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

Abstract

The development of low-frequency-driven liquid crystal displays (LCDs) has recently received intense attention to open up low-power consumption display devices, such as portable displays, advertising panels and price tags. In fringe-field switching (FFS) LCD mode, a unidirectional electric field gives rise to head-tail symmetry breaking in liquid crystals, so that the flexoelectric effect, a coupling between the elastic distortion and the electric polarization, becomes enormously significant. The effect is thus linked to an unusual optical effect, which badly damages the quality of images by image-flickering, and this image-flickering is mainly caused by transmittance difference between the applied signal frames. Here, we intensively investigate the mechanism of the transmittance deviation, and propose an essential and promising approach to solve the poor image-quality, that is, symmetrization of electric fields between the frames. The result of our work clearly demonstrates that the field-symmetry is crucial to reduce the image-flickering, and it can be obtained by optimization of the thickness of an insulation layer with respect to the ratio of the space between electrodes to the electrode width.

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

“…For the analysis on the appearance of the sawtooth‐shaped borderline, on the one hand, we look back to the cross‐sectional view of the schematics shown in Figure a. The field‐potential becomes asymmetric between (+) and (−) frames owing to the insulation layer between pixel and common electrodes . In (+) frame, the order of elements in the circuit is: (1) electrode, (2) liquid crystal, (3) insulation layer, (4) electrode, whereas in (−) frame, it is (1) electrode, (2) insulation layer, (3) liquid crystal, (4) electrode.…”

“…The flexoelectric effect is a coupling between elastic deformation and electric polarization of liquid crystals in which the flexoelectric polarization is spontaneously induced by external electric field at a low f . This effect has been known to occur with high‐flexoelectric constant materials, such as a bent‐core liquid crystal; however, recent reports clearly show that the optical appearance of the flexoelectric effect becomes quite obvious even in rod‐like nematic liquid crystal with relatively small flexoelectric coefficients, e s (splay) and e b (bend) <15 pC m −1 while horizontal electric field is applied …”

“…From this perspective, the FFS mode is less advantageous in power‐saving low‐ f driving mode than the IPS mode . However, a recent report demonstrates the static flickering can be solved by field symmetrization by optimization of electrode structures …”

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

“…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.…”

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

“…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].…”