JP2000344574A - Composition and method for forming pnzt ferroelectric thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition for forming a PNZT ferroelectric thin film excellent in storage stability for a long period of time and to provide a method for forming the same. SOLUTION: In a composition for forming a perovskite-type PNZT ferroelectric thin film, which contains metal alkoxides of Pb, Nb, Zr and Ti and partially hydrolyzed compounds of the alkoxides and/or organic acid salts of these metals, the number of particles having particle sizes of >=0.5 μm is controlled to be not more than 50 pieces/ml. The method for forming the PNZT ferroelectric thin film comprises repeating the process comprising applying the composition for forming the PNZT ferroelectric thin film onto a heat resistant base plate and then heating the coated material in air, or an oxidizing atmosphere or an atmosphere containing steam until a film having a desired thickness is obtained, and then firing the coated film at a temp. equal to or higher than the crystallization temp. in the final heating process of the above process or after heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PN which is expected to be applied to various devices due to its electrical or optical properties.
The present invention relates to a composition and a method for forming a ZT ferroelectric thin film.

[0002]

2. Description of the Related Art PNZT ferroelectric thin films are expected to be applied to various dielectric devices because of their excellent ferroelectric properties. As a method of forming the PNZT ferroelectric thin film, 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. As described in US Pat. Filing No. 09/061362, the sol-gel method applies a PNZT ferroelectric thin film forming composition comprising a solution of an organometallic compound to a substrate, hydrolyzes after application, and forms an oxide thin film. After that, it is a method of forming a ferroelectric thin film by firing and crystallization to form a ferroelectric thin film. As the organometallic compound as a raw material, a metal alkoxide, a partial hydrolyzate thereof, or an organic acid salt is generally used. .

[0003]

SUMMARY OF THE INVENTION Conventionally used P
When the composition for forming an NZT ferroelectric thin film is stored for a long period of time, particles increase due to a polymerization reaction in the solution,
There was a problem of generation of precipitation, and it could not be used stably for a long time.

[0004] The present invention solves the above-mentioned conventional problems, and provides a composition for forming a PNZT ferroelectric thin film having excellent long-term storage stability.
An object of the present invention is to provide a method for forming an NZT ferroelectric thin film.

[0005]

A composition for forming a PNZT ferroelectric thin film according to the present invention is a composition for forming a PNZT ferroelectric thin film comprising an organometallic compound solution for forming a perovskite-type PNZT ferroelectric thin film. In the above, a particle size of 0.
The amount of particles having a size of 5 μm or more is 50 particles / mL or less.

That is, the present inventors have conducted intensive studies to improve the long-term storage stability of the composition for forming a PNZT ferroelectric thin film, and as a result, have found that the composition for forming a PNZT ferroelectric thin film has an organometallic compound solution. Among them, the present inventors have found that by minimizing the number of initial particles serving as initial nuclei for the generation of sediment as much as possible, it is possible to drastically reduce the increase in the number of particles and the generation of sediment during long-term storage.

The method for forming a PNZT ferroelectric thin film according to the present invention comprises applying the composition for forming a PNZT ferroelectric thin film according to the present invention to a heat-resistant substrate, and applying the composition in air, an oxidizing atmosphere, or a steam-containing atmosphere. Repeating the step of heating until a film of a desired thickness is obtained, characterized in that the film is fired at or above the crystallization temperature at least during or after heating in the final step. , PNZT
Even after the ferroelectric thin film forming composition has been stored for a long period of time, a good PNZT ferroelectric thin film having a uniform and high film quality can be formed.

[0008]

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

The raw material of the organometallic compound used in the present invention is, specifically, a metal alkoxide of Pb, Nb, Zr or Ti, a partial hydrolyzate thereof and / or an organic acid salt. Organic acid salts such as lead acetate, and alkoxides such as lead diisopropoxide are exemplified. Ti
Examples of the compound include alkoxides such as titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide, and titanium dimethoxydiisopropoxide. As the Zr compound and the Nb compound, alkoxides similar to the above-mentioned Ti compound are preferable. The metal alkoxide may be used as it is, or its partial hydrolyzate may be used to accelerate the decomposition.

To prepare the composition for forming a PNZT ferroelectric thin film of the present invention, these starting organometallic compounds are dissolved in a suitable solvent at a ratio corresponding to the desired PNZT ferroelectric thin film composition. Adjust to a concentration suitable for application.

The solvent of the composition for forming a PNZT ferroelectric thin film used here is appropriately determined according to the starting organometallic compound, but is generally selected from carboxylic acids, alcohols, esters, ketones (for example, acetone). , Methyl ethyl ketone), ethers (eg, dimethyl ether, diethyl ether), cycloalkanes (eg, cyclohexane, cyclohexanol), aromatics (eg, benzene, toluene, xylene), tetrahydrofuran, and the like, or two or more of these Can be used.

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-dimethylpentane It is preferable to use an acid, 2-ethylhexanoic acid, or 3-ethylhexanoic acid.

Examples of the ester 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. It is preferable to use 1-propanol, 2-propanol, 1-butanol, 2-butanol, iso-butyl alcohol, 1-propanol.
It is preferable to use pentanol, 2-pentanol, 2-methyl-2-pentanol, and 2-methoxyethanol.

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

In this organometallic compound solution, if necessary, β-diketones (eg, acetylacetone, heptafluorobutanoylpivaloylmethane, dipivaloylmethane, trifluoroacetylacetone, benzoyl) may be used as a stabilizer. Acetone, etc.), ketone acids (eg, acetoacetic acid, propionylacetic acid, benzoylacetic acid, etc.), lower alkyl esters of these ketone acids such as methyl, propyl, butyl, etc., and oxyacids (eg, lactic acid, glycolic acid, α-oxy acid) Butyric acid, salicylic acid, etc.), lower alkyl esters of these oxyacids, oxyketones (eg, diacetone alcohol, acetoin, etc.), α-amino acids (eg, glycine, alanine, etc.), alkanolamines (eg, jetanol) Amine, triethanolamine, mono The ethanolamine) 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, the organometallic compound solution thus prepared is filtered to remove particles, and the number of particles having a particle size of 0.5 μm or more is 50 particles / mL or less per 1 mL of the solution. So that

When 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 number of particles having a particle size of 0.5 μm or more in this organometallic compound solution is preferably as small as possible, and particularly preferably 30 particles / mL or less.

The method for treating the prepared organometallic compound solution so that the number of particles is as described above is not particularly limited, but specific examples include the following methods. A filtration method in which a commercially available membrane filter having a pore size of 0.2 μm is used and the solution is pumped by a syringe. A pressure filtration method combining a commercially available membrane filter with a pore size of 0.05 μm and a pressure tank. A circulation filtration method combining the above filter and a solution circulation tank.

In any of the methods, the particle capture rate by the filter differs depending on the solution pressure.
It is generally known that the lower the pressure, the higher the trapping rate. In particular, in order to achieve the condition of 50 particles or less according to the present invention, it is necessary to pass the filter very slowly at a low pressure. There is. In the embodiments described later, the method of (1) does not realize 50 particles or less, but naturally the condition of the present invention can be achieved by lowering the pressure.

In order to form a PNZT ferroelectric thin film according to the method of the present invention from such a composition for forming a PNZT ferroelectric thin film, the above-described composition for forming a PNZT ferroelectric thin film of the present invention is spin-coated. Coat, dip coat, L
SMCD (Liquid Source Misted)
It is applied onto a substrate by a coating method such as a Chemical Deposition method, and is dried (temporarily baked) and baked.

As a specific example of the substrate used, monocrystalline Si, polycrystalline Si, Pt, Pt (top layer) / Ti, Pt (top layer) / Ta, Ru, RuO ₂ ,
Ru (top layer) / RuO ₂ , RuO ₂ (top layer) / Ru,
Perovskite-type conductivity such as 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} ) CoO ₃ A substrate using an oxide or the like can be given, but not limited thereto.

If the desired film thickness cannot be obtained by one coating, the steps of coating and drying are repeated a plurality of times, followed by main baking.

Here, the calcination is performed in air, in an oxidizing atmosphere, or in a steam-containing atmosphere since the calcination is performed to remove the solvent and hydrolyze the organic metal compound to convert it to a complex oxide. Even when heated in the air, the water required for hydrolysis is sufficiently ensured by the humidity in the air. This heating may be performed in two stages of low-temperature heating for removing the solvent and high-temperature heating for decomposing the organometallic compound.

The main baking is a step for baking the thin film obtained by the preliminary baking at a temperature higher than the crystallization temperature to crystallize, and thereby a PNZT ferroelectric thin film is obtained.

Generally, the calcination is performed at 150 to 550 ° C., and the main calcination is performed at 450 to 800 ° C.

[0026]

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

In the following Examples and Comparative Examples,
The following were used as organometallic compound raw materials. Pb compound: lead acetate trihydrate Nb compound: niobium pentaethoxide Zr compound: zirconium tetra-t-butoxide Ti compound: titanium tetraisopropoxide Examples 1-3, Comparative Examples 1-12 2-methoxyethanol as organic solvent Was used to dissolve an organic metal compound (Pb compound) in the form of acetate, and water was removed by azeotropic distillation. Thereafter, an alkoxide-type organometallic compound (Nb, Zr,
Ti compound) is added and dissolved, and acetylacetone is twice as much as the metal alkoxide in order to stabilize the solution.
In addition, a thin film forming solution having the composition shown in Table 1 was obtained. The total concentration of the organometallic compound in this solution was about 15% by weight in terms of metal oxide.

The obtained solution was filtered by the following method, and the number of particles having a particle size of 0.5 μm or more in the solution after the filtration was measured by a submerged particle counter. The results are shown in Table 1. Was. However, Comparative Example 1,
In Nos. 5 and 9, the number of particles was measured without filtering.

[Filtration method] A: 9: 1 mixture of the liquid filtered by the filtration method and the stock solution B: The filtration method C: The filtration method D: The filtration method Then, each solution is shielded from light at room temperature. When stored for a long time, the number of particles having a particle size of 0.5 μm or more in the solution is measured by a submerged particle counter,
The changes over time are shown in Table 1.

In Examples 1 to 3, each solution was stored for 3 months after filtration, and then a thin film was formed by the sol-gel method according to the following method.

That is, each solution was applied on a 6-inch silicon substrate by spin coating at 3000 rpm for 15 seconds. The film quality of the surface of the obtained coating film was confirmed by examining the presence or absence of striation by optical microscopic observation, and evaluated according to the following criteria. The results are shown in Table 1. ：: good △: almost good ×: bad Also, as described above, after application, drying was performed at 400 ° C. for 10 minutes. This application and drying were repeated four times, and then RTA (rapid) was performed in an oxygen atmosphere at 700 ° C. for 1 minute. By baking with a heat treatment device), a PNZT ferroelectric thin film having a thickness of 2800 ° was formed. The dielectric characteristics of the PNZT ferroelectric thin film at an applied voltage of 5 V were examined, and the results are shown in Table 1.

[0032]

[Table 1]

From Table 1, it can be seen that the storage stability can be maintained for more than 3 months by setting the number of initial particles (particles having a particle size of 0.5 μm or more) in the solution to 50 particles / mL or less. It can be seen that a composition for forming a PNZT ferroelectric thin film having excellent properties is provided. Further, by using such a composition for forming a PNZT ferroelectric thin film, a high-quality coating film can be formed even after long-term storage,
This shows that a PNZT ferroelectric thin film excellent in dielectric properties and its reproducibility can be formed.

[0034]

As described above in detail, according to the present invention, PN which has no problem of generation of precipitation and increase of particles even after long-term storage, has extremely good long-term storage stability, and has high practicality.
A composition for forming a ZT ferroelectric thin film is provided. By using such a composition for forming a PNZT ferroelectric thin film, a PNZT ferroelectric thin film having high quality and excellent dielectric properties can be formed with good reproducibility. it can.

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Claims (2)

[Claims] 1. A PNZT comprising an organometallic compound solution for forming a perovskite-type PNZT ferroelectric thin film
In the composition for forming a ferroelectric thin film, the number of particles having a particle size of 0.5 μm or more was 50 particles /
mL or less, a composition for forming a PNZT ferroelectric thin film. 2. The step of applying the composition for forming a PNZT ferroelectric thin film according to claim 1 to a heat-resistant substrate and heating the composition in air, an oxidizing atmosphere, or a water-containing atmosphere. A method of forming a PNZT ferroelectric thin film, wherein the film is fired at or above a crystallization temperature at least during or after heating in a final step.