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

Abstract

The piezoelectric thin film of the present application has a lower layer and a first piezoelectric layer directly or indirectly overlapping the lower layer. The first piezoelectric layer contains a tetragonal crystal 1 of a perovskite-type oxide. A (001) plane of the tetragonal crystal 1 is oriented in a normal direction dn of a surface of the first piezoelectric layer. A spacing of a (100) plane of the tetragonal crystal 1 is al. A spacing of a (100) plane of a crystal contained in the lower layer is aL. A lattice mismatch rate between the first piezoelectric layer and the lower layer is defined as 100 x (aL - al) / al. The lattice mismatch rate is 3.0% or more and 12.1% or less. A rocking curve of a diffraction X-ray of the (001) plane of the tetragonal crystal 1 is measured in an out-of-plane direction of the surface of the first piezoelectric layer. A full width at half maximum of the rocking curve is 1.9° or more and 5.5° or less.

Description

Technical Field

[0001] This disclosure relates to piezoelectric thin films, piezoelectric thin film elements, and piezoelectric transducers. Background Technology

[0002] Piezoelectric materials are processed into a variety of piezoelectric elements for various purposes. For example, piezoelectric actuators convert voltage into force through the inverse piezoelectric effect, which causes deformation of the piezoelectric material by applying voltage. Additionally, piezoelectric sensors convert force into voltage by generating a polarized piezoelectric effect through deformation of the piezoelectric material by applying pressure. These piezoelectric elements are incorporated into a wide variety of electronic devices.

[0003] In recent years, the market has demanded miniaturization and improved performance of electronic devices. Therefore, research has been actively conducted on piezoelectric elements (piezoelectric thin film elements) that utilize piezoelectric thin films. However, the thinner the piezoelectric material, the more difficult it is to obtain the piezoelectric effect and the inverse piezoelectric effect. Therefore, there is a desire to develop piezoelectric materials with excellent piezoelectric properties in the thin film state.

[0004] Currently, lead zirconate titanate (PZT), a perovskite-type ferroelectric material, is widely used as a piezoelectric material (see Japanese Patent Application Publication No. 2008-192868). However, PZT contains lead (Pb), which is harmful to human health and the environment. Therefore, lead-free piezoelectric materials are expected to be developed as alternatives to PZT. For example, BiFeO3 is described as an example of a lead-free piezoelectric material in the following non-patent literature. Among lead-free piezoelectric materials, BiFeO3 exhibits superior piezoelectricity, and its application in piezoelectric thin film elements is particularly anticipated.

[0005] <Non-Patent Literature> Y. Kawahara et al., Control of Crystal Structure of BiFeO3 Epitaxial Thin Films by Adjusting Growth Conditions and Piezoelectric Properties, Japanese Journal of Applied Physics, 51(2012)09LB04 Summary of the Invention

[0006] The main indicator representing the performance of a piezoelectric material (piezoelectric constant) is d. 33,f (Piezoelectric strain constant) and g 33 (Piezoelectric voltage constant). Piezoelectric strain constant d 33,f(Unit: pC / N) is an indicator of the amount of deformation (transmission capacity) per unit electric field. The piezoelectric strain constant d 33,f The larger the value, the better the performance of the piezoelectric element as an actuator. On the other hand, the piezoelectric voltage constant g... 33 (unit × 10) -3 V·m / N) is an indicator of the electric field strength (receiving capacity) generated per unit stress. The piezoelectric voltage constant g 33 The larger the value, the better the performance of the piezoelectric element used as a sensor, such as a converter. 33 Represented as d 33,f / ε r ε0 or d 33,f / ε 33 ε0. ε r or ε 33 ε0 is the relative permittivity of the piezoelectric material (unit: none). ε0 is the permittivity of vacuum (8.854 × 102). －12 Fm －1 ). d 33,f / ε r ε0 is recorded as the "piezoelectric performance index". With d 33,f The piezoelectric property index increases with increasing ε. r The reduction in piezoelectricity increases the piezoelectric property index. That is, through a large piezoelectric strain constant d. 33,f and low relative permittivity ε r The balance between piezoelectric performance index (d) 33,f / ε r ε0) increases.

[0007] One objective of this invention is to provide a piezoelectric performance index (d) with a large piezoelectric performance index. 33,f / ε r A piezoelectric thin film with ε0), a piezoelectric thin film element including the piezoelectric thin film, and a piezoelectric transducer including the piezoelectric thin film element.

[0008] One aspect of the present invention provides a piezoelectric thin film comprising a lower layer and a first piezoelectric layer directly or indirectly superimposed on the lower layer. The first piezoelectric layer comprises a tetragonal crystal 1 of a perovskite-type oxide. The (001) facets of the tetragonal crystal 1 are oriented in the normal direction to the surface of the first piezoelectric layer. The spacing between the (100) facets of the tetragonal crystal 1 is a1. The spacing between the (100) facets of the crystal contained 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-rays of the (001) facets 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 (FWHM) of the rocking curve is 1.9° or more and 5.5° or less.

[0009] aL can also be The above and the following.

[0010] The (001) plane of the crystal contained in the lower layer can also be oriented in the normal direction of the surface of the first piezoelectric layer.

[0011] The crystals contained in the lower layer may also be at least one selected from cubic crystal, tetragonal crystal, rhombohedral crystal, pseudo-cubic crystal, and pseudo-tetragonal crystal.

[0012] The crystals contained in the lower layer may also contain at least one compound of barium titanate and titanium nitride.

[0013] The thickness of the lower layer can also be greater than 10nm and less than 350nm.

[0014] The spacing of the (001) plane of the tetragonal crystal 1 is c1. c1 / a1 can also be greater than 1.050 and less than 1.250.

[0015] Tetragonal crystal 1 can also contain bismuth, iron, and element E. B And oxygen. Element E B It can also be at least one element selected from magnesium, aluminum, zirconium, titanium, nickel and zinc.

[0016] Tetragonal crystal 1 can also be represented by the following chemical formula 1. In the following chemical formula 1, E... AIt can also be at least one element selected from Na, K, and Ag. E in the following chemical formula 1... B It can also be at least one element selected from Mg, Al, Zr, Ti, Ni, and Zn. In the following Chemical Formula 1, x1 can be 0.10 or more and 0.90 or less. In the following Chemical Formula 1, y1 can be 0.05 or more and 0.85 or less. In the following Chemical Formula 1, z1 can be 0.05 or more and 0.85 or less. x1+y1+z1 can also be 1.00. In the following Chemical Formula 1, α can be 0.00 or more and less than 1.00.

[0017] Chemical formula 1: x1(Bi) 1－α E A α E B O3-y1BiFeO3-z1Bi(Fe 0.5 Ti 0.5 O3

[0018] The piezoelectric thin film may also have a second piezoelectric layer. The second piezoelectric layer may also be disposed between the lower layer and the first piezoelectric layer. The second piezoelectric layer may also comprise a tetragonal crystal 2 of perovskite oxide. The (001) facets of the tetragonal crystal 2 may also be oriented in the normal direction to the surface of the first piezoelectric layer. The spacing between the (001) facets of the tetragonal crystal 1 is c1. The spacing between the (001) facets of the tetragonal crystal 2 is c2. The spacing between the (100) facets of the tetragonal crystal 2 is a2. c2 / a2 may also be less than c1 / a1.

[0019] c2 / a2 can also be greater than 1.010 and less than 1.110.

[0020] The peak intensity of the X-ray diffracted from the (001) plane of tetragonal crystal 1 is I1. The peak intensity of the X-ray diffracted from the (001) plane of tetragonal crystal 2 is I2. I1 / (I1+I2) can also be greater than 0.90 and less than 1.00.

[0021] Tetragonal crystal 2 can also contain bismuth, iron, and element E. B And oxygen. Element E B It can also be at least one element selected from magnesium, aluminum, zirconium, titanium, nickel and zinc.

[0022] Tetragonal crystal 2 can also be represented by the following chemical formula 2. The E in the following chemical formula 2... A It can also be at least one element selected from Na, K, and Ag. E in the following chemical formula 2... BIt can also be at least one element selected from Mg, Al, Zr, Ti, Ni, and Zn. In the following chemical formula 2, x² can be 0.10 or more and 0.85 or less. In the following chemical formula 2, y² can be 0.10 or more and 0.85 or less. In the following chemical formula 2, z² can be 0.05 or more and 0.80 or less. x² + y² + z² can also be 1.00. In the following chemical formula 2, α can be 0.00 or more and less than 1.00.

[0023] Chemical formula 2: x2(Bi) 1－α E A α E B O3-y2BiFeO3-z2Bi(Fe 0.5 Ti 0.5 O3

[0024] The thickness of the second piezoelectric layer can also be greater than 10 nm and less than 300 nm.

[0025] One aspect of the present invention provides a piezoelectric thin film element having said piezoelectric thin film.

[0026] The piezoelectric thin film element may also include a crystalline substrate and an electrode layer superimposed on the crystalline substrate. The lower layer may also be directly superimposed on the electrode layer. An intermediate layer may also be disposed between the crystalline substrate and the electrode layer. The intermediate layer may also include ZrO2 and Y2O3.

[0027] Piezoelectric thin film elements can also have an electrode layer. The lower layer can also be directly superimposed on the electrode layer. The electrode layer can also contain platinum crystals. The (002) facet of the platinum crystals can also be oriented in the normal direction of the surface of the electrode layer. The (200) facet of the platinum crystals can also be oriented in the in-plane direction of the surface of the electrode layer.

[0028] One aspect of the present invention provides a piezoelectric transducer comprising the piezoelectric thin film element.

[0029] According to one aspect of the present invention, a piezoelectric performance index (d) is provided. 33,f / ε r A piezoelectric thin film with ε0), a piezoelectric thin film element including the piezoelectric thin film, and a piezoelectric transducer including the piezoelectric thin film element. Attached Figure Description

[0030] Figure 1A This is a schematic cross-sectional view of a piezoelectric thin film element according to an embodiment of the present invention. Figure 1B yes Figure 1A An exploded three-dimensional view of a piezoelectric thin film element.

[0031] Figure 2It is a three-dimensional diagram of the unit cell of a perovskite structure (perovskite oxide).

[0032] Figure 3A This is a schematic three-dimensional diagram of the unit cell of the tetragonal crystal 1 contained in the first piezoelectric layer. Figure 3B It is a schematic three-dimensional diagram of the unit cells of the crystals contained in the lower layer.

[0033] Figure 4 This is a schematic diagram illustrating the method (ω scan) for measuring the rocking curve of the diffracted X-rays originating from the (001) plane of the tetragonal crystal 1 contained in the first piezoelectric layer.

[0034] Figure 5 This is a schematic cross-sectional view of a piezoelectric thin film (lower layer and first piezoelectric layer) according to an embodiment of the present invention.

[0035] Figure 6 This is a schematic cross-sectional view of a piezoelectric thin film element according to another embodiment of the present invention.

[0036] Figure 7A This is a schematic three-dimensional diagram of the unit cell of the tetragonal crystal 1 contained in the first piezoelectric layer. Figure 7B This is a schematic three-dimensional diagram of the unit cell of the tetragonal crystal 2 contained in the second piezoelectric layer.

[0037] Figure 8 This is a schematic cross-sectional view of a piezoelectric thin film (lower layer, second piezoelectric layer and first piezoelectric layer) according to another embodiment of the present invention.

[0038] Figure 9 This is a schematic cross-sectional view of a piezoelectric thin film element (ultrasonic transducer) according to another embodiment of the present invention.

[0039] Figure 10 This is an example of a rocking curve of X-rays diffracted from the (001) plane of the tetragonal crystal 1 contained in the first piezoelectric layer.

[0040] Figure 11 This is an example of a reciprocal space map of a piezoelectric thin film composed of a lower layer, a second piezoelectric layer, and a first piezoelectric layer. Detailed Implementation

[0041] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiment. In the drawings, the same or equivalent elements are labeled with the same symbols. Figure 1A , Figure 1B , Figure 4 , Figure 6 and Figure 9 The X, Y, and Z axes shown are three mutually orthogonal coordinate axes. The directions of each of the three coordinate axes are... Figure 1A , Figure 1B , Figure 4 , Figure 6 and Figure 9 The same applies to both.

[0042] The piezoelectric thin film element of this embodiment includes a piezoelectric thin film. Figure 1A This is a cross-sectional view of the piezoelectric thin film element 10 according to this embodiment. Figure 1B This is an exploded perspective view of the piezoelectric thin film element 10. The cross-section of the 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) directly or indirectly superimposed on the crystalline substrate 8, a piezoelectric thin film P directly superimposed on the first electrode layer 7, and a second electrode layer 4 (upper electrode layer) directly or indirectly superimposed on the piezoelectric thin film P. The piezoelectric thin film P includes: a lower layer 6 directly superimposed on the first electrode layer 7; and a first piezoelectric layer 3A directly or indirectly superimposed on the lower layer 6. The piezoelectric thin film element 10 may also include an intermediate layer 5. The intermediate layer 5 may also be disposed between the crystalline substrate 8 and the first electrode layer 7, and the first electrode layer 7 may also be directly superimposed on the surface of the intermediate layer 5. Figure 1B As shown, the normal direction dn of the surface of the first piezoelectric layer 3A can also be the same as the normal direction D of the surface of the crystalline substrate 8. N Roughly parallel. The normal direction dn of the surface of the first piezoelectric layer 3A can also be referred to as the thickness direction of the piezoelectric thin film P. Figure 1B In the exploded perspective view of the piezoelectric thin film element 10 shown, the intermediate layer 5, the first electrode layer 7, the lower layer 6, and the second electrode layer 4 are omitted.

[0043] A variation of the piezoelectric thin film element 10 may also omit the crystalline substrate 8. For example, the crystalline substrate 8 may be removed after the first electrode layer 7 and the piezoelectric thin film P are formed. A variation of the piezoelectric thin film element 10 may also omit the second electrode layer 4. For example, a piezoelectric thin film element without a second electrode layer may be supplied as a product to an electronic device manufacturer, and then the second electrode layer is added to the piezoelectric thin film element during the manufacturing process of the electronic device. In the case where the crystalline substrate 8 functions as an electrode, a variation of the piezoelectric thin film element 10 may also omit the first electrode layer 7. That is, a variation of the piezoelectric thin film element 10 may include the crystalline substrate 8 and the piezoelectric thin film P superimposed on the crystalline substrate 8. Without the first electrode layer 7, the lower layer 6 of the piezoelectric thin film P may be directly superimposed on the crystalline substrate 8. Without the first electrode layer 7, the lower layer 6 of the piezoelectric thin film P may be superimposed on the crystalline substrate 8 through an intermediate layer 5.

[0044] The piezoelectric film P may also include a lower layer 6 and a first piezoelectric layer 3A, and further include a second piezoelectric layer 3B. Alternatively, the piezoelectric film P may consist only of the lower layer 6, the first piezoelectric layer 3A, and the second piezoelectric layer 3B. When the piezoelectric 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, Figure 6 The piezoelectric thin film element 10a shown includes a piezoelectric thin film P comprising: a lower layer 6 directly superimposed on the first electrode layer 7, a second piezoelectric layer 3B directly superimposed on the lower layer 6, and a first piezoelectric layer 3A directly superimposed on 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 also be composed only of the lower layer 6 and the first piezoelectric layer 3A.

[0045] The first piezoelectric layer 3A comprises a tetragonal crystal 1 of a perovskite oxide. Of course, the perovskite oxide is an oxide with a perovskite structure. The perovskite oxide is the main component of the first piezoelectric layer 3A. The total content of the elements constituting the perovskite oxide in the first piezoelectric layer 3A can also be 99% mol% or more and 100 mol% or less. The tetragonal crystal 1 can also be a single crystal or a polycrystalline form.

[0046] The second piezoelectric layer 3B comprises tetragonal crystals 2 of perovskite oxides. The perovskite oxides are the principal components of each element in the second piezoelectric layer 3B. The total content of the elements constituting the perovskite oxides in the second piezoelectric layer 3B can also be 99% mol% or more and 100 mol% or less. The tetragonal crystal 2 can also be a single crystal or polycrystalline.

[0047] The first piezoelectric layer 3A may also consist solely of tetragonal crystal 1. The first piezoelectric layer 3A may also not contain tetragonal crystal 2. The first piezoelectric layer 3A may also contain a trace amount of tetragonal crystal 2. The second piezoelectric layer 3B may also consist solely of tetragonal crystal 2. The second piezoelectric layer 3B may also not contain tetragonal crystal 1. The second piezoelectric layer 3B may also contain a trace amount of tetragonal crystal 1.

[0048] The first piezoelectric layer 3A may also contain trace amounts of crystals other than tetragonal crystals, in addition to tetragonal crystal 1. The second piezoelectric layer 3B may also contain trace amounts of crystals other than tetragonal crystals, in addition to tetragonal crystal 2. For example, the trace amounts of crystals other than tetragonal crystals may be crystals of at least one perovskite-type oxide selected from cubic, rhombohedral, pseudocubic, and pseudotetragonal crystals.

[0049] The lower layer 6 contains crystals. For example, the crystals contained in the lower layer 6 may be at least one selected from cubic, tetragonal, rhombohedral, pseudocubic, and pseudotetragonal crystals. The crystals contained in the lower layer 6 may also be single crystals or polycrystalline. The lower layer 6 may also consist solely of crystals.

[0050] Tetragonal crystal 1 can also contain bismuth (Bi), iron (Fe), and element E. B And oxygen (O). The element E contained in tetragonal crystal 1. B It can also be at least one element selected from magnesium (Mg), aluminum (Al), zirconium (Zr), titanium (Ti), nickel (Ni), and zinc (Zn). Tetragonal crystal 1 can also contain multiple elements. B Tetragonal crystal 1 can also be, in addition to containing Bi, Fe, and E. B In addition to O, it further includes element E. A The element E contained in tetragonal crystal 1 A It can also be at least one element selected from sodium (Na), potassium (K), and silver (Ag). Tetragonal crystal 1 can also contain multiple E elements. A .

[0051] Tetragonal crystal 2 may also contain bismuth, iron, and element E. B And oxygen. The tetragonal crystal 2 contains element E. B It can also be at least one element selected from magnesium, aluminum, zirconium, titanium, nickel, and zinc. Tetragonal crystal 2 can also be, in addition to containing Bi, Fe, and E. B In addition to O, it further includes element E. A Tetragonal crystal 2 can also contain various E B The element E contained in tetragonal crystal 2 A It can also be at least one element selected from sodium, potassium, and silver. Tetragonal crystal 2 can also contain various E elements. A .

[0052] The composition of tetragonal crystal 1 can be the same as that of tetragonal crystal 2. The composition of tetragonal crystal 1 can also differ from that of tetragonal crystal 2. Both tetragonal crystal 1 and tetragonal crystal 2 can further contain Bi, Fe, and E. A E B And elements other than O. Tetragonal crystal 1 and tetragonal crystal 2 may each not contain Pb. Tetragonal crystal 1 and tetragonal crystal 2 may each contain Pb. Tetragonal crystal 1 and tetragonal crystal 2 may each contain Fe as iron. 2+ (Fe2+) and Fe 3+ (Trivalent iron) Both sides. Tetragonal crystal 1 and tetragonal crystal 2 may each contain only Fe as the element of iron. 3+ (Trivalent iron).

[0053] Figure 2 The unit cell uc represents the perovskite oxide. Figure 2 In the diagram, a, b, and c are each a fundamental vector of the perovskite structure. The element at site A in the unit cell uc can also be Bi or E. A The element located at the B site in the unit cell uc can also be Fe or E. BA portion of the Fe at site B can also be divalent iron (Fe). 2+ The remaining portion of Fe at site B can also be trivalent iron (Fe2+). 3+ Fe at site B can also be only trivalent iron (Fe). 3+ ).

[0054] Figure 3A The unit cell uc1 represents the tetragonal crystal 1. Figure 3B This represents the unit cell ucL of the crystal contained in the lower layer 6. For ease of illustration, the details are omitted. Figure 3A E in the unit cell uc1 B And O (oxygen), but Figure 3A The unit cell uc1 in the middle has the same characteristics as Figure 2 The cell uc in the middle has the same perovskite structure. The crystals contained in the lower layer 6 are recorded as "lower crystal 6c".

[0055] Figure 3A a1, b1, and c1 are each the fundamental vectors of the tetragonal crystal 1. Figure 3A Vector a1 in Figure 2 The vector 'a' in the text corresponds to this. Figure 3A Vector b1 in Figure 2 The vector b in the text corresponds to this. Figure 3A Vector c1 in Figure 2 The vector c corresponds to the vectors a1, b1, and c1. a1, b1, and c1 are perpendicular to each other. The orientation of vector a1 (a-axis) is

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

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

[001] . The length a1 of vector a1 is the spacing between the (100) planes of the tetragonal crystal 1 (i.e., the lattice constant in the

[100] direction). The length b1 of vector b1 is the spacing between the (010) planes of the tetragonal crystal 1 (i.e., the lattice constant in the

[010] direction). The length c1 of vector c1 is the spacing between the (001) planes of the tetragonal crystal 1 (i.e., the lattice constant in the

[001] direction). Length a1 is equal to length b1. Length c1 is greater than length a1.

[0056] Figure 3B aL, bL, and cL are each the basic vectors of the lower crystal 6c. aL, bL, and cL can also be perpendicular to each other. aL, bL, and cL can also not be perpendicular to each other. The orientation of vector aL (a-axis) is

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

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

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

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

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

[001] direction).

[0057] Figure 7A The unit cell uc1 represents the tetragonal crystal 1. Figure 7B Let uc2 represent the unit cell of tetragonal crystal 2. For ease of illustration, the details are omitted. Figure 7B E in the unit cell uc2 B And O (oxygen), but Figure 7B The unit cell uc2 in the middle has the same characteristics as Figure 2 The cell uc in it has the same perovskite structure. Figure 7A The unit cell uc1 and Figure 3A The unit cell uc1 is the same.

[0058] Figure 7B a2, b2, and c2 are each the basic vectors of the tetragonal crystal 2. Figure 7B The vector a2 in Figure 2 The vector 'a' in the text corresponds to this. Figure 7B Vector b2 in Figure 2 The vector b in the text corresponds to this. Figure 7B The vector c2 in Figure 2 The vector c corresponds to the vectors a2, b2, and c2. a2 (a-axis) is oriented at

[100] . b2 (b-axis) is oriented at

[010] . c2 (c-axis) is oriented at

[001] . The length a2 of vector a2 is the spacing between the (100) planes of tetragonal crystal 2 (i.e., the lattice constant in the

[100] direction). The length b2 of vector b2 is the spacing between the (010) planes of tetragonal crystal 2 (i.e., the lattice constant in the

[010] direction). The length c2 of vector c2 is the spacing between the (001) planes of tetragonal crystal 2 (i.e., the lattice constant in the

[001] direction). Length a2 is equal to length b2. Length c2 is greater than length a2.

[0059] like Figure 1B , Figure 3A and Figure 7A As shown, the (001) plane of the tetragonal crystal 1 (cell uc1) is oriented in the normal direction dn of the surface of the first piezoelectric layer 3A. Figure 1B and Figure 7B As shown, the (001) facet of the tetragonal crystal 2 (cell uc2) is also oriented in the normal direction dn of the surface of the first piezoelectric layer 3A. For example, the (001) facets of the tetragonal crystal 1 and the tetragonal crystal 2 can each be approximately parallel to the surface of the first piezoelectric layer 3A, and the

[001] directions of the tetragonal crystal 1 and the tetragonal crystal 2 can each be approximately parallel to the normal direction dn of the surface of the first piezoelectric layer 3A. The (001) facet of the tetragonal crystal 1 can also be oriented in the normal direction dn of the surface of the crystalline substrate 8. N Upward orientation. The (001) plane of the tetragonal crystal 2 can also be aligned in the normal direction D of the surface of the crystalline substrate 8. NUpward orientation. In other words, the (001) plane of tetragonal crystal 1 and the (001) plane of tetragonal crystal 2 can each be approximately parallel to the surface of the crystalline substrate 8, and the

[001] directions of tetragonal crystal 1 and tetragonal crystal 2 can each be aligned with the normal direction D of the surface of the crystalline substrate 8. N Roughly parallel.

[0060] Tetragonal crystals of perovskite oxides tend to be polarized in the

[001] direction. That is,

[001] is the orientation in which tetragonal crystals of perovskite oxides are more likely to be polarized than other crystal orientations. Therefore, by aligning the (001) facets of tetragonal crystal 1 and tetragonal crystal 2 in the normal direction dn of the surface of the first piezoelectric layer 3A, the piezoelectric film P can have excellent piezoelectricity. For the same reason, the piezoelectric film P can also be a ferroelectric material. In the case where the piezoelectric film P only includes the first piezoelectric layer 3A and the second piezoelectric layer 3B, the "crystal orientation" described below refers to the orientation of the (001) facets of tetragonal crystal 1 in the normal direction dn of the surface of the first piezoelectric layer 3A. In the case where the piezoelectric thin film P includes both the first piezoelectric layer 3A and the second piezoelectric layer 3B, the “crystal orientation” described below refers to the orientation of the (001) facet of the tetragonal crystal 1 and the (001) facet of the tetragonal crystal 2 in the normal direction dn of the surface of the first piezoelectric layer 3A.

[0061] The piezoelectric thin film P possesses the aforementioned crystal orientation, thereby enabling it to exhibit a large piezoelectric performance index (d). 33,f / ε r ε0). The aforementioned crystal orientation is an inherent characteristic of thin films. Thin films are crystalline films formed through methods such as vapor phase growth or solution processing. On the other hand, bulk piezoelectric bodies with the same composition as the piezoelectric thin film P are unlikely to possess the aforementioned crystal orientation. This is because the bulk piezoelectric body is a sintered body (ceramic) containing powders of the essential elements for piezoelectricity, making it difficult to control the structure and orientation of the multiple crystals constituting the sintered body. Since the bulk piezoelectric body contains elements such as Fe, its resistivity is lower than that of the piezoelectric thin film P. As a result, leakage current is easily generated in the bulk piezoelectric body. Therefore, it is difficult to polarize the bulk piezoelectric body by applying a high electric field, and the bulk piezoelectric body is unlikely to have a large piezoelectric performance index.

[0062] As described above, the spacing between the (100) planes of the tetragonal crystal 1 is a1, and the spacing between the (100) planes of the crystal contained in the lower layer 6 (lower crystal 6c) 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-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 3A. The full width at half maximum (FWHM) of the rocking curve RC is 1.9° or more and 5.5° or less.

[0063] When the lattice mismatch rate Δa is within the aforementioned range, the FWHM of the rocking curve RC can be easily controlled within this range. When the lattice mismatch rate Δa is less than 3.0%, the FWHM of the rocking curve RC tends to be less than 1.9°. When the lattice mismatch rate Δa is greater than 12.1%, the FWHM of the rocking curve RC tends to be greater than 5.5°. 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. Therefore, by selecting and combining the compositions and crystal structures of the first piezoelectric layer 3A and the lower layer 6, the lattice mismatch rate Δa can also be controlled.

[0064] By using the rocking curve RC with a FWHM greater than 1.9° and less than 5.5°, the piezoelectric thin film P can possess a large piezoelectric performance index (d). 33,f / ε r ε0). That is, the FWHM of the rocking curve RC is above 1.9° and below 5.5°, which can take into account the large piezoelectric strain constant d of the piezoelectric thin film P. 33,f And the low relative permittivity ε of the piezoelectric thin film P r .

[0065] For example, the piezoelectric property index (d) of the piezoelectric thin film P 33,f / ε r ε0) can also be 150×10 －3 V·m / N or higher and 239×10 －3 Below V·m / N, or 155×10 －3 V·m / N or higher and 222×10 －3 Below V·m / N.

[0066] For example, the piezoelectric strain constant d of the piezoelectric thin film P 33,f It can also be 147 pC / N or higher and 179 pC / N or lower and 149 pC / N or higher and 174 pC / N or lower.

[0067] For example, the relative permittivity ε of the piezoelectric thin film P r (or ε) 33 It can also be 85 or higher and 150 or lower, or 88 or higher and 127 or lower.

[0068] The inventors hypothesize that the piezoelectric thin film P can possess a large piezoelectric performance index (d) through the following mechanism. 33,f / ε r ε0).

[0069] Because of lattice mismatches such as a lattice mismatch rate Δa of 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 tends to have a low relative permittivity ε. r Furthermore, due to lattice mismatch such that the lattice mismatch rate Δa is 3.0% or more and 12.1% or less, the (001) plane of the tetragonal crystal 1 is tilted to a degree where the FWHM of the rocking curve RC is 1.9° or more and 5.5° or less. That is, the FWHM of the rocking curve RC represents the degree of tilt of the (001) plane of the tetragonal crystal 1 caused by lattice mismatch, and at least a portion 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, Figure 5 This indicates the tilt of the (001) plane of the tetragonal crystal 1 that constitutes the first piezoelectric layer 3A directly superimposed on the lower layer 6. Figure 8 This indicates the tilt of the (001) plane of the tetragonal crystal 1 that constitutes the first piezoelectric layer 3A, which is directly superimposed on the second piezoelectric layer 3B. That is, even when the second piezoelectric layer 3B is disposed 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 tilted. Since the (001) plane of the tetragonal crystal 1 is tilted to a degree where the FWHM of the rocking curve RC is more than 1.9° and less than 5.5°, the polarization axis of the tetragonal crystal 1 rotates when an electric field is applied, and the piezoelectric thin film P tends to have a large piezoelectric strain constant d. 33,f For the reasons mentioned above, it is possible to achieve a low relative permittivity ε. r and large piezoelectric strain constant d 33,f The piezoelectric thin film P has a large piezoelectric property index (d). 33 / ε r ε0). When the FWHM of the rocking curve RC is less than 1.9°, the (001) plane of the tetragonal crystal 1 is not sufficiently tilted, and the piezoelectric thin film P is difficult to have a large piezoelectric strain constant d. 33,f When the FWHM of the rocking curve RC is greater than 5.5°, the crystal orientation of the first piezoelectric layer 3A is excessively damaged, making it difficult for the piezoelectric thin film P to possess a large piezoelectric strain constant d. 33,f .

[0070] The above mechanism is an assumption, and the technical scope of the present invention is not limited by the above mechanism.

[0071] The spacing and orientation of the crystal planes of tetragonal crystal 1, tetragonal crystal 2, and the lower crystal 6c can also be determined based on the X-ray diffraction (XRD) pattern of the piezoelectric thin film P measured by the 2θ-θ method in both the out-of-plane and in-plane directions of the surface of the first piezoelectric layer 3A. Crystal planes can also be referred to as lattice planes.

[0072] The rocking curve RC of the diffraction X-rays from the (001) plane of the tetragonal crystal 1 was determined by an out-of-plane ω scan of the surface of the first piezoelectric layer 3A. A summary of the ω scan is as follows: Figure 4 As shown. ω-scan is a type of out-of-plane measurement. In an ω-scan, incident X-rays are irradiated from an X-ray source XR onto the surface of the first piezoelectric layer 3A. Direction d1 is the direction of the incident X-rays. The incident X-rays diffract on the (001) plane of the tetragonal crystal 1 contained in the first piezoelectric layer 3A and are detected by the detector D as diffracted X-rays. When the reference point is defined as the position on the surface of the first piezoelectric layer 3A irradiated by the incident X-rays, direction d2 is the direction from the reference point toward the detector D. That is, direction d2 is the direction of the detector D relative to the position irradiated by the incident X-rays. 2θ1 is the diffraction angle with the maximum intensity of the diffracted X-rays originating from the (001) plane of the tetragonal crystal 1. 2θ1 can also be determined using 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 relative to the direction d1 of the incident X-rays. The unit of ω is degrees (°). ω-scan is a method that continuously measures the intensity of diffracted X-rays originating from the (001) plane of tetragonal crystal 1 by fixing the angle between directions d1 and d2 as the diffraction angle 2θ1 and varying ω. The rocking curve RC can also be described as the tilted distribution of the intensity of diffracted X-rays originating from the (001) plane of tetragonal crystal 1.

[0073] Figure 10An example of a rocking curve RC representing the diffracted X-rays from the (001) plane of tetragonal 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 intensity of the diffracted X-rays can also be arbitrary unit. The origin of the horizontal axis of the rocking curve RC corresponds to ω (i.e., θ1) where the intensity of the diffracted X-rays originating from the (001) plane of tetragonal crystal 1 is the greatest. When ω0 is defined as the ω where the intensity of the diffracted X-rays originating from the (001) plane of tetragonal crystal 1 is the greatest, the rocking curve RC is the distribution of the intensity of diffracted X-rays in the range of ω above (ω0 - Δω) and below (ω0 + Δω). The incident X-rays can also be characteristic X-rays (e.g., CuKα rays).

[0074] The spacing and orientation of each crystal facet of tetragonal crystal 1, tetragonal crystal 2, and the lower crystal 6c can also be determined according to the reciprocal space mapping. That is, tetragonal crystal 1, tetragonal crystal 2, and the lower crystal 6c can also be detected and identified by the reciprocal space mapping of the X-ray diffraction pattern described above. The reciprocal space mapping can also be called a distribution map of the intensity of diffracted X-rays in reciprocal space. For example, the reciprocal space mapping can also 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 ω axis, φ axis, χ axis, 2θ axis, and 2θχ axis. For example, the reciprocal space mapping can also be a two-dimensional graph of a coordinate system composed of orthogonal horizontal and vertical axes. The horizontal axis of the two-dimensional reciprocal space mapping can also be 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 reciprocal lattice space diagram can also be a value corresponding to the reciprocal of the spacing a (i.e., 1 / a) of the (100) plane. The vertical axis of the two-dimensional reciprocal lattice space diagram can also be 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 reciprocal lattice space diagram can also be a value corresponding to the reciprocal of the spacing c (i.e., 1 / c) of the (001) plane. The reciprocal lattice space diagram contains multiple spots. A spot corresponds to the diffracted X-ray originating from a crystal plane of any of the tetragonal crystals 1, 2, and the lower crystal 6c. The spacing and orientation direction of a crystal plane of any of the tetragonal crystals 1, 2, and the lower crystal 6c can also be determined based on the coordinates of a spot in the reciprocal lattice space diagram. Figure 11 This is an example of the reciprocal space diagram of a piezoelectric thin film P composed of a lower layer 6, a second piezoelectric layer 3B, and a first piezoelectric layer 3A. Figure 11S3A-(204) is the point corresponding to the (204) face of the tetragonal crystal 1 contained in the first piezoelectric layer 3A. S3B-(204) is the point corresponding to the (204) face of the tetragonal crystal 2 contained in the second piezoelectric layer 3B. S6-(204) is the point corresponding to the (204) face of the lower crystal 6c contained in the lower layer 6. S3A-(004) is the point corresponding to the (004) face of the tetragonal crystal 1 contained in the first piezoelectric layer 3A. S3B-(004) is the point corresponding to the (004) face of the tetragonal crystal 2 contained in the second piezoelectric layer 3B. S6-(004) is the point corresponding to the (004) face of the lower crystal 6c contained in the lower layer 6.

[0075] The spacing aL of the (100) plane of the lower crystal 6c contained in the lower layer 6 can also be The above and The following, or The above and Below. The spacing a1 of the (100) plane of the tetragonal crystal 1 contained in the first piezoelectric layer 3A can also be... The above and The following, or The above and When aL and a1 are within the above range, it is easy to control the lattice mismatch rate Δa within the range of 3.0% or higher and 12.1% or lower.

[0076] like Figure 1B and Figure 3B As shown, the (001) plane of the lower crystal 6c (cell ucL) contained in the lower layer 6 can also be oriented in the normal direction dn of the surface of the first piezoelectric layer 3A. When the (001) plane of the lower crystal 6c (cell ucL) is oriented in the normal direction dn of the surface of the first piezoelectric layer 3A, it is easy to control the lattice mismatch rate Δa within the range of 3.0% or more and 12.1% or less.

[0077] The lower crystal 6c contained in the lower layer 6 may also contain at least one compound selected from strontium ruthenium ruthenium oxide (SrRuO3), barium titanate (BaTiO3), and titanium nitride (TiN). Alternatively, the lower crystal 6c contained in the lower layer 6 may consist only of one compound selected from strontium ruthenium oxide, barium titanate, and titanium nitride. When the lower crystal 6c contained in the lower layer 6 contains at least one compound selected from strontium ruthenium oxide, barium titanate, and titanium nitride, it is easy to control the lattice mismatch rate Δa within the range of 3.0% or more and 12.1% or less.

[0078] The lower crystal 6c, composed of strontium ruthenium ruthenium oxide, has a perovskite-type crystal structure. The spacing aL of the (100) planes of the lower crystal 6c composed of strontium ruthenium ruthenium oxide is approximately... The existing thin film (piezoelectric layer) composed of lead zirconate titanate (PZT) has a spacing a1 on the (100) side that is greater than that of the piezoelectric layer. Large. The spacing a1 of the (100) plane of the existing bismuth ferrite (BiFeO3) thin film (piezoelectric layer) is approximately Therefore, when the lower layer 6 is composed of strontium ruthenate and the first piezoelectric layer is composed of lead zirconate titanate or bismuth ferrite, the lattice mismatch rate Δa is negative. When the lattice mismatch rate Δa is negative, the relative permittivity ε of the piezoelectric thin film P is... r The piezoelectric index is relatively low, but the FWHM of the rocking curve RC is small, making it difficult for piezoelectric thin films P to have a large piezoelectric performance index.

[0079] The lower layer 6, which contains strontium ruthenium ruthenium oxide, is conductive. When the lower layer 6 is conductive, it can also function as the first electrode layer 7; the piezoelectric thin film element may not include a first electrode layer 7 that is different from the lower layer 6.

[0080] The lower crystal 6c, composed of barium titanate, has a perovskite-type crystal structure. The spacing aL of the (100) planes of the lower crystal 6c, composed of barium titanate, is approximately... The lower crystal 6c composed of titanium nitride has a sodium chloride-type structure (face-centered cubic lattice structure). The spacing aL of the (100) planes of the lower crystal 6c composed of titanium nitride is approximately The piezoelectric thin film P formed by crystallizing at least one of barium titanate and titanium nitride in the lower layer 6 tends to have a larger piezoelectric performance index than the piezoelectric thin film P formed by crystallizing strontium ruthenate in the lower layer 6.

[0081] The c2 / a2 ratio of the tetragonal crystal 2 contained in the second piezoelectric layer 3B can also be smaller than the c1 / a1 ratio of the tetragonal crystal 1 contained in the first piezoelectric layer 3A. That is, the anisotropy of the tetragonal crystal 2 can also be lower than that of the tetragonal crystal 1.

[0082] When c1 / a1 is larger than c2 / a2, the relative permittivity of tetragonal crystal 1 is lower than that of tetragonal crystal 2. However, since c1 / a1 is larger than c2 / a2, the crystal structure of tetragonal crystal 1 is more robust than that of tetragonal crystal 2, and the atoms in tetragonal crystal 1 are less mobile than those in tetragonal crystal 2. Therefore, polarization reversal is more difficult to occur in tetragonal crystal 1 than in tetragonal crystal 2, and the piezoelectricity of tetragonal crystal 1 itself is lower than that of tetragonal crystal 2. In other words, when c2 / a2 is smaller than c1 / a1, the relative permittivity of tetragonal crystal 2 is higher than that of tetragonal crystal 1, but the crystal structure of tetragonal crystal 2 is more flexible than that of tetragonal crystal 1, and the atoms in tetragonal crystal 2 are more mobile than those in tetragonal crystal 1. Therefore, polarization reversal is more likely to occur in tetragonal crystal 2 than in tetragonal crystal 1.

[0083] When c2 / a2 is smaller than c1 / a1 and an electric field is applied to the piezoelectric thin film P, the polarization reversal of the tetragonal crystal 2 in the second piezoelectric layer 3B tends to occur before the polarization reversal of the tetragonal crystal 1 in the first piezoelectric layer 3A. Because the polarization reversal of the tetragonal crystal 2 occurs before the polarization reversal of the tetragonal crystal 1, the crystal structure of the tetragonal 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 the tetragonal crystal 2, the polarization of the tetragonal crystal 1 is prone to fluctuation at the interface between the tetragonal crystal 1 and the tetragonal crystal 2. For example, due to the polarization reversal of the tetragonal crystal 2 in the second piezoelectric layer 3B, at the interface between the first piezoelectric layer 3A and the second piezoelectric layer 3B, the charge on the surface of the second piezoelectric layer 3B repels the charge on the surface of the first piezoelectric layer 3A, causing the polarization of the tetragonal crystal 1 to fluctuate.

[0084] Due to the aforementioned mechanism, the polarization reversal of tetragonal crystal 2 triggers the polarization reversal of tetragonal crystal 1. That is, by configuring the second piezoelectric layer 3B as a buffer layer to promote the polarization reversal of the first piezoelectric layer 3A between the lower layer 6 and the first piezoelectric layer 3A, polarization reversal easily occurs across the entire piezoelectric film P. As a result, the overall piezoelectricity of the piezoelectric film P is superior to that of tetragonal crystal 1 itself, easily achieving a large dp polarization. 33,f and low ε r Piezoelectric thin films P tend to have large piezoelectric performance indices.

[0085] However, the above-mentioned mechanisms related to c1 / a1 and c2 / a2 are assumptions, and the technical scope of the present invention is not limited by the above-mentioned mechanisms.

[0086] Compared to piezoelectric thin films (P), it is difficult for stress to cause deformation of the crystal structure in bulk piezoelectric materials. Therefore, most of the perovskite oxides constituting bulk piezoelectric materials are cubic crystals, and bulk piezoelectric materials tend to be less likely to exhibit piezoelectricity caused by the tetragonal crystal structure of perovskite oxides compared to piezoelectric thin films (P).

[0087] The c1 / a1 ratio of the tetragonal crystal 1 can also be 1.050 or higher and 1.250 or lower, or 1.063 or higher and 1.249 or lower. When c1 / a1 is 1.050 or higher, the relative permittivity of the first piezoelectric layer 3A containing the tetragonal crystal 1 and the piezoelectric film P tends to decrease, and the piezoelectric index of the piezoelectric film P tends to increase. When c1 / a1 is 1.250 or lower, polarization reversal of the tetragonal crystal 1 tends to occur, and the piezoelectric index of the piezoelectric film P tends to increase. For example, c1 can also be... The above and the following.

[0088] c2 / a2 can also be 1.010 or higher and 1.110 or lower, or 1.014 or higher and 1.108 or lower. Since c2 / a2 is within these ranges, polarization reversal of tetragonal crystal 2 is more likely to occur than that of tetragonal crystal 1, and polarization reversal of tetragonal crystal 2 easily induces polarization reversal of tetragonal crystal 1, resulting in a large piezoelectric index for the piezoelectric film P. When c2 / a2 is outside these ranges, there is a tendency for the relative permittivity of tetragonal crystal 2 to be too high, or for the piezoelectricity of tetragonal crystal 2 itself to deteriorate. For example, c2 can also be... The above and The following. For example, a2 can also be... The above and the following.

[0089] Alternatively, the relationship between cL, c1, and c2, as well as the relationship between aL, a1, and a2, can be determined by observing the cross-section of the piezoelectric film P parallel to the thickness direction of the piezoelectric film P at atomic energy level resolution using a scanning transmission electron microscope (STEM).

[0090] To determine the specific values ​​of c1 and c2 with high precision, the out-of-plane (OOF) measurement method (2θ-θ method) can be used to measure the peak P1 of the diffracted X-rays from the (001) plane of tetragonal crystal 1 and the peak P2 of the diffracted X-rays from the (001) plane of tetragonal crystal 2. The measured X-ray diffraction pattern includes both peaks P1 and P2. When the diffraction angle 2θ1 of the peak P1 of the diffracted X-rays from the (001) plane of tetragonal crystal 1 is close to the diffraction angle 2θ2 of the peak P2 of the diffracted X-rays from the (001) plane of tetragonal crystal 2, and a peak P3 that coincides with peaks P1 and P2 is measured, peak P1 can be approximated by a Gaussian function g1, and peak P2 can be approximated by another Gaussian function g2. Curve fitting of g1+g2 and peak P3 can also be performed. Alternatively, g1 after curve fitting can be regarded as P1, and g2 after curve fitting can be regarded as P2.

[0091] To determine the specific values ​​of a1 and a2 with high precision, the peaks P1' and P2' of the diffracted X-rays from the (100) plane of tetragonal crystal 1 and tetragonal crystal 2 can be measured using the in-plane measurement method (2θ-θ method) on the surface of the piezoelectric thin film P. A measured X-ray diffraction pattern includes both peaks P1' and P2'. When the diffraction angle 2θ1' of the peak P1' from the (100) plane of tetragonal crystal 1 is close to the diffraction angle 2θ2' of the peak P2' from the (100) plane of tetragonal crystal 2, and a peak P3' that coincides with peaks P1' and P2' is measured, peak P1' can be approximated by a Gaussian function G1, and peak P2' can be approximated by another Gaussian function G2. Curve fitting between G1+G2 and peak P3' can also be performed. Alternatively, the curve-fitted G1 can be regarded as P1', and the curve-fitted G2 can be regarded as P2'.

[0092] The peak intensity (maximum intensity) of the X-ray diffracted from the (001) plane of tetragonal crystal 1 is I1. The peak intensity (maximum intensity) of the X-ray diffracted from the (001) plane of tetragonal crystal 2 is I2. I1 / (I1+I2) can also be 0.90 or higher and less than 1.00, or 0.91 or higher and less than 0.99. When I1 / (I1+I2) is within the above range, it is easy to take into account a large piezoelectric strain constant (d). 33,f and low relative permittivity (ε) r The piezoelectric thin film P tends to have a large piezoelectric property index. The units for I1 and I2 can also be, for example, cps (counts per second). I1 and I2 can also be measured by out-of-plane measurements on the surface of the first piezoelectric layer 3A. The measurement conditions for I1 and I2 can also be set such that I1 and I2 are each at least 3 bits higher than the background intensity.

[0093] I1 can also be proportional to the total area of ​​the (001) faces of the tetragonal crystal 1 oriented in the normal direction dn of the surface of the first piezoelectric layer 3A, and I2 can also be proportional to the total area of ​​the (001) faces of the tetragonal crystal 2 oriented in the normal direction dn of the surface of the first piezoelectric layer 3A. In other words, I1 can also be proportional to the amount of tetragonal crystal 1 contained in the piezoelectric film P, and I2 can also be proportional to the amount of tetragonal crystal 2 contained in the piezoelectric film P. Therefore, I1 / (I1+I2) can also be the ratio of the presence of tetragonal crystal 1 relative to the total amount of tetragonal crystal 1 and tetragonal crystal 2. That is, the ratio of the presence of tetragonal crystal 1 relative to the total amount of tetragonal crystal 1 and tetragonal crystal 2 can also be 90% or more and less than 100%.

[0094] The degree of orientation of the (001) plane of tetragonal crystal 1 and the (001) plane of tetragonal crystal 2 can also be quantified based on the degree of orientation. The greater the degree of orientation of the (001) plane of tetragonal crystal 1 and the (001) plane of tetragonal crystal 2, the easier it is for the piezoelectric thin film P to have a large piezoelectric performance index. The degree of orientation of each crystal plane can also be calculated based on the peaks of diffracted X-rays originating from each crystal plane. The peaks of diffracted X-rays originating from each crystal plane can also be determined by out-of-plane measurement on the surface of the first piezoelectric layer 3A.

[0095] The orientation degree of the tetragonal crystal 1 (001) plane on the normal direction dn of the surface of the first piezoelectric layer 3A can also be expressed as 100×I1 / ΣI 1(hkl) ΣI 1(hkl) It is the sum of the peak intensities of diffracted X-rays from each crystal plane of the tetragonal crystal 1, measured in the out-of-plane direction on the surface of the first piezoelectric layer 3A. ΣI 1(hkl) For example, it can also be I. 1(001) +I 1(110) +I 1(111) I 1(001) This refers to I1 as mentioned above. That is, I... 1(001) The peak intensity (maximum intensity) of the diffracted X-rays from the (001) plane of the tetragonal crystal 1 is measured in the out-of-plane direction on the surface of the first piezoelectric layer 3A. 1(110) The peak intensity (maximum intensity) of the diffracted X-rays from the (110) plane of the tetragonal crystal 1 is measured in the out-of-plane direction on the surface of the first piezoelectric layer 3A. 1(111) The peak intensity (maximum intensity) of the diffracted X-rays on the (111) plane of the tetragonal crystal 1 is measured in the out-of-plane direction on the surface of the first piezoelectric layer 3A.

[0096] The orientation degree of the (001) plane of tetragonal crystal 2 can also be expressed as 100×I² / ΣI 2(hkl) ΣI 2(hkl) It is the sum of the peak intensities of the diffracted X-rays from each crystal plane of the tetragonal crystal 2, measured in the out-of-plane direction on the surface of the first piezoelectric layer 3A. ΣI 2(hkl) For example, it can also be I. 2(001) +I 2(110) +I 2(111) I 2(001) This refers to I2 as mentioned above. That is, I... 2(001) The peak intensity (maximum intensity) of the diffracted X-rays from the (001) plane of the tetragonal crystal 2 is measured in the out-of-plane direction on the surface of the first piezoelectric layer 3A. 2(110)The peak intensity (maximum intensity) of the diffracted X-rays from the (110) plane of the tetragonal crystal 2 is measured in the out-of-plane direction on the surface of the first piezoelectric layer 3A. 2(111) The peak intensity (maximum intensity) of the diffracted X-rays on the (111) plane of the tetragonal crystal 2 is measured in the out-of-plane direction on the surface of the first piezoelectric layer 3A.

[0097] The degree of orientation of the (001) facet of tetragonal crystal 1 and the (001) facet of tetragonal crystal 2 can also be quantified by the degree of orientation F based on the Lotgering method. Even when the degree of orientation is calculated by any of the above methods, the degree of orientation of the (001) facet of tetragonal crystal 1 and the (001) facet of tetragonal crystal 2 can 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) facet of tetragonal crystal 1 can also be oriented in the normal direction dn of the surface of the first piezoelectric layer 3A, which is preferred over the other crystal faces of tetragonal crystal 1. The (001) facet of tetragonal crystal 2 can also be oriented in the normal direction dn of the surface of the first piezoelectric layer 3A, which is preferred over the other crystal faces of tetragonal crystal 2.

[0098] One or both of tetragonal crystal 1 and tetragonal crystal 2 may contain Fe. 2+ One or both of tetragonal crystal 1 and tetragonal crystal 2 contain Fe. 2+ In such cases, the piezoelectric thin film P tends to have a large piezoelectric performance index.

[0099] In the case of a BiFeO3-(Bi,K)TiO3 system piezoelectric thin film having a composition near the morphotropic phase boundary (MPB) between tetragonal and rhombohedral crystals, the piezoelectricity originating from the tetragonal crystal (d 33,f The dielectric constant (ε0ε) increases, but the dielectric constant (ε0ε) decreases. rThe increase in dielectric constant also makes it difficult to improve the piezoelectric performance index. To suppress this increase, it is desirable to improve the piezoelectricity (ferroelectricity) of the piezoelectric film by constructing it solely from tetragonal crystals. The tetragonality of the piezoelectric film is achieved through epitaxial stress (compressive stress caused by lattice mismatch). This is because, due to the epitaxial stress parallel to the surface of the piezoelectric film, the film is compressed in directions parallel to its surface (i.e., the a-axis and b-axis directions), causing deformation. However, the thicker the piezoelectric film, the more difficult it is to improve its tetragonality solely through epitaxial stress. This is because the thicker the film, the more difficult it is to deform the entire film through epitaxial stress. Furthermore, the lattice mismatch rate Δa is positive (above 3.0% and below 12.1%), therefore, tensile stress (not compressive stress) easily acts on the first piezoelectric layer 3A and the second piezoelectric layer 3B. Therefore, even when the piezoelectric film thickens to the point that the epitaxial stress generated within the piezoelectric film weakens, making it difficult for compressive stress to act on the piezoelectric film, it is desirable to maintain the stability of the tetragonal crystal structure of the piezoelectric film. Thus, in one or both of tetragonal crystal 1 and tetragonal crystal 2, it is also possible that the electronic configuration of the element (ion) located at the B site in the perovskite oxide becomes similar to that of Co constituting BiCoO3. 3+ The d6 electron configuration is the same, using Fe 2+ The ions at site B are replaced. As a result, even when the piezoelectric film P is thickened to the point that the epitaxial stress generated within the piezoelectric film P is reduced, the tetragonal crystallinity of the piezoelectric film P is improved. In other words, even when the piezoelectric film P is thickened to the point that the epitaxial stress generated within the piezoelectric film P is reduced, the first piezoelectric layer 3A tends to contain tetragonal crystal 1, and the second piezoelectric layer 3B tends to contain tetragonal crystal 2.

[0100] In the case of the compositional system near the MPB, which is expected to form rhombohedral crystals in the piezoelectric bulk, a portion of the B sites can be affected by Fe. 2+ The rotation (rotation about the c-axis) of the BO6 octahedrons (or BO5 pyramids) within the substituted tetragonal crystals is inhibited, but the polarization rotation caused by the formation of pseudocubic crystals is suppressed. In other words, a portion of the B sites is affected by Fe. 2+ In substituted perovskite oxides, MPB is difficult to exist, making it difficult to cause polarization rotation that alters the direction of the c-axis of tetragonal crystals.

[0101] Through the above mechanism, one or both of tetragonal crystal 1 and tetragonal crystal 2 contain Fe. 2+ In this case, it is easy to take into account a large piezoelectric strain constant (d). 33,f and low relative permittivity (ε) r The piezoelectric index tends to increase with Fe. However, compared to Fe... 2+ The aforementioned mechanisms are assumptions, and the technical scope of this invention is not limited to Fe.2+ The aforementioned mechanisms apply.

[0102] Compared to piezoelectric thin films (P), stress-induced deformation of the crystal structure is less likely to occur in bulk piezoelectric materials. Therefore, most of the perovskite oxides constituting bulk piezoelectric materials are cubic crystals, and bulk piezoelectric materials tend to be less prone to exhibiting piezoelectricity caused by the tetragonal crystal structure of perovskite oxides compared to piezoelectric thin films (P).

[0103] The thicknesses of the crystalline substrate 8, intermediate layer 5, first electrode layer 7, lower layer 6, second piezoelectric layer 3B, first piezoelectric layer 3A, and second electrode layer 4 can all be the same.

[0104] The thickness TL of the lower layer 6 along the normal direction dn of the surface of the first piezoelectric layer 3A can also be 10 nm or more and 350 nm or less. When the thickness TL of the lower layer 6 is within the above range, it is easy to control the lattice mismatch rate Δa within the range of 3.0% or more and 12.1% or less, and it is easy to control the FWHM of the rocking curve RC within the range of 1.9° or more and 5.5° or less.

[0105] The thickness T1 of the first piezoelectric layer 3A along the normal direction dn of its surface can also be greater than the thickness T2 of the second piezoelectric layer 3B along the normal direction dn of its surface. The thickness Tp of the piezoelectric film P can also 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 film P can also 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 can also 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 can also 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 film P tends to have a large piezoelectric performance index. When the thickness T2 of the second piezoelectric layer 3B is less than 300 nm, the relative permittivity of the piezoelectric film P tends to decrease, and the piezoelectric performance index of the piezoelectric film P tends to increase. Even when the thickness Tp of the piezoelectric film P is 510 nm or more, and the piezoelectric film P is relatively thick, the ions located at the B site of the perovskite oxide are subjected to Fe... 2+ Substitution also allows piezoelectric thin films P to easily possess a large piezoelectric index. By adjusting the thickness Tp of the piezoelectric thin film P to below 5350 nm, tetragonal crystals 1 and 2 can be easily formed without relying on epitaxial stress, thus allowing the piezoelectric thin film P to easily possess a large piezoelectric index.

[0106] TL, T1, T2, and Tp are not limited to the ranges mentioned above. There are no limitations on the methods for measuring TL, T1, T2, and Tp. For example, the thickness Tp of the piezoelectric film P can also be measured by scanning electron microscopy (SEM) on a cross-section of the piezoelectric film P parallel to the normal direction dn of the surface of the first piezoelectric layer 3A. Alternatively, the lower layer 6, the first piezoelectric layer 3A, and the second piezoelectric layer 3B can be identified on the cross-section of the piezoelectric film P based on differences in composition or the relationships between cL / aL, c1 / a1, and c2 / a2. TL, T1, and T2 can also be measured by SEM on the cross-section of the piezoelectric film P.

[0107] Tetragonal crystal 1 can also be represented by the following chemical formula 1. The following chemical formula 1 is substantially the same as the following chemical formula 1a.

[0108] Chemical Formula 1:

[0109] x1(Bi 1－α E A α E B O3-y1BiFeO3-z1Bi(Fe 0.5 Ti 0.5 O3

[0110] Chemical formula 1a:

[0111] (Bi x1(1－α)+y1+z1 E A x1α (E) B x1 Fe y1+0.5z1 Ti 0.5z1 )O 3±δ

[0112] In the above chemical formula 1, x1+y1+z1 can also be 1.00. E in the above chemical formula 1... A The elements mentioned above. E in the above chemical formula 1. B For the elements mentioned above.

[0113] The composition of the above chemical formula 1 (Bi) 1－α E A α E B The Bi of O3 is 3-price Bi (Bi 3+ ) or 5-price Bi(Bi 5+ The composition of the above chemical formula 1 (Bi) 1－α E A α E B O3 of E A The sum of the valences (ion valences) is expressed as V. AComposition (Bi) 1－α E A α E B O3 of E B The sum of the valences (ion valences) is expressed as V. B The composition of chemical formula 1 (Bi) 1－α E A α E B O3's Bi, E A and E B The sum of the valences is expressed as 3(1-α)+V A α+V B or 5(1-α)+V A α+V B 3(1-α)+V A α+V B or 5(1-α)+V A α+V B It can also be +6.3(1-α)+V in equilibrium with the sum of the valences (ionic valences) of O (-6). A α, or 5(1-α)+V A α can also be +3. V B It can also be +3. This refers to element E in the above chemical formula 1. B The two elements are represented by element E. B1 and element E B2 In the case of [specific situation], the above chemical formula 1 is substantially the same as the following chemical formula 1'. In the following chemical formula 1', β can also be 0.00 or more and 1.00 or less. E B1 The valence (ionic valence) is expressed as V. B1 E B2 The valence (ionic valence) is expressed as V. B2 E B The sum of valences (ion valences) V B Represented as (1-β)V B1 +βV B2 (1-β)V B1 +βV B2 It can also be +3.

[0114] Chemical formula 1':

[0115] x1(Bi 1－α E A α (E) B1 1－β E B2 β )O3-y1BiFeO3-z1Bi(Fe 0.5 Ti 0.5Bi in the above chemical formula 1a) x1(1－α)+y1+z1 E A x1α The element at site A corresponds to the perovskite structure. E in chemical formula 1a B x1 Fe y1+0.5z1 Ti 0.5z1 It corresponds to the element located at the B site in the perovskite structure.

[0116] The Fe valence of the component y1BiFeO3 in the above chemical formula 1 is 3, but the Fe valence of the component z1Bi(Fe) in the above chemical formula 1 is 3. 0.5 Ti 0.5 The Fe valence of O3 is 2. Therefore, through the Bi and E in the raw material of the first piezoelectric layer 3A... A E B The molar ratios of Fe and Ti are the same as those of Bi and E in the above chemical formula 1. A E B The composition of the raw materials for the first piezoelectric layer 3A is adjusted by ensuring a consistent molar ratio of Fe and Ti, so that the tetragonal crystal 1 can contain Fe. 2+ .

[0117] In the above chemical formula 1, x1 can also be 0.10 or higher and 0.90 or lower, 0.10 or higher and 0.85 or lower, or 0.15 or higher and 0.85 or lower. When x1 is 0.10 or higher and 0.90 or lower, tetragonal crystal 1 tends to have the above crystal orientation, c1 / a1 tends to be within the above range, lattice mismatch rate Δa tends to be within the above range, and the FWHM of the rocking curve RC tends to be within the above range.

[0118] In the above chemical formula 1, y1 can also be 0.05 or higher and 0.85 or lower, or 0.05 or higher and 0.80 or lower. When y1 is 0.05 or higher and 0.85 or lower, tetragonal crystal 1 tends to have the above crystal orientation, c1 / a1 tends to be within the above range, lattice mismatch rate Δa tends to be within the above range, and the FWHM of the rocking curve RC tends to be within the above range.

[0119] In the above chemical formula 1, z1 can also 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, tetragonal crystal 1 tends to have the above crystal orientation, c1 / a1 tends to be within the above range, lattice mismatch rate Δa tends to be within the above range, and the FWHM of the rocking curve RC tends to be within the above range.

[0120] In the above chemical formula 1, α can also be 0.00 or more and less than 1.00. Tetragonal crystal 1 readily exhibits the aforementioned crystal orientation, c1 / a1 is readily within the aforementioned range, the lattice mismatch rate Δa is readily within the aforementioned range, and the FWHM of the rocking curve RC is readily within the aforementioned range; therefore, α can also be 0.50. As described above, in the above chemical formula 1', β can also be 0.00 or more and less than 1.00, or greater than 0.00 and less than 1.00. Tetragonal crystal 1 readily exhibits the aforementioned crystal orientation, c1 / a1 is readily within the aforementioned range, the lattice mismatch rate Δa is readily within the aforementioned range, and the FWHM of the rocking curve RC is readily within the aforementioned range; therefore, β can also be 0.50.

[0121] In the above chemical formula 1a, δ can also be greater than 0. As long as the crystal structure (perovskite structure) of tetragonal crystal 1 is maintained, δ can also be a value other than 0. For example, δ can also be greater than 0 and less than 1.0. δ can also be calculated based on, for example, the valence of each ion located at each of the A and B sites in tetragonal crystal 1. The valence of each ion can also be determined by X-ray photoelectron spectroscopy (XPS).

[0122] Bi and E contained in tetragonal crystal 1 A The total number of moles can also be expressed as [A]1, the Fe, Ti and E contained in tetragonal crystal 1. B The total number of moles can also be expressed as [B]1, and [A]1 / [B]1 can also be 1.0. As long as the tetragonal crystal structure (perovskite structure) is maintained, [A]1 / [B]1 can also be a value other than 1.0. That is, [A]1 / [B]1 can be lower than 1.0, and [A]1 / [B]1 can also be greater than 1.0.

[0123] Tetragonal crystal 2 can also be represented by the following chemical formula 2. The following chemical formula 2 is actually the same as the following chemical formula 2a.

[0124] Chemical formula 2:

[0125] x2(Bi 1－α E A α E B O3-y2BiFeO3-z2Bi(Fe 0.5 Ti 0.5 O3

[0126] Chemical formula 2a:

[0127] (Bi x2(1－α)+y2+z2 E A x2α (E) B x2 Fe y2+0.5z2 Ti0.5z2 )O 3±δ

[0128] In the above chemical formula 2, x² + y² + z² can also be 1.00. E in the above chemical formula 2... A The elements mentioned above. E in chemical formula 2 above. B The elements mentioned above. E in chemical formula 2 above. A It can be combined with E in the above chemical formula 1 A They can be the same, or they can be different. E in the above chemical formula 2... B It can be combined with E in the above chemical formula 1 B They can be the same or different. The valences of the elements in chemical formula 2 above can also be the same as the valences of the elements in chemical formula 1 above. (The text then abruptly shifts to a seemingly unrelated topic about element E in chemical formula 2.) B The two elements are represented by element E. B1 and element E B2 In the case of [specific situation], the above chemical formula 2 is substantially the same as the following chemical formula 2'. In the following chemical formula 2', β can also be 0.00 or more and 1.00 or less.

[0129] Chemical formula 2':

[0130] x2(Bi 1－α E A α (E) B1 1－β E B2 β )O3-y2BiFeO3-z2Bi(Fe 0.5 Ti 0.5 O3

[0131] Bi in the above chemical formula 2a x2(1－α)+y2+z2 E A x2α The element at site A corresponds to the perovskite structure. E in chemical formula 2a. B x2 Fe y2+0.5z2 Ti 0.5z2 It corresponds to the element located at the B site in the perovskite structure.

[0132] In the above chemical formula 2, the Fe valence of y2BiFeO3 is 3, and the Fe valence of z2Bi(Fe) in the above chemical formula 2 is 3. 0.5 Ti 0.5 The Fe valence of O3 is 2. Therefore, through the Bi and E in the raw material of the second piezoelectric layer 3B... A E B The molar ratios of Fe and Ti are the same as those of Bi and E in the above chemical formula 2. A EB The composition of the raw materials for the second piezoelectric layer 3B is adjusted by ensuring that the molar ratio of Fe and Ti is consistent, so that the tetragonal crystal 2 can contain Fe. 2+ .

[0133] In the above chemical formula 2, x2 can also 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 tends to have the above crystal orientation, and c2 / a2 tends to be within the above range.

[0134] In the above chemical formula 2, y2 can also be 0.10 or higher and 0.85 or lower. When y2 is 0.10 or higher and 0.85 or lower, tetragonal crystal 2 tends to have the above crystal orientation, and c2 / a2 tends to be within the above range.

[0135] In the above chemical formula 2, z2 can also be 0.05 or more and 0.80 or less. When z2 is 0.05 or more and 0.80 or less, tetragonal crystal 2 tends to have the above crystal orientation, and c2 / a2 tends to be within the above range.

[0136] In the above chemical formula 2, α can also be 0.00 or more and less than 1.00. Tetragonal crystal 2 readily exhibits the above-mentioned crystal orientation, and c² / a² is readily within the above range; therefore, α can also be 0.50. As described above, in the above chemical formula 2', β can also be 0.00 or more and less than 1.00, or greater than 0.00 and less than 1.00. Tetragonal crystal 2 can also exhibit the above-mentioned crystal orientation, and c² / a² is readily within the above range; therefore, β can also be 0.50.

[0137] In the above chemical formula 2a, δ can also be greater than 0. As long as the crystal structure (perovskite structure) of tetragonal crystal 2 is maintained, δ can also be a value other than 0. For example, δ can also be greater than 0 and less than 1.0. δ can also be calculated based on, for example, the valence of each ion located at each of the A and B sites in tetragonal crystal 2. The valence of each ion can also be determined by XPS.

[0138] Bi and E contained in tetragonal crystal 2 A The total number of moles can also be expressed as [A]2, the Fe, Ti and E contained in tetragonal crystal 2. B The total number of moles can also be expressed as [B]², and [A]² / [B]² can also be 1.0. As long as the tetragonal crystal structure (perovskite structure) is maintained, [A]² / [B]² can also be a value other than 1.0. That is, [A]² / [B]² can be less than 1.0, and [A]² / [B]² can also be greater than 1.0.

[0139] Tetragonal crystal 1 can also be represented by the following chemical formula 1w. In the following chemical formula 1w, E... A The elements mentioned above. The E in the following chemical formula 1w B The elements are as described above. In the following chemical formula 1w, w1 can also be 0.30 or more and 0.80 or less. In the following chemical formula 1w, α can also be 0.00 or more and less than 1.00.

[0140] Chemical formula 1w: (1-w1)Bi 1－α E A α E B O3-w1BiFeO3

[0141] Tetragonal crystal 2 can also be represented by the following chemical formula 2w. The E in the following chemical formula 2w... A The elements mentioned above. The E in the following chemical formula 2w B The elements are as described above. In the following chemical formula 2w, w2 can also be 0.30 or more and 0.80 or less. In the following chemical formula 2w, α can also be 0.00 or more and less than 1.00. In the following chemical formula 2w, E... A It can be combined with E in the above chemical formula 1w A They can be the same or different. The E in the following chemical formula 2w... B It can be combined with E in the above chemical formula 1w B They can be the same, or they can be different.

[0142] Chemical formula 2w: (1-w2)Bi 1－α E A α E B O3-w2BiFeO3

[0143] Piezoelectric thin films P can also be epitaxial films. That is, piezoelectric thin films P can also be formed through epitaxial growth. Through epitaxial growth, piezoelectric thin films P with excellent anisotropy and crystal orientation can be easily formed.

[0144] The surface area of ​​the first piezoelectric layer 3A can be, for example, 1 μm. 2 Above and 500mm 2 The areas of the crystalline substrate 8, intermediate layer 5, first electrode layer 7, lower layer 6, second piezoelectric layer 3B, and second electrode layer 4 can each be the same as the area of ​​the first piezoelectric layer 3A.

[0145] For example, the composition of the piezoelectric thin film P can also be analyzed using X-ray fluorescence (XRF), inductively coupled plasma (ICP) luminescence spectrometry, and X-ray photoelectron spectrometry (XPS). As a method to determine the composition and thickness of the first piezoelectric layer 3A and the second piezoelectric layer 3B, the composition of the piezoelectric thin film P can also be analyzed along its thickness direction using XPS. For example, the thickness Tp of the piezoelectric thin film P can be uniformly reduced by ion milling or sputtering of the surface of the piezoelectric thin film P, while the surface composition of the piezoelectric thin film P is continuously measured using XPS. The composition of the cross-section of the piezoelectric thin film P can also be analyzed along its thickness direction. In the analysis of the cross-sectional composition of the piezoelectric thin film P along its thickness direction, the energy-dispersive X-ray analysis (EDS) apparatus of a scanning electron microscope (SEM) or a scanning transmission electron microscope (STEM) can also be used. The crystal structure and crystal orientation of the first piezoelectric layer 3A and the second piezoelectric layer 3B can also be determined using the aforementioned X-ray diffraction (XRD) method. The crystal structure and crystal orientation of the lower layer 6, the first piezoelectric layer 3A and the second piezoelectric layer 3B mentioned above can also be the crystal structure and crystal orientation at room temperature.

[0146] When the piezoelectric film P is composed of a lower layer 6 and a first piezoelectric layer 3A directly superimposed on the lower layer 6, the first piezoelectric layer 3A is directly formed on the surface of the lower layer 6 through a first film forming process.

[0147] In the case where the piezoelectric film P is composed of a lower layer 6, a second piezoelectric layer 3B directly superimposed on the lower layer 6, and a first piezoelectric layer 3A directly superimposed on the second piezoelectric layer 3B, the second piezoelectric layer 3B is directly formed on the surface of the lower layer 6 through a second film forming process, and the first piezoelectric layer 3A is directly formed on the surface of the second piezoelectric layer 3B through a first film forming process after the second film forming process.

[0148] The lower layer 6 can also be formed by sputtering, vacuum evaporation, printing, spin coating, or sol-gel method.

[0149] In the first film formation step, a first piezoelectric layer 3A is formed using pulsed-laser deposition (PLD) with a first target material. The first target material is the raw material for the first piezoelectric layer 3A. The first target material may also be composed of all the elements common to the first piezoelectric layer 3A (tetragonal crystal 1). The composition of the first target material may also be adjusted so that the molar ratio of each element constituting the first target material is consistent with 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 material may also be consistent with the molar ratio of each element constituting the above-mentioned chemical formula 1 or chemical formula 1'.

[0150] In the second film-forming process, the second piezoelectric layer 3B is directly formed on the surface of the lower layer 6 using a PLD method with a second target. The second target is the raw material for the second piezoelectric layer 3B. The second target may also be composed of all the elements common to the second piezoelectric layer 3B (tetragonal crystal 2). The composition of the second target may also be adjusted so that the molar ratio of each element constituting the second target is consistent with 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 also be consistent with the molar ratio of each element constituting the above-mentioned chemical formula 2 or chemical formula 2'.

[0151] In the PLD method, the elements constituting the target are plasma-ionized and evaporated by irradiating the target with a pulsed laser (e.g., an excimer laser). According to the PLD method, each element constituting the target can be plasma-ionized uniformly in an instant. As a result, the molar ratio of each element in each piezoelectric layer easily matches the molar ratio of each element in each target, and element segregation in each piezoelectric layer is easily suppressed. Furthermore, according to the PLD method, each piezoelectric layer is easily epitaxially grown, readily forming dense piezoelectric layers at the atomic level. In the PLD method, by changing the number of pulses (repetition frequency) of the pulsed laser, 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 decreases, the growth rate of each piezoelectric layer decreases, and the anisotropy and crystal orientation of the tetragonal crystal constituting each piezoelectric layer increase.

[0152] The repetition frequency f1 of the pulsed laser in the first film formation process is less than the repetition frequency f2 of the pulsed laser in the second film formation process. Since f1 is less than f2, a piezoelectric thin film P with c1 / a1 of tetragonal crystal 1 being greater than c2 / a2 of tetragonal crystal 2 can be formed.

[0153] The repetition frequency f1 of the pulsed laser in the first film formation process can also be 10Hz. By adjusting f1 to 10Hz, it is easy to control the c1 / a1 of the tetragonal crystal 1 contained in the first piezoelectric layer 3A within the range of 1.050 or higher and 1.250 or lower.

[0154] The repetition frequency f2 of the pulsed laser in the second film deposition process can also be 20Hz. By adjusting f2 to 20Hz, it is easy to control the c2 / a2 of the tetragonal crystal 2 in the second piezoelectric layer 3B within the range of 1.010 or higher and 1.050 or lower.

[0155] The first and second targets can also be manufactured separately using the following methods.

[0156] Bi and E can also be used as initial raw materials for various targets. A E BOxides of Fe and Ti are used as starting materials. Alternatively, substances that become oxides through calcination, such as carbonates or oxalates, can be used instead of oxides. After thoroughly drying these starting materials at temperatures above 100°C, Bi and E are used as the starting materials. A E B The initial raw materials were weighed in a manner consistent with the molar ratios of Fe and Ti in each piezoelectric layer. In the first and second film-forming processes, Bi in the target material is more volatile than other elements. Therefore, the molar ratio of Bi in each target material can be adjusted to a higher value than the molar ratio of Bi in each piezoelectric layer. When using raw materials containing K as E... A In the case of this, K in the target material is more volatile than other elements in the first and second film-forming processes. Therefore, the molar ratio of K in each target material can be adjusted to a higher value than the molar ratio of K in each piezoelectric layer.

[0157] The weighed initial raw materials are thoroughly mixed in an organic solvent or water. The mixing time can be 5 hours or more but less than 20 hours. The mixing device can be, for example, a ball mill. After thoroughly drying the mixed initial raw materials, the initial raw materials are shaped using a stamping machine. The shaped initial raw materials are calcined to obtain a calcined product. The calcination temperature can be 750°C or more but less than 900°C. The calcination time can be 1 hour or more but less than 3 hours. The calcined product is pulverized in an organic solvent or water. The pulverization time can be 5 hours or more but less than 30 hours. The pulverization device can also be a ball mill. After drying the pulverized calcined product, the calcined product with added binder solution is granulated to obtain a powder of the calcined product. The powder of the calcined product is stamped to obtain a block-shaped shaped body.

[0158] By heating the block-shaped molded body, the binder in the molded body evaporates. The heating temperature can be above 400°C and below 800°C. The heating time can be above 2 hours and below 4 hours.

[0159] After the binder evaporates, the molded body is sintered. The sintering temperature can be above 800°C and below 1100°C. The sintering time can be above 2 hours and below 4 hours. The heating and cooling rates of the molded body during the sintering process can be, for example, above 50°C / hour and below 300°C / hour.

[0160] Through the above processes, the first and second target materials are fabricated respectively. The average grain size of the oxides (perovskite oxides) contained in each target material can, for example, be 1 μm or more and 20 μm or less. Each target material contains Fe... 3+ However, each target material may not necessarily contain Fe. 2+In the first film-forming process, Fe originating from the first target material is reduced. 3+ A portion of which can be obtained containing Fe 2+ The first piezoelectric layer 3A. In the second film formation process, Fe from the second target material is reduced. 3+ A portion of which can be obtained containing Fe 2+ The second piezoelectric layer 3B.

[0161] In the first film-forming process, the elements constituting the first target material are evaporated under a vacuum atmosphere using the PLD method. The evaporated elements adhere to and accumulate on the surface of the lower layer 6 or the second piezoelectric layer 3B to form the first piezoelectric layer 3A.

[0162] In the second film-forming process, the elements constituting the second target material are evaporated under a vacuum atmosphere using the PLD method. The evaporated elements adhere to and accumulate on the surface of the lower layer 6, forming the second piezoelectric layer 3B.

[0163] In the first film-forming process, the first piezoelectric layer 3A can also be formed inside the vacuum chamber while the interior of the vacuum chamber is heated. For example, the temperature inside the vacuum chamber (film-forming temperature) only needs to be above 450°C and below 600°C. With a film-forming temperature above 450°C, Fe originating from the first target material is easily reduced. 3+ Part of it, easily forming a substance containing Fe 2+ The first piezoelectric layer 3A. At film formation temperatures below 450°C, it is difficult to reduce Fe originating from the target material. 3+ It is difficult to obtain Fe 2+ The first piezoelectric layer 3A. A higher film-forming temperature improves the surface cleanliness of the underlying layer 6 or the second piezoelectric layer 3B, increases the crystallinity of the first piezoelectric layer 3A, and makes it easier to increase the orientation of the tetragonal crystal planes 1. However, if the film-forming temperature is too high, excessive reduction of the elements constituting the first piezoelectric layer 3A can occur, making it difficult to obtain a first piezoelectric layer 3A with the desired composition. Furthermore, at excessively high film-forming temperatures, Bi or K can easily detach from the first piezoelectric layer 3A, making it difficult to control the composition of the first piezoelectric layer 3A.

[0164] The oxygen partial pressure within the vacuum chamber can be, for example, 0.1 Pa or more and 3.0 Pa or less, preferably 0.1 Pa or more and 1.0 Pa or less, and more preferably 0.1 Pa or more and 0.5 Pa or less. By maintaining the oxygen partial pressure within the above range, Fe derived from the target material can be easily reduced. 3+ Part of it, easily forming a substance containing Fe 2+ The first piezoelectric layer 3A. Under excessively low oxygen partial pressure, it is difficult to fully oxidize the elements originating from the target material, making it difficult to form perovskite-type oxides, and the orientation degree of the tetragonal crystal 1 is easily reduced. Under excessively high oxygen partial pressure, it is difficult to reduce Fe originating from the target material. 3+It is difficult to obtain Fe 2+ The first piezoelectric layer 3A. In addition, when the oxygen partial pressure is too high, the growth rate of the first piezoelectric layer 3A is prone to decrease, and the orientation degree of the tetragonal crystal 1 is prone to decrease.

[0165] In the first film-forming process, in addition to controlling the repetition frequency f1 of the pulsed laser, the number of times the pulsed laser irradiates the first target material (film-forming time) can also be controlled. As the number of times the pulsed laser irradiates the first target material (film-forming time) increases, the thickness of the first piezoelectric layer 3A tends to increase. In the first film-forming process, in addition to controlling the repetition frequency f1 of the pulsed laser, the distance between the surface of the lower layer 6 or the second piezoelectric layer 3B and the first target material can also be controlled. As the distance between the surface of the lower layer 6 or the second piezoelectric layer 3B and the first target material decreases, the thickness and growth rate of the first piezoelectric layer 3A tend to increase.

[0166] Apart from the composition of the target material and the repetition frequency of the pulsed laser, the second film-forming process can also be implemented in a manner that is roughly the same as the first film-forming process described above.

[0167] Alternatively, after forming the piezoelectric thin film P through the first film-forming process (and the second film-forming process), the piezoelectric thin film P can be annealed (heat-treated). The temperature of the piezoelectric thin film P during annealing (annealing temperature) can 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. Annealing of the piezoelectric thin film P tends to further improve its piezoelectricity. In particular, annealing at 850°C or higher and 1000°C easily improves the piezoelectricity of the piezoelectric thin film P. However, annealing is not mandatory. Annealing can also be performed in a reducing atmosphere such as nitrogen (N2). Annealing in a reducing atmosphere increases the Fe content of the piezoelectric thin film P. 2+ oxidation (Fe) 3+ The formation of Fe is suppressed, making it easier to maintain the Fe content in the piezoelectric thin film P. 2+ .

[0168] During the formation and subsequent cooling processes of the piezoelectric thin film P, compressive stress caused by temperature changes can be generated within the piezoelectric thin film P. This compressive stress compresses the piezoelectric thin film P in directions approximately parallel to the surface of the first piezoelectric layer 3A (a-axis and b-axis directions). As a result, tetragonal crystal 1 (and tetragonal crystal 2) are easily formed.

[0169] The crystalline substrate 8 can also be a single-crystal substrate. For example, the crystalline substrate 8 can 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 can also be a substrate made of a single crystal of an oxide. The single crystal of the oxide can be, for example, MgO or perovskite-type oxide (e.g., SrTiO3). The thickness of the crystalline substrate 8 can be, for example, 10 μm or more and 1000 μm or less. When the crystalline substrate 8 is conductive, the crystalline substrate 8 functions as an electrode, therefore, the first electrode layer 7 may not be required. For example, the conductive crystalline substrate 8 can also be a single crystal of SrTiO3 doped with niobium (Nb). SOI (Silicon-on-Insulator) substrates can also be used as the crystalline substrate 8.

[0170] The crystal orientation of the crystalline substrate 8 and the normal direction D of the surface of the crystalline substrate 8 N Equal. That is, the surface of the crystalline substrate 8 can also be parallel to the crystal plane of the crystalline substrate 8. The crystalline substrate 8 can also be a uniaxially oriented substrate. For example, the (100) plane of the crystalline substrate 8 of Si, etc., can also be parallel to the surface of the crystalline substrate 8. That is, the

[100] direction of the crystalline substrate 8 of Si, etc., can also be parallel to the normal direction D of the surface of the crystalline substrate 8. N parallel.

[0171] When the (100) facet of the crystalline substrate 8 such as Si is parallel to the surface of the crystalline substrate 8, the (001) facest of the tetragonal crystal 1 and the tetragonal crystal 2 are easily oriented in the normal direction dn of the surface of the first piezoelectric layer 3A.

[0172] As described above, the intermediate layer 5 (first intermediate layer) can also be disposed between the crystalline substrate 8 and the first electrode layer 7. The intermediate layer 5 may also contain at least one material selected from, for example, titanium (Ti), chromium (Cr), titanium oxide (TiO2), silicon oxide (SiO2), and zirconium oxide (ZrO2). Through the intermediate layer 5, the first electrode layer 7 can easily adhere to the crystalline substrate 8. The intermediate layer 5 can also be crystalline. The crystal plane of the intermediate layer 5 may also be in the normal direction D of the surface of the crystalline substrate 8. N Upward orientation. The crystal planes of the crystalline substrate 8 and the intermediate layer 5 can also be aligned in the normal direction D of the surface of the crystalline substrate 8. N The intermediate layer 5 can also be formed by sputtering, vacuum evaporation, printing, spin coating, or sol-gel method.

[0173] The intermediate layer 5 may also contain ZrO2 and oxides of rare earth elements. By containing ZrO2 and oxides of rare earth elements, a first electrode layer 7 composed of platinum crystals can be easily formed on the surface of the intermediate layer 5. The (002) facet of the platinum crystals is easily oriented in the normal direction of the surface of the first electrode layer 7, and the (200) facet of the platinum crystals is easily oriented in the in-plane direction of the surface of the first electrode layer 7. The rare earth elements may also be at least one selected from scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0174] Intermediate layer 5 may also contain ZrO2 and Y2O3. For example, intermediate layer 5 may also be composed of yttrium-stabilized zirconium oxide (ZrO2 with added Y2O3). Intermediate layer 5 may also have a first layer composed of ZrO2 and a second layer composed of Y2O3. The first layer composed of ZrO2 may also be directly stacked on the surface of the crystalline substrate 8. The second layer composed of Y2O3 may also be directly stacked on the surface of the first layer. The first electrode layer 7 may also be directly stacked on the surface of the second layer composed of Y2O3. When intermediate layer 5 contains ZrO2 and Y2O3, the first piezoelectric layer 3A (and the second piezoelectric layer 3B) is easily epitaxially grown, and the (001) facet of tetragonal crystal 1 (and the (001) facet of tetragonal crystal 2) is preferentially oriented in the normal direction dn of the surface of the first piezoelectric layer 3A. In addition, when the intermediate layer 5 contains ZrO2 and Y2O3, a first electrode layer 7 composed of platinum crystals is easily formed on the surface of the intermediate layer 5. The (002) facet of the platinum crystals is easily oriented in the normal direction of the surface of the first electrode layer 7, and the (200) facet of the platinum crystals is easily oriented in the in-plane direction of the surface of the first electrode layer 7.

[0175] The first electrode layer 7 may also be composed of at least one metal selected from platinum (Pt), palladium (Pd), rhodium (Rh), gold (Au), ruthenium (Ru), iridium (Ir), molybdenum (Mo), titanium (Ti), tantalum (Ta), and nickel (Ni). The first electrode layer 7 may also be composed of conductive metal oxides such as strontium ruthenium ruthenium oxide (SrRuO3), lanthanum nickel oxide (LaNiO3), or lanthanum strontium cobalt oxide ((La,Sr)CoO3). The first electrode layer 7 may also be crystalline. The crystal plane of the first electrode layer 7 may also be in the normal direction D of the crystalline substrate 8. N Upward orientation. That is, the crystal plane of the first electrode layer 7 can also be approximately parallel to the surface of the crystalline substrate 8. The crystal planes of the crystalline substrate 8 and the first electrode layer 7 can also be aligned in the normal direction D of the crystalline substrate 8. N Upward orientation. In the normal direction D of the crystalline substrate 8.N The crystal plane of the upward-oriented first electrode layer 7 can also be substantially parallel to the (001) plane of the tetragonal crystal 1 (and the (001) plane of the tetragonal crystal 2). The thickness of the first electrode layer 7 can be, for example, 1 nm or more and 1.0 μm or less. The first electrode layer 7 can also be formed by sputtering, vacuum evaporation, printing, spin coating, or sol-gel method. In the case of printing, spin coating, or sol-gel method, in order to improve the crystallinity of the first electrode layer 7, heat treatment (annealing) of the first electrode layer 7 can also be performed.

[0176] The first electrode layer 7 may also contain platinum crystals. The first electrode layer 7 may also be composed solely of platinum crystals. The platinum crystals are cubic crystals with a face-centered cubic (fcc) lattice structure. The (002) facets of the platinum crystals may be oriented in the normal direction to the surface of the first electrode layer 7, and the (200) facets of the platinum crystals may be oriented in the in-plane direction to the surface of the first electrode layer 7. In other words, the (002) facets of the platinum crystals may be approximately parallel to the surface of the first electrode layer 7, and the (200) facets of the platinum crystals may be approximately perpendicular to the surface of the first electrode layer 7. When the (002) and (200) facets of the platinum crystals constituting the first electrode layer 7 have the above-described orientations, the first piezoelectric layer 3A (and the second piezoelectric layer 3B) is easily epitaxially grown, and the (001) facets of the tetragonal crystal 1 (and the (001) facets of the tetragonal crystal 2) are preferentially oriented in the normal direction dn to the surface of the first piezoelectric layer 3A. The surface of the first electrode layer 7 may also be approximately parallel to the surface of the first piezoelectric layer 3A. That is, the normal direction of the surface of the first electrode layer 7 can also be approximately parallel to the normal direction dn of the surface of the first piezoelectric layer 3A.

[0177] The second electrode layer 4 may also be composed of at least one metal selected from, for example, Pt, Pd, Rh, Au, Ru, Ir, Mo, Ti, Ta, and Ni. The second electrode layer 4 may also be composed of at least one conductive metal oxide selected from, for example, LaNiO3, SrRuO3, and (La,Sr)CoO3. The second electrode layer 4 may also be crystalline. The crystal plane of the second electrode layer 4 may also be in the normal direction D of the crystalline substrate 8. N Upward orientation. The crystal plane of the second electrode layer 4 can also be approximately parallel to the surface of the crystalline substrate 8. In the normal direction D of the crystalline substrate 8... N The crystal plane of the upward-oriented second electrode layer 4 can also be approximately parallel to the (001) plane of the tetragonal crystal 1 (and the (001) plane of the tetragonal crystal 2). The thickness of the second electrode layer 4 can be, for example, 1 nm or more and 1.0 μm or less. The second electrode layer 4 can also be formed by sputtering, vacuum evaporation, printing, spin coating, or sol-gel method. In the case of printing, spin coating, or sol-gel method, in order to improve the crystallinity of the second electrode layer 4, heat treatment (annealing) of the second electrode layer 4 can also be performed.

[0178] Alternatively, another intermediate layer (second intermediate layer) can be disposed between the piezoelectric thin film P (first piezoelectric layer 3A) and the second electrode layer 4. Through the intervening intermediate layer, the second electrode layer 4 can easily adhere to the piezoelectric thin film P (first piezoelectric layer 3A). The composition, crystal structure, and formation method of the other intermediate layer (second intermediate layer) can also be the same as those of the aforementioned intermediate layer (first intermediate layer). The other intermediate layer may also contain at least one selected from, for example, SrRuO3, LaNiO3, and (La,Sr)CoO3. The formation method of the other intermediate layer can also be sputtering, vacuum evaporation, printing, spin coating, or sol-gel method.

[0179] At least a portion or all of the surface of the piezoelectric thin film element 10 may also be covered by a protective film. Due to the coverage of the protective film, the durability (moisture resistance, etc.) of the piezoelectric thin film element 10 is improved.

[0180] The piezoelectric thin film element of this embodiment has a wide variety of applications. For example, it can also be used in piezoelectric transducers and piezoelectric sensors. That is, the piezoelectric transducer (e.g., an ultrasonic transducer) of this embodiment can also include the piezoelectric thin film element described above. The piezoelectric transducer can also be an ultrasonic transducer such as an ultrasonic sensor. The piezoelectric thin film element can also be a collector (vibration power generation element). As described above, the piezoelectric thin film element of this embodiment has excellent piezoelectric performance index, therefore, it is suitable for use in ultrasonic transducers. The piezoelectric thin film element can also be a piezoelectric actuator. The piezoelectric actuator can also be used in magnetic head assemblies, magnetic head cantilever assemblies, or hard disk drives. The piezoelectric actuator can also be used in printheads or inkjet printer devices. The piezoelectric actuator can also be a piezoelectric switch. The piezoelectric actuator can also be used for haptics. That is, the piezoelectric actuator can also be used in various devices that require feedback from skin sensation (tactile sensation). Devices that require feedback from skin sensation can also be wearable devices, touchpads, displays, or game controllers. The piezoelectric thin film element can also be a piezoelectric sensor. For example, a piezoelectric sensor can also be a piezoelectric microphone, gyroscope sensor, pressure sensor, pulse wave sensor, or impact sensor. A piezoelectric thin film element can also be a SAW filter, BAW filter, oscillator, or acoustic multilayer film. The microelectromechanical system (MEMS) of this embodiment includes the aforementioned piezoelectric thin film element. That is, the piezoelectric thin film element can also be part or integral to the microelectromechanical system. For example, a piezoelectric thin film element can also be part or integral to a piezoelectric micromachined ultrasonic transducer (PMUT). For example, products using piezoelectric micromachined ultrasonic transducers can also be biometric sensors (fingerprint sensors, vascular sensors, etc.) or medical / healthcare sensors (blood pressure monitors, vascular imaging sensors, etc.), or ToF (Time of Flight) sensors.

[0181] Figure 9This diagram shows a schematic cross-section of an ultrasonic transducer 10b comprising the aforementioned piezoelectric thin film element. The cross-section of the ultrasonic transducer 10b is perpendicular to the surface of the piezoelectric thin film P (first piezoelectric layer 3A). The ultrasonic transducer 10b may also include: substrates 8a and 8b, a first electrode layer 7 disposed on substrates 8a and 8b, 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. A cavity 8c for acoustic purposes may also be provided below the piezoelectric thin film P. Ultrasonic signals are transmitted or received through the flexure or vibration of the piezoelectric thin film P. The second piezoelectric layer 3B may also be disposed between the lower layer 6 and the first piezoelectric layer 3A. An intermediate layer may also be disposed between substrates 8a and 8b and the first electrode layer 7.

[0182] [Example]

[0183] The present invention will be described in detail through the following embodiments and comparative examples. The present invention is not limited to the following embodiments.

[0184] (Example 1)

[0185] In the fabrication of the piezoelectric thin film element in Example 1, a crystalline substrate made of Si was used. The (100) facet of the Si was parallel to the surface of the crystalline substrate. The crystalline substrate was a square of 20 mm × 20 mm. The thickness of the crystalline substrate was 500 μm.

[0186] Within a vacuum chamber, a crystalline intermediate layer composed of ZrO2 and Y2O3 is formed integrally on the surface of a crystalline substrate. The intermediate layer is formed by sputtering. The thickness of the intermediate layer is 30 nm.

[0187] Within a vacuum chamber, a first electrode layer composed of Pt crystals is formed integrally on the surface of the intermediate layer. The first electrode layer is formed by sputtering. The thickness of the first electrode layer is 200 nm. The temperature inside the vacuum chamber is maintained at 500 °C during the formation of the first electrode layer.

[0188] The XRD pattern of the first electrode layer was measured using out-of-plane measurements on its surface. The XRD pattern of the first electrode layer was also measured using in-plane measurements on its surface. These XRD pattern measurements were performed using an X-ray diffraction apparatus (SmartLab) manufactured by Rigaku Corporation. Measurement conditions were set such that the peak intensity in each XRD pattern increased by at least three positions relative to the background intensity. Out-of-plane measurements detected the peaks of the diffracted X-rays from the (002) plane of the Pt crystal. That is, the (002) plane of the Pt crystal is oriented in the normal direction of the surface of the first electrode layer. In-plane measurements detected the peaks of the diffracted X-rays from the (200) plane of the Pt crystal. That is, the (200) plane of the Pt crystal is oriented in the in-plane direction of the surface of the first electrode layer.

[0189] A crystalline lower layer is formed integrally on the surface of the first electrode layer. The lower layer is formed by sputtering. The composition of the lower layer is shown in Table 1 below. The thickness TL of the lower layer is adjusted to the values ​​shown in Table 2 below.

[0190] By performing the first film-forming process (PLD method) described above in a vacuum chamber, a first piezoelectric layer is formed on the entire surface of the lower layer. The repetition frequency f1 of the pulsed laser in the first film-forming process is adjusted to 10 Hz. The oxygen partial pressure in the vacuum chamber during the first film-forming process is maintained at 1 Pa. The internal temperature (film-forming temperature) of the vacuum chamber during the formation of the first piezoelectric layer is maintained at 460°C. The thickness T1 of the first piezoelectric layer is adjusted to the values ​​shown in Table 2 below.

[0191] The composition of the first target material used in the first film-forming process 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 The elements are those shown in Table 1 below. In the case of Example 1, α, β, x1, y1, and z1 in the following chemical formula 1' are the values ​​shown in Table 1 below.

[0192] Chemical formula 1':

[0193] x1(Bi 1－α E A α (E) B1 1－β E B2 β )O3-y1BiFeO3-z1Bi(Fe 0.5 Ti 0.5 O3

[0194] Through the first film-forming process described above, a piezoelectric thin film consisting of a lower layer and a first piezoelectric layer is formed. For the following analysis and measurements, multiple piezoelectric thin films are formed using the above method.

[0195] By sputtering the surface of the piezoelectric thin film, the thickness of the piezoelectric thin film is uniformly reduced while its composition is continuously analyzed along the thickness direction. The composition of the piezoelectric thin film is analyzed using XPS. The results show that the composition of the first piezoelectric layer is consistent with that of the first target material.

[0196] The XRD pattern of the piezoelectric thin film was measured using out-of-plane measurements on the surface of the first piezoelectric layer using the aforementioned X-ray diffraction apparatus. Additionally, another XRD pattern of the piezoelectric thin film was measured using in-plane measurements on the surface of the first piezoelectric layer. Reciprocal space maps of the piezoelectric thin film were obtained using these measurements. Measurement conditions were set such that the peak intensity in each XRD pattern increased by at least three positions relative to the background intensity. The measurement apparatus and conditions for each XRD pattern were the same as described above. A cross-section of the piezoelectric thin film parallel to its thickness direction was observed at atomic-level resolution using a scanning transmission electron microscope (STEM).

[0197] The results of the above analysis using X-ray diffraction and STEM show that the piezoelectric thin film has the following characteristics.

[0198] The (001) plane of the lower crystal forming the lower layer is oriented in the normal direction of the surface of the first piezoelectric layer.

[0199] The first piezoelectric layer is composed of tetragonal crystals of perovskite oxide.

[0200] The (001) facet of the tetragonal crystal 1 is preferentially oriented in the normal direction of the surface of the first piezoelectric layer. That is, the orientation degree of the (001) facet of the tetragonal crystal 1 in the normal direction of the surface of the first piezoelectric layer is 90% or more. As described above, the orientation degree of the (001) facet of the tetragonal crystal 1 is expressed as 100×1 1(001) / (I 1(001) +I 1(110) +I 1(111) The crystal plane of the tetragonal crystal 1 that is preferentially oriented in the normal direction of the surface of the first piezoelectric layer is recorded as the "first orientation plane".

[0201] The spacing aL of the (100) planes that constitute the lower crystals of the lower layer is the value shown in Table 1 below.

[0202] The spacing a1 of the (100) planes of the tetragonal crystal 1 constituting the first piezoelectric layer is the value shown in Table 1 below.

[0203] The lattice mismatch rate Δa is the value shown in Table 1 below. As mentioned above, the lattice mismatch rate Δa is defined as 100×(aL-a1) / a1.

[0204] The full width at half maximum (FWHM) of the rocking curves of diffracted X-rays originating from the (001) plane of tetragonal crystal 1 are the values ​​shown in Table 1 below. The rocking curves of diffracted X-rays originating from the (001) plane of tetragonal crystal 1 in Example 1 are shown in Table 1 below. Figure 10 As shown in the image.

[0205] The c1 / a1 of tetragonal crystal 1 is the value shown in Table 2 below.

[0206] Using the above method, a laminate was fabricated consisting of a crystalline substrate, an intermediate layer directly superimposed on the crystalline substrate, a first electrode layer directly superimposed on the intermediate layer, and a piezoelectric thin film (lower layer and first piezoelectric layer) directly superimposed on the first electrode layer. The following processes were then performed using this laminate.

[0207] Inside a vacuum chamber, a second electrode layer composed of Pt is formed integrally on the surface of the piezoelectric thin film. The second electrode layer is formed by sputtering. The temperature of the crystalline substrate is maintained at 500°C during the formation of the second electrode layer. The thickness of the second electrode layer is 200 nm.

[0208] Through the above processes, a laminate consisting of a crystalline substrate, an intermediate layer directly superimposed on the crystalline substrate, a first electrode layer directly superimposed on the intermediate layer, a lower layer directly superimposed on the first electrode layer, a first piezoelectric layer directly superimposed on the lower layer, and a second electrode layer directly superimposed on the first piezoelectric layer is fabricated. Next, photolithography is used to pattern the laminated structure on the crystalline substrate. After patterning, the laminate is cut and diced.

[0209] Through the above processes, a quadrilateral piezoelectric thin film element of Example 1 is obtained. The piezoelectric thin film element consists of a crystalline substrate, an intermediate layer directly superimposed on the crystalline substrate, a first electrode layer directly superimposed on the intermediate layer, a lower layer directly superimposed on the first electrode layer, a first piezoelectric layer directly superimposed on the lower layer, and a second electrode layer directly superimposed on the first piezoelectric layer. The area of ​​the movable portion of the piezoelectric thin film is 600 μm × 600 μm.

[0210] <Evaluation of piezoelectricity>

[0211] The piezoelectricity of piezoelectric films is evaluated using the following methods.

[0212] [Calculation of relative permittivity]

[0213] The capacitance C of the piezoelectric thin film element was measured. Details of the capacitance C measurement are as follows.

[0214] Measurement apparatus: Impedance Gain-Phase Analyzer 4194A manufactured by Hewlett Packard Corporation

[0215] Frequency: 1kHz

[0216] Electric field: 10V / μm

[0217] Based on the following mathematical formula A, the relative permittivity ε is calculated from the measured value of capacitance C. r .

[0218] ε in Example 1 r As shown in Table 2 below.

[0219] Mathematical expression A: C = ε0 × ε r ×(S / d)

[0220] In mathematical formula A, ε0 is the permittivity of vacuum (8.854 × 10⁻⁶). －12 Fm －1 In mathematical formula A, S represents the surface area of ​​the piezoelectric film. S can also be referred to as the area of ​​the first electrode layer overlapping the piezoelectric film. In mathematical formula A, d represents the thickness of the piezoelectric film.

[0221] [Piezoelectric strain constant d] 33,f [Determination]

[0222] The piezoelectric strain constant d of a piezoelectric thin film was determined using a piezoelectric thin film element. 33,f . d 33,f The details of the measurement are as follows. Example 1: Piezoelectric strain constant d 33,f (The average value of the three measurement points) is shown in Table 2 below. Based on d 33,f and ε r Calculate the piezoelectric performance index (d) 33,f / ε r ε0). d of Example 1 33,f / ε r ε0 is shown in Table 2 below. Measuring apparatus: d... (The sentence is incomplete and requires more context to translate accurately.) 33 Instrument (ZJ-4B)

[0223] Frequency: 110Hz

[0224] Clamping pressure: 0.25N

[0225] (Examples 2-11 and Comparative Examples 1-8)

[0226] The composition of the lower layer of Examples 2-11 and Comparative Examples 6-8 is shown in Table 1 below. The thickness TL of the lower layer of Examples 2-11 and Comparative Examples 6-8 is adjusted to the values ​​shown in Table 2 below. The lower layer of Comparative Examples 1-5 is not formed. That is, the first piezoelectric layer of Comparative Examples 1-5 is formed directly on the surface of the first electrode layer.

[0227] The thickness T1 of the first piezoelectric layer in Examples 2-11 and Comparative Examples 1-8 was adjusted to the values ​​shown in Table 2 below. The composition of the first target material in Examples 2-11 and Comparative Examples 1-8 is represented by the above-described chemical formula 1'. The E of Examples 2-11 and Comparative Examples 1-8... A E B1 and E B2 The elements are shown in Table 1 below. The values ​​of α, β, x1, y1, and z1 for Examples 2-11 and Comparative Examples 1-8 are shown in Table 1 below.

[0228] In addition to the matters described above, piezoelectric thin film elements of Examples 2 to 11 and Comparative Examples 1 to 8 were produced by the same method as in Example 1.

[0229] Measurements related to the first electrode layer of each of Examples 2-11 and Comparative Examples 1-8 were performed using the same method as in Example 1. In any of Examples 2-11 and Comparative Examples 1-8, the (002) planes of the Pt crystal constituting the first electrode layer were oriented in the normal direction of the surface of the first electrode layer, and the (200) planes of the Pt crystal were oriented in the in-plane direction of the surface of the first electrode layer.

[0230] The analyses and measurements related to the piezoelectric films of Examples 2-11 and Comparative Examples 1-8 were performed using the same method as in Example 1.

[0231] In any of Examples 2 to 11 and Comparative Examples 1 to 8, the composition of the first piezoelectric layer is consistent with the composition of the first target material.

[0232] In any of Examples 2 to 11 and Comparative Examples 6 to 8, the (001) facets of the lower crystals constituting the lower layer are oriented in the normal direction of the surface of the first piezoelectric layer.

[0233] In any of Examples 2 to 11 and Comparative Examples 1 to 8, the first piezoelectric layer is composed of tetragonal crystals of perovskite oxide.

[0234] In any of Examples 2-11 and Comparative Examples 1-8, the (001) plane of the tetragonal crystal 1 is preferentially oriented in the normal direction of the surface of the first piezoelectric layer.

[0235] The values ​​of aL, a1, Δa, and FWHM for Examples 2-11 and Comparative Examples 1-8 are shown in Table 1 below. However, only in the cases of Comparative Examples 1-5 and Comparative Example 10 described later, aL is not a spacing between the (100) planes of the lower crystals constituting the lower layer, but a spacing between the (100) planes of the Pt crystals constituting the first electrode layer.

[0236] The c1 / a1 values ​​for Examples 2-11 and Comparative Examples 1-8 are shown in Table 2 below.

[0237] The piezoelectric properties of the piezoelectric films of Examples 2-11 and Comparative Examples 1-8 were evaluated using the same method as in Example 1. The ε-coating properties of the piezoelectric films of Examples 2-11 and Comparative Examples 1-8 were also evaluated. r d 33,f and d 33,f / ε r ε0 is shown in Table 2 below.

[0238]

[0239]

[0240] (Comparative Examples 9-11)

[0241] In Comparative Examples 9-11, the internal temperature (film formation temperature) of the vacuum chamber in the first film formation process was maintained as 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.

[0242] Apart from the matters described above, piezoelectric thin film elements of Comparative Examples 9 to 11 were fabricated using the same method as in Example 1.

[0243] Measurements related to the first electrode layer of each of Comparative Examples 9 to 11 were performed using the same method as in Example 1. In any of Comparative Examples 9 to 11, the (002) planes of the Pt crystals constituting the first electrode layer were oriented in the normal direction of the surface of the first electrode layer, and the (200) planes of the Pt crystals were oriented in the in-plane direction of the surface of the first electrode layer.

[0244] The analyses and measurements related to the piezoelectric films of Comparative Examples 9-11 were performed using the same method as in Example 1.

[0245] In any of the comparative examples 9 to 11, the composition of the first piezoelectric layer is consistent with the composition of the first target material.

[0246] In either of Comparative Examples 9 and 11, the (001) facets of the lower crystals constituting the lower layer are oriented in the normal direction of the surface of the first piezoelectric layer.

[0247] In any of the Comparative Examples 9 to 11, the first piezoelectric layer is composed of a tetragonal crystal 1 of perovskite-type oxide.

[0248] In any of the comparative examples 9 to 11, the (001) plane of the tetragonal crystal 1 is preferentially oriented in the normal direction of the surface of the first piezoelectric layer.

[0249] The values ​​of aL, a1, Δa, and FWHM for Comparative Examples 9 to 11 are shown in Table 3 below.

[0250] The c1 / a1 values ​​for each of Comparative Examples 9 to 11 are shown in Table 4 below.

[0251] The piezoelectricity of the piezoelectric films of Comparative Examples 9-11 was evaluated using the same method as in Example 1. The ε-coating of the piezoelectric films of Comparative Examples 9-11 was also evaluated. r d 33，f and d 33，f / ε r ε0 is shown in Table 4 below.

[0252]

[0253] (Comparative Example 12)

[0254] In Comparative Example 12, the oxygen partial pressure in the vacuum chamber during the first film-forming process was maintained at 0.01 Pa. The thickness T1 of the first piezoelectric layer in Comparative Example 12 was adjusted to the values ​​shown in Table 6 below.

[0255] Apart from the matters described above, a piezoelectric thin film element of Comparative Example 12 was fabricated using the same method as in Example 1.

[0256] Measurements related to the first electrode layer of Comparative Example 12 were performed using the same method as in Example 1. In the case of Comparative Example 12, the (002) facet 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) facet of the Pt crystal was oriented in the in-plane direction of the surface of the first electrode layer.

[0257] The analysis and determination related to the piezoelectric thin film of Comparative Example 12 were carried out using the same method as in Example 1.

[0258] In Comparative Example 12, the composition of the piezoelectric film was inconsistent with that of the first target material in terms of oxygen content.

[0259] The piezoelectric film of Comparative Example 12 does not have sufficient crystal orientation; therefore, the FWHM of Comparative Example 12 cannot be determined.

[0260] The values ​​of aL, a1, and Δa in Comparative Example 12 are shown in Table 5 below.

[0261] The c1 / a1 of Comparative Example 12 is the value shown in Table 6 below.

[0262] The piezoelectricity of the piezoelectric thin film of Comparative Example 12 was evaluated using the same method as in Example 1. The ε... r d 33，f and d 33，f / ε r ε0 is shown in Table 6 below.

[0263]

[0264] (Example 12)

[0265] In the fabrication process of the piezoelectric thin film element of Example 12, no intermediate layer was formed. In the fabrication process of the piezoelectric thin film element of Example 12, a first electrode layer composed of crystalline SrRuO3 was directly formed on the entire surface of the crystalline substrate. The thickness of the first electrode layer in Example 12 was 200 nm.

[0266] Apart from the matters described above, the piezoelectric thin film element of Example 12 was fabricated using the same method as in Example 1.

[0267] Measurements related to the first electrode layer of Example 12 were performed using the same method as in Example 1. In the case of Example 12, the crystal planes of the first electrode layer were not oriented in the in-plane direction on the surface of the first electrode layer. That is, in the case of Example 12, there was no in-plane orientation of the crystals of the first electrode layer.

[0268] The analyses and measurements related to the piezoelectric thin film of Example 12 were performed using the same method as in Example 1.

[0269] The composition of the first piezoelectric layer in Example 12 is consistent with the composition of the first target material.

[0270] In Example 12, the (001) facet of the lower crystal forming the lower layer is oriented in the normal direction of the surface of the first piezoelectric layer.

[0271] The first piezoelectric layer in Example 12 is composed of tetragonal crystals of perovskite oxide 1.

[0272] In Example 12, the (001) plane of the tetragonal crystal 1 is preferentially oriented in the normal direction of the surface of the first piezoelectric layer.

[0273] In Example 12, aL, a1, Δa, and FWHM are the values ​​shown in Table 7 below.

[0274] In Example 12, c1 / a1 are the values ​​shown in Table 8 below.

[0275] The piezoelectricity of the piezoelectric thin film of Example 12 was evaluated using the same method as in Example 1. The ε... r d 33，f and d 33，f / ε r ε0 is shown in Table 8 below.

[0276]

[0277] (Examples 13-19)

[0278] The composition of the lower layer of each of Examples 13 to 19 is shown in Table 9 below.

[0279] In Examples 13-19, a second piezoelectric layer is formed on the entire surface of the lower layer by performing the second film-forming process (PLD method) described above in a vacuum chamber. The repetition frequency f2 of the pulsed laser in the second film-forming process is adjusted to 20 Hz. The oxygen partial pressure in the vacuum chamber in the second film-forming process is maintained at 1 Pa. The internal temperature (film-forming temperature) of the vacuum chamber in the second film-forming process is maintained at 460°C. The thickness T2 of the second piezoelectric layer is adjusted to the values ​​shown in Table 11 below.

[0280] The composition of the second target material used in the second film-forming process of each of Examples 13-19 is represented by the following chemical formula 2'. E in the chemical formula 2' of each of Examples 13-19 A E B1 and E B2 The elements are those shown in Table 9 below. The x2, y2, and z2 values ​​in the chemical formula 2' of Examples 13-19 are those shown in Table 10 below.

[0281] Chemical formula 2':

[0282] x2(Bi 1-α E A α (E) B1 1-β E B2 β )O3-y2BiFeO3-z2Bi(Fe 0.5 Ti 0.5 O3

[0283] In Examples 13-19, a first piezoelectric layer is formed on the entire surface of the second piezoelectric layer through a first film-forming process following the second film-forming process. That is, each piezoelectric film in Examples 13-19 consists of a lower layer, a second piezoelectric layer directly superimposed on the lower layer, and a first piezoelectric layer directly superimposed on the second piezoelectric layer. The thickness T1 of the first piezoelectric layer in Examples 13-19 is adjusted to the values ​​shown in Table 11 below. The composition of the first target material used in the first film-forming process of Examples 13-19 is represented by the above-described chemical formula 1'. E in the chemical formula 1' of Examples 13-19... A E B1 and E B2 The elements are those shown in Table 9 below. The values ​​of α, β, x1, y1, and z1 in the chemical formula 1' of Examples 13-19 are those shown in Table 9 below.

[0284] In any of the examples 13-19, both the first piezoelectric layer (first target) and the second piezoelectric layer (second target) have a common E A E B1 E B2 α and β.

[0285] Apart from the matters described above, the piezoelectric thin film elements of Examples 13 to 19 were fabricated using the same method as in Example 1.

[0286] Measurements related to the first electrode layer of each of Examples 13-19 were performed using the same method as in Example 1. In any of Examples 13-19, the (002) planes of the Pt crystals constituting the first electrode layer were oriented in the normal direction of the surface of the first electrode layer, and the (200) planes of the Pt crystals were oriented in the in-plane direction of the surface of the first electrode layer.

[0287] The analyses and measurements related to the piezoelectric films of Examples 13-19 were performed using the same method as in Example 1. The piezoelectric films of Examples 13-19 each have the following characteristics.

[0288] The composition of the first piezoelectric layer is consistent with that of the first target material.

[0289] The (001) plane of the lower crystal forming the lower layer is oriented in the normal direction of the surface of the first piezoelectric layer.

[0290] The first piezoelectric layer is composed of tetragonal crystals of perovskite oxide.

[0291] The (001) plane of the tetragonal crystal 1 is preferentially oriented in the normal direction of the surface of the first piezoelectric layer.

[0292] The composition of the second piezoelectric layer is consistent with that of the second target material.

[0293] The second piezoelectric layer is composed of tetragonal perovskite oxide.

[0294] The (001) facet of the tetragonal crystal 2 is preferentially oriented in the normal direction of the surface of the first piezoelectric layer. That is, the orientation degree of the (001) facet of the tetragonal crystal 2 in the normal direction of the surface of the first piezoelectric layer is 90% or more. As described above, the orientation degree of the (001) facet of the tetragonal crystal 2 is expressed as 100×1 2(001) / (I 2(001) +I 2(110) +I 2(111) 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 recorded as the "second orientation plane".

[0295] The values ​​of aL, a1, Δa, and FWHM for Examples 13 to 19 are shown in Table 9 below.

[0296] The c1 / a1 of the tetragonal crystal 1 in Examples 13 to 19 are the values ​​shown in Table 11 below.

[0297] The c2 / a2 of the tetragonal crystal 2 in Examples 13-19 are the values ​​shown in Table 11 below. The I1 / (I1+I2) of the tetragonal crystal 2 in Examples 13-19 are the values ​​shown in Table 11 below. The definition of I1 / (I1+I2) is as described above.

[0298] The piezoelectricity of the piezoelectric films of Examples 13-19 was evaluated using the same method as in Example 1. The ε-coating of the piezoelectric films of Examples 13-19 was also evaluated. r d 33，f and d 33，f / ε r ε0 is shown in Table 11 below. The reciprocal space diagram of Example 13 is shown in... Figure 11 As shown in the image.

[0299]

[0300]

[0301] [Industry availability]

[0302] For example, the piezoelectric thin film of one aspect of the present invention can be applied to piezoelectric transducers, piezoelectric actuators, and piezoelectric sensors.

[0303] [Symbol Explanation]

[0304] 1: Tetragonal crystal 1, 2: Tetragonal 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 crystallization), 7: First electrode layer, 8: Crystalline substrate, 10, 10a: Piezoelectric thin film element, 10b: Ultrasonic transducer, D N dn: normal direction of the surface of the crystalline substrate; P: piezoelectric thin film; uc: cell of the perovskite structure; uc1: cell of tetragonal crystal 1; uc2: cell of tetragonal crystal 2; ucL: cell of the crystal contained in the lower layer.

Claims

1. A piezoelectric thin film, wherein, It has a lower layer and a first piezoelectric layer directly or indirectly superimposed on the lower layer. The first piezoelectric layer comprises a tetragonal perovskite oxide. The tetragonal crystal 1 contains bismuth, iron, and element E. B And oxygen, The tetragonal crystal 1 contains the element E. B It is at least one element selected from magnesium, aluminum, zirconium, titanium, nickel, and zinc. The (001) facet of the tetragonal crystal 1 is oriented in the normal direction of the surface of the first piezoelectric layer. The spacing between the (100) planes of the tetragonal crystal 1 is a1. The spacing between the (100) planes of the crystals contained 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 greater than 3.0% and less than 12.1%. The rocking curve of the X-ray diffraction of the (001) plane of the tetragonal crystal 1 was measured in the out-of-plane direction of the surface of the first piezoelectric layer. The full width at half maximum (FWHM) of the swing curve is greater than 1.9° and less than 5.5°. The (001) facet of the crystal contained in the lower layer is oriented in the normal direction of the surface of the first piezoelectric layer.

2. The piezoelectric thin film according to claim 1, wherein, The aL is greater than 3.92 Å and less than 4.29 Å.

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

4. The piezoelectric thin film according to claim 1, wherein, The crystals contained in the lower layer comprise at least one compound selected from barium titanate and titanium nitride.

5. The piezoelectric thin film according to claim 1, wherein, The thickness of the lower layer is greater than 10 nm and less than 350 nm.

6. The piezoelectric thin film according to claim 1, wherein, The spacing of the (001) plane of the tetragonal crystal 1 is c1. c1 / a1 is greater than 1.050 and less than 1.

250.

7. The piezoelectric thin film according to claim 1, wherein, The tetragonal crystal 1 is represented by the following chemical formula 1. E in the following chemical formula 1 A It is at least one element selected from Na, K, and Ag. E in the following chemical formula 1 B It is at least one element selected from Mg, Al, Zr, Ti, Ni and Zn. In the following chemical formula 1, x1 is 0.10 or higher and 0.90 or lower. In the following chemical formula 1, y1 is greater than 0.05 and less than 0.

85. In the following chemical formula 1, z1 is 0.05 or higher and 0.85 or lower. x1 + y1 + z1 = 1.00 In the following chemical formula 1, α is greater than or equal to 0.00 and less than 1.

00. Chemical Formula 1: 。 8. The piezoelectric thin film according to claim 1, wherein, It has a second piezoelectric layer. The second piezoelectric layer is disposed between the lower layer and the first piezoelectric layer. The second piezoelectric layer comprises a tetragonal perovskite oxide. The (001) facet of the tetragonal crystal 2 is oriented in the normal direction of the surface of the first piezoelectric layer. The spacing of the (001) plane of the tetragonal crystal 1 is c1. The spacing of the (001) plane of the tetragonal crystal 2 is c2. The spacing between the (100) faces of the tetragonal crystal 2 is a2. c2 / a2 is less than c1 / a1.

9. The piezoelectric thin film according to claim 8, wherein, The c2 / a2 ratio is greater than 1.010 and less than 1.

110.

10. The piezoelectric thin film according to claim 8, wherein, The peak intensity of the X-ray diffraction from the (001) plane of the tetragonal crystal 1 is I1. The peak intensity of the X-ray diffraction from the (001) plane of the tetragonal crystal 2 is I2. I1 / (I1+I2) is greater than 0.90 and less than 1.

00.

11. The piezoelectric thin film according to claim 8, wherein, The tetragonal crystal 2 contains bismuth, iron, and element E. B And oxygen, The tetragonal crystal 2 contains the element E. B It is at least one element selected from magnesium, aluminum, zirconium, titanium, nickel and zinc.

12. The piezoelectric thin film according to claim 8, wherein, The tetragonal crystal 2 is represented by the following chemical formula 2. E in the following chemical formula 2 A It is at least one element selected from Na, K, and Ag. E in the following chemical formula 2 B It is at least one element selected from Mg, Al, Zr, Ti, Ni and Zn. In the following chemical formula 2, x2 is greater than or equal to 0.10 and less than or equal to 0.

85. In the following chemical formula 2, y2 is greater than 0.10 and less than 0.

85. In the following chemical formula 2, z2 is 0.05 or higher and 0.80 or lower. x² + y² + z² = 1.00 In the following chemical formula 2, α is greater than or equal to 0.00 and less than 1.

00. Chemical formula 2: 。 13. The piezoelectric thin film according to claim 8, wherein, The thickness of the second piezoelectric layer is greater than 10 nm and less than 300 nm.

14. A piezoelectric thin film element, wherein, The piezoelectric thin film comprising any one of claims 1 to 13.

15. The piezoelectric thin film element according to claim 14, wherein, have: Crystalline substrate; and An electrode layer, which overlaps the crystalline substrate, The lower layer directly overlaps the electrode layer. An intermediate layer is disposed between the crystalline substrate and the electrode layer. The intermediate layer contains ZrO2 and Y2O3.

16. The piezoelectric thin film element according to claim 14, wherein, Equipped with an electrode layer, The lower layer directly overlaps the electrode layer. The electrode layer contains platinum crystals. The (002) plane of the platinum crystal is oriented in the normal direction to the surface of the electrode layer. The (200) facet of the platinum crystal is oriented in the in-plane direction of the surface of the electrode layer.

17. A piezoelectric transducer, wherein, The piezoelectric thin film element is provided with any one of claims 14 to 16.

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