Abstract:
A method for fabricating a high efficiency lighting device and the structure thereof are disclosed. The method includes the following steps: providing a light emitting diode structure; attaching a distributed-Bragg reflecting layer (DBR) to the light emitting diode structure by vapor deposition; and connecting the light emitting diode structure to a eutectic layer through the distributed-Bragg reflecting layer to form the high efficiency lighting device.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method of forming a high efficiency lighting device and a structure thereof, and more particularly, to a high efficiency lighting device having a distributed-Bragg reflecting layer (DBR) for increasing the extraction efficiency thereof. 
       BACKGROUND OF THE INVENTION 
       [0002]    With the advancement of epitaxy technology and reduction of manufacture costs, use of light emitting diodes (LEDs) has been gradually introduced to various fields. For example, LEDs have seen use in electronic devices such as mobile phones, multimedia players, PDAs, etc. It is expected that such use will be expended to the general lighting system to replace many conventional lighting devices. 
         [0003]    In popularizing the use of light emitting diodes, one important issue, among others, is to increase the lighting efficiency of LEDs to a highest achievable level. Given that, reducing absorbance and attenuation of light generated by LEDs would be a critical area for improvement. 
         [0004]    In a conventional LED structure, a metal reflecting mirror is used to reduce light attenuation and increase lighting efficiency. For example, in manufacture process where silver paste binding technology is replaced by eutectic, because the gold/tin thin film used tends to absorb light, hence reducing lighting efficiency, a metal reflecting mirror is used at the back side of a LED to lessen the extent of light absorbance. Referring to  FIG. 1 , a lighting device  100  of conventional technology is shown. The lighting device  100  has a light emitting diode structure  110 , a titanium (Ti) layer  120 , an aluminum (Al) layer  130  and a gold/tin (Au/Sn) alloy layer  140 . In the conventional lighting device  100 , the titanium layer  120  of thickness around 10 Å (angatroms) and the aluminum layer  130  of thickness around 2000 Å are used as a metal reflecting layer, whereas the gold/tin alloy layer  140  is used for eutectic binding process, or eutectic welding. However, in structures that employ conventional metal reflecting layers, such as the titanium layer  120  and the aluminum layer  130  shown in  FIG. 1 , the reflectivity rendered is not satisfactory, and particularly, the low reflectivity at the Ultra-Violet (UV) band undermines their applicability. Furthermore, the metal reflective thin film affects the reflectivity due to different vapor deposition conditions, resulting in difficulty in assuring the device quality. 
         [0005]    Therefore, it is desirable to have a high efficiency lighting device with increased lighting and heat dissipating efficiency of the composing elements thereof. 
       SUMMARY OF THE INVENTION 
       [0006]    According to an aspect of the present invention, there is provided a high efficiency lighting device, which utilizes a distributed-Bragg reflecting layer to improve problems caused by undesirable light absorbance and poor reflectivity of the metal reflecting layer thin film in the conventional technology. 
         [0007]    According to another aspect of the present invention, there is provided a high efficiency lighting device, of which the reflectivity is not affected by vapor deposition conditions and which increases the light extraction efficiency. 
         [0008]    According to yet another aspect of the present invention, there is provided a high efficiency lighting device, in which the distributed-Bragg reflector layer has a micro-contact layer array to increase the heat dissipating efficiency of the lighting device. 
         [0009]    In one embodiment of the present invention, a method of fabricating a high efficiency lighting device includes the following steps: providing a light emitting diode structure; attaching a distributed-Bragg reflecting layer (DBR) to the light emitting diode structure by vapor deposition; and connecting the light emitting diode structure to an eutectic layer through the distributed-Bragg reflecting layer to form the high efficiency lighting device. Furthermore, the step of forming the distributed-Bragg reflecting layer may further comprise forming multiple high refraction layers and low refraction layers in an alternating manner, so as to form a stacked thin film having an alternate high/low refraction pattern, or still more, forming a micro-contact layer array in the stacked thin film, to increase the heat dissipating efficiency of materials used. 
         [0010]    The following materials, but not limited to those, may be selectively used in the lighting device of the present invention: titanium dioxide for the high refraction layers, silicon dioxide layers for the low refraction layers, a metal material for the micro-contact layer, and gold/tin alloy for the eutectic layer. 
         [0011]    In another embodiment of the present invention, a high efficiency lighting device includes the following components: a light emitting diode structure; an eutectic layer; and a distributed-Bragg reflecting layer between the light emitting diode structure and the eutectic layer, the distributed Bragg reflecting layer being attached to the light emitting diode structure by vapor deposition. The distributed-Bragg reflecting layer may further include multiple high refraction layers and multiple low refraction layers, wherein said high refraction and said low refraction layers are arranged in an alternating manner, so as to form a stacked thin film having an alternate high/low refraction pattern. Moreover, the distributed-Bragg reflecting layer may further include a micro-contact layer array in the stacked thin film. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1 . shows a lighting device according to the conventional technology. 
           [0013]      FIG. 2 . shows a schematic diagram of a lighting device according to an embodiment of the present invention. 
           [0014]      FIG. 3 . shows a schematic diagram of the distributed-Bragg reflecting layer of  FIG. 2 . 
           [0015]      FIG. 4 . shows a schematic diagram of a lighting device according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIG. 2  shows a schematic diagram of a lighting device  200  according to an embodiment of the present invention. The high efficiency lighting device  200  comprises a light emitting diode structure  220 , a distributed-Bragg reflecting (DBR hereinafter) layer  240  and a eutectic layer  260 . The DBR layer  240  is between the light emitting diode structure  220  and the eutectic layer  260 . In the manufacture process of fabricating the high efficiency lighting device  200 , the light emitting diode structure  220  is first provided. The present invention is applicable to any conventional light emitting diodes, for example, InGaN-based high brightness light emitting diodes, but not limited to those. 
         [0017]    Next, the DBR layer  240  is attached to the light emitting diode structure  220  through vapor deposition, so as to replace the conventional metal reflecting layer and the inherent poor reflectivity thereof. Applying the DBR layer  240  enables the reflectivity of the lighting device  200  to greatly increase to above 90%, and preferably, to almost 100%. At last, via the distributed-Bragg reflecting layer  240 , the light emitting diode structure  220  is connected to the eutectic layer  260  to form the high efficiency lighting device  200 . 
         [0018]    In this embodiment, the eutectic layer  260  is a gold/tin alloy layer, which serves in place of the conventional silver paste binding process, thereby tremendously resolving the heat dissipation issue of dice. However, it is to be noted that the present invention is not limited to the use of gold/tin alloy. Furthermore, in this embodiment, the thickness of the eutectic layer  260  is around 1.5 micrometers, but to which the present invention is not limited. 
         [0019]    Now referring to  FIG. 3 , which further shows the DBR layer  240  of  FIG. 2 . The DBR layer  240  has multiple high refraction layers  240  and multiple low refraction layers  244 . The high refraction layers  242  referred to herein, compared to the low refraction layers  244 , are formed using materials with a higher refractive index. By contrast, the low refraction layers  244  are formed using materials with a lower refractive index compared to the high refraction layers  242 . 
         [0020]    As shown in  FIG. 3 , the multiple high refraction layers  242  and the multiple low refraction layers  244  are formed in an alternating manner, so as to form a stacked film having an alternate high/low refraction pattern. The high-refractive-index materials and the low-refractive-index materials are used in manufacturing the stacked film to form the DBR  240  with high reflectivity, thereby increasing the lighting efficiency of the light emitting diodes undergone eutectic processing. 
         [0021]    It is to be noted that the figures used herein are merely exemplary, and the present invention in itself may contain more different modifications and variations. For example, the DBR layer  240  is not limited to having four layers as shown in  FIG. 3 , but may have more and fewer stacked layers depending on in-field implementation conditions. Furthermore, in this embodiment, the multiple high refraction layers  242  are titanium dioxide layers, whereas the multiple low refraction layers  244  are silicon dioxide layers. The present invention is not limited to these materials. 
         [0022]      FIG. 4  shows a schematic diagram of a lighting device  400  according to another embodiment of the present invention. The high efficiency lighting device  400  includes a light emitting diode structure  420 , a DBR layer  440  and an eutectic layer  460 . The DBR layer  440  is between the light emitting diode structure  420  and the eutectic layer  460 . In the manufacture process of fabricating the high efficiency lighting device  400 , the light emitting diode structure  420  is first provided. The present invention is applicable to any conventional light emitting diodes, for example, InGaN-based high brightness light emitting diodes, but not limited to those. 
         [0023]    In the present embodiment, the DBR layer  440  has multiple high refraction layers  442 , multiple low refraction layers  444  and a micro-contact layer array  445 . As shown in  FIG. 4 , the multiple high refraction layers  442  and the multiple low refraction layers  444  are formed in an alternating manner, so as to form a stacked film having an alternate high/low refraction pattern. The high-refractive-index materials and the low-refractive-index materials are used in manufacturing the stacked film to form the DBR  240  with high reflectivity, thereby increasing the lighting efficiency of the light emitting diodes undergone eutectic processing. 
         [0024]    The micro-contact array  445  is connected to the light emitting diode structure  420  and the eutectic layer  460  to increase the heat dissipating efficiency of the components. For the sake of figurative clarity and convenience, the embodiment the micro-contact array  445  is composed of two micro-contact layers, though the present invention is not limited to this. In the present invention, more or fewer micro-contact layers may also be used to form the micro-contact array  445 . Furthermore, the micro-contact array  445  may employ any metal material. 
         [0025]    The DBR layer  440  is attached to the light emitting diode structure  420  through vapor deposition, so as to replace the conventional metal reflecting layer and the inherent poor reflectivity thereof. Applying the DBR layer  440  enables the reflectivity of the lighting device  400  to greatly increase to above 90%, and preferably, to almost 100%. At last, via the distributed-Bragg reflecting layer  440 , the light emitting diode structure  420  is connected to the eutectic layer  460  to form the high efficiency lighting device  400 . Furthermore, in this embodiment, the thickness of the eutectic layer  460  is around 1.5 micrometers, though the present invention is not limited to this. 
         [0026]    Summing the descriptions above, and in view of the undesirable light absorbance and poor reflectivity of the metal reflecting layer, the present invention utilizes a DBR layer which increases the reflectivity to nearly 100%, thereby greatly increasing the lighting efficiency of the lighting device. Furthermore, conventional metal reflecting thin film has low reflectivity at the UV band, but the DBR layer used in the present invention does not pose such a problem. Moreover, manufacture process of conventional metal reflecting layers is not easy to control in that the reflectivity is affected by vapor deposition conditions. The DBR layer used in the present invention, on the other hand, again does not pose such a problem, therefore further enhancing the flexibility of manufacture process assurance. The selectively disposed micro-contact array in the DBR layer can further increase the heat dissipating efficiency of the components. 
         [0027]    The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.