JP4973050B2 - Manufacturing method of crystalline oxide film of composite oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a crystalline fine particle film of a compound oxide by which a dense crystalline fine particle film can be obtained even at a heat-treating temperature lower than the crystallization temperature. <P>SOLUTION: The method for producing the crystalline fine particle film of a compound oxide includes the steps of: forming a crystalline fine particle film 2 of the compound oxide containing at least one kind of alkaline earth metal elements and titanium on a substrate 1; forming a noble metal film 3 on the crystalline fine particle film 2; and heat-treating the crystalline fine particle film 2 formed with the noble metal film 3 at a temperature of &ge;400&deg;C but &lt;600&deg;C. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a crystalline fine particle film of a composite oxide containing at least one alkaline earth metal element and titanium.

  Attempts have been made to form functional films that can be applied to thin film capacitors, thin film piezoelectric bodies, thin film pyroelectric bodies, and the like by growing various crystalline fine particle films on a substrate.

For example, in Japanese Patent Application Laid-Open No. 04-342422 (hereinafter referred to as Patent Document 1), a sol solution composed of an inorganic salt of zircon, a lanthanum compound, an organic compound of lead and an organic compound of titanium is applied to the substrate, and then the substrate is Ferroelectric material having chemical composition of (Pb _1-x La _x ) (Zr _1-y Ti _y ) O ₃ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) by crystallizing the coating film by heat treatment A method for forming a thin film has been proposed.

In JP-A-07-315810 (hereinafter referred to as Patent Document 2), A and B (where A is an element selected from Group IA, Group IIA, Group IIIA, Group IVB and Group VB, and B is An element selected from Group IVA and Group VA) is hydrolyzed by adding water and an inorganic catalyst or acetic acid at a predetermined molar ratio to a composite metal alkoxide compound containing ABO, and then coated on a substrate and heat-treated, thereby ABO. A method for producing the oxide thin film shown in ₃ has been proposed.

  In each of the methods proposed in Patent Document 1 and Patent Document 2, a thin film is formed with a precursor solution of oxide or composite oxide, and solvent evaporation and chemical reaction occur at a low temperature of about 50 ° C. to 150 ° C. Thus, a thin film of an amorphous oxide or composite oxide is formed. Next, this thin film is crystallized by heat treatment at 600 ° C. or higher (Patent Document 1) or 200 ° C. to 800 ° C. (Patent Document 2).

For this reason, the methods proposed in Patent Document 1 and Patent Document 2 have the following three problems. First, the thin film precursor solution applied to the substrate surface contracts by about 30% by volume or more due to the volume change when the solvent and the organic components in the raw material evaporate, and the density of the thin film is significantly reduced. That is. Second, the above-mentioned heat treatment at a relatively high temperature causes a reaction or diffusion between the thin film and the substrate or between the thin film and another film (for example, an electrode film), thereby reducing the characteristics and reliability of the thin film. It may be reduced. Third, the heat treatment at a relatively high temperature as described above increases the manufacturing cost and causes environmental degradation due to a large amount of energy consumption.
Japanese Patent Laid-Open No. 04-342422 JP 07-315810 A

  An object of the present invention is to solve the above-mentioned problems and to provide a production method capable of obtaining a dense complex oxide crystal particle film even at a heat treatment temperature lower than the crystallization temperature.

  The present invention includes a step of forming a composite oxide crystal fine particle film containing at least one kind of alkaline earth metal element and titanium on a substrate, a step of forming a noble metal film on the crystal fine particle film, And a step of heat-treating the formed crystalline fine particle film at a temperature of 400 ° C. or higher and lower than 600 ° C.

  In the method for producing a crystalline fine particle film of a complex oxide according to the present invention, the complex oxide can contain at least one element selected from the group consisting of Ba, Sr and Ca as an alkaline earth metal element. Further, the step of forming the noble metal can be performed by an ion sputtering method or a vacuum deposition method.

  According to the present invention, it is possible to provide a production method capable of obtaining a dense complex oxide crystal particle film even at a heat treatment temperature lower than the crystallization temperature.

  One embodiment of the method for producing a composite oxide crystal fine particle film according to the present invention is described with reference to FIG. 1. A composite oxide crystal containing at least one alkaline earth metal element and titanium on a substrate 1. The step of forming the fine particle film 2 (FIG. 1A), the step of forming the noble metal film 3 on the crystalline fine particle film 2 (FIG. 1B), and the crystalline fine particle film 2 on which the noble metal film 3 is formed And a step of heat treatment at 400 ° C. or higher and lower than 600 ° C. (FIG. 1C).

In the method for producing a crystalline fine particle film according to the present embodiment, a film formed not from an amorphous fine particle film formed from a precursor of a complex oxide crystalline particle but from a complex oxide crystalline particle instead of being formed on a substrate. Is formed on the substrate, and a noble metal film is formed on the crystal fine particle film of the composite oxide, and heat treatment is performed at 400 ° C. or more and less than 600 ° C., so that the crystallization temperature of the composite oxide (for example, BaTiO ₃ In the case of 800 ° C., and in the case of (Ba, Sr) TiO ₃ 650 ° C. to 750 ° C.), the crystal fine particles in the crystal fine particle film can be grown, and a dense crystal fine particle film is formed. Can do. Here, if the temperature of the heat treatment is less than 400 ° C., it becomes difficult to grow crystal fine particles, and if it is 600 ° C. or higher, aggregation between the fine particles occurs vigorously and massive particles are formed. From this viewpoint, the heat treatment temperature is preferably 450 ° C. or higher and 550 ° C. or lower.

Hereinafter, the method for producing the composite oxide crystal fine particle film of the present embodiment will be described in detail.
(1) Crystal Fine Particle Film Formation Step First, referring to FIG. 1A, a complex oxide crystal fine particle film 2 containing at least one alkaline earth metal element and titanium is formed on a substrate 1. (This process is referred to as a crystal particle film forming process, and the same applies hereinafter).

Here, the composite oxide containing one kind of alkaline earth metal and titanium is an oxide containing two or more metal elements represented by the general formula of (M ₁ ,..., M _n ) TiO _3. Say. Here, M represents an alkaline earth metal element, and (M ₁ ,..., M _n ) TiO ₃ has a molar ratio of all n types of alkaline earth metal elements, Ti atoms and O atoms of 1 : 1: 3. Specific examples of (M ₁ ,..., M _n ) TiO ₃ include BaTiO ₃ (Ba: Ti: O = 1: 1: 3), (Ba, Sr) TiO ₃ ((Ba + Sr): Ti: O = 1: 1: 3).

  The composite oxide preferably includes at least one element selected from the group consisting of Ba, Sr, and Ca as the alkaline earth metal element. This is because a complex oxide containing at least one of Ba, Sr, and Ca as an alkaline earth metal element can form a film having very excellent dielectric characteristics and piezoelectric characteristics.

The method for forming the (M ₁ ,..., M _n ) TiO ₃ crystalline particle film is not particularly limited, but from the viewpoint of easily forming a thin and uniform crystalline particle film, (M ₁ ,..., M _n ) a suspension containing crystal fine particles of TiO ₃ is brought into contact, and the crystal fine particles 2p of (M ₁ ,..., M _n ) TiO ₃ are adsorbed on the surface of the substrate 1 (M ₁ ,..., M _n ) TiO ₃ crystalline fine particle film 2 is preferably used.

Further, in order to uniformly and efficiently adsorb the crystal fine particles 2p on the surface of the substrate 1, the surface of the substrate 1 is easily wetted by the suspension solvent, that is, the contact angle of the suspension on the surface of the substrate 1 is small, and It is preferable that the surface of the substrate 1 and the surface of the crystal fine particle 2p are charged so as to have charges of opposite signs, and an electrostatic attractive force acts between them. For this purpose, it is preferable to treat the surface of the substrate 1 with a silane coupling agent or the like before contacting with the suspension containing crystal fine particles of (M ₁ ,..., M _n ) TiO ₃ .

Therefore, the step of forming the composite oxide crystal fine particle film 2 containing at least one kind of alkaline earth metal element and titanium on the substrate 1 is preferably (M ₁ ,..., M _n ) TiO ₃ crystal particle synthesis step, (M ₁ ,..., M _n ) TiO ₃ crystal particle suspension preparation step, substrate 1 surface treatment step, substrate 1 surface (M ₁ ,..., M _n ) including a step of contacting a suspension of crystalline fine particles of TiO ₃ . Each step will be described below.

(1-1) Step of synthesizing crystal fine particles of (M ₁ ,..., M _n ) TiO ₃ TiO ₂ fine particles are added to an aqueous solution of at least one alkaline earth metal element hydroxide, for example, 80 ° C. or higher. By stirring at this temperature, the alkaline earth metal element hydroxide reacts with TiO ₂ to obtain (M ₁ ,..., M _n ) TiO ₃ crystalline fine particle powder. In addition, by hydrothermally synthesizing at least one alkaline earth metal element carbonate and TiO ₂ under the conditions of, for example, 200 ° C. to 300 ° C. and 1.0 MPa to 3.0 MPa, (M ₁ ,... , M _n ) TiO ₃ fine crystal powder. It can be confirmed by XRD (X-ray diffraction) that the fine particles are crystals.

(1-2) (M ₁ ,..., M _n ) TiO ₃ Crystalline Particle Suspension Preparation Step (M ₁ ,..., M _n ) TiO ₃ obtained in (1-1) above The crystal fine particles are dispersed in an organic solvent, and the aggregated crystal fine particles are pulverized using a bead mill to obtain fine particles having an average particle diameter of about 10 nm to 200 nm. By setting the particle size to this level, a stable suspension can be easily obtained. Next, the same organic solvent as described above is added to obtain a suspension containing a predetermined amount of crystal fine particles. The organic solvent used as the solvent for the suspension is not particularly limited, but preferably has an appropriate polarity from the viewpoint of enhancing the dispersibility of the (M ₁ ,..., M _n ) TiO ₃ crystal fine particles, For example, a mixed solvent of toluene and ethanol is preferable. Here, positive charges are charged on the surface of the crystal fine particles of (M ₁ ,..., M _n ) TiO ₃ in the suspension.

(1-3) Substrate Surface Treatment Step The substrate 1 is not particularly limited, and a Si substrate, a sapphire substrate, a glass substrate, or the like is preferably used. The surface of these substrates is hydrophilic due to the —OH group present on the surface, and is difficult to wet with the organic solvent of the suspension of crystal particles of (M ₁ ,..., M _n ) TiO ₃ . Therefore, the surface of the substrate 1 is treated with a silane coupling agent to make it oleophilic, so that the surface of the substrate is easily wetted with the organic solvent of the suspension of crystal particles of (M ₁ ,..., M _n ) TiO _3. .

  The method for treating the surface of the substrate 1 with a silane coupling agent is not particularly limited, but from the viewpoint of uniformly treating the surface of the substrate, a solution in which a predetermined silane coupling agent is dissolved in an organic solvent (hereinafter referred to as silane). A method in which the substrate 1 is dipped in a coupling agent solution) and then dried is preferable. Although there is no restriction | limiting in particular in the organic solvent used for a silane coupling agent solution, Toluene etc. are suitable from a viewpoint of improving the drying property of a board | substrate.

Further, _{(M 1, ···, M n} ) is the surface of the TiO ₃ crystal particles, the positive charge is charged, to the surface of the substrate _{(M 1, ···, M n} ) of TiO ₃ In order to increase the electrostatic adsorption force of the crystal fine particles, it is preferable to charge a negative charge on the surface of the substrate. From this viewpoint, the silane coupling agent preferably contains a functional group capable of charging a negative charge in the lipophilic portion. For example, a mercapto group is preferred.

(1-4) The step of bringing the suspension of crystal fine particles of (M ₁ ,..., M _n ) TiO ₃ into contact with the surface of the substrate The substrate surface-treated with the silane coupling agent according to the above (1-3) the prepared by _{(1-2) (M 1, ···} , M n) by immersion in a suspension of TiO ₃ crystal particles, the surface of the substrate _{(M 1, ···, M n} ) TiO ₃ is brought into contact, and referring to FIG. 1A, (M ₁ ,..., M _n ) TiO ₃ crystal particles 2p are thinly and uniformly adsorbed on the surface of the substrate 1. .

Next, the substrate 1 on which the (M ₁ ,..., M _n ) TiO ₃ crystal fine particles 2 are adsorbed on the surface is dried (drying process), thereby referring to FIG. A crystalline fine particle film 2 of (M ₁ ,..., M _n ) TiO ₃ is formed thereon.

(2) Noble Metal Film Forming Step Next, referring to FIG. 1B, a noble metal film 3 is formed on the crystalline fine particle film 2 formed by the above (1) (this is called a noble metal film forming step). same as below). Here, the method for forming the noble metal film 3 is not particularly limited, but from the viewpoint of forming a uniform and thin film, an ion sputtering method and a vacuum deposition method are preferable.

  Here, the noble metal forming the noble metal film 3 is not particularly limited as long as it has a catalytic action for growing the crystal fine particles 2p in the crystal fine particle film 2, and includes those containing Pt, Pd, Au, Ag and the like. It is done. Moreover, it may be a simple substance or an alloy. From the viewpoint of high catalytic action, it is preferable to include noble metals Pt and Pd that form the noble metal film 3. Further, the thickness of the noble metal film 3 is not particularly limited, but it is preferably as thin as possible considering the average particle diameter of the crystal fine particles 2p, for example, 20 nm or less.

(3) Heat Treatment Step Next, with reference to FIG. 1C, the crystalline fine particle film 2 on which the noble metal film 3 is formed is heat treated at 400 ° C. or higher and lower than 600 ° C. (this is referred to as a heat treatment step, hereinafter the same). By heat-treating the crystal particle film 2 on which the noble metal film 3 is formed, the crystal particle 2p in the crystal particle film 2 grows, and the dense crystal particle film 2 is obtained. Due to the catalytic action of the noble metal film 3 formed on the crystal particle film 2, the crystal particle 2p can be grown even at a temperature lower than the crystallization temperature. Here, if the temperature of the heat treatment is less than 400 ° C., it becomes difficult to grow crystal fine particles, and if it is 600 ° C. or higher, aggregation between the fine particles occurs vigorously and massive particles are formed. From this viewpoint, the heat treatment temperature is preferably 450 ° C. or higher and 550 ° C. or lower.

Example 1
When 1.0 mol of TiO ₂ fine particles are added to 1.0 liter of a 1.0 mol / l (liter, same hereinafter) aqueous Ba (OH) ₂ solution and stirred at a temperature of 80 ° C. or higher for 1 hour, Ba (OH ₂ ) and TiO ₂ reacted to precipitate BaTiO ₃ fine particles. When this BaTiO ₃ fine particle powder was subjected to XRD (X-ray diffraction), a diffraction peak pattern as shown in FIG. 2 was obtained, confirming that it was a crystalline fine particle.

Next, the BaTiO ₃ crystal fine particles are dispersed in a 1: 1 (volume ratio) mixed solvent of toluene and ethanol, and the aggregated BaTiO ₃ particles are pulverized using a bead mill, so that the concentration of the crystal fine particles is 100 g. / L slurry was obtained. Further, the slurry was diluted with a 1: 1 (volume ratio) mixed solvent of toluene and ethanol to obtain a suspension of BaTiO ₃ crystal particles having a crystal particle concentration of 1 g / l. The particle size distribution of BaTiO ₃ crystal fine particles of this suspension was measured by a dynamic light scattering method using a Zetasizer Nano series manufactured by Malvern. As shown in FIG. 3, the BaTiO ₃ crystal particles in the suspension were monodispersed sharply in an average particle size of 45.6 nm and a particle size of 15 nm to 200 nm.

  On the other hand, the Si substrate as the substrate 1 was ultrasonically cleaned using a mixed solvent of water, ethanol and acetone, and then further dry-cleaned with ultraviolet light. The cleaned Si substrate (substrate 1) was immersed in a 1% by volume 3-mercaptopropyltrimethoxysilane toluene solution at 25 ° C. for 60 minutes to perform surface treatment of the Si substrate (substrate 1).

Next, the surface-treated Si substrate was immersed in the BaTiO ₃ crystal fine particle suspension at 25 ° C. for 20 minutes, and then dried at 0 ° C. for 48 hours or more. With reference to FIG. A BaTiO ₃ crystal particle film (crystal particle film 2) was formed on the Si substrate (substrate 1).

Next, referring to FIG. 1B, a BaTiO ₃ crystal particle film (a noble metal film on the crystal particle film 2 is applied under the condition that a charge current of 15 mA is applied for 3 minutes in an Ar atmosphere using an ion sputtering film forming apparatus. 3, a Pt—Pd alloy film (Pt: Pd = 90: 10 (molar ratio)) having a thickness of about 10 nm was formed. The BaTiO ₃ crystal particle film (crystal particle film 2) at this time was observed with an SEM (scanning electron microscope). An SEM photograph of the BaTiO ₃ crystal particle film (crystal particle film 2) is shown in FIG.

Next, referring to FIG. 1C, using a tubular electric furnace, a BaTiO ₃ crystalline fine particle film (Pt—Pd alloy film (noble metal film 3) formed under a heat treatment condition of 500 ° C. for 2 hours ( The crystalline fine particle film 2) was heat-treated. An SEM photograph of the BaTiO ₃ crystal particle film (crystal particle film 2) after the heat treatment is shown in FIG.

As is clear from comparison between FIG. 5 and FIG. 6, the above heat treatment increases the particle size of the crystal particles 2p in the BaTiO ₃ crystal particle film (crystal particle film 2), that is, the BaTiO ₃ crystal particle film (crystal The crystal particles 2p in the fine particle film 2) grew, and a dense BaTiO ₃ crystal fine particle film (crystal fine particle film 2) was obtained.

(Example 2)
BaCO ₃ , SrCO ₃ and TiO ₂ were mixed at a molar ratio of 0.7: 0.3: 1.0, and hydrothermally synthesized under the conditions of 250 ° C. and 1.013 MPa, (Ba , Sr) TiO ₃ fine particles were obtained. In the same manner as in Example 1, it was confirmed by XRD that the (Ba, Sr) TiO ₃ fine particles were crystal fine particles.

Then, in the same manner as in Example 1, the (Ba, Sr) using TiO ₃ crystal particles, the crystal particles concentration to obtain a suspension of (Ba, Sr) TiO ₃ crystal particles of 1 g / l. When the particle size distribution of the (Ba, Sr) TiO ₃ crystal fine particles of this suspension was measured in the same manner as in Example 1, as shown in FIG. 4, the (Ba, Sr) TiO ₃ crystal fine particles in the suspension were It was monodisperse sharply in a diameter range of 51 nm and a particle size range of 20 nm to 200 nm.

On the other hand, the surface treatment of the Si substrate (substrate 1) was performed in the same manner as in Example 1.
Next, the surface-treated Si substrate was immersed in the above (Ba, Sr) TiO ₃ crystal fine particle suspension at 25 ° C. for 20 minutes, and then dried at 0 ° C. for 48 hours or more. ), A (Ba, Sr) TiO ₃ crystal particle film (crystal particle film 2) was formed on the Si substrate (substrate 1).

Next, referring to FIG. 1B, a BaTiO ₃ crystal particle film (a noble metal film on the crystal particle film 2 is applied under the condition that a charge current of 15 mA is applied for 3 minutes in an Ar atmosphere using an ion sputtering film forming apparatus. Then, a Pt film having a thickness of about 10 nm was formed, and the (Ba, Sr) TiO ₃ crystal particle film (crystal particle film 2) at this time was observed with an SEM (scanning electron microscope) (Ba, Sr). An SEM photograph of the TiO ₃ crystal particle film (crystal particle film 2) is shown in FIG.

Next, referring to FIG. 1C, a (Ba, Sr) TiO ₃ crystal particle film (crystal particle) on which a Pt film (noble metal film 3) is formed at 500 ° C. for 2 hours using a tubular electric furnace. Film 2) was heat treated. FIG. 8 shows an SEM photograph of the (Ba, Sr) TiO ₃ crystal particle film (crystal particle film 2) after the heat treatment.

As is clear from comparison between FIG. 7 and FIG. 8, the above heat treatment increases the particle size of the crystal particles 2p in the (Ba, Sr) TiO ₃ crystal particle film (crystal particle film 2), that is, (Ba , Sr) TiO ₃ crystal particle film (crystal particle film 2) grows, and a dense (Ba, Sr) TiO ₃ crystal particle film (crystal particle film 2) is obtained.

(Comparative Example 1)
After forming the BaTiO ₃ crystal particle film (crystalline particle film 2) on the Si substrate (substrate 1), without forming a noble metal film 3 on the BaTiO ₃ crystal particle film (crystalline particle film 2), except that the heat-treated Produced a BaTiO ₃ crystal particle film (crystal particle film 2) in the same manner as in Example 1. An SEM photograph of the BaTiO ₃ crystal particle film (crystal particle film 2) after the heat treatment is shown in FIG.

As is clear from comparison between FIG. 5 and FIG. 9, even when the above heat treatment is performed, the grain size of the crystal grain 2p in the BaTiO ₃ crystal grain film (crystal grain film 2) is not increased, that is, BaTiO ₃ crystal. The crystal particles 2p in the fine particle film (crystalline fine particle film 2) did not grow, and a dense BaTiO ₃ crystalline fine particle film (crystalline fine particle film 2) could not be obtained.

(Example 3)
A BaTiO ₃ crystal particle film (crystal particle film 2) was produced in the same manner as in Example 1 except that the heat treatment conditions in the heat treatment step were set at 500 ° C. for 8 hours. An SEM photograph of the BaTiO ₃ crystal particle film (crystal particle film 2) after the heat treatment is shown in FIG.

As is clear from comparison between FIG. 5 and FIG. 10, the above heat treatment increases the particle size of the crystal particles 2p in the BaTiO ₃ crystal particle film (crystal particle film 2), that is, the BaTiO ₃ crystal particle film (crystal The crystal particles 2p in the fine particle film 2) grew, and a dense BaTiO ₃ crystal fine particle film (crystal fine particle film 2) was obtained.

Example 4
A (Ba, Sr) TiO ₃ crystal particle film (crystal particle film 2) was produced in the same manner as in Example 2 except that the heat treatment conditions in the heat treatment step were 450 ° C. for 8 hours. FIG. 11 shows an SEM photograph of the (Ba, Sr) TiO ₃ crystal particle film (crystal particle film 2) after the heat treatment.

As is clear from comparison between FIG. 7 and FIG. 11, the above heat treatment increases the particle size of the crystal particles 2p in the (Ba, Sr) TiO ₃ crystal particle film (crystal particle film 2), that is, (Ba , Sr) TiO ₃ crystal particle film (crystal particle film 2) grows, and a dense (Ba, Sr) TiO ₃ crystal particle film (crystal particle film 2) is obtained.

(Comparative Example 2)
A BaTiO ₃ crystal particle film (crystal particle film 2) was produced in the same manner as in Example 1 except that the heat treatment conditions in the heat treatment step were set at 600 ° C. for 20 minutes. FIG. 12 shows an SEM photograph of the BaTiO ₃ crystal particle film (crystal particle film 2) after the heat treatment.

As is clear from the comparison between FIG. 5 and FIG. 12, the above heat treatment causes the crystal particles 2p in the BaTiO ₃ crystal particle film (crystal particle film 2) to aggregate to form massive particles, thereby forming dense BaTiO ₃ crystals. A fine particle film was not obtained.

  For reference, for Tables 1 to 4 and Comparative Examples 1 and 2, a list (Table 1) is prepared that summarizes the composition of the crystalline fine particle film, the noble metal film, the heat treatment conditions, and the SEM photograph numbers before and after the heat treatment. did.

  From Examples 1 to 4, a crystal fine particle film of a composite oxide containing at least one kind of alkaline earth metal element and titanium is formed on a substrate, and a noble metal film is formed on the crystal fine particle film. It was found that a dense crystalline fine particle film can be obtained by heat-treating the crystalline fine particle film on which the film is formed at 400 ° C. or higher and lower than 600 ° C.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic cross section which shows one Embodiment of the manufacturing method of the crystalline fine particle film | membrane of complex oxide concerning this invention. Here, (a) shows a process for forming a crystalline fine particle film, (b) shows a process for forming a noble metal film, and (c) shows a heat treatment process. FIG. 4 is a diagram showing a diffraction peak pattern by XRD of crystal fine particles in the suspension used in Example 1. FIG. 3 is a graph showing the particle size distribution of crystal fine particles in the suspension used in Example 1. FIG. 4 is a graph showing a particle size distribution of crystal fine particles in a suspension used in Example 2. 2 is a SEM photograph of the crystalline fine particle film before the heat treatment step in Example 1. 2 is a SEM photograph of the crystalline fine particle film after the heat treatment step in Example 1. 4 is a SEM photograph of a crystalline fine particle film before a heat treatment step in Example 2. 4 is a SEM photograph of the crystalline fine particle film after the heat treatment step in Example 2. 4 is a SEM photograph of the crystalline fine particle film after the heat treatment step in Comparative Example 1. 4 is a SEM photograph of a crystalline particle film after a heat treatment step in Example 3. 6 is a SEM photograph of the crystalline fine particle film after the heat treatment step in Example 4. 4 is a SEM photograph of a crystalline fine particle film after a heat treatment step in Comparative Example 2.

Explanation of symbols

  1 substrate, 2 crystal particle film, 2p crystal particle, 3 noble metal film.

Claims (3)

Forming a composite oxide crystal particle film containing at least one alkaline earth metal element and titanium on a substrate;
Forming a noble metal film on the crystalline particle film;
And a step of heat-treating the crystalline fine particle film on which the noble metal film is formed at a temperature of 400 ° C. or higher and lower than 600 ° C.   2. The method for producing a fine crystal particle film of a composite oxide according to claim 1, wherein the composite oxide includes at least one element selected from the group consisting of Ba, Sr, and Ca as the alkaline earth metal element.   3. The method for producing a composite oxide crystalline particle film according to claim 1, wherein the step of forming the noble metal is performed by an ion sputtering method or a vacuum deposition method.