Conventional Liquid Crystal Display Research Articles

P‐13: Picture Quality of In‐Plane Switching Liquid Crystal Displays with Deep Black

In‐Plane Switching (IPS) liquid crystal display (LCD) is one of leading technologies in display industrials because of its superior picture quality. This paper provides picture quality of high contrast IPS LCD in terms of color contrast, dynamic range, color expression and PQ‐EOTF accuracy in HDR compared to conventional IPS LCD. Furthermore, to evaluate its performance as a gaming display, reaction time between two IPS LCDs have different contrast ratio was tested. Experimental results indicate that observer's reaction time for high contrast IPS LCD was faster than conventional IPS LCD because of superior color contrast and color gamut at low luminance level.

High fidelity mini-LED backlit liquid crystal displays

ABSTRACT Mini-LED backlit liquid crystal display (LCD) exhibits premium display performance, benefiting from the new design space enabled by the mini-LED backlight unit: the flexibility in subframe sequential illumination enables motion blur reduction; the selective illumination of bright zones and dark zones offers high dynamic range, good sunlight readability and power saving; the high zone density suppresses the visual artefact of ‘halo effect’ that is commonly observed in conventional local dimming LCDs. In this paper, we discuss limiting factors and solutions to achieve high display fidelity regarding the abovementioned performance metrics.

Flexoelectric-effect-based light waveguide liquid crystal display for transparent display

We report a light waveguide liquid crystal display (LCD) based on the flexoelectric effect. The display consists of two parallel flat substrates with a layer of flexoelectric liquid crystal sandwiched between them. A light-emitting diode (LED) is installed on the edge of the display and the produced light is coupled into the display. When no voltage is applied, the liquid crystal is uniformly aligned and is transparent. The incident light propagates through the display by total internal reflection at the interface between the substrate and air, and no light comes out of the viewing side of the display. The display appears transparent. When a voltage is applied, the liquid crystal is switched to a micrometer-sized polydomain state due to flexoelectric interaction and becomes scattering. The incident light is deflected from the waveguide mode and comes out of the viewing side of the display. We achieved thin-film-transistor active matrix compatible driving voltage by doping liquid crystal dimers with large flexoelectric coefficients. The light waveguide LCD does not use polarizers as in conventional LCDs. It has an ultrahigh transmittance near 90% in the voltage-off state. It is very suitable for transparent display, which can be used for head-up display and augmented reality display.

Color mismatch and observer metamerism between conventional liquid crystal displays and organic light emitting diode displays, Part II: Adjacent stimuli with a larger field of view

In part I of this study [Opt. Express 29, 12292 (2021)10.1364/OE.418675], 50 human observers matched the color appearance of six color stimuli produced by four smartphone displays, including one conventional liquid crystal display (LCD) and three organic light emitting diode (OLED) displays, to those produced by a reference smartphone OLED display. The matching and reference stimuli had a field of view (FOV) around 4.77° and were 5.72° apart. In this experiment, we carefully designed and built a new apparatus to make the two stimuli adjacent to each other with an FOV around 20.2°. This not only made the viewing condition in the experiment similar to the typical viewing condition of smartphone displays, but also allowed for an easier color matching, resulting in smaller intra- and inter-observer variations. The performance of the four CMFs, however, were not significantly changed with the increase of the FOV. The CIE 2006 2° CMFs still had the best performance in characterizing the color matches, which did not support the recommendation of using 10° CMFs for stimuli with an FOV beyond 4°. Meanwhile, for the pairs of stimuli with matched color appearance, the LCD display always had the greatest chromaticity differences and degrees of observer metamerism among the four displays, regardless of the CMFs. In particular, the chromaticities of the stimuli produced by the LCD display were always shifted towards the -u’+v’ direction in the CIE 1976 u’v’ chromaticity diagram, when calculated using the CIE 1931 CMFs. This implies that the neutral colors shown on LCD displays would have a yellow-green tint on OLED displays, if they were calibrated to the same chromaticities using the CIE 1931 2° CMFs.

Building a Display Field Leader: SKL's Journey

Building a Display Field Leader: SKL's Journey

A Self-Refreshing Memory-in-Pixel Comprising Low Temperature Poly-Silicon and Oxide TFTs for 3-Bit Liquid Crystal Displays

In this letter, a self-refreshing multi-level memory-in-pixel (MIP) circuit for liquid crystal display (LCD) comprising low temperature poly-silicon and oxide (LTPO) thin film transistors (TFTs) is proposed. Since the proposed MIP circuit features self-refreshing without embedding frame memory, power consumption can be minimized when displaying a still image. Measurement results verify that the proposed circuit successfully enables a 3-bit grayscale. The LCD employing the proposed MIP circuit consumes only 1.22 % of power compared with a conventional LCD when displaying a still image. Thus, the proposed multi-level MIP circuit is expected to enable a low-power LCD featuring higher color depth with a simple structure.

A high transmittance and fast response in-plane switching liquid crystal display with the zero-azimuth anchoring layers on the electrodes

An in-plane switching (IPS) liquid crystal display (LCD) containing the zero-azimuth anchoring layers formed only on the electrodes and rubbed polyimide (PI) covered on the other areas was successfully developed. This configuration was realized using photoreactive PI with photo-radical generation units and the mask exposure technique. The maximum transmittance (Tmax) of this LCD was 1.12 times higher than that of a conventional IPS LCD. This was attributed to a large aperture in the voltage-on state because the nematic liquid crystals (NLCs) on the electrodes were barely anchored to the surface, such that the NLCs could be rotated by applying a small in-plane electric field above the electrodes, and by an elastic torque caused by the twisted NLCs between the electrodes. Furthermore, the response times of this LCD were equivalent to those of a conventional IPS LCD because the NLCs between the electrodes quickly recovered to their initial orientation after removing the electric field, and the NLCs on the electrodes followed this movement. This novel LCD is termed a ‘partially zero-azimuth anchoring IPS (PZ-IPS) LCD’, which is the first practical LCD utilizing these weak anchoring characteristics in the history of LCDs.

Novel in-plane switching liquid crystal display with an extremely high transmittance using a well-designed bottlebrush as a zero-azimuth anchoring material

In this study, a one-side zero-azimuth anchoring in-plane switching (OZ-IPS) liquid crystal display (LCD) employing poly(n-hexyl methacrylate) (PHMA) bottlebrush polymers as an application-type zero-azimuth anchoring material was successfully developed. The twist anchoring coefficient A2 measured for the nematic liquid crystal (NLC) on the PHMA bottlebrush at 25 °C was comparable to that of the same NLC on high-density PHMA brushes. Optimizing the optical design increased the transmission efficiency (TE) of the OZ-IPS cell with the negative NLC to 95%, which was significantly higher than that of conventional IPS cells. Using optical simulation, the OZ-IPS LCDs with a negative NLC clearly exhibited the highest TE (≃107% of TN LCDs) for LCDs developed thus far. Moreover, the higher transmittance of the OZ-IPS LCDs was also confirmed for the practical TFT LCD, which exhibited a maximum luminance that was 30% higher than conventional IPS TFT LCDs.

Self-powered nanodevices for fast UV detection and energy harvesting using core-shell nanowire geometry

Developing multiple functionalities in nanodevices is a desirable objective in current nanotechnology, where the self-powered capability is one of the most demanded functions—without the need of external batteries, nanodevices can be operated independently and maintenance-free for a long period of time. In this study, we fabricated the core-shell nanostructured device employing multi-walled carbon nanotubes (CNTs) as inner cores and ZnO as outer shells, and demonstrate their multiple functionalities of fast UV detection and self-powered capability. The device features high photoconductive gain of 800 and short response time of 0.48 ms in air and 29 ms in vacuum. For energy harvesting, the device shows photovoltaic (PV) capability to drive a conventional liquid crystal display (LCD) with a Voc of 0.85 V and Isc of 5 nA. Those features demonstrate that our CNT-ZnO core-shell nanostructured device, performing both high photoresponsivity and PV capability, can be operated in different functionalities with or without external bias.

Influence of Size and Current Density on the Optoelectrical Properties of Green III-Nitride Micro-Light-Emitting Diodes

High efficiency III-nitride light-emitting diodes (LEDs) have been applied to solid-state lighting. A luminous efficacy (about 150 lm/W) of InGaN/GaN-based LEDs is much higher than those of other self-emissive devices such as organic LEDs (OLEDs). As mobile electronics scale down, display technologies must also move to smaller form factors and ultra-high resolutions while maintaining high efficiencies to extend battery lifetime. III-nitride LEDs are an ideal candidate for achieving these goals. Current technologies including liquid crystal displays (LCDs) and organic light emitting diode (OLED) suffer from low efficiencies and brightness. For the realization of ultrahigh resolutions, around 10 μm or smaller light-emitting pixel sizes are required. In this regard, the InGaN/GaN μLED-based displays have emerged as a promising technology in terms of high brightness, contrast, luminous efficacies, resolution, compactness, operation under harsh conditions, and long lifetime, which cannot be satisfied by conventional LCD and OLED-based display technologies. Several groups have fabricated single-color μLED-based arrays with pixel dimensions as small as 12 μm. This self-emissive technology can be used in applications where high resolution, brightness, and efficiency are necessary such as smartphones, smartwatches, head-mounted and near-eye displays. In addition, μLEDs have exhibited improved thermal management, enhanced light extraction, and operation at higher current densities over their broad-area counterparts. Despite these benefits, surface recombination at small dimensions has been noted as a potential source for reducing device efficiencies. We have investigated the effect of chip size on the forward voltage, light output, emission image and spectral shift of InGaN based green LEDs (518 nm) as a function of current density. The size of the chips was varied from 10 to 100 μm. The smaller chips exhibited higher light output power although the lower output powers were obtained at the higher current densities. Furthermore, the smallest devices showed the better current spreading at higher current densities. It was observed that green μLEDs underwent spectral shift more pronouncedly when dc drive current increased than when chip size increased. It was observed that variation of dc drive current more pronouncedly affected the spectral shift of green μLEDs compared with change of chip size. The relation between the electroluminescence characteristics and current density of different-size devices exhibited that the devices experienced more dominantly blue shift than red shift. However, at the same current density, the peak of the devices was not shifted when the device size changed. Dependence of size and current density on the spectral shift of green μLEDs will be described and discussed in terms of band-filling and stress relaxation effects.

Photoaligned Nanorod Enhancement Films with Polarized Emission for Liquid‐Crystal‐Display Applications

Semiconductor nanorods (NR) emit polarized light, which is expected to bring manifold benefits, in terms of brightness and color enhancement, for modern liquid-crystal displays (LCD). In this regard, photoaligned nanorod enhancement films (NREF) for color and polarization conversion for LCD backlights are introduced here. The photoinduced anchoring forces, by the photoalignment layer, stimulate well-ordered self-assembly of NR in the thin polymer films. Green and red emitting NR with a quantum yield of ≈80% are aligned unidirectionally and in-plane, showing a polarization ratio of >7:1 and a degree of polarization of >0.81. The photoalignment technique facilitates the fabrication of mixed and multiple stacked NREF for LCDs, which improves the color gamut and polarization efficiency, and is thus expected to increase the optical efficiency of conventional LCDs by ≈60%.

Realization of 95% of the Rec. 2020 color gamut in a highly efficient LCD using a patterned quantum dot film.

An optically efficient liquid-crystal display (LCD) structure using a patterned quantum dot (QD) film and a short-pass filter (SPF) was proposed and fabricated. The patterned QD film contributed to the generation of 95% in the area ratio (or 90% in the coverage ratio) of the Rec. 2020 color gamut. This was achieved by avoiding the problem of interaction between white backlight and broad transmittance spectra of color filters (CFs) as seen in a conventional LCD with a mixed QD film as a reference. The patterned QD film can maintain the narrow bandwidth of the green and the red QD colors before passing through the CFs. Additionally, the optical intensities of the red, green, and blue spectra were enhanced to 1.63, 1.72, and 2.16 times the reference LCD values, respectively. This was a result of separated emission of the red and green patterned QD film and reflection of the red and green light to the forward direction by the SPF.

Going beyond the limit of an LCD\u2019s color gamut

In this study, we analyze how a backlight’s peak wavelength, full-width at half-maximum (FWHM), and color filters affect the color gamut of a liquid crystal display (LCD) device and establish a theoretical limit, even if the FWHM approaches 1 nm. To overcome this limit, we propose a new backlight system incorporating a functional reflective polarizer and a patterned half-wave plate to decouple the polarization states of the blue light and the green/red lights. As a result, the crosstalk between three primary colors is greatly suppressed, and the color gamut is significantly widened. In the experiment, we prepare a white-light source using a blue light-emitting diode (LED) to pump green perovskite polymer film and red quantum dots and demonstrate an exceedingly large color gamut (95.8% Rec. 2020 in Commission internationale de l'éclairage (CIE) 1931 color space and 97.3% Rec. 2020 in CIE 1976 color space) with commercial high-efficiency color filters. These results are beyond the color gamut limit achievable by a conventional LCD. Our design works equally well for other light sources, such as a 2-phosphor-converted white LED.

Aggregate‐induced emission in light‐emitting liquid crystal display technology

AbstractNowadays, liquid crystal displays (LCDs) with light‐emission are considered as energy‐efficient devices and are promising alternatives to conventional LCDs. To realize such possibility, strong fluorescent materials with a dichroic properties are required. Aggregate‐induced emission (AIE) is an unusual photophysical phenomenon shown by some luminogenic materials that will be highly emissive in their aggregate state. In this work, we studied the AIE effect of a luminescent liquid crystalline molecule TPE‐PPE in our LC system as a luminophore dopant. The result showed the excellent AIE effect that higher concentration of luminogen in the nematic LC host induced stronger luminescent intensity. Through exposure of a photoisomeriable alignment material sulfonic‐dye‐1, the photopatterning of a light‐emitting LC device was achieved with the use of the TPE‐PPE/nematic LC mixture.

Hybrid driving method for outdoor public information displays

This paper proposes a pixel structure and a hybrid driving method for improving the transmittance of the liquid crystal display (LCD) for the outdoor public information display (PID) while maintaining the image quality. The proposed driving method uses the pixel consisting of subpixels using red (R), green (G), and blue (B) color filters and white (W) subpixels, and performs in either of two operation modes selected according to the amount of sunlight and the temperature. Mode 1 is a hybrid field sequential mode in which W subpixels are operated to increase the transmittance without the simultaneous contrast problem under the very bright condition. Mode 2 is a low-temperature mode in which only red–green–blue (RGB) subpixels are operated to prevent image distortion under a low-temperature condition. The measurement results from the fabricated LCD were 14.5% transmittance, an over 4000 contrast ratio, and 82.5% color gamut. In addition, the ratio of RGB luminance to the W image is similar to that of the conventional LCD. Therefore, the proposed pixel structure and driving method are appropriate for outdoor PIDs.

What monitor can replace the cathode-ray tube for visual stimulation to elicit multifocal electroretinograms?

To compare a conventional cathode-ray tube (CRT) screen to organic light-emitting diode (OLED) and liquid crystal display (LCD) screens as visual stimulators to elicit multifocal electroretinograms (mfERGs), mfERGs were recorded from seven eyes of seven healthy volunteers (21 ± 2 years). The mfERGs elicited by a conventional CRT screen (S710, Compaq Computer Co.) were compared to those elicited by a studio-grade master OLED monitor (PVM-1741, Sony, Japan) and a conventional LCD (S1721, Flexscan, Eizo Nanao Corp., Japan). The luminance changes of each monitor were measured with a photodiode. CRT, OLED, and LCD screens with a frame frequency of 60 Hz were studied. A hexagonal stimulus array with 61 stimulus elements was created on each monitor. The serial white stimuli of the OLED screen at 60 Hz did not fuse, and that of the LCD screens fused. The amplitudes of P1 and P2 of the first-order kernels of the mfERGs were not significantly different from those elicited by the CRT and OLED screens, and the P1 amplitude of the first-order kernel elicited by the LCD stimuli was significantly smaller than that elicited by the CRT in all the groups of the averaged hexagonal elements. The implicit times were approximately 10 ms longer in almost all components elicited by the LCD screen compared to those elicited by the CRT screen. The mfERGs elicited by monitors other than the CRT should be carefully interpreted, especially those elicited by LCD screens. The OLED had good performance, and we conclude that it can replace the CRT as a stimulator for mfERGs; however, a collection of normative data is recommended.

Optical design and roll‐to‐roll fabrication process of microstructure film for wide viewing LCDs

AbstractWe have developed a new microstructure film for wide viewing liquid crystal displays (LCDs). By attaching it to the surface of a conventional LCD, the viewing angle characteristics of LCD has drastically improved without causing a blur of the frontal image and a decrease in the contrast ratio under bright ambient light conditions. This film can be applied to various LC modes including twisted nematic and multidomain vertical alignment by changing its internal micrometer‐size 3D structure. Further, this film can be mass‐produced efficiently by self alignment roll‐to‐roll process.

A Spatiotemporal Four-Primary Color LCD With Quantum Dots

A four-primary liquid crystal display (LCD) by hybrid color processing in spatial and temporal domains is presented. By integrating with quantum dots, the number of LED can be reduced and the emission spectrum optimized. This approach exhibits following advantages over conventional three-primary LCDs: 1) it has 1.5X higher spatial resolution and 2X higher light efficiency; 2) it can achieve 130% color gamut in CIE 1931 and 155% in CIE 1976 color space; and 3) it has a more relaxed LC response time requirement and can be readily integrated into commercial LCD products.

Comparison of organic electroluminescence and liquid crystal displays for clinical utility in orthopedic endoscopic surgery

Organic electroluminescence displays (OELD) use organic materials that self-emit light with the passage of an electric current. OELD provide high contrast, excellent color reproducibility at low brightness, excellent video images, and less restricted viewing angles. OELD are thus promising for medical use. This study compared the utility of an OELD with conventional liquid crystal displays (LCD) for imaging in orthopedic endoscopic surgery. One OELD and two conventional LCD that were indistinguishable in external appearance were used in this study. Images from 18 patients were displayed simultaneously on three monitors and evaluated by six orthopedic surgeons with extensive surgical experience. Images were shown for 2 min, repeated twice, and viewed from the front and side (diagonally). Surgeon rated both clinical utility (12 parameters) and image quality (11 parameters) for each image on a 5-point scale: 1, very good; 2, good; 3, average; 4, poor; and 5, very poor. For clinical utility in 16 percutaneous endoscopic discectomy cases, mean scores for all 12 parameters were significantly better on the OELD than on the LCD, including organ distinguishability (2.1 vs 3.2, respectively), lesion identification (2.2 vs 3.1), and overall viewing impression (2.1 vs 3.1). For image quality, all 11 parameters were better on the OELD than on LCD. Significant differences were identified in six parameters, including contrast (1.8 vs 2.9), color reproducibility in dark areas (1.8 vs 2.9), and viewing angle (2.2 vs 2.9). The high contrast and excellent color reproducibility of the OELD reduced the constraints of imaging under endoscopy, in which securing a field of view may be difficult. Distinguishability of organs was good, including ligaments, dura mater, nerves, and adipose tissue, contributing to good stereoscopic images of the surgical field. These findings suggest the utility of OELD for excellent display of surgical images and for enabling safe and highly accurate endoscopic surgery.

IR Sensor Synchronizing Active Shutter Glasses for 3D HDTV with Flexible Liquid Crystal Lenses

IR sensor synchronizing active shutter glasses for three-dimensional high definition television (3D HDTV) were developed using a flexible liquid crystal (FLC) lens. The FLC lens was made on a polycarbonate (PC) substrate using conventional liquid crystal display (LCD) processes. The flexible liquid crystal lens displayed a maximum transmission of 32% and total response time of 2.56 ms. The transmittance, the contrast ratio and the response time of the flexible liquid crystal lens were superior to those of glass liquid crystal lenses. Microcontroller unit and drivers were developed as part of a reception module with power supply for the IR sensor synchronizing active shutter glasses with the flexible liquid crystal lens prototypes. IR sensor synchronizing active shutter glasses for 3D HDTV with flexible liquid crystal lenses produced excellent 3D images viewing characteristics.