BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a light emitting device.  
         [0003]     2. Related Background Art  
         [0004]     A known light emitting device of this type is one having a semiconductor light-emitting element, and a varistor connected in parallel to this semiconductor light-emitting element (e.g., Japanese Patent Application Laid-Open No. 2001-15815). In the light emitting device described in Patent Document 1, the semiconductor light-emitting element is protected from an ESD (Electrostatic Discharge) surge by the varistor connected in parallel thereto.  
       SUMMARY OF THE INVENTION  
       [0005]     Incidentally, the semiconductor light-emitting element generates heat during its light-emitting operation. As the temperature of the semiconductor light-emitting element becomes higher, the light-emitting operation is affected thereby. For this reason, it is necessary to efficiently dissipate the heat generated. Particularly, in a case where the semiconductor light-emitting element is sealed in an optically transparent resin, it becomes difficult to dissipate the heat generated in the semiconductor light-emitting element.  
         [0006]     An object of the present invention is to provide a light emitting device capable of efficiently dissipating heat generated in a semiconductor light-emitting element.  
         [0007]     A light emitting device according to the present invention is a light emitting device comprising a semiconductor light-emitting element and a multilayer chip varistor, wherein the multilayer chip varistor comprises: a laminate having a varistor layer comprised essentially of ZnO, and a plurality of internal electrodes arranged to sandwich the varistor layer between the internal electrodes; and a plurality of external electrodes formed on an outer surface of the laminate and each connected to a corresponding internal electrode out of the plurality of internal electrodes; wherein the semiconductor light-emitting element comprises: an electroconductive substrate of ZnO or GaN; and a pair of semiconductor layers of ZnO or GaN formed by epitaxial growth on two surfaces of the electroconductive substrate; wherein the semiconductor light-emitting element is placed on an outer surface intersecting with the internal electrodes of the multilayer chip varistor, and wherein one of the pair of semiconductor layers is fixed in face contact to the mentioned outer surface.  
         [0008]     According to the present invention, the multilayer chip varistor is connected in parallel to the semiconductor light-emitting element, whereby the semiconductor light-emitting element can be protected from the ESD surge. In addition, since in the present invention the multilayer chip varistor has the external electrodes connected to the semiconductor light-emitting element and the internal electrodes connected to the external electrodes, the heat generated in the semiconductor light-emitting element is transferred mainly to the external electrodes and the internal electrodes to be dissipated. The configuration of the present invention expands heat-radiation paths of the heat generated in the semiconductor light-emitting element and is thus able to efficiently dissipate the heat generated in the semiconductor light-emitting element Furthermore, the semiconductor layer is fixed in face contact to the outer surface of the multilayer chip varistor, whereby the p-type semiconductor layer or n-type semiconductor layer is thermally, electrically, and mechanically connected to the outer surface, so as to achieve more effective transmission of heat Incidentally, the varistor layer is comprised essentially of ZnO. ZnO has the thermal conductivity equivalent to that of alumina or the like normally used as a heat-radiating substrate and thus has the relatively good thermal conductivity. Therefore, it is feasible to prevent the varistor layer from inhibiting dissipation of heat from the internal electrodes.  
         [0009]     The present invention as described above successfully provides the light emitting device capable of efficiently dissipating the heat generated in the semiconductor light-emitting element. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a drawing showing a sectional configuration of a light emitting device according to an embodiment of the present invention  
         [0011]      FIG. 2  is a schematic top view of the light emitting device according to the embodiment of the present invention.  
         [0012]      FIG. 3  is a schematic bottom view of the light emitting device according to the embodiment of the present invention.  
         [0013]      FIG. 4  is a drawing showing a sectional configuration of a light emitting device as a modification example.  
         [0014]      FIG. 5  is a schematic top view of the light emitting device as the modification example.  
         [0015]      FIG. 6  is a flowchart for explaining a production process of the light emitting device as the embodiment of the present invention.  
         [0016]      FIG. 7  is a drawing for explaining the production process of the light emitting device as the embodiment of the present invention 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     The expertise of the present invention can be readily understood in view of the following detailed description with reference to the accompanying drawings presented by way of illustration only. Subsequently, an embodiment of the present invention will be described with reference to the accompanying drawings. The same portions will be denoted by the same reference symbols as much as possible, without redundant description.  
         [0018]     A configuration of a light emitting device  1  according to the embodiment of the present invention will be described with reference to FIGS.  1  to  3 .  FIG. 1  is a drawing for explaining a sectional configuration of the light emitting device  1  according to the present embodiment, and shows a cross section near the center of the light emitting device  1 .  FIG. 2  is a schematic top view of the light emitting device  1 .  FIG. 3  is a schematic bottom view of the light emitting device  1 .  
         [0019]     The light emitting device  1 , as shown in FIGS.  1  to  3 , is provided with a semiconductor light-emitting element  20  and a multilayer chip varistor  10 . The semiconductor light-emitting element  20  is laid on the multilayer chip varistor  10 . The semiconductor light-emitting element  20  is covered by a silicone layer  30  containing fine particles of a phosphor.  
         [0020]     First, a configuration of the multilayer chip varistor  10  will be described The multilayer chip varistor  10  has a varistor element  11  of approximately a rectangular parallelepiped shape, a plurality (a pair in the present embodiment) of external electrodes  50 , and a plurality (a pair in the present embodiment) of external electrodes  103 ,  104 .  
         [0021]     The pair of external electrodes  50  are formed each on one principal surface (outer surface)  11   a  of the varistor element  11 . The pair of external electrodes  103 ,  104  are formed each on the other principal surface (outer surface)  11   b  of the varistor element  11 . The varistor element  11  is set, for example, to the length of about 0.5 to 2.0 mm, the width of about 0.5 to 2.0 mm, and the thickness of about 0.3 mm. The external electrode  103  functions as an input terminal electrode of the multilayer chip varistor  10 , while the external electrode  104  functions as an output terminal electrode of the multilayer chip varistor  10 . The external electrodes  50  function as pad electrodes electrically connected to the semiconductor light-emitting element  20  described later.  
         [0022]     The varistor element  11  is constructed as a laminate in which a plurality of varistor layers to exhibit the current-voltage nonlinear characteristic (hereinafter referred to as “varistor characteristic”), and a plurality of first internal electrodes  101  and second internal electrodes  102  are stacked. The first internal electrodes  101  and the second internal electrodes  102  are a plurality of layers alternately arranged along a stack direction of the varistor layers (which will be referred to hereinafter simply as “stack direction”) in the varistor element  11 .  
         [0023]     The first internal electrodes  101  and the second internal electrodes  102  are arranged so that at least one varistor layer is sandwiched between the first and second internal electrodes. The pair of principal surfaces  11   a ,  11   b  of the varistor element  11  extend in a direction parallel to the stack direction of the varistor layers. The first internal electrodes  101  and the second internal electrodes  102  are juxtaposed along the stack direction of the varistor layers. In practical multilayer chip varistor  10 , the plurality of varistor layers are integrally formed so that no boundary can be visually recognized between the layers.  
         [0024]     The varistor layers are made of an element material containing ZnO (zinc oxide) as a principal component and containing Co, a rare-earth metal element, or Bi as an accessory component Furthermore, the varistor layers contain single metals such as a IIIb element (B, Al, Ga, In), Si, Cr, Mo, an alkali metal element (K, Rb, Cs), and an alkaline-earth metal element (Mg, Ca, Sr, Ba), or oxides of these. In the present embodiment the varistor layers contain Pr, Co, Cr, Ca, Si, K, Al, etc. as accessory components.  
         [0025]     In the present embodiment Pr is used as a rare-earth metal. Pr is a material for the varistor layers to exhibit the varistor characteristic. The reason for use of Pr is that Pr demonstrates excellent current-voltage nonlinearity and little characteristic variation in mass production. There are no particular restrictions on the content of ZnO in the varistor layers, but it is normally 99.8 to 69.0% by mass, where the total content of all the materials forming the varistor layers is 100% by mass. The thickness of the varistor layers is, for example, approximately 5-60 μm.  
         [0026]     Each first internal electrode  101  includes a first electrode portion  101   a , a second electrode portion  101   b , a third electrode portion  101   c , and a fourth electrode portion  101   d . The fourth electrode portion  101   d  overlaps with a third electrode portion  102   c  of a second internal electrode  102  described later, when viewed from the stack direction. The fourth electrode portion  101   d  is of approximately rectangular shape.  
         [0027]     The third electrode portion  101   c  is drawn out from the fourth electrode portion  101   d  so as to be exposed in one principal surface  11   b , and functions as a lead conductor. The third electrode portion  101   c  is physically and electrically connected to the external electrode  104 .  
         [0028]     The first electrode portion  101   a  and second electrode portion  101   b  are drawn out from the fourth electrode portion  101   d  so as to be exposed in the other principal surface  11   a , and function as lead conductors. The first electrode portion  101   a  and the second electrode portion  101   b  are physically and electrically connected to the pair of external electrodes  50 , respectively.  
         [0029]     The fourth electrode portion  101   d  is electrically connected through the third electrode portion  101   c  to the external electrode  104  and is also electrically connected through the first electrode portion  101   a  and the second electrode portion  101   b  to the pair of external electrodes  50 . The first electrode portion  101   a , second electrode portion  101   b , and third electrode portion  101   c  are formed integrally with the fourth electrode portion  101   d.    
         [0030]     Each second internal electrode  102  includes a first electrode portion  102   a , a second electrode portion  102   b , and a third electrode portion  102   c . The third electrode portion  102   c  overlaps with the fourth electrode portion  101   d  of the first internal electrode  101 , when viewed from the stack direction. The third electrode portion  102   c  is of approximately rectangular shape.  
         [0031]     The second electrode portion  102   b  is drawn out from the third electrode portion  102   c  so as to be exposed in one principal surface  11   b , and functions as a lead conductor. The second electrode portion  102   b  is physically and electrically connected to the external electrode  103 .  
         [0032]     The first electrode portion  102   a  is drawn out from the third electrode portion  102   c  so as to be exposed in the other principal surface  11   a , and functions as a lead conductor. The first electrode portion  102   a  is physically and electrically connected through an external electrode  60  to the semiconductor light-emitting element  20 . It is also preferable to interpose an Au-Sn solder layer between the semiconductor light-emitting element  20  and the external electrode  60 . Each third electrode portion  102   c  is electrically connected through the second electrode portion  102   b  to the external electrode  103  and is also electrically connected through the first electrode portion  102   a  to the semiconductor light-emitting element  20 . The first electrode portion  102   a  and second electrode portion  102   b  are formed integrally with the third electrode portion  102   c.    
         [0033]     The first and second internal electrodes  101 ,  102  contain an electroconductive material. There are no particular restrictions on the electroconductive material in the first and second internal electrodes  101 ,  102 , but it is preferably a material consisting of Pd or Ag—Pd alloy or Ag. The thickness of the first and second internal electrodes  101 ,  102  is, for example, approximately 0.5-5 μm.  
         [0034]     The external electrode  103  and the external electrode  104  are arranged with a predetermined spacing in a direction perpendicular to the stack direction of the varistor layers and parallel to the other principal surface  11   a , on one principal surface  11   b . The external electrodes  103 ,  104  are of rectangular shape.  
         [0035]     The pair of external electrodes  50  are arranged with a predetermined spacing in a direction perpendicular to the stack direction of the varistor layers and parallel to the one principal surface  11   b , on the other principal surface  11   a . The external electrodes  50  are of rectangular shape, and are formed so as to be electrically connected to the first electrode portion  101   a  and the second electrode portion  101   b  of each internal electrode  101 .  
         [0036]     The fourth electrode portion  101   d  of the first internal electrode  101  overlaps with the third electrode portion  102   c  of the second internal electrode  102 , between the fourth electrode portions  101   d  of first internal electrodes  101  adjacent to each other. Therefore, a region in a varistor layer overlapping with the fourth electrode portion  101   d  and the third electrode portion  102   c  functions as a region to exhibit the varistor characteristic. In the multilayer chip varistor  10  having the above-described configuration, one varistor part is constructed of the fourth electrode portions  101   d , the third electrode portions  102   c , and the regions in the varistor layers overlapping with the fourth electrode portions  101   d  and the third electrode portions  102   c.    
         [0037]     Subsequently, a configuration of the semiconductor light-emitting element  20  will be described. The semiconductor light-emitting element  20  is a Light-Emitting Diode (LED) of a ZnO semiconductor. The semiconductor light-emitting element  20  is of approximately a rectangular parallelepiped shape, and has an n-ZnO transparent electrode layer  201 , an n-ZnO substrate  202 , an n-ZnO layer  203 , a luminous layer  204 , and a p-ZnO layer  205  in the order named. Although the present embodiment uses the light-emitting diode of the ZnO semiconductor, it is also possible to use a light-emitting diode of a GaN semiconductor. In that case, the substrate is also a GaN substrate. Since GaN and ZnO have the respective lattice constants and coefficients of thermal expansion close to each other, it is also possible, for example, to adopt a configuration wherein a GaN semiconductor layer is formed on a ZnO substrate.  
         [0038]     The semiconductor light-emitting element  20  is an element wherein the n-ZnO transparent electrode layer  201  being an n-type semiconductor region is formed on one principal surface of the n-ZnO substrate  202  by epitaxial growth and wherein the n-ZnO layer  203  of an n-type semiconductor region, the luminous layer  204 , and the p-ZnO layer  205  of a p-type semiconductor region are formed on the other principal surface of the n-ZnO substrate  202  by epitaxial growth. The n-ZnO substrate  202  is an electrically conductive, transparent substrate.  
         [0039]     The luminous layer  204  is formed on the n-ZnO layer  203  of the n-type semiconductor region and generates light in a luminous region through recombination of carriers (electrons and holes) supplied from the n-ZnO layer  203  and from the p-ZnO layer  205 . The luminous layer  204  can be, for example, of the SQW structure of ZnO. The luminous region is made in a region into which the carriers are injected, in the luminous layer  204 .  
         [0040]     In the semiconductor light-emitting element  20  the p-ZnO layer  205  is fixed onto the principal surface  11   a  of the multilayer chip varistor  10  by the external electrode  60  of an Au-Sn solder. Pad electrodes  40  are formed at six positions on the n-ZnO transparent electrode layer  201  of the semiconductor light-emitting element  20 . Each pad electrode  40  is electrically connected to the external electrode  50  of the multilayer chip varistor  10  by wire bonding. Therefore, a voltage can be applied between the p-ZnO layer  205  of the p-type semiconductor region and the n-ZnO layer  203  of the n-type semiconductor region, whereby the semiconductor light-emitting element  20  emits light according to the voltage applied.  
         [0041]     A modification example of the present embodiment will be described with reference to  FIGS. 4 and 5 .  FIG. 4  is a drawing showing a sectional configuration of a light emitting device  4  as the modification example of the present embodiment  FIG. 5  is a schematic top view of the light emitting device  4 . The light emitting device  4  is provided with a multilayer chip varistor  10  and a semiconductor light-emitting element  20 , the configurations of which are the same as those described above and the description of which is thus omitted herein.  
         [0042]     A conductor layer  80  and conductor layers  70  are formed each on the principal surface  11   a  of the multilayer chip varistor  10  in the light emitting device  4 . The conductor layer  80  is of much the same shape as the external electrode  60  in the light emitting device  1 . Therefore, the conductor layer  80  is electrically connected to each second internal electrode  102  of the multilayer chip varistor  10 . The conductor layers  70  are of much the same shape as the external electrodes  50  in the light emitting device  1 . Therefore, the conductor layers  70  are electrically connected to each first internal electrode  101  of the multilayer chip varistor  10 .  
         [0043]     An insulating layer  90  is formed so as to cover the conductor layers  70  and conductor layer  80 . Contact holes  901  and a contact hole  902  are formed at predetermined positions in the insulating layer  90 . The contact holes  901  are formed at the four corners of the principal surface  11   a  of the multilayer chip varistor  10  and approximately in the central regions of a pair of edges facing each other. The contact hole  902  is formed approximately in the central region of the principal surface  11   a  (the portion where the semiconductor light-emitting element  20  is mounted) and in a shape approximately equal to the contour of the semiconductor light-emitting element  20 .  
         [0044]     Pad electrodes  55  and pad electrodes  57  are formed at the positions corresponding to the contact holes  901 . Since the insulating layer  90  is formed as described above, the shapes and positions of the pad electrodes  55  and pad electrodes  57  can be arbitrarily set. The shapes of the pad electrodes  55  and pad electrodes  57  shown in  FIG. 5  are just an example, and they can also be integrally provided so as to extend along the outer periphery of the principal surface  11   a , for example.  
         [0045]     An external electrode  80  is formed at the position corresponding to the contact hole  902 . The semiconductor light-emitting element  20  is mounted and fixed on this external electrode  80 . Electrodes  40 , electrodes  42 , and electrodes  44  are formed each on the semiconductor light-emitting element  20 . Each electrode  40  is connected to a pad electrode  55 , and each of the electrodes  42  and  44  is connected to a pad electrode  57 . The positions of these electrodes  40 ,  42 ,  44  are also arbitrary, and the connections thereof to the pad electrodes can also be arbitrarily set  
         [0046]     Subsequently, a production process of the light emitting device  1  having the above-described configuration will be described with reference to  FIGS. 6 and 7 .  FIG. 6  is a flowchart for explaining a production process of the multilayer chip varistor according to the present embodiment.  FIG. 7  is a drawing for explaining the production process of the multilayer chip varistor according to the present embodiment  
         [0047]     The first step is to weigh each of ZnO as a principal component and trace additives such as metals or oxides of Pr, Co, Cr, Ca, Si, K, and Al for the varistor layers, at a predetermined ratio and thereafter mix them to prepare a varistor material (step S 101 ). After that, an organic binder, an organic solvent, an organic plasticizer, etc. are added into this varistor material and they are mixed and pulverized for about 20 hours with a ball mill or the like to obtain a slurry.  
         [0048]     This slurry is applied onto a film, for example, of a polyethylene terephthalate by a known method such as the doctor blade method, and thereafter dried to form membranes in the thickness of about 30 μm. The membranes obtained in this manner are stripped off from the film to obtain green sheets (step S 103 ).  
         [0049]     Next, a plurality of electrode portions corresponding to the first and second internal electrodes  101 ,  102  (in the number corresponding to the number of divided chips described later) are formed on the green sheets (step S 105 ). The electrode portions corresponding to the first and second internal electrodes  101 ,  102  are formed by printing an electroconductive paste as a mixture of a metal powder consisting primarily of Pd particles, an organic binder, and an organic solvent, by a printing method such as screen printing, and drying it.  
         [0050]     The next step is to stack the green sheets with the electrode portions and green sheets without the electrode portions in the predetermined order to form a sheet laminate (step S 107 ). The sheet laminate obtained in this manner is cut in chip units to obtain a plurality of divided green bodies GL 1  (cf.  FIG. 7 ) (step S 109 ).  
         [0051]     In the resultant green body GL 1 , the green sheets successively stacked include the green sheets GS 1  on each of which an electrode portion EL 1  corresponding to the first internal electrode  101  is formed, the green sheets GS 2  on each of which an electrode portion EL 2  corresponding to the second internal electrode  102  is formed, and the green sheets GS 3  without the electrode portions EL 1 , EL 2 . The green sheet GS 3  located between a green sheet GS 1  and a green sheet GS 2  may consist of a plurality of sheets, or may be excluded.  
         [0052]     The next step is to deliver an electroconductive paste for the external electrodes  103 ,  104 ,  50  onto outer surfaces of the green body GL 1  (step S 111 ). At this step the electrode portions are formed by printing the electroconductive paste so as to contact the corresponding electrode portions EL 1 , EL 2  on one principal surface of the green body GL 1  by the screen printing technique and thereafter drying it.  
         [0053]     The next step is to subject the green body GL 1  with the electroconductive paste to a thermal treatment at 180-400° C. and for about 0.5-24 hours to effect debindering and thereafter perform baking at 1000-1400° C. and for about 0.5-8 hours (step S 113 ). This baking turns the green sheets GS 1 -S 3  in the green body GL 1 , into varistor layers. Each electrode portion EL 1  turns into the second internal electrode  102 . Each electrode portion EL 2  turns into the first internal electrode  101 .  
         [0054]     The above process results in obtaining the multilayer chip varistor  10 . After the baking, an alkali metal (e.g., Li, Na, or the like) may be diffused from the surface of the varistor element  11 .  
         [0055]     After that, the semiconductor light-emitting element  20  prepared in advance is mounted and fixed on the multilayer chip varistor  10  and is covered by the silicone layer  30  to obtain the light emitting device  1  (step S 115 ).  
         [0056]     In the present embodiment, as described above, the multilayer chip varistor  10  is connected in parallel to the semiconductor light-emitting element  20 , whereby the semiconductor light-emitting element  20  can be protected from the ESD surge.  
         [0057]     Since in the present embodiment the multilayer chip varistor  10  has the external electrodes  50  and external electrode  60  connected to the semiconductor light-emitting element  20  and the internal electrodes  101 ,  102  connected to the external electrodes  50  and to the external electrode  60 , the heat generated in the semiconductor light-emitting element  20  is transferred mainly to the internal electrodes  101 ,  102  to be dissipated. The present embodiment expands the heat-radiation paths of the heat generated in the semiconductor light-emitting element  20 , and is thus able to efficiently dissipate the heat generated in the semiconductor light-emitting element  20 .  
         [0058]     In the present embodiment the varistor layers contain ZnO as a principal component ZnO has the thermal conductivity equivalent to that of alumina or the like normally used as a heat-radiating substrate, and thus has the relatively good thermal conductivity. Therefore, it is feasible to prevent the varistor layers from inhibiting dissipation of the heat from the internal electrodes  101 ,  102 .  
         [0059]     Incidentally, in the multilayer chip varistor  10  of the present embodiment the external electrode  103  functioning as an input terminal electrode and the external electrode  104  functioning as an output terminal electrode are placed both on one principal surface  11   b  of the varistor element  11 . This multilayer chip varistor  10  is mounted on an external substrate, an external device, or the like by electrically and mechanically connecting each of the external electrodes  103 ,  104  to a land corresponding to the external electrode  103 ,  104 , using a solder ball, a bump electrode, or the like.  
         [0060]     In the present embodiment, preferably, the green body GL 1  contains Pr, and the electroconductive paste for the external electrodes  60 ,  80 ,  103 ,  104  contains one of Pd, Au, Ag, Pt, Al, and Ni. Since the green body GL 1  with the electroconductive paste is baked to obtain the varistor element  11  and the electrode layers for the external electrodes  103 ,  104 , the varistor element  11  and the electrode layers are simultaneously baked. This can enhance the adhesive strength between the varistor element  11  and the external electrodes  103 ,  104 . The electroconductive paste may further contain glass for improvement in the adhesive strength.  
         [0061]     When the multilayer chip varistor is constructed in the form of a BGA package, the area of the external electrodes functioning as the input/output terminal electrodes or ground terminal electrode is particularly small. For this reason, the adhesive strength becomes lower between the varistor element and the external electrodes, so that the external electrodes could be delaminated from the varistor element. However, the multilayer chip varistor  10  of the present embodiment is improved in the adhesive strength between the varistor element  11  and the external electrodes  103 ,  104  as described above, whereby the external electrodes  103 ,  104  are prevented from being delaminated from the varistor element  11 .  
         [0062]     In the present embodiment, the pair of external electrodes  103 ,  104  are formed on one principal surface  11   b  of the varistor element  11 , and the pair of external electrodes  50  are formed on the other principal surface  11   a  facing the one principal surface  11   b . The first and second internal electrodes  101 ,  102  include the fourth electrode portions  101   d  and third electrode portions  102   c  overlapping with each other, and the first electrode portions  101   a , second electrode portions  101   b , third electrode portions  101   c , first electrode portions  102   a , and second electrode portions  102   b  drawn out from the fourth electrode portion  101   d  and from the third electrode portion  102   c  so as to be exposed in the one principal surface  11   b  and in the other principal surface  11   a . The plurality of external electrodes  103 ,  104 ,  50 , and the external electrode  60  are electrically connected to the corresponding internal electrodes  101 ,  102  through the first electrode portion  101   a , second electrode portion  101   b , third electrode portion  101   c , first electrode portion  102   a , or second electrode portion  102   b . In this case, the semiconductor light-emitting element  20  is connected to the external electrodes  50  and external electrode  60 , whereby it is mounted on the multilayer chip varistor  10 . Therefore, it is easy and simple to implement mounting for electrically and physically connecting the semiconductor light-emitting element  20  to the external electrodes  50  and the external electrode  60 . The multilayer chip varistor  10  is mounted on an external substrate, an external device, or the like in a state in which the one principal surface  11   b  with the external electrodes  103 ,  104  faces the external substrate, external device, or the like. Therefore, it is also easy and simple to implement mounting of the multilayer chip varistor  10 .  
         [0063]     In the present embodiment the semiconductor light-emitting element can be connected to the plurality of external electrodes  50 ,  55  by wire bonding with a plurality of wires, whereby the heat generated in the semiconductor light-emitting element  20  can be more efficiently dissipated through the wires. The electroconductive paste for the external electrodes  50 ,  55  contains one of Au, Pd, and Ag. Preferably, it contains Au in order to facilitate the wire bonding. In addition, it may further contain glass in order to improve the adhesive strength.
An object is to provide a light emitting device capable of efficiently dissipating heat generated in a semiconductor light-emitting element. The light emitting device 1 for achieving this object is a device wherein a multilayer chip varistor 10 has a varistor element 11 having a varistor layer comprised essentially of ZnO, and a plurality of internal electrodes 101, 102 arranged to sandwich the varistor layer between the internal electrodes; and a plurality of external electrodes 103, 104 formed on an outer surface of the varistor element 11 and each connected to a corresponding internal electrode 101, 102; wherein a semiconductor light-emitting element 20 has an electroconductive substrate 202 of ZnO, and semiconductor layers 201, 203, 205 of ZnO formed by epitaxial growth on two surfaces of the electroconductive substrate 202; wherein the semiconductor light-emitting element 20 is placed on a principal surface 11 a intersecting with the internal electrodes 101, 102 of the multilayer chip varistor 10; wherein the semiconductor layer 205 is fixed in face contact to the principal surface 11 a.