Display device and method of manufacturing the same

Abstract

To provide a display device in which a barrier function is enhanced by improving a color filter layer, and to provide a method for manufacturing the same.SOLUTION: A display device of the present invention includes a display pixel in which a light-emitting element, a color conversion layer, and a color filter layer are laminated in this order on a substrate, wherein the display pixel includes a red display pixel, a green display pixel, and a blue display pixel, and a film reduction rate of the color filter layer is 5.0% or less in a chemical resistance test. In the present invention, the film thickness loss is preferably 2.0% or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a display device and a manufacturing method thereof. [Background technology]

[0002] Patent Document 1 discloses an invention related to a micro LED display device. The micro LED display device in Patent Document 1 includes a sealing portion, a low refractive index layer, and a color conversion layer (wavelength conversion layer) stacked on a micro LED array substrate, and further includes a color filter that may be disposed on the color conversion layer.

[0003] Patent Document 2 discloses an invention relating to a light-emitting device in which a phosphor layer is sandwiched between sealing films having gas barrier properties, and describes that the sealing films are formed to a thickness of about 100 nm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-155737 [Patent Document 1] International Publication No. 2021 / 166785 Summary of the Invention [Problem to be solved by the invention]

[0005] However, oxygen and water permeate the color filter layer and deactivate the phosphor particles, particularly the quantum dots, contained in the color conversion layer, resulting in a problem of reduced color purity and brightness. In Patent Document 2, the sealing film has gas barrier properties, and thus can block oxygen and water to some extent, but the sealing film is thin and does not have sufficient barrier function.

[0006] The present invention has been made in view of the above points, and an object of the present invention is to provide a display device having an improved color filter layer and enhanced barrier function, and a method for manufacturing the same. [Means for solving the problem]

[0007] One embodiment of the display device of the present invention is characterized in that it has display pixels in which a light-emitting element, a color conversion layer, and a color filter layer are stacked in this order on a substrate, and the film loss rate of the color filter layer is 5.0% or less in a chemical resistance test. [Effects of the Invention]

[0008] According to the display device of the present invention, by improving the barrier function of the color filter layer against oxygen and water, deterioration of the phosphor particles, such as quantum dots, contained in the color conversion layer can be suppressed, and color purity and brightness can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a micro LED display as a display device according to the present embodiment. [Figure 2] FIG. 2A is a schematic diagram showing an image of the gas barrier property in Patent Document 1, FIG. 2B is a schematic diagram showing an image of the gas barrier property in Patent Document 2, and FIG. 2C is a schematic diagram showing an image of the gas barrier property in the present embodiment. [Figure 3] FIG. 2 is a schematic diagram illustrating the structure of an evaluation sample. [Figure 4] 10 is a graph showing the relationship between the film reduction rate of the color filter layer and the rate of change in front luminance. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes in detail an embodiment of the present invention, but the following description is an example (typical example) of the embodiment of the present description, and the present invention is not limited to these details as long as it does not deviate from the gist of the present invention. Furthermore, the notation "to" used below includes both the lower limit and the upper limit within the range.

[0011] <Background to the invention of the display device of this embodiment> Liquid crystal on silicon (LCOS), laser beam scanning (LBS), or organic light-emitting diode (OLED) microdisplays are becoming mainstream for applications such as head-mounted displays for AR (Augmented Reality) / MR (Mixed Reality). However, these methods do not provide sufficient brightness in outdoor light, and are therefore primarily used indoors.

[0012] In contrast, the micro LED method is considered to have an advantage over the above methods in terms of brightness, and its application is expected to expand in the future.

[0013] As a method of displaying full color using a micro LED display, a technology has been proposed in which blue light-emitting elements are used as light-emitting elements (LEDs), and color conversion (wavelength conversion) is performed using a color conversion layer using quantum dots to enable RGB display.

[0014] Furthermore, to prevent blue light that has not been fully wavelength converted by the color conversion layer from mixing with the red and green display pixels and reducing color purity, a color filter layer is provided to reduce blue light noise excited from the light-emitting element.

[0015] In this type of micro LED display structure, the quantum dots contained in the color conversion layer are prone to degradation due to oxygen and water that pass through the color filter layer, resulting in a decrease in the brightness and color purity of the micro LED display.

[0016] Therefore, the inventors conducted extensive research and invented a display device that has excellent brightness and color purity by improving the gas barrier properties of the color filter layer, thereby suppressing the deterioration of phosphor particles, particularly quantum dots, due to oxygen and water.

[0017] <Description of the Display Device of the Present Embodiment> The display device in this embodiment is configured as a micro LED (Light Emitting Diode) display 1 shown in Fig. 1. Fig. 1 is a schematic cross-sectional view of the micro LED display 1.

[0018] As shown in Fig. 1, the micro LED display 1 includes a plurality of display pixels 2a, 2b, and 2c. For example, the display pixel 2a shown in Fig. 1 is a red display pixel, the display pixel 2b is a green display pixel, and the display pixel 2c is a blue display pixel.

[0019] 1, a plurality of light-emitting elements 4 are arranged on a substrate 3. For example, the light-emitting elements 4 are arranged in a matrix on the substrate 3. Each light-emitting element 4 is a micro LED that emits blue light.

[0020] As shown in Fig. 1, partition walls 5 are formed on the substrate 3 to separate the light-emitting elements 4 from one another. The partition walls 5 are formed so as to surround the periphery of each light-emitting element 4 in a plan view. In this embodiment, the material of the partition walls 5 is not limited. The partition walls 5 may extend to the position of the color filter layer 11. By providing the partition walls 5 also in the color filter layer 11 in this way, it is possible to expect an effect of suppressing color mixing, etc.

[0021] 1, the internal spaces of the partition walls 5 of the red display pixel 2a and the green display pixel 2b are filled with color conversion layers 6a and 6b. As shown in FIG. 1, the color conversion layers of the red display pixel 2a and the green display pixel 2b have red quantum dots 7 and green quantum dots 8 dispersed therein, respectively.

[0022] The quantum dots 7 and 8 are dispersed in a resin 9. The resin 9 is preferably a transparent resin. There are no limitations on the material of the resin 9, but examples thereof include acrylic resins, polyurethane resins, polyester resins, polyolefin resins, polycarbonate resins, polyethyleneimine resins, epoxy resins, and thioether resins.

[0023] Preferably, the red quantum dots 7 have a fluorescence peak wavelength of 600 nm to 680 nm, and the green quantum dots 8 have a fluorescence peak wavelength of 520 nm to 560 nm. These quantum dots 7 and 8 absorb blue light as excitation light irradiated from the light-emitting element 4, and emit red or green light after color conversion.

[0024] Although there are no limitations on the material, the quantum dots 7 and 8 are preferably cadmium-free because the use of cadmium (Cd) is restricted in various countries due to its toxicity. Furthermore, the quantum dots 7 and 8 preferably have a core-shell structure consisting of a core and a shell covering the core, such as ZnSe / ZnS, ZnSe / ZnSeS, ZnTe / ZnS, ZnSeTe / ZnS, or InP / ZnS. However, the quantum dots 7 and 8 may be composed of only a core. Furthermore, to improve dispersibility, the quantum dots 7 and 8 preferably have a ligand (organic ligand) on their surfaces.

[0025] The particle size of the quantum dots 7 and 8 is several nm to several tens of nm. The fluorescence peak wavelength can be controlled by adjusting the particle size and composition. Note that the color conversion layers 6a and 6b may contain phosphors other than the quantum dots 7 and 8.

[0026] On the other hand, as shown in FIG. 1, the internal space of the partition wall 5 of the blue-displaying pixel 2c is filled with a resin 9, but does not contain quantum dots. The resin 9 is preferably a transparent resin. "Transparent" means that the visible light transmittance is 50% or more, preferably 70% or more, and most preferably 90% or more. The visible light transmittance can be measured in accordance with JIS K 7375:2008. However, the blue-displaying pixel 2c can also contain phosphor particles or quantum dots.

[0027] The color conversion layers 6a and 6b may contain phosphor particles other than the quantum dots in addition to or instead of the quantum dots. However, in this embodiment, it is preferable to use the quantum dots 7 and 8 to obtain excellent color purity.

[0028] 1, the surfaces of color conversion layers 6a, 6b and resin 9 may be formed at substantially the same height as partition walls 5, or may be slightly lower than partition walls 5. The thickness of color conversion layers 6a, 6b is approximately 2 to 10 μm.

[0029] 1, a color filter layer 11 is provided on the surfaces of the color conversion layers 6a, 6b and the resin 9 via a barrier layer 10. The color filter layer 11 includes a red filter layer 11a, a green filter layer 11b, and a blue filter layer 11c.

[0030] Although the barrier layer 10 is not an essential layer, its inclusion can improve gas barrier properties and more effectively prevent oxygen and water-induced deterioration of the quantum dots 7 and 8 contained in the color conversion layers 6a and 6b. Furthermore, the inclusion of the barrier layer 10 can reduce the thermal impact on the quantum dots 7 and 8 in the color conversion layers 6a and 6b when the color filter layer 11 is formed. Furthermore, if there are irregularities between the partition walls 5 and the surfaces of the color conversion layers 6a and 6b and the resin 9, the barrier layer 10 can smooth out the irregularities. This allows the color filter layer 11 to be formed on a flat surface. However, a planarizing layer may be provided separately from the barrier layer 10 to smooth out the irregularities. The material of the barrier layer 10 is not limited, but is preferably an inorganic insulating film such as an oxide film or a nitride film, such as SiO2, SiN, Al2O3, AlN, ZrO2, Ta2O3, or ZnO, and is particularly preferably formed of SiO2. The thickness of the barrier layer 10 is not limited, but is about 50 nm to 1 μm, preferably about 100 nm to 1 μm, more preferably about 300 μm to 1 μm, and even more preferably about 500 μm to 1 μm.

[0031] As shown in FIG. 1, microlenses 12a to 12c can be provided on the surface of the color filter layer 11. The microlenses 12a to 12c are optically transparent. Although not limited thereto, the microlenses 12a to 12c can be formed from organic materials such as acrylic resin, epoxy resin, and silicone resin, or inorganic materials such as SiN and SiO2. As shown in FIG. 1, the microlenses 12a to 12c are convex lenses, but they can also be concave lenses. The surface shapes of the microlenses 12a to 12c can be changed in various ways depending on the relationship between the refractive index and the layer located on the surface of the microlenses 12a to 12c.

[0032] <Characteristic configuration of the micro LED display 1 according to the present embodiment> The micro LED display 1 of this embodiment has the following features. That is, the film loss rate of the color filter layer 11 is 5.0% or less in a chemical resistance test. The "film loss rate" will be explained.

[0033] The "film loss rate" is defined as the change in film thickness before and after a chemical resistance test in which the film is immersed in a specified chemical. The "specified chemical" refers to one or more selected from propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monomethyl ether (PGME), and an aqueous solution containing 0.05% tetramethylammonium hydroxide (TMAH) (hereinafter referred to as "TMAH 0.05%"). For any of the chemicals PGMEA, PGME, and TMAH 0.05%, the film loss rate is preferably 5.0% or less.

[0034] The chemical resistance test is carried out at room temperature and pressure, and the immersion time in the chemical is about 3 to 10 minutes. In the chemical resistance test described below, the immersion time was set to 5 minutes.

[0035] The film thickness t1 of the color filter layer before the chemical resistance test and the film thickness t2 of the color filter layer after the chemical resistance test are measured, and the film thickness reduction rate can be obtained by calculating (t2 / t1) × 100 (%). The film thicknesses t1 and t2 can be taken as average film thicknesses. It is preferable to measure the film thickness at the same position before and after the test.

[0036] It is generally known that improving the degree of crosslinking and crosslink density is effective in reducing the water vapor transmission rate (WVTR). Therefore, we focused on the film loss rate, which is an index of the degree of crosslinking and crosslink density of the color filter layer 11. That is, the higher the degree of crosslinking and crosslink density, the smaller the film loss rate. This is common technical knowledge. Specifically, it is known that a high crosslink density results in excellent barrier properties, liquid crystal contamination resistance, chemical resistance, and heat resistance. Specific examples of heat resistance include the degree of film loss and discoloration due to heating.

[0037] In this embodiment, the color filter layer 11 is made of a material such as a thermosetting resin, a thermoplastic resin, or a UV-curable resin, which has a film loss rate of 5.0% or less.

[0038] The color filter layer 11 contains a colorant and a binder resin. The colorant can be variously changed for the red filter layer 11a, the green filter layer 11b, and the blue filter layer 11c. The colorant is contained in an amount of several mass % to several tens of mass % in the entire coloring material. Examples of the binder resin include polysiloxane, polyimide, polybenzoxazole, a polybenzoxazole precursor, and (meth)acrylic polymer. For example, in order to improve the degree of crosslinking and the crosslinking density, a crosslinking aid may be contained in an amount of several mass %. An example of the crosslinking aid is triallyl isocyanurate. Furthermore, during exposure, the crosslink density can be improved by increasing the exposure dose, increasing the baking temperature, or lengthening the baking time.

[0039] In this embodiment, a low water vapor permeability can be obtained by adjusting the film loss rate to 5.0% or less.

[0040] In the present embodiment, it is preferable that the film thickness reduction rate of each of the red filter layer 11a, the green filter layer 11b, and the blue filter layer 11c constituting the color filter layer 11 is 5.0% or less. Even if the blue-displaying pixel 2c does not contain quantum dots, as shown in Fig. 1, by reducing the film thickness reduction rate of the blue filter layer 11c, the gas barrier property of the blue filter layer 11c can be improved, and the barrier function from the blue-displaying pixel 2c to the adjacent red-displaying pixel 2a and green-displaying pixel 2b can be enhanced.

[0041] 2A is a schematic diagram showing an image of the gas barrier properties in Patent Document 1. In Patent Document 1, oxygen and water 20 pass through color filter layer 21 and deactivate quantum dots 23 contained in color conversion layer 22, resulting in a decrease in color purity and brightness.

[0042] FIG. 2B is a schematic diagram illustrating the gas barrier properties of Patent Document 2. In FIG. 2B, a barrier layer 24 having gas barrier properties is interposed between a color filter layer 21 and a color conversion layer 22. Therefore, the barrier layer 24 can block the permeation of oxygen and water 20 to some extent, but not sufficiently. For example, Patent Document 2 specifies a film thickness of 100 nm for the barrier layer 24. However, an inorganic film having a thickness of about 100 nm is prone to pinholes and cracks, and therefore does not provide sufficient gas barrier properties. Therefore, as shown in FIG. 2B, some oxygen and water 20 permeate the barrier layer 24 and deactivate the quantum dots 23 contained in the color conversion layer 22.

[0043] In contrast, in this embodiment, the film loss rate of the color filter layer 11 is adjusted to 5.0% or less in a predetermined chemical resistance test, so that the color filter layer 11 has a high cross-linking density and an excellent barrier function against oxygen and water 20. As a result, as shown in FIG. 2C , the color filter layer 11 can effectively block oxygen and water 20, and can effectively suppress deactivation of the quantum dots 7 and 8 contained in the color conversion layer 9. As a result, the color purity and brightness of the micro LED display 1 can be improved.

[0044] In this embodiment, the barrier layer 10 is provided between the color filter layer 11 and the color conversion layer 9, but even without the barrier layer 10, a sufficiently excellent barrier function can be exhibited.

[0045] The water vapor transmission rate (WVTR) of color filter layer 11 is preferably lower than that of color conversion layer 9. This allows color filter layer 11 to effectively block oxygen and water 20. In this case, barrier layer 10 can effectively function as a functional layer such as a planarizing film that smooths the surface of color conversion layer 9 or a heat-resistant film when color filter layer 11 is heat-treated.

[0046] Furthermore, the water vapor transmission rate (WVTR) of color filter layer 11 may be equal to or slightly higher than that of color conversion layer 9. This also allows oxygen and water 20 to be effectively blocked by thick color filter layer 11. Even if some oxygen and water 20 permeate color filter layer 11, the amount of permeation can be reduced compared to conventional methods, and they can be effectively blocked by barrier layer 10, which has high gas barrier properties.

[0047] In this embodiment, the film loss rate of the color filter layer is preferably 3.0% or less, and more preferably 2.0% or less. In this embodiment, the film loss rate can be controlled to 3.0% or less, or 2.0% or less for any of the chemicals PGMEA, PGME, and 0.05% TMAH.

[0048] In this embodiment, the thickness of the color filter layer 11 is preferably 0.5 μm or more and 3.0 μm or less, and more preferably 1.0 μm or more and 3.0 μm or less. The thickness of the color filter layer 11 is also preferably thicker than the thickness of the barrier layer 10. This effectively improves the gas barrier property of the color filter layer 11, and can also be appropriately adjusted so that the gas barrier property is higher than that of the barrier layer 10.

[0049] In addition, in this embodiment, the red filter layer 11a and green filter layer 11b constituting the red display pixel 2a and the green display pixel 2b preferably have a transmittance at a wavelength of 460 nm of 20% or less of the emission peak of the excitation light emitted from the light emitting element 4. This allows sufficient transmission of red and green light while effectively blocking blue light. In this embodiment, the transmittance at a wavelength of 460 nm is more preferably 15% or less, even more preferably 10% or less, even more preferably 5% or less, even more preferably 2% or less, and most preferably 1% or less.

[0050] In this embodiment, the refractive index of the red filter layer 11a and the green filter layer 11b at a wavelength of 460 nm is preferably higher than that of the color conversion layers 6a and 6b. Specifically, the refractive index of the red filter layer 11a and the green filter layer 11b at a wavelength of 460 nm is preferably 1.75 or higher.

[0051] <Method of Forming Color Filter Layer 11> In this embodiment, a red filter material is applied onto the color conversion layer 6a that constitutes the red display pixel 2a, a green filter material is applied onto the color conversion layer 6b that constitutes the green display pixel 2b, and a blue filter material is applied onto the resin layer 9 that constitutes the blue display pixel 2c, and these are heat-treated to form a color filter layer 11 of a predetermined thickness. Specifically, the process includes a step of applying each filter material, a step of exposing to i-rays, a step of developing with an alkaline developer, and a step of performing heat treatment.

[0052] In this embodiment, the heat treatment temperature when forming the color filter layer 11 can be set to 150°C or less. As described above, the red filter material and green filter material used in this embodiment are both low-temperature materials, and the heat treatment temperature can be adjusted to a low temperature of 150°C or less, which reduces the thermal influence on the quantum dots 7 and 8 and the light-emitting element 4 and suppresses deterioration. In this embodiment, the heat treatment temperature is preferably set to 130°C or less, and more preferably to 100°C or less.

[0053] Furthermore, in this embodiment, by sandwiching the barrier layer 10 between the color filter layer 11 and the color conversion layer 9, the influence of the heat treatment temperature on the quantum dots 7 and 8 can be further weakened. In this way, the method of forming the color filter layer 11 also makes it possible to suppress deterioration of the quantum dots 7 and 8.

[0054] <Effects of this embodiment> In this embodiment, the film loss rate of the color filter layer 11 is set to 5.0% or less, which increases the crosslink density of the color filter layer 11 and allows the color filter layer 11 to exhibit an excellent barrier function against oxygen and water.

[0055] In this embodiment, the change rate of the front luminance of the display in the high temperature and humidity test can be suppressed to 10% or less. Note that the "change rate of the front luminance" refers to the change rate of the luminance in the normal direction from the light emitting surface before and after the test. [Example]

[0056] The present invention will be described in detail below with reference to examples carried out to clarify the effects of the present invention, but the present invention is not limited to the following examples.

[0057] <Evaluation sample structure> In the experiment, the layered structure shown in Figure 3 was formed. In Figure 3A, a color conversion layer 31 (4 μm), a planarization layer 32 (2 μm), and a barrier layer 33 (500 nm) were layered on a substrate 30. In Figure 3B, a color conversion layer 31 (4 μm), a planarization layer 32 (2 μm), a barrier layer 33 (500 nm), and a color filter layer 34 (2 μm) were layered on a substrate 30. The numbers in parentheses indicate film thicknesses.

[0058] The substrate 30 is a glass substrate. The color conversion layer 31 is formed by applying a quantum dot-containing resist and then performing i-line exposure and heat treatment to a film thickness of 4 μm. The resist material contains a quantum dot dispersion, a monomer, an initiator, an acrylic resin, a light scattering agent, and a PGMEA solvent.

[0059] The barrier layer 33 was a SiO2 film with a thickness of 500 nm formed by the CVD method. The color filter layer 34 was formed by applying the color filter material of each evaluation sample onto the barrier layer 33, and adjusting the rotation speed so as to obtain a predetermined film thickness. At this time, the pre-bake was performed at 70°C for 1 minute, and the illuminance of the exposure was 20,000 W / m 2 , and an exposure dose of 5000 J / m 2 The post-baking was carried out at 100° C. for 15 minutes.

[0060] In Examples 1 to 4 and Comparative Examples 1 and 2, the laminated structure shown in FIG. 3B was used. That is, all of them had a color filter layer 34. A color filter material having a film reduction rate shown in Table 1 in response to a predetermined chemical was used. The color filter material was obtained by curing a photosensitive coloring composition containing at least a colorant, a photopolymerizable monomer, a photopolymerization initiator, an acrylic resin, and a solvent. In Comparative Example 3, the laminated structure shown in FIG. 3A was used. That is, a color filter layer was not formed.

[0061] <Chemical resistance test> The color filter layer constituting each evaluation sample was formed on a glass substrate and immersed in chemicals (PGMEA (undiluted solution), PGME (undiluted solution), TMAH 0.05% (remainder is water)) at room temperature and atmospheric pressure for 5 minutes. Then, the change in the film thickness of the color filter layer before and after the chemical resistance test was measured, and the film thickness reduction rate of the color filter layer was derived.

[0062] <High temperature and humidity test> Each evaluation sample was left in an environment of 85°C temperature and 85% humidity for 500 hours. <Front luminance change rate> Each evaluation sample was placed on a blue light-emitting element (LED), and the rate of change in front luminance before and after the test was measured using a spectroradiometer CS-1000 (manufactured by Konica Minolta). The experimental results are shown in Table 1 below.

[0063] [Table 1]

[0064] As shown in Table 1, in Examples 1 to 4, in a chemical resistance test in which the films were immersed in chemicals containing 0.05% of PGMEA, PGME, and TMAH for 5 minutes, the film loss rate of the color filter layer was found to be 5.0% or less.

[0065] FIG. 4 is a graph showing the relationship between the film loss rate of the color filter layer and the rate of change in front luminance in a chemical resistance test in which the color filter layer was immersed in PGMEA. As shown in Table 1 and FIG. 4, it was found that the rate of change in front luminance in the high temperature and humidity test could be made 10% or less in Examples 1 to 4. [Explanation of symbols]

[0066] 1: Micro LED display 2a: Red display pixel 2b: Green display pixel 2c: Blue display pixel 3, 30: PCB 4: Light emitting element 5: Bulkhead 6a, 6b: color conversion layer 7: Red quantum dots 8: Green quantum dots 9, 22, 31: Color conversion layer 10, 24, 33: Barrier layer 11, 21, 34: Color filter layers 11a: Red filter layer 11b: green filter layer 11c: Blue filter layer 12a~12c: Micro lenses 20: Oxygen and water 23: Quantum dots 32: Flattening layer

Claims

1. a display pixel having a light-emitting element, a color conversion layer, and a color filter layer stacked in this order on a substrate; the film loss rate of the color filter layer is 5.0% or less in a chemical resistance test; A display device characterized by:

2. The film loss rate is 2.0% or less.

2. The display device according to claim 1.

3. The thickness of the color filter layer is 0.5 μm or more and 3.0 μm or less.

2. The display device according to claim 1.

4. the color filter layer has a transmittance of 20% or less at a wavelength of 460 nm; 2. The display device according to claim 1.

5. The light-emitting element is a blue light-emitting element.

2. The display device according to claim 1.

6. A partition wall is formed around the light emitting element, the color conversion layer is embedded in the internal space of the partition wall on the light emitting element; 2. The display device according to claim 1.

7. The color conversion layer contains quantum dots.

2. The display device according to claim 1.

8. a barrier layer is formed between the color conversion layer and the color filter layer; 2. The display device according to claim 1.

9. A method for manufacturing a display device according to claim 1, comprising the steps of: The color filter layer is heat-treated at 150°C or less. A method for manufacturing a display device comprising the steps of:

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