JP2006173646A - Ferroelectric thin-film element, piezoelectric actuator, liquid discharge head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferroelectric thin-film element that has large spontaneous polarization, is suitable for thinning and does not have deterioration in the characteristics, and to provide a piezoelectric actuator and a liquid delivery head that uses the same. <P>SOLUTION: In the ferroelectric thin-film element provided with a substrate and an epitaxial ferroelectric thin-film provided on the substrate, the ferroelectric thin-film element, wherein of the crystal planes of the epitaxial ferroelectric thin-film, when a crystal plane parallel to that of a substrate surface is set as a Z crystal plane, the surface separation of the Z crystal plane as z, and the spacing between Z crystal planes in bulk state of composition material of the epitaxial ferroelectric thin-film as z<SB>0</SB>, z/z<SB>0</SB>>1.003; and when one crystal plane among the crystal planes in the epitaxial ferroelectric thin-film perpendicular to the Z crystal plane is set as a X crystal plane, the inter-plane separation of the X crystal plane as x, the inter-plane separation of the X crystal plane in bulk state of composition material of the epitaxial ferroelectric thin-film is x<SB>0</SB>, the relation 0.997≤x/x<SB>0</SB>≤1.003 holds. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ferroelectric thin film element, and relates to an element such as a nonvolatile memory in which spontaneous polarization of a ferroelectric thin film is involved in improving element characteristics of the thin film element. The present invention also relates to a piezoelectric actuator that utilizes the piezoelectric characteristics of an epitaxial ferroelectric film and a liquid discharge head that includes a piezoelectric actuator portion having a configuration including the piezoelectric actuator.

  In recent years, a storage device (hereinafter referred to as a ferroelectric memory) using a high-performance ferroelectric thin film as a storage medium such as a nonvolatile memory has been demanded. In order to ensure optimal device characteristics and reproducibility in ferroelectric memory, the ferroelectric thin film has a large spontaneous polarization (residual polarization), a small temperature dependence of the remanent polarization, and deterioration due to repeated polarization inversion. Is required to be small.

Currently, lead zirconate titanate [Pb (Zr _, Ti) O ₃ ] (sometimes referred to as PZT) is mainly used as a ferroelectric material. PZT is a solid solution of lead zirconate and lead titanate, but a solid solution with a molar ratio of approximately 1: 1 has a large spontaneous polarization and can be reversed even at a low electric field, and is excellent as a storage medium. It is considered a thing. Since PZT has a relatively high transition temperature (Curie temperature) between the ferroelectric phase and the paraelectric layer of 300 ° C. or higher, it is memorized in the temperature range (120 ° C. or lower) in which ordinary electronic circuits are used. There is little worry that the contents will be lost by heat.

  However, even with an excellent ferroelectric thin film such as a PZT thin film, it is difficult to obtain good device characteristics in a ferroelectric thin film made of a polycrystal due to a disturbance of physical quantities due to grain boundaries. For this reason, when considering the device characteristics of the ferroelectric element, an epitaxial thin film that is as close to a complete single crystal as possible is desired.

  For high integration of ferroelectric devices, it is effective to reduce the thickness of the ferroelectric thin film. Generally, when the thickness of the ferroelectric thin film is set to 100 nm or less, the ferroelectric thin film becomes epitaxial. Even in the case of a film, the spontaneous polarization of the ferroelectric thin film tends to be lost, and the residual polarization of the ferroelectric thin film and the deterioration of the fatigue resistance of the ferroelectric thin film become remarkable. For this reason, in order to reduce the thickness of the ferroelectric thin film, a device for keeping the spontaneous polarization of the ferroelectric thin film sufficiently large is required.

  As a method for increasing the spontaneous polarization of the ferroelectric thin film, a method using a mismatch between the thermal expansion coefficients of the substrate and the ferroelectric thin film (see, for example, Patent Document 1), a lattice misfit between the substrate and the ferroelectric thin film. (For example, refer to Patent Document 2). By adopting these methods, it is possible to apply a compressive stress to the ferroelectric thin film, thereby increasing the spontaneous polarization of the ferroelectric thin film.

  However, the conventional method of increasing the spontaneous polarization by applying compressive stress to the ferroelectric thin film can increase the spontaneous polarization, but the residual polarization of the ferroelectric thin film and the fatigue resistance characteristics of the ferroelectric thin film Deterioration of is not improved. This is because the stress applied to the surface of the ferroelectric thin film in the direction of the substrate surface greatly contributes to the deterioration of the characteristics of the ferroelectric thin film, and a large compressive stress is applied to the ferroelectric thin film by the conventional method. In addition, it is estimated that the stress applied in the direction of the substrate surface acts on the ferroelectric thin film and further promotes the deterioration of the characteristics of the ferroelectric thin film.

  In addition, in recent years, printers using an ink jet recording apparatus as a printing apparatus such as a personal computer have become widespread for reasons such as good printing performance, easy handling, and low cost. The ink jet head used in this ink jet recording apparatus is a liquid discharge head that discharges ink, generates air bubbles in the ink by thermal energy, and discharges ink droplets by pressure waves due to the air bubbles. There are various methods such as those for sucking and discharging ink droplets, and those for sucking and discharging ink droplets using a pressure wave generated by an actuator having a vibrator such as a piezoelectric element or an electrostrictive element.

  In general, a liquid discharge head using a piezoelectric actuator includes, for example, a pressure chamber that communicates with a liquid supply chamber and a liquid discharge port that communicates with the pressure chamber. A directly formed diaphragm is provided. In the liquid discharge head having such a configuration, a predetermined voltage is applied to the piezoelectric actuator to expand and contract the piezoelectric element, thereby causing a flexural vibration to pressurize the liquid in the pressure chamber, thereby causing a droplet from the liquid discharge port. To discharge.

  Currently, color ink jet recording apparatuses have become widespread, but improvement in printing performance, in particular, higher resolution and higher speed printing are required. For this reason, attempts have been made to realize high resolution and high speed printing using a multi-nozzle head structure in which a liquid discharge head for discharging ink is miniaturized. In order to miniaturize the liquid discharge head, it is necessary to reduce the size of the piezoelectric actuator for discharging the liquid.

  Conventionally, in the piezoelectric actuator and the liquid discharge head, in order to reduce the size of the piezoelectric actuator, the piezoelectric body obtained by sintering has been manufactured by micro-molding by techniques such as cutting and polishing as described above. Apart from this, research has been conducted to develop a highly accurate ultra-small piezoelectric actuator by forming a piezoelectric body as a film and making full use of microfabrication technology that has been used in semiconductors. Further, considering the high performance, it is desirable that the piezoelectric film is a single crystal film or a film having crystal orientation, and development of heteroepitaxial growth techniques has been actively conducted.

  In general, when a ferroelectric material is used as the piezoelectric material, one of the characteristics required for the ferroelectric material is that the ferroelectric material has a large spontaneous polarization. However, in the case of a film, when the thickness of the ferroelectric film is decreased, the spontaneous polarization of the epitaxial ferroelectric film tends to be lost even if the ferroelectric film is an epitaxial film. Therefore, a device for keeping the spontaneous polarization of the epitaxial ferroelectric film sufficiently large is required.

  As described above, as a method for increasing the spontaneous polarization of the epitaxial ferroelectric film, as described above, a method using the mismatch between the thermal expansion coefficients of the substrate and the epitaxial ferroelectric film (see, for example, Patent Document 1), the substrate and the epitaxial ferroelectric film. For example, a method using a misfit of the lattice of the body membrane (for example, see Patent Document 2). According to these methods, an epitaxial ferroelectric film in which compressive stress is applied is formed in the film, and an epitaxial ferroelectric film having a large spontaneous polarization can be obtained.

  However, it is possible to increase the piezoelectricity by the conventional method of improving the piezoelectric characteristics by forming an epitaxial ferroelectric film in which a compressive stress acts in the film and increasing the spontaneous polarization, Problems such as deterioration of characteristics during repeated use of the actuator and destruction of the piezoelectric actuator due to leakage current during voltage application cannot be solved. This is because the stress applied to the substrate surface in the plane of the epitaxial ferroelectric film is involved in the deterioration and destruction of the above-mentioned characteristics of the piezoelectric actuator, and is affected by the large compressive stress produced by the conventional method. In the epitaxial ferroelectric film, it is estimated that the stress applied in the substrate surface direction acts on the epitaxial ferroelectric film and further promotes the deterioration of the durability characteristics of the piezoelectric actuator.

Japanese Patent Laid-Open No. 08-186182 Japanese Patent Laid-Open No. 08-139292

  One of the objects of the present invention is that since the stress applied in the direction of the substrate surface in the ferroelectric thin film surface is small, there is no deterioration in the characteristics of the ferroelectric thin film element, and the spontaneous polarization of the ferroelectric thin film is large. It is an object to provide a ferroelectric thin film element suitable for fabrication. Spontaneous polarization of the ferroelectric thin film is effective for an element involved in improving the element characteristics of the ferroelectric thin film element, such as a nonvolatile memory. In the heteroepitaxial growth technique, it is preferable to reduce the stress applied in the substrate surface direction generated in the region near the boundary surface between the substrate and the formed ferroelectric thin film. This is because the stress applied in the direction of the substrate surface caused by misfit between the crystal lattice of the substrate and the ferroelectric thin film contributes to the peeling of the film of the ferroelectric thin film, and the stress applied in the direction of the substrate surface is reduced. This is presumably because the film can be prevented from peeling off.

Another object of the present invention is to provide a ferroelectric thin film element comprising a substrate and an epitaxial ferroelectric thin film provided on the substrate, wherein the epitaxial ferroelectric thin film is a crystal plane of the epitaxial ferroelectric thin film. Among them, the crystal plane parallel to the crystal plane of the substrate surface is a Z crystal plane, and the plane spacing of the Z crystal plane is z, and the interval of the Z crystal plane in the bulk state of the constituent material of the epitaxial ferroelectric thin film is When z ₀ , z / z ₀ > 1.003, and one crystal plane of the epitaxial ferroelectric thin film perpendicular to the Z crystal plane is defined as an X crystal plane, and the plane spacing of the X crystal planes Where x is x and the interplanar spacing of the X crystal plane in the bulk state of the constituent material of the epitaxial ferroelectric thin film is x ₀ , 0.997 ≦ x / x ₀ ≦ 1.003 It is to provide a ferroelectric thin film element. According to the present invention, it is possible to obtain a ferroelectric thin film element that does not deteriorate the characteristics of the ferroelectric thin film element and has large spontaneous polarization and is suitable for thinning.

  Still another object of the present invention is to reduce the stress applied in the direction of the substrate surface acting on the epitaxial ferroelectric film surface, without causing film peeling or characteristic deterioration of the epitaxial ferroelectric film, and enabling a large area. In addition, an object of the present invention is to provide a piezoelectric actuator having excellent characteristics by forming an epitaxial ferroelectric film that is excellent in piezoelectric characteristics and suitable for thinning. Another object of the present invention is to provide a liquid discharge head, particularly a liquid discharge head used in an ink jet recording apparatus, provided with a piezoelectric actuator portion having a configuration including this piezoelectric actuator. In the heteroepitaxial growth technique, it is preferable to reduce the stress applied in the substrate surface direction generated in the vicinity of the boundary surface between the substrate and the formed epitaxial ferroelectric film. By reducing the stress applied in the direction of the substrate surface caused by the misfit of the lattice between the substrate and the epitaxial ferroelectric film, it becomes possible to prevent the film of the epitaxial ferroelectric film from peeling off, thereby increasing the production area of the substrate. It is possible to improve the performance.

Still another object of the present invention is to provide a piezoelectric actuator comprising a substrate and an epitaxial ferroelectric film provided on the substrate, wherein the epitaxial ferroelectric film is a crystal plane of the epitaxial ferroelectric film. The crystal plane parallel to the crystal plane of the substrate surface is the Z crystal plane, the plane spacing of the Z crystal plane is z, and the plane spacing of the Z crystal plane in the bulk state of the constituent material of the epitaxial ferroelectric film is z _{When 0} , z / z ₀ > 1.003, and one crystal plane of the epitaxial ferroelectric film perpendicular to the Z crystal plane is defined as an X crystal plane, and the spacing between the X crystal planes Where x is x and the interplanar spacing of the X crystal plane in the bulk state of the constituent material of the epitaxial ferroelectric film is x ₀ , 0.997 ≦ x / x ₀ ≦ 1.003 A piezoelectric actuator is provided. Still another object of the present invention is to provide a liquid ejection head that ejects liquid using the piezoelectric actuator.

The present invention which has achieved the above object
In a ferroelectric thin film element comprising a substrate and an epitaxial ferroelectric thin film provided on the substrate,
The epitaxial ferroelectric thin film is
Of the crystal planes of the epitaxial ferroelectric thin film, a crystal plane parallel to the crystal plane of the substrate surface is a Z crystal plane, and a plane interval of the Z crystal plane is z, and the bulk of the constituent material of the epitaxial ferroelectric thin film when the distance between the Z crystal face in a state set to z _0, a z / z _0> 1.003,
One crystal plane of the epitaxial ferroelectric thin film perpendicular to the Z crystal plane is defined as an X crystal plane, and the plane spacing of the X crystal plane is defined as x, in the bulk state of the constituent material of the epitaxial ferroelectric thin film. when the spacing of X crystal plane is a x _0, a ferroelectric thin film device which is a _{0.997 ≦ x / x 0 ≦ 1.003} .

The present invention that has achieved the above object
In a piezoelectric actuator comprising a substrate and an epitaxial ferroelectric film provided on the substrate,
The epitaxial ferroelectric film is
Of the crystal planes of the epitaxial ferroelectric film, a crystal plane parallel to the crystal plane of the substrate surface is a Z crystal plane, and a plane interval of the Z crystal plane is z, and the bulk of the constituent material of the epitaxial ferroelectric film Z / z ₀ > 1.003, where z ₀ is the spacing between the Z crystal faces in the state,
One crystal plane of the epitaxial ferroelectric film perpendicular to the Z crystal plane is defined as an X crystal plane, and an interval between the X crystal planes is defined as x, and the bulk state of the constituent material of the epitaxial ferroelectric film The piezoelectric actuator is characterized in that 0.997 ≦ x / x ₀ ≦ 1.003, where x ₀ is the spacing between the X crystal planes.

  Furthermore, the present invention that has achieved the above object is a liquid ejection head that ejects liquid using the piezoelectric actuator of the present invention.

According to the present invention, it is possible to obtain a ferroelectric thin film element that does not deteriorate the characteristics of the ferroelectric thin film element and has large spontaneous polarization and is suitable for thinning.
In addition, according to the present invention, there are provided a piezoelectric actuator and a liquid discharge head which are excellent in piezoelectric characteristics, suitable for film formation / miniaturization, and excellent in large area, with no film peeling or characteristic deterioration of the epitaxial ferroelectric film. be able to.

  The ferroelectric thin film element of the present invention has a structure including at least a substrate and an epitaxial ferroelectric thin film formed on the substrate. The epitaxial ferroelectric thin film formed on the substrate of the ferroelectric thin film element of the present invention is a ferroelectric thin film having a single crystal or crystal orientation.

  The piezoelectric actuator of the present invention has a structure including at least a substrate, an epitaxial ferroelectric film formed on the substrate, and electrodes formed above and below the epitaxial ferroelectric film. The epitaxial ferroelectric film formed on the substrate is an epitaxial ferroelectric film having a single crystal or crystal orientation, and electrodes are provided above and below so as to sandwich the epitaxial ferroelectric film.

In the epitaxial ferroelectric film according to the present invention, the crystal plane parallel to the crystal plane of the substrate surface among the crystal planes is defined as a Z crystal plane, the plane spacing of the Z crystal plane is z, and the constituent material of the epitaxial ferroelectric film is When the interplanar spacing of the Z crystal plane in the bulk state is z ₀ , the relationship of z / z ₀ > 1.003 is satisfied. This epitaxial ferroelectric film preferably satisfies the relationship of z / z ₀ > 1.004, more preferably z / z ₀ > 1.005. When the relationship of z / z ₀ > 1.003 is satisfied, the epitaxial ferroelectric film can increase the spontaneous polarization even when the film thickness is 2 to 100 nm. Further, when the above relationship is satisfied, the epitaxial ferroelectric film has a large spontaneous polarization and can improve the piezoelectric characteristics even if the film thickness is 10 μm or less.

the upper limit of the value of z / z ₀ is not particularly limited, in general, z / z ₀ is 1.050 or less, preferably 1.020 or less, more preferably 1.010 or less. When the upper limit value of z / z ₀ is set to 1.050 or less, an epitaxial film with good crystallinity can be easily formed.

Further, the epitaxial ferroelectric film according to the present invention is a constituent material of an epitaxial ferroelectric film, wherein one crystal plane perpendicular to the Z crystal plane is the X crystal plane and the plane spacing of the X crystal plane is x. The relationship of 0.997 ≦ x / x ₀ ≦ 1.003 is satisfied, where x ₀ is the plane spacing of the X crystal planes in the bulk state. The epitaxial ferroelectric film formed on the substrate of the ferroelectric film element of the present invention is preferably 0.998 ≦ x / x ₀ ≦ 1.002, more preferably 0.999 ≦ x / x. The relation ₀ ≦ 1.001 is satisfied. When the above relationship is satisfied, the stress applied in the direction of the substrate surface in the plane of the epitaxial ferroelectric film is small, the residual polarization of the epitaxial ferroelectric film and the fatigue resistance characteristics of the epitaxial ferroelectric film are not deteriorated, and the film does not peel off A ferroelectric thin film element is obtained. In addition, when the above relationship is satisfied, the stress applied to the epitaxial ferroelectric film in the direction of the substrate surface is small, the characteristic deterioration during repeated use of the piezoelectric actuator, and the breakdown of the epitaxial ferroelectric film due to the leakage current during voltage application Thus, it is possible to obtain a piezoelectric actuator having no problem such as excellent durability characteristics.

  Hereinafter, specific embodiments of the invention required to realize such a ferroelectric element and a piezoelectric actuator will be described.

The constituent material of the epitaxial ferroelectric film is not particularly limited, and can be appropriately selected from those having ferroelectricity. Examples thereof include BaTiO ₃ , PbTiO ₃ , PbZrO ₃ , YMnO ₃ , Bi ₄ Ti ₃ O ₁₂ , SrBi ₂ Ta ₂ O ₉ , (Sr, Ba) NbO _{3 and the} like. As a material having a large ferroelectric property at room temperature, a lead-based perovskite oxide material generally represented by PZT can be exemplified. Further, a composition in which the above main component is doped with a trace amount of element such as La, such as La-doped PZT [(Pb, La) (Zr, Ti,) O ₃ ] (sometimes referred to as PLZT). There may be. In the case of a piezoelectric actuator, as a material having large piezoelectric properties, lead niobate zincate-lead titanate (may be represented as PZN-PT), lead niobate magnesium oxide-lead titanate (may be represented as PMN-PT). It may be a relaxation type ferroelectric (relaxer) material represented by

The substrate that can be used to manufacture the ferroelectric thin film element and the piezoelectric actuator of the present invention is preferably a single crystal that can epitaxially form a ferroelectric film as an upper layer. Preferred examples of the substrate include single crystal substrates such as MgO, SrTiO ₃ , (La, Sr) TiO ₃ , Al ₂ O ₃ , Pt, and Si. In particular, SrTiO ₃ , (La, Sr) TiO ₃ , MgO, Pt, etc., which have a lattice constant close to that of lead-based PZT or the like that generally exhibits excellent ferroelectric properties, are preferable. For example, single crystals of SrTiO ₃ , (La, Sr) TiO ₃ , Pt, and MgO have a cubic crystal structure. The a-axis lattice constants of these bulk crystals are 3.905, 3.907, 3.923, and 4.211, respectively, at room temperature. An epitaxial ferroelectric material having a tetragonal crystal structure on the single crystal substrate prepared from the above material so that the (100) plane is the substrate surface, and the Z crystal plane of the PZT film is the (001) plane. When forming the film, as a constituent material of the ferroelectric film, for example, the crystal system is a tetragonal system, and the lattice constant of the a axis in the bulk state is 4.036% at room temperature. Zr: Ti = 52: 48 PZT having the following composition is preferred.

  Further, it is an effective method for obtaining an epitaxial ferroelectric film having excellent single crystal or crystal orientation by interposing a buffer layer between the substrate and the epitaxial ferroelectric film. The layer thickness of the buffer layer is not particularly limited, but is preferably 0.5 nm or more, preferably 1 nm or more, more preferably 2 nm or more because the buffer layer preferably has high crystallinity.

In the case of a ferroelectric element, a thickness that does not hinder its characteristics is preferable, and the thickness of the buffer layer is usually 100 nm or less, preferably 50 nm or less, more preferably 10 nm or less. For example, when an epitaxial ferroelectric thin film composed of PZT is formed on a Pt substrate, a PbTiO ₃ layer having a thickness of ₂ nm to 10 nm is formed as a buffer layer, and the epitaxial ferroelectric thin film is formed on the buffer layer. Further, a higher quality single crystal epitaxial ferroelectric thin film can be obtained. This is presumed to be because, in the initial growth process of an epitaxial ferroelectric thin film composed of PZT, Ti is richer than Zr because the epitaxial growth of the single crystal is easier to control.

Also in the case of a piezoelectric actuator, a thickness that does not hinder its characteristics is preferable, and the layer thickness of the buffer layer is usually 1000 nm or less, preferably 500 nm or less, more preferably 100 nm or less. For example, when an epitaxial ferroelectric film composed of PZT is formed on a Pt substrate, a PbTiO ₃ buffer layer having a thickness of 2 nm to 1000 nm is formed as the buffer layer, and the epitaxial ferroelectric is formed on the buffer layer. When the film is formed, a higher quality single crystal epitaxial ferroelectric film can be obtained. This is presumed to be because, in the initial growth process of an epitaxial ferroelectric film composed of PZT, Ti is richer than Zr, and the single crystal epitaxial growth is easier to control.

In addition, a buffer layer is used to obtain an epitaxial ferroelectric film having a single crystal or crystal orientation on a substrate manufactured from a material having a large lattice constant difference from PZT, such as Al ₂ O ₃ and Si. Is also effective. For example, on a substrate obtained by epitaxially growing a (100) plane of yttria-stabilized zirconium oxide (sometimes referred to as YSZ) on a Si (100) substrate in parallel with the substrate surface and further epitaxially growing Pt (111) thereon. In addition, by forming an epitaxial ferroelectric film containing PZT (111) as a constituent material through a buffer layer containing PbTiO ₃ (111) as a constituent material, a higher quality single crystal epitaxial ferroelectric film can be obtained. Can do. This is because when the crystal plane perpendicular to the cubic Pt (111) crystal plane is the (-110) plane with respect to the a-axis lattice constant of 5.16 mm in YSZ, this plane spacing is relatively 5.55 mm. This is presumably because it is close to the (100) plane spacing.

Further, even with a substrate having no orientation such as a stainless steel or glass substrate, a ferroelectric film having a single crystal or crystal orientation can be epitaxially grown using the buffer layer. For example, since Pt has a property of spontaneous orientation in [111], for example, when a Pt film is formed on a glass substrate, a highly oriented film whose crystal plane parallel to the substrate surface is the (111) plane is formed. Can do. On top of this, an epitaxial ferroelectric film of PZT (111) can be grown via a buffer layer of PbTiO ₃ (111).

  As described above, the use of the buffer layer is an effective method for obtaining an epitaxial ferroelectric film having a single crystal or crystal orientation.

When the epitaxial ferroelectric film is used as a storage medium such as a nonvolatile memory, electrodes are required above and below the epitaxial ferroelectric film. The piezoelectric actuator has a structure in which electrodes are provided on the upper and lower sides so as to sandwich the epitaxial ferroelectric film. For this reason, it is desirable that at least one of the ferroelectric thin film element, the substrate constituting the piezoelectric actuator or the buffer layer is conductive. Pt and Au are generally used as the electrode material, but other materials such as Cr, Ru, and Ir may be used, and oxide-based electrode materials such as SrRuO ₃ and (La, Sr) TiO ₃ May be used. Moreover, the electrode material of the multilayered structure for the purpose of electrode adhesiveness or ohmic junction like Pt / Ti may be used. The conductive material used as the electrode preferably has a specific resistance of 0.01 Ω · cm or less.

  Next, examples of specific layer structures of the ferroelectric thin film element and the piezoelectric actuator of the present invention will be listed.

  The ferroelectric thin film element of the present invention has a structure including at least a substrate and an epitaxial ferroelectric thin film having a single crystal or crystal orientation formed epitaxially on the substrate. In many cases, electrodes are required above and below the epitaxial ferroelectric thin film. For this reason, the display of the configuration is the upper electrode // ferroelectric thin film // buffer layer // substrate, and an underline is added when the substrate or the buffer layer is a conductive layer. However, this is not the case when a ferroelectric thin film element is used for a device that does not necessarily require a conductive layer as a buffer layer, such as a ferroelectric gate transistor. Of these layers, at least the epitaxial ferroelectric thin film is in an epitaxial relationship with the underlying film.

The piezoelectric actuator according to the present invention includes at least a substrate, an epitaxial ferroelectric film epitaxially formed on the substrate or having crystal orientation, and electrode films arranged vertically so as to sandwich the epitaxial ferroelectric film. It has the structure provided. For this reason, the following display showing the specific layer structure of the piezoelectric actuator is the upper electrode // ferroelectric film // buffer layer // substrate, and the substrate or buffer layer has conductivity to function as an electrode. When it is a layer, it is underlined. The piezoelectric actuator of the present invention is particularly preferably applied to the actuator portion in the liquid discharge head. In the piezoelectric actuator of the present invention, it is particularly preferable that a single crystal Si substrate having a SiO ₂ layer formed by thermally oxidizing the surface of the substrate is used as the substrate, and this substrate is a vibration plate. Of the layers of the substrate, at least the epitaxial ferroelectric film is a layer whose lower layer has crystallinity and is in an epitaxial relationship with this lower layer.
Example 1 Pt // PZT (001) / PbTiO ₃ (001) // Pt (100) / MgO (100) // Si (100)
Example 2 Pt // PZT (001) / PbTiO ₃ (001) // Pt (100) / SrTiO ₃ (100) // Si (100)
Example 3 Au // PZT (001) // ( La, Sr) TiO ₃ (100) / Si (100) / SiO ₂ // Si (100)
Example 4 Pt // PZT (001) / PbTiO ₃ (001) // Pt (100) // Al ₂ O ₃ (100) // Si (100)
Example 5 Pt // PZT (111) / PbTiO ₃ (111) // Pt (111) // YSZ (100) / Zr // Si (100)
Example 6 Ag // PZT (001) / BaTiO ₃ (001) // Pt (100) / LaAlO ₃ (100) // Si (100)
Example 7 Au // PZT (001) / PbTiO ₃ (001) // Pt (100) // YSZ (111) / SiO ₂ // Si (111)
Example 8 Au // PZT (001) // ( La, Sr) TiO ₃ (100) / YSZ (111) // Si (111)
Example 9 Pt // PZT (111) / PbTiO ₃ (111) // Pt (111) / YSZ (100) // Si (100)
Example 10 Pt // PZT (111) // Pt (111) // Glass
Example 11 Pt // PZT (111) // Pt (111) // SUS
Example 12 Pt // PZT (111) / PbTiO ₃ (111) // Pt (111) / MgO (111) // Si (100)
Example 13 Au // PZT (001) // SrRuO ₃ (001) // Si (100)
Example 14 Au // PZT (001) / PbTiO ₃ (001) // Pt (100) // MgO (100)
Example 15 Au // PZT (001) / PbTiO ₃ (001) // Pt (100) // SrTiO (100)
Example 16 Pt // PZT (001) // ( La, Sr) TiO ₃ (100)
Example 17 Au // PZT (001) / PbTiO ₃ (001) // Pt (100) // Al ₂ O ₃ (100)
Example 18 Pt // PZT (001) // Ir (100) / ZrN (100) // Si (100)
Example 19 Pt // YMnO ₃ (0001) / Y ₂ O ₃ (111) // Si (111)
Example 20 Pt // PbZrO ₃ (101) // ( La, Sr) TiO ₃ (100)

As an example of the above, the constituent material of the epitaxial ferroelectric film is mainly exemplified by PZT. However, the constituent material of the ferroelectric film is a trace element such as La such as La-doped PZT. It may be a composition doped with. Further, the constituent material of the ferroelectric film is not lead-based, and may be a lead-free ferroelectric material such as BaTiO ₃ , SrBi ₂ Ta ₂ O ₉ , for example.

  Next, the ferroelectric thin film element of the present invention can be produced by epitaxially forming a ferroelectric thin film on a substrate. The piezoelectric actuator of the present invention can be manufactured by forming a ferroelectric film epitaxially on at least a substrate and providing electrodes above and below the epitaxial ferroelectric film. The piezoelectric actuator according to the present invention includes at least a substrate, a single crystal formed on the substrate or an epitaxial ferroelectric film having crystal orientation, and electrodes having crystal orientation formed above and below the epitaxial ferroelectric film. It has a structure with a film.

  Such an epitaxial ferroelectric film can be formed by a sputtering method, a sol-gel method, a metal organic chemical vapor deposition method (sometimes referred to as MOCVD method), a vapor deposition method, a laser ablation method, or the like. The film formation conditions vary depending on each film formation method and the ferroelectric material used, and appropriate conditions may be determined as appropriate.

For example, when the sputtering method is used, the RF magnetron sputtering method is preferable. The film formation conditions by the RF magnetron sputtering method include a substrate temperature during film formation of 500 ° C. to 700 ° C., an argon / oxygen ratio of 20/1 to 50/1 in an argon / oxygen atmosphere, and a gas pressure. is less 0.5Pa than 0.2 Pa, RF input power 0.5 W / cm ² or more and 1.2 W / cm ² or less, the substrate cooling speed after the film formation is 65 ° C. / min or higher. Further preferable conditions are an argon / oxygen ratio of 30/1 to 50/1 during film formation, a gas pressure of 0.2 Pa to 0.3 Pa, and an RF input power of 0.5 W / cm ^2. The rate of cooling is 0.8 W / cm ² or less and the substrate cooling rate after film formation is 100 ° C./min or more. In particular, cooling to 180 ° C. is preferably performed at the above speed, and pre-sputtering performed before film formation is preferably performed shortly at half or less of the RF input power during film formation and immediately shifted to film formation. . From the above conditions, the film can be formed by appropriately selecting conditions according to the composition of the target epitaxial ferroelectric film. In particular, in a system to which a dopant such as La is added, the substrate temperature can be lowered and the RF input power can be set higher. The substrate is preferably heated by an infrared heating method or a resistance heating method. At this time, by making the variation in the substrate temperature within brass minus 5%, an epitaxial ferroelectric film having uniform and stable characteristics can be obtained even when the epitaxial ferroelectric film is formed using a large area substrate. I can do it.

As a method for forming the epitaxial ferroelectric film according to the present invention, a sputtering method is particularly preferable. This is because, in the case of the sputtering method, an epitaxial ferroelectric film having a crystal structure defined in the present invention and having good crystallinity can be easily formed. For example, in the case of a PZT (001) film epitaxially grown on a Pt (100) film, when the degree of crystal orientation is 90% or more, it is the Z crystal plane of the epitaxial ferroelectric film that exists in a direction parallel to the substrate surface. The ratio z / z ₀ between the (001) plane spacing z and the (001) plane spacing z ₀ , which is the Z crystal plane of PZT in the bulk state, is greater than 1.003 and is perpendicular to the Z crystal plane. Ratio x / x between the (100) plane spacing x which is the X crystal plane of the epitaxial ferroelectric film in the direction and the (100) plane spacing x ₀ of the PZT X crystal plane in the bulk state ₀ becomes 0.997 ≦ x / x ₀ ≦ 1.003. When the degree of crystal orientation further increases, the ratio x / x ₀ between the above-mentioned epitaxial ferroelectric film and bulk (100) plane becomes close to 1.

  In the present invention, the degree of crystal orientation refers to an epitaxial ferroelectric film for all reflection peak intensities measured by the 2θ / θ method, where X-ray incidence angle with respect to the Z crystal plane of the epitaxial ferroelectric film is X in X-ray measurement. The ratio of the reflection peak intensity of all Z planes. For example, in the crystal orientation epitaxial ferroelectric film of tetragonal (001) plane, in the X-ray diffraction pattern of the epitaxial ferroelectric film measured by the 2θ / θ method, for the sum of all the observed reflection peak intensities, The ratio of the sum of all reflection peak intensities attributed to the (00L) plane (L = 1, 2, 3... N).

  The film thickness of the epitaxial ferroelectric thin film of the ferroelectric thin film element of the present invention is preferably 2 nm to 100 nm. Since the ferroelectricity of the epitaxial ferroelectric thin film is expressed depending on the skeleton of the crystal lattice and the arrangement of atoms, the film thickness is usually 2 nm or more, preferably 5 nm or more. On the other hand, when the ferroelectric thin film element of the present invention is used in a highly integrated device such as a ferroelectric memory, it is effective to reduce the thickness of the epitaxial ferroelectric thin film for high integration, and it is also suitable for low voltage driving. Therefore, for the purpose of use in these fields, the thickness of the epitaxial ferroelectric thin film is preferably 100 nm or less.

  The film thickness of the epitaxial ferroelectric film of the piezoelectric actuator of the present invention is preferably as small as possible, particularly preferably from 100 nm to 10 μm. For example, when a large piezoelectric displacement is required for a piezoelectric actuator, such as a liquid ejection head that ejects ink, a larger displacement can be obtained with a smaller voltage when the epitaxial ferroelectric film is thinner. However, in the piezoelectric actuator, a voltage of several tens of volts is applied to the epitaxial ferroelectric film, and the film thickness of the epitaxial ferroelectric film is prevented in order to prevent film breakdown due to the increase or decrease of this voltage or deterioration of piezoelectric characteristics due to leakage current. Is generally 100 nm or more, preferably 500 nm or more. On the other hand, if the thickness of the epitaxial ferroelectric film is increased, the frequency of problems such as film peeling will increase during the film formation, and single crystal or crystal orientation will be required for all the ferroelectric materials described above. In general, it is preferable that the thickness of the epitaxial ferroelectric film is 10 μm or less because it is difficult to obtain an epitaxial ferroelectric film element having a thickness of 10 μm.

  In the present invention, by controlling the crystal system and the plane orientation of the epitaxial ferroelectric film as described below, there is no deterioration in the characteristics of the ferroelectric film, and the spontaneous polarization of the ferroelectric film is large, thereby reducing the thickness. Can be suitable. When the crystal system is a tetragonal epitaxial ferroelectric film, the spontaneous polarization direction of the epitaxial ferroelectric film is [001]. For this reason, when the spacing between the (001) planes of the epitaxial ferroelectric film is longer than the spacing between the bulk (001) planes, the value of spontaneous polarization increases. Therefore, when the crystal system is tetragonal, it is preferable that the Z crystal plane is the (001) plane.

  On the other hand, when the crystal system is a rhombohedral epitaxial ferroelectric film, the spontaneous polarization direction of the epitaxial ferroelectric film is [111]. For this reason, when the interplanar spacing of the (111) plane of the ferroelectric film is longer than the interplanar spacing of the bulk (111) plane, the value of spontaneous polarization increases. Therefore, in the case of a rhombohedral-type epitaxial ferroelectric film, it is preferable that the Z crystal plane is a (111) plane. Similarly, in the case of an epitaxial ferroelectric film having a hexagonal crystal system, the spontaneous polarization direction of the epitaxial ferroelectric film is [0001]. For this reason, when the spacing between the (0001) planes of the epitaxial ferroelectric film is longer than the spacing between the (0001) planes of the bulk crystal, the spontaneous polarization value increases. Therefore, in the case of a hexagonal epitaxial ferroelectric film, it is preferable that the Z crystal plane is a (0001) plane. Similarly, when the crystal system is an orthorhombic epitaxial ferroelectric film, the spontaneous polarization direction of the epitaxial ferroelectric film is [011]. For this reason, when the spacing between the (011) planes of the epitaxial ferroelectric film is longer than the spacing between the (011) planes of the bulk crystal, the value of spontaneous polarization increases. Therefore, in the case of an orthorhombic epitaxial ferroelectric film, it is preferable that the Z crystal plane is the (011) plane.

  Note that the hexagonal system is represented not by the Miller index (hkl), which is generally used in the notation of crystal plane indices, but by the Brave-Miller index (hikl), which is often used in the hexagonal system.

  The liquid discharge head of the present invention includes a liquid discharge port 12, a pressure chamber 15 communicating with the liquid discharge port, and a pressure chamber as shown in the schematic cross-sectional view of an example of the embodiment of the present invention shown in FIG. A diaphragm 10 constituting a part, and a piezoelectric actuator portion 9 for applying vibration to the diaphragm provided outside the pressure chamber are provided. The liquid discharge port usually has a nozzle shape. A part of the pressure chamber is constituted by a diaphragm, and at least the piezoelectric actuator is provided outside the diaphragm, thereby constituting a piezoelectric actuator part of the liquid discharge head.

  In the liquid discharge head having such a configuration, when a predetermined voltage is applied to the epitaxial ferroelectric film of the piezoelectric actuator portion to expand and contract the epitaxial ferroelectric film having piezoelectric characteristics, flexural vibration is generated and the pressure chamber The volume fluctuates, the pressure in the pressure chamber fluctuates, and accordingly, the liquid is supplied from the liquid supply unit, and the liquid is discharged from the discharge port (sometimes referred to as a nozzle). Examples of the liquid to be discharged include liquids such as various solutions and inks.

  In the liquid ejection head of the present invention, when there are a plurality of nozzles that eject liquid, the piezoelectric actuator unit of the present invention has a structure basically divided for each nozzle. However, for example, the structure may be divided for each pressure chamber instead of each nozzle, or may be divided for every several pitches. In addition, when dividing the piezoelectric actuator portion of the liquid discharge head of the present invention, it is not necessary to divide everything from the substrate, which is a component, to the upper electrode. For example, only the epitaxial ferroelectric film and the upper electrode are divided. Alternatively, only the upper electrode may be divided.

  As long as the expansion and contraction of each piezoelectric actuator is not hindered between the divided piezoelectric actuator portions, a resin having low rigidity may exist. The shape of the pressure chamber can be arbitrarily selected, such as a rectangle, a circle, and an ellipse. In the case of a head that discharges liquid in a direction perpendicular to the longitudinal direction of the pressure chamber, the cross-sectional shape of the pressure chamber may be a shape narrowed in the nozzle direction.

  Further, in the liquid discharge head of the present invention, the piezoelectric actuator portion can be configured by joining the piezoelectric actuator to a vibration plate constituting a part of the pressure chamber. For example, the piezoelectric actuator substrate itself is formed. It is good also as a structure made into a diaphragm. In this case, it is preferable that the substrate has characteristics suitable as a vibration plate that can be formed by epitaxially growing at least the lower electrode and the ferroelectric film having crystal orientation. In this case, a substrate obtained by epitaxially growing a ferroelectric film having a single crystal or crystal orientation through a buffer layer on a substrate having no orientation such as stainless steel or a glass substrate can be used as the substrate. . In addition, the liquid discharge head of the present invention may be a liquid discharge head having a configuration including a piezoelectric actuator portion manufactured by attaching the piezoelectric actuator of the present invention to a vibration plate.

  Further, in the above-described piezoelectric actuator or liquid discharge head, when a buffer layer is interposed between the substrate and the epitaxial ferroelectric film and the buffer layer itself has dielectric properties, the piezoelectric displacement is an epitaxial ferroelectric material having piezoelectricity. The buffer layer preferably has a small thickness because it depends on the effective electric field applied to the film.

  The piezoelectric actuator of the present invention is excellent in piezoelectric characteristics because the spontaneous polarization of the epitaxial ferroelectric film is large, and the stress applied to the substrate surface direction in the plane of the epitaxial ferroelectric film is small. The film is not peeled off and the characteristics are not deteriorated, and the area can be easily increased. Further, the liquid discharge head of the present invention has a configuration including the above-described piezoelectric actuator in the piezoelectric actuator portion, so that it has a high density and a large discharge force, is excellent in high-frequency driving, and is excellent in a large area.

Hereinafter, a ferroelectric thin film element and a manufacturing method thereof according to the present invention will be described in detail based on examples with reference to the drawings. In the following examples and comparative examples, z / z ₀ , x / x ₀ and crystal orientation are adjusted by adjusting the epitaxial ferroelectric film forming conditions (sputtering power, film forming temperature, cooling rate, sputter gas pressure, sputter The gas type, the distance between the target and the substrate, the target density, and the like were adjusted.

Example 1
A PZT thin film with a thickness of 70 nm is used as an epitaxial ferroelectric thin film on a (La _0.038 , Sr _0.962 ) TiO ₃ (100) (single crystal production substrate) substrate that also serves as an electrode, using an RF magnetron sputtering system A dielectric thin film device was fabricated by epitaxial growth. At that time, the substrate temperature is 600 ° C., the argon / oxygen ratio is 30/1 during film formation, the gas pressure is 0.2 Pa, the RF input power during film formation is 0.8 W / cm ² , and the cooling rate after film formation is 180 ° C. Control was performed at 100 ° C./min or higher until the following, and pre-sputtering before film formation was performed for 3 min at an RF input power of 0.3 W / cm ² . The composition of the PZT thin film, which is an epitaxial ferroelectric thin film, was Pb (Zr _0.52 , Ti _0.48 ) O ₃ . The single crystallinity of the PZT thin film of the ferroelectric thin film device thus fabricated was measured by XRD. The results are shown in FIG. From the results shown in FIG. 1, it was confirmed that the crystal structure of the PZT thin film was tetragonal, the Z crystal plane was the (001) plane, and the degree of crystal orientation was 100%.

  Further, an electron beam was incident from [010] perpendicular to the normal axis of the Z crystal plane, and electron diffraction was performed on the PZT thin film. The result is shown in FIG. From the results of FIG. 2, it was confirmed that the PZT thin film had a single crystal structure with the film growth surface as the (001) plane.

Next, the diffraction peak of the (004) plane of the PZT thin film obtained by XRD-2θ / θ measurement of the substrate horizontal surface of the PZT thin film and the PZT thin film obtained by XRD-2θχ / φ measurement of the substrate vertical plane of the PZT thin film The lattice constants of the a-axis and c-axis were calculated from the (400) plane diffraction peak. The measurement was performed using an X-ray diffractometer Rint-Inplane (trade name) manufactured by Rigaku Corporation under the conditions of an X-ray output of 40 kV / 50 mA and a slit on the light receiving side and the detecting side of 0.5 °. As a result, a = 4.041 mm and c = 4.162 mm. The lattice constants described in the literature (JCPDS-330784) of PZT tetragonal bulk ceramics having a composition of Zr: Ti = 52: 48 are a ₀ = 4.036Å, c ₀ = 4.146Å, and z / z ₀ = c / c ₀ = 1.0039 and x / x ₀ = a / a ₀ = 1.0012.

A Pt pattern with a diameter of 100 μφ is formed on the ferroelectric thin film element thus obtained by sputtering to form an upper electrode, and the lower electrode is made of (La, Sr) TiO ₃ , and is strong using a Soya tower circuit. The ferroelectricity of the dielectric thin film element was evaluated. As a result, spontaneous polarization Ps = 100μC / cm ^2, the residual polarization Pr = 45μC / cm ^2, became. In addition, fatigue characteristics tests were conducted at 10 locations on the Pt pattern of the ferroelectric thin film element. The evaluation conditions were an applied voltage of ± 5 V, an evaluation temperature of 70 ° C., a frequency of 1 kHz, and a write count of 10 ⁷ times. As a result, no defective element was confirmed in all 10 evaluated locations. The results obtained are summarized and shown in Table 1.

Example 2
A PZT thin film with a thickness of 70 nm is used as an epitaxial ferroelectric thin film on a (La _0.038 , Sr _0.962 ) TiO ₃ (100) (single crystal production substrate) substrate that also serves as an electrode, using an RF magnetron sputtering system A ferroelectric thin film device was fabricated by epitaxial growth. At that time, the substrate temperature is 600 ° C., the argon / oxygen ratio is 30/1 during film formation, the gas pressure is 0.2 Pa, the RF input power during film formation is 0.8 W / cm ² , and the cooling rate after film formation is 180 ° C. Control was performed at 80 ° C./min or higher until the following, and pre-sputtering before film formation was performed for 3 min at an RF input power of 0.3 W / cm ² . The composition of the PZT thin film, which is an epitaxial ferroelectric thin film, was Pb (Zr _0.52 , Ti _0.48 ) O ₃ . The single crystallinity of the PZT thin film of the ferroelectric thin film device thus fabricated was measured by XRD. As a result, it was confirmed that the crystal structure of the PZT thin film was tetragonal, the Z crystal plane was (001), and the degree of crystal orientation was 90%.

  Also, an electron beam was incident from [010] perpendicular to the normal axis of the Z crystal plane, and electron diffraction was performed on the PZT thin film. As a result, it was confirmed that the PZT thin film had a single crystal structure with the (001) plane as the film growth surface.

Next, the diffraction peak of the (004) plane of the PZT thin film obtained by XRD-2θ / θ measurement of the substrate horizontal plane of the PZT thin film and the XZ-2θχ / φ measurement of the PZT thin film vertical plane of the PZT thin film The lattice constants of the a-axis and c-axis of the PZT thin film were calculated from the (400) plane diffraction peak. As a result, a = 4.034 mm, c = 4.163 mm, z / z ₀ = c / c ₀ = 1.0042, and x / x ₀ = a / a ₀ = 0.9995.

On the ferroelectric thin film device thus obtained, a Pt pattern having a diameter of 100 μφ is formed by sputtering to form an upper electrode, and the lower electrode is made of (La, Sr) TiO ₃ , and the ferroelectric thin film device is ferroelectric. Sex was evaluated. As a result, spontaneous polarization Ps = 90μC / cm ^2, the residual polarization Pr = 40μC / cm ^2, became. In addition, fatigue characteristics tests were conducted at 10 locations on the Pt pattern of the ferroelectric thin film element. As a result, no defective element was confirmed in all 10 evaluated locations. The results obtained are summarized and shown in Table 1.

Example 3
The substrate is mirror-polished 15 mm square Si (100), and this surface is first etched with tetramethylammonium hydroxide (sometimes referred to as TMAH) (manufactured by Kanto Chemical) for 10 minutes at room temperature, washed with pure water, Washed with acetone steam bath. Next, a YSZ thin film having a film thickness of 10 nm was formed on the substrate at a substrate temperature of 800 ° C. using an RF magnetron type sputtering apparatus. As a result of XRD measurement after film formation, it was confirmed that the YSZ thin film had a degree of crystal orientation in the [100] direction of 99% or more. Next, Pt was deposited as a lower electrode by sputtering at a substrate temperature of 600 ° C. to a thickness of 100 nm. As a result of XRD measurement after film formation, it was confirmed that Pt had a degree of crystal orientation in the [111] direction of 97% or more. Further, [PbTiO ₃ ] (sometimes referred to as PT) as a buffer layer was formed to a thickness of 7 nm at a substrate temperature of 600 ° C. using the RF magnetron type sputtering apparatus on the laminated film thus far. As a result of XRD measurement after film formation, it was confirmed that PT also had a degree of crystal orientation in the [111] direction of 94% or more. Next, a PZT thin film was formed as an epitaxial ferroelectric thin film at 85 nm using an RF magnetron type sputtering apparatus. At that time, the substrate temperature is 600 ° C., the argon / oxygen ratio is 30/1 during film formation, the gas pressure is 0.2 Pa, the RF input power during film formation is 0.8 W / cm ² , and the cooling rate after film formation is 180 ° C. Control was performed at 100 ° C./min or higher until the following, and pre-sputtering before film formation was performed for 3 min at an RF input power of 0.3 W / cm ² . The single crystallinity of the PZT thin film of the ferroelectric thin film device thus fabricated was measured by XRD. As a result, it was confirmed that the crystal structure of the PZT thin film was rhombohedral, the Z crystal plane was the (111) plane, and the degree of crystal orientation was 92%. The composition of the PZT thin film was Pb (Zr _0.58 , Ti _0.42 ) O ₃ .

Next, the diffraction peak of the (222) plane of the PZT thin film obtained by XRD-2θ / θ measurement of the substrate horizontal plane of the PZT thin film and the PZT thin film obtained by XRD-2θχ / φ measurement of the substrate vertical plane of the PZT thin film From the diffraction peak of the (-220) plane, the interplanar spacing of the (222) plane, which is the Z crystal plane of the rhombohedral PZT thin film, and the interplanar spacing of the (-220) plane, which is a crystal plane perpendicular to the Z crystal plane Was calculated. As a result, d (222) = 1.186 mm and d (−220) = 1.433 mm. The interplanar spacing described in the literature (JCPDS-732022) of PZT rhombohedral bulk ceramics with Zr / Ti = 58/42 is d ₀ (222) = 1.1821 mm, d ₀ (−220) = 1.4346 mm, z / z ₀ = d (222) / d ₀ (222) = 1.0035 and x / x ₀ = d (−220) / d ₀ (−220) = 0.9987.

An Au pattern having a diameter of 100 μφ is formed on the ferroelectric thin film element thus obtained by sputtering to form the upper electrode, the lower electrode is Pt, and the ferroelectric thin film element is strengthened using a Soya Tower circuit. Dielectric properties were evaluated. As a result, spontaneous polarization Ps = 80 μC / cm ² and remanent polarization Pr = 35 μC / cm ² . In addition, fatigue characteristics tests were conducted at 10 locations on the Au pattern of the ferroelectric thin film element. The evaluation conditions were an applied voltage of ± 5 V, an evaluation temperature of 70 ° C., a frequency of 1 kHz, and a write count of 10 ⁷ times. As a result, no defective element was confirmed in all 10 evaluated locations. The results obtained are summarized and shown in Table 1.

≪Comparative Examples 1-3≫
When epitaxially growing a PZT thin film as an epitaxial ferroelectric thin film on a substrate using an RF magnetron sputtering apparatus, the cooling rate after film formation is not controlled below 400 ° C., and pre-sputtering Same as Example 1 except that z / z ₀ , x / x ₀ and crystal orientation were adjusted by adjusting each except that it was the same as the RF input power at the time of film formation and was fixed to 60 min. Thus, a ferroelectric thin film element was fabricated and evaluated. The obtained results are shown in Table 1.

From the results shown in Table 1, z / z ₀ > 1.003 and 0.997 ≦ x in all the epitaxial ferroelectric thin films of the ferroelectric thin film elements of Examples 1 to 3 of the present invention. / X ₀ ≦ 1.003. Further, the epitaxial ferroelectric thin film of the ferroelectric thin film element of the example has a crystal orientation of 90% or more, spontaneous polarization Ps = 80 μC / cm ² or more, and remanent polarization Pr = 35 μC / cm ² or more. It was. Furthermore, the fatigue characteristics of the ferroelectric thin film element cleared 10 ⁷ times.

On the other hand, the ferroelectric thin film of the ferroelectric thin film element of Comparative Example 1 has z / z ₀ ≦ 1.003, and this ferroelectric thin film element has a fatigue characteristic of 10 ⁷ times, The spontaneous polarization was Ps = 70 μC / cm ² , and the remanent polarization was Pr = 28 μC / cm ² , indicating a low ferroelectricity. In addition, the epitaxial ferroelectric thin film of the ferroelectric thin film element of Comparative Example 2 has x / x ₀ <0.997, and although this ferroelectric thin film element has high ferroelectricity, the fatigue characteristics are 10 ^7. Some things could not be cleared. Further, the epitaxial ferroelectric thin film of the ferroelectric thin film element of Comparative Example 3 had x / x ₀ <0.997, the crystal orientation was less than 90%, the spontaneous polarization was Ps = 75 μC / cm ² , and the residual The polarization was Pr = 30μC / cm ² and the ferroelectricity was low, and the fatigue characteristics could not be cleared 10 ⁷ times.

Hereinafter, a piezoelectric actuator, a liquid discharge head, and a manufacturing method thereof according to the present invention will be described in detail with reference to the drawings. In the following examples and comparative examples, z / z ₀ , x / x ₀ and crystal orientation are adjusted by adjusting the epitaxial ferroelectric film forming conditions (sputtering power, film forming temperature, cooling rate, sputter gas pressure, sputter The gas type, the distance between the target and the substrate, the target density, and the like were adjusted. In this embodiment, an ink jet head will be described as an example of the liquid discharge head.

Example 4
A 2.0μm PZT film was epitaxially grown as an epitaxial ferroelectric film on a (La _0.038 , Sr _0.962 ) TiO ₃ (100) (single crystal production substrate) substrate, which also served as an electrode, using an RF magnetron sputtering apparatus. . At that time, the substrate temperature is 600 ° C., the argon / oxygen ratio is 30/1 during film formation, the gas pressure is 0.2 Pa, the RF input power during film formation is 0.8 W / cm ² , and the cooling rate after film formation is 180 ° C. Control was performed at 100 ° C./min or higher until the following, and pre-sputtering before film formation was performed for 3 min at an RF input power of 0.3 W / cm ² . The composition of the PZT film is Pb (Zr _0.52 , Ti _0.48 ) O ₃ . The single crystallinity of the epitaxial ferroelectric film thus prepared was measured by XRD. The result is shown in FIG. From the results shown in FIG. 3, it was confirmed that the crystal structure of the PZT film was tetragonal, the Z crystal plane was the (001) plane, and the degree of crystal orientation was 100%.

  Further, an electron beam was incident from [010] perpendicular to the normal axis of the Z crystal plane, and electron diffraction of the PZT film was performed. The result is shown in FIG. From the results of FIG. 4, it was confirmed that the PZT film had a single crystal structure with the film growth surface as the (001) plane.

Next, the diffraction peak of the PZT (004) film obtained by XRD-2θ / θ measurement of the substrate horizontal plane of the PZT film and the XZ-2θχ / φ measurement of the PZT film vertical plane of the PZT film ( The lattice constants of the a-axis and c-axis of the PZT film were calculated from the diffraction peak of the (400) plane. The measurement was performed using an X-ray diffractometer Rint-Inplane (trade name) manufactured by Rigaku Corporation under the conditions of an X-ray output of 40 kV / 50 mA and a slit on the light receiving side and the detecting side of 0.5 °. As a result, a = 4.042cm and c = 4.171mm. The lattice constants described in the literature (JCPDS-330784) of PZT tetragonal bulk ceramics having a composition of Zr: Ti = 52: 48 are a ₀ = 4.036Å, c ₀ = 4.146Å, and z / z ₀ = c / c ₀ = 1.0060, x / x ₀ = a / a ₀ = 1.0015.

A Pt pattern having a diameter of 100 μmφ was formed on the epitaxial ferroelectric film thus obtained by sputtering to form an upper electrode and a piezoelectric actuator having a lower electrode of (La, Sr) TiO ₃ . For this piezoelectric actuator, the piezoelectric constant d33 was measured using a piezoelectric constant measuring apparatus (manufactured by Toyo Technica). As a result, d33 = 498 pC / N.

  Furthermore, for the purpose of evaluating the displacement amount of this piezoelectric actuator, a piezoelectric actuator in which the LSTO substrate also serves as a diaphragm was fabricated.

First, a 100 μm (La _0.038 , Sr _0.962 ) TiO ₃ (100) (single crystal production substrate) substrate (sometimes referred to as an LSTO substrate) that also serves as an electrode is bonded onto the Si (100) substrate, and the LSTO substrate surface The side was polished until the LSTO thickness was about 5 μm. Next, a PZT film having a thickness of 3.0 μm was formed as an epitaxial ferroelectric film, and a Pt electrode pattern was formed thereon by sputtering. Furthermore, the Si substrate was etched by a dry process with a pattern with a length of 600 μm and a width of 40 μm to produce a unimorph type cantilever in which the LSTO substrate serves as a diaphragm. The upper electrode was patterned to a length of 600 μm and a width of 40 μm, similar to the cantilever shape. The displacement of the unimorph cantilever-shaped piezoelectric actuator thus produced was measured with a laser Doppler measuring device, and it was confirmed that the displacement was 50 nm with an applied voltage of 10V.

Further, the piezoelectric actuator for applying voltage ± 20V, rated temperature 70 ° C., a durability test was carried out at a frequency of 1 kHz, write count 10 ^seven conditions. As a result, no attenuation of displacement due to film deterioration or peeling was observed.

The evaluation results of the durability test of the piezoelectric actuator were evaluated based on the following criteria.
○: The displacement after the durability test was higher than 70% with respect to the displacement before the durability test.
X: The displacement after the durability test was 70% or less with respect to the displacement before the durability test.
The obtained results are summarized in Table 2.

Example 5
On the (La _0.038 , Sr _0.962 ) TiO ₃ (100) (single crystal production substrate) substrate that also serves as an electrode, an epitaxial ferroelectric film is grown as an epitaxial ferroelectric film using a RF magnetron sputtering system. It was. At that time, the substrate temperature is 600 ° C., the argon / oxygen ratio is 30/1 during film formation, the gas pressure is 0.2 Pa, the RF input power during film formation is 0.8 W / cm ² , and the cooling rate after film formation is 180 ° C. Control was performed at 80 ° C./min or higher until the following, and pre-sputtering before film formation was performed for 3 min at an RF input power of 0.3 W / cm ² . The composition of the PZT film was Pb (Zr _0.52 , Ti _0.48 ) O ₃ . The single crystallinity of the epitaxial ferroelectric film thus prepared was measured by XRD. As a result, it was confirmed that the crystal structure of the PZT film was tetragonal, the Z crystal plane was the (001) plane, and the degree of crystal orientation was 90%.

  Further, an electron beam was incident from [010] perpendicular to the normal axis of the Z crystal plane, and electron diffraction was performed on the PZT film. As a result, it was confirmed that the PZT film had a single crystal structure with the film growth surface as the (001) plane.

Next, the diffraction peak of the (004) plane of the PZT film obtained by XRD-2θ / θ measurement of the substrate horizontal plane of the PZT film and the XZ-2θχ / φ measurement of the PZT film vertical plane of the PZT film The lattice constants of the a-axis and c-axis of the PZT film were calculated from the (400) plane diffraction peak. As a result, a = 4.033 mm, c = 4.162 mm, z / z ₀ = c / c ₀ = 1.0039, and x / x ₀ = a / a ₀ = 0.9993.

A Pt pattern having a diameter of 100 μmφ was formed on the epitaxial ferroelectric film thus obtained by sputtering to form an upper electrode, and the lower electrode was made of (La, Sr) TiO ₃ to produce a piezoelectric actuator. Using this piezoelectric actuator, the piezoelectric constant d33 was measured in the same manner as in Example 4. As a result, d33 = 450 pC / N.

  Furthermore, for the purpose of evaluating the displacement of this piezoelectric actuator, a piezoelectric actuator was fabricated in which the LSTO substrate also serves as a diaphragm.

First, a 100 μm (La _0.038 , Sr _0.962 ) TiO ₃ (100) (single crystal production substrate) substrate, which also serves as an electrode, is bonded onto a Si (100) substrate, and the LSTO substrate surface side has an LSTO thickness of about 5 μm. Polished until Next, a PZT film having a thickness of 3.0 μm was formed as an epitaxial ferroelectric film, and a Pt electrode pattern was formed thereon by sputtering. Furthermore, the Si substrate was etched by a dry process with a pattern with a length of 600 μm and a width of 40 μm to produce a unimorph type cantilever in which the LSTO substrate serves as a diaphragm. The upper electrode was patterned to a length of 600 μm and a width of 40 μm, similar to the cantilever shape. The displacement of the unimorph cantilever-shaped piezoelectric actuator thus produced was measured with a laser Doppler measuring device, and it was confirmed that the displacement was 46 nm with an applied voltage of 10V.

Further, the piezoelectric actuator for applying voltage ± 20V, rated temperature 70 ° C., a durability test was carried out at a frequency of 1 kHz, write count 10 ^seven conditions. As a result, no attenuation of displacement due to film deterioration or peeling was observed. The obtained results are summarized in Table 2.

Example 6
The substrate is mirror-polished Si (100), and this surface is first etched with tetramethylammonium hydroxide (TMAH) (manufactured by Kanto Chemical) for 10 minutes at room temperature, washed with pure water, and then acetone vapor bath Washed with. Next, a YSZ film having a film thickness of 10 nm was formed on the substrate at a substrate temperature of 800 ° C. using an RF magnetron type sputtering apparatus. As a result of XRD measurement after film formation, it was confirmed that the YSZ film had a degree of crystal orientation in the [100] direction of 99% or more.

Next, Pt was deposited as a lower electrode by sputtering at a substrate temperature of 600 ° C. to a thickness of 100 nm. As a result of XRD measurement after film formation, it was confirmed that the crystal orientation degree of Pt in the [111] direction was 97% or more. Further, PbTiO ₃ (sometimes referred to as PT) was formed as a buffer layer on the laminated film so far to a thickness of 7 nm at a substrate temperature of 600 ° C. using an RF magnetron type sputtering apparatus. As a result of XRD measurement after film formation, it was confirmed that PT also had a degree of crystal orientation in the [111] direction of 94% or more.

Next, a PZT film as an epitaxial ferroelectric film was formed to a thickness of 3.0 μm using an RF magnetron type sputtering apparatus. At that time, the substrate temperature is 600 ° C., the argon / oxygen ratio is 30/1 during film formation, the gas pressure is 0.2 Pa, the RF input power during film formation is 0.8 W / cm ² , and the cooling rate after film formation is 180 ° C. Control was performed at 100 ° C./min or higher until the following, and pre-sputtering before film formation was performed for 3 min at an RF input power of 0.3 W / cm ² . The single crystallinity of the epitaxial ferroelectric film thus prepared was measured by XRD. As a result, it was confirmed that the crystal structure of the PZT film was rhombohedral, the Z crystal plane was the (111) plane, and the degree of crystal orientation was 92%. The composition of the PZT film was Pb (Zr _0.58 , Ti _0.42 ) O ₃ .

Next, the diffraction peak of the (222) plane of the PZT film obtained by XRD-2θ / θ measurement of the substrate horizontal surface of the PZT film, and the PZT obtained by XRD-2θχ / φ measurement of the substrate vertical plane of the PZT film ( The plane spacing of the (222) plane, which is the Z crystal plane of the rhombohedral PZT film, and the plane spacing of the (-220) plane, which is a crystal plane perpendicular to the Z crystal plane, are calculated from the diffraction peak of the -220) plane. did. As a result, d (222) = 1.187 mm and d (−220) = 1.432 mm. Zr: Ti = 58: 42 PZT rhombohedral bulk ceramic literature (JCPDS-732022) described in the interplanar spacing is d ₀ (222) = 1.1821 mm, d ₀ (−220) = 1.4346 mm, z / z ₀ = d (222) / d ₀ (222) = 1.0041, x / x ₀ = d (−220) / d ₀ (−220) = 0.9982.

A Pt pattern having a diameter of 100 μmφ was formed on the epitaxial ferroelectric film thus obtained by sputtering to form an upper electrode and a piezoelectric actuator having a lower electrode of (La, Sr) TiO ₃ . For this piezoelectric actuator, the piezoelectric constant d33 was measured using a piezoelectric constant measuring apparatus (manufactured by Toyo Technica). As a result, d33 = 471 pC / N.

  Further, for the purpose of evaluating the displacement amount of the piezoelectric actuator of the present invention, the Si substrate is etched by dry process in a range of 600 μm in length and 40 μm in width until the thickness of the Si substrate becomes about 5 μm. A unimorph type cantilever was prepared. The upper electrode was patterned to a length of 600 μm and a width of 40 μm, similar to the cantilever shape. The displacement of the unimorph cantilever-shaped piezoelectric actuator thus produced was measured with a laser Doppler measuring device, and it was confirmed that the displacement was 46 nm with an applied voltage of 10V.

Further, the piezoelectric actuator for applying voltage ± 20V, rated temperature 70 ° C., a durability test was carried out at a frequency of 1 kHz, write count 10 ^seven conditions. As a result, no attenuation of displacement due to film deterioration or peeling was observed. The obtained results are summarized in Table 2.

Example 7
A schematic cross-sectional view of the ink jet head of this embodiment is shown in FIG. Boron (B) doped single crystal Si (100) / SiO ₂ / Si substrate (each film thickness: 2.5μm / 1μm / 250μm) and MgO (100) film on Si (100) layer It was formed with a thickness of 0.3 μm. Further, a 0.2 μm Pt (001) film as an electrode, a 0.1 μm PT (001) film thereon, and then an epitaxial ferroelectric film having piezoelectricity were formed under the same conditions as in Example 4 with a 2 μm thickness. A PZT film having a thickness was formed by epitaxial growth in order. The composition of the PZT film was Pb (Zr _0.52 , Ti _0.48 ) O ₃ . Furthermore, the upper electrode was coated with Au to produce a piezoelectric actuator part.

The Si layer was subjected to plasma etching using SF ₆ and C ₄ F ₈ to form a pressure chamber. Thereafter, the Si substrate and the nozzle plate forming a part of the pressure chamber were joined to obtain the ink jet head shown in FIG. The width of the pressure chamber was 60 μm, the depth was 2.2 mm, and the partition wall width between the pressure chambers was 24 μm.

Obtained by XRD-2θχ / φ measurement of the (004) plane diffraction peak of the PZT film obtained by XRD-2θ / θ measurement of the substrate horizontal surface of the PZT film of the piezoelectric actuator part and the substrate vertical surface of the PZT film From the diffraction peak of the (400) plane of the PZT film, the a-axis and c-axis lattice constants of the PZT film were calculated. As a result, a = 4.040 mm, c = 4.165 mm, z / z ₀ = c / c ₀ = 1.0045, and x / x ₀ = a / a ₀ = 1.0010. As a result of measuring the single crystallinity by XRD, it was confirmed that the crystal structure of the PZT film was tetragonal, the Z crystal plane was the (001) plane, and the degree of crystal orientation was 99%.

As a result of confirming ink ejection from the nozzles using this inkjet head, it was possible to confirm stable ink ejection even at a driving frequency of 3 V at a driving frequency of 10 kHz. In addition, the ink jet head was subjected to a durability test at a driving frequency of 1 kHz and a driving voltage of 0 V / 30 V. As a result, the discharge of up to 10 ⁷ times, there are ink discharge from all the nozzles, film peeling and deterioration of the characteristics of an epitaxial dielectric film even after the durability test was not observed.

<< Comparative Examples 4-6 >>
When epitaxially growing a PZT film as an epitaxial ferroelectric film on a substrate using an RF magnetron type sputtering apparatus, the cooling rate after film formation is not controlled below 400 ° C, and pre-sputtering is not performed. Same as Example 5 except that z / z ₀ , x / x ₀ and crystal orientation were adjusted by adjusting each except that the RF input power at the time of filming was the same and 60 min was fixed. A piezoelectric actuator was fabricated and evaluated.

It was confirmed that the crystal structures of the PZT films of Comparative Examples 4 to 6 were all tetragonal and the Z crystal plane was the (001) plane. In addition, Table 2 shows z / z ₀ and x / x _{0 of} the PZT film, the piezoelectric constant d33 of the piezoelectric actuator, the amount of displacement, and the evaluation results of the endurance test of the piezoelectric actuator. In the piezoelectric constant d33 and the displacement amount of the piezoelectric actuator, the piezoelectric actuator of Comparative Example 4 could not obtain a sufficient value. Further, it was confirmed that the piezoelectric actuator of Comparative Example 5 could not clear 10 ⁷ times and the displacement amount was small. Furthermore, it was confirmed that the piezoelectric actuator of Comparative Example 6 could not clear 10 ⁷ times and the displacement amount was small.

<< Comparative Example 7 >>
As a comparative example of Example 7, an inkjet head having the following configuration was manufactured. Boron (B) doped single crystal Si (100) / SiO ₂ / Si substrate (each film thickness: 2.5μm / 1μm / 250μm) and MgO (100) film on Si (100) layer It was formed with a thickness of 0.3 μm. Further, a 0.2 μm Pt (001) film as an electrode, a 0.1 μm PT (001) film thereon, and then a piezoelectric epitaxial ferroelectric film having a piezoelectric property were formed under the same conditions as in Comparative Example 4. A PZT film having a thickness was formed by epitaxial growth in order. The composition of the PZT film was Pb (Zr _0.52 , Ti _0.48 ) O ₃ . Furthermore, the upper electrode was coated with Au to produce a piezoelectric actuator part.

The Si layer was subjected to plasma etching using SF ₆ and C ₄ F ₈ to form a pressure chamber. Thereafter, the Si substrate and the nozzle plate forming a part of the pressure chamber were joined, and the same ink jet head as in Example 7 was obtained. The width of the pressure chamber was 60 μm, the depth was 2.2 mm, and the partition wall width between the pressure chambers was 24 μm.

Next, from the diffraction peak of PZT (004) obtained by XRD-2θ / θ measurement on the substrate horizontal plane of PZT and the diffraction peak of PZT (400) obtained by XRD-2θχ / φ measurement of the substrate vertical plane of PZT The lattice constant of a-axis and c-axis of tetragonal PZT was calculated. As a result, a = 4.012, c = 4.115, z / z ₀ = c / c ₀ = 1.0012, and x / x ₀ = a / a ₀ = 0.9940. As a result of measuring the single crystallinity by XRD, it was confirmed that the crystal structure of PZT was tetragonal, the Z crystal plane was the (001) plane, and the degree of crystal orientation was 78%.

As a result of confirming ink ejection from the nozzle using this inkjet head, stable ink ejection was confirmed at a driving frequency of 10 kHz and a driving voltage of 7 V, but stable ink ejection was achieved at a driving frequency of 10 kHz and a driving voltage of 3 V. Could not be confirmed. Further, the driving frequency 1 kHz, 0V / 30 V results of the ink durability test at a driving voltage of, in the discharge of up to 10 ⁷ times, ink discharge failure was observed in the plurality of nozzles.

From the results shown in Table 2 and above, the piezoelectric actuators of Examples 4 to 6 of the present invention and the epitaxial ferroelectric film of the ink jet head of Example 7 have z / z ₀ > 1.003 and 0.997. ≦ x / x ₀ ≦ 1.003. Further, the degree of crystal orientation was 90% or more. The piezoelectric constants d33 of the piezoelectric actuators of Examples 4 to 6 were 450 pC / N or more, and the displacement was 46 nm or more. Further, in the piezoelectric actuators of Examples 4 to 6, no displacement attenuation due to deterioration or peeling was observed in the epitaxial ferroelectric film of the piezoelectric actuator part in the durability test. As described above, the ink-jet head of Example 7, after the ejection durability test up to 10 ⁷ times, film peeling and the epitaxial ferroelectric films of the piezoelectric actuator unit, discharge failure was observed.

On the other hand, the epitaxial ferroelectric film of the piezoelectric actuator of Comparative Example 4 has z / z ₀ <1.003, the piezoelectric constant d33 of the piezoelectric actuator of Comparative Example 4 is 347 pC / N, and the displacement is 28 nm. The sex was low.

The epitaxial ferroelectric film of the piezoelectric actuator of Comparative Example 5 was z / z ₀ > 1.003. For this reason, the piezoelectric constant d33 of the piezoelectric actuator of Comparative Example 5 was 505 pC / N, and the displacement was 45 nm, which was as large as in the example, but x / x ₀ <0.997. It was confirmed that 5 piezoelectric actuators could not clear 10 ⁷ times in the durability test.

The epitaxial ferroelectric film of the piezoelectric actuator of Comparative Example 6 had x / x ₀ <0.997, and the crystal orientation degree of the (001) plane of the PZT film was as low as 80%. Further, the piezoelectric actuator of Comparative Example 6 has a piezoelectric constant d33 of 375 pC / N and a displacement amount of 36 nm, which has a low piezoelectric characteristic. Further, in the endurance test, 107 ⁷ times cannot be cleared, and the displacement amount becomes small. Was confirmed.

  The ferroelectric thin film element of the present invention has no deterioration in characteristics, has a large spontaneous polarization, is suitable for thinning, and can be suitably used for a storage medium such as a nonvolatile memory, a storage device, and the like. In addition, the piezoelectric actuator and the liquid discharge head of the present invention are free of epitaxial ferroelectric film peeling and characteristic deterioration, have excellent piezoelectric characteristics, and can be widely used in printing apparatuses such as inkjet recording apparatuses.

The XRD pattern of the PZT thin film of the ferroelectric thin film element of Example 1 of this invention. The electron diffraction pattern of the PZT thin film of the ferroelectric thin film element of Example 1 of the present invention. The XRD pattern of the epitaxial ferroelectric film of the piezoelectric actuator of Example 4 of this invention. The electron beam diffraction image of the epitaxial ferroelectric film of the piezoelectric actuator of Example 4 of this invention. FIG. 10 is a schematic cross-sectional view of an inkjet head according to a seventh embodiment of the present invention.

Explanation of symbols

1 Si layer of substrate 2 SiO ₂ layer of substrate 3 Si (100) layer of substrate 4 MgO (100) film 5 Pt (100) film 6 PT (001) film 7 PZT (001) film 8 Pt film 9 Piezoelectric actuator part DESCRIPTION OF SYMBOLS 10 Diaphragm 11 Main-body part 12 Liquid (ink) discharge port 13 Liquid (ink) supply part 14 Nozzle 15 Pressure chamber

Claims (25)

In a ferroelectric thin film element comprising a substrate and an epitaxial ferroelectric thin film provided on the substrate,
The epitaxial ferroelectric thin film is
Of the crystal planes of the epitaxial ferroelectric thin film, a crystal plane parallel to the crystal plane of the substrate surface is a Z crystal plane, and a plane interval of the Z crystal plane is z, and the bulk of the constituent material of the epitaxial ferroelectric thin film when the distance between the Z crystal face in a state set to z _0, a z / z _0> 1.003,
One crystal plane of the epitaxial ferroelectric thin film perpendicular to the Z crystal plane is defined as an X crystal plane, and the plane spacing of the X crystal plane is defined as x, in the bulk state of the constituent material of the epitaxial ferroelectric thin film. A ferroelectric thin film element characterized in that 0.997 ≦ x / x ₀ ≦ 1.003, where x ₀ is the spacing between X crystal planes.   2. The ferroelectric thin film element according to claim 1, wherein the epitaxial ferroelectric thin film has a thickness of 2 to 100 nm.   2. The ferroelectric thin film element according to claim 1, further comprising at least one buffer layer between the substrate and the epitaxial ferroelectric thin film.   The ferroelectric thin film element according to claim 3, wherein at least one of the substrate and the buffer layer has conductivity.   2. The crystal orientation degree of the Z crystal plane measured by the 2θ / θ method is 90% or more, wherein an X-ray incident angle with respect to the Z crystal plane of the epitaxial ferroelectric thin film is θ. The ferroelectric thin film element described.   2. The ferroelectric thin film element according to claim 1, wherein the crystal orientation degree of the Z crystal plane is 99% or more.   2. The ferroelectric thin film element according to claim 1, wherein the epitaxial ferroelectric thin film has a perovskite type structure.   2. The ferroelectric thin film element according to claim 1, wherein the epitaxial ferroelectric thin film contains lead (Pb) atoms or oxygen (O) atoms as constituent atoms.   2. The ferroelectric thin film element according to claim 1, wherein the epitaxial ferroelectric thin film has a tetragonal crystal structure, and a Z crystal plane thereof is a (001) plane.   2. The ferroelectric thin film element according to claim 1, wherein the epitaxial ferroelectric thin film has a rhombohedral crystal structure, and a Z crystal plane thereof is a (111) plane.   2. The ferroelectric thin film element according to claim 1, wherein the epitaxial ferroelectric thin film has a hexagonal crystal structure, and a Z crystal plane thereof is a (0001) plane.   2. The ferroelectric thin film element according to claim 1, wherein the epitaxial ferroelectric thin film has an orthorhombic crystal structure, and a Z crystal plane thereof is a (011) plane. In a piezoelectric actuator comprising a substrate and an epitaxial ferroelectric film provided on the substrate,
The epitaxial ferroelectric film is
Of the crystal planes of the epitaxial ferroelectric film, a crystal plane parallel to the crystal plane of the substrate surface is a Z crystal plane, and a plane interval of the Z crystal plane is z, and the bulk of the constituent material of the epitaxial ferroelectric film Z / z ₀ > 1.003, where z ₀ is the spacing between the Z crystal faces in the state,
One crystal plane of the epitaxial ferroelectric film perpendicular to the Z crystal plane is defined as an X crystal plane, and an interval between the X crystal planes is defined as x, and the bulk state of the constituent material of the epitaxial ferroelectric film A piezoelectric actuator characterized in that 0.997 ≦ x / x ₀ ≦ 1.003, where x ₀ is the spacing between X crystal planes.   14. The piezoelectric actuator according to claim 13, wherein the epitaxial ferroelectric film has a thickness of 100 nm to 10 [mu] m.   14. The piezoelectric actuator according to claim 13, further comprising at least one buffer layer between the substrate and the epitaxial ferroelectric film.   The piezoelectric actuator according to claim 15, wherein at least one of the substrate and the buffer layer has conductivity.   The X-ray incident angle with respect to the Z crystal plane of the epitaxial ferroelectric film is θ, and the crystal orientation degree of the Z crystal plane measured by the 2θ / θ method is 90% or more. The described piezoelectric actuator.   14. The piezoelectric actuator according to claim 13, wherein the crystal orientation degree of the Z crystal plane is 99% or more.   14. The piezoelectric actuator according to claim 13, wherein the epitaxial ferroelectric film has a perovskite structure.   The piezoelectric actuator according to claim 13, wherein the epitaxial ferroelectric film contains lead (Pb) atoms or oxygen (O) atoms as constituent atoms.   The piezoelectric actuator according to claim 13, wherein the epitaxial ferroelectric film has a tetragonal crystal structure, and a Z crystal plane thereof is a (001) plane.   14. The piezoelectric actuator according to claim 13, wherein the epitaxial ferroelectric film has a rhombohedral crystal structure, and a Z crystal plane thereof is a (111) plane.   The piezoelectric actuator according to claim 13, wherein the epitaxial ferroelectric film has a hexagonal crystal structure, and a Z crystal plane thereof is a (0001) plane.   14. The piezoelectric actuator according to claim 13, wherein the epitaxial ferroelectric film has an orthorhombic crystal structure, and a Z crystal plane thereof is a (011) plane. A liquid ejection head that ejects liquid using the piezoelectric actuator according to claim 13.

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