PATENT DOCUMENT

Publication Number: US-9123668-B2
Application Number: US-201414312416-A
Country: US
Kind Code: B2

Title: Organic light-emitting diode displays with white subpixels

Abstract:
An electronic device may include a display having an array of organic light-emitting diode display pixels that produce light that forms an image. Color filter elements may be used to allow the display to present color images. Each display pixel may have a red subpixel, a blue subpixel, a green subpixel, and a white subpixel. To adjust the color coordinates of the white pixel and thereby ensure that the light from the white pixel has a desired white point, part of the white subpixel may be overlapped by an area of colored color filter material. The white subpixel may, for example have a rectangular white area within which a patch of blue color filter material may be provided to make the white light from the white subpixel more bluish than it would be without the patch of blue color filter material.

Claims:
What is claimed is: 
     
       1. A display pixel in an organic light-emitting diode display, comprising:
 a red subpixel; 
 a green subpixel; 
 a blue subpixel that comprises a first blue color filter; and 
 a white subpixel, wherein the white subpixel has an area that emits light and has a second blue color filter that overlaps part of the area, wherein the first and second blue color filters are separated by portions of the white subpixel, and wherein the second blue color filter is only adjacent to portions of the white subpixel. 
 
     
     
       2. The display pixel defined in  claim 1  wherein the area that emits light has a rectangular outline and wherein the second blue color filter comprises a patch of blue color filter material within the rectangular outline. 
     
     
       3. The display pixel defined in  claim 1  wherein the area that emits light has a first area and wherein the second blue color filter comprises blue polymer having a second area that is smaller than the first area and that overlaps the first area. 
     
     
       4. The display pixel defined in  claim 1  wherein the red subpixel, the green subpixel, the blue subpixel, and the white subpixel each include organic electroluminescent material and thin-film transistor circuitry that applies current to the organic electroluminescent material. 
     
     
       5. An organic light-emitting diode display, comprising:
 an array of display pixels each of which has a white subpixel, wherein each white subpixel has a part that is overlapped by a colored color filter structure and a part that is not overlapped by colored color filter material, and wherein the part that is overlapped by the colored color filter structure is completely surrounded by the part that is not overlapped by colored color filter material. 
 
     
     
       6. The organic light-emitting diode display defined in  claim 5  further comprising:
 control circuitry that directs the display pixels to generate light. 
 
     
     
       7. The organic light-emitting diode display defined in  claim 6  wherein each display pixel includes a red subpixel, a blue subpixel, and a green subpixel that produce the light. 
     
     
       8. The organic light-emitting diode display defined in  claim 7  wherein the colored color filter structure comprises blue material. 
     
     
       9. The organic light-emitting diode display defined in  claim 8  wherein the blue material comprises a patch of blue polymer that overlaps the white subpixel. 
     
     
       10. The organic light-emitting diode display defined in  claim 9  wherein the patch of blue polymer and the blue subpixel are formed from different areas of a common blue polymer layer. 
     
     
       11. The organic light-emitting diode display defined in  claim 9  further comprising:
 organic electroluminescent material; and 
 thin-film transistor circuitry that supplies signals to the organic electroluminescent material. 
 
     
     
       12. The organic light-emitting diode display defined in  claim 11  wherein the display is a bottom-emission display comprising a transparent substrate through which the light passes from the red subpixel, the green subpixel, the blue subpixel, and the white subpixel of each display pixel. 
     
     
       13. The organic light-emitting diode display defined in  claim 11  wherein the display is a top-emission display comprising a first layer on which the thin-film transistor circuitry is formed and a second layer through which the light from the red subpixel, the green subpixel, the blue subpixel, and the white subpixel of each display pixel passes. 
     
     
       14. The organic light-emitting diode display defined in  claim 5  wherein the display is a bottom-emission display comprising a transparent substrate through which light passes from a red subpixel in each display pixel, a green subpixel in each display pixel, a blue subpixel in each display pixel, and the white subpixel of each display pixel. 
     
     
       15. The organic light-emitting diode display defined in  claim 5  wherein the display is a top-emission display comprising a first layer on which the thin-film transistor circuitry is formed and a second layer through which light passes from a red subpixel in each display pixel, a green subpixel in each display pixel, a blue subpixel in each display pixel, and the white subpixel of each display pixel. 
     
     
       16. The organic light-emitting diode display defined in  claim 15  wherein the red subpixel comprises a red color filter, wherein the blue subpixel comprises a blue color filter, wherein the green subpixel comprises a green color filter, and wherein the red color filter, the blue color filter, the green color filter, and the colored color filter material are formed on the second layer. 
     
     
       17. An organic light-emitting diode display, comprising:
 an array of display pixels; and 
 control circuitry that directs the array of display pixels to generate light, wherein each display pixel includes red, blue, and green subpixels, wherein each display pixel comprises a white display pixel, and wherein each white subpixel comprises an area of color filter material that adjusts a white point associated with the white subpixel, wherein each white subpixel has a total surface area, wherein each area of color filter material has a surface area, and wherein the surface area of each area of color filter material is less than one tenth of the total surface area of each white subpixel. 
 
     
     
       18. The organic light-emitting diode display defined in  claim 17  wherein the area of color filter material in each white subpixel comprises a patch of blue color filter material. 
     
     
       19. The organic light-emitting diode display defined in  claim 18  wherein each white subpixel has a rectangular white subpixel area and wherein the patch of blue color filter material comprises a rectangle of blue color filter material formed in part of the rectangular white subpixel area. 
     
     
       20. The organic light-emitting diode display defined in  claim 19  wherein the red subpixel comprises red color filter material, wherein the blue subpixel comprises blue color filter material, and wherein the green subpixel comprises green color filter material.

Description:
This application claims the benefit of provisional patent application No. 61/885,983, filed Oct. 2, 2013, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with organic light-emitting diode displays. 
     Electronic devices often include displays. For example, an electronic device may have an organic light-emitting diode display with rows and columns of display pixels. The display pixels may each have subpixels with respective red, blue, and green color filter elements. There can be non-negligible amounts of optical absorption in the color filter material of red, blue, and green subpixels, so some designs incorporate white subpixels. Pixel rendering operations may covert red-green-blue data to red-green-blue-white data to ensure that the white subpixels are frequently used. This helps reduce power consumption, because the white subpixels are more efficient at emitting light than the colored subpixels. However, the white light emitted from a white organic light-emitting diode subpixel may have white point color coordinates that do not match target white point color coordinates, leading to images that are colored differently than desired. 
     It would therefore be desirable to be able to provide improved displays such as improved organic light-emitting diode displays. 
     SUMMARY 
     An electronic device may be provided with a display. The display may have an array of display pixels. The display pixels may be organic light-emitting diode display pixels. Control circuitry may be used to direct the display pixels to produce light that forms an image on the display. The display may be a top-emission organic light-emitting diode display or may be a bottom-emission organic light-emitting display. 
     Thin-film transistor circuitry on the display may be used to apply currents to organic electroluminescent material to create the light for the image. Color filter elements may be used to allow the display to present color images. 
     Each display pixel may have a red subpixel, a blue subpixel, a green subpixel, and a white subpixel. The red subpixels may be formed using red color filter elements. The blue subpixels may be formed using blue color filter elements. The green subpixels may be formed using green color filter elements. White subpixels may be substantially free of color filter material so that white light from white organic light-emitting diode structures may be emitted from the display. 
     To adjust the color coordinates of the white subpixel and thereby ensure that the white light from the white pixel has a desired white point, the white subpixel may be provided with an area of colored color filter material. The area of the colored color filter material may cover a fraction of the total area of the white subpixel. For example, the area of the colored color filter material may be one fifth or less or one tenth or less of the total area of the white subpixel (as examples). 
     The colored color filter element may be formed from a patch of blue color filter material having a relatively small area relative to the total area of the white subpixel. Because the size of the patch of blue material in the white subpixel is relatively small, the blue patch merely adjusts the white point of the white subpixel and does not substantially alter the white nature of the light being emitted by the white subpixel. The presence of the blue patch also does not significantly degrade white light emission efficiency. When the blue patch is included in the white subpixels, it is no longer necessary to turn on the blue subpixel to make the white light from the white subpixels more bluish in color. Accordingly, the lifetime of the blue subpixels is not undesirably decreased. 
     The white subpixel may, for example, have a rectangular area within which a patch of blue color filter material may be provided to make the white light from the white subpixel more bluish than it would be without the patch of blue color filter material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG. 2  is a diagram of an illustrative organic light-emitting diode display in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of an illustrative organic light-emitting diode display in a bottom emission configuration in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of an illustrative organic light-emitting diode display in a top emission configuration in accordance with an embodiment. 
         FIG. 5  is a top view of an illustrative organic light-emitting diode display pixel showing illustrative subpixels that may be included in the display pixel in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative electronic device of the type that may be provided with an organic light-emitting diode display is shown in  FIG. 1 . As shown in  FIG. 1 , electronic device  10  may have control circuitry  16 . Control circuitry  16  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  16  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Input-output circuitry in device  10  such as input-output devices  12  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  64  may include buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  12  and may receive status information and other output from device  10  using the output resources of input-output devices  12 . 
     Input-output devices  12  may include one or more displays such as display  14 . Display  14  may be a touch screen display that includes a touch sensor for gathering touch input from a user or display  14  may be insensitive to touch. A touch sensor for display  14  may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements. 
     Control circuitry  16  may be used to run software on device  10  such as operating system code and applications. During operation of device  10 , the software running on control circuitry  16  may display images on display  14  in input-output devices. 
     Display  14  may be an organic light-emitting diode display. As shown in the illustrative diagram of  FIG. 2 , display  14  may include layers such as substrate layer  24 . Layers such as substrate  24  may be formed from planar rectangular layers of material such as planar glass layers and planar polymer layers. 
     Display  14  may have an array of display pixels  22  for displaying images for a user. The array of display pixels  22  may be formed from rows and columns of display pixel structures (e.g., display pixels formed from structures on display layers such as substrate  24 ). There may be any suitable number of rows and columns in the array of display pixels  22  (e.g., ten or more, one hundred or more, or one thousand or more). 
     Display driver circuitry such as display driver integrated circuit  28  may be coupled to conductive paths such as metal traces on substrate  24  using solder or conductive adhesive. Display driver integrated circuit  28  (sometimes referred to as a timing controller chip) may contain communications circuitry for communicating with system control circuitry over path  26 . Path  26  may be formed from traces on a flexible printed circuit or other cable. The control circuitry may be located on a main logic board in an electronic device in which display  14  is being used. During operation, the control circuitry on the logic board (e.g., control circuitry  16  of  FIG. 1 ) may supply control circuitry such as display driver integrated circuit  28  with information on images to be displayed on display  14 . 
     To display the images on display pixels  22 , display driver integrated circuit  28  may supply corresponding image data to data lines D while issuing clock signals and other control signals to supporting thin-film transistor display driver circuitry such as gate driver circuitry  18  and demultiplexing circuitry  20 . 
     Gate driver circuitry  18  (sometimes referred to as scan line driver circuitry) may be formed on substrate  24  (e.g., on the left and right edges of display  14 , on only a single edge of display  14 , or elsewhere in display  14 ). Demultiplexer circuitry  20  may be used to demultiplex data signals from display driver integrated circuit  16  onto a plurality of corresponding data lines D. With this illustrative arrangement of  FIG. 1 , data lines D run vertically through display  14 . Each data line D is associated with a respective column of display pixels  22 . Gate lines G (sometimes referred to as scan lines) run horizontally through display  14 . Each gate line G is associated with a respective row of display pixels  22 . If desired, there may be multiple gate lines (scan lines) associated with each row of display pixels. Gate driver circuitry  18  may be located on the left side of display  14 , on the right side of display  14 , or on both the right and left sides of display  14 , as shown in  FIG. 1 . 
     Gate driver circuitry  18  may assert gate signals (sometimes referred to as scan signals) on the gate lines G in display  14 . For example, gate driver circuitry  18  may receive clock signals and other control signals from display driver integrated circuit  16  and may, in response to the received signals, assert a gate signal on gate lines G in sequence, starting with the gate line signal G in the first row of display pixels  22 . As each gate line is asserted, data from data lines D is located into the corresponding row of display pixels. In this way, circuitry  28 ,  20 , and  18  may provide display pixels  22  with signals that direct display pixels  22  to generate light for displaying a desired image on display  14 . 
     Display driver circuitry such as demultiplexer circuitry  20  and gate line driver circuitry  18  may be formed from thin-film transistors on substrate  24 . Thin-film transistors may also be used in forming circuitry in display pixels  22 . The thin-film transistors in display  14  may, in general, be formed using any suitable type of thin-film transistor technology (e.g., silicon-based, semiconducting-oxide-based, etc.). 
     Cross-sectional side views of configurations that may be used for display  14  of device  10  are shown in  FIGS. 3 and 4 .  FIG. 3  is a cross-sectional side view of an illustrative bottom emission organic light-emitting diode display.  FIG. 4  is a cross-sectional side view of an illustrative top emission organic light-emitting diode display. 
     In a bottom-emission display configuration of the type shown in  FIG. 3 , display  14  has a transparent substrate layer such as glass layer  52 . Thin-film transistor circuitry such as thin-film transistor  54  may pass current between cathode  58  and anode  60  of light-emitting diode  62 . As this current passes through organic light-emitting diode emissive electroluminescent layer  56 , white light  64  is generated. The amount of current that is applied to electroluminescent material  56  controls the intensity of the resulting light  64  that is produced. 
     Light  64  passes through color filter element  66 , which imparts a desired color to light  64 . The resulting colored version of light  64  passes through clear substrate  52 . The structures of  FIG. 3  form a single subpixel  22 ′ of a particular color (e.g., red in situations in which color filter element  66  is red, blue in situations in which color filter element  66  is blue, green in situations in which color filter element  66  is green, and white in situations in which color filter element  66  is clear or is absent). There may be four subpixels  22 ′ per display pixel  22  in display  14  (e.g., a first subpixel  22 ′ that is red, a second subpixel  22 ′ that is blue, a third subpixel  22 ′ that is green, and a fourth subpixel  22 ′ that is white). 
     In a top-emission display configuration of the type shown in  FIG. 4 , display  14  has a substrate layer such as substrate  70 . Thin-film transistor structures such as thin-film transistor  54  may pass current between cathode  58  and anode  60  of light-emitting diode  62 . As this current passes through organic light-emitting diode emissive electroluminescent layer  56 , white light  64  is generated. Light  64  passes through color filter element  66 , which imparts a desired color to light  64 , and passes through a transparent layer such as glass layer  52 . Black matrix  72  may prevent stray light from exiting display  14 . Color filter elements  66  are formed on the underside of glass layer  52  within openings in black matrix  72 . 
     The structures of  FIG. 4  form a single subpixel  22 ′ of a particular color (e.g., red in situations in which color filter element  66  is red, blue in situations in which color filter element  66  is blue, green in situations in which color filter element  66  is green, and white in situations in which color filter element  66  is clear or is absent). As with bottom-emission displays, there may be four subpixels  22 ′ per display pixel  22  in display  14  (e.g., a first subpixel  22 ′ that is red, a second subpixel  22 ′ that is blue, a third subpixel  22 ′ that is green, and a fourth subpixel  22 ′ that is white). 
     A top view of an illustrative display pixel  22  showing how display pixels  22  in display  14  may each contain four subpixels  22 ′ is shown in  FIG. 5 . Each subpixel  22  has a respective color filter (e.g., one of color filter elements  66  of  FIGS. 3 and 4 ). Organic light emissive layer  56  is preferably configured to emit white light. Color filters  66  in subpixels  22 ′ impart colors to light  64 . By controlling the amount of light  64  that is emitted from each of the subpixels  22 ′ in a given display pixel  22 , the display driver circuitry of display  14  can control the color of light that is emitted from that display pixel  22 . 
     The presence of a clear color filter element (i.e., a missing color filter layer  66 ′ or a clear layer of material) over white subpixel  22 ′ allows light to be efficiently emitted from that subpixel. During operation, data that is encoded using red-green-blue color coordinates (RGB data) can be transformed (by control circuitry  16 ) into data that is encoded using red-green-blue-white color coordinates (RGBW data). This transformation can be used to turn on the white subpixel in display pixel  22  as often as possible to help reduce drive currents for the display pixels and thereby conserve power. 
     The color coordinates of a purely white subpixel generally will not match the color coordinates for the desired white point for display  14 . A bluish white point for the white subpixels may be desirable for appealing images. Although the blue subpixel  22 ′ could be turned on to contribute a blue component to the white emitted from the white subpixel, doing so excessively can degrade the lifetime of the blue sub-pixel and can consume more power than desired. 
     As shown in  FIG. 5 , white (clear) color filter element region  74  in white subpixel  22 ′ is therefore preferably provided with a colored color filter structure such as blue color filter region  76 . White (clear) region  74  may, for example, have a rectangular outline (i.e., white light may be emitted from within the rectangular outline of region  76  of  FIG. 5 ). Blue color filter region  76  may, for example, contain a square patch of blue color filter material or one or more blue color filter element structures of other shapes within a rectangular area  74  for white subpixel  22 ′. The area of blue patch  76  may be relatively small compared to white area  74 . For example, blue area  76  may be one fifth or less of area  74 , blue area  76  may be one tenth or less of area  74 , etc. Blue area  76  may be formed using one or more rectangular areas or areas of other shapes that overlap the light-emitting region for the white subpixel  22 ′ (area  74 ). Area  74  emits white light, because that portion of display  14  is devoid of colored (red, blue, and green) color filter element material. Because a relatively small part of white subpixel  22 ′ is overlapped by blue color filter structure  74  and a relatively large part of white subpixel  22 ′ is not overlapped by any blue color filter material, white light emission efficiency is not significantly degraded. 
     Color filter elements  66  may be formed from transparent polymer containing dyes (e.g., red-dyed photoimageable polyimide, blue-dyed photoimageable, polyimide, and green-dyed photoimageable polyimide). Clear (white) areas may be formed using clear polyimide or other clear polymers or by forming an opening (e.g., a rectangular opening) overlapping the white subpixel light emitting area. If desired, blue color filter structure  76  and the blue color filter structure for blue subpixel  22 ′ may be formed from the same patterned layer of blue-dyed polyimide (i.e., a common blue photoimageable polymer layer), thereby minimizing the number of photomasks used in forming display  14 . 
     The size of blue color filter area  76  in white subpixel area  74  can be adjusted to adjust the white point for white subpixel  22 ′. If, for example, it is desired for the white subpixels  22 ′ in display  14  to emit light that is more bluish, the size of blue color filter area  76  can be increased relative to the color-filter-element-free region  74  that overlaps the white display pixel. If it is desired to emit white light in the white display subpixels  22 ′ that is less bluish, the ratio of the size of blue color filter  76  to the size of white subpixel  22 ′ can be reduced. 
     During operation of a display that includes a blue color filter structure such as the blue color filter structure in blue color filter area  76  that lies within white subpixel region  74  of white subpixel  22 ′, the presence of blue color filter  76  helps adjust the white point of the white light produced by the white subpixels to a desired set of color coordinates. When blue filter  76  is incorporated into white subpixel  22 ′ in this way, power that might otherwise be expended in operating blue subpixel  22 ′ to make the white light from white subpixel  22 ′ more bluish can instead by entirely directed towards operating the white subpixel  22 ′. It is therefore not necessary to operate the blue subpixel whenever the white subpixel is used, thereby conserving power. 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20140623
Publication Date: 20150901
Grant Date: 20150901
Priority Date: 20131002
Inventors: PARK YOUNG BAE
CHANG SHIH CHANG
GUPTA VASUDHA
Assignee: APPLE INC
CPC Classifications: [{"code": "H01L27/322", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/3213", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/38", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/38", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/351", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/351", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 52739192