JP2001110237A - Ferroelectric thin film forming application liquid, its manufacture and ferroelectric thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferroelectric thin film forming application liquid capable of forming a ferroelectric thin film at a low cost which contains effective components soluble in general organic solvent and has excellent reserving stability and reproductivity, a small leak current and a great film density, its manufacture and the ferroelectric thin film formed by applying and hardening the application liquid. SOLUTION: A ferroelectric thin film forming application liquid contains organic metal compound, the organic metal compound being formed by replacing hydroxyl groups and alkoxyl groups or one of them of hydrolyzed metal alkoxide containing two or more types of metal elements in one molecule with other functional groups than the hydroxyl groups.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating liquid for forming a ferroelectric thin film. More specifically, a ferroelectric thin film containing an active ingredient soluble in a general-purpose organic solvent, having excellent storage stability and reproducibility, and having a small leak current and a large (density) film density. The present invention relates to a coating liquid for forming a ferroelectric thin film which can be formed at low cost, a method for producing the same, and a ferroelectric thin film.

[0002]

_2. Description of the Related Art In recent years, the formula (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O
_{3m + 1} ) Bi-based ferroelectric (BL) having a layered structure shown in ^2-
(SF) thin films have attracted attention. In the above formula, A is 1,
Divalent or trivalent ions (for example, Bi, Pb, Ba, Sr,
B represents ions of Ca, Na, K, and rare earth elements) or a combination of these ions; B represents a 4, 5, 6-valent ion (eg, Ti, Nb, Ta, W, Mo, Fe,
A metal element such as Co or Cr), or a combination of these ions; m is an integer of 1 to 5. Bi-based ferroelectric (BLSF) having such a layered structure
Since the thin film has characteristics such as a small coercive electric field of PE hysteresis and little fatigue of the film due to polarization reversal, it has been spotlighted as a material for semiconductor memories and sensors (Tasashi Takenaka, Bismuth "Layered Structure Ferroelectrics and Particle Orientation", Japan Society of Applied Physics, Applied Electronic Properties Subcommittee Research Report, November 22, 1994, pp. 1-8; "Ceramics" Vol. 30, No. 6, pp. 499 -50
3 (1995)). Among them, SrBi ₂ Ta ₂ O ₉ system, that is, (Bi ₂ O ₂ ) ²⁺ (SrTa ₂ O ₇ ) ^2- BLSF
Thin films have received particular attention as materials that exhibit these properties significantly.

[0003] As a method of forming these BLSF thin films,
Examples of the method include a sputtering method, a CVD method, and a coating film forming method. However, a thin film forming method by a sputtering method or a CVD method requires an expensive apparatus because a large amount of metal oxide is contained as a constituent of the thin film. There are problems such as high cost and difficulty in controlling and managing the composition of the dielectric film. In particular, there is a problem in that application to a large-diameter substrate is difficult. On the other hand, the coating film forming method is promising because it does not require expensive equipment, the film forming cost is relatively low, and the control and management of the composition of the dielectric film are easy.

BLS used in this coating type coating method
As the F-based coating solution, a carboxylate of Sr or Bi (for example, 2-ethylhexanoate) and an alkoxide compound of Ta are dissolved in acetate to form a coating solution (the twelfth ferroelectric substance). Proceedings of the Conference of Applied Conferences; Mitsubishi Materials Corporation; 24-TP-11 (pp. 57-58); 1
995.5.24-27, "Jpn. J. Appl. P.
hys. "Vol. 34 (1995) pp. 5096-
5099) or 2- such as Sr, Bi, Ta, Nb, Ti, etc.
Ethyl hexanoate is dissolved in xylene and MOD (Me
tallo-Organic Decomposition
on) -type coating solution (the same proceedings; Olympus Optical Co., Ltd., Symmetrics Corporation; 26-
TC-10, pp. 139-140, 1995.5.2
4-27) has been reported. However, in these coating solutions, since the 2-ethylhexanoate of each metal component has a long-chain organic group having 8 carbon atoms, the content of the organic component in the entire coating solution is large, and the coating, baking, Due to the high film loss due to the burning off of the organic components during the crystallization treatment, the film obtained is porous, and the surface shape (surface morphology) of the film is not good, and it is difficult to apply it to an VLSI device. It was not always satisfactory. In addition, when a thin film is formed using these coating liquids, baking must be performed twice at a high temperature of about 800 ° C. in order to obtain appropriate electric characteristics. It was not always satisfactory.

Further, the solvent used in the conventional coating solution is a metal salt of a long-chain monobasic carboxylic acid (metal soap), which is generally poorly soluble in a polar solvent. A group-based solvent is used. When these aromatic solvents are used, it is necessary to store the coating liquid tightly in a glass or metal container so that the solvent does not volatilize and disappear outside. However, if a glass or metal container is used, a metal component may ooze out of the inner wall into the coating solution, and a glass or metal container should be used in a semiconductor manufacturing field where metal impurities are not to be mixed. Can not. Therefore, the use of polyethylene or polypropylene containers is preferred from the viewpoint of low metal impurities mixed in the coating solution, ease of handling against impact, low cost, and the like. Even so, use of a solvent having a small degree of volatilization is desired.

Further, since the above-mentioned aromatic solvents adversely affect the human body due to inhalation or the like, there is a tendency that usage methods, management methods, and the like are significantly restricted.

On the other hand, when a metal salt of a short-chain carboxylic acid is used instead of the metal salt of a long-chain monobasic carboxylic acid,
It is practically insoluble in general-purpose organic solvents and is not practical. Although lower alkoxide compounds of metals are also soluble in some polar solvents, they are easily hydrolyzed by moisture in the air and thus lack storage stability, and are not practical because of poor reproducibility during use.

[0008] Under these circumstances, in order to form a high quality film having a small leakage current and a large (dense) film density, the content of the organic component in the entire coating solution is small, and It has been desired to realize a coating liquid that has low film loss due to component burn-out, has little precipitation (segregation) and burn-out of metal elements, and has an active ingredient that is soluble in a general-purpose organic solvent and has excellent storage stability. .

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and contains an active ingredient soluble in a general-purpose organic solvent, and has excellent storage stability and reproducibility.
A coating liquid for forming a ferroelectric thin film capable of forming a ferroelectric thin film having a small leak current and a large film density (dense) at a low cost, a method for producing the same, and applying the coating liquid;
An object of the present invention is to provide a cured ferroelectric thin film.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, all of the conventional BLSF-based coating liquids contain a metal carboxylate and a metal alkoxide compound in an organic solvent. Is only mixed with
This causes a large amount of burning of metal elements and organic components during the firing step, which causes a reduction in film formation density, and also, as an active ingredient, a functional group of a hydrolyzate of a specific metal alkoxide compound. It has been found that a desired coating solution can be obtained by containing an organometallic compound obtained by exchanging with a different functional group, thereby completing the present invention.

According to the present invention, there are provided the following coating liquid for forming a ferroelectric thin film, a method for producing the same, and a ferroelectric thin film obtained by applying and curing the coating liquid.

[1] A coating liquid for forming a ferroelectric thin film containing an organometallic compound, wherein the organometallic compound contains 1
A ferroelectric thin film comprising a hydrolyzate of a metal alkoxide containing two or more metal elements in a molecule, wherein a hydroxyl group and / or an alkoxy group are exchanged for a functional group other than a hydroxyl group. Forming coating solution.

[2] The coating liquid for forming a ferroelectric thin film according to [1], wherein the functional group other than the hydroxyl group is a carboxyl group.

[3] Metal alkoxides containing two or more metal elements in one molecule are hydrolyzed, and the resulting hydrolyzate is converted to a hydroxyl group and / or an alkoxy group to a functional group other than the hydroxyl group. A method for producing a coating liquid for forming a ferroelectric thin film, characterized by exchanging.

[4] After the exchange of the functional group other than the hydroxyl group,
The method for producing a coating liquid for forming a ferroelectric thin film according to the above [3], wherein the obtained functional group exchange product is dissolved in a solvent having an oxygen atom in a molecule.

[5] The method for producing a coating liquid for forming a ferroelectric thin film according to [3] or [4], wherein the functional group other than the hydroxyl group is a carboxyl group.

[6] A ferroelectric thin film obtained by applying and curing the coating liquid for forming a ferroelectric thin film according to [1] or [2].

[7] The ferroelectric thin film according to the above [6], having a structure represented by the following formula (1).

[0019]

Embedded image _{(Bi 2 O 3) (M} 1 l M 2 m O x) (1)

[In the formula (1), M ¹ represents a divalent metal ion, M ² represents a pentavalent metal ion, l and m are positive numbers of 0.5 to 5, and x is It is a positive number calculated from the valences of M ¹ and M ² . ]

[8] The ferroelectric thin film according to the above [6], having a structure represented by the following formula (2).

[0022]

Embedded image M ³ _a M ⁴ _b O _y (2)

In the formula (2), M ³ represents a divalent metal ion, M ⁴ represents a tetravalent metal ion, a and b are positive numbers from 0.5 to 5, and y is It is a positive number calculated from the valences of M ³ and M ⁴ . ]

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below. I. Coating solution for forming a ferroelectric thin film The coating solution for forming a ferroelectric thin film of the present invention is characterized by containing a specific organometallic compound. This specific organometallic compound is obtained by hydrolyzing a specific metal alkoxide with water alone or using water and a catalyst, wherein a hydroxyl group and / or an alkoxy group is a functional group other than a hydroxyl group. It is exchanged. Hereinafter, each component will be specifically described.

1. Metal alkoxide The metal alkoxide used in the present invention contains 2 per molecule.
It contains the above metal elements, and the type of metal element may be one type or two or more types. As the metal element of the metal alkoxide used in the present invention, Bi,
Pb, Ba, Sr, Ca, Li, Na, K, Ti, Z
Examples thereof include r, Nb, Ta, W, Mo, Fe, Co, and Cr.

When there are two or more kinds of metal elements,
A combination of Bi, Sr and Ta is preferred. in this way,
By using a metal alkoxide containing a plurality of metal elements in one molecule, precipitation (segregation) of a single metal element,
The phenomenon of burning can be suppressed.

Specific examples of the metal alkoxide containing a combination of Bi, Sr and Ta include the following. (A) A mixture containing a Ta metal alkoxide and SrBi metal alkoxides. (B) A mixture containing Sr metal alkoxide and BiTa metal alkoxides. (C) A mixture containing Bi metal alkoxide and SrTa metal alkoxide. (D) SrBiTa metal alkoxides.

The above-mentioned SrBi metal alkoxides,
BiTa metal alkoxides, SrTa metal alkoxides and SrBiTa metal alkoxides are SrB
Taking i-metal alkoxides as an example, it means metal alkoxides containing Sr and Bi in one molecule, such as Bi-O-Sr.
Other compounds have the same meaning.

Further, the appropriate values of the contents of the Bi metal element component, the Sr metal element component and the Ta metal element component can be uniformly determined by the application location, conditions, etc. of the coating solution of the present invention. Absent. Therefore, the optimum value of the content depends on the type of the applied device (FRAM, DRAM, etc.).
, MFS, MFIS, MFMIS, etc.), the type and thickness of the upper and lower electrodes used, the type and thickness of the barrier layer, and the presence or absence of a seed layer (alignment film). It is preferable to select as appropriate.

The metal alkoxide used in the present invention is
"Manufacturing technology of glass and ceramics by sol-gel method and its application" (Applied Technology Publishing Co., Ltd., June 4, 1989)
Pp. 46 to 47. Specifically, SrBi (OR ¹ ) _m (OR ² ) ₃ , Ta
Bi (OR ³ ) _n (OR ² ) ₃ , SrTa (OR ¹ ) _m (OR
³ ) _n , ABBi (OR ¹ ) _m (OR ³ ) _n (OR ² ) ₃ , wherein A represents a metal ion having 1 to 3 valences and B represents a metal ion having 4 to 6 valences; Is the valence of the A metal element;
n is the valence of the B metal element; R ¹ , R ² , R ³ are
Each independently represents an alkyl group having 1 to 6 carbon atoms). Above all, ABi (OR ¹ ) _m (OR ² ) ₃ and BBi (OR ³ ) _n (O
R ² ) ₃ and ABBi (OR ¹ ) _m (OR ³ ) _n (OR ² ) ₃ are preferred.

The alcohols forming the metal alkoxide are not particularly limited, but preferred examples include those represented by the following formula (3).

[0032]

Embedded image R ⁴ OH (3)

[In the formula (3), R ⁴ is a group having 1 to 6 carbon atoms.
A saturated or unsaturated hydrocarbon group or further having 1 carbon atom
And represents a hydrocarbon group substituted with an alkoxyl group. ]

When R ⁴ is a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms, examples of the alcohol include methanol, ethanol, propanol, butanol, amyl alcohol and cyclohexanol. it can.

When R ⁴ is a hydrocarbon group further substituted with an alkoxyl group having 1 to 6 carbon atoms, examples of the alcohols include methoxymethanol, methoxyethanol, ethoxymethanol, ethoxyethanol and the like. be able to.

2. Hydrolysis of metal alkoxide The metal alkoxide can be hydrolyzed by adding water or water and a catalyst to the metal alkoxide and stirring the mixture at 20 to 100 ° C for several hours to several days.

The catalyst used in the present invention is not particularly limited, and those known for hydrolysis of metal alkoxides, for example, inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid; and organic acids such as acetic acid, propionic acid and butyric acid. Examples thereof include acid catalysts such as acids, and inorganic and organic alkali catalysts such as sodium hydroxide, potassium hydroxide, ammonia, monoethanolamine, diethanolamine, and tetramethylammonium hydroxide. However, inorganic alkalis such as sodium hydroxide and potassium hydroxide may cause metal ions such as sodium and potassium to remain in the coating solution and affect the electrical properties of the coating film. Nitrogen-containing alkali may form a nitrogen compound having a high boiling point after the hydrolysis reaction, and this may affect the densification of the coating film during the firing step. Preferably, it is used.

The conditions for the above hydrolysis are not limited to the above, and can be appropriately selected according to the use of the film. By performing the hydrolysis treatment in this manner, the content of the organic component in the entire coating film after the drying step can be reduced, and the metalloxane bond (Bi-O-Bi, Bi-O- Ta, Bi-O-
Sr, Ta-O-Bi-O-Sr, etc.).

3. Exchange of the functional group of the hydrolyzate The exchange of the functional group of the hydrolyzate of the metal alkoxide includes, for example, a reaction between a functional group (a hydroxyl group and / or an alkoxy group) of the hydrolyzate and a carboxyl group of a carboxylic acid. Those can be mentioned as preferred examples. The above carboxylic acids can substitute the functional groups of the compound in the coating solution of the present invention and improve the storage stability. Preferred examples of such carboxylic acids include at least one selected from the group consisting of aliphatic carboxylic acids and aromatic carboxylic acids.

As a preferred example of the aliphatic carboxylic acids, at least one selected from the group consisting of aliphatic carboxylic acids represented by the following formula (5) can be given.

[0041]

Embedded image R ⁵ COOH (5)

[In the formula (5), R ⁵ is a group having 1 to 1 carbon atoms.
0 represents a saturated or unsaturated hydrocarbon group. ]

Examples of the aromatic carboxylic acids include salicylic acid, benzoic acid, p-aminobenzoic acid and the like.

II. Method for Producing Coating Liquid The coating liquid of the present invention is obtained by hydrolyzing a metal alkoxide containing two or more metal elements in one molecule described above, and obtaining a hydrolyzate of a hydroxyl group and / or an alkoxy group. Can be produced by exchanging with a functional group other than a hydroxyl group. In this case, after exchanging the functional groups other than the hydroxyl group, it is preferable to dissolve the obtained functional group exchange product (organic metal compound) in a solvent having an oxygen atom in the molecule.

Examples of such solvents include alcohol solvents, polyhydric alcohol solvents, ether solvents,
Examples thereof include ketone solvents, ester solvents, and lower carboxylic acid solvents.

As the alcohol solvent, methanol,
Ethanol, propanol, butanol, amyl alcohol, cyclohexanol, methylcyclohexanol and the like can be mentioned.

Examples of the polyhydric alcohol solvents include ethylene glycol monomethyl ether, ethylene glycol monoacetoester, diethylene glycol monomethyl ether, diethylene glycol monoacetate, propylene glycol monoethyl ether, propylene glycol monoacetate, dipropylene glycol monoethyl ether, and methoxybutanol. And the like.

Examples of the ether solvent include methylal, diethyl ether, dipropyl ether, dibutyl ether, diamyl ether, diethyl acetal, dihexyl ether, trioxane, dioxane and the like.

Examples of the ketone solvents include acetone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl cyclohexyl ketone, diethyl ketone, ethyl butyl ketone, trimethyl nonanone, acetonitrile acetone, dimethyl oxide, holon, cyclohexanone, Examples include diacetone alcohol.

Examples of the ester solvents include ethyl formate, methyl acetate, ethyl acetate, butyl acetate, cyclohexyl acetate, methyl propionate, ethyl butyrate, ethyl oxyisobutyrate, ethyl acetoacetate, ethyl lactate, methoxybutyl acetate, diethyl oxalate, And diethyl malonate. Examples of lower carboxylic acid solvents include acetic acid, propionic acid, butyric acid, valeric acid and the like. The above-mentioned solvents can be used alone or in combination of two or more. In addition, the organometallic compound contained in the coating liquid of the present invention exhibits good solubility even in aromatic hydrocarbon solvents, but as described above, these solvents are used in the method of use and management. Is liable to be significantly restricted, which is not preferable. As the various solvents described above, the most preferable one can be used as appropriate according to the difference in application conditions such as the open spin coating method, the closed spin coating method, the mist-forming LSM-CVD method, and the dipping method.

III. Ferroelectric thin film Preparation of Ferroelectric Thin Film The ferroelectric thin film of the present invention is obtained by applying and curing the above-described ferroelectric thin film-forming coating solution. The method for producing such a ferroelectric thin film using the above-mentioned coating solution is not particularly limited, and examples thereof include the following method.

First, a substrate such as a Si wafer is oxidized to form a Si oxide film on the substrate, and Pt, Ir,
A lower electrode is formed by forming a metal such as Ru and a conductive metal oxide which is a metal oxide thereof by a known method such as a sputtering method or an evaporation method. And on this lower electrode,
The coating liquid of the present invention is applied by a known coating method such as a spinner method or a dipping method, and dried at a temperature of 50 to 250 ° C.

Next, calcination is performed at a temperature of 250 to 800.degree. It is preferable that the operation from coating to calcination is repeated several times to set a desired film thickness.

Next, main firing is performed at a high temperature of 800 ° C. in an oxygen atmosphere to form a ferroelectric thin film having a crystal structure. In the firing step, the temperature is from room temperature to 5 to 20 ° C./mi.
The furnace method in which the temperature is raised to the main firing temperature at a temperature raising rate of about n, and then the main firing temperature is maintained and firing is performed for about 30 to 80 minutes, and the main firing temperature is increased from room temperature to about 30 to 250 ° C./sec. Various firing methods can be selected, such as the RTP method in which the temperature is raised to the maximum firing temperature and then the firing is maintained for about 0.5 to 3 minutes while maintaining the main firing temperature.

Next, an electrode (upper electrode) is formed on the ferroelectric thin film manufactured as described above. As the upper electrode, the metals, metal oxides, and the like mentioned as materials for the lower electrode can be used. These materials are formed on a ferroelectric thin film by a known method such as a sputtering method or a vapor deposition method. At 700 ° C. to produce a ferroelectric memory.
At this time, a material different from that of the lower electrode may be used as the upper electrode. For example, Ir may be used for the lower electrode and Ru may be used for the upper electrode.

2. Specific Examples of Ferroelectric Thin Film As specific examples of the ferroelectric thin film formed by the coating liquid for forming a ferroelectric thin film of the present invention, a ferroelectric thin film having a structure represented by the above formula (1) or (2) A thin film can be mentioned as a preferable example. For convenience of explanation, the formula (1) or the formula (2) is shown below again.

[0057]

Embedded image _{(Bi 2 O 3) (M} 1 l M 2 m O x) (1)

In the formula (1), M ¹ represents a divalent metal ion, M ² represents a pentavalent metal ion, l and m are positive numbers from 0.5 to 5, and x is It is a positive number calculated from the valences of M ¹ and M ² . ]

[0059]

Embedded image M ³ _a M ⁴ _b O _y (2) [In the formula (2), M ³ represents a divalent metal ion, and M ⁴ represents a tetravalent metal ion. 0.5-5
Is a positive number calculated from the valences of M ³ and M ⁴ . ]

In particular, an SBT composed of Sr, Bi and Ta
Examples of the ferroelectric film include those having a structure represented by the following formula (5).

[0061]

Embedded image ^{_{M 3 a M 4 b O y}} Sr a Bi x Ta b O y (5)

[In the formula (5), x is a positive number from 1 to 4, a
Is a positive number from 0.5 to 2, b is a positive number from 2 to 5, y = ｛3
x + a (valence of Sr) + b (valence of Ta)｝ / 2. ]

[0063]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited by these Examples.

Preparation of Coating Solution (Example 1) 46.8 g of Sr (OnC ₄ H ₉ ) ₂ , Bi
_{(OtC 5 H 11) 3 188.2g} , Ta (OC 2 H 5) 5 1
After mixing 62.5 g and 3546.0 g of propylene glycol monopropyl ether, and stirring at 25 ° C. for 1 hour, 3943.43 g of a mixed solution of Sr metal alkoxide, Bi metal alkoxide and Ta metal alkoxide was obtained.

9.0 g of water and 885.6 g of propylene glycol monopropyl ether were mixed, and 3546.0 g of a mixed solution of the above Sr metal alkoxide, Bi metal alkoxide and Ta metal alkoxide was added.
The mixture was heated and stirred for 4 hours, and cooled to room temperature after the completion of the reaction to obtain a solution of an organometallic compound in which SrBiTa metal alkoxides were hydrolyzed.

447.1 g of 2-ethylhexanoic acid was added to the obtained solution of the organometallic compound, and the mixture was stirred at 25 ° C. for 30 minutes to exchange the functional groups of the organometallic compound. C. and stirred under reduced pressure for 30 minutes to remove 600.0 g of the solution from which the low-boiling alcohol was removed.
Obtained. After cooling to room temperature, the mixture was diluted 4-fold with propylene glycol monopropyl ether to prepare a coating liquid 1 for forming an SBT dielectric thin film.

Comparative Example 1 Sr (OnBu) ₂ 46.8
g, Bi (OtC ₅ H ₁₁ ) ₃ 188.2 g, Ta (OE
t) 162.5 g of _{5 and} 3546.0 g of propylene glycol monopropyl ether were mixed and stirred at 25 ° C for 1 hour, and then 3943.43 g of Sr metal alkoxide,
A mixed solution of Bi metal alkoxide and Ta metal alkoxide was obtained.

9.0 g of water and 885.6 g of propylene glycol monopropyl ether were mixed, and 3546.0 g of a mixed solution of the above Sr metal alkoxide, Bi metal alkoxide and Ta metal alkoxide was added.
The mixture was heated and stirred for 4 hours, and cooled to room temperature after the completion of the reaction to obtain a comparative coating liquid 1 for forming an SBT dielectric thin film.

Formation of Ferroelectric Thin Film (Example 2, Comparative Example 2) A 100-nm thick Pt film was formed on a 6-inch diameter silicon wafer on which a thermally oxidized SiO ₂ film of 1000 nm was formed by sputtering.
A lower electrode was formed.

Next, the coating solution 1 and the comparative coating solution 1 obtained in Example 1 and Comparative Example 1 were applied on the Pt lower electrode at 500 rpm for 5 seconds by using a spin coater, and then for 300 seconds.
After spin coating at 0 rpm for 20 seconds and drying at 150 ° C. for 5 minutes, the temperature was increased from 25 ° C. to 25 ° C./sec at a heating rate of 7 ° C.
The temperature was raised to 00 ° C. and calcining was performed for 1 minute, and the operation from the above coating to the preliminary calcining was repeated seven times.
The temperature is raised from 25 ° C. to 800 ° C. at a rate of 25 ° C./sec, and then main firing (primary firing) is performed at 800 ° C. for 60 minutes in an oxygen atmosphere. A thin film was formed.

Then, a 0.2 mm diameter was formed on the ferroelectric thin film by a sputtering method via a metal mask.
Was formed and fired (secondary firing) at 700 ° C. for 30 minutes in an oxygen atmosphere to produce a ferroelectric element. FIG. 1 shows an example of the configuration.

The ferroelectric element formed using the coating liquid 1 showed a good hysteresis curve with a high squareness ratio even at an applied voltage of 3 V. Also, the leakage current is 10 ^-8 A /
cm ² and good characteristics. 2 and 3 show the results.
Shown in

When the comparative coating solution 1 was used, a good hysteresis curve having a high squareness ratio was not obtained.
The leak current was also higher than 10 ⁻³ A / cm ² , exceeding the measurement limit of the measuring instrument. FIG. 4 shows the results.

Hereinafter, the results of evaluating the densities and storage stability of the films obtained in Example 2 and Comparative Example 2 will be described. Density of film: When the cross sections of the films prepared in Example 2 and Comparative Example 2 were observed with a scanning electron microscope, no voids were found at the crystal grain boundaries of the film prepared in Example 2. ,
In the film formed in Comparative Example 2, voids of about several nm were observed.

Storage stability: Coating solution 1 and comparative coating solution 1 were 1
As a result of performing a hysteresis measurement after forming a film at room temperature for a month, the hysteresis curve of the coating solution 1 did not change at all, but the film of the comparative coating solution 1 was deteriorated to such an extent that the hysteresis measurement could not be performed.

[0076]

As described above, according to the present invention,
It contains low-cost ferroelectric thin films that contain active ingredients that are soluble in general-purpose organic solvents, have excellent storage stability and reproducibility, and have low leakage current and high (density) film density. The obtained coating liquid for forming a ferroelectric thin film, a method for producing the same, and a ferroelectric thin film can be provided.

[0077]

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a configuration example of a ferroelectric element formed from a coating solution of the present invention.

FIG. 2 is a graph showing a hysteresis characteristic of the ferroelectric element obtained in Example 2.

FIG. 3 is a graph showing a leakage current characteristic of the ferroelectric element obtained in Example 2.

FIG. 4 is a graph showing hysteresis characteristics of a ferroelectric element obtained in Comparative Example 2.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C01G 35/00 C01G 35/00 C C09D 1/00 C09D 1/00 5/00 5/00 Z (72) Inventor Kinji Yamada F-term (reference) 4D075 CA21 DA06 DB14 DC22 EC02 EC08 4G048 AA04 AB02 AC02 AD02 AE05 AE08 4J038 AA011 JA23 JA35 KA06 NA17 PA19 PB09 PC03 5303 AB20 BA03 BA07 BA12 CA01 CA11 CB05 CB32 CB33 DA06

Claims (8)

[Claims] 1. A coating liquid for forming a ferroelectric thin film containing an organometallic compound, wherein the organometallic compound is a hydroxyl group of a hydrolyzate of a metal alkoxide containing two or more metal elements in one molecule. And a coating liquid for forming a ferroelectric thin film, wherein the coating liquid is obtained by replacing one or both of the alkoxy groups with a functional group other than a hydroxyl group. 2. The coating liquid for forming a ferroelectric thin film according to claim 1, wherein the functional group other than the hydroxyl group is a carboxyl group. 3. A hydrolyzate of a metal alkoxide containing two or more metal elements in one molecule, and
A method for producing a coating liquid for forming a ferroelectric thin film, comprising exchanging a hydroxyl group and / or an alkoxy group with a functional group other than a hydroxyl group. 4. The coating liquid for forming a ferroelectric thin film according to claim 3, wherein after exchanging the functional group other than the hydroxyl group, the obtained functional group exchange product is dissolved in a solvent having an oxygen atom in a molecule. Manufacturing method. 5. The method for producing a coating liquid for forming a ferroelectric thin film according to claim 3, wherein the functional group other than the hydroxyl group is a carboxyl group. 6. A ferroelectric thin film obtained by applying and curing the coating liquid for forming a ferroelectric thin film according to claim 1 or 2. 7. A structure having a structure represented by the following formula (1):
3. The ferroelectric thin film according to 1. ## STR1 _{(Bi 2 O 3) (M} 1 l M 2 m O x) (1) [ Formula (1), M ¹ is a divalent metal ion, M ² is a pentavalent metal ion 1 and m are 0.5 to 5 respectively.
, X is a positive number calculated from the valences of M ¹ and M ² . ] 8. The structure according to claim 6, wherein the structure has the following formula (2).
3. The ferroelectric thin film according to 1. Embedded image M ³ _a M ⁴ _b O _y (2) [In the formula (2), M ³ represents a divalent metal ion, M ⁴ represents a tetravalent metal ion. 0.5-5
Is a positive number calculated from the valences of M ³ and M ⁴ . ]