Color filter substrate and liquid crystal display having the same

This application claims priority to Korean Patent Application No. 2009-109716 filed on Nov. 13, 2009, the contents of which are herein incorporated by reference in its entirety.

1. Technical Field

The present invention relates to a color filter substrate capable of improving a display quality thereof and a liquid crystal display having the color filter substrate.

2. Discussion of the Related Art

In general, a liquid crystal display includes an array substrate, a color filter substrate, a backlight assembly, and a liquid crystal layer disposed between the array substrate and the color filter substrate. The array substrate includes a pixel, the backlight assembly provides a light to the liquid crystal layer, and the color filter substrate includes a color filter through which a white light from the liquid crystal layer is transmitted to allow the white light to have a predetermined color.

As an alternative to a transmissive type color filter as described above, a reflective type color filter used in conjunction with cholesteric liquid crystal has been developed. The reflective color filter reflects light to change a wavelength of the light, so that the light has a desired color. The wavelength of the light reflected by the reflective type color filter is controlled by a pitch of the cholesteric liquid crystal.

Embodiments of the present invention provide a color filter substrate capable of improving a display quality, and a liquid crystal display having the color filter substrate.

According to an embodiment, a color filter substrate includes a base substrate, a non-transmissive layer on the base substrate to absorb light and including concave-convex portions on a surface of the non-transmissive layer, a plurality of color filter layers on the non-transmissive layer and including a cholesteric liquid crystal to change a wavelength of light and reflect the light, and an alignment layer between the non-transmissive layer and the color filter layers to align the cholesteric liquid crystal.

According to an embodiments, a liquid crystal display includes a first base substrate, a second base substrate facing the first base substrate, a liquid crystal layer disposed between the first base substrate and the second base substrate, a non-transmissive layer on the first base substrate to absorb light and including concave-convex portions arranged on a surface of the non-transmissive layer, a plurality of color filter layers on the non-transmissive layer and including a cholesteric liquid crystal to change a wavelength of light and reflect the light, an alignment layer between the non-transmissive layer and the color filter layers to align the cholesteric liquid crystal, a first electrode on the color filter layers, and a second electrode on the second base substrate.

The non-transmissive layer includes convex portions protruded from an upper surface thereof. Further, the alignment layer and the color filter layers sequentially arranged on the non-transmissive layer have a concave-convex shape corresponding to the convex portions. Since the cholesteric liquid crystal of the color filter layers is aligned corresponding to the concave-convex shape of the alignment layer, the wavelength of the light reflected by the cholesteric liquid crystal may be determined by the cholesteric liquid crystal having the same pitch although a viewing angle is changed. Consequently, in the liquid crystal display having a color filter substrate including the color filter layers, the liquid crystal display may prevent deterioration in a display quality, which is caused by the change of the wavelength of the light reflected by the cholesteric liquid crystal as the viewing angle changes.

The embodiments of the present invention will become readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is an enlarged plan view showing part of a color filter substrate according to an exemplary embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along a line I-I′ of FIG. 1 ;

FIG. 3A is an enlarged view showing a first area of FIG. 2 ;

FIG. 3B is an enlarged view showing a second area of FIG. 2 ;

FIG. 3C is an enlarged view showing a third area of FIG. 2 ;

FIG. 4 is a cross-sectional view showing a color filter substrate according to an exemplary embodiment of the present invention;

FIG. 5 is an enlarged plan view showing part of a liquid crystal display according to an exemplary embodiment of the present invention;

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

FIG. 7 is a cross-sectional view taken along a line of FIG. 5 ;

FIG. 8 is an enlarged plan view showing part of a liquid crystal display according to an exemplary embodiment of the present invention;

FIG. 9 is a cross-sectional view taken along a line IV-IV′ of FIG. 8 ; and

FIG. 10 is a cross-sectional view taken along a line V-V′ of FIG. 8 .

It will be understood that when an element or layer is referred to as being “on”, “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. Like numbers may refer to like elements throughout the drawings and the specification.

FIG. 1 is an enlarged plan view showing part of a color filter substrate according to an exemplary embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along a line I-I′ of FIG. 1 .

Referring to FIGS. 1 and 2 , a color filter substrate 100 includes a base substrate 10 , a non-transmissive layer 20 , an alignment layer 30 arranged on the non-transmissive layer 20 , and a plurality of color filter layers arranged on the alignment layer 30 .

The base substrate 10 includes a plurality of pixel areas having a first pixel area PA 1 , a second pixel area PA 2 , and a third pixel area PA 3 and a peripheral area SA surrounding each of the pixel areas. The pixel areas are arranged both in a column direction that is substantially parallel to a first direction D 1 and in a row direction that is substantially perpendicular to the first direction D 1 to have a matrix pattern, and the pixel areas are spaced apart from each other.

The non-transmissive layer 20 includes a material that is not transparent or absorbs light, such as a resin including carbon. The non-transmissive layer 20 is arranged on the base substrate 10 corresponding to the pixel areas and the peripheral area SA. In addition, the non-transmissive layer 20 includes a plurality of concave-convex portions 25 arranged on an upper surface thereof. In a sectional view, a surface of each of the concave-convex portions 25 has a round shape.

The alignment layer 30 is arranged on the non-transmissive layer 20 . The alignment layer 30 has a first concave-convex surface 35 corresponding to the concave-convex portions 25 . The alignment layer 30 aligns cholesteric liquid crystals in the color filter layers.

The color filter layers are arranged on the alignment layer 30 in a one-to-one correspondence with the pixel areas. In other words, each color filter layer CF corresponds to one pixel area PA. According to an exemplary embodiment, the color filter layers include a first color filter layer CF 1 , a second color filter layer CF 2 , and a third color filter layer CF 3 . The first color filter layer CF 1 is arranged on the alignment layer 30 corresponding to the first pixel area PA 1 , the second color filter layer CF 2 is arranged on the alignment layer 30 corresponding to the second pixel area PA 2 , and the third color filter layer CF 3 is arranged on the alignment layer 30 corresponding to the third pixel area PA 3 .

Each of the first to third color filter layers CF 1 , CF 2 , and CF 3 includes the cholesteric liquid crystal twisted at different pitches from each other. In general, in the color filter layer including the cholesteric liquid crystal, the cholesteric liquid crystal is twisted in a helical fashion, and the pitch of the cholesteric liquid crystal is defined as a distance in which cholesteric liquid crystal molecules rotate 360° along the helical axis. In other words, the pitch is the width of one complete helix turn, measured parallel to the axis of the helix. If the pitch is defined as described above, the wavelength of the light reflected by the cholesteric liquid crystal may be increased as the pitch increases. More detailed descriptions of the above will be described with reference to FIGS. 3A to 3C .

FIG. 3A is an enlarged view showing a first area A 1 of FIG. 2 , FIG. 3B is an enlarged view showing a second area A 2 of FIG. 2 , and FIG. 3C is an enlarged view showing a third area A 3 of FIG. 2 .

Referring to FIGS. 3A to 3C , the first color filter layer CF 1 includes a first cholesteric liquid crystal 50 twisted at a first pitch P 1 , the second color filter layer CF 2 includes a second cholesteric liquid crystal 51 twisted at a second pitch P 2 that is smaller than the first pitch P 1 , and the third color filter layer CF 3 includes a third cholesteric liquid crystal 52 twisted at a third pitch P 3 that is smaller than the second pitch P 2 .

Referring again to FIG. 2 , since the first to third cholesteric liquid crystals 50 , 51 , and 52 have different pitches from each other as described above, the lights reflected from the first to third color filter layers CF 1 , CF 2 , and CF 3 have different wavelengths to have different colors from each other. For example, a first light L 1 reflected by the first color filter layer CF 1 may be a red light, a second light L 2 reflected by the second color filter layer CF 2 may be a green light having a smaller wavelength than that of the red light, and a third light L 3 reflected by the third color filter layer CF 3 may be a blue light having a smaller wavelength than that of the green light.

According to an exemplary embodiment, the pitch of the first to third cholesteric liquid crystals 50 , 51 , and 52 is controlled by adjusting an amount of chiral dopant that reacts with the first to third cholesteric liquid crystals 50 , 51 , and 52 . Also, the pitch of the first to third cholesteric liquid crystals 50 , 51 , and 52 may be decided by controlling an amount of light exposure energy provided to a preliminary color filter layers including the cholesteric liquid crystal.

Each of the first to third color filter layers CF 1 , CF 2 , and CF 3 has a second concave-convex surface 40 corresponding to the first concave-convex surface 35 . Thus, a size of surface area of each of the first to third color filter layers CF 1 , CF 2 , and CF 3 increases, thereby enhancing a reflection efficiency of each of the first to third color filter layers CF 1 , CF 2 , and CF 3 .

According to a structure of the color filter substrate 100 shown in FIG. 2 , since the first to third color filter layers CF 1 , CF 2 , and CF 3 are arranged in a one-to-one correspondence with the pixel areas, the non-transmissive layer 20 is not covered by the first to third color filter layers CF 1 , CF 2 , and CF 3 in the peripheral areas SA. Therefore, a light L 0 transmitting through the alignment layer 30 and traveling to the non-transmissive layer 20 is absorbed by the non-transmissive layer 20 , and thus the first, second and third lights L 1 , L 2 , and L 3 respectively reflected by the first, second and third color filter layers CF 1 , CF 2 , and CF 3 are prevented from being mixed with each other.

Referring again to FIGS. 3A to 3C , the first cholesteric liquid crystal 50 is aligned corresponding to the shape of the first concave-convex surface 35 having the round shape in the sectional view. A tangent line direction at a point of the first concave-convex surface 35 is defined as a third direction D 3 and a rotation axis (e.g., a normal line direction) of the first cholesteric liquid crystal 50 adjacent to the point is defined as a fourth direction D 4 , the third direction D 3 is substantially perpendicular to the fourth direction D 4 .

As a result, a vertical light 60 that vertically travels with respect to the color filter substrate 100 (shown in FIG. 1 ) after being reflected by the first color filter layer CF 1 and an inclined light 61 that travels in an inclined direction with respect to the color filter substrate 100 after being reflected by the first color filter layer CF 1 are reflected by the first cholesteric liquid crystal 50 twisted with the same pitch, so that the vertical light 60 and the inclined light 61 have the same wavelength. As a result, a change in the wavelength of the light reflected by the first color filter layer CF 1 , which is caused by a viewing angle, may be prevented, thereby improving a color reproducibility of the color filter substrate 100 .

Similar to the first cholesteric liquid crystal 50 , since the second cholesteric liquid crystal 51 and the third cholesteric liquid crystal 52 are aligned corresponding to the first concave-convex surface 35 , a change in the wavelength of the light reflected by the second color filter layer CF 2 and the third color filter layer CF 3 , which is caused by the viewing angle, may be decreased.

FIG. 4 is a cross-sectional view showing a color filter substrate according to an exemplary embodiment of the present invention. In FIG. 4 , the same reference numerals denote the same or similar elements as in the exemplary embodiment described in connection with FIG. 2 .

Referring to FIG. 4 , when compared to the color filter substrate 100 of FIG. 2 , a color filter substrate 101 further includes a transparent electrode 80 . The transparent electrode 80 may be a transparent conductive film, such as an indium tin oxide or an indium zinc oxide.

When the color filter substrate 101 is coupled with another substrate (not shown), the transparent electrode 80 may form an electric field with another electrode arranged on the substrate. For example, when the color filter substrate 101 is employed in a liquid crystal display, the transparent electrode 80 may form the electric field with a pixel electrode formed on an array substrate to control an alignment of the liquid crystal. More detailed descriptions of the above will be described with reference to FIGS. 5 to 10 .

FIG. 5 is an enlarged plan view showing part of a liquid crystal display according to an exemplary embodiment of the present invention, FIG. 6 is a cross-sectional view taken along a line II-II′ of FIG. 5 , and FIG. 7 is a cross-sectional view taken along a line III-III′ of FIG. 5 .

Referring to FIGS. 5 and 6 , a liquid crystal display 400 includes a first substrate 200 , a second substrate 300 facing the first substrate 200 , and liquid crystal 250 disposed between the first substrate 200 and the second substrate 300 .

The first substrate 200 includes a first base substrate 110 having a plurality of pixel areas and a peripheral area surrounding each of the pixel areas. A structure of the liquid crystal display 400 corresponding to a first pixel area PA 1 , a second pixel area PA 2 , and a third pixel area PA 3 is the same as a structure of the liquid crystal display 400 corresponding to remaining pixel areas.

The first base substrate 110 includes gate lines GL, data lines DL, a thin film transistor TR positioned in each of the first to third pixel areas PA 1 , PA 2 , and PA 3 , first, second, and third pixel electrodes PE 1 , PE 2 , and PE 3 arranged to respectively correspond with the first to third pixel areas PA 1 , PA 2 , and PA 3 , first, second, third color filter layers CF 1 , CF 2 , and CF 3 arranged to respectively correspond with the first to third pixel areas PA 1 , PA 2 , and PA 3 , a first non-transmissive layer 140 , and an alignment layer 150 .

Although not shown in FIGS. 5 and 6 , an additional alignment layer may be arranged on the first to third pixel electrodes PE 1 , PE 2 , and PE 3 to align the liquid crystal 250 .

A structure of the first substrate 200 corresponding to the first pixel area PA 1 is as follows. The gate lines GL and the data lines DL cross each other on the first base substrate 110 , and the thin film transistors TR are electrically connected to their corresponding gate lines GL and data lines DL. More particularly, a thin film transistor TR includes a gate electrode GE branched from the gate line GL, a semiconductor pattern AP arranged on the gate electrode GE, a gate insulating layer 120 interposed between the gate electrode GE and the semiconductor pattern AP, a source electrode SE branched from the data line DL, and a drain electrode DE spaced apart from the source electrode SE.

A protective layer 130 is arranged on the thin film transistor TR. The non-transmissive layer 140 , the alignment layer 150 , the first color filter layer CF 1 , and the first pixel electrode PE 1 are sequentially arranged on the protective layer 130 . In addition, the non-transmissive layer 140 , the alignment layer 150 , and the first color filter layer CF 1 are partially removed from a region corresponding to the drain electrode DE to form a contact hole CH 1 , and the first pixel electrode PE 1 is electrically connected to the drain electrode DE through the contact hole CH 1 .

The structure and function of the non-transmissive layer 140 , the alignment layer 150 , and the first color filter layer CF 1 are the same as those of the non-transmissive layer 20 (shown in FIG. 2 ), the alignment layer 30 (shown in FIG. 2 ), and the first color filter layer CF 1 (shown in FIG. 2 ) except that the non-transmissive layer 140 , the alignment layer 150 , and the first color filter layer CF 1 are partially removed to form the contact hole CH 1 .

The second substrate 300 includes a second base substrate 310 and an opposite electrode 320 arranged on the second base substrate 310 . The opposite electrode 320 forms an electric field with the first pixel electrode PE 1 to control alignment of the liquid crystal 250 .

Although not shown in FIGS. 5 and 6 , according to an exemplary embodiment, an additional alignment layer may be arranged on the opposite electrode 320 in order to align the liquid crystal 250 .

Referring to FIG. 7 , the second color filter layer CF 2 and the second pixel electrode PE 2 are sequentially arranged on the alignment layer 150 corresponding to the second pixel area PA 2 , and the third color filter layer CF 3 and the third pixel electrode PE 3 are sequentially arranged on the alignment layer 150 corresponding to the third pixel area PA 3 .

Thus, a fourth light L 4 transmitting through the second substrate 300 and being reflected by the second color filter layer CF 2 has a wavelength corresponding to the second pitch P 2 (shown in FIG. 3B ) of the second cholesteric liquid crystal 51 (shown in FIG. 3B ) included in the second color filter layer CF 2 . A fifth light L 5 transmitting through the second substrate 300 and being reflected by the third color filter layer CF 3 has a wavelength corresponding to the third pitch P 3 (shown in FIG. 3C ) of the third cholesteric liquid crystal 52 (shown in FIG. 3C ) included in the third color filter layer CF 3 . In addition, a sixth light L 6 that transmits through the second substrate 300 and travels to the peripheral area SA is absorbed by the non-transmissive layer 140 .

FIG. 8 is an enlarged plan view showing part of a liquid crystal display according to an exemplary embodiment of the present invention, FIG. 9 is a cross-sectional view taken along a line IV-IV′ of FIG. 8 , and FIG. 10 is a cross-sectional view taken along a line V-V′ of FIG. 8 .

Referring to FIGS. 8 to 10 , a liquid crystal display 401 includes a color filter substrate 101 and an opposite substrate 201 . The color filter substrate 101 has the same structure and function as those of the color filter substrate shown in FIG. 4 .

The opposite substrate 201 has essentially the same structure as that of the first substrate 200 (shown in FIGS. 6 and 7 ) except that the non-transmissive layer 140 , the alignment layer 150 , and the first to third color filter layers CF 1 , CF 2 , and CF 3 are removed from the opposite substrate 201 . Consequently, first to third pixel electrodes PE 1 , PE 2 , and PE 3 are arranged on a protective layer 130 in the opposite substrate 201 .

Although not shown in FIGS. 9 and 10 , an additional alignment layer may be arranged on the first to third pixel electrodes PE 1 , PE 2 , and PE 3 in order to align a liquid crystal 250 .

In the liquid crystal display 401 having the above-described structure, a seventh light L 7 transmitting through the opposite substrate 201 from an external location and being reflected by the second color filter layer CF 2 has a wavelength corresponding to a pitch of a cholesteric liquid crystal included in the second color filter layer CF 2 , and an eighth light L 8 transmitting through the opposite substrate 201 and being reflected by the third color filter layer CF 3 has a wavelength corresponding to a pitch of a cholesteric liquid crystal included in the third color filter layer CF 3 . Also, a ninth light L 9 that transmits through the opposite substrate 201 from external location and travels to the peripheral area SA is absorbed by the non-transmissive layer 20 .

The structure that includes the non-transmissive layer 20 , the alignment layer 30 , and the first to third color filter layers CF 1 , CF 2 , and CF 3 may be employed in other display devices besides the liquid crystal display 401 in order to provide the white light in any desired color.

Although the exemplary embodiments of the present invention have been described, it is understood that the present invention should not be limited to these exemplary embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the present invention as hereinafter claimed.