Patent Publication Number: US-11653534-B2

Title: Display device and electronic apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to and benefits of Korean Patent Application No. 10-2020-0027982 under 35 U.S.C. § 119, filed in the Korean Intellectual Property Office on Mar. 5, 2020, the entire contents of which is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     Embodiments of the disclosure relate to a display device and an electronic apparatus including the display device. 
     2. Description of the Related Art 
     Display devices have been widely used. Furthermore, as the thickness and weight of a display device have been reduced, a use range thereof has been increased. 
     As the area of a display area in a display device has been increased, various functions combined or linked to a display device have been added. As a method to add various functions while increasing display area, research has been conducted into a display device having an area for both adding various functions and displaying an image. 
     It is to be understood that this background of the technology section is, in part, intended to provide useful background for understanding the technology. However, this background of the technology section may also include ideas, concepts, or recognitions that were not part of what was known or appreciated by those skilled in the pertinent art prior to a corresponding effective filing date of the subject matter disclosed herein. 
     SUMMARY 
     In order to add various functions, a component such as a camera or a sensor may be disposed. A component may be disposed to overlap a display area to secure a larger display area. As a method of displaying a component, a display device may include a transmission area in which a wavelength such as light or sound may be transmitted. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments of the disclosure. 
     According to an embodiment of the disclosure, a display device may include pixel circuits disposed on a substrate, each of the pixel circuits comprising a transistor and a storage capacitor, display elements electrically connected to the pixel circuits, and a metal layer disposed between the substrate and the pixel circuits, the metal layer comprising through-holes, wherein the through-holes of the metal layer may include a first through-hole and a second through-hole disposed adjacent to the first through-hole. 
     The metal layer may include a metal part between the first through-hole and the second through-hole, and the metal part may overlap the pixel circuits and the display elements. 
     The first through-hole may have a shape, a size, or a width which is different from that of the second through-hole. 
     At least one of the first through-hole and the second through-hole may include corner parts disposed in different directions from a center. 
     At least one of the first through-hole and the second through-hole may include a side edge between adjacent corner parts, and the side edge may be curved. 
     The side edge may include an uneven part. 
     The first through-hole may include four corner parts disposed in four different directions from a first center, the second through-hole may include four corner parts disposed in four different directions from a second center, and one or more corner parts of the first through-hole and one or more corner parts of the second through-hole may be adjacent to each other. 
     The first through-hole may entirely surround the second through-hole. 
     At least one of the first through-hole and the second through-hole may include protruding portion. 
     The metal layer may further include a fine hole disposed between the first through-hole and the second through-hole. 
     According to another embodiment of the disclosure, an electronic apparatus may include a display device including at least one transmission area, and a component disposed below the at least one transmission area, wherein the display device may include pixel circuits disposed on a substrate, each of the pixel circuits including a transistor and a storage capacitor, display elements electrically connected to the pixel circuits, and a metal layer disposed between the substrate and the pixel circuits, the metal layer including a first through-hole and a second through-hole. 
     The metal layer may include a metal part between the first through-hole and the second through-hole, and the metal part may overlap the pixel circuits and the display elements. 
     The metal part may include a fine hole. 
     An edge of at least one of the first through-hole and the second through-hole may include an uneven part. 
     At least one of the first through-hole and the second through-hole may include four corner parts disposed in four different directions from a center, and a curved side edge may be between two neighboring corner parts of the four corner parts. 
     At least one of the first through-hole and the second through-hole may include a fine concave portion or a fine protruding portion. 
     Each of the first through-hole and the second through-hole may include four corner parts, and the first through-hole and the second through-hole may be arranged such that at least one of the corner parts of the first through-hole and at least one of the corner parts of the second through-hole may be adjacent to each other. 
     The first through-hole may entirely surround the second through-hole. 
     A width of the first through-hole may be about 200 μm to about 300 μm. 
     The component may include at least one of a sensor and a camera. 
     The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description, the accompanying drawings, and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIGS.  1 A and  1 B  are schematic perspective views of an electronic apparatus according to an embodiment of the disclosure; 
         FIGS.  2 A to  2 C  are schematic cross-sectional views of a part of an electronic apparatus according to an embodiment of the disclosure; 
         FIG.  2 D  is a schematic cross-sectional view of a part of an electronic apparatus according to an embodiment of the disclosure. 
         FIGS.  3 A and  3 B  are schematic plan views of a display device according to an embodiment of the disclosure. 
         FIG.  4    is a schematic circuit diagram of a pixel circuit connected to an organic light-emitting diode of a display device according to an embodiment of the disclosure; 
         FIG.  5    is a schematic plan view of a part of a first display area of a display device according to an embodiment of the disclosure; 
         FIG.  6    is a schematic plan view of a second display area of a display device according to an embodiment of the disclosure; 
         FIG.  7    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; 
         FIG.  8    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; 
         FIG.  9    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; 
         FIG.  10    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; 
         FIG.  11    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; 
         FIG.  12    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; 
         FIG.  13    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; 
         FIG.  14    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; 
         FIG.  15    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; 
         FIG.  16    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; 
         FIG.  17    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; 
         FIG.  18    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; 
         FIG.  19    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure; and 
         FIG.  20    is a schematic cross-sectional view of a part of a display device according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of the description. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. The terms “and” and “or” may be used in the conjunctive or disjunctive sense and may be understood to be equivalent to “and/or.” Throughout the disclosure, the expression “at least one of a, b and c” indicates only a, only b, only c, both a and b, both a and c, both b and c, all of a, b, and c, or variations thereof. 
     Hereinafter, the disclosure will be described in detail by explaining embodiments of the disclosure with reference to the attached drawings, and in the description of the disclosure, certain detailed explanations of related art are omitted when it is deemed that they may unnecessarily obscure the essence of the disclosure. 
     While such terms as “first,” “second,” etc., may be used to describe various components, such components must not be limited to the above terms. The above terms are used only to distinguish one component from another. 
     An expression used in the singular encompasses the expression of the plural, unless it has a clearly different meaning in the context. 
     Terms such as “including,” “having,” and “comprising” are intended to indicate the existence of the features disclosed in the specification, and are not intended to preclude the possibility that one or more other features may exist or may be added. 
     Spatially relative terms such as “below”, “beneath”, “lower”, “behind” “above”, “upper”, or “in front” or the like, may be used herein for ease of description to describe the relations between one element or component and another element or component as illustrated in the drawings. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the drawings. For example, in the case where a device illustrated in the drawing is turned over, elements positioned “below” or “behind” another device may be placed “above” or “in front” of another device. Accordingly, the illustrative term “below” may include both the lower and upper positions. The device may also be oriented in other directions and thus the spatially relative terms may be interpreted differently depending on the orientations. 
     It will be understood that when a component, such as a layer, a film, a region, or a plate, is referred to as being “on” another component, the component can be directly on the other component or intervening components may be present thereon. 
     Sizes of components in the drawings may be exaggerated for convenience of explanation. For example, as sizes and thicknesses of components in the drawings may be arbitrarily illustrated for convenience of explanation, the following embodiments are not limited thereto. 
     When a certain embodiment may be implemented differently, a specific process order may be performed differently from the described order. For example, two consecutively described processes may be performed substantially at the same time or performed in an order opposite to the described order. 
     It will be understood that when a layer, region, or component is referred to as being “connected to” another layer, region, or component, it can be directly connected to the other layer, region, or component or indirectly connected to the other layer, region, or component via intervening layers, regions, or components. For example, in the specification, when a layer, region, or component is referred to as being electrically connected to another layer, region, or component, it can be directly electrically connected to the other layer, region, or component or indirectly electrically connected to the other layer, region, or component via intervening layers, regions, or components. 
     Terms such as “overlap” may include layer, stack, face or facing, extending over, extending under, covering or partly covering or any other suitable term as would be appreciated and understood by those of ordinary skill in the art. 
     “About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” may mean within one or more standard deviations, or within ±30%, 20%, 5% of the stated value. 
     Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those skilled in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an ideal or excessively formal sense unless clearly defined in the specification. 
       FIGS.  1 A and  1 B  are schematic perspective views of an electronic apparatus  1  according to an embodiment of the disclosure. 
     Referring to  FIGS.  1 A and  1 B , the electronic apparatus  1  may include a display area DA and a non-display area NDA outside the display area DA. The electronic apparatus  1  may provide an image through an array of pixels that may be two-dimensionally arranged in the display area DA. Pixels may include first pixels P 1  disposed in a first display area DA 1  and second pixels P 2  disposed in a second display area DA 2 . 
     The electronic apparatus  1  may provide a first image by using light emitted from the first pixels P 1  disposed in the first display area DA 1  and a second image by using light emitted from the second pixels P 2  disposed in the second display area DA 2 . In some embodiments, the first image and the second image may be parts of any one image provided through the display area DA of the electronic apparatus  1 . In some embodiments, the electronic apparatus  1  may provide the first image and the second image that may be independent of each other. 
     The second display area DA 2  may include a transmission area TA between the second pixels P 2 . The transmission area TA may be an area in which light transmits and where no pixel may be disposed. 
     The non-display area NDA may be an area that does not provide an image and is adjacent to the display area DA. For example, the non-display area NDA may surround (e.g., entirely surround) the display area DA. The non-display area NDA may be where drivers for providing electrical signals or power to the first pixels P 1  and the second pixels P 2  may be disposed. The non-display area NDA may be where a pad, to which electronic components or printed circuit boards may be electrically connected, may be disposed. 
     The second display area DA 2  may be circular or oval in plan view, as illustrated in  FIG.  1 A . As another example, the second display area DA 2  may be polygonal such as a rectangular or bar type, as illustrated in  FIG.  1 B . 
     The second display area DA 2  may be disposed inside the first display area DA 1  ( FIG.  1 A ) or at one side of the first display area DA 1  ( FIG.  1 B ). As illustrated in  FIG.  1 A , the second display area DA 2  may be entirely surrounded by the first display area DA 1 . In some embodiments, the second display area DA 2  may be partially surrounded by the first display area DA 1 . For example, the second display area DA 2  may be located at one corner portion of the first display area DA 1  and be partially surrounded by the first display area DA 1 . 
     A ratio of the second display area DA 2  to the display area DA may be less than a ratio of the first display area DA 1  to the display area DA. The electronic apparatus  1 , as illustrated in  FIG.  1 A , may include one second display area or two or more second display areas as the second display area DA 2 . 
     The electronic apparatus  1  may include a mobile phone, a tablet PC, a laptop, or a smart watch or smart band worn around the wrist. 
       FIGS.  2 A to  2 C  are schematic cross-sectional views of a part of the electronic apparatus  1  according to an embodiment of the disclosure.  FIG.  2 D  is a schematic cross-sectional view of a part of the electronic apparatus  1  according to an embodiment of the disclosure. 
     Referring to  FIGS.  2 A to  2 C , the electronic apparatus  1  may include the display device  10  and a component  20  disposed to overlap the display device  10 . 
     The display device  10  may include a substrate  100 , a display layer  200  disposed on the substrate  100 , a thin film encapsulation layer  300 A on the display layer  200 , an input sensing layer  400 , an optical functional layer  500 , an anti-reflection layer  600 , and a window  700 . 
     The component  20  may be located in the second display area DA 2 . The component  20  may be an electronic component that uses light or sound. For example, the electronic component may include a sensor that measures a distance, such as a proximity sensor, a sensor that recognizes a part of the user&#39;s body, such as a fingerprint, an iris, a face, etc., a small lamp that outputs light, or an image sensor that captures an image, such as a camera. An electronic component that uses light may use light in various wavelength bands, such as visible light, infrared light, and ultraviolet light. An electronic component that uses sound may use ultrasound or sound in other frequency bands. In some embodiments, the component  20  may include sub-components such as a light emitting part and a light receiving part. The light emitting part and the light receiving part may have an integrated structure or a physically separated structure in which a pair of the light emitting part and the light receiving part constitute one component as the component  20 . 
     The substrate  100  may include glass, polymer resin, or a combination thereof. For example, the polymer resin of the substrate  100  may include polyether sulfone, polyacrylate, polyether imide, polyethylene naphthalate, polyethylene terephthalate, polyphenylene sulfide, polyarylate, polyimide, polycarbonate, and/or cellulose acetate propionate. The substrate  100  including polymer resin may be flexible, rollable, or bendable. The substrate  100  may have a multilayer structure including a layer including the above-described polymer resin and an inorganic layer (not shown). 
     The display layer  200  may be disposed on the front surface of the substrate  100 , and a lower protection film  175  may be disposed on the rear surface of the substrate  100 . The lower protection film  175  may be attached on the rear surface of the substrate  100 . An adhesive layer may be provided between the lower protection film  175  and the substrate  100 . As another example, the lower protection film  175  may be formed (e.g., directly formed) on the rear surface of the substrate  100 . No adhesive layer may be provided between the lower protection film  175  and the substrate  100 . 
     The lower protection film  175  may support and protect the substrate  100 . The lower protection film  175  may include a first opening  1750 P corresponding to the second display area DA 2 . The first opening  1750 P of the lower protection film  175  may be a concave portion formed as a part of the lower protection film  175  having been removed in a thickness direction (e.g. a z direction). In some embodiments, the first opening  1750 P of the lower protection film  175  may be formed as a part of the lower protection film  175  having been entirely removed in the thickness direction. The first opening  1750 P may have a section of a through-hole as illustrated in  FIGS.  2 A and  2 C . In some embodiments, the first opening  1750 P of the lower protection film  175  may have a section of a blind-hole as illustrated in  FIG.  2 B  as a part of the lower protection film  175  having been partially removed in the thickness direction. 
     As the lower protection film  175  may include the first opening  1750 P, the transmittance of the second display area DA 2 , for example, the light transmittance of the transmission area TA, may be improved. The lower protection film  175  may include an organic insulating material such as polyethylene terephthalate (PET) and/or polyimide (PI). 
     The display layer  200  may include pixels. Each pixel may include a display element and may emit red, green, or blue light. The display element may include an organic light-emitting diode OLED. In some embodiments, an area in the organic light-emitting diode OLED, where light may be emitted, may correspond to a pixel. 
     The display layer  200  may include a display element layer including the organic light-emitting diode OLED that may be a display element, a circuit layer including a thin film transistor TFT electrically connected to the organic light-emitting diode OLED, a buffer layer  111  between the display element layer and the circuit layer, and an insulating layer IL. The thin film transistor TFT and the organic light-emitting diode OLED electrically connected to the thin film transistor TFT may be disposed in each of the first display area DA 1  and the second display area DA 2 . The thin film transistor TFT may include a semiconductor layer Act, a gate electrode GE, a source electrode SE, and a drain electrode DE. 
     The second display area DA 2  may include at least one transmission area TA where the thin film transistor TFT and the organic light-emitting diode OLED may not be disposed. The transmission area TA may be an area in which light that may be emitted from and/or proceeds toward the component  20  transmits. In the display device  10 , the transmittance of the transmission area TA may be about 30% or more, about 40% or more, about 50% or more, about 60% or more, about 70% or more, about 75% or more, about 80% or more, about 85% or more, or about 90% or more. 
     A back metal layer (blocking metal layer, metal layer) BML may be disposed between the substrate  100  and the display layer  200 , for example, between the substrate  100  and the thin film transistor TFT or between the substrate  100  and the buffer layer  111 . The back metal layer BML may include at least one through-hole TH through which the light emitted from or proceeding toward the component  20  may pass. The through-hole TH of the back metal layer BML may be located in the transmission area TA. A metal portion of the back metal layer BML, where the through-hole TH may not be formed, may prevent the diffraction of light by a narrow gap between wirings connected to the pixel circuit PC or a narrow gap between parts of the pixel circuit PC in the second display area DA 2 . 
     The back metal layer BML may be connected to a connection line CL. The connection line CL may be a part of the gate electrode GE, the source electrode SE, or the drain electrode DE of the thin film transistor TFT, or a line electrically connected to the gate electrode GE, the source electrode SE, or the drain electrode DE. The back metal layer BML may have the same voltage level as that of the gate electrode GE, the source electrode SE, or the drain electrode DE through the connection line CL. In an embodiment, in case the thin film transistor TFT may be a driving thin film transistor that is described later with reference to  FIG.  4   , the back metal layer BML may have the same voltage level as that of a gate electrode, a source electrode, or a drain electrode of the driving thin film transistor, and the source electrode or the drain electrode of the driving thin film transistor may be a part of a driving voltage line. In case the back metal layer BML has a certain voltage level, deterioration of the performance of the thin film transistor TFT may be prevented or the performance of the thin film transistor TFT may be improved. 
     The display layer  200  may be sealed with an encapsulation member. In some embodiments, the encapsulation member may include the thin film encapsulation layer  300 A as illustrated in  FIGS.  2 A and  2 B . The thin film encapsulation layer  300 A may include at least one inorganic encapsulation layer and at least one organic encapsulation layer. In an embodiment, the thin film encapsulation layer  300 A may include first and second inorganic encapsulation layers  310  and  330  and an organic encapsulation layer  320  therebetween. 
     In some embodiments, the encapsulation member may include an encapsulation substrate  300 B as illustrated in  FIG.  2 C . The encapsulation substrate  300 B may be disposed to face the substrate  100  with the display layer  200  therebetween. There may be a gap between the encapsulation substrate  300 B and the display layer  200 . The encapsulation substrate  300 B may include glass. A sealant may be disposed between the substrate  100  and the encapsulation substrate  300 B, and the sealant may be disposed in the non-display area NDA that is previously described with reference to  FIG.  1 A or  1 B . The sealant disposed in the non-display area NDA may surround the display area DA to prevent intrusion of moisture through a side surface. 
     An input sensing layer  400  may obtain coordinate information according to an external input, for example, a touch event of an object such as a finger or a stylus pen. The input sensing layer  400  may include a touch electrode and trace lines connected to the touch electrode. The input sensing layer  400  may sense an external input in a mutual-capacitance (mutual cap) method or a self-capacitance (self cap) method. 
     The input sensing layer  400  may be formed on the encapsulation member. As another example, the input sensing layer  400  that may be formed separately may be bonded to the encapsulation member via an adhesive layer such as an optical transparent adhesive OCA. In an embodiment, as illustrated in  FIGS.  2 A to  2 C , the input sensing layer  400  may be formed (e.g., directly formed) on the thin film encapsulation layer  300 A or the encapsulation substrate  300 B. The adhesive layer may not be provided between the input sensing layer  400  and the thin film encapsulation layer  300 A or the encapsulation substrate  300 B. 
     An optical functional layer  500  may improve optical efficiency. For example, the front optical efficiency and/or side visibility of the light emitted from the organic light-emitting diode OLED may be improved, and the diffraction of the light passing through the transmission area TA and then proceeding toward the component  20  may be reduced or prevented. 
     An anti-reflection layer  600  may reduce reflectivity of light (external light) input toward the display device  10  from the outside. 
     In some embodiments, the anti-reflection layer  600  may include an optical plate having a retarder and/or a polarizer. A retarder may be of a film type or a liquid crystal coating type and may include a λ/2 retarder and/or a λ/4 retarder. A polarizer may also be a film type or a liquid crystal coating type. A film type polarizer may include a stretchable synthetic resin film, and the liquid crystal coating-type polarizer may include liquid crystals arranged in a certain array. 
     In some embodiments, the anti-reflection layer  600  may include a filter plate including a black matrix and color filters as illustrated in  FIG.  2 C . A filter plate may include color filters, a black matrix, and an overcoat layer disposed in each pixel. 
     In some embodiments, the anti-reflection layer  600  may include a destructive interference structure. A destructive interference structure may include a first reflective layer and a second reflective layer disposed on different layers. First reflection light and second reflection light respectively reflected from the first reflective layer and the second reflective layer may destructively interfere with each other, and thus, the reflectivity of the external light may be reduced. 
     A window  700  may be disposed on the anti-reflection layer  600  and coupled to the anti-reflection layer  600  through an adhesive layer such as an optical transparent adhesive OCA. Although  FIGS.  2 A to  2 C  illustrate that the window  700  is disposed on the anti-reflection layer  600 , in some embodiments, the positions of the anti-reflection layer  600  and the optical functional layer  500  may be switched with each other. The window  700  may be coupled to the optical functional layer  500  through an adhesive layer such as an optical transparent adhesive OCA. In some embodiments, the optical transparent adhesive OCA may be omitted between the window  700  and a layer under the window  700 , for example, an anti-reflection layer or an optical functional layer. 
     One component or multiple components as the component  20  may be disposed in the second display area DA 2 . In case the electronic apparatus  1  includes multiple components as the component  20 , the electronic apparatus  1  may include multiple second display areas by as many as the number of components  20  as the second display area DA 2 . For example, the electronic apparatus  1  may include multiple second display areas apart from each other as the second display areas DA 2 . In some embodiments, the components  20  may be disposed in one second display area as the second display area DA 2 . For example, the electronic apparatus  1  may include the second display area DA 2  that may be of a bar type as described with reference to  FIG.  1 B , the components  20  may be arranged spaced apart from each other in the length direction, for example, the x direction of  FIG.  1 B , of the second display area DA 2 . 
     Although  FIGS.  2 A to  2 C  illustrate that the display device  10  may include the organic light-emitting diode OLED as a display element, the display device  10  of the disclosure is not limited thereto. In another embodiment, the display device  10  may include a light-emitting display device including an inorganic material such as a micro LED, for example, an inorganic light emitting display or an inorganic display device, or a display device such as a quantum-dot light-emitting display device. For example, the light-emitting layer of the display element provided in the display device  10  may include an organic material, an inorganic material, quantum dots, an organic material and quantum dots, or an inorganic material and quantum dots. 
     Although  FIGS.  2 A to  2 C  illustrate that the display device  10  may include the substrate  100  having a constant thickness, in another embodiment, the thickness of the substrate  100  in the transmission area TA may be less than the thickness in other areas. 
     Referring to  FIG.  2 D , the substrate  100  may include layers, and at least one layer of the layers may include an opening located in the transmission area TA. For example, the substrate  100  may include a first base layer  101 , a first barrier layer  102 , a second base layer  103 , and a second barrier layer  104 , which may be sequentially stacked on each other. 
     The first base layer  101  and the second base layer  103  each may include polymer resin. The polymer resin may include polyethersulphone (PES), polyarylate (PAR), polyetherimide (PEI), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyimide (PI), polycarbonate, cellulose triacetate (TAC), cellulose acetate propionate (CAP), or a combination thereof. The polymer resin may be transparent. 
     The first barrier layer  102  and the second barrier layer  104  each may include, as a barrier layer for preventing intrusion of external foreign materials, a single layer or a multilayer including an inorganic insulating material such as a silicon nitride, a silicon oxynitride, and/or a silicon oxide. 
     As a part of the first base layer  101  corresponding to the transmission area TA may be removed, the first base layer  101  may include a second opening  101 OP. Although  FIG.  2 D  illustrates the second opening  101 OP may have a section of a through-hole, in another embodiment, the second opening  101 OP may have a section of a blind-hole. 
       FIGS.  3 A and  3 B  are schematic plan views of a display device according to an embodiment of the disclosure. 
     Referring to  FIGS.  3 A and  3 B , the display device  10  may include an array of pixels disposed on the substrate  100 . The pixels may include the first pixels P 1  disposed in the first display area DA 1  and the second pixels P 2  disposed in the second display area DA 2 . 
     The display area DA may include the first display area DA 1  and the second display area DA 2 , and the size of the first display area DA 1  and the size of the second display area DA 2  may be different from each other. The size of the first display area DA 1  may be greater than the size of the second display area DA 2 . 
     The first pixels P 1  may be two-dimensionally arranged in the first display area DA 1 , and the second pixels P 2  may be two-dimensionally arranged in the second display area DA 2 . The transmission area TA may be disposed in the second display area DA 2 . The transmission area TA may be disposed between the second pixels P 2  neighboring each other. 
     The non-display area NDA may entirely surround the display area DA. A scan driver or a data driver may be disposed in the non-display area NDA. A pad  230  may be located in the non-display area NDA. The pad  230  may be disposed adjacent to any one of edges of the substrate  100 . The pad  230  may be exposed without being covered by the insulating layer, and may be electrically connected to a flexible printed circuit board FPCB. The flexible printed circuit board FPCB may electrically connect a controller to the pad  230 , and may supply signals or power transmitted from the controller to the pixel circuits or wires. In some embodiments, a data driver may be disposed in the flexible printed circuit board FPCB. The pad  230  may be connected to wirings to transmit signals or voltages of the flexible printed circuit board FPCB to the first pixels P 1  and the second pixels P 2 . 
     In another embodiment, instead of the flexible printed circuit board FPCB, an integrated circuit may be disposed on the pad  230 . The integrated circuit may include, for example, a data driver, and may be electrically connected to the pad  230  via an anisotropic conductive film containing a conductive ball. 
     Each first pixel P 1  and each second pixel P 2  may emit light of a certain color by using the organic light-emitting diode OLED of  FIGS.  2 A to  2 C . Each organic light-emitting diode OLED may emit, for example, red, green, or blue light. Each organic light-emitting diode OLED may be connected to a pixel circuit including a transistor and a capacitor. 
       FIG.  4    is a schematic circuit diagram of a pixel circuit connected to an organic light-emitting diode of a display device according to an embodiment of the disclosure. 
     Referring to  FIG.  4   , the organic light-emitting diode OLED may be electrically connected to the pixel circuit PC. The pixel circuit PC may include a first thin film transistor T 1 , a second thin film transistor T 2 , and a storage capacitor Cst. 
     The second thin film transistor T 2 , as a switching thin film transistor, may be connected to a scan line SL and a data line DL, and may transmit a data voltage, or a data signal Dm, input through the data line DL to the first thin film transistor T 1  on the basis of a switching voltage, or a switching signal Sn, input through the scan line SL. The storage capacitor Cst may be connected to the second thin film transistor T 2  and a driving voltage line PL, and may store a voltage corresponding to a difference between the voltage received from the second thin film transistor T 2  and a first power voltage ELVDD supplied to the driving voltage line PL. 
     The first thin film transistor T 1 , as a driving thin film transistor, may be connected to the driving voltage line PL and the storage capacitor Cst, and may control a driving current flowing in the organic light-emitting diode OLED from the driving voltage line PL corresponding to a value of the voltage stored in the storage capacitor Cst. The organic light-emitting diode OLED may emit light having a certain luminance according to the driving current. A counter electrode, for example, a cathode, of the organic light-emitting diode OLED may receive a second power voltage ELVSS. 
     Although  FIG.  4    illustrates that the pixel circuit PC may include two thin film transistors and one storage capacitor, the disclosure is not limited thereto. The number of thin film transistors and the number of storage capacitors may be variously changed according to the design of the pixel circuit PC. For example, the pixel circuit PC may include three or more thin film transistors. 
       FIG.  5    is a schematic plan view of a part of a first display area of a display device according to an embodiment of the disclosure. 
     Referring to  FIG.  5   , the first pixels P 1  may be disposed in the first display area DA 1 . The first pixels P 1  may include a first red pixel P 1   r , a first green pixel P 1   g , and a first blue pixel P 1   b . In some embodiments, as illustrated in  FIG.  5   , the first red pixel P 1   r , the first green pixel P 1   g , and the first blue pixel P 1   b  may be disposed in a PenTile® type. For example, the first red pixels P 1   r  and the first blue pixels P 1   b  may be alternately arranged in a first row  1 N. The first green pixels P 1   g  may be arranged in a second row  2 N and be apart from each other at certain intervals. The first blue pixels P 1   b  and the first red pixels P 1   r  may be alternately arranged in an adjacent third row  3 N. The first green pixels P 1   g  may be arranged in a fourth row  4 N and be apart from each other at certain intervals. The first red and blue pixels P 1   r  and P 1   b  in the first row  1 N and the first green pixels P 1   g  in the second row  2 N may be shifted each other. The first blue and red pixels P 1   b  and P 1   r  in the third row  3 N and the first green pixels P 1   g  in the fourth row  4 N may be shifted each other. Therefore, the first red pixels P 1   r  and the first blue pixels P 1   b  may be alternately arranged in a first column  1 M. The first green pixels P 1   g  may be arranged in a second column  2 M and be apart from each other at certain intervals. The first blue pixels P 1   b  and the first red pixels P 1   r  may be alternately arranged in a third column  3 M. The first green pixels P 1   g  may be arranged in a fourth column  4 M and be apart from each other at certain intervals. Such pixel arrangement may be repeated up to an M th  column. The pixel arrangement structure described above may be expressed differently as follows: the first red pixels P 1   r  are arranged at first and third vertices facing each other from among the vertices of a virtual rectangle VS having a center point of the first green pixel P 1   g  as a center point of a rectangle, and the first blue pixels P 1   b  are arranged at second and fourth vertices that are the other vertices. In this case, the virtual rectangle VS may be modified in various forms, such as a rectangle, a rhombus, and a square Such a pixel arrangement structure may be referred to as a PenTile® matrix structure or a PenTile® structure, and high resolution may be implemented with a small number of pixels by applying a rendering driving that expresses colors by sharing adjacent pixels. In another embodiment, the first red pixel P 1   r , the first green pixel P 1   g , and the first blue pixel P 1   b  may be disposed in a stripe type. 
     A first red pixel P 1   r , a first green pixel P 1   g , and a first blue pixel P 1   b  may have sizes or widths different from one another. For example, the first blue pixel P 1   b  may be larger than the first red pixel P 1   r  and the first green pixel P 1   g , and the first red pixel P 1   r  may be larger than the first green pixel P 1   g . In some embodiments, the first green pixel P 1   g  may be rectangular, and the first green pixels P 1   g  that neighbor each other may extend in different directions. 
       FIG.  6    is a schematic plan view of a second display area of a display device according to an embodiment of the disclosure. 
     Referring to  FIG.  6   , the second pixels P 2  may be disposed in the second display area DA 2 . The second pixels P 2  may include a second red pixel P 2   r , a second green pixel P 2   g , and a second blue pixel P 2   b . In some embodiments, the second red pixel P 2   r , the second green pixel P 2   g , and the second blue pixel P 2   b  may be disposed in a pentile type. In another embodiment, the second red pixel P 2   r , the second green pixel P 2   g , and the second blue pixel P 2   b  may be disposed in a stripe type. 
     The transmission area TA may be disposed adjacent to the second pixels P 2 . For example, the transmission area TA may be disposed between the second pixels P 2 . The transmission areas TA, as illustrated in  FIG.  6   , may be arranged in the x direction, the y direction and/or a direction oblique to the x and y directions adjacent to each other as illustrated. 
     The back metal layer BML may be disposed in the second display area DA 2 . The back metal layer BML may include through-holes corresponding to the transmission area TA, and in this regard,  FIG.  6    illustrates a first through-hole TH 1  and a second through-hole TH 2 . A metal part may be between the first through-hole TH 1  and the second through-hole TH 2 , and the second red pixel P 2   r , the second green pixel P 2   g , and the second blue pixel P 2   b  may be disposed on the metal part. 
     The first through-hole TH 1  and the second through-hole TH 2  may be apart from each other, but may be disposed adjacent to each other. The first through-hole TH 1  and the second through-hole TH 2  may be different from each other in terms of shape, pattern, size, and/or width (also referred to herein as shapes and/or sizes). Shapes being different from each other may mean that the condition of similarity in geometry, for example, the Euclidean geometry, may not be satisfied. For example, in case one of the first through-hole TH 1  and the second through-hole TH 2  may be magnified or reduced and then overlapped with the other, if the first through-hole TH 1  and the second through-hole TH 2  do not match 100%, it may be stated that the shape of the first through-hole TH 1  and the shape of the second through-hole TH 2  may be different. 
     The first through-hole TH 1  may include corner parts disposed in a first direction, for example, the y direction, and a second direction, for example, the x direction, crossing the first direction from a first center O 1  of the first through-hole TH 1 . For example, the first through-hole TH 1  may include four corner parts (hereinafter, referred to as the first to fourth corner parts C 11 , C 12 , C 13 , and C 14 ) disposed in the left, right, up, and down directions from the first center O 1 . 
     A side edge E 1  between two neighboring corner parts of the first through-hole TH 1  may be largely curved. Each side edge E 1  between the first corner part C 11  and the second corner part C 12 , between the second corner part C 12  and the third corner part C 13 , between the third corner part C 13  and the fourth corner part C 14 , and between the fourth corner part C 14  and the first corner part C 11  may be largely curved. The side edge E 1  being largely curved may be distinguished from a structure that extends in the x direction and suddenly bents in the y direction, for example, a structure that may be bent about 90°. 
     The edges of the first through-hole TH 1  may include an uneven part. For example, the edges of the first through-hole TH 1  may include an uneven part with irregular unevenness. For example, each side edge E 1  between the first corner part C 11  and the third corner part C 13 , between the second corner part C 12  and the third corner part C 13 , between the second corner part C 12  and the fourth corner part C 14 , and between the fourth corner part C 14  and the first corner part C 11  may include irregular unevenness. In some embodiments, the side edge E 1  of the first through-hole TH 1  may be largely curved (or macroscopically) and may include irregular unevenness locally (or microscopically). 
     The second through-hole TH 2  may include corner parts disposed in the first direction, for example, the y direction, and the second direction, for example, the x direction, crossing the first direction, from a second center O 2  of the second through-hole TH 2 . For example, the second through-hole TH 2  may include four corner parts (hereinafter, referred to as the fifth to eighth corner parts C 21 , C 22 , C 23 , and C 24 ) disposed in the left, right, up, and down directions from the second center O 2 . 
     The edges of the second through-hole TH 2  may include an uneven part. For example, the edges of the second through-hole TH 2  may include irregular unevenness. For example, each side edge E 2  between the fifth corner part C 21  and the seventh corner part C 23 , between the sixth corner part C 22  and the seventh corner part C 23 , between the sixth corner part C 22  and the eighth corner part C 24 , and between the eighth corner part C 24  and the fifth corner part C 21  may include irregular unevenness. In some embodiments, the side edge E 2  of the second through-hole TH 2  may be largely curved (or macroscopically) and may include irregular unevenness locally (or microscopically). 
     A first width W 1  of the first through-hole TH 1  may be different from a second width W 2  of the second through-hole TH 2 . For example, the first width (maximum width) W 1  of the first through-hole TH 1  passing the first center O 1  may be greater than the second width (maximum width) W 2  of the second through-hole TH 2  passing the second center O 2 . The first width W 1  may be about 200 μm to about 300 μm or about 250 μm to about 300 μm. In an embodiment, the first width W 1  may be about 270 μm. 
     Multiple first through-holes as the first through-hole TH 1  may be arranged to surround the second through-hole TH 2 . In this respect,  FIG.  6    illustrates that four first through-holes TH 1  may be disposed around one second through-hole TH 2 . In some embodiments, the first through-holes TH 1  may be arranged around the second through-hole TH 2  such that each of the side edge E 1  of the first through-hole TH 1  and the side edge E 2  of the second through-hole TH 2  may be adjacent to each other. The corner parts of the first through-hole TH 1  and the corner parts of the second through-hole TH 2  may be disposed adjacent to each other. For example, the two neighboring corner parts of the second through-holes TH 2 , and the two neighboring corner parts of the first through-holes TH 1  may be disposed adjacent to each other. 
     According to the embodiment described with reference to  FIG.  6   , the first through-hole TH 1  may be approximately a cross type and the second through-hole TH 2  may be approximately a rhombus type, and the first through-hole TH 1  and/or the second through-hole TH 2  may be variously changed as described below with reference to  FIGS.  7  to  19   . 
       FIG.  7    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure. 
     Referring to  FIG.  7   , the back metal layer BML may include the first through-hole TH 1  and the second through-hole TH 2 , which may be different in terms of shape and/or size. A metal part BML-M of the back metal layer BML may overlap the second pixels as described above with reference to  FIG.  6   . 
     The first through-hole TH 1  may include corner parts, for example, the first to fourth corner parts C 11 , C 12 , C 13 , and C 14 , which may be disposed in different directions with respect to the first center O 1 . The side edge E 1  between two neighboring corner parts of the first through-hole TH 1  may be largely curved and may have locally irregular unevenness. According to the embodiment illustrated in  FIG.  7   , a corner edge CE 1  of each of the first to fourth corner parts C 11 , C 12 , C 13 , and C 14  of the first through-hole TH 1  may include irregular unevenness. 
     The second through-hole TH 2  may include corner parts, for example, fifth to eighth corner parts C 21 , C 22 , C 23 , and C 24 , disposed in different directions with respect to the second center O 2 . Unlike the second through-hole TH 2  described with reference to  FIG.  6   , the side edge E 2  of the second through-hole TH 2  of  FIG.  7    may be largely curved. The second through-hole TH 2  may be largely or macroscopically curved and may include irregular unevenness locally or microscopically. Although the second through-hole TH 2  may be approximately a cross type, the shape of the second through-hole TH 2  may be different from that of the first through-hole TH 1 . For example, while the second through-hole TH 2  has a cross shape in which the width of each of the fifth to eighth corner parts C 21 , C 22 , C 23 , and C 24  thereof decreases in a direction away from the second center O 2 , the first through-hole TH 1  has a cross shape, which may be different in a detailed shape, in which the width of each of the first to fourth corner parts C 11 , C 12 , C 13 , and C 14  may be a certain width, for example, about 70 μm to about 90 μm. 
     The first width of the first through-hole TH 1  may be greater than the second width of the second through-hole TH 2 . Multiple first through-holes as the first through-hole TH 1  may be arranged around the second through-hole TH 2  as a center. For example, the side edge E 1  of the first through-hole TH 1  and the side edge E 2  of the second through-hole TH 2  may be disposed adjacent to each other, and/or the corner parts of the first through-hole TH 1  and the corner parts of the second through-hole TH 2  may be disposed adjacent to each other, as described with reference to  FIG.  6   . 
       FIGS.  8  to  10    are schematic plan views of excerpts of a metal layer of a display device according to embodiments of the disclosure. 
     Referring to  FIGS.  8  and  9   , the back metal layer BML may include the first through-hole TH 1  and the second through-hole TH 2  having different shapes and/or sizes. The features regarding the metal part BML-M of the back metal layer BML and the structure and arrangement of the first through-hole TH 1  and the second through-hole TH 2  may be the same as those described with reference to  FIGS.  6  and  7   . 
     Unlike the corner edge CE 1  of each of the first to fourth corner parts C 11 , C 12 , C 13 , and C 14  of the first through-hole TH 1  described with reference to  FIGS.  6  and  7    extending largely in the x direction or the y direction, the corner edge CE 1  of each of the first to fourth corner parts C 11 , C 12 , C 13 , and C 14  of the first through-hole TH 1  of  FIGS.  8  and  9    may be arranged along a virtual line passing the first center O 1  in the x direction or the y direction and may be curved to have a certain radius of curvature 
     The first through-hole TH 1  of  FIGS.  8  and  9    may include the side edge E 1  between adjacent corner parts, and the side edge E 1  may be largely curved and may include an uneven part (e.g., locally irregular unevenness) as described above with reference to  FIG.  6   . While the side edge E 1  of the first through-hole TH 1  illustrated in  FIG.  9    may be largely curved, a degree of curve, for example, a radius of curvature, may be less than a radius of curvature of the side edge E 1  of the first through-hole TH 1  of  FIG.  8   . 
     While the side edge E 1  of the first through-hole TH 1  of  FIGS.  8  and  9    includes locally irregular unevenness, in another embodiment, referring to  FIG.  10   , the side edge E 1  of the first through-hole TH 1  may include a smooth curve in plan view. The corner edge CE 1  of each corner part of the first through-hole TH 1  may also include a smooth curve similar to the side edge E 1 . 
     The side edge E 2  and/or a corner edge CE 2  of the second through-hole TH 2  may include an uneven part (e.g., irregular unevenness), as illustrated in  FIGS.  8  and  9   , or may include a smooth curve as illustrated in  FIG.  10   . 
       FIGS.  11  and  12    are schematic plan views of excerpts of a metal layer of a display device according to an embodiment of the disclosure. 
     Referring to  FIG.  11   , the back metal layer BML may include the first through-hole TH 1  and the second through-hole TH 2  having different shapes and/or sizes. Features regarding the metal part BML-M of the back metal layer BML and the structure and arrangement of the first through-hole TH 1  and the second through-hole TH 2  may be the same as those described with reference to  FIGS.  6  and  7   . 
     Each of the first to fourth corner parts C 11 , C 12 , C 13 , and C 14  of the first through-hole TH 1  may include a fine protruding portion ph, and the side edge E 1  of the first through-hole TH 1  may include a fine concave portion ch. The fine concave portion ch of the first through-hole TH 1  may be a fine protrusion of the metal part BML-M of the back metal layer BML. As the first through-hole TH 1  may be defined by an edge of the metal part BML-M, a fine protrusion of the metal part BML-M may be the fine concave portion ch of the first through-hole TH 1 . The term “fine” in the fine protruding portion ph and the fine concave portion ch may mean that the diameter or width of the fine protruding portion ph and the diameter or width of the fine concave portion ch may be less about ten times or more than the width of the first through-hole TH 1  or the width of the second through-hole TH 2 . For example, a diameter or width s 1  of the fine protruding portion ph and a diameter or width s 2  of the fine concave portion ch may be about 1 μm to about 20 μm. 
     The second through-hole TH 2  may include the fifth to eighth corner parts C 21 , C 22 , C 23 , and C 24 , and the second through-hole TH 2 , as illustrated in  FIG.  11   , unlike the first through-hole TH 1 , may not include a fine concave portion and/or a fine protruding portion. In another embodiment, the second through-hole TH 2 , similar to the first through-hole TH 1 , may include a fine concave portion and/or a fine protruding portion. 
     The second through-hole TH 2 , as illustrated in  FIG.  11   , may have a structure of a left-right symmetry and/or an up-down symmetry with respect to a line passing the second center O 2  as a center. As another example, the second through-hole TH 2 , as illustrated in  FIG.  12   , may not have a structure of a left-right symmetry and/or an up-down symmetry. 
     The metal part BML-M of the back metal layer BML may be between the first through-hole TH 1  and the second through-hole TH 2 , as illustrated in  FIGS.  11  and  12   , and the metal part BML-M of the back metal layer BML may include a fine hole FH. The fine hole FH may be between the first through-hole TH 1  and the second through-hole TH 2 . Although  FIG.  12    illustrates that the fine hole FH may be located adjacent to each of the corner part of the first through-hole TH 1  and the corner part of the second through-hole TH 2 , in another embodiment, the fine hole FH may be between the side edge E 1  of the first through-hole TH 1  and the side edge E 2  of the second through-hole TH 2 . 
     The term “fine” in the fine hole FH may mean that the diameter or width of the fine hole FH may be less about ten times or more, particularly, about twenty times or more, than the width of the first through-hole TH 1  or the width of the second through-hole TH 2 . For example, the diameter or width of the fine hole FH may be about 1 μm to about 10 μm. 
       FIGS.  13  to  15    each are a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure. 
     Referring to  FIGS.  13  and  14   , the back metal layer BML may include the first through-hole TH 1  and the second through-hole TH 2  having different shapes and/or sizes. The features regarding the metal part BML-M of the back metal layer BML and the structure and arrangement of the first through-hole TH 1  and the second through-hole TH 2  may be the same as those described with reference to  FIGS.  6  and  7   . In the embodiments described with reference to  FIG.  6    to  FIG.  12   , the first through-hole TH 1  may be approximately a cross type, whereas the first through-hole TH 1  of  FIGS.  13  to  15    may be approximately a rhombus type. 
     Referring to  FIG.  13   , the first through-hole TH 1  may include the first to fourth corner parts C 11 , C 12 , C 13 , and C 14 , which may be disposed in the left, right, up, and down directions from the first center O 1 , and the second through-hole TH 2  may include the fifth to eighth corner parts C 21 , C 22 , C 23 , and C 24 , which may be disposed in the left, right, up, and down directions from the second center O 2 . The first through-hole TH 1  and the second through-hole TH 2  may be disposed neighboring each other. For example, as described above, the side edge E 1  of the first through-hole TH 1  and the side edge E 2  of the second through-hole TH 2  may be disposed adjacent to each other, and the corner parts of the first through-hole TH 1  and the corner parts of the second through-hole TH 2  may be disposed adjacent to each other. 
     In the first through-hole TH 1  and the second through-hole TH 2  of  FIG.  14   , as described above with reference to  FIG.  13   , each may include corner parts, and at least one of the first through-hole TH 1  and the second through-hole TH 2  may include a fine protruding portion and/or a concave portion. 
     In an embodiment, as illustrated in  FIG.  14   , the first through-hole TH 1  may include the fine protruding portion ph located at the corner part, and the second through-hole TH 2  may include the concave portion (hereinafter, the fine concave portion ch) located at the side edge E 2 . The fine concave portion ch of the second through-hole TH 2  may be a portion of the metal part BML-M of the back metal layer BML protruding toward the second through-hole TH 2 , as described above. The diameter or width s 1  of the fine protruding portion ph and the diameter or width s 2  of the fine concave portion ch may be selected within a range of about 1 μm to about 20 μm. 
     Although  FIG.  14    illustrates that the side edge E 1  of the first through-hole TH 1  and the side edge E 2  of the second through-hole TH 2  each include an uneven part (e.g., irregular unevenness), in another embodiment, at least one of the side edge E 1  of the first through-hole TH 1  and the side edge E 2  of the second through-hole TH 2  may include a smooth curve. In an embodiment,  FIG.  15    illustrates that the side edge E 1  of the first through-hole TH 1  includes a smooth curve and the side edge E 2  of the second through-hole TH 2  includes an uneven part (e.g., irregular unevenness). 
       FIGS.  16  to  18    are schematic plan views of an excerpt of a metal layer of a display device according to an embodiment of the disclosure. 
     Referring to  FIGS.  16  and  17   , the first through-hole TH 1  and/or the second through-hole TH 2  may include the fine protruding portion ph and the fine concave portion ch. 
     Referring to  FIGS.  16  and  17   , the corner parts of the first through-hole TH 1  may include the fine protruding portion ph and the fine concave portion ch, and the second through-hole TH 2  may include the fine protruding portion ph and the fine concave portion ch. The side edge E 2  of the second through-hole TH 2 , as illustrated in  FIG.  16   , may include fine protruding portions as the fine protruding portion ph and the fine concave portion ch between the neighboring fine protruding portions ph. 
     The fine hole FH may be disposed between the first through-hole TH 1  and the second through-hole TH 2 , as illustrated in  FIG.  17   . For example, the fine hole FH may be disposed adjacent to each of the four corner parts of the second through-hole TH 2 . 
     In  FIGS.  16  and  17   , the first through-hole TH 1  and the second through-hole TH 2  may have a left-right symmetry and/or an up-down symmetry with respect to each center. In another embodiment, referring to  FIG.  18   , the first through-hole TH 1  and the second through-hole TH 2  may not have a left-right symmetry and/or an up-down symmetry with respect to each center. For example, the shapes of at least two corner parts selected from the first to fourth corner parts C 11 , C 12 , C 13 , and C 14  of the first through-hole TH 1  may be different from one another. 
     In an embodiment, as illustrated in  FIG.  18   , the shapes of the first to fourth corner parts C 11 , C 12 , C 13 , and C 14  of the first through-hole TH 1  may be different from one another. Although each of the first to fourth corner parts C 11 , C 12 , C 13 , and C 14  may include the fine protruding portion ph and/or the fine concave portion ch, specific arrangements, locations, and/or widths thereof may be different from one another, and accordingly, the shapes of the first to fourth corner parts C 11 , C 12 , C 13 , and C 14  may be different from one another. 
     Similarly, the shapes of the fifth to eighth corner parts C 21 , C 22 , C 23 , and C 24  of the second through-hole TH 2  may be different from one another. One or more of the fifth to eighth corner parts C 21 , C 22 , C 23 , and C 24  may include the fine protruding portion ph and/or the fine concave portion ch. The shapes of the fifth to eighth corner parts C 21 , C 22 , C 23 , and C 24  may be different from one another according to whether the fifth to eighth corner parts C 21 , C 22 , C 23 , and C 24  include the fine protruding portion ph and the fine concave portion ch, or according to a specific arrangement in case the fifth to eighth corner parts C 21 , C 22 , C 23 , and C 24  include the fine protruding portion ph or the fine concave portion ch. 
     According to the embodiments described with reference to  FIGS.  6  to  18   , the side edge E 1  of the first through-hole TH 1  and the side edge E 2  of the second through-hole TH 2  may be disposed adjacent to each other, and the corner parts of the first through-hole TH 1  and the corner parts of the second through-hole TH 2  may be disposed adjacent to each other. However, the disclosure is not limited thereto. In another embodiment, in the first through-hole TH 1  and the second through-hole TH 2 , the side edge E 1  of the first through-hole TH 1  and the corner parts of the first through-hole TH 1  may be disposed adjacent to each other. 
       FIG.  19    is a schematic plan view of an excerpt of a metal layer of a display device according to an embodiment of the disclosure. 
     According to the embodiments described with reference to  FIGS.  6  to  18   , the first through-holes TH 1  apart from each other may be arranged to surround the second through-hole TH 2 , but the disclosure is not limited thereto. Referring to  FIG.  19   , the second through-hole TH 2  may be entirely surrounded by the first through-hole TH 1 . 
     The first through-hole TH 1  may have a mesh structure extending in the first direction, for example, the y direction, and the second direction, for example, the x direction, and multiple metal parts BML-M may be spaced apart from each other in an island type. The second through-hole TH 2  may be apart from the first through-hole TH 1  with the metal part BML-M therebetween, and the second through-hole TH 2  may be disposed at a location corresponding to the center of the metal part BML-M. The side edge of each of the first through-hole TH 1  and/or the second through-hole TH 2  may have an uneven part (e.g., irregular unevenness), as described above. 
     The back metal layer BML having the structure according to the embodiments described with reference to  FIGS.  6  to  19    may reduce or prevent diffraction of light incident on a component through the back metal layer BML. 
     A line spread function (LSF) may be checked by irradiating a line light source to the back metal layer BML having the above-described structure. In a graph regarding data related to the above-described LSF, for example, light intensity to a location, a ratio of the second peak to the first peak was searched for, and the value was found to be about 5% or less, and thus it may be checked that the diffraction of light incident on a component through the back metal layer BML having the above-described structure may be reduced or prevented. It may be checked that the ratio of the second peak to the first peak of the LSF being about 5% or less may be about 50% when converted to a modulation transfer function (MTF). 
       FIG.  20    is a schematic cross-sectional view of a part of a display device according to an embodiment of the disclosure. 
     Referring to  FIG.  20   , the substrate  100  may have a multilayer structure. The substrate  100  may include the first base layer  101 , the first barrier layer  102 , the second base layer  103  and the second barrier layer  104 , which may be sequentially stacked on each other, and detailed materials thereof may be the same as those described above with reference to  FIG.  2 D . Although  FIG.  20    illustrates that the substrate  100  has the above-described multilayer structure, in another embodiment, the substrate  100  may be formed in a single layer like a glass material. 
     The buffer layer  111  may reduce or prevent the intrusion of foreign materials, moisture, or external air from the lower portion of the substrate  100  and may provide a planarized surface on the substrate  100 . The buffer layer  111  may include an inorganic insulating material such as a silicon oxide, a silicon oxynitride, and a silicon nitride, and may have a single layer or multilayer structure including the above-described material. 
     The back metal layer BML may be disposed between the substrate  100  and the buffer layer  111 . The back metal layer BML may include the through-hole TH corresponding to the transmission area TA. The back metal layer BML may include conductive metal such as aluminum (AI), platinum (Pt), palladium (Pd), silver (Ag), magnesium (Mg), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), calcium (Ca), molybdenum (Mo), titanium (Ti), tungsten (W), and/or copper (Cu). The back metal layer BML may have a flat structure as described above with reference to  FIGS.  6  to  19   , and in  FIG.  20   , the through-hole TH of the back metal layer BML may correspond to the first through-hole TH 1  or the second through-hole TH 2 , which is described with reference to  FIGS.  6  to  19   . 
     The back metal layer BML may be electrically connected to the connection line CL. The connection line CL may be electrically connected to a gate electrode, a source electrode, or a drain electrode of the thin film transistor TFT, or electrically connected to any one capacitor plate of the storage capacitor Cst that is described later. As another example, the connection line CL may be electrically connected to the driving voltage line PL of  FIG.  4   . The back metal layer BML may be electrically connected by the connection line CL to the gate electrode, the source electrode, or the drain electrode of the thin film transistor TFT, to any one capacitor plate of the storage capacitor Cst, or to the driving voltage line PL. The back metal layer BML connected to the connection line CL may protect the thin film transistor TFT from the external static electricity or enhance the performance of the thin film transistor TFT. 
     The pixel circuit PC including the thin film transistor TFT and the storage capacitor Cst may be disposed on the buffer layer  111 . The thin film transistor TFT may include the semiconductor layer Act, the gate electrode GE overlapping a channel region of the semiconductor layer Act, and the source electrode SE and the drain electrode DE respectively connected to a source region and a drain region of the semiconductor layer Act. A gate insulating layer  112  may be provided between the semiconductor layer Act and the gate electrode GE, and a first interlayer insulating layer  113  and a second interlayer insulating layer  115  may be disposed between the gate electrode GE and the source electrode SE or between the gate electrode GE and the drain electrode DE. 
     The storage capacitor Cst may be disposed overlapping the thin film transistor TFT. The storage capacitor Cst may include a first capacitor plate Cst 1  and a second capacitor plate Cst 2  that overlap each other. In some embodiments, the gate electrode GE of the thin film transistor TFT may include the first capacitor plate Cst 1  of the storage capacitor Cst. The first interlayer insulating layer  113  may be disposed between the first capacitor plate Cst 1  and the second capacitor plate Cst 2 . 
     The semiconductor layer Act may include polysilicon. In some embodiments, the semiconductor layer Act may include amorphous silicon. In some embodiments, the semiconductor layer Act may include an oxide of at least one material selected from the group consisting of indium (In), gallium (Ga), stannum (Sn), zirconium (Zr), vanadium (V), hafnium (Hf), cadmium (Cd), germanium (Ge), Cr, Ti, and zinc (Zn). The semiconductor layer Act may include the channel region, and the source region and the drain region where impurities may be doped. 
     The gate insulating layer  112  may include an inorganic insulating material such as a silicon oxide, a silicon oxynitride, and a silicon nitride, and may have a single layer or multilayer structure including the above-described material. 
     The gate electrode GE or the first capacitor plate Cst 1  may include a low resistance conductive material such as Mo, Al, Cu, and/or Ti, and may have a single layer or multilayer structure having the above-described material. 
     The first interlayer insulating layer  113  may include an inorganic insulating material such as a silicon oxide, a silicon oxynitride, and a silicon nitride, and may have a single layer or multilayer structure including the above-described material. 
     The second capacitor plate Cst 2  may include Al, Pt, Pd, Ag, Mg, Au, Ni, Nd, Ir, Cr, Ca, Mo, Ti, W, and/or Cu, and may have a single layer or multilayer structure including the above-described material. 
     The second interlayer insulating layer  115  may include an inorganic insulating material such as a silicon oxide, a silicon oxynitride, and a silicon nitride, and may have a single layer or multilayer structure including the above-described material. 
     The source electrode SE or the drain electrode DE may include Al, Pt, Pd, Ag, Mg, Au, Ni, Nd, Ir, Cr, Ca, Mo, Ti, W, and/or Cu, and may have a single layer or multilayer structure including the above-described material. For example, the source electrode SE or the drain electrode DE may have a triple layer structure of a titanium layer/an aluminum layer/a titanium layer. 
     A planarization insulating layer  117  may include a material that may be different from the material of at least one inorganic insulating layer  116  disposed under the planarization insulating layer  117 , for example, the gate insulating layer  112 , the first interlayer insulating layer  113 , and the second interlayer insulating layer  115 . The planarization insulating layer  117  may include an organic insulating material such as acryl, benzocyclobutene (BCB), polyimide, hexamethyldisiloxane (HMDSO), or a combination thereof. 
     A pixel electrode  221  may be formed on the planarization insulating layer  117 . The pixel electrode  221  may be electrically connected to the thin film transistor TFT via a contact hole formed in the planarization insulating layer  117 . 
     The pixel electrode  221  may include a reflective film including Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, or a compound thereof. The pixel electrode  221  may include the reflective film including the above-described material and a transparent conductive film disposed above and/or below the reflective film. The transparent conductive film may include indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium oxide (In 2 O 3 ), indium gallium oxide (IGO), aluminum zinc oxide (AZO), or a combination thereof. In an embodiment, the pixel electrode  221  may have a tri-layer structure of an ITO layer/an Ag layer/an ITO layer that may be sequentially stacked on each other. 
     A pixel defining film  119  may cover the edge of the pixel electrode  221 , and may include a through-hole  119 TH that exposes the center of the pixel electrode  221 . The pixel defining film  119  may include an organic insulating material such as BCB, polyimide, HMDSO, or a combination thereof. The through-hole  119 TH of the pixel defining film  119  may define an emission area EA, and red, green, or blue light may be emitted through the emission area EA. The area or width of the emission area EA may define the area or width of a pixel. 
     A spacer  121  may be formed on the pixel defining film  119 . The spacer  121  may prevent layers below the spacer  121  from being damaged by a mask in a process of forming an intermediate layer  222  that is described later. The spacer  121  and the pixel defining film  119  may include a same material. 
     The intermediate layer  222  may include a light-emitting layer  222   b  overlapping the pixel electrode  221 . The light-emitting layer  222   b  may include an organic material. The light-emitting layer  222   b  may include a polymer organic material or a low molecular weight organic material that emits light of a certain color. The light-emitting layer  222   b  may be formed through a deposition process using a mask, as described above. 
     A first functional layer  222   a  and a second functional layer  222   c  may be disposed above and/or below the light-emitting layer  222   b.    
     The first functional layer  222   a  may be a single layer or multilayer. For example, in case the first functional layer  222   a  may be formed of a polymer material, the first functional layer  222   a  may be formed of poly-(3,4)-ethylene-dihydroxy thiophene (PEDOT) or polyaniline (PANI), as a hole transport layer (HTL) that may be a single layer structure. In case the first functional layer  222   a  may be formed of a low molecular weight material, the first functional layer  222   a  may include a hole injection layer (HIL) and the HTL. 
     The second functional layer  222   c  may be optional. For example, in case the first functional layer  222   a  and the light-emitting layer  222   b  may be formed of a polymer material, the second functional layer  222   c  may be formed. The second functional layer  222   c  may be a single layer or multilayer. The second functional layer  222   c  may include an electron transport layer (ETL) and/or an electron injection layer (EIL). 
     Each of the first functional layer  222   a  and the second functional layer  222   c  may be formed as a single body to largely cover the display area. As illustrated in FIG.  20 , the first functional layer  222   a  and the second functional layer  222   c  may be integrally formed across the display area. 
     A counter electrode  223  may be formed of a conductive material having a relatively low work function. For example, the counter electrode  223  may include a (semi-) transparent layer including Ag, Mg, Al, Ni, Cr, lithium (Li), Ca, or an alloy thereof. As another example, the counter electrode  223  may further include a layer such as ITO, IZO, ZnO, or In 2 O 3  on the (semi-) transparent layer including the above-described material. In an embodiment, the counter electrode  223  may include Ag, Mg, or a combination thereof. The counter electrode  223  may include a fourth hole  223 H located in the transmission area TA, and may be integrally formed across the display area. 
     A stack structure of the pixel electrode  221 , the intermediate layer  222 , and the counter electrode  223 , which may be sequentially stacked on each other, may form a light-emitting diode, for example, the organic light-emitting diode OLED. The display layer  200  including the pixel circuit PC, the insulating layers, and the organic light-emitting diode OLED may be covered by the thin film encapsulation layer  300 A. 
     The thin film encapsulation layer  300 A may include the organic encapsulation layer  320  between the first and second inorganic encapsulation layers  310  and  330 . 
     The first and second inorganic encapsulation layers  310  and  330  each may include one or more inorganic insulating materials. The inorganic insulating material may include aluminum oxide, titanium oxide, tantalum oxide, hafnium oxide, zinc oxide, silicon oxide, silicon nitride, and/or silicon oxynitride. The first and second inorganic encapsulation layers  310  and  330  may be formed by a chemical vapor deposition method. 
     The organic encapsulation layer  320  may include a polymer-based material. The polymer-based material may include acryl-based resin, epoxy-based resin, polyimide, polyethylene, or a combination thereof. For example, the organic encapsulation layer  320  may include acryl-based resin, for example, polymethyl methacrylate or polyacryl acid. The organic encapsulation layer  320  may be formed by curing a monomer or coating a polymer. 
     As the second display area DA 2  may include the transmission area TA, FIG.  20  illustrates that two pixel circuits PC and two organic light-emitting diodes OLED may be disposed adjacent to each other with the transmission area TA therebetween. 
     The insulating layer IL on the substrate  100 , for example, at least one of the inorganic insulating layer  116  and the planarization insulating layer  117 , and the pixel defining film  119  may include a hole corresponding to the transmission area TA. At least one inorganic insulating layer  116  may include any one or more selected from the gate insulating layer  112 , the first interlayer insulating layer  113 , and the second interlayer insulating layer  115 . 
     At least one of a first hole  116 H of the inorganic insulating layer  116 , a second hole  117 H of the planarization insulating layer  117 , and a third hole  119 H of the pixel defining film  119  may overlap each other in the transmission area TA. The counter electrode  223  may include the fourth hole  223 H located in the transmission area TA, and the fourth hole  223 H may overlap the first hole  116 H, the second hole  117 H, and the third hole  119 H. The first hole  116 H may have a shape of a through-hole that penetrates a stack body of the gate insulating layer  112 , the first interlayer insulating layer  113 , and the second interlayer insulating layer  115  or a shape of a blind-hole in which the above-described stack body may be partially removed in a thickness direction. Each of the second hole  117 H, the third hole  119 H, and the fourth hole  223 H may have the shape of a through-hole. 
     Each of the buffer layer  111  and the second barrier layer  104  may not include a hole located in the transmission area TA. For example, as illustrated in  FIG.  20   , the buffer layer  111  and the second barrier layer  104  may cover the transmission area TA. In some embodiments, the buffer layer  111  and/or the second barrier layer  104  may include a hole located in the transmission area TA. 
     The sizes or widths of the first hole  116 H, the second hole  117 H, the third hole  119 H, and the fourth hole  223 H may be different from each other. Although  FIG.  20    illustrates that the width of the first hole  116 H may be substantially the same as the width of the through-hole TH of the back metal layer BML, the disclosure is not limited thereto. In another embodiment, the width of the first hole  116 H may be greater or less than the width of the through-hole TH of the back metal layer BML. 
     Although  FIG.  20    illustrates that the thin film encapsulation layer  300 A may be disposed on the organic light-emitting diode OLED, in another embodiment, the encapsulation substrate  300 B of  FIG.  2 C  may be disposed on the organic light-emitting diode OLED. Although  FIG.  20    illustrates a sectional structure in the second display area DA 2 , the organic light-emitting diode OLED and the pixel circuit PC electrically connected to the organic light-emitting diode OLED may be disposed in the first display area DA 1 , and the structure may be the same as the structure of the organic light-emitting diode OLED and the pixel circuit PC, which are described with reference to  FIG.  20   . 
     The embodiments of the disclosure may provide a display panel which may provide a high quality image, and the diffraction of light that a component receives may be prevented. The effect is exemplary, and the scope of the disclosure is not limited thereby. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims, including any equivalents.