PATENT DOCUMENT

Publication Number: US-9455304-B2
Application Number: US-201514745014-A
Country: US
Kind Code: B2

Title: Organic light-emitting diode display with white and blue diodes

Abstract:
An organic light-emitting diode display may have an array of pixels with sets of pixels arranged in rows and columns. Each set of pixels includes a red pixel, a green pixel, a blue pixel, and a white pixel. The red pixels each have a white diode and a red color filter element to impart a red color to white light from that white diode. The green pixels each have a white diode and a green color filter element to impart a green color to white light from that white diode. The white pixels each have an unfiltered white diode. The blue pixels each have an unfiltered blue diode. The unfiltered white and blue diodes do not have color filters and emit white and blue light for the white and blue pixels, respectively. The white and blue diodes may be tandem diodes having two or more emissive layers.

Claims:
What is claimed is: 
     
       1. An organic light-emitting diode display, comprising:
 white pixels each having an unfiltered tandem white diode; 
 blue pixels each having an unfiltered tandem blue diode; 
 red pixels each having a tandem white diode that produces white light and a red color filter element that imparts a red color to that white light; and 
 green pixels each having a tandem white diode that produces white light and a green color filter element that imparts a green color to that white light. 
 
     
     
       2. The organic light-emitting diode display defined in  claim 1  wherein unfiltered tandem white diode of the white pixels and the tandem white diodes of the red and green pixels are formed from commonly deposited white emissive structures. 
     
     
       3. The organic light-emitting diode display defined in  claim 2  wherein the white emissive structures include a blue emissive layer and a yellow emissive layer. 
     
     
       4. The organic light-emitting diode display defined in  claim 3  wherein the tandem blue diode contains a blue emissive layer and wherein the blue emissive layer of the white emissive structures and the blue emissive layer of the tandem blue diode are formed from a common layer of material. 
     
     
       5. The organic light-emitting diode display defined in  claim 4  wherein the tandem blue diode and the unfiltered tandem white diode have reflective anodes and a transparent cathode. 
     
     
       6. The organic light-emitting diode display defined in  claim 4  wherein the tandem blue diode and the unfiltered tandem white diode have a reflective cathode and transparent anodes. 
     
     
       7. The organic light-emitting diode display defined in  claim 2  wherein the white emissive structures include a blue emissive layer and an emissive layer formed from a stack of red and green emissive layers. 
     
     
       8. The organic light-emitting diode display defined in  claim 7  wherein the tandem blue diode contains a blue emissive layer and wherein the blue emissive layer of the white emissive structures and the blue emissive layer of the tandem blue diode are formed from a common layer of material. 
     
     
       9. The organic light-emitting diode display defined in  claim 8  wherein the tandem blue diode and the unfiltered tandem white diode have reflective anodes and a transparent cathode. 
     
     
       10. The organic light-emitting diode display defined in  claim 8  wherein the tandem blue diode and the unfiltered tandem white diode have a reflective cathode and transparent anodes. 
     
     
       11. The organic light-emitting diode display defined in  claim 8  wherein the tandem blue diode has three blue emissive layers. 
     
     
       12. The organic light-emitting diode display defined in  claim 11  wherein the unfiltered tandem white diode comprises two blue emissive layers. 
     
     
       13. The organic light-emitting diode display defined in  claim 12  wherein the unfiltered tandem white diode further comprises an emissive layer selected from the group consisting of: a yellow emissive layer and a stack of red and green emissive layers. 
     
     
       14. An organic light-emitting diode display, comprising:
 an array of pixels having sets of pixels arranged in rows and columns, each set of pixels including a white pixel, a blue pixel, a red pixel, and a green pixel; 
 a blue tandem diode in each blue pixel; and 
 white tandem diodes respectively in the white pixel, the red pixel, and the green pixel. 
 
     
     
       15. The organic light-emitting diode display defined in  claim 14  wherein the white tandem diodes each have a blue emissive layer and an emissive layer selected from the group consisting of: a yellow emissive layer and a stack of red and green emissive layers and wherein the blue tandem diodes each have two blue emissive layers one of which is common with the blue emissive layer of the white tandem diodes. 
     
     
       16. The organic light-emitting diode display defined in  claim 15  further comprising a circular polarizer. 
     
     
       17. The organic light-emitting diode display defined in  claim 15  further comprising a black matrix having openings aligned with the array of pixels to suppress ambient light reflections. 
     
     
       18. An organic light-emitting diode display, comprising:
 a plurality of sets of pixels, each set of pixels include a white pixel, a blue pixel, a red pixel, and a green pixel; 
 a blue tandem diode in each blue pixel; and 
 white diodes respectively in the white pixel, the red pixel, and the green pixel; and 
 a layer of color filter elements aligned with the pixels, wherein the layer of color filter elements includes red color filter elements and green color filter elements and is free of blue color elements. 
 
     
     
       19. The organic light-emitting diode display defined in  claim 18  wherein each red color filter element is aligned with a respective one of the white diodes to produce red light for a corresponding one of the red pixels and wherein each green color filter element is aligned with a respective one of the white diodes to produce green light for a corresponding one of the green pixels. 
     
     
       20. The organic light-emitting diode display defined in  claim 19  further comprising first and second blue emissive layers, wherein each blue tandem diode contains a respective portion of the first blue emissive layer and a respective portion of the second blue emissive layer and wherein each white diode contains a respective portion of the first blue emissive layer. 
     
     
       21. The organic light-emitting diode display defined in  claim 20  further comprising a third blue emissive layer, wherein each blue tandem diode contains a respective portion of the third blue emissive layer.

Description:
This application claims the benefit of provisional patent application No. 62/017,490 filed on Jun. 26, 2014, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to displays, and, more particularly, to organic light-emitting diode displays. 
     Electronic devices often include displays. Organic light-emitting diode displays may exhibit desirable attributes such as a wide field of view, compact size, and low power consumption. Organic light-emitting diode displays may have individually colored light-emitting diodes such as red, green, and blue diodes or may use an array of white diodes with an overlapping array of red, green, and blue color filter elements. Organic light-emitting diode displays that are based on white diodes may be fabricated using fewer evaporation masks than are generally used when forming a display based on red, green, and blue diodes. 
     White diodes may be implemented using a tandem design in which a first diode and second diode are arranged in series. The first diode may be a blue diode and the second diode may have a yellow emissive layer or a stack of red and green emissive layers. The light produced by the first and second diodes in each tandem organic light-emitting diode collectively forms white light emissions that can be filtered using an overlapping color filter element. Organic light-emitting diodes with tandem designs may be operated at reduced currents relative to other designs and may therefore exhibit extended lifetimes. 
     It can be challenging to form a white diode organic light-emitting diode display with a desired color gamut. Color gamut can be enhanced by using narrowband color filter elements, but this adversely affects power efficiency. The reproduction of blue image content can be particularly challenging. White diodes generally contain blue emissive material, but due to the relatively low efficiency available from the blue emissive material, the white diodes associated with blue pixels may need to be driven with relatively large currents. This can reduce the lifetime of a display. 
     It would therefore be desirable to be able to provide improved organic light-emitting diode displays such as improved organic light-emitting diode displays using an array of white diodes overlapped by a color filter array. 
     SUMMARY 
     An organic light-emitting diode display has array of pixels. The array of pixels has sets of pixels arranged in rows and columns. Each set of pixels includes a red pixel, a green pixel, a blue pixel, and a white pixel. The red pixels each have a white diode and a red color filter element that is aligned with the white diode to impart a red color to white light from that white diode. The green pixels each have a white diode and a green color filter element that is aligned with the white diode to impart a green color to white light from that white diode. The white pixels each have an unfiltered white diode. The blue pixels each have an unfiltered blue diode. The unfiltered white and blue diodes do not have color filters and emit white and blue light for the white and blue pixels, respectively. The white and blue diodes may be tandem diodes having two or more emissive layers. 
     During fabrication, white emissive structures can be deposited through a first mask to form the white diodes for the red, green, and white pixels and blue emissive structures can be deposited through a second mask to form the blue diodes. The blue diodes and the white diodes may share a common blue emissive layer. Each white diode may also have an emissive layer such as a yellow emissive layer or a stack of red and green emissive layers. Each blue diode may contain a portion of the common blue emissive layer and an additional blue emissive layer. 
    
    
     
       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 pixel circuit in accordance with an embodiment. 
         FIG. 3  is a diagram of an illustrative organic light-emitting diode display in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of a portion of an illustrative bottom-emission organic light-emitting diode display in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of illustrative white and blue diode structures that may be used in the display of  FIG. 4  in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of a portion of an illustrative top-emission organic light-emitting diode display in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of illustrative white and blue diode structures that may be used in the display of  FIG. 6  in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of illustrative three-element white and blue diode structures that may be used in displays of the type shown in  FIGS. 4 and 6  in accordance with an embodiment. 
         FIG. 9  is a top view of a set of red, green, white, and blue pixels showing how a first mask may be used when depositing white diode emissive structures for the red, green, and white pixels and how a second mask may be used when depositing blue diode emissive structures for the blue pixels. 
     
    
    
     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 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, 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 . 
     Display  14  may be an organic light-emitting diode display. In an organic light-emitting diode display, each display pixel contains a respective organic light-emitting diode. A schematic diagram of an illustrative pixel circuit for an organic light-emitting diode display pixel is shown in  FIG. 2 . As shown in  FIG. 2 , display pixel  22  may include light-emitting diode  38 . A positive power supply voltage ELVDD may be supplied to positive power supply terminal  34  and a ground power supply voltage ELVSS may be supplied to ground power supply terminal  36 . Diode  38  has an anode (terminal AN) and a cathode (terminal CD). The state of drive transistor  32  controls the amount of current flowing through diode  38  and therefore the amount of emitted light  40  from display pixel  22 . Cathode CD of diode  38  is coupled to ground terminal  36 , so cathode terminal CD of diode  38  may sometimes be referred to as the ground terminal for diode  38 . Cathode CD may be shared among multiple diodes (i.e., the cathodes CD of multiple diodes may be tied to a shared voltage). The voltage on the anode of each diode is independently controlled to control the amount of light the diode produces for the pixel associated with that diode. 
     To ensure that transistor  32  is held in a desired state between successive frames of data, display pixel  22  may include a storage capacitor such as storage capacitor Cst. The voltage on storage capacitor Cst is applied to the gate of transistor  32  at node A to control transistor  32 . Data can be loaded into storage capacitor Cst using one or more switching transistors such as switching transistor  30 . When switching transistor  30  is off, data line D is isolated from storage capacitor Cst and the gate voltage on terminal A is equal to the data value stored in storage capacitor Cst (i.e., the data value from the previous frame of display data being displayed on display  14 ). When gate line G (sometimes referred to as a scan line) in the row associated with display pixel  22  is asserted, switching transistor  30  will be turned on and a new data signal on data line D will be loaded into storage capacitor Cst. The new signal on capacitor Cst is applied to the gate of transistor  32  at node A, thereby adjusting the state of transistor  32  and adjusting the corresponding amount of light  40  that is emitted by light-emitting diode  38 . If desired, the circuitry for controlling the operation of light-emitting diodes for display pixels in display  14  (e.g., transistors, capacitors, etc. in display pixel circuits such as the display pixel circuit of  FIG. 2 ) may be formed using other configurations (e.g., configurations that include circuitry for compensating for threshold voltage variations in drive transistor  32 , etc.). The pixel circuit of  FIG. 2  is merely illustrative. 
     As shown in  FIG. 3 , display  14  may include layers such as substrate layer  24 . Substrate layers such as layer  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. Substrate  24  may have left and right vertical edges and upper and lower horizontal edges. If desired, substrates such as substrate  24  may have non-rectangular shapes (e.g., shapes with curved edges, etc.). 
     Display  14  may have an array of pixels  22  for displaying images for a user. Each pixel may have a light-emitting diode such as organic light-emitting diode  38  of  FIG. 2  and associated thin-film transistor circuitry (e.g., the pixel circuit of  FIG. 2  or other suitable display pixel circuit). Pixels  22  may be arranged in rows and columns. There may be any suitable number of rows and columns in the array of pixels  22  (e.g., ten or more, one hundred or more, or one thousand or more). Display  14  may include pixels  22  of different colors. As an example, display  14  may include red pixels that emit red light, green pixels that emit green light, blue pixels that emit blue light, and white pixels that emit white light. Configurations for display  14  that include pixels of other colors may be used, if desired. 
     Display driver circuitry may be used to control the operation of pixels  22 . The display driver circuitry may be formed from integrated circuits, thin-film transistor circuits, or other suitable circuitry. As shown in  FIG. 3 , display driver integrated circuit  28  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 one or more printed circuits in electronic device  10 . During operation, the control circuitry (e.g., control circuitry  16  of  FIG. 1 ) may supply circuitry such as display driver integrated circuit  28  with information on images to be displayed on display  14 . Circuits such as display driver integrated circuits may be mounted on substrate  24  or may be coupled to substrate  24  through a flexible printed circuit cable or other paths. The circuitry of display driver integrated circuits such as circuit  28  may also be provided using thin-film transistor circuitry on substrate  24 . 
     To display the images on display pixels  22 , display driver circuitry  28  may supply corresponding image data to data lines D while issuing clock signals and other control signals to supporting display driver circuitry such as gate driver circuitry  18  and demultiplexing circuitry  20 . 
     Demultiplexer circuitry  20  may be used to demultiplex data signals from circuit  28  onto a plurality of corresponding data lines D. With the illustrative arrangement of  FIG. 3 , data lines D run vertically through display  14 . Data lines D are associated with respective columns of display pixels  22 . Demultiplexer circuitry  20  may be implemented as part of an integrated circuit such as circuit  28  and/or may be formed from thin-film transistor circuitry on substrate  24 . 
     Gate driver circuitry  18  (sometimes referred to as scan line driver circuitry) may be implemented as part of an integrated circuit such as circuit  28  and/or may be implemented using thin-film transistor circuitry on substrate  24 . Gate lines G (sometimes referred to as scan lines or horizontal control 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. 3 . 
     Gate driver circuitry  18  may assert control signals on the gate lines G in display  14 . For example, gate driver circuitry  18  may receive clock signals and other control signals from circuit  28  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, control circuitry such as display driver 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 . If desired, more complex control schemes may be used to control display pixels using multiple thin-film transistors (e.g., to implement threshold voltage compensation schemes). 
     Display circuits such as demultiplexer circuitry  20 , gate line driver circuitry  18 , and the circuitry of display pixels  22  may be formed using thin-film transistors on substrate  24  such as silicon-based transistors such as polysilicon thin-film transistors, semiconducting-oxide-based transistors such as InGaZnO transistors, or other thin-film transistor circuitry. 
     A cross-sectional side view of a configuration that may be used for the pixels of display  14  of device  10  is shown in  FIG. 4 . In display  14  of  FIG. 4 , light is emitted downward. Accordingly, display  14  of  FIG. 4  may sometimes be referred to as a bottom emission display. As shown in  FIG. 4 , display  14  may have a thin-film transistor substrate such as substrate  58 . Substrate  58  may be formed from a transparent layer of glass or other clear substrate material. During operation, diodes  38  produce light that is emitted in the downward direction. There are four pixels in  FIG. 4 : red pixel  22 R, green pixel  22 G, blue pixel  22 B, and white pixel  22 W. Pixel  22 R emits red light R, pixel  22 G emits green light G, pixel  22 B emits blue light B, and pixel  22 W emits white light W. In display  14 , sets of pixels of the type shown in  FIG. 4  (i.e., sets of red, green, blue, and white pixels) are arranged in rows and columns, as described in connection with  FIG. 3 . 
     A layer of color filter elements such as color filter elements  80  and  82  may be patterned to form an array on the surface of substrate  58 . Diodes  38  include white light diodes based on white emissive structures  76 . Diodes  38  also include a blue diode based on blue emissive structure  78 . The white light diode in pixel  22 W emits white light W. No color filters are used to filter white light W (i.e. the white diode in pixel  22 W is an unfiltered white diode), so white light W from pixel  22 W is emitted through substrate  58 . The blue diode in pixel  22 B emits blue light B. No color filters are used to filter blue light B (i.e., the blue diode in pixel  22 B is an unfiltered blue diode), so blue light B from pixel  22 B is emitted through substrate  58 . The absence of color filters on the blue and white diodes of pixels  22 W and  22 B allows these pixels to emit light efficiently. 
     Red pixel  22 R has a white light diode based on white emissive structure  76 . A red color filter such as red color filter  80  filters white light from the white diode in red pixel  22 R and imparts a red color to the white light, thereby producing red light R. Green pixel  22 G also has a white diode based on a white emissive structure  76 . A green color filter such as green color filter  82  filters white light from the white diode in green pixel  22 G, thereby producing green light G. 
     Color filter elements  80  and  82  are formed on the inner surface of substrate  58 . A planarization layer (e.g., a clear polymer layer or other transparent dielectric layer) such as layer  56  is formed over color filter elements  80  and  82 . Thin-film transistors, capacitors, and other thin-film transistor circuitry  72  (e.g., display pixel circuitry such as the illustrative display pixel circuitry of  FIG. 2 ) may be formed on layer  56 . An array of transparent anodes  70  may be formed on the surface of thin-film transistor circuitry  72 . Transparent anodes may be formed from a transparent conductive material such as indium tin oxide (as an example). Pixel definition layer  68  may be formed from a photoimageable polymer such as black polyimide (as an example). Openings may be formed in pixel definition layer  68 . Each pixel definition layer opening receives diode structures for a respective pixel, as shown in  FIG. 4 . 
     A blanket cathode layer such as cathode  66  may cover organic emissive layer structures  76  for the white light diodes and organic emissive layer structure  78  for the blue light diode. Cathode  66  may extend over all pixels  22  in display  14 . In the bottom-emission configuration of  FIG. 4 , cathode  66  may be a reflective cathode (sometimes referred to as a mirror cathode) and may be formed from aluminum, other metals, or other reflective conductive structures. 
     A thin-film encapsulation layer such as layer  64  may cover cathode  66 . Thin-film encapsulation layer  64  may be formed from a layer of silicon oxide or other dielectric. Adhesive  62  may be used to attach substrate  50  to the structures on substrate  58 . Substrate  50  may be formed from an opaque or transparent layer such as a layer of glass, a layer of plastic, or other materials. Sealant  52  may be used to seal the edges of display  14 . Getter structure  54  may help absorb moisture that intrudes into the interior of display  14 . Circular polarizer  60  may be used to suppress ambient light reflections from reflective cathode  66 . If desired, a black matrix structure (e.g., patterned black masking material aligned with the structures of pixel definition layer  68 ) may be used in place of circular polarizer to help block off-axis ambient light and thereby reduce ambient light reflections from cathode  66 . The use of a circular polarizer may be more effective at reducing ambient light reflections than the use of a black matrix, but the circular polarizer will absorb about 40-60% of the light emitted by diodes  38  and therefore will reduce display efficiency. 
       FIG. 5  shows illustrative layers of material of the type that may be used in forming white and blue diodes  38  for bottom-emission display  14  of  FIG. 4 . As shown in  FIG. 5 , diodes  38  include a white diode W of the type that may be used for red pixel  22 R, green pixel  22 G, and white pixel  22 W and include a blue diode B of the type that may be used for blue pixel  22 B. 
     The organic light-emitting diodes of display  14  are based on layers of emissive material (e.g., organic electroluminescent material). Diodes  38  may have layers of emissive material of different colors. In white light diodes, emissive layers of different colors may collectively produce white light emissions. In blue diodes, blue emissive layers may be used to produce blue light that can be used in forming blue pixels without using blue color filters. 
     In blue diode B, blue diode emissive structures  78  are interposed between reflective cathode  66  and transparent anode  70 . Structures  78  include first and second blue emissive layers such as blue emissive layer  88  and blue emissive layer  96 . Electron transport layer  84  may be interposed between blue emissive layer  88  and reflective cathode  66 . Hole injection layer  90 , charge generation layer  92 , and electron transport layer  94  may be interposed between blue emissive layer  88  and blue emissive layer  96 . Hole transport layer  98  and hole injection layer  100  may be interposed between blue emissive layer  96  and transparent anode  70 . Because there are two blue emissive layers in blue diode B, blue diode B is made up of two blue diodes coupled in series. Blue diodes such as blue diode B of  FIG. 5  may therefore sometimes be referred to as tandem blue diodes. Blue diode B emits blue light for blue pixel  22 B. No blue color filter is needed to produce the blue light, so blue light diode B may sometimes be referred to as an unfiltered blue tandem diode. 
     In white diode W, white emissive structures  76  are interposed between reflective cathode  66  and transparent anode  70 . Structures  76  include first emissive layer  86  and second emissive layer  96 . Electron transport layer  84  may be interposed between emissive layer  86  and reflective cathode  66 . Hole injection layer  90 , charge generation layer  92 , and electron transport layer  94  may be interposed between emissive layer  86  and emissive layer  96 . Hole transport layer  98  and hole injection layer  100  may be interposed between emissive layer  96  and transparent anode  70 . Because there are two emissive layers in white diode W, white diode W is made up of two diodes coupled in series and may therefore sometimes be referred to as a tandem white diode. Emissive layer  96  in white diode W may be formed from the same layer of material as emissive layer  96  in blue diode B (i.e., emissive layer  96  may be a common blue emissive layer having a portion in blue diode B and a portion in white diode W). Layer  86  may be a yellow emissive layer or may be a stack of red and green emissive layers. The light produced by the diode formed from emissive layer  86  and the light produced by the diode formed from emissive layer  96  collectively form white light. This white light can be used with no color filter to form white light for pixel  22 W, can be passed through a red color filter to form red light for red pixel  22 R, or can be passed through a green color filter to form green light for green pixel  22 G. 
       FIG. 6  is a cross-sectional side view of display  14  in an illustrative top-emission configuration. As shown in  FIG. 6 , light from diodes  38  may pass upwards through transparent substrate  58 . Substrate  58  may be formed from a transparent layer of glass or other clear substrate material. Display  14  of  FIG. 6  has red, green, blue, and white pixels such as red pixel  22 R, green pixel  22 G, blue pixel  22 B, and white pixel  22 W. Pixel  22 R emits red light R, pixel  22 G emits green light G, pixel  22 B emits blue light B, and pixel  22 W emits white light W. Sets of the red, green, blue, and white pixels of  FIG. 6  are arranged in rows and columns, as described in connection with  FIG. 3 . 
     Color filter elements  80  and  82  may be patterned in an array on the surface of substrate  58 . Diodes  38  include white light diodes based on white emissive structures  76 . Diodes  38  also include a blue diode based on blue emissive structure  78 . The white light diode in pixel  22 W emits white light W. No color filters are used to filter white light W, so white light W from pixel  22 W is emitted through substrate  58 . The blue diode in pixel  22 B emits blue light B. No color filters are used to filter blue light B, so unfiltered blue light B from pixel  22 B is emitted through substrate  58 . As in the bottom-emission configuration of  FIG. 4 , the absence of color filters on the blue and white diodes of pixels  22 W and  22 B of  FIG. 6  allows these pixels to emit unfiltered light efficiently. 
     Red pixel  22 R has a white light diode based on white emissive structure  76 . A red color filter such as red color filter  80  filters white light from the white diode in red pixel  22 R and imparts a red color to the white light, thereby producing red light R. Green pixel  22 G also has a white diode based on a white emissive structure  76 . A green color filter such as green color filter  82  filters white light from the white diode in green pixel  22 G, thereby producing green light G. 
     The arrangement of  FIG. 6  uses a transparent cathode and reflective anodes. Color filter elements  80  and  82  are formed on the inner surface of substrate  58 . A planarization layer (e.g., a clear polymer layer or other transparent dielectric layer) such as layer  56  is formed over color filter elements  80  and  82 . A black matrix such as black matrix  102  may be formed from a patterned opaque masking layer (e.g., patterned black polymer). Black matrix  102  may help suppress ambient light reflections from reflective the reflective anodes. If desired, a circular polarizer may be incorporated into display  14  to suppress ambient light reflections (e.g., a circular polarizer may be attached to the outer surface of substrate  58  in place of using black matrix  102 ). 
     Thin-film transistors, capacitors, and other thin-film transistor circuitry  72  (e.g., display pixel circuitry such as the illustrative display pixel circuitry of  FIG. 2 ) may be formed on substrate layer  50 . An array of reflective anodes  70  may be formed on the surface of thin-film transistor circuitry  72 . Reflective anodes may be formed from aluminum, other metals, or other reflective conductive material. 
     Pixel definition layer  68  may be formed from a photoimageable polymer such as black polyimide (as an example). Openings may be formed in pixel definition layer  68 . Each pixel definition layer opening receives diode structures for a respective pixel. 
     A blanket cathode layer such as cathode  66  may cover organic emissive layer structures  76  for the white light diodes and organic emissive layer structure  78  for the blue light diode. Cathode  66  may extend over all pixels  22  in display  14 . In the top-emission configuration of  FIG. 6 , cathode  66  may be a transparent cathode that is formed from layers of conductive material that are sufficiently transparent to allow light from diodes  38  to pass upwards through layer  58 . Transparent cathode  66  may, for example, be formed from a thin metal layer (e.g., silver layer, silver and magnesium, etc.), may be formed from silver and indium tin oxide, or may be formed from other materials. A thin-film encapsulation layer such as layer  64  may cover cathode  66 . Thin-film encapsulation layer  64  may be formed from a layer of silicon oxide or other dielectric. Planarization layer  56  may cover color filter elements  80  and  82  and black matrix  102 . Planarization layer  56  may be formed from a transparent material such as a layer of clear polymer. Transparent adhesive  62  (e.g., a clear polymer) may be used to attach substrate  58  to the structures on substrate  50  and may help match the index of refraction of layer  56  to the index of refraction of layer  64  and the other structures on substrate  50 . Substrate  50  may be formed from an opaque or transparent layer such as a layer of glass, a layer of plastic, or other materials. Sealant  52  may be used to seal the edges of display  14 . Getter structure  54  may help absorb moisture that intrudes into the interior of display  14 . 
       FIG. 7  shows illustrative layers of material that may be used to form diodes  38  for top-emission display  14  of  FIG. 6 . As shown in  FIG. 7 , diodes  38  include a white diode W of the type that may be used for red pixel  22 R, green pixel  22 G, and white pixel  22 W and include a blue diode B of the type that may be used for blue pixel  22 B. 
     In blue diode B, blue emissive structures  78  are interposed between transparent cathode  66  and reflective anode  70 . Structures  78  include first and second blue emissive layers such as blue emissive layer  88  and blue emissive layer  96 . Electron transport layer  84  may be interposed between blue emissive layer  88  and transparent cathode  66 . Hole injection layer  90 , charge generation layer  92 , and electron transport layer  94  may be interposed between blue emissive layer  88  and blue emissive layer  96 . Hole transport layer  98  and hole injection layer  100  may be interposed between blue emissive layer  96  and reflective anode  70 . Because there are two blue emissive layers (and therefore two blue diodes) in blue diode B, blue diode B is a tandem blue diode. Blue diode B emits unfiltered blue light for blue pixel  22 B without using a color filter and may therefore sometimes be referred to as an unfiltered blue diode. 
     In white diode W, which also uses a tandem diode configuration, white emissive structures  76  are interposed between transparent cathode  66  and reflective anode  70 . Structures  76  include first emissive layer  86  and second emissive layer  96 . Electron transport layer  84  may be interposed between emissive layer  86  and transparent cathode  66 . Hole injection layer  90 , charge generation layer  92 , and electron transport layer  94  may be interposed between emissive layer  86  and emissive layer  96 . Hole transport layer  98  and hole injection layer  100  may be interposed between emissive layer  96  and reflective anode  70 . Because there are two emissive layers in white diode W, white diode W is made up of two diodes coupled in series and may be referred to as a tandem white diode. Emissive layer  96  may be a blue emissive layer (i.e., a common layer shared with the lower blue emissive material in blue diode B). Layer  86  may be a yellow emissive layer or may be formed from a stack of red and green emissive layers. The light produced by the diode formed from emissive layer  86  and the light produced by the diode formed from emissive layer  96  collectively form white light. This white light can be used with no color filter to form white light for pixel  22 W, can be passed through a red color filter to form red light for red pixel  22 R, or can be passed through a green color filter to form green light for green pixel  22 G. 
     If desired, more than two diodes may be used in each pixel (i.e., three or more diodes may be coupled in series to form within each pixel rather than two diodes). An illustrative three-diode tandem diode configuration that may be used for white and blue diodes  38  is shown in  FIG. 8 . 
     As shown in  FIG. 8 , diodes  38  include a tandem white diode W of the type that may be used for red pixel  22 R, green pixel  22 G, and white pixel  22 W and include a tandem blue diode B of the type that may be used for blue pixel  22 B. The structures of  FIG. 8  may be used in a top-emission display or a bottom-emission display. In a top-emission display, cathode  66  is transparent and anodes  70  are reflective. In a bottom-emission display, cathode  66  is reflective and anodes  70  are transparent. 
     Both the white and blue diodes of  FIG. 8  include diode structures associated with three Diodes—diode D 1 , diode D 2 , and diode D 3 . In blue diode B of  FIG. 8 , blue emissive structures  78  are interposed between cathode  66  and anode  70 . Structures  78  include first, second, and third blue emissive layers such as blue emissive layer  88 , blue emissive layer  96 , and blue emissive layer  108 . Electron transport layer  110  may be interposed between cathode  66  and blue emissive layer  108 . Hole injection layer  106 , charge generation layer  104 , and electron transport layer  84  may be coupled between blue emissive layer  108  and blue emissive layer  88 . Hole injection layer  90 , charge generation layer  92 , and electron transport layer  94  may be interposed between blue emissive layer  88  and blue emissive layer  96 . Hole transport layer  98  and hole injection layer  100  may be interposed between blue emissive layer  96  and reflective anode  70 . Blue diode B emits blue light for blue pixel  22 B. Because there are three diodes D 1 , D 2 , and D 3  in blue diode B, the current through each diode is reduced and blue diode lifetime may be extended. 
     In white diode W, which also uses a tandem diode configuration, white emissive structures  76  are interposed between cathode  66  and anode  70 . Structures  76  include emissive layer  86 , emissive layer  96 , and emissive layer  108 . Electron transport layer  110  may be interposed between cathode  66  and blue emissive layer  108 . Hole injection layer  106 , charge generation layer  104 , and electron transport layer  84  may be interposed between blue emissive layer  108  and emissive layer  86 . Hole injection layer  90 , charge generation layer  92 , and electron transport layer  94  may be interposed between emissive layer  86  and emissive layer  96 . Hole transport layer  98  and hole injection layer  100  may be interposed between emissive layer  96  and anode  70 . Because there are three emissive layers in white diode W, white diode W is made up of three diodes coupled in series. Emissive layer  96  may be a blue emissive layer. Emissive layer  108  may also be a blue emissive layer. Layer  86  may be a yellow emissive layer or may be formed from a stack of red and green emissive layers. The light produced by the diode formed from emissive layer  86  and the light produced by the diodes formed from emissive layers  96  and  108  collectively form white light. This white light can be used with no color filter to form white light for pixel  22 W, can be passed through a red color filter to form red light for red pixel  22 R, or can be passed through a green color filter to form green light for green pixel  22 G. 
       FIG. 9  is a diagram of an illustrative layout that may be used for each set of four pixels ( 22 R,  22 G,  22 W, and  22 B) in display  14 . The pattern of  FIG. 9  may be tiled across the surface of display  14  so that the sets of pixels are arranged in rows and columns. During fabrication, white diode structures (e.g., a yellow emissive layer or a stack formed from red and green emissive layers) may be evaporated through a mask with openings such as opening  114 , thereby forming the emissive layer structures needed for the white diodes associated with pixels  22 R,  22 G, and  22 G. Blue emissive structures that are specific to the blue diodes of pixels  22 B may be evaporated through a mask with openings such as opening  116 . Layers of emissive material and other diode structures that are common to both white and blue diodes may be deposited as blanket films. Because a small number of masks are used in forming display  14 , processing operations are simplified. 
     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: 20150619
Publication Date: 20160927
Grant Date: 20160927
Priority Date: 20140626
Inventors: LEE JUNGMIN
NAM DONGHEE
Assignee: APPLE INC
CPC Classifications: [{"code": "H01L27/3213", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L51/5044", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L27/322", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/38", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/351", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K50/131", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/351", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/38", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/131", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 54931391