JP7764703B2 - Micro LED display device - Google Patents

Description

The present invention relates to a micro LED display device. More specifically, it relates to a partition structure for a micro LED display device.

Organic electroluminescence display devices (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 burn-in to occur when the current is increased. Recently, displays using LEDs (LED displays) made from inorganic materials 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 amount of current (allowing for brighter displays).

In recent years, attention has been focused on a technology for LCD displays that uses direct-type backlights known as mini-LEDs, which are made up of multiple LED chips measuring 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.

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, eliminating the need for liquid crystal shutters.

In micro LED display devices, light-emitting elements, including light-emitting diodes, are point light sources, resulting in a wide distribution of light emission brightness. As a result, some of the light emitted from the light-emitting elements can 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).

However, previously proposed partitions often have wall surfaces that are vertical or inclined at a certain angle, and since light reflected by the partitions is reflected linearly, light at certain angles is emphasized from the perspective of the viewer of the display device, which can result in perceived differences in brightness depending on the viewing angle.

Patent Publication No. 2015-216104

In light of the above circumstances, the present invention aims to provide a micro LED display device that displays images with uniform brightness even when the viewing angle changes.

As a means for solving the above problems, the invention described in claim 1 of the present invention comprises at least:
A micro LED display device having a plurality of LED elements arranged in a grid pattern on a substrate and partitions separating the plurality of LED elements, characterized in that the side wall surfaces of the partitions are spherical.

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.

Furthermore, the invention described in claim 3 is the 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.

Furthermore, the invention described in claim 4 is a micro LED display device described in any one of claims 1 to 3, characterized in that the multiple LED elements emit red, green, or blue light.

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 multiple LED elements are LED elements that emit white light and a color filter substrate is provided on the side walls.

Furthermore, the invention described in claim 6 is a micro LED display device described in any one of claims 1 to 5, characterized in that the light-blocking material layer is a black photosensitive resin layer.

In the micro LED display device of the present invention, the spherical sidewalls cause the light emitted from the LED element to be scattered within the cavity as diffused light, resulting in stable display quality that is independent of the viewer's viewing angle.

3A and 3B are explanatory diagrams showing cross-sectional structures of the partition walls of the micro LED display device according to the first embodiment of the present invention, respectively, with and without a diffuse reflection layer; 1A and 1B are explanatory diagrams showing 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; FIG. 2 is a flow diagram showing the manufacturing process of the first embodiment of the micro LED display device of the present invention. FIG. 4 is a flow diagram showing the manufacturing process of a second embodiment of the micro LED display device of the present invention.

<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.

The first embodiment of the partition wall 10-1 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 multiple LED chips are mounted in an XY matrix is disposed 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.

As the LED chips, LED chips 3-1, 3-2, and 3-3 each having a different light emission color were mounted on a substrate 1.
Furthermore, 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 that converts the wavelength to red or green, or a blue color filter material, to obtain red light, green light, and blue light.

The cavity 5 consists of a space with spherical walls consisting of a bottom surface 8 and side wall surfaces 9. (Since the space and the cavity 5 are the same, hereafter it will also be referred to as the space 5.) The substrate 1 may or may not be exposed on the bottom surface 8.

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

A characteristic of this cavity 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 9 of the cavity 5 is a curve that convex outward from the cavity 5. For example, as shown in Figure 1(a), this applies to a roughly spherical cavity or a cavity in which the side wall 9 of a rectangular parallelepiped bulges outward, but any other three-dimensional cavity can also be used as long as the side wall of the cavity is bulging 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 of such a three-dimensional cavity are all curves that convex outward.

For example, this applies when the cross section of the side wall surface 9 of the cavity 5 forms a reverse-tapered space (a space in which the opening dimensions of the opening 6 are 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.

In addition, the cross section of the side wall surface 9 of the cavity 5 may not be inversely tapered, but may instead be a shape that combines an inverse tapered shape with a tapered shape, as shown in Figure 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 moves from the opening 6 to the bottom surface 8. 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, the curve formed by the surface of the side wall surface 9 of the cavity 5 is sufficient as long as it is a curve that is convex toward the partition 2 side. For example, it may be an arc that is part of a circumference (if the cavity is spherical), or it may be a curve formed by an aspherical cross section.

As described above, because the cross-sectional shape of the partition wall 2 is inversely tapered, of the light emitted in various directions from the LED chip 3, light emitted at angles closer to a direction parallel to the surface of the substrate 1 is less likely to escape through 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, 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 impossible to reduce the component parallel to the plane of the substrate 1. The same applies even if the cross-sectional shape of the partition wall 2 is cylindrical.

Second Embodiment
Next, a second embodiment of the micro LED display device of the present invention will be described with reference to FIG.

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 a diffuse reflection layer 7 is formed on the surface of the side wall surface 9 of the cavity 5 in the second embodiment.
By forming the diffuse reflection layer 7, the intensity of the light emitted from the opening 6 can be increased.

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

The material for the diffuse reflection 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-reflecting 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.

The preferred method for forming the diffuse reflection layer 7 is to mask the flat surfaces of the partition walls of the substrate and the surfaces of LEDs 3-1 to 3-3 shown in Figures 1(a) and 2(a) with a thin film of resin or the like, and then spray coat the white paint described above from a nozzle.

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

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

More specifically, this will be explained below.
The micro LED display device 10-3 has a substrate 1 on which a plurality of LED chips 3 are mounted in an XY matrix, and each LED chip 3 is disposed on the bottom surface 8 of a cavity 5 formed in a light-shielding material layer 4 formed on the substrate 1 including the LED chips 3.

The convex portions of each LED chip 3 on the substrate 1 are planarized by a planarization layer 11 formed on the substrate 1. The thickness of the LED chip 3 may be approximately 150 μm. As a result, the LED chips 3 may have convex or protruding portions with a height of approximately 150 μm from the surface of the substrate 1.

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 would be too great to properly pattern. Therefore, the protrusions formed by each LED chip 3 on the substrate 1 are first planarized using a planarizing resin 11. A photosensitive or non-photosensitive transparent resin can be used as the planarizing resin 11. When using a non-photosensitive transparent resin, a layer of the planarizing resin 11 is applied 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 layer of the planarizing resin 11 can be made thinner only in the area of each LED chip 3, allowing for the creation of taller partition walls 2.

The light-shielding material layer 4 is formed on the substrate 1, which has been planarized so that the top surface of the LED chip 3 on the substrate 1 is flush with the top surface of the planarizing resin layer 11. The subsequent steps are the same as those in the first embodiment.

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

The difference between the micro LED display device 10-4 of the fourth embodiment of the present invention and the micro LED display device 10-3 of 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.

<Method of manufacturing a micro LED display device>
Next, a method for manufacturing a micro LED display device according to the present invention will be described with reference to FIGS.
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. 3A and 4A). The substrate is subjected to a process selected from the following processes.
(1) Substrate surface planarization step (FIG. 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 reflection layer on the sidewall surface of the cavity (FIG. 3(e) and FIG. 4(f))

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) of 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.

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

A coating liquid containing at least a resin and a solvent is applied onto the substrate 1 and dried to form the planarizing layer 11 under conditions such that the thickness of the film after drying is equal to the height of the LED chip 3 formed on the substrate 1. In addition to the resin and the solvent, the coating liquid preferably contains a leveling agent that promotes planarization.

A coating method that can produce a coating thickness equivalent to the height of the LED chip 3 can be selected. Examples include knife coating and bank coating. These coating methods use a medium to high viscosity coating liquid of 1000 mPa·s (1 Pa·s) or more, making it possible to obtain a coating film thickness of 50 μm or more. Other coating methods 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.

Both non-photosensitive and photosensitive coating fluids can be used as coating fluids.

In the case of a non-photosensitive coating liquid, it can be either transparent or opaque. By adjusting the composition and viscosity of the coating liquid, as well as 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 flattening the surface of the coating film.

When using a photosensitive coating, a transparent coating is used. With an opaque coating, the exposure light cannot reach deep into the film thickness, resulting in insufficient exposure and peeling due to insufficient adhesion to the base. The advantage of a photosensitive coating is that it can be flattened by adjusting the composition of the coating, the coating conditions, the exposure conditions, and the development conditions. The disadvantage is that the material is expensive.

Furthermore, a dry film-like planarization film can be used as the material for the planarization layer 11 used in the substrate planarization process, and can be thermally laminated onto the substrate on which the LED chip is mounted. In this case, as in the case of using a coating liquid, both photosensitive and non-photosensitive materials can be used.

(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.

As shown in Figure 3(b), if the thickness of the LED chip 3 is thin enough that there is no need to form a planarization layer 11, the light-blocking material layer 4 can be formed as is.

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

The light-blocking material that forms the light-blocking material layer 4 need not be particularly limited, as long as it can be a light-sensitive light-blocking material that is a mixture of a material capable of blocking light emitted from the LED chip 3 and a negative-type photosensitive resin. For example, a liquid or dry-film black photosensitive resin that is used to form the black matrix of color filters for liquid crystal display devices can be suitably used.

(3) Step of forming a cavity in the light-shielding material layer (see FIGS. 3(c) and 3(d) and FIGS. 4(d) and 4(e))
The light-shielding material layer 4 is exposed to light through a photomask having a desired pattern. Development is then performed (see FIGS. 3( c) and 4(d)). Upon completion of the development, the sidewall surface of the hole that will become the cavity 5 will have 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 development is not necessarily smooth.

Next, a heat treatment is performed at a temperature equal to or higher than the softening temperature of the light-shielding resin 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, rather than a curve that is convex outward from the cavity 5, and the surface of the side wall surface also becomes a smooth surface.

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 (toward the surface of the substrate 1). If the exposure amount 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 partition wall 2 pattern does not peel off after development. The unexposed portions shielded by the photomask are removed by the development process, forming cavities 5.

The amount of light-blocking material layer 4 that is exposed to light decreases as it approaches the substrate, resulting in a greater amount of dissolution and removal during development. Dissolution and removal of the light-blocking material layer 4 proceeds isotropically from the surface. Therefore, during development, the unexposed portions of the light-blocking material layer 4 are dissolved and removed isotropically, forming the cavity 5. The exposed portions of the light-blocking material layer 4 remain undissolved, but the amount of exposure decreases as the thickness increases, allowing for easier dissolution and removal. As development progresses, an inverse tapered shape forms. When the dissolution reaches the substrate 1, the curve formed by the surface of the sidewall 9 of the cavity 5 forms a convex curve outward from the cavity 5 in a cross section taken along a cutting line passing through the center of the cavity 5 in a plan view (see Figure 1(a)). This results in a tapered shape extending from the substrate 1 toward the opening 6. Further development removes more of the light-shielding material layer 4 closer to the base, resulting in an inversely tapered shape for the entire partition wall 2 (not shown). If the current processing is continued further, the base for the partition wall 2 will be completely removed, causing the partition wall 2 to peel off. For this reason, development is preferably performed so that the cross-sectional shape of the partition wall 2 is wider on the upper side (opening 6 side) and base side (substrate 1 side) and is narrowest midway between the upper side (opening 6 side) and the lower side (substrate 1 side), or so that the entire partition wall 2 has an inversely tapered shape.

(4) Step of forming a scattering reflection layer on the sidewall surface of the cavity (see FIG. 3(e) and FIG. 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, a binder, a dispersant, a leveling agent, etc., and a 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.

DESCRIPTION OF SYMBOLS 1... Substrate 2... Partition wall (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 surface 9... Side wall surface 10, 10-1, 10-2, 10-3, 10-4... Micro LED display device 11... Planarization layer

Claims (6)

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. 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. The micro LED display device described in claim 2, characterized in that a diffuse reflection layer is formed between the partition walls and the LED elements on the surface of the substrate bearing the partition walls and the LED elements. A micro LED display device according to any one of claims 1 to 3, characterized in that the plurality of LED elements emit red, green, or blue light. 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 . The micro LED display device described in any one of claims 1 to 5, characterized in that the partition wall is a black photosensitive resin layer.