KR20070007606A - Liquid crystal display device - Google Patents

Abstract

An LCD is provided to prevent the leakage of light due to an electric field between neighboring pixel electrodes, by designing pixel electrodes such that the boundary line between pixel electrodes has an inclination angle with respect to a gate line. A gate line(20) is formed on a substrate(10), and a pixel electrode(40) is formed within each pixel region. Liquid crystal molecules(50) are apart from the substrate, wherein each of the liquid crystal molecules has a positive dielectric anisotropy. An alignment layer is formed to cover the pixel electrode, and aligns the liquid crystal molecules in a horizontal direction. A boundary line between pixel electrodes, which are disposed adjacently at the gate line, has an inclination angle with respect to the gate line.

Description

Liquid Crystal Display Device

1 is a plan view of a substrate used in the liquid crystal display device according to the prior art,

2 is a plan view of a substrate used in the liquid crystal display according to the embodiment of the present invention;

3 is a cross-sectional view taken along the line AA ′ of FIG. 2;

4 is a plan view of a substrate used in a liquid crystal display according to another embodiment of the present invention;

5A and 5B are cross sectional views taken along the line BB ′ of FIG. 4.

♧ explanation of symbols for main parts of drawing

10-substrate 11-gate insulating film

12-Shield 20-Gate Line

30-data line 40-pixel electrode

50-liquid crystal 60-alignment layer

70-Organic Film 80-Color Filter Film

P-pixels

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device in which the pixel electrode is formed to be bent.

A liquid crystal display (LCD) converts an input electrical signal into visual information by using a property in which light transmittance of a liquid crystal, which is an intermediate state material between a liquid and a crystal, changes according to an applied voltage. It is a display device that delivers an image. A general liquid crystal display device includes two substrates on which electrodes are formed and a liquid crystal injected between the substrates. Different voltages are applied to the electrodes of each substrate, thereby applying an electric field to the liquid crystals to change the arrangement of the liquid crystals so as to change the light transmittance of the liquid crystals. Such a liquid crystal display device has an advantage of thinner, lighter, and lower power consumption than other display devices having the same screen size.

The arrangement of the liquid crystal changes depending on the electric field due to the dielectric anisotropy of the liquid crystal. That is, the liquid crystal molecules have different physical properties in the long axis direction and the short axis direction, and thus, when an electric field is applied, the electric forces acting in the long axis direction and the short axis direction of the liquid crystal molecules are different. It becomes a drive source to rotate. The liquid crystal has positive dielectric anisotropy or negative dielectric anisotropy depending on the type. Based on the long axis direction of the liquid crystal, the former is arranged in parallel to the direction of the electric field when the electric field is applied, the latter is arranged perpendicular to the direction of the electric field.

The driving method of the liquid crystal display device is determined according to the type of liquid crystal as described above. That is, the driving method of the liquid crystal display device is classified according to whether the white state is the brightest state or the black state is the darkest state when no electric field is applied to the liquid crystal. At this time, the former liquid crystal display uses a liquid crystal having a positive dielectric anisotropy, and the latter liquid crystal display uses a liquid crystal having a negative dielectric anisotropy. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the former scheme, and in particular, to the arrangement of a substrate used in a liquid crystal display and a polarizing plate coupled thereto. Hereinafter, the problems of the conventional liquid crystal display will be described with reference to the accompanying drawings.

1 is a plan view of a substrate used in a liquid crystal display according to the prior art.

Referring to FIG. 1, a plurality of metal wires 2 and 3 are formed on the substrate 1. Here, the metal lines 2 and 3 include a gate line 2 formed in a row direction and a data line 3 formed in a column direction. A region defined by the intersection of the gate line 2 and the data line 3 corresponds to each pixel P, and each pixel includes a pixel electrode 4. An upper side of the substrate 1 is bonded to a separate substrate provided with a common electrode without distinguishing the pixel P. A polarizing plate for transmitting light in one direction is coupled to the outside of the two substrates as described above. Arrows in FIG. 1 indicate a transmission axis direction for transmitting light of the polarizing plate, and the two polarizing plates are disposed such that the transmission axis directions are perpendicular to each other.

However, the liquid crystal display device as above may be formed of an electric field (E _l) between the pixel electrodes 4 adjacent. Since the data voltage corresponding to the image to be implemented in each pixel P is applied to the pixel electrode 4, when the image information is different, the data voltage applied to the pixel electrode 4 is also different. In this case, the adjacent pixel electrode ( 4) applying an electric field (E _l) according to the voltage difference is between a can be formed. In particular, in order to prevent deterioration as the liquid crystal continues to react in only one direction, a method of applying a data voltage having a different polarity in units of pixels P has been adopted. In this case, a data voltage having a different polarity is applied between the adjacent pixel electrodes 4, so that the electric field _El is further increased. The electric field is (E _l) is named as are formed on the side, which the lateral electric field (lateral field) Hereinafter, the pixel electrodes 4 adjacent.

And the various problems caused by the lateral electric field (E _l), located in the vicinity of the region where the boundary of the pixel (P) and the pixel (P) for example can be light leakage occurs. In the black state, most of the liquid crystals are arranged vertically with respect to the substrate by the inter-substrate electric field. In this case, light cannot pass through two polarizers whose transmission axis directions are perpendicular to each other. However, some of the liquid crystal (5) on the area in which the pixel electrodes 4 adjacent to the side is inclined to a certain arrangement relative to the substrate 1 by the electric field direction (E _l). In this case, the long axis direction of the liquid crystal 5 is at an angle with the transmission axis of the polarizing plate, the light passing through the first polarizing plate is refracted while passing through the liquid crystal 5, the polarization direction is distorted, as a result of the second polarizing plate It penetrates and causes light leakage.

Unlike in FIG. 1, if the transmission axis direction of the polarizing plate is parallel to the row direction and the column direction, even if the light passes through the liquid crystal arranged inclined in the row direction by the lateral electric field, the light has a transmission axis parallel to the column direction. It does not pass through the polarizing plate. Therefore, light leakage and the like can be prevented, but in this case, gray scale inversion occurs in the left and right sides, which causes a problem of poor visibility.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a liquid crystal display device capable of preventing a problem due to an electric field between adjacent pixel electrodes.

The present invention provides a liquid crystal display device to achieve the above technical problem. According to an exemplary embodiment of the present invention, a liquid crystal display includes: a gate line formed in one direction on a substrate and a pixel electrode formed to be distinguished for each pixel; A liquid crystal arranged to be spaced apart from the substrate and having positive dielectric anisotropy; An alignment layer covering the pixel electrode and arranging the liquid crystal in a horizontal direction; A boundary line between pixel electrodes adjacent in the gate line direction is inclined with respect to the gate line. The pixel electrode is also inclined along the boundary line.

The boundary line may be formed in a curved shape having a portion inclined in a first direction and a portion inclined in a second direction, and the first and second directions may be perpendicular to each other.

According to the present invention, a polarizing plate coupled to the substrate and performing a polarizing function is further included, but a transmission axis direction through which light of the polarizing plate passes is parallel or perpendicular to the first direction or the second direction. The polarizers are respectively coupled to two substrates provided in the liquid crystal display, and the transmission axes of the polarizers are perpendicular to each other. Therefore, even if different data voltages are applied to adjacent pixel electrodes to operate an electric field between the pixel electrodes, the direction of the electric field is perpendicular to the direction of the inclination of the pixel electrode and perpendicular to the transmission axis direction of any one of the two polarizing plates. As a result, even if the arrangement of the liquid crystals is changed by the electric field between the pixel electrodes, the alignment direction of the liquid crystals is perpendicular to the transmission axis of the polarizing plate, thereby preventing light leakage by the liquid crystals.

Signal wires are formed on the substrate to transfer signals necessary for applying a data voltage to the pixel electrode. The signal wires include data lines in addition to the gate lines. The electric field may act on the pixel electrode by the signal line while the signal is transmitted to the signal line, and the signal line may be formed so as not to overlap the pixel electrode to prevent this. The gate line may be formed in one direction, for example, in a row direction between the pixel electrodes, and the data line may be formed along the curved shape of the pixel electrode while crossing the gate line. Alternatively, the data line may be formed so as to pass straight in one direction while overlapping the pixel electrode. In this case, a thick insulating layer may be formed between the pixel electrode and the data line to prevent an electric field generated by the data line from affecting the pixel electrode. Can be added.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be applied and modified in various forms. Rather, the following embodiments are provided to more clearly clarify the technical spirit disclosed by the present invention and to further convey the technical spirit of the present invention to those skilled in the art having an average knowledge in the field to which the present invention belongs. Therefore, the scope of the present invention should not be construed as limited by the embodiments described below. In addition, in the drawings presented in conjunction with the following examples, the size of layers and regions are simplified or somewhat exaggerated to emphasize clarity, and like reference numerals in the drawings indicate like elements.

2 is a plan view of a substrate used in the liquid crystal display according to the embodiment of the present invention.

2, a predetermined region on the substrate 10 is divided into a plurality of pixels P, and each pixel P is provided with a pixel electrode 40. The boundary line between the pixel electrodes 40 adjacent in the row direction is inclined and curved with respect to the row direction, and the pixel electrode 40 is also formed bent along the curved line. The pixel electrode 40 may be divided into a first region 41 inclined in the first direction D ₁ and a second region 42 inclined in the second direction D ₂ in a row shape. Can be. A signal for displaying image information is transmitted to the pixel electrode 40, and signal lines such as a gate line 20 and a data line 30 are provided for this purpose. In the embodiment shown in FIG. 2, the gate line 20 is straight in the row direction, and the data line 30 is curved along the curved shape of the pixel electrode 40 while crossing the gate line 20. Is formed. Each pixel P includes a thin film transistor (not shown) including a gate electrode and a source electrode extending from the gate line 20 and the data line 30. The thin film transistor includes a drain electrode formed to face the source electrode, and the drain electrode is in contact with the pixel electrode 40. Therefore, when the gate-on signal is transmitted along the gate line 20, the thin film transistor is turned on and the data voltage transferred along the data line 30 is applied to the pixel electrode 40.

When a voltage is applied to the pixel electrode 40, a voltage is also applied to a substrate provided separately on the substrate 10 of FIG. 2, and an electric field acts on the liquid crystal injected between the two substrates. As a result, the arrangement direction of the liquid crystals is changed, so that the light transmittance of the liquid crystals is changed and the corresponding image information is displayed.

However, since the data voltage corresponding to the image to be implemented in each pixel P is applied to each pixel electrode 40, when the image information is different, the data voltage applied to the pixel electrode 40 is also different, so that adjacent pixel electrodes 40 are different. The lateral fields E _l1 and E _l2 according to the data voltage difference may be formed between the two sides. In particular, in order to prevent the liquid crystals from reacting in only one direction, data voltages having different polarities are applied in units of pixels P, and thus, lateral electric fields due to data voltages having different polarities between adjacent pixel electrodes 40 are applied. (E _l1 , E _l2 ) is further increased.

Since the above-described lateral electric fields E _l1 and E _l2 act between adjacent pixel electrodes 40, the lateral electric fields E _l1 and E _l2 affect the liquid crystals 50 arranged in the vicinity of the boundary of the pixel electrodes 40. When the lateral electric field is applied, the liquid crystal 50 is arranged according to the electric field obtained by synthesizing the lateral electric fields E _l1 and E _l2 in addition to the electric fields between the substrates. For example, in the case of a black state, most liquid crystals are arranged with their long axes perpendicular to the substrate 10, and the liquid crystal 50 receiving some lateral electric fields E _l1 and E _l2 is slightly inclined with respect to the substrate 10. Can cause light leakage.

However, according to the structure of FIG. 2, the influence (for example, light leakage, etc.) caused by the lateral electric fields E _l1 and E _l2 generated near the boundary of the pixel electrode 40 may be blocked. Take a look at this. The arrow direction shown in FIG. 2 relates to a polarizing plate coupled to the substrate 10 to perform a polarizing function. The polarizing plates are respectively coupled to the outside of two substrates provided in the liquid crystal display. The polarizer allows light in one direction to be transmitted, and the two polarizers are disposed such that transmission axes through which light passes are perpendicular to each other. 2, the data line 30 and the liquid crystal 50 illustrated in the array is inclined by a lateral electric field (E _l1, E _l2) between the pixel electrodes 40. Comparing FIG. 1 with respect to the prior art and FIG. 2 with respect to the present invention, in the present invention, the lateral electric fields E _l1 and E _l2 acting on the liquid crystal 50 are caused by the curved shape of the pixel electrode 40. It is changed from the direction to the slope.

At this time, if the inclination of the curved shape of the pixel electrode 40 is appropriately set, the direction of the lateral electric fields E _l1 and E _l2 and the transmission axis direction of the polarizing plate may be perpendicular to each other. For example, as shown in FIG. 2, the first direction D ₁ and the second direction D ₂ are perpendicular to each other, and the first direction D ₁ and the second direction D ₂ are the transmission axes of the polarizing plate ( Or an absorption axis that completely absorbs light). In this case, in the electric fields E _l1 and E _l2 between the adjacent pixel electrodes 40, the lateral electric fields E _l1 and E _{l2 in} the first region 41 or the second region 42 are perpendicular to each other. It is perpendicular to the transmission axis of either polarizer. Therefore, the action of polarizer light is a lateral electric field (E _l1, E _l2) is the transmission axis disposed perpendicular to the, even if the polarization direction is twisted by the liquid crystal 50, the lateral electric field (E _l1, E _l2) acting Transmission of light is blocked. By changing the shape of the pixel electrode 40 as described above, the light leakage is blocked at the boundary portion of the pixel electrode 40 in the black state, and the action by other lateral electric fields E _l1 and E _l2 is canceled.

3 is a cross-sectional view taken along the line AA ′ of FIG. 2.

Referring to FIG. 3, the data line 30 and the pixel electrode 40 are formed on the substrate 10. Insulation films 11 and 12 are interposed between the substrate 10 and the data line 30 and between the data line 30 and the pixel electrode 40, respectively. The former is a gate insulating film 11 for insulating the gate line 20 and the latter is a protective film 12 for protecting a thin film transistor and the like, which may be formed by depositing a silicon nitride film. The data line 30 is formed by applying a sputtering method to a metal such as chromium (Cr), and the pixel electrode 40 is formed of a transparent conductive film using indium tin oxide or indium zinc oxide. After deposition it can be formed by patterning.

As shown in FIG. 2, the gate line 20 and the data line 30 cross each other to define the pixel P, and the pixel electrode 40 is formed by separating each pixel P. Therefore, the data line 30 is a boundary between the pixels P, and as shown in FIG. 3, the data line 30 and the pixel electrode 40 are formed at positions not overlapping each other. If the data line 30 and the pixel electrode 40 overlap, the electric field formed in the data line 30 may affect the overlapping pixel electrode 40 while a signal is transmitted along the data line 30. have.

An alignment layer 60 is formed on the pixel electrode 40 to cover the substrate 10 including the pixel electrode 40. The alignment layer 60 arranges the liquid crystals in one direction through physicochemical interactions such as hydrogen bonding with liquid crystals or Van der Waals interactions. The alignment layer 60 is divided into a horizontal alignment layer and a vertical alignment layer depending on whether the liquid crystal is arranged horizontally or vertically on the surface of the alignment layer 60 based on the long axis of the liquid crystal. Among these, in the present invention, a horizontal alignment film in which the liquid crystals are arranged horizontally on the surface of the alignment film 60 in a state where the electric field is not applied to the liquid crystal is used. The alignment layer is manufactured by a rubbing process of forming a film from a polymer material such as polyimide and rubbing it with a cloth. The direction of rubbing at the time of rubbing determines the alignment direction of the liquid crystal later. In general, the rubbing direction and the alignment direction of the liquid crystal are parallel.

Using this characteristic, the initial arrangement of the liquid crystal can be set in a desired direction. For example, when the rubbing direction is set parallel or perpendicular to the transmission axis direction of the polarizing plate, the liquid crystal in the initial state is arranged parallel or perpendicular to the transmission axis direction of the polarizing plate. In the shape of the curved pixel electrode 40 as shown in FIG. 2, the initial arrangement direction of the liquid crystal (indicated by the dotted line in FIG. 2) is parallel or perpendicular to the directions of the lateral electric fields E _l1 and _El1 . For example, the liquid crystal 51 in the first region 41 is initially parallel to the lateral electric field _El 1 and the liquid crystal 52 in the second region 42 is initially _{equal to the} lateral electric field _{El 1} . Assume that they are arranged vertically. In this case, when a voltage is applied to the pixel electrode 40 to form the lateral electric fields E _l1 and E _l2 , the liquid crystal 51 in the first region 41 is perpendicular to the substrate 10 in the initial arrangement direction. Rotate in the direction. In contrast, the liquid crystal in the second region 42 rotates in the initial arrangement direction and in a direction perpendicular to the substrate 10, and also in the lateral electric field direction _El1 in the second region 42. That is, the liquid crystal 52 of the second region has an extended rotation range, so that some liquid crystals are not arranged in parallel with the lateral electric field _El2 in the black state, and the blocking effect of light leakage is somewhat reduced.

According to the simulation results of the effects of the present invention, when 0V and 8V are applied to the adjacent pixel electrode 40 and 4V is applied to the common electrode facing the pixel electrode 40, the conventional structure is 3.32%. Light leakage occurs, and in the present invention, light leakage of 0.98% (when the arrangement of the initial liquid crystal is parallel to the lateral electric field direction) and 1.68% (when the arrangement of the initial liquid crystal is perpendicular to the lateral electric field direction) is generated. According to the present invention, light leakage is reduced to about half or less as compared with the prior art. In addition, since the blocking effect of light leakage may vary according to the initial arrangement direction of the liquid crystal, in consideration of this point, the rubbing direction of the alignment layer is selected and the initial alignment direction of the liquid crystal is determined.

4 is a plan view of a substrate used in a liquid crystal display according to another exemplary embodiment of the present invention.

Referring to FIG. 4, a predetermined region on the substrate 10 is divided into a plurality of pixels P, and the pixel electrode 40 is formed in each pixel P. Referring to FIG. The pixel electrode 40 is formed to be bent, and is inclined in the first direction D ₁ in the first region 41 and in the second direction D ₂ in the second region 42. This is to ensure that the directions of the lateral electric fields E _l1 and E _l2 between the adjacent pixel electrodes 40 are perpendicular to the transmission axis direction of the polarizing plate, as in the above-described embodiment. Since the effect of this structure is common with the previous embodiment, detailed description is omitted.

The characteristic of this embodiment is that the data line 30 is formed straight. In the embodiment of FIG. 2, the data line 30 is formed to be bent along the curved shape of the pixel electrode 40, and the pixel P region is defined while the data line 30 and the gate line 20 cross each other. . In contrast, in the present exemplary embodiment, the data line 30 overlaps the pixel electrode 40, and the region defined by the crossing of the gate line 20 and the data line 30 and the region of each pixel P are inconsistent. If the data line 30 is formed straight as described above, the length of the data line 30 is reduced, thereby reducing the resistance value proportional to the length of the data line 30. If the resistance value of the data line 30 is high, a signal transmitted along the data line 30 may be distorted, and a higher driving voltage is required to prevent the signal distortion as described above.

5A and 5B are cross sectional views taken along the line BB ′ of FIG. 4.

Referring to FIG. 5A, a gate insulating layer 11, a data line 30, and a protective layer 12 are formed on a substrate 10. In addition, the pixel electrode 40 and the alignment layer 60 are formed on the passivation layer 12. Since the gate insulating film 11, the protective film 12, the alignment film 60, and the like have been described with reference to FIG. 3, a detailed description thereof will be omitted.

In the present embodiment, the data line 30 is formed to overlap the pixel electrode 40, not the boundary portion between the pixel electrode 40 and the pixel electrode 40. In this case, when a signal is transmitted along the data line 30, the electric field formed in the data line 30 may affect the pixel electrode 40 of the overlapping portion. In order to block the electric field effect of the data line 30, a separate thick insulating film is required on the passivation layer 12.

Various films may be used as the insulating film, and FIG. 5A illustrates a case in which the organic film 70 is used. The thicker the organic layer 70 is, the more effective the insulation of the data line 30 is. However, when the organic layer 70 is thick, the parasitic capacitance value formed between the data line 30 and the pixel electrode 40 is also increased. Is increased. In view of this point, in order to reduce the parasitic capacitance value, the organic layer 70 is required to have a low dielectric constant of about 3.2. However, since the low dielectric constant of the organic film 70 is expensive, another film quality may be used instead of the organic film 70 in consideration of cost, and FIG. 5B illustrates an embodiment in which a color filter film is used.

Referring to FIG. 5B, a thick color filter film 80 is formed between the data line 30 and the pixel electrode 40. The color filter film 80 is for realizing color, and the red film / green film / blue film (or three primary colors of yellow (Y), magenta (M), and cyan (C)), which are the three primary colors of light, is provided for each pixel region. Arranged alternately, the red film R and the green film G are shown in the drawing. The color filter film 80 is mainly formed on the upper substrate of the two substrates bonded on the upper and lower sides of the liquid crystal. However, the color filter film 80 may be disposed inconsistently with the pixel region by a miss assembly between the two substrates. In order to prevent this, the color filter film 80 may be formed on the lower substrate. Such a structure is called a COA (Color Filter On Array), and FIG. 5B shows an example in which the above-described COA structure is applied.

The color filter film 80 may be formed by a photo / development process using a color photoresist, and the dielectric constant is about 3.2 to 4.0, which is not larger than that of the organic film, and also excellent in insulation. Since the color filter film 80 is essentially provided for color implementation, according to the present embodiment, there is no need to add an organic film or the like, thereby reducing the process or reducing the cost. However, an organic film may be added on the color filter film 80 to complement the function of the color filter film 80.

The liquid crystal display device of the present invention focuses on matching the shape of the pixel electrode to the direction of the transmission axis of the polarizing plate in order to cancel the effect of the lateral electric field between the pixel electrodes. It can be applied to pixel electrodes of various shapes that are not disclosed. For example, the pixel electrode may be formed in a shape of, for example, a parallelogram, in which the pixel electrode is not formed to be curved but is simply inclined in only one of the first direction and the second direction. Further, in consideration of the electric field effect acting between the adjacent pixel electrodes in the column direction, the pixel electrode may be formed to be inclined at a predetermined slope rather than being parallel to the gate line. Application examples as described above are applied to the technical spirit of the present invention as it is, it can be seen that all belong to the scope of the present invention.

As described above, according to the present invention, there is an effect of preventing various problems such as light leakage caused by an electric field formed between adjacent pixel electrodes acting on a liquid crystal arranged near the boundary of the pixel electrode.

In addition, the present invention has the effect of increasing the aperture ratio. If light leakage is generated by an electric field between pixel electrodes according to the prior art, a black matrix must be formed on the substrate to cover such light leakage so that it does not appear outside. However, according to the present invention, since the light leakage by the lateral electric field is blocked, the black matrix can be formed narrowly, and the opening ratio is increased as it is narrowed.

Claims (10)

A gate line formed in one direction on the substrate and a pixel electrode formed to be separated for each pixel; A liquid crystal arranged to be spaced apart from the substrate and having positive dielectric anisotropy; An alignment layer covering the pixel electrode and arranging the liquid crystal in a horizontal direction; And a boundary line between pixel electrodes adjacent in the gate line direction is inclined with respect to the gate line. The method of claim 1, And the boundary line has a curved shape formed of a portion inclined in a first direction and a portion inclined in a second direction. The method of claim 2, And the first direction and the second direction are perpendicular to each other. The method according to any one of claims 1 to 3, And a polarizing plate coupled to the substrate and performing a polarizing function, wherein a light transmitting direction of the polarizing plate is parallel or perpendicular to an inclination direction of the boundary line. The method of claim 4, wherein And a direction having a maximum refractive index in the white state of the liquid crystal is parallel or perpendicular to a direction through which light of the polarizing plate passes. The method of claim 5, And the alignment layer has an orientation characteristic in a horizontal direction through rubbing, and the rubbing direction is parallel to a direction having a maximum refractive index in the white state of the liquid crystal. The method of claim 4, wherein And a plurality of data lines crossing the gate line and formed along a curved shape of the boundary line. The method of claim 4, wherein And a plurality of data lines formed to intersect the gate lines vertically. The method of claim 8, And an insulating film including a low dielectric constant organic film between the data line and the pixel electrode. The method of claim 8, And an insulating film including a color filter film showing color between the data line and the pixel electrode.

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