JPH09148648A - Manufacture of piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable piezoelectric elements of high quality to be efficiently manufactured by the use of a board without cutting off a piezoelectric film and generating cracking or delamination among a piezoelectric film, an electrode, and a metal board. SOLUTION: The periphery or the periphery and all the one surface of a titanium board 1 are masked with a masking material, a piezoelectric film 3 is formed on a non-masked part of the titanium board 1, an electrode 4 is formed, and the masking material is removed, whereby a piezoelectric bimorph element and a piezoelectric unimorph element are manufactured. Furthermore, the one side or both sides of the titanium board 1 are separated into sections with a masking material, a piezoelectric film 3 and an electrode 4 are formed on each section, the masking material is removed, the titanium board 1 is divided into piezoelectric elements 6 along dividing lines, whereby a piezoelectric bimorph element and a piezoelectric unimorph element are manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a piezoelectric element which expands and contracts when a voltage is applied and generates a voltage by mechanical stress, and more particularly to a thin piezoelectric unimorph element and a bimorph element.

[0002]

2. Description of the Related Art Piezoelectric elements include a unimorph element composed of one piezoelectric body and a bimorph element having a structure in which two piezoelectric bodies having the same thickness are bonded together. When a voltage is applied, the piezoelectric body expands and contracts, and when the voltage changes alternately, vibration according to the frequency of the voltage change is obtained. Therefore, it is widely applied as an oscillator of ultrasonic waves, an oscillator such as an ultrasonic motor or a piezoelectric buzzer, an actuator such as a camera shutter, and the like. Further, since a voltage is generated when the piezoelectric body receives mechanical stress, it is also used as an ultrasonic wave reception, a stress sensor, an igniter, and the like.

Conventionally, piezoelectric elements are produced by compression molding raw material powders.
It is manufactured by adhering electrodes to the piezoelectric body obtained by firing. Further, in the case of forming a thin piezoelectric element up to about 0.1 mm, a method of printing an electrode paste on a green sheet made of a piezoelectric material and then firing it integrally (for example, JP-A-61-239682) is also used. ). Since the resonance frequency of the piezoelectric element is proportional to its thickness, it is necessary to reduce its thickness in order to handle low frequencies. The thinning is also important for downsizing the device. However, it is difficult to form a thin film by the method of compressing and molding the raw material powder among the above-mentioned conventional methods, and in the case of a bimorph element, there is a problem in heat resistance of the element because two piezoelectric bodies are used as an adhesive. Even with the green sheet method, it is difficult to achieve a film thickness of several tens of μm or less.
Further, if it is made too thin, the strength will decrease, so it is necessary to adhere this to an elastic body and reinforce it after integrally firing. The characteristics of this adhesive limit the heat resistance of the device.

A method in which an elastic body is used as a substrate and a piezoelectric film is hydrothermally synthesized on the substrate has also been proposed (JP-A-5-259525).
In this method, as shown in FIG. 4, first, the substrate is placed in an aqueous solution containing a raw material such as lead nitrate and kept at 140 to 160 ° C. to generate crystal nuclei on the surface of the substrate. After the substrate on which the crystal nuclei have been deposited is washed and dried, the substrate is further placed in an aqueous solution containing a titanium source and kept at 100 to 130 ° C. to form the piezoelectric film 3. Further, the side surface of the substrate is covered with a plating resist to form the electrode 4 by electroless plating or sputtering.

According to this method, an extremely thin piezoelectric film of about several μm can be formed, and a bimorph element can be manufactured in one step without using an adhesive, but as shown in FIG. Since the piezoelectric layer is also formed on the side surface of the substrate 1 (4 (a)), it is necessary to mechanically cut and remove the piezoelectric layer on the side end face portion in order to ensure complete insulation between both electrodes ( 4 (b)). However, since the titanium foil and the piezoelectric layer have different coefficients of thermal expansion or expansion and contraction, peeling between the piezoelectric layer and the titanium foil may occur near the cut portion due to shear stress during cutting, The yield rate of piezoelectric device production is reduced.

[0006]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for manufacturing a piezoelectric element in which a piezoelectric layer is formed on an elastic substrate by a hydrothermal synthesis method, at the time of cutting for ensuring insulation between electrodes. It is to solve the problem of peeling between the titanium substrate and the piezoelectric layer and improve the production efficiency.

[0007]

The inventors of the present invention previously masked a titanium substrate portion corresponding to a peripheral end portion of a piezoelectric element, formed a piezoelectric film by hydrothermal synthesis, and then formed an electrode, and then, If the masking material is removed, the insulation between the electrodes can be taken without the need for a cutting operation, and thus the problem of peeling between the piezoelectric layer and the substrate (deterioration of the bondability) can be solved. Masking is performed so that a plurality of sections are formed on the surface, and after the piezoelectric layer and the electrode are formed, the masking material is removed, and each section is cut at the removed portion, so that a plurality of sections can be formed without deteriorating the bondability. It has been confirmed that the piezoelectric element can be efficiently manufactured at one time, and the above problems have been solved.

That is, the present invention provides the following piezoelectric element manufacturing method. 1) A titanium substrate is covered on one side and a peripheral portion with a masking material, a piezoelectric film is formed on a non-masking portion of the substrate by hydrothermal synthesis, electrodes are further formed on the surface of the piezoelectric film, and then the masking material is removed. A method for manufacturing a piezoelectric unimorph element, which is characterized by the above. 2) Cover the periphery of the titanium substrate with a masking material, and form a piezoelectric film by hydrothermal synthesis on the non-masking portions on both sides of the substrate,
Furthermore, after the electrode is formed on the surface of the piezoelectric film, the masking material is removed, and a method for manufacturing a piezoelectric bimorph element. 3) After covering the entire surface of one side of the titanium substrate with a masking material, and dividing the other surface of the substrate into a plurality of compartments with the masking material, forming piezoelectric films and electrodes in each compartment, and removing the masking material, A method for manufacturing a unimorph element, which comprises cutting along the dividing line.

4) Both sides of the titanium substrate are divided by a masking material into a plurality of compartments so that the two compartments are aligned with each other, a piezoelectric film and an electrode are formed in each compartment, and the masking material is removed. A method for manufacturing a bimorph element, which comprises cutting along the dividing line. 5) The masked titanium substrate was kept at a temperature of 140 to 160 ° C. in a mixed aqueous solution containing nitrate, zirconium oxychloride and potassium hydroxide to generate crystal nuclei in the unmasked portion of the substrate, and then the substrate was taken out, It is washed and dried, then 10 times in a mixed aqueous solution containing lead nitrate, zirconium oxychloride, titanium tetrachloride and potassium hydroxide.
5. The manufacturing method according to any one of 1 to 4 above, wherein a piezoelectric film is formed by growing a lead zirconate titanate crystal while maintaining the temperature at 0 to 130 ° C. 6) The manufacturing method according to any one of 1 to 5 above, wherein the substrate is masked by sequentially applying, exposing and developing a resist. 7) The manufacturing method according to any one of 1 to 5 above, wherein the substrate is masked by pattern printing.

[0010]

According to the method of the present invention, both the unimorph element and the bimorph element can be easily and efficiently manufactured by devising the way of masking the titanium substrate. FIG. 1 shows a manufacturing process of an example of a bimorph element. In this example, the masking layer 2 is formed on the substrate 1 (1 (a)), and then the piezoelectric film 3 (1 (b)) and the electrode 4 are formed on the non-masking portion 5 (1 (c)). )) Then, the masking layer 2 is removed to obtain the piezoelectric element 6 in which the piezoelectric film 3 and the electrode 4 are laminated on the substrate 1 (1 (d)).

The manufacturing method of the present invention will be described below. [Substrate] In the present invention, a titanium substrate is used as the piezoelectric element substrate. By using titanium as the substrate, the required strength can be maintained even if the piezoelectric layer is thinned. Further, when hydrothermally synthesizing a titanium-containing PZT (lead zirconate titanate) piezoelectric material having excellent properties, the bondability between titanium of the substrate and PZT formed thereon is improved. In order not to impair the characteristics of the piezoelectric element, a titanium foil of 500 μm or less, preferably 100 μm or less is used.

[Masking Step] In the masking step, the surface of the substrate is covered according to a predetermined pattern. As a masking method, a masking material is formed by a known method such as a printing method or a photoresist method using a photosensitive resin. The photoresist method is preferred. In the photoresist method, first, a photoresist is applied to the entire surface of a titanium substrate whose surface has been washed with a solvent (acetone or the like). The photoresist is not particularly limited as long as it can be maintained without being dissolved during hydrothermal synthesis of the piezoelectric film and electrode formation. An alkali resistant rubber-based resist material, for example, a mixed system of an isoprene rubber component and a photosensitizer component is preferable. Examples of the photosensitizer include bisazide compounds. This is dissolved in a suitable solvent and applied.

The resist coating method is a method commonly used in semiconductor manufacturing and the like, for example, a method of coating with a blade, a method of immersing a substrate in a resist solution, and a method of spinning a substrate while spinning the resist solution onto the resist solution. Any of the coating methods may be used. The thickness of the coating film (when dried) is usually several to ten.
μm. If necessary, the solvent is removed by heating and drying at 100 ° C or lower. The entire surface of the substrate is covered with resist. After drying, exposure is performed. The exposure is performed through a photomask formed in a pattern so that the resist remains at a predetermined place (a peripheral portion of the piezoelectric element in FIG. 1) or by scanning with a light beam. In the case of a negative type resist, the exposed portion gels and remains on the substrate without being dissolved even in the next developing step. In the positive resist, the non-exposed portion remains on the substrate.

Ultraviolet rays are usually used for the exposure. For example, the above-mentioned bisazide compound releases nitrogen to generate nitrene upon irradiation with ultraviolet rays, and this nitrene reacts with a double bond or the like of the cyclized rubber to cause crosslinking.
The development may be performed according to the masking used in the usual semiconductor manufacturing. It is dipped in a developing solution made of a solvent (for example, n-heptane or xylene) that dissolves or softens the masking agent, or after spraying the developing solution, it is thoroughly washed with a washing solution such as isopropyl alcohol and dried. 150 if necessary
The solvent is removed by heating and drying at a temperature of not higher than ℃. In this way, a piezoelectric element manufacturing substrate having a desired portion coated with a resist is obtained.

[Piezoelectric film formation] The piezoelectric material preferably used in the present invention is a piezoelectric material containing a titanium ion component. For example, a solid solution of BaTiO ₃ and PbTiO ₃ or CaTiO ₃ having a perovskite crystal structure, or PbZ
PZT or the like, which is a solid solution of rO ₃ and PbTiO ₃ , is preferable. To form the piezoelectric film, a hydrothermal synthesis method is used in which salts of metal ions corresponding to the intended material are mixed as an aqueous solution and synthesized on a substrate. For example, when forming a PZT film, it is preferable to take a method of generating crystal nuclei and then precipitating PZT as shown below. By this method, a uniform film can be efficiently synthesized.

That is, first, 0.1 to 1.0 mol / l of lead nitrate (Pb (NO ₃ ) ₂ ), 0.05 to 2.0 mol / l of zirconium oxychloride (ZrOCl ₂ ) and 2.5 to
The masked titanium substrate was placed in a mixed aqueous solution containing 8.0 mol / l potassium hydroxide (KOH) and kept at a temperature of 140 to 160 ° C. for 12 to 72 hours to crystallize on the unmasked portion of the substrate. Generate a nucleus. After washing and drying, 0.2 to 1.2 mol / l lead nitrate (Pb (N
O ₃ ) ₂ ), 0.05 to 2.0 mol / l zirconium oxychloride (ZrOCl ₂ ), 0.1 to 2.0 mol / l titanium tetrachloride (TiCl ₄ ) and 1.1 to 5.0 mol / l potassium hydroxide (KOH). The substrate is put into a mixed aqueous solution containing the same and kept at a temperature of 100 to 130 ° C. for 12 to 96 hours to form a PZT piezoelectric film. Several to ten by the above method
A PZT piezoelectric film having a thickness of μm can be formed.

[Electrode formation] As the method for forming the electrodes, any known method can be used as long as it does not destroy the masking pattern formed by the resist. For example, the electroless plating method, the sputtering method, the vapor deposition method, or the like can be used, and the sputtering method is particularly preferable. Examples of the electrode material include Ni, Pt, Au, Ag and Al. The film thickness is usually several tens of nm to 1 μm. If it is less than the lower limit, reliability is poor, and if it exceeds the upper limit, it is easily broken.

[Removal of Masking] The masking is removed by dissolving the masking material in the substrate on which the electrode is formed (for example, an aromatic organic solvent such as toluene or xylene).
If necessary, it is heated and immersed to dissolve and remove the masking. A piezoelectric element piece is obtained through washing and drying.

[Masking Pattern] In the present invention, piezoelectric elements having various piezoelectric film patterns on a substrate can be obtained according to the masking pattern. For example, according to the method of the present invention, both one piezoelectric unimorph element and bimorph element in which insulation between electrodes is secured can be manufactured from one substrate. Although FIG. 1 shows the manufacturing process of the bimorph element, in the case of the unimorph element, as shown in FIG. 2, the peripheral portion including the entire one surface and the side surface of the substrate is covered with the masking agent 2 (FIG. 2b). . After the PZT film 3 and the electrode 4 are formed on the entire surface of the non-masking portion 5 on one surface of the substrate, the masking is removed to obtain a unimorph element. In any case, since the masking material is dissolved and removed, it is not necessary to cut and remove the peripheral edge of the substrate.
It does not cause cracks or cracks in the film and does not impair the bondability between the PZT film and the substrate. Further, since the PZT film does not exist on the peripheral edge of the substrate and the surface of the PZT film can be completely covered with the electrode material, the piezoelectric efficiency is good.

According to the method of the present invention, a plurality of piezoelectric elements can be efficiently manufactured from one substrate. In this mode, as shown in the plan view of FIG. 3, the sections corresponding to the respective elements are divided, for example, the substrate 1
Masking pattern 2 is formed in a grid pattern on (3
(A)). When manufacturing a bimorph element, a masking pattern is formed so that the sections on both sides are aligned. Next, the piezoelectric film 3 and the electrode 4 are formed in each section (3 (b)). Then, after the mask pattern 2 is removed, the substrate is cut along the dividing lines that partition each section to obtain individual piezoelectric element pieces (3 (d)). P on the cutting line
Since the ZT film does not exist, the PZT film is not cracked or cracked during cutting, and the bondability between the PZT film and the substrate is not impaired. Further, in the manufactured piezoelectric element, the PZT film does not exist on the peripheral edge of the substrate, and the surface of the PZT film can be completely covered with the electrode material, so that the piezoelectric efficiency is good.

[0021]

Example 1 A titanium foil having a thickness of 50 μm (10 mm × 30 mm) was thoroughly washed with acetone, dried and then immersed in a photoresist solution (OMR-83 manufactured by Tokyo Ohka Co., Ltd.). The surface of the foil was coated with a resist solution. The film thickness of the resist when dried was about several μm. After the resist was dried, a mask having a light opaque center portion and a light permeable portion corresponding to a peripheral edge width of 1 mm of the substrate was placed on both sides of the substrate, exposed with an ultraviolet lamp for 10 seconds, and developed with n-heptane. did. Pb (NO ₃ ) ₂ (10.00mmo in a Teflon autoclave container
l), ZrOCl ₂ (4.8 mmol) and KOH (13
30 ml of a mixed aqueous solution containing 6.8 mmol) and the substrate subjected to the above treatment were put in an autoclave, and 150
Crystal nuclei were generated at 48 ° C. for 48 hours.

After the substrate was taken out and washed in distilled water by ultrasonic cleaning, Pb (NO ₃ ) ₂ (9.91 mmol), ZrO ₂
Cl ₂ (4.3 mmol) and TiCl ₄ (4.5 mmo
1) and a mixed aqueous solution containing KOH (65.6 mmol) 3
It was added to 0 ml, and hydrothermal synthesis treatment was again carried out at 120 ° C. for 48 hours in the autoclave. After the hydrothermal synthesis, the substrate was taken out, ultrasonically washed with distilled water and dried, and its cross section was measured with a metallographic microscope. As a result, it was found that the Zr: Ti molar ratio of 8 μm was 5 μm on each of the front and back surfaces of the titanium substrate.
It was observed that a zirconium titanate (PZT) crystal of 2:48 was homogeneously deposited. A thickness of 4 is formed on this substrate by an RF sputtering method using an ion sputtering device.
A 0 nm Pt electrode was formed, and then the photoresist was dissolved and removed using a resist dissolving agent (502A manufactured by Tokyo Ohka). When one end of the piezoelectric film manufactured in this way was fixed and the other end was used as a free end, a DC voltage of 1 V was applied,
A maximum displacement of 0.2 mm was observed on the free end side. Also, 1
After driving the vibrator for 1 hour by applying an AC voltage of V and 104 Hz, the surface of the vibrator was observed, and no peeling or cracking between the piezoelectric film and the substrate was observed.

Example 2 A Ti substrate having a size of 30 mm × 60 mm and a thickness of 50 μm was used.
A plurality of sections of 8 mm × 28 mm were formed on the entire surface of one side of the substrate and the other side with a masking material. Example 1
After the PZT film and the electrodes were formed and the masking material was removed in the same manner as in, a plurality of unimorph elements were obtained by cutting along a dividing line using a cutter. When the end face of each element was observed with a magnifying glass, the piezoelectric film and the electrode were uniformly overlaid on each element piece, and no peeling between the substrate and the piezoelectric film was observed. In addition, the end face of the laminated portion had a sharp rectangular shape.

[0024]

According to the method of the present invention, piezoelectric unimorph and bimorph elements can be manufactured without cutting the piezoelectric film. Since it is possible to manufacture a relatively hard and fragile piezoelectric film such as PZT without applying excessive cutting force, it is possible to efficiently obtain a high-quality piezoelectric element that is free from cracks or peeling between the piezoelectric film and the electrodes and the metal substrate. . Moreover, a plurality of piezoelectric unimorph and bimorph elements can be efficiently manufactured from one substrate.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of an example of a piezoelectric bimorph element according to the method of the present invention.

FIG. 2 is a manufacturing process diagram of an example of a piezoelectric unimorph element according to the method of the present invention.

FIG. 3 is an explanatory diagram of a process of manufacturing a plurality of piezoelectric elements by the method of the present invention.

FIG. 4 is an explanatory diagram of a piezoelectric element manufactured by a conventional hydrothermal synthesis method.

[Explanation of symbols]

 1 substrate 2 resist 3 piezoelectric film 4 electrode 5 non-masking part 6 piezoelectric element

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahisa Isaji Komaki City, Aichi 3600 Amigazu, Kita Sotoyama, Tokai Rubber Industry Co., Ltd.

Claims (7)

[Claims] 1. A masking material covering one surface and a peripheral portion of a titanium substrate, a piezoelectric film is formed on the non-masking portion of the substrate by hydrothermal synthesis, and an electrode is further formed on the surface of the piezoelectric film. A method for manufacturing a piezoelectric unimorph element, which comprises: 2. A masking material is applied to the periphery of a titanium substrate, a piezoelectric film is formed on the non-masking parts on both sides of the substrate by hydrothermal synthesis, electrodes are further formed on the surface of the piezoelectric film, and then the masking material is removed. A method for manufacturing a piezoelectric bimorph element, comprising: 3. A titanium substrate is entirely covered on one side with a masking material, and the other surface of the substrate is divided into a plurality of compartments by a masking material. A piezoelectric film and an electrode are formed in each compartment and the masking material is removed. After that, a method for manufacturing a piezoelectric unimorph element, characterized by cutting along the dividing line. 4. A titanium substrate is divided into a plurality of compartments by a masking material so that the compartments on both surfaces are aligned, a piezoelectric film and an electrode are formed in each compartment, and the masking material is removed. A method for manufacturing a piezoelectric bimorph element, which comprises cutting along the dividing line. 5. The masked titanium substrate is kept at a temperature of 140 to 160 ° C. in a mixed aqueous solution containing lead nitrate, zirconium oxychloride and potassium hydroxide to generate crystal nuclei in the unmasked portion of the substrate, The substrate is taken out, washed, dried, and then kept at a temperature of 100 to 130 ° C. in a mixed aqueous solution containing lead nitrate, zirconium oxychloride, titanium tetrachloride and potassium hydroxide to grow a lead zirconate titanate crystal. The method according to any one of claims 1 to 4, wherein the piezoelectric film is formed by the method. 6. The substrate is masked by sequentially applying a resist, exposing and developing the resist.
The manufacturing method according to any one of 1. 7. The manufacturing method according to claim 1, wherein the substrate is masked by pattern printing.