrared camera and characterized its performance parameters, and then we successfully captured shortwave infrared images through the shortwave infrared camera.