Patent Publication Number: US-2015060894-A1

Title: Light Emitting Device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-180679, filed on Aug. 30, 2013; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a light emitting device. 
     BACKGROUND 
     For example, there is a light emitting device that is configured to emit white light by combining a semiconductor light emitting element that emits blue light and a fluorescent body that converts a wavelength of the light. In such a light emitting device, it is preferable that reliability be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  to  FIG. 1C  are schematic views illustrating a light emitting device and a lighting device according to a first embodiment; 
         FIG. 2  is a schematic cross-sectional view illustrating the light emitting device according to the first embodiment; 
         FIG. 3  is a schematic cross-sectional view illustrating a light emitting device according to a second embodiment; 
         FIG. 4A  to  FIG. 4G  are schematic views illustrating a light emitting device according to a third embodiment; 
         FIG. 5A  to  FIG. 5C  are schematic views illustrating the light emitting device according to the embodiment; and 
         FIG. 6  is a graph illustrating characteristics of the light emitting device according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to an embodiment, a light emitting device including a substrate, a plurality of semiconductor elements and a wavelength conversion layer is provided. The semiconductor light emitting elements are provided on the substrate. The wavelength conversion layer covers the semiconductor light emitting elements and converts a wavelength of light emitted from the semiconductor light emitting elements. A first distance between an upper surface of the wavelength conversion layer and the substrate in a first region between two adjacent semiconductor light emitting elements in the semiconductor light emitting elements is shorter than a second distance between the upper surface of the wavelength conversion layer and the substrate in a second region on the two adjacent semiconductor light emitting elements. 
     Various embodiments will be described hereinafter with reference to the accompanying drawings. 
     Moreover, the drawings are schematic or conceptual and a relationship between a thickness and a width of each portion, a ratio of a size between portions, or the like is not necessarily limited to the same as that in reality. Further, even if the same portions are indicated in drawings, dimensions or ratios thereof may be indicated differently from each other depending on the drawings. 
     Moreover, in the specification and each view of the application, the same reference numerals are given to similar elements described already in the foregoing drawings and detailed description thereof is appropriately omitted. 
     First Embodiment 
       FIG. 1A  to  FIG. 1C  are schematic views illustrating a light emitting device and a lighting device according to a first embodiment. 
       FIG. 1A  is a plan view.  FIG. 1B  is a cross-sectional view illustrating a part of a cross-section along line A1-A2 of  FIG. 1A . 
     As illustrated in  FIG. 1A  and  FIG. 1B , a light emitting device  110  according to an embodiment includes a base member  71 , a grease layer  53 , a metal plate  51 , a bonding layer  52 , a mounting substrate section  15  and a plurality of semiconductor light emitting elements  20 . The light emitting device  110  is, for example, utilized in a lighting device  210 . 
     A direction from the base member  71  to the mounting substrate section  15  is referred to as a laminating direction (a Z-axis direction). One direction perpendicular to the Z-axis direction is referred to as an X-axis direction. A direction perpendicular to the Z-axis direction and the X-axis direction is referred to as a Y-axis direction. 
     The grease layer  53 , the metal plate  51 , the bonding layer  52 , the mounting substrate section  15  and the plurality of semiconductor light emitting elements  20  are disposed on the base member  71  in this order. 
     That is, the plurality of semiconductor light emitting elements  20  are separated from the base member  71  in the Z-axis direction. The mounting substrate section  15  includes a substrate  10 . The substrate  10  has an upper surface  10   ue . For the substrate  10 , for example, a member formed of ceramic, a composite ceramic of ceramic and resin or the like is used. For the ceramic, for example, aluminum oxide (Al 2 O 3 ), aluminum nitride (AlN), beryllium oxide (BeO), steatite (MgO.SiO 2 ), zircon (ZrSiO 4 ), silicon nitride (Si 3 N 4 ), or the like is used. The substrate  10  is provided between the base member  71  and the plurality of semiconductor light emitting elements. The metal plate  51  is provided between the base member  71  and the mounting substrate section  15 . 
     As illustrated in  FIG. 1B , the bonding layer  52  is provided between the mounting substrate section  15  and the metal plate  51 . The bonding layer  52  bonds the mounting substrate section  15  to the metal plate  51 . 
     The grease layer  53  is provided between the base member  71  and the metal plate  51 . The grease layer  53  transmits heat of the metal plate  51  to the base member  71 . 
     Hereinafter, an example of the light emitting device  110  (and a lighting device  210 ) shown in  FIG. 1A  and  FIG. 1B  is described. 
     A light emitting section  40  is provided in the light emitting device  110 . The light emitting section  40  is provided on the metal plate  51 . The bonding layer  52  is provided between the metal plate  51  and the light emitting section  40 . 
     In the specification of the application, a state of being provided above also includes a state in which another element is inserted, in addition to the state of being provided above directly. 
     A direction from the metal plate  51  to the light emitting section  40  corresponds to the laminating direction. In the specification of the application, a state of being laminated also includes a state in which another element is inserted and overlapped in addition to a state of being overlapped directly. 
     The metal plate  51  is, for example, a plate-shape. A main surface of the metal plate  51  is, for example, substantially parallel to an X-Y plane. A planar shape of the metal plate  51  is, for example, rectangular. The metal plate  51  has, for example, first to fourth sides  55   a  to  55   d . The second side  55   b  is separated from the first side  55   a . The third side  55   c  connects an end of the first side  55   a  and an end of the second side  55   b . The fourth side  55   d  is separated from the third side  55   c  and connects the other end of the first side  55   a  and the other end of the second side  55   b . A plane-shaped corner section of the metal plate  51  may be curved. A plane shape of the metal plate  51  may not be rectangular and is optional. 
     For the metal plate  51 , for example, a substrate formed of a metal material such as copper or aluminum or a composite material of metal and ceramic. Another metal layer such as Ni plating may be formed on a surface of the metal plate  51 , from the viewpoint of preventing oxidation of the member and improving wettability of a solder. 
     The light emitting section  40  emits light. At the same time, the light emitting section  40  generates heat. The bonding layer  52  efficiently conducts the heat generated in the light emitting section  40  to the metal plate  51 . For the bonding layer  52 , for example, the solder or the like is used. That is, the bonding layer  52  includes the solder. For example, for the bonding layer  52 , the solder including at least one kind or more of gold, silver, copper, bismuth, nickel, indium, zinc, antimony, germanium and silicon in a base of tin can be used. For example, SnAgCu alloy or the like is used. 
     The light emitting section  40  includes the mounting substrate section  15  and a light emitting element section  35 . 
     The mounting substrate section  15  includes the substrate  10 , a first metal layer  11  and a second metal layer  12 . 
     The substrate  10  has a first main surface  10   a  and a second main surface  10   b . The second main surface  10   b  is a surface on the side opposite the first main surface  10   a . The metal plate  51  faces the second main surface of the substrate  10 . In other words, the second main surface  10   b  is a surface on the side of the metal plate  51 . That is, the second main surface  10   b  is a surface on the side of the bonding layer  52 . 
     In the specification of the application, a state of facing also includes a state in which another element is inserted, in addition to a state of facing directly. 
     The first main surface  10   a  includes a mounting region  16 . For example, the mounting region  16  is separated from an outer edge  10   r  of the first main surface  10   a . In the example, the mounting region  16  is provided in a center portion of the first main surface  10   a . The first main surface  10   a  further includes a peripheral region  17 . The peripheral region  17  is provided around the mounting region  16 . 
     The substrate  10  includes, for example, alumina. For the substrate  10 , for example, a ceramic mainly composed of alumina is used. High thermal conductivity and a high insulating property can be obtained. High reliability can be obtained. 
     The first metal layer  11  is provided on the first main surface  10   a . The first metal layer  11  includes a plurality of mounting patterns  11   p . The plurality of mounting patterns  11   p  are provided in the mounting region  16 . At least two or more of the plurality of mounting patterns  11   p  are separated from each other. For example, at least one of the plurality of mounting patterns  11   p  is an island shape. Two of the plurality of mounting patterns  11   p  are independent of each other. The plurality of mounting patterns  11   p  include, for example, a first mounting pattern  11   pa  and a second mounting pattern  11   pb  or the like. 
     Each of the plurality of mounting patterns  11   p  includes, for example, a first mounting portion  11   a  and a second mounting portion  11   b . In the example, the mounting pattern  11   p  further includes a third mounting portion  11   c . The third mounting portion  11   c  is provided between the first mounting portion  11   a  and the second mounting portion  11   b , and connects the first mounting portion  11   a  and the second mounting portion  11   b . Examples of the mounting portions are described below. 
     The first metal layer  11  may further include a connection section  44  connecting the plurality of mounting patterns  11   p  to each other. In the example, the first metal layer  11  further includes a first connector electrode section  45   e  and a second connector electrode section  46   e . The first connector electrode section  45   e  is electrically connected to one of the plurality of mounting patterns  11   p . The second connector electrode section  46   e  is electrically connected to another one which is different from the one of the plurality of mounting patterns  11   p . For example, the semiconductor light emitting element  20  is disposed on a part of one mounting pattern  11   p . The first connector electrode section  45   e  is electrically connected to one of the mounting patterns  11   p  by the semiconductor light emitting element  20 . Further, the semiconductor light emitting element  20  is disposed on a part of another mounting pattern  11   p . The second connector electrode section  46   e  is electrically connected to another mounting pattern  11   p  by the semiconductor light emitting element  20 . 
     In the example, the light emitting section  40  further includes a first connector  45  and a second connector  46  provided on the first main surface  10   a . The first connector  45  is electrically connected to the first connector electrode section  45   e . The second connector  46  is electrically connected to the second connector electrode section  46   e . In the example, the first connector  45  is provided on the first connector electrode section  45   e . The second connector  46  is provided on the second connector electrode section  46   e . The light emitting element section  35  is disposed between the first connector  45  and the second connector  46 . Power is supplied to the light emitting section  40  through the connectors. 
     The second metal layer  12  is provided on the second main surface  10   b . The second metal layer  12  is electrically insulated from the first metal layer  11 . At least a part of the second metal layer  12  overlaps the mounting region  16  when projecting in the X-Y plane (a first plane parallel to the first main surface  10   a ). 
       FIG. 1C  is a perspective plan view illustrating a part of the light emitting device  110 . 
     The second metal layer  12  is separated from the outer edge  10   r . A planar shape of the second metal layer  12  is, for example, rectangular. The second metal layer  12  has first to fourth sides  12   i  to  12   l . The second side  12   j  is separated from the first side  12   i . A third side  12   k  connects an end of the first side  12   i  and an end of the second side  12   j . The fourth side  12   l  is separated from the third side  12   k  and connects the other end of the first side  12   i  and the other end of the second side  12   j . An intersecting point of each side, that is, a corner section may be a curved shape (a rounded shape). A planar shape of the second metal layer  12  may not be rectangular and is optional. 
     As described above, the first metal layer  11  is provided on the upper surface (the first main surface  10   a ) of the substrate  10  and the second metal layer  12  is provided on a lower surface (the second main surface  10   b ) of the substrate  10 . 
     The light emitting element section  35  is provided on the first main surface  10   a  of the substrate  10 . The light emitting element section  35  includes the plurality of semiconductor light emitting elements  20  and a wavelength conversion layer  31 . 
     In the example, the plurality of semiconductor light emitting elements  20  are disposed in an array shape. The semiconductor light emitting elements  20  are, for example, disposed in a substantially circular shape. For example, the semiconductor light emitting elements  20  are disposed in a substantially equal pitch. 
     The plurality of semiconductor light emitting elements  20  are provided on the first main surface  10   a . Each of the plurality of semiconductor light emitting elements  20  emits the light. For example, the semiconductor light emitting element  20  includes a nitride semiconductor. The semiconductor light emitting element  20  includes, for example, In y Al z Ga 1-x-y N (0≦x≦1, 0≦y≦1, x+y≦1). However, in the embodiment, the semiconductor light emitting element  20  is optional. 
     The plurality of semiconductor light emitting elements  20  include, for example, a first semiconductor light emitting element  20   a , a second semiconductor light emitting element  20   b , or the like. 
     Each of the plurality of semiconductor light emitting elements  20  is electrically connected to one mounting pattern  11   p  in the plurality of mounting patterns  11   p  and to another which is adjacent to the one mounting pattern  11   p  in the plurality of mounting patterns  11   p.    
     For example, the first semiconductor light emitting element  20   a  is electrically connected to the first mounting pattern  11   pa  and the second mounting pattern  11   pb  in the plurality of mounting patterns  11   p . The second mounting pattern  11   pb  is equivalent to another mounting pattern  11   p  which is adjacent to the first mounting pattern  11   pa.    
     For example, each of the plurality of semiconductor light emitting elements  20  includes a first semiconductor layer  21  of a first conductive type, a second semiconductor layer  22  of a second conductive type and a light emitting layer  23 . For example, the first conductive type is an n-type and the second conductive type is a p-type. The first conductive type may be the p-type and the second conductive type may be the n-type. 
     The first semiconductor layer  21  includes a first portion (a first semiconductor portion  21   a ) and a second portion (a second semiconductor portion  21   b ). The second semiconductor portion  21   b  lines up with the first semiconductor portion  21   a  in a direction (for example, the X-axis direction) intersecting the laminating direction (the Z-axis direction from the metal plate  51  toward the light emitting section  40 ). 
     The second semiconductor layer  22  is provided between the second semiconductor portion  21   b  and the mounting substrate section  15 . The light emitting layer  23  is provided between the second semiconductor portion  21   b  and the second semiconductor layer  22 . 
     The semiconductor light emitting element  20  is, for example, a flip-chip type LED. 
     For example, the first semiconductor portion  21   a  of the first semiconductor layer  21  faces the first mounting portion  11   a  of the mounting pattern  11   p . The second semiconductor layer  22  faces the second mounting portion  11   b  of the mounting pattern  11   p . The first semiconductor portion  21   a  of the first semiconductor layer  21  is electrically connected to the mounting pattern  11   p . The second semiconductor layer  22  is electrically connected to another mounting pattern  11   p . For the connection, for example, the solder, a gold bump having high electric conductivity and thermal conductivity, or the like is used. The connection is, for example, performed by a metal melting solder bonding. Otherwise, for example, the connection is performed by an ultrasonic thermo-compression bonding method using the gold bump. 
     That is, for example, the light emitting element section  35  further includes a first bonding metal member  21   e  and a second bonding metal member  22   e . The first bonding metal member  21   e  is provided between the first semiconductor portion  21   a  and one mounting pattern  11   p  (for example, the first mounting portion  11   a ). The second bonding metal member  22   e  is provided between the second semiconductor layer  22  and another mounting pattern  11   p  (for example, the second mounting pattern  11   pb ). At least one of the first bonding metal member  21   e  and the second bonding metal member  22   e  includes the solder or the gold bump. Therefore, each cross-sectional area (a cross-sectional area when cutting in the X-Y plane) of the first bonding metal member  21   e  and the second bonding metal member  22   e  can be increased. Therefore, heat can be efficiently transmitted to the mounting substrate section  15  through the first bonding metal member  21   e  and the second bonding metal member  22   e  and heat radiation is improved. 
     For example, another metal layer may be provided between the semiconductor light emitting element  20  and the mounting substrate section  15 . Therefore, oxidation of the first metal layer can be suppressed or wettability of the solder can be enhanced. The metal layer is not electrically connected to the semiconductor light emitting element  20  and the mounting pattern  11   p . The metal layer is not related to a circuit. 
     The wavelength conversion layer  31  covers at least a part of the plurality of semiconductor light emitting elements  20 . The wavelength conversion layer  31  absorbs at least a part of the light (for example, a first light) emitted from the plurality of semiconductor light emitting elements  20 , and emits a second light. A wavelength (for example, a peak wavelength) of the second light is different from a wavelength (for example, a peak wavelength) of the first light. For example, the wavelength conversion layer  31  includes a plurality of wavelength conversion particles such as fluorescent body and a light-transmitting resin in which a plurality of wavelength conversion particles are dispersed. The first light includes, for example, blue light. The second light includes light whose wavelength is longer than that of the first light. For example, the second light includes at least one of yellow light and red light. 
     In the example, the light emitting element section  35  further includes a reflecting layer  32 . The reflecting layer  32  surrounds the wavelength conversion layer  31  in the X-Y plane. The reflecting layer  32  includes, for example, a plurality of particles such as a metal oxide and a light transmitting resin in which the particles are dispersed. The particles such as the metal oxide have light reflective properties. For the particles such as the metal oxide, for example, at least one of TiO 2  and Al 2 O 3  can be used. The light emitted from the semiconductor light emitting element  20  can be efficiently emitted along a direction (for example, an upward direction) along the laminating direction by providing the reflecting layer  32 . 
     The light emitting section  40  is, for example, a chip-on board (COB) type LED module. 
     In the embodiment, a luminous emittance of light emitted from the light emitting element section  35  (the plurality of semiconductor light emitting elements  20 ) is 10 lm/mm 2  (lumens/square millimeter) or more and 100 lm/mm 2  or less. Preferably, the luminous emittance is 20 lm/mm 2  or more. That is, in the embodiment, a ratio (the luminous emittance) for the light emitted from the light emitting element section  35  with respect to a light-emitting area is very high. In the specification of the application, the light-emitting area substantially corresponds to an area of the mounting region  16 . 
     For example, the light emitting device  110  according to the embodiment is used in the lighting device  210  such as a projector. 
     For the grease layer  53 , lubricant (grease) of liquid or solid, or the like is used. For the grease layer  53 , for example, lubricant (insulating grease) having an insulating property, lubricant (conductive grease) having conductivity or the like is also used. The insulating grease includes, for example, silicone and ceramic particles which are dispersed in the silicone. The conductive grease includes, for example, silicone and metal particles which are dispersed in the silicone. In the conductive grease, for example, the thermal conductivity that is higher than that of the insulating grease is obtained. For example, heat of the light emitting element section  35  is transmitted to the base member  71  by the grease layer  53  and radiated. 
     In the light emitting device  110  according to the embodiment, for example, the metal plate  51  has an area of 5 times or more an area of the mounting region  16  when the metal plate  51  is projected in the X-Y plane. That is, in the embodiment, the area of the metal plate  51  is set to be a lot greater than that of the mounting region  16 . Therefore, the heat generated in the light emitting element section  35  provided on the mounting region  16  spreads in an in-plane direction (an in-plane direction of the X-Y plane) by the metal plate  51  having a large area. Then, the heat spread in the in-plane direction is transmitted toward, for example, the base member  71  and is efficiently radiated. 
       FIG. 2  is a schematic cross-sectional view illustrating the light emitting device according to the first embodiment. 
       FIG. 2  illustrates the light emitting element section  35  provided on the mounting region  16 . 
     As illustrated in  FIG. 2 , the wavelength conversion layer  31  has an upper surface (a wavelength conversion layer upper surface  31   u ). As shown in  FIG. 2 , in the example, the wavelength conversion layer upper surface  31   u  is a concave shape in a region between the plurality of semiconductor light emitting elements  20 . 
     The wavelength conversion layer upper surface  31   u  in the region on the semiconductor light emitting element  20  is positioned above the wavelength conversion layer upper surface  31   u  in a region between adjacent semiconductor light emitting elements  20 . 
     For example, the region between two adjacent semiconductor light emitting elements  20  in the plurality of semiconductor light emitting elements  20  is referred to as a first region R1. The region on two adjacent semiconductor light emitting elements  20  is referred to as a second region R2. 
     A distance between the wavelength conversion layer upper surface  31   u  in the first region R1 and the substrate  10  is referred to as a first distance L1. A distance between the wavelength conversion layer upper surface  31   u  in the second region R2 and the substrate  10  is referred to as a second distance L2. 
     In the embodiment, the first distance L1 is shorter than the second distance L2. 
     That is, the concave section is provided on the wavelength conversion layer upper surface  31   u  in the region between the plurality of semiconductor light emitting elements  20 . 
     In the embodiment, for example, the first distance L1 is not less than 0.55 mm and not more than 0.65 mm. The second distance L2 is, for example, not less than 0.6 mm not more than 0.7 mm. An absolute value of a difference between the first distance L1 and the second distance L2 is, for example, not less than 0.07 times not more than 0.83 times the second distance L2. A height of the semiconductor light emitting element  20  is not less than 0.05 mm not more than 0.60 mm. 
     The height of the wavelength conversion layer  31  in the first region R1 between adjacent semiconductor light emitting elements  20  corresponds to the first distance L1. The height of the wavelength conversion layer  31  in the second region on the semiconductor light emitting element  20  corresponds to the second distance L2. For example, the plurality of semiconductor light emitting elements  20  are provided in the array shape in the X-Y plane. For example, a surface shape of the wavelength conversion layer  31  may also be observed as a scale shape. 
     A part of the heat generated in the light emitting element section  35  is accumulated, for example, in the wavelength conversion layer  31 . The heat accumulated in the wavelength conversion layer  31  is, for example, transmitted to the semiconductor light emitting element  20  and is radiated to the mounting substrate section  15 . For example, the heat is accumulated in the wavelength conversion layer  31  in the region between the semiconductor light emitting elements  20 . In the embodiment, the height of the wavelength conversion layer  31  in the region between the semiconductor light emitting elements  20  is low. Therefore, accumulation of the heat between the semiconductor light emitting elements  20  can be suppressed and heat radiation can be increased. 
     According to the embodiment, the light emitting device having high reliability in which the heat radiation is improved is provided. 
     Second Embodiment 
       FIG. 3  is a schematic cross-sectional view illustrating a light emitting device according to a second embodiment. 
       FIG. 3  is a schematic cross-sectional view of a surface perpendicular to the Y-axis of the light emitting device  110 . The mounting region  16  includes a center section  16   c  and an outer periphery section  16   e.    
     A distance L2c is a distance from the wavelength conversion layer upper surface  31   u  to the substrate  10  in the region on the semiconductor light emitting element  20  which is provided in the center section  16   c.    
     A distance L1c is a distance from the wavelength conversion layer upper surface  31   u  to the substrate  10  in the region between the adjacent semiconductor light emitting elements  20  which are provided in the center section  16   c . The distance L1c is shorter than the distance L2c. 
     A distance L2e is a distance from the wavelength conversion layer upper surface  31   u  to the substrate  10  in the region on the semiconductor light emitting element  20  which is provided in the outer periphery section  16   e.    
     A distance L1e is a distance from the wavelength conversion layer upper surface  31   u  to the substrate  10  in the region between adjacent semiconductor light emitting elements  20  which are provided in the outer periphery section  16   e . The distance L1e is shorter than the distance L2e. 
     In the embodiment, the distance L1c is shorter than the distance L1e. That is, the first distance L1 (that is, the distance L1c) with respect to the semiconductor light emitting element  20  which is positioned in the center section  16   c  of the mounting region  16  is shorter than the first distance L1 (that is, the distance L1e) with respect to the semiconductor light emitting element  20  which is positioned in the outer periphery section  16   e.    
     For example, the distance L1c is not less than 0.54 mm not more than 0.67 mm. The distance L1e is not less than 0.7 mm not more than 0.8 mm. An absolute value of a difference between the distance L1c and the distance L1e is, for example, not less than 0.3 times not more than 0.45 times the distance L1c. 
     In the embodiment, the distance L2c is shorter than the distance L2e. That is, the second distance L2 (that is, the distance L2c) with respect to the semiconductor light emitting element  20  which is positioned in the center section  16   c  of the mounting region  16  is shorter than the second distance L2 (that is, the distance L2e) with respect to the semiconductor light emitting element  20  which is positioned in the outer periphery section  16   e.    
     For example, the distance L2c is not less than 0.6 mm not more than 0.7 mm. The distance L2e is not less than 0.75 mm not more than 0.85 mm. An absolute value of difference between the distance L2c and the distance L2e is for example, not less than 0.2 times not more than 0.25 times the distance L2c. 
     A part of the heat generated in the light emitting element section  35  is accumulated, for example, in the wavelength conversion layer  31 . For example, the heat is likely to be accumulated in the wavelength conversion layer  31  in the region on the center section  16   c . In the embodiment, the height (the distance L1c) of the wavelength conversion layer  31  in the region on the center section  16   c  is lower than that (the distance L2c) of the wavelength conversion layer  31  in the region on the outer periphery section  16   e . Then, the distance L2c is shorter than the distance L2e. Therefore, the accumulation of the heat in the wavelength conversion layer  31  in the region on the center section  16   c  can be suppressed. For example, a difference between a temperature of the semiconductor light emitting element  20  in the region on the center section  16   c  and a temperature of the semiconductor light emitting element  20  in the region on the outer periphery section  16   e  is small. According to the embodiment, the light emitting device having high reliability in which the accumulation of the heat is suppressed and the heat radiation is improved is provided. 
     Third Embodiment 
       FIG. 4A  to  FIG. 4G  are schematic views illustrating a light emitting device according to a third embodiment.  FIG. 4A  is a plan view of a part of the mounting region  16  of a light emitting device  110   a  according to the third embodiment. 
       FIG. 4B  is a schematic cross-sectional view illustrating a cross-section along line B1-B2 of  FIG. 4A . 
       FIG. 4C  is a schematic cross-sectional view illustrating a cross-section along line C1-C2 of  FIG. 4A . 
       FIG. 4D  is a schematic cross-sectional view illustrating a cross-section along line D1-D2 of  FIG. 4A . 
       FIG. 4E  is a schematic cross-sectional view illustrating a cross-section along line E1-E2 of  FIG. 4A . 
       FIG. 4F  is a schematic cross-sectional view illustrating a cross-section along line F1-F2 of  FIG. 4A . 
       FIG. 4G  is a schematic cross-sectional view illustrating a cross-section along line G1-G2 of  FIG. 4A . 
     As shown in  FIG. 4A , in the light emitting device  110   a , the plurality of semiconductor light emitting elements  20  are provided on the upper surface of the substrate  10 . The plurality of semiconductor light emitting elements  20  include a first semiconductor element  20   i , a second semiconductor element  20   j , a third semiconductor element  20   k  and a fourth semiconductor element  20   l.    
     The second semiconductor element  20   j  is separated from the first semiconductor element  20   i  in a first direction (for example, the X-axis direction) parallel to the upper surface of the substrate  10 . 
     The third semiconductor element  20   k  is separated from the first semiconductor element  20   i  in a second direction (for example, the Y-axis direction) which is parallel to the upper surface of the substrate  10  and intersecting the first direction. 
     The fourth semiconductor element  20   l  is separated from the third semiconductor element  20   k  in the X-axis direction and is separated from the second semiconductor element  20   j  in the Y-axis direction. 
     The wavelength conversion layer  31  covers the plurality of semiconductor light emitting elements  20 . The wavelength conversion layer  31  includes a first portion P1, a second portion P2, a third portion P3, a fourth portion P4 and a fifth portion P5. 
     The first portion P1 is a region between the first semiconductor element  20   i  and the second semiconductor element  20   j . The second portion P2 is a region between the first semiconductor element  20   i  and the third semiconductor element  20   k . The third portion P3 is a region between the second semiconductor element  20   j  and the fourth semiconductor element  20   l . The fourth portion P4 is a region between the third semiconductor element  20   k  and the fourth semiconductor element  20   l . The fifth portion P5 is a region between the first portion P1 and the fourth portion P4, and between the second portion P2 and the third portion P3. 
     The first portion P1, the second portion P2, the third portion P3 and the fourth portion P4 are a region R1 which is provided in a region between adjacent semiconductor light emitting elements  20 . 
     As shown in  FIG. 4B , a distance between the wavelength conversion layer upper surface  31   u  and the substrate  10  in the fourth portion P4 is the first distance L1. 
     As shown in  FIG. 4C , a distance between the wavelength conversion layer upper surface  31   u  and the substrate  10  in the first portion P1 is the first distance L1. 
     As shown in  FIG. 4D , a distance between the wavelength conversion layer upper surface  31   u  and the substrate  10  in the second portion P2 is the first distance L1. 
     As shown in  FIG. 4E , a distance between the wavelength conversion layer upper surface  31   u  and the substrate  10  in the third portion P3 is the first distance L1. 
     As shown in  FIG. 4F  and  FIG. 4G , a distance between the wavelength conversion layer upper surface  31   u  and the substrate  10  in the fifth portion is a third distance L3. 
     In the light emitting device  110   a  according to the embodiment, the third distance L3 is shorter than the first distance L1. 
     The accumulation of the heat in the wavelength conversion layer  31  between the semiconductor light emitting elements  20  can be suppressed by making the third distance L3 shorter than the first distance L1. Therefore, the light emitting device having high reliability in which the heat radiation is improved is provided. 
     For example, the first portion P1 to fourth portion P4 are sandwiched between two semiconductor light emitting elements. Therefore, a part of the heat of those portions is radiated by a path through the semiconductor light emitting elements. Meanwhile, the fifth portion P5 is sandwiched by the first portion P1 to fourth portion P4 instead of the semiconductor light emitting elements. Thus, the heat of the fifth portion P5 is unlikely to be radiated. The heat of the fifth portion P5 is effectively radiated by making the height of the wavelength conversion layer  31  in the fifth portion P5 lower than those of the other portions. 
       FIG. 5A  to  FIG. 5C  are schematic views illustrating a light emitting device according to an embodiment. 
       FIG. 5A  is a graph illustrating concavity and convexity of the wavelength conversion layer upper surface  31   u  in the X-Y plane of the light emitting device  110   a.    
     A vertical axis of  FIG. 5A  is a height h of the wavelength conversion layer  31 . A horizontal axis of  FIG. 5A  is, for example, a position x in the X-Y plane. The height h is a position in the Z-axis direction. 
     In the example, the height of the semiconductor light emitting element is 0.40 mm and an average value of the thickness (the distance from semiconductor light emitting element to the upper surface of the wavelength conversion layer) of the wavelength conversion layer  31  is 0.25 mm. In the example, the outer periphery section  16   e  is a region in which the position x is the vicinity of 0 mm to 7.0 mm and a region in which the position x is the vicinity of 13.0 mm to 20.0 mm. The center section  16   c  is a region in which the position x is the vicinity of 7.0 mm to 14.0 mm. In the center section  16   c , a depth of the concave section is approximately 0.045 mm to 0.060 mm. 
       FIG. 5B  is a schematic perspective view of the wavelength conversion layer  31  of the light emitting device  110   a . Moreover, the view is obtained by changing the position x and measuring the reflected light while radiating light of optical laser into the light emitting element section. 
       FIG. 5C  is a schematic plan view of the wavelength conversion layer  31  of the light emitting device  110   a.    
     As shown in  FIG. 5B  and  FIG. 5C , a concave section  31   ua  and a convex section  31   ub  are provided in the wavelength conversion layer upper surface  31   u . A shape of the wavelength conversion layer upper surface  31   u  may be observed as a scale shape. Therefore, the light emitting device having high reliability in which the heat radiation is improved is provided. 
       FIG. 6  is a graph illustrating characteristics of a light emitting device of according to embodiment. 
       FIG. 6  illustrates a temperature of the mounting region  16 . A horizontal axis of  FIG. 6  is a depth R1 of a concave section of the concavity and convexity of the wavelength conversion layer  31 . The depth R1 is a ratio of an absolute value of a difference between the first distance L1 and the second distance L2 with respect to the second distance L2. That is, the depth R1 is |L2−L1|/L2. A vertical axis of  FIG. 6  is a temperature T1 of a center section of the mounting region  16  when emitting the light. 
     The temperature T1 is 96.1° C. when the depth R1 is 0.76. 
     The temperature T1 is 96.3° C. when the depth R1 is 0.69. 
     The temperature T1 is 97.8° C. when the depth R1 is 0.62. 
     The depth R1 is, for example, preferably 0.69 or more. The upper limit is 0.90. If the depth R1 is greater than 0.90, moving of the heat is suppressed between adjacent regions and imbalance of the heat may be caused. 
     Moreover, the concave section can be generated, for example, by pouring resin between electrodes on a lower side of a flip chip type LED or by a viscosity of the resin which is poured when manufacturing. A depth of the concave section affects those conditions, the height of the semiconductor light emitting element which is used, or the like. 
     According to the embodiment, the light emitting device having high reliability is provided. 
     Moreover, in the specification of the application, terms of “perpendicular” and “parallel” are not only strictly perpendicular and strictly parallel but also are intended to include variations thereof or the like, for example, in a manufacturing process, and may be substantially perpendicular and substantially parallel. 
     Above, the embodiments are described with reference to specific examples. However, the exemplary embodiment is not limited to the specific examples. For example, specific configurations of each element such as the semiconductor light emitting element, the wavelength conversion layer and the substrate are included within the scope of the exemplary embodiment as long as the configurations can be executed similar to the exemplary embodiment and the same effects can be obtained by those skilled in the art. 
     Further, that two or more elements of each specific example are combined in a technically possible range is included in the scope of the exemplary embodiment as long as the gist of the exemplary embodiment is included. 
     In addition, in the scope of the spirit of the exemplary embodiment, those skilled in the art can conceive various modification examples and alteration examples, and it is understood that the modification examples and the alteration examples belong within the scope of the exemplary embodiment. 
     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.