PIEZOELECTRIC THIN FILM, PIEZOELECTRIC THIN FILM ELEMENT AND PIEZOELECTRIC CONVERTER

Abstract

A piezoelectric thin film contains a metal oxide with a perovskite structure. The metal oxide contains bismuth, potassium, titanium, magnesium, iron, and an element M. The element M is at least one element selected from the group consisting of gallium and cobalt. At least a portion of the metal oxide is at least one crystal selected from the group consisting of a tetragonal crystal and an orthorhombic crystal. One (001) plane of the crystal is oriented in a normal direction to a surface of the piezoelectric thin film.

Description

CROSS REFERENCE TO RELATED APPLICATIONSThis application is based on and claims priority from Japanese Patent Application No. 2023-124586 filed on Jul. 31, 2023, the entire contents of which are incorporated herein by reference.BACKGROUNDField of InterestThe present disclosure relates to a piezoelectric thin film, a piezoelectric thin film element, and a piezoelectric transducer.DESCRIPTION OF THE RELATED ARTA piezoelectric material is processed into different piezoelectric elements in correspondence for different purposes. For example, a piezoelectric actuator converts a voltage into a force by an inverse piezoelectric effect that deforms a piezoelectric material by applying a voltage to the piezoelectric material. For example, a piezoelectric sensor converts a force into a voltage by a piezoelectric effect deforming a piezoelectric material by applying a pressure to the piezoelectric material. These piezoelectric elements are mounted on various electronic devices. In recent markets, reduction in size and improvement in performance of electronic devices are demanded, and thus a piezoelectric element (thin film piezoelectric element) using a piezoelectric thin film has been actively studied. However, the thinner the piezoelectric material, the lower the piezoelectric effect and the reverse piezoelectric effect are to be expected. Therefore, development of a piezoelectric material having excellent piezoelectric properties in a thin film state has been expected.As the piezoelectric material, lead zirconate titanate (so-called PZT), a perovskite-type ferroelectric material, has heretofore been frequently used. However, since PZT contains lead which damages the environment or the human body, development of a lead-free piezoelectric material has been expected as an alternative to PZT. In the following Non-Patent Literature 1, for example, a material based on BaTiO 3 is described as an example of a lead-free piezoelectric material. The BaTiO 3 based material has relatively excellent piezoelectric properties among lead-free piezoelectric materials, and therefore is expected to be used particularly for a thin film piezoelectric element.<Nicht Patent Literature 1>Yiping GUO et al., "Thick Dependence of Electrical Properties of Highly (100)-Oriented BaTiO 3 Thin Films Prepared by One-Step Chemical Solution Deposition" Japanese Journal of Applied Physics, Vol. 45, No. 2A, 2006, pp. 855-859SUMMARYAn object of one aspect of the present invention is to provide a piezoelectric thin film having excellent piezoelectric properties, a piezoelectric thin film element including the piezoelectric thin film, and a piezoelectric transducer including the piezoelectric thin film or the piezoelectric thin film element.An aspect of the present invention relates to, for example, a piezoelectric thin film described in any one of the following [1] to [5], a piezoelectric thin film element described in any one of the following [6] to

[14] , and a piezoelectric transducer described in any one of the following

[15] and

[16] .[1] A piezoelectric thin film containing a metal oxide having a perovskite structure, wherein the metal oxide contains bismuth, potassium, titanium, magnesium, iron, and an element M, the element M is at least one element selected from the group consisting of gallium and cobalt, at least a part of the metal oxide is at least one crystal selected from the group consisting of a tetragonal crystal and an orthorhombic crystal, and a (001) plane of the crystal is oriented in a normal direction of a surface of the piezoelectric thin film.[2] The piezoelectric thin film described in [1], wherein the metal oxide is represented by Chemical Formula 1 below, x, y, and z in Chemical Formula 1 below are each a positive real number, x+y+z is 1, α in Chemical Formula 1 below is greater than 0 and less than 1, β in Chemical Formula 1 below is greater than 0 and less than 1, y in Chemical Formula 1 below is from 0.05 to 0.40, M in Chemical Formula 1 below is represented by Ga1-δCoδ, and δ is from 0 to 1: x(Bi1-αKα)TiO 3- yBi(Ti1-βMgβ)O 3- zBi(Fe1-γMγ)O 3(1)[3] The piezoelectric thin film described in [2], wherein a three-dimensional coordinate system is composed of an X-axis, a Y-axis and a Z-axis, arbitrary coordinates in the coordinate system are represented by (X, Y, Z), coordinates (x, y, z) in the coordinate system correspond to x, y and z in Chemical Formula 1, coordinates A in the coordinate system are (0.250, 0.005, 0.700), coordinates B in the coordinate system are (0.450, 0.250, 0.300), coordinates C in the coordinate system are (0.200, 0.500, 0.300), coordinates D in the coordinate system are (0.005, 0.250, 0.700), and the coordinates (x, y, z) are in a quadrangle having vertices at the coordinates A, the coordinates B, The coordinates C and the coordinates D are located.[4] The piezoelectric thin film described in any one of [1] to [3], wherein the piezoelectric thin film is an epitaxial film.[5] The piezoelectric thin film described in any one of [1] to [4], wherein the piezoelectric thin film is a ferroelectric thin film.[6] A piezoelectric thin film element including the piezoelectric thin film described in any one of [1] to [5].[7] The piezoelectric thin film element described in [6], comprising:a crystalline substrate; andthe piezoelectric thin film directly or indirectly deposited on the crystalline substrate.[8] The piezoelectric thin film element described in [6], comprising:a crystalline substrate; andan electrode layer directly or indirectly deposited on the crystalline substrate; andthe piezoelectric thin film directly or indirectly deposited on the electrode layer.[9] The piezoelectric thin film element described in [6], comprising:an electrode layer; andthe piezoelectric thin film directly or indirectly deposited on the electrode layer.

[10] The piezoelectric thin film element described in [8], further comprising at least one intermediate layer (first intermediate layer), the intermediate layer (first intermediate layer) being disposed between the crystalline substrate and the electrode layer.

[11] The piezoelectric thin film element described in [8], further including at least one intermediate layer (second intermediate layer), the intermediate layer (second intermediate layer) being disposed between the electrode layer and the piezoelectric thin film.

[12] The piezoelectric thin film element described in [9], further including at least one intermediate layer (second intermediate layer), the intermediate layer (second intermediate layer) being disposed between the electrode layer and the piezoelectric thin film.

[13] The piezoelectric thin film element described in [8] or

[11] , wherein the electrode layer contains a platinum crystal, a (002) plane of the platinum crystal is oriented in a normal direction of a surface of the electrode layer, and a (200) plane of the platinum crystal is oriented in a direction in the plane of the surface of the electrode layer.

[14] The piezoelectric thin film element described in [9] or

[12] , wherein the electrode layer contains a platinum crystal, a (002) plane of the platinum crystal is oriented in a normal direction of a surface of the electrode layer, and a (200) plane of the platinum crystal is oriented in a direction in the plane of the surface of the electrode layer.

[15] A piezoelectric transducer including the piezoelectric thin film described in any one of [1] to [5].

[0023]

[16] A piezoelectric transducer including the piezoelectric thin film element described in any one of [6] to

[14] .According to an aspect of the present invention, there are provided a piezoelectric thin film having excellent piezoelectric properties, a piezoelectric thin film element including the piezoelectric thin film, and a piezoelectric transducer including the piezoelectric thin film or the piezoelectric thin film element.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1A is a schematic cross-sectional view of a piezoelectric thin film element according to a specific example of the present invention, FIG. 1B is an exploded perspective view of the piezoelectric thin film element illustrated in FIG. 1A, and a substrate, a first intermediate layer, a second intermediate layer, and a second electrode layer are omitted in FIG. 1B. FIG. 2 is a perspective view of a crystal (unit cell) of a metal oxide having a perovskite structure, and shows the arrangement of the individual elements in the perovskite structure. FIG. 3 is a perspective view of a crystal (unit cell) of a metal oxide having a perovskite structure, and shows the lattice planes and crystal orientations of the crystal. FIG. 4 is a three-dimensional coordinate system for illustrating a composition of a piezoelectric thin film. FIG. 5 is a triangular coordinate system corresponding to a triangle shown in FIG. 4. FIG. 6 is a schematic cross-sectional view of a thin film piezoelectric element (ultrasonic transducer) according to another specific example of the present invention.DETAILED DESCRIPTIONHereinafter, details of a preferred embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment. In the following description, like components or like components having the same function are assigned the same reference numerals with reference to the drawings, and overlapping descriptions are omitted. An X axis, a Y axis, and a Z axis illustrated in FIGS. 1A, 1B, and 6 are three mutually orthogonal coordinate axes. The X-axis, the Y-axis, and the Z-axis are the same as FIGS. 1A, 1B, and 6, but the coordinate systems illustrated in FIGS. 1A, 1B, and 6 have nothing to do with the coordinate systems illustrated in FIGS. 4 and 5.(Piezoelectric thin film element)A piezoelectric thin film element according to the present embodiment includes at least one piezoelectric thin film. For example, as illustrated in FIG. 1A, a piezoelectric thin film element 10 according to the present embodiment may include a crystalline substrate 1, a first electrode layer 2 (lower electrode layer) directly or indirectly deposited on the crystalline substrate 1, a piezoelectric thin film 3 directly or indirectly deposited on the first electrode layer 2, and a second electrode layer 4 (upper electrode layer) directly or indirectly deposited on the piezoelectric thin film 3. The piezoelectric thin film element 10 may further include at least one intermediate layer. For example, the piezoelectric thin film element 10 may include a first intermediate layer 5. The first intermediate layer 5 may be disposed between the crystalline substrate 1 and the first electrode layer 2, and the first electrode layer 2 may be directly deposited on a surface of the first intermediate layer 5. The piezoelectric thin film element 10 may include a second intermediate layer 6. The second intermediate layer 6 may be disposed between the first electrode layer 2 and the piezoelectric thin film 3, and the piezoelectric thin film 3 may be directly deposited on a surface of the second intermediate layer 6. A thickness of the crystalline substrate 1, the first intermediate layer 5, the first electrode layer 2, the second intermediate layer 6, the piezoelectric thin film 3, and the second electrode layer 4 may be uniform. As illustrated in FIG. 1B, a normal direction dn of a surface of the piezoelectric thin film 3 may be substantially or entirely parallel to a normal direction D N of a surface of the first electrode layer 2. That is, the surface of the piezoelectric thin film 3 may be substantially or entirely parallel to the surface of the first electrode layer 2. The normal direction dn of the surface of the piezoelectric thin film 3 may be a polarization direction of the piezoelectric thin film 3. The normal direction dn of the surface of the piezoelectric thin film 3 may also be referred to as the thickness direction of the piezoelectric thin film 3.A modified example of the piezoelectric thin film element 10 may not include the crystalline substrate 1. The crystalline substrate 1 may be removed after the formation of the first electrode layer 2, the piezoelectric thin film 3, and the second electrode layer 4, for example. In a case where the crystalline substrate 1 functions as an electrode, the crystalline substrate 1 may be the first electrode layer 2. That is, in a case where the crystalline substrate 1 functions as an electrode, the modified example of the piezoelectric thin film element 10 may include the crystalline substrate 1 and the piezoelectric thin film 3 deposited on the crystalline substrate 1. When the crystalline substrate 1 functions as an electrode, the piezoelectric thin film 3 may be directly deposited on the crystalline substrate 1. When the crystalline substrate 1 functions as an electrode, the piezoelectric thin film 3 may be deposited on the crystalline substrate 1 through at least one of the first intermediate layer 5 and the second intermediate layer 6.The piezoelectric thin film 3 contains a metal oxide having a perovskite structure. The metal oxide contains bismuth (Bi), potassium (K), titanium (Ti), magnesium (Mg), iron (Fe), and an element M. The element M is at least one element selected from the group consisting of gallium (Ga) and cobalt (Co). The metal oxide having the above composition tends to be at least one crystal selected from the group consisting of a tetragonal crystal and an orthorhombic crystal, and a (001) plane of the crystal tends to be oriented in the normal direction of the surface of the piezoelectric thin film. As a result, the piezoelectric thin film 3 can have excellent piezoelectric properties (large piezoelectric strain constant d 33,f) and ferroelectricity.It is possible that the metal oxide is composed of only Bi, K, Ti, Mg, Fe, the element M, and oxygen (O). The metal oxide may contain other elements besides Bi, K, Ti, Mg, Fe, the element M and O. The metal oxide may further contain at least one element selected from the group consisting of lanthanum (La), yttrium (Y), sodium (Na), lithium (Li), zirconium (Zr), nickel (Ni), zinc (Zn), manganese (Mn), and lead (Pb). However, the metal oxide may not necessarily contain Pb.The metal oxide is a main component of the piezoelectric thin film 3. It is possible that the piezoelectric thin film 3 is made of only the metal oxide. The piezoelectric thin film 3 may contain other elements besides Bi, K, Ti, Mg, Fe, the element M and O as long as the piezoelectric properties of the piezoelectric thin film 3 are not impaired. The piezoelectric thin film 3 may additionally contain, for example, at least one element selected from the group consisting of La, Y, Na, Li, Zr, Ni, Zn, Mn, and Pb. However, the piezoelectric thin film 3 need not contain Pb.Hereinafter, the metal oxide having a perovskite structure will be referred to as a "perovskite-type oxide". FIG. 2 shows a unit cell of a perovskite-type oxide crystal. An element located in the A site of the unit cell uc may be Bi or K. An element located in the B site of the unit cell uc may be Ti, Mg, Fe or the element M. The unit cell uc shown in FIG. 2 is the same as the unit cell uc shown in FIG. 3. However, the B site and oxygen (O) in the unit cell uc in FIG. 3 are omitted to show the lattice planes. A lattice translation vector a (i.e., the a-axis) in the unit cell uc points in a

[100] direction, a lattice translation vector b (i.e., the b-axis) in the unit cell uc points in a

[010] direction, and a lattice translation vector c (i.e., the c-axis) in the unit cell uc points in a

[001] direction. The grating translation vector a, the grating translation vector b and the grating translation vector c are perpendicular to each other. A length a of the lattice translation vector a is a distance a (lattice constant a) from (100) planes of the perovskite-type oxide. A length b of the lattice translation vector b is a distance b (lattice constant b) from (010) planes of the perovskite-type oxide. A length c of the lattice translation vector c is a distance c (lattice constant c) from (001) planes of the perovskite-type oxide. The piezoelectric thin film 3 may be made of a single crystal of perovskite-type oxide. The piezoelectric thin film 3 may be made of a polycrystal of perovskite-type oxide.A part or all of the perovskite-type oxide is at least one crystal selected from the group consisting of a tetragonal crystal and an orthorhombic crystal at normal temperature or at a temperature of Curie temperature or less. Due to the anisotropy along the c-axis of either the tetragonal or orthorhombic crystal, the piezoelectric thin film 3 can have excellent piezoelectric properties and ferroelectricity. In the tetragonal crystal, the lattice constant a is equal to the lattice constant b. In the tetragonal crystal, the lattice constant a is different from the lattice constant c. In the tetragonal crystal, the lattice constant c may be larger than the lattice constant a. In the orthorhombic crystal, the lattice constant a, the lattice constant b, and the lattice constant c are different from each other. In the orthorhombic crystal, the lattice constant c may be larger than the lattice constant a and the lattice constant b. It is possible that the perovskite-type oxide is composed of only the tetragonal crystal. It is possible that the perovskite-type oxide is composed of only the orthorhombic crystal. It is possible that the perovskite-type oxide is composed of only the tetragonal crystal and the orthorhombic crystal. The piezoelectric thin film 3 may also contain a crystal other than the tetragonal crystal and the orthorhombic crystal. For example, the piezoelectric thin film 3 may further include one or both of cubic crystals of perovskite-type oxide and a rhombohedral crystal of perovskite-type oxide.A (001) plane of at least one crystal selected from the group consisting of the tetragonal crystal and the orthorhombic crystal is oriented in the normal direction dn of the surface of the piezoelectric thin film 3. The piezoelectric thin film 3 may include a plurality of crystals, and the (001) plane of a part or all of the crystals in the piezoelectric thin film 3 may be oriented in the normal direction dn of the surface of the piezoelectric thin film 3. For example, the (001) plane of the crystal (unit cell uc) may be substantially or completely perpendicular to the normal direction dn, and

[001] (orientation of the lattice plane) of the crystal (unit cell uc) may be substantially or completely parallel to the normal direction dn. In other words, the (001) plane of the crystal (unit cell uc) may be substantially or entirely parallel to the surface of the piezoelectric thin film 3. A crystal orientation in which the perovskite-type oxide having the above-described composition may be easily polarized is

[001] . Therefore, the piezoelectric thin film 3 can have excellent piezoelectric properties and ferroelectricity because the (001) plane of the perovskite-type oxide crystal is oriented in the normal direction dn of the surface of the piezoelectric thin film 3. For the same reason, c / a of the tetragonal crystal and the orthorhombic crystal may be 1.05 to 1.20, respectively. The lattice constant a of the tetragonal crystal and the orthorhombic crystal may be, for example, between 0.375 Å and 0.395 Å, respectively. The lattice constant b of the tetragonal crystal is equal to the lattice constant a of the tetragonal crystal. The lattice constant b of the orthorhombic crystal may be, for example, between 0.375 Å and 0.395 Å and have a different value than the lattice constant a of the orthorhombic crystal. The lattice constant c of the tetragonal crystal and the orthorhombic crystal may be, for example, between 0.430 Å and 0.450 Å, respectively. c / a of the tetragonal crystal may be the same as or different from c / a of the orthorhombic crystal. The lattice constant a of the tetragonal crystal may be the same as or different from the lattice constant a of the orthorhombic crystal. The lattice constant c of the tetragonal crystal may be the same as or different from the lattice constant c of the orthorhombic crystal.The degree of orientation of each lattice plane of the crystal can be quantified by an orientation degree (unit: %). The degree of orientation of each grating plane can be calculated on the basis of a diffraction peak of the X-ray radiation derived from each grating plane. The X-ray diffraction peak derived from each lattice plane can be measured by out-of-plane measurement on the surface of the piezoelectric thin film 3. A degree of orientation of the (001) plane may be represented as 100×I (001) / ΣI (hkl). A degree of orientation of the (110) plane may be represented as 100×I (110) / ΣI (hkl). A degree of orientation of the (111) plane may be represented as 100×I (111) / ΣI (hkl). I (001) is a maximum value of the X-ray diffraction peak derived from the (001) plane. I (110) is a maximum value of the X-ray diffraction peak derived from the (110) plane. I(111) is the maximum value of the X-ray diffraction peak derived from the (111) plane. ΣI (hkl1) is I (001)+ I (110)+ I (111). The degree of orientation of the (001) plane may be represented as 100×S (001) / ΣS (hkl). The degree of orientation of the (110) plane may be represented as 100×S (110) / ΣS (hkl). The degree of orientation of the (111) plane may be represented as 100×S (111) / ΣS (hkl). S (001) is an area (integration of a peak) of the X-ray diffraction peak derived from the (001) plane. S (110) is an area (integration of the peak) of the X-ray diffraction peak derived from the (110) plane. S (111) is the area (integration of peak) of the X-ray diffraction peak derived from the (111) plane. ES (hkl) is S (001)+ S (110)+ S (111). The degree of orientation of each lattice plane can be quantified by a degree of orientation based on the Lotgering method.For the reason that the piezoelectric thin film 3 is likely to have excellent piezoelectric properties and ferroelectricity, it is preferable that the (001) plane of the crystal is preferably oriented in the normal direction dn of the surface of the piezoelectric thin film 3. That is, the degree of orientation of the (001) plane is preferably higher than the degree of orientation of the (110) plane and the (111) plane. For example, the degree of orientation of the (001) plane may be from 70% to 100%, preferably from 80% to 100% and particularly preferably from 90% to 100%.In contrast to the piezoelectric thin film 3, it is difficult to stress a bulk of a piezoelectric material having a cubic crystal structure or a pseudocubic crystal structure to convert the bulk of the piezoelectric material into a tetragonal crystal or an orthorhombic crystal. Therefore, the bulk of the piezoelectric material tends to hardly have piezoelectric properties attributable to the tetragonal or orthorhombic crystal of the perovskite-type oxide.A crystalline orientation described below means that the (001) plane of at least one crystal selected from the group consisting of a tetragonal crystal and an orthorhombic crystal is oriented in the normal direction dn of the surface of the piezoelectric thin film 3.The piezoelectric thin film 3 is a crystalline film formed by a vapor deposition method or a solution method and is likely to have the above-described crystalline orientation. On the other hand, a bulk of the piezoelectric material having the same composition as that of the piezoelectric thin film 3 tends to have the crystalline orientation as described above with difficulty compared with the piezoelectric thin film 3. This is because the bulk of the piezoelectric material is a sintered body (ceramic) made of a powder containing essential elements of the piezoelectric material, and it is difficult to control the structure and orientation of various crystals constituting the sintered body. Since the bulk of the piezoelectric material contains Fe, the resistivity of the bulk of the piezoelectric material is lower than that of the piezoelectric thin film 3. Therefore, it is difficult to polarize the bulk of the piezoelectric material by applying a high electric field, and it is difficult for the bulk of the piezoelectric material to have the same piezoelectric properties as those of the piezoelectric thin film.The metal oxide contained in the piezoelectric thin film 3 can be represented by Chemical Formula 1 below. Chemical Formula 1 below is substantially the same as Chemical Formula 1a below and Chemical Formula 1b below. M in Chemical Formula 1 and Chemical Formula 1 aabove is represented as Ga1-δCoδ. (Bi1-αKα) x Bi y+z in Chemical Formula 1 aand Chemical Formula 1 bcorresponds to the A site of the unit cell uc of the perovskite-type oxide (ABO 3). Ti x( Ti1-βMgβ) y( Fe1-γMγ) z in Chemical Formula 1 acorresponds to the B site of the unit cell uc of the perovskite-type oxide. Ti x( Ti1-βMgβ) y( Fe1-γ(Ga1-γCoδ)γ) z in the following Chemical Formula 1 bcorresponds to the B site of the unit cell uc of the perovskite-type oxide. In a case where the metal oxide is represented by Chemical Formula 1 below, the piezoelectric thin film 3 is likely to contain at least one crystal selected from the group consisting of a tetragonal crystal and an orthorhombic crystal, the crystal being likely to have the above-described crystalline orientation, and the piezoelectric thin film 3 is likely to have excellent piezoelectric characteristics and ferroelectricity. x(Bi1-αKα)TiO 3- yBi(Ti1-βMgβ)O 3- zBi(Fe1-γMγ)O 3(1) ( Bi1-αKα) x Bi y+z Ti x( Ti1-βMgβ) y( Fe1-γMγ) z O3±ε(1a) (Bi1-αKα) x Bi y+z Ti x( Ti1-βMgβ) y( Fe1-γ(Ga1-δCoδ)γ)O3±ε(1b)A unit of x, y, z, α, β, γ, δ, and ε in each of the chemical formulas described above is the molar ratio. Each of x, y, and z is a positive real number. x+y+z is 1,000. x in each chemical formula is greater than 0.000 and less than 1,000. y in each chemical formula is greater than 0.000 and less than 1,000. z in each chemical formula is greater than 0.000 and less than 1,000. α in each chemical formula is greater than 0.000 and less than 1,000 as long as the crystalline structure of the perovskite-type oxide is maintained. β in each chemical formula is greater than 0.000 and less than 1,000 as long as the crystalline structure of the perovskite-type oxide is maintained. For example, α may be 0.500 and β may be 0.500. γ in each chemical formula is from 0.050 to 0.400. δ in each chemical formula is from 0.000 to 1.000.In a case where y in each chemical formula is from 0.050 to 0.400, the piezoelectric thin film 3 is likely to contain at least one crystal selected from the group consisting of a tetragonal crystal and an orthorhombic crystal, the crystal is likely to have the above-described crystalline orientation, and the piezoelectric thin film 3 is likely to have excellent piezoelectric properties and ferroelectricity.A total value of the substance amounts of Bi and K in the metal oxide may be represented as [A] mol, a total value of the substance amounts of Ti, Mg, Fe, and the element M in the metal oxide may be represented as [B] mol, and [A] / [B] may be 1.000. [A] / [B] may be a value other than 1.000 as long as the metal oxide may have a perovskite structure. That is, [A] / [B] may be less than 1.000 or more than 1.000. ε in Chemical Formula 1 aand Chemical Formula 1 bis 0.000 or more. ε may be a value other than 0.000 as long as the metal oxide may have a perovskite structure. For example, ε may be more than 0.000 and 1.000 or less. ε may be calculated from the valence of each element at the A site and the element at the B site of the perovskite structure. The valence of the individual elements can be measured by X-ray photoelectron spectroscopy (XPS).Hereinafter, (Bi1-αKα)TiO 3 is referred to as BKT. Bi(Ti1-βMgβ)O 3 is referred to as BMT. BiFe1-γMγO 3 is referred to as BFMO. BiFeO 3 is referred to as BFO. A metal oxide whose composition is represented by the sum of BKT and BMT is referred to as BKT-BMT. A metal oxide having a composition represented by the sum of BKT, BMT and BFO is referred to as BKT-BMT-BFO. A metal oxide having a composition represented by Chemical Formula 1 above is referred to as xBKT-yBMT-zBMO. The crystal of each of BKT, BMT, BFMO, BFO, BKT-BMT, BKT-BMT-BFO, and xBKT-yBMT-zBMO has a perovskite structure.Each of bismuth gallate (BiGaO 3; BGO) and bismuth cobaltate (BiCoO 3; BCO) is perovskite-type oxides. c / a of the crystal (tetragonal crystal) of bismuth gallate and bismuth cobaltate is larger than c / a of the crystal (rhombohedral crystal) of BFO. In xBKT-yBMT-zBMO, c / a of the crystal of xBKT-yBMT-zBMO tends to be larger than c / a of conventional BKT-BMT-BFO because a part of BFO is replaced with one or both of BGO and BCO. As a result, the piezoelectric thin film 3 containing xBKT-yBMT-zBMO can have excellent piezoelectric properties and ferroelectricity.The crystal of BKT is a tetragonal crystal at normal temperature, and BKT is a ferroelectric material. The crystal of BMT is a rhombohedral crystal at normal temperature and BMT is a ferroelectric material. The crystal of BFO is a rhombohedral crystal at normal temperature, and BFO is a ferroelectric material. A thin film composed of BKT-BMT is a tetragonal crystal at normal temperature. c / a of the tetragonal crystal of BKT-BMT tends to be larger than c / a of BKT. The thin film consisting of BKT-BMT has excellent ferroelectricity as compared with a thin film consisting of BKT and a thin film consisting of BMT. A thin film consisting of xBKT-yBMT-zBMO tends to be at least one tetragonal crystal or an orthorhombic crystal at normal temperature. c / a of xBKT-yBMT-zBMO tends to be larger than c / a of BKT-BMT and BKT-BMT-BFO. The thin film consisting of xBKT-yBMT-zBMO has excellent ferroelectricity as compared with a thin film consisting of BKT-BMT or BKT-BMT-BFO. That is, the piezoelectric thin film 3 containing xBKT-yBMT-zBMO is likely to be a ferroelectric thin film. It is presumed that the ferroelectricity of the piezoelectric thin film 3 is due to the composition of xBKT-yBMT-zBMO having a morphotropic phase boundary (MPB). However, since the piezoelectric thin film 3 belongs to a tetragonal or orthorhombic crystal system, it is presumed that the ferroelectricity of the piezoelectric thin film 3 is not due solely to the MPB. Since the piezoelectric thin film 3 has ferroelectricity, the piezoelectric thin film 3 is likely to have a large d 33,f. In contrast to the piezoelectric thin film 3, the crystal contained in the bulk of xBKT-yBMT-zBMO is a pseudocubic crystal, and the bulk of xBKT-yBMT-zMo tends to be difficult to have the above-described crystalline orientation and ferroelectricity as compared with the piezoelectric thin film 3.The composition of xBKT-yBMT-zBMO may be represented based on a three-dimensional coordinate system. As shown in FIG. 4, the three-dimensional coordinate system is composed of an X axis, a Y axis, and a Z axis. Arbitrary coordinates in the coordinate system are represented by (X, Y, Z). The coordinates (x, y, z) in the coordinate system correspond to x, y, and z in the above Chemical Formula 1. a sum of x, y, and z in Chemical Formula 1 is 1, and all x, y, and z are positive real numbers. Therefore, the coordinates (x, y, z) are located within a triangle drawn by broken lines in a plane represented by X+Y+Z=1. That is, the coordinates (x, y, z) are located within a triangle whose vertices have the coordinates (1, 0, 0), (1, 1, 0), and (0, 0, 1). This triangle is a triangular coordinate system, and X+Y+Z is 1 in the triangular coordinate system. The triangular coordinate system is shown in FIG. 5. The triangular coordinate system includes coordinates A, B, C and D in addition to coordinates (x, y, z). that is, all coordinates (x, y, z), coordinates A, coordinates B, coordinates C, coordinates D, coordinates E and coordinates F are in the plane represented by X+Y+Z=1. The coordinates A are (0.250, 0.005, 0.700). The coordinates B are (0.450, 0.250, 0.300). The coordinates C are (0.200, 0.500, 0.300). The coordinates D are (0.005, 0.250, 0.700). The coordinates (x, y, z) indicating x, y, and z in Chemical Formula 1 may be within a square having vertices at the coordinates A, the coordinates B, the coordinates C, and the coordinates D. In a case where the coordinates (x, y, z) are within the square ABCD, the composition of xBKT-yBMT-zBMO is likely to have MPB, and the piezoelectric characteristics and the ferroelectricity of the piezoelectric thin film 3 are likely to be improved. In a case where x is y, the coordinates (x, y, z) are on a straight line passing through the coordinates (0.500, 0.500, 0.000) and the coordinates (0.000, 0.000, 1.000). In a case where x is y, the composition xBKT-yBMT-zBMO is likely to have MPB, and the piezoelectric properties and the ferroelectricity of the piezoelectric thin film 3 are likely to be improved.x may be from 0.050 to 0.450, or from 0.100 to 0.350, y may be from 0.050 to 0.500, or from 0.100 to 0.350, and z may be from 0.300 to 0.700. In a case where x, y, and z are in the above-described ranges and x+y+z is 1, the composition of xBKT-yBMT-zBMO is likely to have MPB, and the piezoelectric properties and the ferroelectricity of the piezoelectric thin film 3 are likely to be improved.For example, the thickness of the piezoelectric thin film 3 may be from 10 nm to 10 μm, from 0.3 μm to 10 μm, from 0.3 μm to 5 μm, from 0.5 μm to 5 μm, from 0.3 μm to 3 μm, or from 0.5 μm to 3 μm. The area of the piezoelectric thin film 3 may be, for example, from 1 μm 2 to 500 mm 2. The area of the crystalline substrate 1, the first intermediate layer 5, the first electrode layer 2, the second intermediate layer 6, and the second electrode layer 4 may be identical to or different from the area of the piezoelectric thin film 3.The composition of the piezoelectric thin film 3 can be analyzed by, for example, X-ray fluorescence spectroscopy (XRF method) or inductively coupled plasma emission spectroscopy (ICP). The crystalline structure and the crystalline orientation of the piezoelectric thin film 3 can be determined by an X-ray diffraction (XRD) method.The piezoelectric thin film 3 may be formed by the following method, for example.As a starting material for the piezoelectric thin film 3, a target having the same composition as that of the piezoelectric thin film 3 can be used. A method for manufacturing the target is as follows.As the starting materials, for example, powders of bismuth oxide (Bi 2 O 3), potassium carbonate (K 2 CO 3), titanium oxide (TiO 2), magnesium oxide (MgO), iron oxide (Fe 2 O 3) and an oxide of the element M can be used. The oxide of the element M may be at least one oxide selected from the group consisting of gallium oxide (Ga 2 O 3) and cobalt oxide (Co 2 O 3). As starting materials, instead of the above-described oxides, materials which become oxides by sintering, such as carbonates or oxalates, can also be used. These starting materials are sufficiently dried at 100° C. or more, and then each of the starting materials is weighed so that the substance amount (molar ratio) of Bi, K, Ti, Mg, Fe and the element M is within the range indicated in Chemical Formula 1, Chemical Formula 1 a, or Chemical Formula 1 bdescribed above. In the vapor deposition method described later, Bi and K are likely to be evaporated in the target compared with other elements. Therefore, the molar ratio of Bi in the target can be set to a value higher than the molar ratio of Bi in the piezoelectric thin film 3.The weighed starting materials are sufficiently mixed in an organic solvent or water. A mixing time may be from 5 to 20 hours. A mixing tool may be a ball mill. The raw materials obtained after mixing are sufficiently dried, and then the raw materials are molded by a pressing machine. The molded raw materials are calcined to obtain a calcined product. A calcination temperature may be from 750° C. to 900° C. A calcination time may be from 1 to 3 hours. The calcined product is pulverized in an organic solvent or water. A pulverization time may be from 5 to 30 hours. A pulverizing means may be a ball mill. After the calcined product is pulverized and dried, a powder of the calcined product is obtained by granulating the calcined product with addition of a binder solution. The powder of the calcined product is subjected to press molding to obtain a ingot-shaped compact.The binder in the compact evaporates by heating the ingot-shaped compact. A heating temperature may be from 400° C. to 800° C. A heating time may be from 2 to 4 hours. Subsequently, the compact is sintered to obtain a target. A sintering temperature may have a value of 800° C. to 1100° C. A sintering time may be from 2 hours to 4 hours. A temperature increase rate and a temperature decrease rate of the compact during the sintering process may be, for example, from 50° C. / hr to 300° C. / hr. An average grain size of the crystal grains of the metal oxide contained in the target may be, for example, from 1 μm to 20 μm.The piezoelectric thin film 3 may be formed by a vapor deposition method using the target described above. In the deposition method, the elements constituting the target are evaporated in a vacuum atmosphere. The vapor deposited elements are deposited on one of the surfaces of the second intermediate layer 6, the first electrode layer 2 or the crystalline substrate 1, so that the piezoelectric thin film 3 grows. The vapor deposition method may be, for example, a sputtering method, an electron beam vapor deposition method, a chemical vapor deposition method, or a pulsed laser vapor deposition method. Hereinafter, the pulsed laser deposition method is referred to as a PLD (pulsed-laser deposition) method. With these vapor deposition methods, it is possible to produce a piezoelectric thin film 3 that is dense on the atomic level, and segregation of elements in the piezoelectric thin film 3 is suppressed. The excitation source is different depending on the type of vapor deposition process. An excitation source for a sputtering process is an Ar plasma. An excitation source for an electron beam deposition process is an electron beam. An excitation source for a PLD method is laser light (e.g., an excimer laser). When these excitation sources are irradiated onto the target, the elements constituting the target evaporate.Among the above-described vapor deposition methods, the PLD method is relatively excellent in the following points. In the PLD method, the respective elements constituting a target can be immediately and uniformly converted into a plasma by a pulsed laser. Therefore, the piezoelectric thin film 3 having substantially or entirely the same composition as the target can be easily produced. Moreover, in the PLD method, the thickness of the piezoelectric thin film 3 can be easily controlled by changing the number of laser pulse shots.The piezoelectric thin film 3 may be an epitaxial film. That is, the piezoelectric thin film 3 may be formed by epitaxial growth. The piezoelectric thin film 3 having excellent crystalline orientation can be easily formed by epitaxial growth. When the piezoelectric thin film 3 is formed by the PLD method, the piezoelectric thin film 3 is likely to be formed by epitaxial growth.In the PLD method, the piezoelectric thin film 3 may be formed by heating the crystalline substrate 1 and the first electrode layer 2 in a vacuum chamber. A temperature (film forming temperature) of the crystalline substrate 1 and the first electrode layer 2 may be, for example, from 300° C. to 800° C., from 500° C. to 700° C., or from 500° C. to 600° C. As the film forming temperature increases, the cleanliness of the surface of the crystalline substrate 1 or the first electrode layer 2 is improved, and thus the crystallinity of the piezoelectric thin film 3 is increased, so that the orientation degree of the (001) plane of the piezoelectric thin film 3 is likely to increase. If the film forming temperature is too high, Bi or K is likely to be desorbed from the piezoelectric thin film 3, so that the composition of the piezoelectric thin film 3 is difficult to control.In the PLD method, an oxygen partial pressure in a vacuum chamber may be, for example, more than 10 mTorr and less than 400 mTorr, from 15 mTorr to 300 mTorr, or from 20 mTorr to 200 mTorr. In other words, the oxygen partial pressure in the vacuum chamber may be, for example, more than 1 Pa and less than 53 Pa, 2 Pa to 40 Pa, or 3 Pa to 30 Pa. When the oxygen partial pressure is maintained within the above range, Bi, K, Ti, Mg, Fe and the element M deposited on the crystalline substrate 1 are likely to be sufficiently oxidized. In a case where the oxygen partial pressure is excessively high, the growth rate of the piezoelectric thin film 3 is likely to decrease, and the orientation degree of the (001) plane in the piezoelectric thin film 3 is likely to decrease.Parameters other than those mentioned above controlled in the PLD method include the frequency of laser oscillation and the distance between a substrate and a target. By controlling these parameters, the crystalline structure and crystalline orientation of the piezoelectric thin film 3 can be easily controlled. For example, when the laser oscillation frequency is 10 Hz or less, the degree of orientation of the (001) plane of the piezoelectric thin film 3 is likely to increase.After the growth of the piezoelectric thin film 3, annealing (heating treatment) of the piezoelectric thin film 3 may be performed. A temperature (annealing temperature) of the piezoelectric thin film 3 in the annealing treatment may be, for example, from 300° C. to 1000° C., from 600° C. to 1000° C., or from 850° C. to 1000° C. The piezoelectric properties of the piezoelectric thin film 3 tend to be further improved by the annealing treatment of the piezoelectric thin film 3. The piezoelectric properties of the piezoelectric thin film 3 are likely to be improved by the annealing treatment, particularly at a temperature of 850° C. to 1000° C. However, the annealing treatment is not necessarily required.The crystalline substrate 1 may be, for example, a substrate made of a single crystal of Si or a substrate made of a single crystal of a compound semiconductor such as GaAs. The crystalline substrate 1 may be a substrate made of a single crystal of oxide such as MgO or a perovskite-type oxide (e.g., SrTiO 3). A thickness of the crystalline substrate 1 may be, for example, 10 μm to 1000 μm. When the crystalline substrate 1 is conductive, the crystalline substrate 1 functions as an electrode, so that the first electrode layer 2 is not required. The crystalline substrate 1 having conductivity may be, for example, a single crystal of SrTiO 3 doped with niobium (Nb). As the crystalline substrate 1, an SOI (Siliconon-Insulator) substrate may be used.The crystal orientation of the crystalline substrate 1 may be the same as a normal direction of a surface of the crystalline substrate 1. That is, the surface of the crystalline substrate 1 may be parallel to a lattice plane of the crystalline substrate 1. The crystalline substrate 1 may be a uniaxially oriented substrate. For example, a grating plane selected from the group consisting of a (100) plane, a (001) plane, a (110) plane, a (101) plane, and a (111) plane may be parallel to the surface of the crystalline substrate 1. When the (100) plane of the crystalline substrate 1 (e.g., Si) is parallel to the surface of the crystalline substrate 1, the (001) plane of the crystal in the piezoelectric thin film 3 is likely to be oriented in the normal direction dn of the surface of the piezoelectric thin film 3.As described above, the first intermediate layer 5 may be disposed between the crystalline substrate 1 and the first electrode layer 2. For example, the first intermediate layer 5 may include at least one selected from the group consisting of titanium (Ti), chromium (Cr), titanium oxide (TiO 2), silicon oxide (SiO 2) and zirconium oxide (ZrO 2). The first electrode layer 2 is likely to be in close contact with the crystalline substrate 1 with the first intermediate layer 5 interposed therebetween. The first intermediate layer 5 may be crystalline. A lattice plane of the first intermediate layer 5 may be oriented in the normal direction of the surface of the crystalline substrate 1. Both the lattice plane of the crystalline substrate 1 and the lattice plane of the first intermediate layer 5 may be oriented in the normal direction on the surface of the crystalline substrate 1. The method for forming the first intermediate layer 5 may be a sputtering method, a vacuum deposition method, a printing method, a spin-coat method, or a sol-gel method.The first intermediate layer 5 may include ZrO 2 and an oxide of a rare earth element. When the first intermediate layer 5 contains ZrO 2 and an oxide of a rare earth element, the first electrode layer 2 made of a platinum crystal is likely to be formed on a surface of the first intermediate layer 5, the (002) plane of the platinum crystal is likely to be oriented in the normal direction D N of the surface of the first electrode layer 2, and the (200) plane of the platinum crystal is likely to be oriented in the in-plane direction of the surface of the first electrode layer 2. The rare earth element may be at least one element selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The first intermediate layer 5 can consist of yttria-stabilized zirconia (ZrO 2 with addition of Y 2 O 3). When the first intermediate layer 5 is made of yttria-stabilized zirconia, the first electrode layer 2 made of a platinum crystal is likely to be formed on the surface of the first intermediate layer 5, the (002) plane of the platinum crystal is likely to be oriented in the normal direction D N of the surface of the first electrode layer 2, and the (200) plane of the platinum crystal is likely to be oriented in the in-plane direction of the surface of the first electrode layer 2. For the same reasons, the first intermediate layer 5 may include a first layer consisting of ZrO 2, and a second layer consisting of Y 2 O 3. The first layer may be directly deposited on the surface of the crystalline substrate 1, the second layer may be directly deposited on the surface of the first layer, and the first electrode layer 2 may be directly deposited on the surface of the second layer.The first electrode layer 2 may be made of, for example, at least one metal selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), gold (Au), ruthenium (Ru), iridium (Ir), molybdenum (Mo), titanium (Ti), tantalum (Ta), and nickel (Ni). The first electrode layer 2 may be made of, for example, a conductive metal oxide such as strontium ruthenium oxide (SrRuO 3), lanthanum nickel oxide (LaNiO 3) or lanthanum strontium cobalt oxide ((La,Sr)CoO 3). The first electrode layer 2 may be crystalline. A lattice plane of the first electrode layer 2 may be oriented in the normal direction of the surface of the crystalline substrate 1. The lattice plane of the first electrode layer 2 may be substantially or completely parallel to the surface of the crystalline substrate 1. Both the lattice plane of the crystalline substrate 1 and the lattice plane of the first electrode layer 2 may be oriented in the normal direction on the surface of the crystalline substrate 1. The lattice plane of the first electrode layer 2 may be substantially or entirely parallel to the lattice plane of the perovskite-type oxide oriented in the piezoelectric thin film 3. A thickness of the first electrode layer 2 may be, for example, 1 nm to 1.0 μm. The manufacturing method of the first electrode layer 2 may be a sputtering method, a vacuum deposition method, a printing method, a spin coat method, or a sol-gel method. In the case of a printing method, a spin-coat method, or a sol-gel method, the first electrode layer 2 may be subjected to a heat treatment (annealing) to improve the crystallinity of the first electrode layer 2.The first electrode layer 2 may include a platinum crystal. It is possible that the first electrode layer 2 is made of only a platinum crystal. The platinum crystal is a cubic crystal having a face-centered cubic lattice structure. The (002) plane of the platinum crystal may be oriented in the normal direction D N of the surface of the first electrode layer 2, and the (200) plane of the platinum crystal may be oriented in the in-plane direction of the surface of the first electrode layer 2. In other words, the (002) plane of the platinum crystal may be substantially or entirely parallel to the surface of the first electrode layer 2, and the (200) plane of the platinum crystal may be substantially or entirely perpendicular to the surface of the first electrode layer 2. In a case where the (002) plane and the (200) plane of the platinum crystal constituting the first electrode layer 2 have the above-described orientation, the piezoelectric thin film 3 is likely to epitaxially grow on the surface of the first electrode layer 2, and a lattice stress due to the lattice mismatch between the first electrode layer 2 and the piezoelectric thin film 3 is likely to act on the piezoelectric thin film 3. As a result, the piezoelectric thin film 3 is likely to contain at least one crystal selected from the group consisting of a tetragonal crystal and an orthorhombic crystal, and the (001) plane of the crystal is likely to be preferentially oriented in the normal direction dn of the surface of the piezoelectric thin film 3. As a result, the piezoelectric thin film element 10 is likely to have excellent piezoelectric properties and ferroelectricity.The second intermediate layer 6 may be disposed between the first electrode layer 2 and the piezoelectric thin film 3. The second intermediate layer 6 may contain, for example, at least one compound selected from the group consisting of SrRuO 3, LaNiO 3 and (La,Sr)CoO 3. The piezoelectric thin film 3 is likely to be in close contact with the first electrode layer 2 with the second intermediate layer 6 interposed therebetween. The second intermediate layer 6 may be crystalline. When the second intermediate layer 6 includes at least one of SrRuO 3 and LaNiO 3 the lattice voltage is likely to act on the piezoelectric thin film 3 due to the lattice mismatch between the second intermediate layer 6 and the piezoelectric thin film 3. The lattice stress may be a compressive stress in the plane of the surface of the piezoelectric thin film 3. As a result, the piezoelectric thin film 3 is likely to contain at least one crystal selected from the group consisting of a tetragonal crystal and an orthorhombic crystal, and the (001) plane of the crystal is likely to be preferentially oriented in the normal direction dn of the surface of the piezoelectric thin film 3. As a result, the piezoelectric thin film element 10 is likely to have excellent piezoelectric properties and ferroelectricity. A lattice plane of the second intermediate layer 6 may be oriented in the normal direction D N of the surface of the first electrode layer 2. Both the lattice plane of the crystalline substrate 1 and the lattice plane of the second intermediate layer 6 may be oriented in the normal direction D N of the surface of the first electrode layer 2. The method for forming the second intermediate layer 6 may be a sputtering method, a vacuum deposition method, a printing method, a spin-coat method, or a sol-gel method.The second electrode layer 4 may be made of, for example, at least one metal selected from the group consisting of Pt, Pd, Rh, Au, Ru, Ir, Mo, Ti, Ta, and Ni. The second electrode layer 4 may be made of, for example, at least one conductive metal oxide selected from the group consisting of LaNiO 3, SrRuO 3 and (La,Sr)CoO 3. The second electrode layer 4 may be crystalline. A lattice plane of the second electrode layer 4 may be oriented in the normal direction dn of the surface of the piezoelectric thin film 3. The lattice plane of the second electrode layer 4 may be substantially or completely parallel to the surface of the piezoelectric thin film 3. The lattice plane of the second electrode layer 4 may be substantially or entirely parallel to the (001) plane oriented in the piezoelectric thin film 3. A thickness of the second electrode layer 4 may be, for example, 1 nm to 1.0 μm. The second electrode layer 4 can be produced by sputtering, vacuum deposition, printing, spin-coat method or sol-gel. In the case of a printing method, a spin-coat method, or a sol-gel method, the second electrode layer 4 may be subjected to a heat treatment (annealing) to improve the crystallinity of the second electrode layer 4.A third intermediate layer may be disposed between the piezoelectric thin film 3 and the second electrode layer 4. The second electrode layer 4 is likely to be in close contact with the piezoelectric thin film 3 with the third intermediate layer interposed therebetween. Due to the lattice mismatch between the crystalline third intermediate layer and the piezoelectric thin film 3, the above-described lattice voltage is likely to act on the piezoelectric thin film 3. As a result, the piezoelectric thin film 3 is likely to contain at least one crystal selected from the group consisting of a tetragonal crystal and an orthorhombic crystal, and the (001) plane of the crystal is likely to be preferentially oriented in the normal direction dn of the surface of the piezoelectric thin film 3. As a result, the piezoelectric thin film element 10 is likely to have excellent piezoelectric properties and ferroelectricity. The composition, the crystalline structure, and the manufacturing method of the third intermediate layer may be the same as those of the second intermediate layer 6.The surface of the piezoelectric thin film element 10 may be coated at least partially or entirely with a protective film. For example, by coating the piezoelectric thin film element 10 with the protective film, the moisture resistance of the piezoelectric thin film element 10 is improved.Applications of the piezoelectric thin film element according to the present embodiment are various. For example, the piezoelectric thin film element may be a part or the whole of a device selected from the group consisting of a piezoelectric actuator, a piezoelectric sensor, a piezoelectric transducer, a piezoelectric microphone, a harvester, an oscillator, a resonator, an acoustic multilayer film, a pyroelectric element, and a filter. The piezoelectric actuator can be used, for example, in haptics. That is, the piezoelectric actuator can be used in various devices where feedback due to the feeling of skin (haptic sense) is required. The device that requires feedback due to the skin sensation may be, for example, a portable device, a touchpad, a display, or a game controller. The piezoelectric actuator can be used in, for example, a head assembly, a head stack assembly, or a hard disk drive. The piezoelectric actuator can be used in, for example, a print head or an ink jet printer. The piezoelectric actuator can be used in a piezoelectric switch, for example. The piezoelectric sensor or the piezoelectric transducer can be used in, for example, a gyroscope sensor, a pressure sensor, a pulse sensor, an ultrasonic sensor, an ultrasonic transducer, an infrared sensor, or a shock sensor. The ultrasonic transducer may be a piezoelectric micromachined ultrasonic transducer (PMUT). A product to which the piezoelectric micromachined ultrasonic transducer is applied may be a biometric sensor such as a fingerprint sensor and an ultrasonic sensor for vessel authentication, a medical or health sensor, or a Time of Flight (ToF) sensor. The filter may be, for example, a bulk acoustic wave (BAW) filter or a surface acoustic wave (SAW) filter. Each of the piezoelectric thin film elements described above may be a part or the whole of a microelectromechanical system (MEMS). Each of the piezoelectric thin film elements described above may be a portable device or a portable device.A piezoelectric transducer according to the present embodiment includes the above-described piezoelectric thin film or piezoelectric thin film element. FIG. 6 shows a schematic cross section of an ultrasonic transducer 10 aas an example of a piezoelectric transducer. The cross section of this piezoelectric transducer 10a is substantially or completely parallel to the normal direction dn of the surface of the piezoelectric thin film 3. the piezoelectric transducer 10a may include substrates 1a and 1b, the first electrode layer 2 provided on the substrates 1a and 1b, the piezoelectric thin film 3 deposited on the first electrode layer 2, and the second electrode layer 4 deposited on the piezoelectric thin film 3. Below the piezoelectric thin film 3 an acoustic cavity 1c may be provided. An ultrasonic signal is transmitted or received by displacement or vibration of the piezoelectric thin film 3. The first intermediate layer may be disposed between the substrates 1 aand 1 band the first electrode layer 2. The second intermediate layer may be disposed between the first electrode layer 2 and the piezoelectric thin film 3. The third intermediate layer may be disposed between the piezoelectric thin film 3 and the second electrode layer 4.It is to be understood that not all aspects, advantages, and features described herein are necessarily achieved by or included in a particular example. Having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and details.[Examples]Hereinafter, the present invention will be described in more detail by way of Examples; however, the present invention is not limited to these Examples.(Example 1)For the production of the piezoelectric thin film element of Example 1, a crystalline substrate consisting of a Si single crystal was used. A (100) plane of Si was parallel to the surface of the crystalline substrate. The crystalline substrate had a square shape of 20 mm×20 mm. A thickness of the crystalline substrate was 500 μm.A crystalline first intermediate layer consisting of ZrO 2 and Y 2 O 3, was formed on the entire surface of the crystalline substrate in a vacuum chamber. The first intermediate layer was formed by a sputtering method. A thickness of the first intermediate layer was 30 nm.A first electrode layer consisting of a Pt crystal was formed on the entire surface of the first intermediate layer in a vacuum chamber. The first electrode layer was formed by a sputtering method. A thickness of the first electrode layer was 200 nm. A temperature (film forming temperature) of the crystalline substrate was maintained at 500° C. in the formation of the first electrode layer.An X-ray diffraction (XRD) pattern of the first electrode layer was measured by out-of-plane measurement on the surface of the first electrode layer. Another XRD pattern of the first electrode layer was measured by in-plane measurement on the surface of the first electrode layer. For measurement of these XRD patterns, an X-ray diffraction apparatus (SmartLab) manufactured by Rigaku Corporation was used. The measurement conditions were set so that the intensity of each peak in the XRD patterns is at least three orders of magnitude above the background intensity. An X-ray diffraction peak of the (002) plane of the Pt crystal was detected by out-of-plane measurement. That is, the (002) plane of the Pt crystal was oriented in the normal direction of the surface of the first electrode layer. An X-ray diffraction peak of the (200) plane of the Pt crystal was detected by in-plane measurement. That is, the (200) plane of the Pt crystal was oriented in the in-plane direction of the surface of the first electrode layer.A piezoelectric thin film was formed on the entire surface of the first electrode layer in a vacuum chamber. The piezoelectric thin film was produced by a PLD method. A thickness of the piezoelectric thin film was 2000 nm. A temperature (film forming temperature) of the crystalline substrate in the formation of the piezoelectric thin film was maintained at 500°C. An oxygen partial pressure in the vacuum chamber in the formation of the piezoelectric thin film was maintained at 10 Pa. As a starting material for the piezoelectric thin film, a target (sintered body of raw material powders) was used. In the preparation of the target, the mixing ratio of raw material powders (bismuth oxide, potassium carbonate, titanium oxide, magnesium oxide, iron oxide and gallium oxide) was adjusted to correspond to the intended composition of the piezoelectric thin film. The intended composition of the piezoelectric thin film was represented by Chemical Formula 1A below. That is, the composition of the target was represented by Chemical Formula 1A below. A value of x, y, z, α, β, and γ in Chemical Formula 1A below was a value listed in Table 1 below. x(Bi1-αKα)TiO 3- yBi(Ti1-βMgβ)O 3- zBi(Fe1-γGaγ)O 3(1 A)The composition of the piezoelectric thin film was analyzed by X-ray fluorescence spectroscopy (XRF method). For the analysis, a PW2404 manufactured by Philips Japan, Ltd. was used. As a result of the analysis, the composition of the piezoelectric thin film of Example 1 was represented by Chemical Formula 1A above, and each of the values of x, y, z, α, β, and γ in Chemical Formula 1A above agreed with the value shown in Table 1 below. That is, the composition of the piezoelectric thin film was consistent with the composition of the target.An XRD pattern of the piezoelectric thin film was measured by out-of-plane measurement on the surface of the piezoelectric thin film. Another XRD pattern of the piezoelectric thin film was measured by in-plane measurement in the surface of the piezoelectric thin film. The measurement apparatus and the measurement conditions for the XRD patterns were the same as those described above.The XRD patterns of the piezoelectric thin film indicated that the piezoelectric thin film is composed of a perovskite-type oxide crystal.A lattice constant c of the crystal in the normal direction of the surface of the piezoelectric thin film was obtained by the out-of-plane measurement. The lattice constant c is represented as the distance of the lattice planes parallel to the surface of the piezoelectric thin film. Lattice constants a and b of the crystal in a direction parallel to the surface of the piezoelectric thin film were measured by the in-plane measurement. The lattice constants a and b are represented as the pitch of the lattice planes perpendicular to the surface of the piezoelectric thin film. a and b were substantially the same. Both a and b were smaller than c. That is, at least a part of the crystal contained in the piezoelectric thin film was a tetragonal crystal in which c / a is larger than 1.An X-ray diffraction peak of the (001) plane of the perovskite-type oxide crystal was detected by the out-of-plane measurement. Based on the XRD pattern, the orientation degree of the (001) plane of the crystal was calculated. As described above, the degree of orientation of the (001) plane is represented as 100×I(001) / ( I(001) + I(110) + I(111). The degree of orientation of the (001) plane in the normal direction dn of the surface of the piezoelectric thin film was 90% or more. That is, the (001) plane of the crystal was preferably oriented in the normal direction of the surface of the piezoelectric thin film. The lattice plane, which is preferably oriented in the normal direction dn of the surface of the piezoelectric thin film (a lattice plane having an orientation degree of 90% or more), is referred to as an "oriented plane" in each of the following tables.By the above-described method, a laminate composed of the crystalline substrate, the first intermediate layer stacked on the crystalline substrate, the first electrode layer stacked on the first intermediate layer, and the piezoelectric thin film stacked on the first electrode layer was produced. The following step was further carried out using the laminate.A second electrode layer consisting of Pt was formed on the entire surface of the piezoelectric thin film in a vacuum chamber. The second electrode layer was formed by a sputtering method. A temperature of the crystalline substrate was maintained at 500° C. in the formation of the second electrode layer. A thickness of the second electrode layer was 200 nm.Through the above-described steps, a laminate composed of the crystalline substrate, the first intermediate layer on the crystalline substrate, the first electrode layer on the first intermediate layer, the piezoelectric thin film on the first electrode layer, and the second electrode layer on the piezoelectric thin film was prepared. In the subsequent photolithography, the laminate structure was patterned on the crystalline substrate. After structuring, the laminate was cut by dicing.By the above-described steps, a piezoelectric thin film element in strip form of Example 1 was obtained. The piezoelectric thin film element consisted of the crystalline substrate, the first intermediate layer stacked on the crystalline substrate, the first electrode layer stacked on the first intermediate layer, the piezoelectric thin film stacked on the first electrode layer, and the second electrode layer stacked on the piezoelectric thin film. The area of the movable part of the piezoelectric thin film was 20 mm×1.0 mm.[Measurement of Piezoelectric Strain Constant d33,f]The piezoelectric strain constant d 33,f of the piezoelectric thin film was measured with the piezoelectric thin film element of Example 1. An apparatus including an atomic force microscope (AFM) and a system for evaluating the ferroelectric material in combination was used for measurement of d 33,f. The atomic force microscope was SPA-400 from Seiko Instruments, Inc. and the system for evaluating the ferroelectric material was FCE from TOYO Corporation. A frequency of the alternating electric field (AC voltage) in the measurement of d 33,f was 5 Hz. The maximum value of the voltage applied to the piezoelectric thin film was 20 V. A unit of d 33,f is pm / V. d 33,f of Example 1 is shown in Table 1 below.(Examples 2 to 18 and Comparative Examples 1 to 4)In the preparation of the target of Examples 2 to 18 and Comparative Examples 1 to 4, the mixing ratio of raw material powders (bismuth oxide, potassium carbonate, titanium oxide, magnesium oxide, iron oxide and gallium oxide) was adjusted to correspond to the desired composition of the piezoelectric thin film.As the starting material for the target of Comparative Example 1, no potassium carbonate was used.As the starting material for the target of Comparative Example 2, no magnesium oxide was used.As the starting material for the target of Comparative Example 3, gallium oxide was not used.As the starting material for the target of Comparative Example 4, no iron oxide was used.A piezoelectric thin film element of Examples 2 to 18 and Comparative Examples 1 to 4 was produced by the same method as in Example 1, except that the composition of the target used for forming the piezoelectric thin film was different.The XRD patterns of the first electrode layer of Examples 2 to 18 and Comparative Examples 1 to 4 were measured by the same method as in Example 1. In all the cases of Examples 2 to 18 and Comparative Examples 1 to 4, the (002) plane of the Pt crystal constituting the first electrode layer was oriented in the normal direction of the surface of the first electrode layer, and the (200) plane of the Pt crystal was oriented in the in-plane direction of the surface of the first electrode layer.The composition of the piezoelectric thin film in Examples 2 to 18 and Comparative Examples 1 to 4 was analyzed by the same method as in Example 1. In all the cases of Examples 2 to 18 and Comparative Examples 1 to 4, the composition of the piezoelectric thin film was consistent with the composition (Chemical Formula 1A above) of the target. In each of Examples 2 to 18 and Comparative Examples 1 to 4, a value of each of the x, y, z, α, β, γ, and δ in Chemical Formula 1A was a value shown in Table 1 below. x, y, and z of each of Examples 1 to 14 are shown as coordinates (x, y, z) in FIG. 5 (triangular coordinate system).Coordinates A in FIG. 5 correspond to Example 1.The coordinates B in FIG. 5 correspond to Example 2.The coordinates C in FIG. 5 correspond to Example 3.The coordinates D in FIG. 5 correspond to Example 4.The coordinates E in FIG. 5 correspond to the example 5.The coordinates F in FIG. 5 correspond to Example 6.The coordinates G in FIG. 5 correspond to Example 7.The coordinates H in FIG. 5 correspond to Example 8.Coordinates I in FIG. 5 correspond to Example 9.The coordinates J in FIG. 5 correspond to the example 10.The coordinates K in FIG. 5 correspond to the example 11.The coordinates L in FIG. 5 correspond to the example 12.The coordinates M in FIG. 5 correspond to the example 13.The coordinates O in FIG. 5 correspond to the example 14.The XRD patterns of the piezoelectric thin film of Examples 2 to 18 and Comparative Examples 1 to 4 were measured by the same method as in Example 1. Each of the XRD patterns of Examples 2 to 18 and Comparative Examples 1 to 4 shows that the piezoelectric thin film is composed of a perovskite-type oxide crystal. In all the cases of Examples 2 to 18 and Comparative Examples 1 to 4, at least a part of the crystal contained in the piezoelectric thin film was a tetragonal crystal. In all the cases of Examples 2 to 18 and Comparative Examples 1 to 4, the (001) plane of the crystal was preferably oriented in the normal direction of the surface of the piezoelectric thin film.The piezoelectric strain constant d 33,f of the piezoelectric thin film of Examples 2 to 18 and Comparative Examples 1 to 4 was measured by the same method as in Example 1. d 33,f of Examples 2 to 18 and Comparative Examples 1 to 4 is shown in Table 1 below.(Comparative Example 5)The target of Comparative Example 5 contained no bismuth. The target of Comparative Example 5 had the composition shown in Chemical Formula 5 below. Each numerical value in Chemical Formula 5 below represents a molar ratio. A thin film and a thin film element of Comparative Example 5 were prepared by the same method as in Example 1 except that the composition of the target used for forming the thin film was different.Analysis and measurement of the thin film and the thin film element of Comparative Example 5 were carried out by the same method as in Example 1. Also in the case of Comparative Example 5, the (002) plane of the Pt crystal constituting the first electrode layer was oriented in the normal direction of the surface of the first electrode layer, and the (200) plane of the Pt crystal was oriented in the plane of the surface of the first electrode layer. The composition of the thin film of Comparative Example 5 was the same as the composition of the target of Comparative Example 5. The thin film of Comparative Example 5 was not a crystal having an oriented lattice plane and had no piezoelectric properties. 0.20MgTiO 3-0.10 K 2 O-0 '20TiO 2-0,50( Fe 0,9 Ga 0,1)2 O 3(5) (Comparative Examples 6 to 8)The oxygen partial pressure in the vacuum chamber was maintained at 1 Pa in the production of the piezoelectric thin film of Comparative Example 6.The oxygen partial pressure in the vacuum chamber was maintained at 20 Pa in the production of the piezoelectric thin film of Comparative Example 7.The oxygen partial pressure in the vacuum chamber was maintained at 0.1 Pa in the production of the piezoelectric thin film of Comparative Example 8.A piezoelectric thin film element of each of Comparative Examples 6 to 8 was produced by the same method as in Example 9 except for the oxygen partial pressure in the formation of the piezoelectric thin film.The XRD patterns of the first electrode layer of each of Comparative Examples 6 to 8 were measured by the same method as in Example 1. In all the cases of Comparative Examples 6 to 8, the (002) plane of the Pt crystal constituting the first electrode layer was oriented in the normal direction of the surface of the first electrode layer, and the (200) plane of the Pt crystal was oriented in the in-plane direction of the surface of the first electrode layer.The composition of the piezoelectric thin film of each of Comparative Examples 6 to 8 was analyzed by the same method as in Example 1. In all the cases of Comparative Examples 6 to 8, the composition of the piezoelectric thin film was consistent with the composition of the target. That is, the composition of the piezoelectric thin film in each of Comparative Examples 6 to 8 was the same as the composition of the piezoelectric thin film of Example 9.The XRD patterns of the piezoelectric thin films of Comparative Examples 6 to 8 were measured by the same method as in Example 1.Each of the XRD patterns of Comparative Examples 6 to 8 indicates that the piezoelectric thin film is composed of a perovskite-type oxide crystal.In all the cases of Comparative Examples 6 to 8, at least a part of the crystal contained in the piezoelectric thin film was a tetragonal crystal.In Comparative Example 6, the (110) plane of the crystal in the piezoelectric thin film was preferably oriented in the normal direction of the surface of the piezoelectric thin film.In Comparative Example 7, the (111) plane of the crystal in the piezoelectric thin film was preferably oriented in the normal direction of the surface of the piezoelectric thin film.In the case of Comparative Example 8, a certain lattice plane of the crystal in the piezoelectric thin film was not oriented in the normal direction of the surface of the piezoelectric thin film. That is, in the case of Comparative Example 8, the degree of orientation of an arbitrary lattice plane was less than 50%.The piezoelectric strain constant d 33,f of the piezoelectric thin film of each of Comparative Examples 6 to 8 was measured by the same method as in Example 1. d 33,f of each of Comparative Examples 6 to 8 is shown in Table 2 below. (Examples 19 and 20)In Examples 19 and 20, the second intermediate layer was directly formed on the entire surface of the first electrode layer, and the piezoelectric thin film was directly formed on the entire surface of the second intermediate layer.The second interlayer of Example 19 was crystalline SrRuO 3. A thickness of the second intermediate layer of Example 19 was 50 nm.The second interlayer of Example 20 was crystalline LaNiO 3. A thickness of the second intermediate layer of Example 20 was 20 nm."SRO" in Table 3 below means SrRuO 3. "LNO" in Table 3 below means LaNiO 3.A piezoelectric thin film element of Examples 19 and 20 was produced by the same method as in Example 9 except that the second intermediate layer was formed.XRD patterns of the first electrode layer of Examples 19 and 20 were measured by the same method as in Example 1. In all the cases of Examples 19 and 20, the (002) plane of the Pt crystal constituting the first electrode layer was oriented in the normal direction of the surface of the first electrode layer, and the (200) plane of the Pt crystal was oriented in the in-plane direction of the surface of the first electrode layer.The composition of the piezoelectric thin film of Examples 19 and 20 was analyzed by the same method as in Example 1. In all the cases of Examples 19 and 20, the composition of the piezoelectric thin film was consistent with the composition of the target. That is, the composition of the piezoelectric thin film of each of Examples 19 and 20 was the same as the composition of the piezoelectric thin film of Example 9.XRD patterns of the piezoelectric thin films of Examples 19 and 20 were measured by the same method as in Example 1.Each of the XRD patterns of Examples 19 and 20 indicates that the piezoelectric thin film is composed of a perovskite-type oxide crystal.In all the cases of Examples 19 and 20, at least a part of the crystal contained in the piezoelectric thin film was a tetragonal crystal.In all the cases of Examples 19 and 20, the (001) plane of the crystal was preferably oriented in the normal direction of the surface of the piezoelectric thin film.The piezoelectric strain constant d 33,f of the piezoelectric thin film of Examples 19 and 20 was measured by the same method as in Example 1. d 33,f of Examples 19 and 20 is shown in Table 3 below. (Example 21)In the production of the piezoelectric thin film element of Example 21, the first intermediate layer was not formed. In the production of the piezoelectric thin film element of Example 21, the first electrode layer consisting of crystalline SrRuO 3, was directly formed on the entire surface of the crystalline substrate. A thickness of the first electrode layer of Example 21 was 200 nm. A piezoelectric thin film element of Example 21 was prepared by the same method as in Example 9 except for these points.The XRD patterns of the first electrode layer of Example 21 were measured by the same method as in Example 1. The lattice plane of the first electrode layer of Example 21 was not oriented in the in-plane direction of the surface of the first electrode layer. That is, in the case of Example 21, an in-plane direction orientation of the crystal of the first electrode layer was not present.The composition of the piezoelectric thin film of Example 21 was analyzed by the same method as in Example 1. The composition of the piezoelectric thin film of Example 21 was consistent with the composition of the target. That is, the composition of the piezoelectric thin film of Example 21 was the same as the composition of the piezoelectric thin film of Example 9.The XRD patterns of the piezoelectric thin film of Example 21 were measured by the same method as in Example 1.The XRD patterns of Example 21 showed that the piezoelectric thin film is composed of a perovskite-type oxide crystal.At least a part of the crystal contained in the piezoelectric thin film of Example 21 was a tetragonal crystal.In the case of Example 21, the (001) plane of the perovskite-type crystal was preferably oriented in the normal direction of the surface of the piezoelectric thin film.The piezoelectric strain constant d 33,f of the piezoelectric thin film of Example 21 was measured by the same method as in Example 1. d 33,f of Example 21 is shown in Table 4 below.

[0110] (Examples 22 and 23)In the preparation of the target from Example 22, cobalt oxide was also used as starting material in addition to gallium oxide.In the preparation of the target of Example 23, cobalt oxide was used as the starting material instead of gallium oxide. That is, gallium oxide was not used in the preparation of the target of Example 23.The composition of the target of Examples 22 and 23 was represented by Chemical Formula 1B below. In each of Examples 22 and 23, a value of x, y, z, γ, and δ in Chemical Formula 1B below was a value listed in Table 5 below. x(Bi 0,5 K 0,3) TiO 3- yBi(Ti 0,3 Mg 0,5) O 3- ZBi(Fe1-γ(Ga1-δCoδ)γ)O 3(1 B)A piezoelectric thin film element of Examples 22 and 23 was produced by the same method as in Example 1 except that the composition of the target used for forming the piezoelectric thin film was different.XRD patterns of the first electrode layer of Examples 22 and 23 were measured by the same method as in Example 1. In all the cases of Examples 22 and 23, the (002) plane of the Pt crystal constituting the first electrode layer was oriented in the normal direction of the surface of the first electrode layer, and the (200) plane of the Pt crystal was oriented in the in-plane direction of the surface of the first electrode layer.The composition of the piezoelectric thin film in Examples 22 and 23 was analyzed by the same method as in Example 1. In all the cases of Examples 22 and 23, the composition of the piezoelectric thin film was consistent with the composition of the target. The composition of the piezoelectric thin film in each of Examples 22 and 23 was the same as the composition of the piezoelectric thin film of Example 9 except for Ga1-δCoδin Chemical Formula 1B above.XRD patterns of the piezoelectric thin films of Examples 22 and 23 were measured by the same method as in Example 1.Each of the XRD patterns of Examples 22 and 23 indicates that the piezoelectric thin film is composed of a perovskite-type oxide crystal.In all the cases of Examples 22 and 23, at least a part of the crystal contained in the piezoelectric thin film was a tetragonal crystal.In all the cases of Examples 22 and 23, the (001) plane of the crystal was preferably oriented in the normal direction of the surface of the piezoelectric thin film.The piezoelectric strain constant d 33,f of the piezoelectric thin film of Examples 22 and 23 was measured by the same method as in Example 1. d 33,f of Examples 22 and 23 is shown in Table 5 below.

[0116] [Industrial Applicability]The piezoelectric thin film element according to an aspect of the present invention can be used in, for example, a piezoelectric transducer, a piezoelectric actuator, and a piezoelectric sensor.

[0117] [List of Reference Numerals]10: A piezoelectric thin film element, 10 a: a piezoelectric transducer (ultrasonic transducer), 1: a crystalline substrate, 2: a first electrode layer, 3: a piezoelectric thin film, 4: a second electrode layer, 5: a first intermediate layer, 6: a second intermediate layer, D N: a normal direction of the surface of the first electrode layer, dn: a normal direction of the surface of the piezoelectric thin film, uc: a unit cell of the perovskite-type oxide crystal.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 2023-124586

[0001] Cited Non-Patent LiteratureJapanese Journal of Applied Physics, Vol. 45, No. 2A, 2006, pp. 855-859

[0005]

Claims

A piezoelectric thin film comprising a metal oxide having a perovskite structure, wherein the metal oxide contains bismuth, potassium, titanium, magnesium, iron, and an element M, the element M is at least one element selected from the group consisting of gallium and cobalt, at least a part of the metal oxide is at least one crystal selected from the group consisting of a tetragonal crystal and an orthorhombic crystal, and a (001) plane of the crystal is oriented in a normal direction of a surface of the piezoelectric thin film.The piezoelectric thin film according to claim 1, wherein the metal oxide is represented by Chemical Formula 1 below, x, y, and z in Chemical Formula 1 below are each a positive real number, x + y + z is 1, α in Chemical Formula 1 below is greater than 0 and less than 1, β in Chemical Formula 1 below is greater than 0 and less than 1, γ in Chemical Formula 1 below is from 0.05 to 0.40, M in Chemical Formula 1 below is represented by Ga1-δCoδ, and δ is from 0 to 1, x(Bi1-αKα)TiO 3- yBi(Ti1-βMgβ)O 3- zBi(Fe1-γMγ)O 3(1).The piezoelectric thin film according to claim 2, wherein a three-dimensional coordinate system is composed of an X-axis, a Y-axis and a Z-axis, arbitrary coordinates in the coordinate system are represented by (X, Y, Z), coordinates (x, y, z) in the coordinate system in the above Chemical Formula 1 correspond to x, y and z, coordinates A in the coordinate system (0.250, 0.005, 0.700), coordinates B in the coordinate system (0.450, 0.250, 0.300), coordinates C in the coordinate system (0.200, 0.500, 0.300), coordinates D in the coordinate system (0.005, 0.250, 0.700), and the coordinates (x, y, z) in a quadrangle having vertices at the coordinates A, the coordinates B, are, the coordinates C and the coordinates D are positioned.The piezoelectric thin film according to claim 1, wherein the piezoelectric thin film is an epitaxial film.The piezoelectric thin film according to claim 1, wherein the piezoelectric thin film is a ferroelectric thin film.A piezoelectric thin film element comprising the piezoelectric thin film according to claim 1.The piezoelectric thin film element according to claim 6, comprising: a crystalline substrate; and the piezoelectric thin film directly or indirectly deposited on the crystalline substrate.The piezoelectric thin film element according to claim 6, comprising: a crystalline substrate; an electrode layer directly or indirectly deposited on the crystalline substrate; and the piezoelectric thin film directly or indirectly deposited on the electrode layer.The piezoelectric thin film element according to claim 6, comprising: an electrode layer; and the piezoelectric thin film directly or indirectly applied to the electrode layer.The piezoelectric thin film element according to claim 8, further comprising at least one intermediate layer, wherein the intermediate layer is disposed between the crystalline substrate and the electrode layer.The piezoelectric thin film element according to claim 8, further comprising at least one intermediate layer, wherein the intermediate layer is disposed between the electrode layer and the piezoelectric thin film.The piezoelectric thin film element according to claim 9, further comprising at least one intermediate layer, wherein the intermediate layer is disposed between the electrode layer and the piezoelectric thin film.The piezoelectric thin film element according to claim 8, wherein the electrode layer contains a platinum crystal, a (002) plane of the platinum crystal is oriented in a normal direction of a surface of the electrode layer, and a (200) plane of the platinum crystal is oriented in a direction within the plane of the surface of the electrode layer.The piezoelectric thin film element according to claim 9, wherein the electrode layer contains a platinum crystal, a (002) plane of the platinum crystal is oriented in a normal direction of a surface of the electrode layer, and a (200) plane of the platinum crystal is oriented in a direction within the plane of the surface of the electrode layer.A piezoelectric transducer comprising the piezoelectric thin film according to any one of claims 1 to 5.A piezoelectric transducer comprising the piezoelectric thin film element according to any one of claims 6 to 14.

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