KR19990006887A - LCD and its manufacturing method - Google Patents

Abstract

In the liquid crystal display device of the present invention, a liquid crystal is sandwiched between a pair of substrates, and an active element is disposed for each pixel on one side of the substrate, and on the substrate on which the active element is formed, one or more pairs of pixel electrodes and a common electrode on the line state It is formed in a pixel, and the rubbing direction of the alignment film of both board | substrates is made to be substantially the same direction.

Description

LCD and its manufacturing method

Liquid crystal display devices are thin, light, and low in power consumption, and are widely used in OA devices such as televisions, video display devices, word processors, personal computers, and the like.

Among the liquid crystal display elements, the active matrix type liquid crystal display element in which a large number of switching elements are arranged on an array substrate generally uses a twisted nematic (TN) mode in which the alignment direction of the liquid crystal is twisted by about 90 degrees. Development is progressing as a display capable of high-speed response or high definition.

However, since the liquid crystal display element of TN mode displays the liquid crystal using the optical fluorescence, there exists a fault that a hue and contrast differ according to the angle of viewing a panel. As a solution to this drawback, a method of compensating color tone and contrast using a retardation film, a pixel dividing method or an orientation dividing method which has a plurality of different alignment regions in a pixel, is implemented.

However, even if the above-described method was used, there was a problem that the viewing angle range in the TN mode was narrower than the viewing angle range when the cathode ray tube (CRT) was used.

In order to solve such a problem and to realize a viewing angle characteristic close to the CRT even in the TN mode, a display method of controlling the light transmittance by the electric field control birefringence effect by moving the liquid crystal molecules in a direction substantially horizontal to the substrate surface (hereinafter referred to as "IPS"). Mode ”is proposed.

As an IPS mode, the method of forming the comb-tooth electric field proposed by R.A.Soref on a board | substrate (The Journal of Applied Physics J. Appl. Phys. 45,5446 (1974)) is mentioned. According to this system, the liquid crystal molecules are always viewed from the side (short axis direction). Therefore, even if the viewing directions are different, the refractive index is almost insignificant, and the viewing angle dependency of contrast can be made extremely small.

In the above system, the lower one is preferable as long as the tilt angle of the liquid crystal molecules can be obtained from the viewpoint of the symmetry of the viewing angle characteristics. Therefore, a low pretilt type alignment film is used. However, when a low pretilt film is used for the alignment film in order to obtain a low tilt angle, there is a problem that the voltage holding ratio is generally lowered and traces are easily generated due to charge accumulation.

As described above, in the IPS mode, a low pretilt film is used as the alignment film. However, in the conventional TN mode active matrix panel, a high pretilt angle of 3 ° or more is required in view of the orientation of the active element and the wiring step portion. A high pretilt film is used as the alignment film.

Therefore, when the liquid crystal display panel of the IPS mode and the liquid crystal display panel of the TN mode are made in the same production line, there is a problem that the alignment film cannot be shared, the productivity is poor, and the cost is high.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and also in an IPS mode liquid crystal display panel, a liquid crystal display device having a high pretilt angle for a conventional TN mode can be shared and a wide viewing angle and a fast response speed. To provide. In addition, the liquid crystal display panel of the IPS mode and the liquid crystal display panel of the TN mode can be manufactured in the same production line, to provide a method of manufacturing a liquid crystal display device that can be productive, cost-effective.

In order to solve the above problem, the liquid crystal display device of the present invention is characterized in that the liquid crystal molecules between the two substrates are aligned with the spray deformation.

According to the present invention, a liquid crystal display device having a wide viewing angle characteristic and good symmetry is obtained, and a conventional high pretilt film for TN mode can be used for the alignment film.

In the liquid crystal display device according to claim 1, a liquid crystal is sandwiched between a pair of substrates, an active element is arranged for each pixel on one side of the substrate, and one or more pairs of pixel electrodes and a common electrode on a substrate on which the active element is formed. The liquid crystal display element formed in the pixel is characterized in that the rubbing direction of the alignment films of the two substrates is substantially parallel to each other.

According to this configuration, when a voltage is applied between the electrodes, the liquid crystal molecules are aligned with the spray deformation between the two substrates, and since the central liquid crystal molecules are almost parallel to the substrate, the tilt component of the liquid crystal molecules is optically As the whole thickness direction, it becomes the form cancelled, and a viewing angle is wide and symmetry improves.

The liquid crystal display device according to claim 2 is characterized in that the pretilt angle of liquid crystal molecules existing near the interface of the substrate is 3 ° or more.

According to this configuration, since the pretilt angle is high, a normal high pretilt film for TN mode can be used as the alignment film. The alignment film has a good voltage retention and no trace. In addition, even when manufacturing panels in both the IPS mode and the TN mode in the same manufacturing line, the alignment film does not need to be changed, so productivity can be improved and cost reduction can be expected.

The liquid crystal display device according to claim 3 is characterized in that the pretilt angles of both substrates are the same.

According to this structure, the tilt component of the upper and lower substrate interfaces is completely canceled, and the symmetry of the viewing angle characteristic is further improved.

The liquid crystal display element of Claims 4 and 5 is characterized in that the alignment film is polyimide in any one of Claims 1 to 3.

According to this structure, the orientation stability of liquid crystal molecules becomes favorable by using the polyimide aligning film excellent in orientation stability, and the liquid crystal display element with a high display quality can be obtained.

The liquid crystal display device of Claims 6, 7, and 8 is characterized in that the liquid crystal is a fluorine-based liquid crystal according to any one of Claims 1 to 4.

According to this constitution, impurity ions are hardly accepted at the time of injection of the liquid crystal or from the surrounding material, and the decrease in the voltage holding ratio is eliminated, and the traces are less likely to occur.

In the method of manufacturing a liquid crystal display device according to claim 9, before attaching a pair of substrates to each other, the alignment films of the respective substrates are rubbed so that the rubbing directions are parallel to each other and are in the same direction while the two substrates are bonded to each other. After adhering to each other, the liquid crystal is injected.

According to this configuration, since the liquid crystal molecules line up with the tilt angle in the state of being excited from the substrate interface with respect to the rubbing direction, an alignment state with spray deformation is obtained.

1 is a plan view of a substrate in Example 1;

Fig. 2 is a sectional view of the liquid crystal display panel in Example 1;

3 is a schematic view of an alignment state of liquid crystal molecules in Specific Example 1. FIG.

4 is an isocontrast characteristic of the liquid crystal display device of Example 1;

5 is a schematic view of an alignment state of liquid crystal molecules in Comparative Example 1. FIG.

6 is an isocontrast characteristic of the liquid crystal display device of Comparative Example 1. FIG.

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention is described, referring FIGS.

Example 1

1 and 2 show Embodiment 1 of the present invention.

1 is a plan view of a substrate used in the liquid crystal display panel of the present invention, Figure 2 is a cross-sectional view of the liquid crystal display panel.

As shown in Fig. 1, on one surface of the glass substrate 8a, a plurality of gate electrodes 1 and a source electrode 2 are disposed in a lattice state, and the common electrode 6 is arranged so as to be parallel to the source electrode 2; This common electrode 6 is short-circuited by the drawing electrode 5 provided at the end of the glass substrate 8a.

In addition, the pixel electrodes 7 in a linear state are arranged in portions surrounded by the gate electrode 1 and the source electrode 2, and each end of each pixel electrode 7 intersects the gate electrode 1. A thin film transistor element (hereinafter referred to as "TFT") 4 is provided as an active element. The drain electrode 3 is disposed at the connection portion between the TFT 4 and the pixel electrode 7.

In the liquid crystal display panel of Example 1, as shown in Fig. 2, an alignment film 9a is formed between the glass substrate 8a and each electrode. Similarly, the alignment film 9b is formed on one surface of the glass substrate 8b.

The glass substrates 8a and 8b on which the alignment films 9a and 9b are formed are rubbed in opposite directions, respectively, and are rubbed so that the rubbing directions are substantially parallel and in the same direction when the glass substrates 8a and 8b are bonded to each other.

A space is interposed between the rubbed glass substrates 8a and 8b to maintain a constant distance between the glass substrate 8a and the glass substrate 8b, and the glass substrates 8a and 8b are bonded together. Filled with liquid crystal (not shown).

In such a liquid crystal display panel, when a voltage is applied to the common electrode 6 and the pixel electrode 7, an electric field is generated in the horizontal direction with respect to the surface of the glass substrate 8a, and the liquid crystal molecules are aligned with the spray deformation. It is possible to obtain a liquid crystal display device having a wide viewing angle and good symmetry.

The specific example of the liquid crystal display element in Example 1 is shown below.

(Example 1)

In the first embodiment, the pixel electrode 7 is connected to the drain electrode 3 in parallel with the common electrode 6 and with a thickness of 15 μm therebetween.

In addition, the alignment films 9a and 9b provided on one surface of the glass substrate 8a and the glass substrate 8b have a soluble polyimide varnish having a solid concentration of 6% by weight (for example, Optomer AL-5442: Japanese Synthetic Rubber). Corporation) was offset-printed, and it heated at 170 degreeC for 1 hour, and formed the alignment film 9a, 9b. The film thicknesses of the alignment films 9a and 9b at this time were about 800 GPa, respectively.

The glass substrate 8a was subjected to a rubbing treatment using a rayon spring in the direction of the arrow 10 (see Fig. 1) which appears to be at an angle of about 10 degrees with respect to the direction parallel to the electrode wiring. The glass substrate 8b was rubbed in the reverse direction to the glass substrate 8a. When the glass substrate 8a and the glass substrate 8b were bonded together, the respective rubbing directions were substantially parallel to the same direction.

Subsequently, the substrates 8a and 8b were opposed to each other so that the alignment films 9a and 9b faced each other, and beads 11 having a diameter of 4 탆 were sandwiched and bonded to each other.

A fluorine-based nematic liquid crystal having a Δn of 0.075 and an N-I point of 95 ° C was enclosed by a vacuum injection method in this panel, and the resulting liquid crystal display panel was annealed at 120 ° C higher than the N-I point for 1 hour. As a result, the alignment state of the liquid crystal molecules uniform in the entire liquid crystal panel was obtained.

FIG. 3 is a schematic diagram of the orientation state of liquid crystal molecules when no voltage is applied to the liquid crystal panel in a cross section parallel to the rubbing direction 10. As shown in Fig. 3, the liquid crystal molecules 12 are oriented along with the spray deformation between the upper and lower substrates, and are parallel to the substrates 8a and 8b in the central region. The homogeneous cell of 20 micrometers of cell gaps was produced from the liquid crystal material and alignment film which were used for this liquid crystal panel, and the pretilt angle was measured by the crystal rotation method, and the pretilt angle was 4 degrees.

The polarizing plates were attached to both sides of the liquid crystal panel produced as described above so as to cross each other, thereby obtaining a liquid crystal display device in a normally black mode. At this time, the bonding method of the polarizing plate was such that the rubbing direction 10 on the glass substrate 8a side and the absorption axis of the deflection plate were parallel to each other.

4 shows the viewing angle dependency of the portion where the contrast CR is 100 in this liquid crystal display element. Since the rubbing direction is 10 degrees away from the electrode, the axis is shifted by 10 degrees in both the up, down, left and right directions, but the shape is almost symmetrical and becomes very wide.

As described above, the obtained liquid crystal display device had a wide viewing angle and was excellent in symmetry.

In order to compare and examine the effect of the liquid crystal display device obtained in the specific example 1, the comparative example 1 is shown below.

(Comparative Example 1)

In Example 1, when the glass substrates 8a and 8b were bonded to each other, the rubbing treatment was performed such that the rubbing directions of the glass substrates 8a and 8b were substantially parallel to and in the same direction. In Comparative Example 1, the glass substrates were rubbed. When (8a, 8b) were attached to each other, rubbing treatment was carried out so that the rubbing directions of the respective glass substrates 8a, 8b were almost parallel and reversed.

A liquid crystal display device was manufactured in the same manner as in Example 1 except for the above.

5 schematically illustrates the alignment state of liquid crystal molecules when no voltage is applied to the liquid crystal panel.

The liquid crystal molecules 12 are aligned in parallel with a constant inclination between the upper and lower substrates. The polarizing plates were attached to both sides of this panel so as to cross each other, thereby obtaining a liquid crystal display device in black background mode.

Fig. 6 shows the viewing angle dependency of contrast of this liquid crystal display element.

As is apparent from FIG. 6, the viewing angle dependence of the liquid crystal molecules 12 oriented as shown in FIG. 5 becomes asymmetric in the up, down, left, and right directions, and the liquid crystal display device has a narrow viewing angle.

In addition, in the specific example 1 and the comparative example 1, contrast is represented by the brightness ratio of white display and black display, but the magnitude of the value is largely influenced by the brightness | luminance of black, and since black display mode shows black display when voltage is not applied. In this case, the alignment states of the liquid crystal molecules are compared.

In the specific example 1, as shown in FIG. 3, since the liquid crystal molecules 12 orientate with spray deformation, the liquid crystal molecules 12 are substantially parallel to a board | substrate in the center part of a liquid crystal layer. Therefore, the surface of the liquid crystal molecules 12 in the vicinity of the interface of the glass substrates 8a and 8b becomes optically symmetrical even when viewed from either of the left and right inclinations.

On the other hand, in Comparative Example 1, since the liquid crystal molecules 12 are oriented with the same inclination, as shown in Fig. 5, the liquid crystal molecules 12 are also present at the center of the liquid crystal layer. In addition, when viewed from the upper right side of FIG. 5, the liquid crystal molecules are viewed in a direction close to the long axis of the liquid crystal molecules, and light is easily leaked, and the contrast is decreased.

As a result, in the case of Comparative Example 1, the range where the contrast becomes 100 is narrower in the upper direction than in the lower direction of the liquid crystal display panel, and the isocontrast curve is particularly asymmetric in the vertical direction.

In the specific example 1, the pretilt angle of the liquid crystal molecules 12 near the interface of the glass substrates 8a and 8b is 4 degrees. In the present invention, if the pretilt angle is 3 degrees or more, the normal TN is used. It becomes possible to use the high pretilt alignment film used for a mode, and can lead to the improvement of productivity, and also can expect a cost reduction.

Example 2

In Example 1, the alignment films 9a and 9b of the two substrates were made of the same material. In Example 2, the alignment films 9a and 9b of the two substrates were made of different materials.

In such a configuration, the pretilt angles near the interface of the glass substrates 8a and 8b are different, but an equal contrast region wider than that of FIG. 4 in the specific example 1 can be obtained.

However, in order to obtain more symmetrical viewing angle characteristics, it is preferable that the alignment films of both substrates be made of the same material or that the pretilt angles are the same even if different alignment films are used.

Example 3

In Example 1, a fluorine-based liquid crystal was used as the liquid crystal material. In Example 3, liquid crystal compositions other than fluorine-based compounds such as cyano-based were used as the liquid crystal material.

Also with such a configuration, almost the same effect as in Example 1 was obtained.

However, liquid crystal materials, such as cyano series, tend to accept impurities, and the voltage holding ratio is lower than that of fluorine series materials. In an active matrix type liquid crystal display element, since the fall of voltage retention leads to the fall of a display quality, it is preferable to use a fluorine-type liquid crystal composition.

According to the present invention, the rubbing direction of the alignment film of the two substrates is formed in substantially the same direction so that the liquid crystal molecules are aligned with the spray deformation between the two substrates when voltage is applied between the electrodes. Since it becomes substantially parallel to a board | substrate, the tilt component of the liquid crystal molecule will be canceled in the whole thickness direction, and a viewing angle is wide and symmetry improves.

In addition, since the pretilt angle of the liquid crystal molecules is 3 DEG or more, the high pretilt film for TN mode can be used as the alignment film, and in the case of manufacturing panels in both IPS mode and TN mode in the same production line, the alignment film is used. Since there is no need to change, productivity can be improved and cost can be expected.

Claims (9)

Liquid crystal is sandwiched between a pair of substrates, and an active element is arranged for each pixel on one side of the substrate, and on the substrate on which the active element is formed, a liquid crystal display in which at least one pair of pixel electrodes and a common electrode are formed in the pixel. In the device, A liquid crystal display device in which the rubbing directions of the alignment films of the two substrates are substantially parallel to each other. The liquid crystal display device of claim 1, wherein the pretilt angle of the liquid crystal molecules present near the interface of the substrate is 3 ° or more. The liquid crystal display device according to claim 1 or 2, wherein the pretilt angles of the two substrates are the same. The liquid crystal display device according to claim 1 or 2, wherein the alignment film is polyimide. The liquid crystal display device according to claim 3, wherein the alignment film is polyimide. The liquid crystal display device according to claim 1 or 2, wherein the liquid crystal is a fluorine-based liquid crystal. The liquid crystal display device according to claim 3, wherein the liquid crystal is a fluorine-based liquid crystal. The liquid crystal display device according to claim 4, wherein the liquid crystal is a fluorine-based liquid crystal. Before the pair of substrates are bonded to each other, the alignment films of the respective substrates are rubbed so that the rubbing directions are parallel to each other and are in the same direction while the two substrates are bonded to each other, and after the two substrates are bonded to each other, the liquid crystal is injected. A method of manufacturing a liquid crystal display device, characterized in that.