KR100855482B1 - Modulator for inspecting Liquid Crystal Display - Google Patents

Abstract

The present invention relates to a modulator for inspecting a liquid crystal display device that can reduce driving voltage and improve detection power.

According to the present invention, a modulator for inspecting a thin film transistor substrate on which a pixel electrode is formed includes: a substrate on which a transparent electrode to which a voltage is supplied is formed; A reflecting plate facing the substrate; A polymer dispersed liquid crystal layer injected between the substrate and the reflecting plate and having a liquid crystal droplet and a polymer; The refractive index difference Δn of the liquid crystal droplets is greater than the refractive index difference Δn of the polymer.

Description

Modulator for inspecting Liquid Crystal Display             

1 is a view showing a conventional liquid crystal display device.

FIG. 2 is a view showing a modulator for inspecting the liquid crystal display device shown in FIG.

3 is a view showing the operation principle of the polymer dispersed liquid crystal used in the modulator shown in FIG.

4 is a view showing a polymer dispersed liquid crystal according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating a modulator injecting the polymer dispersed liquid crystal of FIG. 4. FIG.

6 is a view showing a relationship between voltage and light transmittance according to the present invention;

<Description of Symbols for Main Parts of Drawings>

1: lower substrate 6: gate insulating film

8: protective layer 10, 12: alignment film

11: upper substrate 14: common electrode

16 color filter 22 pixel electrode

23 contact hole 24 liquid crystal                 

25 gate electrode 26, 27 semiconductor layer

28 source electrode 29 drain electrode

31: TFT array substrate 33, 69: reflector plate

35, 67: PDLC layer 37, 65: substrate

39: modulator 41: PBSP

43: light source 45: CCD camera

51, 61: polymer 53, 63: liquid crystal droplets

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a modulator for inspecting a liquid crystal display device capable of reducing driving voltage and improving detection power of a high resolution thin film transistor array.

In general, a liquid crystal display (LCD) displays an image corresponding to a video signal on a liquid crystal panel in which liquid crystal cells are arranged in a matrix form by adjusting light transmittance of liquid crystal cells according to a video signal. In the active matrix liquid crystal display device, a thin film transistor (hereinafter referred to as TFT) is mainly used as a switching element. Such liquid crystal display devices can be miniaturized compared to CRTs, and are widely used in personal computers and notebook computers, as well as office automation devices such as photocopiers, mobile devices such as cell phones and pagers. .

Referring to FIG. 1, a conventional liquid crystal display device includes a color filter substrate including a color filter 16, a common electrode 14, and an alignment layer 12 sequentially formed on an upper substrate 11, and a lower substrate 1. TFT array substrate formed sequentially on the substrate, a TFT array substrate composed of the pixel electrode 22 and the alignment film 10, a spacer (not shown) for maintaining a gap between the color filter substrate and the TFT array substrate, and a color filter substrate. And a liquid crystal 24 injected into the internal space provided by the TFT array substrate and the spacer.

In the color filter substrate, color filters 16 of red, green, and blue primary colors are sequentially formed on the upper substrate 11. In this case, each of the three primary color filters 16 is formed by coating and then patterning a material that absorbs a white light source on the front surface of the upper substrate 11 to transmit only a light having a specific wavelength (red, green, or blue). The common electrode 14, which is a transparent conductive film to which a ground potential is supplied, is formed on the upper substrate 11 on which the color filter 16 is formed. The alignment film 12 is formed by applying polyimide on the common electrode 14.

The TFTs for switching the driving of the liquid crystal cell in the TFT array substrate include a gate electrode 25 protruding from a gate line (not shown), a source electrode 28 protruding from a data line (not shown), and a contact hole 23. A drain electrode 29 connected to the pixel electrode 22 is provided. In addition, the TFT is formed by the gate insulating film 6 for insulating the gate electrode 25, the source electrode 28, and the drain electrode 29, and the source electrode 28 by the gate voltage supplied to the gate electrode 25. Semiconductor layers 26 and 27 for forming a conductive channel between the drain electrodes 29 are provided. This TFT selectively supplies the data signal from the data line to the pixel electrode 22 in response to the gate signal from the gate line. The liquid crystal rotates by the voltage difference between the data signal supplied through the TFT and the common voltage Vcom supplied to the common electrode 14, and the light transmittance is determined according to the degree of rotation of the liquid crystal. The pixel electrode 22 is formed of a transparent conductive material having a high light transmittance and positioned in a cell region divided by a data line and a gate line. The pixel electrode 22 is formed on the passivation layer 8 applied to the entire lower substrate 1 and electrically connected to the drain electrode 29 through the contact hole 23 formed in the passivation layer 8. After the alignment layer 10 is coated on the lower substrate 1 on which the pixel electrode 22 is formed, a rubbing process is performed.

After completing the TFT array on the TFT array substrate of the liquid crystal display device, an electrical inspection method using charge and discharge of the storage capacitor and a reflection type liquid crystal display device according to the voltage of the pixel electrode to check whether the TFT of each pixel operates properly. There is an optical inspection method using the optical characteristics of. Among them, an optical inspection method using an optical inspection apparatus will be described.
Referring to FIG. 2, an optical inspection apparatus for a TFT array substrate includes a TFT array substrate 31 to be inspected, a light source 43 for generating light, and a modulator 39 provided on the TFT array substrate 31; And a polarizing beam splitter prism (hereinafter referred to as " PBSP &quot;) 41 for selectively reflecting light from the light source 43 and sending it to the modulator 39, and a CCD (Charged Couple Display) camera 45 It is provided.

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The optical inspection apparatus moves while maintaining a distance of about 10 to 20 µm from the TFT array substrate 31 to inspect the defect of the TFT array substrate 31.

In the optical inspection device, the PBSP 41 selectively transmits and reflects light. The PBSP 41 reflects the linearly polarized S-waves of the light generated by the light source 43 to advance to the modulator 39.

The modulator 39 is composed of a polymer dispersed liquid crystal (hereinafter referred to as " PDLC ") 35 which is injected between the substrate 37 on which the transparent electrode is installed and the reflecting plate 33. As shown in FIG. 3, the PDLC layer 35 is formed of a circular liquid crystal droplet 53 by mixing the liquid crystal and the polymer 51 to irradiate ultraviolet rays and then separating the liquid crystal from the polymer 51. The material of the PDLC layer 35 is an epoxy resin composed of a resin and a curing agent. The PDLC layer 35 is driven by the voltage difference between the transparent electrode formed on the substrate 37 of the modulator 39 and the pixel electrode 22 formed on the TFT array substrate 31. In other words, when the voltage is not applied to the PDLC layer 35, that is, when the voltage difference applied to the transparent electrode and the pixel electrode 22 is less than or equal to the threshold voltage Vth, the liquid crystal droplets 53 are arranged in random order. Scatters light. This is because light is scattered due to a mismatch between the refractive index of the liquid crystal droplets 53 and the polymer refractive index. On the other hand, when the voltage difference between the transparent electrode and the pixel electrode 22 is greater than or equal to the threshold voltage Vth, the liquid crystal molecules in the liquid crystal droplets 53 of the PDLC layer 35 are arranged in a direction parallel to the electric field to transmit incident light. .

By using the principle of the PDLC layer 35, the TFT array substrate is inspected for defects.

When the pixel electrodes 22 of the TFT array substrate 31 operate properly and the PDLC layer 35 is arranged side by side in the electric field, the S-waves via the PBSP 41 reflect the reflector plate 33 of the modulator 39 without changing the polarization. B) and proceeds to PBSP 41. Since there is no change in polarization, light of S-waves is reflected from the PBSP 41 toward the light source 43. As a result, light cannot be detected by the CCD camera 45.

When a defect occurs in the pixel cell of the TFT array substrate 31, no voltage difference occurs between the transparent electrode and the pixel electrode 22, so that the PDLC layer 35 is not driven. In other words, the S-wave from the light source 43 via the PBSP 41 changes the polarization component while passing through the PDLC layer 35. As a result, the S-waves passing through the PDLC layer 35 are converted into P-waves and transmitted through the PBSP 41 so that light is detected by the CCD camera 45. Accordingly, it can be seen that the pixel cells on the TFT array substrate 31 on which light is detected by the CCD camera 45 are defective pixels.

The size of pixel cells will be reduced due to the high resolution and high resolution trend of LCD. In this case, if the LCD is inspected for defects using a conventional modulator, there is a limit in light detection output. That is, the size of the liquid crystal droplets must also be reduced to correspond to the size of the pixel cell to be high definition, and as the size of the liquid crystal droplets is reduced, the driving voltage required to drive the liquid crystal droplets increases accordingly. In this case, the size of the liquid crystal droplets according to the high resolution is about 5 ~ 6㎛, the driving ratio of the liquid crystal droplets of the PDLC layer and the polymer ratio of about 30 to 70 is consumed about 15 ~ 20V.

Accordingly, an object of the present invention is to provide a modulator for inspecting a liquid crystal display device which can reduce driving voltage and improve detection power.

In order to achieve the above object, according to the present invention, a modulator for inspecting a thin film transistor substrate on which a pixel electrode is formed includes: a substrate on which a transparent electrode to which a voltage is supplied is formed; A reflecting plate facing the substrate; A polymer dispersed liquid crystal layer injected between the substrate and the reflecting plate and having a liquid crystal droplet and a polymer; The refractive index difference Δn of the liquid crystal droplets is greater than the refractive index difference Δn of the polymer.
The refractive index difference Δn of the phase liquid crystal drops is 0.2.
The polymer is characterized in that it is formed of an acrylic resin.

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Other objects and features of the present invention in addition to the above object will be apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 4 to 6.

4 and 5, the modulator for inspecting the liquid crystal display according to the exemplary embodiment of the present invention is characterized by changing the mixing ratio of the liquid crystal droplets and the polymer or changing the material properties of the liquid crystal and the polymer.

Referring to FIG. 4, the present invention increases the mixing ratio of polymer components in PDLC of a modulator for detecting a TFT array substrate.

As shown in FIG. 5, the modulator includes a PDLC layer 67 injected between a substrate 65 provided with a transparent electrode and a reflecting plate 69. The PDLC layer 67 is formed by mixing a liquid crystal and a polymer to irradiate ultraviolet rays and then separating the liquid crystal from the polymer to form a circular liquid crystal drop. Often, the material of the PDLC layer 67 is an epoxy resin composed of a resin and a curing agent. The PDLC layer 67 is driven by the voltage difference between the transparent electrode of the modulator and the pixel electrode formed on the TFT array substrate (not shown) to be inspected. In other words, when no voltage is applied, that is, when the voltage difference applied to the transparent electrode and the pixel electrode is less than or equal to the threshold voltage Vth, the liquid crystal droplets are arranged in random order and scatter the incident light. This is because light is scattered due to a mismatch between the refractive index of the liquid crystal droplets and the polymer refractive index. On the other hand, when the voltage difference between the transparent electrode and the pixel electrode is greater than or equal to the threshold voltage Vth, the liquid crystal molecules in the liquid crystal droplet of the PDLC layer 67 are arranged in parallel with the electric field to transmit incident light.

The mixing ratio of the polymer is increased in the mixing ratio of the liquid crystal droplet of the PDLC layer 67 and the polymer. For example, the mixing ratio of the polymer is increased by 70% or more. Accordingly, the detection force of the modulator is improved by widening the interval d between the liquid crystal drops. However, if the mixing ratio of the polymer is increased, the problem of increasing the driving voltage still remains.

In order to improve this, the mixing ratio of the liquid crystal droplets and the polymer is fixed constantly, and then the physical components are changed to match the characteristics of the liquid crystal droplets and the polymer, respectively.

This is described in detail as follows.

The liquid crystal droplets used in the general PDLC layer 67 have refractive index anisotropy characteristics due to different refractive indices corresponding to the long axis and short axis of the liquid crystal, and the difference in refractive index of the liquid crystal is Δn = 0.1. In addition, the polymer, which is another component of the PDLC layer 67, is composed of an epoxy-based material, and the polymer has a refractive index of about 1.5. At this time, since the epoxy resin has a high viscosity, it has a problem of increasing the driving voltage.

Therefore, the present invention increases the difference in refractive index of the liquid crystal to Δn = 0.2. In the OFF state where no voltage is applied to the modulator, the scattering degree of light increases due to a large difference in refractive index of the liquid crystal. Accordingly, as shown in FIG. 6, the light transmittance is decreased in the OFF state, thereby increasing the transmittance difference at the time of ON / OFF. That is, the contrast of the black and white of the contrast is improved, and thus the detection power for the defect of the TFT array substrate is improved.

The present invention also alters the components of the polymer in the PDLC layer 67. That is, while a conventional epoxy resin is used as a polymer, the present invention uses an acrylic resin having the same refractive index as that of the conventional epoxy resin. In this case, the acrylic resin may have an effect of lowering the driving voltage because of low viscosity.

On the other hand, liquid crystal molecules positioned at the interface of the liquid crystal droplets of the PDLC layer 67 tend not to be directed in the electric field direction even when an electric field is applied by an anchoring energy with a polymer. Since the interfacial energy is a main factor for increasing the driving voltage for driving the PDLC layer 67, the interfacial energy can be reduced and the driving voltage can be reduced at the same time by using an acrylic resin in which a flooride group is substituted. .

As described above, the modulator for inspecting the liquid crystal display according to the present invention increases the mixing ratio of the polymer in the liquid crystal droplet and the polymer mixing ratio, increases the refractive index of the liquid crystal drop, or uses the polymer of acrylic resin. As a result, the liquid crystal display inspection modulator according to the present invention can improve the detection power of the high resolution thin film transistor array by reducing the driving voltage required to drive the polymer dispersed liquid crystal and improving the characteristics of the polymer dispersed liquid crystal. .

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (5)

delete delete In a modulator for inspecting a thin film transistor substrate on which a pixel electrode is formed, A substrate on which a transparent electrode to which a voltage is supplied is formed; A reflecting plate facing the substrate; A polymer dispersed liquid crystal layer injected between the substrate and the reflecting plate and having a liquid crystal droplet and a polymer; And a refractive index difference (Δn) of the liquid crystal droplets is larger than the refractive index difference (Δn) of the polymer. The method of claim 3, wherein The refractive index difference (Δn) of the phase liquid crystal droplet is 0.2, wherein the modulator for inspecting the liquid crystal display device. The method of claim 3, wherein And said polymer is formed of an acrylic resin.

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