JP2856599B2 - 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 controlled composition at a stoichiometric ratio.
The present invention relates to a method for manufacturing a thin film of lead zirconate titanate having a thickness of angstrom to several μm.

[0002]

2. Description of the Related Art Lead zirconate titanate exhibits ferroelectricity, piezoelectricity, and pyroelectricity, and is expected to have various applications. Further, with the miniaturization and integration of electronic devices such as ferroelectric elements, piezoelectric elements, and pyroelectric elements, thinning has been attempted.
Until now, thin films of lead zirconate titanate have been deposited by sputtering or C
In these methods, lead zirconate titanate is synthesized by lead, zirconium, titanium,
Since it is a quaternary system composed of oxygen, it was very difficult to control the composition uniformly in the film plane. In addition, since synthesis is performed under reduced pressure or a low oxygen partial pressure atmosphere, the number of oxygen vacancies is extremely large, and problems such as poor insulation have occurred. In order to solve these problems, attempts have been made to synthesize a lead zirconate titanate thin film by a sol-gel method using a solution containing a constituent metal element as a starting material. The sol-gel method is also called the metal alkoxide method in a narrow sense, and the following synthesis examples of lead zirconate titanate are actually reported. For example, According to Fukushima et al., Lead-
2-ethylhexanoate, zirconium acetylacetonate and titanium butoxide in a molar ratio of 1: 0.5:
It is weighed so as to be 0.5 and dissolved and refluxed in alcohol 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 at 500 to 800 ° C. in the air to obtain a crystalline lead zirconate titanate thin film. The composition of the thin film obtained by this method is almost the same as the composition of the starting solution, and it has been reported that the composition uniformity is very good (J. Mate
rial science., 19 (1984) 599-606).

[0003]

However, in the above-mentioned method for producing a lead zirconate titanate thin film by the sol-gel method, an organic substance decomposed from a metal alkoxide or the like as a metal source remains in a precursor solution. During storage of the solution, a phenomenon occurs in which the precursor reacts again with the organic matter and decomposes, and there is a problem in the stability of the solution. In addition, heat treatment at least at 600 ° C. or more was required in order to completely decompose and remove these residual organic substances and obtain a thin film of perovskite single phase having a high dielectric constant. An object of the present invention is to solve such a conventional problem and to provide a method for producing a crystalline lead zirconate titanate thin film by a low-temperature heat treatment using a stable precursor solution. is there.

[0004]

According to the present invention, a molar ratio of lead acetate or lead alkoxide, zirconium alkoxide, and titanium alkoxide is 1: (1-x): x.
(However, a polyhydric alcohol or a derivative thereof that does not form an azeotrope with the lower alcohol is added to a solution obtained by mixing and reacting in a lower alcohol such that 0 <x <1), and then concentrated. A method for producing a lead zirconate titanate thin film, comprising repeating the step of preparing a precursor solution, and applying and drying the precursor solution on a substrate, and then heating and firing at least once, This is a method for producing a lead zirconate titanate thin film, characterized in that the heating and sintering is performed in an ozone-oxygen mixed gas stream at a temperature of 450 ° C. or higher.

The method of the present invention will be described in more detail as follows. As a starting material, an alkoxide of zirconium and an alkoxide of titanium are weighed so that the molar ratio becomes (1-x): x, mixed with dehydrated and purified alcohol, and dissolved. Alcohol may be liquid at room temperature,
Preferably, ethanol is used. Pb: (Zr + Ti) = lead acetate or lead alkoxide in a molar ratio to this solution.
The mixture was refluxed to prepare a precursor of lead zirconate titanate, and the resulting solution was mixed with a polyhydric alcohol or a derivative thereof, a lower alcohol having a low vapor pressure and being a reaction solvent. After adding a solvent that does not form an azeotrope, the mixture is concentrated to prepare a coating solution. The crystal substrate is immersed in this solution and pulled up at a constant speed to form a coating film on the substrate surface. These operations are 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 ozone and oxygen to obtain a thin film of a lead zirconate titanate single phase. Thereafter, the steps of dipping in the coating solution, lifting, drying, and heat treatment are repeated several times to obtain a lead zirconate titanate thin film having a desired thickness.

[0006]

According to the present invention, a lower alcohol as a reaction solvent hardly forms an azeotrope with a polyhydric alcohol or a derivative thereof, so that an organic substance (eg, ester, etc.) generated in the reaction process of preparing a precursor at the time of concentration. In addition, the alcohol solvent can be evaporated, the precursor solution can be kept stable, and the boiling point of the solvent of the precursor solution increases, so that the film is dried slowly to form a uniform film. Can be In addition, by performing the heat treatment in an ozone-oxygen mixed gas stream, a perovskite single-phase lead zirconate titanate thin film can be obtained at a low temperature of 500 ° C. or less, so that a conventional high-temperature heat treatment cannot be performed. A thin film of lead zirconate titanate can be formed on any of these.

[0007]

The present invention will be described below in more detail with reference to examples. However, the scope of the present invention is not limited at all by the following Examples. Tetraethoxy zirconium _{(Zr (OC 2 H 5)} 4) and tetraethoxytitanium (T
i (OC ₂ H ₅ ) ₄ ) when the ratio of Zr: Ti is (1-x): x
(However, 0 <x <1), each was weighed, mixed and dissolved in dehydrated and purified ethanol. The solution was stirred and refluxed for 24 hours. Pb:
(Zr + Ti) = 1: 1, refluxed,
A lead zirconate titanate precursor represented by a composition formula of PbZr _1-x Ti _x O ₃ was produced. Thereafter, a predetermined amount of ethylene glycol was added, and the acetic acid groups and ethanol were evaporated to prepare a lead zirconate titanate precursor solution. However, the solvent to be added may be a polyhydric alcohol or a derivative thereof that is low in saturated vapor pressure at room temperature and hard to form an azeotrope with ethanol, in addition to ethylene glycol, such as cellosolve or carbitol. These operations were performed in a dry nitrogen atmosphere because the metal alkoxide is easily hydrolyzed by moisture in the air.

[0008] A silicon (100) substrate on which platinum was deposited was immersed in the obtained lead zirconate titanate precursor solution, pulled up at a constant speed, applied, and dried. Thereafter, the coating film of the precursor of lead zirconate titanate obtained is placed in a mixed atmosphere of ozone and oxygen (ozone 5%) under four kinds of temperature conditions of 400 ° C., 450 ° C., 500 ° C., and 600 ° C.
For 1 hour to perform a heat treatment. This immersion, lifting, drying, and heat treatment (400 ° C, 450 ° C, 500 ° C,
(600 ° C.), a dense crystalline lead zirconate titanate thin film could be synthesized.

The thin film obtained as described above was examined by a powder X-ray diffraction method using Cu as a target.
When heat treatment was performed in a dry oxygen stream, a perovskite single phase could not be obtained even with heat treatment at 600 ° C. On the other hand, in the ozone-oxygen mixed gas flow, the perovskite phase was not observed in the heat treatment at 400 ° C.
It was confirmed that a perovskite-pyrochlore mixed phase was obtained by the heat treatment at 0 ° C., and a substantially complete perovskite single phase was obtained by the heat treatment at 500 ° C. and 600 ° C. Even at a heat treatment temperature of 700 ° C., an X-ray diffraction peak almost equivalent to that of the heat treatment at 600 ° C. was obtained in an ozone-oxygen mixed gas stream.

FIG. 1 shows an X-ray of a thin film finally obtained in this embodiment by changing the heat treatment temperature in an ozone-oxygen mixed gas stream.
FIG. 2 is a diagram showing a line diffraction peak, and FIG. 2 is a diagram showing an X-ray diffraction peak of a thin film obtained by performing a heat treatment at 500 to 700 ° C. in a dry oxygen stream. 1 and 2,
○ indicates the peak of the perovskite phase of the PbZr _1-x Ti _x O ₃ thin film, ● indicates the peak of the pyrochlore phase, △ indicates the peak of the platinum diffraction line of the substrate, and ▲ indicates the peak of the silicon diffraction line of the substrate. It shows a peak. The raw material Z
If the ratio of r: Ti is (1-x): x and 0 <x <1,
All gave similar results.

[0011]

As described above, according to the method of the present invention, using a stable precursor solution for producing a lead zirconate titanate thin film, a perovskite single-phase zirconate at a lower heat treatment temperature than before. The production of lead titanate thin films has become possible. Therefore, the method of the present invention is expected to be utilized for various applications such as piezoelectric elements and pyroelectric elements using lead zirconate titanate.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a lead zirconate titanate thin film obtained by performing a heat treatment in an ozone-oxygen mixed gas stream in an example of the present invention.

FIG. 2 is an X-ray diffraction diagram of a lead zirconate titanate thin film obtained by performing a heat treatment in a dry oxygen stream.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C01G 25/00 C04B 35/49

Claims (1)

(57) [Claims] 1. A mixture of lead acetate or lead alkoxide, zirconium alkoxide, and titanium alkoxide in a lower alcohol such that the molar ratio thereof is 1: (1-x): x (where 0 <x <1). A step of adding a polyhydric alcohol or a derivative thereof that does not form an azeotrope with the lower alcohol to a solution obtained by the reaction, and then concentrating the solution to prepare a precursor solution; and applying the precursor solution to a substrate. After coating and drying, a method for producing a lead zirconate titanate thin film comprising repeating a heating and firing step at least once or more, wherein the heating and firing step is performed at a temperature of 450 ° C. or higher in an ozone-oxygen mixed gas stream. A method for producing a lead zirconate titanate thin film, which comprises heating and firing.