Micro LED display device

Abstract

To provide a micro LED display device in which an image has the uniform brightness even when a viewing angle changes.SOLUTION: A micro LED display device comprises at least: a plurality of LED elements arranged in the grid shape on a board; and a partition wall which partitions each of the plurality of LED elements. In the micro LED display device, a side wall surface of the partition wall is in the spherical shape. In the micro LED display device, a diffuse reflection layer is formed on the surface of the side wall surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a micro LED display device, and more particularly to a barrier structure of a micro LED display device. [Background technology]

[0002] Organic electroluminescence displays (hereinafter referred to as OLED) are well known as display devices, but they have problems such as low luminous efficiency of the OLED layer, changes in light emission over time, a short lifespan, and a tendency for image burn-in when the current is increased. Recently, LED displays using inorganic LEDs (LED displays) have been expected to contribute to thinner mobile devices. LEDs have attracted increasing attention because they have higher luminous efficiency than OLEDs and their luminance can be easily adjusted by the current (allowing for brighter displays).

[0003] In recent years, attention has been focused on a technology for LCD displays that uses direct-type backlights called mini-LEDs, which are made up of multiple LED chips with sizes ranging from approximately 5 μm to 200 μm arranged in a matrix. Mini-LEDs include a full-color system that uses three types of LED chips (red, green, and blue) to produce full color, and a full-color system that uses LED chips that emit white light containing RGB wavelength components as a light source and further separates the light into RGB colors for each element using color filters.

[0004] In recent years, display devices that use micro LED chips as light sources have been attracting attention because they can display images by individually driving multiple LED chips, without using liquid crystal shutters.

[0005] In micro LED display devices, light emitting elements including light emitting diodes are point light sources, so the distribution of light emission brightness is wide. As a result, some of the light emitted from the light emitting elements may enter adjacent pixels as stray light, causing color mixing and reducing color reproducibility. Therefore, partitions are often provided between adjacent light emitting elements to prevent light from entering the adjacent elements (see Patent Document 1).

[0006] However, the partitions proposed so far often have wall surfaces that are vertical or inclined at a certain angle, and the light reflected by the partitions is reflected linearly. Therefore, from the perspective of the viewer of the display device, light at a specific angle is emphasized, which can result in the appearance of different brightness depending on the viewing angle. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2015-216104 Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above circumstances, an object of the present invention is to provide a micro LED display device that displays images with uniform brightness even when the viewing angle changes. [Means for solving the problem]

[0009] As a means for solving the above problems, the invention described in claim 1 of the present invention comprises at least: A plurality of LED elements arranged in a grid on a substrate, and The micro LED display device has a partition wall that separates the display area, and the side wall surface of the partition wall is spherical.

[0010] Furthermore, the invention described in claim 2 is the micro LED display device described in claim 1, characterized in that a diffuse reflection layer is formed on the surface of the side wall surface.

[0011] Furthermore, the invention described in claim 3 is a micro LED display device described in claim 2, characterized in that a diffuse reflection layer is formed between the partition wall and the LED element on the surface of the substrate having the partition wall and the LED element.

[0012] The invention of claim 4 is the micro LED display device of any one of claims 1 to 3, characterized in that the plurality of LED elements emit any of red, green, and blue light.

[0013] Furthermore, the invention described in claim 5 is a micro LED display device described in any one of claims 1 to 3, characterized in that the plurality of LED elements are LED elements that emit white light and are provided with a color filter substrate on the side walls.

[0014] The invention of claim 6 is the micro LED display device of any one of claims 1 to 5, characterized in that the light-blocking material layer is a black photosensitive resin layer. [Effects of the Invention]

[0015] According to the micro LED display device of the present invention, the spherical sidewalls cause the light emitted from the LED element to be scattered and diffused within the cavity, resulting in stable display quality regardless of the viewer's viewing angle. [Brief explanation of the drawings]

[0016] [Figure 1] 1A and 1B are explanatory diagrams showing the cross-sectional structure of the partition wall in the first embodiment of the micro LED display device of the present invention, with and without a diffuse reflection layer, respectively. [Figure 2] 1A and 1B are explanatory diagrams showing the cross-sectional structures of a micro LED display device according to a second embodiment of the present invention, with and without a diffuse reflection layer, respectively; [Figure 3] FIG. 2 is a flow chart showing the manufacturing process of the first embodiment of the micro LED display device of the present invention. [Figure 4] FIG. 2 is a flow chart showing the manufacturing process of a second embodiment of the micro LED display device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] <Micro LED display device> (First embodiment) A first embodiment of the partition wall of the micro LED display device of the present invention will be described with reference to FIG. 1(a).

[0018] The first embodiment 10-1 of the partition wall of the micro LED display device of the present invention is a micro LED display device 10 in which each LED chip 3 on a substrate 1 on which a plurality of LED chips are mounted in an XY matrix is ​​arranged on the bottom surface 8 of a cavity 5 formed in a light-shielding material layer 4 formed on the substrate 1 containing the LED chip 3.

[0019] As the LED chips, LED chips 3-1, 3-2, and 3-3 each having a different light emission color were mounted on the substrate 1. Although not shown, the LED chips 3-1, 3-2, and 3-3 may be one type of LED element having a peak in the blue or ultraviolet region, and the cavity 5 may be filled with a material for wavelength conversion to red or green, or a blue color filter material, to obtain red light, green light, and blue light. The method may be used.

[0020] The cavity 5 is a space having a spherical wall surface consisting of a bottom surface 8 and a side wall surface 9. (Since the space and the cavity 5 are the same, hereinafter it will also be referred to as the space 5.) The substrate 1 may or may not be exposed to the bottom surface 8.

[0021] On the side of the space 5 opposite to the bottom surface 8, an opening 6 is provided that allows the light emitted from the LED chip 3 to exit the space 5 to the outside.

[0022] A characteristic feature of the cavity 5 is that, in a cross section taken along a cutting line (not shown) passing through the center of the cavity 5 in a plan view, the curve formed by the surface of the side wall surface 9 of the cavity 5 is a curve that is convex outward from the cavity 5. For example, as shown in FIG. 1( a), a nearly spherical cavity or a cavity in which the side wall surface 9 of a rectangular parallelepiped bulges outward is included, but any other three-dimensional cavity may be included as long as the side wall surface of the cavity bulges outward. In a cross section taken along a cutting line passing through the center of the cavity in a plan view, the curves formed by the surface of the side wall surface of such a three-dimensional cavity are all curves that are convex outward.

[0023] For example, this applies to a case where the cross section of the side wall surface 9 of the cavity 5 forms a reverse tapered space (a space in which the opening dimension of the opening 6 is small and the width of the hollow space widens toward the bottom surface 8 of the cavity 5). By placing the LED chip 3 at the bottom 8 of such a space 5, it becomes possible to effectively block the component of the light emitted from the LED chip 3 in a direction parallel to the surface of the substrate 1.

[0024] Furthermore, the cross section of the side wall surface 9 of the cavity 5 may not be inversely tapered, but may instead be a shape in which an inverse tapered shape is combined with a tapered shape, as shown in FIG. 1( a). In this case, the width of the partition 2 is wide at the opening 6 on the substrate 1 side and on the side opposite to the substrate 1 side (bottom surface 8 side) in the cross section, and narrows as it approaches the bottom surface 8 from the opening 6. The width of the partition 2 is narrowest at the midpoint between the opening 6 and the bottom surface 8, and widens again once it passes the midpoint. In this type of configuration, it is sufficient that the curve formed by the surface of the side wall surface 9 of the cavity 5 is a curve that is convex toward the partition 2 side. For example, it may be an arc that is part of a circumference (when the cavity is spherical), or it may be a curve formed by an aspherical cross section.

[0025] As described above, because the cross-sectional shape of the partition wall 2 is inversely tapered, light emitted from the LED chip 3 in various directions at angles closer to a direction parallel to the surface of the substrate 1 is less likely to exit the opening 6 and is blocked by the opening 6. For example, even if light emitted toward the opening 6 is reflected once by the side wall surface 9 toward the opening 6, the concave mirror-like structure prevents it from continuing to reflect toward the opening 6. Repeated reflections attenuate the light intensity. If the side wall surface 9 is black, the light is absorbed without being reflected. This reduces the component parallel to the plane of the substrate 1, thereby suppressing uneven brightness and color. On the other hand, if the cross-sectional shape of the partition wall 2 is tapered, the light emitted from the LED chip 3 that is reflected by the side wall surface 9 exits the opening 6 toward the outside. This makes it difficult to reduce the component parallel to the plane of the substrate 1. This is the same even if the cross-sectional shape of the partition wall 2 is cylindrical.

[0026] (Second embodiment) Next, a second embodiment of the micro LED display device of the present invention will be described with reference to FIG.

[0027] The difference between the second embodiment of the micro LED display device 10-2 of the present invention and the micro LED display device 10-1 of the first embodiment is that the cavity in the second embodiment 5 has a diffuse reflection layer 7 formed on the surface of the side wall surface 9 thereof. By forming the diffuse reflection layer 7, the intensity of the light emitted from the opening 6 can be increased.

[0028] The diffuse reflection layer 7 is preferably made of a light-scattering white layer, and has a surface that can reflect and scatter incident light with a high reflectance of 80% or more in the visible light range.

[0029] The material for the diffuse reflective layer 7 is preferably one containing various white pigments. The white pigment is not particularly limited as long as it has light scattering properties, but zinc oxide (zinc oxide), barium sulfate, lithopone (a mixture of barium sulfate BASO4 and zinc sulfide ZnS), titanium white (titanium (IV) oxide), etc. are preferably used. The white pigment is then mixed with a solvent, binder, dispersant, leveling agent, etc., and the light reflective layer 7 is formed on the inner wall of the cavity 5 using a white paint prepared so as to uniformly disperse the white pigment.

[0030] A suitable method for forming the diffuse reflection layer 7 is to mask the flat surfaces of the partition walls of the substrate shown in Figures 1(a) and 2(a) and the surfaces of LED3-1 to LED3-3 with a thin film of resin or the like, and then spray the above-mentioned white paint from a nozzle to apply it.

[0031] (Third embodiment) Next, a third embodiment of the micro LED display device of the present invention will be described with reference to FIG. 2(a).

[0032] The difference between the micro LED display device 10-3 in the third embodiment of the present invention and the micro LED display device 10-1 in the first embodiment is that the micro LED display device 10-3 in the third embodiment is provided with a planarization layer 11.

[0033] More specifically, this will be explained below. This is a micro LED display device 10-3 in which each LED chip 3 on a substrate 1 on which multiple LED chips 3 are mounted in an XY matrix is ​​placed on the bottom surface 8 of a cavity 5 formed in a light-blocking material layer 4 formed on the substrate 1 containing the LED chips 3.

[0034] The convex portions of the LED chips 3 on the substrate 1 are flattened by a flattening layer 11 formed on the substrate 1. The thickness of the LED chip 3 may be about 150 μm. Therefore, the LED chips 3 may have convex or protruding portions with a height of about 150 μm from the surface of the substrate 1.

[0035] It is difficult to form a light-shielding material layer 4 directly on a substrate 1 with protrusions of such height. While it is possible to form a light-shielding material layer 4 with a thickness of approximately 200 μm, for example, if a black photosensitive resin is used, the thickness is too thick to allow for proper patterning. Therefore, the protrusions consisting of each LED chip 3 on the substrate 1 are first planarized with a planarizing resin 11. The planarizing resin 11 can be a photosensitive or non-photosensitive transparent resin. When using a non-photosensitive transparent resin, the planarizing resin 11 is formed so that each LED chip 3 is embedded, and then planarization is performed. When using a photosensitive transparent resin, planarization can be achieved by adjusting the application, exposure, and development conditions. Furthermore, depending on the exposure conditions, the planarizing resin 11 layer can be made thinner only in the area of ​​each LED chip 3, allowing for the formation of a taller partition wall 2.

[0036] The top surface of the LED chip 3 on the substrate 1 and the top surface of the planarizing resin 11 are flattened to be flush with each other. A light-shielding material layer 4 is formed on the thus-formed substrate. The subsequent steps are the same as those in the first embodiment.

[0037] (Fourth embodiment) Next, a fourth embodiment of the micro LED display device of the present invention will be described with reference to FIG. 2(b).

[0038] The difference between the micro LED display device 10-4 in the fourth embodiment of the present invention and the micro LED display device 10-3 in the third embodiment is that a diffuse reflection layer 7 is formed on the surface of the side wall surface 9 of the cavity 5 in the third embodiment. By forming the diffuse reflection layer 7, the intensity of the light emitted from the opening 6 can be increased. Other than that, it is the same as the third embodiment.

[0039] <Method of manufacturing a micro LED display device> Next, a method for manufacturing a micro LED display device of the present invention will be described with reference to FIGS. 3 and 4. FIG. 3 is an explanatory diagram of a manufacturing method in which the surface on which the LED chip 3 is mounted is not planarized, and FIG. 4 is an explanatory diagram of a manufacturing method in which the surface is planarized. The method for manufacturing a micro LED display device of the present invention includes at least some or all of the following steps: First, a substrate 1 is prepared on which LED chips 3 (3-1, 3-2, 3-3) are mounted in an XY matrix (FIGS. 3(a) and 4(a)). The substrate is then subjected to a process selected from the following processing steps. (1) Planarization of the substrate surface (Figure 4(b)) (2) Step of forming a light-shielding material layer (FIG. 3(b) and FIG. 4(c)) (3) A process of forming a cavity in the light-shielding material layer (FIGS. 3(c), (d), 4(d), ( e)) (4) Step of forming a scattering reflective layer on the sidewall surface of the cavity (Figure 3(e) and Figure 4(f))

[0040] Specifically, the following selections are possible: The manufacturing method of the micro LED display device 10-1 of the first embodiment includes at least the steps (2) and (3) among the above steps. The manufacturing method of the micro LED display device 10-2 of the second embodiment includes at least the steps (2), (3), and (4) of the above steps. The manufacturing method of the micro LED display device 10-3 of the third embodiment includes at least the steps (1), (2), and (3) of the above steps. The manufacturing method of the micro LED display device 10-4 of the fourth embodiment includes at least the steps (1), (2), (3), and (4) of the above steps.

[0041] (1) Planarization of the substrate surface (see Figure 4(b)) When it is necessary to flatten the protrusions caused by the LED chip 3 mounted on the substrate 1, a flattening process is performed on the substrate surface. For example, when a liquid light-blocking material is used to form the light-blocking material layer, and the protrusions caused by the LED chip 3 hinder coating, a flattening process is performed. When a dry film with a thickness equivalent to the protrusions caused by the LED chip 3 is laminated as the material to form the light-blocking material layer, or when the thickness of the LED chip 3 is sufficiently thin, there is no need to perform a flattening process.

[0042] By applying a coating liquid containing at least a resin and a solvent onto the substrate 1 and drying it, the thickness of the film after drying becomes equal to the height of the LED chip 3 formed on the substrate 1. A flattening layer 11 is formed. The coating liquid preferably contains a leveling agent that promotes flattening in addition to the resin and solvent.

[0043] The coating method should be one that can produce a coating thickness equivalent to the height of the LED chip 3. Examples include knife coating and bank coating. These methods use a medium to high viscosity coating liquid of 1000 mPa·s (1 Pa·s) or more, which can produce a coating film thickness of 50 μm or more. Other examples include forward roll coating and slot die coating. These coating methods can be used to form a coating film thickness of approximately 200 μm to 300 μm using a coating liquid with a viscosity of 0.1 Pa·s to 10 Pa·s.

[0044] As the coating liquid, a non-photosensitive coating liquid and a photosensitive coating liquid can be used.

[0045] In the case of a non-photosensitive coating liquid, it may be transparent or opaque. By adjusting the composition and viscosity of the coating liquid and the coating method and conditions, it is possible to form a planarizing film 11 with a thickness equivalent to the protrusions caused by the LED chip 3, thereby achieving planarization of the surface of the coating film.

[0046] In the case of photosensitive coatings, transparent coatings are used. With opaque coatings, the exposure light cannot reach deep parts in the film thickness direction, resulting in insufficient exposure and peeling due to insufficient adhesion to the base. The advantage of photosensitive coatings is that they can be flattened by adjusting the composition of the coating, coating conditions, exposure conditions, and development conditions. The disadvantage is that the materials are expensive.

[0047] In addition, as the material of the planarization layer 11 used in the planarization process of the substrate, a dry film-like A planarizing film can also be used to thermally laminate the LED chip onto the substrate. In this case, as with the coating liquid, both photosensitive and non-photosensitive materials can be used.

[0048] (2) Step of forming a light-shielding material layer (see FIG. 3(b) and FIG. 4(c)) A light-shielding material layer 4 is formed on a substrate 1 having an LED chip 3 mounted thereon (FIG. 3(b)), or on a substrate 1 having an LED chip 3 mounted thereon and further planarized by a planarization layer 11 (FIG. 4(c)). The light-shielding material layer 4 may be formed by applying a liquid photosensitive light-shielding material, or by laminating a dry film-like photosensitive light-shielding material.

[0049] As shown in FIG. 3(b), when the thickness of the LED chip 3 is thin enough that there is no need to form the planarizing layer 11, the light-shielding material layer 4 can be formed as is.

[0050] When it is necessary to form a planarization layer 11, first, as shown in FIG. 4(b), the surface of the substrate 1 (FIG. 4(a)) on which the LED chip 3 is mounted is planarized by forming a planarization layer 11, and then a light-shielding material layer 4 is formed.

[0051] The light-shielding material forming the light-shielding material layer 4 need not be particularly limited as long as it can be a light-sensitive light-shielding material obtained by mixing a material capable of blocking light emitted from the LED chip 3 with a negative photosensitive resin. For example, a liquid or dry film black photosensitive resin used to form the black matrix of a color filter for a liquid crystal display device can be suitably used.

[0052] (3) Step of forming a cavity in the light-shielding material layer (see FIGS. 3(c), (d) and 4(d), (e)) The light-shielding material layer 4 is exposed to light through a photomask with a desired pattern. Next, a development process is performed (see FIGS. 3(c) and 4(d)). After the development process is completed, the sidewall surface of the hole that will become the formed cavity 5 has a curve that is convex outward from the hole in a cross section taken along a cutting line that passes through the center of the hole in a plan view. However, the curve is not necessarily smooth, and the surface after the development process is not necessarily smooth.

[0053] Next, a heat treatment is performed at a temperature equal to or higher than the softening temperature of the resin of the light-shielding material that constitutes the light-shielding material layer 4. As a result of this treatment, as shown in Figures 3(d) and 4(e), in a cross section taken along a cutting line that passes through the center of the cavity 5 in a plan view, the curve formed by the surface of the side wall surface 9 of the cavity 5 becomes a smooth curve that is convex outward from the cavity 5, and the surface of the side wall surface also becomes a smooth surface.

[0054] When the light-shielding material layer 4 is a negative photosensitive resin layer, the photomask pattern is formed so that the partition wall 2 portion is exposed. The surface of the partition wall 2 is most strongly exposed, and the amount of exposure to the light-shielding material decreases as the depth from the surface increases in the film thickness direction (the direction approaching the surface of the substrate 1). If the amount of exposure is insufficient, the adhesion between the underlying substrate 1 or planarization layer 11 and the light-shielding material layer 4 weakens, causing the partition wall 2 to peel off from the underlying substrate. A sufficient amount of exposure is required so that the pattern of the partition wall 2 does not peel off after development. The unexposed portions shielded by the photomask are removed by the development process, forming the cavities 5.

[0055] The amount of the exposed light-shielding material layer 4 that is dissolved and removed by the development process increases as the exposure level decreases from the surface toward the substrate. The dissolution and removal of the light-shielding material layer 4 proceeds isotropically from the surface. Therefore, during the development process, the unexposed portions of the light-shielding material layer 4 are dissolved and removed isotropically, forming the cavity 5. The exposed portions of the light-shielding material layer 4 remain undissolved, but the exposure level decreases as the layer progresses deeper in the film thickness direction, allowing for easier dissolution and removal. As a result, an inverse tapered shape forms as the development process progresses. When the dissolution reaches the substrate 1, the curve formed by the surface of the sidewall surface 9 of the cavity 5 in a cross section taken along a cutting line passing through the center of the cavity 5 in a plan view forms a convex curve outward from the cavity 5 (see Figure 1(a)). This results in a tapered shape from the substrate 1 toward the opening 6. When development is further performed, the light-shielding material layer 4 is removed more toward the base, and the partition walls 2 as a whole assume an inverse tapered shape (not shown). If the current processing is further performed, the base of the partition walls 2 will be completely removed, and the partition walls 2 will peel off. For this reason, development is preferably performed so that the cross-sectional shape of the partition walls 2 becomes wider on the upper side (opening 6 side) and base side (substrate 1 side) and is narrowest in the middle between the upper side (opening 6 side) and the lower side (substrate 1 side), or so that the partition walls 2 as a whole assume an inverse tapered shape.

[0056] (4) A step of forming a scattering reflection layer on the sidewall surface of the cavity (see Figure 3(e) and Figure 4(f)). The procedure for forming the diffuse reflection layer 7 on the side wall surface 9 of the cavity 5 of the substrate shown in FIG. 3(d) or FIG. 4(e) will be described. An appropriate resin mask (not shown) is formed on the flat surface of the partition wall 2 and the surfaces of the LEDs 3-1 to 3-3 in FIG. 3(d) or FIG. 4(e). Next, the white pigment is mixed with a solvent, binder, dispersant, leveling agent, etc., and the white paint in which the white pigment is uniformly dispersed is applied to the inside of the cavity 5 using a spray coater. The solvent in the applied white paint is then evaporated, and a baking process is performed to further increase adhesion, thereby forming the diffuse reflective layer 7. [Explanation of symbols]

[0057] 1. Substrate 2. Partition (made of light-shielding material) 3, 3-1, 3-2, 3-3... LED chip 4...Light-shielding material layer 5. Cavity 6. Opening 7. Diffuse reflection layer 8 Bottom 9. Side wall 10, 10-1, 10-2, 10-3, 10-4... Micro LED display device 11...Planarization layer

Claims

1. A micro LED display device having at least a plurality of LED elements arranged in a grid pattern on a substrate and partition walls separating the plurality of LED elements, The side wall surface of the partition wall is spherical, A micro LED display device, characterized in that the width of the cross section of the partition narrows as it approaches the midpoint of the partition from the side opposite the substrate, and widens as it passes the midpoint and approaches the substrate side.

2. The micro LED display device according to claim 1 , wherein a diffuse reflection layer is formed on the surface of the side wall surface.

3. 3. The micro LED display device according to claim 2, wherein a diffuse reflection layer is formed between the partition walls and the LED elements on the surface of the substrate having the partition walls and the LED elements.

4. 4. The micro LED display device according to claim 1, wherein the plurality of LED elements emit any one of red, green, and blue light.

5. 4. The micro LED display device according to claim 1, wherein the plurality of LED elements are LED elements that emit white light, and a color filter substrate is provided on the partition wall.

6. 6. The micro LED display device according to claim 1, wherein the partition wall is a black photosensitive resin layer.

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