Viewing angle controllable liquid crystal display with high transmittance

The liquid crystal (LC) modes, in-plane switching (IPS) and fringe-field switching (FFS), associated with a transition from a homogenously aligned to twist deformation require rubbing process. In both devices, 1° of misalignment in azimuthal direction could cause voltage–dependent transmittance (V–T) to be different from that in a normal area and consequently results in a rubbing mura. According to our studies, dual domain structure of the FFS and IPS modes could reduce such a V–T difference dependent on the position although 1° of misalignment exists since the LC directors rotate clockwise and anticlockwise.

A single gap transflective liquid crystal display driven by fringe electric field in the transmissive (T) region and vertical electric field in the reflective (R) region was designed with formation of high pretilt angle larger than 45°through polymerization of an UV curable reactive mesogen monomer at the surface in the R region, the effective cell retardation value becomes half of that in the T region where the LCs are homogenously aligned. Consequently, a transflective display driven by a vertical and fringe electric field with a single cell gap and single gamma curves is realized.

This study provides a comprehensive review of the electro-optic effects in the asymmetric optically compensated in-plane switching (IPS), fringe field switching (FFS)–liquid crystal displays (LCDs) and electrically controlled birefringence (ECB) and vertically aligned (VA)-LCDs that produce geometric extra phase in their switching angles accompanying temporal effect. The present review article consists of three parts: in Part I, the effects of the IPS and FFS-LCDs are described, in Part II, the effects of the ECB and VA-LCDs are described, and finally in Part III, the unified treatment of the four LCD operation modes will be described.

As the physical properties of nematic liquid crystals vary with respect to temperature, the performances of liquid crystal displays (LCDs) are highly dependent on temperature. Additionally, it is well known that the electro‐optic characteristics of LCDs, such as transmittance and threshold voltage, also rely on the LCD switching modes. The temperature dependence of the electro‐optic characteristics of the wide‐viewing‐angle LCD modes, such as in‐plane switching (IPS), multidomain vertical alignment by patterned electrode (PVA), and fringe‐field switching (FFS), have been studied, and the results showed that the FFS mode has lower temperature dependence compared to the IPS and PVA modes. Since the liquid crystal (LC) reorients in different ways in each mode, this result is associated with the temperature dependence of LC's bend and twist elastic constants, and also with the position of the main reorientation, either in the middle or on the surface of the LC layer.

We propose a single-cell-gap transflective liquid crystal display (LCD) with dual orientation of LC at an initial state. Owing to hybrid alignment in the reflective region, the effective cell retardation value becomes half of that in the transmissive region where the LCs are homogenously aligned. Consequently, a transflective display driven by a vertical or fringe electric field with a single cell gap and high image quality is realized.

We investigated how surface anchoring strength affects the electro‐optic (EO) characteristics of a fringe‐field switching (FFS) mode. Unlike IPS mode that only azimuthal anchoring mainly contributes to the EO performances, both azimuthal and polar anchoring energies play an important role such that the transmittance increases with decreasing magnitude of azimuthal energy but increasing polar anchoring energy in the FFS mode when using a LC with positive dielectric anisotropy. In addition, weak anchoring at the electrode edge may result in change in initial LC optic axis by applied voltage stress so local control of anchoring energy is proposed.

Multi-layer protruded electrodes for reducing the operating voltage and gamma shift of fringe-field switching LCDs

We present light-emitting liquid crystal (LC) devices with a fluorescent dye-doped nematic LC for the purpose of generating polarized emission. We show that the light-emission characteristics of these devices are nearly independent of the dye concentration, suggesting that the carrier transport is governed mainly by ionic conduction. We discuss the polarized emission properties in the oblique outcoupling directions together with numerically calculated results, which show weakly polarized emission in the oblique direction. Lastly, we present polarized light emission from an LC cell with an inclined emissive layer, which is introduced to efficiently extract the polarized emission in the normal direction.

Single‐gap transflective liquid crystal display (LCD) driven by fringe electric field is proposed. The initial LC orientation is parallel to top polarizer in transmissive (T) region and is 45° with respect to top polarizer in reflective (R) region. The surface pre‐tilt angle of the R‐region is controlled by vertical field and polymerization of an UV curable reactive mesogen and thus, the effective cell retardation in the R‐ region becomes smaller than that in T‐ region. Consequently, a single gap transflective LCD driven by fringe electric field without compensation film or in‐cell retarder is realized.

To improve angular dependence of liquid crystal displays(LCDs), three LCD configurations are proposed. Two of these configurations correspond to transmissive LCDs and the remaining one to reflective LCDs. Each configuration includes negative Δ n compensators whose optical axes take the similar liquid crystal director profile.

Digital halftone is the technique used to convert gray-scale images into binary ones, simulating gray shades by scattering appropriately black and white pixels. Sometimes, there arises the necessity of increasing the resolution of a halftone image. Some recent works have proposed a number of learning-based techniques to zoom binary images. However, they cannot consider a large neighborhood to decide the colors of the resolution-increased pixels, because their running time skyrockets with the growth of the window and the sample images sizes. The use of large window and samples is required to zoom halftone images accurately. This paper presents a new technique to zoom quickly and precisely images generated by any locally-decided halftone algorithm. It is based on decision-tree learning and it is very fast, even using a large window or large samples. The zoomed images obtained by this technique are incredibly sharp and accurate.

Response mechanism of a vertical alignment mode driven by fringe-field switching

This paper proposes an approach to produce high-quality visual QR codes introducing the concept of function icons (FI)—images embedded into QR code. FI design resembled abstract symbols, like identifiable and memorable smartphone app icons or logos. The embedding visually points to the function of a QR code and therefore is more attractive to the end-user than the traditional QR code. Also, the FI perceptual simplicity increases users’ navigation and accessibility over different media. For optimization, the proposed FI design was altered by pixel size, color, and luminance modification, without affecting the decoding reliably. The contrast between dark and light modules of the FI color tone was determined to a minimum of 70% to enable the code reader’s conversion of the image to grayscale and then segmentation it into black and white pixels. The eye-tracking research on QR codes with implemented icons confirmed the subjective attractiveness evaluation. The technical quality of the proposed design was verified with a QR code readability test. Since more than 95% of examinees successfully recognized the content behind a QR code before scanning and evaluated the design as more attractive than a traditional solution, we demonstrated that our approach produces high-quality results for a variety of FI designs.

Fabrication of homogenously self-alignment fringe-field switching mode liquid crystal cell without using a conventional alignment layer

Four different reactive mesogens (RMs) for polymer stabilization of liquid crystal (LC) director in vertical alignment (VA) display have been synthesized and its stabilizing characteristics depending on size of the synthesized group and polarity of RM have been evaluated by studying electro‐optic characteristics of the LC cells. Our results show that the small size of substitute between biphenyls similar to LC molecular with polarity is favored to achieve excellent polymer stabilization without showing any grain size of polymer although photo‐initiator is not used at all.