JPH0419911A - Manufacture of thin ferroelectric film forming precursor solution and manufacture of thin ferroelectric film - Google Patents

Abstract

PURPOSE:To produce precursor solution for forming a thin ferroelectric film by dissolving an organometal compound of lead, lanthanum, titanium, zirconium and other component in organic solvent to form mixed solution, and adding stabilizer in this mixed solution, and thereafter adding water to hydrolize partly. CONSTITUTION:An organometal compound of lead, lanthanum, titanium, zirconium and other component is dissolved in organic solvent. Mixed solution of a metal compound, which is combined with organic group via oxygen, is formed as a result. Next, this solution is added with for instance 0.2-3mol of one of beta-diketones, ketone acids, keto esters, hydroxy acids, higher carboxylic acids and amine acids and is stabilized. After that 0.2-3mol of water against 1mol of total metal atom number is added in the solution and polymerization proceeds by partial hydrolysis. The precursor solution, which forms a thin film of PT, PZT, PLZT and the like, is composed in this way.

Description

Detailed Description of the Invention <Field of Industrial Application> The present invention is applicable to, for example, infrared sensors, piezoelectric filters, vibrators, laser modulation elements, optical shutters, capacitor films, nonvolatile DRAMs, etc. ,PZT,P
The present invention relates to a method for manufacturing a ferroelectric thin film such as LZT and a method for manufacturing a precursor solution for forming the ferroelectric thin film.

<Prior Art> As a conventional method for manufacturing a Pb-based ferroelectric thin film, there is, for example, the method shown below (Japanese Patent Laid-Open No. 60-236404).

First, a dielectric material forming precursor such as lead titanate (PT) is dissolved in an organic solvent such as a lower alcohol to form a dielectric material forming precursor solution.

Next, apply this dielectric formation precursor solution to the metal substrate,
Dry to form a coating on the substrate.

Furthermore, this coating film is calcined at a temperature above the decomposition temperature of the organic substance and below the crystallization temperature of the dielectric.

Then, these coating, drying, and calcining steps are repeated.

Next, it is fired at a temperature equal to or higher than the crystallization temperature of the dielectric.

Alternatively, repeat this application, drying, and baking process.

As a result, two or more dielectric thin films are formed on the metal substrate.

<Problems to be Solved by the Invention> However, in the conventional method of forming a Pb-containing composite metal oxide (dielectric) thin film by coating with a solution, if the precursor compounds are simply mixed together, It was easily hydrolyzed by the moisture inside, making it difficult to obtain a homogeneous film. The state of the film was also in the form of a fine powder.

In other words, even if a compound is stabilized by an organic solvent, it will generate individual metal oxides during thermal decomposition (calcination), and these will become composites through solid phase reactions. During firing, it was difficult to control the formation of the thin film due to the difference in volatility of each metal or compound (PbO is easily volatile at high temperatures). Further, even if the compounds are bonded at a single molecule level, they tend to form a fine powdery film during film formation, which poses problems such as electrical conductivity.

Therefore, an object of the present invention is to obtain a ferroelectric thin film having a composition uniformly containing components such as lead. The present invention also provides a method for producing a ferroelectric thin film forming precursor solution that greatly facilitates the transition to a perovskite crystal, which is a ferroelectric phase, in the ferroelectric thin film forming process, and The purpose of this invention is to provide a method for manufacturing a ferroelectric thin film using a solution.

<Means for Solving the Problems> The present invention involves dissolving metal organic compounds of lead, lanthanum, titanium, zirconium, and other components in an organic solvent, thereby allowing each of these metals to form an organic group via oxygen. A mixed solution of bound metal compounds is formed, a stabilizer is added to this mixed solution, and a predetermined amount of water is added to this mixed solution to cause partial hydrolysis, thereby forming metal-oxygen-metal in the mixed solution. A method of creating a precursor solution for forming a ferroelectric thin film by forming bonds, and a method of applying the precursor solution to a substrate, drying and thermally decomposing it to form an oxide film, and then removing the oxide film. By firing at an appropriate temperature, lead titanate (PT), lead zirconate titanate (PZT), third component-added lead zirconate titanate (three-component PZT), and lanthanum-added zirconate titanate are produced. This is a method for manufacturing a ferroelectric thin film in which a ferroelectric thin film of one type selected from the group consisting of lead (PLZT) is formed.

In addition, the above-mentioned stabilizers include β-diketones, ketone acids,
The stabilizer is one selected from the group consisting of ketoesters, oxyacids, higher carboxylic acids, and amines, and the amount of the stabilizer added is 0.000000000000000000000000000000000,000.
This is a method for producing a ferroelectric thin film forming precursor solution having a concentration of 2 to 3 mo.

<Function> In the method for producing a ferroelectric thin film according to the present invention, lead titanate (PT), lead zirconate titanate (PZT), and a third component constituting the ferroelectric thin film to be produced are added. Dissolving organic compounds of lead, lanthanum, titanium, zirconium and other components in an organic solvent to form lead zirconate titanate (ternary PZT) or lanthanum-doped lead zirconate titanate (PLZT). . As a result, a mixed solution of titanium, lead, lanthanum, zirconium, and a metal compound in which these compounds are bonded to an organic group via oxygen is formed. Note that lower alcohols, β-diketones, ketonic acids, ketoesters, oxyacids, oxyacid esters, etc. are used as the organic solvent.

Next, for example, 0°2 to 3 per 1 m01 of total metal atoms.
A mol of one of β-diketones, ketonic acids, ketoesters, oxyacids, higher carboxylic acids, and amines is added to this solution to stabilize it. The metal-oxygen-metal bond is slowly polymerized as a whole. Stabilizers are added to partially stabilize the solution.

It should be noted that if a large amount of the stabilizer is supplied, there is a risk that hydrolysis will not occur sufficiently and a metal-oxygen bond will not occur, and precipitation may also occur due to solubility problems.

After that, 0.2 to 3 mol per mol of total metal atoms
Water of 1 is added to this solution and polymerization is proceeded by partial hydrolysis.

In this way, a precursor solution for forming a thin film of PT, PZT, PLZT, etc. is formed. It is easy to control the amount of water added, and as a result, the metal-oxygen-metal bond in the precursor solution can be sufficiently controlled.

Next, this precursor solution is applied onto a substrate, dried and thermally decomposed to form an oxide film. Alternatively, by repeating this process, a thin film of a predetermined thickness (for example, about 3°000 A) is obtained.

Furthermore, this oxide film is heated and fired at an appropriate temperature (for example, 600'C) to form a pb gold-containing composite metal oxide thin film having a desired crystalline phase or a mixture of two phases (for example, ferroelectric phase and paraelectric phase). It is something that forms.

Regarding the crystal orientation of the thin film, a film with a specific orientation can be obtained on a specific substrate having a specific orientation.

The bekovskite crystals of the present invention, such as PT and PZT, are cubic crystals above the Curie point and tetragonal or trigonal crystals below the Curie point, and as the temperature decreases, the a-axis of the lattice constant shrinks and the a-axis expands. In particular, we can pay attention to this.

In other words, when using a substrate with a larger thermal expansion coefficient than the thin film, the stress transmitted from the substrate to the thin film due to the difference in thermal expansion coefficient is
When the temperature changes, it acts in a direction consistent with the behavior of the a-axis, and the a-axis tends to be parallel to the substrate, resulting in a c-axis orientation.

Conversely, when a substrate with a smaller thermal expansion than the thin film is used, the C-axis orientation tends to occur.

Therefore, by repeatedly raising and lowering the temperature of the thin film-forming substance near its Curie point, the orientation tendency thereof can be enhanced.

In the present invention, after the heating and baking process, the film material (for example, P
Cooling and heating are repeated around the Curie point of ZT). The orientation is improved by utilizing the difference in thermal expansion coefficient between the PZT film and the substrate (for example, a platinum substrate).

<Examples> Examples of the method for manufacturing a ferroelectric thin film according to the present invention will be described below, but the present invention is not limited thereto.

Strategy 1 Dissolve 12.64 g of lead acetate in 2-methoxyethanol, remove water as an azeotrope with the solvent, and then add 4.55 g of tetraisopropoxytitanium and 6.65 g of tetrabutoxyzirconium. Then, 10 g of acetylacetone (stabilizer) was added.

After thoroughly stirring this mixed solution, 1.8 g of water was added, and the whole solution was mixed with isopropyl alcohol to give a solution of 109.3 g.
g, and it was made into a 10% solution in terms of oxide. A precursor solution for forming a ferroelectric thin film is prepared.

This forming precursor solution was applied to 3,0% by using a spin coater.
After coating on a platinum substrate at 00 rpm, this coating film is dried.

Repeat this coating and drying operation 6 times and then heat to 600°C.
After baking for 1 hour, a thin film of PZT (52/48) was obtained.

When the crystallinity of the 20 PZT thin film was examined using an X-ray diffraction device, it was found to be a single-phase film of perovskite crystals exhibiting ferroelectricity.

Example M 8.13 g of diisopropoxy lead and 7.11 g of tetraisopropoxy titanium were dissolved in isopropyl alcohol, and 9.75 g of ethyl acetoacetate (stabilizer) was added thereto.

After thoroughly stirring this mixed solution, isopropyl alcohol and 0.93 g of water were added to it, resulting in a total of 75.77 g.
g, and a ferroelectric thin film forming precursor solution having a concentration of 10% in terms of oxide was prepared.

This precursor solution was coated at 3°000 using a spin coater.
After coating on a platinum substrate under rpm conditions, this coating film is dried.

This coating and drying operation was repeated six times and then baked at 600° C. for 1 hour to obtain a PT N film.

When the crystallinity of this PT thin film was examined using an X-ray diffraction device, it was found that it was a single-phase film of perovskite crystals exhibiting ferroelectricity.

Example m: 8.63 g of lead acetate and 0.71 g of lanthanum acetate were dissolved in 2-methoxyethanol, and after removing water as an azeotrope with the solvent, 2.43 g of tetraisopropoxytitanium was dissolved.
g and 6.09 g of tetrabutoxyzirconium were added, and further 6.83 g of acetylacetone (stabilizer) was added.

After thoroughly stirring this mixed solution, isopropyl alcohol and 1.23 g of water were added to make a total of 80.85 g to prepare a ferroelectric thin film forming precursor solution having a concentration of 10% in terms of oxide.

This precursor solution was coated at 3°000 using a spin coater.
After coating on a platinum substrate under rpm conditions, the coating film B is dried.

After repeating this coating and drying operation 6 times,
After baking for 1 hour, a thin film of PLZT (9/65/35) was obtained.

When the crystallinity of this PLZT thin film was examined using an X-ray diffraction device, it was found that it was a single-phase film of perovskite crystals exhibiting ferroelectricity.

After mixing each component in the same manner as in the above example except for the step of adding acetylacetone and the step of adding water in the first example above, the mixed solution was heated under reflux at a temperature just below the boiling point for 10 hours. A 10% solution in terms of oxide was obtained.

Using this solution, PZT was prepared in the same manner as in the first example above.
A thin film was obtained. Application to the substrate and drying are repeated.

When we investigated the crystallinity of this PZT thin film using an X-ray diffraction device, we found that it is a mixed crystal film consisting of a perovskite structure crystal that exhibits ferroelectricity and a pyrochlore structure crystal that exhibits paraelectricity. Ta.

<Effects> In the method for manufacturing a ferroelectric thin film and the method for manufacturing a ferroelectric thin film forming precursor solution according to the present invention, even during firing, component elements or compounds such as lead do not volatilize and a uniform strength can be obtained. A dielectric thin film can be obtained. Further, it can be easily transformed into a perovskite crystal which is a ferroelectric phase.

Patent applicant: Mitsubishi Metals Corporation

Claims (3)

[Claims] (1) By dissolving metal organic compounds of lead, lanthanum, titanium, and zirconium in an organic solvent, a mixed solution of metal compounds in which each of these metals is bonded to an organic group via oxygen is formed, and this mixed solution After adding a stabilizer to this mixed solution, a predetermined amount of water is added to cause partial hydrolysis.
By forming a metal-oxygen-metal bond in a mixed solution, lead titanate (PT), lead zirconate titanate (PZT)
, third component added lead zirconate titanate (three-component system PZT
), and lanthanum-doped lead zirconate titanate (PL
A method for producing a ferroelectric thin film forming precursor solution, which comprises preparing a ferroelectric thin film forming precursor solution for forming one type of ferroelectric thin film selected from the group consisting of ZT. (2) The above stabilizers include β-diketones, ketone acids,
One type selected from the group consisting of ketoesters, oxyacids, higher carboxylic acids, and amines, and the amount of the stabilizer added is 0.2 to 3 mol per 1 mol of total metal atoms. A method for producing a ferroelectric thin film forming precursor solution according to claim (1). (3) The ferroelectric thin film forming precursor solution according to claim (1) or (2) above is applied onto a substrate, dried and thermally decomposed to form an oxide film, and then this oxide film is By firing at high temperature, lead titanate (PT), lead zirconate titanate (PZT),
Component-added lead zirconate titanate (three-component PZT) and lanthanum-added lead zirconate titanate (PLZT)
1. A method for producing a ferroelectric thin film, comprising forming one type of ferroelectric thin film selected from the group consisting of: