KR20020002661A - Twisted nematic lcd improved viewing angle - Google Patents

Abstract

PURPOSE: A TN-LCD(Twisted Nematic Liquid Crystal Display) is provided to improve the characteristics of a viewing angle by forming various kinds of electric fields including electric fields bent symmetrically in a single pixel, electric fields vertical to a substrate and electric fields having different strength. CONSTITUTION: A lower substrate(50) having a pixel electrode(51) is positioned opposite to an upper substrate(60) having a counter electrode(61) with a specific distance. Herein, the specific distance is a cell gap. The common electrode is formed in plate type, and plural slits(510) are formed on the pixel electrode. The pixel electrode is divided into first to fourth areas. Forming the slits on the pixel electrode is for generating electric fields(E2) vertical to a substrate surface and electric fields(E1) distorted by the slits at the same time. To form electric fields having different strength in a unit pixel of the lower substrate, a passivation layer(54) is formed at the upper part. The passivation layer is divided to four areas like the pixel electrode. Plural opening are formed in at least one and more areas of the four areas. If an opening is formed on the passivation layer, strength difference of electric fields between the opening-formed area and a non-formed area is generated. If the distorted electric fields(E1) and the vertical electric fields(E2) are generated in a single pixel at the same time, the long axis of LC molecules(70a) is arranged parallel to the electric fields.

Description

Twist nematic liquid crystal display with improved viewing angle {TWISTED NEMATIC LCD IMPROVED VIEWING ANGLE}

The present invention relates to a liquid crystal display, and more particularly, to a twisted-nematic liquid crystal display (TN) having an improved viewing angle.

In general, a liquid crystal display device includes liquid crystal molecules aligned between a pair of light-transmissive substrates, and emits light or blocks light to electrically control the alignment state of the liquid crystal molecules, thereby performing image display. Such liquid crystal displays are widely used as display means for electronic desk calculators and digital clocks, and are rapidly being widely used as display means for laptop computers, television receivers, and word processors.

Here, the conventional liquid crystal display device uses many TN modes that are excellent in optical characteristics, have clear black and white display, and have excellent response characteristics. As shown in FIG. 1, the liquid crystal display of the TN mode is disposed on opposing upper and lower substrates 10 and 20, a pixel electrode 11 disposed on an inner side surface of a lower substrate, and an inner side surface of an upper substrate. The polarizing plates 15 and 25 and the upper and lower substrates 10 and 20 are respectively disposed on the common electrode 21, the alignment film (not shown) disposed on the upper and lower substrate opposing surfaces, and the outer outer surfaces of the upper and lower substrates 10 and 20, respectively. Interposed therebetween, the liquid crystal layer 30 including several liquid crystal molecules is included.

The alignment film (not shown) is a horizontal alignment film, and the rubbing axes 12a and 12b are crossed by 90 degrees, and the upper and lower polarizers are also attached in the direction in which the polarization axes 15a and 25a cross each other. That is, the rubbing axis 12a of the lower alignment layer and the polarization axis 15a of the lower polarizing plate are attached in the same direction, and the rubbing axis 12b of the upper alignment layer and the polarization axis 25a of the upper polarizing plate are attached in the same direction. In addition, the pixel electrode 11 and the common electrode 21 are formed in a plate shape.

Before the electric field is applied between the pixel electrode 11 and the common electrode 21, the liquid crystal molecules 30a are twisted 90 degrees in a left-line direction under the influence of the vertical alignment layer and the chiral dopant, as shown in FIG. 1. . Therefore, the light passing through the lower polarizer 15 passes through the liquid crystal molecules 30a twisted in a left linear manner, and passes through the upper polarizer 25. As a result, the screen becomes white.

On the other hand, when an electric field is applied between the pixel electrode 11 and the common electrode 21, the liquid crystal molecules 30a are not shown in the figure. It is arranged in parallel with an electric field (formed perpendicular to the substrate) formed between the drive electrodes. Accordingly, the light passing through the lower polarizer 15 does not pass through the crossed upper polarizer because the long axis of the liquid crystal molecules 30a is vertically aligned with the substrate surface. Thus, the screen is dark.

However, in the TN liquid crystal display device as described above, since the shape of the liquid crystal molecules interposed between the upper and lower substrates is different from each other, the refractive index anisotropy values are different from each other in the direction of looking at the screen. For this reason, the viewing angle characteristic is very low.

Accordingly, an object of the present invention is to provide a TN liquid crystal display device capable of solving the above-described conventional problems and capable of improving viewing angle characteristics.

1 is an exploded perspective view of a conventional twisted nematic liquid crystal display device.

2 is an exploded perspective view of a TN mode liquid crystal display device according to the present invention;

3 is a plan view of a passivation film according to the present invention.

4 is a cross-sectional view taken along the line IV-IV 'of FIG.

(Explanation of symbols for the main parts of the drawing)

50-lower substrate 51-pixel electrode

54-passivation film 55,65-polarizer

60-upper substrate 61-common electrode

70-liquid crystal molecules

In order to achieve the above object of the present invention, according to an embodiment of the present invention, the present invention provides a display device comprising: a lower substrate having pixel electrodes for each unit pixel; An upper substrate facing the lower substrate and having a common electrode; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A vertical alignment layer disposed on inner surfaces of the lower substrate and the upper substrate and arranged to twist the liquid crystal molecules in the liquid crystal layer by 90 ° before an electric field is formed between the pixel electrode and the common electrode; And first and second polarizing plates disposed on the lower substrate back surface and the upper substrate back surface, respectively, when an electric field is applied between the pixel electrode and the common electrode. In addition to being formed at the same time, it is characterized in that the electric field of different intensities are formed simultaneously.

(Example)

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

2 is an exploded perspective view of a TN mode liquid crystal display device according to the present invention, and FIG. 3 is a plan view of a passivation film according to the present invention. 4 is a cross-sectional view taken along the line IV-IV 'of FIG. 2. Here, the drawings show only one of the plurality of pixels.

Referring to FIG. 2, when the TN mode liquid crystal display according to the present invention is described, the lower substrate 50 including the pixel electrode 51 and the upper substrate 60 including the counter electrode 61 may have a predetermined distance. Left opposite. In this case, the distance between the upper and lower substrates 50 and 60 is called a cell gap. Here, the common electrode 61 is formed in a plate shape, and a plurality of slits 510 are disposed in a predetermined portion of the pixel electrode 51. For example, in the present exemplary embodiment, the pixel electrode 51 is divided into four portions, that is, the first to fourth regions 51A, 51B, 51C, and 51D, and two selected portions thereof, for example, the first And several slits 510 arranged at equal intervals in the fourth regions 51A and 51D. Here, the slit 510 is formed in a predetermined region of the pixel electrode 51 in order to simultaneously generate an electric field perpendicular to the substrate surface and an electric field distorted by the slit 510 in the unit pixel. In this case, the long axis of the slit 510 formed in one pixel electrode 51 may be arranged in parallel or vertically. In addition, in order to form electric fields having different intensities in the unit pixels of the lower substrate 50 on which the pixel electrodes 51 are formed, a passivation film is formed on the upper portion. In this case, as shown in FIG. 3, the passivation film 54 is divided into four regions like the pixel electrode 51, and then the opening H is provided in at least one of the four regions. In this way, when an opening is formed in the passivation film 54, a difference in electric field strength is generated between the region where the opening is formed and the region where the opening is not formed. In the present embodiment, for example, the opening H of the passivation film 54 is positioned in the region where the slit 510 is formed.

An alignment film (not shown) is formed on the surface of the lower substrate 50 and the surface of the upper substrate 60 to determine the arrangement state of the initial liquid crystal molecules. At this time, the alignment layer is a horizontal alignment layer having a pretilt angle of 5 degrees or less, and the two alignment layers are rubbed so that their rubbing axes R1 and R2 are perpendicular to each other.

The liquid crystal layer 70 having several liquid crystal molecules 70a is interposed between the alignment layers of the upper and lower substrates 50 and 60. In this case, the liquid crystal molecules 70a of the liquid crystal layer 70 use a material having a positive dielectric anisotropy Δε.

The first polarizer 55 and the second polarizer 65 are disposed on the rear surface of the lower substrate 50 and the rear surface of the upper substrate 60. These polarizing plates 55 and 65 include polarization axes 55a and 65a in a predetermined direction, and the polarization axes 55a of the first polarizing plate 55 and the polarization axes 25a of the second polarizing plate 65 intersect each other. .

The TN liquid crystal display device of the present invention having such a configuration is operated as follows.

First, when no electric field is formed between the pixel electrode 51 and the common electrode 61, the liquid crystal molecules 70a are arranged in a rubbing state of the horizontal alignment layer. That is, since the alignment film is rubbed at an angle of 90 degrees, the liquid crystal molecules 70a are arranged with a 90 ° twist while the major axis is parallel to the substrate surface. In this case, since the polarization axes of the first and second polarizers 55 and 65 are disposed to cross each other, the light applied from the bottom surface of the lower substrate 10 is transferred to the lower polarizer 55, the liquid crystal layer 30, and the upper polarizer ( Passing 65), the screen becomes white.

On the other hand, if a predetermined voltage difference is generated between the pixel electrode 51 and the common electrode 61, as shown in FIG. An E1 is formed, and an electric field E2 perpendicular to the surface of the substrate 50 is formed in a portion where the slit 510 is not present. Here, since the passivation film 54 is not disposed in the portion where the curved electric field E1 is formed, unlike the portion in which the vertical electric field E2 is formed, the curved electric field E1 has a higher intensity than the vertical electric field E2. Big. As such, when the curved electric field E1 and the vertical electric field E2 are simultaneously formed in one pixel, the liquid crystal molecules 70a are also arranged such that the electric field and the long axis thereof are parallel to each other. Accordingly, the liquid crystal molecules 70a are arranged to be symmetrical at portions where the slit 510 is formed and at portions where the slit 510 is not formed, thereby compensating refractive index anisotropy of the liquid crystal molecules 70a. Thus, the viewing angle characteristic is improved.

As described in detail above, according to the present invention, in the TN liquid crystal display device, a slit is disposed in a predetermined portion of the pixel electrode, a predetermined portion of the passivation film is opened, and an electric field having a symmetrically curved electric field in one pixel; The electric field perpendicular to the substrate surface and the electric field having different intensities are simultaneously formed. Accordingly, the liquid crystal molecules are arranged symmetrically by the shape of the electric field, so that the viewing angle characteristic is improved.

In addition, this invention can be implemented in various changes within the range which does not deviate from the summary.

Claims (3)

A lower substrate having pixel electrodes for each unit pixel; An upper substrate facing the lower substrate and having a common electrode; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A vertical alignment layer disposed on inner surfaces of the lower substrate and the upper substrate and arranged to twist the liquid crystal molecules in the liquid crystal layer by 90 ° before an electric field is formed between the pixel electrode and the common electrode; And A first polarizing plate and a second polarizing plate disposed on the lower substrate back surface and the upper substrate back surface, respectively; When the electric field is applied between the pixel electrode and the common electrode, an electric field perpendicular to the substrate surface and a curved electric field are simultaneously formed in the unit pixel, and electric fields having different intensities are simultaneously formed. Liquid crystal display. The TN liquid crystal display of claim 1, wherein each of the pixel electrodes is divided into several regions, and a plurality of slits are provided in a portion of the several regions. The TN liquid crystal display of claim 1, wherein a passivation layer is formed on the lower substrate on which the pixel electrode is formed, and a portion of the passivation layer is opened to control the intensity of the electric field.