Patent Publication Number: US-2012032175-A1

Title: Display structure

Description:
BACKGROUND OF THE INVENTION 
     a. Field of the Invention 
     The invention relates to a display structure 
     b. Description of the Related Art 
     Nowadays, a portable electronic device such as a tablet computer or a smart phone may fulfill functions of on-line reading, animation display, etc., and these functions are realized by an organic light-emitting diode (OLED) display or a liquid crystal display (LCD). Since a portable electronic device is designed to have as much working hours as possible, how to reduce power consumption becomes a key issue towards current trends. Further, a power-saving electronic book reading device capable of storing massive reading materials may be constructed by a bistable display device, since its bistable characteristics offer the advantage of power saving on performing reading actions. However, compared with the response speed of an OLED device or an LCD device, the response speed of a bistable display device is relatively low. Therefore, the bistable display device is not suitable for animation display. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a display structure having low power consumption and high response speed. 
     Other objects and advantages of the invention may be further illustrated by the technical features broadly embodied and described as follows. In order to achieve one or a portion of or all of the objects or other objects, one embodiment of the invention provides a display structure including a first transparent substrate, a second transparent substrate opposite the first transparent substrate, a display medium interposed between the first transparent substrate and the second transparent substrate, at least one first thin film transistor formed on the first transparent substrate, a first insulation layer formed on the first transparent substrate and covering the first thin film transistor, a first electrode layer formed on the first insulation layer, an organic light-emitting layer formed on the first electrode layer and in a region not overlapping the first thin film transistor, a cathode layer formed on the organic light-emitting layer, and a second electrode layer formed on the second transparent substrate. The second electrode layer is a transparent electrode layer. 
     In one embodiment, a black matrix layer is formed on the first electrode layer or interposed between the first electrode layer and the first insulation layer. 
     In one embodiment, the display medium layer is a cholesterol liquid crystal layer, an electrophoretic layer, or a polymer dispersed liquid crystal layer. 
     In one embodiment, at least one second thin film transistor is formed on the second transparent substrate 
     In one embodiment, either the first electrode layer or the cathode layer serves as a common electrode of the display structure. 
     In one embodiment, the second electrode layer serves as a common electrode of the display structure. 
     Another embodiment of the invention provides a display structure including a first transparent substrate, a second transparent substrate opposite the first transparent substrate, a display medium interposed between the first transparent substrate and the second transparent substrate, at least one first thin film transistor formed on the first transparent substrate, a first insulation layer formed on the first transparent substrate and covering the first thin film transistor, a first electrode layer formed on the first insulation layer, a second electrode layer formed on the second transparent substrate and electrically connected to the first electrode layer, where the second electrode layer is a transparent electrode layer, an organic light-emitting layer formed on the second electrode layer, and a cathode layer formed on the organic light-emitting layer. 
     In one embodiment, a bump structure is formed on the first transparent substrate or the second transparent substrate to connect the first electrode layer with the second electrode layer. 
     In one embodiment, the cathode layer serves as a common electrode of the display structure. 
     Another embodiment of the invention provides a display structure having at least one organic light-emitting diode (OLED) pixel and at least one bistable pixel adjacent to or opposite from each other, where the OLED pixel displays images when the bistable pixel is turned off, and the bistable pixel displays images when the OLED pixel is turned off. 
     In one embodiment, a Vdd voltage signal is in a low-level state when a write-in operation and an erase operation are performed on the bistable pixel, and the Vdd voltage signal is in a high-level state when the OLED pixel is turned on to display images. 
     The embodiment or the embodiments of the invention may have at least one of the following advantages. According to the above embodiments, the OLED pixel is self-luminous and has wide viewing angles, high brightness and high response speed. In comparison, the bistable pixel is power-saving due to bistable characteristics. 
     Other objectives, features and advantages of the invention will be further understood from the further technological features disclosed by the embodiments of the invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram of a display structure according to an embodiment of the invention. 
         FIG. 2  shows a schematic cross-section illustrating electrode structures of a display structure according to an embodiment of the invention. 
         FIG. 3  shows a schematic cross-section illustrating electrode structures of a display structure according to another embodiment of the invention. 
         FIG. 4  shows a schematic cross-section illustrating electrode structures of a display structure according to another embodiment of the invention. 
         FIG. 5  shows a schematic cross-section illustrating electrode structures of a display structure according to another embodiment of the invention. 
         FIG. 6  shows a schematic cross-section illustrating electrode structures of a display structure according to another embodiment of the invention. 
         FIG. 7  shows a schematic cross-section illustrating electrode structures of a display structure shown in  FIG. 6 . 
         FIG. 8  shows a timing diagram illustrating a pixel drive scheme for a display structure according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” etc., is used with reference to the orientation of the Figure(s) being described. The components of the present invention can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. On the other hand, the drawings are only schematic and the sizes of components may be exaggerated for clarity. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. Similarly, the terms “facing,” “faces” and variations thereof herein are used broadly and encompass direct and indirect facing, and “adjacent to” and variations thereof herein are used broadly and encompass directly and indirectly “adjacent to”. Therefore, the description of “A” component facing “B” component herein may contain the situations that “A” component directly faces “B” component or one or more additional components are between “A” component and “B” component. Also, the description of “A” component “adjacent to” “B” component herein may contain the situations that “A” component is directly “adjacent to” “B” component or one or more additional components are between “A” component and “B” component. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
       FIG. 1  shows a schematic diagram of a display structure according to an embodiment of the invention. Referring to  FIG. 1 , the display structure  10  includes a bistable pixel  12  and an organic light-emitting diode (OLED) pixel  14 . The OLED pixel  14  is self-luminous and has wide viewing angles, high brightness and high response speed. In comparison, the bistable pixel  12  is power-saving due to bistable characteristics.  FIG. 2  shows a schematic cross-section illustrating electrode structures of a display structure according to an embodiment of the invention. As shown in a display structure  10   a  of  FIG. 2 , the bistable pixel is a cholesteric liquid crystal pixel  12   a,  and the electrode structures of the cholesteric liquid crystal pixel  12   a  and the OLED pixel  14  are formed on the same side (transparent substrate  16 ). In this embodiment, the cholesteric liquid crystal pixel  12   a  includes at least one thin film transistor T. In the thin film transistor T, a first metal layer M 1  is formed on the transparent substrate  16 , a dielectric gate insulator  22  is formed overlying the first metal layer M 1 . A channel region layer  24  (pure amorphous silicon), an ohmic contact layer  26  (doped amorphous silicon) and a second metal layer M 2  are formed on the gate insulator  22 . A dielectric passivation insulator  28  is formed on the gate insulator  22  and the second metal layer M 2 , and an organic insulation layer  42  is formed on the transparent substrate  16  and covers the thin film transistor T. A transparent electrode layer  32  made from transparent conductive films are formed on the organic insulation layer  42  and electrically connected to the second metal layer M 2  through a via hole  38 . In one embodiment, the transparent electrode layer  32  may be electrically connected to the first metal layer Ml via the second metal layer M 2  to realize a pixel compensation circuit. Besides, a black matrix layer  34  is formed on the transparent electrode layer  32 . A transparent substrate  18  is disposed opposite the transparent substrate  16 , and another transparent electrode layer  36  made from transparent conductive films spreads entirely on one side of the transparent substrate  18  facing the transparent substrate  16 . The cholesteric liquid crystal layer  40  is interposed between the transparent substrate  16  and the transparent substrate  18 . In the OLED pixel  14 , an organic insulation layer  42  is formed on the passivation insulator  28 , and a transparent electrode layer  32 , an organic light-emitting layer  44  and a cathode layer  46  are formed on the organic insulation layer  42  in succession. The transparent electrode layer  32  serves as an anode of the OLED pixel  14 . The cathode layer  46  serves as a cathode of the OLED pixel  14  and may be made from transparent conductive materials. The organic light-emitting layer  44  is formed in a region not overlapping the thin film transistor T, and a light emission area of the organic light-emitting layer  44  is defined by a bank  56 . When the transparent electrode layer  32  is electrically connected to the second metal layer M 2  through the via hole  38 , and the cathode layer  46  serves as a common electrode (Vss) of the OLED pixel  14 , a conventional OLED pixel is formed. In comparison, when the cathode layer  46  is electrically connected to the second metal layer M 2  through the via hole  38 , and the transparent electrode layer  32  serves as a common electrode (Vdd) of the OLED pixel  14 , an inverted OLED pixel is formed. Note the transparent electrode layer  32  is merely illustrated as an example. In an alternate embodiment, the electrode layer formed on the organic insulation layer  42  may be opaque and may be a reflective electrode layer. The cholesteric liquid crystal pixel  12  is suitable for static display, and the OLED pixel  14  is suitable for animation display. For example, when the cholesteric liquid crystal pixel  12   a  is in a planar state, the OLED pixel  14  does not emit light. In comparison, when the cholesteric liquid crystal pixel  12   a  is in a focal conic state, the OLED pixel  14  emits light. Certainly, the OLED pixel is not limited to have a specific emission pattern. When the OLED pixel  14  downwardly emits light and the cholesteric liquid crystal pixel  12   a  displays images on a top side of the display structure  10 , a dual-sided display device is provided. Further, in case the cathode layer  46  is transparent, the OLED pixel  14  may upwardly emit light. Therefore, the OLED pixel  14  may only provide top emission, only provide bottom emission, and provide both top emission and bottom emission. 
     As shown in a display structure  10   b  of  FIG. 3 , in an alternate embodiment, the black matrix layer  34  is formed on the organic insulation layer  42  first, and then the transparent electrode layer  32  is formed on the black matrix layer  34  and covering the black matrix layer  34 . In other words, the black matrix layer  34  may be interposed between the transparent electrode layer  32  and the organic insulation layer  42 . 
       FIG. 4  shows a schematic cross-section illustrating electrode structures of a display structure according to another embodiment of the invention. As shown in a display structure  10   c  of  FIG. 4 , the bistable pixel is cholesteric liquid crystal pixel  12   a , and the electrode structure of the cholesteric liquid crystal pixel  12   a  and the electrode structure of the OLED pixel  14  are formed on different sides. For example, the electrode structure of the cholesteric liquid crystal pixel  12   a  is formed on the transparent substrate  16 , and the electrode structure of the OLED pixel  14  is formed on the transparent substrate  18 . In this embodiment, the cholesteric liquid crystal pixel  12   a  includes at least one thin film transistor T and has an electrode structure similar to that shown in  FIG. 2 . However, compared with the display structure  10   a  of  FIG. 2 , a black matrix layer  34  is omitted from the cholesteric liquid crystal pixel  12   a  shown in  FIG. 4  since the organic insulation layer  42  is made from an opaque material or a low-light-transmittance material. In the electrode structure of the OLED pixel  14 , a transparent electrode layer  36 , an organic light-emitting layer  44  and a cathode layer  46  are formed on the transparent substrate  18  in succession. The cathode layer  46  serves as a common electrode (Vcom) of the display structure  10   c , and a barrier layer  48  covers the organic light-emitting layer  44  and the cathode layer  46 . A bump structure  52  is disposed on the transparent substrate  16  or the transparent substrate  18  to connect the transparent electrode layer  32  on the transparent substrate  16  with the transparent electrode layer  36  on the transparent substrate  18 . In this embodiment, the OLED pixel  14  and the cholesteric liquid crystal pixel  12   a  displays images on the same side of the display structure  10   c . When the cholesteric liquid crystal pixel  12   a  is in a planar state, the OLED pixel  14  does not emit light. In comparison, when the cholesteric liquid crystal pixel  12   a  is in a focal conic state, the OLED pixel  14  upwardly emits light. 
       FIG. 5  shows a schematic cross-section illustrating electrode structures of a display structure according to another embodiment of the invention. As shown in a display structure  10   d  of  FIG. 5 , the bistable pixel is an electrophoretic pixel  12   b,  and the electrode structures of the electrophoretic pixel  12   b  and the OLED pixel  14  are formed on the same side (transparent substrate  16 ). That is, in this embodiment, the display medium layer interposed between the transparent substrate  16  and the transparent substrate  18  is an electrophoretic layer  50 . The electrophoretic pixel  12   b  may include at least one thin film transistor T, and the electrophoretic layer  50  may include multiple micro capsules  54 . When a voltage is applied across the transparent electrode layers  32  and  36 , black and white particles in the micro capsules  54  migrate upwards or downwards to control light reflection and hence fulfill display effects. In this embodiment, when the OLED pixel  14  downwardly emits light and the electrophoretic pixel  12   b  displays images on a top side of the display structure  10 , a dual-sided display device is provided. Further, in case the electrophoretic pixel  12   b  display images, the OLED pixel  14  may not emit light. In comparison, when the electrophoretic pixel  12   b  is in an off state (black state), the OLED pixel  14  may upwardly emit light. 
       FIG. 6  shows a schematic cross-section illustrating electrode structures of a display structure according to another embodiment of the invention. As shown in a display structure  10   e  of  FIG. 6 , the display medium layer interposed between the transparent substrate  16  and the transparent substrate  18  is a polymer dispersed liquid crystal (PDLC) layer  60 . The PDLC layer  60  consists of anisotropic liquid crystal droplets that are dispersed in a polymer matrix. By changing the orientation of the liquid crystal molecules with an electric field, it is possible to vary the intensity of transmitted light to form an off state and an on state and hence achieve display effects. In this embodiment, the display structure  10   e  has two thin film transistors T 1  and T 2 , the thin film transistor T 1  is formed on the transparent substrate  18 , and the thin film transistor T 2  is formed on the transparent substrate  16 . Referring to  FIG. 6 , a polymer dispersed liquid crystal (PDLC) pixel  12   c  and an OLED pixel  14  are respectively formed on two sides of the display structure  10   e.  The PDLC pixel  12   c  may display images on the top side of the display structure  10   e,  and the OLED pixel  14  may upwardly or downwardly emit light. 
       FIG. 7  shows a schematic cross-section illustrating electrode structures of a display structure shown in  FIG. 6 . Referring to the display structure  10   e  of  FIG. 7 , the electrode structure of the PDLC pixel  12   c  is formed on the transparent substrate  18 , and the electrode structure the OLED pixel  14  is formed on the transparent substrate  16 . In this embodiment, the PDLC pixel  12   c  includes at least one thin film transistor T 1 . In the thin film transistor T 1 , a first metal layer M 1  is formed on the transparent substrate  18 , a dielectric gate insulator  22  is formed overlying the first metal layer M 1 . A channel region layer  24  (pure amorphous silicon), an ohmic contact layer  26  (doped amorphous silicon), and a second metal layer M 2  are formed on the gate insulator  22 . A dielectric passivation insulator  28  is formed on the gate insulator  22  and the second metal layer M 2 . A transparent electrode layer  36  made from transparent conductive films are formed on the passivation insulator  28 . In this embodiment, the OLED pixel  14  includes at least one thin film transistor T 2 , and the thin film transistor T 2  is formed at a position overlapping the thin film transistor T 1 . In the thin film transistor T 2 , a first metal layer M 1  is formed on the transparent substrate  16 , a dielectric gate insulator  22  is formed overlying the first metal layer M 1 . A channel region layer  24  (pure amorphous silicon), an ohmic contact layer  26  (doped amorphous silicon), and a second metal layer M 2  are formed on the gate insulator  22 . A dielectric passivation insulator  28  is formed on the gate insulator  22  and the second metal layer M 2 . An organic insulation layer  42  is formed on the transparent substrate  16  and covers the thin film transistor T 2 . A transparent electrode layer  32  made from transparent conductive films are formed on the organic insulation layer  42  and electrically connected to the second metal layer M 2  through a via hole  38 . In one embodiment, the transparent electrode layer  32  may be electrically connected to the first metal layer M 1  via the second metal layer M 2  to realize a pixel compensation circuit. A transparent substrate  18  is disposed opposite the transparent substrate  16 . The PDLC layer  60  is interposed between the transparent substrate  16  and the transparent substrate  18 . In the OLED pixel  14 , a transparent electrode layer  32 , an organic light-emitting layer  44  and a cathode layer  46  are formed on the organic insulation layer  42  in succession. The transparent electrode layer  32  serves as an anode of the OLED pixel  14 , and the cathode layer  46  serves as a cathode of the OLED pixel  14 . The organic light-emitting layer  44  is formed in a region not overlapping the thin film transistor T 2 , and a light emission area of the organic light-emitting layer  44  is defined by a bank  56 . The transparent electrode layer  32  (anode) may be electrically connected to the second metal layer M 2  through the via hole  38 , and the cathode layer  46  may serve as a common electrode (Vss) of the OLED pixel  14 . Besides, the cathode layer  46  may also serve as a common electrode of the PDLC pixel  12   c.    
       FIG. 8  shows a timing diagram illustrating a pixel drive scheme for a display structure according to an embodiment of the invention. Taking the display structure shown in  FIG. 1  as an example, a pixel driving circuit for each display structure includes three kinds of signal control lines, namely data lines, scan lines, and Vdd lines, and the drive scheme may be divided into three stages: 
     1. Write-in of a bistable pixel: the first metal layer M 1  is conducting since the scan lines are in a high-level state. Therefore, low-level signals of date lines are fed in to turn on the bistable pixel  12 . Meanwhile, Vdd voltage signals are set in a low-level state to prevent the OLED pixel  14  from being mistakenly turned on. 
     2. Erase of a bistable pixel: the bistable pixel  12  needs to be erased before the OLED pixel  14  starts to emit light. At this stage, the voltage across a bistable cell is in a high-level state to allow for a dark state of the bistable pixel  12 , and Vdd voltage signals are set in a low-level state to prevent the OLED pixel  14  from being mistakenly turned on; and 
     3. Emission of an OLED pixel: when the first metal layer M 1  is conducting as the scan lines are in a high-level state, signals of date lines are fed in and Vdd voltage signals are set in a high-level state. Therefore, the OLED pixel  14  is allowed to display images in response to different voltage levels transmitted from data lines. 
     The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Accordingly, the foregoing description should be regarded as illustrative rather than restrictive. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. The embodiments are chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable persons skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Therefore, the term “the invention”, “the present invention” or the like does not necessarily limit the claim scope to a specific embodiment, and the reference to particularly preferred exemplary embodiments of the invention does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is limited only by the spirit and scope of the appended claims. The abstract of the disclosure is provided to comply with the rules requiring an abstract, which will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Any advantages and benefits described may not apply to all embodiments of the invention. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention as defined by the following claims. Moreover, no element and component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims.