PATENT DOCUMENT

Publication Number: US-9685486-B2
Application Number: US-201514862006-A
Country: US
Kind Code: B2

Title: Organic light-emitting diode display with color filter layer

Abstract:
A display may have an array of pixels formed from organic light-emitting diodes of different colors. Each organic light-emitting diode may have an anode, a cathode, and an emissive layer between the anode and cathode. To prevent undesired color shifts with off-axis viewing angles, evaporated color filters may be formed on the cathode in alignment with the light-emitting diodes. The color filters may include red color filters that overlap the red diodes but not the green and blue diodes, may include red, blue, and green filters that overlap respective red, green, and blue diodes, or may include an orange filter that overlaps red and green diodes and a blue filter that overlaps blue diodes. The color filters may serve as a capping layer for the diodes or a capping layer that is separate from the color filters can be incorporated into the display.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 a substrate; and 
 an array of organic light-emitting diode pixels on the substrate including organic light-emitting diodes of at least first, second, and third colors, wherein the organic light-emitting diodes of the first color have an emissive layer of a first color and a color filter layer of the first color, wherein the organic light-emitting diodes of the second color have an emissive layer of the second color, wherein the organic light-emitting diodes of the first color have a cathode that is interposed between the color filter layer of the first color and the emissive layer of the first color, and wherein the organic light-emitting diodes of the second and third colors are covered with a color filter layer of a fourth color. 
 
     
     
       2. The display defined in  claim 1  wherein the first color is red and wherein the color filter layer of the first color comprises a red color filter layer. 
     
     
       3. The display defined in  claim 2  further comprising a clear capping layer on the organic light-emitting diodes of the second color. 
     
     
       4. The display defined in  claim 1  wherein the organic light-emitting diodes of the second and third colors are covered with a clear capping layer. 
     
     
       5. The display defined in  claim 1  wherein the first color is blue, wherein the emissive layer of the light-emitting diodes of the first color comprises a blue emissive layer, wherein the color filter layer of the fourth color comprises an orange color filter layer, wherein the second color is red, and wherein the third color is green. 
     
     
       6. The display defined in  claim 1  further comprising a clear capping layer that covers the organic light-emitting diodes of the first, second, and third colors. 
     
     
       7. The display defined in  claim 1  wherein the color filter layer of the first color includes a material selected from the group consisting of: DCM, DCM2, PR254, and PR256. 
     
     
       8. An organic light-emitting diode display with pixels of first, second, and third colors, comprising:
 a substrate; 
 thin-film transistor circuitry on the substrate; 
 a organic light-emitting diode layer on the thin-film transistor circuitry that forms first, second, and third diodes respectively for the pixels of the first, second, and third colors, wherein the first, second, and third diodes include emissive material; 
 a transparent conductive layer that covers the organic light-emitting diode layer; and 
 at least one color filter layer of the first color that overlaps the first diodes, wherein the transparent conductive layer is interposed between the at least one color filter layer and the emissive material of the first diodes and wherein the at least one color filter layer forms a capping layer for the first diodes. 
 
     
     
       9. The organic light-emitting diode display defined in  claim 8  wherein the first color comprises red, the second color comprises green, and the third color comprises blue and wherein the at least one color filter layer comprises a red color filter layer that overlaps the first diodes without overlapping the second and third diodes. 
     
     
       10. An organic light-emitting diode display with pixels of first, second, and third colors, comprising:
 a substrate; 
 thin-film transistor circuitry on the substrate; 
 a organic light-emitting diode layer on the thin-film transistor circuitry that forms first, second, and third diodes respectively for the pixels of the first, second, and third colors, wherein the first, second, and third diodes include emissive material; 
 a transparent conductive layer that covers the organic light-emitting diode layer; 
 at least one color filter layer of the first color that overlaps the first diodes, wherein the transparent conductive layer is interposed between the at least one color filter layer and the emissive material of the first diodes; and 
 a clear capping layer that overlaps the second and third diodes without overlapping the first diodes. 
 
     
     
       11. An organic light-emitting diode display, comprising:
 a substrate; and 
 red light-emitting diodes, green light-emitting diodes, and blue light-emitting diodes formed on the substrate, wherein the red light-emitting diodes include an anode, a red emissive layer, red color filter layer, and a cathode between the red emissive layer and the red color filter layer, and wherein the green light-emitting diodes and the blue light-emitting diodes do not include color filter layers. 
 
     
     
       12. The organic light-emitting diode display defined in  claim 11  wherein the red color filter layer comprises a thermally evaporable material that serves as a capping layer for the red light-emitting diodes and that does not overlap the blue and green light-emitting diodes. 
     
     
       13. The organic light-emitting diode display defined in  claim 11  wherein the red color filter layer comprises a thermally evaporable red color filter layer, the organic light-emitting diode display further comprising a capping layer, wherein a first portion of the capping layer overlaps the blue and green light-emitting diodes and wherein a second portion of the capping layer is interposed between the red color filter layer and the cathodes of the red light-emitting diodes.

Description:
This application claims the benefit of provisional patent application No. 62/153,882 filed on Apr. 28, 2015, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices with displays, and, more particularly, to color displays such as color organic light-emitting diode displays. 
     Electronic devices often include displays. Displays such as organic light-emitting diode displays include arrays of pixels that emit light to display images for a user. The pixels of a display may include emissive material of different colors to provide the display with the ability to display color images. 
     It can be challenging to produce accurate color images with a display. Due to geometrical effects, the spectrum of each pixel&#39;s emitted light in an organic light-emitting diode display can exhibit undesired blue shifts at off-axis viewing angles. This non-ideal behavior can introduce undesired color shifts in the images on a display. 
     It would therefore be desirable to be able to provide improved displays for displaying color images such as improved organic light-emitting diode displays. 
     SUMMARY 
     A display may have an array of pixels on a substrate. The display may be an organic light-emitting diode display and the pixels may include organic light-emitting diodes of different colors. For example, the organic light-emitting diodes may include red organic light-emitting diodes, green organic light-emitting diodes, and blue organic light-emitting diodes. 
     Each organic light-emitting diode may have an anode, a cathode, and an emissive layer between the anode and cathode. To prevent undesired color shifts for off-axis viewing angles, evaporated color filters may be formed on the cathode in alignment with the light-emitting diodes. The color filters may block color-shifted off-axis light. 
     The color filters may include red color filters that overlap the red diodes but not the green and blue diodes, may include red, blue, and green filters that overlap respective red, green, and blue diodes, may include an orange filter that overlaps red and green diodes and a blue filter that overlaps blue diodes, or may include other color filter structures. The color filters may serve as a capping layer for the diodes or a capping layer that is separate from the color filters can be incorporated into the display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG. 3  is a top view of an illustrative display in an electronic device in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of a portion of an illustrative organic light-emitting diode display in accordance with an embodiment. 
         FIG. 5  is a graph showing how pixels in an organic light-emitting diode display may exhibit undesired color shifts as a function of light emission angle in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of an illustrative organic light-emitting diode display layer being coated with an evaporated material that is patterned using a shadow mask in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of an illustrative organic light-emitting diode display in which red pixels are coated with an evaporated red color filter layer in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of an illustrative organic light-emitting diode display in which red, green, and blue pixels are coated with respective evaporated red, green, and blue color filter layers in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an illustrative organic light-emitting diode display in which red and green pixels are coated with an evaporated orange color filter layer and in which blue pixels are coated with an evaporated blue color filter layer in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of an illustrative organic light-emitting diode display in which red, blue, and green pixels are covered with a capping layer and in which the portion of the capping layer overlapping red pixels is coated with a red color filter layer in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative electronic device of the type that may be provided with a display is shown in  FIG. 1 . Electronic device  10  may be a computing device such as a laptop computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, a device embedded in eyeglasses or other equipment worn on a user&#39;s head, or other wearable or miniature device, a computer monitor or other display containing an embedded computer or other electronic equipment, a computer display or other monitor that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. In the illustrative configuration of  FIG. 1 , device  10  is a portable device such as a cellular telephone, media player, tablet computer, wrist device, or other portable computing device. Other configurations may be used for device  10  if desired. The example of  FIG. 1  is merely illustrative. 
     In the example of  FIG. 1 , device  10  includes a display such as display  14  mounted in housing  12 . Housing  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). 
     Display  14  may be a touch screen display that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components (e.g., resistive touch sensor components, acoustic touch sensor components, force-based touch sensor components, light-based touch sensor components, etc.) or may be a display that is not touch-sensitive. Capacitive touch screen electrodes may be formed from an array of indium tin oxide pads or other transparent conductive structures. A touch sensor may be formed using electrodes or other structures on a display layer that contains a pixel array or on a separate touch panel layer that is attached to the pixel array (e.g., using adhesive). 
     Display  14  may include an array of pixels formed from liquid crystal display (LCD) components, an array of electrophoretic pixels, an array of plasma pixels, an array of organic light-emitting diode pixels or other light-emitting diodes, an array of electrowetting pixels, or pixels based on other display technologies. Configurations in which display  14  is an organic light-emitting diode display are sometimes described herein as an example. The use of organic light-emitting diode pixels to form display  14  is merely illustrative. Display  14  may, in general, be formed using any suitable type of pixels. 
     Display  14  may be protected using a display cover layer such as a layer of transparent glass or clear plastic. Openings may be formed in the display cover layer. For example, an opening may be formed in the display cover layer to accommodate a button, a speaker port, or other component. Openings may be formed in housing  12  to form communications ports (e.g., an audio jack port, a digital data port, etc.), to form openings for buttons, etc. 
       FIG. 2  is a schematic diagram of device  10 . As shown in  FIG. 2 , 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  18  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  18  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  18  and may receive status information and other output from device  10  using the output resources of input-output devices  18 . Input-output devices  18  may include one or more displays such as display  14 . 
     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  using an array of pixels in display  14 . 
     Display  14  may have a rectangular shape (i.e., display  14  may have a rectangular footprint and a rectangular peripheral edge that runs around the rectangular footprint) or may have other suitable shapes. Display  14  may be planar or may have a curved profile. 
     A top view of a portion of display  14  is shown in  FIG. 3 . As shown in  FIG. 3 , display  14  may have an array of pixels  22 . Pixels  22  may receive data signals over signal paths such as data lines D and may receive one or more control signals over control signal paths such as horizontal control lines G (sometimes referred to as gate lines, scan lines, emission control lines, etc.). There may be any suitable number of rows and columns of pixels  22  in display  14  (e.g., tens or more, hundreds or more, or thousands or more). Each pixel  22  may have a light-emitting diode  26  that emits light  24  under the control of a pixel control circuit formed from transistor circuitry such as thin-film transistors  28  and thin-film capacitors). Transistors  28  may be polysilicon thin-film transistors, semiconducting-oxide thin-film transistors such as indium gallium zinc oxide transistors, or transistors formed from other semiconductors. 
     A cross-sectional side view of a portion of an illustrative organic light-emitting diode display in the vicinity of one of light-emitting diodes  26  is shown in  FIG. 4 . As shown in  FIG. 4 , display  14  may include a substrate layer such as substrate layer  30 . Substrate  30  may be formed from a polymer or other suitable materials. 
     Thin-film transistor circuitry  44  may be formed on substrate  30 . Thin film transistor circuitry  44  may include layers  32 . Layers  32  may include inorganic layers such as inorganic buffer layers, barrier layers (e.g., barrier layers to block moisture and impurities), gate insulator, passivation, interlayer dielectric, and other inorganic dielectric layers. Layers  32  may also include organic dielectric layers such as a polymer planarization layer. Metal layers and semiconductor layers may also be included within layers  32 . For example, semiconductors such as silicon, semiconducting-oxide semiconductors, or other semiconductor materials may be used in forming semiconductor channel regions for thin-film transistors  28 . Metal in layers  32  such as metal traces  74  may be used in forming transistor gate terminals, transistor source-drain terminals, capacitor electrodes, and metal interconnects. 
     As shown in  FIG. 4 , thin-film transistor circuitry  44  may include diode anode structures such as anode  36 . Anode  36  may be formed from a layer of conductive material such as metal on the surface of layers  32  (e.g., on the surface of a planarization layer that covers underlying thin-film transistor structures). Light-emitting diode  26  may be formed within an opening in pixel definition layer  40 . Pixel definition layer  40  may be formed from a patterned photoimageable polymer such as polyimide. 
     In each light-emitting diode, layers of organic material  38  may be interposed between a respective anode  36  and cathode  42 . Anodes  36  may be patterned from a layer of metal (e.g., silver) and/or one or more other conductive layers such as a layer of indium tin oxide or other transparent conductive material. Cathode  42  may be formed from a common conductive layer that is deposited on top of pixel definition layer  40 . Cathode  42  may be formed from a thin metal layer (e.g., a layer of metal such as a magnesium silver layer) and/or indium tin oxide or other transparent conductive material. Cathode  42  is preferably sufficiently transparent to allow light  24  to exit light emitting diode  26 . During operation, light-emitting diode  26  may emit light  24  in on-axis directions such as on-axis direction  24 - 1  (i.e., a direction parallel to surface normal n of anode  36 ) and off-axis directions such as off-axis direction  24 - 2  (i.e., directions that are oriented at non-zero angles A with respect to surface normal n). 
     If desired, the anode of diode  26  may be formed from a blanket conductive layer and the cathode of diode  26  may be formed from a patterned conductive layer. The illustrative configuration of display  14  in which a transparent blanket cathode layer  42  covers diodes that have individually patterned anodes  36  allows light  24  to be emitted from the top of display  14  (i.e., display  14  in the example of  FIG. 4  is a “top emission” organic light-emitting diode display). Display  14  may be implemented using a bottom emission configuration if desired. Layers such as layers  36 ,  38 , and  42  are used in forming organic light-emitting diodes such as diode  26  of  FIG. 4 , so this portion of display  14  is sometimes referred to as an organic light-emitting diode layer (see, e.g., layer  84  of  FIG. 4 ). 
     Metal interconnect structures may be used to interconnect transistors and other components in circuitry  44 . Metal interconnect lines may also be used to route signals to capacitors, to data lines D and gate lines G, to contact pads (e.g., contact pads coupled to gate driver circuitry), and to other circuitry in display  14 . As shown in  FIG. 4 , layers  32  may include one or more layers of patterned metal for forming interconnects such as metal traces  74  (e.g., traces  74  may be used in forming data lines D, gate lines G, power supply lines, clock signal lines, and other signal lines). 
     If desired, display  14  may have a protective outer display layer such as cover glass layer  70 . The outer display layer may be formed from a material such as sapphire, glass, plastic, clear ceramic, or other transparent material. Protective layer  46  may cover cathode  42 . Layer  46 , which may sometimes be referred to as an encapsulation layer may include moisture barrier structures, encapsulant materials such as polymers, adhesive, and/or other materials to help protect thin-film transistor circuitry. 
     Functional layers  68  may be interposed between layer  46  and cover layer  70 . Functional layers  68  may include a touch sensor layer, a circular polarizer layer, and other layers. A circular polarizer layer may help reduce light reflections from reflective structures such as anodes  36 . A touch sensor layer may be formed from an array of capacitive touch sensor electrodes on a flexible polymer substrate. The touch sensor layer may be used to gather touch input from the fingers of a user, from a stylus, or from other external objects. Layers of optically clear adhesive may be used to attach cover glass layer  70  and functional layers  68  to underlying display layers such as layer  46 , thin-film transistor circuitry  44 , and substrate  30 . 
     Organic layer  38  may include an organic emissive layer (e.g., a red emissive layer in red diodes  26  that emits red light, a green emissive layer in green diodes  26  that emits green light, and a blue emissive layer in blue diodes  26  that emits blue light, etc.). The emissive material may be a material such as a phosphorescent material or fluorescent material that emits light during diode operation. The emissive material in layer  38  may be sandwiched between additional diode layers such as hole injection layers, hole transport layers, electron injection layers, and electron transport layers. These layers of material in layer  38  and the structures of cathode layer  42  and anode layer  36  form an optical etalon that can give rise to undesired color shifts in emitted light  24  at off-axis light emission angles. 
     The dependence of the color spectrum of emitted light  24  on the angle of light emission in an illustrative organic light-emitting diode display shown in the graph of  FIG. 5 . In the graph of  FIG. 5 , normalized emitted light intensity NI has been plotted for light-emitting diodes of three colors. Curve  24 R represents an illustrative light emission spectrum for the red light that is emitted from a red organic light-emitting diode at an angle A of 0° with respect to surface normal n (i.e., curve  24 R corresponds to on-axis red light, which is emitted vertically in the orientation of  FIG. 5 ). Emission spectrums for green and blue on-axis light  24  from respective green and blue diodes  26  are given by curves  24 G and  24 B, respectively. At off-axis angles, the emitted light from the red, green, and blue diodes designs shifts towards blue wavelengths, an effect that tends to be most noticeable to human observers at longer wavelengths (e.g., red wavelengths). As shown in  FIG. 5 , the emission spectrum  24 R′ for off-axis red light  24  (i.e., light emitted at non-zero angle A with respect to surface normal n) includes blue-shifted red diode off-axis light BS-R. Off-axis light  24 G′ from the green diodes includes blue-shifted green diode off-axis light BS-G and off-axis light  24 B′ from the blue diodes includes blue-shifted blue diode off-axis light BS-B. 
     If care is not taken, the wavelength shifts represented by light BS-R, BS-G, and BS-B can lead to undesired color variations that adversely affect the quality of displayed images. To compensate for these potential color shifts, display  14  preferably contains color filter structures in the layers of display  14  above cathode  42 . The color filter structures may include colored layers with transmission spectrums that block blue shifted light such as light BS-R for red diodes  26  in display  14 , BS-G for green diodes  26  in display  14 , and BS-B for blue diodes  26  in display  14  while passing light at wavelengths associated with unshifted curves  24 R,  24 G, and  24 B, respectively. By blocking the wavelengths of light associated with off-axis color shifts, desired spectral shapes may be achieved for the red, green, and blue diodes  26  in display  14 . The color filter structures may be formed from one or more evaporated organic layers or colored layers formed using other deposition techniques. 
     Evaporated color filter layers for display  14  may be formed from organic small molecules that are stable at the temperatures encountered during thermal evaporation operations. 
     The color filter layers may serve as a capping layer (see, e.g., protective layer  46  of  FIG. 4 ) and/or may be used in combination with clear (non-colored) capping layer structures. A shadow mask may be used to accurately define the locations of the deposited color filter elements in each evaporated color filter layer. By avoiding misalignment between the evaporated color filter structures using the shadow mask, undesired effects such as color mixing effects can be avoided. 
     An illustrative evaporation tool for depositing color filter layers in display  14  is shown in  FIG. 6 . As shown in  FIG. 6 , evaporation tool  98  includes a heating element such as heater  80  that heats a source of thermally evaporable color filter layer material such as source  82 . When evaporated, the color filter material travels in directions  96  and passes through patterned pixel-shaped openings  90  in shadow mask  86 . Shadow mask  86  may be formed from a thin layer of metal and may therefore sometimes be referred to as a fine metal mask. 
     The color filter material that passes through openings  90  is deposited onto the surface of display layer  92  to form patterned evaporated color filter layer  94 . Display layer  92  may be a cathode layer such as a layer forming cathode  42  or other layer in display  14 . The emissive layers and color filter layers and other patterned layers of diodes  26  may have an S-stripe pixel layout or other suitable layout (i.e., a layout in which pixels of different colors form columns, checkerboards, etc.). Layers such as layer  94  may be formed from materials such as organic small molecules and may be used in forming red, green, blue, orange, color filter layers (which may also serve as capping layers), color filter layers of other colors, clear capping layers, or other deposited layers for display  14 . 
     Evaporation tool  98  may be used in depositing color filter and/or capping layers such as layer  94  and may be used in depositing layers  38  for display  14  (e.g., red emissive layers, green emissive layers, blue emissive layers, hole and electron transport and injection layers for pixels of different colors, etc.). Evaporated layers in display  14  such as illustrative layer  94  of  FIG. 6  may be formed from small molecules (e.g., organic materials) that are thermally stable when evaporated. The materials that form the emissive layers for diodes  26  may contain diketopyrrolopyrrole dyes such as DCM2 (2-methyl-6-[2,3,6,7-tetrahydro-1H,5H-benjo(ij)quinolizine-9-yl)ethenyl]-4H-pyran-4-ylidene-]propan-dinitrile) and iridium complex materials. The materials that form the color filter layers for display  14  may contain diketopyrrolopyrrole dyes such as DCM (4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran)) and DCM2 and pigments such as PR254 and PR256. Other materials that are thermally stable during evaporation may be evaporated onto display  14  using shadow masks such as mask  88  of  FIG. 6  if desired (e.g., clear capping layers that are free of dyes and pigments). 
     The color filter layer can be formed form multiple materials (dye doped in a clear capping layer, multiple dyes evaporated at the same time from multiple dye sources, etc.). 
     Cross-sectional side views of four illustrative configurations for display  14  are shown in  FIGS. 7, 8, 9, and 10 . 
     As shown in the example of  FIG. 7 , display  14  may include a substrate such as substrate  30  onto which layers  32  are formed, as described in connection with  FIG. 4 . Anode  36  (e.g., a silver/indium-tin-oxide layer or other suitable conductive layer) may be formed on layers  32 . There may be a respective anode  36  for each subpixel in display  14  (i.e., each red pixel may have an anode, each green pixel may have an anode, and each blue pixel may have an anode and these anodes may be electrically isolated from each other to allow independent control). 
     Layers  38  may be formed on anode layer  36 . Layers  38  may include hole injection layer  38 - 1  and hole transport layer  38 - 2 . If desired, layer  38 - 3  may include hole transport layer materials for red pixels (red hole transport layer  38 -R) and green pixels (green hole transport layer  38 -G). 
     Emissive layer  38 - 4  may be formed over the hole transport layer. As shown in  FIG. 7 , emissive layer  38 - 4  may include red emissive layer REL for red diodes  26  in red pixels  22 , green emissive layer GEL for green diodes  26  in green pixels  22 , and blue emissive material BEL for blue diodes  26  in blue pixels  22 . Layer  38 - 4  may also include emissive layers of other colors. 
     Electron transport layer  38 - 5  and electron injection layer  38 - 6  may be formed on top of the emissive material. Cathode layer  42  (e.g., a thin transparent magnesium silver cathode or other conductive transparent layer) may be formed on electronic injection layer  38 - 6 . 
     In the illustrative configuration of  FIG. 7 , the portion of display  14  that is associated with red diode  26 R has been covered with evaporated filter layer material  100  to form red color filter RCF. Filter RCF prevents blue-shifted red light BS-R from being emitted from diode  26 R and may serve as a capping layer. Capping layer structures for display  14  (e.g., the capping layer formed by filter RCF in this example) serve environmental protection layers and are also formed with thicknesses appropriate to maximize light output (e.g., by adjusting diode etalon size and thereby tuning the etalon). In a display with diodes of multiple colors, the optimum etalon tuning for each color of diode may be different and the capping layer for each color of diode may, if desired, be different. In some configurations, a common capping layer may be used for multiple diodes (e.g., using an etalon thickness that maximizes blue light output). In the example of  FIG. 7 , green diode  26 G and blue diode  26 B may be covered with capping layer  102  (e.g., a clear capping layer deposited by evaporation). Capping layer  102  may have the same thickness as layer  100  or may have a different thickness to tune the etalons of the green and blue diodes differently than the red diode etalon. As an example, red color filter RCF may be formed from a layer that is about 50-70 nm thick and layer 102 may be 50-70 nm thick. The capping layer material of display  14  may have an index of refraction of about 1.4-2.0 at 630 nm, as an example. 
     In the example of  FIG. 8 , red diode  26 R has been provided with an evaporated red color filter layer RCF, green diode  26 G has been provided with a green color filter layer GCF (e.g., a color filter that passes spectrum  24 G of  FIG. 5  while blocking light at shifted wavelengths such as light BS-G), and blue diode  26 B has been provided with a blue color filter layer BCF (e.g. a color filter that passes spectrum  24 B of  FIG. 5  while blocking light at shifted wavelengths such as light BS-B). 
     The evaporated materials of filters RCF, GCF, and BCF may allow these layers to simultaneously serve as wavelength filters and as a capping layers that provide environmental protection and etalon tuning. The thicknesses of filters RCF, GCF, and BCF may be  50 - 70  nm or other suitable thicknesses and may be the same or different from each other. In an arrangement of the type shown in  FIG. 7 , two shadow masks may be used to form the layers of material on cathode  42  (i.e., one mask may be used to form patterned red color filter layer RCF and one mask may be used to form patterned capping layer  102 ). In an arrangement of the type shown in  FIG. 8 , three shadow masks may be used (i.e., one mask may be used to form patterned red color filter layer RCF, one mask may be used to form patterned green color filter layer GCF, and one mask may be used to form patterned blue color filter layer BCF). Additional capping layer material (e.g., an additional clear capping layer) can be added below and/or above filters RCF, GCF, and BCF, if desired. 
     Display  14  may be covered with a circular polarizer to suppress ambient light reflections from anodes  36  or the circular polarizer may be omitted from display  14  (in which case the optical properties of the etalons and color filters formed from the diode structures of display  14  such as the diode structures of  FIG. 8  serve to suppress ambient light). 
     In the example of  FIG. 9 , red diode  26 R and green diode  26 G have been coated with an overlapping evaporated orange color filter layer OCF. Orange color filter layer OCF passes red light  24 R and green light  24 G. Orange color filter layer OCF blocks light at wavelengths of 540 nm to 600 nm, thereby blocking blue-shifted red light from red diode  26 R and may absorb blue-shifted green light (light BS-G of  FIG. 5 ). Blue diode  26 B has been covered with blue color filter layer BCF that absorbs blue-shifted light BS-B while passing light  24 B of  FIG. 5 . Filter layers OCF and BCF of layer  100  may be formed from evaporated materials that allow these layers to simultaneously serve as wavelength filters and as a capping layer. A first shadow mask may be used when depositing patterned orange color filter layer OCF and a second shadow mask may be used when depositing patterned blue color filter layer BCF. 
     In the example of  FIG. 10 , capping layer  102  has been deposited as a blanket film on cathode  42  without using a shadow mask. The thickness of layer  102  may be, for example, 50-70 nm. Red color filter layer  26 R may be deposited on layer  102  through a shadow mask (e.g., to a thickness of  150 - 190  nm or other suitable thickness for satisfactory operation of the red diode etalon). Because only a single shadow mask is used in forming the color filter structures of display  14  in the illustrative configuration of  FIG. 10 , the mask count for forming display  14  is minimized. 
     If desired, the number of evaporated color filter layers, the placement of these color filter layers relative to the red, green, and blue diodes, the use of capping layer materials, the order in which layers overlap diodes  26 , and the number of shadow masks used for forming these structures can be varied. The illustrative arrangements of  FIGS. 7, 8, 9, and 10  are merely examples. 
     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: 20150922
Publication Date: 20170620
Grant Date: 20170620
Priority Date: 20150428
Inventors: CHEON KWANG OHK
LIU RUI
CHEN CHENG
Assignee: APPLE INC
CPC Classifications: [{"code": "H01L27/3211", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/5253", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L27/322", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L51/5262", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/5265", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/852", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/35", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/38", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K50/844", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/85", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/38", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/35", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/875", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/873", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 57205234