KR20090108171A - White light emitting device for back light - Google Patents

Abstract

PURPOSE: A white light emitting device for a backlight is provided to simplify a circuit configuration and to omit a separate color correction device. CONSTITUTION: A white light emitting device for a backlight includes a blue light emitting diode chip(21), a green light emitting diode chip(22), and a red phosphor. The red phosphor absorbs a light from the blue light emitting diode chip and a light from the green light emitting diode chip, and emits a light of red color. The blue light emitting diode chip and the green light emitting diode chip are sealed by a sealing member of a light transmitting resin material. The red phosphor is dispersed inside the sealing member.

Description

White light emitting device for backlight {WHITE LIGHT EMITTING DEVICE FOR BACK LIGHT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white light emitting device for a backlight, and more particularly, to a white light emitting device which is used as a backlight light source such as an LCD and which has a simple driving range and a wide color reproduction range.

As the information and communication industry develops, high performance of portable information processing devices and mobile communication terminals is continuously required, and high performance and high quality of various components of the system are continuously required. LCDs, which are commonly applied to monitors of medium and large terminals such as laptops, require a light source with a white backlight on the back. Cold cathode fluorescent lamps (CCFLs) have been widely used as such backlight sources. Cold cathode fluorescent lamps have advantages such as achieving uniform white light with high luminance, but may be used according to mercury regulations in the future. Difficulties are expected. Therefore, research into a backlight light source that can replace CCFL is being actively conducted, and a backlight light source using a white light emitting device including a light emitting diode is being spotlighted as a light source replacing a conventional cold cathode fluorescent lamp.

In the present specification, the light emitting device refers to a device including a light emitting diode that makes a minority carrier (electron or hole) injected by using a pn junction structure of a semiconductor and emits a predetermined light by recombination thereof. As the power consumption is low, the service life is long, can be installed in a narrow space, and the vibration is strong, the use of various information processing and communication devices is increasing.

Korean Patent Laid-Open Publication No. 2002-0041480 discloses a uniform light distribution of an LCD by converting blue light of a blue light emitting diode chip into white light by a phosphor and then injecting the light into a light guide plate. Disclosed is an LCD backlight light source module that has high durability with low power consumption.

The white light emitting device according to the related art disclosed herein can realize uniform white light having high luminance by using a blue light emitting diode chip and a phosphor, but when used as an backlight white light source of an LCD, Since the range of color reproduction that can be represented is very narrow, there is a big limitation in implementing an image closer to natural colors. In particular, it is difficult to realize more realistic colors because it is far below the color reproduction range defined by ADOBE RGB or the color reproduction range defined by NTSC.

As another conventional technology, Korean Patent Laid-Open Publication No. 2004-0087974 is an LCD backlight illumination, which uses a white light emitting element or a red, blue, green tricolor light emitting diode chip to form a white backlight light source, Disclosed is a method of measuring input current and color of each light emitting diode chip using a microcomputer to finally adjust a current supplied to each light emitting diode chip.

The conventional technology disclosed above can satisfy a considerably wider color gamut than conventional CCFLs by using red, blue, and green tricolor LED chips, but the thermal or temporal characteristics of the LED chips are different. As a result, the color tone is changed according to the use environment, and in particular, color uniformity may not be realized.

In addition, the output of each light emitting diode chip changes according to the ambient temperature, so that the color coordinates are different. In particular, the decrease in output according to the ambient temperature of the red light emitting diode chip is more noticeable than the blue and green light emitting diode chips. In addition, the circuit configuration is complicated, manufacturing costs are increased, and space is limited due to space constraints, such as a separate color sensor must be provided to compensate for color tone changes caused by different thermal or temporal characteristics of each LED chip. The disadvantage is that it is impossible to apply to small products such as phones.

One technical problem of the present invention is to realize uniform white light by using light emitting diode chips emitting blue light and green light, and a phosphor emitting red light by absorbing light from the light emitting diode chips, thereby enabling wide color reproduction. It is to provide a white light emitting device for a backlight having a range.

Another technical problem of the present invention is to implement white light, using light emitting diode chips emitting blue light and green light, respectively, instead of the red light emitting diode chip having a relatively low thermal or temporal light output, blue and green light emitting diode chips By using a phosphor having a low thermal or temporal light output degradation that absorbs the green and blue light emitted from the light and emits red light, the circuit configuration is not complicated when driving for white light, and a separate color correction device is provided. There is no need to provide a white light emitting device that is easy to apply to small products.

According to an aspect of the present invention, a white light emitting device for a backlight is provided. The white light emitting device includes a blue light emitting diode chip and a green light emitting diode chip, and a red phosphor that absorbs light from the blue light emitting diode chip and light from the green light emitting diode chip to emit red light. In this case, the blue light emitting diode chip and the green light emitting diode chip may be connected in series or in parallel. The red phosphor absorbs blue light and green light and emits red light, thereby further strengthening the red region of white light, and by connecting a blue light emitting diode chip and a green light emitting diode chip in series or parallel, blue light with only one current flow. And green light at the same time, with which red light can be obtained. Therefore, the above configurations contribute to broadening the color reproduction range of the white light. In this case, the blue light emitting diode chip and the green light emitting diode chip are preferably horizontal light emitting diode chips having two electrodes, that is, a p-type electrode and an n-type electrode on the upper surface, in order to connect in series or in parallel.

The blue light emitting diode chip and the green light emitting diode chip may be encapsulated by an encapsulating member made of a light transmissive resin, and the red phosphor may be dispersed in the encapsulating member. In addition, the spectral height ratio of the light emitted from the blue light emitting diode chip and the light emitted from the green light emitting diode chip is preferably 1: 0.1 to 1: 1.2. Here, the height ratio means the ratio of the peak height of the wavelength, and when the ratio of the blue light and the green light is in the above range, the quality of the white light obtained by using the blue and green LED chips and the red phosphor (particularly, the color reproducibility) ) Was the best.

The light wavelength of the blue light emitting diode chip is 430 nm to 480 nm, the light wavelength of the green light emitting diode chip is 500 to 560 nm, and the light wavelength of the red phosphor is 590 to 700 nm. The red phosphor is preferably a nitride-based or sulfide-based phosphor, and more preferably, the red phosphor is (Ca, Sr, Ba) ₂ Si ₅ N ₈ : Eu, (Mg, Ca, Sr) AlSiN ₃ : At least one nitride-based phosphor selected from Eu, (Ca, Sr, Ba) Si ₇ N ₁₀ : Eu, (Ca, Sr, Ba) SiN ₂ : Eu. In addition, the encapsulation member may further include a scattering material of 0.1 ~ 20㎛ size, more preferably, the scattering material is SiO ₂ , AL ₂ O ₃ , TiO ₂ , Y ₂ O ₃ , CaCO ₃ , MgO At least one selected from is used.

According to the present invention, a uniform white light is realized by using blue and green light emitting diode chips and a phosphor which simultaneously absorbs blue and green light emitted from the light emitting diode chips and emits red light. Can be implemented. In particular, by using a phosphor that can simultaneously absorb blue and green light from the blue and green light emitting diode chips and emit red light, instead of the red light emitting diode chip, a decrease in thermal or temporal light output is relatively lower than that of the blue and green light emitting diode chips. It is possible to omit a severe red light emitting diode chip, thereby realizing a backlight light source (especially a small backlight light source) such as an LCD, in which a circuit configuration is not complicated and a separate color correction device is not required.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided as examples to ensure that the spirit of the present invention can be fully conveyed to those skilled in the art. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. And, in the drawings, the width, length, thickness, etc. of the components may be exaggerated for convenience. Like numbers refer to like elements throughout.

1 is a cross-sectional view showing a white light emitting device for a backlight according to an embodiment of the present invention. Referring to FIG. 1, the white light emitting device 1 according to the present embodiment includes first and second lead terminals 11 and 12 on the base 2, and first and second lead terminals 11 and 12. A blue light emitting diode chip 21 and a green light emitting diode chip 22 are electrically connected to a power source (not shown) by a bonding wire (W). In addition, the white light emitting device 1 includes a red phosphor 31 that absorbs blue light and green light emitted from the blue and green light emitting diode chips 21 and 22 and emits red light. White light is produced by mixing blue light, green light, and red light.

Here, the base 2 may be any means for supporting a printed circuit board, a housing (or a reflector), or other LED chips and / or lead terminals. The printed circuit board as the base 2 may be a general PCB, a metal PCB, or a ceramic substrate having a conductive pattern. In this case, the first and second lead terminals 11 and 12 may be conductive electrodes formed on the printed circuit board. It may be a pattern. In addition, the housing as the base 2 may be a housing made of an injection-molded plastic material or a housing made of laminated ceramic substrates, wherein the first and second lead terminals 11 and 12 may be lead frames or conductive electrodes. It may be a pattern.

In the present embodiment, the blue light emitting diode chip 21 and the green light emitting diode chip 22 are horizontal light emitting diode chips having both a p-type electrode and an n-type electrode on an upper surface thereof, and are bonded wires in a two-bonding manner. The first and second lead terminals 11 and 12 are connected in series by (W).

1, between one electrode of the blue light emitting diode chip 21 and the first lead terminal 11 are connected by one bonding wire W, and the other electrode of the blue light emitting diode chip 21 is connected. The other bonding wire W is connected to one electrode of the green light emitting diode chip 22, and another bonding wire W is connected between the other electrode of the green light emitting diode chip 22 and the second lead terminal 12. Connected by). As such, the blue light emitting diode chip 21 and the green light emitting diode chip 22 are electrically connected in series between the first and second lead terminals 11 and 12 which are the (+) terminal and the (-) terminal, respectively. The blue and green LED chips 21 and 22 emit blue light and green light at the same time by one current flow.

On the other hand, the red phosphor 31 is widely distributed in the transparent member encapsulation member 30 which encapsulates the blue and green light emitting diode chips 21 and 22 together, and the blue and green light emitting diode chips Blue light and green light emitted simultaneously from (21, 22) are absorbed simultaneously, and red light is emitted respectively. In this case, the red phosphor 31 simultaneously absorbs blue light and green light to emit red light, thereby further enhancing the red region of the white light. In addition, the sealing member 30 may further include a scattering material (not shown) having a size of 0.1 to 20 ㎛, most preferably, the scattering material, SiO ₂ , AL ₂ O ₃ , TiO ₂ , At least one selected from Y ₂ O ₃ , CaCO ₃ , MgO can be used.

2 shows a white light emitting device 1 for backlight according to another embodiment of the present invention. Referring to FIG. 2, a blue light emitting diode chip 21 and a green light emitting diode chip 22 are connected in series. The white light emitting device 1 of this embodiment follows almost all the configurations of the white light emitting device of the previous embodiment, such that the red phosphor 31 simultaneously absorbs blue and green light in the encapsulation member 30 to emit red light. . However, the white light emitting device 1 of the present embodiment, in addition to the components of the previous embodiment, is used for protecting both the blue light emitting diode chip 21 and the green light emitting diode chip 22 from static electricity. 23) is further included. In this embodiment, the zener diode 23 is located between the blue light emitting diode chip 21 and the green light emitting diode chip 22 which are connected in series, and for each of the light emitting diode chips 21, 22. It is connected in series.

Unlike the above embodiments, the blue light emitting diode chip 21 and the green light emitting diode chip 22 may be connected in parallel, as shown in the embodiment shown in FIG. 3. Also in this case, the blue light emitting diode chip 21 and the green light emitting diode chip 22 emit blue light and green light at the same time by one current flow. In FIG. 3, the first lead terminal 11, which is a (+) terminal, is connected to the electrodes of the blue and green light emitting diode chips 21 and 22 by bonding wires (W, W), and the (−) terminal. The structure in which the two lead terminals 12 are connected by different bonding wires W and W to the other electrodes of the blue and green LED chips 21 and 22 is well illustrated.

In the above embodiments, the blue light emitting diode chip 21 is an InGaN compound semiconductor, and emits blue light having a wavelength in the range of 430 to 480 nm, and the green light emitting diode chip 22 emits green light having a wavelength in the range of 500 to 560 nm. The red phosphor 31 simultaneously absorbs the above lights and emits red light having a wavelength range of 590 to 700 nm, respectively. And, when the light is emitted in the range of the above wavelength, it was confirmed through experiment that the white light of the optimal color reproducibility range can be obtained (see FIGS. 4 and 5).

In addition, the red phosphor 31 is preferably a nitride-based or sulfide-based phosphor. In particular, the red phosphor 31 has a blue and a light output change depending on temperature in order to prevent thermal or temporal color deviation. (Ca, Sr, Ba) ₂ Si ₅ N ₈ : Eu, (Mg, Ca, Sr) AlSiN ₃ : Eu, (Ca, Sr, Ba) Si ₇ N, similar to the green light emitting diode chips 21, 22. At least one selected from ₁₀ : Eu, (Ca, Sr, Ba) SiN ₂ : Eu or similar nitride-based phosphors is preferably used. Referring to FIG. 6, the change in the light output according to the temperature of the green light emitting diode chip, the blue light emitting diode chip, and the CaAlSiN ₃ : Eu red phosphor is almost similar. As a result, the light output is reduced to a large slope, and it can be seen that the light output of the blue and green LED chips is significantly different from the light output pattern with time.

 (A), (b), and (c) of FIG. 4 show that the red phosphor emitting red light by simultaneously absorbing the light of the blue light emitting diode chip, the green light emitting diode chip, and the blue and green light emitting diode chips realizes white light. 4A shows a spectrum in which a current is applied to a blue light emitting diode chip to emit blue light, and the red phosphor absorbs the blue light to emit red light. (b) shows a spectrum in which a green light is applied when a current is applied to the green light emitting diode chip, and the red phosphor absorbs the green light and emits red light. FIG. 4 (c) shows the above two cases ((a According to the features of the present invention in which both) and (b) occur simultaneously, the spectrum in the case where white light due to a mixture of blue light, green light and red light is generated is shown. At this time, the spectral height ratio of the light emitted from the blue light emitting diode chip and the light emitted from the green light emitting diode chip is preferably 1: 0.1 to 1: 1.2, and in such a range, the blue and green light emitting diodes The quality of white light (particularly color reproducibility) obtained by using a chip and a red phosphor is the best.

5 is a white light emitting device according to the present invention using a blue, a green light emitting diode chip and a red phosphor, as compared with a conventional blue light emitting diode chip and a yellow phosphor combination with the transmittance of an RGB color filter generally used in LCD TVs. The white spectrum of is shown. Referring to FIG. 5, in the case of the conventional blue light emitting diode chip and the yellow phosphor combination, the spectrum of the green and red regions is not sufficient, and the transmittance and consistency of the RGB color filter are very low, so that there is a limit in expressing green and red. Can be. On the contrary, the white spectrum of the white light emitting device according to the present invention has a sufficient spectrum of green and red as well as blue, and has high transmittance and correspondence with the RGB color filter, thereby representing a wider color gamut.

FIG. 7 shows a white spectrum of a light emitting device according to the present invention by a combination of a green and blue LED chip and a red phosphor in comparison with a conventional blue LED chip and yellow phosphor combination in a CIE 1976 color coordinate system. The color reproducing range which appears when transmitted through the RGB color filter used in FIG. Referring to FIG. 7, the color reproduction range of the white light emitting device according to the present invention is significantly improved, compared with the color reproduction range obtained through the conventional blue light emitting diode chip and the yellow phosphor. You can see that it stands out.

1 is a view showing a white light emitting device according to an embodiment of the present invention, including a configuration in which a blue light emitting diode chip and a green light emitting diode chip are connected in series.

2 is a view showing a white light emitting device for a backlight according to another embodiment of the present invention.

3 is a view illustrating a white light emitting device for a backlight according to another embodiment of the present invention in which a blue light emitting diode chip and a green light emitting diode chip are connected in series.

(A), (b) and (c) of FIG. 4 respectively show spectra of blue light emitting diode chips and red phosphors, spectra of green light emitting diode chips and red phosphors, and blue and green light emitting diode chips and red phosphors. Fig. 1 shows the spectra by respectively.

5 is a view showing a white light spectrum of the white light emitting device of the present invention, as compared with a conventional blue light emitting diode chip and yellow phosphor combination with the transmittance of an RGB color filter used in an LCD TV.

6 is a graph for comparing light output changes of LED chips and red phosphors according to temperature change.

7 is a color coordinate graph illustrating a comparison between a conventional white light emitting device and a white light emitting device of the present invention in a CIE 1976 color coordinate system.

Claims (9)

Blue light emitting diode chips; Green light emitting diode chip; And And a red phosphor that absorbs light from the blue light emitting diode chip and light from the green light emitting diode chip to emit red light. The white light emitting device of claim 1, wherein the blue light emitting diode chip and the green light emitting diode chip are encapsulated by an encapsulating member made of a light transmissive resin, and the red phosphor is dispersed in the encapsulating member.  The white light emitting device of claim 1, wherein a spectral height ratio of light emitted from the blue light emitting diode chip and light emitted from the green light emitting diode chip is 1: 0.1 to 1: 1.2. The light wavelength of the blue light emitting diode chip is 430nm ~ 480nm, the light wavelength of the green light emitting diode chip is 500 ~ 560nm, the light wavelength of the red phosphor is 590 ~ 700nm. White light emitting device. The white light emitting device of claim 1, wherein the red phosphor is a nitride-based or sulfide-based phosphor. The method of claim 1, wherein the red phosphor is (Ca, Sr, Ba) ₂ Si ₅ N ₈ : Eu, (Mg, Ca, Sr) AlSiN ₃ : Eu, (Ca, Sr, Ba) Si ₇ N ₁₀ : Eu, (Ca, Sr, Ba) at least one nitride-based phosphor selected from SiN ₂ : Eu. The white light emitting device of claim 2, further comprising a scattering material having a size of about 0.1 μm to about 20 μm in the encapsulation member. The white light emitting device of claim 7, wherein the scattering material is at least one selected from SiO ₂ , AL ₂ O ₃ , TiO ₂ , Y ₂ O ₃ , CaCO ₃ , and MgO. The white light emitting device of claim 1, wherein the blue light emitting diode chip and the green light emitting diode chip are connected in series or in parallel.

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