Patent Document

FIELD OF THE INVENTION 
     The present invention relates to high aperture ratio displays, which include a plurality of tiles aligned to produce an image. 
     BACKGROUND OF THE INVENTION 
     Flat panel displays are found everywhere from hand held electronics to large scale video applications. Larger displays are usually smaller displays tiled together. When the displays are tiled it is important to create a bright image that appears seamless across the tiles. The image brightness is proportional to the size of the aperture ratio in the display as defined by the ratio of the emissive surface area of a pixel to the total surface area of the same pixel. Increasing the aperture ratio of the pixel produces a brighter image. However, increasing the space between pixels allows for a proportional increase in the spacing between adjacent tiles, thereby facilitating the ability to create a seamless tiled display. Therefore, any increase in the area available for each pixel can be distributed optimally to increase the aperture ratio, and to increase the space available between pixels including the space between adjacent pixels on abutting tiles. 
     Flat panel technology has been dominated by liquid crystal displays (LCD&#39;s) in which the liquid crystal material, when activated by an electric field, acts as a valve to transmit light from a back light source. LCD&#39;s require a transparent path that includes a transparent substrate and transparent pixel electrodes. There cannot be anything blocking the pixel from the backlight. In video LCD displays the space available for creating seams between tiles is limited by the rows of circuits that fill the space between pixels. 
     U.S. Pat. No. 5,056,893 describes a technique in which there is increased space for a seam by making the pixels at the edge of a tile smaller. Reducing the size of the pixels is a significant trade-off in brightness and image quality. U.S. Pat. No. 5,903,328 describes tiled LCD displays where the adjacent tile edges are ground at an angle and overlap each other. This allows a small increase in the space for the ground edge relative to the adjacent pixels; however, as the space increases the distance between the image planes of adjacent tiles increases proportionally. U.S. Pat. No. 6,136,621 describes a method for making a high aspect ratio gated emitter wherein the lower gate is partially covered by an insulator and the upper gate; the lower gate extends through a hole in the insulator and the upper gate. U.S. Pat. No. 5,955,744 describes a LCD display wherein the TFT is under the pixel electrode, located just outside the perimeter of the pixel so as not to block light from the backlight. 
     Emissive displays, which produce their own light, do not require a transparent substrate. The pixels do not have to be positioned over a transparent substrate or a transparent electrode. This allows for stacking of the integrated drive circuits and the circuits under the light-emitting layer which contains only an array of light-emitting pixels. These tiles can be arrayed together to make a monolithic tiled display wherein the pixel pitch across the seam of adjacent tiles is substantially equal to that of the pixel pitch within a tile. In order to achieve an emissive device with high aspect ratio pixels, the pixels on each tile are addressed through vertical connections and a conductor layer to the corresponding circuits. The drive circuits are semiconductor electronics that are manufactured directly on the substrate and can be on the same level as the circuits or under the circuits. The drive circuits can also be located on the bottom side of the substrate and connected using vertically connections through the substrate. U.S. Pat. No. 6,091,194 describes an emissive display tile in which discrete drive circuits are attached to the bottom side of the tile. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a high aperture ratio emissive display for use in multiple tile applications. It is another object of the present invention to provide a high aperture ratio emissive tiled display which is particularly suitable for producing video images. 
     This object is achieved by a high aperture ratio display comprising:
         a) at least two tiles having rows and columns of electric field actuable pixels which produce light from one surface of each tile, the pitch between each column of each tile being substantially the same and the pitch between each row of each tile being substantially the same, the tiles being arranged so that, when aligned, the pitch between adjacent pixels in adjacent tiles is the same so that when light is emitted from the surface of the tiles, it does not have intertile artifacts;   b) a plurality of conductors disposed under the pixels of each tile and arranged to provide an electrical connection between the pixels of each tile; and   c) circuits electrically connected to the conductors for producing electrical signals which cause the emission of light in the pixels of each tile to produce an image.       

     ADVANTAGES 
     It is an advantage of the present invention that the pixel aperture ratio can be larger than that of prior art in a tiled display. This high aperture ratio on the light-emitting surface can be achieved by eliminating the need to share space with the electronics. Thus, the pixels can extend to all edges of each display tile wherein the circuits and conductors are on layers under the pixels and are contained in an area defined by the outermost pixels on each tile. 
     It is a further advantage of the present invention that the increased space allowed for each pixel can provide additional space between pixels. The total area available for each pixel can be optimized to establish a large pixel in conjunction with adequate space between pixels. The space between pixels determines the space available for the seam between two or more tiles that are positioned adjacently to create a tiled display. 
     It is a further advantage of the present invention that a high aperture ratio tiled display can be an array of tiles that include island tiles, tiles that do not have an edge along the perimeter of the display. This is accomplished by extending the pixels to all edges of a tile and by utilizing vertical connections to address each pixel. 
     It is a further advantage of the present invention that the integration of the semiconductor drive circuits on the tile significantly reduces the number of external interconnections necessary to address the display. 
     It is a further advantage of the present invention that it is suitable for use in organic electroluminescent displays. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a prior art tiled display with two tiles; 
         FIG. 2  is front view of the tiled display in  FIG. 1 ; 
         FIG. 3  is a top view of an emissive tiled display comprised of four multilayer emissive tiles on a back plate; 
         FIG. 4  is front view of the emissive tiled display in  FIG. 3 ; 
         FIG. 5  is a composite top view of a multilayer emissive tile from the tiled display in  FIG. 3  having the circuits and drive circuits with the pixel cathode and light-emitting layers removed; 
         FIG. 6  is a top view of an alternative multilayer emissive tile from the tiled display in  FIG. 3  showing the layer for the circuits and the drive circuits; 
         FIG. 7  is a top view of a multilayer emissive tile from the tiled display in  FIG. 3  showing the conductor layer for interconnection of the circuits to the pixel electrodes; 
         FIG. 8  is a top view of an alternative multilayer emissive tile from the tiled display in  FIG. 3  showing a tile where pixel electrodes, interconnects, circuits and drive circuits are on separate layers; 
         FIG. 9  is a top view of an alternative multilayer emissive tile from the tiled display in  FIG. 3  with the integrated drive circuits on the back side of the tile and with vertical connections through the tile to the drive circuits on the top; 
         FIG. 10  is a bottom view of the emissive tile shown in  FIG. 9 ; 
         FIG. 11  is a cross section of a multilayer emissive tiled display from the tiled display in  FIG. 3  with light-emitting pixels of different colors; 
         FIG. 12  is a cross section of a multilayer emissive tiled display from the tiled display in  FIG. 3  with light-emitting pixels of different colors and a cover plate; 
         FIG. 13  is a cross section of an alternative multilayer emissive tiled display from the tiled display in  FIG. 3  with a continuous emitting layer for white light-emitting pixels and a cover plate with different color filters aligned to the pixels; 
         FIG. 14  is a cross section of a simple organic light-emitting device; and 
         FIG. 15  is a cross section of an organic light-emitting pixel for emitting light through the top of the pixel, away from the tile. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to  FIGS. 1 and 2  which show a prior art for a tiled display  40  having a plurality of tiles  16   a - 16   b  each with circuits  26  and drive circuits  22  and pixel electrodes  104  or  304 , formed on a back plate  18 . It is understood that the drive circuits  22 , circuits  26  and pixel electrodes  104  or  304  for each tile  16   a - 16   b  exist in the same circuit layer. It is further understood that the circuit  26  includes the thin film transistors and associated capacitors. The pixel aperture ratio is limited by the space required for the circuits  26  and, furthermore, the drive circuits  22  extend beyond the area defined by the outermost pixels on each tile. Alternately, the drive circuits  22  are separate discrete components that are interconnected to the tile using tape automated bonding or other means. The horizontal pitch  80  between adjacent pixels on adjacent tiles, across a seam, is substantially equivalent to the horizontal pixel pitch  80  on a single tile. Additionally, the vertical pixel pitch  82  and the horizontal pixel pitch  80  are substantially the same for all tiles in the display. The vertical pixel length  84  and horizontal pixel length  78  are used in conjunction with the vertical pixel pitch  82  and the horizontal pixel pitch  80  to calculate the aperture ratio using the following equation: (84 ×78)/(82 ×80)=aperture ratio. 
     Referring to  FIGS. 3-5 , an emissive tiled display  42  is comprised of two or more emissive tiles  20   a-d  arrayed, or tiled, together to provide a monolithic seamless display. The stacking of the circuits  26  and drive circuits  22  (see  FIG. 5 ) under the pixels on each tile allows for pixels  300  to be positioned near the edge of tiles  20   a - 20   d  with the distance from the outermost pixel edge to the tile edge at most equal to one-half the space between pixels  300 . Furthermore, the integration of the drive circuits  22  onto each tile reduces the number of external signal connections (not illustrated in this embodiment) needed. The stacking of the drive circuits  22  under the pixels allows for the external signal connections to be made in the limited space at the edge of the tile  20 , or alternately, through vertical connections  36  to the back of the tile  20 . Furthermore, a conductor can be provided along a tile edge to an adjacent tile for the purpose of carrying electrical signals out to the edge of a perimeter tile. The vertical  76  and horizontal pitch  72  between adjacent pixels on adjacent tiles, across a seam, is substantially equivalent to the vertical  76  and horizontal  72  pixel pitch on a single tile. Additionally, the vertical  76  and horizontal  72  pixel pitch is substantially the same for all tiles in the display. The vertical pixel length  74  and horizontal pixel length  62  are used in conjunction with the vertical pixel pitch  76  and the horizontal pixel pitch  72  to calculate the aperture ratio using the following equation: (74 ×62)/(76 ×72)=aperture ratio. 
     The preferred embodiment of emissive tiles for use in the tiled emissive display is shown in  FIGS. 5-7 .  FIG. 5  shows a composite view of an emissive multilayer tile  20  from the tiled display shown in FIG.  3 .  FIG.6  shows the drive circuits  22  and the circuits  26  that are located on the same plane on the tile  20  and are electrically connected by connectors  24 . The tile  20  does not have to be transparent but may be any material compatible with TFT processing including, but not limited to, glass and co-fired ceramic. The pixel electrodes  304  are located above the circuits  26  and separated by insulating layers  60  and  66  shown in cross-sections  FIGS. 11-13 .  FIG. 7  shows the circuits  26  connected to the pixel electrodes  304  by means of an additional layer containing a plurality of conductors  28  shown between the insulating layers  60  and  66  in  FIGS. 11-14 . Also shown in these figures are the components of the TFT circuits: source  30 , insulating layer  58 , gate insulator  64 , anisotropic silicon  68 , and drain  70 . It is the preferred embodiment that the drive circuits  22  and circuits  26  are contained in an area defined by the outermost pixels wherein drive circuits  22  and circuits  26  do not extend past the outermost pixels. It is understood that each circuit  26  is not necessarily located directly under the corresponding pixel electrode  304 . The circuits  26  are electrically connected to the pixel electrode  304  through vertical connections and interconnections  28 . Although the drive circuits  22  and circuits  26  are under the pixel array, the connections to the drive circuits, as shown in  FIG. 5 , can be made through vertical connections  36  that extend to the backside of the tile  20 . Alternately, the external interconnections to the drive circuits  22  can extend to one or more edges of the tile  20 , beyond the outermost pixel. 
     In another embodiment, the drive circuits  22  are integrated on a separate layer under the circuits. As shown in  FIG. 8 , circuits  26  reside above the drive circuits  22  and are separated from the drive circuits by an insulating layer. The pixel electrodes  304  are located above the circuits  26 , separated by another insulating layer. The interconnections  24  from the drive circuits  22  to the circuits  26  and from the circuits  26  to the pixel electrodes  304  are made using vertical connections  36 . Furthermore, a layer containing a plurality of conductors  28  can be used to connect the circuits  26  to the pixel electrodes  304 . External signal connections to the drive circuits can be made along one or more edges of the tile  20 , or through vertical connections  36  to the backside of the tile  20  and on to the drive circuits through drive circuit signal connections  32 . 
     In another embodiment, as shown in  FIGS. 9 and 10 , the drive circuits  22  are integrated on the backside of the tile  20 . The drive circuits  22  are electrically connected to the topside circuits  26  through the tile  20  using vertical connections  36 . It is understood that double side TFT processing is required on the tile. Furthermore, a layer containing a plurality of conductors  28  can be used to connect circuits  26  that are offset from the pixels electrodes  304  to the pixel electrodes  304 . External signal connections to the drive circuits  22  can be made to the backside of the tile  20 . 
       FIG. 11  shows the cross-section of the multilayer emissive tile  20 . In this embodiment, the drive circuits  22  and circuits  26  are electrically connected to the pixels  300  through the conductor layer  28 . As shown in  FIG. 12 , the display includes a cover plate  52  and the display is viewed through the cover plate  52 . The cover plate  52  is a transparent substrate and includes, but is not limited to, glass and plastic. It is understood that a material  56  that has matching index of refraction to the cover plate  52  can be used to fill any gaps between the pixels  300  and the cover plate  52 . This material can also provide moisture and oxygen protection. In the preferred embodiment the cover plate  52  includes a polarization layer  50  to increase the contrast ratio of the display. In another embodiment, as shown in  FIG. 13 , the cover plate  52  includes a color filter array  54 . The patterned color filter array  54  is aligned with the pixel array. When a color filter array  54  is employed on the cover plate  52  the pixels  300  are understood to be white light-emitting. Furthermore, the light-emitting layer  308  can be a continuous coating as shown. The cover plate  52  is bonded to the emissive tile  20  by means including, but not limited to, adhesive, metal and solgel. A desiccant can be positioned in or near the seals between the tile  20  and the cover plate  52 . Furthermore, an oxygen getter can be positioned in or near the seals between the tile  20  and the cover plate  52 . 
     In a further embodiment, the tiles are positioned between the cover plate  52  and a back plate  18 . The tiles can be affixed to either the cover plate  52  or back plate  18 . The back plate  18  does not need to be transparent. Additionally, electrical connections can be made from the tile to the back plate  18 . In a further embodiment, the cover plate  52  and back plate  18  are sealed around the perimeter enclosing the tile array within. In a further embodiment, a desiccant may also be positioned in or near any of the seals previously described. Alternately, an oxygen getter is positioned in or near any of the seals previously described. 
     The present invention is applicable to emissive displays, and is particularly suitable for, but not limited to, use in organic electroluminescent displays.  FIGS. 14 and 15  describe examples of pixels with organic electroluminescent materials. 
     A light-emitting layer of an organic electroluminescent tile comprises a luminescent or fluorescent material where electroluminescence is produced as a result of electron-hole pair recombination in this region. In the simplest construction of a light-emitting pixel  100 , as shown in  FIG. 14 , the light-emitting layer  108  is sandwiched between pixel electrode  104  that is an anode and the cathode  106 . The light-emitting layer  108  is a pure material with a high luminescent efficiency. A well known material is tris (8-quinolinato) aluminum, (Alq), which produces excellent green electroluminescence. 
     The simple pixel structure  100  can be modified to a multilayer structure in which an additional electroluminescent layer is introduced between the hole and electron-transporting layers to function primarily as the site for hole-electron recombination and thus electroluminescence. In this respect, the functions of the individual organic layers are distinct and can therefore be optimized independently. Thus, the electroluminescent or recombination layer can be chosen to have a desirable EL color as well as high luminance efficiency. Likewise, the electron and hole transport layers can be optimized primarily for the carrier transport property. 
     In a preferred embodiment, the pixel  100  is described as a multilayer organic device that emits light from the top. As shown in  FIG. 15 , the multilayer organic device  300  has a substrate  302  on which is disposed a light reflective conductive anode  304 . The anode  304  comprises two layers including a light reflective conductive metal layer  304   a  and a thin transparent layer of a conductive high work function material  304   b . An organic light-emitting structure  308  is formed between the anode  304  and a cathode  306 . The cathode  306  is composed of two layers including a thin transparent conductive layer of a low work function material  306   a  and a transparent conductive layer such as indium tin oxide  306   b . The organic light-emitting structure  308  is comprised of, in sequence, an organic hole-transporting layer  310 , an organic light-emitting layer  312 , and an organic electron-transporting layer  314 . When an electrical potential difference (not shown) is applied between the anode  304  and the cathode  306 , the cathode will inject electrons into the electron-transporting layer  314 , and the electrons will migrate across layer  314  to the light-emitting layer  312 . At the same time, holes will be injected from the anode  304  into the hole-transporting layer  310 . The holes will migrate across layer  310  and recombine with electrons at or near a junction formed between the hole-transporting layer  310  and the light-emitting layer  312 . When a migrating electron drops from its conduction band to a valence band in filling a hole, energy is released as light, and is emitted through the light-transmissive cathode  306 . 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected with the spirit and scope of the invention.

Technology Category: h