JP3164849B2 - Method for producing lead zirconate titanate thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can be fired at a low temperature with a high purity and a composition controlled to a stoichiometric ratio.
The present invention relates to a method for producing a thin film of lead zirconate titanate having a thickness of A to several μm.

[0002]

2. Description of the Related Art Lead zirconate titanate exhibits ferroelectricity, piezoelectricity and pyroelectricity, and is expected for various applications. Also,
With the miniaturization and integration of electronic devices such as ferroelectric elements, piezoelectric elements, and pyroelectric elements, thinning has been attempted.

A thin film of lead zirconate titanate is synthesized by a sputtering method, a CVD method or the like. However, in these methods, since lead zirconate titanate is a quaternary system composed of lead, zirconium, titanium and oxygen, the film is formed. It is very difficult to control the composition uniformly in the plane. In addition, since the synthesis is performed in a vacuum system, the number of oxygen vacancies is extremely large, and there have been problems such as poor insulation.

In order to solve these problems, attempts have been made to synthesize lead zirconate titanate by a sol-gel method using a solution containing constituent metal elements as a starting material. The sol-gel method is also referred to as a metal alkoxide method in a narrow sense. In practice, lead zirconate titanate is synthesized by the following method. Lead acetate and alkoxides of zirconium and titanium are weighed in a molar ratio of 1: 1-x: x, dissolved in alcohol, refluxed, and reacted. The obtained solution is partially hydrolyzed to obtain a precursor solution of lead zirconate titanate. This solution is applied to a substrate to form a dried gel film, which is subjected to a heat treatment to obtain a crystalline lead zirconate titanate thin film. The thin film obtained by this method has a stoichiometric composition, very good in-plane composition uniformity, few oxygen defects, and high insulating properties.

[0005]

In the conventional sol-gel method, a relatively high temperature is required to crystallize the applied gel film, so that there is a problem that the types of substrates are limited. In addition, in the conventional sol-gel method, an acetate group remains in the precursor solution, and the precursor in the solution reacts with the acetate group again during storage of the solution to be decomposed, and there is a problem in the stability of the solution. Was. Also, it was difficult to adjust the solution concentration.

[0006]

According to the present invention, a mixture is obtained by mixing and reacting lead acetate, zirconium alkoxide, and titanium alkoxide in a molar ratio of 1: 1-x: x (where 1>x> 0). The step of coating the substrate surface with the solution and heating it in an oxygen-vapor mixed atmosphere at least once or more to form a lead zirconate titanate thin film on the substrate, A lead acetate, a zirconium alkoxide and a titanium alkoxide having a molar ratio of 1: 1
x: x was mixed and reacted in an alcohol so that x (where 0 <x <1), and a solvent which did not form an azeotrope with the alcohol due to low vapor pressure of the polyhydric alcohol or a derivative thereof was added to the obtained solution. Post-concentration, coating the substrate with the solution and heating and baking at a temperature of 450 ° C. or less in a mixed stream of oxygen and steam at least once or more, and laminating a lead zirconate titanate thin film in multiple layers on the substrate. A method for producing a lead zirconate titanate thin film, comprising:

A more specific example is as follows. An alkoxide of zirconium and an alkoxide of titanium are used as starting materials, and their molar ratio is 1-x: x
And mixed and dissolved in dehydrated and purified alcohol. The alcohol may be a liquid at room temperature, and ethanol is preferably used. Pb: (Zr
+ Ti) = 1: 1, refluxed, and PbZ
A precursor of r _{1 -x} Ti _x O ₃ was prepared, and the obtained PbZ
The r _{1 -x} Ti _x O ₃ precursor is concentrated, or a solvent in which the vapor pressure of a polyhydric alcohol or a derivative thereof is low and does not form an azeotrope with the alcohol is added to the obtained solution, followed by concentration. A coating film was formed on the substrate surface by immersing the crystal substrate in the substrate and lifting it up at a constant speed. These operations were performed in a dry nitrogen atmosphere because the metal alkoxide is easily hydrolyzed by moisture in the air. After drying for several minutes, a heat treatment is performed in a mixed gas stream of oxygen and water vapor and then in a dry oxygen gas stream to obtain a thin film of a single phase of lead zirconate titanate.
Thereafter, the steps of dipping, lifting, drying, and heating are repeated several times, whereby a lead zirconate titanate thin film having a desired thickness can be obtained.

[0008]

According to the present invention, by setting the atmosphere during the heat treatment to an oxygen steam mixed gas stream, the temperature of the heat treatment necessary for finally obtaining lead zirconate titanate is set to 600 ° C. as in the conventional method. The above high temperature can be lowered to 450 ° C. or lower. Thereby, a Si substrate or many glass substrates can be used, and the freedom of selecting the substrate is widened, and application to a piezoelectric element or a pyroelectric element can be expected. Further, according to the present invention, since the solvent alcohol containing an acetic acid group hardly forms an azeotropic mixture with an alcohol solvent that is a polyhydric alcohol or a derivative thereof, the alcohol solvent can be evaporated together with the acetic acid group during concentration, and the precursor The solution can be kept stable. In addition, the precursor solution concentration can be accurately controlled by adding a calculated amount of a polyhydric alcohol or a derivative thereof.

[0009]

The present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited at all by the following Examples.

[0010] Tetraethoxyzirconium: Zr (OC
₂ H _{5) 4} and tetraethoxytitanium: Ti (OC
Mixture were weighed respectively so as to be x, dehydrated, in purified ethanol, which: a ₂ H _{5) 4} Zr: Ti ratio is 1-x
Dissolved. The solution was stirred and refluxed for 24 hours. Lead acetate was added to this solution so that Pb: (Zr + Ti) = 1: 1, and the mixture was refluxed to prepare a precursor of PbZr ₁ -xTi _x O ₃ . The resulting PbZr _{1 - x} Ti _x O ₃ precursor was concentrated, 0.2 m is lead zirconate titanate precursor concentration
ol / l. As another example, a predetermined amount of ethylene glycol was added, and the acetate group and ethanol were evaporated to prepare a lead zirconate titanate precursor solution. However, the solvent to be added may be a polyhydric alcohol or its derivative other than ethylene glycol, such as a cellosolve or carbitol type, which has a low saturated vapor pressure at room temperature and hardly forms an azeotrope with alcohol. These operations were performed in a dry nitrogen atmosphere because the metal alkoxide is easily hydrolyzed by moisture in the air.

The α-Al ₂ O ₃ (012) substrate was immersed in the obtained concentrated solution of the lead zirconate titanate precursor, pulled up at a constant speed, dried, and dried. After that, the coating film of the precursor of lead zirconate titanate obtained was treated with 35
Heat treatment was performed for 1 hour in a mixed atmosphere of oxygen and steam for 1 hour and then for 1 hour in dry oxygen under three temperature conditions of 0 ° C, 400 ° C, and 450 ° C. This dipping, lifting,
The steps of drying and heat treatment (350 ° C., 400 ° C., 450 ° C.) are repeated to obtain a dense crystalline PbZr _{1 -x} Ti _x
An O ₃ thin film could be synthesized.

For comparison with the conventional method, the above-mentioned coating film of the precursor of lead zirconate titanate was heat-treated at the same temperature in a dry oxygen stream to obtain a thin film.

As a result of examining the obtained thin film by a powder X-ray diffraction method using Cu as a target, when the heat treatment was performed in a dry oxygen gas stream, no crystallization was observed even at 450 ° C. On the other hand, in an oxygen steam mixed gas flow, 350
Although crystallization was not observed in the heat treatment at 400 ° C.,
It was confirmed that the film was sufficiently crystallized by the heat treatment at 450 ° C., and the crystalline film was almost completely formed by the heat treatment at 450 ° C.

FIG. 1 (a) shows a thin film finally obtained in an embodiment in a mixed gas stream of oxygen and water vapor, and FIG. X
FIG. 3 shows a line diffraction diagram. FIG. 1 (a) and FIG.
In the figure of (b), those with a circle are PbZr.
The peak of the diffraction line of the _1-x Ti _x O ₃ thin film is shown, and the one marked with a triangle indicates the peak of the α-Al ₂ O ₃ diffraction line of the substrate.

[0015]

As described above, according to the present method, an oriented lead zirconate titanate thin film having high crystallinity can be produced at an extremely low temperature as compared with the conventional method.

The present invention enables low-temperature sintering of such a densely oriented crystalline lead zirconate titanate thin film, and various kinds of piezoelectric elements and pyroelectric elements using the lead zirconate titanate. Its application is expected to be applied.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of the present invention (a) and a conventional example (b).

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shinichi Hirano 2-66 Yadacho, Higashi-ku, Nagoya City Room 123, Yadacho Dormitory, Nagoya University (58) Field surveyed (Int. Cl. ⁷ , DB name) C01G 25 / 00

Claims (2)

(57) [Claims] 1. A mixture of lead acetate, zirconium alkoxide, and titanium alkoxide in a molar ratio of 1: 1-x: x (where 1>x> 0), and the reaction is carried out. A process for producing a lead zirconate titanate thin film, comprising repeating the step of coating and heating in an oxygen / steam mixed atmosphere at least once or more to form a lead zirconate titanate thin film on the substrate. 2. A mixed reaction of lead acetate, zirconium alkoxide and titanium alkoxide in an alcohol such that the molar ratio thereof is 1: 1-x: x (where 0 <x <1). After adding a solvent which does not form an azeotrope with the alcohol, the vapor pressure of the polyhydric alcohol or a derivative thereof is low, and then the mixture is concentrated.
A process for producing a lead zirconate titanate thin film, comprising repeating the step of heating and firing in an oxygen steam mixed gas stream at the above temperature at least once, and laminating the lead zirconate titanate thin film in multiple layers on the substrate. .