JP3237145B2 - Method of forming barium titanate thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for easily forming a barium titanate thin film on a substrate without complicated steps.

[0002]

2. Description of the Related Art Barium titanate (BaTiO ₃ )
It has excellent properties as ferroelectric, piezoelectric, and pyroelectric materials, and is widely used in various devices such as ultrasonic sensors, capacitors, actuators, pyroelectric infrared sensors, and nonvolatile memories. Further applications to many fields are being attempted. When barium titanate is applied to these devices, it is common to use barium titanate as a thin film in order to effectively utilize the characteristics.

[0003] Then, barium titanate (Ba)
As a method for forming a TiO ₃₎ film, conventionally, (1) a method of chemical conversion treatment of titanium metal surface (e.g., JP-A-61-30678), (2) sputter vaporized target material substrate (substrate ) By a sputtering method (for example, JP-A-2-94209) in which a thin film is deposited on the substrate; (3) by a plasma deposition method in which a thin film is formed using plasma (for example, JP-A-2-258700) (4) A method based on a hydrothermal electrochemical method which is a wet-type thin film forming method (for example, JJP Vol. 28 No. 11 (198)
Various formation methods such as 9)) and are known.

[0004]

However, the conventional B
Each of the methods for forming the aTiO ₃ thin film has the following problems. In other words, the method of chemical conversion treatment of the titanium metal surface in (1) is not applicable when the substrate is limited to titanium metal and a material other than titanium is used as the substrate.The sputtering method in (2) is complicated. (3) The plasma deposition method requires complicated and large-scale equipment, and can be applied only to substrates that can withstand high temperatures. (4) Hydrothermal electricity Since the chemical method uses the base material itself as an electrode, it can be applied only to highly conductive metal base materials,
In addition, since the film is formed under a high temperature and a high pressure using an autoclave, it cannot be applied to an organic substrate having low heat resistance.

The present invention solves the above-mentioned problems, and does not require complicated and large-scale facilities and strict film-forming conditions, and can be used for the surface of a substrate made of various materials such as inorganic materials and metal materials. It is an object of the present invention to provide a method for forming a barium titanate thin film that can easily form a barium titanate thin film.

[0006]

Means for Solving the Problems The inventors have heretofore,
An aqueous solution substantially supersaturated with respect to hydroxyapatite contains C
by immersing the aO--SiO ₂ based glass with base, it has proposed a method of forming a hydroxyapatite film on a surface of the substrate (JP-A-1-74829). This method
It is a very simple and economical method of forming a ceramic thin film over a large area on a substrate made of various materials under low temperature conditions. The purpose is to elute an appropriate amount and react with ions in an aqueous solution at an appropriate rate.

[0007] Based on the above findings, the inventors have conducted intensive studies on the composition of the glass to be used, the composition of the aqueous solution in which the substrate and the like are immersed, the ion concentration, and the like. The present inventors have found that a barium titanate thin film can be formed on a substrate by immersing the substrate in an aqueous solution containing acid ions and treating the substrate with an alkali, thereby completing the present invention.

That is, according to the method of forming a barium titanate thin film of the present invention, a base material and a glass containing at least BaO and B ₂ O ₃ are opposed at a predetermined interval, and a hexafluorotitanate ion ( By immersing the glass in the aqueous solution containing TiF ₆ ²⁻ ) to elute its constituents from the glass and forming a thin film of BaTiOF _{4 on} the surface of the substrate, the surface of the substrate is washed with an alkaline aqueous solution. By treating, barium titanate (Ba)
TiO ₃ ) thin film is obtained.

According to the formation method of the present invention, it is considered that the barium titanate thin film is formed by the mechanism described below.

When a glass containing BaO and B ₂ O ₃ is immersed in an aqueous solution containing hexafluorotitanate ions, Ba and B are eluted as ions from the glass, and these eluted ions are converted into TiF ₆ ^{2− in the} aqueous solution. Reacts with the ions to form BaTiO
Generates F ₄ thin film and BF ₄ ^- ions. And BaTi
BaTiOF ₄ is transformed into barium titanate, which is a stable phase in an alkaline region, by immersing a substrate having an OF ₄ thin film formed on its surface in an alkaline aqueous solution (for example, an aqueous sodium hydroxide solution) and treating it. A barium titanate thin film is formed on a substrate.

Next, the configuration of the present invention will be described in detail.

[0012] In order to implement efficiently forming method of barium titanate thin film of the present invention, the composition of the glass is immersed in an aqueous solution containing hexafluoride titanate ions are facing the (1) substrate, (2 ) pH of the aqueous alkali solution to immerse the substrate after the thin film of BaTiOF ₄ is formed, and (3) it is desirable to adjust the temperature of the alkaline aqueous solution, the conditions such as within a predetermined range.

First, it is necessary to use a glass containing at least BaO and B ₂ O ₃ as the glass used in the method for forming a barium titanate thin film of the present invention.
Is preferably those containing BaO and B ₂ O ₃ as a main component, BaO is 1~50mol%, B ₂ O ₃ is 50 to 99 mol%
Is preferably within the range. Table 1 shows examples of preferred glasses. In addition, as glass, MgO, CaO,
A material containing SrO or the like may be used.

[0014]

[Table 1]

In Table 1, the glasses of Nos. 1 to 6 are Ba
Glass containing only O and B ₂ O ₃ , No. 7 to 10
This is a glass containing TiO ₂ in addition to aO and B ₂ O ₃ .
Each of these glasses is made of BaTiOF on various substrates.
_This glass has the ability to form a thin film of ₄ .

The aqueous solution in which the substrate and the glass are immersed is
For example, it can be prepared by weighing a predetermined amount of ammonium hexafluorotitanate or titanate and dissolving it in ion-exchanged water. The concentration of hexafluorotitanate ion affects the film formation rate, but 0.01 mM
/ L or more. As described above, since the film is formed even when the concentration of hexafluorotitanate ion is low, the concentration of hexafluorotitanate ion does not necessarily need to be high.

Further, an alkaline aqueous solution for immersing the substrate on which the BaTiOF ₄ thin film is formed is not preferable because the phase other than barium titanate becomes stable when the pH is less than 13, and the aqueous solution temperature is less than 40 ° C. In the case of the above, since an amorphous phase of BaTiO ₃ is formed,
A stable barium titanate crystal phase cannot be generated. Therefore, the alkaline aqueous solution has a pH of 13
As described above, the temperature of the aqueous solution is desirably 40 ° C. or higher.

[0018]

The present invention will be described below more specifically with reference to examples.

Example 1 Barium carbonate and boric acid were weighed into a platinum crucible so as to have the glass composition of No. 1 in Table 1. And this is 11
After heating to 00 ° C. and melting for 1 hour, the melt is poured onto a metal plate and pressed from above with another metal plate to form a glass plate. Then, this glass plate is cut into a size of 10 mm × 10 mm × 1 mm. Next, the cut glass is made of various materials, that is, alumina sintered body, gold, silver, PMM.
A. The glass and the substrate are fixed via the spacer 4 (FIG. 1) so as to be opposed to the substrate (substrate) made of polyethylene and to keep a distance (gap) of 0.5 mm therebetween. Then, as shown in FIG. 1, the glass 1 and the substrate 2 fixed to each other are immersed in 30 ml of an aqueous solution 3 in which ammonium hexafluorotitanate is dissolved to a concentration of 50 mM, and the liquid temperature is reduced to 25 ° C. Hold and continue immersion for 15 hours. After immersion, the substrate 2 taken out is immersed in a 10 N aqueous solution of sodium hydroxide heated to 80 ° C., and immersion is continued at that temperature for 5 hours. After the immersion for 5 hours, the substrate was taken out, and the formation state of the barium titanate thin film was observed.

As a result, it was confirmed that a BaTiO ₃ thin film having a thickness of about 500 nm was formed on the surface of the substrate facing the glass 1 when immersed in the aqueous solution of hexafluorotitanate ion.

Example 2 Barium carbonate, boric acid and titanium dioxide were weighed so as to have a composition of No. 7 in Table 1, and placed in a platinum crucible to prepare a solution.
After heating to 00 ° C. and melting for 1 hour, the melt is poured out onto a metal plate, and then pressed with another metal plate to form a glass plate. Then, this glass plate was 10mm x 10mm x 1
Cut to the size of mm. Next, the cut glass was opposed to each substrate (base material) made of alumina sintered body, gold, silver, PMMA, and polyethylene, and a distance (gap) of 0.5 mm was maintained between the glass and the base material. Is fixed via a spacer 4 (FIG. 1). Then, as shown in FIG. 1, the glass 1a and the substrate 2 fixed to each other are immersed in 30 ml of an aqueous solution 3a in which ammonium hexafluorotitanate is dissolved to a concentration of 500 mM, and the liquid temperature is reduced to 50 ° C. Keep and continue immersion for 5 hours. After immersion, the substrate 2 taken out is immersed in a 5N sodium hydroxide solution heated to 70 ° C., and immersion is continued at 70 ° C. for 5 hours. And 5
After immersion for a time, the substrate was taken out, and the state of formation of the barium titanate thin film was observed.

As a result, the surface of the substrate facing the glass when immersed in the aqueous solution of hexafluorotitanate ion,
It was confirmed that a BaTiO ₃ thin film having a thickness of about 800 nm was formed.

In the above embodiment, the case where the distance between the glass and the substrate is 0.5 mm has been described. However, the distance between the glass and the substrate is not limited to this. The value can be adjusted to an appropriate value in consideration of conditions such as the concentration of hexafluorotitanate ion in the aqueous solution and the liquid temperature.

The alkaline aqueous solution for immersing the substrate on which the BaTiOF ₄ thin film is formed is not limited to a sodium hydroxide solution, but may be a potassium hydroxide solution or another alkaline aqueous solution.

[0025]

As described above, according to the method of forming a barium titanate thin film of the present invention, a substrate and a glass containing BaO and B ₂ O ₃ are opposed to each other, BaTiOF on the surface of the substrate
_After the thin film of ₄ is formed, the surface of the base material is treated with an aqueous alkaline solution, so complex and large-scale facilities and strict film forming conditions are not required, and inorganic materials, metal materials, A barium titanate thin film can be formed extremely easily on a wide area on a substrate made of various materials such as an organic material.

According to the method for forming a barium titanate thin film of the present invention, in particular, it becomes possible to form a barium titanate thin film on the surface of a substrate made of an organic material. It can be applied not only to resonators and the like but also to wider applications.

[Brief description of the drawings]

FIG. 1 is a view showing one step of a method for forming a barium titanate thin film of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Glass 2 Substrate 3 Aqueous solution containing hexafluorotitanate ion 4 Spacer

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-1-93443 (JP, A) JP-A-2-221121 (JP, A) JP-A-2-258700 (JP, A) JP-A-2- 94209 (JP, A) JP-A-61-30678 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 23/00 CA (STN)

Claims (4)

(57) [Claims] 1. A substrate and a glass containing at least BaO and B ₂ O ₃ are opposed to each other at a predetermined interval, and immersed in an aqueous solution containing hexafluorotitanate ion (TiF ₆ ^2- ). By dissolving the constituents from the glass and forming a thin film of BaTiOF ₄ on the surface of the substrate, the surface of the substrate is treated with an aqueous alkaline solution, whereby titanium Barium acid (BaT
iO ₃ ) A method for forming a barium titanate thin film, comprising obtaining a thin film. Wherein said glass is barium (Ba) and boron (B), respectively in terms BaO, the _{B 2 O 3, BaO: 1~50mol} % B 2 O 3: 50~ 99 mol% of the range The method for forming a barium titanate thin film according to claim 1, wherein: 3. The method for forming a barium titanate thin film according to claim 1, wherein the pH of the alkaline aqueous solution is 13 or more. 4. The method for forming a barium titanate thin film according to claim 1, wherein the temperature of the alkaline aqueous solution is 40 ° C. or higher.