JP2008004781A - Piezoelectric film, piezoelectric element, ink jet recording head, and ink jet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a practical piezoelectric film to be comparatively easily manufactured, capable of obtaining a large piezoelectric distortion due to invertible non-180° domain rotation. <P>SOLUTION: The piezoelectric film 30 is the film which is deposited on a substrate 10 and made of perovskite oxide to be expressed by a general formula ABO<SB>3</SB>(unavoidable impurities can be included). At least a part of the piezoelectric film 30 has a composition where the A site and/or B site of the maternal perovskite oxide are partially substituted with one kind or a plurality of kinds of cation with the smaller number of ionic valency compared with substituted ion. A cationic additive amount is continuously or gradually increased from the side of the substrate 10 toward the side of a film surface 30s when viewing in a film thickness direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric film made of a perovskite oxide and a film forming method thereof, a piezoelectric element provided with the piezoelectric film, an ink jet recording head and an ink jet recording apparatus using the piezoelectric element.

  A piezoelectric element having a piezoelectric film having a piezoelectric property that expands and contracts as the electric field application intensity increases and decreases, and an electrode that applies an electric field to the piezoelectric film is used for applications such as a piezoelectric actuator mounted on an ink jet recording head. in use. As the piezoelectric material, perovskite oxides such as lead zirconate titanate (PZT) are widely used.

  Such a piezoelectric material is a ferroelectric material having spontaneous polarization when no electric field is applied. In a conventional piezoelectric element, a piezoelectric material that extends in the direction of the polarization axis by applying an electric field in a direction that matches the polarization axis of the ferroelectric material. It has been common to use strain (true piezoelectric strain). However, there is a limit to the amount of strain displacement only by using the piezoelectric strain of the ferroelectric material, and a larger amount of strain displacement has been demanded. Under such background, a piezoelectric element using reversible non-180 ° domain rotation has been proposed.

  If the tetragonal system is described as a model, when the a domain in which the a axis is oriented in the electric field application direction is rotated 90 ° domain by the electric field application to the c domain in which the c axis is oriented in the electric field application direction, the major axis of the crystal lattice When the direction is rotated by 90 °, a piezoelectric strain larger than the normal piezoelectric strain is obtained (see FIG. 2B).

  The non-180 ° domain rotation itself as described above has been conventionally known. However, since the non-180 ° domain rotation is usually irreversible, its usefulness is low. Patent Document 1 and Non-Patent Document 1 disclose a piezoelectric material in which a mobile point defect is arranged such that the short-range order symmetry coincides with the crystal symmetry of a ferroelectric phase. It has been reported that reversible non-180 ° domain rotation occurs in materials.

In Patent Document 1 and Non-Patent Document 1, the reason why reversible non-180 ° domain rotation occurs in the piezoelectric material is described as follows (see FIG. 2 of Patent Document 1).
Immediately after the phase transition from the paraelectric phase to the ferroelectric phase by cooling, there is no short-range order of point defects, but short-range order of point defects appears by diffusing point defects by aging treatment. The short range order can be aligned with the crystal symmetry of the ferroelectric domain to which point defects belong. This state is the most stable because the polarization axis due to the short range order of the point defect is aligned with the polarization axis of the domain to which the point defect belongs. When an electric field is applied in this state, non-180 ° domain rotation occurs in some domains. Even if an electric field is applied, the polarization axis due to the short-range order of point defects does not rotate. Therefore, in a domain where non-180 ° domain rotation has occurred, the polarization axis of the point defect is different from the polarization axis of the domain to which the point defect belongs. It becomes. Since this state is unstable, when the electric field is removed, the polarization axis of the point defect tends to return to a stable state aligned with the spontaneous polarization axis of the domain to which the point defect belongs, and non-180 ° domain rotation occurs reversibly. be able to.

In Patent Document 1 and Non-Patent Document 1, (1) a BaTiO ₃ single crystal prepared by a flux method, and a sample subjected to aging treatment at a temperature below the Curie point after cooling (Example 1), (2) K was added to BaTiO _3. Samples (Example 2), (3) (Pb, La) (Zr, Ti) O ₃ prepared by a small amount of (BaK) TiO ₃ single crystal prepared by the flux method and aged at a temperature below the Curie point after cooling. Sample (Example 3) obtained by aging ceramics (PLZT) at room temperature for 30 days, (4) Single crystal (Fe-BT) obtained by adding a small amount of Fe to BaTiO ₃ and aging treatment at a temperature of 80 ° C. for 5 days Samples (Example 5) and the like have been prepared.

FIG. 9 shows the electric field distortion characteristics of the sample (4) as a representative (this figure is FIG. 7 of Patent Document 1). The figure also shows the field strain characteristics of PZT-PT single crystals and PZT ceramics that use only normal piezoelectric strain that extends in the direction of the polarization axis by applying an electric field in the direction that matches the polarization axis of the ferroelectric. It is shown together.
In this figure, by using reversible non-180 ° domain rotation, by applying an electric field in the direction in line with the polarization axis of the ferroelectric, only the normal piezoelectric strain extending in the polarization axis direction is used. However, it has been shown that a much larger piezoelectric strain can be obtained.
JP 2004-363557 A Xiaobing Ren, Nature-Materials 3 (2004) p91

  In Patent Document 1, a sample is prepared only for a single crystal body or a bulk ceramic body, and there is no description about a manufacturing method of a piezoelectric film that causes non-180 ° domain rotation reversibly, and the application to a piezoelectric film is specific. Is not listed.

In addition, as shown in FIG. 9, by applying an electric field in a direction that matches the polarization axis of the ferroelectric, normal strain (true piezoelectric strain) that extends in the direction of the polarization axis, the amount of strain displacement is the applied electric field. While directly proportional to the strength, in the case of piezoelectric strain due to reversible non-180 ° domain rotation, the electric field strain characteristic has a large hysteresis. With such an electric field distortion characteristic, the strain does not change greatly even if the electric field application intensity is increased within a certain range, and when the electric field application characteristic exceeds a certain range, the distortion tends to increase abruptly as the electric field application intensity increases. Such electric field distortion characteristics with a large hysteresis have great practical limitations and are difficult to put into practical use.
In addition, a domain rotated by a non-180 ° domain by applying an electric field needs to be restored to the original domain state when the electric field is lowered. However, when the electric field marking speed (frequency) is increased, there is a possibility that desired domain rotation does not occur. .

The present invention has been made in view of the above circumstances, and an object thereof is to provide a practical piezoelectric film that can obtain a large piezoelectric strain due to reversible non-180 ° domain rotation and is relatively easy to manufacture. It is what. Another object of the present invention is to provide a practically suitable piezoelectric film that can improve the hysteresis and frequency characteristics of electric field distortion characteristics when reversible non-180 ° domain rotation is used.
Another object of the present invention is to provide a piezoelectric element using the piezoelectric film, an ink jet recording head and an ink jet recording apparatus using the piezoelectric element.

The piezoelectric film of the present invention has a general formula ABO ₃ (wherein A: at least one metal element forming an A site, B: at least one metal element forming a B site, O : The standard number of moles of oxygen atoms and A-site elements is 1.0 and the number of moles of B-site elements is 1.0, but the number of moles of A-site elements and B-site elements is a perovskite structure. In a piezoelectric film (which may contain inevitable impurities) made of a perovskite oxide represented by the following formula:
At least a part has a composition in which part of the A site and / or B site of the parent perovskite oxide is substituted with one or more kinds of cations having a smaller ionic valence than the substituted ion. ,
In addition, the addition amount of the cation increases continuously or stepwise from the substrate side toward the film surface side as viewed in the film thickness direction.

  In the piezoelectric film of the present invention, the cation should be added continuously or stepwise from the substrate side to the film surface side as viewed in the film thickness direction. There may be undoped regions. Further, in the configuration in which the cation addition amount increases stepwise from the substrate side toward the film surface side in the film thickness direction, the change in the cation addition amount may be one step or a plurality of steps.

  Examples of the cation include at least one selected from the group consisting of Li, Na, and K. In this case, the cation can replace the A site of the parent perovskite oxide.

  When the B site of the parent perovskite oxide contains one or more group IV elements, the cation can substitute a part of the group IV element. Examples of the group IV element contained in the B site include Ti and / or Zr. When the B site contains one or more group IV elements, the cations include Li, Na, K, Mg, Ca, Cr, Mo, Mn, Fe, Co, Ni, Cu, Ag, Examples thereof include at least one selected from the group consisting of Zn, Al, Ga, In, Sb, Bi, and rare earth.

  When the B site of the parent perovskite oxide contains one or more group V elements, the cation can substitute a part of the group V element. Examples of the group V element contained in the B site include Nb and / or Ta. When the B site contains one or a plurality of V group elements, the cations include Li, Na, K, Mg, Ca, Ti, Zr, Hf, Cr, Mo, Mn, Fe, Co, Examples thereof include at least one selected from the group consisting of Ni, Cu, Ag, Zn, Al, Ga, In, Si, Ge, Sn, Sb, Bi, Se, Te, and rare earth.

  According to the present invention, it is possible to provide a piezoelectric film in which a domain in which the polarization axis is reversibly rotated by non-180 ° by the increase or decrease of the electric field applied intensity is formed by adding the cation.

  The crystal structure of the piezoelectric film of the present invention is preferably any one of a tetragonal system, an orthorhombic system, a rhombohedral system, and a crystal system in which a plurality of these crystal systems are mixed. The piezoelectric film of the present invention preferably has crystal orientation. Here, “a crystal system in which a plurality of crystal systems are mixed” refers to a state in which a plurality of crystal phases coexist at the morphotropic phase boundary. In addition, the “film having crystal orientation” refers to a film in which only some diffraction lines appear greatly in the X-ray diffraction pattern on the surface of the piezoelectric film.

  When the crystal structure of the piezoelectric film of the present invention is a tetragonal system, or a crystal system in which a tetragonal system and another crystal system are mixed, the domain structure of the piezoelectric film of the present invention is as follows when no electric field is applied: A domain in which tetragonal a-axis is preferentially oriented in a direction perpendicular to the substrate surface of the substrate; and c domain in which tetragonal c-axis is preferentially oriented in a direction perpendicular to the substrate surface of the substrate. A structure in which at least a part of the a domain is a domain in which the polarization axis reversibly rotates non-180 ° by increasing or decreasing the electric field application intensity can be given.

  The piezoelectric film of the present invention is preferably made of a material having a larger coefficient of thermal expansion at room temperature to 500 ° C. than the constituent material of the substrate.

In this specification, “the coefficient of thermal expansion of the constituent material of the substrate” means a general linear expansion coefficient measured for a bulk body made of the constituent material of the substrate. Similarly, the “thermal expansion coefficient of the constituent material of the piezoelectric film” means a general linear expansion coefficient of the piezoelectric film measured for a bulk body made of the constituent material of the piezoelectric film. Although the piezoelectric film of the present invention has a composition distribution in which the cation addition amount in the film thickness direction is different, the linear expansion coefficient does not vary greatly depending on the cation addition amount, so that the piezoelectric film has the piezoelectric expansion coefficient of the parent perovskite oxide. The coefficient of thermal expansion of the film shall be specified. Since it is difficult to accurately measure the linear expansion coefficient of the film itself, in the present invention, the relationship between the linear expansion coefficient of the substrate and the piezoelectric film is defined by the linear expansion coefficient of the bulk material.
The linear expansion coefficient represents the rate of change of the length L of one side of the bulk body with respect to the change of the temperature T, and is generally represented by the following formula.
α = (ΔL / L) / ΔT

  The piezoelectric film of the present invention can be formed by a vapor deposition method. For example, the piezoelectric film of the present invention can be formed by preparing a plurality of targets having different cation contents and changing the rate of film formation from the plurality of targets during film formation.

Conventionally, Japanese Unexamined Patent Publication No. 2000-208828 has been known regarding the composition gradient of a piezoelectric film. An object of the present invention is to solve the problem in the sol-gel method in which a crystalline film is obtained by heating a precursor film.
In JP-A-2000-208828, it is considered that c-axis orientation is effective for perovskite tetragonal crystals in order to express piezoelectricity more effectively. It is described that tensile stress is generated in the piezoelectric film due to the volume shrinkage, and the c-axis direction tends to be parallel to the substrate surface (paragraph [0005] of Japanese Patent Laid-Open No. 2000-208828).
In view of this, Japanese Patent Application Laid-Open No. 2000-208828 proposes, for example, a composition gradient in the film thickness direction from Ti-rich to Zr-rich in a PZT film. In PZT, when the amount of Ti is large, the crystal structure tends to be tetragonal, and when the amount of Zr is large, the crystal structure tends to be rhombohedral. Therefore, by adopting the composition gradient as described above, a film structure in which the rhombohedral crystal lattice is continuously connected to the tetragonal crystal lattice after the temperature lowering process after crystallization can be obtained. It is described that the c-axis orientation can be easily realized because the crystal lattice of the crystal system can be constrained (paragraph [0013], etc. of JP-A-2000-208828).

  That is, the invention described in Japanese Patent Application Laid-Open No. 2000-208828 is one in which the composition of the base perovskite oxide (main composition of the piezoelectric film) referred to in the present invention is inclined, and the main composition of the piezoelectric film is Without changing, the composition gradient is different from the present invention in which the amount of added cation is changed in the film thickness direction. Further, the invention described in Japanese Patent Laid-Open No. 2000-208828 is not a system that uses reversible non-180 ° domain rotation.

  In addition, although it is described in JP-A-2000-208828 that it is preferable to increase the c-axis orientation, in the present invention, since reversible non-180 ° domain rotation is used, if it is a tetragonal system, As described above, there is preferably an a domain in which the a axis is preferentially oriented in the direction perpendicular to the substrate surface and a c domain in which the c axis is preferentially oriented in the direction perpendicular to the substrate surface.

The method for forming the piezoelectric film of the present invention includes:
On the substrate, the general formula ABO ₃ (wherein A: at least one metal element forming an A site, B: at least one metal element forming a B site, O: oxygen atom, and the number of moles of the A site element) The standard is 1.0 and the number of moles of the B-site element is 1.0, but the number of moles of the A-site element and the B-site element deviates from 1.0 within a range where a perovskite structure can be obtained. In the method for forming a piezoelectric film for forming a piezoelectric film (which may contain inevitable impurities) made of a perovskite oxide represented by:
At least a part of the piezoelectric film has a composition in which a part of the A site and / or B site of the base perovskite oxide is substituted with one or more kinds of cations having a smaller ionic valence than the substituted ion. Have
The piezoelectric film is formed such that the addition amount of the cation increases continuously or stepwise from the substrate side toward the film surface side in the film thickness direction. It is.

  When the film formation is performed by a vapor deposition method, the film formation may be performed by increasing the addition amount of the cation continuously or stepwise as the film formation time elapses. For example, it is preferable to prepare a plurality of targets having different cation contents, and perform the film formation by changing the ratio of film formation from the plurality of targets during the film formation.

The piezoelectric element of the present invention is characterized by comprising the above-described piezoelectric film of the present invention and an electrode for applying an electric field in the film thickness direction of the piezoelectric film.
When manufacturing the piezoelectric element of the present invention, the substrate used for forming the piezoelectric film can be removed. Therefore, the piezoelectric element of the present invention may have a substrate or may not have a substrate.

The ink jet recording head of the present invention comprises the above-described piezoelectric element of the present invention,
And an ink storage and discharge member having an ink discharge port through which the ink is discharged from the ink chamber to the outside.
An ink jet recording apparatus of the present invention includes the above ink jet recording head of the present invention.

  In the present invention, for at least a part of the piezoelectric film, a part of the A site and / or the B site of the base perovskite oxide is substituted with one or more kinds of cations having a smaller ionic valence than the substituted ion. In addition, the cation addition is performed so that the addition amount of the cation increases continuously or stepwise from the substrate side to the film surface side as viewed in the film thickness direction. .

  In such a configuration, a domain in which the polarization axis reversibly rotates non-180 ° is formed by the point defect due to the addition of the cation, and a large piezoelectric strain due to the reversible non-180 ° domain rotation can be obtained. In addition, since the amount of cation added is relatively small on the substrate side, there are fewer point defects at the initial stage of film formation than when cation is added at a high concentration from the beginning, crystal structure and crystal orientation are easier to control, and manufacturing is also compared. Easy.

  Since the proportion of domains in which the polarization axis reversibly rotates non-180 ° is determined by the amount of cation added, in the present invention, the ratio of domains in which the polarization axis reversibly rotates non-180 ° is relatively small on the substrate side, The film surface side has a relatively large configuration. In such a configuration, reversible non-180 ° domain rotation does not occur on the substrate side, or even if reversible non-180 ° domain rotation occurs, the amount is small, and reversible non-180 ° domain rotation is relatively on the film surface side. It will happen greatly. Therefore, as compared with the case where reversible non-180 ° domain rotation occurs uniformly throughout the film, the hysteresis of the electric field distortion characteristic when reversible non-180 ° domain rotation is utilized can be reduced.

  In addition, since it is sufficient that reversible non-180 ° domain rotation occurs at least on the film surface side, even if the electric field marking speed (frequency) increases, the desired domain rotation can occur stably and reversible. The frequency characteristics when non-180 ° domain rotation is used can also be improved.

"Piezoelectric element, inkjet recording head"
With reference to FIG. 1, a piezoelectric element according to an embodiment of the present invention and the structure of an ink jet recording head provided with the piezoelectric element will be described. FIG. 1 is a cross-sectional view of the main part of an ink jet recording head. In order to facilitate visual recognition, the scale of the constituent elements is appropriately changed from the actual one.

  The piezoelectric element 1 according to this embodiment is an element in which a lower electrode 20, a piezoelectric film 30, and an upper electrode 40 are sequentially stacked on a substrate 10. An electric field is applied to the piezoelectric film 30 in the thickness direction by the lower electrode 20 and the upper electrode 40. In this embodiment, the film structure of the piezoelectric film 30 is characteristic.

  The lower electrode 20 is formed on substantially the entire surface of the substrate 10, and a piezoelectric film 30 having a pattern in which line-shaped convex portions 31 extending from the front side to the rear side in the drawing are arranged in a stripe shape is formed thereon. An upper electrode 40 is formed on 31. An adhesion layer made of Ti or the like may be interposed between the substrate 10 and the lower electrode 20 in order to enhance these adhesion properties.

  The pattern of the piezoelectric film 30 is not limited to that shown in the figure, and is appropriately designed. The piezoelectric film 30 may be a continuous film. However, the piezoelectric film 30 is not a continuous film, but is formed by a pattern composed of a plurality of protrusions 31 separated from each other, so that the expansion and contraction of the individual protrusions 31 occurs smoothly, so that a larger amount of displacement can be obtained, preferable.

The substrate 10 is not particularly limited, and examples thereof include silicon, glass, stainless steel (SUS), yttrium stabilized zirconia (YSZ), alumina, sapphire, and silicon carbide. As the substrate 10, a laminated substrate such as an SOI substrate in which a SiO ₂ film and a Si active layer are sequentially laminated on a silicon substrate may be used.

The main component of the lower electrode 20 is not particularly limited, and examples thereof include metals or metal oxides such as Au, Pt, Ir, IrO ₂ , RuO ₂ , LaNiO ₃ , and SrRuO ₃ , and combinations thereof.
The main component of the upper electrode 40 is not particularly limited, and examples thereof include materials exemplified for the lower electrode 20, electrode materials generally used in semiconductor processes such as Al, Ta, Cr, and Cu, and combinations thereof.
The thickness of the lower electrode 20 and the upper electrode 40 is not particularly limited and is preferably 50 to 500 nm. The film thickness of the piezoelectric film 30 is not particularly limited and is, for example, 1 to 10 μm.

The piezoelectric film 30 is a film made of a perovskite oxide represented by the following general formula (may contain inevitable impurities).
General formula ABO ₃
(Wherein A: at least one metal element forming A site,
B: at least one metal element forming the B site,
O: oxygen atom,
The standard is the case where the number of moles of the A-site element is 1.0 and the number of moles of the B-site element is 1.0, but the number of moles of the A-site element and the B-site element is within a range where a perovskite structure can be taken. May deviate from 1.0. )

In the present embodiment, at least a part of the piezoelectric film 30 is composed of one or more kinds of cations having an ionic valence smaller than that of the substituted ion, at least part of the A site and / or B site of the parent perovskite oxide. A film structure having a substituted composition and having a cation addition amount increased continuously or stepwise from the substrate 10 side toward the film surface 30s side in the film thickness direction. Have.
That is, in this embodiment, the film structure of the piezoelectric film 30 is a structure in which the amount of cations to be added is changed in the film thickness direction without changing the main composition.

  The piezoelectric film 30 only needs to have a cation addition amount continuously or stepwise from the substrate 10 side toward the film surface 30s side as viewed in the film thickness direction. There may be regions that are not doped. In the configuration in which the amount of cation added increases stepwise from the substrate 10 side toward the film surface 30s side in the film thickness direction, the change in the amount of cation added may be one-step or multiple steps.

The composition of the parent perovskite oxide is not particularly limited, and examples thereof include those represented by the following general formula.
General formula ABO ₃
(Wherein A: at least one element selected from the group consisting of Pb, Ba, Nb, La, Li, Sr, Bi, Na, and K;
B: at least one element selected from the group consisting of Cd, Fe, Ti, Ta, Mg, Mo, Ni, Nb, Zr, Zn, W, and Yb,
O: oxygen atom)

  The parent perovskite oxide having the above composition includes lead titanate, lead zirconate titanate (PZT), lead zirconate, lead lanthanum titanate, lead lanthanum zirconate titanate, lead zirconium titanate magnesium niobate, and Lead-containing compounds such as nickel zirconium niobate lead titanate, and non-lead-containing compounds such as barium titanate, potassium niobate, and bismuth sodium titanate can be mentioned.

  The cation to be added is appropriately selected according to the matrix composition, and is not particularly limited as long as it has a smaller ionic valence than the substituted ion.

  Examples of the cation to be added include at least one alkali metal selected from the group consisting of Li, Na, and K. These are all +1 valent cations. Alkali metal can replace the A site and / or the B site, and tends to replace the A site.

When one or a plurality of group IV elements are contained in the B site of the parent perovskite oxide, the added cation can substitute a part of the group IV element. Examples of the group IV element contained in the B site include Ti and / or Zr.
The added cation for substituting the group IV element contained in the B site may be any cation having a valence of +1 to +3, such as Li, Na, K, Mg, Ca, Cr, Mo, Mn, Fe, Co, Ni, Cu. , Ag, Zn, Al, Ga, In, Sb, Bi, and at least one selected from the group consisting of rare earths.
Since alkali metals tend to easily replace the A site, when replacing group IV elements contained in the B site, the added cations include Mg, Ca, Cr, Mo, Mn, Fe, Co, Ni, Cu, At least one selected from the group consisting of Ag, Zn, Al, Ga, In, Sb, Bi, and rare earth is preferable.

When one or more V group elements are contained in the B site of the parent perovskite oxide, the cation to be added can replace a part of the V group element. Examples of the group V element contained in the B site include Nb and / or Ta.
The added cation for substituting the group V element contained in the B site may be a cation having a valence of +1 to +4. Li, Na, K, Mg, Ca, Ti, Zr, Hf, Cr, Mo, Mn, Fe , Co, Ni, Cu, Ag, Zn, Al, Ga, In, Si, Ge, Sn, Sb, Bi, Se, Te, and at least one selected from the group consisting of rare earths.
Alkali metals tend to easily replace the A site. Therefore, when substituting group V elements contained in the B site, the added cations include Mg, Ca, Ti, Zr, Hf, Cr, Mo, Mn, Fe, At least one selected from the group consisting of Co, Ni, Cu, Ag, Zn, Al, Ga, In, Si, Ge, Sn, Sb, Bi, Se, Te, and rare earths is preferable.

  By adding one or more kinds of cations having an ionic valency smaller than the substituted ions of the parent perovskite oxide to the piezoelectric film 30, point defects due to the added cations can be generated in the piezoelectric film 30. Due to the point defect due to the added cation, a domain in which the polarization axis reversibly rotates non-180 ° by increasing or decreasing the electric field applied intensity can be formed.

  In addition, since the ratio of the domain in which the polarization axis reversibly rotates non-180 ° is determined by the addition amount of the cation, in the piezoelectric film 30, the ratio of the domain in which the polarization axis reversibly rotates non-180 ° is relative to the substrate 10 side. Therefore, the film surface 30s side is relatively large. In such a configuration, reversible non-180 ° domain rotation does not occur on the substrate 10 side, or the amount of reversible non-180 ° domain rotation is small, and reversible non-180 ° domain rotation is relative to the film surface 30s side. Will happen greatly.

  The mechanism of reversible non-180 ° domain rotation in this embodiment is considered as follows. Here, a tetragonal system will be described as a model.

FIG. 2A is a diagram showing a state of normal piezoelectric strain. In the figure, E is a code indicating the electric field application intensity and the electric field application direction. Arrow P ₀ is no electric field is applied during the polarization direction and magnitude, the arrow P _E represents the polarization direction and magnitude of when an electric field is applied.
When an electric field is applied in the polarization axis direction to the c domain in which the c axis is oriented in the electric field application direction (E> 0), the crystal lattice extends in the electric field application direction. This is normal piezoelectric strain (true piezoelectric strain).
On the other hand, FIG. 2B shows the state of piezoelectric strain due to non-180 ° domain rotation. As shown in FIG. 2 (b), when the a domain with the a axis oriented in the direction of electric field application is rotated by 90 ° to the c domain with the c axis oriented in the direction of electric field application (E> 0), The major axis direction of the crystal lattice is rotated by 90 °, and a piezoelectric strain larger than the normal piezoelectric strain in FIG.

In this embodiment, the point defect due to the addition of a cation has a valence smaller than that of the ion to be substituted and is negatively charged. This point defect and oxygen vacancies (positive charge) in the vicinity thereof constitute a defect D having short range order, and this defect D is considered to have polarizability due to a charged pair. In the figure, a small arrow in the defect D indicates the direction of defect polarization.
The state in which the polarization direction of the defect D in the domain matches the polarization direction of the domain to which the defect D belongs is stable. That is, the state where the polarization axis of the defect D in the a domain coincides with the polarization axis of the a domain is stable.
Since the polarization axis of the defect D does not rotate even when an electric field is applied, the polarization axis of the defect D is different from the polarization axis of the domain to which the defect D belongs when the a domain is rotated to the c domain by the application of the electric field. . Since this state is unstable, when the electric field is removed, the polarization axis of the defect D tends to return to a stable state aligned with the polarization axis of the domain to which the defect D belongs, and non-180 ° domain rotation can occur reversibly. It is considered possible.

Although the case where the tetragonal system is used as a model and the domain rotation is orderly performed from the a domain to the c domain has been described, the actual piezoelectric film 30 is an aggregate of various domains having different polarization axis directions.
The domain is roughly divided into a domain X in which the polarization axis does not rotate even when an electric field is applied, a domain Y in which the polarization axis rotates (inverts) 180 degrees when an electric field is applied, and a polarization axis that does not rotate when an electric field is applied. There is a domain Z that rotates 180 °. Further, the domain Z includes a domain Z1 in which non-180 ° domain rotation occurs irreversibly and a domain Z2 in which non-180 ° domain rotation occurs reversibly.

  Hereinafter, the domains X to Z will be described with reference to FIG. As will be described later, the piezoelectric film 30 preferably has crystal orientation, but here, the piezoelectric film 30 which is an aggregate of a large number of crystal grains whose polarization axes are completely random is illustrated.

  3A is a diagram showing a state of the piezoelectric film 30 before the polarization treatment, FIG. 3B is a diagram showing a state (E = 0) of the polarization-treated piezoelectric film 30 when no electric field is applied, and FIG. ) Is a diagram showing a state (E> 0) in which an electric field is applied to the polarization-treated piezoelectric film 30. FIG. Here, a case where one crystal grain is one domain is illustrated.

  The piezoelectric film 30 before the polarization treatment shown in FIG. 3A is an aggregate of a large number of crystal grains with random polarization axes. When a polarization process is performed on the piezoelectric film 30 before the polarization process and an electric field is further applied, the polarization axis does not rotate in the domain X as shown in FIG. A rotation (inversion) occurs, and in domain Z, a non-180 ° rotation of the polarization axis occurs. Since 180 ° domain rotation only changes the vertical direction of the crystal lattice, piezoelectric distortion due to domain rotation does not occur, whereas non-180 ° domain rotation causes piezoelectric strain due to domain rotation.

  Further, in the domain Z1 of the domain Z in which the polarization axis rotates non-180 ° by applying an electric field, as shown in FIG. 3B, the polarization axis does not return to the original state even when the electric field is removed, and the distortion remains. (Residual strain). As shown in FIG. 3B, in the domain Z in which the polarization axis rotates non-180 ° by applying an electric field, as shown in FIG. 3B, when the electric field is removed, the polarization axis returns to the original, and reversible non-180 ° domain rotation occurs. In this embodiment, the ratio of the domain Z2 in which reversible non-180 ° domain rotation occurs is relatively small on the substrate 10 side and relatively large on the film surface 30s side.

  In the piezoelectric film 30, when the vector component of the spontaneous polarization axis coincides with the electric field application direction, normal piezoelectric strain (true piezoelectric strain) that expands and contracts in the electric field application direction due to increase / decrease of the electric field application intensity and reversible non-180 ° Both effects of piezoelectric strain due to domain rotation can be obtained. In piezoelectric strain due to reversible non-180 ° domain rotation, a large strain can be obtained by rotating the crystal lattice. Therefore, by combining normal piezoelectric strain and piezoelectric strain due to reversible non-180 ° domain rotation, normal piezoelectric strain can be obtained. A piezoelectric strain larger than the strain alone can be obtained.

  The piezoelectric film 30 preferably has crystal orientation. More specifically, on the substrate 10 side, when the vector component of the spontaneous polarization axis coincides with the electric field application direction, the piezoelectric film 30 is a normal piezoelectric strain that expands and contracts in the electric field application direction due to increase / decrease of the electric field application intensity. It is preferable to increase the ratio of the alignment region where the vector component of the polarization axis and the electric field application direction coincide with each other so that is effectively expressed. Moreover, it is preferable that the piezoelectric film 30 has a high ratio of orientation regions in which piezoelectric strain due to reversible non-180 ° domain rotation is effectively developed on the film surface 30s side.

In PZT, etc., there are three types of crystal systems, cubic, tetragonal and rhombohedral, and in barium titanate, etc., cubic, tetragonal, orthorhombic and rhombohedral There are four types of crystal systems. Since the cubic system is a paraelectric material and does not exhibit piezoelectricity, the piezoelectric film 30 is any one of a tetragonal system, an orthorhombic system, a rhombohedral system, and a crystal system in which a plurality of these crystal systems are mixed. Need to be. The spontaneous polarization axis of each crystal system is as follows. Therefore, it is preferable to design the crystal orientation in consideration of the crystal system, the spontaneous polarization axis, the electric field application direction, and the principle of piezoelectric strain.
Tetragonal system: <001>, orthorhombic system: <110>, rhombohedral system: <111>

  For example, when the crystal structure of the piezoelectric film 30 is a tetragonal system or a crystal system in which a tetragonal system and another crystal system are mixed, the domain structure of the piezoelectric film 30 is an a-axis when no electric field is applied. Includes a domain preferentially oriented in the direction perpendicular to the substrate surface of the substrate 10 and c domain preferentially oriented in the direction perpendicular to the substrate surface of the substrate 10. The ratio is relatively large, the ratio of the a domain is relatively large on the film surface 30 s side, and at least a part of the a domain is a domain in which the polarization axis reversibly rotates non-180 ° by increasing or decreasing the electric field application intensity. Structure.

In the present embodiment, it is preferable to select a combination of the material of the substrate 10 and the piezoelectric film 30 so that the constituent material of the piezoelectric film 30 has a higher thermal expansion coefficient from room temperature to 500 ° C. than the constituent material of the substrate 10.
The reason for this will be described with reference to FIG. 4 using a tetragonal system as a model. FIG. 4 schematically illustrates a case where the piezoelectric film 30 includes only the a domain when no electric field is applied, and all the a domains rotate to the c domain by applying an electric field. In the figure, reference numeral 30a indicates the a domain and reference numeral 30c indicates the c domain, and the illustration of the electrodes is omitted.

  If the thermal expansion coefficient relationship is as described above, after the film formation of the piezoelectric film 30 is completed and the temperature returns to room temperature, the piezoelectric film 30 is As shown in the upper diagram of FIG. 4, a tensile stress is generated in the piezoelectric film 30, as it expands relatively larger in the lateral direction than the substrate 10 (this amount is very small). A ferroelectric crystal, which is an anisotropic crystal, has a stable crystal structure in which the major axis direction is aligned with the direction of the tensile stress in order to relax the stress under a tensile stress. That is, in this state, the a domain is crystallinely stable. As shown in the lower diagram of FIG. 4, domain rotation from the a domain to the c domain occurs by applying an electric field, but after removing the electric field, the crystallized stable a domain in which the major axis is aligned with the direction of the tensile stress. Therefore, it is considered that non-180 ° domain rotation can occur reversibly and stably.

The linear expansion coefficient from room temperature to 500 ° C. is 4.0 to 8.0 × 10 ⁻⁶ (/ ° C.) for a general piezoelectric material such as PZT. The linear expansion coefficients of room temperature to 500 ° C. of main substrate materials are as follows.
Si: 2.6 × 10 ⁻⁶ (/ ° C.), Alumina: 7.0 × 10 ⁻⁶ (/ ° C.)
In order for the constituent material of the piezoelectric film 30 to have a higher coefficient of thermal expansion at room temperature to 500 ° C. than the constituent material of the substrate 10, it is preferable to use a Si substrate or the like as the substrate 10.
In the present invention, taking into account that the film forming temperature of the piezoelectric film is usually about 500 ° C. or higher, the coefficient of thermal expansion from room temperature to 500 ° C., which is considered to be approximately within the film forming temperature, is specified.

  In this specification, “having crystal orientation” is defined as an orientation rate F measured by the Lottgering method being 50% or more.

The orientation rate F is represented by the following formula.
F (%) = (P−P0) / (1−P0) × 100 (i)
In formula (i), P is the ratio of the total reflection intensity from the orientation plane to the total reflection intensity. In the case of (001) orientation, P is the sum ΣI (00l) of the reflection intensity I (00l) from the (00l) plane and the sum ΣI (hkl) of the reflection intensity I (hkl) from each crystal plane (hkl). ({ΣI (00l) / ΣI (hkl)}). For example, in the case of (001) orientation in the perovskite crystal, P = I (001) / [I (001) + I (100) + I (101) + I (110) + I (111)].
P0 is P of a sample having a completely random orientation.
When the orientation is completely random (P = P0), F = 0%, and when the orientation is complete (P = 1), F = 100%.

  The method for forming the piezoelectric film 30 is not particularly limited, and vapor phase growth methods such as sputtering, MOCVD, and pulse laser deposition; chemical solution deposition (CSD) such as sol-gel method and organometallic decomposition method; aerosol Examples include the deposition method.

In the present embodiment, the piezoelectric film 30 is formed so that the addition amount of cations increases continuously or stepwise from the substrate 10 side toward the film surface 30s side as viewed in the film thickness direction.
In the vapor phase growth method, the piezoelectric film 30 may be formed by increasing the cation addition amount continuously or stepwise as the film formation time elapses. For example, by preparing a plurality of targets having different cation contents and changing the rate of film formation from the plurality of targets during film formation, the piezoelectric films 30 having different cation addition amounts in the film thickness direction are formed. (See Examples 1-3 below).
In the chemical solution deposition method (CSD), the piezoelectric films 30 having different cation addition amounts in the film thickness direction can be formed by stacking layers having different compositions by changing the composition of the raw material solution.

  In the normal temperature state after film formation, the symmetry of the defect may not match the crystal symmetry of the ferroelectric domain to which the defect belongs. In such a case, by performing an aging treatment that anneals at a temperature below the Curie point after film formation, the point defect is diffused to a stable position, and the symmetry of the point defect is related to the crystal symmetry of the domain to which the point defect belongs. And a stable state (see the left diagram in FIG. 2B).

In general, in a bulk piezoelectric body without a substrate, when a positive electric field is applied in the spontaneous polarization axis direction, the bulk piezoelectric body expands in the electric field application direction (33 mode deformation) and contracts in a direction orthogonal to the electric field application direction (31 mode deformation). On the other hand, in the piezoelectric film formed on the substrate, when a positive electric field is applied in the spontaneous polarization axis direction, the film surface side of the piezoelectric film extends in the electric field application direction as in the bulk piezoelectric body (33 Mode deformation), and contracts in a direction orthogonal to the electric field application direction (31 mode deformation). However, on the substrate side, the deformation is constrained by the substrate, and the contraction in the direction orthogonal to the electric field application direction is reduced. It is known that it is slightly bent (31-mode bending deformation).
In this embodiment, since the piezoelectric strain due to reversible non-180 ° rotation is relatively increased on the film surface 30 s side of the piezoelectric film 30, it is considered that 31-mode bending deformation occurs more significantly. This is schematically shown in FIG. 5 (illustration of electrodes is omitted). In addition, in order to make it easy to see on the drawing, the 31-mode bending deformation is exaggerated, but the level is very slight.

  In the ink jet recording head 2, a vibration plate 50 that vibrates due to expansion and contraction of the piezoelectric film 30 is attached to the lower surface of the substrate 10 of the piezoelectric element 1, and an ink chamber 61 and ink are stored on the lower surface of the vibration plate 50. An ink nozzle (ink storage and discharge member) 60 having an ink discharge port 62 through which ink is discharged from the chamber 61 to the outside is attached. A plurality of ink chambers 61 are provided corresponding to the number and pattern of the convex portions 31 of the piezoelectric film 30.

  Instead of attaching the vibration plate 50 and the ink nozzle 60 which are members independent of the substrate 10, a part of the substrate 10 may be processed into the vibration plate 50 and the ink nozzle 60. For example, when the substrate 10 is made of a laminated substrate such as an SOI substrate, the substrate 10 is etched from the lower surface side to form the ink chamber 61, and the vibration plate 50 and the ink nozzle 60 are formed by processing the substrate itself. Can do.

  The piezoelectric element 1 and the ink jet recording head 2 of the present embodiment are configured as described above.

  In the present embodiment, at least part of the piezoelectric film 30 is one or more kinds of cations in which part of the A site and / or B site of the parent perovskite oxide has a smaller ionic valence than the substituted ion. In addition, cation addition is performed so that the addition amount of the cation increases continuously or stepwise from the substrate 10 side toward the film surface 30 s side as viewed in the film thickness direction. It is configured to do.

  In such a configuration, a domain in which the polarization axis reversibly rotates non-180 ° is formed by the point defect due to the addition of the cation, and a large piezoelectric strain due to the reversible non-180 ° domain rotation can be obtained. Moreover, since the amount of cation added is relatively small on the substrate 10 side, there are fewer point defects at the initial stage of film formation than when cation is added at a high concentration from the beginning, the crystal structure, crystal orientation, etc. can be easily controlled, and the production is also easy It is relatively easy.

  Since the ratio of the domain in which the polarization axis reversibly rotates non-180 ° is determined by the addition amount of the cation, in this embodiment, the ratio of the domain in which the polarization axis reversibly rotates non-180 ° is relatively higher on the substrate 10 side. There are few, and the film surface 30s side becomes a relatively large structure. In such a configuration, reversible non-180 ° domain rotation does not occur on the substrate 10 side, or the amount of reversible non-180 ° domain rotation is small, and reversible non-180 ° domain rotation is relative to the film surface 30s side. Will happen greatly.

  In the section “Background Art”, it was described that in the piezoelectric strain using reversible non-180 ° domain rotation, the electrostrictive characteristics have large hysteresis and large practical limitations (see FIG. 9). In addition, it is necessary to return to the original domain state when the electric field drops, but it has been stated that if the electric field marking speed (frequency) increases, the desired domain rotation may not occur.

  In this embodiment, since the ratio of the domain in which the polarization axis reversibly rotates non-180 ° is changed in the film thickness direction, compared with the case where reversible non-180 ° domain rotation occurs uniformly in the entire film, Hysteresis of the electric field distortion characteristic when reversible non-180 ° domain rotation is used can be reduced. In addition, since it is sufficient that reversible non-180 ° domain rotation occurs at least on the film surface 30s side, domain rotation can be stably performed as desired even when the electric field marking speed (frequency) increases, and reversible. The frequency characteristics when the non-180 ° domain rotation is used can also be improved.

  In the present embodiment, as described above, the 31-mode bending deformation is effectively caused by the increase / decrease of the electric field application intensity, and therefore, the electric field lateral strain generated by the 31-mode bending deformation can be positively used. For example, the piezoelectric element 1 can be used as a diaphragm or the like by using electric field lateral strain generated by 31-mode bending deformation.

"Inkjet recording device"
A configuration example of an ink jet recording apparatus including the ink jet recording head 3 according to the above embodiment will be described with reference to FIGS. 6 is an overall view of the apparatus, and FIG. 7 is a partial top view.

  The illustrated ink jet recording apparatus 100 includes a printing unit 102 having a plurality of ink jet recording heads (hereinafter simply referred to as “heads”) 2K, 2C, 2M, and 2Y provided for each ink color, and each head 2K, An ink storage / loading unit 114 that stores ink to be supplied to 2C, 2M, and 2Y, a paper feeding unit 118 that supplies recording paper 116, a decurling unit 120 that removes curling of the recording paper 116, and a printing unit An adsorption belt conveyance unit 122 that conveys the recording paper 116 while maintaining the flatness of the recording paper 116, and a print detection unit that reads a printing result by the printing unit 102. 124 and a paper discharge unit 126 that discharges printed recording paper (printed matter) to the outside.

  The heads 2K, 2C, 2M, and 2Y that form the printing unit 102 are the ink jet recording heads 2 of the above-described embodiment.

  In the decurling unit 120, heat is applied to the recording paper 116 by the heating drum 130 in the direction opposite to the curl direction, and the decurling process is performed.

  In the apparatus using roll paper, as shown in FIG. 6, a cutter 128 is provided at the subsequent stage of the decurling unit 120, and the roll paper is cut into a desired size by this cutter. The cutter 128 includes a fixed blade 128A having a length equal to or larger than the conveyance path width of the recording paper 116, and a round blade 128B that moves along the fixed blade 128A. The fixed blade 128A is provided on the back side of the print. The round blade 128B is arranged on the print surface side with the conveyance path interposed therebetween. In an apparatus using cut paper, the cutter 128 is unnecessary.

  The decurled and cut recording paper 116 is sent to the suction belt conveyance unit 122. The suction belt conveyance unit 122 has a structure in which an endless belt 133 is wound between rollers 131 and 132, and at least portions facing the nozzle surface of the printing unit 102 and the sensor surface of the printing detection unit 124 are horizontal ( Flat surface).

  The belt 133 has a width that is wider than the width of the recording paper 116, and a plurality of suction holes (not shown) are formed on the belt surface. An adsorption chamber 134 is provided at a position facing the nozzle surface of the printing unit 102 and the sensor surface of the print detection unit 124 inside the belt 133 that is stretched between the rollers 131 and 132. The recording paper 116 on the belt 133 is sucked and held by suctioning at 135 to make a negative pressure.

  The power of a motor (not shown) is transmitted to at least one of the rollers 131 and 132 around which the belt 133 is wound, so that the belt 133 is driven in the clockwise direction in FIG. 6 and held on the belt 133. The recording paper 116 is conveyed from left to right in FIG.

  Since ink adheres to the belt 133 when a borderless print or the like is printed, the belt cleaning unit 136 is provided at a predetermined position outside the belt 133 (an appropriate position other than the print region).

  A heating fan 140 is provided on the upstream side of the printing unit 102 on the paper conveyance path formed by the suction belt conveyance unit 122. The heating fan 140 heats the recording paper 116 by blowing heated air onto the recording paper 116 before printing. Heating the recording paper 116 immediately before printing makes it easier for the ink to dry after landing.

  The printing unit 102 is a so-called full line type head in which a line type head having a length corresponding to the maximum paper width is arranged in a direction (main scanning direction) orthogonal to the paper feeding direction (see FIG. 7). Each of the print heads 2K, 2C, 2M, and 2Y is a line-type head in which a plurality of ink discharge ports (nozzles) are arranged over a length that exceeds at least one side of the maximum size recording paper 116 targeted by the ink jet recording apparatus 100. It is configured.

  Heads 2K, 2C, 2M, and 2Y corresponding to the respective color inks are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 116. ing. A color image is recorded on the recording paper 116 by ejecting the color inks from the heads 2K, 2C, 2M, and 2Y while conveying the recording paper 116, respectively.

  The print detection unit 124 includes a line sensor that images the droplet ejection result of the print unit 102 and detects ejection defects such as nozzle clogging from the droplet ejection image read by the line sensor.

  A post-drying unit 142 including a heating fan or the like for drying the printed image surface is provided at the subsequent stage of the print detection unit 124. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  A heating / pressurizing unit 144 is provided downstream of the post-drying unit 142 in order to control the glossiness of the image surface. The heating / pressurizing unit 144 presses the image surface with a pressure roller 145 having a predetermined surface irregularity shape while heating the image surface, and transfers the irregular shape to the image surface.

  The printed matter obtained in this manner is outputted from the paper output unit 126. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. In the ink jet recording apparatus 100, there is provided sorting means (not shown) for switching the paper discharge path in order to select the print product of the main image and the print product of the test print and send them to the discharge units 126A and 126B. It has been.

When the main image and the test print are simultaneously printed on a large sheet of paper, the cutter 148 may be provided to separate the test print portion.
The ink jet recording apparatus 100 is configured as described above.

  Examples and comparative examples according to the present invention will be described.

(Example 1)
As a substrate for forming a piezoelectric film, an electrode-attached substrate in which a Ti adhesion layer (10 nm thickness) and a Pt lower electrode (100 nm thickness) are sequentially stacked on a (001) Si single crystal substrate having a natural oxide film on the surface. Prepared.
The piezoelectric film was formed using an RF sputtering apparatus in which two types of targets can be installed and the substrate holder can be rotated to form films from the two types of targets simultaneously. A first target and a second target having the following two compositions were set in the apparatus. The temperature of the substrate holder was 550 ° C.
First target: BaTiO ₃ ,
Second target: 2% Mn—BaTiO ₃ (Ti of BaTiO ₃ substituted with 2 mol% of Mn: BaTi _0.98 Mn _0.02 O ₃ )

Film formation was performed by rotating the substrate holder, and the RF power applied to the first target was fixed at 80W. The RF power applied to the second target was 0 W at the start of film formation, and 20 W of RF power was applied to the second target 30 minutes after the start of film formation. Thereafter, the RF power applied to the second target was increased by 10 W every 20 minutes, and the RF power applied to the second target was finally set to 80 W. The total deposition time including deposition from only the first target was 180 minutes. The film thickness of the obtained piezoelectric film was 1.5 μm.
After the formation of the piezoelectric film, an Au upper electrode (100 nm thickness) was vacuum deposited to obtain the piezoelectric element of the present invention.

  In this example, the RF power applied to the second target was changed over time to change the film composition in the thickness direction, but the applied power to the first target and the second target were both fixed. The film composition in the thickness direction can also be changed by repeating the rotation and stop of the substrate holder and controlling the stop time.

(Example 2)
A piezoelectric element of the present invention was obtained in the same manner as in Example 1 except that a piezoelectric film was formed using a first target and a second target having the following composition.
First target: KNaNb ₂ O ₆ ,
Second target: 2% Mn—KNaNb ₂ O ₆ (Nb in KNaNb ₂ O ₆ substituted with 2 mol% of Mn: KNaNb _1.96 Mn _0.04 O ₆ )

(Example 3)
A substrate with an electrode in which a Ti adhesion layer and a Pt lower electrode are sequentially laminated on a (0001) sapphire substrate (the film thickness of the Ti adhesion layer and the Pt lower electrode is the same as in Example 1) as a piezoelectric film deposition substrate. A piezoelectric element of the present invention was obtained in the same manner as in Example 1 except that it was prepared.

(Comparative Examples 1, 2, 4)
A comparative piezoelectric element was obtained in the same manner as in Examples 1 and 2 except that the piezoelectric film was formed using only one type of target having the composition shown in Table 1.
(Comparative Example 3)
A comparative piezoelectric element was obtained in the same manner as in Example 1 except that the piezoelectric film was formed using the first target and the second target having the composition shown in Table 1.

<Evaluation>
<XRD measurement>
When film formation of the piezoelectric film was completed, X-ray diffraction (XRD) measurement of the piezoelectric film was performed with Cu-Kα characteristic X-rays.
<Piezoelectric constant>
The piezoelectric constant d ₃₁ of the obtained piezoelectric element was measured with a cantilever technique.

<Result>
As a representative, the XRD pattern of the piezoelectric film obtained in Example 1 is shown in FIG. The diffraction lines near 22 ° and 45 ° were large, and the 45 ° diffraction lines were split. That is, the obtained piezoelectric film had a film structure in which the c-axis and a-axis were preferentially oriented perpendicular to the substrate surface. Similar diffraction patterns were obtained in other examples and comparative examples.

Table 1 shows the target composition and evaluation results used in each example.
In Examples 1 to 3 in which the piezoelectric film was formed so that the amount of Mn added was relatively small on the substrate side and relatively large on the film surface side, a higher piezoelectric constant than in Comparative Examples 1 to 3 was obtained. It was. In contrast to Example 1, in Comparative Example 3 in which the piezoelectric film was formed such that the amount of Mn added was relatively large on the substrate side and relatively small on the film surface side, a high piezoelectric constant was obtained. The Mn concentration was almost the same as in Comparative Example 2.
In Examples 1 and 2 in which the combination of the material of the substrate and the piezoelectric film was selected so that the material of the piezoelectric film had a higher coefficient of thermal expansion at room temperature to 500 ° C. than the material of the substrate, the piezoelectric constant was particularly high. was gotten.

  The piezoelectric film of the present invention is preferably used for an ink jet recording head, a magnetic recording / reproducing head, a MEMS (Micro Electro-Mechanical Systems) device, a micro pump, an ultrasonic probe mounted on an ultrasonic probe, and a diaphragm. it can.

1 is a cross-sectional view of a principal part showing the structure of a piezoelectric element according to an embodiment of the present invention and an ink jet recording head including the same (A) is a diagram showing a state of normal piezoelectric strain, (b) is a diagram showing a state of piezoelectric strain due to reversible non-180 ° domain rotation. (A) is a figure which shows the state of the piezoelectric film before polarization processing, (b) is a figure which shows the state at the time of no electric field application of the piezoelectric film after polarization processing, (c) is with respect to the piezoelectric film after polarization processing The figure which shows the state which applied the electric field Explanatory drawing explaining that reversible non-180 ° domain rotation can be stably caused by defining the relationship between the thermal expansion coefficients of the substrate and the piezoelectric film. Explanatory drawing of 31 mode bending deformation 1 is a diagram illustrating a configuration example of an ink jet recording apparatus including the ink jet recording head of FIG. Partial top view of the ink jet recording apparatus of FIG. XRD pattern of the piezoelectric film obtained in Example 1 The figure which shows the example of the electric field distortion characteristic of the piezoelectric element using a reversible non-180 degree domain rotation

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric element 2, 2K, 2C, 2M, 2Y Inkjet recording head 10 Substrate 20, 40 Electrode 30 Piezoelectric film 30a a domain 30c c domain 30s Piezoelectric film surface 50 Diaphragm 60 Ink nozzle (ink storage and discharge member)
61 Ink chamber 62 Ink discharge port 100 Inkjet recording apparatus D Defect with short range order X Domain whose polarization axis does not rotate even when an electric field is applied Y Domain where the polarization axis rotates 180 ° when an electric field is applied When a Z1 electric field is applied Domain where the polarization axis rotates non-180 °, and the polarization axis does not return even if the electric field is removed Z2 The domain where the polarization axis rotates non-180 ° when an electric field is applied, and the polarization axis returns to the original state when the electric field is removed (polarization axis Is a reversible non-180 ° domain)

Claims (21)

The general formula ABO ₃ (A: at least one metal element forming an A site, B: at least one metal element forming a B site, O: oxygen atom, A site element formed on a substrate) It is standard that the number of moles of the B site element is 1.0 and the number of moles of the B site element is 1.0, but the number of moles of the A site element and the B site element is 1 within a range that can take a perovskite structure. In the piezoelectric film (which may contain inevitable impurities) made of a perovskite oxide represented by:
At least a part has a composition in which part of the A site and / or B site of the parent perovskite oxide is substituted with one or more kinds of cations having a smaller ionic valence than the substituted ion. ,
In addition, the piezoelectric film is characterized in that the addition amount of the cation increases continuously or stepwise from the substrate side toward the film surface side as viewed in the film thickness direction.   2. The piezoelectric film according to claim 1, wherein the cation is at least one selected from the group consisting of Li, Na, and K. 3.   The piezoelectric film according to claim 2, wherein the cation substitutes an A site of the base perovskite oxide.   The B site of the parent perovskite oxide contains one or more group IV elements, and the cation substitutes a part of the group IV element. Piezoelectric film.   The piezoelectric film according to claim 4, wherein the group IV element is Ti and / or Zr.   The cation is selected from the group consisting of Li, Na, K, Mg, Ca, Cr, Mo, Mn, Fe, Co, Ni, Cu, Ag, Zn, Al, Ga, In, Sb, Bi, and rare earths. 6. The piezoelectric film according to claim 4, wherein the piezoelectric film is at least one kind.   The B site of the parent perovskite oxide contains one or more V group elements, and the cation substitutes a part of the V group elements. Piezoelectric film.   The piezoelectric film according to claim 7, wherein the group V element is Nb and / or Ta.   The cations are Li, Na, K, Mg, Ca, Ti, Zr, Hf, Cr, Mo, Mn, Fe, Co, Ni, Cu, Ag, Zn, Al, Ga, In, Si, Ge, Sn, 9. The piezoelectric film according to claim 7, wherein the piezoelectric film is at least one selected from the group consisting of Sb, Bi, Se, Te, and rare earth.   10. The piezoelectric film according to claim 1, wherein a domain in which a polarization axis reversibly rotates non-180 ° by an increase or decrease in electric field application intensity is formed by the addition of the cation.   The crystal structure is any one of a tetragonal system, an orthorhombic system, a rhombohedral system, and a crystal system obtained by mixing a plurality of these crystal systems. Piezoelectric film.   The piezoelectric film according to claim 11, wherein the piezoelectric film has crystal orientation. The crystal structure is a tetragonal system, or a crystal system in which a tetragonal system and other crystal systems are mixed,
When no electric field is applied, the a-domain of the tetragonal crystal is preferentially oriented in the direction perpendicular to the substrate surface of the substrate, and the c-axis of the tetragonal crystal is preferentially oriented in the direction perpendicular to the substrate surface of the substrate. 13. The piezoelectric film according to claim 12, wherein the piezoelectric film has a c domain, and at least a part of the a domain is a domain whose polarization axis is reversibly rotated by 180 ° by an increase or decrease in electric field applied intensity. .   The piezoelectric film according to any one of claims 1 to 13, wherein the piezoelectric film is made of a material having a thermal expansion coefficient of room temperature to 500 ° C higher than that of the constituent material of the substrate. It was formed by vapor deposition,
The plurality of targets having different cation contents are prepared, and the film is formed by changing the rate of film formation from the plurality of targets during film formation. The piezoelectric film according to any one of the above. On the substrate, the general formula ABO ₃ (wherein A: at least one metal element forming an A site, B: at least one metal element forming a B site, O: oxygen atom, and the number of moles of the A site element) The standard is 1.0 and the number of moles of the B-site element is 1.0, but the number of moles of the A-site element and the B-site element deviates from 1.0 within a range where a perovskite structure can be obtained. In the method for forming a piezoelectric film for forming a piezoelectric film (which may contain inevitable impurities) made of a perovskite oxide represented by:
At least a part of the piezoelectric film has a composition in which a part of the A site and / or B site of the base perovskite oxide is substituted with one or more kinds of cations having a smaller ionic valence than the substituted ion. Have
The piezoelectric film is formed such that the amount of the cation added increases continuously or stepwise from the substrate side toward the film surface side in the film thickness direction. A film forming method. The film formation is film formation by vapor deposition,
17. The method for forming a piezoelectric film according to claim 16, wherein the film formation is performed by increasing the addition amount of the cation continuously or stepwise as the film formation time elapses.   18. The piezoelectric film according to 17, wherein a plurality of targets having different cation contents are prepared, and the film formation is performed by changing a ratio of film formation from the plurality of targets during the film formation. The film forming method.   A piezoelectric element comprising: the piezoelectric film according to claim 1; and an electrode for applying an electric field in a film thickness direction of the piezoelectric film. The piezoelectric element according to claim 19,
An ink jet recording head, comprising: an ink chamber in which ink is stored; and an ink storage and discharge member having an ink discharge port through which the ink is discharged from the ink chamber to the outside.   An ink jet recording apparatus comprising the ink jet recording head according to claim 20.

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