Piezoelectric thin film, piezoelectric thin film element, and piezoelectric transducer

Abstract

The piezoelectric thin film of the present disclosure includes a metal oxide having a perovskite structure. The metal oxide contains bismuth, potassium, titanium, magnesium, iron, and an element M. Element M is at least one element selected from gallium and cobalt. At least a portion of the metal oxide is at least one crystal selected from tetragonal crystals and orthorhombic crystals. The (001) plane of the crystal is oriented in the normal direction of the surface of the piezoelectric thin film.

Description

[0001] This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2023-124586 filed in Japan on Jul. 31, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present disclosure relates to a piezoelectric film, a piezoelectric film element, and a piezoelectric transducer. Background Art

[0003] Piezoelectric bodies are processed into various piezoelectric elements according to various purposes. For example, piezoelectric actuators convert voltage into force by applying voltage to the piezoelectric body and causing the piezoelectric body to deform due to the inverse piezoelectric effect. For example, piezoelectric sensors convert force into voltage by applying pressure to the piezoelectric body and causing the piezoelectric body to deform due to the piezoelectric effect. These piezoelectric elements are mounted on various electronic devices. In recent years, in the market, due to the requirements for miniaturization and improved performance of electronic devices, piezoelectric elements (piezoelectric thin film elements) using piezoelectric films have been widely studied. However, the thinner the piezoelectric body, the more difficult it is to obtain the piezoelectric effect and the inverse piezoelectric effect. Therefore, it is expected to develop a piezoelectric body with excellent piezoelectric properties in a thin film state.

[0004] At present, lead zirconate titanate (so-called PZT), which is a perovskite-type ferroelectric, is often used as a piezoelectric. However, since PZT contains lead that is harmful to the human body and the environment, it is expected that a lead-free piezoelectric will be developed as a substitute for PZT. For example, in the following non-patent document 1, BaTiO 3 BaTiO 3 This material has relatively excellent piezoelectric properties among lead-free piezoelectric bodies, and is particularly expected to be used in piezoelectric thin-film elements.

[0005] <Non-Patent Document 1>

[0006] Yiping GUO et al., "Highly (100) oriented BaTiO prepared by one-step chemical solution deposition 3 Thickness 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. 855-859. Summary of the invention

[0007] An object of one aspect of the present invention is to provide a piezoelectric film having excellent piezoelectric characteristics, a piezoelectric thin-film element including the piezoelectric film, and a piezoelectric transducer including the piezoelectric film or the piezoelectric thin-film element.

[0008] For example, one aspect of the present invention relates to the piezoelectric film described in any one of the following [1] to [5], the piezoelectric film element described in any one of the following [6] to

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

[15] and

[16] .

[0009] [1] A piezoelectric film comprising a metal oxide having a perovskite structure,

[0010] The metal oxides include bismuth, potassium, titanium, magnesium, iron, and element M.

[0011] The element M is at least one element selected from gallium and cobalt,

[0012] At least a portion of the metal oxide is at least one crystal selected from tetragonal crystal and orthorhombic crystal.

[0013] The (001) plane of the crystal is oriented in the normal direction of the surface of the piezoelectric film.

[0014] [2] The piezoelectric film according to [1], wherein

[0015] The metal oxide is represented by the following chemical formula 1:

[0016] In the following chemical formula 1, x, y and z are positive real numbers.

[0017] x+y+z=1,

[0018] In the following chemical formula 1, α is greater than 0 and less than 1.

[0019] In the following chemical formula 1, β is greater than 0 and less than 1.

[0020] In the following chemical formula 1, γ is 0.05 or more and 0.40 or less,

[0021] In the following chemical formula 1, M represents Ga 1－δ Co δ ,

[0022] δ is greater than 0 and less than 1,

[0023] x(Bi 1－α K α )TiO 3 -yBi(Ti1－β Mg β ) 3 -zBi(Fe 1－γ M γ ) 3 (1).

[0024] [3] The piezoelectric film according to [2], wherein

[0025] The three-dimensional coordinate system consists of the X-axis, Y-axis, and Z-axis.

[0026] Any coordinate in the coordinate system is represented by (X, Y, Z).

[0027] The coordinates (x, y, z) in the coordinate system represent x, y, and z in Chemical Formula 1.

[0028] The coordinate A in the coordinate system is (0.250, 0.005, 0.700),

[0029] The coordinate B in the coordinate system is (0.450, 0.250, 0.300),

[0030] The coordinate C in the coordinate system is (0.200, 0.500, 0.300),

[0031] The coordinate D in the coordinate system is (0.005, 0.250, 0.700)

[0032] The coordinate (x, y, z) is inside a quadrilateral whose vertices are coordinate A, coordinate B, coordinate C, and coordinate D.

[0033] [4] The piezoelectric film according to any one of [1] to [3], wherein the piezoelectric film is an epitaxial film.

[0034] [5] The piezoelectric film according to any one of [1] to [4], wherein the piezoelectric film is a ferroelectric film.

[0035] [6] A piezoelectric thin-film element comprising the piezoelectric thin film according to any one of [1] to [5].

[0036] [7] The piezoelectric thin film element according to [6], comprising:

[0037] Crystalline substrate, and

[0038] A piezoelectric film that is directly or indirectly overlapped with a crystalline substrate.

[0039] [8] The piezoelectric thin film element according to [6], comprising:

[0040] Crystalline substrate,

[0041] An electrode layer directly or indirectly overlapping the crystalline substrate, and

[0042] A piezoelectric film that overlaps directly or indirectly with an electrode layer.

[0043] [9] The piezoelectric thin film element according to [6], comprising:

[0044] The electrode layer and

[0045] A piezoelectric film that overlaps directly or indirectly with an electrode layer.

[0046]

[10] The piezoelectric thin film element according to [8], wherein

[0047] further comprising at least one intermediate layer (first intermediate layer),

[0048] The intermediate layer (first intermediate layer) is disposed between the crystalline substrate and the electrode layer.

[0049]

[11] The piezoelectric thin film element according to [8], wherein

[0050] further comprising at least one intermediate layer (second intermediate layer),

[0051] The intermediate layer (second intermediate layer) is disposed between the electrode layer and the piezoelectric film.

[0052]

[12] The piezoelectric thin film element according to [9], wherein:

[0053] further comprising at least one intermediate layer (second intermediate layer),

[0054] The intermediate layer (second intermediate layer) is disposed between the electrode layer and the piezoelectric film.

[0055]

[13] The piezoelectric thin film element according to [8] or

[11] , wherein

[0056] The electrode layer contains platinum crystals,

[0057] The (002) plane of the platinum crystal is oriented in the normal direction of the surface of the electrode layer.

[0058] The (200) plane of the platinum crystal is oriented in the in-plane direction of the surface of the electrode layer.

[0059]

[14] The piezoelectric thin film element according to [9] or

[12] , wherein:

[0060] The electrode layer contains platinum crystals,

[0061] The (002) plane of the platinum crystal is oriented in the normal direction of the surface of the electrode layer.

[0062] The (200) plane of the platinum crystal is oriented in the in-plane direction of the surface of the electrode layer.

[0063]

[15] A piezoelectric transducer comprising the piezoelectric film according to any one of [1] to [5].

[0064]

[16] A piezoelectric transducer comprising the piezoelectric thin film element according to any one of [6] to

[14] .

[0065] According to one aspect of the present invention, it is possible to provide a piezoelectric film having excellent piezoelectric characteristics, a piezoelectric film element including the piezoelectric film, and a piezoelectric transducer including the piezoelectric film or the piezoelectric film element. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1A is a schematic cross-sectional view of a piezoelectric thin film element according to a specific example of the present invention, Figure 1B yes Figure 1A The three-dimensional exploded view of the piezoelectric film element shown in Figure 1B The substrate, the first intermediate layer, the second intermediate layer and the second electrode layer are omitted.

[0067] Figure 2 It is a three-dimensional diagram of a crystal (unit cell) of a metal oxide having a perovskite structure, and shows the arrangement of each element in the perovskite structure.

[0068] Figure 3 It is a three-dimensional diagram of a crystal (unit cell) of a metal oxide having a perovskite structure, showing the crystal lattice planes and crystal orientation.

[0069] Figure 4 It is a three-dimensional coordinate system used to represent the composition of the piezoelectric film.

[0070] Figure 5 is with Figure 4 The triangle shown is equivalent to the triangular coordinate system.

[0071] Figure 6 It is a schematic cross-sectional view of a piezoelectric thin film element (ultrasonic transducer) according to another specific example of the present invention. DETAILED DESCRIPTION

[0072] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. In the following description, with reference to the accompanying drawings, the same reference numerals are used for the same components or similar components having the same functions, and repeated descriptions are omitted. Figure 1A , Figure 1B and Figure 6 The X-axis, Y-axis, and Z-axis shown in the figure are three mutually orthogonal coordinate axes. Figure 1A , Figure 1B and Figure 6 is common, but, Figure 1A , Figure 1B and Figure 6 The coordinate system shown in Figure 4 and Figure 5 The coordinate system shown in is completely irrelevant.

[0073] (Piezoelectric film element)

[0074] The piezoelectric thin film element of this embodiment includes at least a piezoelectric thin film. Figure 1A As shown, the piezoelectric thin film element 10 of the present embodiment may include: a crystalline substrate 1, a first electrode layer 2 (lower electrode layer) directly or indirectly overlapping the crystalline substrate 1, a piezoelectric thin film 3 directly or indirectly overlapping the first electrode layer 2, and a second electrode layer 4 (upper electrode layer) directly or indirectly overlapping the piezoelectric thin film 3. The piezoelectric thin film element 10 may also 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 arranged between the crystalline substrate 1 and the first electrode layer 2, and the first electrode layer 2 may directly overlap with the 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 arranged between the first electrode layer 2 and the piezoelectric thin film 3, and the piezoelectric thin film 3 may directly overlap with the surface of the second intermediate layer 6. The 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 Figure 1B As shown, the normal direction dn of the surface of the piezoelectric film 3 can be aligned with the normal direction D N Approximately parallel or completely parallel. That is, the surface of the piezoelectric film 3 may be approximately parallel or completely parallel to the surface of the first electrode layer 2. The normal direction dn of the surface of the piezoelectric film 3 is the polarization direction of the piezoelectric film 3. The normal direction dn of the surface of the piezoelectric film 3 may be alternatively referred to as the thickness direction of the piezoelectric film 3.

[0075] A modification of the piezoelectric thin film element 10 may not include the crystalline substrate 1. For example, after forming the first electrode layer 2, the piezoelectric thin film 3, and the second electrode layer 4, the crystalline substrate 1 may be removed. In the case where the crystalline substrate 1 functions as an electrode, the crystalline substrate 1 may be the first electrode layer 2. That is, in the case where the crystalline substrate 1 functions as an electrode, a modification of the piezoelectric thin film element 10 may include the crystalline substrate 1 and the piezoelectric thin film 3 overlapping the crystalline substrate 1. In the case where the crystalline substrate 1 functions as an electrode, the piezoelectric thin film 3 may directly overlap the crystalline substrate 1. In the case where the crystalline substrate 1 functions as an electrode, the piezoelectric thin film 3 may also overlap the crystalline substrate 1 via at least one of the first intermediate layer 5 and the second intermediate layer 6.

[0076] The piezoelectric film 3 includes a metal oxide having a perovskite structure. The metal oxide includes bismuth (Bi), potassium (K), titanium (Ti), magnesium (Mg), iron (Fe), and element M. Element M is at least one element selected from gallium (Ga) and cobalt (Co). The metal oxide having the above composition easily forms at least one crystal selected from tetragonal and orthorhombic, and the (001) plane of the crystal easily orients in the normal direction of the surface of the piezoelectric film. As a result, the piezoelectric film 3 can have excellent piezoelectric characteristics (large piezoelectric strain constant d 33,f ) and ferroelectricity.

[0077] The metal oxide may consist only of Bi, K, Ti, Mg, Fe, element M, and oxygen (O). In addition to Bi, K, Ti, Mg, Fe, element M, and O, the metal oxide may also contain other elements. The metal oxide may also contain at least one element selected from 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 contain Pb.

[0078] Metal oxide is the main component of the piezoelectric film 3. The ratio of all elements constituting the metal oxide in the piezoelectric film 3 can be more than 99 mol% and less than 100 mol%. The piezoelectric film 3 can be composed only of metal oxide. As long as the piezoelectric properties of the piezoelectric film 3 are not impaired, the piezoelectric film 3 may contain other elements in addition to Bi, K, Ti, Mg, Fe, element M, and O. For example, the piezoelectric film 3 may also contain at least one element selected from La, Y, Na, Li, Zr, Ni, Zn, Mn, and Pb. However, the piezoelectric film 3 may not contain Pb.

[0079] Hereinafter, the above-mentioned metal oxide having a perovskite structure is expressed as a “perovskite-type oxide”. Figure 2 The unit cell of the crystal of the perovskite oxide is shown. The element located at the A site of the unit cell uc is Bi or K. The element located at the B site of the unit cell uc is Ti, Mg, Fe or the element M. Figure 2 The unit cell uc shown is Figure 3 The unit cell uc shown is the same. However, in Figure 3In order to indicate the lattice plane, the B site and oxygen (O) in the unit cell uc are omitted. The lattice translation vector a (i.e., the a-axis) in the unit cell uc is oriented in the

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

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

[001] direction. The lattice translation vector a, the lattice translation vector b, and the lattice translation vector c are perpendicular to each other. The length a of the lattice translation vector a is the spacing a (lattice constant a) of the (100) plane of the perovskite oxide. The length b of the lattice translation vector b is the spacing b (lattice constant b) of the (010) plane of the perovskite oxide. The length c of the lattice translation vector c is the spacing c (lattice constant c) of the (001) plane of the perovskite oxide. The piezoelectric film 3 may be composed of a single crystal of the perovskite oxide. The piezoelectric film 3 may also be composed of a polycrystal of the perovskite oxide.

[0080] At room temperature or a temperature below the Curie temperature of the perovskite oxide, a part or all of the perovskite oxide is at least one crystal selected from tetragonal crystal and orthorhombic crystal. Due to the anisotropy on any c-axis of the tetragonal crystal and the orthorhombic crystal, the piezoelectric 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 can be greater 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 can be respectively greater than the lattice constant a and the lattice constant b. The perovskite oxide can be composed only of tetragonal crystals. The perovskite oxide can also be composed only of orthorhombic crystals. The perovskite oxide can be composed only of tetragonal crystals and orthorhombic crystals. The piezoelectric thin film 3 may include crystals other than tetragonal crystals and orthorhombic crystals. For example, the piezoelectric thin film 3 may include one or both of cubic crystals of perovskite oxide and rhombohedral crystals of perovskite oxide.

[0081] The (001) plane of at least one crystal selected from tetragonal crystal and orthorhombic crystal is oriented in the normal direction dn of the surface of the piezoelectric film 3. The piezoelectric film 3 may include a plurality of crystals, and the (001) planes of a portion of the crystals or all of the crystals in the piezoelectric film 3 may be oriented in the normal direction dn of the surface of the piezoelectric film 3. For example, the (001) plane of the crystal (unit cell uc) may be approximately perpendicular or completely perpendicular to the normal direction dn, and the

[001] (orientation of the lattice plane) of the crystal (unit cell uc) may be approximately parallel or completely parallel to the normal direction dn. In other words, the (001) plane of the crystal (unit cell uc) may be approximately parallel or completely parallel to the surface of the piezoelectric film 3. The crystal orientation of the perovskite-type oxide having the above-mentioned composition that is easily polarized is

[001] . Therefore, by orienting the (001) plane of the crystal of the perovskite-type oxide in the normal direction dn of the surface of the piezoelectric film 3, the piezoelectric film 3 can have excellent piezoelectric properties and ferroelectricity. For the same reason, for example, the c / a of the tetragonal crystal and the orthorhombic crystal can be 1.05 or more and 1.20 or less. For example, the lattice constant a of the orthorhombic crystal and the orthorhombic crystal can be above The lattice constant b of the tetragonal crystal is equal to the lattice constant a of the tetragonal crystal. For example, the lattice constant b of the orthorhombic crystal can be above Below, and it only needs to be a value different from the lattice constant a of the orthorhombic crystal. For example, the lattice constant c of the tetragonal crystal and the orthorhombic crystal can be above The following. The c / a of the tetragonal crystal and the c / a of the orthorhombic crystal may be the same or different. The lattice constant a of the tetragonal crystal and the lattice constant a of the orthorhombic crystal may be the same or different. The lattice constant c of the tetragonal crystal and the lattice constant c of the orthorhombic crystal may be the same or different.

[0082] The degree of orientation of each lattice plane of the crystal can be quantified by the orientation degree (unit: %). The orientation degree of each lattice plane can be calculated based on the peak of the diffracted X-ray from each lattice plane. The peak of the diffracted X-ray from each lattice plane can be measured by out-of-plane measurement on the surface of the piezoelectric film 3. The orientation degree of the (001) plane can be expressed as 100×I (001) / ∑I (hkl) The orientation degree of the (110) plane can be expressed as 100×I (110) / ∑I (hkl) The orientation degree of the (111) plane can be expressed as 100×I (111) / ∑I (hkl) I (001) It is the maximum value of the peak of diffracted X-rays from the (001) plane. (110) It is the maximum value of the peak of diffracted X-rays from the (110) plane.(111) is the maximum value of the peak of diffracted X-rays from the (111) plane. (hkl) isI (001) +I (110) +I (111) The orientation degree of the (001) plane can be expressed as 100×S (001) / ∑S (hkl) The orientation degree of the (110) plane can be expressed as 100×S (110) / ∑S (hkl) The orientation degree of the (111) plane can be expressed as 100×S (111) / ∑S (hkl) . S (001) S is the peak area (peak integral) of diffracted X-rays from the (001) plane. (110) S is the peak area (peak integral) of diffracted X-rays from the (110) plane. (111) ∑S is the peak area (integral of the peak) of diffracted X-rays from the (111) plane. (hkl) YesS (001) +S (110) +S (111) The degree of orientation of each lattice plane can be quantified by the degree of orientation based on the Lotgering method.

[0083] For the reason that the piezoelectric film 3 is easy to have excellent piezoelectric characteristics and ferroelectricity, it is preferred that the (001) plane of the crystal is preferentially oriented in the normal direction dn of the surface of the piezoelectric film 3. That is, it is preferred that the orientation degree of the (001) plane is higher than the orientation degrees of the (110) plane and the (111) plane. For example, the orientation degree of the (001) plane can be 70% to 100%, preferably 80% to 100%, and more preferably 90% to 100%.

[0084] In contrast to the piezoelectric film 3, it is difficult to deform a bulk piezoelectric body having a cubic crystal structure or a pseudo cubic crystal structure to make the bulk piezoelectric body tetragonal or orthorhombic. Therefore, the bulk piezoelectric body tends to be difficult to have piezoelectric properties caused by tetragonal or orthorhombic perovskite oxides.

[0085] The crystal orientation described below means that the (001) plane of at least one crystal selected from tetragonal crystal and orthorhombic crystal is oriented in the normal direction dn of the surface of the piezoelectric thin film 3 .

[0086] The piezoelectric film 3 is a crystalline film formed by a vapor phase growth method or a solution method, and is likely to have the above-mentioned crystal orientation. On the other hand, compared with the piezoelectric film 3, the bulk of the piezoelectric body having the same composition as the piezoelectric film 3 tends to be difficult to have the above-mentioned crystal orientation. This is because the bulk of the piezoelectric body is a sintered body (ceramic) containing powders of essential elements of the piezoelectric body, and it is difficult to control the structure and orientation of the multiple crystals constituting the sintered body. Since the bulk of the piezoelectric body contains Fe, the resistivity of the bulk of the piezoelectric body is lower than that of the piezoelectric film 3. As a result, leakage current is likely to occur in the bulk of the piezoelectric body. Therefore, it is difficult to polarize the bulk of the piezoelectric body by applying a high electric field, and it is difficult for the bulk of the piezoelectric body to have the same piezoelectric properties as the piezoelectric film.

[0087] The metal oxide contained in the piezoelectric thin film 3 can be represented by the following chemical formula 1. The following chemical formula 1 is substantially the same as the following chemical formula 1a and the following chemical formula 1b. In the following chemical formula 1 and the chemical formula 1a, M is Ga. 1－δ Co δ In the chemical formula 1a and the chemical formula 1b, (Bi 1-α K α ) x Bi y+z Equivalent to perovskite oxide (ABO 3 ) of the unit cell uc. Ti in chemical formula 1a x (Ti 1-β Mg β ) y (Fe 1-γ M γ ) z It corresponds to the B site of the unit cell uc of the perovskite oxide. Ti in the following chemical formula 1b x (Ti 1-β Mg β ) y (Fe 1-γ (Ga 1-δ Co δ ) γ ) z The B site is equivalent to the unit cell uc of the perovskite oxide. When the metal oxide is represented by the following chemical formula 1, the piezoelectric film 3 easily contains at least one crystal selected from tetragonal and orthorhombic crystals, and the crystals easily have the above-mentioned crystal orientation, and the piezoelectric film 3 easily has excellent piezoelectric properties and ferroelectricity.

[0088] x(Bi 1-α K α )TiO 3 -yBi(Ti 1-β Mg β ) 3 -zBi(Fe 1-γM γ ) 3 (1)

[0089] (Bi 1-α K α ) x Bi y+z Ti x (Ti 1-β Mg β ) y (Fe 1-γ M γ ) z O 3±ε (1a)

[0090] (Bi 1-α K α ) x Bi y+z Ti x (Ti 1-β Mg β ) y (Fe 1-γ (Ga 1-δ Co δ ) γ ) z O 3±ε (1b)

[0091] The units of x, y, z, α, β, γ, δ, and ε in the above chemical formulas are moles or molar ratios. x, y, and z are each positive real numbers. 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. Within the range of maintaining the crystal structure of the perovskite oxide, α in each chemical formula is greater than 0.000 and less than 1.000. Within the range of maintaining the crystal structure of the perovskite oxide, β in each chemical formula is greater than 0.000 and less than 1.000. For example, α may be 0.500 and β may be 0.500. γ in each chemical formula is greater than 0.050 and less than 0.400. δ in each chemical formula is greater than 0.000 and less than 1.000.

[0092] When γ in each chemical formula is greater than or equal to 0.050 and less than or equal to 0.400, the piezoelectric film 3 easily contains at least one crystal selected from tetragonal crystals and orthorhombic crystals, the crystals easily have the above-mentioned crystal orientation, and the piezoelectric film 3 easily has excellent piezoelectric properties and ferroelectric properties.

[0093] The total amount of Bi and K in the metal oxide can be expressed as [A] mole, the total amount of Ti, Mg, Fe and element M in the metal oxide can be expressed as [B] mole, and [A] / [B] can be 1.000. As long as the metal oxide can have a perovskite structure, [A] / [B] can be a value other than 1.000. That is, [A] / [B] can be less than 1.000 or greater than 1.000. ε in Chemical Formula 1a and Chemical Formula 1b is greater than 0.000. As long as the metal oxide can have a perovskite structure, ε can be a value other than 0.000. For example, ε can be greater than 0.000 and less than 1.000. ε can be calculated based on the valence of the element at the A site and the element at the B site of the perovskite structure. The valence of each element can be determined by X-ray photoelectron spectroscopy (XPS).

[0094] In the following, (Bi 1-α K α )TiO 3 Expressed as BKT. 1-β Mg β ) 3 Expressed as BMT. 1-γ M γ O 3 Described as BFMO. 3 Expressed as BFO. A metal oxide having a composition represented by the sum of BKT and BMT is expressed as BKT-BMT. A metal oxide having a composition represented by the sum of BKT, BMT and BFO is expressed as BKT-BMT-BFO. A metal oxide having a composition represented by the above chemical formula 1 is expressed as xBKT-yBMT-zBFMO. Each crystal of BKT, BMT, BFMO, BFO, BKT-BMT, BKT-BMT-BFO, and xBKT-yBMT-zBFMO has a perovskite structure.

[0095] Bismuth gallate (BiGaO 3 ; BGO) and bismuth cobalt oxide (BiCoO 3 ; BCO) are all perovskite oxides. The c / a of each crystal (tetragonal crystal) of bismuth gallate and bismuth cobaltate is greater than the c / a of BFO crystal (rhombohedral crystal). In xBKT-yBMT-zBFMO, since part of BFO is replaced by one or both of BGO and BCO, the c / a of the crystal of xBKT-yBMT-zBFMO tends to be greater than the c / a of the existing BKT-BMT-BFO. As a result, the piezoelectric film 3 including xBKT-yBMT-zBFMO can have excellent piezoelectric characteristics and ferroelectricity.

[0096] The crystal of BKT is tetragonal at room temperature, and BKT is a ferroelectric. The crystal of BMT is rhombohedral at room temperature, and BMT is a ferroelectric. The crystal of BFO is rhombohedral at room temperature, and BFO is a ferroelectric. The thin film composed of BKT-BMT is tetragonal at room temperature. The c / a of the tetragonal crystal of BKT-BMT tends to be greater than the c / a of BKT. The ferroelectricity of the thin film composed of BKT-BMT is superior to that of the thin film composed of BKT and the thin film composed of BMT. The thin film composed of xBKT-yBMT-zBFMO tends to be at least one of tetragonal and orthorhombic at room temperature. The c / a of xBKT-yBMT-zBFMO tends to be greater than the c / a of BKT-BMT and BKT-BMT-BFO. The ferroelectricity of the film composed of xBKT-yBMT-zBFMO is superior to that of the film composed of BKT-BMT or BKT-BMT-BFO. That is, the piezoelectric film 3 containing xBKT-yBMT-zBFMO is likely to become a ferroelectric film. It is speculated that the ferroelectricity of the piezoelectric film 3 is caused by the fact that the composition of the xBKT-yBMT-zBFMO has a morphotropic phase boundary (MPB). However, since the piezoelectric film 3 belongs to the tetragonal system or the orthorhombic system, it is speculated that the ferroelectricity of the piezoelectric film 3 is not only caused by the MPB. Since the piezoelectric film 3 has ferroelectricity, the piezoelectric film 3 is likely to have a large d 33,f In contrast to the piezoelectric thin film 3 , the crystals contained in the bulk of xBKT-yBMT-zBFMO are pseudo-cubic crystals, and the bulk of xBKT-yBMT-zBFMO tends to be less likely to have the above-mentioned crystal orientation and ferroelectricity than the piezoelectric thin film 3 .

[0097] The composition of xBKT-yBMT-zBFMO can be expressed based on a three-dimensional coordinate system. Figure 4 As shown, the three-dimensional coordinate system is composed of an X-axis, a Y-axis, and a Z-axis. Any coordinate in the coordinate system is represented by (X, Y, Z). The coordinates (x, y, z) in the coordinate system represent x, y, and z in the above chemical formula 1. The sum of x, y, and z in chemical formula 1 is 1, and x, y, and z are all positive real numbers. Therefore, the coordinates (x, y, z) are located on the inside of the triangle drawn by the dotted line in the plane represented by X+Y+Z=1. That is, the coordinates (x, y, z) are located on the inside of the triangle whose vertices are coordinates (1, 0, 0), coordinates (1, 1, 0), and coordinates (0, 0, 1). The triangle is a triangular coordinate system, and in the triangular coordinate system, X+Y+Z is 1. The triangular coordinate system is as follows Figure 5As shown. In addition to the coordinates (x, y, z), the triangular coordinate system also includes coordinates A, B, C, and D. That is, the coordinates (x, y, z), A, B, C, D, E, and F are all located in the plane represented by X+Y+Z=1. Coordinate A is (0.250, 0.005, 0.700). Coordinate B is (0.450, 0.250, 0.300). Coordinate C is (0.200, 0.500, 0.300). Coordinate D is (0.005, 0.250, 0.700). The coordinates (x, y, z) representing x, y, and z in Chemical Formula 1 can be located within a quadrilateral whose vertices are coordinates A, B, C, and D. When the coordinates (x, y, z) are within the quadrilateral ABCD, the composition of xBKT-yBMT-zBFMO is likely to have MPB, and the piezoelectric characteristics and ferroelectricity of the piezoelectric film 3 are likely to be improved. When x is equal to y, the coordinates (x, y, z) are located on a straight line passing through the coordinates (0.500, 0.500, 0.000) and the coordinates (0.000, 0.000, 1.000). When x is equal to y, the composition of xBKT-yBMT-zBFMO is likely to have MPB, and the piezoelectric characteristics and ferroelectricity of the piezoelectric film 3 are likely to be improved.

[0098] x can be 0.050 to 0.450, or 0.100 to 0.350, y can be 0.050 to 0.500, or 0.100 to 0.350, and z can be 0.300 to 0.700. When x, y, and z are within the above ranges and x+y+z is 1, the composition of xBKT-yBMT-zBFMO easily has MPB, and the piezoelectric properties and ferroelectricity of the piezoelectric film 3 are easily improved.

[0099] For example, the thickness of the piezoelectric film 3 may be 10 nm to 10 μm, 0.3 μm to 10 μm, 0.3 μm to 5 μm, 0.5 μm to 5 μm, 0.3 μm to 3 μm, or 0.5 μm to 3 μm. For example, the area of ​​the piezoelectric film 3 may be 1 μm 2 Above 500mm 2 The following describes that the areas 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 the same as or different from the area of ​​the piezoelectric thin film 3 .

[0100] For example, the composition of the piezoelectric thin film 3 can be analyzed by X-ray fluorescence analysis (XRF) or inductively coupled plasma (ICP) emission spectroscopy. The crystal structure and crystal orientation of the piezoelectric thin film 3 can be determined by X-ray diffraction (XRD).

[0101] For example, the piezoelectric thin film 3 can be formed by the following method.

[0102] As a raw material of the piezoelectric thin film 3, a target material having the same composition as that of the piezoelectric thin film 3 can be used. The method of producing the target material is as follows.

[0103] As a starting material, for example, 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 powders of the oxide of element M. The oxide of element M may be selected from gallium oxide (Ga 2 O 3 ) and cobalt oxide (Co 2 O 3 ) is at least one oxide of the above chemical formula 1. As a starting material, a substance that becomes an oxide by sintering, such as a carbonate or oxalate, can be used instead of the above oxides. After these starting materials are fully dried at above 100°C, each starting material is weighed in a manner so that the amount (molar ratio) of each Bi, K, Ti, Mg, Fe, and element M is within the range specified by the above chemical formula 1, chemical formula 1a or chemical formula 1b. In the vapor phase growth method described later, Bi and K in the target are easier to volatilize than other elements. Therefore, the molar ratio of Bi in the target can be adjusted to a value higher than the molar ratio of Bi in the piezoelectric film 3. The molar ratio of K in the target can also be adjusted to a value higher than the molar ratio of K in the piezoelectric film 3.

[0104] The weighed raw materials are fully mixed in an organic solvent or water. The mixing time can be more than 5 hours and less than 20 hours. The mixing device can be a ball mill. After the mixed starting raw materials are fully dried, the starting raw materials are formed by a press. A calcined product is obtained by calcining the formed starting raw materials. The calcination temperature can be more than 750°C and less than 900°C. The calcination time can be more than 1 hour and less than 3 hours. The calcined product is crushed in an organic solvent or water. The crushing time can be more than 5 hours and less than 30 hours. The crushing device can be a ball mill. After the crushed calcined product is dried, the calcined product to which the binder solution is added is granulated to obtain a powder of the calcined product. A block-shaped compact is obtained by press-forming the powder of the calcined product.

[0105] By heating the block-shaped molded body, the binder in the molded body is volatilized. The heating temperature can be from 400°C to 800°C. The heating time can be from 2 hours to 4 hours. Then, the target material is obtained by sintering the molded body. The sintering temperature can be from 800°C to 1100°C. The sintering time can be from 2 hours to 4 hours. The heating rate and cooling rate of the molded body during the sintering process can be, for example, from 50°C / hour to 300°C / hour. The average particle size of the crystal grains of the metal oxide contained in the target material can be, for example, from 1 μm to 20 μm.

[0106] The piezoelectric film 3 can be formed by using a vapor phase growth method using the above-mentioned target material. In the vapor phase growth method, the elements constituting the target material are evaporated in a vacuum atmosphere. The evaporated elements adhere to and accumulate on the surface of any one of the second intermediate layer 6, the first electrode layer 2 or the crystalline substrate 1, thereby growing the piezoelectric film 3. The vapor phase growth method can be, for example, a sputtering method, an electron beam evaporation method, a chemical evaporation method (chemical vapor deposition (Chemical Vapor Deposition)) or a pulsed laser deposition (Pulsed Laser Deposition) method. Hereinafter, the pulsed laser deposition method is referred to as the PLD method. By using these vapor phase growth methods, a piezoelectric film 3 that is dense at the atomic level can be formed, and the segregation of elements in the piezoelectric film 3 is suppressed. Depending on the type of vapor phase growth method, the excitation source is different. The excitation source of the sputtering method is Ar plasma. The excitation source of the electron beam evaporation method is an electron beam. The excitation source of the PLD method is a laser (for example, an excimer laser). When these excitation sources are irradiated onto the target material, the elements constituting the target material evaporate.

[0107] Among the above-mentioned vapor phase growth methods, the PLD method is superior in the following aspects. In the PLD method, each element constituting the target material can be plasmatized instantly and spotlessly by pulsed laser. Therefore, it is easy to form a piezoelectric thin film 3 having a composition substantially the same as or completely the same as that of the target material. In addition, in the PLD method, by changing the number of laser pulses emitted, it is easy to control the thickness of the piezoelectric thin film 3.

[0108] The piezoelectric thin film 3 may be an epitaxial film. That is, the piezoelectric thin film 3 may be formed by epitaxial growth. By epitaxial growth, it is easy to form a piezoelectric thin film 3 having excellent crystal orientation. When the piezoelectric thin film 3 is formed by the PLD method, the piezoelectric thin film 3 is easily formed by epitaxial growth.

[0109] In the PLD method, the piezoelectric thin film 3 may be formed while heating the crystalline substrate 1 and the first electrode layer 2 in the vacuum chamber. The temperature (film forming temperature) of the crystalline substrate 1 and the first electrode layer 2 may be, for example, 300°C to 800°C, 500°C to 700°C, or 500°C to 600°C. The higher the film forming temperature, the more the cleanliness of the surface of the crystalline substrate 1 or the first electrode layer 2 is improved, the higher the crystallinity of the piezoelectric thin film 3 is, and the easier it is to improve the orientation of the (001) plane in the piezoelectric thin film 3. When the film forming temperature is too high, Bi or K is easily separated from the piezoelectric thin film 3, and it is difficult to control the composition of the piezoelectric thin film 3.

[0110] In the PLD method, the oxygen partial pressure in the vacuum chamber can be, for example, greater than 10 mTorr and less than 400 mTorr, greater than 15 mTorr and less than 300 mTorr, or greater than 20 mTorr and less than 200 mTorr. In other words, the oxygen partial pressure in the vacuum chamber can be, for example, greater than 1 Pa and less than 53 Pa, greater than 2 Pa and less than 40 Pa, or greater than 3 Pa and less than 30 Pa. By maintaining the oxygen partial pressure within the above range, Bi, K, Ti, Mg, Fe and element M deposited on the crystalline substrate 1 are easily fully oxidized. When the oxygen partial pressure is too high, the growth rate of the piezoelectric film 3 is easily reduced, and the orientation degree of the (001) plane in the piezoelectric film 3 is easily reduced.

[0111] Parameters other than those mentioned above that are controlled by the PLD method include, for example, the laser oscillation frequency and the distance between the substrate and the target. By controlling these parameters, it is easy to control the crystal structure and crystal orientation of the piezoelectric film 3. For example, when the laser oscillation frequency is below 10 Hz, the orientation degree of the (001) plane in the piezoelectric film 3 is easy to increase.

[0112] After the piezoelectric film 3 is grown, an annealing treatment (heat treatment) of the piezoelectric film 3 may be performed. The temperature of the piezoelectric film 3 during the annealing treatment (annealing temperature) may be, for example, 300°C to 1000°C, 600°C to 1000°C, or 850°C to 1000°C. By performing the annealing treatment of the piezoelectric film 3, the piezoelectric characteristics of the piezoelectric film 3 tend to be further improved. In particular, by performing the annealing treatment at 850°C to 1000°C, the piezoelectric characteristics of the piezoelectric film 3 are easily improved. However, the annealing treatment is not essential.

[0113] For example, the crystalline substrate 1 may be a substrate composed of a single crystal of Si or a substrate composed of a single crystal of a compound semiconductor such as GaAs. The crystalline substrate 1 may also be a substrate composed of MgO or a perovskite-type oxide (such as SrTiO 3) or other oxides. For example, the thickness of the crystalline substrate 1 may be 10 μm to 1000 μm. When the crystalline substrate 1 is conductive, the crystalline substrate 1 functions as an electrode, and therefore, the first electrode layer 2 may not be present. That is, for example, the conductive crystalline substrate 1 may be SrTiO doped with niobium (Nb). 3 As the crystalline substrate 1, an SOI (Silicon-on-Insulator) substrate may be used.

[0114] The crystal orientation of the crystalline substrate 1 may be equal to the normal direction of the surface of the crystalline substrate 1. That is, the surface of the crystalline substrate 1 may be parallel to the lattice plane of the crystalline substrate 1. The crystalline substrate 1 may be a uniaxially oriented substrate. For example, one lattice plane selected from the (100) plane, the (001) plane, the (110) plane, the (101) plane, and the (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 film 3 is easily oriented in the normal direction dn of the surface of the piezoelectric film 3.

[0115] 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 a material selected from titanium (Ti), chromium (Cr), titanium oxide (TiO 2 ), silicon oxide (SiO 2 ), and zirconium oxide (ZrO 2 ). Due to the presence of the first intermediate layer 5, the first electrode layer 2 is easily in close contact with the crystalline substrate 1. The first intermediate layer 5 may be crystalline. The lattice planes of the first intermediate layer 5 may be oriented in the normal direction of the surface of the crystalline substrate 1. Both the lattice planes of the crystalline substrate 1 and the lattice planes of the first intermediate layer 5 may be oriented in the normal direction of the surface of the crystalline substrate 1. The first intermediate layer 5 may be formed by sputtering, vacuum evaporation, printing, spin coating or sol-gel method.

[0116] The first intermediate layer 5 may contain ZrO 2 and oxides of rare earth elements. The first intermediate layer 5 contains ZrO 2 The oxides of rare earth elements easily form a first electrode layer 2 composed of platinum crystals on the surface of the first intermediate layer 5. The (002) plane of the platinum crystals easily extends in the normal direction D of the surface of the first electrode layer 2. NThe (200) plane of the platinum crystal is easily oriented in the in-plane direction of the surface of the first electrode layer 2. The rare earth element is at least one element selected from 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 ruthenium (Lu). The first intermediate layer 5 can be made of yttria-stabilized zirconia (added with Y 2 O 3 ZrO 2 ). Since the first intermediate layer 5 is composed of yttria-stabilized zirconia, the first electrode layer 2 composed of platinum crystals is easily formed on the surface of the first intermediate layer 5, and the (002) plane of the platinum crystals is easily in the normal direction D of the surface of the first electrode layer 2. N The (200) plane of the platinum crystal is easily oriented in the in-plane direction of the surface of the first electrode layer 2. For the same reason, the first intermediate layer 5 may have a ZrO 2 The first layer consists of Y 2 O 3 The first layer may be directly laminated on the surface of the crystalline substrate 1, the second layer may be directly laminated on the surface of the first layer, and the first electrode layer 2 may be directly laminated on the surface of the second layer.

[0117] For example, the first electrode layer 2 may be composed of at least one metal selected from 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 composed of, for example, strontium ruthenate (SrRuO 3 ), lanthanum nickel oxide (LaNiO 3 ), or lanthanum strontium cobaltate ((La,Sr)CoO 3 ) and other conductive metal oxides. The first electrode layer 2 may be crystalline. The 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 approximately parallel 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 of the surface of the crystalline substrate 1. The lattice plane of the first electrode layer 2 may be approximately parallel or completely parallel to the lattice plane of the perovskite-type oxide oriented in the piezoelectric film 3. For example, the thickness of the first electrode layer 2 may be greater than 1 nm and less than 1.0 μm. The method for forming the first electrode layer 2 may be sputtering, vacuum evaporation, printing, spin coating, or sol-gel. In the case of printing, spin coating, or sol-gel, in order to improve the crystallinity of the first electrode layer 2, the first electrode layer 2 may be subjected to a heat treatment (annealing).

[0118] The first electrode layer 2 may include platinum crystals. The first electrode layer 2 may be composed only of platinum crystals. The platinum crystals are cubic crystals having a face-centered cubic lattice structure. The (002) plane of the platinum crystals may be in the normal direction D of the surface of the first electrode layer 2. N 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 approximately parallel or completely parallel to the surface of the first electrode layer 2, and the (200) plane of the platinum crystal may be approximately perpendicular or completely perpendicular to the surface of the first electrode layer 2. In the case where the (002) plane and the (200) plane of the platinum crystal constituting the first electrode layer 2 have the above-mentioned orientation, the piezoelectric film 3 is easy to grow epitaxially on the surface of the first electrode layer 2, and the lattice stress caused by the lattice mismatch between the first electrode layer 2 and the piezoelectric film 3 is easy to act on the piezoelectric film 3. The lattice stress may be a compressive stress in the in-plane direction of the surface of the piezoelectric film 3. As a result, the piezoelectric film 3 is easy to contain at least one crystal selected from tetragonal crystals and orthorhombic crystals, and the (001) plane of the crystal is easy to be preferentially oriented in the normal direction dn of the surface of the piezoelectric film 3. As a result, the piezoelectric film element 10 is easy to have excellent piezoelectric characteristics and ferroelectricity.

[0119] The second intermediate layer 6 may be disposed between the first electrode layer 2 and the piezoelectric film 3. The second intermediate layer 6 may include, for example, SrRuO 3 、LaNiO 3 , and (La,Sr)CoO 3 At least one compound in the second intermediate layer 6. Since the second intermediate layer 6 is interposed, the piezoelectric film 3 is easily adhered to the first electrode layer 2. The second intermediate layer 6 may be crystalline. The second intermediate layer 6 may contain SrRuO 3 and LaNiO 3 In at least one of the cases, the lattice stress caused by the lattice mismatch between the second intermediate layer 6 and the piezoelectric film 3 is likely to act on the piezoelectric film 3. The lattice stress can be a compressive stress in the in-plane direction of the surface of the piezoelectric film 3. As a result, the piezoelectric film 3 is likely to contain at least one crystal selected from tetragonal crystals and orthorhombic crystals, and the (001) plane of the crystal is likely to be preferentially oriented in the normal direction dn of the surface of the piezoelectric film 3. As a result, the piezoelectric film element 10 is likely to have excellent piezoelectric properties and ferroelectricity. The lattice plane of the second intermediate layer 6 can be in the normal direction Dn of the surface of the first electrode layer 2. N 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 of the surface of the first electrode layer 2. N The second intermediate layer 6 may be formed by sputtering, vacuum evaporation, printing, spin coating, or sol-gel method.

[0120] The second electrode layer 4 may be composed of 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 composed of at least one metal selected from the group consisting of LaNiO 3 、SrRuO 3 , and (La,Sr)CoO 3 The second electrode layer 4 may be composed of at least one conductive metal oxide. The second electrode layer 4 may be crystalline. The lattice plane of the second electrode layer 4 may be oriented in the normal direction dn of the surface of the piezoelectric film 3. The lattice plane of the second electrode layer 4 may be approximately parallel or completely parallel to the surface of the piezoelectric film 3. The lattice plane of the second electrode layer 4 may be approximately parallel or completely parallel to the (001) plane oriented in the piezoelectric film 3. For example, the thickness of the second electrode layer 4 may be greater than 1 nm and less than 1.0 μm. The formation method of the second electrode layer 4 may be sputtering, vacuum evaporation, printing, spin coating, or sol-gel method. In the case of printing, spin coating or sol-gel method, in order to improve the crystallinity of the second electrode layer 4, the second electrode layer 4 may also be subjected to a heat treatment (annealing).

[0121] The third intermediate layer can be arranged between the piezoelectric film 3 and the second electrode layer 4. Due to the presence of the third intermediate layer, the second electrode layer 4 is easily in close contact with the piezoelectric film 3. Since the lattice between the crystalline third intermediate layer and the piezoelectric film 3 is not matched, the above-mentioned lattice stress is easily applied to the piezoelectric film 3. As a result, the piezoelectric film 3 is likely to contain at least one crystal selected from tetragonal crystals and orthorhombic crystals, and the (001) plane of the crystal is likely to be preferentially oriented in the normal direction dn of the surface of the piezoelectric film 3. As a result, the piezoelectric film element 10 is likely to have excellent piezoelectric properties and ferroelectricity. The composition, crystal structure and formation method of the third intermediate layer can be the same as those of the second intermediate layer 6.

[0122] At least a part or the whole of the surface of the piezoelectric thin-film element 10 may be covered with a protective film. When the piezoelectric thin-film element 10 is covered with a protective film, for example, the moisture resistance of the piezoelectric thin-film element 10 is improved.

[0123] The use of the piezoelectric film element of the present embodiment involves multiple aspects. For example, the piezoelectric film element can be a part or the whole of a device selected from a piezoelectric actuator, a piezoelectric sensor, a piezoelectric transducer, a piezoelectric microphone, a collector (Harvester), an oscillator, a resonator, an acoustic multilayer film, a thermoelectric element, and a filter. For example, a piezoelectric actuator can be used for haptics. That is, a piezoelectric actuator can be used for various devices that require feedback from skin sensation (tactile sensation). For example, the device requiring feedback from skin sensation can be a wearable device, a touch pad, a display, or a game controller. For example, a piezoelectric actuator can be used for a head assembly, a head stack assembly, or a hard disk drive. For example, a piezoelectric actuator can be used for a print head or an inkjet printing device. For example, a piezoelectric actuator can be used for a piezoelectric switch. For example, a piezoelectric sensor or a piezoelectric transducer can be used for a gyroscope sensor, a pressure sensor, a pulse sensor, an ultrasonic sensor, an ultrasonic transducer, an infrared sensor, or an impact sensor. The ultrasonic transducer can be a piezoelectric micromachined ultrasonic transducer (PMUT). Products that use piezoelectric micromachined ultrasonic transducers can be biometric authentication sensors such as fingerprint sensors and ultrasonic blood vessel authentication sensors, sensors for medical or health care, or ToF (Time of Flight) sensors. For example, the filter can be a BAW (Bulk Acoustic Wave) filter or a SAW (Surface Acoustic Wave) filter. Each of the above-mentioned piezoelectric thin film elements can be part or all of a micro electro mechanical system (MEMS). The above-mentioned piezoelectric thin film element can be a wearable device or a portable device.

[0124] The piezoelectric transducer of this embodiment includes the above-mentioned piezoelectric film or piezoelectric film element. Figure 6A schematic cross section of an ultrasonic transducer 10a as an example of a piezoelectric transducer is shown. The cross section of the ultrasonic transducer 10a is approximately parallel or completely parallel to the normal direction dn of the surface of the piezoelectric film 3. The ultrasonic transducer 10a may include substrates 1a and 1b, a first electrode layer 2 disposed on the substrates 1a and 1b, a piezoelectric film 3 overlapping the first electrode layer 2, and a second electrode layer 4 overlapping the piezoelectric film 3. A cavity 1c for sound may be provided below the piezoelectric film 3. Ultrasonic signals are transmitted or received by the deflection or vibration of the piezoelectric film 3. The first intermediate layer may be disposed between the substrates 1a and 1b and the first electrode layer 2. The second intermediate layer may be disposed between the first electrode layer 2 and the piezoelectric film 3. The third intermediate layer may be disposed between the piezoelectric film 3 and the second electrode layer 4.

[0125] It should be understood that all aspects, advantages and features described herein may not all be achieved by any specific embodiment, or may not all be included in any specific embodiment. In fact, after describing and illustrating various examples, other examples can be modified in arrangement and detail, which is self-evident.

[0126] [Example]

[0127] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0128] (Example 1)

[0129] When the piezoelectric thin film element of Example 1 was produced, a crystalline substrate made of single crystal Si was used. The (100) plane of Si was parallel to the surface of the crystalline substrate. The crystalline substrate was a square of 20 mm×20 mm. The thickness of the crystalline substrate was 500 μm.

[0130] In a vacuum chamber, a ZrO2 layer is formed on the entire surface of a crystalline substrate. 2 and Y 2 O 3 The first intermediate layer is formed by sputtering and has a thickness of 30 nm.

[0131] In the vacuum chamber, a first electrode layer composed of Pt crystals is formed on the entire surface of the first intermediate layer. The first electrode layer is formed by sputtering. The thickness of the first electrode layer is 200 nm. The temperature of the crystalline substrate (film forming temperature) during the formation of the first electrode layer is maintained at 500°C.

[0132] The X-ray diffraction (XRD) pattern of the first electrode layer is measured by out-of-plane measurement on the surface of the first electrode layer. The XRD pattern of the first electrode layer is measured by in-plane measurement on the surface of the first electrode layer. In the measurement of these XRD patterns, an X-ray diffraction device (SmartLab) manufactured by Rigaku Co., Ltd. is used. The measurement conditions are set in such a way that the intensity of each peak in the XRD pattern is increased by at least 3 digits relative to the background intensity. The peak of the diffracted X-ray of the (002) plane of the Pt crystal is detected by the out-of-plane measurement. That is, the (002) plane of the Pt crystal is oriented in the normal direction of the surface of the first electrode layer. The peak of the diffracted X-ray of the (200) plane of the Pt crystal is detected by the in-plane measurement. That is, the (200) plane of the Pt crystal is oriented in the in-plane direction of the surface of the first electrode layer.

[0133] In a vacuum chamber, a piezoelectric film is formed on the entire surface of the first electrode layer. The piezoelectric film is formed by the PLD method. The thickness of the piezoelectric film is 2000nm. The temperature of the crystalline substrate (film forming temperature) during the formation of the piezoelectric film is maintained at 500°C. The oxygen partial pressure in the vacuum chamber during the formation of the piezoelectric film is maintained at 10Pa. The raw material of the piezoelectric film uses a target material (sintered body of raw material powder). When making the target material, the mixing ratio of the raw material powder (bismuth oxide, potassium carbonate, titanium oxide, magnesium oxide, iron oxide, and gallium oxide) is adjusted according to the composition of the target piezoelectric film. The composition of the target piezoelectric film is represented by the following chemical formula 1A. That is, the composition of the target material is represented by the following chemical formula 1A. The respective values ​​of x, y, z, α, β and γ in the following chemical formula 1A are the values ​​shown in the following Table 1.

[0134] x(Bi 1-α K α )TiO 3 -yBi(Ti 1-β Mg β ) 3 -zBi(Fe 1-γ Ga γ ) 3 (1A)

[0135] The composition of the piezoelectric film was analyzed by fluorescent X-ray analysis (XRF). The analysis was performed using a device PW2404 manufactured by Philips Corporation of Japan. The results of the analysis are as follows: The composition of the piezoelectric film of Example 1 is represented by the above chemical formula 1A, and the values ​​of x, y, z, α, β, and γ in the above chemical formula 1A are consistent with the values ​​shown in the following Table 1. That is, the composition of the piezoelectric film is consistent with the composition of the target material.

[0136] The XRD pattern of the piezoelectric film was measured by out-of-plane measurement on the surface of the piezoelectric film. The XRD pattern of the piezoelectric film was measured by in-plane measurement on the surface of the piezoelectric film. The measuring device and measuring conditions of the XRD pattern are the same as those described above.

[0137] The XRD pattern of the piezoelectric film shows that the piezoelectric film is composed of crystals of perovskite-type oxide.

[0138] By out-of-plane measurement, the lattice constant c of the above-mentioned crystal in the normal direction of the surface of the piezoelectric film was measured. The lattice constant c can be referred to as the spacing of the lattice planes parallel to the surface of the piezoelectric film. By in-plane measurement, the lattice constants a and b of the above-mentioned crystal in the direction parallel to the surface of the piezoelectric film were measured. The lattice constants a and b can be referred to as the spacing of the lattice planes perpendicular to the surface of the piezoelectric film. a and b are approximately equal to each other. a and b are both smaller than c. That is, at least a portion of the above-mentioned crystals contained in the piezoelectric film are tetragonal crystals with c / a greater than 1.

[0139] Through out-of-plane measurement, the peak of diffraction X-rays of the (001) plane of the perovskite oxide crystal was detected. Based on the XRD pattern, the orientation degree of the (001) plane of the crystal was calculated. As mentioned above, the orientation degree of the (001) plane is expressed as 100×I (001) / (I (001 )+I (110) +I (111) . The orientation degree of the (001) plane in the normal direction dn of the surface of the piezoelectric film is greater than 90%. That is, the (001) plane of the crystal is preferentially oriented in the normal direction of the surface of the piezoelectric film. In the following tables, the lattice plane (the lattice plane with an orientation degree of greater than 90%) preferentially oriented in the normal direction dn of the surface of the piezoelectric film is expressed as an "orientation plane".

[0140] By the above method, a stacked body composed of a crystalline substrate, a first intermediate layer overlapping the crystalline substrate, a first electrode layer overlapping the first intermediate layer, and a piezoelectric film overlapping the first electrode layer was prepared. The following steps were further performed using the stacked body.

[0141] In a vacuum chamber, a second electrode layer made of Pt is formed on the entire surface of the piezoelectric thin film. The second electrode layer is formed by sputtering. The temperature of the crystalline substrate during the formation of the second electrode layer is maintained at 500° C. The thickness of the second electrode layer is 200 nm.

[0142] Through the above process, a stacked body consisting of a crystalline substrate, a first intermediate layer overlapping the crystalline substrate, a first electrode layer overlapping the first intermediate layer, a piezoelectric film overlapping the first electrode layer, and a second electrode layer overlapping the piezoelectric film is manufactured. The stacked structure on the crystalline substrate is patterned by subsequent photolithography. After patterning, the stacked body is cut by dicing.

[0143] Through the above process, a rectangular piezoelectric thin film element of Example 1 was obtained. The piezoelectric thin film element is composed of a crystalline substrate, a first intermediate layer overlapping the crystalline substrate, a first electrode layer overlapping the first intermediate layer, a piezoelectric thin film overlapping the first electrode layer, and a second electrode layer overlapping the piezoelectric thin film. The area of ​​the movable part of the piezoelectric thin film is 20 mm×1.0 mm.

[0144] [Piezoelectric strain constant d 33,f Determination of

[0145] The piezoelectric strain constant d of the piezoelectric film was measured using the piezoelectric film element of Example 1. 33,f .d 33,f The measurement was performed using a device that combined an atomic force microscope (AFM) and a ferroelectric evaluation system. The atomic force microscope was SPA-400 manufactured by Seiko Instruments Co., Ltd., and the ferroelectric evaluation system was FCE manufactured by TOYO Corporation. 33,f The frequency of the alternating electric field (AC voltage) in the measurement is 5 Hz. The maximum value of the voltage applied to the piezoelectric film is 20 V. 33,f The unit of d is pm / V. 33,f As shown in the following Table 1.

[0146] (Examples 2 to 18 and Comparative Examples 1 to 4)

[0147] When preparing the target materials of Examples 2 to 18 and Comparative Examples 1 to 4, the mixing ratio of the raw material powders (bismuth oxide, potassium carbonate, titanium oxide, magnesium oxide, iron oxide, and gallium oxide) was adjusted according to the composition of the target piezoelectric thin film.

[0148] As a raw material of the target material in Comparative Example 1, potassium carbonate was not used.

[0149] As a raw material of the target material of Comparative Example 2, magnesium oxide was not used.

[0150] As a raw material of the target material of Comparative Example 3, gallium oxide was not used.

[0151] As a raw material of the target material of Comparative Example 4, iron oxide was not used.

[0152] Piezoelectric thin film elements of Examples 2 to 18 and Comparative Examples 1 to 4 were produced by the same method as in Example 1, except that the composition of the target material for forming the piezoelectric thin film was different.

[0153] The XRD patterns of the first electrode layers of Examples 2 to 18 and Comparative Examples 1 to 4 were measured by the same method as in Example 1. In any 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.

[0154] The composition of the piezoelectric film of each of Examples 2 to 18 and Comparative Examples 1 to 4 was analyzed by the same method as in Example 1. In any case of Examples 2 to 18 and Comparative Examples 1 to 4, the composition of the piezoelectric film is consistent with the composition of the target material (the above-mentioned chemical formula 1A). In each of Examples 2 to 18 and Comparative Examples 1 to 4, the values ​​of x, y, z, α, β, γ and δ in Chemical Formula 1A are the values ​​shown in Table 1 below. The x, y and z of each of Examples 1 to 14 are shown as coordinates (x, y, z) in Figure 5 (triangular coordinate system).

[0155] Figure 5 The coordinate A in corresponds to Example 1.

[0156] Figure 5 Coordinate B in corresponds to Example 2.

[0157] Figure 5 The coordinate C in corresponds to Example 3.

[0158] Figure 5 The coordinate D in corresponds to Example 4.

[0159] Figure 5 The coordinate E in corresponds to Example 5.

[0160] Figure 5 The coordinate F in corresponds to Example 6.

[0161] Figure 5 The coordinate G in corresponds to Example 7.

[0162] Figure 5 The coordinate H in corresponds to Example 8.

[0163] Figure 5 Coordinate I in corresponds to Example 9.

[0164] Figure 5 The coordinate J in corresponds to Example 10.

[0165] Figure 5 The coordinate K in corresponds to Example 11.

[0166] Figure 5 The coordinate L in corresponds to Example 12.

[0167] Figure 5 The coordinate M in corresponds to Example 13.

[0168] Figure 5 The coordinate O in corresponds to Example 14.

[0169] The XRD patterns of the piezoelectric films of Examples 2 to 18 and Comparative Examples 1 to 4 were measured by the same method as in Example 1. Any XRD pattern in Examples 2 to 18 and Comparative Examples 1 to 4 shows that the piezoelectric film is composed of crystals of a perovskite-type oxide. In any case of Examples 2 to 18 and Comparative Examples 1 to 4, at least a portion of the crystals contained in the piezoelectric film are tetragonal. In any case of Examples 2 to 18 and Comparative Examples 1 to 4, the (001) plane of the crystal is preferentially oriented in the normal direction of the surface of the piezoelectric film.

[0170] The piezoelectric strain constant d of each of the piezoelectric films of Examples 2 to 18 and Comparative Examples 1 to 4 was measured by the same method as in Example 1. 33,f . The d of each of Examples 2 to 18 and Comparative Examples 1 to 4 33,f As shown in the following Table 1.

[0171] (Comparative Example 5)

[0172] The target material of Comparative Example 5 does not contain bismuth. The target material of Comparative Example 5 has a composition represented by the following chemical formula 5. Each numerical value in the following chemical formula 5 represents a molar ratio. The thin film and thin film element of Comparative Example 5 were prepared by the same method as Example 1 except that the composition of the target material used for forming the thin film was different.

[0173] The thin film and thin film element of Comparative Example 5 were analyzed and measured in the same manner as in Example 1. 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 in-plane direction of the surface of the first electrode layer. The composition of the thin film of Comparative Example 5 was consistent with the composition of the target material of Comparative Example 5. The thin film of Comparative Example 5 was not a crystal having an oriented lattice plane and did not have piezoelectric properties.

[0174] 0.20MgTiO 3 -0.10K 2 O-0.20TiO 2 -0.50(Fe 0.9 Ga 0.1 )2 O 3 (5)

[0175] [Table 1]

[0176] Table 1 x y z α β γ Orientation plane <![CDATA[d 33,f ]]> Example 1 0.250 0.050 0.700 0.500 0.500 0.400 (001) 192 Example 2 0.450 0.250 0.300 0.500 0.500 0.400 (001) 183 Example 3 0.200 0.500 0.300 0.500 0.500 0.050 (001) 181 Example 4 0.050 0.250 0.700 0.500 0.500 0.100 (001) 193 Example 5 0.400 0.200 0.400 0.500 0.500 0.100 (001) 185 Example 6 0.200 0.400 0.400 0.500 0.500 0.100 (001) 184 Example 7 0.300 0.100 0.600 0.500 0.500 0.100 (001) 191 Example 8 0.100 0.300 0.600 0.500 0.500 0.100 (001) 188 Example 9 0.200 0.200 0.600 0.500 0.500 0.100 (001) 194 Example 10 0.150 0.150 0.700 0.500 0.500 0.050 (001) 191 Embodiment 11 0.350 0.150 0.500 0.500 0.500 0.200 (001) 190 Example 12 0.150 0.350 0.500 0.500 0.500 0.300 (001) 182 Embodiment 13 0.250 0.250 0.500 0.500 0.500 0.250 (001) 181 Embodiment 14 0.350 0.350 0.300 0.500 0.500 0.100 (001) 180 Embodiment 15 0.200 0.200 0.600 0.500 0.500 0.150 (001) 192 Example 16 0.200 0.200 0.600 0.500 0.500 0.050 (001) 194 Embodiment 17 0.200 0.200 0.600 0.500 0.500 0.200 (001) 187 Embodiment 18 0.200 0.200 0.600 0.500 0.500 0.400 (001) 185 Comparative Example 1 0.000 0.500 0.500 0.000 0.500 0.300 (001) 45 Comparative Example 2 0.400 0.000 0.600 0.500 0.000 0.400 (001) 106 Comparative Example 3 0.300 0.500 0.200 0.500 0.500 0.000 (001) 40 Comparative Example 4 0.400 0.400 0.200 0.500 0.500 1.000 (001) 60

[0177] (Comparative Examples 6 to 8)

[0178] The oxygen partial pressure in the vacuum chamber during the formation of the piezoelectric thin film of Comparative Example 6 was maintained at 1 Pa.

[0179] The oxygen partial pressure in the vacuum chamber during the formation of the piezoelectric thin film of Comparative Example 7 was maintained at 20 Pa.

[0180] The oxygen partial pressure in the vacuum chamber during the formation of the piezoelectric thin film of Comparative Example 8 was maintained at 0.1 Pa.

[0181] Piezoelectric thin film elements of Comparative Examples 6 to 8 were produced in the same manner as in Example 9 except for the oxygen partial pressure during the formation of the piezoelectric thin film.

[0182] The XRD patterns of the first electrode layers of Comparative Examples 6 to 8 were measured by the same method as in Example 1. In any 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.

[0183] The composition of the piezoelectric film of each of Comparative Examples 6 to 8 was analyzed by the same method as Example 1. In any case of Comparative Examples 6 to 8, the composition of the piezoelectric film was consistent with the composition of the target material. That is, the composition of the piezoelectric film of each of Comparative Examples 6 to 8 was the same as the composition of the piezoelectric film of Example 9.

[0184] By the same method as in Example 1, the XRD pattern of each of the piezoelectric thin films of Comparative Examples 6 to 8 was measured.

[0185] All the XRD patterns of Comparative Examples 6 to 8 showed that the piezoelectric thin film was composed of perovskite-type oxide crystals.

[0186] In any of Comparative Examples 6 to 8, at least a portion of the crystals included in the piezoelectric thin film were tetragonal crystals.

[0187] In the case of Comparative Example 6, the (110) plane of the crystal in the piezoelectric film is preferentially oriented in the normal direction of the surface of the piezoelectric film.

[0188] In the case of Comparative Example 7, the (111) planes of the crystals in the piezoelectric film are preferentially oriented in the normal direction of the surface of the piezoelectric film.

[0189] In the case of Comparative Example 8, a specific lattice plane of crystals in the piezoelectric film is not oriented in the normal direction of the surface of the piezoelectric film. That is, in the case of Comparative Example 8, the orientation degree of any lattice plane is less than 50%.

[0190] The piezoelectric strain constant d of each of the piezoelectric films of Comparative Examples 6 to 8 was measured by the same method as in Example 1. 33,f . The d of each of Comparative Examples 6 to 8 33,f As shown in Table 2 below.

[0191] [Table 2]

[0192] Table 2 x y z α β γ Orientation plane <![CDATA[d 33,f ]]> Example 9 0.200 0.200 0.600 0.500 0.500 0.100 (001) 194 Comparative Example 6 0.200 0.200 0.600 0.500 0.500 0.100 (110) 76 Comparative Example 7 0.200 0.200 0.600 0.500 0.500 0.100 (111) 85 Comparative Example 8 0.200 0.200 0.600 0.500 0.500 0.100 none 37

[0193] (Examples 19 and 20)

[0194] In the case of Examples 19 and 20, the second intermediate layer is formed directly on the entire surface of the first electrode layer, and the piezoelectric film is formed directly on the entire surface of the second intermediate layer.

[0195] The second intermediate layer of Example 19 is composed of crystalline SrRuO 3 The thickness of the second intermediate layer in Example 19 was 50 nm.

[0196] The second intermediate layer of Example 20 is made of crystalline LaNiO 3 The thickness of the second intermediate layer in Example 20 is 20 nm.

[0197] "SRO" in Table 3 below refers to SrRuO 3 "LNO" in Table 3 below refers to LaNiO 3 .

[0198] Piezoelectric thin-film elements of Examples 19 and 20 were produced by the same method as that of Example 9 except that the second intermediate layer was formed.

[0199] The XRD patterns of the first electrode layers of Examples 19 and 20 were measured by the same method as in Example 1. In either 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.

[0200] The composition of each piezoelectric film of Examples 19 and 20 was analyzed by the same method as Example 1. In any case of Examples 19 and 20, the composition of the piezoelectric film was consistent with the composition of the target material. That is, the composition of each piezoelectric film of Examples 19 and 20 was the same as the composition of the piezoelectric film of Example 9.

[0201] By the same method as in Example 1, the XRD patterns of the piezoelectric thin films of Examples 19 and 20 were measured.

[0202] All the XRD patterns of Examples 19 and 20 show that the piezoelectric thin film is composed of perovskite-type oxide crystals.

[0203] In any of Examples 19 and 20, at least a portion of the crystals included in the piezoelectric film are tetragonal crystals.

[0204] In both cases of Examples 19 and 20, the (001) plane of the crystal is preferentially oriented in the normal direction of the surface of the piezoelectric film.

[0205] The piezoelectric strain constant d of each piezoelectric film of Examples 19 and 20 was measured by the same method as in Example 1. 33,f . The d of each of Examples 19 and 20 33,f This is shown in Table 3 below.

[0206] [Table 3]

[0207]

[0208] (Example 21)

[0209] In the process of manufacturing the piezoelectric thin-film element of Example 21, the first intermediate layer was not formed. In the process of manufacturing the piezoelectric thin-film element of Example 21, a crystalline SrRuO 3 The thickness of the first electrode layer of Example 21 was 200 nm. A piezoelectric thin-film element of Example 21 was produced in the same manner as in Example 9 except for these matters.

[0210] The XRD pattern of the first electrode layer of Example 21 was measured by the same method as Example 1. The crystal 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, there was no in-plane orientation of the crystals of the first electrode layer.

[0211] The composition of the piezoelectric film of Example 21 was analyzed by the same method as Example 1. The composition of the piezoelectric film of Example 21 was consistent with the composition of the target material. That is, the composition of the piezoelectric film of Example 21 was the same as the composition of the piezoelectric film of Example 9.

[0212] By the same method as in Example 1, the XRD pattern of the piezoelectric thin film of Example 21 was measured.

[0213] The XRD pattern of Example 21 also shows that the piezoelectric thin film is composed of crystals of perovskite-type oxide.

[0214] At least a portion of the crystals contained in the piezoelectric film of Example 21 are tetragonal crystals.

[0215] In the case of Example 21, the (001) plane of the perovskite crystal is also preferentially oriented in the normal direction of the surface of the piezoelectric film.

[0216] The piezoelectric strain constant d of the piezoelectric film of Example 21 was measured by the same method as in Example 1. 33,f Example 21d 33,f This is shown in Table 4 below.

[0217] [Table 4]

[0218]

[0219] (Examples 22 and 23)

[0220] In the production of the target material of Example 22, cobalt oxide was used as a raw material in addition to gallium oxide.

[0221] In the preparation of the target material of Example 23, cobalt oxide was used as a raw material instead of gallium oxide. That is, in the preparation of the target material of Example 23, gallium oxide was not used.

[0222] The composition of each target material of Examples 22 and 23 is represented by the following Chemical Formula 1B. In each of Examples 22 and 23, the values ​​of x, y, z, γ, and δ in the following Chemical Formula 1B are the values ​​shown in Table 5 below.

[0223] x(Bi 0.5 K 0.5 )TiO 3 -yBi(Ti 0.5 Mg 0.5 ) 3 -zBi(Fe 1-γ (Ga 1-δ Co δ ) γ ) 3 (1B)

[0224] Piezoelectric thin film elements of Examples 22 and 23 were prepared in the same manner as in Example 1 except that the composition of the target material for forming the piezoelectric thin film was different.

[0225] The XRD patterns of the first electrode layers of Examples 22 and 23 were measured by the same method as in Example 1. In either 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.

[0226] The composition of each piezoelectric film of Examples 22 and 23 was analyzed by the same method as Example 1. In either case of Examples 22 and 23, the composition of the piezoelectric film was consistent with the composition of the target material. 1－δ Co δ In addition, the composition of the piezoelectric film of each of Examples 22 and 23 is the same as the composition of the piezoelectric film of Example 9.

[0227] By the same method as in Example 1, the XRD patterns of the piezoelectric thin films of Examples 22 and 23 were measured.

[0228] All the XRD patterns of Examples 22 and 23 show that the piezoelectric thin film is composed of perovskite-type oxide crystals.

[0229] In any of Examples 22 and 23, at least a portion of the crystals included in the piezoelectric film are tetragonal crystals.

[0230] In both cases of Examples 22 and 23, the (001) plane of the crystal is preferentially oriented in the normal direction of the surface of the piezoelectric film.

[0231] The piezoelectric strain constant d of each piezoelectric film of Examples 22 and 23 was measured by the same method as in Example 1. 33,f . The d of each of Examples 22 and 23 33,f This is shown in Table 5 below.

[0232] [Table 5]

[0233] Table 5 x y z α β γ δ Orientation plane <![CDATA[d 33,f ]]> Example 9 0.200 0.200 0.600 0.500 0.500 0.100 0.000 (001) 194 Embodiment 22 0.200 0.200 0.600 0.500 0.500 0.100 0.500 (001) 190 Embodiment 23 0.200 0.200 0.600 0.500 0.500 0.100 1.000 (001) 192

[0234] [Industrial Applicability]

[0235] For example, the piezoelectric thin film element according to one aspect of the present invention can be applied to a piezoelectric transducer, a piezoelectric actuator, and a piezoelectric sensor.

[0236] [Explanation of Reference Numerals]

[0237] 10: piezoelectric thin film element, 10a: piezoelectric transducer (ultrasonic transducer), 1: crystalline substrate, 2: first electrode layer, 3: piezoelectric thin film, 4: second electrode layer, 5: first intermediate layer, 6: second intermediate layer, D N: normal direction of the surface of the first electrode layer, dn: normal direction of the surface of the piezoelectric film, uc: unit cell of the crystal of the perovskite type oxide.

Claims

1. A piezoelectric film, wherein: Contains a metal oxide having a perovskite structure, The metal oxide comprises bismuth, potassium, titanium, magnesium, iron, and element M, The element M is at least one element selected from gallium and cobalt, At least a portion of the metal oxide is at least one crystal selected from tetragonal and orthorhombic, The (001) plane of the crystal is oriented in the normal direction of the surface of the piezoelectric film.

2. The piezoelectric film according to claim 1, wherein: The metal oxide is represented by the following chemical formula 1: In the following chemical formula 1, x, y and z are positive real numbers. x+y+z=1, In the following chemical formula 1, α is greater than 0 and less than 1. In the following chemical formula 1, β is greater than 0 and less than 1. In the following chemical formula 1, γ is 0.05 or more and 0.40 or less, In the following chemical formula 1, M represents Ga 1－δ Co δ , δ is greater than 0 and less than 1, <h2 style=";text-align:left;direction:ltr">x(Bi<h2 style=";text-align:left;direction:ltr"> 1－α <h2 style=";text-align:left;direction:ltr"> K<h2 style=";text-align:left;direction:ltr"> α <h2 style=";text-align:left;direction:ltr"> TiO3-yBi(Ti)<h2 style=";text-align:left;direction:ltr"> 1－β <h2 style=";text-align:left;direction:ltr"> Mg<h2 style=";text-align:left;direction:ltr"> β <h2 style=";text-align:left;direction:ltr"> )O3-zBi(Fe<h2 style=";text-align:left;direction:ltr"> 1－γ <h2 style=";text-align:left;direction:ltr"> M<h2 style=";text-align:left;direction:ltr"> γ <h2 style=";text-align:left;direction:ltr"> )O3 (1)。 3. The piezoelectric film according to claim 2, wherein: The three-dimensional coordinate system consists of the X-axis, Y-axis, and Z-axis. Any coordinate in the coordinate system is represented by (X, Y, Z), The coordinates (x, y, z) in the coordinate system represent x, y and z in the chemical formula 1. The coordinate A in the coordinate system is (0.250, 0.005, 0.700), The coordinate B in the coordinate system is (0.450, 0.250, 0.300), The coordinate C in the coordinate system is (0.200, 0.500, 0.300), The coordinate D in the coordinate system is (0.005, 0.250, 0.700) The coordinate (x, y, z) is located within a quadrilateral whose vertices are the coordinate A, the coordinate B, the coordinate C, and the coordinate D.

4. The piezoelectric film according to claim 1, wherein: The piezoelectric film is an epitaxial film.

5. The piezoelectric film according to claim 1, wherein: The piezoelectric film is a ferroelectric film.

6. A piezoelectric thin film element, wherein: A piezoelectric film according to claim 1 is provided.

7. The piezoelectric thin film element according to claim 6, wherein: have: Crystalline substrate, and The piezoelectric film is directly or indirectly overlapped with the crystalline substrate.

8. The piezoelectric thin film element according to claim 6, wherein: have: Crystalline substrate, an electrode layer directly or indirectly overlapping the crystalline substrate, and the piezoelectric film directly or indirectly overlapping the electrode layer.

9. The piezoelectric thin film element according to claim 6, wherein: have: The electrode layer and The piezoelectric film directly or indirectly overlaps the electrode layer.

10. The piezoelectric thin film element according to claim 8, wherein: Also having at least one intermediate layer, The intermediate layer is disposed between the crystalline substrate and the electrode layer.

11. The piezoelectric thin film element according to claim 8, wherein: Also having at least one intermediate layer, The intermediate layer is disposed between the electrode layer and the piezoelectric film.

12. The piezoelectric thin film element according to claim 9, wherein: Also having at least one intermediate layer, The intermediate layer is disposed between the electrode layer and the piezoelectric film.

13. The piezoelectric thin film element according to claim 8, wherein: The electrode layer comprises platinum crystals, The (002) plane of the platinum crystal is oriented in the normal direction of the surface of the electrode layer, and the (200) plane of the platinum crystal is oriented in the in-plane direction of the surface of the electrode layer.

14. The piezoelectric thin film element according to claim 9, wherein: The electrode layer comprises platinum crystals, The (002) plane of the platinum crystal is oriented in the normal direction of the surface of the electrode layer, and the (200) plane of the platinum crystal is oriented in the in-plane direction of the surface of the electrode layer.

15. A piezoelectric transducer, wherein: A piezoelectric film according to any one of claims 1 to 5 is provided.

16. A piezoelectric transducer, wherein: A piezoelectric thin-film element according to any one of claims 6 to 14 is provided.

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