JP2014183076A - Piezoelectric material thin film element, method for manufacturing the same, piezoelectric actuator, droplet discharge head, and droplet discharge device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric material thin film element which allows a droplet discharge characteristic to be kept well, and allows a stable droplet discharge characteristic to be achieved even when continuously discharging a droplet.SOLUTION: A piezoelectric material thin film element comprises: a vibration plate formed on a substrate; a lower electrode formed on the vibration plate; a piezoelectric material thin film formed on the lower electrode; and an upper electrode formed on the piezoelectric material thin film. The lower electrode includes: a metal film containing a platinum group or an alloy including a platinum group metal, and having (111) orientation; LaNiOformed on the metal film; and SrRuOformed on the LaNiO. The SrRuOhas a thickness of 60-80 nm.

Description

  The present invention relates to a piezoelectric thin film element used as a drive source for a droplet discharge head for discharging a droplet of ink or the like provided in an image forming apparatus such as an ink jet printer, facsimile, or copying machine, and the piezoelectric The present invention relates to a method for manufacturing a body thin film element, and a piezoelectric actuator, a droplet ejection head, and a droplet ejection apparatus including the piezoelectric thin film element.

An ink jet recording apparatus (droplet discharge apparatus) and a liquid discharge head used as an image recording apparatus or an image forming apparatus such as a printer, a facsimile machine, a copying apparatus, etc. have the configuration as shown in FIG.
The liquid discharge head 1 includes a nozzle 11 that discharges ink droplets (droplets), a pressurizing chamber 21 that communicates with the nozzles 11 (an ink channel, a pressurized liquid chamber, a pressure chamber, a discharge chamber, a liquid chamber, and the like). And an energy generating means for pressurizing the ink in the pressurizing chamber 21. The energy generating means includes a piezoelectric thin film element 40. Ink droplets are ejected from the nozzle 11 by pressurizing the ink in the pressurizing chamber 21 with the energy generated by the energy generating means.

There are two types of liquid ejection heads, one that uses a longitudinal vibration mode piezoelectric actuator that extends and contracts in the axial direction of the piezoelectric element, and one that uses a flexural vibration mode piezoelectric actuator.
For example, an actuator in the flexural vibration mode is used. For example, a uniform piezoelectric material layer is formed over the entire surface of the diaphragm by a film formation technique, and the piezoelectric material layer is cut into a shape corresponding to the pressure generating chamber by lithography. It is known that a piezoelectric thin film element is formed so as to be independent of each pressure generating chamber.
When the vector component of the spontaneous polarization axis of the piezoelectric film matches the electric field application direction, the expansion and contraction accompanying the increase and decrease of the electric field application intensity occurs effectively, and a large piezoelectric constant is obtained. At this time, it is most preferable that the spontaneous polarization axis of the piezoelectric film completely coincides with the electric field application direction. Further, in order to suppress variations in the ink discharge amount, it is preferable that the in-plane variation in the piezoelectric performance of the piezoelectric film is small. Considering these points, a piezoelectric film having excellent crystal orientation is preferable.

Patent Document 1 describes that a piezoelectric film having excellent crystal orientation can be formed by forming a piezoelectric film on a titanium-containing noble metal electrode on which titanium is deposited in an island shape.
Patent Document 2 describes that a piezoelectric film having excellent crystal orientation can be formed by using an MgO substrate as a substrate.
Further, Patent Document 3 discloses a method for manufacturing a ferroelectric film in which an amorphous ferroelectric film is formed, and then the film is crystallized by a rapid heating method.
Further, in Patent Document 4, in the film forming process, a perovskite complex oxide (including inevitable impurities) having any one of a tetragonal system, an orthorhombic system, and a rhombohedral system is included. And forming the piezoelectric film having a preferential orientation on any one of the (100) plane, the (001) plane, and the (111) plane and having an orientation degree of 95% or more. A method for manufacturing a piezoelectric film is described.

For the above-mentioned patent documents, many are made of lead zirconate titanate (PZT) on platinum.
Conventionally, metal materials such as Pt, Ir, Ru, Ti, Ta, Rh, and Pd have been used as the electrode material. Although generally platinum is utilized, the background having platinum frequently has strong self-orientation since a face-centered cubic lattice (FCC) structure, which is a close-packed structure, the SiO ₂ which is a material of the diaphragm This is because even if the film is formed on such an amorphous layer, it is strongly oriented to (111), and the piezoelectric film thereon is also well oriented. However, since the orientation is strong, columnar crystals grow, and there is a problem that Pb and the like are easily diffused into the base electrode along the grain boundary.

By the way, in order to form a piezoelectric thin film, a conductive oxide electrode immediately below the piezoelectric thin film is important. Moreover, the possibility that oxygen deficiency in the piezoelectric body increases with time during the operation of the piezoelectric body has been recognized as a problem.
Thus, a conductive oxide electrode has been used at the contact interface with the piezoelectric thin film as a supply source of the deficient oxygen component of the piezoelectric thin film. Specifically used material systems include IrO ₂ , LaNiO ₃ , RuO ₂ , SRO, LaNiO ₃ , SrRuO ₃ , CaRuO _3, etc. as the oxide electrode layer, and Pt, Ir, Ru, Ti, Ta, Rh, Pd, etc. are used.
Among them, SrRuO ₃ (strontium ruthenate) has the same perovskite crystal structure as PZT, so it has excellent bonding properties at the interface, facilitates the epitaxial growth of PZT, and has the characteristics of Pb as a diffusion barrier layer. Are better. (See Patent Documents 5 to 7)

Further, as a conventional lower electrode, a laminated structure in which titanium, platinum, and an SrRuO ₃ film are sequentially formed on a vibration plate has been used. The reason for using the titanium film is to improve the adhesion between the diaphragm and the lower electrode.
In contrast, the present inventors have found that the lower electrode formed of LaNiO ₃ / platinum obtains a larger piezoelectric constant than the lower electrode formed of SrRuO ₃ / platinum or the like. On the other hand, it has been found that the piezoelectric performance of a piezoelectric thin film element having a lower electrode formed of LaNiO ₃ / platinum deteriorates with time during operation of the piezoelectric body. Therefore, it has been difficult to obtain stable ink ejection characteristics during continuous ejection.

Therefore, the present inventors realize a large piezoelectric constant by controlling the film thickness range of SRO / LaNiO ₃ / platinum as the lower electrode and controlling the film thickness range of SRO, and suppress deterioration of piezoelectric performance over time. I found that I can do it. When the piezoelectric thin film element is used as a piezoelectric actuator, a sufficient initial displacement can be obtained, and a stable driving characteristic can be realized even when continuously operating.
When a piezoelectric thin film element is used as an electromechanical conversion element, the adhesion between the piezoelectric thin film, the lower electrode and the diaphragm is improved, and the diaphragm is not affected by the displacement vibration generated in the piezoelectric thin film. It is necessary not to deteriorate the vibration characteristics.

Generally, platinum group metal films have poor adhesion, and it is sometimes necessary to devise a technique for improving adhesion between the upper and lower layers of the platinum group metal film. On the other hand, the present inventors have found that a LaNiO film is excellent in adhesion with a platinum film. By adopting a laminated structure of SRO / LaNiO ₃ / platinum, it is possible to improve the adhesion of the laminated structure between the lower electrodes, and to realize stable driving characteristics even when the piezoelectric thin film element is used as an electromechanical conversion element. .

Here, Patent Document 8 discloses a first fluorite oxide layer, a second fluorite oxide layer, a third ABO ₃ perovskite oxide conductive layer, and a fourth ABO ₃ perovskite oxide on a substrate. The present invention relates to a piezoelectric thin film element having a physical conductive layer and a perovskite type dielectric layer having a {100} orientation on a fourth ABO ₃ perovskite type oxide conductive layer.

  Further, the piezoelectric thin film element described in Patent Document 9 includes a substrate, a first conductive layer formed above the substrate, and a piezoelectric body having a perovskite structure formed above the first conductive layer. A buffer made of a lanthanum-based layered perovskite compound that is preferentially oriented to (001), and a second conductive layer electrically connected to the piezoelectric layer. Contains one or more layers. With this piezoelectric thin film element, good piezoelectric characteristics can be obtained.

  However, in any of the techniques described in Patent Documents 1 to 9, a piezoelectric thin film element that can maintain good droplet discharge characteristics and can obtain stable droplet discharge characteristics even when continuously discharged. It was difficult.

  The present invention has been made in view of the above problems in the prior art, and is a piezoelectric thin film that can maintain good droplet discharge characteristics and can obtain stable droplet discharge characteristics even when continuously discharged. An object is to provide an element.

In order to solve the above problems, a piezoelectric thin film element according to the present invention includes a diaphragm formed on a substrate, a lower electrode formed on the diaphragm, and a piezoelectric thin film formed on the lower electrode. And an upper electrode formed on the piezoelectric thin film, wherein the lower electrode is a metal film having a (111) orientation made of a platinum group or an alloy containing a platinum group metal, and on the metal film. It comprises the formed LaNiO ₃ and SrRuO ₃ formed on the LaNiO ₃ , wherein the thickness of the SrRuO ₃ is 60 nm or more and 80 nm or less.

  According to the present invention, it is possible to provide a piezoelectric thin film element that can maintain good droplet ejection characteristics and can obtain stable droplet ejection characteristics even when continuously ejected.

2 is a cross-sectional view illustrating the configuration of a droplet discharge head according to the present invention. FIG. It is sectional drawing which illustrates the structure of the piezoelectric thin film element which concerns on this invention. FIG. 6 is an exploded perspective view illustrating the configuration of a droplet discharge head according to a second embodiment of the invention. It is a perspective explanatory view showing a configuration in an example of a droplet discharge device according to the present invention. It is side explanatory drawing which shows the structure of the mechanism part in an example of the droplet discharge apparatus which concerns on this invention.

A piezoelectric thin film element according to the present invention includes a vibration plate formed on a substrate, a lower electrode formed on the vibration plate, a piezoelectric thin film formed on the lower electrode, and the piezoelectric thin film. An upper electrode formed on a metal film having a (111) orientation made of a platinum group or an alloy containing a platinum group metal, LaNiO ₃ formed on the metal film, SrRuO ₃ formed on the LaNiO ₃ , wherein the thickness of the SrRuO ₃ is 60 nm or more and 80 nm or less.

Next, the piezoelectric thin film element according to the present invention will be described in more detail.
Although the embodiments described below are preferred embodiments of the present invention, various technically preferable limitations are attached thereto, but the scope of the present invention is intended to limit the present invention in the following description. Unless otherwise described, the present invention is not limited to these embodiments.

FIG. 1 is a cross-sectional view illustrating the configuration of a droplet discharge head according to the present invention. FIG. 2 is a cross-sectional view illustrating the configuration of the piezoelectric thin film element according to the invention.
FIG. 2 shows the configuration of the piezoelectric thin film element 40 shown in FIG. 1 in detail. In other words, the piezoelectric thin film element 40 is shown in a simplified manner in FIG.

  Referring to FIGS. 1 and 2, the droplet discharge head 1 generally includes a nozzle plate 10, a substrate 20, a vibration plate 30, and a piezoelectric thin film element 40. The nozzle plate 10 is formed with nozzles 11 for discharging liquid droplets (ink droplets). A pressure chamber 21 (also referred to as an ink flow path, a pressurized liquid chamber, a pressurized chamber, a discharge chamber, or a liquid chamber) that communicates with the nozzle 11 by the nozzle plate 10, the substrate 20, and the vibration plate 30. Is formed. The diaphragm 30 forms part of the wall surface of the pressure chamber 21.

  In short, the piezoelectric thin film element 40 includes a lower electrode 41, a piezoelectric thin film 42, and an upper electrode 43. The piezoelectric thin film element 40 is an element that converts an electric signal into a mechanical displacement or converts a mechanical displacement into an electric signal. The piezoelectric thin film element 40 is mounted on the vibration plate 30 formed on one surface of the substrate 20 at a position overlapping the pressure chamber 21 in plan view.

  The droplet discharge head 1 is a head that discharges ink droplets from the nozzles 11 when the piezoelectric thin film element 40 is driven. Specifically, the droplet discharge head 1 supplies power to the lower electrode 41 and the upper electrode 43 to generate stress in the piezoelectric thin film 42 to vibrate the vibration plate 30. 11 has a function of ejecting ink in the pressure chamber 21 into droplets. Note that illustration and description of ink supply means for supplying ink into the pressure chamber 21, ink flow paths, fluid resistance, and the like are omitted.

Hereinafter, each component of the droplet discharge head 1 will be described in detail.
In the droplet discharge head 1, for example, a silicon single crystal substrate can be used as the substrate 20. The thickness of the board | substrate 20 can be about 100-650 micrometers, for example. When a silicon single crystal substrate is used as the substrate 20, the pressure chamber 21 can be manufactured by processing the silicon single crystal substrate using etching such as anisotropic etching, for example.

The vibration plate 30 is deformed and displaced by the force generated by the piezoelectric thin film element 40, and has a function of ejecting ink in the pressure chamber 21 from the nozzle 11 in the form of droplets (hereinafter also referred to as ink droplets). By applying a voltage to the piezoelectric thin film element 40 to bend and vibrate, the diaphragm 30 can be displaced in the bending direction of the piezoelectric thin film element 40. The piezoelectric thin film element 40 and the diaphragm 30 on which the piezoelectric thin film element 40 is mounted may be referred to as a piezoelectric actuator.
The diaphragm 30 preferably has a predetermined strength. For example, Si, SiO ₂ , Si ₃ N ₄ or the like can be used as the material of the vibration plate 30, but it is preferable to select a material close to the linear expansion coefficient of the lower electrode 41 and the piezoelectric thin film 42.

As will be described later, lead zirconate titanate (PZT) may be used as the material of the piezoelectric thin film 42. Therefore, it is preferable to use a material having a linear expansion coefficient of about 5 × 10 ⁻⁶ to 10 × 10 ⁻⁶ close to the linear expansion coefficient 8 × 10 ⁻⁶ (1 / K) of PZT as the diaphragm 30. It is more preferable to use a material having a linear expansion coefficient of about × 10 ^{−6 to} 9 × 10 ⁻⁶ .
Examples of the material of the diaphragm 30 having a linear expansion coefficient close to that of PZT include aluminum oxide, zirconium oxide, iridium oxide, ruthenium oxide, tantalum oxide, hafnium oxide, osmium oxide, rhenium oxide, rhodium oxide, palladium oxide, and compounds thereof. Etc. The diaphragm 30 using these materials can be manufactured by a spin coater using a sputtering method or a Sol-gel (sol-gel) method.

The film thickness of the diaphragm 30 is preferably 0.1 to 10 μm, and more preferably 0.5 to 3 μm. If the film thickness of the vibration plate 30 is smaller than this range, the processing of the pressure chamber 21 becomes difficult, and if it is larger than this range, the vibration plate 30 itself becomes difficult to be deformed and displaced, and the discharge of droplets becomes unstable.
The film thickness of each diaphragm constituting film is set so that desired diaphragm rigidity and stress can be obtained in the entire diaphragm.

In the piezoelectric thin film element 40, the diaphragm 30, the lower electrode 41, the piezoelectric thin film 42, and the upper electrode 43 are arranged on the substrate 20 in this order by a technique used in manufacturing a film structure such as a semiconductor manufacturing process. It is formed by forming a film.
The lower electrode 41 of the piezoelectric thin film element 40 includes an adhesion layer 41a, a metal film 41b, a LaNiO ₃ film 41c, and a SrRuO ₃ film 41d. The thickness of the lower electrode 41 (the total thickness of the adhesion layer 41a, the metal film 41b, the LaNiO ₃ film 41c, and the SrRuO ₃ film 41d) can be set to, for example, about 50 to 400 nm.

The metal film 41b is indirectly formed on the vibration plate 30 via the adhesion layer 41a. However, the adhesion layer 41 a may be omitted and the metal film 41 b may be formed directly on the vibration plate 30.
As the material of the adhesion layer _{41a, Cr, TiW, Ti,} is formed by laminating before the _{TiO 2, Ta, Ta 2 O} 5, Ta 3 N 5 like the lower electrode 41 other than the adhesion layer 41a and. This is inserted when the adhesion between the diaphragm 30 and the metal film 41b is low.
The metal film 41b includes a layer having (111) orientation. Examples of the material of the metal film 41b include platinum group metals such as platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and these platinum group metals. An alloy material containing can be used.
For example, the thickness of the metal film 41b is preferably 250 nm or less. The metal film 41b can be formed by, for example, sputtering or vacuum deposition.

The LaNiO ₃ film 41c is formed on the metal film 41b. The thickness of the LaNiO ₃ film 41c can be, for example, about 40 to 150 nm. The LaNiO ₃ film 41c can be formed by, for example, sputtering.
LaNiO ₃ film 41c will vary the quality of LaNiO ₃ film by sputtering conditions. For example, it is preferable to form a LaNiO ₃ film by heating at a film formation temperature of 200 ° C. or higher and 600 ° C. or lower. If it is out of this range, sufficient characteristics cannot be obtained with respect to the initial displacement as the piezoelectric actuator in which the piezoelectric thin film is subsequently formed.

The SrRuO ₃ film 41d is formed on the LaNiO ₃ film 41c. The SrRuO ₃ film 41d has a function of replenishing the deficient oxygen component when oxygen deficiency occurs in the piezoelectric thin film 42 over time. The thickness of the SrRuO ₃ film 41d is preferably in the range of 60 to 80 nm. If it is out of this range, sufficient characteristics cannot be obtained for displacement deterioration after continuous driving as a piezoelectric actuator having a piezoelectric thin film formed thereon.
In the SrRuO ₃ film 41d, the film quality of the SrRuO ₃ film varies depending on the sputtering conditions. For example, it is preferable to form a SrRuO ₃ film by heating at a deposition temperature of 450 ° C. or higher and 600 ° C. or lower. If it is out of this range, sufficient characteristics cannot be obtained with respect to the initial displacement as the piezoelectric actuator in which the piezoelectric thin film is subsequently formed.

Regarding the composition ratio of Sr and Ru after film formation, Sr / Ru is preferably 0.82 or more and 1.22 or less. If it is out of this range, the specific resistance increases, and sufficient conductivity as an electrode cannot be obtained.
The SrRuO ₃ film 41d preferably has a surface roughness of 15 nm or less.

The possibility that oxygen deficiency in the piezoelectric body increases with time during the operation of the piezoelectric body has been recognized as a conventional problem. A conductive oxide electrode has come to be used as a supply source of the deficient oxygen component. That is, the oxide electrode layer (41d) is used at the contact interface with the dielectric material. Among them, SrRuO ₃ (strontium ruthenate) has the same perovskite crystal structure as PZT, so it has excellent bondability at the PZT interface, facilitates the epitaxial growth of PZT, and has the characteristics as a Pb diffusion barrier layer. Is also excellent.

The piezoelectric thin film 42 is made of PZT. PZT is a solid solution of lead zirconate (PbTiO ₃ ) and titanic acid (PbTiO ₃ ), and the characteristics differ depending on the ratio. In general, the composition exhibiting excellent piezoelectric properties has a ratio of PbZrO ₃ and PbTiO ₃ of 53:47. When expressed by a chemical formula, Pb (Zr0.53, Ti0.47) O ₃ , general PZT (53/47 ). Examples of composite oxides other than PZT include barium titanate. In this case, it is also possible to prepare a barium titanate precursor solution by dissolving barium alkoxide and a titanium alkoxide compound in a common solvent. is there.

These materials are described by the general formula ABO ₃ and correspond to composite oxides containing A = Pb, Ba, Sr, B = Ti, Zr, Sn, Ni, Zn, Mg, and Nb as main components. Specific descriptions thereof are (Pb _1-x , Ba _x ) (Zr, Ti) O ₃ , (Pb _1-x , Sr _x ) (Zr, Ti) O ₃ , and this is part of Pb at the A site. This is the case when it is replaced with Ba or Sr. Such substitution is possible with a divalent element, and the effect thereof has an effect of reducing characteristic deterioration due to evaporation of lead during heat treatment.

As a manufacturing method, it is possible to manufacture by a spin coater using a sputtering method or a Sol-gel (sol-gel) method. In that case, since patterning is required, a desired pattern is obtained by photolithography etching or the like.
When PZT is produced by the Sol-gel method, a PZT precursor solution is produced by using lead acetate, zirconium alkoxide, and titanium alkoxide compound as starting materials and dissolving in methoxyethanol as a common solvent to obtain a uniform solution. Since the metal alkoxide compound is easily hydrolyzed by moisture in the atmosphere, an appropriate amount of a stabilizer such as acetylacetone, acetic acid or diethanolamine may be added to the precursor solution as a stabilizer.
When a PZT film is obtained on the entire surface of the base substrate, it is obtained by forming a coating film by a solution coating method such as spin coating and performing heat treatments such as solvent drying, thermal decomposition, and crystallization. Since the transformation from the coating film to the crystallized film involves volume shrinkage, it is necessary to adjust the precursor concentration so that a film thickness of 100 nm or less can be obtained in one step in order to obtain a crack-free film.

  The film thickness of the piezoelectric thin film 42 is preferably 0.5 to 5 μm, more preferably 1 μm to 2 μm. If it is smaller than this range, it will not be possible to generate a sufficient displacement, and if it is larger than this range, many layers will be laminated, resulting in an increase in the number of steps and a longer process time.

  Unlike the lower electrode 41, the upper electrode 43 does not have a high-temperature process as in the formation of the piezoelectric thin film 42, and does not require lattice constant matching with the piezoelectric thin film 42. An upper electrode 43 is formed on the upper layer of the piezoelectric thin film 42.

  As the material of the upper electrode 43, the same material as that of the lower electrode 41 can be used. The material of the upper electrode is different from the material of the lower electrode 41, because a high-temperature process such as the formation of the piezoelectric thin film 42 is not a subsequent process, and lattice constant matching with the piezoelectric thin film 42 is not required. The material selection width is wider than that of the lower electrode 41. However, since the possibility that oxygen vacancies in the piezoelectric thin film 42 increase with time during the operation of the piezoelectric body has been recognized as a problem, a conductive oxide electrode is used as a supply source of the deficient oxygen component. It has been used. That is, the oxide electrode layer (41d) described in the material section of the lower electrode 41 is used at the contact interface with the dielectric material.

Therefore, the material system specifically used is the same as that of the lower electrode, and SrRuO ₃ and LaNiO ₃ are used as the oxide electrode layer, and IrO ₂ , RuO ₂ , SrO, and CaRuO ₃ are used as the other electrode layers. Moreover, Pt, Ir, Ru, Ti, Cr, Ta, Rh, Pd, etc. are used as a metal electrode layer.

As a process for forming the upper electrode, a sputter film formation method is mainly employed. In addition, it can carry out by well-known methods, such as a vacuum evaporation method and CVD (Chemical Vapor Deposition) method.
The film thickness of the upper electrode can be formed in the range of about 50 to 300 nm in total from the oxide electrode layer to the electrode layer.

In order to obtain the piezoelectric thin film element 40 processed into a predetermined shape, for example, after the upper electrode 43 is formed, a mask layer at the time of etching is formed on the upper electrode 43 by patterning a photosensitive resist, and dry etching or wet etching is performed. . The patterning of the photosensitive resist can be performed by a known photolithography technique.
That is, a photosensitive resist is applied on the upper electrode 43 by a spin coater or a roll coater, and then exposed to ultraviolet rays with a glass photomask on which a desired pattern has been formed in advance, followed by pattern development → water washing → drying to form a photosensitive resist mask layer. Form. In the formed photosensitive resist mask layer, since the edge inclination of the pattern affects the inclined cross section during etching, the resist selectivity (the etching rate between the etching target material and the mask material depends on the desired inclination angle). Ratio). The photosensitive resist remaining on the film after etching can be removed by a dedicated stripping solution or oxygen plasma ashing.

Etching is often selected from dry etching using a reactive gas because of the stability of the shape. However, the etching gas is a halogen-based gas such as chlorine or fluorine, or Ar or oxygen is added to the halogen-based gas. It can be carried out with a mixed gas. By changing the etching gas or etching conditions, the upper electrode 43 and the piezoelectric thin film 42 can be continuously etched, or the resist pattern can be re-formed once and etched in several times. .
Instead of the above-described method, the electromechanical conversion film 42 is processed (etched) into a predetermined shape before the upper electrode 43 is formed, and then the upper electrode 43 is formed only on the piezoelectric thin film 42 having a predetermined shape. May be.

  As can be seen from the above description, the piezoelectric thin film element 40 can be formed by a simple manufacturing process, has performance equivalent to that of bulk ceramics, and is etched away from the back surface for forming the pressure chamber 31 thereafter. The droplet discharge head 1 can be manufactured by joining the nozzle plate 10 having the nozzles 11.

  A piezoelectric actuator according to the present invention includes the above-described piezoelectric thin film element, and a droplet discharge head according to the present invention includes the piezoelectric actuator. Further, the droplet discharge apparatus according to the present invention includes: The droplet discharge head is provided. For these, well-known and conventional ones can be used except for the structure of the piezoelectric thin film element described above. These details will be described later in Examples.

Hereinafter, examples of the present invention and comparative examples compared with the examples will be described.
In these examples, the configuration of the electromechanical conversion element as the piezoelectric thin film element is the same as that shown in FIG. In addition, about the matter which is not stated in the following description, the already stated matter is used suitably.

<Example 1>
In Example 1, the diaphragm 30 was formed on the substrate 20 and the piezoelectric thin film element 40 was formed on the diaphragm 30 in the following procedure, and the droplet discharge head 1 shown in FIG. However, the processing of the pressure chamber 21 and the adhesion of the nozzle plate 10 are not performed.
The vibration plate 30 can be formed by forming a single layer film or a laminated film of oxide or nitride on the substrate 20 made of silicon by LPCVD (Low Pressure CVD), plasma CVD, sputter film formation, thermal oxidation, or the like. In simple terms, it is often formed by thermally oxidizing the substrate 20 made of silicon. However, when used as a piezoelectric actuator, particularly as a droplet discharge head (inkjet head), the required strength and vibration characteristics are taken into consideration. Formed. Specifically, a SiO ₂ thermal oxide film, a SiO ₂ film, a laminated film of a silicon film and a SiN film, a ZrO ₂ film, a laminated film of a SiO ₂ film and a ZrO ₂ film, or the like is used. The total film thickness is about several μm. This laminated film becomes the vibration plate 30.

In Example 1, an SiO ₂ film and a laminated film (film thickness: 2 μm) of a silicon film and a SiN film were formed on the substrate 20 made of silicon by the heat treatment film forming method and the LPCVD method as the vibration plate 30. Next, the lower electrode 41 was formed on the vibration plate 30. Specifically, first, a titanium film (film thickness: 50 nm) was formed on the diaphragm 30 by sputtering. Subsequently, the titanium film is thermally oxidized in an O ₂ atmosphere at 700 ° C. for 5 minutes using an RTA (rapid thermal annealing) apparatus to form the titanium film as a titanium oxide film. The titanium oxide film becomes the adhesion layer 41a. Then, a platinum film (thickness: 125 nm) was formed by sputtering as the metal film 41b on the titanium oxide film 41a.

Further, a LaNiO ₃ film 41c (film thickness 80 nm) was formed on the metal film 41b by sputtering. Further, a SrRuO ₃ film 41d (film thickness 70 nm) was formed by sputtering on the LaNiO ₃ film 41c, and the lower electrode 41 was completed. The substrate heating temperature during sputtering of the SrRuO ₃ film was 550 ° C. The substrate heating temperature during the LaNiO ₃ film sputtering was 300 ° C.

  Next, in order to produce the piezoelectric thin film 42 on the lower electrode 41, a solution prepared with a composition ratio of Pb: Zr: Ti = 110: 53: 47 was prepared. For the synthesis of a specific precursor coating solution, lead acetate trihydrate, isopropoxide titanium and isopropoxide zirconium were used as starting materials. Crystal water of lead acetate was dissolved in methoxyethanol and then dehydrated. The lead amount is excessive with respect to the stoichiometric composition. This is to prevent crystallinity deterioration due to so-called lead loss during heat treatment.

  Isopropoxide titanium and isopropoxide zirconium were dissolved in methoxyethanol, the alcohol exchange reaction and the esterification reaction were advanced, and the PZT precursor solution was synthesized by mixing with the methoxyethanol solution in which the lead acetate was dissolved. The PZT concentration was 0.5 mol / l. Using this solution, a PZT precursor was deposited on the lower electrode 41 by spin coating, dried at 120 ° C., and subjected to thermal decomposition at 500 ° C.

  After the thermal decomposition treatment of the third layer, crystallization heat treatment (temperature 750 ° C.) of the PZT precursor was performed by RTA treatment (rapid heat treatment). At this time, the film thickness of PZT was 240 nm. This process was performed a total of 8 times (24 layers) to obtain a PZT film having a thickness of about 2 μm as the piezoelectric thin film 42.

Next, the upper electrode 43 was formed on the piezoelectric thin film 42. Specifically, first, a conductive oxide film SrRuO ₃ film (film thickness 40 nm) was formed on the piezoelectric thin film 42 by sputtering. The substrate temperature at the time of sputtering film formation was 300 ° C. Thereafter, post-annealing at 550 ° C./300 s was performed in an oxygen atmosphere by RTA treatment. Thereafter, a platinum metal film (film thickness: 60 nm) was formed by sputtering, and the upper electrode 43 was completed.

  Thereafter, a photoresist (TSMR8800) manufactured by Tokyo Ohka Co., Ltd. is formed by a spin coat method, a resist pattern is formed by a normal photolithography method, and then the piezoelectric thin film element 40 is processed into a predetermined shape using an ICP etching apparatus ( Patterning).

Next, an oxide of Al ₂ O ₃ is applied to the cross section of the piezoelectric thin film element 40 processed into a predetermined shape (the cross section of each of the lower electrode 41, the piezoelectric thin film 42, and the upper electrode 43) using an ALD process. A protective layer consisting of layers was formed. The protective layer is a layer disposed for the purpose of shielding the cross-sectional portion of the piezoelectric thin film element 40 from a driving environment such as humidity. The thickness of the protective layer is preferably about 30 to 100 nm.

  Next, an interlayer insulating layer was formed on the piezoelectric thin film element 40. The interlayer insulating layer is used as an insulating layer for contact between the wiring electrode laminated on the piezoelectric thin film element 40 and the lower electrode 41 and the upper electrode 43 of the piezoelectric thin film element 40. It is preferable that an oxide, a nitride, a mixture thereof, or the like is used as the material of the interlayer insulating layer and the thickness of the interlayer insulating layer is about 300 to 700 nm.

  After the interlayer insulating layer was formed, through-holes were formed for contact between the wiring electrode laminated on the piezoelectric thin film element 40 and the lower electrode 41 and the upper electrode 43 of the piezoelectric thin film element 40. The through hole was formed by etching after using photolithography. The remaining resist was removed by ashing or the like with oxygen plasma.

Since the wiring electrode layer is for taking out the individual electrodes and the common electrode of the piezoelectric thin film element 40, the material is selected from materials that can make ohmic contact with the materials of the lower electrode 41 and the upper electrode 43. Specifically, as the wiring electrode layer, a wiring material in which pure Al or Al was mixed with a component for preventing the formation of heat lock such as Si at several atomic% was used.
As the wiring electrode layer, a wiring material for a semiconductor containing Cu as a main component may be used from the viewpoint of conductivity. The thickness of the wiring electrode layer is set so as to have a wiring resistance that does not hinder the driving of the piezoelectric thin film element 40 in consideration of the resistance due to the routing distance. Specifically, the film thickness is about 1 μm for Al wiring.

  As described above, the wiring electrode layer is formed into a desired shape by using a photolithography technique. The remaining resist is removed by ashing or the like using oxygen plasma. The wiring material layer is preferably covered with an oxide or nitride protective layer in order to ensure environmental resistance except for portions necessary for electrical connection. As described above, the droplet discharge head 1 was completed except for processing of the pressure chamber 21 and adhesion of the nozzle plate 10.

<Example 2>
A piezoelectric thin film element was fabricated in the same manner as in Example 1 except that the film thickness of the SrRuO ₃ film 41d was 60 nm.

<Example 3>
A piezoelectric thin film element was fabricated in the same manner as in Example 1 except that the film thickness of the SrRuO ₃ film 41d was 80 nm.

<Example 4>
A piezoelectric thin film element was fabricated in the same manner as in Example 1 except that the adhesion layer 41a was changed to Ti. The RTA process is not performed.

<Example 5>
A piezoelectric thin film element was fabricated in the same manner as in Example 1 except that the adhesion layer 41a was changed to an alumina film. An alumina film was formed by the ALD method.

<Comparative Example 1>
A piezoelectric thin film element was fabricated in the same manner as in Example 1 except that the film thickness of the SrRuO ₃ film 41d was 50 nm.

<Comparative example 2>
A piezoelectric thin film element was fabricated in the same manner as in Example 1 except that the film thickness of the SrRuO ₃ film 41d was 90 nm.

<Comparative Example 3>
A piezoelectric thin film element was fabricated in the same manner as in Example 1 except that the SrRuO ₃ film 41d was removed.

<Comparative example 4>
A piezoelectric thin film element was fabricated in the same manner as in Example 1 except that the LaNiO ₃ film 41c was omitted.

<Comparative Example 5>
A piezoelectric thin film element was fabricated in the same manner as in Example 1 except that the SrRuO ₃ film 41d was replaced with an ITO film.

For the piezoelectric thin film elements fabricated in Examples 1, 2, 3 and Comparative Examples 1 and 2, in the process, immediately after the SrRuO ₃ film 41d was formed by LPCVD, the surface was used using NanoScope IIIaAFM manufactured by Beiko Japan The roughness was evaluated. This surface roughness is the arithmetic average roughness.

In AFM measurement, the measurement mode was tapping mode, the measurement range was 3 μm × 3 μm, and the scanning speed was 1 Hz. Electrical characteristics and electromechanical conversion ability (piezoelectric constant) were evaluated using the produced piezoelectric thin film element. The electromechanical conversion capacity was calculated from the amount of deformation due to electric field application (150 kV / cm) measured by a laser Doppler vibrometer and adjusted by simulation. After evaluating the initial characteristics, the droplet discharge head 30 shown in FIG. 1 was manufactured, and durability (characteristics immediately after applying the applied voltage 10 ¹⁰ times) was evaluated.
These detailed results are summarized in Table 1.

About Example 1, 2, 3, and the comparative example 1, it had the characteristic equivalent to a general ceramic sintered compact also about the initial characteristic and the result after a durability test.
In the Vj characteristics immediately after the durability test after 10 ¹⁰ times, that is, 10 ¹⁰ times repeatedly applied voltage, it was confirmed that Comparative Example 1 was deteriorated by 10% or more compared with Examples 1 to 3. It was inferior in sex and judged to be NG. In Comparative Example 1, since the SRO film thickness was 50 nm, the effect as a supply source of a deficient oxygen component for suppressing deterioration of the piezoelectric performance over time was insufficient.
On the other hand, in Comparative Example 2, in the durability test after applying the applied voltage 10 ¹⁰ times later, that is, 10 ¹⁰ times repeatedly, in other words, in the characteristics immediately after the deterioration test, electrode leakage occurred during the deterioration test, and evaluation was made in the middle. I can't.
From the comparison of such characteristics with Examples 1, 2, and 3 and Comparative Examples 1 and 2, it was found that the SRO film thickness is preferably in the range of 60 to 80 nm. Moreover, it turned out that it is preferable that the arithmetic surface roughness of SRO is 15 nm or less.

Using the piezoelectric thin film elements fabricated in Examples 1 to 5 and Comparative Examples 1 to 5, the droplet ejection head 30 shown in FIG. 1 was fabricated and the ejection of the liquid was evaluated. Using an ink whose viscosity was adjusted to 5 cp, the discharge situation when applying an applied voltage of −10 to −30 V was confirmed by a simple Push waveform, and it was confirmed that all the nozzle holes were discharging.
Table 2 shows the deterioration rate of the droplet velocity Vj after the durability test in this case.

Compared with Examples 1-5 and Comparative Example 4, Comparative Examples 1, 2, 3, and 5 were 10 in comparison with Examples 1-5 and Comparative Example 4 in the Vj characteristics immediately after ¹⁰ times, that is, 10 ¹⁰ times repeatedly. % Was confirmed to be NG because the durability was inferior. Since the lower electrode configuration is not appropriate, the drop velocity Vj is greatly deteriorated. In Examples 1 to 5, compared with Comparative Examples 1, 2, 3, and 5, the deterioration of the droplets can be reduced, and good results were shown as the durability test. On the other hand, Comparative Example 4 is slightly inferior in initial characteristics.

(Example 6)
In the structure shown in FIG. 1, a piezoelectric thin film element was configured. The manufacturing method adds processing of the liquid chamber part and adhesion of the nozzle plate. Good characteristics were also obtained in a piezoelectric thin film element having a liquid chamber structure.

(Example 7)
In the second embodiment, an example of a droplet discharge head having a plurality of electromechanical conversion elements is shown. FIG. 3 is an exploded perspective view illustrating a droplet discharge head according to the second embodiment. Referring to FIG. 3, the droplet discharge head 2 generally includes a first substrate 50, a second substrate 60, and a nozzle plate 70.

  The first substrate 50 is a protective substrate that protects the electromechanical conversion element and the like of the second substrate 60, and is configured to include a liquid supply path 51 and the like for supplying ink liquid. The first substrate 50 is preferably made of a material that does not greatly differ from the second substrate 60 in thermal expansion coefficient, and the first substrate 50 is formed using, for example, a glass substrate. The liquid supply path 51 is formed by, for example, sand blasting, but may be formed by, for example, laser processing or the like, or may be formed by machining or etching depending on the material of the substrate.

  The second substrate 60 is a flow path forming substrate made of, for example, a silicon single crystal substrate and having an ink liquid flow path formed therein. The second substrate 60 includes a plurality of pressure chambers 61 as spaces (voids) for accommodating ink liquid, a plurality of electromechanical transducers 40 formed in portions corresponding to the pressure chambers 61, A flexible substrate 62 on which a drive circuit (not shown) for driving the electromechanical transducer 40 is formed, a common liquid chamber 63 formed in a portion corresponding to the liquid supply path 51, each pressure chamber 61, and a common liquid A plurality of communication passages 64 and the like communicating with the chamber 63 are provided. The second substrate 60 and the first substrate 50 are bonded by, for example, an epoxy or polyimide adhesive.

  The nozzle plate 70 has a plurality of nozzle holes 71 for discharging ink droplets. The nozzle plate 70 is made of, for example, stainless steel having a thickness of about 30 μm, and after opening the nozzle holes 71 by press working, a fluorine-based resin is deposited on the surface on the liquid outlet side by vapor deposition as a liquid repellent film. doing. For the nozzle plate 70, for example, glass ceramics, a silicon single crystal substrate, or the like may be used. The nozzle plate 70 and the second substrate 60 are bonded by, for example, an epoxy or polyimide adhesive.

In the droplet discharge head 2, each electromechanical conversion element 40 is driven by a drive circuit, whereby droplets can be discharged independently from each nozzle hole 71.
In this manner, the droplet discharge head 2 that can discharge droplets independently from each nozzle hole 71 can be realized by using a plurality of electromechanical conversion elements 40 described in the first embodiment. The droplet discharge head 2 has the same effect as that of the first embodiment.

(Example 8)
Next, an example of a droplet discharge apparatus (hereinafter referred to as an inkjet recording apparatus) equipped with a droplet discharge head (hereinafter referred to as an inkjet head) according to the present invention will be described with reference to FIGS. 4 is an explanatory perspective view of the recording apparatus, and FIG. 5 is an explanatory side view of a mechanism portion of the recording apparatus.

  This ink jet recording apparatus includes a carriage movable in the main scanning direction inside the recording apparatus main body 81, a recording head composed of an ink jet head embodying the present invention mounted on the carriage, an ink cartridge for supplying ink to the recording head, and the like. A sheet feeding cassette (or a sheet feeding tray) 84 on which a large number of sheets 83 can be stacked from the front side is detachably attached to the lower part of the apparatus main body 81. The manual feed tray 85 for manually feeding the paper 83 can be opened, the paper 83 fed from the paper feed cassette 84 or the manual feed tray 85 is taken in, and the printing mechanism 82 After recording a required image, the image is discharged to a paper discharge tray 86 mounted on the rear side.

  The printing mechanism 82 holds a carriage 93 slidably in the main scanning direction by a main guide rod 91 and a sub guide rod 92 which are guide members horizontally mounted on left and right side plates (not shown). (Y), cyan (C), magenta (M), black (Bk) A head 94 comprising an ink jet head according to the present invention for ejecting ink droplets of each color has a plurality of ink ejection openings (nozzles) as the main scanning direction. They are arranged in the intersecting direction and mounted with the ink droplet ejection direction facing downward. In addition, each ink cartridge 95 for supplying ink of each color to the head 94 is replaceably mounted on the carriage 93.

  The ink cartridge 95 has an air port that communicates with the atmosphere upward, a supply port that supplies ink to the inkjet head below, and a porous body filled with ink inside, and the capillary force of the porous body. Thus, the ink supplied to the inkjet head is maintained at a slight negative pressure. Further, although the heads 94 of the respective colors are used here as the recording heads, a single head having nozzles for ejecting ink droplets of the respective colors may be used.

  Here, the carriage 93 is slidably fitted to the main guide rod 91 on the rear side (downstream side in the paper conveyance direction), and is slidably mounted on the sub guide rod 92 on the front side (upstream side in the paper conveyance direction). doing. In order to move and scan the carriage 93 in the main scanning direction, a timing belt 100 is stretched between a driving pulley 98 and a driven pulley 99 that are rotationally driven by a main scanning motor 97, and the timing belt 100 is moved to the carriage 93. The carriage 93 is driven to reciprocate by forward and reverse rotation of the main scanning motor 97.

  On the other hand, in order to convey the paper 83 set in the paper feed cassette 84 to the lower side of the head 94, the paper feed roller 101 and the friction pad 102 for separating and feeding the paper 83 from the paper feed cassette 84 and the paper 83 are guided. A guide member 103, a transport roller 104 that reverses and transports the fed paper 83, a transport roller 105 that is pressed against the peripheral surface of the transport roller 104, and a leading end that defines a feed angle of the paper 83 from the transport roller 104 A roller 106 is provided. The transport roller 104 is rotationally driven by a sub-scanning motor 107 through a gear train.

  A printing receiving member 109 is provided as a paper guide member that guides the paper 83 sent from the transport roller 104 below the recording head 94 in accordance with the movement range of the carriage 93 in the main scanning direction. A conveyance roller 111 and a spur 112 that are rotationally driven to send the paper 83 in the paper discharge direction are provided on the downstream side of the printing receiving member 109 in the paper conveyance direction, and the paper 83 is further delivered to the paper discharge tray 86. A roller 113 and a spur 114, and guide members 115 and 116 that form a paper discharge path are disposed.

  At the time of recording, the recording head 94 is driven according to the image signal while moving the carriage 93, thereby ejecting ink onto the stopped sheet 83 to record one line. Record the line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 83 has reached the recording area, the recording operation is terminated and the paper 83 is discharged.

  Further, a recovery device 117 for recovering defective ejection of the head 94 is disposed at a position outside the recording area on the right end side in the movement direction of the carriage 93. The recovery device 117 includes a cap unit, a suction unit, and a cleaning unit. The carriage 93 is moved to the recovery device 117 side during printing standby and the head 94 is capped by the capping means, and the ejection port portion is kept in a wet state to prevent ejection failure due to ink drying. Further, by ejecting ink that is not related to recording during recording or the like, the ink viscosity of all the ejection ports is made constant and stable ejection performance is maintained.

  When a discharge failure occurs, the discharge port (nozzle) of the head 94 is sealed with a capping unit, and bubbles and the like are sucked out from the discharge port with the suction unit through the tube. Is removed by the cleaning means to recover the ejection failure. Further, the sucked ink is discharged to a waste ink reservoir (not shown) installed at the lower part of the main body and absorbed and held by an ink absorber inside the waste ink reservoir.

As described above, in this ink jet recording apparatus, since the electrode layer does not peel off, there is no ejection failure of the droplet (ink droplet) due to a drive failure, and stable ejection characteristics of the droplet (ink droplet) are obtained. The image quality is improved without any omission of the image.
The present invention can be directly used as a droplet discharge device in the printing field, particularly in the digital printing field, an inkjet printer equipped with a droplet discharge device, a three-dimensional molding technique using an inkjet technique, and the like.

DESCRIPTION OF SYMBOLS 1, 2 Droplet discharge head 10, 70 Nozzle plate 11 Nozzle 20 Substrate 21, 61 Pressure chamber 30 Vibrating plate 40 Electromechanical transducer 41 Lower electrode 41a Adhesion layer 41b, 43b Metal film 41c LaNiO ₃ film 41d SrRuO ₃ film 42 Electricity Mechanical conversion film 43 Upper electrode

JP 2004-186646 A JP 2004-262253 A JP 2003-218325 A JP 2007-258389 A Japanese Patent No. 3249696 Japanese Patent No. 3472877 Japanese Patent Laid-Open No. 11-195768 JP 2005-316628 A Japanese Patent No. 4431891

Claims (10)

A diaphragm formed on a substrate;
A lower electrode formed on the diaphragm;
A piezoelectric thin film formed on the lower electrode;
An upper electrode formed on the piezoelectric thin film,
The lower electrode includes a metal film having a (111) orientation made of a platinum group or an alloy containing a platinum group metal, LaNiO ₃ formed on the metal film, and SrRuO ₃ formed on the LaNiO _3. With
The piezoelectric thin film element, wherein the thickness of the SrRuO ₃ is 60 nm or more and 80 nm or less. The piezoelectric thin film element according to claim 1, wherein the SrRuO ₃ has a surface roughness of 15 nm or less. _3. The piezoelectric thin film element according to claim 1, wherein the SrRuO ₃ has a composition ratio Sr / Ru between Sr and Ru of 0.82 or more and 1.22 or less.   4. The piezoelectric thin film element according to claim 1, wherein the piezoelectric thin film is formed by a sol-gel method.   The piezoelectric thin film element according to any one of claims 1 to 4, wherein the piezoelectric thin film is lead zirconate titanate. A method for manufacturing a piezoelectric thin film element for manufacturing the piezoelectric thin film element according to any one of claims 1 to 5,
A method of manufacturing a piezoelectric thin film element, wherein the SrRuO _{3 is formed} by sputtering at 450 to 600 ° C. A method for manufacturing a piezoelectric thin film element for manufacturing the piezoelectric thin film element according to any one of claims 1 to 5, or a method for manufacturing a piezoelectric thin film element according to claim 6,
A method of manufacturing a piezoelectric thin film element, wherein the LaNiO _{3 is formed} by sputtering at 200 to 600 ° C.   A piezoelectric actuator comprising the piezoelectric thin film element according to any one of claims 1 to 5.   A droplet discharge head comprising the piezoelectric actuator according to claim 8.   A droplet discharge apparatus comprising the droplet discharge head according to claim 9.