JP2020198366A - Thin-film piezo electric element, manufacturing method for the same, actuator, ink jet head, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film piezoelectric element in which a decrease in a displacement amount of a piezoelectric body with time is suppressed when a pulse is driven for a long period of time in a high temperature environment.
A thin-film piezoelectric element having an upper electrode and a lower electrode, and a piezoelectric body having a perovskite structure arranged between the upper electrode and the lower electrode. At least one of the upper electrode and the lower electrode is made of an Ir—Ti alloy containing Ir as a main component, and both Ir and Ti are partially oxidized.
[Selection diagram] Fig. 1

Description

The present invention relates to a thin film piezoelectric element, a method for manufacturing the same, an actuator, an inkjet head, and an image forming apparatus.

A thin-film piezoelectric element having a thin-film piezoelectric body and upper and lower electrodes for applying a voltage to the piezoelectric body in the thickness direction is widely used as an actuator in an inkjet head, a hard disk drive (HDD), or the like. ..

As the piezoelectric material, lead zirconate titanate (PZT) having a perovskite structure, which has ferroelectricity and good piezoelectric characteristics, is generally used. Further, it is known that a wide variety of metals or oxides thereof can be used for the upper and lower electrodes (see Patent Document 1 and Patent Document 2).

Patent Documents 3 to 5 describe a piezoelectric element in which a perovskite-type oxide is used as a piezoelectric material, and a noble metal containing titanium (Ti) or titanium oxide and iridium (Ir) is used for the upper and lower electrodes. Have been described. Patent Documents 3 to 5 describe that the electrode can be produced by a sputtering method using a target containing Ti or Ir.

Japanese Unexamined Patent Publication No. 2016-36006 Japanese Unexamined Patent Publication No. 2005-228838 Japanese Unexamined Patent Publication No. 2004-47928 Japanese Unexamined Patent Publication No. 2004-186646 Japanese Unexamined Patent Publication No. 2005-119166

As described in Patent Documents 1 to 5, thin-film piezoelectric elements using a piezoelectric material having a perovskite structure are widely used.

For example, when the thin-film piezoelectric element is used in an inkjet head, if the displacement amount of the piezoelectric body decreases when the piezoelectric element is pulse-driven for a long period of time, the ejection speed of droplets from the inkjet head also changes with time. From the viewpoint of improving the durability of the thin-film piezoelectric element, the piezoelectric body is required to have little change in the amount of displacement due to long-term use. In particular, according to the findings of the present inventors, when a piezoelectric material having a perovskite structure is pulse-driven for a long period of time in a high temperature environment, the amount of displacement is significantly reduced.

The present invention has been made based on the above findings, and is a thin-film piezoelectric element in which a decrease in the amount of displacement of the piezoelectric body with time is suppressed when the piezoelectric body is pulse-driven for a long period of time in a high temperature environment, and a method for manufacturing the same. An object of the present invention is to provide an actuator having the thin-film piezoelectric element, an inkjet head having the actuator, and an image forming apparatus having the inkjet head.

The above problem is solved by a thin film piezoelectric element having an upper electrode and a lower electrode, and a piezoelectric body having a perovskite structure arranged between the upper electrode and the lower electrode. At least one of the upper electrode and the lower electrode is made of an Ir—Ti alloy containing Ir as a main component, and both Ir and Ti are partially oxidized.

Further, the above-mentioned problems are a step of forming a lower electrode on one surface of a substrate, a step of forming a piezoelectric body on the side of the lower electrode opposite to the substrate, and an upper electrode on the side of the piezoelectric body opposite to the substrate. It is solved by a method for manufacturing a thin-film piezoelectric element having a step of forming. At least one of the steps of forming the lower electrode and the step of forming the upper electrode is performed by using an Ir—Ti alloy sintered body target containing Ir as a main component in the presence of an atmospheric gas containing oxygen. The process includes a step of forming an electrode film by a reactive sputtering method while heating a substrate, and a step of annealing the formed electrode film in an oxygen atmosphere.

Further, the above problem is solved by the actuator having the thin film piezoelectric element.

Further, the above problem is solved by an inkjet head having the above actuator or the like.

Further, the above-mentioned problem is solved by the image-forming apparatus having the above-mentioned inkjet head.

According to the present invention, a thin-film piezoelectric element in which a decrease in the displacement amount of the piezoelectric body is suppressed over time when pulse-driven for a long period of time in a high-temperature environment, a method for manufacturing the same, an actuator having the thin-film piezoelectric element, An inkjet head having an actuator and an image forming apparatus having the inkjet head are provided.

FIG. 1 is a cross-sectional view in the thickness direction showing a schematic configuration of a thin-film piezoelectric element according to the first embodiment of the present invention. FIG. 2 is a flowchart showing a method for manufacturing a thin-film piezoelectric element according to a second embodiment of the present invention. FIG. 3 is a flowchart showing each step included in the step of forming the upper electrode (step S110) in the second embodiment of the present invention. FIG. 4 is a flowchart showing each step included in the step of forming the lower electrode (step S150) in the second embodiment of the present invention. FIG. 5 is a graph showing the relationship between the number of applied pulses and the reduction rate of the displacement amount of the actuator when a drive voltage of 10 billion pulses is applied to each of ACT-1 and ACT-2 in the embodiment. is there. FIG. 6 shows the number of applied pulses and the rate of decrease in injection speed when a drive voltage of 10 billion pulses was applied to each of the inkjet head having ACT-1 and the inkjet head having ACT-2 in the embodiment. It is a graph which shows the relationship of.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The common members in each figure are designated by the same reference numerals. Moreover, the present invention is not limited to the following forms.

[Thin film piezoelectric element]
FIG. 1 is a cross-sectional view in the thickness direction showing a schematic configuration of the thin film piezoelectric element 100 according to the first embodiment of the present invention.

As shown in FIG. 1, the thin-film piezoelectric element 100 has an upper electrode 110, an orientation control layer 120, a piezoelectric body 130, a low dielectric constant layer 140, a lower electrode 150, and a diaphragm 160 arranged in this order.

The upper electrode 110 is an electrode made of an Ir—Ti alloy containing iridium (Ir) and titanium (Ti) as main components. A part of Ir and Ti is oxidized. The lower electrode 150 can be a thin film member having a film thickness of 0.1 μm to 0.4 μm.

The orientation control layer 120 is a layer arranged between the upper electrode 110 and the piezoelectric body 130 and formed of a material having a relative permittivity lower than that of the piezoelectric body 130. The orientation control layer 120 is a layer for controlling the crystallinity of the material of the piezoelectric body 130 at the time of manufacturing the thin-film piezoelectric element 100 to increase the degree of orientation toward the (001) plane. The orientation control layer 120 may be made of a material having a perovskite-type crystal structure, and may be made of lead lanthanate titanate (PLT), PLZT with zirconium added to PLT, PLT or an alloy with magnesium or manganese added to PLZT, strontium ruthenium oxide, It can be a thin film member having a film thickness of 0.01 μm to 0.2 μm, which is formed of a material such as titanium oxide and magnesium oxide.

The material of the orientation control layer 120 is preferably preferentially oriented on the (001) plane. Thereby, the material (PZT) of the piezoelectric body 130 formed in contact with the surface of the orientation control layer 120 can be preferentially oriented to the (001) plane. From the viewpoint of further enhancing the orientation of the material of the piezoelectric body 130, the PLT which is the material of the orientation control layer 120 preferably has a lanthanum (La) content of more than 0 mol% and 25 mol% or less. Further, it is preferable that the content of Pb is 0 mol% or more and 30 mol% or less excess of the stoichiometric composition.

In this embodiment, the piezoelectric body 130 is made of a material having a rhombohedral crystal system or a tetragonal crystal system perovskite type crystal structure. The material of the piezoelectric body 130 is not particularly limited as long as it has the above-mentioned perovskite type crystal structure, but it is preferable that the A site of the perovskite structure (ABO ₃ ) contains lead (Pb), and lead zirconate titanate (PZT) is used. It is preferable to have. The piezoelectric body 130 can be a thin film-like member having a film thickness of 0.5 μm to 5.0 μm.

The PZT is preferentially oriented toward the (001) plane, and for example, the degree of orientation toward the (001) plane can be 90% or more. The degree of orientation to the (001) plane was measured using Cu—Kα rays in the X-ray diffraction method, and each crystal plane of PZT having a perovskite-type crystal structure in the range of 2θ of 10 ° to 70 °. It is the ratio of the peak intensity from the (001) plane to the total of the peak intensities.

The composition of the above PZT is such that the composition ratio of zirconium (Zr) and titanium (Ti) entering the B site is near the boundary between the tetragonal crystal and the rhombic crystal (morphoscopic boundary, Zr / Ti = 53/47). It is preferable that there is Zr / Ti = 30/70 to 70/30. Further, the PZT may contain strontium (Sr), niobium (Nb), Al and the like, and lead magnesium niobate (PMN-PT) and lead zirconate titanate (PZN-PT). And so on.

The low dielectric constant layer 140 is a layer arranged between the lower electrode 150 and the piezoelectric body 130 and formed of a material having a dielectric constant lower than that of the piezoelectric body 130. The low dielectric constant layer 140 suppresses a leak current that tends to occur during long-term driving by relaxing the stress generated in the piezoelectric body 130 when a voltage is applied. The low dielectric constant layer 140 is formed of materials such as PLT, PLZT, PLT or PLZT with magnesium or manganese added, strontium oxide ruthenium oxide, strontium oxide titanium oxide, and magnesium oxide, and has a thickness of 0.01 μm to 0. It can be a thin film member of .2 μm.

The lower electrode 150 is an electrode made of an Ir—Ti alloy containing Ir as a main component. A part of Ir and Ti is oxidized. The lower electrode 150 can be a thin film member having a film thickness of 0.1 μm to 0.4 μm.

The diaphragm 160 is a thin film-like member that vibrates by being displaced in the thickness direction by the volume fluctuation (displacement) of the piezoelectric body 130 due to the piezoelectric effect. In the present embodiment, the diaphragm has a laminated structure having a diaphragm 160a and a diaphragm 160b.

The diaphragm 160a is made of a material (metal) having a Young's modulus smaller than that of the diaphragm 160b. Such a diaphragm 160a relaxes the stress during manufacturing, and cracks occur in the piezoelectric body 130 (or the upper electrode 110, the orientation control layer 120, the low dielectric constant layer 140, the lower electrode 150, etc.) due to the stress. Suppress.

The diaphragm 160b is made of a material (metal) having a Young's modulus larger than that of the diaphragm 160a. Such a diaphragm 160b makes it possible to extract a larger generated pressure from the displacement generated by the piezoelectric body 130.

Further, the diaphragm 160 has the diaphragm 160a having a smaller Young ratio on the side closer to the piezoelectric body 130 and the diaphragm 160a having a larger Young ratio on the side farther from the piezoelectric body 130, whereby the vibration center is centered. The position can be changed to a position farther from the piezoelectric body 130 to make it easier to displace the diaphragm 160.

The material and composition of the vibrating plate are not particularly limited, but for example, chromium (Cr), nickel (Ni), aluminum (Al), copper (Cu), gold (Au), tantalum (Ta), tungsten (W), molybdenum. Formed from (Mo), platinum (Pt), iridium (Ir) and silicon (Si), and oxides or nitrides thereof (eg, silicon dioxide, aluminum oxide, zirconium oxide, and silicon nitride), etc. It can be a thin film-like member having a film thickness of 2.0 μm to 10.0 μm. The combination of the materials used for the diaphragm 160a and the diaphragm 160b is not particularly limited, but for example, the diaphragm 160a is formed to include Au, Cu, Al and the like, and the diaphragm 160b is Cr, Mo, Ti, W, etc. It is preferably formed containing Pt, Ir and the like.

In the present embodiment, the upper electrode 110 and the lower electrode 150 are electrodes made of an Ir—Ti alloy containing Ir as a main component, and both Ir and Ti are partially oxidized. The Ir-Ti alloy containing Ir as a main component means an alloy having an Ir content higher than that of Ti.

According to the findings of the present inventors, when the thin-film piezoelectric element is pulse-driven for a long period of time in a high temperature environment, oxygen is released from the piezoelectric body 130, which shifts the hysteresis curve of the piezoelectric body and causes the piezoelectric body. The amount of displacement of 130 decreases with time. The change over time in the amount of displacement is particularly remarkable in an inkjet head or the like that changes the applied voltage in a complicated manner (applies a complicated waveform).

On the other hand, when the upper electrode 110 and the lower electrode 150 contain Ir in which a part thereof is oxidized and Ti in which a part thereof is oxidized, a decrease in the displacement amount of the piezoelectric body 130 with time is suppressed. Will be done. It is considered that this is because the oxide contained in the upper electrode 110 and the lower electrode 150 prevents oxygen from escaping from the piezoelectric body 130.

In this embodiment, the oxide of the Ir comprises IrO _2. Further, in the present embodiment, the oxides of Ti are TiO ₂ and Ti ₂ O ₃ . Oxides of the above Ti is may include either one of TiO ₂ and _Ti 2 _{O 3,} it is preferable to include both TiO ₂ and _Ti 2 _{O 3.}

Of the Ir atoms contained in the upper electrode 110 and the lower electrode 150, the ratio of the Ir atoms that are the oxide (IrO ₂ ) is the bond spectrum obtained by X-ray photoelectron spectroscopy XPS analysis measurement with respect to the total amount of Ir atoms. From the strength ratio, it is preferably 5% to 50% or less, more preferably 10% to 40%, and even more preferably 15% to 35%. Ir, which is a noble metal, is difficult to oxidize, but by annealing as in the production method described later, oxidation of Ir can be promoted, and the proportion of Ir atoms that are oxides can be within the above range. Further, by increasing the proportion of Ir atoms as oxides as in the above range, the escape of oxygen from the piezoelectric body 130 can be more effectively suppressed, and the displacement amount of the piezoelectric body 130 over time can be suppressed. The decrease can be further suppressed.

Of the Ti atoms contained in the upper electrode 110 and the lower electrode 150, the proportion of oxides that are TiO ₂ and Ti ₂ O ₃ is preferably 90% or more, which is close to 100%. Still converted the ratio of TiO ₂ and _Ti 2 _{O 3} than the analysis of the binding spectrum intensity ratio by X-ray photoelectron spectroscopy XPS analysis measurement, when the strength of the TiO ₂ of TiO ₂ and _Ti 2 _{O 3} and 100%, Ti ₂ preferably the ratio of O ₃ is 40% or less 5%, more preferably from 10% to 30%, more preferably from 10% and 20%. Since TiO ₂ is also an oxidized state necessary for orientation control, it is preferable that the ratio is superior to that of Ti ₂ O ₃ . The presence of the oxide of Ti in the state of TiO ₂ and Ti ₂ O ₃ more effectively suppresses the escape of oxygen from the piezoelectric body 130, further reducing the displacement amount of the piezoelectric body 130 with time. It can be suppressed.

Further, in the present embodiment, the unoxidized Ir is a (111) oriented Ir crystal and a (002) oriented Ir crystal. The unoxidized Ir may be present as either a (111) oriented Ir crystal or a (002) oriented Ir crystal, but the (111) oriented Ir crystal and the (002) oriented Ir crystal. It is preferable that both Ir crystals are present.

Ir contained in the upper electrode 110 and the lower electrode 150 is the sum of the diffraction intensities of the (111) plane and the (002) plane in the range of the diffraction angle of θ-2θ measurement of the X-ray diffraction measurement in the range of 10 ° to 70 °. When it is 100%, the degree of orientation to (111) is preferably 70% or more and 95% or less, more preferably 80% or more and 95% or less, and further preferably 85% or more and 95% or less. ..

Further, Ir contained in the upper electrode 110 and the lower electrode 150 preferably has an orientation degree to the (002) plane of 5% or more and 30% or less, more preferably 5% or more and 20% or less. It is more preferably% or more and 15% or less. Since the (111) orientation is an orientation necessary for controlling the orientation of the piezoelectric body, it is preferable to have a significant degree of orientation with respect to the (002) orientation.

The Ti enhances the adhesion of the upper electrode 110 to the substrate used in manufacturing and the adhesion of the lower electrode 150 to the diaphragm 160. Further, the Ti facilitates preferential alignment of the material (PLT) of the orientation control layer 120 on the (001) plane when the orientation control layer 120 is crystal-grown on the surface of the upper electrode 110. On the other hand, in order to suppress the decrease in conductivity due to the increase in the content of Ti having a higher specific resistance, the content of Ti in the upper electrode 110 and the lower electrode 150 is based on the total mass of Ir and Ti. It is preferably more than 0% by mass and 10% by mass or less, more preferably 0.1% by mass or more and 0.8% by mass or less, and 0.1% by mass or more and 0.4% by mass or less. It is more preferable, and it is particularly preferable that it is 0.2% by mass or more and 1.0% by mass or less.

The upper electrode 110 and the lower electrode 150 may contain metal atoms other than Ir and Ti.

[Manufacturing method of thin film piezoelectric element]
FIG. 2 is a flowchart showing a method of manufacturing the thin film piezoelectric element 100 according to the second embodiment of the present invention.

In the thin film piezoelectric element 100, the upper electrode 110 is formed on one surface of the substrate (step S110), and then the orientation control layer 120 is formed (step S120), the piezoelectric body 130 is formed (step S130), and the low dielectric constant layer 140 is formed. (Step S140), the lower electrode 150 (step S150), and the vibrating plate 160 (step S160) are formed in this order.

The substrate is not particularly limited, and a silicon (Si) wafer, a glass substrate, a metal substrate, a ceramic substrate, or the like can be used.

An adhesion layer may be formed on the surface of the substrate on which the thin-film piezoelectric element 100 is formed. The adhesion layer is a layer for enhancing the adhesion of the upper electrode 110 to the substrate. The adhesion layer is preferably a layer formed of Ti, Ta, iron (Fe), cobalt (Co), Ni and Cr, and an alloy containing these atoms, and further enhances the adhesion of the upper electrode 110. From the viewpoint, a layer containing Ti is more preferable. The adhesion layer can be a layer having a film thickness of 0.005 to 1 μm.

In the step of forming the upper electrode 110 (step S110), the upper electrode 110 is formed on the surface of the substrate or the surface of the adhesion layer.

FIG. 3 is a flowchart showing each step included in the step of forming the upper electrode 110 (step S110).

The upper electrode 110 is formed by a step of forming an electrode film by a reactive sputtering method (step S112) and a step of annealing the formed electrode film in an oxygen atmosphere (step 114).

In the film formation of the electrode film (step S112), an alloy sintered body target made of an Ir—Ti alloy is used, and while heating the substrate, a mixed gas of argon and oxygen is used as an RF power source (high frequency power source) in the presence of an atmospheric gas. ) Is performed to form an electrode film.

Since the alloy sintered body target makes it easy to control the composition ratio of Ir and Ti in the formed upper electrode 110 and makes it easier to distribute Ti more uniformly in the upper electrode 110, the Ir target and the Ti target It is preferable to use two kinds of. The Ti content in the alloy sintered body target can be substantially the same as the Ti content in the upper electrode to be formed, and is more than 0% by mass with respect to the total mass of Ir and Ti. It is preferably 0.1% by mass or less, more preferably 0.1% by mass or more and 0.8% by mass or less, further preferably 0.1% by mass or more and 0.4% by mass or less, and 0.2. It is particularly preferable that it is mass% or more and 1.0 mass% or less.

The heating temperature of the substrate is preferably 300 ° C. or higher and 500 ° C. or lower. In order to effectively prevent oxygen from escaping from the piezoelectric body 130, it is important that Ir contained in the upper electrode 110 is also sufficiently oxidized. By raising the heating temperature, not only Ti but also Ir, which is a precious metal, can be more actively oxidized. Raising the heating temperature of the substrate is advantageous for oxidation, but the heating temperature is more preferably 300 ° C. to 400 ° C. in consideration of the fact that the stress due to the difference in the coefficient of linear expansion from the substrate increases. , 300 ° C to 350 ° C, more preferably.

The atmospheric gas may be a gas obtained by mixing oxygen with an inert gas. The oxygen partial pressure in the atmospheric gas is preferably more than 0% and 30% or less, more preferably 2% or more and 30% or less, from the viewpoint of more sufficiently oxidizing Ir and Ti. It is more preferably% or more and 30% or less, and particularly preferably more than 10% and 30% or less. The degree of vacuum of the atmospheric gas is not particularly limited, but is preferably 0.05 Pa or more and 5.0 Pa or less, and more preferably 0.5 Pa or more and 2.0 Pa or less.

The input power and the sputtering time from the RF power supply are not particularly limited, and for example, the film formation may be performed for 10 minutes with an input power of 500 W.

Annealing of the formed electrode film (step S114) is performed in order to promote the oxidation of the electrode film and particularly to more positively oxidize Ir, which is a noble metal.

The substrate temperature at the time of annealing is preferably higher than the substrate temperature at the time of forming the electrode film, for example, preferably 350 ° C. to 600 ° C., more preferably 400 ° C. to 550 ° C., 400 ° C. More preferably, the temperature is from ° C to 500 ° C.

The annealing is performed in an oxygen atmosphere. The pressure of the atmospheric gas (oxygen gas) at this time is preferably 0.5 Pa to 30 Pa, more preferably 1 Pa to 10 Pa, and further preferably 3 Pa to 5 Pa. The annealing time is not particularly limited, but may be about 5 minutes.

In the step of forming the orientation control layer 120 (step S120), the orientation control layer 120 is formed on the surface (the surface opposite to the substrate) of the formed upper electrode 110.

The orientation control layer 120 uses a sintered target made of the material of the orientation control layer 120, and sputters a mixed gas of argon and oxygen in the presence of an atmospheric gas by an RF power supply (high frequency power supply) while heating the substrate. Do the law and form.

The sintered body target can be an alloy having substantially the same metal atomic ratio as the orientation control layer 120 to be formed, for example, the La content is more than 0 mol% and 25 mol% or less, and , PB can be a PLT in which the content of Pb is 0 mol% or more and 30 mol% or less excess of the stoichiometric composition.

The heating temperature of the substrate at this time is preferably 450 ° C. or higher and 750 ° C. or lower, and more preferably 500 ° C. or higher and 650 ° C. or lower. By setting the heating temperature to 450 ° C. or higher, the crystallinity of the material of the orientation control layer 120 can be sufficiently enhanced, and the perovskite-type crystal structure can be formed in preference to the pyrochlore-type crystal structure. By setting the heating temperature to 750 ° C. or lower, it is possible to suppress a decrease in crystallinity due to evaporation of Pb from the formed film.

The oxygen partial pressure of the atmospheric gas is preferably more than 0% and 10% or less, and preferably 0.5% or more and 10 or less. When the atmospheric gas contains oxygen, the crystallinity of the material of the orientation control layer 120 can be sufficiently enhanced. When the oxygen partial pressure is 10% or less, the orientation of the material of the orientation control layer 120 toward the (001) plane can be sufficiently enhanced.

The degree of vacuum of the atmospheric gas is preferably 0.05 Pa or more and 5 Pa or less, and more preferably 0.1 Pa or more and 2 Pa or less. When the degree of vacuum is 0.05 Pa or more, the variation in crystallinity of the orientation control layer 120 can be suppressed. When the degree of vacuum is 5 Pa or less, the orientation of the material of the orientation control layer 120 toward the (001) plane can be sufficiently enhanced.

The input power and sputtering time from the RF power supply are not particularly limited, and for example, the film formation may be performed for 12 minutes with an input power of 300 W.

In the step of forming the piezoelectric body 130 (step S130), the piezoelectric body 130 is formed on the surface (the surface opposite to the substrate) of the formed orientation control layer 120.

The piezoelectric body 130 uses a sintered body target made of the material of the piezoelectric body 130, and while heating the substrate, a mixed gas of argon and oxygen is sputtered by an RF power source (high frequency power source) in the presence of an atmospheric gas. Go and form.

The sintered body target can be an alloy having substantially the same metal atom ratio as the piezoelectric body 130 to be formed. For example, the composition ratio of zirconium (Zr) and titanium (Ti) entering the B site can be determined. It can be a PZT with Zr / Ti = 30/70 to 70/30.

The heating temperature of the substrate at this time is preferably 450 ° C. or higher and 750 ° C. or lower, and more preferably 525 ° C. or higher and 625 ° C. or lower. By setting the heating temperature to 450 ° C. or higher, the crystallinity of the material of the piezoelectric body 130 can be sufficiently enhanced, and the perovskite-type crystal structure can be formed in preference to the pyrochlore-type crystal structure. By setting the heating temperature to 750 ° C. or lower, it is possible to suppress a decrease in crystallinity due to evaporation of Pb from the formed film.

The oxygen partial pressure of the atmospheric gas is preferably more than 0% and 30% or less, and preferably 1% or more and 10 or less. When the atmospheric gas contains oxygen, the crystallinity of the material of the piezoelectric body 130 can be sufficiently enhanced. When the oxygen partial pressure is 30% or less, the orientation of the material of the piezoelectric body 130 toward the (001) plane can be sufficiently enhanced.

The degree of vacuum of the atmospheric gas is preferably 0.1 Pa or more and 1 Pa or less, and more preferably 0.15 Pa or more and 0.8 Pa or less. When the degree of vacuum is 0.1 Pa or more, it is possible to suppress variations in the crystallinity of the material of the piezoelectric body 130. When the degree of vacuum is 1 Pa or less, the orientation of the material of the piezoelectric body 130 with respect to the (001) plane can be sufficiently enhanced.

The input power and sputtering time from the RF power supply are not particularly limited, and for example, the film formation may be performed for 3 hours with an input power of 250 W.

In the step of forming the low dielectric constant layer 140 (step S140), the low dielectric constant layer 140 is formed on the surface (the surface opposite to the substrate) of the formed piezoelectric body 130.

Since the formation of the low dielectric constant layer 140 can be performed in the same manner as the formation of the orientation control layer 120, overlapping description will be omitted.

In the step of forming the lower electrode 150 (step S150), the lower electrode 150 is formed on the surface (the surface opposite to the substrate) of the formed low dielectric constant layer 140.

FIG. 4 is a flowchart showing each step included in the step of forming the lower electrode 150 (step S150).

The lower electrode 150 is formed by a step of forming an electrode film by a reactive sputtering method (step S152) and a step of annealing the formed electrode film in an oxygen atmosphere (step 154).

Since the film formation and annealing of the electrode film can be performed in the same manner as the film formation and annealing of the electrode film in the formation of the upper electrode 110, overlapping description will be omitted.

In the step of forming the diaphragm 160 (step S160), the diaphragm 160 is formed on the surface (the surface opposite to the substrate) of the formed lower electrode 150.

The method for forming the diaphragm 160 is not particularly limited. For example, using a target made of the material of the diaphragm 160a, argon gas is sputtered with an RF power source (high frequency power source) at room temperature in the presence of atmospheric gas. After that, using a target made of the material of the diaphragm 160b, argon gas can be formed by performing a sputtering method with an RF power source (high frequency power source) in the presence of an atmospheric gas at room temperature.

In this way, a thin-film piezoelectric element 100 is produced in which the upper electrode 110, the orientation control layer 120, the piezoelectric body 130, the low dielectric constant layer 140, the lower electrode 150, and the diaphragm 160 are laminated in this order on the substrate. can do.

The produced thin-film piezoelectric element 100 may then be further processed depending on the use of various actuators. For example, in the produced thin-film piezoelectric element 100, the vibrating plate 160 is electrodeposited on the pressure chamber member (or the material of the pressure chamber member before processing) of the inkjet head using an adhesive, and the substrate and the adhesion layer are further formed. It may be removed by etching, and the upper electrode 110, the orientation control layer 120, and the piezoelectric body 130 may be individualized for each pressure chamber by etching. After that, the inkjet head can be manufactured by adhering them to the ink flow path member and the nozzle plate.

[Use]
The thin-film piezoelectric element can be applied to various applications in which an actuator is used, such as an inkjet head, a memory device, an ultrasonic sensor, and a gyro sensor.

[Other Embodiments]
It should be noted that the above embodiment is merely an example of the embodiment of the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

For example, in each of the above embodiments, both the upper electrode and the lower electrode are made of an Ir-Ti alloy containing Ir as a main component, and both Ir and Ti are electrodes in which a part thereof is oxidized. However, even if only one of the upper electrode and the lower electrode is used as the electrode, the effect of preventing oxygen leakage and suppressing a decrease in the displacement amount of the piezoelectric body with time is exhibited.

Further, the upper electrode and the lower electrode are other than the above Ir—Ti alloy unless the effect of suppressing a decrease in the displacement amount of the piezoelectric body with time when pulse-driven for a long period of time in a high temperature environment is significantly impaired. It may contain other components.

Further, the upper electrode, the orientation control layer, the piezoelectric material, the low dielectric constant layer, and the lower electrode may all have a laminated structure composed of a plurality of layers. Further, the diaphragm may be made of a single layer or may have a laminated structure of three or more layers.

Hereinafter, specific examples of the present invention will be described together with comparative examples, but the present invention is not limited thereto.

(Analysis of Ir-Ti thin film)
Using a sintered target in which 1.0 wt% of Ti was added to Ir, while heating the substrate to 350 ° C., in a mixed gas atmosphere of 0.5 Pa of argon and oxygen (oxygen partial pressure: 20%). An Ir—Ti thin film was formed on one surface of the substrate by reactive sputtering for 10 minutes with the input power from the RF power supply (high frequency power supply) being 500 W. Then, the substrate temperature was raised to 400 ° C., and annealing was performed for 5 minutes while maintaining an atmosphere of 1.0 Pa for oxygen only.

When the Ir-Ti thin film thus annealed was subjected to X-ray diffraction measurement using Cu-Kα rays, peaks (in order of peak intensity) of Ir and Ir oxides and Ti and Ti oxides were observed. It was. As peaks showing Ir crystals, peaks of Ir oriented on the (111) plane (alignment degree: 90%) and the (002) plane (alignment degree: 10%) were observed. The degree of orientation is the ratio of each peak intensity to the total peak intensity of the peaks showing the two Ir crystals.

From this result, it can be seen that the Ir-Ti thin film is made of an Ir-Ti alloy containing Ir as a main component, and a part of both Ir and Ti is oxidized.

Further, when the annealed Ir-Ti thin film was measured by XPS and the peak of Ti2p _3/2 was peak-fitted, it could be separated into valence trivalent (Ti ₂ O ₃ ) and valence divalent (TIO ₂ ). was. Moreover, when the Ir4f _7/2 peak was peak-fitted, it was possible to separate Ir and Ir oxide. Ir ₂ O ₃ is unstable, it is considered that can not exist, the Ir oxide was determined to be IrO _2.

In addition, the bonded spectrum of each atom of the annealed Ir-Ti thin film was measured by X-ray photoelectron spectroscopy XPS analysis measurement. First, among the Ir atoms, the ratio of the Ir atoms that are the oxide (IrO ₂ ) was 30% of the total amount of the Ir atoms from the intensity ratio.

Next, it was determined from the peak fitting analysis that the proportion of oxides of Ti O ₂ and Ti ₂ O ₃ among Ti atoms was 95% or more of the total amount from the spectral ratio. Also from peak fitting analysis Ti2p3 / 2 spectral intensity ratio, it is separated into TiO ₂ and _Ti 2 _{O 3,} when converting the ratio, when the TiO ₂ of TiO ₂ and _Ti 2 _{O 3} and 100, _Ti 2 _{O 3} The ratio of was determined to be approximately 25%.

(Displacement characteristics of actuator)
Using a sintered target containing 1.0 wt% of Ti on a Si substrate, while heating the substrate to 350 ° C., in a mixed gas atmosphere of 0.5 Pa of argon and oxygen (oxygen partial pressure: 20%). ), The Ir-Ti thin film was formed by reactive sputtering for 10 minutes with the input power from the RF power supply (high frequency power supply) being 500 W. Then, the substrate temperature was raised to 400 ° C., and annealing was performed for 5 minutes while maintaining an atmosphere of 1.0 Pa for oxygen only to form an upper electrode.

Using a sintered target prepared by adding lead oxide (PbO) in an excess of 12 mol% from the stoichiometric composition to PLT containing 14 mol% of La on the surface of the formed upper electrode, a substrate was used. In an atmosphere of a mixed gas of argon and oxygen (oxygen partial pressure: 5%) at a temperature of 600 ° C. and a vacuum degree of 0.8 Pa, RF sputtering was performed for 12 minutes with an input power of 300 W to form an orientation control layer.

On the surface of the formed orientation control layer, a PZT sintered body or other 0 get having a composition ratio of Zr and Ti of Zr / Ti = 53/47 was used, and the substrate temperature was 610 ° C. and the degree of vacuum was 0. In an atmosphere of a mixed gas of argon and oxygen (oxygen partial pressure: 5%) at 3 Pa, RF sputtering was performed for 3 hours with an input power of 250 W to form a piezoelectric body.

Using a sintered target prepared by adding lead oxide (PbO) in an excess of 12 mol% from the stoichiometric composition to PLT containing 14 mol% of La on the surface of the formed piezoelectric body, a substrate was used. A low dielectric constant layer was formed by RF sputtering for 12 minutes with an input power of 300 W in an atmosphere of a mixed gas of argon and oxygen (oxygen partial pressure: 5%) at a temperature of 600 ° C. and a vacuum degree of 0.8 Pa.

Using a sintered target to which 1.0 wt% of Ti was added to the surface of the formed low dielectric constant layer, while heating the substrate to 350 ° C., in a mixed gas atmosphere of 0.5 Pa of argon and oxygen. An Ir-Ti thin film was formed by reactive sputtering for 10 minutes at (oxygen partial pressure: 20%) and the input power from the RF power source (high frequency power source) was 500 W. Then, the substrate temperature was raised to 400 ° C., and the lower electrode was formed by annealing for 5 minutes while maintaining an atmosphere of 1.0 Pa for oxygen only.

On the surface of the formed lower electrode, a diaphragm is formed by sputtering for 6 hours at room temperature in a 1 Pa argon gas atmosphere with an input power of 200 W from an RF power source (high frequency power source) using a Cr target. Formed.

Then, the substrate was removed by etching to obtain an actuator-1 (ACT-1).

The upper and lower electrodes are formed by sputtering for 12 minutes in a 1 Pa argon gas atmosphere while heating the substrate to 400 ° C. using a Pt target and setting the input power from the RF power supply (high frequency power supply) to 200 W. Actuator-2 (ACT-2) was obtained in the same manner as in the production of ACT-1 except for the above.

A pulse drive voltage of 15 V, AC, and 60 kHz was applied between both electrodes of ACT-1 and ACT-2, and a drive durability test was performed in a high temperature environment of 50 ° C.

FIG. 5 is a graph showing the relationship between the number of applied pulses and the reduction rate of the displacement amount of the actuator when a driving voltage of 10 billion pulses is applied to each of ACT-1 and ACT-2.

As is clear from FIG. 5, it is composed of an Ir-Ti alloy containing Ir as a main component, and in each of the above Ir and Ti, an Ir-Ti thin film in which a part thereof is oxidized is used for the upper electrode and the lower electrode. In ACT-1, the decrease in the displacement amount of the piezoelectric material with time was suppressed as compared with ACT-2 in which the Pt thin film was used for the upper electrode and the lower electrode.

(Injection characteristics of inkjet head)
ACT-1 and ACT-2 were electrodeposited on the pressure chamber member using an adhesive, and the upper electrode, the low dielectric constant layer and the piezoelectric body were separated for each pressure chamber by etching. Then, these were adhered to the ink flow path member and the nozzle plate to obtain an inkjet head, respectively.

The above-mentioned inkjet head was mounted on an image forming apparatus, and the waveform was adjusted so that the initial speed was 7 m / sec in a high temperature environment of 50 ° C., and a pulse drive durability test of 60 kHz was performed.

FIG. 6 shows the relationship between the number of applied pulses and the rate of decrease in injection speed when a drive voltage of 10 billion pulses is applied to each of the inkjet head having ACT-1 and the inkjet head having ACT-2. It is a graph.

As is clear from FIG. 6, it is composed of an Ir-Ti alloy containing Ir as a main component, and both of the above Ir and Ti use an Ir-Ti thin film in which a part thereof is oxidized is used for the upper electrode and the lower electrode. Compared to ACT-2 in which the Cr thin film was used for the upper electrode and the lower electrode, ACT-1 was suppressed from a decrease in injection speed over time when used in an inkjet head.

According to the thin-film piezoelectric element of the present invention, it is possible to suppress a decrease in the displacement amount of the piezoelectric body with time when the piezoelectric body is pulse-driven for a long period of time in a high temperature environment. Therefore, in the present invention, it is possible to improve the long-term reliability of the thin-film piezoelectric element, especially in applications where the thin-film piezoelectric element is used for a long period of time at high temperature, such as an inkjet head, and the durability of each device provided with the thin-film piezoelectric element is improved. It is expected to contribute to.

100 Thin-film piezoelectric element 110 Upper electrode 120 Orientation control layer 130 Piezoelectric body 140 Low dielectric constant layer 150 Lower electrode 160, 160a, 160b Diaphragm

Claims (17)

A thin-film piezoelectric element having an upper electrode and a lower electrode, and a piezoelectric body having a perovskite structure arranged between the upper electrode and the lower electrode.
At least one of the upper electrode and the lower electrode contains an Ir-Ti alloy containing Ir as a main component, and both Ir and Ti are partially oxidized.
Thin film piezoelectric element. The thin-film piezoelectric element according to claim 1, wherein the Ir-Ti alloy contains IrO ₂ . The thin-film piezoelectric element according to claim 1 or 2, wherein the Ir-Ti alloy contains TiO ₂ and Ti ₂ O ₃ . The thin-film piezoelectric element according to any one of claims 1 to 3, wherein the Ir-Ti alloy contains (111) oriented Ir crystals and (002) oriented Ir crystals. The thin-film piezoelectric element according to any one of claims 1 to 4, wherein the Ir-Ti alloy contains Ti in an amount of more than 0% by mass and 10% by mass or less with respect to the total mass of Ir and Ti. The thin film piezoelectric according to any one of claims 1 to 5, wherein the Ir-Ti alloy contains Ti of 0.2% by mass or more and 1.0% by mass or less with respect to the total mass of Ir and Ti. element. The thin-film piezoelectric element according to any one of claims 1 to 6, which has a low dielectric constant layer arranged between the at least one electrode and the piezoelectric body. The thin-film piezoelectric element according to any one of claims 1 to 7, wherein both the upper electrode and the lower electrode contain the Ir—Ti alloy. The process of forming the lower electrode on one surface of the substrate,
A step of forming a piezoelectric body on the side of the lower electrode opposite to the substrate, and a step of forming an upper electrode on the side of the piezoelectric body opposite to the substrate.
Have,
At least one of the steps of forming the lower electrode and the step of forming the upper electrode is performed by using an Ir-Ti alloy sintered body target containing Ir as a main component in the presence of an atmospheric gas containing oxygen. The process of forming an electrode film by the reactive sputtering method while heating the substrate, and
The step of annealing the formed electrode film in an oxygen atmosphere and
including,
A method for manufacturing a thin film piezoelectric element. The method for manufacturing a thin-film piezoelectric element according to claim 9, wherein the Ir-Ti alloy sintered body target contains Ti in an amount of more than 0% by mass and 10% by mass or less with respect to the total mass of Ir and Ti. The thin-film piezoelectric element according to claim 9 or 10, wherein the Ir-Ti alloy sintered body target contains Ti of 0.2% by mass or more and 1.0% by mass or less with respect to the total mass of Ir and Ti. Manufacturing method. The thin film form according to any one of claims 9 to 11, wherein the film forming step is a step of forming an electrode film by a reactive sputtering method while heating the substrate to 300 ° C. or higher and 500 ° C. or lower. Manufacturing method of piezoelectric element. The step of forming an electrode film is a step of forming an electrode film by a reactive sputtering method in the presence of the atmospheric gas having an oxygen partial pressure of 2% or more and 30% or less, any one of claims 9 to 12. The method for manufacturing a thin film piezoelectric element according to the section. The thin film according to any one of claims 9 to 13, wherein both the steps of forming the lower electrode and the step of forming the upper electrode include the step of forming the film and the step of annealing. A method for manufacturing a state piezoelectric element. An actuator having the thin-film piezoelectric element according to any one of claims 1 to 8, or the thin-film piezoelectric element manufactured by the method according to any one of claims 9 to 14. An inkjet head having the actuator according to claim 15. The image forming apparatus having the inkjet head according to claim 16.

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