JP2008112959A - Light emitting diode element, and light emitting diode device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting diode element for improving light take-out efficiency and having high light emitting efficiency by forming a cover layer wherein the change of an antireflection effect by the heat generation of a light emitting diode chip is small without the need of microfabrication to a substrate and the light emitting diode chip or an optical member for converging light, and to provide a light emitting diode device using it. <P>SOLUTION: In the light emitting diode element comprising the light emitting diode chip and the cover layer formed on the surface, the cover layer is provided with an antireflection function to light emitted from the light emitting diode chip, the thickness is ≤50 μm and the absolute value of the temperature coefficient of a refractive index is ≤15×10<SP>-6</SP>/°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light emitting diode element and a light emitting diode device using the same.

  Today, light-emitting diode devices (LED devices) can emit light with various wavelengths such as red, green, blue, and ultraviolet, and coupled with the development of wavelength conversion technology in combination with fluorescent materials, It is an indispensable light source for various displays and lighting equipment. These instruments are strongly required to obtain a large luminous flux with less electric power, that is, high luminous efficiency.

One method for improving the light emission efficiency is to increase the light extraction efficiency from the light emitting diode element (LED element). In general, a material having a high refractive index such as a gallium nitride-based material is used as a material of a light emitting diode element. Therefore, a phenomenon occurs in which light emitted from the element is reflected at an interface with a surrounding substance in contact with the element and cannot be extracted from the element. . In order to reduce this influence, for example, as disclosed in Patent Document 1, a method for improving the extraction efficiency by providing irregularities on the element substrate and the light emitting diode element to control the incident angle of light, As disclosed, there has been devised a method for effectively using the light extracted by arranging a condensing optical component on a light emitting diode element. Further, Patent Document 3 discloses a method of coating a light-emitting diode element with a synthetic resin having a refractive index adjusted, and Patent Document 4 emits an antireflection film having a refractive index of 2.2 to 2.7. A method of forming a protective film on a diode element and a protective film on an antireflection film is disclosed.
Japanese Patent Laid-Open No. 2003-204079 JP 2005-166733 A JP-A-4-22352 Japanese Patent No. 2924580

  Among the above-described conventional techniques, the techniques disclosed in Patent Document 1 and Patent Document 2 require microfabrication of a substrate and a light-emitting diode element and additional optical components. Or there exists a problem which causes a raise of member cost. Further, when the coating layer is formed on the light emitting diode chip to reduce reflection as in the methods described in Patent Documents 3 and 4, even if the temperature changes due to the heat generation of the light emitting diode chip, the refraction of the coating layer is performed. It is important that the refractive index is difficult to change, but in the method using a resin for the coating layer, the absolute value of the temperature coefficient of the refractive index of the resin is large, that is, the refractive index of the resin is likely to change with temperature. There is a problem that the antireflection effect changes due to heat generation of the chip, that is, the light emission efficiency of the light emitting diode element changes due to temperature change. Furthermore, there is a problem that the resin is likely to be deteriorated by heat and light emitted from the light emitting diode chip, and these are particularly serious problems in a light emitting diode element having a high light output. In addition, the method described in Patent Document 4 has a problem that a material having a predetermined refractive index is limited and a protective layer is provided on the antireflection film, so that the manufacturing process is complicated and the practicality is poor. There is.

  On the other hand, it is conceivable to reduce the reflection at the element interface by sealing the light emitting diode element with a highly durable material such as glass, but generally the light emitting diode element is weak against heat and sealing that softens the glass. There is a problem that the characteristics of the light-emitting diode element deteriorate due to the temperature of the process.

  The present invention has been made in view of such circumstances, and does not require fine processing of a substrate or a light-emitting diode chip or a condensing optical member, and changes in the antireflection effect due to heat generation of the light-emitting diode chip. An object of the present invention is to provide a light-emitting diode element having high light emission efficiency and a light-emitting diode device using the same, by improving the light extraction efficiency by forming a small covering layer on the light-emitting diode chip.

  The inventor forms the thin coating layer on the light emitting diode chip by forming a thin coating layer having an antireflection function for light emitted from the light emitting diode chip and having a small absolute value of the temperature coefficient of refractive index. It is found that the object can be achieved and is proposed as the present invention.

That is, the light-emitting diode element of the present invention is a light-emitting diode element that includes a light-emitting diode chip and a coating layer formed on the surface thereof, and the coating layer has an antireflection function for light emitted from the light-emitting diode chip. The thickness is 50 μm or less, and the absolute value of the temperature coefficient of refractive index is 15 × 10 ⁻⁶ / ° C. or less.

  Since the light-emitting diode element of the present invention has the above-described configuration, it does not require fine processing of the light-emitting diode chip or a condensing optical member, and the change in the antireflection effect due to heat generation of the light-emitting diode chip is small. (The light emission efficiency of the light emitting diode element is not easily changed by a temperature change), and the light extraction efficiency is improved by forming the coating layer on the light emitting diode chip, and the light emission efficiency is high.

  Further, if the thickness of the coating layer is larger than 50 μm, the influence of the thermal expansion coefficient of the coating layer cannot be ignored, and a stress is generated due to the difference in thermal expansion between the coating layer and the light emitting diode element. The risk of breakage increases, and the refractive index changes due to the stress generated in the coating layer, and the desired antireflection effect cannot be obtained. A preferable range of the thickness of the coating layer is 25 μm or less, and a more preferable range is 10 μm or less.

In addition, when the absolute value of the temperature coefficient of the refractive index is greater than 15 × 10 ⁻⁶ / ° C., the coating layer has a large change in the refractive index of the coating layer due to heat generation of the light emitting diode element. Varies greatly with temperature. For example, since the absolute value of the temperature coefficient of the refractive index of a general resin is 100 × 10 ⁻⁶ / ° C. or higher, when the temperature of the light emitting diode chip is increased by 200 ° C., the refractive index is 0.02 or higher. It corresponds to changing. This means that when the incident angle of light on the coating layer is large, the change is sufficient to change the antireflection effect. A preferable range of the absolute value of the temperature coefficient of the refractive index is 10 × 10 ⁻⁶ / ° C. or less, and a more preferable range is 8 × 10 ⁻⁶ / ° C. or less.

  In the above-described configuration, it is preferable that the coating layer is a single layer, and the refractive index of the coating layer is smaller than the refractive index of the light emitting diode chip and larger than the refractive index of the layer outside the coating layer or air.

  If it does in this way, the extraction efficiency of light improves by the buffer layer (buffer layer) effect of a coating layer refractive index, and higher luminous efficiency is obtained.

  Furthermore, when the wavelength of light emitted from the light emitting diode chip is λ, the thickness of the coating layer is d, and the refractive index of the coating layer is n, nd = aλ / 4 (a is an odd number of 1 or more). It is preferable to satisfy.

  In this way, the light extraction efficiency is greatly improved and higher light emission efficiency is obtained due to the synergistic effect of interference between light and the buffer layer (buffer layer) having the refractive index of the coating layer described above. That is, the covering layer increases the critical angle of light emitted from the light emitting diode chip at the interface between the light emitting diode chip and the covering layer and the interface between the covering layer and the outer layer or air, and the light at these interfaces. Is canceled by the interference of light, and light can be efficiently emitted from the light emitting diode chip.

In the above configuration, the refractive index of the light-emitting diode chip is n1, the refractive index of the layer or air outside the coating layer is n2, and the refractive index of the coating layer is n3 = (n1 × n2) ^0.5 + A (n1-n2 ), A is preferably -0.35 to +0.55.

  In this way, a particularly high extraction efficiency can be obtained. A preferable range of A is −0.15 to +0.2.

The optical interference effect described above appears when the light emitted from the light emitting diode chip is continuous light having a length exceeding 2nd, and the relationship (1) of nd = aλ / 4 (a is an odd number of 1 or more). In addition to satisfying the above, it is maximized when the reflection intensity at the interface between the light emitting diode chip and the coating layer and the interface between the coating layer and the outer layer or air is equal (2). Note that the condition (2) where the reflection intensities are equal refers to a condition in which the refractive index n3 = (n1 × n2) ^0.5 of the coating layer which is a single layer is derived from the Fresnel equation.

  Further, in the above-described configuration, when the coating layer is a multilayer, it is preferable to sequentially decrease the refractive index of each layer from the side closer to the light emitting diode chip. In this way, it is possible to effectively prevent reflection and increase the light extraction efficiency as compared with the case where the coating layer is a single layer.

In the above-described configuration, it is preferable that the coating layer is made of silicate multicomponent glass, borate multicomponent glass, or phosphate multicomponent glass. In this way, the absolute value of the temperature coefficient of refractive index can be reduced, and a coating layer having excellent durability against heat and light can be obtained. In Patent Document 3, germanium-based glass is described as a coating layer. Generally, the absolute value of the temperature coefficient of refractive index of germanium-based glass is large. For example, the absolute value of the temperature coefficient of refractive index of GeO ₂ glass is 19 × 10 ⁻⁶ / ° C., the change in the antireflection effect due to heat generation of the light emitting diode chip cannot be sufficiently suppressed. In contrast, silicate-based multicomponent glass, borate-based multicomponent glass or phosphate-based multicomponent glass has a small absolute value of the temperature coefficient of refractive index. Since the refractive index can be adjusted over a wide range and the coefficient of thermal expansion and durability can be adjusted, it is suitable for the purpose of the present invention. In particular, silicate-based multicomponent glass is more preferable because of its excellent durability.

  Further, the coating layer is preferably made of a silicate-based multicomponent glass that substantially does not contain an alkali metal element and a halogen element. When the coating layer is formed of a plurality of layers, at least a layer that contacts the light emitting diode chip is provided. It is preferable that it consists of a silicate type | system | group multicomponent glass which does not contain an alkali metal element and a halogen element substantially. That is, alkali metal elements and halogen elements may deteriorate the electrodes, wirings, and the like on the light emitting diode chip. In particular, it is more preferable that all the layers of the coating layer are made of a silicate-based multicomponent glass that does not substantially contain an alkali metal element and a halogen element. In addition, that it does not contain substantially means that the total amount of an alkali metal element and a halogen element is 1 mass% or less.

In the above-described configuration, when the coating layer is a multilayer, the coating layer is preferably formed by alternately forming a layer having a high refractive index and a layer having a low refractive index. In this way, since the effect of suppressing reflection at the interface over a wide wavelength range can be obtained using the interference effect of light, the same film configuration can be used for light emitting diodes with different wavelengths of emitted light. Can also increase luminous efficiency. In this case, materials for optical thin films such as SiO ₂ and MgF ₂ can be used as the low refractive index layer, and TiO ₂ and Ta ₂ O ₅ can be used as the high refractive index layer.

In the above configuration, the coating layer preferably has a photoelastic constant of 10 (nm / cm) / (kg / cm ² ) or less. In this way, even if stress is generated due to the difference in thermal expansion between the coating layer and the light emitting diode chip, the change in the refractive index of the coating layer can be minimized. A preferable range of the photoelastic constant is 6 (nm / cm) / (kg / cm ² ) or less, and a more preferable range is 4 (nm / cm) / (kg / cm ² ) or less.

  In the above-described structure, each of the coating layers is formed by sputtering, vapor deposition, CVD (chemical vapor deposition), CSD (chemical solution deposition), LPE (liquid crystal growth). Method: It is preferably formed by at least one method selected from the group consisting of Liquid Phase Deposition), AD Method (Aerosol Deposition), and Sol-Gel Method. In this way, the coating layer can be formed at a low temperature so that the characteristics of the light-emitting diode chip are not deteriorated. Moreover, if such a formation method is used, a coating layer can be formed on light emitting diode elements having various shapes. For example, when electrodes are arranged on a light emitting diode chip or unevenness is formed. Even in this case, the coating layer can be easily formed.

  In the above configuration, as the light emitting diode chip, it is possible to use aluminum gallium arsenide, gallium arsenide phosphorus, gallium phosphide, zinc selenide, aluminum indium gallium phosphide, etc. in addition to gallium nitride. The covering layer material having a refractive index corresponding to these materials and the forming method thereof may be selected.

  Further, when the light-emitting diode chip has a structure in which light from the light-emitting diode chip is emitted through a substrate such as silicon nitride or sapphire, that is, in a case where these substrates are installed on the light-emitting diode chip. May be provided with a coating layer on these substrates, and such a light emitting diode element is also included in the scope of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a light emitting diode device, and FIG. 2 is an explanatory view of the light emitting diode device in which a transparent resin is formed on a light emitting diode element. Table 1 shows Examples 1 to 6 and Comparative Examples.

  The light emitting diode device 10 of the embodiment includes an alumina substrate 1, a light emitting diode chip 2a having a refractive index of 3 made of a gallium nitride material disposed on the alumina substrate 1, and a coating layer 2b on the light emitting diode chip 2a. I have. The light emitting diode element 2 includes a light emitting diode chip 2a and a covering layer 2b.

Coating layer 2b in Examples 1 and 2, the SiO ₂ 60% by weight percentage, the _{Al 2 O 3 15%, B} 2 O 3 and 10%, CaO, SrO, silicic acid containing 15% total of BaO It has a single-layer structure of a salt-based multicomponent glass, its photoelastic constant is 3 (nm / cm) / (kg / cm ² ), its refractive index is 1.5, and its temperature coefficient is 8 × 10 ^-6 / ° C.

  In the coating layers 2b of Examples 1 and 2, the light emitting diode chip 2a disposed on the alumina substrate 1 is disposed in the chamber of the sputtering apparatus, and sputtered in Ar gas using a glass target having the above glass composition. This was formed on the light emitting diode chip 2a.

Further, the coating layer 2b of Example 3 has a single layer structure made of only amorphous Al ₂ O ₃ formed by the AD method, has a refractive index of 1.7, and has a refractive index temperature coefficient of It was 13 × 10 ⁻⁶ / ° C.

Example 4 is configured in the same manner as Example 3 except that a transparent resin layer 3 (FIG. 2) having a refractive index of 1.5 is formed on the outside of a coating layer made of a single layer of Al ₂ O ₃ . ing.

The coating layer 2b of Example 5 has a single layer structure made of only MgF ₂ formed by vapor deposition, has a refractive index of 1.4, and a refractive index temperature coefficient of 2.3 × 10 ⁻⁶ / ° C.

The coating layer 2b of Example 6 has a single layer structure made of only SiO ₂ formed by the sol-gel method, has a refractive index of 1.5, and a refractive index temperature coefficient of 12 × 10 ⁻⁶ / ° C. there were.

  The comparative example is configured in the same manner as the example except that the coating layer 2b is not formed.

  As is apparent from Table 1, the light emission efficiency (light extraction efficiency) of Examples 1 to 6 is improved by about 9 to 20% as compared with the comparative example. In particular, in Examples 1 to 5, the light emission efficiency is improved by 11% or more than the comparative example. This is because a coating layer having a refractive index of 1.4 to 1.7 is formed between a light-emitting diode chip having a refractive index of 3 and air having a refractive index of 1, which provides an optical interference effect in addition to the buffer layer effect. It seems that this is the result of improved light extraction efficiency from the light-emitting diode chip. The luminous efficiency of Example 6 is about 9% higher than that of the comparative example, which is considered to be due only to the buffer layer (buffer layer) effect of the transparent resin.

  In Examples 1 and 2, since the absolute value of the temperature coefficient of the refractive index of the coating layer is small and the change in the refractive index due to thermal stress is small due to the small photoelastic constant, the light emitting diode chip generates heat. Even when the temperature rises, the light extraction efficiency does not substantially change. Furthermore, since the coating layer is made of a stable silicate-based multicomponent glass, it has high thermal and chemical durability, and is resistant to light and heat from the light-emitting diode chip or moisture in the surrounding environment. Very good durability. Of course, it is possible to further improve the extraction efficiency by making the coating layer multi-layered and making the refractive index gradient between the light emitting diode element and air gentler.

  Further, as shown in FIG. 2, the same effect can be obtained even if a substance other than air, for example, the transparent resin 3 or the like is arranged on the light extraction side (the air side of the coating layer). In this case, the refractive index of the covering layer 2b is selected to be a refractive index between the refractive index of the light emitting diode chip 2a and the refractive index of the transparent resin 3 or the like (for example, Example 4).

  The light emission efficiency is measured by applying a voltage of 3.5 V to the light emitting diode device 10 and introducing light of a wavelength of 470 nm obtained when a current of 300 mA is passed into the integrating sphere to measure the luminous flux. Went by.

  As described above, according to the present invention, the light-emitting diode chip and the substrate need not be finely processed and no additional optical member is required, and the antireflection effect is not substantially changed by the heat generated from the light-emitting diode chip. A high-efficiency coating layer can be formed by a low-temperature process, and a light-emitting diode element with high light extraction efficiency and a light-emitting diode device using the same can be provided. And is extremely effective for the manufacture of lighting equipment.

It is explanatory drawing of the light emitting diode apparatus in this invention. It is explanatory drawing of the light emitting diode apparatus in this invention which formed transparent resin on the light emitting diode element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Alumina substrate 2 Light emitting diode element 2a Light emitting diode chip 2b Covering layer 3 Transparent resin 10 Light emitting diode device

Claims (10)

In a light emitting diode element comprising a light emitting diode chip and a coating layer formed on the surface thereof, the coating layer has an antireflection function for light emitted from the light emitting diode chip, has a thickness of 50 μm or less, and A light-emitting diode device having an absolute value of a temperature coefficient of refractive index of 15 × 10 ⁻⁶ / ° C. or less.   2. The light emitting device according to claim 1, wherein the coating layer is a single layer, and the refractive index of the coating layer is smaller than the refractive index of the light emitting diode chip and larger than the refractive index of a layer outside the coating layer or air. Diode element.   When the wavelength of light emitted from the light emitting diode chip is λ, the thickness of the coating layer is d, and the refractive index of the coating layer is n, the relationship of nd = aλ / 4 (a is an odd number of 1 or more) is satisfied. The light-emitting diode element according to claim 2. When the refractive index of the light emitting diode chip is n1, the refractive index of the layer or air outside the coating layer is n2, and the refractive index of the coating layer is n3 = (n1 × n2) ^0.5 + A (n1−n2), The light emitting diode element according to claim 2 or 3, wherein A is -0.35 to +0.55.   The light emitting diode element according to claim 1, wherein the coating layer is formed of a plurality of layers, and the refractive index of each layer is sequentially decreased from the side closer to the light emitting diode chip.   6. The light emitting diode device according to claim 1, wherein the coating layer is made of a silicate multicomponent glass, a borate multicomponent glass, or a phosphate multicomponent glass.   The covering layer is composed of a plurality of layers, and at least the layer in contact with the light-emitting diode chip is composed of a silicate-based multicomponent glass substantially not containing an alkali metal element and a halogen element. The light emitting diode element as described in. The light emitting diode element according to claim 1, wherein the coating layer has a photoelastic constant of 10 (nm / cm) / (kg / cm ² ) or less.   Each of the coating layers is formed by at least one method selected from sputtering, vapor deposition, CVD, CSD, LPE, AD, or sol-gel method. The light emitting diode element in any one.   A light-emitting diode device comprising the light-emitting diode element according to claim 1.