JP2013232502A - Method for manufacturing electromechanical conversion film, electromechanical conversion element, and liquid discharge head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromechanical conversion film capable of obtaining stable drive characteristics when a large crystal grain is applied to an electromechanical conversion element.SOLUTION: A method for manufacturing an electromechanical conversion film by a chemical solution deposition method comprises the steps of: (1) forming a coating film by applying a coating liquid including a precursor of the electromechanical conversion film; (2) drying the coating film; (3) irradiating the dried coating film with ultraviolet light; (4) temporarily calcining the coating film irradiated with ultraviolet light; (5) repeating the step (1) to the step (4) to a desired first film thickness; and (6) finally calcining the coating film of the first film thickness.

Description

  The present invention relates to an electromechanical conversion film manufacturing method, an electromechanical conversion element, and a droplet discharge head.

  A droplet discharge head of a droplet discharge device used as an image forming apparatus includes an electromechanical conversion element in which an electromechanical conversion film is stacked. Lead zirconate titanate (PZT) is mainly used as the electromechanical conversion film material, but lead-free complex oxide materials are widely studied from the viewpoint of work safety and environment. It has been broken.

  Barium titanate is known as a lead-free complex oxide material. For example, Patent Document 1 discloses an electromechanical conversion film that includes bismuth sodium potassium titanate and barium titanate as lead-free composite oxide materials and is formed by chemical solution deposition (CSD). Yes.

  However, the electromechanical conversion film obtained by the method of Patent Document 1 or the like may not have a sufficient crystal grain size and cannot obtain stable driving characteristics.

  Therefore, an object of the present invention is to provide an electromechanical conversion film having large crystal grains and capable of obtaining stable driving characteristics when applied to an electromechanical conversion element.

A method for producing an electromechanical conversion film by chemical solution deposition,
(1) A coating film forming step of forming a coating film by applying a coating liquid containing a precursor of the electromechanical conversion film;
(2) a drying step of drying the coating film;
(3) An ultraviolet irradiation step of irradiating the dried coating film with ultraviolet rays,
(4) a calcining step of calcining the coating film irradiated with ultraviolet rays;
(5) repeating the step (4) to the desired first film thickness from the step (1);
(6) a main baking process of baking the coating film having the first film thickness;
A method for producing an electromechanical conversion film is provided.

  An electromechanical conversion film having large crystal grains and capable of obtaining stable driving characteristics when applied to an electromechanical conversion element can be provided.

FIG. 1 is an example of a differential thermothermal gravimetric simultaneous measurement (TG-DTA) analysis result of a dried gel obtained by drying a barium titanate CSD coating solution under reduced pressure. FIG. 2 is a flowchart for explaining an example of a production process of the electromechanical conversion film according to the present embodiment. FIG. 3 is a schematic diagram for explaining a method for preparing a CSD coating solution. FIG. 4 is an example of FT-IR measurement results of the film before and after ultraviolet irradiation for explaining the effect of ultraviolet irradiation. FIG. 5 is a schematic diagram for explaining the characteristics of the barium titanate film obtained in the present embodiment. FIG. 6 is a schematic cross-sectional view for explaining an example of the structure of the droplet discharge head according to the present embodiment.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

[Preparation of CSD coating solution]
The electromechanical conversion element (piezoelectric element) according to this embodiment has a structure in which a lower electrode, an electromechanical conversion film (piezoelectric film, electrostrictive film), and an upper electrode are stacked on a substrate.

The electromechanical conversion film uses a lead-free complex oxide material. As the lead-free complex oxide material, specifically, a complex oxide containing Ba and Ti such as barium titanate (BaTiO ₃ ) can be used. In addition, a material in which a complex oxide material containing Ba and Ti is substituted with any one element of tin (Sn), strontium (Sr), calcium (Ca), or zirconium (Zr) is used. Can do. Specifically, a composite oxide described by the general formula ABO ₃ and having A = Ba, Sr, Ca B = Ti, Sn, Zr as main components is applicable. In this embodiment, as an example, the case where barium titanate is used will be described, but the present invention is not limited in this respect.

When the BaTiO ₃ film is produced by the CSD method, barium ethoxide and titanium isopropoxide are used as starting materials. When a part of the Ba and / or Ti element of the BaTiO ₃ film is substituted with the above-mentioned elements, an alkoxide compound of the substitution element or an acetate or acetylacetonate salt such as strontium acetate may be used as a starting material. it can.

  As a common solvent for dissolving the starting material, methoxyethanol can be used, and it is preferable to prepare a uniform coating solution according to a conventional method for preparing a CSD coating solution (precursor solution).

  In addition, when using barium alkoxide as a starting material, since this material has poor solubility in a common solvent, it is preferable to add methanol to the common solvent.

  Since the prepared CSD coating solution is usually insufficiently stable under normal temperature and normal pressure, it is preferable to add monoethanolamine, diethanolamine, triethanolamine or the like as a peptizer. By adding these peptizers, a CSD coating solution that can be stored for a long time can be obtained.

A sintering aid for promoting crystal grain growth may be further added to the CSD coating solution. Although it does not specifically limit as a sintering aid, For example, as a sintering aid effective when forming a film of barium titanate, silicon oxide (SiO ₂ ), boron oxide (B ₂ O ₃ ), lithium oxide (Li ₂ O ₃ ), bismuth oxide (Bi ₂ O ₃ ), and the like. These materials may be used alone or in combination of two or more.

[Production of Electromechanical Conversion Film According to this Embodiment]
The electromechanical conversion film production process of the present invention includes (1) a CSD coating film coating process, (2) a drying process, (3) an ultraviolet irradiation process, (4) a calcination process, and (5) process (1 ) To step (4) to a desired first film thickness, (6) including a firing step, and if necessary, (7) steps (1) to (6) to the desired second film Including the step of repeating to thickness.

  Usually, the electromechanical conversion film production process by the CSD method includes (i) a CSD coating solution coating process, (ii) a coating film drying process, (iii) a dry film thermal decomposition process, and (iv) a thermal decomposition process. A film crystallization step. At this time, the organic solvent is not present after the step (ii), the organic component is not left after the step (iii) or is in an amorphous state, and a crystallized film is obtained after the step (iv). State.

  In FIG. 1, the CSD coating liquid of barium titanate is dried under reduced pressure, and the example of the differential thermothermal weight simultaneous measurement (TG-DTA) analysis result of the obtained dried gel is shown. As shown in FIG. 1, the DTA curve has four peaks due to the heat balance. The peak P1 is a peak due to the first organic matter combustion (weight reduction is recognized in the TG curve), and the peak P2 is a peak due to the second organic matter combustion (weight reduction is recognized in the TG curve) ), Peak P3 is a peak resulting from the combustion of the organic amine component coordinated as a metal complex (weight reduction is observed in the TG curve). The first organic substance is an organic substance that has been incorporated into the network of the dried gel, and the second organic substance corresponds to the combustion of the alkoxide group of the metal alkoxide.

  In the peak P4, the barium oxide generated by the thermal history up to the peak P3 reacts with carbon dioxide existing in the system to generate barium carbonate, and the barium carbonate is thermally decomposed by the further increase in temperature to self-decompose barium oxide. This is due to decomposition (weight loss is observed in the TG curve). This self-decomposition ends at about 680 ° C., and after self-decomposition, it reacts with titanium oxide existing in the vicinity of the barium oxide particles to produce barium titanate.

  The conventional pyrolysis process is merely to lead to an amorphous state due to the combustion of organic matter, and is not a process that is optimized in consideration of the above-described reaction path. Therefore, in the present embodiment, (4) in the calcination step, the autolysis of barium carbonate and the solid phase reaction with the titanium oxide present in the vicinity are advanced. Specifically, it is preferable to perform the calcination step at a heat treatment temperature of 650 ° C to 800 ° C.

  The amine that forms the metal complex decomposes and leaves at a temperature of about 550 ° C. to 600 ° C. indicated by the peak P3 due to a relatively strong coordination bond. This reaction promotes a carbonate formation reaction with carbon dioxide in the system, leads to film expansion due to the bulkiness of the carbonate, and causes volume shrinkage in subsequent thermal decomposition. Specifically, the volume shrinkage occurs when a void is formed. Due to the voids, the reactivity of the solid phase reaction with titanium dioxide is reduced, and pores (holes) are formed in the crystallized film. It is important that the pores are not reduced in order to deteriorate the film characteristics of the obtained electromechanical conversion film.

  Therefore, in the present embodiment, the generation of pores is suppressed by the above-described (3) ultraviolet irradiation process. Although details will be described below, the generation of pores is suppressed not by cleavage of coordination bonds by thermal energy but by cleavage using a photochemical reaction.

  The reactivity of barium oxide carbonate increases with increasing temperature. That is, when thermal energy is used, coordination bond breakage by thermal energy is performed at about 550 ° C. or more, and carbonate is immediately formed in this temperature range.

  On the other hand, when a photochemical reaction is used, the coordination bond can be broken at room temperature. Carbonation of barium oxide at room temperature proceeds very slowly as compared to the case at about 550 ° C. described above. At this time, the formation of carbonate is further suppressed by performing a photochemical reaction in a treatment atmosphere having a low partial pressure of carbon dioxide. Conventional pyrolysis treatment is performed in an oxygen atmosphere, but it is difficult to remove the influence of residual carbon dioxide, but when using the photochemical reaction of this embodiment, it is at room temperature, so the influence of residual carbon dioxide. Can be removed.

  In the ultraviolet irradiation step, it is preferable to use an ultraviolet region having a wavelength equal to or less than the wavelength corresponding to the bond energy of the CN bond and NH bond constituting the amine molecule.

  The CN bond energy is 64 kcal / mol at room temperature, and the NH bond energy is 92 kcal / mol. Therefore, photodecomposition of C—N bonds and N—H bonds can be easily achieved by irradiation with ultraviolet rays having a wavelength of 310 nm or less.

  For example, since the emission wavelength of a low-pressure mercury lamp is usually 254 nm or 185 nm, it is preferable to use this. In addition, it is preferable to use an excimer lamp or the like. In the case of an excimer lamp, xenon chloride (XeCl; emission wavelength 308 nm), krypton fluoride (KrF; emission wavelength 248 nm), krypton chloride (KrCl; emission wavelength 222 nm), argon fluoride (ArF; emission wavelength 193 nm), xenon (Xe A light emission wavelength of 172 nm). When an excimer lamp is used, it can be preferably used because it exhibits an ultraviolet generation efficiency that is about one digit higher than that of a mercury lamp.

  In addition, among the lamps described above, when a lamp having an emission wavelength of 200 nm or more is used, there is no generation of ozone due to a photochemical reaction of oxygen present in the system, and CN bonds and NH bonds due to ultraviolet irradiation are not generated. Direct decomposition proceeds. On the other hand, when a lamp having an emission wavelength of 200 nm or less is used, a decomposition reaction via ozone proceeds instead of the direct decomposition of the bonds described above.

  Next, each process of the electromechanical conversion film creation process of this embodiment will be described in more detail. FIG. 2 is a flow chart for explaining an example of the production process of the electromechanical conversion film according to this embodiment. As described above, the electromechanical conversion film production process of the present embodiment includes (1) a CSD coating film coating process S101, (2) a drying process S103, (3) an ultraviolet irradiation process S105, and (4) a calcination process. S107, (5) Steps S109 and (6) Repeat the steps (1) to (4) to the desired first film thickness, (6) The firing step S111, and if necessary, (7) Steps (1) to (Steps) It includes a step S113 of repeating (6) to a desired second film thickness.

(1) CSD coating liquid coating film forming process The CSD coating liquid coating film forming process is a process in which a CSD coating liquid is prepared and formed on a substrate by spin coating.

  FIG. 3 is a schematic diagram for explaining a method for preparing a CSD coating solution. A CSD coating solution having a concentration of 0.1 mol / l to 0.5 mol / l was prepared by the procedure shown in FIG. A coating film is formed on the substrate by spin coating (for example, 4000 rpm, 20 seconds).

  Although there is no restriction | limiting in particular as a board | substrate, What deposited the Pt film | membrane etc. as a 1st electrode on the silicon | silicone (Si) wafer in which the dielectric film was formed can be used.

At this time, in order to improve the adhesion between the Pt film and the dielectric film, an aluminum oxide (Al ₂ O ₃ ) film, a zirconium oxide (ZrO ₂ ) film, a tantalum oxide (Ta ₂ O ₅ ) film, and It is preferable to use one kind of titanium oxide (TiO ₂ ) film or two or more kinds of laminated films.

  In addition, it is preferable that the adhesion film has a thickness of usually 3 nm to 100 nm. When the thickness of the adhesion film is less than 3 nm, the adhesion may not be exhibited. On the other hand, when the film thickness of the adhesion film exceeds 100 nm, the electromechanical conversion efficiency of the obtained electromechanical conversion element may be lowered.

(2) Drying process A drying process is a process of drying the solvent of the produced coating film. Specifically, the solvent is dried at a temperature not higher than the boiling point of the main solvent contained in the CSD coating solution. As a specific example, drying within a processing time of 5 minutes is performed on a hot plate or the like maintained at a predetermined temperature. In this embodiment, after drying at 120 ° C. for 1 minute, drying was performed at 300 ° C. for 1 minute.

(3) Ultraviolet irradiation step The ultraviolet irradiation step is a step of removing organic components in the molecular bonds constituting the gel network of the film after the drying step out of the membrane system by a photochemical reaction.

  In this embodiment, a xenon (Xe; emission wavelength: 172 nm) lamp was used to irradiate ultraviolet rays under irradiation conditions at room temperature for 10 minutes.

(4) Calcination process The calcination process is a process in which a self-decomposition of barium carbonate and a solid-phase reaction with titanium oxide present in the surrounding progress. The film after the ultraviolet irradiation step is in an amorphous state of an oxide corresponding to the contained metal element or in an amorphous state of some composite oxide. For this reason, in the calcination step, heat is applied to convert the composite oxide to be produced into a crystalline state.

  When alkaline earth metal elements such as barium, strontium and calcium are included, oxides of these elements easily react with carbon dioxide present in the system to form carbonates. At temperatures below the thermal decomposition temperature of carbonate, the complex oxide formation reaction is suppressed and the reaction does not proceed. Even if heat treatment is performed at the thermal decomposition temperature of carbonate, part of it returns to carbonate when it is returned to room temperature. For this reason, in the calcining step, it is preferable to perform heat treatment at a temperature equal to or higher than the thermal decomposition temperature of the carbonate to generate complex oxide microcrystals.

  Specifically, in the calcination step, it is preferable to perform heat treatment at a temperature higher by 50 ° C. or more than the thermal decomposition temperature of carbonate recognized by TG-DTA. More specifically, in the case of producing a composite oxide containing barium titanate as a main component, it is preferably calcined at a temperature of 650 ° C. or higher and 800 ° C. or lower.

(5) Step of repeating step (1) to step (4) to a desired first film thickness The film thickness of the film obtained in step (1) to step (4) is usually 100 nm or less, preferably 60 nm. The following. When the film thickness obtained in one step exceeds 100 nm, pores are generated in the obtained film, and the piezoelectric performance of the film may deteriorate. On the other hand, the film thickness obtained in one step is preferably 10 nm or more. When the film thickness is less than 10 nm, a crystal film having a very dense columnar structure can be obtained, but the steps (1) to (4) for producing an electromechanical conversion film having a sufficient function required. ) Is too economical, so it is not economical. In general, the electromechanical conversion film has a thickness of about 1 μm to 2 μm.

(6) Main firing step The main firing step is a step of growing complex oxide crystal grains. At this time, for example, when the target film thickness is 1 μm, it is not preferable to repeat the steps (1) to (4) and prepare a film corresponding to 1 μm, and then perform the firing step. The film after the calcination process has complex oxide crystals, but the volume changes due to crystal growth due to the main firing (usually the volume decreases due to shrinkage), and cracks occur in the film due to this volume change. Because there is. Therefore, it is preferable to perform the firing step for each film thickness that does not generate cracks (corresponding to the first film thickness described above). The first film thickness at which cracks do not occur can be appropriately selected by those skilled in the art depending on the conditions of the film forming process.

  In the firing step, as described above, crystal grains of the complex oxide crystal are grown. In order to finally grow into giant crystal grains having sufficient electromechanical conversion performance by thermal energy, it is preferable that the heat treatment temperature in the main firing step is higher than the heat treatment temperature in the calcining step. In addition, the upper limit temperature of the main baking process depends on the heat resistance of the substrate, the dielectric film disposed in the lower layer of the composite oxide film, the adhesion film, and the electrode film. A heat treatment is performed at a temperature of ℃ or less.

  As the heat treatment temperature in the main firing step increases, the diffusion rate on the surface of the crystal grains of the composite oxide increases, so that a huge grain structure is obtained. This contributes to the improvement of the characteristics of the electromechanical conversion film.

  The sintering aid described above melts to form a liquid phase at the heat treatment temperature in the main baking step. The movement of atoms on the surface of the complex oxide is facilitated through this liquid phase, and as a result, the growth of crystal grains is promoted even at a relatively low temperature. Therefore, it is preferable to add the above-mentioned sintering aid.

(7) Step of repeating step (1) to step (6) to a desired second film thickness In the case of forming a complex oxide film containing barium titanate as a main component, usually, about 10 times until calcination. Cracks do not occur when firing is performed after repeating. When an electromechanical conversion film having a thickness larger than that is formed, it is preferable to perform the firing step for every deposition of about 500 nm. Therefore, in order to obtain an electromechanical conversion film having a desired film thickness, those skilled in the art repeat Step (1) to Step (6) as appropriate.

  The above-described heat treatment such as calcination and main firing can be performed by a normal electric furnace, a tubular furnace that can control the processing atmosphere, a rapid heat treatment (RTA) by lamp irradiation that can control the atmosphere, and the like.

  Among the above, heat treatment using RTA is preferable because the temperature rising rate and the temperature falling rate are fast and effective in shortening the time of each step. Furthermore, the calcination step is preferable because the reaction time of the carbonate formation reaction can be shortened, and further, the crystallization inhibition factor in the subsequent crystallization can be reduced.

  More specifically, in the RTA treatment in an oxygen atmosphere, it is preferable to perform heat treatment at a temperature increase rate of 10 ° C./second or more because the production of carbonate is reduced.

  The heat treatment in the main baking process is preferably performed in an oxygen atmosphere, and the high temperature treatment in a pressurized oxygen atmosphere promotes the growth of composite oxide grains and improves the properties of the resulting electromechanical conversion film. Therefore, it is more preferable.

  In addition, when performing heat treatment under pressure, it is preferable to pressurize to a pressure of about 0.3 MPa or more, and as the pressure increases, the crystal grain growth rate increases. Usually, the crystal grain growth rate is about 1 MPa. Saturates.

  In addition, in order to obtain the electromechanical conversion film having a predetermined film thickness, when performing the firing process a plurality of times, it is not necessary to perform all the firing processes under pressure. An electromechanical conversion film having sufficient characteristics can be obtained by performing heat treatment under pressure (by RTA) in the final firing step.

[Example 1]
Hereinafter, based on an Example, this invention is demonstrated in detail.

<Preparation of substrate>
A thermal oxide film having a thickness of 2 μm was formed as a dielectric film on a 6-inch silicon wafer by a steam oxidation method.

Next, an aluminum oxide (Al ₂ O ₃ ) film having a thickness of 50 nm was formed as an adhesion layer by an atomic layer deposition (ALD) method.

Next, in order to promote the crystallinity of a platinum (Pt) film, which is a first electrode described later, a titanium oxide (TiO _x ) film was deposited with a thickness of 5 nm.

  Next, a 100 nm Pt film was formed as a first electrode at a substrate temperature of 550 ° C. by DC magnetron sputtering.

<(1) Coating Forming Process of CSD Coating Solution>
In this embodiment, a method for preparing a CSD coating solution for a barium titanate composite oxide film will be described as an example.

  As starting materials, diethoxybarium (manufactured by High Purity Chemical Co., Ltd.) and tetraisopropoxide titanium (manufactured by High Purity Chemical Co., Ltd.) were used. Methoxyethanol was selected as a common solvent.

  The starting material was dissolved in a common solvent under a nitrogen atmosphere, and an alcohol exchange reaction was performed at a reaction temperature of 125 ° C. After fractionating ethanol and isopropyl alcohol as exchange reaction products, reflux treatment was performed for 12 hours. At this time, monoethanolamine was added in order to increase the stability of the alkoxide compound. Monoethanolamine was added in an amount twice as much as the number of moles of barium titanate. In addition, methanol was added as a second organic solvent by 1/3 times the amount of methoxyethanol. These were refluxed at 80 ° C. for 2 hours to prepare a CSD coating solution having a barium titanate concentration of 0.3 mol / l.

  1 vol% of formamide was added to this CSD coating solution. Formamide is used for wettability control with a substrate and drying rate control.

  A precursor coating film was formed on the substrate on which the Pt electrode was formed by spin coating (4000 rpm, 20 seconds).

<(2) Drying process>
The organic solvent was dried by allowing to stand for 1 minute on a hot plate (under the atmosphere) set to 120 ° C.

<(3) UV irradiation process>
An excimer lamp (Xe, emission wavelength = 172 nm) was used, and ultraviolet irradiation was performed under the irradiation conditions of lamp output = 10 mW / cm ² , lamp light source-substrate distance = 10 mm, and irradiation time = 5 minutes.

  In FIG. 4, the example of the FT-IR measurement result of the precursor film | membrane before and behind ultraviolet irradiation for demonstrating the effect of ultraviolet irradiation is shown.

From FIG. 4, it was confirmed that the precursor film not irradiated with ultraviolet rays had a spectrum caused by C—O bond, CH ₃ bond, carbonate, and N—H bond. On the other hand, in the precursor film of this embodiment irradiated with ultraviolet rays, the peak due to the above-described organic functional group has generally disappeared, and the peak due to the metal-oxygen bond was confirmed.

<(4) Calcination process>
The sample after the ultraviolet irradiation process was inserted into an electric furnace set to 500 ° C. in advance. Then, it heated up to 800 degreeC with the temperature increase rate of 30 degreeC / min, and hold | maintained for 5 minutes. Thereafter, the temperature was lowered to 600 ° C., and a sample was taken out.

<(5) Step of Repeating Step (1) to Step (4) to a Desired First Film Thickness>
Step (1) to step (4) described above were repeated 10 times.

<(6) Main firing process>
After the tenth repeated calcination step, the temperature was raised to 1000 ° C. at a rate of temperature rise of 30 ° C./min, and held for 5 minutes. Thereafter, the temperature was lowered to 600 ° C., and a sample was taken out.

  After this firing step, a film having a thickness of 0.6 μm was obtained.

<(7) Step of Repeating Step (1) to Step (6) to a Desired Second Film Thickness>
The above-described steps (1) to (6) were repeated to obtain a film of Example 1 having a thickness of 1.2 μm.

[Example 2]
The heat treatment in the calcination step and the main firing step was changed to heat treatment using RTA, and step (7) was not performed (that is, a film having a thickness of 0.6 μm was obtained). A film of Example 2 was obtained by the same method.

  By performing the heat treatment using RTA, the temperature increase rate can be executed at 10 ° C./second or more, so that the process can be shortened. In addition, since the heat treatment using RTA is indirect heating by light radiation, the atmosphere of the heat treatment can be easily controlled in an oxygen atmosphere. Therefore, it becomes possible to suppress the carbonation reaction of barium oxide especially in the calcination process, particularly at the time of temperature rise. As described above, at the temperature rising rate of 10 ° C./second, preferably 30 ° C./second, the formation of carbonate that inhibits the complex oxide reaction was not observed even in the X-ray diffraction (XRD) measurement.

[Comparative Example 1 and Comparative Example 2 (conventional method)]
(2) The same steps as in Example 1 were performed until the drying step. Thereafter, the temperature was raised from room temperature to 600 ° C. or 800 ° C. in an oxygen atmosphere at the rate of temperature rise shown in Table 1, and held for 60 minutes. The heat treatment step at 600 ° C. is generally called degreasing and is a treatment for preventing the organic components in the dry film from remaining inside the film.

  After the calcination step, the temperature was raised to the firing temperature at the rate of temperature shown in Table 1 and held for 5 minutes or 60 minutes to grow a complex oxide crystal. Then, it cooled to 200 degreeC.

  The above process was repeated 20 times to obtain a film of Comparative Example 1. In the methods such as Example 1 and Example 2 described above, when a main baking process is performed once every 10 times and a total of 20 calcining processes are performed, usually several hours (when RTA is used) ) Within a day (when using an electric furnace), a desired film can be obtained. On the other hand, this conventional method required several days of treatment before obtaining the film of Comparative Example 1. In the conventional method using an atmosphere-controlled annular furnace, a long cooling time is one of the factors that require a long processing time.

得られた膜は、走査型電子顕微鏡（ＳＥＭ）観察により、平均の結晶粒径を求めた。表１には、各実施例及び各比較例で得られた膜の結晶粒径の値も示している。

The average crystal grain size of the obtained film was determined by observation with a scanning electron microscope (SEM). Table 1 also shows the values of the crystal grain sizes of the films obtained in the examples and the comparative examples.

  In general, it is known that the characteristics (relative permittivity and electromechanical conversion coefficient) of complex oxides such as barium titanate depend on the size of crystal grains. If it is 0.3 μm or more, those skilled in the art will determine that sufficient grain growth has been achieved. Also in the determination of Table 1, a crystal grain size of 0.3 μm or more was set as “◯”, and less than 0.3 μm was set as “Δ” or “X”.

[Example 3]
An embodiment for explaining the effect of adding the sintering aid will be described.

In Example 2, triethoxyboron was added to the CSD coating solution in order to add boron oxide (B ₂ O ₃ ) as a sintering aid. The amount of triethoxyboron added was 0.25 mol% with respect to 1 mol of barium titanate.

Moreover, in order to confirm the addition effect, the temperature of the baking process was changed from 1050 ° C. to 800 ° C. at intervals of 50 ° C. (Examples 3-1 to 3-6). As another example, an example in which silicon oxide (SiO ₂ ) is used as a sintering aid is also shown (Example 3-7). In this example, 0.05 mol% of tetraethoxysilane was added to the CSD coating solution with respect to 1 mol of barium titanate.

  Membranes of Example 3-1 to Example 3-7 were obtained in the same manner as in Example 2 except that the sintering aid was used.

  The average crystal grain size of the obtained film was determined by observation with a scanning electron microscope (SEM). Table 2 shows the value of the crystal grain size of the film obtained in Example 3.

表２により、焼結助剤としてＢ_２Ｏ_３（又はＳｉＯ_２）を使用した場合、８００℃の本焼（結晶化）温度においても、チタン酸バリウムの結晶粒成長が確認された。このとき、結晶化温度の増加に伴い、結晶粒が大きくなり、およそ１０００℃で結晶粒が大きくなる効果が飽和した。

According to Table 2, when B ₂ O ₃ (or SiO ₂ ) was used as a sintering aid, crystal grain growth of barium titanate was confirmed even at a firing (crystallization) temperature of 800 ° C. At this time, as the crystallization temperature increased, the crystal grains increased, and the effect of increasing the crystal grains at about 1000 ° C. was saturated.

[Example 4]
The Example which verified about the heat processing temperature of a calcination process is described. As shown in Table 3, the temperature of the calcining step was changed from 650 ° C. to 850 ° C. at intervals of 50 ° C. (Examples 4-1 to 4-5).

仮焼温度を表３に示したように変更し、本焼工程の温度を９５０℃に変更した以外は、実施例２と同様の方法により、実施例４−１〜４−５の膜を得た。

Films of Examples 4-1 to 4-5 were obtained by the same method as Example 2 except that the calcining temperature was changed as shown in Table 3 and the temperature of the main baking process was changed to 950 ° C. It was.

  From Table 3, it was found that a sufficient crystal grain size can be obtained even when the temperature of the heat treatment in the calcination step is lowered. Usually, an electromechanical conversion element with higher reliability and smaller variations can be obtained by reducing the total sum of the total heat history applied to the sample. The method for manufacturing an electromechanical conversion film according to the present embodiment can reduce the calcining temperature, and an electromechanical conversion film having good reliability, stability of characteristics, and variation can be obtained.

[Example 5]
In Example 2 to Example 4, Step (1) to Step (4) were repeated 10 times, and Step (6) was performed once to obtain a film having a thickness of 0.6 μm. Step (6) was repeated twice to obtain a film having a thickness of 1.2 μm. By repeating the steps (1) to (6), a film having a larger film thickness can be obtained.

  In this example, the film of Example 5 having a film thickness of 3 μm was obtained by repeating the steps (1) to (6) five times. At this time, heat treatment was performed in a pressurized oxygen atmosphere during the fifth firing step.

  FIG. 5 is a schematic diagram for explaining the characteristics of the barium titanate film obtained in this embodiment. More specifically, FIG. 5 shows a case in which a voltage is applied to the upper electrode by an atomic force microscope (AFM) for a sample in which an upper electrode of φ100 μm is formed by shadow mask and vapor deposition after the fourth firing step. This is the result of measuring the displacement in the film thickness direction.

  From FIG. 5, the strain at the maximum applied electric field from 0 to plus in the charge application direction was 0.15%. The slope of the straight line connecting this value and the origin was defined as the electric strain proportional constant X33 of the film of this embodiment. The electrostriction proportional constant X33 of the film of this embodiment when a positive electric field was applied was 85 pm / V. Similarly, when the electric field distortion proportional constant was determined from the maximum distortion when a negative electric field was applied, X33 was 94 pm / V. This is a value sufficient to use the film obtained in this embodiment as an electromechanical conversion film.

  Moreover, the electric field distortion proportional constant was similarly calculated | required about the sample which processed the 4th main baking process in the pressurized oxygen atmosphere of 0.9 Mpa. The electric strain proportional constant X33 when a positive electric field was applied was 100 pm / V, and the electric strain proportional constant X33 when a negative electric field was applied was 104 pm / V. From this, it was found that the characteristics of the obtained film are improved by performing the heat treatment in a pressurized oxygen atmosphere.

[Electromechanical transducer and droplet discharge head]
The electromechanical conversion film according to this embodiment can be applied to an electromechanical conversion element and a droplet discharge head.

  The electromechanical conversion element usually has a structure in which a lower electrode, an electromechanical conversion film according to this embodiment, and an upper electrode are stacked.

  FIG. 6 is a schematic sectional view for explaining an example of the structure of the droplet discharge head according to the present embodiment. FIG. 6B is a diagram in which a plurality of liquid droplet ejection heads of FIG.

  The droplet discharge head 30 according to the present embodiment includes a nozzle 31 that discharges droplets and a pressure chamber 32 (an ink flow path, a pressurized liquid chamber, a pressurized chamber, a discharge chamber, a liquid chamber, and the like) that communicate with the nozzle. An electromechanical conversion element 33 that pressurizes ink in the pressurizing chamber, and a diaphragm 34 that forms the wall surface of the ink flow path. The electromechanical conversion element 33 is formed of a lower electrode 37, an electromechanical conversion film (piezoelectric thin film) 38 and an upper electrode 39.

  The pressure chamber 32 communicates with the nozzle 31 and is partitioned from a nozzle plate 35, a vibration plate 34, and a pressure chamber plate 36. Then, an electromechanical conversion element 33 according to the present embodiment for pressurizing the droplet in the pressure chamber 32 via the vibration plate 34 is provided.

  The pressure chamber 32 is formed by etching away a part of the Si substrate from the back surface as will be described later.

  The nozzles 31 can be formed in a part of the nozzle plate 35, for example, in two lines in a straight line. As the nozzle plate 35, for example, one formed by nickel (Ni) electroforming or the like can be used.

  An etching method for forming the pressure chamber 32 will be briefly described. When producing a pressure chamber of a droplet discharge head, a silicon single crystal substrate is usually processed using etching. As an etching method, anisotropic etching is usually used. Anisotropic etching uses a difference in etching rate between plane orientations of a crystal structure. For example, when a silicon single crystal substrate is immersed in an alkaline solution such as potassium hydroxide (KOH), the etching rate of the (111) plane is about 1/400 compared to the (100) plane. A person skilled in the art can appropriately select etching conditions (type of etching solution, concentration, etching temperature) and the like in order to perform patterning into a desired shape.

  Thereafter, by joining a nozzle plate having a predetermined nozzle hole, the droplet discharge head of this embodiment can be manufactured.

DESCRIPTION OF SYMBOLS 30 Droplet discharge head 31 Nozzle 32 Pressure chamber 33 Electromechanical conversion element 34 Vibrating plate 35 Nozzle plate 36 Pressure chamber plate 37 Lower electrode 38 Electromechanical conversion film 39 Upper electrode

JP 2011-187672 A

Claims (9)

A method for producing an electromechanical conversion film by chemical solution deposition,
(1) A coating film forming step of forming a coating film by applying a coating liquid containing a precursor of the electromechanical conversion film;
(2) a drying step of drying the coating film;
(3) An ultraviolet irradiation step of irradiating the dried coating film with ultraviolet rays,
(4) a calcining step of calcining the coating film irradiated with ultraviolet rays;
(5) repeating the step (4) to the desired first film thickness from the step (1);
(6) a main baking process of baking the coating film having the first film thickness;
A method for producing an electromechanical conversion film.   The method for producing an electromechanical conversion film according to claim 1, further comprising a step of repeating the step (1) to the step (6) to a desired second film thickness.   The method for producing an electromechanical conversion film according to claim 1, wherein the ultraviolet irradiation step irradiates ultraviolet rays having a wavelength of 310 nm or less.   The said calcination process is a manufacturing method of the electromechanical conversion film as described in any one of Claims 1 thru | or 3 which is a process heat-processed in the temperature range of 650 degreeC or more and 800 degrees C or less.   The electromechanical conversion according to any one of claims 1 to 4, wherein the firing step is a step of performing a heat treatment in a temperature range of 800 ° C or higher and 1050 ° C or lower under atmospheric pressure or under a pressure of 1 MPa or lower. A method for producing a membrane. Manufactured by the method for producing an electromechanical conversion film according to any one of claims 1 to 5,
A composite oxide containing barium and titanium, or a composite oxide in which a composite oxide containing barium and titanium is substituted with one or more elements of tin, strontium, calcium and zirconium,
Electromechanical conversion membrane.   The electromechanical conversion film according to claim 6, comprising silicon oxide and / or boron oxide as a sintering aid.   An electromechanical conversion element in which a first electrode, the electromechanical conversion film according to claim 6 or 7, and a second electrode are sequentially laminated on a substrate.   A liquid droplet ejection head comprising the electromechanical transducer according to claim 8.

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