Emissive displays and methods for encapsulating same - Patent Application 20070122997

Abstract

The emissive display includes a substrate, an array of light-emitting diode (LED) pixels on the substrate, a cover plate adhered to the substrate with an optically clear adhesive (OCA), and a light-scattering layer between the array of LED pixels and the front surface of the cover plate.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application No. 63 / 448,699, filed February 28, 2023, the contents of which are herein relied upon and incorporated by reference in their entirety.

[0002] This disclosure relates to emissive electronic displays, and more particularly to LED-based emissive display structures that include encapsulation for controlling and enhancing the light output of the LED display. [Background technology]

[0003] Organic light-emitting diodes (OLEDs) are an emissive electronic display technology consisting of an array of light-emitting diodes (LEDs) that define individual picture elements (pixels). In OLED pixels, an organic electroluminescent or emissive layer is disposed between two electrodes and emits light based on an electric current. MicroLEDs are an emissive electronic display technology consisting of an array of microscopic LEDs that define individual pixels using inorganic (e.g., gallium nitride) materials. These LED-based emissive display technologies do not require backlighting and can be thinner and lighter, have higher contrast ratios, and have shorter response times than comparable liquid crystal displays (LCDs). Because organic materials degrade over time, the inorganic nature of microLED pixels gives them a longer lifetime than OLED pixels. Such emissive display technologies can be used as the basis for electronic display products such as smartphones, computer monitors, tablets, head-mounted displays, smartwatches, automotive instrumentation, digital signage, televisions, and tiled displays.

[0004] LED-based emissive display structures can include color conversion elements such as phosphors or quantum dots. For example, a color-converting LED-based display structure can include an array of LEDs emitting in the UV range with pixelated RGB quantum dots. In another example, a layer of phosphor can be placed over the LEDs to shift the color of individual LEDs.

[0005] OLED and micro-LED display structures traditionally need to be encapsulated to address environmental and mechanical reliability issues, including moisture penetration, oxygenation, and fragility of device structures and electrical interconnects. Traditional encapsulation methods involve laminating a light-transmitting cover plate (e.g., glass or polymer) to the LED display using an optically clear adhesive (OCA). However, such encapsulation can cause optical problems for the LED display, such as a significant reduction in display brightness and light leakage from the edges of the LED display. Edge light leakage can result in undesirable visibility of tile joints, for example, in tiled micro-LED displays.

[0006] These optical problems are primarily due to two causes: 1) changes in the LED's angular emission distribution due to refractive index changes in the encapsulant materials (cover plate and OCA) surrounding the LED's light-emitting surface, and 2) optical restriction and guiding of the emitted light due to Fresnel reflections by the waveguide defined by the cover plate and OCA layers.

[0007] FIG. 1 is a cross-sectional view of a portion of a conventional LED display structure according to the related art. As used throughout this specification, the term "LED display" is meant to encompass related display technologies, such as OLED, micro-LED, color-converting OLED, color-converting micro-LED, and those based on emissive elements. As shown in FIG. 1, the LED display 10 includes a substrate 12 on which LED pixels 14 are disposed. As commonly understood, each LED pixel 14 may include red R, green G, and blue B sub-pixels. A cover plate 16 may be laminated to the substrate 12 using a layer 18 of OCA material. Typically, both the cover plate 16 and the OCA layer 18 are highly transparent in the visible spectrum and may or may not have light scattering. The variable t p and t o represent the thickness of the cover plate and the thickness of the OCA layer, respectively.

[0008] Conventional methods for controlling LED emission include fabricating optical elements on the LED surface and placing the LED within a reflector cavity. These methods affect the LED emission pattern but do not suppress internal reflections of the emitted light (i.e., waveguiding) in the encapsulation (cover glass and OCA), which is the root cause of reduced light output. These approaches also require additional processing and complexity in either the LED display structure or backplane, which already suffers from low yield. Therefore, there is a need for a solution that addresses light waveguiding in the encapsulation to increase light output and reduce light emission from the edges of the display. Summary of the Invention

[0009] The present disclosure relates to emissive display structures and methods for encapsulating an emissive (e.g., microLED or OLED) display panel to enhance the display panel's light output through the design and management of the optical properties of encapsulation layers, such as a cover plate and / or an optically clear adhesive (OCA).

[0010] The disclosed embodiments include encapsulation structures and methods that address the above-identified problems. In these structures, a light-scattering layer can be introduced behind the cover plate to manage / enhance the angular distribution / perceived brightness of the LED display. Additionally, the light-scattering properties of the optically clear adhesive used to laminate the cover plate to the LED display substrate can also be used to manage and enhance the angular distribution of light emitted from the LED display.

[0011] In disclosed embodiments, a scattering layer within the display panel (rather than on the outer surface) increases perceived brightness and reduces edge emission. This scattering layer can be on the inner (back) surface of the cover glass (for top-emitting LED displays), the inner surface of the substrate (for bottom-emitting LED displays), or in the adhesive layer.

[0012] The LED display structures and methods described herein reduce degradation of display brightness due to encapsulation. The LED display structures and methods also suppress edge light leakage due to encapsulation, which can cause undesirable tile joint visibility issues in tiled displays. The LED display structures and methods are easily implemented because there is no need to align optical features with the LED light emitters, as is the case with some currently used methods.

[0013] In one embodiment, an emissive display includes an array of emissive pixels on a substrate and an optically clear adhesive (OCA) between the substrate and a cover plate that includes a light-scattering layer.

[0014] In one embodiment, the emissive pixel includes a light emitting diode (LED), wherein the LED is an organic light emitting diode (OLED), a color-converting OLED, wherein the LED is a micro LED, or wherein the LED is a color-converting micro LED.

[0015] In one embodiment, the light scattering layer is behind the cover plate.

[0016] In one embodiment, the light scattering layer comprises particles dispersed in a resin.

[0017] In one embodiment, the OCA is a light scattering layer.

[0018] In one embodiment, the scattering coefficient of the light-scattering layer is 1 to 30 degrees, and can be 15 to 25 degrees.

[0019] In one embodiment, the ratio of the light scattering layer distance to the array of emissive pixels to the pixel pitch is less than one.

[0020] In one embodiment, the scattering coefficient of an OCA with a layer thickness of 2 μm is less than 15 degrees.

[0021] In one embodiment, a light emitting diode (LED) display includes a substrate, an array of LED pixels on the substrate, a cover plate adhered to the substrate with an optically clear adhesive (OCA), and a light scattering layer between the array of LED pixels and the front surface of the cover plate.

[0022] In one embodiment, the light scattering layer is behind the cover plate.

[0023] In one embodiment, the OCA is a light scattering layer.

[0024] In one embodiment, a method for encapsulating an LED display includes providing an array of LED pixels on a substrate and laminating a cover plate to the substrate, wherein a light-scattering layer is between the array of LED pixels and the front surface of the cover plate.

[0025] The above and other features, elements, characteristics, steps, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.

[0026] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a cross-sectional view of a portion of a conventional LED display structure according to the related art; [Figure 2A] 1 illustrates an encapsulated LED display structure used to enhance display brightness and reduce display edge light leakage, according to disclosed embodiments. [Figure 2B] 1 illustrates an encapsulated LED display structure used to enhance display brightness and reduce display edge light leakage, according to disclosed embodiments. [Figure 2C] 1 illustrates an encapsulated LED display structure used to enhance display brightness and reduce display edge light leakage, according to disclosed embodiments. [Figure 2D] 1 illustrates an encapsulated LED display structure used to enhance display brightness and reduce display edge light leakage, according to disclosed embodiments. [Figure 2E] 1 illustrates an encapsulated LED display structure used to enhance display brightness and reduce display edge light leakage, according to disclosed embodiments. [Figure 2F] 1 illustrates an encapsulated LED display structure used to enhance display brightness and reduce display edge light leakage, according to disclosed embodiments. [Figure 3A] 1 shows the LED display without encapsulation for the reference case. [Figure 3B] 1 shows the LED display without encapsulation for the reference case. [Figure 4] 1 shows a cross-sectional view of a conventional encapsulated LED display of Case 0. [Figure 5A] 1 shows the luminance distribution in angle space for a conventional LED display before and after encapsulation. [Figure 5B] 1 shows the luminance distribution in angle space for a conventional LED display before and after encapsulation. [Figure 6] 4 is a graph of curves showing cross sections of luminance distribution in angle space for an LED display before and after encapsulation. [Figure 7] 1 is a cross-sectional view of an LED display of Case 1. [Figure 8] 1A-1C are cross-sectional views of LED displays with the disclosed encapsulation configurations, Examples 2-5. [Figure 9] 10 is a graph of the curve of brightness reduction in the normal direction due to encapsulation as a function of the scattering coefficient of the scattering layer for LED display case 1 and LED display case 2. [Figure 10A] 1 shows the simulated luminance distribution in angular space for different configurations of LED displays. [Figure 10B] 1 shows the simulated luminance distribution in angular space for different configurations of LED displays. [Figure 10C] 1 shows the simulated luminance distribution in angular space for different configurations of LED displays. [Figure 10D] 1 shows the simulated luminance distribution in angular space for different configurations of LED displays. [Figure 10E] 1 shows the simulated luminance distribution in angular space for different configurations of LED displays. [Figure 10F] 1 shows the simulated luminance distribution in angular space for different configurations of LED displays. [Figure 11A] The following shows a simulation of the LED display image with 4x5 illuminated pixels for different LED display configurations. [Figure 11B] The following shows a simulation of the LED display image with 4x5 illuminated pixels for different LED display configurations. [Figure 11C]The following shows a simulation of the LED display image with 4x5 illuminated pixels for different LED display configurations. [Figure 11D] The following shows a simulation of the LED display image with 4x5 illuminated pixels for different LED display configurations. [Figure 11E] The following shows a simulation of the LED display image with 4x5 illuminated pixels for different LED display configurations. [Figure 11F] The following shows a simulation of the LED display image with 4x5 illuminated pixels for different LED display configurations. [Figure 12A] The following shows a simulation of the LED display image with 4x5 illuminated pixels for different LED display configurations. [Figure 12B] The following shows a simulation of the LED display image with 4x5 illuminated pixels for different LED display configurations. [Figure 12C] The following shows a simulation of the LED display image with 4x5 illuminated pixels for different LED display configurations. [Figure 12D] The following shows a simulation of the LED display image with 4x5 illuminated pixels for different LED display configurations. [Figure 13] 1 is a graph of curves of edge light leakage reduction as a function scattering coefficient of the scattering layer of LED display case 1 and LED display case 2. [Figure 14A] 1 shows images of LED displays of different OCA thicknesses and Case 3 with 4x5 pixels illuminated. [Figure 14B] 1 shows images of LED displays of different OCA thicknesses and Case 3 with 4x5 pixels illuminated. [Figure 14C] 1 shows images of LED displays of different OCA thicknesses and Case 3 with 4x5 pixels illuminated. [Figure 14D] 1 shows images of LED displays of different OCA thicknesses and Case 3 with 4x5 pixels illuminated. [Figure 14E] 1 shows images of LED displays of different OCA thicknesses and Case 3 with 4x5 pixels illuminated. [Figure 14F] 1 shows images of LED displays of different OCA thicknesses and Case 3 with 4x5 pixels illuminated. [Figure 15] 10 is a graph of the curves of the brightness reduction in the normal direction of the display due to encapsulation as a function of the scattering coefficient of the scattering layer for Cases 1, 2, and 4. [Figure 16A] Images of an LED display with 4x5 pixels lit are shown for the reference case (without a scattering layer) and case 4. [Figure 16B] Images of an LED display with 4x5 pixels lit are shown for the reference case (without a scattering layer) and case 4. [Figure 16C] Images of an LED display with 4x5 pixels lit are shown for the reference case (without a scattering layer) and case 4. [Figure 16D] Images of an LED display with 4x5 pixels lit are shown for the reference case (without a scattering layer) and case 4. [Figure 16E] Images of an LED display with 4x5 pixels lit are shown for the reference case (without a scattering layer) and case 4. [Figure 16F] Images of an LED display with 4x5 pixels lit are shown for the reference case (without a scattering layer) and case 4. [Figure 17] A comparison of edge light leakage reduction as a function of the scattering coefficient of the scattering layer for cases 1, 2, and 4 is shown. [Figure 18] 1 is a graph of the curve of display normal brightness reduction due to encapsulation as a function of OCA scattering coefficient. [Figure 19A] For Case 0 and Case 5, images of an LED display with 4x5 pixels lit are included. [Figure 19B] For Case 0 and Case 5, images of an LED display with 4x5 pixels lit are included. [Figure 19C]For Case 0 and Case 5, images of an LED display with 4x5 pixels lit are included. [Figure 19D] For Case 0 and Case 5, images of an LED display with 4x5 pixels lit are included. [Figure 19E] For Case 0 and Case 5, images of an LED display with 4x5 pixels lit are included. [Figure 20] 10 is a graph of curves showing a comparison of edge light leakage reduction as a function of OCA scattering coefficient for Case 5. DETAILED DESCRIPTION OF THE INVENTION

[0028] In the following description, reference is made to the accompanying drawings, which form a part hereof, and which are shown for the purpose of illustrating specific exemplary embodiments in which the present disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the concepts disclosed herein, it being understood that various modifications to the disclosed embodiments may be made and other embodiments may be utilized without departing from the scope of the present disclosure. Accordingly, the following detailed description is not to be construed in a limiting sense.

[0029] Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0030] 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 each endpoint of the range is significant both in relation to the other endpoint, and independently of the other endpoint.

[0031] Directional terms used herein (e.g., up, down, right, left, front, back, top, bottom, vertical, horizontal) are merely to refer to the figures as drawn and are not intended to imply absolute orientation.

[0032] Unless otherwise expressly stated, it is in no way intended that any method described herein be construed as requiring its steps to be performed in a particular order, or that any apparatus require a particular orientation. Thus, where a method claim does not actually recite the order in which its steps are to be followed, or where any apparatus claim does not actually recite an order or orientation for individual components, or where the claim or the specification otherwise specifically states that the steps are to be limited to a particular order, or where no particular order or orientation for the apparatus components is recited, no order or orientation is intended to be inferred in any sense. This applies to all possible implicit bases for interpretation, including logical considerations regarding the arrangement of steps, operational flow, component order, or component orientation, the plain meaning derived from grammatical organization or punctuation, and the number or type of embodiments described herein.

[0033] 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" element includes aspects having two or more such elements unless the context clearly dictates otherwise.

[0034] 2A-2F illustrate an encapsulated LED display structure used to enhance display brightness and reduce display edge light leakage according to disclosed embodiments. All of FIGS. 2A-2F show emissive pixels 24 on a substrate 22. The variable t p , t o , and t s represent the thicknesses of the cover plate, the OCA layer, and the light scattering layer, respectively.

[0035] In one embodiment, as shown in FIG. 2A , a light-scattering layer 27 is included on the rear side of the cover plate 26 before the cover plate 26 is laminated to the substrate 22 using the OCA 28. For example, the light-scattering layer 27 can include a material with light-scattering particles or a light-scattering material dispersed or dissolved in an adhesive medium, which is coated on the rear side of the cover plate 26. The light-scattering layer 27 can be coated onto the cover plate 26 as a liquid or gel and then cured or solidified, or can be applied as a sheet layer or placed on the cover plate 26 using any suitable method or technique. The cover plate 26 can be glass, ceramic, glass-ceramic, polymer, or other optically translucent material. It can have a thickness of less than 3 mm, less than 1 mm, less than 0.7 mm, less than 0.5 mm, less than 0.3 mm, less than 0.2 mm, or less than 0.1 mm.

[0036] 2B, in one embodiment, a light scattering layer 27 is included on the back side of the cover plate 26, and light scattering properties are included in the OCA layer 29. Light scattering particles or materials can be dispersed or dissolved in the OCA layer 29 to encapsulate the pixels 24 and scatter light emitted from the pixels 24.

[0037] As shown in FIG. 2C, in one embodiment, OCA layer 29 includes a material with light scattering properties to encapsulate pixel 24 and scatter light.

[0038] 2D, in one embodiment, an encapsulation layer 25 includes a material with light scattering properties to encapsulate the pixels 24 and scatter light. A cover plate 26 is attached to the encapsulation 25 layer by an OCA layer 28.

[0039] 2E, in one embodiment, a light scattering layer 27 is included on the back side of the cover plate 26, and an OCA layer 28 is adhered to the top surface of the LED pixels 24, but not between the LED pixels 24. Because there is no OCA material between the LED pixels 24, the encapsulation in this configuration has less effect on changing the angular distribution of the LED light emission and therefore less effect on the brightness of the display.

[0040] 2F, in one embodiment, a light scattering layer 27 is included on the back side of the cover plate 26, and the material having light scattering properties is included in an OCA layer 29 that is adhered to the top surface of the LED pixels 24 but not between the LED pixels 24. Because there is no OCA material between the LED pixels 24, this encapsulation configuration has less impact on changing the angular distribution of the LED light emission and therefore less impact on the brightness of the display.

[0041] In addition to the embodiments shown in Figures 2A-2F, the light-scattering layer and / or light-scattering OCA and / or light-scattering encapsulant material can be patterned. As an example, these light-scattering layers can be patterned in 2D shapes within the plane of the LED display. In such cases, the scattering elements can occupy any one of 90% or less of the pixel area, 70% or less of the pixel area, 50% or less of the pixel area, 30% or less of the pixel area, and 10% or less of the pixel area. The patterned light-scattering layer can have a rectangular shape, a circular shape, a ring shape, or other shape, or a combination of shapes. The patterned light-scattering layer can extend beyond the dimensions of the LED pixel. Similarly, the patterned light-scattering layer material can be an inorganic or organic material or combination of materials. The patterned light-scattering layer can be a coating, a surface modification, or integrated into a substrate. While Figures 2A-2F show a cover glass 26, additional examples are possible where the bottom-emitting substrate is integrated with the associated light-scattering elements. For example, the LED display can be a top-emitting, bottom-emitting, or dual-emitting display with light-scattering elements associated with the emission direction. The LED display can be a translucent or semi-translucent display. The LED display configurations shown in Figures 2A-2F can include displays with native red, green, blue, and white LED emitters and color conversion layers. Displays with color conversion can include, for example, native blue emitters with color conversion elements to achieve red and green. As an alternative to OLED and microLED emitters, the emitters can be other electroluminescent or photoluminescent materials and structures.

[0042] The light-scattering layer can be created by including randomly ordered particles in a resin, OCA material, or the like. Alternatively, the scattering elements can be present in the cover glass or substrate glass itself. The scattering elements can be arranged in an ordered orientation rather than a random orientation. The optical properties of the encapsulation material for the disclosed embodiment shown in FIG. 2 can be as follows: The transmittance of the layer(s) with light scattering (FIGS. 2A and 2E: scattering layer behind the cover plate; FIG. 2B and 2F: scattering layer behind the cover plate and OCA layer with scattering; FIG. 2C: OCA layer with scattering; and FIG. 2D: encapsulation layer with scattering) at visible wavelengths is greater than 50%. To characterize this property, the output power of a collimated light source with a bandwidth covering visible wavelengths (P) is measured by an optical power meter. The output light of the collimated light source is incident on the encapsulation layer from the scattering layer side. The incident light is normal to the surface of the encapsulation layer. The transmitted light was collected by an integrating sphere and then measured with an optical power meter. The transmittance of the encapsulation layer (%) is 100 (Pout / Pin). The visible transmittance through its thickness of the non-scattering layer of the cover plate is greater than 60%. The refractive index of the scattering layer, cover plate, OCA with and without scattering, or encapsulation layer with scattering ranges from 1.25 to 2.0 at a wavelength of 550 nm.

[0043] The scattering properties of the scattering layer can be characterized by using a collimated laser beam with a wavelength of 550 nm, which illuminates the scattering layer from the surface normal, and the angular intensity distribution of the transmitted light can be described by the Gaussian scattering function in equation (1):

number

[0044] 3A and 3B show an LED display without encapsulation, which is used as a reference case when modeling the optical performance of different display configurations. FIG. 3A is a plan view of the LED display 30. FIG. 3B is a side view of a portion of the LED display 30 before encapsulation. The LED display 30 includes a substrate 32 and an array of pixels 34, each of which includes R, G, and B subpixels. As shown in FIG. 3A, the LED display 30 consists of an array of 25×25 pixels 34, with a pitch of 200 μm and a spacing of 25 μm between two adjacent subpixels. The size of the subpixels is 30 μm×20 μm.

[0045] Figure 4 shows a cross-sectional view of an LED display 40 after conventional encapsulation (Case 0). In this encapsulation, a highly light-transmitting glass cover plate 46 with a thickness of 0.5 mm is laminated to the LED display 40 using an OCA 48 with a thickness of 20 μm. The transmittance of the glass cover plate 46 and OCA 48 materials at a wavelength of 550 nm and a propagation distance of 5 mm is 99% and 48%, respectively. These transmittance parameters of the glass cover plate 46 and OCA 48 are used for all the following modeling cases. Other parameters for Case 0 are provided in Table 1. In this Case 0, both the cover plate 46 and the OCA 48 do not include light scattering. Table 1 includes the geometric and material parameters of Case 0 (LED display with conventional encapsulation). [Table 1]

[0046] 5A and 5B are polar plot models of the luminance distribution in angle space of LED display 30 before (reference case) and after conventional encapsulation (case 0). Fig. 5A shows the luminance distribution in angle space of LED display 30 before encapsulation. Fig. 5B shows the luminance distribution in angle space of LED display 40, which is LED display 30 after encapsulation.

[0047] FIG. 6 is a graph showing cross sections of the luminance distribution in angular space for the LED display 30 before encapsulation (top two curves) and the LED display 40 after encapsulation (bottom two curves), with normalized luminance along the y-axis and viewing angle (degrees) along the x-axis. The green dotted line in the graph represents the central cross section of the horizontal luminance distribution in FIG. 5A. The red dotted line in the graph represents the central cross section of the vertical luminance distribution in FIG. 5A. The green line in the graph represents the central cross section of the horizontal luminance distribution in FIG. 5B. The red line in the graph represents the central cross section of the vertical luminance distribution in FIG. 5B. As shown in FIGS. 5A, 5B, and 6, the luminance of the LED display 40 at all spatial angles decreases by more than 48% after encapsulation compared to the LED display 30, and the luminance in the normal direction of the LED display 40 decreases by approximately 49%.

[0048] 7 is a cross-sectional view of an LED display 70 of Case 1 according to one embodiment. As shown in FIG. s A light scattering layer 77 having a thickness t is included on the front side of the cover plate 76, which is laminated to the LED display 70 using the OCA 48. f A pre-coating layer 79 having a thickness of 1000 nm is provided on top of the scattering layer 77. The introduction of the pre-coating layer 79 is to simulate the case of the scattering layer 77 near the front surface of the encapsulated LED display 70, rather than at the front surface of the encapsulated LED display 70. The geometric and material parameters of the model for Case 1 are provided in Table 2. [Table 2] [Table 3]

[0049] 8 is a cross-sectional view of an LED display 80 with the disclosed encapsulation configurations (Cases 2-5) used for modeling. In the disclosed encapsulation configurations, a light-scattering layer 87 is provided on the back side of the cover plate 86, and light-scattering properties may also be introduced into the OCA 88 used to laminate the cover plate 86 to the LED display. The geometric and material parameters for modeling Cases 2-5 are provided in Table 3. [Table 4] [Table 5]

[0050] FIG. 9 is a graph showing the curves of brightness reduction in the normal direction due to encapsulation as a function of the scattering coefficient of the scattering layer for LED display 70—Case 1 (the scattering layer is disposed on the front side of the cover plate) and LED display 80—Case 2 (the scattering layer is disposed on the back side of the cover plate). For both Cases 1 and 2, when the scattering coefficient σ of the scattering layer is greater than 10 degrees, an improvement in display brightness can be achieved. The larger the scattering coefficient σ, the greater the brightness improvement in the normal direction can be achieved by reducing brightness reduction. For Cases 1 and 2, when the scattering coefficient σ is approximately 27 degrees and 24 degrees, respectively, the brightness in the normal direction can be fully restored to the level before the cover plate was laminated. The improvement in display brightness in the normal direction is due to the scattering layer redistributing the direction of light propagation within the encapsulation layer. Therefore, the effect of internal reflection of the emitted light (i.e., waveguiding) in the encapsulation (cover glass and OCA) is reduced.

[0051] 10A-10F show simulated luminance distributions in angular space for different configurations of LED displays. FIG. 10A shows the luminance distribution in angular space for LED display 30 without encapsulation (reference case). FIG. 10B shows the luminance distribution in angular space for LED display 40 with encapsulation and without scattering (case 0). FIGS. 10C-10F show the luminance distribution in angular space for different configurations of LED displays in which the back side of the cover plate is provided with a scattering layer having different scattering coefficients σ of 4, 10, 20, and 30 degrees, respectively. As shown with respect to FIGS. 10C-10F, by increasing the scattering coefficient, more light emitted from the pixel is directed from higher angles to lower angles, toward the normal angle (0 degrees) of the display. Therefore, a display with more light at lower angles closer to the normal presents more light to the user and is perceived as brighter than an LED display without a scattering layer. For case 1, a similar evaluation of the luminance distribution in angular space with scattering coefficient σ is observed.

[0052] As shown and described, introducing a light-scattering layer on the cover plate can improve the brightness of the enclosed LED display by directing more light toward the user. However, introducing a light-scattering layer can also cause crosstalk between adjacent pixels, which can result in reduced display contrast and / or image distortion. Therefore, crosstalk simulations were also performed. In all simulations, a 4x5 pixel array located in the center of the display was illuminated.

[0053] 11A-11F show simulated images of the relative luminance of LED displays with 4×5 illuminated pixels for different LED display configurations. FIG. 11A shows the relative luminance of the 4×5 pixels of LED display 40 with encapsulation and no scattering (see Case 0—FIG. 4). FIGS. 11B-11F show the relative luminance of the 4×5 pixels of LED display 70 with encapsulation and a scattering layer 77 in front of cover plate 79 (see Case 1—FIG. 7) with different scattering coefficients σ of 1, 4, 5, 10, and 30 degrees, respectively. As shown, crosstalk between pixels begins to be observed at a scattering coefficient σ of 4 degrees, and the crosstalk increases with increasing scattering coefficient σ.

[0054] 12A-12D show simulated images of the relative brightness of 4x5 illuminated pixels for LED displays with different configurations. FIG. 12A shows the relative brightness of 4x5 pixels for an LED display 40 with encapsulation and no scattering (Case 0—see FIG. 4). FIGS. 12B-12D show simulated images of 4x5 illuminated pixels for an LED display 80 (Case 2—see FIG. 8) that includes a scattering layer 87 on the rear side of a cover plate 86, with different scattering coefficients σ of 10, 20, and 30 degrees, respectively. Unlike Case 1, when the scattering layer is on the front side of the cover plate, no significant crosstalk between pixels is observed for scattering coefficients σ up to 30 degrees. This result indicates that the LED display configuration of Case 2 can improve display brightness without introducing significant crosstalk between pixels when the scattering layer's scattering coefficient is less than 30 degrees.

[0055] The introduction of a scattering layer can also reduce light leakage from the sides of an LED display caused by the waveguiding (total internal reflection) effect. Figure 13 shows the curves of edge light leakage reduction as a function of the scattering coefficient of the scattering layer for LED display 70 (Case 1—scattering layer on the front side of the cover plate) and LED display 80 (Case 2—scattering layer on the back side of the cover plate). The edge light leakage reduction shown in the curves refers to the edge light leakage reduction of LED display 40 (Case 0—conventional encapsulation). For LED display 70 (Case 1) and LED display 80 (Case 2), edge light leakage reduction is achieved when the scattering coefficient σ is greater than 6 degrees. As shown, edge light leakage reduction increases with increasing scattering coefficient σ. This shows that including a scattering layer on the back side of the cover plate, as in Case 2, has a greater impact than a scattering layer on the front side of the cover plate, as in Case 1, for the same scattering coefficient σ.

[0056] For the LED configuration shown in Figure 2C (Case 3), we investigated the effect of OCA thickness (i.e., the distance of the scattering layer to the LED pixels) on pixel-to-pixel crosstalk. Figures 14A-14F show images of the relative luminance of the LED display of Case 3 with different OCA thicknesses and 4 × 5 illuminated pixels. The LED display configurations shown in Figures 14A-14F were fabricated with OCAs of thickness t = 20, 30, 40, 60, 80, and 100 μm, respectively. o The OCA layer has the following structure:

[0057] The crosstalk between pixels is t o= 60 μm (see FIG. 14D ). This optimal OCA thickness or separation dimension can depend on the pixel pitch. Smaller pixel pitches may require smaller OCA thicknesses. As an example, for Case 3, the maximum distance of the scattering layer from the LED pixel emitter is 60 μm. The distance / pitch ratio is 60 / 200 or less. For purposes of controlling the brightness of the LED emission, the ratio of the scattering layer distance from the emitter to the pixel pitch can be less than 1. In another embodiment, the ratio of the scattering layer distance from the emitter to the pixel pitch can be 0.5 or less. In another embodiment, the ratio of the scattering layer distance from the emitter to the pixel pitch can be 0.25 or less.

[0058] The effect of the thickness of the scattering layer (volume scattering) located behind the cover plate on brightness was investigated for the LED configuration shown in Figure 2A (Case 4). Figure 15 shows the curves of the display normal brightness reduction due to encapsulation as a function of the scattering coefficient of the scattering layer for Cases 1, 2, and 4. Similar to Case 1 (scattering layer located on the front side of the cover plate) and Case 2 (0 μm thick scattering layer (surface scattering) located behind the cover plate), an improvement in display brightness for an LED display configured like Case 4 (2 μm thick scattering layer (volume scattering) located behind the cover plate) can be achieved when the scattering coefficient of the scattering layer exceeds 10°. The larger the scattering coefficient, the greater the brightness improvement in the normal direction. However, unlike Cases 1 and 2, where the scattering layer thickness is close to or 0 μm, the normal brightness reduction curve for Case 4 begins to saturate at approximately 10% when the scattering coefficient is 25°.

[0059] For the LED configuration shown in Figure 2A (Case 4), we also investigated the effect of the thickness of the scattering layer located behind the cover plate on pixel-to-pixel crosstalk. Figures 16A-16F contain images of LED displays with 4 x 5 illuminated pixels for the reference case (no scattering layer) (see Figure 16A) and Case 4 (a 2 μm-thick scattering layer). The LED display configurations shown in Figures 16B-16F have scattering layers with scattering coefficients σ of 2.5, 15, 20, 25, and 30 degrees, respectively. Crosstalk between pixels begins to be observed when the scattering coefficient σ is increased to 25 degrees, indicating that the optimal range of the scattering coefficient σ for increasing the brightness of LED displays is between 15 and 25 degrees.

[0060] 17 shows a comparison of the edge light leakage reduction (%) of the scattering layer versus the scattering coefficient σ for Cases 1, 2, and 4. In Case 4, edge light leakage reduction is achieved when the scattering coefficient σ exceeds about 7 degrees, and increasing the scattering coefficient σ increases the edge light leakage reduction.

[0061] The effect of the OCA scattering coefficient σ on brightness was investigated for the LED display configuration (Case 5) shown in Figure 2B. Here, the back side of the cover plate contains a 2 μm-thick light-scattering layer with a scattering coefficient σ of 10°, and a 20 μm-thick OCA layer introduces different levels of light scattering. Figure 18 shows the curve of the display's normal brightness reduction due to encapsulation as a function of the OCA scattering coefficient σ. Here, the OCA scattering coefficient is defined by Equation (1) when light passes through a 2 mm-thick OCA material. As shown, the normal brightness reduction decreases with increasing OCA scattering coefficient σ, and the brightness of the LED display can be restored to the level of the LED display before encapsulation at an OCA scattering coefficient σ of approximately 15°.

[0062] We also investigated the effect of the OCA scattering coefficient σ on pixel-to-pixel crosstalk for the LED configuration shown in Figure 2B (Case 5). Figures 19A-19E contain images of LED displays with 4 × 5 illuminated pixels for Case 0 (no scattering layer) (see Figure 19A) and Case 5 (a 2 μm-thick light-scattering layer with a scattering coefficient σ of 10° and a 20 μm-thick light-scattering OCA layer on the back side of the cover plate). The LED display configurations shown in Figures 19B-19E have OCA layers with scattering coefficients σ of 5, 7.5, 10, and 15°, respectively. Pixel-to-pixel crosstalk began to be observed when the OCA scattering coefficient σ was increased to 15°, indicating that the optimal range for the OCA scattering coefficient σ to enhance the brightness of LED displays is 10° or less.

[0063] Figure 20 shows a comparison of edge light leakage reduction (%) as a function of OCA scattering coefficient σ for Case 5. As shown in Case 5, edge light leakage reduction can be achieved by adding light scattering to the OCA layer, and edge light leakage reduction increases by increasing the OCA scattering coefficient σ.

[0064] It should be understood that the foregoing description is only illustrative of the present invention. Those skilled in the art may devise various alternatives and modifications without departing from the scope of the present invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications, and variations that fall within the scope of the appended claims.

Claims

1. An emissive display, an array of emissive pixels on a substrate; an optically clear adhesive (OCA) between the substrate and a cover plate including a first light-scattering layer.

2. 10. The emissive display of claim 1, wherein the array of emissive pixels comprises light emitting diodes (LEDs).

3. The emissive display of claim 2 , wherein the LEDs are inorganic light emitting diodes.

4. 3. The emissive display of claim 2, wherein the LEDs consist of micro-LEDs emitting multiple colors and color-converting micro-LEDs, or single-color micro-LEDs for color conversion.

5. 10. The emissive display of claim 1, wherein the first light-scattering layer is behind the cover plate.

6. The emissive display of claim 1 , wherein the first light-scattering layer comprises particles dispersed in a resin.

7. The emissive display of claim 1 , wherein the OCA is a second light scattering layer.

8. 6. The emissive display of claim 5, wherein the scattering coefficient of the first light-scattering layer is 1 to 30 degrees.

9. 6. The emissive display of claim 5, wherein the scattering coefficient of the first light-scattering layer is 10 to 25 degrees.

10. 6. The emissive display of claim 5, wherein the ratio of the first light-scattering layer distance for the array of emissive pixels to the pixel pitch is less than 1.

11. The emissive display of claim 7 , wherein the OCA has a scattering coefficient of less than 15 degrees.

12. 1. A light emitting diode (LED) display, comprising: A substrate; an array of LED pixels on the substrate; a cover plate adhered to the substrate with an optically clear adhesive (OCA); a light scattering layer between the array of LED pixels and the front surface of the cover plate.

13. 13. The LED display of claim 12, wherein the light scattering layer is behind the cover plate.

14. The LED display of claim 12 , wherein the OCA is the light scattering layer.

15. the light scattering layer is behind the cover plate; 13. The LED display of claim 12, wherein the OCA is light scattering.

16. 13. The LED display of claim 12, wherein the light-scattering layer has a scattering coefficient of 1 to 30 degrees.

17. 13. The LED display of claim 12, wherein the light-scattering layer has a scattering coefficient of 10 to 25 degrees.

18. 13. The LED display of claim 12, wherein the ratio of the distance from the light scattering layer to the array of LED pixels to the pixel pitch is less than 1.

19. The LED display of claim 12 , wherein the scattering coefficient of the OCA is less than 15 degrees.

20. 1. A method of encapsulating a light emitting diode (LED) display, the method comprising: providing an array of LED pixels on a substrate; and laminating a cover plate to the substrate; The method wherein there is a light scattering layer between the array of LED pixels and the front surface of the cover plate.

Images