Abstract:
A display device useful to create an interactive image having different sizes by employing one display panel that is allowed to emit the light toward both directions.

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. § 119 from an application entitled DISPLAY DEVICE earlier filed in the Korean Intellectual Property Office on the 7 Jun. 2007 and there duly assigned Serial No. 10-2007-0055468. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image display device, and more particularly, to varying image display devices capable of providing dual light emission. 
     2. Description of the Related Art 
     Generally, varying image display panels with dual light emission have configurations with two display panels that emit light toward top and bottom directions and that are doubly overlapped with each other. 
     Contemporary display devices with dual light emission are typically used in folding-type mobile phones.  FIG. 1  shows a perspective view of a conventional folder-type mobile phone. The folder-type mobile phone is composed of a main panel  1 A and a subpanel  1 B to realize an image with the dual light emission. At this time, the subpanel  1 B that emits the light toward the outside of the folder operates if a folder of the conventional mobile phone is close, whereas the main panel  1 A that emits the light toward the inside of the folder goes into action if a folder of the conventional mobile phone is open. 
     At this time, the subpanel  1 B is manufactured at a smaller size than the main panel  1 A. This is done for preventing use of an additional space used for attachment of the flexible printed circuit boards in which parts required for driving is installed by forming the flexible printed circuit boards around the subpanel  1 B. 
     At this time, a liquid crystal display (LCD), an organic light emitting display (OLED) and the like have been generally used as the panel used for the display device. 
     With such contemporary designs for consumer products such as folding mobile phones, if two panels are used to realize an image with dual light emission, problem occur because products must be made thick in order to accommodate both panels and their address, drive and other ancillary circuits, and the manufacturing costs of the products are higher than consumers are willing to pay. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improve dual light emitting panel and an improved process for fabricating dual light emitting panels. 
     These and other objects may be achieved with a designed to solve such drawbacks of the prior art, and therefore it is another object of the present invention is to provide a display device which is composed of one panel while realizing variable visual images having different areas presented to opposite directions. 
     One embodiment of the present invention may be achieved by providing a display device including a first light-emitting surface for displaying varying visual images toward a first direction. The display device includes a second light-emitting surface for displaying variable visual images toward the directly opposite direction of the first light-emitting surface. The second light-emitting surface includes a light emitting region and a non-light emitting region. A display panel includes a first light emitting diode that emits the light toward the first direction in its inside, and a second light emitting diode that emits the light toward the second direction; and a light shading apparatus having the light emitting region formed on the display panel and selectively intercepting the light from the light emitting region. 
     The display device constructed according to the principles of the present invention has a desired effect to display an interactive image having different sizes by employing one dual light emitting display panel. Also, if one display panel is used in the display device, the manufacturing costs may be reduced and the images on both surfaces may all be realized with a fine pitch assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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 indicate the same or similar components, wherein: 
         FIG. 1A  and  FIG. 1B  are perspective views showing a contemporary design for a mobile phone equipped with a conventional display device. 
         FIG. 2  is an exploded perspective view showing a display device constructed as one exemplary embodiment of the principles of the present invention. 
         FIG. 3A  is a cross-sectional, elevation view showing a light emitting region of the display panel shown in  FIG. 1B . 
         FIG. 3B  is a cross-sectional, elevation view showing a non-light emitting region of the display panel as shown in  FIG. 1B . 
         FIG. 4  is a circuit schematic diagram showing one exemplary embodiment of a pixel circuit in the display device constructed according to the principles of the present invention. 
         FIG. 5  is a cross-sectional, elevation view showing a light shading apparatus constructed according to the principles of the present invention, as may be applied to the mobile phone shown in  FIGS. 1A and 1B . 
         FIG. 6  is a cross-sectional view showing a non-light emitting region of the display panel in a display panel constructed as another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings,  FIG. 1A  shows a simplified representation of a contemporary folding-type mobile cellphone (e.g., a “clamshell)  5  equipped with a visual display device providing with dual light emitting displays, in an opened position, while  FIG. 1B  shows the same mobile phone  5  in its closed, or folded position. Mobile phone  5  is constructed with a main panel  1   a  and a subpanel  1   b  to realize an image with the dual light emitting panels. At this time, subpanel  1   b  that emits light toward the outside of folded mobile phone  5 , operates to display variable visual images when this contemporary mobile phone is closed with its main display panel  1   a  facing its keypad, whereas main display panel  1   a  emits light towards the inside of the mobile phone goes into action when mobile phone  5  is in an opened state as is shown in  FIG. 1A . 
     In the contemporary designs shown in  FIGS. 1A ,  1 B, subpanel  1   b  is manufactured with a smaller size and light emitting display area than main panel  1   a . This is done in order to minimize the requirement for additional space to be used to attach flexible printed circuit boards bearing the circuits required for powering, addressing and driving subpanel  1   b , by the expedient of positioning those flexible printed circuit boards around subpanel  1   b.    
     At this time, either a liquid crystal display (LCD), or an organic light emitting display (OLED) or the like, have generally been used as light emitting display panels  1   a ,  1   b  for mobile phone  5 . 
     If two display panels are used however, to construct a device equipped with dual light emitting display panels, the device is necessarily thick, and the manufacturing costs of the device tends to be higher than is comfortable for many consumers. 
     Hereinafter, certain exemplary embodiments according to the present invention will be described with reference to the accompanying drawings. Here, when a first element is described as being coupled to a second element, the first element may not only be directly coupled to the second element, but may also be indirectly coupled to the second element via a third element. Additional elements that are not essential to the complete understanding of the invention are omitted for clarity to this detailed description. Also, like reference numerals tend to refer to like elements throughout. 
     Referring now to  FIG. 2 , an exploded perspective view showing a display device constructed as one exemplary embodiment of the present invention, display device  6  includes display panel  10  and light shading apparatus  20 . 
     Display panel  10  may be constructed with organic light-emitting display panels in this embodiment. In order to realize a visual image with dual light emission in a single panel, organic light-emitting display panel  10  includes a first light-emitting surface  10   a  that emits the light toward the top surface in a general direction aligned with arrow A; and a second light-emission surface  10   b  that emits the light in a diametrically opposite direction, toward the bottom surface in a general direction aligned with arrow B. 
     At this time, the entirety of the area of first light-emission surface  10   a  is a light emitting region, and area of second light-emission surface  10   b  is divided into a light emitting region  10   c  and a non-light emitting region  10   d , wherein the second light-emission surface  10   b  does not emit light toward the non-light emission region  10   d . Non-light emission region  10   d , is formed to ensure a space to accommodate flexible printed circuit boards (not shown) coupled to the display panel  10 . 
     That is to say, if the entirety of the major surface areas of first light-emitting surface  10   a  and second light-emitting surface  10   b  are both completely light emitting surfaces, the accompanying flexible printed circuit boards necessary to address and drive display device  6  to present varying visual images on both first and second light emitting surfaces  10   a ,  10   b  must be fitted along an edge  10   e  of display panel  10  within a separate area of the consumer product; this causes a deterioration of the quality, ornamental and visual presentation of the product. Consequently, disposition of these and their flexible printed circuit board along edge  10   e  detracts from the compactness of the consumer product and from its slim appearance, and thus reduces the marketability of the consumer product. This is why, in contemporary designs for consumer products, the flexible printed circuit boards must overlie non-light emitting region  10   d , B, of second light-emitting surface  10   b.    
       FIG. 3A  is a cross-sectional, elevation view showing an organic light-emitting display panel corresponding to light emitting region  10   c  of second light-emission surface  10   b , and  FIG. 3B  is a cross-sectional, elevation view showing one preferred embodiment of an organic light-emitting display panel corresponding to non-light emitting region  10   d , B, of second light-emission surface  10   b.    
     First, the display panel of the organic light-emitting display device corresponding to the light emitting region  10   c , B, of the second light-emitting surface  10   b  includes a plurality of dual light emitting pixels. 
     Each dual light emitting pixel includes a first light emitting diode  30  that may emit light from the top surface; and a second light emitting diode  40  that may emit light from the bottom surface. 
     First light emitting diode  30  includes first lower electrode (i.e., anode electrode)  31 , a first light-emitting layer  36  formed on first lower electrode  31 , and first upper electrode (i.e., cathode electrode)  37  formed on first light-emitting layer  36 . More particularly, multi-layered first anode electrode  31  includes lower conductive layer  32 , and reflective conductive layer  33  formed on lower conductive layer  32 . Here, lower conductive layer  32  is formed of transparent, conductive metal oxides to form an electrically conductive layer  32  that is transparent to light within the visible spectrum, such as, by way of example, ITO (indium tin oxide) and IZO (indium zinc oxide) and the like, and the reflective conductive layer  33  is formed of silver (Ag), aluminum (Al), silver alloys and aluminum alloys. Generally, lower conductive layer  32  is formed on substrate  11  so as to improve adhesivity between reflective conductive layer  33  and its lower layer conductive layer  32 . 
     First light-emitting layer  36  emits light by forming excitons through recombination of electrons and holes supplied from first anode electrode  31  and first cathode electrode  37 , respectively. First light-emitting layer  36  may include at least one layer (not shown) selected from among a hole injection layer, a hole transporting layer, an electron transporting layer, and an electron injection layer so as to improve the injection of the electrons and holes. First cathode electrode  37  may be formed of compounds selected from among Al, Ca, MgAg, Ag, etc. In order to enhance transmittance of cathode electrode  37 , MgAg or Ca may be deposited at a thickness of approximately 100 Å, and a transparent electrode such as IZO may be formed as an auxiliary layer (not shown) on the MgAg or Ca layer. 
     The second light emitting diode  40  includes a second anode electrode  41  formed on the substrate  11 ; a second light-emitting layer  46  formed on the second anode electrode  41 ; and a first cathode electrode  47  formed on the second light-emitting layer  46 . First light emitting diode  30  and second light emitting diode  40  are electrically isolated from each other because second anode electrode  41  is formed to be spaced apart by a predetermined distance form first anode electrode  31 . Second anode electrode  41  is formed of transparent conductive metal oxides, for example ITO, IZO and the like to form an electrically conductive layer  41  that is transparent to light within the visible spectrum, such as, by way of example, and the second cathode electrode  47  are formed of compounds selected from Al, Ca, MgAg, Ag, etc. In order to enhance transmittance of cathode electrode  47 , MgAg or Ca may also be deposited at a thickness of approximately 100 Å, and a transparent electrode such as IZO may be formed as an auxiliary layer (not shown) on the MgAg or Ca layer. 
     An upper auxiliary electrode layer  49  covering at least second light-emitting layer  46  is formed on second cathode electrode  47 . Compounds such as Al, Ag, Al alloys, Ag alloys and the like may be used in the formation of upper auxiliary electrode layer  49  to prevent light emanating from bottom light emitting diode  40  leaking to the top surface, and to enhance the reflectance in the bottom surface. Second cathode electrode  47  constituting the second light emitting diode  40  and the first cathode electrode  37  constituting the first light emitting diode  30  are not formed separately and are used as a common electrode. Second light-emitting layer  46  emits light in the same manner as in the above-mentioned first light emitting layer  36 . 
     Meanwhile, first and second transistors  38 ,  48  are electrically coupled to the first light emitting diode  30  and the second light emitting diode  40  via multi-layered anode electrode  31  and transparent second anode electrode  41 . At this time, first and second transistors  310 ,  320  are formed on lower regions of the light emitting element  38 ,  48  on the substrate  1 , respectively. At this time, preferably, no other elements are arranged in the lower region of second light emitting diode  40  so as to improve efficiency of the bottom light emission. 
     As configured above, an electrical power source may be separately applied to first light emitting diode  30  and second light emitting element  40 , or an electrical power source may be applied to first and second light emitting diodes  30 , 40  at the same time. If user applies an electrical power source to first light emitting element  30 , only first light emitting diode  30  emits light, and therefore an image is displayed on the top surface since light is emitted through first cathode electrode  37  in the configuration of first light emitting diode  30 . Meanwhile, if the user applies an electrical power source to second light emitting diode  40 , only second light emitting diode  40  emits light, and therefore an image is displayed on the bottom surface since light is emitted through second anode electrode  41  in the configuration of second light emitting element  40 . 
     Reference numerals  12 ,  13 ,  14 ,  15 ,  16  refer to a buffer layer  12 , a gate insulating layer  13 , an interlayer insulating layer  14 , a passivation layer  15  and a pixel definition layer  16 , respectively. 
     Next, display panel  10  of the organic light-emitting display device  6  corresponding to non-light emission region  10   d  of second light-emission surface  10   b  is identical to the light emission region in the aspect of the configuration of the inside light emitting elements, but further includes a light-shading layer  50  formed on a light emission path of second light emitting diode  40 . Accordingly, the light is intercepted from emitting from the non-light emission region  10   d  and is thereby prevented from emanating at the bottom surface. Light-shading layer  50  may be, for example, formed of a liquid crystal or similar structure. 
       FIG. 4  is a circuit schematic diagram showing one preferred embodiment of a dual light emission pixel circuit of the above-mentioned display panel, when constructed with a first pixel circuit I and a second pixel circuit II. 
     First pixel circuit I may be constructed with a first transistor (e.g., a switching transistor) M 1 , a capacitor C 1  and a second transistor (e.g., a driving transistor) M 2 , and second pixel circuit II may be constructed with a first transistor (e.g., a switching transistor) M 7 , a capacitor C 2  and a second transistor (e.g., a driving transistor) M 8 . 
     Here, first transistor M 1  is electrically coupled to scan line Sn- 1  and first data line Dm- 1 , capacitor C 1  is coupled to first transistor M 1  to charge a voltage corresponding to a first data signal applied from first data line Dm- 1 . Second transistor M 2  has a gate electrode coupled to capacitor C 1 , and one of the source or drain electrodes electrically coupled to first light emitting element  30 . 
     In second pixel circuit II, the gate electrode of first transistor M 7  is electrically coupled to scan line Sn- 1  and either the source or drain electrode is coupled to second data line Dm. Capacitor C 2  is coupled to the other one of the source or drain electrode of first transistor M 7  to charge a voltage corresponding to a second data signal applied from second data line Dm. Second transistor M 8  has a gate electrode coupled to capacitor C 2 , and one of its source or drain electrodes electrically coupled to second light emitting diode  40 . First pixel circuit I and second pixel circuit II as configured above may be neighboring along at least one side. 
     In the configuration of the above-mentioned first pixel circuit I, the top light emission of the first light emitting diode  33  is performed according to the following driving principle. First, if switching transistor M 1  is turned on by the scan signal applied through scan line Sn- 1 , a data signal is supplied to first light emitting diode  30  through first data line Dm- 1 . At this time, a voltage is stored in capacitor C 1 ; the magnitude of the voltage being obtained by subtracting a voltage level of the data signal from a voltage level of the light emitting element&#39;s power source. And, the voltage stored in capacitor C 1  is applied to a gate electrode of driving transistor M 2 , and therefore a constant electric current flows from a source electrode to a drain electrode of driving transistor M 2 . As a result, an electric current flows in the first light emitting diode  30 , and then first light emitting diode  30 , shown in  FIGS. 3A ,  3   b  and in  FIG. 4  as a top-light emitting element, emits light. At this time, first light emitting diode  30  is a top light emitting element that emits the light generated in first light emitting layer  36 , through the first cathode electrode  37 . 
     In second pixel circuit II, the principle of operation by second light emitting diode  40  is also identical to the light emission principle for first light emitting diode  30  in first pixel circuit I. First, if a scan signal is applied to switching transistor M 7  through the scan line Sn- 1  and switching transistor M 7  is turned on, a data signal is supplied to second light emitting diode  40  through second data line Dm. At this time, a voltage is stored in capacitor C 2 , the magnitude of the voltage that is stored is obtained by subtracting a voltage level of the data signal from a voltage level of the light emitting diode&#39;s power source. And, the voltage stored in the capacitor C 2  is applied to a gate electrode of driving transistor M 8 , and therefore, a constant electric current flows from a source electrode to a drain electrode of driving transistor M 8 . As a result, an electric current flows in second light emitting diode  40 , and then second light emitting diode  40  emits light as a bottom light emitting diode. At this time, second light emitting diode  40  is a bottom light emitting diode that emits the light, which is generated in the second light-emitting layer  46  by the upper auxiliary electrode layer  49  formed on cathode electrode  47 , toward second anode electrode  41 . 
     At this time, first pixel circuit I and second pixel circuit II share power source line ELVdd and scan line Sn, and have different data lines Dm- 1 , Dm coupled to their respective light emitting diodes  30 ,  40 . 
     Accordingly, by virtue of employing a single integrated circuit using different data lines Dm- 1 , Dm coupled to their respective light emitting diodes  30 ,  40 , first pixel circuit I and second pixel circuit II and their respective first light emitting diode  30  and second light emitting diode  40  may separately emit light according to their selection by a user, or alternatively, may emit light at the same time, by employing one driving integrated circuit (i.e., “IC”). That is to say, users may separately display an image in the top and bottom surfaces at the same time, or alternatively, may simultaneously display different visual images on oppositely directed (i.e., top and bottom) display panels. 
     In the foregoing descriptions of these exemplary embodiments, pixel circuits are described with two transistors and one capacitor coupled to one light emitting diode, but implementation of the principles of the present invention are not particularly limited thereto. And the light emitting diode may further include a compensation circuit which compensates for a threshold voltage and a voltage drop. 
     Light shading apparatus  20  is installed in the light emission region  10   c  of second light-emission surface  10   b  (i.e., the bottom surface). Light shading apparatus  20  selectively intercepts the light emitted from the light emission region. For example, if a folding cover, or lid, of a folding-type mobile phone is closed, a user will be enabled to see a visible image on the second light-emission surface  10   b , and therefore the light shading apparatus  20  does not need to intercept the light emitted from the display panel  10 . Meanwhile, if a cover, or lid, of a folding type mobile phone is open, the user will be able to see an image on first light-emission surface  10   a  (i.e., the top surface), and therefore light shading apparatus  20  may intercept the light and may reflect the light toward first light-emitting surface in order to display an image of the first light-emission surface  10   a  clearly. At this time, light shading apparatus  20  may include a liquid crystal layer, an E-paper or an electrochromic layer. 
       FIG. 5  shows a cross-sectional view of a light shading apparatus  20  using a liquid crystal layer. Light shading apparatus  20  is arranged so that first substrate  23  can face the second substrate  27 . In the construction of light shading apparatus  20 , first transparent electrode  24  and second transparent electrode  26  are formed in inner surfaces of first substrate  23  and second substrate  27 , respectively. And, liquid crystal layer  25  is interposed between first transparent electrode  24  and second transparent electrode  26 , and first polarizer  22  and second polarizer  28  are further provided respectively, on opposite outside surfaces of first substrate  23  and second substrate  27 . 
     At this time, light shading apparatus  20  may selectively intercept, or alternatively, transmit light generated by the integrated circuit as a signal that applied to the transparent electrode  24  and the second transparent electrode  26 . 
     For example, a light source may be passed through first polarizer  22  when first polarizer  22  is in a turned-off state, thereby to transmit only first linearly polarized light matching with a first polarizing axis, and a polarizing state of the first linearly polarized light may be changed into that of a second linearly polarized light while passing through the 90° twisted liquid crystal layer  25 , and the second linearly polarized light may match with a transmission axis of second polarizer  28  to pass through a substrate as it is, thereby to transmit the light. 
     Also, a light source may be passed through first polarizer  22  while first polarizer is in its turned-on state, thereby to transmit only a first linearly polarized light matching with a first polarizing axis, and the first linearly polarized light may transit liquid crystal layer  25  arranged vertically to the substrate as it is, but intercept the light since the first linearly polarized light is intercepted by the second polarizer  28 . 
     Alternatively, the display panel of the organic light-emitting display device, which corresponds to the non-light emission region  10   d  of the second light-emission surface  10   b  in display panel  10 , may be composed only of first light emitting diodes  30  that emit light toward the top surface, unlike the above-mentioned embodiment. For example,  FIG. 6  shows a section in which non-light emission region  10   d  of second light-emission surface  10   b  in the display panel is composed only of the first light emitting diodes  30 . Accordingly, the light which is emitted toward the bottom surface is intercepted in the non-light emission region  10   d , and this embodiment may have the same effect as in the first embodiment. 
     The description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention as apparent to those skilled in the art. For example, the inside structure of the display panel, the materials of the light-shading layer, the inside configuration of the light shading apparatus, etc. may be changed or modified without departing from the spirit and scope of the invention. 
     Although exemplary embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes might be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.