JP2001072926A - Starting solution for formation of perovskite-type oxide thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a starting solution for forming a perovskite-type oxide thin film which is capable of forming a thick film by one coating operation, does not suffer any striation after coating, is excellent in stability with time, is free of crack in the perovskite-type oxide thin film, is satisfactorily densified, has no irregularity in thickness after coating, and is crystallized into a perovskite at a low annealing temperature. SOLUTION: The starting solution for forming a Pb-containing perovskite-type oxide thin film is made of a solution comprising, in an organic solvent, a partial hydrolyzate and/or partial polycondensate of a metal compound containing two or more constituent metals wherein propylene glycol and/or triethylene glycol is used as the organic solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a metal oxide-based perovskite oxide thin film which can be expected to be applied to various dielectric devices due to its electrical and / or optical properties.
The present invention relates to a raw material solution for forming a perovskite oxide thin film to be formed by a sol-gel method or the like.

[0002]

2. Description of the Related Art Metal oxide thin films, in particular, lead zirconate titanate (PZT) and lanthanum-doped (PLZT)
_{ZT: Pb x La 1-x} (Zr y Ti 1-y) 1-x / 4 O 3) is their high dielectric constant, is applied from the excellent ferroelectric characteristics to the various dielectric device it has been expected. As a method of forming these metal oxide thin films, there are a sputtering method, an MOCVD method, and the like. As a relatively inexpensive and simple method of forming a thin film, there is a sol-gel method of applying an organic metal solution to a substrate.

In the sol-gel method, a raw material solution containing a hydrolyzable compound of each component metal as a raw material, a partial hydrolyzate thereof and / or a partial polycondensate thereof is applied to a substrate, and the coating film is dried. Thereafter, the film is heated, for example, to about 400 ° C. in the air to form a metal oxide film, and then fired at a temperature equal to or higher than the crystallization temperature of the metal oxide (eg, about 700 ° C.) to crystallize the film. This is a method of forming a ferroelectric thin film.

As a method similar to the sol-gel method, there is an organic metal decomposition (MOD) method. In the MOD method, a raw material solution containing a thermally decomposable organometallic compound, for example, a metal β-diketone complex (for example, metal acetylacetonate) or a carboxylate (for example, acetate) is applied to a substrate, Heating in air or an oxygen-containing atmosphere, etc., causes evaporation of the solvent in the coating film and thermal decomposition of the metal compound to form a metal oxide film, which is then fired (annealed) at a crystallization temperature or higher. Crystallize the film. Therefore, the film forming operation is almost the same as that of the sol-gel method except for the type of the starting compound.

As described above, since the sol-gel method and the MOD method have the same film forming operation, a method using both of them is also possible. That is, the raw material solution may contain both a hydrolyzable metal compound and a thermally decomposable metal compound. In this case, hydrolysis and thermal decomposition of the raw material compound occur during heating of the coating film, and the metal Oxide forms.

Accordingly, in the following, the sol-gel method, MO
The D method and the method using these methods in combination are referred to as “sol-gel method”, and the raw material solution used in such a method is referred to as “sol-gel liquid”.

The sol-gel method and the like have the advantages of being inexpensive, simple, and suitable for mass production.
An excellent feature is that the film thickness is relatively uniform. Therefore, it can be said that this is the most advantageous film forming method for forming a ferroelectric thin film on a relatively flat substrate.

Metal alkoxides or organic acid salts are generally used as an organic metal raw material for the sol-gel method or the like. As the organic solvent for dissolving these organometallic raw materials, alcohols, ethylene glycol derivatives, xylene, toluene and the like can be used.
As an organic solvent for the raw material solution for forming a perovskite oxide thin film, an ethylene glycol derivative is considered to be good, and in particular, ethylene glycol monomethyl ether (2-methoxyethanol) has been widely used (for example, Jp.
nJAppl.Phys.Vol.33 (1994) pp.5196-5200, JP-A-9
-28415 publication).

However, in general, when a film is formed by a sol-gel method using a sol-gel solution using 2-methoxyethanol as an organic solvent, the thickness of a crack-free thin film formed by one application is at most 0. .About.1 μm (film thickness after annealing), which caused a reduction in production efficiency and an increase in film formation cost.

Therefore, as a method of increasing the film formation throughput by one coating to increase the film formation throughput and lowering the film formation cost, 1,3-propanediol is used as the organic catalyst of the sol-gel liquid. (Journal of Materials Science 30 (1995) pp.2507-
2516).

In the case of a sol-gel solution using this 1,3-propanediol solvent, a high-quality film having a fine structure equivalent to that of a sol-gel solution using a 2-methoxyethanol solvent can be reduced to a maximum of 0 in a single application. The film can be formed to a thickness of about 0.5 to 1 μm (the thickness after annealing). But,
This 1,3-propanediol solvent sol-gel solution has a high boiling point of 213.5 ° C. and is not dried immediately after coating, so that the film thickness changes before the drying step after coating, and the film is in the middle of the film. There is a disadvantage that the film thickness differs at the film edge (Journal of Materials Science 30 (1995) pp.2507-25
16). In addition, even during drying, since the solvent has a high boiling point, the evaporation occurs smoothly, so that the film thickness becomes uneven due to the evaporation after the evaporation. Furthermore, since 1,3-propanediol is expensive, when 1,3-propanediol is used as a solvent, there is also a problem that the cost of the sol-gel liquid increases.

On the other hand, it has been proposed to use propylene glycol as a solvent as a sol-gel liquid having excellent long-term storage properties and easy quality control (Japanese Patent Laid-Open No. 4-342).
422). However, Japanese Patent Application Laid-Open No. 4-342422 discloses
The publication discloses that metal alkoxide is used only for one component Ti of the multi-component system raw material. Since only one kind of metal alkoxide is used, the hydrolysis characteristics are easily controlled and quality control is performed. Although it is easy, the metal-O-metal bond due to hydrolysis and condensation polymerization is small due to the small amount of alkoxide, and most of the ceramics are formed by thermal decomposition, so the obtained ferroelectric thin film is not dense. In addition, there is a problem that a low-quality film having many voids is formed and the crystallization temperature is high. Further, in order to produce a thick film, it is necessary to increase the concentration of the sol-gel solution. However, since the alkoxide is small, the amount of the composite alkoxide generated is also small, and it is difficult to increase the concentration.

[0013]

As described above, conventionally, a relatively thin film having a relatively large thickness can be formed by a single coating without unevenness of the film thickness, and it is inexpensive, has excellent storage stability, and has a high density. In fact, no sol-gel solution capable of easily forming a thin film has been provided.

The present invention solves the above-mentioned conventional problems, and a thick film can be formed by one coating. No striations after application. Excellent stability over time. Cracks do not occur in the perovskite oxide thin film. There are no voids in the perovskite type oxide thin film, and the oxide is sufficiently densified. In addition, there is no unevenness in film thickness after coating. Can be crystallized into perovskite at low annealing temperature.

It is an object of the present invention to provide a raw material solution for forming a perovskite-type oxide thin film having the above-mentioned effects.

[0016]

The raw material solution for forming a perovskite oxide thin film of the present invention is a raw material solution for forming a perovskite oxide thin film containing Pb, and comprises two or more component metals. In a raw material solution comprising a solution containing a partial hydrolyzate of a metal compound and / or a partial polycondensate thereof in an organic solvent, the solution contains propylene glycol and / or triethylene glycol. .

That is, the present inventors have the following characteristics:
Furthermore, as a result of intensive studies for realizing a sol-gel solution having the characteristics described above, propylene glycol and / or triethylene glycol were used as the main solution, and preferably, the raw material compounds of Zr and Ti were converted to an alkoxy group or an alkoxy group and β. -It has been found that by having a diketone group, a sol-gel solution satisfying the above-mentioned characteristics or-can be obtained, thereby completing the present invention.

Due to the high stability of the metal alkoxide in propylene glycol and triethylene glycol,
Compared with the case where a 3-propanediol solvent is used, the stability of the sol-gel liquid over time is improved (characteristics).

By using an alkoxy group or a compound having an alkoxy group and a β-diketone group as a raw material compound of Zr and Ti, a perovskite oxide thin film without voids can be obtained (characteristics). This densification is performed because a complex alkoxide of Pb and Zr or Pb and Ti is present in the sol-gel liquid to form a complex that easily forms a perovskite structure at a molecular level, or metal-oxygen by partial hydrolysis and partial polycondensation. It is considered that many bonds are generated.

In particular, the boiling point of propylene glycol is 18
Since the temperature is relatively low at 7.4 ° C., the film thickness becomes uniform, and no film thickness unevenness due to evaporation occurs. When it is desired to reduce the film thickness, it may be diluted with propylene glycol and an organic solvent having a low viscosity (eg, alcohol) (characteristics).

Further, propylene glycol is used as an organic solvent used as a main solvent, and a raw material compound of Zr and Ti is an alkoxy group or a compound having an alkoxy group and a β-diketone group. It was clarified that even after baking for 60 minutes, the perovskite crystallized (characteristics). Triethylene glycol has a slightly higher crystallization temperature than propylene glycol, but is much lower than other solvents. Note that 1,
When a 3-propanediol solvent is used, Zr and T
i is an alkoxy group or an alkoxy group and β-
Even those having a diketone group did not crystallize under the above conditions. In the comparison between the two, it is not clear why the crystallization temperature of the sol-gel liquid of the present invention is lowered, but it is presumed that the sol-gel liquid has some relationship with the aging stability. When propylene glycol or triethylene glycol was used, and only Ti was used as a raw material compound, the compound having an alkoxy group did not crystallize under these conditions. This is considered to be because most of the sol-gel solution contains only a small amount of alkoxide groups with Ti, and most of the sol-gel solution is crystallized by thermal decomposition.

Such a raw material solution for forming a perovskite oxide thin film of the present invention is particularly suitable for a perovskite oxide thin film containing Pb and Zr and / or Ti, especially a perovskite oxide film containing Pb, Zr and Ti. It is suitable as a raw material solution for forming a type oxide thin film.

In the present invention, the content of propylene glycol and / or triethylene glycol with respect to the organic solvent present in the raw material solution is preferably at least 20% by weight, and the concentration of the metal compound in the raw material solution in terms of oxide is preferred. Is preferably 10% by weight or more.

In the present invention, β-diketones are added in an amount of 0.1 to the total number of metal elements present in the raw material solution.
It is preferable that the compound is contained with a molecular number of up to 5 times, whereby a more excellent effect can be obtained.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The perovskite oxide thin film formed in the present invention is preferably made of one or both of Pb, Ti and Zr,
Particularly preferred is an oxide material containing Pb, Ti and Zr. As an example of such a perovskite oxide thin film, a perovskite oxide thin film (lead zirconate titanate: PZT thin film) composed of Pb and Zr and / or Ti can be mentioned.

This oxide material can contain a trace amount of a doping element. Examples of doping elements include C
a, Sr, Ba, Hf, Sn, Th, Y, Sm, Dy,
Ce, Bi, Sb, Nb, Ta, W, Mo, Cr, C
o, Ni, Fe, Cu, Si, Ge, U, Sc, V, P
r, Nd, Eu, Gd, Tb, Ho, Er, Tm, Y
b, Lu, La, and the like, and the content thereof is preferably 0.1 or less in terms of the atomic fraction of metal atoms in the thin film.

In the present invention, propylene glycol and / or triethylene glycol are used as the organic solvent. A single solvent of propylene glycol, a single solvent of triethylene glycol, a mixed catalyst of propylene glycol and triethylene glycol, A mixed solvent of another organic solvent, a mixed solvent of triethylene glycol and another organic solvent, or a mixed solvent of propylene glycol, triethylene glycol and another organic solvent may be used. When a mixed solvent of propylene glycol and / or triethylene glycol and another organic solvent is used, in order to achieve the above-mentioned, particularly the above-mentioned or the above-mentioned characteristics, propylene glycol and / or Preferably, the proportion of triethylene glycol is at least 20% by weight, especially at least 30% by weight.

Other organic solvents that can be used in combination include:
Alcohols other than propylene glycol and / or triethylene glycol, carboxylic acids, esters, ketones,
Examples include ethers, cycloalkanes, and aromatic solvents. Among them, alcohols include ethanol, 1-
Propanol, 2-propanol, 1-butanol, 2
-Alkanols such as butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol and 2-methyl-2-pentanol, cycloalkanols such as cyclohexanol, and Alkoxy alcohols such as 2-methoxyethanol and 1-ethoxy-2-propanol can be used.

Examples of the carboxylic acid solvent include n-
Butyric acid, α-methylbutyric acid, i-valeric acid, 2-ethylbutyric acid,
2,2-dimethylbutyric acid, 3,3-dimethylbutyric acid, 2,3
-Dimethylbutyric acid, 3-methylpentanoic acid, 4-methylpentanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 2,3-dimethylpentane Acid, 2-ethylhexanoic acid, 3-ethylhexanoic acid and the like.

Examples of the ester solvents include ethyl acetate, propyl acetate, n-butyl acetate, sec-butyl acetate, tert-butyl acetate, isobutyl acetate, n-amyl acetate, sec-amyl acetate, tert-amyl acetate, and isoamyl acetate. And the like.

The ketone solvents include acetone, methyl ethyl ethone, and methyl isobutyl ketone. The ether solvents include chain ethers such as dimethyl ether and diethyl ether, and cyclic ethers such as tetrahydrofuran and dioxane. As the cycloalkane-based solvent, cycloheptane,
Cyclohexane and the like, and aromatic solvents include toluene, xylene and the like.

In the present invention, it is preferable to mix β-diketones as a stabilizer in the raw material solution.
By adding a stabilizer, the rate of accelerated decomposition and the rate of polycondensation of the raw material solution are suppressed, and the storage stability is improved. In this case, the amount of β-diketones added as a stabilizer is β-diketone relative to the total number of metal elements present in the raw material solution.
The amount is preferably 0.1 to 5 times, more preferably 0.2 to 3 times, the number of molecules of the diketones. If the amount of the β-diketone is too large, the stability may be reduced. If the amount is too small, the effect of the β-diketone cannot be sufficiently obtained. As the β-diketones to be used, acetylacetone, benzoylacetone, dibenzoylacetone, diisobutylmethane, dipivaloylmethane, 3-methylpentane-2,4
-Dione, 2,2-dimethylpentane-3,5-dione, heptafluorobutanoylpivaloylmethane, trifluoroacetylacetone and the like, among which economicalness, denseness of the film, and halides are included. Acetylacetone is desirable from the viewpoint that there is no acetylacetone.

The β-diketones as a stabilizer may be added at any stage in the production process of the raw material solution, but when azeotropic distillation described below is performed, it is preferable to add after the distillation. In the case where the metal alkoxide is partially hydrolyzed, it is preferable to add β-diketones before the partial hydrolysis because the hydrolysis rate can be easily controlled. When β-diketones are added, a small amount of water may be added to the raw material solution in order to promote hydrolysis after coating.

The raw material solution for forming a perovskite oxide thin film of the present invention uses propylene glycol and / or triethylene glycol as an organic solvent.
As the Ti raw material compound, one having an alkoxy group or an alkoxy group and a β-diketone group is used, and as the Zr raw material compound, one having an alkoxy group or an alkoxy group and a β-diketone group is used.
It can be prepared according to a conventional method except that diketones are blended.

As the starting metal compound, a metal compound containing each component metal or two or more component metals, a partial hydrolyzate thereof and a partial polycondensate thereof can be used, and a particularly preferable metal compound is a hydrolyzable metal compound. Alternatively, it is a thermally decomposable organometallic compound. For example, alkoxides, organic acid salts, β-diketone complexes and the like are typical examples, but various other complexes such as amine complexes can be used for metal complexes. Here, examples of the β-diketone include acetylacetone (= 2,4-pentanedione), heptafluorobutanoylpivaloylmethane, dipivaloylmethane, trifluoroacetylacetone, and benzoylacetone.

Specific examples of organometallic compounds suitable as raw materials include, as the lead compound and the lanthanum compound, organic acid salts such as acetates (lead acetate and lanthanum acetate) and alkoxides such as diisopropoxy lead. Examples of the titanium compound include tetraethoxy titanium, tetra isopropoxy titanium, tetra n-butoxy titanium, tetra i
Alkoxides such as -butoxytitanium, tetra-t-butoxytitanium and dimethoxydiisopropoxytitanium are preferred, but organic acid salts or organometallic complexes can also be used. The zirconium compound is the same as the above-mentioned titanium compound.

The starting metal compound may be a complex metal compound containing two or more component metals in addition to the compound containing one kind of metal as described above. Examples of such composite metal compounds include PbO
₂ [Ti (OC ₃ H ₇ ) ₃ ] ₂ , PbO ₂ [Zr (OC ₄ H ₉ )
₃ ] _{2 and the} like.

In the present invention, in particular, Ti
As the raw material compound and the Zr raw material compound, an alkoxide group or a compound having an alkoxide group and a β-diketone group is preferable.As the Ti raw material compound having an alkoxide group and a β-diketone group, for example, titanium diisopropoxide bisacetyl acetate is used. Examples of the Zr raw material compound include zirconium dinormal propoxide bisacetyl acetate.

In the present invention, a metal compound used as a raw material for each of these component metals is dissolved in propylene glycol and / or triethylene glycol, or an organic solvent containing propylene glycol and / or triethylene glycol, and is preferably dissolved. A β-diketone is added as a stabilizer to prepare a raw material solution containing a precursor of a composite metal oxide (an oxide containing two or more metals) of a perovskite oxide thin film to be formed.

The ratio of each metal compound contained in the raw material solution may be substantially the same as the metal atomic ratio of the perovskite oxide thin film to be formed. However, lead compounds generally have high volatility, and lead deficiency may occur due to evaporation during heating for changing to a metal oxide or during firing for crystallization. Therefore, in anticipation of this deficiency, lead may be present in a slight excess (for example, a 2 to 20% excess).
The degree of lead deficiency varies depending on the type of lead compound and film forming conditions, and can be determined in advance by experiments.

The concentration of the metal compound in the raw material solution is not particularly limited, and varies depending on the coating method to be used and the presence or absence of partial hydrolysis. Generally, the total metal content in terms of metal oxide is 10 to 40% by weight, particularly The range is preferably 15% by weight or more and 40% by weight or less. By using such a relatively high-concentration material solution, a thick film having a thickness of 100 nm or more can be formed by one application.

The metal compound is propylene glycol and / or
Alternatively, a solution dissolved in an organic solvent containing triethylene glycol or propylene glycol and / or triethylene glycol can be used as it is as a raw material solution for film formation by a sol-gel method or the like. Alternatively, in order to promote film formation, the solution may be heated to promote partial hydrolysis or partial polycondensation of a hydrolyzable metal compound (for example, alkoxide).

The heating for the partial hydrolysis is controlled by controlling the temperature and time so that the hydrolysis does not proceed completely.
When the hydrolysis is completely performed, the stability of the raw material solution is remarkably reduced, gelation is easily caused, and uniform film formation is difficult. The heating conditions are a temperature of 80 to 200 ° C. and a temperature of 0.5 to 50.
Time is appropriate. During the hydrolysis, the hydrolyzate
Polycondensation may occur partially due to the MO-bond (M = metal), but such polycondensation is acceptable if it is partial.

When the raw material solution contains both a metal alkoxide and a metal carboxylate, water of crystallization accompanying the metal carboxylate may be removed before mixing with the metal alkoxide. The removal of the water of crystallization can be carried out by first dissolving only the metal carboxylic acid in a solvent, distilling the solution and dehydrating the solution by azeotropic distillation with the solvent. Therefore, in this case, a solvent that can be azeotropically distilled with water is used. When mixed with a metal alkoxide without removing the water of crystallization of the metal carboxylate, the hydrolysis of the metal alkoxide may progress excessively or may be difficult to control, and when precipitation may occur after partial hydrolysis. Alternatively, water of crystallization may be removed.

According to such a raw material solution for forming a perovskite oxide thin film of the present invention, a perovskite oxide thin film can be formed according to the following procedure in the same manner as in a conventional sol-gel method. .

First, a raw material solution for forming a perovskite oxide thin film of the present invention is applied on a substrate. The coating is generally performed by spin coating, but other coating methods such as roll coating, spraying, dipping, curtain flow coating, and doctor blade can also be applied. After application, the coating is dried and the solvent is removed. The drying temperature varies depending on the type of the solvent, but is usually about 80 to 200C, and preferably in the range of 100 to 180C. However,
Since the solvent is removed during the heating in the next step for converting the metal compound in the raw material solution to the metal oxide, the drying step of the coating film is not necessarily required.

Thereafter, as a calcining step, the applied substrate is heated to completely hydrolyze or thermally decompose the organometallic compound and convert it to a metal oxide, thereby forming a film made of the metal oxide. This heating is generally performed in an atmosphere containing water vapor in a sol-gel method requiring hydrolysis, for example, air or an atmosphere containing water vapor (for example, a nitrogen atmosphere containing water vapor).
The MOD method for thermal decomposition is performed in an oxygen-containing atmosphere. The heating temperature varies depending on the type of the metal oxide, but is usually in the range of 150 to 550 ° C, preferably 300 to 450 ° C. The heating time is selected so that the hydrolysis and thermal decomposition proceed completely, but is usually about 1 minute to 2 hours.

In the case of the sol-gel method or the like, it is often difficult to obtain the film thickness required for the perovskite oxide thin film by one application, so that the above application and (drying) By repeating baking, a metal oxide film having a desired film thickness is obtained. The film obtained in this way is amorphous or crystalline, but the crystallinity is insufficient, so the polarization is low,
Cannot be used as a ferroelectric thin film. Therefore, finally, as a crystallization annealing step, firing is performed at a temperature equal to or higher than the crystallization temperature of the metal oxide to obtain a crystalline metal oxide thin film having a perovskite crystal structure. The firing for crystallization may not be performed once at the end, but may be performed after the above-described calcination for each applied coating film, but it is necessary to repeat firing at a high temperature many times. Therefore, it is economically advantageous to perform the operation at the end.

The firing temperature for this crystallization is usually 50
A relatively low temperature of 0 to 800 ° C., for example, 550 to
700 ° C. Therefore, a substrate having heat resistance enough to withstand this firing temperature is used. The firing (annealing) time for crystallization is usually about 1 minute to 2 hours, and the firing atmosphere is not particularly limited, but is usually air or oxygen.

As a heat-resistant substrate material used for forming such a perovskite-type oxide thin film, metals such as silicon (single crystal or polycrystal), platinum and nickel,
Perovskite-type conductive oxides such as ruthenium oxide, iridium oxide, strontium ruthenate (SrRuO ₃ ) or lanthanum strontium cobaltate ((La _x Sr _{1 -x} ) CoO ₃ ); quartz; aluminum nitride; titanium oxide; Inorganic compounds. In the case of a capacitor film, the substrate is a lower electrode, and for example, Pt, Pt / Ti, Pt / Ta, R
u, RuO ₂ , Ru / RuO ₂ , RuO ₂ / Ru, Ir,
IrO ₂ , Ir / IrO ₂ , Pt / Ir, Pt / Ir
Perovskite-type conductive oxides such as O ₂ , SrRuO ₃ or (La _x Sr _1-x ) CoO ₃ (a two-layer structure using “/” means “upper layer / lower layer” ").)

The thickness of the perovskite-type oxide thin film thus formed varies depending on the use of the derivative device, but is usually preferably about 500 ° to 1 μm.
The obtained ferroelectric thin film is useful for various derivative devices.

[0053]

The present invention will be described more specifically below with reference to examples and comparative examples.

The starting metal compounds used in the examples and comparative examples are as follows.

Pb raw material compound: lead acetate trihydrate La raw material compound: lanthanum acetate hemihydrate Ti raw material compound: titanium tetraisopropoxide titanium diisopropoxide bisacetyl acetate Zr raw material compound: zirconium tetra n- Butoxide Zirconyl nitrate Examples 1-16, Comparative Examples 1-16 Zirconium tetra n-butoxide and the stabilizers shown in Tables 1 and 2 were added to the reaction vessel in an amount of 2 mol times that of the zirconium tetra n-butoxide. Refluxed in a nitrogen atmosphere for hours. To this, titanium tetraisopropoxide and the stabilizers shown in Tables 1 and 2 were added in an amount of 2 mol times of titanium tetraisopropoxide, and the mixture was further refluxed at 150 ° C. for 3 hours in a nitrogen atmosphere. Next, lead acetate trihydrate and lanthanum acetate hemihydrate were added, and the main solvents shown in Tables 1 and 2 were added to the total of lead acetate trihydrate and lanthanum acetate hemihydrate. 5
The mixture was added in a molar amount and refluxed at 150 ° C. for 3 hours in a nitrogen atmosphere. Thereafter, by-products were removed by vacuum distillation at 150 ° C. to remove by-products, and the concentration was adjusted by adding the main solvents shown in Tables 1 and 2 to obtain a solution containing a metal compound having a concentration of 30% by weight in terms of oxide. I got The solution was further refluxed in a nitrogen atmosphere at 150 ° C. for 3 hours, allowed to cool under stirring, and diluted with alcohol shown in Tables 1 and 2 to adjust the concentration, thereby obtaining a metal atom ratio shown in Tables 1 and 2. A sol-gel solution containing a metal compound at a concentration of 25% by weight in terms of oxide was obtained.

Further, this sol-gel solution was converted to Pt (2000)
Å) / Ti (200Å) / SiO ₂ (5000Å) / S
An i (100) wafer was applied on a substrate by a spin coating method (1500 rpm, 60 seconds) and calcined in air at 400 ° C. for 5 minutes. After that, the ferroelectric material is fired in an RTA furnace (rapid heat treatment furnace) at 700 ° C. for 1 minute in an oxygen atmosphere, or fired in a hot plate at 430 ° C. for 60 minutes in air and crystallized and annealed. A thin film was formed.

The film properties of this ferroelectric thin film were examined by the following methods, and the results are shown in Tables 3 and 4. Tables 3 and 4
The table also shows the results of investigation on the presence or absence of gelation and the occurrence of precipitation when the prepared sol-gel solution was left at room temperature for six months.

[Presence / absence of striation] Confirmation of film after calcination by optical microscope [Presence / non-uniformity of film thickness] Visual confirmation of film after calcination [Presence / absence of crack] Confirmation by optical microscope after crystallization [Crystallization] Presence / absence] Confirmed by X-ray diffraction after annealing at 430 ° C. [Film thickness (nm)] Confirmed by SEM photograph after annealing at 700 ° C. Examples 17 to 27, Comparative Examples 17 to 27 In Example 1, titanium tetraisopropoxy was used. In the same manner except that titanium diisopropoxide bisacetyl acetate was added instead of adding titanium oxide and stabilizer, the same procedure was carried out using the main solvent alcohol, diluent alcohol and stabilizer shown in Tables 1 and 2. A sol-gel liquid having a metal atomic ratio shown in 1 and 2 was prepared.

Using this sol-gel solution, a film was formed in the same manner as in Example 1, and the film properties and liquid properties were evaluated in the same manner. The results are shown in Tables 3 and 4.

Examples 28 and 29 In Example 1, normal butanol was used as a diluting alcohol, and a sol-gel solution containing a metal compound having a concentration in terms of oxide shown in Table 1 was prepared. Film formation and liquid properties were evaluated in the same manner as described above, and the results are shown in Table 3.

Examples 30 and 31 In Example 17, normal butanol was used as a diluting alcohol, and a sol-gel solution containing a metal compound having a concentration in terms of oxide as shown in Table 1 was prepared. Film formation and liquid properties were evaluated in the same manner as described above, and the results are shown in Table 3.

Comparative Example 28 Acetic acid trihydrate, lanthanum acetate hemihydrate and zirconyl nitrate were added to propylene glycol and dissolved at 80 ° C., and titanium isopropoxide was added.
Reflux with heating for hours. Then, propylene glycol was added to adjust the concentration, thereby obtaining a sol-gel liquid containing a metal compound at a concentration of 10% by weight in terms of oxide in terms of a metal atomic ratio shown in Table 2.

Using this sol-gel solution, a film was formed in the same manner as in Example 1, and the film properties and liquid properties were evaluated in the same manner. The results are shown in Table 4.

[0064]

[Table 1]

[0065]

[Table 2]

[0066]

[Table 3]

[0067]

[Table 4]

Examples 32 to 49 Using the main solvent alcohol, diluent alcohol and stabilizer shown in Table 5, the main solvent alcohol was changed to zirconium tetra n
-A sol-gel solution having a metal atom ratio and an oxide-converted concentration shown in Table 5 was prepared in the same manner as in Example 1 except that the butoxide and titanium tetraisopropoxide were added in a molar amount of 4.5 times the total amount, and A ferroelectric thin film was formed in the same manner as in Example 1, and the obtained ferroelectric thin film was examined for film properties (presence or absence of striation, presence or absence of cracks, and film thickness) in the same manner as in Example 1. The results are shown in Table 6. Table 6 also shows the results of investigation of the presence or absence of gelation and the presence or absence of precipitation when the prepared sol-gel solution was left at room temperature for one year.

Examples 50 to 62 The procedure of Example 32 was repeated, except that titanium diisopropoxide bisacetyl acetate was added instead of titanium tetraisopropoxide and a stabilizer. A sol-gel solution having a metal atom ratio and a concentration in terms of oxide as shown in Table 5 was prepared using the main solvent alcohol, the dilute alcohol and the stabilizer shown below.

Using this sol-gel liquid, a film was formed in the same manner as in Example 32, and the film properties and liquid properties were evaluated in the same manner. The results are shown in Table 6.

[0071]

[Table 5]

[0072]

[Table 6]

From the above results, the raw material solution for forming a perovskite-type oxide thin film of the present invention is a good sol-gel solution having the above-mentioned characteristics, and also a β-diketone as a stabilizer. It can be seen that the stability of the composition is further improved by the combination of the compounds.

On the other hand, in Comparative Examples 1 to 27 in which 1,3-propanediol was used as the main solvent alcohol, film thickness was uneven, crystallization at low temperature was difficult, and the sol-gel liquid The stability is also poor.

Further, in Comparative Example 28 using zirconyl nitrate as the Zr raw material compound, many voids were formed, only a low-density thin film was formed, and crystallization could not be performed at a low temperature.

[0076]

As described in detail above, according to the present invention, 1
Thick film can be formed by a single application; no striation after application; excellent stability over time; no cracks in perovskite oxide thin film; no voids in perovskite oxide thin film; Further, the present invention provides a raw material solution for forming a perovskite-type oxide thin film, which has excellent effects such as: a non-uniform film thickness after coating; and a perovskite crystallization at a low annealing temperature.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Nobuyuki Soyama 12-6 Techno Park, Mita City, Hyogo Prefecture Mitsubishi Materials Corporation Mita Plant (72) Inventor Kensuke Kageyama 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Mitsubishi Materials F-term (reference) in New Frontier Materials Research Laboratory, R & D Co., Ltd. 4J038 DM021 JA23 JC38 KA06

Claims (6)

[Claims] 1. A raw material solution for forming a perovskite-type oxide thin film containing Pb, wherein a partial hydrolyzate of a metal compound containing two or more component metals and / or a partial polycondensate thereof is converted to an organic compound. In a raw material solution comprising a solution contained in a solvent, propylene glycol and / or
Alternatively, a raw material solution for forming a perovskite oxide thin film, comprising triethylene glycol. 2. A raw material solution for forming a perovskite-type ferroelectric oxide thin film containing Pb and Zr and / or Ti, wherein the Ti raw material compound is an alkoxy group or an alkoxy group. And a Zr raw material compound having an alkoxy group or an alkoxy group and a β-diketone group. 3. The method according to claim 2, wherein Pb, Zr and Ti are used.
A material solution for forming a perovskite-type oxide thin film, which is a material solution for forming a perovskite-type ferroelectric oxide thin film containing: 4. The perovskite type according to claim 1, wherein the content of propylene glycol and / or triethylene glycol with respect to the organic solvent present in the raw material solution is 20% by weight or more. Raw material solution for oxide thin film formation. 5. The raw material solution for forming a perovskite oxide thin film according to claim 1, wherein the concentration of the metal compound in the raw material solution in terms of oxide is 10% by weight or more. 6. The method according to claim 1, wherein the β-diketones are contained in an amount of 0.1 to 5 times the total number of atoms of the metal elements present in the raw material solution. A raw material solution for forming a perovskite oxide thin film, comprising: