Patent Publication Number: US-2015076529-A1

Title: Light-emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-191190, filed Sep. 13, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to light-emitting devices. 
     BACKGROUND 
     The development of light-emitting devices using a luminous body such as a light emitting diode (LED) and a phosphor in combination has been advancing. Modularizing a plurality of luminous bodies within these light-emitting devices is potentially effective for increasing the light output and also making these light-emitting devices more efficient. By integrating a plurality of luminous bodies at the wafer level and configuring the luminous bodies as a one-chip module, miniaturization may be implemented with reduce costs. However, when the plurality of luminous bodies is integrated at the chip level, the light extraction efficiency is sometimes reduced by mutual interference between phosphor layers arranged on the luminous bodies. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1C  are schematic diagrams depicting a light-emitting device according to an embodiment. 
         FIGS. 2A to 2C  are schematic sectional views depicting production processes of the light-emitting device according to the embodiment. 
         FIGS. 3A to 3C  are schematic sectional views depicting additional production processes of the light-emitting device according to the embodiment continued from  FIGS. 2A to 2C . 
         FIGS. 4A to 4C  are schematic sectional views depicting additional production processes of the light-emitting device according to the embodiment continued from  FIGS. 3A to 3C . 
         FIGS. 5A to 5C  are schematic sectional views, each depicting a light-emitting device according to a modified example of the embodiment. 
         FIGS. 6A and 6B  are schematic sectional views, each depicting a light-emitting device according to another modified example of the embodiment. 
         FIG. 7  is a schematic sectional view depicting a light-emitting device according to a comparative example. 
     
    
    
     DETAILED DESCRIPTION 
     A light-emitting device with reduced mutual interference between phosphor layers arranged on a plurality of luminous bodies within the light-emitting device is described as an example embodiment of the present disclosure. 
     In general, according to one embodiment, a light-emitting device includes a resin layer and a plurality of luminous bodies disposed on the resin layer. The luminous bodies are disposed so as to be spaced from each other in a direction generally parallel to the resin layer plane. The luminous bodies each have a first side with a first surface that is contacting the resin layer and a second side, which is opposite the first side, with a second surface. A wiring (wiring element) electrically connects the luminous bodies to each other. For example, the luminous bodies may be wired in series with each other or in parallel with each other. The wiring contacts the luminous bodies on the first side. At least some portion of the wiring is in the resin layer. For example, a vertical (generally perpendicular to the resin layer plane) portion of the wiring can be within the resin layer and a horizontal (generally parallel to the resin layer plane) portion of the wiring can be on a back-side surface of the resin layer. A phosphor layer is disposed on the second surface of each luminous body and each phosphor layer is spaced from each other phosphor layer that may be adjacent. 
     Hereinafter, embodiments will be described with reference to the drawings. Identical portions in the drawings are identified with common reference numerals and the detailed descriptions thereof may be omitted as appropriate, and only different portions may be described in discussing the various figures. Incidentally, the drawings are schematic or conceptual diagrams, and the relationship between the thickness and the width of each portion, the size ratio between one portion and the other portion, and the like are not necessarily identical to the relationship, the size ratio, and the like of an actual device. Moreover, even when the same portion is depicted, the dimensions and ratio thereof may be different in different drawings. 
       FIGS. 1A to 1C  are schematic diagrams depicting a light-emitting device  1  according to an embodiment.  FIG. 1A  is a top view depicting a light-emitting face side of the light-emitting device  1 .  FIG. 1B  is a sectional view taken on the line A-A depicted in  FIG. 1A .  FIG. 1C  is a schematic diagram depicting a circuit configuration of the light-emitting device  1 . 
     The light-emitting device  1  includes a resin layer  10 , a plurality of luminous bodies  15  arranged on the resin layer  10 , wiring  20  that electrically connect the adjacent luminous bodies  15 , and phosphor layers  30  provided on the luminous bodies  15 . 
     Each luminous body  15  is, for example, an LED and has a first face  15   a  on the side where the luminous body  15  is in contact with the resin layer  10  and a second face  15   b  on aside opposite to the first face  15   a . The luminous body  15  may be a laminated body including, for example, an n-type semiconductor layer (first semiconductor layer)  11 , a p-type semiconductor layer (second semiconductor layer)  12 , and an emission layer (light-emitting layer)  13  provided between the n-type semiconductor layer  11  and the p-type semiconductor layer  12  (see  FIGS. 2A to 2C ). 
     As depicted in  FIG. 1B , each wiring  20  electrically connects the adjacent two luminous bodies  15  on the side of the luminous body  15  where the first face  15   a  is located—that is, each wiring  20  connects to the luminous bodies  15  at the first face  15   a . The luminous bodies  15  may be connected in series with each other via the wiring  20  as depicted in  FIG. 1C  or may be connected in parallel with each other. 
     At least part of each wiring  20  is provided in the resin layer  10 . In an example depicted in  FIG. 1B , a portion of the wiring  20 , the portion that is connected to the luminous body  15 , is provided in the resin layer  10 , and a another portion of the wiring  20 , the portion extending between the adjacent luminous bodies  15 , is provided on a face (hereinafter, a rear face) of the resin layer  10  on the side opposite to a face of the resin layer  10  that is in contact with the luminous body  15 . As depicted in  FIG. 1B , the vertical (up-down page direction) portions of wiring  20  are within the resin layer  10  and the horizontal (left-right page direction) portions of wiring  20  are outside the resin layer  10  on a surface of resin layer  10 . The disclosure is not limited to this example arrangement, and, for example, the whole of the wiring  20  may be provided in the resin layer  10  instead of just a portion. 
     On the side of the luminous body  15  where the second face  15   b  is located, the phosphor layer  30  is provided. The phosphor layer  30  contains, for example, a phosphor  31  that is excited by a light emitted from the luminous body  15  and emits a light with a wavelength which is different from the wavelength of the light emitted from the luminous body  15 . That is, the phosphor layer  30  has a wavelength conversion function in that it absorbs light emitted by luminous body  15  at a first wavelength and then emits light at a different, second wavelength. In another embodiment, a structure in which a transparent resin layer, whose principal ingredient is silicone resin or the like, is provided on the second face  15   b  in place of the phosphor layer  30  to directly extract the light emitted from the luminous body  15  may also be adopted. 
     The phosphor layer  30  is provided on each of the luminous bodies  15 . In addition, the phosphor layers  30  are disposed separated from one another on the resin layer  10 . For example, as depicted in  FIG. 1A , the phosphor layers  30  may be disposed in a matrix with a spacing or gap between adjacent phosphor layers  30 . 
       FIG. 7  is a schematic sectional view depicting a light-emitting device  7  according to a comparative example. The light-emitting device  7  includes a resin layer  10 , a plurality of luminous bodies  15  arranged on the resin layer  10 , wiring  20  that electrically connect the adjacent luminous bodies  15 , and a phosphor layer  50  provided on the luminous bodies  15 . As depicted in  FIG. 7 , the phosphor layer  50  is provided on the resin layer  10  in a continuous manner in such a way as to cover the second faces  15   b  of the luminous bodies  15 . 
     In the light-emitting device  7 , a drive current is supplied to the luminous bodies  15  via the wiring  20  to make the luminous bodies  15  emit light. The light emitted from the luminous bodies  15  passes through the phosphor layer  50  and is released to the outside. In the course of this process, the phosphor  31  contained in the phosphor layer  50  absorbs part of the emitted light of the luminous bodies  15  and emits a light with a wavelength which is different from the wavelength of the light emitted from the luminous bodies  15 . As a result, the light-emitting device  7  may output a mixed light of the emitted light of the luminous bodies  15  and the emitted light of the phosphor  31 . In addition, by appropriately selecting the type of the phosphor  31 , lights of various colors may be output from the light-emitting device  7 . 
     On the other hand, the process of wavelength conversion in the phosphor  31  involves a loss of light energy. For example, as depicted in  FIG. 7 , when the phosphor layer  50  is formed in a continuous manner, the optical path length of a light that propagates in the phosphor layer  50  in a transverse direction (not perpendicular to the face  15   b ) increases and the light is attenuated accordingly. Furthermore, in a region B of the phosphor layer  50  between the adjacent luminous bodies  15 , the intensity of the excited light is reduced by attenuation. As a result, the energy loss caused by the absorption by the phosphor  31  becomes relatively greater, resulting in a reduction in efficiency of light extraction from the phosphor layer  50 . 
     On the other hand, the phosphor layers  30  are provided on the luminous bodies  15  in such a way that the phosphor layers  30  are separated from one another. As a result, the potential optical path length of a light that propagates in the phosphor layer  30  in a transverse direction may be shortened as the phosphor layer  30  does not extend between luminous bodies  15 . Furthermore, since the phosphor  31  is not present in a portion in which the luminous body  15  is not arranged, the energy loss caused by the absorption by the phosphor  31  may be reduced. As a result, in the light-emitting device  1 , the efficiency of light extraction from the phosphor layer  30  may be improved. 
     Next, with reference to  FIGS. 2A to 4C , a method for producing light-emitting device  1  will be described.  FIGS. 2A to 4C  are schematic sectional views depicting an example of a production process of the light-emitting device  1  according to the embodiment. 
       FIG. 2A  is a sectional view depicting an n-type semiconductor layer  11 , a p-type semiconductor layer  12 , and an emission layer  13  which are formed on a principal surface of a substrate  100 . For example, by using metal organic chemical vapor deposition (MOCVD), the n-type semiconductor layer  11 , the emission layer  13 , and the p-type semiconductor layer  12  are grown, sequentially, on the substrate  100 . The substrate is, for example, a silicon substrate. The n-type semiconductor layer  11 , the emission layer  13 , and the p-type semiconductor layer are, for example, nitride semiconductors and can contain gallium nitride (GaN). 
     Next, as depicted in  FIG. 2B , for example, by using reactive ion etching (RIE), the p-type semiconductor layer  12  and the emission layer  13  are selectively etched, whereby the n-type semiconductor layer  11  is exposed. Patterning is performed on the p-type semiconductor layer  12  and the emission layer  13  so that portions of the p-type semiconductor layer  12  and the emission layer  13  are left like islands on the n-type semiconductor layer  11 . These island-like portions are used to form a plurality of light-emitting regions on the substrate  100 . 
     Then, as depicted in  FIG. 2C , the n-type semiconductor layer  11  is selectively removed such that the exposed portions of n-type layer  11  that are between the island-like portions of p-type semiconductor  12  and emission layer  13  are removed, whereby a plurality of luminous bodies  15  are formed on the substrate  100 . 
     For example, an etching mask (not shown) that covers the p-type semiconductor layer  12  and the emission layer  13  is provided on the n-type semiconductor layer  11 . Then, by using RIE, the n-type semiconductor layer  11  is etched, whereby grooves  80  reaching the substrate  100  are formed. As a result, for example, as depicted in  FIG. 1A , the plurality of luminous bodies  15  disposed in matrix may be formed on the substrate  100 . Each luminous body  15  is a laminated body including the n-type semiconductor layer  11 , the p-type semiconductor layer  12 , and the emission layer  13  provided between the n-type semiconductor layer  11  and the p-type semiconductor layer  12 . 
     Next, as depicted in  FIG. 3A , on the side of the luminous body  15  where a second face  15   a  is located, a p-electrode  16  and an n-electrode  17  are formed. The p-electrode  16  is formed on the p-type semiconductor layer  12 . The n-electrode  17  is formed on the n-type semiconductor layer  11 . 
     The p-electrode  16  and the n-electrode  17  are formed using, for example, sputtering or evaporative deposition. The p-electrode  16  may be formed before the n-electrode  17  and vice versa. The p-electrode  16  and the n-electrode  17  may also be formed of the same material and at the same time. Preferably, the p-electrode  16  is formed in such a way as to reflect a light emitted from the emission layer  13 , for example. The p-electrode  16  may contain, for example, silver, a silver alloy, aluminum, or an aluminum alloy. Moreover, to prevent sulfuration and oxidation of the p-electrode  16 , a structure including a metal protection film (a barrier metal film) may also be adopted. 
     Next, as depicted in  FIG. 3B , an insulating film  18  that covers the luminous bodies  15  and the substrate  100  is formed. In the insulating film  18 , a first opening communicating with the p-electrode  16  and a second opening communicating with the n-electrode  17  are formed—that is, insulating film  18  has a hole/opening through which a connection to the p-electrode  16  can be made and another hole/opening through which a connection to then-electrode  17  can be made. The insulating film  18  is, for example, a silicon oxide film or a silicon nitride film and may be formed using chemical vapor deposition (CVD). 
     Then, on the insulating film  18 , a p-side wiring layer  21  and an n-side wiring layer  22  are formed. The p-side wiring layer  21  is electrically connected to the p-electrode  16  via the first opening provided in the insulating film  18 . Moreover, the n-side wiring layer  22  is electrically connected to the n-electrode  17  via the second opening provided in the insulating film  18 . Furthermore, a p-side pillar (contact)  23  is formed on the p-side wiring layer  21 , and an n-side pillar (contact)  24  is formed on the n-side wiring layer  22 . The p-side wiring layer  21 , the n-side wiring layer  22 , the p-side pillar  23 , and the n-side pillar  24  are, for example, metal whose principal ingredient is copper formed using electrolytic plating. 
     The p-side wiring layer  21  and the n-side wiring layer  22  determine the area ratio between the p-electrode  16  and the n-electrode  17  to form the pillars. 
     For example, to increase the light output of the luminous body  15 , the area of the emission layer  13  can be increased. Therefore, the area of the p-type semiconductor layer  12  formed on the emission layer  13  can be larger than an exposed portion of the n-type semiconductor layer  11  in which the n-electrode  17  is provided. To make the current injected into the emission layer  13  more nearly uniform, the p-electrode  16  can be formed in such a way as to cover the entire surface of the p-type semiconductor layer  12 . As a result, the p-electrode  16  is wider than the n-electrode  17 . 
     On the other hand, to form a wiring connected to the p-electrode  16  and the n-electrode  17 , preferably, the area ratio between the p-electrode  16  and the n-electrode  17  is close to 1. Thus, by providing the p-side wiring layer  21  and the n-side wiring layer  22 , the area ratio between the p-electrode  16  and the n-electrode  17  is optimized. As a result, the p-side pillar  23  and the n-side pillar  24  which are part of the wiring  20  are formed easily. 
     Next, as depicted in  FIG. 3C , a resin layer  10  that covers the p-side wiring layers  21 , the n-side wiring layers  22 , the p-side pillars  23 , the n-side pillars  24 , the luminous bodies  15 , and the insulating film  18  is formed. 
     The resin layer  10  contains carbon black, for example, and blocks the emitted light of the luminous bodies  15 . Moreover, the resin layer  10  may contain, for example, a component, such as titanium oxide, which reflects the emitted light of the luminous bodies  15 . 
     Next, processing is performed on the sides of the luminous bodies  15  where second faces  15   b  are located.  FIGS. 4A to 4C  are sectional views obtained by turning  FIG. 3C  upside down. 
     As depicted in  FIG. 4A , the substrate  100  is removed from the luminous bodies  15 . For example, when a silicon substrate is used as the substrate  100 , the substrate  100  may be selectively removed by wet etching. Preferably, minute projections and depressions (sometimes referred to as concave-convex structures or a frosting process) are formed on the surfaces (the second faces  15   b ) of the luminous bodies  15  from which the substrate  100  is removed. By doing so, the efficiency of light extraction from the luminous bodies  15  to the phosphor layer  30  may be improved by reducing interfacial reflections. 
     Next, as depicted in  FIG. 4B , on the second faces  15   b  of the luminous bodies  15 , phosphor layers  30  are formed. The phosphor layer  30  is formed, for example, as a continuous layer on the luminous bodies  15  and the resin layer  10 . Then, grooves  33  are formed between the adjacent luminous bodies  15  to obtain a plurality of phosphor layers  30  separated from one another. The grooves  33  are formed in such away as to communicate with the insulating film  18 . Thus, for example, the grooves  33  may extend from an upper surface (as depicted in  FIG. 4B ) of phosphor layers  30  to an upper surface of insulating film  18 . 
     Next, a rear face side of the resin layer  10  is ground (or otherwise processed) to expose the end faces of the p-side pillars  23  and the n-side pillars  24 . 
     Then, as depicted in  FIG. 4C , on a rear face of the resin layer  10 , wiring  25 , each electrically connecting the p-side pillar  23  and the n-side pillar  24  of the adjacent luminous bodies  15 , are formed. That is, each wiring  20  that electrically connects the adjacent luminous bodies  15  includes, for example, the p-side pillar  23 , the n-side pillar  24 , and the wiring  25 . 
     Then, between the adjacent luminous bodies  15 , the insulating film  18  and the resin layer  10  are cut to obtain individual light-emitting devices  1 , each as depicted in  FIGS. 1A to 1C . 
     The light-emitting device  1  produced by the processes described above is a one-chip module inside which the plurality of luminous bodies  15  are encapsulated in resin and includes the wiring that electrically connect the plurality of luminous bodies  15 . The light-emitting device  1  with such a structure may implement significant miniaturization and reduction in cost. 
     Next, with reference to  FIGS. 5A to 5C  and  FIGS. 6A and 6B , light-emitting devices according to modified examples of the embodiment will be described.  FIGS. 5A  to  6 B are schematic sectional views depicting light-emitting devices  2  to  6  according to the modified examples of the embodiment. 
       FIG. 5A  is a sectional view depicting the light-emitting device  2 . The light-emitting device  2  includes a resin layer  10 , a plurality of luminous bodies arranged on the resin layer  10 , wiring  20  that electrically connect the adjacent luminous bodies  15 , and phosphor layers  35  provided on the luminous bodies  15 . Each phosphor layer  35  contains a phosphor  31 . 
     The phosphor layer  35  has a shape in which a face (a top face  35   b ) on a side opposite to the luminous body  15  is narrower than a face in contact with the luminous body  15 . That is, the phosphor layer  35  has inwardly inclined side faces  35   c.    
     For example, in the phosphor layer obtained by division into the size of the luminous body  15 , the light emitted not only from the top face thereof but also from the side face thereof is Lambertian (directionally diffuse) and contributes to light output. In this example, by processing the end of the phosphor layer  35  into a tapered shape, the light distribution angle of the light emitted from the side faces  35   c  is shifted upward. As a result, absorption by another phosphor layer  35  adjacent to the phosphor layer  35  is suppressed and the light extraction efficiency may be improved. 
       FIG. 5B  is a sectional view depicting the light-emitting device  3 . The light-emitting device  3  includes a resin layer  10 , a plurality of luminous bodies arranged on the resin layer  10 , wiring  20  that electrically connects the adjacent luminous bodies  15 , and phosphor layers  30  provided on the luminous bodies  15 . Each phosphor layer  30  contains a phosphor  31 . 
     Furthermore, the phosphor layer  30  has side faces  30   c  intersecting a face which is parallel to the second face  15   b  of the luminous body  15  and reflectors  41  provided on the side faces  30   c . Each reflector  41  reflects the light emitted from the luminous body  15  and the emitted light of the phosphor  31 . 
     In the light-emitting device  3 , the light from the side faces  30   c  of the phosphor layer  30  is reflected by the reflectors  41  and is extracted upward. Each reflector is, for example, a dielectric multilayer film. Moreover, as the reflector  41 , for example, metal having a high reflectivity, such as aluminum or silver, may be used. The light that propagates toward the side faces  30   c  of the phosphor layer  30  is reflected upward by the reflectors  41  and is released from a top face  30   b  of the phosphor layer  30 . As a result, the luminous efficiency of the light-emitting device  3  may be improved. 
       FIG. 5C  is a sectional view depicting the light-emitting device  4 . The light-emitting device  4  includes a resin layer  10 , a plurality of luminous bodies arranged on the resin layer  10 , wiring  20  that electrically connect the adjacent luminous bodies  15 , and phosphor layers  30  provided on the luminous bodies  15 . Each phosphor layer  30  contains a phosphor  31 . 
     Furthermore, between the phosphor layers  30  provided on the adjacent two luminous bodies  15 , a reflector  43  that reflects the emitted lights of the two luminous bodies  15  is provided. The reflector  43  extends in such a way as to surround each of the plurality of phosphor layers  30 . 
     The reflector  43  is formed using, for example, metal having a high reflectivity, such as aluminum or silver, or a multilayer dielectric film. Preferably, the reflector  43  is formed into a tapered shape so that the reflector  43  reflects upward the light released from the phosphor layer  30 . As a result, absorption by another phosphor layer  30  adjacent to the phosphor layer  30  is suppressed and the light extraction efficiency may be improved. 
       FIG. 6A  is a sectional view depicting the light-emitting device  5 . The light-emitting device  5  includes a resin layer  10 , a plurality of luminous bodies arranged on the resin layer  10 , wiring  20  that electrically connects the adjacent luminous bodies  15 , and phosphor layers  30  provided on the luminous bodies  15 . Each phosphor layer  30  contains a phosphor  31 . 
     Furthermore, the light-emitting device  5  includes a resin body  45  that is provided between the phosphor layers  30  provided on the adjacent two luminous bodies  15 . The resin body  45  contains a scattering material  47  that scatters the emitted lights of the two luminous bodies  15  and the emitted light of the phosphor  31 . 
     For example, the inside of the groove  33  dividing the phosphor layer  30  is filled with the resin body  45 . The scattering material  47  is, for example, silica particles and scatters the emitted lights of the luminous body  15  and the phosphor  31  in multiple directions. As a result, the percentage of the light released from a top face  30   b  of the phosphor layer  30  is increased, whereby the luminous efficiency may be improved. 
       FIG. 6B  is a sectional view depicting the light-emitting device  6 . The light-emitting device  6  includes a resin layer  10 , a plurality of luminous bodies arranged on the resin layer  10 , wiring  20  that electrically connects the adjacent luminous bodies  15 , and phosphor layers  30  provided on the luminous bodies  15 . Each phosphor layer  30  contains a phosphor  31 . 
     Furthermore, the light-emitting device  6  includes a lens  51  provided on each of the plurality of phosphor layers  30 . The lens  51  is formed by, for example, molding a transparent resin such as silicone on the phosphor layer  30 . By collecting the emitted lights of the luminous body  15  and the phosphor  31  with the lens, absorption by the adjacent phosphor layer  30  is reduced and the light extraction efficiency may be improved. 
     As described above, in the embodiment, between the phosphor layers provided on the luminous bodies  15 , a gap, a reflector, or the like is disposed. As a result, absorption of the emitted light of the luminous body  15  by the adjacent phosphor layer is suppressed and the light extraction efficiency of the light-emitting device including the plurality of luminous bodies  15  may be improved. Moreover, the lens  51  used in the light-emitting device  6  may be formed on the phosphor layers of the light-emitting devices  2  to  5 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.