KR100286978B1 - Reflective typed LCD and method for fabricating the same - Google Patents

Abstract

The present invention discloses a reflective liquid crystal display and a method of manufacturing the same that can improve the reflection efficiency. In the reflective liquid crystal display device of the present invention, the projections of the reflective electrodes are arranged in an irregular polygon, and the width between the projections is constant. In this way, the projections are irregular in size in each direction, and the flat area is reduced as much as possible, so that the light efficiency is high and the unevenness of the orientation caused by the deep recesses is minimized.

Description

Reflective liquid crystal display and manufacturing method therefor {Reflective typed LCD and method for fabricating the same}

The present invention relates to a reflective liquid crystal display device, and more particularly, to a reflective liquid crystal display device having a reflective electrode having an uneven structure and a manufacturing method thereof.

Cathode ray tubes (CRTs) employed in displays such as televisions and computer monitors are limited in their installation and movement because of their large weight, device space, and power consumption. In order to compensate for these disadvantages, display panels using flat panel panels, such as liquid crystal displays using liquid crystals, plasma display panels (PDPs) using surface discharge, and displays using electroluminescence, have been proposed and are widely used.

Among the flat panel displays, the liquid crystal display has low power consumption, low voltage operation, high definition, full color display, close to the cathode ray tube, and other electronic devices due to the ease of manufacturing process. It is applied in the field.

Such liquid crystal displays include a projection type liquid crystal display using an external light source and a reflection type liquid crystal display using natural light instead of an external light source.

The reflective liquid crystal display has the advantages of low power consumption, a thin, light weight requiring no backlight device, and excellent display outdoors. Because of this feature, portable devices have the best conditions.

However, since the display screen of the current reflective liquid crystal display is dark and does not support high-definition display and color display, it has been used only in extremely low price products requiring only simple pattern display such as numbers among portable devices.

In order to use the reflective liquid crystal display in a portable information device having a function such as a Document Viewer, Internet Viewer, etc., not only the improvement of reflection luminance but also high definition and colorization are required.

In order to make a monochromatic display liquid crystal display mainly displaying characters in a portable information device easy to see, improvement in reflection brightness and high definition are required, and an active matrix substrate including a switching element such as a thin film transistor is required for the realization. However, since the displayable information is limited in a monochromatic display device, the price setting of the entire device is inevitably low, and the adoption of a thin film transistor having a high panel cost is fatal for a monochromatic display device.

In addition, in the future, the coloration of the portable information device is essential, and thus, the product life of the monochromatic display device may be short. Accordingly, the development of the reflective liquid crystal display is in progress in the coloration direction.

However, despite the large development in both panel technology and the market, reflective color liquid crystals have not been practically used until now. The reason is the lack of performance in terms of brightness, contrast and response speed.

The improvement of brightness is realized by the combination of two techniques, namely, the technique of increasing the reflection efficiency of the reflective electrode and the ultra-high opening ratio technique. A technique for improving the reflection efficiency has already been used in the conventional guest host liquid crystal, and a technique for maximizing the reflection efficiency by making fine irregularities in the electrode provided with the reflection function is disclosed in US Patent No. 5,610,741.

1 is a plan view schematically showing the surface of a reflective electrode in the above-described reflective type liquid crystal display.

Referring to FIG. 1, the reflective electrode 10 has a structure in which protruding hemispherical micro lenses are irregularly arranged.

However, in the above prior art, since the microlenses 2 are hemispherical, the spaces 4 between the microlenses differ in size from each other depending on their position. This difference in the size of each space 4 appears as a height difference between the micro lenses, resulting in non-uniformity of reflectance in different areas. Such nonuniformity of reflectance causes nonuniformity in the alignment of liquid crystal molecules, and thus, there is a disadvantage in that contrast ratio of black and white is inferior in expressing an image.

In addition, since the size of the space between the hemispherical micro lens and the lens is different depending on the position, it is difficult to form an accurate lens such as a design value.

Accordingly, one object of the present invention is to increase the contrast ratio while realizing a more efficient reflectance than the prior art.

Another object of the present invention is to form the microlens of the reflective electrode exactly as the design value.

1 is a plan view of a reflective electrode of a conventional reflective liquid crystal display device.

2 is a schematic partial cross-sectional view of a typical reflective liquid crystal display device.

3 is a partial plan view of a reflective electrode according to an embodiment of the present invention.

4 is a cross-sectional view taken along line II ′ of FIG. 3.

5 is a partial plan view of a reflective electrode according to another embodiment of the present invention.

FIG. 6 is a cross-sectional view taken along the line II-II ′ of FIG. 5.

7A and 7B are graphs of reflectances measured in a vertical direction and a horizontal direction in a reflection type liquid crystal display according to an exemplary embodiment of the present invention.

8A is a view for explaining a manufacturing process of a photo mask for forming the reflective electrode of FIG.

8B is a view for explaining a manufacturing process of the photomask for forming the reflective electrode of FIG.

FIG. 9A is a partial cross-sectional view of the photomask of FIG. 8A taken along an arbitrary direction; FIG.

FIG. 9B is a partial cross-sectional view of the photomask of FIG. 8B cut in an arbitrary direction; FIG.

10 is a partial plan view of a thin film transistor substrate of a reflective liquid crystal display device according to still another embodiment of the present invention;

11A through 11C are flowcharts illustrating a process of manufacturing the reflective thin film transistor substrate of FIG. 10.

In order to achieve the above object, in the reflective liquid crystal display device of the present invention, the projections of the reflective electrodes are arranged in an irregular polygon, and the width between the projections is constant. In this way, the projections are irregular in size in each direction, and the flat area is reduced as much as possible, so that the light efficiency is high and the unevenness of the orientation caused by the deep recesses is minimized.

Optionally, by placing a recess recessed to a predetermined depth from the surface of the projection, the reflectance at the front is increased.

According to another aspect of the invention, in the method of manufacturing a reflective liquid crystal display device, first, a photosensitive organic insulating film is coated on the entire surface of the insulating substrate on which the switching element is formed. The surface of the organic insulating film has an irregular polygonal projection, and the organic insulating film is first exposed so that the width of the valley between the projections is constant. Next, the predetermined portion of the organic insulating film is secondarily exposed so that the drain electrode of the switching element is exposed. The first and second exposed portions are developed at once. The developed organic insulating film is reflowed at a predetermined temperature. Next, a reflective metal such as aluminum is deposited on the entire surface and patterned to form a reflective electrode having the same uneven structure as that of the organic insulating film.

Other objects, features and advantages of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

2 is a schematic cross-sectional view of a reflective thin film transistor liquid crystal display device.

Referring to FIG. 2, the reflective liquid crystal display includes a first pixel having a pixel electrode (hereinafter referred to as a reflective electrode) 118 composed of a thin film transistor 114 serving as a switching element and a reflecting plate having a shape of a protrusion on an inner surface thereof. The insulating substrate 112, the retardation plate 146, and the polarizing plate 148 are sequentially attached to the outer surface, and on the inner surface side, the black matrix 134, the color filters 136 of red, green, and blue, and the transparent common electrode ( The liquid crystal material 144 is interposed between the light-transmissive second insulating substrate 132 made of 138 at regular intervals using the spacer 142.

On the inner surface of the first insulating substrate 112 including the reflective electrode 118 and the inner surface of the second insulating substrate 132 including the common electrode, alignment layers 120 and 140 for alignment of liquid crystal are disposed, respectively. .

This invention relates to the structure and shape of the reflective electrode 118 especially in the said structure.

<Example 1>

3 is a partial plan view of the reflective electrode 118 of FIG. 2.

As shown in FIG. 3, the reflective electrode 118 has a polygonal structure in which individual closed curves are different in shape and size. For example, each closed curve 118a, 118c may be composed of at least two polygons having different numbers of angles. Each closed curve 118a, 118c has a protruding structure, and each closed curve 118a, 118c, that is, the space 118b between the projections corresponds to the bone. Preferably, each valley 118b has a constant line width that falls within about 50% of the average distance between the ridges of the protrusions 118a and 118c. Preferably, the average of the distance between the ridges (peaks) of the protrusions 118a and 118c and the adjacent ridge is in the range of about 8-30 μm, for example, when the average distance is about 10 μm, the line width of the bone is about It has a range of 1 to 5 μm.

4 is a cross-sectional view taken along the line II ′ of FIG. 3, showing characteristics of the first embodiment.

As shown in FIG. 4, the reflective electrode 118 of the present invention is made of metal, particularly aluminum having high reflectance. In order to increase the light efficiency, the reflective electrode 118 has a protrusion shape in which a plurality of polygons are irregularly arranged, and is formed on the organic insulating film 116 having the same structure. That is, the reflective electrode 118 has a shape corresponding to that of the organic insulating film 116.

Preferably, the distances W, W ', W' between the bones 118b of each closed curve in the selection direction are different from each other. The heights of the projections 118a and 118c are in proportional relationship depending on the distance between the valleys in the adjacent valleys 118b but the height of the valleys is configured substantially the same from the surface of the substrate 112.

As shown in Fig. 4, the present embodiment does not have such a feature in a specific direction, but also in the cross-sectional view in any direction in Fig. 3. For example, a cross section similar to FIG. 4 is also obtained in a cross-sectional view (not shown) cut along the line II-II 'of FIG. 3.

<Example 2>

In the second embodiment of the present invention, in order to increase the reflectance at the front in the first embodiment, a concave auxiliary shape is formed at the center of the closed curve as shown in FIG.

FIG. 5 is a plan view of a second embodiment, and FIG. 6 is a cross-sectional view taken along line III-III ′ of FIG. 5. 3 and 4, the reflective electrode 218 of the second embodiment is further formed with small craters 218d and 218e recessed to a predetermined depth from the ridges of the protrusions 218a and 218c.

The craters 218d and 218e may be about the same as or different from the closed curve of the polygon around their vertices, but about 30% of the diameter of the projections 218a and 218c.

7A and 7B are graphs showing the change of reflectance according to the reflection angle when the structure of the reflecting electrode is different, and FIG. 7A shows the change of reflectance in the vertical direction and FIG. 7B shows the change of reflectance in the horizontal direction. . Here, the measured reflectance is a change value of the reflectance from the front of the screen (that is, 0 degrees) to 50 degrees when the incident angle is -30 degrees.

As shown in Fig. 7A, the structure of the reflective electrode is circular as shown in Fig. 1, the shape of the polygon shown in Fig. 3, and the crater in the center of the projection of the shape of the polygon shown in Fig. 5 In the case of forming, in the range of 0 degrees to about 23 degrees, and in the range of about 37 degrees to 50 degrees, the crater is formed at the center of the polygonal reflective electrode shown in FIG. 3 and the projection of the polygonal shape shown in FIG. Compared with the circular structure of FIG. 1, the reflective electrode has a very high vertical reflectance.

As shown in FIG. 7B, the horizontal reflectance is a reflection electrode of the polygon shown in FIG. 3 and projections of the polygonal shape shown in FIG. 5 in the range of 0 degree to about 18 degree and about 38 degree to about 50 degree. The reflective electrode with the crater formed at the center is much higher than the circular structure of FIG.

In addition, the above measurement results, in the vertical reflectance, when viewed from the front, it can be seen that the polygonal structure with the crater is higher than the polygonal structure without the crater. Also, it shows that the polygonal structure with the crater has less change in reflectance at the measurement angle than the polygonal structure without the crater.

On the other hand, in addition to the above-described reflectance, the contrast ratio is also an important factor in determining display quality.

Table 1 below shows an incident angle of −30 degrees in a reflective liquid crystal display employing a circular reflective electrode shown in FIG. 1 and a reflective electrode having a polygonal structure shown in FIG. As a result of the measurement, it is shown that the reflective electrode of the polygonal structure of the present invention has a much higher contrast ratio than the conventional circular structure.

division reflectivity(%) Contrast Original lens structure (circle) 20 2: 1 New lens structure (polygon) 30 15: 1

<Example 3>

Next, a design method capable of designing a mask to form the structure of the reflective electrodes described in the first and second embodiments will be described.

First, define the pixel area, and use the computer's random function generator to determine the coordinates (x, y) of each point with one side of it as the x-axis and the other side intersecting the x-axis as the y-axis. To generate. In this case, the average distance of neighboring coordinates is determined by how many coordinates per unit area. For example, if the distance between vertices is set to 10 μm on average, approximately 14,000 coordinate values or more per mm ² are obtained.

As shown in Fig. 8A, polygons 152 are formed by connecting adjacent points at the obtained coordinate values, and drawing a straight line in a direction perpendicular to the midpoint. Preferably, each polygon 152 has a different shape and size. Lines corresponding to the valleys 154 are drawn on either side of each side of each polygon in a width of about 1 to 5 μm, that is, within 50% of the average distance between the vertices of the polygon.

As shown in FIG. 8A, when the polygonal pattern and the valley are designed, a mask is formed as the designed pattern. That is, for example, when the photosensitive organic insulating layer is a positive type, a light shielding area for blocking incident light is formed in a portion corresponding to the polygonal pattern 152, and a light transmitting region for transmitting incident light in a portion corresponding to the valley 152. To form a mask 150. On the other hand, for exposing the negative photosensitive organic insulating film, the light transmitting area and the light blocking area are switched to each other.

In addition, when the crater is placed in the middle of the projection, the polygon pattern and the valley pattern are designed in the same manner as described with reference to FIG. 8A, and as shown in FIG. Although different, draw a polygonal crater 256 about 30% of the diameter.

Based on the above data, portions corresponding to the valleys 218b and the craters 218e of the reflective electrode 218 shown in FIGS. 5 and 6 become light transmitting regions, and portions corresponding to the projections 218a and 218c. The photomask 250 which becomes this light shielding area is produced.

9A and 9B are cross-sectional views of the photomask produced by the above method.

9A is a photomask 150 for forming a reflective electrode having a polygonal structure without craters, and is used to expose an organic insulating film having positive photoresist characteristics formed under the reflective electrode.

In FIG. 9A, reference numeral 151 denotes a quartz substrate, reference numeral 152 corresponds to a polygonal region as a light shielding region for blocking incident light, and reference numeral 154 corresponds to a valley region as a light transmitting region for transmitting incident light.

If the negative photoresist component is an organic insulating layer, when the same shape as in FIG. 9A is patterned, a portion formed in the opposite direction to transmit light corresponds to a protrusion, and a region that does not transmit light corresponds to a valley.

FIG. 9B is a photomask 250 in the case where a concave portion in the form of a crater is provided in the projection, and is used for exposure of an organic insulating film having positive photoresist characteristics. Of course, when a negative photoresist film is used, it forms in a reversed phase.

<Example 4>

10 is a schematic partial plan view of a reflective liquid crystal display using a thin film transistor as a switching element, showing a unit pixel area and a peripheral portion thereof.

Referring to FIG. 10, a gate line 103a arranged in a row direction and a gate electrode 103 vertically branched from the gate line 103a are disposed on an insulating substrate. The storage electrode 162 is spaced apart from the gate line 103a by a predetermined distance and disposed on the insulating substrate to be arranged in parallel with the gate line 103a.

The semiconductor film pattern 106 made of amorphous silicon or the like is disposed on the gate electrode 103. The semiconductor film pattern 107 is selectively disposed in a portion where the gate line 103a and the data line 111 to be described later intersect. The semiconductor film pattern 107 serves to prevent an open defect of the data line 111 or a short defect between the gate line 103a and the data line 111.

Although not shown in FIG. 10, a gate insulating film made of, for example, a silicon nitride film is interposed between the gate electrode and the semiconductor film pattern 106 for insulation.

On the gate insulating film, the data line 111 is disposed to be orthogonal to the gate line 103a. The source electrode 110a branched at a predetermined position of the data line 111 extends to one side edge of the semiconductor film pattern 106. It extends to the other edge of the semiconductor film pattern 106 so as to face the source electrode 110a at a predetermined interval.

Although not shown in FIG. 10, an ohmic contact layer doped with a high concentration of n-type impurities is interposed between the source electrode 110a and the semiconductor film pattern 106 and between the drain electrode 110b and the semiconductor film pattern. .

The gate electrode 103, the semiconductor film pattern 106, the source electrode 110a, and the drain electrode 110b constitute a thin film transistor.

An insulating film (not shown) having a polygonal uneven structure, preferably an organic insulating film having a function of a photosensitive film, is disposed on the entire surface of the resultant including the thin film transistor and the gate insulating film. A reflective electrode 118 having a polygonal uneven structure is disposed on the organic insulating layer as illustrated in FIGS. 3 to 6. In FIG. 10, reference numeral 118BL denotes a boundary line of the reflective electrode.

The reflective electrode 118 is electrically contacted with the drain electrode 110b through the contact hole 164 formed in the organic insulating layer.

In FIG. 10, the reflective electrode 118 extends from the unit pixel region defined as the region where the pair of gate lines 103a and the pair of data lines 111 intersect to the adjacent unit pixel region. This is an option for increasing the reflectance of the reflective electrode, and the boundary region can be changed in various ways. For example, the reflective electrode may be formed in the unit pixel region except for the thin film transistor portion.

A manufacturing process of the thin film transistor substrate of the reflective liquid crystal display shown in FIG. 10 will be described with reference to FIGS. 11A to 11C. FIG. 11C is a cross-sectional view taken along the line IV-IV 'of FIG. 10.

10 and 11A, the gate electrode 103 and the gate line 103a are formed by patterning a metal film on an insulating substrate 112, for example, a glass substrate. In this case, the storage electrode pattern 162 is formed together. The gate insulating layer 104 is formed on the entire surface of the substrate 112 including the gate electrode 103, the gate line 103a, and the storage electrode pattern 162. As the gate insulating film 104, a silicon nitride film (Si _x N _y , x, y is an integer) or a silicon oxide film (SiO ₂ ) is used, and these are formed by a plasma chemical vapor deposition method.

Next, an ohmic made of a semiconductor layer 106 made of an amorphous silicon layer on the gate insulating film 104 and an amorphous silicon layer doped with a high concentration of n-type impurities such as phosphorus so that one end thereof is positioned at the gate electrode 103. The contact layer 108 is formed. In FIG. 11A, the semiconductor layer 106 and the ohmic contact layer 108 extend to both sides of the gate electrode 103, but, alternatively, they may be formed only on the top of the gate electrode.

Next, the source electrode 110a, the drain electrode 110b, and the data line 111 are formed of metal so as to be in electrical contact with the ohmic contact layer 108. Through the above steps, a thin film transistor is formed.

Next, referring to FIG. 11B, an organic insulating film is formed on the resultant substrate on which the thin film transistor is formed by coating or the like with a thickness of 1 to 3 μm, and the protrusions for forming the polygonal protrusions shown in FIGS. A primary photoexposure process is performed. The photomask shown in FIGS. 9A and 9B is used for the primary exposure process.

The second exposure is performed through a separate photo mask (not shown) to form a contact hole for connecting the reflective electrode 118 and the drain electrode 110b. Next, the first exposed portion and the second exposed portion are developed once. Next, the contact hole 264 and the projection of the polygonal structure are formed by heating the developed organic insulating film at a predetermined temperature to flow.

Referring to FIG. 11C, a metal layer such as aluminum is deposited on the entire surface, and then patterned by a general photolithography process to form a reflective electrode 118 having a polygonal pattern of an uneven structure.

Although not shown in the drawing, an alignment layer for pretilting liquid crystal molecules at a selected angle is coated on the entire surface of the organic insulating layer 116 including the reflective electrode 118.

Hereinafter, the operation of the reflective liquid crystal display device having the above-described configuration will be described with reference to FIG. 2.

In the off state where no voltage is applied to the liquid crystal, the light incident from the upper portion of the color filter substrate is converted into linearly polarized light while passing through the polarizing plate 148, and left circularly polarized light while passing through the phase difference plate 146 again. Becomes At this time, the polarized light 144 changes to linearly polarized light while passing through the liquid crystal layer and reaches the reflective electrode 118. The reflected linearly polarized light is changed to the left circle (right) polarized light while passing through the liquid crystal layer 144 again, and is converted to linearly polarized light at the time of incidence while passing through the phase difference plate 146 to pass through the polarizer 148 and is in a white state. Indicates.

On the contrary, when a voltage is applied to the liquid crystal 144, the left circle (right) polarization entering the liquid crystal layer 144 does not feel birefringence and passes through the liquid crystal layer as it is. Will change. The reversed right circularly polarized light is converted into linearly polarized light which is rotated 90 degrees from the time of incidence while passing through the retardation plate, absorbed by the polarizer, and exhibits a dark state.

As described above, the reflective liquid crystal display of the present invention comprises a microlens of the reflective electrode of the reflective electrode composed of a plurality of protrusions having an irregular polygonal structure, and the width of the valley between the protrusions is made constant so that the different areas are different. It prevents the nonuniformity of the orientation of liquid crystal molecules in. As a result, in expressing an image, not only the reflectance is improved but also the contrast ratio of black and white is improved.

In addition, in the manufacturing method of the reflective liquid crystal display device of the present invention, since the spatial size between the hemispherical microlens and the lens is almost the same according to the position, accurate lens formation such as a design value is possible.

Meanwhile, although specific embodiments of the present invention have been described and illustrated herein, modifications will be made by those skilled in the art from the detailed description of the present invention. Accordingly, the following claims are to be embraced as including such variations and modifications without departing from the spirit and spirit of the invention.

Claims (11)

A transparent first insulating substrate having a transparent electrode on an inner surface thereof; A second electrode including a reflective electrode including a plurality of protrusions having a valley and a ridge, wherein a plurality of lines formed by neighboring valleys of the protrusions and a line connecting boundary lines of the reflective electrode define a plurality of closed closed curve regions; Insulating substrate; A liquid crystal layer interposed between the first insulating substrate and the second insulating substrate and having an arrangement changed according to an electric field applied to the transparent electrode and the reflective electrode; And an electric field generating means for generating an electric field between the transparent electrode and the reflective electrode. The reflective liquid crystal display of claim 1, wherein the closed curve is a polygon. The reflective liquid crystal display device according to claim 2, wherein the polygon comprises at least two polygons having at least angles different from each other. The reflective liquid crystal display device according to claim 1, wherein the reflective electrode further comprises a recess recessed to a predetermined depth from the surface of the floor. The reflective liquid crystal display device according to claim 1, wherein the average of the distances of the vertices of neighboring floors from the vertex of each floor is about 8 to 30 탆. The reflective liquid crystal display device according to claim 1, wherein the line width of the valleys does not exceed 50% of the distance between the vertices of neighboring floors. The reflective liquid crystal display device according to claim 1, wherein the heights of the valleys are substantially the same from the surface of the second insulating substrate, and the heights of the floors are different from each other. The reflective liquid crystal display device according to claim 1, wherein the heights of the floors are substantially the same from the surface of the second insulating substrate, and the heights of the valleys are different from each other. Applying a photosensitive organic insulating film to a predetermined thickness on an entire surface of an insulating substrate on which a switching element including a source, a drain, and a gate electrode is formed; Firstly exposing the organic insulating film to a depth smaller than the thickness of the organic insulating film by using a mask having a light blocking area having an irregular polygonal structure and a light transmitting area having a predetermined width between the light blocking areas; Secondarily exposing a portion of the organic insulating film to expose the drain electrode of the switching element; Developing the first and second exposed portions; Heating and developing the developed organic insulating layer at a predetermined temperature; And And depositing and patterning a reflective metal on the entire surface of the resultant product. The method of manufacturing a reflective liquid crystal display device according to claim 9, wherein the photosensitive organic insulating film has a thickness of about 1 to 3 탆. 10. The method of claim 9, wherein the mask has a light transmitting area at a predetermined portion within the light blocking area.