JP2006100622A - Unimorph type piezoelectric film element, manufacturing method therefor and liquid discharge head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent degradation of piezoelectric performance by suppressing a 90° domain caused by tensile stress acting on a piezoelectric film in a process for crystallizing the piezoelectric film. <P>SOLUTION: A vibrating plate 2 is formed on a substrate 1 being an Si substrate. An intermediate film 3, which is made of an MgO film having a thermal expansion coefficient larger than that of the piezoelectric film 5, is laminated on the vibrating plate 2. The intermediate film 3 is patterned corresponding to a movable region of the vibrating plate 2 located on a hollow part 1a of the substrate 1. After that, film forming of an electrode film 4 and the piezoelectric film 5 is executed. The piezoelectric film 5 is crystallized by heat treatment during film forming or after film forming. A thermal expansion coefficient, a Young's modulus, and a thickness of each of the vibrating plate 2, the intermediate film 3, and the piezoelectric film 5, are set so as to satisfy prescribed conditions. Consequently, the 90° domain in crystallization of the piezoelectric film 5 can be suppressed by changing the stress of the piezoelectric film 5 occurring in the crystallization process from tensile stress to compression stress. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a unimorph piezoelectric film element, a liquid discharge head, and a method for manufacturing a unimorph piezoelectric film element used in a driving unit of a micropump, a liquid discharge recording apparatus, and the like.

  In recent years, research on devices using functional thin films has been actively conducted, and realization of excellent functions is expected by making functional materials into thin films and applying them to various devices.

  For example, devices such as piezoelectric film elements and sensors that use physical properties of ferroelectrics such as piezoelectricity, pyroelectricity, and polarization inversion, and non-volatile memory are actively researched. In particular, liquids such as ink are ejected by piezoelectric driving force. The liquid ejection type recording device enables high-speed, high-density, high-definition and high-quality recording, and is also suitable for colorization and compactness. It is suitable not only for printers but also for copiers, facsimiles, etc. Applied, has achieved rapid development in recent years. In such a recording technology field, there is an increasing demand for recording technology with higher quality and higher definition in the future. One method for realizing this is a piezoelectric film element using a piezoelectric film (piezoelectric film), which is expected to be applied to next-generation high-quality and high-definition recording technology.

  There are various methods for producing the piezoelectric film. For example, Patent Document 1 describes a method for forming a PZT film using RF sputtering. Patent Document 2 describes a method of forming a PZT film 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 a piezoelectric film. In particular, a unimorph type piezoelectric film element in which a piezoelectric film is laminated on a diaphragm having a different Young's modulus from a piezoelectric body is very simple and excellent. Therefore, it is easy to adapt to the liquid discharge head.

  As an example of a liquid discharge head using a unimorph type piezoelectric film element as a drive source, a piezoelectric film formed on another substrate is transferred to a glass substrate (glass diaphragm) that is anodically bonded to a Si substrate that is a flow path substrate. A configuration is mentioned. Since the glass substrate is excellent as a vibration plate and has a linear expansion coefficient close to that of Si, it is suitable for forming a unimorph type piezoelectric film element by anodic bonding on a Si substrate on which a liquid channel is formed in advance.

Since a piezoelectric film is generally a complex oxide, a high temperature is required for crystallization. Therefore, for crystallization, a method of forming a piezoelectric film without heating the substrate and annealing after the film formation, or a method of forming a film while heating and crystallizing the substrate has been developed. However, since crystallization occurs at a high temperature, the substrate on which the piezoelectric film is formed needs a single crystal substrate that can withstand high temperatures. Typical examples of the single crystal substrate include MgO and SrTiO ₃ , but after bonding to the glass substrate serving as the vibration plate, only the single crystal substrate must be dissolved and removed by hot phosphoric acid and transferred. In addition, not only the cost but also the throughput is very disadvantageous, which becomes a large barrier to mass production.

In order to solve such problems, a method of directly forming a piezoelectric film on a heat-resistant diaphragm without using a transfer process is effective. Regarding a method of directly forming a piezoelectric film on a heat-resistant diaphragm, as disclosed in Patent Document 3, there is a method in which the surface of a Si substrate is thermally oxidized to form a SiO ₂ layer and used as a diaphragm. .

  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. A method of easily producing a liquid discharge head using a unimorph type piezoelectric film element using a piezoelectric film as a drive source by forming a film at a temperature below the strain point or annealing at a temperature after forming the film at a room temperature. is suggesting.

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 mentioned. In the configuration disclosed in Patent Document 3 above, a SiO ₂ layer is formed on a Si substrate, and after a PZT film is directly formed and crystallized thereon, the Si substrate is opposite to the PZT film surface. A liquid flow path such as a pressure chamber is formed by etching back from the surface. In the case of such a manufacturing method, when the PZT film is crystallized at a high temperature and cooled to room temperature, the lattice constant is greatly influenced by the thermal expansion coefficient of the Si substrate, which is the film formation substrate, and the PZT film The piezoelectricity is greatly deteriorated. The reason for this phenomenon has not been fully clarified, but is thought to be as follows.

Although the thermal expansion coefficient of the PZT film 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 Si substrate is 3 × 10 ⁻⁶ (/ ° C.), which is considerably smaller than PZT. For this reason, when the PZT film is crystallized and cooled to room temperature via the Curie point, the PZT film tends to shrink greatly, whereas the shrinkage amount of the Si substrate is small, so the PZT film receives a force in the pulling direction. It will be. 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, there are many so-called 90 ° domains in which the polarization direction is perpendicular to the vertical direction of the substrate surface to which an electric field is applied, causing a large deterioration in piezoelectricity. Conceivable.

On the other hand, Patent Document 4 discloses a configuration in which an intermediate film for applying a tensile stress to a PZT film is provided in a structure in which a PZT film is formed on a Si substrate provided with a SiO ₂ layer serving as a vibration plate. This is because the thermal expansion coefficient of PZT is larger than that of SiO _{2 serving as a} vibration plate. When a liquid flow path such as a pressure chamber is formed from the side opposite to the PZT film, which is a piezoelectric film, the vibration of SiO ₂ thinned to several microns. An intermediate film is provided for the purpose of preventing the plate from being deformed to the liquid flow path side by receiving a force in the compression direction due to a difference in thermal expansion with the PZT film. However, in this method, the above-described tensile stress tends to increase the 90 ° domain that does not contribute to the piezoelectricity of the PZT film, and the piezoelectricity is significantly deteriorated.

Patent Document 5 discloses a method of forming a PZT film through SiN film for the purpose of preventing lead diffusion on SiN as a diaphragm sputtered on a Si substrate. Since the zirconia film has a thermal expansion coefficient larger than that of PZT and thus has a different purpose, providing such a film between the diaphragm and the piezoelectric film is also effective in reducing the tensile stress of the piezoelectric film. However, since the stress is the product of Young's modulus and strain, the stress 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. And since the length of the cross-sectional area where the films are in contact with each other is the same, the problem is the film thickness, and if the specific film thickness relationship is not satisfied, the tensile stress to the PZT film is reduced. I can't.
Japanese Patent Laid-Open No. 06-290983 JP-A-11-220185 JP 2000-52550 A JP 2000-141644 A JP 07-246705 A

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and completely eliminates the tensile stress to the piezoelectric film in the crystallization process, and more preferably by making the stress in the compression direction. Manufacture of unimorph-type piezoelectric film elements, liquid-discharge heads, and unimorph-type piezoelectric film elements that can suppress the generation of the 90 ° domain and significantly improve the piezoelectric characteristics of the piezoelectric film to realize an inexpensive and high-quality liquid-discharge head, etc. It is intended to provide a method.

In order to achieve the above object, a unimorph type piezoelectric film element of the present invention is a unimorph type piezoelectric film element comprising a diaphragm and a piezoelectric film laminated on the diaphragm, and is more thermally expanded than the piezoelectric film. The piezoelectric film is laminated on the diaphragm via an intermediate film having a large coefficient, the intermediate film is patterned so as to correspond to a movable region of the diaphragm, and the diaphragm, the intermediate film, The following relationship is established among the respective thermal expansion coefficient, Young's modulus, and thickness of the piezoelectric film.
(Thermal expansion coefficient of intermediate film × Young's modulus × thickness) − (thermal expansion coefficient of diaphragm × Young's modulus × thickness) ≧ (thermal expansion coefficient of piezoelectric film × Young's modulus × thickness)

When a Si substrate is used as a substrate for forming a liquid flow path (hollow part) such as a pressure chamber, the probability of separation due to thermal history increases unless a diaphragm having a thermal expansion coefficient close to Si is used. The Si substrate has a considerably small thermal expansion coefficient of about 3 × 10 ⁻⁶ (/ ° C.), and it is necessary to select a glass material having a relatively small thermal expansion coefficient for the diaphragm. Even when the SiO ₂ layer is formed by oxidizing the surface of the Si substrate, and the Si substrate is used as a diaphragm by being back-sided, the thermal expansion coefficient of SiO ₂ is about 0.2 × 10 ⁻⁶ (/ ° C.). The diaphragm is very small and has a small coefficient of thermal expansion.

On the other hand, many piezoelectric materials forming the piezoelectric film have a large thermal expansion coefficient, 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 tensile stress is applied to the piezoelectric film when the piezoelectric film is crystallized and cooled.

  As an example, FIG. 4 shows an X-ray diffraction pattern when a PZT film is formed on a sufficiently thick MgO substrate, fired and crystallized. FIG. 5 shows the relationship between the thermal expansion coefficient when a PZT film is formed and fired on a sufficiently thick Si substrate and the interplanar spacing d of the PZT (112) (211) mixed peak obtained by X-ray diffraction. Indicates. The PZT film shown in FIG. 4 is non-oriented, and PZT (211) is precisely a PZT (112) (211) mixed peak. Focusing on this PZT (112) (211) mixed peak, as shown in FIG. 5, the surface interval d is reduced on the Si substrate having a small thermal expansion coefficient, and the surface interval is formed on MgO having a larger thermal expansion coefficient than PZT. It can be seen that d increases and is compressed.

  FIG. 6 explains the cause of piezoelectric degradation. When a film is formed on a substrate having a small coefficient of thermal expansion such as Si, the film is pulled when it is cooled from the crystallization temperature to the room temperature beyond the Curie point. Stress is applied at the time of crystal phase transition, and in a tetragonal crystal such as PZT, 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. For example, a tetragonal crystal with a crystallization temperature of (100) (010) (001) equivalent plane faces (100) due to in-plane pulling when passing through the Curie point and transitioning to a tetragonal crystal. Many of them are (110) (101) (011) equivalent planes at the crystallization temperature, and many are facing (110). As described above, since the number of polarization axes that are perpendicular to the electric field increases, the piezoelectricity is considered to be greatly deteriorated.

  FIG. 7 shows the electrical characteristics when a PZT film is formed on an MgO substrate having a large thermal expansion coefficient, and FIG. 8 shows the electrical characteristics when a PZT film is formed on an Si substrate having a small thermal expansion coefficient. Show. Comparing the graphs of FIG. 7 and FIG. 8, the relationship between the electric field and the electric flux density (PE curve) shows a good hysteresis with a high squareness ratio and a high saturation electric flux density on the MgO substrate. It can be seen that on the Si substrate, the squareness ratio is lowered, the saturation electric flux density is low, the hysteresis is deteriorated, and the piezoelectricity is also lowered.

  The present inventors have conducted extensive research and provided an intermediate film having a thermal expansion coefficient larger than that of the piezoelectric film between a thin diaphragm having a thickness of 10 μm or less and the piezoelectric film, and (thermal expansion coefficient of the intermediate film × Young's modulus × thickness )-(The thermal expansion coefficient of the diaphragm × Young's modulus × thickness) ≧ (Thermal expansion coefficient of the piezoelectric film × Young's modulus × thickness) By designing to satisfy the relationship, cooling from the crystallization temperature to room temperature In the process, stress in the compression direction was applied to the piezoelectric film, and the increase in the 90 ° domain was successfully suppressed.

  As a result of further intensive research, an intermediate film having a larger thermal expansion coefficient than that of the piezoelectric film is patterned to correspond to the driving region of the unimorph type piezoelectric film element on the diaphragm, thereby making the piezoelectric film more efficient. A stress in the compression direction was applied to successfully suppress the generation of the 90 ° domain.

  That is, an intermediate film having a large thermal expansion coefficient that satisfies the above relationship is interposed between the diaphragm and the piezoelectric film, and the intermediate film is patterned in the same manner as the piezoelectric film in accordance with the movable region of the diaphragm, thereby transferring the transfer process. It is possible to form an excellent unimorph type piezoelectric film element by directly forming a piezoelectric film on the vibration plate without using the material. In addition, it is possible to realize a high-performance and inexpensive liquid discharge head using a unimorph type piezoelectric film element manufactured using this method as a drive source.

  As shown in FIG. 1, a diaphragm 2 is formed on a substrate 1 having a hollow portion 1a, and an electrode film 4 and a piezoelectric film 5 are laminated via an intermediate film 3 such as an MgO film. The intermediate film 3 has a thermal expansion coefficient larger than that of the piezoelectric film 5, and the intermediate film 3, the electrode film 4, and the piezoelectric film 5 are patterned corresponding to the shape of the hollow portion 1 a of the substrate 1 that is the movable region of the diaphragm 2. The surface of the diaphragm 2 is exposed at a portion other than the upper portion of the hollow portion 1a.

Various materials can be used for the diaphragm material, but SiO ₂ and SiN obtained by oxidizing or nitriding Si are less likely to peel off from Si used as a substrate material, and the thickness of the diaphragm This is preferable because it can be freely controlled in a thin range that is difficult to polish. In addition, a glass substrate having a low Young's modulus and high heat resistance is also preferable. In particular, a borosilicate glass, an aluminosilicate glass, or an aluminoborosilicate that is close to the Si substrate and has a high thermal expansion coefficient and hardly peels off after anodic bonding. A glass substrate is preferred.

  Any film forming method can be used as the method for forming the piezoelectric film, and examples include RF sputtering, ion beam sputtering, ion plating, EB deposition, plasma CVD, MO-CVD, and laser ablation. Although any film formation method can produce an oxide thin film, the composition greatly contributes to the characteristics in the production of a piezoelectric film. Therefore, the composition of the substrate can be varied and the composition can be controlled by gas pressure. Easy RF sputtering is preferred.

As the piezoelectric film, various films having piezoelectricity can be used, and a perovskite structure oxide containing Pb is particularly desirable. For example, Pb (Zr, Ti) O ₃ , (Pb, La) (Zr, Ti) O _{3 and the} like can be 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 (represented as so-called PZN-PT) and Pb (Mg, Nb) O ₃ —PbTiO ₃ solid solution (represented as so-called PMN-PT). Etc.) has a very large piezoelectric characteristic that greatly exceeds PZT and is preferable as a material.

For the intermediate film having a larger thermal expansion coefficient than that of the piezoelectric film, various film materials having a large thermal expansion coefficient can be used. In particular, MgO having a thermal expansion coefficient of 13.0 × 10 ⁻⁶ (/ ° C.), heat ZrO _{2 with} an expansion coefficient of 11.5 × 10 ⁻⁶ (/ ° C.) and Cu with a thermal expansion coefficient of 16.8 × 10 ⁻⁶ (/ ° C.) have a particularly large thermal expansion coefficient and are also heat resistant. It is also excellent as a material.

  The intermediate film and the piezoelectric film are preferably patterned so as to leave only a movable region facing the hollow part of the substrate so that the compressive stress at the time of cooling can be effectively used by deforming the diaphragm. The same effect can be obtained simply by making the intermediate film discontinuous at the peripheral part of the movable region facing the surface. Further, even if a part of the peripheral portion of the movable region facing the hollow portion is discontinuous, it is more effective than the case where it is completely continuous.

  FIGS. 2 and 3 show a liquid discharge head on which a unimorph type piezoelectric film element is mounted. On a substrate 21 provided with a liquid flow path such as a pressure chamber 21a, a discharge port (nozzle) 21b, a liquid supply port 21c. A thin diaphragm 22 is formed. On the diaphragm 22 located on the liquid flow path, the intermediate film 23 having a larger thermal expansion coefficient than the piezoelectric film 25 is the thermal expansion coefficient of the intermediate film 23 x Young's modulus x thickness-thermal expansion coefficient of the diaphragm 22 x Young's modulus. × Thickness ≧ thermal expansion coefficient of piezoelectric film 25 × Young's modulus × thickness is satisfied, and the intermediate film 23 is not formed on the partition between the liquid flow paths and is discontinuous. On the intermediate film 23, a first electrode film 24 of a noble metal that also serves to prevent diffusion of atoms is formed, and a piezoelectric film 25 is formed thereon. Further, a second electrode film 26 is formed thereon.

  In this way, a thin diaphragm is bonded onto a substrate such as a Si substrate that has been processed in advance, and an intermediate film having a larger thermal expansion coefficient than that of the piezoelectric film is laminated thereon, and the intermediate film is a liquid that is a hollow portion of the substrate. Patterning is performed so as to be located only in the movable region of the diaphragm that deforms in opposition to the flow path. A first electrode film such as a noble metal is provided on the intermediate film, and then the piezoelectric film is formed by heating or crystallization while being heated or non-heated and then crystallized by firing, thereby applying a compressive stress to the piezoelectric film when the temperature is lowered. The configuration allows the piezoelectric film to be formed directly on the diaphragm without deteriorating the piezoelectricity.

  A second electrode film made of a noble metal or the like is formed on the piezoelectric film, and a liquid discharge head using a unimorph type piezoelectric film element as a drive source is manufactured. Since it is possible to form a diaphragm by anodic bonding after processing the pressure channel and the liquid flow path that becomes the discharge port on the Si substrate, it is possible to directly form a high-performance piezoelectric film on it. High-definition and high-quality liquid discharge heads can be produced with high yield.

As shown in FIG. 1, an intermediate film 3 and an electrode film 4 are laminated on a SiO ₂ diaphragm ₂ formed by thermal oxidation on a substrate 1 which is a Si substrate having a hollow structure, and RF sputtering is used as a film forming method. A PZT film was formed without using heat, and then baked to form the piezoelectric film 5 to produce a unimorph type piezoelectric film element. The specific manufacturing process is as follows.

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 a groove (hollow part), and a SiO ₂ film serving as a diaphragm was formed on a hollow Si substrate. The thermal expansion coefficient of SiO ₂ constituting the diaphragm is 0.2 × 10 ⁻⁶ (/ ° C.), and the Young's modulus is 7.2 × 10 ¹⁰ (N / m ² ). On this, an intermediate film of 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 at room temperature. Thereafter, post-heat treatment was performed at 750 ° C.

The graphs of FIGS. 9 and 10 show X-ray diffraction patterns before and after firing on the SiO ₂ of the MgO intermediate film. Both before and after firing are preferentially oriented to MgO (111). MgO (200) is also seen, and is 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 ). The MgO film having a large thermal expansion coefficient was removed by wet etching, leaving only the portion corresponding to the hollow portion of the substrate. 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 to a thickness of 150 nm. On top of that, an amorphous PZT layer was formed on the surface of 1 μm by RF sputtering at a substrate heater OFF and a display Ar gas pressure of 3.0 Pa. This amorphous PZT layer is usually crystallized by post-heat treatment at 650 ° C. on an MgO substrate to become a PZT film which is a piezoelectric film. 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 amorphous PZT layer was annealed in an oxygen atmosphere at an elevated temperature of 1 ° C./min and 650 ° C. for 5 hours to perform crystallization. As the cooling process proceeds from the crystallization temperature, the thermal contraction of the diaphragm is very small as shown by the arrow in FIG. The intermediate film of MgO having a large thermal expansion coefficient cancels tension and tries to work in the compression direction.

(Thermal expansion coefficient of the intermediate film MgO × Young's modulus × thickness) − (Thermal expansion coefficient of the diaphragm SiO ₂ × Young's modulus × thickness) ≧ (Thermal expansion coefficient of the piezoelectric film PZT × Young's modulus × thickness) Since the thickness of each film is set so as to satisfy the relationship, and (thermal expansion coefficient of the intermediate film MgO)> (thermal expansion coefficient of the piezoelectric film PZT), the temperature range from the crystallization temperature to room temperature is satisfied. A compression force acts on the piezoelectric film PZT.

Furthermore, the diaphragm SiO ₂ is as thin as 1 μm, and the intermediate film MgO is formed only in the movable region of the diaphragm that deforms facing the hollow portion of the Si substrate. There is little restraint from the diaphragm, and the diaphragm facing the hollow portion of the Si substrate is greatly deformed toward the hollow portion with respect to the large shrinkage of the MgO layer during the cooling process, and the compression stress is not lost (( b)).

As a result, an increase in 90 ° domain was suppressed when PZT was cooled from the firing temperature to room temperature. Further, the diaphragm SiO ₂ was provided on the Si substrate by thermal oxidation, and no problem occurred even when baked at 650 ° C. Thereafter, Pt serving as the second electrode film was formed on the crystallized PZT surface by RF sputtering. Pt on the piezoelectric film PZT was patterned by dry etching in accordance with the shape of the hollow portion of the Si substrate. Further, the piezoelectric film PZT was etched by wet etching along the Pt pattern.

  When the electrical characteristics of the piezoelectric film PZT were measured, it showed a good squareness ratio and a high saturation electric flux density in the PE curve, which is the relationship between the electric field strength and the electric flux density, and showed good hysteresis characteristics. Further, when the unimorph type piezoelectric film element thus produced 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.

  As shown in FIG. 2, a thermal oxide film serving as a vibration plate 22 is transferred onto a substrate 21 which is a Si substrate provided with liquid flow paths such as a pressure chamber 21a, a nozzle 21b, and a liquid supply port 21c. After the MgO intermediate film 23 having a very large thermal expansion coefficient is formed on the first electrode film 24, the first electrode film 24 is laminated, and further, RF sputtering is used as the film formation method, and the piezoelectric film 25 is made of an amorphous material. A PZT layer was formed without heating, followed by firing, and a second electrode film 26 was formed thereon, thereby producing a liquid discharge head using the unimorph piezoelectric film element 20 as a drive source. The specific manufacturing process is as follows.

A groove serving as a liquid flow path including a pressure chamber, a liquid supply port, a discharge port, and the like was formed on the Si (100) substrate using an ICP dry etching technique. Thereafter, the Si substrate on which the thermal oxide film 1 μm is formed is attached to the Si substrate on which the liquid flow path is formed by using solid phase bonding, and the Si substrate on which the thermal oxide film is formed is wet-etched from the back surface. Thus, a diaphragm made of a thermal oxide film SiO ₂ having a thickness of 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 controlled by RF sputtering to display Ar gas pressure = 0.14 Pa, O ₂ flow rate / Ar flow rate = 5%, and a thickness of 1.0 μm was formed at room temperature. Thereafter, post-heat treatment was performed at 750 ° C.

Before and after firing the MgO film, both are preferentially oriented to MgO (111). However, MgO (200) is also observed, and it is 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 ). The MgO film having a large thermal expansion coefficient was removed by wet etching while leaving only the portion corresponding to the liquid flow path of the substrate. 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 film was formed thereon by RF sputtering to a thickness of 150 nm. An amorphous PZT layer having a thickness of 1 μm was formed thereon by RF sputtering with a substrate heater OFF and a display Ar gas pressure of 3.0 Pa. This amorphous PZT layer becomes a PZT layer crystallized by post-heat treatment at 650 ° C. 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 amorphous PZT layer was annealed in an oxygen atmosphere at an elevated temperature of 1 ° C./min and 650 ° C. for 5 hours to perform crystallization. In the thermal contraction of each layer from the crystallization temperature to room temperature, the thermal contraction of the diaphragm is very small and acts on the other layers, and the MgO layer having a large thermal expansion coefficient cancels the tension and works in the compression direction. And (Thermal expansion coefficient of the intermediate film MgO × Young's modulus × thickness) − (Thermal expansion coefficient of the diaphragm SiO ² × Young's modulus × thickness) ≧ (Thermal expansion coefficient of the piezoelectric film PZT × Young's modulus × thickness) Since the relationship is satisfied and (thermal expansion coefficient of intermediate film MgO)> (thermal expansion coefficient of piezoelectric film PZT), compression force acts on PZT in the temperature range from the crystallization temperature to room temperature ( (See (b) of FIG. 2). Further, since the diaphragm SiO ₂ is as thin as 1 μm and the intermediate film MgO layer is formed only in the movable region of the diaphragm facing the pressure chamber or the like, there are few constraints from the undeformed diaphragm facing the partition wall portion. . Therefore, the diaphragm facing the pressure chamber is greatly deformed to the pressure chamber side with respect to the large shrinkage of the MgO layer in the cooling process, and the compression stress is not lost. As a result, an increase in 90 ° domain was suppressed when PZT was cooled from the firing temperature to room temperature.

Further, the diaphragm SiO ₂ is a thermal oxidation acid of Si, and no problem occurred even when baked at 650 ° C. Thereafter, Pt serving as the second electrode film was formed on the crystallized PZT surface by RF sputtering. The electrode film Pt on the PZT film was patterned by dry etching according to the flow path of the Si substrate. Further, the PZT film 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.

  In this embodiment, a unimorph type piezoelectric film element is used in which a diaphragm is attached to one surface of a piezoelectric film element in which electrode films are provided above and below the piezoelectric film. By performing various processes on the Si substrate in advance, various devices using unimorph type piezoelectric film elements can be manufactured. In order to confirm the discharge of the liquid discharge head on which the unimorph type piezoelectric film element of this embodiment is mounted, the liquid discharge head is filled with IPA and driven by the drive waveform as shown in FIG. I was able to confirm.

  The liquid discharge head using the unimorph type piezoelectric film element 20 having the film configuration shown in FIG. 2 as a drive source is preliminarily used for the liquid flow such as the pressure chamber 21a, the discharge port 21b, and the liquid supply port 21c by using RF sputtering as a film forming method. An aluminosilicate glass SD2 (registered trademark of HOYA Co., Ltd.) serving as a diaphragm 22 is anodically bonded on a substrate 21 which is a Si substrate provided with a path, and an MgO intermediate film 23 having a very large thermal expansion coefficient is formed thereon. A PZT film to be a piezoelectric film 25 was formed thereon by non-heated film formation and post-baking, and a liquid discharge head using a unimorph type piezoelectric film element as a drive source was produced. A specific manufacturing method is as follows.

A groove serving as a liquid flow path was formed on the Si (100) substrate using the ICP dry etching technique in the same manner as in Example 2. Thereafter, an aluminosilicate glass SD2 having a thickness of 30 μm was attached to the Si substrate having the grooves as an oscillating plate by anodic bonding, and the aluminosilicate glass SD2 was thinned to 3 μm by polishing. The aluminosilicate glass SD2 has a thermal expansion coefficient of 3.2 × 10 ⁻⁶ (/ ° C.) and a Young's modulus of 8.9 × 10 ¹⁰ (N / m ² ). On the aluminosilicate glass thinned by polishing, MgO having a large thermal expansion coefficient is controlled by RF sputtering to display Ar gas pressure = 0.14 Pa, O ₂ flow rate / Ar flow rate = 5%, and a thickness of 1 at room temperature. A film was formed to a thickness of 0.0 μm. 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 ). The MgO film having a large thermal expansion coefficient was removed by wet etching while leaving only the portion corresponding to the liquid flow path of the substrate. 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 film was formed thereon by RF sputtering to a thickness of 150 nm. An amorphous PZT layer having a thickness of 1 μm was formed thereon by RF sputtering with a substrate heater OFF and a display Ar gas pressure of 3.0 Pa. This amorphous PZT layer becomes non-oriented PZT even after post-heat treatment at 650 ° C., which is lower than the strain point of the aluminosilicate glass SD2. 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 amorphous PZT layer was annealed in an oxygen atmosphere at an elevated temperature of 1 ° C./min and 650 ° C. for 5 hours to perform crystallization. As shown in FIG. 2 (b), the thermal contraction of the diaphragm 22 is very small and acts on the other layers. The intermediate film MgO layer 23 having a large thermal expansion coefficient cancels the tension and tries to work in the compression direction.

  (Thermal expansion coefficient of the intermediate film MgO × Young's modulus × thickness) − (Thermal expansion coefficient of the diaphragm SD2 × Young's modulus × thickness) ≧ (Thermal expansion coefficient of the piezoelectric film PZT × Young's modulus × thickness) And (the thermal expansion coefficient of the intermediate film MgO)> (thermal expansion coefficient of the piezoelectric film PZT), the compression force acts on PZT in the temperature range from the crystallization temperature to room temperature. Further, since the glass serving as the vibration plate is as thin as 3 μm, and the intermediate film MgO layer is formed only on the vibration plate that deforms facing the liquid flow path of the Si substrate, the partition walls other than the liquid flow path of the Si substrate There is little constraint from the diaphragm that does not deform in the non-movable region facing the part, and the diaphragm on the Si substrate is greatly deformed to the pressure chamber side due to the large shrinkage of the MgO layer during the cooling process, and the compression stress is lost. Absent. As a result, an increase in 90 ° domain was suppressed when PZT was cooled from the firing temperature to room temperature. The aluminosilicate glass SD2 had a strain point of 667 ° C., and no problem occurred even when baked at 650 ° C.

  FIG. 12 shows the change in thermal expansion coefficient with respect to the temperature of the Si substrate and the aluminosilicate glass SD2 (extracted from HOYA catalog). As can be seen from this graph, the Si substrate and the aluminosilicate glass SD2 have very close thermal expansion coefficients up to a high temperature, and no problems such as peeling occurred even after firing.

  Thereafter, Pt serving as the second electrode film was formed on the crystallized PZT surface by RF sputtering, and the first electrode film Pt on the PZT was patterned by dry etching in accordance with the liquid flow path of the Si substrate. . 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 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 having a diaphragm attached is formed on one surface of a piezoelectric film element in which electrodes are provided above and below the piezoelectric film. By performing various processes on the Si substrate in advance, not only the liquid ejection head but also various devices using unimorph type piezoelectric film elements can be manufactured. When the liquid discharge head of this example was filled with IPA and driven by the drive waveform as shown in FIG. 11, the discharge of droplets could be confirmed.

  The liquid ejection head using the unimorph type piezoelectric film element 20 having the film configuration shown in FIG. 2 as a driving source is formed on the substrate 21 which is a Si substrate provided with a liquid channel in advance by using RF sputtering as a film forming method. An aluminosilicate glass SD2 to be 22 is anodically bonded, and a PZT film to be a piezoelectric film 25 is formed thereon while heating the substrate 21 to crystallize, and a liquid discharge head using a unimorph type piezoelectric film element as a drive source is formed. Produced. A specific manufacturing method will be described below.

A groove serving as a liquid flow path was formed on the Si (100) substrate using the ICP dry etching technique in the same manner as in Example 2. Thereafter, an aluminosilicate glass SD2 having a thickness of 30 μm was attached as a vibration plate on the Si substrate having grooves formed by anodic bonding, and the aluminosilicate glass SD2 was thinned to 5 μm by polishing. The aluminosilicate glass SD2 has a thermal expansion coefficient of 3.2 × 10 ⁻⁶ (/ ° C.) and a Young's modulus of 8.9 × 10 ¹⁰ (N / m ² ). MgO having a large thermal expansion coefficient is displayed on the aluminosilicate glass thinned by polishing by RF sputtering, Ar gas pressure = 0.14 Pa, O ₂ flow rate / Ar flow rate = 5%, and a thickness of 1. A film was formed to 0 μm. 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 ).

The MgO layer having a large thermal expansion coefficient was removed by wet etching, leaving only the portion corresponding to the liquid flow path of the Si substrate. 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 film was formed thereon by RF sputtering to a thickness of 150 nm. On top of this, a PZT film as a piezoelectric film was formed to a thickness of 3 μm while crystallizing at a substrate temperature of 650 ° C. and a display Ar gas pressure of 3.0 Pa. 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 ).

  (Thermal expansion coefficient of intermediate film MgO × Young's modulus × thickness) − (thermal expansion coefficient of diaphragm × Young's modulus × thickness) ≧ (thermal expansion coefficient of piezoelectric film PZT × Young's modulus × thickness) And satisfying the relationship of (thermal expansion coefficient of the intermediate film MgO)> (thermal expansion coefficient of the piezoelectric film PZT), the compression force acts on the PZT in the temperature range from the crystallization temperature to room temperature, Furthermore, the glass to be the vibration plate is as thin as 5 μm, and the MgO layer is formed only on the vibration plate deformed to oppose the pressure chamber of the Si substrate, so that it faces the partition walls other than the pressure chamber of the Si substrate. The restraint from the diaphragm that is not deformed in the non-movable region is small, and the diaphragm is largely deformed to the pressure chamber side with respect to the large contraction of the MgO layer in the cooling process, and the compression stress is not lost. For this reason, an increase in 90 ° domain was suppressed when PZT was cooled from the firing temperature to room temperature. Further, as shown in FIG. 12, the Si substrate and the aluminosilicate glass have very close thermal expansion coefficients up to a high temperature, and no peeling occurred even when the substrate temperature was raised, held, and lowered to 650 ° C.

  Pt serving as the second electrode film was formed on the crystallized PZT surface by RF sputtering. The first electrode film Pt on PZT was patterned by dry etching in accordance with the liquid flow path of the Si substrate. 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.

  When the liquid discharge head of this example was filled with IPA and driven by the drive waveform as shown in FIG. 11, the discharge of droplets could be confirmed.

  The unimorph type piezoelectric film element of the present invention is not limited to a liquid discharge head, and can be widely applied to various devices using a piezoelectric driving force.

BRIEF DESCRIPTION OF THE DRAWINGS The unimorph type piezoelectric film element by one Embodiment is shown, (a) is the schematic cross section, (b) is a figure explaining the compressive stress in the crystallization process of a piezoelectric film. 4A and 4B show a liquid discharge head according to another embodiment, in which FIG. 5A is a schematic cross-sectional view taken along a liquid flow path, and FIG. 5B is a schematic cross-sectional view taken along line AA in FIG. It is. FIG. 3 is a perspective view showing the liquid discharge head of FIG. 2. It is a figure which shows the X-ray-diffraction pattern of a PZT film | membrane. It is a graph explaining the surface interval of the crystal plane (112) of a PZT film | membrane. It is a figure explaining the condition where a 90 degree domain increases by tensile stress. It is a graph which shows the electrical property of a PZT film | membrane when a 90 degree domain increases. It is a graph which shows the electrical property of the PZT film | membrane at the time of suppressing a 90 degree domain. It is a figure which shows the X-ray-diffraction pattern before baking of intermediate film MgO. It is a figure which shows the X-ray-diffraction pattern after baking of intermediate film MgO. It is a figure which shows the drive waveform of a unimorph type piezoelectric film element. It is a graph which compares the thermal expansion of aluminosilicate glass SD2 and Si.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 21 Substrate 1a Hollow part 2, 22 Diaphragm 3, 23 Intermediate film 4, 24, 26 Electrode film 5, 25 Piezoelectric film 20 Unimorph type piezoelectric film element 21a Pressure chamber 21b Discharge port 21c Liquid supply port

Claims (8)

A unimorph piezoelectric film element comprising a diaphragm and a piezoelectric film laminated on the diaphragm, wherein the piezoelectric film is placed on the diaphragm via an intermediate film having a larger thermal expansion coefficient than the piezoelectric film. The intermediate film is patterned so as to correspond to the movable region of the diaphragm, and between the thermal expansion coefficient, Young's modulus, and thickness of each of the diaphragm, the intermediate film, and the piezoelectric film. A unimorph type piezoelectric film element characterized in that the following relationship is established.
(Thermal expansion coefficient of intermediate film × Young's modulus × thickness) − (thermal expansion coefficient of diaphragm × Young's modulus × thickness) ≧ (thermal expansion coefficient of piezoelectric film × Young's modulus × thickness) The unimorph type piezoelectric film element according to claim 1, wherein the intermediate film is an MgO film, a ZrO ₂ film, or a Cu film.   The unimorph type piezoelectric film element according to claim 1 or 2, wherein the piezoelectric film is an oxide having a perovskite structure containing at least Pb.   4. A unimorph type piezoelectric film element according to claim 1, wherein the diaphragm has a thickness of 10 [mu] m or less.   5. The unimorph type piezoelectric film element according to claim 1, wherein the diaphragm is formed by oxidizing or nitriding a Si substrate.   The unimorph type piezoelectric film element according to any one of claims 1 to 4, wherein the vibration plate is formed of a glass plate. A liquid discharge head that pressurizes liquid in a liquid flow path by a piezoelectric driving force and discharges the liquid from a discharge port, the substrate having the liquid flow path, a vibration plate integrated with the substrate, and laminated on the vibration plate. A piezoelectric film and electrode means for supplying piezoelectric driving power to the piezoelectric film, and the piezoelectric film is laminated on the diaphragm via an intermediate film having a larger thermal expansion coefficient than the piezoelectric film. The intermediate film is patterned so as to correspond to the liquid flow path, and the following relationship is established between the thermal expansion coefficient, Young's modulus, and thickness of the diaphragm, the intermediate film, and the piezoelectric film: A liquid discharge head characterized by being established.
(Thermal expansion coefficient of intermediate film × Young's modulus × thickness) − (thermal expansion coefficient of diaphragm × Young's modulus × thickness) ≧ (thermal expansion coefficient of piezoelectric film × Young's modulus × thickness) A method for producing a unimorph-type piezoelectric film element comprising a diaphragm and a piezoelectric film laminated on the diaphragm,
Laminating an intermediate film having a larger thermal expansion coefficient than the piezoelectric film on the diaphragm;
Patterning the intermediate film corresponding to the movable region of the diaphragm;
Laminating and crystallizing a piezoelectric film on the intermediate film, and the following relationship is established among the thermal expansion coefficient, Young's modulus, and thickness of each of the diaphragm, the intermediate film, and the piezoelectric film: A method for producing a unimorph type piezoelectric film element.
(Thermal expansion coefficient of intermediate film × Young's modulus × thickness) − (thermal expansion coefficient of diaphragm × Young's modulus × thickness) ≧ (thermal expansion coefficient of piezoelectric film × Young's modulus × thickness)

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