PATENT DOCUMENT

Publication Number: US-10658441-B2
Application Number: US-201816114039-A
Country: US
Kind Code: B2

Title: Organic light-emitting diode displays with reflectors

Abstract:
A display may have an array of pixels formed from organic light-emitting diodes and thin-film transistor circuitry. Each pixel may include organic layers interposed between an anode and a cathode. The organic layers may emit out-coupled light that escapes the display and waveguided light that is waveguided within the organic layers. A reflector may be placed at the edge of the organic layers to reflect the waveguided light out of the display. The reflector may be located within a pixel definition layer and may be formed from metal or may be formed from one or more interfaces between high-refractive-index material and low-refractive-index material. The reflector may be formed from an extended portion of the pixel anode. The reflector may be formed from light-reflecting particles that are suspended in the pixel definition layer.

Claims:
What is claimed is: 
     
       1. An organic light-emitting diode display, comprising:
 a substrate having an upper surface; 
 first and second light-emitting diodes on the substrate each comprising organic layers interposed between a reflective electrode and a transparent electrode; 
 a pixel definition layer between the first and second light-emitting diodes; and 
 a reflector embedded within the pixel definition layer, wherein the reflector is separate from the reflective electrode and has a surface that reflects light from the organic layers out of the display through the transparent electrode, and wherein the surface is angled with respect to the upper surface of the substrate. 
 
     
     
       2. The organic light-emitting diode display defined in  claim 1  wherein the reflective electrode and the transparent electrode comprise an anode and a cathode, respectively. 
     
     
       3. The organic light-emitting diode display defined in  claim 1  wherein the reflector comprises metal. 
     
     
       4. The organic light-emitting diode display defined in  claim 1  wherein the reflector surrounds the first light-emitting diode. 
     
     
       5. The organic light-emitting diode display defined in  claim 4  further comprising an additional reflector in the pixel definition layer. 
     
     
       6. The organic light-emitting diode display defined in  claim 5  wherein the additional reflector surrounds the second light-emitting diode. 
     
     
       7. The organic light-emitting diode display defined in  claim 1  wherein the reflector comprises light-reflective particles suspended in the pixel definition layer. 
     
     
       8. The organic light-emitting diode display defined in  claim 7  further comprising a light-blocking layer in the pixel definition layer, wherein a first group of the light-reflective particles are located on a first side of the light-blocking layer and are configured to reflect light emitted from the first light-emitting diode out of the display, and wherein a second group of the light-reflective particles are located on a second side of the light-blocking layer and are configured to reflect light emitted from the second light-emitting diode out of the display. 
     
     
       9. The organic light-emitting diode display defined in  claim 1  wherein the pixel definition layer has a refractive index below 1.6. 
     
     
       10. A display, comprising:
 a substrate having an upper surface; 
 a pixel definition layer having an array of openings; 
 an array of organic light-emitting diodes in the openings, wherein each of the organic light-emitting diodes comprises a transparent electrode; and 
 a reflector surrounding each organic light-emitting diode in the display, wherein the reflector is located within the pixel definition layer and has a surface that reflects light out of the display through the transparent electrode, wherein the surface is angled with respect to the upper surface of the substrate. 
 
     
     
       11. The display defined in  claim 10  wherein the reflector comprises light-reflective particles. 
     
     
       12. The display defined in  claim 10  wherein each organic light-emitting diode has an anode, wherein the anode has a first portion that is parallel to the substrate and a second portion that is angled relative to the substrate, and wherein the second portion forms the reflector. 
     
     
       13. The display defined in  claim 10  wherein the transparent electrode comprises a cathode, wherein each organic light-emitting diode has organic layers interposed between an anode and the cathode, and wherein the pixel definition layer has a refractive index that is lower than a refractive index of the organic layers. 
     
     
       14. An organic light-emitting diode pixel, comprising:
 a cathode; 
 an anode having an upper surface; 
 organic layers between the cathode and the anode, wherein the organic layers emit out-coupled light that escapes the organic light-emitting diode pixel and waveguided light that is waveguided within the organic layers; 
 a reflector at the edge of the organic layers having a surface that reflects the waveguided light out of the organic light-emitting diode pixel, wherein the surface is angled with respect to the anode; and 
 a pixel definition layer surrounding the organic light-emitting diode, wherein the reflector is located within the pixel definition layer and is separated from the anode by the pixel definition layer. 
 
     
     
       15. The organic light-emitting diode pixel defined in  claim 14 , wherein the reflector comprises metal. 
     
     
       16. The organic light-emitting diode pixel defined in  claim 14  wherein the reflector comprises light-reflecting particles suspended in the pixel definition layer, wherein the pixel definition layer has an opaque portion, and wherein the light-reflecting particles are interposed between the opaque portion and the organic layers.

Description:
This application claims the benefit of provisional patent application No. 62/551,140, filed Aug. 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 efficiency from an organic light-emitting diode display without sacrificing off-axis viewing quality. Typically, higher on-axis efficiency results in worse off-axis color variation. Off-axis color variation can be reduced, but usually this is at the expense of on-axis efficiency. 
     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. 
     Each organic light-emitting diode may have an anode, a cathode, and organic layers between the anode and cathode. The organic layers may emit out-coupled light that escapes the display and waveguided light that is waveguided within the organic layers. A reflector may be placed at the edge of the organic layers to reflect the waveguided light out of the display. The reflector may completely or partially surround each organic light-emitting diode in the display. 
     The reflector may be located within a pixel definition layer or may replace a pixel definition layer in the display. The reflector may be formed from metal or may be formed from one or more interfaces between high-refractive-index material and low-refractive-index material. The reflector may be formed from an extended portion of the pixel anode. The reflector may be formed from light-reflecting particles that are suspended in the pixel definition layer. An opaque portion of the pixel definition layer may be used to prevent color mixing between adjacent pixels. 
     By reflecting the waveguided light out of the organic layers, the reflector may help increase the overall extraction efficiency of the display. Additionally, the reflector may help mitigate cavity effects at wide viewing angles by increasing off-axis efficiency and reducing off-axis color variation. 
    
    
     
       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 cross-sectional side view of a portion of an illustrative organic light-emitting diode subpixel having a reflector in accordance with an embodiment. 
         FIG. 6  is a top view of illustrative subpixels having reflectors that surround the organic layers of the subpixels in accordance with an embodiment. 
         FIG. 7  is a graph showing how recycling the waveguide mode light of an organic light-emitting diode subpixel increases efficiency at wide viewing angles in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of a portion of an illustrative display including first and second angled reflectors between first and second light-emitting diodes in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of a portion of an illustrative display including an angled reflector between first and second light-emitting diodes in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of a portion of an illustrative display including first and second reflectors formed from angled anodes between first and second light-emitting diodes in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of a portion of an illustrative display including light-scattering particles between first and second light-emitting diodes in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of a portion of an illustrative display including light-scattering particles on opposing sides of a light-blocking material between first and second light-emitting diodes in accordance with an embodiment. 
         FIG. 13  is a cross-sectional side view of a portion of an illustrative display including low-refractive-index material between first and second light-emitting diodes in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of a portion of an illustrative display including reflective coatings within a pixel definition layer between first and second light-emitting diodes in accordance with an embodiment. 
         FIG. 15  is a cross-sectional side view of a portion of an illustrative display including reflective coatings on a pixel definition layer between first and second light-emitting diodes 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. 
     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 , 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  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. 
     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, 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. 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 . 
     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, etc.) and a bottom layer of reflective metal (e.g., silver, aluminum, a compound of reflective metals, etc.). 
     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 configuration of display  14  in which a transparent blanket cathode layer  42  covers diodes that have individually patterned anodes  36  allows light  80  to be emitted from the top of display  14  (i.e., the example of  FIG. 4  in which display  14  is a “top emission” organic light-emitting diode display) is also merely illustrative. 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  130  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 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 . 
     Organic 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 red, green, and blue 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 layer  38  may be sandwiched between additional diode layers such as hole injection layers, hole transport layers, electron injection layers, and electron transport layers. 
     During operation, holes and electrons are injected into organic layers  38  from anode  36  and cathode  42 , respectively. When an electron meets a hole, an electron-hole pair is formed and photons are released. The photons generated in organic layers  38  may be emitted at different angles. Some of the light generated in organic layers  38  such as light  80  will be emitted parallel to (or within a given angle of) the z-axis of  FIG. 4  and will escape display  14 . This type of light is sometimes referred to as “air mode” light or “out-coupled mode” light. Other light generated in organic layers  38  such as light  80 ′ may be emitted at a non-zero angle relative to the z-axis of  FIG. 4  and may be reflected when it strikes an interface between a low-refractive-index layer and a high-refractive-index layer at a certain angle. Light that bounces back and forth within the organic layers of an organic light-emitting diode is sometimes referred to as “waveguide mode” light because the light is waveguided within the organic layers. 
     If care is not taken, waveguide mode light may become trapped and absorbed within the light-emitting diode device and may be unable to escape the display, thereby sacrificing light extraction efficiency (i.e., the ratio of photons generated in a light-emitting diode to photons escaping the display). 
     To increase the light extraction efficiency of display  14 , reflective structures may be used to help extract the waveguide mode light from display  14 .  FIG. 5  is a cross-sectional side view of a portion of display  14  illustrating how a reflective structure may be used to help extract waveguide mode light from display  14 . As shown in  FIG. 5 , light-emitting diode  26  may include organic layers  38  interposed between cathode  42  and anode  36 . Light-emitting diode  26  may emit light in different directions. Light  80  that is emitted within a given angle of the z-axis is extracted from display  14  as air mode light. Light  80 ′ that is emitted at wider angles, however, may be reflected at interfaces between low-refractive-index materials and a high-refractive-index materials and may be guided within device  26  via total internal reflection. To help extract waveguide mode light  80 ′, a reflector such as reflector  72  may be placed at one or more edges of organic layers  38 . Reflector  72  may have an angled surface relative to the z-axis (i.e., angled relative to the surface normal of substrate  30  of  FIG. 4 ) such that waveguide mode light  80 ′ is directed out of display  14  towards viewer  82 . Reflector  72  may, for example, be angled between 25 and 35 degrees from the z-axis, between 20 degrees and 45 degrees from the z-axis, between 0 and 90 degrees from the z-axis, about 30 degrees from the z-axis, less than 30 degrees from the z-axis, or more than 30 degrees from the z-axis. 
     Reflector  72  may be formed from metal that has been deposited and patterned, sheet metal (e.g., stamped sheet metal), metallized polymer film, a thin-film metal on a plastic carrier, a dielectric thin-film stack that forms a dielectric mirror (a thin-film interference mirror) on a polymer film or molded plastic carrier, an interface between a high-refractive-index material and a low-refractive index material, a white reflective film (e.g., a glossy white polymer sheet formed from a white ink layer or other white layer on a polymer carrier covered with a glossy coating such as a glossy polymer coating), or other suitable reflector structure. Reflector  72  may have a rectangular ring-shaped outline (e.g., a rectangular footprint when viewed from above) or may have other suitable shapes. 
     By reflecting waveguide mode light  80 ′ out of organic layers  38 , reflector  72  may help increase the overall extraction efficiency of display  14 . Additionally, whereas air mode light  80  may be subject to spectrum narrowing and color variation at wide viewing angles (e.g., due to cavity effects), waveguide mode light  80 ′ has a broader spectrum and less sensitivity to viewing angle. As such, not only does reflector  72  increase the overall extraction efficiency of display  14 , but it also mitigates cavity effects at wide viewing angles (sometimes referred to as off-axis viewing angles) by increasing off-axis efficiency and reducing off-axis color variation. 
       FIG. 6  is a top view of illustrative pixels in display  14 . Pixels in display  14  may include color pixels (sometimes referred to as subpixels) such as red pixel  22 R, blue pixel  22 B, and green pixel  22 G. As shown in  FIG. 6 , each pixel may include an organic light-emitting diode surrounded by an associated reflector. For example, red pixel  22 R may include light-emitting diode  26 R surrounded by reflector  72 R, blue pixel  22 B may include light-emitting diode  26 B surrounded by reflector  72 B, and green pixel  22 G may include light-emitting diode  26 G surrounded by reflector  72 G. The example of  FIG. 6  in which reflectors  72  completely surround light-emitting diodes  26  is merely illustrative. If desired, reflectors  72  may only partially surround light-emitting diodes  26 , reflectors  72  may be located on one, two, three, or four sides of light-emitting diodes  26 , a reflector  72  on one side of light-emitting diode  26  need not contact a reflector  72  on an adjacent side of light-emitting diode  26 , reflectors  72  in one pixel need not contact reflectors  72  in an adjacent pixel, etc. Reflectors  72  may be located in the non-emitting portion of each pixel  22  (sometimes referred to as the inactive area of pixels  22 ). Reflectors  72  may have the same structure for all pixels in display  14  or reflectors  72  may have different structures for different pixels. For example, reflectors  72  may have a different shape, size, and/or structure for different color pixels, if desired. 
       FIG. 7  is a graph showing how off-axis viewing of display  14  may be improved using a reflector such as reflector  72  to extract waveguide mode light from organic layers  38 . Curve  84  represents air mode light (e.g., light  80  of  FIG. 5 ) emitted from display  14 , and curve  86  represents waveguide mode light (e.g., light  80 ′ of  FIG. 5 ) emitted from display  14 . For on-axis viewing (e.g., around 0°), air mode light is highly efficient and therefore achieves relatively high luminance. In arrangements where the light-emitting diodes of display  14  include micro-cavities (e.g., in which light is reflected up and down within the pixel layers before exiting display  14 ), a spectral narrowing can occur that causes off-axis efficiency to decrease and color variation to increase at wide viewing angles. The recycling of waveguide mode light  80 ′ (curve  86 ) mitigates these affects by adding broader spectrum light with less color variation at wide viewing angles. 
       FIGS. 8-15  show cross-sectional side views of illustrative reflectors  72  that may be used to recycle waveguide mode light  80 ′ as discussed in connection with  FIGS. 5-7 . In these examples, reflectors  72  are located between red pixel  22 R and blue pixel  72 B. However, it should be understood that this is merely illustrative and that the reflectors of  FIGS. 8-15  may be used between any suitable pair of pixels in display  14 . It should also be understood that any one of the embodiments shown in  FIGS. 8-15  may be combined with any one or more of the other embodiments shown in  FIGS. 8-15 , if desired. 
     In the example of  FIG. 8 , reflectors  72 R and  72 B are located in pixel definition layer  60 . Reflector  72 R may be used to reflect waveguide mode light within organic layers  38 R out of display  14 , and reflector  72 B may be used to reflect waveguide mode light within organic layers  38 B out of display  14 . As discussed in connection with  FIG. 5 , reflector  72  may be formed from sheet metal (e.g., stamped sheet metal), metallized polymer film, a thin-film metal on a plastic carrier, a dielectric thin-film stack that forms a dielectric mirror (a thin-film interference mirror) on a polymer film or molded plastic carrier, an interface between a high-refractive-index material and a low-refractive index material, a white reflective film (e.g., a glossy white polymer sheet formed from a white ink layer or other white layer on a polymer carrier covered with a glossy coating such as a glossy polymer coating), or other suitable reflector structure. In arrangements where reflector  72  is formed from an interface between a high-refractive-index material and a low-refractive index material, reflector  72  may be formed from a material that has a lower or higher refractive index than surrounding pixel definition layer  60 . For example, if pixel definition layer  60  has a refractive index of about 1.7, reflectors  72 R and  72 B may have a lower refractive index at about 1.4, or may have a higher refractive index at about 2.3. Materials having other refractive indices may be used, if desired. These examples are merely illustrative. 
     In the example of  FIG. 9 , reflector  72  between adjacent pixels  22 R and  22 B is formed from a single structure (rather than the two separate structures shown in  FIG. 8 ). The structure may have a first angled surface that reflects waveguide mode light from organic layers  38 R out of display  14  and a second opposing angled surface that reflects waveguide mode light from organic layers  38 B out of display  14 . 
     In the example of  FIG. 10 , reflectors  72  are formed from extended portions of the anodes in pixels  22 . Anode  36 R of red pixel  22 R has a first portion  36 R 1  that is parallel to substrate  30  and a second portion  36 R 2  that is angled relative to substrate  30 . Anode  36 B of blue pixel  22 B has a first portion  36 B 1  that is parallel to substrate  30  and a second portion  36 B 2  that is angled relative to substrate  30 . Because anodes  36 R and  36 B are reflective (e.g., around 95% reflective), extended portion  36 R 2  may reflect waveguide mode light from organic layers  38 R out of display  14  and extended portion  36 B 2  may reflect waveguide mode light from organic layers  38 B out of display  14 . 
     In the example of  FIG. 11 , reflector  72  is formed from light-reflective particles  88  within pixel definition layer  60 . Particles  88  may be titanium dioxide particles, silica composite particles, other ceramic particles, or other reflective particles. In the example of  FIG. 11 , particles  88  are suspended in pixel definition layer  60 . If desired, particles  88  may be suspended in other materials (e.g., particles  88  may be suspended within a matrix such as a matrix formed from epoxy, acrylic, silicone, or other polymer materials within or on layer  60 ). 
     In the example of  FIG. 12 , reflector  72  is formed from light-reflective particles  88  on opposing sides of a light-blocking structure such as light-blocking structure  90 . Light-blocking structure  90  may be an opaque (e.g., black) portion of pixel definition layer  60  or may be other suitable light-blocking structure or opaque coating. Light-blocking structure  90  may help prevent color mixing between adjacent pixels. 
     In the example of  FIG. 13 , reflector  72  is formed from a low-refractive-index material  96 . The difference in refractive index between organic layers  38  and low-refractive index material  96  may cause waveguide mode light out of diode  26 . Low-refractive-index material  96  may have a refractive index that is less than 1.6, for example, or may have other suitable refractive index that is lower than the refractive index of organic layers  38 R and  38 B. If desired, low-refractive index material  96  may replace pixel definition layer  60 . 
     In the example of  FIG. 14 , reflector  72  is formed from reflective coatings  76  on structure  78 . Structure  78  may be formed from polymer, metal, or other suitable material. If desired, structure  78  may be formed from the same material as pixel definition layer  60 . Coating  76  may be metallized polymer film, a thin-film metal, a dielectric thin-film stack that forms a dielectric mirror (a thin-film interference mirror) on a polymer film or molded plastic carrier, an interface between a high-refractive-index material and a low-refractive index material, a white reflective film (e.g., a glossy white polymer sheet formed from a white ink layer or other white layer on a polymer carrier covered with a glossy coating such as a glossy polymer coating), or may be a coating of reflective particles suspended in a matrix. 
     In the example of  FIG. 15 , reflectors  72  are formed from reflective coatings  76  that are formed on opposing outer surfaces of pixel definition layer  60  (rather than being formed within pixel definition layer  60  as in the example of  FIG. 14 ). 
     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: 20180827
Publication Date: 20200519
Grant Date: 20200519
Priority Date: 20170828
Inventors: CHEON, KWANG OHK
CHEN, CHENG
LU, CHIEN
CHEN, CHIH-LEI
HSU, CHIN WEI
LU, HUI
KIM, KIBEOM
TSAI, LUN
HO, MENG-HUAN
Kao, Nai-Chih
LIN, PEI-LING
LIU, RUI
YU, SHAN-JEN
CHANG, Wendi
FUJINO, YUSUKE
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G3/3225", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3225", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/323", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/3211", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/5092", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/3283", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/3246", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L51/5237", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2251/5369", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L51/56", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/5209", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/5212", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/5271", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/5056", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/171", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/814", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K2102/331", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/813", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/15", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K2102/331", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K71/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/35", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/856", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3225", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/122", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/173", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/122", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K50/84", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/173", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/80516", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/878", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/80515", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 65435638