Patent Publication Number: US-2007096612-A1

Title: Flat display panel

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention is related to a flat display panel, and more particularly, to a flat display panel comprising a black matrix pattern and a brightness enhancement sheet; wherein in each pixel region an area ratio of the black matrix pattern to the pixel region is between 70% and 95%.  
      2. Description of the Prior Art  
      An organic light emitting display device is one kind of electroluminescene (EL) display devices. The organic light emitting display has the advantages of high brightness, rapid reaction time, low power consumption, and wide viewing angle. It may replace liquid display devices and plasma display devices and become the main stream of the new generation flat display devices.  
      However, the internal part of the organic light emitting display device has conducting patterns or electrodes, which are made from metal. Thus, the organic light emitting display device has a problem of poor contrast. Therefore, the organic light emitting display device has to install a device to eliminate the environmental illumination and improve the poor contrast problem. Two main methods of conventional techniques for raising the contrast are illustrated as follows. The first conventional method is to dispose a polarizer on the surface of the substrate of the organic light emitting display device, for instance, a circular polarizer, to reduce the reflection of the environmental illumination. Although the polarizer may reduce the reflection of the environmental illumination, it may also reduce the transmission of light generated by the organic emitting display device itself to 43% only and result in poor efficiency of light emission. In order to attain sufficient brightness, it is necessary to increase the power consumption of the organic light emitting display device. The second conventional method is to install a black matrix pattern on the non-display area of the organic light emitting display device that may reduce the reflection of the environmental illumination. However, the black matrix disposed on the non-display area may reduce only part of the reflection, for example, the reflection of the environmental illumination resulted from the metal conducting wire and thin-film transistor. The reflection of the environment illumination coming from the cathode disposed in the display area is not reduced. Thus, the contrast of the organic light emitting display is still poor.  
     SUMMARY OF THE INVENTION  
      The present invention provides a flat display panel with improved contrast of the flat display panel.  
      According to the claimed invention, a flat display panel is disclosed. The flat display panel comprises a first substrate; a second substrate divided into a plurality of pixel regions, each pixel region comprising a display area and a non-display area; a black matrix pattern disposed on a surface of the second substrate, the black matrix pattern being disposed on each non-display area of the second substrate; and a brightness enhancement sheet disposed on a surface of the second substrate opposite the first substrate; wherein in each pixel region an area ratio of the black matrix pattern to the pixel region is between 70% and 95%.  
      These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic diagram illustrating an organic light-emitting display (OLED) panel according to a first preferred embodiment of the present invention.  FIG. 2  is a schematic diagram illustrating an OLED panel according to a second embodiment.  
       FIG. 3  is a schematic diagram illustrating the distribution of a pixel region of the OLED panel according to the present invention.  
       FIG. 4  is a schematic diagram illustrating an OLED panel according to a third embodiment.  
       FIG. 5  is a schematic diagram illustrating an OLED panel according to a fourth embodiment. 
    
    
     DETAILED DESCRIPTION  
      Please refer to  FIG. 1 .  FIG. 1  is a schematic diagram illustrating an organic light-emitting display (OLED) panel according to a first preferred embodiment of the present invention; wherein only a single pixel region is presented to manifest the major characteristic of the present invention. As shown in  FIG. 1 , an OLED panel  10  of the present invention has a first substrate (upper substrate)  12  and a second substrate (lower substrate)  14 . The first substrate  12  is connected with the second substrate  14  by a sealant (not shown in the diagram) to maintain a distance between two substrates. The OLED panel  10  is a rear-emission type display panel. Therefore, the second substrate  14  is a display panel and the second substrate  14  comprises a transparent material, such as glass, plastic, or quartz. The material of the first substrate may include a transparent material or an opaque material. The second substrate  14  has a plurality of pixel regions  16 , and each pixel region  16  may be divided into a non-display area  18  and a display area  20 . The OLED panel  10  comprises a black matrix pattern  22  disposed on a surface of the second substrate  14  facing the first substrate  12 . As a result, it may reduce the reflection of the environmental illumination from the direction of the second substrate  14  to the first substrate  12 ; wherein the material of the black matrix pattern may include chromium, chromium oxide, chromium nitride or other materials with good anti-reflection properties. In addition, the surface of the second substrate  14  and the black matrix pattern  22  is covered with an inter-layer dielectric layer  24 . A switch element  26 , such as a thin-film transistor, is disposed on the inter-layer dielectric layer  24  in the non-display area  18 . Moreover, a pixel electrode (anode)  28 , an organic light-emitting layer  30 , and a cathode (reflective electrode)  32  are stacked on the switch element  26  and inter-layer dielectric layer  24 ; wherein the pixel electrode  28  is a transparent electrode and electrically connected to the switch element  26 . The organic light-emitting layer  30  includes organic light-emitting materials and is powered by the pixel electrode  28  and the cathode  32 .  
      The cathode  32  of the OLED panel  10  comprises materials with high-reflective properties, such as metal, that reflects the light generated by the organic light-emitting layer  30  and raises the brightness. However, the cathode  32  may also reflect the environmental illumination from the direction of the second substrate  14  and affect the contrast of the OLED panel  10 . Therefore, the major characteristic of the present invention is to raise the area ratio of the non-display area; in other words, the area ratio of the display area  20  may be reduced correspondingly. Thus, in the display area  20 , the environmental illumination reflected by the cathode  32  may be reduced and the contrast of the OLED panel  10  may be raised effectively. Because the reduction of the display area  20  may also result in the reduction of the brightness of the OLED panel  10  itself. For this reason, the OLED panel  10  of the present invention further comprises a brightness enhancement sheet  34  disposed on a surface of the second substrate  14  opposite to the first substrate  12  to improve the brightness of the OLED panel  10 ; wherein the brightness enhancement sheet  34  may be brightness enhancement film (BEF) or dual brightness enhancement film (DBEF) as required. Depending on the different kinds of the brightness enhancement sheet  34 , the surface of the brightness enhancement sheet  34  may include patterns capable of guiding light, such as a round-shape lens pattern, a trench pattern or a pyramid pattern. In addition, the brightness enhancement sheet  34  may be a multi-layer interference thin-film or any other available structure to enhance brightness.  
      According to the first embodiment, the brightness enhancement sheet  34  is attached to the surface of the second substrate  14 , as shown in  FIG. 1 . The application of the claimed invention is not limited to the present embodiment. The brightness enhancement sheet may be formed on the second substrate  13  by other methods. Please refer to  FIG. 2 .  FIG. 2  is a schematic diagram illustrating an OLED panel according to a second embodiment. In order to more easily distinguish the difference between the present embodiment and the above-mentioned embodiment, the same elements of  FIG. 2  use the same notation as the first embodiment. As shown in  FIG. 2 , the brightness enhancement sheet  34  of the OLED panel  10  of the second embodiment is fabricated directly on the surface of the second substrate  14 . For instance, the method of fabricating the brightness enhancement sheet  34  may use chemical processes such as etching, or mechanical processes such as sand blasting. Both are different from the attachment of the brightness enhancement sheet  34  of the first embodiment.  
      Please refer to  FIG. 3  (also  FIG. 1  and  FIG. 2 ).  FIG. 3  is a schematic diagram illustrating the distribution of a pixel region of the OLED panel according to the present invention. As shown in  FIG. 2 , the pixel area  16  of the OLED panel  10  comprises a non-display area  18  and a display area  20 , wherein in each pixel region an area ratio of the non-display area  18  to the pixel region  16  is between 70% and 95%. That means the area ratio of the black matrix pattern  22  to the total pixel region  16  is between 70% and 95%. In coordination with the disposition of brightness enhancement sheet  34 , the reflection of the environmental illumination is reduced and the brightness of the OLED panel  10  is maintained. Moreover, the shapes of the non-display area  18  and the display area  20  are not limited. It may be modified according to different designs of the OLED panel  10 .  
      Please refer to  FIG. 4 .  FIG. 4  is a schematic diagram illustrating an OLED panel according to a third embodiment. As shown in  FIG. 4 , the OLED panel  50  of the claimed invention comprises a first substrate (upper substrate)  52  and a second substrate (lower substrate)  54 ; wherein the second substrate  54  includes a plurality of pixel regions  56  and each pixel region  56  comprises a non-display area  58  and a display area  60 . The OLED panel  50  comprises a black matrix pattern  62 , which is disposed on a surface of the second substrate  54  facing the first substrate  52 . The black matrix pattern  62  may reduce the reflection of the environmental illumination from the direction of the second substrate  54  to the first substrate  52 . In addition, in the display area  60 , a surface of the second substrate  54  further comprises a color filter pattern  76 . An inter-layer dielectric layer  64  is covered on the surface of the color filter pattern  76  and the black matrix pattern  62 . In the non-display area  58 , a switch element  66  such as a thin-film transistor, is disposed above the inter-layer dielectric layer  64 . In addition, a pixel electrode (anode)  68 , an organic light-emitting layer  70  and a cathode (reflective electrode)  72  are stacked on the switch element  66  and the inter-layer dielectric layer  64 . Moreover, the OLED panel  50  further comprises a brightness enhancement sheet  74  disposed on a surface of the second substrate  54  opposite to the first substrate  54 . The brightness enhancement sheet  74  may raise the brightness of the OLED panel  50 .  
      Similar to the above-described embodiments, according to the OLED panel  50  of the third embodiment, the area ratio of the non-display area  58  to the pixel region  56  is between 70% and 95%. That means the area ratio of the black matrix pattern  62  to the pixel region  56  is between 70% and 95%. Different from the above-described embodiments, in the display area  60 , a color filter pattern  76  is disposed on the surface of the second substrate  54 . The function of the color filter  76  is to absorb a part of the environmental illumination illuminating to the display area  60 . For instance, if the color filter pattern  76  is a blue filter pattern, the environmental illumination (white light) in the range of the red-light wavelength may be absorbed. Thus, it may reduce the environmental illumination illuminating to the display area  60 , and may further reduce the environmental illumination reflected by the cathode  72  in the display area  60 . These factors may raise the contrast of the OLED panel  50 .  
      Please refer to  FIG. 5 .  FIG. 5  is a schematic diagram illustrating an OLED panel according to a fourth embodiment. As shown in  FIG. 5 , the OLED panel  80  of the present invention comprises a first substrate (lower substrate)  82  and a second substrate (upper substrate)  84 . The first substrate  82  is connected to the second substrate  84  by a sealant (not shown in the diagram) to maintain a distance between two substrates. The OLED panel  80  of the present embodiment is a front-emission type panel; thus, the second substrate  84  comprises a transparent material, such as glass, plastic or quartz. The material of the first substrate  82  may comprise transparent material or opaque glass. The second substrate  84  comprises a plurality of pixel regions  86  and each pixel region  86  may be divided into a non-display area  88  and a display area  90 . In the non-display area  88 , a switch element  92  such as a transistor, is disposed on the first substrate  82 . Furthermore, in the display area  90 , a pixel electrode  94 , an organic light-emitting layer  96  and a cathode  98  are stacked on the switch element  92  and the first substrate  82 . Because the OLED panel  80  of the third embodiment is a front-emission type panel, the pixel electrode  94  comprises materials with high-reflective properties such as metal, to reflect the light generated by organic light-emitting layer  96  and to raise the brightness. The cathode  98  comprises transparent conductive material.  
      Moreover, in the non-display area  88 , a black matrix pattern  100  is installed on the second substrate  84 . The black matrix pattern  100  further comprises a brightness enhancement sheet  102 . Inside the display area  90 , a color filter pattern  104  may be disposed selectively on the second substrate  84 . What distinguishes the present embodiment from the above-mentioned embodiment is that the OLED panel  80  is a front-emission type panel. Thus, the black matrix pattern  100 , the brightness enhancement sheet  102 , and the color filter  104  are installed on different locations. However, the OLED panel  80  has the same characteristic of the area ratio of the non-display area  88  to the pixel region  86  being between 70% and 95%. Functions of the black matrix pattern  100 , the brightness enhancement sheet  102 , and the color filter pattern  104  are described above.  
      In conclusion, the major characteristic of the OLED panel of the present invention is to control the area ratio of the black matrix pattern to the pixel region to be between 70% and 90%. In coordination with the brightness enhancement sheet, the contrast of the OLED panel is raised without affecting the brightness. The characteristic of the present invention is the distribution of the display area and the non-display area, and the use of the brightness enhancement sheet. Therefore, other designs of the OLED panel, for example, the composition of the light emitting diode and the material of the electrode may be modified according to the present technique. In addition, the above-mentioned embodiments are illustrated by the example of the OLED panel, but the flat display panel according to the claimed invention is not limited to the OLED panel only.  
      Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.