Field-symmetrization to solve luminance deviation between frames in a low-frequency-driven fringe-field switching liquid crystal cell

Advanced Optical Materials

et al. 2018

Self Cite

for the additional power reduction in the liquid crystal driving scheme, for example, by reducing the driving frequency f. Displaying smooth and dynamic motion at high-frame rate has been an unquestionable direction to improve the performance of displays, but static images are also becoming significantly important as the application of displays diverges. Thus, as the f is in linear dependence on the power consumption of a module, low-f driving LCD is desired.In driving scheme of LCDs, some amount of electromagnetic radiant energy from the backlight is cut off by the combination of crossed polarizers and liquid crystalline medium while modulating polarization. In terms of energy loss in a liquid crystal layer, therefore, maximizing transmittance is an important factor to improve for better electro-optic performance. From this perspective, achieving both high optical transmittance and low-f driving would be a remarkable breakthrough in terms of power savings.There are two main streams of the initially homogeneous aligned light modulating mode in LCDs: fringe-field switching (FFS) and in-plane switching (IPS) modes. Both modes have a patterned electrode on the one side of two sandwiched substrates. In the IPS mode, patterned pixel (signal-swung) and common electrodes are interdigitated such that symmetrical lateral fields, which have the same translational periodicity with the electrode patterns, are formed between these two electrodes to rotating the liquid crystal director in plane; thus, reorientation occurs only in between the electrodes. In the FFS mode, on the other hand, a plain common electrode and a patterned pixel electrode are not on the same layer and separated by an insulation layer. With this structure, the electric fields form nonsymmetrical fringe shape and the field periodicity is half of the pitch of the electrode patterns. Thus, the rotation of the liquid crystal director takes place over the entire electrode area, which contributes more to the optical transmittance. [4,5] The FFS mode has been dominating the LCD market, especially in portable devices owing to the high aperture ratio, high transmittance, low operation voltage, wide-viewing angle, and touchscreen tolerance. [4,6] Consequently, intensive efforts to reduce the power consumption of this mode have been attempted by using the low-f driving when static images are being displayed. However, severe issues regarding image quality arise in the low-f driving, including image-flickering owing to flexoelectric effect. [7][8][9][10][11][12][13][14] The flexoelectric effect is a An advantageous factor for the technology of displays is low power consumption. For power-saving, low-frequency driving of liquid crystal displays (LCDs) is useful. However, an unacceptable performance drop, from image-flickering, occurs due to occurrence of the flexoelectric effect. Here, based on close agreement between experimental and simulated results, a new electro-optic mode with optimization of both electrode structures and physical properties of the liquid crystal...

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Liquid Crystals for Superior Electro‐Optic Performance Display Device with Power‐Saving Mode

Kim

Jin

Advanced Optical Materials

et al. 2018

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“…Although fringe-field switching (FFS) LC displays (LCDs) are widely used in high-resolution and high-end displays and become a standard display for mobile devices, the development of the performance is yet ongoing [1][2][3][4][5][6]. In display technology, one of the performance enhancements is low power consumption mode for static images [7][8][9]. The power consumption of LCDs is determined as fCV 2 where f is a driving frequency, C is a capacitance of a panel, and V is an applied voltage to a panel.…”

Section: Introductionmentioning

confidence: 99%

P‐149: Maximization of Transmittance and Minimization of Image‐Flickering due to Flexoelectric Effect in Low‐Frequency Driving Fringe‐Field Switching (FFS) Mode Using LCs with Negative Dielectric Anisotropy

Symp Digest of Tech Papers

Choi

Ham

et al. 2017

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Image-flickering due to flexoelectric effect in a low frequency driven fringe-field switching (FFS) LCD is troublesome. Maximization of transmittance in the FFS mode is achieved using LCs with negative dielectric anisotropy but still the flickering exists. The paper describes in detail on optimal solutions how it can be solved by controlling the ratio of electrode width to distance and thickness of passivation layer. The results greatly contribute to achieve high transmittance and image-flickering free FFS LCD. Author KeywordsFFS mode, image-flicker, flexoelectric effect, negative liquid crystal, fine-patterned electrode.

“…Thus, a static image-flickering, which is mainly caused by the integral brightness difference between frames, does not exist, unlike in FFS mode as schematically described in Fig. 1 [11]. However, IPS mode is relatively disadvantageous to FFS mode from a perspective of aperture ratio and transmittance [12,13].…”

Section: Introductionmentioning

confidence: 99%

P‐150: Flexoelectric Effect in Fine‐patterned In‐plane Switching (IPS) Mode

Cho

Ham

Symp Digest of Tech Papers

et al. 2017

Self Cite

Low-frequency driving of liquid crystal displays can greatly reduce the power consumption, but the flexoelectric effect badly occurs as an optical fluctuation in space and time, so-called image-flickering. In a fringe-field switching (FFS) mode, both dynamic and static image flickering occur whereas, for an inplane switching (IPS) mode, dynamic image-flicker takes placewith no static flicker. However, the overall transmittance in IPS mode is relatively poor as compared to that of FFS mode. Here, we demonstrate that fine-patterned electrodes and negative dielectric anisotropy liquid crystal can greatly enhance the transmittance as high as that of FFS mode while keeping no static image flicker. The remained dynamic flicker can be also significantly reduced by increasing the magnitude of dielectric anisotropy of liquid crystals. We report the detailed behavior of voltage-and time-dependent transmittances.