PATENT DOCUMENT

Publication Number: US-9620686-B2
Application Number: US-201514853580-A
Country: US
Kind Code: B2

Title: Display light sources with quantum dots

Abstract:
A display may be provided with light sources. The light sources may include light-emitting diodes. The light sources may have packages formed from package bodies to which the light-emitting diodes are mounted. Layers such as quantum dot layers, light-scattering layers, spacer layers, and diffusion barrier layers may be formed over the package bodies and light-emitting diodes. Quantum dots of different colors may be stacked on top of each other. A getter may be incorporated into one or more of the layers to getter oxygen and water. Quantum dots may be formed from semiconductor layers that are doped with n-type and p-type dopant to adjust the locations of their conduction and valance bands and thereby enhanced quantum dot performance.

Claims:
What is claimed is: 
     
       1. A packaged light-emitting diode, comprising:
 a package body; 
 a light-emitting diode mounted to the package body; and 
 a plurality of layers on the package body and light-emitting diode, wherein the layers include at least one quantum dot layer, wherein the at least one quantum dot layer has microparticles, wherein each microparticle includes metal oxide nanoparticles and quantum dot nanoparticles surrounded by a coating, wherein the microparticles of the at least one quantum dot layer are formed in a polymer matrix, and wherein the polymer matrix also includes at least some getter that getters a material selected from the group consisting of oxygen and water. 
 
     
     
       2. The packaged light-emitting diode defined in  claim 1  wherein the getter comprises a molecular getter. 
     
     
       3. The packaged light-emitting diode defined in  claim 1  wherein the getter comprises a particulate getter. 
     
     
       4. The packaged light-emitting diode defined in  claim 1  wherein the getter comprises an oxygen getter. 
     
     
       5. The packaged light-emitting diode defined in  claim 1  wherein the getter comprises a water getter. 
     
     
       6. The packaged light-emitting diode defined in  claim 1  wherein the layers include a light-scattering layer interposed between the quantum dot layer and the light-emitting diode and wherein the light-scattering layer includes metal oxide particles. 
     
     
       7. The packaged light-emitting diode defined in  claim 1  wherein the layers include a spacer layer formed from transparent polymer and wherein the spacer layer is interposed between the quantum dot layer and the light-emitting diode. 
     
     
       8. The packaged light-emitting diode defined in  claim 1  wherein the quantum dot layer includes thermally conductive particles to enhance the thermal conductivity of the quantum dot layer. 
     
     
       9. The packaged light-emitting diode defined in  claim 1  wherein the quantum dot layer is a green quantum dot layer and wherein the layers include a red quantum dot layer and wherein the layers include a yellow quantum dot layer interposed between the red and green quantum dot layers. 
     
     
       10. The packaged light-emitting diode defined in  claim 9  further comprising a light-scattering layer having metal particles in a polymer, wherein the light-scattering layer is interposed between the light-emitting diode and the red quantum dot layer. 
     
     
       11. The packaged light-emitting diode defined in  claim 1  wherein the layers include a diffusion barrier layer. 
     
     
       12. A packaged light-emitting diode, comprising:
 a package body; 
 a light-emitting diode mounted to the package body; and 
 a plurality of layers on the package body and light-emitting diode, wherein the layers include at least one quantum dot layer and at least some getter that getters a material selected from the group consisting of oxygen and water, wherein the layers include a diffusion barrier layer, and wherein the diffusion barrier layer comprises plate-shaped particles in a polymer. 
 
     
     
       13. A packaged light-emitting diode, comprising:
 a package body; 
 a light-emitting diode mounted to the package body; 
 a plurality of layers on the package body and light-emitting diode, wherein the layers include at least one quantum dot layer and at least some getter that getters a material selected from the group consisting of oxygen and water, wherein the package body has a recess, and wherein a diffusion barrier layer is formed in the recess over the light-emitting diode and under the quantum dot layer; and 
 an additional diffusion barrier layer that covers the quantum dot layer and that contacts the diffusion barrier layer in the recess, wherein the quantum dot layer is interposed between the diffusion barrier layer and the additional diffusion barrier layer. 
 
     
     
       14. The packaged light-emitting diode defined in  claim 1  wherein the layers include a layer of plate-shaped particles in polymer that serves as a diffusion barrier for the quantum dot layer. 
     
     
       15. The packaged light-emitting diode defined in  claim 1  wherein the quantum dot layer comprises quantum dots each of which has a semiconductor core and at least one semiconductor shell surrounding the semiconductor core and wherein a selected one of the semiconductor core and the at least one semiconductor shell includes dopant. 
     
     
       16. The packaged light-emitting diode defined in  claim 12 , wherein the plate-shaped particles comprise a material selected from the group consisting of: alumina, clay, and mica. 
     
     
       17. The packaged light-emitting diode defined in  claim 16 , wherein the plate-shaped particles have a diameter and a thickness, and wherein the diameter is between 100 and 10,000 times greater than the thickness. 
     
     
       18. The packaged light-emitting diode defined in  claim 17 , wherein the thickness is less than 200 nanometers. 
     
     
       19. The packaged light-emitting diode defined in  claim 12 , wherein the plate-shaped particles are embedded in the polymer. 
     
     
       20. The packaged light-emitting diode defined in  claim 19 , wherein the polymer comprises silicone.

Description:
This application claims the benefit of provisional patent application No. 62/108,961 filed on Jan. 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 light sources for displays. 
     Electronic devices such as computers and cellular telephones have displays. Some displays are based on light-emitting diodes. For example, organic light-emitting diode displays have arrays of organic light-emitting diodes. Light-emitting diode displays based on arrays of crystalline light-emitting diode dies have also been developed. Liquid crystal displays have arrays of liquid crystal pixels that are backlit using backlight structures based on light-emitting diodes. These light-emitting diodes may be arranged in an array to support local diming or may be used to edge light a light guide plate in a backlight unit. 
     Display performance can be enhanced by using narrow linewidth light-emitting diode light sources. For example, color saturation in a display can be enhanced by using light-emitting diode sources that emit narrowband red, green, and blue light. Light sources of this type may exploit the ability of phosphors and quantum dots to produce output light of desired wavelengths and linewidths. For example, a display may include red and green quantum dots to convert some of the blue light from a blue light source to narrowband red and green light. 
     There are challenges associated with forming this type of display. Quantum dots and phosphors can be sensitive to moisture and oxygen. Quantum dot lifetimes can also be adversely affected by exposure to high pump light intensities and elevated temperatures. Quantum dot performance is also affected by the type of structures used to form the quantum dots. If care is not taken, quantum dots will exhibit insufficient quantum confinement and instability. 
     It would therefore be desirable to be able to provide enhanced light sources for display. 
     SUMMARY 
     A display may be provided with light sources. The light sources may include light-emitting diodes. The light-sources may have packages to which the light-emitting diodes are mounted. The packages may have chip-scale and wire-bond package bodies formed from dielectric. Layers of material may be formed over the light-emitting diodes and packages. These layers may include quantum dot layers, light-scattering layers, spacer layers, and diffusion barrier layers. Quantum dots of different colors may be stacked on top of each other. A getter may be incorporated into one or more of the layers to getter oxygen and water. 
     Quantum dots may be formed from semiconductor layers that are doped with n-type and p-type dopant to adjust the locations of the conduction and valance bands in the layers of the quantum dots and thereby enhanced quantum dot performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of an illustrative diffusion barrier structure for protecting structures such as quantum dots in an electronic device display in accordance with an embodiment. 
         FIGS. 3, 4, 5, 6, and 7  are side views of illustrative light sources with diffusion barrier structures during various phases of fabrication in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of an illustrative wired-bonded packaged light-emitting diode with quantum dots in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an illustrative light-emitting diode with quantum dots that has been packaged in a chip scale package in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of an illustrative light-emitting diode with quantum dots that has been mounted on the upper surface of a chip scale package in accordance with an embodiment. 
         FIGS. 11, 12, 13, and 14  are cross-sectional side views of an illustrative light source with diffusion barrier structures during various phases of fabrication in accordance with an embodiment. 
         FIG. 15  is a cross-sectional side view of an illustrative light source having a light-emitting diode packaged under layers of quantum dots in accordance with an embodiment. 
         FIG. 16  is a diagram containing a cross-section of an illustrative quantum dot and a corresponding energy band diagram in accordance with an embodiment. 
         FIGS. 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, and 29  are diagrams illustrating how quantum dot layers may be doped to adjust their conduction and valance bands in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative electronic device of the type that may be provided with a display having light sources based on light-emitting diodes is shown in  FIG. 1 . As shown in  FIG. 1 , electronic device  10  may have control circuitry  16 . Control circuitry  16  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  16  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc. 
     Input-output circuitry in device  10  such as input-output devices  12  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  12  may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  12  and may receive status information and other output from device  10  using the output resources of input-output devices  12 . 
     Input-output devices  12  may include one or more displays such as display  14 . Display  14  may be a touch screen display that includes a touch sensor for gathering touch input from a user or display  14  may be insensitive to touch. A touch sensor for display  14  may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements. 
     Control circuitry  16  may be used to run software on device  10  such as operating system code and applications. During operation of device  10 , the software running on control circuitry  16  may display images on display  14 . 
     Device  10  may be a tablet computer, laptop computer, a desktop computer, a television, a cellular telephone, a media player, a wristwatch device or other wearable electronic equipment, or other suitable electronic device. 
     Display  14  for device  10  includes an array of pixels. The array of pixels may be formed from liquid crystal display (LCD) components, rows and columns of light-emitting diode dies, organic light-emitting diodes, or other suitable display structures. Light-emitting diodes may be arranged in a backlight array (e.g., to form a backlight with local dimming capabilities for a display), may supply light to the edge of a light guide plate in a backlight unit, may be used as individual pixels in an array of pixels that form a display, or may be used to provide light for a display in other display configurations. Display  14  may include a color filter array (e.g., an array having red, green, and blue color filter elements to impart color to display backlight) or other arrangements for providing display  14  with the ability to display color content may be used. 
     A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer, thin-film transistor layer, or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . The outermost display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
     Light sources for display  14  may be based on quantum dot structures. If desired, some or all of the quantum dots in the light sources may be supplemented with or replaced with phosphors (e.g., doped YAG particles). Light sources with quantum dots may sometimes be described as an example. This is, however, merely illustrative. Light sources based on phosphors or mixtures of quantum dots and phosphors may also be used in display  14 . 
     A light-emitting diode such as a blue light-emitting diode may emit pump light (i.e., blue pump light). The quantum dots may be excited by the blue pump light. The quantum dots may include dots of one or more different colors (e.g., red, yellow, green, etc.). When excited by pump light (e.g., blue pump light), red quantum dots will emit red light, yellow quantum dots will emit yellow light, and green quantum dots will emit green light. 
     Light sources may be formed by packaging quantum dots with light-emitting diodes. The light sources may include one or more different colors of quantum dots. For example, a packaged blue light-emitting diode may include red and green quantum dots. When blue light is produced by the light-emitting diode, the red and green quantum dots will be excited and will emit red and green light, respectively. As a result, the light source will emit blue light (i.e., residual blue light that has not been converted to red and green light by the red and green quantum dots), red light (i.e., red light emitted from the red quantum dots), and green light (i.e., green light emitted from the green quantum dots). The linewidths of the blue, red, and green light emitted by the light source may be relatively narrow, allowing a display that includes this type of light source to exhibit good performance (e.g., good color saturation and efficiency). 
     Quantum dots may be formed from nanoparticles of semiconductor material. The semiconductor material of the quantum dots may be degraded in the presence of moisture and oxygen. To prevent exposure to moisture and oxygen, diffusion barrier layers (sometimes referred to as moisture barrier layers) may be used to protect the quantum dots. 
     An illustrative technique that may be used for protecting quantum dots in a light source from moisture and oxygen is shown in  FIG. 2 . As shown in  FIG. 2 , quantum dots  20  may be embedded in a supporting matrix such as polymer  24 . Polymer  24  may be silicone or other material that is transparent and stable under extended exposure to light and heat. Polymer  24  may be deposited in thin coating layers on a support structure such as support structure  26 . Support structure  26  may be a polymer carrier film or other substrate (e.g., an inorganic substrate, an organic substrate, a light-emitting diode die in a packages, quantum dot layers, light scattering layers, other layers in a light source, part of a package, etc.). 
     Diffusion barrier layers  28  may be interposed between respective quantum dot films  22 . One of diffusion barrier layers  28  may also be used to cover the outermost of quantum dot films  22 . Each diffusion barrier film may include a supporting matrix such as polymer  30 . As with polymer  24  of quantum dot layers  22 , polymer  30  of diffusion barrier layers  28  may be silicone or other material that is transparent and stable under extended exposure to heat and light. Inorganic plate-shaped particles  32  may be embedded within polymer  30 . Plate-shaped particles  32  may be plate-shaped alumina particles, clay, mica, or other plate shaped particles. The thickness of the plate-shaped particles may be, for example, 10-100 nm, more than 5 nm, less than 200 nm, or other suitable thickness. The diameter of plate-shaped particles  32  may be 10-50 microns, more than 5 microns, less than 100 microns, or any other suitable diameter. With this type of arrangement, the diameter of the plate-shaped particles may be 100-10,000 times greater than the thickness of the plate-shaped particles (as an example). 
     The thickness of each quantum dot film may be 10-20 microns, less than 25 microns, more than 5 microns, or other suitable thickness. The thickness of barrier films  28  may be less than 40 microns, more than 30 microns, less than 50 microns, or other suitable thickness. The total thickness of layers  22  and  28  may be less than 100 microns (when a compact set of quantum dot layers is desired) or may be larger or smaller than 100 microns. 
     When the plate-shaped particles are arranged in a thin diffusion barrier layer (e.g., using blade coating, spray coating, or other deposition techniques), the presence of the plate-shaped particles will create a long diffusion path for contaminants such as oxygen and water vapor. Accordingly, each diffusion barrier layer (film)  28  will serve as an oxygen and water barrier that helps protect quantum dots  20  from exposure to oxygen and water. If desired, light scattering material such as metal oxide particles may be incorporated into the layers of the structure of  FIG. 2  (as separate layers, as portions of quantum dot layers  22 , and/or as part of diffusion barrier layers  28 ). Quantum dot films may be deposited onto a light-emitting diode die as a conformal coating to down-convert blue light to red, green, and blue light, or may be deposited on other suitable substrates. 
       FIGS. 3, 4, 5, 6, and 7  are cross-sectional side views of quantum dot structures during a fabrication process in which packaged quantum dot light sources are being produced. 
     As shown in  FIG. 3 , light-emitting diodes  36  may be mounted on substrate  34 . Substrate  34  may be a flexible polymer carrier tape (e.g., a flexible printed circuit), part of a plastic structure for a package, or any other suitable substrate. Solder joints, conductive adhesive connections, or other mounting structures may be used to mount light-emitting diodes  36  to metal traces on substrate  34 . Light-emitting diodes  36  may be blue light emitting diodes or other suitable light-emitting diodes. 
     As shown in  FIG. 4 , a coating such as white reflector coating  38  may be deposited on the upper surface of substrate  34  so that coating  38  covers the tops and sides of light-emitting diodes  36 . Coating  38  may be formed from titanium dioxide particles, silica composite particles, other ceramic particles, or other reflective particles. The particles of coating  38  may be suspended within a matrix such as a matrix formed from epoxy, acrylic, silicone, or other polymer materials. 
     After depositing coating  38 , the top portion of coating  38  may be removed (e.g., using polishing, bead blasting, etc.) so that the upper surface of coating  38  lies flush with the upper surfaces of light-emitting diodes  36 . Layers  40  and  42  may then be formed on light-emitting diodes  36  and reflective coating  38 . Layer  40  may be a quantum dot layer(s). For example, layer  40  may include layers of red and green quantum dots in a matrix such as a silicone matrix or other polymer matrix (see, e.g., layers  22  of  FIG. 2 ). Layer  42  may be a diffusion barrier layer (see, e.g., layers  28  of  FIG. 2 ). 
     As shown in  FIG. 6 , channels  44  may be formed between respective light-emitting diodes. Channels  44  may be formed by sawing or other material removal techniques. 
     After channels  44  have been formed, additional white reflective coating material  38 ′ may be deposited on the exposed edges of layers  40  and  42  (e.g., material  38 ′ may be deposited by overloading or spray coating followed by bead blasting), as shown in  FIG. 7 . Material  38 ′ may help laterally confine light emitted from light-emitting diodes  36  (e.g., to enhance the amount of light passing through quantum dots  20 ). The light-emitting diodes structures of  FIG. 7  may serve as backlight light sources, pixels in a pixel array, or other display light sources. 
       FIGS. 8, 9, and 10  show how quantum dots may be incorporated into the same package as a light-emitting diode. 
       FIG. 8  is a cross-sectional side view of a light source having a light-emitting diode and quantum dots that is based on a wire-bonded package structure. As shown in  FIG. 8 , light-emitting diode  36  may be mounted in package  48 . Light-emitting diode  36  may include semiconductor die  54  and contacts (terminals) such as terminals  50  and  52 . Package  48  may be formed from plastic structure  60 . Package body  60  may have a recess such as recess  66 . Recess  66  may have a tapered shape as shown in  FIG. 8  or may have other shapes. Inner package contacts  74  and  68  may be formed on the bottom surface of recess  66 . Terminal  50  of light-emitting diode  36  may be wire bonded to contact  74  of package  48 . Terminal  52  of light-emitting diode  36  may be soldered to contact  68  using solder  70 . 
     Package  48  may have vias such as vias  62  and  56  that extend through package body  60 . Via  62  may electrically connect inner package contact  74  to outer package contact (terminal)  64 . Portions  64 ′ of contact  64  may, if desired, extend around the sides and/or top surface of package body  60 . Via  56  may electrically connect inner package contact  68  to outer package contact (terminal)  58 . Portions  58 ′ of contact  58  may extend around the sides and/or top surface of package body  60 . 
     Recess  66  in package body  60  may be filled with quantum dot material. For example, one or more layers of quantum dots  20  may be embedded in matrix  24 . Matrix  24  may be a polymer such as silicone or other material that withstands extended exposure to light and heat. Quantum dots  20  may include red quantum dots and green quantum dots and/or quantum dots of other colors (e.g., yellow quantum dots). Light-emitting diode  36  may emit blue light. Some of the blue light is transmitted through the quantum dot material and is emitted as a blue portion of emitted light  47 . Other blue light from light-emitting diode  36  is absorbed by the quantum dots and reemitted by the quantum dots as red, green, and/or yellow light components in emitted light  46 . 
     To protect quantum dots  20  from oxygen and water, package  48  may be covered with a protective layer such as layer  82 . Layer  82  may be a diffusion barrier coating such as film  28  of  FIG. 2  or other protective layer. Layer  82  may be deposited onto the silicone or other matrix material (material  24 ) into which quantum dots  20  have been embedded. Layer  82  may be deposited from a solution, may be deposited using sputtering or other physical vapor deposition techniques, may be deposited using atomic layer deposition, may be deposited using chemical vapor deposition, may be blade coated, screen printed, dripped, sprayed, pad printed, ink-jet printed, spin-coated, or deposited using other suitable deposition techniques. The thickness of layer  82  may, if desired, be less than 10 microns, less than 20 microns, more than 1 micron, 5-15 microns, or other suitable thickness. The thermal coefficient of expansion of layer  82  may, if desired, be close to or equal to the thermal coefficient of expansion of matrix material  24  (e.g., silicone) to prevent cracking during heating of material  24  during use of light source  24 . Illustrative materials that may be used in forming layer  82  include polymer films such as polyimide, aminosilane, sol-gel materials such as sol-gel metal oxides that are deposited as a liquid and solidified by dehydration, spin-on glass, sputtered metal oxides such as aluminum oxide or other metal oxides, metal oxides applied by atomic layer deposition or other deposition techniques, plate-shaped particles such as particles  32  of  FIG. 2 , or other materials for forming a protective layer over quantum dots  20  and the other structures of light source  46 . Layer  82  may be deposited as a coating (e.g., a conformal coating) or may be a film that is attached to the upper surface of light-source  46 . If desired, layer  82  may be impregnated with quantum dots (e.g., red, green, or yellow dots) or may be impregnated with phosphors. Light diffusing material such as metal oxide particles may also be incorporated into layer  82 ). 
     In the illustrative arrangement for light source  46  of  FIG. 9 , via  76  passes through semiconductor die  54  of light-emitting diode  36 . Light-emitting diode contact  78  is connected to via  76  and is attached to inner package contact  74  of package  48  using solder  80 . Contact (terminal)  52  of light-emitting diode  36  may be coupled to inner package contact  68  of package  48  by solder  70 . 
     Vias  62  and  56  may extend through body  60  of package  48  and may connect contacts  74  and  68  to respective outer contacts such as contacts  64  and  58 . Contacts  64  and  58  may, if desired, extend to the sides and front of package  48 . Quantum dots  20  in polymer matrix  24  may fill recess  66 . During operation, light from light-emitting diode  36  may excite quantum dots  20 . Light  47  may be emitted outwards from recess  66  from light-emitting diode  36  and dots  20 . As with light source  46  of  FIG. 8 , light source  46  of  FIG. 9  may be covered with protective layer  82  (i.e., protective layer  82  may form a coating that covers matrix material  24  and quantum dots  20 ). 
     In the illustrative arrangement for light source  46  of  FIG. 10 , light-emitting diode  36  is covered with quantum dot material that is enclosed within encapsulant  82 . In light-emitting diode  36 , via  76  passes through semiconductor die  54 . Light-emitting diode contact  78  is connected to via  76  and is attached to upper surface package contact  74  of package  48  using solder  80 . Contact (terminal)  52  of light-emitting diode  36  may be coupled to inner package contact  68  of package  48  by solder  70 . 
     Vias  62  and  56  may extend through body  60  of package  48  and may connect contacts  74  and  68  to respective outer contacts such as contacts  64  and  58 . Contacts  64  and  58  may, if desired, extend to the sides and front of package  48 . If desired, vias  62  and  56  may be omitted (e.g., in a configuration in which front-side contacts extend outwardly from under light-emitting diode  36 ). Quantum dots  20  in polymer matrix  24  may cover light-emitting diode  36 . Protective layer  82  (e.g., a conformal coating, a film, or other protect layer such as layers  82  of  FIGS. 8 and 9 ) may be used to cover and protect matrix material  24  and quantum dots  20 . 
     If desired, the material of protective layer  82  may be extended under and around the sides of matrix material  24  and quantum dots  20  to form an encapsulation structure that encloses and surrounds material  24  and quantum dots  20 . An illustrative technique for forming this type of encapsulation for light source  46  is shown in  FIGS. 11, 12, 13, and 14 . As shown in  FIG. 11 , light-emitting diode  36  may be soldered or otherwise mounted in recess  66  of package body  60 . As shown in  FIG. 12 , following mounting of light-emitting diode  36  in package body  60 , a first portion of protective (diffusion barrier) layer  82  may be deposited such as layer  82 A. Layer  82  may be formed from plate-shaped particles in a polymer matrix or other suitable diffusion barrier materials. 
     After forming layer  82 A, one or more layers of quantum dots  20  in polymer matrix material  24  and/or other layers of material (e.g., light-scattering layers, spacer layers, etc.) may be deposited over light-emitting diode  36 , as shown in  FIG. 13 . If desired, optional particles  84  may be included in matrix  24  (e.g., in one or more of the layers of material covering light-emitting diode  36 ). Particles  84  may be, for example, a getter that getters oxygen and/or water. In the illustrative package configuration of  FIG. 13 , quantum dots  20  and matrix material  24  fill recess  66 . In other types of package (e.g., packages of the type shown in  FIG. 10 ), matrix material  24  may cover light-emitting diode  36  on the upper surface of package body  60 . As shown in  FIG. 14 , after quantum dots  20  in matrix material  24  have been formed over light-emitting diode  36 , a second portion of protective layer  82  such as layer  82 B may be deposited. Layers  82 A and  82 B may be formed from a transparent material that serves as a diffusion barrier to oxygen and water (see, e.g., layer  82  of  FIGS. 8, 9, and 10 ). Because layers  82 A and  82 B surround the top, bottom, and sides of material  24 , material  24  and quantum dots  20  in material  24  may be protected from oxygen and moisture. 
     In configurations in which particles  84  include a getter, the getter may be an oxygen and/or water getter and may be implemented in particle or molecular form. The getter may be incorporated into quantum dot matrix material  24 , layer  82 , or other structures supporting dots  20  to absorb and/or react with oxygen and/or water. This helps prevent the oxygen and water from interacting with quantum dots  20  and lowering quantum dot lifetime. 
     The getter may be a water getter such as STAYDRY™ getter material from Cookson Electronics, zeolites, other mineral-type compounds that are good water absorbers (e.g., microporous particles formed from aluminosilicate minerals such as Na 2 Al 2 Si 3 O 10 .2H 2 O), bentonite clay (a calcium rich montmorillonite layered structure that attracts and binds water molecules to its inner and outer surface area), moisture adsorbent silica gel (made of highly porous amorphous silicon oxide, which binds water molecules in random intersection channels of various diameters), calcium sulfate, and calcium chloride. If desired, the getter may be an oxygen getter such as SAES Getters St101 or St777P, pyrogallol (a molecular oxygen getter), Ca metal (an oxygen scavenger), mannitol (an oxygen scavenger), sodium azide (an oxygen scavenger), catechol (also known as pyrocatechol or 1, 2 dihydrobenzene, which is an oxygen scavenger), ascorbic acid (an oxygen scavenger), MnTBAP also known as manganese(III)-tetrakis(4-benzoic acid) porphyrin (an oxygen scavenger), hydrazine, a protocatechuic acid/protocatechuate-3,4-dioxygenase system, zirconium-aluminum-iron alloys, zirconium-aluminum alloys such as Zr—Al—Fe or other alloys from the IV-A Group (Ti, Zr, Th) of the periodic table of elements (oxygen scavengers that work by chemically binding gaseous molecules to their surfaces and that are activated at relatively low temperatures such as temperatures below 500 C), etc. 
     The getter may be included with quantum dots  20  in matrix  24 , may be included in a film that is located above or below matrix  24  and/or above or below dots  20  (e.g., a film such as layer  82  and/or a layer of material inside of layer  82 ), may be formed in a ring or other shape that runs along the periphery of quantum dot material  24  and dots  20  (e.g., along a seal formed to enclose material  24  and dots  20  within a protective film such as film  82  and/or a package body such as body  60 ), and/or may be included in other areas within light source  46  to help prevent materials such as oxygen and/or water from interacting with quantum dots  20 . 
     If desired, particles  84  may include inorganic particles that form an inorganic supporting matrix for quantum dots  20  (e.g., matrix  24  may be formed from inorganic particles in addition to or instead of a polymer). The inorganic matrix particles may be, for example, closely packed semiconductor or metal oxide nanoparticles that help separate quantum dots  20  from direct contact with each other. This helps prevent quantum dots  20  from chemically reacting with each other and helps prevent energy transfer between an excited quantum dot and a neighboring quantum dot (e.g., the separation provided by particles  84  may help avoid undesired nonradiative relaxation of the excited quantum dots). The nanoparticles of the inorganic matrix may be configured to not absorb blue light from light-source  36  and may be formed from materials that are stable in the presence of heat, light, oxygen, and water. Examples of metal oxides that may be used in forming the particles include ZnO, MnO, SiO 2 , TiO 2 , Al 2 O 3 , MgO, CaO, WO 3 , V 2 O 5 , Ta 2 O 5 , La 2 O 3 , BeO, CeO 2 , ZrO 2 , and SrO. The nanoparticles may be of the same size as quantum dots  20  or may be similar in size to quantum dots  20  to help avoid phase separation and aggregation (e.g., to help ensure that the mixture of dots  20  and nanoparticles in the supporting matrix remains homogeneous). 
     If desired, the surfaces of the inorganic matrix particles that are supporting dots  20  (and, if desired, dots  20 ) may be coated with an organic or inorganic ligands (e.g., ultra small ligands such as inorganic ligands, small chain or aromatic carboxylates, amines, phosphoric acids, etc.) so that the particles may closely pack in an ultra dense manner. Coating the surfaces of the nanoparticles with organic or inorganic ligands may help allow the particles to be dispensable in a solvent such as alcohol. During formation of the mixed quantum dot and nanoparticle layer, heating may be used to drive out solvent and cause the nanoparticle matrix to densify around quantum dots  20 . The nanoparticle matrix may be used to fill a cavity in light source  46  (see, e.g., recess  66 ) or may be used to form microparticles that could then be coated with metal oxides (e.g., using atomic layer deposition or other coating techniques) and/or water barrier or oxygen barrier polymers to provide further stabilization. The coating may, for example, form a barrier to both oxygen and water. Coated microparticles may each contain multiple quantum dots and multiple matrix particles. Coated microparticles may be dispensed into a polymer (e.g., silicone) and placed on or inside package body  60 . If desired, additional protective layers may be used to protect the microparticles (e.g., diffusion barrier layers, metal oxides, polymer films, etc.). 
       FIG. 15  shows how light source  46  may be provided with multiple layers of material over light-emitting diode  36 . In the example of  FIG. 14 , light source  46  includes four layers (layers  90 ,  92 ,  94 , and  96 ). If desired, light source  46  may have only a single layer, may have two or more layers, may have three layers, may have five or more layers, or may have any other suitable number of layers. These layers may be formed within recess  66  of package body  60  or may be used to cover light-emitting diode  36  in other types of package configurations. The layers of light source  46  such as layers  90 ,  92 ,  94 , and  96  may include light diffusion layers, quantum dot layers, phosphor layers, diffusion barrier layers, layers with getter material, other suitable layers, and/or combinations of any two or more or three or more of these types of structures. 
     Examples of particles that can help scatter light and that may therefore be incorporated into a light diffusion layer include metal oxides (e.g., titanium dioxide particles, barium oxide, etc.). These particles may be embedded in a matrix such as a silicone matrix or a matrix formed from other polymer materials. Quantum dots of different colors may be mixed together and/or quantum dots of different colors may be provided in different layers. 
     If desired, a light scattering layer (e.g., a layer of light scattering particles such as metal oxide particles) may be formed as the first layer (layer  90 ) of light source  46 . A second layer (e.g., layer  92 ) may be a red quantum dot layer. A third layer (e.g., layer  94 ) may be a green quantum dot layer. The excitation density (number of turn-over events) for the quantum dots and the temperature of the quantum dots may be reduced with this type of arrangement (i.e., by interposing a light scattering layer between light-emitting diode  36  and the quantum dots). By spreading out excitation of the quantum dots more uniformly, excitation hot spots may be reduced and more uniform color output as a function of angle may be achieved. 
     If desired, an additional color of quantum dots (e.g., yellow quantum dots) may be included in one or more of the layers of light source  46  (e.g., the same layer that contains the red and green quantum dots, a yellow layer that is interposed between red and green layers, etc.). 
     To provide a desired thermal characteristic, the silicone resin of one or more of the layers (e.g., matrix  24 ) may be modified by adding inorganic microparticles or nanoparticles. The additional particles may be incorporated into any of the layers of light source  46  (e.g., layers above the quantum dot layers, etc.). The layer into which the particles have been incorporated may be transparent, may be highly scattering, or may have other optical properties. The incorporation of the additional particles may modify the thermal characteristics of light source  46 . For example, the matrix that has been filled with the additional particles may be highly thermally conductive or may exhibit thermally insulating properties (e.g., above the quantum dot layers and away from light-emitting diode  36 ). In a multi-layer light source, a first of the layers (e.g., layer  90 ) may be a light scattering layer that includes particles that provide high thermal conductivity. If desired, layer  90  may include a microporous or nonporous material, with the pores providing insulating and/or light-scattering properties. Thermal control layers may, if desired, be incorporated higher in the stack of layers of source  46  (see, e.g., layers  92 ,  94 , and  96 ). 
     A layer in light source  46  such as layer  90  may be configured to enhance heat conduction using a resin filler (e.g., matrix  24 ) with enhanced heat conduction properties. With this type of approach, package body  60  can be thermally bonded to a heat sink to improve heat conduction away from the device. 
     Red quantum dots may be more stable than green quantum dots. Accordingly, a red quantum dot layer may be placed lower in the stack of layers on package  60  than a green layer. The lowest layer (layer  90 ) may be a red layer and the next layer up (layer  92 ) may be a green layer. Alternatively, layer  90  may be a light scattering layer, layer  92  may be a red quantum dot layer, and layer  94  may be a green quantum dot layer. If desired, one or more layers may be interposed between the green and red layers (e.g., a yellow quantum dot layer, one or more light scattering layers, a getter layer, a diffusion barrier layer, etc.). As an example, layer  90  may be a light scattering layer, layer  92  may be a red quantum dot layer, layer  94  may be a yellow quantum dot layer, and layer  96  may be a green quantum dot layer. The topmost layer and, if desired, the lowermost layer may be a diffusion barrier layer (e.g., a diffusion barrier layer with plate-shaped particles in a polymer matrix) and/or other diffusion barrier layers may be included. 
     When green quantum dots are located in a layer above the red quantum dots (i.e., when the less stable quantum dots are located farther away from light-emitting diode  36  than the more stable quantum dots), light source lifetime and efficiency may be enhanced. In particular, because the less stable green quantum dots are farther away from the light source than the red quantum dots, the green quantum dots will have a lower turnover rate. Excitation of the green emitting quantum dots will also be spread out more uniformly, reducing excitation hot spots and providing more uniform color over angle. 
     If desired, a spacer layer may be incorporated into the layers above light-emitting diode  36 . For example, layer  90  may be a transparent spacer layer (e.g., layer of silicone or other polymer) that adds more distance between light-emitting diode  36  and the quantum dots or layer  90  may be a scattering layer and layer  92  may be a spacer layer. 
     Phosphors (e.g., YAG phosphors or other phosphors) may exhibit enhanced stability relative to quantum dots. Accordingly, a stable green phosphor in silicone or another polymer may be used in forming layer  90 . This layer will scatter blue light creating more uniform excitation for red quantum dots in layer  92 . If desired, a yellow quantum dot layer may be interposed between the green phosphor layer and the red phosphor layer. Scattering layers, spacer layers, and other layers may also be incorporated into a layer stack that includes quantum dot layers and/or phosphor layers interspersed with optional diffusion barrier layers, getter layers, thermally conductive layers (heat transport layers) and/or the particles used in forming one or more of these layers may be combined into a single layer. If desired, layer  90  may be a red phosphor layer in which red phosphors are embedded in silicone or another polymer. Layer  92  may be a green quantum dot or green phosphor layer. A layer of yellow quantum dots or phosphors may be interposed between the red and green layers and/or other layers of material may be incorporated into light source  46 . 
     Quantum dots  20  may be formed from nested layers of semiconductors. Variables such as the number of semiconductor layers used, the types of semiconductor compounds used, lattice mismatch, stability, carrier confinement, and size can influence quantum efficiency. Ease of manufacturing and use of nontoxic materials are generally desirable. Balancing these considerations to produce quantum dots that perform optimally can be challenging. 
     With one suitable arrangement, dopant is added to one or more semiconductor quantum dot layers. The dopant will shift the conduction and valence bands in the semiconductor quantum dot layers. These energy band shifts can be exploited to design enhanced quantum dots (e.g., carrier confinement can be enhanced by deepening the energy wells formed within the quantum dots). 
     Consider, as an example, quantum dot  20  of  FIG. 16 . As shown in  FIG. 16 , quantum dot  20  may have multiple layers of semiconductor such as inner (core) layer  20 - 1  and outer layers such as intermediate layer  20 - 2 , and outermost layer  20 - 3 . The core of dot  20  is spherical. The layers surrounding the core are hollow spheres and are therefore sometimes referred to as shells. There are three layers of semiconductor in the example of  FIG. 16 , but quantum dots  20  may, if desired, have two layers, three or more layers, four layers, etc. 
     As shown in the energy band diagram in the lower portion of  FIG. 16 , each semiconductor layer in quantum dot  20  has a different respective set of conduction and valence bands. For example, layer  20 - 1  is characterized by valence band  112  and conduction band  116  separated by bandgap  114 , layer  20 - 2  is characterized by valance band  108  and conduction band  106  separated by bandgap  110 , and layer  20 - 3  is characterized by valance band  102  and conduction band  100  separated by bandgap  104 . To enhance quantum dot performance, one or more of the layers of quantum dots  20  may be doped, thereby shifting the conduction and valance bands so that the Fermi levels of the semiconductor layers are aligned. 
     The way in which the energy bands of a quantum dot are altered by doping depends on the doping type (n or p), which quantum dot layers have been doped, and the identity of the semiconductor materials used. 
     Consider, as an example, the quantum dot structure of  FIG. 17 . The diagram of  FIG. 17  shows the conduction band (upper band) and valence band (lower band) energy levels for a quantum dot having a CdSe core, a CdS inner shell, and a ZnS outer shell.  FIG. 18  shows how both the conduction band and valance band of the CdSe core may be shifted to lower energy levels (to provide a deeper quantum well in the center of the quantum dot) by incorporation of n-type dopant (i.e., the use of n-type CdSe to form the core results in lower conduction and valance band energies relative to the conduction and valance bands of the CdS inner shell than the undoped CdSe core of  FIG. 17 ). Examples of n-type dopant for the CdSe core include Sn, In, Al, Cl, Br, I, and Ga. 
     The diagram of  FIG. 19  shows how an enhanced quantum well for the quantum dot may be formed by incorporating p-type dopant into the inner CdS shell and the outer ZnS shell. The p-type dopant may be, for example, N, P, As, SbCu, Li, Na, or Ag. 
     Another illustrative doping scheme for this type of quantum dot semiconductor system is shown in  FIGS. 20, 21, and 22 .  FIG. 20  shows the undoped case—i.e., an undoped CdSe core, an undoped CdS inner shell, and an undoped ZnS outer shell. With the configuration of  FIG. 21 , the depth of the core well relative to the inner shell has been enhanced by doping the CdS inner shell with p-type dopant (e.g., N, P, As, Sb, Cu, Li, Na, or Ag). With the illustrative configuration of  FIG. 22 , the inner shell has been doped n-type (e.g., with Sn, In, Al, Cl, Br, I, or Ga) and the core and outer shell have been left undoped as in the configuration of  FIG. 21 . 
       FIGS. 23, 24, 25, 26, 27, 28, and 29  illustrate how quantum dots  20  may be formed using an InP (cadmium-free) system. 
     The configurations of  FIGS. 23 and 24  are four layer configurations. The undoped case is shown in  FIG. 23 . The quantum dot core is formed from InP, the first shell is formed from GaP, the second shell is formed from ZnSe, and the third shell is formed from ZnS. Quantum dot performance can be enhanced by doping the GaP shell with n-type dopant (e.g., Te, Si, S, or Se), as shown in  FIG. 24 . 
     The configurations of  FIGS. 25 and 26  are three layer configurations. The undoped case is shown in  FIG. 25 . The core is formed from InP, the inner shell is formed from GaP, and the outer shell is formed from ZnS. The example of  FIG. 26  shows how the conduction and valance bands in the InP core may shift when doped with p-type dopant (e.g. Zn, Mg, N, Si, Ga, or Be). 
     The configurations of  FIGS. 27, 28, and 29  correspond to InP core systems with three layers and ZnSe inner shells.  FIG. 27  is the undoped case. The core is formed from InP, the inner shell is formed from ZnSe, and the outer shell is formed from ZnS.  FIG. 28  shows how the bands align when the inner shell is doped with n-type dopant (e.g., Sn, In, Al, Cl, Br, I, or Ga).  FIG. 29  shows how the bands align when the inner shell is doped with p-type dopant (e.g., N, P, As, Sb, Cu, Li, Na, or Ag). 
     The examples of  FIGS. 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, and 29  are merely illustrative. In general, any suitable quantum dot semiconductor layers and dopant types (n-type or p-type) may be used to enhance performance. Quantum dots  20  may have semiconductor cores formed from semiconductors such as CdSe, CdZnSe, CdZnS, CdZnSeS, InP, InZnP, InZnSP, InZnSeP, and InSeP. Shells for these quantum dots may be formed from II-VI semiconductor materials (e.g., CdS, ZnSe, ZnS, etc.) or III-V semiconductor materials (e.g., GaP, AlP, MnS, MnSe, etc.). These materials can be doped to enhance confinement in the doped or undoped cores of the quantum dots. 
     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: 20150914
Publication Date: 20170411
Grant Date: 20170411
Priority Date: 20150128
Inventors: STECKEL JONATHAN S.
KHAN SAJJAD A.
DROLET JEAN-JACQUES P.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01L2224/16225", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/1403", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/181", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/0002", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/1403", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/16225", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/181", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/0002", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L33/56", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/00012", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/16225", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L33/501", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L2224/1403", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/181", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/0002", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/8511", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/856", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/855", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/854", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/823", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/8511", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/811", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10H20/854", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133614", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 56433492