KR20060092368A - The repair method of lc modulator and tft array tester using it - Google Patents

Abstract

The present invention relates to a method of repairing a liquid crystal modulator that finds a voltage applied to a pixel electrode 104 of a TFT substrate using voltage imaging and an apparatus using the same. The thickness of the lower substrate 215 of the liquid crystal modulator is usually several tens of micrometers or less. Such thin substrates were easily scratched by dust or other mechanical impacts during the movement, and their use period was limited. The repair method was not known, and thus was disposed of rather than recycled. The present invention relates to a liquid crystal modulator for repairing a scratched lower substrate and a repair method thereof. The protective thin film was coated on the lower substrate of the liquid crystal modulator by spin coating, or after the protective thin film of the inorganic material was coated, the protective thin film was polished to planarize scratches on the lower substrate. The smaller the difference in dielectric constant between the lower substrate and the protective layer, the greater the effect of repair. The liquid crystal modulator of the present invention and the TFT substrate inspection apparatus using the same extend the use time of the liquid crystal modulator, and after the liquid crystal modulator is used for a certain period of time, the protective film is coated and flattened before the scratches become large. Can be saved.

TFT, large substrate, liquid crystal modulator, operating time, TV,

Description

Repair Method of LC Modulator and TFT array tester using it

1 is an equivalent circuit diagram of a TFT substrate.

Fig. 2 is a schematic diagram of an inspection apparatus for a TFT substrate by voltage imaging.

3 is an equivalent circuit diagram for obtaining a voltage applied to a liquid crystal layer.

4 is an optical characteristic curve of a liquid crystal modulator.

5 is a discrimination diagram for determining a defect of a pixel electrode.

Fig. 6 is a sectional view of the liquid crystal modulator for TFT substrate inspection.

7 is an explanatory diagram for obtaining a voltage applied to a liquid crystal layer.

8 is a cross-sectional view of a scratched liquid crystal modulator.

9 is an explanatory diagram showing that the accumulation capacity is changed due to scratches.

10 is a cross-sectional view of a liquid crystal modulator with a protective film formed by spin coating.

11 is a cross-sectional view of a liquid crystal modulator in which a protective film is deposited on a scratched liquid crystal modulator.

FIG. 12 is a cross-sectional view when the protective film of the liquid crystal modulator of FIG. 11 is polished.

Fig. 13 is a liquid crystal modulator of the present invention for easy repair of scratches.

※ Explanation of codes for main parts of drawing

10: light source unit 20: beam splitter 30: image detector

100 TFT substrate 101 scanning line 102 signal line

103 TFT 104 pixel electrode 200 liquid crystal modulator

210: liquid crystal cell 211: upper substrate 212: liquid crystal electrode

213: liquid crystal layer 214: reflective film 215: lower substrate

216: spin coating protective film 217: deposited protective film 218: scratch

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of repairing a liquid crystal modulator that finds a voltage applied to a pixel electrode 104 of a TFT substrate using characteristics of liquid crystals whose arrangement varies with voltage, and an apparatus using the same.

TFT is widely used as a device for driving LCD. 1 is an equivalent circuit diagram of a TFT substrate. On the TFT substrate, a gate line 101, a signal line 102, a TFT 103, and a pixel electrode 104 are formed. In the case where the TFT is an n-channel, when a voltage higher than that of the signal line is applied to the gate line, the resistance of the TFT channel is reduced, so that the voltage of the signal line is applied to the pixel electrode.

Among the methods for inspecting bad pixels on a TFT substrate, the Voltage Image Method of PDI (Photon Dynamic, Inc.) of the United States is widely used. (Reference SID DIGEST 1994, p755) The voltage imaging method applies a bias voltage between the pixel electrode 104 of the TFT substrate and the liquid crystal electrode 212 of the liquid crystal modulator 200, and applies the light transmission or reflection characteristics of the liquid crystal modulator. Again, the defect of the pixel electrode is found therefrom. The liquid crystal modulator can be made of both a transmissive type and a reflective type. However, in the case of a transmissive type, the light source unit 10 and the image detecting unit 30 must be separated from each other with the TFT substrate 100 interposed therebetween, so that the configuration of the inspection apparatus is complicated. In the reflection type, the light source unit 10 and the image detection unit 30 can be integrated, so that the inspection apparatus is simple. Therefore, the liquid crystal modulator 200 is mainly made of a reflective type as shown in FIG. Fig. 2 is a schematic diagram of a TFT substrate inspection device of the voltage imaging method. The liquid crystal modulator is placed on the TFT substrate with a gap of about 20 mu m. A bias voltage V is applied between the pixel electrode 104 of the TFT substrate 100 and the liquid crystal electrode 212 of the liquid crystal modulator. Of the light emitted from the light source unit 10, only the light reflected by the beam splitter 20 enters the liquid crystal modulator. The light entering the liquid crystal modulator is modulated by the polarization and the brightness of the light while passing through the liquid crystal layer, and reflected by the reflective film of the liquid crystal modulator. The light reflected from the reflective film passes through the liquid crystal layer again, and the brightness or polarization of the light is changed, so that only light transmitted through the beam splitter enters the image detector 30. The image detection unit is mainly composed of a CCD (Charge Coupled Device) camera. Each pixel of the CCD is configured to correspond to each pixel electrode of the TFT substrate. If the pixel electrode of the TFT substrate is defective, the voltage applied to the liquid crystal layer corresponding to the pixel electrode is changed. Therefore, the image detecting unit detects this and determines whether the pixel electrode is defective. The size of the liquid crystal modulator is usually about 20 cm in the length of the diagonal, the TFT substrate is more than 100 cm in the length of the diagonal. Therefore, the liquid crystal modulator moves to various places on the TFT substrate and checks for defects.

An equivalent circuit for grasping the operation of the liquid crystal modulator is shown in FIG. The equivalent circuit has a structure in which two capacitors of the liquid crystal layer C _L and the insulating layer C _d are connected in series between the pixel electrode and the liquid crystal electrode of the liquid crystal modulator as shown in FIG. 3. The insulating layer has a structure in which an air layer in which the liquid crystal modulator floats from the TFT substrate and a storage capacity of the lower substrate of the liquid crystal modulator are connected in series. If the voltage induced in the pixel electrode is Vp and the bias voltage applied between the pixel electrode and the liquid crystal electrode of the liquid crystal modulator is V _B , the voltage V _L applied to the liquid crystal layer is as follows.

[Equation 1]

The storage capacitance C _d of the air insulating layer and the lower layer of the liquid crystal modulator connected in series can be calculated by the following equation when the storage capacitance C _A of the air layer and the storage capacitance C _S of the lower substrate are known.

[Equation 2]

The storage capacity C of a unit area insulator having a dielectric constant of ε and a thickness of δ is as follows.

[Equation 3]

Knowing the storage capacitance, the voltage across the liquid crystal layer can be calculated.

The defect of the pixel electrode is found by measuring the intensity of the reflected light of the light passing through the liquid crystal modulator. 4 is an electro-optical curve showing the optical characteristics of the liquid crystal modulator. The horizontal axis represents voltage applied to the liquid crystal layer, and the vertical axis represents reflectance. In FIG. 4, the liquid crystal layer has a high reflectivity when no voltage is applied to the liquid crystal layer, and a reflectance is lowered when a voltage higher than a threshold is applied. As shown in Equation 1, when the voltage Vp applied to the pixel electrode is different, the voltage applied to the liquid crystal layer of the liquid crystal modulator corresponding to each pixel is different, so that the reflectance is differently detected by the image detector. The defective pixel electrode in the TFT substrate has a voltage difference from the normally operating pixel electrode, and the intensity of light reflected from the normal pixel electrode and the defective pixel electrode is changed by the voltage difference. As shown in FIG. 5, the upper limit value R1 and the lower limit value R2 are determined for the reflectivity of the liquid crystal modulator operating normally, and it is determined whether there is any defect or not.

6 is a cross-sectional view of the liquid crystal modulator. The liquid crystal modulator includes a liquid crystal cell 210 and a substrate unit 220. The substrate unit 220 is attached to the liquid crystal cell 210 to prevent the liquid crystal cell from bending. The liquid crystal cell has a structure in which a reflective film 214, a liquid crystal layer 213, and a transparent liquid crystal electrode 212 are disposed between the lower substrate 215 and the upper substrate 211. The liquid crystal mode is a polymer dispersed liquid crystal (PDLC), which is formed by coating a film. The polymer dispersed liquid crystal layer 213 is coated on the upper substrate 211 on which the transparent conductive film 212 is coated, and then a thin plastic film on which the anti-desert 214 is coated is attached. In the polymer dispersed liquid crystal, the light scattering degree is reduced by the long axis of the liquid crystal molecules aligned in the direction of the electric field in the polymer doplet above the threshold voltage. In the polymer dispersed liquid crystal, the doplet has an irregular direction at or below a threshold voltage, so that light is scattered between the doplet and the dopant to become milky. (Reference LCD Engineering p53 Sungandang Publishing Co., Ltd.)

7 is an explanatory diagram for obtaining a voltage applied to a liquid crystal layer. The voltage induced in A of the liquid crystal layer in contact with the lower substrate can be obtained by knowing the voltage applied to the adjacent pixel electrode 104 and the liquid crystal electrode 212 and the distance away from each electrode. In FIG. 7, it is assumed that there is no lower substrate for convenience. As shown in FIG. 7, it is assumed that the voltage applied to the liquid crystal electrode 212 of the liquid crystal modulator is V3, there are only two pixel electrodes, and the voltages applied to each of the voltages are V1 and V2, and A is an electrode having a very small area. Assuming that the storage capacitance is C3 between A and the liquid crystal electrode 212 of the liquid crystal modulator, and the storage capacitances formed by the pixel electrodes subjected to the V1 and V2 voltages are C1 and C2, the voltage V induced in A is as follows. The voltage induced in the floated electrode can be obtained from the storage capacitance and the voltage with the surrounding electrode.

[Equation 2]

The thicker the lower substrate, the smaller the capacitance C1 and C2, so the voltage induced by A approaches V3. The difference in the voltage across the liquid crystal layer (the difference in voltage between the liquid crystal electrode and A) converges to 0V as the lower substrate becomes thicker. If the thickness of the lower substrate is d and the relative dielectric constant is ε, the effect of the lower substrate thickness is converted into the effective distance of the air layer, and d is equal to the value of the relative dielectric constant divided by ε. If the lower substrate is a TiO ₂ layer having a dielectric constant of 24, if the thickness of the lower substrate is 24 µm, the effect is the same as that of 1 µm in air.

The lower substrate of the liquid crystal modulator has a thickness of several tens of micrometers or less, and the lower substrate of the liquid crystal modulator is made of a plastic resin called a pellicle. The material of the pellicle is organic compounds such as NC (Nitro Cellulose), CE (Cellulose Ester) and FC (Flurocarbon polymer). In addition, even when the lower substrate of the liquid crystal modulator is made thin by polishing glass or GaAs, the strength of the substrate is high, but the lower substrate is weak to impact. As the liquid crystal modulator moves on the TFT substrate and measures the image of the pixel electrode, the lower substrate is easily scratched by the impact of dust or other debris on the TFT substrate. In the scratched portion, the reflecting film was cracked or the surface flatness was changed, resulting in a difference in reflectance of light. Scratched liquid crystal modulators are not well known for their repairs and were disposed of rather than recycled. The present invention relates to a liquid crystal modulator for repairing a scratched lower substrate and a repair method thereof.

8 is a cross-sectional view of a scratched liquid crystal modulator. The lower substrate 215 is low in strength and easily scratched. In the scratched portion, the reflecting film is curved due to mechanical impact, and thus the optical characteristics of the scratched portion are changed. In addition, if a scratch occurs, the voltage across the liquid crystal layer also changes. As shown in Fig. 9, assuming that the liquid crystal modulator is separated from the TFT substrate by g, the thickness of the lower substrate is d, and the average thickness of the scratch is h, the electric field change due to the scratch can be obtained from Equations 1, 2, and 3 have. If the accumulation capacity of the air layer when there is no scratch is C _A and the accumulation capacity of the lower substrate of the liquid crystal modulator is C _G , the thickness of the air layer when the scratch is increased by h, so the accumulation capacity is g / (g + h) As a result, the liquid crystal modulator lower substrate is reduced in thickness by h, so that the storage capacitance is increased by d / (dg). Therefore, the voltage received by the liquid crystal in the scratched liquid crystal layer is also different. The scratched part should be filled with a material having a similar dielectric constant to the lower substrate and planarized. When the lower substrate at the time of scratching of the substrate is flattened with a material having a different dielectric constant, the storage capacity of the air layer is the same, but the storage capacity of the lower substrate of the liquid crystal modulator is different. Therefore, the lower substrate and the dielectric constant should be flattened with a material having a small difference.

FIG. 10 is a cross-sectional view of a liquid crystal modulator in which an organic protective film 216 is coated and cured by spin coating on a scratched liquid crystal modulator as shown in FIG. 8. In the case of spin coating, since the scratches are flattened immediately by filling the organic protective film, the shape of the scratch is hardly revealed on the protective film. If the scratch is large, coating and curing the organic protective film several times can reduce the volume change of the organic film during curing, thereby making it possible to uniformly flatten the portion where the scratch occurs. If the lower substrate is an organic film like a pellicle, the organic protective film is coated by spin coating. 11 shows a case where a scratched lower substrate is formed by vapor deposition. If the deposition rate is low, some scratches remain on the protective film as shown in FIG. In the case of Fig. 11, the lower substrate is an inorganic material such as glass or GaAs, and the protective film is a sectional view of the liquid crystal modulator in which scratches are left when vacuum-depositing an oxide having a high dielectric constant such as TiO ₂ or Al ₂ O ₃ Ta ₂ O ₅ . FIG. 12 polishes the protective film of FIG. 11 to remove scratches from the protective film.

In the case where the lower substrate is an organic film, as shown in Fig. 13, the scratches are flattened with a thin organic material by spin coating, and a protective film made of an inorganic material is coated by about 10 mu m or more. Since the hardness of the inorganic protective film is high, scratches are less likely to occur, and even when the scratch is formed, depositing and polishing the inorganic protective film can flatten the lower substrate of the liquid crystal modulator.

The liquid crystal modulator of the present invention and the TFT substrate inspection apparatus using the same extend the use time of the liquid crystal modulator, and after the liquid crystal modulator is used for a certain period of time, the protective film is coated and flattened before the scratches become large. Can reduce the cost. Since the liquid crystal modulator of the present invention and the TFT substrate inspection apparatus using the same have a long life time, they can be used in a TFT LCD inspection process for a large TV with a large inspection area.

Claims (5)

The liquid crystal layer 213 is formed between the upper substrate 211 and the lower substrate 215, the liquid crystal electrode 212 is formed between the upper substrate 211 and the liquid crystal layer 213, and the reflective film 214 is formed on the lower substrate. ) And a liquid crystal modulator repairing method for flattening the scratches of the lower substrate by applying a protective thin film to the lower substrate by spin coating, or after the protective thin film is coated. The liquid crystal layer 213 is formed between the upper substrate 211 and the lower substrate 215, the liquid crystal electrode 212 is formed between the upper substrate 211 and the liquid crystal layer 213, and the reflective film 214 is formed on the lower substrate. ), And a liquid crystal modulator to apply a protective thin film to the lower substrate by spin coating or to deposit the protective thin film and then to flatten the protective film. The liquid crystal modulator of claim 2, wherein a difference between the dielectric constant of the lower substrate and the dielectric constant of the protective layer is less than 20%. The liquid crystal modulator according to claim 2, wherein the lower substrate is an organic substrate, and an organic protective film and an inorganic protective film are coated thereon. A device for inspecting a defect of a TFT substrate by an electric field generated by a voltage applied between a pixel electrode of a TFT substrate and a liquid crystal modulator electrode while moving a liquid crystal modulator at regular intervals on a TFT substrate. A TFT substrate inspection apparatus using a liquid crystal modulator for flattening scratches of a liquid crystal modulator by polishing the protective thin film after coating with a film or coating a protective thin film.

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