Abstract:
A backframe may be utilized to align a plurality of emissive display tiles precisely with respect to one another. The individual display tiles may be removable from the backframe for replacement or other reasons. As a result, the spacing between individual tiles in an overall large format display may be precisely controlled in some cases. In addition, regularly occurring gaps between adjacent tiles may be filled with a suitable light absorbing material to reduce the visibility of seams.

Description:
BACKGROUND  
         [0001]    This invention relates generally to large format emissive displays.  
           [0002]    Large format displays may be utilized to create displays of a size greater than the size of conventional displays. For example, large format displays may combine the images produced from a plurality of conventional displays. The composite display may be able to produce an image which is much larger and more economical than that possible with existing display technologies.  
           [0003]    Emissive displays include light emitting diodes, liquid crystal displays, and organic light emitting displays. These displays actually emit light at the pixel level which can perceived by viewers. Emissive displays may be combined together to create a large format display.  
           [0004]    When emissive displays are combined to create a large format display, those displays may suffer from visible seams. The visible seams arise from the joints between the combined displays. The user looking at the large format display notices the individual displays which together are combined to create the overall image. Thus in some cases, the large format display may not produce a seamless image.  
           [0005]    Another problem with large format displays is that the individual displays that are combined to form the large format display may be misaligned with respect to one another. Even the slightest misalignment may result in an irregularity in the overall image that may be noticeable to anyone viewing the large format display.  
           [0006]    Thus, there is a need for better ways to combine emissive displays into large format displays. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a perspective view of an emissive display tile in accordance with one embodiment of the present invention;  
         [0008]    [0008]FIG. 2 is a side elevational view of an emissive display module in accordance with one embodiment of the present invention; and  
         [0009]    [0009]FIG. 3 is a front elevational view of a large format display in accordance with one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0010]    Referring to FIG. 1, an emissive display tile  100  may include a plurality of electroluminescent cells  20  each producing a pixel or subpixel of monochrome or color light. Thus, the cells  20  in a given display tile  100  may produce one or more pixels or subpixels of light which can contribute to the display of an image. In some cases, a large number of cells  20  may be utilized. In another case, fewer cells may be appropriate.  
         [0011]    The display tile  100  may include an integrated circuit driver chip  10 . The chip  10 , mounted on the lower surface of the display tile  100 , actually drives the display cells  20  by way of electrical connections in feedthroughs (not shown).  
         [0012]    The tile  100  may include a body  24 . In one embodiment, the body  24  may be a ceramic layer. Over the body  24  is a transparent layer  104  which may be formed of glass. A black material  102  is applied in a grid pattern on the top surface of the transparent layer  104 .  
         [0013]    The emissive cells  20  may actually be formed on the bottom surface of the transparent layer  104 . The cells  20  are then visible from above, as shown in FIG. 1, because of the transparent nature of the transparent layer  104 . In one embodiment, each cell  20  may include three light emitting elements such as a red, green and blue light emitting element.  
         [0014]    The black material  102  includes an intermediate section  102   a  of greater width and a peripheral section  102   b  that may be less than one-half the width of the material  102   a . Thus, when tiles  100  are butted one against the other and a slight gap is left between adjacent tiles, the combined sections  102   b  from two adjacent tiles  100  have a resulting width approximately equal to that of the section  102   a . As a result, when the combined display is viewed, it has a consistent matrix pattern of pixels.  
         [0015]    The black material  102  forms a matrix that covers the voids between individual cells  20 . This may reduce reflection from electrode structures (not shown) on the bottom surface of the transparent layer  104  thereby increasing pixel contrast. The matrix  102  may be a grid of optically black absorbing material that covers the horizontal and vertical spaces between the cells  20  in the form of horizontal and vertical stripes. In one embodiment black material  102   a  may have a width that is a fraction, usually between 0.25 and 0.5 of the pixel-to-pixel spacing, to allow for misalignment between tiles when formed onto an array of tiles. Patterning may be achieved by transfer screen printing, ink jet printing or other methods capable of producing spatial positioning tolerances and feature sizes on the order of 10 microns.  
         [0016]    The black matrix material  102  may be optically absorbing to visible wavelengths of light and resistant to removal during cleaning of the completed assembly with water or mild solvents. As one example, a black emulsion, as typically used in photomask fabrication may be used for this purpose.  
         [0017]    Referring to FIG. 2, the tile  100  may be mounted on a backplate  110 . Each module  101 , composed of a tile  100  with a backplate  110 , may be optically, electrically and mechanically interchangeable with a plurality of other components in accordance with one embodiment of the present invention. The module assembly is performed at an optical alignment station that provides x,y and z dimensions to tolerances of about 10 microns in each direction. This means that the smallest pixel pitch for a seamless appearance is about one millimeter.  
         [0018]    The backplate  110  may provide mechanical support to the display tile  100 . The backplate  110  may assembled to the display tile  100  using a thin, flexible epoxy adhesive in one embodiment.  
         [0019]    A pair of alignment elements  112  on the backplate  110  provide x and y alignment control at display assembly between the display tile  100  and the backplate  110 . A variety of alignment elements  112  may be used including holes, grooves, tabs, and a variety of pin shapes as a few examples. An exemplary backplate  110  thickness may be one millimeter or more.  
         [0020]    The backplate  110  may be smaller in size than the tile  100  by about one millimeter or more in one embodiment. Cut out regions (not shown) in the backplate  110  may provide clearance for tile electronics such as the chip  10  and connectors that are disposed on the back side of the tile  100 . The backplate  110  may also include fastener extensions  114  for attachment to a backframe (not shown in FIG. 2).  
         [0021]    Referring to FIG. 3, the backframe  120  may include a number of alignment devices  124  to receive the alignment elements  112  and fasteners  114  of a plurality of modules  101 . The alignment devices  124  may be pins, holes, grooves, or tabs, as a few examples. The alignment devices  124  mate with and align the alignment elements  112 . As a result, a large number of modules  101  may be secured on the backframe  120  in precise relative alignment. The fasteners  114  may be secured onto the backframe  120  using nuts  122  as one example. However, any of a variety of other fasteners may be utilized as well, including rivets, releasable catches, friction welds, and solder, as additional examples.  
         [0022]    The seams between adjacent modules  101  can then be filled by an optically clear, substantially index matching gap material  128 . The gap material  128  may be an adhesive such as an acrylic or silicone adhesive. The gap material  128 , for example, may be dispensed by syringe from the front side of the large format display  200 . The gap material  128  may reduce the amount light scattered from the edges of each panel which would otherwise cause a seam to be visible, particularly when viewed off-axis.  
         [0023]    To aid in the replacement of the individual display modules  101 , a reworkable adhesive may be utilized as the gap material  128  in one embodiment. For example, an ultraviolet degradable epoxy may be used.  
         [0024]    A black patterned coating  126  may be applied to the front of the large format display  200  in a form of horizontal and vertical stripes to cover the front of the seams, for example using a syringe. The width of the coating  126  may substantially match the width of the stripes of material  102   a  patterned on the individual tiles  100 . The material used in the coating  126  may be identical to or similar in optical and mechanical properties to the material  102  used to pattern the stripes on the individual tiles  100 .  
         [0025]    The patterning results in a visual effect that presents a low contrast mesh pattern superimposed over the displayed image. This pattern may become part of the pixelated structure of the display, at a spatial frequency equal to that of the pixels. For normal viewing the distances between the fine structure of this pattern may not be resolvable in some embodiments. If one tile  100  must be replaced, its module  101  may be readily disconnected from the backframe  120 .  
         [0026]    While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.