JPH08133735A - Production of dielectric crystal film - Google Patents

Abstract

PURPOSE: To obtain an a-axis oriented dielectric crystal film having crystallographic axes in a certain direction and not requiring film formation or heat treatment at a high temp. by combining two processes each carried out under specified conditions when a lead titanate zirconate dielectric crystal film is formed on a substrate by hydrothermal synthesis. CONSTITUTION: When a dielectric crystal film made of Pb(Zrx Ti1-x )O3 (where 0<=x<=1) is formed on a substrate by hydrothermal synthesis, the objective dielectric crystal film with a-axes oriented perpendicularly to the substrate is obtd. by the following two processes. The 1st process in which crystal nuclei are formed under the conditions of 50-500mmol/l Pb-contg. stock compd., 20-500 mmol/l Zr-contg. stock compd. and 0.002-5mmol/l Ti-contg. stock compd. The 2nd process in which crystals are grown under the conditions of 50-500mmol/l Pb-contg. stock compd., 5-400mmol/l Zr-contg. stock compd. and 10-500mmol/l Ti-contg. stock compd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an a-axis oriented dielectric crystal film by hydrothermal synthesis. The dielectric crystal film obtained by the present invention is used as an a-axis oriented dielectric crystal film for producing a piezoelectric actuator, a piezoelectric sensor, a pyroelectric sensor, or a dielectric element utilizing anisotropy of dielectric constant. be able to.

[0002]

2. Description of the Related Art Conventionally, in order to obtain an oriented dielectric crystal film, it is general that a single crystal of MgO or SrTiO ₃ is used as a substrate and is formed by a sputtering method or a MOCVD method.

However, when an oriented dielectric crystal film is formed by the above method, the type of substrate is limited, film formation at high temperature or heat treatment after film formation is required, and composition control is difficult. However, there is a problem such as poor mass productivity when increasing the film thickness.

On the other hand, regarding a piezoelectric element, for example, in the case of non-orientation, that is, the piezoelectric ceramics produced by the conventional solid phase method, the crystal axes of the piezoelectric ceramics are not aligned, so that those having a large electromechanical coupling coefficient can be obtained. There is a problem that minute cracks are generated by the polarization treatment, hysteresis is generated in the displacement due to the existence of the 90 degree domain, large creep and shift are caused, or unnecessary mode vibration is generated.

Therefore, attempts have been made to produce a dielectric crystal film by the hydrothermal synthesis method, but no a-axis oriented dielectric crystal film has been obtained yet. For example, Tsurumi et al. [Technical Research Report of IEICE, 92 (No. 262), US9
2-18, 35], a synthesis of a PZT thin film by a hydrothermal synthesis method has been studied. However, the XRD pattern of FIG. 9 and the SEM of the surface of the PZT thin film of FIG.
The orientation of the thin film obtained from the photograph is low.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has an a-axis oriented dielectric crystal whose crystal axis directions are uniform and which does not require film formation or heat treatment at a high temperature. The purpose is to provide a membrane.

[0007]

According to the present invention, Pb (Zr _x Ti _1-x ) O ₃ (provided that
0 ≦ x ≦ 1. In the method for forming a dielectric crystal film of (1), the Pb-containing raw material compound is 50 mmol / l.
~ 500 mmol / l, Zr-containing raw material compound is 20 mm
ol / l to 500 mmol / l and a Ti-containing starting compound forming a crystal nucleus under the condition of 0.002 mmol / l to 5 mmol / l, and a Pb-containing starting compound containing 50 mmol / l to 500 mmol / l and Zr The raw material compound is 5 mmol / l to 400 mmol / l and the Ti-containing raw material compound is 10 mmol / l to 400 mmo.
The present invention relates to a method for producing a dielectric crystal film in which the a-axis is oriented perpendicularly to the substrate, which is characterized by comprising a second step of crystal growth under the condition of 1 / l.

The a-axis oriented dielectric crystal film by hydrothermal synthesis is obtained by first forming crystal nuclei by hydrothermal synthesis on the substrate at the concentration of each raw material compound described above, and then performing crystal growth. According to the present invention, an a-axis oriented dielectric crystal film can be obtained by allowing a Ti-containing raw material compound to be present in the formation of crystal nuclei to undergo a hydrothermal reaction and then performing a growth reaction. In the second step, by setting the molar ratio (Zr / Ti ratio) of the Zr-containing raw material compound and the Ti-containing raw material compound to be less than 1, preferably 0.4 to 0.8, the a-axis orientation is An even better dielectric crystal film can be obtained.

In the present invention, the formation of crystal nuclei by hydrothermal synthesis has a Reynolds number of 2000 or less, preferably 100.
A dielectric thin film having further excellent a-axis orientation can be obtained by performing the crystal growth under the condition of 0 or less and then crystal growth. The conditions for crystal growth may be laminar flow or turbulent flow, but the film formation rate can be increased by appropriate stirring.

The substrate used in the present invention is not particularly limited, but the structure of the dielectric crystal film is increased in order to increase the adhesion between the crystal film and the substrate due to the reaction between the substrate and the metal ions in the solution during the formation of crystal nuclei. A substrate containing at least one element is preferable. It is also possible to use a substrate coated with the element forming the dielectric crystal film.

The raw material compounds containing the constituent elements of Pb, Zr and Ti used in the hydrothermal reaction in the present invention include chloride, oxychloride, nitrate, alkoxide, acetate, hydroxide, oxide and the like. preferable. In addition, examples of the alkali compound used in the hydrothermal reaction include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The concentration of the alkali compound in the hydrothermal reaction was 0.1 mol / l when the crystal nuclei were formed.
~ 8.0 mol / l, 0.12 mol during growth reaction
/ L to 8.0 mol / l is preferable.

A specific example of the manufacturing method of the present invention will be described in detail below. A Ti substrate or a Ti-coated one is used as a substrate, and a dielectric crystal film having crystal axes aligned in the a-axis direction is produced on the substrate by hydrothermal synthesis. The formation of this a-axis oriented dielectric crystal film is performed as follows.

First, 50 mmol of Pb (NO ₃ ) ₂ aqueous solution
/ L~500mol / l, ZrOCl ₂ aqueous solution 20mm
ol / l to 500 mmol / l, TiCl ₄ aqueous solution 0.
In a mixed solution of 002 mmol / l to 5 mmol / l and a KOH aqueous solution of 1 mol / l to 8 mol / l, the substrate was placed and fixed on the upper part of the solution, and the Reynolds number was 2000 or less, that is, turbulent flow did not occur. ~ 1
Surface treatment by hydrothermal treatment is performed at a temperature of 90 ° C. for 1 to 24 hours to form crystal nuclei in which the a-axis crystal axes are aligned with the substrate surface.

Next, in order to grow a crystal, Pb (N
O ₃ ) ₂ aqueous solution 50 mmol / l to 500 mmol /
1, ZrOCl ₂ aqueous solution 5 mmol / l to 400 mmo
l / l, TiCl ₄ aqueous solution 10 mmol / l to 500 m
mol / l and KOH aqueous solution 2 mol / l-8 mol
The substrate on which the oriented crystal nuclei are formed is put in a mixed solution of 1 / l, and hydrothermal treatment is performed at 100 to 140 ° C. for 1 to 96 hours. As a result, a highly oriented piezoelectric crystal film is formed on the substrate. The heating method in the hydrothermal treatment is an oil bath or an electric furnace. After that, general cleaning is performed. For example, ultrasonic cleaning is performed in pure water, then ultrasonic cleaning in an acetic acid aqueous solution, and then ultrasonic cleaning in pure water.
Dry at 20 ° C. for about 12 hours.

The composition of the piezoelectric crystal film thus formed is P
b (Zr _x Ti _1-x ) O ₃ (where 0 ≦ x ≦ 1). The crystal state of the obtained piezoelectric crystal film is confirmed by X-ray diffraction or the like.

The electrode used when the dielectric crystal film obtained in the present invention is formed into an element is not particularly limited, but an optimum electrode is selected in consideration of cost and mass productivity. For example, there are Ni by a sputtering method, Ni by an electroless plating method, baking type Ag, and the like. In addition, Al by vapor deposition, Pt or Au by sputtering method, etc. are also used. When a resin is used for the substrate, the baking type Ag electrode is not preferable because it cannot be heated to a high temperature.

[0017]

EXAMPLES Hereinafter, specific examples of the present invention will be described in more detail.

Example 1 Pb (NO ₃ ) ₂ aqueous solution 16 mmol, ZrOCl ₂ aqueous solution 8 mmol, TiCl ₄ aqueous solution 0.08 mmol and KOH aqueous solution 0.3 mol mixed solution (total solution amount 150 ml, filling rate 50%) Then, a Ti substrate was installed and fixed, and hydrothermal treatment was performed at 180 ° C. for 12 hours without any special stirring operation, and Pb (Zr
Ti) O ₃ crystal nuclei were generated. The crystals thus obtained were oriented in the a-axis direction as compared with the ceramics prepared by the usual solid phase method as shown in the X-ray diffraction pattern in FIG. Next, for crystal growth, 16 mmol of Pb (NO ₃ ) ₂ aqueous solution, 1.6 mmol of ZrOCl ₂ aqueous solution, T
It was placed and fixed on the top of a mixed solution of 14.4 mmol of iCl ₄ aqueous solution and 2.3 mol of KOH aqueous solution (total solution amount 640 ml), and at 130 ° C., 4 without special stirring.
A hydrothermal treatment was performed for 8 hours to form a Pb (ZrTi) O ₃ film. Then, ultrasonic cleaning in pure water for 3 minutes x 2
Ultrasonic cleaning in 1 mol / l acetic acid aqueous solution 3 minutes x 2
And further, ultrasonic cleaning in pure water for 3 minutes × 2 times, and dried at 100 ° C. for 12 hours. The X-ray diffraction pattern and SEM photograph of the crystal film thus obtained are shown in FIGS. 2 and 3, respectively. Lotgerling
The expression given by (eg, F. K. Lotger
Ling, J. et al. Inorg. Nucl. Chem, 9,
113 (see 1959)), the degree of orientation in the (100) direction was determined to be 0.75, which was more oriented in the a-axis direction than the ceramics produced by the usual solid phase method. A gold electrode was formed by vapor deposition on the oriented crystal film thus obtained.

The Pb (Zr _x Ti thus obtained was
_The piezoelectric element made of _1-x ) O ₃ (where X is 0.1) is a bimorph element having a length of 20 mm.
Displaced when a voltage was applied without polarization,
It was also confirmed electrically that the polarization directions were aligned. This film had a dielectric constant of about 200 and a dielectric loss of about 0.02.

[0020]

As described above, according to the present invention, an a-axis oriented dielectric crystal film can be obtained by hydrothermal synthesis. The dielectric crystal film obtained by the present invention has a small displacement hysteresis, shift, and creep when used as an actuator, has high sensitivity when used as a sensor, and has an effect that unnecessary modes do not occur. .

[Brief description of drawings]

FIG. 1 Pb after the crystal nucleation reaction obtained by the present invention
Is a diagram showing an X-ray diffraction pattern of (ZrTi) _{O 3} oriented crystalline film.

FIG. 2 Pb after the crystal growth reaction obtained by the present invention
Is a diagram showing an X-ray diffraction pattern of (ZrTi) _{O 3} a-axis orientation crystal film.

FIG. 3 Pb after the crystal growth reaction obtained by the present invention
Is an SEM photograph showing in place of a drawing showing the crystal structure of (ZrTi) _{O 3} a-axis orientation crystal film.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01L 41/24 (72) Inventor Takayuki Kimura 5 1978, Ogushi Kogushi, Ube City, Yamaguchi Prefecture Ube Institute of Industrial Science Co., Ltd.

Claims (1)

[Claims] 1. Pb (Zr _{x is formed} on the substrate by hydrothermal synthesis.
In the method of forming a dielectric crystal film made of Ti _1-x ) O ₃ (where 0 ≦ x ≦ 1), the Pb-containing raw material compound is 50 mmol / l to 500 mmol / l, Z
r-containing raw material compound is 20 mmol / l to 500 mmol
/ L and Ti-containing raw material compound is 0.002 mmol /
The first step of forming crystal nuclei under the condition of 1 to 5 mmol / l, and the Pb-containing starting compound is 50 mmol / l to 5
00 mmol / l, Zr-containing raw material compound is 5 mmol / l
1 to 400 mmol / l and 1 containing Ti-containing raw material compound
2. A method for producing a dielectric crystal film in which the a-axis is oriented perpendicularly to the substrate, which comprises a second step of crystal growth under the condition of 0 mmol / l to 500 mmol / l.