JP5024858B2 - Piezoelectric actuator - Google Patents

Description

  The present invention relates to a piezoelectric actuator, and more particularly to a piezoelectric actuator having a PNN-PZT type piezoelectric film.

  An example of forming a piezoelectric actuator by forming a piezoelectric film on an inexpensive metal substrate such as stainless steel is disclosed in Patent Document 1 including a piezoelectric film made of a PZT material.

JP 2006-93346 A

  An object of the present invention is to provide a piezoelectric actuator provided with a piezoelectric film having even better piezoelectric characteristics than Patent Document 1.

  There is a PNN-PZT material as a material having excellent piezoelectric characteristics. However, as a result of trial production and verification by the present inventors, there were some that did not show piezoelectricity and lacked reliability. As a result of further investigations, the present inventors have determined that a piezoelectric film as a parameter for selecting a piezoelectric film having good piezoelectricity and high reliability from piezoelectric films made of PNN-PZT materials. It has been found that the average particle size of the crystals constituting the is appropriate.

The present invention is based on such knowledge. More specifically, according to the present invention, the substrate, the first electrode formed on the substrate, the piezoelectric film formed on the first electrode, and the A piezoelectric actuator comprising a second electrode formed on a piezoelectric film,
The piezoelectric film is made of a Pb (Ni _1/3 Nb _2/3 ) O ₃ —PbZrO ₃ —PbTiO ₃ material, and a piezoelectric actuator made of a crystal having an average particle diameter of 0.2 μm to 2.0 μm is obtained. It is done.

When a piezoelectric film composed of a Pb (Ni _1/3 Nb _2/3 ) O ₃ —PbZrO ₃ —PbTiO ₃ based material and made of a crystal having an average particle diameter of 0.2 μm to 2.0 μm is used, a good piezoelectric property is obtained. A piezoelectric actuator having characteristics and high reliability can be obtained.

  As shown in FIG. 1, a piezoelectric actuator 100 according to an embodiment of the present invention includes a substrate 10, a diffusion barrier layer 20 formed on the substrate 10, a first electrode 30 formed on the diffusion barrier layer 20, a first electrode A piezoelectric film 40 formed on one electrode 30 and a second electrode 50 formed on the piezoelectric film 40 are provided.

  The substrate 10 in the present embodiment is made of stainless steel. As the substrate 10, instead of stainless steel, other metal materials may be used, or a semiconductor single crystal such as a silicon single crystal, a ceramic, or the like may be used.

The diffusion barrier layer 20 in the present embodiment is made of an Al ₂ O ₃ film directly formed on the substrate 10. The diffusion barrier layer 20, in place of the _Al 2 _{O 3} film may be used a film made of other oxides and nitrides such ZrO2 and MgO. Since this diffusion barrier layer 20 is for preventing the reaction between the substrate 10 and the piezoelectric film 40 during the heat treatment for crystal grain growth constituting the piezoelectric film, as in the present embodiment. In the case of the substrate 10 made of stainless steel, it is preferably provided. However, for example, when the substrate 10 is made of ceramic or the like, it can be omitted.

  The first electrode 30 in the present embodiment is made of a Pt film formed on the diffusion barrier layer 20 by sputtering. The first electrode 30 may be formed by other methods, and the first electrode 30 may be formed using a noble metal other than Pt, such as Ir. Assuming that the oxygen partial pressure is controlled during the heat treatment, a base metal such as Cu or Ni may be used as the material of the first electrode 30. Furthermore, when a metal substrate is used as in the present embodiment, the substrate and the first electrode may be combined.

The piezoelectric film 40 in the present embodiment is made of a Pb (Ni _1/3 Nb _2/3 ) O ₃ —PbZrO ₃ —PbTiO ₃ based material and made of crystals having an average particle diameter of 0.25 μm. The average particle diameter should just be in the range of 0.2 micrometer-2.0 micrometers. As a result of verification by the present inventors, when the average particle diameter is less than 0.2 μm, it is confirmed that the piezoelectricity is not exhibited and the displacement characteristics are extremely low, and the average particle diameter is from 2.0 μm. This is because it has been confirmed that the probability of cracking is high in the polarization treatment step for imparting electrical anisotropy to the piezoelectric film, and that the displacement is reduced by continuous driving. Furthermore, in order to obtain good withstand voltage characteristics, it is preferable that the average particle diameter is in the range of 0.2 μm to 0.5 μm.

The average grain size of the crystals constituting the piezoelectric film 40 is based on the following literature, and a line is drawn from the SEM photograph of the film surface or cross section so that more than 100 crystal grains cross, The average value of the length per grain was calculated, the crystal grain was assumed to be a sphere, and the value multiplied by the correction factor of 1.5 was taken as the crystal grain size.
Reference: “Ceramic Processing”
Published by Jun Mizutani et al., March 1985

In addition, the piezoelectric film 40 in the present embodiment is made of Pb (Ni _{1 /} N _1/3 Nb _2/3 ) O ₃ containing 50 mol%, PbZrO ₃ 15 mol%, and PbTiO ₃ 35 mol%. ₃ Nb _2/3 ) O ₃ —PbZrO ₃ —PbTiO ₃ material. As the composition, when Pb (Ni _1/3 Nb _2/3 ) O ₃ is x mol%, PbZrO ₃ is y mol%, and PbTiO ₃ system is z mol% (where x + y + z = 100), FIG. In the ternary phase diagram as shown in
A (x = 55, y = 5, z = 40)
B (x = 55, y = 15, z = 30)
C (x = 20, y = 45, z = 35)
D (x = 20, y = 35, z = 45)
It is preferable to have a composition that exists in a quadrangular region having the four points of the above. This is because, in the case of the piezoelectric film 40 having a composition included in this rectangular region, a value of 100 pm / V or more can be obtained as the absolute value | d ₃₁ | of the piezoelectric constant.

For the purpose of improving characteristics and other purposes, Pb in Pb (Ni _1/3 Nb _2/3 ) O ₃ —PbZrO ₃ —PbTiO ₃ may be replaced with Sr or rare earth elements as long as it is 3% or less. Further, 0.05 to 0.5% of MnO or Fe2O3 may be added to Pb (Ni _1/3 Nb _2/3 ) O ₃ —PbZrO ₃ —PbTiO ₃ .

  The film thickness of the piezoelectric film 40 in the present embodiment is 10 μm. The film thickness of the piezoelectric film 40 may be thicker or thinner than 10 μm, but is preferably 5 μm or more in order to obtain the generated force required for the actuator. For the same reason, the film density is preferably 90% or more in terms of relative density.

In actually forming the piezoelectric film 40 according to the embodiment of the present invention described above, first, the substrate 10 formed up to the first electrode 30 was ultrasonically cleaned in isopropyl alcohol. Thereafter, the piezoelectric film 40 was formed on the first electrode 30 by an aerosol deposition (AD) method using ceramic powder having a composition of 50 Pb (Ni _1/3 Nb _2/3 ) O ₃ -15PbZrO ₃ -35PbTiO ₃ . It is preferable that the specific surface area of the powder used for AD method is 1-4 m < ² > / g. Regarding the temperature at the time of film formation, the film formation may be performed at room temperature or may be performed while the substrate is heated.

  After forming the piezoelectric film by the AD method, heat treatment was performed in order to grow the grain size of the crystals constituting the piezoelectric film. If the heat treatment temperature is too low, the particle size becomes small, and if it is too high, it becomes too large, so an appropriate temperature range should be selected. In this embodiment mode, heat treatment is performed at 900 ° C. The temperature range should be determined in consideration of the relationship with the crystal before heat treatment, etc., but if it is in the range of 850 to 900 ° C., the average particle diameter is in the range of 0.2 μm to 0.5 μm almost certainly. Can fit inside.

  The second electrode 50 in the present embodiment is made of Au deposited on the piezoelectric film 40. Like the 1st electrode 30, you may be comprised from other noble metals.

  After forming the second electrode 50, the piezoelectric film 40 was subjected to polarization treatment by applying an electric field of 40 kV / cm at 100 ° C. for 15 minutes.

Hereinafter, using FIG. 3 and FIG. 4, the piezoelectric actuator 100 according to the present embodiment is compared with a piezoelectric actuator having a piezoelectric film made of crystals whose average particle diameter is outside the range of 0.2 μm to 0.5 μm. The results will be described. As comparative examples, two types prepared by the same method as the piezoelectric actuator 100 according to the present embodiment described above were prepared by changing only the heat treatment temperature. One is heat-treated at 800 ° C. and has a crystal grain size of 0.18 μm. The other is heat-treated at 1050 ° C. and has a crystal grain size of 2.2 μm. Referring to FIG. 3, the result of a displacement characteristic measurement test for the former is shown. Displacement characteristic measurement test (piezoelectric constant measurement test) is, _{P 1} point in FIG. 1, in a cantilever while holding the _{P 2} points, _{P 5} while applying a voltage of 0V~50V _three points and _{P 4} point _P This was done by measuring the point displacement with a laser displacement system. Although the same measurement was attempted for the latter, the latter piezoelectric film was cracked during polarization treatment and could not be evaluated. On the other hand, FIG. 4 shows a result obtained by performing the same measurement on the present embodiment.

  As can be seen from a glance at FIG. 3, when the average particle size is 0.18 μm, the displacement change with respect to the voltage has a quadratic curve shape and does not show ferroelectricity, but the average particle size is 0. In the case of .25 μm, a displacement characteristic accompanied with polarization inversion was obtained.

Further, the durability test (continuous driving test) by applying a voltage of 10 ⁹ times for cantilevered piezoelectric actuator also performed. As a result, it was confirmed that a piezoelectric film made of crystals having an average particle diameter of 0.2 μm to 0.5 μm exhibits excellent reliability.

  As can be understood from the above-described embodiments including these comparison results, according to the present invention, a piezoelectric actuator having a piezoelectric film having good piezoelectricity and high reliability can be obtained.

  The piezoelectric actuator of the present invention can be used for positioning elements in ultrasonic motors and HDDs, inkjet heads, speakers, and the like.

It is a ternary phase diagram showing the composition range of the piezoelectric film used in the piezoelectric actuator according to the embodiment of the present invention. It is sectional drawing which shows the piezoelectric actuator by embodiment of this invention. It is a figure which shows the characteristic of a comparative example. It is a figure which shows the characteristic of the piezoelectric actuator by embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Board | substrate 20 Diffusion barrier layer 30 1st electrode 40 Piezoelectric film 50 2nd electrode 100 Piezoelectric actuator.

Claims (13)

A piezoelectric actuator comprising a substrate, a first electrode formed on the substrate, a piezoelectric film formed on the first electrode, and a second electrode formed on the piezoelectric film,
The piezoelectric film is a piezoelectric actuator made of a crystal made of a Pb (Ni _1/3 Nb _2/3 ) O ₃ —PbZrO ₃ —PbTiO ₃ based material and having an average grain size of 0.2 μm to 0.5 μm . The piezoelectric film has _three components when Pb (Ni _1/3 Nb _2/3 ) O ₃ is x mol%, PbZrO ₃ is y mol%, and PbTiO ₃ system is z mol% (where x + y + z = 100). In the component phase diagram,
A (x = 55, y = 5, z = 40)
B (x = 55, y = 15, z = 30)
C (x = 20, y = 45, z = 35)
D (x = 20, y = 35, z = 45)
It has a composition that exists in a quadrangular region with the four points of
The piezoelectric actuator according to claim 1 . The piezoelectric actuator according to claim 1, wherein the substrate is made of metal. The piezoelectric actuator according to claim 3 , wherein the substrate is made of stainless steel. The piezoelectric actuator according to claim 1, wherein the substrate is made of a semiconductor single crystal. The piezoelectric actuator according to any one of claims 1 to 5 , further comprising a diffusion barrier layer for preventing a reaction between the substrate and the piezoelectric film between the substrate and the piezoelectric film. The piezoelectric actuator according to claim 6 , wherein the diffusion barrier layer is an oxide layer or a nitride layer formed on the substrate surface. The piezoelectric actuator according to any one of claims 1 to 7 , wherein 3% or less of Pb is substituted with Sr or a rare earth element in the piezoelectric film. Wherein the piezoelectric film, formed by addition of MnO or _Fe 2 _{O 3 0.05~0.5%,} the piezoelectric actuator according to any one of claims 1 to 8. The piezoelectric actuator according to claim 1, wherein the piezoelectric film has a film thickness of at least 5 μm. Forming a first electrode on a substrate;
Pb (Ni _1/3 Nb _2/3 ) O ₃ —PbZrO ₃ —PbTiO ₃ system by aerosol deposition method using Pb (Ni _1/3 Nb _2/3 ) O ₃ —PbZrO ₃ —PbTiO ₃ system powder as material After the film is formed on the first electrode, the Pb (Ni _1/3 Nb _2/3 ) O ₃ —PbZrO ₃ —PbTiO ₃ system film is subjected to heat treatment to cause grain growth, whereby 0.2 μm to Forming a piezoelectric film made of crystals having an average grain size of 0.5 μm on the first electrode;
Forming a second electrode on the piezoelectric film. The specific surface area of the powder used in the aerosol deposition method is 1 to 4 m. ² / G
The method for manufacturing a piezoelectric actuator according to claim 11. The temperature range of the heat treatment is 850 to 900 ° C.
A method for manufacturing a piezoelectric actuator according to claim 11 or 12.

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