High performance color‐converted micro‐LED displays

A full‐color micro‐LED display can be achieved by red, green, and blue (RGB) chips or by a blue/ultraviolet (UV) micro‐LED array to pump downconverters. The latter helps relieve the burden of epitaxial growth of tri‐color micro‐LED chips. However, such a color‐converted micro‐LED system usually suffers from color crosstalk and low efficiency due to limited optical density of color converters. With funnel‐tube array and reflective coating on its inner surface, the crosstalk is eliminated, and the optical efficiency can be improved by more than two times. In addition, the ambient contrast ratio is also improved because of higher light intensity. The color gamut of this device is approximately 92% of DCI‐P3 standard.     

Ten micrometer pixel,quantum dots color conversion layer for high resolution and full color active matrix micro‐LED display

A fine patternable quantum dots (QDs) color conversion layer (CCL) for high resolution and full color active matrix (AM) micro‐LED (μ‐LED) display is demonstrated. QDs CCL could be patterned until 10 μm using photolithography process. It is found that multicoatings with red and green QDs (R‐ and G‐QDs) CCLs on LED array can provide full color AM display.     

Inorganic light‐emitting diode displays using micro‐transfer printing

Large quantities of microscopic red, green, and blue light‐emitting diodes (LEDs) made of crystalline inorganic semiconductor materials micro‐transfer printed in large quantities onto rigid or flexible substrates form monochrome and color displays having a wide range of sizes and interesting properties. Transfer‐printed micro‐LED displays promise excellent environmental robustness, brightness, spatial resolution, and efficiency. Passive‐matrix and active‐matrix inorganic LED displays were constructed, operated, and their attributes measured. Tests demonstrate that inorganic micro‐LED displays have outstanding color, viewing angle, and transparency. Yield improvement techniques include redundancy, physical repair, and electronic correction. Micro‐transfer printing enables revolutionary manufacturing strategies in which microscale LEDs are first assembled into miniaturized micro‐system “light engines,” and then micro‐transfer printed and interconnected directly to metallized large‐format panels. This paper reviews micro‐transfer printing technology for micro‐LED displays.     

High‐resolution and high‐brightness full‐colour “Silicon Display” for augmented and mixed reality

High‐brightness micro‐LED display bonded onto silicon backplane has been successfully demonstrated. The 0.38‐inch full‐colour active matrix LED microdisplay system consists of 352 × 198 pixels. Each pixel is 24 μm square composed of red, green, and blue (RGB) subpixels corresponding to a pixel resolution of 1053 ppi. Quantum‐dot materials are formed on III‐nitride blue micro‐LED array to convert blue light into red and green for full‐colour operation. We have confirmed that this microdisplay, which we call “Silicon Display” has wide colour gamut exceeding 120% of sRGB. We describe the advantage of this colour‐converting approach for the full‐colour micro‐LEDs. Progress toward higher resolution is also described. Brightness of more than 30 000 cd/m² has been confirmed at a driving current density of 4 A/cm² for 3000 ppi blue monochrome micro‐LED prepared for full‐colour Silicon Display. We believe our “Silicon Display” is ideally suited for near‐to‐eye displays for augmented and mixed reality.     

Fully‐integrated active matrix programmable UV and blue micro‐LED display system‐on‐panel (SoP)

High pixel per inch and high‐resolution micro‐LED displays are attracting more and more attentions. The increasing pixel number requires a large amount of bonding pads and brings huge difficulties to micro‐LED system design and lowers power efficiency as well. It is urgent to integrate row and column driving circuits onto the micro‐LED panel. Here, we report a fully integrated active matrix programmable micro‐LED system on panel (SoP) with ultraviolet and blue emission wavelengths. The micro‐LED SoP has a resolution of 60 × 60 and pixel pitch of 70 μm. The micro‐LED SoP was achieved by integrating micro‐LED arrays with silicon‐based p‐channel metal‐oxide semiconductor driving panel using fine‐toned flip‐chip bonding technology. With fully integrated scan and data circuits, the number of bonding pads was greatly reduced from 136 to 28, and large amount of metal interconnection lines were saved. The micro‐LED SoP panel was mounted on a periphery driving board, and representative characters were displayed successfully.     

In‐pixel temperature sensor for high‐luminance active matrix micro‐light‐emitting diode display using low‐temperature polycrystalline silicon and oxide thin‐film‐transistors

We propose an in‐pixel temperature sensor using low‐temperature polycrystalline silicon and oxide (LTPO) thin‐film transistor (TFTs) for high‐luminance active matrix (AM) micro‐light‐emitting diode (LED) displays. By taking advantage of the different off‐current characteristics of p‐type LTPS TFTs and n‐type a‐IGZO TFTs under temperature change, we designed and fabricated a temperature sensor consists of only LTPO TFTs without additional sensing component or material. The fabricated sensor exhibits excellent temperature sensitivity of up to 71.8 mV/°C. In addition, a 64 × 64 temperature sensor array with 3T sensing pixel and integrated gate driver has also been fabricated, which demonstrates potential approach for maxing out the performance of high‐luminance AM micro‐LED display with real‐time in‐pixel temperature monitoring.     

Prospects and challenges of mini‐LED and micro‐LED displays

We review the emerging mini/micro–light‐emitting diode (LED) displays featuring high dynamic range and good sunlight readability. For mini‐LED backlit liquid crystal displays (LCDs), we quantitatively evaluate how the device contrast ratio, local dimming zone number, and local light profile affect the image quality. For the emissive mini/micro‐LED displays, the challenges of ambient contrast ratio and size‐dependent power efficiency are analyzed. Two figure‐of‐merits are proposed for optimizing the optical and electrical performances of mini/micro‐LED displays.     

Backlight unit with double‐surface light emission using a single micro‐structured lightguide plate

Abstract— A novel illumination system for a liquid‐crystal‐display (LCD) module used in a dual‐display cellular phone has been developed. A double‐surface light‐emitting backlight uses a single light‐guide plate to illuminate both LCDs. A single lightguide, two prism sheets, and four light‐emitting diodes (LED) were used in the new structure, compared with ten components and two sets of light sources with six LEDs in the current backlight. The thickness and power consumption of the new backlight were reduced by a factor of 0.59 and 0.67, respectively.     

Electro‐optic properties of an intrinsic half‐V‐mode FLCD and its application to field‐sequential full‐color LCDs using a poly‐Si TFT matrix array

Abstract— An intrinsic half‐V‐mode ferroelectric liquid‐crystal display (FLCD) exhibiting a high contrast ratio (300:1), owing to defect‐free gray‐scale capability, with a high response speed (τ ? 400 μsec) and good switchability with TFTs, has been developed. Furthermore, this FLCD features high‐temperature reliability owing to the use of a special hybrid alignment technique. We successfully fabricated an active‐matrix poly‐Si TFT field‐sequential full‐color (FS FC) LCD with XGA specifications and a 0.9‐in. diagonal using a half‐V‐mode FLCD and an RGB light‐emitting‐diode (LED) array microdisplay. It is shown that the fabricated active‐matrix FS FCLCD exhibits good moving‐image performance with high full‐color display capability.     

Wafer‐scale monolithic hybrid integration of Si‐based IC and III–V epi‐layers—A mass manufacturable approach for active matrix micro‐LED micro‐displays

Hybridization of silicon integrated circuits (ICs) with compound semiconductor device arrays are crucial for making functional hybrid chips, which are found to have enormous applications in many areas. Although widely used in manufacturing hybrid chips, the flip‐chip technology suffers from several limitations that are difficult to overcome, especially when the demand is raised to make functional hybrid chips with higher device array density without sacrificing the chip footprint. To address those issues, Beida Jade Bird Display Limited has developed its unique wafer‐level monolithic hybrid integration technology and demonstrated its advantages in making large‐scale hybrid integration of functional device arrays on Si IC wafers. Active matrix micro‐light‐emitting diode micro‐displays with a resolution of 5000+ pixel per inch were successfully fabricated using Beida Jade Bird Display Limited's monolithic hybrid integration technology. The general fabrication method is described, and the result is presented in this paper. The fabricated monochromatic micro‐light‐emitting diode micro‐displays exhibit improved device performance than do other micro‐display technologies and have great potentials in applications such as portable projectors and near‐to‐eye projection for augmented reality. More importantly, the wafer‐scale monolithic hybrid integration technology offers a clear path for low‐cost mass production of hybrid optoelectronic IC chips.     

Design of micro‐machined modified Sierpinski gasket fractal antenna for satellite communications

Modified Sierpinski gasket fractal patch antenna for earth exploration satellite services has been proposed in this article. The proposed antenna is designed up to third iterative fractal geometry on the FR4 substrate having dielectric constant of 4.4 with height of 0.8 mm. The proposed design shows multiband characteristics at 2.8, 6.1, 7.96, 16, and 17 GHz frequencies. The maximum gain of the proposed design is 9.6 dBi has been achieved in Ku‐band. The resonating performance characteristics and radiation characteristics of the final iteration are investigated using simulator and experimentally to verify the results of the proposed design. The simulated and measured performance parameters show quite resemblance. Further, proposed design has been simulated on the micro‐machined high resistive silicon substrate which causes the improvement in gain and efficiency. Micro‐machined fractal antenna is compatible with monolithic microwave integrated circuits (MMICs).     

High‐efficiency quantum dot light‐emitting diodes with blue cadmium‐free quantum dots

We report outstanding electroluminescence properties of high‐efficiency blue cadmium‐free quantum dot light‐emitting diodes (QD‐LED). External quantum efficiency (EQE) of 14.7% was achieved for QD‐LED emitting at 428 nm. Furthermore, we developed high‐efficiency and narrow wavelength emission zinc selenide (ZnSe) nanocrystals emitting at 445 nm and achieved QD‐LED with an EQE of 10.7%. These new QDs have great potential to be used in next‐generation QD‐LED display with wide color gamut.     

Wide gamut LCD using locally dimmable four‐primary‐color LED backlight

This paper proposes a wide gamut LCD using locally dimmable four‐primary‐color (4PC) LED backlight. Although the color gamut of LCDs has been improved in recent years, it is insufficient to reproduce all the colors in the real world. The objective of this paper is to propose a wide gamut LCD that reproduces all the colors in the real world while keeping the cost increases to a minimum. We evaluated the color gamut reproduced by LEDs of multiple primary colors and selected cyan as the optimal color to be added to the three primary colors to reproduce all the colors in the real world. Therefore, we designed an LED backlight consisting of an additional only‐cyan LED with three‐primary‐color LEDs and developed a prototype LCD with 4PC LED backlight. Furthermore, we developed a local dimming algorithm for the 4PC LED backlight. As a result, we confirmed that the prototype LCD with the 4PC LED backlight is able to cover almost all the colors in the real world and also able to display natural images with highly saturated colors by local dimming.     

Color performance of an MVA‐LCD using an LED backlight

Abstract— The color performance, including color gamut, color shift, and gamma curve, of a multi‐domain vertical‐alignment (MVA) liquid‐crystal display (LCD) using an LED backlight are calculated quantitatively. Simulation results indicate that an LED backlight exhibits better angular color uniformity and smaller color shifts than a CCFL backlight. Color gamut can be further widened and color shift reduced when using a color‐sequential RGB‐LED backlight without color filters, while the angular‐dependent gamma curves are less influenced using different backlights. The obtained quantitative results are useful for optimizing the color performance and color management of high‐end LCD monitors and LCD TVs.     

Viewing‐angle‐enhanced integral imaging system using high‐refractive‐index medium and curved micro‐lens array

In the integral imaging (II) system using a curved micro‐lens array (MLA), the viewing angle is limited by the gap mismatch. Here, we propose a system to decrease the gap mismatch for enhancing the viewing angle. In the proposed system, a layer of high‐refractive‐index medium is assembled between the display panel and the curved MLA. The principle of the proposed II system is studied in detail. Simulations based on ray tracing are performed, and the results show that the proposed II system can effectively enhance the viewing angle.     

High‐efficiency PDP micro‐discharges

Abstract— High‐efficiency plasma‐display‐panel micro‐discharge characteristics will be discussed. An increase in the discharge efficiency for a higher‐Xe‐content gas mixture is well known. In this article, the interdependency of the capacitive design, the sustain voltage, and the Xe content will be discussed. A high panel efficacy was obtained, especially for the design and driving conditions that govern the development of a fast discharge. A fast discharge was observed for a higher discharge field at sustain voltages higher than 200 V. A +C‐buffer design, where the extra capacitance acts as a local on the panel power source that lowers the voltage decrease inherent to the discharge of the discharge capacitance upon firing, and efficient priming of the discharge at higher sustain frequency, also stimulates a fast‐discharge development. Apparently, a “high‐efficiency fast‐discharge mode” exists. It is proposed that in this mode the cathode sheath is not, or incompletely, formed during the increase in the discharge current, and the electric field in the discharge cell is dominated not by the space charges but by the externally applied voltage. The effective discharge field is lowered, resulting in a lower effective electron temperature and more efficient Xe excitation. Also, under a fast discharge build‐up condition, the electron‐heating efficiency increases, due to a decrease in the ion heating losses in the cathode sheath. In a 4‐in. color plasma‐display test panel, operating in a high‐efficiency discharge mode and containing a 50%Xe in Ne gas mixture, a panel efficacy of 5 lm/W concurrent with a luminance of 5000 cd/m² was realized. This result was obtained at a sustain voltage of 260 V. These data compare favorably with alternative high‐efficacy panel design approaches.     

Spatio‐temporal scanning backlight mode for field‐sequential‐color optically‐compensated‐bend liquid‐crystal display

Abstract— A spatially and temporally scanning backlight consisting of ten isolated micro‐structured light guides has been developed to be combined with a fast‐response optically‐compensated‐bend‐mode field‐sequential‐color LCD in which the liquid‐crystal cell does not contain color filters. The sequential fields of three primary colors are generated by illumination of the red‐, green‐, and blue‐light‐emitting diodes, each illuminating for one‐half of the field, resulting in a luminance of 200 cd/m² for the LCD. The effect of light leakage between the blocks in the scanning backlight in field‐sequential‐color applications was measured and will be described.     

lmbench: an extensible micro‐benchmark suite

lmbench is a powerful and extensible suite of micro‐benchmarks that measures a variety of important aspects of system performance. It has a powerful timing harness that manages most of the ‘housekeeping’ chores associated with benchmarking, making it easy to create new benchmarks that analyze systems or components of specific interest to the user. In many ways lmbench is a Swiss army knife for performance analysis. It includes an extensive suite of micro‐benchmarks that give powerful insights into system performance. For those aspects of system or application performance not covered by the suite, it is generally a simple task to create new benchmarks using the timing harness. lmbench is written in ANSI‐C and uses POSIX interfaces, so it is portable across a wide variety of systems and architectures. It also includes powerful new tools that measure performance under scalable loads to analyze SMP and clustered system performance. Copyright © 2005 John Wiley & Sons, Ltd.     

Sequential‐color LCD based on OCB with an LED backlight

We have fabricated a 13.3‐in. XGA (1024 × 768) TFT sequential‐color liquid‐crystal display using optically compensated birefringency (OCB), illuminated by an LED backlight. We fabricated the sequential‐color display feasible process technology, and examined the performance and potential of a field‐sequential‐color scheme. The display was connected to a laptop computer and examined for flicker.     

Transfer printing for fabrication of flexible RGB color e‐paper

Electrophoretic display (EPD) has been a prevailing paper‐like display technology for years, owing to its advantages of flexibility, low‐power consumption, and good sunlight readability. However, it is regrettable that the black/white EPD still dominates the majority of the market while a commercially sold full‐color EPD is still unavailable. In this paper, we proposed a facile yet feasible method to fabricate a color EPD by a tape‐assisted transfer method, which is the first demonstration using transfer method to achieve color micro‐encapsulated EPD.