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유전율 이방성이 음인 액정을 이용한 이중 도메인 FFS 모드의 전기광학 특성
김향율,고재완,노정동,서대식,이승희 한국전기전자재료학회 2002 전기전자재료학회논문지 Vol.15 No.8
The fringe-field switching (FFS) mode was known to exhibit both a wide viewing angle and high transmittance, especially when using the liquid crystal (LC) with negative dielectric anisotropy. In the device, the LC director rotates almost in-plane. However, in the bright state the device shows bluish and yellowish color along parallel and perpendicular to the LC director at off-normal directions since the LC director rotates only in one direction. Such a problem was greatly improved using a wedge shape of only pixel electrodes. In this way two different field directions exist in a pixel, enabling the LC director to rotate in two opposite directions. Consequently, owing to dual domain effect when using the LC with negative dielectric anisotropy, the viewing angle characteristics are greatly improved.
광 최소/최대법을 이용한 IPS-LCD의 잔류 DC특성 연구
김향율,한은주,서대식 한국전기전자재료학회 2001 전기전자재료학회논문지 Vol.14 No.7
The residual DC properties in the in-plane switching (IPS) liquid crystal displays(LCDs) which have different concentrations of cynao NLCs and different resistivities of fluorine NLCs were studied. We also propose a new residual DC measurement method, named 'light minimum/maximum method'. We confirmed the precision of residual DC measurement by light minimum/maximum method compared with the flicker minimizing method and found that new measurement method of residual DC is more accurate than that of the conventional flicker minimizing method since the resolution level of measurements is in 0.1V.
김향율,서대식,남상희 한국전기전자재료학회 2002 전기전자재료학회논문지 Vol.15 No.2
The voltage holding ratio(VHR) and the residual DC property in the in-plane switching (IPS) cells on a polyimide surface was studied. Several IPS cells which have different concentrations of cyano liquid crystals (LCs) were fabricated. We found that the VHR of the IPS cell was decreased with increasing concentration of cyano LCs. Also, the VHR of the IPS cell was increased with increasing specific resistivity of fluorine LCs. The residual DC voltage of the IPS cell by capacitance-voltage (C-V) hysteresis method was decreased with increasing concentration of cyano LCs. The residual DC property of the IPS cell on the rubbed PI surface can be improved by high polarity of cyano LC.
IPS-LCD의 전압-투과율 히스테리시스법을 이용한 잔류 DC 전압 특성
김향율,서대식,김재형 한국전기전자재료학회 2001 전기전자재료학회논문지 Vol.14 No.6
Residual DC voltage of the in-plane switching (IPS)-liquid crystal display(LCD) by voltage-transmittance (V-T) hysteresis method was studied. Several IPS-LCD which have different concentrations of cynao LCs and different resistivities of fluorine LCs were fabricated. We found that the residual DC voltage of the IPS-LCD was decreasing with increasing concentration of cyano LCs and increasing with decreasing specific resistivity of fluorine LC materials. The residual DC voltage property can be improved by low molecular weight and high polarity of cyano LC.
프린지 필드에 의해 구동되는 하이브리드형 네마틱 액정 디스플레이의 전기광학 특성
정연학,김향율,이승희 한국전기전자재료학회 2002 전기전자재료학회논문지 Vol.15 No.6
Conventional hybrid aligned nematic liquid crystal display (HAN-LCD) has several advantages on low operating voltage, fast response time and rubbing free on one substrate. We have fabricated a new hybrid aligned nematic display driven by fringe field. The new device exhibits much wider viewing: angle than that of the conventional HAN mode, owing to almost in-plane rotation of the LC director. Furthermore, we have developed the device that reveals more efficient electro-optic characteristics by placing common electrode on top and bottom substrates. In this paper, the electro-optic characteristics of the novel cell are investigated.
프린즈 전기장에 의해 구동되는 수평 배향 액정셀에서 black matrix의 전기적 특성이 셀의 전기광학 특성에 미치는 영향에 관한 연구
김미숙,김향율,고재완,이승희 한국전기전자재료학회 2003 전기전자재료학회논문지 Vol.16 No.11
We have studied the effect of black matrix (BM) according to the dielectric anisotropy of liquid crystals (LCs) for a homogeneously aligned LC cell driven by fringe-electric field. The results show that for a LC with positive dielectric anisotropy (+LC) there is a large transmittance change when using a conductive BM, whereas the transmittance change is low for a LC with negative dielectric anisotropy (-LC). The conductive BM existing on top substrate produces vertical electric field, which makes the LC molecules be tilt upward from the substrate and have small twist angle for the +LC. However, for the -LC the conductive BM affects the LC distribution only slightly due to characteristic of the -LC orienting perpendicular to the field. Therefore, for the +LC the electro-optic characteristics are strongly dependent on conductivity of the BM on top substrate in a homogeneous liquid crystal cell driven by fringe-electric field.
유전율 이방성이 양인 액정을 이용한 Fringe-Field Driven 수평 배향셀의 위상지연값 연구
정송희,김향율,송성훈,이승희 한국전기전자재료학회 2004 전기전자재료학회논문지 Vol.17 No.3
We have studied the optimal phase retardation value of a homogeneously aligned liquid crystal (LC) driven by fringe-field when using the LC with positive dielectric anisotropy. In general, the transmittance of a homogeneous aligned LC cell under crossed polarizer is maximum when a twist angle of LC by in-plane rotation is 45$^{\circ}$ with polarizer and the cell retardation becomes λ/2. However, the device using the LC with positive dielectric anisotropy does not follow this since the degree of rotation of the LC is dependent on electrode position and in addition the LCs tilt up along the fringe-field. At the center of common and pixel electrode, the LC is most twisted around a middle position of a cell whereas at the edge position of pixel electrode, the LC is most twisted near bottom surface of a cell. Consequently, the optimal phase retardation of the device becomes much larger than λ/2 and the transmittance can be described using the combination of the in-plane switching and twisted nematic mode.
Fringe-Field Switching (FFS) 모드에서 액정의 유전율 이방성에 따른 동력학 안정성에 관한 연구
김미숙,김향율,이승희 한국전기전자재료학회 2003 전기전자재료학회논문지 Vol.16 No.3
The voltage-dependent transmittance curve of a homogeneously aligned liquid crystal (LC) cell driven by fringe-electric field(named FFS mode) was studied, while changing dielectric anisotropy of a LC. The results show that for a LC with positive dielectric anisotropy while positioning at initial position. Therefore, we conclude that the dynamic stability is strongly dependent on the types of the LCs and voltage-dependent dynamics of the LC with negative dielectric anisotropy is staler than that of the LC with positive dielectric anisotropy in the FFS mode.
유전율 이방성의 음인 액정을 이용한 Fringe-Field Switching mode의 cell gap 변화에 따른 전기광학 특성
정송희,김향율,이종문,이승희 한국전기전자재료학회 2003 전기전자재료학회논문지 Vol.16 No.10
The FFS (fringe-field switching) mode was known to exhibit both a wide viewing angle and high transmittance, especially when using a liquid crystal with negative dielectric anisotropy. We have studied cell gap-dependent electrode-optic characteristics of the FFS mode using the LC with negative dielectric anisotropy. In case of a small cell gap of 2 ${\mu}$m, the transmittance at the center of pixel and common electrodes is relatively low because effect of surface anchoring that holds the LC to the initial state is larger than that in a large cell gap of 4 .urn such that the LCs in those regions cannot rotate enough. However, in case of a large cell gap of 4 .urn, the effect of surface anchoring becomes relatively small so that the LCs at the center of pixel and common electrode can be twisted enough by applied voltage, giving rise to high transmittance. Therefore, we can conclude that the light efficiency is dependent on the cell gap.
유전율 이방성이 양인 액정을 이용한 고속응답용 FFS 모드
김미숙,김향율,송성훈,양석만,이성규,임영진,이승희 한국전기전자재료학회 2004 전기전자재료학회논문지 Vol.17 No.7
We have studied the fringe field switching (FFS) mode with the positive dielectric anisotropy for the fast response time. The factors such as the physical properties of the LC, the cell gap, and the rubbing angle were critical for the fast response time of the FFS mode. The response time became 10 ms faster when the rotational viscosity of the new LC is 20 mPa.s lower than the conventional LC. When the cell gap changed from 3.6 ${\mu}{\textrm}{m}$ to 3.0 ${\mu}{\textrm}{m}$, it was possible to achieve the total response time and response times associated with grey-to-grey transitions under 16 ms. And the response times including grey-to-grey transitions become fast as the rubbing angle decreases.