Patent Publication Number: US-2021175308-A1

Title: Transparent display device and method of manufacturing a transparent display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation application of U.S. patent application Ser. No. 16/532,110 filed on Aug. 5, 2019, which is a continuation application of U.S. patent application Ser. No. 16/101,149 filed on Aug. 10, 2018 (now U.S. Pat. No. 10,403,699), which is a divisional application of U.S. patent application Ser. No. 15/447,798 filed on Mar. 2, 2017 (now U.S. Pat. No. 10,074,705), which claims priority under 35 USC § 119 to Korean Patent Application No. 10-2016-0059528, filed on May 16, 2016 in the Korean Intellectual Property Office (KIPO), the entire disclosures of which are incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Field 
     Example embodiments relate generally to display devices. More specifically, example embodiments relate to transparent display devices and methods of manufacturing the transparent display devices. 
     2. Description of the Related Art 
     Recently, a display device (e.g., an organic light-emitting display (OLED) device) having transparent or light-transmitting properties has been developed. 
     To manufacture a transparent display device, various variables (e.g., a composition, a disposition, a thickness, etc.) of components (e.g., substrates, electrodes, insulation layers, etc.) of the transparent display device, and their various advantages and disadvantages, may be addressed. For example, the OLED device may include a stack of insulation layers that contain different materials. In this case, the insulation layers may cause optical characteristics (e.g., transmittance) of the OLED device to be unsatisfactory. 
     SUMMARY 
     Example embodiments provide methods of manufacturing transparent display devices with reduced manufacturing time and cost. 
     Example embodiments provide transparent display devices with improved light transmittance and luminescent efficiency. 
     According to an aspect of example embodiments, in a method of manufacturing a transparent display device, a substrate may be provided, the substrate including a pixel region and a transmission region. A first electrode may be formed over the substrate in the pixel region, and a display layer may be formed on the first electrode. A second electrode may be formed on the display layer to face the first electrode. A capping structure may be formed on the second electrode, the capping structure including a first capping layer and a second capping layer. The first capping layer may be formed on the second electrode in the pixel region and a first region of the transmission region, by using a mask that has an opening. The mask may then be shifted. The second capping layer may be formed on the second electrode in the pixel region and a second region of the transmission region by using the shifted mask. 
     In example embodiments, a width of the opening may be substantially equal to the sum of a width of the pixel region and a half of a width of the transmission region. An end portion of the first region may be adjacent to an end portion of the second region in the transmission region. The capping structure may have a first thickness in the pixel region and may have a second thickness substantially less than the first thickness in the transmission region. 
     In some example embodiments, a width of the opening may be substantially greater than the sum of a width of the pixel region and a half of a width of the transmission region and substantially less than the sum of the width of the pixel region and the width of the transmission region. The transmission region may further include a third region in which the first region overlaps the second region. The capping structure may have a first thickness in the pixel region and the third region of the transmission region and may have a second thickness substantially less than the first thickness in a remaining region of the transmission region, the remaining region being outside the third region. 
     In some example embodiments, a width of the opening may be substantially greater than a width of the pixel region, and substantially less than the sum of the width of the pixel region and a half of a width of the transmission region. The transmission region may further include a third region positioned between the first region and the second region. The capping structure may have a first thickness in the pixel region and may have a second thickness in the first region and the second region, wherein the second thickness is less than the first thickness. 
     In example embodiments, an aperture may be formed in the second electrode. The aperture may overlap at least a portion of the transmission region. 
     According to an aspect of example embodiments, in a method of manufacturing a transparent display device, a substrate may be provided, the substrate including a first pixel region, a first transmission region, a second pixel region, and a second transmission region. 
     A first electrode may be formed over the substrate in each of the first pixel region and the second pixel region, and a display layer may be formed on the first electrode. A second electrode may be formed on the display layer to face the first electrode. A capping structure may be formed on the second electrode, the capping structure including a first capping layer and a second capping layer. The first capping layer may be formed on the second electrode in the first pixel region, the first transmission region, and the second pixel region by using a mask that has an opening. The mask may then be shifted. The second capping layer may be formed on the second electrode in the first pixel region, the second pixel region, and a second transmission region by using the shifted mask. 
     In example embodiments, a width of the opening may be substantially equal to the sum of a width of the first pixel region, a width of the first transmission region, and a width of the second pixel region. The capping structure may have a first thickness in the first pixel region and the second pixel region and may have a second thickness less than the first thickness in the first transmission region and the second transmission region. 
     According to another aspect of example embodiments, a transparent display device may include a substrate including a pixel region and a transmission region which are arranged along a first direction, a first electrode disposed over the substrate in the pixel region, a display layer disposed on the first electrode, a second electrode facing the first electrode and disposed on the display layer, and a capping structure disposed on the second electrode. The capping structure may include a first capping layer disposed on the second electrode in the pixel region and a first region of the transmission region and a second capping layer disposed on the second electrode in the pixel region and a second region of the transmission region. 
     In example embodiments, an end portion of the first region may be adjacent to an end portion of the second region in the transmission region. The capping structure may have a first thickness in the pixel region, and may have a second thickness less than the first thickness in the transmission region. 
     In some example embodiments, the transmission region may further include a third region in which the first region overlaps the second region. The capping structure may have a first thickness in the pixel region and the third region of the transmission region and may have a second thickness less than the first thickness in a remaining region of the transmission region, the remaining region being outside the third region. 
     In some example embodiments, the transmission region may further include a third region positioned between the first region and the second region. The capping structure may have a first thickness in the pixel region and may have a second thickness less than the first thickness in the first region and the second region. 
     In example embodiments, a thickness of the first capping layer may be substantially equal to a thickness of the second capping layer. 
     In example embodiments, the transparent display device may further include a plurality of unit pixels each including one of the pixel regions and one of the transmission regions, the plurality of unit pixels being arranged along a second direction perpendicular to the first direction. The capping structure may be provided in at least one unit pixel of the plurality of unit pixels. 
     In example embodiments, the capping structure may extend across more than one unit pixel of the plurality of unit pixels. In some example embodiments, a plurality of the capping structures may be provided, and ones of the capping structures may be provided separately in respective ones of the unit pixels. 
     In example embodiments, the pixel region may include a red sub-pixel region, a green sub-pixel region, and a blue sub-pixel region which are arranged along a second direction perpendicular to the first direction. 
     In example embodiments, the second electrode may include an aperture overlapping at least a portion of the transmission region. 
     According to another aspect of example embodiments, a transparent display device may include a substrate including a first pixel region, a first transmission region, a second pixel region, and a second transmission region, a first electrode disposed over the substrate in each of the first pixel region and the second pixel region, a display layer disposed on the first electrode, a second electrode facing the first electrode and disposed on the display layer, and a capping structure disposed on the second electrode. The capping structure may include a first capping layer disposed on the second electrode in the first pixel region, the first transmission region, and the second pixel region and a second capping layer disposed on the second electrode in the first pixel region, the second pixel region, and the second transmission region. 
     In example embodiments, the capping structure may have a first thickness in the first pixel region and the second pixel region, and may have a second thickness less than the first thickness in the first transmission region and the second transmission region. 
     According to example embodiments, in methods of manufacturing a transparent display device, a first capping layer and a second capping layer which have substantially the same area may be formed by shifting one mask, so that a resulting capping structure that has substantially different thicknesses in the pixel region and the transmission region may be formed. According to example embodiments, the transparent display device may include the capping structure that has substantially different thicknesses in the pixel region and the transmission region, so that light transmittance and luminescent efficiency of the transparent display device may be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative, non-limiting example embodiments will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. 
         FIG. 1  is a plan view illustrating a transparent display device in accordance with example embodiments. 
         FIG. 2  is a plan view illustrating further details of an area I of the transparent display device in  FIG. 1 . 
         FIG. 3  is a cross-sectional view illustrating a transparent display device in accordance with example embodiments. 
         FIG. 4  is a cross-sectional view illustrating a transparent display device in accordance with some example embodiments. 
         FIG. 5  is a cross-sectional view illustrating a transparent display device in accordance with some example embodiments. 
         FIGS. 6 to 8  are cross-sectional views illustrating transparent display devices in accordance with some example embodiments. 
         FIGS. 9 to 15  are cross-sectional views illustrating a method of manufacturing a transparent display device in accordance with example embodiments. 
         FIGS. 16 and 17  are cross-sectional views illustrating a method of manufacturing a transparent display device in accordance with some example embodiments. 
         FIGS. 18 and 19  are cross-sectional views illustrating a method of manufacturing a transparent display device in accordance with some example embodiments. 
         FIG. 20  is a cross-sectional view illustrating a method of manufacturing a transparent display device in accordance with some example embodiments. 
         FIG. 21  is a plan view illustrating a transparent display device in accordance with example embodiments. 
         FIG. 22  is a plan view illustrating a transparent display device in accordance with some example embodiments. 
         FIG. 23  is a plan view illustrating further details of an area II of the transparent display device in  FIG. 1 . 
         FIG. 24  is a cross-sectional view illustrating a transparent display device in accordance with example embodiments. 
         FIGS. 25 to 31  are cross-sectional views illustrating a method of manufacturing a transparent display device in accordance with example embodiments. 
         FIG. 32  is a plan view illustrating a transparent display device in accordance with example embodiments. 
         FIG. 33  is a plan view illustrating a transparent display device in accordance with some example embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, transparent display devices and methods of manufacturing the transparent display devices in accordance with example embodiments will be explained in detail with reference to the accompanying drawings. The various figures are not necessarily to scale. All numerical values are approximate, and may vary. All examples of specific materials and compositions are to be taken as nonlimiting and exemplary only. Other suitable materials and compositions may be used instead. 
       FIG. 1  is a plan view illustrating a transparent display device in accordance with example embodiments.  FIG. 2  is a plan view illustrating further details of an area I of the transparent display device in  FIG. 1 .  FIG. 3  is a cross-sectional view illustrating a transparent display device in accordance with example embodiments. For example,  FIG. 3  may be a cross sectional view cut along a line III-III′ in  FIG. 2 . 
     Referring to  FIGS. 1 and 2 , the transparent display device may include a plurality of unit pixels PX. The unit pixels PX may be arranged along a first direction and a second direction which are substantially parallel with a top surface of a substrate ( 100  in  FIG. 3 ) and substantially perpendicular to each other. 
     Each of the unit pixels PX may include a pixel region  10  and a transmission region  20 . A plurality of sub-pixel regions may be disposed in the pixel region  10 . In example embodiments, the pixel region  10  may include a red sub-pixel region  11 , a green sub-pixel region  12 , and a blue sub-pixel region  13 . For example, the sub-pixel regions  11  to  13  may be arranged along the second direction. 
       FIGS. 1 and 2  illustrate that the sub-pixel regions  11  to  13  have substantially the same area. However, the red sub-pixel region  11 , the green sub-pixel region  12 , and the blue sub-pixel region  13  may have different relative sizes or areas, so as to improve luminescent efficiency. 
     The transmission region  20  may extend to be adjacent to the red sub-pixel region  11 , the green sub-pixel region  12 , and the blue sub-pixel region  13 . In example embodiments, the transmission region  20  may be provided individually to each of the unit pixels PX. In some example embodiments, the transmission region  20 , for example, may extend along the second direction, and may be provided commonly to a plurality of the unit pixels PX. That is, a separate transmission region  20  may be provided for each sub-pixel region, or a common transmission region  20  may be provided for more than one, or for all, sub-pixel regions. 
     In example embodiments, a pixel circuit for implementation of an image may be disposed in the pixel region  10 . External light may pass through the transmission region  20 , so that an external image may be observed. 
     A transistor (e.g., a thin film transistor; TFT) may be disposed in each of the sub-pixel regions of the pixel region  10 . The transistor may be electrically connected to a data line  151  and a scan line  136 . As illustrated in  FIG. 2 , the data line  151  and the scan line  136  may cross each other. In example embodiments, the pixel circuit may include the data line  151 , the scan line  136 , the transistor, etc. 
     The pixel circuit, for example, may further include a power supply line (not shown in  FIG. 2 ) substantially parallel with the data line  151 . The pixel circuit may further include a capacitor electrically connected between the power supply line and the transistor. 
       FIG. 2  illustrates that one transistor is disposed in each of the sub-pixel regions. However, two or more transistors may be disposed in each of the sub-pixel regions. For example, a switching transistor and a driving transistor may be disposed in each of the sub-pixel regions. The capacitor may be electrically connected between the switching transistor and the driving transistor. 
     Referring to  FIG. 3 , the transistor may be disposed on the substrate  100  in the pixel region  10 . The transistor may include an active pattern  120 , a gate insulation layer  130 , a gate electrode  135 , an insulation interlayer  140 , a source electrode  150  and a drain electrode  155 . The transistor may be covered by a via insulation layer  160 , and a first electrode  170  electrically connected to the drain electrode  155  of the transistor may be disposed on the via insulation layer  160 . 
     A transparent insulation substrate may be used as the substrate  100 . For example, the substrate  100  may include glass or polymer that is transparent and flexible. The transparent display device may be provided as a transparent flexible display device when the substrate  100  includes a polymer. For example, the substrate  100  may include a high molecular material such as polyimide, polysiloxane, epoxy based resin, acryl based resin, polyester, etc. 
     The substrate  100  may be divided into the pixel region  10  and the transmission region  20  as mentioned above.  FIG. 3  illustrates a first pixel region  10   a  and a first transmission region  20   a  included in a first unit pixel PXa, and a second pixel region  10   b  and a second transmission region  20   b  included in a second unit pixel PXb. However, unless otherwise specified, the first pixel region  10   a  and the second pixel region  10   b  will be referred as the pixel region  10  and the first transmission region  20   a  and the second transmission region  20   b  will be referred as the transmission region  20 , since the first unit pixel PXa and the second unit pixel PXb are substantially the same. 
     The buffer layer  110  may be formed on the top surface of the substrate  100 . In some example embodiments, the buffer layer  110  may be provided commonly in the pixel region  10  and the transmission region  20  on the substrate  100 . In some example embodiments, the buffer layer  110  may be substantially provided only in the pixel region  10  on the substrate  100 . The buffer layer  110  may block a permeation of vapor through the substrate  100 , and may block a diffusion of impurities between the substrate  100  and a structure disposed thereon. For example, the buffer layer  110  may include silicon oxide, silicon nitride or silicon oxynitride. These may be used alone or in any combination thereof. In some example embodiments, the buffer layer  110  may have a multi-layered structure including a silicon oxide layer and a silicon nitride layer. 
     The active pattern  120  may be disposed on the buffer layer  110  in the pixel region  10 . The active pattern  120  may include a silicon compound such as polysilicon. In some example embodiments, a source region and a drain region each including p-type or n-type impurities may be disposed on opposing ends of the active pattern  120 . 
     In some example embodiments, the active pattern  120  may include an oxide semiconductor, e.g., indium gallium zinc oxide (IGZO), zinc tin oxide (ZTO), indium tin zinc oxide (ITZO), or the like. 
     The gate insulation layer  130  may be disposed on the buffer layer  110 , and may cover the active pattern  120 . In example embodiments, the gate insulation layer  130  may include silicon oxide, silicon nitride or silicon oxynitride. In some example embodiments, the gate insulation layer  130  may have a multi-layered structure including a silicon oxide layer and a silicon nitride layer. 
     As illustrated in  FIG. 3 , the gate insulation layer  130  may extend across both the pixel region  10  and the transmission region  20 , similar to the buffer layer  110 . In some example embodiments, the gate insulation layer  130  may be substantially selectively disposed only in the pixel region  10 . 
     The gate electrode  135  may be disposed on the gate insulation layer  130 . The gate electrode  135  may substantially overlap the active pattern  120  with respect to the gate insulation layer  130 . 
     The gate electrode  135  may be electrically connected to the scan line  136 . For example, as illustrated in  FIG. 2 , the gate electrode  135  may formed to extend from the scan line  136 . 
     The gate electrode  135  may include a metal such as silver (Ag), magnesium (Mg), aluminum (Al), tungsten (W), copper (Cu), nickel (Ni), chromium (Cr), molybdenum (Mo), titanium (Ti), platinum (Pt), tantalum (Ta), neodymium (Nd) and scandium (Sc), an alloy thereof, or a nitride thereof. These may be used alone or in any combination thereof. The gate electrode  135  may include at least two metal layers having different physical and/or chemical properties. For example, the gate electrode  135  may have a multi-layered structure such as an Al/Mo structure or a Ti/Cu structure. 
     The insulation interlayer  140  may be disposed on the gate insulation layer  130 , and may cover the gate electrode  135 . In example embodiments, the insulation interlayer  140  may include silicon oxide, silicon nitride and/or silicon oxynitride. In some example embodiments, the insulation interlayer  140  may have a multi-layered structure including a silicon oxide layer and a silicon nitride layer. 
     As illustrated in  FIG. 3 , the insulation interlayer  140  may commonly extend across both the pixel region  10  and the transmission region  20 , similar to the buffer layer  110 . In some example embodiments, the insulation interlayer  140  may be substantially selectively disposed only in the pixel region  10 . 
     The source electrode  150  and the drain electrode  155  may contact the active pattern  120  through the insulation interlayer  140  and the gate insulation layer  130 . Each of the source electrode  150  and the drain electrode  155  may include a metal such as Ag, Mg, Al, W, Cu, Ni, Cr, Mo, Ti, Pt, Ta, Nd and Sc, an alloy thereof, or a nitride thereof. These may be used alone or in some combination thereof. For example, each of the source electrode  150  and the drain electrode  155  may have a multi-layered structure having at least two metal layers which have different physical and/or chemical properties, such as an Al layer and a Mo layer. 
     The source electrode  150  and the drain electrode  155  may contact the source region and the drain region of the active pattern  120 , respectively. A portion of the active pattern  120  between the source region and the drain region may serve as a channel through which charges may be moved or transferred. 
     As illustrated in  FIG. 2 , the source electrode  150  may be electrically connected to the data line  151 . For example, the source electrode  150  may extend from the data line  151 . 
       FIG. 3  illustrates that the transistor has a top gate structure in which the gate electrode  135  is disposed over the active pattern  120 . However, the transistor may have a bottom gate structure in which the gate electrode  135  is disposed under the active pattern  120 . 
     The via insulation layer  160  may be disposed on the insulation interlayer  140 , and may cover the source electrode  150  and the drain electrode  155 . A via structure electrically connecting the first electrode  170  and the drain electrode  155  to each other may be accommodated in the via insulation layer  160 . The via insulation layer  160  may have a substantially planar or leveled top surface, and may serve as a planarization layer for structures thereon. 
     The via insulation layer  160  may include an organic material, e.g., polyimide, an epoxy-based resin, an acryl-based resin, polyester, or the like. In example embodiments, the via insulation layer  160  may be commonly disposed in both the pixel region  10  and the transmission region  20 . In some example embodiments, the via insulation layer  160  may be substantially selectively disposed in just the pixel region  10 . 
     The first electrode  170  may be disposed on the via insulation layer  160 , and may include a via structure extending through the via insulation layer  160  to be in contact with, or electrically connected to, the drain electrode  155 . In example embodiments, the first electrode  170  may be individually disposed per each of the sub-pixel regions. The first electrode  170  may serve as a pixel electrode or an anode. 
     In an embodiment, the first electrode  170  may include a transparent conductive material having a relatively high work function. For example, the first electrode  170  may include indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide, or indium oxide. In this case, a light transmittance of the transparent display device may be further improved. 
     In an embodiment, the first electrode  170  may serve as a reflective electrode. In this case, the first electrode  170  may include a metal, e.g., Al, Mg, Ag, W, Cu, Ni, Cr, Mo, Ti, Pt, Ta, Nd or Sc, or an alloy thereof. 
     In an embodiment, the first electrode  170  may have a multi-layered structure including the transparent conductive material and the metal. 
     A pixel defining layer  180  may be disposed on the via insulation layer  160 , and may cover a peripheral portion of the first electrode  170 . The pixel defining layer  180  may include a transparent organic material such as polyimide or an acryl-based resin. 
     Each of the sub-pixel regions included in the pixel region  10  may be exposed by the pixel defining layer  180 . An area of the first electrode  170  which is not covered by the pixel defining layer  180  may be substantially equal to a light emitting area of each of the sub-pixel regions. In example embodiments, the pixel defining layer  180  may extend to the transmission region  20 . In some example embodiments, the pixel defining layer  180  may not extend to the transmission region  20 , and may be substantially selectively disposed only in the pixel region  10 . 
     A display layer  200  may be disposed on the pixel defining layer  180  and the first electrode  170 . For example, the display layer  200  may be disposed on a sidewall of the pixel defining layer  180  and a top surface of the first electrode  170  exposed by the pixel defining layer  180 . 
     The display layer  200  may include an organic light emitting layer patterned individually for the red sub-pixel region  11 , the green sub-pixel region  12 , and the blue sub-pixel region  13  to generate a different color at each of the sub-pixel regions. The organic light emitting layer may include a host material excited by holes and electrons, and a dopant material facilitating an emitting efficiency through absorbing and releasing energy. 
     In some embodiments, the display layer  200  may further include a hole transport layer (HTL) between the first electrode  170  and the organic light emitting layer. The display layer  200  may further include an electron transport layer (ETL) on the organic light emitting layer. 
     The HTL may include a hole transport material, e.g., 4,4′-bis [N-(1-naphtyl)-N-phenylamino]biphenyl (NPB), 4,4′-bis [N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD), N,N′-di-1-naphtyl-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPD), N-phenylcarbazole, polyvinylcarbazole, or a combination thereof. 
     The ETL may include an electron transport material, e.g., tris(8-quinolinolato)aluminum (Alq3), 2-(4-biphenylyl)-5-4-tert-butylphenyl-1,3,4-oxadiazole (PBD), bis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum (BAlq), bathocuproine (BCP), triazole (TAZ), phenylquinazoline, or a combination thereof. 
     In example embodiments, different from the organic light emitting layer, each of the HTL and the ETL may not be patterned individually for the red sub-pixel region  11 , the green sub-pixel region  12  and the blue sub-pixel region  13 , and may instead be provided commonly for the sub-pixel regions  11 ,  12  and  13 . 
     In some embodiments, at least one of the organic light emitting layer, the HTL and the ETL may not be individually patterned for each of the sub-pixel regions, and may instead be provided commonly for a plurality of the sub-pixel regions. In an embodiment, the organic light emitting layer may be provided commonly for the plurality of the sub-pixel regions, and a color of each of the sub-pixel regions may be achieved by a color filter. In this case, the transparent display device may serve as a white-OLED (W-OLED) device. 
     In some embodiments, the display layer  200  may include a liquid crystal layer instead of the organic light emitting layer. In this case, the transparent display device may be provided as a liquid crystal display (LCD) device. 
     A second electrode  210  may be disposed on the pixel defining layer  180  and the display layer  200 . The second electrode  210  may face the first electrode  170  with respect to the display layer  200 . 
     In example embodiments, the second electrode  210  may serve as a common electrode commonly provided for a plurality of the sub-pixel regions. The second electrode  210  may serve as a cathode of the transparent display device. 
     In example embodiments, the second electrode  210  may include a metal having a low work function such as Ag, Mg, Al, W, Cu, Ni, Cr, Mo, Ti, Pt, Ta, Nd, Sc, or an alloy thereof. In some example embodiments, the second electrode  210  may include an alloy of Ag and Mg (e.g., Ag x Mg 1-x ). 
     The second electrode  210  may continuously extend across both the pixel region  10  and the transmission region  20 . A thickness of the second electrode  210  may be determined in consideration of a luminescent efficiency in the pixel region  10  and a desired light transmittance in the transmission region  20 . In some embodiments, the second electrode  210  may be substantially removed in the transmission region  20 . 
     A capping structure  220  may be disposed on the second electrode  210 . In example embodiments, the capping structure  220  may substantially cover a top surface of the second electrode  210 , and may be commonly provided across both the pixel region  10  and the transmission region  20 . 
     The capping structure  220  may include a first capping layer  222  and a second capping layer  224 . The first capping layer  222  may be disposed on the second electrode  210  in the pixel region  10 , and on a first region  21  of the transmission region  20 . In example embodiments, the first capping layer  222  may cover the top surface of the second electrode  210 , and may be commonly provided in both the pixel region  10  and the first region  21  of the transmission region  20 . For example, the first region  21  may be a region adjacent to the first pixel region  10   a  in the first transmission region  20   a.    
     The second capping layer  224  may be disposed on the second electrode  210  in the pixel region  10 , and in a second region  22  of the transmission region  20 . In example embodiments, the second capping layer  224  may cover the top surface of the second electrode  210  and a top surface of the first capping layer  222 , and may be commonly provided across the pixel region  10  and the second region  22  of the transmission region  20 . For example, the second region  22  may be a region spaced apart from the first pixel region  10   a  in the first transmission region  20   a . In other words, the second region  22  may be adjacent to the second pixel region  10   b.    
     In example embodiments, an end portion of the first region  21  and an end portion of the second region  22  may be substantially adjacent to each other in the transmission region  20 . In other words, the first region  21  and the second region  22  may not overlap, and may not be spaced apart from each other. In example embodiments, an area of the first region  21  and an area of the second region  22  may be substantially the same. For example, each of the area of the first region  21  and the area of the second region  22  may be substantially equal to a half of an area of the transmission region  20 . 
     In example embodiments, the capping structure  220  may have a first thickness in the pixel region  10 , and may have a second thickness less than the first thickness in the transmission region  20 . For example, the first thickness may correspond to the sum of a thickness of the first capping layer  222  and a thickness of the second capping layer  224 . 
     In example embodiments, the first capping layer  222  and the second capping layer  224  may have substantially the same thickness. In this case, the capping structure  220  may have a substantially uniform thickness throughout the transmission region  20 . 
     Each of the first capping layer  222  and the second capping layer  224  may include an organic material having an improved transmissive property. In some embodiments, each of the first capping layer  222  and the second capping layer  224  may include a material substantially the same as or similar to the hole transport material. Thus, a light emitting property in the pixel region  10  may not be disturbed by the second electrode  210  serving as the cathode. 
     In example embodiments, the thickness of the first capping layer  222  and the thickness of the second capping layer  224  may be determined in consideration of improving or maximizing luminescent efficiency in the pixel region  10  and improving or maximizing light transmittance in the transmission region  20 . 
     As mentioned above, when the capping structure  220  has a first thickness substantially equal to the sum of the thickness of the first capping layer  222  and the thickness of the second capping layer  224  in the pixel region  10 , and has a second thickness substantially equal to the thickness of the first capping layer  222  or the thickness of the second capping layer  224  in the transmission region  20 , the luminescent efficiency in the pixel region  10  as well as the light transmittance in the transmission region  20  may be improved. 
     In a conventional transparent display device, a capping layer having a substantially uniform thickness and provided commonly across both the pixel region and the transmission region may be disposed on the second electrode. However, luminescent efficiency in the pixel region may be reduced when the capping layer has a relatively small thickness, and light transmittance in the transmission region may be reduced when the capping layer has a relatively large thickness. 
     According to example embodiments then, the capping structure  220  may have a first thickness in the pixel region  10  and may have a second thickness less than the first thickness in the transmission region  20 , so that luminescent efficiency in the pixel region  10  as well as light transmittance in the transmission region  20  may both be improved. 
     In some example embodiments, as illustrated in  FIG. 3 , an encapsulation substrate  250  may be disposed over the capping structure  220 , and a filling layer  240  may be interposed between the capping structure  220  and the encapsulation substrate  250 . A bonding member may be disposed between a peripheral portion of the substrate  100  and a peripheral portion of the encapsulation substrate  250  to store the filling layer  240  and to combine the substrate  100  and the encapsulation substrate  250 . 
     The encapsulation substrate  250  may include a glass substrate or a polymer substrate. The filling layer  240  may include, e.g., a substantially transparent or transmissive organic material. In some embodiments, an organic/inorganic complex layer may be utilized as a sealing film instead of the encapsulation substrate  250  and the filling layer  240 . In this case, the bonding member may not be needed. 
       FIG. 4  is a cross-sectional view illustrating a transparent display device in accordance with some example embodiments. 
     The transparent display device illustrated in  FIG. 4  may have elements and/or constructions substantially the same as or similar to the transparent display device illustrated in  FIG. 3 , except for constructions of the first capping layer  222  and the second capping layer  224  in the transmission region  20 . Therefore, detailed descriptions of repeated elements and/or constructions are omitted, and like reference numerals are used to designate like elements. 
     Referring to  FIG. 4 , the transmission region  20  may further include a third region  23  in which at least a portion of the first region  21  and at least a portion of the second region  22  overlap. In other words, the first region  21  in which the first capping layer  222  is disposed, and the second region  22  in which the second capping layer  224  is disposed, may at least partially overlap, and the area of overlap may be defined as the third region  23 . For example, the first capping layer  222  may be disposed on the second electrode  210  and the second capping layer  224  may be disposed on the first capping layer  222  in the third region  23 , similar to the pixel region  10 . 
     In example embodiments, an area of the first region  21  and an area of the second region  22  may be substantially the same. For example, each of the area of the first region  21  and the area of the second region  22  may be substantially greater than a half of an area of the transmission region  20 . 
     In example embodiments, the capping structure  220  may have a first thickness in the pixel region  10  and in the third region  23  of the transmission region  20 , and may have a second thickness less than the first thickness in a remaining transmission region  20  outside the third region  23 . For example, the first thickness may be substantially equal to the sum of a thickness of the first capping layer  222  and a thickness of the second capping layer  224 , and the second thickness may be substantially equal to either the thickness of the first capping layer  222  or the thickness of the second capping layer  224 . 
     In example embodiments, the first capping layer  222  and the second capping layer  224  may have substantially the same thickness. In this case, the capping structure  220  may have a substantially uniform thickness throughout the remaining transmission region  20  except for the third region  23 . 
       FIG. 5  is a cross-sectional view illustrating a transparent display device in accordance with some example embodiments. 
     The transparent display device illustrated in  FIG. 5  may have elements and/or constructions substantially the same as or similar to the transparent display device illustrated in  FIGS. 3 and 4 , except for constructions of the first capping layer  222  and the second capping layer  224  in the transmission region  20 . Therefore, detailed descriptions of repeated elements and/or constructions are omitted, and like reference numerals are used to designate like elements. 
     Referring to  FIG. 5 , the transmission region  20  may further include a third region  23  between the first region  21  and the second region  22 . In other words, the first region  21  in which the first capping layer  222  is disposed, and the second region  22  in which the second capping layer  224  is disposed, may be spaced apart from each other. The intervening space between the first region  21  and the second region  22  may be defined as the third region  23 . For example, an opening defined by a sidewall of the first capping layer  222 , a sidewall of the second capping layer  224  and an exposed top surface of the second electrode  210  may be formed in the third region  23 . 
     In example embodiments, an area of the first region  21  and an area of the second region  22  may be substantially the same. For example, each of the area of the first region  21  and the area of the second region  22  may be substantially less than a half of an area of the transmission region  20 . 
     In example embodiments, the capping structure  220  may have a first thickness in the pixel region  10 , and may have a second thickness less than the first thickness in the first region  21  and the second region  22 . For example, the first thickness may be substantially equal to a sum of a thickness of the first capping layer  222  and a thickness of the second capping layer  224 , and the second thickness may be substantially equal to the individual thickness of the first capping layer  222  or the individual thickness of the second capping layer  224 . 
     In example embodiments, the first capping layer  222  and the second capping layer  224  may have substantially the same thickness. In this case, the capping structure  220  may have a substantially uniform thickness throughout a remaining transmission region  20  except for the third region  23 . 
       FIGS. 6 to 8  are cross-sectional views illustrating transparent display devices in accordance with some example embodiments. 
     The transparent display device illustrated in  FIGS. 6 to 8  may have elements and/or constructions substantially the same as or similar to the transparent display device illustrated in  FIG. 3 , except for constructions of the second electrode  210 , the pixel defining layer  180 , the via insulation layer  160 , the insulation interlayer  140 , the gate insulation layer  130  and/or the buffer layer  110  in the transmission region  20 . Therefore, detailed descriptions of any repeated elements and/or constructions are omitted, and like reference numerals are used to designate like elements. 
     Referring to  FIG. 6 , the second electrode  210  may include an aperture  215  that overlaps at least a portion of the transmission region  20 . In some example embodiments, the aperture  215  may overlap substantially all of the transmission region  20 . For example, the capping structure  220  may be disposed on a top surface of the pixel defining layer  180  which is exposed by the aperture  215  of the second electrode  210 . As the second electrode  210  includes apertures  215 , the light transmittance of the transmission region  20  may be improved. 
     Referring to  FIG. 7 , at least portions of the pixel defining layer  180  and the via insulation layer  160  may be substantially removed. In example embodiments, a transparent window  260  may be defined by a top surface of the insulation interlayer  140 , a sidewall of the via insulation layer  160 , and a sidewall of the pixel defining layer  180  in the transmission region  20 . As the transparent window  260  is formed, the light transmittance of the transmission region  20  may be improved. In this case, the capping structure  220  may be formed conformally along a surface of the second electrode  210  and a surface of the transparent window  260 . 
     Referring to  FIG. 8 , at least portions of the insulation interlayer  140 , the gate insulation layer  130  and the buffer layer  110  may be substantially removed. In example embodiments, a transparent window  260  may be defined by a top surface of the substrate  100 , a sidewall of the buffer layer  110 , a sidewall of the gate insulation layer  130 , a sidewall of the insulation interlayer  140 , a sidewall of the via insulation layer  160 , and a sidewall of the pixel defining layer  180  in the transmission region  20 . As the transparent window  260  is formed, the light transmittance of the transmission region  20  may be improved. In this case, the capping structure  220  may be formed conformally along a surface of the second electrode  210  and a surface of the transparent window  260 . 
       FIGS. 6 to 8  illustrate that the first capping layer  222  and the second capping layer  224  are adjacent to each other as illustrated in  FIG. 3 , but the invention is not limited thereto. The aperture  215  of the second electrode  210  and the transparent window  260  in the transmission region  20  illustrated in  FIGS. 6 to 8  may be applied to a transparent display device in which the first capping layer  222  and the second capping layer  224  overlap as illustrated in  FIG. 4 , or a transparent display device in which the first capping layer  222  and the second capping layer  224  are spaced apart as illustrated in  FIG. 5 . 
       FIGS. 9 to 15  are cross-sectional views illustrating a method of manufacturing a transparent display device in accordance with example embodiments. For example,  FIGS. 9  to  15  illustrate a method of manufacturing the transparent display device in  FIG. 3 . 
     Referring to  FIG. 9 , a substrate  100  may be provided on a carrier substrate  50 , and then a buffer layer  110  may be formed on the substrate  100 . 
     The carrier substrate  50  may serve as a supporter for the substrate  100  during a manufacturing process of the transparent display device. For example, a glass substrate or a metal substrate may be utilized as the carrier substrate  50 . 
     The substrate  100  may be formed using glass or a transparent polymer such as a polyimide-based resin. For example, a precursor composition containing a polyimide precursor may be coated on the carrier substrate  50  by, e.g., a spin coating process to form a coating layer. The coating layer may be thermally cured to form the substrate  100 . The polyimide precursor may include a diamine and a dianhydride. The precursor composition may be prepared by dissolving the polyimide precursor in an organic solvent. The organic solvent may include, e.g., N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), tetrahydrofuran (THF), triethylamine (TEA), ethylacetate, dimethylsulfoxide (DMSO) or an ethylene glycol-based ether solvent. These may be used alone or in any combination thereof. 
     The diamine and the dianhydride may be polymerized by the thermal curing process so that a polyamic acid may be created, and the polyamic acid may be additionally cured and condensed to form the polyimide-based resin. In one embodiment, when a glass substrate is utilized as the substrate  100 , a process of using the carrier substrate  50  may be omitted. 
     The substrate  100  may be divided into a pixel region  10  and a transmission region  20 .  FIG. 9  illustrates a first pixel region  10   a , a first transmission region  20   a , a second pixel region  10   b , and a second transmission region  20   b . However, unless otherwise specified, the first pixel region  10   a  and the second pixel region  10   b  will be referred as the pixel region  10 , and the first transmission region  20   a  and the second transmission region  20   b  will be referred as the transmission region  20 , since the first pixel region  10   a  and the first transmission region  20   a  are substantially the same as the second pixel region  10   b  and the second transmission region  20   b , respectively. 
     The buffer layer  110  may substantially cover a top surface of the substrate  100 , and may be formed using silicon oxide, silicon nitride and/or silicon oxynitride. As illustrated in  FIG. 9 , the buffer layer  110  may be commonly formed across both the pixel region  10  and the transmission region  20 . In some embodiments, the buffer layer  110  may be selectively formed in only the pixel region  10 . 
     Referring to  FIG. 10 , an active pattern  120 , a gate electrode  135 , a source electrode  150 , a drain electrode  155 , and additional insulation layers may be formed on the buffer layer  110 . 
     The active pattern  120  may be formed on the buffer layer  110  in the pixel region  10 . For example, a semiconductor layer including amorphous silicon or polysilicon may be formed on the buffer layer  110 , and then may be patterned to form the active pattern  120 . In some embodiments, a crystallization process, e.g., a low temperature polycrystalline silicon (LTPS) process or a laser crystallization process, may be further performed after the formation of the semiconductor layer. In some embodiments, the semiconductor layer may be formed of an oxide semiconductor such as IGZO, ZTO or ITZO. 
     A gate insulation layer  130  covering the active pattern  120  may be formed on the buffer layer  110 . The gate insulation layer  130  may be formed of silicon oxide, silicon nitride and/or silicon oxynitride. 
     As illustrated in  FIG. 10 , the gate insulation layer  130  may extend continuously across both the pixel region  10  and the transmission region  20 . In some embodiments, the gate insulation layer  130  may be patterned to be present selectively in the pixel region  10 . 
     The gate electrode  135  may be formed on the gate insulation layer  130 , and may substantially overlap the active pattern  120 . For example, a first conductive layer may be formed on the gate insulation layer  130 . The first conductive layer may be patterned by, e.g., a photo-lithography process, to form the gate electrode  135 . The first conductive layer may be formed using a metal, an alloy or a metal nitride. The first conductive layer may also be formed by depositing a plurality of metal layers. 
     The gate electrode  135  may be formed together with a scan line  136  illustrated in  FIG. 2 . For example, the gate electrode  135  and the scan line  136  may be formed from the first conductive layer by substantially the same etching process, and the scan line  136  may be integral with the gate electrode  135 . 
     In some embodiments, impurities may be implanted into the active pattern  120  using the gate electrode  135  as an ion-implantation mask, such that a source region and a drain region may be formed at both ends of the active pattern  120 . 
     An insulation interlayer  140  covering the gate electrode  135  may be formed on the gate insulation layer  130 . The insulation interlayer  140  may include stepped portions according to profiles of the active pattern  120  and the gate electrode  135 . The insulation interlayer  140  may be formed of silicon oxide, silicon nitride and/or silicon oxynitride. 
     As illustrated in  FIG. 10 , the insulation interlayer  140  may extend commonly across both the pixel region  10  and the transmission region  20 . In some embodiments, at least a portion of the insulation interlayer  140  formed in the transmission region  20  may be removed. 
     The insulation interlayer  140  and the gate insulation layer  130  may be partially removed by, e.g., a photo process, to form contact holes. The contact holes may be formed through the insulation interlayer  140  and the gate insulation layer  130 , such that a top surface of the active pattern  120  may be partially exposed. For example, the source region and the drain region of the active pattern  120  may be exposed through the contact holes. 
     A source electrode  150  and a drain electrode  155  may be formed in the contact holes. The source electrode  150  and the drain electrode  155  may be in contact with the source region and the drain region, respectively. For example, a second conductive layer sufficiently filling the contact holes may be formed on the insulation interlayer  140 . The second conductive layer may be patterned by a photo-lithography process, to form the source electrode  150  and the drain electrode  155 . The second conductive layer may be formed using a metal, a metal nitride or an alloy. 
     Accordingly, a transistor, e.g., a thin film transistor including the active pattern  120 , the gate insulation layer  130 , the gate electrode  135 , the source electrode  150  and the drain electrode  155  may be formed on the substrate  100  in the pixel region  10 . For example, a plurality of sub-pixel regions may be included in the pixel region  10  as illustrated in  FIGS. 1 and 2 , and at least one transistor may be formed in each of the sub-pixel regions. 
     Additionally, a pixel circuit including the transistor, a data line  151  and the scan line  136  may be formed on the substrate  100 . The source electrode  150  may be electrically connected to the data line  151  as illustrated in  FIG. 2 . For example, the source electrode  150 , the drain electrode  155  and the data line  151  may be formed from the second conductive layer by substantially the same etching process. 
     A via insulation layer  160  may be formed to cover the insulation interlayer  140 , the source electrode  150  and the drain electrode  155 . The via insulation layer  160  may extend commonly across both the pixel region  10  and the transmission region  20 , and may have a substantially planar or leveled upper surface. Indeed, the via insulation layer  160  may serve as a planarization layer for the transparent display device. 
     The via insulation layer  160  may be formed using an organic material such as polyimide, an epoxy-based resin, an acryl-based resin or polyester, by a spin coating process or a slit coating process. For example, the via insulation layer  160  may be partially removed by, e.g., a photo process, to form a via hole. In example embodiments, a top surface of the drain electrode  155  may be at least partially exposed through the via hole. 
     As illustrated in  FIG. 10 , the via insulation layer  160  may extend commonly across each of the pixel region  10  and the transmission region  20 . In some embodiments, the via insulation layer  160  may be patterned to be present selectively in the pixel region  10 . 
     Referring to  FIG. 11 , a first electrode  170  and a pixel defining layer  180  may be formed on the via insulation layer  160 . 
     For example, a third conductive layer filling the via hole may be formed on the via insulation layer  160  and the exposed drain electrode  155 , and may be patterned to form the first electrode  170 . The first electrode  170  may serve as a pixel electrode and/or an anode of the transparent display device. The third conductive layer may be formed of a metal such as Ag, Mg, Al, W, Cu, Ni, Cr, Mo, Ti, Pt, Ta, Nd, Sc, etc., or an alloy thereof. 
     The buffer layer  110 , the semiconductor layer, the gate insulation layer  130 , the insulation interlayer  140 , and the first to third conductive layers may be formed by at least one of a chemical vapor deposition (CVD) process, a plasma enhanced chemical vapor deposition (PECVD) process, a high density plasma-chemical vapor deposition (HDP-CVD) process, a thermal evaporation process, a vacuum deposition process, a spin coating process, a sputtering process, an atomic layer deposition (ALD) process and a printing process. 
     The pixel defining layer  180  may be formed on the via insulation layer  160  to cover a peripheral portion of the first electrode  170 . For example, a photosensitive organic material such as a polyimide resin or an acryl resin may be coated, and then exposure and developing processes may be performed to form the pixel defining layer  180 . In some embodiments, the pixel defining layer  180  may be formed of a polymeric material or an inorganic material by a printing process, e.g., an inkjet printing process. 
     As illustrated in  FIG. 11 , the pixel defining layer  180  may extend commonly across both the pixel region  10  and the transmission region  20 . In some embodiments, the pixel defining layer  180  may be patterned to be present selectively in the pixel region  10 . 
     In example embodiments, the pixel defining layer  180  and the via insulation layer  160  formed in the transmission region  20  may be selectively removed, so that the pixel defining layer  180  and the via insulation layer  160  may remain only in the pixel region  10 . Accordingly, the light transmittance of the transmission region  20  may be improved. In some example embodiments, the insulation interlayer  140 , the gate insulation layer  130 , and the buffer layer  110  formed in the transmission region  20 , as well as the pixel defining layer  180  and the via insulation layer  160  formed in the transmission region  20 , may be selectively removed so that the insulation interlayer  140 , the gate insulation layer  130 , and the buffer layer  110  may selectively remain only in the pixel region  10 . Accordingly, the light transmittance of the transmission region  20  may be further improved. 
     Referring to  FIG. 12 , a display layer  200  and a second electrode  210  may be sequentially formed on the pixel defining layer  180  and the first electrode  170 . 
     The display layer  200  may be formed using an organic light emitting material for generating a red color of light, a green color of light or a blue color of light per each of the sub-pixel regions on the first electrode  170  exposed by the pixel defining layer  180 . For example, the display layer  200  may be formed by a spin coating process, a roll printing process, a nozzle printing process, an inkjet process, etc., using a fine metal mask (FMM) that may include an opening through which a region corresponding to a red sub-pixel region, a green sub-pixel region, or a blue sub-pixel region is exposed. Accordingly, an organic light emitting layer, including the organic light emitting material, may be individually formed in each of the sub-pixel regions. 
     A hole transport layer may be formed before the formation of the organic light emitting layer, using the above-mentioned hole transport material. An electron transport layer may be also formed on the organic light emitting layer, using the above-mentioned electron transport material. In some example embodiments, unlike the organic light emitting layer, the hole transport layer and the electron transport layer may extend commonly over every sub-pixel region, rather than being individually patterned for each sub-pixel region. In some example embodiments, the hole transport layer and the electron transport layer may be included in the display layer  200 , and may be patterned or printed per each of the sub-pixel regions. For example, as illustrated in  FIG. 12 , the display layer  200  of each of the sub-pixel regions may be confined by a sidewall of the pixel defining layer  180 . 
     In some embodiments, at least one of the organic emitting layer, the hole transport layer and the electron transport layer may not be individually patterned for each of the sub-pixel regions, and may instead be formed commonly across a plurality of the sub-pixel regions. In an embodiment, the organic light emitting layer may be formed for a plurality of the sub-pixel regions, and a color of each of the sub-pixel regions may be achieved by a color filter. In this case, the transparent display device may serve as a white-OLED (W-OLED) device. 
     A metal having a low work function such as Al, Mg, Ag, W, Cu, Ni, Cr, Mo, Ti, Pt, Ta, Nd or Sc, or an alloy of these metals, may be deposited on the display layer  200  to form a second electrode  210 . The second electrode  210  may serve as a common electrode and/or a cathode of the transparent display device. For example, an open mask, including an opening through which the pixel region  10  and the transmission region  20  are commonly exposed, may be used to deposit the metal by, e.g., a sputtering process, for the formation of the second electrode  210 . The second electrode  210  may be formed common to the pixel region  10  and the transmission region  20  without an additional patterning process, so that the overall fabrication process may be simplified, and an electrical resistance of the second electrode  210  may be reduced. 
     In some example embodiments, the second electrode  210  may be formed of Ag, Mg or an alloy thereof. Further, a thickness of the second electrode  210  may be determined according to a desired luminescent efficiency in the pixel region  10  and a desired light transmittance in the transmission region  20 . 
     Referring to  FIGS. 13 and 14 , a capping structure  220  may be formed on the second electrode  210 . 
     A first capping layer  222  may be formed on the second electrode  210 , in both the pixel region  10  and a first region  21  of the transmission region  20 . A second capping layer  224  may then be formed on the first capping layer  222  in the pixel region  10 , and in a second region  22  of the transmission region  20 . For example, the first region  21  may be a region adjacent to a first pixel region  10   a  in a first transmission region  20   a , and the second region  22  may be a region spaced apart from the first pixel region  10   a  in the first transmission region  20   a . In other words, the first region  21  may be adjacent to the first pixel region  10   a , and the second region  22  may be adjacent to a second pixel region  10   b.    
     As illustrated in  FIG. 13 , the first capping layer  222  may be formed in the pixel region  10  and the first region  21  by using a mask  310  that includes an opening  315 . Specifically, after disposing the mask  310  such that the opening  315  corresponds to the first pixel region  10   a  and the first region  21 , the first capping layer  222  may be formed using the hole transport material line of organic material. The mask  310  may be, for example, a fine metal mask (FMM). 
     Then, as illustrated in  FIG. 14 , the second capping layer  224  may be formed in the pixel region  10  and the second region  22  by shifting the mask  310 . Specifically, after shifting the mask  310  such that the opening  315  corresponds to the second pixel region  10   b  and the second region  22 , the second capping layer  224  may be formed using the hole transport material line of organic material. For example, the second capping layer  224  may be formed of material substantially the same as that of the first capping layer  222 .  FIG. 14  illustrates that the mask  310  is shifted along the first direction, but the invention need not be limited thereto. For example, the mask  310  may be shifted along a direction substantially opposite to the first direction. 
     The same mask  310  may be used in the formation of both the first capping layer  222  and the second capping layer  224 , so that the first capping layer  222  and the second capping layer  224  may have substantially the same size areas. In this manner, a capping structure  220  including the first capping layer  222  and the second capping layer  224  may be formed. 
     In example embodiments, a width of the opening  315  may be substantially equal to the sum of a width of the pixel region  10  and a half of a width of the transmission region  20 . Accordingly, the first capping layer  222  and the second capping layer  224  may overlap each other across the entirety of the pixel region  10 . An end portion of the first region  21  in which the first capping layer  222  is formed, and an end portion of the second region  22  in which the second capping layer  224  is formed, may be substantially adjacent to each other in the transmission region  20 . In other words, in the transmission region  20 , the first capping layer  222  and the second capping layer  224  may not overlap and also may not be spaced apart from each other. 
     In example embodiments, the capping structure  220  may have a first thickness in the pixel region  10 , and may have a second thickness less than the first thickness in the transmission region  20 . In some embodiments, the first capping layer  222  and the second capping layer  224  may have a substantially the same thickness. Accordingly, the capping structure  220  may have the second thickness in the transmission region  20 , and may have the first thickness, which is about twice the second thickness, in the pixel region  10 . 
     As mentioned above, the capping structure  220  having different thickness in the pixel region  10  and the transmission region  20  may be formed by shifting one mask  310 , so that manufacturing time and cost of the capping structure  220  may be reduced, and a transparent display device with improved luminescent efficiency and light transmittance may be manufactured. 
     Referring to  FIG. 15 , a filling layer  240  and an encapsulation substrate  250  may be layered on the capping structure  220 . The carrier substrate  50  may also be detached from the substrate  100 . For example, when the substrate  100  is a plastic substrate, the carrier substrate  50  may be detached from the substrate  100  by a laser-lifting process or by applying a mechanical tension. 
       FIGS. 16 and 17  are cross-sectional views illustrating a method of manufacturing a transparent display device in accordance with some example embodiments. 
     For example,  FIGS. 16 and 17  illustrate a method of manufacturing the transparent display device illustrated in  FIG. 4 . Detailed descriptions of processes and/or elements already described with reference to  FIGS. 9 to 15  will be omitted. 
     Referring to  FIGS. 16 and 17 , the capping structure  220  may be formed on the second electrode  210 . 
     As illustrated in  FIG. 16 , the first capping layer  222  may be formed in the pixel region  10  and the first region  21  by using a mask  320  that includes an opening  325 . Specifically, after disposing the mask  320  such that the opening  325  corresponds to the first pixel region  10   a  and the first region  21 , the first capping layer  222  may be formed using the hole transport material line of organic material. The mask  320  may be, for example, a fine metal mask (FMM). 
     Then, as illustrated in  FIG. 17 , the second capping layer  224  may be formed in the pixel region  10  and the second region  22  by shifting the mask  320 . Specifically, after shifting the mask  320  such that the opening  325  corresponds to the second pixel region  10   b  and the second region  22 , the second capping layer  224  may be formed using the hole transport material line of organic material. For example, the second capping layer  224  may be formed of material substantially the same as that of the first capping layer  222 .  FIG. 17  illustrates that the mask  320  is shifted along the first direction, but the invention need not be limited thereto. For example, the mask  320  may be shifted along a direction substantially opposite to the first direction. 
     The same mask  320  may be used for the formation of the first capping layer  222  and the second capping layer  224 , so that the first capping layer  222  and the second capping layer  224  may have substantially the same size areas. In this manner, the capping structure  220  including the first capping layer  222  and the second capping layer  224  may be formed. 
     In example embodiments, a width of the opening  325  may be substantially greater than the sum of a width of the pixel region  10  and a half of a width of the transmission region  20 . Accordingly, the first capping layer  222  and the second capping layer  244  may overlap each other throughout the entirety of the pixel region  10 . Additionally, the first capping layer  222  and the second capping layer  224  may overlap in at least a portion of the transmission region  20 . In other words, the transmission region  20  may further include a third region  23  in which the first capping layer  222  and the second capping layer  224  overlap each other. 
     In example embodiments, the capping structure  220  may have a first thickness in the pixel region  10 , may have the first thickness in the third region  23 , and may have a second thickness less than the first thickness in the rest of transmission region  20  outside the third region  23 . In some embodiments, the first capping layer  222  and the second capping layer  224  may have substantially the same thickness. Accordingly, the capping structure  220  may have the second thickness in that portion of transmission region  20  outside the third region  23 , and may have the first thickness about twice of the second thickness in the pixel region  10  and the third region  23 . Here, light transmittance in the third region  23  may be reduced when the third region  23  has the first thickness. However, an area of the third region  23  in the transmission region  20  may be minimized, so that reduction of light transmittance in the transmission region  20  may be prevented or minimized. 
       FIGS. 18 and 19  are cross-sectional views illustrating a method of manufacturing a transparent display device in accordance with some example embodiments. 
     For example,  FIGS. 18 and 19  illustrate a method of manufacturing the transparent display device illustrated in  FIG. 5 . Detailed descriptions of processes and/or elements already described with reference to  FIGS. 9 to 15 , and  FIGS. 16 and 17  will be omitted. 
     Referring to  FIGS. 18 and 19 , the capping structure  220  may be formed on the second electrode  210 . 
     As illustrated in  FIG. 18 , the first capping layer  222  may be formed in the pixel region  10  and the first region  21  by using a mask  330  that includes an opening  335 . Specifically, after disposing the mask  330  such that the opening  335  corresponds to the first pixel region  10   a  and the first region  21 , the first capping layer  222  may be formed using the hole transport material line of organic material. The mask  330  may be, for instance, a fine metal mask (FMM). 
     Then, as illustrated in  FIG. 19 , the second capping layer  224  may be formed in the pixel region  10  and the second region  22  by shifting the mask  330 . Specifically, after shifting the mask  330  such that the opening  335  corresponds to the second pixel region  10   b  and the second region  22 , the second capping layer  224  may be formed using the hole transport material line of organic material. For example, the second capping layer  224  may be formed of material substantially the same as that of the first capping layer  222 .  FIG. 19  illustrates that the mask  330  is shifted along the first direction, but the invention need not be limited thereto. For example, the mask  330  may instead be shifted along a direction substantially opposite to the first direction. 
     The same mask  330  may be used for the formation of the first capping layer  222  and the second capping layer  224 , so that the first capping layer  222  and the second capping layer  224  may have substantially the same size areas. In this manner, a capping structure  220  including the first capping layer  222  and the second capping layer  224  may be formed. 
     In example embodiments, a width of the opening  335  may be substantially greater than a width of the pixel region  10 , and may be substantially less than a sum of the width of the pixel region  10  and half of a width of the transmission region  20 . Accordingly, the first capping layer  222  and the second capping layer  244  may overlap across an entirety of the pixel region  10 . Additionally, the first capping layer  222  and the second capping layer  224  may not be formed in, or absent from, at least a portion of the transmission region  20 . In other words, the transmission region  20  may further include a third region  23  between the first region  21  and the second region  22 , in which the first capping layer  222  and the second capping layer  224  are both absent. 
     In example embodiments, the capping structure  220  may have a first thickness in the pixel region  10 , and may have a second thickness less than the first thickness in the first region  21  and the second region  22 . Additionally, an opening defined by a sidewall of the first capping layer  222 , a sidewall of the second capping layer  224 , and an exposed top surface of the second electrode  210  may be formed. In some embodiments, the first capping layer  222  and the second capping layer  224  may have substantially the same thickness. Accordingly, the capping structure  220  may have the second thickness in the first region  21  and the second region  22 , and may have the first thickness, which is about twice the second thickness, in the pixel region  10 . Here, light transmittance in the third region  23  may be reduced when the opening is formed in the third region  23 . However, an area of the third region  23  in the transmission region  20  may be minimized, so that reduction of light transmittance in the transmission region  20  may be prevented or minimized. 
       FIG. 20  is a cross-sectional view illustrating a method of manufacturing a transparent display device in accordance with some example embodiments. 
     In particular,  FIG. 20  illustrates a method of manufacturing the transparent display device illustrated in  FIG. 6 . Detailed descriptions on processes and/or elements already described with reference to  FIGS. 9 to 15  will be omitted. 
     Referring to  FIG. 20 , an aperture  215  overlapping at least a portion of the transmission region  20  may be formed in the second electrode  210 . As illustrated in  FIG. 12 , a portion of the second electrode  210  is removed from the transmission region  20  to form the aperture  215 . As an aperture  215  is formed in the second electrode  210 , a light transmittance in the transmission region  20  may be improved. 
     In some example embodiments, the aperture  215  may substantially cover the entirety of the transmission region  20 . In this case, as an area of the aperture  215  increases, the light transmittance in the transmission region  20  may be further improved. 
       FIG. 21  is a plan view illustrating a transparent display device in accordance with example embodiments.  FIG. 22  is a plan view illustrating a transparent display device in accordance with some example embodiments. 
     For example,  FIGS. 21 and 22  illustrate a transparent display device as described in  FIG. 3 . However, the invention may be not limited thereto, and  FIGS. 21 and 22  may be applied to other transparent display devices such as those illustrated in  FIGS. 4 to 8 . 
     Referring to  FIGS. 21 and 22 , the transparent display device may include a plurality of unit pixels PX. The unit pixels PX may be arranged along the first direction and the second direction, which as shown are substantially perpendicular to each other. For example, N pixel rows may be arranged along the first direction, and M pixel columns may be arranged along the second direction in the transparent display device. Here, each of N and M may be a positive integer. Each of the unit pixels PX may include a pixel region  10  and a transmission region  20 . 
     The capping structure  220  may cover the pixel region  10  and the transmission region  20 . The capping structure  220  may include the first capping layer  222  and the second capping layer  224 . In example embodiments, the first capping layer  222  may cover the pixel region  10  of a k-th pixel row, and a transmission region  20  adjacent thereto. The second capping layer  224  may cover the pixel region  10  of a (k+1)-th pixel row and part of the transmission region  20  of the k-th pixel row. Here, k may be a positive integer between 1 through N−1. 
     In some example embodiments, as illustrated in  FIG. 21 , the capping structure  220  may be commonly disposed on multiple unit pixels PX arranged along the second direction. In this case, each of the first capping layer  222  and the second capping layer  224  may have a stripe shape. 
     In some example embodiments, as illustrated in  FIG. 22 , the capping structure  220  may be individually disposed on each of the unit pixels PX arranged along the second direction. In this case, each of the first capping layer  222  and the second capping layer  224  may have an island shape. 
       FIG. 23  is a plan view illustrating an area II of the transparent display device in  FIG. 1 .  FIG. 24  is a cross-sectional view illustrating a transparent display device in accordance with example embodiments. For example,  FIG. 24  is a cross-sectional view cut along a line IV-IV′ in  FIG. 23 . 
     The transparent display device illustrated in  FIG. 24  may have elements and/or constructions substantially the same as or similar to the transparent display device illustrated in  FIGS. 3 to 5 , except for constructions of the first capping layer  222  and the second capping layer  224 . Therefore, detailed descriptions of repeated elements and/or constructions are omitted, and like reference numerals are used to designate like elements. 
     Referring to  FIGS. 1, 23, and 24 , the transparent display device may include a pixel region  10  and a transmission region  20 .  FIG. 24  illustrates a first pixel region  10   a  and a first transmission region  20   a  included in a first unit pixel PXa, a second pixel region  10   b  and a second transmission region  20   b  included in a second unit pixel PXb, and a third pixel region  10   c  included in a third unit pixel PXc. However, unless otherwise specified, the first pixel region  10   a , the second pixel region  10   b , and the third pixel region  10   c  will be referred as the pixel region  10  and the first transmission region  20   a  and the second transmission region  20   b  will be referred as the transmission region  20 , since the first unit pixel PXa, the second unit pixel PXb, and the third unit pixel PXc are substantially the same. 
     A capping structure  220  may be disposed on the second electrode  210 . In example embodiments, the capping structure  220  may substantially cover a top surface of the second electrode  210 , and may be provided commonly across both the pixel region  10  and the transmission region  20 . 
     The capping structure  220  may include a first capping layer  222  and a second capping layer  224 . The first capping layer  222  may be disposed on the second electrode  210  in the first pixel region  10   a , the first transmission region  20   a , and the second pixel region  10   b . In example embodiments, the first capping layer  222  may cover the top surface of the second electrode  210 , and may be provided commonly across each of the first pixel region  10   a , the first transmission region  20   a , and the second pixel region  10   b . For example, the first transmission region  20   a  may be disposed between the first pixel region  10   a  and the second pixel region  10   b.    
     The second capping layer  224  may be disposed on the second electrode  210  in the first pixel region  10   a , the second pixel region  10   b , and the second transmission region  20   b . In example embodiments, the second capping layer  224  may cover the top surface of the second electrode  210 , and may be provided commonly across each of the first pixel region  10   a , the second pixel region  10   b , and the second transmission region  20   b . For example, the second transmission region  20   b  may be disposed between the second pixel region  10   b  and the third pixel region  10   c.    
     In example embodiments, the capping structure  220  may have a first thickness in the pixel region  10 , and may have a second thickness less than the first thickness in the transmission region  20 . For example, the first thickness may be substantially equal to the sum of a thickness of the first capping layer  222  and a thickness of the second capping layer  224 , and the second thickness may be substantially equal to just the thickness of the first capping layer  222  or the thickness of the second capping layer  224 . 
     In example embodiments, the first capping layer  222  and the second capping layer  224  may have substantially the same thickness. In this case, the capping structure  220  may have a substantially uniform thickness throughout in the first transmission region  20   a  and the second transmission region  20   b.    
     Each of the first capping layer  222  and the second capping layer  224  may include an organic material having an improved transmissive property. In some embodiments, each of the first capping layer  222  and the second capping layer  224  may include a material substantially the same as or similar to the hole transport material. Thus, a light emitting property in the pixel region  10  may not be disturbed by the second electrode  210  serving as the cathode. 
     In example embodiments, the thickness of the first capping layer  222  and the thickness of the second capping layer  224  may be determined in consideration of improving or maximizing luminescent efficiency in the pixel region  10  and improving or maximizing light transmittance in the transmission region  20 . 
     As mentioned above, when the capping structure  220  has the first thickness substantially equal to the sum of the thickness of the first capping layer  222  and the thickness of the second capping layer  224  in the pixel region  10 , and has the second thickness substantially equal to the thickness of the first capping layer  222  or the thickness of the second capping layer  224  in the transmission region  20 , the luminescent efficiency in the pixel region  10  as well as the light transmittance in the transmission region  20  may be improved. 
       FIGS. 25 to 31  are cross-sectional views illustrating a method of manufacturing a transparent display device in accordance with example embodiments. 
     As an example,  FIGS. 25 to 31  illustrate a method of manufacturing the transparent display device illustrated in  FIG. 24 . Detailed descriptions on processes and/or elements previously described with reference to  FIGS. 9 to 15 ,  FIGS. 16 and 17 , and  FIGS. 18 and 19  will be omitted. 
     Referring to  FIGS. 25 to 28 , processes substantially the same as or similar to the processes explained in reference with  FIGS. 9 to 12  may be performed. Accordingly, a substrate  100  and a buffer layer  110  may be formed on a carrier substrate  50 , and a transistor including an active pattern  120 , a gate insulation layer  130 , a gate electrode  135 , an insulation interlayer  140 , a source electrode  150 , a drain electrode  155 , and a via insulation layer  160  covering the transistor may be formed. A first electrode  170  and a pixel defining layer  180  may be formed, and a display layer  200  and a second electrode  210  may be formed. 
     Referring to  FIGS. 29 and 30 , a capping structure  220  may be formed on the second electrode  210 . The capping structure  220  may include a first capping layer  222  and a second capping layer  224 . 
     The first capping layer  222  may be formed on the second electrode  210  in the first pixel region  10   a , the first transmission region  20   a , and the second pixel region  10   b . The second capping layer  224  may be formed on the second electrode  210  in the first pixel region  10   a , the second pixel region  10   b , and the second transmission region  20   b . The first transmission region  20   a  may be disposed between the first pixel region  10   a  and the second pixel region  10   b , and the second transmission region  20   b  may be disposed between the second pixel region  10   b  and the third pixel region  10   c.    
     As illustrated in  FIG. 29 , the first capping layer  222  may be formed in the first pixel region  10   a , the first transmission region  20   a , and the second pixel region  10   b  by using a mask  340  that includes an opening  345 . Specifically, after disposing the mask  340  such that the opening  345  corresponds to the first pixel region  10   a , the first transmission region  20   a , and the second pixel region  10   b , the first capping layer  222  may be formed using the hole transport material line of organic material. As one example, the mask  340  may be a fine metal mask (FMM). 
     Then, as illustrated in  FIG. 30 , the second capping layer  224  may be formed in the second pixel region  10   b , the second transmission region  20   b , and the third pixel region  10   c  by shifting the mask  340 . Specifically, after shifting the mask  340  such that the opening  345  corresponds to the second pixel region  10   b , the second transmission region  20   b , and the third pixel region  10   c , the second capping layer  224  may be formed using the hole transport material line of organic material. For example, the second capping layer  224  may be formed of material substantially the same as that of the first capping layer  222 .  FIG. 30  illustrates that the mask  340  is shifted along the first direction, but the invention is not limited thereto. For example, the mask  340  may be shifted along a direction substantially opposite to the first direction. 
     The same mask  340  may be used for the formation of the first capping layer  222  and the second capping layer  224 , so that the first capping layer  222  and the second capping layer  224  may have substantially the same area sizes. In this manner, a capping structure  220  including the first capping layer  222  and the second capping layer  224  may be formed. 
     In example embodiments, a width of the opening  345  may be substantially equal to the sum of a width of the first pixel region  10   a , a width of the first transmission region  20   a , and a width of the second pixel region  10   b . In other words, the width of the opening  345  may be substantially the same as the sum of twice a width of the pixel region  10  and a width of the transmission region  20 . Accordingly, the first capping layer  222  and the second capping layer  224  may overlap across an entirety of the pixel region  10 . Additionally, either the first capping layer  222  or the second capping layer  224  may be formed in the transmission region  20 . For example, only the first capping layer  222  may be formed in the first transmission region  20   a , and only the second capping layer  224  may be formed in the second transmission region  20   b.    
     In example embodiments, the capping structure  220  may have a first thickness in the first pixel region  10   a , the second pixel region  10   b , and the third pixel region  10   c , and may have a second thickness less than the first thickness in the first transmission region  20   a  and the second transmission region  20   b . In other words, the capping structure  220  may have the first thickness in the pixel region  10 , and may have the second thickness in the transmission region  20 . In some embodiments, the first capping layer  222  and the second capping layer  224  may have substantially the same thickness. Accordingly, the capping structure  220  may have the second thickness in the transmission region  20 , and may have the first thickness, which is about twice of the second thickness, in the pixel region  10 . 
     As mentioned above, a capping structure  220  having different thicknesses in the pixel region  10  and the transmission region  20  may be formed by shifting one mask  340 , so that manufacturing time and cost of the capping structure  220  may be reduced, and a transparent display device with improved luminescent efficiency and light transmittance may be manufactured. Additionally, the capping structure  220  with an uniform thickness in the transmission region  20  may be formed. 
     Referring to  FIG. 31 , processes substantially the same as or similar to the processes explained in reference with  FIG. 15  may be performed. More specifically, a filling layer  240  and an encapsulation substrate  250  may be formed on the capping structure  220 , and the carrier substrate  50  may be detached from the substrate  100 . 
       FIG. 32  is a plan view illustrating a transparent display device in accordance with example embodiments.  FIG. 33  is a plan view illustrating a transparent display device in accordance with some example embodiments.  FIGS. 32 and 33  may illustrate, among others, the transparent display device illustrated in  FIG. 24 . 
     The transparent display device illustrated in  FIGS. 32 and 33  may have elements and/or constructions substantially the same as or similar to the transparent display device illustrated in  FIGS. 21 and 22 , except for constructions of the first capping layer  222  and the second capping layer  224 . Therefore, detailed descriptions of repeated elements and/or constructions are omitted, and like reference numerals are used to designate like elements. 
     Referring to  FIGS. 32 and 33 , the capping structure  220  may cover the pixel region  10  and the transmission region  20 . The capping structure  220  may include the first capping layer  222  and the second capping layer  224 . In example embodiments, the first capping layer  222  may cover the pixel region  10  of a (2k−1)-th pixel row, the transmission region  20  of the (2k−1)-th pixel row, and the pixel region  10  of the (2k)-th pixel row. The second capping layer  224  may cover the pixel region  10  of the (2k)-th pixel row, the transmission region  20  of the (2k)-th pixel row, and the pixel region  10  of a (2k+1)-th pixel row. Here, k may be a positive integer between 1 through (N−1)/2. 
     In some example embodiments, as illustrated in  FIG. 32 , the capping structure  220  may be commonly disposed on the unit pixels PX arranged along the second direction. In this case, each of the first capping layer  222  and the second capping layer  224  may have a stripe shape. 
     In some example embodiments, as illustrated in  FIG. 33 , the capping structure  220  may be individually disposed per each of the unit pixels PX arranged along the second direction. In this case, each of the first capping layer  222  and the second capping layer  224  may have an island shape. 
     The transparent display devices according to example embodiments may be applied to various electronic devices such as computers, notebooks, cell phones, smart phones, smart pads, personal media players (PMPs), personal digital assistances (PDAs), MP3 players, or the like, as well as display devices with improved light transmittance such as navigation systems for automobiles, head-up displays, or the like. 
     Although a few example embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the novel teachings and advantages of the present inventive concept. Various features of the above described and other embodiments can thus be mixed and matched in any manner, to produce further embodiments consistent with the invention.