Patent Publication Number: US-2007115251-A1

Title: Electro phoretic display device and driving method of the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of Korean Patent Application No. 2005-0112034, filed on Nov. 22, 2005, 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 electro phoretic display device and a manufacturing method of an electro phoretic indication display.  
      2. Description of the Related Art  
      An electro phoretic display device is one type of flat display device, and is typically used for e-book (electronic book) applications. An electro phoretic display device comprises two substrates with electrodes formed thereon and facing one another, and includes charged particles between the two substrates. An electro phoretic display device applies a potential difference between the electrodes that are positioned facing one another. The charged particles move away from the electrode with the same polarity and toward the electrode having the opposite polarity with respect to the charged particles, and the device thereby displays an image.  
      An electro phoretic display device has high reflectivity and contrast ratio, and the display does not depend on a viewing angle. As a result, an electro phoretic display device can stably display the image like paper. Further, the electro phoretic display device is bistable and maintains the image without needing to continuously apply the voltage, thereby reducing power consumption. Unlike a liquid crystal display (LCD), an electro phoretic display device does not need a polarizing plate, an arrangement layer, liquid crystals, etc., and thus may be manufactured at a lower cost.  
      However, for some applications, electro phoretic display devices are not flexible enough.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an aspect of the present invention to provide an electro phoretic display device with improved flexibility.  
      Another aspect of the present invention is to provide a manufacturing method of an electro phoretic display device which has excellent flexibility.  
      The foregoing and/or other aspects of the present invention are achieved by providing an electro phoretic display device comprising: a first substrate including a first electrode; a second substrate including a second electrode positioned facing the first substrate; a plurality of spaces formed between the first electrode and the second electrode; fluid including a plurality of charged particles disposed in the spaces; and one or more gel members dividing the spaces.  
      According to an embodiment of the present invention, at least a one of the plurality of spaces is in direct contact with at least one of the first substrate and the second substrate.  
      According to an embodiment of the present invention, at least a part of one of the plurality of spaces extends in a substantially perpendicular direction to a surface of the first substrate.  
      According to an embodiment of the present invention, at least one the plurality of spaces is encompassed by the one or more gel members.  
      According to an embodiment of the present invention, an average cross-sectional small dimension of the plurality of spaces is 100 times to 10000 times an average cross-sectional large dimension of the plurality of charged particles.  
      According to an embodiment of the present invention, an average diameter of the plurality of spaces is included in the range extending from 10 μm to 100 μm.  
      According to an embodiment of the present invention, the one or more gel members comprise an inorganic material.  
      According to an embodiment of the present invention, the one or more gel members comprise silica.  
      According to an embodiment of the present invention, the first electrode and the second electrode are configured to generate an electric field therebetween, and wherein the plurality of charged particles are configured to move up and down in response to the electric field generated between the first electrode and the second electrode.  
      According to an embodiment of the present invention, the plurality of charged particles comprise white sub-particles.  
      According to an embodiment of the present invention, the plurality of charged particles comprise white sub-particles and black sub-particles, where the white sub-particles and black sub-particles have opposite polarities.  
      According to an embodiment of the present invention, the first substrate comprises an insulating substrate and a TFT formed on the insulating substrate, and wherein the first electrode is connected to the TFT.  
      According to an embodiment of the present invention, the first electrode is included in a plurality of first electrodes, and at least one of the plurality of spaces face at least two first electrodes.  
      According to an embodiment of the present invention, the first electrode is included in a plurality of first electrodes, and at least one of the plurality of first electrodes face at least two spaces.  
      According to an embodiment of the present invention, at least one of the first substrate and the second substrate comprises a plastic insulating substrate.  
      According to an embodiment of the present invention, the fluid is a transparent organic solution.  
      According to an embodiment of the present invention, the total volume of the one or more gel members is 20% to 100% of the total volume of the plurality of spaces.  
      The foregoing and/or other aspects of the present invention are also achieved by providing a manufacturing method of an electro phoretic display device comprising: providing a first substrate including a first electrode; adhering a film-type gel member comprising a plurality of spaces to the first electrode; providing a fluid and charged particles into the plurality of spaces; and adhering a second substrate including a second electrode to the gel member.  
      According to an embodiment of the present invention, the gel member comprises an inorganic material.  
      According to an embodiment of the present invention, the first electrode is included in a plurality of first electrodes, and at least a one of the plurality of spaces face at least two first electrodes.  
      According to an embodiment of the present invention, the first electrode is included in a plurality of first electrodes, and at least a one of the first electrodes face at least two spaces. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which:  
       FIG. 1  schematically illustrates a driving principle of an electro phoretic display device according to an exemplary embodiment of the present invention;  
       FIG. 2  is a sectional view of an electro phoretic display device according to a first embodiment of the present invention;  
       FIG. 3  is an exploded perspective view of the electro phoretic display device according to the first embodiment of the present invention;  
       FIG. 4  is a flow chart to illustrate a manufacturing method of the electro phoretic display device according to the first embodiment of the present invention; and  
       FIG. 5  is a sectional view of an electro phoretic display device according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
      Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.  
      First, a driving principle of an electro phoretic display device according to an exemplary embodiment of the present invention will be described with reference to  FIG. 1 .  
      As shown in  FIG. 1 , an electro phoretic display device according to an exemplary embodiment of the present invention comprises a pair of electrodes  10  and  20 . By applying a potential difference between electrode  10  and electrode  20  an electric field is generated between the electrodes. The pair of electrodes  10  and  20  comprise a pixel electrode and a common electrode. The potential difference between electrode  10  and electrode  20  depends on a voltage applied by a power supply  30 . A fluid  40  is dispersed between electrode  10  and electrode  20 , and charged particles  50  are dispersed in the fluid  40 . The charged particles  50  are either positive or negative and either black or white.  
      In an electro phoretic display device according to the exemplary embodiment of the present invention, if a voltage is applied to electrodes  10  and  20  to generate the potential difference (+, −) therebetween, the charged particles  50  move up and down from one electrode to the other electrode having the opposite polarity. Accordingly, an observer recognizes light reflected by the charged particles. If the charged particles  50  move up to (toward) the observer, the observer perceives the colors of the charged particles  50  as more intense. If the charged particles  50  move down (away), the observer perceives the colors of the charged particles  50  as less intense (paler).  
      The charged particles  50  move by electrophoresis, a phenomenon in which a particle of a surface charge moves in an electric field to an electrode having an opposite charge. Electrophoresis is not merely an electromagnetic phenomenon, but can be interpreted by colloidal science and fluid mechanics.  
      An electro phoretic display device  1  according to a first embodiment of the present invention will be described with reference to  FIGS. 2 and 3 .  
      The electro phoretic display device  1  comprises a first substrate  100 , a second substrate  200  facing the first substrate  100 , and a gel member  350  disposed between first substrate  100  and second substrate  200 . The gel member  350  divides spaces  310 . Fluid  321  and charged particles  331  and  332  dispersed in the fluid  321  are disposed in each space  310 .  
      A gate electrode  121  is formed on a first insulating substrate  110 . The gate electrode  121  may be a single layer structure with low resistivity, or may be a multi-layer structure including a -layer with low resistivity and a layer with good contact properties. For example, a single layer structure for gate electrode  121  may comprise a low resistivity material such as silver (Ag), silver alloy, aluminum (Al) or aluminum alloy. A multi-layer structure for gate electrode  121  may include the low resistivity layer and another layer comprising chrome (Cr), titanium (Ti), tantalum (Ta) or other material with good contact properties.  
      A gate insulating layer  131  of silicon nitride (SiNx) covers the gate electrode  121  on the first insulating substrate  110 .  
      A semiconductor layer  132  of amorphous silicon is formed on the gate insulating layer  131 . An ohmic contact layer  133  made of n+ hydrogenated amorphous silicon which is highly doped with silicide or n-type dopant is formed on the semiconductor layer  132 . The ohmic contact layer  133  is divided into two regions with respect to the gate electrode  121 .  
      A data line assembly  141  and  142  is formed on the ohmic contact layer  133  and the gate insulating layer  131 . The data line assembly  141  and  142  may comprise silver or aluminum which has low resistivity, and/or a conductive material with good contact properties. The data line assembly  141  and  142  comprises a source electrode  141  disposed on one region of the ohmic contact layer  133 , and a drain electrode  142  separated from the source electrode  141  and disposed on the region of ohmic contact layer  133  opposite the source electrode  141 , across the gate electrode  121 .  
      A passivation layer  151  is formed on the data line assembly  141  and  142  and a portion of the semiconductor layer  132  which is not covered with the data line assembly  141  and  142 . The passivation layer  151  comprises a material such as silicon nitride, an a-Si:C:O layer or an a-Si:O:F which is deposited by a plasma enhanced chemical vapor deposition (PECVD) method, an acrylic organic insulating layer, or the like. A contact hole  152  exposing the drain electrode  142  is formed in the passivation layer  151 .  
      A pixel electrode  161  is formed on the passivation layer  151 . The pixel electrode  161  generally comprises a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).  
      A plurality of pixel electrodes  161  are connected to the TFTs T is arranged regularly on the first substrate  100 , as shown in  FIG. 3 .  
      Referring to a second substrate  200 , a common electrode  220  is formed on a second insulating substrate  210 .  
      The common electrode  220  generally comprises a transparent conductive material such as ITO or IZO. The common electrode  220  is formed across the second insulating substrate  210  and a potential difference between common electrode  220  and each of the pixel electrodes  161  forms an electric field in the region between the common electrode  220  and a pixel electrode  161  to drive charged particles  331  and  332  which are positive or negative.  
      At least one of the first insulating substrate  110  and the second insulating substrate  210  may be transparent, and at least one of-the first insulating substrate  110  and the second insulating substrate  210  may comprise a plastic material. The plastics may be polycarbon, polyimide, polyethersulfone (PES), polyarylate (PAR), polyethylenenaphthalate (PEN), polyethyleneterephthalate (PET), or other appropriate plastic material. If the insulating substrates  110  and  210  comprise plastics, the electro phoretic display device  1  may be relatively light, slim and flexible.  
      The gel member  350  is disposed between the first substrate  100  and the second substrate  200  to divide the spaces  310 , in which the fluid  321  and the charged particles  331  and  332  are disposed.  
      The fluid  321  may have a low viscosity so that the charged particles  331  and  332  may have high mobility. Further, the fluid  321  may have a low dielectric constant to restrict chemical reaction. Preferably, the fluid  321  is transparent to improve reflecting brightness. The fluid  321  comprises, for example, hydrocarbon such as decahydronaphthalene, 5-ethylidene-2-norbornene, fat oil or paraffin oil; aromatic hydrocarbon such as toluene, xylene, phenylxylylethane, dodecyl benzene or alkylnaphthalene; and a halogenated solvent such as perfluorodecalin, perfluorotoluene, perfluoroxylene, dichlorobenzotrifluoride, 3,4,5-trichlorobenzotrifluoride, chloropentafluoro-benzene, dichlorononane or pentachlorobenzene.  
      The charged particles  331  and  332  dispersed in the fluid  321  comprise white sub-particles  331  and black sub-particles  332 . The white sub-particles  331  and the black sub-particles  332  are charged with different polarities from each other, and thus they move in opposite directions in an electric field. The white sub-particles  331  comprise titanium oxide (TiO 2 ) or silica (SiO 2 ). The black sub-particles  332  comprise carbon black, or TiO 2  or SiO 2  colored with a black pigment.  
      The charged particles  331  and  332  move up and down in response to the electric field generated between the pixel electrode  161  and the common electrode  220 , to adjust the amount of reflected light. For example, when the white sub-particles  331  move up and the black sub-particles  332  move down, a white color is displayed. By contrast, when the white sub-particles  331  move down and the black sub-particles  332  move up, a black color is displayed. A single pixel electrode  161  can display a gray color as well.  
      The charged particles  331  and  332  may have their own charges, be charged by a charge control agent, or obtain charges while drifting in the solvent. The charge control agent may be polymer or non-polymer, ionic or non-ionic, and may comprise sodium dodecylsulfonate, metal soap, polybutene succineimide, maleic anhydride copolymer, vinyl piridine copolymer, vinylpirolidone copolymer, acrylic(metacryl) acid copolymer, or other appropriate material.  
      Particles dispersed in the fluid  321 , such as charged particles  331  and  332 , charge control agent particles, or the like, should be in colloidal stability each other. The colloidal stability may be achieved by adjusting the size of the particles and a surface charge thereof.  
      The gel member  350  divides the spaces  310 . The gel member  350  has a porous shape, i.e. a film shape in which the spaces  310  are scattered, as shown in  FIG. 3 . Preferably, the gel member  350  is transparent.  
      A gel is formed from a colloidal solution (sol) when the colloidal solution (sol) reaches or exceeds a certain concentration, and the colloidal solution forms a network to form the gel. Examples of gels are agar, silica gel, and other gel types which are formed by hardening of the material in a dispersion medium, such as water, in which the network of colloidal particles is dispersed. The gel becomes fluid by heating, since the network is broken by molecular motions or the like. A hydrogel is a gel in which water is the dispersion medium. A xerogel is a porous gel in which air is the dispersion medium. Xerogels include, for example, diatomite, acid clay, etc.  
      Referring again to the spaces  310 , the spaces  310  are disposed between the first substrate  100  and the second substrate  200 . In the illustrated embodiment, spaces  310  extend in a direction perpendicular to surfaces of the substrates  100  and  200 . Preferably, the volume of each space  310  exceeds the size of the charged particles  331  and  332  sufficiently, so that the charged particles  331  and  332  (typically of nanometer dimension) may move up and down easily. In an embodiment, the spaces  310  have an average diameter d 1  of 10 μm to 100 μm, which is about 100 times to 10,000 times an average diameter of the charged particles  331  and  332 . For embodiments in which the spaces  310  and/or particles  331  and  332  do not have a single diameter, the applicable dimensions may have the above relationship. For example, the average cross-sectional small dimension of spaces  310  may be in the range from 10 μm to 100 μm, which may be about 100 to 10,000 times the average cross-sectional large dimension of particles  331  and  332 . For example, for a particular space  310  with an elliptical cross section that varies along the longitudinal extent of the space, the cross-sectional small dimension refers to the smallest minor axis. For particles  331  and  332 , the cross-sectional large dimension refers to the largest straight-line distance between points on the surface.  
      One or more spaces  310  directly contact one or more pixel electrodes  161  on the first substrate  100  and the common electrode  220  on the second substrate  200 . Some spaces  310  face a single pixel electrode  161 , but other spaces  310  face two or more pixel electrodes  161 . Likewise, some pixel electrodes  161  face two or more spaces  310 . The charged particles  331  and  332  in a particular space  310  move in different directions if they face different pixel electrodes  161 . Although the spaces  310  do not generally correspond to the pixel electrodes  161  one-by-one, the movement of the charged particles  331  and  332  is controlled by the pixel electrodes  161  to form a desired image.  
      The volume occupied by the gel member  350  positioned between the first substrate  100  and the second substrate  200  may be in a range of 20% and 100% of the volume of the space  310 . If the volume of the gel member  350  is less than 20% of the volume of the space  310 , the strength of the gel member  350  may not be sufficient. On the contrary, if the volume of the gel member  350  is more than 100% of the volume of the spaces  310 , the volume of spaces  310  may be insufficient to provide the desired resolution.  
      As mentioned above, the electro phoretic display device  1  uses the gel member  350  to divide the spaces  310 . The gel member  350  is improved in flexibility compared to that of a conventional wall, thereby increasing flexibility of the electro phoretic display device  1 . The gel member  350  reduces loss of the fluid  321  and the charged particles  331  and  332  if the electro phoretic display device  1  is broken. Further, the gel member  350  in a solid state maintains a cell gap between the first substrate  100  and the second substrate  200 . Therefore, an additional spacer is not needed. In some embodiments, the height (h) of the gel member  350  may be several micrometers to tens of nanometers.  
      The response time of the electro phoretic display device  1  may be controlled by adjusting the thickness of the gel member  350  and the voltage applied to the pixel electrodes  161  and common electrode  220 .  
      A method  400  to manufacture an electro phoretic display device according to the first embodiment of the present invention will be described, with reference to  FIGS. 1-4 .  
      First, the first substrate  100  where the pixel electrodes  161  are formed is provided (at  410 ). The first substrate  100  comprises TFTs T and the pixel electrodes  161  connected to the TFTs T. The first substrate  100  may be manufactured by methods known to persons skilled in the art, which are not described here.  
      The gel member  350  adheres to the pixel electrodes  161  (at  420 ). For example, a film-type gel member  350  may be laminated on the pixel electrodes  161  so that gel member  350  is adhered to first substrate  100 . Pores, i.e. the spaces  310 , are randomly distributed in the gel member  350  and extend in a thickness direction of the gel member  350 .  
      The fluid  321  and the charged particles  331  and  332  are injected into the spaces  310  of the gel member  350  (at  430 ). This is performed, for example, by depositing part or all of the gel member  350  into the fluid  321  in which the charged particles  331  and  332  are dispersed. In this example, the fluid  321  comprising the charged particles  331  and  332  is injected to the spaces  310  by capillarity or the like.  
      At  440 , the second substrate  200  (where the common electrode  220  is formed) adheres to the gel member  350 , to complete the electro phoretic display device  1  shown in  FIG. 2 .  
      A sealant (not shown) may be used to attach the first substrate  100  and the second substrate  200 .  
      In some embodiments, the gel member  350  may adhere to the pixel electrode  161  with at least one of the fluid  321  and the charged particles  331  and  332  already injected into the spaces  310 . In some embodiments, the gel member  350  may adhere to the second substrate  200  first, and may then be attached to the first substrate  100 .  
      Hereinafter, an electro phoretic display device  1  according to a second embodiment of the present invention will be described with reference to  FIG. 5 . It should be noted that the following description emphasizes the features that are different than those of the first embodiment, and discussion of similar features may not be repeated herein.  
      A first substrate  100  further comprises a first sealing/adhering layer  171  formed on a pixel electrode  161 . A second substrate  200  further comprises a second sealing/adhering layer  230  in contact with a fluid  321  and a gel member  350 . The sealing/adhering layers  171  and  230  adhere to the gel member  350  to prevent charged particles  332  in one space  310  from moving to another space  310 . The sealing/adhering layers  171  and  230  may comprise polymer.  
      In some embodiments, display device  1  is formed by adhering the sealing/adhering layers  171  and  230  to opposite sides of the gel member  350 , and then adhering layers  171  and  230  to the first substrate  100  and the second substrate  200 . In some embodiments, display device  1  is formed by adhering the sealing/adhering layers  171  and  230  to the first substrate  100  and the second substrate  200 , and then adhering layers  171  and  230  to the gel member . 350 .  
      By contrast to the first embodiment described above, the charged particles  332  are only black. The charged particles  332  move up to display a black color, and move down to display a white color. The spaces  310  in the second embodiment may be provided in various configurations. For example, the gel member  350  may be disposed between one or more of the spaces  310  and the second substrate  200  as shown in ‘A’, or one or more of the spaces  310  may be encompassed by the gel member  350  as shown in ‘B’. These different configurations for spaces  310  may also be used in other embodiments, such as the first embodiment.  
      The movement of the charged particles  332  is controlled by the pixel electrode  161  disposed therebelow, and thus an image is formed regardless of the shape of the space  310 .  
      As described above, embodiments of the present invention provide an electro phoretic display device with improved flexibility.  
      Further, embodiments of the present invention provide a manufacturing method for an electro phoretic display device with improved flexibility.  
      Although a few embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.