KR20030061584A - 2-domain ffs-va mode liquid crystal display device - Google Patents

Abstract

PURPOSE: A 2-domain FFS-VA(Fringe Field Switching-Vertial Aligned) mode liquid crystal display is provided to prevent the transmissivity from lowering by minimizing a disclination line generated area, thereby improving viewing angle and transmissivity characteristics. CONSTITUTION: A lower substrate(10) includes a counter electrode(4) and a pixel electrode(7) to form a fringe field. An upper substrate(20) faces the lower substrate and has color filters and black matrices. A liquid crystal layer is interposed between the lower substrate and the upper substrate. Vertical alignment films(8,17) are formed on top sides of lower and upper glass substrates(1,11). A lower polarizing plate(9a) is a circularly polarized light plate transmitting only circularly polarized light. An upper polarizing plate(19) is a linearly polarized light plate transmitting only linearly polarized light. A quarter phase compensating plate(18) is inserted between the upper glass substrate and the upper polarizing plate. A phase delay value of a liquid cell is set as a half.

Description

2-domain F-V mode liquid crystal display {2-DOMAIN FFS-VA MODE LIQUID CRYSTAL DISPLAY DEVICE}

The present invention relates to a liquid crystal display device, and more particularly, to a two-domain F-V (FFS-VA) mode liquid crystal display device capable of improving transmittance.

As is well known, TN (Twist Nematic) mode liquid crystal display has advantages of excellent light efficiency, but has a disadvantage of poor viewing angle and response speed. Accordingly, in order to improve the narrowness of the viewing angle and response speed of the TN mode liquid crystal display device, the V (V) mode, the IPS (In-Plane Switching) mode, and the FSF (FFS: Fringe Field Switching) Mode liquid crystal display devices and the like have been developed and are currently being used.

Among them, the VA mode has the advantages of pure dark and fast response time at the front, but has a disadvantage of poor viewing angle. Accordingly, in order to improve the viewing angle, a technique of forming 2-domain, 4-domain, etc. in one pixel has been proposed. Although such a technique can realize a wide viewing angle, the pixels are divided, which inevitably leads to a decrease in transmittance. In particular, in order to solve such a problem, the power of the backlight must be increased, so there is another problem of increased power consumption.

Therefore, in order to improve the disadvantage of the VA mode, an IPS-VA mode combining the VA mode and the IPS mode, or an FFS-VA mode combining the VA mode and the FFS mode has been researched and developed.

1 and 2 are views for explaining a conventional FFS-VA mode liquid crystal display device, FIG. 1 is a plan view showing a schematic pixel structure, and FIG. 2 is a FFS-VA mode liquid crystal along line AA ′ of FIG. 1. It is sectional drawing of a display apparatus.

Referring to FIG. 1, a gate bus line 2 and a data bus line 6 are intersected and a common bus line 3 is disposed in parallel between the gate bus lines 2. A thin film transistor (TFT) is disposed near the intersection of the gate bus line 2 and the data bus line 6. A plate-shaped counter electrode 4 made of ITO is disposed in each pixel region partitioned by the gate bus line 2 and the data bus line 6, and a gate insulating film is formed on the counter electrode 4. A slit-shaped pixel electrode 7 made of ITO is disposed under (not shown).

Here, the slit of the pixel electrode 7 is formed in a " " shape in a unit pixel so as to divide one pixel into two, and is formed to have a width of 5 μm or less and an interval of 12 μm or less, in particular, a bus It is formed to have an acute angle of 45 ° with the line.

Referring to FIG. 2, a plate-type counter electrode 4 and a slit-type pixel electrode 8 are formed on the inner side surface of the lower glass substrate 1 with the insulating film 5 interposed therebetween. The upper substrate 20 formed by forming a color filter and a black matrix (not shown) on the inner surface of the upper glass substrate 11 is disposed to face each other, and a plurality of liquid crystal molecules (between the substrates 10 and 20). A liquid crystal layer 30 composed of 21 is interposed.

In addition, the vertical alignment layers 8 and 17 are formed on the uppermost inner surfaces of the glass substrates 1 and 11, where the vertical alignment layers 8 and 17 are not rubbing, but in some cases. By rubbing in a specific direction, it is possible to have a pretilt angle of 85 to 90 degrees. In addition, a lower polarizing plate 9 and an upper polarizing plate 19 are attached to the outer surfaces of the glass substrates 1 and 11, wherein each of the lower polarizing plate 9 and the upper polarizing plate 19 transmits only linearly polarized light. It is a linear polarizing plate which is attached to have mutually perpendicular optical axis.

Such an FFS-VA mode liquid crystal display has advantages of pure dark and fast response time at the front because the liquid crystal molecules are vertically aligned at the beginning, and most liquid crystal molecules are driven by the fringe field. Therefore, it exhibits good transmittance and aperture ratio characteristics. In addition, since the pixel electrode is provided with a slit having a " " shape, the refractive index anisotropy of the liquid crystal molecules is compensated because the electric fields are formed in two symmetrical directions in one pixel, thereby exhibiting good viewing angle characteristics.

However, the conventional two-domain FFS-VA mode liquid crystal display as described above has the advantages of wide viewing angle and high speed response, but a disclination line is generated between the electrodes and at the upper end of the electrode to improve the transmittance. There is a problem that degradation occurs.

Accordingly, an object of the present invention is to provide a two-domain FFS-VA mode liquid crystal display device, which is designed to solve the above problems and can improve the transmittance decrease caused by the occurrence of the disclination line. .

1 is a plan view of a conventional two-domain FFS-VA mode liquid crystal display device.

FIG. 2 is a cross-sectional view of the 2-domain FFS-VA mode liquid crystal display device taken along the line AA ′ of FIG. 1.

3 is a cross-sectional view illustrating a two-domain FFS-VA mode liquid crystal display according to an exemplary embodiment of the present invention.

4 is a view for explaining the driving principle of the liquid crystal display device according to the present invention.

5 is a cross-sectional view illustrating a two-domain FFS-VA mode liquid crystal display according to another embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

1: lower glass substrate 4: counter electrode

5 insulating film 7 pixel electrode

8,17 vertical alignment layer 9a lower polarizing plate

10: lower substrate 11: upper glass substrate

18: lambda / 4 plate 19: upper polarizing plate

20: upper substrate 21: liquid crystal molecules

30 liquid crystal layer 40 ITO electrode

In the two-domain FFS-VA mode liquid crystal display of the present invention for achieving the above object, the plate-type counter electrode and the " " -shaped slits are formed under the insulating film so as to form a fringe field on the lower glass substrate. A lower substrate having a slit-shaped pixel electrode formed thereon; An upper substrate disposed to face the lower substrate and having a color filter and a black matrix formed on the upper glass substrate; A liquid crystal layer composed of several liquid crystal molecules interposed between the lower substrate and the upper substrate; A vertical alignment layer formed on an uppermost side of the inner surface of each glass substrate; And a lower polarizer plate and an upper polarizer plate attached to an outer surface of each glass substrate, wherein the lower polarizer plate is a circular polarizer plate that transmits only circularly polarized light, and The upper polarizing plate is composed of a linear polarizing plate that transmits only light of linear polarization, and a phase compensation plate of λ / 4 is inserted between the upper glass substrate and the upper polarizing plate, and the phase delay value of the liquid crystal cell (refractive index anisotropy (Δn) × cell gap (d)). )} Is set to λ / 2.

In addition, the two-domain FFS-VA mode liquid crystal display of the present invention is characterized in that the ITO electrode is further provided on the vertical alignment layer on the upper substrate.

According to the present invention, while applying a circularly polarizing plate as a lower polarizing plate and a linear polarizing plate as an upper polarizing plate, a phase compensation plate of? / 4 is provided on the upper glass substrate, and the phase delay value of the liquid crystal cell is? / 2. By designing to such an extent, it is possible to reduce the disclination line generation area as much as possible, thereby providing a liquid crystal display device having an improved transmittance.

(Example)

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

3 is a cross-sectional view of a two-domain FFS-VA mode liquid crystal display according to an exemplary embodiment of the present invention. Here, the same parts as in Fig. 2 are designated by the same reference numerals.

As shown, the two-domain FFS-VA mode liquid crystal display device of the present invention, as in the prior art, has a counter electrode 4 and an interposed portion of the insulating film 5 so as to form a fringe field on the lower glass substrate 11. The lower substrate 10 formed by forming the pixel electrode 7 and the upper substrate 20 formed by forming a color filter and a black matrix (not shown) on the inner surface of the upper glass substrate 11 have several liquid crystal molecules. It has a structure bonded together by the interposition of the liquid crystal layer 30 comprised from (21).

Here, the counter electrode 4 is preferably formed in a plate shape, and the pixel electrode 7 is preferably formed in a slit shape, in which the slits of the pixel electrode 7 divide one pixel into two. It has a "<" shape and is formed to have a width of 5 µm or less and an interval of 12 µm or less, and in particular, to have an acute angle of 45 ° with the bus line.

Subsequently, as shown, vertical alignment layers 8 and 17 are formed at the top of the inner side surfaces of the glass substrates 1 and 11 so that the liquid crystal molecules 21 are initially arranged in the vertical direction. Each of the vertical alignment layers 8 and 17 is not based on rubbing, but may have a pretilt angle of 85 to 90 ° through a rubbing process in a specific direction.

In addition, the lower polarizing plate 9a and the upper polarizing plate 19 are attached to the outer surfaces of the glass substrates 1 and 11, respectively, in which the upper polarizing plate 19 transmits only linearly polarized light as in the prior art. On the other hand, the lower polarizing plate 9a is formed of a circularly polarizing plate that transmits only light of circularly polarized light.

In addition, in the upper substrate 20, a phase compensation plate of λ / 4 (hereinafter referred to as λ / 4 plate) is interposed between the upper glass substrate 11 and the upper polarizing plate 19.

In addition, although not shown, the liquid crystal display of the present invention is represented by the product of the refractive index anisotropy (Δn) of the liquid crystal molecules 21 and the cell gap d, which is an interval between the lower substrate 10 and the upper substrate 20. The phase delay value (Δn × d) of the liquid crystal cell is preferably designed to be λ / 2. For example, the phase delay value is designed to be about 0.25 to 0.5.

The driving principle of the two-domain FFS-VA mode liquid crystal display of the present invention will be described with reference to FIG. 4 as follows.

As shown, the light emitted from the backlight 50 passes through the lower polarizing plate 9a attached to the lower glass substrate (not shown), that is, the circularly polarizing plate that transmits only the circularly polarized light, for example, the left circularly polarized light ( left handed). Here, the circularly polarizing plate transmits only circularly polarized light in one direction and absorbs or reflects light that rotates in the opposite direction, and the light of the right circularly polarized light is reflected and enters the backlight 50 again. By the reflective layer 51 provided at the lower portion of 50, the left circularly polarized light is finally passed through the circularly polarized plate.

Subsequently, the left circularly polarized light that has passed through the lower polarizing plate 9a maintains the left circularly polarized light in the dark state where the electric field is not applied to the liquid crystal layer 30, as shown in the left side of FIG. And then linearly polarized through the λ / 4 plate 18, and this linearly polarized light is absorbed by the upper polarizing plate 19, i.e., the linear polarizing plate, on the upper substrate (not shown) having a vertical optical axis. Will remain the same.

On the other hand, the left circularly polarized light passing through the lower polarizing plate 9a has a phase delay value of λ / 2 due to the electric field in an on state in which an electric field is applied to the liquid crystal layer 30 as shown in the right side of FIG. 5. Through the 30, it becomes a right circularly polarized light, and while passing through the λ / 4 plate 18, it becomes a linearly polarized light in a dark state and a linearly polarized light 90 degrees, and passes through the upper polarizing plate 19 on the upper substrate (not shown). So, it implements the white state.

On the other hand, the lower polarizing plate (9a) in the above can be provided so that the left circularly polarized light as well as the right circularly polarized light has a characteristic, therefore, according to this principle in a large area in the pixel generated when the liquid crystal is initially vertically aligned is driven The generation of the disclination line of is significantly reduced, so that the decrease in transmittance due to the generation of the disclination line is improved, resulting in an improvement in viewing angle and transmittance characteristics.

As a result, the liquid crystal display device of the present invention using both circularly polarized light and linearly polarized light can considerably reduce the size of the declining generation region, compared with the conventional method using only linearly polarized light, and thus obtains light efficiency similar to that of the conventional TN mode. Can be. In addition, since the circularly polarizing plate can be directly applied to the backlight to improve the transmittance, the lower polarizing plate in the pure liquid crystal cell can be omitted, and thus, the cost reduction effect can be obtained and the liquid crystal alignment can be achieved. Regarding the possibility of omitting the alignment process, process simplification can also be obtained.

FIG. 5 is a cross-sectional view showing a two-domain FFS-VA mode liquid crystal display device according to another embodiment of the present invention. As shown, the liquid crystal display device in this embodiment has an upper substrate compared with that of the previous embodiment. In more detail, the plate-shaped ITO electrode 40 may be further provided at the top of the inner surface of the upper glass substrate 11.

In this case, since the equipotential lines have a symmetrical structure between the electrodes and on the electrodes, a better symmetrical viewing angle characteristic can be obtained, so that the screen quality of the liquid crystal display device can be further improved.

As described above, the present invention is provided with a phase compensation plate of λ / 4 on the upper glass substrate while applying a circularly polarizing plate as a lower polarizing plate and a linear polarizing plate as an upper polarizing plate, and adding a phase delay value of the liquid crystal cell to λ. By designing about / 2, the disclination line generation area can be reduced as much as possible to prevent the decrease in transmittance caused by the disclination line generation, thereby providing a liquid crystal display device having improved viewing angle and transmittance characteristics. can do.

In addition, the present invention can provide a liquid crystal display device having better viewing angle characteristics by providing an ITO electrode on the upper substrate in addition to the above-described configuration.

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

Claims (2)

A lower substrate comprising a plate type counter electrode and a slit pixel electrode having "<" shaped slits formed therebetween so as to form a fringe field on the lower glass substrate; An upper substrate disposed to face the lower substrate and having a color filter and a black matrix formed on the upper glass substrate; A liquid crystal layer composed of several liquid crystal molecules interposed between the lower substrate and the upper substrate; A vertical alignment layer formed on an uppermost side of the inner surface of each glass substrate; And a lower polarizing plate and an upper polarizing plate attached to an outer surface of each glass substrate, wherein the two-domain FFS-VA mode liquid crystal display device includes: The lower polarizing plate is a circular polarizing plate for transmitting only light of circular polarization, and the upper polarizing plate is made of a linear polarizing plate for transmitting only light of linear polarization, A phase compensation plate of λ / 4 is inserted between the upper glass substrate and the upper polarizing plate, The phase delay value (refractive anisotropy (Δn) x cell gap d) of the liquid crystal cell is set to lambda / 2, 2-domain FFS-VA mode liquid crystal display device. 2. The two-domain FFS-VA mode liquid crystal display of claim 1, further comprising an ITO electrode on the vertical alignment layer of the upper substrate.