JP3026310B2 - Method for producing precursor solution for forming ferroelectric thin film and method for producing ferroelectric thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to, for example, a PT applied to an infrared sensor, a piezoelectric filter, a vibrator, a laser modulation element, an optical shutter, a capacitor film, a nonvolatile DRAM, and the like. The present invention relates to a method for producing a ferroelectric thin film such as PZT, PLZT and PLZT and a method for producing a precursor solution for forming a ferroelectric thin film.

<Prior Art> As a conventional method for producing a Pb-based ferroelectric thin film, there is, for example, the following method (JP-A-60-236404).

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

Next, this dielectric-forming precursor solution is applied to a metal substrate and dried to form a coating film on the substrate.

Further, this coating film is calcined at a temperature not lower than the decomposition temperature of the organic substance and not higher than the crystallization temperature of the dielectric.

 Then, the application, drying, and calcination are repeated.

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

 Alternatively, the application, drying and baking are repeated.

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

<Problems to be Solved by the Invention> However, in such a conventional method of forming a Pb-containing composite metal oxide (dielectric) thin film by solution coating, it is difficult to simply mix a precursor compound with air. It was easily hydrolyzed by the moisture therein, and it was difficult to obtain a homogeneous film. The state of the film was also in a fine powder state.

In other words, even when a compound is stabilized by an organic solvent, during thermal decomposition (during firing), each forms a single metal oxide and is complexed by their solid-phase reaction. Because of the difference in volatility of each metal or compound during firing (PbO tends to volatilize at high temperatures), it was difficult to control the composition of the thin film. Further, even if the compound is bonded only at the single-molecule level, there is a problem that a fine powder film is easily formed at the time of film formation, and conduction is easily generated.

Accordingly, an object of the present invention is to obtain a ferroelectric thin film having a composition in which components such as lead are uniformly contained. Further, the present invention provides a method for producing a ferroelectric thin film forming precursor solution which makes it very easy to transfer to a perovskite crystal which is a ferroelectric phase in the ferroelectric thin film forming step, It is an object of the present invention to provide a method for producing a ferroelectric thin film using a solution.

<Means for Solving the Problems> The present invention provides a metal compound bonded to an organic group via oxygen for each of these metals by dissolving a metal organic compound of lead, lanthanum, titanium, and zirconium in an organic solvent. After forming a mixed solution of, and adding a stabilizer to the mixed solution, a predetermined amount of water is added to the mixed solution,
By partially hydrolyzing and forming a metal-oxygen-metal bond in the mixed solution, lead titanate (PT), lead zirconate titanate (PZT), and third component-added lead zirconate titanate (three-component system) PZT) and lanthanum-added lead zirconate titanate (PLZT) to form a ferroelectric thin film forming precursor solution for forming one type of ferroelectric thin film selected from the group consisting of ferroelectric thin film formation In the method for producing a precursor solution, the amount of the stabilizer is 0.2 to 3 mol based on 1 mol of total metal atoms, and the amount of water is 1 mol of total metal atoms.
This is a method for producing a precursor solution for forming a ferroelectric thin film in an amount of 0.2 to 3 mol per 1.

Further, the present invention provides the stabilizer, β-diketones,
The method for producing a precursor solution for forming a ferroelectric thin film according to claim 1, wherein the precursor solution is one selected from the group consisting of ketone acids, keto esters, oxy acids, higher carboxylic acids, and amines.

Further, the present invention provides a method for applying a precursor solution for forming a ferroelectric thin film according to claim 1 or 2 on a substrate,
After drying and thermal decomposition to form an oxide film, this oxide film is fired at an appropriate temperature to obtain lead titanate (PT),
One type of ferroelectric selected from the group consisting of lead zirconate titanate (PZT), lead zirconate titanate with a third component (ternary PZT), and lead zirconate titanate with a lanthanum (PLZT) This is a method for manufacturing a ferroelectric thin film having a thin film formed thereon.

<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, which constitute the ferroelectric thin film to be produced, are added. Dissolve organic compounds of lead, lanthanum, titanium, zirconium and other components in an organic solvent to form lead zirconate titanate (ternary PZT) or lanthanum-added 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. As the organic solvent, lower alcohols, β-diketones, ketone acids, keto esters, oxy acids, oxy acid esters, and the like are used.

Next, for example, 0.2 to 3 mol of β-diketones, ketone acids, keto esters, oxy acids, higher carboxylic acids, and one of amines are added to the solution with respect to 1 mol of the total number of metal atoms in the solution. Stabilize. The metal-oxygen-metal bond is gradually polymerized as a whole.
A stabilizer is added to partially stabilize the solution. When a large amount of the stabilizer is supplied, hydrolysis may not be sufficiently generated, and a metal-oxygen-metal bond may not be generated. In addition, precipitation may occur due to a solubility problem.

Thereafter, 0.2 to 3 mol of water per 1 mol of total metal atoms is added to this solution, and polymerization is promoted by partial hydrolysis.

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

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

Further, this oxide film is heated and fired at an appropriate temperature (eg, 600 ° C.) to form a Pb-containing composite metal oxide thin film having a desired crystal phase or a mixture of two phases (eg, a ferroelectric phase and a paraelectric phase). Is what you do.

With respect to the crystal orientation of the thin film, a specific alignment film can be obtained on a specific substrate having a specific orientation.

The perovskite-type crystals such as PT and PZT according to the present invention take a cubic system at or above the Curie point, and take a tetragonal or trigonal system below the Curie point, and as the temperature decreases, the a-axis of the lattice constant decreases and the c-axis extends. In particular, attention can be paid.

That is, when a substrate having a larger coefficient of thermal expansion than a thin film is used, the stress transmitted from the substrate to the thin film due to the difference in the coefficient of thermal expansion acts in a direction that matches the behavior of the a-axis when the temperature changes, and the a-axis It tends to be parallel to the substrate and has a c-axis orientation.

Conversely, when a substrate having a smaller thermal expansion than the thin film is used, a
It tends to be axially oriented.

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

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

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

First Example 12.64 g of lead acetate was dissolved in 2-methoxyethanol,
After removing water as an azeotrope with the solvent, 4.55 g of tetraisopropoxytitanium and 6.65 g of tetrabutoxyzirconium were added, and acetylacetone (stabilizer) 1
0 g was added.

After sufficiently stirring this mixed solution, 1.8 g of water was added,
Then make the whole 109.3g with isopropyl alcohol,
It was a 10% solution in terms of oxide. This is for preparing a precursor solution for forming a ferroelectric thin film.

Using a spin coater, the formed precursor solution
After coating on a platinum substrate under the condition of 0 rpm, this coating film is dried.

This coating and drying operation is repeated 6 times and then 600 ° C
For 1 hour to obtain a thin film of PZT (52/48).

When the crystallinity of this PZT thin film was examined using an X-ray diffractometer, it was found that the thin film was a perovskite-type single-phase film exhibiting ferroelectricity.

Second Example 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 sufficiently stirring this mixed solution, 0.93 g of isopropyl alcohol and water was added thereto to make a total of 75.77 g,
A precursor solution for forming a ferroelectric thin film having a concentration of 10% in terms of oxide was prepared.

Using a spin coater, this precursor solution is 3,000 rpm
After coating on a platinum substrate under the conditions described above, this coating film is dried.

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

When the crystallinity of the PT thin film was examined using an X-ray diffractometer, it was found that the PT thin film was a single-phase film of a perovskite crystal showing ferroelectricity.

Third Example After dissolving 8.63 g of lead acetate and 0.71 g of lanthanum acetate in 2-methoxyethanol and removing water as an azeotropic mixture with a solvent, 2.43 g of tetraisopropoxytitanium and 6.09 g of tetrabutoxyzirconium were added. Then, 6.83 g of acetylacetone (stabilizer) was added.

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

Using a spin coater, this precursor solution is 3,000 rpm
After coating on a platinum substrate under the conditions described above, this coating film is dried.

After repeating this coating and drying operation six times,
For 1 hour to obtain a PLZT (9/65/35) thin film.

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

Comparative Example After the components were mixed in the same manner as in the above Example, except that the step of adding acetylacetone and the step of adding water in the first example were performed, the mixed solution was heated and refluxed at a temperature just below the boiling point for 10 hours. The reaction was performed to obtain a 10% solution in terms of oxide.

Using this solution, PZT
A thin film was obtained. Coating on a substrate and drying are repeated.

Examination of the crystallinity of this PZT thin film using an X-ray diffractometer revealed that it was a mixed crystal film of a perovskite-type crystal exhibiting ferroelectricity and a pyrochlore-type crystal exhibiting paraelectricity. Was.

<Effects> In the method for producing a ferroelectric thin film and the method for producing a precursor solution for forming a ferroelectric thin film according to the present invention, a homogeneous ferroelectric thin film is obtained without volatilization of component elements or compounds such as lead even during firing. A dielectric thin film can be obtained. Further, it can be easily transformed into a perovskite crystal which is a ferroelectric phase.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroto Uchida 1-6-1, Otemachi, Chiyoda-ku, Tokyo Mitsubishi Metals Corporation (56) References JP-A-2-6335 (JP, A)

Claims (3)

(57) [Claims] (1) dissolving a metal organic compound of lead, lanthanum, titanium, and zirconium in an organic solvent to form a mixed solution of a metal compound bonded to an organic group via oxygen for each of these metals; After adding a stabilizer to the mixed solution, a predetermined amount of water is added to the mixed solution to cause partial hydrolysis,
By forming metal-oxygen-metal bonds in the mixed solution, lead titanate (PT), lead zirconate titanate (PZT), third component-added lead zirconate titanate (ternary PZT), and Manufacture of a ferroelectric thin film forming precursor solution for forming one type of ferroelectric thin film selected from the group consisting of lanthanum-added lead zirconate titanate (PLZT) In the method, the amount of the stabilizer added is 0.
A method for producing a precursor solution for forming a ferroelectric thin film, wherein the addition amount of water is 2 to 3 mol and the addition amount of water is 0.2 to 3 mol based on 1 mol of total metal atoms. 2. The method according to claim 1, wherein the stabilizer is one selected from the group consisting of β-diketones, ketone acids, keto esters, oxy acids, higher carboxylic acids, and amines. The method for producing a precursor solution for forming a ferroelectric thin film according to the above. 3. A ferroelectric thin film forming precursor solution according to claim 1 or 2 is coated on a substrate, dried and thermally decomposed to form an oxide film. By firing at an appropriate temperature, lead titanate (PT), lead zirconate titanate (PZT), lead zirconate titanate with a third component (ternary PZT), and lead zirconate titanate with lanthanum A method for producing a ferroelectric thin film, wherein one type of ferroelectric thin film selected from the group consisting of (PLZT) is formed.