PATENT DOCUMENT

Publication Number: US-11054696-B2
Application Number: US-201816629537-A
Country: US
Kind Code: B2

Title: Electronic devices having displays with direct-lit backlight units

Abstract:
An array of pixels in a display may be illuminated by a backlight having an array of light sources such as light-emitting diodes. The light-emitting diodes may be mounted on a printed circuit. A reflector may be formed on the printed circuit to help reflect light from the light-emitting diodes upwards through the pixels. The reflector may include two white ink layers. Multifunctional layers and other optical films may be incorporated into the backlight. These layers may include diffusers, microlens array layers, thin-film interference filters, phosphor layers, light-collimating layers, and reflective polarizers.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 pixels configured to display images; 
 a backlight configured to produce backlight illumination for the pixels, wherein the backlight comprises:
 a two-dimensional array of light sources that are configured to emit light; and 
 a light conversion layer interposed between the two-dimensional array of light sources and the pixels, wherein the light conversion layer comprises:
 a polymer substrate layer; 
 a phosphor layer on the substrate layer; 
 a first filter layer on the phosphor layer; 
 a diffuser layer; 
 polymer material that attaches the diffuser layer to the first filter layer; and 
 a second filter layer on the diffuser layer. 
 
 
 
     
     
       2. The display defined in  claim 1  wherein the first filter layer comprises a blue-transmitting-and-red-and-green-reflecting thin-film interference filter. 
     
     
       3. The display defined in  claim 1  wherein the second filter layer comprises a blue-reflecting thin-film interference filter configured to partially reflect blue light. 
     
     
       4. The display defined in  claim 1  wherein the two-dimensional array of light sources comprises an array of blue light-emitting diodes. 
     
     
       5. The display defined in  claim 4  further comprising:
 a printed circuit to which the blue light-emitting diodes are mounted; and 
 a reflector on the printed circuit with openings that receive the blue light-emitting diodes. 
 
     
     
       6. The display defined in  claim 5  wherein the reflector comprises:
 an ultraviolet-light-cured white ink layer on the printed circuit; and 
 a thermally cured white ink layer on the ultraviolet-light-cured white ink layer. 
 
     
     
       7. The display defined in  claim 1  wherein the first and second filter layers are thin-film interference filters formed from stacks of dielectric layers. 
     
     
       8. The display defined in  claim 1  further comprising a microlens array layer interposed between the light conversion layer and the two-dimensional array of light sources. 
     
     
       9. The display defined in  claim 8  wherein the microlens array layer has opposing first and second surfaces, wherein the first surface has concave lenses facing the two-dimensional array of light sources, and wherein the second surface has convex lenses facing the light conversion layer. 
     
     
       10. The display defined in  claim 8  wherein the microlens array layer includes a plurality of lenses with non-uniform lens powers. 
     
     
       11. The display defined in  claim 8  wherein the microlens array layer includes a plurality of lenses with non-uniform sizes. 
     
     
       12. The display defined in  claim 8  wherein the microlens array layer includes lenses having randomized lens center locations. 
     
     
       13. The display defined in  claim 8  wherein the microlens array layer has an array of lenses arranged in rows and columns, wherein each of the lenses has a lens center that is offset from a nominal lens center position in the array by an offset value, and wherein the offset value for each lens differs from that of the lenses in neighboring rows and columns. 
     
     
       14. The display defined in  claim 1  further comprising a prism-and-microlens layer interposed between the pixels and the light conversion layer, wherein the prism-and-microlens layer includes a polymer layer, a layer of microlenses on a first surface of the polymer layer, and an array of light-collimating prisms on an opposing second surface of the polymer layer. 
     
     
       15. The display defined in  claim 14  further comprising a reflective polarizer interposed between the prism-and-microlens layer and the pixels. 
     
     
       16. The display defined in  claim 15  further comprising a layer of light-collimating structures between the reflective polarizer and the prism-and-microlens layer. 
     
     
       17. A display, comprising:
 a two-dimensional array of light sources; 
 pixels; 
 optical films between the array of light sources and the pixels, wherein the optical films include a prism-and-microlens layer having a first surface facing the pixels and a second surface facing the two-dimensional array of light sources, wherein the prism-and-microlens layer has light-collimating structures on the first surface and an array of microlenses on the second surface; and 
 an additional microlens array layer interposed between the prism-and-microlens layer and the two-dimensional array of light sources. 
 
     
     
       18. The display defined in  claim 17  wherein the additional microlens array layer has concave microlenses facing the two-dimensional array of light sources. 
     
     
       19. The display defined in  claim 18  wherein the two-dimensional array of light sources comprises a two-dimensional array of blue light sources configured to produce blue light and wherein the display further comprises a light conversion layer between the prism-and-microlens layer and the additional microlens array layer that is configured to convert at least part of the blue light to red and green light. 
     
     
       20. The display defined in  claim 19  wherein the light conversion layer comprises:
 a polymer substrate layer; 
 a phosphor layer on the substrate layer; and 
 a blue-transmitting-and-red-and-green reflecting thin-film interference filter on the phosphor layer. 
 
     
     
       21. The display defined in  claim 20  wherein the light conversion layer further comprises:
 a diffuser layer; 
 polymer material coupled between the diffuser layer and the first filter layer; and 
 a blue-reflecting thin-film interference filter on the diffuser layer that is configured to partially reflect blue light. 
 
     
     
       22. A display, comprising:
 a two-dimensional array of light sources that produce light; 
 pixels illuminated by the light; 
 a first microlens array layer, wherein the first microlens array layer is between the pixels and the two-dimensional array of light sources; 
 a diffuser between the microlens array layer and the pixels; 
 a filter-and-phosphor layer having phosphor and a thin-film interference filter, wherein the filter-and-phosphor layer is between the diffuser and the pixels; and 
 a second microlens array layer, wherein the second microlens array layer is between the filter-and-phosphor layer and the pixels. 
 
     
     
       23. The display defined in  claim 22  further comprising:
 a first light-collimating prism film between the second microlens array layer and the pixels; and 
 a second light-collimating prism film between the first light-collimating prism film and the pixels; and 
 a reflective polarizer between the pixels and the second light-collimating prism film.

Description:
This application claims priority to U.S. provisional patent application No. 62/563,557, filed on Sep. 26, 2017, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to displays, and, more particularly, to backlit displays. 
     Electronic devices often include displays. For example, computers and cellular telephones are sometimes provided with backlit liquid crystal displays. Edge-lit backlight units have light-emitting diodes that emit light into an edge surface of a light guide plate. The light guide plate then distributes the emitted light laterally across the display to serve as backlight illumination. Direct-lit backlight units have arrays of light-emitting diodes that emit light vertically through the display. 
     Direct-lit backlights may have locally dimmable light-emitting diodes that allow dynamic range to be enhanced. If care is not taken, however, a direct-lit backlight may be bulky or may produce non-uniform backlight illumination. 
     SUMMARY 
     An array of pixels in a display may be illuminated by a backlight. The backlight may have an array of light sources such as a two-dimensional array of light-emitting diodes. The light-emitting diodes may be mounted on a printed circuit. A reflector may be formed on the printed circuit to help reflect light from the light-emitting diodes upwards through the pixels. The reflector may one or more layers of material such as one or more white ink layers or a reflective multilayer film. 
     Optical films may be incorporated into the backlight between the two-dimensional array of light-emitting diodes and the pixels. The optical films may include layers such as diffusers, microlens array layers, thin-film interference filters, phosphor layers, light-collimating layers, and reflective polarizers. In some configurations, multifunctional films may be formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of an illustrative display in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of an illustrative array of pixels in accordance with an embodiment. 
         FIGS. 4 and 5  are cross sectional side view of illustrative displays having reflective polarizer layers in accordance with embodiments. 
         FIGS. 6 and 7  are cross-sectional side views of illustrative two-dimensional light source arrays for a backlight in accordance with embodiments. 
         FIG. 8  is a cross-sectional side view of an illustrative diffuser in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an illustrative dielectric stack for a thin-film interference filter in accordance with an embodiment. 
         FIG. 10  is a graph of light reflection for an illustrative blue-light-reflecting thin-film interference filter in accordance with an embodiment. 
         FIG. 11  is a diagram of an illustrative filter-and-diffuser layer and associated light-emitting source array in accordance with an embodiment. 
         FIG. 12  is a graph of light reflection for an illustrative blue-light-transmitting-and-red-and-green-light-reflecting thin-film interference filter in accordance with an embodiment. 
         FIG. 13  is a cross-sectional side view of an illustrative filter-and-phosphor layer that may be used as a light conversion layer for light from an associated two-dimensional array of blue light-emitting diodes in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of an illustrative two-dimensional array of white light-emitting diodes in accordance with an embodiment. 
         FIGS. 15 and 16  are cross-sectional side views of illustrative filter-and-phosphor layers in accordance with embodiments. 
         FIGS. 17, 18, and 19  are cross-sectional side views of illustrative microlens array layers in accordance with embodiments. 
         FIG. 20  is a cross-sectional side view of an illustrative light-collimating layer such as a prism film in accordance with an embodiment. 
         FIG. 21  is a cross-sectional side view of an illustrative prism-and-microlens array layer in accordance with an embodiment. 
         FIG. 22  is a cross-sectional side view of an illustrative light conversion layer in accordance with an embodiment. 
         FIGS. 23 and 24  are cross-sectional side views of illustrative backlights in accordance with embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with backlit displays. The backlit displays may include liquid crystal pixel arrays or other display structures that are backlit by light from a direct-lit backlight unit. A front view of an illustrative electronic device of the type that may be provided with a display having a direct-lit backlight unit is shown in  FIG. 1 . Electronic device  10  of  FIG. 1  may be a computing device such as a laptop computer, a computer monitor containing an embedded 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 television, a computer display 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. 
     As shown in  FIG. 1 , device  10  may have a display such as display  14 . Display  14  may be 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.). 
     Housing  12  may have a stand, may have multiple parts (e.g., housing portions that move relative to each other to form a laptop computer or other device with movable parts), may have the shape of a cellular telephone or tablet computer (e.g., in arrangements in which no stand is present), and/or may have other suitable configurations. The arrangement for housing  12  that is shown in  FIG. 1  is illustrative. 
     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. 
     Display  14  may include an array of pixels  16  formed from liquid crystal display (LCD) components or may have an array of pixels based on other display technologies. A cross-sectional side view of display  14  is shown in  FIG. 2 . 
     As shown in  FIG. 2 , display  14  may include a pixel array such as pixel array  50 . Pixel array  50  may be a liquid crystal display or other display having an array of pixels  16  configured to display images for a user such as viewer  20  who is viewing display  14  in direction  22 . Backlight unit  42  (sometimes referred to as backlight structures or a backlight) may be used to provide backlight illumination  44  for pixels  16 . 
     Backlight unit  42  may include a light source array having cells with light sources such as light-emitting diodes or lasers that produce backlight illumination  44 . Backlight unit  42  may, for example, have an array of light-emitting diodes such as light-emitting diode array  36 . Light-emitting diode array  36  may contain a two-dimensional array of light-emitting diode cells  38 . Light-emitting diode cells  38  may, as an example, be arranged in rows and columns and may lie in the X-Y plane of  FIG. 2 . Each light-emitting diode cell  38  may include one or more light-emitting diodes that produce light  44 . The light produced by light-emitting diode cells  38  may be blue light, ultraviolet light, white light, and/or light of other colors. Configurations in which cells  38  include lasers may also be used, if desired. 
     During operation, light-emitting diode cells  38  may be controlled in unison by control circuitry in device  10  or may be individually controlled (e.g., to implement a local dimming scheme that helps improve the dynamic range of images displayed on pixel array  50 ). The light produced by each light-emitting diode cell  38  may travel upwardly along dimension Z through and optical films (layers)  52  before passing through pixel array  50 . Layers  52  may include diffuser layers and/or microlens array layers for diffusing and homogenizing light, light-collimating films such as brightness enhancement films (prism films) for collimating light, photoluminescent films such as phosphor layers for producing white illumination  44  from a narrowband light source (e.g., blue or ultraviolet light light-emitting diodes or lasers), thin-film interference filters and/or reflective polarizers (e.g., to help contain and/or recycle light), and/or other optical films. 
       FIG. 3  shows how pixel array  50  may be formed from liquid crystal display pixels. As shown in  FIG. 3 , pixel array  50  may form a liquid crystal display having a liquid crystal layer such as liquid crystal layer  50 C sandwiched between thin-film transistor layer  50 B and color filter layer  50 D. Configurations in which the thin-film transistor layer is located on top of layer  50 C and the color filter layer is integrated with the thin-film transistor layer or located under layer  50 C may also be used. Layers  50 D,  50 C, and  50 B may be interposed between upper polarizer  50 E and lower polarizer  50 A. 
     If desired, optical films  52  ( FIG. 2 ) may include a reflective polarizer to help recycle light and thereby enhance backlight efficiency. A reflective polarizer passes light of a given polarization while reflecting light of an orthogonal polarization. In the example of  FIG. 4 , reflective polarizer  54  has been laminated onto the underside of pixel array  50 . This type of configuration may be used, for example, where device  10  is compact and portable. In the example of  FIG. 5 , reflective polarizer  54  rests on top of other optical films  52  in backlight unit  42 . This type of arrangement may be used, for example, where device  10  is a desktop device with a stand or a wall-mounted device. 
     Illustrative configurations for light-emitting diode array  36  are shown in  FIGS. 6 and 7 . In the example of  FIG. 6 , an array of light-emitting diodes  62  is mounted (e.g., soldered) to metal traces in printed circuit board  56 . Light-emitting diode array  36  may include reflector  58  to help recycle light and enhance backlight efficiency (e.g., by reflecting any light that has been emitted from light-emitting diodes  62  back in the upwards (+Z) direction). Reflector  58  may be formed from reflective layer  60  on printed circuit board  56  (or, if desired, curved cavities formed from a reflective layer). Layer  60  may be formed from a layer of white ink (e.g., a polymer containing titanium oxide particles or other light-scattering particles) or may be formed from a thin-film interference filter film configured to form a highly reflective layer. 
     Diodes  62  may have lateral dimensions (in the X-Y plane) of about 100-150 microns (as an example). Openings may be formed in layer  60  to allow diodes  62  to be soldered to printed circuit  56 . 
     In the illustrative configuration of  FIG. 7 , reflector  58  has two layers. Initially a first layer of white ink is deposited such as white ink layer  64 . Ink layer  64  may be photopatterned titanium oxide ink that is cured by exposure to ultraviolet light. Ultraviolet-light-cured ink layer  64  may be patterned accurately to minimize gaps between layer  64  and diodes  60 . After layer  64  has been deposited and patterned, a second layer of white link such as layer  66  may be deposited. Layer  66  may be deposited and patterned using screen printing and may be cured using thermal curing. Thermally-cured white ink layer  66  may have openings that are aligned with the openings in layer  64 . Screen printing tends to be less accurate than photopatterning, so the openings in layer  66  may be made larger than the openings in layer  64  to provide a margin for slight misalignment during the deposition of layer  66 . Ink layer  66  may be more reflective than ink layer  64 , which enhances the reflectivity of reflector  58 . 
     Optical layers  52  may include one or more light-diffuser layers. In the illustrative configuration of  FIG. 8 , light-diffuser layer  68 , which may sometimes be referred to as a diffuser or diffuser layer, has a polymer substrate such as substrate  70  in which light-scattering particles  72  (e.g., titanium oxide particles) have been embedded. Other diffuser configurations may be used, if desired. 
     Optical layers  52  may include thin-film interference filter layers. These layers may be formed from a stack of inorganic and/or organic dielectric layers of alternating index of refraction (see, e.g., the dielectric stack of layers  74  of  FIG. 9 ). Thin-film interference filters may form broadband (white light) reflectors (sometimes referred to as mirrors or partial mirrors) and/or may form filters that reflect some colors of light more than others (e.g., to form a filter that has a non-flat visible light reflection spectrum). Thin-film interference filters may be configured to transmit light that is not reflected (e.g., so that light transmission is high at wavelengths that are not reflected). Dielectric stacks such as the stack of layer  74  of  FIG. 9  may be formed on polymer or glass substrates and/or may be combined with layers of material that perform other functions (e.g., as thin-film interference filter coating layers). 
     In the graph of  FIG. 10 , the reflectivity R of an illustrative thin-film interference filter for optical layers  52  has been plotted as a function of wavelength. In the example of  FIG. 10 , the thin-film interference filter forms a blue-light-reflecting filter (sometimes referred to as a partially reflecting or partially transparent filter) exhibiting a reflectivity RH for blue light. The value of reflectivity RH may be, for example, between 50% and 90%, at least 60%, less than 80%, or other suitable value (e.g., the filter may be a partially transmitting blue-reflecting filter that is partially transparent to blue light). At red and green wavelengths, this filter may have more or less reflectivity than at blue wavelengths. 
       FIG. 11  shows how a blue-reflecting thin-film interference filter of this type such as blue-light-reflecting filter  76  may be formed as a coating on diffuser  70  to form filter-and-diffuser layer  71 . During operation, light-emitting diode array  36  may emit blue light B that is partially transmitted and partially reflected by blue-light reflecting filter  76 . Transmitted light B passes upwards in the Z direction through diffuser  70  for use as backlight illumination  44 . Reflected blue light B spreads laterally in dimensions X and Y before reflecting upwards off of structures in array  36  such as reflector  58  ( FIGS. 6 and 7 ). This reduces hotspots. 
     In the graph of  FIG. 12 , the reflectivity R of another illustrative thin-film interference filter for optical layers  52  has been plotted as a function of wavelength. In the example of  FIG. 12 , the thin-film interference filter forms a blue-transmitting-and-red-and-green-reflecting filter. This type of filter may be used to control red and green light that has been produced by illuminating a phosphor layer with blue light. As shown in  FIG. 13 , for example, light-emitting diode array  36  may produce blue light B. Blue-transmitting-and-red-and-green-reflecting filter  78  may transmit blue light to a photoluminescent layer such as yellow phosphor layer  80 . In layer  80 , some of blue light B is converted into red light R and green light G for use as white backlight illumination  44 . Filter  78  may be formed as a coating on the lower surface of phosphor layer  80  to form filter-and-phosphor layer  81 . The presence of filter  78  helps reflect red and green light produced in layer  80 , thereby preventing red and green light from leaking laterally. If desired, light-emitting diode array  36  may contain white light-emitting diodes to emit white light W ( FIG. 14 ). 
     Filter  78  may be formed by depositing a dielectric stack ( FIG. 9 ) on a polymer film and laminating this film to phosphor layer  80 , as shown in  FIG. 15 . Phosphor layer  80  may include phosphor coating  84 . Coating  84  may be deposited and cured on polymer substrate  82 . In the illustrative configuration of  FIG. 16 , phosphor layer  80  includes a polymer barrier layer  86  on which filter  78  is deposited. 
     Microlens array layers such as illustrative layers  88  of  FIGS. 17, 18, and 19  may be used to spread and homogenize light  44 . Layers  88  may be relatively thin so as not to overly increase the thickness of display  14 . For example, layers  88  may be 5-100 microns thick, at least 10 microns thick, or less than 150 microns thick. In the example of  FIG. 17 , upper (outwardly facing) surface  90  of layer  88  has an array of convex lenses such as convex microlenses  94  and lower (inwardly facing) surface  92  of layer  88  has an array of concave lenses such as concave microlenses  94 . In the example of  FIG. 18 , upper surface  90  has concave microlenses  94  and lower surface  92  has concave microlenses  94 . As shown in  FIG. 19 , layer  88  may, if desired, have a planar upper surface  90  (no microlenses) and a lower surface  92  with an array of concave microlenses  94 . Configurations in which the illustrative layers  88  of  FIGS. 17, 18 , and/or  19  have lower surfaces with an array of convex microlenses  94  may also be used. 
     Microlenses  94  may have lateral dimensions of about 15-25 microns, at least 1 micron, at least 2 microns, at least 4 microns, at least 7 microns at least 10 microns, at least 20 microns, at least 40 microns, at least 100 microns, less than 300 microns, less than 150 microns, less than 75 microns, less than 30 microns, less than 15 microns, less than 5 microns, or other suitable lateral (X-Y plane) dimensions and may have heights of about 3-20 microns, at least 0.5 microns, at least 1 micron, at least 2 microns, at least 5 microns, at least 25 microns, at least 100 microns, less than 250 microns, less than 125 microns, less than 60 microns, less than 30 microns, or other suitable heights. 
     A non-uniform pattern may be used for microlenses  94  to reduce Moiré effects and to enhance light uniformity. For example, the heights, diameters, and/or center locations of lenses  94  may be randomized (e.g., lenses  94  may have a random distribution of powers produced by varying the lens curvature and clear aperture for lenses  94 , while configuring the array of lenses  94  to exhibit a desired average power). If desired, microlenses  94  may be configured to form an array of lenses of a desired periodicity (e.g., a desired pitch) but each lens in the array (e.g., the lens at each row and/or column of the array) may have a lens center position that is offset by a random (non-uniform) amount relative to its nominal position within the array. The magnitude of the random lens center offset (in one or both lateral dimensions of the array) may be 1-30% of the nominal lens-center-to-lens-center spacing (pitch) of the array, may be at least 5% of the nominal spacing, may be at least 10% of the nominal spacing, may be less than 90% of the nominal spacing, may be less than 20% of the nominal spacing, etc. With this type of arrangement, the lens center of each lens in the array may be offset from the periodic pitch of the array by an amount that differs from that of its neighboring lenses in the array. The microlens array layer has an array of lenses arranged in rows and columns, each of the lenses has a lens center that is offset from a nominal lens center position in the array by an offset value, and the offset values of the lenses are different in different rows and columns (e.g., the offset value for each lens differs from that of the lenses in neighboring rows and/or columns). The use of intentionally offset lens center locations and/or lens powers and/or other non-uniform attributes lenses  94  may help reduce frequency contrast (e.g., periodic hot spots from light-emitting diodes). 
     If desired, brightness enhancement films (sometimes referred to as prism films or light-collimating prism layers) may be used in collimating light  44 .  FIG. 20  is a cross-sectional side view of an illustrative prism film. As shown in  FIG. 20 , prism film  96  has a series of parallel ridges  98  that extend into the page and that have triangular cross-sectional shapes. Ridges  98  may face upwards (outwardly) towards the viewer to help collimate light  44  towards the viewer. 
     If desired, microlenses, light-collimating prisms, diffuser layers, phosphor layers, and/or other structures in layers  52  may be consolidated into multifunction films by sharing substrate films and/or other layers. Consider, as an example, the arrangement of  FIG. 21 . In the example of  FIG. 21 , a layer of light-collimating structures such as light-collimating prism film layer  102  has been formed on an upper surface of layer  104  and microlens array  106  has been formed on an opposing lower surface of layer  104 . Layer  104  may be formed from a low-index-of-refraction polymer (e.g., a polymer film, a cured liquid polymer layer, etc.). Layers  102  and  106  may be formed by patterning and curing liquid polymer or other transparent material to form coatings on the upper and lower surfaces of layer  104  and/or may be formed from films that are laminated to each other (e.g., using layer  104 ). 
     Another illustrative multifunction optical film structure is shown in  FIG. 22 . In the example of  FIG. 22 , filter  78  has been formed on the lower surface of filter-and-phosphor layer  81 . Filter-and-phosphor layer  81  includes substrate  82  and phosphor coating layer  80 . Filter-and-diffuser layer  71  includes filter  76  on diffuser  70 . A single optical film such as light conversion sheet  110  (sometimes referred to as a light conversion layer or conversion layer) may be formed by coupling filter  78  and layer  81  to layer  71  using polymer layer  108 . Polymer layer  108  may be formed from a low-index-of-refraction polymer material that helps reduce reflections. Use of a multifunctional layer such as conversion sheet  110  and/or other multifunctional layers (e.g., layer  100  of  FIG. 21 ) may help reduce assembly complexity when forming display  14 . 
     Illustrative backlight structures for display  14  are shown in  FIGS. 23 and 24 . 
     As shown in the illustrative configuration of  FIG. 23 , backlight unit  42  may include a light source such as light-emitting diode array  36 . Light from array  36  passes upwards in the +Z direction through the layers stacked on top of array  36  and exits backlight unit  42  as backlight illumination  44 . Microlens array layer  88  may be located above array  36 . Layer  88  may be an array layer of the type shown in  FIG. 17  or, if desired, an array layer of other types such as arrays  88  of  FIGS. 18 and 19 ). Filter-and-diffuser layer  71  may be located above layer  88 . Filter-and-phosphor layer  81  may be located above layer  71 . 
     Layer  112  may be a multifunctional layer such as layer  100  of  FIG. 21  (e.g., a layer that includes a first side with a microlens array and a second side with light-collimating prisms). In another illustrative configuration, layer  112  is formed from a lower layer (e.g., a microlens array such as lens array layer  88  of  FIG. 18  or, if desired, a microlens array layer such as layer  88  of  FIG. 17 , layer  88  of  FIG. 19 , etc.) and from an upper layer that lies above the lower layer (e.g., an upper layer such as a light-collimating prism film). 
     Light-collimating prism layer  96  may be located above layer  112 . The prisms of layer  96  may run perpendicular to the prisms of layer  112 . For example, if the prisms of layer  112  are parallel to the X axis, the prisms of layer  96  may be parallel to the Y axis. Reflective polarizer  54  may be located above layer  96 . 
     If desired, a multifunctional light-conversion layer such as conversion sheet  110  of  FIG. 22  and a multifunctional layer such as prism-and-microlens layer  100  of  FIG. 21  may be incorporated into backlight unit  42 . This type of arrangement is shown in  FIG. 24 . As shown in  FIG. 24 , microlens array layer  88  may be located above array  36 . Layer  88  may be an array layer of the type shown in  FIG. 17  or, if desired, an array layer of other types such as arrays  88  of  FIGS. 18 and 19  or other microlens array layers). Conversion sheet  110  may be located above layer  88 . Prism-and-microlens layer  100  may be located above layer  110 . Light-collimating prism layer  96  may be located above layer  100 . The prisms of layer  96  may run perpendicular to the prisms of layer  100 . For example, if the prisms of layer  100  run parallel to the X axis, the prisms of layer  96  may run parallel to the Y axis. Reflective polarizer  54  may be located above layer  96 . 
     In accordance with an embodiment, a display is provided that includes pixels configured to display images, a backlight configured to produce backlight illumination for the pixels, the backlight includes a two-dimensional array of light sources that are configured to emit light, a light conversion layer interposed between the two-dimensional array of light sources and the pixels, the light conversion layer includes a polymer substrate layer, a phosphor layer on the substrate layer, a first filter layer on the phosphor layer, a diffuser layer, polymer material that attaches the diffuser layer to the first filter layer and a second filter layer on the diffuser layer. 
     In accordance with another embodiment, the first filter layer includes a blue-transmitting-and-red-and-green-reflecting thin-film interference filter. 
     In accordance with another embodiment, the second filter layer includes a blue-reflecting thin-film interference filter configured to partially reflect blue light. 
     In accordance with another embodiment, the two-dimensional array of light sources includes an array of blue light-emitting diodes. 
     In accordance with another embodiment, the display includes a printed circuit to which the blue light-emitting diodes are mounted and a reflector on the printed circuit with openings that receive the blue light-emitting diodes. 
     In accordance with another embodiment, the reflector includes an ultraviolet-light-cured white ink layer on the printed circuit and a thermally cured white ink layer on the ultraviolet-light-cured white ink layer. 
     In accordance with another embodiment, the first and second filter layers are thin-film interference filters formed from stacks of dielectric layers. 
     In accordance with another embodiment, the display includes a microlens array layer interposed between the light conversion layer and the two-dimensional array of light sources. 
     In accordance with another embodiment, the display includes the microlens array layer has opposing first and second surfaces, the first surface has concave lenses facing the two-dimensional array of light sources, and the second surface has convex lenses facing the light conversion layer. 
     In accordance with another embodiment, the display includes the microlens array layer includes a plurality of lenses with non-uniform lens powers. 
     In accordance with another embodiment, the display includes the microlens array layer includes a plurality of lenses with non-uniform sizes. 
     In accordance with another embodiment, the display includes the microlens array layer includes lenses having randomized lens center locations. 
     In accordance with another embodiment, the microlens array layer has an array of lenses arranged in rows and columns, each of the lenses has a lens center that is offset from a nominal lens center position in the array by an offset value, and the offset value for each lens differs from that of the lenses in neighboring rows and columns. 
     In accordance with another embodiment, the display includes a prism-and-microlens layer interposed between the pixels and the light conversion layer, the prism-and-microlens layer includes a polymer layer, a layer of microlenses on a first surface of the polymer layer, and an array of light-collimating prisms on an opposing second surface of the polymer layer. 
     In accordance with another embodiment, the display includes a reflective polarizer interposed between the prism-and-microlens layer and the pixels. 
     In accordance with another embodiment, the display includes a layer of light-collimating structures between the reflective polarizer and the prism-and-microlens layer. 
     In accordance with an embodiment, a display is provided that includes a two-dimensional array of light sources, pixels and optical films between the array of light sources and the pixels, the optical films include a prism-and-microlens layer having light-collimating structures facing the pixels and an array of microlenses facing the two-dimensional array of light sources. 
     In accordance with another embodiment, the display includes a microlens array layer interposed between the prism-and-microlens layer and the two-dimensional array of light sources. 
     In accordance with another embodiment, the display includes the microlens array layer has concave microlenses facing the two-dimensional array of light sources. 
     In accordance with another embodiment, the display includes the two-dimensional array of light sources includes a two-dimensional array of blue light sources configured to produce blue light and the display further includes a light conversion layer between the prism-and-microlens layer and the microlens array layer that is configured to convert at least part of the blue light to red and green light. 
     In accordance with another embodiment, the light conversion layer includes a polymer substrate layer, a phosphor layer on the substrate layer, and a blue-transmitting-and-red-and-green reflecting thin-film interference filter on the phosphor layer. 
     In accordance with another embodiment, the light conversion layer includes a diffuser layer, polymer material coupled between the diffuser layer and the first filter layer, and a blue-reflecting thin-film interference filter on the diffuser layer that is configured to partially reflect blue light. 
     In accordance with an embodiment, a display is provided that includes a two-dimensional array of light sources that produce light, pixels illuminated by the light, a first microlens array layer, the first microlens array layer is between the pixels and the two-dimensional array of light sources, a diffuser between the microlens array layer and the pixels, a filter-and-phosphor layer having phosphor and a thin-film interference filter, the filter-and-phosphor layer is between the diffuser and the pixels, a second microlens array layer, the second microlens array layer is between the filter-and-phosphor layer and the pixels. 
     In accordance with another embodiment, the display includes a first light-collimating prism film between the second microlens array layer and the pixels, and a second light-collimating prism film between the first light-collimating prism film and the pixels, and a reflective polarizer between the pixels and the second light-collimating prism film. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20180809
Publication Date: 20210706
Grant Date: 20210706
Priority Date: 20170926
Inventors: LIU, RONG
QI, JUN
YIN, VICTOR H.
LUO, Zhenyue
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133611", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133521", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133606", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133607", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133606", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133607", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133521", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133621", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133611", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133521", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133607", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133621", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133611", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133606", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 63405406