WO2008156280A1

WO2008156280A1 - Method of repairing flat pannel display

Info

Publication number: WO2008156280A1
Application number: PCT/KR2008/003409
Authority: WO
Inventors: Il Ho Kim
Original assignee: Cowindst Co., Ltd.
Priority date: 2007-06-18
Filing date: 2008-06-17
Publication date: 2008-12-24

Abstract

Disclosed herein is a method of repairing a bright pixel defect of a display device that is capable of very effectively repairing a bright pixel defect using laser of a wavelength band having high absorption spectrum with respect to respective pixels. When repairing a bright pixel defect of a display device having no polarizing plate attached thereto, the method includes, when a color filter having a bright pixel defect is a red (R) region, irradiating laser having a wavelength of 270 to 550 nm, when a color filter having a bright pixel defect is a green (G) region, irradiating laser having a wavelength of 270 to 480 nm or 600 to 750 nm, and/or, when a color filter having a bright pixel defect is a blue (B) region, irradiating laser having a wavelength of 270 to 390 nm or 520 to 750 nm.

Description

Description METHOD OF REPAIRING FLAT PANNEL DISPLAY

Technical Field

[1] The present invention relates to a method of repairing a bright pixel defect of a display device, and, more particularly, to a method of repairing a bright pixel defect of a display device that is capable of selectively using laser of a wavelength band having high absorption spectrum with respect to a color filter having a bright pixel defect, thereby effectively repairing the bright pixel defect of the color filter. Background Art

[2] In recent years, liquid crystal displays have been in the spotlight as a next-generation high-technology display device which has low power consumption and high portability, is technology-intensive, and is highly value-added. Among them, an active matrix type liquid crystal display including a switching device for switching voltage applied for each pixel has attracted the greatest attention because of its high resolution and excellent motion picture implementation.

[3] Referring to FIG. 1, a liquid crystal panel 500 is constructed in a structure in which a color filter substrate 530, which is an upper substrate, and a thin film transistor (TFT) array substrate 510, which is a lower substrate, are joined to each other while being opposite to each other, and a liquid crystal layer 520 is disposed between the substrates. The liquid crystal panel 500 is driven in a way in which TFTs attached to hundreds of thousands of pixels are switched, through address wires for pixel selection, to apply voltage to corresponding pixels. Here, the color filter substrate 530 includes a glass 531, red/green/blue (RGB) color filters 532, black matrices 533 formed between the color filters 532, an overcoat layer, an indium tin oxide (ITO) film 535 for a αmmon electrode, and an alignment film 536. To the top of the glass is attached a polarizing plate 537.

[4] A thin film transistor array substrate process, a color filter substrate process, and a liquid crystal cell process are performed to manufacture such a liquid crystal pane.

[5] The thin film transistor array substrate process is a process for repeatedly performing deposition, photolithography, and etching to form gate wires, data wires, thin film transistors, and pixel electrodes on the glass substrate.

[6] The color filter substrate process is a process for manufacturing RGB color filters which are arranged on a glass having black matrices in a predetermined sequence to implement colors and forming an ITO film for a common electrode. [7] The liquid crystal cell process is a process for joining the thin film transistor array substrate and the color filter substrate, such that a predetermined gap is maintained between the thin film transistor array substrate and the color filter substrate, and injecting liquid crystal into the gap between the thin film transistor array substrate and the color filter substrate, to form a liquid crystal layer. Alternatively, in recent years, there has been used a one drop filling (ODF) process for uniformly applying liquid crystal to the thin film transistor array substrate and then joining the thin film transistor array substrate and the color filter substrate.

[8] At the time of inspecting such a liquid crystal display, a test pattern is displayed on a screen of the liquid crystal panel to detect whether a defective pixel exists. When the defective pixel is found, a process for repairing the defective pixel is carried out. liquid crystal defects may include a spot defect, a line defect, and display nonuniformity. The spot defect may occur due to poor TFT devices, poor pixel electrodes, or poor color filter wires. The line defect may occur due to an open circuit between wires, a short circuit between wires, breakdown of TFTS by static electricity, or poor connection with a drive circuit. The display nonuniformity may occur due to nonuniform cell thickness, nonuniform liquid crystal alignment, TFT distribution at specific places, or relatively large wire time constant.

[9] Among them, the spot defect and the line defect generally occur due to poor wires. In the conventional art, when open-circuit wires are found, the open-circuit wires are merely connected to each other, and, when short-circuit wires are found, the short- circuit wires are merely separated from each other.

[10] In addition to above-described defects, impurities, including dust, organic matter, metal, etc., may be adsorbed to the liquid crystal panel, during the manufacture of the liquid crystal panel. When such impurities are adsorbed to the region near seme color filters, pixels corresponding to the color filters emit much brighter light than the brightness of the remaining normal pixels, which is called a light-leakage phenomenon. A method of using laser to repair such a bright pixel defect is now under study.

[11] Japanese Patent Application Publication No. 2006-72229 discloses a technology for irradiating laser to an alignment film, such that the alignment film is damaged, to weaken an arrangement property of liquid crystal and thus lower light transmittance of the liquid crystal, thereby eliminating a light-leakage phenomenon. However, this technology has problems in that it is not possible to completely eliminate the arrangement property of liquid crystal, and a large amount of time is required to αmplete the process.

[12] In order to solve the above-mentioned problems, Korean Patent Application No.

10-2006-86569 has been filed in the name of the applicant of the present application. This patent application discloses a method of blackening a defective pixel using femtosecond laser.

[13] When the femtosecond laser is used, it is possible to efficiency blackening the defective pixel; however, there is a problem in that equipment for oscillating the femtosecond laser is very expensive. Disclosure of Invention Technical Problem

[14] Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of repairing a bright pixel defect of a display device that is capable of very effectively repairing a bright pixel defect using laser of a wavelength band having high absorption spectrum with respect to respective pixels.

[15]

Technical Solution

[16] In accordance with the present invention, the above and other objects can be accomplished by the provision of a method of repairing a bright pixel defect of a display device having no polarizing plate attached thereto, the method including, when a color filter having a bright pixel defect is a red (R) region, irradiating laser having a wavelength of 270 to 550 nm, when a color filter having a bright pixel defect is a green (G) region, irradiating laser having a wavelength of 270 to 480 nm or 600 to 750 nm, and/or, when a color filter having a bright pixel defect is a blue (B) region, irradiating laser having a wavelength of 270 to 393 nm or 520 to 750 nm.

[17] Preferably, the laser has a pulse duration of 100 ns or less, and the laser has a repetitive frequency of 1 Hz to 1 kHz.

[18] Preferably, the method further includes adjusting the intensity of the laser.

[19] Preferably, the laser has a flat top profile.

[20] Preferably, the method further includes adjusting the intensity and focal distance of the laser such that 20 % to 90 % of the thickness of the color filter is blackened by the laser.

[21] Preferably, when the display device has no overcoat layer, the laser has a pulse duration of 50 ns or less, the laser has a repetitive frequency of 1 Hz to 100 Hz, and the laser has a power of 10 mW or less. [22] Preferably, the laser is irradiated to the color filter by a scan type laser irradiation method. Alternatively, the laser may be irradiated to the color filter by a block shot type laser irradiation method or a multi block shot type laser irradiation method. [23] Preferably, the laser is created using at least one selected from a group consisting of

Ytterbium laser, Ti-Sapphire laser, Nd: YLF laser, Nd:Glass laser, Nd: Vanadate

(YV04) laser, Nd: YAG laser, Fiber laser, and Dye laser. [24]

Advantageous Effects

[25] According to the present invention, as apparent from the above description, it is possible to very effectively repair a bright pixel defect of a oolor filter by selectively using laser of a wavelength band having high absorption spectrum with respect to the color filter. [26] In particular, when a polarizing plate is attached to a display device, it is possible to more effectively blacken the oolor filter in consideration of the transmittance of the polarizing plate according to its wavelength.

Brief Description of the Drawings [27] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[28] FIG. 1 is a sectional view illustrating a liquid crystal panel containing impurities;

[29] FIG. 2 is a graph illustrating transmittance of a color filter according to its wavelength;

[30] FIGS. 3 to 5 are views illustrating various laser irradiation methods;

[31] FIG. 6 is a view illustrating a process for irradiating laser while adjusting the focal distance;

[32] FIG. 7 is a flow chart illustrating a blackening process;

[33] FIG. 8 is a sectional view illustrating a liquid crystal panel having no overcoat layer;

[34] FIG. 9 is a graph illustrating light absorption of an overcoat layer; and

[35] FIG. 10 is a graph illustrating a laser beam profile (shape) according to the present invention. [36]

Best Mode for Carrying Out the Invention [37] Now, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[38] A method of repairing a bright pixel defect of a display device according to the present invention is to irradiate a pixel (a oolor filter and its neighboring black matrices) having a bright pixel defective to blacken the defective pixel.

[39] When laser is irradiated to an organic film, such as a color filter, molecular coupling of organic matter constituting the film is broken, with the result that the organic film is ablated while emitting radicals, clusters, electrons, and photons, including plasma comprising neutral atoms, molecules, and positive and negative ions, whereby the organic film is blackened.

[40] Ablation is a phenomenon in which organic matter is decomposed into molecules and ions due to the dissociation of the molecular coupling of the organic matter. In order to achieve such dissociation, however, it is required to absorb energy greater than the energy level of the organic matter.

[41] The light transmittance of the blackened pixel is lowered, and therefore, the blackened pixel does not transmit but absorbs light generated from a light source (a backlight unit) of the display device. In this way, the defective pixel is repaired such that the bright pixel of the defective pixel becomes a dark pixel.

[42] Consequently, it is required for laser to be irradiated with a wavelength having low transmittance, i.e., a wavelength having high absorptivity, of a pixel to be blackened.

[43] This wavelength is selected with reference to FIG. 2. For example, when a color filter having a bright pixel defect is a red (R) region, it can be seen that a wavelength having high absorptivity of the red region is 550 nm or less. When laser having a wavelength of more than 550 nm is irradiated to the red (R) region, the transmittance is high, and therefore, a larger amount of energy is needed, with the result that several film layers, such as an overcoat layer, an ITO film, and an alignment film, below the color filter may be seriously damaged. If the film layers below the color filter are damaged, liquid crystal comes up to the damaged regions, with the result that bubbles are generated, which leads to more serious defect of the color filter.

[44] Meanwhile, laser having a wavelength of less than 270 nm is not transmitted through the glass, with the result that the laser does not reach the color filter. Laser having a wavelength of more than 750 nm is transmitted through the color filter, with the result that the laser does not react on the color filter.

[45] In conclusion, when a color filter having a bright pixel defect is a red region, it is preferred for laser having a wavelength of 270 to 550 nm to be irradiated to the color filter, whereby it is possible to very effectively blacken the color filter, such that the bright pixel defect of the color filter is repaired, without the damage to the film layers below the color filter.

[46] In this way, when such a bright pixel defect is to be repaired, it is required to irradiate laser having a wavelength of low color filter transmittance. For a red (R) region, it is preferred to irradiate laser having a wavelength of 270 to 550 nm, as previously described. For a green (G) region, it is preferred to irradiate laser having a wavelength of 270 to 480 nm or 600 to 750 nm. For a blue (B) region, it is preferred to irradiate laser having a wavelength of 270 to 390 nm or 520 to 750 nm.

[47]

Mode for the Invention

[48] FIGS. 3 to 5 are views illustrating various methods of irradiating laser to a pixel having a bright pixel defect. Specifically, FIG. 3 illustrates a scan type laser irradiation method, FIG. 4 illustrates a block shot type laser irradiation method, and FIG. 5 illustrates a multi block shot type laser irradiation method.

[49] Here, the scan type laser irradiation method is to scan laser having a beam size (see

'S' of FIG. 3) corresponding to a portion of area of a pixel having a bright pixel defect to irradiate the laser to the entire area of the pixel. The block shot type laser irradiation method is to irradiate laser having a beam size corresponding to the entire area of a pixel having a bright pixel defect at once. The multi block shot type laser irradiation method is a αmbination of the scan type laser irradiation method and the block shot type laser irradiation method. That is, the multi block shot type laser irradiation method is to irradiate laser according to the block shot type laser irradiation method and, at the same time, continuously irradiate laser according to the scan type laser irradiation method.

[50] Although any of the laser irradiation methods is used, it is preferred to irradiate laser to a portion of each black matrix neighboring to the color filter as well as the color filter.

[51] Referring to FIG. 6, it is preferred to irradiate laser several times to satisfactorily blacken the color filter.

[52] Specifically, when laser is firstly irradiated (Sl), a Z-axis moving scanner is used to locate a depth of focus (DOF) at a region corresponding to 10 % of the thickness of the color filter, and then the color filter is blackened using an XY-axis moving scanner. When the blackened degree of the color filter is confirmed by a charge coupled device (CCD) camera, and it is determined that the blackened degree of the color filter is insufficient, the Z-axis moving scanner is driven, such that the DOF is located at a region corresponding to 20 % of the thickness of the color filter, and then laser is secondly irradiated (S2) using the XY-axis moving scanner. When this process is repeatedly carried out 2 to 4 times, it is possible to satisfactorily blacken the color filter to a desired blackened degree.

[53] FIG. 7 is a flow chart illustrating a process for blackening a color filter while moving the focal distance according to the above-described method.

[54] As shown in FIG. 7, laser is firstly irradiated to a color filter (SlO) to blacken a color filter to a blackened degree of approximately 10 % (S20), and then the blackened degree of the color filter is confirmed (S30) to determine whether the color filter has been blackened to a satisfied degree (S40). When it is determined that the color filter has been blackened to a desired degree, the procedure is ended (S50). On the other hand, when it is determined that the color filter has not been blackened to the desired degree, the focal distance is moved (S60), and then laser is re-irradiated to the color filter so as to further blacken the color filter.

[55] The depth of focus (DOF) is calculated by the focal distance between the Z-axis moving scanner and a scanning lens and the diameter of an incident beam within a range of 2 μm or less.

[56] [Mathematical equation 1]

[57] DOF = λ/2(NA)2

[58] [Mathematical equation 2]

[59] NA = nsinθ

[60] [Mathematical equation 3]

[61] f/# = 1/2(NA)

[62] [Mathematical equation 4]

[63] f/# = efl/φ

[64] Mathematical equation 5 may be derived from a combination of Mathematical equation 3 and Mathematical equation 4.

[65] [Mathematical equation 5]

[66] NA = φ/2(efl)

[67] In the mathematical equations above, NA indicates an effective numerical aperture, λ

(lambda) indicates a wavelength of laser, and efl indicates effective focal length.

[68] It can be confirmed that the larger the diameter of an incident beam is and the shorter the wavelength of laser is, the shallower the depth of focus (DOF) is. It can be also confirmed that the shorter the focal distance (efl) of the lens is, the larger the numerical aperture (NA) is, and therefore, the shallower the depth of focus (DOF) is. [69] It is preferred for the blackened thickness to be less than 93 % to the maximum, preferably 20 to 40 %, of the thickness of the color filter, to prevent the occurrence of a light-leakage phenomenon within a viewing angle range of a liquid crystal panel. When less than 20% of the thickness of the color filter is blackened, it may not be possible to fully (100 %) prevent the occurrence of light leakage. On the other hand, when not less than 90% of the thickness of the color filter is blackened, films stacked below the color filter may be damaged. Also, laser energy plays an important role to blacken an organic film to an appropriate thickness. In other words, it is possible to adjust the blackened thickness according to output energy of laser.

[70] Referring to FIG. 8, there is illustrated a display device having no overcoat layer to reduce the manufacturing costs and simplify the manufacturing process.

[71] Meanwhile, an overcoat layer has a light absorptivity as shown in FIG. 9. It can be seen from FIG. 9 that transmission is little achieved at a region below an ultraviolet (UV) region, and approximately 80 % of absorption and approximately 20 % of transmission are achieved at the UV region.

[72] Consequently, it is required that a display device having no overcoat layer be repaired differently from a display device having an overcoat layer. This is because energy generated from laser irradiated to repair a bright pixel defect is absorbed by the overcoat layer. Consequently, when a bright pixel defect of a display device having no overcoat layer is repaired, energy, transmitted through a color filter, reaches a liquid crystal layer, with the result that the liquid crystal layer may be damaged.

[73] For this reason, it may be possible to use laser having low energy to prevent the damage to the liquid crystal layer; however, in this case, no reaction can occur.

[74] Consequently, in consideration of the above problem, conditions in which laser has low energy and energy application time is short must be satisfied. Experiment results revealed that a bright pixel defect of a display device having no overcoat layer was satisfactorily repaired when laser having a plus duration of 50 ns or less, a repetitive frequency of 1 Hz to 100 Hz, and a power of 10 mW or less was used.

[75] FIG. 10 is a graph illustrating a laser beam profile according to the present invention.

[76] Laser initially irradiated from a laser oscillator is a Gaussian type laser beam of which energy concentrates on a central region. When this laser beam passes through a beam shaper or a beam homogenizer, the intensity of the laser beam is uniformalized at a specific range, with the result that the laser beam is converted into a flat top profile of an expanded size. At this time, the area of the laser irradiated is also changed along with the change of the beam profile. The flat top profile may be changed into the shape of a rectangular flat top 300 or a circular flat top 301.

[77] It is possible to change the magnitude and intensity of the laser beam irradiated using the beam shaper and a beam adjustor. The smaller the area of the laser beam irradiated is, the more time is required to wholly blackening a plurality of pixels. The magnitude of the laser beam may be uniformly converted to increase blackening speed, whereby the present invention is applicable to a production line to mass-produce products. The laser converted into the rectangular flat top 300 or the circular flat top 301 having appropriate intensity can blacken RGB pixels, among a plurality of organic films constituting a liquid crystal panel, to a desired thickness by the Z-axis moving scanner.

[78] Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[I] A method of repairing a bright pixel defect of a display device having no polarizing plate attached thereto, the method αmprising: when a color filter having a bright pixel defect is a red (R) region, irradiating laser having a wavelength of 270 to 550 nm; when a color filter having a bright pixel defect is a green (G) region, irradiating laser having a wavelength of 270 to 480 nm or 600 to 750 nm; and/or when a color filter having a bright pixel defect is a blue (B) region, irradiating laser having a wavelength of 270 to 390 nm or 520 to 750 nm. [2] The method according to claim 1, wherein the laser has a pulse duration of 100 ns or less. [3] The method according to claim 1, wherein the laser has a repetitive frequency of

1 Hz to 1 kHz. [4] The method according to claim 1, further comprising: adjusting the intensity of the laser.

[5] The method according to claim 1, wherein the laser has a flat top profile.

[6] The method according to claim 1, further comprising: adjusting the intensity and focal distance of the laser such that 20 % to 90 % of the thickness of the color filter is blackened by the laser. [7] The method according to claim 1, wherein, when the display device has no overcoat layer, the laser has a pulse duration of 50 ns or less. [8] The method according to claim 7, wherein the laser has a repetitive frequency of

1 Hz to 100 Hz. [9] The method according to claim 7, wherein the laser has a power of 10 mW or less. [10] The method according to claim 1, wherein the laser is irradiated to the color filter by a scan type laser irradiation method.

[I I] The method according to claim 1, wherein the laser is irradiated to the color filter by a block shot type laser irradiation method or a multi block shot type laser irradiation method.

[12] The method according to claim 10 or 11, wherein the laser is irradiated to the color filter and black matrices neighboring to the color filter.

[13] The method according to claim 1, wherein the laser is created using at least one selected from a group consisting of Ytterbium laser, Ti-Sapphire laser, Nd: YLF laser, Nd:Glass laser, Nd: Vanadate (YV04) laser, Nd: YAG laser, Fiber laser, and Dye laser.