Patent Publication Number: US-11650441-B2

Title: Display device and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Divisional of U.S. patent application Ser. No. 15/883,064, filed on Jan. 29, 2018, and claims priority from and the benefit of Korean Patent Application No. 10-2017-0112734, filed on Sep. 4, 2017, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
    
    
     BACKGROUND 
     Field 
     Exemplary embodiments relate to a display device and a method of manufacturing the same. 
     Discussion of the Background 
     With the development of multimedia, display devices are becoming increasingly important. Accordingly, various types of display devices such as liquid crystal displays (LCDs) and organic light-emitting displays (OLEDs) are being used. 
     Of these display devices, LCDs are one of the most widely used types of flat panel displays. An LCD includes a pair of substrates having field generating electrodes, such as pixel electrodes and a common electrode, and a liquid crystal layer interposed between the two substrates. In the LCD, voltages are applied to the field generating electrodes to generate an electric field in the liquid crystal layer. Accordingly, the alignment of liquid crystal molecules of the liquid crystal layer is determined, and the polarization of incident light is controlled. As a result, a desired image is displayed on the LCD. 
     As one way to make each pixel uniquely display one primary color, a color conversion pattern may be placed in each pixel on an optical path extending from a light source to a viewer. For example, a color filter may realize a primary color by transmitting only a specific wavelength band. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the inventive concept, and, therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY 
     Exemplary embodiments provide a display device which can improve light output efficiency by including a low refractive layer and a method of manufacturing the display device. 
     Exemplary embodiments provide a display device which provides flatness to a low refractive layer and a planarization layer by placing a light transmission pattern in a valley area between wavelength conversion patterns and a method of manufacturing the display device. 
     Additional aspects will be set forth in the detailed description which follows, and, in part, will be apparent from the disclosure, or may be learned by practice of the inventive concept. 
     According to exemplary embodiments, a display device comprises: a first substrate; first through third subpixel electrodes which are disposed on the first substrate to neighbor each other; a second substrate which is opposite the first substrate; wavelength conversion patterns which are disposed on the second substrate and comprise a first wavelength conversion pattern at least partially overlapping the first subpixel electrode and a second wavelength conversion pattern at least partially overlapping the second subpixel electrode; light transmission patterns which comprise a first light transmission pattern at least partially overlapping the third subpixel electrode and a second light transmission pattern disposed between the first wavelength conversion pattern and the second wavelength conversion pattern; a planarization layer which is disposed on the wavelength conversion patterns and the light transmission patterns; and a low refractive layer which has a lower refractive index than the wavelength conversion patterns. The low refractive layer may comprise at least one of a first low refractive layer disposed between the wavelength conversion patterns and the second substrate and a second low refractive layer disposed between the wavelength conversion patterns and the planarization layer. 
     According to exemplary embodiments, a display device comprises: a backlight unit which emits light displaying a first color; and a display panel which receives the light displaying the first color. The display panel nay comprise: a substrate; wavelength conversion patterns which are disposed on the substrate and comprise a first wavelength conversion pattern converting the light displaying the first color into light displaying a second color different from the first color and a second wavelength conversion pattern converting the light displaying the first color into light displaying a third color different from the first color; light transmission patterns which comprise a first light transmission pattern transmitting the light displaying the first color and a second light transmission pattern disposed between the first wavelength conversion pattern and the second wavelength conversion pattern; and a low refractive layer which has a lower refractive index than the wavelength conversion patterns. The low refractive layer may comprise at least one of a first low refractive layer disposed between the wavelength conversion patterns and the substrate and a second low refractive layer disposed on the wavelength conversion patterns. 
     According to exemplary embodiments, a method of manufacturing a display device comprises: forming a first low refractive layer on a substrate; forming wavelength conversion patterns, which comprise a first wavelength conversion pattern converting light having a first wavelength band into light having a second wavelength band and a second wavelength conversion pattern converting the light having the first wavelength band into light having a third wavelength band, on the first low refractive layer; forming light transmission patterns which comprise a first light transmission pattern transmitting the light having the first wavelength band and a second light transmission pattern disposed between the first wavelength conversion pattern and the second wavelength conversion pattern; and forming a second low refractive layer on the wavelength conversion patterns and the light transmission patterns. Refractive indices of the first low refractive layer and the second low refractive layer may be lower than those of the wavelength conversion patterns. 
     The foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the inventive concept, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the inventive concept, and, together with the description, serve to explain principles of the inventive concept. 
         FIG.  1    is a cross-sectional view of a display device according to an embodiment; 
         FIG.  2    is a schematic view of a first subpixel illustrated in  FIG.  1   ; 
         FIG.  3    is an enlarged view of an area A illustrated in  FIG.  1   ; 
         FIGS.  4 A through  5 B  illustrate optical paths in the display device according to the embodiment; 
         FIG.  6 A  illustrates the area A of  FIG.  1    turned over; 
         FIG.  6 B  illustrates the area A of  FIG.  1    turned over in a case where a second light transmission pattern is omitted; 
         FIG.  7    illustrates the flatness of a surface of a planarization layer among elements of the display device according to the embodiment; 
         FIG.  8    is a view for explaining the color mixing reducing effect of the display device according to the embodiment; 
         FIGS.  9  through  14    illustrate other embodiments of the display device of  FIG.  1   ; 
         FIG.  15    is a graph illustrating the luminance according to the position of a low refractive layer in a display device according to an embodiment; 
         FIG.  16    illustrates an embodiment of the display device of  FIG.  1   ; and 
         FIGS.  17  through  22    illustrate a method of manufacturing a display device according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of various exemplary embodiments. It is apparent, however, that various exemplary embodiments may be practiced without these specific details or with one or more equivalent arrangements. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring various exemplary embodiments. 
     In the accompanying figures, the size and relative sizes of layers, films, panels, regions, etc., may be exaggerated for clarity and descriptive purposes. Also, like reference numerals denote like elements. 
     When an element or layer is referred to as being “on,” “connected to,” or “coupled to” another element or layer, it may be directly on, connected to, or coupled to the other element or layer or intervening elements or layers may be present. When, however, an element or layer 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. For the purposes of this disclosure, “at least one of X, Y, and Z” and “at least one selected from the group consisting of X, Y, and Z” may be construed as X only, Y only, Z only, or any combination of two or more of X, Y, and Z, such as, for instance, XYZ, XYY, YZ, and ZZ. 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. 
     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 used to distinguish one element, component, region, layer, and/or section from another element, component, region, layer, and/or section. Thus, a first element, component, region, layer, and/or section discussed below could be termed a second element, component, region, layer, and/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 descriptive purposes, and, thereby, to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the drawings. Spatially relative terms are intended to encompass different orientations of an apparatus in use, operation, and/or manufacture in addition to the orientation depicted in the drawings. For example, if the apparatus in the drawings 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. Furthermore, the apparatus may be otherwise oriented (e.g., rotated 90 degrees or at other orientations), and, as such, the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting. 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. Moreover, the terms “comprises,” “comprising,” “includes,” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Various exemplary embodiments are described herein with reference to sectional illustrations that are schematic illustrations of idealized exemplary embodiments and/or intermediate structures. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, exemplary embodiments disclosed herein should not be construed as limited to the particular illustrated shapes of regions, but are to include deviations in shapes that result from, for instance, manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the drawings are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to be limiting. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure is a part. 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, exemplary embodiments rill be described with reference to the accompanying drawings. 
       FIG.  1    is a cross-sectional view of a display device  1  according to an embodiment. 
     Referring to  FIG.  1   , the display device  1  according to the embodiment includes a display panel  10  and a backlight unit  20 . 
     The display panel  10  displays an image. The display panel  10  may include a lower display panel  100 , an upper display panel  200 , and a liquid crystal layer  300 . Here, the terms ‘lower’ and ‘upper’ are used for ease of description and are based on  FIG.  1   . The lower display panel  100  may be placed to face the upper display panel  200 . The liquid crystal layer  300  may be interposed between the lower display panel  100  and the upper display panel  200  and may include a plurality of liquid crystal molecules  310 . In an embodiment, the lower display panel  100  may be bonded to the upper display panel  200  by sealing. 
     The backlight unit  20  provides light to the display panel  10 . More specifically, the backlight unit  20  may be disposed under the display panel  10  to provide light having a specific wavelength band to the display panel  10 . Hereinafter, light provided from the backlight unit  20  to the display panel  10  will be referred to as light L 1  having a first wavelength band. 
     The backlight unit  20  may emit the light L 1  having the first wavelength band to the display panel  10 . Here, the light L 1  having the first wavelength band is defined as light displaying a first color. The first color may be blue having a center wavelength of about 420 to 480 nm in an embodiment. The center wavelength can also be expressed as a peak wavelength. That is, the light L 1  having the first wavelength band is also defined as blue light whose center wavelength is in the range of about 420 to 480 nm. Therefore, the backlight unit  20  can provide blue light to the display panel  10 . The display panel  10  is disposed on the path of the light L 1  having the first wavelength band emitted from the backlight unit  20  and displays an image based on received light. The arrangement relationship between the display panel  10  and the backlight unit  20  is not limited to that illustrated in  FIG.  1    as long as the display panel  10  is disposed on the path of light emitted from the backlight unit  20 . 
     The backlight unit  20  may include a light source which emits the above light and a light guide plate which guides the light received from the light source to the display panel  10 . The type of the light source is not particularly limited. The light source may include a light emitting diode (LED) or a laser diode (LD) in an embodiment. In addition, the material of the light guide plate is not particularly limited. The light guide plate may be made of glass, quartz, or a plastic material such as polyethylene terephthalate or polycarbonate in an embodiment. 
     Although not illustrated in the drawing, the backlight unit  20  may include at least one optical sheet. The optical sheet may include at least one of a prism sheet, a diffusion sheet, a lenticular lens sheet, and a micro lens sheet. The optical sheet can improve the display quality of the display device  1  by modulating optical characteristics of light emitted from the backlight unit  20 , such as condensing, diffusion, scattering, or polarization characteristics. 
     The lower display panel  100 , the upper display panel  200  and the liquid crystal layer  300  will hereinafter be described in more detail. 
     First, the lower display panel  100  will be described. The lower display panel  100  may include a lower substrate  110 , a first polarizing layer  120 , a plurality of pixels including a first pixel PX 1 , a first insulating layer  130 , and a lower alignment film  140 . 
     The lower substrate  110  may be a transparent insulating substrate in an embodiment. Here, the transparent insulating substrate may include a glass material, a quartz material, or a translucent plastic material. The lower substrate  110  may have flexibility in an embodiment. 
     The first polarizing layer  120  may be disposed on an optical path between the lower substrate  110  and the backlight unit  20 . In an embodiment, the first polarizing layer  120  may be disposed under the lower substrate  110 . However, the position of the first polarizing layer  120  is not limited to that illustrated in  FIG.  1   . In an embodiment, the first polarizing layer  120  may be disposed between the lower substrate  110  and the liquid crystal layer  300 . The first polarizing layer  120  may be a reflective polarizing layer in an embodiment. When the first polarizing layer  120  is a reflective polarizing layer, it may transmit a polarization component parallel to a transmission axis and reflect a polarization component parallel to a reflection axis. 
     The first polarizing layer  120  may be in direct contact with the lower substrate  110  in an embodiment. That is, the first polarizing layer  120  may be formed on a surface of the lower substrate  110  through a continuous process. 
     In an embodiment, the first polarizing layer  120  may be bonded to the surface of the lower substrate  110  by an adhesive member. Here, the adhesive member may be a pressure sensitive adhesive member (PSA) or an optically clear adhesive member (OCA, OCR) in an embodiment. 
     The pixels including the first pixel PX 1  may be disposed on the lower substrate  110 . The pixels will hereinafter be described based on the first pixel PX 1 . 
     The first pixel PX 1  may include first through third subpixels SPX 1  through SPX 3 . Here, the first through third subpixels SPX 1  through SPX 3  display different colors. Each of the first through third subpixels SPX 1  through SPX 3  includes a switching element and a subpixel electrode. This will be described based on the first subpixel SPX 1  by referring to  FIG.  2   . 
       FIG.  2    is a schematic view of the first subpixel SPX 1  illustrated in  FIG.  1   . 
     Referring to  FIGS.  1  and  2   , a first switching element Q 1  may be a three-terminal element such as a thin-film transistor in an embodiment. The first switching element Q 1  may have a control electrode electrically connected to a first scan line GL 1  and have one electrode electrically connected to a first data line DL 1 . The other electrode of the first switching element Q 1  may be electrically connected to a first subpixel electrode SPE 1 . The first scan line GL 1  may extend in a first direction d 1  in an embodiment. The first data line DL 1  may extend in a second direction d 2 , which is different from the first direction d 1 , in an embodiment. The first direction d 1  intersects the second direction d 2 . 
     The first switching element Q 1  may be turned on by a scan signal received from the first scan line GL 1  to provide a data signal received from the first data line DL 1  to the first subpixel electrode SPE 1 . In the present specification, the first subpixel SPX 1  includes only one first switching element Q 1 . However, the inventive concept is not limited to this case, and two or more switching elements can be included. 
     The first subpixel electrode SPE 1  may be disposed in the lower display panel  100 . More specifically, the first subpixel electrode SPE 1  may be disposed on the first insulating layer  130  located on the lower substrate  110 . A common electrode CE may be located in the upper display panel  200  to be described later. The first subpixel electrode SPE 1  may be overlapped by at least part of the common electrode CE. Therefore, the first subpixel SPX 1  may further include a first liquid crystal capacitor Clc 1  formed by the overlap of the first subpixel electrode SPE 1  and the common electrode CE. In the present specification, when ‘two elements overlap each other,’ it means that the two elements overlap in a direction perpendicular to the lower substrate  110 , unless otherwise specified. 
     Referring again to  FIG.  1   , the first insulating layer  130  may be disposed on the first through third switching elements Q 1  through Q 3 . The first insulating layer  130  electrically insulates elements disposed under the first insulating layer  130  from elements disposed on the first insulating layer  130 . 
     In an embodiment, the first insulating layer  130  may be made of an inorganic material such as silicon nitride or silicon oxide. In an embodiment, the first insulating layer  130  may include an organic material having an excellent planarization property and having photosensitivity. In an embodiment, the first insulating layer  130  may be formed as a stacked structure of a layer made of an organic material and a layer made of an inorganic material. The first insulating layer  130  may include a plurality of contact holes for electrically connecting the first through third switching elements Q 1  through Q 3  to the first through third subpixel electrodes SPE 1  through SPE 3 , respectively. 
     The first through third subpixel electrodes SPE 1  through SPE 3  may be disposed on the first insulating layer  130  to neighbor each other. Each of the first through third subpixel electrodes SPE 1  through SPE 3  may be a transparent electrode or a translucent electrode or may be made of a reflective metal such as aluminum, silver, chromium or an alloy of these materials. Here, the transparent electrode or the translucent electrode may include one or more of indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium oxide (In 2 O 3 ), indium gallium oxide (IGO), and aluminum zinc oxide (AZO). Although not illustrated in the drawing, each of the first through third subpixel electrodes SPE 1  through SPE 3  may include a plurality of slits. 
     The lower alignment film  140  may be disposed on the first through third subpixel electrodes SPE 1  through SPE 3 . The lower alignment film  140  may induce the initial alignment of the liquid crystal molecules  310  in the liquid crystal layer  300 . The lower alignment film  140  may include a polymer organic material having an imide group in a repeating unit of a main chain in an embodiment. 
     Next, the upper display panel  200  will be described. The upper display panel  200  may include an upper substrate  210 , a black matrix BM, wavelength conversion patterns WC, light transmission patterns TC, a first filter  220 , a first low refractive layer  230 , a second filter  240 , a second low refractive layer  250 , a planarization layer  260 , a second insulating layer  270 , a second polarizing layer  280 , the common electrode CE, and an upper alignment film  290 . 
     The upper substrate  210  is placed to face the lower substrate  110 . The upper substrate  210  may be made of transparent glass or plastic. In an embodiment, the upper substrate  210  may be made of the same material as the lower substrate  110 . 
     The black matrix BM may be disposed on the upper substrate  210 . The black matrix BM is disposed at boundaries between the pixels and prevents transmission of light, thereby preventing color mixing between neighboring pixels. Based on  FIG.  1   , the black matrix BM is disposed at the boundaries between the first through third subpixels SPX 1  through SPX 3 . The material of the black matrix BM is not particularly limited as long as it can block the transmission of light provided to the black matrix BM. In an embodiment, the black matrix BM may include an organic material or a metal material such as chromium. 
     Although not illustrated in the drawing, a protective layer may be disposed on the black matrix BM. More specifically, the protective layer may be disposed between the black matrix BM and the first filter  220  to described later. The protective layer can prevent the black matrix BM from being damaged or corroded during the process of manufacturing the upper display panel  200 . The material of the protective layer is not particularly limited. However, the protective layer may include an inorganic insulating material such as silicon nitride or silicon oxide. The protective layer can be omitted. 
     Although not illustrated in the drawing, the black matrix BM can also be disposed in the lower display panel  100 . When the black matrix BM is disposed in the lower display panel  100 , it may be located between the first insulating layer  130  and the lower alignment film  140  in an embodiment. The black matrix BM disposed in the lower display panel  100  can prevent light scattered by the light transmission patterns TC from entering the wavelength conversion patterns WC, thereby suppressing color mixing. 
     In the present specification, when “a third element is disposed between a first element and a second element,” it means that the position of the third element varies depending on the arrangement of the first element and the second element. That is, when the first element and the second element are arranged to overlap each other in the direction perpendicular to the lower substrate  110 , the third element may be placed to overlap each of the first element and the second element in the direction perpendicular to the lower substrate  110 . On the other hand, when the first element and the second element are arranged to overlap each other in a direction horizontal to the lower substrate  110 , the third element may be placed to overlap each of the first element and the second element in the direction horizontal to the lower substrate  110 . In the latter case, a second light transmission pattern TC 2 , which will be described later, is disposed between a first wavelength conversion pattern WC 1  and a second wavelength conversion pattern WC 2  which overlap each other in the direction horizontal to the lower substrate  110 . This means that the second light transmission pattern TC 2  is placed to overlap each of the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2  in the direction horizontal to the lower substrate  110 . 
     The first filter  220  may be disposed on the black matrix BM. More specifically, the first filter  220  may be disposed on the black matrix BM to overlap the wavelength conversion patterns WC and the second light transmission pattern TC 2 . In addition, the first filter  220  may not overlap with a first light transmission pattern TC 1 . 
     The first filter  220  may include an organic material having photosensitivity in an embodiment. The first filter  220  may have a thickness of about 0.5 to 2 μm or about 0.5 to 1.5 μm in an embodiment. When having a thickness of 0.5 μm or more, the first filter  220  can have sufficient absorptive power for light of a specific wavelength band. When the thickness of the first filter  220  is 2 μm or less, the height of a step formed by the first filter  220  can be minimized, and the distance between the wavelength conversion patterns WC and the black matrix BM can be minimized. Accordingly, a color mixing defect can be suppressed. 
     The first filter  220  may be a cut-off filter that transmits light having a specific wavelength band and blocks light having another specific wavelength band. This will be described later together with the wavelength conversion patterns WC by referring to  FIG.  4   . 
     The position of the filter  220  is not limited to that illustrated in  FIG.  1    as long as the first filter  220  overlaps the wavelength conversion patterns WC and the second light transmission pattern TC 2 . For example, the black matrix BM can be disposed on the first filter  220 . In an embodiment, the first filter  220  and the black matrix BM can be disposed on the same layer. 
     The first low refractive layer  230  may be disposed on the first filter  220 . The first low refractive layer  230  may be disposed on the entire surfaces of the black matrix BM and the first filter  220  in an embodiment. Accordingly, the first low refractive layer  230  may overlap each of the first wavelength conversion pattern WC 1 , the second wavelength conversion pattern WC 2 , the first light transmission pattern TC 1 , and the second light transmission pattern TC 2  in the direction perpendicular to the lower substrate  110 . 
     The first low refractive layer  230  may be in contact with the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 . On the other hand, the first low refractive layer  230  is not in contact with the first light transmission pattern TC 1  and the second light transmission pattern TC 2 . 
     As used herein, the term ‘low refractive layer’ refers to a layer having a relatively low refractive index as compared with an adjacent element. Therefore, the first low refractive layer  230  may have a lower refractive index than the wavelength conversion patterns WC to be described later. For example, the first low refractive layer  230  may have a refractive index of about 1.1 to 1.4. On the other hand, the wavelength conversion patterns WC may have a refractive index of about 1.8 to 1.9 in an embodiment. 
     The first low refractive layer  230  may reflect a portion of light, which is emitted from the wavelength conversion patterns WC toward the upper substrate  210 , back to the wavelength conversion patterns WC. That is, the first low refractive layer  230  may recycle at least a portion of the light emitted from the wavelength conversion patterns WC toward the upper substrate  210 , thereby improving the light output efficiency. This will be described in more detail later with reference to  FIG.  4   . 
     The first low refractive layer  230  may include a resin and nano particles (such as zinc oxide (ZnO) or titanium dioxide (TiO 2 )) dispersed in the resin. However, the material of the first low refractive layer  230  is not particularly limited as long as the refractive index of the first low refractive layer  230  is lower than those of the wavelength conversion patterns WC. In an embodiment, the first low refractive layer  230  may include one of hollow silica, nano silicate, and porogen. 
     The wavelength conversion patterns WC and the light transmission patterns TC will now be described in more detail with reference to  FIG.  3   . 
       FIG.  3    is an enlarged view of an area A illustrated in  FIG.  1   . For ease of description, one first wavelength conversion material WC 1   a , one second wavelength conversion material WC 2   a , and one light scattering material TC 1   a  are illustrated in  FIG.  3   . In addition, the optical path change according to the refractive index is not taken into consideration in  FIG.  3   . 
     Referring to  FIGS.  1  and  3   , the wavelength conversion patterns WC may be disposed on the first low refractive layer  230 . The wavelength conversion patterns WC may include a material capable of converting or shifting the wavelength band of light received from the outside. Accordingly, the wavelength conversion patterns WC can convert the display color of light emitted to the outside into a display color different from the display color of the light incident on the wavelength conversion patterns WC. The wavelength conversion patterns WC may include the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 . 
     The first wavelength conversion pattern WC 1  may be disposed on the first low refractive layer  230  and may overlap the first subpixel electrode SPE 1  in the direction perpendicular to the lower substrate  110 . The second wavelength conversion pattern WC 2  may be disposed on the first low refractive layer  230  and may overlap the second subpixel electrode SPE 2  in the direction perpendicular to the lower substrate  110 . 
     More specifically, the first wavelength conversion pattern WC 1  may receive the light L 1  having the first wavelength band from the backlight unit  20 , convert or shift the center wavelength of the light L 1 , and emit the light L 1  having the converted or shifted center wavelength to the outside. The light L 1  whose center wavelength has been converted by the first wavelength conversion pattern WC 1  will be referred to as light L 2  having a second wavelength band. 
     The light L 2  having the second wavelength band displays a second color different from the first color. Here, the second color may be red having a center wavelength of about 600 to 670 nm in an embodiment. That is, the light L 2  having the second wavelength band is also defined as red light whose center wavelength is in the range of about 600 to 670 nm. Therefore, the first wavelength conversion pattern WC 1  can receive blue light from the backlight unit  20  and convert the blue light into red light. 
     The first wavelength conversion pattern WC 1  will be described in more detail below. The first wavelength conversion pattern WC 1  may include the first wavelength conversion material WC 1   a  and a first light transmitting resin WC 1   b.    
     The first wavelength conversion material WC 1   a  may be a material that converts the light L 1  having the first wavelength band into the light L 2  having the second wavelength band. The first wavelength conversion material WC 1   a  may include first quantum dots in an embodiment. The particle size of the first quantum dots is not particularly limited as long as the first wavelength conversion material WC 1   a  can convert the light L 1  having the first wavelength band into the light L 2  having the second wavelength band. 
     The first quantum dots may have a core-shell structure. The core may be a semiconductor nanocrystalline material. In an embodiment, the core of the first quantum dots may be selected from a group II-VI compound, a group III-V compound, a group IV-VI compound, a group IV element, a group IV compound, and combinations of these materials. 
     The group II-VI compound may be selected from a binary compound selected from CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS and mixtures of these materials; a ternary compound selected from CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS and mixtures of these materials; and a quaternary compound selected from HgZnTeS, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe and mixtures of these materials. 
     The group III-V compound may be selected from a binary compound selected from GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb and mixtures of these materials; a ternary compound selected from GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP and mixtures of these materials; and a quaternary compound selected from GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb and mixtures of these materials. 
     The group IV-VI compound may be selected from a binary compound selected from SnS, SnSe, SnTe, PbS; PbSe, PbTe and mixtures of these materials; a ternary compound selected from SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbSe and mixtures of these materials; and a quaternary compound selected from SnPbSSe, SnPbSeTe, SnPbSTe and mixtures of these materials. The group IV element may be selected from Si, Ge, and a mixture of these materials. The group IV compound may be a binary compound selected from SiC, SiGe, and a mixture of these materials. 
     Here, the binary compound, the ternary compound, or the quaternary compound may be present in particles at a uniform concentration or may be present in the same particles at non-uniform concentrations. In addition, the binary compound, the ternary compound, or the quaternary compound may have a core/shell structure in which one quantum dot surrounds another quantum dot. The interface between the core and the shell may have a concentration gradient in which the concentration of an element existing in the shell becomes lower toward the core. 
     The first wavelength conversion material WC 1   a  may be dispersed in a naturally coordinated form in the first light transmitting resin WC 1   b . The first light transmitting resin WC 1   b  is not particularly limited as long as it is a transparent medium that does not affect the wavelength conversion performance of the first wavelength conversion material WC 1   a  and does not cause light absorption. For example, the first light transmitting resin WC 1   b  may include an organic material such as epoxy resin or acrylic resin. 
     The second wavelength conversion pattern WC 2  may receive the light L 1  having the first wavelength band from the backlight unit  20 , convert or shift the center wavelength of the light L 1 , and emit the light L 1  having the converted or shifted center wavelength to the outside. The light L 1  whose center wavelength has been converted by the second wavelength conversion pattern WC 2  will be referred to as light L 3  having a third wavelength band. The light L 3  having the third wavelength band displays a third color different from the first color and the second color. Here, the third color may be green having a center wavelength of about 500 to 570 nm in an embodiment. That is, the light L 3  having the third wavelength band is also defined as green light whose center wavelength is in the range of about 500 to 570 nm. Therefore, the second wavelength conversion pattern WC 2  can receive blue light from the backlight unit  20  and convert the blue light into green light. 
     A sidewall of the second wavelength conversion pattern WC 2  may be spaced apart from a sidewall of the first wavelength conversion pattern WC 1 . More specifically, the second light transmission pattern TC 2  to be described later is disposed between the sidewall of the second wavelength conversion pattern WC 2  and the sidewall of the first wavelength conversion pattern WC 1 . Accordingly, light emitted from the first wavelength conversion material WC 1   a  in the first wavelength conversion pattern WC 1  and light emitted from the second wavelength conversion material WC 2   a  in the second wavelength conversion pattern WC 2  can be prevented from being mixed with each other. This will be described later. 
     The second wavelength conversion pattern WC 2  will now be described in more detail. The second wavelength conversion pattern WC 2  may include the second wavelength conversion material WC 2   a  and a second light transmitting resin WC 2   b.    
     The second wavelength conversion material WC 2   a  may be a material that converts the light L 1  having the first wavelength band into the light L 3  having the third wavelength band. The second wavelength conversion material WC 2   a  may include second quantum dots in an embodiment. The particle size of the second quantum dots is not particularly limited as long as the second wavelength conversion material WC 2   a  can convert the light L 1  having the first wavelength band into the light L 3  having the third wavelength band. In an embodiment, the core of the second quantum dots may be selected from a group II-VI compound, a group III-V compound, a group IV-IV compound, a group IV element, a group IV compound, and combinations of these materials. Examples of each compound or element are the same as those described above in relation to the first quantum dots and thus will not be described. 
     The second wavelength conversion material WC 2   a  may be dispersed in a naturally coordinated form in the second light transmitting resin WC 2   b . The second light transmitting resin WC 2   b  is not particularly limited as long as it is a transparent medium that does not affect the wavelength conversion performance of the second wavelength conversion material WC 2   a  and does not cause light absorption. For example, the second light transmitting resin WC 2   b  may include an organic material such as epoxy resin or acrylic resin. 
     The first and second quantum dots may have a full width at half maximum (FWHM) of an emission wavelength spectrum of about 45 nm or less, preferably about 40 nm or less, more preferably about 30 nm or less in an embodiment. In this range, the first and second quantum dots can improve color purity or color reproducibility. In addition, since light emitted through the first quantum dots and the second quantum dots is radiated in all directions, a wide viewing angle can be improved. 
     The size (e.g., particle size) of the first quantum dots may be greater than the size of the second quantum dots in an embodiment. For example, the size of the first quantum dots may be about 55 to 65 Å. Also, the size of the second quantum dots may be about 40 to 50 Å Light emitted from each of the first and second quantum dots is radiated in various directions regardless of the incident angle of incident light. 
     In addition, each of the first and second quantum dots may be in the form of a spherical, pyramidal, multi-arm, or cubic nanoparticle, nanotube, nanowire, nanofiber, plate-like nanoparticle, or the like. 
     The light L 2  having the second wavelength band emitted from the first wavelength conversion pattern WC 1  and the light L 3  having the third wavelength band emitted from the second wavelength conversion pattern WC 2  may be in an unpolarized state through depolarization. As used herein, ‘unpolarized light’ refers to light that is not composed only of polarization components in a specific direction, that is, light that is not polarized only in a specific direction, in other words, light that is composed of random polarization components. An example of the unpolarized light is natural light. 
     In an embodiment, the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2  may include a phosphor, a quantum rod or a phosphor material, in addition to the first and second quantum dots. Here, the phosphor may have a size of about 100 to 3000 nm in an embodiment. In addition, the phosphor may include a yellow, green, or red fluorescent material. 
     Before describing the light transmission patterns TC, the second filter  240  will be described first. 
     The second filter  240  may be disposed on the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 . The second filter  240  may cover outer surfaces of the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 . In addition, the second filter  240  may be disposed under the light transmission patterns TC which will be described later. In other words, the second filter  240  may be formed in the upper display panel  200  before the light transmission patterns TC. 
     The second filter  240  may be formed between the first wavelength conversion pattern WC 1 , the second wavelength conversion pattern WC 2  and the light transmission patterns TC, so that the first wavelength conversion pattern WC 1 , the second wavelength conversion pattern WC 2 , and the light transmission patterns TC do not contact each other. Accordingly, this can prevent the color mixing of light emitted from the first wavelength conversion pattern WC 1 , the second wavelength conversion pattern WC 2 , and the light transmission patterns TC. 
     The second filter  240  may consist of a single layer or multiple layers. When consisting of multiple layers, the second filter  240  may include a SiNx layer and a SiOx layer stacked alternately in an embodiment. The second filter  240  may have an average thickness of about 0.5 to 2 μm or about 1 μm in an embodiment. 
     The second filter  240  may transmit light having a specific wavelength band and reflect light having another specific wavelength band. Here, the center wavelength of the light reflected by the second filter  240  may be longer than the center wavelength of the light transmitted through the second filter  240 . That is, the second filter  240  may transmit the light L 1  having the first wavelength band and reflect the light L 2  having the second wavelength band and the light L 3  having the third wavelength band, wherein the center wavelength of the light L 2  having the second wavelength band and the center wavelength of the light L 3  having the third wavelength band are longer than the center wavelength of the light L 1  having the first wavelength band. Therefore, the second filter  240  may transmit blue light and reflect red light and green light. 
     The second filter  240  may reflect the light L 2  having the second wavelength band, which is emitted from the first wavelength conversion pattern WC 1  toward the lower substrate  110 , back toward the upper substrate  210 , thereby improving the light output efficiency. In addition, the second filter  240  may transmit the light L 1  having the first wavelength band provided from the backlight unit  20  but reflect light whose center wavelength is longer than that of the light L 1  having the first wavelength band. Therefore, the color purity of the light L 1  having the first wavelength band provided from the backlight unit  20  can be improved. The path of light provided to the second filter  240  will be described in more detail later with reference to  FIG.  5   . 
     The light transmission patterns TC will now be described. The light transmission patterns TC may be disposed on the second filter  240 . The light transmission patterns TC may transmit light incident from the outside without changing the color of the light. 
     More specifically, the light transmission patterns TC may include the first light transmission pattern TC 1  and the second light transmission pattern TC 2 . 
     The first light transmission pattern TC 1  may be disposed on the second filter  240  and may overlap the third subpixel electrode SPE 3  in the direction perpendicular to the lower substrate  110 . The second light transmission pattern TC 2  may be disposed on the second filter  240  and may be located between the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 . That is, the second light transmission pattern TC 2  overlaps the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2  in the direction horizontal to the lower substrate  110 . 
     More specifically, the first light transmission pattern TC 1  may receive the light L 1  having the first wavelength band from the backlight unit  20  and transmit the light L 1  as it is without converting or shifting the center wavelength of the light L 1 . The first light transmission pattern TC 1  may not overlap the first filter  220 . The first light transmission pattern TC 1  may include the light scattering material TC 1   a  and a third light transmitting resin TC 1   b.    
     The light scattering material TC 1   a  may be dispersed in the third light transmitting resin TC 1   b  to scatter light provided to the first light transmitting pattern TC 1  and emit the scattered light to the outside. More specifically, the first light transmission pattern TC 1  may scatter the light L 1  having the first wavelength band received from the backlight unit  20  and emit the scattered light L 1  to the outside. That is, the first light transmission pattern TC 1  may receive blue light and transmit the blue light as it is. 
     The light scattering material TC 1   a  may scatter incident light in various directions regardless of the incident angle and emit the scattered light. Here, the emitted light may be in the unpolarized state through depolarization. That is, the light scattering material TC 1   a  may scatter the light L 1  having the first wavelength band, which is received from the backlight unit  20 , in various directions regardless of the incident angle without converting the center wavelength of the light L 1 . Accordingly, the lateral visibility of the display device  1  according to the embodiment can be improved. 
     The light scattering material TC 1   a  may be a material having a different refractive index from the third light transmitting resin TC 1   b  in an embodiment. In addition, the light scattering material TC 1   a  is not particularly limited as long as it can scatter incident light. For example, the light scattering material TC 1   a  may be a metal oxide or organic particles. The metal oxide may include titanium oxide (TiO 2 ), zirconium oxide (ZrO 2 ), aluminum oxide (Al 2 O 3 ), indium oxide (In 2 O 3 ), zinc oxide (ZnO), or tin oxide (SnO 2 ). The organic material may include acrylic resin or urethane resin. 
     The third light transmitting resin TC 1   b  may be a transparent light transmitting resin in an embodiment. The third light transmitting resin TC 1   b  may be made of the same or different material from the first light transmitting resin WC 1   b  and the second light transmitting resin WC 2   b.    
     The second light transmission pattern TC 2  may be formed in the same process as the first light transmission pattern TC 1 . In an embodiment, the second light transmission pattern TC 2  may be formed at the same time as the first light transmission pattern TC 1  using the same mask. Accordingly, the second light transmission pattern TC 2  may include the same material as the first light transmission pattern TC 1 . 
     Since the second light transmission pattern TC 2  is located between the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 , the height of a valley step formed between the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2  can be minimized. Accordingly, the flatness of the planarization layer  260  to be described later can be improved. This will be described later with reference to  FIGS.  6  and  7   . 
     The second low refractive layer  250  may be disposed on the light transmission patterns TC and the second filter  240 . The second low refractive layer  250  may be disposed on the entire surfaces of the light transmission patterns TC and the second filter  240  in an embodiment. Accordingly, the second low refractive layer  250  may overlap each of the first wavelength conversion pattern WC 1 , the second wavelength conversion pattern WC 2 , the first light transmission pattern TC 1 , and the second light transmission pattern TC 2  in the direction perpendicular to the lower substrate  110 . 
     The second low refractive layer  250  may not be in contact with the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 . On the other hand, the second low refractive layer  250  may be in contact with the first light transmission pattern TC 1  and the second light transmission pattern TC 2 . That is, unlike the first low refractive layer  230 , the second low refractive layer  250  may not contact the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2  but may contact the first light transmission pattern TC 1  and the second light transmission pattern TC 2 . 
     The refractive index of the second low refractive layer  250  is not particularly limited as long as it is lower than the refractive indices of the wavelength conversion patterns WC. For example, the second low refractive layer  250  may have a refractive index of about 1.1 to 1.4. In addition, the refractive index of the first low refractive layer  230  and the refractive index of the second low refractive layer  250  can be equal to or different from each other as long as they are lower than the refractive indices of the wavelength conversion patterns WC. 
     Of light emitted from the wavelength conversion patterns WC, light emitted toward the lower substrate  110  may be reflected back toward the wavelength conversion patterns WC by the second low refractive layer  250 . That is, the second low refractive layer  250  can improve the light output efficiency by recycling at least a portion of the light emitted from the wavelength conversion patterns WC. 
     The second low refractive layer  250  may include a resin and nano particles (such as zinc oxide (ZnO) or titanium dioxide (TiO 2 )) dispersed in the resin. However, the material of the second low refractive layer  250  is not particularly limited as long as the refractive index of the second low refractive layer  250  is lower than those of the wavelength conversion patterns WC. In an embodiment, the second low refractive layer  250  may include one of hollow silica, nano silicate, and porogen. In an embodiment, the materials of the first low refractive layer  230  and the second low refractive layer  250  may be the same. In an embodiment, the materials of the first low refractive layer  230  and the second low refractive layer  250  may be different from each other. 
     Referring again to  FIG.  1   , the planarization layer  260  may be disposed on the second low refractive layer  250 . The planarization layer  260  may provide flatness to the second polarizing layer  280  which will be described later. That is, when the first wavelength conversion pattern WC 1 , the second wavelength conversion pattern WC 2 , the first light transmission pattern TC 1  and the second light transmission pattern TC 2  are formed to different thicknesses in a process, the planarization layer  260  may make the heights of the above elements uniform. 
     The material of the planarization layer  260  is not particularly limited as long as it has planarization characteristics. In an embodiment, the planarization layer  260  may include an organic material. For example, the organic material may include cardo resin, polyimide resin, acrylic resin, siloxane resin, or silsesquioxane resin. 
     The second insulating layer  270  may be disposed on the planarization layer  260 . The second insulating layer  270  may consist of at least one layer having an insulating inorganic material. The insulating inorganic material may include silicon nitride or silicon oxide in an embodiment. The second insulating layer  270  can prevent the planarization layer  260  from being damaged in the process of forming the second polarizing layer  280  which will be described later. In addition, the second insulating layer  270  can improve the adhesion of the second polarizing layer  280  and can prevent the second polarizing layer  280  from being corroded or damaged by air or moisture. The second insulating layer  270  can be omitted. 
     The second polarizing layer  280  may be disposed on the second insulating layer  270 . The second polarizing layer  280  may be a wire grid polarizer in an embodiment. The second polarizing layer  280  will hereinafter be described as a wire grid polarizer. 
     The second polarizing layer  280  may include a plurality of wire grid patterns. In an embodiment, the wire grid patterns may include a conductive material through which a current flows. Here, the conductive material may include a metal such as aluminum (Al), silver (Ag), gold (Au), copper (Cu), or nickel (Ni) in an embodiment. In addition, the conductive material may further include titanium (Ti) or molybdenum (Mo). In an embodiment, the wire grid patterns may be a stacked structure of at least two pattern layers. 
     For example, when light provided to the second polarizing layer  280  passes through the second polarizing layer  280 , components parallel to the second polarizing layer  280  may be absorbed or reflected, and components perpendicular to the second polarizing layer  280  may be transmitted to form polarized light. The second polarizing layer  280  may be formed by a method such as nanoimprinting in an embodiment. 
     A capping layer  281  may be disposed on the second polarizing layer  280 . The capping layer  281  may be disposed directly on the wire grid patterns to cover and protect the wire grid patterns. The capping layer  281  can prevent the second polarizing layer  280  from being damaged or corroded by penetration of air or moisture. The capping layer  281  may be made of an inorganic insulating material such as silicon nitride or silicon oxide in an embodiment. 
     The common electrode CE may be disposed on the capping layer  281 . At least part of the common electrode CE may overlap the first through third subpixel electrodes SPE 1  through SPE 3 . The common electrode CE may be in the form of a whole plate in an embodiment. In addition, the common electrode CE may include a plurality of slits. The common electrode CE may be a transparent electrode or a translucent electrode or may be made of a reflective metal such as aluminum, silver, chromium or an alloy of these materials. Here, the transparent electrode or the translucent electrode may include one or more of indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium oxide (In 2 O 3 ), indium gallium oxide (IGO), and aluminum zinc oxide (AZO). 
     The upper alignment film  290  may be disposed on the common electrode CE. The upper alignment film  290  may induce the initial alignment of the liquid crystal molecules  310  in the liquid crystal layer  300 . The upper alignment film  290  may include a polymer organic material having an imide group in a repeating unit of a main chain in an embodiment. 
     Next, the liquid crystal layer  300  will be described. The liquid crystal layer  300  includes a plurality of initially aligned liquid crystal molecules  310 . The liquid crystal molecules  310  may have negative dielectric anisotropy and may be vertically aligned in the initial alignment state. The liquid crystal molecules  310  may have a predetermined pretilt angle in the initial alignment state. The initial alignment of the liquid crystal molecules  310  can be induced by the lower alignment film  140  and the upper alignment film  290 . When an electric field is formed between the lower display panel  100  and the upper display panel  200 , the liquid crystal molecules  310  may be tilted or rotated in a specific direction to change the polarization state of light transmitted through the liquid crystal layer  300 . 
     The path of light provided from the backlight unit  20  will now be described based on the first wavelength conversion pattern WC 1  by referring to  FIGS.  3  through  5   .  FIGS.  4 A through  5 B  illustrate optical paths in the display device  1  according to the embodiment. For ease of description, different paths of the light L 1  having the first wavelength band and different paths of the light L 2  having the second wavelength band are indicated by different reference numerals in  FIGS.  4  and  5   . 
     The path of light emitted toward the upper substrate  210  will first be described again with reference to  FIG.  3   . 
     As described above, the light L 1  having the first wavelength band is provided to the second filter  240  that covers the first wavelength conversion pattern WC 1 . The second filter  240  provides the received light L 1  having the first wavelength band to the first wavelength conversion pattern WC 1  by transmitting the light L 1 . The first wavelength conversion material WC 1   a  of the first wavelength conversion pattern WC 1  converts the light L 1  having the first wavelength band into the light L 2  having the second wavelength band by shifting the center wavelength of the light L 1 . The light L 2  having the second wavelength band is emitted toward the outside, that is, toward the upper substrate  210 . 
     Hereinafter, the path of light that fails to be emitted toward the upper substrate  210  will be described with reference to  FIGS.  4  and  5   . 
     Referring to  FIG.  4 A , light L 1   a  having the first wavelength band is converted into the light L 2  having the second wavelength band by the first wavelength conversion material WC 1   a  of the first wavelength converting pattern WC 1 . However, when the light L 2  having the second wavelength band is emitted toward the upper substrate  210 , it can be provided to the black matrix BM and absorbed by the black matrix BM without being emitted out of the upper display panel  200 . This light is defined as ineffective light NL that does not affect luminance. The ineffective light NL may be a factor that reduces the light output efficiency. 
     In addition, although not illustrated in the drawing, the light L 2  having the second wavelength band can be totally reflected due to the difference between the refractive index of the upper substrate  210  and the refractive index of outside air. Accordingly, the light L 2  having the second wavelength band can be incident on the wavelength conversion patterns WC or the light transmission patterns TC of another pixel. The light incident on another pixel is defined as noise light. The noise light can reduce color purity and cause deterioration of image quality. 
     The display device  1  according to the embodiment may include the first low refractive layer  230  disposed between the first wavelength conversion pattern WC 1  and the upper substrate  210 . The first low refractive layer  230  has a lower refractive index than the first wavelength conversion pattern WC 1 . 
     Since the refractive index of the first low refractive layer  230  is lower than that of the first wavelength conversion pattern WC 1  as described above, when the incident angle of the light L 2  having the second wavelength band illustrated in  FIG.  4 A  is equal to or greater than a total reflection critical angle, the light L 2  having the second wavelength band is totally reflected toward the first wavelength conversion pattern WC 1  at a first interface B 1  between the first low refractive layer  230  and the first wavelength conversion pattern WC 1 . Accordingly, the light L 2  having the second wavelength band is incident toward the first wavelength conversion pattern WC 1  again. The light L 2  re-incident toward the first wavelength conversion pattern WC 1  is defined as recycled light RL. 
     The recycled light RL can have an opportunity to be emitted toward the upper substrate  210  again by the second filter  240  or the second low refractive layer  250 . That is, the first low refractive layer  230  can prevent the light L 2  having the second wavelength band from becoming the ineffective light NL or the noise light, thereby improving light output efficiency, color purity, and display quality. 
     When the incident angle of the light L 2  having the second wavelength band illustrated in  FIG.  4 A  is smaller than the total reflection critical angle, the incident angle of light incident from the upper substrate  210  to the outside air is reduced due to the first low refractive layer  230  formed between the first wavelength conversion pattern WC 1  and the upper substrate  210  (in a case where the refractive index of the upper substrate  210  is higher than that of the first low refractive layer  230 ). Accordingly, the total reflection ratio of the light incident from the upper substrate  210  to the outside air is reduced, and the light incident from the upper substrate  210  to the outside air can be concentrated close to a direction perpendicular to the upper substrate  210 . 
     If the light incident from the upper substrate  210  to the outside air is incident again on the upper display panel  200  through total reflection, the re-incident light may be absorbed by the black matrix BM to become the ineffective light NL or may be provided to another pixel to become the noise light. This causes a reduction in the light output efficiency and display quality of the display device  1 . 
     However, since the display device  1  according to the embodiment includes the first low refractive layer  230  between the upper substrate  210  and the first wavelength conversion pattern WC 1 , the total reflection ratio of the light incident from the upper substrate  210  to the outside air can be reduced, which, in turn, improves the light output efficiency and the display quality. 
     Referring to  FIG.  4 B , light L 1   b  having the first wavelength band does not contact the first wavelength conversion material WC 1   a  of the first wavelength conversion pattern WC 1 . Therefore, the center wavelength of the light L 1   b  having the first wavelength band may not be converted. As described above, the refractive index of the first low refractive layer  230  is lower than that of the first wavelength conversion pattern WC 1 . Therefore, when the incident angle of the light L 1   b  which has the first wavelength band and whose center wavelength has not been converted is equal to or greater than the total reflection critical angle, the first low refractive layer  230  may totally reflect the light L 1   b , which has the first wavelength band and whose center wavelength has not been converted, into the first wavelength conversion pattern WC 1  at a second interface B 2 . 
     Accordingly, the totally reflected light L 1   b  has an opportunity to contact the first wavelength conversion material WC 1   a  within the first wavelength conversion pattern WC 1 . That is, the first low refractive layer  230  totally reflects the light L 1   b , which has the first wavelength band and whose center wavelength has not been converted, back into the first wavelength conversion pattern WC 1  in order to give an opportunity for the center wavelength of the light L 1   b  to be converted. As a result, the light output efficiency can be improved. 
     Next, referring to  FIG.  4 C , light L 1   c  having the first wavelength band does not contact the first wavelength conversion material WC 1   a  of the first wavelength conversion pattern WC 1 . Therefore, the center wavelength of the light L 1   c  having the first wavelength band may not be converted. Further, when the incident angle of the light L 1   c  having the first wavelength band is smaller than the total reflection critical angle, the light L 1   c  may not be totally reflected at a third interface B 3  between the first low refractive layer  230  and the first wavelength conversion pattern WC 1 . In this case, the light L 1   c  having the first wavelength band may be provided to the first filter  220 . 
     The first filter  220  may block (filter) the light L 1   c , which has the first wavelength band and whose center wavelength has not been converted, from being emitted to the outside of the upper substrate  210 . That is, the first filter  220  can prevent the light L 2  having the second wavelength band and the light L 1  having the first wavelength band, which display different colors, from being mixed with each other, thereby improving color purity. 
     While a case where the first filter  220  blocks the light L 1  having the first wavelength band has been described above, the wavelength band blocked by the first filter  220  can vary according to the wavelength band of light emitted from the backlight unit  20 . 
     Next, the path of light emitted from the first wavelength conversion pattern WC 1  toward the lower substrate  110  will be described with reference to  FIG.  5   . 
     Referring to  FIG.  5 A , some L 2 _ a   1  of the light L 2  having the second wavelength band may travel toward the lower substrate  110  without being emitted toward the upper substrate  210 . As described above, the second filter  240  may transmit the light L 1  having the first wavelength band and reflect the light L 2  having the second wavelength band and the light L 3  having the third wavelength band, wherein the center wavelength of the light L 2  having the second wavelength band and the center wavelength of the light L 3  having the third wavelength band are longer than the center wavelength of the light L 1  having the first wavelength band. In an embodiment, the second filter  240  may be a dichroic filter. 
     Therefore, the second filter  240  may reflect the light L 2 _ a   1  having the second wavelength band back to the upper substrate  210  at a first interface C 1  between the first wavelength conversion pattern WC 1  and the second filter  240 . The light L 2 _ a   2  reflected by the second filter  240  may enter the first wavelength conversion pattern WC 1  and have an opportunity to be emitted toward the upper substrate  210 . 
     While a case where the second filter  240  transmits the light L 1  having the first wavelength band and reflects light having a wavelength band whose center wavelength is longer than the center wavelength of the light L 1  has been described above, the center wavelength band reflected by the second filter  240  can vary according to the wavelength band of light emitted from the backlight unit  20 . 
     Referring to  FIG.  5 B , when the incident angle of light L 1   d  having the first wavelength band and not contacting the first wavelength conversion material WC 1   a  is equal to or greater than the total reflection critical angle, the light L 1   d  may be reflected by the second low refractive layer  250  back to the first wavelength conversion pattern WC 1 . Thus, the light L 1   d  incident on the first wavelength conversion pattern WC 1  can have an opportunity to contact the first wavelength conversion material WC 1   a  within the first wavelength conversion pattern WC 1  and an opportunity to be output again toward the upper substrate  210 . 
     Here, the light L 1   d  having the first wavelength band illustrated in  FIG.  5 B  may be, for example, the light L 1   b  input to the first wavelength conversion pattern WC 1  by the total reflection at the second interface B 2  between the first wavelength conversion pattern WC 1  and the first low refractive layer  320  in  FIG.  4 B . 
     Since the second filter  240  transmits the light L 1  having the first wavelength band as described above, the light L 1   d  having the first wavelength band may be transmitted through the second filter  240  and provided to the second low refractive layer  250 . The refractive index of the second low refractive layer  250  is smaller than that of the first wavelength conversion pattern WC 1 . 
     Therefore, when the incident angle of the light L 1   d  having the first wavelength band and travelling toward the second low refractive layer  250  is equal to or greater than the total reflection critical angle, the light L 1   d  having the first wavelength band may be totally reflected back into the first wavelength conversion pattern WC 1  at an interface C 2  between the second filter  240  and the second low refractive layer  250 . The light L 1   d  incident on the first wavelength conversion pattern WC 1  has an opportunity to contact the first wavelength conversion material WC 1   a  within the first wavelength conversion pattern WC 1  and an opportunity to be output toward the upper substrate  210  again. 
     That is, the second low refractive layer  250  totally reflects the light L 1   d , which has the first wavelength band and whose center wavelength has not been converted, back into the first wavelength conversion pattern WC 1 , thereby providing an opportunity for the center wavelength of the light L 1   d  to be converted. As a result, the light output efficiency can be improved. 
     Although not illustrated in the drawing, of the light L 2  which has the second wavelength band and whose center wavelength has been converted by the first wavelength conversion material WC 1   a , a portion of light directed toward the lower substrate  110  may travel toward the second refractive layer  250  without being reflected by the second filter  240 . In this case, the second low refractive layer  250  may totally reflect the received light L 2  having the second wavelength band back into the first wavelength conversion pattern WC 1 . That is, since the light L 2  having the second wavelength band is given an opportunity to be emitted toward the upper substrate  210  again, the light output efficiency can be improved. 
     Next, the flatness of the planarization layer  260  will be described in more detail with reference to  FIGS.  6 A and  6 B and  7   . 
       FIG.  6 A  illustrates the area A of  FIG.  1    turned over.  FIG.  6 B  illustrates the area A of  FIG.  1    turned over in a case where the second light transmission pattern TC 2  is omitted.  FIG.  7    illustrates the flatness of the planarization layer  260  among the elements of the display device  1  according to the embodiment. 
     Referring to  FIG.  6 A , the planarization layer  260  includes a first surface  260   a  which contacts the second insulating layer  270  (see  FIG.  1   ) and a second surface  260   b  which contacts the second low refractive layer  250 . The second low refractive layer  250  includes a first surface  250   a  which contacts the second surface  260   b  of the planarization layer  260  and a second surface  250   b  which is opposite the first surface  250   a.    
     The second light transmission pattern TC 2  is disposed in a valley area GA between the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 . Thus, the second light transmission pattern TC 2  can provide flatness to the second low refractive layer  250 . That is, the second light transmission pattern TC 2  is formed to fill the valley area GA between the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 , thereby minimizing a step height h 1  of the second surface  250   b  of the second low refractive layer  250 . As the step height h 1  of the second surface  250   b  of the second low refractive layer  250  is minimized, a step height h 2  of the first surface  250   a  of the second low refractive layer  250  may also be minimized. Here, the step height of a specific surface refers to a height difference between a lowest part and a highest part of the specific surface. 
     As the step heights h 2  and h 1  of the first surface  250   a  and the second surface  250   b  of the second low refractive layer  250  are minimized, the thickness of the second low refractive layer  250  for step height compensation may also be reduced. In an embodiment, the second low refractive layer  250  may be formed to a thickness de 2  of about 1 μm or less. The reduction in the thickness de 2  of the second low refractive layer  250  can reduce the cost of forming the second low refractive layer  250  and reduce the occurrence of cracks. 
     Furthermore, when the step height h 2  of the first surface  250   a  of the second low refractive layer  250  is minimized, the step height of the first surface  260   a  of the planarization layer  260  disposed on the second low refractive layer  250  may also be minimized. In an embodiment, the first surface  260   a  of the planarization layer  260  may have a step height h 3  of about 0 to 40 nm. Thus, the flatness of the planarization layer  260  can be sufficiently secured. In addition, as the step height of the planarization layer  260  is minimized, a thickness de 3  of the planarization layer  260  necessary for step height compensation may also be reduced. In an embodiment, the thickness de 3  of the planarization layer  260  may be about 2 to 3 μm. The reduction in the thickness de 3  of the planarization layer  260  can reduce the cost of forming the planarization layer  260  and prevent the warpage of the planarization layer  260 . 
       FIG.  6 A  will be described in more detail through comparison with  FIG.  6 B . For ease of description, the same reference numerals as those of  FIG.  6 A  will be used in  FIG.  6 B . 
     When the second light transmission pattern TC 2  is absent as illustrated in  FIG.  6 B , the second low refractive layer  250  is formed to fill the valley area GB between the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 . Here, the absence of the second light transmission pattern TC 2  denotes that the first light transmission pattern TC 1  is disposed under the second filter  240 . 
     Therefore, a step height h 4  of the first surface  250   a  of the second low refractive layer  250  is increased by the height of the valley step. Accordingly, the step height h 4  of the first surface  250   a  of the second low refractive layer  250  illustrated in  FIG.  6 B  is greater than the step height h 2  of the first surface  250   a  of the second low refractive layer  250  illustrated in  FIG.  6 A . Therefore, in order to compensate for the step height h 4 , the second low refractive layer  250  illustrated in  FIG.  6 B  should have a large thickness de 4 . The increase in the thickness de 4  of the second low refractive layer  250  causes the occurrence of cracks in the second low refractive layer  250  and an increase in the cost of forming the second low refractive layer  250 . In an embodiment, the thickness de 4  of the second low refractive layer  250  illustrated in  FIG.  6 B  may be about 3 to 4 μm. 
     In addition, the step height h 4  of the first surface  250   a  of the second low refractive layer  250  affects the step height h 5  of the first surface  260   a  of the planarization layer  260 . Since the planarization layer  260  is formed on the second low refractive layer  250 , a thickness de 5  of the planarization layer  260  should be large enough to compensate for the step height h 4  of the first surface  250   a  of the second low refractive layer  250 . In an embodiment, the thickness de 5  of the planarization layer  260  illustrated in  FIG.  6 B  may be about 4 to 6 μm. The increase in the thickness de 5  of the planarization layer  260  causes an increase in the overall thickness of the upper display panel  200  and the warpage of the planarization layer  260 . 
     That is, the display device  1  according to the embodiment can provide flatness to the second low refractive layer  250  and the planarization layer  260  by including the second light transmission pattern TC 2 . Therefore, the occurrence of cracks in the second low refractive layer  250  and the warpage of the planarization layer  260  can be prevented. Furthermore, the cost of forming the second low refractive layer  250  and the planarization layer  260  can be reduced. 
     A thickness de 1  of the first low refractive layer  230  illustrated in  FIG.  6 A  is not particularly limited. However, in an embodiment, the thickness de 1  of the first low refractive layer  230  may be set to about 1 μm or less in consideration of crack occurrence and cost. That is, the thickness de 1  of the first low refractive layer  230  may be the same as the thickness de 2  of the second low refractive layer  250 . However, the inventive concept is not limited to this case, and the thickness de 1  of the first low refractive layer  230  can also be different from the thickness de 2  of the second low refractive layer  250 . 
       FIG.  7    illustrates the flatness of the first surface  260   a  of the planarization layer  260  among the elements of the display device  1  according to the embodiment. 
     Referring to  FIG.  7   , the first surface  260   a  of the planarization layer  260  may have different step heights at different positions D 1  through D 9  in consideration of process conditions and the positional relationship with other elements. However, since the display device  1  according to the embodiment includes the second light transmission pattern TC 2  located between the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 , the step heights of the first surface  260   a  of the planarization layer  260  can be minimized. In an embodiment, the step heights at the positions D 1  through D 9  on the first surface  260   a  of the planarization layer  260  may all be in the range of 0 to 40 nm. 
     The color mixing reducing effect of the display device  1  according to the embodiment will now be described with reference to  FIG.  8   . 
     As described above, the display device  1  according to the embodiment includes the first low refractive layer  230  to prevent light emitted toward the upper substrate  210  from being totally reflected to an adjacent pixel. Therefore, color mixing can be prevented. 
     The color mixing can also be suppressed by the second light transmission pattern TC 2 . 
       FIG.  8    is a view for explaining the color mixing reducing effect of the display device  1  according to the embodiment. 
     Referring to  FIG.  8   , the display device  1  according to the embodiment includes the second light transmission pattern TC 2  disposed between the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 . The light L 2  having the second wavelength band scattered by the first wavelength conversion pattern WC 1  may not enter an adjacent wavelength conversion pattern or an adjacent light transmission pattern due to the second filter  240 . In some cases, however, the light L 2  having the second wavelength band scattered by the first wavelength conversion pattern WC 1  can transmit through the second filter  240  to enter the adjacent second wavelength conversion pattern WC 2 . 
     Here, the second light transmission pattern TC 2  disposed between the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2  in the display device  1  according to the embodiment may block the light L 2  having the second wavelength band scattered by the first wavelength conversion pattern WC 1  from entering the second wavelength conversion pattern WC 2 . Thus, color mixing can be prevented. 
     The prevention of the color mixing can improve color reproducibility. This will now be described with reference to Table 1 below. Table 1 compares the luminance of a conventional display device with the color reproducibility of the display device  1  according to the embodiment. The color reproducibility comparison is based on Commission Internationale de L&#39;eclairage (CIE) 1931 and CIE 1976 established by the CIE. The conventional display device in Table 1 refers to a display device without the second light transmission pattern TC 2  among display devices displaying quantum dots. 
     Referring to Table 1, the color reproducibility of the display device  1  according to the embodiment is better than that of the conventional display device by about 2.6%. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 Conventional Display 
                 Inventive Display 
               
               
                   
                 Category 
                   
                 Device 
                 Device 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 DCI 
                 1931 
                 90.3 
                 92.9 
               
               
                   
                   
                 1976 
                 94.8 
                 96.1 
               
               
                   
                   
               
            
           
         
       
     
     Next, the optical characteristic effect of the display device  1  according to the embodiment will be described with reference to Table 2 below. Table 2 compares the luminance of a conventional display device with the luminance of the display device  1  according to the embodiment. The conventional display device in Table 2 refers to a display device without a low refractive layer among display devices displaying quantum dots. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Conventional Display 
                 Inventive Display 
               
               
                 Category 
                 Device 
                 Device 
               
               
                   
               
             
            
               
                 Luminance (nit) 
                 120 
                 212 
               
               
                 Color difference 
                 Δx 0.010, Δy 0.018 
                 Δx 0.010, Δy 0.020 
               
               
                 0 degrees/60 degrees 
               
               
                   
               
            
           
         
       
     
     Referring to Table 2, the luminance of the display device  1  according to the embodiment is higher than the luminance of the conventional display device by 77%. In addition, the display device  1  according to the embodiment has substantially the same color difference as the conventional display device. That is, since the display device  1  according to the embodiment includes the first low refractive layer  230  and the second low refractive layer  250 , it can have improved luminance while maintaining the same color difference as the conventional display device. 
     The luminance characteristics according to the refractive index values of the first low refractive layer  230  and the second low refractive layer  250  included in the display device  1  according to an embodiment will now be described with reference to Tables 3 and 4. 
     Table 3 below shows the luminance in a case where the first low refractive layer  230  and the second low refractive layer  250  have the same refractive index value. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
             
            
               
                 Refractive index 
                 First low refractive layer 230 
                 1.4 
                 1.3 
                 1.2 
               
               
                   
                 Second low refractive layer 250 
                 1.4 
                 1.3 
                 1.2 
               
            
           
           
               
               
               
               
            
               
                 Average refractive index 
                 1.4 
                 1.3 
                 1.2 
               
               
                 Luminance 
                 1.32 
                 1.52 
                 1.77 
               
               
                   
               
            
           
         
       
     
     Referring to Table 3, in the case where the first low refractive layer  230  and the second low refractive layer  250  have the same refractive index value, the luminance is highest when the average of the refractive index values of the first low refractive layer  230  and the second low refractive layer  250  is lowest. 
     Table 4 below shows the luminance in a case where the first low refractive layer  230  and the second low refractive layer  250  have different refractive index values. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
             
            
               
                 Refractive index 
                 First low refractive layer 230 
                 1.2 
                 1.2 
                 1.3 
               
               
                   
                 Second low refractive layer 250 
                 1.3 
                 1.4 
                 1.4 
               
            
           
           
               
               
               
               
            
               
                 Difference in refractive index 
                 0.1 
                 0.2 
                 0.1 
               
               
                 Average refractive index 
                 1.25 
                 1.3 
                 1.35 
               
               
                 Luminance 
                 1.59 
                 1.44 
                 1.38 
               
               
                   
               
            
           
         
       
     
     Referring to Table 4, even in the case where the first and second low refractive layers  230  and  250  have different refractive index values, the luminance is highest when the average of the refractive index values of the first low refractive layer  230  and the second low refractive layer  250  is lowest. 
     As is apparent from the above, the luminance is more affected by the average of the refractive index values of the first and second low refractive layers  230  and  250  than by the difference between the refractive index values. Accordingly, the display device  1  according to the embodiment can improve the luminance by reducing the average of the refractive index values of the first low refractive layer  230  and the second low refractive layer  250 . 
       FIGS.  9  through  14    illustrate other embodiments of the display device  1  of  FIG.  1   . For simplicity, a description of elements and features identical to those described above with reference to  FIGS.  1  through  8    will be omitted. 
     Referring to  FIG.  9   , a display device  2  according to an embodiment may not include a second filter  240 . That is, the display device  2  of  FIG.  9    is different from the display device  1  of  FIG.  1    in that it does not include the second filter  240 . 
     However, the display device  2  according to the embodiment may further include third insulating layer  295  in order to prevent a first wavelength conversion pattern WC 1 , a second wavelength conversion pattern WC 2 , a first light transmission pattern TC 1 , and a second light transmission pattern TC 2  from directly contacting each other. The third insulating layer  295  may consist of at least one layer including an inorganic material in an embodiment. The inorganic material may include a silicon nitride (SiNx) layer and a silicon oxide (SiOx) layer in an embodiment. The thickness of the third insulating layer  295  is not limited to that illustrated in  FIG.  9    as long as the wavelength conversion patterns WC and the light transmission patterns TC do not directly contact each other. 
     Even if the display device  2  according to the embodiment does not include the second filter  240 , the light output efficiency can be maintained because some of the light emitted from the first wavelength conversion pattern WC 1  can be input again into the first wavelength conversion pattern WC 1  by a second low refractive layer  250 . 
     Referring to  FIG.  10   , a display device  3  according to an embodiment may not include a first filter  220 . That is, the display device  3  of  FIG.  10    is different from the display device  1  of  FIG.  1    in that it does not include the first filter  220 . 
     Even if the display device  3  according to the embodiment does not include the first filter  220 , the light output efficiency can be maintained because some of the light emitted from a first wavelength conversion pattern WC 1  can be input again into the first wavelength conversion pattern WC 1  by a first low refractive layer  230 . 
     Although not illustrated in the drawing, the display device  3  according to the embodiment may also not include both the first filter  220  and a second filter  240 . 
     Referring to  FIG.  11   , a display device  4  according to an embodiment may include a first inorganic layer  231  instead of a first low refractive layer  230 . That is, the display device  4  of  FIG.  11    is different from the display device  1  of  FIG.  1    in that the first low refractive layer  230  is replaced with the first inorganic layer  231 . 
     The first inorganic layer  231  may have a refractive index of about 1.3 to 1.5 in an embodiment. If the refractive index condition is satisfied, the material of the first inorganic layer  231  is not particularly limited. In an embodiment, the first inorganic layer  231  may include a silicon nitride (SiNx) layer or a silicon oxide (SiOx) layer and may be formed as a single layer or may be formed by stacking a plurality of layers. 
     Referring to  FIG.  12   , a display device  5  according to an embodiment may include a second inorganic layer  251  instead of a second low refractive layer  250 . That is, the display device  5  of  FIG.  12    is different from the display device  1  of  FIG.  1    in that the second low refractive layer  250  is replaced with the second inorganic layer  251 . 
     The second inorganic layer  251  may have a refractive index of about 1.3 to 1.5 in an embodiment. If the refractive index condition is satisfied, the material of the second inorganic layer  251  is not particularly limited. In an embodiment, the second inorganic layer  251  may include a silicon nitride (SiNx) layer or a silicon oxide (SiOx) layer and may be formed as a single layer or may be formed by stacking a plurality of layers. 
     Although not illustrated in the drawing, both a first low refractive layer  230  and the second low refractive layer  250  can be replaced with a first inorganic layer  231  and the second inorganic layer  251 , respectively. Here, the refractive indexes of the first inorganic layer  231  and the second inorganic layer  251  are not necessarily the same, and the materials of the first inorganic layer  231  and the second inorganic layer  251  can be different from each other. 
     Referring to  FIG.  13   , a display device  6  according to an embodiment may not include a first low refractive layer  230 . That is, the display device  6  of  FIG.  13    is different from the display device  1  of  FIG.  1    in that it does not include the first low refractive layer  230 . 
     Referring to  FIG.  14   , a display device  7  according to an embodiment may not include a second low refractive layer  250 . That is, the display device  7  of  FIG.  14    is different from the display device  1  of  FIG.  1    in that it does not include the second low refractive layer  250 . 
     The relationship between the position of a low refractive layer and luminance will now be described in more detail with reference to  FIG.  15   . 
       FIG.  15    is a graph illustrating the luminance according to the position of a low refractive layer in a display device according to an embodiment. In  FIG.  15   , ref represents a case where no low refractive layer is included, (a) represents a case where only a first low refractive layer is included, (b) represents a case where only a second low refractive layer is included, and (c) represents a case where both the first low refractive layer and the second low refractive layer are included. In addition, p1 represents a case where the average refractive index is 1,2, p2 represents a case where the average refractive index is 1.3, and p3 represents a case where the average refractive index is 1.4. 
     Referring to  FIG.  15   , assuming that the refractive indices are the same, the luminance is highest when both the first and second low refractive layers  230  and  250  are included. In addition, assuming that the number of refractive layers included is the same, the luminance is highest when the average refractive index is lowest, as described above. 
     Therefore, the display device according to the embodiment can improve luminance by including both the first low refractive layer  230  and the second low refractive layer  250  and minimizing the average of the refractive indices of the first low refractive layer  230  and the second low refractive layer  250 . However, the refractive indices of low refractive layers and the positions and number of the low refractive layers can be variously set in consideration of the relationship with other elements, the required luminance, and the production cost. 
       FIG.  16    illustrates an embodiment of the display device  1  of  FIG.  1   . 
     Referring to an area F of  FIG.  16   , a display device  8  according to an embodiment may include a second light transmission pattern TC 2 ′ and a first light transmission pattern TC 1  having different thicknesses. That is, since the second light transmission pattern TC 2 ′ is formed in a narrower area than the first light transmission pattern TC 1 , it may be thinner than the first light transmission pattern TC 1 . In other words, even if the first light transmission pattern TC 1  and the second light transmission pattern TC 2 ′ are simultaneously formed through the same process, they do not necessarily have the same thickness. 
     Hereinafter, a method of manufacturing the upper display panel  200  among the elements of the display device  1  according to the embodiment of  FIG.  1    will be described with reference to  FIGS.  17  through  22   .  FIGS.  17  through  22    illustrate a method of manufacturing a display device according to an embodiment. For simplicity, a description of elements and features identical to those described above with reference to  FIGS.  1  through  8    will be omitted. 
     Referring to  FIG.  17   , the black matrix BM and the first filter  220  are formed on the upper substrate  210 . The black matrix  13119  may be formed on the upper substrate  210  to include a plurality of openings. The first filter  220  may be formed on the black matrix BM to vertically overlap the first subpixel electrode SPE 1  and the second subpixel electrode SPE 2  described above with reference to  FIG.  1   . That is, the first filter  220  does not overlap the third subpixel electrode SPE 3  to be described later. 
     In an embodiment, the first filter  220  may be formed by forming an organic material having photosensitivity on the entire surfaces of the black matrix BM and the upper substrate  210  and then patterning the organic material such that the first filter  220  is located only in areas vertically overlapping the first sub pixel electrode SPE 1  and the second sub pixel electrode SPE 2 . The organic material having photosensitivity may be a yellow photoresist in an embodiment. In an embodiment, the first filter  220  may be formed by depositing an inorganic material using a method such as chemical vapor deposition. The first filter  220  may be formed as a single layer or may be formed by stacking a plurality of layers. When the first filter  220  consists of a plurality of layers, the transmission wavelength band and the blocking wavelength band of the first filter  220  can be controlled by adjusting the material, the refractive index, the deposition thickness, etc. of each layer. 
     Referring to  FIG.  18   , the first low refractive layer  230  is formed on the first filter  220 , the black matrix BM, and the upper substrate  210 . The first low refractive layer  230  may be formed on the entire surfaces of the first filter  220 , the black matrix BM and the upper substrate  210  to vertically overlap all of the wavelength conversion patterns WC and the light transmission patterns TC to be described later. The thickness of the first low refractive layer  230  may be about 1 μm or less. 
     The material of the first low refractive layer  230  is not particularly limited as long as the refractive index of the first low refractive layer  230  is about 1.1 to 1.4. That is, the first low refractive layer  230  may include a resin and nano particles (such as zinc oxide (ZnO) or titanium dioxide (TiO 2 )) dispersed in the resin. In an embodiment, the first low refractive layer  230  may include one of hollow silica, nano silicate, and porogen. In addition, the first inorganic layer  231  can be formed instead of the first low refractive layer  230 . 
     Next, referring to  FIG.  19   , the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2  are formed on the first low refractive layer  230 . The formation order of the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2  is not particularly limited. 
     More specifically, a material including a plurality of first quantum dots that convert blue light into red light is deposited on a transparent organic material or a transparent photoresist and then patterned to leave only an area overlapping the first subpixel electrode SPE 1  in the direction perpendicular to the lower substrate  110 . As a result, the first wavelength conversion pattern WC 1  is formed. 
     In addition, a material including a plurality of second quantum dots that convert blue light into green light is deposited on a transparent organic material or a transparent photoresist and then patterned to leave only an area overlapping the second subpixel electrode SPE 2  in the direction perpendicular to the lower substrate  110 . As a result, the second wavelength conversion pattern WC 2  is formed. 
     After the formation of the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 , the second filter  240  is formed on the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 . The second filter  240  may be formed as a single layer or may be formed by stacking a plurality of layers. When the second filter  240  consists of a plurality of layers, the transmission wavelength band and the reflection wavelength band of the second filter  240  can be controlled by adjusting the material, the refractive index, the deposition thickness, etc. of each layer. 
     Next, referring to  FIG.  20   , the light transmission patterns TC including the first light transmission pattern TC 1  and the second light transmission pattern TC 2  are formed on the second filter  240 . The light transmission patterns TC are formed by stacking a material including a light scattering material for dispersing incident light on a transparent organic material or a transparent photoresist and then patterning the stacked material to leave an area overlapping the third subpixel electrode SPE 3  in the direction perpendicular to the lower substrate  110  and an area located between the first wavelength conversion pattern WC 1  and the second wavelength conversion pattern WC 2 . 
     That is, the first light transmission pattern TC 1  and the second light transmission pattern TC 2  may be formed simultaneously through the same mask process in an embodiment. Accordingly, the first light transmission pattern TC 1  and the second light transmission pattern TC 2  may be made of the same material. In an embodiment, each of the first light transmission pattern TC 1  and the second light transmission pattern TC 2  may include the light scattering material TC 1   a  capable of scattering light and the third light transmitting resin TC 1   b  in which the light scattering material TC 1   a  is coordinated. 
     Referring to  FIG.  21   , the second low refractive layer  250  is formed on the light transmission patterns TC and the second filter  240 . The second low refractive layer  250  may be formed on the entire surfaces of the light transmission patterns TC and the second filter  240 . The thickness of the second low refractive layer  250  may be about 1 μm or less. 
     The material of the second low refractive layer  250  is not particularly limited as long as the refractive index of the second low refractive layer  250  is about 1.1 to 1.4. The refractive index of the second low refractive layer  250  may be the same as or different from that of the first low refractive layer  230 . In addition, the material of the second low refractive layer  250  may be the same as or different from that of the first low refractive layer  230 . For example, the second low refractive layer  250  may include a resin and nano particles (such as zinc oxide (ZnO) or titanium dioxide (TiO 2 )) dispersed in the resin. In an embodiment, the second low refractive layer  250  may include one of hollow silica, nano silicate, and porogen. In addition, the second inorganic layer  251  can be formed instead of the second low refractive layer  250 . 
     Since the second light transmission pattern TC 2  provides flatness to the second low refractive layer  250 , the step height of the second low refractive layer  250  can be minimized. 
     Next, the planarization layer  260  is formed on the second low refractive layer  250 . More specifically, the forming of the planarization layer  260  may include applying a planarizing material and curing the planarizing material. The planarizing material may include an organic material such as a thermosetting resin in an embodiment. 
     As described above, as the step height of the second low refractive layer  250  is minimized, the step height of the planarization layer  260  may also be minimized, thereby improving the flatness of the planarization layer  260 . 
     Next, referring to  FIG.  22   , the second insulating layer  270 , the second polarizing layer  280 , the capping layer  281 , the common electrode CE, and the upper alignment film  290  are formed on the planarization layer  260 . Here, since the flatness of the planarization layer  260  has been improved, a plurality of wire grid patterns included in the second polarizing layer  280  can be formed uniformly. 
     According to embodiments, the light output efficiency can be improved due to the presence of a low refractive layer. 
     In addition, since a light transmission pattern is placed in a valley area between wavelength conversion patterns, flatness can be given to the low refractive layer and a planarization layer. 
     Since the thickness of the low refractive layer is minimized, the occurrence of cracks can be reduced, and the cost of forming the low refractive layer can be reduced. 
     Also, since the thickness of the planarization layer is minimized, the warpage of the planarization layer can be prevented. 
     Although certain exemplary embodiments and implementations have been described herein, other embodiments and modifications will be apparent from this description. Accordingly, the inventive concept is not limited to such embodiments, but rather to the broader scope of the presented claims and various obvious modifications and equivalent arrangements.