JP4174858B2 - Light emitting diode - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light emitting diode capable of emitting multicolor light and used for light sources such as various pilot lamps, backlights and displays, and in particular, achieves both improvement in luminous intensity and contrast ratio of the light emitting diode.
[0002]
[Prior art]
Today, light-emitting diodes (hereinafter also referred to as LEDs) have been used for various light sources because of their small size, light weight, long life, and high reliability. Examples of the LED include a chip type LED using an LED chip that is a semiconductor element. The chip type LED uses a resin package to protect the LED chip from the external environment and improve workability. Since the package itself is insulative, a lead electrode is provided to supply current to the LED chip mounted in the recess of the package. The lead electrode exposed to the outside from the inside of the package and each electrode of the LED chip are electrically connected inside by Ag paste or wire. A light-transmitting resin is molded in the recess in which the LED chip, the wire, and the like are arranged for the purpose of protecting the LED chip. The LED chip can emit light by supplying power to the lead electrode. The light emitted from the LED chip is not only directly emitted from the LED chip through the mold member but emitted to the outside, and also emitted from the LED chip by being reflected by the bottom surface or the side wall of the recess for housing the LED chip.
[0003]
When importance is attached to the luminous intensity extracted from the LED, the luminous intensity can be improved relatively easily by using the side wall of the recess in which the LED chip is disposed. Specifically, a white material or a metal material excellent in light reflectivity is selected as the resin constituting the package. Alternatively, by adding a white pigment having excellent light reflectivity to the package, the side surface and bottom surface of the concave portion of the package can be used as a reflective surface having excellent light reflectivity. As a result, the amount of light extracted from the LED can be increased by 10% or more.
[0004]
On the other hand, the contrast ratio, which is the ratio of the brightness of the LED in the dark place, the brightness of the entire LED when the LED in the bright place is emitted, and the brightness of the entire LED when the LED in the bright place is turned off On the other hand, in contrast to the above, a dark color coloring material such as black is included in the entire package including the LED chip. Alternatively, it is conceivable to select a material in which the package itself is colored black. Thereby, reflection of the extraneous light irradiated to LED can be suppressed and contrast ratio can be improved. In particular, in the case of an LED display or the like, a high contrast ratio is desired. This is because if the contrast ratio is high, the difference between lighting and non-lighting becomes clear and a good gray scale can be achieved. Similarly, when used as a light source of an optical sensor, noise can be reduced and sensitivity can be improved.
[0005]
[Problems to be solved by the invention]
However, in order to effectively use the light from the LED chip, if it has white, silver white or silver side walls with excellent reflectivity, it not only reflects the light from the LED chip and efficiently emits it to the outside. The light from the outside is also reflected by the side wall. Therefore, there is a problem that the contrast ratio of the light emitting diode is lowered. In addition, when the package is colored in a dark color system in order to improve the contrast ratio, there is a problem that light emitted from the LED chip is absorbed and the light extracted from the LED is greatly reduced. That is, it has been extremely difficult to achieve both improvement in the brightness of the LED and improvement in the contrast ratio. As the luminous intensity of the LED chip improves, higher brightness and higher contrast ratio tend to be particularly demanded along with the variety of usage environments such as outdoor use. Therefore, the LED having the above configuration is not sufficient and further improvement is required.
[0006]
[Means for Solving the Problems]
The present invention includes a substrate having a recess and a plurality of light emitting elements disposed in the recess and having different emission colors, and the light emitted from the plurality of light emitting elements is reflected by a sidewall of the recess. The side wall has a plurality of colorants having different colors, and each light emission color of the plurality of light emitting elements is substantially the same as any one of the plurality of colorants. It is a light emitting diode characterized by being the same. As a result, the contrast ratio can be greatly improved while preventing a decrease in luminous intensity.
[0007]
The light emitting diode according to claim 2 of the present invention is such that the plurality of light emitting elements include a first light emitting element and a second light emitting element having a height higher than that of the first light emitting element. The colorant includes a first colorant having substantially the same color as the emission color of the first light-emitting element and a second colorant having a color substantially the same as the emission color of the second light-emitting element. The sidewall has the first colorant on the bottom side and the second colorant on the upper side. As described above, the light emitting elements have different directivity characteristics, and the colorants are mainly arranged independently according to the directivity characteristics. In the case where the light emitted from the light emitting element has different directivity, a colorant that reflects the light is disposed at the site most irradiated with the light emitted from the light emitting element. Although the colorants are arranged independently, they are arranged very close to each other, so that they can be visually recognized as mixed colors by human eyes. Therefore, it can be set as the light emitting diode which can suppress the fall of luminous intensity more.
[0008]
The light-emitting diode according to claim 3 of the present invention is a light-emitting diode in which at least three types of light-emitting elements capable of emitting red, green, and blue light are mounted in a recess. In particular, at least a part of the surface of the recess that reflects light emitted from the light emitting element is colored by mixing a colorant substantially the same as the light emitting color of each light emitting element. A light emitting diode capable of full color display with a good contrast ratio while maintaining the luminous intensity can be obtained.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
As a result of various experiments, the present inventor has improved the contrast ratio while preventing a significant decrease in light emission luminance by establishing a specific relationship between the emission wavelength of the light emitting element and the portion that reflects the light from the light emitting element. As a result, the present invention has been found.
[0010]
A colorant reflects a wavelength corresponding to the color of the colorant and absorbs other colors. Further, while the color mixture of light approaches white light, the color mixture of colors approaches black. In the present invention, the color mixture of light and the color mixture of colors are used for an LED in which a plurality of LED chips are arranged in one place. That is, the light emitted from the plurality of light emitting elements of the LED is reflected by the side walls containing the colorant substantially the same as the light emitting color of the light emitting elements. In this case, although it is absorbed by a colorant different from the emission color from the light emitting element, it is reflected by at least the same colorant as the emission color of the light emitting element. For this reason, the decrease in luminous intensity is far less than that of an LED composed of a side wall containing a black colorant.
[0011]
On the other hand, when different colorants are separated to a distance that cannot be discerned by human eyes, they are visually expressed by color mixing. For example, when a red, green, and blue pigment is mixed and formed in a resin, a dark color system such as amber color can be expressed. Therefore, the light from the outside is absorbed by each colorant. Accordingly, the present invention can efficiently absorb light from external light and selectively reflect light from the light emitting element, thereby improving the contrast ratio. In particular, a light emitting element that emits a monochromatic light emission wavelength with a sharp emission peak and a colorant that has a peak corresponding to the light emission peak of the light emitting element and a relatively broad absorption wavelength produce a particularly great effect.
[0012]
Hereinafter, LED200 which is an example of this invention is demonstrated using FIG. In FIG. 2, a package 202 having recesses in which the LED chips 204 and 205 can be disposed is formed by containing yellow and black coloring dyes in a ratio of 5: 1. One of the packages 202 is exposed as a lead electrode 206 on the surface of the recess, and the other is exposed on the outer wall of the package. An LED chip 204 capable of emitting blue light and an LED chip 205 capable of emitting yellow light are disposed in the cup of the package 202. Each LED chip is electrically connected to each lead electrode using a gold wire and Ag paste so that it can be driven independently. The LED chip 204 capable of emitting blue light is a light emitting element having a pn junction as a light emitting layer on sapphire as a light emitting layer, and the LED chip 205 capable of emitting yellow light as a light emitting layer on a gallium phosphorous substrate. It is a light-emitting element having a pn junction made of indium, aluminum, and gallium phosphide.
[0013]
The directivity characteristic of the blue LED chip 204 tends to be more intensely irradiated in the layer direction than the yellow LED chip 205. Further, the blue LED chip 204 is formed lower than the height of the yellow LED chip 205. Therefore, the light emitted from the blue LED chip 204 is strongly irradiated to the side surface of the recess parallel to the active layer of the LED chip. On the other hand, the ratio of the light emitted from the yellow LED chip 205 to the side of the concave portion higher than that is high. Accordingly, in the present invention, the epoxy resin 201 containing a blue coloring pigment is applied and cured on the bottom surface side of the concave side wall to be colored blue. On the other hand, the side surfaces 202 above the surface appear yellow and black color pigments contained in the package on the surface. When viewed from a distance by coloring, the inside of the recess is visually recognized as dark green as a mixed color of black, yellow, and blue. Moreover, when each LED is lighted simultaneously, white light can be obtained by color mixture of light. Such an LED can instantaneously determine the color of the light emitting element even when LED chips of a plurality of colors are arranged. Even if extraneous light is irradiated, the reflected light is green, so it is gentle on the eyes. Hereinafter, each configuration of the present invention will be described.
[0014]
(Coloring agent)
As the colorant of the present invention, a colorant having substantially the same color as each emission color of the light emitting element can be used. The colorant efficiently reflects light from a light emitting element that emits the same color as the colorant and absorbs other colors. If the colorant is in close proximity and has a plurality of colors, the color mixture approaches black. Accordingly, the plurality of colorants of the present invention may be used by mixing each other, or may be provided independently at positions close enough to cause color mixing. The colorant can be contained in the substrate, or a colorant contained in a resin or the like may be applied to the surface of the substrate. In the case where the contrast is important, in addition to a plurality of colorants, a dark package material or the like can be selected or a dark colorant can be added. The contents of the plurality of colorants are not necessarily contained in equal amounts, and can be variously adjusted in consideration of the luminous intensity of the light emitting element, the reflectivity of the colorant, and the like. Various coloring agents such as various dyes and pigments can be selected. Similarly, the colorant may be an inorganic member or an organic member. Specific examples include perylene red, condensed azo red, quinacridone red, copper phthalocyanine blue, copper phthalocyanine green, curcumin, and coal tar dyes. The colorant preferably has a broad absorption spectrum while the light emitting element has a monochromatic peak wavelength. Thereby, extraneous light can be efficiently absorbed, reflecting the light of the light emitting element of the same color as a coloring agent. Such a colorant is preferably 5 to 40% by weight and more preferably 10 to 30% by weight in order to increase the reflection efficiency.
[0015]
(Substrate 102, 202)
The bases 102 and 202 of the present invention have portions where the light emitting elements 103, 104, 105, 204, and 205 can be arranged and at least a part of the light emitted from the light emitting elements can be reflected. Examples of the base of the light emitting diode include a chip-type LED housing having a concave portion in which the light emitting element can be disposed and a substantially flat plate on which the LED chip can be mounted. As long as the effects of the present invention are exhibited, the mount lead cup can also be used as the substrate. In order to obtain a substrate containing a colorant having the same color as the light emission color corresponding to the plurality of light emitting elements of the present invention, a substrate material that can easily be uniformly dispersed and mixed uniformly is selected. It is preferable.
[0016]
Various base resin colors can be selected depending on the material used for the package, but in order to improve the light utilization efficiency, the base resin color is white and various light-transmitting agents can be added to the light. It is preferable to use a functional resin. This is to prevent light from the light emitting element from being unnecessarily absorbed by the concave side surface 101 and the bottom surface. In addition, the light emitted from the light emitting element can be reflected by utilizing the side wall of the concave portion of the package, or a reflecting member that efficiently reflects the light from the light emitting element can be formed separately from the concave side wall of the package. May be. In addition, even if the color of base resin itself is a dark color system, since the light from a light emitting element is reflected with the coloring pigment to contain, it can produce an effect similarly.
[0017]
Further, a similar effect can be obtained by applying a colorant that matches the emission color of the light-emitting element to the inner wall surface of the package recess, instead of including a colorant in the package. The coloring material can also be applied using various translucent resins and glass. As such a substrate, an insulating resin such as a liquid crystal polymer, PBT, melamine, epoxy resin, or acrylic resin can be suitably used. Moreover, the package formed using the ceramic as an inorganic member can also be utilized as a base | substrate.
[0018]
In the case where the light emitting element is disposed in the recess of the package, a translucent mold resin 109 can be provided to protect the light emitting element and the like. As such a translucent resin, a resin excellent in weather resistance such as an epoxy resin, a silicon resin, a silicon resin, and an acrylic resin is preferably exemplified.
[0019]
In addition, since the package normally has an insulating property, the package includes lead electrodes 106 and 107 for supplying electric power to the light emitting elements in the package from the outside. The lead electrodes 106 and 107 use a light emitting element and a wire 108 such as gold and aluminum, as well as a conductive paste such as Ag paste, carbon paste and ITO, as well as solder or gold tin eutectic. Can be connected. Various materials can be selected for the lead electrodes 106 and 107 in consideration of the electrical conductivity and the adhesiveness to the wire and the package material. Specifically, various metals and alloys such as iron, copper, iron-containing copper, and stainless steel can be used.
[0020]
(Light emitting elements 103, 104, 105, 204, 205)
The light-emitting element of the present invention is a semiconductor light-emitting element and emits light when supplied with current. Various emission colors emitted from the light emitting element by the semiconductor material can be selected. That is, when a semiconductor with a large band gap is used, a light emitting element capable of emitting a short wavelength can be obtained, and when a semiconductor material with a small band gap is used, a light emitting element capable of emitting a relatively long wavelength can be obtained. As a specific material for such a semiconductor element, SiC, GaN, GaP, GaAlAs, GaAsP, InGaN, InAlGaN, AlGaInP, or the like can be preferably used. Examples of the structure of the semiconductor element include a MIS structure using a homojunction, a heterojunction, and a double heterojunction, a pn structure, and a PIN structure. Furthermore, it is possible to improve the light emission efficiency by using a single well structure or a multiple quantum well structure in which the quantum effect is generated in the light emitting layer. Such a light emitting element can be formed using a liquid phase growth method and various CVD methods.
[0021]
Currently, a nitride semiconductor (Al _x In _y Ga _1-xy N, where 0 ≦ x, 0 ≦ y, x + y ≦ 1) is used as a light-emitting element capable of emitting light with high brightness even on the short wavelength side of visible light. Is preferred. Specific examples of the structure of a light emitting device using a nitride semiconductor include a buffer layer, an n-type contact / cladding layer made of GaN on a sapphire substrate, and a light emitting layer made of InGaN having a thickness considered to have a quantum effect. A p-type cladding layer made of AlGaN and a p-type contact layer made of GaN may be stacked. If the In composition of the light emitting layer is large, the emission wavelength is on the long wavelength side, and if the In composition is small, the emission wavelength is on the short wavelength side. For example, In _0.4 Ga _0.6 N emits a monochromatic peak wavelength exhibiting a blue color having a wavelength of about 475 nm, and In _0.6 Ga _0.4 N emits a monochromatic peak wavelength exhibiting a green color having a wavelength of about 535 nm. Thus, various selections can be made to obtain a desired emission color. Similarly, as a light emitting element capable of emitting red light with high brightness, a buffer layer on a semiconductor substrate such as GaAs or GaP, an n-type cladding layer made of AlInGaP, a light-emitting layer made of AlInGaP, a p-type cladding layer made of AlInGaP, and an InGaP The light emitting element etc. which laminated | stacked the p-type contact layer which become can be utilized suitably. Mixed light can be obtained by arranging such different light emitting elements in proximity to each other and emitting light simultaneously. For example, in order to obtain white, at least three types of light emitting elements capable of emitting red, green and blue, respectively, at least three types of light emitting elements capable of emitting cyan, magenta and yellow, respectively, blue and yellow can emit light respectively. It can be obtained by mixing light emission from at least two kinds of light emitting elements.
[0022]
In addition, as described above, a light emitting element capable of emitting blue and green light with high luminance and a light emitting element capable of emitting red light with high luminance have different stacked structures, and thus are emitted from light emitting elements using nitride semiconductors. Light tends to be more strongly irradiated in a direction parallel to the light emitting layer than the other. In addition, a red light emitting device using a light emitting layer made of AlInGaP has a higher light emitting layer height than a blue or green light emitting device using a light emitting layer made of InGaN. By using different directivity characteristics of the light emitting elements, each colorant can be arranged independently according to the directivity characteristics to increase the luminous intensity. Hereinafter, although the Example of this invention is described in full detail, it cannot be overemphasized that it is not limited only to this.
[0023]
【Example】
(Example 1)
FIG. 1 shows a schematic sectional view and a plan view of a light emitting diode 100 of the present invention. In FIG. 1, a package is formed using a liquid crystal polymer as a substrate 102 on which a light emitting element is arranged. A perfect circular recess having a diameter of 2 mm is provided in the center of the package as seen from the light emission observation surface side. LED chips 103, 104, and 105 capable of emitting RGB light are disposed in the recesses that become the depressions. A lead electrode 107 is provided on the bottom surface of the recess of the package so that each LED chip can supply current independently. A total of four lead electrodes are provided, that is, three lead electrodes 107 wire-bonded via electrodes of each LED chip and gold wires, and lead electrodes 106 commonly connected to the common of each LED. Each lead electrode is silver-plated on the surface of phosphor bronze and exposed at the bottom of the recess of the package, and is also exposed outside the back surface of the light emitting surface through the inside of the insulating package.
[0024]
A package using a liquid crystal polymer as an insulating resin is used. Although the base resin of the liquid crystal polymer is substantially white, substantially red, green and blue colored dyes are mixed in the base resin in proportions of 15% by weight, corresponding to the emission color of the LED chip. Perylene red, copper phthalocyanine green and copper phthalocyanine blue are used as coloring dyes. The package is formed by forming a molding material containing red, green and blue colorants in advance. The molding material is placed in an injection molder hopper (not shown) and heated and melted, and then a lead electrode plated with silver on the surface of bronze is injected into a pre-arranged mold, and a package for a light emitting diode is formed using injection molding. Formed. After taking out from the mold, the lead electrode is cut into a desired shape to form a package as shown in FIG. In the formed package, the resin containing red, green and blue has an amber color close to black. Therefore, except for the exposed lead electrode, the concave surface 101 of the package is dark.
[0025]
Each LED chip is a blue LED chip 103 using InGaN, on a sapphire substrate, a buffer layer made of GaN, an n-type contact / cladding layer made of GaN, and light emission made of InGaN with a thickness that is supposed to have a quantum effect. An LED chip of about 350 μm square is used in which a layer, a p-type cladding layer made of AlGaN, and a p-type contact layer made of GaN are stacked. Similarly, the green LED chip 104 and the red LED chip 105 using InGaAlAs have the same configuration except that the composition of In is changed. The red LED chip 105 has a buffer layer, an n-type cladding layer made of AlInGaP, a light emitting layer made of AlInGaP, a p-type cladding layer made of AlInGaP, and a p-type contact layer made of InGaP on a GaP substrate. . Each LED chip emits light having monochromatic peak wavelengths of 470 nm, 555 nm and 620 nm.
[0026]
In addition, since the contact layers of the blue and green LED chips are exposed on the same surface and positive and negative electrodes are provided, die bonding is performed on the lead electrodes with epoxy resin. Each electrode of the LED chip provided on the same surface side and the lead electrode are connected by a gold wire. On the other hand, a red LED chip is formed with a pair of positive and negative electrodes via a semiconductor element. For this reason, a lead electrode common to each LED chip and an Ag paste are used for die bonding so as to be conductive. On the other hand, the other electrode of the LED chip and another lead electrode are wire-bonded using a gold wire. In addition, an epoxy resin is disposed as a translucent mold resin for protecting each LED chip, a gold wire, and the like in the concave portion of the package in which the LED chip is connected to the lead electrode. 500 light emitting diodes thus formed were formed.
[0027]
(Comparative Example 1)
500 light emitting diodes having a black package were formed in the same manner as in Example 1 except that only a black pigment was added in place of the RGB colored pigment in the package. Further, 500 light emitting diodes were formed in the same manner as in Example 1 except that no pigment was added. This is a light emitting diode having a white package reflecting the color of the base resin. The average values of the luminance and contrast ratio of the light-emitting diode of Example 1 and the light-emitting diodes having black and white packages were measured. When the number of light emitting diodes of the present invention is 100, the brightness of the light emitting diode in the white package is 162 and the contrast ratio is 41. The luminance of the light emitting diode in the black package was 64 and the contrast ratio was 108. The brightness × contrast ratio is 66 for the white package light emitting diode and 69 for the black package light emitting diode, compared to 100 of the present invention. Therefore, it can be seen that the light emitting diode of the present invention is remarkably superior.
[0028]
(Example 2)
Example 1 except that the light emitting device of Example 1 uses a nitride semiconductor capable of emitting blue and yellow, and uses an acrylic resin in which blue, yellow and black colorants are mixed and uniformly contained in the package. A light emitting diode was formed in the same manner as described above. The lead electrode is provided so that each light emitting element can be driven independently. The formed light emitting diode can emit white light by color mixture when the light emitting elements are turned on simultaneously. When the light emitting element emits light, it is reflected by a colorant having the same color as the light emitted from the light emitting element to suppress a decrease in luminous intensity. Further, when the light emitting element is turned off, the colorant becomes dark green due to a mixture of blue, yellow and black colorants, and the contrast ratio can be improved.
[0029]
【The invention's effect】
As described above, in the present invention, the light extraction side surface of the package constituting the light emitting diode, that is, the portion that is visible from the outside when the display element or display body is formed with the light emitting diode, is colored with the same color as the light emitting element. Apply. As a result, the coloring has a reflection effect for the light from the light emitting element because it is the same color, while it absorbs light of a color other than the same as the coloring for the substantially white light from the outside. . Therefore, the light-emitting diode according to the present invention can achieve the contradictory characteristics of improving the contrast ratio while suppressing a decrease in luminance.
[Brief description of the drawings]
FIG. 1A is a schematic plan view showing a light emitting diode of the present invention, and FIG. 1B is a sectional view taken along line XX in FIG.
FIG. 2 is a schematic cross-sectional view showing another light emitting diode of the present invention.
[Explanation of symbols]
100, 200... Light emitting diode 101... Recessed side wall 102 of package.. Base 103 on which LED chip is arranged... Blue LED chip 104... Green LED chip 105. 107, 206 ... lead electrodes 108, 208 ... wires 109, 209 ... translucent mold resin 201 ... resin 202 containing a colorant ... sidewall 204 containing a colorant ..Blue LED chip 205 ... Yellow LED chip

Claims (3)

Light emission that has a base having a recess and a plurality of light emitting elements that are arranged inside the recess and have different emission colors , and that can emit light from the plurality of light emitting elements at a sidewall of the recess. A diode,
The side wall has a plurality of colorants having different colors from each other,
Each light emitting color of the plurality of light emitting elements is substantially the same as any color of the plurality of coloring materials . The plurality of light emitting elements include a first light emitting element and a second light emitting element having a height higher than that of the first light emitting element.
The plurality of colorants include a first colorant having substantially the same color as the emission color of the first light-emitting element and a second colorant having substantially the same color as the emission color of the second light-emitting element. Have
2. The light emitting diode according to claim 1 , wherein the side wall includes the first colorant on a bottom surface side and the second colorant on an upper side thereof. 2. The light emitting diode according to claim 1, wherein the plurality of light emitting elements include at least three types of light emitting elements capable of emitting red, green, and blue light respectively.

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