JP3107084B1 - Composition for forming ferroelectric thin film and method for forming ferroelectric thin film - Google Patents

Abstract

A perovskite-type PLZT ferroelectric thin film having a uniform surface morphology and excellent electrical property uniformity is formed. A composition for forming a ferroelectric thin film comprising a metal compound solution for forming a perovskite-type PLZT ferroelectric thin film, wherein the composition contains hydroxydimethylacetophenone in the solution.
The composition for forming a ferroelectric thin film is applied to a heat-resistant substrate, calcined, and fired to form a ferroelectric thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition for forming a ferroelectric thin film and a method for forming a ferroelectric thin film, and more particularly, to a perovskite type which is expected to be applied to various devices due to its electrical or optical properties. PLZT ferroelectric thin film with crystal structure (eg, PT thin film, PZT thin film, PLZT thin film)
The present invention relates to a composition for forming a ferroelectric thin film for forming a thin film and a method for forming a ferroelectric thin film using the composition for forming a ferroelectric thin film.

[0002]

2. Description of the Prior Art Lead zirconate titanate (PZT) and P
PLZT in which ZT is further doped with lanthanum is expected to be applied to various dielectric devices because of its high dielectric constant and excellent ferroelectric properties.

As a method for forming the PLZT ferroelectric thin film, there are a sputtering method, an MOCVD method and the like, and a sol-gel method is a relatively inexpensive and simple method for forming a thin film.
The sol-gel method is a method of forming a ferroelectric thin film by applying a solution of an organometallic compound and an inorganic compound to a substrate, hydrolyzing the coating to form an oxide thin film, and then firing and crystallizing the oxide thin film. As raw material organometallic compounds,
Generally, metal alkoxides and organic acid salts are used.

[0004]

The PLZT ferroelectric thin film formed by the conventional sol-gel method has a disadvantage that the particle size of the thin film forming particles is not uniform. That is, P
The LZT ferroelectric thin film generally has a non-uniform surface morphology divided into a perovskite coarse particle region and a zirconia fine particle region having a particle diameter of about 1000 nm. In the case of such a thin film having a non-uniform surface morphology, the electric characteristics are also non-uniform depending on the location, which is an obstacle to producing a fine capacitor.

The present invention solves the above-mentioned conventional problems, and provides a PLZT having a uniform surface state and excellent electrical property uniformity.
An object of the present invention is to provide a composition for forming a ferroelectric thin film capable of forming a ferroelectric thin film and a method for forming a ferroelectric thin film using the composition for forming a ferroelectric thin film.

[0006]

The composition for forming a ferroelectric thin film according to the present invention is a composition for forming a ferroelectric thin film comprising an organometallic compound solution for forming a perovskite-type PLZT ferroelectric thin film. The solution is characterized by containing hydroxydimethylacetophenone.

The method for forming a ferroelectric thin film of the present invention includes a step of applying the composition for forming a ferroelectric thin film to a heat-resistant substrate and heating the composition in air, an oxidizing atmosphere, or a steam-containing atmosphere. The process is repeated until a film having a thickness is obtained, and the film is fired at a crystallization temperature or higher at least during or after heating in the final step.

That is, the present inventors have studied the component compositions of various organic metal compound solutions for the purpose of improving the surface morphology of the formed ferroelectric thin film. The present inventors have found that when hydroxydimethylacetophenone is added to a compound solution, a drastic improvement in the surface morphology of the formed ferroelectric thin film is recognized, and the present invention has been achieved.

In the present invention, the content of hydroxydimethylacetophenone in the starting organometallic compound solution is 10%.
5,000 ppm, preferably 500-500 ppm.
It is preferably 3000 ppm.

[0010]

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

In the present invention, a ferroelectric thin film forming composition is formed by a conventional method except that a predetermined amount of hydroxydimethylacetophenone is added to the organometallic compound solution of the ferroelectric thin film forming composition. Preparation and formation of a ferroelectric thin film can be performed.

Examples of the starting organic metal compound include a metal alkoxide constituting a ferroelectric thin film, a partial hydrolyzate thereof, and an organic acid salt.

Specifically, examples of the lead compound and the lanthanum compound include organic acid salts such as acetates (lead acetate and lanthanum acetate) and alkoxides such as lead diisopropoxide. Examples of the titanium compound include alkoxides such as titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide, and titanium dimethoxydiisopropoxide. As the zirconium compound, alkoxides similar to the above-mentioned titanium compounds 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 ferroelectric thin film of the present invention, a raw material organometallic compound is dissolved in a suitable solvent in a ratio corresponding to a desired ferroelectric thin film composition, and the composition is suitable for coating. Adjust to a concentration that is

In the present invention, hydroxydimethylacetophenone is added to the organometallic compound solution of the composition for forming a ferroelectric thin film. The timing of addition of the hydroxydimethylacetophenone is not particularly limited, and may be added together with the organometallic compound when the organometallic compound is dissolved in the solvent or separately from the organometallic compound in preparing the organometallic compound solution. Further, the organic metal compound may be added to a solvent before the addition, or may be added to a solution after dissolving the organic metal compound.

If the content of hydroxydimethylacetophenone in the obtained organometallic compound solution is too small, the effect of improving the surface morphology due to the addition thereof cannot be sufficiently obtained, and if it is too large, the thermal decomposition characteristics of the solution are impaired. Or
Since the surface morphology starts to deteriorate, this content is 10
It is preferably from 5000 to 5000 ppm, particularly preferably from 500 to 3000 ppm.

The solvent of the composition for forming a ferroelectric thin film is appropriately determined according to the organometallic compound used.
In general, carboxylic acids, alcohols, esters, ketones (eg, acetone, methyl ethyl ketone), ethers (eg, dimethyl ether, diethyl ether), cycloalkanes (eg, cyclohexane, cyclohexanol), aromatic compounds (eg, Benzene, toluene, xylene), tetrahydrofuran or the like, or a mixed solvent of two or more thereof.

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 ferroelectric thin film is preferably about 0.1 to 20% by weight in terms of metal oxide.

To form the ferroelectric thin film of the present invention, the above-described composition for forming a ferroelectric thin film of the present invention is spin-coated, dip-coated, LSMCD (Liquid So
source Misted Chemical Depo
The composition is applied onto a heat-resistant substrate by a coating method such as a method of drying (pre-firing) and main firing.

Specific examples of the heat-resistant substrate used include:
Monocrystalline Si, polycrystalline Si, Pt, Pt
(Top layer) / Ti, Pt (top layer) / Ta, Ru, Ru
O 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 , SrR
Substrates using a perovskite-type conductive oxide such as uO ₃ or (La _x Sr _1-x ) CoO ₃ are exemplified, 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 firing.

Here, the calcination is performed in air, in an oxidizing atmosphere, or in a steam-containing atmosphere because the calcination is performed to remove the solvent and hydrolyze the organometallic 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 firing is a process for firing the thin film obtained by the preliminary firing at a temperature higher than the crystallization temperature to crystallize the thin film, thereby obtaining a ferroelectric thin film.

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

[0027]

The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples unless it exceeds the gist.

[0028] Examples 1-10, Comparative Examples 1 and 2 lead acetate trihydrate _{(Pb (O-Ac) 2} · 3H 2 O) and lanthanum acetate 1.5 hydrate (La (O-Ac) ₃・ 1.5H ₂
O) was dissolved in 2-methoxyethanol, and water was removed by azeotropic distillation. In addition, zirconium tetratertiary butoxide [Zr (Ot-Bu) ₄ ] and titanium tetraisopropoxide (Ti (Oi-Pr) ₄ )
Was further added, and a predetermined amount of hydroxydimethylacetophenone was added to obtain a raw material organometallic compound solution (however, in Comparative Examples 1 and 2, hydroxydimethylacetophenone was not added). The total concentration of the organometallic compound in the starting organometallic compound was about 10% by weight in terms of oxide, and the content of hydroxydimethylacetophenone was as shown in Table 1.
As shown in FIG.

The composition for forming a ferroelectric thin film is made of Pt / S
It was applied on an iO ₂ / Si substrate by a spin coating method, and was heated in air on a hot plate at 400 ° C. for 10 minutes to obtain a metal oxide thin film. This coating and heating operation were repeated five times, and finally, the resultant was baked at 600 ° C. for 1 minute with an RTA (rapid heating apparatus) to obtain a PLZT ferroelectric thin film having a perovskite crystal structure with a thickness of 200 nm. The composition of this PLZT ferroelectric thin film is as shown in Table 1.

SEM of the surface of this PLZT ferroelectric thin film
By observing the photograph, the average grain size of the crystals of the perovskite phase constituting the thin film, the presence or absence of variation in the grain size, and the presence or absence of a phase other than the perovskite phase (for example, a sirconia-rich phase) are examined. Indicated. The average particle size was represented by an average intercept length of particles calculated from an SEM photograph of the thin film surface.

[0031]

[Table 1]

Table 1 shows that the addition of hydroxydimethylacetophenone makes it possible to form a good PLZT ferroelectric thin film having uniform surface morphology and fine crystal grains.

[0033]

As described above in detail, according to the present invention, a high-performance PLZT ferroelectric thin film having a uniform surface morphology and excellent electrical property uniformity is provided.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazumasa Maki 12-6 Techno Park, Mita City, Hyogo Prefecture Mitsubishi Materials Corporation Mita Plant (72) Inventor Masaya Matsuura 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Mitsui Material Inside Research Institute, Inc. (72) Akira Mori 12-6 Techno Park, Mita City, Hyogo Prefecture Mitsubishi Materials Corporation Mita Plant (72) Katsumi Ogi 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Mitsubishi Materials Corporation Within the Research Institute (56) References JP-A-9-34113 (JP, A) JP-A-7-187669 (JP, A) JP-A-9-263969 (JP, A) JP-A-7-268637 (JP, A) A) JP-A-8-225950 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 25/00 H01G 4/12 397 H01G 4/12 400 H01G 13/00 391 C0 1G 1/00 CA (STN)

Claims (3)

(57) [Claims] 1. A ferroelectric thin film forming composition comprising an organometallic compound solution for forming a perovskite-type PLZT ferroelectric thin film, characterized in that said solution contains hydroxydimethylacetophenone. A composition for forming a body thin film. 2. The composition for forming a ferroelectric thin film according to claim 1, wherein the content of the hydroxydimethylacetophenone is from 10 to 5000 ppm. 3. The step of applying the composition for forming a ferroelectric thin film according to claim 1 to a heat-resistant substrate and heating the composition in air, an oxidizing atmosphere, or a steam-containing atmosphere to a desired thickness. A method for forming a ferroelectric thin film, characterized in that the film is repeatedly fired at or above a crystallization temperature during or after heating in a final step at least until a film is obtained.