High Pixel Density Research Articles

Compact Foveated AR Displays with Polarization Selective Planar Lenses

The rapid development of powerful microprocessors, high-pixel density display panels, thin and small formfactor optics, and precise device fabrication capabilities enable wearable near-eye displays for augmented reality (AR) and virtual reality (VR) applications. However, in traditional near-eye displays, there is often a trade-off between field of view (FoV) and angular resolution when a single microdisplay light engine is employed. A high-resolution display panel helps overcome this conflict, but the device fabrication remains a challenge, not to mention the issues like huge data transfer, circuit overheating, and high computational load. Here, we propose a Maxwellian-type foveated AR display based on a single microdisplay light engine by using a temporal polarization multiplexing method, enabled by two polarization selective flat cholesteric liquid crystal lenses. One polarization lens provides a large FoV while the other realizes a high angular resolution imaging in a small fovea region. Moreover, the vergence-accommodation conflict issue is inherently nonexistent in the Maxwellian display, and the aberration can be eliminated for each view by matching the recording and reconstructing signals. In an experiment, we constructed a display breadboard and demonstrated that the angular resolution of the foveal view is enhanced by 3.12× while maintaining a compact formfactor. This work paves the way for implementing high-performance foveated AR displays while keeping a compact formfactor.

Coupling Quantum Random Walks with Long- and Short-Term Memory for High Pixel Image Encryption Schemes.

This paper proposes an encryption scheme for high pixel density images. Based on the application of the quantum random walk algorithm, the long short-term memory (LSTM) can effectively solve the problem of low efficiency of the quantum random walk algorithm in generating large-scale pseudorandom matrices, and further improve the statistical properties of the pseudorandom matrices required for encryption. The LSTM is then divided into columns and fed into the LSTM in order for training. Due to the randomness of the input matrix, the LSTM cannot be trained effectively, so the output matrix is predicted to be highly random. The LSTM prediction matrix of the same size as the key matrix is generated based on the pixel density of the image to be encrypted, which can effectively complete the encryption of the image. In the statistical performance test, the proposed encryption scheme achieves an average information entropy of 7.9992, an average number of pixels changed rate (NPCR) of 99.6231%, an average uniform average change intensity (UACI) of 33.6029%, and an average correlation of 0.0032. Finally, various noise simulation tests are also conducted to verify its robustness in real-world applications where common noise and attack interference are encountered.

Electrically Driven Sub-Micrometer Light-Emitting Diode Arrays Using Maskless and Etching-Free Pixelation.

For decades, group-III-nitride-based light-emitting diodes (LEDs) havebeen regarded as a light emitting source for future displays by virtue of their novel properties such as high efficiency, brightness, and stability. Nevertheless, realization of high pixel density displays is still challenging due to limitations of pixelation methods. Here, a maskless and etching-free micro-LED (µLED) pixelation method is developed via tailored He focused ion beam (FIB) irradiation technique, and electrically driven sub-micrometer-scale µLED pixel arrays are demonstrated. It is confirmed that optical quenching and electrical isolation effects are simultaneously induced at a certain ion dose (≈1014 ions cm-2 ) without surface damage. Furthermore, highly efficient µLED pixel arrays at sub-micrometer scale (square pixel, 0.5µm side length) are fabricated. Their pixelation and brightness are verified by various optical measurements such as cathodo-, photo-, and electroluminescence. It is expected that the FIB-induced optical quenching and electrical isolation method can pioneer a new defect engineering technology not only for µLED fabrication, but also for sub-micrometer-scale optoelectronic devices.

Sub-Micron Monolithic Full-Color Nanorod LEDs on A Single Substrate

The extended reality (XR) display, including augmented reality (AR) and virtual reality (VR), requires ultrahigh-resolution and high-luminance pixel technology. GaN-based micro-LEDs are the most promising for high-density pixel applications. However, it is necessary to simultaneously fabricate full-color R/G/B emitters on a single substrate. Moreover, the efficiency droop at long wavelengths with high-indium InGaN still remains a challenge. The InGaN nanorod has the potential to realize monolithic R/G/B LEDs on a single substrate, and the Al reflector has a light reflectance that can dramatically improve light extraction efficiency. Here, we designed sub-micron monolithic full-color R/G/B nanorod LEDs with an Al core-shell reflector on single chip. The optimal structures for light confinement and vertical light extraction by single InGaN nanorod R/G/B LED structures were identified. The single nanorod with Al core-shell structure dramatically increased the light extraction efficiency, and showed an improvement of more than 20%, especially in the red wavelength. As a result, by introducing a long-length nanorod structure, we have successfully designed a new submicron pixel with full-color R/G/B LEDs operating within 1 μm × 1 μm size. This unique design will be a key factor in enabling the next generation of AR and VR displays that require ultra-small and compact pixels.

Modeling Insights Into the Assembly Challenges of Focal Plane Arrays

Ongoing technological advances in photodetector material growth and processing, readout integrated circuits, and robust hybridization (packaging) methods for assembling high-resolution and small-pitch size pixel arrays are the main enabling factors for pushing the frontiers of high-performance Focal Plane Array (FPA) technologies for imaging systems. This paper details the development of analytical and numerical models and demonstrates their use to generate insights into the feasibility of two flip-chip assembly processes for packaging infrared (IR) detector chips. The modelling studies focus on the challenges of forming the indium interconnection arrays in the case of the FPA technologies using Group III-V compound semiconductor materials and ultra-fine pitch pixel array layouts. The accurate alignment of the IR detector chip onto the readout chip in the case of high-density pixel architectures is a critical requirement for the packaging process. To gain better understanding of this requirement, which has a clear implication for the quality and subsequent reliability performance of the FPA, compression and reflow bonding process models are developed using suitable modeling approaches and methods and then demonstrated for two distinctive focal plane array design configurations. The novelty of this work is in the developed modeling capabilities utilizing different computational methods, from large deformation and contact analysis finite element to energy-based and harmonic motion mechanics, to characterize and optimize the mechanical and dynamic non-linear behavior of the indium solder joints and their formation during FPA packaging. The feasibility of bonding techniques for different resolution FPAs and under flip-chip misalignment conditions is assessed. The modeling results pointed to a very strict, sub-micrometer flip-chip placement accuracy requirement for the assembly of FPAs with ultra-fine indium bump array resolution.

Design of Atomic Layer Deposited Oxide Channel Transistor for High-Performance, High-Pixel Density AMOLED

Design of Atomic Layer Deposited Oxide Channel Transistor for High-Performance, High-Pixel Density AMOLED

Spectral imaging at high definition and high speed in the mid-infrared.

Spectral imaging in the mid-infrared (MIR) range provides simultaneous morphological and chemical information of a wide variety of samples. However, current MIR technologies struggle to produce high-definition images over a broad spectral range at acquisition rates that are compatible with real-time processes. We present a novel spectral imaging technique based on nondegenerate two-photon absorption of temporally chirped optical MIR pulses. This approach avoids complex image processing or reconstruction and enables high-speed acquisition of spectral data cubes (xyω) at high-pixel density in under a second.

Freestanding High-Resolution Quantum Dot Color Converters with Small Pixel Sizes

Designing the next generation of high-resolution displays requires high pixel density per area and small pixel sizes without compromising the optical quality. Quantum dots (QDs) have been demonstrated as a promising material system for down-conversion of blue emission as they provide pure colors on the wide color gamut. However, for high color-conversion efficiency, the required QD film thickness has not been compatible with small pixel sizes. In this work, we develop a new type of freestanding QD-based color converter for efficient optical down-conversion from inorganic blue light-emitting diodes (LEDs) in a color-by-blue configuration. CdSe/ZnS core-shell QDs in a UV-curable polymer matrix are encapsulated within cavities formed by patterning and bonding a pair of patterned quartz substrates. By controlling the required QD thickness and the pixel size independently, we demonstrate freestanding monochrome red and green converters with small pixel sizes down to 5 × 5 μm2 and a high resolution of >3600 ppi. The optical studies show that the QD film thickness required for efficient color conversion can be successfully realized even for the small pixel sizes. We further combine green and red pixels in a single converter to achieve white emission when combined with blue LED emission. The QD color converter design and processing are decoupled from the LED fabrication and can be easily scaled to wafer-size integration with arbitrary pixel sizes for QD-based RGB displays with ultrahigh resolution.

Evaluation of a High-Resolution Large-Area Two-Dimensional Detector Array for Pre-Treatment Verification of Multiple-Target SRS Plans Using a Single Isocenter

<h3>Purpose/Objective(s)</h3> Pre-treatment verification of multiple-target SRS plans using a single isocenter is challenging because of small target sizes and multiple off-isocenter targets. Targets located further away from the isocenter are more sensitive to rotational setup variations, increasing the risk of geometrical miss. It demands high-resolution detector for small target sizes and large detector area for measuring multiple targets at once. The purpose of this study is to evaluate a high-resolution large-area two-dimensional (2D) detector array for pre-treatment verification of multiple-target SRS plans using a single isocenter. <h3>Materials/Methods</h3> A 2D detector array was evaluated for this purpose. It is based on a silicon complementary metal-oxide-semiconductor platform, which enables a compact design, fast read-out, and high pixel density with each pixel comprising a radiation-sensitive photodiode, a capacitor and three transistors. Its spatial resolution is 0.4 mm, with 105,000 pixels across a large active area of 120 × 140 mm². Ten multiple-target SRS plans were selected such that each plan has at least 2 targets appear on a longitudinal plane cross the isocenter. All plans were created in a treatment planning system using 6 MV flattening filter free photon beam. The typical plan consisted of one or two coplanar arcs, and two to three non-coplanar arcs. All plans were delivered in patient geometry with the detector center aligned to the plan isocenter. The detector plane was rotated to the corresponding desired longitudinal plane to measure the composite dose in a single measurement. The smallest target measured was 0.12 cc. The largest center-to-center target separation measured was 12 cm. Six of the plans in which the target separations were relatively short were able to be cross verified with a patient-specific quality assurance (PSQA) tool, whose detector area is of 77 × 77 mm². The measured 2D dose distributions in true composite were compared with the calculated dose distributions. Gamma index analysis was performed using 3%/1 mm criteria with a 10% dose threshold. <h3>Results</h3> With the 2D detector array, the gamma passing rates are all greater than 95% except one, which is 93%. The average gamma-passing rate is 97.7%. For the 6 plans cross verified, the average gamma-passing rates are 98.2% and 96.1% with the 2D detector array and PSQA tool, respectively. <h3>Conclusion</h3> The 2D detector array was demonstrated to be suitable and offers an efficient way for pre-treatment verification of multiple-target SRS plans using a single isocenter. The advantages of this 2D array include: 1) High-resolution of 0.4 mm avoids dose interpolations for plans calculated with 0.5 -1.0 mm dose grid and potentially avoids "false positive" results due to more measured points; 2) Large active area of 120 × 140 mm² allows simultaneous verification of multiple targets in true composite in patient geometry.

Improved Deep CNN-based Two Stream Super Resolution and Hybrid Deep Model-based Facial Emotion Recognition

Humans have traditionally found it easy to determine emotions from facial expressions, but doing so by utilizing a computer algorithm is far more challenging. It is now feasible to discern emotions from photographs because of recent advances in computer vision as well as artificial intelligence. The following issues afflict existing face expression detection systems throughout the application process: As the extant shallow feature extraction framework has lost a great deal of effective feature data and also has limited detection performance, the paper proposes a novel technique termed “Improved Deep CNN-based Two Stream Super Resolution and Hybrid Deep Model-based Facial Emotion Detection”, which consists of three working phases: super-resolution, facial emotion recognition, as well as classification. Improved Deep CNN has been used in the super-resolution phase for two streams, structure and texture stream super-resolution, that delivers high pixel density to the pictures with minimal cross-entropy loss. The facial emotion identification phase involves face recognition utilizing the Viola–Jones face detection algorithm and feature extraction using three traditional methods: Texton, Bag of Words (BOW), and GLCM, as well as improved LGXP features. In addition, classification was performed in our work utilizing RNN as well as Bi-GRU neural networks. A voting mechanism known as Score level fusion was used to get precise categorization results. Our unique Deep CNN-based facial emotion recognition system provides 95% accuracy, which is superior to other traditional approaches, according to the results. Positive and negative performance metrics for various databases have also been assessed and compared with our proposed methodology, proving that our novel strategy surpasses conventional approaches.

29.2: Invited Paper: A Brief Introduction to Advantages of LTPS Technology in High‐end NB

The electron mobility based on low temperature polysilicon is almost 100 times that of amorphous silicon, so low temperature polysilicon technology has overwhelming advantages in high pixel density, high refresh rate, narrow frame and other aspects. This paper will focus on the application of LTPS technology in the future high‐end notebook, mainly from the four dimensions of narrow border, power consumption, wide frame rate (WFR) ,low power consumption and incell, and discuss the industry trends, the technical bottlenecks of LTPS process and the current progress made by CSOT in these points. At present, LTPS technology has took a piece of the cake in the high‐end notebook market, and definitely present. Through the above introduction we believe that with the continuous breakthrough of LTPS technology bottleneck, it will bring a new chapter in the development of high‐end notebook.

(Invited, Digital Presentation) Oxide TFTs Based on Semiconductors and Semimetals

A bottleneck issue of oxide TFTs is the instability under bias stresses and illuminations. Furthermore, the carrier mobility needs improvement for high pixel density and high brightness displays. Here, we use a high work-function Schottky source contact to enable depletion around the TFT source region. This results in a high intrinsic immunity to negative bias illumination stress, no obvious short channel effect, and extremely flat current saturation at low drain voltages. A voltage gain reaching 23,000 V/V is obtained due to the flat saturation current, which is the highest ever achieved with a solid-state transistor. Furthermore, the Schottky barrier depletion allows to utilize ITO to replace IGZO as the channel layer, which significantly enhances carrier mobility. Because ITO is used for both channel and drain electrode, the TFT appears to have no channel, enabling aggressive scaling for a significant increase in flat-panel display pixel aperture ratio, brightness and pixel density.

Well-Designed Smartphone-Based Imaging Biosensor

With the development of hardware and software for smartphones, more and more well-designed smartphone-based imaging biosensors have been created and broadly applied in point-of-care testing (POCT). Imaging biosensors can get clear images through the high pixel density of smartphones’ camera systems. And smartphones also provide a chance for imaging processing thanks to smartphones' central processing units (CPUs) and graphics processing units (GPUs). Different approaches have extensively explored smartphone-based imaging biosensors. The commonly used imaging methods are generally implemented by the bright field with the light source or by fluorescence with a fluorescence microscope. Smartphones have enabled the widespread application of imaging-based methods in clinical chemistry, environmental monitoring, flow cytometry, food analysis, drug screening, and medical diagnostics. In detail, this article discusses various imaging biosensors and specific applications of smartphone-based imaging biosensors for bright-field imaging and fluorescence bioimaging. Meanwhile, the opportunities and challenges of smartphone-based imaging biosensors are also analyzed here.

Pixel-density enhanced integral three-dimensional display with two-dimensional image synthesis.

Integral three-dimensional (3D) displays can display naturally viewable 3D images. However, displaying 3D images with high pixel density is difficult because the maximum pixel number is restricted by the number of lenses of a lens array. Therefore, we propose a method for increasing the maximum pixel density of 3D images by optically synthesizing the displayed images of an integral 3D display and high-definition two-dimensional display using a half mirror. We evaluated the improvements in 3D image resolution characteristics through simulation analysis of the modulation transfer function. We developed a prototype display system that can display 3D images with a maximum resolution of 4K and demonstrated the effectiveness of the proposed method.

3200 ppi Matrix-Addressable Blue MicroLED Display.

In this article, an active matrix (AM) micro light-emitting diode (MicroLED) display with a resolution of 1920 × 1080 and a high pixel density of 3200 pixels per inch (ppi) is reported. The single pixel with a diameter of 5 μm on the MicroLED array exhibits excellent characteristics, including a forward voltage of 2.8 V at 4.4 μA, an ideality factor of 1.7 in the forward bias of 2–3 V, an extremely low leakage current of 131 fA at −10 V, an external quantum efficiency of 6.5%, and a wall-plug efficiency of 6.6% at 10.2 A/cm2, a light output power of 28.3 μW and brightness of 1.6 × 105 cd/m2 (nits) at 1 mA. The observed blue shift in the electroluminent peak wavelength is only 6.6 nm from 441.2 nm to 434.6 nm with increasing the current from 5 μA to 1 mA (from 10 to 5 × 103 A/cm2). Through flip-chip bonding technology, the 1920 × 1080 bottom-emitting MicroLED display through the backside of a sapphire substrate can demonstrate high-resolution graphic images.

Multi-view density-based field-road classification for agricultural machinery: DBSCAN and object detection

Field-road classification that automatically identifies the operation modes (either in-field or on-road) of GNSS (Global Navigation Satellite System) points plays an important role for the operational performance analysis of agricultural vehicles. Intuitively, a field often has high point density because in-field driving speed is rather low and the distance between consecutive strips is closed. In this paper, two methods were used to capture the in-field high-density characteristic: DBSCAN (Density-Based Spatial Clustering of Applications with Noise) and an object detection model. DBSCAN is a widely-used density-based clustering algorithm, which clusters the points with high point density into a cluster. Alternatively, a trajectory can be transformed into an image, and an object detection model can be applied to detect objects in the image, where an object is a set of pixels with high pixel density (i.e., a set of points with high point density). Finally, the two field-road classification results are combined using DBI (Davis Bouldin index), a metric which can evaluate the quality of either classification result. The developed method was validated by the harvesting trajectories of two crops (wheat and paddy), and the density-based field-road classification achieved 85.97% and 73.34% accuracy on the wheat data and the paddy data, respectively.

A review on Single Image Super Resolution techniques using generative adversarial network

Single Image Super Resolution (SISR) is a process to obtain a high pixel density and refined details from a low resolution (LR) image to get upscaled and sharper high-resolution (HR) image. In last decade, SISR based on Convolutional Neural Networks (CNN) have achieved impressive results for generating super-resolved images up to the size of ×3. This technique focuses on minimizing L1/L2 loss between real HR image and generated HR image without considering the perceptual quality of images. To improve upon, SISR based on Generative Adversarial Network (GAN) has gained researchers attention for generating visually pleasing images with reasonably minimizing L1/L2 loss for ×4 size images. The basic idea of GAN is to train two networks simultaneously, a Generator and a Discriminator such that generator can produce the super-resolved image for a given input LR image by learning real HR image distribution. This paper presents an overview of GAN based SISR techniques for further research as there are a few surveys in this area. Different GAN models have been classified in terms of architecture, algorithms, and loss functions including their benefits and limitations. Lastly, the research gaps as well as some possible solutions for the existing methods have been discussed.

A Stacked p‐Type Low‐Temperature Polycrystalline Silicon Thin‐Film Transistor for Future Display Applications

AbstractIn this study, a novel structural design of the p‐type low‐temperature polycrystalline silicon thin‐film transistors (p‐type LTPS TFTs) applied to the pixel structure of displays is proposed. Compared to the conventional pixel structure of displays, the proposed architecture can achieve the aperture ratio improvement by stacking the switch thin‐film transistor and the storage capacitor in a pixel region to enlarge the active space. Therefore, the demands of high‐resolution characteristics, such as a high aperture ratio, and high pixel densities for high‐end displays or novel technologies, can be satisfied by the adoption of the proposed design concept. Furthermore, the discussion of experimental and simulated results in terms of device physics of the transistor indicates that proposed TFTs possess higher performance and reliability properties. By modulating the geometry of the drain‐connected bottom metal in stacked TFTs, output characteristics and hot carrier phenomenon in devices can be further improved. Time‐dependent transfer characteristics, extracted electrical parameters, and numerical simulation results are performed to support our design.

Vertical Oxide Channel Thin Film Transistor for Ultra-High-Resolution Display

The significance of backplane devices for ultra-high-resolution (UHR) display has increased with the recent development of augmented reality (AR) and virtual reality (VR) devices. Since the human visual resolution can distinguish up to 60 pixels per degree (PPD), the AR/VR device panel needs at least 3000 pixels per inch (PPI) to exceed the human retina resolution limit for clear display without screen effect. As a results, the unit pixel pitch of thin film transistor (TFT) for UHR display should be not only smaller than a few micrometers (~3 μm), TFT channel length should also be sub-micrometers level. In active matrix organic light emitting diode (AMOLED) display type, self-aligned top gate (SATG) TFT has been widely used as a planar backplane device structure because of its low parasitic capacitance and tolerance of illumination degradation caused by the light from emitting layer [1-2]. However, SATG TFT has fundamental disadvantages for device miniaturization due to its essentially required area of metallization region for reducing contact resistance and scaling limit of channel induced by carrier diffusion shrinking effective channel length. For this reason, we suggested a size tunable oxide channel VTFT structure that can achieve a high pixel density on account of structural benefit on device footprint.In this work, we fabricated amorphous indium gallium zinc oxide (a-IGZO) based VTFT. The previously published VTFT structure, channel length is determined by the thickness of spacer between source and drain electrodes [3]. Owing to spacer etching process, uneven backchannel roughness and high off current has become well-known issues of VTFT. On the contrary, the proposed VTFT structure has a controllability of effective channel aspect ratio because source and drain electrodes are able to be patterned by photolithography process. Furthermore, the parasitic capacitance is also relatively less than the formerly reported VTFTs controlled by inevitable thickness limit structurally due to the electrodes.To sum up, we not only realized the oxide channel VTFT that meets high performance for AR/VR display, but opened new application possibility to UHR electronic devices platform. Figure 1. (a) Schematic of the proposed VTFT (b) Transfer characteristic of VTFT Acknowledgement This work was supported by the Korea Evaluation Institute of Industrial Technology(KEIT) grant funded by the Korea government (MOTIE) (No. 2021-11-1283) References Kang, Dong Han, et al. "Self-aligned coplanar a-IGZO TFTs and application to high-speed circuits." IEEE electron device letters 32.10 (2011): 1385-1387.Wang, Guoying, et al. "8.3: High Stability Against Light and Heat Based on the Top Gate Self‐Aligned a‐IGZO TFTs under OLED Dislplay." SID Symposium Digest of Technical Papers. Vol. 49. 2018.Petti, Luisa, et al. "Flexible quasi-vertical In-Ga-Zn-O thin-film transistor with 300-nm channel length." IEEE Electron Device Letters36.5 (2015): 475-477. Figure 1

41‐3: Invited Paper: High Resolution Stretchable Micro‐LED Displays

The RGB micro‐LED display has been demonstrated to withstand mechanical strain during out‐of‐plane periodically deformation. In this work, the high pixel density (&gt;139‐PPI) and high strain tolerance of circuits were achieved by utilizing the novel design of the island‐bridge structure under the compact pixel arrangement. Light absorbent was adopted into a stretchable display to reduce ambient back light and ambient reflection for the dark mode of a panel