JP2005129670A - Unimorph type piezoelectric film element and its manufacturing method, and unimorph type ink jet head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost and high-quality ink jet head. <P>SOLUTION: On a diaphragm; a bottom electrode, a film having piezo-electricity, and a top electrode are formed in order. Between the diaphragm and the film having piezo-electricity, a film having a coefficient of thermal expansion larger than that of the film having piezo-electricity is formed in such a manner that satisfied: (coefficient of thermal expansion of the film having a coefficient of thermal in expansion larger than that of the film having piezo-electricity × thickness × Young's modulus)-(coefficient of thermal expansion of the diaphragm × thickness × Young's modulus)≥(coefficient of thermal expansion of the film having piezo-electricity × thickness × Young's modulus). The film having piezo-electricity is formed by sputtering so as to satisfy a formula of (average free path of metal atoms knocked out of a target)≥(distance between target and substrate). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a structure of a unimorph type piezoelectric film element using a piezoelectric film and a diaphragm, which is used in a device such as a micropump or a droplet ejecting apparatus, and an ink jet head and a unimorph type piezoelectric element using this structure. The present invention relates to a method for manufacturing a film element.

  In recent years, device research using functional thin films has been active. Realization of superior functions is expected by thinning functional materials and applying them to devices.

  For example, devices such as piezoelectric elements and sensors that use physical properties of ferroelectrics such as piezoelectricity, pyroelectricity, and polarization inversion, and non-volatile memories are actively researched. In particular, ink is ejected using piezoelectric elements. The inkjet method is capable of high-speed, high-density, high-definition, high-quality recording, and is suitable for colorization and compactness. It has been applied to printers, copiers, facsimiles, etc. Accomplished. In such a recording technology field, there is an increasing demand for further high-quality and high-definition recording technology in the future. One method for realization is a piezoelectric film element using a film having piezoelectricity, and application to next-generation high-quality and high-definition recording technology is expected.

  There are various methods for producing a piezoelectric film. For example, Patent Document 1 discloses a method for forming a PZT film with improved crystallinity using RF sputtering. Patent Document 2 and the like describe a method of forming PZT oriented in the (100) plane by controlling the precursor decomposition temperature of the sol-gel method.

  There are various types of piezoelectric film elements using piezoelectric films. Among them, a unimorph type piezoelectric film element in which a diaphragm having a different Young's modulus from a piezoelectric film and a piezoelectric film are stacked is used. It is a very simple and excellent piezoelectric film element, and can be applied to various devices. In particular, various proposals have been made because it is easy to adapt to an inkjet head.

  As an example of an inkjet head using a unimorph type piezoelectric film element using a piezoelectric film as a drive source, a structure in which a piezoelectric film is transferred onto a glass substrate that has been anodically bonded to a Si substrate on which a flow path has been formed in advance. Is mentioned. The glass substrate is excellent as a vibration plate and has a thermal expansion coefficient close to that of Si, and is suitable for forming a unimorph type piezoelectric element by anodic bonding on a Si substrate on which a flow path is formed. As an example of anodic bonding between a glass substrate and a Si substrate during ink jet production, representative methods are described in Patent Documents 3 to 5 and the like.

  Several methods have been proposed in which a piezoelectric film is directly formed on a diaphragm without using a transfer process. Since a film having piezoelectricity is generally a complex oxide, a high temperature is required for crystallization. In order to crystallize, there are a method of forming a film without heating the substrate and annealing after the film formation and a method of forming the film while heating and crystallizing the substrate, but because high temperature is required for crystallization, A substrate on which a piezoelectric film is formed needs a material that can withstand high temperatures.

Typical materials that can withstand high temperatures include expensive single crystal substrates such as MgO and SrTiO ₃ , but after bonding onto the diaphragm, only the single crystal substrate is dissolved and removed with hot phosphoric acid or the like. Therefore, not only the cost but also the throughput is very disadvantageous and becomes a big barrier to mass production. In order to solve such problems, a method of directly forming a film having piezoelectricity on a heat-resistant diaphragm material without using a transfer process is effective. Regarding a method for directly forming a piezoelectric film on a heat-resistant diaphragm material, Patent Document 6 describes a method in which the surface of a Si substrate is thermally oxidized to form a diaphragm as an SiO ₂ layer.

  In addition, the present inventors also performed anodic bonding to a Si substrate in which a flow path was previously formed using heat-resistant glass having a high strain point as a vibration plate, and the vibration plate was polished and sliced. An ink jet head using a unimorph type piezoelectric element using a piezoelectric film as a drive source, by forming a film having a property at a temperature below the strain point or annealing at a room temperature after film formation at room temperature. A method of manufacturing is proposed.

JP-A-6-290983 JP-A-11-220185 Japanese Patent Laid-Open No. 01-266376 Japanese Patent Laid-Open No. 04-132877 JP-A-11-192712 JP 2000-52550 A

  However, in the case of a method of forming a piezoelectric film on a diaphragm without using a transfer process, the following major problems can be cited.

That is, in Patent Document 6, after a SiO ₂ layer is formed on Si and a piezoelectric PZT film is directly formed thereon and crystallized, the Si substrate is opposite to the PZT film surface. Then, the flow path is formed by being etched back by etching. In such a method, when the piezoelectric PZT film is crystallized at a high temperature and cooled to room temperature, it greatly affects the thermal expansion coefficient of the Si substrate as the film formation substrate and the SiO ₂ layer as the vibration plate. In response, the lattice constant changes, and the piezoelectricity of PZT is greatly degraded. The reason for this phenomenon has not been fully clarified, but is thought to be as follows.

Although the thermal expansion coefficient of PZT varies depending on the composition, it is about 9 × 10 ⁻⁶ (/ ° C.) in the vicinity of the MPB composition having the highest piezoelectricity (Zr: Ti = 0.53: 0.47). On the other hand, the thermal expansion coefficient of the Si substrate is 3 × 10 ⁻⁶ (/ ° C.), and the SiO ₂ layer serving as the diaphragm is 0.2 × 10 ⁻⁶ (/ ° C.), which is considerably smaller than that of PZT. For this reason, when the PZT film having piezoelectricity is crystallized and cooled to room temperature via the Curie point, the PZT film tends to shrink greatly, whereas the shrinkage of the Si substrate and the SiO ₂ diaphragm is small. The PZT film receives a force in the pulling direction. In order to relieve this force, the orientation of tetragonal PZT crystals tends to be in the in-plane direction of the Si substrate where the C-axis having a long crystal axis receives tensile force. Since the polarization axis of PZT which is a tetragonal crystal is the C-axis direction, the crystal whose polarization direction is perpendicular to the vertical direction of the substrate surface to which an electric field is applied = 90 ° domain increases. It is thought to cause great deterioration.

Japanese Patent Application Laid-Open No. 2000-141644 describes the provision of a film for applying a tensile stress to the PZT film in a structure in which a piezoelectric PZT film is formed on a Si substrate provided with SiO ₂ . The object of the present invention is that the thermal expansion coefficient of PZT is larger than that of SiO _{2 serving as a} vibration plate. Therefore, when the ink flow path is formed from the opposite side to the piezoelectric PZT film, the SiO ₂ vibration plate thinned to several microns becomes the PZT film. This is for the purpose of preventing the ink flow path from being deformed by receiving a force in the compression direction due to the difference in thermal expansion. However, in the method of the present invention, the crystal orientation of the PZT film having piezoelectricity generated by the tensile stress does not contribute to the piezoelectricity = 90 ° domain tends to increase on the contrary, and the deterioration of the piezoelectricity is prevented. Can not.

  Japanese Patent Application Laid-Open No. 07-246705 describes a method of directly forming a PZT film on SiN as a diaphragm sputtered on a Si substrate through a zirconia film for the purpose of preventing lead diffusion. Yes. The purpose of zirconia film is different from that of PZT because its thermal expansion coefficient is larger than that of PZT. However, providing such a film between the diaphragm and the piezoelectric film is effective in reducing the tensile stress of the piezoelectric film. It is.

  However, stress is a product of Young's modulus and strain, and stress is a force per unit area. Therefore, the force generated by the thermal history is proportional to the product of the thermal expansion coefficient, the cross-sectional area and the Young's modulus of the material. Since the lengths of the cross-sectional areas that are in contact with each other are the same, the problem is the film thickness. That is, (thermal expansion coefficient of film having thermal expansion coefficient larger than PZT × Young's modulus × thickness) − (thermal expansion coefficient of diaphragm × Young's modulus × thickness) ≧ (thermal expansion coefficient of PZT film having piezoelectricity × Unless the relationship of Young's modulus × thickness) is satisfied, the tensile stress on the piezoelectric PZT film cannot be completely eliminated.

  The present invention solves the above problems and provides a method for realizing a more excellent piezoelectric element. That is, the tensile stress on the piezoelectric film is completely eliminated, more preferably the stress is in the compression direction, and the piezoelectric film is formed under the condition of being oriented in a specific direction. Even in direct film formation without using a transfer process, the piezoelectric film is preferentially oriented so that the direction of the polarization axis that exhibits the most effective piezoelectricity is perpendicular to the film surface. The object is to realize a high-quality inkjet head.

  In order to achieve the above object, according to the first aspect of the present invention, a lower electrode, a piezoelectric film, and an upper electrode are sequentially formed on a diaphragm, and the diaphragm and the piezoelectric film are formed. In the meantime, a film having a larger thermal expansion coefficient than the piezoelectric film is formed, and (thermal expansion coefficient of the film having a larger thermal expansion coefficient than the piezoelectric film × thickness × Young's modulus) − (the vibration Each plate is formed so as to satisfy the thermal expansion coefficient of the plate × thickness × Young's modulus) ≧ (thermal expansion coefficient of the film having piezoelectricity × thickness × Young's modulus), and the piezoelectric film is sputtered. The method is characterized in that film formation is performed so as to satisfy (mean free process of each metal atom knocked out of the target) ≧ (target-substrate distance).

  According to a second aspect of the present invention, in the first aspect of the present invention, the film formation is performed only with an inert gas.

  According to a third aspect of the present invention, in the second aspect of the present invention, the inert gas is Ar gas.

  According to a fourth aspect of the present invention, in the second or third aspect of the present invention, the partial pressure of the inert gas is 0.5 Pa or less.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the (target-substrate distance) is 150 mm or more.

  The invention according to claim 6 is the invention according to any one of claims 1 to 5, characterized in that the oxide thin film is crystallized by post-baking after completion of the film formation.

  The invention according to claim 7 is the invention according to claim 6, wherein the post-baking is performed at a temperature exceeding 700 ° C.

The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein MgO, ZrO ₂ or Cu is used as the film having a larger thermal expansion coefficient than the film having piezoelectricity. .

  The invention according to claim 9 is the invention according to any one of claims 1 to 8, wherein a film having a perovskite structure oxide containing at least Pb is used as the piezoelectric film.

  A tenth aspect of the invention is characterized in that, in the invention according to any one of the first to ninth aspects, a film having a larger thermal expansion coefficient than the piezoelectric film is formed by vacuum film formation.

  According to an eleventh aspect of the present invention, in the invention according to any one of the first to tenth aspects, the thickness of the diaphragm is 10 μm or less.

  According to a twelfth aspect of the present invention, in the invention according to any one of the first to eleventh aspects, the diaphragm is formed on a processed Si substrate.

  A thirteenth aspect of the invention is characterized in that, in the invention according to any one of the first to twelfth aspects, the diaphragm is produced by oxidizing or nitriding a Si substrate.

  The invention according to claim 14 is the invention according to any one of claims 1 to 12, characterized in that the diaphragm is crystallized glass.

  A fifteenth aspect of the invention is the invention according to any one of the first to twelfth or fourteenth aspects, wherein the diaphragm has impurity ions that act as movable ions during anodic bonding, and the Si substrate and the vibration The plates are joined by anodic bonding.

  The invention according to claim 16 is the invention according to any one of claims 1 to 12 or 14, wherein the thermal expansion coefficient of the diaphragm is in the range from room temperature to the heat treatment temperature of the piezoelectric film. It is within 50% of the substrate.

  The unimorph-type piezoelectric film element according to claim 17, wherein a lower electrode, a piezoelectric film, and an upper electrode are sequentially provided on the diaphragm without using an adhesive, and the polarization of the piezoelectric film is provided. The axial direction is preferentially oriented in a direction perpendicular to the film surface having piezoelectricity.

  The invention according to claim 18 is the invention according to claim 17, wherein a film having a larger thermal expansion coefficient than the film having piezoelectricity is provided between the diaphragm and the film having piezoelectricity, and ( Thermal expansion coefficient x thickness x Young's modulus of a film having a larger thermal expansion coefficient than the piezoelectric film-(thermal expansion coefficient x thickness x Young's modulus of the diaphragm) ≥ (heat of the piezoelectric film The relationship of expansion coefficient × thickness × Young's modulus is satisfied.

A nineteenth aspect of the invention is characterized in that, in the eighteenth aspect of the invention, the film having a larger thermal expansion coefficient than the piezoelectric film is MgO, ZrO ₂ or Cu.

  A twentieth aspect of the invention is characterized in that, in the invention of any one of the seventeenth to nineteenth aspects, the piezoelectric film is a perovskite structure oxide containing at least Pb.

  The invention according to claim 21 is the invention according to any one of claims 17 to 20, wherein the piezoelectric film is a polycrystalline film.

  A twenty-second aspect of the invention is characterized in that, in the invention of any of the seventeenth to twenty-first aspects, the piezoelectric film element is formed on a processed Si substrate.

  The invention according to claim 23 is the invention according to any one of claims 17 to 22, wherein the diaphragm has a thickness of 10 μm or less.

According to a twenty-fourth aspect of the invention, in the invention according to any one of the seventeenth to twenty- _third aspects, the diaphragm is made of SiO ₂ or SiN.

  A twenty-fifth aspect of the invention is the invention according to any one of the seventeenth to twenty-third aspects, wherein the diaphragm is crystallized glass.

  According to a twenty-sixth aspect of the present invention, in the invention according to any one of the seventeenth to twenty-third or twenty-fifth aspects, the thermal expansion coefficient of the diaphragm is in the range from room temperature to a heat treatment temperature of the piezoelectric film. It is within 50% of the substrate.

  According to a twenty-seventh aspect of the present invention, in the invention according to any one of the seventeenth to twenty-third, twenty-five, or twenty-sixth aspects, the diaphragm has impurity ions, and the impurity ions act as movable ions during anodic bonding. The material is characterized by being easily anodic bonded.

  A unimorph-type ink jet head according to claim 28 uses a Si substrate in which grooves serving as nozzles, pressure chambers, flow paths, and ink chambers are formed, and is provided on any one of claims 17 to 27 on the Si substrate. The piezoelectric film element described is formed.

When Si is used for the substrate for forming the flow path, the vibration plate has a higher probability of peeling due to thermal history unless a diaphragm having a thermal expansion coefficient close to that of Si is used. The Si substrate has a coefficient of thermal expansion as small as about 3 × 10 ⁻⁶ (/ ° C.), and it is necessary to select a diaphragm having a relatively small thermal expansion coefficient. It is also possible to produce SiO ₂ by oxidizing Si without using bonding and use it as a diaphragm by backing it out. However, the thermal expansion coefficient of SiO ₂ is 0.2 × 10 ⁻⁶ ( / [Deg.] C.) and a diaphragm having a small thermal expansion coefficient is still used.

However, many films having piezoelectricity have a large coefficient of thermal expansion, and typical PZT is particularly large at about 9 × 10 ⁻⁶ (/ ° C.) in the MPB composition having the highest piezoelectricity. Therefore, a piezoelectric film having a large thermal expansion coefficient is formed on a diaphragm having a small thermal expansion coefficient, and when the piezoelectric film is crystallized and cooled, a tensile stress is applied to the piezoelectric film. Will be added.

  As an example, FIG. 1 shows an X-ray diffraction pattern when PZT is formed on a sufficiently thick MgO substrate under non-oriented conditions, fired and crystallized, and FIG. 2 shows PZT on a sufficiently thick substrate. The relationship between the thermal expansion coefficient when film-forming and baking is carried out under the same non-oriented condition and the interplanar spacing of the PZT (112) (211) mixed peak obtained by X-ray diffraction is shown.

  As shown in FIG. 1, PZT is non-oriented, and PZT (211) is precisely a PZT (112) (211) mixed peak. Focusing on this PZT (112) (211) mixed peak, the surface spacing becomes smaller on the Si substrate having a small thermal expansion coefficient as shown in FIG. 2, and the surface spacing becomes larger on MgO having a larger thermal expansion coefficient than PZT. You can see how it is compressed.

  FIG. 3 shows a model of the cause of piezoelectric deterioration. When a film is formed on a substrate having a small coefficient of thermal expansion such as Si, a tensile stress is applied at the phase transition of the crystal when the film is cooled from the crystallization temperature to the room temperature exceeding the Curie point, and is square like PZT. In the crystal, the so-called 90 ° domain in which the C-axis direction, which is the polarization axis, faces in a plane perpendicular to the electric field to which tensile stress is applied increases. That is, for example, when the crystallization temperature is tetragonal (100) (010) (001) equivalent plane, it passes through the Curie point and transitions to the tetragonal crystal by in-plane tension ( 100 is more oriented, and (110) (101) (011) equivalent planes at the crystallization temperature are more oriented to (110), so the polarization axis is perpendicular to the electric field. It is considered that the piezoelectricity is greatly deteriorated.

  FIG. 4 shows electrical characteristics when PZT is formed on MgO having a large thermal expansion coefficient, and FIG. 5 shows electrical characteristics when PZT is formed on a Si substrate having a small thermal expansion coefficient. In the relationship between the electric field and the electric flux density (PE curve), the squareness ratio is high on MgO and the saturation electric flux density is high, and the piezoelectricity is high, but the squareness ratio is lowered on the Si substrate, The saturation electric flux density is also low, the hysteresis is deteriorated, and the piezoelectricity is also lowered.

  The present inventor has intensively studied, and in the previously filed invention, between the sufficiently thin diaphragm of 10 μm or less of the unimorph type piezoelectric film element and the film having piezoelectricity, the coefficient of thermal expansion is larger than that of the film having piezoelectricity. The film is (thermal expansion coefficient of film having a larger thermal expansion coefficient than piezoelectric film × Young's modulus × thickness) − (thermal expansion coefficient of diaphragm × Young's modulus and thickness) ≧ (film having piezoelectricity) The thermal expansion coefficient x Young's modulus x thickness) was applied to the film, and the stress in the compression direction was applied to the piezoelectric film to successfully suppress the increase in the 90 ° domain.

  In addition, the inventor of the present invention has formed a piezoelectric film in a sputtering film formation so as to satisfy (average free process of each metal atom knocked out of the target) ≧ (target-substrate distance). By performing the film, the piezoelectric film was successfully preferentially oriented in a specific direction (in a state of being oriented at about 50% or more). The present invention will be described as follows.

  That is, the introduced sputter gas particles are ionized and collide with the target, atoms in the target are knocked out, and the sputtered atoms fly through the sputter gas and reach the substrate to form a film. Is called. Normally, atoms struck out from the target repeatedly hit the sputter gas particles introduced during the flight and reach the substrate while losing their energy.

  Here, an average free path L, which is an average distance that a certain particle can fly without colliding in a space where only the particle exists, is expressed by the following equation.

・粒子直径：Ｄ
・粒子密度：ｎ
ここで、空間内の粒子の圧力Ｐは以下の式であらわされる。

-Particle diameter: D
-Particle density: n
Here, the pressure P of the particles in the space is expressed by the following equation.

・ P = nkT
Boltzmann constant: k
-Absolute particle temperature: T
However, since the absolute temperature of the particle is the particle temperature in the plasma during sputtering, it is several hundred to several hundred hundred K, and is assumed to be 1000 K in the present invention.

  From the expression of the pressure P, the mean free path L can be rewritten as the following expression.

更に、この式を拡張して、スパッタガス粒子Ａが飛び交う中に微量の被スパッタ粒子Ｂが飛行する場合、被スパッタ粒子Ｂの平均自由工程Ｌ_Ｂ は、被スパッタ粒子Ｂはスパッタガス粒子Ａのみと衝突すると仮定して以下のように表される。

Further, by extending this equation, if the flight is the sputtered particles B traces in the sputtered gas particles A flurry, mean free L _B of the sputtered particles B is the sputtered particles B is only sputtering gas particles A Assuming that it collides with

・Ｐ_Ａ
：粒子Ａの圧力
・Ｄ_Ａ
：粒子Ａの直径
・Ｄ_Ｂ
：粒子Ｂの直径
・ｍ_Ａ
：粒子Ａの重量
・ｍ_Ｂ
：粒子Ｂの重量
本発明者は、酸化物薄膜の成膜時に、スパッタリング中にターゲットから叩き出された原子のエネルギーに注目し、他の原子・分子と衝突せずにエネルギーを失わないで基板に到達する原子が多くなる場合の酸化物薄膜の配向性について検討を行った。

· _{P A}
: Pressure of particle A ・ D _A
: Of particle A diameter · _{D B}
: Of particle B diameter · _{m A}
: Weight of particle A · m _B
: Weight of particle B The inventor pays attention to the energy of atoms knocked out of the target during sputtering during the formation of the oxide thin film, and does not lose energy without colliding with other atoms / molecules. The orientation of the oxide thin film when the number of atoms reaching the surface increases is investigated.

  Here, the ratio of the particles B to be sputtered that fly directly through the sputter gas particles A and reach the substrate is expressed by the following equation.

・Ｎ_Ｂ
＝基板まで衝突しないで到達する粒子Ｂの個数
・Ｎ_０
＝出発点（ターゲット）からスパッタされた粒子Ｂの個数
・Ｘ＝粒子Ｂが飛行する出発点（ターゲット）からの基板までの距離
本発明者はこの検討において、他の原子・分子と衝突せずにエネルギーを失わないで基板に到達する原子が多くなる程酸化物薄膜の特定の方位面に優先的に配向する傾向が強まり、
直接基板に到達する原子が４０％程度以上に達する、叩き出される原子の平均自由工程がターゲット基板間距離以上になる（Ｌ_Ｂ ≧Ｘ）条件で成膜された膜は、後焼成においても或る特定温度以上の焼成でほぼ完全に特定方位面に優先配向する実験事実を見出した。この条件で作製された膜は基板を選ばず、
電極を形成した様々な基板上で特定方向に優先配向することも明らかになった。

· _{N B}
= Number of particles B that reach the substrate without colliding -N ₀
= Number of sputtered particles B from the starting point (target) X = Distance from the starting point (target) where the particle B flies to the substrate In this study, the present inventors did not collide with other atoms / molecules As more atoms reach the substrate without losing energy, the tendency to preferentially align in a specific orientation plane of the oxide thin film becomes stronger.
A film formed under the condition that the number of atoms directly reaching the substrate reaches about 40% or more, and the mean free path of the knocked-out atoms is equal to or greater than the distance between the target substrates (L _B ≧ X). The experimental fact that preferential orientation in the specific orientation plane was found almost completely by firing at a specific temperature or higher. The film produced under these conditions does not choose the substrate,
It has also been revealed that preferential orientation in a specific direction on various substrates on which electrodes are formed.

  The present inventor conducted further earnest research, and formed a film having piezoelectricity directly on the diaphragm via a film having a large thermal expansion coefficient (mean free process of each metal atom knocked out from the target) ≧ (target− By forming the film so as to satisfy the distance between the substrates), the specific direction in which the piezoelectric film is preferentially oriented is the film surface that indicates the polarization direction of the piezoelectric film that is most effective for expressing the piezoelectricity. It was found that it can be controlled vertically. In other words, it is possible to preferentially orient the film having piezoelectricity in the polarization direction of the film having piezoelectricity that is most effective for expressing the piezoelectricity by directly forming the film on the diaphragm without using an adhesive. Became. Thus, an excellent unimorph type piezoelectric film element can be formed, and an excellent ink jet head can be realized by using a unimorph type piezoelectric film element manufactured by this method as a drive source.

  Hereinafter, the present invention will be described in detail. In this embodiment, an example in which a unimorph type piezoelectric film element and an ink jet head using the same are manufactured using a film having specific piezoelectricity is shown.

Various materials can be used for the diaphragm in the present invention, but SiO ₂ or SiN obtained by oxidizing or nitriding Si is hardly peeled off from Si used as a base, and It is preferable because the thickness can be freely controlled in a thin range that is difficult to polish. In addition, a crystallized glass substrate having a low Young's modulus, high heat resistance, close to a temperature range where the thermal expansion coefficient is high with that of the Si substrate, and hardly peeled off after anodic bonding is preferable.

  Various film formation methods using sputtering can be used as a method for producing a functional oxide thin film in the present invention. In particular, the gas can be maintained up to a low gas pressure due to the electron confinement effect of the magnet. RF magnetron sputtering with a wide control range of the mean free process of sputtered particles by pressure is preferable.

As the film having piezoelectric characteristics, various films having piezoelectricity can be used. In particular, a perovskite structure oxide containing Pb is desirable. For example, Pb (Zr, Ti) O ₃ , (Pb, La) (Zr, Ti) O _{3, and the} like are given as typical examples. In particular, Pb (Zr, Ti) O ₃ (expressed as so-called PZT) is excellent in piezoelectric characteristics and is preferable as a material. Recently, Pb (Zn, Nb) O ₃ —PbTiO ₃ solid solution (referred to as PZN-PT) and Pb (Mg, Nb) O ₃ —PbTiO ₃ solid solution (referred to as PMN-PT) Etc.) has a very large piezoelectric characteristic that greatly exceeds PZT, and is preferable as a material.

Various films having a large thermal expansion coefficient can be used as the film having a larger thermal expansion coefficient than the film having piezoelectricity, and in particular, MgO having a thermal expansion coefficient of 13.0 × 10 ⁻⁶ (/ ° C.), ZrO _{2 with} a thermal expansion coefficient of 11.5 × 10 ⁻⁶ (/ ° C.), Cu with a thermal expansion coefficient of 16.8 × 10 ⁻⁶ (/ ° C.) has a particularly large thermal expansion coefficient, and heat resistance It is also excellent as a material and is preferable as a material.

  The structure of an inkjet head using a unimorph type piezoelectric film element using a piezoelectric film according to the present invention as a drive source will be briefly described with reference to FIG.

  FIG. 8 is a cross-sectional view that best represents the present invention. As shown in FIG. 8, a thin diaphragm 12 is formed on a Si substrate 11 provided with a flow path. A film 13 having a larger coefficient of thermal expansion than the film having piezoelectricity on the diaphragm located on the flow path is (the coefficient of thermal expansion × Young's modulus × thickness−the coefficient of thermal expansion of the diaphragm × Young's modulus × thickness ≧ piezoelectric. The film is formed so as to satisfy the relationship of thermal expansion coefficient × Young's modulus × thickness of the film having the property. Further, a noble metal first electrode layer 14 that serves as an electrode for preventing diffusion of atoms and an electrode is formed thereon, and a piezoelectric film 15 is formed thereon as a second layer. A second electrode layer 16 is formed thereon. Specific examples are shown below.

A unimorph-type piezoelectric film is formed by non-thermally forming a PZT film having piezoelectricity using RF sputtering as a film forming method on a vibrating plate SiO ₂ provided on a Si substrate having a hollow structure, and using post-firing. The example which produced the element is given.

A 1 μm thick SiO ₂ film was formed on the Si (100) substrate by thermal oxidation. This was etched from the surface opposite to the SiO ₂ surface to form grooves, and a structure was obtained in which SiO _{2 serving as a} diaphragm was formed on a hollow Si substrate. The thermal expansion coefficient of SiO ₂ is 0.2 × 10 ⁻⁶ (/ ° C.), and the Young's modulus is 7.2 × 10 ¹⁰ (N / m ² ). On top of this, MgO having a large thermal expansion coefficient was formed by RF sputtering, with an Ar gas pressure = 0.14 Pa, an O ₂ flow rate / Ar flow rate = 5%, and a thickness of 1.0 μm formed at room temperature. Thereafter, a post heat treatment was performed at 750 ° C. The X-ray diffraction patterns before and after firing the MgO film on SiO ₂ are shown in FIGS.

Both pre- and post-firing are preferentially oriented to MgO (111), but MgO (200) is also observed, resulting in a polycrystalline film. MgO has a thermal expansion coefficient of 13.0 × 10 ⁻⁶ (/ ° C.) and a Young's modulus of 20.6 × 10 ¹⁰ (N / m ² ). Thereafter, Ti was formed as an adhesion layer on the MgO side having a large thermal expansion coefficient by a thickness of 4 nm, and further, Pt as a first electrode was formed thereon by RF sputtering with a thickness of 150 nm. On top of that, an amorphous PZT layer was formed on the surface of 1 μm by RF sputtering with substrate heater OFF, display Ar gas pressure 0.2 Pa, target-substrate distance = 160 mm. This amorphous PZT layer is usually a crystallized PZT layer preferentially oriented to (001) as shown in FIG. 14 by post-heat treatment at 450 ° C. on an MgO substrate, but it is 450 ° C. on a Si substrate having a small thermal expansion coefficient. A tensile stress is applied during cooling after crystallization by post-heat treatment, and a PZT film preferentially oriented at (100) is obtained as shown in FIG. The thermal expansion coefficient of PZT is 9.0 × 10 ⁻⁶ (/ ° C.) near the MPB composition, and the Young's modulus is 8.0 × 10 ¹⁰ (N / m ² ).

  The formed film was annealed in an oxygen atmosphere at an elevated temperature of 1 ° C./min and 750 ° C. for 5 hours for crystallization. FIG. 6 and FIG. 7 show the contraction force relationship and shape change acting on each layer from the crystallization temperature to room temperature.

As the cooling process proceeds from the crystallization temperature, the thermal contraction of the diaphragm 12 is very small as shown in FIG. The MgO layer 13 having a large thermal expansion coefficient cancels the tension and tries to work in the compression direction. It satisfies the relationship of (thermal expansion coefficient of MgO × Young's modulus × thickness) − (thermal expansion coefficient of diaphragm SiO ₂ × Young's modulus × thickness) ≧ (thermal expansion coefficient of PZT × Young's modulus × thickness) In addition, since there is a relationship of (thermal expansion coefficient of MgO)> (thermal expansion coefficient of PZT), a compressive force acts on PZT in the temperature range from the crystallization temperature to room temperature.

Furthermore, the SiO ₂ that becomes the diaphragm is as thin as 1 μm, and the diaphragm facing the hollow part is greatly deformed to the pressure chamber side as shown in FIG. 7 due to the large shrinkage of the MgO layer in the cooling process, and the compression stress is lost. I will not. As a result, compressive stress was applied when the PZT was cooled from the firing temperature to room temperature, and the polarization axis direction (C axis) of the PZT was preferentially oriented in the direction perpendicular to the film surface, resulting in a preferential orientation of (001). .

SiO ₂
Was provided on the Si substrate by thermal oxidation, and no problem occurred even when baked at 750 ° C. Thereafter, Pt serving as the second electrode was formed on the crystallized PZT surface by RF sputtering. Patterning was performed by dry etching with the first electrode Pt on PZT aligned with the groove on Si. Further, PZT was etched by wet etching along the Pt pattern. When the electrical characteristics of the PZT were measured, the P-E curve, which is the relationship between the electric field strength and the electric flux density, showed a good squareness ratio and a high saturated electric flux density, and showed good hysteresis characteristics. Further, when the unimorph type piezoelectric film element manufactured in this way was measured with a laser Doppler displacement meter by applying a rectangular wave as shown in FIG. 11, a sufficient displacement as a unimorph type piezoelectric film element was confirmed.

  A thermal oxide film to be a vibration plate is transferred onto a Si substrate provided with a flow path in advance, and MgO having a very large thermal expansion coefficient is formed on the vibration plate, and further, RF sputtering is used as a film formation method thereon. An example in which an ink jet head using a unimorph type piezoelectric film element as a drive source is manufactured by forming a piezoelectric PZT film without heating and post-baking.

  A groove serving as an ink flow path was formed on the Si (100) substrate using an ICP dry etching technique. FIG. 9 is a cross-sectional view of the completed inkjet head viewed from the nozzle direction. FIG. 10 shows a top view of the inkjet head.

An ink supply chamber, a communication nozzle, a pressure chamber, and a discharge nozzle are formed, and a part of the ink supply chamber penetrates. After that, the Si substrate on which the thermal oxide film 1 μm is formed is pasted onto the Si substrate on which a groove described later is formed using solid phase bonding, and the Si substrate on which the thermal oxide film is formed is wet-etched from the back surface. A diaphragm having a thermal oxide film SiO ₂ = 1 μm was formed.

SiO ₂
Has a thermal expansion coefficient of 0.2 × 10 ⁻⁶ (/ ° C.) and a Young's modulus of 7.2 × 10 ¹⁰ (N / m ² ). On top of this, MgO having a large thermal expansion coefficient was formed by RF sputtering, with an Ar gas pressure = 0.14 Pa, an O ₂ flow rate / Ar flow rate = 5%, and a thickness of 1.0 μm formed at room temperature. Thereafter, a post heat treatment was performed at 750 ° C. The X-ray diffraction patterns before and after firing the MgO film on SiO ₂ are shown in FIGS.

Both pre- and post-firing are preferentially oriented to MgO (111), but MgO (200) is also observed, resulting in a polycrystalline film. MgO has a thermal expansion coefficient of 13.0 × 10 ⁻⁶ (/ ° C.) and a Young's modulus of 20.6 × 10 ¹⁰ (N / m ² ). Thereafter, Ti was formed as an adhesion layer on the MgO side having a large thermal expansion coefficient by a thickness of 4 nm, and further, Pt as a first electrode was formed thereon by RF sputtering with a thickness of 150 nm. On top of that, an amorphous PZT layer was formed on the surface of 1 μm by RF sputtering with substrate heater OFF, display Ar gas pressure 0.2 Pa, target-substrate distance = 160 mm. This amorphous PZT layer is usually a crystallized PZT layer preferentially oriented to (001) as shown in the figure by post-heat treatment at 750 ° C. on the MgO substrate, but after 750 ° C. on the Si substrate having a small thermal expansion coefficient. A tensile stress is applied during cooling after crystallization by heat treatment, and a PZT film preferentially oriented at (100) as shown in the figure. The thermal expansion coefficient of PZT is 9.0 × 10 ⁻⁶ (/ ° C.) near the MPB composition, and the Young's modulus is 8.0 × 10 ¹⁰ (N / m ² ).

The formed film was annealed in an oxygen atmosphere at an elevated temperature of 1 ° C./min and 750 ° C. for 5 hours for crystallization. FIG. 9 shows the relationship of thermal shrinkage of each layer from the crystallization temperature to room temperature. The thermal contraction of the diaphragm 12 is very small and acts as a tension against the other layers. The MgO layer 13 having a large thermal expansion coefficient cancels the tension and tries to work in the compression direction. It satisfies the relationship of (thermal expansion coefficient of MgO × Young's modulus × thickness) − (thermal expansion coefficient of diaphragm SiO ₂ × Young's modulus × thickness) ≧ (thermal expansion coefficient of PZT × Young's modulus × thickness) In addition, since there is a relationship of (thermal expansion coefficient of MgO)> (thermal expansion coefficient of PZT), a compressive force acts on PZT in the temperature range from the crystallization temperature to room temperature.

Further, since SiO _{2 serving as} a diaphragm is as thin as 1 μm, the diaphragm facing the hollow portion is greatly deformed toward the pressure chamber as shown in FIG. Not lost. As a result, compressive stress was applied when PZT was cooled from the firing temperature to room temperature, and the polarization axis direction (C axis) of PZT was preferentially oriented in the direction perpendicular to the film surface, and (001) became preferential orientation. .

SiO ₂
Was bonded to the Si substrate by solid phase bonding, and no problem occurred even when baked at 750 ° C. Thereafter, Pt serving as the second electrode was formed on the crystallized PZT surface by RF sputtering. Patterning was performed by dry etching with the first electrode Pt on PZT aligned with the groove on Si. Further, PZT was etched by wet etching along the Pt pattern. When the electrical characteristics of the PZT were measured, the P-E curve, which is the relationship between the electric field strength and the electric flux density, showed a good squareness ratio and a high saturated electric flux density, and showed good hysteresis characteristics. Further, when the unimorph type piezoelectric film element thus fabricated was applied with a rectangular wave as shown in FIG. 11 and measured with a laser Doppler displacement meter, a sufficient displacement as a unimorph type piezoelectric film element was confirmed.

  In this embodiment, a unimorph type piezoelectric film element having a vibration plate attached is formed on one surface of a piezoelectric element in which electrodes are provided above and below a piezoelectric film. By performing various processes on the Si substrate in advance, various devices using unimorph type piezoelectric film elements can be manufactured. In this embodiment, an ink jet head using a unimorph type piezoelectric film element is formed by forming a groove in a Si substrate.

  The ejection was confirmed using the ink jet head for ink ejection thus prepared. When this ink jet head was filled with IPA and driven with a drive waveform as shown in FIG. 11, ejection of droplets could be confirmed.

  Using RF sputtering as the film formation method, MgO with a very high thermal expansion coefficient is formed on crystallized glass, which is a vibration plate that has been anodically bonded to a Si substrate that has been previously provided with a flow path, and piezoelectric film is further formed thereon. An example in which an ink-jet head using a unimorph type piezoelectric film element as a drive source is produced by forming a PZT film having the property into a non-heated film and post-baking it.

A groove serving as an ink flow path was formed on the Si (100) substrate using the ICP dry etching technique in the same manner as in Example 2. Thereafter, crystallized glass having a thickness of 30 μm was attached as a vibration plate on a Si substrate on which grooves described later were formed using anodic bonding, and the crystallized glass was thinned to 3 μm by polishing. The thermal expansion coefficient of crystallized glass is 3.2 × 10 ⁻⁶ (/ ° C.), and the Young's modulus is 8.9 × 10 ¹⁰ (N / m ² ). MgO having a large thermal expansion coefficient was formed on the crystallized glass sliced by polishing by RF sputtering, and a thickness of 1.0 μm was formed at room temperature with Ar gas pressure = 0.14 Pa, O ₂ flow rate / Ar flow rate = 5%.

MgO has a thermal expansion coefficient of 13.0 × 10 ⁻⁶ (/ ° C.) and a Young's modulus of 20.6 × 10 ¹⁰ (N / m ² ). Thereafter, Ti was formed as an adhesion layer on the MgO side having a large thermal expansion coefficient by a thickness of 4 nm, and further, Pt as a first electrode was formed thereon by RF sputtering with a thickness of 150 nm. On top of that, an amorphous PZT layer was formed on the surface of 1 μm by RF sputtering with substrate heater OFF, display Ar gas pressure 0.2 Pa, target-substrate distance = 160 mm. This amorphous PZT layer is usually a crystallized PZT layer preferentially oriented to (001) as shown in FIG. 14 by post-heat treatment at 750 ° C. on the MgO substrate, but it is 750 ° C. on the Si substrate having a small thermal expansion coefficient. A tensile stress is applied during cooling after crystallization by post-heat treatment, and a PZT film preferentially oriented at (100) is obtained as shown in FIG. The thermal expansion coefficient of PZT is 9.0 × 10 ⁻⁶ (/ ° C.) near the MPB composition, and the Young's modulus is 8.0 × 10 ¹⁰ (N / m ² ).

  The formed film was annealed in an oxygen atmosphere at an elevated temperature of 1 ° C./min and 750 ° C. for 5 hours for crystallization. FIG. 9 shows the relationship of thermal shrinkage of each layer from the crystallization temperature to room temperature. The thermal contraction of the diaphragm 12 is very small and acts as a tension against the other layers. The MgO layer 13 having a large thermal expansion coefficient cancels the tension and tries to work in the compression direction. The relationship of (thermal expansion coefficient of MgO × Young's modulus × thickness) − (thermal expansion coefficient of crystallized glass as vibration plate × Young's modulus × thickness) ≧ (thermal expansion coefficient of PZT × Young's modulus × thickness) And satisfying the relationship (thermal expansion coefficient of MgO)> (thermal expansion coefficient of PZT), a compressive force acts on PZT in the temperature range from the crystallization temperature to room temperature, and the diaphragm Since the crystallized glass becomes as thin as 3 μm, the diaphragm facing the hollow part is greatly deformed to the pressure chamber side as shown in FIG. 7 due to the large shrinkage of the MgO layer in the cooling process, and the compression stress is not lost. . As a result, compressive stress was applied when PZT was cooled from the firing temperature to room temperature, and the polarization axis direction (C axis) of PZT was preferentially oriented in the direction perpendicular to the film surface, and (001) became preferential orientation. . In addition, the crystallized glass has a strain point of about 1000 ° C., and no problem occurred even when fired at 750 ° C. Further, the thermal expansion coefficients of the Si substrate and the crystallized glass were very close to a high temperature, and no problems such as peeling occurred even after firing.

  Thereafter, the first electrode Pt on PZT in which Pt to be the second electrode was formed by RF sputtering on the crystallized PZT surface was patterned by dry etching in accordance with the groove on Si. Further, PZT was etched by wet etching along the Pt pattern. When the electrical characteristics of the PZT were measured, the P-E curve, which is the relationship between the electric field strength and the electric flux density, showed a good squareness ratio and a high saturated electric flux density, and showed good hysteresis characteristics. Furthermore, when the produced unimorph type piezoelectric film element was applied with a rectangular wave as shown in FIG. 11 and measured by a laser Doppler displacement meter, a sufficient displacement as a unimorph type piezoelectric film element was confirmed.

  In this embodiment, a unimorph type piezoelectric film element in which a vibration plate is attached is formed on one surface of a piezoelectric element in which electrodes are provided above and below a piezoelectric film. By performing various processes on the Si substrate in advance, various devices using unimorph type piezoelectric film elements can be manufactured. In this embodiment, an ink jet head using a unimorph type piezoelectric film element is formed by forming a groove in a Si substrate.

  The ejection was confirmed using the ink jet head for ink ejection thus prepared. When this ink jet head was filled with IPA and driven with a drive waveform as shown in FIG. 11, ejection of droplets could be confirmed.

  According to the present invention, a thin diaphragm is bonded to a Si substrate that has been processed in advance, and a film having a larger thermal expansion coefficient than a film having piezoelectricity is formed thereon as a first layer (from a film having piezoelectricity). Thermal expansion coefficient of a film having a large thermal expansion coefficient × Young's modulus × thickness) − (Thermal expansion coefficient of the diaphragm × Young's modulus × thickness) ≧ (Thermal expansion coefficient of the film having piezoelectricity × Young's modulus × thickness) An electrode layer made of noble metal or the like is provided as a second layer thereon, and a piezoelectric film as a third layer is further formed thereon using a sputtering method (each metal atom struck out from the target). The average free process) ≧ (target-to-substrate distance) is formed while heating or crystallizing so as to satisfy the target-substrate distance and then crystallized by post-baking to cause compressive stress on the piezoelectric film when the temperature is lowered. A piezoelectric film with its pressure. Can be directly formed on the diaphragm so that the polarization axis direction (C axis) that exhibits the most effective property is in the (001) preferential orientation state in which the orientation is approximately 50% or more perpendicular to the film surface. It was.

  An electrode layer such as a noble metal is formed as a third layer on the piezoelectric film, and a device such as an ink jet head using a unimorph type piezoelectric film element using the piezoelectric film as a driving source can be manufactured. However, after processing the ink flow path and the ink supply port on the Si substrate, a diaphragm is formed by bonding or the like, and a piezoelectric film is further formed on the Si substrate without deteriorating its piezoelectricity. Therefore, it is possible to directly form a film so as to exhibit the efficiency more efficiently. Therefore, it is possible to produce a high-definition and extremely high-quality ink jet head with a high yield compared to the related art.

It is a figure which shows the X-ray-diffraction pattern of non-oriented PZT applied to description of an effect | action of this invention, and an Example. It is a figure which shows the relationship between the surface space | interval by the X-ray diffraction of the thermal expansion coefficient of the sufficiently thick board | substrate applied for description of an effect | action of this invention, and the PZT (112) (211) mixed peak formed on it. It is a model figure of the piezoelectric deterioration of the film | membrane which has the piezoelectricity formed on the board | substrate with a small thermal expansion coefficient applied for description of an effect | action of this invention. It is a figure which shows the relationship between the electrical property on the MgO board | substrate which the compression force acts on PZT = electric field and electric flux density applied to description of an effect | action of this invention. It is a figure which shows the relationship between the electrical property on Si substrate in which the tension | pulling force acts on PZT applied to description of an effect | action of this invention = electric field and electric flux density. It is sectional drawing of the unimorph type piezoelectric film element using the film | membrane which has a piezoelectric property applied to description of the Example of this invention. It is sectional drawing which shows the shape change at the time of cooling from the crystallization temperature of the unimorph type | mold piezoelectric film element using the film | membrane which has a piezoelectric property applied to description of the Example of this invention. FIG. 2 is a cross-sectional view of an inkjet head using a unimorph type piezoelectric element using a piezoelectric film as a drive source, which is applied to the description of an embodiment of the invention. It is sectional drawing seen from the nozzle direction of the inkjet head which uses the unimorph type piezoelectric element using the film | membrane which has a piezoelectric property applied to description of the Example of this invention as a drive source. It is a top view of the inkjet head which uses the unimorph type piezoelectric element using the film | membrane which has a piezoelectric property applied to description of the comparative example of this invention as a drive source. It is a figure which shows the drive waveform used for evaluation of the piezoelectric element applied to description of the Example of this invention. It is a figure which shows the X-ray-diffraction pattern before baking of the MgO film | membrane applied for description of the Example of this invention. It is a figure which shows the X-ray-diffraction pattern after baking of the MgO film | membrane applied for description of the Example of this invention. It is a figure which shows the X-ray-diffraction pattern after baking of the priority orientation PZT film | membrane formed into a film on the MgO substrate applied to description of the Example of this invention. It is a figure which shows the X-ray-diffraction pattern after baking of the priority orientation PZT film | membrane formed into a film on the Si substrate applied to description of the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Si substrate used as the base of a piezoelectric film element 11 Si substrate in which the groove | channel for inkjets was formed 12 Vibration plate 13 Film | membrane with a larger thermal expansion coefficient than the film | membrane which has piezoelectricity 14 1st electrode 15 Film | membrane which has piezoelectricity
16 Second electrode 17 Ink discharge groove 21 Si substrate and anode bonded diaphragm 22 Ink supply chamber through hole 23 Ink supply chamber 24 Connecting nozzle 25 Pressure chamber and unimorph piezoelectric element 26 Discharge nozzle 27 on the pressure chamber Droplet

Claims (28)

  A lower electrode, a piezoelectric film, and an upper electrode are sequentially formed on the diaphragm, and a thermal expansion coefficient is larger between the diaphragm and the piezoelectric film than the piezoelectric film. In addition to forming a film, (thermal expansion coefficient of the film having a larger thermal expansion coefficient than the piezoelectric film × thickness × Young's modulus) − (thermal expansion coefficient of the diaphragm × thickness × Young's modulus) ≧ (the above Each is formed so as to satisfy the thermal expansion coefficient × thickness × Young's modulus of the film having piezoelectricity, and the film having piezoelectricity is sputtered (average of each metal atom knocked out from the target) A method for producing a unimorph type piezoelectric film element, wherein film formation is performed so as to satisfy a free step) ≧ (target-substrate distance).   The method for producing a unimorph type piezoelectric film element according to claim 1, wherein the film formation is performed only with an inert gas.   3. The method for producing a unimorph type piezoelectric film element according to claim 2, wherein the inert gas is Ar gas.   4. The method for producing a unimorph type piezoelectric film element according to claim 2, wherein the partial pressure of the inert gas is 0.5 Pa or less.   The method for producing a unimorph type piezoelectric film element according to any one of claims 1 to 4, wherein the (target-substrate distance) is 150 mm or more.   6. The method for producing a unimorph type piezoelectric film element according to claim 1, wherein the oxide thin film is crystallized by post-baking after completion of the film formation.   The method for producing a unimorph type piezoelectric film element according to claim 6, wherein the post-baking is performed at a temperature exceeding 700 ° C. The method for producing a unimorph type piezoelectric film element according to any one of claims 1 to 7, wherein MgO, ZrO ₂ or Cu is used as the film having a larger thermal expansion coefficient than the film having piezoelectricity.   9. The method for manufacturing a unimorph type piezoelectric film element according to claim 1, wherein a film having a perovskite structure oxide containing at least Pb is used as the piezoelectric film.   The method for producing a unimorph type piezoelectric film element according to any one of claims 1 to 9, wherein a film having a larger thermal expansion coefficient than the film having piezoelectricity is formed by vacuum film formation.   The method for producing a unimorph type piezoelectric film element according to any one of claims 1 to 10, wherein the diaphragm has a thickness of 10 m or less.   The method for producing a unimorph type piezoelectric film element according to claim 1, wherein the vibration plate is formed on a processed Si substrate.   The method for manufacturing a unimorph type piezoelectric film element according to claim 1, wherein the diaphragm is manufactured by oxidizing or nitriding a Si substrate.   The method for manufacturing a unimorph type piezoelectric film element according to claim 1, wherein the diaphragm is crystallized glass.   15. The diaphragm according to claim 1, wherein the diaphragm has impurity ions that act as movable ions during anodic bonding, and the Si substrate and the diaphragm are bonded by anodic bonding. A production method of the unimorph type piezoelectric film element described.   15. The thermal expansion coefficient of the diaphragm is within 50% of the Si substrate in a range from room temperature to a heat treatment temperature of the piezoelectric film. Of manufacturing a unimorph type piezoelectric film element.   A lower electrode, a piezoelectric film, and an upper electrode are sequentially provided on the diaphragm without using an adhesive, and the polarization axis direction of the piezoelectric film is perpendicular to the piezoelectric film surface. A unimorph type piezoelectric film element characterized by being preferentially oriented in a direction.   A film having a larger thermal expansion coefficient than the piezoelectric film is provided between the diaphragm and the piezoelectric film, and (thermal expansion of a film having a larger thermal expansion coefficient than the piezoelectric film) Coefficient × thickness × Young's modulus) − (thermal expansion coefficient of the diaphragm × thickness × Young's modulus) ≧ (thermal expansion coefficient of the film having piezoelectricity × thickness × Young's modulus) The unimorph type piezoelectric film element according to claim 17. The unimorph type piezoelectric film element according to claim 18, wherein the film having a larger thermal expansion coefficient than the piezoelectric film is MgO, ZrO ₂ or Cu.   The unimorph type piezoelectric film element according to any one of claims 17 to 19, wherein the piezoelectric film is a perovskite structure oxide containing at least Pb.   21. The unimorph type piezoelectric film element according to claim 17, wherein the piezoelectric film is a polycrystalline film.   The unimorph piezoelectric film element according to any one of claims 17 to 21, wherein the piezoelectric film element is formed on a processed Si substrate.   23. The unimorph type piezoelectric film element according to claim 17, wherein the diaphragm has a thickness of 10 [mu] m or less. The unimorph type piezoelectric film element according to any one of claims 17 to 23, wherein the diaphragm is made of SiO ₂ or SiN.   The unimorph type piezoelectric film element according to any one of claims 17 to 23, wherein the vibration plate is crystallized glass.   26. The thermal expansion coefficient of the diaphragm is within 50% of the Si substrate in a range from room temperature to a heat treatment temperature of the piezoelectric film. Unimorph type piezoelectric film element.   27. The diaphragm according to claim 17, wherein the diaphragm has impurity ions, and the impurity ions act as movable ions at the time of anodic bonding so that the anodic bonding is easy. The unimorph type piezoelectric film element described in 1.   A Si substrate on which grooves for forming nozzles, pressure chambers, flow paths and ink chambers are formed, and the piezoelectric film element according to any one of claims 17 to 27 is formed on the Si substrate. A unimorph type inkjet head characterized by

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