Display device

Abstract

To provide a display device that offers improved color conversion efficiency.SOLUTION: A display device of the present invention comprises light-emitting elements provided on a substrate, a partition wall formed around each of the light-emitting elements, and color conversion layers, each filling a space above the light-emitting element inside the partition wall, where the partition walls have a surface roughness of 10 Å or greater and less than 500 Å, and preferably 50 Å or greater and less than or equal to 200 Å.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a display device. [Background technology]

[0002] Patent Document 1 discloses an invention relating to a photosensitive resin composition for forming partition walls and a display device using the same. Patent Document 1 states that by including a white pigment in the partition walls, it is possible to impart reflective properties to light directed toward the partition walls, thereby improving light efficiency.

[0003] Patent Document 2 discloses an invention relating to a micro LED display device having a light-shielding portion in which the cross section of the partition is inverted tapered or T-shaped, and a reflecting portion provided on the side of the light-shielding portion. Patent Document 2 states that the display device has high brightness and contrast and can suppress color mixing between adjacent pixels. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-081724 [Patent Document 1] Japanese Patent Publication No. 2020-205417 Summary of the Invention [Problem to be solved by the invention]

[0005] Both Patent Documents 1 and 2 aim to improve the reflectivity of the partition walls. However, even if the reflectivity is increased, the color conversion layer filled inside the partition walls fails to convert the excitation light completely, resulting in some of the excitation light reaching the light-receiving surface. This makes it impossible to effectively improve color conversion efficiency, which also leads to a decrease in color purity.

[0006] The present invention has been made in view of the above points, and has an object to provide a display device that can improve color conversion efficiency. [Means for solving the problem]

[0007] One aspect of the display device of the present invention is characterized in that it comprises a light-emitting element provided on a substrate, a partition wall formed around the light-emitting element, and a color conversion layer on the light-emitting element and filling an internal space of the partition wall, wherein the surface roughness of the partition wall is 10 Å or more and less than 500 Å. [Effects of the Invention]

[0008] According to the display device of the present invention, by adjusting the surface roughness of the partition walls, the optical path length of the excitation light can be extended, the color conversion efficiency can be increased, and a display device with excellent color purity can be provided. [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. 2 is a schematic diagram for explaining the mechanism by which the optical path length of blue light (excitation light) is extended. [Figure 3] FIG. 1 is a schematic diagram of an optical simulation model used in a simulation experiment. [Figure 4] 1A to 1C are diagrams illustrating a process for explaining a method for forming partition walls that constitute the display device of the present embodiment. [Figure 5] 1A to 1C are diagrams illustrating a process for explaining a method for forming partition walls that constitute the display device of the present embodiment. [Figure 6] 1A to 1C are diagrams illustrating a process for explaining a method for forming partition walls that constitute the display device of the present embodiment. [Figure 7] 10 shows the results of a simulation experiment showing the relationship between the number of refractions of blue light and the amount of light when the surface roughness of the partition wall is different. 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).

[0012] However, these methods do not provide sufficient brightness in outdoor light, and are therefore primarily used indoors.

[0013] 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.

[0014] 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.

[0015] However, there is a problem that the color purity decreases when the blue light that cannot be completely converted mixes with the red light and the green light. In Patent Documents 1 and 2, although the reflection characteristics of the partition walls are improved, the color conversion efficiency cannot be sufficiently increased.

[0016] As a result of intensive research, the inventors have invented a display device that can extend the optical path length of excitation light by controlling the surface roughness of the partition walls, thereby improving color conversion efficiency.

[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] 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. In the present embodiment, the material of the partition walls 5 is not limited, but for example, the partition walls 5 are formed of a material containing a white pigment, or a reflective film made of metal or the like is formed on the side surface of the partition walls 5.

[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 display 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.

[0027] The color conversion layers 6a and 6b may contain fluorescent particles other than quantum dots in addition to or instead of quantum dots. However, in this embodiment, it is preferable to use 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, color filters 11 are provided on the surfaces of color conversion layers 6a, 6b and resin 9 via barrier layers 10. Color filters 11 include red color filters 11a, green color filters 11b, and blue color filters 11c. The thickness of color filters 11 is not limited, but is, for example, about 0.5 μm to 2.0 μm.

[0030] 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. The material of the barrier layer 10 is not limited, but is preferably an oxide film or a nitride film, and is formed, for example, from SiO2. The film thickness of the barrier layer 10 is not limited, but is approximately 50 nm to 1 μm.

[0031] As shown in FIG. 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 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: The surface roughness of the partition walls 5 provided around the light emitting elements 4 is 10 Å or more and less than 500 Å.

[0033] The "surface roughness" refers to the surface roughness of the side surface 5a of the partition wall 5, and it is preferable that the surface roughness be within the above range for preferably 50% or more of the area of ​​the side surface 5a, more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, even more preferably 90% or more, and most preferably 95% or more.

[0034] The surface roughness can be measured by obtaining an SEM image of a cross section and calculating the calculated average roughness Ra of the side surface 5 a of the partition wall 5 from the SEM image, or by using an atomic force microscope. For example, an SU3500 manufactured by Hitachi High-Tech Corporation can be used as the scanning microscope, and an NX20 manufactured by Park Systems Co., Ltd. can be used as the atomic force microscope. Furthermore, the surface roughness may be calculated by measuring approximately 50% of the center of the height of the partition wall 5 rather than the entire side surface 5 a of the partition wall 5.

[0035] In this way, by appropriately roughening the side surfaces 5a of the partition walls 5, the optical path length of blue light as excitation light can be extended, and color conversion efficiency can be improved.

[0036] Figure 2 is a schematic diagram illustrating the mechanism by which the optical path length of blue light (excitation light) is extended. While Figure 2 shows a red display pixel 2a, the same applies to a green display pixel 2b. As shown in Figure 2, blue light L1 emitted from the light-emitting element 4 is converted into red light L4 by the red quantum dots 7. The red light L4 passes through the red color filter 11a.

[0037] On the other hand, blue light L2 and L3 traveling toward the barrier ribs 5 is refracted by the moderately roughened side surfaces 5a of the barrier ribs 5, returned to the inside of the color conversion layer 6a, and eventually converted into red light L4 by the red quantum dots 7. At this time, like the blue light L3, the light is refracted by the barrier ribs 5 multiple times, thereby extending the optical path length and, in other words, the residence time within the color conversion layer 6a. As a result, the probability of conversion into red light L4 by the red quantum dots 7 increases, improving the color change efficiency and, ultimately, the color purity.

[0038] Increasing the surface roughness of the partition walls 5 makes light more easily diffused, increasing the number of times it is refracted by the partition walls. On the other hand, if the surface roughness is too high, the amount of light that enters the color filter from the color conversion layer decreases, leading to a decrease in brightness.

[0039] Therefore, in this embodiment, the surface roughness of the partition walls 5 is set to a range of 10 Å or more and less than 500 Å. The surface roughness of the partition walls 5 is preferably 30 Å or more, and more preferably 50 Å or more. The surface roughness of the partition walls 5 is preferably 400 Å or less, more preferably 300 Å or less, and even more preferably 200 Å or less. The surface roughness of the partition walls 5 is more preferably in the range of 50 Å or more and 200 Å or less, and even more preferably 100 Å or more and 200 Å or less, or 50 Å or more and 100 Å or less.

[0040] This increases the number of refractions at the partition 5, thereby extending the optical path length and suppressing a decrease in the amount of light on the light-receiving side. The amount of light is evaluated, for example, based on the total amount of light when the side surface 5a of the partition 5 is a mirror surface (surface roughness = 0 Å).

[0041] The height dimension t of the partition walls 5 is preferably 1 μm or more and 10 μm or less, more preferably 2 μm or more and 8 μm or less, and even more preferably 4 μm or more and 6 μm or less, which allows the optical path length to be appropriately extended and effectively suppresses a reduction in the amount of light.

[0042] Furthermore, the side surfaces 5a of the partition walls 5 are preferably formed perpendicular to the substrate 3, or are inclined so that the width of the partition walls 5 gradually narrows in the direction away from the substrate 3 (upward in the drawing). In this case, the inclination angle θ between the side surfaces 5a and the substrate 3 is preferably 80° or more and 90° or less. This makes it possible to effectively extend the optical path length while suppressing a reduction in the amount of light, thereby achieving high brightness and color purity. In addition, this is adaptable to higher resolution image sizes.

[0043] <Method of forming partition wall 5> 3, a plurality of light-emitting elements 4 are formed on a substrate 3. The plurality of light-emitting elements 4 constitute an RGB pixel region.

[0044] Next, a partition wall material layer 22 is formed over the entire surface of the substrate 3. The partition wall material is not limited, and for example, a partition wall material containing a white pigment can be used. After applying the partition wall material layer 22, a heat treatment is performed. The heat treatment temperature is not limited, but is about 70°C to 150°C. The heat treatment time is about several minutes to several tens of minutes.

[0045] Next, as shown in FIG. 3, a resist layer 23 is applied to the upper surface 22a of the partition wall material layer 22. An existing material can be selected for the resist layer 23. As shown in FIG. 3, a mask 24 is placed above the resist layer 23. The mask 24 has light-transmitting portions 24a and non-transmitting portions 24b. If the resist layer 23 is a positive type, the unexposed portions remain, and if the resist layer 23 is a negative type, the exposed portions remain. The patterns of the light-transmitting portions 24a and non-transmitting portions 24b of the mask 24 are changed depending on the type of resist layer 23. The mask 24 has a planar pattern of the partition walls 5. The resist layer 23 is exposed through the mask 24 and developed to form a resist pattern 23a shown in FIG. 4 on the upper surface 22a of the partition wall material layer 22.

[0046] Then, the partition material layer 22 that is not covered with the resist pattern 23a is removed by dry etching, and then the resist pattern 23a is removed (see FIG. 5).

[0047] By anisotropic dry etching, the side surfaces 5a of the partition walls 5 can be formed as substantially vertical or inclined surfaces.

[0048] Furthermore, existing dry etching methods such as reactive ion etching and reactive gas etching can be used. While the dry etching conditions are not limited, a mixed gas of two or more of CHF3, CF4, F2, HBr, Ar, O2, etc. was used as the etching gas. For the dry etching conditions, the flow rate of each gas was adjusted to a range of several sccm to 300 sccm. For the reactive ion etching, the RF power was adjusted to approximately 500 W to 3000 W, the magnetic field output was adjusted to approximately 500 W to 2000 W, and the etching time was set to several minutes to several tens of minutes.

[0049] By adjusting the etching conditions described above, the surface roughness of the partition wall can be set within a range of 10 Å or more and less than 500 Å, and the range of the surface roughness can be further narrowed stepwise, and particularly preferably, it can be appropriately adjusted within a range of 50 Å or more and 200 Å or less.

[0050] <Effects of this embodiment> In this embodiment, the surface roughness of the partition walls 5 is adjusted to a range of 10 Å or more and less than 500 Å. As a result, in the red display pixel 2a and the green display pixel 2b, even if the blue light (excitation light) emitted from the light emitting element 4 cannot be completely color converted, the optical path length can be extended so that the blue light remains in the color conversion layers 6a, 6b without being mixed with the red light or green light, thereby improving the color conversion efficiency and increasing the color purity.

[0051] By adjusting the surface roughness to a range of 10 Å or more and less than 500 Å, and more preferably to a range of 50 Å or more and 200 Å or less, it is possible to effectively suppress the reduction in the amount of light on the light-receiving side, increase the number of refractions, and effectively extend the optical path length. [Example]

[0052] 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.

[0053] Using the optical simulation model shown in Figure 3, evaluation was carried out using partition walls with different surface roughness.

[0054] 3 are partition walls A, color conversion layer B, color filter C, adhesive layer D, and cover glass F. The refractive index n of cover glass F was 1.52, the refractive index n of adhesive layer was 1.523, the refractive index n of color filter was between 1.6 and 2.0, the refractive index n of color conversion layer B was 1.6, and the reflectance of partition walls A was 100%.

[0055] In the experiment, Experimental Examples 1 to 16, in which the surface roughness of the partition walls was different, were used. No surface roughness was applied in Experimental Examples 1 and 9. In Experimental Examples 2 to 8 and 10 to 16, the surface roughness was set to 10 Å, 50 Å, 100 Å, 200 Å, 500 Å, 1000 Å and 5000 Å.

[0056] The number of times that blue light emitted from the light-emitting element is refracted at the side surface of the partition wall was calculated in terms of light dose. The light dose was measured using the surface of cover glass F shown in Figure 6 as the light-receiving surface. Table 1 shows an example in which the partition wall height was 4 μm, and Table 2 shows an example in which the partition wall height was 6 μm.

[0057] [Table 1]

[0058] [Table 2]

[0059] Figure 7 shows the results of a simulation experiment that shows the relationship between the number of refractions of blue light and the amount of light when the surface roughness of the partition walls is different. Note that Figure 7 shows the experimental results of Table 2.

[0060] As shown in Figure 7, Tables 1 and 2, it was found that the number of refractions or the average number of refractions increases as the surface roughness increases. However, when the surface roughness is 500 Å or more, the total light dose is significantly reduced when compared to the total light dose when there is no surface roughness (surface roughness = 0 Å). For this reason, a surface roughness of 500 Å or more was rated as x. Furthermore, when the surface roughness is 0 Å, the number of refractions does not exceed 6, and the rating is x. For this reason, the surface roughness is set to a range less than 500 Å, preferably 200 Å or less.

[0061] It was found that if the surface roughness is 10 Å or more, six or more refractions are possible, and the optical path length can be extended. Also, if the surface roughness is 50 Å or more, the proportion of refractions of 10 or more increases, and the average optical path length can be extended further. Therefore, a surface roughness in the range of 50 Å to 200 Å was judged to be good.

[0062] From the above, the surface roughness of the partition walls is set to a range of 10 Å or more and less than 500 Å, and more preferably, 50 Å or more and 200 Å or less. [Explanation of symbols]

[0063] 1: Micro LED display 2a: Red display pixel 2b: Green display pixel 2c: Blue display pixel 3: Substrate 4: Light emitting element 5: Bulkhead 5a: Side 6a, 6b: color conversion layer 7: Red quantum dots 8: Green quantum dots 10: Barrier layer 11: Color filter 11a: Red color filter 11b: Green color filter 11c: Blue color filter 12a~12c: Micro lenses 22: Partition material layer 23: Resist layer 23a: Resist pattern 24: Mask 24a: Light transmitting part 24b: Non-transparent part A: Bulkhead B: Color conversion layer C: Color filter D: Adhesive layer F: Cover glass L1~L3: Blue light L4: Red light

Claims

1. a light emitting element provided on a substrate; a partition wall formed around the light emitting element; a color conversion layer on the light emitting element, the color conversion layer filling the internal space of the partition; and The surface roughness of the partition wall is 10 Å or more and less than 500 Å. A display device characterized by:

2. the surface roughness of the partition wall is 50 Å or more and 200 Å or less; 2. The display device according to claim 1.

3. The side surface of the partition wall is formed in a direction perpendicular to the substrate, or is inclined so that the width of the partition wall gradually narrows in a direction away from the substrate.

2. The display device according to claim 1.

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

2. The display device according to claim 1.

5. The color conversion layer contains quantum dots.

2. The display device according to claim 1.

Images