Patent Publication Number: US-2019196089-A1

Title: Display apparatus with backlight unit and method of fabricating backlight unit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2017-0181146, filed on Dec. 27, 2017, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a display apparatus and, in particular, to a display apparatus with a backlight unit, and a method of fabricating the backlight unit. 
     DISCUSSION OF THE RELATED ART 
     Generally, a display apparatus includes a display panel, which is configured to display an image, and a backlight unit, which is configured to provide light to the display panel. 
     According to a disposition of a light source, the backlight unit can be classified as either an edge-type backlight or a direct-type backlight. In the direct-type backlight unit, the light source is provided along a back surface of the display panel (the surface opposite to the surface through which an image is displayed), and in the edge-type backlight unit, the light source is provided at a lateral side of the display panel. In the edge-type backlight unit, a light guide plate is used to direct light, which is emitted from the light source, along the back surface of the display panel. 
     SUMMARY 
     A display apparatus includes a display panel and a backlight unit. The backlight unit is configured to provide light to the display panel. The backlight unit includes a light source portion configured to produce light. The light source portion includes a light source and a supporting part. A light guide plate is configured to receive the light from the light source portion, and to direct the received light toward the display panel. One or more optical sheets are disposed on the light guide plate. The light guide plate includes a first section having a first side surface and a second section having an incidence surface facing to the light source portion, and a second side surface, which is opposite to the incidence surface and is coupled to the first side surface of the first section. The first section is disposed below the display panel and has a different composition from that of the second section. The first side surface of the first section is thinner than the incidence surface of the second section. 
     A method of fabricating a backlight unit includes preparing a first light guide plate, which has a first composition and includes a first side surface. A second light guide plate is formed. The second light guide plate includes a second composition, different from the first composition, and includes an incidence surface, a second side surface, and an inclined surface. The second side surface is opposite to the incidence surface and has a vertical length that is less than that of the incidence surface. The second side surface is coupled to the first side surface of the first light guide plate. The inclined surface of the second light guide plate is between the incidence surface and the second side surface and has a vertical length increasing closer to the incidence surface. A light source is provided to face the incidence surface of the second light guide plate. One or more optical sheets is provided on the first light guide plate and the second light guide plate. 
     A method of fabricating a backlight unit includes preparing a first light guide plate having a first composition and including a first side surface. A light source including a light emitting surface is prepared. A second light guide plate, having a second composition different from the first composition and including an incidence surface, a second side surface, and an inclined surface is prepared. One or more optical sheets are placed on the first light guide plate and the second light guide plate. The incidence surface is coupled to the light emitting surface of the light source. The second side surface is opposite to the incidence surface. A vertical height of the second side surface is less than that of the incidence surface. The second side surface is coupled to the first side surface. The inclined surface is between the incidence surface and the second side surface and is inclined to have a vertical height that increases closer to the incidence surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the present disclosure and many of the attendant aspects thereof will be more clearly understood by reference to the following detailed description taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an exploded perspective view illustrating a display apparatus according to exemplary embodiments of the inventive concept; 
         FIG. 2  is a perspective view illustrating a portion of a backlight unit according to exemplary embodiments of the inventive concept; 
         FIG. 3  is a cross-sectional view taken along line I-I′ of  FIG. 2 ; 
         FIGS. 4 to 8  are cross-sectional views illustrating backlight units according to exemplary embodiments of the inventive concept; 
         FIG. 9  is a flow chart illustrating a method of fabricating a backlight unit, according to exemplary embodiments of the inventive concept; 
         FIG. 10  is a flow chart illustrating the step S 110  of  FIG. 9 ; 
         FIGS. 11A to 11D  are cross-sectional views illustrating the step S 110  of  FIG. 9 ; 
         FIG. 12  is a flow chart illustrating the step S 110  of  FIG. 9  according to exemplary embodiments of the inventive concept; 
         FIG. 13  is a flow chart illustrating a method of fabricating a backlight unit according to exemplary embodiments of the inventive concept; 
         FIG. 14  is a flow chart illustrating the step S 220  of  FIG. 13 ; and 
         FIGS. 15A to 15D  are cross-sectional views illustrating the step S 220  of  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments of the inventive concept will now be described more fully with reference to the accompanying drawings, in which example embodiments are shown. In the drawings, the thicknesses of layers and regions may be exaggerated for clarity and some elements might not be drawn to scale. Like reference numerals in the drawings may denote like elements throughout the specification and drawings. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. 
     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 element, component, 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 example embodiments. 
     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. 
       FIG. 1  is an exploded perspective view illustrating a display apparatus according to exemplary embodiments of the inventive concept. 
     In some exemplary embodiments of the present inventive concept, a light guide plate may be used as a part of a display apparatus. The light guide plate may be configured to guide light, which is emitted from a light source in a specific direction. In some exemplary embodiments of the present inventive concept, the light guide plate may be used as a part of a backlight unit of the display apparatus. Thus, in the present specification, a display apparatus, a light guide plate, and a backlight unit with the light guide plate will be described. Thereafter, a method of fabricating the light guide plate and the backlight unit will be described. 
     A display apparatus according to exemplary embodiments of the inventive concept is illustrated in  FIG. 1 . 
     As shown in  FIG. 1 , a display apparatus  1000  may include a display panel  100 , a backlight unit  200 , and a top cover  150 . 
     In the display panel  100 , light, which is provided from the backlight unit  200 , may be used to display an image. The display panel  100  may be a non-emitting type display panel, such as a liquid crystal display panel, and the description that follows will refer to an example in which the display panel  100  is a liquid crystal display panel, although it is to be understood that other forms of non-emitting type display panels may be used. 
     The display panel  100  may include a first substrate  110 , which is configured to display an image, a second substrate  120 , which is provided to face the first substrate  110 , and a liquid crystal layer disposed between the first and second substrates  110  and  120 . A plurality of pixels may be arranged in a matrix shape on the first substrate  110 , and each of the plurality of pixels may include a gate line, a data line, and a pixel electrode. HI-ere, the data line may be electrically disconnected from the gate line and may be disposed along a direction that crosses the gate line. In addition, each of the plurality of pixels may include a thin-film transistor and the thin film transistor may be connected to the gate line, the data line, and the pixel electrode. A color filter and a common electrode, that faces the pixel electrode, may be provided on the second substrate  120 . The color filter and the common electrode may also be provided on the first substrate  110 . The arrangement of liquid crystal molecules in the liquid crystal layer may be controlled by adjusting an electric field established between the pixel electrodes and the common electrode, and this electric field may be used to control a transmittance of the light provided from the backlight unit  200 . In this way, a desired gradation level of the image is realized. 
     The display apparatus  1000  may further include a driving IC  130 , which is configured to provide a driving signal to the display panel  100 , and a printed circuit board  140 , which is electrically connected to the display panel  100 . 
     The display panel  100  may be configured to display an image on a top/front surface thereof. The display panel  100  may include a liquid crystal layer, which is interposed between the first substrate  110  and the second substrate  120 . When viewed in a plan view, the display panel  100  may include a display region DA, which is used to display an image, and a non-display region NDA, which may at least partially surround the display region. As the plurality of pixels is disposed entirely within the display region DA, the non-display region NDA is not used to display an image. The non-display region NDA may be veiled by the top cover  150 . 
     The driving IC  130  may be provided on a side region of the first substrate  110 , when viewed in a plan view, and may be configured to apply data signals to the data lines. The driving IC  130  may generate the data signals, which will be applied to the data lines of the display panel  100 , in response to an externally supplied signal. The externally supplied signal may include signals transmitted from the printed circuit board  140  and may include image signals, various control signals, driving voltages, or the like. 
     In some exemplary embodiments of the present inventive concept, the driving IC  130  may include two or more chips (e.g., including a data driving IC and a gate driving IC) and may be mounted on the first substrate  110  by a chip-on-film process. 
     In some exemplary embodiments of the present inventive concept, the printed circuit board  140  may be flexible. In some exemplary embodiments of the present disclosure, the printed circuit board  140  may be electrically connected to the display panel  100  via a plurality of tape carrier packages. The driving IC  130  may be mounted on the tape carrier packages. The tape carrier packages may be bent to enclose a side surface of a bottom cover  270 . The printed circuit board  140  connected to the tape carrier packages may be provided below the bottom cover  270 . In this case, the display apparatus  1000  may further include a shield case, which is provided below the bottom cover  270  to protect the printed circuit board  140 . The printed circuit board  140  may be provided on the side surface of the bottom cover  270 . 
     The backlight unit  200  may be provided below the display panel  100  and may be configured to provide light to the display panel  100 . 
     The backlight unit  200  may include a mold frame  160 , a light source portion  210 , a light guide plate  220 , one or more optical sheets  250 , and a reflection plate  260 . The mold frame  160  may be configured to support the display panel  100 . The light source portion  210  may be configured to produce light. The light guide plate  220  may be configured to guide the light, which is provided from the light source portion  210 , toward the display panel  100 . The optical sheets  250  may be configured to increase optical efficiency of the display panel  100 . The reflection plate  260  may be configured to change a propagation path of the light. 
     In some exemplary embodiments of the present disclosure, the backlight unit  200  may be an edge-type backlight unit. For example, the light source portion  210  of the backlight unit  200  may be provided below the display panel  100  and may be configured to direct the light toward at least one side surface of the light guide plate  220 , and the light guide plate  220  may be configured to guide the light to the display panel  100 . 
     The light guide plate  220  may include a first light guide plate  230  and a second light guide plate  240 , which may be formed of different materials, but the inventive concept is not limited thereto. Being formed of different materials may be understood herein as including all different materials (i.e. no common material is found between the two structures), or at least one constituent material is different (i.e. some, but not all, materials may be the same). Alternatively, being formed of different materials may mean that all of the constituent materials are the same but the relative proportion of each constituent material may differ from structure to structure. Thus, “being formed of different materials” may be understood to mean that the two structures do not include all identical materials in identical proportions. 
     The mold frame  160  may be disposed along an edge region of the display panel  100  and the mold frame  160  may support a bottom portion of the display panel  100 . The mold frame  160  may include a fastening element, which is configured to fasten or support other elements (e.g., the light source portion  210 , the optical sheets  250 , and so forth) except for the display panel  100 . The mold frame  160  may support four sides of the display panel  100  or at least a portion of one or more of the four sides. For example, the mold frame  160  may have a letter “U” shape supporting three sides of the display panel  100 . In some exemplary embodiments of the present inventive concept, the mold frame  160  may be provided in the form of a single object, but where desired, the mold frame  160  may include a plurality of assembled parts. The mold frame  160  may be formed of or include a polymer region, but the inventive concept is not limited thereto. For example, the mold frame  160  may be formed of or include a different material having substantially the same shape and substantially the same function. 
     The light source portion  210  may include a light source  211  and a supporting part  212  and may be configured to provide light to the display panel  100 . In some exemplary embodiments of the present inventive concept, the light source portion  210  may include one or more light sources  211 , which are each mounted on the supporting part  212  and are each configured to emit light using electric power supplied through the supporting part  212 . The light source  211  may be a light emitting diode (LED). The supporting part  212  may be configured to deliver the electric power from the outside the light source  211 . For the sake of simplicity, the description herein will refer to an example of the present embodiment in which the light source  211  is a light emitting diode, but the light source  211  may be a cold cathode fluorescent lamp (CCFL), a flat fluorescent lamp (FFL), or some other light source. 
     The reflection plate  260  may be disposed below the light guide plate  220 . The reflection plate  260  may be configured to reflect light which is emitted from the light source  211  but does not propagate toward the light guide plate  220 . This light may be referred to herein as leaked light. 
     The optical sheets  250  may be provided on the light guide plate  220  to increase an intensity of the light emitted from the light guide plate  220 . 
     The optical sheets  250  may include a diffusion sheet  251 , a prism sheet  252 , and a protection sheet  253 , which are sequentially stacked. The diffusion sheet  251  may be configured to diffuse an incident light. The prism sheet  252  may be configured to condense the light diffused by the diffusion sheet  251 , thereby increasing an intensity of light emitted therefrom. The protection sheet  253  may be configured to protect the prism sheet  252  and to realize a desired viewing angle. As shown in  FIG. 1 , the optical sheets  250  may have three layers, but in certain embodiments, the optical sheets  250  may have four or more layers. 
     The bottom cover  270  may define a storage space, which is configured to house the light source portion  210 , the light guide plate  220 , the reflection plate  260 , the optical sheets  250 , and the mold frame  160 . The bottom cover  270  may include a bottom portion, in which the backlight unit  200  is disposed, and a side wall, which is extended from the bottom portion in a vertical direction (e.g., a third direction D 3 ). 
     The top cover  150  may cover a portion of a top surface of the display panel  100 . The top cover  150  may support a top edge of the display panel  100  and may cover a side surface of the mold frame  160  or a side surface of the bottom cover  270 . 
       FIG. 2  is a perspective view illustrating a portion of the backlight unit  200  constituting the display apparatus  1000 , according to exemplary embodiments of the inventive concept. For convenience in illustration, the mold frame  160 , the optical sheets  250 , and the bottom cover  270  are omitted in the perspective view of  FIG. 2 . 
       FIG. 3  is a cross-sectional view taken along line I-I′ of  FIG. 2 . For convenience in illustration, the optical sheets  250 , which are omitted from the perspective view of  FIG. 2 , are additionally illustrated in the cross-sectional view of  FIG. 3 . 
     As shown in  FIGS. 2 and 3 , the backlight unit  200  may include the light source portion  210 , the light guide plate  220 , the reflection plate  260 , and the optical sheets  250 . 
     Referring to  FIGS. 2 and 3 , the light source portion  210  may be configured to produce light and may include a plurality of the light sources  211  and the supporting part  212  supporting the light sources  211 . The supporting part  212  may be a circuit board, in which interconnection lines for supplying an electric power to the light source  211  are printed. The supporting part  212  may be configured to control the supply of the electric power, and may have the shape of an elongated rectangular plate. 
     The light guide plate  220  may be disposed on a side surface of the light source portion  210  and may be configured to provide light, which is incident from the light source  211 , to have a propagation path toward the display panel  100 . The light guide plate  220  may be formed of a transparent material. For example, the light guide plate  220  may be formed of polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), and/or metastyrene (MS). In some exemplary embodiments of the present disclosure, the light guide plate  220  may be formed of glass or the like. However, the inventive concept is not limited to using glass in the light guide plate  220 . For example, the light guide plate  220  may include two or more layers, which are formed of different materials and are coupled to each other by a double injection method or using an adhesive member, as will be described in more detail below. 
     The light guide plate  220  may include the first light guide plate  230  and the second light guide plate  240 , which are formed of different materials and are coupled to each other. 
     The first light guide plate  230  may have a uniform thickness and may include a first side surface  231 , a first flat surface  233 , which is adjacent to the first side surface  231  and is parallel to the display panel  100 , and a first bottom surface  232 , which is parallel to and opposite to the first flat surface  233 . The first light guide plate  230  may be configured to allow light, which is incident into the first flat surface  233  from the light source  211 , to propagate toward the display panel  100 . In some exemplary embodiments of the present inventive concept, the first light guide plate  230  may be formed of a first material (e.g., glass), but other materials may be used. 
     The second light guide plate  240  may include a second side surface  241 , a second bottom surface  242 , an inclined surface  243 , an incidence surface  244 , and a second flat surface  245  and may be formed of a second material that is different from a first material of the first light guide plate  230 . The second material may be polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), and/or metastyrene (MS), but other materials may be used. 
     The second light guide plate  240  may be provided on the side surface of the light source portion  210 . The second light guide plate  240  may include the incidence surface  244  that faces the light sources  211  of the light source portion  210 . Light emitted from the light source  211  may be incident into the second light guide plate  240  through the incidence surface  244  and may then be incident into the first light guide plate  230 . 
     The second light guide plate  240  may include the second side surface  241 , which is provided to face the incidence surface  244  and to have a vertical length less than that of the incidence surface  244 . The second side surface  241  and the first side surface  231  may be coupled to each other in such a way that the second light guide plate  240  and the first light guide plate  230  constitute the light guide plate  220 . In some exemplary embodiments of the present inventive concept, the first light guide plate  230  and the second light guide plate  240  may be coupled to each other by a double injection method, as will be described in more detail below. 
     The second light guide plate  240  may include the second bottom surface  242 , which is extended from the incidence surface  244  and runs parallel to the first bottom surface  232  of the first light guide plate  230 . 
     The second light guide plate  240  may include the inclined surface  243 , which is provided between the incidence surface  244  and the second side surface  241  and is inclined toward the first bottom surface  232  or the second bottom surface  242 . A height of the inclined surface  243  from the second bottom surface  242  may decrease with increasing distance from the incidence surface  244 . The inclined surface  243  may be inclined at an obtuse angle relative to the first flat surface  233  of the first light guide plate  230 . 
     The second light guide plate  240  may further include the second flat surface  245 , which is parallel to the second bottom surface  242  and is located between the incidence surface  244  and the inclined surface  243 . Thus, the inclined surface  243  may be located between the first flat surface  233  and the second flat surface  245 . In some exemplary embodiments of the present inventive concept, the second light guide plate  240  may not have the second flat surface  245 . 
     In some exemplary embodiments of the present inventive concept, the optical sheets  250  provided on the light guide plate  220  may be at least partially overlapped with the first flat surface  233 . However, the inventive concept is not limited thereto, and in some exemplary embodiments of the present disclosure, the optical sheets  250  may also be at least partially overlapped with the inclined surface  243  or the second flat surface  245  of the second light guide plate  240 . 
     In some exemplary embodiments of the present inventive concept, a vertical length of the first side surface  231  of the first light guide plate  230  may be less than that of the light source  211 . In the case where the first side surface  231  of the first light guide plate  230  has a small vertical length, it may be possible to reduce a total thickness of the display apparatus  1000 . If the first light guide plate  230  is formed of glass, it may be possible to reduce a thermal deformation, even when the glass is relatively thin. 
     However, reducing the thickness of the light source  211  may make it difficult to produce a desired amount of light. Also the thickness of the incidence surface  244  should be substantially equal to or greater than that of the light source  211 . For example, the light guide plate should have an increasing thickness in the direction of the incidence surface  244 , but if it is formed of glass, it is difficult to realize an integrated shape having a varying thickness. 
     In the fabrication methods according to some exemplary embodiments of the inventive concept, the light guide plate  220  of the backlight unit  200  may be fabricated in such a way that the first light guide plate  230 , whose thickness is uniform, and the second light guide plate  240 , whose thickness increases in the direction of the incidence surface  244 , are formed of different materials, as will be described. 
     For example, in the display apparatus  1000 , according to some exemplary embodiments of the inventive concept, the first light guide plate  230 , that is at least partially overlapped with the display panel  100 , may be relatively thin, thereby allowing for a slim display apparatus. The second light guide plate  240  can have a thickness greater than that of the first light guide plate  230  to accommodate the thickness of the light source  211 , thereby alleviating the need to reduce the thickness of the light source  211 , which could cause the display brightness to be decreased. 
       FIGS. 4 to 8  are cross-sectional views illustrating backlight units according to exemplary embodiments of the inventive concept. Except for a difference in the structure of the light guide plate, the backlight units of  FIGS. 4 to 8  may have substantially same features as those of the backlight unit  200  of  FIGS. 2 and 3 . Thus, in the following description of  FIGS. 4 to 8 , an element previously described with reference to  FIGS. 2 and 3  may be identified by a similar or identical reference number without repeating an overlapping description thereof, for concise description. 
     In the display apparatus  1000  of  FIG. 4 , a backlight unit  300  may include a light source portion  210 , a light guide plate  320 , a reflection plate  260 , and optical sheets  250 . The light guide plate  320  may include a first light guide plate  330  and a second light guide plate  340 , which are formed of different materials. The first light guide plate  330  is provided in a plate-like shape having a first side surface  331 , a first flat surface  333 , and a first bottom surface  332  and having a constant thickness (e.g. an identical thickness throughout the entire structure such as a rectangular prism shape). The second light guide plate  340  includes a second side surface  341 , a second bottom surface  342 , an inclined surface  343 , an incidence surface  344 , and a second flat surface  345 . 
     The incidence surface  344  of the second light guide plate  340  may have a rough surface (e.g. not smooth). Due to the rough surface, the incidence surface  344  may scatter light provided from a light source  211 , thereby suppressing or preventing brightness non-uniformity, which may occur when the light emitting diode, which is a point-like light source, is used as the light source  211 . 
     A reflecting member  380  may be further provided on the inclined surface  343  and the second flat surface  345  of the second light guide plate  340  to reflect an incident light. The reflecting member  380  may be formed of or include a reflective resin and/or a reflective tape, but the inventive concept is not limited thereto. The reflecting member  380  may prevent light, which is incident into the incidence surface  344  of the second light guide plate  340 , from being leaked to the inclined surface  343  and the second flat surface  345  or may reflect the light into the light guide plate  320 , and this may increase optical characteristics of the display apparatus. 
     In the display apparatus  1000  of  FIG. 5 , a backlight unit  400  may include a light source portion  210 , a light guide plate  420 , a reflection plate  260 , and optical sheets  250 . The light guide plate  420  may include a first light guide plate  430  and a second light guide plate  440 , which are formed of different materials. The first light guide plate  430  is provided in a plate-like shape (e.g. a rectangular prism in which the thickness is less than the length and width) having a first side surface  431 , a first flat surface  433 , and a first bottom surface  432  and having a constant thickness. The second light guide plate  440  includes a second side surface  441 , a second bottom surface  442 , an inclined surface  443 , and an incidence surface  444 . 
     Referring to  FIG. 5 , at least one (e.g., the second flat surface) of the surfaces shown in  FIGS. 3 to 4  may be omitted from the backlight unit  400 . Thus, a side of the inclined surface  443  of the second light guide plate  440  may be connected to the first flat surface  433  of the first light guide plate  430 , and an opposite side of the inclined surface  443  of the second light guide plate  440  may be connected to the incidence surface  444 . 
     In the display apparatus  1000  of  FIG. 6 , a backlight unit  500  may include a light source portion  210 , a light guide plate  520 , a reflection plate  260 , and optical sheets  250 . The light guide plate  520  may include a first light guide plate  530  and a second light guide plate  540 , which are formed of different materials. The first light guide plate  530  is provided in a plate-like shape having a first side surface  531 , a first flat surface  533 , and a first bottom surface  532  and having a constant thickness. The second light guide plate  540  includes a second side surface  541 , a second bottom surface  542 , an inclined surface  543 , an incidence surface  544 , and a second flat surface  545 . 
     Referring to  FIG. 6 , the light guide plate  520  may be formed by combining the first light guide plate  530  and the second light guide plate  540  with each other using an adhesive member. 
     An adhesive member  521  may be disposed between the first side surface  531  of the first light guide plate  530  and the second side surface  541  of the second light guide plate  540 . The adhesive member  521  may be formed of or include a transparent material. For example, the adhesive member  521  may be an optical clear adhesive (OCA), which is a transparent tape having an adhesive property, or an optical clear resin (OCR), which is a liquid transparent resin adhesive material. The inventive concept is not limited to a specific material of the adhesive member  521 , and other adhesive materials may be included within the adhesive member  521 . 
     The optical sheets  250  may be provided on the first flat surface  533  of the first light guide plate  530 , but the inventive concept is not limited thereto. For example, the optical sheets  250  may be at least partially overlapped with the first flat surface  533  of the first light guide plate  530  and may be at least partially overlapped with the inclined surface  543  and the second flat surface  545  of the second light guide plate  540 . 
     In the display apparatus  1000  of  FIG. 7 , a backlight unit  600  may include a light source portion  210 , a light guide plate  620 , a reflection plate  260 , and optical sheets  250 , and the light guide plate  620  may include a first light guide plate  630  and a second light guide plate  640 , which are formed of different materials. The first light guide plate  630  is provided in a plate-like shape having a first side surface  631 , a first flat surface  633 , and a first bottom surface  632  and having a constant thickness. The second light guide plate  640  includes a second side surface  641 , a second bottom surface  642 , an inclined surface  643 , an incidence surface  644 , and a second flat surface  645 . 
     Referring to  FIG. 7 , the second light guide plate  640  may further include a third flat surface  646  connected to the inclined surface  643 . The third flat surface  646  may be parallel to the first flat surface  633 . An adhesive member  621  may be provided between the first side surface  631  of the first light guide plate  630  and the second side surface  641  of the second light guide plate  640 , and the adhesive member  621  may be formed of or include a transparent material. 
     Accordingly, the optical sheets  250  may be at least partially overlapped with the first flat surface  633  of the first light guide plate  630  and the third flat surface  646  of the second light guide plate  640 . In some exemplary embodiments of the present inventive concept, the optical sheet  250  may be extended to be further overlapped with the inclined surface  643  and the second flat surface  645  of the second light guide plate  640 . 
     In the display apparatus  1000  of  FIG. 8 , a backlight unit  700  may include a light source portion  710 , a light guide plate  720 , a reflection plate  760 , and optical sheets  750 . The light guide plate  720  may include a first light guide plate  730  and a second light guide plate  740 , which are formed of different materials. The second light guide plate  740  may be coupled to a light source  711  by a double injection method. The optical sheets  750  may sequentially include a diffusion sheet  751 , a prism sheet  752 , and a protective sheet  753 . 
     Referring to  FIG. 8 , the light source portion  710  may include a light source  711 , which has a light emitting surface  713 , and a supporting part  712 , on which the light source  711  is mounted. The first light guide plate  730  may have a plate-like shape having a first side surface  731 , a first flat surface  733 , and a first bottom surface  732  and having a constant thickness. The second light guide plate  740  includes a second side surface  741 , a second bottom surface  742 , an inclined surface  743 , an incidence surface  744 , and a second flat surface  745 . The light emitting surface  713  of the light source  711  may be in contact with the incidence surface  744  of the second light guide plate  740 , and the light source  711  and the second light guide plate  740  may be coupled to each other by a double injection method. 
     The second side surface  741  facing the incidence surface  744  of the second light guide plate  740  may include a portion having a rough shape. 
     The light guide plate  720  may further include an adhesive member  721 , which is provided between the first side surface  731  of the first light guide plate  730  and the rugged portion of the second side surface  741  of the second light guide plate  740 . 
       FIG. 9  is a flow chart illustrating a fabrication method of a backlight unit, according to some exemplary embodiments of the inventive concept. 
     Referring to  FIG. 9 , a method of fabricating a backlight unit according to some exemplary embodiments of the inventive concept may include preparing a first light guide plate (Step S 100 ), forming a second light guide plate (Step S 110 ), disposing a light source (Step S 120 ), and disposing optical sheets (Step S 130 ). 
     For example, the first light guide plate may include a first side surface and may be formed of a first material (Step S 100 ). The first material may be glass, but other materials may be used. 
     Next, the second light guide plate may include an incidence surface, a second side surface, and an inclined surface and may be formed of a second material (Step S 110 ). Here, the second side surface may face the incidence surface and to have a vertical length less than that of the incidence surface and may be coupled to the first side surface. The inclined surface may be provided between the incidence surface and the second side surface and may be inclined to have an increasing height closer to the incidence surface. The second material may be polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), and/or metastyrene (MS), but the inventive concept is not limited thereto. 
     The second light guide plate may be adhered to the first light guide plate by a double injection method. Alternatively, the second light guide plate may be adhered to the first light guide plate using an adhesive member. This will be described in more detail below. 
     Thereafter, the light source portion may face the incidence surface of the second light guide plate (Step S 120 ), and the optical sheets may be disposed on the first light guide plate and the second light guide plates (Step S 130 ). 
       FIG. 10  is a flow chart illustrating step S 110  of  FIG. 9  for forming the second light guide plate using the double injection method, and  FIGS. 11A to 11D  are cross-sectional views illustrating a process of forming the second light guide plate using a mold. 
     Referring to  FIGS. 10 and 3 , the step of forming the second light guide plate using the double injection method may include steps of preparing a mold including a first portion and a second portion (Step S 111 ), placing the first light guide plate in a first space of the mold (Step S 112 ), filling a second space of the mold with a second material (Step S 113 ), and solidifying the second material (Step S 114 ). 
     Referring to  FIGS. 3, 10, and 11A , in the step of preparing the mold (Step S 111 ), a mold MD may have a first portion  10 , in which a first space  11  is defined, and a second portion  20 , in which a second space  21  and an injection hole  22  are defined. Here, the first space  11  may have a uniform internal height, and the second space  21  may be connected to the first space  11  and may have an internal height increasing with increasing distance from the first space  11 . The injection hole  22  may allow a material to be injected into the second space  21 . 
     Referring to  FIGS. 3, 10, and 11B , the step of placing the first light guide plate in the first space of the mold (Step S 112 ) may include placing the first light guide plate  230  to allow the first side surface  231  to face the second space  21  in the first space  11  of the mold MD. 
     Referring to  FIGS. 3, 10, 11B, and 11C , the step of filling the second space of the mold with the second material (Step S 113 ) may include connecting the first portion  10  to the second portion  20 , injecting a second material MT into the second space  21  through the injection hole  22 , and solidifying the second material MT to form the second light guide plate. The second material MT may be injected to be in contact with the first side surface  231  of the first light guide plate  230 , and thus, the first side surface  231  of the first light guide plate  230  may be in contact with, and attached to, the second side surface  241  of the second light guide plate  240 . 
     Referring to  FIGS. 3, 10, and 11D , the second material MT may be solidified, and then the mold may be removed. As a result, the light guide plate  220  including the first and second light guide plates  230  and  240  connected to each other may be formed. 
       FIG. 12  is a flow chart illustrating a method of forming the light guide plate using an adhesive member (e.g., Step S 110  of  FIG. 9 ). Hereinafter, a process of coupling the first light guide plate  530  to the second light guide plate  540  using the adhesive member  521  to form the light guide plate will be described with reference to  FIGS. 12 and 6 . 
     Firstly, a mold including a third portion may be prepared (Step S 116 ). The third portion may have a third space, whose internal height increases in a specific direction, and an injection hole, which is formed to allow a material to be injected into the third space. The second light guide plate  540  may be formed by filling the third space of the mold with a second material (Step S 117 ). Thereafter, an adhesive member  522  may be used to couple the first side surface  531  of the first light guide plate  530  to the second side surface  541  of the second light guide plate  540  and thereby to form the light guide plate  520  including the first light guide plate  530  and the second light guide plate  540 , which are connected to each other (Step S 118 ). 
       FIG. 13  is a flow chart illustrating a method of fabricating a backlight unit, according to exemplary embodiments of the inventive concept.  FIG. 14  is a flow chart illustrating step S 220  of  FIG. 13 , and  FIGS. 15A to 15D  are cross-sectional views illustrating a process of forming a part, in which a second light guide plate and a light source are combined, using a mold, in step S 220 . 
     Referring to  FIG. 13 , a method of forming a light guide plate, according to exemplary embodiments of the inventive concept, may include preparing a first light guide plate (Step S 200 ), preparing a light source (Step S 210 ), forming a second light guide plate (Step S 220 ), combining the first light guide plate to the second light guide plate (Step S 230 ), and placing optical sheets (Step S 240 ). This will be described in more detail below. 
     For example, the first light guide plate may include a first side surface and may be formed of a first material (Step S 200 ). The first material may be glass, but other materials may be used. 
     Next, the light source including a light emitting surface may be prepared (Step S 210 ). 
     Thereafter, the second light guide plate may include an incidence surface, a second side surface, and an inclined surface and may be formed of a second material (Step S 220 ). Here, the second side surface may face the incidence surface and have a vertical length less than that of the incidence surface and may be coupled to the first side surface. The inclined surface may be disposed between the incidence surface and the second side surface and may be inclined to have an increasing height with decreasing distance from the incidence surface. The second material may be polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), and/or metastyrene (MS), but other materials may be used. 
     Next, an adhesive member may be used to couple the first side surface of the first light guide plate to the second side surface of the second light guide plate (Step S 230 ). 
     Thereafter, the optical sheets may be placed on the first light guide plate and the second light guide plates (Step S 240 ). 
     Referring to  FIGS. 8 and 14 , the forming the second light guide plate (Step S 220 ) may include preparing a mold (Step S 221 ), placing a light source in the mold (Step S 222 ), and forming a second light guide plate by filling the mold with a second material (Step S 224 ). 
     Referring to  FIGS. 8, 14, and 15A , a mold MD 1  may include a fourth portion  40 , in which a fourth space  41  is provided, and a fifth portion  50 , in which a fifth space  51  and an injection hole  52  are provided. The fifth space  51  may have a vertical height decreasing with increasing distance from the fourth space  41 , and the injection hole  52  may allow a material to be injected into the fifth space  51  therethrough. 
     Referring to  FIGS. 8, 14, and 15B , the light source  711  may be placed in the fourth space  41  to have the light emitting surface  713  facing the fifth space  51 . 
     Referring to  FIGS. 8, 14, and 15C , the fourth portion  40  and the fifth portion  50  of the mold MD 1  may be connected to each other, and then, a second material MT 1  may be supplied through the injection hole  52  of the fifth portion  50  to fill the fifth space  51 , thereby forming the second light guide plate. 
     Referring to  FIGS. 8, 14, and 15D , the mold MD 1  may be removed to remain a part, in which the light source  711  and the second light guide plate  740  are connected. Thereafter, an adhesive member may be used to couple the first side surface  731  of the first light guide plate  730  to the second side surface  741  of the second light guide plate  740  and thereby to form the light guide plate  720  including the first light guide plate  730  and the second light guide plate  740 , which are connected to each other. 
     In a display apparatus according to some exemplary embodiments of the inventive concept, a first light guide plate, which is at least partially overlapped with a display panel, may be relatively thin, allowing for a slim structure of the display apparatus. Owing to a second light guide plate, a light source may have a vertical height larger than that of the first light guide plate and thereby may prevent loss in brightness of the display panel that would otherwise be caused by reducing the height of the light source. 
     In a method of fabricating a backlight unit according to some exemplary embodiments of the inventive concept, the light guide plate can have the above features. 
     Exemplary embodiments described herein are illustrative, and many variations can be introduced without departing from the spirit of the disclosure or from the scope of the appended claims. For example, elements and/or features of different exemplary embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.