KR20060078136A - Transmissive and reflective type liquid crystal display - Google Patents

Abstract

A reflection-transmissive liquid crystal display device capable of suppressing light leakage, removing afterimages, and improving transmission contrast ratio is provided. A reflective transmissive liquid crystal display device includes a protective film having a first thickness corresponding to a transmissive region and having a second thickness thicker than the first thickness corresponding to a reflective region, a common electrode formed on the protective film, and formed on the common electrode. A color filter substrate having a first alignment layer rubbed in one direction, a liquid crystal layer substantially in contact with the first alignment layer, a thin film transistor, a transparent electrode connected to a drain electrode of the thin film transistor, and defining a pixel region, and transparent A reflective electrode formed on the electrode and formed at a position corresponding to the stepped portion where displacement of the liquid crystal layer occurs and defining a transmissive region and a reflective region, and formed on the transparent electrode and the reflective electrode and different from the first direction. And a TFT substrate having a second alignment film rubbed in two directions.

Reflection, transmission, liquid crystal, light leakage

Description

Transmissive and reflective type liquid crystal display

1 is a view illustrating a process of forming an alignment layer on a substrate.

FIG. 2 is a view illustrating a state in which liquid crystals are aligned depending on the alignment layer of FIG. 1.

3 is a layout view illustrating a structure of a TFT substrate in a reflective transmissive liquid crystal display according to an exemplary embodiment of the present invention.

4 is a cross-sectional view of the liquid crystal display including the TFT substrate and the color filter substrate illustrated in FIG. 3 taken along the line IV-IV ′.

6A, 7A, 8A, 9A, and 10A are layout views of a TFT substrate in an intermediate process of manufacturing a TFT substrate for a reflective transmissive liquid crystal display device according to an embodiment of the present invention.

FIG. 6B is a cross-sectional view taken along the line VIb-VIb ′ in FIG. 6A.

FIG. 7B is a cross-sectional view taken along the line VIIb-VIIb ′ in FIG. 7A and illustrates the next step of FIG. 6B.

FIG. 8B is a cross-sectional view taken along the line VIIIb-VIIIb 'of FIG. 8A and illustrates the next step of FIG. 7B.

FIG. 9B is a cross-sectional view taken along the line IXb-IXb 'of FIG. 9 and illustrates the next step of FIG. 8B.                 

FIG. 10B is a cross-sectional view taken along the line Xb-Xb ′ in FIG. 10A and illustrates the next step of FIG. 9B.

(Explanation of symbols for the main parts of the drawing)

100: TFT substrate 110: insulating substrate

121: gate line 123: gate electrode

140: gate insulating film 150: semiconductor layer

163 and 165: ohmic contact layer 171: data line

173: source electrode 175: drain electrode

180: lower protective film 196: transmission window

200: color filter substrate 220: black matrix

231: color filter 240: upper protective film

250: common electrode 300: liquid crystal layer

310: spacer 901: transparent electrode

902: reflective electrode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a reflection transmissive liquid crystal display device for suppressing a light leak phenomenon to improve a black characteristic of a screen and a transmission contrast ratio.                         

Liquid crystal display (LCD) is one of the most widely used flat panel display devices. The liquid crystal display (LCD) is composed of a TFT substrate including an electrode, a color filter substrate, and a liquid crystal layer interposed therebetween. A display device adjusts a transmittance of light passing through a liquid crystal layer by rearranging liquid crystal molecules of the liquid crystal layer by adjusting a voltage. In this case, the light transmittance is determined by phase retardation caused by the optical properties of the liquid crystal material when passing through the liquid crystal layer, and the phase retardation is controlled by adjusting the refractive index anisotropy of the liquid crystal material and the distance between the two substrates. Decide

Among the liquid crystal display devices, a liquid crystal display device having a thin film transistor (TFT) that has electrodes on each of two substrates and switches a voltage applied to the electrode is a liquid crystal display device. It is generally formed in.

Such a liquid crystal display displays an image by transmitting light emitted by a backlight, which is a specific light source, to the liquid crystal layer to display an image, and external light such as natural light reflected by the reflective electrode of the liquid crystal display to the liquid crystal layer. It can be divided into a reflection type, and recently, a reflection transmission mode that operates in both a reflection mode and a transmission mode has been developed.

However, in the reflection-transmissive liquid crystal display device, since the phase retardation with respect to the light passing through the liquid crystal layer is different in each mode, there is a problem in that display characteristics are deteriorated. That is, in the transmissive mode, light passes through the liquid crystal layer only once and reaches the eyes of the user. In the reflective mode, the light passes through the liquid crystal layer twice. Therefore, the light paths are different in both modes.

In order to overcome this, it is possible to reduce the light path difference between the two modes by reducing the cell gap of the reflection region rather than the transmission region. That is, the organic insulating film corresponding to the reflective region on the substrate may be formed thicker than the transmissive region to have different thicknesses. However, at the interface between the reflection area and the transmission area, an afterimage remains on the screen due to a disclination phenomenon occurring early in the frame due to the distortion of liquid crystal alignment, and a light leakage phenomenon occurring throughout the frame. There is a problem that the contrast ratio is lowered.

Hereinafter, with reference to FIGS. 1 and 2, the problem of the distortion of the liquid crystal alignment and the resulting display characteristics will be described.

FIG. 1 is a view illustrating a process of forming an alignment layer on a substrate, and FIG. 2 is a view illustrating a shape in which liquid crystals are aligned depending on the alignment layer of FIG. 1. Referring to FIG. 1, the alignment layer 30 is rubbed in the left direction 45 while applying the alignment layer 30 by the roller 40 rotating on the substrate 10 on which the structure 20 is formed. Referring to FIG. 2, in the portion where the roller 40 rides up the stepped portion A formed by the structure 20, the liquid crystal 50 is generally pretilted. However, in the portion where the roller 40 rides down the stepped portion B formed by the structure 20, the liquid crystal 50 is reversely pretilted relative to the other portion, so that the liquid crystal 50 is oriented in a certain direction when an electric field is applied. It is not known whether this will form, which can cause serious light leakage.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reflection-transmissive liquid crystal display device which is employed in a reflection-transmission liquid crystal display device having a multi-cell gap structure to suppress light leakage, eliminate afterimages, and improve transmission contrast ratio. will be.

Technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a reflective transmissive liquid crystal display device comprising: a protective film having a first thickness corresponding to a transmissive region and a second thickness thicker than the first thickness corresponding to a reflective region; A color filter substrate comprising a common electrode formed on the passivation layer, a first alignment layer formed on the common electrode and rubbed in a first direction, a liquid crystal layer substantially contacting the first alignment layer, a thin film transistor; And a transparent electrode connected to the drain electrode of the thin film transistor to define a pixel region, and formed at a position corresponding to the stepped portion formed on the transparent electrode and generating disclination of the liquid crystal layer. A reflective electrode defined on the transparent electrode and the transparent electrode and rubbed in a second direction different from the first direction; It includes a TFT substrate having a second alignment layer.                     

Specific details of other embodiments are included in the detailed description and the drawings.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, the structure of a reflective transmissive liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 3 to 5.

First, the structure of the liquid crystal display according to the exemplary embodiment of the present invention will be described in detail with reference to FIGS. 3 and 4.

3 is a layout view of a TFT substrate for a reflective transmissive liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 4 is a line along the line IV-IV 'of the liquid crystal display including the TFT substrate and the color filter substrate shown in FIG. It is sectional drawing cut out.

As shown in FIG. 3 and FIG. 4, the liquid crystal display according to the exemplary embodiment of the present invention includes a spacer 310 that uniformly supports an interval between two substrates 100 and 200 and two substrates 100 and 200 facing each other. ) And the liquid crystal layer 300 injected between the two substrates 100 and 200. The spacer 310 is made of an organic insulating material and is formed through a photolithography process.

On the TFT substrate 100, a gate line 121 and a data line 171 are formed crossing each other to define the unit pixel region P of the matrix array. Each pixel region P includes a thin film transistor TFT connected to the gate line 121 and a data line 171, and a pixel electrode electrically connected to the thin film transistor TFT. The pixel electrode includes a transparent electrode 901 made of a transparent conductive film and a reflective electrode having a reflectance and a reflective electrode 902 having a transmission window 196. From now on, the area occupied by the transmission window 196 will be referred to as the "transmission area" T, and the remaining area of the pixel area P will be referred to as the "reflection area" R. In addition, the region of the TFT substrate 100 corresponding to the transparent region T and the reflective region R is also referred to using the same name and the same reference numeral.

In the color filter substrate 200 according to the exemplary embodiment of the present invention facing the TFT substrate 100, a black matrix 220 having an opening corresponding to the pixel region P is formed, and each pixel region P is formed. ), Red, green, and blue color filters 231 are formed, and the color filter 231 is covered with an upper passivation layer 240 made of an organic insulating material, and a common electrode 250 is disposed on the upper passivation layer 240. ) Is formed. In this case, the upper passivation layer 240 has a thickness different according to the display regions R and T, and the organic insulating material corresponding to the transmission region T is removed.

Here, the reflecting region R is mainly used to display an image using the light reflected from the reflecting electrode 902, and the transmitting region T is used to display the image using the backlight, that is, light from its own light source. Mainly used to                     

In the liquid crystal display according to the exemplary embodiment of the present invention, in the transmission region T, light emitted from the backlight passes through the TFT substrate 100 and then passes through the liquid crystal layer 300 once to be displayed as an image. The light displaying the image in the area R experiences the liquid crystal layer 300 when it reaches the reflective electrode from the outside, is reflected by the reflective electrode 902 and then experiences the liquid crystal layer 300 again. In consideration of this, the thickness of the upper passivation layer 240 of the reflective region R is greater than the thickness of the upper passivation layer 240 of the transmission region T. In this way, the path of the light displaying the image can experience the liquid crystal layer 300 in each of the display mode regions T and R to be uniform, whereby the light in the two display mode regions T and R The phase delay with respect to can be made uniform, and the display characteristic of a liquid crystal display device can be improved. In particular, in the liquid crystal display of the electrically controlled birefringence mode (ECB) having various cell gaps, the liquid crystal in the transmission region T and the reflection region R is satisfied to satisfy the condition of Δnd = λ / 2. By adjusting the path d of the light passing through the layer 300, the path of the light displayed in the image can be made uniform.

Next, the structure of the lower substrate in the liquid crystal display according to the exemplary embodiment of the present invention will be described in more detail.

The TFT substrate 100 includes an insulating substrate 110. A plurality of gate lines 121 extending mainly in the horizontal direction are formed on the insulating substrate 110. The gate line 121 may include a single layer made of a low resistivity material, for example, silver or silver alloy or aluminum or aluminum alloy. Alternatively, the gate line 121 may be formed of a multilayer film including at least one film including the above-described material and at least one film for pads having excellent contact properties with other materials. The portion 125 positioned near one end of the gate line 121 transmits a gate signal from the outside to the gate line, and the plurality of branches 123 of each gate line 121 are the gate electrode 123 of the thin film transistor. To achieve.

The gate insulating layer 140 made of silicon nitride (SiNx) covers the gate line 121.

An island-like semiconductor layer 150 made of hydrogenated amorphous silicon or the like is formed on the gate insulating layer 140 of the gate electrode 123, and silicide or n-type impurities are heavily doped on the semiconductor layer 150. A plurality of pairs of ohmic contacts 163 and 165 made of n + hydrogenated amorphous silicon are formed. Each pair of ohmic contacts 163 and 165 are separated from each other with respect to the corresponding gate line 121.

A plurality of data lines 171 and a plurality of drain electrodes 175 are formed on the ohmic contacts 163 and 165 and the gate insulating layer 140. The data line 171 and the drain electrode 175 include a conductive film made of a low resistance conductive material such as aluminum or silver. The data line 171 mainly extends in the vertical direction and crosses the gate line 121. The plurality of branches 173 of the data line 171 extends to an upper portion of one of the pair of ohmic contacts 163 and 165 to form the source electrode 173 of the thin film transistor. The portion 179 located near one end of the data line 171 transmits an image signal from the outside to the data line 171. The drain electrode 175 of the thin film transistor is separated from the data line 171 and positioned above the ohmic contact layer 165 opposite to the source electrode 173 with respect to the gate electrode 123.

A lower passivation layer 180 made of silicon nitride or an organic material having excellent planarization characteristics is formed on the data line 171 and the drain electrode 175 and the semiconductor layer 150 which is not covered.

In the lower passivation layer 180, contact holes 185 and 189 respectively exposing the drain electrode 175 and the end portion 179 of the data line 171 are formed, and the gate line 121 together with the gate insulating layer 140 is formed. A contact hole 182 is formed that exposes the end portion 125 of the.

A transparent electrode 901 is formed on the lower passivation layer 180 and is electrically connected to the drain electrode 175 through the contact hole 185 and positioned in the pixel region P. Further, on the passivation layer 180, the gate contact auxiliary member 192 connected to the end portion 125 of the gate line 121 and the end portion 179 of the data line 171 through the contact holes 182 and 189, respectively. ) And a data contact assistant member 199 are formed. Here, the transparent electrode 901 and the contact auxiliary members 192 and 199 are made of indium tin oxide (ITO), indium zinc oxide (IZO), or the like, which is a transparent conductive material.

A plurality of reflective electrodes 902 having a transmission window 196 are formed on each of the transparent electrodes 901. The reflective electrode 902 is made of a conductive film having a high reflectance such as aluminum or an aluminum alloy, silver or silver alloy, molybdenum or molybdenum alloy, or the like. Although not illustrated, the surface of the lower passivation layer 180 may be roughened to cause irregularities in the reflective electrode 902, thereby improving reflection efficiency. The reflective electrode 902 and the transparent electrode 901 are paired to become pixel electrodes. Here, the transmission window 196 of the reflective electrode 902 may be formed in various shapes, a plurality of may be formed in one pixel area.

Here, the pixel electrodes 901 and 902 overlap with the gate line 121 of the previous stage for transmitting the gate signal to the thin film transistors in the adjacent pixel row to form a storage capacitor. It is also possible to add a conductor made of the same layer to add another storage capacitor formed by superimposing the pixel electrodes 901 and 902 or other conductors connected thereto. As such, the conductor layer (not shown) separately added for the storage capacitor is preferably positioned under the reflective electrode 902 so as not to block light passing through the transmission region T from the backlight.

The reflective transmissive liquid crystal display according to the exemplary embodiment of the present invention is applicable to an electrically controlled birefringence mode (ECB) having various cell gaps, and as shown in FIG. From the observer's point of view, the TFT substrate is rubbed upward and the color filter substrate is rubbed downward to ensure optimal viewing angle characteristics at 12 o'clock. That is, referring to FIG. 4, the liquid crystal provided in the liquid crystal layer 300 is homogeneous aligned. The alignment film (not shown) provided in the TFT substrate is rubbed in a left direction, which is a first direction, and provided on the color filter substrate. The oriented film (not shown) is rubbed in a second direction, ie, in a right direction, opposite to the first direction.

FIG. 5 is a diagram illustrating an interface between the reflective region R and the transmissive region T of FIG. 4.                     

Referring to FIG. 5, the upper passivation layer 240 formed on the color filter substrate in the boundary region C between the reflection region R and the transmission region T has a predetermined step, and the alignment layer of the alignment layer with respect to the color filter substrate is described above. In consideration of the rubbing direction, the liquid crystal in the boundary region C is pretilted inversely compared to other portions, such that an afterimage or light leakage may occur. However, the discretization occurs at the beginning of the frame by overlapping the reflective electrode 902 provided in the TFT substrate according to the embodiment of the present invention with the boundary region C and extending a predetermined portion to the transmission region T. Phenomenon and light leakage that occur throughout the frame can be prevented. In this case, when the stepped portion of the upper passivation layer 240 is defined as the boundary region C between the reflective region and the transmissive region, the reflective electrode 902 passes through the boundary region C, and It is preferred that at least about 4-5 μm overlap.

As shown in FIG. 3, the reflective transmissive liquid crystal display according to the exemplary embodiment of the present invention may prevent light leakage by forming a reflective electrode 902 and an upper passivation layer 240 corresponding thereto on the pixel. have. In addition, as shown in FIG. 4, the liquid crystal may be partially pretilted in the region D where the upper passivation layer 240 starts in consideration of the rubbing direction of the alignment layer with respect to the color filter substrate. Since the 220 shields the upper portion of the region D, the disclination phenomenon or the light leakage phenomenon can be prevented.

Hereinafter, a method of manufacturing a color filter substrate in a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to FIG. 4.

An organic insulating material is coated on the substrate 210 on which the color filter 231 and the black matrix 220 are formed by spin coating to transmit the upper passivation layer 240 through a photolithography process using a mask. The part corresponding to the area | region T is removed. In this case, the upper passivation layer 240 may not be completely removed from the transmission region T by using a mask that may partially adjust the light transmittance in order to uniformly control the light paths of the transmission region T and the reflection region R. You can leave some without.

Finally, a transparent conductive material such as ITO or IZO is laminated and the common electrode 250 is formed on the color filter 231 and the upper passivation layer 240, as shown in FIGS. 3 and 4. 4).

Meanwhile, a method of manufacturing a TFT substrate according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 6A to 10B and FIGS. 3 and 4.

First, as illustrated in FIGS. 6A and 6B, a low-resistance conductive material is stacked and patterned on the lower insulating substrate 110 to form a horizontal gate line 121 including the gate electrode 123. .

Next, as shown in FIGS. 7A and 7B, a three-layer film of a gate insulating layer 140 made of silicon nitride, a semiconductor layer made of amorphous silicon, and a doped amorphous silicon layer is successively laminated, and the semiconductor layer is formed by a patterning process using a mask. The doped amorphous silicon layer is patterned to form an island-type semiconductor layer 150 and an island-type doped amorphous silicon layer 160 on the gate insulating layer 140 facing the gate electrode 125.

Next, as shown in FIGS. 8A to 8B, after the conductive films are stacked, the plurality of data lines 171 and the plurality of drain electrodes 175 crossing the gate lines 121 are patterned by a photolithography process using a mask. To form. Each data line 171 includes a source electrode 173 extending to the upper portion of the doped amorphous silicon layer 160. The drain electrode 175 is separated from the data line 171 and faces the source electrode 173 around the gate electrode 123.

Subsequently, portions of the doped amorphous silicon layer 160 that are not covered by the data line 171 and the drain electrode 175 are removed, and each island-shaped doped amorphous silicon layer 160 is centered on the gate electrode 123. The two resistive contact layers 163 and 165 are separated while exposing a portion of the island-like semiconductor layer 150 below. Subsequently, in order to stabilize the exposed part surface of the semiconductor layer 150, it is preferable to perform oxygen plasma.

Next, as shown in FIGS. 9A and 9B, the lower passivation layer 180 is formed by stacking an insulating material such as an organic material or silicon nitride having a low dielectric constant and excellent planarization characteristics. Subsequently, the photolithography pattern is patterned by dry etching together with the gate insulating layer 140 to form an end portion 125 of the gate line 121, a drain electrode 175, and an end portion of the data line 171. A plurality of contact holes 182, 185, 189 exposing 179 are formed.

Next, as shown in FIGS. 10A and 10B, a transparent electrode 901 and a contact hole 182, which are connected to the drain electrode 175 through the contact hole 185 by stacking an ITO or IZO film and performing a patterning using a mask, are formed. Gate contact auxiliary members 192 and data contact auxiliary members 199 respectively connected to the end portion 125 of the gate line 121 and the end portion 179 of the data line 171 through the first and second reference numerals 189, respectively. do.

Next, as shown in FIGS. 3 and 4, a conductive film including aluminum, silver, molybdenum, or the like having a high reflectance is stacked and patterned to form a reflective electrode 902 having a transmission window 196 of the opening. .

Although embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. I can understand that. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

As described above, according to the reflection-transmitting liquid crystal display device according to the present invention, by forming the protective film thickness of the transmissive area smaller than the protective film thickness of the reflective area, the degree of phase retardation experienced by the light displaying the image in each area is uniform. It can be done. In particular, in the electrically controlled birefringent mode liquid crystal display having multiple cell gaps to improve the luminance of the transmission region and the reflection region, an alignment layer light leakage phenomenon and a display are formed by forming a reflective electrode and a corresponding upper protective layer on the pixel. Clearance can be prevented. In addition, the black matrix shields the upper portion of the upper passivation layer in consideration of the rubbing direction of the alignment layer with respect to the color filter substrate, thereby preventing the screening phenomenon or the light leakage phenomenon.

Claims (5)

A protective film having a first thickness corresponding to the transmissive region and having a second thickness thicker than the first thickness corresponding to the reflective region, a common electrode formed on the protective film, and rubbing in the first direction on the common electrode; A color filter substrate having a first alignment layer formed thereon; A liquid crystal layer in substantially contact with the first alignment layer; And A transmissive region formed at a position corresponding to a thin film transistor, a transparent electrode connected to a drain electrode of the thin film transistor to define a pixel region, and a step portion formed on the transparent electrode and where disclination of the liquid crystal layer occurs And a TFT substrate including a reflective electrode defining a reflective region, and a second alignment layer formed on the transparent electrode and the reflective electrode and rubbed in a second direction different from the first direction. According to claim 1, And wherein the first direction is a direction from the thin film transistor toward the reflective region in one pixel. The method of claim 2, The homogeneous orientation is performed by the said 1st alignment film and a 2nd alignment film, The reflection-transmissive liquid crystal display device characterized by the above-mentioned. According to claim 1, And wherein the stepped portion is positioned at a boundary area between the transmission area and the reflection area. The method of claim 4, wherein And the reflective electrode extends from the point corresponding to the stepped portion toward the transmission area by a predetermined length.

Images