PATENT DOCUMENT

Publication Number: US-11164911-B2
Application Number: US-201816649590-A
Country: US
Kind Code: B2

Title: Displays with white organic light-emitting diodes

Abstract:
A display may have an array of pixels formed from organic light-emitting diodes and thin-film transistor circuitry. The organic light-emitting diodes may be interposed between a substrate (30) and a cover layer (70). The organic light-emitting diodes may be white light-emitting diodes (26) that emit white light that is filtered through a color filter array (76) to produce colored light. The color filter array may be located above or below the array of light-emitting diodes. A microcavity may be formed between the substrate (30) and each light-emitting diode (26). The microcavity may be formed from an anode (36) in the light-emitting diode and first (86) and second layers (78) with different refractive indices. The low-refractive-index layer may be formed from a color filter in the color filter array. Light from the light-emitting diode may resonate within the microcavity beneath each light-emitting diode before exiting the display as colored light.

Claims:
What is claimed is: 
     
       1. An organic light-emitting diode display, comprising:
 a substrate; 
 a cover layer; 
 a white organic light-emitting diode interposed between the substrate and the cover layer; 
 a color filter interposed between the white organic light-emitting diode and the substrate; and 
 a layer interposed between the substrate and the color filter, wherein the layer has a higher refractive index than the color filter. 
 
     
     
       2. The organic light-emitting diode display defined in  claim 1  further comprising a reflective layer interposed between the layer and the substrate. 
     
     
       3. The organic light-emitting diode display defined in  claim 2  wherein the reflective layer comprises metal. 
     
     
       4. The organic light-emitting diode display defined in  claim 3  wherein the layer comprises a material selected from the group consisting of: titanium dioxide and silicon nitride. 
     
     
       5. The organic light-emitting diode display defined in  claim 1  wherein the white organic light-emitting diode comprises an anode, and wherein the anode, the layer, and the color filter form a microcavity that causes light from the light-emitting diode to resonate between the layer and the anode. 
     
     
       6. The organic light-emitting diode display defined in  claim 1  wherein the white organic light-emitting diode comprises an emissive layer that mixes three primary colors to form white light. 
     
     
       7. The organic light-emitting diode display defined in  claim 1  wherein the white organic light-emitting diode comprises multiple emissive layers that each emit light of an associated color and wherein the light from the multiple emissive layers combines to form white light. 
     
     
       8. The organic light-emitting diode display defined in  claim 1  wherein the white organic light-emitting diode comprises a blue emissive layer that emits blue light and a phosphor that converts some of the blue light to yellow light and wherein the blue light and the yellow light combine to form white light. 
     
     
       9. The organic light-emitting diode display defined in  claim 1  wherein the white organic light-emitting diode comprises at least two light-emitting diode units stacked in tandem and coupled in series. 
     
     
       10. An organic light-emitting diode pixel, comprising:
 a substrate; 
 a white organic light-emitting diode on the substrate, wherein the white organic light-emitting diode comprises an anode; 
 a cover layer formed over the white organic light-emitting diode; and 
 a first layer having a first refractive index and a second layer having a second refractive index that is higher than the first refractive index, wherein the first and second layers are interposed between the white organic light-emitting diode and the substrate, wherein the anode, the first layer, and the second layer form a microcavity, wherein light from the white organic light-emitting diode resonates within the microcavity, and wherein the first layer comprises a color filter layer. 
 
     
     
       11. The organic light-emitting diode pixel defined in  claim 10  further comprising a metal reflector interposed between the second layer and the substrate. 
     
     
       12. The organic light-emitting diode pixel defined in  claim 10  further comprising a capping layer interposed between the cover layer and the white organic light-emitting diode. 
     
     
       13. A display, comprising:
 a substrate; 
 an array of organic light-emitting diodes on the substrate that emit white light; 
 a color filter array that filters the white light to produce colored light; 
 a cover layer over the array of organic light-emitting diodes, wherein the colored light passes through the cover layer; and 
 a microcavity between each organic light-emitting diode and the substrate, wherein at least some of the white light resonates in the microcavity before passing through the cover layer as colored light, wherein the microcavity is formed from first and second layers having different indices of refraction, and wherein the first layer of the microcavity is formed from a portion of the color filter array. 
 
     
     
       14. The display defined in  claim 13  further comprising a metal reflector interposed between the microcavity and the substrate. 
     
     
       15. The display defined in  claim 14  further comprising a capping layer interposed between the array of organic light-emitting diodes and the cover layer.

Description:
This application claims priority to U.S. provisional patent application No. 62/564,732, filed on Sep. 28, 2017, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices with displays and, more particularly, to electronic devices with 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 subpixels of different colors to provide the display with the ability to display color images. The organic light-emitting diodes are controlled by thin-film transistor circuitry. 
     It can be challenging to achieve high resolution displays with organic light-emitting diode pixels. Displays sometimes use white organic light-emitting diodes with red, green, and blue color filters to achieve higher resolution. If care is not taken, however, displays with white organic light-emitting diodes may not exhibit desired levels of optical performance. 
     It would therefore be desirable to be able to provide 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. The display may include thin-film transistor circuitry that controls the organic light-emitting diode pixels. 
     The organic light-emitting diodes may be interposed between a substrate and a cover layer. The organic light-emitting diodes may be white light-emitting diodes that emit white light that is filtered through a color filter array to produce colored light. The color filter array may be located above or below the array of light-emitting diodes. 
     A microcavity may be formed between the substrate and each light-emitting diode. The microcavity may be formed from an anode of the light-emitting diode and first and second layers with different refractive indices. In one illustrative arrangement, the color filter array is located below the light-emitting diode array and is used as the low-refractive-index layer in the microcavity. Light from the light-emitting diode may resonate within the microcavity beneath each light-emitting diode, passing through the color filter multiple times before exiting the display as colored light. 
     In another suitable arrangement, the color filter array is located above the light-emitting diode array and an oxide layer is used as the low-refractive-index layer in the microcavity beneath each light-emitting diode. 
     The white light-emitting diodes may be formed from an emissive layer that mixes primary or complementary colors to produce white light, may be formed from multiple emissive layers that mix primary or complementary colors to produce white light, may be formed from an emissive layer and a phosphor that together produce white light, or may be formed from multiple light-emitting diode units that are stacked in tandem and connected in series to produce white light. 
    
    
     
       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 atop 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 cross-sectional side view of an illustrative white organic light-emitting diode having a single emissive layer in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of an illustrative white organic light-emitting diode having two emissive layers in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of an illustrative white organic light-emitting diode having three emissive layers in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of an illustrative white organic light-emitting diode having an emission layer and a phosphor in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an illustrative white organic light-emitting diode having first and second stacked light-emitting diode units coupled in series in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of an illustrative white organic light-emitting diode having first, second, and third stacked light-emitting diode units coupled in series in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of an illustrative pixel having a white organic light-emitting diode with a bottom color filter that forms part of a microcavity in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of an illustrative pixel having a white organic light-emitting diode with a top color filter and a second microcavity 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  80  under the control of a pixel control circuit formed from transistor circuitry such as thin-film transistors  58  and thin-film capacitors). Transistors  58  may be polysilicon thin-film transistors, semiconducting-oxide thin-film transistors such as indium gallium zinc oxide transistors, or transistors formed from other semiconductors. 
     Display  14  may include pixels of different colors (sometimes referred to as subpixels). For example, display  14  may include red, green, and blue pixels or may include pixels of other colors. In one illustrative arrangement, color pixels  22  in display  14  may be formed using light-emitting diodes that emit light of the desired color. For example, red, green, and blue pixels may be formed by depositing red, green, and blue organic emissive material side-by-side on a substrate. With this type of arrangement, each light-emitting diode  26  emits colored light such as red light, blue light, or green light. 
     In another suitable configuration, color pixels  22  in display  14  may be formed using white organic light-emitting diodes that emit white light that is filtered through color filters such as color filters  76  to produce colored light. Color filters  76  may be formed from colored polymers that are deposited and patterned to form a color filter array. For example, red pixels  22  may be formed from white organic light-emitting diodes that are paired with red color filters  76 R, green pixels  22  may be formed from white organic light-emitting diodes that are paired with green color filters  76 G, and blue pixels  22  may be formed from white organic light-emitting diodes that are paired with blue color filters  76 B. Display  14  may include pixels of other colors, if desired. Arrangements that pair white organic light-emitting diodes with red, green, and blue color filters are sometimes described herein as an example. 
     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 polymer, glass, sapphire, a semiconductor material such as silicon, 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  58  ( FIG. 3 ). 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 , light-emitting diode  26  may be formed within an opening in pixel definition layer  60 . Pixel definition layer  60  may be formed from a patterned photoimageable polymer such as polyimide and/or may be formed from one or more inorganic layers such as silicon nitride, silicon dioxide, or other suitable materials. 
     Each light-emitting diode  26  may include light-emitting diode layers  38  interposed between a respective anode  36  and cathode  42 . Anodes  36  may be patterned from a layer of metal (e.g., silver, aluminum, or other suitable metal) and/or one or more other conductive layers such as a layer of indium tin oxide, molybdenum oxide (MoOx), titanium nitride (TiNx), or other transparent conductive material. In one illustrative arrangement, anode  36  may be formed from one or more layers of non-conducting materials (e.g., silicon oxide (SiOx), silicon nitride (SiNx), or polymers) with a top layer of conductive transparent material (e.g., indium tin oxide, indium gallium zinc oxide, other transparent conductive oxides, etc.) and a bottom layer of reflective metal (e.g., silver, aluminum, a compound of reflective metals, etc.). Cathode  42  may be formed from a common conductive layer that is deposited on top of pixel definition layer  60 . 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  80  to exit light-emitting diode  26 . 
     The example of  FIG. 4  in which the anode of diode  26  is formed from a patterned conductive layer and the cathode of diode  26  is formed from a blanket conductive layer is merely illustrative. If desired, anode  36  may be formed from a blanket conductive layer and cathode  42  may be formed from a blanket conductive layer. 
     The example of  FIG. 4  in which diode  26  is a “top emission” organic light-emitting diode is merely illustrative. Display  14  may be implemented using bottom emission organic light-emitting diodes, if desired. 
     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 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 a thin film 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  and cathode  42 . 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 layer  70  (e.g., a layer of glass, sapphire, polymer, or other suitable material) and functional layers  68  to underlying display layers such as layer  46 , thin-film transistor circuitry  44 , and substrate  30 . 
     Light-emitting diode layers  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, a blue emissive layer in blue diodes  26  that emits blue light, a combination of emissive materials that emit white 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 light-emitting diode layers  38  may be sandwiched between additional diode layers such as hole injection layers, hole transport layers, electron injection layers, and electron transport layers. 
     As discussed in connection with  FIG. 3 , pixels  22  may include white organic light-emitting diodes  26  that emit white light that is filtered through a color filter to produce colored light. Color filters  76  ( FIG. 3 ) may be located below light-emitting diodes  26  (e.g., between substrate  30  and diodes  26 ), or may be located above light-emitting diodes  26  (e.g., between cover layer  70  and diodes  26 ). 
     White emission from organic light-emitting diodes  26  of  FIG. 4  may be achieved using one or more emissive layers and/or one or more phosphor layers to mix three primary colors (e.g., red, green, and blue) or two complementary colors (e.g., yellow/orange and blue).  FIGS. 5-10  illustrate various examples of structures that may be used to form white light-emitting diodes  26  of display  14 . 
     As shown in  FIG. 5 , white light-emitting diode  26  may include light-emitting diode layers  38  sandwiched between anode  36  and cathode  42 . Light-emitting diode layers  38  include electron transport layer  48 , emissive layer  50 , hole transport layer  52 , and hole injection layer  54 . 
     In the example of  FIG. 5 , white light-emitting diode  26  includes a single emissive layer  50  that mixes emissive materials of different colors to produce white light  80 W. For example, emissive layer  50  may be a mix of primary color emissive materials that combine to form white light  80 W such as red, green, and blue emissive materials, or emissive layer  50  may be a mix of complementary color emissive materials that combine to form white light  80 W such as blue and yellow (or orange) emissive materials. 
     In the example of  FIG. 6 , emissive layer  50  of white light-emitting diode  26  includes first emissive layer  50 - 1  and second emissive layer  50 - 2 . Emissive layer  50 - 1  and emissive layer  50 - 2  may be emissive materials of complementary colors that combine to form white light  80 W (e.g., layer  50 - 1  may be blue emissive material and layer  50 - 2  may be yellow or orange emissive material or vice versa), or one of emissive layers  50 - 1  and emissive layer  50 - 2  may include a mix of two primary color emissive materials and the other emissive layer may include a third primary color emissive material that combine to form white light  80 W (e.g., layer  50 - 1  may be blue emissive material and layer  50 - 2  may be a mix of red and green emissive materials, or vice versa). 
     In the example of  FIG. 6 , emissive layer  50  of white light-emitting diode  26  includes first emissive layer  50 - 1 , second emissive layer  50 - 2 , and third emissive layer  50 - 3 . Emissive layers  50 - 1 ,  50 - 2 , and  50 - 2  may be emissive materials of primary colors that combine to form white light  80 W. For example, layer  50 - 1  may be blue emissive material, layer  50 - 2  may be green emissive material, and layer  50 - 3  may be red emissive material. This ordering of layers is merely illustrative. In general, red, green, and blue emissive layers in layer  50  of diode  26  may be stacked in any suitable order. 
     In the example of  FIG. 8 , white light  80 W is formed by pairing emissive layer  50  with a phosphor layer such as phosphor layer  56 . Phosphor layer  56  may be formed on substrate  30  (e.g., phosphor  56  may be formed below substrate  30  as shown in the example of  FIG. 8 , may be formed above substrate  30 , may be formed above emissive layer  50 , or may be formed in other suitable locations in diode  26 ). Emissive layer  50  and phosphor layer  56  may produce light of complementary colors that combine to form white light  80 W. For example, emissive layer  50  may emit blue light and phosphor  56  may be a yellow phosphor. Some of the blue photons from blue emissive layer  50  will be emitted from diode  26  unaltered to form blue light. Other blue photons from blue emissive layer  50  will be converted by yellow phosphor layer  56  into yellow light. The blue light and yellow light may combine to form white light  80 W. The use of blue emissive material and yellow phosphor is merely illustrative. If desired, emissive layer  50  may emit ultraviolet light and/or phosphor layer  56  may emit green and/or red light. 
     In the example of  FIG. 9 , white light  80 W is formed from a pair of light-emitting diode units  38 - 1  and  38 - 2  stacked in tandem. Light-emitting diode unit  38 - 1  includes electron transport layer  48 - 1 , emissive layer  50 - 1 , hole transport layer  52 - 1 , and hole injection layer  54 - 1 . Light-emitting diode unit  38 - 2  includes electron transport layer  48 - 2 , emissive layer  50 - 2 , hole transport layer  52 - 2 , and hole injection layer  54 - 2 . Light-emitting diode units  38 - 1  and  38 - 2  may emit light of complementary colors (e.g., blue and yellow or other suitable complementary colors) that combine to form white light  80 W. For example, emissive layer  50 - 1  may emit blue light and emissive layer  50 - 2  may emit yellow light, or vice versa. 
     Light-emitting diode units  38 - 1  and  38 - 2  may be electrically connected in series. A charge-generating interconnect layer such as charge generating layer  62  may be located between units  38 - 1  and  38 - 2  and may be used to couple unit  38 - 1  to unit  38 - 2 . Charge generating layer  62  may, for example, be formed from an n-type layer (sometimes referred to as an electron injecting conductive layer) and a p-type layer (sometimes referred to as a hole injecting conductive layer). 
     In the example of  FIG. 10 , white light  80 W is formed from three light-emitting diode units  38 - 1 ,  38 - 2 , and  38 - 3  stacked in tandem. Light-emitting diode unit  38 - 1  includes electron transport layer  48 - 1 , emissive layer  50 - 1 , hole transport layer  52 - 1 , and hole injection layer  54 - 1 . Light-emitting diode unit  38 - 2  includes electron transport layer  48 - 2 , emissive layer  50 - 2 , hole transport layer  52 - 2 , and hole injection layer  54 - 2 . Light-emitting diode unit  38 - 3  includes electron transport layer  48 - 3 , emissive layer  50 - 3 , hole transport layer  52 - 3 , and hole injection layer  54 - 3 . Light-emitting diode units  38 - 1 ,  38 - 2 , and  38 - 3  may emit light of primary colors (e.g., red, green, and blue light) that combine to form white light  80 W. For example, emissive layer  50 - 1  may emit blue light, emissive layer  50 - 2  may emit green light, and emissive layer  50 - 3  may emit red light. This ordering of units is merely illustrative. In general, red, green, and blue light-emitting units  38 - 1 ,  38 - 2 , and  38 - 3  may be stacked in any suitable order. 
     Light-emitting diode units  38 - 1 ,  38 - 2 , and  38 - 3  may be electrically connected in series. A first charge-generating interconnect layer such as charge generating layer  62 - 1  may be located between units  38 - 1  and  38 - 2  and may be used to couple unit  38 - 1  to unit  38 - 2 . A second charge-generating interconnect layer such as charge generating layer  62 - 2  may be located between units  38 - 2  and  38 - 3  and may be used to couple unit  38 - 2  to unit  38 - 3 . Charge generating layers  62 - 1  and  62 - 2  may each be formed from an n-type layer (sometimes referred to as an electron injecting conductive layer) and a p-type layer (sometimes referred to as a hole injecting conductive layer). 
     In displays that form color pixels by filtering white light through color filters, care must be taken to avoid light source efficiency loss, color filter alignment errors, and color shifts at wide viewing angles.  FIGS. 11 and 12  show illustrative arrangements for forming color pixels  22  using white light-emitting diodes and color filters with increased optical efficiency, reduced alignment errors, and minimal color shifts at wide viewing angles. 
     In the example of  FIG. 11 , pixel  22  of display  14  includes white light-emitting diode  26  and a color filter such as color filter  76 . White light-emitting diode  26  may be formed using one of the arrangements of  FIGS. 5-10  or may be formed using other light-emitting diode structures. Color filter  76  may be a red color filter, a green color filter, a blue color filter, or other suitable color filter. Color filter  76  may be formed on a high-refractive-index material such as layer  78 . Layer  78  may be formed from titanium dioxide, silicon nitride, silicon oxide, or other suitable inorganic material having a relatively high refractive index. A reflective layer such as reflective layer  84  may be formed on substrate  30  below light-emitting diode  26  to reflect light upwards and out of display  14 . 
     A capping layer such as capping layer  64  may be formed on cathode  42 . Capping layer  64  may be an organic layer that helps increase transmittance through cathode  42 . Barrier layers  92  may include organic layers such as organic layer  72  (e.g., manganese or other suitable organic material) and inorganic layers such as inorganic layers  66  and  74  (e.g., silicon nitride, silicon oxide, or other suitable inorganic material). Additional layers such as the layers described in connection with  FIG. 4  may be used in display  14 . For example, layer  102  may include protective layer  46  and/or functional layers  68  ( FIG. 4 ). Cover layer  70  may cover organic light-emitting diodes  26 . 
     Reflective materials such as metal and reflective interfaces (e.g., interfaces between a high-refractive-index material and a low-refractive-index material) may cause light to resonate within pixel  22 . For example, electrodes  42  and  36  may be at least partially reflective and may exhibit similar effects as a micro-resonator with parallel mirrors, sometimes referred to as a microcavity (e.g., a Fabry Pérot interferometer). The spectral emission of pixel  22  may depend on the resonator properties of the microcavity (or multiple microcavities) within pixel  22 . Optical efficiency of the pixel may increase when constructive interference occurs between the incident light and the reflected light in the microcavity. Microcavity effects can be optimized by tuning the thicknesses of the layers in pixel  22  and/or by selecting certain materials to achieve the desired resonant effect (e.g., selecting materials with different indices of refraction, different reflectivity levels, etc.). 
     Pixel  22  may include one or more microcavities that increase optical efficiency of the pixel. A first microcavity may be formed between anode  36  and cathode  42  (as illustrated by resonating light  94 ), a second microcavity may be formed between barrier layers  92  (as illustrated by resonating light  96 ), and a third microcavity may be formed between anode  36  and high-refractive-index layer  78  (as illustrated by light  98 ). These microcavities may be tuned to optimize optical efficiency of pixel  22 . 
     During operation, white light from diode  26  resonates in the microcavities within pixel  22  and is filtered by color filter  76  to produce colored light  80 C. The microcavity formed from anode  36 , color filter layer  76 , and high-refractive index layer  78  may serve multiple purposes. First, the difference in refractive index between color filter layer  76  (e.g., a low-refractive-index material such as polymer) and high-refractive-index layer  78  causes light  98  to resonate within layers  76  and  78 , leading to constructive interference and therefore increased optical efficiency and better viewing angle performance. The difference in refractive index between layers  78  and  76  may be 0.4, 0.5, 0.6, 0.8, 1, greater than 1, or less than 1. Second, this microcavity effect means that light  98  passes through color filter  76  multiple times before it exits pixel  22  as colored light  80 C. Because light  98  passes through filter  76  multiple times, color filter  76  may be relatively thin. Thin color filter layers may in turn reduce unnecessary absorption in pixel  22 . 
     Additionally, color filter  76  of  FIG. 11  is formed below light-emitting diode  26  and may therefore allow for greater flexibility in the types of deposition methods that are used to deposit color filter material  76  on substrate  30 . For example, layers  88  may be formed using thin-film-transistor array processes and layers  90  may be formed from organic light-emitting diode and thin-film encapsulation processes. Because layers  88  are formed on substrate  30  prior to organic light-emitting diode layers  38 , photolithographic techniques, fine metal mask techniques, or other techniques may be used to deposit color filters (e.g., red, green, and blue color filters) on substrate  30  without the risk of damaging organic light-emitting diode layers  38 . 
     This is, however, merely illustrative. If desired, color filter layer  76  may be formed above light-emitting diode  26 . An example of this type of arrangement is illustrated in  FIG. 12 . 
     As shown in  FIG. 12 , pixel  22  of display  14  includes white light-emitting diode  26  and a color filter such as color filter  76 . White light-emitting diode  26  may be formed using one of the arrangements of  FIGS. 5-10  or may be formed using other light-emitting diode structures. Color filter  76  may be a red color filter, a green color filter, a blue color filter, or other suitable color filter. Color filter  76  may be formed on barrier layers  92 . A reflective layer such as reflective layer  84  may be formed on substrate  30  below light-emitting diode  26  to reflect light upwards and out of display  14 . 
     Additional layers such as the layers described in connection with  FIG. 4  may be used in display  14 . For example, layer  102  may include protective layer  46  and/or functional layers  68  ( FIG. 4 ). Cover layer  70  may cover organic light-emitting diodes  26 . 
     A capping layer such as capping layer  64  may be formed on cathode  42 . Capping layer  64  may be an organic layer that helps increase transmittance through cathode  42 . Barrier layers  92  may include organic layers such as organic layer  72  (e.g., manganese or other suitable organic material) and inorganic layers such as inorganic layers  66  and  74  (e.g., silicon nitride, silicon oxide, or other suitable inorganic material). 
     Pixel  22  may include one or more microcavities that increase optical efficiency of the pixel. A first microcavity may be formed between anode  36  and cathode  42  (as illustrated by resonating light  94 ), a second microcavity may be formed between barrier layers  92  (as illustrated by resonating light  96 ), and a third microcavity may be formed between anode  36  and high-refractive-index layer  78  (as illustrated by light  98 ). Low-refractive-index layer  86  may be formed from an inorganic layer (e.g., an oxide material or other inorganic material) or an organic layer (e.g., a polymer material or other organic material). High-refractive-index layer  78  may be formed from titanium dioxide, silicon nitride, silicon oxide, or other suitable inorganic material having a relatively high refractive index. The difference in refractive index between layers  78  and  86  may be 0.4, 0.5, 0.6, 0.8, 1, greater than 1, or less than 1. The microcavities in pixel  22  may be tuned to optimize optical efficiency of pixel  22 . 
     During operation, white light from diode  26  resonates in the microcavities within pixel  22  and is filtered by color filter  76  to produce colored light  80 C. The difference in refractive index between low-refractive-index layer  86  and high-refractive-index layer  78  causes light  98  to resonate within layers  86  and  78 , leading to constructive interference and therefore increased optical efficiency and better viewing angle performance. 
     In accordance with an embodiment, an organic light-emitting diode display is provided that includes a substrate, a cover layer, a white organic light-emitting diode interposed between the substrate and the cover layer, and a color filter interposed between the white organic light-emitting diode and the substrate. 
     In accordance with another embodiment, the organic light-emitting diode display includes a high-refractive-index layer interposed between the substrate and the color filter. 
     In accordance with another embodiment, the organic light-emitting diode display includes a reflective layer interposed between the high-refractive-index layer and the substrate. 
     In accordance with another embodiment, the reflective layer includes metal. 
     In accordance with another embodiment, the high-refractive-index layer includes a material selected from the group consisting of titanium dioxide and silicon nitride. 
     In accordance with another embodiment, the white organic light-emitting diode includes an anode, and the anode, the high-refractive-index layer, and the color filter form a microcavity that causes light from the light-emitting diode to resonate between the high-refractive-index layer and the anode. 
     In accordance with another embodiment, the white organic light-emitting diode includes an emissive layer that mixes three primary colors to form white light. 
     In accordance with another embodiment, the white organic light-emitting diode includes multiple emissive layers that each emit light of an associated color and the light from the multiple emissive layers combines to form white light. 
     In accordance with another embodiment, the white organic light-emitting diode includes a blue emissive layer that emits blue light and a phosphor that converts some of the blue light to yellow light and the blue light and the yellow light combine to form white light. 
     In accordance with another embodiment, the white organic light-emitting diode includes at least two light-emitting diode units stacked in tandem and coupled in series. 
     In accordance with an embodiment, an organic light-emitting diode pixel is provided that includes a substrate, a white organic light-emitting diode on the substrate, the white organic light-emitting diode includes an anode, a cover layer formed over the white organic light-emitting diode, and a first layer having a first refractive index and a second layer having a second refractive index that is higher than the first refractive index, the first and second layers are interposed between the white organic light-emitting diode and the substrate, the anode, the first layer, and the second layer form a microcavity, and light from the white organic light-emitting diode resonates within the microcavity. 
     In accordance with another embodiment, the organic light-emitting diode pixel includes a color filter interposed between the cover layer and the white organic light-emitting diode. 
     In accordance with another embodiment, the first layer includes a color filter layer. 
     In accordance with another embodiment, the organic light-emitting diode pixel includes a metal reflector interposed between the second layer and the substrate. 
     In accordance with another embodiment, the organic light-emitting diode pixel includes a capping layer interposed between the cover layer and the white organic light-emitting diode. 
     In accordance with an embodiment, a display is provided that includes a substrate, an array of organic light-emitting diodes on the substrate that emit white light, a color filter array that filters the white light to produce colored light, a cover layer over the array of organic light-emitting diodes, the colored light passes through the cover layer; and a microcavity between each organic light-emitting diode and the substrate, at least some of the white light resonates in the microcavity before passing through the cover layer as colored light. 
     In accordance with another embodiment, the microcavity is formed from first and second layers having different indices of refraction. 
     In accordance with another embodiment, the first layer of the microcavity is formed from a portion of the color filter array. 
     In accordance with another embodiment, the display includes a metal reflector interposed between the microcavity and the substrate. 
     In accordance with another embodiment, the display includes a capping layer interposed between the array of organic light-emitting diodes and the cover layer. 
     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: 20180924
Publication Date: 20211102
Grant Date: 20211102
Priority Date: 20170928
Inventors: LU, Chun-yang
LIU, RUI
TSAI, LUN
Assignee: APPLE INC
CPC Classifications: [{"code": "H01L51/5265", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2251/303", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L27/322", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L51/5271", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/852", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/38", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K2102/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/856", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/38", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/878", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/876", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 63862203