JP3750446B2 - Piezoelectric film and method of manufacturing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric film and a piezoelectric actuator, and more particularly, to a piezoelectric film having high piezoelectric characteristics according to a predetermined preferred orientation direction, and a piezoelectric actuator capable of obtaining a large displacement using the piezoelectric film.
[0002]
[Prior art]
Piezoelectric films generate distortion when an electric field is applied (reverse piezoelectric effect), and are applied to various piezoelectric actuators using this property. Conventionally, efforts have been made to obtain a piezoelectric body having high piezoelectric characteristics in order to improve the amount of displacement in the piezoelectric actuator.
[0003]
For example, in Japanese Patent Laid-Open No. 10-81016, the crystal structure of the piezoelectric film is a rhombohedral crystal and is strongly oriented in the crystal plane of the plane orientation (111), the crystal plane of the plane orientation (100), or both. A piezoelectric thin film element is described. In addition, a piezoelectric thin film element is described in which the crystal structure of the piezoelectric film is a tetragonal crystal and is strongly oriented in the crystal plane of the plane orientation (001).
[0004]
Japanese Patent Application Laid-Open No. 11-238921 discloses that the piezoelectric layer has a tetragonal system and (001) plane orientation and (111) plane orientation are mixed, and the (111) plane orientation with respect to the entire plane orientation. Describes a piezoelectric element in which the ratio is set larger than the ratio of the (001) plane orientation.
[0005]
[Problems to be solved by the invention]
According to the above conventional technique, a piezoelectric film having high piezoelectric characteristics can be obtained. However, future piezoelectric actuators are required to have a larger displacement, lower power, and smaller size, and a piezoelectric film having higher piezoelectric characteristics is desired.
[0006]
An object of the present invention is to provide a piezoelectric film having higher piezoelectric characteristics and a piezoelectric actuator that realizes a larger displacement. It is another object of the present invention to provide a method for manufacturing such a piezoelectric film.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the piezoelectric film of the present invention is characterized in that crystals are preferentially oriented in the {221} plane .
[0008]
The piezoelectric film may be polycrystalline or single crystal.
[0009]
High piezoelectric characteristics can be achieved by increasing the proportion of crystal grains in which the crystal plane parallel to the substrate is the {221} plane. In particular, a piezoelectric film having a large displacement can be provided.
[0010]
In the piezoelectric film of the present invention, the crystal is a pseudo cubic system or a crystal system in which at least two of a pseudo cubic system, a rhombohedral system, or a tetragonal system are mixed. Features .
[0011]
In the case of pseudo-cubic (psudocubic), or plural such as pseudo-cubic, rhombohedoral or tetragonal crystal phase boundary (hereinafter referred to as MPB) It has been found that even higher piezoelectric properties can be obtained when the crystal system is mixed.
[0012]
The piezoelectric film of the present invention is characterized in that the crystal has an ABO ₃ type perovskite crystal structure .
[0013]
The complex oxide having this crystal structure has high piezoelectric characteristics. In addition, an additive may be included such as (A ₁ A ₂ ) BO ₃ or a multi-component system such as A (B ₁ B ₂ ) O ₃ may be used.
[0014]
In the piezoelectric film of the present invention, the crystal is composed of barium titanate (BaTiO ₃ : BTO), lead zirconate titanate (Pb (Zr, Ti) O ₃ : PZT), lead zinc niobate (Pb (Zn)). , Nb) O ₃ ) and lead titanate (PbTiO ₃ ) solid solution (PZN-PT) or lead magnesium niobate (Pb (Mg, Nb) O ₃ ) and lead titanate (PbTiO ₃ ) PMN-PT) as a main component .
[0015]
In the piezoelectric film of the present invention, the crystal is formed by epitaxial growth in a {221} plane orientation on a substrate .
[0016]
By epitaxial growth, the degree of orientation in the {221} plane orientation can be increased.
[0017]
In the piezoelectric film of the present invention, the substrate is made of any one of single crystal silicon (Si), strontium titanate (SrTiO ₃ : STO), or magnesium oxide (MgO) whose principal surface is the (221) plane. It is characterized by being.
[0018]
In addition, a piezoelectric actuator according to the present invention includes the above-described piezoelectric film, and is configured such that a voltage can be applied to the piezoelectric film in a film thickness direction .
[0019]
Examples of piezoelectric actuators include drive elements such as (positioning) positioners, piezoelectric fans, piezoelectric motors, piezoelectric pumps, piezoelectric relays, and piezoelectric valves. By applying to a piezoelectric actuator, an actuator capable of obtaining a high displacement can be obtained.
[0020]
In addition, an electric device according to the present invention includes the above-described piezoelectric film, and is configured such that a voltage can be applied to the piezoelectric film in a film thickness direction .
[0021]
An electrical device generally refers to a mechanical instrument driven by electricity, and examples thereof include a piezoelectric fan, a piezoelectric motor, a piezoelectric pump, a piezoelectric relay, a piezoelectric valve, and the like.
[0022]
The method for manufacturing a piezoelectric film of the present invention is characterized in that a piezoelectric crystal is epitaxially grown in a {221} plane orientation on a substrate .
[0023]
By epitaxially growing a piezoelectric crystal in the {221} plane orientation, a piezoelectric film having excellent crystal orientation and high piezoelectric characteristics can be provided.
[0024]
In the piezoelectric film manufacturing method of the present invention, the substrate is made of single crystal silicon (Si), strontium titanate (SrTiO ₃ : STO), or magnesium oxide (MgO) whose principal surface is the (221) plane. It is either .
[0025]
By epitaxially growing a piezoelectric crystal using (221) -oriented single crystal silicon, strontium titanate, or magnesium oxide as a substrate, the (221) plane of the piezoelectric film can be preferentially oriented.
[0026]
In the method for manufacturing a piezoelectric film of the present invention , {221} preferentially oriented ceria / ceria zirconia (CeO ₂ / Ce · ZrO ₂ ) is formed on the substrate, and a piezoelectric crystal is epitaxially grown thereon. It is characterized by.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
(Principle explanation)
In the inverse piezoelectric effect that generates strain when an electric field is applied to the piezoelectric material, the strain is caused by the spontaneous strain stretching (the original part of the piezoelectric effect) and the spontaneous strain rotating. It is expressed as the sum of (unnatural part). In order to obtain a large amount of displacement, it is effective to use the rotation of the spontaneous strain together with the extension of the spontaneous strain.
[0028]
FIG. 1 is a graph obtained by measuring the X-ray diffraction intensity before and after voltage application for a certain PZT piezoelectric film. This piezoelectric body is preferentially oriented in the {111} plane, but there are also crystal grains oriented in other planes. From this graph, it can be seen that the crystal grains oriented in the {221} plane have a higher rate of change in diffraction intensity before and after voltage application than the crystal grains oriented in other crystal planes.
[0029]
In this graph, the diffraction intensity of the {221} plane oriented crystal and the diffraction intensity of the {300} plane oriented crystal are displayed in the vicinity of 2θ = 68 ° in the figure. However, the change rate of the diffraction intensity of the {300} plane oriented crystal should be the same as the change rate of the diffraction intensity of the {200} plane oriented crystal in the vicinity of 2θ = 44 ° shown in the figure, and the {200} plane oriented crystal The change rate of the diffraction intensity is extremely small as shown in the figure. Therefore, it can be seen that the change rate of the diffraction intensity of the {300} plane oriented crystal is small and the change rate of the diffraction intensity of the {221} plane oriented crystal is large.
[0030]
From this, it can be derived that the {221} plane oriented crystal is most likely to rotate spontaneously. Accordingly, the piezoelectric film preferentially oriented in the {221} plane has high piezoelectric characteristics, and a piezoelectric actuator using the piezoelectric film can obtain a large displacement characteristic.
[0031]
When spontaneous distortion occurs, it takes longer to change the shape than when spontaneous distortion does not occur. For example, when driven at a high frequency on the order of megahertz (MHz) or more, the response may be inferior. There is also. However, when driven at a relatively low frequency, it is possible to obtain responsiveness enough for practical use as a piezoelectric actuator, and the advantage is that a large displacement can be obtained.
[0032]
(Crystal structure)
FIG. 2 is a schematic diagram of an ABO ₃ type perovskite crystal structure which is a kind of crystal structure of a piezoelectric body. In this crystal structure, element A is a divalent metal element (such as Pb), element B is a tetravalent metal element (such as Ti or Zr), and element O is usually oxygen (O). In addition, an additive may be included such as (A ₁ A ₂ ) BO ₃ or a multi-component system such as A (B ₁ B ₂ ) O ₃ may be used.
[0033]
In the figure, the surface indicated by diagonal lines in the triangular frame is the (221) plane, and the normal line is directed to the [221] direction as indicated by the arrow in the figure. The piezoelectric film of the present invention is controlled in orientation so that the proportion of crystal grains whose crystal plane parallel to the substrate is the {221} plane, that is, the (221) plane, the (212) plane, or the (122) plane increases. Manufactured.
[0034]
(Production method)
FIG. 3 is a process diagram illustrating the method for manufacturing the piezoelectric film according to the present embodiment. As shown in FIG. 3A, a {221} preferentially oriented ceria / ceria as a buffer layer (underlayer) 5 is formed on a single crystal silicon (s-Si) substrate 1 having a plane orientation (221) and a thickness of 220 μm. Zirconia (CeO ₂ / Ce · ZrO ₂ ) is epitaxially formed by electron beam evaporation to a thickness of 0.5 μm. The composition of the substrate 1 is not limited to the single crystal silicon, but may be a single crystal STO (SrTiO ₃ ) substrate or an MgO substrate having a plane orientation (221). When an STO substrate or an MgO substrate is used, a piezoelectric film 7 (described later) may be formed directly on the substrate or via a lower electrode 6 (described later).
[0035]
Next, a {221} preferentially oriented platinum (Pt) film to be the lower electrode 6 is epitaxially grown on the buffer layer 5 to a thickness of 100 nm. As the lower electrode 6, the piezoelectric film 7 may be formed directly on the buffer layer 5 without forming a platinum film. Further, instead of the platinum film, another conductive material that can be epitaxially grown, for example, iridium (Ir), iridium oxide, or the like may be used as the lower electrode 6.
[0036]
Next, as shown in FIG. 3B, {221} is obtained by a CVD method while appropriately adjusting the supply amounts of a source gas, an oxygen-containing gas, a carrier gas, and the like, which are vaporized organic metal sources constituting the piezoelectric material. } A PZT crystal to be the preferentially oriented piezoelectric film 7 is epitaxially grown to a thickness of about 1 μm.
[0037]
In general, in the case of bulk PZT, as a result of crystal phase identification by X-ray diffraction measurement for a crystal system near room temperature, the constituent element ratio of the B site in the perovskite structure, that is, the molar ratio of Zr / Ti is 0/1 or more and 0. When it is in the range of less than 53 / 0.47, it constitutes a tetragonal system, and when it is in the range of more than 0.53 / 0.47 and not more than 0.90 / 0.10, it constitutes a rhombohedral system. It has been found crystallographically that a tetragonal / rhombohedral crystal phase boundary, that is, MPB exists when the molar ratio of Zr / Ti is around 0.53 / 0.47. Therefore, in this example, the Zr / Ti molar ratio was 0.56 / 0.44, and the piezoelectric film 7 had a crystal structure near the MPB.
[0038]
The crystal system of the piezoelectric film 7 may be a pseudo cubic system or a crystal system in which at least two of a pseudo cubic system, a rhombohedral system, and a tetragonal system are mixed.
[0039]
As described above, since the substrate 1, the base layer 5 and the lower electrode 6 are preferentially oriented in the (221) plane orientation, the piezoelectric film 7 epitaxially grown thereon is also preferentially oriented in the (221) plane orientation. become.
[0040]
Note that the piezoelectric film may be formed not only by the CVD method but also by another method capable of forming the piezoelectric film by epitaxial growth, such as a sol-gel method. The sol-gel method is a method in which a hydrated complex (sol) of a metal component hydroxide constituting a piezoelectric film is applied on a substrate, dried and degreased, and then subjected to a crystallization heat treatment.
[0041]
In the present embodiment, PZT is used as the piezoelectric body. However, the present invention is not limited to this, but barium titanate (BaTiO ₃ : BTO), solid solution of lead zinc niobate and lead titanate (PZN-PT), or magnesium niobium A solid solution (PMN-PT) of lead acid and lead titanate may be used.
[0042]
Further, as shown in FIG. 3C, platinum is deposited on the piezoelectric film 7 as the upper electrode 8 to a thickness of 100 nm by DC sputtering. Thereafter, a resist is applied on the upper electrode 8 and patterned into a predetermined shape, and the upper electrode 8 and the piezoelectric film 7 are etched using the remaining resist as a mask, thereby forming a piezoelectric element.
[0043]
According to the present embodiment, since the piezoelectric film 7 is strongly oriented in the (221) plane by epitaxial growth and has a crystal structure near the MPB, high displacement characteristics are obtained when the piezoelectric element is used as an actuator. Obtainable.
[0044]
(Application example of piezoelectric film)
FIG. 4 is a schematic cross-sectional view of a piezoelectric pump using a piezoelectric film manufactured according to the present invention. The piezoelectric pump 20 includes a piezoelectric element 21, a pump chamber 26, a suction-side check valve 27a, a discharge-side check valve 27b, a suction port 28a, and a discharge port 28b. The piezoelectric element 21 includes a two-layer piezoelectric film 22, a three-layer electrode 23, a signal line 24, and a covering material 25.
[0045]
When a voltage is supplied to the signal line 24, a voltage is applied in the film thickness direction of the piezoelectric film 22, and the piezoelectric element 21 is distorted. For this reason, the pressure in the pump chamber 26 changes, the fluid flows from the suction port 28a into the pump by the action of the check valves 27a and 27b, and is discharged to the outside from the discharge port 28b.
[0046]
Such a piezoelectric pump is strongly required to have a large deformation of the piezoelectric element, but is not so required to respond to a high frequency. Therefore, it is possible to provide a piezoelectric pump with high fluid conveyance efficiency by taking advantage of the characteristics of the piezoelectric film of the present invention.
[0047]
In addition to the above, the piezoelectric film of the present invention can be used in various electrical devices such as (positioning) positioners, piezoelectric fans, piezoelectric motors, piezoelectric relays, piezoelectric valves, etc. Thus, highly efficient electrical equipment can be created. The piezoelectric film of the present invention includes a filter, a lead selector, a tuning fork oscillator, a tuning fork clock, a transceiver, a piezoelectric pickup, a piezoelectric earphone, a piezoelectric microphone, a SAW filter, an RF modulator, a resonator, a delay element, a multistrip coupler, and a piezoelectric. It can also be applied to accelerometers, piezoelectric speakers, and the like.
[0048]
【The invention's effect】
According to the present invention, it is possible to provide a piezoelectric film having higher piezoelectric characteristics and a piezoelectric actuator that realizes a larger displacement. In addition, a method for manufacturing such a piezoelectric film can be provided.
[Brief description of the drawings]
FIG. 1 is a graph showing X-ray diffraction intensities before and after voltage application for a PZT piezoelectric film.
FIG. 2 is a schematic diagram of an ABO ₃ type perovskite crystal structure.
FIG. 3 is a process diagram illustrating the method of manufacturing the piezoelectric film according to the present embodiment.
FIG. 4 is a schematic cross-sectional view of a piezoelectric pump using a piezoelectric film manufactured according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Substrate, 5 ... Buffer layer, 6 ... Lower electrode, 7 ... Piezoelectric film, 8 ... Upper electrode, 20 ... Piezoelectric pump, 21 ... Piezoelectric element, 22 ... Piezoelectric film, 23 ... Electrode, 24 ... Signal line, 25 ... Coating material, 26 ... Pump chamber, 27a ... Suction side check valve, 27b ... Discharge side check valve, 28a ... Suction port, 28b ... Discharge port

Claims (7)

A piezoelectric film,
  The crystals of the piezoelectric film are preferentially oriented in the {221} plane,
  The crystal is a pseudo-cubic system or a crystal system in which at least two of a pseudo-cubic system, a rhombohedral system, and a tetragonal system are mixed, and ABO ₃ A piezoelectric film having a type perovskite crystal structure and epitaxially grown in a {221} plane orientation on a substrate. The crystal is
Barium titanate (BaTiO ₃ : BTO),
Lead zirconate titanate (Pb (Zr, Ti) O ₃ : PZT),
Solid solution (PZN-PT) of lead zinc niobate (Pb (Zn, Nb) O ₃ ) and lead titanate (PbTiO ₃ ), or lead magnesium niobate (Pb (Mg, Nb) O ₃ ) and lead titanate 2. The piezoelectric film according to claim 1 , wherein any one of a solid solution (PMN-PT) with (PbTiO ₃ ) is a main component. The substrate is a single crystal silicon is a major surface (221) plane (Si), strontium titanate _(SrTiO 3: STO), or is any one of magnesium oxide (MgO) in claim 1, wherein The piezoelectric film according to the description. It comprising a piezoelectric film according to any one of claims 1 to 3, energizable to the through each electrode respectively formed on both sides of the piezoelectric film in the thickness direction with respect to the piezoelectric film A piezoelectric actuator characterized by comprising. Comprising a piezoelectric film according to any one of claims 1 to 3, energizable to the through each electrode respectively formed on both sides of the piezoelectric film in the thickness direction with respect to the piezoelectric film An electric device characterized by comprising. A method of manufacturing a piezoelectric film,
A step of epitaxially growing a piezoelectric crystal in a {221} plane orientation on a substrate whose principal surface is a (221) plane ,
The substrate is one of single crystal silicon (Si), strontium titanate (SrTiO ₃ : STO), or magnesium oxide (MgO) whose principal surface is a (221) plane ,
The crystal is a pseudo-cubic crystal system or a crystal system in which at least two of a pseudo-cubic crystal system, a rhombohedral system, or a tetragonal system are mixed, and has an ABO ₃ type perovskite crystal structure. ,
A method of manufacturing a piezoelectric film characterized by the above. The piezoelectric body according to claim 6, wherein the forming the {221} preferred orientation ceria / ceria zirconia _{(CeO 2 / Ce · ZrO 2} ) on a substrate, epitaxially growing the piezoelectric crystal thereon A method for producing a membrane.

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