Abstract:
The viewing angle of a Liquid Crystal Display (LCD) apparatus is expanded by means of a sampled light redirecting layer, In one embodiment, the sampled light redirecting layer is formed as a compensation layer disposed between a top polarizing plate and the rest of a liquid crystal display panel having a first substrate, a second substrate, and a liquid crystal layer interposed therebetween. The compensation layer includes at least two optical path changing patterns disposed in interleaved manner. The two optical path changing patterns have different refractive indexes. As a result of the different refractive indices and shapes of the at least two different optical path changing patterns some of the light rays sampled out of the output of the rest of a liquid crystal display panel are directed in a first direction by means of reflection or refraction and some are directed in a different second direction, thereby improving a side visibility of the display apparatus.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 13/188,779 filed on Jul. 22, 2011, which relies for priority upon Korean Patent Application No. 10-2010-0093412 filed on Sep. 27, 2010, the contents of which are herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field of Disclosure 
     The present disclosure of invention relates to a display apparatus and a method of manufacturing the display apparatus. More particularly, the present invention relates to a liquid crystal display apparatus capable of improving image visibility and a method of manufacturing the liquid crystal display apparatus. 
     2. Description of Related Technology 
     In general, a liquid crystal display (LCD) includes an array substrate, an opposite substrate facing the array substrate, and a liquid crystal layer disposed between the array substrate and the opposite substrate. The array substrate is provided with a pixel electrode, and the opposite substrate is provided with a common electrode facing the pixel electrode. Liquid crystal molecules included in the liquid crystal layer are aligned in a direction decided by an electric field generated between the pixel electrode and the common electrode, and a transmittance of a light depends upon the alignment directions of the liquid crystal molecules. A to-be perceived image may be formed by controlling light transmittance of various pixels. 
     However, since the liquid crystal molecules have anisotropic refractive index, the visibility of the to-be perceived image may be changed according to a viewing angle of the viewer. That is, the visibility when the user watches/views the display panel at a side portion of the display panel may be significantly worse than the visibility when the user watches the display panel from a frontal head-on position relative to the display panel. Thus, when compared to a cathode ray tube display apparatus, the liquid crystal display has a defect of a narrow acceptable viewing angle due to light ray directivity characteristics of the conventional LCD device. 
     It is to be understood that this background of the technology section is intended to provide useful background for understanding the here disclosed technology and as such, the technology background section may include ideas, concepts or recognitions that were not part of what was known or appreciated by those skilled in the pertinent art prior to corresponding invention dates of subject matter disclosed herein. 
     SUMMARY 
     Exemplary embodiments in accordance with the present disclosure provide a liquid crystal display apparatus having a wider viewing angle and improved visibility compared to conventional LCD devices. 
     Exemplary teachings of the present disclosure also provide a method of manufacturing the liquid crystal display apparatus. 
     More specifically, the viewing angle of a Liquid Crystal Display (LCD) apparatus is expanded by means of a sampled light redirecting layer, In one embodiment, the sampled light redirecting layer is formed as a compensation layer disposed between a top polarizing plate and the rest of a liquid crystal display panel having a first substrate, a second substrate, and a liquid crystal layer interposed therebetween. The compensation layer includes at least two different optical path changing patterns disposed in interleaved manner. The at least two optical path changing patterns have different refractive indexes. As a result of the different refractive indices and shapes of interface surfaces where the at least two different optical path changing patterns contact one another, some of the light rays sampled out of the output of the rest of a liquid crystal display panel are directed in a first direction by means of reflection or refraction and some are directed in a different second direction by means of reflection or refraction, thereby improving a side visibility of the display apparatus. 
     Yet more specifically, in one embodiment, a liquid crystal display apparatus includes a first substrate, a second substrate, and a liquid crystal layer. The first substrate includes a first base substrate and a plurality of pixel units arranged on the first base substrate. The second substrate includes a second base substrate facing the first base substrate and the compensation layer is arranged on one surface of the second base substrate. The compensation layer includes two interleaved (interdigitated) optical path changing patterns that function to change the output directions of incident light rays, where the two optical path changing patterns have different indexes and are alternately arranged in a direction substantially in parallel to the one surface. The liquid crystal layer is disposed between the first substrate and the second substrate. 
     A method of manufacturing a liquid crystal display apparatus is provided as follows. A first substrate including a first base substrate and a plurality of pixels arranged on the first base substrate is formed. A second substrate including a second base substrate facing the first base substrate and a compensation layer arranged on one surface of the second base substrate to change a path of an incident light is formed. A liquid crystal layer is disposed between the first and second substrates. A first layer having a first refractive index is formed on the one surface of the second base substrate. The first layer is patterned to form a plurality of first optical path changing patterns arranged substantially in parallel to the first base substrate. A second layer having a second refractive index different from the first refractive index is formed on the second base substrate on which the first optical path changing patterns are formed. The second layer is patterned to form a plurality of second optical path changing patterns each arranged between two first optical path changing patterns adjacent to each other. 
     Other aspects of the present teachings will become apparent from the below detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other advantages of the present disclosure of invention will become readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a cross-sectional view showing a display apparatus according to an exemplary embodiment; 
         FIG. 2  is a cross-sectional view showing a compensation layer of  FIG. 1 ; 
         FIGS. 3 to 5  are cross-sectional views showing compensation layers according to respective other exemplary embodiments; 
         FIG. 6  is a perspective view showing a first polarizing plate, a compensation layer, and a second polarizing plate of  FIG. 1 ; 
         FIG. 7  is a perspective view showing a first polarizing plate, a compensation layer, and a second polarizing plate according to another exemplary embodiment; 
         FIG. 8A  is a graph showing a brightness of each gray scale level according to upper and lower viewing angles of a normal TN display; 
         FIG. 8B  is a graph showing a brightness of each gray scale level according to left and right viewing angles of a normal TN display; 
         FIG. 9A  is a graph showing a brightness of each gray scale level according to upper and lower viewing angles of a display apparatus having a compensation layer of  FIG. 6 ; 
         FIG. 9B  is a graph showing a brightness of each gray scale level according to left and right viewing angles of a display apparatus having a compensation layer of  FIG. 6 ; 
         FIG. 10A  is a graph showing a brightness of each gray scale level according to upper and lower viewing angles of a display apparatus having a compensation layer of  FIG. 7 ; 
         FIG. 10B  is a graph showing a brightness of each gray scale level according to left and right viewing angles of a display apparatus having a compensation layer of  FIG. 7 ; 
         FIG. 11A  is a graph showing a transmittance according to a thickness of a second optical path changing pattern in a white gray scale when the second optical path changing pattern is extended in a direction that is substantially in parallel to an x-axis of  FIG. 6 ; 
         FIG. 11B  is a graph showing a transmittance according to a thickness of a second optical path changing pattern in a black gray scale when the second optical path changing pattern is extended in a direction that is substantially in parallel to an x-axis of  FIG. 6 ; 
         FIG. 12A  is a graph showing a transmittance according to a thickness of a second optical path changing pattern in a white gray scale when the second optical path changing pattern is extended while being inclined by about 135° with respect to an x-axis of  FIG. 7 ; 
         FIG. 12B  is a graph showing a transmittance according to a thickness of a second optical path changing pattern in a black gray scale when the second optical path changing pattern is extended while being inclined by about 135° with respect to an x-axis of  FIG. 7 ; 
         FIG. 13A  is a graph showing a contrast ratio of a display apparatus in the case that a second optical path changing pattern is extended in a direction that is substantially in parallel to an x-axis of  FIG. 6 ; 
         FIG. 13B  is a graph showing a contrast ratio of a display apparatus in the case that a second optical path changing pattern is extended in a direction that is inclined by about 135° with respect to an x-axis of  FIG. 7 ; 
         FIGS. 14A to 14E  are cross-sectional views showing a manufacturing method of a compensation layer according to an exemplary embodiment in accordance with the disclosure; and 
         FIGS. 15A to 15H  are cross-sectional views showing a manufacturing method of a compensation layer according to another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     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. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout. 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, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present disclosure. 
     Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship 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” or “beneath” other elements or features would then be oriented “above” 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. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms, “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, 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. 
     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 the present disclosure most closely pertains. 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. 
     Hereinafter, the present disclosure of invention will be explained in detail with reference to the accompanying drawings. 
       FIG. 1  is a cross-sectional view showing a display apparatus according to a first exemplary embodiment in accordance with the disclosure. 
     Referring to  FIG. 1 , a display apparatus  500  includes a display panel  350  structured to control transmittance of incident light rays using a liquid crystal. The display apparatus  500  further includes a first polarizing plate  410  that polarizes light rays provided to the display panel  350  and a second polarizing plate  420  that polarizes light rays as they exit from the display panel  350 . The display panel  350  is disposed between the first and second polarizing plates  410  and  420 . 
     The display apparatus  500  yet further includes a backlight unit  450  that generates the incident light rays and provides the light rays to the display panel  350 . The backlight unit  450  is arranged under the first polarizing plate  410 . Thus, light generated from the backlight unit  450  is output to a viewing user of the display apparatus  500  after sequentially passing through the first polarizing plate  410 , the display panel  350 , and the second polarizing plate  420 . 
     The display panel  350  includes a first substrate  100 , a second substrate  200  facing the first substrate  100 , and a liquid crystal material layer  300  disposed between the first substrate  100  and the second substrate  200 . The first substrate  100  is disposed adjacent to the first polarizing plate  410 , and the second substrate  200  is disposed adjacent to the second polarizing plate  420 . 
     The first substrate  100  includes a first base substrate  110  and a pixel array layer  120  disposed on the first base substrate  110 . Although not explicitly shown in  FIG. 1 , the pixel array layer  120  is understood to be a layer on which a plurality of pixel units are arranged in a matrix configuration, and each pixel unit may include a thin film transistor (TFT), a pixel electrode and optionally a storage capacitance. 
     The second substrate  200  includes a second base substrate  210  facing the first base substrate  110 , a compensation layer  220  disposed on a first major surface  211  of the second base substrate  210 , and a color filter layer  230  disposed on the compensation layer  220 . The first major surface  211  of the second base substrate  210  may face the liquid crystal layer  300  or the second polarizing plate  420 . In  FIG. 1 , the compensation layer  220  is shown disposed on the first major surface  211  and facing away from the liquid crystal layer  300 . 
     The compensation layer  220  includes a first optical path changing pattern  221  and a second optical path changing pattern  222  having different refractive indexes from each other. Each of the first and second optical path changing patterns  221  and  222  is provided as a plurality of spaced apart regions, and in one embodiment, the first and second optical path changing patterns  221  and  222  are alternately arranged one after the next in a repeat direction which is substantially parallel to the first major surface  211  of the second base substrate  210 . As an example of the present embodiment, the first optical path changing pattern  221  has a first refractive index (n 1 ) and the second optical path changing pattern  222  has a second refractive index (n 2 ) that is lower than the first refractive index (n 2 &lt;n 1 ). 
     The first optical path changing pattern  221  may have its regions formed of an organic resin having for example an acrylic-based resin or polyamide-based resin with relatively large refractive index. In addition, the first optical path changing pattern  221  may have its regions formed to exhibit the first refractive index (n 1 ) in the range of about 1.2 to about 2.1 (while n 1  remains &gt;n 2 ). In order to increase the first refractive index (n 1 ) of the first optical path changing pattern  221 , a titanium oxide (TiOx) may be added into the organic resin. 
     The second optical path changing pattern  222  may include at least one of low refractive index and light-passing materials such as a silicon nitride (SiNx), a silicon oxide (SiOx), a titanium oxide (TiOx), an indium tin oxide (ITO), an indium zinc oxide (IZO), or a zinc oxide. The microstructure of the second pattern/region  222  may be made less dense (e.g., more hollowed) than that of the first pattern/region  221  so as to thereby reduce the refractive index (n 2 ) of the second pattern/region  222 . Also, the second optical path changing pattern  222  may have its regions formed to exhibit the second refractive index (n 2 ) in a range of about 1 to about 1.6, where the second refractive index (n 2 ) is lower than the first refractive index (n 1 ). The second pattern/region  222  may be filled with air. 
     As shown in  FIG. 1 , the compensation layer  220  may further include at least one supportive/protective cover layer  223  that protectively covers and/or supports the first and second optical path changing patterns  221  and  222  (e.g., protecting  221 / 222  from chemicals that might be present in layer  230 ). As an example of the present embodiment, the cover layer  223  may include the same material as the first optical path changing pattern  221 . 
     The color filter layer  230  disposed on the compensation layer  220  may include a red color filter R, a green color filter G, and a blue color filter B. As another exemplary embodiment, an organic layer colored with corresponding pigments or dyes may be used as part of the first optical path changing pattern  221 . In case that the organic layer colored with pigments or dyes is used for the first optical path changing pattern  221 , the red colored, green colored and the blue colored pixel filters may be integrally formed by the first optical path changing pattern  221 . Therefore, the first optical path changing pattern  221  may perform a dual function as substituting for or supplementing the color filter layer  230 , and thus, in one case the color filter layer  230  may be omitted from the second substrate  200 . 
     Although not shown in  FIG. 1 , the second substrate  200  may further include a common electrode (not shown) and a black matrix (not shown) in addition to the color filter layer  230 . 
     Meanwhile, the liquid crystal material of layer  300  may include a twisted nematic (TN) liquid crystal, a vertical alignment (VA) liquid crystal, or a cholesteric liquid crystal. 
       FIG. 2  is a cross-sectional view showing the compensation layer of  FIG. 1 . 
     Referring to  FIG. 2 , the compensation layer  220  includes a plurality of first optical path changing patterns or regions  221  having the first refractive index n 1  and a plurality of second optical path changing patterns or regions  222  having the second refractive index n 2  that is lower than the first refractive index n 1 . Each of the second optical path changing patterns  222  is arranged between two spaced apart first optical path changing patterns  221  that neighbor each other. 
     An area or region between a first pair of spaced apart but adjacent second optical path changing patterns  222  is defined in  FIG. 2  as a first area R 1  through which incident light rays may pass. In the first area R 1 , the compensation layer  220  includes a first material having the greater first refractive index n 1 . A second region or area between a pair of spaced apart but adjacent first areas R 1  is defined in  FIG. 2  as a second area R 2  from which incident light rays (e.g., L 2 , L 3 ) may be reflected, totally reflected or refracted therethrough. In the second area R 2 , the compensation layer  220  includes the first material having the first refractive index n 1  and the second material having the lesser second refractive index n 2 . 
     Since the compensation layer  220  includes one homogenous light-passing medium in the first area R 1 , a first light ray L 1  incident to the first area R 1  mostly passes through the first area R 1  without being refracted. However, the compensation layer  220  includes two light-passing media having different refractive indexes (n 2 &gt;n 1 ) in the second area R 2 , a second light ray L 2  and a third light ray L 3  incident to the second area R 2  may be respectively essentially totally reflected and essentially totally refracted due to the different refractive indexes of the two media in second area R 2 . 
     More particularly, an interface or contact surface  222   a  at which the first optical path changing pattern  221  comes into contact with the second optical path changing pattern  222  is provided in the second area R 2 , and the second light ray L 2  and the third light ray L 3  (which light rays may be pre-polarized and directed in the vertical (+Z) direction or another direction as they enter cover layer  223 ) are respectively totally reflected or refracted at that contact surface  222   a  due to angle of incidence and difference in refractive indices (n 1 /n 2 ). As an exemplary embodiment of the present invention, the contact surface  222   a  is inclined by a predetermined angle θ with respect to the one surface  211 . The angle θ may be set in a range of about 30° to about 85°. Therefore, as shown in  FIG. 2 , the second light ray L 2  vertically incident to a light incident surface of the compensation layer  220  is totally reflected in the second area R 2 , and the third light ray L 3  incident to the light incident surface of the compensation layer  220  while being inclined (unlike L 1  and L 2 ) by the angle θ may be refracted. 
     A total reflection angle of the second light ray L 2  may be decided by a difference between the first refractive index n 1  and the second refractive index n 2  and an inclination degree (that is, the angle θ) of the contact surface  222   a . The second light L 2  that is totally reflected at the contact surface  222   a  may be exited while being largely inclined with respect to a hypothetical normal line of the screen that is substantially perpendicular to the first surface  211  of the second base substrate  210 . Therefore, a side visibility of the display apparatus  500  may be improved since light rays such as L 2  are intentionally reflected essentially totally in the direction of an aside user while light rays such as L 1  are intentionally caused to be passed in the direction of a head-on viewer of the LCD device  500 . 
     Since the second light ray L 2  vertically incident to the light incident surface of the compensation layer  220  has been already processed by the liquid crystal layer  300  and the color filters layer  230 , it includes an accurate gray scale and color information, and therefore the angle θ of the contact surface  222   a  may be set to totally reflect the second light ray L 2  vertically incident to the light incident surface of the compensation layer  220 . 
     Meanwhile, the third light ray L 3  incident to the light incident surface of the compensation layer  220  while being inclined generally does not include the accurate gray scale and/or color information intended for it. Thus, the second optical path changing pattern  222  may further include a direction sensitive optical absorbent to absorb (attenuate) the third light ray L 3  refracted at the contact surface  222   a . As an example of the present embodiment, the second optical path changing pattern  222  may include black carbon particles oriented to absorb mis-directed incident light rays such as L 3 . 
     The second optical path changing pattern  222  may be in the form of a triangular prism (see also  FIG. 6 ) or another shape having the illustrated triangular cross section and may have a triangle base width w 1  of about 0.5 μm to about 10 μm and a thickness (triangle height) t 1  of about 0.1 μm to about 3 μm. The first optical path changing pattern  221  may be in the form of a trapezoidal prism (see also  FIG. 6 ) or another shape having the illustrated trapezoidal cross section and may have a trapezoid base width w 2  of about 3 μm to about 30 μm and a thickness (trapezoid height) t 2  of about 1 μm to about 10 μm. That is, the first optical path changing pattern  221  may have a thickness t 1  equal to or thicker than that of the second optical path changing pattern  222 . 
       FIGS. 3 to 5  are cross-sectional views showing a compensation layer according to another exemplary embodiment in accordance with the present disclosure. 
     Referring to  FIG. 3 , a compensation layer  220   a  includes a first optical path changing pattern  224  having a first refractive index n 1  and a second optical path changing pattern  225  having a second refractive index n 2  that is lower than the first refractive index n 1 . The first optical path changing pattern  224  and the second optical path changing pattern  225  are alternately arranged in a direction that is substantially in parallel to one surface  211  of a second base substrate  210 . 
     The second optical path changing pattern  225  in  FIG. 3  has a half circle cross sectional shape in its cross-sectional view. As an exemplary embodiment of the present invention, the second optical path changing pattern  225  may have a curvature of about 0.5 or less. Vertically directed light rays (not shown, see L 1 , L 2  of  FIG. 2 ) striking the inclined portions of the n 1 &gt;n 2  optical interface are refracted in respective inclined directions depending on the instant angle of incline and on the refractive index ratio (n 1 /n 2 ). 
     An area or region between adjacent second optical path changing patterns  225  is defined in  FIG. 3  as a first area R 1  through which incident light rays may pass. In the first area R 1 , the compensation layer  220   a  includes a first material having the greater first refractive index n 1 . A second region or area between adjacent first areas R 1  is defined as a second area R 2  from which incident light rays may be reflected, totally reflected or refracted therethrough. In the second area R 2 , the compensation layer  220   a  includes the first material having the first refractive index n 1  and the second material having the lesser second refractive index n 2 . 
     Since the compensation layer  220   a  includes one homogenous light-passing medium in the first area R 1 , a first light ray L 1  vertically incident to the light incident surface of the compensation layer  220   a  in the first area R 1  mostly passes through the first area R 1  without being refracted. However, a second light ray L 2  vertically incident to the light incident surface of the compensation layer  220   a  in the second area R 2  may be respectively essentially totally reflected and essentially totally refracted due to the different refractive indexes of the two media in second area R 2 . 
     Therefore, a side visibility of the display apparatus  500  may be improved since light rays such as L 2  are intentionally reflected essentially totally in the direction of an aside user while light rays such as L 1  are intentionally caused to be passed in the direction of a head-on viewer of the LCD device  500 . 
     Referring to  FIG. 4 , a compensation layer  220   b  includes a first optical path changing pattern  226  having a first refractive index n 1  and a second optical path changing pattern  227  having a second refractive index n 2  that is lower than the first refractive index n 1 . The first optical path changing pattern  226  and the second optical path changing pattern  227  are alternately arranged in a direction that is substantially in parallel to one surface of a second base substrate  210 . 
     The first and second optical path changing patterns  226  and  227  may have a rectangular shape in a cross-sectional view. In this case, a medium interface or contact surface  227   a  at which the first optical path changing pattern  226  comes into contact with the second optical path changing pattern  227  may be substantially perpendicular to the one surface  211 . 
     Since the compensation layer  220   b  includes one homogenous light-passing medium in the first area R 1 , the first light ray L 1  and the second light ray L 2  vertically incident to a light incident surface of the compensation layer  220   b  in the first area R 1  mostly passes through the first area R 1  and the second area R 2  without being refracted, respectively. 
     However, a fourth light ray L 4  ray incident to the contact surface  227   a  of the compensation layer  220   b  may be respectively essentially totally reflected and essentially totally refracted due to the different refractive indexes of the two media. As an exemplary embodiment in accordance with the present disclosure, the fourth light ray L 4  may be approximately vertically incident to the light incident surface of the compensation layer  220   b.    
     Therefore, a side visibility of the display apparatus  500  may be improved since light rays such as L 2  are intentionally reflected essentially totally in the direction of an aside user while light rays such as L 1  are intentionally caused to be passed in the direction of a head-on viewer of the LCD device  500 . 
     Referring to  FIG. 5 , a compensation layer  220   c  includes a first optical path changing pattern  228  having a first refractive index n 1  and a second optical path changing pattern  229  having a second refractive index n 2  that is lower than the first refractive index n 1 . The first optical path changing pattern  228  and the second optical path changing pattern  229  are alternately arranged in a direction that is substantially in parallel to one surface  211  of a second base substrate  210 . 
     The second optical path changing pattern  229  may have a trapezoid shape in a cross-sectional view, and the first optical path changing pattern  228  may have a reverse trapezoid shape. As in the case of  FIG. 3 , vertically directed light rays (not shown, see L 1 , L 2  of  FIG. 2 ) striking the inclined portions of the n 1 &gt;n 2  optical interfaces are refracted in respective inclined directions depending on the instant angle of incline and on the refractive index ratio (n 1 /n 2 ). 
     Since the compensation layer  220   c  includes one homogenous light-passing medium in the first area R 1 , a first light ray L 1  vertically incident to a light incident surface of the compensation layer  220   c  in the first area R 1  mostly passes through the first area R 1  without being refracted. However, a second light ray L 2  vertically incident to the light incident surface of the compensation layer  220   c  in the second area R 2  may be respectively essentially totally reflected and essentially totally refracted due to the different refractive indexes of the two media in second area R 2 . 
     Therefore, a side visibility of the display apparatus  500  may be improved since light rays such as L 2  are intentionally reflected essentially totally in the direction of an aside user while light rays such as L 1  are intentionally caused to be passed in the direction of a head-on viewer of the LCD device  500 . 
       FIG. 6  is a perspective view showing the first polarizing plate, the compensation layer, and the second polarizing plate of  FIG. 1 . 
     Referring to  FIG. 6 , the compensation layer  220  and the liquid crystal layer  300  are disposed between the first polarizing plate  410  and the second polarizing plate  420 . As an example embodiment in accordance with the present disclosure, the liquid crystal layer  300  may include a twisted nematic liquid crystal. In this case, the first polarizing plate  410  may have a first light absorption axis  411  and the second polarizing plate  420  may have a second absorption axis  421  that is substantially perpendicular to the first absorption axis  411 . The first absorption axis  411  is inclined by about 45° with respect to an x-axis, and the second absorption axis  421  is inclined by about 135° with respect to the x-axis to be substantially perpendicular to the first absorption axis  411 . The x-axis may be parallel to the D 2  direction. 
     The compensation layer  220  includes the first optical path changing pattern  221  having the first refractive index n 1  and the second optical path changing pattern  222  having the second refractive index n 2  that is lower than the first refractive index n 1 . The first optical path changing pattern  221  and the second optical path changing pattern  222  are alternately arranged along a first direction D 1 , and each of the first and second optical path changing patterns  221  and  222  is extended in a second direction D 2  that is substantially perpendicular to the first direction D 1 . As illustrated, the second optical path changing pattern  222  may have a triangular prism shape. 
     As an exemplary embodiment in accordance with the present disclosure, the second direction D 2  may be a direction that is substantially in parallel to the x-axis. Then, the second optical path changing pattern  222  is inclined by about 135° with respect to the second absorption axis  421  of the second polarizing plate  420  and is inclined by about 45° with respect to the first absorption axis  411  of the first polarizing plate  410 . 
       FIG. 7  is a perspective view showing a first polarizing plate, a compensation layer, and a second polarizing plate according to another exemplary embodiment in accordance with the present disclosure. 
     Referring to  FIG. 7 , a compensation layer  220  and a liquid crystal layer  300  are disposed between a first polarizing plate  410  and a second polarizing plate  420 . As an example, the liquid crystal layer  300  may include a twisted nematic liquid crystal. The first polarizing plate  410  includes a first absorption axis  411  that is inclined by about 45° with respect to an x-axis, and the second polarizing plate  420  includes a second absorption axis  421  that is inclined by about 135° with respect to the x-axis to be substantially perpendicular to the first absorption axis  411 . 
     The compensation layer  220  includes a first optical path changing pattern  221  having a first refractive index n 1  and a second optical path changing pattern  222  having a second refractive index n 2  that is lower than the first refractive index n 1 . The first optical path changing pattern  221  and the second optical path changing pattern  222  are alternately arranged in a first direction D 1 , and each of the first and second optical path changing patterns  221  and  222  is extended in a second direction D 2  that is substantially perpendicular to the first direction D 1 . Thus, the second optical path changing pattern  222  may have a triangular prism shape. 
     In this particular example, the first direction D 1  may be substantially in parallel to the first absorption axis  411 , and the second direction D 2  may be substantially in parallel to the second absorption axis  421  and thus the medium interface surfaces where  221  meets  222  may extend as being substantially perpendicular to the first absorption axis  411  and thus as substantially parallel to the light transmission axis (not shown) of the first polarizing plate  410 . 
       FIG. 8A  is a graph showing a brightness of each of selected gray scale levels according to upper and lower viewing angles of a conventional TN display (not shown), and  FIG. 8B  is a graph showing a brightness of each of selected gray scale levels according to left and right viewing angles of a conventional TN display. 
     Referring to  FIGS. 8A and 8B , the brightness of each gray scale level is measured according to upper and lower viewing angles and left and right viewing angles in a conventional TN display. A gray scale inversion does not occur in a range of about −60° to about 60° in the case of left and right directions, however, the gray scale inversion occurs at a point of about −20° in the case of upper and lower directions. 
     That is, a viewing angle in the left and right directions is narrower than a viewing angle of the upper and lower directions. 
       FIG. 9A  is a graph showing a brightness of each gray scale level according to upper and lower viewing angles of a display apparatus in accordance with the present disclosure and having the compensation layer of  FIG. 6 .  FIG. 9B  is a graph showing a brightness of each gray scale level according to left and right viewing angles of the display apparatus having the compensation layer of  FIG. 6 . 
     Referring to  FIGS. 9A and 9B , a brightness of each gray scale level is measured according to the upper and lower viewing angles and the left and right viewing angles in a display apparatus having the compensation layer  220  of  FIG. 6 . The compensation layer  220  of  FIG. 6  includes the second optical path changing pattern  222  that is substantially in parallel to the x-axis shown in  FIG. 6 . 
     Similar to the TN liquid crystal, perceived gray scale inversion does not occur in the range of about −60° to about 60° in the case of the left and right directions. Also, perception of the gray scale inversion does not occur in the range of about −60° to about 30° in the case of the upper and lower directions. Therefore, when the display apparatus employs the compensation layer  220  of  FIG. 6 , the upper and lower viewing angles are improved compared to the conventional TN display ( FIGS. 8A-8B ). 
       FIG. 10A  is a graph showing a brightness of each gray scale level according to upper and lower viewing angles of a display apparatus having the compensation layer of  FIG. 7 , and  FIG. 10B  is a graph showing a brightness of each gray scale level according to left and right viewing angles of a display apparatus having the compensation layer of  FIG. 7 . 
     Referring to  FIGS. 10A and 10B , a brightness of each gray scale level is measured according to the upper and lower viewing angles and the left and right viewing angles of the display apparatus having the compensation layer of  FIG. 7 . The compensation layer  220  of  FIG. 7  includes the second optical path changing pattern  222  that is inclined by about 135° with respect to the x-axis of  FIG. 7 . 
     Similar to the TN liquid crystal, the gray scale inversion does not occur in the range of about −60° to about 60° in the case of the left and right directions. Also, the gray scale inversion does not occur in the range of about −60° to about 20° in the case of the upper and lower directions. Thus, when the display apparatus employs the compensation layer  220  shown in  FIG. 7 , the upper and lower viewing angles are improved when compared to the TN display. 
       FIG. 11A  is a graph showing resultant transmittance according to change of inclination angle of the incident light rays and also according to change of thickness (t 1 ) of the second optical path changing pattern (graph plots G 1 -G 4 ) where the thickness of the second optical path changing pattern is varied and the width w 1  is correspondingly extended in a direction that is substantially in parallel to the y-axis of  FIG. 6 .  FIG. 11B  is a graph showing a resultant transmittance according to change of inclination angle of the incident light rays and also according to change of thickness (t 1 ) of the second optical path changing pattern in a black gray scale in case that the second optical path changing pattern is varied and the width (w 1 ) is correspondingly extended in a direction that is substantially in parallel to the y-axis of  FIG. 6 . The plotted result graphs include a first graph G 1  and a fifth graph G 5  representing the transmittance when the second optical path changing pattern  222  has a thickness t 1  of about 1.5 μm, a second graph G 2  and a sixth graph G 6  representing the transmittance when the second optical path changing pattern  222  has a thickness t 1  of about 3 μm, a third graph G 3  and a seventh graph G 7  representing the transmittance when the second optical path changing pattern  222  has a thickness t 1  of about 4.5 μm, and a fourth graph G 4  and an eighth graph G 8  representing the transmittance when the second optical path changing pattern has a thickness t 1  of about 6 μm. In addition, in  FIGS. 11A and 11B , an x-axis represents an angle (that is, an incident angle θi) formed by an incident light and a normal line that is substantially perpendicular to the one surface  211  of the second base substrate  210 . 
     Referring to details of  FIG. 11A , when the display apparatus displays its maximum white gray scale, a transmittance of a light (hereinafter, referred to as a front transmittance) incident to a front surface of the second base substrate  210  becomes higher as the incident angle θi becomes smaller. In addition, in the case that the thickness t 1  of the second optical path changing pattern  222  is more than 3.0 μm, the front transmittance is higher than 0.6. Thus, the thickness t 1  of the second optical path changing pattern  222  may be set in consideration of desired consistency of the front transmittance. 
     Referring to  FIG. 11B , when the display apparatus displays the black gray scale (dark output), the front transmittance becomes lower as the incident angle θi becomes smaller. Also, the front transmittance is close to zero (0) regardless of the thickness t 1  of the second optical path changing pattern  222 . However, a transmittance of a leakage light (hereinafter, referred as a lateral transmittance) incident while being inclined by about 50° with respect to the second base substrate  210  becomes higher as the thickness t 1  of the second optical path changing pattern  222  becomes smaller. Therefore, in order to decrease the lateral transmittance, the thickness t 1  of the second optical path changing pattern  222  may be set to about 3.0 μm or larger. 
     As described above, the transmittance in the white gray scale may be improved and the undesired transmittance of leakage light when in the black gray scale displaying mode may be decreased by controlling the thickness t 1  of the second optical path changing pattern  222 . 
       FIG. 12A  is a graph showing a transmittance according to a thickness of the second optical path changing pattern in a white gray scale display mode when the second optical path changing pattern is extended while being inclined by about 135° with respect to the x-axis of  FIG. 7 .  FIG. 12B  is a graph showing a transmittance according to a thickness of the second optical path changing pattern in a black gray scale display mode when the second optical path changing pattern is extended while being inclined by about 135° with respect to the x-axis of  FIG. 7 . The graph plots include a ninth graph G 9  and a thirteenth graph G 13  representing the transmittance when the second optical path changing pattern  222  has a thickness t 1  of about 1.5 μm, a tenth graph G 10  and fourteenth graph G 14  representing the transmittance when the second optical path changing pattern  222  has a thickness t 1  of about 3 μm, an eleventh graph G 11  and a fifteenth graph G 15  representing the transmittance when the second optical path changing pattern  222  has a thickness t 1  of about 4.5 μm, and a twelfth graph G 12  and a sixteenth graph G 16  representing the transmittance when the second optical path changing pattern  222  has a thickness t 1  of about 6 μm. In  FIGS. 12A and 12B , the graph&#39;s x-axis represents an angle (that is, an incident angle θi) formed by an incident light and a normal line that is substantially perpendicular to the one surface  211  of the second base substrate  210 . 
     Referring to  FIG. 12A , when the display apparatus displays a white gray scale, a transmittance of a light (hereinafter, referred as a front transmittance) incident to a front surface of the second base substrate  210  becomes higher as the incident angle θi becomes smaller. Also, when the second optical path changing pattern  222  has a thickness t 1  larger than 3.0 μm, the front transmittance becomes larger than 0.6. Thus, the thickness t 1  of the second optical path changing pattern  222  may be set in consideration of the desired amount and consistency of front transmittance. 
     Referring to  FIG. 12B , when the display apparatus displays a black gray scale, the front transmittance becomes lower as the incident angle θi becomes smaller. Also, the front transmittance is close to zero (0) regardless to the thickness t 1  of the second optical path changing pattern  222 . However, a transmittance of a side leakage light (hereinafter, referred as a lateral transmittance) incident while being inclined by about 50° with respect to the second base substrate  210  becomes higher as the thickness t 1  of the second optical path changing pattern  222  becomes smaller. Therefore, in order to decrease the undesired lateral transmittance, the thickness t 1  of the second optical path changing pattern  222  may be set to about 3.0 μm or larger. 
     As described above, the transmittance in the white gray scale may be improved and the transmittance of leakage light when in the black gray scale display mode may be decreased by controlling the thickness t 1  of the second optical path changing pattern  222 . 
       FIG. 13A  is a graph showing a contrast ratio of a display apparatus in the case that the second optical path changing pattern is extended in a direction that is substantially in parallel to the x-axis of  FIG. 6 .  FIG. 13B  is a graph showing a contrast ratio of a display apparatus in the case that the second optical path changing pattern is extended in a direction that is inclined by about 135° with respect to the x-axis of  FIG. 7 . 
     In  FIGS. 13A and 13B , a seventeenth graph G 17  and a twenty-first graph G 21  show a contrast ratio in the case that the second optical path changing pattern  222  has a thickness t 1  of about 1.5 μm, an eighteenth graph G 18  and a twenty-second graph G 22  show a contrast ratio in the case that the second optical path changing pattern  222  has a thickness t 1  of about 3 μm, a nineteenth graph G 19  and a twenty-third graph G 23  show a contrast ratio in the case that the second optical path changing pattern  222  has a thickness t 1  of about 4.5 μm, and a twentieth graph G 20  and a twenty-fourth graph G 24  show a contrast ratio in the cast that the second optical path changing pattern  222  has a thickness t 1  of about 6 μm. 
     Referring to  FIG. 13A , when the second optical path changing pattern  222  is extended in a direction that is substantially in parallel to the x-axis of  FIG. 6 , the contrast ratio of the display apparatus is the highest when the second optical path changing pattern  222  has the thickness t 1  of about 6 μm. 
     Referring to  FIG. 13B , when the second optical path changing pattern  222  is extended in a direction that is inclined by about 135° with respect to the x-axis of  FIG. 7 , the contrast ratio of the display apparatus is the highest when the second optical path changing pattern  222  has the thickness t 1  of about 1.5 μm. 
     However, a contrast ratio of the display apparatus when the second optical path changing pattern  222  is extended in a direction substantially in parallel to the x-axis of  FIG. 6  is much lower than a contrast ratio of the display apparatus when the second optical path changing pattern  222  is extended in a direction that is inclined by about 135° with respect to the x-axis of  FIG. 7 . Thus, in order to improve the contrast ratio of the display apparatus, the second optical path changing pattern  222  should be longitudinally extended in the direction that is inclined by about 135° with respect to the x-axis. 
       FIGS. 14A to 14E  are cross-sectional views showing a manufacturing method usable for manufacturing a compensation layer according to an exemplary embodiment of the present disclosure. Variations in shape and angle may be obtained with slit mask technologies. 
     Referring to  FIG. 14A , an organic layer  241  having a relatively large refractive index (n 1 ) due for example to it including at least one of an acrylic-based resin or a polyamide-based resin is formed on a second base substrate  210 . As an example, when the organic layer  241  includes the acrylic-based resin or the polyamide-based resin, the organic layer  241  may have a refractive index of about 0.2 to about 0.5. As another example, the organic layer  241  may be formed by adding a titanium oxide (TiOx) to the acrylic-based resin or the polyamide-based resin. When the titanium oxide (TiOx) is added to the organic layer  241 , the refractive index (n 1 ) of the organic layer  241  may increase to about 1.9 to about 2.1 
     Then, a photosensitive layer (photoresist or PR)  242  is formed on the organic layer  241 . Although not shown in figures, a mask (not shown) is disposed on the photosensitive layer  242 . An opening is formed through the mask corresponding to a second area R 2  that is positioned adjacent to a first area R 1  in which a first optical path changing pattern  243  is formed. When a light is irradiated onto the photosensitive layer  242  after the mask is disposed, the photosensitive layer  242  and the organic layer  241  arranged in the second area R 2  are substantially simultaneously exposed to the light. Then, the exposed photosensitive layer  242  and the organic layer  241  are substantially simultaneously developed. After that, as shown in  FIG. 14B , a hardened photosensitive pattern  244  and a first optical path changing pattern  243  are formed in the first area R 1  of the second base substrate  210 . 
     An inorganic layer  245  having a relatively low refractive index (n 2 ) due for example to it including at least one of a silicon nitride (SiNx), a silicon oxide (SiOx), a titanium oxide (TiOx), indium tin oxide (ITO), indium zinc oxide (IZO), or zinc oxide ZnOx is formed on the second base substrate  210  on which the hardened photosensitive pattern  244  and the first optical path changing pattern  243  are formed. The inorganic layer  245  may be deposited by a plasma-enhanced chemical vapor deposition (PECVD) process. In the case that the inorganic layer  245  is formed with a silicon nitride (SiNx), the refractive index of the inorganic layer  245  may be controlled by a ratio between an ammonia gas (NH 3 ) and a silane gas (SiH 4 ) during CVD deposition. Meanwhile, in the case that the inorganic layer  245  is formed with a silicon oxide layer (SiOx), the refractive index of the inorganic layer  245  may be controlled by a ratio between a silane gas (SiH 4 ) and an oxide nitrogen gas (N 2 O) during CVD deposition. 
     Then, an etching mask (not shown) including a photosensitive layer and an optional ITO layer (not shown) is arranged on the inorganic layer  245 , and the inorganic layer  245  is selectively dry-etched. The inorganic layer  245  may be dry-etched by an inductively coupled plasma (ICP) method or a reactive ion etching (RIE) method. 
     In the dry etching process, a sulfur hexafluoride (SF 6 ) gas or a mixture gas of the sulfur hexafluoride (SF 6 ) gas and an oxygen gas (O 2 ) may be used as the etching gas. 
     As shown in  FIG. 14D , the inorganic layer  245  is etched to form a second optical path changing pattern  246  on the second base substrate  210 . the thickness t 1  of the second optical path changing pattern  246  may be independently changed by changing an amount of the etching gas used, and/or changing the etching duration, and/or a temperature, pressure or power of the etching chamber. 
     Then, when the photosensitive pattern  244  is stripped, the first optical path changing pattern  243  is formed in the first area R 1  of the second base substrate  210  and the second optical path changing pattern  246  is formed in the second area R 2 . Thus, the compensation layer  220  may be completely formed on the second base substrate  210 . 
       FIGS. 15A to 15H  are cross-sectional views showing a manufacturing method of a compensation layer according to another exemplary embodiment. 
     Referring to  FIG. 15A , a photosensitive layer  251  is formed on a second base substrate  210 . Although not shown in  FIG. 15A , a mask (not shown) having an opening formed therethrough corresponding to a second area R 2  is arranged on the photosensitive layer  251 . When a light is irradiated onto the photosensitive layer  251  after the mask is arranged, the photosensitive layer  251  arranged in a first area R 1  is exposed to the light. Then, when the exposed photosensitive layer  251  is developed, as shown in  FIG. 15B , a hardened photosensitive pattern  252  is formed in the first area R 1  of the second base substrate  210 . 
     Referring to  FIG. 15C , an inorganic layer  253  including at least one of a silicon nitride (SiNx), a silicon oxide (SiOx), a titanium oxide (TiOx), indium tin oxide (ITO), indium zinc oxide (IZO), or zinc oxide (ZnOx) is formed. The inorganic layer  253  may be deposited by a plasma-enhanced chemical vapor deposition (PECVD) process. 
     Then, an etching mask (not shown) including a photosensitive layer or an ITO layer (optional) is arranged on the inorganic layer  253  and the inorganic layer  253  is dry-etched. The inorganic layer  253  may be dry-etched by an inductively coupled plasma (ICP) method or a reactive ion etching (RIE) method. 
     In the dry etching process, a sulfur hexafluoride (SF 6 ) gas or a mixture gas of the sulfur hexafluoride (SF 6 ) gas and an oxygen gas (O 2 ) may be used as an etching gas. 
     As shown in  FIG. 15D , the inorganic layer  253  is etched to form a second optical path changing pattern  254  on the second base substrate  210 . The thickness t 1  of the second optical path changing pattern  254  may be independently changed according to an amount of the etching gas, an etching duration, and a temperature and pressure of an etching chamber. 
     Then, when the hardened photosensitive pattern  252  is selectively stripped away, the second optical path changing pattern  254  is left behind on the second base substrate  210  as shown in  FIG. 15E . 
     Referring to  FIG. 15F , an organic layer  255  including at least an acrylic-based resin or a polyamide-based resin is formed on the second base substrate  210  on which the second optical path changing pattern  254  is formed. As an exemplary embodiment of the present invention, the organic layer  255  including the acrylic-based resin or the polyamide-based resin may have a refractive index of about 0.2 to about 0.5. As another exemplary embodiment of the present invention, the titanium oxide (TiOx) may be added into the acrylic-based resin or the polyamide-based resin when forming the organic layer  255 . When the titanium oxide (TiOx) is added into the acrylic-based resin or the polyamide-based resin, the refractive index of the organic layer  255  may increase to about 1.9 to about 2.1 
     Then, a patterned photosensitive layer  256  is formed on the organic layer  255 . Although not shown in figures, a mask (not shown) having an opening formed therethrough is arranged on the photosensitive layer  256  corresponding to a second area R 2  of the second base substrate  210 . When a light is irradiated onto the photosensitive layer  256  after the mask is arranged, the photosensitive layer  256  and the organic layer  255  arranged on the second area R 2  are substantially simultaneously exposed to the light. Then, the exposed photosensitive layer  256  and the organic layer  255  are substantially simultaneously developed. As a result, a photosensitive pattern  258  and a first optical path changing pattern  257  are formed in a first area R 1  of the second base substrate  210  as shown in  FIG. 15G . 
     Then, when the photosensitive pattern  258  is selectively stripped away, the first optical path changing pattern  257  is formed in the first area R 1  of the second base substrate  210 , and the second optical path changing pattern  254  is formed in the second area R 2 . Consequently, a compensation layer  220  may be completely formed on the second base substrate  210 . 
     In  FIGS. 14A to 14E and 15A to 15H , a method of forming the compensation layer  220  on the second substrate  210  has been described. In the manufacturing process of the display apparatus  500 , the additional methods of forming the first substrate  100  and interposing the liquid crystal layer  300  between the first substrate  100  and the second substrate  200  will be known to one ordinary skilled in the art, and therefore detailed description thereof will be omitted here. 
     Although the exemplary embodiments of the present teachings have been described, it is understood that the present teachings should not be limited to these exemplary embodiments but various changes and modifications can be made by one ordinary skilled in the art in light of the foregoing and within the spirit and scope of the present teachings.