JPH1064335A - Precursor for forming ferroelectric thin film, manufacture thereof, and manufacture of ferroelectric thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable precursor for forming a ferroelectric thin film with high quality (such as high density) at low temperature. SOLUTION: A metal acetate and a metal alcoxide are dissolved in an organic solvent, then while the organic solvent is replenished in the solution dissolved, they are heated and distilled. A precursor for forming a ferroelectric thin film containing a metal organic compound formed by the reaction and the non-reacted remaining metal acetate is obtained. The precursor for forming a ferroelectric thin film containing 52 mole % or less of non-reacted remaining metal acetate of the total metal acetate used is manufactured. By heating the precursor obtained, a ferroelectric thin film is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitor element, a memory element, a piezoelectric element, a sensor element, a light modulation element, an optical switching element, and an organic metal compound.
The present invention relates to a precursor for producing a ferroelectric thin film that can be used for an optical deflection element, a wavelength conversion element, and the like, a method for producing the same, and a method for producing the ferroelectric thin film.

[0002]

2. Description of the Related Art As oxides, many materials such as superconducting thin films, conductive thin films, insulating thin films, high dielectric constant thin films, and ferroelectric thin films have been tried. Among these, ferroelectric thin films are expected to be applied in many fields of electronics due to the many properties of ferroelectrics such as ferroelectricity, piezoelectricity, pyroelectricity, electro-optic effect, and nonlinear optical effect. Surface acoustic wave device, infrared pyroelectric device, acousto-optic device, light modulation device, light switching device,
Many applications, such as light deflection elements and wavelength conversion elements, are being studied. Conventionally, as a method for manufacturing an oxide thin film, a dry process such as a sputtering method, a vacuum evaporation method, and an MOCVD method has been mainly used. However, in the case of film formation in a dry process, the equipment used for these is very expensive, and the vapor pressure differs for each element, so that a thin film with excellent stoichiometry cannot be manufactured stably, However, there are drawbacks such as deterioration of productivity, low productivity, and high cost, and it is far from practical use.

On the other hand, a method for producing a ferroelectric thin film by a sol-gel method using an organometallic compound requires precise chemical composition control,
It has advantages in terms of uniformity at the molecular level, low temperature of the process, large area, low equipment cost, etc., and research is being conducted in various fields.

[0004] For example, Japanese Patent Publication No. Sho 62-27482 discloses that a solution containing an organometallic compound is applied on a glass substrate and dried in air at room temperature for 30 minutes and further in a thermostat at 110 ° C for 30 minutes. To terminate the hydrolysis, and forcing 550 to 8
A method for producing an oxide thin film that is fired at a temperature of 00 ° C. has been proposed. However, according to this publication, a solution containing an organometallic compound is obtained only by weighing a raw material into a butanol solution, and since a heating reaction such as distillation or reflux is not performed, the solution is left as it is. Otherwise, there is a problem that the viscosity is gradually increased or changed and the viscosity is unstable.

Japanese Patent Laid-Open Publication No. 4-19911 discloses that
After dissolving a metal organic compound of lead, lanthanum, titanium, and zirconium in an organic solvent, using a solution obtained by adding a stabilizer and a predetermined amount of water, lead titanate (PT), lead zirconate titanate (PZT), A method of forming a ferroelectric thin film of PZT with a third component and lead zirconate titanate with a lanthanum (PLZT) has been proposed. However, according to this publication, only sufficient stirring is carried out after dissolving the raw material in an organic solvent, and 0.1 to 1.5 per mole of metal atom.
In order to utilize the hydrolysis by adding moles of H ₂ O, there is a problem that the viscosity of the solution is gradually increased or changed due to the remaining H ₂ O, which is unstable, and a problem that the density of the obtained thin film is low. was there.

Therefore, the following method is noteworthy.
That is, a metal alkoxide is reacted with a metal salt such as lead acetate in a reactive solvent 2-methoxyethanol [actually, the following formula (1) in which the metal alkoxide reacts with 2-methoxyethanol results in A series of reactions such as the following formula (2) in which the metal alkoxide reacts with the lead acetate proceeds], and the obtained precursor for producing a ferroelectric thin film (a mixed solution containing a double alkoxide) is placed on a substrate. This is an application approach. This approach is described in Mat. Re
s. Soc. Symp. Proc. Vol. 73, 71
1, (1986) by Budd et al. _{Ti (O-i- C 3 H} 7) 4 + 4ROH → Ti (OR) 4 + 4i-C 3 H 7 OH (1) Pb (OOCCH 3) 2 + Ti (OR) 4 → PbTiO 2 (OR) 2 + 2OCCH 3 OR (2) [R = CH ₃ OCH ₂ CH _2- ] Since the obtained mixed solution contains a metal alkoxide or the like which is difficult to separate and purify, it is used for coating on a substrate without purification. used.

[0007] It is noteworthy that in this method, the reaction between the metal alkoxide and the metal salt can be achieved by oxygen between the different metals without using a hydrolysis reaction. That is, by doing so, there is no residual moisture due to the hydrolysis, and the instability of the product due to the moisture can be avoided.

[0008]

However, in the method disclosed above, since the reaction between the metal alkoxide and the metal salt progresses only slightly, the residual metal acetate is reduced to 5%.
5% or more, and because of such a large amount of residual metal acetate, crystallization of the formed thin film requires a high temperature, and the properties of the precursor itself are also affected by moisture from the surroundings such as the atmosphere. There was a problem of instability of changing.
Due to this, the density, refractive index, smoothness, transparency and the like of the ferroelectric thin film may not be at desired levels.

The present invention has been made in view of the above situation. That is, a first object of the present invention is to use various kinds of electronic devices and optoelectronic devices on a substrate using an organometallic compound as a raw material.
An object of the present invention is to provide a stable precursor for producing a ferroelectric thin film having high quality (high density or the like) at a low temperature.

A second object of the present invention is to provide a method for producing such a precursor. A third object of the present invention is to provide a method for producing such a high-quality ferroelectric thin film.

[0011]

That is, a first object of the present invention is to dissolve a metal acetate and a metal alkoxide in an organic solvent, and to react with an organometallic compound obtained by a reaction in the system without unreacted metal salt. A ferroelectric thin film-forming precursor containing a residual metal acetate of the formula (I), wherein the precursor for producing a ferroelectric thin film comprises 52 mol% or less of the unreacted residual metal acetate, Achieved.

In the precursor for producing a ferroelectric thin film, the amount of unreacted residual metal acetate is small. This is considered to contribute to the stability of the precursor and the production of a ferroelectric thin film having high quality (high density or the like) at a low temperature.

A second object of the present invention is to provide a dissolving step of dissolving a metal acetate and a metal alkoxide in an organic solvent, and a step of heating and distilling the system obtained in the above step while replenishing the organic solvent. And a precursor for producing a ferroelectric thin film including an organometallic compound obtained by a reaction in the system and an unreacted residual metal acetate, wherein the unreacted residual metal acetate is used. This is achieved by a method for producing a precursor for producing a ferroelectric thin film, which comprises producing a precursor for producing a ferroelectric thin film containing not more than 52 mol% of the prepared metal acetate.

By proceeding the reaction while replenishing the organic solvent as described above, it becomes possible to produce a precursor for producing a ferroelectric thin film having little unreacted residual metal acetate.

Further, a third object of the present invention is a method for producing a ferroelectric thin film, comprising the steps of: applying the precursor for producing a ferroelectric thin film on a substrate; Heat-treating the substrate on which the precursor has been applied.

By using the above precursor, a ferroelectric thin film having high quality (high density, etc.) can be produced through a lower temperature heat treatment than before.

[0017]

Embodiments of the present invention will be described below in detail.

The metal acetate salt used as a raw material of the precursor for producing a ferroelectric thin film of the present invention is selected from one or more kinds of salts of a specific metal having an organic ligand of CH ₃ OCO—. The specific metal referred to here is any metal (for example, Pb, Bi, La) that can be a constituent metal element of the ferroelectric thin film. Specific examples of the metal acetate include lead acetate, bismuth acetate, bismuth acetate oxide, lanthanum acetate and the like.

The use of an organic acid salt other than the metal acetate, for example, a propionate, a butyrate, or an organic acid having a larger number of carbon atoms can be considered, but it is difficult to obtain.

The metal alkoxide is a well-known organic compound. In the present invention, the metal is any metal that can be a constituent metal element of the ferroelectric thin film together with the specific metal. As the metal, for example, Mg, La,
It is selected from one or more of Pb, Bi, Ti, Zr, and Nb.

The organic ligand of the metal alkoxide is arbitrary as long as it binds to the above-mentioned metal to form a metal alkoxide, and typically, R'O- or R "O-
R ′ ″ O— (wherein, R ′ and R ″ represent an aliphatic hydrocarbon group, and R ′ ″ represents a divalent aliphatic hydrocarbon group which may have an ether bond). The carbon number of R ′ is preferably 1 to 4, more preferably 1 to 3. R ″
Has preferably 1 to 4, more preferably 1
~ 2. R ′ ″ preferably has 2 to 4 carbon atoms.

Specific examples of the organic ligand R'O- include C
_{H 3 O-, C 2 H 5} O-, C 3 H 7 O-, C 4 H 9 O-
Etc. Specific examples of the organic ligand R "OR '" O-, CH 3 OC 2 H 4 O-, C 2 H 5 OC 2 H 4 O-,
_{C 3 H 7 OC 2 H 4} O-, C 4 H 9 OC 2 H 4 O-, C
_{2 H 5 OC 2 H 4 OC} 2 H 4 O- , etc. These metal acetate and metal alkoxides include, at a predetermined composition (i.e., composition corresponding to the thin film composition), the solvent (preferably at atmospheric pressure Solvent having a boiling point of 80 ° C. or higher). Thus, after both the metal acetate metal salt and the metal alkoxide are dissolved in the solvent, or after both are dissolved in the solvent and at least one of the two is reacted with the solvent (such as an alcohol exchange reaction), (Including those whose chemical structure has changed by reacting with).

The solvent may have a boiling point of 80 ° C. or higher.
By using this, the surface is smoother and pores are
And a more uniform thin film can be obtained. As a solvent
For example, (CH_Three)_TwoCHOH, CH_Three(C_TwoH
_Five) CHOH, (CH_Three)_TwoCHCH_TwoOH, C_FourH₉
OH, (CH_Three)_TwoCHC_TwoH_FourOH, CH_ThreeOC_TwoH
_FourOH, C_TwoH_FiveOC_TwoH_FourOH, C_FourH₉OC_TwoH_Four
Alcohols such as OH are most preferred, but various ethers
Le, C_TwoH_FiveOC_TwoH_FourOC_TwoH_FourOH etc. can be used
is there. These may be used alone or in combination of two or more.
Is also good.

In the mixture containing the precursor obtained after the above-mentioned reaction, that is, the organometallic compound which is a reaction product, the unreacted residual metal acetate is determined based on the metal acetate used (the same applies to other places). , 52 mol% (see Example 5), preferably 30 mol% or less, more preferably 20 mol% or less, for producing a stable ferroelectric thin film precursor. This is effective for producing a ferroelectric thin film having high density and good crystallinity at a low temperature. Since it is usually impossible to completely eliminate the unreacted residual metal acetate, 0 mol% is not intended to be included in "52 mol% or less" in the present invention.

In consideration of shortening of the production time, unreacted residual metal acetate is usually contained in an amount of 1 to 52 mol%, preferably 5 to 30 mol%, more preferably 10 to 20 mol%. It is effective.

When the amount of the residual metal acetate is more than 52 mol%, the crystallization temperature of the thin film becomes high, the density of the obtained thin film becomes low, and in addition to the perovskite phase which is a ferroelectric phase, a non-ferroelectric phase is formed. A non-uniform thin film containing a certain pyrochlore phase is likely to be formed, and the stability of the precursor to moisture is also deteriorated. On the other hand, if the residual metal acetate is less than 1 mol%, the synthesis reaction time becomes considerably long, which is usually not preferred.

As described above, in addition to the organometallic compound product, the ferroelectric thin film precursor containing 52 mol% or less of the residual metal acetate usually contains 0.01 to 10 mol of the metal acetate and the metal alkoxide. / L, preferably 0.05 to
After dissolving in an organic solvent at a concentration of 2.0 mol / l,
The synthesis is performed by including at least the step of heating and distillation while replenishing the organic solvent, and the relatively volatile components such as acetate, which is a by-product, are removed. The ratio between the metal acetate and the metal alkoxide can be easily determined in consideration of the stoichiometric amount.

In order to obtain a ferroelectric thin film precursor containing 52 mol% or less of the residual metal acetate in a relatively short time, it is necessary to carry out the heating distillation while replenishing the organic solvent as described above. Not required, but required.

The replenishment method and replenishment timing of the organic solvent are arbitrary, but it is preferable that the replenishment is carried out continuously during the reaction.

The replenishing amount of the organic solvent is usually 0.1 to 100 times, preferably 1 to 50 times, more preferably 3 to 20 times the volume of the initially used organic solvent.

When the amount of the solvent is less than 1 time, the amount of the unreacted residual metal acetate is not more than 52 mol%, which requires a considerable amount of time. . Further, even if the solvent is used in an amount of more than 100 times the volume, not only does the amount of the residual metal acetate remain unchanged, but it is economically undesirable.

The heating distillation time is desirably 1 to
48 hours, more preferably 2 to 24 hours. If the time is shorter than this time, unreacted residual metal acetate is removed by 52%.
It may be difficult to reduce the amount to less than mol%, and it is not desirable to carry out the reaction for longer than this time because the amount of the residual metal acetate does not change. It is also effective to carry out a reflux reaction for 0.5 to 48 hours after this heat distillation reaction. The same solvent can be used as the solvent initially used and the solvent to be replenished, but different solvents may be used.

The distillation temperature is conveniently the boiling point of the solvent used, and the atmospheric pressure is conveniently normal pressure.

The content of the residual metal acetate in the precursor is ¹
Although it can be identified by NMR (nuclear magnetic resonance) spectra such as H, in some cases, it can also be identified by infrared spectroscopy.

The formed ferroelectric thin film precursor (mixed solution form) is used as a substrate (Al ₂ O ₃ , MgO, MgAl ₃ O ₄ ,
A single crystal substrate of SrTiO ₃ , ZnO or the like, a single crystal substrate of Si or MgO epitaxially grown on MgO, a single crystal substrate of GaAs or the like epitaxially grown on MgO, and Pt / Ti / S
iO ₂ / Si, is applied to the polycrystalline substrate, etc.), such as ITO glass. The method is preferably a spin coating method, dipping method, spray method, screen printing method,
Selected from the inkjet method. In this case, it is also possible to apply the precursor after further hydrolyzing the organometallic compound-containing precursor, but in order to obtain an epitaxial, or highly oriented ferroelectric thin film, do not hydrolyze and use a single crystal as it is. It is desirable to apply it on a substrate.

Next, pre-processing is performed as desired,
A heat treatment is performed to obtain a ferroelectric thin film.

For example, as a pretreatment, the substrate is rapidly heated at a temperature rising rate of 1 to 500 ° C./sec in an atmosphere containing oxygen, desirably in oxygen, and crystallized at 100 to 500 ° C. The coating layer is thermally decomposed in a temperature range in which no occurrence occurs. This application and thermal decomposition are repeated one or more desired times.

The heat treatment may be performed in an atmosphere containing oxygen, in an atmosphere containing no oxygen (eg, nitrogen), or in an atmosphere containing oxygen followed by an atmosphere containing no oxygen.
Usually, the substrate is rapidly heated at a temperature rising rate of 1 to 500 ° C./sec. Generally, the ferroelectric thin film is epitaxially, highly oriented, or polycrystalline in a temperature range of 300 ° C. to 1200 ° C. Allow to crystallize. As these atmospheres, a dry atmosphere or a forcedly humidified atmosphere can be used. The pressure of the atmosphere is usually 0.01 to 10
Atmospheric pressure is possible, but generally 1 atm (normal pressure) is often used.

Although the individual heating temperature varies depending on the material, the type of the substrate, and the like, heating can be performed at a relatively low temperature as compared with the corresponding conventional method. For example, conventionally 650-7
What is heated at 00 ° C. can be heated at about 600 ° C.

By the above method, a high-density ferroelectric thin film usable for various electronic devices and optoelectronic devices can be manufactured.

When a single crystal substrate is used as the substrate,
The thin film formed thereon is epitaxial or highly oriented, has a density and a refractive index similar to that of a single crystal, and has an optically smooth surface such as PbTiO ₃ , Pb (Zr
_1-X Ti _X ) O ₃ (PZT), Pb _1-X La _X (Zr
_1-Y Ti _Y ) _1-X / ₄ O ₃ (PLZT), Bi ₄ Ti ₃
O1 _2, the ferroelectric thin film, such as _{Pb (Mg 1/3 Nb 2/3) O} 3 is obtained.

[0042]

【Example】

Example 1 tetraisopropoxytitanium (Ti (O-i-C 3 H 7)
₄ ) with 2-methoxyethanol (CH ₃ OCH ₂ CH)
Was dissolved in ₂ OH), followed by acetic anhydride lead was vacuum dried at _{100 ° C (Pb (OOCCH 3} ) 2) Pb: Ti =
Dissolve at a molar composition ratio of 1.0: 1.0, 0.6 mol
/ L. Thereafter, while gradually adding 2-methoxyethanol three times the volume of 2-methoxyethanol used first, the mixture was reacted at a temperature of about 125 ° C. for 12 hours as shown in the reaction formulas (1) and (2). To reduce the amount of unreacted lead acetate, and the metal complex PbTiO ₂ (OCH ₂ CH ₂ O
CH ₃ ) ₂ and by-product CH ₃ COO
CH ₂ CH ₂ OCH ₃ was removed.

Thus, a Pb concentration of 0.6 mol / l
A stable precursor solution was obtained. Also, a part of the solution is dried under reduced pressure
Thus, a viscous polymer precursor was obtained. The above operation is
All N_TwoI went in the atmosphere. Precursors dried under reduced pressure
O_TwoThermogravimetric analysis (TGA)
Analysis shows that when the thermogravimetric change disappears, the thermogravimetric loss is
31.3%, PbTiO_Two(OCH_TwoCH_TwoOC
H_Three)_TwoFrom PbTiO_Three30.7 of theoretical weight loss to
%. In addition, this precursor is
Dissolved in Lum-d¹Measure 1 H NMR spectrum
And Pb (OOCC) found at around 1.9 ppmH _Three)
_TwoAround 3.4 ppm with the integrated intensity of the signal due to H
Ti (OCH_TwoCH_TwoOCH _Three)_FourBy H
The ratio of the signal to the integrated intensity is about 0.5 before the reaction.
0.021 from which the amount of residual lead acetate was calculated.
As a result, it was found that the content was 2.1 mol%. These
Thus, the obtained precursor had 2.1 mol% of residual lead acetate and
PbTiO_Two(OCH_TwoCH _TwoOCH_Three)_TwoConsisting of
It is clear that it is a precursor. This precursor is_TwoDuring ~
Analysis by scanning differential thermal analysis (DSC)
The oxidative decomposition temperature of the organic ligand is 210 ° C and the crystallization temperature is 4
It was 90 ° C.

This precursor solution was placed on an ITO (indium-tin oxide) glass substrate at room temperature in an N ₂ atmosphere for 2000 hours.
Spin coating was performed at rpm. The spin-coated substrate was heated at 425 ° C. after heating at 300 ° C. in an O ₂ atmosphere. Despite heating at only 425 ° C., the thin film having a thickness of 1,000 Å was a single polycrystalline perovskite thin film of PbTiO ₃ when analyzed by X-ray diffraction pattern.

Next, after spin coating this precursor solution on an ITO (indium tin oxide) glass substrate,
Heat at 300 ° C for 1 minute in O ₂ atmosphere,
Heated at 00 ° C. When the obtained thin film having a thickness of 1000 Å was analyzed for its X-ray diffraction pattern,
It was a single thin film of polycrystalline perovskite of bTiO ₃ .

Further, spin coating and baking are further performed.
The film thickness is 3000 angstroms by repeating twice
A polycrystalline thin film was obtained. PbTiO_ThreeThe composition of the thin film
When analyzed with an X-ray microanalyzer, Pb: T
The i ratio is 0.99: 1.00, which is a deviation from the Pb: Ti ratio.
The difference is within the error range, and the composition control is extremely good.
Was. In addition, the refractive index is measured by a He-Ne ellipsometer.
Observation showed a value close to that of a single crystal. In addition, the surface
When observed with a scanning electron microscope, PbTiO _ThreeThin film
Was extremely dense. Comparative Example 1 Only the reaction conditions were changed from those of Example 1, and 2-methoxyethanol
Example 1 except that distillation was performed only for 1 hour without adding
The precursor solution and the precursor dried under reduced pressure
Done. The precursor dried under reduced pressure is converted into chloroform-d.
Dissolve¹When the 1 H NMR spectrum was measured, it was 1.9.
Pb (OOCC)H _Three)_TwoBy H
Of the integrated signal and T around 3.4 ppm
i (OCH_TwoCH_TwoOCH _Three)_FourOf signal by H
The ratio to the integrated intensity is 0.35, which indicates that the residual lead acetate
The calculated amount was found to be 54%. these
Thus, the resulting precursor contains 54% residual lead acetate.
It is clear that this is a precursor. This precursor is_Two
Analysis by scanning differential thermal analysis (DSC)
The oxidative decomposition temperature of the organic ligand is 290 ° C, and the crystallization temperature is
510 ° C., the oxidative decomposition temperature higher than in the case of Example 1,
Both crystallization temperatures were high. In addition, this precursor solution is
When left inside, the example (due to the effect of atmospheric moisture)
Gelation occurred in a shorter time as compared to the precursor solution of No. 1.

This precursor solution was treated in the same manner as in Example 1 with ITO.
(Indium-tin oxide) Spin coating was performed on a glass substrate. The spin-coated substrate is O ₂
After heating at 300 ° C in an atmosphere, heating was performed at 425 ° C. When the obtained thin film having a thickness of 1000 angstroms was analyzed for its X-ray diffraction pattern, most of the thin film including a pyrochlore phase was an amorphous phase, and no perovskite phase was observed.

Next, after spin coating this precursor solution on an ITO (indium tin oxide) glass substrate,
Heat at 300 ° C. in O ₂ atmosphere, then 600 °
When heated at C, the thin film having a thickness of 1000 angstroms was found to be polycrystalline PbTiO according to the X-ray diffraction pattern.
_Although it was a ₃ perovskite phase, it contained a slight pyrochlore phase, and the X-ray diffraction by the perovskite phase was considerably weaker than that of Example 1. When the composition of the PbTiO ₃ layer was analyzed with an X-ray microanalyzer, the Pb: Ti ratio was 0.95: 1.00, and the deviation from the Pb: Ti ratio was considerably larger than that in Example 1. Further, the refractive index is set to He.
When observed by a -Ne ellipsometer, the value was much smaller than that of the single crystal. Further, when the surface was observed with a scanning electron microscope, it was found that pores were observed in the PbTiO ₃ thin film, and thus the refractive index was low. Thus, it can be seen that the formation of the precursor structure by the reaction of Example 1 is effective for producing a PbTiO ₃ thin film having a controlled composition and a high density. Example 2 (metal alkoxide changes, reaction time changes) tetraisopropoxytitanium (Ti (O-i-C 3 H 7)
₄ ), tetraisopropoxy zirconium (Zr (O-
i-C ₃ H ₇ ) ₄ ), dried anhydrous lead acetate (Pb (OOCCH ₃ ) ₂ ) dried in vacuo at 100 ° C. in 2-methoxyethanol (CH ₃ OCH ₂ CH ₂ OH) with Pb: Zr: T
It was dissolved at a molar composition ratio of i = 1.0: 0.52: 0.48, and the Pb concentration was 0.6 mol / l. Thereafter, distillation was conducted at about 125 ° C. for 6 hours while adding 2-methoxyethanol eight times the volume of the used 2-methoxyethanol, and reflux was further performed for 18 hours to reduce unreacted lead acetate. complex _{Pb (Zr 0. 52 Ti 0.48} ) O 2 (OCH
₂ CH ₂ OCH ₃ ) ₂ and by-product CH
₃ COOCH ₂ CH ₂ OCH ₃ was removed. Thereafter, a part of the solution was concentrated under reduced pressure to finally obtain a Pb concentration of 0.1%.
A 5M stable precursor solution was obtained. All of the above operations are N
Performed in _two atmospheres.

Thereafter, the precursor dried under reduced pressure in the same manner as in Example 1 was analyzed for the thermogravimetric change by thermogravimetric analysis (TGA) in O ₂ , and the thermogravimetric loss when the thermogravimetric change disappeared was 33. 0.3%, and Pb (Zr _0.52 T
i _0.48 ) O ₂ (OCH ₂ CH ₂ OCH ₃ ) ₂ to Pb
29.2 theoretical weight loss to (Zr _0.52 Ti _0.48 ) O ₃
%. Further, when the amount of residual lead acetate was calculated from the ¹ H NMR spectrum, it was 6.2 mol%. From these facts, the obtained precursor was composed of about 6% of residual lead acetate and Pb (Zr _0.52 Ti _0.48 ) O ₂ (OCH ₂ C).
It is clear that this is a precursor consisting of H ₂ OCH ₃ ) ₂ .

[0050] After the spin coating onto the precursor solution Al ₂ O ₃ (sapphire R face) 3 in O ₂ atmosphere
Heat at 00 ° C for 1 minute, and further heat at 650 ° C for 30 minutes.
Heated for minutes. The obtained thin film having a thickness of 1000 Å was analyzed by the X-ray diffraction pattern and the pole figure shown in FIG.
It was an epitaxial thin film having a single orientation only on the 0) plane.
When the composition was analyzed with an X-ray microanalyzer, the composition deviation from the precursor was within the error range, and the composition control was extremely good. In addition, when the refractive index was observed with a He-Ne ellipsometer, it showed a value equivalent to that of a single crystal. Further, when the surface was observed with a scanning electron microscope, the thin film was extremely dense and uniform without pinholes or the like. Comparative Example 2 (without solvent replenishment) For comparison with Example 2, tetraisopropoxy titanium,
Tetraisopropoxy zirconium, anhydrous lead acetate vacuum-dried at 100 ° C., was treated with Pb: Zr: Ti = 1.0
At 0: 0.52: 0.48, a precursor only dissolved in 2-methoxyethanol was prepared.

This precursor¹H NMR spectrum
The amount of residual lead acetate was slightly lower than the amount charged
It was about. This precursor solution was prepared in the same manner as in Example 2.
Al _TwoO_Three(Sapphire R surface)
Many pyrochlore phases instead of single perovskite phases
It was a thin film containing, and the surface was uneven. This precursor solution
When the solution is left in the air, it is compared with the precursor solution of Example 2.
Gelation occurred in a short time (several days). X of the obtained thin film
The line diffraction pattern is shown in FIG. Example 3 (Change in amount of solvent supply) In Example 2, the amount of solvent to be supplied during heating distillation was changed to 3
Except that the volume was doubled, the precursor solution was dissolved in the same manner as in Example 2.
A liquid and a precursor dried under reduced pressure were synthesized. Vacuum dried
Precursor¹From the 1 H NMR spectrum, determine the amount of residual lead acetate
The calculated value was 13.9 mol%. So before got
The precursor was about 14 mol% residual lead acetate and Pb (Zr_0.52Ti
_0.48) O_Two(OCH_TwoCH_TwoOCH_Three)_TwoConsisting of a precursor
It turns out that it is a body.

The precursor solution was treated with M in the same manner as in Example 2.
When a thin film was formed on the gO (100) plane and analyzed by an X-ray diffraction pattern and a pole figure, it was a single-oriented epitaxial thin film having only the (001) plane. He-N
Observation with an e-ellipsometer showed a value equivalent to that of a single crystal, and observation of the surface with a scanning electron microscope revealed that the thin film was extremely dense and uniform. Example 4 (a metal alkoxide modified) in substantially the same manner as in Example 2, tetraisopropoxytitanium (Ti (O-i-C 3 H 7) 4), tetra-isopropoxy zirconium (Zr (O-i-C 3 H ₇ ) ₄ ), 100
Anhydrous lead acetate (Pb (OOCC)
H _{3) 2),} and iso-propoxy lanthanum 2-methoxyethanol _{(CH 3 OCH 2 CH 2 OH} ) Pb:
La: Zr: Ti = 0.91: 0.09: 0.65:
It was dissolved at a molar composition ratio of 0.35 and the Pb concentration was 0.6
mol / l. Thereafter, distillation was performed at about 125 ° C. for 6 hours while adding 2-methoxyethanol four times the volume of the used 2-methoxyethanol, and reflux was further performed for 18 hours to reduce unreacted lead acetate. And a by-product CH ₃ COOCH ₂ CH
₂ OCH ₃ was removed to obtain a 0.6M stable precursor solution.

The precursor dried under reduced pressure¹1 H NMR spec
Calculating the amount of residual lead acetate from Torr
there were. This precursor solution was treated with SrT in the same manner as in Example 2.
iO _ThreePreparation of thin film on (100) plane and X-ray diffraction pattern
Analysis by pole figure, single orientation of (100) plane only
Was obtained. He-Ne refractive index
Observed with a lipsometer, the same value as a single crystal
The surface was observed with a scanning electron microscope.
Was extremely dense and the surface was uniform and smooth. Example 5 (Change in amount of solvent) In Example 2, the amount of solvent to be replenished during heating distillation was 1
A precursor solution was prepared in the same manner as in Example 2 except that the volume was doubled.
And a precursor dried under reduced pressure was synthesized. Before drying under reduced pressure
Carcass¹Measure the amount of residual lead acetate from the 1 H NMR spectrum
It was 52.3 mol% when calculated. Thus the precursor obtained
The body contains about 52 mol% of residual lead acetate and Pb (Zr_0.52Ti
_0.48) O_Two(OCH_TwoCH_TwoOCH_Three)_TwoConsisting of a precursor
It turns out that it is a body.

The precursor solution was prepared in the same manner as in Example 2
When a thin film was formed on l ₂ O ₃ (sapphire R plane) and analyzed by the X-ray diffraction pattern and the pole figure shown in FIG. 3, it was a single-phase (110) epitaxial thin film of perovskite single phase. However, the crystallinity was lower than that of Example 2.

[0055]

According to the present invention, since the heating distillation is carried out while replenishing the solvent to the reaction system as described above, the stable distillation containing not more than 52 mol% of unreacted residual metal acetate in addition to the organometallic compound is carried out. A precursor for producing a ferroelectric thin film can be produced. The ferroelectric thin film obtained by using the precursor according to the present invention has a surface that is optically smooth, transparent, has a high refractive index, and when formed on a single crystal substrate, is monocrystalline or It has high orientation. Therefore, using an organometallic compound solution that has the advantages of precise chemical composition control, large area, low equipment cost, etc., a ferroelectric thin film that can be used for electro-optical elements using optical waveguides etc. It has become possible to make the manufacturing method more effective.

[Brief description of the drawings]

FIG. 1 is a diagram showing an X-ray diffraction pattern in one example.

FIG. 2 is a diagram showing an X-ray diffraction pattern in a comparative example.

FIG. 3 is a diagram showing an X-ray diffraction pattern in one example.

Claims (13)

[Claims] 1. A precursor for producing a ferroelectric thin film comprising an organometallic compound obtained by dissolving a metal acetate metal salt and a metal alkoxide in an organic solvent, and an unreacted residual metal acetate salt in the system. A precursor for producing a ferroelectric thin film, comprising a non-reacted residual metal acetate in an amount of not more than 52 mol% of the metal acetate used. 2. The precursor for producing a ferroelectric thin film according to claim 1, wherein the metal of the metal acetate is one or more selected from the group consisting of Pb, Bi, and La. 3. The metal of the metal alkoxide is Mg, L
2. The precursor for producing a ferroelectric thin film according to claim 1, wherein the precursor is one or more selected from the group consisting of a, Pb, Bi, Ti, Zr, and Nb. 4. An organic ligand of the metal alkoxide,
R'O- or R "OR '" O- (wherein R' and R "represent an aliphatic hydrocarbon group, and R '" represents a divalent aliphatic hydrocarbon group which may have an ether bond. The precursor for producing a ferroelectric thin film according to claim 1, wherein 5. A dissolving step of dissolving a metal acetate metal salt and a metal alkoxide in an organic solvent, and a step of heating and distilling the system obtained in the above step while supplying an organic solvent to the system. An organometallic compound obtained by the reaction,
A precursor for producing a ferroelectric thin film comprising an unreacted residual metal acetate, comprising a ferroelectric thin film comprising not more than 52 mol% of the unreacted residual metal acetate. For producing a precursor for producing a ferroelectric thin film. 6. The method according to claim 5, wherein the organic solvent reacts with a metal alkoxide. 7. The method according to claim 5, wherein the boiling point of the organic solvent is 80 ° C. or higher. 8. The method according to claim 5, wherein 0.1 to 100 times the volume of the organic solvent used in the dissolving step is replenished. 9. The distillation time is from 1 to 48 hours.
The manufacturing method as described. 10. A method for producing a ferroelectric thin film, comprising: dissolving a metal acetate and a metal alkoxide in an organic solvent;
An organometallic compound obtained by a reaction in the system,
A precursor for producing a ferroelectric thin film comprising an unreacted residual metal acetate, comprising a ferroelectric thin film comprising not more than 52 mol% of the unreacted residual metal acetate. A method for producing a ferroelectric thin film, comprising: a step of applying a substrate on a substrate; and a step of heat-treating the substrate to which the precursor for producing a ferroelectric thin film has been applied. 11. The metal of the metal acetate salt is Pb, Bi,
11. The method for producing a ferroelectric thin film according to claim 10, wherein the ferroelectric thin film is one or more selected from the group consisting of La and La. 12. The metal of the metal alkoxide is Mg,
The method for producing a ferroelectric thin film according to claim 10, wherein the ferroelectric thin film is one or more selected from the group consisting of La, Pb, Bi, Ti, Zr, and Nb. 13. An organic ligand of the metal alkoxide, wherein R′O— or R ″ OR ′ ″ O— (wherein R ′ and R ″ represent an aliphatic hydrocarbon group, and R ′ ″ represents an ether). 11. The method for producing a ferroelectric thin film according to claim 10, which represents a divalent aliphatic hydrocarbon group which may have a bond.