Patent Publication Number: US-2011069001-A1

Title: Electronic paper display device and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2009-0088740 filed on Sep. 18, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic paper display device, and more particularly, to an electronic paper display device which has a high contrast ratio and is capable of guaranteeing a low driving voltage, and a method of manufacturing the same. 
     2. Description of the Related Art 
     Recently, with the increasing development of mobile terminals and information communication networks, the demand for devices having excellent portability characteristics is increasing. A great deal of attention is being paid to electronic paper display devices as display devices which may satisfy such demand. 
     Since electronic paper display devices may have flexibility, they are easy to carry and handle. Furthermore, the electronic paper display devices may be driven by a low voltage, may maintain a clear screen even after power is cut off, and may provide a high resolution and a wide viewing angle. 
     The technical approach to the realization of electronic paper display paper may be accomplished using liquid crystals, organic electro luminescence (EL) displays, reflective film reflection-type displays, electrophoretic displays, or electrochromic displays. 
     In the method using electrophoretic capsules or twist balls, a single-layer structure is converted into a multilayer arrangement structure to implement a more close-packed arrangement, thereby obtaining a higher contrast ratio. 
     However, since such a multilayer structure may cause a result in which a distance between electrodes increases, a voltage required for diving capsules or balls may increase relatively. Further, since it is difficult to control the respective capsules or balls with a uniform driving voltage, the distribution of a driving voltage for each pixel may increase. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides an electronic paper display device which has a monolayer structure to reduce a driving voltage and a high contrast ratio through a close-packed arrangement. 
     Another aspect of the present invention provides a method of manufacturing an electronic paper display device which reduces a driving voltage, implements a high contrast ratio through a close-packed arrangement, and may simplify the manufacturing process. 
     According to an aspect of the present invention, there is provided an electronic paper display device including: a display-side electrode disposed at a display side and formed of a transparent material; a back electrode disposed to face the display-side electrode; a substrate provided as a single layer disposed between the display-side electrode and the back electrode and including a plurality of first and second micro cups which are arranged in a two-dimensionally close-packed manner such that one micro cup is surrounded by different adjacent micro cups; and a plurality of first and second optical anisotropic elements disposed in the first and second micro cups, respectively, and having an optical characteristic changing in response to an electromagnetic change and a different driving voltage to change the optical characteristic. 
     The plurality of first and second micro cups may have the same size and are arranged in a plurality of lines such that a predetermined distance is provided between the respective lines, and the line arrangements of the first and second micro cups may be alternately repeated in such a manner that the position of a first micro cup is offset by a distance equal to half of the cup size from the position of a second micro cup adjacent to the first micro cup. 
     The plurality of first and second micro cups may have a periodic square-lattice arrangement in which one micro cup is positioned substantially in the center of a square lattice formed by different adjacent micro cups. 
     The second optical anisotropic element may have a smaller size than the first optical anisotropic element. The second micro cup may have a smaller size than the first micro cup. 
     The depth of the second micro cup may be less than that of the first micro cup. 
     The second micro cup may have such a small size so as not to contain the first optical anisotropic element. 
     According to another aspect of the present invention, there is provided an electronic paper display device including: a display-side electrode disposed at a display side and formed of a transparent material; a back electrode disposed to face the display-side electrode; a plurality of embossed patterns disposed as a single layer disposed between the display-side electrode and the back electrode and arranged in a two-dimensionally close-packed manner to provide first and second spaces which are regularly repeated; and a plurality of first and second optical anisotropic elements disposed in the first and second spaces, respectively, and having an optical characteristic changing in response to an electromagnetic change and a different driving voltage to change the optical characteristic. 
     According to another aspect of the present invention, there is provided a method of manufacturing an electronic paper display device, including: forming a back electrode on a base member; providing a substrate having a single layer structure on the back electrode; forming a plurality of first and second micro cups in the substrate, the first and second micro cups being arranged in a two-dimensionally close-packed manner such that one micro cup is surrounded by different adjacent micro cups; disposing first and second anisotropic elements in the first and second micro cups, respectively, the first and second anisotropic elements having an optical characteristic changing in response to an electromagnetic change and a different driving voltage in order to change the optical characteristic; and forming a display-side electrode formed of a transparent material on the substrate such that the display-side electrode faces the back electrode. 
     The disposing of the first and second optical anisotropic elements may include disposing the first optical anisotropic elements in the first micro cups using a first mask which opens only the first micro cups, and disposing the second optical anisotropic elements in the second micro cups using a second mask which opens only the second micro cups. 
     The second optical anisotropic element may have a smaller size than the first optical anisotropic element. The second micro cup may have a smaller size than the first micro cup. The second micro cup may be formed to have such a small size so as not to contain the first optical anisotropic element. 
     The disposing of the first and second optical anisotropic elements may include providing the first optical anisotropic elements on the substrate to dispose in the first micro cups, respectively, and providing the second optical anisotropic elements on the substrate to dispose in the second micro cups, respectively. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a top plan view of a substrate which may be adopted in an electronic paper display device according to an embodiment of the present invention; 
         FIGS. 2A to 2C  are side cross-sectional views of the electronic paper display device according to the embodiment of the present invention, taken in different directions; 
         FIG. 3  is a graph showing drive characteristics of anisotropic elements depending on applied voltages in the electronic paper display device according to the embodiment of the present invention; 
         FIG. 4  is a top plan view of a substrate which may be adopted in an electronic paper display device according to another embodiment of the present invention; 
         FIG. 5  is a side cross-sectional view of the electronic paper display device according to the embodiment of the present invention, taken along a line B-B′ of  FIG. 4 ; 
         FIG. 6  is a graph showing drive characteristics of anisotropic elements depending on applied voltages in the electronic paper display device according to the embodiment of the present invention; 
         FIGS. 7A to 7D  are cross-sectional views explaining a method of manufacturing an electronic paper display device according to another embodiment of the present invention; 
         FIG. 8  is a top plan view of a substrate which may be adopted in an electronic paper display device according to another embodiment of the present invention; and 
         FIG. 9  is a side cross-sectional view of the electronic paper display device according to the embodiment of the present invention, taken along a line C-C′ of  FIG. 8 ; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like reference numerals in the drawings denote like elements, and thus their description will be omitted. 
       FIG. 1  is a top plan view of a substrate which may be adopted in an electronic paper display device according to an embodiment of the present invention.  FIGS. 2A to 2C  are side cross-sectional views of the electronic paper display device according to the embodiment of the present invention, taken in different directions. 
     Referring to  FIGS. 1 and 2A  to  2 C, the electronic paper display device according to this embodiment of the present invention includes a display-side electrode  14  formed of a transparent conductive material, a back electrode  12  facing the display-side electrode  14 , and a substrate  11  disposed between the display-side electrode  14  and the back electrode  12 . 
     Referring to  FIG. 1 , the substrate  11  has a plurality of first and second micro cups H 1  and H 2  for containing optical anisotropic particles  15   a  and  15   b  having a different drive characteristic. Specifically, the first optical anisotropic particles  15   a  are disposed in the first micro cups H 1 , and the second optical anisotropic particles  15   b  are disposed in the second micro cups H 2  (refer to  FIGS. 2A to 2C ). 
     The substrate  11  used in the embodiment of the present invention has a single-layer structure in which the first and second micro cups H 1  and H 2  are arranged in a two-dimensionally close-packed pattern. 
     To implement such a close-packed arrangement, one micro cup (for example, the first micro cup) may be disposed to be surrounded by different adjacent micro cups (for example, the second micro cup). 
     As in this embodiment, when the first and second micro cups H 1  and H 2  have the same size, the plurality of first and second micro cups H 1  and H 2  are arranged in a plurality of lines such that a constant distance is provided between the respective lines. Therefore, as illustrated in  FIG. 2A , the first optical anisotropic elements may be disposed in the first micro cups positioned along a direction indicted by a line A 1 -A 1 ′ of  FIG. 1 . Furthermore, as illustrated in  FIG. 2B , the second optical anisotropic elements may be disposed in the second micro cups positioned along a direction indicated by a line A 2 -A 2 ′ of  FIG. 1 . 
     Furthermore, referring to  FIG. 1 , the line arrangements of the first and micro cups H 1  and H 2  are alternately repeated in such a manner that the position of a first micro cup H 1  is offset by a distance equal to half of the cup size from the position of a second micro cup H 2  adjacent to the first micro cup H 1 . Such line arrangements may implement an arrangement in which the first and second micro cups containing the first and second optical anisotropic elements, respectively, are alternately disposed in a direction indicated by a line B-B′ of  FIG. 1 . 
     In such an arrangement, a specific second micro cup C may be disposed in a rectangular lattice L formed by the first micro cups H 1  adjacent to the second micro cup C, as illustrated in  FIG. 1 . 
     In the arrangement of the first and second micro cups H 1  and H 2  according to this embodiment of the present invention, the first and second optical anisotropic elements may be repetitively arranged in a predetermined pattern. Such an arrangement may be understood as a form in which a hexagonal close-packed pattern H is repeated. 
     As such, the close-packed arrangement of the respective micro cups  15   a  and  15   b  may be implemented with a barrier rib interposed therebetween, the barrier rib having a constant and small thickness. Therefore, it is possible to increase a contrast ratio. Furthermore, since the substrate is implemented as a single layer, a distance between the electrodes  12  and  14  may be reduced, and a relatively low driving voltage may be expected. 
     In this embodiment, the first and second optical anisotropic elements  15   a  and  15   b  refer to an element whose optical characteristic changes in response to an electromagnetic change. Examples of the optical anisotropic element may include an electrophoretic microcapsule and a twist ball. 
     The first and second optical anisotropic elements  15   a  and  15   b  adopted in this embodiment have a different driving voltage to change the optical characteristic. As such, different drive characteristics may be obtained by various methods. For example, an electrolyte component and/or a surface charge related to the optical anisotropic elements may be treated in a different manner to obtain optical anisotropic elements having different drive characteristics. Furthermore, a method of diversifying the size (that is, diameter) of microcapsules or twist balls may be used separately from or together with the above-described method (refer to  FIG. 5 ). 
     Therefore, the first and second optical anisotropic elements  15   a  and  15   b  may be selectively driven depending on the voltages applied from the electrodes  11  and  14 . 
     In a specific embodiment, the first optical anisotropic element  15   a  may be designed to have a higher driving voltage V 2  than a driving voltage V 1  of the second optical anisotropic element  15   b . In this case, when the voltage V 1  is applied as illustrated in  FIG. 3 , the optical characteristic of the second optical anisotropic element  15   b  changes. Subsequently, when the voltage V 2  is applied, the optical characteristic of the first optical anisotropic element  15   a  also changes with the second optical anisotropic element  15   b.    
     Such a selective drive may be utilized for implementing additional functions. For example, optical anisotropic element groups having different drive characteristics may be implemented to have different color characteristics. Then, a function of controlling color characteristics depending on voltage selection may be additionally implemented. 
     In the above embodiment, it has been described that the first and second optical anisotropic elements have the same size. Referring to  FIGS. 4 and 5 , however, an electronic paper display device according to another embodiment of the present invention includes optical anisotropic particles (for example, capsules or twist balls) having different sizes. 
     Referring to  FIGS. 4 and 5 , the electronic paper display device according to the embodiment of the present invention includes a display-side electrode  44  formed of a transparent conductive material, a back electrode  42  facing the display-side electrode  44 , and a substrate  41  disposed between the display-side electrode  44  and the back electrode  42 . 
     The substrate  41  has a plurality of first and second micro cups H 1  and H 2  for containing first and second optical anisotropic particles  45   a  and  45   b . The first and second optical anisotropic particles  45   a  and  45   b  adopted in this embodiment have a different size. Thus, the first and second optical anisotropic particles  45   a  and  45   b  may have a different drive characteristic. 
     The first and second micro cups H 1  and H 2  formed in the substrate  41  used in this embodiment may have a different size from each other unlike those illustrated in  FIG. 1 , in order to contain the first and second optical anisotropic particles  45   a  and  45   b  having a different size. 
     That is, the first micro cup H 1  containing the first optical anisotropic particle  45   a  with a large size has a larger diameter d 1  than the diameter d 2  of the second micro cup H 2  containing the second optical anisotropic particle  45   b  with a small size. 
     The substrate  41  of this embodiment also has a single-layer structure, similar to the above-described embodiment. However, the first and second micro cups H 1  and H 2  may be arranged in a form similar to a three-dimensional arrangement such that the first and second optical anisotropic particles  45   a  and  45   b  are arranged in a more close-packed manner. 
     More specifically, the depth of the second micro cup H 2  having a relatively small size may be less than that of the first micro cup H 1  having a relatively large size, as illustrated in  FIG. 5 . 
     As such, the first and second optical anisotropic particles adopted in this embodiment of the present invention have a different size. Therefore, the first and second optical anisotropic particles may not only have a different drive characteristic, but interstitials between the respective particles having a large size may be effectively utilized to implement a more close-packed arrangement. 
     That is, interstitials between the respective particles having a relatively large size may be utilized to dispose micro cups in which the small particles are positioned. Then, it is possible to implement a more close-packed arrangement, as illustrated in  FIG. 4 . 
     In this embodiment, the plurality of micro cups H 1  and H 2  have a periodic square-lattice arrangement. In such an arrangement, one micro cup is positioned substantially in the center of a square lattice L formed by the adjacent micro cups having a different size. However, the arrangement is not limited thereto. 
     For example, the first micro cups may be arranged in a hexagonal close-packed pattern (refer to the entire arrangement of the first and second micro cups illustrated in  FIG. 1 ), and each of the second micro cups may be disposed in an interstitial among three first micro cups forming a triangle lattice. 
     In this embodiment, it is possible to increase packing density as much as more than 10%, compared with a typical arrangement of the first optical anisotropic elements  45   a  using the first micro cups H 1 . Therefore, a contrast ratio may be improved more effectively. Further, since the basic structure with a single layer is maintained as it is, it is possible to expect a relatively low driving voltage. 
     Furthermore, since the first and second optical anisotropic elements  45   a  and  45   b  are contained in different micro cups so as to be spatially separated from each other, it is possible to prevent the elements from adhering to each other through the contact between the particles or interfering with each other when driven. 
     In this embodiment, the first optical anisotropic element  45   a  having a relatively large size may require a large driving voltage than the second optical anisotropic element  45   b . Therefore, they may be selectively driven depending on voltages applied from the electrodes  41  and  44 . 
     Referring to  FIG. 6 , when a voltage Va is applied, the optical characteristic of the second optical anisotropic element  45   b  changes. Subsequently, when a voltage Vb is applied, the optical characteristic of the first optical anisotropic element  45   a  also changes with the second optical anisotropic element  45   b . For example, when the first and second optical anisotropic elements  45   a  and  45   b  have a different color characteristic, it is possible to control their color depending on the voltages. 
     Hereinafter, a method of manufacturing an electronic paper display device according to another embodiment of the present invention will be described. The method may start with a process of forming a back electrode on a base member. The back electrode may be implemented as an electric field application unit or a matrix address electrode which enables optical anisotropic particles contained in micro cups to be driven independently. 
     Then, a substrate with a single-layer structure is provided on the back electrode, and a plurality of first and second micro cups are formed in the substrate so as to be arranged in a two-dimensionally close-packed manner. In such an arrangement, one cup is surrounded by different adjacent micro cups.  FIGS. 1 and 4  illustrate such a substrate structure. 
     Subsequently, first and second optical anisotropic elements having a different driving voltage to change an optical characteristic are disposed in the first and second micro cups, respectively. A display-side electrode composed of a transparent material is formed on the substrate so as to face the back electrode. 
     The disposing of the first and second optical anisotropic elements may include disposing the first optical anisotropic elements in the first micro cups using a first mask which opens only the first micro cups and disposing the second optical anisotropic elements in the second micro cups using a second mask which opens only the second micro cups. 
     As such, the mask or filter which selectively opens the formed micro cups may be disposed to selectively supply the respective optical anisotropic particles using a squeezer or the like. Then, a desired arrangement may be implemented. 
     On the other hand, the embodiment illustrated in  FIGS. 4 and 5 , in which the balls and the micro cups have a different size, may be implemented by a simplified process. Such a process may be described with reference to  FIGS. 7A to 7D . 
     First, referring to  FIG. 7A , a substrate  71  is prepared on a base member  61  having a back electrode  72  formed thereon. Then, a plurality of first and second micro cups H 1  and H 2  are formed in the substrate  71 . The first and second micro cups H 1  and H 2  are arranged in a two-dimensionally close-packed manner such that each of the first micro cups H 1  is surrounded by the adjacent second micro cups H 2  and each of the second micro cups H 2  is surrounded by the adjacent first micro cups H 1 . In the substrate adopted in this embodiment of the present invention, the first and second micro cups H 1  and H 2  having a different size are adopted to contain balls having a different size, as illustrated in  FIGS. 4 and 5 . 
     Subsequently, first and second optical elements having a different driving voltage to change an optical characteristic are disposed in the first and second micro cups, respectively. Then, a display-side electrode composed of a transparent material is formed on the substrate so as to face the back electrode. 
     In a specific embodiment, the substrate may be provided by applying liquid resin onto a base member to a thickness of 100-200 μm, the base member having a back electrode formed of a thin metallic film or thin metallic film pattern. Such an application process may be performed using a doctor blade or die coater. 
     Subsequently, first and second micro cups H 1  and H 2  having a different size are formed by imprinting, laser drilling, lithography, or sand blasting. 
     The process of disposing the first and second optical anisotropic elements (capsules or balls) in the respective micro cups may be simply performed by using a difference in cup size or a difference in capsule or ball size without using a mask which selectively opens the micro cups. 
     In order for the simplification of the process, the second micro cup H 2  may have such a size as to contain the second optical anisotropic element  75   b  but not to contain the first optical anisotropic element  75   a . Furthermore, the second optical anisotropic element  75   b  may have such a size so as not to be contained in the remaining space of the first micro cup H 1  in which the first optical anisotropic element  75   a  is contained. 
     The disposing process will be described in more detail with reference to  FIGS. 7B and 7C . 
     Referring to  FIG. 7B , the first optical anisotropic elements  75   a  having a large size are disposed in the first micro cups H 1 . 
     Then, a solution  75  containing the first optical anisotropic elements  75   a  formed in a micro-capsule or twist-ball shape is poured onto the substrate  71  from a container  76 . At this time, since the second micro cups H 2  have such a small size so as not to contain the first optical anisotropic elements  75   a , the first optical anisotropic elements  75   a  are not contained in the second micro cups H 2 , but contained in the first micro cups H 1 , respectively. 
     Subsequently, referring to  FIG. 7C , the second optical anisotropic elements  75   b  having a small size are disposed in the second micro cups H 2 , respectively. 
     Similar to the above-described process, a solution  75  containing the second optical anisotropic elements  75   b  is poured onto the substrate  71  from the container  76 . At this time, when each of the second optical anisotropic elements  75   b  has such a size so as not be contained in the remaining space of a first micro cup H 1  in which the first optical anisotropic element  75   a  is contained, the second optical anisotropic element  75  may be effectively contained in the second micro cup H 2 , not in the first micro cup H 1 . 
     The process of disposing balls having a different size in the micro cups may be performed by the simplified process without a mask or filter. 
     Next, the respective micro cups H 1  and H 2  are filled with a fluid such as oil. Then, referring to  FIG. 7D , a display-side electrode  74  formed of a transparent electrode is provided to cover the top, thereby forming the electronic paper display device. The electronic paper manufactured by using balls or capsules having a different size according to the embodiment of the present invention may improve a packing factor as much as 10% or more in a single layer structure. 
       FIG. 8  is a top plan view of a substrate which may be adopted in an electronic paper display device according to another embodiment of the present invention.  FIG. 9  is a side cross-sectional view of the electronic paper display device according to the embodiment of the present invention, taken along a line C-C′ of  FIG. 8 . 
     The electronic paper display device  100  according to the embodiment of the present invention includes a display-side electrode  104  disposed at a display side and formed of a transparent material, aback electrode  102  disposed to face the display-side electrode  104 , and a plurality of embossed patterns  101  provided between the display-side electrode  104  and the back electrode  102 . 
     Instead of the substrate structure having the micro cups formed therein which is adopted in the above-described embodiment, spaces for containing optical anisotropic elements are formed by arranging the plurality of embossed patterns  101 . Such embossed patterns  101  are arranged as a single layer disposed between the display-side electrode  104  and the back electrode  102 . 
     Referring to  FIG. 8 , first and second spaces R 1  and R 2  defined by the plurality of embossed patterns  101  are arranged in a two-dimensionally close-packed manner, and first and second optical anisotropic elements  105   a  and  105   b  are disposed in the first and second spaces R 1  and R 2 , respectively. The plurality of first and second spaces R 1  and R 2  are arranged in a regular and repetitive manner. 
     Seen from the top, the embossed patterns  105  adopted in this embodiment are formed in such a Y shape that they may be easily partitioned. Furthermore, the embossed patterns  105  are arranged to provide hexagonal spaces. However, a plurality of embossed patterns having various shapes such as circle, triangle, straight line, and cross may be adopted. Furthermore, the plan shape of the space may be implemented in various manners. 
     Since the first and second optical anisotropic elements adopted in this embodiment have a different drive characteristic as in the above-described embodiment, the first and second optical anisotropic elements may be driven independently on the basis of their drive characteristics. In this case, since the first and second anisotropic elements are disposed in separate spaces, it is possible to prevent a problem caused by the contact with different optical anisotropic elements. 
     According to the embodiments of the present invention, the electronic paper display device having the monolayer-structure substrate, in which the optical anisotropic elements such as twist balls or electrophoretic capsules are arranged in a two-dimensionally close-packed manner, is manufactured to implement a high contrast ratio and a low driving voltage. As the balls or capsules serving as the optical anisotropic elements are separated from each other using the micro cups, the interaction between the respective balls and capsules may be reduced, making it possible to expect a smooth drive. Furthermore, as the anisotropic elements having a different size are disposed, it is possible to simplify the manufacturing process. 
     While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.