Patent Publication Number: US-2012032217-A1

Title: White led device and manufacturing method thereof

Description:
CLAIM OF PRIORITY 
     This application claims the priority benefit of Taiwan Application Ser. No. 099126317, filed on Aug. 6, 2010. All disclosure of the Taiwan application is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     The present invention is related to a white light emitting diode (LED) device and a manufacturing method thereof. 
     B. Description of the Prior Art 
     In a conventional LED device, such as the LED device disclosed in U.S. Pat. No. 5,998,925, a phosphor layer with a wavelength converting function is frequently provided to change the wavelength of a light emitted by the LED device. However, the phosphor layer usually has a thicker thickness and contacts with the LED device directly, thereby causing various adverse problems. For examples, the distribution of phosphor powder in the phosphor layer is uneven; the aging of phosphor layer is speeded up due to the heat generated by the LED device, which would significantly reduce the life of the LED device; and so on. Furthermore, in the LED device disclosed in U.S. Pat. No. 5,998,925, the color of the light emitted by the LED device was measured after the assembly or package of the entire LED device is completed. If it is found that the wavelength of the light emitted fails to meet the specification, the production cost would be significantly increased because the rework is very difficult, or even the failed products must be scrapped right away. Moreover, since the conventional method of coating a phosphor layer is generally performed by a dispensing process, the conventional phosphor layer may have a larger thickness. Therefore, there will be a yellow ring issue and phosphor powder may sink down in the phosphor layer due to gravity, thereby reducing the color uniformity of LED device. The brightness of LED will drop by reducing the thickness of phosphor layer. The heat generated by the LED device also ages the phosphor layer and decrease its life. Accordingly, it is strongly required that a LED device and manufacturing method thereof can overcome the foregoing problems. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a method of manufacturing a white light emitting diode is provided, the method includes the following steps: providing an optical layer; providing a wavelength converting layer on the optical layer to form a first stack structure including the optical layer and the wavelength converting layer; providing a conductive substrate; forming a multilayered light emitting semiconductor epitaxial structure on the conductive substrate to form a second stack structure including the conductive substrate and the multilayered light emitting semiconductor epitaxial structure; cutting the first stack structure into a size matching the second stack structure; and bonding the wavelength converting layer of the first stack structure to the multilayered light emitting semiconductor epitaxial structure of the second stack structure, while providing a transparent layer between the wavelength converting layer and the multilayered light emitting semiconductor epitaxial structure. 
     According to another aspect of the invention, a white light emitting diode device is provided, the device includes: a conductive substrate; a multilayered light emitting semiconductor epitaxial structure formed on the conductive substrate; a contact provided on the multilayered light emitting semiconductor epitaxial structure; a transparent layer provided on the multilayered light emitting semiconductor epitaxial structure; a wavelength converting layer provided on the transparent layer; and an optical layer provided on the wavelength converting layer. 
     Other aspects and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating exemplifications of the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings of the invention, like reference numerals refer to similar elements, in which: 
         FIG. 1  is a schematic cross sectional view of a white light emitting diode device according to an embodiment of the invention; 
         FIGS. 2   a - 2   g  illustrate exemplary steps of manufacturing the white light emitting diode device in  FIG. 1 ; 
         FIG. 3  shows a schematic cross sectional view of a white light emitting diode device according to another embodiment of the invention; 
         FIGS. 4   a - 4   e  illustrate exemplary steps of manufacturing the white light emitting diode device in  FIG. 3 ; 
         FIG. 5  is a schematic cross sectional view of a white light emitting diode device according to yet another embodiment of the invention; and 
         FIGS. 6   a - 6   g  illustrate exemplary steps of manufacturing the white light emitting diode device in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a schematic cross sectional view of a white light emitting diode (LED) device  100  according to an embodiment of the invention. As shown in  FIG. 1 , white light emitting diode device  100  includes: a conductive substrate  41 ; a multilayered light emitting semiconductor epitaxial structure  43  formed on the conductive substrate  41 ; a contact (electrode)  45  provided on the multilayered light emitting semiconductor epitaxial structure  43 ; a transparent layer  53  provided on the multilayered light emitting semiconductor epitaxial structure  43 ; a wavelength converting layer  55  provided on the transparent layer  53 ; and an optical layer  57  provided on the wavelength converting layer  55 . The conductive substrate  41  may be a metal or an alloy, such as copper or copper alloy, or may be silicon (Si). The multilayered light emitting semiconductor epitaxial structure  43  may include a p-type semiconductor layer, an active layer formed on the p-type semiconductor layer, and an n-type semiconductor layer formed on the active layer. In one example of the invention, the p-type semiconductor layer is formed on and adjacent to the conductive substrate  41 ; while in another example, the n-type semiconductor layer is formed on and adjacent to the conductive substrate  41 . The transparent layer  53  may be made of a polymer, such as a silicone resin, an epoxy resin, or other transparent resins. The refractive index of the transparent layer  53  is more than or equal to 1.40, and preferably 1.50 or above. Furthermore, the transparent layer  53  is provided between the multilayered light emitting semiconductor epitaxial structure  43  and the wavelength converting layer  55 . In one embodiment of the invention, the wavelength converting layer  55  may consist of a plurality of wavelength converting sublayers. For example, it may include two wavelength converting sublayers, i.e. a first wavelength converting sublayer and a second wavelength converting sublayer provided on the first wavelength converting sublayer (not shown), in which each of the first wavelength converting sublayer and the second wavelength converting sublayer includes phosphors and organic resins. Furthermore, the first wavelength converting sublayer and the second wavelength converting sublayer may have similar or different phosphors and organic resins. The thickness of the wavelength converting layer  55  is less than about 200 μm, preferably less than about 50 μm. However, in other examples, the wavelength converting layer  55  may also be a single wavelength converting layer. The optical layer  57  may have a roughened surface to increase the light extraction efficiency of the white light emitting diode device  100 . The optical layer  57  may be made of a polymer, such as a silicone resin, an epoxy resin, or other transparent resins. The thickness of the optical layer  57  is between about 150 μm and about 400 μm, preferably about 200 μm. In various embodiments of the invention, the optical layer may be in the form of a dome, a convex, a concave, a flat, or a Fresnel lens, and the surface of the optical layer may be roughened optionally. 
       FIGS. 2   a - 2   g  illustrate exemplary steps of manufacturing the white light emitting diode device  100  in  FIG. 1 . As shown in  FIGS. 2   a - 2   g,  the optical layer  57  is provided on a rough surface mold  31  by injection molding, compress molding, or casting and so on. The roughing of the mold surface is achieved by a sand blasting or etching process, so that the surface of the optical layer  57  may have a predetermined roughness. In another embodiment of the invention, the mold  31  may be provided without the surface roughening treatment. Instead of the treatment, the surface of the optical layer  57  is directly treated by a sand blasting or etching process. Therefore, the optical layer  57  may have a surface with a predetermined roughness. The mold  31  can be made of a material such as glass, stainless steel, or rubber. 
     The wavelength converting layer  55  (as a carrier) is provided on the optical layer  57  by spraying coating, spin coating, jet printing, or screen printing and so on. The transparent layer  53  is provided on the wavelength converting layer  55  by spraying coating, spin coating, jet printing, or screen printing and so on. The first stack structure including the transparent layer  53 , the wavelength converting layer  55  and the optical layer  57  is given by removing the mold  31 . 
     In another embodiment of the invention, a transparent polymer film that does or does not undergo a surface roughening treatment can be provided as the optical layer  57 . 
     The multilayered light emitting semiconductor epitaxial structure  43  is formed on the conductive substrate  41 , so as to form a second stack structure including the conductive substrate  41  and the multilayered light emitting semiconductor epitaxial structure  43 . The contact (electrode)  45  is provided on the multilayered light emitting semiconductor epitaxial structure  43 . 
     Then, the first stack structure is cut into a size fitting the second stack structure. 
     In the embodiment, the mold  31  is removed before the first stack structure is cut. However, in other embodiments, the mold  31  can be removed after the optical layer  57  is provided but before the wavelength converting layer  55  is provided. Alternatively, the mold  31  may be removed after the wavelength converting layer  55  is provided but before the transparent layer  53  is provided. 
     Finally, the first stack structure is bonded to the second stack structure. Specifically, the wavelength converting layer  55  of the first stack structure is bonded to the multilayered light emitting semiconductor epitaxial structure  43  of the second stack structure, and the transparent layer  53  is provided therebetween, so as to produce the white light emitting diode device  100 . However, in other embodiments of the invention, the transparent layer  53  can be provided on the second stack structure rather than on the first stack structure, as shown in  FIGS. 4   a - 4   e  and  FIGS. 6   a - 6   g.  Alternatively, the transparent layer  53  can be provided on the first stack structure and the second stack structure, respectively, as long as the transparent layer  53  is placed between the multilayered light emitting semiconductor epitaxial structure  43  and the wavelength converting layer  55  after the bonding, i.e. the transparent layer  53  is provided between the multilayered light emitting semiconductor epitaxial structure  43  and the wavelength converting layer  55 . 
       FIG. 3  shows a schematic cross sectional view of a white light emitting diode device  200  according to another embodiment of the invention. The white light emitting diode device  200  in  FIG. 3  is similar to the white light emitting diode device  100  in  FIG. 1 , the difference therebetween is that an optical layer  67  of the white light emitting diode device  200  in  FIG. 3  dose not have a roughened surface, and it is a transparent window to increase the light extraction efficiency.  FIGS. 4   a - 4   e  illustrate the steps of manufacturing the white light emitting diode device  200  in  FIG. 3 .  FIGS. 4   a - 4   e  illustrate the embodiment without applying the mold. In another embodiment, the mold can be employed to provide the optical layer  67 , as shown in  FIG. 2 . 
     As shown in  FIGS. 4   a - 4   e,  the optical layer  67  is provided. Then the wavelength converting layer  55  is provided on the optical layer  67  to form a first stack structure including the optical layer  67  and the wavelength converting layer  55 . The multilayered light emitting semiconductor epitaxial structure  43  and the transparent layer  53  are formed sequentially on the conductive substrate  41 , such that a second stack structure having the transparent layer  53  thereon is formed. The second stack structure includes the conductive substrate  41  and the multilayered light emitting semiconductor epitaxial structure  43 . The contact (electrode)  45  is provided on the multilayered light emitting semiconductor epitaxial structure  43 . 
     Then, the first stack structure is cut into a size fitting the second stack structure. 
     Finally, the first stack structure is bonded to the second stack structure, so as to produce the white light emitting diode device  200 . 
       FIG. 5  shows a schematic cross sectional view of a white light emitting diode device  300  according to another embodiment of the invention. The white light emitting diode device  300  in  FIG. 5  is similar to the white light emitting diode device  100  in  FIG. 1 , the difference therebetween is that an optical layer  77  of the white light emitting diode device  300  in  FIG. 5  is a dome lens, such that the light pattern of the white light emitting diode device  300  can be changed.  FIGS. 6   a - 6   g  illustrate the steps of manufacturing the white light emitting diode device  300  in  FIG. 5 . As shown in  FIGS. 6   a - 6   g,  the optical layer  77  is provided on a mold  81 , which does or does not undergo a surface roughening treatment, and can be made of a material such as glass, stainless steel or rubber. Next, the wavelength converting layer  55  is provided on the optical layer  77 . After that, the mold  81  is removed, so as to give a first stack structure including the optical layer  77  and the wavelength converting layer  55 . 
     The multilayered light emitting semiconductor epitaxial structure  43  and the transparent layer  53  are formed sequentially on the conductive substrate  41  The second stack structure includes the conductive substrate  41 , the multilayered light emitting semiconductor epitaxial structure  43 , and the transparent layer  53 . The contact (electrode)  45  is provided on the multilayered light emitting semiconductor epitaxial structure  43 . 
     Then, the first stack structure is cut into a size fitting the second stack structure. 
     Finally, the first stack structure is bonded to the second stack structure to produce the white light emitting diode device  300 . Specifically, the wavelength converting layer  55  of the first stack structure is bonded to the multilayered light emitting semiconductor epitaxial structure  43  of the second stack structure, and the transparent layer  53  is provided between the wavelength converting layer  55  and the multilayered light emitting semiconductor epitaxial structure  43 . 
     As compared with the prior art, the present invention has following advantages: having the better color uniformity without the yellow ring issue; the wavelength converting layer not directly contacting with the multilayered light emitting semiconductor epitaxial structure (since the transparent layer is provided therebetween), thereby increasing the life of the LED device and improving the stability; the light extraction efficiency being improved and/or the light pattern being changed via the optical layer; and so on. Moreover, the wavelength converting layer has been provided on the optical layer, the color of the wavelength converting layer can be tested before the assembly or package of the entire light emitting diode device is completed to determine whether the color falls within the specification. If not, the LED device of the invention can be easily reworked, thereby reducing the production cost significantly. 
     While the present invention has been described in details with reference to preferred embodiments and figures thereof, it should be apparent to a person skilled in the art that various modifications, alterations and equivalent substitutions could be made without departing from the spirit and scope of the present invention. However, such modifications, alterations and equivalent substitutions are intended to be embraced in the appended claims.