US20120074442A1 - Light emitting diode module - Google Patents

Abstract

A light emitting diode module having improved luminous efficiency is provided. The light emitting diode module includes: a light emitting chip; a phosphor layer formed of phosphor materials emitting light having a wavelength longer than the light emitted from the light emitting chip using light emitted from the light emitting chip as an excitation source; and a reflection plate that is disposed between the light emitting chip and the phosphor layer and that reflects the light emitted by the phosphor layer.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATION
• This application is a divisional of U.S. application Ser. No. 11/513,221, filed Aug. 31, 2006, and claims the benefit of Korean Patent Application No. 10-2006-0010179, filed on Feb. 2, 2006 in the Korean Intellectual Property Office, the entire contents of which is incorporated herein by reference.
BACKGROUND OF THE DISCLOSURE
• 1. Field of the Disclosure
• The present disclosure relates to a light emitting diode module, and more particularly, to a light emitting diode module with an improved structure providing an improved luminous efficiency for realizing white light or colored light while using a light emitting diode emitting blue or ultraviolet light and phosphor materials.
• 2. Description of the Related Art
• A light emitting diode (LED) is formed of a light emitting source using compound semiconductors, such as GaAS, AlGaN, and AlGaAs, to generate various colors of light. LEDs can be easily manufactured and controlled compared to semiconductor lasers and have longer life spans than fluorescent lamps, and thus have replaced fluorescent lamps as the illumination light sources for next generation display devices. Recently, blue light emitting diodes and ultraviolet light emitting diodes which are produced using nitride materials and having excellent physical and chemical characteristics, have been introduced. In addition, as white light and other colors can be produced using blue or ultraviolet light emitting diodes together with phosphor materials, the application range of light emitting diodes has been enlarged.
• LED modules using phosphor materials produce white light or other colors of light according to the principle that light emitted from the blue or ultraviolet light emitting diode and incident on the phosphor material transmits energy to the phosphor material, and thus light with a longer wavelength than incident light is emitted. For example, in a white light emitting diode module, photons of ultraviolet light emitted from the LED chip excite the phosphor material and thus a combination of red, green, and blue light or a combination of yellow and blue light is emitted from the excited phosphor material. The wavelengths of the visible light emitted from the phosphor material vary according to the composition of the phosphor material, and this combination of visible light appears as white light to human eyes.
• FIG. 1 is a schematic view of a conventional LED module. Referring toFIG. 1, in the LED module, a light emitting chip1 is disposed in a concave recess on abase6, afirst resin layer3 is coated inside thebase6, and asecond resin layer4 and athird resin layer5 are coated sequentially on top of thefirst resin layer3.
• However, in the configuration described above, the light extraction efficiency is low. Light extraction efficiency refers to the ratio of the amount of the light generated in the light emitting chips1 to the amount of the light actually emitted from the LED module, and is directly related to the luminous efficiency, which denotes the illuminating performance of the LED module.
• FIG. 2 illustrates the path of the light emitted by excited phosphor layers in the structure of the LED module ofFIG. 1. Referring toFIG. 2, the light is emitted by the excited phosphor materials over 360°. Accordingly, light that is not fully emitted outward and is instead emitted in the downward direction ofFIG. 2 is thus counted as loss resulting in a decrease in the luminous efficiency of the LED module.
SUMMARY OF THE DISCLOSURE
• The present invention may provide a light emitting diode (LED) module with a structure having high luminous efficiency.
• According to an aspect of the present invention, there may be provided a light emitting diode module comprising: a light emitting chip; a phosphor layer formed of phosphor materials emitting light having a longer wavelength than the light emitted from the light emitting chip using light emitted from the light emitting chip as an excitation source; and a reflection plate that is disposed between the light emitting chip and the phosphor layer, and that reflects the light emitted from the phosphor layer.
BRIEF DESCRIPTION OF THE DRAWINGS
• The above and other features and advantages of the present invention are illustrated in detailed exemplary embodiments thereof with reference to the attached drawings in which:
• FIG. 1 is a cross-sectional view of a conventional light emitting diode (LED) module;
• FIG. 2 is a schematic view illustrating directions of light emitted from a phosphor layer in the conventional LED module ofFIG. 1;
• FIG. 3 is a cross-sectional view of an LED module according to an embodiment of the present invention;
• FIGS. 4A through 4D are perspective views illustrating reflection plates according to various embodiments of the present invention; and
• FIG. 5 is a schematic view illustrating light that is emitted from the phosphor layer of the LED module ofFIG. 3.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
• The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.
• FIG. 3 is a cross-sectional view of an LED module according to an embodiment of the present invention; andFIGS. 4A through 4D illustrate a number of reflection plates according to various embodiments of the present invention.
• Referring toFIG. 3, the LED module includes alight emitting chip22, aphosphor layer25 using the light emitted from thelight emitting chip22 as an excitation source and emitting light of a longer wavelength than the light emitted from thelight emitting chip22, and areflection plate28 that is disposed between thephosphor layer25 and thelight emitting chip22 and reflects the light emitted in the downward direction ofFIG. 3 by theexcited phosphor layer25.
• Thelight emitting chip22 is disposed on asubmount34 that is mounted in a dispensingmember33 having a cup-shapedinner surface33a. Afirst lead frame37 and asecond lead frame40 are fixed in the lower portion of the dispensingmember33 and protrude from the dispensingmember33.
• Thefirst lead frame37 and thesecond lead frame40 are electrically connected to an n-electrode and a p-electrode of thelight emitting chip22 respectively.
• Thelight emitting chip22 includes a p-type semiconductor layer and an n-type semiconductor layer. When power is supplied through the first andsecond lead frames37 and40 between the n-electrode and the p-electrode, holes of the p-type semiconductor layer and electrons of the n-type semiconductor layer are combined in an active layer and thus light is generated Light is therefore emitted from thelight emitting chip22.
• The wavelength of light generated in thelight emitting chip22 is determined according to the material and structure of the active layer, and according to the wavelength of light that is to be realized by the LED module.
• The light generated and emitted by thelight emitting chip22 is transmitted through thereflection plate28 and is incident on thephosphor layer25 formed of a phosphor material. The incident light transmits energy to and excites the phosphor material, thereby changing the color of the light. Essentially, white light or other colors of monochromic light can be produced by the proper combination of thelight emitting chip22 and thephosphor layer25 in the LED module.
• For example, in one method of realizing white light, thelight emitting chip22 generates blue light, and thephosphor layer25 is formed of a yellow phosphor material. Alternatively, thelight emitting chip22 generates ultraviolet light, and thephosphor layer25 is formed of a mixture of red, green, and blue phosphor materials.
• Also, thelight emitting chip22 can generate ultraviolet or blue light, and thephosphor layer25 can be formed of a single color phosphor material such that an LED module emitting light of a single color having a longer wavelength than the light generated in thelight emitting chip22 can be produced.
• Thereflection plate28 is disposed between thelight emitting chip22 and thephosphor layer25, and a concavo-convex pattern is formed on the upper surface of thereflection plate28 facing thephosphor layer25.
• Referring toFIG. 4A, the concavo-convex pattern is a pattern of concave rectangular cavities. The concavo-convex pattern ofFIG. 4 is illustrated as an example, and the pattern may be convex or have other forms. For example, as illustrated inFIG. 4B, areflection plate29 with a concavo-convex pattern of concave hemispheres can be employed. The concave-convex pattern in a preferred embodiment can be a hemispherical array or a polygonal cavity array.
• The concavo-convex pattern may be formed on the upper surface of thereflection plate28 or29 facing the phosphor layer or on the lower surface of thereflection plate28 or29 facing thelight emitting chip22.
• Afirst resin layer43 may be formed between thelight emitting chip22 and thereflection plate28 or29. Thefirst resin layer43 protects thelight emitting chip22 and reduces the difference between the refractive index of thelight emitting chip22 and the refractive index of the region into which the light is emitted from thelight emitting chip22. As the refractive index of thefirst resin layer43 is similar to the refractive index of thelight emitting chip22, the amount of the light that is totally internally reflected at aboundary surface22aof thelight emitting chip22 is decreased, thus increasing the amount of the light that is emitted out of thelight emitting chip22.
• Asecond resin layer46 may be included between thereflection plate28 or29 and thephosphor layer25.
• Some light may be internally totally reflected at a surface where a concavo-convex pattern is not formed depending on the incidence angle, which may reduce the amount of light emitted from the LED module and thus reduce the luminous efficiency. Accordingly, when a concavo-convex pattern is formed only on the upper surface of thereflection plate28 or29 facing thephosphor layer25 and the lower surface of thereflection plate28 or29 facing thelight emitting chip22 is flat, the refractive index of thefirst resin layer43 may preferably be smaller than the refractive index of thereflection plate28 or29.
• Also, when a concavo-convex pattern is formed only on the lower surface of thereflection plate28 or29 facing thelight emitting chip22 and the surface of thereflection plate28 or29 facing thephosphor layer25 is flat, the refractive index of thesecond resin layer46 may preferably be greater than the refractive index of thereflection plate28 or29.
• Referring toFIG. 4C, areflection plate30 may have a flat upper surface facing thephosphor layer25 and a flat lower surface facing thelight emitting chip22. In this case, the refractive index of thefirst resin layer43 may be smaller than the refractive index of thereflection plate30, and the refractive index of thesecond resin layer46 may be greater than the refractive index of thereflection plate30 in order to reduce the loss of the light emitted from thelight emitting chip22 due to total internal reflection of some of the light at two boundary surfaces of thereflection plate30. Also, this relatively higher refractive index of thesecond resin layer46 is preferable in consideration of the light emitted from theexcited phosphor layer25 since the amount of the light that is reflected back towards thephosphor layer25 by thereflection plate30 increases.
• Referring toFIG. 4D, areflection plate31 may be formed of multiple layers of different materials having different refractive indices. In this instance, the refractive index of the layer that is disposed closer to thephosphor layer25 may preferably be greater. Thus, as described above, for the light emitted from thelight emitting chip22 and transmitted through thereflection plate31 and through the phosphor layer and emitted from the LED module, the loss due to the total internal reflection is minimized and for the light emitted from thephosphor layer25, the amount of light that is reflected back toward thephosphor layer25 is increased.
• FIG. 5 is a schematic view illustrating the light emitted from thelight emitting chip22 and the light emitted from theexcited phosphor layer25. Referring toFIG. 5, the light emitted from thelight emitting chip22 is transmitted through thereflection plate28 and is incident on thephosphor layer25.
• The light incident on thephosphor layer25 transmits energy to the phosphor materials, and consequently light having a longer wavelength than the incident light is emitted. The light is emitted in all directions above and below thephosphor layer25. Thereflection plate28, disposed between thephosphor layer25 and thelight emitting chip22, reflects the light which is not emitted from the LED module by thephosphor layer25 but which is incident on thereflection plate28 back towards thephosphor layer25, thereby increasing the luminous efficiency.
• Also, the concavo-convex pattern formed on thereflection plate28 effectively diverges the light emitted by thephosphor layer25 so as to emit the light from the LED module, which is preferred. The material forming thereflection plate28, or the size and arrangement periods of the cavities of the concavo-convex pattern may be determined according to the wavelength of the light emitted from thelight emitting chip22 and the wavelength of the light emitted from thephosphor layer25 or other related properties.
• Examples of materials which can form thereflection plates28 through31 are SiO₂, Al₂O₃, AlN, and ZnSe.
• Table 1 shows a comparison between the illumination efficiency of an LED module according to an embodiment of the present invention and the illumination efficiency of a conventional LED module.

• TABLE 1
  			Brightness	Illumination
  	Current (A)	Power (W)	(lm)	Efficiency (lm/W)

  Present	0.35	0.151	32.96	26.6
  Embodiment
  Comparative	0.35	0.097	27.99	22.7
  Example

• The LED modules used to obtain these results included a light emitting chip emitting light of a wavelength of around 400 nm and a phosphor layer formed of a mixture of red, green, and blue phosphor materials. The first and second resin layers were formed of silicon resin, and the concavo-convex pattern of the reflection plate was the same as the pattern ofFIG. 4B. The light emitted from the light emitting chip was incident on the phosphor layer and excited the phosphors to emit red, blue, and green light, which were used to realize white light.
• Luminous efficiency is used as an index denoting the illuminating performance of the LED module, which refers to the brightness sensed by a human eye per watt of supplied power, the brightness being measured in units of lumens (lm). The luminous efficiency of the LED module according to the present embodiment was 26.6 lm/W and the luminous efficiency of the conventional LED module was 22.7 lm/W. Thus the LED module according to the present embodiment had a luminous efficiency that was 17% higher than the luminous efficiency of the conventional LED module.
• In the LED module described above according to the present invention, a reflection plate reflecting the light emitted from the phosphor layer between the phosphor layer and the light emitting chip is used to improve the luminous efficiency of an LED module for realizing white light or single color light using a light emitting chip and a phosphor layer. Also, a fine concavo-convex pattern is formed on at least one surface of the reflection plate to increase the luminous efficiency.
• While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims (4)

1. A light emitting diode module comprising:

a light emitting chip;

a phosphor layer formed of phosphor materials emitting light having a longer wavelength than the light emitted from the light emitting chip using light emitted from the light emitting chip as an excitation source; and

a reflection plate that is disposed between the light emitting chip and the phosphor layer, and that reflects light emitted from the phosphor layer,

wherein a concavo-convex pattern is formed on the surface of the reflection plate which faces the light emitting chip.

2. The light emitting diode module of1, wherein the concavo-convex pattern is a hemispherical array or a polygonal cavity array.

3. The light emitting diode module ofclaim 1, further comprising a resin layer that has a refractive index greater than the refractive index of the reflection plate and is formed between the reflection plate and the phosphor layer.

4. The light emitting diode module ofclaim 1, wherein the reflection plate is formed of a material selected from the group consisting of SiO₂, Al₂O₃, AlN, and ZnSe.

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