Abstract:
A display device may include a cell containing a suspension fluid and at least one suspension particle dispersed within the suspension fluid. The suspension particle may be adapted to migrate in the suspension fluid under the influence of an electric field. A light waveguide layer may extend adjacent to a side of the cell. The light waveguide layer may be adapted to conduct light laterally into the cell through the side of the cell.

Description:
BACKGROUND  
       [0001]     Display devices of various types are used to produce displays of images for viewing by users of the devices. The effectiveness of a display may depend on the ability of a viewer to comfortably perceive a displayed image. This effectiveness may be based on the ability of a display device to provide sufficient contrast between image elements, in combination with the amount of light that is emitted overall by the display device. Contrast typically is inherent in a device, since it is related to the size and quantity of display elements used to produce an image, and to the brightness of individual display elements of the display device. Accordingly, for a given type of device, such as a CRT, liquid crystal display, or electrophoretic display, an increase in the amount of light emitted by the device can result in an improved display. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0002]      FIG. 1  is a simplified illustration of a display device according to an embodiment of the invention.  
         [0003]      FIG. 2  is an illustration of a display device having a plurality of display cells according to another embodiment of the invention.  
         [0004]      FIGS. 3A-3C  illustrate the formation of a display cell according to yet another embodiment of the invention.  
         [0005]      FIGS. 4A-4D  illustrate the formation of a display cell according to another embodiment of the invention.  
         [0006]      FIGS. 5A-5D  illustrate the formation of a display cell according to another embodiment of the invention.  
         [0007]      FIG. 6  illustrates a display device according to another embodiment of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0008]     An electrophoretic cell may be a cell that includes particles suspended in a fluid and may use an electric field to migrate the particles through the fluid between different positions in the cell. The electrophoretic cell can serve as a display element when the particles can be made to move between a first position in which the particles are distributed along a surface of the cell where it can be viewed and a second position in which the particles are substantially hidden from view. The cell can produce different effects depending on the intended display. For instance, the particles can be reflective, colored, white or black in visual character. The fluid in which the particles are suspended can be colorless or colored. In certain combinations of these characteristics, the cell can function as a light valve, with the particles selectively blocking light from passing through the cell or allowing light to pass through the cell. An array of cells along a display surface positioned between a light source and the viewer can be used to create images for display by blocking light from being transmitted through selected cells.  
         [0009]     Referring now to the drawings and more particularly to  FIG. 1 , there is illustrated a display device  10  that may include a cell  12  and a light-conducting waveguide layer  14 . Device  10  may also include a base layer  16 . Cell  12  may form a microcapsule, or more generally, a capsule  18  that includes an enclosing light-conducting membrane  20 . The cell may have a first portion  12   a , including a first end  12   b  that extends into or through layer  14 . The cell may also include one or more sides, such as side  12   c , exposed to layer  14 . A second portion  12   d  of the cell may include a second end  12   e  that may extend beyond layer  14 . Base layer  16  may enclose, support or surround second end  12   e.    
         [0010]     Cell  12  may contain a light-conducting suspension fluid  22 , and one or more particles  24  suspended in the fluid. When particles  24  have an electrostatic charge, and an appropriate electric field is induced in cell  12 , device  10  may function as an electrophoretic display device. The charged suspension particles are caused to migrate to one or the other of ends  12   b  and  12   e  depending on the direction of the applied electric field. Incident light  26  may be directed along waveguide layer  14 . When incident light contacts side  12   c , at least a portion of it may be conducted through the cell and toward end  12   e . When particles  24  are positioned in the first end  12   b , as shown, received light  28  may be conducted through cell end  12   e  and out of the cell as display light  30 . Since the particles are not in the path of the light, light incident on the side of the cell is not blocked by the particles. As a result, more of the light can be emitted from the cell than would be possible if the cell were backlit. This, in turn, may result in brighter cells, more contrast, and an overall brighter display. Display light  30  may be characterized as having a color corresponding to the color of fluid  22 , the color of incident light  26 , or a combination of the colors of the fluid and the incident light. However, if particles  24  cover cell end  12   e , no or little light may escape through end  12   e , and the cell may appear to have the color of the particles.  
         [0011]     An observer may see light transmitted through the cell, which may form a display that may include one cell, or a plurality of cells, such as in an array with each cell forming an image element, or a component of a display element. Accordingly, display device  10  may be a display element of a display device including a plurality of display elements. A display element, when viewed, may represent an image element, also known as a pixel or pel, or a component of an image element. For example, different adjacent cells can have differently colored particles or differently colored solutions. Optionally, a cell may have differently colored particles of different electrostatic charges. A combination of adjacent differently colored cells may thus form, in combination, an image element.  
         [0012]     As mentioned, some electrophoretic display devices may include a plurality of display elements. An example of such a display device  40  is depicted in  FIG. 2 . Device  40  may include an array  42  of cells, as represented by cells  43 ,  44 ,  45  and  46 , and a multi-layer assembly  48  in which the cells may be supported. Each cell may include a suspension fluid  50  and respectively charged particles  52 . Assembly  48  can include an intermediate light-conducting waveguide layer  54  that may be sandwiched between outer support layers  56  and  58 . Each cell may have a relatively narrow end, such as end  46   a , that may be supported in layer  56 , an intermediate portion having sides, such as side  46   b , that may be exposed to or surrounded by waveguide layer  54 , and a relatively enlarged end  46   c  that may be supported in layer  58 .  
         [0013]     A continuous layer  60 , attached to layer  58 , may be adapted to conduct light emitted from the cells, as well as hold an electrical charge. Accordingly, layer  60  may also function as an electrode  61 . The opposite side of assembly  48  may include a layer  62  attached to layer  56 . Individually addressable electrodes  64  may be positioned in layer  62 , with an electrode in line with a narrow end of each cell, such as end  46   a . Electrodes  61  and  64  may produce the charges that cause the charged particles  52  to migrate to a selected end of each cell. Other electrode and cell configurations may be used.  
         [0014]     As with display device  10 , incident light  66 , from a corresponding light source, may be directed along waveguide layer  54 . The incident light may enter each cell from the side, as illustrated. For those cells in which particles  52  are collected adjacent the narrow ends of the cells, such as with cells  44  and  46 , the incident light directly enters the cells, as transmitted light  68 , without being diminished by the particles. The transmitted light in each cell may then be transmitted through the broad end of the cells to become viewable display light  70 . For those cells in which particles  52  are collected adjacent the broad ends of the cells, such as with cells  43  and  45 , the transmitted light may be prevented from passing through the broad ends of the cells, preventing these cells from contributing to the viewable display light.  
         [0015]     There are various methods that may be used to make a tapered cell.  FIGS. 3A-3C  illustrate one such method. A deformable cell  80 , that may contain a fluid  82  and electrophoretic particles  84 , may be positioned adjacent one end of a passageway  86  formed in a substrate  88 . The passageway may be tapered, having a broad end  86   a  and a narrow end  86   b . Optionally, passageway  86  may be closed at the narrow end, making it a cavity or chamber, or it may have other shapes, such as a cylindrical shape. In the case of a cavity or chamber, a cell may be formed using the sides of the cavity or chamber as the cell walls or membrane. In the latter case, the cell may be formed by inserting the fluid and particles, and sealing the cavity or chamber.  
         [0016]     Cell  80  may be inserted into the passageway. This may be accomplished in various ways. For instance, the cell may be pressed into the passageway, such as by applying a force  90  onto a plate  92  or other force-applying element or material, placed against the cell, such as shown. Optionally, the cell may be pulled into the passageway, such as by applying a reduced ambient atmosphere or vacuum to the opposite end of the passageway, as represented by arrow  94 .  
         [0017]      FIG. 3B  shows cell  80  partially inserted into the passageway. In some embodiments, this may be sufficient. In other embodiments, it may be desired to have the cell positioned entirely in the passageway, or even through the passageway, such as shown in  FIG. 3C . In this latter figure, it is seen that a portion  80   c  of the cell may extend beyond the narrow end of the passageway.  
         [0018]     Substrate  88  may be formed of one or more layers, such as a first layer  96  and a second layer  98 . Substrate  88  and cell  80  may be part of a display device. If first layer  96  is a light waveguide layer, then the position of the cell in  FIG. 3B  may be appropriate to cause light to enter into the cell from the side, as described above. Similarly, if second layer  98  is a waveguide layer, then the position of the cell in  FIG. 3C  also may be appropriate to allow light to enter the cell from the side.  
         [0019]     The method illustrated in  FIGS. 3A, 3B  and  3 C may also be appropriate where the outer membrane of the cell is in a pliable condition, and can be treated to make it rigid. For example, the cell membrane may be a thermoplastic. In this example, the cell may be heated before inserting it into the passageway, and cooled after it is in the passageway. As a further example, an epoxy or other resin-based material may be used to form the membrane, in which case the membrane may harden with the passage of time.  
         [0020]     Referring now to  FIGS. 4A-4D , another method for forming a shaped electrophoretic cell and or a display device is illustrated. An electrode  100  may be attached to or positioned in a first end  102   a  of an electrophoretic cell  102 , such as during making of the cell. Although not shown, cell  102  may include a suspension fluid and electrophoretic particles, as has been described in the preceding embodiments. The electrode may be attached to a conductor  104  or other member that extends away from the cell and with which the electrode may be manipulated.  
         [0021]     An end  102   b  of the cell spaced from electrode  100  may be restrained. This may be accomplished in various ways. One way may be by securing end  102   b  in a base layer  106 . As illustrated in  FIG. 4A , this may be accomplished by inserting the cell end into the base layer when the layer is in a liquid state, as may exist for resin-based or thermoplastic materials. When the layer is transformed into a solid state, as illustrated in  FIG. 4B , the cell end may be embedded in the layer and secured to it.  
         [0022]     Layer  106  may be of various thicknesses and may leave cell end  102   a  exposed. Optionally, a second layer  108  of material may be applied to cell  102 , similar to the application of the base layer. As is illustrated in  FIG. 4C , a force  110  may be applied to cell end  102   a  directed away from cell end  102   b , until the cell deforms, as illustrated in  FIG. 4D . Depending on the weight of the cell relative to the deformability of cell end  102   a , it may be sufficient to use gravity to restrain the cell. If cell  102  is formed of a thermoplastic material, heat  112  may be applied to cell end  102   a  to transform it into a deformable state. Holding the cell end in a deformed state, heat  112  may be removed, thereby cooling the cell end and transforming it into a rigid state in the shape shown in  FIG. 4D .  
         [0023]     The assembly of electrode  100 , cell  102 , conductor  104  and base layer  106  may form a display device  114 , similar to display devices  10  and  40 , in which base layer  106  may be a light waveguide layer. In some embodiments, a second layer  108  may be included in the display device, with the second layer forming a light waveguide layer.  
         [0024]     Yet another method of forming an electrophoretic cell is illustrated in  FIGS. 5A-5D . An electrophoretic cell  120  may be made of a thermoplastic material, and may include a suspension fluid and charged particles as described in the previous embodiments. As shown in  FIG. 5A , cell  120  may be secured by an apparatus  122 , such as an extruder from which the cell may be formed, or a device with an aperture through which a vacuum may be applied to a first portion  120   a  of the cell.  
         [0025]     Cell  120  may be suspended from apparatus  122 . A suitable energy  124 , such as heat or infrared radiation, may be applied to the cell, allowing it to deform into an elongate shape, such as a teardrop shape as shown in  FIG. 5B . Once the cell exists in an elongate shape, a second portion  120   b , spaced from portion  120   a , may be broadened. This broadening may be provided in various ways, such as by applying a force  126  to portion  120   b  with an external surface, such as surface  128 . This may be achieved by pressing surface  128  against the bottom of the cell as the cell is suspended. Optionally and as shown, the cell may be released from apparatus  122  and allowed to land on surface  128 . In this latter method, gravity acting on the cell or force of extraction from extrusion apparatus  122  may produce sufficient momentum in the cell to cause cell portion  120   b  to broaden as it lands on the surface.  
         [0026]     As cell portion  120   a  elongates during this process, this cell portion may be maintained in the elongated shape. This may be accomplished, at least in part, by removing heat  124  from this cell portion, as illustrated in  FIG. 5C . Further, once cell portion  120   b  has formed into a broadened shape, the broadened shape may be maintained, such as by the further removal of heat  124  from the cell. This may be accompanied by the continued appropriate application of force  126  to cell portion  120   b . The weight of cell  120  on surface  128  may be sufficient to broaden cell portion  120   b  or to maintain cell portion  120   b  in the broadened shape while the cell is cooled.  
         [0027]     The resulting cell, which may have a narrow portion  120   a  and broadened portion  120   b , may be used in a display device, such as display device  10  or  40 .  
         [0028]     Referring now to  FIG. 6 , yet another embodiment of a display device is shown generally at  140 . Device  140  may include an array  142  of cells, as represented by cells  144 ,  145  and  146 , and a multi-layer assembly  148  in which the cells may be supported, positioned or embedded. Each cell may include a suspension fluid  150  and respectively charged particles  152 . Assembly  148  can include an intermediate light conducting waveguide layer  154  that may be sandwiched between outer layers  156  and  158 . Each cell may include a chamber  160  in waveguide layer  154 . Chamber  160  may be a cavity, passageway, compartment, channel or other space defined by an opening in waveguide layer  154 , or in a combination of layers including layer  154 . The cell chambers may be formed by etching, embossing, casing, injection molding, photolithographic processes, drilling, embedding a preformed element, or other suitable technique. The cell chambers also may have a variety of shapes, for example, having a relatively narrow end, such as end  146   a , an intermediate portion having sides, such as side  146   b , and a relatively enlarged end, such as end  146   c.    
         [0029]     Layer  156  may be a continuous layer attached to layer  154  and sealing chambers  160 , may be adapted to conduct light emitted from the cells, and may hold an electrical charge. Accordingly, layer  156  may also be an electrode  162 . Individually addressable electrodes  164  may be positioned in layer  158 , with an electrode in line with a narrow end of each cell, such as end  146   a . Electrodes  162  and  164  may produce the charges that cause the charged particles  152  to migrate to a selected end of each cell. Other electrode and cell configurations may be used.  
         [0030]     Incident light  166 , from a corresponding light source, may be directed along waveguide layer  154 . The incident light may enter each cell from the side, as illustrated. For those cells in which particles  152  are collected adjacent to the narrow ends of the cells, such as with cells  145  and  146 , the transmitted light  168  in each cell may then be transmitted through the broad end of the cells to become viewable display light  170 . For those cells in which particles  152  are collected adjacent to the broad ends of the cells, such as with cell  144 , the transmitted light may be prevented from passing through the broad ends of the cells, preventing these cells from contributing to the viewable display light.  
         [0031]     While the present disclosure has been provided with reference to the foregoing embodiments, those skilled in the art will understand that many variations may be made therein without departing from the spirit and scope defined in the following claims. The foregoing embodiments are illustrative, and no single feature, procedure or element is essential to all possible combinations that may be claimed in this or a later application. Moreover, the description should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. Where the claims recite “an”, “a first”, or “another” element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.