KR100724746B1 - Ferroelectric Liquid Crystal Display And Manufacturing Method Thereof - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric liquid crystal display device in which color characteristics are improved without impairing alignment characteristics or cell gap uniformity of liquid crystals.

A ferroelectric liquid crystal display device according to the present invention includes an upper substrate on which color filters, a common electrode, and an alignment layer are sequentially formed, a lower substrate on which pixel electrodes and an alignment layer are sequentially formed, and a sealing material for maintaining a gap between the upper and lower substrates. And a spacer and a liquid crystal interposed between the upper and lower substrates, and the thicknesses of the alignment layers formed on the upper and lower substrates are formed differently for each color pixel.

By such a configuration, the ferroelectric liquid crystal display according to the present invention can improve color characteristics without disturbing alignment characteristics or cell gap uniformity.

Description

Ferroelectric Liquid Crystal Display And Manufacturing Method Thereof             

1 is a cross-sectional view of a liquid crystal display device for explaining the prior art.

2 is a cross-sectional view of a conventional liquid crystal display device which improves color characteristics by making a cell gap different for each color.

3 is a cross-sectional view showing a liquid crystal display device according to an embodiment of the present invention.

4A through 4C are process diagrams illustrating a manufacturing process of the liquid crystal display shown in FIG. 3.

           <Explanation of symbols for the main parts of the drawings>

101,105,211,210,309,310: polarizer

102,106,201,202,301,304,401: transparent substrate

103,203,302,402: TFT array

104,109,208,209,307,303,403,404,405: alignment film

107,207,305 Color filter 108,204,306 Common electrode

110,206,311 Liquid crystal 111,205,308 Spacer                 

406,407,408: PI resin plate 212,312: Black matrix

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric liquid crystal display device and a method for manufacturing the same, and more particularly, to a ferroelectric liquid crystal display device and a method for manufacturing the same, which improve color characteristics of a liquid crystal using a ferroelectric liquid crystal.

In general, an active matrix liquid crystal display device displays a moving image using a thin film transistor (hereinafter referred to as TFT) as a switching element. The display mode of the LCD may be classified into a polarization type, an absorption type, and a scattering type according to the availability of light. Among them, the liquid crystal of the polarization type ferroelectric liquid crystal display device has the property of spontaneous polarization.

The ferroelectric liquid crystal display device is formed by injecting and sealing a liquid crystal between an upper substrate and a lower substrate that maintain a predetermined interval to face each other.

Referring to FIG. 1, a polarizing plate 101, a transparent substrate 102, a TFT array 103, and an alignment layer 104 are sequentially formed on a lower substrate of an FLC mode liquid crystal display device. In the upper substrate, the polarizer 105, the transparent substrate 106, the color filter 107, the common electrode 108, and the alignment layer 109 are sequentially stacked.

In the TFT array 103, a pixel having a TFT and a pixel electrode connected to the TFT as a basic unit is vertically and horizontally arranged on the transparent substrate 102, and a plurality of gate bus lines and data bus lines electrically connected to the respective TFTs are provided. Formed. The gate electrode of the TFT provided near the intersection of the gate bus line and the data bus line branches off the gate bus line, and the source electrode branches off the data bus line. The color filter 107 is a color filter having one of R, G, and B colors on the transparent substrate 106, and a plurality of color filters are formed corresponding to each pixel. The black matrix (not shown) is installed between each color filter 107 R, G, and B so that each color does not interfere. The liquid crystal 110 is injected and sealed between the upper substrate and the lower substrate, and a spacer 111 is provided to maintain a constant gap between the upper substrate and the lower substrate.

Such a liquid crystal display displays an image by rearranging liquid crystals by applying a voltage to an arbitrary pixel to generate a voltage difference between a pixel electrode positioned in the pixel and a common electrode on the upper substrate. In other words, when one gate bus line and one data bus line are selected and a voltage is applied, only the TFT to which the gate voltage is applied is turned on. The charge is accumulated by the voltage on the data bus line to the pixel electrode connected to the drain electrode of the turned on TFT so that only the liquid crystal portion between the pixel electrode and the common electrode is applied to the voltage. Accordingly, the angle of the liquid crystal molecules is changed, and light is transmitted or blocked according to the angle of the liquid crystal molecules, thereby selectively controlling the transmission and blocking of light for each pixel electrode to display an image.

In the LCD, color filters of R, G, and B corresponding to the three primary colors of light are used to implement colors. Colors are expressed by arranging color filters adjacently and controlling brightness by applying a color signal corresponding to each color filter. In detail, the amount of light passing through the color filter is controlled using a liquid crystal, and the voltage required to operate the liquid crystal is output from a source driver integrated circuit (IC) and supplied through the pixel TFT. The voltage supplied to the liquid crystal changes the liquid crystal array, and the light transmittance is changed. At this time, the number of colors that can be expressed is determined by how many steps the liquid crystal can be controlled. For example, the NW (Normally White) ECB mode becomes a white state when no voltage is applied and becomes the darkest state when the highest voltage of the driving range is applied. In this case, when the color filter exists for each pixel and an intermediate voltage is applied to each color filter pixel, an intermediate gray scale may be generated according to the combination. Accordingly, brightness and saturation can be adjusted.

The most common method used for the manufacture of color filters in TFT LCD is pigment dispersion

It is a law. Pigment particles are generally opaque because they scatter light, but are transparent because the particle size is smaller than the wavelength of light. The smaller the size of the pigment particles, the higher the transparency and excellent dispersion properties.

The light transmittance of the ferroelectric liquid crystal display device is given by the following equation.

는 입사광 쪽의 편광판 투과축과 액정방향 사이의 각도,

는 위상차를 나타낸다. 위상차는 다음의 식으로 주어진다. Where T is the light transmittance,

Is the angle between the transmissive axis of the polarizing plate and the liquid crystal direction

Represents a phase difference. The phase difference is given by the following equation.

는 빛의 파장,

는 액정의 프리틸트각을 고려한 유효 굴절율 이방성을 나타낸다.Where d is the cell gap,

Is the wavelength of light,

Represents effective refractive index anisotropy in consideration of the pretilt angle of the liquid crystal.

Therefore, the light transmittance is given by the angle and phase difference between the polarizing plate transmission axis of the incident light and the liquid crystal direction, and this phase difference is given by the cell gap and the wavelength of light and the refractive index anisotropy of the liquid crystal. When the cell gap is constant, the color transmittance characteristics according to voltage application are different. As the wavelength of each of R, G, and B pixels is different, the phase difference is different even in the same liquid crystal array. As a result, the color balance is broken because of the difference in transmittance. In addition, since the voltage at which the maximum transmittance is made is also different for each of the R, G, and B pixels, it is difficult to produce an optimal white light. The proposed method to solve this problem is to form a cell gap differently.

In order to make the phase difference of light affecting the light transmittance equal, the refractive index anisotropy of the liquid crystal is a constant, so the longer the wavelength of the light, the larger the cell gap. Accordingly, it is possible to solve the problem of color balance by varying the cell gap for each color.

Referring to FIG. 2, in the conventional liquid crystal display device, a liquid crystal 206 is sealed while maintaining a predetermined gap by a spacer 205 with an alignment layer 208 and 209 interposed between two opposing transparent substrates 201 and 202. It is injected into, and provided with a different thickness of the color filter 207. As the transmittance (T _R , T _G , T _B ) for each color is different when the same voltage is applied to the liquid crystal, color balance in the middle gray due to voltage application is broken for each color. Compensation by changing the cell gap (d _R , d _G , d _B ).

However, in the prior art to improve the color characteristics by varying the thickness of the color filter for each color, it is difficult to secure the orientation stability due to the difficulty of securing the gap uniformity and the step difference for each R, G, and B pixels. For this reason, when the orientation is unstable, undesired microdomains are generated, and due to the step difference on the surface of the alignment layer, the orientation is poor compared to the flat substrate during rubbing. In addition, since the alignment force is not stable at the boundary where the step occurs, a problem arises in that a disclination line in which liquid crystal alignment between the domains discontinuously changes occurs.

Accordingly, it is an object of the present invention to provide a ferroelectric liquid crystal display device and a method of manufacturing the same, which have improved color characteristics while securing cell gap uniformity without inhibiting the alignment characteristics of the liquid crystal.

In order to achieve the above object, a ferroelectric liquid crystal display device according to the present invention comprises an upper substrate on which a color filter, a common electrode and an alignment layer are sequentially formed, a lower substrate on which a pixel electrode and an alignment layer are sequentially formed, and between the upper and lower substrates. And a sealing material and a spacer for maintaining a gap, and a liquid crystal interposed between the upper and lower substrates, wherein the thicknesses of the alignment layers formed on the upper and lower substrates are formed differently for each color pixel.

Other objects and features of the present invention in addition to the above object will become 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 FIG. 3.

Referring to FIG. 3, a liquid crystal display according to the present invention includes a lower substrate including a pixel electrode 302 including a TFT array formed on a transparent substrate 301, and an alignment film 303 formed thereon; In addition, the spacer 308 and the sealing material may include a color filter array 305 formed on the transparent substrate 304, and an upper substrate on which the common electrode 306 and the alignment film 307 that are aligned are sequentially formed. A ferroelectric liquid crystal 311 is injected therebetween, and polarizers 309 and 310 are attached to the upper and lower substrates, respectively.

m 정도이며, 색필터의 각 색깔별에 해당하는 배향막의 두께 차이를 0.1

m 이하로 변화시킨다. 이러한 배향막의 두께 변화로 색특성 보상 효과를 얻을 수 있다. 또한, R', G', B' 배향막의 단차가 크지 않기 때문에 배향 안정성과 셀갭 균일성을 높일 수 있다.The alignment layer 303 formed on the lower substrate has different thicknesses at positions corresponding to R, G, and B of the color filters 305, and the color filter 305 differs in the thickness of each of the R, G, and B color filters. Maintain the flatness of the upper substrate by making it free. An alignment film R 'at a position corresponding to the first color element R, an alignment film G' at a position corresponding to the second color element G, and an alignment film at a position corresponding to the third color element B ( The thickness of B ') has a predetermined thickness that can be balanced by reducing the difference in transmittance in the middle gray for each color when the same voltage is applied to each pixel, and d _R' <d _{G '} <d _B' Satisfies the relationship. At this time, d _{x '} is the thickness of the alignment film of the corresponding element for each color. Cell gap is 2.0

m, the thickness difference of the alignment layer corresponding to each color of the color filter is 0.1

to m or less. The color characteristic compensation effect can be obtained by the thickness change of this alignment film. In addition, since the step difference between the R ', G', and B 'alignment films is not large, the orientation stability and the cell gap uniformity can be improved.

4A to 4C illustrate cross-sectional views for explaining a method of manufacturing a liquid crystal display, step by step, according to an embodiment of the present invention.

4A shows that the alignment layer 403 is formed only on the R pixel region through a roll coating process on the lower substrate 401 on which the TFT array 402 is formed. At this time, the resin plate used for roll coating is patterned so that the alignment film 403 may rise only on the R pixel region. After the alignment layer forming process, the solvent (Solvent) remaining in the alignment layer is blown through the alignment layer firing process.

4B, the alignment layer 404 is formed only on the R and G pixel regions through a roll coating process on the lower substrate 401 and the alignment layer 403 on which the TFT array 402 is formed. At this time, the resin plate used for roll coating is patterned so that the alignment film 44 may rise only on the R and G pixel regions. After the alignment layer forming process, the solvent (Solvent) remaining in the alignment layer is blown through the alignment layer firing process.

FIG. 4C shows that the alignment layer 405 is formed over the entire active region through a roll coating process on the lower substrate 401 and the alignment layer 404 on which the TFT array 402 is formed. At this time, the resin plate used for roll coating is patterned so that the oriented film 405 may rise over the active whole area | region. After the alignment layer forming process, the solvent (Solvent) remaining in the alignment layer is blown through the alignment layer firing process.

According to the method of manufacturing the ferroelectric liquid crystal display device, the alignment layer has a different thickness between the region corresponding to R of the color filter, the region corresponding to G of the color filter, and the region corresponding to B of the color filter.

The above embodiment of the present invention represents only one example, the selection of the order of the resin plate for coating the alignment film may be carried out by changing the advantageous side in the process, and the coating by using a different combination of resin plate also It is possible to form the thickness of the alignment film corresponding to each color pixel which is the object of the present invention differently.

By changing the thickness of the alignment layer, color characteristics of the ferroelectric liquid crystal display device can be compensated, and an alignment stability can be secured by securing a uniform alignment layer.

As described above, the ferroelectric liquid crystal display device and the manufacturing method thereof according to the present invention can achieve color characteristics compensation by changing the thickness of the alignment layer. In addition, as compared with the conventional method of compensating color by adjusting the thickness of the color filter, a stable orientation and a uniform cell gap can be achieved.

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 (10)

An upper substrate on which a color filter, a common electrode and an alignment layer are sequentially formed; A lower substrate on which the pixel electrode and the alignment layer are sequentially formed; A sealing member and a spacer for maintaining a gap between the upper and lower substrates; It is provided with a liquid crystal interposed between the upper and lower substrates, The thickness of the alignment layers formed on the upper and lower substrates is formed differently for each color pixel. The method of claim 1, And the liquid crystal is a ferroelectric liquid crystal. The method of claim 1, Wherein the alignment layer of B color pixels is greater than or equal to the alignment thickness of G color pixels among the alignment layers. The method of claim 1, Wherein the alignment layer of the G color pixel is greater than or equal to the thickness of the alignment layer of the R color pixel among the alignment layers. The method according to any one of claims 1, 2, 3 and 4, The thickness difference of the alignment layers is 0.01 ~ 0.1

Liquid crystal display characterized in that. The method of claim 1, The pixel electrode is a liquid crystal display, characterized in that the voltage is applied through a thin film transistor (TFT). An upper substrate on which color filters, a common electrode and an alignment layer are sequentially formed, a lower substrate on which pixel electrodes and an alignment layer are sequentially formed, a sealing material and a spacer for maintaining a gap between the upper and lower substrates, and the upper and lower substrates In the manufacturing method of a liquid crystal display device having a liquid crystal interposed therebetween, A method of manufacturing a liquid crystal display device, wherein the thickness of the alignment film corresponding to each color pixel is formed differently. The method of claim 7, wherein And the liquid crystal is a ferroelectric liquid crystal. The method according to any one of claims 7 and 8, The process of differently forming the thickness of the alignment film corresponding to each of the color pixels, Forming an alignment layer at a position corresponding to the color element R region of the color filter; Forming an alignment layer corresponding to the color elements R and G regions of the color filter; Forming an alignment layer over the entire active region. The method of claim 9, And firing an alignment film after each of the alignment film forming steps.

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