Piezoelectric laminate, and piezoelectric element

Abstract

To improve the etching treatment efficiency of a piezoelectric film made of alkaline niobium oxide.SOLUTION: A piezoelectric laminate includes a board, an electrode film, and a piezoelectric film composed of an alkali niobium oxide having a perovskite structure represented by a composition formula (K1-xNax)NbO3 (0<x<1). The standard deviation of the particle size of the crystals constituting the piezoelectric film is more than 0.42 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a piezoelectric laminate, a method for manufacturing the piezoelectric laminate, and a piezoelectric element.

Background Art

[0002] Piezoelectric materials are widely used in functional electronic components such as sensors and actuators. As piezoelectric materials, lead-based materials, particularly, perovskite-type ferroelectrics represented by the composition formula Pb(Zr 1-x Ti x )O3 are widely used. Since the PZT-based piezoelectric material contains lead, it is not preferable from the viewpoint of pollution prevention. Therefore, potassium sodium niobate (KNN) has been proposed as a lead-free piezoelectric material (see, for example, Patent Documents 1 and 2). In recent years, there has been a strong demand to further improve the performance of piezoelectric materials made of lead-free materials such as KNN.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to improve the etching efficiency of a piezoelectric film made of an alkali niobate oxide.

Means for Solving the Problems

[0005] According to one aspect of the present invention, a substrate, an electrode film, a composition formula (K 1-x Na x)A piezoelectric laminate comprising a piezoelectric film made of an alkaline niobate oxide having a perovskite structure represented by )NbO3(0 < x < 1), and related technologies thereof are provided, wherein the standard deviation of the crystal grain size of the crystal constituting the piezoelectric film is more than 0.42 μm. [Advantages of the Invention]

[0006] According to the present invention, it is possible to improve the etching efficiency of the piezoelectric film made of alkaline niobate oxide. [Brief Description of the Drawings]

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[0008] [One Embodiment of the Present Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] (1) Configuration of the piezoelectric laminate As shown in FIG. 1, a laminate (laminated substrate) 10 having a piezoelectric film according to this embodiment (hereinafter also referred to as a piezoelectric laminate 10) includes a substrate 1, a lower electrode film 2 formed on the substrate 1, a piezoelectric film (piezoelectric thin film) 3 formed on the lower electrode film 2, and an upper electrode film 4 formed on the piezoelectric film 3.

[0010] As the substrate 1, a single-crystalline silicon (Si) substrate 1a having a surface oxide film (SiO2 film) 1b such as a thermal oxide film or a CVD (Chemical Vapor Deposition) oxide film, that is, an Si substrate having a surface oxide film can be preferably used. Further, as the substrate 1, as shown in FIG. 2, an Si substrate 1a having an insulating film 1d formed of an insulating material other than SiO2 on its surface can also be used. Further, as the substrate 1, an Si substrate 1a having an exposed Si(100) plane or Si(111) plane or the like on its surface, that is, an Si substrate having no surface oxide film 1b or insulating film 1d can also be used. Further, as the substrate 1, an SOI (Silicon On Insulator) substrate, a quartz glass (SiO2) substrate, a gallium arsenide (GaAs) substrate, a sapphire (Al2O3) substrate, or a metal substrate formed of a metal material such as stainless steel (SUS) can also be used. The thickness of the single-crystalline Si substrate 1a can be, for example, 300 to 1000 μm, and the thickness of the surface oxide film 1b can be, for example, 1 to 4000 nm.

[0011] The lower electrode film 2 can be formed using, for example, platinum (Pt). The lower electrode film 2 becomes a single crystal film or a polycrystalline film (hereinafter, these are also referred to as Pt films). The crystal constituting the Pt film is preferably preferentially oriented in the (111) plane direction with respect to the surface of the substrate 1. That is, the surface of the Pt film (the surface that becomes the base of the piezoelectric film 3) is preferably mainly composed of the Pt(111) plane. The Pt film can be formed using techniques such as sputtering and vapor deposition. In addition to Pt, the lower electrode film 2 can also be formed using various metals such as gold (Au), ruthenium (Ru), or iridium (Ir), alloys having these as main components, metal oxides such as strontium ruthenate (SrRuO3, abbreviation: SRO) or lanthanum nickelate (LaNiO3, abbreviation: LNO). Note that, between the substrate 1 and the lower electrode film 2, an adhesion layer 6 mainly composed of, for example, titanium (Ti), tantalum (Ta), titanium oxide (TiO2), nickel (Ni), ruthenium oxide (RuO2), iridium oxide (IrO2), etc. may be provided to enhance their adhesion. The adhesion layer 6 can be formed using techniques such as sputtering and vapor deposition. The thickness of the lower electrode film 2 can be, for example, 100 to 400 nm, and the thickness of the adhesion layer 6 can be, for example, 1 to 200 nm.

[0012] The piezoelectric film 3 contains, for example, potassium (K), sodium (Na), and niobium (Nb), and has a composition formula (K 1-x Na x)A film can be formed using an alkali niobium oxide represented by NbO3, that is, potassium sodium niobate (KNN). The coefficient x [=Na / (K+Na)] in the above composition formula should be in the range of 0 < x < 1. The piezoelectric film 3 is a polycrystalline film of KNN (hereinafter also referred to as the KNN film 3). The crystal structure of KNN is a perovskite structure. The KNN film 3 may contain substances other than K, Na, and Nb. Here, a film with a composition of 90% or more of K, Na, and Nb is defined as the KNN film 3. Examples of substances other than K, Na, and Nb include calcium zirconate (CaZrO3, abbreviation: CZO), barium zirconate (BaZrO3, abbreviation: BZO), etc. The KNN film 3 can be formed using techniques such as sputtering, PLD (Pulsed Laser Deposition), and sol-gel methods. The thickness of the KNN film 3 can be, for example, 0.5 to 5 μm.

[0013] The crystals constituting the KNN film 3 are preferably preferentially oriented in the (001) plane orientation with respect to the surface of the substrate 1 (when the substrate 1 is, for example, an Si substrate 1a having a surface oxide film 1b or an insulating film 1d, etc., it is the surface of the Si substrate 1a). That is, the surface of the KNN film 3 (the surface that becomes the base of the upper electrode film 4) is preferably mainly composed of the KNN (001) plane orientation. By directly forming the KNN film 3 on a Pt film preferentially oriented in the (111) plane orientation with respect to the surface of the substrate 1, it becomes easy to preferentially orient the crystals constituting the KNN film 3 in the (001) plane orientation with respect to the surface of the substrate 1. For example, it becomes easy to orient 80% or more of the crystals in the crystal group constituting the KNN film 3 in the (001) plane orientation with respect to the surface of the substrate 1, and to make 80% or more of the area of the surface of the KNN film 3 the KNN (001) plane.

[0014] It is preferable that more than half of the crystals constituting the KNN film 3 have a columnar structure. Further, the boundaries between the crystals constituting the KNN film 3, that is, the grain boundaries present in the KNN film 3, preferably penetrate in the thickness direction of the KNN film 3. For example, in the KNN film 3, it is preferable that the grain boundaries penetrating in the thickness direction are more numerous than the grain boundaries that do not penetrate in the thickness direction of the KNN film 3 (for example, grain boundaries parallel to the plane direction of the substrate 1).

[0015] The standard deviation of the particle size of each crystal constituting the KNN film 3 (hereinafter also referred to as the "crystal grain size of KNN") (hereinafter also referred to as the "standard deviation of the KNN film 3") is more than 0.42 μm, preferably 0.45 μm or more, and more preferably 0.50 μm or more. The upper limit value of the standard deviation of the KNN film 3 is not particularly limited, but in the current technology, it is usually about 0.6 μm.

[0016] By making the initial film formation rate slower than the later film formation rate when forming the KNN film 3, the standard deviation of the KNN film 3 can be increased. For example, the initial film formation rate is less than 0.5 μm / hr, preferably 0.2 μm / hr or more and less than 0.5 μm / hr, more preferably 0.2 μm / hr or more and 0.4 μm / hr or less, and the later film formation rate is, for example, 0.5 μm / hr or more and 2 μm / hr or less, preferably 0.5 μm / hr or more and 1.5 μm / hr or less, more preferably 0.5 μm / hr or more and 1 μm / hr or less. In this way, the standard deviation of the KNN film 3 can be made more than 0.42 μm, preferably 0.45 μm or more.

[0017] The initial film formation rate refers to the film formation rate in the initial stage of forming the KNN film 3. The initial stage of film formation refers to the nucleation stage of forming nuclei of KNN (crystal nuclei of KNN) on the lower electrode film 2 (the base of the KNN film 3). The initial stage of film formation refers to, for example, the period from the start of forming the KNN film 3 to 3 to 5 minutes. The later film formation rate refers to the film formation rate in the later stage of forming the KNN film 3. The later stage of film formation is a stage later than the initial stage of film formation, and is the nucleation growth stage of growing the nuclei formed in the initial stage of film formation to form the KNN film 3.

[0018] By reducing the film formation rate at the time of nucleus formation (i.e., the initial film formation rate), the number of nuclei generated on the lower electrode film 2 can be reduced (the nucleus density can be lowered). As a result, at the initial stage of film formation, nuclei are formed roughly (sparsely, in an island-like manner) on the lower electrode film 2.

[0019] By forming nuclei roughly at the initial stage of film formation, the size of the nuclei can be made more non-uniform and the sizes of the respective crystal grains constituting the KNN film 3 can be made uneven, compared to the case of forming nuclei densely (forming nuclei so that the nucleus density becomes high). As a result, the standard deviation of the KNN film 3 can be increased.

[0020] Also, by forming nuclei roughly at the initial stage of film formation, in the later stage of film formation, while the nuclei formed at the initial stage of film formation start to grow, nuclei are formed with a delay in the portions where no nuclei are formed on the lower electrode film 2. The nuclei formed in the later stage of film formation have a shorter growth time than the nuclei formed in the initial stage of film formation. For this reason, the crystal grains formed by the growth of the nuclei formed in the later stage of film formation become smaller than the crystal grains formed by the growth of the nuclei formed in the initial stage of film formation. By forming nuclei also in the later stage of film formation in this way, the standard deviation of the KNN film 3 can be increased.

[0021] The nuclei formed in the later stage of film formation grow so as to fill the spaces between the nuclei that were formed in the initial stage of film formation and have already started to grow. In the present embodiment, since nuclei are formed roughly at the initial stage of film formation, the spaces between adjacent nuclei are wider than in the case where nuclei are formed densely at the initial stage of film formation. For this reason, even when the KNN film 3 is grown until it reaches a predetermined thickness, it is difficult to completely fill the spaces between the nuclei that were formed and grew in the initial stage of film formation with the nuclei that were formed and grew in the later stage of film formation. Thus, when the standard deviation of the KNN film 3 is large, the gaps between the crystal grains constituting the KNN film 3 become large.

[0022] Since the gaps between the crystal grains constituting the KNN film 3 are large, the wet etching rate (hereinafter also referred to as "WER") of the KNN film 3 with respect to a predetermined etching solution (for example, an etching solution containing an alkaline aqueous solution of a chelating agent and not containing hydrofluoric acid) can be increased. That is, since the gaps between the crystal grains constituting the KNN film 3 are large, the etching of the KNN film 3 with respect to a predetermined etching solution can be made to proceed easily. For example, by setting the standard deviation of the KNN film 3 to more than 0.42 μm, when the KNN film 3 is immersed in an etching solution obtained by mixing ethylenediaminetetraacetic acid (abbreviation: EDTA, 5 g, 0.01 mol / L or more and 0.1 mol / L or less (0.01 M or more and 0.1 M or less)) as a chelating agent, aqueous ammonia (NH4OH, 29%, 37 mL), and hydrogen peroxide solution (30%, 125 mL), the etching rate of the KNN film 3 can be made 0.1 μm / min or more, preferably 0.2 μm / min or more. Note that as the chelating agent, ethylenediaminetetraacetic acid (EDTA) compounds, diethylenetriaminepentaacetic acid (DTPA) compounds, etc. can be used. As the EDTA compounds, at least one selected from the group consisting of ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA·2Na), ethylenediaminetetraacetic acid trisodium salt trihydrate (EDTA·3Na), ethylenediaminetetraacetic acid tetrasodium salt tetrahydrate (EDTA·4Na), ethylenediaminetetraacetic acid dipotassium salt dihydrate (EDTA·2K), ethylenediaminetetraacetic acid tripotassium salt dihydrate (EDTA·3K), and ethylenediaminetetraacetic acid diammonium salt (EDTA·2NH3) can be preferably used in addition to EDTA.

[0023] The average value of the particle size of the crystal (crystal group) constituting the KNN film 3 (hereinafter also referred to as the "average particle size of the KNN film 3") can be, for example, more than 1.0 μm and 5 μm or less, preferably 1.5 μm or more and 4 μm or less. The average particle size of the KNN film 3 here refers to the average particle size in the cross section of the KNN film 3 in the plane direction of the substrate 1. The average particle size of the KNN film 3 can be obtained by image analysis of a field of view of an image taken with a scanning electron microscope (for example, an SEM image) or an image taken with a transmission electron microscope (for example, a TEM image). As the image analysis software, for example, "ImageJ" manufactured by Wayne Rasband can be used.

[0024] When the average particle size of the KNN film 3 is more than 1.0 μm, it becomes possible to easily obtain the KNN film 3 having a standard deviation of more than 0.42 μm. When the average particle size of the KNN film 3 is 1.5 μm or more, it becomes possible to more easily obtain the KNN film 3 having a standard deviation within the above range. Note that when the average particle size of the KNN film 3 is 1.0 μm or less, since it is necessary to densely form nuclei on the lower electrode film 2, it may not be possible to obtain the KNN film 3 having a standard deviation within the above range.

[0025] When the average particle size of the KNN film 3 is 5 μm or less, the distribution of the physical property values of the KNN film 3 can be made uniform in the plane, and when the average particle size of the KNN film 3 is 4 μm or less, the distribution of the physical property values of the KNN film 3 can be made more uniform in the plane. The "physical property values of the KNN film 3" referred to here are, for example, the piezoelectric constant, leakage current density, dielectric constant, etc. of the KNN film 3.

[0026] The KNN film 3 preferably contains a metal element selected from the group consisting of copper (Cu) and manganese (Mn) at a concentration in the range of, for example, 0.2 at% or more and 2.0 at% or less. When both Cu and Mn are added to the KNN film 3, Cu and Mn are added to the KNN film 3 so that the total concentration of Cu and Mn is within the above concentration range.

[0027] By adding at least one of Cu or Mn to the KNN film 3 within the above-mentioned concentration range, it becomes possible to improve the film properties of the KNN film 3. For example, it becomes possible to enhance the insulation property (leakage resistance) of the KNN film 3 or to make the relative permittivity of the KNN film 3 an appropriate magnitude according to the application of the piezoelectric laminate 10.

[0028] For example, when the total concentration of Cu and Mn in the KNN film 3 is within the above-mentioned range, the leakage current density when an electric field of 250 kV / cm is applied to the KNN film 3 in its thickness direction is 500 μA / cm 2 Hereinafter, preferably 250 μA / cm 2 Hereinafter, more preferably 200 μA / cm 2 It can be made below.

[0029] Also, for example, when the total concentration of Cu and Mn in the KNN film 3 is within the above-mentioned range, it becomes possible to make the relative permittivity of the KNN film 3 measured under the conditions of a frequency of 1 kHz and ±1 V to be 1500 or less, preferably 300 or more and 1200 or less. When the relative permittivity of the KNN film 3 is within the above-mentioned range, when the piezoelectric laminate 10 is applied to a sensor, for example, there is a tendency that a decrease in sensitivity is less likely to occur. This is considered as one of the reasons that the addition amounts of Cu and Mn are appropriate and the crystals constituting the KNN film 3 can be preferentially oriented in the (001) plane orientation with respect to the surface of the substrate 1.

[0030] In addition, by adding Cu to the KNN film 3 within the above-described concentration range, it becomes possible to extend the life of the KNN film 3. This is because oxygen vacancies (oxygen vacancies) exist at a predetermined ratio inside the crystals (crystallite grains) constituting the KNN film 3 and at the grain boundaries of the KNN film 3. The oxygen vacancies at the grain boundaries of the KNN film 3 may move, for example, when an electric field is applied to the KNN film 3. When the oxygen vacancies move and reach the electrode film (the lower electrode film 2 or the upper electrode film 4), the oxygen vacancies react with the metal contained in the electrode film and cause a short circuit. By adding Cu to the KNN film 3 within the above-described concentration range, this Cu pairs with the oxygen vacancies at the grain boundaries of the KNN film 3, that is, the Cu at the grain boundaries traps the oxygen vacancies, and it is possible to reduce the oxygen vacancies at the grain boundaries of the KNN film 3 that move toward the electrode film when an electric field is applied or the like. As a result, the life of the KNN film 3 can be extended.

[0031] In addition, by adding Cu to the KNN film 3 within the above-described concentration range, in addition to making the WER with respect to an etching solution containing an alkaline aqueous solution of a chelating agent within the above-described range and improving the above-described film characteristics, it is also possible to enhance the resistance (etching resistance) to a fluorine-based etching solution (for example, a buffered hydrofluoric acid (BHF) solution containing hydrogen fluoride (HF) and ammonium fluoride (NH4F) at predetermined concentrations respectively). As a result, it becomes unnecessary to form a protective film for protecting the exposed surface of the KNN film 3. That is, it becomes possible to use a BHF solution as the etching solution without forming a protective film. As a result, the processing process in the treatment after forming the piezoelectric laminate 10 can be simplified.

[0032] The KNN film 3 may contain elements other than K, Na, Nb, Cu, and Mn such as lithium (Li), Ta, and antimony (Sb) at a concentration that can maintain the standard deviation of the KNN film 3 within the above-described range, for example, a concentration of 5 at% or less.

[0033] The upper electrode film 4 can be formed using various metals such as Pt, Au, aluminum (Al), Cu, or alloys thereof. The upper electrode film 4 can be formed using techniques such as sputtering, vapor deposition, plating, or the metal paste method. The upper electrode film 4 does not significantly affect the crystal structure of the KNN film 3 like the lower electrode film 2. Therefore, the material, crystal structure, and film formation technique of the upper electrode film 4 are not particularly limited. Note that an adhesion layer mainly composed of, for example, Ti, Ta, TiO2, Ni, etc. may be provided between the KNN film 3 and the upper electrode film 4 to enhance their adhesion. The thickness of the upper electrode film 4 can be, for example, 10 to 5000 nm, and when an adhesion layer is provided, the thickness of the adhesion layer can be, for example, 1 to 200 nm.

[0034] (2) Configuration of the piezoelectric device Fig. 3 shows a schematic configuration diagram of a device 30 having the KNN film 3 in the present embodiment (hereinafter also referred to as the piezoelectric device 30). The piezoelectric device 30 includes at least an element 20 obtained by shaping the above-described piezoelectric laminate 10 into a predetermined shape (the element 20 having the KNN film 3, hereinafter also referred to as the piezoelectric element 20), and a voltage application unit 11a or a voltage detection unit 11b connected to the piezoelectric element 20. The voltage application unit 11a is a means for applying a voltage between the lower electrode film 2 and the upper electrode film 4 (between the electrodes), and the voltage detection unit 11b is a means for detecting the voltage generated between the lower electrode film 2 and the upper electrode film 4 (between the electrodes). As the voltage application unit 11a and the voltage detection unit 11b, various known means can be used.

[0035] By connecting the voltage application unit 11a between the lower electrode film 2 and the upper electrode film 4 of the piezoelectric element 20, the piezoelectric device 30 can function as an actuator. By applying a voltage between the lower electrode film 2 and the upper electrode film 4 with the voltage application unit 11a, the KNN film 3 can be deformed. By this deformation operation, various members connected to the piezoelectric device 30 can be actuated. In this case, examples of the applications of the piezoelectric device 30 include a head for an inkjet printer, a MEMS mirror for a scanner, a vibrator for an ultrasonic generator, etc.

[0036] By connecting the voltage detection unit 11b between the lower electrode film 2 and the upper electrode film 4 of the piezoelectric element 20, the piezoelectric device 30 can function as a sensor. When the KNN film 3 deforms with a change in some physical quantity, a voltage is generated between the lower electrode film 2 and the upper electrode film 4 due to the deformation. By detecting this voltage with the voltage detection unit 11b, the magnitude of the physical quantity applied to the KNN film 3 can be measured. In this case, examples of the applications of the piezoelectric device 30 include an angular velocity sensor, an ultrasonic sensor, a pressure sensor, an acceleration sensor, and the like.

[0037] (3) Manufacturing methods of piezoelectric laminate, piezoelectric element, and piezoelectric device Hereinafter, the manufacturing methods of the above-described piezoelectric laminate 10, piezoelectric element 20, and piezoelectric device 30 will be described.

[0038] First, prepare the substrate 1, and form a adhesion layer 6 (Ti layer) and a lower electrode film 2 (Pt film) in this order on any one of the main surfaces of the substrate 1 by, for example, sputtering method. Note that, a substrate 1 on which the adhesion layer 6 or the lower electrode film 2 is previously formed on any one of the main surfaces may be prepared.

[0039] As conditions for forming the adhesion layer 6, the following conditions are exemplified. Temperature (substrate temperature): 100°C or higher and 500°C or lower, preferably 200°C or higher and 400°C or lower Discharge power: 1000 W or higher and 1500 W or lower, preferably 1100 W or higher and 1300 W or lower Atmosphere: Argon (Ar) gas atmosphere Atmospheric pressure: 0.1 Pa or higher and 0.5 Pa or lower, preferably 0.2 Pa or higher and 0.4 Pa or lower Time: 30 seconds or longer and 3 minutes or shorter, preferably 30 seconds or longer and 2 minutes or shorter

[0040] As conditions for forming the lower electrode film 2, the following conditions are exemplified. Film formation temperature (substrate temperature): 100°C or higher and 500°C or lower, preferably 200°C or higher and 400°C or lower Discharge power: 1000 W or more and 1500 W or less, preferably 1100 W or more and 1300 W or less Film formation atmosphere: Ar gas atmosphere Atmospheric pressure: 0.1 Pa or more and 0.5 Pa or less, preferably 0.2 Pa or more and 0.4 Pa or less Film formation time: 3 minutes or more and 10 minutes or less, preferably 4 minutes or more and 7 minutes or less

[0041] Subsequently, a KNN film 3 is formed on the lower electrode film 2 by, for example, sputtering. The composition ratio of the KNN film 3 can be adjusted by controlling the composition of the target material used during sputtering film formation. The target material can be produced by, for example, mixing K2CO3 powder, Na2CO3 powder, Nb2O5 powder, Cu powder (or CuO powder, Cu2O powder), MnO powder, etc. and firing them. The composition of the target material can be controlled by adjusting the mixing ratio of K2CO3 powder, Na2CO3 powder, Nb2O5 powder, Cu powder (or CuO powder, Cu2O powder), MnO powder.

[0042] As conditions for forming the KNN film 3, the following conditions are exemplified. Note that the film formation time is appropriately set according to the thickness of the KNN film 3 to be formed. Film formation temperature (substrate temperature): 500 °C or more and 700 °C or less, preferably 550 °C or more and 650 °C or less Discharge power: 2000 W or more and 2400 W or less, preferably 2100 W or more and 2300 W or less Film formation atmosphere: Ar gas + oxygen (O2) gas atmosphere Atmospheric pressure: 0.2 Pa or more and 0.5 Pa or less, preferably 0.2 Pa or more and 0.4 Pa or less Partial pressure of Ar gas with respect to O2 gas (Ar / O2 partial pressure ratio): 30 / 1 to 20 / 1, preferably 27 / 1 to 23 / 1 Initial film formation: Period from the start of film formation (0 minute) to 5 minutes, preferably from the start of film formation to 3 minutes Late stage of film formation: Period after the initial film formation Initial film formation rate: Less than 0.5 μm / hr, preferably 0.2 μm / hr or more and less than 0.5 μm / hr, more preferably 0.2 μm / hr or more and 0.4 μm / hr or less Post-film formation speed: 0.5 or more and 2 μm / hr or less, preferably 0.5 μm / hr or more and 1.5 μm / hr or less, more preferably 0.5 μm / hr or more and 1 μm / hr or less

[0043] Then, on the KNN film 3, an upper electrode film 4 is formed, for example, by sputtering. The conditions for forming the upper electrode film 4 can be the same as those for forming the lower electrode film 2 described above. Thereby, a piezoelectric laminate 10 having a substrate 1, a lower electrode film 2, a KNN film 3, and an upper electrode film 4 as shown in FIG. 1 is obtained.

[0044] Then, by shaping the piezoelectric laminate 10 into a predetermined shape by etching or the like, a piezoelectric element 20 as shown in FIG. 3 is obtained, and by connecting at least one of a voltage application unit 11a or a voltage detection unit 11b to the piezoelectric element 20, a piezoelectric device 30 is obtained.

[0045] (4) Effects obtained by this embodiment According to this embodiment, one or more of the following effects can be obtained.

[0046] (a) Since the standard deviation of the KNN film 3 is large, that is, since the standard deviation of the KNN film 3 exceeds 0.42 μm, the WER of the KNN film 3 (for example, the WER with respect to an etching solution containing an alkaline aqueous solution of a chelating agent and not containing hydrofluoric acid) can be increased without adversely affecting the physical properties of the KNN film 3. By increasing the above-described WER of the KNN film 3, for example, the following merits can be obtained.

[0047] For example, consider the process after forming the piezoelectric laminate 10 by depositing an adhesion layer 6, a lower electrode film 2, a KNN film 3, and an upper electrode film 4 in this order on a substrate 1. In the process of forming the piezoelectric element 20 or the piezoelectric device 30, when shaping the piezoelectric laminate 10 into a predetermined shape, a process of shaping the KNN film 3 into a predetermined shape may be performed by wet etching using an etching solution containing an alkaline aqueous solution of a chelating agent. By increasing the WER of the KNN film 3 as described above, it becomes possible to increase the efficiency of the above-described etching process of the KNN film 3. As a result, it becomes possible to increase the productivity of the piezoelectric element 20 or the piezoelectric device 30.

[0048] Also, the time for immersing the KNN film 3 (piezoelectric laminate 10) in the etching solution can be shortened. As a result, it is also possible to suppress the etching damage of the KNN film 3 due to the etching process. That is, the influence of the etching process on the physical properties of the KNN film 3 can be minimized.

[0049] (b) By adding at least one of Cu or Mn to the KNN film 3 within the above-described concentration range, it becomes possible to improve the film characteristics of the KNN film 3 while maintaining a high WER of the KNN film 3. Also, by adding Cu to the KNN film 3 within the above-described concentration range, it becomes possible to suppress the movement of oxygen vacancies on the grain boundaries of the KNN film 3. As a result, it becomes possible to improve the lifespan of the KNN film 3.

[0050] (c) When the average particle size of the KNN film 3 is more than 1.0 μm and 5 μm or less, the physical property value distribution of the KNN film 3 can be made in-plane uniform while keeping the standard deviation of the KNN film 3 within the above-described range. When an electric field is applied to the piezoelectric element 20 or the piezoelectric device 30 manufactured by processing the piezoelectric laminate 10 to drive the KNN film 3, deterioration of the KNN film 3 (for example, a decrease in the piezoelectric constant, etc.) can be suppressed because the physical property value distribution of the KNN film 3 is in-plane uniform.

[0051] <Other Embodiments> The embodiments of the present invention have been specifically described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist thereof.

[0052] (a) For example, the piezoelectric laminate 10 may not include the lower electrode film 2. The piezoelectric laminate 10 may be configured to include a substrate 1, a KNN film (piezoelectric film) 3 formed on the substrate 1, and an upper electrode film 4 (electrode film 4) formed on the KNN film 3. Also in this case, by the standard deviation of the KNN film 3 being more than 0.42 μm, the WER of the KNN film 3 can be increased as described above.

[0053] Fig. 4 shows a cross-sectional configuration diagram of a piezoelectric laminate 10A without the lower electrode film 2. The piezoelectric laminate 10A can be obtained by forming an adhesion layer 6 on the substrate 1, forming the KNN film 3 on the adhesion layer 6, and forming the electrode film 4 on the KNN film 3. The conditions for forming each film (layer) of the piezoelectric laminate 10A can be the same as the conditions for forming each film (layer) of the piezoelectric laminate 10 shown in the above-described embodiment. Also in the piezoelectric laminate 10A, by making the initial film formation rate of the KNN film 3 slower than the later film formation rate, the standard deviation of the KNN film 3 can be made within the above-described range. Note that the piezoelectric laminate 10A may not have the adhesion layer 6. That is, the KNN film 3 may be directly formed on the substrate 1.

[0054] Fig. 5 shows a schematic configuration diagram of a piezoelectric device 30A manufactured using the piezoelectric laminate 10A. The piezoelectric device 30A is configured to include at least a piezoelectric element 20A obtained by shaping the piezoelectric laminate 10A into a predetermined shape, and a voltage application unit 11a and a voltage detection unit 11b connected to the piezoelectric element 20A. In the present embodiment, the piezoelectric element 20A has a pattern electrode formed by shaping the electrode film 4 into a predetermined pattern. For example, the piezoelectric element 20A has a pair of positive and negative pattern electrodes 4p1 on the input side and a pair of positive and negative pattern electrodes 4p2 on the output side. Examples of the pattern electrodes 4p1 and 4p2 include interdigitated transducers (abbreviation: IDT).

[0055] By connecting the voltage application unit 11a between the pattern electrodes 4p1 and connecting the voltage detection unit 11b between the pattern electrodes 4p2, the piezoelectric device 30A can function as a filter device such as a surface acoustic wave (SAW) filter. By applying a voltage between the pattern electrodes 4p1 by the voltage application unit 11a, SAWs can be excited on the surface of the KNN film 3. The adjustment of the frequency of the SAWs to be excited can be performed, for example, by adjusting the pitch of the pattern electrodes 4p1. For example, the shorter the pitch of the IDT as the pattern electrode 4p1, the higher the frequency of the SAWs, and the longer the pitch, the lower the frequency of the SAWs. Among the SAWs excited by the voltage application unit 11a and propagated through the KNN film 3 to reach the pattern electrode 4p2, a voltage is generated between the pattern electrodes 4p2 by the SAWs having a predetermined frequency (frequency component) determined according to the pitch of the IDT as the pattern electrode 4p2 and the like. By detecting this voltage by the voltage detection unit 11b, the SAWs having a predetermined frequency among the excited SAWs can be extracted. Here, the term "predetermined frequency" may include not only a predetermined frequency but also a predetermined frequency band whose center frequency is a predetermined frequency.

[0056] (b) For example, an orientation control layer for controlling the orientation of the crystals constituting the KNN film 3 may be provided between the lower electrode film 2 and the KNN film 3, that is, directly under the KNN film 3. When the lower electrode film 2 is not provided, the orientation control layer may be provided between the substrate 1 and the KNN film 3. The orientation control layer is, for example, a metal oxide such as SRO, LNO, strontium titanate (SrTiO3, abbreviated: STO), and can be formed using a material different from the material constituting the lower electrode film 2. The crystals constituting the orientation control layer are preferably preferentially oriented in the (100) plane with respect to the surface of the substrate 1.

[0057] (c) For example, in addition to or instead of Cu or Mn, the KNN film 3 may contain another metal element that exhibits an effect equivalent to that of Cu or Mn at a concentration that can obtain the above-described effects related to insulation, relative permittivity, or suppression of oxygen vacancy migration while maintaining the high WER of the KNN film 3. Even in this case, the same effects as those of the above-described embodiments can be obtained.

[0058] (d) For example, when forming the above-described piezoelectric laminates 10, 10A into piezoelectric elements 20, 20A, the substrate 1 may be removed from the piezoelectric laminates 10, 10A as long as the piezoelectric devices 30, 30A fabricated using the piezoelectric laminates 10, 10A (piezoelectric elements 20, 20A) can be applied to desired applications such as sensors or actuators.

[0059] <Preferred Embodiments of the Present Invention> The preferred embodiments of the present invention are appended below.

[0060] (Appendix 1) According to one embodiment of the present invention, a substrate, an electrode film, a piezoelectric film made of an alkaline niobate oxide having a perovskite structure represented by the composition formula (K 1-x Na x ) NbO3 (0 <x <1), and a piezoelectric laminate is provided in which the standard deviation of the crystal grain size of the crystal constituting the piezoelectric film is more than 0.42 μm, preferably 0.45 μm or more.

[0061] (Appendix 2) The piezoelectric laminate of Appendix 1, preferably, when the piezoelectric film is etched using an etching solution prepared by mixing 5 g of ethylenediaminetetraacetic acid as a chelating agent at 0.1 M or less, 37 mL of aqueous ammonia having an ammonia concentration of 29%, and 125 mL of aqueous hydrogen peroxide having a concentration of 30%, the etching rate is 0.1 μm / min or more, preferably 0.2 μm / min.

[0062] (Appendix 3) The piezoelectric laminate according to Supplementary Note 1 or 2, preferably, the piezoelectric film contains a metal element selected from the group consisting of copper (Cu) and manganese (Mn) at a concentration of 0.2 at% or more and 2.0 at% or less.

[0063] (Supplementary Note 4) The piezoelectric laminate according to Supplementary Note 3, preferably, the metal element is Cu.

[0064] (Supplementary Note 5) The piezoelectric laminate according to any one of Supplementary Notes 1 to 4, preferably, the average particle diameter of the crystals constituting the piezoelectric film is more than 1.0 μm and 5 μm or less, preferably 1.5 μm or more and 4 μm or less.

[0065] (Supplementary Note 6) According to another aspect of the present invention, a step of forming an electrode film on a substrate, a step of forming a piezoelectric film made of an alkali niobate oxide having a perovskite structure represented by the composition formula (K 1-x Na x )NbO3 (0 <x <1) on the electrode film, and a method for manufacturing a piezoelectric laminate is provided in which, in the step of forming the piezoelectric film, the initial film formation rate is made slower than the later film formation rate.

[0066] (Supplementary Note 7) According to still another aspect of the present invention, a step of forming a piezoelectric film made of an alkali niobate oxide having a perovskite structure represented by the composition formula (K 1-x Na x )NbO3 (0 <x <1) on a substrate is provided, a method for manufacturing a piezoelectric laminate is provided in which, in the step of forming the piezoelectric film, the initial film formation rate is made slower than the later film formation rate.

[0067] (Supplementary Note 8) The method according to Supplementary Note 6 or 7, preferably, The initial film formation rate is less than 0.5 μm / hr, and the later film formation rate is 0.5 μm / hr or more and 2 μm / hr or less.

[0068] (Appendix 9) According to still another aspect of the present invention, a substrate, a lower electrode film formed on the substrate, a piezoelectric film formed on the lower electrode film and composed of an alkali niobate oxide having a perovskite structure represented by the composition formula (K 1-x Na x ) NbO3 (0 <x <1), and an upper electrode film formed on the piezoelectric film, There is provided a piezoelectric element (piezoelectric device) in which the standard deviation of the crystal grain size of the crystal constituting the piezoelectric film exceeds 0.42 μm, preferably 0.45 μm or more.

[0069] (Appendix 10) According to still another aspect of the present invention, a substrate, a piezoelectric film formed on the substrate and composed of an alkali niobate oxide having a perovskite structure represented by the composition formula (K 1-x Na x ) NbO3 (0 <x <1), and an electrode film formed on the piezoelectric film, There is provided a piezoelectric element (piezoelectric device) in which the standard deviation of the crystal grain size of the crystal constituting the piezoelectric film exceeds 0.42 μm, preferably 0.45 μm or more.

Explanation of Reference Numerals

[0070] 1 Substrate 3 Piezoelectric film 10 Piezoelectric laminate

Claims

1. A substrate, An electrode film, Composition formula (K １－ｘ Na ｘ ) NbO ３ A piezoelectric film made of an alkali niobate oxide having a perovskite structure represented by (0 < x < 1), and Among the crystals constituting the piezoelectric film, more than half of the crystals have a columnar structure, The crystals constituting the piezoelectric film are preferentially oriented in the (001) plane orientation with respect to the surface of the substrate, A piezoelectric laminate in which the standard deviation of the particle size of the crystals constituting the piezoelectric film exceeds 0.42 μm.

2. The piezoelectric laminate according to claim 1, wherein the piezoelectric film has an etching rate of 0.2 μm / min or more when etched using an etching solution obtained by mixing 5 g of ethylenediaminetetraacetic acid as a chelating agent at 0.1 M or less, 37 mL of aqueous ammonia having an ammonia concentration of 29%, and 125 mL of aqueous hydrogen peroxide having a concentration of 30%.

3. The piezoelectric laminate according to claim 1 or 2, wherein the piezoelectric film contains a metal element selected from the group consisting of Cu and Mn at a concentration of 0.2 at% or more and 2.0 at% or less.

4. The piezoelectric laminate according to any one of claims 1 to 3, wherein the average particle size of the crystals constituting the piezoelectric film exceeds 1.0 μm and is 5 μm or less.

5. A substrate, A lower electrode film formed on the substrate, formed on the lower electrode film and composed of a piezoelectric film made of an alkaline niobium oxide having a perovskite structure represented by the composition formula (K １－ｘ Na ｘ )NbO ３ (0 < x < 1), and An upper electrode film formed on the piezoelectric film, and Among the crystals constituting the piezoelectric film, more than half of the crystals have a columnar structure, The crystals constituting the piezoelectric film are preferentially oriented in the (001) plane orientation with respect to the surface of the substrate, A piezoelectric element in which the standard deviation of the particle size of the crystals constituting the piezoelectric film exceeds 0.42 μm.

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