PATENT DOCUMENT

Publication Number: US-9231034-B1
Application Number: US-201414466111-A
Country: US
Kind Code: B1

Title: Organic light-emitting diode displays

Abstract:
An electronic device may include a display having an array of organic light-emitting diode display pixels. Color filter elements may be used to allow the display to present color images. A blue subpixel may be formed using part of an emissive layer and red and green subpixels may share a separate second part of the emissive layer. In four-subpixel designs, a white or yellow subpixel may also share the emissive layer with the red and green subpixels. Tandem diode configurations may be used in which a blue subpixel has two blue diodes connected in series and other subpixels are formed from respective pairs of series-connected diodes. A pixel definition layer may be formed from a light-absorbing material to suppress ambient light reflections.

Claims:
What is claimed is: 
     
       1. A display pixel in an organic light-emitting diode display, comprising:
 a red subpixel with a red color filter; 
 a green subpixel with a green color filter; and 
 a blue subpixel, wherein the blue subpixel comprises a tandem subpixel having a pair of diodes connected in series, wherein the red subpixel comprises a tandem subpixel having a pair of diodes connected in series, wherein the green subpixel comprises a tandem subpixel having a pair of diodes connected in series, and wherein the blue subpixel is a blue subpixel without a blue color filter. 
 
     
     
       2. The display pixel defined in  claim 1  further comprising an upper emissive layer and a lower emissive layer, wherein the upper emissive layer has a first portion in the blue subpixel and has a separate second portion common to the red and green subpixels. 
     
     
       3. The display pixel defined in  claim 2  wherein the first portion of the upper emissive layer is a blue emissive layer. 
     
     
       4. The display pixel defined in  claim 3  wherein the second portion of the upper emissive layer is a layer selected from the group consisting of: a green emissive layer, a red emissive layer, and a yellow emissive layer. 
     
     
       5. The display pixel defined in  claim 3  wherein the lower emissive layer includes blue emissive material. 
     
     
       6. The display pixel defined in  claim 1  wherein the blue subpixel has an upper blue emissive layer associated with a first blue light-emitting diode and has a lower blue emissive layer associated with a second blue light-emitting diode that is coupled in series with the first blue light-emitting diode. 
     
     
       7. The display pixel defined in  claim 1  further comprising a blue emissive layer in the blue subpixel and a separate emissive layer shared by the red and green subpixels. 
     
     
       8. The display pixel defined in  claim 7  further comprising a yellow subpixel that shares the separate emissive layer with the red and green subpixels. 
     
     
       9. The display pixel defined in  claim 7  further comprising a white subpixel without a color filter, wherein the white subpixel shares the separate emissive layer with the red and green subpixels. 
     
     
       10. The display pixel defined in  claim 7  wherein the separate emissive layer comprises a red-green emissive layer that emits red and green light. 
     
     
       11. The display pixel defined in  claim 7  further comprising:
 an additional blue emissive layer, wherein the blue emissive layer and the additional blue emissive layer are parts of respective diodes connected in series in the blue subpixel. 
 
     
     
       12. The display pixel defined in  claim 1  wherein the red subpixel and the green subpixel have hole injection layers of different thicknesses. 
     
     
       13. The display pixel defined in  claim 12  further comprising a transreflective cathode common to the blue, red, and green subpixels. 
     
     
       14. A display pixel in an organic light-emitting diode display, comprising:
 a red subpixel with a red color filter; 
 a green subpixel with a green color filter; and 
 a blue subpixel having a first diode coupled in series with a second diode, wherein the first diode has a first blue emissive layer and wherein the second diode has a second blue emissive layer. 
 
     
     
       15. The display pixel defined in  claim 14  wherein the red subpixel has a pair of diodes connected in series. 
     
     
       16. The display pixel defined in  claim 15  wherein the green subpixel has a pair of diodes connected in series. 
     
     
       17. The display pixel defined in  claim 16  wherein the red and green subpixels share at least one common emissive layer. 
     
     
       18. The display pixel defined in  claim 17  wherein the display pixel has a pixel definition layer and wherein the pixel definition layer comprises a black polymer. 
     
     
       19. A display pixel in an organic light-emitting diode display, comprising:
 a red subpixel with a red color filter; 
 a green subpixel with a green color filter; 
 a blue subpixel; 
 an organic emissive layer that emits light, wherein the organic emissive layer has a first portion in the blue subpixel and a second portion that is separate from the first portion and that is shared by the green and red subpixels; and 
 a yellow subpixel that shares the second portion of the organic emissive layer with the red and green subpixels. 
 
     
     
       20. The display pixel defined in  claim 19 , wherein the blue subpixel is a blue subpixel without a blue color filter. 
     
     
       21. The display pixel defined in  claim 20 , wherein the yellow subpixel is a yellow subpixel without a color filter.

Description:
This application claims the benefit of provisional patent application No. 61/924,634, filed Jan. 7, 2014, 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 an array of display pixels. The display pixels may each have subpixels. Color filter elements of different colors may be included in the subpixels to provide the subpixels with the ability to emit light of different colors. As an example, each pixel in a display may have a red subpixel, a green subpixel, and a blue subpixel. 
     There are challenges associated with optimizing display performance in an organic light-emitting diode display. If care is not taken, pixel pitch will be low, pixel apertures will be small, and light emitting efficiency will be poor. 
     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 include a display having an array of organic light-emitting diode display pixels. Color filter elements may be used to allow the display to present color images to a viewer. A blue subpixel may be formed using a first part of an emissive layer and red and green subpixels may share a second part of the emissive layer. In four-subpixel designs, a white or yellow subpixel may share the second part of the emissive layer with the red and green subpixels. Tandem diode configurations may be used in which a blue subpixel has two blue diodes connected in series each with a respective blue emissive organic layer. Additional (non-blue) subpixels in a display pixel may also be implemented in a tandem configuration so that each of these subpixels has a respective pair of series-connected diodes. 
     A pixel definition layer may be formed form a light-absorbing material to suppress ambient light reflections. The pixel definition layer may be coated with a moisture barrier to prevent outgassing of water vapor from the pixel definition layer. 
     A display pixel may be provided with optical cavity structures. Cavity modification layers formed of transparent material of different thicknesses may be used to tune the wavelength resonances of cavities for subpixels of different colors. For example, an optical cavity for a red subpixel may be tuned to resonate at red wavelengths by making cavity length adjustments and other optical cavity adjustments. If desired, a hole injection layer may be deposited with locally varying thicknesses using inkjet printing or other localized deposition techniques. The varying thicknesses of the hole injection layer may be used to tune that optical cavities of the subpixels of different colors.2 
    
    
     
       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 cross-sectional side view of an illustrative bottom-emission organic light-emitting diode display pixel with a two-stripe design having red and green color filters and having a blue subpixel without a blue color filter in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of an illustrative bottom-emission organic light-emitting diode display pixel with a two-stripe design having red and green color filters and having a blue subpixel with a blue color filter in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of an illustrative top-emission organic light-emitting diode display pixel having a weak cavity and having a two-stripe design with red and green color filters and with a blue subpixel without a blue color filter in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of an illustrative top-emission organic light-emitting diode display pixel having a weak cavity and having a two-stripe design with red and green color filters and with a blue subpixel with a blue color filter in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an illustrative top-emission organic light-emitting diode display pixel having a strong cavity and having a two-stripe design with red and green color filters and a blue subpixel without a blue color filter in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of an illustrative top-emission organic light-emitting diode display pixel having a strong cavity and having a two-stripe design with red and green color filters and a blue subpixel with a blue color filter in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of an illustrative tandem bottom-emission organic light-emitting diode display pixel having a two-stripe design with red and green color filters and with a blue subpixel without a blue color filter in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of an illustrative tandem bottom-emission organic light-emitting diode display pixel having a two-stripe design with red and green color filters and with a blue subpixel with a blue color filter in accordance with an embodiment. 
         FIG. 13  is a cross-sectional side view of an illustrative tandem top-emission organic light-emitting diode display pixel having a weak cavity and having a two-stripe design with red and green color filters and with a blue subpixel without a blue color filter in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of an illustrative tandem top-emission organic light-emitting diode display pixel having a weak cavity and having a two-stripe design having red and green color filters and with a blue subpixel with a blue color filter in accordance with an embodiment. 
         FIG. 15  is a cross-sectional side view of an illustrative tandem top-emission organic light-emitting diode display pixel having a strong cavity and having a two-stripe design with red and green color filters and with a blue subpixel without a blue color filter in accordance with an embodiment. 
         FIG. 16  is a cross-sectional side view of an illustrative top-emission organic light-emitting diode display pixel having a strong cavity and having a two-stripe design with red and green color filters and with a blue subpixel with a blue color filter in accordance with an embodiment. 
         FIG. 17  is a cross-sectional side view of an illustrative four-subpixel tandem bottom-emission organic light-emitting diode display pixel having a two-stripe design with a blue subpixel that does not have a blue color filter and having a yellow subpixel in accordance with an embodiment. 
         FIG. 18  is a cross-sectional side view of an illustrative four-subpixel tandem bottom-emission organic light-emitting diode display pixel having a two-stripe design with a blue subpixel that has a blue color filter and having a yellow subpixel in accordance with an embodiment. 
         FIG. 19  is a cross-sectional side view of an illustrative four-subpixel tandem top-emission organic light-emitting diode display pixel with a weak cavity having a two-stripe design with a blue subpixel that does not have a blue color filter and having a yellow subpixel in accordance with an embodiment. 
         FIG. 20  is a cross-sectional side view of an illustrative four-subpixel tandem top-emission organic light-emitting diode display pixel with a weak cavity having a two-stripe design with a blue subpixel that has a blue color filter and having a yellow subpixel in accordance with an embodiment. 
         FIG. 21  is a cross-sectional side view of an illustrative four-subpixel tandem bottom-emission organic light-emitting diode display pixel having a two-stripe design with a blue subpixel that does not have a blue color filter and having a white subpixel in accordance with an embodiment. 
         FIG. 22  is a cross-sectional side view of an illustrative four-subpixel tandem bottom-emission organic light-emitting diode display pixel having a two-stripe design with a blue subpixel that has a blue color filter and having a white subpixel in accordance with an embodiment. 
         FIG. 23  is a cross-sectional side view of an illustrative four-subpixel tandem top-emission organic light-emitting diode display pixel with a weak cavity having a two-stripe design with a blue subpixel that does not have a blue color filter and having a white subpixel in accordance with an embodiment. 
         FIG. 24  is a cross-sectional side view of an illustrative four-subpixel tandem top-emission organic light-emitting diode display pixel with a weak cavity having a two-stripe design with a blue subpixel that has a blue color filter and having a white subpixel in accordance with an embodiment. 
         FIGS. 25 ,  26 , and  27  are top views of illustrative display pixels showing subpixel layouts that may be used in accordance with an embodiment. 
         FIG. 28  is a cross-sectional side view of a display pixel showing how one or more subpixel hole injection layer thicknesses may be locally adjusted to control the resonant wavelength of optical cavities in subpixels of the display pixel in accordance with an embodiment. 
         FIG. 29  is a cross-sectional side view of a display having a pixel definition layer formed from a light-absorbing material such as a black polymer in accordance with an embodiment. 
         FIG. 30  is a cross-sectional side view of the pixel definition layer of  FIG. 29  after coating with an optional moisture barrier coating 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  12  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, planar polymer layers, composite films that include polymer and inorganic materials, metallic foils, etc. 
     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(s)  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 . Data lines D are associated with a respective columns of display pixels  22 . There may be distinct data lines D for each of the subpixels in a display pixel  22 . For example, in a display pixel that has separately controlled red, green, and blue subpixels, there may be three corresponding data lines for carrying respective red, green, and blue data. 
     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 horizontal control lines such as gate lines G 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 horizontal control signals (sometimes referred to as scan signals or gate 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 . More complex control schemes may be used to control display pixels with multiple thin-film transistors (e.g., to implement threshold voltage compensation schemes) if desired. 
     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  (e.g., a reflective metal layer formed from one or more metals such as aluminum and silver) and anode  60  (e.g., a transparent conductive layer such as a layer of indium tin oxide or indium zinc oxide) of light-emitting diode  62 . As this current passes through organic light-emitting diode emissive electroluminescent layer  56  (sometimes referred to as a light emitting layer or emissive layer), 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, yellow or white or blue or other colors determined by the nature of emissive layer  56  in situations in which color filter element  66  is clear or is absent, etc.). There may be three or four subpixels  22 ′ per display pixel  22  in display  14  or display pixels with other numbers of subpixels may be used. As an example, in a three-subpixel design display pixel  22  may have a first subpixel  22 ′ that is red, a second subpixel  22 ′ that is blue, and a third subpixel  22 ′ that is green. In a four-subpixel design, display pixel  22  may have 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 yellow or white (as examples). If desired, subpixels can be shared between neighboring pixels. for example, subpixels of red, blue, or both red and blue may be shared between neighboring pixels so that the effective resolution of display  14  appears higher than the physical number of pixels. 
     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  (e.g., a transparent conductive layer such as indium tin oxide or indium zinc oxide) and anode  60  (e.g., a light reflecting metal layer) of light-emitting diode  62 . As this current passes through organic light-emitting diode emissive electroluminescent layer (emissive layer)  56 , 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 layer  52  (e.g., a transparent color filter substrate such as a layer of glass or plastic that is sometimes referred to as an encapsulation substrate). Black matrix  72  may prevent stray light from exiting display  14 . Color filter elements  66  are formed on the underside of substrate  52  within openings in black matrix  72 . 
     The structures of  FIG. 4  form a single subpixel  22 ′ of a particular color. As with bottom-emission displays, there may be three or four subpixels  22 ′ per display pixel  22  or other suitable number of subpixels per display pixel  22  in display  14 . 
     An illustrative display pixel using a bottom emission design is shown in  FIG. 5 . As shown in  FIG. 5 , display pixel  22  may have a common cathode, an electron injection layer (and electron transport layer) such as layer  80  that is common to all subpixels in pixel  22  and that is therefore sometimes referred to as a common electron injection layer, a segmented layer of emissive material including portion  56 - 1  and separate portion  56 - 2 , a common hole injection layer (and hole transport layer)  82 , a patterned anode layer  60  that forms separate respective anodes for blue subpixel  22 -B, red subpixel  22 ′-R, and green subpixel  22 ′-G, color filter elements formed from a photoimageable polymer with colored dye or pigment (see, e.g., red color filter element  66 R and green color filter element  66 G), substrate  52  (including thin-film transistor circuitry for controlling pixel  22 , sometimes referred to as backplane circuitry or a backplane), and circular polarizer  90  (to reduce ambient light reflections from metal structures in display  14  such as cathode  58 ). Blue subpixel  22 ′-B emits blue light  64 B, red subpixel  22 ′-R emits red light  64 R, and green subpixel  22 ′-G emits green light  64 G. In bottom-emission designs such as the bottom-emission display pixel designs of  FIGS. 5 and 6 , common cathode  58  may be formed from a light-reflecting metal layer such as a layer of aluminum or silver. Anode  60  may be formed from a transparent conductive material such as indium tin oxide or indium zinc oxide. 
     The presence of color filter material in the light path of a subpixel tends to reduce light output efficiency, due to the absorption of the color filter material. Accordingly, display efficiency (i.e., the amount of output light generated for a given input power) may be maximized in some embodiments by omitting one or more color filters. In the configuration of  FIG. 5 , for example, blue subpixel  22 ′ contains a blue emissive layer  56 - 1  that emits blue light  64 B without using a blue color filter element on substrate  52 . Blue light emission materials tend to be less efficient than red and green light emitting materials, so the size of blue subpixel  22 ′-B (and therefore the size of its emissive layer) may be larger than that of red subpixel  22 ′-R and may be larger than that of green subpixel  22 ′-G. 
     Emissive layers  56 - 1  and  56 - 2  of  FIG. 5  serve to emit light under the control of current passing between cathode  58  and respective independently controllable separate anodes  60 . The emissive layers of pixel  22  may be formed from an organic material (e.g., an emissive polymer layer or an emissive small molecule layer). If desired, different subpixels may be provided with different emissive materials by segmenting an emissive layer. As an example, a blue subpixel may be provided with an emissive material that emits blue light (sometimes referred to as a blue emissive layer), whereas other subpixels may be provided with an emissive material that emits light of different wavelengths. In configurations of the type shown in  FIGS. 5 and 6 , the emissive layer has a first portion  56 - 1  that is used by the blue subpixel and a separate second portion  56 - 2  that is used by non-blue subpixels (i.e., red and green subpixels in the example of  FIGS. 5 and 6 ). By segmenting the emissive layer in this way, portions  56 - 1  and  56 - 2  need not emit light of the same color. Portion  56 - 1  may be a blue emissive layer, whereas portion  56 - 2  may be an emissive layer that emits red and green light (and not blue light). Portion  56 - 2  is used as a common emissive layer for both red subpixel  22 ′-R and green subpixel  22 ′-G (each having a respective color filter element). Portion  56 - 2  may be formed by stacked red and green layers or may be formed from a material that is formed from a mixture of red and green emitters rather than two separate stacked layers. If desired, the upper emissive layer (e.g., portion  56 - 2  may be formed from a yellow emissive layer rather than a red and green layer. 
     Shadow masks are used to pattern emissive layers such as emissive layers  56  of  FIGS. 3 and 4 . An emissive layer shadow mask has horizontal and vertical stripes of shadow mask material arranged in a grid to divide up the areas on a display into which emissive layers are being deposited. In the illustrative configuration of  FIG. 5 , the display pixels on display  14  such as display pixel  22  are being patterned using two shadow mask lines (stripes) per display pixel: shadow mask stripe  88 - 1  and shadow mask stripe  88 - 2 . This shadow mask pattern repeats itself across the surface of display  14 . The shadow mask is adjacent to display  14  during fabrication (e.g., during evaporation of emissive layer material) and is removed after emissive layer patterning is complete. 
     Using a two-stripe design of the type shown in  FIG. 5 , two shadow-mask stripes are used in creating two corresponding regions of subpixel structures. In particular, blue subpixels such as blue subpixel  22 ′-B form a first region (i.e., a first stripe) of subpixel structures in a column of display pixels  22  and red and green subpixel structures  22 ′-R and  22 ′-G form a second region (i.e., a second stripe) of subpixel structures. A first dead zone stripe (i.e., a first area in which no light is emitted because no emissive material is present) is formed under mask line  88 - 1 . A second dead zone stripe is formed under mask line  88 - 2  (and so forth, for each display pixel in display  14 ). Configurations of the type shown in  FIG. 5  are therefore sometimes referred to as using a two-stripe design. 
     In some conventional displays, a three-stripe design is used in which three separate shadow mask lines are used in patterning emissive material for three separate stripes of subpixels—blue, green, and red. In this type of design, there are three dead zones (areas in which no light is emitted) per display pixel. In a two-stripe display pixel array of the type shown in  FIG. 5  a common emissive layer is shared between two adjacent subpixels so that there are only two stripes and therefore only two dead zones per display pixel. This reduces that area of the dead zone per display pixel and therefore allows display pixel aperture to be increased and/or the pixel pitch for display  14  to be increased. 
     As shown in  FIG. 5 , red subpixel  22 ′-R and green subpixel  22 ′-G share common emissive layer  56 - 2 . Emissive layer  56 - 2  may emit red and green light (and not blue light). Red subpixel  22 ′-R may have a red color filter (color filter element)  66 R, so output light  64 R from subpixel  22 ′-R will be red. Green subpixel  22 ′-G may have a green color filter (color filter element) such as green color filter  66 G, so that light  64 G that is output from subpixel  22 ′-G will be green. Emissive material  56 - 1  may emit blue light (and not red or green light), so that output light  64 B is blue. In the configuration of  FIG. 5 , blue subpixel  22 ′-B has no color filter on substrate  52 , so blue output efficiency is enhanced. In the configuration of  FIG. 6 , blue subpixel  22 ′-B has a blue color filter (color filter element)  66 B to enhance the purity of emitted blue light  64 B. 
       FIGS. 7 and 8  are cross-sectional side views of an illustrative top-emission organic light-emitting diode configuration that may be used for forming display pixel  22 . Display pixel  22 ′-B of  FIG. 7  does not have a blue color filter so that efficiency is enhanced, whereas display pixel  22 ′-B of  FIG. 8  has blue color filter  66 B to enhance blue color purity in emitted blue light  64 B. 
     In the top-emission configuration of  FIG. 7 , cathode  58  may be formed from a transparent conductive material such as indium tin oxide or indium zinc oxide. Anode  60  may be formed from a light-reflecting metal such as aluminum or silver. Because there are weak light reflections from transparent cathode  58 , configurations of the type shown in  FIG. 7  are sometimes said to form a weak optical cavities for the subpixels of pixel  22 . 
     A strong optical cavity configuration for an illustrative top-emission display is shown in  FIGS. 9 and 10 . In the arrangement of  FIG. 9 , blue subpixel  22 ′-B is unfiltered (i.e., subpixel  22 ′-B does not have a blue color filter). In the arrangement of  FIG. 10 , blue color filter element  66 B is present to enhance color purity for blue light  64 B. Display pixels  22  of  FIGS. 9 and 10  have a transreflective cathode. In particular, cathode  58  may be formed from a thin layer of metal or other material that exhibits comparable levels of transmission and reflection. As an example, cathode  58  may have a transmittance of 50% and a reflectance of 50%, may have a transmittance of 60% and a reflectance of 40% or may have other suitable amounts of transmission and reflection so that layer  58  is transreflective. Because display pixels  22  of  FIGS. 9 and 10  have a transreflective cathode, light reflections within the diodes are strong. This type of configuration is therefore sometimes referred to as a strong cavity configuration. 
     Display pixel  22  may have transparent layers such as layers  92  and  94 . Layers  92  and  94  may be formed from layers of clear material such as indium tin oxide or other transparent layers and may serve as cavity modification layers. The cavities (etalons) that are formed in the subpixels serve as optical filters with defined wavelength resonances and can therefore be used to enhance color purity. If desired, optical cavity modification layers such as layers  92  and  94  may be used to adjust the lengths of the cavities (and other optical properties of the cavities) and therefore their resonant wavelengths. The thickness of layer  92  may, for example, be adjusted to control the optical resonance of the cavity in red subpixel  22 ′-R. The thickness of layer  94 , which is generally different than the thickness of layer  92 , may be adjusted to control the resonant peak associated with the cavity of green subpixel  22 ′-G. By configuring the cavity resonances in the subpixels of pixel  22 , the colors of light  64 B,  64 R, and  64 G may be adjusted. 
     If desired, top-emission and bottom-emission pixel configurations may use a tandem design in which each subpixel has multiple emissive layers (and associated light-emitting diodes) operating in series. A tandem bottom-emission configuration is shown in  FIGS. 11 and 12 . Blue color filter layer  66 B is absent in blue subpixel  22 ′-B of  FIG. 11  and is present in blue subpixel  22 ′-B of  FIG. 12 . 
     Blue subpixel  22 ′-B of  FIG. 11  has an upper diode formed from electronic injection layer (and electron transport layer)  80 T, blue emissive layer  56 - 1 T, and hole injection layer (and hole transport layer)  82 T and has a lower diode formed from electronic injection layer (and electron transport layer)  80 B, blue emissive layer  56 - 1 B, and hole injection layer (and hole transport layer)  82 B. Charge generation layer  96  may be interposed between the upper and lower diodes in each subpixel to ensure satisfactory diode operation. Charge generation layer  96  may be a conductive organic material or other material (e.g., a doped inorganic layer, etc.). The use of tandem blue diodes may enhance blue subpixel performance (e.g., diode lifetime may be increased since the current flowing through each diode is about half of what it would be in a non-tandem configuration). 
     Red subpixel  22 ′-R and green subpixel  22 ′-G may also each have a pair of series-connected organic light-emitting diodes. The upper diode in red subpixel  22 ′-R and the upper diode in green subpixel  22 ′-G share common emissive layer  56 - 2 T. Layer  56 - 2 T and layer  56 - 1 T are formed at the same vertical location in pixel  22  but represent separate portions of the emissive layer at this vertical location. Because portions  56 - 1 T and  56 - 2 T are laterally separated from each other, they may be formed from different materials (i.e., materials that emit light at different wavelengths). 
     The lower diode in red subpixel  22 ′-R and the lower diode in subpixel  22 ′-G share common emissive layer  56 - 2 B. Emissive layer  56 - 2 B may be separate from layer  56 - 1 B and may therefore emit light at different wavelengths than layer  56 - 1 B. With one suitable arrangement, emissive layer  56 - 2 T may be a green emissive layer producing green light  64 G and emissive layer  56 - 2 B may be a red emissive layer producing red light  64 R (or vice versa). The use of tandem diodes for the red and green subpixels may help enhance color gamut and extend diode lifetime. 
       FIGS. 13 and 14  show top-emission weak cavity display pixels with tandem diodes. Subpixel  22 ′-B of display pixel  22  of  FIG. 13  does not have a blue color filter element. Subpixel  22 ′-B of display pixel  22  of  FIG. 14  has blue color filter element  66 B to enhance blue color purity of blue light  64 B. 
       FIGS. 15 and 16  show top-emission strong cavity display pixels with tandem diodes. Cavity modification layers such as layers  92  and  94  may be used in independently adjusting optical cavity properties for the blue, red, and green subpixels. Subpixel  22 ′-B of display pixel  22  of  FIG. 15  does not have a blue color filter element. Subpixel  22 ′-B of display pixel  22  of  FIG. 16  has blue color filter element  66 B to enhance blue color purity of blue light  64 B. 
       FIGS. 17 and 18  show how display pixels  22  may be formed using a four subpixel design (e.g., a tandem four-pixel design). A two-strip design is used in which blue subpixels use a first pair of upper and lower emissive layers and in which the yellow, red, and green subpixels each share a common second pair of upper and lower emissive layers. 
     In the arrangements of  FIGS. 17 and 18 , emissive layers  56 - 1 T and  56 - 1 B may be blue emissive layers that produce blue light  64 B for tandem blue diodes. Emissive layer  56 - 2 T may be a green emissive layer and emissive layer  56 - 2 B may be a red emissive layer (or vice versa). Red emissive layer  56 - 2 T may produce red light  64 R for red subpixel  22 ′-R. Green emissive layer  56 - 2 B may produce green light  64 G for green subpixel  22 ′-G. The combined green and red emissions of layers  56 - 2 T and  56 - 2 B may produce light that appears yellow to a viewer (i.e., yellow light  64 Y in yellow subpixel  22 ′-Y may be produced partly by light from green emissive layer  56 - 2 T and partly by light from red emissive layer  56 - 2 B). In the configuration of  FIG. 17 , blue subpixel  22 ′-B has no blue color filter element so as to enhance efficiency and yellow subpixel  22 ′-Y has no color filter so as to enhance efficiency. If desired, blue and/or yellow subpixels may be provided with color filter elements. As shown in  FIG. 18 , for example, blue color filter  66 B may be used to enhance the blue color purity of emitted blue light  64 B. 
       FIGS. 19 and 20  show top-emission weak cavity display pixels with tandem diodes using a four-subpixel design in a two-stripe configuration. In the configuration of  FIG. 19 , blue subpixel  22 ′-B has no blue color filter element so as to enhance efficiency and yellow subpixel  22 ′-Y has no color filter so as to enhance efficiency. If desired, color filters may be added. For example, blue subpixel  22 ′-B may have a color filter such as blue color filter  66 B to enhance the blue color purity of emitted blue light  64 B, as shown in  FIG. 20 . 
       FIGS. 21 and 22  show bottom-emission weak cavity display pixels with tandem diodes using a four-subpixel design in a two-stripe configuration. In the configuration of  FIG. 21 , blue subpixel  22 ′-B has no blue color filter element to enhance efficiency and white subpixel  22 ′-W has no color filter to enhance efficiency. In the configuration of  FIG. 22 , blue subpixel  22 ′-B has blue color filter  66 B to enhance the blue color purity of emitted blue light  64 B. 
     The four-subpixel design of  FIGS. 19 and 20  contained yellow subpixels  22 ′-Y. The four-subpixel design of  FIGS. 21 and 22  has white subpixels  22 ′-W. The upper layer of emissive material is segmented. Portion (layer)  56 - 1 T is a blue emissive layer that is used by the upper diode in blue subpixel  22 ′-B. Portion (layer)  56 - 2 T is green-red emissive layer that produces green and red light. The red light is emitted as red light  64 R by red subpixel  22 ′-R. The green light is emitted as green light  64 G by green subpixel  22 -G. Lower emissive layer  56 B in pixel  22  of  FIGS. 21 and 22  is a common (shared) blue emissive layer that is shared by all subpixels. In blue subpixel  22 ′-B, layers  56 - 1 T and  56 B produce blue light. In white subpixel  22 ′-W, blue light from emissive layer  56 B combines with the red and green light from layer  56 - 2 T to produce white light  64 W. In the red and green subpixels, respective color filters  66 R and  66 G filter out all but the respective red and green light contributions from layer  56 - 2 T. 
       FIGS. 23 and 24  show top-emission weak cavity display pixels with tandem diodes using a four-subpixel design in a two-stripe configuration. In the configuration of  FIG. 23 , blue subpixel  22 ′-B has no blue color filter element to enhance efficiency and white subpixel  22 ′-W has no color filter to enhance efficiency. In the configuration of  FIG. 24 , blue subpixel  22 ′-B has blue color filter  66 B to enhance the blue color purity of emitted blue light  64 B. 
     As with the pixels of  FIGS. 21 and 22 , the upper emissive region in the pixels of  FIGS. 23 and 24  is formed from layers of two different materials. Layer  56 - 1 T is a blue emission layer that is used by the upper diode in blue subpixel  22 ′-B. Layer  56 - 2 T is green-red emissive layer that produces green and red light. The red light is emitted as red light  64 R by red subpixel  22 ′-R. The green light is emitted as green light  64 G by green subpixel  22 -G. Lower emissive layer  56 B in pixel  22  of  FIGS. 23 and 24  is a blue emissive layer that is common to all four subpixels. In white subpixel  22 ′-W, blue light from emissive layer  56 B combines with the red and green light from layer  56 - 2 T to produce white light  64 W. In the red and green subpixels, layer  56  produces red light and green light, respectively. 
       FIGS. 25 ,  26 , and  27  are top views of illustrative layouts that may be used for display pixels  22 . Illustrative emissive layer  56  may include a blue emissive layer  56  (blue), a yellow emissive layer  56  (yellow) or a white emissive layer  56  (white) (as examples). Data lines D run vertically through the pixels and gate lines (e.g., scan lines or other horizontal control lines) run horizontally through the pixels. Blue subpixels  22  ‘-B are generally larger than the other subpixels because blue emissive layers are relatively less efficient. The subpixel boundaries shown for illustrative subpixels  22 ’-B,  22 ′-R,  22 ′-G, and  22 ′-Y or  22 ′-W correspond to the outlines of openings in a dielectric pixel definition layer in which anodes  66  are formed.  FIG. 25  is an illustrative layout that may be used for a three-subpixel design.  FIGS. 26 and 27  are illustrative four-subpixel designs. Other layouts for pixels  22  may be used if desired. The configurations of  FIGS. 25 ,  26 , and  27  are merely illustrative. 
     If desired, the optical properties of the subpixel cavities in pixels  22  (i.e., strong cavity pixel designs) may be modified using one or more cavity modification layers formed from an organic material. For example, the thicknesses in vertical dimension Z of one or more of the layers of material in pixels  22  may be adjusted by performing material deposition using inkjet printing or by performing material deposition using thermal jet technology (i.e., inkjet printing in which the inkjet printing nozzle deposits a desired amount of material in a container on a resistive heater, which is then raised in temperature to heat the deposited material and to cause the heated material to be evaporated onto a desired target). Cavity modification layers such as layers  92  and  94  may, if desired, be omitted and the thickness of the subpixel cavities controlled by independently controlling the thicknesses of hole injection layer  82  (or layer  82 T and/or layer  82 B in tandem configurations) for each subpixel using inkjet printing and/or thermal jet deposition. Organic vapor phase jet technology may also be used in locally controlling the thicknesses of the hole injection layers or other layers of material in individual subpixels, if desired.  FIG. 28  shows how three illustrative subpixels SP 1 , SP 2 , and SP 3  in a three-subpixel design (and optionally an additional fourth subpixel SP 4  in a four-subpixel design) may be provided with different respective hole injection layer thicknesses T 1 , T 2 , T 3  and optionally T 4  in vertical dimension Z (e.g., using inkjet printing, thermal jet deposition, or organic vapor phase jet deposition to deposit these layers). 
     Ambient light reflections are partially suppressed using circular polarizers in display  14  and by using color filter elements (which partly suppress white ambient light by only transmitting light that is colored the same as the color of the color filter element in each subpixel). Additional ambient light reflection suppression may be achieved by implementing a pixel definition layer in display  14  with a light absorbing material. Consider, as an example, display  14  of  FIG. 29 . Patterned pixel definition layer  204  may be formed on other display layers such as substrate and backplane layers  200  (e.g., thin-film transistor layer circuits). Openings  210  in pixel definition layer  204  are aligned with color filter element CF in respective subpixels  22 ′ and contain diode layers  202  (e.g., anodes  60 , organic layers, etc.). Color filter layer  206  may include color filter elements CF (e.g., red color filters, blue color filters, etc.) and black mask BM formed on substrate  208 . Ambient light  212  may be transmitted through color filters CF, but, due to the light absorbing qualities of pixel definition layer  204 , light  212  is absorbed by layer  204  and not reflected back out of display  14  towards viewer  214 . 
     Pixel definition layer  204  may, as an example, be implemented using black masking material (e.g., a photoimageable polymer containing a black filler such as carbon black or other light-absorbing filler material). Organic light-emitting diode structures can be sensitive to the presence of water vapor, so pixel definition layer  204  is preferably formed from a polymer that has low water vapor retention. Water vapor outgassing from pixel definition layer  204  may therefore be minimized. If desired, pixel definition layer  204  may be coated with a water vapor barrier layer such a moisture barrier layer  214  of  FIG. 30 . Layer  214  may be formed from one or more inorganic dielectric layers (e.g., one or more layers of silicon nitride, silicon oxide, etc.) or other suitable moisture vapor barrier material. When a black pixel definition layer is used in display  14 , the circular polarizer in the display may be omitted or may be implemented using a weaker design that enhances light output efficiency from the light-emitting diodes. 
     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: 20140822
Publication Date: 20160105
Grant Date: 20160105
Priority Date: 20140107
Inventors: CHEN CHIEH-WEI
DRZAIC PAUL S.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01L27/322", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/3209", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/3213", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/3218", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/351", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/32", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/38", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/353", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/38", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/32", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/352", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/352", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/353", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/351", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 54939300