41.4: Advanced ASM Mode (Axially Symmetric Aligned Microcell Mode): Improvement of Display Performances by Using Negative Dielectric Liquid Crystal

Kume, Y.; Yamada, Nobuaki; Kozaki, Shuichi; Kishishita, H.; Funada, Fumiaki; Hijikigawa, Masaya

doi:10.1889/1.1833676

Cited by 11 publications

(7 citation statements)

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“…The first work on polymer stabilization in VA mode appeared in 1998. 20,21 Especially, Kume et al 20 reported for the first time that the alignment direction and surface tilt angle can be controlled by using a polymer, as demonstrated by their SEM photograph of the alignment layer and model of the polymer-controlled surface tilt angle. In both of their reports, they used a position controllable resin spacer and gibbous lattice structure.…”

Section: History Of Related Technologymentioning

confidence: 99%

Review Paper: Emerging vertical‐alignment liquid‐crystal technology associated with surface modification using UV‐curable monomer

Lee¹,

Kim²,

Wu³

2009

J Soc Info Display

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-The recent development of polymer-induced pretilt angle in multi-domain vertical-alignment liquid-crystal (LC) structures is reviewed. To create a small but well-defined pretilt angle, 0.1 wt.% of a photo-curable monomer was mixed in an LC host and a bias voltage was applied to reorient the LC directors within each domain. The monomers are polymerized near the substrate surfaces by UV exposure. The formed polymer layers change the surface pretilt angle of the LC from 90°t o about 89°with a defined azimuthal orientation. Consequently, within each domain the LC reorientation direction responding to the external field is well-defined which leads to faster rise time and higher transmittance. This new technology overcomes the long standing problems of conventional MVA devices and is therefore expected to play a dominant role in the future.Keywords -Multi-domain vertical alignment, liquid crystal, polymerization, surface tilt angle. DOI # 10.1889/JSID17.7.551 1 IntroductionAt present, two major wide-view liquid-crystal (LC) approaches are commonly practiced: homogenous alignment (HA) and vertical alignment (VA) in the initial state. The HA camp includes in-plane switching (IPS) 1,2 and fringe-field switching (FFS), 3,4 in which the LC directors essentially rotate in plane so that wide view is a built-in feature. While in the VA camp, multi-domain VA (MVA) using protrusion 5-8 and patterned VA (PVA) 9,10 are the two major approaches. In both types of VA devices, the LCs are vertically aligned with respect to the substrate with the help of a polymer alignment layer under crossed polarizers and their normalized transmittance T/T o can be described aswhere ψ is the angle between one of the transmission axes of the crossed polarizers and the LC director, ∆n eff is the voltage-dependent effective birefringence of the LC medium, and λ and T o are the wavelength and intensity of the incident light, respectively. In the absence of an electric field, ψ = 0°and the device appears black. In the presence of an electric field, the effective retardation (d∆n eff ) starts to occur. Ideally, the transmittance will reach a maximum at ψ = 45°. In both MVA and PVA devices, the LC directors are reoriented by the oblique fields. In MVA, the oblique field is generated by a protrusion and patterned pixel electrode, whereas in PVA the oblique field originates from a patterned common and pixel electrode, as depicted in Fig. 1. Both MVA and PVA devices have been successfully commercialized; however, their performance and cost still need to be improved.Recently, a new type of VA technology which enables the control of the surface pretilt angle of the LC by using a UV curable monomer was introduced. This technique improves the rise time and transmittance and has become a strong contender for future wide-view VA technology. Major issues in VA technologiesLet us first describe the general problems associated with VA devices and the demerits of conventional MVA and PVA devices.In the initial state, the LC directors are perfectly aligned...

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Section: History Of Related Technologymentioning

confidence: 99%

Review Paper: Emerging vertical‐alignment liquid‐crystal technology associated with surface modification using UV‐curable monomer

Lee¹,

Kim²,

Wu³

2009

J Soc Info Display

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“…Many works have been reported to overcome such drawbacks with their own particular features, e.g. multidomain vertical alignment (MVA), which has protrusions on the surface [8,9]; advanced super-view (ASV) [10]; patterned vertical alignment (PVA), which utilizes an oblique electric field formed by electrodes of desired patterns [11][12][13]; and polymer-stabilized vertical alignment (PS-VA), in which a pretilt angle is achieved by a certain polymer morphology on the surface [14][15][16]. In all VA modes, vertically aligned LCs tilt down in four different azimuthal directions, to improve the viewing-angle property.…”

Section: Introductionmentioning

confidence: 99%

Reduction of Gamma Distortion in Oblique Viewing Directions in Polymer-stabilized Vertical Alignment Liquid Crystal Mode

김효중¹,

Lim²,

Murali³

et al. 2017

Current Optics and Photonics

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In large liquid crystal displays, the image quality in an oblique viewing direction is a crucial issue. From this perspective, 8-domain polymer-stabilized vertical alignment (PS-VA) mode has been developed to suppress the color shift in oblique viewing directions, compared to that in 4-domain PS-VA mode. To realize the 8-domain PS-VA, the four domains in a pixel are each divided into two regions, such that applying different electric potentials result in different tilt angles in these two regions, while keeping four azimuthal directions in each domain. However, applying different voltages in a pixel causes drawbacks, such as requiring additional processes to construct a capacitor and a transistor, which will further reduce the aperture ratio. Here we propose a different approach to form the 8-domain, by controlling surface polar anchoring energy and the width of patterned electrodes in two regions of a pixel. As a result, the gamma-distortion index (GDI), measured at an azimuthal angle of 0°, is reduced by about 23% and 8%, compared to that of a conventional 4-domain at polar angles of 30° and 60° respectively.

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“…However, the voltage-dependent reflectance (VR) and transmittance (VT) curves do not match each other, and these devices are difficult to manufacture. To produce intermediate pretilt angles for a nematic LC cell, the surface polymer-stabilization manufacturing process has been widely developed [14][15][16][17][18][19] in recent years, e.g., doping photocurable monomers in a LC cell and stabilizing the LC alignment by UV exposure, 14 using a position-controllable resin spacer and gibbous lattice structure. 17,18 In this paper, we propose a single-cell-gap TR-LCD using low intermediate pretilt angles in the T region based on the in-plane-switching (IPS) mode with positive-dielectric-anisotropy nematic LC and a large LC layer, in which the T region is almost homeotropically aligned with the rubbed surfaces at parallel directions while the R region has a homeotropic liquid-crystal alignment to accumulate greater phase change for the T region.…”

Section: Introductionmentioning

confidence: 99%

A single‐cell‐gap transflective liquid‐crystal display using different pretilt angles in transmissive and reflective regions

Song¹,

Wang²,

Li³

et al. 2011

J Soc Info Display

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Abstract— A single‐cel l‐gap transflective liquid‐crystal display with two types of liquid‐crystal alignment based on an in‐plane‐switching structure is proposed. The transmissive region is almost homeotropically aligned with the rubbed surfaces at parallel directions while the reflective region has a homeotropic liquid‐crystal alignment. For every driving voltage for a positive‐dielectric‐anisotropy nematic liquid crystal, the effective cell‐retardation value in the transmissive region becomes larger than that in the reflective region because of optical compensation film which is generated by low‐pretilt‐angle liquid crystal in the transmissive region. Under the optimization of the liquid‐crystal cell and alignment used in the transmissive and reflective areas, the transmissive and reflective parts have similar gamma curves. An identical response time in both the transmissive and reflective regions and a desirable viewing angle for personal portable displays can also be obtained.

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41.4: Advanced ASM Mode (Axially Symmetric Aligned Microcell Mode): Improvement of Display Performances by Using Negative Dielectric Liquid Crystal

Cited by 11 publications

References 1 publication

Review Paper: Emerging vertical‐alignment liquid‐crystal technology associated with surface modification using UV‐curable monomer

Review Paper: Emerging vertical‐alignment liquid‐crystal technology associated with surface modification using UV‐curable monomer

Reduction of Gamma Distortion in Oblique Viewing Directions in Polymer-stabilized Vertical Alignment Liquid Crystal Mode

A single‐cell‐gap transflective liquid‐crystal display using different pretilt angles in transmissive and reflective regions

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