Abstract:
A display may be formed of a plurality of abutted tiles, each tile contributing a portion of the overall displayed image. Optical elements may be selectively situated between pixels to improve the optical performance of the display. In some embodiments, these optical elements may facilitate the use of relatively thicker cover glasses over the display tiles.

Description:
BACKGROUND  
         [0001]    This invention relates generally to emissive displays including organic light emitting device (OLED) displays, light emitting diode (LED) displays and electro luminescence (EL) displays.  
           [0002]    Emissive displays generally include a cover glass or transparent sheet over the light emissive elements. The transparent sheet generally is substantially transparent to light emissions. The thinner the glass sheet, normally the less its optical effects.  
           [0003]    In displays made by combining a plurality of tiles, each including a cover glass, gaps may exist between adjacent tiles. The thicker the glass that is utilized, the more apparent are these gaps to viewers of such displays.  
           [0004]    While the use of thin cover glasses has many advantages, it also has concomitant cost disadvantages. Thinner glass generally breaks more easily. In addition, manufacturing equipment is designed for certain minimum glass thicknesses. Using thinner glass may result in cost penalties or require the development of specialized equipment for handling glass processing.  
           [0005]    Thus, the thicker the cover glass that is utilized, the more apparent are any gaps between adjacent tiles. The composite image of a large area display is the result of the images contributed by each of the tiles making up the large area display. To the extent that the individual tiles may be delineated because of the inter-tile gaps, the overall seamless effect of the display is lessened. Therefore, it is desirable to produce large area displays in which the individual tiles making up the displays are as invisible and undiscernible as possible.  
           [0006]    Thus, while using thicker glass has many practical advantages, it may also increase the likelihood that seams between adjacent tiles become visible. Therefore, there is a need for a way to make the gaps between adjacent tiles less visible in large area displays.  
           [0007]    State of the art tile displays, such as video walls, use mullions between individual tiles to hide the physical gap. However, if these mullions are discernible to the user, they are objectionable because they break the continuity of the image.  
           [0008]    Another structure commonly found in non-tiled displays is a pattern of black lines. The black lines, like a mullion, produce inter-pixel black lines. A black line is put between the pixels to absorb ambient light in those areas in order to increase the display contrast. Black lines are found in non-modular displays such as cathode ray tubes and liquid crystal displays. With these displays, the black lines are smaller than the mullions. They are placed in the plane of the pixels, located between the pixels. Because the pattern of black lines is periodic and placed between pixels, it does not break the continuity of the image.  
           [0009]    Thus, there is a need for ways to make the seams of large area displays less visible. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a schematic depiction of one embodiment of the present invention;  
         [0011]    [0011]FIG. 2 is a partial, enlarged cross-sectional view of another embodiment of the present invention;  
         [0012]    [0012]FIG. 3 is a partial, enlarged cross-sectional view of still another embodiment of the present invention;  
         [0013]    [0013]FIG. 4 is a partial, enlarged cross-sectional view of still another embodiment of the present invention;  
         [0014]    [0014]FIG. 5 is a partial, enlarged cross-sectional view of still another embodiment of the present invention;  
         [0015]    [0015]FIG. 6 is a partial, enlarged cross-sectional view of yet another embodiment of the present invention;  
         [0016]    [0016]FIG. 7 is a partial, enlarged cross-sectional view of another embodiment of the present invention;  
         [0017]    [0017]FIG. 8 is a partial, enlarged cross-sectional view of another embodiment of the present invention; and  
         [0018]    [0018]FIG. 9 is a partial, enlarged cross-sectional view of another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]    Referring to FIG. 1, a pair of adjacent display tiles  10  and  12  may combine to create a portion of an overall large area display made up of a plurality of tiles  10  and  12 . The region between display tiles  10  and  12 , indicated as A, is described herein as the gap. The gap A includes an upper surface which is closest to the viewer and a gap region that proceeds along the entire thickness of the tiles  10  and  12 . At the top of the gap A, differences in surface reflection, such as the angle of reflection and its intensity, are most important. Below the top of the gap surface in the gap region, the differences in refraction, reflection and absorption are important if they are different in the region of the tiles between the pixels that are not straddling a gap.  
         [0020]    Two rays are shown emanating from the lower surface of the gap A and extending upwardly at an angle θ c  called the critical angle. At the critical angle, a ray is refracted to an angle parallel to the top surface of each layer  10  or  12 . Light reaching the surface with angles less than the critical angle exits the layers  10  and  12  and light reaching the surface with angles larger than the critical angle is totally internally reflected.  
         [0021]    Because of the critical angle, light emitted from a point within the layers  10  and  12  can escape from the panels by traveling at most a lateral distance of dc which is equal to the thickness of the layers  10  or  12  times the tangent of the critical angle. Therefore, light from any part of the gap A can be completely blocked by putting a black strip  14  of width W m  equal to 2d c  over the gap A. Because of the symmetry of the relevant optics, this same black strip  14  also blocks any external rays (not shown) from detecting the gap A.  
         [0022]    If the strip  14  width is less than 2d c  but wider than the width of the top of the gap A, then it will completely hide the top of the gap A and a portion of a gap region near the top of the gap A. Thus, the strip  14  makes the top of the gap A and part or all of the underlying gap region invisible to a user. In practice, the black strip  14  may be slightly wider to account for any finite width of the gap A and for any tolerance for the mis-positioning of the black strip  14  directly over the gap A.  
         [0023]    Using a black strip  14  that is wide enough to hide the entire gap A top and gap region makes the gap A substantially invisible. If mullions (not shown) are used around the edges of the display, a visual discontinuity may result because of the difference in widths of the mullions versus the black strips  14 . Making the black strips  14  identical to the mullions may make this discontinuity less noticeable. Also the use of the strips  14  may increase the contrast of the displayed image. In some embodiments, the same techniques may be used over the regions between pixels that are used between the layers  10  and  12  to provide greater uniformity.  
         [0024]    Referring to FIG. 2, a pair of transparent layers  10  and  12  may be abutted together to form part of an overall large area display. The gap A may be defined between the layers  10  and  12 . Each of the layers  10  and  12  may have coated on its lower surface one or more light emitting elements  15 . In the case shown in FIG. 2, a set of three light emitting elements  15  are provided, one for each color of a tricolor color space such as red, green, blue (RGB) color space.  
         [0025]    Each of the light emitting elements  15  closest to the gap A emits light having a ray most adjacent to the gap A and indicated by the letters B and C. As a result, a space D may be defined over the strip  14  that is not impacted by any emitted light. In particular, the strip  14  may be sized so that it obscures the gap A while refraining from blocking substantial light emitted by the light emitting elements  15 .  
         [0026]    In some embodiments of the present invention, the light emitting elements  15  may be any emissive elements including an organic light emitting device (OLED), a light emitting diode (LED), or an electroluminescent display (EL), to mention a few examples. However, the other display technologies may be utilized including liquid crystal display technologies in some embodiments.  
         [0027]    In FIG. 3, each layer  10  and  12  is overlaid by a layer  16 . In some embodiments, the layers  10  and  12  may be formed of glass. In some embodiments, the layer  16  may be formed of glass or plastic that is, at least in part, transparent. In particular, the layer  16  may include transparent regions  20  positioned more directly over the light emitting elements  15  and non-transparent regions  18  intermediate between adjacent regions  20 . The layers  10  and  12  may be integrated to a layer  16  for example by conventional bonding techniques including heat welding and adhesive bonding as two examples.  
         [0028]    In some embodiments, the non-transparent regions  18  may be rectangular or square and may be black in color throughout their thickness. The sides  19  of the region  18  may be coated to make them more reflective. This may be done by providing a mirrored or white surface as two examples. As a result, the rays B and C described in connection with FIG. 2 may be reflected from the sides  19  as indicated at E and F. In this way, light may still not be blocked, as was the case in FIG. 2, but a gap blocking, non-transparent region  18  of greater vertical dimensions may be provided.  
         [0029]    Because of the imposition of the region  18  close to the light emitting elements  15 , the gap A may be more effectively hidden. Also, in some cases the layers  10  and  12 , reinforced by the layer  16 , may be thinner.  
         [0030]    In some cases, the layer  16  may be abutted against an adjacent layer  16  producing gaps between adjacent layers  16 . These gaps may be obscured in some cases by using an overlying sheet  40 . This overlying sheet  40 , which may be called an optical integrating plate, may be utilized to assemble the various tiles that include the layers  10  and  12 . The plate  40  may include mullions  42  to cover the gaps A. Those tiles together form the composite image of a large area display. In addition, an optical integrating plate may provide a diffusing effect to obscure any gaps between layers  16  in some cases.  
         [0031]    The layer  16  may be formed in a variety of different fashions. It may be possible to diffuse a non-transparent material into the regions  18  while masking the transparent regions  20 . However, as another embodiment, a lithography process may be used to etch a plurality of holes in the layer  16 . The layer  16  may be transparent in general. Each of those holes may then be coated with a suitably reflective layer to form the sides  19 . The remaining holes may then be filled with a dark or black material to form the regions  18 .  
         [0032]    Turning next to FIG. 4, in this case, black material  22  is formed in the layer  16   a  in a triangular shape. The sides  23  of the black material  22  may be oriented at an angle so as not to block the emitted rays B and C. Thus, in some cases, the sides  23  need not be made reflective, as was the case in the embodiment shown in FIG. 3.  
         [0033]    However, in some cases, it may still be possible for some light to impact the sides  23  of the triangular black material  22 . In such cases, it may still be desirable to make the sides  23  reflective. For example, as shown in FIG. 5, reflective sides  26  may be provided on a black triangular material  24  in a sheet  16   b . The resulting reflected rays E and F reduce the loss of light which might otherwise occur. The embodiment shown in FIG. 5 may be advantageous, particularly in situations where relatively thick layers  10  and  12  are utilized. In the embodiments of FIGS. 4 and 5, an optical integrating plate  40  may be used as described in connection with FIG. 3.  
         [0034]    In some cases, if the index of refraction of the material  24  is sufficiently lower than the index of refraction of the surrounding region  20 , it may not be necessary to make the sides  26  reflective. Instead, the rays may be reflected due to the differences in indices of refraction between the material  24  and the region  20 . In some cases, embodiments of the type shown in FIGS. 4 and 5 may exhibit less contrast improvement for the overall display compared to those of the type shown in FIG. 7 because of reflections off of the tapered sides  26  or  23 . Thus, in situations where high contrast is desired, embodiments of the type shown in FIG. 3 may be preferable. In cases where the redistribution of the light may become a problem, embodiments of the type shown in FIG. 4 may be preferable.  
         [0035]    Referring next to FIG. 6, an optical structure may be provided that improves the optical separation between pixels. This structure may be made as a vertically laminated or multilayer structure, as shown in FIG. 6, or may be formed from a single layer. Each of the layers  10  and  12  may be associated with one or more hemispherical lenses  20   a  that may be described as microlenses. The lenses  20   a  may be formed of glass, plastic or other transparent materials.  
         [0036]    The lenses  20   a  provide a means of concentrating emitted light from a pixel light emitting element  15  into the viewing space, providing a brighter display. Lenses  20   a  may also reduce the internally reflected light by waveguiding the light outwardly from the display. This is because the lenses  20   a  may increase the critical angle of the outbound light in some embodiments. Each lens  20   a  may be either one or two dimensional. In the case of linear lenses or one dimensional lenses, the lens  20   a  may be oriented horizontally so as to concentrate the light into a smaller vertical viewing zone.  
         [0037]    Between each adjacent layer  10  or  12 , over the gap A, a dark region  28  may be formed for example by deposition. The dark region  28  obscures the underlying gap A as was the case in previously described embodiments. In this case, the lateral extension of the region  28  may avoid obscuring the outbound light from the light emitting elements  15 . The effect of the lenses  20   a  is indicated by the rays B and C, which are the rays most adjacent to gap A. The rays B and C are refracted, as indicated at G and H, towards the center of each lens  20   a , effectively concentrating the resulting outbound light.  
         [0038]    The use of lenses  20   b  (with a greater aspect ratio than those shown in FIG. 6) is illustrated in FIG. 7. In some cases, the lenses  20   b  may use refraction as well as internal reflection as indicated by the arrows E and F in FIG. 7. In some cases, a reflective coating may be applied to the external sides  30  of the lenses  20   b . In other cases, total internal reflection may be utilized. A black matrix material  28   a  is situated between adjacent lenses  20   b . In the embodiment shown in FIG. 7, the matrix material  28   a  may cover the sides  30  of the lenses  20   b  because of the use of internal reflection.  
         [0039]    The use of a unitary cover plate  32  is shown in FIG. 8. In this example, the plate  32  may replace both the layers  10  and  12  and any overlying layer such as the layer  20 . This may be possible because the plate  32  may be formed with integral optical elements  38 . The plate  32  may be molded to the shape that is desired using plastic as one example. In other cases, the desired shape may be formed by grinding, sawing, abrasive jets, etching or other formation techniques. The elements  38  defined in the plate  32  may be triangular in one embodiment of the present invention. The triangular elements  38  reflect incoming light and obscure underlying gaps.  
         [0040]    The elements  38  may be coated or filled with black or reflective materials to make optics that isolate or concentrate light from the pixels defined by elements  15 . Thus, as shown in FIG. 9, a filler  40  is used in place of the open spaces (FIG. 8) that may make up part of the elements  38 .  
         [0041]    Where a coating is utilized as indicated at  38  in FIG. 8, the remaining opening area  34  may be utilized to locate electrodes, connections and other features. Thus, a contact  36  may be provided to metal or other conductive lines to reach the light emitting layer  15  in one embodiment.  
         [0042]    The elements  38  may be open spaces with air which has a relatively low index of refraction. This may create, in some embodiments, total internal reflection without the need for a coating. Gaps may be defined between adjacent plates  32 .  
         [0043]    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.