Liquid crystal display device and repairing method thereof

An LCD and an LCD repairing method are provided. The LCD repairing method includes forming a hole on a first or second substrate at a position corresponding to a defective pixel and forming a pigment in the hole. The LCD includes a first substrate on which a pixel electrode and a TFT are formed in a pixel region formed in a matrix pattern, a second substrate on which a color filter layer and a black matrix are formed, the second substrate facing the first substrate, a hole formed on an outer surface of the first or second substrate to repair a defective pixel, and a repair pattern formed in the hole.

This application claims the benefit of Korean Patent Application No. 87278/2004, filed Oct. 29, 2004, which is hereby incorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device (LCD), and more particularly, to an LCD constructed to repair its defective cell and a repairing method thereof.

2. Discussion of the Related Art

LCDs have low power consumption and good portability and thus are considered to be a next-generation display device.

Generally, liquid crystal is manufactured as a liquid crystal cell for use in the LCD.

The liquid crystal cell is constructed in such a way that liquid crystal is filled between two glass substrates or between two transparent plastic substrates. Transparent electrodes (common electrode, pixel electrode) are formed on the substrate to apply a voltage to the liquid crystal, thereby controlling the switching on or off of the liquid crystal cell.

More specifically, the light transmittance of the LCD is controlled by a voltage applied to the transparent electrodes, and thus text and an images can be displayed by a light shutter effect.

An active matrix (AM) LCD is provided with a switching element capable of controlling whether or not to apply a voltage to each pixel. The AM LCD is widely used because it can provide high resolution and excellent reproduction of motion pictures and video.

FIG. 1is a perspective view illustrating a portion of a related art LCD, particularly an active region thereof.

Referring toFIG. 1, upper and lower substrates110and130are disposed in such a way that they face each other and are spaced apart from each other by a predetermined distance. A liquid crystal layer150is interposed between the upper and lower substrates110and130.

A plurality of gate and data lines132and134are arranged to intersect each other, and a thin film transistor (TFT) T is formed at an intersection of the data and gate lines132and134. A pixel electrode146connected to the TFT T is formed in a pixel region P defined by the intersected gate and data lines132and134.

Although not shown inFIG. 1, the TFT T includes a gate electrode supplied with a gate voltage, source/drain electrodes supplied with a data voltage, and a channel for controlling whether or not to apply a voltage by a difference between the gate and data voltages.

A color filter layer112and a common electrode116are sequentially formed on an inner surface of the upper substrate110.

The color filter layer112includes an R/G/B color filter transmitting only light of a specific wavelength, and a black matrix disposed between the color filter layers to block light in the region where the alignment of liquid crystal is or cannot be controlled.

Upper and lower polarizers152and154are disposed on outer surfaces of the upper and lower substrates110and130, respectively, to transmit only light parallel to a polarization axis. A backlight unit is disposed under the lower polarizer154.

The LCD is completely manufactured by performing an array substrate manufacturing process for forming the switching elements and the pixel electrodes, a color filter substrate manufacturing process for forming the color filters and the common electrodes, and a liquid crystal cell process for interposing liquid crystal between the two substrates.

The liquid crystal cell process is roughly divided into an alignment layer forming process for aligning liquid crystal molecules, a cell cutting process, and a liquid crystal forming process. A polarizer is attached on an outer surface of a liquid crystal panel completed through the above processes, and a driving circuit is connected to it, thereby completing the LCD.

FIG. 2is a view illustrating a related art process of repairing a defective cell of a liquid crystal panel.

Referring toFIG. 2, a plurality of gate and data lines262and274are formed on a liquid crystal panel290in such a way to intersect each other. A TFT T is formed at an intersection of the gate and data lines262and274. A pixel electrode276is connected to the TFT T in each pixel.

A dielectric material (not shown) is interposed between the gate line262and the pixel electrode276, thereby forming a storage capacitor Cst.

After the liquid crystal panel290is completely manufactured through this liquid crystal cell process, a cell checking process is performed for checking whether or not a defective pixel exists. This is performed by displaying a test pattern on a screen of the liquid crystal panel290. Thereafter, any detected defective pixels are repaired.

Defects of the liquid crystal panel290include a color defect in each pixel, a point defect, and a light defect. The point defect includes a bright point (always-on cell) and a dark point (always-off cell). The light defect is due to disconnection between the drain electrode of TFT and the pixel electrode276or the broken channel of a TFT (normally white mode TN).

These defects appear when the test pattern is displayed on the liquid crystal pattern290. The positions of defective pixels are detected and then the defective pixels are repaired.

FIG. 2illustrates an exemplary process for repairing a defective cell I, which appears as a bright point due to a broken defect or a signal defect when a black pattern is displayed on the screen, by darkening the bright point.

A pixel electrode276of the defective cell I is shorted by laser from the drain electrode of TFT or is shorted by laser between the drain electrode and the source electrode of TFT. Accordingly the defective cell I is darkened to repair the bright point.

A white point A may occur due to an alignment layer printing process or environments.

Also, when the disconnection of the pixel electrode276from the gate line262and the ITO cutting process is unsuccessfully performed, the gate and data lines262and274become shorted together, thereby causing the line defect.

As above, there may occur a case where it is impossible to repair the point defect, such as the white point A. In this case, the yield and production of the liquid crystal panel is degraded.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an LCD and a repairing method thereof that substantially obviate one or more problems due to limitations and disadvantages of the related art.

An advantage of the present invention is to provide an LCD that is constructed to provide an easy repair process therefore by darkening its defective cell.

To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a method of repairing an LCD, including: forming a hole on a liquid crystal panel at a position corresponding to a defective pixel; and forming a repair pattern in the hole.

In another aspect of the present invention, there is provided a method of repairing an LCD, including: forming a hole on a first or second substrate at a position corresponding to a defective pixel; and forming a pigment in the hole.

In a further another aspect of the present invention, there is provided a method of repairing an LCD, including: forming a hole on a first or second substrate at a position corresponding to a defective pixel; and inserting a wedge into the hole.

In a still further another aspect of the present invention, there is provided an LCD including: a first substrate on which a pixel electrode and a TFT are formed in a pixel region formed in a matrix pattern; a second substrate on which a color filter layer and a black matrix are formed, the second substrate facing the first substrate; a hole formed on an outer surface of the first or second substrate to repair a defective pixel; and a repair pattern formed in the hole.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 3is a schematic view illustrating a process of repairing a defective cell of a liquid crystal panel according to the present invention.

Referring toFIG. 3, a plurality of gate lines362are formed on a first substrate of a liquid crystal panel390in a first direction, and a plurality of data lines374are formed on the first substrate in a second direction intersecting the first direction.

A pixel region P is defined by the gate and data lines362and374intersecting each other. A TFT T is disposed at an intersection of the gate and data lines362and374in each pixel region. A pixel electrode376is connected to the TFT T.

A dielectric material (not shown) is interposed between the gate line362and the pixel electrode376, thereby forming a storage capacitor Cst.

Although not shown inFIG. 3, a color filter layer and a common electrode are sequentially formed on a second substrate facing the first substrate.

The color filter layer includes an R/G/B color filter transmitting only light of a specific wavelength, and a black matrix disposed between the color filter layers to block light on a region where alignment of liquid crystal is not controlled.

When a bright point occurs due to a defective cell II, it is repaired by forming a darkening pattern on the first or second substrate to cover the defective cell II.

That is, a hole is formed on an outer surface of the first or second substrate at a position corresponding to the bright point by using a micro-drill. Thereafter, a material such as a pigment is filled in the formed hole, and the bright point is darkened to prevent light from being transmitted at the defective position.

The pigment may be any material capable of blocking light, such as an acryl series material or a Novolac series material.

The bright point defects occurring in the liquid crystal panel390include not only a bright point defect occurring due to an electrical short at a gate or data line and the TFT, but also a bright point defect occurring due to particles remaining in the pixel region during the corresponding process.

Micro-drilling is a method of forming a hole of a predetermined depth on the first or second substrate at a position corresponding to the defect by using a micro-drill having a fine or small diameter.

Alternatively, a hole is formed on an outer surface of the first or second substrate at a position corresponding to the bright point by using a micro-screw device. Thereafter, a wedge is inserted into the formed hole, and the bright point is darkened to prevent light from being transmitted at the defective position.

Here, the repairing method may be applied to one or both of the first and second substrates.

The wedge may be made of a solid polymer or a metal with a polymer.

FIG. 4is a view illustrating a method of repairing a defective cell of a liquid crystal panel according to an embodiment of the present invention. AlthoughFIG. 4illustrates a TN mode liquid crystal display panel, this is by way of example only, and it is understood that the present invention encompasses other liquid crystal display panels, such as in-plane switching (IPS) mode, vertical alignment (VA) mode, and fringe field switching (FFS) mode panels as well.

Referring toFIG. 4, first and second substrates410and430are disposed to face each other, and a liquid crystal layer450is interposed between the first and second substrates410and430.

An array element420is formed on a transparent substrate400of the first substrate410, and R/G/B color filters434A,434B and434C are sequentially arranged on a transparent substrate410of the second substrate430. A black matrix432is formed at each boundary between the R/G/B color filters434A,434B and434C. An overcoat layer438and a common electrode440are sequentially formed on the R/G/B color filters434A,434B and434C and the black matrix432.

The array element420includes a TFT disposed at an intersection of gate and data lines in each pixel region defined by the gate and data lines, and a pixel electrode connected to the TFT.

When a bright point and a white point occur in the liquid crystal panel due to a defective cell X, a hole460is formed on an outer surface of the transparent substrate400or401of the first or second substrate410or430at a position corresponding to the defective cell by using a micro-drill. Thereafter, a pigment461is filled in the hole460, thereby darkening the bright point.

The pigment461may be any material capable of blocking light, such as an acryl series material or a Novolac series material.

The micro-drilling is a method of forming the hole460of a predetermined depth on the transparent substrates400or401at a position corresponding to the defective cell X by using a micro-drill having a fine diameter.

Preferably, the substrate is micro-drilled to remain about 20 μm thick. This is to prevent the liquid crystal inside the substrate from being contaminated due to the pigment when the substrate is completely perforated.

To fill the hole460with the pigment461, an inkjet method, a printing method, an injection method or the like can be used.

The inkjet method prints pigment on a desired site (hole).

The printing method includes printing pigment on a substrate and removing the pigment printed on a non-desired site when the pigment is filled in the desired site (hole).

In the liquid crystal panel of the above construction, since light incident into a failure site is shielded by the pigment filled in the micro hole of the substrate. The light does not pass through the liquid crystal panel, so a bright point defect or foreign particle white point can be readily prevented.

The repair method that converts the defect point into a dark point may be applied to either the first substrate or the second substrate, or both of the first and second substrates.

FIGS. 5A and 5Bare views illustrating a relationship between a hole depth and an angle at which a light leakage occurs in a defective cell region.

Referring toFIGS. 5A and 5B, when a bright point defect occurs in any one of cell regions of an liquid crystal panel, a hole is formed at the defective cell region and a pigment is filled in the formed hole to darken the bright point.

The bright point defect is generated because light generated from a backlight is undesirably refracted or scattered by the electrical short defect at the gate or data line and the TFT or the particle defect occurring in the pixel region during the corresponding process.

In the present invention, an angle (hereinafter referred to as an identification angle (I/A)) between a reference line perpendicular to the pixel region and a point at which an observer can perceive an initial bright point defect is maximized so that the bright point defect cannot be viewed by the observer while the liquid crystal panel is displayed.

That is, the I/A is maximized so that the observer cannot sense the bright point defect in the range of a viewing angle.

Particularly, since the I/A increases as the hole filled with the pigment increased in depth, that is, as the pigment approaches the bright point defect region, it is possible to adjust a region where the bright point defect is sensed.

For example, when a particle defect of about 30 μm occurs the pixel region, if the pigment is filled in the hole of 650 μm, the I/A θ approaches 60° toward one surface of the liquid crystal panel with respect to the reference line perpendicular to the pixel region.

That is, a refracting or scattering angle of a traveling light is increased with an increase in the depth of the hole, and thus the observer cannot sense the bright point (light leakage) defect in the range of left and right 60° from the front of the liquid crystal panel (that is, a total of 120°).

According to the present invention, the leaking light due to the bright point defect is sensed only a region of 30° toward the reference line from the surface of the liquid crystal panel, and the bright point defect cannot be perceived by the observer in the display region (that is, the 120° region). That is, in the 120° region, the bright point defect is blocked by the pigment formed in the hole such that it cannot be sensed by the observer.

The inventive method of forming the hole to repair the cell defective region is differentiated from a conventional method of dotting a light blocking or reflecting ink on a substrate to prevent the cell defective region.

The conventional ink dotting method merely blocks the light generated at the backlight from traveling toward the bright point defective region, thereby preventing the bright point defect in the perpendicular front region. However, the ink dotting method cannot prevent the light leakage defect in an inclined direction.

Moreover, when the dotted region is increased so as to completely prevent the light leakage defect region, a bright point defect is undesirably generated due to a light reflection or scattering by the dotted ink.

However, the inventive light leakage blocking method can adjust the light leakage blocking region only by the adjustment of the hole depth (that is, the distance between the pigment and the defective region), thereby making it possible to greatly increase the view angle range where the light leakage is blocked.

FIG. 6is a view illustrating a process of forming a hole with a micro drill for the repairing method according to the present invention.

Referring toFIG. 6, a hole is formed on a substrate400by using a micro drill470. The formed hole corresponds to a region where the bright point defect occurs, and the diameter of the hole may be varied according to the type and range of the bright point defect.

That is, when the bright point defect occurs in the entire sub-pixel due to the electrical short of the data line of the TFT, the hole is formed to a size corresponding to the sub-pixel. When the bright point occurs due to a small amount of particle in the sub-pixel, the hole is formed to a size corresponding to the particle.

FIG. 7is a view illustrating a method of repairing a defective cell of a liquid crystal panel according to another embodiment of the present invention.

Referring toFIG. 7, when a bright point or foreign particle white point is generated due to a defective cell ‘X’ in a completed liquid crystal panel, a hole560is formed at an outer corresponding site of a transparent substrate400or401of a first substrate410or a second substrate430to the site of the defective cell ‘X’, using a micro-screw. A wedge561is inserted into the hole560to convert the defective cell ‘X’ into a dark point.

The wedge561is manufactured to have the same shape as the micro drill, is inserted into the hole region, and is then cut suitably.

The wedge561is formed of a polymer or a metal by a polymer.

The hole560formed in the defect site is made in a diameter of about 20 to 400 μm.

The repair method that converts the defect point into a dark point may be applied to either the first substrate or the second substrate, or to both of the first and second substrates.

As described above, the hole is formed on the external surface of the substrate at a position corresponding to the bright point or the white point generated in the liquid crystal panel, and the pigment or the wedge are filled in the hole. Accordingly, the liquid crystal panel can be easily repaired and the yield and production thereof can be greatly enhanced.

Also, the defective cell of the liquid crystal panel can be repaired even after the substrates are attached together. Accordingly, the product quality and reliability can be greatly enhanced.