JP3704941B2 - Light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light-emitting device using an LED chip that can be used as a writing light source or backlight light source for various indicators, displays, and optical printers, and in particular, provides a light-emitting device that further improves light extraction efficiency from the LED chip. There is to do.
[0002]
[Prior art]
One of the various light sources used today is an LED chip. The LED chip is a semiconductor light emitting device, has no ball breakage, and has excellent ON / OFF drive characteristics. Further, since it has low power consumption and has a monochromatic peak wavelength, it is used in various fields. Such an LED chip is usually as small as about 300 μm square. Therefore, for the purpose of improving the handling efficiency such as placement on the mounting board, electrical connection and light utilization efficiency, chip type LED etc. in which the LED chip is placed inside the package in which the lead electrode capable of conducting to the outside is embedded Is being used.
[0003]
Specifically, as shown in FIG. 4, a package 407 in which lead electrodes 405 are embedded in a liquid crystal polymer is used as an envelope for protecting the LED chip 403 from the outside. The package 407 has a recess, and a part of the lead electrode 405 is exposed inside. A part of the exposed lead electrode 405 and the electrode of the LED chip 403 fixed with the die bond resin 406 inside the package are electrically connected by a gold wire 404 or the like. The concave portion of the package 407 is covered with a translucent epoxy resin 402 to protect the LED chip 403. When a current is supplied to the chip type LED 400 formed in this way, the LED chip 403 emits light, and directly from the LED chip 403 to the outside of the chip type LED 400 via the translucent sealing material 402 or once on the bottom surface or side surface of the package. Reflected light is emitted outside the package.
[0004]
[Problems to be solved by the invention]
Of the light emitted from the LED chip 403, the light directed toward the bottom surface of the concave portion of the package 407 is reflected by the smooth metal lead electrode 405 or the bottom surface of the smooth package and is transmitted to the outside of the light emitting device via the translucent epoxy resin 402. Is taken out efficiently.
[0005]
However, in the present day when higher light extraction efficiency is required with low power consumption, the light-emitting device having the above configuration is not sufficient, and further improvement in light extraction efficiency is required. Therefore, the present invention eliminates the above problems and forms a light emitting device with higher light extraction efficiency.
[0006]
[Means for Solving the Problems]
The present invention provides a light emitting device having a package including a lead electrode, an LED chip disposed on a bottom surface of a concave portion of the package, and a light scattering layer that scatters light from the LED chip. The resin is made of a resin containing a light scattering material, and is disposed with a thickness smaller than the height from the bottom surface to the light emitting layer of the LED chip from the surface of the lead electrode exposed in the recess and from the bottom surface to the side surface of the recess. It is characterized by being. This relatively simple configuration effectively scatters and diffuses the light reflected from the LED chip and the surface of the package bottom and lead electrodes that efficiently reflect the light to the front, and the light totally reflected by the translucent sealing material. The function is separated from the light scattering layer extracted outside. This enhances the light extraction efficiency from the light emitting device. That is, the light emitted from the LED chip is inherently highly reflective on the mirror surface. However, there is a light-transmitting sealing material in which light from the LED chip is totally reflected and confined. In the present invention, a light reflection layer is used to scatter and diffuse light totally reflected by a translucent resin while a flat reflection surface is provided in a direction directly below the LED chip.
[0007]
Furthermore, it is preferable that the LED chip has a double hetero structure, and the light scattering layer further covers an end face of the LED chip. Thereby, the light emission luminance emitted from the end face of the light emitting layer of the LED chip is not lowered. In addition, it is possible to increase the external extraction efficiency by selecting light that is critically reflected.
[0008]
In the light emitting device of the present invention, it is preferable that the light scattering layer is colored substantially the same as the emission color of the LED chip. Thereby, the LED chip does not emit dots in the package. In other words, the light emitting part can be observed more largely as if the LED chip is arranged over the entire opening part during lighting as well as during non-lighting.
[0009]
The light scattering material is preferably at least one selected from titanium oxide, barium titanate, aluminum oxide, silicon oxide, zinc oxide, metal pieces, or phosphor. Or it is preferable that the said light-scattering material is at least 1 type selected from a melamine resin, a guanamine resin, or a benzoguanamine resin. As a result, a light-emitting device that can dramatically improve the light extraction efficiency can be obtained.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
As a result of various experiments, the present inventor has found that the light emission efficiency is drastically improved by disposing a light scattering layer that scatters light from the LED chip on the bottom surface of the package on which the LED chip is disposed. It came to be accomplished.
[0011]
That is, the present invention improves the light extraction efficiency by changing the structure of the light emitting device according to the path of light emitted from the LED chip.
[0012]
More specifically, FIG. 2 schematically shows a path of light emitted from the LED chip at an angle θ greater than the critical angle in an example of the light emitting device shown for comparison with the present invention. The light 208 having an angle equal to or larger than the critical angle emitted from the light emitting point 203 of the LED chip as viewed schematically is a critical angle in the symmetry direction at the same angle as the incident angle at the interface between the translucent sealing material 202 and the outside. Reflected. The light 209 reflected by the critical angle is incident on the lead electrode or the bottom surface of the package, and is reflected on this surface in the symmetrical direction at the same angle as the incident.
[0013]
The light 210 again enters the interface between the translucent sealing material and the outside at the same angle, and is reflected at a critical angle toward the inside of the package. As described above, the path of the light 208 emitted from the LED chip at a critical angle or more is inside the translucent sealing material 203 as long as the bottom surface of the package or the lead electrode is substantially smooth without any change in angle. And the reflection at the interface of the translucent sealing material 202 and the lead electrode or the bottom of the package is repeated. During this time, none of the transmissivity of the translucent sealing material 202 and the reflectivity of the lead electrode and the package bottom is completely 1. Therefore, each time transmission and reflection are repeated once, light is absorbed and extinguished at (1−transmittance × reflectance). Even if the resin transmittance is high, it is about 90%, and the reflectance is also about 90% even for highly reflective metal members. Therefore, if you repeat transmission and reflection three times, more than 50% of the emitted light above the critical angle disappears. To do.
[0014]
FIG. 3 schematically shows the path of light emitted from the LED chip at an angle greater than the critical angle in the light emitting device of the present invention, as in FIG.
[0015]
The light emitted from the light emitting point 303 of the LED chip as viewed schematically at an angle θ greater than the critical angle is reflected at the critical angle at the interface between the translucent sealing material 302 and the outside, and travels toward the inside to be scattered and diffusely reflected. The light scattering layer 301 having the property. The light reaching the light scattering layer 301 is scattered, diffused and reflected to be scattered and reflected to the hemispherical light path 310. Of the scattered light, light 302 having a critical angle or less is extracted from the translucent sealing material 302 as it is. Further, although light having a critical angle greater than the critical angle of the scattered light is reflected at the critical angle at the interface between the translucent sealing material 302 and the outside, if it reaches the light scattering layer 301 again, it is scattered and diffusely reflected as described above. Therefore, most of the light reflected by the critical angle is extracted to the outside.
[0016]
On the other hand, the light 311 directed downward from the LED chip 303 is efficiently reflected on the flat surface and extracted outside through the light-transmitting sealing material 302. As described above, according to the present invention, light emitted from the LED chip 303 is efficiently used by separately utilizing light directed toward the package bottom surface where the LED chip is disposed and light directed toward the package side wall. It is an enhanced one. The critical angle in the present invention refers to the critical angle α between the translucent sealing material and the external space, and is defined as follows. Critical angle α = Sin ⁻¹ (n ₂ / n ₁ ), where n ₁ = refractive index of translucent sealing material and n ₂ = refractive index of external space.
[0017]
In the LED chip having a double hetero structure, the composition of the semiconductor is changed in order to confine the current. Therefore, the refractive index of the light emitting layer and the clad layer sandwiching the light emitting layer are different. For this reason, the light generated in the light emitting layer plays a role like a kind of waveguide. Therefore, more light is emitted from the end of the light emitting layer. Whether or not the light emitted from the end portion can be effectively used greatly contributes to the light utilization efficiency.
[0018]
Furthermore, an LED chip using a nitride semiconductor is generally formed on sapphire because crystal growth is difficult and the physical properties of the nitride semiconductor. For this reason, the positive electrode and the negative electrode are formed on the semiconductor laminated surface side formed on the sapphire substrate. Further, a full-surface electrode that covers almost the front surface on the light emitting layer is formed. The electrode material that can make such ohmic contact is limited, and light is extracted through this metal electrode layer. Since the metal electrode layer has a light-transmitting property, there is inevitably light reflected by the metal electrode layer. For this reason, LED chips using nitride semiconductors tend to have greater lateral light leakage. Hereinafter, an embodiment of the present invention will be described.
[0019]
In the manufacture of a light emitting device, first, an LED chip made of AlGaInP as a light emitting element is mounted in a recess of a package with Ag paste using a die bond apparatus. Note that the back electrode of the LED chip that contacts the Ag paste is a metal electrode that is smooth and efficiently reflects the light of the LED chip. The electrode on the light emitting surface side of the mounted LED chip and the lead electrode of the package are wire bonded using a wire bonding apparatus. Next, the resin mixed with the diffusing material is injected into the recess of the package around the LED chip.
[0020]
After the injection, the diffusion material flows to cover the bottom surface of the package. After the resin containing the diffusing material is cured, the resin of the translucent sealing material is injected and cured to complete the light emitting device of the present invention. Thus, a light emitting device with high light extraction efficiency can be obtained. Hereinafter, the constituent members of the present invention will be described in detail.
[0021]
(Light scattering layer 101)
The light scattering layer 101 of the present invention is for extracting light emitted from the LED chip 103 with a vector in the horizontal direction to the outside without being guided in the translucent sealing material 102. Therefore, any device can be used as long as it is arranged around the LED chip 103 and can efficiently scatter and diffusely reflect the light from the LED chip 103. Specific examples include light scattering / diffusing inorganic members such as titanium oxide, barium titanate, aluminum oxide, silicon oxide, titanium oxide, zinc oxide, metal pieces, and various phosphors. Furthermore, instead of the inorganic member, an organic resin such as a melamine resin, a CTU guanamine resin, or a benzoguanamine resin can be used.
[0022]
The resin containing the light scattering / diffusing inorganic member has high translucency with respect to the light from the LED chip 103, adhesion to the diffusing material, the translucent sealing material 102, and the package 107 and heat resistance. It is desirable that the property is high. Specifically, silicone-based, epoxy-based, acrylic resin, and the like are preferably used as such a resin. The light scattering layer 101 can be formed relatively easily by pouring and curing in the recesses of the package 107 in which the LED chip 103 is arranged in advance. If the viscosity of the resin constituting the light scattering layer 101 is lowered, the resin tends to spread into the recesses of the package 107. Therefore, not only the bottom surface of the package 107 but also the side surface constituting the recess of the package and the side surface of the LED chip 103 are crawled.
[0023]
Since the LED chip 103 using a nitride semiconductor has a large amount of light emitted from the end face of the light emitting layer, it is particularly effective to effectively use the light emitted from the end face. If the height of the light emitting layer of the LED chip 103 from the bottom surface of the package 107 is higher than the thickness of the light scattering layer 101, the light emitted from the end face is effectively emitted. Thereafter, the light totally reflected at the interface between the translucent resin 102 and the outside is emitted isotropically in the light scattering layer.
[0024]
Further, when the light scattering layer partially crawls up and covers the light emitting layer of the LED chip thinly, light can be used more effectively because it is easily emitted isotropically from the end face of the LED chip. Also in this case, the thickness of the light scattering layer is thinner than the height of the light emitting layer. This scooping up can be controlled to some extent by adjusting the viscosity of the resin constituting the light scattering layer. Such a light scattering layer can obtain uniform light emission with a relatively simple configuration in which the light scattering layer is formed on a smooth package.
[0025]
(Translucent sealing material 102)
The translucent sealing material 102 is provided in the recess of the package 107, and efficiently transmits the light from the LED chip 103 to the outside and protects the LED chip 103, the wire 104, and the like from external force and dust. Is. As such a translucent sealing material 102, an epoxy resin, a silicone resin, an acrylic resin, or the like is preferably used. In order to give a filter effect to the light from the LED chip 103, the light-transmitting sealing material 102 can be added with a coloring dye or a coloring pigment.
[0026]
(LED chip 103)
The LED chip 103 can be formed by stacking a semiconductor light emitting layer such as GaP, GaAlAs, GaAlInP, InN, GaN, AlN, InGaN, or InGaAlN on a substrate by MOCVD, liquid phase growth, or the like. Examples of the structure of the LED chip include a homostructure having a MIS junction, a PIN junction, a pn junction, and the like, a heterostructure, and a double heterostructure. In particular, in the case of a double hetero structure through the active layer, light generated in the active layer 108 propagates like a waveguide in the active layer and is easily emitted from the end face of the active layer. Therefore, the effect of the present invention is great.
[0027]
Similarly, a nitride semiconductor (In _X Ga _Y Al _1-XY N, 0 ≦ X, 0 ≦ Y, 0 ≦ X + Y ≦ 1) is formed on an insulating sapphire substrate that is difficult to grow crystals. In order to supply power to the nitride semiconductor formed on the sapphire substrate, the positive electrode and the negative electrode have to be formed on the same surface side, and in order to inject current efficiently with ohmic contact, translucency A gold thin film or the like is used as the electrode. Although such an electrode is made of a metal although it is a thin film, light generated in the active layer of the LED chip is partially reflected. Therefore, an LED chip using a nitride semiconductor has a large amount of light emitted from the end portion, and the effect of the present invention is great.
[0028]
Such an LED chip 103 can be mounted on the package 107 using a die-bonding device. In addition, the electrode provided on the LED chip can be electrically connected using the wire 104 or the like.
[0029]
(Package 107)
The package 107 is provided with a lead electrode 105 in which the LED chip 103 is arranged and current from the outside is supplied to the LED chip 103. As a specific material of such a package 107, an insulating support member such as ceramics, liquid crystal polymer, PBT resin, or the like is preferably used. As the package 107, a package having a side wall in order to efficiently extract light from the LED chip 103 is preferably cited.
[0030]
When the package 107 is molded with resin, the lead electrode 105 that supplies power to the LED chip 103 disposed therein can be formed relatively easily by insert molding or the like. The lead electrode 105 can be formed of a metallized material such as nickel or a good electrical conductor such as phosphor bronze. In order to improve the reflectivity of light from the LED chip 103, the surface of the lead electrode 105 can be subjected to smooth metal plating such as silver, aluminum, copper or gold. In order to efficiently reflect the light from the LED chip 103, a white pigment such as barium titanate can be mixed into the resin constituting the package 107.
[0031]
When the package 107 is made of ceramic, a conductive paste containing a refractory metal is printed in a desired pattern on a green sheet that is a raw material before firing the ceramic. A plurality of green sheets are stacked into a package shape and then fired to form a ceramic package. The conductive paste is left as an electrode layer that can be electrically connected to the outside when the resin component jumps during firing.
[0032]
The smooth bottom surface of the package refers to a plane that can reflect most of the light from the LED chip 103 incident from a certain direction, such as a mirror surface, in a specific direction. Light in the vertical direction emitted from the LED chip 103 arranged on such a plane can be efficiently emitted to the front surface.
[0033]
【Example】
Hereinafter, specific examples of the present invention will be described in detail, but it is needless to say that the present invention is not limited thereto. As a chip type LED, an LED chip having a nitride semiconductor capable of emitting blue light (470 nm) in a light emitting layer was disposed in a resin package. The LED chip is formed by laminating a buffer layer made of gallium nitride, an n-type contact / cladding layer made of GaN, a p-type cladding layer made of GaAlN, and a p-type contact layer made of GaN on a sapphire substrate. An InGaN layer having a single quantum well structure is formed between the n-type contact layer and the p-type cladding layer. In order to form positive and negative electrodes from the semiconductor layer side formed on the sapphire substrate, a part of the nitride semiconductor is etched to expose the n-type contact layer. A gold thin film is formed as an ohmic electrode on the p-type contact layer.
[0034]
The package was molded by placing a pre-formed lead electrode in a mold and injecting and curing a liquid crystal polymer. In the formed package, a part of the lead electrode is exposed at the bottom surface of the opening, and the surface of the lead electrode, the bottom surface and the side surface of the package are smooth surfaces that can efficiently reflect the light from the LED chip.
[0035]
The LED chip described above was mounted using a die-bonding device using a translucent epoxy resin in the opening of the package. Each electrode of the LED chip and the lead electrode in the opening of the package are wire-bonded using a gold wire so as to be electrically connected.
[0036]
As a light scattering layer, 100 g of a silicone resin containing 5 g of barium titanate and a blue dye was injected into the package opening while being mixed and stirred. After the injection, the mixture was cured at 150 ° C. for 30 minutes to form a light scattering layer. Although the height of the formed light scattering layer was lower than the light emitting layer of the LED chip, the light scattering layer ran up thinly at the end. In the recess of the package, an epoxy resin is injected and cured as a light-transmitting sealing material at 120 ° C. for 2 hours. In this way, 500 chip type LEDs were formed, and the light emission characteristics were examined.
[0037]
For comparison, 500 chip-type LEDs were formed in the same manner as the chip-type LED of the present invention except that no light scattering layer was formed.
[0038]
Although current was supplied to the formed chip type LED and all emitted light, the chip type LED of the present invention emitted blue light entirely, whereas the chip type formed for comparison with the present invention The LED emits significantly blue light near the LED chip. Further, assuming that the average light emission luminance of the chip type LED not provided with the light scattering layer was 100, the chip type LED provided with the light scattering layer was detected brightly by about 20%. Thus, it was found that the light emitting device of the present invention can greatly improve the light emission output with a very simple configuration.
[0039]
【The invention's effect】
With the configuration of the present invention, the function is separated into a reflective surface that directly reflects from the LED chip to the front surface and a light scattering layer that scatters and diffuses the light totally reflected by the translucent sealing material and efficiently extracts the light to the outside. This enhances the light extraction efficiency from the light emitting device. In addition, when LED chips emitting a plurality of different emission wavelengths are arranged in a package, light can be emitted with good color mixing because light is spread uniformly by the light scattering layer.
[0040]
Since the substantial thickness of the light scattering layer is thinner than the height from the bottom surface of the concave portion of the LED chip to the light emitting layer, only the extraction efficiency can be improved without affecting the light emission from the LED chip. That is, the luminance of light emitted from the end of the light emitting layer is not lowered. In addition, it is possible to increase the external extraction efficiency by selecting light that is critically reflected.
[0041]
Since the light scattering layer is colored substantially the same as the emission color of the LED chip, the LED chip does not emit dots in the package. In other words, the light emitting part can be observed more largely as if the LED chip is arranged over the entire opening part during lighting as well as during non-lighting. For example, if the emission wavelength of the light-emitting element is in the blue region, add a light-scattering / diffusible blue pigment to the light-scattering layer to make it a blue-colored color. You can also. In this case, if the light emission color of the light emitting element is matched with the color of the light scattering layer, the light emission color of the light emitting device can be easily discriminated visually without actually emitting light.
[0042]
The LED chip is preferably made of a nitride semiconductor having a double hetero structure, and the light scattering layer preferably covers the end face of the light emitting layer of the LED chip. Thereby, even in the case of a light emitting element that emits a lot of light in the lateral direction, the light extraction efficiency can be dramatically improved.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a chip type LED according to an embodiment of the present invention.
FIG. 2 schematically shows a path of light emitted from an LED chip at an angle greater than a critical angle in a chip type LED shown for comparison with the present invention.
FIG. 3 schematically shows a path of light emitted from the LED chip at an angle greater than a critical angle in the chip type LED of the present invention.
FIG. 4 is a schematic cross-sectional view of a chip type LED shown for comparison with the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 ... Light-emitting device 101 ... Light-scattering layer 102 ... Translucent sealing material 103 ... LED chip 104 ... Wire 105 ... Lead electrode 106 ... Mount resin 107 ... Package 108 ··· Active layer 200 ··· Light emitting device 202 ··· Translucent resin 203 · · · Light emitting point 208 of LED chip as seen schematically · · · Light emitted from the LED chip at a critical angle or more 209... Critical angle reflected light 210... Light repeatedly reflected by the light-transmitting sealing material 301... Light scattering layer 302... Translucent resin 303. Light emitting point 308 of the LED chip ... Light 309 emitted from the LED chip at a critical angle or more ... Light reflected by the critical angle 310 ... Light 311 diffused and reflected and emitted hemispherically ... Directly below the LED chip 400 ... light-emitting device 402 ... translucent sealing material 403 ... LED chips 404 ... gold wires 405 ... lead electrodes 406 ... die bonding resin 407 ... package

Claims (5)

In a light emitting device having a package including a lead electrode, an LED chip disposed on the bottom surface of the recess of the package, and a light scattering layer that scatters light from the LED chip,
The light scattering layer is made of a resin containing a light scattering material. From the surface of the lead electrode exposed in the recess and from the bottom surface to the side surface of the recess, from the height from the bottom surface to the light emitting layer of the LED chip. The light emitting device is characterized by being arranged with a thin thickness. The light emitting device according to claim 1, wherein the LED chip has a double hetero structure, and the light scattering layer further covers an end face of the LED chip .   The light-emitting device according to claim 1, wherein the light scattering layer is colored substantially the same as a light emission color of the LED chip.   4. The light emitting device according to claim 1, wherein the light scattering material is at least one selected from titanium oxide, barium titanate, aluminum oxide, silicon oxide, zinc oxide, a metal piece, and a phosphor. 4. The light emitting device according to claim 1, wherein the light scattering material is at least one selected from a melamine resin, a guanamine resin, or a benzoguanamine resin.

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