Patent Publication Number: US-9853242-B2

Title: Sealing structure and organic electroluminescence device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sealing structure and an organic electroluminescence device. 
     2. Description of the Related Art 
     Research and development have been extensively conducted on organic electroluminescence elements. In the fundamental structure of the organic electroluminescence element, a layer containing a light-emitting organic compound is interposed between a pair of electrodes. By applying voltage to this element, light emission from the light-emitting organic compound can be obtained. 
     The light-emitting device using an organic electroluminescence element is, for example, a lighting device, or an image display device including a thin film transistor. The organic electroluminescence element can be formed in a film shape and thus easily increased in area, which allows a lighting device with a planar light source to be realized. In addition, an image display device using an organic electroluminescence element needs no backlight which is necessary for liquid crystal display devices and the like; therefore, thin, lightweight, high contrast, and low power consumption display devices can be obtained. 
     It is known that when the organic electroluminescence element is exposed to the air (including moisture, oxygen, and the like), its performance degrades rapidly. It is thus required that the organic electroluminescence element be hermitically sealed with a material having a high gas barrier property so as not to be exposed to the air. 
     A sealing technique using glass frit including a low-melting-point glass is known as a technique that realizes sealing with a high gas barrier property. The technique disclosed in Patent Document 1 is as follows: a paste containing a binder and a frit material including a low-melting-point glass is applied onto a glass substrate; the binder is removed through prebaking; and the glass frit is irradiated with laser light while a counter glass substrate is provided over the glass substrate, whereby the glass frit is melted and the substrates are bonded to each other and sealed with the glass frit. When a device using an organic electroluminescence element is sealed with such glass frit, the organic electroluminescence element can be isolated from the external air and a light-emitting device with high reliability can be realized. 
     In a light-emitting device to which an organic electroluminescence element is applied, there are common power supply lines between a substrate and glass frit and the number of common power supply lines overlapping the glass frit varies depending on the location. For example, there is a plurality of common power supply lines between the glass frit and the substrate at an edge portion of one side of a sealing structure and there is one common power supply line between the glass frit and the substrate at the middle portion of the one side of the sealing structure. When the glass frit is irradiated with laser light, the laser light is absorbed or reflected by the common power supply lines. Therefore, in the case where the degree of overlap between the common power supply lines and the glass frit varies depending on the location, there is a problem in that a difference is generated in the temperature distribution of the glass frit and the glass frit cannot be sufficiently melted; thus, a sealing structure with high air-tightness and an organic electroluminescence device with high air-tightness cannot be manufactured. 
     REFERENCE 
     
         
         [Patent Document 1] Japanese Published Patent Application No. 2011-65895 
       
    
     SUMMARY OF THE INVENTION 
     Therefore, the present invention was made to solve the above problem and an object of the present invention is to provide a sealing structure with high air-tightness and an organic electroluminescence device with high air-tightness regardless of a pattern of a common power supply line overlapping with glass frit. 
     In order to achieve the above object, one embodiment of the present invention is a sealing structure including a first substrate including a first metal layer, a first insulating layer covering the first metal layer, a second metal layer overlapping with at least part of the first metal layer with the first insulating layer therebetween, and a second insulating layer over the second metal layer, which are provided over a first surface; a second substrate facing the first surface with a space kept between the first substrate and the second substrate; and a sealant for sealing the space between the first substrate and the second substrate, in which the first metal layer has a pattern crossing the sealant, and the sealant is in contact with the second insulating layer on the first substrate side and overlaps with the second metal layer at an intersection of the first metal layer and the sealant. 
     In the above structure, it is preferable that a material of the sealant be a low-melting-point glass. 
     In the above structure, it is preferable that the first metal layer have a linear pattern. 
     Further, one embodiment of the present invention is an organic electroluminescence device including a first substrate provided with a pixel region and a non-pixel region which is a region other than the pixel region; a second substrate facing the first substrate with a space kept between the first substrate and the second substrate; and a sealant for sealing the space between the first substrate and the second substrate, in which the pixel region comprises a thin film transistor including a semiconductor layer, a gate insulating layer, a gate electrode layer, a source electrode layer, and a drain electrode layer, a first electrode layer electrically connected to a source electrode or a drain electrode of the thin film transistor, a partition wall covering an edge portion of the first electrode layer, a light-emitting layer provided over the first electrode layer and the partition wall, and a second electrode layer provided over the light-emitting layer, in which the non-pixel region comprises a first metal layer, the gate insulating layer covering the first metal layer, a second metal layer overlapping with at least part of the first metal layer with the gate insulating layer therebetween, and a second insulating layer over the second metal layer, in which the first metal layer has a pattern crossing the sealant, and in which the sealant is in contact with the second insulating layer on the first substrate side and overlaps with the second metal layer at an intersection of the first metal layer and the sealant. 
     In the above structure, it is preferable that a material of the sealant be a low-melting-point glass. 
     In the above structure, it is preferable that the first metal layer be a common power supply line. 
     In the above structure, it is preferable that the first metal layer be electrically connected to any one of the gate electrode layer, the source electrode layer, the drain electrode layer, and the first electrode layer. 
     With the structures of a sealing structure and an organic electroluminescence device of one embodiment of the present invention, a sealing structure with high air-tightness and an organic electroluminescence device with high air-tightness can be obtained. Further, flexibility in the layout of the first metal layer serving as a common power supply line can be increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a top view and  FIG. 1B  is a cross-sectional view of a sealing structure according to one embodiment of the present invention. 
         FIG. 2A  is a top view and  FIG. 2B  is a cross-sectional view of a sealing structure according to one embodiment of the present invention. 
         FIG. 3A  is a top view and  FIG. 3B  is a cross-sectional view of an organic electroluminescence device according to one embodiment of the present invention. 
         FIG. 4A  is a top view and  FIG. 4B  is a cross-sectional view of an organic electroluminescence device according to one embodiment of the present invention. 
         FIGS. 5A and 5B  are each a cross-sectional view of a light-emitting element which can be used for an organic electroluminescence device according to one embodiment of the present invention. 
         FIGS. 6A to 6E  each illustrate an electronic device to which an organic electroluminescence device according to one embodiment of the present invention is applied. 
         FIGS. 7A to 7C  illustrate an electronic device to which an organic electroluminescence device according to one embodiment of the present invention is applied. 
         FIG. 8  is a cross-sectional view illustrating a modification example of a sealing structure according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the invention disclosed in this specification will be described with reference to the accompanying drawings. Note that the present invention is not limited to the following description, and it is easily understood by those skilled in the art that modes and details of the present invention can be modified in various ways. Therefore, the invention disclosed in this specification is not construed as being limited to the description of the following embodiments. 
     Embodiment 1 
     A structure of a sealing structure which is one embodiment of the present invention is described below in detail. 
       FIG. 1A  and  FIG. 2A  are top views of a sealing structure, and  FIG. 1B  and  FIG. 2B  are schematic cross-sectional views of part of the sealing structure. 
     &lt;Structure of Sealing Structure&gt; 
     In the sealing structure illustrated in  FIG. 1B , a light-emitting element  131  is sealed by a first substrate  901 , a second substrate  902 , and a sealant  500 . A first metal layer  107  is provided over the first substrate  901  and a first insulating layer  105  is provided in contact with the first metal layer  107 . A second metal layer  113  is provided so as to overlap with the sealant  500  and be in contact with the first insulating layer  105 . A second insulating layer  114  is provided in contact with the first insulating layer  105  and the sealant  500 . The first metal layer  107  is covered with the second metal layer  113  with the first insulating layer  105  therebetween, and the second metal layer  113  is provided between the first metal layer  107  and the sealant  500  in a region where the first metal layer  107  and the sealant  500  overlap with each other. 
     &lt;Members Forming Sealing Structure&gt; 
     Members forming the sealing structure which is one embodiment of the present invention are described below. 
     (First Substrate and Second Substrate) 
     As each of the first substrate  901  and the second substrate  902 , a glass substrate, a quartz substrate, a sapphire substrate, a ceramic substrate, a metal substrate, or the like can be used. For at least one of the first substrate  901  and the second substrate  902 , a substrate transmitting laser light used for forming the sealant  500  is used. 
     (First Metal Layer) 
     The first metal layer  107  includes a region overlapping with the sealant  500 . The first metal layer  107  is preferably formed using a metal material such as molybdenum, titanium, tantalum, tungsten, aluminum, copper, chromium, neodymium, or scandium, or an alloy material which contains any of these materials as a main component. The first metal layer  107  is led from the inside of the sealant  500  having a frame-shape to the outside to cross the sealant  500 . Therefore, in a cross section of a portion where the first metal layer  107  overlaps with the sealant  500 , a plurality of first metal layers  107  crosses the sealant  500  at an end of one side of the sealing structure ( FIG. 1B ). The number of the first metal layers  107  crossing the sealant  500  at the middle of the one side of the sealing structure is smaller than that at the end of the one side of the sealing structure ( FIG. 2B ). 
     In the case where the second metal layer  113  described later is not provided, when glass frit provided in a sealant formation region is irradiated with laser light, the laser light is absorbed or reflected by the first metal layer  107  overlapping with the sealant formation region. Therefore, heat applied to the glass fit varies depending on the layout of the first metal layer  107  crossing the sealant formation region. When there is a difference in heat applied to the glass frit, a crack is easily generated in a low-melting-point glass included in the sealant  500 . Therefore, for the pitch or the width of the first metal layer  107 , absorption or reflectance of the laser light or the like has needed to be considered. However, in the case where the second metal layer  113  described later is provided, the laser light is absorbed or reflected by the second metal layer  113  and thus the glass frit can be uniformly heated. Therefore, the layout of the first metal layer  107  overlapping with the sealant formation region (e.g., the pitch or the width of the first metal layer  107 ) can be freely set. 
     (First Insulating Layer) 
     The first insulating layer  105  is provided in order to prevent an electrical short circuit between the first metal layer  107  and the second metal layer  113 . The first insulating layer  105  is preferably formed using a silicon nitride film which is deposited by a plasma CVD method in which a mixed gas of silane (SiH 4 ) and nitrogen (N 2 ) is supplied. As the first insulating layer  105 , another inorganic insulating film can be used; for example, a material similar to the material which can be used for a buffer layer described in Embodiment 2 can be used. 
     (Second Metal Layer) 
     The second metal layer  113  is provided so that the glass frit can be heated uniformly with laser light to be melted. By provision of the second metal layer  113 , the layout of the first metal layer  107  overlapping with the sealant formation region can be freely set. The second metal layer  113  is provided so as to be in contact with the first insulating layer  105  and overlap with the sealant  500 . As a material of the second metal layer  113 , a material similar to the material which can be used for the first metal layer  107  can be used. 
     (Second Insulating Layer) 
     In order to increase the adhesion of the sealant  500  to a layer in contact with the sealant  500 , it is preferable that the second insulating layer  114  and the sealant  500  be provided in contact with each other in the sealing structure. The second insulating layer  114  is preferably formed using a silicon nitride film which is deposited by a plasma CVD method in which a mixed gas of silane (SiH 4 ) and nitrogen (N 2 ) is supplied. As the second insulating layer  114 , another inorganic insulating film can be used; for example, a material similar to the material which can be used for a buffer layer or a gate insulating layer described in Embodiment 2 can be used. 
     (Sealant) 
     The sealant  500  seals an object to be sealed and forms a sealing structure with high air-tightness together with the first substrate  901  and the second substrate  902 . The sealant  500  is provided in contact with the second insulating layer  114 . The sealant  500  is provided so as to overlap with the second metal layer  113 . The sealant  500  is preferably formed using a low-melting-point glass. The low-melting-point glass is formed by irradiating glass frit with laser light and the laser light is absorbed or reflected by the glass frit and the second metal layer. Since the second metal layer  113  is formed so as to overlap with a region where the first metal layer  107  and a region where a paste including glass fit is applied overlap with each other, heat of the laser light is applied to the glass frit uniformly and the low-melting-point glass uniform in quality can be formed. Thus, the sealing structure with high air-tightness can be obtained. A material which can be used for the glass frit preferably contains one or more compounds selected from, for example, the following group: magnesium oxide, calcium oxide, barium oxide, lithium oxide, sodium oxide, potassium oxide, boron oxide, vanadium oxide, zinc oxide, tellurium oxide, aluminum oxide, silicon dioxide, lead oxide, tin oxide, phosphorus oxide, ruthenium oxide, rhodium oxide, iron oxide, copper oxide, titanium oxide, tungsten oxide, bismuth oxide, antimony oxide, lead borate glass, tin phosphate glass, vanadate glass, and borosilicate glass. 
     In the structure of the sealing structure which is one embodiment of the present invention, the second metal layer  113  is provided between the sealant  500  and the first metal layer  107 ; therefore, the layout of the first metal layer  107  overlapping with the sealant  500  can be freely set. Further, laser light is absorbed or reflected by the second metal layer  113 ; therefore, a low-melting-point glass uniform in quality can be formed and a sealing structure with high air-tightness can be obtained. 
     Modification Example 
       FIG. 8  illustrates a modification example of the sealing structure of  FIG. 2B  and the second metal layer  113  is provided with holes. The second insulating layer  114  provided in contact with the second metal layer  113  has an uneven surface due to the holes. The sealant  500  fills in the unevenness provided in the second insulating layer  114 ; thus, an anchor effect is caused. Therefore, the adhesion between the sealant  500  and the second insulating layer  114  is increased and a sealing structure with high air-tightness can be obtained. 
     This embodiment can be combined with any of the other embodiments disclosed in this specification as appropriate. 
     Embodiment 2 
     A structure of an organic electroluminescence device which is one embodiment of the present invention is described below in detail. 
     &lt;Structure of Organic Electroluminescence Device&gt; 
       FIG. 3A  and  FIG. 4A  are top views of an organic electroluminescence device, and  FIG. 3B  and  FIG. 4B  are schematic cross-sectional views of part of the organic electroluminescence device, in which specific structures of a sealing portion  4501 , a pixel portion  4502 , and a signal line circuit portion  4503  are shown. 
     As illustrated in  FIG. 3B , the organic electroluminescence device includes the first substrate  901 , a buffer layer  103 , a plurality of transistors, the second insulating layer  114 , a planarization layer  116 , a light-emitting element  130 , partition walls  124 , and the second substrate  902  in the pixel portion  4502 . 
     As illustrated in  FIG. 3B , the plurality of transistors is provided over the first substrate  901 , and the light-emitting element  130  is provided over each of transistors  150  and  151 . Each transistor includes a gate electrode layer  106 , a source electrode layer  112   a , a drain electrode layer  112   b , a semiconductor layer  110 , and a gate insulating layer  108 . The transistors  150  and  151  are transistors for driving the light-emitting elements. The light-emitting element  130  is provided over the planarization layer  116 , and a first electrode layer  118  of the light-emitting element  130  is electrically connected to the transistor through a contact hole provided in the planarization layer  116 . The light-emitting element  130  is sealed by the first substrate  901 , the sealant  500 , and the second substrate  902 . A color filter or a touch panel may be provided on the first substrate  901  side of the second substrate  902 . 
     In this embodiment, the organic electroluminescence device having a top emission structure is described; however, the organic electroluminescence device may have a bottom emission structure or a dual emission structure. 
     The light-emitting element  130  includes the first electrode layer  118  which is electrically connected to the transistor, an organic compound-containing layer  120  over the first electrode layer  118 , and a second electrode layer  122  over the organic compound-containing layer  120 . Edge portions of the first electrode layer  118  are covered with the partition walls  124 . The second electrode layer  122  is formed over the entire area of the pixel portion  4502 . 
     As illustrated in  FIG. 3B , the organic electroluminescence device includes a transistor  152  in the signal line circuit portion  4503 . 
     &lt;Members Forming Organic Electroluminescence Device&gt; 
     Members forming the organic electroluminescence device which is one embodiment of the present invention are described below. 
     (Buffer Layer) 
     It is preferable that the buffer layer  103  have a function of preventing diffusion of impurities such as mobile ions into the semiconductor layer  110 . For example, the buffer layer  103  can be formed using one or more insulating films selected from the following: an oxide insulating film such as a silicon oxide film, a gallium oxide film, a hafnium oxide film, an yttrium oxide film, or an aluminum oxide film; a nitride insulating film such as a silicon nitride film or an aluminum nitride film; an oxynitride insulating film such as a silicon oxynitride film or an aluminum oxynitride film; or a nitride oxide insulating film such as a silicon nitride oxide film. Note that “nitride oxide” contains more nitrogen than oxygen and “oxynitride” contains more oxygen than nitrogen. 
     (Gate Electrode Layer) 
     The gate electrode layer  106  serves as a gate electrode of each of the transistors. The gate electrode layer  106  can be formed using a metal material such as molybdenum, titanium, tantalum, tungsten, aluminum, copper, chromium, neodymium, or scandium, or an alloy material containing any of these materials as its main component. Alternatively, a semiconductor film typified by a polycrystalline silicon film doped with an impurity element such as phosphorus, or a silicide film such as a nickel silicide film may be used as the gate electrode layer  106 . The gate electrode layer  106  may have a single-layer structure or a stacked-layer structure. 
     (First Metal Layer) 
     The first metal layer  107  is electrically connected to any one of the gate electrode layer, the source electrode layer, and the drain electrode layer of the transistor and the first electrode layer  118 , and serves as a common power supply line. The first metal layer  107  includes a region overlapping with the sealant  500 . It is preferable that the first metal layer  107  be formed using a material similar to the material of the gate electrode layer  106 . The first metal layer  107  is led as a common power supply line. Therefore, in a cross section of a portion where the first metal layer  107  overlaps with the sealant  500 , a plurality of first metal layers  107  crosses the sealant  500  at an end of one side of the organic electroluminescence device ( FIG. 3B ). The number of the first metal layers  107  crossing the sealant  500  at the middle of the one side of the organic electroluminescence device is smaller than that at the end of the one side of the organic electroluminescence device ( FIG. 4B ). 
     In the case where the second metal layer  113  described later is not provided, when glass frit provided in a sealant formation region is irradiated with laser light, the laser light is absorbed or reflected by the first metal layer  107  overlapping with the sealant formation region. Therefore, heat applied to the glass frit varies depending on the layout of the first metal layer  107  crossing the sealant formation region. When there is a difference in heat applied to the glass frit, a crack is easily generated in a low-melting-point glass included in the sealant  500 . Therefore, for the pitch or the width of the first metal layer  107 , absorption or reflectance of the laser light or the like has needed to be considered. However, in the case where the second metal layer  113  described later is provided, the laser light is absorbed or reflected by the second metal layer  113  and thus the glass frit can be uniformly heated. Therefore, the layout of the first metal layer  107  overlapping with the sealant formation region (e.g., the pitch or the width of the first metal layer  107 ) can be freely set. 
     (Gate Insulating Layer) 
     The gate insulating layer  108  can be formed using a material similar to the material which can be used for the buffer layer. 
     The gate insulating layer  108  is formed by a plasma chemical vapor deposition (CVD) method or a sputtering method. In the case where a plasma CVD method is used, it is particularly preferable to use a plasma CVD method in which plasma is generated utilizing electric-field energy of a microwave and a source gas for the gate insulating film is excited by the plasma, and the excited source gas is reacted on a surface of an object to deposit a reactant (also referred to as a microwave plasma CVD method). The thickness of the gate insulating layer  108  is greater than or equal to 5 nm and less than or equal to 300 nm. 
     (Semiconductor Layer) 
     For the semiconductor layer  110 , silicon or an oxide semiconductor can be used. In the manufacturing method of the present invention, the semiconductor layer  110  is formed over the first substrate  901 . Therefore, the semiconductor layer  110  can be deposited at a temperature higher than or equal to 500° C. or can be subjected to annealing treatment. Thus, a transistor with high field effect mobility and high on-state current can be manufactured. Note that an oxide semiconductor which can be used for the semiconductor layer  110  is described in detail in Embodiment 3. 
     (Source Electrode Layer and Drain Electrode Layer) 
     The source electrode layer  112   a  and the drain electrode layer  112   b  are electrically connected to source and drain formation regions of the semiconductor layer  110 . As a conductive film used for the source electrode layer  112   a  and the drain electrode layer  112   b , for example, a metal film including an element selected from Al, Cr, Cu, Ta, Ti, Mo, and W, a metal nitride film including any of these elements (a titanium nitride film, a molybdenum nitride film, or a tungsten nitride film), or the like can be used. Alternatively, a film of a high-melting-point metal such as Ti, Mo, or W or a metal nitride film thereof (e.g., a titanium nitride film, a molybdenum nitride film, or a tungsten nitride film) may be formed over or/and below a metal film such as an Al film or a Cu film. Alternatively, the conductive film used for the source electrode layer  112   a  and the drain electrode layer  112   b  may be formed using a conductive metal oxide. As the conductive metal oxide, indium oxide (In 2 O 3  or the like), tin oxide (SnO 2  or the like), zinc oxide (ZnO), indium tin oxide (ITO), indium zinc oxide (In 2 O 3 —ZnO or the like), or any of these metal oxide materials in which silicon oxide is contained can be used. 
     (Second Metal Layer) 
     The second metal layer  113  is provided so that the glass frit can be heated uniformly with laser light to be melted. By provision of the second metal layer  113 , the layout of the first metal layer  107  overlapping with the sealant formation region can be freely set. The second metal layer  113  is provided so as to be in contact with the gate insulating layer  108  and overlap with the sealant  500 . As a material of the second metal layer  113 , the same material as the source electrode layer  112   a  and the drain electrode layer  112   b  can be used. 
     (Second Insulating Layer) 
     The second insulating layer  114  is provided in order to protect the transistors. The second insulating layer  114  can be formed using the material described in Embodiment 1 or the material which can be used for the gate insulating layer. In order to increase the adhesion of the sealant  500  to a layer in contact with the sealant  500 , it is preferable that the second insulating layer  114  and the sealant  500  be provided in contact with each other in the organic electroluminescence device. 
     (Planarization Layer) 
     The planarization layer  116  is provided in order to reduce unevenness which is caused by the source electrode layer  112   a  and the drain electrode layer  112   b . The planarization layer  116  can be formed using an organic resin material such as polyimide or acrylic, an inorganic insulating film such as a silicon oxide film, or the like. It is preferable that the planarization layer  116  in the sealant formation region be removed (that is, the sealant  500  and the planarization layer  116  do not overlap with each other). This is in order that the adhesion between the sealant  500  and a layer which is in contact with the sealant  500  and is provided over the first substrate  901  can be increased and thus an organic electroluminescence device with high air-tightness can be formed. 
     (Light-Emitting Element) 
     In the organic electroluminescence device which is one embodiment of the present invention, light emission is obtained from the light-emitting element  130 . The light-emitting element  130  includes the organic compound-containing layer  120  between the first electrode layer  118  and the second electrode layer  122 . The organic compound-containing layer  120  includes at least a light-emitting layer and has a plurality of layers. The organic compound-containing layer  120  is described in Embodiment 4. 
     In this embodiment, the organic electroluminescence device having a top emission structure is described; therefore, a conductive film that transmits visible light is used for the second electrode layer  122 . It is preferable that a conductive film that reflects visible light be used for the first electrode layer  118 . With the use of the conductive film that reflects visible light, efficiency of light extraction from the light-emitting element can be improved. One of the first electrode layer  118  and the second electrode layer  122  serves as an anode and the other serves as a cathode. 
     The conductive film that transmits visible light can be formed using, for example, indium oxide, ITO, indium zinc oxide, ZnO, or ZnO to which gallium is added. Alternatively, a film of a metal material such as gold, platinum, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, or titanium, or a nitride of any of these metal materials (e.g., titanium nitride) can be formed thin so as to have a light-transmitting property. Further alternatively, graphene or the like may be used. 
     The conductive film that reflects visible light can be formed using, for example, a metal material such as aluminum, gold, platinum, silver, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium; an aluminum-containing alloy (aluminum alloy) such as an alloy of aluminum and titanium, an alloy of aluminum and nickel, or an alloy of aluminum and neodymium; or a silver-containing alloy such as an alloy of silver and copper. An alloy of silver and copper is preferable because of its high heat resistance. The metal material or the alloy may include lanthanum, neodymium, or germanium. 
     (Partition Wall) 
     The partition wall  124  can be formed using an inorganic insulating material or an organic insulating material. As the organic insulating material, for example, a negative or positive photosensitive resin material, a non-photosensitive resin material, or the like can be used. Specifically, a polyimide resin, an acrylic resin, or the like can be used. It is preferable that the partition wall  124  have a forward tapered shape so that a film formed over the partition wall  124  is prevented from being broken. In a forward tapered shape, a layer gradually increases in thickness and is in contact with a layer serving as a base. 
     (Sealant) 
     The sealant  500  seals the light-emitting element  130  and forms an organic electroluminescence device with high air-tightness together with the first substrate  901  and the second substrate  902 . The sealant  500  is provided in contact with the second insulating layer  114 . The sealant  500  is provided so as to overlap with the second metal layer  113 . The sealant  500  is preferably formed using a low-melting-point glass. The low-melting-point glass is formed by irradiating glass frit with laser light and the laser light is absorbed or reflected by the glass frit and the second metal layer. Since the second metal layer  113  is formed so as to overlap with a region where the first metal layer  107  and a region where a paste including glass frit is applied overlap with each other, heat of the laser light is applied to the glass frit uniformly and the low-melting-point glass uniform in quality can be formed. Thus, the organic electroluminescence device with high air-tightness can be obtained. 
     In the structure of the organic electroluminescence device which is one embodiment of the present invention, the second metal layer  113  is provided between the sealant  500  and the first metal layer  107 ; therefore, the layout of the first metal layer  107  overlapping with the sealant  500  can be freely set. Further, laser light is absorbed or reflected by the second metal layer  113 ; therefore, the sealant  500  uniform in quality can be formed and an organic electroluminescence device with high air-tightness can be obtained. 
     This embodiment can be combined with any of the other embodiments disclosed in this specification as appropriate. 
     Embodiment 3 
     In this embodiment, an oxide semiconductor which can be used for the semiconductor layer in Embodiment 2 is described in detail. 
     For example, an In-based metal oxide, a Zn-based metal oxide, an In—Zn-based metal oxide, or an In—Ga—Zn-based metal oxide can be used as the oxide semiconductor. Alternatively, a metal oxide including another metal element instead of part or all of Ga in the In—Ga—Zn-based metal oxide may be used. 
     As the aforementioned another metal element, for example, a metal element that is capable of combining with more oxygen atoms than gallium can be used, and one or more elements of titanium, zirconium, hafnium, germanium, and tin can be used, for instance. Alternatively, as the aforementioned another metal element, one or more elements of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium may be used. These metal elements function as a stabilizer. Note that the amount of such a metal element added is determined so that the metal oxide can function as a semiconductor. When a metal element that is capable of combining with more oxygen atoms than gallium is used and oxygen is supplied to a metal oxide, oxygen defects in the metal oxide can be reduced. 
     Further, the semiconductor layer  110  may be a stacked layer of a first oxide semiconductor layer having an atomic ratio of In:Ga:Zn=1:1:1, a second oxide semiconductor layer having an atomic ratio of In:Ga:Zn=3:1:2, and a third oxide semiconductor layer having an atomic ratio of In:Ga:Zn=1:1:1. With the above stacked layer structure of the semiconductor layer  110 , for example, field effect mobility of the transistor can be increased. 
     The oxide semiconductor may be a c-axis aligned crystalline oxide semiconductor (also referred to as CAAC-OS). 
     The CAAC-OS is one of oxide semiconductors including a plurality of crystal parts. In each of the crystal parts, for example, a c-axis is aligned in a direction parallel to a normal vector of a surface where an oxide semiconductor layer is formed or a normal vector of a surface of the oxide semiconductor layer. Further, in each of the crystal parts, metal atoms are arranged in a triangular or hexagonal configuration when seen from the direction perpendicular to the a-b plane, and metal atoms are arranged in a layered manner or metal atoms and oxygen atoms are arranged in a layered manner when seen from the direction perpendicular to the c-axis. In this specification, a simple term “perpendicular” includes a range from 85° to 95°. In addition, a simple term “parallel” includes a range from −5° to 5°. 
     For example, the CAAC-OS can be formed by a sputtering method with a polycrystalline oxide semiconductor sputtering target. When ions collide with the sputtering target, a crystal region included in the sputtering target may be separated from the target along an a-b plane; in other words, a sputtered particle having a plane parallel to an a-b plane (flat-plate-like sputtered particle or pellet-like sputtered particle) may flake off from the sputtering target. In that case, the flat-plate-like sputtered particle reaches a substrate while maintaining their crystal state, whereby a crystal state of the sputtering target is transferred to a substrate. In this manner, the CAAC-OS is formed. 
     For the deposition of the CAAC-OS, the following conditions are preferably used. 
     For example, the CAAC-OS is formed while the impurity concentration is reduced, whereby the crystal state of the oxide semiconductor can be prevented from being broken by the impurities. For example, impurities (e.g., hydrogen, water, carbon dioxide, or nitrogen) which exist in a deposition chamber are preferably reduced. Further, impurities in a deposition gas are preferably reduced. For example, a deposition gas whose dew point is −80° C. or lower, preferably −100° C. or lower is preferably used as a deposition gas. 
     By increasing the substrate heating temperature during the deposition, migration of a sputtered particle is likely to occur after the sputtered particle is attached to a substrate surface. Specifically, the substrate heating temperature during the deposition is 100° C. or higher and 740° C. or lower. By increasing the substrate heating temperature during the deposition, when the flat-plate-like sputtered particle reaches the substrate, migration occurs on the substrate surface, so that a flat plane of the flat-plate-like sputtered particle is attached to the substrate. 
     Furthermore, it is preferable that the proportion of oxygen in the deposition gas be increased and the power be optimized in order to reduce plasma damage at the deposition. The proportion of oxygen in the deposition gas is 30 vol % or higher, preferably 100 vol %. 
     As an example of the sputtering target, an In—Ga—Zn—O compound target is described below. 
     The In—Ga—Zn—O compound target, which is polycrystalline, is made by mixing InO x  powder, GaO Y  powder, and ZnO X  powder in a predetermined ratio, applying pressure, and performing heat treatment at a temperature higher than or equal to 1000° C. and lower than or equal to 1500° C. Note that X, Y, and Z are each a given positive number. Here, the predetermined ratio of InO X  powder to GaO Y  powder and ZnO Z  powder is, for example, 2:2:1, 8:4:3, 3:1:1, 1:1:1, 4:2:3, or 3:1:2. The kinds of powder and the molar ratio for mixing powder may be determined as appropriate depending on the desired sputtering target. 
     A transistor whose channel formation region contains the CAAC-OS has high reliability because change in electric characteristics of the transistor due to irradiation with visible light or ultraviolet light is small. 
     The transistor containing the oxide semiconductor has low leakage current due to thermal excitation because of its wide bandgap. Further, the effective mass of a hole is large, which is 10 or more, and the height of the tunnel barrier is high, which is 2.8 eV or higher. Thus, the amount of tunnel current is small. Furthermore, the number of carriers in the semiconductor layer is very small; therefore, the off-state current can be made low. For example, the off-state current per micrometer of the channel width of the transistor at room temperature (25° C.) is lower than or equal to 1×10 −19  A (100 zA), preferably lower than or equal to 1×10 −22  A (100 yA). It is preferable that the off-state current of the transistor be as low as possible; the lowest value of the off-state current of the transistor is estimated to be about 1×10 −3 ° A/μm. 
     This embodiment can be combined with any of the other embodiments disclosed in this specification as appropriate. 
     Embodiment 4 
     In this embodiment, the light-emitting element in Embodiment 1 is described in detail. 
     The light-emitting element  130  illustrated in  FIG. 5A  has a structure in which the organic compound-containing layer  120  is sandwiched between a pair of electrodes (the first electrode layer  118  and the second electrode layer  122 ). Note that the first electrode layer  118  is used as an anode and the second electrode layer  122  is used as a cathode as an example in the following description of this embodiment. 
     The organic compound-containing layer  120  includes at least a light-emitting layer and may have a stacked-layer structure including a functional layer other than the light-emitting layer. Examples of the functional layer other than the light-emitting layer include a layer containing a substance having a high hole-injection property, a substance having a high hole-transport property, a substance having a high electron-transport property, a substance having a high electron-injection property, a bipolar substance (a substance having high electron and hole transport properties), or the like. Specifically, functional layers such as a hole-injection layer, a hole-transport layer, an electron-transport layer, and an electron-injection layer can be used in combination as appropriate. 
     The light-emitting element  130  illustrated in  FIG. 5A  emits light when current flows because of a potential difference generated between the first electrode layer  118  and the second electrode layer  122 , and holes and electrons are recombined in the organic compound-containing layer  120 . That is, a light-emitting region is formed in the organic compound-containing layer  120 . 
     In this invention, light emission from the light-emitting element  130  is extracted to the outside from the first electrode layer  118  or the second electrode layer  122  side. Therefore, one or both of the first electrode layer  118  and the second electrode layer  122  are formed using a substance having a light-transmitting property. 
     Note that a plurality of organic compound-containing layers  120  may be stacked between the first electrode layer  118  and the second electrode layer  122  as illustrated in  FIG. 5B . In the case where n (n is a natural number of 2 or more) layers are stacked, a charge generation layer  120   a  is preferably provided between the m-th (m is a natural number of 1 or more and n−1 or less) organic compound-containing layer  120  and the (m+1)-th organic compound-containing layer  120 . 
     The charge generation layer  120   a  may be formed of a composite material of an organic compound and a metal oxide, a metal oxide, or a composite material of an organic compound and an alkali metal, an alkaline earth metal, or a compound thereof; alternatively, these materials may be combined as appropriate. Examples of the composite material of an organic compound and a metal oxide include composite materials of an organic compound and a metal oxide such as vanadium oxide, molybdenum oxide, and tungsten oxide. As the organic compound, various compounds can be used; for example, a low molecular compounds such as an aromatic amine compound, a carbazole derivative, or aromatic hydrocarbon and a compound in which the basic skeleton is any of the low molecular compounds, such as oligomer, dendrimer, or polymer. As the organic compound, it is preferable to use the organic compound which has a hole-transport property and has a hole mobility of 10 −6  cm 2 /Vs or higher. However, another substance may be used instead of the above described materials as long as the substance has a hole-transport property higher than an electron-transport property. These materials used for the charge generation layer  120   a  are excellent in carrier-injection property and carrier-transport property, and thus the light-emitting element  130  can be driven with low current and with low voltage. 
     It is to be noted that the charge generation layer  120   a  may be formed with a combination of a composite material of an organic compound and a metal oxide and another material. For example, a layer containing a composite material of the organic compound and the metal oxide may be combined with a layer containing a compound of a substance selected from substances with an electron-donating property and a compound with a high electron-transport property. Moreover, a layer containing a composite material of the organic compound and the metal oxide may be combined with a transparent conductive film. 
     As for the light-emitting element  130  having such a structure, problems such as energy transfer, quenching, and the like are unlikely to occur, and a light-emitting element which has both high light emission efficiency and long lifetime is easily obtained due to expansion in the choice of materials. Further, a light-emitting element which provides phosphorescence from one of light-emitting layers and fluorescence from the other of the light-emitting layers can be easily obtained. 
     Note that the charge generation layer  120   a  has a function of injecting holes to one of the organic compound-containing layers  120 , which is formed in contact with the charge generation layer  120   a , and a function of injecting electrons to the other of the organic compound-containing layers  120 , when voltage is applied between the first electrode layer  118  and the second electrode layer  122 . 
     The light-emitting element  130  illustrated in  FIG. 5B  can provide a variety of emission colors by changing the type of the light-emitting substance which is used for the organic compound-containing layer  120 . In addition, a plurality of light-emitting substances of different colors are used as the light-emitting substance, whereby light emission having a broad spectrum or white light emission can also be obtained. 
     In the case where white light emission is obtained using the light-emitting element  130  illustrated in  FIG. 5B , as for a combination of a plurality of organic compound-containing layers  120 , a structure for emitting white light including red light, blue light, and green light may be used. For example, the structure may include a first light-emitting layer containing a blue fluorescent substance as a light-emitting substance and a second light-emitting layer containing green and red phosphorescent substances as light-emitting substances. Alternatively, a structure including a first light-emitting layer exhibiting red light, a second light-emitting layer exhibiting green light, and a third light-emitting layer exhibiting blue light may be employed. Also with a structure including light-emitting layers emitting light of complementary colors, white light emission can be obtained. When light emitted from the first light-emitting layer and light emitted from the second light-emitting layer have complementary colors to each other in a stacked-layer element including two light-emitting layers, the combination of colors are as follows: blue and yellow, blue-green and red, and the like. 
     In the structure of the above-described stacked-layer element, by providing the charge generation layer between the stacked light-emitting layers, the element can have long lifetime in a high-luminance region while keeping the current density low. In addition, a voltage drop due to the resistance of the electrode material can be reduced, whereby uniform light emission in a large area is possible. 
     This embodiment can be implemented in appropriate combination with the structures described in the other embodiments. 
     Embodiment 5 
     In this embodiment, examples of electronic devices or a lighting device using the organic electroluminescence device which is one embodiment of the present invention are described with reference to  FIGS. 6A to 6E  and  FIGS. 7A to 7C . 
     Examples of the electronic devices to which the organic electroluminescence device is applied are a television device (also referred to as television or television receiver), a monitor of a computer or the like, a camera such as a digital camera or a digital video camera, a digital photo frame, a mobile phone (also referred to as cellular phone or cellular phone device), a portable game machine, a portable information terminal, an audio reproducing device, and a large-sized game machine such as a pachinko machine. Specific examples of these electronic devices are shown in  FIGS. 6A to 6E . 
       FIG. 6A  illustrates an example of a television device. In the television device  7100 , a display portion  7103  is incorporated in a housing  7101 . Images can be displayed by the display portion  7103 , and the organic electroluminescence device can be used for the display portion  7103 . In addition, here, the housing  7101  is supported by a stand  7105 . 
     The television device  7100  can be operated by an operation switch of the housing  7101  or a separate remote controller  7110 . With operation keys  7109  of the remote controller  7110 , channels and volume can be controlled and images displayed on the display portion  7103  can be controlled. Furthermore, the remote controller  7110  may be provided with a display portion  7107  for displaying data output from the remote controller  7110 . 
     Note that the television device  7100  is provided with a receiver, a modem, and the like. With the receiver, a general television broadcast can be received. Furthermore, when the television device  7100  is connected to a communication network by wired or wireless connection via the modem, one-way (from a transmitter to a receiver) or two-way (between a transmitter and a receiver, between receivers, or the like) data communication can be performed. 
       FIG. 6B  illustrates a computer, which includes a main body  7201 , a housing  7202 , a display portion  7203 , a keyboard  7204 , an external connection port  7205 , a pointing device  7206 , and the like. This computer is manufactured by using the organic electroluminescence device for the display portion  7203 . 
       FIG. 6C  illustrates a portable game machine having two housings, a housing  7301  and a housing  7302 , which are connected with a joint portion  7303  so that the portable game machine can be opened or folded. A display portion  7304  is incorporated in the housing  7301  and a display portion  7305  is incorporated in the housing  7302 . In addition, the portable game machine illustrated in  FIG. 6C  includes a speaker portion  7306 , a recording medium insertion portion  7307 , an LED lamp  7308 , an input unit (an operation key  7309 , a connection terminal  7310 , a sensor  7311  (sensor having a function of measuring force, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, odor, or infrared rays), or a microphone  7312 ), and the like. It is needless to say that the structure of the portable game machine is not limited to the above as far as the organic electroluminescence device can be used for at least either the display portion  7304  or the display portion  7305 , or both, and may include other accessories arbitrarily. The portable game machine illustrated in  FIG. 6C  has a function of reading a program or data stored in a recording medium to display it in the display portion, and a function of sharing information with another portable game machine by wireless communication. Note that the functions of the portable game machine illustrated in  FIG. 6C  are not limited to these functions, and the portable game machine can have various functions. 
       FIG. 6D  illustrates an example of a mobile phone. The mobile phone  7400  is provided with a display portion  7402  incorporated in a housing  7401 , operation buttons  7403 , an external connection port  7404 , a speaker  7405 , a microphone  7406 , and the like. Note that the mobile phone  7400  is manufactured using the organic electroluminescence device for the display portion  7402 . 
     When the display portion  7402  of the mobile phone  7400  illustrated in  FIG. 6D  is touched with a finger or the like, data can be input into the mobile phone  7400 . Further, operations such as making a call and composing e-mail can be performed by touch on the display portion  7402  with a finger or the like. 
     There are mainly three screen modes of the display portion  7402 . The first mode is a display mode mainly for displaying images. The second mode is an input mode mainly for inputting data such as text. The third mode is a display-and-input mode in which two modes of the display mode and the input mode are combined. 
     For example, in the case of making a call or composing an e-mail, a text input mode mainly for inputting text is selected for the display portion  7402  so that text displayed on a screen can be inputted. In this case, it is preferable to display a keyboard or number buttons on almost the entire screen of the display portion  7402 . 
     When a detection device including a sensor for detecting inclination, such as a gyroscope sensor or an acceleration sensor, is provided inside the mobile phone  7400 , display on the screen of the display portion  7402  can be automatically changed by determining the orientation of the mobile phone  7400  (whether the mobile phone is placed horizontally or vertically for a landscape mode or a portrait mode). 
     The screen modes are switched by touch on the display portion  7402  or operation with the operation buttons  7403  of the housing  7401 . Alternatively, the screen modes can be switched depending on kinds of images displayed on the display portion  7402 . For example, when a signal of an image displayed on the display portion is a signal of moving image data, the screen mode is switched to the display mode. When the signal is a signal of text data, the screen mode is switched to the input mode. 
     Moreover, in the input mode, when input by touching the display portion  7402  is not performed within a specified period while a signal detected by an optical sensor in the display portion  7402  is detected, the screen mode may be controlled so as to be switched from the input mode to the display mode. 
     The display portion  7402  may function as an image sensor. For example, an image of a palm print, a fingerprint, or the like is taken by touch on the display portion  7402  with the palm or the finger, whereby personal authentication can be performed. Further, by providing a backlight or a sensing light source which emits a near-infrared light in the display portion, an image of a finger vein, a palm vein, or the like can be taken. 
       FIG. 6E  illustrates an example of a lighting device. In a lighting device  7500 , light-emitting devices  7503   a ,  7503   b ,  7503   c , and  7503   d  to which one embodiment of the present invention is applied are incorporated in a housing  7501  as light sources. The lighting device  7500  can be attached to a ceiling, a wall, or the like. 
     Further, the light-emitting device includes a light-emitting panel which emits light having high brightness and a pale color and causing less eyestrain even in the case of long-time use, light of a bright red color, and light of a bright color different from the other colors. By adjusting conditions under which the light-emitting element is driven for each emission color, a lighting device whose hue can be adjusted by a user can be achieved. 
       FIGS. 7A and 7B  illustrate a tablet terminal that can be folded. In  FIG. 7A , the tablet terminal is opened, and includes a housing  9630 , a display portion  9631   a , a display portion  9631   b , a display-mode switching button  9034 , a power button  9035 , a power-saving-mode switching button  9036 , a clip  9033 , and an operation button  9038 . The tablet terminal is manufactured using the organic electroluminescence device for one or both of the display portion  9631   a  and the display portion  9631   b.    
     A touch panel region  9632   a  can be provided in a part of the display portion  9631   a , in which area, data can be input by touching displayed operation keys  9637 . Note that  FIG. 7A  shows, as an example, that half of the area of the display portion  9631   a  has only a display function and the other half of the area has a touch panel function. However, the structure of the display portion  9631   a  is not limited to this, and all the area of the display portion  9631   a  may have a touch panel function. For example, all the area of the display portion  9631   a  can display keyboard buttons and serve as a touch panel while the display portion  9631   b  can be used as a display screen. 
     Like the display portion  9631   a , part of the display portion  9631   b  can be a touch panel region  9632   b . When a finger, a stylus, or the like touches the place where a button  9639  for switching to keyboard display is displayed in the touch panel, keyboard buttons can be displayed on the display portion  9631   b.    
     Touch input can be performed concurrently on the touch panel regions  9632   a  and  9632   b.    
     The display-mode switching button  9034  allows switching between a landscape mode and a portrait mode, color display and black-and-white display, and the like. With the power-saving-mode switching button  9036 , the luminance of display can be optimized in accordance with the amount of external light at the time when the tablet terminal is in use, which is detected with an optical sensor incorporated in the tablet terminal. In addition to the optical sensor, other detecting devices such as sensors for detecting inclination, like a gyroscope sensor or an acceleration sensor, may be incorporated in the tablet terminal. 
     Although the display portion  9631   a  and the display portion  9631   b  have the same display area in  FIG. 7A , one embodiment of the present invention is not limited to this example. The display portion  9631   a  and the display portion  9631   b  may have different areas or different display quality. For example, one of them may be a display panel that can display higher-definition images than the other. 
       FIG. 7B  illustrates the tablet terminal folded, which includes the housing  9630 , a solar battery  9633 , a charge and discharge control circuit  9634 , a battery  9635 , and a DCDC converter  9636 . Note that  FIG. 7B  shows an example in which the charge and discharge control circuit  9634  includes the battery  9635  and the DCDC converter  9636 . 
     Since the tablet terminal can be folded in two, the housing  9630  can be closed when the tablet terminal is not in use. Thus, the display portions  9631   a  and  9631   b  can be protected, thereby providing a tablet terminal with high endurance and high reliability for long-term use. 
     The tablet terminal illustrated in  FIGS. 7A and 7B  can have other functions such as a function of displaying various kinds of data (e.g., a still image, a moving image, and a text image), a function of displaying a calendar, a date, the time, or the like on the display portion, a touch-input function of operating or editing the data displayed on the display portion by touch input, and a function of controlling processing by various kinds of software (programs). 
     The solar battery  9633 , which is attached on the surface of the tablet terminal, supplies electric power to a touch panel, a display portion, an image signal processor, and the like. Note that the solar battery  9633  can be provided on one or both surfaces of the housing  9630 , so that the battery  9635  can be charged efficiently, which is preferable. When a lithium ion battery is used as the battery  9635 , there is an advantage of downsizing or the like. 
     The structure and operation of the charge and discharge control circuit  9634  illustrated in  FIG. 7B  are described with reference to a block diagram of  FIG. 7C . The solar battery  9633 , the battery  9635 , the DCDC converter  9636 , a converter  9638 , switches SW 1  to SW 3 , and the display portion  9631  are illustrated in  FIG. 7C , and the battery  9635 , the DCDC converter  9636 , the converter  9638 , and the switches SW 1  to SW 3  correspond to the charge and discharge control circuit  9634  illustrated in  FIG. 7B . 
     First, an example of operation in the case where power is generated by the solar battery  9633  using external light is described. The voltage of power generated by the solar battery  9633  is raised or lowered by the DCDC converter  9636  so that a voltage for charging the battery  9635  is obtained. When the power from the solar battery  9633  is used for the operation of the display portion  9631 , the switch SW 1  is turned on and the voltage of the power is raised or lowered by the converter  9638  to a voltage needed for operating the display portion  9631 . In addition, when display on the display portion  9631  is not performed, the switch SW 1  may be turned off and the switch SW 2  may be turned on so that the battery  9635  is charged. 
     Here, the solar battery  9633  is shown as an example of a power generation means; however, there is no particular limitation on a way of charging the battery  9635 , and the battery  9635  may be charged with another power generation means such as a piezoelectric element or a thermoelectric conversion element (Peltier element). For example, the battery  9635  may be charged with a non-contact power transmission module that transmits and receives power wirelessly (without contact) to charge the battery or with a combination of other charging means. 
     It is needless to say that one embodiment of the present invention is not limited to the electronic devices or the lighting device illustrated in  FIGS. 6A to 6E  and  FIGS. 7A to 7C  as long as the sealing structure or the organic electroluminescence device described in any of the above embodiments is included. 
     The electronic devices and the lighting device described above each include the sealing structure or the organic electroluminescence device to which one embodiment of the present invention is applied. Therefore, a highly reliable electronic device or a highly reliable lighting device can be manufactured. 
     This embodiment can be combined with any of the other embodiments disclosed in this specification as appropriate. 
     This application is based on Japanese Patent Application serial no. 2012-168388 filed with Japan Patent Office on Jul. 30, 2012, the entire contents of which are hereby incorporated by reference.