KR20020067270A - Liquid crystal display device and method for fabricating the same - Google Patents

Abstract

The present invention relates to a multi-domain liquid crystal display device for securing a wide viewing angle by forming electric field distortion means only on the lower substrate, and a method of manufacturing the same. Particularly, the multi-domain liquid crystal display device according to the present invention includes a first and a second substrate; A thin film transistor formed on a first substrate, a first transparent conductive film connected to the thin film transistor and having a first field distortion means, a dielectric film formed on the first transparent conductive film and having a second field distortion means; And a liquid crystal layer formed between the second transparent conductive film formed on the second substrate and the first and second substrates.

Description

Multi-domain liquid crystal display device and manufacturing method therefor {LIQUID CRYSTAL DISPLAY DEVICE AND METHOD FOR FABRICATING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device (LCD), and more particularly, to a multi-domain liquid crystal display device that realizes a wide viewing angle by distorting an electric field by forming slits or structures in a transparent conductive film, and a manufacturing method thereof. .

One of the liquid crystal display devices currently used is a liquid crystal display device of twisted nematic (TN) mode.

The TN mode liquid crystal display device forms electrodes on two substrates, and the liquid crystal molecules filled therebetween are parallel to the substrate, twisted in a spiral with a constant pitch, and then a voltage is applied to the electrodes to drive the liquid crystal director. That's the way it is.

However, since the TN mode liquid crystal display does not completely block the light in the off state, the contrast ratio is not good and the contrast ratio changes with the angle, and the brightness of the halftone is reversed as the angle changes. Hard to get In addition, there is a viewing angle problem such as that the image quality is not symmetrical with respect to the front face.

Conventionally, studies to solve the narrow viewing angle problem of the liquid crystal display device are active, and a film compensation mode (Film-compensated Mode) for compensating the viewing angle with a compensation film, and the viewing angle of each domain by dividing pixels into multiple domains Multi-Domain Mode for compensating viewing angles in different directions, In-Plane Switching mode for placing two electrodes on the same substrate to generate a horizontal electric field, and OCB ( There are techniques such as Optically Compensated Birefringence Mode.

On the other hand, the vertical alignment (VA) mode liquid crystal display uses a negative liquid crystal having a negative dielectric anisotropy and a vertical alignment layer. In the state where no voltage is applied, the long axis of the liquid crystal molecules is vertically aligned with the plane of the alignment layer. The polarization axis of the polarizer attached to the vertical axis of the liquid crystal molecule is arranged perpendicularly to display a black mode (normally black mode). On the other hand, when a voltage is applied, the long axis of the liquid crystal molecules moves toward the alignment layer plane in the vertical direction of the alignment layer plane due to the property of being oriented obliquely with respect to the electric field of the negative liquid crystal molecule to transmit light.

Such a vertically aligned liquid crystal display device is superior in various aspects, such as contrast ratio and response speed, compared to the twisted nematic method. In addition, when the alignment direction of the liquid crystal molecules are divided into a plurality of directions and a compensation film is used, there is an advantage in that a wide viewing angle can be effectively realized.

Recently, instead of the alignment process, structures such as side-electrodes, ribs, or slits are formed on the substrate, thereby distorting the electric field applied to the liquid crystal layer to position the director of the liquid crystal molecules in a desired direction. do.

Examples include a patterned vertical alignment (PVA), a multi-domain vertical alignment (MVA), and the like.

Hereinafter, a multi-domain liquid crystal display device according to the related art will be described with reference to the accompanying drawings.

1A to 1C are cross-sectional views for explaining the problem of the TN LCD, and FIGS. 2A to 2C are process charts for explaining the orientation division by the rubbing process.

3 and 4 are cross-sectional views of a multi-domain liquid crystal display device according to the prior art.

First, although TN mode LCDs are in the spotlight for providing excellent contrast and color reproducibility, they have a problem that the viewing angle is narrow.

Referring to the drawings in detail, in a nominally white mode TN LCD, first, when the electric field is not applied between the two substrates 112 and 113 of the LCD as shown in FIG. It is arranged in an oblique direction, and light is transmitted from any direction to display the white level. When an electric field above a threshold is applied, as shown in FIG. 1C, the liquid crystal molecules 114 of the intermediate layer except for the liquid crystal molecules positioned near the substrates 112 and 113 are arranged in the vertical direction. At this time, the linearly polarized incident light is not distorted and is displayed in black. Since light incident at an angle to the substrate is twisted to some extent through the liquid crystal molecules arranged in the vertical direction, the polarized axis direction is not completely displayed.

In addition, when a medium electric field is applied, the birefringence of the liquid crystal is alleviated to some extent, and as shown in FIG. 1B, the liquid crystal molecules near the alignment layer are arranged in the horizontal direction, and the liquid crystal molecules in the intermediate layer rise about half, thereby transmitting light. This is interrupted and gray levels are displayed. However, this is limited to light incident perpendicularly to the substrate, and light incident at an angle looks different from the left side or the right side. That is, the light passing from the right to the left is arranged in parallel with respect to the liquid crystal molecules, and the black level is displayed when viewed from the left, while the light passing from the bottom to the right is perpendicular to the liquid crystal molecules, so the birefringence of the liquid crystal White level is displayed.

As described above, the display state of the TN LCD varies greatly depending on the viewing position, and the viewing angle characteristics can be improved by forming the alignment directions of the liquid crystal molecules in many directions.

In general, the alignment direction and pretilt angle of the liquid crystal molecules in contact with the substrate surface are controlled by the alignment film rubbed in different directions.

That is, as shown in FIG. 2A, the alignment layer 122 is formed on the glass substrate 116 on which the plurality of patterns (not shown) are formed, and rubbed in one direction using the rotating rubbing roll 201. Next, a photoresist is formed on the alignment layer 122, and the photoresist 202 is patterned as shown in FIG. 2B using a photolithography process. Next, as shown in FIG. 2C, the rubbing roll 201 is rotated in the opposite direction so that the alignment film 122 of the photoresist pattern opening is rubbed in the opposite direction. In this way, a plurality of regions having different alignment directions of the liquid crystal are formed in each pixel by using the direction in which the alignment film varies depending on the direction in which the rubbing roll rotates.

On the other hand, VA LCD (Vertical Alignment Liquid Crystal Display Device) applying vertical alignment film and negative liquid crystal divides the alignment direction of liquid crystal molecules to improve the viewing angle, and at this time, the same contrast ratio and operation speed as conventional LCD are possible. It is desirable to improve the viewing angle characteristic as much as the IPS mode.

The method of uniformizing the domains in VA mode is possible by initially making the liquid crystals arranged at an angle be uniformly oriented in a plurality of directions within each pixel when an electric field is applied, wherein at least one domain on one substrate must be divided. In addition, an inclined surface must be formed on at least one of the substrates in which the domain is divided. It also includes surfaces that are inclined substantially perpendicular to the substrate.

And it is not necessary to perform a rubbing process with respect to a vertical alignment film.

The liquid crystal molecules when no voltage is applied to the VA LCD formed as described above are arranged perpendicularly to the substrate surface, and are inclined with respect to the substrate as a result of the inclined substrate surface.

Thereafter, when voltage is applied, the liquid crystal molecules are tilted according to the strength of the electric field. At this time, since the electric field is formed perpendicular to the substrate, the tilt azimuth angle caused by the electric field has a rotational direction of 360 °.

If there are pretilted liquid crystal molecules around the liquid crystal molecules, the surrounding liquid crystal molecules are tilted in that direction. For example, the azimuth angle of the liquid crystal molecules lying in the gap between the protrusion and the protrusion is also in contact with the surface of the protrusion. Controlled by

In addition, the negative liquid crystal molecules used in VA LCD have a property of tilting in the vertical direction with respect to the electric field.

On the other hand, the following description relates to a method for dividing a domain into several regions by forming an electric field distortion means for distorting an electric field on a substrate.

Referring to the multi-domain liquid crystal display device including the conventional electric field distortion means, as shown in FIG. 3, between the first and second substrates 1 and 2 of the transparent material, and between the first and second substrates 1 and 2. First and second transparent conductive films 3 and 4 having a liquid crystal layer 7 injected and injected into the liquid crystal layer and slits 6 formed on the first and second substrates 1 and 2 to cause electric field distortion, respectively. It is composed of

At this time, although not shown, the first substrate 1 and the first transparent conductive layer 3 may be formed to cross each other to define a gate line and a data line, and a thin film transistor formed at an intersection of the two lines. In addition, there is a color filter layer between the second substrate 2 and the second transparent conductive film 4 to express color on the screen.

In more detail through the manufacturing method, a gate wiring and a gate electrode are formed of a metal on a first substrate, and a gate insulating film is coated thereon to insulate the gate wiring.

After the semiconductor layer is formed on the gate electrode, a data line is formed to cross the gate line to distinguish the pixel region, and at the same time, a source / drain electrode is formed on the semiconductor layer.

The laminated film of the gate electrode, the semiconductor layer, and the source / drain electrodes thus formed is referred to as a thin film transistor.

Thereafter, a protective film is coated on the entire surface including the data line, and a first transparent conductive film electrically connected to the drain electrode is formed on the protective film.

Next, a black matrix, a color filter layer, and a second transparent conductive film are formed on the first substrate.

Here, a plurality of slits are formed in the first and second transparent conductive films to control the liquid crystal director by distorting an electric field.

This can be done by selectively removing the first and second transparent conductive films.

At this time, in addition to the method of forming the slit as described above, as shown in Figure 4, even if the structure 10, such as a rib (rib) is formed on a predetermined portion of the transparent conductive film, the electric field distortion phenomenon occurs.

Finally, after bonding the first and second substrates to face each other, the liquid crystal is injected and encapsulated therebetween to produce a liquid crystal display device.

In this case, the liquid crystal is a negative liquid crystal having dielectric anisotropy so that the long axis of the liquid crystal molecules 9 is initially aligned perpendicular to the substrate plane.

When the voltage above the threshold is applied to the multi-domain liquid crystal display device formed as described above, the long axis of the liquid crystal molecules is inclined in the horizontal direction. At this time, the electric field is distorted by the slit 6 so that the liquid crystal molecules are different from each other around the slits. Inclined to

As a result, the liquid crystal directors face each other and the viewing angle is compensated, thereby ensuring a wide viewing angle.

However, at the point where the liquid crystal director is divided, that is, the disclination line (indicated by the dotted line) that is the boundary region of the domain, light is not transmitted and a black part appears on the screen.

Therefore, an electric field deformation region through which light does not penetrate is enlarged, so that display quality is deteriorated and a defect such as a low viewing angle occurs.

In addition, when the upper and lower substrates are not correctly bonded, the area ratio of the domain is changed, so that the viewing angle characteristic is deteriorated, and the display quality is deteriorated.

To prevent this problem, expensive alignment equipment should be used.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a multi-domain liquid crystal display device having a viewing angle improved by forming an electric field distortion means only on a lower substrate, and a manufacturing method thereof.

1A to 1C are cross-sectional views for explaining the problem of a TN LCD.

2A to 2C are process drawings for explaining orientation splitting by rubbing treatment.

3 and 4 are cross-sectional views of a multi-domain liquid crystal display device according to the prior art.

5 is a cross-sectional view of a multi-domain liquid crystal display device according to the present invention.

6A to 6E are cross-sectional views of a manufacturing process of a multi-domain liquid crystal display device according to the present invention.

7 is a plan view showing various pixel structures according to the present invention.

* Explanation of symbols on the main parts of the drawings

21: first substrate 22: second substrate

23: first transparent conductive film 24: second transparent conductive film

25a, 25b: first and second alignment layers 26 slit

27 liquid crystal layer 28 dielectric film

29: liquid crystal molecules 31: depression

30a, 30b: first and second photoresist patterns

Multi-domain liquid crystal display device of the present invention for achieving the above object is a first transparent conductive film having a first, a second substrate, a first field distortion means formed on the first substrate, and the first transparent conductive film And a liquid crystal layer formed between the dielectric film having a second electric field distortion means formed on the second substrate, the second transparent conductive film formed on the second substrate, and the first and second substrates.

That is, the present invention is characterized by improving the viewing angle by forming distortion means such as slits or structures only on the lower substrate.

Hereinafter, a multi-domain liquid crystal display device and a manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings.

5 is a cross-sectional view of a multi-domain liquid crystal display device according to the present invention, and FIGS. 6A to 6E are cross-sectional views of a manufacturing process of the multi-domain liquid crystal display device according to the present invention.

7 is a plan view illustrating various pixel electrodes according to the present invention.

As shown in FIG. 5, the multi-domain liquid crystal display device according to the present invention includes a liquid crystal layer formed by being injected between the first and second substrates 21 and 22 and the first and second substrates 21 and 22. 27. The first substrate 21 includes a gate wiring and a data wiring arranged in a matrix to distinguish unit pixel regions, a thin film transistor formed at an intersection of the two wirings, and the thin film transistor. A dielectric film 28 having a protective film formed on the entire surface thereof, a first transparent conductive film 23 having a field distortion means formed on the protective film, and a depression 31 formed on the first transparent conductive film 23. And a first alignment layer 25a formed on the entire surface including the dielectric layer 28.

In addition, the second substrate 22 includes a black matrix formed at a predetermined portion to prevent light leakage, a color filter layer formed between the black matrix, a second transparent conductive film 24 formed on the color filter layer, and the second There is a second alignment film 25b formed on the entire surface including the transparent conductive film 24.

As described above, the present invention is characterized in that the field distortion means is not formed on the second substrate.

That is, when the field distortion means are formed on each of the upper and lower plates as in the prior art, the field distortion means is formed with an error of about 5 μm of the bonding process of the upper and lower plates, but only in the lower plate as in the present invention. In the case of forming the field distortion means, the bonding margin of the upper and lower plates does not affect the error range of the field distortion means formed on the lower plate.

In other words, since the error range generated in the present invention is about 1 to 2 µm, the error range of the electric field distortion means of the lower panel is also about 1 to 2 µm, thereby eliminating the process problems caused by the upper and lower plate bonding margins.

Further, by further comprising a dielectric film 28 having a recessed portion in the lower plate, a multi-domain of the same type as in the prior art is realized.

Thus, when the depression is formed, the texture of the liquid crystal is stabilized and the domain area is uniform compared to the existing protrusions.

In more detail through the manufacturing method, although not shown first, a metal is deposited on the first substrate and then patterned to form a plurality of gate lines and gate electrodes.

Subsequently, a gate insulating film is formed over the entire surface including the gate wiring, and a semiconductor layer is formed over the gate electrode.

Further, metal is deposited and patterned to form a data line crossing the gate line to separate pixel regions, and at the same time, a source / drain electrode is formed on the semiconductor layer to form a gate electrode, a semiconductor layer, and a source / drain electrode. A thin film transistor consisting of a laminated film of the drain electrode is completed.

Here, the metal used for the formation of the gate wiring and the data wiring is deposited by sputtering with copper (Cu), aluminum (Al), molybdenum (Mo) and aluminum alloy or a double layer thereof having low resistance, and the gate insulating film. Silver is deposited using plasma enhanced chemical vapor deposition (PECVD) using inorganic materials such as silicon nitride (SiNx) or silicon oxide (SiOx) having excellent adhesion to the metal and having high dielectric breakdown voltage.

Thereafter, a protective film is coated on the entire surface including the data line using a material such as silicon nitride film (SiNx) or silicon oxide film (SiOx), and a first transparent conductive film is formed on the protective film.

In this case, as the protective layer, BCB (Benzocyclobutene), acryl, polyimide, or the like having a low dielectric constant may be used.

Next, as shown in FIG. 6A, the first photoresist is applied onto the first transparent conductive film 23, and then patterned by a photolithography process using a mask to form the first photoresist pattern 30a.

Subsequently, as shown in FIG. 6B, a portion of the first transparent conductive film 23 is removed using the first photoresist pattern 30a as an etching mask to form a slit 26.

At this time, a structure such as an auxiliary electrode or a protrusion may be formed at a predetermined portion on the first transparent conductive film without forming a slit to form an electric field distortion means.

Subsequently, as shown in FIG. 6C, the dielectric film 28 and the second photoresist are sequentially formed on the entire surface including the first transparent conductive film 23, and the second photoresist 30b is patterned. The recess 31 is formed as shown in FIG. 6D by partially removing the dielectric film using the photoresist pattern 30b as an etching mask.

The depression of the dielectric film acts as an electric field distortion means, and may form a structure instead of the depression.

Here, the dielectric film 28 is an example of a material that is patternable, transparent and flat, and is formed of a material such as an acrylic resin.

The material may be a material of an overcoat layer used after the color filter layer is formed.

That is, unlike the conventional method of forming the field distortion means on the upper substrate, by forming a dielectric film having the field distortion means on the lower substrate without forming the field distortion means on the upper substrate, misalignment may occur when the upper and lower substrates are bonded. It is possible to prevent the failure caused by.

Here, the field distortion means 26 and 31 formed on the first transparent conductive layer 23 and the dielectric layer 28 may be modified in various forms as shown in FIG. 5.

Next, a black matrix is formed on the second substrate using a metal having a high reflectance, an RGB color filter layer is formed between the black matrices, and a second transparent conductive film is formed on the color filter layer.

The first and second transparent conductive films are formed of an indium tin oxide (ITO), indium zinc oxide (IZO), or the like, which is a transparent conductive material.

In this case, the first and second alignment films 25a and 25b may be formed on the entire surface including the first and second transparent conductive films 23 and 24, respectively, or may not be formed.

The alignment layer may be formed of polyimide, polyamide, or polysiloxane-cinnamate, cellulose-cinnamate, or the like as a photo-alignment layer.

Next, as shown in FIG. 6E, the first and second substrates 21 and 22 are opposed to each other, and then the liquid crystal 27 is injected therebetween.

The liquid crystal is a liquid crystal having a negative dielectric anisotropy, and initially causes the long axis of the liquid crystal molecules to be perpendicular to the substrate plane.

The liquid crystal may include a chiral dopant.

In this case, the liquid crystal may be injected by a drop method such as a dispensing method.

That is, a seal pattern for adhering the two substrates is formed on the edge of the first substrate on which various patterns are formed, and a liquid crystal is partially dropped inside the seal pattern by a dispensing method to spread the liquid crystal.

Next, after uniformly dispersing a spacer for spaced apart two substrates on a second substrate, the first and second substrates are bonded. At this time, the seal pattern is cured using UV to completely adhere the first and second substrates.

On the other hand, in addition to the drop method, a method in which the inside of the bonded substrate is made in a vacuum state and then the liquid crystal is filled in the inside of the substrate using a pressure difference may be used.

For reference, when the drop method is applied to a large area of the substrate, the liquid crystal layer formation time is reduced, and when the negative liquid crystal is used, the liquid crystal injection time is shortened because the viscosity of the liquid crystal is large.

In addition, a column spacer may be used as the spacer, or a sealant which is easily cured at room temperature may be used as a sealant.

Lastly, although not shown, a phase difference film is attached to at least one of the first substrate and the second substrate.

The retardation film is a negative uniaxial film having one axis and compensates for a viewing angle.

Therefore, the area without gray inversion is enlarged, the contrast ratio in the oblique direction is increased, and the multi-domain in one pixel is realized, so that the viewing angles in the left and right directions are effectively compensated.

In addition to the negative uniaxial film as the retardation film, a negative biaxial film having two axes may be used. Negative biaxial films ensure wider viewing angle characteristics than negative uniaxial films.

After attaching the retardation film, a polarizing plate is attached to each of the first and second substrates to complete the liquid crystal display element. Moreover, the said retardation film and a polarizing plate can also be comprised integrally and affixed.

When the electric field is applied to the liquid crystal display device formed as described above, the long axis 29 of the liquid crystal molecules standing vertically with respect to the substrate surface is inclined in different directions with respect to the depression 31 as shown in FIG. 5 to compensate for the viewing angle. By doing so, it realizes a wide viewing angle.

In addition, display margins are improved because process margins due to misalignment are minimized when substrates are bonded.

In addition, since the rubbing treatment is not required, the static electricity generated by the rubbing is prevented and the production yield is improved.

As described above, the multi-domain liquid crystal display device and the method of manufacturing the same of the present invention have the following effects.

First, the electric field deformation region is formed only on the lower substrate, thereby minimizing defects caused by the upper and lower plate bonding process margins and minimizing the electric field deformation region.

Second, the wide viewing angle is secured by implementing the multi-domain.

Thus, a liquid crystal display device having excellent image quality can be obtained.

Claims (8)

First and second substrates; A thin film transistor formed on the first substrate; A first transparent conductive film connected to the thin film transistor and having a first field distortion means; A dielectric film formed on the first transparent conductive film and having a second field distortion means; A second transparent conductive film formed on the second substrate; And a liquid crystal layer formed between the first and second substrates. The multi-domain liquid crystal display device according to claim 1, wherein the second field distortion means is a depression or a structure. Forming a first transparent conductive film having a first field distortion means on the first substrate; Forming a dielectric film having a second field distortion means on the first transparent conductive film; Forming a second transparent conductive film on the second substrate; A method of manufacturing a multi-domain liquid crystal display device comprising the step of bonding the first and second substrates to each other and forming a liquid crystal layer therebetween. 4. The method according to claim 3, further comprising forming a gate wiring, a data wiring and a thin film transistor between the first substrate and the first transparent conductive film. 4. The method of claim 3, wherein the first field distortion means is a slit formed by selectively removing the first transparent conductive film. 4. The method according to claim 3, wherein the first field distortion means is a structure further formed at a predetermined portion on the first transparent conductive film. 4. The method according to claim 3, wherein the second field distortion means is a depression formed by selectively removing the dielectric film. 4. The method of claim 3, wherein the second field distortion means is a structure further formed at a predetermined portion on the dielectric film.