Light emitting device

A light emitting device includes: a substrate; a light emitting element disposed on the substrate, the light emitting element having an upper surface and a lateral surface; a reflecting layer located on the upper surface of the light emitting element; a first light-transmissive member having a first surface in contact with the lateral surface of the light emitting element, and a second surface that is inclined toward the substrate in a direction outward from the light emitting element; and a second light-transmissive member in contact with the second surface and covering the light emitting element. A refractive index of the first light-transmissive is smaller than a refractive index of the second light-transmissive member.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-108389, filed May 31, 2016. The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND

The present disclosure relates to a light emitting device.

In recent years, various electronic components have been proposed and come into practical use, and higher performance is required for those components. For example, applications for backlights of liquid crystal displays and for general lighting, appearance is highly valued, and there have been high demands for further thinner type and downsizing of the light emitting device.

For example, Japanese Unexamined Patent Application Publication No. 2006-114863 discloses a light emitting device in which a secondary lens is combined with an LED. Thus, light can be dispersed uniformly in a short irradiating distance, allowing for a reduction in the thickness of the device.

SUMMARY

However, in combining an LED and a lens, when light reflected at an interface between the lens and air layer, and/or direct light from the LED is incident on a light-diffusing and reflecting part provided on an upper surface of the substrate located under the lens, luminous intensity in a substantially upward direction with respect to the substrate increases due to an emission in upper surface directions of the lens caused by scattering of the light. For this reason, sufficient decrease in the luminous intensity in the substantially upward direction may not be obtained, which may result in failure to achieve desired light distribution properties.

Certain embodiments of the present invention can provide a light emitting device in which the amount of light leaking in the upper surface directions can be reduced and desired light distributing properties can be achieved.

A light emitting device according to one embodiment includes a substrate, a light emitting element having a lateral surface mounted on the substrate and having a reflecting layer on its upper surface, a first light-transmissive member having a first surface being in contact with the lateral surface of the light emitting element and a second surface tapering toward the substrate as separating from the light emitting element, and a second light-transmissive member covering the light emitting element. The first light-transmissive member has a smaller refractive index than the second light-transmissive member.

In the light emitting device according to certain embodiments of the present invention, the amount of light leaking in the upper surface direction can be reduced and desired light distributing properties can be achieved.

DETAILED DESCRIPTION

Embodiments of the present invention will be described below with reference to the accompanying drawings. It is to be noted that the light emitting device described below is intended for implementing the technical concept of the present invention, and the present invention is not limited to those described below unless otherwise specified. The sizes and the positional relationships of the members in each of the drawings are occasionally shown exaggerated for ease of explanation.

First Embodiment

FIG. 1is a schematic top view of a light emitting device according to a first embodiment.FIG. 2is a schematic cross-sectional view of the light emitting device taken along line II-II ofFIG. 1. The light emitting device includes a substrate25, a light emitting element12disposed on the substrate25and having an upper surface on which a reflecting layer17is provided, a first light-transmissive member16, and a second light-transmissive member20. The first light-transmissive member16includes a first surface16ain contact with a lateral surface of the light emitting element12, and a second surface16bthat is inclined so as to become closer to the substrate25in an outward direction from the light emitting element12. The second light-transmissive member20is in contact with the second surface16bof the first light-transmissive member16, and covers the light emitting element12. A refractive index α of the first light-transmissive member16is smaller than a refractive index β of the second light-transmissive member20.

1. Structure of Substrate25

The substrate25includes, for example, as shown inFIG. 2, a base body24, wiring parts13aand13b, and a protective layer15. The substrate24is made of an insulating material, examples thereof include, insulating resins such as glass epoxy, bismaleimide triazine, polyimide (PI), polyethylene naphthalate (PEN), and polyethylene terephthalate (PET), ceramics such as alumina. The base body24may be made of a copper foil or aluminum foil which is covered with an insulating resin. The base body24may have a thickness in a range of, for example, about 10 μm to about 100 μm.

The wiring parts13aand13bare arranged on a main surface of the base body24. The wiring parts13aand13bare arranged spaced apart from each other. The wiring parts13aand13bas described above are made of, for example, a metal film such as a copper foil or an aluminum foil. The wiring parts13aand13bmay have a thickness in a range of, for example, about 10 μm to about 60 μm. When a flexible the base body24is used, the wiring parts13aand13bhave a thickness which does not impair the flexibility of the substrate25, and for example, a thickness in a range of 8 μm to 150 μm is preferable.

In the first embodiment, the substrate10includes a pair of wiring parts13aand13b, but is not limited thereto. The substrate25at least includes a pair of wiring portions, but may include three or more wiring parts. In this case, the light emitting elements12may be arranged over three or more wiring parts.

The protective layer15covers the surfaces of the base member24and the wiring parts13a,13b. Thus, the protective layer15covers approximately the entire upper surface of the substrate25except for the opening portions15S to be described below. Such a reflective layer15is made of a material adapted to reflect the emitted light (including the wavelength-converted light by a wavelength converting member) from the light emitting element12. As an example of the material of the protective layer15, an insulating white ink (i.e., a white resist) made of a silicone-based resin containing titanium oxide can be preferably used.

The protective layer15defines an opening15S at least in and around the region where the light emitting element12to be arranged.FIG. 1shows an opening15S formed in a portion including portions of the wiring parts13aand13b. As shown inFIG. 2, parts of the two wiring parts13aand13bare exposed in the opening15S.

The openings15S can be formed in an appropriate shape such as a circular shape or a quadrangular shape adapted to surround the light emitting element12in a plan view. InFIG. 1, the opening15S is formed in a circular shape. After the light emitting element12is mounted in the opening15S, the opening15S is covered by the first light-transmissive member16. The opening15S may be covered by the first light-transmissive member16, or by both the first light-transmissive member16and a second light-transmissive member20.

The size of the opening15S allows a region for electrically connecting to the electrodes of the light emitting element12. For example, a peripheral defining the opening15S is preferably located at about 50 to 2000 μm outer side with respect to each side of outline of the light emitting element12in a plan view. In the first embodiment, the opening15S is defined outward of an outer periphery of the second light-transmissive member20.

Also, the protective layer15may be disposed extending below the light emitting element12with the openings15S smaller than the shape in a plan view of the light emitting elements12. The protective layer15may be disposed to surround a bonding member18connecting the light emitting element12and the substrate25so that the opening is not substantially formed.

The wiring parts13aand13balso serve as the terminal portions, which are connected to external wirings that are connected to an external power source. The terminal portions are preferably formed at an end portion at the main surface-side of the base member25, and the external wirings may be connected to a known connectors disposed on the substrate25.

2. Configuration of Light Emitting Element12

The light emitting element12is disposed on the substrate25. As shown inFIG. 1, when the base member25includes the protective layer15, the light emitting element12is arranged in the opening15S defined in the protective layer15.

The light emitting element12has a reflecting layer17on its upper surface. The reflecting layer17is adapted to reflect light from the light emitting element12. With the reflecting layer17, light emitted from the light emitting element12can be emitted in lateral directions from the surfaces of the light emitting element12where the reflecting layer17is not formed. Accordingly, an amount of light directly over the light emitting element12can be reduced and a batwing light distributing properties can be obtained. When the reflecting layer17is disposed directly on the light emitting element12, a primary lens and/or a secondary lens becomes unnecessary, which allows for a reduction in the thickness of the light emitting device compared to the case where a batwing light distribution is obtained by the use of a primary lens and/or a secondary lens.

The reflecting layer17is adapted to reflect light from the light emitting element12. For example, the reflecting layer17preferably can reflect 70% or greater, more preferably 80% or greater, of light emitted from the light emitting element12. For example, the reflecting layer17may be made of a metal film, or may be made of a dielectric multilayer film (DBR film).

The reflecting layer17preferably has an incident angle dependence of reflectance for a light emission wavelength of the light emitting element12. More specifically, the reflecting layer17preferably has a reflectance smaller to oblique incident light than to perpendicularly incident light. With this arrangement, moderate change in the luminance directly above the light emitting element can be obtained, so that occurrence of an extremely dark portion such as a dark spot directly above the light emitting element can be sufficiently reduced.

In the embodiment, each of the light emitting elements12is, as shown inFIG. 2, mounted on the substrate25in a flip-chip manner. The light emitting element12is connected to the wiring parts13aand13bvia corresponding bonding members18respectively. The bonding member18can be made of, for example, a solder such as a Sn—Ag—Cu based alloy, a Au—Sn based alloy, a Sn—Cu based alloy, a metal such as Au, an anisotropic conductive paste, or an Ag paste.

The light emitting element12includes, for example, an n-type layer, an active layer, and a p-type layer, which are stacked in order on a light-transmissive sapphire substrate. The n-type layer, the active layer and the p-type layers can be made of, for example, gallium nitride-based semiconductors. The n-side electrode connected to the n-type layer and the p-side electrode connected to the p-type layer are electrically connected to corresponding wiring parts13and13via respective bonding members18.

In the present embodiment, the use of the first light-transmissive member16and the second light-transmissive member20allows for changing of light extracting direction of light emitted from the light emitting element12that has the reflecting layer17, and obtaining an improvement in the light extraction efficiency.

The first light-transmissive member16configured to receive light emitted in lateral directions from the light emitting element12is arranged in contact with the lateral surfaces of the light emitting element12. The surface of the first light emitting element16in contact with the lateral surfaces of the light emitting element12will be indicated as a first surface16a. Further, the first light-transmissive member16has a second surface16bthat tapers toward the upper substrate25in a direction outward from the light emitting element12(in other words, the first light-transmissive member16has a thickness decreasing in a direction outward from the light emitting element12). The second surface16bis sloped with respect to the substrate25or to the surfaces of the wiring parts13a,13b.

The upper surface of the light emitting element12, that is, the upper surface of the reflecting layer17, is exposed from the first light-transmissive member16. The lateral surfaces of the reflecting layer17are covered by the first light-transmissive member16. The first light-transmissive member16may be arranged so as to cover an entirety of the light emitting element12provided with the reflecting layer17.

The first light-transmissive member16preferably has a circular outline shape in a top view, as shown inFIG. 1. In this case, as shown inFIG. 1, the first light-transmissive member16is preferably arranged to surround the light emitting element12such that the light emitting element12is approximately centered in the first light-transmissive member16.

The second light-transmissive member20is arranged on the substrate25, is in direct contact with the second surface16bof the first light-transmissive member16, and indirectly or directly covers the light emitting element12. The second light-transmissive member20may have a cylindrical shape, a hemisphere shape, or the like.

The second light-transmissive member20may be disposed, as shown in the plan view ofFIG. 1, so as to cover the entire upper surface of the first light-transmissive member16and to be larger than the first light-transmissive member16. In this case, the second light-transmissive member20covers the upper surface of the substrate25at the outer periphery of the first light-transmissive member16, without the first light-transmissive member16interposed therebetween. For example, in a plan view, the outermost end of the second light-transmissive member20is preferably located about 50 to 1000 μm outward of the outer end of the first light-transmissive member16.

In the present embodiment, the refractive index α of the first light-transmissive member16is smaller than the refractive index β of the second light-transmissive member20. In the present specification, the term “refractive index” refers to a refractive index to the emission wavelength of the light emitting element12. When α<β, as shown by arrows inFIG. 2, light emitted in a lateral direction of the light emitting element12enters the first light-transmissive member16from the first surface16aand propagates toward an interface between the second surface16bof the first light-transmissive member16and the second light-transmissive member20. The light L1propagating from the first light-transmissive member16to the second light-transmissive member20is propagating from a medium having a smaller refractive index to a medium having a larger refractive index. Thus, total reflection will not occur at the interface between the first light-transmissive member16and the second light-transmissive member20. The second surface16bof the second light-transmissive member16, that is, an interface between the first light-transmissive member16and the second light-transmissive member20, is sloped, tapering toward the substrate25in a direction outward from the light emitting element12, so that the light reflected at the interface L2will be directed upward.

With this arrangement, the amount of light leaking in the upper surface direction can be reduced by the reflecting layer17and the light extraction efficiency can be improved. As described above, in order to refract light in an upward direction, most of light emitted from the light emitting element12is preferably directed to pass through the first light-transmissive member16, so that all the lateral surfaces of the light emitting element12are preferably covered by the first light-transmissive member16.

FIG. 3illustrates a state of extracting of light from the light emitting element12when α>β is satisfied. The light emitted in a lateral direction of the light emitting element12enters the first light-transmissive member16from the first surface16aand propagates toward an interface between the second surface16bof the first light-transmissive member16and the second light-transmissive member20. The light L1propagating from the first light-transmissive member16to the second light-transmissive member20is propagating from a medium having a larger refractive index to a medium having a smaller refractive index. Thus, total reflection will occur at the interface between the first light-transmissive member16and the second light-transmissive member20. In particular, when light is emitted from a lateral surface of the light emitting element12, light L1tends to enter the second surface16bat an angle greater than a critical angle. Thus, a large amount of light is totally reflected toward the substrate25side, as shown in the arrow L3inFIG. 3, and may be absorbed by the substrate25, which may result in a reduction of the light extraction efficiency.

Also, in order to reduce optical absorption by the substrate25, for example, increasing the reflectance of the wiring parts13a,13b, and/or employing a light-reflecting protective layer15to extract totally-reflected light, luminous intensity in directly upper direction of the light emitting element12is increased by scattering of light, and the effect of the reflecting layer17decreases.

FIG. 4illustrates a state of extracting of light from the light emitting element12when α=β is satisfied. In this case, total reflection at the interface between the first light-transmissive member16and the second light-transmissive member20does not occur. Refracting of light at the interface also does not occur, so that light L4enters the second light-transmissive member20and propagates in the second light-transmissive member20while retaining the incident angle. When a plurality of light sources are aligned and used, light emitted in a direction of the alignment enters the adjacent light source and may be absorbed. Thus, in the embodiment described above, light emitted in a lateral direction should be directed in an upward direction by refracting the light at the interface between the first light-transmissive member16and the second light-transmissive member20.

When a reflecting member33that can reflect light emitted in a lateral direction is arranged to be lateral of the light emitting element12as shown inFIG. 6, due to a thickness of the reflecting member33, light that hits an end portion35of the reflecting member33is scattered to increase the luminous intensity in directly upper direction of the light emitting element12, and the effect of the reflecting layer17decreases. Thus, in the present embodiment described above, light emitted in a lateral direction can be directed in an upward direction by refracting the light at the interface between the first light-transmissive member16and the second light-transmissive member20.

Taking the extraction of light from the light emitting element12to the first light-transmissive member16into consideration, for example, a refractive index of a light emitting element12that includes a sapphire substrate is generally higher than a refractive index of a light emitting element12that includes a resin substrate. In such a case, in order to increase the light extraction efficiency from the light emitting element12, a smaller difference in the refractive indices of the light emitting element12and the first light-transmissive member16is preferable. In the present embodiment, when the first light-transmissive member16and the second light-transmissive member20are respectively made of resin material, the difference in the refractive indices of the light emitting element12and the second light-transmissive member20is greater than the difference in the refractive indices of the light emitting element12and the first light-transmissive member16. This may result in a low light extraction efficiency from the light emitting element12to the first light-transmissive member16, but according to the present embodiment, optical absorption by the substrate25can be reduced, so that the light extraction efficiency to the outside of the second light-transmissive member20(where air exists) can be increased.

The refractive index can be measured with, for example, an Abbe refractometer. When the refractive index cannot be measured with the Abbe refractometer, due to the size of the member or the like, the refractive index can be measured by determining the material of the member and measuring a similar member of the same material to obtain the refractive index of the member.

The first light-transmissive member16and the second light-transmissive member20are preferably resin members. When using a resin material, a material having a desired refractive index can be selected. Examples of the resin material include an epoxy resin material, a urea resin material, a silicone resin material, a fluororesin material, and a hybrid resin material that contains at least one of those resin materials. The first light-transmissive member16and the second light-transmissive member20do not substantially contain any materials that disturb the straight-line propagation of light. In order to adjust the viscosity of resin, a material such as a nano-filler material that barely produces scattering of light may be contained in the light-transmissive members16,20.

Other than the resin materials described above, a material satisfying the relationship of the refractive indices α<β, such as a light-transmissive glass material may be used for the first light-transmissive member16and the second light-transmissive member20. In this case, the first light-transmissive member16and the second light-transmissive member20may be made of different materials, such that the first light-transmissive member16may be made of a resin material and the second light-transmissive member20may be made of a glass material.

Second Embodiment

In a light emitting device according to a second embodiment, the light emitting element12is not flip-chip mounted but the light emitting element12is mounted on an upper surface of the substrate25.

The light emitting element12according to the second embodiment is, as shown inFIG. 5, mounted so that the p-side electrode and the n-side electrodes are located above the light emitting element12, and the electrodes are electrically connected to the wiring parts13a,13bvia wires22respectively. The surface of the light emitting element12having the electrodes is provided with a reflecting layer17. For example, portions of the electrodes may be masked and the reflecting layer17may be disposed on other unmasked portions, or a reflecting layer17may be disposed with approximately a flat upper surface via a protective layer and the electrodes may be provided on the reflecting layer17. In the second embodiment, the protective layer15defining an opening15S is disposed so that the opening15S is located inward of the end portion of the second light-transmissive member20.

The first light-transmissive member16is arranged at the lateral surfaces of the light emitting element12as in the first embodiment, and connecting portions of the wires22and the wiring parts13aand13bare covered by the first light-transmissive member16. The connecting portions of the wires22and the light emitting element12are covered by the second light-transmissive member20. Other configurations may be similar to that in the first embodiment, and similar effects can be obtained.

Next, configurations and members that can be used in the first embodiment and the second embodiment will be described.

Surface Light-Emitting Device

The light emitting device according to the second embodiment preferably includes a plurality of the light emitting devices shown inFIG. 1andFIG. 5disposed on a single substrate. Accordingly, a surface light source with little luminance unevenness can be formed. A light diffusing plate or a wavelength-converting sheet may be provided on the surface light source. As examples, surface light-emitting device are shown inFIG. 6andFIG. 7.

FIG. 6is a schematic cross-sectional view showing a surface light-emitting device including the light emitting devices according to the first embodiment. The light emitting devices illustrated in the first embodiment are mounted on a common substrate25with predetermined intervals, and the reflecting member33is arranged between adjacent light emitting devices. That is, the surface light-emitting device is provided with a plurality of light emitting devices of the first embodiments, and a reflecting member33that can reflect light from the light emitting element12is arranged on each region of the substrate25exposed from the second light-transmissive member20between the light emitting devices. A height of the reflecting members33is greater than the heights of the second light-transmissive members20. Further, a light diffusing plate30for diffusing light from the light emitting devices is placed over the reflecting members33, so that the light diffusing plate30is approximately parallel to the upper surfaces of the light emitting elements12. Moreover, a wavelength converting layer32that is configured to convert the wavelength of a portion of light into different wavelength is arranged approximately in parallel to and above the light diffusing plate30.

Generally, the smaller the ratio of the distance between the substrate25and the light diffusing plate30(which hereinafter may also be referred to as an optical distance OD) to the interval of the light emitting elements (which hereinafter may also be referred to as Pitch), i.e., OD/Pitch, the smaller the luminous intensity between the light emitting devices on the light diffusing plate30, resulting in occurrence of dark portions on the light diffusing plate30. However, with the reflecting members33arranged as in the second embodiment, the luminous intensity between the light emitting devices can be compensated by the reflecting members33. Thus, even in a region having small OD/Pitch, luminance unevenness on the light diffusing plate33can be reduced. A material that can at least reflect the emission wavelength of the light emitting element12can be used for the material of the reflecting member33. For example, a metal plate or a resin material containing a white filler can be suitably used.

The height of the reflecting member33and the tilting angle of the light-reflecting surface with respect to the surface of the substrate25can be appropriately determined. The reflecting surface may be a flat surface or a curved surface, which can be selected to obtain desired light distributing properties. The height of the reflecting member33may be 0.3 times or less, preferably 0.2 times or less, with respect to the distance between the light emitting elements. With this arrangement, unevenness in the luminance can be reduced.

The reflecting members33preferably form an overall plate-shape in which a plurality of the reflecting members33are connected to each other, with a plurality of through-holes that allow arrangement of the light emitting devices. InFIG. 6, a schematic cross-sectional view that includes two light emitting devices is illustrated, but for example, as shown in the schematic top view ofFIG. 7, several tens to several hundreds light emitting devices may be arranged in matrix.

EXAMPLES

FIG. 1andFIG. 2are respectively a top view and a cross-sectional view of a light emitting device according to Example 1. As shown inFIG. 1, in Example 1, a light emitting element12is flip-chip mounted on the substrate25, in which the light emitting element12is straddling the wiring parts13aand13bdisposed on the upper surface of the base body24, via the respective bonding members18. Of the wiring parts13aand13b, regions that are not used to establish electrical connection is provided with a protective layer15. The upper surface of the light emitting element12is provided with a reflecting layer17.

The first light-transmissive member16is disposed to have a second surface16bthat is in contact with the lateral surfaces of the light emitting element12, and to expose the reflecting layer17located on the upper surface of the light emitting element12, tapering toward the substrate25as separating from the light emitting element12. Further, a second light-transmissive member20is disposed to directly in contact with the second surface16bof the first light-transmissive member16and the reflecting layer17. The second light-transmissive member20has a circular shape in a top view, and having a curved surface. The second light-transmissive member20is formed in a convex shape with a height smaller than its radius and covering the light emitting element12and the first light-transmissive member16.

In Example 1, the base body24is made of glass epoxy base material, the wiring parts13a,13bare made of a Cu material with a thickness of 35 μm, the protective layer15is made of an epoxy-based white solder resist and has light-reflecting properties.

The light emitting element12is a nitride-based blue LED with a peak emission wavelength of 450 nm, having a substantially square shape with a side of 600 μm and a thickness of 150 μm, with a dielectric multilayer film disposed as a reflecting layer17on the upper surface of the light emitting element12.

In Example 1, the first light-transmissive member16is made of dimethyl silicone (refractive index 1.41), and the second light-transmissive member20is made of phenyl silicone (refractive index 1.50). In Example 1, the refractive index at 589 nm is shown, but at 450 nm, which is the emission wavelength of the light emitting element12, the relationship of “a refractive index α of the first light-transmissive member16<refractive index β of the second light-transmissive member20” is still satisfied.

The second light-transmissive member20of Example 1 preferably does not have light scattering properties, but in order to provide thixotropic properties, a silica-based nano-filler material (average particle diameter of about 12 nm) that does not create scattering of light is added.

Comparative Example 1

As shown inFIG. 3, Comparative Example 1 is performed as in Example 1, except that the first light-transmissive member16is made of phenyl silicone (refractive index 1.50) and the second light-transmissive member20is made of dimethyl silicone (refractive index 1.41). The refractive indices satisfy a relationship of “a refractive index α of the first light-transmissive member16>refractive index β of the second light-transmissive member20”.

Comparative Example 2

As shown inFIG. 4, Comparative Example 2 is performed as in Example 1, except that the first light-transmissive member16and the second light-transmissive member20are made of phenyl silicone (refractive index 1.50). The refractive indices satisfy a relationship of “a refractive index α of the first light-transmissive member16=refractive index β of the second light-transmissive member20”.

Comparative Example 3

As shown inFIG. 4, Comparative Example 3 is performed as in Example 1, except that the first light-transmissive member16and the second light-transmissive member20are made of dimethyl silicone (refractive index 1.41). The refractive indices satisfy “refractive index α of the first light-transmissive member16=refractive index β of the second light-transmissive member20”.

Results

Light distributing properties of the light emitting devices according to Example 1, and Comparative Examples 1 to 3 are shown inFIG. 8.

The diagram shows that, in Example 1, where α<β, light emitted in a lateral direction is refracted in upward direction, which reduces the amount of light in a right-lateral direction, and accordingly, increases the peak height. With the increase in the peak height, the amount of light directly above the light emitting element, that is, the amount of light near 0° is relatively lowered. Accordingly, relative luminous intensity with respect to the peak luminous intensity in the substantially upward direction can be decreased compared to that in Comparative Examples 1 to 3, and desired light distributing properties can be obtained.

The light emitting devices can be used for the display devices such as backlights of liquid crystal displays and TV-screens, and lighting devices.

It is to be understood that although the present disclosure has been described with regard to example embodiments thereof, various other embodiments and variants may occur to those skilled in the art, which are within the scope and spirit of the disclosure, and such other embodiments and variants are intended to be covered by the following claims.