White light emitting diode

The present invention relates to a white light emitting diode comprising a blue light emitting diode chip; a green light emitting diode chip; and a molding member that encapsulates the blue light emitting diode chip and the green light emitting diode chip, the molding member containing a red fluorescent substance.

This application claims priority under 35 USC 119 by virtue of Korean Patent Application No. 10-2005-0116520 filed on Dec. 1, 2005, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a white light emitting diode, and more particularly, to a white light emitting diode, wherein a molding member with a red fluorescent substance mixed therein is formed on a blue light emitting diode chip and a green light emitting diode chip.

2. Description of the Related Art

As red, orange, green, blue and white light emitting diodes with high luminance have recently appeared with the development of compound semiconductor technology, light emitting diodes, which were mainly used for simple indicators, dial plates and the like in the prior art, have been applicable to a variety of fields in which full colors, high reliability, low power consumption and miniaturization are required. In particular, as the illumination efficiency of a white light emitting diode is superior to that of an incandescent bulb, the appearance of the white light emitting diode shows possibility of use as an illumination light source, and the white light emitting diode has been also used as a backlight source of a liquid crystal display (LCD). There have been developed a variety of methods for implementing such white light emitting diodes, which include a method of obtaining white light by coupling a fluorescent substance on a blue or ultraviolet light emitting diode chip as a single chip type, a method of obtaining white light by combining two or three light emitting diodes as a multi-chip type, and the like.

Among conventional techniques, in a case where a blue light emitting diode is used, the blue light emitting diode is used as an excitation light source and excited light is passed through a fluorescent substance of YAC (Yttrium Aluminum Garnet) emitting yellow light so as to implement a white light emitting diode. However, this method has disadvantages in that a flicker effect frequently occurs due to color separation resulting from a wide wavelength interval between blue and yellow light, and it is difficult to control color temperature and a color rendering evaluation index. Further, there is a method of implementing a white light emitting diode by applying red, green and blue fluorescent substances on an ultraviolet light emitting diode chip. However, there is a problem in that the ultraviolet light emitting diode chip has a short life span and low efficiency.

Meanwhile, although red, green and blue light emitting diode chips are combined to implement a white light emitting diode with multi-chips, there is a problem in that the operation voltage of each of the chips is not uniform, and the output of each of the chips varies depending on an ambient temperature.

FIGS. 1A and 1Bare perspective and sectional views of a white light emitting diode according to a prior art. Referring toFIGS. 1A and 1B, there is shown a case where a blue light emitting diode is used as an excitation light source and excited light is passed through a fluorescent substance of YAG (Yttrium Aluminum Garnet) emitting yellow light so as to implement a white light emitting diode. The white light emitting diode shown inFIGS. 1A and 1Bis a side view type fight emitting diode used as a backlight source of an LCD. The white light emitting diode comprises a substrate110, a first lead terminal120, a second lead terminal130, a blue light emitting diode chip140, a reflection portion150, a wire160, a fluorescent substance170and a molding member180.

In the side view type white light emitting diode, the first lead terminal120and the second lead terminal130are arranged on the substrate110, and the blue light emitting diode chip140is mounted on the second lead terminal130. The reflection portion150for laterally reflecting light emitted from the blue light emitting diode chip140is formed on the substrate110, the molding member180encapsulates the blue light emitting diode chip140, and the fluorescent substance170, e.g., YAG (Yttrium Aluminum Garnet) is mixed in the molding member180. As a result, blue light emitted from the blue light emitting diode chip140excites the fluorescent substance170to generate yellow light, and white light is emitted due to constructive interference of the yellow light and the blue light. Thus, since only the blue light and the yellow light exist, there is limitation on expression of red and green, which causes a problem of deterioration of color reproducibility. Further, as described above, since white light emitting diodes implemented according to the prior art have problems, there is a current need for white light emitting diodes that solve these problems.

SUMMARY OF THE INVENTION

The present invention solves the aforementioned problems by providing a white light emitting diode wherein red, green and blue lights are emitted to improve color reproducibility. According to an aspect of the present invention, the white light emitting diode comprises a blue light emitting diode chip; a green light emitting diode chip; a molding member such as a resin that encapsulates the blue light emitting diode chip and the green light emitting diode chip and which contains a red fluorescent substance. The red fluorescent substance may advantageously comprise (Sr1-xEux)S or (Ca1-xEux)S, where x is 0.001 to 0.02. The white light emitting diode may further include a reflection portion arranged on the substrate to reflect light emitted from the light emitting diode chips in a predetermined direction.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Light emitting diodes have been fabricated in various forms and fabricated as surface mount devices (SMD) adapted to be mounted directly on printed circuit boards. A SMD type light emitting diode is fabricated as a side view type or a top view type according to the desired application. SMD type white light emitting diodes of a side view and a top view will be described below with reference toFIGS. 2 and 3.

FIGS. 2A and 2Bare perspective and sectional views of a white light emitting diode according to a first embodiment of the present invention. The white light emitting diode shown inFIGS. 2A and 2Bis a side view type white light emitting diode, which may be used as a backlight source of an LCD. The white light emitting diode comprises a substrate210, a first lead terminal220, a second lead terminal230, a blue light emitting diode240a, a green light emitting diode240b, a reflection portion250, wires260aand260b, a red fluorescent substance270and a molding member280. The first lead terminal220and the second lead terminal230are formed on the substrate210. The blue light emitting diode chip240aand the green light emitting diode240bare mounted on the first lead terminal220, and the blue light emitting diode chip240aand the green light emitting diode240bare connected to the second lead terminal230through the wires260aand260b. Although the blue light emitting diode chip240aand the green light emitting diode240bare connected in series in this embodiment, they are not limited thereto but may be connected in parallel.

The reflection portion250is formed on the substrate such that one side of the reflection portion is open to allow light emitted from the light emitting chips to be reflected in a lateral direction. The molding member280is contained in the reflection portion250so as to function to encapsulate the blue light emitting diode chip240aand the green light emitting diode chip240band to fix the first lead terminal220and the second terminal230. At this time, a transparent resin such as epoxy resin or silicone resin is used for the molding member.

The red fluorescent substance270is included in the molding member280, and light emitted from the blue light emitting diode chip240aor the green light emitting diode chip240bexcites the red fluorescent substance270to generate red light. Thus, blue, green and red light are mixed with one another so that white light can be emitted. Here, (Sr1-xEux)S or (Ca1-xEux)S where x is 0.001 to 0.02 is used as the red fluorescent substance270. Besides, a variety of red substances may be used.

The blue light emitting chip240amay be fabricated using IV group semiconductors such as silicone carbide (SiC), II-IV group semiconductors such as ZnSe and ZnS, GaN-based III-V group semiconductors, or the like, preferably using GaN-based semiconductors. In case of GaN, red light to near ultraviolet rays can be emitted depending on a composition ratio of In. Thus, it is possible to fabricate not only a blue light emitting diode chip but also a green light emitting diode chip.

FIGS. 3A and 3Bare plan and sectional views of a white light emitting diode according to a second embodiment of the present invention. The white light emitting diode shown inFIGS. 3A and 3Bis a top view type white light emitting diode. This embodiment is different from the first embodiment in that light is emitted upwardly contrary to the first embodiment in which light is emitted in a lateral direction. Remaining components are similar to each other.

The white light emitting diode comprises a substrate310, first lead terminals320aand320b, second lead terminals330aand330b, a blue light emitting diode chip340a, a green light emitting diode chip340b, a reflection portion350, wires360aand360b, a red fluorescent substance370, and a molding member380.

The two first lead terminals320aand320b, and the two second lead terminals330aand330bare formed on the substrate310. The blue light emitting diode chip340ais mounted on the first lead terminal320a, and the green light emitting diode chip340bis mounted on the first lead terminal320b. The blue light emitting diode chip340aand the green light emitting diode chip340bare connected to the second lead terminals330aand330bthrough the wires360aand360b, respectively.

The reflection portion350is formed to surround the blue and green light emitting diodes340aand340bon the substrate310. At this time, to improve luminance and a light focusing ability, an inner wall of the reflection portion350surrounding the blue and green light emitting diode chips340aand340bmay be formed to have a predetermined slope. As described above, the reflection portion350is formed so that reflection of light emitted from the blue and green light emitting diode chips340aand340bcan be maximized.

The molding member380is applied in the reflection portion350so as to function to encapsulate the blue light emitting diode chip340aand the green light emitting diode chip340band to fix the first lead terminals320aand320band the second lead terminals330aand330b. At this time, a transparent resin such as epoxy resin or silicone resin is used for the molding member380.

The red fluorescent substance370is included in the molding member380, and light emitted from the blue light emitting diode chip340aor the green light emitting diode chip340bexcites the red fluorescent substance370to generate red light. Thus, blue, green and red light are mixed with one another so that white light can be emitted. As described above, (Sr1-xEux)S or (Ca1-xEux)S wherein x is 0.001 to 0.02 is used as the red fluorescent substance370.

FIG. 4is a sectional view of a white light emitting diode according to a third embodiment of the present invention. The white light emitting diode according to the third embodiment is a chip type light emitting diode. This embodiment is different from the second embodiment in that there is no reflection portion, and remaining components are similar to each other. Further, although the molding member380is shown in the form of a hemisphere in this embodiment, it is not limited thereto but may be fabricated in various forms. Although white light emitting diodes in various forms are shown inFIGS. 2A to 4, the present invention is not limited thereto but may be applied to white light emitting diodes in other forms except these illustrative forms.

FIGS. 5A and 5Bare views showing emission spectra of white light emitting diodes according to the prior art and the present invention, respectively, andFIGS. 5C and 5Dare views showing color coordinates according to the prior art and the present invention.FIG. 5Ashows the emission spectrum of the white light emitting diode according to the prior art, i.e., shown inFIG. 1, andFIG. 5Bshows the emission spectrum of the white light emitting diode according to the present invention. As shown inFIG. 5A, emission peaks exist only in the vicinity of blue and yellow, and there is no emission peak in the vicinity of green and red. Thus, there is limitation on expression of red and green, resulting in deterioration of color reproducibility.

Referring toFIG. 5B, contrary to the emission spectrum shown inFIG. 5A, it can be seen that emission peaks exist in the vicinity of not only blue but also green and red. Thus, red and green can be readily expressed and color reproducibility is improved.

Referring toFIGS. 5C and 5D, it can be seen that there is little difference between the RGB color coordinates of white light emitted from the white light emitting diode according to the prior art and those of white light emitted from the white light emitting diode according to the present invention. In this simulation, a CIE 1931 (International Commission for Illumination) color coordinate is used, and a color reproducibility defined in the NTSC (National Television Standard Committee) is used. The color reproducibility is defined as follows;
Color reproducibility=(the triangular area of the RGB color coordinate/the triangular area of the NTSC standard color coordinate)*100%

The values of color coordinates shown inFIGS. 5C and 5Dare shown in the following Table 1.

The color reproducibility of the white light emitting diode according to the prior art is about 56.2%, but that of the white light emitting diode according to the present invention is about 78.1%. Thus, according to the present invention, the color reproducibility of a white light emitting diode is improved considerably.

The foregoing are merely exemplary embodiments of the white light emitting diode according to the present invention. The present invention is not limited to the aforementioned embodiments, and it will be understood by those skilled in the art that various modifications and changes can be made thereto without departing from the technical spirit and scope of the present invention as defined by the appended claims.