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

Abstract

To provide a piezoelectric thin film having a large piezoelectric performance index (d33,f / εrε0).SOLUTION: A piezoelectric thin film P includes a lower layer 6, and a first piezoelectric layer 3A which directly or indirectly overlaps the lower layer 6. The first piezoelectric layer 3A contains tetragonal crystal 1 of perovskite oxide. The (001) planes of the tetragonal crystal 1 are oriented in a normal direction dn of the surface of the first piezoelectric layer 3A. The spacing of the (100) planes of the tetragonal crystal 1 is a1. The spacing of the (100) planes of crystal 6c included in the lower layer 6 is aL. The lattice mismatch rate between the first piezoelectric layer 3A and the lower layer 6 is defined as 100×(aL-a1) / a1. The lattice mismatch rate is 3.0% or more and 12.1% or less. The rocking curve of diffracted X-rays of the (001) planes of the tetragonal crystal 1 is measured in an out-of-plane direction of the surface of the first piezoelectric layer 3A. The full width at half maximum of the rocking curve is 1.9° or more and 5.5° or less.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] A piezoelectric material is processed into various piezoelectric elements according to various purposes. For example, a piezoelectric actuator converts a voltage into a force by the inverse piezoelectric effect of applying a voltage to the piezoelectric material to deform the piezoelectric material. Also, a piezoelectric sensor converts a force into a voltage by the piezoelectric effect of applying a pressure to the piezoelectric material to deform the piezoelectric material and generate electric polarization. These piezoelectric elements are mounted on various electronic devices.

[0003] In recent years' market, since miniaturization and performance improvement of electronic devices are required, piezoelectric elements (piezoelectric thin film elements) using piezoelectric thin films have been actively studied. However, since it is difficult to obtain the piezoelectric effect and the inverse piezoelectric effect as the piezoelectric material becomes thinner, development of a piezoelectric material having excellent piezoelectricity in a thin film state is expected.

[0004] Conventionally, lead zirconate titanate (so-called PZT), which is a perovskite-type ferroelectric, has been frequently used as a piezoelectric material. (See Patent Document 1 below.) However, since PZT contains lead (Pb) that is harmful to the human body and the environment, development of a lead-free piezoelectric material is expected as an alternative to PZT. For example, Non-Patent Document 1 below describes, as an example of a lead-free piezoelectric material, BiFeO 3 is described. BiFeO 3 has relatively excellent piezoelectricity among lead-free piezoelectric materials, and its application to piezoelectric thin film elements is particularly expected.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Literature

[0006]

Non-Patent Literature 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The main index (piezoelectric constant) indicating the performance of a piezoelectric material is d 33,f (piezoelectric strain constant), and g 33 (voltage output constant). The piezoelectric strain constant d 33,f (unit: pC / N) is an index of the amount of strain per unit electric field (transmission ability). The larger the piezoelectric strain constant d 33,f , the better the performance of the piezoelectric material as an actuator. On the other hand, the voltage output constant g 33 (unit × 10 -3 V·m / N) is an index of the generated electric field strength per unit stress (reception ability). The larger the voltage output constant g 33 , the better the performance of the piezoelectric material as a sensor such as a transducer. g 33 is expressed as d 33,f / ε r ε 0 or d 33,f / ε 33 ε 0 ε r or ε 33 is the relative permittivity of the piezoelectric material (unit: none). ε 0 is the permittivity of vacuum (8.854×10 -12 Fm -1 ). d 33,f / ε r ε 0 is denoted as the "piezoelectric performance index". d 33,fAs increases, the piezoelectric performance index increases, and ε r As decreases, the piezoelectric performance index increases. That is, a large piezoelectric strain constant d 33,f and a low relative permittivity ε r are compatible, and the piezoelectric performance index (d 33,f / ε r ε 0 ) increases.

[0008] An object of one aspect of the present invention is to provide a piezoelectric thin film having a large piezoelectric performance index (d 33,f / ε r ε 0 ), a piezoelectric thin film element including the piezoelectric thin film, and a piezoelectric transducer.

Means for Solving the Problems

[0009] The piezoelectric thin film according to one aspect of the present invention includes a lower layer and a first piezoelectric layer that directly or indirectly overlaps the lower layer. The first piezoelectric layer includes a tetragonal 1 of a perovskite-type oxide. The (001) plane of the tetragonal 1 is oriented in the normal direction of the surface of the first piezoelectric layer. The interval between the (100) planes of the tetragonal 1 is a1. The interval between the (100) planes of the crystal included in the lower layer is aL. The lattice mismatch rate between the first piezoelectric layer and the lower layer is defined as 100×(aL - a1) / a1. The lattice mismatch rate is 3.0% or more and 12.1% or less. The rocking curve of the diffracted X-ray of the (001) plane of the tetragonal 1 is measured in the out-of-plane direction of the surface of the first piezoelectric layer. The full width at half maximum (FWHM) of the rocking curve is 1.9° or more and 5.5° or less.

[0010] aL may be 3.92 Å or more and 4.29 Å or less.

[0011] The (001) plane of the crystal included in the lower layer may be oriented in the normal direction of the surface of the first piezoelectric layer.

[0012] The crystal contained in the lower layer may be at least one crystal selected from the group consisting of cubic crystal, tetragonal crystal, rhombohedral crystal, pseudo-cubic crystal, and pseudo-tetragonal crystal.

[0013] The crystal contained in the lower layer may contain at least one compound of barium titanate and titanium nitride.

[0014] The thickness of the lower layer may be 10 nm or more and 350 nm or less.

[0015] The spacing between the (001) planes of tetragonal crystal 1 is c1. c1 / a1 may be 1.050 or more and 1.250 or less.

[0016] Tetragonal crystal 1 may contain bismuth, iron, element E B and oxygen. Element E B may be at least one element selected from the group consisting of magnesium, aluminum, zirconium, titanium, nickel, and zinc.

[0017] Tetragonal crystal 1 may be represented by the following Chemical Formula 1. E in the following Chemical Formula 1 A may be at least one element selected from the group consisting of Na, K, and Ag. E in the following Chemical Formula 1 B may be at least one element selected from the group consisting of Mg, Al, Zr, Ti, Ni, and Zn. x1 in the following Chemical Formula 1 may be 0.10 or more and 0.90 or less. y1 in the following Chemical Formula 1 may be 0.05 or more and 0.85 or less. z1 in the following Chemical Formula 1 may be 0.05 or more and 0.85 or less. x1 + y1 + z1 may be 1.00. α in the following Chemical Formula 1 may be 0.00 or more and less than 1.00. x1(Bi 1-α E A α )E B O 3 -y1BiFeO3 -z1Bi(Fe 0.5 Ti 0.5 )O 3 (1)

[0018] The piezoelectric thin film may include a second piezoelectric layer. The second piezoelectric layer may be disposed between the lower layer and the first piezoelectric layer. The second piezoelectric layer may include a tetragonal crystal 2 of a perovskite-type oxide. The (001) plane of the tetragonal crystal 2 may be oriented in the normal direction of the surface of the first piezoelectric layer. The interval between the (001) planes of the tetragonal crystal 1 is c1. The interval between the (001) planes of the tetragonal crystal 2 is c2. The interval between the (100) planes of the tetragonal crystal 2 is a2. c2 / a2 may be smaller than c1 / a1.

[0019] c2 / a2 may be 1.010 or more and 1.110 or less.

[0020] The peak intensity of the diffracted X-ray of the (001) plane of the tetragonal crystal 1 is I 1 . The peak intensity of the diffracted X-ray of the (001) plane of the tetragonal crystal 2 is I 2 . I 1 / (I 1 +I 2 ) may be 0.90 or more and less than 1.00.

[0021] The tetragonal crystal 2 may include bismuth, iron, element E B and oxygen. Element E B may be at least one element selected from the group consisting of magnesium, aluminum, zirconium, titanium, nickel, and zinc.

[0022] The tetragonal crystal 2 may be represented by the following chemical formula 2. E in the following chemical formula 2 A may be at least one element selected from the group consisting of Na, K, and Ag. E in the following chemical formula 2 Bmay be at least one element selected from the group consisting of Mg, Al, Zr, Ti, Ni, and Zn. x2 in the following Chemical Formula 2 may be 0.10 or more and 0.85 or less. y2 in the following Chemical Formula 2 may be 0.10 or more and 0.85 or less. z2 in the following Chemical Formula 2 may be 0.05 or more and 0.80 or less. x2 + y2 + z2 may be 1.00. α in the following Chemical Formula 2 may be 0.00 or more and less than 1.00. x2(Bi 1-α E A α )E B O 3 ‐y2BiFeO 3 ‐z2Bi(Fe 0.5 Ti 0.5 )O 3 (2)

[0023] The thickness of the second piezoelectric layer may be 10 nm or more and 300 nm or less.

[0024] The piezoelectric thin film element according to one aspect of the present invention includes the above piezoelectric thin film.

[0025] The piezoelectric thin film element may include a crystalline substrate and an electrode layer overlapping the crystalline substrate. The lower layer may directly overlap the electrode layer. The intermediate layer may be disposed between the crystalline substrate and the electrode layer. The intermediate layer may include ZrO 2 and Y 2 O 3 .

[0026] The piezoelectric thin film element may include an electrode layer. The lower layer may directly overlap the electrode layer. The electrode layer may include platinum crystals. The (002) plane of the platinum crystals may be oriented in the normal direction of the surface of the electrode layer. The (200) plane of the platinum crystals may be oriented in the in-plane direction of the surface of the electrode layer.

[0027] The piezoelectric transducer according to one aspect of the present invention includes the above piezoelectric thin film element.

Advantages of the Invention

[0028] According to one aspect of the present invention, there are provided a piezoelectric thin film having a large piezoelectric performance index (d 33,f / ε r ε 0 ), a piezoelectric thin film element including the piezoelectric thin film, and a piezoelectric transducer.

Brief Description of the Drawings

[0029]

Figure 1

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Figure 11

DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, with reference to the drawings, details of a preferred embodiment of the present invention will be described. However, the present invention is not limited to the following embodiments. In the drawings, the same or equivalent elements are denoted by the same reference numerals. The X-axis, Y-axis, and Z-axis shown in FIGS. 1, 4, 6, and 9 are three mutually orthogonal coordinate axes. The directions of each of the three coordinate axes are common to FIGS. 1, 4, 6, and 9.

[0031] The piezoelectric thin film element according to this embodiment includes a piezoelectric thin film. FIG. 1 is a cross-sectional view and a perspective exploded view of a piezoelectric thin film element 10 according to this embodiment. The cross-section of this piezoelectric thin film element 10 is perpendicular to the surface of the piezoelectric thin film P. The piezoelectric thin film element 10 includes a crystalline substrate 8, a first electrode layer 7 (lower electrode layer) that directly or indirectly overlaps the crystalline substrate 8, a piezoelectric thin film P that directly overlaps the first electrode layer 7, and a second electrode layer 4 (upper electrode layer) that directly or indirectly overlaps the piezoelectric thin film P. The piezoelectric thin film P includes a lower layer 6 that directly overlaps the first electrode layer 7, and a first piezoelectric layer 3A that directly or indirectly overlaps the lower layer 6. The piezoelectric thin film element 10 may further include an intermediate layer 5. The intermediate layer 5 may be disposed between the crystalline substrate 8 and the first electrode layer 7, and the first electrode layer 7 may directly overlap the surface of the intermediate layer 5. As shown in FIG. 1, the normal direction dn of the surface of the first piezoelectric layer 3A may be substantially parallel to the normal direction D of the surface of the crystalline substrate 8. The normal direction dn of the surface of the first piezoelectric layer 3A may be alternatively referred to as the thickness direction of the piezoelectric thin film P. In the perspective exploded view of the piezoelectric thin film element 10 shown in FIG. 1, the intermediate layer 5, the first electrode layer 7, the lower layer 6, and the second electrode layer 4 are omitted. N and may be substantially parallel. The normal direction dn of the surface of the first piezoelectric layer 3A may be alternatively referred to as the thickness direction of the piezoelectric thin film P. In the perspective exploded view of the piezoelectric thin film element 10 shown in FIG. 1, the intermediate layer 5, the first electrode layer 7, the lower layer 6, and the second electrode layer 4 are omitted.

[0032] A modified example of the piezoelectric thin film element 10 may not include the crystalline substrate 8. For example, after the formation of the first electrode layer 7 and the piezoelectric thin film P, the crystalline substrate 8 may be removed. A modified example of the piezoelectric thin film element 10 may not include the second electrode layer 4. For example, after a piezoelectric thin film element without the second electrode layer is supplied to a manufacturer of electronic devices as a product, the second electrode layer may be added to the piezoelectric thin film element during the manufacturing process of the electronic device. When the crystalline substrate 8 functions as an electrode, a modified example of the piezoelectric thin film element 10 may not include the first electrode layer 7. That is, a modified example of the piezoelectric thin film element 10 may include the crystalline substrate 8 and the piezoelectric thin film P overlapping the crystalline substrate 8. When there is no first electrode layer 7, the lower layer 6 included in the piezoelectric thin film P may directly overlap the crystalline substrate 8. When there is no first electrode layer 7, the lower layer 6 included in the piezoelectric thin film P may overlap the crystalline substrate 8 via the intermediate layer 5.

[0033] In addition to the lower layer 6 and the first piezoelectric layer 3A, the piezoelectric thin film P may further include a second piezoelectric layer 3B. The piezoelectric thin film P may consist only of the lower layer 6, the first piezoelectric layer 3A, and the second piezoelectric layer 3B. When the piezoelectric thin film P includes the second piezoelectric layer 3B, the second piezoelectric layer 3B is disposed between the lower layer 6 and the first piezoelectric layer 3A. For example, the piezoelectric thin film P included in the piezoelectric thin film element 10a shown in FIG. 6 includes a lower layer 6 directly overlapping the first electrode layer 7, a second piezoelectric layer 3B directly overlapping the lower layer 6, and a first piezoelectric layer 3A directly overlapping the second piezoelectric layer 3B. However, the second piezoelectric layer 3B is not essential for the piezoelectric thin film P, and the piezoelectric thin film P may not include the second piezoelectric layer 3B. For example, the piezoelectric thin film P may consist only of the lower layer 6 and the first piezoelectric layer 3A.

[0034] The first piezoelectric layer 3A includes a tetragonal crystal 1 of a perovskite-type oxide. Needless to say, a perovskite-type oxide is an oxide having a perovskite-type structure. The perovskite-type oxide is the main component of the first piezoelectric layer 3A. The total content of the elements constituting the perovskite-type oxide in the first piezoelectric layer 3A may be 99 mol% or more and 100 mol% or less. The tetragonal crystal 1 may be a single crystal or a polycrystal. The second piezoelectric layer 3B contains a tetragonal crystal 2 of a perovskite-type oxide. The perovskite-type oxide is the main component of each of the second piezoelectric layers 3B. The total content of the elements constituting the perovskite-type oxide in the second piezoelectric layer 3B may be 99 mol% or more and 100 mol% or less. The tetragonal crystal 2 may be a single crystal or a polycrystal. The first piezoelectric layer 3A may consist only of the tetragonal crystal 1. The first piezoelectric layer 3A may not contain the tetragonal crystal 2. The first piezoelectric layer 3A may contain a trace amount of the tetragonal crystal 2. The second piezoelectric layer 3B may consist only of the tetragonal crystal 2. The second piezoelectric layer 3B may not contain the tetragonal crystal 1. The second piezoelectric layer 3B may contain a trace amount of the tetragonal crystal 1. In addition to the tetragonal crystal 1, the first piezoelectric layer 3A may contain a trace amount of crystals other than the tetragonal crystal. The second piezoelectric layer 3B may also contain a trace amount of crystals other than the tetragonal crystal 2. For example, the trace amount of crystals other than the tetragonal crystal may be crystals of at least one perovskite-type oxide selected from the group consisting of cubic crystals, rhombohedral crystals, pseudo-cubic crystals, and pseudo-tetragonal crystals.

[0035] The lower layer 6 contains crystals. For example, the crystals contained in the lower layer 6 may be at least one crystal selected from the group consisting of cubic crystals, tetragonal crystals, rhombohedral crystals, pseudo-cubic crystals, and pseudo-tetragonal crystals. The crystals contained in the lower layer 6 may be single crystals or polycrystals. The lower layer 6 may consist only of crystals.

[0036] The tetragonal crystal 1 may contain bismuth (Bi), iron (Fe), element E B and oxygen (O). Element E B may be at least one element selected from the group consisting of magnesium (Mg), aluminum (Al), zirconium (Zr), titanium (Ti), nickel (Ni), and zinc (Zn). The tetragonal crystal 1 may contain a plurality of types of E B The tetragonal crystal 1 may contain Bi, Fe, E B and O, and may further contain element E A Element E A may be at least one element selected from the group consisting of sodium (Na), potassium (K), and silver (Ag). The tetragonal crystal 1 may contain a plurality of types of E Amay include. Cubic crystal 2 may also contain bismuth, iron, and element E. B and oxygen. Element E contained in cubic crystal 2 B may also be at least one element selected from the group consisting of magnesium, aluminum, zirconium, titanium, nickel, and zinc. Cubic crystal 2 may also be Bi, Fe, E B and O, and in addition, may further contain element E A may include. Cubic crystal 2 may also contain multiple types of E B may include. Element E contained in cubic crystal 2 A may also be at least one element selected from the group consisting of sodium, potassium, and silver. Cubic crystal 2 may also contain multiple types of E A may include. The composition of cubic crystal 1 may be the same as that of cubic crystal 2. The composition of cubic crystal 1 may also be different from that of cubic crystal 2. Each of cubic crystals 1 and 2 may further contain elements other than Bi, Fe, E A , E B and O. Each of cubic crystals 1 and 2 may not contain Pb. Each of cubic crystals 1 and 2 may contain Pb. Each of cubic crystals 1 and 2 may contain Fe as Fe 2+ (divalent iron) and Fe 3+ (trivalent iron). The perovskite-type oxide may contain only Fe 3+ (trivalent iron).

[0037] Figure 2 shows the unit cell uc of the perovskite-type oxide. Each of a, b, and c in Figure 2 is a basic vector of the perovskite structure. The element located at the A site of the unit cell uc may be Bi or E A The element located at the B site of the unit cell uc may be Fe or E B . A part of the Fe located at the B site may be divalent iron (Fe 2+ ), and the remainder of the Fe located at the B site may be trivalent iron (Fe 3+ ). The Fe located at the B site may be only trivalent iron (Fe 3+ ).

[0038] Figure 3 shows the unit cell uc1 of the cubic crystal 1 and the unit cell ucL of the crystal included in the lower layer 6. For the sake of illustration, E B and O (oxygen) included in Figure 3 are omitted, but the unit cell uc1 in Figure 3 has the same perovskite structure as the unit cell uc in Figure 2. The crystal included in the lower layer 6 is denoted as "lower crystal 6c".

[0039] Each of a1, b1, and c1 in Figure 3 is a basic vector of the cubic crystal 1. The vector a1 in Figure 3 corresponds to the vector a in Figure 2. The vector b1 in Figure 3 corresponds to the vector b in Figure 2. The vector c1 in Figure 3 corresponds to the vector c in Figure 2. a1, b1, and c1 are perpendicular to each other. The orientation of the vector a1 (a-axis) is

[0100] . The orientation of the vector b1 (b-axis) is

[0010] . The orientation of the vector c1 (c-axis) is

[0001] . The length a1 of the vector a1 is the spacing of the (100) plane of the cubic crystal 1 (i.e., the lattice constant in the

[0100] direction). The length b1 of the vector b1 is the spacing of the (010) plane of the cubic crystal 1 (i.e., the lattice constant in the

[0010] direction). The length c1 of the vector c1 is the spacing of the (001) plane of the cubic crystal 1 (i.e., the lattice constant in the

[0001] direction). The length a1 is equal to the length b1. The length c1 is greater than the length a1.

[0040] Each of aL, bL, and cL in Figure 3 is a basic vector of the lower crystal 6c. aL, bL, and cL may be perpendicular to each other. aL, bL, and cL may not be perpendicular to each other. The orientation of the vector aL (a-axis) is

[0100] . The orientation of the vector bL (b-axis) is

[0010] . The orientation of the vector cL (c-axis) is

[0001] . The length aL of the vector aL is the spacing of the (100) plane of the lower crystal 6c (i.e., the lattice constant in the

[0100] direction). The length bL of the vector bL is the spacing of the (010) plane of the lower crystal 6c (i.e., the lattice constant in the

[0010] direction). The length cL of the vector cL is the spacing of the (001) plane of the lower crystal 6c (i.e., the lattice constant in the

[0001] direction).

[0041] Figure 7 shows the unit cell uc1 of cubic crystal 1 and the unit cell uc2 of cubic crystal 2. For the sake of illustration, E B and O (oxygen) that make up the unit cell uc2 in Figure 7 are omitted, but the unit cell uc2 in Figure 7 has the same perovskite structure as the unit cell uc in Figure 2. The unit cell uc1 in Figure 7 is the same as the unit cell uc1 in Figure 3.

[0042] Each of a2, b2, and c2 in Figure 7 is a basic vector of cubic crystal 2. The vector a2 in Figure 7 corresponds to the vector a in Figure 2. The vector b2 in Figure 7 corresponds to the vector b in Figure 2. The vector c2 in Figure 7 corresponds to the vector c in Figure 2. a2, b2, and c2 are perpendicular to each other. The orientation of the vector a2 (a-axis) is

[0100] . The orientation of the vector b2 (b-axis) is

[0010] . The orientation of the vector c2 (c-axis) is

[0001] . The length a2 of the vector a2 is the spacing of the (100) plane of cubic crystal 2 (i.e., the lattice constant in the

[0100] direction). The length b2 of the vector b2 is the spacing of the (010) plane of cubic crystal 2 (i.e., the lattice constant in the

[0010] direction). The length c2 of the vector c2 is the spacing of the (001) plane of cubic crystal 2 (i.e., the lattice constant in the

[0001] direction). The length a2 is equal to the length b2. The length c2 is greater than the length a2.

[0043] As shown in Figures 1, 3, and 7, the (001) plane of cubic crystal 1 (unit cell uc1) is oriented in the normal direction dn of the surface of the first piezoelectric layer 3A. As shown in Figures 1 and 7, the (001) plane of cubic crystal 2 (unit cell uc2) is also oriented in the normal direction dn of the surface of the first piezoelectric layer 3A. For example, each of the (001) plane of cubic crystal 1 and the (001) plane of cubic crystal 2 may be substantially parallel to the surface of the first piezoelectric layer 3A, and the

[0001] direction of each of cubic crystal 1 and cubic crystal 2 may be substantially parallel to the normal direction dn of the surface of the first piezoelectric layer 3A. The (001) plane of cubic crystal 1 may be oriented in the normal direction D N of the surface of the crystalline substrate 8. The (001) plane of cubic crystal 2 is also in the normal direction D NIt may be oriented. In other words, the (001) plane of the cubic crystal 1 and the (001) plane of the cubic crystal 2 may each be substantially parallel to the surface of the crystalline substrate 8, and the

[0001] direction of each of the cubic crystal 1 and the cubic crystal 2 may be substantially parallel to the normal direction D of the surface of the crystalline substrate 8. N and may be substantially parallel.

[0044] The cubic crystal of the perovskite-type oxide is easily polarized in the

[0001] direction. That is,

[0001] is the direction in which the cubic crystal of the perovskite-type oxide is more easily polarized than other crystal orientations. Therefore, when the (001) plane of the cubic crystal 1 and the (001) plane of the cubic crystal 2 are each oriented in the normal direction dn of the surface of the first piezoelectric layer 3A, the piezoelectric thin film P can have excellent piezoelectric properties. For the same reason, the piezoelectric thin film P may be a ferroelectric material. When the piezoelectric thin film P includes only the first piezoelectric layer 3A among the first piezoelectric layer 3A and the second piezoelectric layer 3B, the "crystal orientation" described below means that the (001) plane of the cubic crystal 1 is oriented in the normal direction dn of the surface of the first piezoelectric layer 3A. When the piezoelectric thin film P includes both the first piezoelectric layer 3A and the second piezoelectric layer 3B, the "crystal orientation" described below means that the (001) plane of the cubic crystal 1 and the (001) plane of the cubic crystal 2 are each oriented in the normal direction dn of the surface of the first piezoelectric layer 3A.

[0045] Since the piezoelectric thin film P has the above-described crystal orientation, the piezoelectric thin film P has a large piezoelectric performance index (d 33,f / ε r ε 0) can have. The above crystal orientation is a characteristic peculiar to the thin film. A thin film is a crystalline film formed by a vapor growth method, a solution method, or the like. On the other hand, it is difficult for a bulk piezoelectric material having the same composition as the piezoelectric thin film P to have the above crystal orientation. The bulk piezoelectric material is a sintered body (ceramics) of powder containing essential elements of the piezoelectric material, and it is difficult to control the structure and orientation of a large number of crystals constituting the sintered body. Due to the fact that the bulk piezoelectric material contains elements such as Fe, the resistivity of the bulk piezoelectric material is lower than that of the piezoelectric thin film P. As a result, leakage current is likely to occur in the bulk piezoelectric material. Therefore, it is difficult to polarize the bulk piezoelectric material by applying a high electric field, and it is difficult for the bulk piezoelectric material to have a large piezoelectric performance index.

[0046] As described above, the interval between the (100) planes of the tetragonal crystal 1 is a1, and the interval between the (100) planes of the crystal (lower crystal 6c) contained in the lower layer 6 is aL. aL is larger than a1. The lattice mismatch rate Δa between the first piezoelectric layer 3A and the lower layer 6 is defined as 100×(aL - a1) / a1. The lattice mismatch rate Δa is 3.0% or more and 12.1% or less, or 3.01% or more and 12.03% or less. That is, 100×(aL - a1) / a1 is 3.0 or more and 12.1 or less, or 3.01 or more and 12.03 or less. The rocking curve RC of the diffracted X-ray of the (001) plane of the tetragonal crystal 1 is measured in the out-of-plane direction of the surface of the first piezoelectric layer 3A. The full width at half maximum FWHM of the rocking curve RC is 1.9° or more and 5.5° or less.

[0047] When the lattice mismatch rate Δa is within the above range, the full width at half maximum FWHM of the rocking curve RC is easily controlled within the above range. When the lattice mismatch rate Δa is less than 3.0%, the full width at half maximum FWHM tends to be less than 1.9°. When the lattice mismatch rate Δa is larger than 12.1%, the full width at half maximum FWHM tends to be larger than 5.5°. Since a1 depends on the composition and crystal structure of the first piezoelectric layer 3A, and aL depends on the composition and crystal structure of the lower layer 6, the lattice mismatch rate Δa may be controlled by selecting and combining the compositions and crystal structures of the first piezoelectric layer 3A and the lower layer 6 respectively.

[0048] Since the full width at half maximum FWHM of the rocking curve RC is 1.9° or more and 5.5° or less, the piezoelectric thin film P can have a large piezoelectric performance index (d 33,f / ε r ε 0 ). That is, since the full width at half maximum FWHM is 1.9° or more and 5.5° or less, a large piezoelectric strain constant d 33,f of the piezoelectric thin film P and a low relative permittivity ε r of the piezoelectric thin film P can be made compatible. For example, the piezoelectric performance index (d 33,f / ε r ε 0 ) of the piezoelectric thin film P may be 150×10 -3 V·m / N or more and 239×10 -3 V·m / N or less, or 155×10 -3 V·m / N or more and 222×10 -3 V·m / N or less. For example, the piezoelectric strain constant d 33,f of the piezoelectric thin film P may be 147 pC / N or more and 179 pC / N or less, or 149 pC / N or more and 174 pC / N or less. For example, the relative permittivity ε r (or ε 33 ) of the piezoelectric thin film P may be 85 or more and 150 or less, or 88 or more and 127 or less.

[0049] The inventor infers that the piezoelectric thin film P can have a large piezoelectric performance index (d 33,f / ε r ε 0 ) due to the following mechanism.

[0050] Due to the lattice mismatch with the lattice mismatch rate Δa being 3.0% or more and 12.1% or less, the c1 / a1 of the tetragonal crystal 1 constituting the first piezoelectric layer 3A tends to increase. Due to the increase in c1 / a1 of the tetragonal crystal 1, the piezoelectric thin film P has a low relative permittivity ε ris likely to have. Also, due to the lattice mismatch where the lattice mismatch rate Δa is 3.0% or more and 12.1% or less, the (001) plane of the tetragonal crystal 1 is inclined to such an extent that the full width at half maximum FWHM of the rocking curve RC is 1.9° or more and 5.5° or less. That is, the full width at half maximum FWHM indicates the degree of inclination of the (001) plane of the tetragonal crystal 1 due to the lattice mismatch, and at least a part of the (001) plane of the tetragonal crystal 1 constituting the first piezoelectric layer 3A is not completely parallel to the surface of the first piezoelectric layer 3A. For example, FIG. 5 shows the inclination of the (001) plane of the tetragonal crystal 1 constituting the first piezoelectric layer 3A directly overlapping the lower layer 6. FIG. 8 shows the inclination of the (001) plane of the tetragonal crystal 1 constituting the first piezoelectric layer 3A directly overlapping the second piezoelectric layer 3B. That is, even when the second piezoelectric layer 3B is interposed between the lower layer 6 and the first piezoelectric layer 3A, the (001) plane of the tetragonal crystal 1 constituting the first piezoelectric layer 3A is inclined. Due to the inclination of the (001) plane of the tetragonal crystal 1 to such an extent that the full width at half maximum FWHM is 1.9° or more and 5.5° or less, the rotation of the polarization axis of the tetragonal crystal 1 occurs when an electric field is applied, and the piezoelectric thin film P has a large piezoelectric strain constant d 33,f is likely to have. For the above reasons, a low relative permittivity ε r and a large piezoelectric strain constant d 33,f are compatible, and the piezoelectric thin film P can have a large piezoelectric performance index (d 33 / ε r ε 0 ). When the full width at half maximum FWHM is less than 1.9°, the (001) plane of the tetragonal crystal 1 is not inclined sufficiently, and it is difficult for the piezoelectric thin film P to have a large piezoelectric strain constant d 33,f . When the full width at half maximum FWHM is greater than 5.5°, the crystal orientation of the first piezoelectric layer 3A is excessively impaired, and it is difficult for the piezoelectric thin film P to have a large piezoelectric strain constant d 33,f .

[0051] The above mechanism is a hypothesis, and the technical scope of the present invention is not limited by the above mechanism.

[0052] The intervals and orientation directions of the respective crystal planes of the tetragonal crystal 1, the tetragonal crystal 2, and the lower crystal 6c may be specified based on the X-ray diffraction (XRD) pattern of the piezoelectric thin film P measured by the 2θ-θ method in the out-of-plane direction and in-plane direction of the surface of the first piezoelectric layer 3A.

[0053] The rocking curve RC of the diffracted X-rays of the (001) plane of the cubic crystal 1 is measured by ω-scan in the out-of-plane direction of the surface of the first piezoelectric layer 3A. The outline of the ω-scan is shown in FIG. 4. The ω-scan is a kind of out-of-plane measurement. In the ω-scan, the incident X-rays are irradiated from the X-ray source XR onto the surface of the first piezoelectric layer 3A. The direction d1 is the direction of the incident X-rays. The incident X-rays are diffracted at the (001) plane of the cubic crystal 1 contained in the first piezoelectric layer 3A and detected by the detector D as diffracted X-rays. When the reference point is defined as the position where the incident X-rays are irradiated on the surface of the first piezoelectric layer 3A, the direction d2 is the direction from the reference point to the detector D. That is, the direction d2 is the direction of the detector D with respect to the position where the incident X-rays are irradiated. 2θ 1 is the diffraction angle at which the intensity of the diffracted X-rays derived from the (001) plane of the cubic crystal 1 is maximum. 2θ 1 may be specified by the 2θ-θ method in the out-of-plane direction. ω is the angle between the surface of the first piezoelectric layer 3A and the direction d1 of the incident X-rays. That is, ω is the tilt angle of the surface of the first piezoelectric layer 3A with respect to the direction d1 of the incident X-rays. The unit of ω is degree (°). The ω-scan is a method of fixing the angle between the direction d1 and the direction d2 to the diffraction angle 2θ 1 and continuously measuring the intensity of the diffracted X-rays derived from the (001) plane of the cubic crystal 1 as ω changes. The rocking curve RC may be paraphrased as the tilt distribution of the intensity of the diffracted X-rays derived from the (001) plane of the cubic crystal 1.

[0054] FIG. 10 shows an example of the rocking curve RC of the diffracted X-rays of the (001) plane of the cubic crystal 1. The horizontal axis of the rocking curve RC is Δω. The vertical axis of the rocking curve RC is the intensity of the diffracted X-rays. For example, the unit of the intensity of the diffracted X-rays may be an arbitrary unit. The origin on the horizontal axis of the rocking curve RC corresponds to ω (that is, θ 1 ) at which the intensity of the diffracted X-rays derived from the (001) plane of the cubic crystal 1 is maximum. ω 0When defined as ω at which the intensity of the diffracted X-ray derived from the (001) plane of the cubic crystal 1 is maximum, the rocking curve RC is the distribution of the intensity of the diffracted X-ray in the range where ω is equal to or greater than (ω 0 -Δω) and equal to or less than (ω 0 +Δω). The incident X-ray may be a characteristic X-ray (for example, CuKα ray).

[0055] The intervals and orientation directions of the crystal planes of cubic crystal 1, cubic crystal 2, and lower crystal 6c may each be specified by inverse lattice space mapping. That is, cubic crystal 1, cubic crystal 2, and lower crystal 6c may be detected by the inverse lattice space map of the above X-ray diffraction pattern and distinguished from each other. The inverse lattice space map may be paraphrased as a distribution diagram of the intensity of diffracted X-rays in the inverse lattice space. For example, the inverse lattice space map may be obtained by measuring the intensity of diffracted X-rays of the piezoelectric thin film P along two or more scanning axes selected from the group consisting of the ω-axis, φ-axis, χ-axis, 2θ-axis, and 2θχ-axis. For example, the inverse lattice space map may be a two-dimensional map in a coordinate system composed of an orthogonal horizontal axis and vertical axis. The horizontal axis of the two-dimensional inverse lattice space map may indicate a value corresponding to the reciprocal of the lattice constant in the in-plane direction of the surface of the first piezoelectric layer 3A. For example, the horizontal axis of the inverse lattice space map may indicate a value corresponding to the reciprocal of the interval a of the (100) plane (that is, 1 / a). The vertical axis of the two-dimensional inverse lattice space map may indicate a value corresponding to the reciprocal of the lattice constant in the normal direction dn of the surface of the first piezoelectric layer 3A. For example, the vertical axis of the inverse lattice space map may indicate a value corresponding to the reciprocal of the interval c of the (001) plane (that is, 1 / c). The inverse lattice space map includes a plurality of spots. One spot corresponds to diffracted X-rays derived from one crystal plane of any of cubic crystal 1, cubic crystal 2, and lower crystal 6c. From the coordinates of one spot in the inverse lattice space map, the interval and orientation direction of one crystal plane of any of cubic crystal 1, cubic crystal 2, and lower crystal 6c may be specified. FIG. 11 is an example of an inverse lattice space map of the piezoelectric thin film P composed of the lower layer 6, the second piezoelectric layer 3B, and the first piezoelectric layer 3A. S3A-(204) in FIG. 11 is a spot corresponding to the (204) plane of cubic crystal 1 included in the first piezoelectric layer 3A. S3B-(204) is a spot corresponding to the (204) plane of cubic crystal 2 included in the second piezoelectric layer 3B. S6-(204) is a spot corresponding to the (204) plane of lower crystal 6c included in the lower layer 6. S3A-(004) is a spot corresponding to the (004) plane of cubic crystal 1 included in the first piezoelectric layer 3A. S3B-(004) is a spot corresponding to the (004) plane of cubic crystal 2 included in the second piezoelectric layer 3B.S6-(004) is a spot corresponding to the (004) plane of the lower crystal 6c contained in the lower layer 6.

[0056] The spacing aL between the (100) planes of the lower crystal 6c contained in the lower layer 6 may be 3.92 Å or more and 4.29 Å or less, or 3.93 Å or more and 4.24 Å or less. The spacing a1 between the (100) planes of the tetragonal crystal 1 contained in the first piezoelectric layer 3A may be 3.650 Å or more and 3.940 Å or less, or 3.73 Å or more and 3.92 Å or less. When aL and a1 are within the above ranges, the lattice mismatch rate Δa is easily controlled within the range of 3.0% or more and 12.1% or less.

[0057] As shown in FIGS. 1 and 3, the (001) plane of the lower crystal 6c (unit cell ucL) contained in the lower layer 6 may be oriented in the normal direction of the surface of the first piezoelectric layer 3A. When the (001) plane of the lower crystal 6c (unit cell ucL) is oriented in the normal direction of the surface of the first piezoelectric layer 3A, the lattice mismatch rate Δa is easily controlled within the range of 3.0% or more and 12.1% or less.

[0058] The lower crystal 6c contained in the lower layer 6 may contain at least one compound of strontium ruthenate (SrRuO 3 ), barium titanate (BaTiO 3 ), and titanium nitride (TiN). The lower crystal 6c contained in the lower layer 6 may consist of only one compound of strontium ruthenate, barium titanate, and titanium nitride. When the lower crystal 6c contained in the lower layer 6 contains at least one compound of strontium ruthenate, barium titanate, and titanium nitride, the lattice mismatch rate Δa is easily controlled within the range of 3.0% or more and 12.1% or less. The crystal structure of the lower crystal 6c made of strontium ruthenate is a perovskite-type structure. The spacing aL between the (100) planes of the lower crystal 6c made of strontium ruthenate is about 3.93 Å. The spacing a1 between the (100) planes of a conventional thin film (piezoelectric layer) made of lead zirconate titanate (PZT) is larger than 4.00 Å. Conventional bismuth ferrite (BiFeO 3) The interval a1 between the (100) planes of the thin film (piezoelectric layer) composed of is about 3.96 Å. Therefore, when the lower layer 6 is made of strontium ruthenate and the first piezoelectric layer is made of lead titanate zirconate or bismuth ferrite, the lattice mismatch rate Δa is a negative value. When the lattice mismatch rate Δa is a negative value, the relative permittivity ε of the piezoelectric thin film P r is relatively low, but the full width at half maximum FWHM is small, and it is difficult for the piezoelectric thin film P to have a large piezoelectric performance index. The lower layer 6 containing strontium ruthenate has conductivity. When the lower layer 6 has conductivity, the lower layer 6 may function as the first electrode layer 7, and the piezoelectric thin film element may not include a first electrode layer 7 different from the lower layer 6. The crystal structure of the lower crystal 6c made of barium titanate is a perovskite structure. The interval aL between the (100) planes of the lower crystal 6c made of barium titanate is about 3.99 Å. The crystal structure of the lower crystal 6c made of titanium nitride is a sodium chloride structure (face-centered cubic lattice structure). The interval aL between the (100) planes of the lower crystal 6c made of titanium nitride is about 4.24 Å. The piezoelectric thin film P in which the lower layer 6 is composed of crystals of at least one compound of barium titanate and titanium nitride is more likely to have a larger piezoelectric performance index than the piezoelectric thin film P in which the lower layer 6 is composed of crystals of strontium ruthenate.

[0059] The c2 / a2 of the tetragonal crystal 2 included in the second piezoelectric layer 3B may be smaller than the c1 / a1 of the tetragonal crystal 1 included in the first piezoelectric layer 3A. That is, the anisotropy of the tetragonal crystal 2 may be lower than the anisotropy of the tetragonal crystal 1.

[0060] When c1 / a1 is larger than c2 / a2, the relative permittivity of cubic crystal 1 is lower than that of cubic crystal 2. However, since c1 / a1 is larger than c2 / a2, the crystal structure of cubic crystal 1 is stronger than that of cubic crystal 2, and the atoms in cubic crystal 1 are more difficult to move than the atoms in cubic crystal 2. Therefore, the polarization reversal of cubic crystal 1 is less likely to occur than that of cubic crystal 2, and the piezoelectricity of cubic crystal 1 itself is inferior to that of cubic crystal 2 itself. In other words, when c2 / a2 is smaller than c1 / a1, the relative permittivity of cubic crystal 2 is higher than that of cubic crystal 1, but the crystal structure of cubic crystal 2 is softer than that of cubic crystal 1, and the atoms in cubic crystal 2 are easier to move than the atoms in cubic crystal 1. Therefore, the polarization reversal of cubic crystal 2 is more likely to occur than that of cubic crystal 1. When c2 / a2 is smaller than c1 / a1 and an electric field is applied to the piezoelectric thin film P, the polarization reversal of cubic crystal 2 in the second piezoelectric layer 3B is more likely to occur earlier than the polarization reversal of cubic crystal 1 in the first piezoelectric layer 3A. Due to the polarization reversal of cubic crystal 2 preceding the polarization reversal of cubic crystal 1, the crystal structure of cubic crystal 1 becomes unstable at the interface between the first piezoelectric layer 3A and the second piezoelectric layer 3B. In other words, due to the polarization reversal of cubic crystal 2, the polarization of cubic crystal 1 is likely to fluctuate at the interface between cubic crystal 1 and cubic crystal 2. For example, due to the polarization reversal of cubic crystal 2 in the second piezoelectric layer 3B, at the interface between the first piezoelectric layer 3A and the second piezoelectric layer 3B, the charges on the surface of the second piezoelectric layer 3B repel the charges on the surface of the first piezoelectric layer 3A, causing the polarization of cubic crystal 1 to fluctuate. Due to the mechanism as described above, the polarization reversal of cubic crystal 2 induces the polarization reversal of cubic crystal 1. That is, by disposing the second piezoelectric layer 3B as a buffer layer that promotes the polarization reversal of the first piezoelectric layer 3A between the lower layer 6 and the first piezoelectric layer 3A, polarization reversal is likely to occur in the entire piezoelectric thin film P. As a result, the piezoelectricity of the entire piezoelectric thin film P is superior to and larger than the piezoelectricity of cubic crystal 1 itself, with a large d 33,f and a low ε r being compatible, and the piezoelectric thin film P is likely to have a large piezoelectric performance index. However, the above mechanism regarding c1 / a1 and c2 / a2 is a hypothesis, and the technical scope of the present invention is not limited by the above mechanism.

[0061] In contrast to the piezoelectric thin film P, in the bulk of the piezoelectric body, distortion of the crystal structure due to stress hardly occurs. Therefore, most of the perovskite-type oxides constituting the bulk of the piezoelectric body are cubic, and the bulk of the piezoelectric body tends to have less piezoelectricity due to the tetragonality of the perovskite-type oxide compared to the piezoelectric thin film P.

[0062] c1 / a1 of the tetragonal crystal 1 may be 1.050 or more and 1.250 or less, or 1.063 or more and 1.249 or less. When c1 / a1 is 1.050 or more, the relative permittivity of each of the first piezoelectric layer 3A containing the tetragonal crystal 1 and the piezoelectric thin film P tends to decrease, and the piezoelectric performance index of the piezoelectric thin film P tends to increase. When c1 / a1 is 1.250 or less, polarization reversal of the tetragonal crystal 1 easily occurs, and the piezoelectric performance index of the piezoelectric thin film P tends to increase. For example, c1 may be 3.980 Å or more and 4.750 Å or less.

[0063] c2 / a2 may be 1.010 or more and 1.110 or less, or 1.014 or more and 1.108 or less. Due to c2 / a2 being within the above range, polarization reversal of the tetragonal crystal 2 more easily occurs than polarization reversal of the tetragonal crystal 1, polarization reversal of the tetragonal crystal 2 easily induces polarization reversal of the tetragonal crystal 1, and the piezoelectric thin film P tends to have a large piezoelectric performance index. When c2 / a2 is outside the above range, the relative permittivity of the tetragonal crystal 2 tends to be too high, or the piezoelectricity of the tetragonal crystal 2 itself tends to deteriorate. For example, c2 may be 3.920 Å or more and 4.390 Å or less. For example, a2 may be 3.890 Å or more and 3.950 Å or less.

[0064] By observing a cross-section of the piezoelectric thin film P parallel to the thickness direction of the piezoelectric thin film P with atomic-level resolution using a scanning transmission electron microscope (STEM), the magnitude relationships of cL, c1, and c2, as well as the magnitude relationships of aL, a1, and a2, may be specified. To specify the specific values of c1 and c2 with high precision, the peak P1 of the diffracted X-ray of the (001) plane of cubic crystal 1 and the peak 2 of the diffracted X-ray of the (001) plane of cubic crystal 2 may be measured by out-of-plane measurement (2θ-θ method) on the surface of the piezoelectric thin film P. One measured X-ray diffraction pattern includes both the peak P1 and the peak 2. The diffraction angle 2θ of the peak P1 of the diffracted X-ray of the (001) plane of cubic crystal 1 1 is close to the diffraction angle 2θ of the peak P2 of the diffracted X-ray of the (001) plane of cubic crystal 2 2 When the peaks P1 and P2 overlap and a peak P3 is measured, the peak P1 may be approximated by a Gaussian function g1, the peak P2 may be approximated by another Gaussian function g2, and curve fitting of g1 + g2 and the peak P3 may be performed. After curve fitting, g1 may be regarded as P1, and after curve fitting, g2 may be regarded as P2. To specify the specific values of a1 and a2 with high precision, the peak P1' of the diffracted X-ray of the (100) plane of cubic crystal 1 and the peak P2' of the diffracted X-ray of the (100) plane of cubic crystal 2 may be measured by in-plane measurement (2θ-θ method) on the surface of the piezoelectric thin film P. One measured X-ray diffraction pattern includes both the peak P1' and the peak 2'. The diffraction angle 2θ of the peak P1' of the diffracted X-ray of the (100) plane of cubic crystal 1 1 ' is close to the diffraction angle 2θ of the peak P2' of the diffracted X-ray of the (100) plane of cubic crystal 2 2 ' When the peaks P1' and P2' overlap and a peak P3' is measured, the peak P1' may be approximated by a Gaussian function G1, the peak P2' may be approximated by another Gaussian function G2, and curve fitting of G1 + G2 and the peak P3' may be performed. After curve fitting, G1 may be regarded as P1', and after curve fitting, G2 may be regarded as P2'.

[0065] The peak intensity (maximum intensity) of the diffracted X-ray of the (001) plane of cubic crystal 1 is I 1 is. The peak intensity (maximum intensity) of the diffracted X-ray of the (001) plane of cubic crystal 2 is I 2 is. I 1 / (I1 +I 2 ) may be 0.90 or more and less than 1.00, or 0.91 or more and 0.99 or less. I 1 / (I 1 +I 2 ) is within the above range, a large piezoelectric strain constant (d 33,f ) and a low relative permittivity (ε r ) are likely to coexist, and the piezoelectric thin film P is likely to have a large piezoelectric performance index. I 1 And I 2 Each unit may be, for example, cps (counts per second). I 1 And I 2 may be measured by out-of-plane measurement on the surface of the first piezoelectric layer 3A. I 1 And I 2 So that each of them is at least three digits or more higher than the background intensity, I 1 And I 2 The measurement conditions for each may be set.

[0066] I 1 may be proportional to the total area of the (001) plane of the tetragonal crystal 1 oriented in the normal direction dn of the surface of the first piezoelectric layer 3A, I 2 may be proportional to the total area of the (001) plane of the tetragonal crystal 2 oriented in the normal direction dn of the surface of the first piezoelectric layer 3A. In other words, I 1 may be proportional to the amount of the tetragonal crystal 1 contained in the piezoelectric thin film P, I 2 may be proportional to the amount of the tetragonal crystal 2 contained in the piezoelectric thin film P. Therefore, I 1 / (I 1 +I 2 ) may be the abundance ratio of the tetragonal crystal 1 to the total amount of the tetragonal crystal 1 and the tetragonal crystal 2. That is, the abundance ratio of the tetragonal crystal 1 to the total amount of the tetragonal crystal 1 and the tetragonal crystal 2 may be 90% or more and less than 100%.

[0067] The degree of orientation of the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2 may be quantified by the degree of orientation. The higher the degree of orientation of the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2, the more likely the piezoelectric thin film P has a large piezoelectric performance index. The degree of orientation of each crystal plane may be calculated based on the peak of the diffracted X-ray derived from each crystal plane. The peak of the diffracted X-ray derived from each crystal plane may be measured by the out-of-plane measurement on the surface of the first piezoelectric layer 3A. The degree of orientation of the (001) plane of the tetragonal crystal 1 in the normal direction dn of the surface of the first piezoelectric layer 3A may be expressed as 100×I 1 / ΣI 1(hkl) ΣI 1(hkl) is the sum of the peak intensities of the diffracted X-rays of each crystal plane of the tetragonal crystal 1 measured in the out-of-plane direction of the surface of the first piezoelectric layer 3A. ΣI 1(hkl) For example, may be 1(001) +I 1(110) +I 1(111) I 1(001) is the above-mentioned I 1 That is, I 1(001) is the peak intensity (maximum intensity) of the diffracted X-ray of the (001) plane of the tetragonal crystal 1 measured in the out-of-plane direction of the surface of the first piezoelectric layer 3A. I 1(110) is the peak intensity (maximum intensity) of the diffracted X-ray of the (110) plane of the tetragonal crystal 1 measured in the out-of-plane direction of the surface of the first piezoelectric layer 3A. I 1(111) is the peak intensity (maximum intensity) of the diffracted X-ray of the (111) plane of the tetragonal crystal 1 measured in the out-of-plane direction of the surface of the first piezoelectric layer 3A. The degree of orientation of the (001) plane of the tetragonal crystal 2 may be expressed as 100×I 2 / ΣI 2(hkl) ΣI 2(hkl) is the sum of the peak intensities of the diffracted X-rays of each crystal plane of the tetragonal crystal 2 measured in the out-of-plane direction of the surface of the first piezoelectric layer 3A. ΣI 2(hkl) For example, may be 2(001) +I 2(110) +I 2(111) I 2(001) is the above-mentioned I 2 That is, I2(001) is the peak intensity (maximum intensity) of the diffracted X-ray of the (001) plane of the tetragonal crystal 2 measured in the out-of-plane direction of the surface of the first piezoelectric layer 3A. I 2(110) is the peak intensity (maximum intensity) of the diffracted X-ray of the (110) plane of the tetragonal crystal 2 measured in the out-of-plane direction of the surface of the first piezoelectric layer 3A. I 2(111) is the peak intensity (maximum intensity) of the diffracted X-ray of the (111) plane of the tetragonal crystal 2 measured in the out-of-plane direction of the surface of the first piezoelectric layer 3A. The degree of orientation of the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2 may be quantified by the orientation degree F based on the Lotgering method. Even when the orientation degree is calculated by any of the above methods, the orientation degree of the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2 may be 70% or more and 100% or less, preferably 80% or more and 100% or less, more preferably 90% or more and 100% or less. In other words, the (001) plane of the tetragonal crystal 1 may be oriented in the normal direction dn of the surface of the first piezoelectric layer 3A, preferentially to other crystal planes of the tetragonal crystal 1, and the (001) plane of the tetragonal crystal 2 may also be oriented in the normal direction dn of the surface of the first piezoelectric layer 3A, preferentially to other crystal planes of the tetragonal crystal 2.

[0068] One or both of the tetragonal crystal 1 and the tetragonal crystal 2 may contain Fe 2+ When one or both of the tetragonal crystal 1 and the tetragonal crystal 2 contain Fe 2+ the piezoelectric thin film P is likely to have a large piezoelectric performance index. BiFeO 3 -(Bi,K)TiO 3 When the piezoelectric thin film of the BiFeO 33,f -(Bi,K)TiO system has a composition near the Morphotropic Phase Boundary (MPB) between the tetragonal crystal and the rhombohedral crystal, the piezoelectricity (d 0 ε rSince [it] also increases, it is difficult to improve the piezoelectric performance index. In order to suppress the increase in dielectric constant, it is desirable to improve the piezoelectricity (ferroelectricity) of the piezoelectric thin film by configuring the piezoelectric thin film only from tetragonal crystals. The tetragonality of the piezoelectric thin film is realized by epitaxial stress (compressive stress due to lattice mismatch). This is because the piezoelectric thin film is compressed in the directions parallel to the surface of the piezoelectric thin film (that is, the a-axis direction and the b-axis direction) by the epitaxial stress parallel to the surface of the piezoelectric thin film, causing the piezoelectric thin film to be distorted. However, the thicker the piezoelectric thin film, the more difficult it is to improve the tetragonality of the piezoelectric thin film only by epitaxial stress. This is because the thicker the piezoelectric thin film, the more difficult it is to distort the entire piezoelectric thin film by epitaxial stress. Also, since the lattice mismatch rate Δa is a positive value (3.0% or more and 12.1% or less), tensile stress rather than compressive stress is likely to act on the first piezoelectric layer 3A and the second piezoelectric layer 3B. Therefore, even when the piezoelectric thin film is thick to the extent that the epitaxial stress generated in the piezoelectric thin film weakens and compressive stress hardly acts on the piezoelectric thin film, it is desirable to stabilize the tetragonal structure of the piezoelectric thin film. Therefore, in one or both of the tetragonal crystal 1 and the tetragonal crystal 2, the electronic configuration of the element (ion) located at the B site of the perovskite-type oxide is such that it is the same as the d6 electronic configuration of Co 3 constituting 3+ , the ions at the B site may be replaced with Fe 2+ . As a result, even when the piezoelectric thin film P is thick to the extent that the epitaxial stress generated in the piezoelectric thin film P weakens, the tetragonality of the piezoelectric thin film P is improved. In other words, even when the piezoelectric thin film P is thick to the extent that the epitaxial stress generated in the piezoelectric thin film P weakens, the first piezoelectric layer 3A is likely to contain the tetragonal crystal 1, and the second piezoelectric layer 3B is likely to contain the tetragonal crystal 2. In the case of a composition system near the MPB where it is expected that rhombohedral crystals are formed in the bulk of the piezoelectric material, even though rotation (rotation around the c-axis) of the BO 2+ octahedron (or BO 6 ) in the tetragonal crystal substituted with Fe 5 at a part of the B site (or BO 2+In the perovskite oxide replaced by , it is difficult for the MPB to exist, and the polarization rotation in which the direction of the c-axis of the tetragonal crystal changes hardly occurs. Due to the above mechanism, one or both of the tetragonal crystal 1 and the tetragonal crystal 2 contain Fe 2+ When included, a large piezoelectric strain constant (d 33,f ) and a low relative permittivity (ε r ) are likely to coexist, and the piezoelectric performance index is likely to increase. However, the above mechanism regarding Fe 2+ is a hypothesis, and the technical scope of the present invention is not limited by the above mechanism regarding Fe 2+ .

[0069] In contrast to the piezoelectric thin film P, in the bulk of the piezoelectric body, it is difficult for the strain of the crystal structure caused by stress to occur. Therefore, most of the perovskite-type oxides constituting the bulk of the piezoelectric body are cubic crystals, and the bulk of the piezoelectric body tends to have less piezoelectricity due to the tetragonality of the perovskite-type oxide compared to the piezoelectric thin film P.

[0070] The thicknesses of the crystalline substrate 8, the intermediate layer 5, the first electrode layer 7, the lower layer 6, the second piezoelectric layer 3B, the first piezoelectric layer 3A, and the second electrode layer 4 may each be uniform.

[0071] The thickness TL of the lower layer 6 in the normal direction dn of the surface of the first piezoelectric layer 3A may be 10 nm or more and 350 nm or less. When the thickness TL of the lower layer 6 is within the above range, the lattice mismatch rate Δa is easily controlled within the range of 3.0% or more and 12.1% or less, and the full width at half maximum of the rocking curve RC is easily controlled within the range of 1.9° or more and 5.5° or less.

[0072] The thickness T1 of the first piezoelectric layer 3A in the normal direction dn of the surface of the first piezoelectric layer may be greater than the thickness T2 of the second piezoelectric layer 3B in the normal direction dn of the surface of the first piezoelectric layer 3A. The thickness Tp of the piezoelectric thin film P may be equal to the sum of the thickness TL of the lower layer 6, the thickness T1 of the first piezoelectric layer 3A, and the thickness T2 of the second piezoelectric layer 3B. The thickness Tp of the piezoelectric thin film P may be 510 nm or more and 5350 nm or less, or 590 nm or more and 5100 nm or less. The thickness T1 of the first piezoelectric layer 3A may be 490 nm or more and 4700 nm or less, or 500 nm or more and 4920 nm or less. The thickness T2 of the second piezoelectric layer 3B may be 10 nm or more and 300 nm or less, or 10 nm or more and 290 nm or less. When the thickness T2 of the second piezoelectric layer 3B is 10 nm or more, the polarization reversal of the tetragonal crystal 2 in the second piezoelectric layer 3B easily induces the polarization reversal of the tetragonal crystal 1 in the first piezoelectric layer 3A. As a result, the piezoelectric thin film P easily has a large piezoelectric performance index. When the thickness T2 of the second piezoelectric layer 3B is 300 nm or less, the relative permittivity of the piezoelectric thin film P easily decreases, and the piezoelectric performance index of the piezoelectric thin film P easily increases. When the thickness Tp of the piezoelectric thin film P is 510 nm or more, even when the piezoelectric thin film P is thick, ions located at the B site of the perovskite-type oxide are Fe 2+ substituted by, and the piezoelectric thin film P easily has a large piezoelectric performance index. By adjusting the thickness Tp of the piezoelectric thin film P to 5350 nm or less, the tetragonal crystal 1 and the tetragonal crystal 2 are easily formed regardless of the epitaxial stress, and the piezoelectric thin film P easily has a large piezoelectric performance index.

[0073] TL, T1, T2, and Tp are not limited to the above ranges. The measurement methods of TL, T1, T2, and Tp are not limited. For example, the thickness Tp of the piezoelectric thin film P may be measured by a scanning electron microscope (SEM) in a cross-section of the piezoelectric thin film P parallel to the normal direction dn of the surface of the first piezoelectric layer 3A. Based on the difference in composition or the magnitude relationship of cL / aL, c1 / a1, and c2 / a2, the lower layer 6, the first piezoelectric layer 3A, and the second piezoelectric layer 3B may be identified in the cross-section of the piezoelectric thin film P. TL, T1, and T2 may be measured by SEM in the cross-section of the piezoelectric thin film P.

[0074] The cubic crystal 1 may be represented by the following Chemical Formula 1. The following Chemical Formula 1 is substantially the same as the following Chemical Formula 1a. x1(Bi 1-α E A α )E B O 3 -y1BiFeO 3 -z1Bi(Fe 0.5 Ti 0.5 )O 3 (1) (Bi x1(1-α)+y1+z1 E A x1α )(E B x1 Fe y1+0.5z1 Ti 0.5z1 )O 3±δ (1a)

[0075] x1 + y1 + z1 in the above Chemical Formula 1 may be 1.00. E in the above Chemical Formula 1 A is the element described above. E in the above Chemical Formula 1 B is the element described above.

[0076] Bi constituting (Bi 1-α E A α )E B O 3 is trivalent Bi (Bi 3+ ) or pentavalent Bi (Bi 5+ ). The total valence (ionic valence) of E 1-α E A α )E B O 3 constituting is represented as V A . The total valence (ionic valence) of E A constituting (Bi 1-α E A α )E B O 3 is represented as V B . In Chemical Formula 1, (Bi B E 1-α E A α )E B O 3Bi and E that make up A and E B The sum of the valences is 3(1 - α)+V A α + V B or 5(1 - α)+V A α + V B and is expressed as. 3(1 - α)+V A α + V B or 5(1 - α)+V A α + V B may be +6 to balance with the sum of the valences (ionic valences) of O (-6). 3(1 - α)+V A α, or 5(1 - α)+V A α may be +3. V B may be +3. Element E in the above Chemical Formula 1 B Two elements corresponding to B1 element E B2 and element E B1 The valence (ionic valence) of E is expressed as V B1 The valence (ionic valence) of E is expressed as V B2 The valence (ionic valence) of E is expressed as V B2 The sum of the valences (ionic valences) of E B V B is expressed as (1 - β)V B1 +βV B2 and is expressed as. (1 - β)V B1 +βV B2 may be +3. x1(Bi 1-α E A α )(E B1 1-β E B2 β )O 3 -y1BiFeO 3 -z1Bi(Fe 0.5 Ti 0.5 )O 3 (1’)

[0077] Bi in the above Chemical Formula 1a x1(1-α)+y1+z1 E A x1αcorresponds to the element located at the A site of the perovskite structure. E in Chemical Formula 1a B x1 Fe y1+0.5z1 Ti 0.5z1 corresponds to the element located at the B site of the perovskite structure.

[0078] The valence of Fe that constitutes y1BiFeO in Chemical Formula 1 above is trivalent, but the valence of Fe that constitutes z1Bi(Fe 3 Ti 0.5 Ti 0.5 )O 3 above is divalent. Therefore, by adjusting the composition of the raw material of the first piezoelectric layer 3A so that the molar ratio of each of Bi, E A E B Fe, and Ti in the entire raw material of the first piezoelectric layer 3A matches the molar ratio of Bi, E A E B Fe, and Ti in Chemical Formula 1 above, tetragonal crystal 1 can contain Fe 2+ .

[0079] x1 in Chemical Formula 1 above may be 0.10 or more and 0.90 or less, 0.10 or more and 0.85 or less, or 0.15 or more and 0.85 or less. When x1 is 0.10 or more and 0.90 or less, tetragonal crystal 1 is likely to have the above crystal orientation, c1 / a1 is likely to fall within the above range, the lattice mismatch rate Δa is likely to fall within the above range, and the full width at half maximum FWHM is likely to fall within the above range.

[0080] y1 in Chemical Formula 1 above may be 0.05 or more and 0.85 or less, or 0.05 or more and 0.80 or less. When y1 is 0.05 or more and 0.85 or less, tetragonal crystal 1 is likely to have the above crystal orientation, c1 / a1 is likely to fall within the above range, the lattice mismatch rate Δa is likely to fall within the above range, and the full width at half maximum FWHM is likely to fall within the above range.

[0081] In Chemical Formula 1 above, z1 may be 0.05 or more and 0.85 or less, or 0.05 or more and 0.80 or less. When z1 is 0.05 or more and 0.85 or less, the cubic crystal 1 is likely to have the above crystal orientation, c1 / a1 is likely to fall within the above range, the lattice mismatch rate Δa is likely to fall within the above range, and the full width at half maximum FWHM is likely to fall within the above range.

[0082] In Chemical Formula 1 above, α may be 0.00 or more and less than 1.00. Since the cubic crystal 1 is likely to have the above crystal orientation, c1 / a1 is likely to fall within the above range, the lattice mismatch rate Δa is likely to fall within the above range, and the full width at half maximum FWHM is likely to fall within the above range, α may be 0.50. As described above, in Chemical Formula 1' above, β may be 0.00 or more and 1.00 or less, or greater than 0.00 and less than 1.00. Since the cubic crystal 1 is likely to have the above crystal orientation, c1 / a1 is likely to fall within the above range, the lattice mismatch rate Δa is likely to fall within the above range, and the full width at half maximum FWHM is likely to fall within the above range, β may be 0.50.

[0083] In Chemical Formula 1a above, δ may be 0 or more. As long as the crystal structure (perovskite structure) of the cubic crystal 1 is maintained, δ may be a value other than 0. For example, δ may be greater than 0 and 1.0 or less. δ may be calculated, for example, from the valences of the respective ions located at each of the A-site and B-site in the cubic crystal 1. The valence of each ion may be measured by X-ray photoelectron spectroscopy (XPS).

[0084] The total number of moles of Bi and E contained in the cubic crystal 1 A may be represented as [A], 1 and the total number of moles of Fe, Ti and E contained in the cubic crystal 1 B may be represented as [B], 1 [A] 1 / [B] 1 may be 1.0. As long as the crystal structure (perovskite structure) of the cubic crystal 1 is maintained, [A] 1 / [B] 1 may be a value other than 1.0. That is, [A] 1 / [B] 1 may be less than 1.0, [A] 1 / [B] 1 may be greater than 1.0.

[0085] The cubic crystal 2 may be represented by the following chemical formula 2. The following chemical formula 2 is substantially the same as the following chemical formula 2a. x2(Bi 1-α E A α )E B O 3 -y2BiFeO 3 -z2Bi(Fe 0.5 Ti 0.5 )O 3 (2) (Bi x2(1-α)+y2+z2 E A x2α )(E B x2 Fe y2+0.5z2 Ti 0.5z2 )O 3±δ (2a)

[0086] x2 + y2 + z2 in the above chemical formula 2 may be 1.00. E in the above chemical formula 2 A is the element described above. E in the above chemical formula 2 B is the element described above. E in the above chemical formula 2 A is the same as E in the above chemical formula 1 A and may be different. E in the above chemical formula 2 B is the same as E in the above chemical formula 1 B and may be different. The valence of each element in the above chemical formula 2 may be the same as the valence of each element in the above chemical formula 1. The element E in the above chemical formula 2 B corresponding to two kinds of elements is represented as element E B1 and element E B2 In this case, the above chemical formula 2 is substantially the same as the following chemical formula 2'. β in the following chemical formula 2' may be 0.00 or more and 1.00 or less. x2(Bi 1-α E A α )(E B1 1-β E B2β )O 3 -y2BiFeO 3 -z2Bi(Fe 0.5 Ti 0.5 )O 3 (2’)

[0087] Bi in the above chemical formula 2a x2(1-α)+y2+z2 E A x2α corresponds to the element located at the A site of the perovskite structure. E in chemical formula 2a B x2 Fe y2+0.5z2 Ti 0.5z2 corresponds to the element located at the B site of the perovskite structure.

[0088] The Fe valence number constituting y2BiFeO in the above chemical formula 2 3 is trivalent, but the Fe valence number constituting z2Bi(Fe 0.5 Ti 0.5 )O 3 is divalent. Therefore, by adjusting the composition of the raw material of the second piezoelectric layer 3B so that the molar ratios of Bi, E A E B Fe, and Ti respectively are consistent with the molar ratios of Bi, E A E B Fe, and Ti in the above chemical formula 2, tetragonal crystal 2 can contain Fe 2+ .

[0089] x2 in the above chemical formula 2 may be 0.10 or more and 0.85 or less, 0.10 or more and 0.80 or less, or 0.10 or more and 0.70 or less. When x2 is 0.10 or more and 0.85 or less, tetragonal crystal 2 is likely to have the above crystal orientation, and c2 / a2 is likely to fall within the above range.

[0090] y2 in the above chemical formula 2 may be 0.10 or more and 0.85 or less. When y2 is 0.10 or more and 0.85 or less, tetragonal crystal 2 is likely to have the above crystal orientation, and c2 / a2 is likely to fall within the above range.

[0091] In Chemical Formula 2 above, z2 may be 0.05 or more and 0.80 or less. When z2 is 0.05 or more and 0.80 or less, the tetragonal crystal 2 is likely to have the above crystal orientation, and c2 / a2 is likely to fall within the above range.

[0092] In Chemical Formula 2 above, α may be 0.00 or more and less than 1.00. Since the tetragonal crystal 2 is likely to have the above crystal orientation and c2 / a2 is likely to fall within the above range, α may be 0.50. As described above, in Chemical Formula 2', β may be 0.00 or more and 1.00 or less, or greater than 0.00 and less than 1.00. Since the tetragonal crystal 2 is likely to have the above crystal orientation and c2 / a2 is likely to fall within the above range, β may be 0.50.

[0093] In Chemical Formula 2a above, δ may be 0 or more. As long as the crystal structure (perovskite structure) of the tetragonal crystal 2 is maintained, δ may be a value other than 0. For example, δ may be greater than 0 and 1.0 or less. δ may be calculated from the valence of each ion located at each of the A-site and B-site in the tetragonal crystal 2, for example. The valence of each ion may be measured by the XPS method.

[0094] Bi and E contained in the tetragonal crystal 2 A The total value of the number of moles may be represented as [A] 2 and the total value of the number of moles of Fe, Ti, and E contained in the tetragonal crystal 2 B may be represented as [B] 2 and [A] 2 / [B] 2 may be 1.0. As long as the crystal structure (perovskite structure) of the tetragonal crystal 2 is maintained, [A] 2 / [B] 2 may be a value other than 1.0. That is, [A] 2 / [B] 2 may be less than 1.0, and [A] 2 / [B] 2 may also be greater than 1.0.

[0095] The tetragonal crystal 1 may be represented by the following Chemical Formula 1w. E in the following Chemical Formula 1w Ais the element described above. E in the following Chemical Formula 1w B is the element described above. w1 in the following Chemical Formula 1w may be 0.30 or more and 0.80 or less. α in the following Chemical Formula 1w may be 0.00 or more and less than 1.00. (1 - w1)Bi 1-α E A α E B O 3 -w1BiFeO 3 (1w)

[0096] The tetragonal crystal 2 may be represented by the following Chemical Formula 2w. E in the following Chemical Formula 2w A is the element described above. E in the following Chemical Formula 2w B is the element described above. w2 in the following Chemical Formula 2w may be 0.30 or more and 0.80 or less. α in the following Chemical Formula 2w may be 0.00 or more and less than 1.00. E in the following Chemical Formula 2w A may be the same as E in the above Chemical Formula 1w A or may be different. E in the following Chemical Formula 2w B may be the same as E in the above Chemical Formula 1w B or may be different. (1 - w2)Bi 1-α E A α E B O 3 -w2BiFeO 3 (2w)

[0097] The piezoelectric thin film P may be an epitaxial film. That is, the piezoelectric thin film P may be formed by epitaxial growth. By epitaxial growth, it is easy to form a piezoelectric thin film P excellent in anisotropy and crystal orientation.

[0098] The surface area of the first piezoelectric layer 3A is, for example, 1 μm 2 or more and 500 mm 2 or less. The areas of the crystalline substrate 8, the intermediate layer 5, the first electrode layer 7, the lower layer 6, the second piezoelectric layer 3B, and the second electrode layer 4 may be the same as the area of the first piezoelectric layer 3A.

[0099] The composition of the piezoelectric thin film P may be analyzed, for example, by fluorescence X-ray analysis (XRF) method, inductively coupled plasma (ICP) optical emission spectrometry, and X-ray photoelectron spectroscopy (XPS) method. As a method for specifying the composition and thickness of each of the first piezoelectric layer 3A and the second piezoelectric layer 3B, the composition of the piezoelectric thin film P may be analyzed along the thickness direction of the piezoelectric thin film P by the XPS method. For example, by ion milling or sputtering on the surface of the piezoelectric thin film P, while uniformly reducing the thickness Tp of the piezoelectric thin film P, the composition of the surface of the piezoelectric thin film P may be continuously measured by the XPS method. The composition of the cross-section of the piezoelectric thin film P may also be analyzed along the thickness direction of the piezoelectric thin film P. For the compositional analysis of the cross-section of the piezoelectric thin film P along the thickness direction, an energy dispersive X-ray analysis (EDS) device provided in a scanning electron microscope (SEM) or a scanning transmission electron microscope (STEM) may be used. The crystal structure and crystal orientation of each of the first piezoelectric layer 3A and the second piezoelectric layer 3B may be specified by the X-ray diffraction (XRD) method described above. The crystal structure and crystal orientation of each of the lower layer 6, the first piezoelectric layer 3A, and the second piezoelectric layer 3B described above may be the crystal structure and crystal orientation at room temperature.

[0100] When the piezoelectric thin film P is composed of the lower layer 6 and the first piezoelectric layer 3A directly overlapping the lower layer 6, the first piezoelectric layer 3A is directly formed on the surface of the lower layer 6 by the first film formation process. When the piezoelectric thin film P is composed of the lower layer 6, the second piezoelectric layer 3B directly overlapping the lower layer 6, and the first piezoelectric layer 3A directly overlapping the second piezoelectric layer 3B, the second piezoelectric layer 3B is directly formed on the surface of the lower layer 6 by the second film formation process, and the first piezoelectric layer 3A is directly formed on the surface of the second piezoelectric layer 3B by the first film formation process following the second film formation process. The method for forming the lower layer 6 may be a sputtering method, a vacuum evaporation method, a printing method, a spin coating method, or a sol-gel method.

[0101] In the first film formation step, a first piezoelectric layer 3A is formed by a pulsed-laser deposition (PLD) method using a first target. The first target is a raw material for the first piezoelectric layer 3A. The first target may be composed of all the elements common to the first piezoelectric layer 3A (tetragonal crystal 1). The composition of the first target may be adjusted so that the molar ratio of each element constituting the first target matches the molar ratio of each element constituting the first piezoelectric layer 3A (tetragonal crystal 1). For example, the molar ratio of each element constituting the first target may match the molar ratio of each element constituting the above chemical formula 1 or 1'.

[0102] In the second film formation step, a second piezoelectric layer 3B is directly formed on the surface of the first piezoelectric layer 3A by a PLD method using a second target. The second target is a raw material for the second piezoelectric layer 3B. The second target may be composed of all the elements common to the second piezoelectric layer 3B (tetragonal crystal 2). The composition of the second target may be adjusted so that the molar ratio of each element constituting the second target matches the molar ratio of each element constituting the second piezoelectric layer 3B (tetragonal crystal 2). For example, the molar ratio of each element constituting the second target may match the molar ratio of each element constituting the above chemical formula 2 or 2'.

[0103] In the PLD method, by irradiating a pulsed laser beam (for example, an excimer laser) onto the target, the elements constituting the target are turned into plasma and evaporated. According to the PLD method, each element constituting the target can be turned into plasma uniformly in an instant. As a result, the molar ratio of each element in each piezoelectric layer is likely to be substantially the same as the molar ratio of each element in each target, and segregation of elements in each piezoelectric layer is likely to be suppressed. Also, according to the PLD method, each piezoelectric layer is likely to grow epitaxially, and each piezoelectric layer that is dense at the atomic level is likely to be formed. In the PLD method, by changing the number of pulses (repetition frequency) of the pulsed laser beam, the growth rate of each piezoelectric layer, the anisotropy of the tetragonal crystal constituting each piezoelectric layer, and the crystal orientation can be controlled. As the repetition frequency of the pulsed laser beam decreases, the growth rate of each piezoelectric layer decreases, and the anisotropy of the tetragonal crystal constituting each piezoelectric layer and the crystal orientation increase.

[0104] The repetition frequency f1 of the pulsed laser light in the first film formation step is smaller than the repetition frequency f2 of the pulsed laser light in the second film formation step. Due to f1 being smaller than f2, it is possible to form a piezoelectric thin film P in which c1 / a1 of the tetragonal crystal 1 is larger than c2 / a2 of the tetragonal crystal 2. The repetition frequency f1 of the pulsed laser light in the first film formation step may be 10 Hz. By adjusting f1 to 10 Hz, it is easy to control c1 / a1 of the tetragonal crystal 1 contained in the first piezoelectric layer 3A within the range of 1.050 or more and 1.250 or less. The repetition frequency f2 of the pulsed laser light in the second film formation step may be 20 Hz. By adjusting f2 to 20 Hz, it is easy to control c2 / a2 of the tetragonal crystal 2 in the second piezoelectric layer 3B within the range of 1.010 or more and 1.050 or less.

[0105] The first target and the second target may be individually manufactured by the following method.

[0106] As starting materials for each target, for example, oxides of Bi, E A 、E B 、Fe, and Ti may each be used. As starting materials, instead of oxides, substances that become oxides by firing, such as carbonates or oxalates, may also be used. After these starting materials are sufficiently dried at 100 °C or higher, Bi, E A 、E B 、Fe, and Ti are each weighed so that the molar ratio of each starting material matches the molar ratio of each element in each piezoelectric layer. In the first film formation step and the second film formation step, Bi in the target is more likely to volatilize than other elements. Therefore, the molar ratio of Bi in each target may be adjusted to a higher value than the molar ratio of Bi in each piezoelectric layer. E A When a raw material containing K is used as E, in the first film formation step and the second film formation step, K in the target is more likely to volatilize than other elements. Therefore, the molar ratio of K in each target may be adjusted to a higher value than the molar ratio of K in each piezoelectric layer.

[0107] The weighed 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, for example, a ball mill. After the starting materials after mixing are sufficiently dried, the starting materials are formed by a press machine. By calcining the formed starting materials, a calcined product is obtained. The calcining temperature may be 750 °C or more and 900 °C or less. The calcining time may be 1 hour or more and 3 hours or less. The calcined product is pulverized in an organic solvent or water. The pulverizing time may be 5 hours or more and 30 hours or less. The pulverizing means may be a ball mill. After drying the pulverized calcined product, powder of the calcined product is obtained by granulating the calcined product to which a binder solution has been added. A block-shaped compact is obtained by press-molding the powder of the calcined product.

[0108] By heating the block-shaped compact, the binder in the compact volatilizes. The heating temperature may be 400 °C or more and 800 °C or less. The heating time may be 2 hours or more and 4 hours or less.

[0109] After the volatilization of the binder, the compact is sintered. The sintering temperature may be 800 °C or more and 1100 °C or less. The sintering time may be 2 hours or more and 4 hours or less. The heating rate and cooling rate of the compact during the sintering process may be, for example, 50 °C / hour or more and 300 °C / hour or less.

[0110] By the above steps, the first target and the second target are individually produced. The average particle size of the crystal grains (perovskite-type oxide) of the oxide contained in each target may be, for example, 1 μm or more and 20 μm or less. Each target contains Fe 3+ but each target does not necessarily contain Fe 2+ In the first film-forming step, by reducing a part of Fe 3+ derived from the first target, a first piezoelectric layer 3A containing Fe 2+ can be obtained. In the second film-forming step, by reducing a part of Fe 3+ derived from the second target, Fe 2+A second piezoelectric layer 3B containing it can be obtained.

[0111] In the first film formation step, in a vacuum atmosphere, the elements constituting the first target are evaporated by the PLD method. The evaporated elements adhere and deposit on the surface of the lower layer 6 or the second piezoelectric layer 3B, whereby the first piezoelectric layer 3A is formed. In the second film formation step, in a vacuum atmosphere, the elements constituting the second target are evaporated by the PLD method. The evaporated elements adhere and deposit on the surface of the lower layer 6, whereby the second piezoelectric layer 3B is formed.

[0112] In the first film formation step, the first piezoelectric layer 3A may be formed in the vacuum chamber while heating the inside of the vacuum chamber. For example, the temperature (film formation temperature) inside the vacuum chamber may be 450°C or higher and 600°C or lower. When the film formation temperature is 450°C or higher, a part of Fe 3+ derived from the first target is easily reduced, and the first piezoelectric layer 3A containing Fe 2+ is easily formed. When the film formation temperature is less than 450°C, Fe 3+ derived from the target is difficult to be reduced, and it is difficult to obtain the first piezoelectric layer 3A containing Fe 2+ . The higher the film formation temperature, the better the cleanliness of the surface of the lower layer 6 or the second piezoelectric layer 3B, the higher the crystallinity of the first piezoelectric layer 3A, and the easier the orientation degree of the crystal plane of tetragonal crystal 1 is increased. When the film formation temperature is too high, each element constituting the first piezoelectric layer 3A is excessively reduced, and it is difficult to obtain the first piezoelectric layer 3A having a desired composition. Also, when the film formation temperature is too high, Bi or K is easily desorbed from the first piezoelectric layer 3A, and it is difficult to control the composition of the first piezoelectric layer 3A.

[0113] The oxygen partial pressure in the vacuum chamber may be, for example, 0.1 Pa or higher and 3.0 Pa or lower, preferably 0.1 Pa or higher and 1.0 Pa or lower, more preferably 0.1 or higher and 0.5 Pa or lower. By maintaining the oxygen partial pressure within the above range, a part of Fe 3+ derived from the target is easily reduced, and Fe 2+It is easy to form the first piezoelectric layer 3A containing [it]. When the oxygen partial pressure is too low, each element derived from the target is difficult to be sufficiently oxidized, it is difficult to form a perovskite-type oxide, and the degree of orientation of the crystal plane of the tetragonal crystal 1 is likely to decrease. When the oxygen partial pressure is too high, Fe 3+ derived from the target is difficult to be reduced, and it is difficult to obtain the first piezoelectric layer 3A containing Fe 2+ . Further, when the oxygen partial pressure is too high, the growth rate of the first piezoelectric layer 3A is likely to decrease, and the degree of orientation of the crystal plane of the tetragonal crystal 1 is likely to decrease.

[0114] In the first film formation step, in addition to the repetition frequency f1 of the pulsed laser light, the number of irradiations (film formation time) of the pulsed laser light on the first target may be controlled. As the number of irradiations (film formation time) of the pulsed laser light on the first target increases, the thickness of the first piezoelectric layer 3A tends to increase. In the first film formation step, in addition to the repetition frequency f1 of the pulsed laser light, the distance between the surface of the lower layer 6 or the second piezoelectric layer 3B and the first target may be controlled. As the distance between the surface of the lower layer 6 or the second piezoelectric layer 3B and the first target decreases, the thickness and growth rate of the first piezoelectric layer 3A tend to increase.

[0115] Except for the composition of the target and the repetition frequency of the pulsed laser light, the second film formation step may be carried out in substantially the same manner as the above-described first film formation step.

[0116] After the piezoelectric thin film P is formed by the first film formation step (and the second film formation step), annealing treatment (heat treatment) of the piezoelectric thin film P may be performed. The temperature (annealing temperature) of the piezoelectric thin film P in the annealing treatment may be, for example, 300 ° C or higher and 1000 ° C or lower, 600 ° C or higher and 1000 ° C or lower, or 850 ° C or higher and 1000 ° C or lower. By annealing the piezoelectric thin film P, the piezoelectricity of the piezoelectric thin film P tends to be further improved. In particular, by annealing at 850 ° C or higher and 1000 ° C or lower, the piezoelectricity of the piezoelectric thin film P is likely to be improved. However, the annealing treatment is not essential. The annealing treatment may be carried out in a reducing atmosphere such as nitrogen gas (N 2 ). By annealing in a reducing atmosphere, Fe in the piezoelectric thin film P associated with the annealing treatment 2+Oxidation (Fe 3+ generation) is suppressed, and Fe in the piezoelectric thin film P 2+ is easily maintained.

[0117] In the formation process of the piezoelectric thin film P described above and the subsequent temperature drop process, compressive stress due to temperature change may be generated in the piezoelectric thin film P. Due to the compressive stress, the piezoelectric thin film P is compressed in the directions (a-axis direction and b-axis direction) substantially parallel to the surface of the first piezoelectric layer 3A. As a result, tetragonal crystal 1 (and tetragonal crystal 2) is easily formed.

[0118] The crystalline substrate 8 may be a single crystal substrate. For example, the crystalline substrate 8 may be a substrate made of a single crystal of Si, or a substrate made of a single crystal of a compound semiconductor such as GaAs. The crystalline substrate 8 may also be a substrate made of a single crystal of an oxide. The single crystal of the oxide may be, for example, MgO or a perovskite-type oxide (for example, SrTiO 3 ). The thickness of the crystalline substrate 8 may be, for example, 10 μm or more and 1000 μm or less. When the crystalline substrate 8 has conductivity, since the crystalline substrate 8 functions as an electrode, the first electrode layer 7 may not be provided. For example, the conductive crystalline substrate 8 may be a single crystal of SrTiO 3 doped with niobium (Nb). As the crystalline substrate 8, an SOI (Silicon-on-Insulator) substrate may be used.

[0119] The crystal orientation of the crystalline substrate 8 may be equal to the normal direction D N of the surface of the crystalline substrate 8. That is, the surface of the crystalline substrate 8 may be parallel to the crystal plane of the crystalline substrate 8. The crystalline substrate 8 may be a uniaxially oriented substrate. For example, the (100) plane of the crystalline substrate 8 such as Si may be parallel to the surface of the crystalline substrate 8. That is, the

[0100] direction of the crystalline substrate 8 such as Si may be parallel to the normal direction D N of the surface of the crystalline substrate 8.

[0120] When the (100) plane of the crystalline substrate 8 such as Si is parallel to the surface of the crystalline substrate 8, the (001) plane of each of the tetragonal crystal 1 and the tetragonal crystal 2 is likely to be oriented in the normal direction dn of the surface of the first piezoelectric layer 3A.

[0121] As described above, the intermediate layer 5 (first intermediate layer) may be disposed between the crystalline substrate 8 and the first electrode layer 7. The intermediate layer 5 may contain, for example, at least one selected from the group consisting of titanium (Ti), chromium (Cr), titanium oxide (TiO 2 ), silicon oxide (SiO 2 ), and zirconium oxide (ZrO 2 ). By interposing the intermediate layer 5, the first electrode layer 7 can be easily adhered to the crystalline substrate 8. The intermediate layer 5 may be crystalline. The crystal plane of the intermediate layer 5 may be oriented in the normal direction D N of the surface of the crystalline substrate 8. Both the crystal plane of the crystalline substrate 8 and the crystal plane of the intermediate layer 5 may be oriented in the normal direction D N of the surface of the crystalline substrate 8. The method for forming the intermediate layer 5 may be a sputtering method, a vacuum evaporation method, a printing method, a spin coating method, or a sol-gel method.

[0122] The intermediate layer 5 may contain ZrO 2 and an oxide of a rare earth element. By the intermediate layer 5 containing ZrO 2 and an oxide of a rare earth element, the first electrode layer 7 made of platinum crystals is easily formed on the surface of the intermediate layer 5, the (002) plane of the platinum crystals is easily oriented in the normal direction of the surface of the first electrode layer 7, and the (200) plane of the platinum crystals is easily oriented in the in-plane direction of the surface of the first electrode layer 7. The rare earth element may be at least one 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).

[0123] The intermediate layer 5 may contain ZrO 2 and Y 2 O 3 . For example, the intermediate layer 5 may be yttria-stabilized zirconia (Y 2 O3 ZrO added with 2 ) may be composed of. The intermediate layer 5 is ZrO 2 A first layer composed of, and Y 2 O 3 It may have a second layer composed of. The first layer composed of ZrO 2 May be directly laminated on the surface of the crystalline substrate 8. Y 2 O 3 The second layer composed of may be directly laminated on the surface of the first layer. The first electrode layer 7 is Y 2 O 3 It may be directly laminated on the surface of the second layer composed of. When the intermediate layer 5 contains ZrO 2 And Y 2 O 3 In the case of including, the first piezoelectric layer 3A (and the second piezoelectric layer 3B) is likely to grow epitaxially, and the (001) plane of the tetragonal crystal 1 (and the (001) plane of the tetragonal crystal 2) is likely to be preferentially oriented in the normal direction dn of the surface of the first piezoelectric layer 3A. Also, when the intermediate layer 5 contains ZrO 2 And Y 2 O 3 In the case of including, the first electrode layer 7 made of platinum crystals is likely to be formed on the surface of the intermediate layer 5, the (002) plane of the platinum crystals is likely to be oriented in the normal direction of the surface of the first electrode layer 7, and the (200) plane of the platinum crystals is likely to be oriented in the in-plane direction of the surface of the first electrode layer 7.

[0124] The first electrode layer 7 may be composed of at least one metal selected from the group consisting of, for example, 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 7 may be composed of a conductive metal oxide such as, for example, strontium ruthenate (SrRuO 3 ), lanthanum nickelate (LaNiO 3 ), or lanthanum strontium cobaltate ((La,Sr)CoO 3 ). The first electrode layer 7 may be crystalline. The crystal plane of the first electrode layer 7 is in the normal direction D of the crystalline substrate 8 Nmay be oriented. That is, the crystal plane of the first electrode layer 7 may be substantially parallel to the surface of the crystalline substrate 8. Both the crystal plane of the crystalline substrate 8 and the crystal plane of the first electrode layer 7 are in the normal direction D of the crystalline substrate 8 N may be oriented. The normal direction D of the crystalline substrate 8 N The crystal plane of the first electrode layer 7 that is oriented in the direction D may be substantially parallel to the (001) plane of the cubic crystal 1 (and the (001) plane of the cubic crystal 2). The thickness of the first electrode layer 7 may be, for example, 1 nm or more and 1.0 μm or less. The method for forming the first electrode layer 7 may be a sputtering method, a vacuum evaporation method, a printing method, a spin coating method, or a sol-gel method. In the case of the printing method, the spin coating method, or the sol-gel method, heat treatment (annealing) of the first electrode layer 7 may be performed to enhance the crystallinity of the first electrode layer 7.

[0125] The first electrode layer 7 may contain platinum crystals. The first electrode layer 7 may consist only of platinum crystals. The platinum crystals are cubic crystals having a face-centered cubic lattice structure (fcc structure). The (002) plane of the platinum crystals may be oriented in the normal direction of the surface of the first electrode layer 7, and the (200) plane of the platinum crystals may be oriented in the in-plane direction of the surface of the first electrode layer 7. In other words, the (002) plane of the platinum crystals may be substantially parallel to the surface of the first electrode layer 7, and the (200) plane of the platinum crystals may be substantially perpendicular to the surface of the first electrode layer 7. When the (002) plane and the (200) plane of the platinum crystals constituting the first electrode layer 7 have the above-mentioned orientation, the first piezoelectric layer 3A (and the second piezoelectric layer 3B) is likely to grow epitaxially, and the (001) plane of the cubic crystal 1 (and the (001) plane of the cubic crystal 2) is likely to be preferentially oriented in the normal direction dn of the surface of the first piezoelectric layer 3A. The surface of the first electrode layer 7 may be substantially parallel to the surface of the first piezoelectric layer 3A. That is, the normal direction of the surface of the first electrode layer 7 may be substantially parallel to the normal direction dn of the surface of the first piezoelectric layer 3A.

[0126] The second electrode layer 4 may be made of, for example, at least one metal selected from the group consisting of Pt, Pd, Rh, Au, Ru, Ir, Mo, Ti, Ta, and Ni. The second electrode layer 4 may be, for example, LaNiO 3 , SrRuO3 and at least one kind of conductive metal oxide selected from the group consisting of (La,Sr)CoO 3 It may be made of. The second electrode layer 4 may be crystalline. The crystal plane of the second electrode layer 4 may be oriented in the normal direction D N of the crystalline substrate 8. The crystal plane of the second electrode layer 4 may be substantially parallel to the surface of the crystalline substrate 8. The normal direction D N of the crystalline substrate 8, the crystal plane of the second electrode layer 4 that is oriented may be substantially parallel to the (001) plane of the cubic crystal 1 (and the (001) plane of the cubic crystal 2). The thickness of the second electrode layer 4 may be, for example, 1 nm or more and 1.0 μm or less. The method for forming the second electrode layer 4 may be a sputtering method, a vacuum evaporation method, a printing method, a spin coating method, or a sol-gel method. In the case of the printing method, the spin coating method, or the sol-gel method, heat treatment (annealing) of the second electrode layer 4 may be performed to enhance the crystallinity of the second electrode layer 4.

[0127] Another intermediate layer (second intermediate layer) may be disposed between the piezoelectric thin film P (first piezoelectric layer 3A) and the second electrode layer 4. By interposing another intermediate layer, the second electrode layer 4 is likely to adhere to the piezoelectric thin film P (first piezoelectric layer 3A). The composition, crystal structure, and formation method of another intermediate layer (second intermediate layer) may be the same as those of the above-described intermediate layer (first intermediate layer). Another intermediate layer is, for example, SrRuO 3 , LaNiO 3 and at least one selected from the group consisting of (La,Sr)CoO 3 may be included. The method for forming another intermediate layer may be a sputtering method, a vacuum evaporation method, a printing method, a spin coating method, or a sol-gel method.

[0128] At least a part or the whole of the surface of the piezoelectric thin film element 10 may be covered with a protective film. By covering with the protective film, the durability (such as moisture resistance) of the piezoelectric thin film element 10 is improved.

[0129] The applications of the piezoelectric thin film element according to this embodiment are diverse. For example, the piezoelectric thin film element may be used in a piezoelectric transducer and a piezoelectric sensor. That is, the piezoelectric transducer according to this embodiment (for example, an ultrasonic transducer) may include the above-described piezoelectric thin film element. The piezoelectric transducer may be, for example, an ultrasonic transducer such as an ultrasonic sensor. The piezoelectric thin film element may be, for example, a harvester (vibration power generation element). As described above, since the piezoelectric thin film element according to this embodiment has excellent piezoelectric performance indices, the piezoelectric thin film element according to this embodiment is suitable for an ultrasonic transducer. The piezoelectric thin film element may be a piezoelectric actuator. The piezoelectric actuator may be used in a head assembly, a head stack assembly, or a hard disk drive. The piezoelectric actuator may be used in a print head or an inkjet printer device. The piezoelectric actuator may be a piezoelectric switch. The piezoelectric actuator may be used in haptics. That is, the piezoelectric actuator may be used in various devices that require feedback by skin sensation (tactile sense). Devices that require feedback by skin sensation may be, for example, wearable devices, touch pads, displays, or game controllers. The piezoelectric thin film element may be a piezoelectric sensor. For example, the piezoelectric sensor may be a piezoelectric microphone, a gyro sensor, a pressure sensor, a pulse wave sensor, or a shock sensor. The piezoelectric thin film element may be a SAW filter, a BAW filter, an oscillator, or an acoustic multilayer film. The micro electro mechanical systems (MEMS) according to this embodiment include the above-described piezoelectric thin film element. That is, the piezoelectric thin film element may be part or all of the micro electro mechanical system. For example, the piezoelectric thin film element may be part or all of a piezoelectric micromachined ultrasonic transducer (PMUT).For example, a product applying a piezoelectric micromachined ultrasonic transducer may be a biometric sensor (such as a fingerprint authentication sensor, a blood vessel authentication sensor, etc.) or a medical / healthcare sensor (such as a sphygmomanometer, a blood vessel imaging sensor, etc.), or a ToF (Time of Flight) sensor.

[0130] FIG. 9 shows a schematic cross-section of an ultrasonic transducer 10b including the above piezoelectric thin film element. The cross-section of this ultrasonic transducer 10b is perpendicular to the surface of the piezoelectric thin film P (the first piezoelectric layer 3A). The ultrasonic transducer 10b may include substrates 8a and 1b, a first electrode layer 7 provided on the substrates 8a and 1b, a piezoelectric thin film P overlapping the first electrode layer 7, and a second electrode layer 4 overlapping the piezoelectric thin film P. The piezoelectric thin film P includes a lower layer 6 directly overlapping the first electrode layer 7 and a first piezoelectric layer 3A overlapping the lower layer 6. An acoustic cavity 8c may be provided below the piezoelectric thin film P. An ultrasonic signal is transmitted or received by the bending or vibration of the piezoelectric thin film P. A second piezoelectric layer 3B may be disposed between the lower layer 6 and the first piezoelectric layer 3A. An intermediate layer may be interposed between the substrates 8a and 1b and the first electrode layer 7.

Example

[0131] The present invention will be described in detail by the following examples and comparative examples. The present invention is not limited by the following examples.

[0132] (Example 1) For the fabrication of the piezoelectric thin film element of Example 1, a crystalline substrate made of Si was used. The (100) plane of Si was parallel to the surface of the crystalline substrate. The crystalline substrate was a 20 mm × 20 mm square. The thickness of the crystalline substrate was 500 μm.

[0133] In a vacuum chamber, a crystalline intermediate layer composed of ZrO 2 and Y 2 O 3 was formed over the entire surface of the crystalline substrate. The intermediate layer was formed by a sputtering method. The thickness of the intermediate layer was 30 nm.

[0134] Inside the vacuum chamber, a first electrode layer composed of Pt crystals was formed over the entire surface of the intermediate layer. The first electrode layer was formed by sputtering. The thickness of the first electrode layer was 200 nm. The temperature inside the vacuum chamber during the formation process of the first electrode layer was maintained at 500 °C.

[0135] The XRD pattern of the first electrode layer was measured by out-of-plane measurement on the surface of the first electrode layer. The XRD pattern of the first electrode layer was measured by in-plane measurement on the surface of the first electrode layer. For the measurement of these XRD patterns, an X-ray diffractometer (SmartLab) manufactured by Rigaku Corporation was used. The measurement conditions were set such that each peak intensity in each XRD pattern was at least three orders of magnitude higher than the background intensity. By out-of-plane measurement, a peak of diffracted X-rays from the (002) plane of Pt crystals was detected. That is, the (002) plane of Pt crystals was oriented in the normal direction of the surface of the first electrode layer. By in-plane measurement, a peak of diffracted X-rays from the (200) plane of Pt crystals was detected. That is, the (200) plane of Pt crystals was oriented in the in-plane direction of the surface of the first electrode layer.

[0136] A crystalline lower layer was formed over the entire surface of the first electrode layer. The lower layer was formed by sputtering. The composition of the lower layer is shown in Table 1 below. The thickness TL of the lower layer was adjusted to the value shown in Table 2 below.

[0137] By performing the above-described first film-forming process (PLD method) inside the vacuum chamber, a first piezoelectric layer was formed over the entire surface of the lower layer. The repetition frequency f1 of the pulsed laser light in the first film-forming process was adjusted to 10 Hz. The oxygen partial pressure inside the vacuum chamber in the first film-forming process was maintained at 1 Pa. The temperature (film-forming temperature) inside the vacuum chamber during the formation process of the first piezoelectric layer was maintained at 460 °C. The thickness T1 of the first piezoelectric layer was adjusted to the value shown in Table 2 below.

[0138] The composition of the first target used in the first film-forming step is represented by the following chemical formula 1'. In the case of Example 1, E in the following chemical formula 1' A , E B1 and E B2 were the elements shown in Table 1 below. In the case of Example 1, α, β, x1, y1, and z1 in the following chemical formula 1' were the values shown in Table 1 below. x1(Bi 1-α E A α )(E B1 1-β E B2 β )O 3 -y1BiFeO 3 -z1Bi(Fe 0.5 Ti 0.5 )O 3 (1')

[0139] By the above first film-forming step, a piezoelectric thin film composed of a lower layer and a first piezoelectric layer was formed. For the following analysis and measurement, a plurality of piezoelectric thin films were formed by the above method.

[0140] By sputtering the surface of the piezoelectric thin film, while uniformly reducing the thickness of the piezoelectric thin film, the composition of the piezoelectric thin film was continuously analyzed along the thickness direction of the piezoelectric thin film. The composition of the piezoelectric thin film was analyzed by the XPS method. The analysis results showed that the composition of the first piezoelectric layer was consistent with the composition of the first target.

[0141] By the out-of-plane measurement on the surface of the first piezoelectric layer using the above X-ray diffractometer, the XRD pattern of the piezoelectric thin film was measured. Further, by the in-plane measurement on the surface of the first piezoelectric layer, another XRD pattern of the piezoelectric thin film was measured. By these measurements, the reciprocal lattice space mapping of the piezoelectric thin film was performed. The measurement conditions were set so that each peak intensity in each XRD pattern was at least three digits or more higher than the background intensity. The measurement apparatus and measurement conditions for each XRD pattern were the same as the above conditions. A cross-section of the piezoelectric thin film parallel to the thickness direction of the piezoelectric thin film was observed at atomic-level resolution using a scanning transmission electron microscope (STEM).

[0142] The results of the above analysis using the X-ray diffractometer and STEM indicated that the piezoelectric thin film had the following characteristics.

[0143] The (001) plane of the lower crystal constituting the lower layer was oriented in the normal direction of the surface of the first piezoelectric layer. The first piezoelectric layer was composed of tetragonal crystal 1 of perovskite-type oxide. The (001) plane of tetragonal crystal 1 was preferentially oriented in the normal direction of the surface of the first piezoelectric layer. That is, the degree of orientation of the (001) plane of tetragonal crystal 1 in the normal direction of the surface of the first piezoelectric layer was 90% or more. As described above, the degree of orientation of the (001) plane of tetragonal crystal 1 was 100×I 1(001) / (I 1(001) +I 1(110) +I 1(111) ) and was represented as such. The crystal plane of tetragonal crystal 1 that was preferentially oriented in the normal direction of the surface of the first piezoelectric layer was denoted as the "first orientation plane".

[0144] The interval aL between the (100) planes of the lower crystal constituting the lower layer was the value shown in Table 1 below. The interval a1 between the (100) planes of tetragonal crystal 1 constituting the first piezoelectric layer was the value shown in Table 1 below. The lattice mismatch rate Δa was the value shown in Table 1 below. As described above, the lattice mismatch rate Δa was defined as 100×(aL - a1) / a1. The full width at half maximum FWHM of the rocking curve of the diffracted X-rays derived from the (001) plane of tetragonal crystal 1 was the value shown in Table 1 below. The rocking curve of the diffracted X-rays derived from the (001) plane of tetragonal crystal 1 in Example 1 is shown in FIG. 10. c1 / a1 of tetragonal crystal 1 was the value shown in Table 2 below.

[0145] Using the above method, a laminate composed of a crystalline substrate, an intermediate layer directly overlapping the crystalline substrate, a first electrode layer directly overlapping the intermediate layer, and a piezoelectric thin film (lower layer and first piezoelectric layer) directly overlapping the first electrode layer was fabricated. Using this laminate, the following steps were further carried out.

[0146] Inside the vacuum chamber, a second electrode layer made of Pt was formed over the entire surface of the piezoelectric thin film. The second electrode layer was formed by sputtering. The temperature of the crystalline substrate during the formation process of the second electrode layer was maintained at 500 °C. The thickness of the second electrode layer was 200 nm.

[0147] Through the above steps, a laminate composed of a crystalline substrate, an intermediate layer directly overlapping the crystalline substrate, a first electrode layer directly overlapping the intermediate layer, a lower layer directly overlapping the first electrode layer, a first piezoelectric layer directly overlapping the lower layer, and a second electrode layer directly overlapping the first piezoelectric layer was fabricated. Subsequently, patterning of the laminated structure on the crystalline substrate was performed by photolithography. After patterning, the laminate was cut by dicing.

[0148] Through the above steps, a piezoelectric thin film element of Example 1 having a square shape was obtained. The piezoelectric thin film element was composed of a crystalline substrate, an intermediate layer directly overlapping the crystalline substrate, a first electrode layer directly overlapping the intermediate layer, a lower layer directly overlapping the first electrode layer, a first piezoelectric layer directly overlapping the lower layer, and a second electrode layer directly overlapping the first piezoelectric layer. The area of the movable part of the piezoelectric thin film was 600 μm × 600 μm.

[0149] <Evaluation of piezoelectricity> The piezoelectricity of the piezoelectric thin film was evaluated by the following method.

[0150] [Calculation of relative permittivity] The capacitance C of the piezoelectric thin film element was measured. The details of the measurement of the capacitance C were as follows. Measuring device: Impedance Gain‐Phase Analyzer 4194A manufactured by Hewlett Packard Co., Ltd. Frequency: 1 kHz Electric field: 10 V / μm

[0151] Based on the following mathematical formula A, the relative permittivity ε was calculated from the measured value of the capacitance C. r The ε of Example 1 r is shown in Table 2 below. C = ε 0×ε r ×(S / d) (A) ε in formula A 0 is the permittivity of vacuum (8.854×10 -12 Fm -1 ). S in formula A is the surface area of the piezoelectric thin film. S can be rephrased as the area of the first electrode layer overlapping the piezoelectric thin film. d in formula A is the thickness of the piezoelectric thin film.

[0152] [Measurement of piezoelectric strain constant d 33,f Using the piezoelectric thin film element, the piezoelectric strain constant d of the piezoelectric thin film 33,f was measured. The details of the measurement of d 33,f were as follows. The piezoelectric strain constant d of Example 1 33,f (average value of three measurement points) is shown in Table 2 below. d 33,f and ε r were used to calculate the piezoelectric performance index (d 33,f / ε r ε 0 ). The d 33,f / ε r ε 0 of Example 1 is shown in Table 2 below. Measuring device: d meter (ZJ-4B) manufactured by the Chinese Academy of Sciences 33 Frequency: 110 Hz Clamp pressure: 0.25 N

[0153] (Examples 2 to 11 and Comparative Examples 1 to 8) The compositions of the lower layers of Examples 2 to 11 and Comparative Examples 6 to 8 are shown in Table 1 below. The thickness TL of the lower layers of Examples 2 to 11 and Comparative Examples 6 to 8 was adjusted to the values shown in Table 2 below. The lower layers of Comparative Examples 1 to 5 were not formed. That is, the first piezoelectric layers of Comparative Examples 1 to 5 were formed directly on the surface of the first electrode layer.

[0154] The thickness T1 of the first piezoelectric layer of each of Examples 2 to 11 and Comparative Examples 1 to 8 was adjusted to the values shown in Table 2 below. The composition of the first target of each of Examples 2 to 11 and Comparative Examples 1 to 8 is represented by the above chemical formula 1'. Each of Examples 2 to 11 and Comparative Examples 1 to 8 has E A , E B1 ​​and E B2 was the element shown in Table 1 below. α, β, x1, y1, and z1 in Examples 2 to 11 and Comparative Examples 1 to 8 were the values shown in Table 1 below.

[0155] Piezoelectric thin film elements of Examples 2 to 11 and Comparative Examples 1 to 8 were fabricated in the same manner as in Example 1 except for the above matters.

[0156] Measurements regarding the first electrode layer of Examples 2 to 11 and Comparative Examples 1 to 8 were performed in the same manner as in Example 1. In all cases of Examples 2 to 11 and Comparative Examples 1 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.

[0157] Analysis and measurement regarding the piezoelectric thin films of Examples 2 to 11 and Comparative Examples 1 to 8 were performed in the same manner as in Example 1. In all cases of Examples 2 to 11 and Comparative Examples 1 to 8, the composition of the first piezoelectric layer was consistent with the composition of the first target. In all cases of Examples 2 to 11 and Comparative Examples 6 to 8, the (001) plane of the lower crystal constituting the lower layer was oriented in the normal direction of the surface of the first piezoelectric layer. In all cases of Examples 2 to 11 and Comparative Examples 1 to 8, the first piezoelectric layer was composed of tetragonal crystal 1 of perovskite-type oxide. In all cases of Examples 2 to 11 and Comparative Examples 1 to 8, the (001) plane of the tetragonal crystal 1 was preferentially oriented in the normal direction of the surface of the first piezoelectric layer. aL, a1, Δa, and FWHM in Examples 2 to 11 and Comparative Examples 1 to 8 were the values shown in Table 1 below. However, only in the cases of Comparative Examples 1 to 5 and Comparative Example 10 described later, aL was the interval of the (100) plane of the Pt crystal constituting the first electrode layer, not the interval of the (100) plane of the lower crystal constituting the lower layer. c1 / a1 in Examples 2 to 11 and Comparative Examples 1 to 8 were the values shown in Table 2 below.

[0158] In the same manner as in Example 1, the piezoelectric properties of the piezoelectric thin films of Examples 2 to 11 and Comparative Examples 1 to 8 were evaluated. The ε of each of Examples 2 to 11 and Comparative Examples 1 to 8 r , d 33,f and d 33,f / ε r ε 0 are shown in Table 2 below.

[0159]

Table 1

[0160]

Table 2

[0161] (Comparative Examples 9 to 11) In the first film formation step of each of Comparative Examples 9 to 11, the temperature inside the vacuum chamber (film formation temperature) was maintained at the temperature shown in Table 3 below. The lower layer of Comparative Example 10 was not formed. That is, the first piezoelectric layer of Comparative Example 10 was formed directly on the surface of the first electrode layer.

[0162] Except for the above matters, piezoelectric thin film elements of each of Comparative Examples 9 to 11 were fabricated in the same manner as in Example 1.

[0163] Measurements regarding the first electrode layer of each of Comparative Examples 9 to 11 were carried out in the same manner as in Example 1. In all cases of Comparative Examples 9 to 11, 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.

[0164] Analysis and measurement regarding the piezoelectric thin film of each of Comparative Examples 9 to 11 were carried out in the same manner as in Example 1. In all cases of Comparative Examples 9 to 11, the composition of the first piezoelectric layer was consistent with the composition of the first target. In both cases of Comparative Examples 9 and 11, the (001) plane of the lower crystal constituting the lower layer was oriented in the normal direction of the surface of the first piezoelectric layer. In all cases of Comparative Examples 9 to 11, the first piezoelectric layer was composed of tetragonal crystal 1 of perovskite-type oxide. In all cases of Comparative Examples 9 to 11, the (001) plane of tetragonal crystal 1 was preferentially oriented in the normal direction of the surface of the first piezoelectric layer. The aL, a1, Δa, and FWHM of each of Comparative Examples 9 to 11 were the values shown in Table 3 below. The c1 / a1 of each of Comparative Examples 9 to 11 was the value shown in Table 4 below.

[0165] In the same manner as in Example 1, the piezoelectric properties of the piezoelectric thin films of each of Comparative Examples 9 to 11 were evaluated. The ε r , d 33,f and d 33,f / ε r ε 0 are shown in Table 4 below.

[0166]

Table 3

[0167]

Table 4

[0168] (Comparative Example 12) In the first film-forming step of Comparative Example 12, the oxygen partial pressure in the vacuum chamber was maintained at 0.01 Pa. The thickness T1 of the first piezoelectric layer of Comparative Example 12 was adjusted to the value shown in Table 6 below.

[0169] A piezoelectric thin film element of Comparative Example 12 was fabricated in the same manner as in Example 1, except for the above matters.

[0170] In the same manner as in Example 1, measurements regarding the first electrode layer of Comparative Example 12 were carried out. In the case of Comparative Example 12, 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.

[0171] In the same manner as in Example 1, analysis and measurement of the piezoelectric thin film of Comparative Example 12 were performed. In the case of Comparative Example 12, the composition of the piezoelectric thin film did not match the composition of the first target in terms of the oxygen content. Since the piezoelectric thin film of Comparative Example 12 did not have sufficient crystal orientation, the FWHM of Comparative Example 12 could not be specified. aL, a1, and Δa of Comparative Example 12 were the values shown in Table 5 below. c1 / a1 of Comparative Example 12 was the value shown in Table 6 below.

[0172] In the same manner as in Example 1, the piezoelectricity of the piezoelectric thin film of Comparative Example 12 was evaluated. ε of Comparative Example 12 r , d 33,f and d 33,f / ε r ε 0 are shown in Table 6 below.

[0173]

Table 5

[0174]

Table 6

[0175] (Example 12) In the process of fabricating the piezoelectric thin film element of Example 12, an intermediate layer was not formed. In the process of fabricating the piezoelectric thin film element of Example 12, a first electrode layer made of crystalline SrRuO 3 was directly formed on the entire surface of the crystalline substrate. The thickness of the first electrode layer of Example 9 was 200 nm.

[0176] Except for the above matters, a piezoelectric thin film element of Example 12 was fabricated in the same manner as in Example 1.

[0177] The measurement of the first electrode layer of Example 12 was carried out in the same manner as in Example 1. In the case of Example 12, the crystal plane of the first electrode layer was not oriented in the in-plane direction of the surface of the first electrode layer. That is, in the case of Example 12, there was no in-plane orientation of the crystal of the first electrode layer.

[0178] Analysis and measurement of the piezoelectric thin film of Example 12 were carried out in the same manner as in Example 1. The composition of the first piezoelectric layer of Example 12 was consistent with the composition of the first target. The (001) plane of the lower crystal constituting the lower layer of Example 12 was oriented in the normal direction of the surface of the first piezoelectric layer. The first piezoelectric layer of Example 12 was composed of tetragonal crystal 1 of perovskite-type oxide. The (001) plane of tetragonal crystal 1 of Example 12 was preferentially oriented in the normal direction of the surface of the first piezoelectric layer. aL, a1, Δa and FWHM of Example 12 were the values shown in Table 7 below. c1 / a1 of Example 12 was the value shown in Table 8 below.

[0179] The piezoelectricity of the piezoelectric thin film of Example 12 was evaluated in the same manner as in Example 1. ε of Example 12 r , d 33,f and d 33,f / ε r ε 0 are shown in Table 8 below.

[0180]

Table 7

[0181]

Table 8

[0182] (Examples 13 to 19) The compositions of the lower layers of Examples 13 to 19 are shown in Table 9 below.

[0183] In the case of Examples 13 to 19, by performing the above-described second film formation step (PLD method) in a vacuum chamber, a second piezoelectric layer was formed over the entire surface of the lower layer. The repetition frequency f2 of the pulsed laser light in the second film formation step was adjusted to 20 Hz. The oxygen partial pressure in the vacuum chamber in the second film formation step was maintained at 1 Pa. The internal temperature (film formation temperature) of the vacuum chamber in the second film formation step was maintained at 460°C. The thickness T2 of the second piezoelectric layer was adjusted to the values shown in Table 11 below.

[0184] The composition of the second target used in each of the second film formation steps of Examples 13 to 19 is represented by the following Chemical Formula 2'. E in Chemical Formula 2' of each of Examples 13 to 19 A , E B1 and E B2 were the elements shown in Table 9 below. x2, y2, and z2 in Chemical Formula 2' of each of Examples 13 to 19 were the values shown in Table 10 below. x2(Bi 1-α E A α )(E B1 1-β E B2 β )O 3 -y2BiFeO 3 -z2Bi(Fe 0.5 Ti 0.5 )O 3 (2')

[0185] In the case of Examples 13 to 19, by the first film formation step following the second film formation step, a first piezoelectric layer was formed over the entire surface of the second piezoelectric layer. That is, each of the piezoelectric thin films of Examples 13 to 19 consisted of a lower layer, a second piezoelectric layer directly overlapping the lower layer, and a first piezoelectric layer directly overlapping the second piezoelectric layer. The thickness T1 of each of the first piezoelectric layers of Examples 13 to 19 was adjusted to the values shown in Table 11 below. The composition of the first target used in each of the first film formation steps of Examples 13 to 19 is represented by the above Chemical Formula 1'. E in Chemical Formula 1' of each of Examples 13 to 19 A , E B1 and E B2It was the element shown in Table 9 below. In each of Chemical Formulas 1' in Examples 13 to 19, α, β, x1, y1, and z1 were the values shown in Table 9 below. In any of Examples 13 to 19, E A , E B1 , E B2 , α and β are common to the first piezoelectric layer (first target) and the second piezoelectric layer (second target).

[0186] Piezoelectric thin film elements of Examples 13 to 19 were fabricated in the same manner as in Example 1, except for the above matters.

[0187] Measurements regarding the first electrode layers of Examples 13 to 19 were carried out in the same manner as in Example 1. In any of Examples 13 to 19, 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.

[0188] Analysis and measurements regarding the piezoelectric thin films of Examples 13 to 19 were carried out in the same manner as in Example 1. The piezoelectric thin films of Examples 13 to 19 had the following characteristics. The composition of the first piezoelectric layer was consistent with the composition of the first target. The (001) plane of the lower crystal constituting the lower layer was oriented in the normal direction of the surface of the first piezoelectric layer. The first piezoelectric layer was composed of tetragonal crystal 1 of perovskite-type oxide. The (001) plane of tetragonal crystal 1 was preferentially oriented in the normal direction of the surface of the first piezoelectric layer. The composition of the second piezoelectric layer was consistent with the composition of the second target. The second piezoelectric layer was composed of tetragonal crystal 2 of perovskite-type oxide. The (001) plane of tetragonal crystal 2 was preferentially oriented in the normal direction of the surface of the first piezoelectric layer. That is, the orientation degree of the (001) plane of tetragonal crystal 2 in the normal direction of the surface of the first piezoelectric layer was 90% or more. As described above, the orientation degree of the (001) plane of tetragonal crystal 2 was 100×I 2(001) / (I 2(001)+I 2(110) +I 2(111) ) is represented as such. The crystal plane of the tetragonal crystal 2 that is preferentially oriented in the normal direction of the surface of the first piezoelectric layer is denoted as the "second orientation plane".

[0189] For each of Examples 13 to 19, aL, a1, Δa, and FWHM were the values shown in Table 9 below. For each of Examples 13 to 19, c1 / a1 of the tetragonal crystal 1 was the value shown in Table 11 below. For each of Examples 13 to 19, c2 / a2 of the tetragonal crystal 2 was the value shown in Table 11 below. For each of Examples 13 to 19, I 1 / (I 1 +I 2 ) was the value shown in Table 11 below. The definition of I 1 / (I 1 +I 2 ) is as described above.

[0190] In the same manner as in Example 1, the piezoelectric properties of the piezoelectric thin films of Examples 13 to 19 were evaluated. For each of Examples 13 to 19, ε r , d 33,f and d 33,f / ε r ε 0 are shown in Table 11 below. The reciprocal lattice space map of Example 13 is shown in FIG. 11.

[0191]

Table 9

[0192]

Table 10

[0193]

Table 11

Industrial Applicability

[0194] For example, the piezoelectric thin film according to one aspect of the present invention may be applied to a piezoelectric transformer, a piezoelectric actuator, and a piezoelectric sensor.

Explanation of Signs

[0195] 1…Cubic crystal 1, 2…Cubic crystal 2, 3A…First piezoelectric layer, 3B…Second piezoelectric layer, 4…Second electrode layer, 5…Intermediate layer, 6…Lower layer, 6c…Crystal contained in the lower layer (lower crystal), 7…First electrode layer, 8…Crystalline substrate, 10, 10a…Piezoelectric thin film element, 10b…Ultrasonic transducer, D N …Normal direction of the surface of the crystalline substrate, dn…Normal direction of the surface of the first piezoelectric layer, P…Piezoelectric thin film, uc…Unit cell of the perovskite structure, uc1…Unit cell of cubic crystal 1, uc2…Unit cell of cubic crystal 2, ucL…Unit cell of the crystal contained in the lower layer.

Claims

1. a bottom layer and a first piezoelectric layer directly or indirectly overlying the bottom layer; The first piezoelectric layer includes a tetragonal crystal 1 of a perovskite oxide, The (001) plane of the tetragonal crystal 1 is oriented in a normal direction to the surface of the first piezoelectric layer, The spacing between the (100) planes of the tetragonal crystal 1 is a1, The spacing between (100) planes of the crystals included in the lower layer is aL, the lattice mismatch between the first piezoelectric layer and the bottom layer is defined as 100×(aL−a1) / a1; the lattice mismatch rate is 3.0% or more and 12.1% or less, The rocking curve of the diffracted X-rays of the (001) plane of the tetragonal crystal 1 is measured in the out-of-plane direction of the surface of the first piezoelectric layer; The full width at half maximum of the rocking curve is 1.9° or more and 5.5° or less, The (001) plane of the crystal included in the lower layer is oriented in the normal direction of the surface of the first piezoelectric layer. Piezoelectric thin film.

2. The aL is 3.92 Å or more and 4.29 Å or less. The piezoelectric thin film according to claim 1 .

3. The crystal contained in the lower layer is at least one crystal selected from the group consisting of a cubic crystal, a tetragonal crystal, a rhombohedral crystal, a pseudocubic crystal, and a pseudotetragonal crystal. The piezoelectric thin film according to claim 1 or 2.

4. The crystals contained in the lower layer include at least one compound of barium titanate and titanium nitride. The piezoelectric thin film according to any one of claims 1 to 3.

5. The thickness of the lower layer is 10 nm or more and 350 nm or less. The piezoelectric thin film according to any one of claims 1 to 4.

6. The spacing between the (001) planes of the tetragonal crystal 1 is c1, c1 / a1 is equal to or greater than 1.050 and equal to or less than 1.250; The piezoelectric thin film according to any one of claims 1 to 5.

7. The tetragonal crystal 1 is composed of bismuth, iron, and element E. Ｂ and oxygen, The element E Ｂ is at least one element selected from the group consisting of magnesium, aluminum, zirconium, titanium, nickel and zinc; The piezoelectric thin film according to any one of claims 1 to 6.

8. The tetragonal crystal 1 is represented by the following chemical formula 1: E in the following chemical formula 1 Ａ is at least one element selected from the group consisting of Na, K, and Ag, E in the following chemical formula 1 Ｂ is at least one element selected from the group consisting of Mg, Al, Zr, Ti, Ni and Zn, In the following chemical formula 1, x1 is 0.10 or more and 0.90 or less, In the following chemical formula 1, y1 is 0.05 or more and 0.85 or less, In the following chemical formula 1, z1 is 0.05 or more and 0.85 or less, x1+y1+z1 is 1.00, In the following chemical formula 1, α is 0.00 or more and less than 1.

00. The piezoelectric thin film according to any one of claims 1 to 7. ^1(SAN) １－α E Ａ α )E Ｂ Oh ３ ‐y1iaet ３ ‐ζ1Bi(Fe ０．５ Till ０．５ )O ３ (1)

9. A second piezoelectric layer is provided. the second piezoelectric layer is disposed between the bottom layer and the first piezoelectric layer; The second piezoelectric layer includes a tetragonal crystal 2 of a perovskite oxide, The (001) plane of the tetragonal crystal 2 is oriented in the normal direction of the surface of the first piezoelectric layer, The spacing between the (001) planes of the tetragonal crystal 1 is c1, The spacing between the (001) planes of the tetragonal crystal 2 is c2, The spacing between the (100) planes of the tetragonal crystal 2 is a2, c2 / a2 is smaller than c1 / a1; The piezoelectric thin film according to any one of claims 1 to 8.

10. The c2 / a2 is 1.010 or more and 1.110 or less. The piezoelectric thin film according to claim 9.

11. The peak intensity of the diffracted X-rays from the (001) plane of the tetragonal crystal 1 is I １ and The peak intensity of the diffracted X-rays from the (001) plane of the tetragonal crystal 2 is I ２ and I １ / (I １ +I ２ ) is equal to or greater than 0.90 and less than 1.00; The piezoelectric thin film according to claim 9 or 10.

12. The tetragonal crystal 2 is composed of bismuth, iron, and element E. Ｂ and oxygen, The element E Ｂ is at least one element selected from the group consisting of magnesium, aluminum, zirconium, titanium, nickel and zinc; The piezoelectric thin film according to any one of claims 9 to 11.

13. The tetragonal crystal 2 is represented by the following chemical formula 2: E in the following chemical formula 2 Ａ is at least one element selected from the group consisting of Na, K, and Ag, E in the following chemical formula 2 Ｂ is at least one element selected from the group consisting of Mg, Al, Zr, Ti, Ni and Zn, In the following chemical formula 2, x2 is 0.10 or more and 0.85 or less, In the following chemical formula 2, y2 is 0.10 or more and 0.85 or less, In the following chemical formula 2, z2 is 0.05 or more and 0.80 or less, x2+y2+z2 is 1.00, In the following chemical formula 2, α is 0.00 or more and less than 1.

00. The piezoelectric thin film according to any one of claims 9 to 12. x2(Bi １－α E Ａ α )E Ｂ O ３ ‐y2BiFeO ３ -z2Bi(Fe ０．５ Ti ０．５ ) ３ (2)

14. The thickness of the second piezoelectric layer is 10 nm or more and 300 nm or less. The piezoelectric thin film according to any one of claims 9 to 13.

15. A piezoelectric thin film according to any one of claims 1 to 14, Piezoelectric thin film element.

16. A crystalline substrate; an electrode layer overlying the crystalline substrate; Equipped with the bottom layer directly overlies the electrode layer; an intermediate layer is disposed between the crystalline substrate and the electrode layer; The intermediate layer is made of ZrO ２ and Y ２ O ３ Including, 16. The piezoelectric thin film element according to claim 15.

17. An electrode layer is provided, the bottom layer directly overlies the electrode layer; the electrode layer includes platinum crystals; the (002) plane of the platinum crystal is oriented in a direction normal 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.

16. The piezoelectric thin film element according to claim 15.

18. The electrode layer comprises platinum crystals, the (002) plane of the platinum crystal is oriented in a direction normal 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.

17. The piezoelectric thin film element according to claim 16.

19. A piezoelectric thin film element according to any one of claims 15 to 18, Piezoelectric transducer.

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