METHOD FOR FABRICATING THE BACKLIGHT

BACKGROUND

Field

[0001] The present disclosure relates generally to backlights for displays. More particularly, it relates to backlights including patterned reflectors.

Technical Background

[0002] Liquid crystal displays (LCDs) are commonly used in various electronics, such as cell phones, laptops, electronic tablets, televisions, and computer monitors. LCDs are light valve-based displays in which the display panel includes an array of individually addressable light valves. LCDs may include a backlight for producing light that may then be wavelength converted, filtered, and/or polarized to produce an image from the LCD. Backlights may be edge-lit or direct-lit. Edge-lit backlights may include a light emitting diode (LED) array edge- coupled to a light guide plate that emits light from its surface. Direct-lit backlights may include a two-dimensional (2D) array of LEDs directly behind the LCD panel.

[0003] Direct-lit backlights may have the advantage of improved dynamic contrast as compared to edge-lit backlights. For example, a display with a direct-lit backlight may independently adjust the brightness of each LED to set the dynamic range of the brightness across the image. This is commonly known as local dimming. To achieve desired light uniformity and/or to avoid hot spots in direct-lit backlights, however, a diffuser plate or film may be positioned at a distance from the LEDs, thus making the overall display thickness greater than that of an edge-lit backlight. Lenses positioned over the LEDs have been used to improve the lateral spread of light in direct-lit backlights. The optical distance (OD) between the LEDs and the diffuser plate or film in such configurations (e.g., from at least 10 to typically about 20-30 millimeters), however, still results in an undesirably high overall display thickness and/or these configurations may produce undesirable optical losses as the backlight thickness is decreased. While edge-lit backlights may be thinner, the light from each LED may spread across a large region of the light guide plate such that turning off individual LEDs or groups of LEDs may have only a minimal impact on the dynamic contrast ratio. SUMMARY

[00041 Some embodiments of the present disclosure relate to a backlight. The backlight includes a substrate, a plurality of light sources, a reflective layer, a light guide plate, and a plurality of first patterned reflectors. The plurality of light sources are proximate the substrate. The reflective layer is on the substrate. The light guide plate is proximate the plurality of light sources. The light guide plate includes a pattern of light extractors. The plurality of first patterned reflectors are on the light guide plate. Each first patterned reflector is aligned with a corresponding light source.

[0005] Yet other embodiments of the present disclosure relate to a backlight. The backlight includes a substrate, a plurality of light sources, a reflective layer, a light guide plate, a plurality of patterned reflectors, and a low index material. The plurality of light sources are proximate the substrate. The reflective layer is on the substrate. The light guide plate is proximate the plurality of light sources. The light guide plate comprises a pattern of light extractors and a refractive index. The plurality of patterned reflectors are over the light guide plate. Each patterned reflector is aligned with a corresponding light source. The low index material is between the light guide plate and the plurality of patterned reflectors. The low index material comprises a refractive index less than the refractive index of the light guide plate.

[0006] Yet other embodiments of the present disclosure relate to a method for fabricating a backlight. The method includes arranging a plurality of light sources on a substrate and applying a reflective layer on the substrate. The method further includes applying a pattern of light extractors to a light guide plate and applying a plurality of first patterned reflectors on the light guide plate. The method further includes arranging the light guide plate over the plurality of light sources such that each patterned reflector is aligned with a corresponding light source.

[0007} The backlights disclosed herein are thin direct-lit backlights with improved light efficiency. The backlights have an improved ability to hide light sources resulting in a thinner backlight. The improved ability to hide the light sources allows for the removal of so-called “hot” spots directly above the light sources of the backlight, thus resulting in a uniform brightness across the display.

[0008] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings. [0009] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIGS. 1A-1D are various views of an exemplary backlight including patterned reflectors;

[0011] FIGS. 2A-2D are cross-sectional views of exemplary patterned reflectors on a light guide plate;

[0012] FIG. 3 is a cross-sectional view of an exemplary liquid crystal display (LCD) including a separate layer including patterned reflectors;

[0013] FIG. 4 is a cross-sectional view of an exemplary LCD including a diffuser plate with patterned reflectors;

]0014] FIGS. 5A-5C are various views of an exemplary backlight including patterned reflectors and absorptive elements;

[0015] FIG. 6 is a simplified cross-sectional view of an exemplary backlight including a patterned reflector and an absorptive element;

[0016] FIGS. 7A and 7B are cross-sectional views of exemplary backlights including patterned reflectors and a low index material;

[0017] FIG. 8 is a simplified cross-sectional view of an exemplary backlight including a top emitting light source, a patterned reflector, and a low index material; and

[0018] FIGS. 9A-9C are flow diagrams illustrating an exemplary method for fabricating a backlight.

DETAILED DESCRIPTION

|0019] Reference will now be made in detail to embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. However, this disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. [0020] Ranges can be expressed herein as from“about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent“about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0021] Directional terms as used herein - for example up, down, right, left, front, back, top, bottom, vertical, horizontal - are made only with reference to the figures as drawn and are not intended to imply absolute orientation.

[0022] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus, specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification.

[0023] As used herein, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Thus, for example, reference to“a” component includes aspects having two or more such components, unless the context clearly indicates otherwise.

[0024] Referring now to FIGS. 1 A-1 D, various views of an exemplary backlight 100 are depicted. FIG. 1A is a cross-sectional view of backlight 100. Backlight 100 may include a substrate 102, a reflective layer 104, a plurality of light sources 106, a light guide plate 108, and a plurality of patterned reflectors 1 12. The plurality of light sources 106 are arranged on substrate 102 and are in electrical communication with the substrate 102. The reflective layer 104 is on the substrate 102 and surrounds each light source 106. The light guide plate 108 is over the plurality of light sources 106 and optically coupled to each light source 106. In certain exemplary embodiments, an optical adhesive 109 may be used to couple the plurality of light sources 106 to the light guide plate 108. The optical adhesive (e.g., phenyl silicone) may have a refractive index greater than or equal to a refractive index of the _. light guide plate 108. The plurality of patterned reflectors 112 are arranged on the upper surface of the light guide plate 108. Each patterned reflector 1 12 is aligned with a corresponding light source 106.

[0025] FIG. IB is a top view of the plurality of light sources 106 and reflective layer 104 on substrate 102. Light sources 106 are arranged in a 2D array including a plurality of rows and a plurality of columns. While nine light sources 106 are illustrated in FIG. IB in three rows and three columns, in other embodiments backlight 100 may include any suitable number of light sources 106 arranged in any suitable number of rows and any suitable number of columns. Light sources 106 may also be arranged in other periodic patterns, for example, a hexagonal or triangular lattice, or as quasi-periodic or non-strictly periodic patterns. For example, the spacing between light sources 106 may be smaller at the edges and/or corners of the backlight. Substrate 102 may be a printed circuit board (PCB), a glass or plastic substrate, or another suitable substrate for passing electrical signals to each light source 106 for individually controlling each light source. Substrate 102 may be a rigid substrate or a flexible substrate. The reflective layer 104 may include, for example, metallic foils, such as silver, platinum, gold, copper, and the like; dielectric materials (e.g., polymers such as polytetrafluoroethylene (PTFE)); porous polymer materials, such as polyethylene terephthalate (PET), Poly(methyl methacrylate) (PMMA), polyethylene naphthalate (PEN), polyethersulfone (PES), etc., multilayer dielectric interference coatings, or reflective inks, including white inorganic particles such as titania, barium sulfate, etc., or other materials suitable for reflecting light.

[0026] Each of the plurality of light sources 106 may, for example, be an LED, a micro- LED, an organic LED (OLED), or another suitable light source having a wavelength ranging from about 100 nanometers to about 750 nanometers. The light from each light source 106 is optically coupled to the light guide plate 108. As used herein, the term“optically coupled” is intended to denote that a light source is positioned at a surface of the light guide plate 108 and is in an optical contact with the light guide plate 108 directly or through an optically clear adhesive 109, so as to introduce light into the light guide plate that at least partially propagates due to total internal reflection. The light from each light source 106 is optically coupled to the light guide plate 108 such that a first portion of the light travels laterally in the light guide plate 108 due to the total internal reflection and is extracted out of the light guide plate by the pattern of light extractors 1 10, and a second portion of the light travels laterally between the reflective layer 104 and the patterned reflectors 1 12 due to multiple reflections at the reflective surfaces of the reflective layer 104 and the patterned reflectors 1 12 or between an optical film stack (shown in Fig. 3) and the reflective layer 104.

[0027] According to various embodiments, the light guide plate 108 may include any suitable transparent material used for lighting and display applications. As used herein, the term“transparent” is intended to denote that the light guide plate has an optical transmission of greater than about 70 percent over a length of 500 millimeters in the visible region of the spectrum (about 420-750 nanometers). In certain embodiments, an exemplary transparent material may have an optical transmittance of greater than about 50 percent in the ultraviolet (UV) region (about 100-400 nanometers) over a length of 500 millimeters. According to various embodiments, the light guide plate may include an optical transmittance of at least 95 percent over a path length of 50 millimeters for wavelengths ranging from about 450 nanometers to about 650 nanometers.

[0028] The optical properties of the light guide plate may be affected by the refractive index of the transparent material. According to various embodiments, the light guide plate 108 may have a refractive index ranging from about 1.3 to about 1.8. In other embodiments, the light guide plate 108 may have a relatively low level of light attenuation (e.g., due to absorption and/or scattering). The light attenuation (a) of the light guide plate 108 may, for example, be less than about 5 decibels per meter for wavelengths ranging from about 420-750 nanometers. The light guide plate 108 may include polymeric materials, such as plastics (e.g., polymethyl methacrylate (PMMA), methylmethacrylate styrene (MS), polydimethylsiloxane (PDMS)), polycarbonate (PC), or other similar materials. The light guide plate 108 may also include a glass material, such as aluminosilicate, alkali-aluminosilicate, borosilicate, alkali-borosilicate, aluminoborosilicate, alkali-aluminoborosilicate, soda lime, or other suitable glasses. Nonlimiting examples of commercially available glasses suitable for use as a glass light guide plate 108 include EAGLE XG®, Lotus™, Willow®, Iris™, and Gorilla® glasses from Corning Incorporated.

[0029] FIG. 1C is a top view of the pattern of light extractors 110 of the light guide plate 108. The pattern of light extractors 1 10 includes a plurality of gaps 1 1 1. Each gap 1 1 1 is aligned with a corresponding light source 106 and a corresponding patterned reflector 1 12. The light guide plate 108 includes a pattern of light extractors 1 10 on the lower surface of the light guide plate. In certain exemplary embodiments, light guide plate 108 may include a pattern of light extractors on the upper surface (e.g., see FIGS. 3-4) of the light guide plate in place of or in addition to the pattern of light extractors 1 10 on the lower surface of the light guide plate. As used herein, the term“pattern” is intended to denote that the light extractors are present on or under the surface of the light guide plate in any given pattern or design, which may, for example, be random or arranged, repetitive or non-repetitive, uniform or non-uniform. In other embodiments, the light extractors may be located within the matrix of the light guide plate adjacent to the surface (e.g., below the surface). For example, the light extractors may be distributed across the surface (e.g., as textural features making up a roughened or raised surface) or may be distributed within and throughout the light guide plate or portions thereof (e.g., as laser-damaged sites or features).

f0030] Suitable methods for creating such light extractors may include printing, such as inkjet printing, screen printing, microprinting, and the like, embossing or micro-replication, such as UV or thermal embossing in a light guide plate material itself or an additional material coated on the surface of the light guide plate, texturing, mechanical roughening, etching, injection molding, coating, laser damaging, or any combination thereof. Non-limiting examples of such methods include, for instance, acid etching a surface, coating a surface with TiCh, particle filled ink or paint, coating a surface with a transparent ink containing micro polymer or glass beads of varying sizes, and laser damaging the substrate by focusing a laser on a surface or within the substrate matrix. Each gap 1 11 may be square, circular, or any other suitable shape. In one aspect, each gap 1 1 1 allows the corresponding light source 106 to be optically coupled to the light guide plate 108. In another aspect, the size of each gap 111 controls the impact of the pattern of light extractors 110 on the luminance around each light source 106. For example, a larger gap 1 1 1 means a larger distance between the pattern of light extractors 110 and each light source 106, resulting in a lower luminance near each light source. In comparison, a smaller gap 1 1 1 means a smaller distance between the pattern of light extractors and the light source 106, resulting in a higher luminance near the light source. (0031) FIG. ID is a top view of the plurality of patterned reflectors 1 12 on the light guide plate 108. Each patterned reflector 1 12 may include a first area 1 13 and a second area 1 14. The first area 1 13 may be more reflective than the second area 114, and the second area 114 may be more transmissive than the first area 1 13. The patterned reflector 1 12 may additionally have a third, a fourth and so on areas with different properties, or its properties may be changing in a continuous and smooth way with distance from its center. While in the embodiment illustrated in FIG. ID, each patterned reflector 1 12 is circular in shape, in other embodiments each patterned reflector 1 12 may have another suitable shape (e.g., rectangular, hexagonal, etc.). With the patterned reflectors 1 12 fabricated directly on the upper surface of the light guide plate 108, the patterned reflectors 1 12 increase the ability of hiding the light sources 106. Fabricating patterned reflectors 1 12 directly on the upper surface of the light guide plate 108 also saves space. In certain exemplary embodiments, each patterned reflector 1 12 is a diffuse reflector, such that each patterned reflector 1 12 further enhances the performance of the backlight 100 by scattering some light rays at high enough angles such that they can propagate in the light guide plate 108 by total internal reflection. Such rays will then not experience multiple bounces between the patterned reflectors 1 12 and the reflective layer 104 or between an optical film stack and the reflective layer 104 and therefore avoid loss of optical power, thereby increasing the backlight efficiency. In certain exemplary embodiments, each patterned reflector 112 is a specular reflector. In other embodiments, some areas of each patterned reflector 1 12 have a more diffuse character of reflectivity and some areas have a more specular character of reflectivity.

[0032] FIG. 2A is a cross-sectional view of an exemplary patterned reflector 1 12a. In certain exemplary embodiments, patterned reflector 1 12a may be used for each patterned reflector 112 of FIGS. 1A and ID. Patterned reflector 112a is arranged on the upper surface of the light guide plate 108 and is aligned with the light source 106. Patterned reflector 1 12a includes a single layer having a constant thickness. Patterned reflector 1 12a may be formed, for example, by printing (e.g., inkjet printing, screen printing, microprinting, etc.) a pattern with white ink, black ink, metallic ink, or other suitable ink. Patterned reflector 1 12a may also be formed by first depositing a continuous layer of a white or metallic material, for example by physical vapor deposition (PVD) or any number of coating techniques such as for example slot die or spray coating, and then patterning the layer by photolithography or other known methods of area-selective material removal. Patterned reflector 1 12a may have a varying optical density. The varying optical density may be achieved, for example, by printing a variable proportion of clear and reflective ink on light guide plate 108 or by printing an ink of variable thickness. The varying optical density may also be achieved by making the patterned reflector 1 12a discontinuous, meaning that the reflective material is present in some places and not present in some other places, according to a predetermined pattern. In certain exemplary embodiments, the patterned reflector 1 12a could be a continuous layer with small gaps where the reflective material is not present. In other embodiments, the patterned reflector 1 12a may consist of relatively small isolated patches of reflective material separated by relatively large empty space. The proportion of covered and empty space within the patterned reflector may vary between 0 and 100 percent.

[0033| FIG. 2B is a cross-sectional view of an exemplary patterned reflector 1 12b. In certain exemplary embodiments, patterned reflector 1 12b may be used for each patterned reflector 1 12 of FIGS. 1 A and I D. Patterned reflector 1 12b is arranged on the upper surface of the light guide plate 108 and is aligned with the light source 106. Patterned reflector 1 12b includes a first layer 120 on the upper surface of the light guide plate 108 and a second layer 122 on the upper surface of the first layer 120. In certain exemplary embodiments, each of the first layer 120 and the second layer 122 may have a constant thickness. The constant thickness of the first layer 120 and the second layer 122, however, may be different for each layer. In other embodiments, each of the first layer 120 and the second layer 122 may have a variable thickness.

[00341 Each of the first layer 120 and the second layer 122 may have a varying optical density. The second layer 122 may vary from the first layer 120 in reflection, absorption, and/or transmission. Each of the first layer 120 and the second layer 122 may be absorptive, for example, by containing black material. Each of the first layer 120 and the second layer 122 may be reflective, for example, by containing white or metallic material. Each of the first layer 120 and the second layer 122 may also be both absorptive and reflective by containing more than one type of material, such as inks with added metal particles (e.g., silver, aluminum, etc.). In this case, the absorptive and or reflective properties may vary over the patterned reflector area.

[00351 FIG· 2C is a cross-sectional view of an exemplary patterned reflector 1 12c. In certain exemplary embodiments, patterned reflector 1 12c may be used for each patterned reflector 112 of FIGS. 1A and ID. Patterned reflector 1 12c is arranged on the upper surface of the light guide plate 108 and is aligned with the light source 106. Patterned reflector 1 12c includes a first layer 124 on the upper surface of the light guide plate 108, a second layer 126 on the upper surface of the first layer 124, and a third layer 128 on the upper surface of the second layer 126. In certain exemplary embodiments, each of the first layer 124, the second layer 126, and the third layer 128 may have a constant thickness. The constant thickness of the first layer 124, the second layer 126, and the third layer 128, however, may be different for each layer.

[0036] Each of the first layer 124, the second layer 126, and the third layer 128 may have a varying optical density. Each of the first layer 124, the second layer 126, and the third layer 128 may vary from each other in reflection, absorption, and/or transmission. Each of the first layer 124, the second layer 126, and the third layer 128 may be absorptive, for example, by containing black material. Each of the first layer 124, the second layer 126, and the third layer 128 may be reflective, for example, by containing white or metallic material. Each of the first layer 124, the second layer 126, and the third layer 128 may also be both absorptive and reflective by containing more than one type of material, such as inks with added metal particles (e.g., silver, aluminum, etc.). In this case, the absorptive and/or reflective properties may vary over the patterned reflector area. In certain exemplary embodiments, the first layer 124 and the third layer 128 are more reflective than the second layer 126, and the second layer 126 is more absorptive than the first layer 124 and the third layer 128. In this case, patterned reflector 1 12c reflects most of the light emitted from the top surface of the light source 106 as well as light redirected from a diffuser plate or other optical film above the light guide plate 108, while effectively blocking most of the light going directly through the patterned reflector 1 12c. Each of the layers 124, 126, and 128 could also be discontinuous with the proportion of the layer area where the reflective or absorptive material is present versus the layer area where it is not present being between 0 and 100 percent. Although all three layers 124, 126, and 128 are shown in FIG. 2C as having the same size (i.e., width), in various embodiments they may have different sizes. For example, the size of the layer 126 may be smaller than the layers 124 and 128, in which case layers 124 and 128 will be directly on top of each other at the periphery of the patterned reflector 1 12c. In other embodiments, the size of the layer 126 may be larger than layers 124 and 128, in which case the periphery of the layer 126 will be directly on the light guide plate top surface. In reference to Fig. ID, different areas 113, 114 of the patterned reflector 1 12 could have a different number of layers and/or a different pattern within the layers.

[0037] FIG. 2D is a cross-sectional view of an exemplary patterned reflector 112d. In certain exemplary embodiments, patterned reflector 1 12d may be used for each patterned reflector 112 of FIGS. 1 A and ID. Patterned reflector 1 12d is arranged on the upper surface of the light guide plate 108 and is aligned with the light source 106. Patterned reflector 1 12d includes a first layer 130 on the upper surface of the light guide plate 108, a second layer 132 on the upper surface of the first layer 130 and on the upper surface of the light guide plate 108, and a third layer 134 on the upper surface of the second layer 132 and on the upper surface of the light guide plate 108. In certain exemplary embodiments, each of the first layer 130, the second layer 132, and the third layer 134 may have a varying thickness such that patterned reflector 1 12d may have a varying thickness. The varying thickness of each of the first layer 130, the second layer 132, and the third layer 134 may, for example, be formed by printing each respective layer to include a different amount of ink versus position for each respective layer. The maximum thickness of each of the first layer 130, the second layer 132, and the third layer 134 may be centered with the light source 106.

[0038] Each of the first layer 130, the second layer 132, and the third layer 134 may have a varying optical density. Each of the first layer 130, the second layer 132, and the third layer 136 may vary from each other in reflection, absorption, and/or transmission. Each of the first layer 130, the second layer 132, and the third layer 134 may be absoiptive, for example, by containing black material. Each of the first layer 130, the second layer 132, and the third layer 134 may be reflective, for example, by containing white or metallic material. Each of the first layer 130, the second layer 132, and the third layer 134 may also be both absorptive and reflective by containing more than one type of material, such as inks with added metal particles (e.g., silver, aluminum, etc.). In this case, the absorptive and/or reflective properties may vary over the patterned reflector area. In certain exemplary embodiments, the first layer 130 and the third layer 134 are more reflective than the second layer 132, and the second layer 132 is more absorptive than the first layer 130 and the third layer 134. In this case, patterned reflector 1 12d reflects most of the light emitted from the top surface of the light source 106 as well as light redirected from a diffuser plate or other optical film above the light guide plate 108, while effectively blocking most of the light going directly through the patterned reflector 112d.

[00391 In certain exemplary embodiments where white light sources 106 are used, the presence of different reflective and absorptive materials in variable density in the patterned reflectors 112a-l 12d may be beneficial for minimizing the color shift across each of the dimming zones of the backlight. Multiple bounces of light rays between the patterned reflectors and the reflective layer 104 (FIG. 1 A) may cause more loss of light in the red part of the spectrum than in the blue, or vice versa. In this case, engineering the reflection to be color neutral, for example by using slightly colored reflective/absorptive materials, or materials with the opposite sign of dispersion (in this case, dispersion means spectral dependence of the reflection and/or absorption) may minimize the color shift.

[0040] FIG. 3 is a cross-sectional view of an exemplary liquid crystal display (LCD) 140. LCD 140 includes a backlight 100 including first patterned reflectors 1 12 as previously described and illustrated with reference to FIGS. 1A-1 D. In addition, LCD 140 includes a layer 142 over backlight 100, optionally a diffuser plate 146 over the layer 140, optionally a quantum dot film 148 over the diffuser plate 146, optionally a prismatic film 150 over the quantum dot film 148, optionally a reflective polarizer 152 over the prismatic film 150, and a display panel 154 over the reflective polarizer 152. Layer 142 includes a plurality of second patterned reflectors 144. Each of the second patterned reflectors 144 is aligned with a corresponding first patterned reflector 1 12.

|0041 | Layer 142 may include a glass or transparent plastic material on which patterned reflectors 144 are formed. In certain exemplary embodiments, layer 142 may include the same or similar material as light guide plate 108. Each patterned reflector 144 may include the same or similar materials as patterned reflectors 1 12 and may be fabricated using the same or similar processes as those used to fabricate patterned reflectors 1 12. Using two separate patterned reflectors (i.e., first patterned reflectors 1 12 and second patterned reflectors 144) may add thickness and cost to the backljght, however, using two separate patterned reflectors may allow the use of a reduced number of reflective layers and/or a reduced layer thickness for both the first patterned reflectors 112 and the second patterned reflectors 144. As a result, both of the first patterned reflectors 1 12 and the second patterned reflectors 144 may be easier to fabricate. Additionally, both of the first patterned reflectors 1 12 and the second patterned reflectors 144 may be more durable due to better adhesion strength when the total thickness is less.

[0042] FIG. 4 is a cross-sectional view of an exemplary LCD 160. LCD 160 is similar to LCD 140 previously described and illustrated with reference to FIG. 3, except that in LCD 160 second patterned reflectors 144 are formed on diffuser plate 146 instead of on the separate layer 142. In this example, each patterned reflector 144 may include the same or similar materials as patterned reflectors 1 12 and may be fabricated using the same or similar processes as those used to fabricate patterned reflectors 1 12. While second patterned reflectors 144 are formed on the lower surface of diffuser plate 146 in FIG. 4, in other embodiments second patterned reflectors 144 maybe formed on the upper surface of diffuser plate 146. In other embodiments, second patterned reflectors 144 may be formed on the upper or lower surface of another adjacent optical component of LCD 160. Compared to LCD 140 ofFIG. 3, LCD 160 may have a smaller overall thickness.

[0043] The optical component (e.g., diffuser plate) on which the second patterned reflectors 144 are fabricated should be accurately aligned with the light guide plate 108 for the first reflectors 112 and the second reflectors 144 to work correctly together. Since the material of the diffuser plate or other optical component on which the second reflectors 144 may be fabricated may have different coefficients of thermal expansion than the light guide plate 108, a small misalignment between the light sources 106, the first patterned reflectors 1 12 on the light guide plate 108, and the second patterned reflectors 144 may occur because of environmental changes. This small misalignment, however, should not be a significant issue when the size of the backlight is small or when the pitch of the light sources 106 is large.

[0044] To maintain the alignment between the light sources 106 and the patterned reflectors 1 12 on the light guide plate 108 for the proper functioning of the backlight 100, it is advantageous if the light guide plate 108 and the substrate 102 are made of the same or similar type of material so that both the patterned reflectors 112 on the light guide plate 108 and the light sources 106 on the substrate 102¾re registered well to each over a large range of operating temperatures. Similarly, when the second patterned reflectors 144 are included, it is advantageous tf the second patterned reflectors 144 are made on the same or similar type of material as the light guide plate 108, so the second patterned reflectors 144 and the first patterned reflectors 1 12 on the light guide plate 108 are registered well to each other over a large range of operating temperatures. In certain exemplary embodiments, the light guide plate 108 and the substrate 102 are made of the same plastic material. In other embodiments, the light guide plate 108 and the substrate 102 are made of the same type of glass. In yet other embodiments, the light guide plate 108, the substrate 102, and the layer 142 (FIG. 3) are all made of the same type of glass.

[0045] An alternative solution to keep the light guide plate 108 and light sources 106 on the substrate 102 in alignment is to use a highly flexible substrate. The highly flexible substrate may be made of a polyimide or other high temperature resistant polymer film to allow component soldering. The highly flexible substrate may also be made of materials such as FR4 or fiberglass, but of a significantly lower thickness than usual. In certain exemplary embodiments, an FR4 material of 0.4 millimeters thickness may be used for substrate 102, which may be sufficiently flexible to absorb the dimensional changes resulting from changing operating temperatures.

[0046] FIGS. 5A-5C are various views of an exemplary backlight 200. FIG. 5A is a cross- sectional view of backlight 200. Backlight 200 may include a substrate 102, a reflective layer 104, a plurality of light sources 106, a light guide plate 108, and a plurality of patterned reflectors 1 12 as previously described and illustrated with reference to FIGS. 1 A-1D. In addition, backlight 200 includes a plurality of absorptive elements 202. Each absorptive element 202 laterally surrounds a corresponding light source 106. The reflective layer 104 is on the substrate 102 and surrounds each absorptive element 202. Each absorptive element 202 has a lower reflectance than the reflective layer 104. In certain exemplary embodiments, each absorptive element 202 may have a reflectance lower than about 4 percent, or within a range between about 1 and about 85 percent. In other embodiments, each absorptive element 202 might have a reflectance that varies depending on the radial distance to the center of the light source 106, for example is smaller closer to the light source and larger away from the light source 106. Each absorptive element 202 may also have a shape of a ring, meaning that it might start at a certain distance from the light source 106 and end at a larger distance.

[0047] FIG. 5B is a top view of the plurality of light sources 106, reflective layer 104, and absorptive elements 202 on substrate 102. While in the embodiment illustrated in FIG. 5B each absorptive element 202 is circular in shape, in other embodiments each absorptive element 202 may have another suitable shape (e.g., rectangular, hexagonal, etc.). FIG. 5C is a top view of the pattern of light extractors 1 10 and absorptive elements 202. The pattern of light extractors 1 10 includes a plurality of gaps 11 1. Each gap 1 11 is aligned with a corresponding light source 106, a corresponding absorptive element 202, and a corresponding patterned reflector 1 12.

[0048] The absorptive elements 202 may be a black paper, black plastic, black paint, black ink, a chemically altered (e.g., anodized) metal, or another suitable optically absorptive material. The absorptive elements 202 may be positioned anywhere between the substrate 102 and the lower surface of the light guide plate 108. For example, the absorptive elements 202 may be painted or laminated directly to the substrate 102 surface or wrapped around each light source 106.

[0049] FIG. 6 is a simplified cross-sectional view of an exemplary backlight 200 including a patterned reflector 1 12 and an absorptive element 202. Light rays 210 indicate light escaping from backlight 200. Light ray 212 indicates light that is reflected by patterned reflector 112 and then absorbed by absorptive element 202 and thus does not escape backlight 200. Light ray 214 indicates light that is reflected by patterned reflector 1 12 and then reflected by reflective layer 104 back to light guide plate 108 where the light may escape backlight 200.

[00501 The function of the absorptive elements 202 is to increase the luminance uniformity of the backlight 200. More specifically, it has been observed that placing a high reflectivity reflector (i.e., patterned reflector 1 12) on the upper surface of the light guide plate 108 directly above the light sources 106 may cause a bright ring or halo to appear adjacent to the outer edge of the reflector. This is due to the light rays emitted from the light source 106 at a small angle (i.e., nearly vertical) that, after multiple bounces between the light source and the patterned reflector 1 12, and/or reflective layer 104 and the patterned reflector 112, escape upwards as soon as the light rays hit the top surface of the light guide plate 108 where the light guide plate is not covered by the patterned reflector 1 12. The absorptive elements may eliminate or reduce the number of such rays and thereby may remove or reduce the halo.

[0051] The same effect may be achieved if the size of the patterned reflector 1 12 is increased, while making the patterned reflector less and less dense from the center towards the edge. Increasing the size of the patterned reflector 1 12 to suppress the halo, however, may lead to a decreased backlight efficiency. When the absorptive element 202 is included, the size of the patterned reflector 1 12 may be reduced and the backlight efficiency may be improved. In certain exemplary embodiments, the size of each absorptive clement 202 is within the range of about 0.5 to 5 times the thickness of the light guide plate 108 on all sides of the light source 106. For example, if the light source 106 is a 1 by 1 millimeter LED chip and the light guide plate thickness is 1 millimeter, the size of the absorptive clement may be between 2 by 2 millimeters and 11 by 11 millimeters. The absorptive element may also be a rectangle with rounded corners, or a circle with the diameter between 2 and 11 millimeters.

[0052] FIG. 7A is a cross-sectional view of an exemplary backlight 300a. Backlight 300a may include a substrate 102, a reflective layer 104, a plurality of light sources 106, and a light guide plate 108 as previously described and illustrated with reference to FIGS. 1A-1 D. In addition, backlight 300a may include a single continuous layer of low index material 302a on the upper surface of the light guide plate 108. Patterned reflectors 1 12 are on the upper surface of the layer of low index material 302a and aligned with light sources 106. In the example illustrated in FIG. 7A, each patterned reflector 1 12 has a varying thickness.

[0053] As a result of the layer of low index material 302a presence on the upper surface of the light guide plate 108, and the patterned reflectors 1 12 placed over the layer of low index material 302a, low angle rays, such as ray 304 (i.e., nearly along the normal direction of the light guide plate 108), may be reflected back into the light guide plate 108 by the thicker portions of the patterned reflector 112. High angle rays, such as ray 306, may be reflected back into the light guide plate 108 due to the total internal reflection at the interface of the light guide plate 108 and the layer of low index material 302a despite the fact that the patterned reflector 112 is thin above the location where ray 306 intersects the upper surface of the light guide plate 108. Both low angle and high angle rays may then be subsequently extracted out of the light guide plate 108 by the light extractors 1 10 with variable density to achieve improved luminance uniformity. Without the layer of low index material 302a, high angle rays may be undesirably extracted out of the backlight by the thinner portions of the patterned reflector 1 12, which may reduce the luminance uniformity.

[0054] The low index material 302a has a lower refractive index than the light guide plate material. In certain exemplary embodiments, the low index material 302a has a refractive index equal to about 1.25 (e.g., for a polymer filled with hollow silica particles), about 1.3 (e.g., for fluorinated polymers), or about 1.37 (e.g., for magnesium fluoride). As a result, some high angle light from the light source 106 may be trapped inside the light guide plate 108 without getting into the low index material 302a, but may still be extracted out by the light extractors 1 10 on the lower surface of the light guide plate 108.

[0055] FIG. 7B is a cross-sectional view of an exemplary backlight 300b. Backlight 300b is similar to backlight 300a previously described and illustrated with reference to FIG. 7A except that in backlight 300b, layer of low index material 302a is replaced with a plurality of low index material layers 302b. Each patterned reflector 1 12 is aligned with a corresponding low index material layer 302b. The plurality of low index material layers 302b provide the same function as the layer of low index material 302a of FIG. 7 A.

[0056] FIG. 8 is a simplified cross-sectional view of the exemplary backlight 300b of FIG. 7B. Referring to FIG. 8, the light guide plate 108 has a thickness T1 indicated at 324 and a refractive index nl at the wavelength of interest, while the low index material 302b has a thickness T2 indicated at 326 and a refractive index n2 at the wavelength of interest. The wavelength of interest may, for example, be 450 ± 30 nanometers for a blue light source, 550 ± 30 nanometers for a green or white light source, or 650 ± 30 nanometers for a red light source. The size SO (i.e., width or diameter) of the light source 106 or 107 is indicated at 320. The size S2 (i.e., width or diameter) of the low index material 302b is indicated at 322.

[0057] In certain exemplary embodiments, the minimum size S2 of the low index material is given by:

52 = 50 + 2G1 * tan (0c) where 0c is the total internal critical angle for rays incident from the light guide plate 108 upon the low index material 302b, and is determined by:

Or

TABLE: Various examples showing the dependence of the minimum size S2 of the low index material and the critical angle 0c on light source size SO, light guide plate thickness Tl, light guide plate refractive index nl, and the low index material refractive index n2.

[0058] The table shows in various examples the dependence of the minimum size S2 of the low index material and the critical angle 0c on light source size SO, light guide plate thickness Tl , light guide plate refractive index nl, and the low index material refractive index n2. In general, S2 increases with light guide plate thickness Tl and the ratio n2/nl . The refractive index of the low index material may be slightly smaller than that of the light guide plate, such as by a difference of about 0.01 , 0.04, 0.1, 0.2, 0.3, or 0.4. The refractive index of the low index material may be slightly larger than 1 , such as by a difference of about 0.005, 0.1, 0.2, 0.3, 0.3, or 0.4.

[0059] FIGS. 9 A-9C are flow diagrams illustrating an exemplary method 400 for fabricating a backlight. Method 400 may, for example, be used to fabricate backlight 100 previously described and illustrated with reference to FIGS. 1A-1D, backlight 200 previously described and illustrated with reference to FIGS. 5A-5C, or backlights 300a or 300b previously described and illustrated with reference to FIGS. 7A-8. As illustrated in FIG. 9A, at 402 method 400 includes arranging a plurality of light sources on a substrate. For example, a plurality of light sources 106 may be arranged on and electrically connected to a substrate 102 as illustrated in FIG. 1 A. At 404, method 400 includes applying a reflective layer on the substrate. For example, a reflective layer 104 may be applied to substrate 102 as illustrated in FIG. 1 A. The reflective layer may be applied to the substrate via a printing process, a deposition process, a film application process, or another suitable process.

[0060] At 406, method 400 includes applying a pattern of light extractors to a light guide plate. For example, a pattern of light extractors 1 10 may be applied to a light guide plate 108as illustrated in FIG. 1A. At 408, method 400 includes applying a plurality of first patterned reflectors on the light guide plate. For example, a plurality of first patterned reflectors 1 12 may be applied to light guide plate 108 as illustrated in FIG. 1 A and as further described with reference to FIGS. 2A-2D. At 410, method 400 includes arranging the light guide plate over the plurality of light sources such that each patterned reflector is aligned with a corresponding light source. The light guide plate may be arranged over the light sources such that gaps in the pattern of light extractors (e.g., gaps 1 11 of pattern of light extractors 1 10 illustrated in FIG. 1C) are aligned with corresponding light sources. In certain exemplary embodiments, an optical adhesive (e.g., phenyl silicone) may be used to couple the plurality of light sources to the light guide plate.

[00611 In certain exemplary embodiments, applying the plurality of first patterned reflectors includes printing the plurality of first patterned reflectors on the light guide plate. Printing the plurality of first patterned reflectors may include, for example, printing a layer of white ink, black ink, or metallic ink for each first patterned reflector. In other examples, printing the plurality of first patterned reflectors may include printing a layer including a different amount of ink versus position for each first patterned reflector. In other examples, printing the plurality of first patterned reflectors includes printing a layer including a variable proportion of clear and reflective ink for each first patterned reflector.

f0062] As illustrated in FIG. 9B, at 412 method 400 may further include applying a plurality of second patterned reflectors over and aligned with the plurality of first patterned reflectors. For example, a plurality of patterned reflectors 144 as part of a separate layer 142 or as part of a diffuser plate 146 may be applied over and aligned with a plurality of patterned reflectors 112 as illustrated in FIGS. 3 and 4, respectively. As illustrated in FIG. 9C, at 414 method 400 may further include applying a plurality of absorptive elements such that each absorptive element laterally surrounds a corresponding light source. For example, a plurality of absorptive elements 202 may be applied such that each absorptive element laterally surrounds a corresponding light source 106 as illustrated in FIGS. 5A-5C. The absorptive elements may be applied, for example, by applying black paper, black plastic, black paint, black ink, a chemically altered (anodized) metal, or another suitable optically absorptive material to the portions of the substrate laterally surrounding each light source, to each light source itself, or to the portions of the lower surface of the light guide plate laterally surrounding each light source. The absorptive elements may be applied prior to arranging the light guide plate over the plurality of light sources.

[00631 It will be apparent to those skilled in the art that various modifications and variations can be made to embodiments of the present disclosure without departing from the spirit and scope of the disclosure. Thus it is intended that the present disclosure cover such modifications and variations provided they come within the scope of the appended claims and their equivalents.