JP2011181478A - Distributed inorganic el element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distributed inorganic EL fluorescent element having sufficient high luminance for a light emitting element. <P>SOLUTION: The distributed inorganic EL element has a luminous layer between a transparent electrode and a metal layer, and the surface on the luminous layer side of the metal layer is oxidized and an oxide film of a film-thickness of 0.1 μm-2.0 μm is formed. Its manufacturing method is also provided. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a high-intensity dispersed inorganic EL element and a method for manufacturing the same.

  A cross-sectional view of the basic configuration of a conventional dispersion-type inorganic EL element is shown in FIG. Formed by dispersing electroluminescent phosphor powder in which zinc sulfide is added with an activator such as copper or manganese and a coactivator such as chlorine, aluminum or bromine in an organic binder resin having a high dielectric constant A light emitting layer and a dielectric layer formed by dispersing high dielectric constant insulator particles such as barium titanate in a high dielectric constant organic binder resin on one side of a transparent substrate made of glass, film, etc. The outer electrode is arranged between a transparent electrode made of tin oxide (ITO) and a back electrode made of a metal such as aluminum or a metal oxide having conductivity such as ITO, and these are further excellent in moisture resistance. Wrapped with film. As the organic binder resin, fluorinated resins such as cyanoethylated cellulose, cyanoethylated hydroxycellulose, cyanoethylated polyvinyl alcohol, cyanoethylated pullulan, and tetrafluoroethylene are used.

  The dispersion-type inorganic EL element configured as described above has excellent characteristics such as being able to be thinly formed with a thickness of 1 mm or less, obtaining uniform surface light emission, and being able to manufacture elements having various shapes. It is being put to practical use as a backlight for liquid crystal display devices, various types of lighting, or decoration.

  As a configuration method of the back electrode of such a dispersion type inorganic EL element, a method of producing a back electrode by a printing method using a silver paste (see, for example, Patent Document 1), a metal foil such as aluminum is used as a back electrode. A method of forming an element by thermocompression bonding (for example, see Patent Document 2) is known. Furthermore, a method of thinning a dielectric layer using a ceramic material is known (see, for example, Patent Document 3).

JP 2005-158491 A JP 2006-156358 A JP 2004-235167 A JP 2005-132947 A JP 2004-2867 A JP 2003-318069 A

  Patent Documents 1 and 2 disclose a method for constructing a reliable insulating structure by a dielectric layer and a method for producing an electrode as an important element for electroluminescence, but the dielectric layer of a dispersed inorganic EL element is thinned. Thus, there is no description regarding a method for increasing the brightness of the element. In order to increase the light emission luminance of the dispersion type EL element, it is necessary to increase the distribution of voltage applied to the light emitting layer with respect to the dielectric layer. By increasing the capacitance of the dielectric layer, when the same voltage is applied to the entire device, the voltage distribution applied to the light emitting layer is increased, so that the light emission luminance is improved. Here, in order to increase the capacitance of the dielectric layer, it is necessary to increase the dielectric constant of the film, reduce the thickness of the dielectric layer, or both. Patent Document 3 describes that the luminance is improved by thinning the dielectric layer and increasing the dielectric constant. However, in Patent Document 3, the ceramic dielectric layer is formed by sintering by a sol-gel method. Therefore, the formation process is complicated, the heat treatment is performed several times, and the smoothness of the electrode is easily impaired. Further, the ceramic dielectric layer and the back electrode manufactured in this way This interface has problems such as that sufficient electrical conductivity is not imparted because it does not have a chemical bond.

  In view of these problems, an object of the present invention is to provide a dispersion-type inorganic EL fluorescent element having sufficiently high luminance for a light-emitting element.

As a result of intensive studies to achieve the above object, the present inventors have found a configuration capable of stably obtaining high luminance in a dispersion-type inorganic EL element, and have reached the present invention.
That is, according to the present invention, the following is provided.
[1]
A light emitting layer is provided between the transparent electrode and the metal layer, and the surface of the metal layer on the light emitting layer side is oxidized to form an oxide film having a thickness of 0.1 μm to 2.0 μm. Dispersive inorganic EL element.
[2]
The dispersion-type inorganic EL device according to [1], wherein the metal constituting the metal layer is aluminum.
[3]
The dispersion inorganic EL element according to [1] or [2], wherein the specific surface area of the metal layer is 0.50 to 50.00 m ² / g.
[4]
(A) a step of forming an oxide film having a thickness of 0.1 μm to 2.0 μm by oxidizing at least one surface of the metal layer;
(B) forming a light emitting layer on the transparent electrode;
(C) laminating the metal layer on which the oxide film is formed in the step (a) on the light emitting layer so that the oxide film faces the light emitting layer;
A method for producing a dispersion-type inorganic EL element.
[5]
[4] The manufacturing method according to [4], wherein the metal constituting the metal layer is aluminum.
[6]
The production method according to [4] or [5], wherein an anodizing method is used in the step (a) of oxidizing the surface of the metal layer to form an oxide film.

  In the present invention, by using an oxide film obtained by oxidizing a part of the metal layer (back electrode) as the dielectric layer, the dielectric layer can be greatly thinned and a large capacitance can be obtained. Therefore, the dispersion-type inorganic EL fluorescent element of the present invention has high luminance for a light emitting element.

FIG. 1 is a cross-sectional view showing a basic configuration of a dispersion-type inorganic EL element of the present invention. FIG. 2 is a cross-sectional view showing a basic configuration of a conventional dispersion-type inorganic EL element.

As the light emitting layer constituting the dispersion type inorganic EL fluorescent element of the present invention, a phosphor layer in which phosphor particles are dispersed in a binder is used.
The phosphor used in the light-emitting layer constituting the dispersion-type inorganic EL fluorescent element of the present invention is not particularly limited, but is zinc sulfide, calcium sulfide, strontium sulfide, zinc selenide, cadmium selenide, and the like. In view of chemical stability, use of zinc sulfide is preferable.

  The method for preparing the phosphor is not particularly limited, and a method of firing a precursor obtained by a liquid phase reaction as shown in Patent Document 4, or a zinc sulfide powder as shown in Patent Document 5 is used. What was prepared by the method of baking by mixing an activator solid as a light emission center, etc. can be used.

  An activator may be used for the phosphor, and the activator to be used is not particularly limited, but transition metals such as copper, manganese, silver, and gold, cerium, europium, terbium, and the like. Rare earth metals can be used. From the viewpoint of orientation due to external field force, it is preferable to use copper, gold, or rare earth.

  The amount of the activator can be appropriately adjusted depending on the desired emission color, but is not particularly limited, and is usually added in the range of 100 ppm to 50000 ppm, more preferably in the range of 120 ppm to 30000 ppm.

  A coactivator may be further used in the phosphor of the present invention. The coactivator to be used is not particularly limited, and halogens such as chlorine, bromine and iodine, and metals such as aluminum and gallium can be used. The amount to be used is not particularly limited, and is usually 0.2 to 10 times by weight, more preferably 0.3 to 5 times by weight with respect to the activator. can do.

  The binder used in the light emitting layer constituting the dispersion-type inorganic EL fluorescent element of the present invention is not particularly limited as long as it is a material that does not absorb emitted light. For example, a polymer having a relatively high dielectric constant such as cyanoethyl cellulose resin, polyethylene, polypropylene, polystyrene resin, silicone resin, epoxy resin, vinylidene fluoride, acrylic resin, or the like can be used. These may have characteristics such as photo-curing properties and thermosetting properties, but the glass transition temperature is sufficiently higher than 40 ° C. so that the properties do not change due to heat generated during light emission or heat generated by energization. It needs to be expensive.

The dielectric constant can be adjusted by appropriately mixing fine particles having a high dielectric constant such as BaTiO ₃ or SrTiO _{3 with the} binder used in the light emitting layer of the present invention. As a method of dispersing these fine particles in the binder, a homogenizer, a planetary kneader, a roll kneader, an ultrasonic disperser, a centrifugal defoamer, or the like can be used.

  The light emitting layer can be coated on the transparent electrode by using a spin coating method, a dip coating method, a bar coating method, a spray coating method, or the like. In particular, it is preferable to use a method that does not select a printing surface, such as a screen printing method, or a method that allows continuous application, such as a slide coating method. For example, the screen printing method is a method in which a dispersion liquid in which fine particles of phosphor or dielectric are dispersed in a polymer solution having a high dielectric constant is applied through a screen mesh. In this method, the film thickness can be controlled by selecting the mesh thickness, the aperture ratio, the number of times of application, and the like. In addition, this method has an advantage that the area can be easily increased by changing the size of the screen.

Any transparent electrode material that is generally used can be used for the transparent electrode that constitutes the dispersion-type inorganic EL element of the present invention. For example, indium tin oxide, fluorine-doped tin oxide, antimony-doped tin oxide, aluminum-doped zinc oxide, gallium-doped zinc oxide and other oxides, conductive pastes composed of fine particles of these oxides and organic binders, silver thin films Or a π-conjugated polymer such as polyaniline or polypyrrole can be used.
The surface resistivity of the transparent electrode is preferably 1000Ω / □ or less, more preferably 0.1Ω / □ to 800Ω / □, and most preferably 0.2Ω / □ to 500Ω / □. The surface resistivity of the transparent electrode can be measured according to the method described in JIS K6911.

  As a method for producing the transparent electrode, a vapor phase method such as sputtering or vacuum deposition may be used. It may be produced by coating or screen printing using paste-like ITO or tin oxide, or may be produced by heating the entire film or heating with a laser.

  The metal layer constituting the dispersion-type inorganic EL element of the present invention is not particularly limited as long as it is a conductive material, and can be made from any material. Specifically, it is selected from metals such as gold, silver, platinum, copper, iron, and aluminum in a timely manner in consideration of the form of the element to be manufactured, the temperature of the manufacturing process, and the like. From the viewpoint of workability, electrical conductivity, and economy of the transparent electrode, it is preferable to use aluminum. When aluminum is used, the form may be foil, mesh, or woven, but from the viewpoint of surface workability and durability, it is preferable to use a foil.

In the present invention, in order to make the metal layer function not only as a back electrode but also as a dielectric layer, the surface of the metal layer is oxidized to form an oxide film.
The oxide film is preferably formed using a method in which the metal layer is heated in the presence of oxygen to oxidize the surface, or a method in which it is electrically oxidized. From the viewpoint of electrode strength and oxidation homogeneity, It is preferable to use an electrically oxidizing method.

  It is preferable that the thickness of the oxide film is appropriately selected in view of the insulating properties. For example, when the constituent material of the metal layer is aluminum, it is not preferable that the oxide film made of alumina is too thick because the capacitance is lowered. On the other hand, if the oxide film is too thin, insulation cannot be secured, which is not preferable. Therefore, a preferable thickness of the oxide film when using aluminum is 0.1 μm or more and 2.0 μm or less, and more preferably 0.2 μm or more and 1.0 μm or less.

In the present invention, the capacitance can be further increased by increasing the specific surface area of the metal layer. In this case, the specific surface area of the metal layer is preferably 0.50 to 50.00 m ² / g. The method for increasing the specific surface area of the metal layer is not particularly limited, and the surface area may be physically increased by using sandblasting or the like, or a chemical method such as electrolytic etching or electroless etching is used. The surface area may be increased. Among these, it is preferable to use electrolytic etching from the viewpoint of maintaining strength of the aluminum foil and homogeneous etching. Specifically, a metal layer and an oxide film can be prepared according to a method for producing an electrode for an aluminum electrolytic capacitor as disclosed in Patent Document 6.

  In the present invention, an organic layer is provided between the light emitting layer and the surface layer of the formed oxide film in order to reduce unevenness on the surface of the metal layer on which the oxide film is formed and to further improve the adhesion to the light emitting layer. It doesn't matter. It is preferable to make the organic layer as thin as possible, and increasing the thickness is not preferable because the dielectric constant decreases depending on the organic material used. Accordingly, the preferable thickness of the organic layer is 0.1 μm or more and 2.0 μm or less, and more preferably 0.2 μm or more and 1.0 μm or less. The organic layer to be laminated is not particularly limited as long as it does not absorb emitted light. Polymers having a relatively high dielectric constant such as cyanoethyl cellulose resin, polyethylene, polypropylene, polystyrene resin, silicone Resins, epoxy resins, vinylidene fluoride, acrylic resins, and the like can be used. In order to further increase the dielectric constant and reflectance of the organic material layer, the organic material layer may contain a high dielectric such as barium titanate, titanium oxide, zirconia, lead zirconate. In this case, since the oxide film formed on the metal layer also functions as a dielectric layer, the film thickness of the organic layer containing the high dielectric particles can be significantly reduced as compared with the conventional dielectric layer.

  The method for adhering the metal layer on which the oxide film is formed and the light emitting layer is not particularly limited, and a dispersed inorganic EL element can be easily formed by a method such as a thermocompression bonding method.

  The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited by the specific examples shown below.

(Reference Example 1) Aluminum foil etching method An aluminum foil having a thickness of 100 μm and a purity of 99.9% was immersed in a 1.0 wt% sulfuric acid aqueous solution at 80 ° C. for 60 seconds to remove a natural oxide film formed on the surface. did. Next, the aluminum foil was immersed in a 90 ° C. aqueous solution having a phosphoric acid concentration of 1.0 wt% for 60 seconds. Next, an aqueous solution at a temperature of 30 ° C. adjusted to 5.0 wt% hydrochloric acid, 2.0 wt% aluminum chloride, 0.1 wt% sulfuric acid, 0.5 wt% phosphoric acid, and 0.2 wt% nitric acid (the aluminum concentration in the electrolyte is The aluminum foil is immersed in 0.1 wt%), a sine wave current having a current density of 0.5 A / cm ² and a frequency of 40 Hz is applied to the aluminum foil, and etching is performed for 300 seconds. Shaped holes were formed. Next, in order to enlarge the pit hole, the aluminum foil was immersed in a 10 wt% sulfuric acid aqueous solution at a liquid temperature of 60 ° C. for 5 minutes, followed by a hydration treatment with a 0.1 wt% ethanolamine aqueous solution at 50 ° C. Thereafter, a heat treatment was performed for 3 minutes in an atmosphere at 250 ° C. to obtain an etched aluminum foil.

Reference Example 2 Method for Forming Oxide Film on Etched Aluminum Foil An aqueous solution of ammonium adipate having a liquid temperature of 80 ° C. and a concentration of 200 g / l was applied to the etched aluminum foil produced in Reference Example 1. The aluminum etching foil was subjected to chemical conversion treatment by immersing in and applying a voltage of 15 V at a low current density of 25 mA / cm ² to form an oxide film on the surface (anodic oxidation method). When the film thickness of the oxide film was measured, it was 0.6 μm. It was 4.60 m < ² > / g when the specific surface area was measured with the vapor | steam adsorption amount measuring apparatus (Nippon Bell company_made: BELSORP-18PLUS (brand name)).

(Reference Example 3) Preparation of phosphor High-purity zinc sulfide powder (manufactured by Sakai Chemical Industry Co., Ltd .: RAK-N (trade name)) is added to 150 g of 2.0 g of copper acetate hydrate (Cu (CH ₃ CO ₂ ) _2. H ₂ O) and a mixture of 30 g of magnesium chloride (MgCl ₂ ), 20 g of sodium chloride (NaCl), and 10 g of potassium chloride (KCl) as a flux were added to a planetary stirring deaerator ( Sinky Corporation: AR-250 (trade name)) and mixed well for 10 minutes. Next, this raw material powder is sealed in a magnetic crucible, baked at 1050 ° C. for 3 hours, washed with 3 liters of ion-exchanged water 10 times and filtered, and the flux is completely washed away, dried and subjected to intermediate fluorescence. A body powder (average particle size 22 μm) was obtained. Next, 120 g of this intermediate phosphor powder was dispersed in 600 g of ion-exchanged water, and continuously irradiated for 5 minutes at an output of 60% using an ultrasonic vibrator (manufactured by BRANSON: Digital Sonifier (trade name)) for 5 minutes. A stop cycle was performed three times. Then, it dehydrated and it dried at 80 degreeC with the hot air dryer for 12 hours. To 100 g of the obtained dried intermediate phosphor powder, 2.5 g of copper sulfate pentahydrate and 25 g of zinc sulfate heptahydrate were mixed, and a planetary stirring deaerator (AR-250 (trade name, manufactured by Shinky Corporation) was mixed. )) And mixed well for 10 minutes. Next, this raw material powder was sealed in a magnetic crucible, refired at 700 ° C. for 3 hours in a nitrogen atmosphere, and cooled to room temperature. The obtained fired product is stirred for 30 minutes in 1200 g of 5% hydrochloric acid aqueous solution, the remaining salt is washed, the surface is etched, washed with ion-exchanged water, and further 500 g of 1% KCN aqueous solution. To remove copper sulfide on the particle surface. Then, it was washed twice with 2 liters of ion exchanged water and dried with hot air at 80 ° C. for 12 hours to obtain 80 g of phosphor powder.

(Reference Example 4) Method of forming oxide film on unetched aluminum foil An aluminum foil having a thickness of 10 μm was immersed in an aqueous solution of ammonium adipate having a liquid temperature of 80 ° C. and a concentration of 200 g / l, and 25 mA / The aluminum foil was subjected to chemical conversion treatment by applying a voltage of 15 V at a low current density of cm ² to form an oxide film on the surface (anodic oxidation method). It was 0.7 micrometer when the film thickness of the oxide film was measured. It was 0.14 m < ² > / g when the specific surface area was measured with the vapor | steam adsorption amount measuring apparatus (Nippon Bell company_made: BELSORP-18PLUS (brand name)).

Example 1
To 1.5 g of the phosphor obtained in Reference Example 3, 1.0 g of a fluorine-based binder (manufactured by DuPont: 8155 (trade name)) was added as a binder, mixed and degassed to prepare a light emitting layer paste. Using a screen plate (200 mesh, 25 μm) on a 20 mm square PET film with ITO, a light emitting layer paste was made with a film thickness of 40 μm and dried at 100 ° C. for 10 minutes to form a light emitting layer. The aluminum foil electrode in which the oxide film was formed in Reference Example 2 as a metal layer was laid at 18 mm square. This element was sandwiched between PET films, passed through a pressure sealing machine at 140 ° C., the electrode and the light emitting layer were brought into close contact with each other, and waterproof sealing was performed to constitute a dispersion-type inorganic EL element. About the obtained element, the EL element was made to emit light at 200 V and 1 kHz, and the luminance was measured with a color luminance meter (Topcon Co., Ltd .: BM7 (trade name)). The luminance meter was installed at a height of 50 cm from the EL element, and the measurement was performed in a measurement range of 0.2 °. The results are shown in Table 1.

(Example 2)
In Example 1, except that an aluminum foil electrode on which an oxide film was formed was previously formed using a screen printer with a barium titanate paste (manufactured by DuPont: 8153 (trade name)) with a thickness of 1 μm. Was carried out in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)
To 1.5 g of the phosphor obtained in Reference Example 3, 1.0 g of a fluorine-based binder (manufactured by DuPont: 8155 (trade name)) was added as a binder, mixed and degassed to prepare a light emitting layer paste. Using a screen plate (200 mesh, 25 μm) on a 20 mm square PET film with ITO, a light emitting layer paste was made with a film thickness of 40 μm and dried at 100 ° C. for 10 minutes to form a light emitting layer. An aluminum foil electrode that was not subjected to etching in which an oxide film was formed in Reference Example 4 was laid in an 18 mm square. This element was sandwiched between PET films, passed through a pressure sealing machine at 140 ° C., the electrode and the light emitting layer were brought into close contact with each other, and waterproof sealing was performed to constitute a dispersion-type inorganic EL element. About the obtained element, the EL element was made to emit light at 200 V and 1 kHz, and the luminance was measured with a color luminance meter (Topcon Co., Ltd .: BM7 (trade name)). The luminance meter was installed at a height of 50 cm from the EL element, and the measurement was performed in a measurement range of 0.2 °. The results are shown in Table 1.

(Comparative Example 1)
To 1.5 g of the phosphor obtained in Reference Example 3, 1.0 g of a fluorine-based binder (manufactured by DuPont: 7155 (trade name)) was added as a binder, mixed and degassed to prepare a light emitting layer paste. Using a screen plate (200 mesh, 25 μm) on a 20 mm square PET film with ITO, a light emitting layer paste is made with a film thickness of 40 μm, and a barium titanate paste (manufactured by DuPont: 8153 (trade name)) is used as a screen plate. (150 mesh, 25 μm), and the plate was dried at 100 ° C. for 10 minutes. Thereafter, a barium titanate paste was again made in the same manner and dried at 100 ° C. for 10 minutes to form a dielectric layer having a total thickness of 20 μm. On the upper surface, as an electrode, silver paste (manufactured by Atchison: 461SS (trade name)) was made using a screen plate (150 mesh, 25 μm), dried at 100 ° C. for 10 minutes to form an electrode, A printing EL element was constructed. About the obtained element, the EL element was made to emit light at 200 V and 1 kHz, and the luminance was measured with a color luminance meter (Topcon Co., Ltd .: BM7 (trade name)). The luminance meter was installed at a height of 50 cm from the EL element, and the measurement was performed in a measurement range of 0.2 °. The results are shown in Table 1.

(Comparative Example 2)
In Example 1, 15 μm of alumina sol (manufactured by Nissan Chemical Industries, Ltd .: Alumina Sol 100 (trade name)) was applied to an aluminum foil having a thickness of 10 μm and sintered at 300 ° C. for 1 hour in place of the metal layer. Used as an electrode. The thickness of the alumina film was measured and found to be 0.7 μm. The results are shown in Table 1.

(Comparative Example 3)
To 1.5 g of the phosphor obtained in Reference Example 3, 1.0 g of a fluorine-based binder (manufactured by DuPont: 8155 (trade name)) was added as a binder, mixed and degassed to prepare a light emitting layer paste. Using a screen plate (200 mesh, 25 μm) on a 20 mm square PET film with ITO, a light emitting layer paste was made with a film thickness of 40 μm and dried at 100 ° C. for 10 minutes to form a light emitting layer. The aluminum foil electrode to which the etching produced in the reference example 1 was performed was laid in 18 square mm there. This element was sandwiched between PET films, passed through a pressure sealing machine at 140 ° C., the electrode and the light emitting layer were brought into close contact with each other, and waterproof sealing was performed to constitute a dispersion-type inorganic EL element. About the obtained element, the EL element was made to emit light at 200 V, 1 kHz, and the luminance was measured with a color luminance meter (Topcon Co., Ltd .: BM7 (trade name)), but the emission was unstable and black spots due to dielectric breakdown were observed. Many occurred and the brightness could not be evaluated.

  As shown in Table 1, in accordance with the method of the present application, the oxide film formed on the back electrode and used instead of the dielectric layer had an oxide film thickness of 0.6 μm (Example 1), 1.6 μm (Example 1) Since Example 2) and 0.7 μm (Example 3) were very thin, higher luminance than that using 20 μm of barium titanate paste as a dielectric layer (Comparative Example 1) was obtained. Further, comparing Example 1 and Example 3, it can be seen that the luminance is further improved by increasing the specific surface area of the metal layer by etching.

  Further, in each of the examples of the present invention, high brightness was obtained even when compared with the one in which a 0.7 μm oxide film was formed with alumina sol (Comparative Example 2). This is probably because the dielectric layer formed by sintering the alumina sol is not chemically well bonded to the back electrode, causing electrical loss at the interface and not fully functioning as a dielectric layer. This is probably because of this.

1: Transparent electrode 2: Light emitting layer 3: Dielectric layer 4: Metal layer 4a: Back electrode portion 4b: Oxide film 5: Skin film

Claims (6)

  A light emitting layer is provided between the transparent electrode and the metal layer, and the surface of the metal layer on the light emitting layer side is oxidized to form an oxide film having a thickness of 0.1 μm to 2.0 μm. Dispersive inorganic EL element.   2. The dispersion-type inorganic EL device according to claim 1, wherein the metal constituting the metal layer is aluminum. 3. The dispersion type inorganic EL device according to claim 1, wherein the metal layer has a specific surface area of 0.50 to 50.00 m ² / g. (A) a step of forming an oxide film having a thickness of 0.1 μm to 2.0 μm by oxidizing at least one surface of the metal layer;
(B) forming a light emitting layer on the transparent electrode;
(C) laminating the metal layer on which the oxide film is formed in the step (a) on the light emitting layer so that the oxide film faces the light emitting layer;
A method for producing a dispersion-type inorganic EL element.   The manufacturing method according to claim 4, wherein the metal constituting the metal layer is aluminum.   The manufacturing method according to claim 4 or 5, wherein an anodizing method is used in the step (a) of forming an oxide film by oxidizing the surface of the metal layer.