Transient flickering behavior in fringe-field switching liquid crystal mode analyzed by positional asymmetric flexoelectric dynamics

Advanced Optical Materials

Jin

Lee

et al. 2018

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: Introductionmentioning

confidence: 99%

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

Advanced Optical Materials

Jin

Lee

et al. 2018

“…As above mentioned, the flexoelectricity of the calamitic liquid crystal has been known as small effect; however, the optical property associated with such small effect turns out to be remarkably significant even an image-flickering being noticed by human eyes because the voltage-dependent transmittance curves, as well as the time-dependent transmittance curve, of positive and negative field frames in the FFS mode are deviated each other due to collective splay and bend deformation 8 13 23 . Furthermore, despite of the reasonable studies according to the detailed mechanism of the flexoelectric effect in the FFS mode, inconsistency of the local transmittance curves among the reported results has been found, especially in the region above each electrode 18 19 20 21 . In the FFS mode, a stack of one transparent electrode and another transparent interdigitated electrode is separated by an insulation layer; however, in in-plane switching (IPS) mode, only one layer of a transparent electrode is interdigitated so that the electric field shape is much simpler than that in the FFS mode.…”

mentioning

confidence: 90%

“…In liquid crystal displays, usually the driving frequency is 60 Hz or higher; it seems no flexoelectric effect has been an issue from such a device application perspective. Recently, however, the scientific interests 1 11 13 14 15 16 in the flexoelectricity induced by the external electric field 4 10 14 are exposed to the practical display applications and actively explored under low-frequency driving (below 30 Hz) with fringe-field switching (FFS) mode for saving power consumption 17 18 19 20 21 22 . As above mentioned, the flexoelectricity of the calamitic liquid crystal has been known as small effect; however, the optical property associated with such small effect turns out to be remarkably significant even an image-flickering being noticed by human eyes because the voltage-dependent transmittance curves, as well as the time-dependent transmittance curve, of positive and negative field frames in the FFS mode are deviated each other due to collective splay and bend deformation 8 13 23 .…”

mentioning

confidence: 99%

Flexoelectric effect in an in-plane switching (IPS) liquid crystal cell for low-power consumption display devices

Bos

et al. 2016

Sci Rep

Technology of displaying static images in portable displays, advertising panels and price tags pursues significant reduction in power consumption and in product cost. Driving at a low-frequency electric field in fringe-field switching (FFS) mode can be one of the efficient ways to save powers of the recent portable devices, but a serious drop of image-quality, so-called image-flickering, has been found in terms of the coupling of elastic deformation to not only quadratic dielectric effect but linear flexoelectric effect. Despite of the urgent requirement of solving the issue, understanding of such a phenomenon is yet vague. Here, we thoroughly analyze and firstly report the flexoelectric effect in in-plane switching (IPS) liquid crystal cell. The effect takes place on the area above electrodes due to splay and bend deformations of nematic liquid crystal along oblique electric fields, so that the obvious spatial shift of the optical transmittance is experimentally observed and is clearly demonstrated based on the relation between direction of flexoelectric polarization and electric field polarity. In addition, we report that the IPS mode has inherent characteristics to solve the image-flickering issue in the low-power consumption display in terms of the physical property of liquid crystal material and the electrode structure.

“…However, with increasing pixel density, the mobile display panels suffer from power consumption issues. Because the power consumption level in driving circuits is proportional to the operation frequency [6,7], extensive efforts have been made to reduce the operation frequency level of FFS LC modes without degrading the image quality [8][9][10][11][12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Photocontrollable Resistivity Change in Nanoparticle-Doped Liquid Crystal Alignment Layer: Voltage Holding and Discharging Properties of Fringe-Field Switching Liquid Crystal Modes

Choi

Lee

et al. 2021

Crystals

Self Cite

In liquid crystal (LC) displays, deriving an optimum resistance level of an LC alignment polyimide (PI) layer is important because of the trade-off between the voltage holding and surface-discharging properties. In particular, to apply a power-saving low-frequency operation scheme to fringe-field switching (FFS) LC modes with negative dielectric LC (n-LC), delicate material engineering is required to avoid surface-charge-dependent image flickering and sticking problems, which severely degrade with lowering operation frequency. Therefore, this paper proposes a photocontrolled variable-resistivity PI layer in order to systematically investigate the voltage holding and discharging properties of the FFS n-LC modes, according to the PI resistivity (ρ) levels. By doping fullerene into the high-ρ PI as the photoexcited charge-generating nanoparticles, the ρ levels of the PI were continuously controllable with a wide tunable range (0.95 × 1015 Ω∙cm to 5.36 × 1013 Ω∙cm) through Ar laser irradiation under the same LC and LC alignment conditions. The frequency-dependent voltage holding and discharge behaviors were analyzed with photocontrolled ρ variation. Thus, the proposed experimental scheme is a feasible approach in PI engineering for a power-saving low-frequency FFS n-LC mode without the image flickering and image sticking issues.