JP2001139329A - METHOD FOR FORMING Pb-BASE PEROVSKITE TYPE METAL OXIDE THIN FILM AND Pb-BASE PEROVSKITE TYPE METAL OXIDE THIN FILM - Google Patents

Abstract

PROBLEM TO BE SOLVED: To crystallize a metal oxide at a low temperature of <=450 deg.C in a method for forming a Pb-base perovskite type metal oxide thin film by applying a raw material solution for forming the metal oxide thin film on a substrate, then heating the substrate to crystallize the metal oxide. SOLUTION: This method for forming the Pb-base perovskite type metal oxide thin film has a stage for applying the raw material for forming the Pb-Ti- base metal oxide thin film on the substrate, then applying a raw material solution for forming the Pb-Zr-Ti-base metal oxide thin film. In the method, a crystallization stage is executed at least one time in such a manner that the thickness of the metal oxide thin film formed by one time of the crystallization stage attains <=30 nm in the film thickness after the crystallization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a Pb-based perovskite-type metal oxide thin film, which can be expected to be applied to various dielectric devices due to its electrical and / or optical properties, by a sol-gel method or the like. In particular, the present invention relates to a method for forming a Pb-based perovskite-type metal oxide thin film having a low crystallization temperature of a metal oxide and capable of forming a film at a low temperature.

[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, the application of the excellent ferroelectric characteristics to the various dielectric device is 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 ferroelectric thin film is formed, for example, by heating to about 400 ° C. in the air to form a metal oxide film, and further firing at a temperature higher than the crystallization temperature of the metal oxide to crystallize the film. How to

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 at a crystallization temperature or higher to crystallize the film. To 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 methods using these methods in combination are referred to as “sol-gel method”.

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.

In the conventional sol-gel method, a raw material solution is applied to a substrate, dried, calcined, and the application, drying and calcining are repeated until a desired film thickness is obtained. Film formation is performed by baking at a temperature higher than the crystallization temperature of the product and crystallizing the product.

[0009]

However, formation of a PZT thin film by a sol-gel method or the like requires a high heating temperature of generally 650 ° C. or higher for firing for crystallization.

On the other hand, in a memory using such a ferroelectric thin film, an adverse effect on a transistor of a device and a peripheral circuit thereof due to a heat treatment has been regarded as a problem as the device chip is downsized. Therefore, it is indispensable to lower the crystallization temperature when forming a Pb-based perovskite-type metal oxide thin film.
Also, in applications other than ferroelectric memory, reducing the crystallization temperature during film formation enables film formation on a glass substrate or the like, which was difficult to form at the conventional crystallization temperature,
Since it is expected to expand the application range of ferroelectrics, piezoelectrics, current collectors, and the like, it is strongly desired to reduce the crystallization temperature.

Conventionally, as a technique for reducing the crystallization temperature of a PZT thin film, a raw material solution for forming a metal oxide thin film containing Pb and Ti is applied, and then a raw material solution for forming a metal oxide thin film containing Pb, Zr and Ti is formed. Has been proposed to crystallize by coating (Journal of the European Ceramic S
society 19 (1999) 1397-1401). In this method, a PT layer having a low crystallization temperature is first crystallized, and the PZ is
By crystallization of the T layer at a low temperature, the activation energy for crystallization of the PZT thin film is reduced, and the crystallization temperature can be reduced. This method is called PT seeding and is effective to some extent in lowering the crystallization temperature, but it is still not enough, and further improvement is desired.

The present invention solves the above-mentioned conventional problems, and when forming a Pb-based perovskite-type metal oxide thin film by a sol-gel method or the like, a Pb-based perovskite capable of performing crystallization even at a low temperature of 450 ° C. or less. It is an object of the present invention to provide a method for forming a metal oxide thin film of a type and a high-quality Pb-based perovskite metal oxide thin film formed by the low-temperature crystallization method.

[0013]

According to a first aspect of the present invention, there is provided a method for forming a Pb-based perovskite-type metal oxide thin film, which comprises applying a raw material solution for forming a metal oxide thin film on a substrate and heating the substrate. In the method of forming a Pb-based perovskite-type metal oxide thin film by crystallization, the thickness of the metal oxide thin film formed in one crystallization step may be 30 nm or less as a thickness after crystallization. The crystallization step is performed once or more.

By setting the thickness of the metal oxide thin film formed in one crystallization step to be 30 nm or less in terms of the thickness after crystallization, the crystallization temperature of the metal oxide can be reduced. Can be done. The details of this reason are not clear, but the effect that carbon is easily decomposed at the time of calcination after coating and the crystal growth after nucleation from the interface between the substrate and the amorphous layer due to the extremely thin film thickness are in progress. It is presumed to be due to the effect of crystallization to the surface without interruption. That is,
As in the conventional method, when the film is fired and crystallized at a relatively low temperature of about 450 ° C. so that the film thickness after crystallization becomes 30 nm or more, the crystal growth of the perovskite oxide is interrupted in the middle of the thin film, and the film grows to the surface. It is not crystallized and a fine pyrochlore layer is formed on the surface. On the other hand, when crystallization is performed by firing at a relatively low temperature of about 450 ° C. so that the film thickness after crystallization becomes 30 nm or less, complete crystallization is performed.

In the present invention, the crystallization step is performed one or more times so that the thickness of the metal oxide thin film formed in one crystallization step is 30 nm or less in thickness after crystallization. In addition to the above, it is preferable to use PT seeding in combination, whereby the crystallization temperature can be further reduced in combination with the above-mentioned crystallization temperature reduction effect, and even at a low temperature of 450 ° C. or lower. Crystallization is promoted, and a high-quality Pb-based perovskite-type metal oxide thin film can be formed.

The Pb-based perovskite-type metal oxide thin film of the present invention is formed by such a method of forming the Pb-based perovskite-type metal oxide thin film of the present invention, and is sintered at a low temperature to achieve high cost at low cost. This realizes a high quality dielectric device.

[0017]

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

As the Pb-based perovskite-type metal oxide thin film formed in the present invention, a perovskite-type oxide thin film composed of Pb and Zr and / or Ti, in particular, a lead zirconate titanate: PZT thin film can be mentioned.

This oxide material can contain a small 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.

The raw material solution for forming a metal oxide thin film used in the present invention is obtained by dissolving a raw metal compound in an organic solvent. Examples of the organic solvent used herein include alcohols, carboxylic acids, esters, ketones, ethers, and the like. Cycloalkanes, aromatic solvents and the like can be mentioned. Among them, alcohols include ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, and 2-methyl-2. -Alkanols such as propanol, 1-pentanol, 2-pentanol, 2-methyl-2-pentanol, cycloalkanols such as cyclohexanol, and 2-
Alkoxy alcohols such as 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 later is performed, it is preferably added after this 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.

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 compound 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, it is particularly preferable to use titanium alkoxide as the Ti raw material compound, zirconium alkoxide as the Zr raw material compound, and lead acetate trihydrate and / or anhydrous lead acetate as the Pb raw material compound. .

In the present invention, a metal compound used as a raw material for each of these component metals is dissolved in the above-mentioned organic solvent,
Preferably, a raw material solution containing a precursor of a composite metal oxide (oxide containing two or more metals) of a Pb-based perovskite-type metal oxide thin film to be formed by adding a β-diketone as a stabilizer. Is prepared.

The ratio of each metal compound contained in the raw material solution may be substantially the same as the metal atomic ratio of the Pb-based perovskite-type metal 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, an excess of 2 to 30%). 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 0.1 to 20% by weight. Is preferable.

A solution in which a metal compound is dissolved in an organic solvent 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 partially hydrolyze or partially polycondense a hydrolyzable metal compound (eg, alkoxide) and use the film for film formation. That is, in this case, the raw material solution contains a partial hydrolyzate and / or a partial polycondensate of at least a part of the metal compound.

The heating for the partial hydrolysis controls 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, it is preferable to remove water of crystallization accompanying the metal carboxylate 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. If the metal carboxylate is mixed with the metal alkoxide without removing the water of crystallization, the hydrolysis of the metal alkoxide may progress too much or its control may be difficult, and precipitation may occur after partial hydrolysis.

In the present invention, the raw material solution for forming a metal oxide thin film thus prepared is used under the following conditions:
Preferably, a Pb-based perovskite-type metal oxide thin film can be formed according to the following procedure in the same manner as in a conventional sol-gel method except that the film formation is performed under the following conditions.

The crystallization step is performed one or more times so that the thickness of the metal oxide thin film formed in one crystallization step is 30 nm or less in thickness after crystallization. In this case,
The thinner the metal oxide thin film formed in one crystallization step, the more advantageous the crystallization temperature is. However, excessively thinning leads to a decrease in film formation efficiency. It is preferable that the thickness of the metal oxide thin film formed by one crystallization is 5 to 30 nm.

After forming a coating film by applying a metal oxide thin film forming raw material solution containing a Pb raw material compound and a Ti raw material compound, a metal containing the Pb raw material compound, the Zr raw material compound and the Ti raw material compound is formed on the coating film. An oxide thin film forming raw material solution is applied to form a coating film. Preferably Pb on the substrate
After forming a coating film by applying a raw material solution for forming a metal oxide thin film containing a raw material compound and a Ti raw material compound, forming a metal oxide thin film containing a Pb raw material compound, a Zr raw material compound and a Ti raw material compound on the coated film. The raw material solution is applied a plurality of times to form a laminated film.

First, a raw material solution for forming a metal oxide thin film 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. This drying temperature depends on the type of solvent,
Usually, it is about 80 to 200 ° C., preferably 100 to 200 ° C.
The temperature may be in the range of 180 ° C. However, the solvent is removed during the heating in the next step for converting the metal compound in the raw material solution into the metal oxide, so that the step of drying 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 450 ° C, preferably 200 to 400 ° 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, etc.
Since it is often difficult to obtain a film thickness required for a b-based perovskite-type metal oxide thin film, the above-described coating and (drying) calcination are repeated as necessary to obtain a metal oxide having a desired film thickness. To obtain a film. The film obtained in this way is amorphous or crystalline and has insufficient crystallinity, so that it has low polarizability and 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.

When the above conditions are adopted, the firing for crystallization is appropriately performed such as coating, drying, calcining and calcination so that the thickness of the crystallized film obtained by one firing is 30 nm or less. The firing step is repeated, or the coating, drying and calcining steps are repeated, and then the firing step is repeated to form a Pb-based perovskite-type metal oxide thin film having a desired film thickness.

In the present invention, the aforementioned, preferably
By adopting the above conditions, the temperature for this crystallization is set to 450 ° C. or lower, for example, 420 to 450.
° C.

Therefore, a substrate having heat resistance enough to withstand the firing temperature may be used. The baking (annealing) time for crystallization is usually 1 minute to 2 minutes.
It is about time, and the firing atmosphere is not particularly limited, but is usually air or oxygen.

Such a Pb-based perovskite-type metal acid
Heat-resistant substrate material used for forming oxide thin films
Are silicon (single crystal or polycrystal), platinum, nickel
Which metals, ruthenium oxide, iridium oxide, rutheni
Strontium titanate (SrRuO)₃) Or cobalt acid
Lanthanum strontium ((La_XSr_1-X) CoO
₃), Such as perovskite-type conductive oxides, quartz,
Inorganic compounds such as aluminum nitride and titanium oxide
Can be In the case of a capacitor film, the substrate is the lower electrode
Yes, as the lower electrode, for example, Pt, Pt / Ti,
Pt / Ta, Ru, RuO₂, Ru / RuO₂, RuO
₂/ Ru, Ir, IrO₂, Ir / IrO ₂, Pt / I
r, Pt / IrO₂, SrRuO₃Or (La_XSr
_1-X) CoO₃Perovskite-type conductive oxides such as
(A two-layer structure using “/”)
The structures are shown as "upper / lower". ).

The thickness of the Pb-based perovskite-type metal oxide thin film thus formed varies depending on the use of the derivative device, but is usually preferably about 50 to 400 nm. It is useful for various derivative devices.

[0047]

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: a raw material solution for forming a Pb-Ti-based metal oxide thin film and a raw material solution for forming a Pb-La-Zr-Ti-based metal oxide thin film. Each solution was produced by the following method.

Pb raw material compound: lead acetate trihydrate La raw material compound: lanthanum acetate sesquihydrate Ti raw material compound: titanium tetraisopropoxide Zr raw material compound: zirconium tetra n-butoxide

[Production Method of Raw Material Solution for Forming Pb-Ti Metal Oxide Thin Film] Titanium tetraisopropoxide and acetylacetone as a stabilizer were added to a reaction vessel in an amount of 2 mol times of titanium tetraisopropoxide. 3 at ℃
Refluxed in a nitrogen atmosphere for hours. Next, lead acetate trihydrate was added, and alcohol (propylene glycol) was added as a main solvent at a molar ratio of 5 times the amount of lead acetate trihydrate, and the resulting mixture was added to the mixture.
Reflux at 0 ° C. for 3 hours in a nitrogen atmosphere. Then 150
The by-product was removed by distillation under reduced pressure at ℃, and the concentration was adjusted by further adding propylene glycol to obtain a liquid containing a metal compound at a concentration of 30% by weight in terms of oxide.
The solution was further refluxed at 150 ° C. for 3 hours in a nitrogen atmosphere, and then allowed to cool under stirring, and diluted alcohol (n-propanol)
Is added to adjust the concentration, so that Pb: Ti = 12
A sol-gel solution containing 5% by weight (atomic ratio) of a metal compound at a concentration of 1% by weight in terms of oxide (hereinafter referred to as "PT sol-gel solution") was obtained.

[Method for Producing Raw Material Solution for Forming Pb-La-Zr-Ti-Based Metal Oxide Thin Film] In a reaction vessel, zirconium tetra-n-butoxide and acetylacetone as a stabilizing agent are 2 mol times of zirconium tetra-n-butoxide. The mixture was refluxed at 150 ° C. for 3 hours in a nitrogen atmosphere. Titanium tetraisopropoxide and acetylacetone as a stabilizer were added to titanium tetraisopropoxide.
The mixture was added in a molar amount, and refluxed at 150 ° C. for 3 hours in a nitrogen atmosphere. Then, lead acetate trihydrate and lanthanum acetate 1.
A pentahydrate was added, and alcohol (propylene glycol) was added as a main solvent to lead acetate trihydrate and lanthanum acetate 1.5.
The hydrate was added in an amount of 5 mol times the total, and refluxed at 150 ° C. for 3 hours in a nitrogen atmosphere. Then, by-product distillation was performed at 150 ° C. under reduced pressure to remove by-products, and propylene glycol was added to adjust the concentration to obtain a liquid containing a metal compound at a concentration of 30% by weight in terms of oxide. The solution was further refluxed in a nitrogen atmosphere at 150 ° C. for 3 hours, allowed to cool under stirring, and diluted with alcohol (n-propanol) to adjust the concentration, whereby Pb: La: Zr: Ti = 1
A sol-gel solution (hereinafter referred to as “P”) containing a metal compound at a concentration of 5% by weight in terms of oxide at a ratio of 25: 1: 40: 60 (atomic ratio).
LZT sol-gel liquid ". ) Got.

Example 1 Pt (2000 °) / SiO ₂ (5000 °) / Si
First, a PT sol-gel solution is applied on a substrate of a (100) wafer by a spin coating method (3000 rpm, 15
S) at 150 ° C. for 1 minute in the air (hot plate). Next, a PLZT sol-gel solution is applied on the dried film by a spin coating method (3000 rpm, 15 rpm).
Second) and dried in the same manner as described above, and then calcined at 400 ° C. for 1 minute in the air (hot plate). Then 430
C. for 10 minutes in air (hot plate) for crystallization.

Further, the same steps of applying, drying, calcining and baking a PLZT sol-gel solution as described above were repeated five times to form a 150 nm-thick PLZT thin film.

The SE on the surface of the obtained PLZT thin film was
The crystal phase was observed from the M photograph. In addition, the presence or absence of a perovskite peak was examined by X-ray diffraction, and the presence or absence of hysteresis characteristics was examined by applying a voltage. The results are shown in Table 1, FIG. 1 and FIG.

Comparative Example 1 Pt (2000 °) / SiO ₂ (5000 °) / Si
First, a PT sol-gel solution is applied on a substrate of a (100) wafer by a spin coating method (3000 rpm, 15
S) at 150 ° C. for 1 minute in the air (hot plate). Next, a PLZT sol-gel solution is applied on the dried film by a spin coating method (3000 rpm, 15 rpm).
Second) and dried in the same manner as described above, and then calcined at 400 ° C. for 1 minute in the air (hot plate). The steps of applying, drying and calcining the PLZT sol-gel solution are further repeated 5 times, and then at 430 ° C. for 50 minutes in the air (hot plate).
And crystallized to form a PLZT thin film having a thickness of 150 nm.

The SE on the surface of the obtained PLZT thin film was
The crystal phase was observed from the M photograph. In addition, the presence or absence of a perovskite peak was examined by X-ray diffraction, and the presence or absence of a hysteresis characteristic was examined by applying a voltage. The effects are shown in Table 1, FIG. 2 and FIG.

[0057]

[Table 1]

From the above results, when applying the raw material solution for an oxide thin film so that the film thickness to be crystallized in one crystallization is 30 nm or less after crystallization, first, Pb and Ti are used. A raw material solution containing
The step of applying and crystallizing a raw material solution containing b, Zr and Ti is performed at least once or more, whereby 450
It can be seen that crystallization is promoted even at a low temperature of not more than ℃, and a high-quality Pb-based perovskite-type metal oxide thin film can be formed.

[0059]

As described above in detail, according to the method for forming a Pb-based perovskite-type metal oxide thin film of the present invention, the crystallization temperature is increased when forming a Pb-based perovskite-type metal oxide thin film by a sol-gel method or the like. Therefore, it is possible to form a complete high-quality Pb-based perovskite-type metal oxide thin film of perovskite crystals by low-temperature firing.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a metal oxide thin film formed in Example 1.

FIG. 2 is an X-ray diffraction diagram of a metal oxide thin film formed in Comparative Example 1.

FIG. 3 shows a voltage of a metal oxide thin film formed in Example 1.
It is a graph which shows a polarization curve.

FIG. 4 shows a voltage of a metal oxide thin film formed in Comparative Example 1.
It is a graph which shows a polarization curve.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Nobuyuki Soyama 12-6 Techno Park, Mita City, Hyogo Prefecture Mitsubishi Materials Corporation Mita Plant F-term (reference) 4G048 AA03 AB02 AC02 AD02 AD08 AE05 5G303 AA10 AB15 AB20 BA03 CA01 CB15 CB25 CB35 CB39 DA02

Claims (5)

[Claims] In a method of forming a Pb-based perovskite-type metal oxide thin film by applying a raw material solution for forming a metal oxide thin film to a substrate and then heating the solution to crystallize the metal oxide, A Pb-based perovskite-type metal oxide thin film, wherein the crystallization step is performed at least once so that the thickness of the metal oxide thin film formed in the crystallization step is 30 nm or less in thickness after crystallization. Formation method. 2. The method according to claim 1, wherein the Pb-based perovskite-type metal oxide thin film is composed of Pb and Zr and / or Ti.
A method for forming a Pb-based perovskite-type metal oxide thin film, which is a perovskite-type metal oxide thin film containing: 3. The method according to claim 1, wherein a coating film is formed by applying a raw material solution for forming a metal oxide thin film containing Pb and Ti to the substrate, and then Pb, Zr and A step of applying a raw material solution for forming a metal oxide thin film containing Ti to form a coating film
A method for forming a perovskite-type metal oxide thin film. 4. A method for forming a Pb-based perovskite-type metal oxide thin film according to claim 1, wherein a heating temperature for crystallization is 450 ° C. or less. 5. A Pb-based perovskite-type metal oxide thin film formed by the method for forming a Pb-based perovskite-type metal oxide thin film according to any one of claims 1 to 4.