JP2011129746A - Piezoelectric film actuator and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric film actuator using a piezoelectric film that does not contain lead and has high piezoelectric constant, which has high performance and is superior in temperature characteristic, and the method of manufacturing the same. <P>SOLUTION: A piezoelectric film actuator is formed of a piezoelectric film 2 formed on a substrate 1 and a lower electrode 3 and an upper electrode 4 for applying voltage to the piezoelectric film 2. The piezoelectric film actuator drives an object using displacement produced in the piezoelectric film 2 by applying voltage between the electrodes. The piezoelectric film 2 is composed of polycrystals of barium titanate (BaTiO<SB>3</SB>) whose particle size is 0.2-0.5 μm. The piezoelectric film 2 is formed by an aerosol deposition method, and then heat-treated at a temperature of 850 to 1,100°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a piezoelectric film type actuator for driving an object using displacement generated by applying a voltage to a piezoelectric film formed on a substrate, and a method for manufacturing the same, and in particular, a material for a piezoelectric film used for a piezoelectric actuator. And a manufacturing method thereof.

  Piezoelectric devices have advantages such as high energy density, low power consumption, and reduced electromagnetic noise. As electronic devices become smaller, camera autofocus mechanisms, thin speakers, and inkjet printer heads It is used for sensor elements such as actuators and gyros, and its application fields are expanding.

  These piezoelectric devices are required to be further reduced in size and thickness. In recent years, a piezoelectric film type in which a piezoelectric film is formed on a substrate and an object is driven using a displacement generated by applying a voltage to the piezoelectric film. Development of piezoelectric film type devices such as actuators has been actively conducted. As a material for the piezoelectric film, a lead-based piezoelectric material having excellent piezoelectric performance, for example, lead zirconate titanate (PZT) is generally used.

  On the other hand, in recent years, the EU (European Union) has begun to enforce the RoHS Directive that regulates the use of specific harmful substances such as lead in electronic devices in consideration of the environment and safety. Piezoelectric materials are not subject to regulation because there are no alternative materials yet, but lead-free piezoelectric materials are being actively developed.

In general, non-lead materials have lower piezoelectric characteristics than lead-based materials, and if the phase transition temperature of the material is within the operating temperature range of the device, temperature characteristics become a problem. Barium titanate (BaTiO ₃ ), one of the lead-free materials, has a large piezoelectric constant in bulk crystals, but it is difficult to produce a high-quality film while keeping the piezoelectric constant large, and the phase transition temperature is Since it is low, there is a problem that a stable temperature characteristic cannot be obtained even if a conventional crystal film is applied to a device.

  As a conventional technology, a lead-free piezoelectric material that has barium titanate as the main component and a part of which is replaced with an additive has been sintered to be used as a field-induced strain element. This is described in Patent Document 1. Also, barium titanate by a gas deposition method in which fine particles such as ceramics are suspended in a gas, aerosolized and collided with a substrate, and the heat energy at that time is used to sinter between the fine particles or between the fine particles and the substrate. Patent Document 2 describes a method for manufacturing a dielectric film. Furthermore, in Patent Document 3, as a method for producing a ceramic film or the like, an aerosol containing fine particles such as ceramics is collided with a substrate at high speed, and the resulting crystal plane shift, crystal grain refinement, and interparticle spacing due to mechanochemical reaction. An aerosol deposition method (AD method) using bonding is shown. In Non-Patent Document 1, a contact probe using a barium titanate film by this AD method is shown. On the other hand, Non-Patent Document 2 shows the relationship between the piezoelectric constant and the crystal grain size that determine the performance of a piezoelectric actuator when bulk barium titanate is sintered.

JP 2001-172077 A Japanese Patent Laid-Open No. 4-188503 Japanese Patent No. 3348154

“From the basics to the application of the aerosol deposition method” 2007, CMC Publishing, p. 199-208 “Japanese Journal of Applied Physics” 2007, 46, 10B, p. 7044-7047

However, in the above-mentioned Patent Document 1, since the piezoelectric film is formed by the printing method, it is necessary to fire at a high temperature of 1300 ° C. or higher for densification, and there is a problem that the substrate is limited to ceramic. In addition, since BaTiO ₃ is the main component and fired at a high temperature, the particle size is large, so there is a phase transition temperature near room temperature. There is.

  In the method of Patent Document 2, the firing temperature can be lowered as compared with the method of Patent Document 1, but there is a problem that the substrate is restricted because it is manufactured at a high temperature. In addition, the method for producing barium titanate disclosed in Patent Document 2 is a method for producing a capacitor utilizing the high dielectric constant, and titanic acid that can be used for an actuator that has a large piezoelectric constant and requires stable temperature characteristics. There is no description of the production of barium films.

  On the other hand, since the AD method shown in Patent Document 3 can be formed at room temperature, it is effective as a method for producing various films. In Non-Patent Document 1, since the contact probe has a function of a capacitor, A method for producing a barium titanate film using the AD method is described. However, the purpose of this barium titanate film is to obtain a film having a high dielectric constant for obtaining a capacitor, and the piezoelectric constant and its temperature characteristics are unknown. In order to obtain a large piezoelectric constant, elements such as an elastic constant and a coupling coefficient are important in addition to the dielectric constant, and temperature characteristics are important in practical use.

  Non-Patent Document 2 shows the relationship between the piezoelectric constant and the crystal grain size of barium titanate prepared by sintering, and shows that a high piezoelectric constant can be obtained when the crystal grain size is 2.5 μm. However, as will be described later in the description of the present invention, the above grain size value is different from the optimum crystal grain size for a piezoelectric film type actuator using a barium titanate film produced by the AD method.

  As described above, in the prior art, a high-performance piezoelectric film type actuator using a lead-free piezoelectric material and using a piezoelectric film having a high piezoelectric constant has not been obtained. In addition, no means for stabilizing temperature characteristics, which is indispensable for the practical application of piezoelectric film type actuators, has been obtained.

  Accordingly, an object of the present invention is to provide a piezoelectric film type actuator using a piezoelectric film having a high piezoelectric constant not containing lead and having excellent temperature characteristics and a method for manufacturing the same.

The present invention has been made to solve the above problems, and the piezoelectric film type actuator of the present invention comprises a piezoelectric film formed on a substrate and an electrode for applying a voltage to the piezoelectric film, A piezoelectric film type actuator for driving an object using displacement generated in the piezoelectric film by applying a voltage to the electrode, wherein the piezoelectric film has a particle diameter of 0.2 to 0.5 μm. characterized in that it consists polycrystalline (BaTiO _3).

  In the method for manufacturing a piezoelectric film type actuator according to the present invention, the piezoelectric film is formed by an AD method, and then heat treated at a temperature of 850 to 1100 ° C.

  The present invention is based on the fact that the inventors have studied the conditions for producing a barium titanate film by the AD method, and found the structure and manufacturing conditions of the film excellent in piezoelectric characteristics and temperature characteristics.

  According to the present invention, a lead-free piezoelectric film having excellent piezoelectric characteristics and temperature characteristics can be obtained by forming a barium titanate film by the AD method and then controlling the particle size by heat treatment. As a result, a piezoelectric film type actuator using a piezoelectric film having a high piezoelectric constant not containing lead and having excellent temperature characteristics and a manufacturing method thereof can be obtained.

1 is a cross-sectional view showing an embodiment of a piezoelectric film type actuator according to the present invention. The photograph which shows an example of the observation result of the surface of the piezoelectric film which consists of a polycrystal of the barium titanate of an Example. The figure which shows an example of the result of having measured the displacement characteristic of the piezoelectric film of an Example. The figure which shows an example of the measurement result of the temperature characteristic of the dielectric constant of the piezoelectric film of an Example compared with the piezoelectric film obtained by sintering of the conventional bulk crystal.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of a piezoelectric film type actuator according to the present invention. In FIG. 1, a piezoelectric film type actuator according to the present embodiment includes a piezoelectric film 2 formed on a substrate 1 and a lower electrode 3 and an upper electrode 4 for applying a voltage to the piezoelectric film 2. A piezoelectric film type actuator for driving an object by utilizing a displacement generated in a piezoelectric film 2 by applying a voltage between electrodes, wherein the piezoelectric film 2 has a particle diameter of 0.2 to 0.5 μm. and a polycrystalline (BaTiO _3).

Next, a specific example of the piezoelectric film type actuator of the present invention and the manufacturing method thereof shown in FIG. 1 will be described. Here, a stainless steel plate is used as the substrate 1, and aluminum oxide (Al) is used as a barrier layer 5 on the surface of the substrate 1 to prevent mutual diffusion between the components of the substrate 1 and the components of the lower electrode 3 and the piezoelectric film 2. ₂ O ₃ ) film is formed, and a platinum (Pt) film is formed thereon as the lower electrode 3. The material of the substrate 1 may be ceramic or silicon as long as mutual diffusion of components can be prevented. The substrate 1 has a shape of several tens of μm to 30 mm, a width of several tens of μm to 10 mm, a thickness of about 10 to 500 μm, and the thicknesses of the lower electrode 3 and the upper electrode 4 are several tens of nm depending on the application of the actuator. The value can be about several μm.

The piezoelectric film 2 was produced by the AD method using a barium titanate powder having a particle size of 0.1 to 0.5 μm formed by a hydrothermal synthesis method as a material. The powder may be produced by a solid phase method as long as film formation by the AD method is possible. The piezoelectric film 2 was formed by the AD method using N ₂ gas as a carrier gas so that the film thickness was about 10 μm at room temperature. The film thickness is not limited to 10 μm, and there is no problem even if it is thin as long as the electric withstand voltage can be secured, and it does not matter if cracks or peeling do not occur even if it is thick. The formed film was heat-treated at a temperature of 850 to 1100 ° C. in the atmosphere.

  The surface of the heat-treated piezoelectric film 2 was observed with a scanning electron microscope (SEM), and the particle size of the barium titanate crystal constituting the piezoelectric film 2 was measured. As a result, it was confirmed that the piezoelectric film 2 was a polycrystalline film made of crystals having a particle size of 0.2 to 0.5 μm. FIG. 2 is a photograph showing an example of the observation result of the surface of the piezoelectric film made of a barium titanate polycrystal of the example.

Next, a metal mask was placed on the surface of the piezoelectric film 2 and gold (Au) was deposited by sputtering to form the upper electrode 4. The piezoelectric characteristic of the piezoelectric film 2 is that of the structure shown in FIG. 1, that is, the piezoelectric unimorph is held in a cantilever structure and the electric field strength in the piezoelectric film 2 due to the applied voltage is 20 kV / cm. From this, the piezoelectric constant d ₃₁ was determined. FIG. 3 is a diagram showing an example of the result of measuring the displacement characteristics of the piezoelectric film of the example. It can be seen that better piezoelectric characteristics are obtained.

  Since the piezoelectric characteristics are proportional to the square root of the dielectric constant, the temperature characteristics of the piezoelectric film used in the present invention were evaluated by measuring the relative dielectric constant in the temperature range of -20 to 140 ° C. FIG. 4 is a diagram showing an example of the measurement result of the temperature characteristic of relative permittivity in comparison with a piezoelectric film obtained by sintering a conventional bulk crystal. Thus, it can be seen that stable characteristics are obtained in a wide temperature range as compared with the conventional piezoelectric film. In the present invention, it is shown that the peak of the relative dielectric constant due to the phase transition can be suppressed without reducing the piezoelectric characteristics so much by reducing the particle size.

In order to confirm the effectiveness of the present invention, as a comparative example, a piezoelectric film was prepared by the AD method in the same manner as described above, and then heat treated at 750 ° C., 1200 ° C., and 1250 ° C., respectively, and a comparative example having the same structure as FIG. A sample of was prepared. Table 1 summarizes the evaluation results of the crystal grain size, piezoelectric constant, and temperature characteristics of the sample of the example using the piezoelectric film manufactured by heat treatment at each temperature of 850 ° C., 950 ° C., 1000 ° C., and 1100 ° C. and the above comparative example. Shown in A piezoelectric constant d ₃₁ having an absolute value of 50 pm / V or more can be used as a non-defective product, and a temperature characteristic of a piezoelectric constant d ₃₁ that does not show a remarkable inflection point in the temperature range of −20 to 80 ° C. .

  From Table 1, it can be seen that both the piezoelectric constant and the temperature characteristics of the examples of the present invention satisfy the conditions for non-defective products. Furthermore, it is desirable for the device to have a positive temperature coefficient in the range of use. Therefore, the embodiment and the conventional example were compared with respect to the temperature characteristics of the relative dielectric constant. FIG. 4 is a diagram showing an example of the measurement result of the temperature characteristic of the relative dielectric constant of the piezoelectric film of the example in comparison with a piezoelectric film obtained by sintering a conventional bulk crystal. As shown in the example of FIG. 4, in the example, a positive temperature coefficient is obtained in a wide range from −20 ° C. to around 100 ° C.

  As described above, in the present invention, a piezoelectric film type actuator having excellent piezoelectric characteristics and excellent temperature characteristics can be realized by controlling the crystal grain size of the piezoelectric film made of barium titanate to 0.2 to 0.5 μm.

  The piezoelectric film type actuator according to the present invention can be used in devices such as inkjet heads, medical micropumps, ultrasonic motors, ultrasonic transducers, and optical scanners.

  It goes without saying that the present invention is not limited to the above-described embodiments and examples, and the design can be changed according to the purpose and application. For example, the production method and particle size of the barium titanate powder that is the material of the substrate and electrode, and the piezoelectric film by AD method can be changed. The structure of the piezoelectric film type actuator is a multilayer of piezoelectric film and electrode film. Or you may comprise.

1 Substrate 2 Piezoelectric film 3 Lower electrode 4 Upper electrode 5 Barrier layer

Claims (2)

A piezoelectric film comprising a piezoelectric film formed on a substrate and an electrode for applying a voltage to the piezoelectric film, and for driving an object using a displacement generated in the piezoelectric film by applying a voltage to the electrode A piezoelectric film type actuator, wherein the piezoelectric film is made of a polycrystal of barium titanate (BaTiO ₃ ) having a particle diameter of 0.2 to 0.5 μm.   2. The method of manufacturing a piezoelectric film type actuator according to claim 1, wherein the piezoelectric film is formed by an aerosol deposition method and then heat-treated at a temperature of 850 to 1100 [deg.] C.

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