Abstract:
A display device that increases visibility and that reduces the entire thickness of the device and is suitable for mobile appliances and other applications. The display device includes a display panel that has a display area and a non-display area, a transparent protective unit that is positioned at the front of the display panel, an adhesive layer that is formed between the display area and the transparent protective unit to attach the transparent protective unit to the display panel, an adhesive tape that is positioned between the non-display area and the transparent protective unit while enclosing the adhesive layer, and a bezel that is coupled to the display panel at the rear of the display panel. The adhesive tape forms at least one opening.

Description:
CLAIM OF PRIORITY 
       [0001]    This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for DISPLAY DEVICE earlier filed in the Korean Intellectual Property Office on 9 Jan. 2008 and there duly assigned Serial No. 10-2008-0002587. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a display device. More particularly, the present invention relates to a transparent protective unit that is positioned at the front of a display panel to protect the display panel. 
         [0004]    2. Description of the Related Art 
         [0005]    Organic light emitting diode (OLED) display device use an OLED display panel to display images. The OLED display panel includes organic light emitting elements that include an anode electrode which is a hole injection electrode, an organic emission layer, and a cathode electrode which is an electron injection electrode. When the anode electrode and the cathode electrode inject holes and electrons, respectively, to the organic emission layer, excitons to which electrons and holes are coupled are generated within the organic emission layer, and light emitting is performed by energy generated when the excitons drop from an exited state to a ground state. 
         [0006]    An active matrix type of OLED display panel includes pixels on a substrate arranged in a matrix format, and a thin film transistor (TFT) as a switching element is disposed in each pixel to independently control the corresponding pixel. 
         [0007]    A display device having the OLED display panel or other display panels can be applied to small mobile appliances such as a cellular phone, a personal digital assistant (PDA), and a portable multimedia player (PMP). In this case, the display device should have excellent visibility, a small thickness, and excellent impact resistance. 
         [0008]    In a conventional display device, a lower bezel is provided at the rear of the display panel to fix and support the display panel. An upper bezel having a transparent protective unit is provided at the front of the display panel to protect the display panel. 
         [0009]    However, in a common case, the transparent protective unit is positioned apart the display panel with a predetermined gap therebetween. In this case, because light that is emitted from the display panel is emitted to the outside through the gap and the transparent protective unit, visibility is deteriorated due to a refractive index difference between the transparent protective unit and the gap and transmittance deterioration that is generated by the gap. Further, because the gap has a considerable thickness of about 0.5 mm or more, the gap functions as a detrimental element in making the display device slim. 
         [0010]    The above information disclosed in this Related Art section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention has been made in an effort to provide a display device having advantages of minimizing deterioration of visibility and reducing an entire thickness thereof to be more suitable for mobile appliances and other applications. 
         [0012]    An exemplary embodiment of the present invention provides a display device includes a display panel that has a display area and a non-display area enclosing the display area, a transparent protective unit that is positioned at the front of the display panel, an adhesive layer that is formed between the display area and the transparent protective unit to attach the transparent protective unit to the display panel, an adhesive tape that is positioned between the non-display area and the transparent protective unit while enclosing the adhesive layer and that forms at least one opening; and a bezel that is coupled to the display panel at the rear of the display panel. 
         [0013]    The adhesive layer may be made of a transparent synthetic resin material. The adhesive tape may be formed with a double-sided adhesive tape having two adhesive surfaces. The adhesive layer and the adhesive tape may have a thickness of 0.15 to 0.25 mm. The adhesive tape may form a pair of longitudinal sides and a pair of lateral sides, and an opening of the adhesive tape may be positioned at each of the pair of longitudinal sides and the pair of lateral sides. 
         [0014]    The bezel may include a bottom portion at which the display panel is placed, and a side wall that is extended toward the transparent protective unit from an edge of the bottom portion. A height of the side wall may be equal to or greater than the sum of a thickness of the display panel and a thickness of the adhesive layer. 
         [0015]    The display panel may include a front substrate and a rear substrate. A polarizing film may be positioned at an outer surface of the front substrate, and the adhesive layer may have the same refractive index as that of the transparent protective unit. A polarizing film may be positioned at an outer surface of the transparent protective unit, and the adhesive layer may have the same refractive index as that of the transparent protective unit and the front substrate. The display panel may be an organic light emitting diode (OLED) display panel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicated the same or similar components, wherein: 
           [0017]      FIG. 1  is an exploded perspective view of a display device according to a first exemplary embodiment of the present invention. 
           [0018]      FIG. 2  is a perspective view illustrating a coupled state of the display device that is shown in  FIG. 1 . 
           [0019]      FIG. 3  is a partial cross-sectional view of a dotted line portion that is taken along line I-I of  FIG. 2 . 
           [0020]      FIG. 4  is a partial cross-sectional view of a display device according to a second exemplary embodiment of the present invention. 
           [0021]      FIG. 5  is a schematic diagram of an organic light emitting diode (OLED) display panel. 
           [0022]      FIG. 6  is a partial cross-sectional view of an OLED display panel. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
         [0024]      FIG. 1  is an exploded perspective view of a display device according to a first exemplary embodiment of the present invention, and  FIG. 2  is a perspective view illustrating a coupled state of the display device that is shown in  FIG. 1 . 
         [0025]    Referring to  FIGS. 1 and 2 , a display device  100  of the present exemplary embodiment includes a display panel  12  that displays an image, a bezel  14  that is disposed at the rear of the display panel  12  to receive and fix the display panel  12  and various parts, and a transparent protective unit  16  that is disposed at the front of the display panel  12  to protect the display panel  12 . 
         [0026]    The display panel  12  may be an organic light emitting diode (OLED) display panel. Alternatively, the display panel  12  may be another display panel, for example a liquid crystal display panel. The display panel  12  is electrically connected to a printed circuit board (PCB)  20  through a flexible printed circuit board (FPCB)  18 . In  FIG. 1 , for convenience, the FPCB  18  is shown to be cut, but the FPCB  18  is actually connected as shown in  FIG. 2 . 
         [0027]    Pixels, which are a basic unit of image expression, are arranged in a matrix format on a first substrate  22  of the display panel  12 , and a second substrate  24  is bonded to the first substrate  22  through a sealing member (not shown) to protect the pixels. The first substrate  22  may be a rear substrate, and the second substrate  24  may be a front substrate. 
         [0028]    As an example, in an active matrix type of OLED display panel, a pixel includes an organic light emitting element (not shown) that includes an anode electrode, an organic emission layer, and a cathode electrode, and a driving circuit (not shown) that drives the organic light emitting element. The driving circuit may be a TFT. A data line is connected to a source terminal of the TFT, and a gate line is connected to a gate terminal thereof. One of the anode electrode and the cathode electrode of the organic light emitting element is connected to a drain terminal thereof. 
         [0029]    The data line and the gate line of the TFT are connected to the PCB  20  through the FPC  18 . When an electric signal is input to the source terminal and the gate terminal of the TFT through the PCB  20 , the TFT is turned on or turned off according to the input signal to output an electric signal that is necessary for driving a pixel to the drain terminal. 
         [0030]    An integrated circuit chip  26  is mounted on the first substrate  22  to control the display panel  12 . The integrated circuit chip  26  generates timing signals for applying a data driving signal and a gate driving signal at an appropriate time. The integrated circuit chip  26  applies each of the signals to a data line and a gate line of the display panel  12 . A protective layer  28  is formed around the integrated circuit chip  26  to protect the integrated circuit chip  26 . 
         [0031]    Electronic elements (not shown) for processing a driving signal are mounted in the PCB  20 . The PCB  20  includes a connector  30  and an extension unit  32 , and the extension unit  32  transmits an outside signal that is transferred to the connector  30  to the PCB  20 . In a cellular phone, the connector  30  can be connected to a keypad. 
         [0032]    The transparent protective unit  16  that protects the display panel  12  is positioned at the front of the display panel  12 . The transparent protective unit  16  may be made of a synthetic resin material, and performs a function of protecting the display panel  12  from breaking by an external impact. 
         [0033]    A predetermined thickness of an adhesive layer  34  and an adhesive tape  36  that encloses the adhesive layer  34  are positioned between the display panel  12  and the transparent protective unit  16  to attach the transparent protective unit  16  to the display panel  12 . The adhesive layer  34  and the adhesive tape  36  protect the display panel  12  together with the transparent protective unit  16  to improve impact-resistance integrity of the display device  100 . The adhesive layer  34  may be made of a transparent synthetic resin material, and the adhesive tape  36  may be formed as a double-sided adhesive tape having two adhesive surfaces of an upper surface and a lower surface. 
         [0034]    The adhesive layer  34  is formed with the same size as that of a display area of the second substrate  24 , and is positioned at an upper part of the display area. The adhesive tape  36  is positioned at a non-display area that encloses the display area. The transparent protective unit  16  is formed with an area that is greater than that defined by outer edges of the adhesive tape  36 , for example with the same size as that of the second substrate  24 . An air gap does not exist between the display area and the transparent protective unit  16  because of the adhesive layer  34 . 
         [0035]    The adhesive layer  34  is formed with a uniform thickness on the display area, and the thickness thereof can be adjusted as needed. For example, the adhesive layer  34  can be formed with a thickness of 0.15 to 0.25 mm. If the thickness of the adhesive layer  34  is less than 0.15 mm, impact-resistance integrity thereof deteriorates, and the display panel  12  may be damaged by an external impact. If the thickness of the adhesive layer  34  exceeds 0.25 mm, because material consumption increases without increasing impact-resistance intensity, production cost may increase. 
         [0036]    The adhesive tape  36  can be formed with a uniform width, and performs a function of a guide when the adhesive layer  34  is formed. That is, the adhesive layer  34  can be formed by attaching the adhesive tape  36  to the non-display area of the second substrate  24 , and coating and pressing a liquid high polymer resin on the display area of the second substrate  24 . In this process, the adhesive tape  36  confines the high polymer resin to the inside thereof as a guide to form the adhesive layer  34 . 
         [0037]    Further, at least one opening  361  for discharging bubbles is formed in the adhesive tape  36 . The opening  361  performs a function of discharging bubbles to the outside when coating and pressing the liquid high polymer resin at the inside of the adhesive tape  36 . Therefore, because the completed adhesive layer  34  does not contain bubbles, when light that is emitted from the display panel  12  passes through the adhesive layer  34 , visibility is not deteriorated. 
         [0038]    The adhesive tape  36  may form a pair of longitudinal sides and a pair of lateral sides, and one opening  361  may be formed in each of the pair of longitudinal sides and the pair of lateral sides.  FIG. 1  illustrates, as an example, one opening  361  positioned at each of the center of a longitudinal side and the center of a lateral side of the adhesive tape  36 . The position, size, and number of openings  361  are not limited to the illustrated example, and can be variously changed. 
         [0039]    As the adhesive tape  36  performs a function of guiding the adhesive layer  34 , the thickness of the adhesive layer  34  is determined by the thickness of the adhesive tape  36 . Therefore, by forming the adhesive tape  36  at a thickness of 0.15 to 0.25 mm, the adhesive layer  34  can be formed at the same thickness. 
         [0040]    Because the adhesive layer  34  and the adhesive tape  36  have a smaller thickness than a conventional air gap (an interval between a display panel and a transparent protective unit), the adhesive layer  34  and the adhesive tape  36  contribute to slimness of the display device  100 . Further, the display panel  12  of the display device  100  can be more safely protected from an external impact that is applied to the front of the display panel  12  and an upper bezel that is generally disposed at the circumference of the transparent protective unit  16  to be coupled to the bezel  14  may be omitted, thereby simplifying the structure and manufacture thereof. 
         [0041]    The bezel  14  is positioned between the display panel  12  and the PCB  20 , and receives and fixes the display panel  12  and various parts at the inside thereof at the rear of the display panel  12 . The bezel  14  is made of a material having greater integrity than the transparent protective unit  16 . For example, the bezel  14  is made of a metal material such as stainless steel, cold rolled steel, and an aluminum-nickel-silver alloy. 
         [0042]    The bezel  14  includes a bottom portion  38  that comes in contact with the first substrate  22  of the display panel  12 , and a side wall  40  that is extended toward the transparent protective unit  16  from an edge of the bottom portion  38 . The side wall  40  has an opening  401  through which the FPCB  18  passes, and encloses and supports a side surface of the display panel  12  except for a portion at which the opening  401  is formed. 
         [0043]      FIG. 3  is a partial cross-sectional view of a dotted line portion that is taken along line I-I of  FIG. 2 . 
         [0044]    Referring to  FIG. 3 , a height of the side wall  40  of the bezel  14  is equal to or greater than the sum of a thickness of the display panel  12  and a thickness of the adhesive layer  34  or the adhesive tape  36 . Therefore, the side wall  40  encloses a side surface of the display panel  12  and the outside of the adhesive tape  36  to protect them. 
         [0045]    For example, as shown in  FIG. 3 , the height of the side wall  40  may be equal to the sum of a thickness of the display panel  12 , a thickness of the adhesive layer  34  or the adhesive tape  36 , and a thickness of the transparent protective unit  16 . In this case, the side wall  40  encloses the side surface of the display panel  12 , the outside of the adhesive tape  36 , and a side surface of the transparent protective unit  16  to support them. The shape and height of the side wall  40  are not limited to the above-described example, and can be variously changed. 
         [0046]    In this way, in the display device  100  of the present exemplary embodiment, as the adhesive layer  34  and the adhesive tape  36  are positioned between the display panel  12  and the transparent protective unit  16 , the entire thickness thereof can be reduced and impact-resistance integrity can be improved. By using the bezel  14  of the above-described structure, the display panel  12  and the transparent protective unit  16  can be firmly fixed. 
         [0047]    Further, in the present exemplary embodiment, as shown in  FIG. 3 , a polarizing film  42  is disposed at an outer surface of the transparent protective unit  16 , and the adhesive layer  34  may have the same refractive index as that of the transparent protective unit  16  and the second substrate  24  of the display panel  12 . Alternatively, in the second exemplary embodiment of the present invention as shown in  FIG. 4 , the polarizing film  42  is disposed at an outer surface of the second substrate  24 , and the adhesive layer  34  may have the same refractive index as that of the transparent protective unit  16 . 
         [0048]    In the display device  100  that is shown in  FIG. 3 , external light is reflected only from a surface of the polarizing film  42 , and external light reflection generated at an upper surface of the transparent protective unit  16 , an upper surface of the adhesive layer  34 , and an upper surface of the second substrate  24  can be eliminated. In a display device  101  that is shown in  FIG. 4 , external light reflection generated at the upper surface of the adhesive layer  34  can be eliminated. 
         [0049]    Therefore, the display devices  100  and  101  of the first and second exemplary embodiments can improve external light visibility (visibility that is measured in a condition in which external light exists the device). 
         [0050]    An organic light emitting diode (OLED) display panel, which is a kind of a display panel, is described hereinafter. 
         [0051]      FIG. 5  is a schematic diagram of an OLED display panel, and  FIG. 6  is a partial cross-sectional view of an OLED display panel and illustrates one sub-pixel area. 
         [0052]    Referring to  FIGS. 5 and 6 , in a color OLED display panel  120 , a plurality of sub-pixels  46  are disposed in a matrix format in a display area  44  of the first substrate  22 , and a scan driver  48  and a data driver  50  that drive the sub-pixels  46  are positioned at the outside of the display area  44 . 
         [0053]    Each sub-pixel  46  includes an organic light emitting element L 1  and a driving circuit, and the organic light emitting element L 1  includes an anode electrode  52 , an organic emission layer  54 , and a cathode electrode  56 . The driving circuit includes, as an example, a switching first thin film transistor (hereinafter referred to as a “first TFT”) T 1 , a driving second thin film transistor (hereinafter referred to as a “second TFT”) T 2 , and a storage capacitor Cst.  FIG. 6  shows the second TFT T 2 . 
         [0054]    The first TFT T 1  is connected to a scan line SL 1  and a data line DL 1 , and transmits a data voltage that is input from the data line DL 1  to the second TFT T 2  according to a switching voltage that is input to the scan line SL 1 . The storage capacitor Cst is connected to the first TFT T 1  and a power line VDD, and stores a voltage Vgs corresponding to a difference between a voltage that is received from the first TFT T 1  and a voltage that is supplied to the power line VDD. 
         [0055]    The second TFT T 2  is connected to the power line VDD and the storage capacitor Cst to supply an output current that is in proportion to the square of a difference between a voltage Vgs that is stored in the storage capacitor Cst and a threshold voltage Vth to an organic light emitting element L 1 , and the organic light emitting element L 1  emits light by an output current. 
         [0056]    For a display device to which the OLED display panel is applied, optical characteristics that are measured in a display device of a comparative example and display devices of Exemplary Embodiments 1 and 2 are represented in Table 1. In the display device of the comparative example, an adhesive layer is not provided and a polarizing film is attached to an outer surface of the second substrate. The display devices of Exemplary Embodiments 1 and 2 have an adhesive layer, and in Exemplary Embodiment 1, a polarizing film is attached to an outer surface of a transparent protective unit, while in Exemplary Embodiment 2, a polarizing film is attached to an outer surface of a second substrate. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Comparative 
                 Exemplary 
                 Exemplary 
               
               
                   
                 Example 
                 Embodiment 1 
                 Embodiment 2 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Luminance (cd/m 2 ) 
                 180 
                 206 
                 206 
               
               
                   
                 (100%) 
                 (114%) 
                 (114%) 
               
               
                 External light contrast 
                 1.74 
                 6 
                 2.45 
               
               
                 ratio 
               
               
                 (at 10,000 lux) 
               
               
                 External light color 
                 5.3 
                 42.6 
                 14.5 
               
               
                 representation 
               
               
                 (at 10,000 lux) 
               
               
                 Transmittance of 
                 91.8 
                 91.8 
                 91.8 
               
               
                 transparent protective 
               
               
                 unit (%) 
               
               
                 Reflectivity of 
                 7.44 
                 1 or less 
                 4.35 
               
               
                 transparent protective 
               
               
                 unit + display panel 
               
               
                 (%) 
               
               
                   
               
             
          
         
       
     
         [0057]    As described in Table 1, the display devices of Exemplary Embodiments 1 and 2 show improved results in terms of luminance, external light contrast ratio, and external light color representation, compared with the display device of the comparative example. Further, in the display device of Exemplary Embodiment 1, the external light contrast ratio and external light color representation are remarkably improved and reflectivity of a transparent protective unit and a display panel are remarkably reduced, compared with the display device of Exemplary Embodiment 2. 
         [0058]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.