JP2010206151A - Composition for ferroelectric thin film formation, method for ferroelectric thin film formation, and ferroelectric thin film formed by the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composition for ferroelectric thin film formation that has nearly the same relative permittivity with a conventional ferroelectric thin film and also has low leakage current density, and is suitable for use in a thin film capacitor with high capacity density, a method for ferroelectric thin film formation, and a ferroelectric thin film formed by the method. <P>SOLUTION: The composition for ferroelectric thin film formation is used in the formation of the ferroelectric thin film of one material selected from the group consisting of PLZT, PZT, and PT. The composition for ferroelectric thin film formation is a liquid composition for the formation of a thin film of a mixed composite metal oxide formed of a mixture of a composite metal oxide A represented by general formula (Pb<SB>x</SB>La<SB>y</SB>)(Zr<SB>z</SB>Ti<SB>(1-z)</SB>)O<SB>3</SB>(wherein 0.9<x<1.3, 0≤y<0.1, and 0≤z<0.9 are satisfied) with a composite oxide B containing Ce, and consists of an organic metal compound solution having the respective raw materials dissolved in an organic solvent at rates for imparting the metal atom ratio shown by the general formula. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a composition for forming a ferroelectric thin film suitable for use in a thin film capacitor having a high capacity density and a low leakage current density, a method for forming a ferroelectric thin film, and a ferroelectric thin film formed by the method. is there.

  As a method of manufacturing this type of ferroelectric film, a mixed solution in which each component metal alkoxide or organic acid salt is dissolved in a polar solvent is used. It is generally known to form a dielectric thin film by heating to a temperature equal to or higher than the crystallization temperature and firing (see, for example, Patent Documents 1 and 2).

  However, it has been confirmed that a PZT film, which is a typical ferroelectric substance, has a high leakage current density and a dielectric breakdown when a voltage is applied after being thinned.

  Therefore, attempts have been made to improve the leak characteristics by adding trace elements to a ferroelectric thin film such as a PZT film, but it has not been sufficient.

  Attempts have also been made to reduce the leakage current density by using a thick film, but in this case, there is a problem that the capacitance is lowered.

  As a countermeasure against the above-mentioned problem, it is possible to improve the non-doped PZT film having a relative dielectric constant of about 400 to about 700 by doping the PZT film having a thickness of about 1 μm with 1 at.% Cerium nitrate. Although it is shown that the relative dielectric constant is still low, it is an insufficient value for practical use (for example, see Non-Patent Document 1).

JP-A-60-236404 (page 3, lower right column, line 11 to page 4, lower left column, line 10; page 5, upper right column, line 10 to same page, lower left column, line 17) JP-A-8-153854 (Claim 1)

SB Majumder, DC Agrawal, YN Mohopatra, and RS Katiyar, "Effect of Cerium Doping on the Microstructure and Electrical Properties of Sol-Gel Derived Pb1.05 (Zr0.53-dCedTi0.47) O3 (d = 10at%) Thin Films ", Materials Science and Engineering, B98, 2003, pp.25-32 (Fig.2)

  If the thickness of the formed ferroelectric thin film is not sufficient, the leakage current density is high and there is a possibility of dielectric breakdown. Therefore, the performance as a capacitor could not be sufficiently exhibited.

  Further, if the film thickness is too thick, there is a problem that sufficient electrostatic capacity and relative dielectric constant cannot be obtained.

  An object of the present invention is a ferroelectric material suitable for high-capacity density thin film capacitor applications that has a relative dielectric constant comparable to that of a conventional ferroelectric thin film and a low leakage current density by a simple technique. An object of the present invention is to provide a composition for forming a thin body film, a method for forming a ferroelectric thin film, and a ferroelectric thin film formed by the method.

A first aspect of the present invention is a composition for forming a ferroelectric thin film for forming one kind of ferroelectric thin film selected from the group consisting of PLZT, PZT, and PT, and has a general formula: (Pb _x La _{y) (Zr z Ti (1} -z)) O 3 (0.9 <x <1.3,0 ≦ y <0.1,0 ≦ z composite metal oxide represented by <0.9) wherein A liquid composition for forming a thin film in the form of a mixed composite metal oxide in which a composite metal oxide B containing Ce is mixed with A, a raw material for forming the composite metal oxide A, and a composite metal oxide The raw material for composing the product B is composed of an organometallic compound solution dissolved in an organic solvent at a ratio that gives a metal atomic ratio represented by the above general formula.

  A second aspect of the present invention is an invention based on the first aspect, wherein the raw material for constituting the composite metal oxide A and the composite metal oxide B is an organic group via its oxygen or nitrogen atom. It is a compound that is bonded to a metal element.

  The third aspect of the present invention is the invention based on the second aspect, and the raw materials for constituting the composite metal oxide A and the composite metal oxide B are metal alkoxide, metal diol complex, metal triol complex. , A metal carboxylate, a metal β-diketonate complex, a metal β-diketoester complex, a metal β-iminoketo complex, and one or more selected from the group consisting of metal amino complexes.

  A fourth aspect of the present invention is an invention based on the first to third aspects, further comprising a β-diketone, β-ketone acid, β-ketoester, oxyacid, diol, triol, higher carboxylic acid, alkanolamine And further containing one or more stabilizers selected from the group consisting of polyamines in a proportion of 0.2 to 3 moles relative to 1 mole of the total amount of metals in the composition. Features.

  A fifth aspect of the present invention is the invention based on the first to fourth aspects, wherein the molar ratio B / A between B and A is 0 <B / A <0.05. To do.

  A sixth aspect of the present invention is the invention based on the fifth aspect, further characterized in that the molar ratio B / A between B and A is 0.005 ≦ B / A ≦ 0.03. .

  According to a seventh aspect of the present invention, there is provided a step of applying a ferroelectric thin film forming composition based on the first to sixth aspects to a heat resistant substrate and heating in air, an oxidizing atmosphere or a water-containing atmosphere. It is a method for forming a ferroelectric thin film characterized in that it is repeated once or until a film having a desired thickness is obtained, and the film is fired at a temperature equal to or higher than the crystallization temperature at least after heating in the final step.

  An eighth aspect of the present invention is a ferroelectric thin film formed by a method based on the seventh aspect.

  A ninth aspect of the present invention is a thin film capacitor having a ferroelectric thin film based on the eighth aspect, a capacitor, an IPD (Integrated Passive Device), a DRAM memory capacitor, a multilayer capacitor, a gate insulator of a transistor, and a nonvolatile memory , A pyroelectric infrared detecting element, a piezoelectric element, an electro-optical element, an actuator, a resonator, an ultrasonic motor, or an LC noise filter element.

  A tenth aspect of the present invention is a thin film capacitor having a ferroelectric thin film, a capacitor, an IPD, a DRAM memory capacitor, a multilayer capacitor, and a gate insulator of a transistor corresponding to a frequency band of 100 MHz or more based on the ninth aspect. , A composite electronic component of a nonvolatile memory, a pyroelectric infrared detection element, a piezoelectric element, an electro-optical element, an actuator, a resonator, an ultrasonic motor, or an LC noise filter element.

The composition for forming a ferroelectric thin film of the present invention has a general formula: (Pb _x La _y ) (Zr _z Ti _(1-z) ) O ₃ (where 0.9 <x <1.3, 0 ≦ y <0.1, 0 ≦ z <0.9) An organic metal compound solution so as to take the form of a mixed composite metal oxide in which a composite metal oxide A containing Ce is mixed with a composite metal oxide A represented by Ce The raw material for constituting the composite metal oxide A and the raw material for constituting the composite metal oxide B are dissolved in an organic solvent so as to have a predetermined ratio. By using this composition to form a ferroelectric thin film, it has the same dielectric constant as that of a conventional ferroelectric thin film, and a low leakage current density can be obtained. There is an advantage that a ferroelectric thin film suitable for the above can be obtained by a simple method. Therefore, when the leakage current density is about the same as that of the prior art, further thinning is possible, and a higher dielectric constant can be obtained.

  Next, the form for implementing this invention is demonstrated.

The composition for forming a ferroelectric thin film of the present invention is a composition for forming one kind of ferroelectric thin film selected from the group consisting of PLZT, PZT and PT. A ferroelectric thin film formed using this composition has a general formula: (Pb _x La _y ) (Zr _z Ti _(1-z) ) O ₃ (where 0.9 <x <1.3, 0 It takes the form of mixed composite metal oxide in which composite metal oxide A represented by ≦ y <0.1, 0 ≦ z <0.9) is mixed with composite metal oxide B containing Ce. In the above equation, when y ≠ 0 and z ≠ 0, it is PLZT, when y = 0 and z ≠ 0, it is PZT, and when y = 0 and z = 0, it is PT. This composition is organic so that the raw material for constituting the composite metal oxide A and the raw material for constituting the composite metal oxide B have a ratio that gives the metal atomic ratio represented by the above general formula. It consists of an organometallic compound solution dissolved in a solvent.

  The raw material for composite metal oxide A and the raw material for composite metal oxide B is preferably a compound in which an organic group is bonded to each metal element of Pb, La, Zr, Ti and Ce via its oxygen or nitrogen atom. It is. For example, one kind selected from the group consisting of metal alkoxide, metal diol complex, metal triol complex, metal carboxylate, metal β-diketonate complex, metal β-diketoester complex, metal β-iminoketo complex, and metal amino complex Or 2 or more types are illustrated. Particularly suitable compounds are metal alkoxides, partial hydrolysates thereof, and organic acid salts. Among these, as Pb compound, La compound, and Ce compound, organic acid salts such as acetate (lead acetate, lanthanum acetate), cerium 2-ethylhexanoate, cerium 2-ethylbutyrate, lead diisopropoxide, cerium tri-n -Alkoxides such as butoxide and cerium triethoxide, and metal β-diketonate complexes such as tris (acetylacetonate) cerium. Examples of the Ti compound include alkoxides such as titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide, and titanium dimethoxydiisopropoxide. The Zr compound is preferably an alkoxide similar to the Ti compound. Although the metal alkoxide may be used as it is, a partially hydrolyzed product thereof may be used in order to promote decomposition.

  In order to prepare the composition for forming a ferroelectric thin film of the present invention, these raw materials are dissolved in an appropriate solvent at a ratio corresponding to the desired ferroelectric thin film composition, and prepared to a concentration suitable for coating.

  The molar ratio B / A between B and A is adjusted to be in the range of 0 <B / A <0.05. Within the above range, it is possible to obtain a specific dielectric constant comparable to that of the conventional ferroelectric thin film, which is the effect of the present invention, and a low leakage current density. If the upper limit value is exceeded, there will be a problem of deterioration of the relative dielectric constant. Among these, 0.005 ≦ B / A ≦ 0.03 is particularly preferable.

  The solvent for the composition for forming a ferroelectric thin film used here is appropriately determined according to the raw material to be used. Generally, carboxylic acid, alcohol, ester, ketones (for example, acetone, methyl ethyl ketone), ether (E.g., dimethyl ether, diethyl ether), cycloalkanes (e.g., cyclohexane, cyclohexanol), aromatics (e.g., benzene, toluene, xylene), other tetrahydrofuran, or a mixture of two or more of these be able to.

  Specific examples of the carboxylic acid 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-dimethylpentanoic acid, 2- It is preferable to use ethylhexanoic acid or 3-ethylhexanoic acid.

  As the ester, ethyl acetate, propyl acetate, n-butyl acetate, sec-butyl acetate, tert-butyl acetate, isobutyl acetate, n-amyl acetate, sec-amyl acetate, tert-amyl acetate, isoamyl acetate are used. As the alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, iso-butyl alcohol, 1-pentanol, 2-pentanol, 2-methyl-2-pentanol, 2-methoxy It is preferred to use ethanol.

  The total concentration of the organometallic compound in the organometallic compound solution of the ferroelectric thin film forming composition is preferably about 0.1 to 20% by mass in terms of metal oxide.

  In this organometallic compound solution, β-diketones (for example, acetylacetone, heptafluorobutanoylpivaloylmethane, dipivaloylmethane, trifluoroacetylacetone, benzoylacetone, etc.) are used as stabilizers as necessary. , Β-ketone acids (for example, acetoacetic acid, propionylacetic acid, benzoylacetic acid, etc.), β-ketoesters (for example, lower alkyl esters such as methyl, propyl, and butyl of the above ketone acids), oxyacids (for example, lactic acid, Glycolic acid, α-oxybutyric acid, salicylic acid, etc.), lower alkyl esters of the above oxyacids, oxyketones (eg, diacetone alcohol, acetoin, etc.), diols, triols, higher carboxylic acids, alkanolamines (eg, diethanolamine, Triethanolamine, Roh ethanolamine), a polyvalent amine or the like, may be added from 0.2 to 3 approximately at (stabilizer number of molecules) / (number of metal atoms).

  In the present invention, particles are removed from the prepared organometallic compound solution by filtration or the like, and the number of particles having a particle size of 0.5 μm or more (especially 0.3 μm or more, especially 0.2 μm or more) per 1 mL of the solution. It is preferable to be 50 / mL or less.

  A light scattering particle counter is used for measuring the number of particles in the organometallic compound solution.

  If the number of particles having a particle size of 0.5 μm or more in the organometallic compound solution exceeds 50 particles / mL, the long-term storage stability becomes poor. The smaller the number of particles having a particle size of 0.5 μm or more in this organometallic compound solution, the more preferable, and particularly preferably 30 particles / mL or less.

  The method for treating the organometallic compound solution after preparation so as to achieve the number of particles is not particularly limited, and examples thereof include the following method. The first method is a filtration method in which a commercially available membrane filter having a pore size of 0.2 μm is used and pressure-fed with a syringe. The second method is a pressure filtration method in which a commercially available membrane filter having a pore size of 0.05 μm and a pressure tank are combined. The third method is a circulation filtration method in which the filter used in the second method and the solution circulation tank are combined.

  In any method, the particle capture rate by the filter varies depending on the solution pressure. It is generally known that the lower the pressure, the higher the capture rate. In particular, in the first method and the second method, the number of particles having a particle size of 0.5 μm or more is set to 50 or less. In order to achieve, it is preferable to pass the solution through the filter very slowly at low pressure.

  By using the composition for forming a ferroelectric thin film of the present invention, a mixed metal oxide B containing Ce is mixed with one kind of mixed metal oxide A selected from the group consisting of PLZT, PZT, and PT. A ferroelectric thin film in the form of a composite metal oxide can be easily formed.

  In order to form a ferroelectric thin film by using the composition for forming a ferroelectric thin film of the present invention, the composition is heat-resistant by a coating method such as spin coating, dip coating, or LSMCD (Liquid Source Misted Chemical Deposition). It apply | coats on a board | substrate and performs drying (temporary baking) and main baking.

As a specific example of the heat-resistant substrate to be used, the surface layer portion of the substrate includes single crystal Si, polycrystal Si, Pt, Pt (top layer) / Ti, Pt (top layer) / Ta, Ru, RuO ₂ , Ru ( Top layer) / RuO ₂ , RuO ₂ (top layer) / Ru, Ir, IrO ₂ , Ir (top layer) / IrO ₂ , Pt (top layer) / Ir, Pt (top layer) / IrO ₂ , SrRuO ₃ or _{(La x Sr (1-x} )) is a substrate with CoO ₃ perovskite-type conductive oxide such like, but not limited thereto.

  In addition, when a desired film thickness cannot be obtained by one application, the application and drying steps are repeated a plurality of times, followed by firing. Here, the desired film thickness refers to the thickness of the ferroelectric thin film obtained after the main firing, and in the case of a high capacity density thin film capacitor, the film thickness of the ferroelectric thin film after the main firing is 50 to 500 nm. Range.

  In addition, the preliminary calcination is performed in order to remove the solvent and thermally decompose or hydrolyze the organometallic compound to convert it into a composite oxide. Therefore, the calcination is performed in air, in an oxidizing atmosphere, or in a steam-containing atmosphere. Even in heating in the air, the moisture required for hydrolysis is sufficiently secured by the humidity in the air. This heating may be performed in two stages: low temperature heating for removing the solvent and high temperature heating for decomposing the organometallic compound.

The main firing is a step for firing and crystallizing the thin film obtained by the pre-firing at a temperature equal to or higher than the crystallization temperature, whereby a ferroelectric thin film is obtained. The firing atmosphere in this crystallization step is preferably O ₂ , N ₂ , Ar, N ₂ O, H _2, or a mixed gas thereof.

  The pre-baking is performed at 150 to 550 ° C. for about 5 to 10 minutes, and the main baking is performed at 450 to 800 ° C. for about 1 to 60 minutes. The main baking may be performed by rapid heating treatment (RTA treatment). When the main baking is performed by the RTA treatment, the heating rate is preferably 10 to 100 ° C./second.

  The ferroelectric thin film of the present invention formed in this way has a relative dielectric constant comparable to that of a conventional ferroelectric thin film, and a low leakage current density can be obtained. Suitable for use. Therefore, when the leakage current density is about the same as that of the conventional ferroelectric thin film, further thinning is possible, a higher capacity density is obtained, and the basic characteristics as a capacitor are excellent. Further, by using a thin film, there is another advantage that the use of raw materials can be reduced. The ferroelectric thin film of the present invention is also excellent in basic characteristics as an IPD.

  The ferroelectric thin film of the present invention includes a thin film capacitor, a capacitor, an IPD, a DRAM memory capacitor, a multilayer capacitor, a transistor gate insulator, a nonvolatile memory, a pyroelectric infrared detection element, a piezoelectric element, an electro-optical element, It can be used as a constituent material in composite electronic parts of actuators, resonators, ultrasonic motors, or LC noise filter elements. Among these, it can also be used especially for the thing corresponding to the frequency band of 100 MHz or more.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Examples 1-5>
First, zirconium tetra-n-butoxide and acetylacetone as a stabilizer were added to a reaction vessel, and refluxed at a temperature of 150 ° C. in a nitrogen atmosphere. Titanium tetraisopropoxide and acetylacetone as a stabilizer were added thereto and refluxed at a temperature of 150 ° C. in a nitrogen atmosphere. Next, lead acetate trihydrate and propylene glycol as a solvent were added thereto and refluxed at a temperature of 150 ° C. in a nitrogen atmosphere. Thereafter, the by-product was removed by distillation under reduced pressure at 150 ° C., and further, propylene glycol was added and the concentration was adjusted to obtain a liquid containing a 30% by mass metal compound in terms of oxide. Furthermore, by adding diluted alcohol, a sol-gel solution containing a metal compound having a concentration of 10% by mass with a metal ratio of Pb / Zr / Ti = 110/52/48 in terms of oxide was obtained.

  Next, the sol-gel solution is divided into five equal parts, and 0.5 mol% of various cerium compounds (cerium 2-ethylhexanoate, cerium 2-ethylbutyrate, cerium triethoxide, cerium tri-n-butoxide) are divided into these sol-gel solutions. , Tris (acetylacetonate) cerium) were added to obtain 5 types of thin film forming solutions.

Using these five types of thin film forming solutions, thin films were formed by the CSD method by the following method. That is, a 6-inch silicon substrate (Pt / TiO ₂ / SiO ₂ / Si (100) on which a Pt thin film was formed on the surface by a spin coating method at 500 rpm for 3 seconds and then at 3000 rpm for 15 seconds. ) Substrate). Subsequently, using a hot plate, heating was performed at 350 ° C. for 5 minutes to perform temporary baking. This coating and pre-baking process was repeated 6 times, and then baked with an RTA (rapid heat treatment apparatus) at 700 ° C. for 1 minute in a 100% oxygen atmosphere to form a 270 nm thick ferroelectric thin film.

<Examples 6 to 10>
A ferroelectric thin film was formed on the substrate in the same manner as in Examples 1 to 5, except that 1.0 mol% of various cerium compounds were added to the sol-gel solution to obtain a thin film forming solution.

<Examples 11 to 15>
A ferroelectric thin film was formed on the substrate in the same manner as in Examples 1 to 5 except that 3.0 mol% of various cerium compounds were added to the sol-gel solution to obtain a thin film forming solution.

<Example 16>
Other than adding 1.0 mol% of lanthanum compound (lanthanum acetate hemihydrate) and 1.0 mol% of cerium compound (cerium 2-ethylhexanoate) to the sol-gel solution to make a thin film forming solution In the same manner as in Examples 1 to 5, a ferroelectric thin film was formed on the substrate.

<Example 17>
Except for adding 1.0 mol% lanthanum compound (lanthanum acetate hemihydrate) and 1.0 mol% cerium compound (cerium triethoxide) to the sol-gel solution, A ferroelectric thin film was formed on the substrate in the same manner as in Examples 1-5.

<Comparative Example 1>
A ferroelectric thin film was formed on the substrate in the same manner as in Examples 1 to 5 except that the cerium compound was not added to the sol-gel solution and the solution was used for forming a thin film.

<Comparative example 2>
Example 1 except that no cerium compound was added to the sol-gel solution, and instead 1.0 mol% of a lanthanum compound (lanthanum acetate hemihydrate) was added to form a thin film forming solution. In the same manner as in 5, a ferroelectric thin film was formed on the substrate.

<Examples 18 to 22>
First, zirconium tetra n-butoxide and diethanolamine as a stabilizer were added to a reaction vessel, and the mixture was refluxed at a temperature of 150 ° C. in a nitrogen atmosphere. Titanium tetraisopropoxide and diethanolamine as a stabilizer were added thereto, and the mixture was refluxed at a temperature of 150 ° C. in a nitrogen atmosphere. Next, lead acetate trihydrate and propylene glycol as a solvent were added thereto and refluxed at a temperature of 150 ° C. in a nitrogen atmosphere. Thereafter, the by-product was removed by distillation under reduced pressure at 150 ° C., and further, propylene glycol was added and the concentration was adjusted to obtain a liquid containing a 30% by mass metal compound in terms of oxide. Furthermore, by adding diluted alcohol, a sol-gel solution containing a metal compound having a concentration of 10% by mass with a metal ratio of Pb / Zr / Ti = 110/52/48 in terms of oxide was obtained.

  Next, the sol-gel solution is divided into five equal parts, and 0.5 mol% of various cerium compounds (cerium 2-ethylhexanoate, cerium 2-ethylbutyrate, cerium triethoxide, cerium tri-n-butoxide) are divided into these sol-gel solutions. , Tris (acetylacetonate) cerium) were added to obtain 5 types of thin film forming solutions.

Using these five types of thin film forming solutions, thin films were formed by the CSD method by the following method. That is, a 6-inch silicon substrate (Pt / TiO ₂ / SiO ₂ / Si (100) on which a Pt thin film was formed on the surface by a spin coating method at 500 rpm for 3 seconds and then at 3000 rpm for 15 seconds. ) Substrate). Subsequently, using a hot plate, heating was performed at 350 ° C. for 5 minutes to perform temporary baking. This coating and pre-baking process was repeated 6 times, and then baked with an RTA (rapid heat treatment apparatus) at 700 ° C. for 1 minute in a 100% oxygen atmosphere to form a 270 nm thick ferroelectric thin film.

<Examples 23 to 27>
A ferroelectric thin film was formed on the substrate in the same manner as in Examples 18 to 22 except that 1.0 mol% of various cerium compounds were added to the sol-gel solution to obtain a thin film forming solution.

<Examples 28 to 32>
A ferroelectric thin film was formed on the substrate in the same manner as in Examples 18 to 22, except that 3.0 mol% of various cerium compounds were added to the sol-gel solution to obtain a thin film forming solution.

<Example 33>
Other than adding 1.0 mol% of lanthanum compound (lanthanum acetate hemihydrate) and 1.0 mol% of cerium compound (cerium 2-ethylhexanoate) to the sol-gel solution to make a thin film forming solution In the same manner as in Examples 18 to 22, a ferroelectric thin film was formed on a substrate.

<Example 34>
Except for adding 1.0 mol% lanthanum compound (lanthanum acetate hemihydrate) and 1.0 mol% cerium compound (cerium triethoxide) to the sol-gel solution, A ferroelectric thin film was formed on the substrate in the same manner as in Examples 18-22.

<Comparative Example 3>
A ferroelectric thin film was formed on the substrate in the same manner as in Examples 18 to 22, except that the sol-gel solution was not added with a cerium compound and used as a thin film forming solution.

<Comparative example 4>
Except that the cerium compound was not added to the sol-gel solution, and instead, 1.0 mol% of lanthanum compound (lanthanum acetate hemihydrate) was added to obtain a solution for forming a thin film. In the same manner as in No. 22, a ferroelectric thin film was formed on the substrate.

<Examples 35 to 39>
First, zirconium tetra-n-butoxide and acetylacetone as a stabilizer were added to a reaction vessel, and refluxed at a temperature of 150 ° C. in a nitrogen atmosphere. Titanium tetraisopropoxide and acetylacetone as a stabilizer were added thereto and refluxed at a temperature of 150 ° C. in a nitrogen atmosphere. Next, lead acetate trihydrate and propylene glycol as a solvent were added thereto and refluxed at a temperature of 150 ° C. in a nitrogen atmosphere. Thereafter, the by-product was removed by distillation under reduced pressure at 150 ° C., and further, propylene glycol was added and the concentration was adjusted to obtain a liquid containing a 30% by mass metal compound in terms of oxide. Furthermore, by adding diluted alcohol, a sol-gel solution containing a metal compound having a concentration of 10% by mass with a metal ratio of Pb / Zr / Ti = 110/52/48 in terms of oxide was obtained.

  Next, the sol-gel solution is divided into five equal parts, and 0.5 mol% of various cerium compounds (cerium 2-ethylhexanoate, cerium 2-ethylbutyrate, cerium triethoxide, cerium tri-n-butoxide) are divided into these sol-gel solutions. , Tris (acetylacetonate) cerium) were added to obtain 5 types of thin film forming solutions.

Using these five types of thin film forming solutions, thin films were formed by the CSD method by the following method. That is, a 6-inch silicon substrate (Pt / TiO ₂ / SiO ₂ / Si (100) on which a Pt thin film was formed on the surface by a spin coating method at 500 rpm for 3 seconds and then at 3000 rpm for 15 seconds. ) Substrate). Subsequently, using a hot plate, heating was performed at 350 ° C. for 5 minutes to perform temporary baking. This coating and pre-baking process was repeated 6 times, and then a 270 nm thick ferroelectric thin film was formed by baking at 700 ° C. for 1 minute in a dry air atmosphere with an RTA (rapid heat treatment apparatus).

<Examples 40 to 44>
A ferroelectric thin film was formed on the substrate in the same manner as in Examples 35 to 39 except that 1.0 mol% of various cerium compounds were added to the sol-gel solution to obtain a thin film forming solution.

<Examples 45-49>
A ferroelectric thin film was formed on the substrate in the same manner as in Examples 35 to 39 except that 3.0 mol% of various cerium compounds were added to the sol-gel solution to obtain a thin film forming solution.

<Example 50>
Other than adding 1.0 mol% of lanthanum compound (lanthanum acetate hemihydrate) and 1.0 mol% of cerium compound (cerium 2-ethylhexanoate) to the sol-gel solution to make a thin film forming solution A ferroelectric thin film was formed on the substrate in the same manner as in Examples 35-39.

<Example 51>
Except for adding 1.0 mol% lanthanum compound (lanthanum acetate hemihydrate) and 1.0 mol% cerium compound (cerium triethoxide) to the sol-gel solution, In the same manner as in Examples 35 to 39, a ferroelectric thin film was formed on the substrate.

<Comparative Example 5>
A ferroelectric thin film was formed on the substrate in the same manner as in Examples 35 to 39 except that a cerium compound was not added to the sol-gel solution and a thin film forming solution was used.

<Comparative Example 6>
Except that the cerium compound was not added to the sol-gel solution, instead of adding 1.0 mol% of a lanthanum compound (lanthanum acetate hemihydrate) to obtain a solution for forming a thin film, Example 35 to Example 35 In the same manner as in 39, a ferroelectric thin film was formed on the substrate.

<Comparison evaluation>
About the board | substrate which formed the ferroelectric thin film obtained in Examples 1-51 and Comparative Examples 1-6, about 250 micrometers square Pt upper electrode was produced with the sputtering method on the surface, and the ferroelectric A DC voltage was applied between the Pt lower electrodes immediately below the thin film, and the IV characteristics (voltage dependence of leakage current density) were evaluated. Also, CV characteristics (voltage dependence of capacitance) are evaluated in the range of -5 to 5 V at a frequency of 1 kHz between the Pt lower electrodes directly below the ferroelectric thin film, and the ratio is compared with the maximum value of capacitance The dielectric constant εr was calculated. The results are shown in the following Tables 1 to 3, respectively. The IV characteristics were measured using a 236 SMU manufactured by Keithley under the conditions of bias step 0.5 V, delay time 0.1 sec, temperature 23 ° C., and hygrometry 50 ± 10%. In addition, for measurement of the CV characteristics, 4284A precision LCR meter manufactured by HP was used, Bias step 0.1V, Frequency 1 kHz, Oscillation level 30 mV, Delay time 0.2 sec, Temperature 23 ° C., Hygrometer 10 ° C. Measured under conditions.

表１〜表３から明らかなように、Ｃｅを添加した実施例１〜５１の強誘電体薄膜では、２７０ｎｍ程度の薄い膜厚で、Ｃｅを含まない比較例１〜６のＰＺＴ強誘電体薄膜よりも低いリーク電流密度を得ることができた。

As is clear from Tables 1 to 3, in the ferroelectric thin films of Examples 1 to 51 to which Ce was added, the PZT ferroelectric thin film of Comparative Examples 1 to 6 having a thin film thickness of about 270 nm and not containing Ce. A lower leakage current density could be obtained.

  Further, in comparison with the PLZT ferroelectric thin films of Comparative Examples 2, 4, and 6 containing La, it was confirmed that the leakage current density was reduced when 5V was applied and when 20V was applied.

  In addition, regarding the capacitance and relative dielectric constant, the ferroelectric thin films of Examples 1 to 51 were slightly lower in numerical values than the ferroelectric thin films of Comparative Examples 1 to 6, but overall The result is not inferior, and it can be said that a numerical value comparable to the conventionally known ferroelectric thin film was obtained.

  However, when the ferroelectric thin film of Examples 1 to 51 is set to a level of leakage current density comparable to that of the ferroelectric thin film of Comparative Examples 1 to 6, further thinning is possible and the thinning is achieved. Thus, there is an advantage that a higher relative dielectric constant can be obtained.

  From these results, the ferroelectric thin films of Examples 1 to 51 have an excellent effect of reducing the leakage current density without reducing the relative dielectric constant, and can be made thin. Capacity density can be achieved.

  Composition for forming ferroelectric thin film, method for forming ferroelectric thin film, and ferroelectric thin film formed by the method of the present invention are excellent in basic characteristics as a capacitor, and have a high density and a high breakdown voltage. Is available. In addition, it has excellent basic characteristics as an IPD. IPD, DRAM memory capacitor, multilayer capacitor, transistor gate insulator, nonvolatile memory, pyroelectric infrared detector, piezoelectric element, electro-optical element, actuator, resonator It can be used for composite electronic parts such as ultrasonic motors or LC noise filter elements.

Claims (10)

In the ferroelectric thin film forming composition for forming one kind of ferroelectric thin film selected from the group consisting of PLZT, PZT and PT,
General formula: (Pb _x La _y ) (Zr _z Ti _(1-z) ) O ₃ (where 0.9 <x <1.3, 0 ≦ y <0.1, 0 ≦ z <0.9) A liquid composition for forming a thin film in the form of a mixed composite metal oxide in which a composite metal oxide B containing Ce is mixed with the composite metal oxide A represented by
The organic material dissolved in the organic solvent at such a ratio that the raw material for constituting the composite metal oxide A and the raw material for constituting the composite metal oxide B give the metal atomic ratio represented by the above general formula A composition for forming a ferroelectric thin film comprising a metal compound solution.   2. The ferroelectric thin film formation according to claim 1, wherein the raw material for constituting the composite metal oxide A and the composite metal oxide B is a compound in which an organic group is bonded to a metal element via its oxygen or nitrogen atom. Composition.   The raw materials for constituting the composite metal oxide A and the composite metal oxide B are metal alkoxide, metal diol complex, metal triol complex, metal carboxylate, metal β-diketonate complex, metal β-diketoester complex, metal β The composition for forming a ferroelectric thin film according to claim 2, wherein the composition is one or more selected from the group consisting of an iminoketo complex and a metal amino complex.   Composition of one or more stabilizers selected from the group consisting of β-diketone, β-ketone acid, β-ketoester, oxyacid, diol, triol, higher carboxylic acid, alkanolamine and polyvalent amine The composition for forming a ferroelectric thin film according to any one of claims 1 to 3, further comprising 0.2 to 3 moles per mole of the total amount of metals in the product.   The composition for forming a ferroelectric thin film according to any one of claims 1 to 4, wherein a molar ratio B / A between B and A is 0 <B / A <0.05.   6. The composition for forming a ferroelectric thin film according to claim 5, wherein the molar ratio B / A between B and A is 0.005 ≦ B / A ≦ 0.03.   The process for applying the ferroelectric thin film forming composition according to any one of claims 1 to 6 to a heat resistant substrate and heating in air, in an oxidizing atmosphere or in a steam-containing atmosphere once or in a desired manner A method for forming a ferroelectric thin film, which is repeated until a film having a thickness is obtained, and the film is fired at a temperature equal to or higher than a crystallization temperature at least during or after heating in the final step.   A ferroelectric thin film formed by the method according to claim 7.   A thin film capacitor having a ferroelectric thin film according to claim 8, a capacitor, an IPD, a DRAM memory capacitor, a multilayer capacitor, a gate insulator of a transistor, a nonvolatile memory, a pyroelectric infrared detection element, a piezoelectric element, an electro-optical element, Composite electronic components of actuators, resonators, ultrasonic motors, or LC noise filter elements.   A thin film capacitor having a ferroelectric thin film, a capacitor, an IPD, a capacitor for DRAM memory, a multilayer capacitor, a transistor gate insulator, a non-volatile memory, a pyroelectric infrared, corresponding to a frequency band of 100 MHz or more according to claim 9 A composite electronic component including a detection element, a piezoelectric element, an electro-optical element, an actuator, a resonator, an ultrasonic motor, or an LC noise filter element.