PATENT DOCUMENT

Publication Number: US-11513392-B1
Application Number: US-202117519358-A
Country: US
Kind Code: B1

Title: Direct-lit backlight units with optical films

Abstract:
A display may have a pixel array such as a liquid crystal pixel array. The pixel array may be illuminated with backlight illumination from a direct-lit backlight unit. The backlight unit may include an array of light-emitting diodes (LEDs) on a printed circuit board. The display may have a notch to accommodate an input-output component. Reflective layers may be included in the notch. The backlight may include a color conversion layer with a property that varies as a function of position. The light-emitting diodes may be covered by a slab of encapsulant with recesses in an upper surface.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 a liquid crystal display panel; and 
 a backlight unit that provides backlight for the liquid crystal display panel, wherein the backlight unit comprises:
 an array of light-emitting diodes, wherein each light-emitting diode emits blue light; and 
 a color conversion layer, wherein the color conversion layer converts the blue light to white light, wherein the color conversion layer has a central area and an edge, wherein the central area overlaps multiple light-emitting diodes of the array of light-emitting diodes, wherein the color conversion layer has a thickness that varies as a function of position across the color conversion layer, wherein the thickness is uniform in the central area of the color conversion layer, and wherein the thickness increases from the central area towards the edge. 
 
 
     
     
       2. The electronic device defined in  claim 1 , wherein the color conversion layer has a phosphor layer that includes red quantum dots and green quantum dots distributed in a resin. 
     
     
       3. The electronic device defined in  claim 2 , wherein the color conversion layer includes an additional film over the phosphor layer and wherein the additional film also has a varying thickness. 
     
     
       4. The electronic device defined in  claim 2 , wherein the color conversion layer includes an additional film over the phosphor layer and wherein the additional film has a uniform thickness. 
     
     
       5. The electronic device defined in  claim 2 , wherein the color conversion layer further includes light-redirecting structures formed over the phosphor layer that recycle a percentage of light from the array of light-emitting diodes. 
     
     
       6. An electronic device comprising:
 a liquid crystal display panel; and 
 a backlight unit that provides backlight for the liquid crystal display panel, wherein the backlight unit comprises:
 an array of light-emitting diodes; 
 at least one light spreading layer formed over the array of light-emitting diodes; 
 a color conversion layer formed over the at least one light spreading layer; 
 a first brightness-enhancement film that is formed over the color conversion layer, wherein the color conversion layer includes a first plurality of protrusions that extend towards the first brightness-enhancement film and wherein each protrusion in the first plurality of protrusions has a rounded tip with a radius of curvature between 0.4 microns and 1.5 microns; 
 a second brightness-enhancement film that is formed over the first brightness-enhancement film; and 
 a diffusion film that is formed over the second brightness-enhancement film, wherein the second brightness-enhancement film includes a second plurality of protrusions that extend towards the diffusion film and wherein each protrusion in the second plurality of protrusions has a tip with a radius of curvature that is less than 0.3 microns. 
 
 
     
     
       7. The electronic device defined in  claim 6 , wherein the first brightness-enhancement film includes a third plurality of protrusions that extend towards the second brightness-enhancement film and wherein each protrusion in the third plurality of protrusions has a rounded tip with a radius of curvature between 0.4 microns and 1.5 microns. 
     
     
       8. The electronic device defined in  claim 6 , wherein each protrusion in the first plurality of protrusions is a pyramidal protrusion. 
     
     
       9. The electronic device defined in  claim 6 , wherein the first brightness-enhancement film has a base film and a third plurality of protrusions that extend from an upper surface of the base film away from the color conversion layer and wherein the first brightness-enhancement film includes a plurality of clear dots on a lower surface of the base film. 
     
     
       10. The electronic device defined in  claim 9 , wherein the clear dots are concentrated at an edge of the lower surface of the base film. 
     
     
       11. An electronic device comprising:
 a liquid crystal display panel; and 
 a backlight unit that provides backlight for the liquid crystal display panel, wherein the backlight unit comprises:
 an array of light-emitting diodes; 
 a slab of encapsulant formed over the array of light-emitting diodes, wherein the slab of encapsulant conforms to and directly contacts the array of light-emitting diodes; 
 a plurality of color conversion patches formed directly on an upper surface of the slab of encapsulant, wherein each color conversion patch overlaps a respective light-emitting diode in the array of light-emitting diodes; 
 at least one light spreading layer formed over the array of light-emitting diodes; and 
 a color conversion layer formed over the at least one light spreading layer. 
 
 
     
     
       12. The electronic device defined in  claim 11 , wherein each color conversion patch has a non-uniform thickness. 
     
     
       13. The electronic device defined in  claim 11 , wherein the plurality of color conversion patches is formed in corresponding recesses in the slab of encapsulant and wherein upper surfaces of the plurality of color conversion patches are coplanar with an upper surface of the slab of encapsulant.

Description:
This application claims the benefit of provisional patent application No. 63/247,715, filed Sep. 23, 2021, provisional patent application No. 63/247,722, filed Sep. 23, 2021, and provisional patent application No. 63/247,735, filed Sep. 23, 2021, which are hereby incorporated by reference herein in their entireties. 
    
    
     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. If care is not taken, however, a direct-lit backlight may be bulky or may produce non-uniform backlight illumination. 
     SUMMARY 
     A display may have a pixel array such as a liquid crystal pixel array. The pixel array may be illuminated with backlight illumination from a direct-lit backlight unit. The backlight unit may include an array of light-emitting diodes (LEDs) on a printed circuit board. 
     The backlight unit may include first, second, and third light spreading layers formed over the array of light-emitting diodes. A color conversion layer may be formed over the first, second, and third light spreading layers. First and second brightness enhancement films may be formed over the color conversion layer. A diffusion film may be formed over the brightness enhancement films. 
     The display may have a notch to accommodate an input-output component. Reflective layers may be included in the notch. An inner surface of a housing sidewall may have a mitigated reflectance portion. A bracket and foam may be included in the notch between the optical films and the liquid crystal display panel. A shielding ring may be included in the liquid crystal display panel to mitigate electrostatic discharge. Foam may be included in an upper housing with the same footprint as a high-rigidity portion of a lower housing. 
     The color conversion layer may have a property that varies as a function of position. The property may be the thickness of a phosphor layer in the color conversion layer, the concentration of red quantum dots in the color conversion layer, the concentration of green quantum dots in the color conversion layer, or the concentration of scattering dopants in the color conversion layer. Protrusions in the optical films may have rounded tips to mitigate scratching and reduce friction between adjacent optical films. 
     The light-emitting diodes may be covered by a slab of encapsulant with recesses in an upper surface. Each recess may overlap a respective light-emitting diode. The light-emitting diodes may be arranged in cells. Cells may have different sizes in different portions of the backlight. An adhesive layer having a low dielectric constant and adhesive strips may attach an LED substrate to a housing wall. A conductive adhesive may also attach the LED substrate to the housing wall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a 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 display in accordance with an embodiment. 
         FIG. 3  is a top view of an illustrative light-emitting diode array for a direct-lit backlight unit in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of an illustrative display having a direct-lit backlight unit with three light spreading layers, a color conversion layer, two brightness enhancement films, and a diffusion film in accordance with an embodiment. 
         FIG. 5  is a top view of an illustrative light spreading layer showing the layout of pyramidal protrusions in the light spreading layer in accordance with an embodiment. 
         FIG. 6  is a top view of an illustrative display with a notch that accommodates input-output components in accordance with an embodiment. 
         FIG. 7A  is a top view of an illustrative display with a notch that includes reflective patches in accordance with an embodiment. 
         FIG. 7B  is a top view of an illustrative diffusion film that includes reflective patches in accordance with an embodiment. 
         FIG. 8  is a top view of an illustrative display with a notch that has a reflective wall in accordance with an embodiment. 
         FIG. 9A  is a cross-sectional side view of an illustrative display with adhesive patches between optical films, a bracket, and foam in accordance with an embodiment. 
         FIG. 9B  is a top view of an illustrative optical film with adhesive patches in accordance with an embodiment. 
         FIG. 9C  is a top view of an illustrative diffusion film with an overlying bracket in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of an illustrative device with a housing having an interior wall having a region with mitigated reflectance in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of an illustrative device having a shielding ring to mitigate electrostatic discharge in accordance with an embodiment. 
         FIG. 12A  is a top view of an illustrative lower housing having a rigid portion in accordance with an embodiment. 
         FIG. 12B  is a top view of an illustrative upper housing having a foam structure that overlaps the rigid portion of the lower housing in accordance with an embodiment. 
         FIG. 13  is a top view of an illustrative display having electronic components along a lower edge of a LED substrate in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of an illustrative display having a chassis with a bent portion that protects electronic components along the edge of a substrate in accordance with an embodiment. 
         FIG. 15  is a cross-sectional side view of a color conversion layer with quantum dots and scattering dopants in accordance with an embodiment. 
         FIG. 16  is a graph illustrating the color variation from a light-emitting diode cell in −Δv′ (negative delta v′), quantifying the bluishness of the light, across the width of the light-emitting diode cell in accordance with an embodiment. 
         FIG. 17  is a graph illustrating how −Δv′ (negative delta v′), quantifying the bluishness of the light from a display, may vary across the width of the display in accordance with an embodiment. 
         FIG. 18  is a graph of a color conversion layer property as a function of a position within a LED cell in accordance with an embodiment. 
         FIG. 19  is a graph of a color conversion layer property as a function of a position across a display in accordance with an embodiment. 
         FIG. 20A  is a cross-sectional side view of an illustrative color conversion layer with a phosphor layer having a varying thickness and covered by an additional film having a varying thickness in accordance with an embodiment. 
         FIG. 20B  is a cross-sectional side view of an illustrative color conversion layer with a phosphor layer having a varying thickness and covered by an additional film having a uniform thickness in accordance with an embodiment. 
         FIG. 21  is a cross-sectional side view of an illustrative color conversion layer having light-redirecting structures with different shapes in accordance with an embodiment. 
         FIG. 22  is a cross-sectional side view of an illustrative backlight with color conversion patches formed on an upper surface of a slab of encapsulant in accordance with an embodiment. 
         FIG. 23  is a cross-sectional side view of an illustrative light-redirecting structure with a rounded tip in accordance with an embodiment. 
         FIG. 24  is a cross-sectional side view of an illustrative backlight unit with multiple optical films having light-redirecting structures with rounded tips in accordance with an embodiment. 
         FIG. 25  is a cross-sectional side view of an illustrative light-emitting diode that emits light with a peak brightness at a non-zero angle in accordance with an embodiment. 
         FIG. 26  is a cross-sectional side view of an illustrative backlight unit with light-emitting diodes covered by an encapsulant layer with recesses over the light-emitting diodes in accordance with an embodiment. 
         FIGS. 27A-27E  are cross-sectional side views showing illustrative recesses in encapsulant having various shapes in accordance with various embodiments. 
         FIG. 28  is a top view of an illustrative LED array having LED cells with varying pitch in accordance with an embodiment. 
         FIG. 29  is a cross-sectional side view of an illustrative electronic device showing how multiple adhesive layers may attach the LED array to a housing wall in accordance with an embodiment. 
         FIG. 30  is a top view of an illustrative electronic device showing strips of adhesive in accordance with an embodiment. 
         FIG. 31  is a rear view of an illustrative LED array showing how conductive adhesive may be formed around the periphery of the array and an adhesive layer with an array of holes is attached to a central portion of the LED array in accordance with an embodiment. 
     
    
    
     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 perspective 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, and/or may have other suitable configurations. In the arrangement of  FIG. 1 , housing  12  includes an upper housing  12 A that is rotatably coupled to lower housing  12 B. Upper housing  12 A houses display  14  and may therefore sometimes be referred to as display housing  12 A. Lower housing  12 B houses keyboard  8  and may therefore sometimes be referred to as keyboard housing  12 B. Upper housing  12 A may be coupled to lower housing  12 B by hinge structures  18 . Upper housing  12 A may rotate relative to lower housing  12 B around a bend axis that is colinear with hinge structures  18 . 
     Each one of lower housing  12 B and upper housing  12 A 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. Each one of lower housing  12 B and upper housing  12 A may be formed using a unibody configuration in which some or all of that housing 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.). 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. 
     Electronic device  10  may include additional input-output components in addition to display  14 . As shown in  FIG. 1 , electronic device  10  may include a keyboard  8  (including a plurality of keys that are pressed by the user to provide input) and a touch-sensitive area  6  (that a user may touch to control the position of a mouse on display  14 ). Touch-sensitive area  6  may sometimes be referred to as a touchpad or a trackpad. The touch-sensitive area  6  is formed on a surface of lower housing  12 B that is exposed when upper housing  12 A is opened to expose display  14 . 
     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  24 . Pixel array  24  (sometimes referred to as a display panel or liquid crystal display panel) may include an array of pixels such as pixels  16  of  FIG. 1  (e.g., an array of pixels having rows and columns of pixels  16 ). Pixel array  24  may be formed from a liquid crystal display module (sometimes referred to as a liquid crystal display or liquid crystal layers) or other suitable pixel array structures. A liquid crystal display panel for forming pixel array  24  may, as an example, include upper and lower polarizers, a color filter layer and a thin-film transistor layer interposed between the upper and lower polarizers, and a layer of liquid crystal material interposed between the color filter layer and the thin-film transistor layer. Liquid crystal display structures of other types may be used in forming pixel array  24 , if desired. 
     During operation of display  14 , images may be displayed on pixel array  24 . Backlight unit  42  (which may sometimes be referred to as a backlight, direct-lit backlight, direct-lit backlight unit, backlight layers, backlight structures, a backlight module, a backlight system, etc.) may be used in producing backlight illumination  45  that passes through pixel array  24 . This illuminates any images on pixel array  24  for viewing by a viewer such as viewer  20  who is viewing display  14  in direction  22 . 
     Backlight unit  42  may include a plurality of optical films  26  formed over light-emitting diode array  36 . Light-emitting diode array  36  may contain a two-dimensional array of light sources such as light-emitting diodes  38  that produce backlight illumination  45 . Light-emitting diodes  38  may, as an example, be arranged in rows and columns and may lie in the X-Y plane of  FIG. 2 . Light-emitting diodes  38  may be mounted on printed circuit board  50  (sometimes referred to as substrate  50 ) and may be encapsulated by encapsulant  52  (sometimes referred to as transparent encapsulant  52 , encapsulant slab  52 , etc.). The slab of encapsulant  52  may be formed continuously across the LED array and may have a planar upper surface. 
     Light-emitting diodes  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  24 ). The light produced by each light-emitting diode  38  may travel upwardly along dimension Z through optical films  26  before passing through pixel array  24 . 
     Optical films  26  may include films such as one or more light spreading layers  28 , color conversion layer  34 , one or more brightness-enhancement films  44  (sometimes referred to as collimating layers  44 ), a diffusion film  30 , and/or other optical films. 
     Light-emitting diodes  38  may emit light of any suitable color (e.g., blue, red, green, white, etc.). With one illustrative configuration described herein, light-emitting diodes  38  emit blue light. To help provide uniform backlight across backlight unit  42 , light from light-emitting diodes  38  may be spread by light spreading layer  28 . The light from the at least one light spreading layer  28  then passes through color conversion layer  34  (which may sometimes be referred to as a photoluminescent layer). 
     Color conversion layer  34  may convert the light from LEDs  38  from a first color to a different color. For example, when the LEDs emit blue light, color conversion layer  34  may include a phosphor layer (e.g., a layer of white phosphor material or other photoluminescent material) that converts blue light into white light. If desired, other photoluminescent materials may be used to convert blue light to light of different colors (e.g., red light, green light, white light, etc.). For example, one layer  34  may have a phosphor layer that includes quantum dots that convert blue light into red and green light (e.g., to produce white backlight illumination that includes, red, green, and blue components, etc.). Configurations in which light-emitting diodes  38  emit white light (e.g., so that layer  34  may be omitted, if desired) may also be used. 
     By the time light from light-emitting diodes  38  reaches the one or more brightness-enhancement films  44 , the light has been converted from blue to white and has been homogenized (e.g., by the light spreading layer). Brightness-enhancement films  44  may then collimate off-axis light to increase the brightness of the display for a viewer viewing the display in direction  22 . Diffusion film  30  may further diffuse the light to homogenize the light ultimately provided to pixel array  24 . 
       FIG. 3  is a top view of an illustrative light-emitting diode array for backlight  42 . As shown in  FIG. 3 , light-emitting diode array  36  may contain rows and columns of light-emitting diodes  38 . Each light-emitting diode  38  may be associated with a respective cell (tile area)  38 C. The length D of the edges of cells  38 C may be 2 mm, 18 mm, 1-10 mm, 1-4 mm, 10-30 mm, more than 5 mm, more than 10 mm, more than 15 mm, more than 20 mm, less than 25 mm, less than 20 mm, less than 15 mm, less than 10 mm, less than 1 mm, less than 0.1 mm, greater than 0.01 mm, greater than 0.1 mm, or any other desired size. If desired, hexagonally tiled arrays and arrays with light-emitting diodes  38  that are organized in other suitable array patterns may be used. In arrays with rectangular cells, each cell may have sides of equal length (e.g., each cell may have a square outline in which four equal-length cell edges surround a respective light-emitting diode) or each cell may have sides of different lengths (e.g., a non-square rectangular shape). The configuration of  FIG. 3  in which light-emitting diode array  36  has rows and columns of square light-emitting diode regions such as cells  38 C is merely illustrative. 
     If desired, each cell  38 C may have a light source that is formed form an array of light-emitting diode dies (e.g., multiple individual light-emitting diodes  38  arranged in an array such as a 2×2 cluster of light-emitting diodes in cell  38 C). For example, light source  38 ′ in the leftmost and lowermost cell  38 C of  FIG. 3  has been formed from a 2×2 array of light-emitting diodes  38  (e.g., four separate light-emitting diode dies). In general, each cell  38 C may include a light source  38 ′ with a single light-emitting diode  38 , a pair of light-emitting diodes  38 , 2-10 light-emitting diodes  38 , at least two light-emitting diodes  38 , at least 4 light-emitting diodes  38 , at least eight light-emitting diodes  38 , fewer than five light-emitting diodes  38 , or other suitable number of light-emitting diodes. Illustrative configurations in which each cell  38 C has a single light-emitting diode  38  may sometimes be described herein as an example. Illustrative configurations in which each cell  38 C has four light-emitting diodes  38  may also sometimes be described herein as an example. These examples are, however, merely illustrative. Each cell  38 C may have a light source  38  with any suitable number of one or more light-emitting diodes  38 . When multiple LEDs are included in a single cell, the multiple LEDs may be controlled in unison (e.g., to have the same brightness). The diodes  38  in light-emitting diode array  36  may be mounted on a printed circuit board substrate ( 50 ) that extends across array  36  or may be mounted in array  36  using other suitable arrangements. 
     As previously mentioned, more than one light spreading layer  28  and more than one brightness-enhancement film may be included in the optical films  26  of the backlight unit  42 .  FIG. 4  is a cross-sectional side view of an illustrative display having three light spreading layers, two brightness-enhancement films, and one diffusion film. 
     As shown in  FIG. 4 , a first light spreading layer  28 - 1 , a second light spreading layer  28 - 2 , and a third light spreading layer  28 - 3  are formed between light-emitting diode array  36  and color conversion layer  34 . Each light spreading layer has a similar structure, with protrusions (sometimes referred to as prisms or light-redirecting structures) extending from a substrate (base film). Light spreading layer  28 - 1  includes protrusions  102 - 1  that extend from substrate  104 - 1 . Light spreading layer  28 - 2  includes protrusions  102 - 2  that extend from substrate  104 - 2 . Light spreading layer  28 - 3  includes protrusions  102 - 3  that extend from substrate  104 - 3 . 
     Substrates  104 - 1 ,  104 - 2 , and  104 - 3  may sometimes be referred to as base film portions and may be formed from a transparent material such as polyethylene terephthalate (PET) or any other desired material. Light-redirecting structures  102 - 1 ,  102 - 2 , and  102 - 3  may be formed from the same material as base film portions  104 - 1 ,  104 - 2 , and  104 - 3  or may be formed from a different material than the base film portion. Different materials may be used in each light spreading layer if desired or the light spreading layers may be formed from the same material(s). 
     For each light spreading layer, the protrusions  102  may be formed in an array across the light spreading layer. Each protrusion  102  (sometimes referred to as light-redirecting structure  102  or prism  102 ) may split an incoming point light source into three or more points. The protrusions may have a pyramidal shape (e.g., with a square base and four triangular faces that meet at a vertex), a triangular pyramidal shape (e.g., with a triangular base and three triangular faces that meet at a vertex), partial-cube shape (e.g., corner-cubes by three square faces that meet at a vertex), a tapered pyramid structure (where each face of the pyramid has an upper portion and a lower portion that are at an angle relative to one another), or any other desired shape. Square-based pyramidal protrusions may split a point light source into four points, whereas triangular pyramidal protrusions may split a point light source into three points. 
       FIG. 5  is a top view of light spreading layer  28 - 1  showing how protrusions  102 - 1  may be arranged in an array. In this case, each protrusion has a pyramidal shape with a square base and four triangular faces that meet at a vertex  106 . 
     The example in  FIGS. 4 and 5  of the light-redirecting structures  102  being formed from protrusions from a substrate is merely illustrative. In another possible arrangement, the light-redirecting structures may be formed as recesses in the corresponding substrate film  104 . The recesses may have any desired shape (e.g., a square-based pyramidal shape, a triangular-based pyramidal shape, etc.). Additionally, the example in  FIG. 4  of light-redirecting structures  102  being formed on the lower surface of the light-redirecting layers is merely illustrative. Light-redirecting structures  102  may alternatively be formed on the upper surface in one or more of the light-redirecting layers. 
     Substrates  104 - 1 ,  104 - 2 , and  104 - 3  in  FIG. 4  may each have a matte upper surface (e.g., the surface that is higher in the positive Z-direction may be matte). The matte upper surface may mitigate undesired reflections in the backlight unit. 
     Light spreading layer  28 - 3  (e.g., substrate  104 - 3  and/or prisms  102 - 3 ) may be formed from a diffusive material such that light travelling along the Z-axis is diffused by light spreading layer  28 - 3 . In contrast, light spreading layers  28 - 1  and  28 - 2  are not formed from diffusive material. In one arrangement, substrate  104 - 3  is formed from an entirely different (and more diffusive) material than substrate  104 - 2  and  104 - 1 . In another possible arrangement, substrates  104 - 1 ,  104 - 2 , and  104 - 3  are formed from the same base material and substrate  104 - 3  includes an additive that increases the diffusion of substrate  104 - 3  relative to substrates  104 - 1  and  104 - 2  (which do not include the diffusion-increasing additive). 
     As shown in  FIG. 4 , color conversion layer  34  may include a phosphor layer  40  (e.g., a layer of white phosphor material or other photoluminescent material) that converts blue light into white light. If desired, other photoluminescent materials may be used to convert blue light from LEDs  38  to light of different colors (e.g., red light, green light, white light, etc.). For example, phosphor layer  40  may include red quantum dots  112 -R that convert blue light into red light and green quantum dots  112 -G that convert blue light into green light (e.g., to produce white backlight illumination that includes, red, green, and blue components, etc.). 
     In addition to phosphor layer  40 , color conversion layer  34  may include a partially reflective layer  41 . Partially reflective layer  41  (sometimes referred to as a dichroic layer or dichroic filter layer) may reflect all red and green light and partially reflect blue light, for example. Partially reflective layer  41  therefore allows for some of the blue light to be recycled through optical films  26 . 
     An additional film such as film  108  may also be included in the color conversion layer. The additional film  108  (sometimes referred to as an optical film, substrate, base film, etc.) may be formed from a polymer material (e.g., polyethylene terephthalate). Light-redirecting structures such as protrusions  102 - 4  may be formed on an upper surface of additional film  108 . Protrusions  102 - 4  may have any one of the arrangements described above in connection with protrusions  102 - 1 ,  102 - 2 , and  102 - 3  (e.g., an array of pyramids as shown in  FIG. 5 ). Light-redirecting structures  102 - 4  may be formed from the same material as film  108  or may be formed from a different material than the film  108 . 
     In the example of  FIG. 4 , a first brightness and enhancement film  44 - 1  and a second brightness-enhancement film  44 - 2  are included in the backlight unit. Each brightness-enhancement film has a similar structure, with protrusions (sometimes referred to as prisms or light-redirecting structures) extending from a substrate (base film). Brightness-enhancement film  44 - 1  includes protrusions  110 - 1  that extend from substrate  114 - 1 . Brightness-enhancement film  44 - 2  includes protrusions  110 - 2  that extend from substrate  114 - 2 . 
     Substrates  114 - 1  and  114 - 2  may sometimes be referred to as base film portions and may be formed from a transparent material such as polyethylene terephthalate (PET) or any other desired material. Light-redirecting structures  110 - 1  and  110 - 2  may be formed from the same material as base film portions  114 - 1  and  114 - 2  or may be formed from a different material than the base film portions. Different materials may be used in each brightness-enhancement film if desired or the light spreading layers may be formed from the same material(s). 
     In each brightness-enhancement film, the protrusions  110  may extend in strips across the light spreading layer. For example, protrusions  110 - 1  may be elongated, parallel protrusions (sometimes referred to as ridges) that extend along a longitudinal axis across the layer (e.g., parallel to the Y-axis in  FIG. 4 ). Protrusions  110 - 2  may have a similar structure as protrusions  110 - 1  (with elongated, parallel protrusions extending across the brightness-enhancement film). Protrusions  110 - 2  may be rotated (e.g., by 90°) relative to the protrusions  110 - 1 . 
     As yet another possible arrangement, protrusions  110 - 1  may have any one of the arrangements described above in connection with protrusions  102 - 1 ,  102 - 2 , and  102 - 3  (e.g., an array of pyramids as shown in  FIG. 5 ). Similarly, protrusions  110 - 2  may have any one of the arrangements described above in connection with protrusions  102 - 1 ,  102 - 2 , and  102 - 3  (e.g., an array of pyramids as shown in  FIG. 5 ). 
     The example in  FIG. 4  of the light-redirecting structures  110  being formed from protrusions from a substrate is merely illustrative. In another possible arrangement, the light-redirecting structures  110  may be formed as recesses in the corresponding substrate film  114 . Additionally, the example in  FIG. 4  of light-redirecting structures  110  being formed on the upper surface of the brightness-enhancement films is merely illustrative. Light-redirecting structures  110  may alternatively be formed on the lower surface in one or more of the brightness-enhancement films. 
     In  FIG. 4 , each adjacent pair of optical films may be separated by an air gap. The air gap may provide a refractive index difference as light enters and exits each optical film, ensuring the light from LEDs  38  is spread by the light spreading layers  28  (e.g., via refraction and/or diffraction). Alternatively, instead of including air gaps between the optical films, a low-index filler material may be formed between each adjacent optical film. 
       FIG. 6  is a top view of display  14  showing how the display may have a footprint with a notch along one of its edges. As shown in  FIG. 6 , display  14  has left and right edges that are connected by upper and lower edges. Along the upper edge of the display, a notch  62  is present. One or more input-output components  64  is included in the region of notch  62 . Input-output components  64  may include sensors components such as a camera or an ambient light sensor, light-emitting components, or any other desired input-output components. 
     LEDs for backlight unit  42  and/or other display components are omitted in notch  62 . In other words, every layer of display  14  (e.g., the liquid crystal display panel, the optical films, the LED array, etc.) may optionally have a respective notch in region  62  to accommodate input-output components  64 . As a result, no light is emitted by display  14  in notch  62 . Additionally, the area of display  14  adjacent to notch  62  (e.g., area  66  in  FIG. 6 ) may be dimmer than the remaining portions of display  14 . To better illuminate this area and ensure the display has a uniform brightness adjacent to notch  62  as in other portions of the display, one or more reflective layers may be incorporated in notch  62 . 
       FIG. 7A  is a top view of display  14  showing LED array  36 . As shown in  FIG. 7A , there is a notch in the LED array (e.g., a notch in printed circuit board  50 ) where no backlight LED components are present. Input-output components  64  may be formed in notch  62 . The input-output components may be formed on a substrate  72  (e.g., a printed circuit or other desired substrate). The display may also include protrusions  68  (sometimes referred to as alignment structures  68 , attachment structures  68 , alignment protrusions  68 , attachment structures  68 , etc.). Protrusions  68  may protrude into recesses in one or more optical films  26  for the backlight unit  42 . In this way, protrusions  68  align the optical films  26  for the backlight unit and ensure the optical films  26  do not undesirably shift during operation of the electronic device. Protrusions  68  may be formed integrally with upper housing  12 A (see  FIG. 1 ) or may be separate structures that are attached to upper housing  12 A. 
     To increase the luminance in regions of the display adjacent to notch  62 , reflective layers  70  may be formed in notch  62 . In the example of  FIG. 7A , first and second reflective layers (sometimes referred to as reflective patches) are incorporated on either side of substrate  72 . The first and second reflective layers are therefore formed on first and second opposing sides of notch  62 . The reflective layers  70  and substrate  72  may be coplanar. The reflective layers  70  and LED array (e.g., substrate  50 , LEDs  38 , and/or encapsulant  52 ) may be coplanar. Each reflective layer  70  may have an opening that receives a corresponding protrusion  68 . In other words, each protrusion  68  protrudes through the opening in a respective reflective layer. 
     Reflective layers  70  may be formed from white ink, metal, or any other desired material. Reflective layers  70  may have a reflectance that is greater than 50%, greater than 60%, greater than 70%, greater than 80%, greater than 90%, etc. Reflective layers  70  may therefore recycle light emitted from the active area of the backlight unit/display back into the active area to increase luminance in region  66  adjacent to the notch, increasing display uniformity around the notch. 
       FIG. 7B  is a top view of diffuser film  30  for backlight unit  42 . In addition to reflective layers  70 , display  14  may include reflective layers  74  on diffuser film  30 . Diffuser film  30  may have openings  76  that receive protrusions  68 . In other words, protrusions  68  protrude through the openings  76  in diffuser film  30 , thus maintaining the position of diffuser film  30 . 
     The dashed line shows the position of the LED array  36  relative to diffuser film  30 . As shown, diffuser film  30  includes portions that overlap the notch  62  in the LED array. These portions of the diffuser film  30  may overlap reflective layers  70 . The width of the notch in diffuser film  30  is therefore less than the width of the notch in LED array  36 . 
     First and second reflective layers  74  (sometimes referred to as reflective patches  74 ) are formed on diffuser film  30  on either side of the notch in the diffuser film. Each reflective layer  74  may have a footprint that overlaps a footprint of a corresponding, underlying reflective layer  70 . Reflective layers  74  may be formed from white ink, metal, or any other desired material. Reflective layers  74  may have a reflectance that is greater than 50%, greater than 60%, greater than 70%, greater than 80%, greater than 90%, etc. Reflective layers  74  may therefore recycle light emitted from the active area of the backlight/display back into the active area to increase luminance in region  66  adjacent to the notch, increasing display uniformity around the notch. 
     As shown in  FIG. 7B , each reflective patch  74  may accommodate a respective opening  76  in the diffusion film  30 . In other words, the diffusion film  30  has an upper edge. A notch is formed in the upper edge of diffusion film  30 . Diffusion film  30  has side edges and an inset edge that define the notch in the diffusion film  30 . A first portion of reflective patch  74  is formed between a respective opening  76  and the upper edge of the diffusion film  30 . A second portion of reflective layer  74  is formed between a respective opening  76  and a respective side (notch-defining) edge of the diffusion film  30 . 
     In  FIG. 7A , reflective layer  70  may have a width (e.g., the dimension parallel to the X-axis), length (e.g., the dimension parallel to the Y-axis) and height/thickness (e.g., the dimension parallel to the Z-axis). In  FIG. 7A , the reflective layer  70  has a width and length that are greater than the thickness of the reflective layer. However, this example is merely illustrative. In another desired arrangement, shown in  FIG. 8 , reflective layer  70  has a width and/or length that is smaller than the thickness of the reflective layer. 
     As shown in  FIG. 8 , reflective layer  70  may be formed in notch  62  at the interface between the notch and the active area of display  14 . In other words, reflective layer  70  is formed along the border of LED array  36  within the notch. Reflective layer  70  may be sufficiently thick to be adjacent to the edges of one or more optical films  26  in addition to LED array  36 . In other words, the height of reflective layer  70  may be equal to or greater than the height of the optical film stack such that the edge of each optical film is adjacent to a portion of reflective layer  70 . This may result in the same boundary condition for display  14  along notch  62  as along the remaining display edges (where the display and optical films are adjacent to a housing wall of upper housing  12 A). As a result, the reflection performance is consistent in notch  62  as the other active area edges, resulting in a uniform luminance adjacent to notch  62 . 
     Reflective layer  70  in  FIG. 8  (sometimes referred to as reflective wall  70 ) may be formed integrally with display housing  12 A or may be formed from a separate structure that is attached to display housing  12 A. Reflective layer  70  in  FIG. 8  may have a reflectance that is greater than 40%, greater than 50%, greater than 60%, greater than 70%, greater than 80%, greater than 90%, etc. 
     The reflective wall in  FIG. 8  may extend along the entire notch  62  (e.g., first, second, and third edges of the display that define notch  62 ) or may be discontinuous within notch  62 . For example, the reflective wall may have two or more portions separated by gaps. As an example, first and second portions of the reflective wall may be separated by a gap in region  80  in  FIG. 8 . 
     In the arrangement of  FIG. 8 , reflective wall  70  may serve as a protrusion that aligns optical films  26  within the backlight unit. In other words, optical films  26  may have openings that align with reflective wall  70  such that reflective wall  70  secures the position of optical films  26 . 
       FIG. 7A  shows an example where protrusions  68  are used to secure optical films within the display. However, other structures may additionally or instead be used to secure optical films  26  within display  14 . 
       FIG. 9A  is a cross-sectional side view of display  14  in notch region  62  showing how adhesive patches may be included between optical films in the display to ensure the optical films do not move or rotate during operation of the electronic device.  FIG. 9A  shows LED array  36  formed over a wall of housing  12 A. A portion of LED array  36  is omitted in notch region  62 . Substrate  72  (with input-output components  64  as shown in  FIG. 7A ) and reflective patches  70  are included in the notch in LED array  36 . 
     Optical films  26  including light spreading layer  28 - 1 , light spreading layer  28 - 2 , light spreading layer  28 - 3 , color conversion layer  34 , brightness-enhancement film  44 - 1 , brightness-enhancement film  44 - 2 , and diffusion film  30  are formed over LED array  36 . The optical films may have one or more portions that overlap some of notch region  62  (e.g., as shown with diffusion film  30  in  FIG. 7B ). 
     To prevent rotation, movement, and/or wrinkling of the optical films, first and second adhesive patches  82  are formed between brightness-enhancement film  44 - 1  and brightness-enhancement film  44 - 2 . Additionally, first and second adhesive patches  84  are formed between brightness-enhancement film  44 - 2  and diffusion film  30 . A first reflective patch  70 , a first adhesive patch  82 , and a first adhesive patch  84  (e.g., on the left in  FIG. 9A ) may have footprints that overlap in the Z-direction. A second reflective patch  70 , a second adhesive patch  82 , and a second adhesive patch  84  (e.g., on the right in  FIG. 9A ) may also have footprints that overlap in the Z-direction. 
     As shown in  FIG. 9A , display  14  may also include a bracket  86  and foam  88  between the upper-most optical film (diffusion film  30 ) and the bottom of pixel array  24  (sometimes referred to as display panel  24 ). A first layer of adhesive  90  is interposed between an upper surface of diffusion film  30  and a lower surface of bracket  86 . Bracket  86  may apply compressive force on the optical films  26  (e.g., in the negative Z-direction) to keep the optical films from sliding off alignment protrusions  68 . Bracket  86  may have one or more openings to accommodate input-output components  64  that are formed in the notch region. Bracket  86  may be formed from stainless steel or another desired rigid material. A second layer of adhesive  92  is interposed between an upper surface of bracket  86  and a lower surface of foam  88 . Foam  88  may be formed from a compressive material and applies compressive force on the optical films  26  (e.g., in the negative Z-direction) to keep the optical films from sliding off alignment protrusions  68 . Foam  88  also fills the gap between pixel array  24  and the optical films  26 , thus preventing deflection in the Z-direction of the pixel array and improving the structural integrity of the display. 
     Similar to as shown by openings  76  in diffusion film  30  in  FIG. 7B , each optical film  26  may have openings to accommodate protrusions  68  (e.g., in  FIG. 7A ). The alignment of the optical films is maintained by the protrusions  68 . 
       FIG. 9B  is a top view of an illustrative optical film with adhesive patches on the top surface. Specifically,  FIG. 9B  is a top view of brightness-enhancement film  44 - 1  for backlight unit  42 . As shown, brightness-enhancement film  44 - 1  may have openings  94  that receive protrusions  68 . In other words, protrusions  68  protrude through the openings  94  in brightness-enhancement film  44 - 1 , thus maintaining the position of brightness-enhancement film  44 - 1 . 
     The dashed line shows the position of the LED array  36  relative to brightness-enhancement film  44 - 1 . As shown, brightness-enhancement film  44 - 1  includes portions that overlap the notch  62  in the LED array. These portions of the brightness-enhancement film  44 - 1  may overlap reflective layers  70  (see  FIGS. 7A and 9A ). The width of the notch in brightness-enhancement film  44 - 1  is less than the width of the notch in LED array  36 . The optical films may all have a notch with the same or similar dimensions as the notch shown in  FIG. 9B . 
     First and second adhesive patches  82  (sometimes referred to as adhesive layers  82 ) are formed on brightness-enhancement film  44 - 1  on either side of the notch in the brightness-enhancement film  44 - 1 . Each adhesive layer  82  may have a footprint that overlaps a footprint of a corresponding, underlying reflective layer  70 . 
     As shown in  FIG. 9B , each adhesive patch  82  may accommodate a respective opening  94  in the brightness-enhancement film  44 - 1 . In other words, the brightness-enhancement film  44 - 1  has an upper edge. A notch is formed in the upper edge of brightness-enhancement film  44 - 1 . Brightness-enhancement film  44 - 1  has side edges and an inset edge that define the notch in the brightness-enhancement film  44 - 1 . A first portion of adhesive layer  82  is formed between a respective opening  94  and the upper edge of the brightness-enhancement film  44 - 1 . A second portion of adhesive layer  82  is formed between a respective opening  94  and a respective side (notch-defining) edge of the brightness-enhancement film  44 - 1 . 
     Brightness-enhancement film  44 - 2  may have the same or similar footprint as brightness-enhancement film  44 - 1 . Similarly, adhesive patches  84  on brightness-enhancement film  44 - 2  may have the same or similar arrangement as adhesive patches  82  on brightness-enhancement film  44 - 1 . In other words, each adhesive patch  84  may accommodate a respective opening and may overlap with a respective reflective layer  70  (and respective adhesive patch  82 ). 
       FIG. 9C  is a top view of diffusion film  30  showing the position of bracket  86  relative to the notch and openings in the diffusion film. As shown, bracket  86  extends over the notch and has a portion that covers the notch of the optical films and LED array. The portion of bracket  86  in the notch has openings  96  that accommodate input-output components  64  that are positioned in the notch. In other words, input-output components  64  may have a thickness in the Z-direction that protrudes through openings  96  in the bracket  86 . First and second opposing sides of the bracket  86  overlap the diffusion film  30  and other optical films  26  in the backlight unit. The bracket does not overlap openings  76  in the diffusion film (and the other corresponding openings in the optical films that are aligned with openings  76 ). 
     Foam  88 , meanwhile, extends over the notch and has a portion that covers the notch of the optical films and LED array. The portion of foam in the notch has openings with the same footprint as bracket openings  96 . The openings in the foam accommodate input-output components  64  that are positioned in the notch. In other words, input-output components  64  may have a thickness in the Z-direction that protrudes through the openings in the foam  88 . First and second opposing sides of the foam  88  overlap the diffusion film  30  and other optical films  26  in the backlight unit. Unlike bracket  86 , foam  88  overlaps openings  76  in the diffusion film (and the other corresponding openings in the optical films that are aligned with openings  76 ). 
       FIG. 10  is a cross-sectional side view of display  14 .  FIG. 10  shows how display  14  is formed within display housing  12 A. Display  12 A has an exterior surface  142  that forms an exterior (outer-most) surface of the electronic device  10  and an interior surface  144 . Interior surface  144  may define a cavity that contains the backlight unit  42  and pixel array  24  for display  14 . 
     As shown in  FIG. 10 , optical films  26  may be formed over LED array  36  within display housing  12 A. Optical films  26  and LED array  36  may be parallel to a rear wall  146  of the display housing. The rear wall  146  (sometimes referred to as rear wall portion  146 ) extends parallel to the XY-plane. In addition to rear wall  146 , display housing  12 A has a sidewall portion  148  (sometimes referred to as sidewall  148 ) that extends in the Z-direction. Sidewall portion  148  has a portion  150  of interior surface  144  that faces the optical films  26 . 
       FIG. 10  additionally shows how a spacer  152  may be formed between LED array  36  and optical films  26 . Spacer  152  may optionally be an adhesive spacer. Similarly, a spacer  154  may be formed between housing  12 A and pixel array  24 . Spacer  154  may optionally be an adhesive spacer. The electronic device also includes a trim structure  156 . Trim structure  156  may have a rounded upper surface. 
     To minimize the width of the border region of the display, the edges of optical films  26  may be positioned very close to portion  150  of interior surface  144  of display housing  12 A. The magnitude of gap  158  between the edge of films  26  and interior surface  144  may be less than 30 millimeters, less than 15 millimeters, less than 10 millimeters, less than 5 millimeters, less than 3 millimeters, less than 2 millimeters, less than 1 millimeter, less than 0.5 millimeters, less than 0.3 millimeters, less than 0.1 millimeters, less than 0.05 millimeters, etc. 
     If care is not taken, light may exit the edges of optical films  26  and reflect off of the interior surface  144  of display housing  12 A towards a viewer. This may cause the edge of the display to have a blue tint, particularly at off-axis viewing angles. To mitigate this issue, portion  150  of interior surface  144  of housing  12 A may be treated or coated to mitigate the reflectance of portion  150 . 
     As one example, portion  150  of housing  12 A may be laser treated to mitigate the reflectance of the housing  12 A. Housing  12 A may be formed from a metal material such as aluminum. Laser darkening may be performed on the aluminum housing to reduce reflectance. The example of using laser darkening to mitigate the reflectance in portion  150  of housing  12 A is merely illustrative. A double anodization technique may instead be used if desired. As yet another example, a black or gray ink or a less reflective metal than the rest of housing  12 A may be coated/plated on the housing in region  150 . 
     Ultimately, portion  150  of interior surface  144  of housing  12 A may have a lower reflectance (at visible light wavelengths) than the adjacent portions of interior surface  144 . Portion  150  of interior surface  144  of housing  12 A may also have a lower reflectance than exterior surface  142  of housing  12 A. The reflectance in portion  150  may be selected to be sufficiently low to mitigate the blue tint in the display at off-axis viewing without causing a dark edge in the display. The reflectance in portion  150  may be greater than 20%, greater than 30%, greater than 35%, greater than 40%, greater than 50%, less than 80%, less than 60%, less than 50% less than 45%, less than 40%, between 35% and 45%, between 30% and 50%, etc. The difference in reflectance between portion  150  of housing  12 A and the adjacent/remaining portions of housing  12 A may be greater than 10%, greater than 20%, greater than 30%, greater than 40%, greater than 50%, between 30% and 50%, etc. As one specific example, portion  150  may have a reflectance between 35% and 45% while the rest of housing  12 A has a reflectance between 70% and 80%. In some cases, the bulk of housing  12 A may have a reflectance that is within the target range for portion  150 . Therefore, portion  150  may match the rest of the housing (because no modification is required to optimize the reflectance in portion  150 ). For example, the entire housing  12 A may have a reflectance between 35% and 45%. 
       FIG. 11  is a cross-sectional side view of display  14  showing additional details regarding trim structure  156  and pixel array  24 . As shown in  FIG. 11 , pixel array  24  includes a polarizer  172 , first substrate  160  (e.g., a thin-film transistor substrate), one or more layers  162  that are formed over substrate  160 , a sealant  164  that is formed over layers  162 , one or more layers  166  that are formed over sealant  164 , a second substrate  168  (e.g., a color filter substrate) that is formed over layers  166 , and a polarizer  170  that is formed over substrate  168 . 
     Polarizers  170  and  172  may be linear polarizers that control the light emitted by the liquid crystal display. Polarizer  172  (sometimes referred to as a lower polarizer or rear polarizer) may ensure light enters the display panel with a uniform polarization. A liquid crystal layer may be formed between substrates  168  and  160  (e.g., coplanar with sealant  164 ). Thin-film transistor circuitry within substrate  160  may control the liquid crystal layer in the display to selectively rotate or not rotate the polarization of the light. Light that exits the liquid crystal layer with a polarization aligned with the pass-axis of polarizer  170  will exit the display and be viewable to a user. Light that exits the liquid crystal layer with a polarization not aligned with the pass-axis of polarizer  170  will be blocked and not be viewable to a user. Layers  162  may include multiple dielectric layers (e.g., passivation layers, liquid crystal alignment layers, etc.). Layers  166  may include multiple dielectric layers (e.g., adhesive layers, liquid crystal alignment layers, black masking layers, etc.). An additional encapsulant material  174  (sometimes referred to as potting  174 ) may be formed along the edge of display panel  24 . Color filter substrate  168  may include an array of color filter elements that impart desired colors to the light emitted by pixels within the display panel. 
     A first spacer  154  may be formed between housing  12 A and display panel  24 . Spacer  154  may optionally be an adhesive spacer. A second spacer  176  may be formed between housing  12 A and display panel  24 . Spacer  176  may optionally be an adhesive spacer. Spacers  154  and  176  may directly contact substrate  160 . Trim structure  156  may be attached to housing  12 A with an adhesive layer  178 . Trim structure  156  may have a rounded upper surface. 
     To minimize the width of the non-light-emitting border of display  14 , pixel array  24  may include traces that are close to the display edges, making the display susceptible to electrostatic discharge (ESD) damage. To prevent electrostatic discharge damage, a shield ring  180  may be formed around the periphery of the display. Shield ring  180  may have a ring shape with a footprint that matches the footprint of the edges of the display (e.g., the shield ring extends around the entire periphery of the display and accommodates the notch). Shield ring  180  therefore has a central opening in which the active area of the display is formed. Shield ring  180  may be electrically connected to ground and therefore may sometimes be referred to as grounding ring  180 . 
     Additionally, to prevent electrostatic discharge damage, sealant  164  may overlap the metal traces on the edge of substrate  160 . Thin-film transistor substrate  160  may include a number of metal traces that form thin-film transistor circuitry for the display. Sealant  164  may extend to the edge of the display panel to overlap ground ring  180  and other traces at the edges of the display panel. As previously mentioned, sealant  164  may be a liquid crystal sealant that contains the liquid crystal layer within the display. 
     Trim structure  156  may be positioned such that air gaps are present between the trim structure  156  and adjacent display panel structures to prevent electrostatic discharge damage. As shown in  FIG. 11 , trim structure  156  is separated from substrate  160  by gap  182  in the X-direction and gap  184  in the Z-direction. Gaps  182  and  184  may be greater than 5 micron, greater than 10 micron, greater than 20 micron, greater than 50 micron, greater than 100 micron, between 10 micron and 50 micron, etc. Trim structure  156  may be formed from a plastic material in some embodiments. Alternatively, trim structure  156  may be formed from a conductive material and electrically connected to housing  12 A using a conductive adhesive  178 . This type of arrangement may provide an electrostatic discharge path from trim structure  156  to housing  12 A (through adhesive  178 ). 
       FIG. 12A  is a top view of lower housing  12 B of electronic device  10 . As previously discussed, lower housing  12 B includes a keyboard  8  and a touch-sensitive area (touch pad)  6 . To maintain the structural integrity of lower housing  12 B and the input-output devices (e.g., keyboard  8  and touchpad  6 ) in the lower housing  12 B, wall structures may be included in the interior of housing  12 B. The wall structures may be aligned with the lower edge of keyboard  8  and the left and right edges of touch pad  6 . The wall structures may have a footprint that results in the lower housing  12 B having a high rigidity in region  186  of the housing. The rigidity of housing  12 B (and associated internal components) is higher in region  186  than in surrounding portions of housing  12 B. Region  186  has a first portion that extends along (and overlapping) a lower edge of keyboard  8 , a second portion that extends from the first portion and orthogonal to the first portion along (and overlapping) a left edge of touchpad  6 , and a third portion that extends from the first portion and orthogonal to the first portion along (and overlapping) a right edge of touchpad  6 . 
     The high-rigidity portion  186  may have the potential to cause damage display  14  in upper housing  12 A in an impact event. To prevent damage of this type, housing  12 A may include a foam structure.  FIG. 12B  is a top view of an upper housing  12 A with a foam structure. As shown, foam structure  188  is formed in upper housing  12 A. The foam structure  188  may be, for example, embedded in a pocket in the rear wall  146  of housing  12 A. The rear wall of housing  12 A may cover foam structure  188  on both sides in one possible arrangement. Alternatively, rear wall portion  146  of housing  12 A may cover foam structure  188  on the exterior side of the device but not the interior side of the device. In other words, foam structure  188  may be exposed at the interior of the device if desired. 
     As shown in  FIG. 12B , foam  188  has a footprint that overlaps the footprint of high-rigidity region  186  in lower housing  12 B (shown in  FIG. 12A ). When the laptop computer of  FIG. 1  is closed, foam  188  aligns with and overlaps high-rigidity region  186 . Having the foam in this area may prevent damage to display  14  during operation of the electronic device. For example, during an impact event on upper housing  12 A when the laptop computer is closed, damage to the display is mitigated by foam  188 . 
     To further improve the mechanical strength of the electronic device, the pocket in display housing  12 A that contains foam  188  may be formed with rounded corners to prevent high stress concentration areas from forming. 
       FIG. 13  is a top view of an illustrative LED array with LEDs  38  formed across printed circuit board  50 . As shown, LEDs  38  may be distributed across an active area (AA) of the display. The active area is the footprint of the display that actually emits light, and may optionally be defined by an opaque masking layer in the display stack-up. Herein, the display panel, printed circuit board, backlight unit, optical films, and other desired display layers may all be referred to as having an active area. The active area of each layer may simply refer to the footprint of each layer that overlaps with the light-emitting area of the display. In the example of  FIG. 13 , the active area has right-angled corners and a notch  62 . This example is merely illustrative. In general, the active area may have any desired shape. Printed circuit board  50  may have an inactive area (e.g., an area that does not vertically overlap the light-emitting footprint of the display) in addition to the active area. 
     In addition to LEDs being mounted on printed circuit board  50 , additional electronic components  190  (sometimes referred to as surface mount components) may be mounted to printed circuit board  50 . The printed circuit board may have an edge  50 E in the inactive area that includes components  190 . Components  190  may include, for example, driving circuitry (e.g., one or more display driver integrated circuits) that is used to control LEDs  38  in the LED array. Components  190  may be attached to the upper surface of the printed circuit board using solder. As shown in  FIG. 13 , the components  190  are consolidated in one edge  50 E of the printed circuit board. This allows only one edge of the printed circuit board to have a larger gap between the edge of the printed circuit board and the active area (e.g., distance  192  in  FIG. 13 ). The remaining three edges of the printed circuit board have a smaller gap between the edge of the printed circuit board and the active area (e.g., distance  194  in  FIG. 13 ). In other words, distance  194  is less than distance  192 . 
     During a drop or impact event, one or more optical films  26  in the backlight unit may shift into the edge of the printed circuit board with the electronic components  190 . If care is not taken, one of the optical films may strike an electronic component  190  and dislodge the electronic component from the printed circuit board. To ensure the reliability of electronic components  190 , a mechanical structure may be included along the edge of the printed circuit board to prevent the electronic components from being dislodged or damaged during a drop event. 
       FIG. 14  is a cross-sectional side view of display  14 . As shown in  FIG. 14 , substrate  50  (for LED array  36 ) extends across the display parallel to the rear wall of housing  12 A. An array of LEDs is mounted on substrate  50 . Additionally, along the edge  50 E of substrate  50 , additional electronic components  190  are mounted. 
     Display panel  24  may be mounted to a stiffening component  196 . Stiffening component  196  may sometimes be referred to as a chassis, stiffener, bracket, etc. Chassis  196  may have a first portion (e.g., portion  196 - 1 ) parallel to substrate  50 , the rear housing wall, and the XY-plane that serves as a mounting substrate for display panel  24 . In other words, an edge of the display panel  24  is mounted on portion  196 - 1  of component  196  (as shown in  FIG. 14 ). Component  196  may be formed from metal (e.g., stainless steel) and may have a high rigidity. 
     To protect electronic components  190  along the edge  50 E, chassis  196  includes an additional portion  196 - 2  that is orthogonal to substrate  50 , the rear housing wall, portion  196 - 1 , and the XY-plane. Portion  196 - 2  is parallel to the XZ-plane. Portion  196 - 2  extends between the edge of optical films  26  and electronic components  190 . Portion  196 - 2  therefore serves as a physical barrier that prevents optical films  26  from striking electronic components  190 . If a drop event causes optical films  26  to shift in the negative Y-direction, the optical films will be blocked by portion  196 - 2  of chassis  196  (and thus not reach or contact electronic components  190  along edge  50 E of substrate  50 ). 
       FIG. 15  is a cross-sectional side view of an illustrative color conversion layer  34  with scattering dopants for increasing the amount of off-axis blue light. As shown in the inset portion of  FIG. 15 , red quantum dots  112 -R output light in a random direction (e.g., the direction that red light is output is not correlated to the direction that blue light is received). Similarly, green quantum dots  112 -G output light in a random direction (e.g., the direction that green light is output is not correlated to the direction that blue light is received). To make the emission direction of blue light more random (and therefore equalize the off-axis emission of blue light to the off-axis emission of red and green light), scattering dopants  130  may be included in the phosphor layer. Scattering dopants  130  may elastically scatter blue light. This means that no energy is lost when the scattering dopants  130  receive blue light and that the wavelength of the light is not changed by the scattering dopants. However, the scattering dopants randomize the direction of the blue light. The blue light will be scattered by the scattering dopants while the red and green light will tend not to be scattered by the scattering dopants. Consequently, the distribution of red, blue, and green light may be equalized both on-axis and off-axis. 
     The average diameter of the scattering dopants may be between 5 and 20 nanometers, less than 500 nanometers, less than 100 nanometers, less than 50 nanometers, less than 20 nanometers, more than 5 nanometers, more than 1 nanometer, or any other desired diameter. The average diameter of quantum dots  112 -R and  112 -G may be more than 500 nanometers, more than 1 micron, more than 2 microns, between 1 and 3 microns, less than 5 microns, or any other desired diameter. 
     The quantum dots  112 -R and  112 -G as well as scattering dopants  130  may be distributed in a resin  132  (sometimes referred to as host resin  132 ). Resin  132  may have an index of refraction of less than 1.5, less between 1.45 and 1.55, less than 1.6, less than 1.55, greater than 1.4, between 1.4 and 1.6, or any other desired index of refraction. To achieve the desired scattering using the scattering dopants, the scattering dopants may be formed using a transparent material that has an index of refraction that is greater than 1.5, greater than 1.55, greater than 1.6, greater than 1.65, greater than 1.7, between 1.6 and 1.7, between 1.55 and 1.7, or any other desired index of refraction. The difference in refractive index between resin  132  and scattering dopants  130  may be greater than 0.05, greater than 0.1, greater than 0.15, greater than 0.2, between 0.1 and 0.2, between 0.15 and 0.2, or any other desired magnitude. 
     In general, the scattering dopants may be formed from any desired material (e.g., silicone, melamine, etc.). As one example, the scattering dopants may be formed from melamine (C 3 H 6 N 6 , having an index of refraction of 1.66) whereas the resin  132  may have a refractive index of 1.49. The density of scattering dopants  130  within the phosphor layer may be less than 10 g/m 3 , less than 5 g/m 3 , less than 3 g/m 3 , less than 2 g/m 3 , more than 1 g/m 3 , more than 2 g/m 3 , more than 3 g/m 3 , between 1 g/m 3  and 3 g/m 3 , between 1.5 g/m 3  and 2.5 g/m 3 , between 1 g/m 3  and 5 g/m 3 , or any other desired density. 
     It should be noted that the example of including red and green quantum dots in the color conversion layer is merely illustrative. In general, any desired red/green color conversion materials may be included (e.g., red and green phosphor, quantum dots, perovskite, etc.). 
     Returning to  FIG. 3  which shows LED cells  38 C, the light from the edge of a cell  38 C tends to have been recycled more than light emitted from the center of the cell. Therefore, light from the edge of the cell may be less blue than light from the middle of the cell.  FIG. 16  is a graph illustrating this effect. As shown by curve  442  in  FIG. 16 , light from the center of cell is bluer than light from the edges of the cell. The shape of the profile shown in  FIG. 16  is merely illustrative. In general, the profile may have any desired shape. 
     Within the display (e.g., the middle of the display), light from a given cell is mixed with light from neighboring cells to produce display light of a uniform color (with a particular amount of blue light). However, at the edges of the display, there may be a shortage of yellow light (because at an edge, yellow light from a neighboring cell is absent at the border). This makes light from the edge of the display bluer than light from the middle of the display. This effect is shown in the graph of  FIG. 17 . As shown by curve  444 , light from the edge of the display is bluer than light from the middle of the display. Each mark along the X-axis indicates the border of a respective cell  38 C. As shown, light exiting from the two cells closest to the edge of the display is bluer than the remaining cells in the display. This example is merely illustrative, and light exiting from any desired number of cells may be bluer than the remaining cells in the display depending on the specific display design. The curve shown in  FIG. 17  is merely illustrative and may have a different shape if desired. 
     To mitigate the color non-uniformity of the emitted light from the display, color conversion layer  34  may have non-uniformities across the active area of the display. In  FIG. 15 , phosphor layer  40  has a uniform thickness (e.g., the dimension in the Z-direction is uniform across the phosphor layer). To mitigate non-uniformities, the phosphor may instead have varying thickness. 
       FIG. 18  is a graph showing how a color conversion layer property may vary across the width of a cell in LED array  36 . The property may follow profile  200 . In the example of  FIG. 18 , the cell has two light-emitting diodes along the width of the cell. For example, the cell may include four total light-emitting diodes arranged in a 2×2 grid. Profile  200  has a local maximum over each light-emitting diode. Between the light-emitting diodes (e.g., in portions not overlapping the light-emitting diodes), the profile dips and the property has a lower magnitude. 
     Consider the example where phosphor thickness is the varied property shown in  FIG. 18 . In the areas over the LEDs, the phosphor thickness is greater than in portions between the LEDs. The greater phosphor thickness results in more blue light being converted to red and green light, mitigating the high bluishness of the light over the LEDs (as shown in  FIG. 16 ). 
     Phosphor thickness is merely one property of many that may be varied in the color conversion layer to increase the uniformity of light in the display. As other examples, the concentration of red quantum dots  112 R may be the varied property in  FIG. 18  (with a higher concentration of red quantum dots over the LEDs), the concentration of green quantum dots  112 G may be the varied property in  FIG. 18  (with a higher concentration of green quantum dots over the LEDs), the concentration of scattering particles  130  may be the varied property in  FIG. 18  (with a higher concentration of scattering particles over the LEDs), the recycling percentage achieved by light-redirecting structures  102 - 4  may be the varied property in  FIG. 18  (with the light-redirecting structures having a shape that results in higher recycling percentage over the LEDs than in portions not overlapping the LEDs), etc. 
       FIG. 19  is a graph showing how a color conversion layer property may vary across the width of the display. The property may follow profile  202 . In the example of  FIG. 19 , profile  202  increases towards the edge of the display. 
     Consider the example where phosphor thickness is the varied property as shown in  FIG. 19 . Towards the edge of the LED array, the phosphor thickness is greater than in portions in a central area of the LED array. The greater phosphor thickness results in more blue light being converted to red and green light, mitigating the high bluishness of the light in the edges of the display (as shown in  FIG. 17 ). 
     Phosphor thickness is merely one property of many that may be varied in the color conversion layer to increase the uniformity of light in the display. As other examples, the concentration of red quantum dots  112 R may be the varied property in  FIG. 19  (with a higher concentration of red quantum dots at the edges of the color conversion layer), the concentration of green quantum dots  112 G may be the varied property in  FIG. 19  (with a higher concentration of green quantum dots at the edges of the color conversion layer), the concentration of scattering particles  130  may be the varied property in  FIG. 19  (with a higher concentration of scattering particles at the edges of the color conversion layer), the recycling percentage achieved by light-redirecting structures  102 - 4  may be the varied property in  FIG. 19  (with the light-redirecting structures having a shape that results in higher recycling percentage at the edges of the color conversion layer than at a central portion of the color conversion layer), etc. 
     In  FIGS. 18 and 19 , profiles  200  and  202  both have gradual changes. This example is merely illustrative. The profiles may instead have one or more step changes if desired. In general, profiles  200  and  202  may have any desired shapes. 
     The techniques of  FIG. 18  (e.g., intra-cell color conversion layer non-uniformity) and the techniques of  FIG. 19  (e.g., inter-cell color conversion layer non-uniformity) may both be used in a single color conversion layer if desired. 
     When the phosphor layer has a varying thickness, the additional film  108  formed over the phosphor layer may also have a varying thickness such that the additional film has a planar upper surface (as shown in  FIG. 20A ). Alternatively, the color conversion layer  34  may be embossed such that the phosphor layer  40  has a varying thickness and additional film  108  has a uniform thickness across the color conversion layer (as shown in  FIG. 20B ). 
       FIG. 21  is a cross-sectional side view of an illustrative color conversion layer  34  that includes light-redirecting structures having a varying shape. In other words, for the color conversion layer  34  in  FIG. 21 , the recycling percentage of the light-redirecting structures is the property that varies as in  FIG. 18  or  FIG. 19 . A first subset  204 - 1  of the light-redirecting structures may have a first shape with a first corresponding reflectance (e.g., reflectance of light received from underlying optical films, sometimes referred to as the recycling percentage). A first second  204 - 2  of the light-redirecting structures may have a second shape with a second corresponding reflectance (recycling percentage). The shapes of the light-redirecting structures may change according to a step function or may gradually change. 
     The examples of  FIGS. 18-21  to mitigate color non-uniformity in the backlight unit are merely illustrative. Instead or in addition to these techniques, a color conversion material may be formed on encapsulant layer  52  of LED array  36 .  FIG. 22  is a cross-sectional side view showing an arrangement of this type. In this example, color conversion layer  34  is uniform across the display. The color non-uniformity is mitigated using color conversion patches  206  that are formed on an upper surface of encapsulant  52  over LEDs  38 . The color conversion patches may convert the color of light emitted by LEDs  38  (e.g., blue) to a different color (e.g., white). In other words, the wavelength of light having the peak brightness is different for light received by color conversion patches  206  than light exiting the color conversion patches. The color conversion patches may be formed from ink, quantum dots (as in phosphor layer  40 ), or any other desired material. 
     In  FIG. 22 , the color conversion patches  206  are formed in recesses in an upper surface  208  of encapsulant  52 . In this arrangement, some or all of color conversion patches  206  may be formed beneath a plane defined by upper surface  208 . In one example, shown in  FIG. 22 , the upper surface of patches  206  and upper surface  208  are coplanar (thus defining a smooth, continuous upper surface). As another possible arrangement, encapsulant  52  may have a planar upper surface without recesses. The color conversion patches  206  are then formed on the upper surface (e.g., above the plane defined by surface  208 ). Regardless of whether the color conversion patches are formed entirely below upper surface  208 , partially below upper surface  208  and partially above upper surface  208 , or entirely above upper surface  208 , the color conversion patches  206  may have either a uniform thickness or a non-uniform thickness (as in  FIG. 22 ). 
     As shown in  FIG. 4 , color conversion layer  34  includes light-redirecting structures  102 - 4  on an upper surface of film  108 . Brightness-enhancement film  44 - 1  includes light-redirecting structures  110 - 1  on an upper surface of film  114 - 1 . Brightness-enhancement film  44 - 2  includes light-redirecting structures  110 - 2  on an upper surface of film  114 - 2 . Due to this arrangement, the lower surface of film  114 - 1  may be susceptible to being scratched by the tips of light-redirecting structures  102 - 4 , the lower surface of film  114 - 2  may be susceptible to being scratched by the tips of light-redirecting structures  110 - 1 , and the lower surface of film  30  may be susceptible to being scratched by the tips of light-redirecting structures  110 - 2 . Scratching of this type may result in damage to the optical films that causes optical artifacts in the display. 
     To mitigate scratching caused by protrusions within the backlight unit, the protrusions may have rounded tips.  FIG. 23  is a cross-sectional side view of an illustrative light-redirecting structure  102 - 4 . As shown in  FIG. 23 , each light-redirecting structure  102 - 4  has a rounded tip  210 . Rounded tip  210  may be less likely to scratch the overlying film than when a non-rounded tip is used. 
     Rounded tip  210  may have a radius of curvature that is greater than 0.3 microns, greater than 0.4 microns, greater than 0.5 microns, greater than 0.7 microns, greater than 1.0 micron, less than 1.5 microns, less than 3 microns, less than 1.0 micron, between 0.4 microns and 1.5 microns, etc. 
       FIG. 24  is a cross-sectional side view of an illustrative backlight unit showing how light-redirecting structures  102 - 4  in color conversion layer  34  and light-redirecting structures  110 - 1  in brightness-enhancement film  44 - 1  may both have rounded tips similar to as shown in  FIG. 23 . The rounded tips of both structures  102 - 4  and  110 - 1  may have a radius of curvature that is greater than 0.3 microns, greater than 0.4 microns, greater than 0.5 microns, greater than 0.7 microns, greater than 1.0 micron, less than 1.5 microns, less than 3 microns, less than 1.0 micron, between 0.4 microns and 1.5 microns, etc. Structures  102 - 4  and  110 - 1  may have rounded tips regardless of whether structures  102 - 4  and  110 - 1  have a pyramidal shape (e.g., with a square base and four triangular faces that meet at a vertex), a triangular pyramidal shape (e.g., with a triangular base and three triangular faces that meet at a vertex), a partial-cube shape (e.g., corner-cubes by three square faces that meet at a vertex), a tapered pyramid structure, an elongated structure (as discussed earlier in connection with structures  110 - 1  and  110 - 2 ), etc. 
     In some cases, light-redirecting structures  110 - 2  may have rounded tips similar to as shown in  FIG. 23  (and in structures  110 - 1  and  102 - 4  in  FIG. 24 ). However, scratching the underlying surface of diffusion film  30  may not produce detrimental optical artifacts in the display. Therefore, structures  110 - 2  may have sharp tips (e.g., not rounded tips). Said another way, the radius of curvature of the tips of structures  110 - 2  may be less than the radius of curvature of the tips of structures  110 - 1  and  102 - 4  (e.g., by greater than 0.1 microns, greater than 0.2 microns, greater than 0.3 microns, greater than 0.4 microns, greater than 0.5 microns, greater than 0.7 microns, greater than 1.0 micron, less than 1.5 microns, less than 3 microns, less than 1.0 micron, between 0.4 microns and 1.5 microns, etc.). The radius of curvature of the tips of structures  110 - 2  may be less than 0.1 microns, less than 0.2 microns, less than 0.3 microns, less than 0.4 microns, etc. 
     In addition to preventing scratching, the rounded tips of structures  110 - 1  and  102 - 4  may reduce the coefficient of friction between the adjacent optical films in the backlight unit (e.g., between films  34  and  44 - 1  and between films  44 - 1  and  44 - 2 ). This reduction in friction may reduce the likelihood of the optical films wrinkling during operation of the device (e.g., due to shifting from an impact event or thermal expansion). The coefficient of friction between adjacent optical films may additionally be reduced by including clear dots  212  on the bottom surface of base film  114 - 1  and/or  114 - 2 . The clear dots  212  may be optically invisible (e.g., the clear dots do not impact the optical performance of the backlight). However, the clear dots  212  further reduce the coefficient of friction between adjacent optical films in the backlight unit. The clear dots may have a uniform distribution across the optical films (e.g., distributed evenly across a given optical film), may be concentrated at an edge of the optical films (e.g., included in a ring shape around the periphery of a given optical film but not in a central portion of that optical film), etc. The clear dots  212  may be formed from clear ink or any other desired material. 
       FIG. 25  is a cross-sectional side view of an illustrative light-emitting diode in LED array  36 . As shown, LED  38  may be mounted on substrate  50 . LED  38  may have conductive contact pads  214  that are physically and electrically connected to respective conductive contact pads  216  on substrate  50  by solder  218 . Each light-emitting diode may be formed in a respective package (e.g., that includes sapphire) that is attached to the substrate  50 . 
     A distributed Bragg reflector (DBR)  220  may be included over an upper surface of each LED  38 . In some cases, DBR  220  may reflect substantially all light generated by LED  38  such that the LED serves as a side-emitter (and emits light primarily in a direction that is parallel to the XY-plane and substrate  50 ). Alternatively, the reflectance of DBR  220  may be tuned to allow some but not all light to pass through DBR  220 . For example, angled light  222  may pass through DBR  220  instead of being reflected. 
     The tuning of DBR  220  may result in LED  38  having a peak emission angle  224  (e.g., the angle relative to the substrate  50  and XY-plane with the highest intensity of emitted light from LED  38 ) that is greater than 0 degrees, greater than 10 degrees, greater than 20 degrees, greater than 30 degrees, greater than 45 degrees, greater than 60 degrees, greater than 70 degrees, less than 10 degrees, less than 20 degrees, less than 30 degrees, less than 45 degrees, less than 60 degrees, less than 70 degrees, less than 90 degrees, between 5 degrees and 85 degrees, between 5 degrees and 45 degrees, between 1 degree and 30 degrees, between 45 degrees and 85 degrees, between 60 degrees and 89 degrees, etc. Tuning DBR  220  in this manner may increase the efficiency of the display (relative to arrangements where LED  38  is a side-emitter). 
     A reflective layer  226  may be formed on an upper surface of substrate  50  to increase the efficiency of the display. Reflective layer  226  may have a reflectance that is greater than 60%, greater than 70%, greater than 80%, greater than 90%, greater than 95%, greater than 99%, etc. Reflective layer  226  may be formed from any desired material (e.g., a white solder resist layer). Each LED may be formed in a respective opening in reflective layer  226 . 
     To mitigate hotspots in the display caused by LEDs  38 , encapsulant  52  may have recesses formed over the LEDs.  FIG. 26  is a cross-sectional side view of an illustrative backlight unit  42  of this type. As shown in  FIG. 26 , a recess  228  is formed over each LED  38  within LED array  36 . Each recess increases the amount of light from LED  38  that is reflected via total internal reflection (at the encapsulant-air interface). This better disperses light from LED  38  within the XY-plane, mitigating hotspots caused by the LEDs. 
     Recesses  228  may have any desired shape. In  FIG. 26 , the recesses  228  have a conical shape. In other words, an edge surface  230  extends in a circle (or oval) around the footprint of LED  38 . This example is merely illustrative.  FIG. 27A  shows an alternate example where recess  228  has a semi-spherical shape (e.g., the recess has spherical curvature). In  FIG. 26 , the conical shape of recesses  228  terminates at a flat surface  232 . This example is merely illustrative.  FIG. 27B  shows an alternate example where recess  228  has a conical shape with an edge surface  230  that meets at a vertex (instead of a flat surface as in  FIG. 26 ). 
     In  FIG. 27C , edge surfaces  230  of the recess are curved and meet at a vertex. In  FIG. 27D , edge surfaces  230  of the recess are curved and meet at a flat surface  232 . Recess  228  may have multiple portions with different widths. In the example of  FIG. 27E , a first portion of the recess has a first width  234  whereas a second portion of the recess has a second width  236 . The second (lower) portion may have a smaller width than the first (upper) portion of the recess. In other words, width  236  is smaller than width  234 . 
     In general, each encapsulant recess  228  may have any desired shape. Regardless of the shape of the recess, a portion of encapsulant  52  may remain present between an upper surface of LED  38  (and DBR  220 ) and the recess. The width of each recess may be greater than the width of the LED, may be greater than the 1.5 times the width of the LED, may be greater than the 2 times the width of the LED, may be less than the 3 times the width of the LED, etc. 
     Regardless of the shape of the recess, the recess may optionally be filled by a filler material  238  (as shown in  FIG. 27A , for example). The filler material may be a gray ink or a color conversion material, as possible examples. When the filler material is omitted, the recesses may instead be filled with air. 
     Incorporating recesses of the type shown in  FIGS. 26 and 27  may mitigate hotspots cased by LEDs  38  in LED array  36 . This may allow one or more optical films to be omitted from the backlight unit, reducing the thickness, manufacturing cost, and manufacturing complexity of the display. For example, when recesses  228  are included in encapsulant  52 , only five or six optical films may be needed to provide sufficiently uniform backlight to display panel  24  (instead of seven as in  FIG. 4  when no encapsulant recesses are included). 
     As shown in  FIG. 26 , an opaque dam  240  may optionally be formed between adjacent LEDs in LED array  36 . Alternatively, opaque dam  240  may be formed at the border between adjacent LED cells  38 C (see  FIG. 3 ). Dam  240  may have the same thickness  242  as encapsulant  52  or may have a smaller thickness than encapsulant  52  (such that the encapsulant is formed over and covers an upper surface of each dam  240 ). 
     An air gap may also be formed in place of dam  240 . The air gap may extend completely through encapsulant  52  (such that the encapsulant has a thickness  242  of  0 ) or only partially through encapsulant  52  (such that the encapsulant has a non-zero thickness  242  overlapped by the air gap). 
       FIG. 28  is a top view of LED array  36  showing how the pitch of the LEDs and/or the dams may be adjusted to mitigate non-uniformities in the display. As shown in  FIG. 28 , the LEDs  38  in LED array  36  are arranged in a plurality of cells  38 C. In the example of  FIG. 28 , each cell includes a 2×2 grid of LEDs  38 . The LEDs have a horizontal pitch  244  and a vertical pitch  246 . Cells  38 C are defined by dams (e.g., opaque dams) that have a horizontal pitch  248  and a vertical pitch  250 . 
     The display may be susceptible to having a lower than desired luminance at the edges. To mitigate this non-uniformity, the pitch of the LEDs and/or dams may be reduced at the edges of the display. In the example of  FIG. 28 , there are m rows and n columns of LED cells  38 C. The left-most column of LED cells (COL  1 ) and the right-most column of LED cells (COL N) may have a lower horizontal dam pitch  248  (and, correspondingly, a lower cell width) than the remaining, central columns of LED cells. Similarly, the row of LED cells that is below notch  62  (ROW  2 ) may have a lower vertical dam pitch  250  (and, correspondingly, a lower cell height) than the remaining, central rows of LED cells. The final row of LED cells in the LED array (not explicitly shown in  FIG. 28 ) may also have a lower vertical dam pitch  250  than the remaining, central rows of LED cells. Reducing the dam pitch adjacent to the edges of the display in this manner may mitigate non-uniformities at the edges of the display. 
     In  FIG. 28 , the vertical dam pitch  250  in the first row of LED cells (that is interrupted by the notch) is larger than the row  2  vertical dam pitch and the vertical dam pitch of the central rows. The vertical dam pitch in the first row is set to match the height  252  of notch  62 . This example is merely illustrative. In an alternate arrangement, multiple rows of LED cells  38 C may be interrupted by notch  62  (instead of just 1 as in  FIG. 28 ) and those rows of LED cells  38 C may have a vertical dam pitch  250  that is lower than the notch height  262 . 
     In the example of  FIG. 28 , LEDs  38  have a uniform pitch across the LED array (whether or not the LEDs are in the smaller edge cells). Alternatively, the LEDs  38  at the edge of the array (e.g., in the smaller edge cells) may also have a smaller LED pitch (in the horizontal and/or vertical direction) than in the central portion of the array. 
       FIGS. 29-31  show adhesive layers that may be used to attach LED array  36  to display housing  12 A.  FIG. 29  is a cross-sectional side view of device  10 . As shown, a first adhesive layer  254  is attached to a lower surface of LED array  36  (e.g., a lower surface of substrate  50  in LED array  36 ). Adhesive layer  254  (sometimes referred to as spacer layer  254 ) may be a single-sided adhesive where the surface coupled to LED array  36  is adhesive and the opposing surface is not adhesive. A plurality of adhesive strips  256  attach spacer layer  254  to rear wall  146  of housing  12 A. Adhesive strips  256  may be formed from discrete, elongated, and double-sided adhesive strips. A first side of each adhesive strip is attached to spacer  254  and a second side of each adhesive strip is attached to an interior surface of the rear wall of housing  12 A. 
     Additionally, a conductive adhesive  258  may be attached between an interior surface of the rear wall of housing  12 A and LED array  36  (e.g., a lower surface of substrate  50  in LED array  36 ). Specifically, the conductive adhesive  258  may be physically and electrically connected to a ground trace  260  in LED array  36 . Ground trace  260  may extend partially or completely around the periphery of LED array  36 . Conductive adhesive  258  therefore electrically connects ground trace  260  to housing  12 A (which may be conductive and serve as a ground structure). The conductive adhesive  258  has a thickness that is equal to the sum of the thickness of adhesive layer  254  and the thickness of adhesive strips  256 . In addition to serving as a grounding structure, conductive adhesive  258  may mitigate undesired electrostatic discharge in device  10 . 
     Adhesive layer  256  may be formed in strips (instead of a continuous plane like layer  254 ) to increase the reworkability of the display. In other words, stretching and heating may be used to deliberately remove adhesive strips  256  if desired. 
     Adhesive layer  254  may be formed from a layer having a low dielectric constant to mitigate parasitic capacitances and corresponding system power loss. The dielectric constant of adhesive layer  254  may be less than 10, less than 6.0, less than 5.0, less than 4.0, less than 3.0, less than 2.0, etc. 
     The thickness of the strips  256  (e.g., the dimension parallel to the Z-direction) may be less than 100 microns, less than 80 microns, less than 60 microns, greater than 30 microns, between 30 microns and 70 microns, etc. The thickness of the spacer  254  (e.g., the dimension parallel to the Z-direction) may be less than 150 microns, less than 100 microns, less than 80 microns, less than 60 microns, greater than 50 microns, greater than 70 microns, between 50 microns and 100 microns, etc. The thickness of the conductive adhesive  258  (e.g., the dimension parallel to the Z-direction) may be less than 250 microns, less than 150 microns, less than 100 microns, greater than 100 microns, greater than 120 microns, between 100 microns and 150 microns, etc. 
       FIG. 30  shows how adhesive strips  256  may be elongated in the Y-direction. Each strip extends along a longitudinal axis that is parallel to the Y-direction. In other words, the length of each strip may be longer than the width of each strip and the length of each strip may extend parallel to the Y-axis. This example is merely illustrative. The adhesive strips may instead extend parallel to the X-axis if desired. Each strip may have a length that is more than 3× greater than the width, more than 5× greater than the width, more than 10× greater than the width, more than 20× greater than the width, more than 50× greater than the width, etc. 
       FIG. 31  is a rear view of LED array  36  showing the relative positions of conductive adhesive  258  and adhesive layer  254 . As shown, conductive adhesive  258  extends around the periphery of the LED array. In the example of  FIG. 31 , conductive adhesive  258  extends along the left, upper, and right edges of the LED array (but not the lower edge of the LED array). The conductive adhesive  258  therefore surrounds the LED array on three out of four sides. The footprint of ground trace  260  (shown explicitly in  FIG. 29 ) may be the same or approximately the same as the footprint of conductive adhesive  258 . In other words, the ground trace  260  also surrounds the LED array on three out of four sides (along the left, upper, and right edges). The conductive adhesive  258  (and grounding trace  260  may be routed around the notch  62  in LED array  36 , as shown in  FIG. 31 . 
     Adhesive layer  254  covers a central area of the LED array  36 . The adhesive layer  254  may have a notch to accommodate notch  62  in the LED array  36 . Adhesive layer  254  may have an array of openings  264 . Each opening  264  may be a through-hole that extends entirely through the adhesive layer (e.g., from a first surface of the adhesive layer to a second, opposing surface of the adhesive layer). The openings  264  allow for the passage of air during the lamination process, mitigating bubble formation. Each opening  264  may have a diameter (or width) that is greater than 0.1 millimeters, greater than 0.5 millimeters, greater than 1.0 millimeter, greater than 1.5 millimeters, greater than 3.0 millimeters, less than 0.1 millimeters, less than 0.5 millimeters, less than 1.0 millimeter, less than 1.5 millimeters, less than 3.0 millimeters, between 1.0 millimeters and 2.0 millimeters, etc. The total number of openings  264  in adhesive layer  254  may be greater than 200, greater than 300, greater than 400, greater than 500, greater than 750, greater than 1000, less than 200, less than 300, less than 400, less than 500, less than 750, less than 1000, between 250 and 750, etc. 
     It should be noted that any of the adhesive layers mentioned herein (e.g., layers  82 ,  84 ,  90 ,  92 ,  152 ,  154 ,  176 ,  178 ,  254 ,  256 , and  258 ) may be formed from pressure sensitive adhesive (PSA), optically clear adhesive (OCA), liquid optically clear adhesive (LOCA), a cured adhesive, or any other desired type of adhesive. 
     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: 20211104
Publication Date: 20221129
Grant Date: 20221129
Priority Date: 20210923
Inventors: LUO, Zhenyue
AMOOREZAEI, MORTEZA
WANG, QINGBING
YOU, CHENHUA
JIAO, MEIZI
LEE, CHUNGJAE
SPECHLER, JOSHUA A.
ZHU, XINYU
GU, MINGXIA
QI, JUN
BENSON, ERIC L.
YIN, VICTOR H.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133607", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133614", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133611", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133609", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0053", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133607", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133614", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133611", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0058", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133608", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133605", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/169", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1662", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2202/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133606", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13338", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133614", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133607", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133601", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 84230892