KR100966230B1 - Viewing angle controllable liquid crystal display device - Google Patents

Abstract

The present invention discloses a viewing angle control liquid crystal display using a single panel of Fringe-Field Switching (FFS) mode using hybrid oriented liquid crystals. The disclosed invention has a structure in which an upper common electrode is additionally disposed on an upper substrate in an electrode structure of a conventional FFS mode. The liquid crystals of the lower substrate are horizontally arranged, and the liquid crystals of the upper substrate are hybridly aligned in a vertical arrangement. When driven by the pixel electrode and the lower common electrode of the lower substrate, a narrow viewing angle appears due to the narrow viewing angle characteristic of the hybrid arrayed liquid crystal, and the liquid crystal having a negative dielectric anisotropy is generated by the vertical electric field generated between the upper common electrode and the lower common electrode. When driven by the pixel electrode and the lower common electrode positioned on the lower substrate while lying parallel to the substrate, a wide viewing angle appears. The present viewing angle control liquid crystal display device has a merit of being thin, lightweight, and capable of adjusting the viewing angle without reducing the aperture ratio since a single panel is used.

Viewing angle adjustment, liquid crystal display, single panel, wide viewing angle, narrow viewing angle

Description

LCD with adjustable viewing angle {VIEWING ANGLE CONTROLLABLE LIQUID CRYSTAL DISPLAY DEVICE}

The present invention relates to a liquid crystal display (LCD), which is made of a single panel and has an adjustable viewing angle, and more particularly, high-quality display information viewed from the front according to the user's environment or preference is maintained in the front-out direction. The present invention relates to an adjustable liquid crystal display device which is either (wide viewing angle) or invisible (narrow viewing angle).

The liquid crystal display uses a birefringent liquid crystal and a polarizing plate together to change the polarization state of the liquid crystal to act as a light modulator. Due to the birefringence of the liquid crystal, the image quality of the display is deteriorated in the out-of-front viewing angle direction. Has the problem. In order to solve the viewing angle problem of the liquid crystal display, wide-viewing angle twisted nematic (WV-TN), film-compensated vertical alignment (VA), and fringe-field switching (FFS) modes for obtaining high quality characteristics in a wide viewing angle direction This was studied. This wide viewing angle characteristic has also been a major issue for the liquid crystal display device entering the mobile and TV market in the flat panel display market. However, in recent years, the problem of privacy invasion due to the increase in the value of information and the increase of portable displays has become important, and a narrow viewing angle display having a tendency opposite to that of a liquid crystal display having a wide viewing angle has emerged.

 In this regard, the viewing angle control liquid crystal display device, in which a portable display can be actively adjusted according to a change of user's preference and surrounding environment from a wide viewing angle to a narrow viewing angle or a narrow viewing angle to a wide viewing angle, has emerged. Looking at the characteristics of the conventional viewing angle control liquid crystal display device, in terms of the structure of the liquid crystal cell, a method of adjusting the viewing angle using birefringence anisotropy of the liquid crystal layer itself by stacking additional liquid crystal cells on the liquid crystal cell representing an image, and one pixel in two regions Divided into, the method of composing the main image and the pixel part serving as the viewing angle is presented. In the former case, since the liquid crystal cell is additionally stacked, the thickness becomes thicker than that of the existing display, and the power consumption is also increased. In the latter case, the fraction of aperture and brightness is reduced compared to conventional displays because the part of the pixel that acts as the viewing angle control of one pixel operates only by changing the viewing angle dependency of the dark state. In this case, the pixel is divided into two regions, which complicates the driving method and increases the production cost.

Accordingly, an object of the present invention is to provide a viewing angle control liquid crystal display device using a single panel and having a wide viewing angle and a narrow viewing angle that can be adjusted according to a user's use and environment without reducing an aperture ratio.

According to an aspect of the present invention, there is provided a liquid crystal display device capable of adjusting a viewing angle, the hybrid liquid crystal layer having an upper portion vertically aligned and a lower portion horizontally aligned, a vertical alignment layer positioned on the hybrid liquid crystal layer, and the vertical alignment layer. An upper common electrode of an unpatterned planar shape positioned on an upper portion of the upper common electrode, an upper substrate positioned on the upper common electrode, an upper polarizer positioned on the upper substrate, a horizontal alignment layer positioned below the hybrid liquid crystal layer, A patterned pixel electrode under the horizontal alignment layer, an insulating layer under the pixel electrode, an unpatterned planar lower common electrode under the insulating layer, and a lower portion of the lower common electrode And a lower polarizing plate disposed below the lower substrate. It shall be.
In another aspect, the present invention provides a liquid crystal display device, wherein a hybrid liquid crystal layer having one surface vertically aligned and the other surface horizontally aligned, an upper common electrode positioned above the hybrid liquid crystal layer, and a lower common positioned below the hybrid liquid crystal layer And a patterned pixel electrode disposed under the hybrid liquid crystal layer, wherein the viewing angle is controlled by a vertical electric field applied between the upper common electrode and the lower common electrode.
According to the present invention, in the structure of the lower common electrode and the pixel electrode of the conventional FFS mode, the upper common electrode is additionally positioned in a plane shape in which the upper common electrode is not patterned. It is vertically hybrid oriented. Switching between the wide viewing angle and the narrow viewing angle mode is controlled by the upper common electrode, and implements the wide viewing angle mode when the upper common electrode has a constant potential difference with respect to the lower common electrode, and implements the narrow viewing angle mode when there is no potential difference.

Since the present invention does not use an additional liquid crystal panel and does not use an additional pixel, the present invention has an aperture ratio and a thickness corresponding to an existing display, and the viewing angle control can provide excellent characteristics in both directions without biasing either the wide viewing angle or the narrow viewing angle. . In particular, the viewing angle control liquid crystal display according to the present invention makes white and dark appear white and dark in white, and reduces or reverses the luminance difference for each gray level to secure a narrow viewing angle. The liquid crystals are rotated in a state of lying down to secure transmittance and wide viewing angle characteristics.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

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1 is a view schematically showing an embodiment of a viewing angle control liquid crystal display using a single panel according to the present invention. As shown, the lower common electrode 7 is positioned in an unpatterned plane shape on the lower substrate 8, and the pixel electrode 5 is disposed on the upper portion of the lower substrate 8 with an insulating layer 6 interposed therebetween. Patterned at regular intervals. The upper common electrode 3 and the upper substrate 2 having a plane shape are positioned on the negative liquid crystal layer 4. In this case, the upper polarizing plate 1 and the lower polarizing plate 9 have a transmission axis of 90 ° to each other and are positioned at the outer portions of the upper substrate 2 and the lower substrate 8, respectively. The liquid crystal layer 4 is hybridly aligned from the horizontal orientation to the vertical orientation from the lower substrate 9 to the upper substrate 2.

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When the driving method is described in detail, the wide viewing angle and the narrow viewing angle can be adjusted by the potential difference of the upper common electrode 3 with respect to the lower common electrode 7, and the image representation of each mode is the lower common electrode 7 and the pixel. This is enabled by the electrode 5.
In the case of the wide viewing angle mode, this occurs when the upper common electrode 3 of the upper substrate generates a vertical electric field between the common electrodes 7 of the lower substrate, and the negative liquid crystal is laid down parallel to the substrate by the vertical electric field. The liquid crystals are twisted by the lower fringe field to express transmittance. When the liquid crystals lie parallel to the substrate by a vertical electric field, the initial liquid crystal director is in agreement with the absorption axis of the polarizing plate to represent the dark state, and exhibits a wide viewing angle due to the small viewing angle dependence of the horizontally arranged liquid crystal layers.
In the narrow viewing angle mode, when there is no potential difference between the upper common electrode 3 and the lower common electrode 7, the upper portion is driven in the same manner as the conventional HAN-FFS (Hybrid Aligned Nematic-Fringe-Field Switching) mode. The liquid crystal molecules standing perpendicular to each other show a narrow viewing angle.

Since the image quality and viewing angle characteristics of the display depend on the dark state of the panel, it can be confirmed by observing the liquid crystal director in the dark state in the wide viewing angle and the narrow viewing angle mode.

2 is a liquid crystal array showing the dark state of the narrow-view angle mode. The upper common electrode 3 is in a state before voltage is applied to the lower common electrode 7, and the pixel electrode 5 is also in a state before voltage is applied. Exists as. Since the liquid crystal 4 is not affected by any electric field, it maintains the hybrid alignment which is an initial alignment condition. Due to the hybrid orientation of the liquid crystal 4, the half of the liquid crystal layer 4 is erected so that light leakage occurs in the viewing angle direction, thereby realizing a narrow viewing angle in the dark state.
In the wide viewing angle mode, the electrodes of the upper and lower substrates 2 and 8 are used as shown in the right figure of FIG. The electric field is generated, and the vertical electric field causes the negative liquid crystals 4 to lie parallel to the substrate, thereby representing a dark state having a wide viewing angle characteristic.

Such a structure can be applied to a multi-domain FFS in which the direction of the electric field is different by changing the pattern of the pixel electrode as shown in FIGS. 3A and 3B. The following describes the structure and operation of FFS adopting multiple domains. 3A is a plan view illustrating a lower substrate of a viewing angle control liquid crystal display using a multi-domain FFS electrode structure according to an exemplary embodiment of the present invention.

As shown, a gate bus line 10 and a data bus line 11 are arranged and intersected on the lower substrate 8, and a switching element is provided at an intersection point of the gate bus line 10 and the data bus line 11. A thin film transistor TFT is disposed. The pixel electrode 5, the lower common electrode 7 and the upper common electrode (not shown) are disposed by the crossed lines 10 and 11, and the pixel electrode 5 has a center slit to form multiple domains. Based on S1, the upper slit S2 and the lower slit S3 exist to have a symmetrical slope of + θ or -θ. When negative liquid crystal is used, the directions 12a and 13b of the initial liquid crystal molecules are rubbed parallel to the data bus line 11. At this time, the inclination of the upper and lower slits (S2, S3) can be used up to 0 ~ 90 °, but should be less than ± 45 ° by the transmittance generation principle, and limited to ± 2 ~ 20 ° for high transmittance. Under these conditions, the widths of the slits S1, S2, and S3 are about 1 to 10 µm, and the spacing between the slits is also limited to 1 to 10 µm. 3B is a cross-sectional view taken along line AA ′ of FIG. 3A. The upper common electrode 3 is located opposite to the lower common electrode 7 in an unpatterned plane.

In this structure, in the implementation of the mid-gradation and the white state, the mid-gradation and the white state of the wide viewing angle and the narrow viewing angle are expressed by applying a voltage to the pixel electrode 5 with respect to the lower common electrode 7.

4 illustrates a phenomenon in which light leaks in a viewing angle direction of a dark state in order to prove the effect of the present invention. Referring to FIG. 4, light is not leaked from the front side even when switching from the wide viewing angle mode to the narrow viewing angle mode, whereas light is leaked approximately 10 times in the left and right viewing angle directions. As the left and right viewing angles leak light only in the viewing angle direction, a narrow viewing angle can be realized without a large loss of front brightness and contrast ratio.

FIG. 5 is a curve illustrating brightness, contrast, and contrast ratio of light, dark states according to the viewing angle in the wide viewing angle mode and the narrow viewing angle mode. Referring to the bright state of the wide viewing angle mode of Figure 4 it can be seen that the brightness is the highest in the front, and evenly distributed luminance according to the viewing angle. On the other hand, in the bright state of the narrow viewing angle mode, the brightness at the front side decreases rapidly toward the viewing angle direction, which means that the white at the front side becomes dark in the viewing angle direction. Compared to the dark state, the light leakage of 0.014778, which is 70% of the maximum light leakage in the wide viewing angle mode, appeared in the viewing angle of 60 ° or more, whereas the corresponding light leakage appeared in the viewing angle of 10 ° or more in the narrow viewing angle mode. Suddenly the light can see the fountain. Therefore, it can be seen that the region having a contrast ratio of 5 or more is limited to the viewing angle of 20 ° in the narrow viewing angle mode, and the wide viewing angle mode appears at 70 ° or more.

As described above, the viewing angle control liquid crystal display using the single panel according to the present invention uses a liquid crystal arranged in a hybrid arrangement and introduces a common electrode on the upper side to enable switching between wide viewing angle mode and narrow viewing angle mode in a single panel. It was possible to manufacture a display device.

The upper common electrode introduced for the control of the viewing angle may be applied to the viewing angle control liquid crystal display in the form of a patterned common electrode, instead of an unpatterned planar shape. However, in the case of using the patterned common electrode, since the oblique electric field generated causes light leakage in the dark state, it is necessary to use film compensation or to have a small gap between the patterned electrodes.

In addition, the effective phase delay value of this panel should be manufactured within the phase delay range that can bring the dark state of the narrow viewing angle, and the width and electrode spacing of the fringe field electrode are important for the wide viewing angle and the narrow viewing angle. Adjustable according to

1 is a cross-sectional view schematically illustrating a viewing angle adjusting liquid crystal display using a single panel according to an exemplary embodiment of the present invention.

FIG. 2 is a view for explaining a liquid crystal arrangement in a dark state of the viewing angle control liquid crystal display device of a narrow viewing angle and a wide viewing angle according to the present invention.

3A is a plan view of a viewing angle control liquid crystal display for explaining an embodiment according to the present invention.

3B is a cross-sectional view of the present invention taken along the line AA ′ of FIG. 3A.

4 is a view illustrating a phenomenon in which light leaks in the narrow viewing angle mode compared to the wide viewing angle of the viewing angle control liquid crystal display according to the present invention.

5 is a view illustrating luminance characteristics and contrast curves according to viewing angles of the viewing angle control liquid crystal display according to the present invention.

Claims (3)

In the liquid crystal display device capable of adjusting the viewing angle, A hybrid liquid crystal layer in which the upper portion is vertically aligned and the lower portion is horizontally aligned; A vertical alignment layer on the hybrid liquid crystal layer; An upper common electrode of an unpatterned planar shape positioned on the vertical alignment layer; An upper substrate positioned on the upper common electrode; An upper polarizer positioned on the upper substrate; A horizontal alignment layer disposed under the hybrid liquid crystal layer; A patterned pixel electrode disposed under the horizontal alignment layer; An insulating layer under the pixel electrode; A lower common electrode of an unpatterned planar shape positioned under the insulating layer; A lower substrate positioned below the lower common electrode; A lower polarizer disposed under the lower substrate; The liquid crystal display device characterized by the above-mentioned. The method of claim 1, And the pixel electrode is patterned to form multiple domains having different electric field directions for each unit pixel. In the liquid crystal display device, A hybrid liquid crystal layer having one surface vertically aligned and the other surface horizontally aligned; An upper common electrode disposed on the hybrid liquid crystal layer; A lower common electrode disposed under the hybrid liquid crystal layer; A patterned pixel electrode disposed under the hybrid liquid crystal layer; And a viewing angle is controlled by a vertical electric field applied between the upper common electrode and the lower common electrode.

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