JPH08133736A - Production of pyroelectric crystal film - Google Patents

Abstract

PURPOSE: To obtain an oriented pyroelectric 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 pyroelectric crystal film is formed on a substrate by hydrothermal synthesis. CONSTITUTION: When a pyroelectric crystal film made of Pb(Zrx Ti1-x )O3 where 0<=x<=1) is formed on a substrate by hydrothermal synthesis, the following two processes are adopted. The 1st process in which crystal nuclei are formed under the conditions of 50-500mmol/l Pb-contg. stock compd., 20-500mmol/l Zr-contg. stock compd. and 0.002-7mmol/l Ticontg. stock compd. The 2nd process in which crystals are grown under the conditions of 50-50Ommol/l Pb-contg. stock compd., 10-400mmol/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 a pyroelectric crystal film by hydrothermal synthesis. The pyroelectric crystal film obtained by the present invention can be used as an oriented pyroelectric crystal film for producing a pyroelectric element utilizing pyroelectric anisotropy.

[0002]

2. Description of the Related Art Conventionally, in order to obtain an oriented pyroelectric 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 pyroelectric crystal film is produced 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 required. There are problems such as difficulty and poor mass productivity when increasing the film thickness.

On the other hand, as for a pyroelectric element, for example, a non-oriented pyroelectric body manufactured by the conventional solid phase method is
Since the directions of the crystal axes are not aligned, there are problems that a material having a large electromechanical coupling coefficient cannot be obtained, and minute cracks are generated by the polarization treatment.

Therefore, attempts have been made to produce a pyroelectric crystal film by the hydrothermal synthesis method, but an oriented pyroelectric crystal film has not been obtained. For example, Tsurumi et al. [Technical Report of IEICE, 92 (No. 262), US 92-1
8, 35], a synthesis of a PZT thin film by a hydrothermal synthesis method has been examined.
The degree of orientation of the obtained thin film is low when viewed from the RD pattern and the SEM photograph of the surface of the PZT thin film of FIG.

[0006]

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

[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 pyroelectric 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 the Ti-containing starting compound forms a crystal nucleus under the condition of 0.002 mmol / l to 5 mmol / l, and the Pb-containing starting compound contains 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 500 mmo.
The present invention relates to a method for producing a pyroelectric crystal film, which comprises a second step of growing crystals under the condition of 1 / l.

The oriented pyroelectric crystal film produced by hydrothermal synthesis is
It is obtained by first forming crystal nuclei on the substrate by the hydrothermal synthesis at the concentrations of the respective raw material compounds described above, and then performing crystal growth. According to the present invention, an oriented pyroelectric crystal film can be obtained by allowing a small amount of a Ti-containing raw material compound to be present during the formation of crystal nuclei to carry out a hydrothermal reaction and then carrying out a growth reaction. Second
In the step, the molar ratio of the Zr-containing raw material compound and the Ti-containing raw material compound (Zr / Ti ratio) is larger than 0.1, preferably 0.2 to 9.0, whereby the orientation is further excellent. A pyroelectric crystal film is obtained.

In the present invention, the formation of crystal nuclei by hydrothermal synthesis has a Reynolds number of 2000 or less, preferably 100.
The dielectric thin film having more excellent orientation can be obtained by performing the crystal growth under the condition of 0 or less, and then performing 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 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, the pyroelectric crystal film is used. A substrate containing at least one or more constituent elements is preferable. It is also possible to use a substrate coated with the element forming the pyroelectric 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 substrate is used as a substrate, and a pyroelectric crystal film with aligned crystal axes is produced on the substrate by hydrothermal synthesis. The formation of this oriented pyroelectric crystal film is performed as follows.

First, Pb (NO ₃ ) ₂ aqueous solution 50 mol /
1 to 500 mmol / l, ZrOCl ₂ aqueous solution 20 mm
ol / l to 500 mmol / l, TiCl ₄ aqueous solution 0.
The substrate was placed and fixed on the top of the solution in a mixed solution of 002 mmol / l to 5 mmol / l and a KOH aqueous solution of 0.1 mol / l to 8 mol / l, and Reynolds number was 200.
120 or less, that is, no turbulence
Surface treatment by hydrothermal treatment is performed at a temperature of ˜200 ° C. for 0.25 to 24 hours to form crystal nuclei with crystal axes 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 10 mmol / l to 500 mm
ol / l, TiCl ₄ aqueous solution 5 mmol / l to 400 m
mol / l and KOH aqueous solution 0.12 mol / l-8
The substrate on which the oriented crystal nuclei are formed is put into a mol / l mixed solution, and hydrothermal treatment is performed at 100 to 140 ° C. for 1 to 96 hours. As a result, a highly oriented pyroelectric 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 in pure water, then ultrasonic cleaning in acetic acid aqueous solution, further ultrasonic cleaning in pure water,
It is dried at 100 to 120 ° C. for about 12 hours.

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

The electrode used when the pyroelectric 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 0.02 mmol and KOH aqueous solution 0.3 mol mixed solution (total solution amount 150 ml, filling rate 50%) were added to the middle part. 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 c-axis 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, a Pb (NO ₃ ) ₂ aqueous solution 16
mmol, ZrOCl ₂ aqueous solution 8.32 mmol, Ti
Cl ₄ aqueous solution 8 mmol and KOH aqueous solution 2.3 mo
The mixed solution (total solution amount: 640 ml) of 1 was placed and fixed on the upper portion, and a Pb (ZrTi) O ₃ film was formed under hydrothermal conditions at 130 ° C. for 48 hours without any special stirring operation. Then, ultrasonic cleaning in pure water 3 minutes x 2 times, 1 mol / l
Perform ultrasonic cleaning in an acetic acid aqueous solution for 3 minutes × 2 times, and further in pure water for 3 minutes × 2 times, and perform 1 time at 100 ° C.
It was dried for 2 hours. The X-ray diffraction pattern and the SEM photograph of the pyroelectric crystal film thus obtained are shown in FIGS. 2 and 3, respectively. The expression given by Lotgerling (eg, F. K. Lotgerling,
J. Inorg. Nucl. Chem, 9, 113 (1
959)), the degree of orientation in the (001) direction was calculated to be 0.56, and the orientation was in the c-axis direction as compared with the ceramics produced by the usual solid phase method. Gold electrodes were formed by vapor deposition on the oriented pyroelectric crystal film thus obtained.

The Pb (Zr _x Ti thus obtained was
_{For the} pyroelectric element made of _1-x ) O ₃ (where x is 0.52), a voltage was applied without polarization treatment to measure the pyroelectric current, and the pyroelectric current was 0. .8 nA /
It was also electrically confirmed that the polarization directions were uniform at mV. The measurement result of the pyroelectric current is shown in FIG.

[0020]

As described above, according to the present invention, an oriented pyroelectric crystal film can be obtained by hydrothermal synthesis. The pyroelectric crystal film obtained by the present invention has high sensitivity and excellent directivity when used as an infrared sensor.

[Brief description of drawings]

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

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

FIG. 4 Pb after the crystal growth reaction obtained by the present invention
Is a graph showing measurement results of the pyroelectric current (ZrTi) _{O 3} pyroelectric crystal film.

Front page continuation (72) Inventor Takayuki Kimura 5 Ube City, Ube City, Yamaguchi Prefecture 5 1978, Kogushi, Ube Ube Laboratory Ltd.

Claims (1)

[Claims] 1. Pb (Zr _{x is formed} on the substrate by hydrothermal synthesis.
In the method of forming a pyroelectric 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 10 mmol
/ L to 400 mmol / l and a Ti-containing raw material compound in the second step of crystal growing under conditions of 10 mmol / l to 500 mmol / l.