Display device and method for manufacturing same

Abstract

The objective of the present invention is to provide a display device which has reduced blue light noise and excellent color purity, by improving color filters that constitute red display pixels and green display pixels, and to provide a method for manufacturing the display device. The display device of the present invention is characterized by including display pixels in which a light emitting element, a color conversion layer, and a color filter are stacked in the stated order on a substrate, the display pixels including red display pixels, green display pixels, and blue display pixels, wherein the color filters constituting the red display pixels and the green display pixels are formed of yellow color filters. Alternatively, the colors filters constituting the red display pixels and the green display pixels are characterized by having a transmittance of 2.0% or less at a wavelength of 460 nm, and a transmittance of 85% or more at wavelengths of 550 nm and 620 nm.

Description

Display device and manufacturing method thereof

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

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

[0003] Patent Document 2 discloses an invention related to a display device. The display device in Patent Document 2 includes a light source unit, a wavelength conversion unit, a reflective layer, and an optical member, and describes that the reflective layer is a dielectric multilayer film and further that a low refractive index layer is disposed between the wavelength conversion unit and the optical member. The patent also describes that the light source unit emits blue light and the reflective layer reflects blue light.

[0004] JP 2022-155737 A JP 2022-096625 A

[0005] However, Patent Document 1 does not provide a detailed explanation of the color filter. Patent Document 2 requires a low refractive index layer and a reflective layer on the wavelength conversion unit to suppress leakage of excitation light toward the optical component, and the dielectric multilayer film serving as the reflective layer has a layered structure of a low refractive index material and a high refractive index material, resulting in a complex structure. Patent Document 2 also does not describe the spectral characteristics of the low refractive index layer and the reflective layer combined together.

[0006] The present invention has been made in view of the above-mentioned points, and aims to provide a display device having excellent color purity and reduced blue light noise by improving the color filters constituting red display pixels and green display pixels, and a method for manufacturing the same.

[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 are stacked in this order on a substrate, the display pixels comprising red display pixels, green display pixels, and blue display pixels, and the color filters constituting the red display pixels and the green display pixels are formed of yellow color filters.

[0008] Alternatively, one embodiment of the display device of the present invention has display pixels in which a light-emitting element, a color conversion layer, and a color filter are stacked in this order on a substrate, the display pixels comprising red display pixels, green display pixels, and blue display pixels, and the color filters constituting the red display pixels and the green display pixels have a transmittance of 2.0% or less at a wavelength of 460 nm and a transmittance of 85% or more at wavelengths of 550 nm and 620 nm.

[0009] According to the display device of the present invention, by using yellow color filters as color filters constituting red display pixels and green display pixels, it is possible to transmit red light and green light while effectively removing blue light (excitation light).

[0010] According to the display device manufacturing method of the present invention, the yellow color filter can be formed at a low temperature of 150° C. or less, which makes it possible to suppress deterioration of fluorescent particles, such as quantum dots, contained in the color conversion layer.

[0011] Fig. 1 is a cross-sectional schematic diagram of a micro LED display as a display device in this embodiment. Fig. 2 is a schematic diagram for explaining the mechanism for cutting blue light (excitation light). Fig. 3 is a schematic diagram of an optical simulation model used in a simulation experiment.

[0012] 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.

[0013] <Background to the Invention of the Display Device of the Present 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).

[0014] However, these methods do not provide sufficient brightness in outdoor light, and are therefore primarily used indoors.

[0015] In contrast, the micro LED method is considered to be more advantageous than the above methods in terms of brightness, and is expected to see expanded application in the future.

[0016] As a method for 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.

[0017] However, there was a problem in that blue light that could not be fully wavelength-converted by the color conversion layer mixed with the red and green display pixels, reducing color purity. For this reason, there was a need for a technology that could effectively block blue light excited by the light-emitting element.

[0018] Therefore, as a result of intensive research, the inventors have invented a display device that reduces blue light noise and has excellent color purity by using yellow color filters for the color filters that make up the red display pixels and green display pixels.

[0019] <Description of Display Device of the Present Embodiment> The display device of the present 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.

[0020] 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.

[0021] 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 blue-emitting micro LED.

[0022] 1, partition walls 5 that separate the light-emitting elements 4 are formed on the substrate 3. The partition walls 5 are formed so as to surround the outer periphery of each light-emitting element 4 in a plan view. The material of the partition walls 5 is not limited in this embodiment.

[0023] 1, the internal spaces of the partition walls 5 of the red display pixels 2a and the green display pixels 2b are filled with color conversion layers 6a and 6b. As shown in FIG. 1, the color conversion layers of the red display pixels 2a and the green display pixels 2b have red quantum dots 7 and green quantum dots 8 dispersed therein, respectively.

[0024] 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.

[0025] The red quantum dots 7 preferably have a fluorescence peak wavelength of 600 nm to 680 nm, and the green quantum dots 8 preferably 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.

[0026] Although the materials are not limited, 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.

[0027] The particle size of the quantum dots 7 and 8 is several nanometers to several tens of nanometers. The fluorescence peak wavelength can be controlled by adjusting the particle size and composition. Note that the color conversion layers 6 a and 6 b may contain phosphors other than the quantum dots 7 and 8.

[0028] On the other hand, as shown in Figure 1, the internal space of the partition wall 5 of the blue display pixel 2c is filled with 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.

[0029] The color conversion layers 6 a and 6 b may contain fluorescent particles other than the quantum dots in addition to or instead of the quantum dots, but in this embodiment, it is preferable to use the quantum dots 7 and 8 in order to obtain excellent color purity.

[0030] 1, the surfaces of the color conversion layers 6a, 6b and resin 9 may be formed at substantially the same height as the partition walls 5, or may be slightly lower than the partition walls 5. The thickness of the color conversion layers 6a, 6b is about 2 to 10 μm.

[0031] 1, a color filter 11 is provided on the surfaces of the color conversion layers 6a, 6b and the resin 9 via a barrier layer 10. The configuration of the color filter 11 will be described later.

[0032] Although the barrier layer 10 is not an essential layer, providing the barrier layer 10 can reduce the thermal influence on the quantum dots 7 and 8 in the color conversion layers 6a and 6b when the color filter 11 is formed. Furthermore, if there are irregularities between the surfaces of the partition wall 5 and 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 11 to be formed on a flat surface. There are no restrictions on the material of the barrier layer 10, but it is preferably an oxide film or a nitride film, for example, SiO ２ The thickness of the barrier layer 10 is not limited, but is about 50 nm to 1 μm.

[0033] 1, microlenses 12a to 12c can be provided on the surface of the color filter 11. The microlenses 12a to 12c are optically transparent. Although not limited thereto, the microlenses 12a to 12c can be made of organic materials such as acrylic resin, epoxy resin, and silicon resin, or SiN, SiO ２ 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.

[0034] <Characteristic Configuration of the Micro LED Display 1 of the Present Embodiment> The micro LED display 1 of the present embodiment has the following characteristics. Specifically, the color filters constituting the red display pixels 2 a and the green display pixels 2 b are formed of yellow color filters 11 a. This blocks blue light (wavelength 460 nm) that is excitation light for the light emitting elements 4, while allowing red light (wavelength 620 nm) and green light (wavelength 550 nm) to pass through.

[0035] Conventionally, a red color filter is used for the red display pixel 2a and a green color filter is used for the green display pixel 2b, but by unifying them with a yellow color filter 11a rather than using individual color filters, a display with high color purity and less blue light noise can be effectively achieved. Moreover, since the red display pixel 2a and the green display pixel 2b can be unified with the yellow color filter 11a, the manufacturing process can be simplified, which is also advantageous. As shown in Figure 1, a blue color filter 11b is used for the blue display pixel 2c.

[0036] Fig. 2 is a schematic diagram illustrating the mechanism for cutting blue light (excitation light). Fig. 2 shows a red display pixel 2a, but the same applies to a green display pixel 2b. As shown in Fig. 2, blue light L1 emitted from the light-emitting element 4 is converted into red light L2 by the red quantum dots 7. The red light L2 passes through the yellow color filter 11a.

[0037] On the other hand, blue light L1 that has not been wavelength-converted by the red quantum dots 7 is reflected at the interface between the yellow color filter 11a and the color conversion layer 6a. The blue light L1 is also reflected by the partition wall 5 and returned to the color conversion layer 6a, where it is wavelength-converted by the red quantum dots 7, thereby improving the conversion efficiency.

[0038] Furthermore, when a portion of the blue light L1 is not reflected and enters the yellow color filter 11a, it is absorbed within the color filter.

[0039] As described above, by using the yellow color filter 11a, the blue light L1 can be effectively cut off.

[0040] The yellow color filter 11a preferably has a transmittance of 2.0% or less at a wavelength of 460 nm and a transmittance of 85% or more at wavelengths of 550 nm and 620 nm. This allows sufficient transmission of red and green light while effectively blocking blue light. The transmittance can be measured, for example, by spectrophotometer transmittance. Alternatively, the transmittance can be determined by identifying the material of the color filter.

[0041] The transmittance at a wavelength of 460 nm indicates the transmittance of blue light, but the measured wavelength may deviate slightly from 460 nm. Alternatively, the measured wavelength may be within a range, for example, 450 nm to 470 nm, and the transmittance may be the average transmittance.

[0042] In this embodiment, the transmittance at a wavelength of 460 nm is preferably 2% or less, more preferably 1.5% or less, even more preferably 1.3% or less, even more preferably 1.2% or less, and most preferably 1.0% or less.

[0043] The transmittance at a wavelength of 550 nm indicates the transmittance of green light, but the measured wavelength may deviate slightly from 550 nm. Alternatively, the measured wavelength may be within a range, for example, 530 nm to 570 nm, and the transmittance may be the average transmittance.

[0044] In this embodiment, the transmittance at a wavelength of 550 nm is preferably 85% or more, more preferably 90% or more, even more preferably 92% or more, and even more preferably 95% or more.

[0045] The transmittance at a wavelength of 620 nm indicates the transmittance of red light, but the measured wavelength may deviate slightly from 620 nm. Alternatively, the measured wavelength may be within a range, for example, 600 nm to 640 nm, and the transmittance may be the average transmittance.

[0046] In this embodiment, the transmittance at a wavelength of 620 nm is preferably 85% or more, more preferably 90% or more, even more preferably 92% or more, and even more preferably 95% or more.

[0047] In addition, the refractive index of yellow color filter 11a at a wavelength of 460 nm in this embodiment is preferably higher than that of color conversion layer 6a. Specifically, the refractive index of yellow color filter 11a at a wavelength of 460 nm is preferably 1.75 or higher, more preferably 1.80 or higher, even more preferably 1.85 or higher, and most preferably 1.90 or higher. The refractive index at a wavelength of 550 nm is preferably 1.65 or higher, and the refractive index at a wavelength of 640 nm is preferably 1.60 or higher.

[0048] The thickness t of the yellow color filter 11a is preferably 0.1 μm or more and 2.0 μm or less. This allows the transmittance at a wavelength of 460 nm to be 1% or less, and the transmittance at wavelengths of 550 nm and 620 nm to be 85% or more with high precision. The thickness t is preferably 0.3 μm or more and 1.8 μm or less, and more preferably 0.5 μm or more and 1.5 μm or less.

[0049] The yellow material forming the yellow color filter 11a can be a commercially available product, a developed product, or a product manufactured by a known method that satisfies the above-mentioned transmittance. While not limited to this, the yellow material includes, for example, a colorant and a binder resin. Examples of colorants include C.I. Pigment Yellow 139, C.I. Pigment Yellow 150, and C.I. Pigment Yellow 185. The colorant is contained in an amount ranging from several percent to several tens of percent of the entire yellow material. Examples of binder resins include polysiloxane, polyimide, polybenzoxazole, polybenzoxazole precursor, and (meth)acrylic polymer.

[0050] <Method of forming yellow color filter 11a> In this embodiment, a yellow material is applied onto the color conversion layer 6a that constitutes the red display pixel 2a and the color conversion layer 6b that constitutes the green display pixel 2b, and then heat-treated to form a yellow color filter 11a of a predetermined thickness.

[0051] In this embodiment, the yellow color filter 11a can be formed integrally with the red display pixel 2a and the green display pixel 2b, which reduces the number of manufacturing steps compared to the conventional manufacturing method in which a color filter is formed individually for each of the red display pixel 2a and the green display pixel 2b, thereby providing advantages in terms of the manufacturing process.

[0052] Furthermore, in this embodiment, the heat treatment temperature when forming the yellow color filter 11a can be set to 150° C. or less. Since the heat treatment temperature can be set to a low temperature, the thermal influence on the quantum dots 7 and 8 and the light emitting element 4 can be reduced, and deterioration can be suppressed. In contrast, for example, in the dielectric multilayer film described in Patent Document 2, the heat treatment temperature is higher than 150° C., which makes the quantum dots more susceptible to deterioration.

[0053] <Effects of the Present Embodiment> In the present embodiment, the color filters constituting the red display pixels 2 a and the green display pixels 2 b are formed of yellow color filters, or the color filters constituting the red display pixels 2 a and the green display pixels 2 b are formed of a yellow material having a transmittance of 2.0% or less at a wavelength of 460 nm and a transmittance of 85% or more at wavelengths of 550 nm and 620 nm.

[0054] This allows the red display pixel 2 a and the green display pixel 2 b to block blue light as excitation light emitted from the light emitting element 4, while allowing red light and green light to be appropriately transmitted, thereby reducing blue light noise and providing a display device with high color purity.

[0055] Furthermore, since the yellow color filter 11a can be integrally formed with the red display pixel 2a and the green display pixel 2b, the number of manufacturing steps can be reduced, improving production efficiency. Furthermore, since the heat treatment temperature for forming the color filter can be lowered, deterioration of the quantum dots 7 and 8 can be suppressed, and high luminous efficiency can be maintained.

[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] Using the optical simulation model shown in FIG. 3, evaluation was carried out using color filters with different refractive indices.

[0058] 3 are a partition wall A, a color conversion layer B, a color filter C, an adhesive layer D, and a cover glass F. The refractive index n of the cover glass F was 1.52, the refractive index n of the adhesive layer was 1.523, the refractive index n of the color conversion layer B was 1.6, and the reflectance of the partition wall A was 100%.

[0059] In the experiments, Experimental Examples 1 to 5 were used, in which the refractive index of the color filters was different. In Experimental Examples 1 to 3, a yellow color filter was formed using a yellow material. In Experimental Example 4, a green color filter was formed using a green material. In Experimental Example 5, a red color filter was formed using a red material.

[0060] The yellow color filters of Experimental Examples 1 to 3 have different refractive indices at a wavelength of 460 nm.

[0061] The experiment software for the simulation was Light Tools by Synopsys, and a transmittance simulation was performed for blue light (wavelength 460 nm), green light (wavelength 550 nm), and red light (wavelength 620 nm) using a ray tracing method. The experimental results are shown in Table 1 below.

[0062]

[0063] As shown in Table 1, in Experimental Example 4, the transmittance of blue light was about 1%, the transmittance of green light was about 90%, but the transmittance of red light was only about 3%, and it was found that the film could not be used as a common color filter for red and green display pixels.

[0064] In Experimental Example 5, the transmittance of blue light was about 1%, the transmittance of red light was about 95%, but the transmittance of green light was only about 1%, which meant that the film could not be used as a common color filter for red and green display pixels. Therefore, Experimental Examples 4 and 5 were judged as "X."

[0065] On the other hand, in Experimental Examples 1 to 3, which used a yellow color filter, simulation experiments were conducted by changing the film thickness, and it was found that the transmittance of blue light was 2.0% or less, and the transmittance of red light and green light was 85% or more, regardless of the film thickness. It was also found that it is possible to preferably make the transmittance of blue light about 1.0%, and the transmittance of red light and green light 90% or more. Therefore, Experimental Examples 1 to 3 were all judged as △, ○, or ◎.

[0066] In the yellow color filters of Experimental Examples 1 and 3, the transmittance of blue light was 1.0% or more, but the transmittance of red light and green light was 90% or more, so they were rated as fair.

[0067] It was found that the yellow color filter of Experimental Example 2 could achieve a blue light transmittance of 1.0% or less and a red and green light transmittance of 85% or more, or a blue light transmittance of 2.0% or less and a red and green light transmittance of 95% or more. Therefore, Experimental Example 2 was superior to the yellow color filters of Experimental Examples 1 and 3, and was judged as ○ or ◎.

[0068] In Experimental Example 2, when the film thickness was set to 0.5 μm to 1.5 μm, the transmittance of blue light could be set to 1.0% or less, and the transmittance of red light and green light could be set to 95% or more, which was the best result, and was therefore judged as ⊚.

[0069] As shown in Table 1, Experimental Examples 1 to 3, which used a yellow color filter, had a higher refractive index than Experimental Example 4, which used a green color filter, and Experimental Example 5, which used a red color filter. Specifically, it was found that the refractive index could be made 1.75 or higher, preferably 1.8 or higher, more preferably 1.85 or higher, and even more preferably 1.9 or higher. This increased the difference in refractive index with the color conversion layer, increasing the reflectance of blue light and enabling the production of a display device with excellent color purity.

[0070] This application is based on Japanese Patent Application No. 2024-071286, filed April 25, 2024, the contents of which are incorporated herein in their entirety.

Claims

1. A display device comprising display pixels each having a light-emitting element, a color conversion layer, and a color filter stacked in this order on a substrate, the display pixels comprising red, green, and blue display pixels, and the color filters constituting the red and green display pixels are formed of yellow color filters.

2. A display device having display pixels in which a light-emitting element, a color conversion layer, and a color filter are stacked in this order on a substrate, the display pixels comprising red, green, and blue display pixels, and the color filters constituting the red and green display pixels have a transmittance of 2.0% or less at a wavelength of 460 nm and a transmittance of 85% or more at wavelengths of 550 nm and 620 nm.

3. The display device according to claim 2, wherein the color filter has a higher refractive index at a wavelength of 460 nm than the color conversion layer.

4. The display device according to claim 2, wherein the refractive index (at a wavelength of 460 nm) of said color filter is 1.75 or more.

5. A display device according to claim 1 or 2, characterized in that the film thickness of the color filters constituting the red display pixels and the green display pixels is 0.1 μm or more and 2.0 μm or less.

6. The display device according to claim 1 or 2, wherein the light-emitting element is a blue light-emitting element.

7. A display device according to claim 1 or 2, characterized in that a partition wall is formed around the light-emitting element, and a color conversion layer is embedded in the internal space of the partition wall above the light-emitting element.

8. The display device according to claim 1 or 2, wherein the color conversion layer contains quantum dots.

9. The display device according to claim 1 or 2, wherein a microlens is formed on the color filter.

10. A method for manufacturing a display device according to claim 1 or 2, characterized in that the color filter is heat-treated at a temperature of 150°C or less.

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