Color filter plate and thin film transistor plate for liquid crystal display, and methods for fabricating the plates

A color filter substrate for a liquid crystal display includes a substrate, a black matrix formed on the substrate, and a plurality of color filters formed on the substrate with the black matrix. Each color filter has a flat central portion, and a peripheral portion placed on the black matrix with a thickness smaller than the central portion. A common electrode is formed on the plurality of color filters. A thin film transistor array substrate for the liquid crystal display includes a substrate, a plurality of gate lines formed on the substrate, a plurality of data lines crossing over the gate lines while defining pixel regions, a thin film transistor formed at each pixel region, and a plurality of color filters. Each color filter has a flat central portion, and a peripheral portion placed on the data lines with a thickness smaller than the central portion. Contact holes expose the drain electrodes, and pixel electrodes are connected to the drain electrodes through the contact holes.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a color filter substrate and a thin film transistor array substrate for a liquid crystal display.

(b) Description of the Related Art

Generally, a liquid crystal display has two substrates with electrodes, and a liquid crystal layer sandwiched between the two substrates. Voltages are applied to the electrodes so that the liquid crystal molecules in the liquid crystal layer are re-oriented to thereby control the light transmission. The electrodes may be all formed at one of the substrates. Furthermore, in order to make color expressions on the screen, color filters of red, green and blue may be formed at one of the substrates.

Recently, in the case of monitors or televisions, the thickness of the color filter has been enlarged to enhance the color representation thereof. However, in this case, the periphery of the color filter may involve a stepped difference so large as to change the molecular orientation of the liquid crystal while causing disclination. Furthermore, the periphery of the color filter is liable to be under-cut while causing leakage of light at the black display state, and deteriorating the picture quality.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a liquid crystal display which exhibits improved picture quality while preventing miss-orientation of liquid crystal molecules and leakage of light.

This and other objects may be achieved by a liquid crystal display with a color filter substrate, and a thin film transistor array substrate.

The color filter substrate includes a substrate, a black matrix formed on the substrate, and a plurality of color filters formed on the substrate with the black matrix. Each color filter has a flat central portion, and a peripheral portion placed on the black matrix with a thickness smaller than the central portion. A common electrode is formed on the plurality of color filters.

The neighboring color filters are overlapped with each other over the black matrix. The neighboring color filters are structured such that the peripheral portion of the overlying color filter is overlapped with the peripheral portion of the underlying color filter. Alternatively, the peripheral portion of the overlying color filter may be overlapped with the peripheral portion of the underlying color filter as well as partially with the central portion of the underlying color filter. Furthermore, the neighboring color filters may be spaced apart from each other with a predetermined distance.

In a method of fabricating the color filter substrate, a black matrix is first formed on a substrate. A plurality of color filters are sequentially formed on the substrate with the black matrix. Each color filter has a flat central portion, and a peripheral portion placed on the black matrix with a thickness smaller than the central portion. A common electrode is formed on the plurality of color filters.

The color filters are formed using a mask differentiated in the light transmission while bearing a transparent pattern, an opaque pattern and a semitransparent pattern. The semitransparent pattern of the mask is placed over the peripheral portion of the color filter during the formation of the color filter.

The thin film transistor array substrate includes a substrate, a plurality of gate lines formed on the substrate, a plurality of data lines crossing over the gate lines while defining pixel regions, a thin film transistor formed at each pixel region, and a plurality of color filters. Each color filter has a flat central portion, and a peripheral portion placed on the data lines with a thickness smaller than the central portion. Contact holes expose the drain electrodes, and pixel electrodes are connected to the drain electrodes through the contact holes. The neighboring color filters are overlapped with each other over the data lines.

The neighboring color filters are structured such that the peripheral portion of. the overlying color filter is overlapped with the peripheral portion of the underlying color filter. Alternatively, the neighboring color filters may be structured such that the peripheral portion of the overlying color filter is overlapped with the peripheral portion of the underlying color filter as well as partially with the central portion of the underlying color filter. Furthermore, the neighboring color filters may be spaced apart from each other with a predetermined distance.

In a method of fabricating the thin film transistor array substrate, a substrate is processed such that it has a plurality of gate lines, a plurality of data lines crossing over the gate lines while defining pixel regions, and thin film transistors provided at the pixel regions while being electrically connected to the gate lines and the data lines. A plurality of color filters are formed in a sequential manner such that each color filter has a flat central portion, and a peripheral portion placed on the data lines with a thickness smaller than the central portion. Contact holes are processed such that they expose drain electrodes of the thin film transistors. A plurality of pixel electrodes are processed such that they are connected to the drain electrodes through the contact holes.

The color filters are formed using a mask differentiated in the light transmission while bearing a transparent pattern, an opaque pattern and a semitransparent pattern. The semitransparent pattern of the mask is placed over the peripheral portion of the color filter during the formation of the color filter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of this invention will be explained with reference to the accompanying drawings.

FIG. 1is a liquid crystal display with a color filter substrate according to a preferred embodiment of the present invention, andFIG. 2is a cross sectional view of the liquid crystal display taken along the II-II′ line ofFIG. 1.

In the thin film transistor array substrate, a gate line assembly is formed on a first insulating substrate10with a metallic material such as molybdenum (Mo), a molybdenum-tungsten (MoW) alloy, chrome (Cr), tantalum (Ta), and titanium (Ti). The gate line assembly includes gate lines22proceeding in the horizontal direction, and gate electrodes26connected to the gate lines22as parts of the thin film transistors. The gate line assembly may have a multiple-layered structure where one layer is formed with an aluminum-based conductive material bearing a low resistance, and the other layer with a material bearing a good contact characteristic in relation to other materials.

A gate insulating layer30is formed on the first insulating substrate10with silicon nitride while covering the gate line assembly.

A semiconductor pattern42is formed on the gate insulating layer30with amorphous silicon while corresponding to the gate electrodes26. Ohmic contact patterns55and56are formed on the semiconductor pattern42with amorphous silicon where impurities are doped at high concentration.

A data line assembly is formed on the ohmic contact patterns55and56, and the gate insulating layer30with molybdenum (Mo), a molybdenum-tungsten (MoW),alloy, chrome (Cr), tantalum (Ta), and titanium (Ti). The data line assembly includes data lines62crossing over the gate lines22while defining pixel regions, source electrodes65protruded from the data lines62while contacting the one-sided ohmic contact pattern55, and drain electrodes66contacting -the, opposite-sided ohmic contact pattern56while being separated from the source electrodes65around the gate electrodes26.

The data line assembly may have a multiple-layered structure where one layer is formed with an aluminum-based conductive material bearing a low resistance, and the other layer with a material bearing a good contact characteristic in relation to other materials.

A protective layer70is formed on the gate insulating layer30with an insulating material such as silicon nitride while covering the data line assembly and the semiconductor pattern42.

Contact holes72are formed at the protective layer70while exposing the drain electrodes66. Pixel electrodes82are formed on the protective layer70such that they are connected to the drain electrodes66through the contact holes72.

In the color filter substrate, a black matrix210is formed on a second insulating substrate200such that it is overlapped with the gate lines22, the data lines62and the semiconductor pattern42of the thin film transistor array substrate while exposing the internal area of the pixel electrode82.

Stripe-shaped color filters of R, G and B each with a predetermined width are alternately formed on the second insulating substrate200with the black matrix210.

Each color filter is patterned to bear a flat central portion, and a peripheral -portion positioned on the black matrix210with a thickness-smaller than the central portion.

The peripheral portion of the color filter gradually slopes down. The peripheral portions of the neighboring color filters are overlapped with each other over the black matrix210. The difference t1in height between the overlapped peripheral portion H1of the color filter with a smallest thickness and the central portion thereof should be established to be ½ or less of the thickness of the central portion of the color filter to reduce the stepped difference of the color filter.

In the above structure, the step coverage characteristic of the layers covering the color filters to be processed later can be enhanced, and the resulting color filter substrate can be flattened while preventing miss-orientation of the liquid crystal molecules.

A common electrode230is formed on the color filters with ITO or IZO while covering the latter.

The steps of fabricating the color filter substrate will be now explained with reference toFIGS. 3 to 7.

As shown inFIG. 3, a metallic layer based on chrome or a chrome alloy is deposited onto an insulating substrate200, and processed through photolithography to thereby form a black matrix210. The black matrix210may bear a single or double-layered structure. Furthermore, the black matrix210may be formed with a black organic insulating material.

Thereafter, red color filters R are formed on the insulating substrate200with the black matrix210. The central portion R1of each color filter R is formed with a flat shape, and the peripheral portions thereof R2and R3are placed on the black matrix210with a thickness smaller than the central portion R1.

The color filters R may be formed through one photolithography process based on a mask differentiated in the light transmission. This process will be now explained with reference toFIG. 4.

A negative photosensitive organic film221of red color is coated onto the insulating substrate200with the black matrix210, and exposed to light using a mask M differentiated in the light transmission.

The mask M has a transparent pattern M1, an opaque pattern M3, and a semitransparent pattern M2. The semitransparent pattern M2of the mask M may be formed with a slit or lattice pattern, or a semitransparent film. In the case of the slit pattern, it is preferable that the slit width should be smaller than the light decomposition capacity of the light-exposing device. In the case of the semitransparent film, the mask M may be formed with thin films differentiated in the light transmission, or the thickness.

When the photosensitive organic film22is exposed to light using the mask M, the portion A thereof directly exposed to the light is completely hardened, the portion B thereof corresponding to the semitransparent pattern M2is hardened by a predetermined thickness, and the portion C thereof intercepted by the opaque pattern M3is not hardened. When the light exposing time is too long, the organic film221is liable to be completely hardened.

When the selectively light-exposed organic film is developed, as shown inFIG. 3, only the hardened portions thereof are left over. At this time, the portion B of the organic film corresponding to the semitransparent pattern M2bears a thickness smaller than the portion A thereof corresponding to the transparent pattern M1. The A portion of the organic film becomes to be the central portion R1of the red color filter, and the B portion thereof to be the peripheral portions R2and R3while bearing a thickness smaller than the central portion R1.

When the developed organic film is heat-treated, the peripheral portions R2and R3of the color filter R become to bear a smooth slope-down profile.

In order to obtain a uniform color representation, it is preferable that the peripheral color filter portions R2and R3should be placed only over the black matrix210. For this purpose, the semitransparent mask pattern M2is established to bear a width smaller than the pattern with of the black matrix210while being positioned corresponding to the black matrix210through aligning the mask M and the substrate200.

Thereafter, as shown inFIG. 5, green color filters G are formed at the substrate200such that each green color filter G has a flat central portion G1, and a peripheral portion G2placed on the black matrix210with a thickness smaller than the central portion G1.

For that purpose, a negative photosensitive film of green color is coated onto the entire surface of the substrate, exposed to light, and developed as with the formation of the red color filters R. In this process, the peripheral portion G2of the green color filter G is overlapped with the peripheral portion R2of the neighboring red color filter R over the black matrix210.

It is required that the end of the semitransparent pattern M2of the mask corresponding to the end of the peripheral portion G2of the green color filter G should be placed within the peripheral portion R2of the neighboring red color filter R. When the light-exposing and developing operations are made under such a condition, a color filter portion H1bearing the smallest thickness is existent at the overlapping area of the red and green color filters. The difference in height t1between the H1portion of the color filter and the flat central portion of thereof is preferably controlled to be ½ or less of the thickness of the central color filter portion.

In this way, the stepped difference of the color filter is reduced, and the layers covering the color filters to be processed later become to bear improved step coverage characteristic while flattening the resulting substrate.

Thereafter, as shown inFIG. 6, blue color filters B are formed in the same way as with the formation of the green color filters G such that the central portion thereof is flat, and the peripheral portion thereof has a thickness smaller than the central portion while being placed over the black matrix210.

For that purpose, a negative photosensitive film of blue color is coated onto the entire surface of the substrate, exposed to light, and developed. Then the subsequent processing steps are made with respect to the photosensitive film. In this way, the color filter substrate is completed.

Meanwhile, as shown inFIG. 7, when the green color filter G is formed after the formation of the red color filters R, the end of the semitransparent mask pattern M2corresponding to the end of the peripheral portion G2of the green color filter G may be placed at the central portion R1of the neighboring red color filter R. When the light-exposing and developing operations are, made, the peripheral portion G2of the green color filter G covers the neighboring red color filter R. In this case, a color filter layer portion H2with a largest thickness is existent at the overlapping area of the R and G color filters. The difference in height t2between the color filter layer portion H2and the central color filter portion is preferably established to be ½ or less of the thickness of the central color filter portion.

Blue color filters are subsequently formed at the substrate in the same way as with the formation of the green color filters G.

In the subsequent process, when an alignment film is coated, and rubbed by way of a rubbing roll wound with a rubbing cloth, alignment failure is liable to be made with the stepped difference due to the overlapping of the neighboring color filters. In order to prevent such an alignment failure, the slightly stepped portion is preferably located in the rubbing direction standing with the side of entrance of the rubbing roll.

As the peripheral portion G2of the green color filter G covering the peripheral portion R2of the red color filter R bears a slow upward slope R, the rubbing is preferably established to be directed toward the slope R.

Meanwhile, the blue color filter may cover another peripheral portion R3of the red color filter R. In this case, the stepped difference due to the overlapping of the blue color filter and the red color filter is so small as to not cause the rubbing failure.

Furthermore, as shown inFIG. 8, the mask and the substrate may be aligned such that when the green color filters G are formed after the formation of the red color filters R, the end of the semitransparent mask pattern M2corresponding to the end of the peripheral portion G2of the green color filter G does not reach the peripheral portion R1of the neighboring red color filter R. In this case the green color filter G is spaced apart from the red color filter R with a predetermined distance. In order to reduce the stepped difference, the peripheral portions R2and G2of the red and green color filters R and G are established to bear an inclination degree of 40° or less. For this purpose, it is required that the light transmission of the semitransparent mask pattern M2should be controlled in an appropriate manner. For instance, one or two slits with a width of 3-4 μm may be formed within the mask area with a width of 10 μm.

Blue color filters are subsequently formed in the same way as with the formation of the green color filters.

Alternatively, a positive photosensitive organic film may be used to form the color filters. In this case, the transparent pattern and the opaque pattern are formed in the reverse order. Furthermore, the sequence of formation of red, green and blue color filters may be changed in various manners.

FIG. 9is a plan view of a thin film transistor array substrate for a liquid crystal display according to another preferred embodiment of the present invention, andFIG. 10is a cross sectional view of the thin film transistor array substrate taken along the X-X′ line ofFIG. 9.

A gate line assembly is formed on an insulating substrate10with a metallic material such as molybdenum (Mo), a molybdenum-tungsten (MoW) alloy, chrome (Cr), tantalum (Ta), and titanium (Ti). The gate line assembly includes gate lines22proceeding in the horizontal direction and gate electrodes26connected to the gate lines22as parts of thin film transistors. The gate line assembly may have a multiple-layered structure where one layer is formed with an aluminum-based conductive material bearing a low resistance, and the other layer with a material bearing a good contact characteristic in relation to other materials.

A gate insulating layer30is formed on the insulating substrate10with silicon nitride while covering the gate line assembly.

A semiconductor pattern42is formed on the gate insulating layer30with amorphous silicon while corresponding to the gate electrodes26. Ohmic contact patterns55and56are formed on the semiconductor pattern42with amorphous silicon where impurities are doped at high concentration.

A data line assembly is formed on the ohmic contact patterns55and56, and the gate insulating layer30with a metallic material such as molybdenum (Mo), a molybdenum-tungsten (MoW) alloy, chrome (Cr), tantalum (Ta), and titanium (Ti). The data line assembly includes data lines62crossing over the gate lines22while defining pixel regions, source electrodes65protruded from the data lines62while contacting the one-sided ohmic contact pattern55, and drain electrodes66contacting the opposite-sided ohmic contact pattern56while being separated from the source electrodes65around the gate electrodes26.

The data line assembly may have a multiple-layered structure where one layer is formed with an aluminum-based conductive material bearing a low resistance, and the other layer with a material bearing a good contact characteristic in relation to other materials.

Color filters of red R, green G and blue B are formed on the gate insulating layer30with colored organic materials while covering the data line assembly and the semiconductor pattern42.

The RGB color filters are repeatedly formed each with a vertical stripe in an alternate manner while bearing a predetermined width. Each color filter has a flat central portion and a peripheral portion with a thickness smaller than the central portion. The peripheral portions of the neighboring color filters are overlapped with each other over the data line62. The overlapped portion of the color filter has a smallest thickness. It is preferable that the difference in thickness between the central portion of the color filter and the overlapped portion thereof should be established by ½ or less of the central portion, thereby reducing the stepped difference of the color filter.

Alternatively, it is possible that the peripheral portion of the color filter partially covers the central portion of the neighboring color filter. In this case, the color filter layer bears a largest thickness at the overlapping area. It is preferable that the difference in thickness between the central portion of the color filter and the largest thickness portion of the color filter layer should be established to be ½ or less of the central portion.

Furthermore, the RGB color filters may be spaced apart from each other with a predetermined distance over the data lines62. In this case, it is preferable that the peripheral portion of the color filter has an inclination angle of 40° or less.

When the stepped difference of the color filter is reduced in such a way, the step coverage characteristic of the layers covering the color filters to be processed later can be improved while resulting in flattening of the substrate.

The RGB color filters72are provided with contact holes72exposing the drain electrodes66. Pixel electrodes82are formed on the color filters such that they are connected to the drain electrodes66through the contact holes72.

The steps of fabricating the thin film transistor array substrate will be now explained with reference toFIGS. 11A to 13B.

As shown inFIGS. 11A and 11B, a metallic layer is deposited onto a substrate10, and patterned through photolithography to thereby form a gate line assembly. The gate line assembly includes gate lines22, and gate electrodes26.

Thereafter, a gate insulating layer30, a semiconductor layer and an impurities-doped semiconductor layer are sequentially deposited onto the substrate10. The impurities-doped semiconductor layer and the semiconductor layer are etched through photolithography to thereby form an island-shaped semiconductor pattern42, and an ohmic contact layer52.

As shown inFIGS. 12A and 12B, a metallic layer is deposited onto the substrate10, and patterned through photolithography to thereby form a data line assembly. The data line assembly includes data lines62, source electrodes65, and drain electrodes66.

Thereafter, the island-shaped ohmic contact layer52is etched using the source and the drain electrodes65and66as a mask to thereby form a first ohmic contact pattern55contacting the source electrodes65, and a second ohmic contact pattern56contacting the drain electrodes66.

As shown inFIGS. 13A and 13B, RGB color filters are sequentially formed on the data line assembly, the semiconductor pattern, and the gate insulating layer30, It is preferable that the overlapping of the neighboring color filters should be made over the data lines63.

As shown inFIGS. 9 and 10, the RGB color filters are patterned through photolithography to thereby form contact holes72exposing the drain electrodes66.

Thereafter, a transparent conductive layer is deposited onto the color filters and the drain electrodes66with ITO or IZO. The transparent conductive layer is patterned through photolithography to thereby form pixel electrodes82. The pixel electrodes82are connected to the drain electrodes66through the contact holes72.

The subsequent processing steps are then made to thereby complete a thin film transistor array substrate.

As described above, the peripheral portion of each color filter is reduced in thickness while flattening the substrate, thereby preventing miss-alignment of the liquid crystal molecules and leakage of light occurring due to the stepped difference of the color filter, thereby improving the picture quality.