Patent Application
20250031496
The present disclosure relates to a light emission device and an image display apparatus including the same.
For example, Patent Literature 1 discloses a light-emitting diode (LED) device that includes a wavelength conversion member. The wavelength conversion member includes a first resin layer and a second resin layer stacked in this order on an LED element. In the first resin layer, only light-scattering materials are dispersed. In a second resin layer, light-scattering materials and quantum dots are dispersed.
PTL 1: Japanese Unexamined Patent Application Publication No. 2020-43353
Meanwhile, a light emission device including quantum dots as a wavelength conversion material is required to have both of light extraction efficiency and reliability.
It is desirable to provide a light emission device and an image display apparatus that makes it possible to have both of the light extraction efficiency and the reliability.
A light emission device according to an embodiment of the present disclosure includes a light source unit and a wavelength conversion layer. The light source unit has a light emission surface and emits first light from the light emission surface. The wavelength conversion layer is disposed on a side of the light emission surface of the light source unit, has a first surface disposed to face the light emission surface and a second surface disposed on an opposite side of the first surface, includes a plurality of wavelength conversion materials that converts the first light into second light in a different wavelength band and a plurality of scattering particles, and has a lower absorption coefficient of the first light in the vicinity of the first surface than in the vicinity of the second surface.
An image display apparatus according to an embodiment of the present disclosure includes the light emission device according to the embodiment.
In the light emission device according to the embodiment of the present disclosure and the image display apparatus according to the embodiment of the present disclosure, the wavelength conversion layer includes the plurality of wavelength conversion materials that converts the first light emitted from the light source unit into the second light in the different wavelength band and the plurality of scattering particles. The wavelength conversion layer has a lower absorption coefficient of the first light in the vicinity of a surface on the side of the light source unit (the first surface) than in the vicinity of a light extraction surface (the second surface). This reduces a rate of absorption of excitation light in the vicinity of the light source unit.
Hereinafter, an embodiment of the present disclosure is described in detail with reference to the drawings. The following description is one specific example of the present disclosure, and the present disclosure is not limited to the following modes. In addition, the arrangement, dimensions, dimension ratios, and the like of components of the present disclosure are not limited to those illustrated in each drawing. Note that the description is made in the following order.
The light emission device 1 is preferably used, for example, for a display pixel P of an image display apparatus (for example, image display apparatus 100, refer to
The light emission device 1 according to the present embodiment includes a light source
unit 10 that emits excitation light EL, and a wavelength conversion layer 20 that is disposed on a side of a light emission surface (surface 10S2) of the light source unit 10, absorbs the excitation light EL, and emits light with a different wavelength. For example, in the wavelength conversion layer 20, a plurality of quantum dot phosphors 21 and a plurality of scattering particles 22 are dispersed in a resin 23, and the wavelength conversion layer 20 includes a first region 20A and a second region 20B in order from the side of the surface 10S2 of the light source unit 10. The first region 20A has a configuration in which only the plurality of quantum dot phosphors 21 is dispersed in the resin 23, and has an absorption coefficient of the excitation light EL lower than that of the second region 20B.
The light source unit 10 corresponds to a specific example of a “light source unit” in the present disclosure. The light source unit 10 is a solid-state light emission device that emits light in a predetermined wavelength band from a top surface (light emission surface). The light source unit 10 is, for example, a light-emitting diode (LED) chip. The LED chip refers to a cut piece of a wafer used for crystal growth and does not refer to a package type covered with a molded resin or the like. The LED chip has a size equal to or greater than 1 μm and equal to or less than 100 μm, for example, and is a so-called micro-LED.
The light source unit 10 includes a first conductive type layer 11, an active layer 12, and a second conductive type layer 13 that are stacked in this order. A top surface of the second conductive type layer 13 serves as a light emission surface. The light source unit 10 has a pillar mesa portion M including the first conductive type layer 11 and the active layer 12 and includes a step including a recess portion from which the first conductive type layer 11 is exposed and a projection portion from which the second conductive type layer 13 is exposed, on a surface (surface 10S1) on an opposite side of the light emission surface. In the present embodiment, a surface, including the recess portion and the projection portion, on an opposite side of the light extraction surface 10S2 (side of surface 10S1) is assumed as a bottom surface. The light source unit 10 further includes a first electrode 14 that is electrically coupled to the first conductive type layer 11 and a second electrode 15 that is electrically coupled to the second conductive type layer 13. Each of the first electrode 14 and the second electrode 15 is provided on the side of the surface 10S1. Specifically, the first electrode 14 is disposed on the surface 10S1 of the first conductive type layer that is the recess portion of the bottom surface, and the second electrode 15 is disposed on the surface 10S1 of the second conductive type layer that is the projection portion of the bottom surface.
A side surface of the light source unit 10 including the first conductive type layer 11, the active layer 12, and the second conductive type layer 13 is covered with a laminated film 16 including an insulation film 16A and a reflection film 16B. For example, the laminated film 16 extends to peripheral edges of the first electrode 14 and the second electrode 15 and has openings 16H1 and 16H2 respectively on the first electrode 14 and the second electrode 15. That is, the first electrode and the second electrode are exposed outside through the openings 16H1 and 16H2, respectively.
A material of the first conductive type layer 11, the active layer 12, and the second conductive type layer 13 is appropriately selected in accordance with light in a desired wavelength band. In a case where a III-V compound semiconductor material is used, the light source unit 10 emits ultraviolet rays of which an emission wavelength is, for example, equal to or greater than 360 nm and equal to or less than 430 nm, or light in a blue band (blue light) of which an emission wavelength is, for example, equal to or greater than 430 nm and equal to or less than 500 nm. As the III-V compound semiconductor material, for example, an AlGaInN based material is exemplified. In addition, a ZnSe-based material or a ZnO-based material may be used. It is possible to form the active layer 12, for example, using a GaInN-based material.
It is to be noted that the light emitted from the light source unit 10 is not limited to the ultraviolet rays or the blue light, and may be, for example, infrared rays or light in a red band (red light). In that case, as a III-V compound semiconductor material that emits the infrared rays, for example, an AlGaInAs-based material is exemplified. As a III-V compound semiconductor material that emits the red light, for example, an AlGaInP-based material is exemplified.
The first electrode 14 is in contact with the first conductive type layer 11 and electrically coupled to the first conductive type layer 11. That is, the first electrode 14 is brought into ohmic contact with the first conductive type layer 11. The first electrode 14 is, for example, a metal electrode and is formed as a multi-layer film (Ni/Au) including nickel (Ni) and gold (Au). In addition, the first electrode 14 may include a transparent conductive material such as indium-tin oxide (ITO), for example.
The second electrode 15 is in contact with the second conductive type layer 13 and is electrically coupled to the second conductive type layer 13. That is, the second electrode 15 is brought into ohmic contact with the second conductive type layer 13. The second electrode 15 is, for example, a metal electrode, and is formed as a multi-layer film (Ti/Al) including titanium (Ti) and aluminum (Al) or a multi-layer film (Cr/Au) including chromium (Cr) and Au. In addition, the second electrode 15 may include a transparent conductive material such as ITO, for example.
The laminated film 16 is formed from the side surface of the light source unit 10 to the bottom surface as described above. Each of the insulation film 16A and the reflection film 16B is a thin film, and it is possible to form the insulation film 16A and the reflection film 16B through a thin-film formation process, for example, CVD, vapor deposition, or sputtering.
The insulation film 16A electrically isolates the reflection film 16B from the first conductive type layer 11, the active layer 12, and the second conductive type layer 13. It is preferable to form the insulation film 16A using a transparent material with respect to light emitted from the active layer 12. As such a material, for example, SiO2, Si2N3, Al2O3, TiO2, and TiN are exemplified. The insulation film 16A has a thickness of, for example, about 50 nm to 1 μm.
The reflection film 16B reflects light emitted from an active layer 122. The reflection film 16B is provided with the insulation film 16A on its inner side. Specifically, the reflection film 16B extends to the side surface and the bottom surface of the light source unit 10, and is formed, for example, to a position slightly backward from an end portion of the insulation film 16A in the openings 16H1 and 16H2 of the insulation film 16A. As a result, the reflection film 16B is isolated and separated (electrically separated) from the first conductive type layer 11, the active layer 12, the second conductive type layer 13, the first electrode 14, and the second electrode 15, by the insulation film 16A. It is preferable to use a material that reflects the light emitted from the active layer 12, as a material of the reflection film 16B. Such a material includes, for example, Ti, Al, silver (Ag), copper (Cu), Au, Ni, or an alloy thereof. The reflection film 16B has a thickness of, for example, about 50 nm to 1 μm.
It is to be noted that an insulation film may be further formed on the reflection film 16B. In that case, it is preferable that the insulation film be formed on the first electrode 14 and the second electrode 15 so as to extend to the insulation film 16A and cover an end portion of the reflection film 16B. As a result, when the light emission device 1 (1B, 1G, and 1R) to be described later is mounted on a driving substrate 41, it is possible to prevent short circuit of bumps 44 and 45 with respect to the reflection film 16B. The bump 44 joins a pad electrode 42 on the driving substrate 41 and the first electrode 14, and the bump 45 joins a pad electrode 43 on the driving substrate 41 and the second electrode 15 (refer to
The wavelength conversion layer 20 corresponds to a specific example of a “wavelength conversion layer” in the present disclosure. The wavelength conversion layer 20 is disposed on the side of the surface 10S2 of the light source unit 10 and converts the light emitted from the light source unit 10 into light in a desired wavelength band (for example, red light Lr, green light Lg, and blue light Lb). The wavelength conversion layer 20 has a surface 20S1 and a surface 20S2 as a pair of opposed surfaces. The surface 20S1 corresponds to a “first surface” in the present disclosure and is disposed to face the surface 10S2 of the light source unit 10. The surface 20S2 corresponds to a “second surface” in the present disclosure and serves as a surface from which wavelength-converted light is extracted.
In the wavelength conversion layer 20, the plurality of quantum dot phosphors 21 and the plurality of scattering particles 22 are dispersed in the resin 23, as described above.
The quantum dot phosphor 21 corresponds to a specific example of a “wavelength conversion material” of the present disclosure. The quantum dot phosphor 21 absorbs the light emitted from the light source unit 10 as the excitation light EL and emits fluorescence. Specifically, for example, the quantum dot phosphor 21 is a particle-shaped phosphor that emits fluorescence in a blue wavelength band equal to or greater than 430 nm and equal to or less than 500 nm, a green wavelength band equal to or greater than 500 nm and equal to or less than 550 nm, or a red wavelength band equal to or greater than 610 nm and equal to or less than 780 nm.
The largest factor that determines the fluorescence wavelength (fluorescence color) of the quantum dot phosphor is bandgap energy of a material included in the quantum dot. Therefore, it is desirable to select a material depending on a desired fluorescence color. For example, in a case where red fluorescence (red light Lr) is obtained, it is possible to select the quantum dot phosphor 21, for example, from among InP, GaInP, InAsP, CdSe, CdZnSe, CdTeSe, or CdTe. In a case where green fluorescence (green light Lg) is obtained, it is possible to select the quantum dot phosphor 21, for example, from among InP, GaInP, ZnSeTe, ZnTe, CdSe, CdZnSe, CdS, or CdSeS. In a case where blue fluorescence (blue light Lb) is obtained, it is possible to select the quantum dot phosphor 21 from among ZnSe, ZnTe, ZnSeTe, CdSe, CdZnSe, CdS, CdZnS, or CdSeS, for example. It is to be noted that, the quantum dot phosphor 21 is not limited to the above, and for example, CuInSe2, CuInS2, CuInGaS, and AgInS2 may be used. In addition, for example, perovskite nano phosphor including CsPb (Cl/Br)3, CsPbBr3, CsPb (I/Br)3, and CsPbI3 may be used.
Furthermore, it is possible for the quantum dot phosphor 21 to control the fluorescence color depending on a particle diameter thereof. For example, as the particle diameter decreases, the fluorescence wavelength is shortened. To obtain fluorescence with high color purity, it is desirable to select a quantum dot phosphor having a controlled particle diameter.
The quantum dot phosphor 21 has, for example, an average particle diameter of equal to or greater than 5 nm and equal to or less than 100 nm. For example, the quantum dot phosphor 21 has a core-shell structure that includes a core emitting light and having an average particle diameter of about 2 nm to 10 nm, and a shell covering and protecting the core. The shell includes a single or a plurality of layers. In addition, the shell may be covered with an inorganic film including silicon oxide (SiO2) or aluminum oxide (Al2O3), for example. On a surface of the quantum dot phosphor 21, a large number of organic ligands are coordinated. With this organic ligands, when the quantum dot phosphors are mixed with a solvent, agglomeration of the quantum dot phosphors 21 is prevented, and dispersibility is improved.
To charge the quantum dot phosphor 21, for example, an ink-jet type dispenser or a needle-type dispenser that discharges or applies the quantum dot phosphor 21 is used depending on the viscosity of the resin 23 to be mixed with the quantum dot phosphor 21. This is classified into a plateless type printing method, and with this method, it is possible to selectively fill only a wall with the quantum dot phosphor 21. Therefore, it is possible to enhance use efficiency of the quantum dot phosphor 21. The quantum dot phosphor 21 may be applied to a determined place using screen printing or gravure printing technology that are plate printing methods. In addition, as in a spin coater or a PR method, for example, the quantum dot phosphor 21 may be applied to an entire substrate.
It is to be noted that, for the wavelength conversion layer 20, an inorganic phosphor or an organic phosphor may be used as the wavelength conversion material, instead of the quantum dot phosphor 21.
The scattering particle 22 improves light extraction efficiency by scattering the excitation light EL emitted from the light source unit 10 and the fluorescence emitted from the quantum dot phosphor 21 to change an incident angle of the fluorescence on the light extraction surface 20S2. Furthermore, the scattering particle 22 improves an absorption rate of the excitation light EL by increasing an effective optical path length of the excitation light EL. It is preferable for the scattering particle 22 to have a larger average particle diameter than the quantum dot phosphor 21 and a larger refractive index than the resin 23. For example, for the scattering particle 22, it is preferable to use a dielectric substance having a particle diameter of equal to or greater than 100 nm and equal to or less than 1000 nm. As a specific material of the scattering particle 22, for example, silicon oxide (SiO2), titanium oxide (TiO2), aluminum oxide (Al2O3), aluminum nitride (AlN), boron nitride (BN), and zinc oxide (ZnO) are exemplified.
It is to be noted that the scattering particle 22 may be, for example, an air bubble mixed into a filling material 123 or an agglomerated quantum dot phosphor 21.
The resin 23 is used to disperse the quantum dot phosphors 21 and the scattering particles 22, and it is possible to form the resin 23, for example, using a material having light transparency with respect to the excitation light EL. As a specific material of the resin 23, for example, an ultraviolet curing resin and a thermosetting resin are exemplified. Specific examples thereof include polypropylene, polyethylene, polystyrene, an AS resin, an ABS resin, a methacryl resin, polyvinyl chloride, polyacetal, polyamide, polycarbonate, modified polyphenylene ether, polybutylene telephthalate, polyethylene terephthalate, polysulfone, polyethersulfone, polyphenylene sulfide, polyamidimide, polymethylpentene, liquid crystal polymer, an epoxy resin, an acryl resin, a phenol resin, a urea resin, a melamine resin, a diallyl phthalate resin, an unsaturated polyester resin, polyimide, polyurethane, a silicone resin, and a mixture thereof. In addition, sol-gel glass may be used, for example.
It is to be noted that the resin 23 is not necessarily necessary, and the quantum dot phosphors 21 and the scattering particles 22 may be sealed in a hollow structure.
In the present embodiment, the wavelength conversion layer 20 includes the first region 20A and the second region 20B having the absorption coefficients of the excitation light EL different from each other, in order from the side of the surface 10S2 of the light source unit 10. The first region 20A does not include the plurality of scattering particles 22 in the resin 23 and has a configuration in which only the plurality of quantum dot phosphors 21 is dispersed. The second region 20B has a configuration in which both of the plurality of quantum dot phosphors 21 and the plurality of scattering particles 22 are dispersed in the resin 23. As a result, the first region 20A has the absorption coefficient of the excitation light EL lower than that of the second region 20B.
The excitation light EL having entered the wavelength conversion layer 20 is scattered by the scattering particles 22, which increases the optical path length. As a result, the rate of absorption of the excitation light EL in the wavelength conversion layer 20 increases in the wavelength conversion layer 20 (Example and Comparative Example 2) in which the plurality of quantum dot phosphors 21 and the plurality of scattering particles 22 are dispersed, as compared with a case where the plurality of scattering particles 22 is not included (Comparative Example 2). Furthermore, the fluorescence emitted from the quantum dot phosphor 21 is scattered by the scattering particles 22, which improves the light extraction efficiency (
In contrast, in Example, the first region 20A in which the plurality of scattering particles 22 is not included in the resin 23 and only the plurality of quantum dot phosphors 21 is dispersed is provided on the side of the light source unit 10. As a result, a light density adjacent to the side of the light source unit 10 is reduced, and the amount of the absorbed excitation light EL per unit length is reduced to be substantially equal to Comparative Example 2 (
A side surface (surface 20S3) of the wavelength conversion layer 20 is sealed, for example, with a side wall 24. As a material included in the side wall 24, for example, SiO2, silicon (Si), a resist, a resin, and a metal material such as Cu or Al are exemplified.
A light reflection film 25 may be formed between the wavelength conversion layer 20 and the side wall 24. The light reflection film 25 reflects the excitation light EL emitted from the light source unit 10 and scattered with, for example, the scattering particles 22, and the fluorescence emitted from the quantum dot phosphor 21 into the wavelength conversion layer 20. It is preferable to form the light reflection film 25 using a material having a high reflection rate with respect to the excitation light EL and the fluorescence regardless of a light incident angle. As a material of the light reflection film 25, for example, a metal material such as gold (Au), Ag, aluminum (Al), or platinum (Pt) and a dielectric multi-layer film obtained by combining RiO2, Ta2O5, TiO2, SiN, SiO2, and Al2O3 are exemplified.
In the image display apparatus 100 to be described later, the plurality of display pixels P is arranged in a display region 100A in a two-dimensional array. In each of the plurality of display pixels P, a light emission unit 2 including the plurality of light emission devices 1 is provided.
In the light emission unit 2, for example, the plurality of light emission devices 1 is disposed in line. For example, the light emission unit 2 has an elongated shape extending in a direction in which the plurality of light emission devices 1 is provided.
For example, the display pixel P of the image display apparatus 100 includes three color pixels Pr, Pg, and Pb corresponding to RGB, for example. In the color pixels Pr, Pg, and Pb, the light emission devices 1 that emit light in respectively corresponding wavelength bands are provided.
Each of the light emission devices 1R, 1G, and 1B is mounted on the driving substrate 41 via the pad electrodes 42 and 43 and the bumps 44 and 45, for example. It is to be noted that mounting on the driving substrate 41 may be performed using another bonding method such as Cu—Cu bonding.
In each of the light emission devices 1R, 1G, and 1B, for example, the wavelength conversion layer 20 including the plurality of quantum dot phosphors 21 that wavelength-converts the excitation light EL into the light in the predetermined wavelength band is disposed on the light source unit 10 that emits the blue light as the excitation light EL. For example, in the wavelength conversion layer 20 of the light emission device 1R, the plurality of quantum dot phosphors 21 that emits red fluorescence and the plurality of scattering particles 22 are dispersed in the resin 23, and the excitation light EL emitted from the light source unit 10 is converted into the red light with the quantum dot phosphors 21, scattered with the scattering particles 22, and extracted as the red light Lr. In the wavelength conversion layer 20 of the light emission device 1G, the plurality of quantum dot phosphors 21 that emits green fluorescence and the plurality of scattering particles 22 are dispersed in the resin 23, and the excitation light EL emitted from the light source unit 10 is converted into the green light with the quantum dot phosphors 21, scattered with the scattering particles 22, and extracted as the green light Lg. In the wavelength conversion layer 20 disposed in the light emission device 1B, for example, only the scattering particles 22 are dispersed in the resin 23, and the excitation light EL emitted from the light source unit 10 is scattered with the scattering particles 22 and is extracted as the blue light Lb.
Furthermore, on the wavelength conversion layers 20 of the light emission devices 1R and 1G, an excitation light reflection film 31 may be provided as a wavelength selection layer that selectively reflects the excitation light EL. As a result, the excitation light EL emitted from the light extraction surface 20S2 of the wavelength conversion layer 20 is reduced, and it is possible to improve a color gamut. Furthermore, it is possible to improve a contrast of outside light. Furthermore, instead of the excitation light reflection film 31, a yellow filter that selectively absorbs the blue light may be disposed.
Furthermore, in a case where the light source unit 10 that emits ultraviolet rays as the excitation light EL is used, for example, as illustrated in
In the light emission device 1 according to the present embodiment, the wavelength conversion layer 20 includes the first region 20A and the second region 20B from the side of the light source unit 10. Only the plurality of quantum dot phosphors 21 is dispersed in the resin 23 in the first region 20A, and both of the plurality of quantum dot phosphors 21 and the plurality of scattering particles 22 are dispersed in the resin 23 in the second region 20B. The first region 20A has a lower absorption coefficient of the excitation light EL than the second region 20B. This reduces the rate of absorption of the excitation light EL in the vicinity of the light source unit 10. Hereinafter, a description is given in this regard.
In recent years, due to high color gamut of liquid crystal televisions, a product using a QD sheet for a backlight unit has been commercialized. In addition, a display device for augmented reality (AR) applications obtained by combining a blue LED array with a color conversion layer including the quantum dot (QD) has been developed. For the color conversion layer using the QD, a QD layer with high color conversion efficiency is required for high luminance and power saving. Regarding the color conversion efficiency of the QD layer, light extraction efficiency from the QD layer is also important as well as a QD quantum yield. For example, because fluorescence is isotopically emitted from the QD, high-angle components are totally reflected at an interface between the QD and air. This reduces fluorescence to be extracted in the air.
To solve this problem, a method for adding scattering substances to the QD layer is used. As a result, an effect of the total reflection at the interface between the QD and the air is reduced, and the light extraction efficiency is improved by changing an angle of the fluorescence. In addition, an advantage is also obtained that the rate of absorption of the excitation light increases due to the increase in the optical path length of the excitation light in the QD layer by adding the scattering substances. As a result, it is possible to improve the color conversion efficiency of the QD layer by adding the scattering substance to the QD layer.
On the other hand, there is also a problem caused by adding the scattering substance. An excitation light density in the QD layer is increased due to the increase in the optical path length of the excitation light, which lowers reliability. The reliability of the QD layer is lowered as the excitation light density and a temperature of the QD layer become higher. The light density is the highest in the vicinity of the LED because an intensity distribution of the excitation light in the QD layer is exponentially attenuated as being away from the LED, regardless of whether there is the scattering substance. Furthermore, even in a case where the rate of absorption of the excitation light is the same, a total amount of the absorbed excitation light increases as the intensity of the excitation light increases. This increases heat generation caused by an energy loss at the time of color conversion in the vicinity of the LED. For these reasons, a region in the vicinity of the LED in the QD layer has the highest light density and the highest temperature, and deterioration is thus large in the QD. In a case where the scattering substance is included, the rate of absorption of the excitation light in the vicinity of the LED becomes higher, which increases the temperature of the QD layer in the vicinity of the LED and lowers the reliability. An attainment luminance of a light emission element using the color conversion layer including the QD is often limited in accordance with the reliability. Accordingly, both of light extraction efficiency and reliability of a device structure are to be achieved in order to improve the luminance of the light emission device.
Whereas, as described above, an LED device has been proposed that includes a layer to which only the scattering substance is added (scattering substance layer) between the LED and the QD layer to which the scattering substance is added. In this method, the reliability is improved by uniformizing the excitation light in a lateral direction with the scattering substance between the LED and the QD layer or by expanding an area of the excitation light by increasing a distance between the LED and the QD layer. On the other hand, the excitation light from the LED is returned to the LED by the scattering substance layer, which lowers the amount of light incident on the QD layer. Therefore, the light extraction efficiency of both of the LED and the color conversion layer is lowered. In addition, in a case where a narrow pitch is required as in the AR applications, the angle of a QD side wall becomes vertical, which limits a light density reduction effect caused by increasing the distance between the LED and the QD.
Whereas, according to the present embodiment, the wavelength conversion layer 20 includes the first region 20A provided on the side of the light source unit 10, and the second region 20B provided on the side of the light extraction surface 20S2. In the first region 20A, only the plurality of quantum dot phosphors 21 is dispersed in the resin 23, and in the second region 20B, both of the plurality of quantum dot phosphors 21 and the plurality of scattering particles 22 are dispersed in the resin 23. As a result, the absorption coefficient of the excitation light EL in the vicinity of the light source unit 10 is lower than the absorption coefficient of the excitation light
EL in the vicinity of the light extraction surface 20S2, and the absorption rate of the excitation light EL in the vicinity of the light source unit 10 is reduced. That is, the heat generation and the deterioration in the quantum dot phosphor 21 are reduced in the vicinity of the light source unit 10.
As described above, according to the light emission device 1 of the present embodiment, it is possible to achieve both of the improvement in the light extraction efficiency and the improvement in the reliability.
Next, Modification Examples 1 to 13 of the present disclosure are described. It is to be noted that components corresponding to those in the light emission device 1 according to the above embodiment are denoted with the same reference numerals, and a description thereof is omitted.
In the above embodiment, an example has been described in which only the plurality of quantum dot phosphors 21 is dispersed in the resin 23 in the first region 20A on the side of the light source unit 10, and the absorption coefficient of the excitation light EL in the vicinity of the light source unit 10 is lower than the absorption coefficient of the excitation light EL in the vicinity of the light extraction surface 20S2; however, the embodiment is a non-limiting example. For example, the plurality of scattering particles 22 may be dispersed in the first region 20A at a lower concentration than in the second region 20B.
In this way, in the present modification example, both of the plurality of quantum dot phosphors 21 and the plurality of scattering particles 22 are dispersed in the first region 20A, and the concentration of the plurality of scattering particles in the first region 20A is lower than the concentration of the plurality of scattering particles in the second region 20B. As a result, it is possible to obtain effects similar to those of the above embodiment.
For example, a concentration of the plurality of quantum dot phosphors 21 dispersed in the first region 20A may be lower than a concentration of the plurality of quantum dot phosphors 21 dispersed in the second region 20B.
In this way, in the present modification example, the concentration of the plurality of quantum dot phosphors 21 in the first region 20A is lower than the concentration of the plurality of scattering particles in the second region 20B. As a result, as compared with the above-described embodiment, a heat generation amount in the first region 20A is further reduced, and it is possible to further improve the reliability. Furthermore, as compared with the above-described embodiment, it is possible to realize a higher luminance.
A plurality of quantum dot phosphors 26 having a different material, a different composition, or a different core-shell structure from that of the plurality of quantum dot phosphors 21 dispersed in the second region 20B may be dispersed in the first region 20A. For example, the quantum dot phosphors 2, having a lower absorption coefficient of the excitation light EL than the quantum dot phosphors 21 dispersed in the second region 20B are dispersed in the first region 20A.
In this way, in the present modification example, the quantum dot phosphors 26 having a lower absorption coefficient of the excitation light EL than the quantum dot phosphors 21 dispersed in the second region 20B are dispersed in the first region 20A. As a result, as compared with the above-described embodiment, the heat amount in the first region 20A is further reduced, and it is possible to further improve the reliability. Furthermore, as compared with the above-described embodiment, it is possible to realize a higher luminance.
In the above embodiment, an example has been described in which only the plurality of quantum dot phosphors 21 is dispersed in the resin 23 in the first region 20A on the side of the light source unit 10 and the absorption coefficient of the excitation light EL adjacent to the light source unit 10 is made to be lower than the absorption coefficient of the excitation light EL adjacent to the light extraction surface 20S2. However, the embodiment is not limited to this. For example, a region 20X including only the resin 23 may be provided between the first region 20A in which only the plurality of quantum dot phosphors 21 is dispersed in the resin 23 and the second region 20B in which both of the plurality of quantum dot phosphors 21 and the plurality of scattering particles 22 are dispersed.
In this way, in the present modification example, the region 20X including only the resin 23 has been provided between the first region 20A and the second region 20B, and the first region 20A and the second region 20B have been spatially separated. As a result, it is possible to reduce an effect of the heat generation on the second region 20B, in the first region 20A. Therefore, as compared with the above-described embodiment, it is possible to further improve the reliability. Furthermore, as compared with the above-described embodiment, it is possible to realize a higher luminance.
In the above-described embodiment, an example has been described in which the first region 20A in which only the plurality of quantum dot phosphors 21 is dispersed in the resin 23 and the second region 20B in which both of the plurality of quantum dot phosphors 21 and the plurality of scattering particles 22 are dispersed are provided in this order from the side of the light source unit 10. However, the wavelength conversion layer 20 is not limited to this configuration. For example, the wavelength conversion layer 20 is divided into, for example, three regions including the first region 20A, the second region 20B, and a third region 20C from the side of the light source unit 10. Only the plurality of scattering particles 22 is dispersed in the first region 20A, and the second region 20B and the third region 20C may have configurations similar to the respective configurations of the first region 20A and the second region 20B in the above-described embodiment.
In this way, in the present modification example, the wavelength conversion layer 20 is divided into, for example, the three regions including the first region 20A, the second region 20B, and the third region 20C from the side of the light source unit 10, and only the plurality of scattering particles 22 is dispersed in the first region 20A. As a result, the excitation light EL having entered from the light source unit 10 into the wavelength conversion layer 20 is equalized with the first region 20A. It is therefore possible to improve in-plane uniformity of the excitation light EL entering the second region 20B in which only the plurality of quantum dot phosphors 21 is dispersed in the resin 23. Therefore, as compared with the above-described embodiment, it is possible to further improve the reliability.
In the above embodiment, an example has been described in which the first region 20A in which only the plurality of quantum dot phosphors 21 is dispersed in the resin 23 and the second region 20B in which both of the plurality of quantum dot phosphors 21 and the plurality of scattering particles 22 are dispersed are provided in this order from the side of the light source unit 10. However, the wavelength conversion layer 20 is not limited to this configuration. For example, the third region 20C in which both of a plurality of quantum dot phosphors 21B and the plurality of scattering particles 22 are dispersed may be further provided on the second region 20B of the above-described embodiment.
In the present modification example, a plurality of quantum dot phosphors 21A dispersed in the first region 20A and the second region 20B and the plurality of quantum dot phosphors 21B dispersed in the third region 20C include different materials from each other. In general, a so-called Cd-based quantum dot phosphor has a higher light resistance than a Cd-free quantum dot phosphor. In the present modification example, the Cd-based quantum dot phosphor is used for the first region 20A and the second region 20B, and the Cd-free quantum dot phosphor is used for the third region 20C.
In this way, by providing the first region 20A in which only the plurality of quantum dot phosphors 21 is dispersed in the resin 23 on the side of the light source unit 10 in the wavelength conversion layer 20, it is possible to use the Cd-free quantum dot phosphors for other regions (for example, the third region 20C farthest from the light source unit 10). Therefore, it is possible to reduce a Cd concentration in the wavelength conversion layer 20, and it is possible to reduce an environment load.
In the above embodiment, an example has been described in which the first region 20A in which only the plurality of quantum dot phosphors 21 is dispersed in the resin 23 and the second region 20B in which both of the plurality of quantum dot phosphors 21 and the plurality of scattering particles 22 are dispersed are provided in this order from the side of the light source unit 10. However, the wavelength conversion layer 20 is not limited to this configuration. For example, as illustrated in
In this way, in the present modification example, the concentration of the plurality of quantum dot phosphors 21 in the wavelength conversion layer 20 is changed in the lateral direction. As a result, in plan view, light extraction efficiency relatively increases near the middle of the light emission device 9. Therefore, by combining with a microlens array 32 to be described later, it is possible to improve controllability of light distribution characteristics of the light emission device 9.
The microlens array 32 corresponds to a specific example of a “light distribution control structure” in the present disclosure. As the light distribution control structure, a photonic crystal, a moth-eye structure, a nanoantenna, and a metamaterial may be provided, other than the microlens array 32. As a result, for example, it is possible to enhance a luminance on a low angle side.
It is to be noted that, in the present modification example, an example has been described in which the texture structure 34 is additionally provided on the light extraction surface (surface 20S2) of the wavelength conversion layer 20. However, for example, a texture structure may be formed on the light extraction surface of the wavelength conversion layer 20.
In the display panel 110, a mounting substrate 120 and a counter substrate 130 are stacked on each other. A surface of the counter substrate 130 serves as a video display surface, the display region 100A is provided in a middle portion, and a frame region 100B that is a non-display region is provided therearound.
The scan wiring line 1022 is formed, for example, on an outermost layer, and is formed, for example, on an insulation layer (not illustrated) formed on a base material surface. Note that the base material of the mounting substrate 120 includes, for example, a silicon substrate or a resin substrate, and the insulation layer on the base material includes, for example, SiN, SiO, aluminum oxide (AlO), or a resin material. On the other hand, the data wiring line 1021 is formed in a layer (for example, layer lower than outermost layer) different from the outermost layer including the scan wiring line 1022 and is formed, for example, in the insulation layer on the base material. On a surface of the insulation layer, for example, a black is provided as necessary, in addition to the scan wiring line 1022. The black enhances a contrast and includes a light-absorbing material. For example, the black is formed in at least a non-forming region of pad electrodes 1021B and 1022B to be described later, in the surface of the insulation layer. Note that, it is possible to omit the black, as necessary.
The vicinity of an intersecting portion between the data wiring line 1021 and the scan wiring line 1022 serves as the display pixel P, and the plurality of display pixels P is disposed in the display region 100A, for example, in a matrix. In each display pixel P, for example, the light emission unit 2 including the plurality of light emission devices 1 corresponding to RGB is mounted. In
Note that the image display apparatus 100 illustrated in
In a passive matrix type driving method, because a time allocated to each light emission device is shortened if the number of scan wiring lines increases, an injection current is necessary to be increased along with a decrease in a duty ratio, and there is a possibility that luminance efficiency or a device lifetime is lowered. To avoid this, it is necessary to lower the maximum luminance setting value. Furthermore, due to problems such as a voltage drop or a signal delay caused by a wiring resistance and a parasitic capacitance, for a large screen with a large number of scanning lines or a high-definition image display apparatus, a system for dividing a screen into a plurality of partial screens and performing passive-matrix-driving on the screens in parallel or a system for performing active-driving on the light emission device is adopted. The parallel passive matrix driving makes a structure of an entire display device be more complicated and increases a circuit size, like it is necessary to extract a wiring line to a rear surface for each partial screen to couple the wiring line to a driving circuit, and to divide and parallelize an image signal in accordance with each partial screen. On the other hand, with the active driving system, by holding a signal voltage in pixel unit and providing a voltage-current conversion circuit, it is possible to obtain a higher luminance than the passive matrix driving, in a state where the screen division as described above is not performed or at least the number of divisions is smaller.
In the light emission unit 2, for example, a pair of terminal electrodes is provided for each of the light emission devices 1R, 1G, and 1B. Then, the one terminal electrode is, for example, electrically coupled to the data wiring line 1021, and the other terminal electrode is, for example, electrically coupled to the scan wiring line 1022. For example, the terminal electrode is electrically coupled to the pad electrode 1021B at a front end of a branch 1021A provided in the data wiring line 1021. Furthermore, for example, the terminal electrode is electrically coupled to the pad electrode 1022B at a front end of a branch 1022A provided in the scan wiring line 1022.
The pad electrodes 1021B and 1022B are formed, for example, on the outermost layer, and for example, as illustrated in
On the mounting substrate 120, for example, a plurality of pillars (not illustrated) that controls an interval between the mounting substrate 120 and the counter substrate 130 is further provided. The pillar may be provided in an opposing region to the display region 100A or may be provided in an opposing region to the frame region 100B.
The counter substrate 130 includes, for example, a glass substrate, a resin substrate, or the like. Although a surface of the counter substrate 130 on the side of the light emission device 1 may be flat, it is preferable that the surface be a rough surface. The rough surface may be provided across the entire opposing region to the display region 100A or may be provided only on an opposing region to the display pixel P. The rough surface has fine bumps and dips in which light emitted from the display pixel P enters. It is possible to form the bumps and dips on the rough surface, for example, by sandblasting or dry etching.
The control circuit 140 drives each display pixel P (each light emission unit 2) on the basis of a picture signal. The control circuit 140 includes, for example, a data driver that drives the data wiring line 1021 coupled to the display pixel P and a scan driver that drives the scan wiring line 1022 coupled to the display pixel P. For example, as illustrated in
In the display panel 210, a mounting substrate 220 and a counter substrate 230 are stacked on each other. A surface of the counter substrate 230 serves as a video display surface, a display region is provided in a middle portion, and a frame region that is a non-display region is provided therearound (both are not illustrated). The counter substrate 230 is disposed at a position opposing to the mounting substrate 220, for example, with a predetermined gap. Note that, the counter substrate 230 may have contact with a top surface of the mounting substrate 220.
In the transparent display 300, a substrate having light transparency is used as a mounting substrate. Each electrode provided in the light emission device 1 is formed using a conductive material having light transparency, similarly to the mounting substrate. Alternatively, each electrode has a structure that is difficult to be visually recognized by narrowing a wiring line width or thinning a thickness of the wiring line. Furthermore, for example, it is possible for the transparent display 300 to realize black display by stacking a liquid crystal layer including a driving circuit and to switch transmission and black display by controlling a light distribution direction of the liquid crystal.
As described above, the present disclosure has been described using the embodiment, the modification examples 1 to 13, and the application examples. However, the present disclosure is not limited to the above embodiment, and it is possible to make various modifications. For example, in the above example or the like, an example has been described in which the LED chip having the mesa portion M is used as the light source unit 10. However, the shape of the LED chip is not limited to this.
Furthermore, in the above embodiment or the like, although an example has been described in which the LED chip using an inorganic semiconductor is used as the light source unit 10, the light source unit 10 is not limited to this. As the light source unit 10, for example, it is possible to use an LED using an organic semiconductor (OLED) and a semiconductor laser (laser diode: LD).
In addition, it is possible to apply the light emission device (for example, light emission device 1) according to the above embodiment or the like to a smartphone, a television, a laptop computer, an AR/VR device, a projector, a head-up display (HUD), a smart watch, a video wall, or the like, in addition to the application examples 1 to 3 described above.
Note that the effects described herein are examples and not limited, and may be other effects.
Note that the present disclosure may have the following configurations. According to the present technology having the following configuration, in the wavelength conversion layer including the plurality of wavelength conversion materials that converts the first light emitted from the light source unit into the second light in the different wavelength band and the plurality of scattering particles, the absorption coefficient of the first light adjacent to the surface (first surface) on the side of the light source unit is made to be lower than the absorption coefficient of the first light adjacent to the light extraction surface (second surface). This reduces the absorption rate of the excitation light adjacent to the light source unit. Therefore, it is possible to achieve both of the light extraction efficiency and the reliability.
A light emission device including:
The light emission device according to (1), in which
The light emission device according to (2), in which the first region does not include the plurality of scattering particles.
The light emission device according to any one of (1) to (3), in which
The light emission device according to any one of (2) to (4), in which the first region extends toward the second surface to surround the second region.
The light emission device according to any one of (2) to (5), in which the wavelength conversion layer further includes a region that does not include the plurality of wavelength conversion materials and the plurality of scattering particles between the first region and the second region.
The light emission device according to any one of (1) to (6), in which
The light emission device according to any one of (1) to (6), in which
The light emission device according to (8), in which
The light emission device according to any one of (1) to (9), in which
The light emission device according to any one of (1) to (10), in which a light reflection structure is formed on a side surface between the first surface and the second surface of the wavelength conversion layer.
The light emission device according to (11), in which the side surface is an inclined surface extending from the first surface toward the second surface.
The light emission device according to any one of (1) to (12), further including an irregular structure on the second surface of the wavelength conversion layer.
The light emission device according to any one of (1) to (13), further including:
The light emission device according to (14), further including a wavelength selection layer on the second surfaces of at least the first wavelength conversion layer and the second wavelength conversion layer, the wavelength selection layer selectively reflecting the first light.
The light emission device according to (14) or (15), further including a light distribution control structure on the second surfaces of the first wavelength conversion layer, the second wavelength conversion layer, and the third wavelength conversion layer.
The light emission device according to (16), in which the light distribution control structure is any one of a microlens array, a photonic crystal, a moth-eye structure, a nanoantenna, and a metamaterial.
The light emission device according to any one of (1) to (17), further including:
The light emission device according to any one of (1) to (18), in which the light source unit is a blue light-emitting diode or an ultraviolet ray light-emitting diode.
An image display apparatus including
The present application claims the benefit of Japanese Priority Patent Application No. 2021-185012 filed with the Japan Patent Office on Nov. 12, 2021, the entire contents of which are incorporated herein by reference.
It should be understood by those skilled in the art that various modifications, combinations, sub-combinations, and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-185012 | Nov 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/038786 | 10/18/2022 | WO |
