Trapping of defect point to improve response time via controlled azimuthal anchoring in a vertically aligned liquid crystal cell with polymer wall

Kim, Sang Gyun; Kim, Sung Min; Kim, Youn Sik; Lee, Hee Kyu; Lee, Seung Hee; Lyu, Jae‐Jin; Kim, Kyeong Hyeon; Lü, Renguo; Wu, Shin‐Tson

doi:10.1088/0022-3727/41/5/055401

Cited by 24 publications

(10 citation statements)

References 19 publications

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“…They claimed that the proposed device exhibits a higher transmittance, better dark state, and faster response time as compared to the MVA device. In 2007 and 2008, our group [23][24][25][26] reported the surface polymer stabilization of the LC director in a PVA device and other VA devices using a reactive mesogen (RM), showing a considerable improvement in the rise time, in which the doping amount of the RM was about 0.1 wt.% in the LC host. Recently, Hsu et al 27 reported detailed results on the optical performance of a polymer-stabilized mobile MVA-LCD according to the curing process of the reactive monomer with a doping amount of 0.05 wt.%.…”

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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“…The conventional multi-domain VA (MVA) [2][3][4][5][6] and patterned VA (PVA) [7][8][9] have shortcomings, such as low transmittance and slow rise response time. In order to overcome the slow rise response time of such VA modes, the polymer-stabilized VA (PS-VA) mode [16][17][18][19][20] has recently been proposed, but the low-transmittance issue still persists and furthermore gives rise to a power consumption issue when employed in high resolution LCDs such as ultra-high-definition (UHD) LCDs. In a PS-VA device as shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

Transmittance Improvement with Reversed Fishbone-Shape Electrode in Vertical Alignment Liquid Crystal Display

Lim¹,

Kim²,

Kim³

et al. 2016

Journal of the Optical Society of Korea

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A polymer-stabilized vertical alignment (PS-VA) mode with fishbone-shaped pixel electrode structure is mainly used in large-sized liquid crystal displays (LCDs) owing to its advantages such as wide viewing angle, good transmittance and fast response time. One drawback of this mode is a main bone electrode, which crosses in the center of a pixel. It causes the transmittance to decrease badly because LCs cannot be reoriented in this region, and thus, it is particularly unfavorable in an ultra-high-definition LCD. Here, we propose an innovative structure with the main bone electrode relocated to the edge area in a pixel, and investigate how this reverse directed fishbone-shaped pixel electrode structure affects electro-optic characteristics. The proposed structure shows enhanced electro-optic performance, such as the higher transmittance and the faster response time than the conventional VA mode with fishbone-shaped pixel electrode structure.

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“…[12,13] For instance, Kim et al [14] proposed a robust vertically aligned LC cell, where the LC were locked by polymer walls, and the azimuthal anchoring on the surface of the alignment layer was controlled by the polymerisation of a UV curable reactive mesogen monomer. As a result, the defect points were trapped at a single position, resulting in a greatly improved response time.…”

Section: Introductionmentioning

confidence: 99%

Reverse-mode polymer dispersed liquid crystal films prepared by patterned polymer walls

et al. 2015

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This article proposes a methodology to prepare polymer dispersed liquid crystal (PDLC) films working in the reverse-mode operation, where the ion-doped nematic liquid crystals (NLCs) with negative dielectric anisotropy (Δε) were locked by polymer walls. On-state and off-state of films were controlled by an electric field. In the absence of an electric field, it appears to be transparent. In the field, the homogeneous alignment NLCs form dynamic scattering, giving rise to opaque. The effect of the cylindrical holes with different diameters of photo masks and liquid crystal Δε on the electro-optical properties and transmittance wavelength range of 400-3000 nm light of samples were investigated. It was found that it exhibited very good electro-optical characteristics, high contrast ratio and excellent infrared energy-efficient of films used as switchable windows.Keywords: reverse-mode polymer dispersed liquid crystal; polymer walls; nematic liquid crystal; negative dielectric anisotropy; electro-optical properties IntroductionPolymer dispersed liquid crystal (PDLC) films are technologically important class of materials that find numerous applications as electrically switchable optical devices.[1-3] PDLC films are formed by liquid crystal (LC) microdroplets embedded in a polymer matrix. They can exhibit either a droplet morphology in which droplets of LC are embedded in a polymer matrix, or a polymer ball morphology in which the LC takes up the voids and the crevices of a network structure formed by small polymer balls. In the normal-mode operation, they are in an opaque state (offstate) and can be turned into a transparent state (onstate) by controlling the LC molecule orientation by means of a suitable voltage. The reverse-mode PDLC films are transparent in its off-state and can be turned into an opaque on-state. A greater interest has been aroused by reverse-mode PDLC films that are useful as switchable windows, automotive applications [4,5] and used in a wide range of applications that need a transparent state in the absence of any applied voltage.Several authors have reported examples of reverse-mode PDLC films obtained by modification of the polymer surface energy,[6] by functionalising the LC/polymer matrix interface,[7] by using dualfrequency addressable LC,[8] by means of rough surfaces [9,10] or by increasing the LC content. [11]

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Trapping of defect point to improve response time via controlled azimuthal anchoring in a vertically aligned liquid crystal cell with polymer wall

Cited by 24 publications

References 19 publications

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

Transmittance Improvement with Reversed Fishbone-Shape Electrode in Vertical Alignment Liquid Crystal Display

Reverse-mode polymer dispersed liquid crystal films prepared by patterned polymer walls

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