WO2005013380A1

WO2005013380A1 - Semiconductor led device

Info

Publication number: WO2005013380A1
Application number: PCT/KR2004/001925
Authority: WO
Inventors: Tae Kyung Yoo; Chang Tae Kim
Original assignee: Epivalley Co., Ltd.
Priority date: 2003-07-30
Filing date: 2004-07-30
Publication date: 2005-02-10
Also published as: KR20050014341A; KR100586678B1

Abstract

The present invention relates to a semiconductor LED device for producing a white light using a plurality of LEDs and provides for a semiconductor LED device comprising a red LED and a diode connected serially to the red LED, a blue LED connected in parallel to the serially connected red LED and diode, a green LED connected in parallel to the serially connected red LED and diode and to the blue LED; and one driving voltage for operating the serially connected red LED and diode, the blue LED and the green LED, thereby a semiconductor LED device emitting a white light which is operated by one driving voltage in a package is provided.

Description

SEMICONDUCTOR LED DEVICE

[Technical Field] The present invention relates to a semiconductor LED (Light Emitting Diode) device for producing a multiwavelength light source by using a single driving voltage and a l ow voltage as well as red, blue and green LEDs, and more particularly, to a semiconductor LED device for implementing a multiwavelength light source by serially connecting a red LED element having a low driving voltage to a silicon diode having a much lower driving voltage than the red LED, connecting a blue LED element to the serially connected red LED element and silicon diode in parallel, connecting a green LED element to the serially connected red LED element and silicon diode, and packaging these diodes so as to operate at the same driving voltage.

[Background Art] In general, there have been proposed five methods for obtaining a white light source using LEDs. The first method uses an LED for emitting ultraviolet (UV) light, and a phosphor material for emitting red, green and blue lights by absorbing energy from the LED. By this method, reproducible white light with a high color rendering index can be acquired and it is easy to manufacture the device. However, there may be skin d amage caused by the ultraviolet light and it is hard to achieve the LED with high efficiency. The second method, which is the most widely used method, uses a blue LED and a yellow phosphor material to obtain reproducible white light. However, the white light obtained by this method exhibits a low color rendering index and it is difficult to obtain the phosphor having high efficiency. The third method utilizes a blue LED and blue and green phosphor materials. In t his case, white light having various color temperatures can be obtained. The fourth method uses red, green and blue LEDs. By this m ethod, light efficiency is higher than the method using blue LED and the phosphor material. Moreover, white light obtained by this method has high reliability, a high color rendering index, and light quality similar to solar light. However, since a driving voltage of the red LED is remarkably lower than that of the blue or green LED, separate d riving voltages should be applied to the respective LEDs. Therefore, a circuit configuration becomes complicated. In the fifth method, two LEDs with complementary colors, that is, a yellow LED and a cyan LED are used. The white light source obtained by this method has high reliability and higher light efficiency than that obtained by the method using the blue LED and the phosphor material, but it has a low color rendering index. FIG. 1 illustrates a circuit diagram of a conventional LED device. Blue

LEDs and a yellow phosphor material are used to obtain white light having a high o utput. Three blue LEDs are connected i n parallel to one a nother. T he blue LEDs connected in parallel to one another are assembled into a package as illustrated in FIG. 2. A circuit of connecting three LEDs in parallel is used in, for example, a camera flash of a cellular phone. This L ED circuit has a low driving voltage of about 3.1 volts and it is convenient to use because its voltage is lower than a voltage of a battery of a generally used cellular phone. As can be seen in a package structure of FIG. 2, a blue LED chip 12 is located on a substrate 10 of the package. Although not shown in the drawing, the blue LED chip 12 is electrically connected to a metal pad on the substrate 10 through an electrode pad on the chip using bonding wire. Light emitted from the blue LED chip 12 proceeds to an epoxy 13 including a phosphor material. A part of the light is absorbed into the phosphor material to produce yellow light and the other part of the light is emitted to the exterior. FIG. 3 illustrates a light output for a light wavelength of white light obtained by the method shown in FIG. 2. Generally, a mixed light can be obtained by combining a primary wavelength light with a secondary wavelength light. If they form a complementary color relation, white light can be obtained only the mixture of the two light wavelengths. For example, if a phosphor material including YAG is exited by a blue wavelength (450 nm) LED to generate a yellow wavelength (590 nm) which is a complementary color of the 450 wavelength, it is possible to make white LED by the mixture of the two 450 nm and 590 nm wavelengths. In this case, a color temperature can be adjusted by tuning the yellow wavelength through modifying components of the YAG phosphor layer, and white light in which the proportion of light intensity of the two light wavelengths is adjusted can be obtained by adjusting the thickness of the phosphor layer. Although this method is easily performed, the reliability of the phosphor material is not stable in comparison with a semiconductor device. Therefore, a color may vary according to used time, or efficiency may deteriorate. Moreover, since the efficiency of the phosphor material is low, the efficiency of the white light deteriorates and a color rendering index is also low.

[Disclosure]

[Technical Problem] It is an object of the present invention to provide a semiconductor LED device which has high light efficiency in comparison with a conventional method using a blue LED and a phosphor material, and has superior reliability and a high color rendering index to obtain light quality similar to natural light.

[Technical Solution] According to an aspect of the present invention, a semiconductor LED device includes a diode, a first LED connected serially to the diode, for emitting a first color, a second LED connected in parallel to the diode and the first diode serially connected to the d iode, for emitting a second color, and one driving voltage for operating the serially connected first LED and diode and the second

LED. Preferably, the first LED and the second LED emit complementary colors to produce white light. Preferably, the semiconductor LED device further includes a third LED driven by the driving voltage, for emitting a third color. Preferably, the first, second and third LEDs produce white light by their combination, and preferably, the first, second and third LEDs emit red, blue and green light, respectively. Preferably, the first color of the first LED is amber and an operating voltage of the first LED is 1.0 - 2.5 volts at a current of 20 mA. Preferably, t he d iode i s a s ilicon p -n or p-i-n d iode a nd i ts o perating voltage is 0.5 - 2.5 volts at a current of 20 mA. Preferably, the diode is a silicon Schottky diode and its operating voltage is 0.5 - 2.5 volts at a current of 20 mA. Preferably, the diode is a GaAs-based p-n or p-i-n diode and its operating voltage is 0.5 - 2.5 volts at a current of 20 mA. Preferably, the diode is a GaAs-based Schottky diode and its operating voltage is 0.5 - 2.5 volts at a current of 20 mA. Preferably, the second color of the second LED is cyan and the operating voltage of the second LED is 2.5 - 5 volts at a current of 20 mA. According to another aspect of the present invention, a semiconductor LED device includes a red LED and a diode which is connected serially to the red LED, a blue LED connected in parallel to the serially connected red LED and diode, a green LED connected in parallel to the serially connected red LED and diode and to the blue LED, and one driving voltage for operating the serially connected red LED and diode, the blue LED and the green LED. Preferably, the red, blue and green LEDs have different light intensity and form white light by a combination of the different light intensity. Preferably, an operating voltage of the red LED is 1.0 - 2.5 volts at a current of 20 mA. Preferably, t he d iode i s a s ilicon p -n or p-i-n d iode a nd i ts o perating voltage is 0.5 - 2.5 volts at a current of 20 mA. Preferably, the diode is a silicon Schottky diode and its operating voltage is 0.5 - 2.5 volts at a current of 20 mA. Preferably, the diode is a GaAs-based p-n or p-i-n diode and its operating voltage is 0.5 - 2.5 volts at a current of 20 mA. Preferably, the diode is a GaAs-based Schottky diode and its operating voltage is 0.5 - 2.5 volts at a current of 20 mA. Preferably, an operating voltage of the blue LED is 2.5 - 5 volts at a current of 20 mA. Preferably, an operating voltage of the green LED is 2.5 - 5 volts at a current of 20 mA. Preferably, the red, blue and green LEDs have different light intensity and form a light source emitting a color by a combination of the different light intensity. Preferably, the semiconductor LED device further includes a silicon sub-mount wherein the diode is installed within the silicon sub-mount, and the blue and green LEDs are formed on the silicon sub-mount by a flip chip bonding method. [Advantageous Effects] There is provided a semiconductor LED device for achieving a multiwavelength light source by a package so as to operate at one driving voltage. The semiconductor LED device has high light efficiency in comparison with a conventional method u sing a b lue L ED a nd a p hosphor m aterial, a nd has superior reliability and a high color rendering index to obtain light quality similar to natural light.

[Description of Drawings] Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which: FIG. 1 is a circuit diagram illustrating an LED device in which blue LEDs are connected in parallel to one another; FIG. 2 is a schematic view illustrating a white light source device using blue LEDs and a phosphor material; FIG. 3 is a graph illustrating a wavelength-light intensity characteristic of a white LED using a phosphor; FIG. 4 is a circuit diagram illustrating an LED device in which a red LED, a silicon diode, a blue LED and a green LED are connected according to one embodiment of the present invention; FIG. 5 is a graph illustrating current-voltage characteristics of a red

LED, a silicon diode, a blue LED and a green LED used in the present invention; FIG. 6 is a graph illustrating current-voltage characteristics of a serially connected a red LED and silicon diode and of a single blue or green LED according to the present invention; FIG. 7 is a graph illustrating light intensity for red, blue and green wavelengths according to the present invention; FIG. 8 is a graph illustrating a color coordinate; FIG. 9 is a circuit diagram illustrating an LED device according to another embodiment of the present invention; and FIG. 10 is a diagram illustrating an LED device according to still another embodiment of the present invention.

[Mode for Invention] The present invention will now be described in detail in connection with preferred embodiments with reference to the accompanying drawings. For reference, like reference characters designate corresponding parts throughout several views. Referring to FIG. 4, there is shown a multiwavelength LED device according to the present invention. A red LED having a low operating voltage is serially connected to a p-n diode to raise an operating voltage of an entire circuit. A blue LED and a green LED each having a high operating voltage are connected i n parallel t o t he s erially connected r ed L ED and p -n diode t o be driven at t he s ame o perating v oltage. These e lements are a ssembled i nto a single package to obtain various colors by appropriately adjusting the brightness of each LED. FIG. 5 illustrates current-voltage characteristics of the respective LEDs and the p-n diode shown in FIG. 4. A reference numeral 40 denotes a current-voltage characteristic of an AIGalnN-based green LED. A typical operating voltage at a current of 20 mA is in a range from 2.9 to 4.0 volts. A reference numeral 41 denotes a current-voltage characteristic of an AIGalnN-based blue LED showing an operating voltage in a range from 2.9 to 4.0 volts at 20 mA. The blue LED has the same operating voltage as the green LED. A reference numeral 42 designates a current-voltage characteristic of an AIGalnP-based red LED. A typical operating voltage of the AIGalnP-based red LED at 20 mA ranges from 1.5 to 2.5 volts. As described above, since the red LED has an operating voltage much lower than the green or blue LED, it can't be u sed at the s ame driving voltage as the g reen or blue L ED. A reference numeral 53 denotes a current-voltage characteristic of a silicon-based diode having an operating voltage at 20 mA in a range from 0.8 to 1.5 volts. As the silicon-based diode, a GaAs-based p-n diode, a Schottky diode, or a silicon-based Schottky diode can be used. Referring to FIG. 6, a reference numeral 51 indicates a current-voltage characteristic of the serially connected AIGalnP-based red LED and silicon-based p-n diode having an operating v oltage of 3.02 volts at 20 mA. Meanwhile, an operating voltage of an AIGalnN-based blue LED is 3.05 volts as indicated by a reference numeral 50. When comparing these two curves, it can be seen that it is possible to operate the serially connected AIGalnP-based red LED and silicon-based p-n diode and the blue LED at the same driving voltage. As shown, even though an operating voltage varies, since an operating current varies at a s imilar rate, they c an b e o perated at the same driving voltage. FIG. 7 illustrates light intensity for red, blue and green LEDs according to the present invention. Various colors can be obtained by adjusting the ratio of light intensity to each wavelength and a white LED can also be obtained. FIG. 8 illustrates a color coordinate. Red, blue and green colors are shown on the color coordinate. When an LED of a coordinate (x1, y1) around a wavelength of 470 nm is combined with an LED of a coordinate (x2, y2) around a wavelength of 560 nm, light of a color of a coordinate^, y) can be produced.

A white LED region is also indicated. Referring to FIG. 9, an example for obtaining a white LED is shown. An AIGalnP-based amber LED is serially connected to a silicon-based p-n diode. An AIGalnN-based cyan LED is connected in parallel to the serially connected amber LED and p-n diode. This device uses a complementary color to obtain high reliability and high light efficiency in comparison with the conventional device in which a blue LED and a phosphor material are used. Referring to FIG. 10, there is shown a semiconductor LED device according to still another embodiment of the present invention. A red LED, a blue LED and a green LED are mounted by a flip chip bonding process on a silicon sub-mount 100 having a p-n or p-i-n diode therein. The red LED is serially connected to the diode within the silicon sub-mount. The blue LED is connected in parallel to the serially connected two elements through a bump 101. The green LED is also connected in the same way as the blue LED. Thus each LED operates at the same driving voltage, and light generated from the blue and green LEDs is effectively emitted. While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.

Claims

1. A semiconductor LED deivce compirising: a red LED(Light Emitting Diode) and a diode which is connected serially to the red LED; a blue LED connected in parallel to the serially connected red LED and diode; a green LED connected in parallel to the serially connected red LED and diode and to the blue LED; and a driving voltage for operating the serially connected red LED and diode, the blue LED and the green LED.

2. The semiconductor LED device of claim 1 , wherein the red, blue and green LEDs have different light intensity and form white light by a combination of the different light intensity.

3. The semiconductor LED device of claim 1 , wherein the operating voltage of the red LED is 1.0 - 2.5 volts at a current of 20 mA.

4. The semiconductor LED device of claim 1 , wherein the diode is a silicon p-n o r p-i-n diode and the operating voltage of the diode is 0.5 - 2.5 volts at a current of 20 mA.

5. The semiconductor LED device of claim 1 , wherein the diode is a silicon Schottky diode and the operating voltage of the diode is 0.5 - 2.5 volts at a current of 20 mA.

6. The semiconductor LED device of claim 1 , wherein the diode is a

GaAs-based p-n or p-i-n diode and the operating voltage of the diode is 0.5 - 2.5 volts at a current of 20 mA.

7. The semiconductor LED device of claim 1, wherein the diode is a GaAs-based Schottky diode and the operating voltage of the diode is 0.5 - 2.5 volts at a current of 20 mA.

8. The semiconductor LED device of claim 1, wherein the operating voltage of the blue LED is 2.5 - 5 volts at a current of 20 mA.

9. The semiconductor LED device of claim 1, wherein the operating voltage of the green LED is 2.5 - 5 volts at a current of 20 mA.

10. The semiconductor LED device of claim 1 , wherein the red, blue and green LEDs have different light intensity and form a light source emitting a color by a combination of the different light intensity.

11. The semiconductor LED device of claim 1 further comprising: a silicon sub-mount wherein the diode is installed within the silicon sub-mount, and the blue and green LEDs are formed on the silicon sub-mount by a flip chip bonding method.

5 12. A semiconductor LED device comprising: a diode; a first LED(Light Emitting Diode) connected serially to the diode, for emitting a first color; a second LED connected in parallel to the serially conneted diode and0 first diode, for emitting a second color; and a driving voltage for operating the serially connected diode and first LED and the second LED.

13. The semiconductor LED device of claim 12, wherein the first and5 second LEDs have different light intensity and form a light source emitting a white light.

14. The semiconductor LED device of claim 12, wherein the first color of the first LED is amber and the operating voltage of the first LED is 1.0 - 2.5 o volts at a current of 20 mA.

15. The semiconductor LED device of claim 12, wherein the diode is a silicon p-n o r p-i-n diode and the operating voltage of the diode is 0.5 - 2.5 volts at a current of 20 mA.

16. The semiconductor LED device of claim 12, wherein the diode is a silicon Schottky diode and the operating voltage of the diode is 0.5 - 2.5 volts at a current of 20 mA.

17. The semiconductor LED device of claim 12, wherein, the diode is a GaAs-based p-n or p-i-n diode and the operating voltage of the diode is 0.5 - 2.5 volts at a current of 20 mA.

18. The semiconductor LED device of claim 12, wherein the diode is a GaAs-based Schottky diode and the operating voltage of the diode is 0.5 - 2.5 volts at a current of 20 mA.

19. The s emiconductor LED device of claim 12, wherein the s econd color of the second LED is cyan and the operating voltage of the second LED is 2.5 - 5 volts at a current of 20 mA.

20. The semiconductor LED device of claim 12, wherein the first LED and the second LED emit complementary colors to produce white light.

21. The semiconductor LED device of claim 12 furtehr comprising: a silicon sub-mount wherein the diode is installed within the silicon sub-mount, and the second LED is formed on the silicon sub-mount by a flip chip bonding method.

22. The semiconductor LED device of claim 12 further comprising: a third LED for emitting a third color, the third LED operated by the driving voltage.