Light emitting device having multiple light emitting elements

A light emitting device includes a first light emitting element including a rectangular first light extraction surface, a second light emitting element including a rectangular second light extraction surface and emitting light having an emission peak wavelength different from an emission peak wavelength of the first light emitting element, and a light-transmissive member covering the first light extraction surface and the second light extraction surface. The light-transmissive member includes a first light-transmissive layer facing the first light extraction surface and the second light extraction surface, a wavelength conversion layer located on the first light-transmissive layer, and a second light-transmissive layer located on the wavelength conversion layer. The first light-transmissive layer contains a first matrix and first diffusive particles. The wavelength conversion layer contains a second matrix and wavelength conversion particles. The second light-transmissive layer contains a third matrix and second diffusive particles.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2017-246293, filed on Dec. 22, 2017, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND

The present disclosure relates to a light emitting device.

A white light emitting diode is known in which a blue light emitting diode chip and a green light emitting diode chip are mounted on a first lead terminal, the blue light emitting diode chip and the green light emitting diode chip are encapsulated in a molded portion, and a red phosphor is contained in the molded portion (see, for example, Japanese Patent Publication No. 2007-158296).

SUMMARY

Certain non-limiting and exemplary embodiment provides a light emitting device in which the color non-uniformity is less likely to occur.

In certain general aspect, a light emitting device according to the present disclosure includes a first light emitting element including a rectangular first light extraction surface, a first electrodes formation surface located opposite to the first light extraction surface, a first lateral surface located between the first light extraction surface and the first electrodes formation surface, and a pair of first electrodes formed on the first electrodes formation surface;

a second light emitting element including a rectangular second light extraction surface, a second electrodes formation surface located opposite to the second light extraction surface, a second lateral surface located between the second light extraction surface and the second electrodes formation surface, and a pair of second electrodes formed on the second electrodes formation surface, the second light emitting element emitting light having an emission peak wavelength different from an emission peak wavelength of the first light emitting element, a shorter side of the first light extraction surface and a shorter side of the second light extraction surface facing each other;

a light guide member continuously covering the first light extraction surface, the first lateral surface, the second light extraction surface and the second lateral surface;

a light-transmissive member covering the first light extraction surface and the second light extraction surface via the light guide member; and a first reflective member covering the first lateral surface and the second lateral surface via the light guide member.

The light-transmissive member includes a first light-transmissive layer facing the first light extraction surface and the second light extraction surface, a wavelength conversion layer located on the first light-transmissive layer, and a second light-transmissive layer located on the wavelength conversion layer.

The first light-transmissive layer contains a first matrix and first diffusive particles.

The wavelength conversion layer contains a second matrix and wavelength conversion particles.

The second light-transmissive layer contains a third matrix and second diffusive particles.

According to the above aspect, it is possible to provide a light emitting device in which the color non-uniformity is less likely to occur.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described with reference to the attached drawings when necessary. Light emitting devices described below embody the technological idea of the present invention, and the present invention is not limited to any of the following embodiments unless otherwise specified. A content described in one embodiment is applicable to other embodiments and modifications. In the drawings, the size, positional arrangement or the like may be emphasized for clear illustration.

A light emitting device1000in an embodiment according to the present disclosure will be described with reference toFIG. 1AthroughFIG. 10. The light emitting device1000includes a first light emitting element20A, a second light emitting element20B, a light guide member50, a light-transmissive member30, and a first reflective member40. The first light emitting element20A includes a rectangular first light extraction surface201A, a first electrodes formation surface203A located opposite to the first light extraction surface201A, a first lateral surfaces202A located between the first light extraction surface201A and the first electrodes formation surface203A, and a pair of first electrodes21A and22A formed on the first electrodes formation surface203A. The second light emitting element20B includes a rectangular second light extraction surface201B, a second electrodes formation surface203B located opposite to the second light extraction surface201B, a second lateral surfaces202B located between the second light extraction surface201B and the second electrodes formation surface203B, and a pair of second electrodes21B and22B formed on the second electrodes formation surface203B. The second light emitting element20B has an emission peak wavelength different from an emission peak wavelength of the first light emitting element20A. In this specification, the term “rectangle” refers to a quadrangle including two longer sides, two shorter sides, and four right-angled corners. In this specification, the “right angle” includes tolerance of about +3° from 90°.

A shorter side2011A of the first light extraction surface201A and a shorter side2011B of the second light extraction surface201B face each other. The light guide member50continuously covers the first light extraction surface201A, the first lateral surfaces202A, the second light extraction surface201B and the second lateral surfaces202B. The light-transmissive member30covers the first light extraction surface201A and the second light extraction surface201B via the light guide member50. The light-transmissive member30includes a first light-transmissive layer31A facing the first light extraction surface201A and the second light extraction surface201B, a wavelength conversion layer31B located on the first light-transmissive layer31A, and a second light-transmissive layer31C located on the wavelength conversion layer31B. The first light-transmissive layer31A includes a first matrix312A and first diffusive particles311A. The wavelength conversion layer31B includes a second matrix312B and wavelength conversion particles311B. The second light-transmissive layer31C includes a third matrix312C and second diffusive particles311C.

As shown inFIG. 2AandFIG. 2B, the light-transmissive member30includes the first light-transmissive layer31A facing the first light extraction surface201A and the second light extraction surface201B. With such a structure, light from the first light emitting element20A and light from the second light emitting element20B are diffused by the first light-transmissive layer31A. This allows the light from the first light emitting element20A and the light from the second light emitting element20B to be mixed together in the first light-transmissive layer31A. This can reduce a color non-uniformity of the light emitting device1000.

It is preferable that the first light-transmissive layer31A substantially includes no wavelength conversion particles. The wavelength conversion particles absorb a part of the light from the first light emitting element20A and/or the second light emitting element20B when being excited by the light from the first light emitting element20A and/or the second light emitting element20B. Because the first light-transmissive layer31A is located between the first light extraction surface201A/the second light extraction surface201B and the wavelength conversion layer31B, the light from the first light emitting element20A, and/or the light from the second light emitting element20B are mixed together before being absorbed by the wavelength conversion particles. This can suppress a decline in the light extraction efficiency of the light emitting device. The expression that “substantially includes no wavelength conversion particles” indicates that unavoidable contamination with the wavelength conversion particles is not eliminated. It is preferable that the first light-transmissive layer31A has a content of the wavelength conversion particles of 0.05% by weight or lower.

As shown inFIG. 2A, the light guide member50continuously covers the first light extraction surface201A, the first lateral surfaces202A, the second light extraction surface201B and the second lateral surfaces202B. With such a structure, the light from the first light emitting element20A and the light from the second light emitting element20B are mixed together in the light guide member50. This can reduce the color non-uniformity of the light emitting device.

It is preferable that the light guide member50substantially includes no wavelength conversion particles. The structure in which the light guide member50substantially includes no wavelength conversion particles suppresses a situation where apart of the light from the first light emitting element20A and/or the second light emitting element20B is absorbed into the wavelength conversion particles in the light guide member. This can alleviate a decline in the light extraction efficiency of the light emitting device.

As shown inFIG. 2AandFIG. 2B, the second light-transmissive layer31C is located on the wavelength conversion layer31B. With such a structure, the light from the first light emitting element20A and the light from the second light emitting element20B are mixed, in the second light-transmissive layer31C, with light from the wavelength conversion particles311B excited by the first light emitting element20A and/or the second light emitting element20B. This can reduce the color non-uniformity of the light emitting device. In addition, the second light-transmissive layer31C is located on the wavelength conversion layer31B. With such a structure, even if the wavelength conversion layer31B includes wavelength conversion particles, which are weak against moisture, the second light-transmissive layer31C serves as a protective layer.

This can alleviate deterioration of the wavelength conversion particles. Examples of the wavelength conversion particles weak against moisture include, for example, a manganese-activated fluoride phosphor. The manganese-activated fluoride phosphor emits light having a relatively narrow spectral line width, which is preferable from the point of view of color reproducibility.

It is preferable that the second light-transmissive layer31C substantially includes no wavelength conversion particles. The structure in which the second light-transmissive layer31C substantially includes no wavelength conversion particles can reduce a possibility where a part of the light from the first light emitting element20A, and/or the second light emitting element20B is absorbed into the wavelength conversion particles in the second light-transmissive layer31C. This can alleviate a decline in the light extraction efficiency of the light emitting device.

It is preferable that the first matrix312A, the second matrix312B and the third matrix312C contain the same resin material as each other. The structure in which the first matrix312A and the second matrix312B contain the same resin material as each other can increase a joining strength between the first matrix312A and the second matrix312B. The structure in which the second matrix312B and the third matrix312C contain the same resin material as each other can increase a joining strength between the second matrix312B and the third matrix312C.

The first light emitting element20A includes at least a first semiconductor stack body23A, and the pair of first electrodes21A, and22A are formed on the first semiconductor stack body23A. In this embodiment, the first light emitting element20A includes a first element substrate24A, but the first element substrate24A may be removed. Similarly, the second light emitting element20B includes at least a second semiconductor stack body23B, and the pair of second electrodes21B and22B are formed on the second semiconductor stack body23B. In this embodiment, the second light emitting element20B includes a second element substrate24B, but the second element substrate24B may be removed. Typically, the first element substrate24A and the second element substrate24B are each an element substrate formed of sapphire or the like described below.

The emission peak wavelength of the first light emitting element20A and the emission peak wavelength of the second light emitting element20B merely need to be different from each other. It is preferable that the emission peak wavelength of the first light emitting element20A is in the range of 430 nm or longer and shorter than 490 nm (i.e., wavelength range of blue light) and that the emission peak wavelength of the second light emitting element20B is in the range of 490 nm or longer and 570 nm or shorter (i.e., wavelength range of green light). With such an arrangement, the light emitting device1000can have an improved color rendering properties. In the case where the emission peak wavelength of the second light emitting element20B is in the range of 490 nm or longer and 570 nm or shorter, it is preferable that the second light emitting element20B has a half width of 5 nm or longer and 40 nm or shorter. Setting the half width of the second light emitting element20B is 5 nm or longer can improve the optical output of the second light emitting element20B. Setting the half width of the second light emitting element20B is 40 nm or shorter can exhibit a sharp peak having a strong green light component. This can realize a high color reproducibility in the case where the light emitting device1000is used for a liquid crystal display device. Use of a light emitting element that emits green light can shorten the half width of the green light more easily than the green light provided by use of a green phosphor.

In the case where the emission peak wavelength of the first light emitting element20A is in the range of 430 nm or longer and shorter than 490 nm (i.e., wavelength range of blue light) and the emission peak wavelength of the second light emitting element20B is in the range of 490 nm or longer and 570 nm or shorter (i.e., wavelength range of green light), it is preferable that the emission peak wavelength of the wavelength conversion particles311B is in the range of 580 nm or longer and shorter than 680 nm (i.e., wavelength range of red light). Such an arrangement increases the color rendering properties of the light emitting device1000.

As shown inFIG. 3A, the shorter side2011A of the first light extraction surface201A and the shorter side2011B of the second light extraction surface201B face each other. Such a structure allows the light emitting device1000to be thinner in a Y direction.

The first reflective member40covers the first lateral surface202A and the second lateral surface202B via the light guide member50. With such a structure, light traveling in an X direction and/or the Y direction from the first light emitting element20A and the second light emitting element20B is reflected by the first reflective member40to increase the amount of light traveling in a Z direction. This allows the light from the first light emitting element20A and the light from the second light emitting element20B to pass the light-transmissive member30more easily, and thus the color non-uniformity of the light emitting device can be reduced.

As shown inFIG. 2A, it is preferable that a lateral surface of the light-transmissive member30is covered with the first reflective member40. With such a structure, the light emitting device1000has a high contrast between a light emitting region and a non-light emitting region, namely, has a highly clear border between the light emitting region and the non-light emitting region.

As shown inFIG. 2A, the light emitting device1000includes three light emitting elements, in other words, the first light emitting element20A, the second light emitting element20B and a third light emitting element20C. However, as in a light emitting device2000shown inFIG. 4AthroughFIG. 4D, a light emitting device in an embodiment according to the present disclosure may include two light emitting elements, in other words, the first light emitting element20A and the second light emitting element20B.

As in a light emitting device3000shown inFIG. 4E, a light emitting device in an embodiment according to the present disclosure may include four light emitting elements, in other words, the first light emitting element20A, the second light emitting element20B, the third light emitting element20C and a fourth light emitting element20D. A light emitting device in an embodiment according to the present disclosure may include five or more light emitting elements.

The third light emitting element20C includes a third light extraction surface201C, a third electrodes formation surface203C located opposite to the third light extraction surface201C, a third lateral surfaces202C located between the third light extraction surface201C and the third electrodes formation surface203C, and a pair of third electrodes21C and22C formed on the third electrodes formation surface203C. In the exemplary construction illustrated inFIG. 2A, the light guide member50continuously covers the third light extraction surface201C and the third lateral surfaces202C. The light-transmissive member30covers the third light extraction surface201C via the light guide member50. The first reflective member40covers the third lateral surfaces202C via the light guide member50.

As shown inFIGS. 1B and 2B, the light emitting device1000may include an insulating film18covering a part of a second wiring portion13. The insulating film18can ensure insulation property and prevent shortcircuiting of the light emitting device1000. The insulating film18also can prevent or alleviate the second wiring portion13from being peeled off from a base member11.

As shown inFIG. 2A, the first light extraction surface201A of the first light emitting element20A and the second light extraction surface201B of the second light emitting element20B may have substantially the same height as each other in the Z direction. Alternatively, the first light extraction surface201A of the first light emitting element20A and the second light extraction surface201B of the second light emitting element20B may have different heights from each other in the Z direction. For example, as in a light emitting device1000A shown inFIG. 2C, the first light extraction surface201A may be positioned lower than that of the second light extraction surface201B in the Z direction. With the structure in which the first light extraction surface201A is positioned lower than that of the second light extraction surface201B in the Z direction, a portion of the light guide member50that is located on the first light extraction surface201A can be made thicker in the Z direction. Therefore, the light from the first light emitting element20A and the light from the second light emitting element20B can be mixed together more easily in the light guide member50. This can reduce the color non-uniformity of the light emitting device. As in a light emitting device1000B shown inFIG. 2D, the first light extraction surface201A may be positioned higher than that of the second light extraction surface201B in the Z direction. With the structure in which the first light extraction surface201A is positioned higher than that of the second light extraction surface201B in the Z direction, a portion of the light guide member50that is located on the second light extraction surface201A can be made thicker in the Z direction. Therefore, the light from the first light emitting element20A and the light from the second light emitting element20B are mixed together more easily in the light guide member50. This can reduce the color non-uniformity of the light emitting device.

As shown inFIG. 3A, it is preferable that the second light emitting element20B is located between the first light emitting element20A and the third light emitting element20C as seen in a front view. With such a structure, the first light emitting element20A, the second light emitting element20B and the third light emitting element20C are arrayed in one direction. This allows the light emitting device to be thinner in the Y direction. In the case where the third light extraction surface201C is rectangular, it is preferable that a shorter side2012B of the second light extraction surface201B and a shorter side2011C of the third light extraction surface201C face each other. Such a structure allows the light emitting device to be thinner in the Y direction.

As shown inFIG. 3A, the shorter side2011A of the first light extraction surface201A of the first light emitting element20A and the shorter side2011B of the second light extraction surface201B of the second light emitting element20B may have the same length as each other. Alternatively, the shorter side2011A of the first light extraction surface201A of the first light emitting element20A and the shorter side2011B of the second light extraction surface201B of the second light emitting element20B may have different lengths from each other. For example, as shown inFIG. 3B, the shorter side2011A of the first light extraction surface201A may be longer than the shorter side2011B of the second light extraction surface201B. With such a structure, a portion of the light guide member50positioned along a longer lateral surfaces of the second light emitting element20B can be made thicker in the Y direction. Therefore, the light from the first light emitting element20A and the light from the second light emitting element20B are mixed together more easily in the light guide member50. This can reduce the color non-uniformity of the light emitting device1000. As shown inFIG. 3C, the shorter side2011A of the first light extraction surface201A may be shorter than the shorter side2011B of the second light extraction surface201B. With such a structure, a portion of the light guide member50positioned along a longer lateral surfaces of the first light emitting element20A can be made thicker in the Y direction. Therefore, the light from the first light emitting element20A and the light from the second light emitting element20B are mixed together more easily in the light guide member50. This can reduce the color non-uniformity of the light emitting device.

The third light emitting element20C may have an emission peak wavelength same as, or different from, the emission peak wavelength of the first light emitting element20A or the emission peak wavelength of the second light emitting element20B. In the case where the second light emitting element20B is located between the first light emitting element20A and the third light emitting element20C, it is preferable that the emission peak wavelength of the third light emitting element20C is the same as the emission peak wavelength of the first light emitting element20A. Such an arrangement can reduce the color non-uniformity of the light emitting device. In this specification, the expression that the “emission peak wavelength is the same” indicates that a tolerance of about +10 nm is allowed. In the case where, for example, the emission peak wavelength of the first light emitting element20A is in the range of 430 nm or longer and shorter than 490 nm (i.e., wavelength range of blue light), it is preferred that the emission peak wavelength of the third light emitting element20C is in the range of 430 nm or longer and shorter than 490 nm. With such an arrangement, wavelength conversion particles having an excitation efficiency peak in the range of 430 nm or longer and shorter than 490 nm may be selected, and thus the excitation efficiency of the wavelength conversion particles can be improved.

As in a light emitting device1000C shown inFIG. 5A, a light emitting device in an embodiment according to the present disclosure may include a cover member31D covering the second light extraction surface201B of the second light emitting element20B. In this example, the cover member31D is located between the second light extraction surface201B of the second light emitting element20B and the light guide member50. In the case where the cover member31D contains third diffusive particles311D, the cover member31D covering the second light extraction surface201B can decrease the amount of light traveling in the Z direction from the second light emitting element20B and thus can increase the amount of light traveling in the X direction and/or the Y direction. This can diffuse the light from the second light emitting element20B in the light guide member50, and thus can reduce the color non-uniformity of the light emitting device. It is preferable that the cover member31D containing the third diffusive particles311D is disposed such that at least a part of the second lateral surfaces202B is exposed. Such a structure can alleviate a decrease in the amount of the light traveling in the X direction and/or the Y direction from the second light emitting element20B.

The cover member31D may include wavelength conversion particles. The provision of the cover member31D covering the second light extraction surface201B of the second light emitting element20B and containing the wavelength conversion particles allows color adjustment of the light emitting device to be performed easily. The wavelength conversion particles312D contained in the cover member31D may be formed of a material comprising same as, or different from, that of the wavelength conversion particles311B included in the wavelength conversion layer31B. In the case where, for example, the emission peak wavelength of the second light emitting element20B is in the range of 490 nm or longer and 570 nm or shorter (i.e., wavelength range of green light), the wavelength conversion particles may be formed of a CASN-based phosphor and/or an SCASN-based phosphor, which is excited by light in the range of 490 nm or longer and 570 nm or shorter. Alternatively, the wavelength conversion particles may be formed of a phosphor of (Sr, Ca)LiAl3N4:Eu. The cover member31D may cover the first light extraction surface201A of the first light emitting element20A and/or the third light extraction surface201C of the third light emitting element20C.

As in the light emitting device1000C shown inFIG. 5A, one cover member31D may cover the element light extraction surface of one light emitting element. Alternatively, as in a light emitting device1000D shown inFIG. 5B, a plurality of the cover members31D may cover the element light extraction surface of one light emitting element. In this case, a part of the element light extraction surface of the light emitting element is exposed from the cover members31D, and thus the light extraction efficiency of the light emitting element can be improved.

As shown inFIG. 2A, the light emitting device1000may include a second reflective member41covering the first electrodes formation surface203A and the second electrodes formation surface203B. In the case where the light emitting device1000includes a substrate on which the first light emitting element20A and the second light emitting element20B are placed, the structure in which the first electrodes formation surface203A and the second electrodes formation surface203B are covered with the second reflective member41to alleviate the light from the first light emitting element20A and the light from the second light emitting element20B from being absorbed into the substrate. This can improve the light extraction efficiency of the light emitting device1000. In the case where the light emitting device1000does not include the substrate on which the first light emitting element20A and the second light emitting element20B are placed, the structure in which the first electrodes formation surface203A and the second electrodes formation surface203B are covered with the second reflective member41can alleviate the light from the first light emitting element20A and the light from the second light emitting element20B from being absorbed into a mounting substrate on which the light emitting device1000is mounted. This can improve the light extraction efficiency of the light emitting device1000. It is preferable that the second reflective member41includes an inclining portion having a greater thickness in the Z direction as being farther from the first light emitting element20A and/or the second light emitting element20B. With the structure in which the second reflective member41includes the inclining portion, the extraction efficiency of the light from the first light emitting element20A and/or the second light emitting element20B can be improved.

As in a light emitting device1000E shown inFIG. 5C, the first electrodes formation surface203A and the second electrodes formation surface203B may be covered with the first reflective member40. Such a structure improves the light extraction efficiency of the light emitting device1000E.

As shown inFIG. 2A, the light emitting device1000may include a third reflective member42provided between the light guide member50and the first reflective member40. The third reflective member42covers the first lateral surface202A and the second lateral surface202B via the light guide member50. After the third reflective member42is formed, the light guide member50may be formed by potting or the like, so that shape of the light guide member50is less likely to be varied. It is preferable that a surface of the third reflective member42that faces the light-transmissive member30is flat. With such a structure, the light-transmissive member30is easily formed after the third reflective member42is formed. In the case where the light emitting device1000includes the third reflective member42, the first reflective member40covers the first lateral surface202A and the second lateral surface202B via the third reflective member42and the light guide member50.

As shown inFIG. 2A, the light emitting device1000may include the substrate10on which the first light emitting element20A and the second light emitting element20B are placed. In the case where the substrate10is included, the strength of the light emitting device1000can be increased. However, as in a light emitting device1000F shown inFIG. 5D, a light emitting device in an embodiment according to the present disclosure does not need to include a substrate for which the first light emitting element20A and the second light emitting element20B are placed. In the case where the substrate10is not included, the light emitting device1000F can be thinner in the Z direction.

In the case where the substrate10is not included as in the light emitting device1000F shown inFIG. 5D, it is preferable that the first light emitting element20A and the second light emitting element20B are connected with each other by a metal film122formed by sputtering or the like. The provision of the metal film122allows the first light emitting element20A and the second light emitting element20B to be electrically connected with each other.

The substrate10includes, for example, the base member11in which at least one via15is formed, a first wiring portion12, and the second wiring portion13. The base member11includes a front surface111extending in a longer direction and a shorter direction, a rear surface112located opposite to the front surface111, a bottom surface113adjacent and perpendicular to the front surface111, and a top surface114located opposite to the bottom surface113(see, e.g.,FIG. 10). The first wiring portion12is located on the front surface111of the base member11. The second wiring portion13is located on the rear surface112of the base member11. The first light emitting element20A and the second light emitting element20B are electrically connected with, and are located on, the first wiring portion12. The first reflective member40covers the first lateral surface202A, the second lateral surface202B and the front surface111of the substrate10. The via15electrically connects the first wiring portions12and the second wiring portions13to each other.

As shown inFIG. 1B, the base member11may have at least one recessed portion16. The recessed portion16is opened at the rear surface112and the bottom surface113. An inner wall of the recessed portion16is covered with a third wiring portion14. In the case where the base member11have the recessed portion16, the light emitting device1000is allowed to be secured to the mounting substrate by a joining member such as a solder member or the like formed in the recessed portion16. This can increase the joining strength between the light emitting device and the mounting substrate. Alternatively, as in a light emitting device1000G shown inFIG. 6AthroughFIG. 6D, the base member11does not need to have any recessed portion. In the case where the base member11includes no recessed portion, the strength of the base member11can be increased.

The light emitting device1000may be secured to the mounting substrate by the joining member such as a solder member or the like formed in the recessed portion16. The number of the recessed portion16may be one or more. In the case where the plurality of recessed portions16is formed on the base member11, the joining strength between the light emitting device1000and the mounting substrate can be increased. The recessed portion16may be a central recessed portion16A opened on the rear surface112and the bottom surface113and apart from a shorter lateral surface105(FIG. 7) of the base member11, or may be an end recessed portion16B opened on the rear surface112, the bottom surface113and the shorter lateral surface105of the base member11. In this specification, the term “recessed portion” refers to the central recessed portion and/or the end recessed portion.

The recessed portion16may have an equal depth on the top surface114side and the bottom surface113side, or may be deeper on the bottom surface113side than on the top surface114side. In the case where as shown inFIG. 2B, the recessed portion16is deeper in the Z direction on the bottom surface113side than on the top surface114side, thickness W1of a portion of the base member11that is located on the top surface114side with respect to the recessed portion16is greater than thickness W2of a portion of the base member11that is located on the bottom surface113side with respect to the recessed portion16. This can alleviate a decrease in the strength of the base member. In addition, a depth W3of the recessed portion16on the bottom surface113side is greater than a depth W4of the recessed portion16on the top surface114side. This can increase the volume of the joining member formed in the recessed portion16. Therefore, the joining strength between the light emitting device1000and the mounting substrate can be increased. The light emitting device1000may be either a top emission type or side emission type. The top emission type has a structure in which the rear surface112of the base member11and the mounting substrate face each other. The side view type has a structure in which the bottom surface113of the base member11and the mounting substrate face each other. In either case, the increase in the volume of the joining member can increase the joining strength between the light emitting device1000and the mounting substrate.

The joining strength between the light emitting device1000and the mounting substrate can be increased especially in the case where the light emitting device1000is used as the side view type. Because the recessed portion16is deeper in the Z direction on the bottom surface113side than on the top surface114side, the surface area size of the opening of the recessed portion16at the bottom surface113can be made large. Because the surface area size of the opening of the recessed portion at the bottom surface, which faces the mounting substrate, is made large, the surface area size of the joining member located on the bottom surface can also be made large. In this manner, the surface area size of the joining member located on the surface facing the mounting substrate can be increased. This can increase the joining strength between the light emitting device1000and the mounting substrate.

It is preferable that the maximum depth of each of the recessed portions16in the Z direction is 0.4 to 0.9 times the thickness of the base member11in the Z direction. With the structure in which the depth of the recessed portion16is larger than 0.4 times the thickness of the base member11, the volume of the joining member formed in the recessed portion16can be increased. This can increase the joining strength between the light emitting device1000and the mounting substrate. With the structure in which the depth of the recessed portion16is smaller than 0.9 times the thickness of the base member11, the strength of the base member11is less likely to be decreased.

As shown inFIG. 2B, it is preferable that the recessed portion16includes a parallel portion161extending from the rear surface112in a direction parallel to the bottom surface113(in the Z direction) as seen in a cross-sectional view. The provision of the parallel portion161can increase the volumetric capacity of the recessed portion16even though the surface area size of the opening of the recessed portion16at the rear surface112is the same. With such an increased volumetric capacity of the recessed portion16, the amount of the joining member such as a solder member or the like that may be formed in the recessed portion16can be increased. This can increase the joining strength between the light emitting device1000and the mounting substrate. In this specification, the term “parallel” indicates that a tolerance of about ±3 degrees is allowed. As seen in a cross-sectional view, the recessed portion16has an inclining portion162inclining so as to increase the thickness of the base member11from the bottom surface113. The inclining portion162may be defined by a straight line or a curved line.

At the bottom surface113, the central recessed portion16A may have a substantially constant depth in the Z direction, or the depth of the central recessed portion16A may be different between in a central portion and an end portion. It is preferable that as shown inFIG. 7, at the bottom surface113, a depth D1of the central portion of the central recessed portion16A is the maximum depth of the central recessed portion16A in the Z direction. With such a structure, a thickness D2of the base member11in the Z direction can be large at an end of the central recessed portion16A in the X direction, as seen in a bottom view. This can increase the strength of the base member11. In this specification, the term “central” indicates that a tolerance of about 5 μm is allowed.

At the bottom surface113, the end recessed portion16B may have a substantially constant depth in the Z direction. Alternatively, a depth D3of the end recessed portion16B at an end corresponding to the lateral surface105of the base member11may be larger than a depth of the end recessed portion16B at an end not corresponding to the lateral surface105of the base member11. With such a structure, thickness D4of the base member11in the Z direction can be large at the end of the end recessed portion16B not corresponding to the lateral surface105of the base member11. This can increase the strength of the base member11.

As shown inFIG. 8, it is preferable that the central recessed portion16A has a substantially semicircular shape at the rear surface112. It is preferable that the end recessed portion16B has a shape of about ¼ of a circle at the rear surface112. Because the shape of the recessed portion16B at the rear surface112has rounded or nonangular portion, a stress is less likely to concentrate to any particular position of the recessed portion16. This can alleviate breakage of the base member11.

As shown inFIG. 2A, it is preferable that each of the vias15is in contact with corresponding ones of the first wiring portions12, the second wiring portions13and the third wiring portions14. With such a structure, heat from the light emitting elements is transmitted from the first wiring portions12to the second wiring portions13and/or the third wiring portions14through the vias15. This can improve the heat dissipation of the light emitting device1000.

The vias15may include a conductive member filling a through-hole of the vias formed in the base member11. As shown inFIG. 2A, the vias15may each include a fourth wiring portion151covering an inner surface of the through-hole in the base member11and a filling member152filling a space enclosed by the fourth wiring portion151. The filling member152may be conductive or insulating.

In the case where the first light emitting element20A and/or the second light emitting element20B is flip-chip-mounted on the substrate10, it is preferable that the first wiring portion12includes at least one protrusion121at a position overlapping the first electrodes21A and22A of the first light emitting element20A and/or the second electrodes21B and22B of the second light emitting element20B as seen in a front view. With the structure in which the first wiring portion12includes the protrusion121, when the first wiring portion12is connected with the first electrodes21A and22A and/or the second electrodes21B and22B via at least one conductive bonding member60, the positional alignment between the substrate10and the first light emitting element20A and/or the second light emitting element20B can be easily realized by a self-alignment effect. The shape, height, size or the like of the protrusion121used herein is not particularly specified, but may be appropriately adjusted depending on the size of the substrate10, the thickness of the first wiring portion12, the size of the first light emitting element20A and/or the second light emitting element20B, and the like. Lateral surfaces of the protrusion121may be inclined or perpendicular to the rest of the first wiring portion12. In the case where the lateral surfaces of the protrusions121are perpendicular to the rest of the first wiring portion12, the first light emitting element20A and/or the second light emitting element20B located on the protrusions121is less likely to move, and thus is stably mounted. In this specification, the term “perpendicular” indicates that a tolerance of about ±3 degrees is allowed.

As shown inFIG. 7, it is preferable that a shorter lateral surface405of the first reflective member40and the shorter lateral surface105of the substrate10are substantially flush with each other. With such a structure, the width of the light emitting device in the longer direction (i.e., X direction) is shortened. Thus, the size of the light emitting device is decreased.

As shown inFIG. 2AandFIG. 9, the base member11may include at least one concaved portion111A in the front surface111. With the state where the first reflective member40covers the front surface111of the base member11, the concaved portion111A in the front surface111can increase the contact area size of the first reflective member40and the base member11. This can increase the joining strength between the first reflective member40and the base member11. It is preferable that the concaved portion111A is located at both of two ends of the front surface111in the longer direction (i.e., X direction). Such a structure can increase the joining strength between the first reflective member40and the base member11at both of the two ends thereof. Therefore, the reflective member40is less likely to be delaminated from the base member.

As shown inFIG. 10, it is preferable that a longer lateral surface403of the first reflective member40on the bottom surface113side is inclined inward while extending in the Z direction. With such a structure, when the light emitting device1000is to be mounted on the mounting substrate, the lateral surface403of the first reflective member40and the mounting substrate are less likely to be in contact each other. Therefore, the light emitting device1000can be easily mounted. It is preferable that a longer lateral surface404of the first reflective member40on the top surface114side is inclined inward while extending in the Z direction. Such a structure can alleviate the lateral surface404of the first reflective member40from being in contact with a collet (i.e., suction hole), and thus the first reflective member40is less likely to be damaged when the light emitting device1000is sucked by the collet. As described above, it is preferable that the longer lateral surface403of the first reflective member40on the bottom surface113side, and the longer lateral surface404of the first reflective member40on the top surface114side, are inclined inward in the light emitting device1000while extending from the rear surface112toward the front surface111while extending in the Z direction. The inclination angle θ of the first reflective member40may be appropriately selected. From the points of view of ease of providing the above-described effects and of the strength of the first reflective member40, the inclination angle θ is preferably 0.3 degrees or larger and 3 degrees or smaller, more preferably 0.5 degrees or larger and 2 degrees or smaller, and still more preferably 0.7 degrees or larger and 1.5 degrees or smaller. It is preferable that a right side of lateral surfaces and a left side of lateral surfaces of the light emitting device1000have substantially the same shape as each other. With such a structure, the size of the light emitting device1000can be reduced.

Hereinafter, components of the light emitting device in an embodiment according to the present disclosure will be described. Light Emitting Element (first light emitting element, second light emitting element, third light emitting element and/or fourth light emitting element)

The “light emitting element” refers to the first light emitting element, the second light emitting element, the third light emitting element and/or the fourth light emitting element. The light emitting element is a semiconductor element that itself emits light when being applied with a voltage. For the light emitting element, a known semiconductor element formed of a nitride semiconductor or the like can be used. The light emitting element may be, for example, an LED chip. The light emitting element includes at least a semiconductor stack body, and in many cases, further includes a substrate (hereinafter referred to as an “element substrate”). The semiconductor stack body may have a quadrangular shape, specifically, a square shape or a rectangular shape longer in one direction, when seen in a plan view. Alternatively, the semiconductor stack body may have other shapes, for example, a hexagonal shape. In the case where the semiconductor stack body has a hexagonal shape, the light emission efficiency can be improved. A lateral surfaces of the light emitting element may be perpendicular to the top surface, or inclined inward or outward with respect to the top surface. The light emitting element includes positive and negative electrodes. The positive and negative electrodes may be formed of gold, silver, tin, platinum, rhodium, titanium, aluminum, tungsten, palladium, nickel or an alloy thereof. The emission peak wavelength of the light emitting element may be selected from a range of an ultraviolet region to an infrared region depending on the type of the semiconductor material or the mixed crystal ratios of materials. A preferable material for the semiconductor stack body may be a nitride semiconductor, which may emit light of a short wavelength that excites wavelength conversion particles at a high efficiency. The nitride semiconductor is generally expressed by general formula InxAlyGa1-x-yN (0≤x, 0≤y, x+y≤1). Other examples of usable semiconductor material include an InAlGaAs-based semiconductor, an InAlGaP-based semiconductor, zinc sulfide, zinc selenide, silicon carbide and the like. The element substrate of the light emitting element is generally a substrate for crystal growth, from which a semiconductor crystal forming the semiconductor stack layer may grow. Alternatively, the element substrate may be a support substrate which supports the semiconductor element structure that has been separated from the substrate for crystal growth. The element substrate may be light-transmissive, thereby enabling flip-chip mounting and exhibition of improved light extraction efficiency. The element substrate may be a substrate mainly containing sapphire, gallium nitride, aluminum nitride, silicon, silicon carbide, gallium arsenide, gallium phosphide, indium phosphide, zinc sulfide, zinc oxide, zinc selenide, diamond or the like. Among these materials, sapphire is preferable. The thickness of the element substrate may be appropriately selected, and is, for example, 0.02 mm or greater and 1 mm or less. From the point of view of the strength of the element substrate and/or the thickness of the light emitting device, it is preferred that the thickness of the element substrate is 0.05 mm or greater and 0.3 mm or less.

The light-transmissive member is provided on or above the light emitting element, and protects the light emitting element. The light-transmissive member includes the first light-transmissive layer, the wavelength conversion layer and the second light-transmissive layer provided in a stacked manner. The first light-transmissive layer contains the first matrix and the first diffusive particles. The wavelength conversion layer contains the second matrix and the wavelength conversion particles. The second light-transmissive layer contains the third matrix and the second diffusive particles.

Matrix of Light-Transmissive Member (First Matrix, Second Matrix and/or Third Matrix)

The “matrix of the light-transmissive member” refers to the first matrix, the second matrix and/or the third matrix. The matrix of the light-transmissive member may be formed of any material that is transmissive to light emitted by the light emitting element. The term “light-transmissive” refers to having a light transmittance of 60% or higher, preferably 70% or higher, and more preferably 80% or higher, respectively at the emission peak wavelength of the light emitting element. The matrix of the light-transmissive member may be formed of a silicone resin, an epoxy resin, a phenol resin, a polycarbonate resin, an acrylic resin, or a modified resin thereof. Alternatively, the matrix of the light-transmissive member may be formed of glass. Among these materials, a silicone resin and a modified silicone resin, which are highly resistant against heat and light, are preferable. Examples of the silicone resin include dimethyl silicone resin, phenyl-methyl silicone resin, and diphenyl silicone resin. In this specification, the term “modified resin” encompasses a hybrid resin.

The “diffusive particles of the light-transmissive member” refers to the first diffusive particles and/or the second diffusive particles. The diffusive particles of the light-transmissive member may be formed of titanium oxide, silicon oxide, aluminum oxide, zirconium oxide, zinc oxide or the like. The first diffusive particles and the second diffusive particles may be formed of the same material as, or different materials from, each other. For example, the second diffusive particles may be formed of a material having a refractive index lower than that of the material of the first diffusive particles. In this case, the amount of light diffused by the second diffusive particles is decreased, and thus the light extraction efficiency of the light emitting device can be improved. To realize such a refractive index relationship between the first diffusive particles and the second diffusive particles, the first diffusive particles can be formed of titanium oxide, and the second diffusive particles can be formed of silicon oxide. The diffusive particles contained in the matrix may be of a single material or of a combination of two or more materials. The wavelength conversion layer may contain the diffusive particles. With a structure in which the wavelength conversion layer includes the diffusive particles, the light emitted by the light emitting element is diffused in the wavelength conversion layer. This can decrease the amount of the wavelength conversion particles to be used. The diffusive particles have size of, for example, about 0.1 μm or longer and about 3 μm of shorter on average. In this specification, the “particle size” is defined by, for example, D50(i.e., median for a volume distribution).

Wavelength Conversion Particles

The wavelength conversion particles absorb at least a part of primary light emitted by the light emitting element and emit secondary light having a wavelength different from that of the primary light. The wavelength conversion particles may comprise one material or a combination of two or more materials among the examples shown below.

Examples of materials of the wavelength conversion particles emitting green light include a yttrium-aluminum-garnet-based phosphor (e.g., Y3(Al, Ga)5O12:Ce), a lutetium-aluminum-garnet-based phosphor (e.g., Lu3(Al, Ga)5O12:Ce), a terbium-aluminum-garnet-based phosphor (e.g., Tb3(Al, Ga)5O12:Ce), a silicate-based phosphor (e.g., (Ba, Sr)2SiO4:Eu), a chlorosilicate-based phosphor (e.g., Ca8Mg(SiO4)4Cl2:Eu), a β-SiAlON-based phosphor (e.g., Si6-zAlzOzN8-z:Eu (0<z<4.2)), an SGS-based phosphor (e.g., SrGa2S4:Eu), and the like. Examples of materials of the wavelength conversion particles emitting yellow light include an α-SiAlON-based phosphor (e.g., Mz(Si, Al)12(O/N)16(0≤z≤2; M is Li, Mg, Ca, Y, or a lanthanide element excluding La and Ce), and the like. The above-described examples of material of the wavelength conversion particles emitting green light include a material usable as the wavelength conversion particles emitting yellow light. For example, the emission peak wavelength is shifted toward the longer side so as to emit yellow light by substituting Gd for a part of Y in the yttrium-aluminum-garnet-based phosphor. The above-described examples of material of the wavelength conversion particles emitting yellow light include a material usable as wavelength conversion particles emitting orange light. Examples of materials of the wavelength conversion particles emitting red light include a nitrogen-containing calcium aluminosilicate (e.g., CASN or SCASN)-based phosphor, for example, (Sr, Ca)AlSiN3:Eu, and the like. Another example of material of the wavelength conversion particles emitting red light may be a manganese-activated fluoride-based phosphor (phosphor represented by general formula (I): A2[M1-aMnaF6] (in general formula (I), A is at least one selected from the group consisting of K, Li, Na, Rb, Cs and NH4; M is at least one element selected from the group consisting of the group IV elements and the group XIV elements; and “a” satisfies 0<a<0.2)). A representative example of the manganese-activated fluoride-based phosphor is a phosphor of manganese-activated potassium fluorosilicate (e.g., K2SiF6:Mn).

Reflective Member (First Reflective Member, Second Reflective Member and/or Third Reflective Member)

The “reflective member” refers to the first reflective member, the second reflective member and/or the third reflective member. From the point of view of the light extraction efficiency in the Z direction, the reflective member has a light reflectance of preferably 70% or higher, more preferably 80% or higher, and still more preferably 90% or higher, respectively at the emission peak wavelength of the light emitting element. It is also preferable that the reflective member is white. Therefore, it is preferable that the reflective member contains a white pigment in the matrix. The reflective member is put into a liquid state before being cured. The reflective member may be formed by transfer molding, injection molding, compressing molding, potting or the like. In the case where the light emitting device includes the first reflective member, the second reflective member and/or the third reflective member, the third reflective member may be formed by drawing whereas the first reflective member and the second reflective member may be formed by potting, for example.

Matrix of Reflective Member

The matrix of the reflective member may be formed of a resin, for example, a silicone resin, an epoxy resin, a phenol resin, a polycarbonate resin, an acrylic resin or a modified resin thereof. Among these resins, a silicone resin and a modified silicone resin, which are highly resistant against heat and light, are preferable. Examples of the silicone resin include dimethyl silicone resin, phenyl-methyl silicone resin, and diphenyl silicone resin.

White Pigment

The white pigment may be formed of a single material or a combination of two or more materials selected from the group consisting of titanium oxide, zinc oxide, magnesium oxide, magnesium carbonate, magnesium hydroxide, calcium carbonate, calcium hydroxide, calcium silicate, magnesium silicate, barium titanate, barium sulfate, aluminum hydroxide, aluminum oxide, zirconium oxide and silicon oxide. The white pigment may have an appropriate shape, and may be irregular or crushed. It is preferable that the white pigment is spherical from the point of view of the fluidity. The white pigment may have an average particle size of, for example, about 0.1 μm or longer and about 0.5 μm or shorter. It is preferable that the white pigment is as small as possible in order to improve the effects of light reflection and covering. The content of the white pigment in the light-reflective member may be of any appropriate value, and is, for example, preferably 10 wt. % or higher and 80 wt. % or lower, more preferably 20 wt. % or higher and 70 wt. % or lower, and still more preferably 30 wt. % or higher and 60 wt. % or lower, from the points of view of the light reflectance, the viscosity in a liquid state and the like. The term “wt. %” herein refers to percent by weight, and represents the weight ratio of a material of interest with respect to the total weight of the light-reflective member.

Light Guide Member50

The light guide member bonds the light emitting element and the light-transmissive member to each other, and guides the light from the light emitting element to the light-transmissive member. The matrix of the light guide member may be formed of a silicone resin, an epoxy resin, a phenol resin, a polycarbonate resin, an acrylic resin or a modified resin thereof. Among these resins, a silicone resin and a modified silicone resin, which are highly resistant against heat and light, are preferable. Examples of the silicone resin include dimethyl silicone resin, phenyl-methyl silicone resin, and diphenyl silicone resin. In the matrix of the light guide member, diffusive particles the same as or similar to those in the above-described light-transmissive member may be contained.

Cover Member

The cover member covers the light extraction surface of the light emitting element (i.e., the first light extraction surface, the second light extraction surface and/or the third light extraction surface), and diffuses the light from the light emitting element or converts the light from the light emitting element into light having an emission peak wavelength different from that of the light from the light emitting element.

Matrix of Cover Member

The matrix of the cover member may be formed of a material the same as or similar to that of the matrix of the light-transmissive member.

Diffusive Particles of Cover Member

The “diffusive particles of the cover member” refers to the third diffusive particles. The diffusive particles of the cover member may be formed of a material the same as or similar to that of the diffusive particles of the light-transmissive member.

The substrate10is a component on which the light emitting element is placed. The substrate10includes, for example, the base member11, the first wiring portion12, the second wiring portion13, and the vias15. In the case where the base member11has at least one recessed portion, the substrate10may include the at least one third wiring portion14covering the inner wall of the recessed portion.

The base member11may be formed of an insulating material such as a resin, a ceramic material, glass or the like. Examples of the resin includes epoxy, bismaleimide triazine (BT), polyimide, and the like. The base member11may be formed of a fiberglass-reinforced plastic (e.g., glass epoxy resin). Examples of the ceramic material include aluminum oxide, aluminum nitride, zirconium oxide, zirconium nitride, titanium oxide, titanium nitride, a mixture thereof, and the like. Among these materials, it is preferable to use, especially, a material having a coefficient of linear thermal expansion close to that of the light emitting element. The lower limit of the thickness of the base member11may be appropriate selected. From the point of view of the strength of the base member11, the thickness of the base member11is preferably 0.05 mm or greater, and more preferably 0.2 mm or greater. From the point of view of the thickness (i.e., depth in the Z direction) of the light emitting device, the thickness of the base member11is preferably 0.5 mm or less, and more preferably 0.4 mm or less.

First Wiring Portion12, Second Wiring Portion13, Third Wiring Portion14)

The at least one first wiring portion is located on the front surface of the substrate, and is electrically connected with the at least one light emitting element. The at least one second wiring portion is located on the rear surface of the substrate, and is electrically connected with the first wiring portion through the via. The at least one third wiring portion covers the inner wall of the recessed portion, and is electrically connected with the second wiring portion. The first wiring portion, the second wiring portion and the third wiring portion may be formed of material comprising copper, iron, nickel, tungsten, chromium, aluminum, silver, gold, titanium, palladium, rhodium, or an alloy thereof. The first wiring portion, the second wiring portion and the third wiring portion may each be formed of a single layer or a plurality of layers of any of the above-listed metal materials and alloys. From the point of view of, especially, the heat dissipation, it is preferable to use copper or a copper alloy. The first wiring portion and/or the second wiring portion may include a surface layer of silver, platinum, aluminum, rhodium, gold or an alloy thereof from the point of view of, for example, the wettability on the conductive bonding member and/or the light reflectance.

The at least one via15is provided in the through-hole extending from the front surface to the rear surface of the base member11, and electrically connects the first wiring portion and the second wiring portion to each other. The via15may include the fourth wiring portion151covering the inner surface of the through-hole in the base member and a filling member152filling a space enclosed by the fourth wiring portion151. The fourth wiring portion151may be formed of a conductive material the same as or similar to that of the first wiring portion, the second wiring portion and the third wiring portion. The filling member152may be formed of a conductive material or an insulating material.

The insulating film18ensures insulation at the rear surface of the light emitting device and prevention of short-circuiting of the light emitting device. The insulating film may be formed of a material that is used in the field. The insulating film may be formed of, for example, a thermosetting resin, a thermoplastic resin or the like.

The conductive bonding member electrically connects the electrodes of the light emitting element and the first wiring portion to each other. The conductive bonding member may be any one of: bumps mainly containing gold, silver, copper or the like; metal pastes containing metal powder of silver, gold, copper, platinum, aluminum, palladium or the like and a resin binder; solder based on tin-bismuth, tin-copper, tin-silver, gold-tin or the like; and brazing material of a low melting-point metal material; and the like.

A light emitting device in an embodiment according to the present disclosure can be used for, for example, backlight devices of liquid crystal display devices; various lighting devices; large-scale displays; various display devices for advertisements, destination guides and the like; projector devices; and image reading devices for digital video cameras, facsimiles, copiers, scanners and the like.