JP7268487B2 - Thin-film piezoelectric element and manufacturing method thereof - Google Patents

Description

The present invention relates to a thin film piezoelectric element and its manufacturing method, 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 voltage to the piezoelectric body in the thickness direction is widely used as an actuator in inkjet heads, hard disk drives (HDD), and the like. .

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

Patent Documents 3 to 5 disclose piezoelectric elements using a perovskite-type oxide as a piezoelectric material and using noble metals containing titanium (Ti) or titanium oxide and iridium (Ir) for the upper and lower electrodes. Are listed. Patent Documents 3 to 5 describe that the electrodes can be produced by a sputtering method using a target containing Ti or Ir.

Japanese Patent Application Laid-Open No. 2016-36006 JP 2005-228838 A JP-A-2004-47928 JP 2004-186646 A JP 2005-119166 A

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 of the piezoelectric body decreases during long-term pulse driving, the ejection speed of droplets from the inkjet head also changes with time. From the viewpoint of enhancing the durability of the thin-film piezoelectric element, the piezoelectric body is required to have little change in 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 significantly decreases.

The present invention has been made based on the above findings, and provides a thin-film piezoelectric element that suppresses a decrease in the amount of displacement of the piezoelectric body over time when subjected to long-term pulse driving in a high-temperature environment, and a method for manufacturing the same. , 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, a lower electrode, and a piezoelectric body having a perovskite structure disposed 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.

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

Moreover, the above problems are solved by an actuator having the above thin-film piezoelectric element.

Further, the above problems are solved by an inkjet head having the above actuator and others.

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

INDUSTRIAL APPLICABILITY According to the present invention, a thin-film piezoelectric element in which a decrease in the amount of displacement of a piezoelectric body over time is suppressed when subjected to long-term pulse driving in a high-temperature environment, a method for manufacturing the same, an actuator having the thin-film piezoelectric element, and the like. 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 flow chart showing a method of manufacturing a thin film piezoelectric element according to the second embodiment of the present invention. FIG. 3 is a flowchart showing steps included in the step of forming an upper electrode (step S110) according to the second embodiment of the present invention. FIG. 4 is a flowchart showing steps included in the step of forming a lower electrode (step S150) according to the second embodiment of the present invention. FIG. 5 is a graph showing the relationship between the number of applied pulses and the decrease rate of displacement of the actuator when 10 billion pulses of drive voltage were applied to each of ACT-1 and ACT-2 in the example. be. FIG. 6 shows the number of applied pulses and the reduction rate of ejection speed when 10 billion pulses of driving voltage were applied to each of the inkjet head having ACT-1 and the inkjet head having ACT-2 in the example. is a graph showing the relationship of

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code|symbol is attached|subjected to the member which is common in each figure. 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 a 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 vibration plate 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. Both Ir and Ti are partially oxidized. The lower electrode 150 can be a thin film member with a thickness of 0.1 μm to 0.4 μm.

The orientation control layer 120 is a layer formed between the upper electrode 110 and the piezoelectric body 130 and made of a material having a dielectric constant 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 and increasing the degree of orientation to the (001) plane when the thin-film piezoelectric element 100 is manufactured. The orientation control layer 120 may be made of a material having a perovskite crystal structure, such as lead lanthanum titanate (PLT), PLZT in which zirconium is added to PLT, an alloy in which magnesium or manganese is added to PLT or PLZT, strontium ruthenium oxide, A thin film member having a film thickness of 0.01 μm to 0.2 μm made of a material such as strontium titanium oxide and magnesium oxide can be used.

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

The piezoelectric body 130 is made of a material having a rhombohedral or tetragonal perovskite crystal structure in this embodiment. The material of the piezoelectric body 130 is not particularly limited as long as it has the above-described perovskite crystal structure, but it preferably contains lead (Pb) in the A site of the perovskite structure (ABO ₃ ), such as lead zirconate titanate (PZT). Preferably. The piezoelectric body 130 can be a thin film member with a thickness of 0.5 μm to 5.0 μm.

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

The composition of the 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 rhombohedral crystal (morphotropic boundary, Zr/Ti = 53/47). preferably Zr/Ti=30/70 to 70/30. In addition, the PZT may contain strontium (Sr), niobium (Nb), Al, etc., or may contain lead magnesium niobate titanate (PMN-PT) and lead zinc niobate titanate (PZN-PT). and so on.

The low dielectric constant layer 140 is a layer formed between the lower electrode 150 and the piezoelectric body 130 and made of a material having a lower dielectric constant than the piezoelectric body 130 . The low dielectric constant layer 140 reduces the stress generated in the piezoelectric body 130 when a voltage is applied, thereby suppressing leakage current that tends to occur during long-term driving. The low dielectric constant layer 140 is made of a material such as PLT, PLZT, an alloy of PLT or PLZT with magnesium or manganese added, strontium ruthenium oxide, strontium titanium oxide, and magnesium oxide, and has a thickness of 0.01 μm to 0.01 μm. 0.2 μm thin film member.

The lower electrode 150 is an electrode made of an Ir--Ti alloy containing Ir as a main component. Both Ir and Ti are partially oxidized. The lower electrode 150 can be a thin film member with a thickness of 0.1 μm to 0.4 μm.

The vibration plate 160 is a thin-film member that vibrates while being displaced in the thickness direction due to the volume change (displacement) of the piezoelectric body 130 due to the piezoelectric effect. In this embodiment, the diaphragm has a laminated structure with diaphragm 160a and 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 vibration plate 160a relaxes the stress during manufacturing, and cracks are generated 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 vibration plate 160b makes it possible to take out a larger generated pressure from the displacement generated by the piezoelectric body 130. As shown in FIG.

In addition, diaphragm 160 has diaphragm 160a with a smaller Young's modulus on the side closer to piezoelectric body 130 and diaphragm 160a with a larger Young's modulus on the side farther from piezoelectric body 130. The position can be changed to a position further away from the piezoelectric body 130 to make it easier to displace the diaphragm 160 .

Although the material and configuration of the diaphragm are not particularly limited, for example, chromium (Cr), nickel (Ni), aluminum (Al), copper (Cu), gold (Au), tantalum (Ta), tungsten (W), molybdenum (Mo), platinum (Pt), iridium (Ir) and silicon (Si), and their oxides or nitrides (e.g., silicon dioxide, aluminum oxide, zirconium oxide, silicon nitride, etc.), A thin film member having a film thickness of 2.0 μm to 10.0 μm can be obtained. The combination of materials used for diaphragm 160a and diaphragm 160b is not particularly limited. It is preferably formed containing Pt, Ir, and the like.

In this 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 the main component means an alloy containing more Ir than Ti.

According to the findings of the present inventors, when the thin-film piezoelectric element is pulse-driven in a high-temperature environment for a long period of time, oxygen escapes from the piezoelectric body 130, which shifts the hysteresis curve of the piezoelectric body, The amount of displacement of 130 decreases with time. The change over time in the amount of displacement is conspicuous particularly in an inkjet head 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 partially oxidized Ir and partially oxidized Ti, the decrease in the amount of displacement of the piezoelectric body 130 over time is suppressed. be done. It is believed that this is because the oxides contained in the upper electrode 110 and the lower electrode 150 prevent oxygen from escaping from the piezoelectric body 130 .

In this embodiment, the Ir oxide includes _IrO2 . In the present embodiment, the oxides of Ti are TiO ₂ and Ti ₂ O ₃ . The oxide of Ti may contain either one of TiO ₂ and Ti ₂ O ₃ , but preferably contains both TiO ₂ and Ti ₂ O ₃ .

Among the Ir atoms contained in the upper electrode 110 and the lower electrode 150, the ratio of the Ir atoms forming the oxide (IrO ₂ ) is determined by X-ray photoelectron spectroscopy XPS analysis measurement of the Ir atoms. The strength ratio is preferably from 5% to 50%, more preferably from 10% to 40%, and even more preferably from 15% to 35%. Ir, which is a noble metal, is difficult to oxidize, but by annealing as in the manufacturing method described later, the oxidation of Ir can be accelerated and the proportion of Ir atoms forming oxides can be within the above range. In addition, by increasing the ratio of Ir atoms that form oxides to the above range, oxygen escape from the piezoelectric body 130 is more effectively suppressed, and the amount of displacement of the piezoelectric body 130 changes over time. A decrease can be further suppressed.

Among the Ti atoms contained in the upper electrode 110 and the lower electrode 150, it is preferable that the ratio of the oxides forming TiO ₂ and Ti ₂ O ₃ is 90% or more, and is close to 100%. Furthermore, when the ratio of TiO ₂ and Ti ₂ O ₃ is converted from the analysis of the bond spectrum intensity ratio by X-ray photoelectron spectroscopy XPS analysis measurement, if the intensity of TiO ₂ among TiO ₂ and Ti ₂ O ₃ is 100%, Ti ₂ The proportion of _O3 is preferably 5% to 40% or less, more preferably 10% to 30%, even more preferably 10% to 20%. Since TiO ₂ is in an oxidized state necessary for orientation control, it is preferable that the ratio is superior to that of Ti ₂ O ₃ . Since the oxides of Ti exist in the states of TiO ₂ and Ti ₂ O ₃ , oxygen escape from the piezoelectric body 130 is more effectively suppressed, and the displacement amount of the piezoelectric body 130 is further prevented from decreasing with time. can be suppressed.

In this embodiment, the unoxidized Ir is a (111) oriented Ir crystal and a (002) oriented Ir crystal. The non-oxidized Ir may exist as either (111) oriented Ir crystals or (002) oriented Ir crystals. Preferably both Ir crystals are present.

The Ir contained in the upper electrode 110 and the lower electrode 150 has a diffraction angle of 10° to 70° in θ-2θ measurement of X-ray diffraction measurement, and the sum of the diffraction intensities of the (111) plane and the (002) plane is When 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, the Ir contained in the upper electrode 110 and the lower electrode 150 preferably has a degree of orientation to the (002) plane of 5% or more and 30% or less, more preferably 5% or more and 20% or less. % or more and 15% or less. Since the (111) orientation is an orientation required for controlling the orientation of the piezoelectric material, it is preferable that the orientation be significant with respect to the (002) orientation.

The above Ti enhances the adhesion of the upper electrode 110 to the substrate used during manufacturing and the adhesion of the lower electrode 150 to the vibration plate 160 . Also, Ti makes it easier to preferentially align the material (PLT) of the orientation control layer 120 to 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, which has a higher specific resistance, the content of Ti in the upper electrode 110 and the lower electrode 150 is set to the total mass of Ir and Ti. 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 is more preferable, and it is particularly preferable to be 0.2% by mass or more and 1.0% by mass or less.

Note that 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 flow chart showing a method for manufacturing the thin film piezoelectric element 100 according to the second embodiment of the invention.

The thin-film piezoelectric element 100 is formed by forming the upper electrode 110 on one surface of the substrate (step S110), forming the orientation control layer 120 (step S120), forming the piezoelectric body 130 (step S130), and forming the low dielectric constant layer 140. (Step S140), formation of lower electrode 150 (Step S150), and formation of diaphragm 160 (Step S160) 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 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, or an alloy containing these atoms, and further enhances the adhesion of the upper electrode 110. From the point of view, the layer containing Ti is more preferable. The adhesion layer can be a layer having a 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 steps included in the step of forming upper electrode 110 (step S110).

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

In the deposition of the electrode film (step S112), an alloy sintered target made of an Ir--Ti alloy is used, and while the substrate is heated, a mixed gas of argon and oxygen is supplied in the presence of an atmosphere gas by an RF power source (high frequency power source ) to form an electrode film by reactive sputtering.

The alloy sintered target facilitates control of the composition ratio of Ir and Ti in the upper electrode 110 to be formed, and facilitates more uniform distribution of Ti in the upper electrode 110. Therefore, the Ir target and the Ti target It is more preferable than using two kinds of. The content of Ti in the alloy sintered body target can be substantially the same as the content of Ti in the upper electrode to be formed, and the total mass of Ir and Ti is more than 0% by mass and 10% by mass. % by mass or less, more preferably 0.1% by mass or more and 0.8% by mass or less, even more preferably 0.1% by mass or more and 0.4% by mass or less, and 0.2% by mass or less. It is particularly preferable that the amount is not less than 1.0% by mass and not more than 1.0% by mass.

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 the Ir contained in the upper electrode 110 is also sufficiently oxidized. By increasing the heating temperature, not only Ti but also Ir, which is a noble metal, can be oxidized more positively. Raising the substrate heating temperature is advantageous for oxidation, but considering that the stress due to the difference in coefficient of linear expansion with the substrate increases, the heating temperature is more preferably 300° C. to 400° C. , 300°C to 350°C.

The atmosphere gas may be any gas in which oxygen is mixed with an inert gas. From the viewpoint of sufficiently oxidizing Ir and Ti, the oxygen partial pressure in the atmosphere gas is preferably more than 0% and 30% or less, more preferably 2% or more and 30% or less. % or more and 30% or less, and particularly preferably more than 10% and 30% or less. Although the degree of vacuum of the atmosphere gas is not particularly limited, it 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 power supplied from the RF power source and the sputtering time are not particularly limited. For example, the film formation may be performed with a power of 500 W for 10 minutes.

Annealing of the deposited electrode film (step S114) is performed to accelerate the oxidation of the electrode film, 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 which the electrode film is formed. °C to 500 °C is more preferred.

The annealing is performed in an oxygen atmosphere. At this time, the pressure of the atmosphere gas (oxygen gas) is preferably 0.5 Pa to 30 Pa, more preferably 1 Pa to 10 Pa, even more preferably 3 Pa to 5 Pa. Although the annealing time is not particularly limited, it 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 of the formed upper electrode 110 (the surface opposite to the substrate).

The orientation control layer 120 is formed by sputtering a mixed gas of argon and oxygen with an RF power source (high frequency power source) in the presence of an atmospheric gas while heating the substrate using a sintered body target made of the material of the orientation control layer 120. Practice and form the law.

The sintered body target can be an alloy having substantially the same metal atomic ratio as the orientation control layer 120 to be formed. , and Pb in excess of the stoichiometric composition by 0 mol % or more and 30 mol % or less.

At this time, the heating temperature of the substrate 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 improved, and the perovskite crystal structure can be preferentially formed over the pyrochlore crystal structure. By setting the heating temperature to 750° C. or lower, it is possible to suppress deterioration in crystallinity due to evaporation of Pb from the formed film.

The oxygen partial pressure of the atmosphere gas is preferably more than 0% and 10% or less, more preferably 0.5% or more and 10% or less. By including oxygen in the atmosphere gas, 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 atmosphere 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, variations 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 power supplied from the RF power source and the sputtering time are not particularly limited. For example, the film formation may be performed with an input power of 300 W for 12 minutes.

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 orientation control layer 120 that has been formed.

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 atomic ratio as the piezoelectric body 130 to be formed. For example, the composition ratio of zirconium (Zr) and titanium (Ti) entering the B site is It can be PZT with Zr/Ti=30/70 to 70/30.

At this time, the heating temperature of the substrate 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 improved, and the perovskite crystal structure can be preferentially formed over the pyrochlore crystal structure. By setting the heating temperature to 750° C. or lower, it is possible to suppress deterioration 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, more preferably 1% or more and 10% or less. By including oxygen in the atmosphere gas, 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 atmosphere 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, variations in the crystallinity of the material of the piezoelectric body 130 can be suppressed. When the degree of vacuum is 1 Pa or less, the orientation of the material of the piezoelectric body 130 toward the (001) plane can be sufficiently enhanced.

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

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

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, so redundant description will be omitted.

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

FIG. 4 is a flow chart showing steps 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 reactive sputtering (step S152) and a step of annealing the formed electrode film in an oxygen atmosphere (step 154).

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, so redundant description will be omitted.

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

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

In this manner, the thin-film piezoelectric element 100 is fabricated by laminating 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 vibration plate 160 on the substrate in this order. can do.

The fabricated thin-film piezoelectric element 100 may then undergo further processing depending on the application of various actuators. For example, the manufactured thin-film piezoelectric element 100 is produced by electrodepositing the vibration plate 160 on the pressure chamber member of the inkjet head (or the material of the pressure chamber member before processing) using an adhesive, and then attaching the substrate and the adhesion layer. 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 produced by bonding these to the ink channel member and the nozzle plate.

[Use]
The thin-film piezoelectric element can be applied to various applications in which actuators are used, such as inkjet heads, memory devices, ultrasonic sensors, and gyro sensors.

[Other embodiments]
It should be noted that the above-described embodiment merely shows an example of implementation of the present invention, and the technical scope of the present invention should not be construed in a limited manner. Thus, the invention may be embodied in various forms without departing from its spirit or essential characteristics.

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

In addition, the upper electrode and the lower electrode are made of a material other than the Ir--Ti alloy unless the effect of suppressing the temporal decrease in the amount of displacement of the piezoelectric body when subjected to long-term pulse driving in a high-temperature environment is significantly hindered. It may contain other ingredients.

Moreover, the upper electrode, the orientation control layer, the piezoelectric body, the low dielectric constant layer, and the lower electrode may all have a laminated structure consisting of a plurality of layers. Further, the diaphragm may consist of a single layer, or may have a laminated structure of three or more layers.

EXAMPLES Specific examples of the present invention will be described below together with comparative examples, but the present invention is not limited to these.

(Analysis of Ir--Ti thin film)
While heating the substrate to 350 ° C. using a sintered body target in which 1.0 wt% of Ti is added to Ir, 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 with an RF power supply (high frequency power supply) of 500 W for 10 minutes. Thereafter, the substrate temperature was raised to 400° C., and annealing was performed for 5 minutes while maintaining an atmosphere of 1.0 Pa of only oxygen.

When the Ir--Ti thin film thus annealed was subjected to X-ray diffraction measurement using Cu--Kα rays, peaks of Ir, Ir oxide, Ti, and Ti oxide were observed (in order of peak intensity). rice field. As peaks indicating Ir crystals, peaks of Ir oriented in the (111) plane (degree of orientation: 90%) and (002) plane (degree of orientation: 10%) were observed. The degree of orientation is the ratio of the intensity of each peak to the sum of the peak intensities of the two peaks representing 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 that both Ir and Ti are partially oxidized.

In addition, when the annealed Ir-Ti thin film was subjected to XPS measurement and the peak of Ti2p _3/2 was peak-fitted, it was possible to separate it into trivalent (Ti ₂ O ₃ ) and divalent (TiO ₂ ). was. Also, when the Ir4f7 _/2 peak was peak-fitted, it was possible to separate Ir and Ir oxide. The Ir oxide was determined to be _IrO2 , since _Ir2O3 is considered _unstable and cannot exist.

Also, the annealed Ir--Ti thin film was subjected to X-ray photoelectron spectroscopy XPS analysis to measure the bond spectrum of each atom. First, among the Ir atoms, the ratio of the Ir atoms forming the oxide (IrO ₂ ) was 30% with respect to the total amount of the Ir atoms based on the intensity ratio.

Next, it was determined from the peak fitting analysis that the ratio of oxides to be TiO ₂ and Ti ₂ O ₃ among the Ti atoms was 95% or more of the total amount from the spectral ratio. Also, from the peak fitting analysis of the Ti2p3/2 spectrum intensity ratio, it was possible to separate into TiO ₂ and Ti ₂ O ₃ , and when converting the ratio, if TiO ₂ of TiO 2 and Ti ₂ O ₃ is ₁₀₀ , Ti ₂ O ₃ ratio was determined to be approximately 25%.

(Actuator displacement characteristics)
Using a sintered body target to which 1.0 wt% of Ti is added 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% ), an Ir--Ti thin film was formed by reactive sputtering for 10 minutes with an input power of 500 W from an RF power source (high frequency power source). After that, the substrate temperature was raised to 400° C., and annealing was performed for 5 minutes while maintaining an oxygen atmosphere of 1.0 Pa to form an upper electrode.

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

A sintered body of PZT having a Zr/Ti composition ratio of Zr/Ti of 53/47 was used on the surface of the orientation control layer formed as described above. RF sputtering was performed for 3 hours at an input power of 250 W in a mixed gas atmosphere of argon and oxygen (oxygen partial pressure: 5%) at 3 Pa to form a piezoelectric body.

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

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

Sputtering was performed on the surface of the lower electrode formed above using a Cr target at room temperature in an argon gas atmosphere of 1 Pa at a power of 200 W from an RF power supply (high frequency power supply) for 6 hours to form a diaphragm. formed.

After that, the substrate was removed by etching to obtain Actuator-1 (ACT-1).

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

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

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

As is clear from FIG. 5, an Ir--Ti alloy containing Ir as a main component is used, and both Ir and Ti are partially oxidized Ir--Ti thin films used for the upper and lower electrodes. In ACT-1, the decrease in the amount of displacement of the piezoelectric body over time was suppressed as compared with ACT-2 in which the Pt thin film was used for the upper electrode and the lower electrode.

(Ejection characteristics of inkjet head)
ACT-1 and ACT-2 were electrodeposited on pressure chamber members using an adhesive, and the upper electrode, low dielectric constant layer and piezoelectric were individualized for each pressure chamber by etching. After that, these were adhered to the ink channel member and the nozzle plate, respectively, to form an inkjet head.

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

FIG. 6 shows the relationship between the number of applied pulses and the reduction rate of ejection speed when 10 billion pulses of drive voltage are applied to each of an inkjet head having ACT-1 and an inkjet head having ACT-2. graph.

As is clear from FIG. 6, an Ir--Ti alloy containing Ir as a main component is used, and both Ir and Ti are partially oxidized Ir--Ti thin films used for the upper and lower electrodes. When ACT-1 was used in an ink jet head, the drop in ejection speed over time was suppressed more than ACT-2, in which Cr thin films were used for the upper and lower electrodes.

According to the thin-film piezoelectric element of the present invention, when the piezoelectric body is pulse-driven for a long period of time in a high-temperature environment, the amount of displacement of the piezoelectric body is suppressed from decreasing with time. Therefore, in the present invention, it is possible to improve the long-term reliability of the thin-film piezoelectric element in applications such as inkjet heads, which are used for a long time at high temperatures, and to improve the durability of each device equipped with the thin-film piezoelectric element. expected to contribute to

Reference Signs List 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 (18)

A thin-film piezoelectric element having an upper electrode, a lower electrode, and a piezoelectric body having a perovskite structure disposed between the upper electrode and the lower electrode,
at least one of the upper electrode and the lower electrode comprises an Ir—Ti alloy containing Ir as a main component, and both the Ir and Ti are partially oxidized;
the Ir-Ti _alloy comprises _TiO2 and _Ti2O3 ;
Thin-film piezoelectric element. A thin-film piezoelectric element having an upper electrode, a lower electrode, and a piezoelectric body having a perovskite structure disposed between the upper electrode and the lower electrode,
at least one of the upper electrode and the lower electrode comprises an Ir—Ti alloy containing Ir as a main component, and both the Ir and Ti are partially oxidized;
The Ir—Ti alloy comprises (111) oriented and (002) oriented Ir crystals,
Thin-film piezoelectric element. A thin-film piezoelectric element having an upper electrode, a lower electrode, and a piezoelectric body having a perovskite structure disposed between the upper electrode and the lower electrode,
at least one of the upper electrode and the lower electrode comprises an Ir—Ti alloy containing Ir as a main component, and both the Ir and Ti are partially oxidized;
The Ir-Ti alloy contains more than 0% by mass and no more than 10% by mass of Ti with respect to the total mass of Ir and Ti,
Thin-film piezoelectric element. A thin-film piezoelectric element having an upper electrode, a lower electrode, and a piezoelectric body having a perovskite structure disposed between the upper electrode and the lower electrode,
both the upper electrode and the lower electrode comprise an Ir—Ti alloy containing Ir as a main component, and both the Ir and Ti are partially oxidized;
Thin-film piezoelectric element. The thin film piezoelectric element according to any one of claims 2 to 4, wherein said Ir-Ti alloy contains TiO ₂ and Ti ₂ O ₃ . 5. The thin-film piezoelectric element according to claim 1, wherein said Ir--Ti alloy contains (111)-oriented and (002)-oriented Ir crystals. The thin film piezoelectric element according to any one of claims 1, 2 and 4, wherein the Ir-Ti alloy contains more than 0 mass% and 10 mass% or less of Ti with respect to the total mass of Ir and Ti. . The thin-film piezoelectric according to any one of claims 1 to 3, further comprising a low dielectric constant layer interposed between the electrode containing an Ir-Ti alloy containing Ir as a main component and the piezoelectric body. element. 9. The thin-film piezoelectric element according to claim 1, wherein both the upper electrode and the lower electrode contain the Ir--Ti alloy. The thin film piezoelectric element according to any one of claims 1 to 9, wherein said Ir-Ti alloy contains _IrO2 . The thin-film piezoelectric according to any one of claims 1 to 10, wherein said Ir-Ti alloy contains 0.2% by mass or more and 1.0% by mass or less of Ti with respect to the total mass of Ir and Ti. element. forming a lower electrode on one surface of the substrate;
forming a piezoelectric body on a side of the lower electrode opposite to the substrate; and forming an upper electrode on a side of the piezoelectric body opposite to the substrate;
has
At least one of the step of forming the lower electrode and the step of forming the upper electrode contains Ir as a main component and contains 0.2% by mass or more and 1.0% by mass or less of the total mass of Ir and Ti. A step of forming an electrode film by a reactive sputtering method using an Ir--Ti alloy sintered body target containing Ti while heating the substrate in the presence of an atmospheric gas containing oxygen;
annealing the deposited electrode film in an oxygen atmosphere;
including,
A method for manufacturing a thin-film piezoelectric element. forming a lower electrode on one surface of the substrate;
forming a piezoelectric body on a side of the lower electrode opposite to the substrate; and forming an upper electrode on a side of the piezoelectric body opposite to the substrate;
has
In both the step of forming the lower electrode and the step of forming the upper electrode, an Ir—Ti alloy sintered body target containing Ir as a main component is used in the presence of an oxygen-containing atmospheric gas. A step of forming an electrode film by a reactive sputtering method while heating the
annealing the deposited electrode film in an oxygen atmosphere;
including,
A method for manufacturing a thin-film piezoelectric element. 14. The method of manufacturing a thin-film piezoelectric element according to claim 13, wherein said Ir--Ti alloy sintered body target contains Ti in an amount of more than 0% by mass and not more than 10% by mass with respect to the total mass of Ir and Ti. 15. The thin film piezoelectric element according to claim 13, wherein the Ir--Ti alloy sintered body target contains 0.2% by mass or more and 1.0% by mass or less of Ti with respect to the total mass of Ir and Ti. manufacturing method. 13. The method of manufacturing a thin-film piezoelectric element according to claim 12, wherein both the step 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. The thin film according to any one of claims 12 to 16, wherein the step of forming a film 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. A method for manufacturing a piezoelectric element. 18. The step of forming the 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. 10. A method for manufacturing the thin film piezoelectric element according to claim 1.

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