Curved display device including trenches in substrate

Abstract

A curved display device includes a first substrate, a pixels and a second substrate. The first substrate is curved along a first direction and includes a pixel area through which light is transmitted and a non-pixel area which blocks light transmission therethrough. The pixel is disposed in the pixel area. The second substrate is curved along the first direction, and is opposite to and coupled to the first substrate. First trenches are defined in at least one substrate among the first and second substrates and extending in a second direction intersecting the first direction.

Claims

What is claimed is: 1 . A curved display device comprising: a first substrate curved along a first direction, and comprising a pixel area through which light is transmitted and a non-pixel area which blocks light transmission therethrough; a pixel in the pixel area; and a second substrate curved along the first direction, and opposite to and coupled to the first substrate, wherein first trenches are defined in one substrate among the first and second substrates and extending in a second direction intersecting the first direction. 2 . The curved display device of claim 1 , wherein the first trenches are in the non-pixel area. 3 . The curved display device of claim 2 , wherein the first trenches are defined in the first and second substrates, and comprise: first sub-trenches defined in the first substrate; and second sub-trenches defined in the second substrate. 4 . The curved display device of claim 1 , wherein each of the first trenches has a first depth from a surface of the one substrate among the first and second substrates, and the first depth is in a range of about 10% to about 50% a thickness of the one substrate among the first and second substrates. 5 . The curved display device of claim 1 , wherein each of the first and second substrates comprises an outer surface exposed outwardly, and an inner surface opposite to the outer surface, and the first trenches are defined recessed from the outwardly exposed outer surface of the one substrate among the first and second substrates. 6 . The curved display device of claim 1 , wherein each of the first and second substrates comprises an outer surface exposed outwardly, and an inner surface opposite to the outer surface, and the first trenches are defined recessed from the inner surface of the one substrate among the first and second substrates. 7 . The curved display device of claim 1 , wherein the first and second substrates are further curved along the second direction intersecting the first direction, and second trenches are defined in the one substrate among the first and second substrates, and extending in the second direction. 8 . The curved display device of claim 7 , wherein the second trenches are in the non-pixel area. 9 . The curved display device of claim 8 , wherein the second trenches are defined in the first and second substrates, and comprise: third sub-trenches defined in the first substrate; and fourth sub-trenches defined in the second substrate. 10 . The curved display device of claim 7 , wherein each of the second trenches has a first depth from a surface of the one substrate among the first and second substrates, and the first depth is in a range of about 10% to about 50% a thickness of the one substrate among the first and second substrates. 11 . The curved display device of claim 7 , wherein each of the first and second substrates comprises an outer surface exposed outwardly, and an inner surface opposite to the outer surface, and the second trenches are defined recessed from at least one of the outer surface and the inner surface of the one substrate among the first and second substrates. 12 . The curved display device of claim 7 , further comprising: a light blocking layer on the first substrate or the second substrate, the light blocking layer overlapping the first trenches and the second trenches. 13 . The curved display device of claim 7 , wherein the first direction is perpendicular to the second direction. 14 . The curved display device of claim 7 , wherein an extending direction of each of the first trenches is perpendicular to an extending direction of each of the second trenches. 15 . The curved display device of claim 7 , further comprising: a thin film transistor electrically connected to the pixel; a gate line which is electrically connected to the thin film transistor and transfers a gate signal to the thin film transistor; and a data line which is electrically connected to the thin film transistor and transfers a data signal to the thin film transistor, wherein each of the gate line and the data line is provided in plural, the first trenches overlap the plurality of data lines, and the second trenches overlap the plurality of gate lines. 16 . The curved display device of claim 7 , wherein the first trenches are discontinuous in the first direction; and the second trenches are discontinuous in the second direction. 17 . The curved display device of claim 1 , wherein the first and second substrates comprise glass substrates. 18 . The curved display device of claim 1 , further comprising: a light blocking layer on the first substrate or the second substrate, the light blocking layer overlapping the first trenches. 19 . The curved display device of claim 1 , further comprising: a thin film transistor electrically connected to the pixel; a gate line which is electrically connected to the thin film transistor and transfers a gate signal to the thin film transistor; and a data line which is electrically connected to the thin film transistor and transfers a data signal to the thin film transistor, wherein each of the gate line and the data line is provided in plural, and the first trenches overlap the plurality of data lines or the plurality of gate lines.
[0001] This application claims priority to Korean Patent Application No. 10-2014-0018591, filed on Feb. 18, 2014, and all the benefits accruing therefrom under 35 U.S.C. §119, the disclosure of which is hereby incorporated by reference in its entirety. BACKGROUND [0002] The invention relates to a curved display device. More particularly, the invention relates to a curved display device including a curved display area. [0003] Flat display devices, such as a liquid crystal display device and an organic electroluminescence display device, have been used in order to display an image in a variety of information processing devices, such as a television, a monitor, a notebook and a portable phone. [0004] A curved display device including the flat display device has been developed. The curved display device includes a display area having a curved shape to provide an image with improved three-dimensional effect, immersion effect and presence effect to users. SUMMARY [0005] One or more exemplary embodiment of the invention provides a curved display device having improved display quality. [0006] One or more exemplary embodiment of the invention provides a curved display device including a first substrate, a pixel and a second substrate. The first substrate is curved along a first direction, and includes a pixel area through which light is transmitted and a non-pixel area which blocks light transmission therethrough. The pixel is in the pixel area. The second substrate is curved along the first direction, and is opposite to and coupled to the first substrate. First trenches are defined in one substrate among the first and second substrates, and extending in a second direction intersecting the first direction. [0007] In an exemplary embodiment, the first and second substrates may be curved along the first direction and the second direction. At least one substrate among the first and second glass substrates may have second trenches defined in the one substrate among the first and second substrates, and extending in a direction intersecting the second direction. BRIEF DESCRIPTION OF THE DRAWINGS [0008] The above and other features of this disclosure will become more apparent in view of the attached drawings and accompanying detailed description, in which: [0009] FIG. 1A is a perspective view of an exemplary embodiment of a curved display device according to the invention; [0010] FIG. 1B is a cross-sectional view of the curved display device shown in FIG. 1A ; [0011] FIG. 1C is a perspective view showing an exemplary embodiment of a display panel included in the curved display device of FIG. 1A ; [0012] FIG. 2 is an enlarged plan view of an exemplary embodiment of pixels included in the display panel of FIG. 1C ; [0013] FIG. 3A is a cross-sectional view taken along line I-I′ of FIG. 2 ; [0014] FIG. 3B is a cross-sectional view taken along line II-II′ of FIG. 2 ; [0015] FIG. 4A is a perspective view of another exemplary embodiment of a curved display device according to the invention; [0016] FIG. 4B is a cross-sectional side view of the curved display device shown in FIG. 4A ; [0017] FIG. 4C is a perspective view showing an exemplary embodiment of a display panel included in the curved display device of FIG. 4A ; [0018] FIG. 5A is an enlarged plan view of an exemplary embodiment of pixels included in the display panel of FIG. 4C ; [0019] FIG. 5B is a cross-sectional view taken along line III-III′ of FIG. 5A ; [0020] FIG. 6 is a cross-sectional view showing another exemplary embodiment of a display panel included in a curved display device according to the invention; [0021] FIG. 7 is an enlarged plan view of another exemplary embodiment of pixels of a display panel included in a curved display device according to the invention; and [0022] FIG. 8 is a cross-sectional view of yet another exemplary embodiment of a display panel included in a curved display device according to the invention. DETAILED DESCRIPTION [0023] The inventions will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The advantages and features of the invention and methods of achieving them will be apparent from the following exemplary embodiments that will be described in more detail with reference to the accompanying drawings. It should be noted, however, that the invention is not limited to the following exemplary embodiments, and may be implemented in various forms. Accordingly, the exemplary embodiments are provided only to disclose the invention and let those skilled in the art know the category of the invention. In the drawings, exemplary embodiments of the invention are not limited to the specific examples provided herein and are exaggerated for clarity. [0024] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular terms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element or intervening elements may be present. As used herein, connected may refer to elements being physically and/electrically connected to each other. [0025] Similarly, it will be understood that when an element such as a layer, region or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may be present. In contrast, the term “directly” means that there are no intervening elements. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. [0026] Spatially relative terms, such as “below,” “upper” and the like, may be used herein for ease of description to describe the relationship of one element or feature to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” relative to other elements or features would then be oriented “above” relative to the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. [0027] Additionally, the exemplary embodiments in the detailed description will be described with sectional views as ideal exemplary views of the invention. Accordingly, shapes of the exemplary views may be modified according to manufacturing techniques and/or allowable errors. Therefore, the embodiments of the invention are not limited to the specific shape illustrated in the exemplary views, but may include other shapes that may be created according to manufacturing processes. Areas exemplified in the drawings have general properties, and are used to illustrate specific shapes of elements. Thus, this should not be construed as limited to the scope of the invention. [0028] It will be also understood that although the terms first, second, third etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, a first element in some exemplary embodiments could be termed a second element in other exemplary embodiments without departing from the teachings of the invention. Exemplary embodiments of the invention explained and illustrated herein include their complementary counterparts. The same reference numerals or the same reference designators denote the same elements throughout the specification. [0029] “About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations, or within ±30%, 20%, 10%, 5% of the stated value. [0030] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. [0031] Hereinafter, the invention will be described in detail with reference to the accompanying drawings. [0032] FIG. 1A is a perspective view of an exemplary embodiment of a curved display device according to the invention. FIG. 1B is a cross-sectional view of the curved display device shown in FIG. 1A . FIG. 1C is a perspective view showing an exemplary embodiment of a display panel included in the curved display device of FIG. 1A . [0033] Referring to FIGS. 1A , 1 B and 1 C, a curved display device 500 includes a receiving member 350 , a display panel 300 and a cover member 360 . In the illustrated exemplary embodiment, the display panel 300 may be a liquid crystal display panel. Where the display panel 300 is a liquid crystal display panel, the curved display device 500 may further include a backlight unit (not shown) received in the receiving member 350 . The backlight unit generates and outputs light to the display panel 300 . The display panel 300 is provided with the light to display an image through a display area DA thereof. The display area DA includes a pixel area PA through which light is transmitted, and a non-pixel area N-PA which blocks light transmittance therethrough. [0034] In the illustrated exemplary embodiment, the curved display device 500 has a curved shape. In more detail, the curved display device 500 has a shape curved along a first direction DR 1 . Where the curved display device 500 has a shape curved along the first direction DR 1 , the display panel 300 has a shape curved along the first direction DR 1 to correspond to the curved shape of the curved display device 500 . The display panel 300 has a long side E 1 and a short side E 2 . Where the curved display panel 300 has a shape curved along the first direction DR 1 , the long side E 1 of the display panel 300 has a shape curved along the first direction DR 1 . In FIG. 1C , a dotted line at long sides E 1 of the display panel 300 indicates a location at which the long sides E 1 may be disposed for a flat display panel 300 , however, since the display panel 300 is curved in FIG. 1C , the long sides E 1 are deviated from the dotted line positions. [0035] Referring to FIG. 3A and FIG. 3B , the display panel 300 may include a first glass substrate GS 1 of and a second glass substrate GS 2 of FIG. 2 that face each other and are coupled with each other. The first and second glass substrates include a transparent and relatively hard or rigid material such as glass. However, in the illustrated exemplary embodiment, a size (e.g., 46 inches or 55 inches) of the display panel 300 may be greater than a size of a display panel applied to a portable display device, and a thickness of each of the first and second glass substrates may be several millimeters (mm) or less. Thus, the display panel 300 may be curved in the first direction DR 1 with a radius of curvature of about 2 meters to about 10 meters. [0036] As described above, where the display panel 300 has the curved shape, the display area DA of the display panel 300 may also have the curved shape. Thus, the curved display device 500 may display the image with improved three-dimensional effect, immersion effect and presence effect through the display area DA. [0037] The receiving member 350 receives the display panel 300 , and the cover member 360 is coupled with the receiving member 350 including the display panel 300 received therein. The cover member 360 covers an edge portion of the display panel 300 . In addition, an opening may be defined in the cover member 360 corresponding to the display area DA of the display panel 300 to expose the display region DA. Each of the cover member 360 and the receiving member 350 may be curved to correspond to the shape of the display panel 300 , so the curved shape of the display panel 300 may be maintained. [0038] FIG. 2 is an enlarged plan view of an exemplary embodiment of pixels included in the display panel of FIG. 1C . FIG. 3A is a cross-sectional view taken along line I-I′ of FIG. 2 . FIG. 3B is a cross-sectional view taken along line II-II′ of FIG. 2 . The display panel 300 includes a plurality of pixels disposed in the display region DA of FIG. 1C . FIG. 2 shows a portion of the plurality of pixels disposed in the display region DA of FIG. 1C . The plurality of pixels disposed in the display region DA of FIG. 1C may have the same structure or similar structures to each other. Thus, descriptions to pixels other than those illustrated in FIG. 2 will be omitted. [0039] Referring to FIGS. 2 and 3A , the display panel 300 includes a display substrate 100 , an opposite substrate 200 , and a liquid crystal layer LC disposed between the display substrate 100 and the opposite substrate 200 . [0040] The display substrate 100 includes the first glass substrate GS 1 , a plurality of gate lines such as first to third gate lines GL 1 , GL 2 and GL 3 , a plurality of data lines DL such as first to third data lines DL 1 , DL 2 and DL 3 , a plurality of thin film transistors TR, and a plurality of pixel electrodes PE. [0041] The first glass substrate GS 1 includes a glass material. As described above, the first glass substrate GS 1 has the shape curved along the first direction DR 1 . Each of the first to third gate lines GL 1 , GL 2 and GL 3 may extend in the first direction DR 1 . Each of the first to third data lines DL 1 , DL 2 and DL 3 may extend in a second direction DR 2 perpendicular to the first direction DR 1 . [0042] In the illustrated exemplary embodiment, the plurality of thin film transistors TR may be disposed at crossing points of the first to third gate lines GL 1 , GL 2 and GL 3 and the first to third data lines DL 1 , DL 2 and DL 3 in one-to-one correspondence, and the plurality of pixel electrodes PE may be electrically connected to the plurality of thin film transistors TR in one-to-one correspondence. [0043] However, the invention is not limited to the structures of the gate lines GL 1 , GL 2 and GL 3 , the structures of the data lines DL 1 , DL 2 and DL 3 , the structures of the thin film transistors TR, and the structures of the pixel electrodes PE illustrated herein. In other exemplary embodiments, each of the pixel electrodes PE may include two sub-pixel electrodes. The two sub-pixel electrodes may be electrically connected to data lines different from each other, so data signals different from each other may be applied to the two sub-pixel electrodes. [0044] The first gate line GL 1 and one thin film transistor TR electrically connected to the first gate line GL 1 will be described hereinafter. [0045] The thin film transistor TR may be disposed in the non-pixel area N-PA. The thin film transistor TR may include a gate electrode GE, an active pattern AP, a source electrode SE and a drain electrode DE. [0046] The gate electrode GE may diverge from a main portion of the first gate electrode GL 1 and may be disposed on the first glass substrate GS 1 . The active pattern AP may be disposed on the gate electrode GE, with a first insulating layer L 1 therebetween. The source electrode SE may diverge from a main portion of the first data line DL 1 and may be disposed on the active pattern AP. The drain electrode DE may be on the active pattern AP and spaced apart from the source electrode SE. A portion of the active pattern AP may be exposed by the spaced apart source and drain electrodes SE and DE. [0047] In the illustrated exemplary embodiment, the active pattern AP may include a semiconductor material such as amorphous silicon. However, the invention is not limited to the above-described semiconductor material of the active pattern AP. In other exemplary embodiments, the active pattern AP may include at least one of an oxide semiconductor such as indium gallium zinc oxide (“IGZO”), ZnO, SnO 2 , In 2 O 3 , Zn 2 SnO 4 , Ge 2 O 3 and HfO 2 . In still other exemplary embodiments, the active pattern AP may include at least one of a compound semiconductor such as GaAs, GaP and InP. [0048] A first pixel electrode PE 1 among the pixel electrodes PE will be described as an example. The first pixel electrode PE 1 may be disposed in the pixel area PA and may be electrically connected to the thin film transistor TR. In more detail, the first pixel electrode PE 1 is disposed on a second insulating layer L 2 and a third insulating layer L 3 that cover the thin film transistor TR. The first pixel electrode PE 1 is electrically connected to the drain electrode DE of the thin film transistor TR through a contact hole CH penetrating the second and third insulating layers L 2 and L 3 . [0049] The opposite substrate 200 may include the second glass substrate GS 2 , a light blocking layer BM, a color filter CF and a common electrode CE. The second glass substrate GS 2 includes a glass material. The second glass substrate GS 2 has a curved shape along the first direction DR 1 similar to that of the first glass substrate GS 1 . [0050] The light blocking layer BM is disposed on the second glass substrate GS 2 to correspond to the non-pixel area N-PA, and the color filter CF is disposed on the second glass substrate GS 2 to correspond to the pixel area PA. The common electrode CE is disposed on the second glass substrate GS 2 to cover the light blocking layer BM and the color filter CF. The common electrode CE and the pixel electrodes PE are configured to generate an electric field therebetween, which controls directors of liquid crystal molecules of the liquid crystal layer LC. [0051] However, the invention is not limited to the aforementioned structures of the light blocking layer BM, the color filter CF and the common electrode CE. In other exemplary embodiments, the color filter CF may be disposed on the first glass substrate GS 1 to correspond to the pixel area PA, and the light blocking layer BM may be disposed on the first glass substrate GS 1 to correspond to the non-pixel area N-PA. The common electrode CE may be disposed on the first glass substrate GS 1 but spaced apart from the pixel electrodes PE. [0052] In the illustrated exemplary embodiment, first trenches TH 1 may be defined in the first glass substrate GS 1 and the second glass substrate GS 2 . The first trenches TH 1 may be disposed in the non-pixel area N-PA and may overlap with the light blocking layer BM. Thus, even though light transmitted through the first or second glass substrate GS 1 or GS 2 is scattered by an inclined plane defining each of the first trenches TH 1 , the scattered light is blocked by the light blocking layer BM, so that deterioration of a display quality of the display panel 300 by the scattered light may be reduced or effectively prevented. [0053] Where each of the first and second glass substrates GS 1 and GS 2 are curved along the first direction DR 1 as described above, each of the first trenches TH 1 may extend in a direction intersecting the first direction DR 1 . In the illustrated exemplary embodiment, each of the first trenches TH 1 may extend in the second direction DR 2 perpendicular to the first direction DR 1 . [0054] In the illustrated exemplary embodiment, the first trenches TH 1 may include first sub-trenches TH 1 - 1 defined in the first glass substrate GS 1 and second sub-trenches TH 1 - 2 defined in the second glass substrate GS 2 . The first sub-trenches TH 1 - 1 may disperse or relieve stress that is applied to the first glass substrate GS 1 owing to the curved shape of the first glass substrate GS 1 . Likewise, the second sub-trenches TH 1 - 2 may disperse or relieve stress that is applied to the second glass substrate GS 2 owing to the curved shape of the second glass substrate GS 2 . As a result, the display quality of the display panel 300 may be improved. This will be described using the first sub-trenches TH 1 - 1 as an example in more detail hereinafter. In a conventional curved display device, if the first sub-trenches TH 1 - 1 are not defined in a first glass substrate, unlike the exemplary embodiments of the invention, stress may be locally applied to the first glass substrate owing to the curved shape of the first glass substrate. When light is transmitted through a portion of the first glass substrate to which the stress is locally applied, a refractive index of the light may be varied according to a travelling direction of the light to cause retardation of a phase of the light. If the first glass substrate is not curved, the first glass substrate generally has transparent and non-optical characteristics. In contrast, where the first glass substrate is curved, the phase retardation of the light may occur to cause deterioration of the display quality of the conventional curved display device, e.g., a light leakage phenomenon. [0055] However, in one or more exemplary embodiment according to the invention, the first sub-trenches TH 1 - 1 may be defined in the first glass substrate GS 1 to disperse or relieve the stress locally applied to the first glass substrate GS 1 , so that phase retardation of the light transmitted through the first glass substrate GS 1 may be reduced or effectively prevented. As a result, the transparent and non-optical characteristics of the first glass substrate GS 1 may be maintained in a curved display device. [0056] Since the first and second sub-trenches TH 1 - 1 and TH 1 - 2 have substantially the same structure or similar structures to each other, repeated descriptions will be omitted for the purpose of ease and convenience in explanation. [0057] In the illustrated exemplary, the first trenches TH 1 may overlap with the first to third data lines DL 1 , DL 2 and DL 3 as well as the light blocking layer BM. In an exemplary embodiment, for example, the first trenches TH 1 may overlap with the first to third data lines DL 1 , DL 2 and DL 3 in one-to-one correspondence, as illustrated in FIG. 2 . Where the first trenches TH 1 overlap with the first to third data lines DL 1 , DL 2 and DL 3 in one-to-one correspondence, a first pitch of the first trenches TH 1 may be similar to a second pitch of the first to third data lines DL 1 , DL 2 and DL 3 . In other exemplary embodiments, the first pitch may be greater than the second pitch. In an exemplary embodiment, for example, the first pitch may be several times to tens of times greater than the second pitch. The first and second pitches may be defined as a distance between adjacent data lines and a distance between adjacent trenches, taken from common references points thereof and in a direction perpendicular to extension directions thereof. [0058] In the illustrated exemplary embodiment, an interface of the first glass substrate GS 1 and the first insulating layer L 1 contacting each other is defined as an inner surface S 1 . In an exemplary embodiment of manufacturing a curved display device, a portion of the first glass substrate GS 1 may be partially removed at the inner surface S 1 to form each of the first sub-trenches TH 1 - 1 . The first sub-trench TH 1 - 1 has a first depth D 1 taken from the inner surface S 1 . The first depth D 1 may be in a range of about 10% to about 50% of a cross-sectional thickness of the first glass substrate GS 1 . In an exemplary embodiment, for example, if the cross-sectional thickness of the first glass substrate GS 1 is about 1 mm, the first depth D 1 may be in a range of about 0.1 mm to about 0.5 mm. [0059] In the illustrated exemplary embodiment, the first trenches TH 1 include the first and second sub-trenches TH 1 - 1 and TH 1 - 2 . However, the invention is not limited thereto. In other exemplary embodiments, the first trenches TH 1 may include only the first sub-trenches TH 1 - 1 defined in the first glass substrate GS 1 or the second sub-trenches TH 1 - 2 defined in the second glass substrate GS 2 . [0060] In other exemplary embodiments, the display panel 300 may include an organic electroluminescence display panel, and a window substrate covering the organic electroluminescence display panel. The organic electroluminescence display panel may include a base substrate and a plurality of pixels disposed on the base substrate. Each of the pixels of the organic electroluminescence display panel may include an anode, a cathode and an organic light emitting layer disposed between the anode and the cathode. Where the curved display panel 300 includes the organic electroluminescence display panel and the window substrate, as described above, a plurality of trenches TH 1 may be defined in each of the base substrate and the window substrate. Thus, the stress locally applied to the base and window substrates owing to the curved shape of the display panel 300 may be dispersed or relieved by the plurality of trenches, so that phase retardation of light transmitted through the base and window substrates may be minimized or effectively prevented. [0061] FIG. 4A is a perspective view of another exemplary embodiment of a curved display device according to the invention. FIG. 4B is a side view of the curved display device shown in FIG. 4A . FIG. 4C is a perspective view of an exemplary embodiment of a display panel included in the curved display device of FIG. 4A . [0062] The curved display device 500 of FIG. 1A has the shape curved only along the first direction DR 1 . However, referring to FIGS. 4A , 4 B, and 4 C, a curved display device 501 has a shape curved along a second direction DR 2 as well as the first direction DR 1 . A display panel 301 included in the curved display device 501 has a long side E 1 and a short side E 2 . The long side E 1 is curved along the first direction DR 1 , and the short side E 2 is curved along the second direction DR 2 . [0063] FIG. 5A is an enlarged plan view of an exemplary embodiment of pixels included in the display panel of FIG. 4C . FIG. 5B is a cross-sectional view taken along line III-III′ of FIG. 5A . In the illustrated embodiment, the same elements as described in the aforementioned exemplary embodiments will be indicated by the same numerals or the same designators. The descriptions to the same elements as described in the aforementioned exemplary embodiments will be omitted or mentioned briefly for the purpose of ease and convenience in explanation. [0064] Referring to FIGS. 5A and 5B , the display panel 301 includes a display substrate 101 and an opposite substrate 201 . The display substrate 101 includes a first glass substrate GS 1 - 1 , and the opposite substrate 201 includes a second glass substrate GS 2 - 1 . [0065] In the illustrated exemplary embodiment, first trenches TH 1 and second trenches TH 2 may be defined in each of the first and second glass substrates GS 1 - 1 and GS 2 - 1 . Each of the second trenches TH 2 may extend in a direction intersecting the second direction DR 2 . In the illustrated exemplary, each of the second trenches TH 2 may extend in the first direction DR 1 perpendicular to the second direction DR 2 . [0066] The second trenches TH 2 may be disposed in a non-pixel area N-PA to overlap with a light blocking layer BM. The second trenches TH 2 may disperse or relieve stress that is locally applied to the first and second glass substrates GS 1 - 1 and GS 2 - 1 by the first and second glass substrates GS 1 - 1 and GS 2 - 1 being curved along the second direction DR 2 . As a result, phase retardation of light transmitted through the first and second glass substrates GS 1 - 1 and GS 2 - 1 may be minimized or effectively prevented, so the first and second glass substrates GS 1 - 1 and GS 2 - 1 may maintain their transparent and non-optical characteristics. [0067] Since the first and second trenches TH 1 and TH 2 have substantially the same structure or similar structures to each other, repeated descriptions will be omitted for the purpose of ease and convenience in explanation. [0068] In the illustrated exemplary embodiment, the second trenches TH 2 may overlap with the first to third gate lines GL 1 , GL 2 and GL 3 as well as the light blocking layer BM. In an exemplary embodiment, for example, the second trenches TH 2 may overlap with the first to third gate lines GL 1 , GL 2 and GL 3 in one-to-one correspondence, as shown in FIG. 5A . Where the second trenches TH 2 overlap with the first to third gate lines GL 1 , GL 2 and GL 3 in one-to-one correspondence, a first pitch of the second trenches TH 2 may be similar to a second pitch of the first to third gate lines GL 1 , GL 2 and GL 3 . In other exemplary embodiments, the first pitch may be greater than the second pitch. In an exemplary embodiment, for example, the first pitch may be several times to tens of times greater than the second pitch. [0069] In the illustrated exemplary embodiment, the second trenches TH 2 may include first sub-trenches TH 2 - 1 defined in the first glass substrate GS 1 - 1 and second sub-trenches TH 2 - 2 defined in the second glass substrate GS 2 - 1 . The first sub-trenches TH 2 - 1 may disperse or relieve stress which is applied to the first glass substrate GS 1 - 1 owing to the curved shape of the first glass substrate GS 1 - 1 . The second sub-trenches TH 2 - 2 may disperse or relieve stress which is applied to the second glass substrate GS 2 - 1 owing to the curved shape of the first glass substrate GS 2 - 1 . [0070] In the illustrated exemplary embodiment, the second trenches TH 2 include the first sub-trenches TH 2 - 1 and the second sub-trenches TH 2 - 2 . However, the invention is not limited thereto. In other exemplary embodiments, the second trenches TH 2 may include only the first sub-trenches TH 2 - 1 defined in the first glass substrate GS 1 - 1 or the second sub-trenches TH 2 - 2 defined in the second glass substrate GS 1 - 1 . [0071] FIG. 6 is a cross-sectional view of another exemplary embodiment of a display panel included in a curved display device according to the invention. A position of the cross-sectional view of a display panel 302 shown in FIG. 6 corresponds to a position of a cross-sectional view taken along line II-II′ of FIG. 2 . In the illustrated exemplary embodiment, the same elements as described in the aforementioned exemplary embodiments will be indicated by the same numerals or the same designators. The descriptions to the same elements as described in the aforementioned embodiments will be omitted or mentioned briefly for the purpose of ease and convenience in explanation. [0072] Referring to FIG. 6 , the display panel 302 includes a display substrate 102 and an opposite substrate 202 . The display substrate 102 includes a first glass substrate GS 1 - 2 , and the opposite substrate 202 includes a second glass substrate GS 2 - 2 . [0073] In the illustrated exemplary embodiment, each of the first and second glass substrates GS 1 - 2 and GS 2 - 2 has an outer surface S 2 exposed outwardly. Each of first trenches TH 1 ′ may have a depth taken from the outer surface S 2 . Even though the first trenches TH 1 ′ have a depth from the outer surfaces S 2 (not the inner surfaces S 1 like in FIG. 3B ), stress caused owing to the curved shapes of the first and second glass substrates GS 1 - 2 and GS 2 - 2 may be dispersed or relieved by the first trenches TH 1 ′. As a result, phase retardation of light transmitted through the first and second glass substrates GS 1 - 2 and GS 2 - 2 may be minimized or effectively prevented. [0074] In an exemplary embodiment of manufacturing a curved display device, where the first trenches TH 1 ′ are defined at the outer surfaces S 2 , a laser or an etching solution may be provided to the outer surfaces S 2 to form the first trenches TH 1 ′ after manufacture of the display panel 302 is completed. [0075] FIG. 7 is an enlarged plan view of another exemplary embodiment of pixels of a display panel included in a curved display device according to the invention. In the illustrated exemplary embodiment, the same elements as described in the aforementioned exemplary embodiments will be indicated by the same numerals or the same designators. The descriptions to the same elements as described in the aforementioned embodiments will be omitted or mentioned briefly for the purpose of ease and convenience in explanation. [0076] Referring to FIG. 7 , a display panel 303 includes a display substrate 103 and an opposite substrate 203 . A glass substrate included in the display panel 103 has first trenches TH 11 defined therein, and a glass substrate included in the opposite substrate 203 has second trenches TH 22 defined therein. [0077] Referring again to FIG. 5A , each of the first trenches TH 1 is continuously disposed along the second direction DR 2 , and each of the second trenches TH 2 is continuously disposed along the first direction DR 1 . In the illustrated exemplary embodiment of FIG. 7 , each of the first trenches TH 11 is discontinuously disposed along the second direction DR 2 , and each of the second trenches TH 22 is discontinuously disposed along the first direction DR 1 , as indicated by the separated groups of dotted lines. As used herein, in an area between adjacent groups of dotted lines, the first and second trenches TH 11 and TH 22 are not defined in the respective glass substrate. [0078] Even though the first and second trenches TH 11 and TH 22 are discontinuously disposed as described above, the first and second trenches TH 11 and TH 22 may disperse or relieve stress applied to the display panel 303 . In addition, if the stress is locally applied to the display panel 303 , the first and second trenches TH 11 and TH 22 may be selectively defined in portions of the display panel 303 applied with the stress. [0079] Among the display substrate 103 and the opposite substrate 203 , while FIG. 7 shows both the first and second trenches TH 11 and TH 22 , the invention is not limited thereto. In an exemplary embodiment, among the display substrate 103 and the opposite substrate 203 , one of the first and second trenches TH 11 and TH 22 may be continuously disposed in one of the respective glass substrates, while the other one of the first and second trenches TH 11 and TH 22 may be discontinuously disposed in the other one of the respective glass substrates. In another exemplary embodiment, among the display substrate 103 and the opposite substrate 203 and referring again to FIG. 2 , one of the first and second trenches TH 11 and TH 22 may be disposed in one of the respective glass substrates, while no trenches are disposed in the other one of the respective glass substrates. [0080] FIG. 8 is a cross-sectional view of yet another exemplary embodiment of a display panel included in a curved display device according to the invention. A position of the cross-sectional view of a display panel 304 shown in FIG. 8 corresponds to a position of a cross-sectional view taken along line II-II′ of FIG. 2 . In the illustrated exemplary embodiment, the same elements as described in the aforementioned exemplary embodiments will be indicated by the same numerals or the same designators. The descriptions to the same elements as described in the aforementioned exemplary embodiments will be omitted or mentioned briefly for the purpose of ease and convenience in explanation. [0081] Referring to FIG. 8 , a display panel 304 includes a display substrate 100 - 1 and an opposite substrate 200 - 1 . Similar to the exemplary embodiment shown in FIG. 3B , the display panel 304 of the illustrated exemplary embodiment includes a first glass substrate GS 1 in which first sub-trenches TH 1 - 1 are defined, and the opposite substrate 200 - 1 includes a second glass substrate GS 2 in which second sub-trenches TH 1 - 2 are defined. [0082] Unlike the exemplary embodiment shown in FIG. 3B , the opposite substrate 200 - 1 of the illustrated exemplary embodiment does not include an electrode for controlling directors of liquid crystal molecules of a liquid crystal layer LC. However, the display substrate 100 - 1 includes pixel electrodes, and a common electrode CE- 1 disposed under the pixel electrodes. The common electrode CE- 1 generates an electric field together with the pixel electrodes. In an exemplary embodiment, for example, the pixel electrodes may include a first pixel electrode PE 1 - 1 and a second pixel electrode PE 2 - 1 that face each other with the third insulating layer L 3 therebetween. Slits may be defined in each of the first and second pixel electrodes PE 1 - 1 and PE 2 - 1 , which define respective portions of the first and second pixel electrodes PE 1 - 1 and PE 2 - 1 . The first and second pixel electrodes PE 1 - 1 and PE 2 - 1 having the slits defined therein generate the electric field together with the common electrode CE- 1 . [0083] In the illustrated exemplary embodiment, the first and second sub-trenches TH 1 - 1 and TH 1 - 2 may disperse or relieve the stress which is locally applied to the first and second glass substrates GS 1 and GS 2 owing to the curved shape of the display panel 304 , and thus, phase retardation of light transmitted through the first and second glass substrates GS 1 and GS 2 may be minimized or effectively prevented. As a result, the first and second glass substrates GS 1 and GS 2 may maintain their transparent and non-optical characteristics. [0084] According to one or more exemplary embodiment of the invention, the trenches are defined in the glass substrate and extend in a direction intersecting the curved direction of the glass substrate, in the curved display device. The trenches may disperse or relieve the stress which is locally applied to the glass substrate owing to the curved shape of the glass substrate. Thus, phase retardation of the light transmitted through the glass substrates is minimized or effectively prevented, so the non-optical characteristics of the glass substrates may be maintained to improve the display quality of the curved display device. [0085] While the invention has been described with reference to exemplary embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. Therefore, it should be understood that the above exemplary embodiments are not limiting, but illustrative. Thus, the scope of the invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing description.

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