• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.180-182
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• 1996

In this study, we have investigated the characteristics of the response time and the viewing angle on twisted nematic (TN)-liquid crystal display (LCD) and amorphous (a) TN-LCD without rubbing. To measure the transmission-voltage, response time, and viewing angle characteristics, we prepared three kinds of LC cells and then studied the surface liquid crystal alignment effect. We studied that the response time on a-TN-LCD is fast compared to the TN-LCD. We suggest that the weak anchoring strength is attributed to the fast response time on a-TN-LCD. Also, we obtained the uniform viewing angle characteristics on a-TN-LCD. From these results, we consider that the liquid crystal alignment on LCD device are very important factor for electro-optical characteristics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.05a
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• pp.54-57
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• 2005

We have designed a single gap transflective liquid crystal display (LCD) driven by a fringe electric field, in which the +LC (${\Delta}{\varepsilon}$=7.4, rubbing angle= $80^{\circ}$) is homogeneously aligned in the initial state. This device is a problem that the voltage-dependent transmittance and reflectance curves do not match each other. Thus a dual driving circuit is required. This study shows that optimization of the rubbing angle in the transmissive and reflective regions solves this problem so that the transflective display with a single cell gap and single gamma curve for reflective and transmissive region is possible.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.186-186
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• 2009

Most liquid crystal display modes, including the twisted nematic (TN) $mode^1$, the in-plane switching (IPS) $mode^2$, the fringe field switching (FFS) $mode^3$, and the vertically aligned (VA) $mode^4$ are based on either a horizontal or a vertical alignment. However, for some applications, such as no-bias-bend (NBB) pi cell or bistable bend-splay display, an intermediate pretilt angle is essential$^5$. NBB pi cells have been a focus of interest because of their fast response time; however, the reliable control of the intermediate pretilt angle of liquid crystals that is required for the fabrication of NBB pi cells is challenging. The controllable pre-tilt angle of liquid crystals was investigated using a blend of horizontal and vertical polyimide prepared by a rubbing method. Various pretilt angles in the range from 0^{\circ}$ to 90^{\circ}$ were achieved as a function of the vertical polyimide content. We observed uniform liquid crystal alignment on the rubbing-treated blended polyimide layer. A NBB pi cell with an intermediate pretilt angle of 47.8^{\circ}$ was manufactured. This cell had no initial bias voltage and a low threshold voltage, which indicates that it has low power consumption. In addition, the response time of the NBB pi cell was rapid.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.04a
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• pp.43-43
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• 2008

Recently, it is widely studied to liquid crystal (LC) alignment using ion-beam exposure. Because conventional rubbing method has some problems such as defects from dust and electrostatic charges and rubbing scratch during rubbing process. Moreover rubbing method needs cleaning process to remove these defects. Therefore rubbing-free techniques like ion-beam method are strongly required. We studied LC alignment by controlling ion-beam irradiation angles and electro-optical (EO) characteristics of twisted nematic LC on the polyimide surface. In this experiment, a good uniform alignment of the nematic liquid crystal (NLC) with the ion-beam exposure on the polyimide (PI) surface was observed. We also achieved low pretilt angle as function of ion-beam irradiation angles. X-ray photoelectron spectroscopic (XPS) analysis provided chemical evidence for LC alignment by controlling ion-beam irradiation angles. In addition, it can be achieved the good EO properties of the ion-beam-aligned twisted nematic liquid crystal display (TN-LCD) on PI surface. Some other experiments results and discussion will be included in the presentation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.199-202
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• 2003

We have investigated the generation of pretilt angle for a nematic liquid crystal (NLC) alignment with rubbing alignment method on two kinds of polyimide (PI) surfaces using thin plastic substrates. The generated NLC pretilt angles on the pre-imidized type PI are about $3.8^{\circ}$ by the rubbing alignment method with thin plastic substrates, However, the pretilt angle measured at about $2.8^{\circ}$ lower on the polyamic acid type PI than by pre-imidized type PI surface with thin polymer film. The tilt angle increases as increasing curring temperature for making polyimide layer using polyamic acid type PI. It was concluded that pretilt angle in the polyimide surface is attributable to the increasing of imide rato.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.2
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• pp.151-156
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• 2000

Effects of alignment layers on pretilt nagle generation and electrical characteristics in nematic liquid crystal(NLC) by using photo-alignment techniques on polyimide PI) surface with side chain were studied. The generated pretilt angle of the NLC on rubbed PI surface with 1-layer is almost the same as that with the 2-layers. However, the generated pretilt angle of the NLC on photo-induced PI surface with 2-layers is larger than that with the 1-layer. The different mechanism of pretilt generation in NLC was observed on the rubbing and photo-alignment method. Therefore, the pretilt angle of the NLC on photo-induced PI surface is attributed to surface roughness due to photo-dissociation on the polymer with UV light irradiation on PI surface. We observed the same characteristics of voltage-transmittance (V-T) and response time for 1- and 2-layers on PI surface. Consequently, we sugest that the VHR of photo-aligned TN-LCD is higher than that of the rubbing-aligned TN-LCD.

• Journal of Satellite, Information and Communications
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• v.10 no.1
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• pp.67-70
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• 2015

We studied the state of the dual liquid crystal (LC) alignment which displays both homeotropic and homogeneous alignment on blended polyimide (PI) layer. The research was conducted using rubbing method at different imidizing temperatures and the blended PI was made using homeotropic PI having an alkyl side chain and homogeneous PI without the side chain. The uniform LC alignments were achieved, and have thermal stability. The results of contact angles were similar to that of pretilt angles.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.531-533
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• 2007

A new method is developed for the measurement of twist angles of LC molecules in an LC panel with angular resolution of 0.01degree, which allows measurement of LC panels with small twist angles. The method is based on the analysis of the change in polarization state of a light beam as it passes through the LC panel in test is rotated in-plane. Compared to other traditional method, including the analysis of transmittance change, our method is more sensitive and more precise. This method allows accurate determination of anchoring energy and close analysis of the rubbing process in the fabrication of IPS mode LC panels.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.12
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• pp.1068-1071
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• 2007

When a dielectric layer, in-cell retarder (ICR) is formed between electrode and LC layer to get a single gap transflective fringe-field switching (FFS) display, the operating voltage ($V_{op}$) is highly increased due to the thickness of dielectric material. But, we also knew the phenomenon that the increasing rate of Vop is different whether the 1st common electrode was composed of plate type or slit type. In this paper, the common electrode in transmissive part was composed of slit type which had less steepness effect of the Vop and in reflective part was composed of plate type. The rubbing angle of reflective part can be adjusted properly to match the voltage dependent transmittance and reflectance.

• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.218-222
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• 1997

We fabricated a bistable TN LCD with 180$^{\circ}$ twist angle and confirmed that it has a fast switching response time and a high contrast ratio. We also investigated the effects of the amplitude and width of the reset and selection pulses on a bistable TN LC cell and the conditions of the bistability and the memory time. The range of d/p values showing the bistability is determinded for the pretilt angle according to the rubbing depth.