Piezoelectric laminate and method for manufacturing piezoelectric laminate

Abstract

To provide a piezoelectric laminate having a piezoelectric film improved in adhesion to an upper electrode film.SOLUTION: A piezoelectric device comprising: a substrate; a piezoelectric film on the substrate; an upper adhesive layer on the piezoelectric film; and a lower adhesive layer on the upper adhesive layer, wherein the piezoelectric film is composed of a perovskite compound expressed by a general formula ABO3, where an A site includes K and Na, and a B site includes Nb, when the piezoelectric film is divided into a surface layer region extending from an upper surface of the piezoelectric film to a predetermined depth toward the substrate and a bulk region that is a region other than the surface layer region, a total atomic concentration of K and Na in the surface layer region is lower than a total atomic concentration of K and Na in the bulk region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to piezoelectric stacks and methods for manufacturing piezoelectric stacks. [Background technology]

[0002] Piezoelectrics are widely used in functional electronic components (devices) such as sensors and actuators. One type of piezoelectric material is a ferroelectric (i.e., a KNN-based ferroelectric) composed of a perovskite-type oxide represented by the general formula ABO3, with the A site containing K and Na and the B site containing Nb. A laminate has been proposed that includes a piezoelectric film (KNN film) formed using a KNN-based ferroelectric. In such a laminate, an upper electrode film is sometimes formed on the piezoelectric film, and high adhesion between the piezoelectric film and the upper electrode film is required. Therefore, an IrO x or RuO x A piezoelectric laminate provided with an adhesive layer made of the above has been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-207055 Summary of the Invention [Problem to be solved by the invention]

[0004] However, there is a problem that the IrO x or RuO x Even when an adhesive layer made of IrO x or RuO x As a result, the adhesion between the piezoelectric film and the upper electrode film may be poor.

[0005] An object of the present disclosure is to provide a piezoelectric stack having a piezoelectric film with improved adhesion to an upper electrode film. [Means for solving the problem]

[0006] According to one aspect of the present disclosure, A substrate; a lower electrode film on the substrate; a piezoelectric film on the lower electrode film, the piezoelectric film being composed of a perovskite oxide represented by the general formula ABO3, the A site containing K and Na, and the B site containing Nb; an upper adhesive layer on the piezoelectric film; an upper electrode film on the upper adhesive layer, When the piezoelectric film is divided into a surface region extending from an upper surface of the piezoelectric film to a predetermined depth toward the substrate, and a bulk region other than the surface region, the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region. A piezoelectric stack is provided.

[0007] According to another aspect of the present disclosure, providing a substrate; A step of preparing a target composed of a perovskite-type oxide represented by a general formula ABO3, in which the A site contains K and Na and the B site contains Nb; forming a lower electrode film on the substrate; forming a piezoelectric film composed of a perovskite oxide represented by a general formula ABO3, the A site of which contains K and Na, and the B site of which contains Nb, on the lower electrode film by a sputtering method using the target; forming an upper adhesive layer on the piezoelectric film; forming an upper electrode film on the upper adhesive layer, In the step of preparing the target, a first target and a second target are prepared, the second target having a ratio of the total number of K atoms and Na atoms contained per unit volume to the number of Nb atoms contained per unit volume smaller than that of the first target, In the step of depositing the piezoelectric film, the first target and the second target are used, and the steps of (a) applying equal power to the first target and the second target, and (b) applying a power to the second target that is greater than the power to the first target are carried out in this order, and (b) is started immediately before the end of deposition of the piezoelectric film. A method for manufacturing a piezoelectric stack is provided. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a piezoelectric stack having a piezoelectric film with improved adhesion to an upper electrode film. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating an example of a cross-sectional structure of a piezoelectric laminate according to an embodiment of the present disclosure. [Figure 2] 1A and 1B are diagrams illustrating an example of the structure of a simplified piezoelectric element according to an embodiment of the present disclosure. [Figure 3] 1 is a diagram illustrating an example of a schematic configuration of a piezoelectric element according to an aspect of the present disclosure. [Figure 4] 1 is a diagram illustrating an example of a schematic configuration of a piezoelectric device module according to an aspect of the present disclosure. [Figure 5] FIG. 10 is a diagram illustrating an example of a cross-sectional structure of a piezoelectric laminate according to a modified example of an aspect of the present disclosure. [Figure 6] FIG. 1 is a diagram illustrating how a StudPull test is performed. [Figure 7] FIG. 1(a) is a diagram showing an example of the schematic configuration of a simple unimorph cantilever fabricated using each sample, and FIG. 1(b) is a diagram illustrating a method for measuring the amount of piezoelectric displacement. DETAILED DESCRIPTION OF THE INVENTION

[0010] <One aspect of the present disclosure> Hereinafter, one embodiment of the present disclosure will be described with reference to the drawings.

[0011] (1) Structure of the piezoelectric laminate As shown in FIG. 1, a laminate 10 having a piezoelectric film according to this embodiment (hereinafter also referred to as piezoelectric laminate 10) comprises a substrate 1, a lower electrode film 2, a piezoelectric film (piezoelectric thin film) 3, an upper adhesion layer 7, and an upper electrode film 4.

[0012] The substrate 1 can be preferably a single-crystal silicon (Si) substrate 1a on which a surface oxide film (SiO2 film) 1b, such as a thermal oxide film or a CVD (Chemical Vapor Deposition) oxide film, is formed, i.e., a Si substrate having a surface oxide film. Alternatively, the substrate 1 can be a Si substrate 1a having an insulating film formed of an insulating material other than SiO2 instead of the surface oxide film 1b. Alternatively, the substrate 1 can be a Si substrate 1a with an exposed Si(100) or Si(111) surface, i.e., a Si substrate without a surface oxide film 1b or insulating film. Alternatively, the substrate 1 can be an SOI (Silicon-On-Insulator) substrate or a quartz glass (SiO2) substrate. The thickness of the single-crystal Si substrate 1a can be, for example, 300 μm to 1000 μm, and the thickness of the surface oxide film 1b can be, for example, 1 nm to 4000 nm.

[0013] The lower electrode film 2 is formed on the substrate 1. That is, the lower electrode film 2 is provided between the substrate 1 and the piezoelectric film 3. The lower electrode film 2 can be formed using, for example, platinum (Pt). The lower electrode film 2 is a polycrystalline film. Hereinafter, a polycrystalline film formed using Pt will also be referred to as a Pt film. It is preferable that the (111) plane of the Pt film is parallel to the main surface of the substrate 1 (including the case where the (111) plane is inclined at an angle of ±5° or less with respect to the main surface of the substrate 1), that is, the Pt film is oriented in the (111) plane. The Pt film being oriented in the (111) plane means that no peaks other than those attributable to the (111) plane are observed in the X-ray diffraction pattern obtained by X-ray diffraction (XRD) measured on the surface of the piezoelectric film 3. Thus, it is preferable that the main surface of the lower electrode film 2 (the surface underlying the piezoelectric film 3) is composed of the Pt (111) plane. The lower electrode film 2 can be formed by a method such as sputtering or vapor deposition. The lower electrode film 2 can be formed using various metals other than Pt, such as gold (Au), ruthenium (Ru), or iridium (Ir), alloys containing these metals as main components, or metal oxides such as strontium ruthenate (SrRuO3, abbreviated as SRO) or lanthanum nickelate (LaNiO3, abbreviated as LNO). When the lower electrode film 2 is formed using a metal oxide, the crystals constituting the lower electrode film 2 preferably have a (001) plane orientation with respect to the surface of the substrate 1. That is, the main surface of the lower electrode film 2 is preferably primarily composed of the SRO (001) plane or the LNO (001) plane. The crystals constituting the lower electrode film 2 being oriented in the (001) plane orientation means that the (001) plane of the crystals constituting the lower electrode film 2 is parallel or substantially parallel to the main surface of the substrate 1. Furthermore, the crystals constituting the lower electrode film 2 being preferentially oriented in the (001) plane direction means that there are many crystals whose (001) plane is parallel or approximately parallel to the main surface of the substrate 1. The lower electrode film 2 can be a single layer film formed using the above-mentioned metals, alloys containing the above-mentioned metals as main components, metal oxides, or the like. The lower electrode film 2 may also be a laminate of a Pt film and a film containing SRO as main component provided on the Pt film, or a laminate of a Pt film and a film containing LNO as main component provided on the Pt film, or the like.The thickness of the lower electrode film 2 (if the lower electrode film 2 is a laminate, the total thickness of each layer) can be set to, for example, 100 nm or more and 400 nm or less.

[0014] A lower adhesion layer 6 may be provided between the substrate 1 and the lower electrode film 2 to enhance adhesion therebetween. The lower adhesion layer 6 may be, for example, a layer containing zinc (Zn) and oxygen (O) as main components (hereinafter also referred to as a "ZnO layer"). The ZnO layer may be formed using, for example, zinc oxide. The Zn:O composition ratio constituting the ZnO layer preferably satisfies the relationship Zn:O = 1:1, but is not limited thereto and may vary somewhat. The ZnO layer is a polycrystalline layer. The ZnO layer preferably has its (0001) plane parallel to the main surface of the substrate 1 (including cases where the (0001) plane is inclined at an angle of ±5° or less with respect to the main surface of the substrate 1), i.e., the ZnO layer is preferably oriented in the (0001) plane direction. The ZnO layer being oriented in the (0001) plane direction means that the intensity of the peak due to the (0002) plane is high in the X-ray diffraction pattern obtained by XRD measured on the surface of the piezoelectric film 3. Thus, the main surface of the ZnO layer (the surface underlying the lower electrode film 2) is preferably configured as a ZnO (0001) plane. The ZnO layer can be formed by a method such as sputtering or vapor deposition. The thickness of the ZnO layer can be, for example, 1 nm to 200 nm, preferably 10 nm to 50 nm. The lower adhesion layer 6 may be a layer containing, for example, titanium (Ti), tantalum (Ta), titanium oxide (TiO), nickel (Ni), ruthenium oxide (RuO), iridium oxide (IrO), or the like as a main component. Such a lower adhesion layer 6 can also be formed by a method such as sputtering or vapor deposition, and the thickness of the lower adhesion layer 6 can be, for example, 1 nm to 200 nm, preferably 10 nm to 50 nm.

[0015] The piezoelectric film 3 is formed on the lower electrode film 2. The piezoelectric film 3 is composed of a perovskite-type oxide represented by the general formula ABO3, where the A site contains potassium (K) and sodium (Na), and the B site contains niobium (Nb). That is, the piezoelectric film 3 can be a film mainly composed of an alkali niobate containing K, Na, Nb, and oxygen (O) and having a perovskite-type crystal structure. The piezoelectric film 3 can be formed using an alkali niobate represented by the composition formula (K 1-x Na x )NbO3, that is, potassium sodium niobate (KNN). The coefficient x [=Na / (K + Na)] in the above composition formula can be within the range of 0 < x < 1, preferably 0.4 ≤ x ≤ 0.8. The piezoelectric film 3 is a polycrystalline film of KNN (hereinafter also referred to as the KNN film 3).

[0016] In addition, the alkali niobate constituting the KNN film 3 may further contain at least one element (dopant) selected from the group consisting of lithium (Li), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), bismuth (Bi), antimony (Sb), vanadium (V), indium (In), tantalum (Ta), molybdenum (Mo), tungsten (W), chromium (Cr), Ti, zirconium (Zr), hafnium (Hf), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), copper (Cu), zinc (Zn), silver (Ag), manganese (Mn), iron (Fe), cobalt (Co), Ni, aluminum (Al), Si, germanium (Ge), tin (Sn), and gallium (Ga). The concentration of these elements in the alkali niobate can be, for example, 5 at% or less (when containing a plurality of the above elements, the total concentration is 5 at% or less).

[0017] The crystals constituting the KNN film 3 are preferentially oriented in the (001) plane with respect to the main surface of the substrate 1 (for example, the Si substrate 1a when the substrate 1 is a Si substrate 1a having a surface oxide film 1b or an insulating film, etc.). That is, the main surface of the KNN film 3 (the surface underlying the upper electrode film 4) is mainly composed of the KNN (001) plane. For example, by directly depositing the KNN film 3 on a Pt film (lower electrode film 2) whose main surface is mainly composed of the Pt (111) plane, a KNN film 3 whose main surface is mainly composed of the KNN (001) plane can be obtained. In this specification, the crystals constituting the KNN film 3 being oriented in the (001) plane means that the (001) plane of the crystals constituting the KNN film 3 is parallel or approximately parallel to the main surface of the substrate 1. Furthermore, the crystals constituting the KNN film 3 being preferentially oriented in the (001) plane means that many of the crystals have their (001) plane parallel or approximately parallel to the main surface of the substrate 1. In this specification, the crystal system of KNN is considered to be a tetragonal system. The thickness of the KNN film 3 can be, for example, 0.5 μm to 5 μm, preferably 1 μm to 3 μm.

[0018] The KNN film 3 in this embodiment is formed by a two-stage sputtering technique in which two types of targets, a first target and a second target described below, each having different compositions, are simultaneously used and the conditions for applying power to each target are changed. As a result, the KNN film 3 in this embodiment has the novel features described below, specifically, feature 1 described below. The KNN film 3 in this embodiment can further have at least one of features 2 to 8 described below.

[0019] The crystals constituting the KNN film 3 obtained by sputtering deposition include crystals having a columnar structure. It is preferable that at least half of the crystals constituting the KNN film 3 have a columnar structure. Furthermore, it is preferable that the boundaries between the crystals constituting the KNN film 3, i.e., the grain boundaries present in the KNN film 3, run through the KNN film 3 in the film thickness direction. For example, it is preferable that the number of grain boundaries running through the KNN film 3 in the film thickness direction is greater than the number of grain boundaries that do not run through the KNN film 3 in the film thickness direction (for example, grain boundaries parallel to the direction along the main surface of the substrate 1 (the surface direction of the substrate 1)).

[0020] The upper electrode film 4 is formed on the KNN film 3. The upper electrode film 4 is mainly composed of various metals, such as Pt, Au, Al, and Cu, or alloys thereof. The upper electrode film 4 can be formed by techniques such as sputtering, vapor deposition, plating, and metal paste deposition. Unlike the lower electrode film 2, the upper electrode film 4 does not significantly affect the crystalline structure of the KNN film 3. Therefore, the material, crystalline structure, and deposition technique of the upper electrode film 4 are not particularly limited. An upper adhesion layer 7 is provided between the KNN film 3 and the upper electrode film 4 to improve adhesion therebetween. The upper adhesion layer 7 can be formed using a metal oxide, such as RuO2, IrO2, TiO2, SRO, or LNO. The thickness of the upper electrode film 4 can be, for example, 50 nm to 5000 nm, preferably 50 nm to 300 nm, and the thickness of the upper adhesion layer 7 can be, for example, 1 nm to 200 nm, preferably 5 nm to 50 nm.

[0021] Feature 1 possessed by the KNN film 3 of this embodiment and features 2 to 8 that the KNN film 3 of this embodiment may possess will be described below.

[0022] (Feature 1) The KNN film 3 has a feature (feature 1) that "when the KNN film 3 is divided into a surface region and a bulk region, the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region."

[0023] Here, the "surface region" refers to a region of the KNN film 3 extending from the upper surface of the KNN film 3 to a predetermined depth (for example, a depth of 3 nm) toward the substrate 1. The "bulk region" refers to a region of the KNN film 3 other than the surface region of the KNN film 3.

[0024] In addition, in this specification, "the upper surface of the KNN film 3" means one of the two main surfaces of the KNN film 3 that is located on the upper electrode film 4 side, that is, the surface that is located opposite to the substrate 1.

[0025] In addition, the "total atomic concentration of K and Na in the surface region" in this specification is the ratio of the total number of K and Na atoms in the surface region to the total number of atoms in the KNN film 3 that constitutes the surface region, and is expressed in at%. That is, the "total atomic concentration of K and Na in the surface region" in this specification is a value calculated using the following (Equation 1).

[0026] (Number 1) Total atomic concentration of K and Na in the surface region (at%) = (total number of K and Na atoms in the surface region / total number of atoms in the KNN film constituting the surface region) × 100

[0027] In the above (Equation 1), the "total number of K and Na atoms in the surface region" is the total number of K and Na atoms contained in the KNN film 3 constituting the surface region, and the "total number of atoms in the KNN film constituting the surface region" is the total number of K, Na, Nb, and O atoms contained in the KNN film 3 constituting the surface region. Note that the "KNN film 3 constituting the surface region" refers to the KNN film 3 deposited in the second film deposition step described below, and is hereinafter also referred to as KNN film 3a.

[0028] The "total atomic concentration of K and Na in the bulk region" in this specification is the ratio of the total number of K and Na atoms in the bulk region to the total number of atoms in the KNN film constituting the bulk region, and is expressed in at%. That is, the "total atomic concentration of K and Na in the bulk region" in this specification is a value calculated using the following (Equation 2).

[0029] (Number 2) Total atomic concentration of K and Na in the bulk region (at%) = (total number of K and Na atoms in the bulk region / total number of atoms in the KNN film constituting the bulk region) × 100

[0030] In the above (Equation 2), the "total number of K and Na atoms in the bulk region" is the total number of atoms of K and Na contained in the KNN film 3 constituting the bulk region, and the "total number of atoms in the KNN film constituting the bulk region" is the total number of atoms of K, Na, Nb, and O contained in the KNN film 3 constituting the bulk region. Note that the "KNN film 3 constituting the bulk region" refers to the KNN film 3 deposited in the first deposition step described below, and is hereinafter also referred to as KNN film 3b.

[0031] The total number of K and Na atoms in the surface region and the bulk region, the total number of atoms in the KNN film 3a, and the total number of atoms in the KNN film 3b can be measured by, for example, time-of-flight secondary ion mass spectrometry (TOF-SIMS). Measurement by TOF-SIMS can be performed using, for example, a TOF SIMS5 manufactured by ION-TOF.

[0032] When calculating the total atomic concentrations of K and Na in each of the surface and bulk regions using values ​​measured by TOF-SIMS, TOF-SIMS measurements are performed at multiple locations throughout each of the surface and bulk regions, and the average of the measurement results is used for calculation. In this case, the total atomic concentrations of K and Na in each of the surface and bulk regions can also be considered as the average of the total atomic concentrations of K and Na in each of the surface and bulk regions. This also applies to the total atomic concentrations of K and Na in the lower region of the bulk region, which will be described later.

[0033] It is difficult to accurately measure the number of O atoms contained in the KNN film 3 (the O atomic concentration in the KNN film 3) in TOF-SIMS measurements. However, it is known that the O atomic concentration is approximately 60% in perovskite-type oxide crystals represented by the general formula ABO3. Therefore, in this embodiment, assuming that the O atomic concentration in the KNN film 3 (KNN film 3a, KNN film 3b) is exactly 60%, the total number of atoms in each of the KNN films, the total number of atoms in the KNN film 3a, and the total number of atoms in the KNN film 3b are calculated using the results of composition measurements using TOF-SIMS. This also applies to the calculation of the total number of K and Na atoms in a measurement length of 10 nm, the total number of atoms in a measurement length of 10 nm, the total number of K and Na atoms in the lower layer region, and the total number of atoms in the KNN film constituting the lower layer region, which will be described later.

[0034] The composition of the surface region and the bulk region can also be measured by Auger electron spectroscopy (AES) or X-ray photoelectron spectroscopy (XPS). That is, the composition of the surface region and the bulk region can also be measured by measuring the composition distribution in the depth direction (thickness direction) of the KNN film 3 using AES or XPS. However, with techniques using AES or XPS, it is difficult to accurately measure the number of K, Na, and Nb atoms in the surface region, especially, because the analytical sensitivity of the surface region is low. The composition of the surface region and the bulk region can also be measured by energy dispersive X-ray spectroscopy (EDS), X-ray fluorescence analysis (XRF), or inductively coupled plasma atomic emission spectroscopy (ICP-AES). However, these techniques have low analytical sensitivity for K and Na, so the number of K, Na, and Nb atoms in the surface region and the bulk region may not be accurately measured. For these reasons, when calculating the total atomic concentration of K and Na in each of the surface region and the bulk region, it is not preferable to use the total atomic number measured by AES, XPS, EDS, XRF, or ICP-AES.

[0035] The KNN film 3 having the feature 1 can improve the adhesion between the KNN film 3 and the upper adhesive layer 7, and further the adhesion between the KNN film 3 and the upper electrode film 4. For example, in a StudPull test described in the examples below, the maximum stress when the upper electrode film 4 peeled off from the KNN film 3 was 20 N / m 2 It can be made super.

[0036] The fact that the composition of the surface region (KNN film 3a) of the KNN film 3 affects the adhesion between the KNN film 3 and the upper adhesion layer 7 is a new finding that was first discovered as a result of intensive studies by the present inventors, etc. In other words, the fact that the adhesion between the KNN film 3 and the upper adhesion layer 7 can be improved by making the total atomic concentration of K and Na in the surface region lower than the total atomic concentration of K and Na in the bulk region is a new finding that was first discovered as a result of intensive studies by the present inventors, etc.

[0037] (Feature 2) The KNN film 3 may further have the feature (feature 2) that "the difference between the total atomic concentration of K and Na in the surface region and the total atomic concentration of K and Na in the bulk region is 1 at % or more and 11 at % or less." That is, the KNN film 3 may further have the feature that "the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region by, for example, 1 at % or more and 11 at % or less."

[0038] This makes it possible to reliably increase the adhesion between the KNN film 3 and the upper adhesive layer 7, and further to suppress a decrease in the dielectric strength voltage of the KNN film 3.

[0039] Even if the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region, if the difference between the total atomic concentration of K and Na in the surface region and the total atomic concentration of K and Na in the bulk region is less than 1 at%, the effect of improving the adhesion between the KNN film 3 and the upper adhesion layer 7 described above may not be sufficiently obtained.

[0040] By making the difference between the total atomic concentration of K and Na in the surface region and the total atomic concentration of K and Na in the bulk region 1 at % or more, the adhesion between the above-mentioned KNN film 3 and the upper adhesion layer 7 can be reliably improved.

[0041] Even if the total atomic concentration of K and Na in the surface region is lower than that in the bulk region, if the difference between the total atomic concentrations of K and Na in the surface region and the bulk region exceeds 11 at% (i.e., if the total atomic concentration of K and Na in the surface region is lower than that in the bulk region by more than 11 at%), the total atomic concentration of K and Na in the surface region is likely to be less than 10 at%. If the total atomic concentration of K and Na in the surface region is less than 10 at%, the KNN crystals constituting the KNN film 3a may not be able to maintain a perovskite crystal structure (the KNN film 3a may not have a perovskite crystal structure), and as a result, different crystal phases and amorphous substances may be likely to be present in the KNN film 3a. If the proportion of different crystalline phases or amorphous substances in the KNN film 3a becomes high, the effect of improving adhesion between the KNN film 3 and the upper adhesive layer 7 may not be obtained, or an appropriate potential barrier may not be formed at the interface between the KNN film 3 and the upper electrode film 4 (upper adhesive layer 7), resulting in a decrease in the dielectric strength voltage of the KNN film 3.

[0042] By making the difference between the total atomic concentration of K and Na in the surface region and the total atomic concentration of K and Na in the bulk region 11 at % or less, even if the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region, the effect of improving adhesion between the KNN film 3 and the upper adhesion layer 7 can be reliably obtained while suppressing a decrease in the dielectric strength voltage of the KNN film 3.

[0043] (Feature 3) The KNN film 3 may further have a feature (feature 3) that "the total atomic concentration of K and Na in the surface layer region is 10 at % or more."

[0044] This more reliably achieves the effect of improving the adhesion between the KNN film 3 and the upper adhesive layer 7. It also reliably suppresses a decrease in the dielectric strength of the KNN film 3. For example, even if the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region, a KNN film 3 having a dielectric strength of 350 kV / cm or more can be obtained.

[0045] Even if the total atomic concentration of K and Na in the surface region is lower than that in the bulk region, or even if the difference between the total atomic concentrations of K and Na in the surface region and the bulk region is, for example, 1 at% or more and 11 at% or less, if the total atomic concentration of K and Na in the surface region is less than 10 at%, as described above, the KNN crystals constituting the KNN film 3a may not maintain a perovskite-type crystal structure, and the proportion of other crystalline phases or amorphous substances in the KNN film 3a may increase. As a result, as described above, the effect of improving the adhesion between the KNN film 3 and the upper adhesive layer 7 may not be obtained, or the KNN film 3 may not have a dielectric strength of 350 kV / cm or more.

[0046] The upper limit of the total atomic concentration of K and Na in the surface region is not particularly limited as long as it is lower than the total atomic concentration of K and Na in the bulk region. The total atomic concentration of K and Na in the bulk region is not particularly limited, but can be, for example, 18 at% or more and 22 at% or less.

[0047] (Feature 4) The KNN film 3 may further have the feature (feature 4) that "the surface roughness (Ra) is 5 nm or less."

[0048] This further enhances the adhesion between the KNN film 3 and the upper adhesive layer 7.

[0049] The surface roughness (Ra) is the arithmetic mean roughness measured in accordance with JIS B0601:2013.

[0050] (Feature 5) The KNN film 3 may further have the feature (feature 5) that "in the KNN film 3 (KNN film 3b) constituting the bulk region, the difference (deviation) between the total atomic concentration of K and Na when the measurement length is 10 nm in the film thickness direction at a position including the center of the surface of the KNN film 3b parallel to the direction along the main surface of the substrate 1 (surface direction of the substrate 1) and the total atomic concentration of K and Na in the bulk region is within 5% at any position in the film thickness direction of the KNN film 3b excluding the interface regions on the upper and lower sides." In other words, the KNN film 3 may further have the feature that "the composition of the KNN film 3b is almost uniform in the film thickness direction."

[0051] Here, the "interface region on the upper surface side of the KNN film 3b" refers to a region ranging from the interface with the KNN film 3a toward the substrate 1 at a distance of 0.1% of the thickness of the KNN film 3b. The "interface region on the lower surface side of the KNN film 3b" refers to a region ranging from the interface with the lower electrode film 2 toward the upper electrode film 4 at a distance of 0.1% of the thickness of the KNN film 3b.

[0052] In this specification, "the total atomic concentration of K and Na at a position including the center of the surface of the KNN film 3b parallel to the surface direction of the substrate 1, when the measurement length is 10 nm in the film thickness direction" is also simply referred to as "the total atomic concentration of K and Na at a measurement length of 10 nm."

[0053] In this specification, the "total atomic concentration of K and Na in a measurement length of 10 nm" refers to the ratio of the total number of K and Na atoms in a measurement length of 10 nm to the total number of atoms in a measurement length of 10 nm, and is expressed in at%. That is, the "total atomic concentration of K and Na in a measurement length of 10 nm" in this specification is a value calculated using the following (Equation 3).

[0054] (Number 3) Total atomic concentration of K and Na in a measurement length of 10 nm (at%) = (total number of K and Na atoms in a measurement length of 10 nm / total number of atoms in a measurement length of 10 nm) × 100

[0055] In the above (Equation 3), the "total number of K and Na atoms in a measurement length of 10 nm" is the total number of K and Na atoms contained in the KNN film 3b at a measurement point of 10 nm. Also, the "total number of atoms in a measurement length of 10 nm" is the total number of K, Na, Nb, and O atoms contained in the KNN film 3b at a measurement point of 10 nm.

[0056] Measurement of a measurement length of 10 nm can be performed using, for example, TOF-SIMS. Measurement by TOF-SIMS can be performed using, for example, TOF SIMS5 manufactured by ION-TOF.

[0057] Furthermore, in addition to the total atomic concentration of K and Na at a measurement length of 10 nm at a position including the center of the surface of the KNN film 3b parallel to the surface direction of the substrate 1, it is preferable that the deviation between the total atomic concentration of K and Na at a measurement length of 10 nm in the film thickness direction at any position excluding the peripheral region of the surface of the KNN film 3b parallel to the surface direction of the substrate 1 and the total atomic concentration of K and Na in the bulk region is within 5% at any position in the film thickness direction of the KNN film 3b excluding the interface regions on the upper and lower sides.

[0058] Here, the "peripheral region of the KNN film 3b" means a region on the surface of the KNN film 3b parallel to the surface direction of the substrate 1, ranging from the outer periphery of the KNN film 3b to 5 mm toward the center.

[0059] Since the KNN film 3 in this embodiment is formed by, for example, sputtering, the composition of the KNN film 3b can be prevented from varying in the thickness direction compared to when the KNN film 3 is formed by a chemical solution deposition method (CSD method) such as a sol-gel method. This reduces the deviation in the bulk region between the total atomic concentration of K and Na when the measurement length in the thickness direction is set to a short length of 10 nm and the total atomic concentration of K and Na in the bulk region. As a result, the KNN film 3 in this embodiment has the above-mentioned feature 5.

[0060] The KNN film 3 has feature 5, i.e., the bulk region has a substantially uniform composition in the film thickness direction, which can prevent the occurrence of crystal defects due to composition variations in the film thickness direction and can prevent the shortening of the DC stress lifetime caused by the presence of these crystal defects. Note that, in this specification, "shortening the DC stress lifetime" means that when a (DC) voltage is applied to the KNN film 3 via the upper electrode film 4 so that an electric field of a predetermined magnitude is generated between the lower electrode film 2 and the upper electrode film 4 (i.e., in the KNN film 3), the time from the start of voltage application until the KNN film 3 experiences dielectric breakdown is shortened.

[0061] In contrast, when a KNN film is formed by the CSD method, the composition of the KNN film fluctuates (varies) periodically (approximately every 50 nm) due to the manufacturing method. Therefore, in the bulk region of a KNN film formed by the CSD method, the deviation between the total atomic concentration of K and Na measured at a length of 50 nm in the film thickness direction and the total atomic concentration of K and Na in the bulk region may be within 5%. However, in the bulk region of a KNN film formed by the CSD method, the deviation between the total atomic concentration of K and Na measured at a length of 10 nm in the film thickness direction and the total atomic concentration of K and Na in the bulk region exceeds 5% due to the manufacturing method. Thus, when a KNN film is formed by the CSD method, the above-mentioned feature 5 cannot be obtained.

[0062] (Feature 6) The KNN film 3 may further have the feature (feature 6) that "the difference (deviation) between the total atomic concentration of K and Na in the lower layer region of the bulk region and the total atomic concentration of K and Na in the bulk region is within 5%."

[0063] In this specification, the "lower region of the bulk region (hereinafter also simply referred to as the "lower region")" refers to the region of the bulk region that extends from the lower surface of the KNN film 3 to a height of 10 nm toward the upper surface of the KNN film 3. In other words, the lower region is a part of the bulk region. In addition, in this specification, the "lower surface of the KNN film 3" refers to the surface of the two main surfaces of the KNN film 3 that is opposite to the upper surface of the KNN film 3, i.e., the surface located on the substrate 1 side.

[0064] In addition, the "total atomic concentration of K and Na in the lower layer region" in this specification is the ratio of the total number of K and Na atoms in the lower layer region to the total number of atoms in the KNN film 3 that constitutes the lower layer region, and is expressed in at%. That is, the "total atomic concentration of K and Na in the lower layer region" in this specification is a value calculated using the following (Equation 4).

[0065] (Number 4) Total atomic concentration of K and Na in the lower layer region (at%) = (total number of K and Na atoms in the lower layer region / total number of atoms in the KNN film constituting the lower layer region) × 100

[0066] In the above (Equation 4), the "total number of K and Na atoms in the lower region" refers to the total number of K and Na atoms contained in the KNN film 3 constituting the lower region, and the "total number of atoms in the KNN film constituting the lower region" refers to the total number of K, Na, Nb, and O atoms contained in the KNN film 3 constituting the lower region. Hereinafter, the KNN film 3 constituting the lower region will also be referred to as KNN film 3b1, and the KNN film 3 constituting the bulk region other than the lower region of the KNN film 3b constituting the bulk region will also be referred to as KNN film 3b2. Thus, the KNN film 3b is a laminate of the KNN film 3b1 and the KNN film 3b2.

[0067] The total number of K and Na atoms in the lower layer region and the total number of atoms in the KNN film 3b1 can be measured by TOF-SIMS, for example, using a TOF SIMS5 manufactured by ION-TOF.

[0068] Since the KNN film 3 in this embodiment is formed by, for example, sputtering, diffusion (migration) of alkali metal elements (K element, Na element) in the KNN film 3 into the lower electrode film 2 is suppressed during the formation of the KNN film 3. This suppresses deviation of the composition of the KNN film 3b1 from the composition of the KNN film 3 (KNN film 3b) constituting the bulk region. As a result, the KNN film 3 in this embodiment can have the above-mentioned feature 6. When the KNN film 3 has the above-mentioned feature 6, a KNN film 3 highly oriented in the (001) plane direction, i.e., a KNN film 3 with a high (001) orientation rate, can be reliably obtained. For example, a KNN film 3 with a (001) orientation rate of 70% or more, preferably 80% or more, can be reliably obtained.

[0069] Here, the (001) orientation rate of the KNN film 3 refers to the orientation rate of the crystals constituting the KNN film 3 in the (001) plane direction. "The (001) orientation rate of the KNN film 3 is 70% or more" means that 70% or more of the crystals constituting the KNN film 3 are oriented in the (001) plane direction with respect to the main surface of the substrate 1. Note that the "orientation rate" in this specification is a value calculated by the following (Equation 5) based on the peak intensity of the X-ray diffraction pattern (2θ / θ) obtained by performing XRD measurement on the KNN film 3.

[0070] (Number 5) Orientation rate (%) = {(001) peak intensity / ((001) peak intensity + (110) peak intensity)} × 100

[0071] The "(001) peak intensity" in the above equation (5) refers to the intensity of a diffraction peak due to crystals oriented in the (001) plane direction (i.e., crystals whose (001) plane is parallel to the main surface of the substrate 1) among the crystals constituting the KNN film 3 in the X-ray diffraction pattern obtained by performing XRD measurement on the KNN film 3, and is the intensity of a peak appearing within a 2θ range of 20° to 23°. When multiple peaks appear within a 2θ range of 20° to 23°, it is the intensity of the highest peak. Furthermore, the "(110) peak intensity" in the above equation (5) refers to the intensity of a diffraction peak due to crystals oriented in the (110) plane direction (i.e., crystals whose (110) plane is parallel to the main surface of the substrate 1) among the crystals constituting the KNN film 3 in the X-ray diffraction pattern obtained by performing XRD measurement on the KNN film 3, and is the intensity of a peak appearing within a 2θ range of 30° to 33°. When multiple peaks appear within the 2θ range of 30° to 33°, the intensity is that of the highest peak.

[0072] In order for the KNN film 3 to have a (001) orientation rate of 70% or more, the KNN film 3 must have a perovskite crystal structure. If the KNN film 3 does not have a perovskite crystal structure, no peak can be observed within the 2θ range of 20° to 23° in the X-ray diffraction pattern obtained by XRD measurement, and as a result, the (001) orientation rate cannot be calculated.

[0073] If the KNN film 3 does not have the above-mentioned feature 6, that is, if the composition of the KNN film 3b1 is different from the composition of the KNN film 3 (KNN film 3b) constituting the bulk region, the (001) orientation rate of the KNN film 3 tends to be low. This is because, in the KNN film 3 formed by sputtering, a deviation in the composition of the KNN film 3b1 means a deviation in the composition of the KNN film 3 at the start of film formation. The deviation in the composition of the KNN film 3 at the start of film formation adversely affects the orientation of the crystals constituting the KNN film 3 formed thereafter (on top of it), and as a result, may cause a decrease in the (001) orientation rate of the KNN film 3.

[0074] When the KNN film 3 is formed by the CSD method, the alkali metal elements in the KNN film 3 may diffuse into the lower electrode film 2 due to the method. As a result, the composition of the KNN film 3b1 may differ from the composition of the KNN film 3b. Thus, when the KNN film 3 is formed by the CSD method, the above-mentioned feature 6 may not be obtained.

[0075] (Feature 7) The KNN film 3 may further have the feature (feature 7) that "the dielectric strength voltage is 350 kV / cm or more."

[0076] Since the KNN film 3 in this embodiment is formed by, for example, sputtering, the KNN film 3 has high quality even if the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region. Here, the "high-quality KNN film 3" refers to, for example, a fully crystallized KNN film 3, i.e., a KNN film 3 in which a perovskite-type crystal structure is properly formed. As a result, the KNN film 3 has a high dielectric strength voltage. That is, the KNN film 3 in this embodiment achieves the above-mentioned feature 7.

[0077] After the KNN film 3 is formed, the KNN film 3 may be heated during the formation of the upper electrode film 4, heat treatment, etc. It is said that this heating causes some alkali metal elements in the KNN film 3 to be desorbed (volatilized) from the vicinity of the upper surface of the KNN film 3. However, the present inventors have confirmed that in a sufficiently crystallized KNN film 3, even if heat treatment (heating) at a temperature of, for example, 800° C. or less is performed after the formation of the KNN film 3, desorption of alkali metal elements from the upper surface of the KNN film 3 does not occur.

[0078] In contrast, the present inventors have confirmed that alkali metal elements are easily desorbed from KNN films deposited by the CSD method when heated. This is thought to be because KNN films deposited by the CSD method are less crystallized (because the perovskite-type crystal structure is not properly formed) than KNN films deposited by, for example, sputtering. Furthermore, in a stack having an insufficiently crystallized KNN film (i.e., a KNN film from which alkali metal elements are easily desorbed when heated), an appropriate potential barrier is not formed at the interface between the KNN film and the upper electrode film, resulting in a low dielectric strength. In other words, when a KNN film is deposited by the CSD method, the above-mentioned feature 7 cannot be obtained. A stack having such an insufficiently crystallized KNN film with a low dielectric strength is difficult to use in the practical piezoelectric element 20 or piezoelectric device module 30 described below.

[0079] There is no particular upper limit to the dielectric strength voltage, but with current technology, the upper limit is approximately 2 MV / cm.

[0080] (Feature 8) The KNN film 3 has a piezoelectric constant e 31 is 8C / m 2 The present invention may further include the feature (Feature 8) that the above is true.

[0081] In this specification, the "piezoelectric constant e 31 " is a value measured under the condition that a negative voltage (for example, a triangular wave or sine wave voltage) is applied to the upper electrode film 4 while the lower electrode film 2 is grounded so as to generate an electric field of 100 kV / cm between the lower electrode film 2 and the upper electrode film 4 (i.e., the KNN film 3). "Piezoelectric constant e 31 " can be measured, for example, by the method described in the Examples.

[0082] By forming the KNN film 3 in this embodiment by, for example, a technique described below, it is possible to reduce only the total atomic concentration of K and Na in the surface region. The proportion of the KNN film 3 that is occupied by the KNN film 3a (surface region) is extremely small. Therefore, by reducing only the total atomic concentration of K and Na in the surface region, it is possible to avoid adversely affecting the piezoelectric properties of the entire KNN film 3, i.e., to prevent a decrease in the piezoelectric constant. As a result, the KNN film 3 can further have the above-mentioned feature 8.

[0083] The KNN film 3 in this embodiment is formed by, for example, the method described below, which results in a KNN film 3 having the above-mentioned feature 1, preferably a KNN film 3 having the above-mentioned feature 1 and at least one of the above-mentioned features 2 to 8, and more preferably a KNN film 3 having all of the above-mentioned features 1 to 8.

[0084] (2) Methods for manufacturing piezoelectric laminates, piezoelectric elements, and piezoelectric device modules A method for manufacturing the above-mentioned piezoelectric laminate 10, piezoelectric element, and piezoelectric device module will now be described.

[0085] (Deposition of lower adhesive layer and lower electrode film) First, a substrate 1 is prepared, and a lower adhesive layer 6 (e.g., a ZnO layer) and a lower electrode film 2 (e.g., a Pt film) are formed in this order by, for example, sputtering on one of the main surfaces of the substrate 1. Alternatively, a substrate 1 may be prepared on which the lower adhesive layer 6 and the lower electrode film 2 have already been formed on one of the main surfaces.

[0086] The following conditions are exemplified as conditions for depositing a ZnO layer as the lower adhesion layer 6. The deposition time for the lower adhesion layer 6 is adjusted appropriately depending on the target thickness of the lower adhesion layer 6. Target: ZnO sintered body Temperature (substrate temperature): 200°C or higher and 700°C or lower, preferably 300°C or higher and 700°C or lower, more preferably 500°C or higher and 700°C or lower Applied power (power density): 2W / cm 2 More than 6W / cm 2 Less than 3W / cm, preferably 3W / cm 2More than 5W / cm 2 below Atmosphere: a mixed gas atmosphere of argon (Ar) gas and oxygen (O2) gas (hereinafter also referred to as "Ar / O2 mixed gas atmosphere") Ratio of partial pressure of Ar gas to O gas (Ar gas partial pressure / O gas partial pressure): 5 / 1 to 30 / 1, preferably 7 / 1 to 20 / 1, more preferably 10 / 1 to 15 / 1 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 Thickness: 1 nm or more and 200 nm or less, preferably 10 nm or more and 50 nm or less

[0087] In this specification, when a numerical range is expressed, such as "5 / 1 to 30 / 1," it means that the lower limit and the upper limit are included in the range. The same applies to other numerical ranges.

[0088] The conditions for forming the Ti layer or the like as the lower adhesive layer 6 are exemplified as follows. Target: Ti plate, etc. Temperature (substrate temperature): 100°C or higher and 500°C or lower, preferably 200°C or higher and 400°C or lower 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 Other conditions can be the same as those used when providing the ZnO layer.

[0089] The following conditions are exemplified as conditions for depositing a Pt film as the lower electrode film 2. The deposition time for the lower electrode film 2 is adjusted appropriately depending on the target thickness of the lower electrode film 2. Target: Pt plate Temperature (substrate temperature): 200°C or higher and 600°C or lower, preferably 300°C or higher and 500°C or lower Applied power (power density): 1W / cm 2 More than 5W / cm 2 Less than 2 W / cm, preferably 2 More than 4W / cm 2 below 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 Thickness: 100nm or more and 400nm or less

[0090] (Preparation of target, deposition of KNN film) After the formation of the lower adhesive layer 6 and the lower electrode film 2 is completed, the KNN film 3 is subsequently formed on the lower electrode film 2 by a sputtering method such as RF magnetron sputtering. The composition of the KNN film 3 can be adjusted, for example, by controlling the composition of the target used during sputtering.

[0091] First, as a target to be used for sputtering deposition of the KNN film 3, a target composed of a perovskite-type oxide (i.e., KNN) represented by the general formula ABO3, in which the A site contains K and Na and the B site contains Nb, is prepared (preparation of target).

[0092] As targets, a first target and a second target in which the ratio of the total number of K atoms and Na atoms contained per unit volume to the total number of Nb atoms contained per unit volume is smaller than that of the first target. That is, when the numbers of K, Na, and Nb atoms per unit volume contained in the first target are K1, Na1, and Nb1, respectively, and the numbers of K, Na, and Nb atoms per unit volume contained in the second target are K2, Na2, and Nb2, respectively, the first target and the second target are prepared so that they satisfy the relationship "(K1 + Na1) / Nb1 > (K2 + Na2) / Nb2." For example, the first target and the second target are prepared so that they satisfy the relationship "total atomic concentration of K and Na in the first target > total atomic concentration of K and Na in the second target."

[0093] The target can be prepared by mixing and firing K2CO3 powder, Na2CO3 powder, Nb2O5 powder, etc. The composition of the target can be controlled by adjusting the mixing ratio of K2CO3 powder, Na2CO3 powder, Nb2O5 powder, etc. When depositing a KNN film 3 containing the above-mentioned dopant elements such as Cu and Mn, a target prepared by mixing the above-mentioned powders with Cu powder (or CuO powder), Mn powder (or MnO powder), etc. in a predetermined ratio can be used.

[0094] The prepared first and second targets are simultaneously used to deposit the KNN film 3 (deposition of KNN film).

[0095] In the deposition of the KNN film 3, a step (first deposition step) of depositing the KNN film 3 (KNN film 3b) constituting the bulk region and a step (second deposition step) of depositing the KNN film 3 (KNN film 3a) constituting the surface region are carried out in this order.

[0096] In addition, in the deposition of the KNN film 3, the power applied to the target in the first deposition step and the power applied to the target in the second deposition step are adjusted so that the total atomic concentration of K and Na in the KNN film 3a deposited in the second deposition step is lower than the total atomic concentration of K and Na in the KNN film 3b deposited in the first deposition step. Specifically, in the first deposition step, the power applied to the first target and the second target is made equal, and in the second deposition step, the power applied to the second target is made greater than the power applied to the first target.

[0097] In this specification, "making the power applied to the first target and the second target equal" not only means making the power applied to the first target and the second target equal, but also includes cases where the power applied to the first target and the power applied to the second target are each within a range of ±20% of the average value of the power applied to the first target and the power applied to the second target.

[0098] <First film-forming step> First, the first film deposition step is carried out to deposit the KNN film 3b (the KNN film 3 that constitutes the bulk region).

[0099] The conditions for the first film-forming step are exemplified as follows: The film-forming time is adjusted appropriately depending on the target thickness of the KNN film 3b in the bulk region. First target: A target with a total atomic concentration of K and Na in the range of 22 at% to 40 at% Second target: A target with a total atomic concentration of K and Na in the range of 3 at% to 18 at% Applied power to the first target (power density): 10 W / cm 2 More than 70W / cm 2 Within the following range, the same power as that applied to the second target Power applied to the second target (power density): 10 W / cm 2 More than 70W / cm 2 Within the following range, the same power as that applied to the first target Temperature (substrate temperature): 500°C or higher and 800°C or lower, preferably 600°C or higher and 700°C or lower Atmosphere: an atmosphere containing at least Ar gas, preferably an Ar / O2 mixed gas atmosphere Atmospheric pressure: 0.03 Pa or more and 0.5 Pa or less, preferably 0.04 Pa or more and 0.4 Pa or less Ratio of partial pressure of O2 gas to Ar gas (O2 gas partial pressure / Ar gas partial pressure): 0 to 1 / 20, preferably 0 to 1 / 30 Film formation rate: 0.5 μm / hr or more and 4 μm / hr or less, preferably 0.5 μm / hr or more and 2 μm / hr or less Thickness of the KNN film constituting the bulk region: 0.5 μm or more and 5 μm or less, preferably 1 μm or more and 3 μm or less

[0100] Note that "O2 gas partial pressure / Ar gas partial pressure is 0 (zero)" means a state in which the O2 gas partial pressure is 0, that is, an atmosphere of only Ar gas.

[0101] When a predetermined time has elapsed since the start of the first film-forming step, the discharge (application of power to both targets) is stopped, and the first film-forming step is completed.

[0102] <Second film-forming step> Subsequently, the power applied to the first target and the second target is changed to start the second deposition step, and a KNN film 3a (KNN film 3 constituting the surface layer region) is deposited. The second deposition step is started immediately before the end of deposition of the KNN film 3. The inventors have confirmed that the length of time during which discharge is stopped when switching from the first deposition step to the second deposition step, i.e., the length of time from the end of the first deposition step to the start of the second deposition step, does not affect the effects obtained by the present disclosure.

[0103] Furthermore, after a predetermined time has elapsed since the start of the first film deposition step, the power applied to both targets may be gradually or stepwise changed to start the second film deposition step. In this case, the change in the power applied to the first target and the second target is performed immediately before the end of the deposition of the KNN film 3.

[0104] In the second film forming step, the powers applied to the first target and the second target are changed so that the power applied to the second target is greater than the power applied to the first target.

[0105] The conditions for the second film-forming step are exemplified as follows: The film-forming time is adjusted appropriately so that the thickness of the KNN film 3a in the surface layer region becomes, for example, 3 nm. Applied power to the first target (power density): 10 W / cm 2 More than 70W / cm 2 A power smaller than the power applied to the second target within the following range: Power applied to the second target (power density): 10 W / cm 2 More than 70W / cm 2 A power greater than the power applied to the first target within the following range: Other conditions can be the same as those in the first film-forming step.

[0106] In the second deposition step, the power applied to the second target is preferably set to be higher than the power applied to the second target in the first deposition step within the above-mentioned range, thereby reliably obtaining a KNN film 3 in which the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region.

[0107] In the second deposition step, the power applied to the first target is preferably set to be smaller than the power applied to the first target in the first deposition step within the above-mentioned range, thereby more reliably obtaining a KNN film 3 in which the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region.

[0108] In this way, the KNN film 3 is formed in two stages by simultaneously using two types of targets, the first target and the second target, and by changing the power (power density) applied to each target.

[0109] By depositing the KNN film 3 under the above conditions, the total atomic concentration of K and Na in the surface region deposited in the second deposition step can be made lower than the total atomic concentration of K and Na in the bulk region deposited in the first deposition step. As a result, the KNN film 3 having the above-mentioned feature 1 can be obtained.

[0110] Furthermore, by depositing the KNN film 3 under the above conditions, the total atomic concentration of K and Na in the surface region can be made lower than that in the bulk region, and the difference between the total atomic concentrations of K and Na in the surface region and the bulk region can be made 1 at % or more and 11 at % or less. As a result, the KNN film 3 can further have the above-mentioned feature 2.

[0111] Furthermore, by depositing the KNN film 3 under the above conditions, the total atomic concentration of K and Na in the surface region can be made lower than the total atomic concentration of K and Na in the bulk region, and the total atomic concentration of K and Na in the surface region can be made, for example, 10 at% or more. As a result, the KNN film 3 can further have the above-mentioned feature 3.

[0112] Furthermore, by depositing the KNN film 3 under the above conditions, not only can the total atomic concentration of K and Na in the surface region be made lower than the total atomic concentration of K and Na in the bulk region, but also the surface roughness (Ra) of the upper surface of the KNN film 3 can be made 5 nm or less. As a result, the KNN film 3 can further have the above-mentioned feature 4.

[0113] Furthermore, by depositing the KNN film 3b by performing the first deposition step under the above-mentioned conditions, the composition of the KNN film 3b can be made substantially uniform in the thickness direction. That is, by depositing the KNN film 3 under the above-mentioned conditions, not only can the total atomic concentration of K and Na in the surface region be made lower than the total atomic concentration of K and Na in the bulk region, but the composition of the KNN film 3b can also be made substantially uniform in the thickness direction. As a result, the KNN film 3 can further have the above-mentioned feature 5.

[0114] Furthermore, by depositing the KNN film 3 under the above conditions, not only can the total atomic concentration of K and Na in the surface region be made lower than the total atomic concentration of K and Na in the bulk region, but also the alkali metal elements contained in the KNN film 3 can be prevented from diffusing into the lower electrode film 2 during the deposition of the KNN film 3. As a result, the KNN film 3 can further have the above-mentioned feature 6.

[0115] Furthermore, by depositing the KNN film 3 under the above conditions, not only can the total atomic concentration of K and Na in the surface region be made lower than the total atomic concentration of K and Na in the bulk region, but also a high-quality KNN film 3 can be obtained. That is, the dielectric strength voltage of the KNN film 3 can be made 350 kV / cm or more. As a result, the KNN film 3 can further have the above-mentioned feature 7.

[0116] Furthermore, by forming the KNN film 3 under the above conditions, it is possible to reduce the total atomic concentration of K and Na only in the surface region. This makes it possible to avoid adversely affecting the piezoelectric properties of the entire KNN film 3. That is, by forming the KNN film 3 under the above conditions, not only is it possible to lower the total atomic concentration of K and Na in the surface region compared to the total atomic concentration of K and Na in the bulk region, but it is also possible to prevent a decrease in the piezoelectric constant of the KNN film 3. As a result, the KNN film 3 can further have the above-mentioned feature 8.

[0117] In this way, by simultaneously using two types of targets having different compositions, the first target and the second target, and performing the first film formation step and the second film formation step under the above-mentioned conditions in this order to form the KNN film 3, it is possible to obtain a KNN film 3 having the above-mentioned feature 1, preferably a KNN film 3 having the above-mentioned feature 1 and at least one of the above-mentioned features 2 to 8, and more preferably a KNN film 3 having all of the above-mentioned features 1 to 8.

[0118] (Deposition of upper adhesive layer and upper electrode film) After the deposition of the KNN film 3 is completed, an upper adhesive layer 7 (for example, a RuO2 layer) and an upper electrode film 4 (for example, a Pt film) are deposited in this order on the KNN film 3 by, for example, sputtering.

[0119] The following conditions are exemplified as conditions for depositing a RuO2 layer or the like as the upper adhesion layer 7. The deposition time for the upper adhesion layer 7 is adjusted appropriately depending on the target thickness of the upper adhesion layer 7. Target: Ru plate, etc. Temperature (substrate temperature): Room temperature (25℃) or higher and 500℃ or lower Applied power (power density): 0.3W / cm 2 More than 2W / cm 2 Less than or equal to 0.5 W / cm 2 More than 1W / cm 2 below Atmosphere: Ar / O2 mixed gas atmosphere Ratio of partial pressure of Ar gas to O gas (Ar gas partial pressure / O gas partial pressure): 3 / 5 to 1 / 1, preferably 3 / 4 to 1 / 1 Atmospheric pressure: 0.1 Pa or more and 1.0 Pa or less, preferably 0.2 Pa or more and 0.7 Pa or less Thickness: 1 nm or more and 200 nm or less, preferably 5 nm or more and 50 nm or less

[0120] The following conditions are exemplified as conditions for depositing a Pt film or the like as the upper electrode film 4. The deposition time for the upper electrode film 4 is adjusted appropriately depending on the target thickness of the upper electrode film 4. Target: Pt plate, etc. Temperature (substrate temperature): Room temperature (25℃) or higher and 500℃ or lower Applied power (power density): 1W / cm 2 More than 5W / cm 2 Less than 2 W / cm, preferably 2 More than 4W / cm 2 below 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 Thickness: 50 nm or more and 5000 nm or less, preferably 50 nm or more and 300 nm or less

[0121] As described above, the lower adhesive layer 6, the lower electrode film 2, the KNN film 3 (KNN film 3b, KNN film 3a), the upper adhesive layer 7, and the upper electrode film 4 are deposited in this order to obtain the piezoelectric laminate 10 shown in FIG. 1.

[0122] (Fabrication of piezoelectric elements) After the piezoelectric laminate 10 shown in FIG. 1 is produced, the piezoelectric laminate 10 is processed to form an element having a KNN film 3 (also referred to as a piezoelectric element 20).

[0123] Specifically, first, the upper electrode film 4 (including the upper adhesive layer 7) and the KNN film 3 are individually patterned by dry etching using, for example, Ar gas or a reactive gas. In the patterning, the upper electrode film 4 (including the upper adhesive layer 7) and the KNN film 3 are each formed into a predetermined shape, and a portion of the lower electrode film 2 is exposed. In the patterning, a photoresist can be used as an etching mask. Figure 2 shows the piezoelectric stack 10 after patterning, i.e., a piezoelectric element 20. The piezoelectric element 20 shown in Figure 2 is also referred to as a simple piezoelectric element.

[0124] 2, the lower electrode film 2 and the lower adhesive layer 6 are patterned by dry etching using, for example, Ar gas or a reactive gas, to form the lower electrode film 2 and the lower adhesive layer 6 into predetermined shapes. In this patterning, a photoresist can be used as an etching mask.

[0125] After the patterning of the lower electrode film 2 and the lower adhesive layer 6 is completed, the insulating film 8 and metal wirings 9a, 9b are provided. Specifically, first, a layer made of an insulating material is provided from the upper electrode film 4 to the substrate 1 so as to cover the side surfaces of the KNN film 3. Then, the layer made of the insulating material is patterned by dry etching using a reactive gas such as Ar gas or CF4 gas, or by wet etching, to provide the insulating film 8. The insulating film 8 can be formed using oxides such as silicon oxide (SiO2), aluminum oxide (Al2O3), and tantalum oxide (Ta2O5). The insulating film 8 may be a single-layer film or a laminated body having multiple layers stacked on top of one another. The insulating film 8 can be provided by a method such as CVD or sputtering.

[0126] After the insulating film 8 is formed, a layer (metal wiring layer) made of a material containing metal is formed. Then, the metal wiring layer is patterned by dry etching using Ar gas or a reactive gas or wet etching to form metal wirings 9a and 9b. The metal wiring 9a is formed (patterned) so as to be connected (contacted) to the lower electrode film 2 but not connected (not contacted) to the upper electrode film 4, while the metal wiring 9b is formed so as to be connected to the upper electrode film 4 but not connected to the lower electrode film 2. The metal wirings 9a and 9b can be formed using various metals such as Au, Al, Ti, and Cr, or alloys containing these metals as main components. The metal wirings 9a and 9b can be single-layer films or laminates of multiple layers. The metal wirings 9a and 9b (metal wiring layer) can be formed by methods such as sputtering, vapor deposition, plating, and metal paste deposition.

[0127] Further, by deep-RIE or wet etching, a part of the substrate 1 is removed from the back surface side of the substrate 1 (one of the two main surfaces of the substrate 1 opposite to the surface on which the lower electrode film 2 and the like are formed). As a result, a piezoelectric element 20 having a membrane structure, a cantilever structure, or the like, such as a membrane-type MEMS piezoelectric element 20 as shown in FIG. 3, is obtained.

[0128] The etching conditions for pattern processing when forming the insulating film 8 and the metal wiring 9a, 9b, and the etching conditions for the substrate 1 when processing the piezoelectric laminate 10 into the piezoelectric element 20 can be general etching conditions used in semiconductor device manufacturing processes, as long as the conditions do not deteriorate the insulating properties of the KNN film 3.

[0129] (Fabrication of piezoelectric device modules) A device module 30 (hereinafter also referred to as piezoelectric device module 30) having a KNN film 3 is obtained by connecting a voltage detection means 11a or a voltage application means 11b to the obtained piezoelectric element 20. FIG. 4 shows a schematic configuration diagram of the piezoelectric device module 30 according to this embodiment. The piezoelectric device module 30 includes at least a piezoelectric element 20 and a voltage detection means 11a or a voltage application means 11b connected to the piezoelectric element 20. The voltage detection means 11a is a means for detecting a voltage generated between the lower electrode film 2 and the upper electrode film 4 (between the electrodes). The voltage application means 11b is a means for applying a voltage between the lower electrode film 2 and the upper electrode film 4 (between the electrodes). Various known means can be used as the voltage detection means 11a and the voltage application means 11b.

[0130] By connecting the voltage detection means 11a between the lower electrode film 2 and the upper electrode film 4 of the piezoelectric element 20, the piezoelectric device module 30 can function as a sensor. When the KNN film 3 deforms in response to 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 means 11a, it is possible to measure the magnitude of the physical quantity applied to the KNN film 3. In this case, the piezoelectric device module 30 can be used, for example, as an angular velocity sensor, an ultrasonic sensor, a pressure sensor, an acceleration sensor, etc.

[0131] By connecting the voltage application means 11b between the lower electrode film 2 and the upper electrode film 4 of the piezoelectric element 20, the piezoelectric device module 30 can function as an actuator. By applying a voltage between the lower electrode film 2 and the upper electrode film 4 by the voltage application means 11b, the KNN film 3 can be deformed. This deformation can actuate various members connected to the piezoelectric device module 30. In this case, examples of applications of the piezoelectric device module 30 include a head for an inkjet printer, a MEMS mirror for an optical scanner, and a vibrator for an ultrasonic generator.

[0132] (3) Effects According to this aspect, one or more of the following effects can be obtained.

[0133] (a) In the KNN film 3, the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region, which can improve the adhesion between the KNN film 3 and the upper adhesive layer 7, and in turn, the adhesion between the KNN film 3 and the upper electrode film 4. For example, in a StudPull test described in the Examples below, the maximum stress when the upper electrode film 4 peeled off from the KNN film 3 was 20 N / m 2 As a result, the reliability and versatility of the piezoelectric element 20 (piezoelectric device module 30) obtained by processing the piezoelectric laminate 10 can be improved.

[0134] (b) The total atomic concentration of K and Na in the surface region is, for example, 1 at % or more and 11 at % or less lower than the total atomic concentration of K and Na in the bulk region, thereby reliably achieving the effect of improving adhesion between the KNN film 3 and the upper adhesion layer 7 and suppressing a decrease in the dielectric strength voltage of the KNN film 3.

[0135] (c) Not only is the total atomic concentration of K and Na in the surface region lower than that in the bulk region, but the composition of the KNN film 3b in the thickness direction is also nearly uniform, which can prevent the occurrence of crystal defects due to composition fluctuations in the KNN film 3 in the thickness direction. As a result, it is possible to prevent the shortening of the lifespan of DC stress caused by the presence of these crystal defects.

[0136] (d) When the deviation between the total atomic concentration of K and Na in the lower layer region and the total atomic concentration of K and Na in the bulk region is within 5%, a KNN film 3 highly oriented in the (001) plane direction can be reliably obtained.

[0137] (e) Since the KNN film 3 has a dielectric strength of 350 kV / cm or more, the piezoelectric laminate 10 can be reliably used in practical applications of the piezoelectric element 20 (piezoelectric device module 30).

[0138] (f) When the total atomic concentration of K and Na in the surface layer region is, for example, 10 at % or more, a KNN film 3 having a dielectric strength of 350 kV / cm or more can be reliably obtained.

[0139] (g) Since only the total atomic concentration of K and Na in the surface region is low, a decrease in the piezoelectric constant of the entire KNN film 3 can be avoided. That is, even if the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region, the piezoelectric constant e 31 8C / m 2 As described above, in this embodiment, the adhesion between the KNN film 3 and the upper adhesive layer 7 can be improved without decreasing the piezoelectric constant of the KNN film 3.

[0140] (4) Variations This aspect can be modified as follows. In the following description of the modifications, the same components as those in the above aspect are denoted by the same reference numerals, and the description thereof will be omitted. The above aspect and the following modifications can be combined in any way.

[0141] (Variation 1) In the above-described embodiment, the piezoelectric laminate 10 includes the lower electrode film 2, but the present invention is not limited thereto. The piezoelectric laminate 10 does not necessarily include the lower electrode film 2. That is, the piezoelectric laminate 10 may include a substrate 1, a KNN film (piezoelectric film) 3 on the substrate 1, an upper adhesive layer 7 on the KNN film 3, and an upper electrode film 4 (electrode film 4) on the upper adhesive layer 7. A lower adhesive layer 6 may be provided between the substrate 1 and the KNN film 3. Note that the lower adhesive layer 6 may be omitted if a predetermined adhesiveness can be ensured. The piezoelectric laminate 10 of this modification, and thus the piezoelectric element 20 (piezoelectric device module 30) obtained by processing the piezoelectric laminate 10 of this modification, can function as a filter device such as a surface acoustic wave (SAW) filter.

[0142] In this modification, for example, by simultaneously using two types of targets, a first target and a second target, and performing the first film deposition step and the second film deposition step in this order under the same conditions as those described in the above embodiment to deposit the KNN film 3, it is possible to obtain a KNN film 3 having the above-mentioned feature 1, preferably a KNN film 3 having the above-mentioned feature 1 and at least one of the above-mentioned features 2 to 8, and more preferably a KNN film 3 having all of the above-mentioned features 1 to 8. As a result, in this modification as well, the same effects as in the above embodiment can be obtained.

[0143] (Variation 2) In the above embodiment, the KNN film 3 is a KNN polycrystalline film, but this is not limiting. The piezoelectric film 3 may be a single crystal film (epitaxial film) of perovskite-type alkali niobium oxide (KNN) containing K, Na, Nb, and O. Hereinafter, the KNN single crystal film will also be referred to as the epi-KNN film 3. The crystals constituting the epi-KNN film 3 preferably have a (001) plane orientation relative to the surface of the substrate 1.

[0144] In this modification, a single crystal Si substrate 1a or the like similar to the above embodiment can be suitably used as the substrate 1. Alternatively, a substrate made of single crystal strontium titanate (SrTiO), single crystal magnesium oxide (MgO), or single crystal fluorite (calcium fluoride, CaF) can also be used as the substrate 1.

[0145] 5, in this modification, a buffer layer 13 is provided between the substrate 1 and the lower electrode film 2 (or the lower adhesive layer 6 if provided). The buffer layer 13 is made of, for example, zirconia (composition formula (ZrO)) stabilized with yttrium (Y) oxide (YO). 1-x (Y2O3) x The buffer layer 13 can be formed by using a YSZ (Yttria Stabilized Zirconia). The composition of the buffer layer 13 is preferably such that the crystal structure of the buffer layer 13 is a cubic crystal (cubic structure, cubic phase). For example, the composition formula (ZrO2) 1-x (Y2O3) xThe coefficient x in the formula (1) is preferably within the range of 0.065≦x≦0.155. The buffer layer 13 may have a thickness of, for example, 5 nm to 300 nm, and preferably 10 nm to 200 nm. By forming the buffer layer 13 on the substrate 1 by a method such as PLD (Pulsed Laser Deposition) or sputtering, the buffer layer 13 grows epitaxially to become a single-crystal epitaxial film.

[0146] Then, by forming the lower adhesive layer 6 and the lower electrode film 2 in this order on the buffer layer 13, the lower electrode film 2 is epitaxially grown, and the lower electrode film 2 can be made into a single-crystal epitaxial film. Then, by forming the KNN film 3 on this lower electrode film 2, KNN crystals are epitaxially grown, and the epi-KNN film 3 is obtained.

[0147] The conditions for depositing the YSZ layer as the buffer layer 13 by the PLD method are exemplified below: The deposition time for the buffer layer 13 is adjusted appropriately depending on the target thickness of the buffer layer 13. Substrate temperature: 500°C or higher and 1000°C or lower, preferably 600°C or higher and 800°C or lower Atmosphere: an atmosphere containing at least oxygen (O2), preferably an O2 gas atmosphere Ambient pressure: 5.0 x 10 -2 Pa or more 10.0×10 -2 Pa or less, preferably 7 x 10 -2 Pa or more 8.0×10 -2 Pa or less Laser frequency: 5 Hz or more and 10 Hz or less, preferably 6 Hz or more and 8 Hz or less

[0148] The conditions for depositing the lower adhesive layer 6, the lower electrode film 2, the KNN film 3 (epi-KNN film 3), the upper adhesive layer 7, and the upper electrode film 4 can be the same as those in the above-mentioned embodiment.

[0149] In this modification, for example, two types of targets, a first target and a second target, are used simultaneously, and the first and second film deposition steps are performed in this order under the same conditions as those described in the above embodiment to deposit the KNN film 3, thereby obtaining an epi-KNN film 3 having the above-mentioned feature 1, preferably an epi-KNN film 3 having the above-mentioned feature 1 and at least one of the above-mentioned features 2 to 8, and more preferably an epi-KNN film 3 having all of the above-mentioned features 1 to 8. As a result, in this modification, the same effects as those in the above embodiment can be obtained.

[0150] (Variation 3) In the above embodiment, an example has been described in which the piezoelectric film 3 is composed of a perovskite-type oxide represented by the general formula ABO3, the A site containing K and Na, and the B site containing Nb, i.e., the piezoelectric film 3 is a KNN film 3. However, the A site may contain at least one element selected from the group consisting of, for example, lithium (Li), sodium (Na), potassium (K), lead (Pb), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), lanthanum (La), cadmium (Cd), bismuth (Bi), manganese (Mn), and copper (Cu). The B site may contain at least one element selected from the group consisting of, for example, titanium (Ti), zirconium (Zr), scandium (Sc), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), iron (Fe), ruthenium (Ru), cobalt (Co), iridium (Ir), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), and antimony (Sb). Cu and manganese may be contained in either the A site or the B site depending on the deposition conditions of the piezoelectric film 3.

[0151] In this modified example, the piezoelectric film 3 also has the feature (feature 1) that "the total atomic concentration of elements contained in the A site in the surface region is lower than the total atomic concentration of elements contained in the A site in the bulk region," thereby achieving at least the effect of increasing adhesion between the piezoelectric film 3 and the upper adhesion layer 7.

[0152] <Other aspects> The above describes one embodiment of the present disclosure. However, the present disclosure is not limited to the above embodiment and can be modified in various ways without departing from the spirit of the present disclosure. Furthermore, these embodiments can be combined in any manner.

[0153] For example, when the above-mentioned piezoelectric laminate 10 is molded into the piezoelectric element 20, the substrate 1 from the piezoelectric laminate 10 may be replaced with another substrate, as long as the piezoelectric device module 30 made using the piezoelectric laminate 10 (piezoelectric element 20) can be used for a desired purpose such as a sensor.

[0154] In the above embodiment, an example in which one laminate is formed on one substrate 1 has been described, but the present invention is not limited to this. For example, a plurality of laminates may be formed on one substrate 1. In this case, each of the plurality of laminates includes (a lower adhesive layer 6,) a lower electrode film 2, a KNN film 3, an upper adhesive layer 7, and an upper electrode film 4. A substrate 1 on which one or more laminates are formed is also referred to as a piezoelectric laminate substrate. [Example]

[0155] The following describes experimental results that support the effects of the above-described embodiment.

[0156] (Preparation of samples 1 to 21) A Si substrate with a (100) surface orientation, a thickness of 610 μm, and a diameter of 6 inches (also referred to as "φ6 inches"), and a thermally oxidized film (200 nm thick) was prepared as the substrate. Then, on the thermally oxidized film of this Si substrate, a ZnO layer (25 nm thick) as a lower adhesive layer, a Pt film (200 nm thick, preferentially oriented in the (111) plane with respect to the substrate surface) as a lower electrode film, a KNN (polycrystalline) film (2 μm thick) as a piezoelectric film, a RuO layer (10 nm thick) as an upper adhesive layer, and a Pt film (100 nm thick) as an upper electrode film were deposited in this order to produce Samples 1 to 21, which are piezoelectric laminates. In Samples 1 to 21, the lower adhesive layer, lower electrode film, KNN film, upper adhesive layer, and upper electrode film were all deposited by RF magnetron sputtering under the following conditions. In Samples 1 to 21, when depositing the KNN film, two targets with different compositions were simultaneously used, and the first and second deposition steps described in the above-described embodiment were carried out. In addition, in Samples 1 to 21, after depositing the KNN film and before depositing the upper adhesive layer, a heat treatment was carried out under the conditions shown below.

[0157] <Conditions for forming the ZnO layer as the lower adhesion layer> Target: ZnO sintered body Substrate temperature: 500℃ Applied power (power density): 4W / cm 2 Atmosphere: Ar / O2 mixed gas atmosphere Ambient pressure: 0.3 Pa Ar gas partial pressure / O2 gas partial pressure: 10 / 1 Film formation time: 3 minutes (thickness 25 nm)

[0158] <Deposition conditions of Pt film as bottom electrode film> Target: Pt plate Substrate temperature: 500℃ Applied power (power density): 2W / cm 2 Atmosphere: Ar gas atmosphere Ambient pressure: 0.3 Pa Film formation time: 14 minutes (thickness 200 nm)

[0159] <Conditions for the first deposition step (deposition conditions for the KNN film that constitutes the bulk region)> First target: KNN target with a total atomic concentration of K and Na of 35 at% Second target: KNN target with a total atomic concentration of K and Na of 5 at% The power (power density) applied to the first target was as shown in Table 1 below. The power (power density) applied to the second target was as shown in Table 1 below. Atmosphere: Ar / O2 mixed gas atmosphere Ambient pressure: 0.1 Pa O2 gas partial pressure / Ar gas partial pressure: 1 / 20 Film forming temperature: 600℃ Film deposition time: 60 minutes (target thickness: 2000 nm (2 μm))

[0160] <Conditions for the second film deposition step (deposition conditions for the KNN film that constitutes the surface layer region)> Target: The same target as used to deposit the KNN film that constitutes the bulk region The power (power density) applied to the first target was as shown in Table 1 below. The power (power density) applied to the second target was as shown in Table 1 below. Atmosphere: Ar / O2 mixed gas atmosphere Ambient pressure: 0.1 Pa O2 gas partial pressure / Ar gas partial pressure: 1 / 20 Film forming temperature: 600℃ Film deposition time: 6 seconds (target thickness: 3 nm)

[0161] <Heat treatment conditions> Atmosphere: Atmospheric Temperature: 850℃ Duration: 2 hours

[0162] <Deposition conditions for RuO2 layer as upper adhesion layer> Target: Ru plate Substrate temperature: Room temperature (25°C) Applied power (power density): 0.5W / cm 2 Atmosphere: Ar / O2 mixed gas atmosphere Ambient pressure: 0.3 Pa Ar gas partial pressure / O2 gas partial pressure: 1 / 1 Film formation time: 6 minutes (thickness 10 nm)

[0163] <Film formation conditions for the Pt film as the upper electrode film> Target: Pt plate Substrate temperature: Room temperature (25 °C) Applied power (power density): 2 W / cm 2 Atmosphere: Ar gas atmosphere Ambient pressure: 0.3 Pa Film formation time: 7 minutes (thickness 100 nm)

[0164] The applied power to the first target and the second target of Samples 1 to 21 is as shown in Table 1 below.

[0165]

Table 1

[0166] (Fabrication of Sample 22) Sample 22, a piezoelectric laminate, was fabricated in the same manner as Sample 1, except that the KNN film was formed under the conditions shown below. In Sample 22, after the KNN film was formed, heat treatment was performed under the same conditions as Sample 1 (at a high temperature of 850 °C or higher). By this heat treatment, the alkali metal elements (K element and Na element) in the vicinity of the surface layer region of the KNN film were evaporated, and the total atomic concentration of K and Na in the surface layer region was made lower than the total atomic concentration of K and Na in the bulk region.

[0167] <Film formation conditions for the KNN film> Target: KNN target Applied power to the target (power density): 4 W / cm 2 Atmosphere: Ar / O2 mixed gas atmosphere Ambient pressure: 0.1 Pa O2 gas partial pressure / Ar gas partial pressure: 1 / 20 Film formation temperature: 600 °C Film deposition time: 60 minutes (target thickness: 2000 nm (2 μm))

[0168] <Rating 1> For each of Samples 1 to 21, the total atomic concentration of K and Na in the surface region and the total atomic concentration of K and Na in the bulk region were measured, and the adhesion, dielectric strength, and piezoelectric constant e 31 was evaluated.

[0169] (Measurement of the total atomic concentration of K and Na in each region of the surface and bulk regions) The total atomic concentrations of K and Na in the surface region and bulk region of Samples 1 to 21 were measured using the following apparatus, conditions, and method.

[0170] Equipment: ION-TOF TOF SIMS5 Measurement method: For each sample, the total number of K and Na atoms in each of the surface and bulk regions, the total number of atoms in the KNN film constituting the surface region, and the total number of atoms in the KNN film constituting the bulk region were calculated using TOF-SIMS. Assuming that the O atomic concentration in the KNN film was exactly 60%, the total atomic concentrations of K and Na in each of the surface and bulk regions were calculated using the above (Equation 1) and (Equation 2).

[0171] (Evaluation of Adhesion) To evaluate the adhesion between the KNN film and the upper adhesive layer (upper electrode film), the following StudPull test was carried out using the following apparatus, conditions, and method.

[0172] Equipment: Shimadzu Corporation AUTOGRAPH AGS-H Evaluation item: Load at peeling Test temperature: Room temperature (25°C) Test atmosphere: Air Tensile speed: 0.5 mm / min Adhesion area (jig area): 6mmφ Adhesive: Epoxy adhesive Measurement method: Multiple small pieces were prepared from one sample. Then, as shown in Figure 6, tensile jigs were fixed to both sides (the upper surface of the upper electrode film and the lower surface of the substrate) of the laminate (each prepared small piece) with an adhesive. Then, using a tensile tester, the tensile jig fixed to the upper electrode film was pulled upward in a direction perpendicular to the upper surface of the upper electrode film. For each prepared small piece, the load when the upper electrode film peeled off from the KNN film (laminate) was measured. The maximum load among the measured loads was used to calculate the maximum stress. The maximum stress is the value obtained by dividing the maximum load by the jig area (adhesion area). Note that the "upper surface of the upper electrode film" refers to the main surface opposite the KNN film side of the two main surfaces of the upper electrode film, and the "lower surface of the substrate" refers to the main surface opposite the main surface on which the lower electrode film and the like are formed of the two main surfaces of the substrate.

[0173] (Evaluation of dielectric strength voltage) The dielectric strength voltage of the KNN film was measured using the following equipment, conditions, and method.

[0174] Equipment: DBLI equipment manufactured by aixACCT Measurement atmosphere: Air Measurement temperature: room temperature (25℃) Measurement method: A voltage was applied to the upper electrode film from 0 V to -100 V in 1 V steps (1 V intervals), and the current density was measured at each voltage. The holding time at each voltage (the application time of each voltage) was 2 seconds. When the current density reached 1 mA / cm 2 When the KNN film had a thickness of approximately 2 μm, as in samples 1 to 21, if the KNN film did not experience dielectric breakdown when a voltage of −70 V (a voltage with an absolute value of 70 V) was applied, the KNN film was determined to have a dielectric strength of 350 kV / cm or more.

[0175] (piezoelectric constant e 31 ) Piezoelectric constant e of KNN film 31 was measured using the following equipment, conditions, and method.

[0176] Equipment: Laser Doppler vibrometer (model number: V100) manufactured by Iwasaki Communications Co., Ltd. (IWATSU) Measurement atmosphere: Air Temperature: Room temperature (25℃) Measurement method: First, small strips measuring 20 mm in length and 2.5 mm in width were cut from each of Samples 1 to 21. Then, as shown in Figure 7(a), one longitudinal end of each small piece from Samples 1 to 21 was fixed with a clamp, and a voltage application means (not shown) was connected between the lower electrode film and the upper electrode film to fabricate a simple unimorph cantilever. Then, using the voltage application means, a 350 Hz sine wave negative voltage was applied to the KNN film via the upper electrode film while the lower electrode film was grounded, so as to generate an electric field of 100 kV / cm between the lower electrode film and the upper electrode film (i.e., the KNN film), thereby expanding and contracting (deforming) the KNN film. The deformation of the KNN film caused the entire cantilever to bend and stretch (vibrate), and the tip of the cantilever to reciprocate up and down. The displacement Δ (piezoelectric displacement) of the tip of the cantilever at this time was measured by irradiating the tip of the cantilever with laser light L from a laser Doppler displacement meter, as shown in Figure 7(b). Then, using the displacement Δ of the tip of the cantilever, the length of the cantilever, and the applied voltage, the piezoelectric constant e at an applied electric field of 100 kV / cm was calculated. 31 was calculated.

[0177] The results of these measurements are shown in Table 2. In Table 2, a "+" in the "Difference in Total Atomic Concentration of K and Na" column means that the total atomic concentration of K and Na in the surface region is higher than that in the bulk region, and a "-" in the same column means that the total atomic concentration of K and Na in the surface region is lower than that in the bulk region. For example, in Table 2, "+2 at%" in the same column means that the total atomic concentration of K and Na in the surface region is 2 at% higher than that in the bulk region, and "-2 at%" in the same column means that the total atomic concentration of K and Na in the surface region is 2 at% lower than that in the bulk region.

[0178] [Table 2]

[0179] The laminates of samples 3 to 5, 9, 10, 14, 15, 19, and 20 all had a maximum stress of 20 N / m 2 It was confirmed that the total atomic concentration of K and Na in the surface region is lower than that in the bulk region, which improves the adhesion between the KNN film and the upper adhesive layer, and ultimately the adhesion between the KNN film and the upper electrode film. It is also found that the adhesion between the KNN film and the upper adhesive layer is reliably improved by keeping the difference between the total atomic concentration of K and Na in the surface region and the total atomic concentration of K and Na in the bulk region between 1 at% and 11 at%.

[0180] Furthermore, it was confirmed that the laminates of Samples 3 to 5, 9, 10, 14, 15, 19, and 20 all had a dielectric strength voltage of 350 kV / cm or more. This shows that a total atomic concentration of K and Na in the surface region of 10 at% or more can improve adhesion between the KNN film and the upper adhesive layer while obtaining a KNN film with a high dielectric strength voltage. Furthermore, the laminates of Samples 3 to 5, 9, 10, 14, 15, 19, and 20 have a dielectric strength voltage of 350 kV / cm or more, even when heat treatment is performed at 850°C after the KNN film is formed but before the upper adhesive layer is formed, and therefore it is clear that the KNN film is sufficiently crystallized.

[0181] In addition, the laminates of Samples 3 to 5, 9, 10, 14, 15, 19, and 20 all had a piezoelectric constant e 31 is 8C / m 2 This indicates that reducing the total atomic concentration of K and Na only in the surface layer region does not affect the piezoelectric properties of the entire KNN film.

[0182] In contrast, the laminates of samples 1, 2, 7, 8, 12, 13, 17, and 18 all had a maximum stress of 10 N / m 2This confirms that in a laminate in which the total atomic concentration of K and Na in the surface region is equal to or higher than that in the bulk region, the adhesion between the KNN film and the upper adhesive layer, and in turn the adhesion between the KNN film and the upper electrode film, is low.

[0183] In addition, for the laminates of samples 6, 11, 16, and 21, the maximum stress in the StudPull test was 10 N / m 2 It was confirmed that the total atomic concentration of K and Na in the surface region was less than 10 at% and the dielectric strength was less than 60 kV / cm. This shows that even if the total atomic concentration of K and Na in the surface region is lower than that in the bulk region, when the total atomic concentration of K and Na in the surface region is less than 10 at% the adhesion between the KNN film and the upper adhesive layer is reduced and the dielectric strength is reduced.

[0184] In addition, the laminates of Samples 6, 11, 16, and 21 all had a dielectric strength voltage of less than 60 kV / cm. Therefore, in these samples, the piezoelectric constant e 31 When a voltage was applied to the laminate to generate an electric field of 100 kV / cm in the KNN film, the piezoelectric constant e 31 Before the measurement of the piezoelectric constant e 31 could not be measured.

[0185] Furthermore, it was confirmed that the dielectric strength voltage was 100 kV / cm for the laminate of Sample 22. This confirmed that the dielectric strength voltage was low for a laminate in which the alkali metal elements were evaporated by heat treatment and the total atomic concentration of K and Na in the surface region was lower than the total atomic concentration of K and Na in the bulk region.

[0186] <Rating 2> For each of Samples 1 to 21, the deviation between the total atomic concentration of K and Na in a measurement length of 10 nm and the total atomic concentration of K and Na in the bulk region was evaluated.

[0187] (Measurement of total atomic concentration of K and Na in a measurement length of 10 nm) For each of Samples 1 to 21, the total atomic concentration of K and Na within a measurement length of 10 nm was measured using the following device, conditions, and method.

[0188] Equipment: ION-TOF TOF SIMS5 Measurement position: A position including the center of the surface of the KNN film that constitutes the bulk region, parallel to the surface direction of the substrate Measurement length: 10 nm in the film thickness direction Measurement method: For each sample, TOF-SIMS was performed in the film thickness direction at the measurement position. Then, the total number of K and Na atoms contained in the KNN film at the measurement position when the measurement length was 10 nm in the film thickness direction, and the total number of atoms constituting the KNN film at the measurement position were calculated. At this time, assuming that the O atomic concentration of the KNN film was exactly 60%, the total atomic concentration of K and Na at the measurement length of 10 nm was calculated using the above (Equation 3).

[0189] (Total atomic concentration of K and Na in the bulk region) Measurement was carried out in the same manner as described in Evaluation 1 above.

[0190] (Calculation of deviation) For each of Samples 1 to 21, the deviation between the total atomic concentration of K and Na in a measurement length of 10 nm and the total atomic concentration of K and Na in the bulk region was calculated.

[0191] In the KNN films constituting the bulk regions of Samples 1 to 21, it was confirmed that the deviation between the total atomic concentration of K and Na at a measurement length of 10 nm and the total atomic concentration of K and Na in the bulk region was within 5% at any position in the KNN film except for the interface regions on the upper and lower sides. This shows that in the stacks of Samples 1 to 21 in which the KNN film was deposited by sputtering, the composition of the KNN film in the bulk region was almost uniform in the film thickness direction.

[0192] <Rating 3> For each of Samples 1 to 21, the deviation between the total atomic concentration of K and Na in the lower layer region and the total atomic concentration of K and Na in the bulk region was evaluated.

[0193] (Measurement of total atomic concentration of K and Na in the lower layer region) For each of Samples 1 to 21, the total atomic concentration of K and Na in the lower layer region of the bulk region was measured using the following device, conditions, and method.

[0194] Equipment: ION-TOF TOF SIMS5 Measurement method: For each sample, the total number of K and Na atoms in the lower layer region and the total number of atoms in the KNN film constituting the lower layer region were calculated using TOF-SIMS. At this time, assuming that the O atomic concentration in the KNN film is exactly 60%, the total atomic concentration of K and Na in the lower layer region was calculated using the above (Equation 4).

[0195] (Total atomic concentration of K and Na in the bulk region) Measurement was carried out in the same manner as described in Evaluation 1 above.

[0196] (Calculation of deviation) For each of Samples 1 to 21, the deviation between the total atomic concentration of K and Na in the lower layer region and the total atomic concentration of K and Na in the bulk region was calculated.

[0197] In the laminates of Samples 1 to 21 in which the KNN film was deposited by sputtering, it was confirmed that the deviation between the total atomic concentration of K and Na in the lower layer region and the total atomic concentration of K and Na in the bulk region was within 5%. This indicates that in the laminates of Samples 1 to 21, the diffusion of alkali metal elements into the lower electrode film during the deposition of the KNN film was suppressed.

[0198] <Preferred aspects of the present disclosure> Preferred aspects of the present disclosure will be described below.

[0199] (Appendix 1) According to one aspect of the present disclosure, A substrate; a lower electrode film on the substrate; a piezoelectric film on the lower electrode film, the piezoelectric film being composed of a perovskite oxide represented by the general formula ABO3, the A site containing K and Na, and the B site containing Nb; an upper adhesive layer formed on the piezoelectric film; an upper electrode film formed on the upper adhesive layer, When the piezoelectric film is divided into a surface region extending from an upper surface of the piezoelectric film to a predetermined depth toward the substrate, and a bulk region other than the surface region, the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region. A piezoelectric stack is provided.

[0200] (Appendix 2) The piezoelectric laminate according to Supplementary Note 1, preferably The surface region is a region extending from the top surface of the piezoelectric film to a depth of 3 nm toward the substrate.

[0201] (Appendix 3) The piezoelectric laminate according to Supplementary Note 1 or 2, preferably The difference between the total atomic concentration of K and Na in the surface region and the total atomic concentration of K and Na in the bulk region is 1 at % or more and 11 at % or less.

[0202] (Appendix 4) The piezoelectric laminate according to any one of Supplementary Notes 1 to 3, preferably The total atomic concentration of K and Na in the surface layer region is 10 at % or more.

[0203] (Appendix 5) The piezoelectric laminate according to any one of Supplementary Notes 1 to 4, preferably In the piezoelectric film constituting the bulk region, the difference (deviation) between the total atomic concentration of K and Na when the measurement length is 10 nm in the film thickness direction at a position including the center of the surface of the piezoelectric film parallel to the direction along the main surface of the substrate and the total atomic concentration of K and Na in the bulk region is within 5% at any position in the film thickness direction of the piezoelectric film except for each interface region on the upper and lower sides.

[0204] (Appendix 6) The piezoelectric laminate according to any one of Supplementary Notes 1 to 5, preferably The difference (deviation) between the total atomic concentration of K and Na in a lower layer region of the bulk region extending from the lower surface of the piezoelectric film to a height of 10 nm toward the upper surface of the piezoelectric film and the total atomic concentration of K and Na in the bulk region is within 5%.

[0205] (Appendix 7) The piezoelectric laminate according to any one of Supplementary Notes 1 to 6, preferably The dielectric strength of the piezoelectric film is 350 kV / cm or more.

[0206] (Appendix 8) The piezoelectric laminate according to any one of Supplementary Notes 1 to 7, preferably The piezoelectric constant e of the piezoelectric film 31 is 8C / m 2 That's all.

[0207] (Appendix 9) The piezoelectric laminate according to any one of Supplementary Notes 1 to 8, preferably The piezoelectric film is a polycrystalline film of the perovskite-type oxide or a single-crystalline film of the perovskite-type oxide.

[0208] (Appendix 10) According to another aspect of the present disclosure, providing a substrate; A step of preparing a target composed of a perovskite-type oxide represented by a general formula ABO3, in which the A site contains K and Na and the B site contains Nb; forming a lower electrode film on the substrate; forming a piezoelectric film composed of a perovskite oxide represented by a general formula ABO3, the A site of which contains K and Na, and the B site of which contains Nb, on the lower electrode film by a sputtering method using the target; forming an upper adhesive layer on the piezoelectric film; forming an upper electrode film on the upper adhesive layer, In the step of preparing the target, a first target and a second target are prepared, the second target having a ratio of the total number of K atoms and Na atoms contained per unit volume to the number of Nb atoms contained per unit volume smaller than that of the first target, In the step of depositing the piezoelectric film, the first target and the second target are used, and the steps of (a) applying equal power to the first target and the second target, and (b) applying a power to the second target that is greater than the power to the first target are carried out in this order, and (b) is started immediately before the end of deposition of the piezoelectric film. A method for manufacturing a piezoelectric stack is provided.

[0209] (Appendix 11) According to yet another aspect of the present disclosure, A substrate; a lower electrode film on the substrate; a piezoelectric film on the lower electrode film, the piezoelectric film being composed of a perovskite oxide represented by the general formula ABO3, the A site containing K and Na, and the B site containing Nb; an upper adhesive layer formed on the piezoelectric film; an upper electrode film formed on the upper adhesive layer, When the piezoelectric film is divided into a surface region extending from an upper surface of the piezoelectric film to a predetermined depth toward the substrate, and a bulk region other than the surface region, the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region. A piezoelectric laminate substrate or a piezoelectric element (piezoelectric device module) is provided. [Explanation of symbols]

[0210] 1 board 2 Lower electrode film 3 Piezoelectric film 3a Piezoelectric film that forms the surface layer 3b Piezoelectric film that constitutes the bulk region 3b1 Piezoelectric film that constitutes the lower layer region of the bulk region 3b2 Piezoelectric film constituting the bulk region other than the lower layer region 4 Upper electrode film 6 Lower adhesive layer 7 Upper adhesive layer 10 Piezoelectric laminate 20 Piezoelectric element 30 Piezoelectric Device Module

Claims

1. A substrate; a lower electrode film on the substrate; General formula ABO ３ a piezoelectric film on the lower electrode film, the piezoelectric film being composed of a perovskite oxide, the A site of which contains K and Na, and the B site of which contains Nb; an upper adhesive layer on the piezoelectric film; an upper electrode film on the upper adhesive layer, When the piezoelectric film is divided into a surface region extending from an upper surface of the piezoelectric film to a predetermined depth toward the substrate, and a bulk region other than the surface region, the total atomic concentration of K and Na in the surface region is lower than the total atomic concentration of K and Na in the bulk region. Piezoelectric stack.

2. The piezoelectric stack according to claim 1 , wherein the surface region is a region ranging from the top surface of the piezoelectric film to a depth of 3 nm toward the substrate.

3. 3. The piezoelectric stack according to claim 1, wherein a difference between the total atomic concentration of K and Na in the surface region and the total atomic concentration of K and Na in the bulk region is 1 at % or more and 11 at % or less.

4. 3. The piezoelectric stack according to claim 1, wherein the total atomic concentration of K and Na in the surface layer region is 10 at % or more.

5. 3. The piezoelectric stack according to claim 1, wherein in the piezoelectric film constituting the bulk region, a difference between the total atomic concentration of K and Na when the measurement length is 10 nm in the film thickness direction at a position including the center of a surface of the piezoelectric film parallel to a direction along the main surface of the substrate and the total atomic concentration of K and Na in the bulk region is within 5% at any position in the film thickness direction of the piezoelectric film excluding each interface region on the upper and lower sides.

6. 3. The piezoelectric stack according to claim 1, wherein a difference between a total atomic concentration of K and Na in a lower layer region of the bulk region extending from a lower surface of the piezoelectric film to a height of 10 nm toward the upper surface of the piezoelectric film and the total atomic concentration of K and Na in the bulk region is within 5%.

7. 3. The piezoelectric laminate according to claim 1, wherein the dielectric strength of the piezoelectric film is 350 kV / cm or more.

8. The piezoelectric constant e of the piezoelectric film ３１ is 8 C / m ２ 3. The piezoelectric laminate according to claim 1 or 2, wherein:

9. 3. The piezoelectric stack according to claim 1, wherein the piezoelectric film is a polycrystalline film of the perovskite oxide or a single crystalline film of the perovskite oxide.

10. providing a substrate; General formula ABO ３ a step of preparing a target composed of a perovskite oxide represented by the formula: forming a lower electrode film on the substrate; General formula ABO ３ a step of depositing a piezoelectric film made of a perovskite oxide represented by the formula (I) on the lower electrode film by a sputtering method using the target, the perovskite oxide having an A site containing K and Na and a B site containing Nb; forming an upper adhesive layer on the piezoelectric film; forming an upper electrode film on the upper adhesive layer, In the step of preparing the target, a first target and a second target are prepared, the second target having a ratio of the total number of K atoms and Na atoms contained per unit volume to the number of Nb atoms contained per unit volume smaller than that of the first target, In the step of depositing the piezoelectric film, the first target and the second target are used, and the steps of (a) applying equal power to the first target and the second target, and (b) applying a power to the second target that is greater than the power to the first target are performed in this order, and (b) is started immediately before the end of deposition of the piezoelectric film. A method for manufacturing a piezoelectric laminate.

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