Piezoelectric thin film, piezoelectric thin film element and piezoelectric transducer

Abstract

To provide a piezoelectric thin film exhibiting a large performance index expressed as -e31,f / ε0εr.SOLUTION: A piezoelectric thin film contains metal oxides. The metal oxide contains bismuth, iron, and a plurality of elements EB. The plurality of elements EB contain divalent elements. Furthermore, the plurality of elements EB include at least one element selected from the group consisting of trivalent elements, tetravalent elements, pentavalent elements, and hexavalent elements. The average valence of the plurality of elements EB is 3. The metal oxide contains a main component with a perovskite structure and a secondary component with a non-perovskite structure.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a piezoelectric thin film, a piezoelectric thin film element, and a piezoelectric transducer. [Background technology]

[0002] With the development and widespread adoption of various technologies such as wearable devices, healthcare, smartphones, connected cars, smart cities, and smart homes, there is a growing demand for small piezoelectric thin film elements (elements including a thin film as a piezoelectric body) that are applied to these technologies (see Patent Document 1 below and Non-Patent Documents 1 and 2 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5832091 [Non-patent literature]

[0004] [Non-Patent Document 1] Asif Ali et al., Dielectric properties of Bi(M2 / 3Nb1 / 3)O3(M = Ni, Mg, Zn) ceramics, J Mater Sci: Mater Electron (2022) 33:15067-15073. [Non-patent document 2] Zenghui Liu et al., Micro- / nanodomains and their switching in a highCurie-temperature ferroelectric single crystal of Bi(Zn2 / 3Nb1 / 3)O3-PbTiO3,Ceramics International 44 (2018) S189-S194. Summary of the Invention [Problem to be solved by the invention]

[0005] One of the figures of merit for piezoelectric thin films is -e 31,f / ε0ε r It is expressed as -e 31,f (Unit: C / m 2 ) is the piezoelectric stress constant of the longitudinal transverse vibration (in-plane vibration) of the piezoelectric thin film. ε0 is the dielectric constant of vacuum (8.854×10 -12 Fm -1 ) is ε r (No unit) is the relative permittivity of the piezoelectric thin film.

[0006] An object of one aspect of the present disclosure is to provide a method for 31,f / ε0ε r The present invention provides a piezoelectric thin film having a large figure of merit, which is expressed as: [Means for solving the problem]

[0007] For example, as described in [1] to

[18] below, one aspect of the present disclosure relates to a piezoelectric thin film, a piezoelectric thin film element, and a piezoelectric transducer.

[0008] [1] A piezoelectric thin film containing a metal oxide, The metal oxide comprises bismuth, iron, and a plurality of elements E B and, The plurality of elements E B teeth, a divalent element, at least one element selected from the group consisting of trivalent elements, tetravalent elements, pentavalent elements, and hexavalent elements; Including, The plurality of elements E B The average value of the valence of is 3, The metal oxide is a main component having a perovskite structure; a minor component having a non-perovskite structure; Including, Piezoelectric thin film.

[0009] [2] The metal oxide includes a first component and a second component, The first component is a plurality of elements E A containing Bi(Fe 1-y Co y ) 1-x E A x O3, The second component is the plurality of elements E B Including BiE B O3, The plurality of elements E A teeth, a divalent element, at least one element selected from the group consisting of trivalent elements, tetravalent elements, pentavalent elements, and hexavalent elements; Including, The plurality of elements E A The average value of the valence of is 3, wherein x is greater than 0 and less than 1; The y is equal to or greater than 0 and less than 1. [1] The piezoelectric thin film according to [1].

[0010] [3] the plurality of elements E A teeth, At least one of Zn and Mg; At least one of Ti and Zr, Including, The piezoelectric thin film according to [1] or [2].

[0011] [4] the plurality of elements E B teeth, Zn and At least one of Nb and Ta, Including, The piezoelectric thin film according to any one of [1] to [3].

[0012] [5] At least a portion of the main component is tetragonal. The piezoelectric thin film according to any one of [1] to [4].

[0013] [6] It is an epitaxial film. The piezoelectric thin film according to any one of [1] to [5].

[0014] [7] Ferroelectric thin films, The piezoelectric thin film according to any one of [1] to [6].

[0015] [8] A piezoelectric thin film comprising the piezoelectric thin film according to any one of [1] to [7]. Piezoelectric thin film element.

[0016] [9] a crystalline substrate; the piezoelectric thin film directly or indirectly overlapping the crystalline substrate; Including, [8] The piezoelectric thin film element according to [8].

[0017]

[10] a crystalline substrate; an electrode layer directly or indirectly overlying the crystalline substrate; the piezoelectric thin film directly or indirectly overlapping the electrode layer; Including, [8] The piezoelectric thin film element according to [8].

[0018]

[11] an electrode layer; the piezoelectric thin film directly or indirectly overlapping the electrode layer; Including, [8] The piezoelectric thin film element according to [8].

[0019]

[12] Further comprising at least one intermediate layer; the intermediate layer is disposed between the crystalline substrate and the electrode layer;

[10] The piezoelectric thin film element according to

[10] .

[0020]

[13] Further comprising at least one intermediate layer; the intermediate layer is disposed between the electrode layer and the piezoelectric thin film;

[10] The piezoelectric thin film element according to

[10] .

[0021]

[14] Further comprising at least one intermediate layer. the intermediate layer is disposed between the electrode layer and the piezoelectric thin film;

[11] The piezoelectric thin film element according to

[11] .

[0022]

[15] The electrode layer includes platinum crystals, the (002) plane of the platinum crystal is oriented in the normal direction to the surface of the electrode layer, the (200) plane of the platinum crystal is oriented in the in-plane direction of the surface of the electrode layer; The piezoelectric thin film element according to

[10] ,

[12] , or

[13] .

[0023]

[16] The electrode layer includes platinum crystals, the (002) plane of the platinum crystal is oriented in the normal direction to the surface of the electrode layer, the (200) plane of the platinum crystal is oriented in the in-plane direction of the surface of the electrode layer; The piezoelectric thin film element according to

[11] or

[14] .

[0024]

[17] A piezoelectric thin film comprising the piezoelectric thin film according to any one of [1] to [7]. Piezoelectric transducer.

[0025]

[18] A piezoelectric thin film element according to any one of [8] to

[17] . Piezoelectric transducer. [Effects of the Invention]

[0026] According to one aspect of the present disclosure, -e 31,f / ε0ε r The present invention provides a piezoelectric thin film having a large figure of merit, which is expressed as: [Brief explanation of the drawings]

[0027] [Figure 1] (a) in Figure 1 is a schematic cross-sectional view of a piezoelectric thin film element according to one embodiment of the present disclosure, and (b) in Figure 1 is an oblique exploded view of the piezoelectric thin film element shown in (a) in Figure 1, with the substrate, first intermediate layer, second intermediate layer and second electrode layer omitted in (b) in Figure 1. [Figure 2]FIG. 2 is a perspective view of a crystal (unit cell) of a main component (metal oxide) having a perovskite structure, showing the arrangement of each element in the perovskite structure. [Figure 3] FIG. 3 is a perspective view of a crystal (unit cell) of the main component (metal oxide) having a perovskite structure, showing the lattice planes and crystal orientation of the crystal. [Figure 4] FIG. 4 is a schematic cross-sectional view of a piezoelectric thin film element (ultrasonic transducer) according to another specific example of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0028] Preferred embodiments of the present disclosure will be described below with reference to the drawings. In the drawings, equivalent components are designated by equivalent reference numerals. The present disclosure is not limited to the following embodiments. X, Y, and Z shown in Figure 1(a), Figure 1(b), and Figure 4 represent three mutually orthogonal coordinate axes. The directions of the X-axis, Y-axis, and Z-axis are common to Figure 1(a), Figure 1(b), and Figure 4. The units of variables and numerical values ​​in each chemical formula in the present disclosure are moles or molar ratios.

[0029] (Piezoelectric thin film and piezoelectric thin film element) The piezoelectric thin film element according to this embodiment includes at least a piezoelectric thin film. For example, as shown in FIG. 1(a), the piezoelectric thin film element 10 according to this 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 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 directly overlap 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 disposed between the first electrode layer 2 and the piezoelectric thin film 3, and the piezoelectric thin film 3 may directly overlap the surface of the second intermediate layer 6. The thicknesses 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 shown in FIG. 1(b), the normal direction dn of the surface (main surface) of the piezoelectric thin film 3 is perpendicular to the normal direction D N The normal direction dn to the surface of the piezoelectric thin film 3 may be approximately or completely parallel to the surface of the first electrode layer 2. In other words, the surface of the piezoelectric thin film 3 may be approximately or completely parallel to the surface of the first electrode layer 2. The normal direction dn to the surface of the piezoelectric thin film 3 may be the polarization direction of the piezoelectric thin film 3. The normal direction dn to the surface of the piezoelectric thin film 3 may be rephrased as the thickness direction of the piezoelectric thin film 3.

[0030] A modified example of the piezoelectric thin film element 10 does not need to include the crystalline substrate 1. For example, the crystalline substrate 1 may be removed after the first electrode layer 2, the piezoelectric thin film 3, and the second electrode layer 4 are formed. When the crystalline substrate 1 functions as an electrode, the crystalline substrate 1 may be the first electrode layer 2. In other words, when the crystalline substrate 1 functions as an electrode, a modified example of the piezoelectric thin film element 10 may include the crystalline substrate 1 and the piezoelectric thin film 3 overlying the crystalline substrate 1, and the first electrode layer 2 does not need to be disposed between the crystalline substrate 1 and the piezoelectric thin film 3. When the crystalline substrate 1 functions as an electrode, the piezoelectric thin film 3 may directly overly the crystalline substrate 1. When the crystalline substrate 1 functions as an electrode, the piezoelectric thin film 3 may overly the crystalline substrate 1 via at least one intermediate layer selected from the first intermediate layer 5 and the second intermediate layer 6.

[0031] The piezoelectric thin film 3 includes a metal oxide. The piezoelectric thin film 3 may be made of only a metal oxide. The metal oxide may be made of bismuth (Bi), iron (Fe), and a plurality of elements E. B The metal oxide may further contain cobalt (Co) in addition to iron. The piezoelectric thin film 3 may be a ferroelectric thin film. Multiple elements E B contains one or more divalent elements. B includes one or more elements selected from the group consisting of one or more trivalent elements, one or more tetravalent elements, one or more pentavalent elements, and one or more hexavalent elements. Multiple elements E B The average valence of the element E is 3. B The mole ratio of divalent elements in B d, and multiple elements E B The molar ratio of trivalent elements in B tr, and multiple elements E B The molar ratio of tetravalent elements in B te, and multiple elements E B The mole ratio of pentavalent elements in B p, and multiple elements E B The molar ratio of hexavalent elements in B h, where the average valence of multiple elements E is 3. B satisfies both the following formula 1 and formula 2. M B d+M B tr+M B te+M B p+M B h=1.00 (1) 2M B d+3M B tr+4M B te+5M B p+6M B h=3.00 (2)

[0032] Metal oxides include a main component and a secondary component. Metal oxides may consist only of the main component and the secondary component. The main component has a perovskite structure at room temperature and atmospheric pressure. For example, room temperature may be 20°C ± 15°C. The secondary component has a non-perovskite structure (a crystal structure different from the perovskite structure) under any conditions (room temperature and atmospheric pressure, and high temperature and pressure). In other words, the secondary component does not have a perovskite structure under any conditions. For example, Bi(Mg,Ti)O3 and Bi(Zn,Ti)O3 do not have a perovskite structure at room temperature and atmospheric pressure, but do have a perovskite structure at high temperature and pressure. Therefore, Bi(Mg,Ti)O3 and Bi(Zn,Ti)O3 are not considered secondary components.

[0033] The relative dielectric constant ε of the metal oxide increases when a part of the perovskite structure (main component) in the metal oxide is replaced by a non-perovskite structure (secondary component). r Furthermore, the non-perovskite structure (secondary component) mixed with the perovskite structure (main component) in the piezoelectric thin film 3 acts like a local defect, softening the hard perovskite structure. As a result of the softening of the perovskite structure, polarization reversal of each domain in the metal oxide becomes more likely to occur. Therefore, the piezoelectric properties (e.g., -e 31,f ) improves. Relative permittivity ε r Decrease in -e 31,f As a result of the increase in the absolute value of the figure of merit (-e 31,f / ε0ε r ) increases. The inventors speculate that the above mechanism is a phenomenon specific to epitaxial films, and is difficult to realize in piezoelectric thin films and piezoelectric ceramics (sintered bodies made of piezoelectric materials) that have poor crystallinity. In other words, the piezoelectric thin film 3 may be an epitaxial film (a thin film formed by epitaxial growth) because the figure of merit is likely to increase. As mentioned above, -e 31,f is the piezoelectric stress constant of the longitudinal vibration (in-plane vibration) of the piezoelectric thin film 3. 31,fThe unit is [C / m 2 The longitudinal lateral vibration is vibration (expansion and contraction) of the piezoelectric thin film 3 in a direction perpendicular to the polarization direction (thickness direction) of the piezoelectric thin film 3. In other words, the longitudinal lateral vibration is vibration (expansion and contraction) of the piezoelectric thin film 3 in a direction substantially or completely parallel to the surfaces (principal surfaces) of the first electrode layer 2 and the second electrode layer 4.

[0034] The major component (perovskite structure) and minor component (non-perovskite structure) may be detected and distinguished based on the X-ray diffraction (XRD) pattern of the piezoelectric thin film 3. The XRD pattern of the piezoelectric thin film 3 may be measured by θ-2θ scanning in the out-of-plane direction of the main surface (surface) of the piezoelectric thin film 3. When the metal oxide in the piezoelectric thin film 3 contains a minor component in addition to the major component, the XRD pattern will include not only diffracted X-ray peaks specific to the perovskite structure, but also diffracted X-ray peaks specific to the non-perovskite structure (diffracted X-ray peaks not derived from the perovskite structure). For example, when the incident X-rays used to measure the XRD pattern are CuKα rays, the diffraction angle 2θ of the maximum peak of diffracted X-rays specific to the perovskite structure of the major component may be measured. P When the incident X-rays used to measure the XRD pattern are CuKα rays, the diffraction angle 2θ of the maximum peak of the diffracted X-rays specific to the non-perovskite structure of the minor component may be about 20°. NP The maximum peak of the diffracted X-rays (the diffraction angle is 2θ Pで The intensity of the peak) is I P The maximum peak of the diffracted X-rays (diffraction angle 2θ NPで The intensity of the peak) is I NP It can be expressed as I P / I NP can be greater than 1.0. That is, I greater than 1.0 P / I NP may mean that the crystal structure of the main component is a perovskite structure. In other words, an I P / I NP may mean that the crystal structure of the main component is a non-perovskite structure. For example, IP and I NP Each unit may be cps (counts per second) or an arbitrary unit.

[0035] The metal oxide may include a first component and a second component. The first component is composed of Bi, Fe, and several elements E. A The first component may include Bi(Fe 1-y Co y ) 1-x E A x O3. Bi(Fe 1-y Co y ) 1-x E A x In O3, x may be greater than 0.00 and less than 1.00. For example, x may be 0.40. Bi(Fe 1-y Co y ) 1-x E A x The y in O3 may be 0.00 or more and less than 1.00. 1-y Co y ) 1-x E A x O3) itself has a perovskite structure. The first component in the metal oxide may be a main component having a perovskite structure. The first component (Bi(Fe 1-y Co y ) 1-x E A x O3) A may contain one or more divalent elements. A may contain one or more elements selected from the group consisting of one or more trivalent elements, one or more tetravalent elements, one or more pentavalent elements, and one or more hexavalent elements. Multiple elements E A The average valence of the elements E may be 3. For example, A The mole ratio of divalent elements in A d, and multiple elements EA The molar ratio of trivalent elements in A tr, and multiple elements E A The molar ratio of tetravalent elements in A te, and multiple elements E A The mole ratio of pentavalent elements in A p, and multiple elements E A The molar ratio of hexavalent elements in A h, where the average valence of multiple elements E is 3. A may satisfy both the following formula 3 and the following formula 4. M A d+M A tr+M A te+M A p+M A h=1.00 (3) 2M A d+3M A tr+4M A te+5M A p+6M A h=3.00 (4) The second component is Bi, Fe, and several elements E. B The second component may include BiE. B O3. The second component (BiE B E in O3) B is a plurality of elements E B The second component (BiE B O3) itself has a non-perovskite structure. The second component in the metal oxide may be a minor component having a non-perovskite structure. When the metal oxide contains the first component and the second component, the metal oxide is likely to contain a main component having a perovskite structure and a subcomponent having a non-perovskite structure, and the figure of merit of the piezoelectric thin film 3 containing the metal oxide is likely to increase. The metal oxide may consist only of the first component (main component) and the second component (subcomponent). Multiple elements E in the first component A At least one of the E B The first component may be composed of at least one of the elements E A At least one of the EB The first component may be different from at least one of the elements E. A All of the above are the E of multiple elements in the second component. B The first component may contain multiple elements E. A All of the above are the E of multiple elements in the second component. B may be different from all of the above.

[0036] The metal oxide may be represented by the following chemical formula A1: The following chemical formula A1 is substantially the same as the following chemical formula A2: The variables γ, x, y, δ, and each numerical value in each chemical formula are in moles or molar ratios. (1-γ)Bi(Fe 1-y Co y ) 1-x E A x O3-γBiE B O3(A1) Bi(Fe 1-y Co y ) (1-γ)(1-x) E A (1-γ)x E B γ O 3±δ (A2) In Chemical Formula A1 and Chemical Formula A2, x may be greater than 0.00 and less than 1.00. In Chemical Formula A1 and Chemical Formula A2, y may be 0.00 or greater and less than 1.00. In Chemical Formula A1 and Chemical Formula A2, 1-γ may be the molar ratio of the first component (or main component) in the metal oxide. γ in Chemical Formula A1 and Chemical Formula A2 may be the molar ratio of the second component (or subcomponent) in the metal oxide. Because metal oxides tend to contain a major component having a perovskite structure and a minor component having a non-perovskite structure, and the figure of merit of the piezoelectric thin film 3 containing the metal oxide tends to increase, γ in chemical formula A1 and chemical formula A2 may be greater than 0.00 and less than 0.20, greater than 0.00 and 0.15 or less, greater than 0.00 and 0.10 or less, 0.06 or more and less than 0.20, 0.06 or more and 0.15 or less, or 0.06 or more and 0.10 or less. Chemical formula A1 is (1-γ)Bi(Fe1-y Co y ) 1-x E A x O3+γBiE B It is essentially the same as O3. In Chemical Formula A2, δ may be 0.000 or more. As long as the main component in the metal oxide has a perovskite structure, δ may be a value other than 0.000. For example, δ may be greater than 0.000 and less than or equal to 1.000. δ may be back-calculated from the valence of each element other than oxygen (O) contained in the metal oxide. The valence of each element may be measured by X-ray photoelectron spectroscopy (XPS). The amount of Bi in the metal oxide can be expressed as [A] moles, and the amount of Fe, Co, and multiple elements E in the metal oxide can be expressed as [A] moles. A , and several elements E B The total amount of these substances may be expressed as moles [B], and the ratio [A] / [B] may be 1.000. As long as the main component in the metal oxide has a perovskite structure, the ratio [A] / [B] may be a value other than 1.000. In other words, the ratio [A] / [B] may be less than 1.000 or greater than 1.000.

[0037] The first component (or the main component) is likely to have a perovskite structure, and the figure of merit of the piezoelectric thin film 3 containing a metal oxide is likely to increase. Therefore, the first component is preferably made of a plurality of elements E A may contain divalent and tetravalent elements. For the same reason, the plurality of elements E in the first component A may contain at least one of zinc (Zn) and magnesium (Mg), and at least one of titanium (Ti) and zirconium (Zr). A The divalent element contained in may be at least one of zinc (Zn) and magnesium (Mg), and the plurality of elements E A The tetravalent element contained therein may be at least one of titanium (Ti) and zirconium (Zr). For example, multiple elements E AThe trivalent element contained in may be one or more elements selected from the group consisting of aluminum (Al), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), gallium (Ga), indium (In), and rare earth elements. A The rare earth element contained in 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). For example, multiple elements E A The pentavalent element contained in may be one or more elements selected from the group consisting of niobium (Nb), tantalum (Ta), and vanadium (V). For example, multiple elements E A The hexavalent element contained in may be one or more elements selected from the group consisting of tungsten (W) and molybdenum (Mo).

[0038] The second component (or subcomponent) is likely to have a non-perovskite structure, and the figure of merit of the piezoelectric thin film 3 containing a metal oxide is likely to increase. Therefore, the second component (or subcomponent) is likely to have a non-perovskite structure, and the figure of merit of the piezoelectric thin film 3 containing a metal oxide is likely to increase. B may contain divalent and pentavalent elements. For the same reason, the plurality of elements E in the second component B may contain zinc (Zn) and may further contain at least one of niobium (Nb) and tantalum (Ta). B The divalent element contained in may be zinc (Zn), and the plurality of elements E B The pentavalent element contained in may be at least one of niobium (Nb) and tantalum (Ta). B The pentavalent element contained therein may be at least one selected from the group consisting of niobium (Nb), tantalum (Ta), and vanadium (V). For example, multiple elements E BThe trivalent element contained in may be one or more elements selected from the group consisting of aluminum (Al), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), gallium (Ga), indium (In), and rare earth elements. B The rare earth element contained in 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). For example, multiple elements E B The tetravalent element contained in may be one or more elements selected from the group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf), germanium (Ge), and tin (Sn). For example, multiple elements E B The hexavalent element contained in may be one or more elements selected from the group consisting of tungsten (W) and molybdenum (Mo).

[0039] The ratio of all elements constituting the metal oxide in the piezoelectric thin film 3 may be 99 mol% or more and 100 mol% or less. For example, Bi, Fe, Co, and a plurality of elements E in the piezoelectric thin film 3 A , multiple elements E B The proportion of Bi, Fe, Co, and O may be 99 mol % or more and 100 mol % or less. As long as the piezoelectric properties of the piezoelectric thin film 3 are not impaired, the piezoelectric thin film 3 may contain Bi, Fe, Co, and a plurality of elements E. A , multiple elements E B In addition to O and 0, other elements may be contained. The piezoelectric thin film 3 may contain or not contain lead (Pb). However, the piezoelectric thin film 3 does not need to contain Pb.

[0040] Hereinafter, the above-mentioned main component having a perovskite structure will be referred to as a "perovskite oxide." FIG. 2 shows a unit cell of a perovskite oxide crystal. The element located at the A site of the unit cell uc is Bi. The element located at the B site of the unit cell uc is Fe, Co, or a plurality of elements E. A The unit cell uc in Figure 2 is the same as the unit cell uc in Figure 3. However, in Figure 3, the B site and oxygen (O) in the unit cell uc are omitted to show the lattice planes. The lattice translation vector a (i.e., the a-axis) in the unit cell uc points in the

[0100] direction, the lattice translation vector b (i.e., the b-axis) in the unit cell uc points in the

[0010] direction, and the lattice translation vector c (i.e., the c-axis) in the unit cell uc points in the

[0001] direction. The lattice translation vectors a, b, and c are perpendicular to each other. The length a of the lattice translation vector a is the spacing a between the (100) planes of the perovskite oxide (lattice constant a). The length b of the lattice translation vector b is the spacing b between the (010) planes of the perovskite oxide (lattice constant b). The length c of the lattice translation vector c is the spacing c (lattice constant c) between (001) planes of the perovskite oxide. The perovskite oxide (main component) in the piezoelectric thin film 3 may be polycrystalline or imperfectly crystalline.

[0041] At room temperature or a temperature below the Curie temperature of the perovskite oxide, at least a portion or all of the perovskite oxide (main component) may be at least one crystal selected from the group consisting of tetragonal crystal and orthorhombic crystal. Due to the anisotropy in the c-axis of both the tetragonal crystal and the orthorhombic crystal, the piezoelectric thin film 3 is likely to 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 other words, c / a in the tetragonal crystal may be larger than 1. In the orthorhombic crystal, the lattice constant a, lattice constant b, and lattice constant c are different from each other. In the orthorhombic crystal, the lattice constant c may be larger than both the lattice constant a and the lattice constant b. In other words, c / a and c / b in the orthorhombic crystal may be larger than 1. The perovskite oxide may consist solely of tetragonal crystals. The perovskite oxide may consist solely of orthorhombic crystals. The perovskite oxide may consist solely of tetragonal crystals and orthorhombic crystals. The perovskite oxide may further contain crystals other than tetragonal crystals and orthorhombic crystals. For example, the perovskite oxide may further contain one or more crystals selected from the group consisting of cubic crystals, pseudo cubic crystals, and rhombohedral crystals.

[0042] The (001) plane of at least one crystal selected from the group consisting of tetragonal and orthorhombic crystals may be oriented in the normal direction dn to the surface of the piezoelectric thin film 3. The perovskite oxide may include multiple crystals, and the (001) planes of some or all of the crystals in the perovskite oxide may be oriented in the normal direction dn to the surface of the piezoelectric thin film 3. For example, the (001) plane of the crystal (unit cell uc) may be approximately or completely perpendicular to the normal direction dn, and the

[0001] (lattice plane orientation) of the crystal (unit cell uc) may be approximately or completely parallel to the normal direction dn. In other words, the (001) plane of the crystal (unit cell uc) may be approximately or completely parallel to the surface (main surface) of the piezoelectric thin film 3. The crystal orientation that is most likely to polarize the perovskite oxide (main component) is

[0001] . Therefore, since the (001) plane of the crystal of the perovskite oxide is oriented in the normal direction dn to the surface of the piezoelectric thin film 3, the piezoelectric thin film 3 tends to have excellent piezoelectric properties (and ferroelectricity).

[0043] The degree of orientation of each lattice plane of the crystal may be quantified by the degree of orientation (unit: %). The degree of orientation of each lattice plane may be calculated based on the peak of the diffracted X-rays originating from each lattice plane. The peak of the diffracted X-rays originating from each lattice plane may be measured in the out-of-plane direction of the surface of the piezoelectric thin film 3. The degree of orientation of the (001) plane is calculated by the following formula: (001) / ΣI (hkl) The orientation of the (110) plane can be expressed as 100×I (110) / ΣI (hkl) The orientation of the (111) plane can be expressed as 100×I (111) / ΣI (hkl) It can be expressed as: I (001) is the maximum peak of the diffracted X-rays originating from the (001) plane. (110) is the maximum peak of the diffracted X-rays originating from the (110) plane. (111) is the maximum peak of the diffracted X-rays originating from the (111) plane. (hkl) I (001) +I (110) +I (111) The unit of the maximum value of each peak may be cps or an arbitrary unit. The orientation of the (001) plane is 100×S(001) / ΣS (hkl) The orientation of the (110) plane can be expressed as 100×S (110) / ΣS (hkl) The orientation of the (111) plane can be expressed as 100×S (111) / ΣS (hkl) It may be expressed as S (001) is the area of ​​the diffracted X-ray peak (peak integral) originating from the (001) plane. (110) is the area of ​​the diffracted X-ray peak (peak integral) originating from the (110) plane. (111) is the area of ​​the diffracted X-ray peak (peak integral) originating from the (111) plane. (hkl) is S (001) +S (110) +S (111) is. The degree of orientation of each lattice plane may be quantified by the degree of orientation based on the Lotgering method.

[0044] Because this tends to result in excellent piezoelectric properties and ferroelectricity for the piezoelectric thin film 3, it is preferable that the (001) plane of the crystal of the perovskite oxide (main component) be preferentially oriented in the normal direction dn to the surface of the piezoelectric thin film 3. In other words, it is preferable that the degree of orientation of the (001) plane be higher than the degrees of orientation of the (110) plane and the (111) plane. For example, the degree of orientation of the (001) plane may be 70% or more and 100% or less, 80% or more and 100% or less, or 90% or more and 100% or less.

[0045] In contrast to the piezoelectric thin film 3, it is difficult to distort the bulk of a piezoelectric body having a cubic or pseudo-cubic structure to make the bulk of the piezoelectric body a tetragonal or orthorhombic structure, and therefore the bulk of the piezoelectric body tends to have little piezoelectric properties due to the tetragonal or orthorhombic structure of perovskite oxides.

[0046] The crystal orientation described below means that the (001) plane of at least one crystal selected from the group consisting of tetragonal and orthorhombic crystals is oriented in the normal direction dn to the surface of the piezoelectric thin film 3 .

[0047] The piezoelectric thin film 3 is a crystalline film formed by vapor deposition or solution deposition, and is likely to have the above-mentioned crystal orientation. On the other hand, a bulk piezoelectric body having the same composition as the piezoelectric thin film 3 tends to be less likely to have the above-mentioned crystal orientation than the piezoelectric thin film 3. This is because the bulk piezoelectric body is a sintered body (ceramic) of powder containing the essential elements of the piezoelectric body, and it is difficult to control the structure and orientation of the numerous crystals that make up the sintered body. Because the bulk piezoelectric body contains Fe, the resistivity of the bulk piezoelectric body is lower than that of the piezoelectric thin film 3. As a result, leakage current is likely to occur in the bulk piezoelectric body. Therefore, it is difficult to polarize the bulk piezoelectric body by applying a high electric field, and it is difficult for the bulk piezoelectric body to have the same piezoelectric properties as the piezoelectric thin film.

[0048] For example, the thickness of the piezoelectric thin film 3 may be 10 nm or more and 10 μm or less. 2 Over 500mm 2 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.

[0049] For example, the composition of the piezoelectric thin film 3 may be analyzed by X-ray fluorescence analysis (XRF) or inductively coupled plasma (ICP) optical emission spectroscopy. The crystal structure and crystal orientation of the piezoelectric thin film 3 may be identified by X-ray diffraction (XRD).

[0050] (Method of manufacturing piezoelectric thin film and piezoelectric thin film element) For example, the piezoelectric thin film 3 and the piezoelectric thin film element 10 may be manufactured by the following method.

[0051] A target having the same composition as that of the piezoelectric thin film 3 may be used as the raw material for the piezoelectric thin film 3. The target is produced as follows.

[0052] For example, the starting material (target material) is composed of bismuth oxide (Bi2O3), iron oxide (Fe2O3), and several elements E. A Each oxide and several elements EB The starting material may contain oxides of each of these elements. The starting material may further contain cobalt oxide (CO2O3). Instead of the above oxides, substances that become the above oxides by sintering, such as carbonates or oxalates, may be used as the starting material. The starting material may be in the form of powder. After the starting material is sufficiently dried at 100°C or higher, Bi, Fe, Co, and multiple elements E are added. A , and several elements E B Each component in the starting material is weighed out so that the amount of each substance (molar ratio) falls within the range specified by Chemical Formula A1 or Chemical Formula A2. In the vapor phase epitaxy described below, Bi in the target is more easily volatilized than other elements. Therefore, the molar ratio of Bi in the target may be adjusted to a value higher than the molar ratio of Bi in Chemical Formula A1 or Chemical Formula A2.

[0053] The starting materials are thoroughly mixed in an organic solvent or water. The mixing time may be 5 hours or more and 20 hours or less. The mixing means may be a ball mill. After the mixed starting materials are thoroughly dried, the starting materials are molded in a press. A calcined product is obtained by calcining the molded starting materials. The calcination temperature may be 750°C or more and 900°C or less. The calcination time may be 1 hour or more and 3 hours or less. The calcined product is pulverized in an organic solvent or water. The pulverization time may be 5 hours or more and 30 hours or less. The pulverization means may be a ball mill. After drying the pulverized calcined product, a binder solution is added to the calcined product and the calcined product is granulated to obtain a calcined powder. The calcined powder is press-molded to obtain a block-shaped compact.

[0054] By heating the block-shaped compact, the binder in the compact is volatilized. The heating temperature may be 400°C or higher and 800°C or lower. The heating time may be 2 hours or higher and 4 hours or lower. The compact is then sintered to obtain a target. The sintering temperature may be 800°C or higher and 1100°C or lower. The sintering time may be 2 hours or higher and 4 hours or lower. The heating rate and cooling rate of the compact during the sintering process may be, for example, 50°C / hour or higher and 300°C / hour or lower. For example, the average particle size of the crystal grains of the metal oxide contained in the target may be 1 μm or higher and 20 μm or lower.

[0055] The piezoelectric thin film 3 may be formed by vapor deposition using the target. In vapor deposition, elements constituting the target are evaporated in a vacuum atmosphere. The evaporated elements adhere to and deposit on the surface of either the second intermediate layer 6, the first electrode layer 2, or the crystalline substrate 1, thereby growing the piezoelectric thin film 3. For example, the vapor deposition may be sputtering, electron beam evaporation, chemical vapor deposition, or pulsed-laser deposition. Hereinafter, pulsed-laser deposition will be referred to as PLD. By using these vapor deposition methods, it is possible to form a piezoelectric thin film 3 that is dense at the atomic level, and segregation of elements in the piezoelectric thin film 3 is suppressed. The excitation source differs depending on the type of vapor deposition method. The excitation source for sputtering is Ar plasma. The excitation source for electron beam evaporation is an electron beam. The excitation source for PLD is laser light (e.g., an excimer laser). These excitation sources are irradiated onto the target, causing the elements that make up the target to evaporate.

[0056] Among the above vapor phase growth methods, the PLD method is relatively superior in the following respects. In the PLD method, a pulsed laser can instantly and uniformly convert each element constituting the target into plasma. Therefore, it is easy to form a piezoelectric thin film 3 having substantially or exactly the same composition as the target. Furthermore, in the PLD method, it is easy to control the thickness of the piezoelectric thin film 3 by changing the number of laser pulse shots. When the piezoelectric thin film 3 is formed by the PLD method, the piezoelectric thin film 3 is easily formed by epitaxial growth. Epitaxial growth makes it easy to form a piezoelectric thin film 3 with excellent crystal orientation.

[0057] 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 a vacuum chamber. For example, the temperature (film formation temperature) of the crystalline substrate 1 and the first electrode layer 2 during the formation of the piezoelectric thin film 3 may be 300°C or higher and 800°C or lower. The higher the film formation temperature, the more improved the cleanliness of the surface of the crystalline substrate 1 or the first electrode layer 2, the higher the crystallinity of the piezoelectric thin film 3, and the more likely it is that the degree of orientation of the (001) plane in the main component (perovskite oxide) will increase. If the film formation temperature is too high, Bi will be easily desorbed from the piezoelectric thin film 3, making it difficult to control the composition of the piezoelectric thin film 3.

[0058] For example, in the PLD method, the oxygen partial pressure in the vacuum chamber may be greater than 10 mTorr and less than 400 mTorr. In other words, the oxygen partial pressure in the vacuum chamber may be greater than 1 Pa and less than 53 Pa. By maintaining the oxygen partial pressure within the above range, the elements deposited on the crystalline substrate 1 are likely to be sufficiently oxidized, and a metal oxide (piezoelectric thin film 3) containing the main component and the subcomponent is likely to be formed. If the oxygen partial pressure is too high, the growth rate of the piezoelectric thin film 3 is likely to decrease, and the degree of orientation of the (001) plane in the main component is likely to decrease.

[0059] For example, other parameters that can be controlled in the PLD method include the laser oscillation frequency and the distance between the substrate and the target. Controlling these parameters makes it easy to control the crystal structure and crystal orientation of the piezoelectric thin film 3. For example, when the laser oscillation frequency is 10 Hz or less, the degree of orientation of the (001) plane in the main component tends to increase.

[0060] After the piezoelectric thin film 3 is grown, the piezoelectric thin film 3 may be annealed (heat-treated). For example, the temperature (annealing temperature) of the piezoelectric thin film 3 during the annealing may be 300°C or higher and 1000°C or lower. Annealing the piezoelectric thin film 3 tends to further improve the piezoelectric properties of the piezoelectric thin film 3. However, the annealing is not essential.

[0061] For example, the crystalline substrate 1 may be a substrate made of single crystal Si or a substrate made of single crystal compound semiconductor (such as GaAs). The crystalline substrate 1 may be a substrate made of single crystal MgO or a substrate made of single crystal other oxide (such as SrTiO3) having a perovskite structure. For example, the thickness of the crystalline substrate 1 may be 10 μm or more and 1000 μm or less. If the crystalline substrate 1 is conductive, the crystalline substrate 1 functions as an electrode, and the first electrode layer 2 may be omitted. For example, the conductive crystalline substrate 1 may be a single crystal SrTiO3 doped with Nb. An SOI (Silicon-on-Insulator) substrate may be used as the crystalline substrate 1.

[0062] The crystal orientation of the crystalline substrate 1 may be the same as the normal direction to the surface of the crystalline substrate 1. In other words, 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 group consisting of 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 piezoelectric thin film 3 (main component) is likely to be oriented in the normal direction dn to the surface of the piezoelectric thin film 3.

[0063] 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 contain at least one selected from the group consisting of titanium (Ti), chromium (Cr), titanium oxide (TiO2), silicon oxide (SiO2), and zirconium oxide (ZrO2). The first intermediate layer 5 facilitates adhesion of the first electrode layer 2 to the crystalline substrate 1. The first intermediate layer 5 may be crystalline. The lattice plane of the first intermediate layer 5 may be oriented in the normal direction to 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 to the surface of the crystalline substrate 1. The first intermediate layer 5 may be formed by sputtering, vacuum deposition, printing, spin coating, or a sol-gel method.

[0064] The first intermediate layer 5 may contain ZrO2 and an oxide of a rare earth element. When the first intermediate layer 5 contains ZrO2 and an oxide of a rare earth element, the first electrode layer 2 made of platinum crystals is easily formed on the surface of the first intermediate layer 5, and the (002) plane of the platinum crystals is aligned in the normal direction D of the surface of the first electrode layer 2. N 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 may be made of yttria-stabilized zirconia (ZrO2 with added Y2O3). Since the first intermediate layer 5 is made of yttria-stabilized zirconia, the first electrode layer 2 made of platinum crystals is easily formed on the surface of the first intermediate layer 5, and the (002) plane of the platinum crystals is aligned in the normal direction D of the surface of the first electrode layer 2. NThe (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 reason, the first intermediate layer 5 may have a first layer made of ZrO2 and a second layer made of Y2O3. The first layer may be stacked directly on the surface of the crystalline substrate 1, the second layer may be stacked directly on the surface of the first layer, and the first electrode layer 2 may be stacked directly on the surface of the second layer.

[0065] For example, the first electrode layer 2 may be made of 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). For example, the first electrode layer 2 may be made of a conductive metal oxide such as strontium ruthenate (SrRuO), lanthanum nickelate (LaNiO), or lanthanum strontium cobaltate ((La,Sr)CoO). The first electrode layer 2 may be crystalline. The lattice plane of the first electrode layer 2 may be oriented in the normal direction to the surface of the crystalline substrate 1. The lattice plane of the first electrode layer 2 may be approximately 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 to the surface of the crystalline substrate 1. The lattice plane of the first electrode layer 2 may be approximately or completely parallel to the lattice plane (e.g., the (001) plane) of the perovskite oxide (main component) in the piezoelectric thin film 3. For example, the thickness of the first electrode layer 2 may be 1 nm or more and 1.0 μm or less. The first electrode layer 2 may be formed by sputtering, vacuum deposition, printing, spin coating, or a sol-gel method. In the case of the printing, spin coating, or sol-gel method, the first electrode layer 2 may be subjected to a heat treatment (annealing) in order to enhance the crystallinity of the first electrode layer 2.

[0066] The first electrode layer 2 may contain platinum crystals. The first electrode layer 2 may consist solely of platinum crystals. Platinum crystals are cubic crystals with a face-centered cubic lattice structure. The (002) plane of the platinum crystals is aligned with the normal direction D of the surface of the first electrode layer 2. NThe (002) plane of the platinum crystal may be oriented in the in-plane direction 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 approximately or completely parallel to the surface of the first electrode layer 2, and the (200) plane of the platinum crystal may be approximately or completely perpendicular to the surface of the first electrode layer 2. When the (002) plane and the (200) plane of the platinum crystal constituting the first electrode layer 2 have the above-mentioned orientation, the piezoelectric thin film 3 is likely to grow epitaxially on the surface of the first electrode layer 2, and lattice stress due to lattice mismatch between the first electrode layer 2 and the piezoelectric thin film 3 is likely to act on the piezoelectric thin film 3. The lattice stress may be compressive stress in the in-plane direction of the surface of the piezoelectric thin film 3. As a result, the main component (perovskite oxide) in the piezoelectric thin film 3 is likely to contain at least one crystal selected from the group consisting of tetragonal and orthorhombic crystals, and the (001) plane of the crystal in the main component is likely to be preferentially oriented in the normal direction dn to 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).

[0067] A 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 SrRuO3, LaNiO3, and (La,Sr)CoO3. The second intermediate layer 6 facilitates adhesion of the piezoelectric thin film 3 to the first electrode layer 2. The second intermediate layer 6 may be crystalline. When the second intermediate layer 6 contains at least one of SrRuO3 and LaNiO3, lattice stress due to lattice mismatch between the second intermediate layer 6 and the piezoelectric thin film 3 is likely to act on the piezoelectric thin film 3. The lattice stress may be compressive stress in the in-plane direction of the surface of the piezoelectric thin film 3. As a result, the main component (perovskite-type oxide) in the piezoelectric thin film 3 is likely to contain at least one crystal selected from the group consisting of tetragonal and orthorhombic crystals, and the (001) plane of the crystal in the main component is likely to be preferentially oriented in the normal direction dn to 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). 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 NThe second intermediate layer 6 may be formed by a sputtering method, a vacuum deposition method, a printing method, a spin coating method, or a sol-gel method.

[0068] For example, the second electrode layer 4 may be made 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 made of at least one conductive metal oxide selected from the group consisting of LaNiO3, SrRuO3, and (La,Sr)CoO3. 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 to the surface of the piezoelectric thin film 3. The lattice plane of the second electrode layer 4 may be approximately or completely parallel to the surface of the piezoelectric thin film 3. The lattice plane of the second electrode layer 4 may be approximately or completely parallel to the lattice plane (e.g., the (001) plane) of the perovskite-type oxide (main component) in the piezoelectric thin film 3. For example, the thickness of the second electrode layer 4 may be 1 nm or more and 1.0 μm or less. The second electrode layer 4 may be formed by sputtering, vacuum deposition, printing, spin coating, or a sol-gel method. When the printing, spin coating, or sol-gel method is used, the second electrode layer 4 may be subjected to heat treatment (annealing) in order to enhance the crystallinity of the second electrode layer 4.

[0069] A third intermediate layer may be disposed between the piezoelectric thin film 3 and the second electrode layer 4. The third intermediate layer facilitates adhesion of the second electrode layer 4 to the piezoelectric thin film 3. Due to the lattice mismatch between the crystalline third intermediate layer and the piezoelectric thin film 3, the lattice stress described above is likely to act on the piezoelectric thin film 3. As a result, the main component (perovskite-type oxide) in the piezoelectric thin film 3 is likely to contain at least one crystal selected from the group consisting of tetragonal and orthorhombic crystals, and the (001) plane of the crystal in the main component is likely to be preferentially oriented in the normal direction dn to 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, crystal structure, and formation method of the third intermediate layer may be the same as those of the second intermediate layer 6.

[0070] At least a part or the entire surface of the piezoelectric thin film element 10 may be covered with a protective film. By covering the piezoelectric thin film element 10 with a protective film, the moisture resistance of the piezoelectric thin film element 10 is improved.

[0071] (Example of a piezoelectric thin film element) The piezoelectric thin film element according to this embodiment has a wide range of applications. For example, the piezoelectric thin film element may be a part or the entirety of one 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. For example, the piezoelectric actuator may be used in haptics. That is, the piezoelectric actuator may be used in various devices requiring cutaneous (tactile) feedback. For example, devices requiring cutaneous feedback may be wearable devices, touchpads, displays, or game controllers. For example, the piezoelectric actuator may be used in a head assembly, a head stack assembly, or a hard disk drive. For example, the piezoelectric actuator may be used in a printer head or an inkjet printer device. For example, the piezoelectric actuator may be used in a piezoelectric switch. For example, the piezoelectric sensor or piezoelectric transducer may be used in a gyro sensor, a pressure sensor, a pulse wave 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). Products applying the piezoelectric micromachined ultrasonic transducer may be biometric sensors such as fingerprint sensors and ultrasonic blood vessel authentication sensors, medical or healthcare sensors, or ToF (Time of Flight) sensors. For example, the filter may be a BAW (Bulk Acoustic Wave) filter or a SAW (Surface Acoustic Wave) filter. Each of the above-described thin film piezoelectric elements may be a part or the whole of a micro electro mechanical system (MEMS). Each of the above-described thin film piezoelectric elements may be a wearable device or a portable device. -e 31,f / ε0ε rAs described above, the piezoelectric thin film 3 according to this embodiment has a large -e 31,f / ε0ε r (That is, excellent sensor sensitivity) Therefore, according to this embodiment, the sensor sensitivity of the piezoelectric sensor or piezoelectric transducer is improved.

[0072] The piezoelectric transducer according to this embodiment includes the piezoelectric thin film or piezoelectric thin film element described above. FIG. 4 shows a schematic cross section of an ultrasonic transducer 10a, which is an example of a piezoelectric transducer. The cross section of the ultrasonic transducer 10a is approximately or completely parallel to the normal direction dn to the surface of the piezoelectric thin 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 thin film 3 overlapping the first electrode layer 2, and a second electrode layer 4 overlapping the piezoelectric thin film 3. An acoustic cavity 1c may be provided below the piezoelectric thin film 3. An ultrasonic signal is transmitted or received by deflection or vibration of the piezoelectric thin film 3. A first intermediate layer may be interposed between the substrates 1a and 1b and the first electrode layer 2. A second intermediate layer may be interposed between the first electrode layer 2 and the piezoelectric thin film 3. A second intermediate layer may be interposed between the piezoelectric thin film 3 and the second electrode layer 4.

[0073] The present disclosure is not necessarily limited to the above-described embodiments. Various modifications of the present disclosure are possible without departing from the spirit of the present disclosure, and these modifications are also included in the present disclosure. [Example]

[0074] The present disclosure will be described in detail with reference to the following examples and comparative examples, but the present disclosure is not limited to the following examples.

[0075] Example 1 A single crystal substrate (Si wafer) made of Si was used to fabricate the piezoelectric thin film element of Example 1. The (100) plane of Si was parallel to the surface (main surface) of the single crystal substrate. The diameter φ of the single crystal substrate was 3 inches. The thickness of the single crystal substrate was 400 μm.

[0076] In a vacuum chamber, a crystalline first intermediate layer consisting of ZrO2 and Y2O3 was formed on the entire surface of the single crystal substrate by sputtering. The thickness of the first intermediate layer was 30 nm.

[0077] In a vacuum chamber, a first electrode layer made of Pt crystals was formed on the entire surface of the first intermediate layer. The first electrode layer was formed by sputtering. The thickness of the first electrode layer was 200 nm. The temperature of the single crystal substrate (film formation temperature) during the formation of the first electrode layer was maintained at 500°C.

[0078] The laminate produced by the above method was cut (diced) to produce a plurality of rectangular laminates each consisting of a single crystal substrate, a first intermediate layer, and a first electrode layer. That is, a plurality of laminates were produced as samples for the analysis and measurement described below. The dimensions of each laminate in the direction perpendicular to the stacking direction were adjusted to 10 mm x 10 mm.

[0079] An X-ray diffraction (XRD) pattern of the first electrode layer was measured in the out-of-plane direction of the surface (main surface) of the first electrode layer. Another XRD pattern of the first electrode layer was measured in the in-plane direction of the surface of the first electrode layer. These XRD patterns were measured using an X-ray diffractometer (SmartLab) manufactured by Rigaku Corporation. The measurement conditions were set so that the peak intensity in each XRD pattern was at least three orders of magnitude higher than the background intensity. In the XRD pattern measured in the out-of-plane direction, a diffracted X-ray peak from the (002) plane of the Pt crystal was detected. This means that the (002) plane of the Pt crystal was oriented in the normal direction to the surface of the first electrode layer. In the XRD pattern measured in the in-plane direction, a diffracted X-ray peak from the (200) plane of the Pt crystal was detected. This means that the (200) plane of the Pt crystal was oriented in the in-plane direction of the surface of the first electrode layer.

[0080] In a vacuum chamber, a second intermediate layer made of crystalline LaNiO3 was formed on the entire surface of the first electrode layer by sputtering. The thickness of the second intermediate layer was 50 nm.

[0081] In a vacuum chamber, a piezoelectric thin film was formed on the entire surface of the second intermediate layer. The piezoelectric thin film was formed by a PLD method. The thickness of the piezoelectric thin film in Example 1 was adjusted to 10.0 μm. The temperature (film formation temperature) of the single crystal substrate during the piezoelectric thin film formation process was maintained at 500°C. The oxygen partial pressure in the vacuum chamber during the piezoelectric thin film formation process was maintained at 10 Pa. A target (sintered body of raw material powder) was used as the raw material for the piezoelectric thin film.

[0082] When preparing the target, the amount of bismuth oxide, iron oxide, and divalent element E in the raw material powder is adjusted according to the composition of the desired piezoelectric thin film (metal oxide). Ad oxides of titanium oxide, zinc oxide, and pentavalent element E Bp The compounding ratio of the oxides was adjusted. The composition of the target piezoelectric thin film (metal oxide) was expressed by the following chemical formula A3. In other words, the composition of the target roughly matched the following chemical formula A3. (1-γ)BiFe 0.60 E Ad 0.20 Ti 0.20 O3-γBiZn 2 / 3 E Bp 1 / 3 O3(A3) BiFe in formula A3 0.60 E Ad 0.20 Ti 0.20 O3 corresponds to the first component (main component). 1-γ in chemical formula A3 is the molar ratio of the first component. E in chemical formula A3 Ad is a divalent element contained in the first component, and is a plurality of elements E A The divalent element E in Example 1 is one of the following: Ad are shown in Table 1 below. A (i.e., E Ad 0.20 Ti 0.20 The average valence of ) was 3. BiZn in chemical formula A3 2 / 3 E Bp 1 / 3 O3 corresponds to the second component (minor component). γ in chemical formula A3 is the molar ratio of the second component. E in chemical formula A3 Bp is a pentavalent element contained in the first component, and is a plurality of elements E B The pentavalent element E in Example 1 is one of the following: Bp are shown in Table 1 below. B (i.e., Zn 2 / 3 E Bp 1 / 3 The average valence of ) was 3. In Example 1, γ was adjusted to the value shown in Table 1 below. Chemical formula A3 is (1-γ)BiFe 0.60 E Ad 0.20 Ti 0.20 O3+γBiZn 2 / 3 E Bp 1 / 3 It is essentially the same as O3.

[0083] The composition of the piezoelectric thin film was analyzed by X-ray fluorescence spectroscopy (XRF). A PW2404 instrument manufactured by Philips Japan Ltd. was used for the analysis. The analysis results showed that the piezoelectric thin film of Example 1 was made of a metal oxide represented by the above chemical formula A3. In other words, the composition of the piezoelectric thin film was approximately the same as the composition of the target.

[0084] The XRD pattern of the piezoelectric thin film was measured in the out-of-plane direction of the surface (main surface) of the piezoelectric thin film. In addition, another XRD pattern of the piezoelectric thin film was measured in the in-plane direction of the surface (main surface) of the piezoelectric thin film. The measurement equipment and measurement conditions for each XRD pattern were the same as those described above. The crystal structures of the main and subcomponents in the piezoelectric thin film (metal oxide) were analyzed using the method described in the above embodiment. The analysis results based on the XRD patterns showed that the piezoelectric thin film (metal oxide) contained a main component with a perovskite structure and a subcomponent with a non-perovskite structure. Out-of-plane measurements were used to measure the lattice constant c of the main component (perovskite oxide) in the normal direction to the surface of the piezoelectric thin film. Lattice constant c can be rephrased as the spacing between lattice planes parallel to the surface of the piezoelectric thin film. In-plane measurements were used to measure the lattice constants a and b of the main component (perovskite oxide) in the direction parallel to the surface of the piezoelectric thin film. Lattice constants a and b can be rephrased as the spacing between lattice planes perpendicular to the surface of the piezoelectric thin film. a and b were approximately equal to each other. Both a and b were smaller than c. In other words, the main component (perovskite oxide) contained in the piezoelectric thin film was a tetragonal crystal with c / a greater than 1. In the XRD pattern measured in the out-of-plane direction, a peak of diffracted X-rays from the (001) plane of the perovskite oxide crystal was detected. Based on the XRD pattern, the degree of orientation of the (001) plane of the crystal was calculated. As mentioned above, the degree of orientation of the (001) plane is 100×I 1(001) / (I 1(001) +I 1(110) +I 1(111) The degree of orientation of the (001) plane in the normal direction dn of the surface of the piezoelectric thin film was over 90%. In other words, the (001) plane of the main component (perovskite-type oxide) was preferentially oriented in the normal direction of the surface of the piezoelectric thin film.

[0085] The capacitance C of the piezoelectric thin film was measured by the following method. A number of dot-shaped electrodes arranged in a grid pattern were formed on the surface of the piezoelectric thin film. Each dot-shaped electrode was made of silver. The diameter φ of each dot-shaped electrode was 100 μm. The spacing between the dot-shaped electrodes was 300 μm. The details of the measurement of the capacitance C were as follows: Measurement equipment: LCR meter (E4980A) manufactured by Agilent Technologies, Inc. Frequency: 10kHz Electric field: 1V / μm Based on the following formula A, the relative permittivity ε of the piezoelectric thin film is calculated from the measured value of the capacitance C. r was calculated. ε0 in formula A is the dielectric constant of a vacuum (8.854×10 -12 Fm -1) In formula A, S is the surface area of ​​the piezoelectric thin film. S can be rephrased as the total area of ​​the dot-shaped electrodes (silver electrodes) that overlap the surface of the piezoelectric thin film. T in formula A is the thickness of the piezoelectric thin film. C=ε0×ε r ×(S / T) (A) The relative permittivity ε determined by the above method r are shown in Table 1 below.

[0086] The following steps were further carried out using the above laminate (excluding the silver dot electrodes) consisting of the single crystal substrate, the first intermediate layer, the first electrode layer, the second intermediate layer and the piezoelectric thin film.

[0087] In a vacuum chamber, a third intermediate layer made of crystalline LaNiO3 was formed on the entire surface of the piezoelectric thin film by sputtering. The thickness of the third intermediate layer was 50 nm.

[0088] In a vacuum chamber, a second electrode layer made of Pt was formed on the entire surface of the third intermediate layer. The second electrode layer was formed by sputtering. The temperature of the single crystal substrate during the formation of the second electrode layer was maintained at 500°C. The thickness of the second electrode layer was 200 nm.

[0089] Through the above steps, a laminate was produced including a single crystal substrate, a first intermediate layer overlying the single crystal substrate, a first electrode layer overlying the first intermediate layer, a second intermediate layer overlying the first electrode layer, a piezoelectric thin film overlying the second intermediate layer, a third intermediate layer overlying the piezoelectric thin film, and a second electrode layer overlying the third intermediate layer. Subsequently, photolithography was used to pattern the laminate structure on the single crystal substrate. After patterning, the laminate was cut by dicing.

[0090] The above steps resulted in the production of a rectangular piezoelectric thin film element of Example 1. The piezoelectric thin film element included a single crystal substrate, a first intermediate layer overlying the single crystal substrate, a first electrode layer overlying the first intermediate layer, a second intermediate layer overlying the first electrode layer, a piezoelectric thin film overlying the second intermediate layer, a third intermediate layer overlying the piezoelectric thin film, and a second electrode layer overlying the third intermediate layer.

[0091] <piezoelectric stress constant -e 31,f Measurement of Piezoelectric stress constant of piezoelectric thin film -e 31,f To measure this, a rectangular sample (cantilever) was prepared as the piezoelectric thin film element. The dimensions of the sample were 2 mm wide x 10 mm long. The dimensions of each electrode layer were 1.6 mm wide x 6 mm long. Except for these dimensions, the sample was the same as the piezoelectric thin film element in Example 1. A homemade evaluation system was used for the measurement. One end of the sample was fixed, and the other end of the sample was a free end. While applying a voltage to the piezoelectric thin film in the sample, the displacement of the free end of the sample was measured with a laser. Then, -e was calculated from the following formula B: 31,f was calculated. Note that E in formula B s is the Young's modulus of the single crystal substrate. h s is the thickness of the single crystal substrate. L is the length of the sample (cantilever). ν s is the Poisson's ratio of the single crystal substrate. out is the output displacement based on the measured displacement. V in is the voltage applied to the piezoelectric thin film. Piezoelectric constant -e 31,f The frequency of the AC electric field (AC voltage) in the measurement was 100 Hz. The maximum voltage applied to the piezoelectric thin film was 50 V. 31,f The unit is C / m 2 Example 1-e 31,f are shown in Table 1 below.

number

[0092] Dielectric constant of vacuum ε0, relative permittivity ε r Measurement values ​​of -e 31,f From the measured values, -e 31,f / ε0ε r was calculated. 31,f / ε0ε r The unit is GV / m (i.e., × 10 9 V / m). 31,f / ε0ε r are shown in Table 1 below.

[0093] (Examples 2 to 4 and Comparative Examples 1 to 6) Divalent element E in Examples 2 to 4 and Comparative Examples 1 to 6 Ad The pentavalent element E in each of Examples 2 to 4 and Comparative Examples 1 and 3 to 5 is shown in Table 1 below. Bp is shown in the following Table 1. γ in each of Examples 2 to 4 and Comparative Examples 1 to 6 was adjusted to the value shown in Table 1 below. The piezoelectric thin films and piezoelectric thin film elements of Examples 2 to 4 and Comparative Examples 1 to 6 were fabricated in the same manner as in Example 1, except for the differences shown in Table 1 below. The piezoelectric thin films of Examples 2 to 4 and Comparative Examples 1 to 6 were analyzed in the same manner as in Example 1.

[0094] Except for the differences shown in Table 1 below, the piezoelectric thin films of Examples 2 to 4 and Comparative Examples 1 to 6 each had the same characteristics as Example 1 described above. In Table 1 below, "P" means a perovskite structure. In Table 1 below, "NP" means a non-perovskite structure. In Table 1 below, "present" in the "NP" column means that not only a perovskite structure but also a non-perovskite structure exists in the piezoelectric thin film (metal oxide). In Table 1 below, "none" in the "NP" column means that a non-perovskite structure was not detected in the piezoelectric thin film (metal oxide). The "P" in the "Main Structure" column in Table 1 below means that the crystal structure of the main component is a perovskite structure. "NP" in the "Main Structure" column in Table 1 below means that the crystal structure of the main component is a non-perovskite structure.

[0095] Measurements were carried out using the piezoelectric thin film elements of Examples 2 to 4 and Comparative Examples 1 to 5 in the same manner as in Example 1. r , -e 31,f , and -e 31,f / ε0ε r is shown in Table 1 below.

[0096] [Table 1] [Industrial Applicability]

[0097] For example, a piezoelectric thin film according to one aspect of the present disclosure may be applied to a piezoelectric transducer, a piezoelectric sensor, or a piezoelectric actuator. [Explanation of symbols]

[0098] 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 to the surface of the first electrode layer, dn...normal direction to the surface of the piezoelectric thin film, uc...unit cell of a crystal of perovskite oxide (main component having a perovskite structure).

Claims

1. A piezoelectric thin film comprising a metal oxide, The metal oxide contains bismuth, iron, and a plurality of elements E Ｂ and The plurality of elements E Ｂ teeth, a divalent element; at least one element selected from the group consisting of trivalent elements, tetravalent elements, pentavalent elements, and hexavalent elements; Including, The plurality of elements E Ｂ The average value of the valence of is 3, The metal oxide is a main component having a perovskite structure; a minor component having a non-perovskite structure; Including, Piezoelectric thin film.

2. the metal oxide comprises a first component and a second component; The first component is a plurality of elements E Ａ Bi(Fe １－ｙ Co ｙ ) １－ｘ E Ａ ｘ O ３ and The second component is the plurality of elements E Ｂ BiE including Ｂ O ３ and The plurality of elements E Ａ teeth, a divalent element; at least one element selected from the group consisting of trivalent elements, tetravalent elements, pentavalent elements, and hexavalent elements; Including, The plurality of elements E Ａ The average value of the valence of is 3, x is greater than 0 and less than 1; The y is equal to or greater than 0 and less than 1. The piezoelectric thin film according to claim 1 .

3. The plurality of elements E Ａ teeth, At least one of Zn and Mg; At least one of Ti and Zr; Including, The piezoelectric thin film according to claim 2 .

4. The plurality of elements E Ｂ teeth, Zn and At least one of Nb and Ta; Including, The piezoelectric thin film according to claim 1 .

5. At least a portion of the main component is tetragonal. The piezoelectric thin film according to claim 1 .

6. It is an epitaxial film, The piezoelectric thin film according to claim 1 .

7. A ferroelectric thin film, The piezoelectric thin film according to claim 1 .

8. A piezoelectric thin film according to claim 1, Piezoelectric thin film element.

9. a crystalline substrate; the piezoelectric thin film directly or indirectly overlapping the crystalline substrate; Equipped with 9. The piezoelectric thin film element according to claim 8.

10. a crystalline substrate; an electrode layer directly or indirectly overlying the crystalline substrate; the piezoelectric thin film directly or indirectly overlapping the electrode layer; Equipped with 9. The piezoelectric thin film element according to claim 8.

11. an electrode layer; the piezoelectric thin film directly or indirectly overlapping the electrode layer; Equipped with 9. The piezoelectric thin film element according to claim 8.

12. further comprising at least one intermediate layer; the intermediate layer is disposed between the crystalline substrate and the electrode layer; The piezoelectric thin film element according to claim 10.

13. further comprising at least one intermediate layer; the intermediate layer is disposed between the electrode layer and the piezoelectric thin film; The piezoelectric thin film element according to claim 10.

14. further comprising at least one intermediate layer; the intermediate layer is disposed between the electrode layer and the piezoelectric thin film; The piezoelectric thin film element according to claim 11.

15. the electrode layer includes platinum crystals, the (002) plane of the platinum crystal is oriented in the normal direction to the surface of the electrode layer, the (200) plane of the platinum crystal is oriented in the in-plane direction of the surface of the electrode layer; The piezoelectric thin film element according to claim 10.

16. the electrode layer includes platinum crystals, the (002) plane of the platinum crystal is oriented in the normal direction to the surface of the electrode layer, the (200) plane of the platinum crystal is oriented in the in-plane direction of the surface of the electrode layer; The piezoelectric thin film element according to claim 11.

17. A piezoelectric thin film according to any one of claims 1 to 7, Piezoelectric transducer.

18. A piezoelectric thin film element according to any one of claims 8 to 16, Piezoelectric transducer.

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