Piezoelectric film, piezoelectric film element and piezoelectric transducer

Abstract

The piezoelectric film includes a first piezoelectric layer and a second piezoelectric layer directly overlapping the first piezoelectric layer. The first piezoelectric layer includes tetragonal crystals 1 of a perovskite-type oxide. The second piezoelectric layer includes tetragonal crystals 2 of a perovskite-type oxide. The (001) plane of the tetragonal crystal 1 is oriented in a normal direction dn to the surface of the piezoelectric film. The (001) plane of the tetragonal crystal 2 is oriented in a normal direction dn to the surface of the piezoelectric film. The spacing of the (001) planes of the tetragonal crystal 1 is c1. The spacing of the (100) planes of the tetragonal crystal 1 is a1. The spacing of the (001) planes of the tetragonal crystal 2 is c2. The spacing of the (100) planes of the tetragonal crystal 2 is a2. c2 / a2 is greater than c1 / a1. c1 / a1 is greater than 1.015 and less than 1.050.

Description

Technical Field

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

[0002] Piezoelectric materials are processed into various piezoelectric elements for various purposes. For example, piezoelectric actuators convert voltage into force through the inverse piezoelectric effect, in which voltage is applied to the piezoelectric body to deform the piezoelectric body. In addition, piezoelectric sensors convert force into voltage through the piezoelectric effect, in which pressure is applied to the piezoelectric body to deform the piezoelectric body. These piezoelectric elements are installed in various electronic devices.

[0003] In recent years, the market has required the miniaturization and performance improvement of electronic devices, and therefore, piezoelectric elements (piezoelectric thin film elements) using piezoelectric thin films have been actively studied. However, the thinner the piezoelectric body is, the more difficult it is to obtain the piezoelectric effect and the inverse piezoelectric effect. Therefore, the development of piezoelectric bodies with excellent piezoelectricity in a thin film state is expected.

[0004] At present, as a piezoelectric body, lead zirconate titanate (so-called PZT), which is a perovskite type ferroelectric, is mostly used. However, PZT contains lead (Pb) which is harmful to the human body and the environment. Therefore, as a substitute for PZT, the development of lead-free piezoelectric bodies is expected. For example, in the following non-patent literature, BiFeO 3 .BiFeO 3 It has relatively excellent piezoelectricity among lead-free piezoelectric materials, and is particularly expected to be applied to piezoelectric thin film elements. In Japanese Patent Publication No. 2013-191870, a piezoelectric material having a higher piezoelectricity than the conventional BiFeO 3 Excellent piezoelectric material, made of Bi(Co,Fe)O 3 A piezoelectric material composed of a mixture of tetragonal crystals and rhombohedral crystals.

[0005] Non-patent literature: K. Ujimoto et al, Direct piezoelectric properties of (100) and (111) BiFeO 3 epitaxial thin films,APPLIED PHYSICS LETTERS.100,102901(2012) Summary of the invention

[0006] (-e 31,f ) 2 / ε0 ε r It is a piezoelectric performance index that indicates the piezoelectricity of the piezoelectric film. 31,f A type of piezoelectric constant, -e 31,f The unit is C / m 2 ε 0 is the dielectric constant of vacuum, ε 0 The unit is F / m. ε r is the relative dielectric constant of the piezoelectric film, ε r No units. (-e 31,f ) 2 / ε 0 ε r The unit is Pa. Piezoelectric films with a large piezoelectric performance index are suitable for piezoelectric thin film elements such as piezoelectric transducers (sensors). However, the existing piezoelectric body in which tetragonal crystals and rhombohedral crystals are mixed has excellent piezoelectricity, but has a high relative dielectric constant, and therefore does not have a sufficiently large piezoelectric performance index. Therefore, the existing piezoelectric body is not fully suitable for piezoelectric thin film elements such as piezoelectric transducers (sensors).

[0007] One aspect of the present invention is to provide a piezoelectric film having a large piezoelectric performance index, a piezoelectric film element including the piezoelectric film, and a piezoelectric transducer.

[0008] One aspect of the present invention provides a piezoelectric film, comprising a first piezoelectric layer and a second piezoelectric layer directly overlapping the first piezoelectric layer, wherein the first piezoelectric layer comprises tetragonal crystals 1 of a perovskite-type oxide, the second piezoelectric layer comprises tetragonal crystals 2 of a perovskite-type oxide, the (001) planes of the tetragonal crystals 1 are oriented in the normal direction of the surface of the piezoelectric film, the (001) planes of the tetragonal crystals 2 are oriented in the normal direction of the surface of the piezoelectric film, the spacing of the (001) planes of the tetragonal crystals 1 is c1, the spacing of the (100) planes of the tetragonal crystals 1 is a1, the spacing of the (001) planes of the tetragonal crystals 2 is c2, the spacing of the (100) planes of the tetragonal crystals 2 is a2, c2 / a2 is greater than c1 / a1, and c1 / a1 is greater than 1.015 and less than 1.050.

[0009] c2 / a2 may be greater than or equal to 1.051 and less than or equal to 1.250.

[0010] The peak intensity of the diffracted X-rays from the (001) plane of tetragonal crystal 1 is I 1 The peak intensity of the diffracted X-rays from the (001) plane of the tetragonal crystal 2 is I 2 , I 2 / (I 1 +I 2 ) can be greater than 0.90 and less than 1.00.

[0011] Perovskite oxides can contain bismuth, iron, element EB and oxygen, element E B It may be at least one element selected from magnesium, aluminum, zirconium, titanium, nickel and zinc.

[0012] The tetragonal crystal 1 can be represented by the following chemical formula 1. In the following chemical formula 1, E A It can be at least one element selected from Na, K and Ag. E in the following chemical formula 1 B It may be at least one element selected from Mg, Al, Zr, Ti, Ni and Zn, x1 in the following chemical formula 1 may be greater than or equal to 0.10 and less than or equal to 0.90, y1 in the following chemical formula 1 may be greater than or equal to 0.05 and less than or equal to 0.85, z1 in the following chemical formula 1 may be greater than or equal to 0.05 and less than or equal to 0.85, x1+y1+z1 may be 1.00, and α in the following chemical formula 1 may be greater than or equal to 0.00 and less than 1.00

[0013] x1(Bi 1-α E A α )E B O 3 -y1BiFeO 3 -z1Bi(Fe 0.5 Ti 0.5 ) 3 (1).

[0014] The tetragonal crystal 2 can be represented by the following chemical formula 2. In the following chemical formula 2, E A It can be at least one element selected from Na, K and Ag. E in the following chemical formula 2 B It may be at least one element selected from Mg, Al, Zr, Ti, Ni and Zn, x2 in the following chemical formula 2 may be greater than or equal to 0.10 and less than or equal to 0.85, y2 in the following chemical formula 2 may be greater than or equal to 0.10 and less than or equal to 0.85, z2 in the following chemical formula 2 may be greater than or equal to 0.05 and less than or equal to 0.80, x2+y2+z2 may be 1.00, and α in the following chemical formula 2 may be greater than or equal to 0.00 and less than 1.00

[0015] x2(Bi 1-α E A α )E B O 3 -y2BiFeO 3 -z2Bi(Fe 0.5 Ti 0.5 ) 3 (2).

[0016] The thickness of the first piezoelectric layer may be greater than or equal to 10 nm and less than or equal to 300 nm.

[0017] One aspect of the present invention provides a piezoelectric film element including the piezoelectric film.

[0018] The piezoelectric thin film element of one aspect of the present invention may include a single crystal substrate, an electrode layer overlapped on the single crystal substrate, and a piezoelectric thin film overlapped on the electrode layer. The first intermediate layer may be arranged between the single crystal substrate and the electrode layer. The first intermediate layer may include ZrO 2 and Y 2 O 3 .

[0019] The piezoelectric thin film element of one aspect of the present invention may include an electrode layer and a piezoelectric thin film overlapped with the electrode layer, the second intermediate layer may be arranged between the electrode layer and the piezoelectric thin film, and the second intermediate layer may include SrRuO 3 and LaNiO 3 At least one of .

[0020] The piezoelectric film element of one aspect of the present invention may include an electrode layer and a piezoelectric film overlapping the electrode layer. The electrode layer may include platinum crystals. The (002) planes of the platinum crystals may be oriented in the normal direction of the surface of the electrode layer, and the (200) planes of the platinum crystals may be oriented in the in-plane direction of the surface of the electrode layer.

[0021] One aspect of the present invention provides a piezoelectric transducer including the piezoelectric thin film element.

[0022] According to one aspect of the present invention, a piezoelectric film having a large piezoelectric performance index, a piezoelectric film element including the piezoelectric film, and a piezoelectric transducer are provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1A is a schematic cross-sectional view of a piezoelectric thin-film element according to one embodiment of the present invention, Figure 1B yes Figure 1A A three-dimensional exploded view of the piezoelectric film element shown.

[0024] Figure 2 It is a three-dimensional diagram of a unit cell of a perovskite structure (perovskite oxide), and shows the arrangement of each element in the perovskite structure.

[0025] Figure 3A is a schematic three-dimensional diagram of a unit cell of a tetragonal crystal 1, Figure 3B It is a schematic three-dimensional diagram of a unit cell of a tetragonal crystal 2.

[0026] Figure 4 This is a schematic cross-sectional view of a piezoelectric thin-film element (ultrasonic transducer) according to another embodiment of the present invention. DETAILED DESCRIPTION

[0027] Hereinafter, the details of a preferred embodiment of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. In the accompanying drawings, the same or equivalent elements are marked with the same reference numerals. Figure 1A , Figure 1B and Figure 4 The X-axis, Y-axis, and Z-axis shown are three mutually orthogonal coordinate axes. The directions of the three coordinate axes are Figure 1A , Figure 1B and Figure 4 same.

[0028] The piezoelectric thin-film element according to this embodiment includes a piezoelectric thin film. Figure 1A The cross section of the piezoelectric thin film element 10 of the present embodiment is shown. The cross section of the piezoelectric thin film element 10 is perpendicular to the surface of the piezoelectric thin film 3. The piezoelectric thin film element 10 may have a single crystal substrate 1, a first electrode layer 2 (lower electrode layer) overlapping the single crystal substrate 1, a piezoelectric thin film 3 overlapping the first electrode layer 2, and a second electrode layer 4 (upper electrode layer) overlapping the piezoelectric thin film 3. The piezoelectric thin film element 10 may further include a first intermediate layer 5. The first intermediate layer 5 may be arranged between the single crystal substrate 1 and the first electrode layer 2, and the first electrode layer 2 may directly overlap the surface of the first intermediate layer 5. The piezoelectric thin film element 10 may further include a second intermediate layer 6. The second intermediate layer 6 may be arranged between the first electrode layer 2 and the piezoelectric thin film 3, and the piezoelectric thin film 3 may directly overlap the surface of the second intermediate layer 6. The thickness of each of the single crystal substrate 1, the first intermediate layer 5, the first electrode layer 2, the second intermediate layer 6, the piezoelectric thin film 3 and the second electrode layer 4 may be uniform. As Figure 1B As shown, the normal direction dn of the surface of the piezoelectric film 3 can be aligned with the normal direction D N The normal direction dn of the surface of the piezoelectric film 3 can be referred to as the thickness direction of the piezoelectric film 3 . Figure 1B In the embodiment, the first electrode layer, the first intermediate layer, the second intermediate layer and the second electrode layer are omitted.

[0029] A modified example of the piezoelectric thin film element 10 may not include the single crystal substrate 1. For example, the single crystal substrate 1 may be removed after the first electrode layer 2 and the piezoelectric thin film 3 are formed. A modified example of the piezoelectric thin film element 10 may not include the second electrode layer 4. For example, after the piezoelectric thin film element not including the second electrode layer is supplied as a product to a manufacturer of electronic equipment, the second electrode layer is added to the piezoelectric thin film element during the manufacturing process of the electronic equipment. In the case where the single crystal substrate 1 functions as an electrode, a modified example of the piezoelectric thin film element 10 may include the first electrode layer 2. That is, a modified example of the piezoelectric thin film element 10 may include the single crystal substrate 1 and the piezoelectric thin film 3 overlapped on the single crystal substrate 1. In the absence of the first electrode layer 2, the piezoelectric thin film 3 may be directly overlapped on the single crystal substrate 1. In the absence of the first electrode layer 2, the piezoelectric thin film 3 may also be overlapped on the single crystal substrate 1 via at least one of the first intermediate layer 5 and the second intermediate layer 6.

[0030] The piezoelectric film 3 includes a first piezoelectric layer 3A overlapping the first electrode layer 2 and a second piezoelectric layer 3B directly overlapping the first piezoelectric layer 3A. The piezoelectric film 3 may be composed only of the first piezoelectric layer 3A and the second piezoelectric layer 3B. The first piezoelectric layer 3A includes tetragonal crystals 1 (first tetragonal crystals) of a perovskite-type oxide. The second piezoelectric layer 3B includes tetragonal crystals 2 (second tetragonal crystals) of a perovskite-type oxide. Of course, the perovskite-type oxide is an oxide having a perovskite-type structure. The perovskite-type oxide is the main component of each of the first piezoelectric layer 3A and the second piezoelectric layer 3B. The total content of the elements constituting the perovskite-type oxide in the first piezoelectric layer 3A may be greater than 99 mol % and less than 100 mol %. The total content of the elements constituting the perovskite-type oxide in the second piezoelectric layer 3B may be greater than 99 mol % and less than 100 mol %. The first piezoelectric layer 3A may be composed only of tetragonal crystals 1. The first piezoelectric layer 3A may not include tetragonal crystals 2. The first piezoelectric layer 3A may contain a trace amount of tetragonal crystals 2. The second piezoelectric layer 3B may be composed only of tetragonal crystals 2. The second piezoelectric layer 3B may contain tetragonal crystals 1. The second piezoelectric layer 3B may contain a trace amount of tetragonal crystals 1. The first piezoelectric layer 3A may contain trace amounts of crystals other than tetragonal crystals in addition to tetragonal crystals 1. The second piezoelectric layer 3B may contain trace amounts of crystals other than tetragonal crystals in addition to tetragonal crystals 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 crystals and rhombohedral crystals. Tetragonal crystals 1 may be single crystals or polycrystalline. Tetragonal crystals 2 may be single crystals or polycrystalline. The composition of tetragonal crystals 1 may be different from that of tetragonal crystals 2. The composition of tetragonal crystals 1 may also be the same as that of tetragonal crystals 2.

[0031] The perovskite type oxide may contain bismuth (Bi), iron (Fe), and oxygen (O). The perovskite type oxide may contain Fe 2+ (divalent iron) and Fe 3+(trivalent iron) both as iron. The perovskite-type oxide may contain only Fe 3+ (trivalent iron) as iron. The perovskite-type oxide may contain element E in addition to Bi, Fe and O. A , element E A It may be at least one element selected from sodium (Na), potassium (K) and silver (Ag). The perovskite-type oxide may contain a plurality of elements as E. A Perovskite oxides may contain elements E in addition to Bi, Fe and O. B , element E B It may be at least one element selected from magnesium (Mg), aluminum (Al), zirconium (Zr), titanium (Ti), nickel (Ni) and zinc (Zn). The perovskite-type oxide may contain a plurality of elements as E B Perovskite oxides can contain Bi, Fe, E A 、E B The piezoelectric film 3 may further contain Bi, Fe, E A 、E B and other elements other than O. The piezoelectric film 3 may not contain Pb. The piezoelectric film 3 may contain Pb.

[0032] Figure 2 represents the unit cell uc of the perovskite oxide. Figure 2 Each of a, b and c in the perovskite structure is a basic vector. The element located at the A site of the unit cell uc can be Bi or E A The element located at the B site of the unit cell uc can be Fe or E B Part of the Fe at the B site can be divalent iron (Fe 2+ ), the rest of the Fe at site B may also be trivalent iron (Fe 3+ The Fe at the B site can be only trivalent iron (Fe 3+ ).

[0033] Figure 3A Represents the unit cell uc1 of tetragonal crystal 1. Figure 3B represents the unit cell uc2 of tetragonal crystal 2. For the convenience of illustration, E in the unit cells uc1 and uc2 are omitted. B and O (oxygen), but each of the unit cells uc1 and uc2 can have Figure 2 The unit cell in uc is the same perovskite structure.

[0034] Figure 3A Each of a1, b1, and c1 in φ is a basic vector of the tetragonal crystal 1. Figure 3A The vector a1 in Figure 2 corresponds to the vector a in . Figure 3A The vector b1 in Figure 2 corresponds to the vector b in . Figure 3A The vector c1 in Figure 2 The vector c in corresponds to 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 of the (100) planes of tetragonal crystal 1 (i.e., the lattice constant in the

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

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

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

[0035] Figure 3B Each of a2, b2 and c2 is a basic vector of the tetragonal crystal 2. Figure 3B The vector a2 in Figure 2 corresponds to the vector a in . Figure 3B The vector b2 in Figure 2 corresponds to the vector b in . Figure 3B The vector c2 in Figure 2 The vector c in corresponds to a2, b2 and c2. a2, b2 and c2 are perpendicular to each other. The orientation of vector a2 (a-axis) is

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

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

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

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

[0036] like Figure 1B and Figure 3A As shown, the (001) plane of the tetragonal crystal 1(uc1) is oriented in the normal direction dn of the surface of the piezoelectric film 3. Figure 1B and Figure 3B As shown, the (001) plane of the tetragonal crystal 2 (uc2) is also oriented in the normal direction dn of the surface of the piezoelectric film 3. For example, each of the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2 can be substantially parallel to the surface of the piezoelectric film 3, and the

[001] directions of the tetragonal crystal 1 and the tetragonal crystal 2 can be substantially parallel to the normal direction dn of the surface of the piezoelectric film 3. The (001) plane of the tetragonal crystal 1 can be oriented in the normal direction Dn of the surface of the single crystal substrate 1. N The (001) plane of the tetragonal crystal 2 may be oriented in the normal direction D of the surface of the single crystal substrate 1.N In other words, each of the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2 can be substantially parallel to the surface of the single crystal substrate 1, and the

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

[0037] The tetragonal crystals of perovskite-type oxides are easily polarized in the

[001] direction. That is,

[001] is an orientation that makes it easier to polarize the tetragonal crystals of perovskite-type oxides than other crystal orientations. Therefore, each of the (001) planes of the tetragonal crystal 1 and the (001) planes of the tetragonal crystal 2 is oriented in the normal direction dn of the surface of the piezoelectric film 3, thereby enabling the piezoelectric film 3 to have excellent piezoelectricity. For the same reason, the piezoelectric film 3 can be a ferroelectric material. The crystal orientation described below refers to each of the (001) planes of the tetragonal crystal 1 and the (001) planes of the tetragonal crystal 2 being oriented in the normal direction dn of the surface of the piezoelectric film 3.

[0038] The piezoelectric film 3 has the above-mentioned crystal orientation, and thus the piezoelectric film 3 can have a large (-e 31,f ) 2 / ε 0 ε r (Piezoelectric Performance Index). The above-mentioned crystal orientation is an inherent feature of the thin film. The thin film is a crystalline film formed by a vapor phase growth method or a solution method. On the other hand, the bulk material of the piezoelectric body having the same composition as the piezoelectric thin film 3 is difficult to have the above-mentioned crystal orientation. This is because the bulk material of the piezoelectric body is a sintered body (ceramic) of powder containing essential elements of the piezoelectric body, and it is difficult to control the structure and orientation of multiple crystals constituting the sintered body. Since the bulk material of the piezoelectric body contains Fe, the resistivity of the bulk material of the piezoelectric body is lower than that of the piezoelectric thin film 3. As a result, leakage current is easily generated in the bulk material of the piezoelectric body. Therefore, it is difficult to polarize the bulk material of the piezoelectric body by applying a high electric field, and the bulk material of the piezoelectric body is difficult to have a large piezoelectric performance index.

[0039] c2 / a2 of the tetragonal crystals 2 included in the second piezoelectric layer 3B is larger than c1 / a1 of the tetragonal crystals 1 included in the first piezoelectric layer 3 A. That is, the anisotropy of the tetragonal crystals 2 is higher than the anisotropy of the tetragonal crystals 1 .

[0040] c2 / a2 is greater than c1 / a1, so the relative dielectric constant of tetragonal crystal 2 is smaller than that of tetragonal crystal 1. However, c2 / a2 is greater than c1 / a1, so the crystal structure of tetragonal crystal 2 is stronger than that of tetragonal crystal 1, and atoms in tetragonal crystal 2 are more difficult to move than atoms in tetragonal crystal 1. Therefore, polarization reversal of tetragonal crystal 2 is more difficult to cause than polarization reversal of tetragonal crystal 1, and the piezoelectricity of tetragonal crystal 2 itself is worse than that of tetragonal crystal 1 itself. In other words, c1 / a1 is less than c2 / a2, so the relative dielectric constant of tetragonal crystal 1 is higher than that of tetragonal crystal 2, but the crystal structure of tetragonal crystal 1 is softer than that of tetragonal crystal 2, and atoms in tetragonal crystal 1 are more likely to move than atoms in tetragonal crystal 2. Therefore, polarization reversal of tetragonal crystal 1 is more likely to cause than polarization reversal of tetragonal crystal 2, and the piezoelectricity of tetragonal crystal 1 itself is better than that of tetragonal crystal 2 itself.

[0041] When an electric field is applied to the piezoelectric film 3, the polarization reversal of the tetragonal crystal 1 in the first piezoelectric layer 3A is likely to occur earlier than the polarization reversal of the tetragonal crystal 2 in the second piezoelectric layer 3B. Since the polarization reversal of the tetragonal crystal 1 occurs earlier than the polarization reversal of the tetragonal crystal 2, the crystal structure of the tetragonal crystal 2 at the interface between the first piezoelectric layer 3A and the second piezoelectric layer 3B becomes unstable. In other words, due to the polarization reversal of the tetragonal crystal 1, the polarization of the tetragonal crystal 2 is likely to fluctuate at the interface between the tetragonal crystal 1 and the tetragonal crystal 2. For example, due to the polarization reversal of the tetragonal crystal 1 in the first piezoelectric layer 3A, at the interface between the first piezoelectric layer 3A and the second piezoelectric layer 3B, the surface charge of the first piezoelectric layer 3A and the surface charge of the second piezoelectric layer 3B repel each other, and the polarization of the tetragonal crystal 2 fluctuates.

[0042] Due to the mechanism described above, the polarization reversal of the tetragonal crystal 1 induces the polarization reversal of the tetragonal crystal 2. That is, the first piezoelectric layer 3A is introduced between the first electrode layer 2 and the second piezoelectric layer 3B as a buffer layer to promote the polarization reversal of the second piezoelectric layer 3B, thereby facilitating the polarization reversal of the entire piezoelectric film 3. As a result, the piezoelectricity (-e) of the entire piezoelectric film 3 is reduced. 31,f ) has a higher piezoelectricity than the tetragonal crystal 2 itself, and has a large -e 31,f and low relative dielectric constant (ε r ), the piezoelectric film 3 can have a large (-e 31,f ) 2 / ε 0 ε r (Piezoelectric Performance Index).

[0043] However, the above-mentioned mechanism is a hypothesis, and the technical scope of the present invention is not limited to the above-mentioned mechanism.

[0044] In contrast to the piezoelectric film 3, the bulk material of the piezoelectric body is less likely to cause deformation of the crystal structure due to stress. Therefore, most of the perovskite oxides constituting the bulk material of the piezoelectric body are cubic crystals, and the bulk material of the piezoelectric body is less likely to have piezoelectricity caused by the tetragonal perovskite oxide.

[0045] c1 / a1 is greater than 1.015 and less than 1.050. Since c1 / a1 is greater than 1.015 and less than 1.050, the polarization reversal of tetragonal crystal 1 is easier to cause than the polarization reversal of tetragonal crystal 2, the piezoelectricity of tetragonal crystal 1 itself is better than the piezoelectricity of tetragonal crystal 2 itself, and the -e of piezoelectric film 3 is 31,f When c1 / a1 is outside the above range, the relative dielectric constant of the tetragonal crystal 1 is too high, or the piezoelectricity of the tetragonal crystal 1 itself is degraded. As a result, the piezoelectric performance index of the piezoelectric film 3 is reduced. c1 can be, for example, Above and Below. a1 can be, for example, Above and the following.

[0046] c2 / a2 can be greater than 1.051 and less than 1.250, or greater than 1.051 and less than 1.249. When c2 / a2 is greater than 1.051, the relative dielectric constants of the second piezoelectric layer 3B including the tetragonal crystals 2 and the piezoelectric film 3 are easily reduced, and the piezoelectric performance index of the piezoelectric film 3 is easily increased. When c2 / a2 is less than 1.250, the polarization reversal of the tetragonal crystals 2 is easily caused, and the piezoelectric performance index of the piezoelectric film 3 is easily increased. For example, c2 can be Above and Below. a2 can be, for example, Above and the following.

[0047] By observing a cross section of the piezoelectric film 3 parallel to the thickness direction of the piezoelectric film 3 with atomic level resolution using a scanning transmission electron microscope (STEM), the magnitude relationship between c1 and c2 and the magnitude relationship between a1 and a2 can be identified.

[0048] In order to identify the specific values ​​of c1 and c2 with high precision, the peak P1 of the diffracted X-rays of the (001) plane of the tetragonal crystal 1 and the peak P2 of the diffracted X-rays of the (001) plane of the tetragonal crystal 2 can be measured by out-of-plane measurement (2θ-θ method) on the surface of the piezoelectric film 3. The measured X-ray diffraction pattern contains both peaks P1 and P2. The diffraction angle 2θ of the peak P1 of the diffracted X-rays of the (001) plane of the tetragonal crystal 1 is 1 The diffraction angle 2θ of the peak P2 of the diffracted X-ray close to the (001) plane of the tetragonal crystal 2 is 2, and when a peak P3 where peaks P1 and P2 overlap is measured, peak P1 can be approximated by a Gaussian function g1, and peak P2 can be approximated by another Gaussian function g2, and a curve fitting of g1+g2 and peak P3 can be performed. After the curve fitting, g1 can be regarded as P1, and g2 can be regarded as P2.

[0049] In order to determine the specific values ​​of a1 and a2 with high precision, the peak P1' of the diffracted X-rays of the (100) plane of the tetragonal crystal 1 and the peak P2' of the diffracted X-rays of the (100) plane of the tetragonal crystal 2 can be measured by In-plane measurement (2θ-θ method) of the surface of the piezoelectric film 3. The measured X-ray diffraction pattern contains both the peak P1' and the peak P2'. The diffraction angle 2θ of the peak P1' of the diffracted X-rays of the (100) plane of the tetragonal crystal 1 1 The diffraction angle 2θ of the peak P2' of the diffracted X-ray close to the (100) plane of the tetragonal crystal 2 is 2 ', and when a peak P3' where peak P1' and peak P2' overlap is measured, peak P1' can be approximated by a Gaussian function G1, peak P2' can be approximated by another Gaussian function G2, and curve fitting of G1+G2 and peak P3' can be performed. G1 after curve fitting can be regarded as P1', and G2 after curve fitting can be regarded as P2'.

[0050] I 2 / (I 1 +I 2 ) may be 0.90 or more and less than 1.00, or 0.91 or more and 0.99 or less. 1 It is the peak intensity (maximum intensity) of the diffracted X-rays of the (001) plane of tetragonal crystal 1. 2 is the peak intensity (maximum intensity) of the diffracted X-rays from the (001) plane of the tetragonal crystal 2. 2 / (I 1 +I 2 ) increases, there is -e 31,f decreases, and the relative dielectric constant (ε r ) tends to decrease. 2 / (I 1 +I 2 ) is within the above range, it is easy to obtain a large (-e 31,f ) 2 and low relative dielectric constant (ε r ), the piezoelectric film 3 tends to have a large (-e 31,f ) 2 / ε 0 ε r (Piezoelectric Performance Index). 1 and I 2The respective units may be, for example, cps (counts per second). 1 and I 2 The measurement can be performed by out-of-plane measurement of the surface of the piezoelectric film 3. 1 and I 2 In the manner where the intensity of each of the above is increased by at least 3 digits relative to the background intensity, set I 1 and I 2 The respective measurement conditions.

[0051] I 1 It can be proportional to the total area of ​​the (001) planes of the tetragonal crystals 1 oriented in the normal direction dn of the surface of the piezoelectric film 3. 2 It can be proportional to the total area of ​​the (001) planes of the tetragonal crystals 2 oriented in the normal direction dn of the surface of the piezoelectric film 3. In other words, I 1 It can be proportional to the amount of tetragonal crystals 1 contained in the piezoelectric film 3. 2 It can be proportional to the amount of tetragonal crystals 2 contained in the piezoelectric film 3. Therefore, I 2 / (I 1 +I 2 ) may be the abundance ratio of tetragonal crystal 2 to the total amount of tetragonal crystal 1 and tetragonal crystal 2. That is, the abundance ratio of tetragonal crystal 2 to the total amount of tetragonal crystal 1 and tetragonal crystal 2 may be 90% or more and less than 100%.

[0052] The degree of orientation of the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2 can also be quantified based on the orientation degree. The greater the orientation degree of the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2, the easier it is for the piezoelectric film 3 to have a large piezoelectric performance index. The orientation degree of each crystal plane can be calculated based on the peak of the diffraction X-ray from each crystal plane. The peak of the diffraction X-ray from each crystal plane can be measured by out-of-plane measurement of the surface of the piezoelectric film 3.

[0053] The orientation degree of the (001) plane of the tetragonal crystal 1 in the normal direction dn of the surface of the piezoelectric film 3 can be expressed as 100×I 1 / ΣI 1(hkl) ΣI 1(hkl) It is the sum of the peak intensities of the diffracted X-rays of each crystal plane of the tetragonal crystal 1 measured in the out-of-plane direction of the surface of the piezoelectric thin film 3. ΣI 1(hkl) For example, it can be 1(001) +I 1(110) +I 1(111) I 1(001) For the above I 1 . That is I 1(001)It is the peak intensity (maximum intensity) of the diffracted X-ray of the (001) plane of the tetragonal crystal 1 measured in the out-of-plane direction of the surface of the piezoelectric thin film 3. 1(110) I is the peak intensity (maximum intensity) of the diffracted X-rays of the (110) plane of the tetragonal crystal 1 measured in the out-of-plane direction of the surface of the piezoelectric thin film 3. 1(111) It is the peak intensity (maximum intensity) of the diffracted X-rays of the (111) plane of the tetragonal crystal 1 measured in the out-of-plane direction of the surface of the piezoelectric thin film 3 .

[0054] The orientation degree of the (001) plane of tetragonal crystal 2 can be expressed as 100×I 2 / ΣI 2(hkl) ΣI 2(hkl) ΣI is the sum of the peak intensities of diffracted X-rays from each crystal plane of the tetragonal crystal 2 measured in the out-of-plane direction of the surface of the piezoelectric thin film 3. 2(hkl) For example, it can be 2(001) +I 2(110) +I 2(111) I 2(001) For the above I 2 . That is I 2(001) It is the peak intensity (maximum intensity) of the diffracted X-rays of the (001) plane of the tetragonal crystal 2 measured in the out-of-plane direction of the surface of the piezoelectric thin film 3. 2(110) It is the peak intensity (maximum intensity) of the diffracted X-rays of the (110) plane of the tetragonal crystal 2 measured in the out-of-plane direction of the surface of the piezoelectric thin film 3. 2(111) It is the peak intensity (maximum intensity) of the diffracted X-rays of the (111) plane of the tetragonal crystal 2 measured in the out-of-plane direction of the surface of the piezoelectric thin film 3 .

[0055] The degree of orientation of the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2 can be quantified according to the orientation degree F based on the Lotgering (orientation degree) method. When the orientation degree is calculated by any of the above methods, the orientation degree of the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2 is 70% or more and 100% or less, preferably 80% or more and 100% or less, and more preferably 90% or more and 100% or less. In other words, the (001) plane of the tetragonal crystal 1 can be oriented in the normal direction dn of the surface of the piezoelectric film 3 in priority to the other crystal planes of the tetragonal crystal 1, and the (001) plane of the tetragonal crystal 2 can be oriented in the normal direction dn of the surface of the piezoelectric film 3 in priority to the other crystal planes of the tetragonal crystal 2.

[0056] One or both of the tetragonal crystals 1 and 2 may contain Fe 2+One or both of the tetragonal crystals 1 and 2 contain Fe. 2+ In the case of Fe, the piezoelectric film 3 tends to have a large piezoelectric performance index. 2+ The reason why the piezoelectric thin film 3 tends to have a large piezoelectric performance index is not limited to the following reason.

[0057] In BiFeO 3 -(Bi,K)TiO 3 When the piezoelectric film of the system has a composition near the morphotropic phase boundary (MPB) between tetragonal crystals and rhombohedral crystals, the piezoelectricity (-e 31,f ) increases, but the dielectric constant (ε 0 ε r ) also increases, so it is difficult to improve the piezoelectric performance index. In order to suppress the increase in dielectric constant, it is expected that the piezoelectric film can be improved by forming the piezoelectric film only with tetragonal crystals. The tetragonal crystallinity (tetragonality) of the piezoelectric film is achieved by epitaxial stress (compression stress caused by lattice mismatch). This is because, through the epitaxial stress parallel to the surface of the piezoelectric film, the piezoelectric film is compressed in the direction parallel to the surface of the piezoelectric film (that is, the a-axis direction and the b-axis direction), and the piezoelectric film is deformed. However, the thicker the piezoelectric film, the more difficult it is to improve the tetragonal crystallinity of the piezoelectric film only through epitaxial stress. This is because the thicker the piezoelectric film, the more difficult it is to deform the entire piezoelectric film through epitaxial stress. Therefore, in the case where the piezoelectric film is so thick that the epitaxial stress generated in the piezoelectric film becomes weak, it is also expected to stabilize the tetragonal crystal structure of the piezoelectric film. Therefore, in one or both of the tetragonal crystals 1 and the tetragonal crystals 2, in order to make the electronic configuration of the element (ion) located at the B site of the perovskite-type oxide and the structure of BiCoO 3 Co 3+ The d6 electron configuration of Fe 2+ As a result, when the piezoelectric film 3 is thick enough to weaken the epitaxial stress generated in the piezoelectric film 3, the tetragonal crystal property of the piezoelectric film 3 is also improved. In other words, when the piezoelectric film 3 is thick enough to weaken the epitaxial stress generated in the piezoelectric film 3, the first piezoelectric layer 3A is likely to include the tetragonal crystal 1, and the second piezoelectric layer 3B is likely to include the tetragonal crystal 2.

[0058] It is predicted that when a composition system near MPB is formed in the bulk material of the piezoelectric body, a part of the B site is replaced by Fe. 2+ BO in the substitutional tetragonal crystal 6 Octahedron (or BO 5The rotation of the pyramid (rotation around the c-axis) inhibits the polarization rotation caused by the formation of the pseudo cubic crystal. In other words, part of the B site is occupied by Fe 2+ In substituted perovskite oxides, MPB is less likely to exist, and polarization rotation that changes the direction of the c-axis of the tetragonal crystal is less likely to occur.

[0059] Through the above mechanism, one or both of tetragonal crystals 1 and 2 contain Fe 2+ In the case of piezoelectricity, it is easy to obtain both 31,f ) and the dielectric constant (ε 0 ε r ) decreases, the piezoelectric performance index tends to increase.

[0060] However, with Fe 2+ The above-mentioned mechanism is a hypothesis, and the technical scope of the present invention is not limited to Fe 2+ The above mentioned mechanism is relevant.

[0061] In contrast to the piezoelectric film 3, the crystal structure of the bulk material of the piezoelectric body is not easily deformed by stress. Therefore, most of the perovskite oxides constituting the bulk material of the piezoelectric body are cubic crystals, and the bulk material of the piezoelectric body is unlikely to have piezoelectricity caused by the tetragonal perovskite oxides.

[0062] The thickness Tp of the piezoelectric film 3 may be equal to the sum of the thickness Ta of the first piezoelectric layer 3A and the thickness Tb of the second piezoelectric layer 3B. The thickness Tb of the second piezoelectric layer 3B may be greater than the thickness Ta of the first piezoelectric layer 3A. The thickness Tp of the piezoelectric film 3 may be greater than 500nm and less than 5000nm. The thickness Ta of the first piezoelectric layer 3A may be greater than 10nm and less than 300nm, or greater than 80nm and less than 300nm. The thickness Tb of the second piezoelectric layer 3B may be greater than 490nm and less than 4700nm, or greater than 420nm and less than 4700nm. When the thickness Ta of the first piezoelectric layer 3A is greater than 10nm, the polarization reversal of the tetragonal crystals 1 in the first piezoelectric layer 3A easily induces the polarization reversal of the tetragonal crystals 2 in the second piezoelectric layer 3B. As a result, the piezoelectric film 3 easily has a large piezoelectric performance index. When the thickness Ta of the first piezoelectric layer 3A is less than 300 nm, the relative dielectric constant of the piezoelectric film 3 is likely to be reduced, and the piezoelectric performance index of the piezoelectric film 3 is likely to be increased. When the thickness Tp of the piezoelectric film 3 is greater than 500 nm and the piezoelectric film 3 is thick, the ions at the B site of the perovskite type oxide are Fe 2+Replacement, the piezoelectric film 3 is also likely to have a large piezoelectric performance index. By adjusting the thickness Tp of the piezoelectric film 3 to less than 5000nm, tetragonal crystals 1 and tetragonal crystals 2 are easily formed regardless of the epitaxial stress, and the piezoelectric film 3 is likely to have a large piezoelectric performance index. Ta, Tb and Tp are not limited to the above ranges. The method for measuring Ta, Tb and Tp is not limited. For example, the thickness Tp of the piezoelectric film 3 can be measured by a scanning electron microscope (SEM) on a cross section of the piezoelectric film 3 parallel to the normal direction dn of the piezoelectric film 3. The first piezoelectric layer 3A and the second piezoelectric layer 3B can be identified on the cross section of the piezoelectric film 3 based on the difference in composition, or the size relationship between c1 / a1 and c2 / a2, and the thickness Ta of the first piezoelectric layer 3A and the thickness Tb of the second piezoelectric layer 3B can be measured on the cross section of the piezoelectric film 3 by SEM. Each of the thickness Tp of the piezoelectric thin film 3 , the thickness Ta of the first piezoelectric layer 3A, and the thickness Tb of the second piezoelectric layer 3B may be substantially uniform.

[0063] The tetragonal crystal 1 can be represented by the following Chemical Formula 1. The following Chemical Formula 1 is substantially the same as the following Chemical Formula 1a.

[0064] x1(Bi 1-α E A α )E B O 3 -y1BiFeO 3 -z1Bi(Fe 0.5 Ti 0.5 ) 3 (1)

[0065] (Bi x1(1-α)+y1+z1 E A x1α )(E B x1 Fe y1+0.5z1 Ti 0.5z1 ) 3±δ (1a)

[0066] In the above chemical formula 1, x1+y1+z1 may be 1.00. In the above chemical formula 1, E A The E in the above chemical formula 1 is B For the above elements.

[0067] In the above chemical formula 1, (Bi 1-α E A α )E B O 3 Bi is 3-price Bi (Bi 3+ ) or 5-price Bi(Bi 5+ ) constitutes (Bi in the above chemical formula 11-α E A α )E B O 3 E A The sum of the valences (ion valences) is expressed as V A . Composition (Bi 1-α E A α )E B O 3 E B The sum of the valences (ion valences) is expressed as V B . (Bi in Chemical Formula 1 1-α E A α )E B O 3 Bi, E A and E B The sum of the valence numbers 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 be +6 which is balanced with the total valence (ion valence) of O (-6). 3(1-α)+V A α or 5(1-α)+V A α can be +3. V B It can be +3. B The two elements are represented as elements E B1 and element E B2 In the case of, the above chemical formula 1 is substantially the same as the following chemical formula 1'. β in the following chemical formula 1' may be greater than or equal to 0.00 and less than or equal to 1.00. B1 The valence (ion valence) is expressed as V B1 . E B2 The valence (ion valence) is expressed as V B2 . E B The sum of the valences (ion valences) V B Expressed as (1-β)V B1 +βV B2 (1-β)V B1 +βV B2 It can be +3.

[0068] x1(Bi 1-α E A α )(EB1 1-β E B2 β ) 3 -y1BiFeO 3 -z1Bi(Fe 0.5 Ti 0.5 ) 3 (1')

[0069] In the above chemical formula 1a, Bi x1(1-α)+y1+z1 E A x1α Corresponds to the element located at the A site of the perovskite structure. E in Formula 1a B x1 Fe y1+0.5z1 Ti 0.5z1 Corresponding to the element located at the B site of the perovskite structure.

[0070] The y1BiFeO in the above chemical formula 1 3 The Fe valence is 3, but the z1Bi(Fe 0.5 Ti 0.5 ) 3 The valence of Fe is 2. Therefore, by using Bi, E A 、E B The molar ratio of each of Fe and Ti is the same as that of Bi, E in the above chemical formula 1. A 、E B The composition of the raw material of the first piezoelectric layer 3A is adjusted in such a way that the molar ratio of Fe and Ti is consistent, and the tetragonal crystal 1 can contain Fe 2+ .

[0071] In the above Chemical Formula 1, x1 may be 0.10 to 0.90, or 0.15 to 0.85. When x1 is 0.10 to 0.90, the tetragonal crystal 1 easily has the above crystal orientation, and c1 / a1 easily falls within the above range.

[0072] In the above chemical formula 1, y1 may be 0.05 to 0.85, or 0.05 to 0.80. When y1 is 0.05 to 0.85, the tetragonal crystal 1 easily has the above crystal orientation, and c1 / a1 easily falls within the above range.

[0073] In the above Chemical Formula 1, z1 may be 0.05 to 0.85, or 0.05 to 0.80. When z1 is 0.05 to 0.85, the tetragonal crystal 1 easily has the above crystal orientation, and c1 / a1 easily falls within the above range.

[0074] α in the above chemical formula 1 may be greater than or equal to 0.00 and less than 1.00. Tetragonal crystal 1 easily has the above crystal orientation, c1 / a1 easily falls within the above range, and therefore, α may be 0.50. As described above, β in the above chemical formula 1' may be greater than or equal to 0.00 and less than or equal to 1.00, or greater than 0.00 and less than 1.00. Tetragonal crystal 1 easily has the above crystal orientation, c1 / a1 easily falls within the above range, and therefore, β may be 0.50.

[0075] δ in the above chemical formula 1a may be greater than 0. As long as the crystal structure (perovskite structure) of the tetragonal crystal 1 is maintained, δ may be a value other than 0. For example, δ may be greater than 0 and less than 1.0. δ can be calculated, for example, based on the valence of each ion located at the A site and the B site in the tetragonal crystal 1. The valence of each ion can be measured by X-ray photoelectron spectroscopy (XPS).

[0076] Bi and E contained in tetragonal crystal 1 A The total number of moles can be expressed as [A] 1 , Fe, Ti and E contained in tetragonal crystal 1 B The total number of moles can be expressed as [B] 1 , [A] 1 / [B] 1 It can be 1.0. As long as the tetragonal crystal structure (perovskite structure) is maintained, [A] 1 / [B] 1 It can be a value other than 1.0. That is, [A] 1 / [B] 1 Can be less than 1.0, [A] 1 / [B] 1 It can also be greater than 1.0.

[0077] The tetragonal crystal 2 can be represented by the following chemical formula 2. The following chemical formula 2 is substantially the same as the following chemical formula 2a.

[0078] x2(Bi 1-α E A α )E B O 3 -y2BiFeO 3 -z2Bi(Fe 0.5 Ti 0.5 ) 3 (2)

[0079] (Bi x2(1-α)+y2+z2 E A x2α )(E B x2 Fey2+0.5z2 Ti 0.5z2 ) 3±δ (2a)

[0080] In the above chemical formula 2, x2+y2+z2 may be 1.00. In the above chemical formula 2, E A The E in the above chemical formula 2 is B The E in the above chemical formula 2 is A It can be combined with E in the above chemical formula 1 A The same or different. E in the above chemical formula 2 B It can be combined with E in the above chemical formula 1 B The valence of each element in the above chemical formula 2 may be the same as the valence of each element in the above chemical formula 1. B The two elements are represented as elements E B1 and element E B2 In the case of , the above Chemical Formula 2 is substantially the same as the following Chemical Formula 2'. β in the following Chemical Formula 2' may be greater than or equal to 0.00 and less than or equal to 1.00.

[0081] x2(Bi 1-α E A α )(E B1 1-β E B2 β ) 3 -y2BiFeO 3 -z2Bi(Fe 0.5 Ti 0.5 ) 3 (2')

[0082] In the above chemical formula 2a, Bi x2(1-α)+y2+z2 E A x2α Corresponds to the element located at the A site of the perovskite structure. E in Formula 2a B x2 Fe y2+0.5z2 Ti 0.5z2 Corresponding to the element located at the B site of the perovskite structure.

[0083] The y2BiFeO in the above chemical formula 2 3 The Fe valence is 3, but the z2Bi(Fe 0.5 Ti 0.5 ) 3 The valence of Fe is 2. Therefore, by using Bi, E A 、EB The molar ratio of each of Fe and Ti is the same as that of Bi, E in the above chemical formula 2. A 、E B The composition of the raw material of the second piezoelectric layer 3B is adjusted in such a way that the molar ratio of Fe and Ti is consistent, and the tetragonal crystal 2 can contain Fe 2+ .

[0084] In the above chemical formula 2, x2 may be 0.10 to 0.85, or 0.10 to 0.80. When x2 is 0.10 to 0.85, the tetragonal crystal 2 easily has the above crystal orientation, and c2 / a2 easily falls within the above range.

[0085] In the above chemical formula 2, y2 may be 0.10 or more and 0.85 or less. When y2 is 0.10 or more and 0.85 or less, the tetragonal crystal 2 easily has the above crystal orientation, and c2 / a2 easily falls within the above range.

[0086] In the above chemical formula 2, z2 may be 0.05 or more and 0.80 or less. When z2 is 0.05 or more and 0.80 or less, the tetragonal crystal 2 easily has the above crystal orientation, and c2 / a2 easily falls within the above range.

[0087] α in the above chemical formula 2 may be greater than or equal to 0.00 and less than 1.00. Tetragonal crystal 2 easily has the above crystal orientation, c2 / a2 easily falls within the above range, and therefore, α may be 0.50. As described above, β in the above chemical formula 2' may be greater than or equal to 0.00 and less than or equal to 1.00, or greater than 0.00 and less than 1.00. Tetragonal crystal 2 easily has the above crystal orientation, c2 / a2 easily falls within the above range, and therefore, β may be 0.50.

[0088] δ in the above chemical formula 2a may be greater than 0. As long as the crystal structure (perovskite structure) of the tetragonal crystal 2 is maintained, δ may be a value other than 0. For example, δ may be greater than 0 and less than 1.0. Δ may be calculated based on, for example, the valence of each ion located at the A site and the B site of the tetragonal crystal 2, respectively. The valence of each ion is determined by the XPS method.

[0089] Bi and E contained in tetragonal crystal 2 A The total number of moles can be expressed as [A] 2 , Fe, Ti and E contained in tetragonal crystal 2 B The total number of moles can be expressed as [B] 2 , [A] 2 / [B] 2 It can be 1.0. As long as the tetragonal crystal structure (perovskite structure) is maintained, [A] 2 / [B]2 It can be a value other than 1.0. That is, [A] 2 / [B] 2 Can be less than 1.0, [A] 2 / [B] 2 It can also be greater than 1.0.

[0090] The tetragonal crystal 1 can also be represented by the following chemical formula 1w. A The E in the following chemical formula 1w is B The above-mentioned elements may be used. w1 in the following chemical formula 1w may be 0.30 or more and 0.80 or less. α in the following chemical formula 1w may be 0.00 or more and less than 1.00.

[0091] (1-w1)Bi 1-α E A α E B O 3 -w1BiFeO 3 (1w)

[0092] The tetragonal crystal 2 can also be represented by the following chemical formula 2w. A The E in the following chemical formula 2w is B The above elements. w2 in the following chemical formula 2w may be 0.30 or more and 0.80 or less. α in the following chemical formula 2w may be 0.00 or more and less than 1.00. E in the following chemical formula 2w A It can be combined with E in the above chemical formula 1w A The same or different. E in the following chemical formula 2w B It can be combined with E in the above chemical formula 1w B The same, or different.

[0093] (1-w2)Bi 1-α E A α E B O 3 -w2BiFeO 3 (2w)

[0094] The piezoelectric thin film 3 may be an epitaxial film. That is, the piezoelectric thin film 3 may be formed by epitaxial growth. By epitaxial growth, it is easy to form a piezoelectric thin film 3 with excellent anisotropy and crystal orientation.

[0095] The surface area of ​​the piezoelectric film 3 can be, for example, 1 μm 2 Above and 500mm 2The single crystal substrate 1 , the first intermediate layer 5 , the first electrode layer 2 , the second intermediate layer 6 , and the second electrode layer 4 may each have the same area as the piezoelectric thin film 3 .

[0096] The composition of the piezoelectric film 3 can be analyzed, for example, by X-ray fluorescence analysis (XRF), inductively coupled plasma (ICP) emission spectroscopy, and photoelectron spectroscopy (XPS). As a method for specifying the composition and thickness of each of the first piezoelectric layer 3A and the second piezoelectric layer 3B, the composition of the piezoelectric film 3 can be analyzed along the thickness direction of the piezoelectric film 3 by the XPS method. For example, the thickness Tp of the piezoelectric film 3 can be uniformly reduced by ion milling or sputtering of the surface of the piezoelectric film 3, and the composition of the surface of the piezoelectric film 3 can be continuously measured by the XPS method. The composition of the cross section of the piezoelectric film 3 can be analyzed along the thickness direction of the piezoelectric film 3. The energy dispersive X-ray analysis (EDS) device provided in the scanning electron microscope (SEM) or the scanning transmission electron microscope (STEM) can be used in the composition analysis of the cross section of the piezoelectric film 3 along the thickness direction of the piezoelectric film 3. The crystal structure and crystal orientation of each of the first piezoelectric layer 3A and the second piezoelectric layer 3B can be specified by the X-ray diffraction (XRD) method. The crystal structure and crystal orientation of each of the first piezoelectric layer 3A and the second piezoelectric layer 3B may be the crystal structure and crystal orientation at room temperature.

[0097] The process of forming the piezoelectric thin film 3 includes a first film forming process and a second film forming process subsequent to the first film forming process. In the first film forming process, the first piezoelectric layer 3A is formed by a pulsed laser deposition (PLD) method using a first target. In the second film forming process, the second piezoelectric layer 3B is directly formed on the surface of the first piezoelectric layer 3A by a PLD method using a second target.

[0098] The first target is a raw material for the first piezoelectric layer 3A. The first target may be composed of all the same elements as the first piezoelectric layer 3A (tetragonal crystal 1). The composition of the first target may be adjusted in such a way that the molar ratio of each element constituting the first target 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 may be consistent with the molar ratio of each element constituting the above chemical formula 1.

[0099] The second target is a raw material for the second piezoelectric layer 3B. The second target may be composed of all the same elements as the second piezoelectric layer 3B (tetragonal crystal 2). The composition of the second target may be adjusted in such a way 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 be consistent with the molar ratio of each element constituting the above chemical formula 2.

[0100] In the PLD method, by irradiating a target material with a pulsed laser (e.g., an excimer laser), the elements constituting the target material are plasmatized and evaporated. According to the PLD method, each element constituting the target material can be plasmatized instantly and uniformly. As a result, the molar ratio of each element in each piezoelectric layer is likely to be roughly consistent with the molar ratio of each element in each target material, and the segregation of the elements in each piezoelectric layer is likely to be suppressed. In addition, according to the PLD method, each piezoelectric layer is likely to grow epitaxially, and each piezoelectric layer that is dense and at the atomic level is likely to be formed. In the PLD method, by changing the number of pulses (repetition frequency) of the pulsed laser, the growth rate of each piezoelectric layer, the anisotropy of the tetragonal crystals 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 crystals constituting each piezoelectric layer become higher.

[0101] The repetition frequency f2 of the pulsed laser in the second film-forming process is less than the repetition frequency f1 of the pulsed laser in the first film-forming process. Since f2 is less than f1, a piezoelectric film 3 can be formed in which c2 / a2 of the tetragonal crystal 2 is greater than c1 / a1 of the tetragonal crystal 1. For example, the repetition frequency f1 of the pulsed laser in the first film-forming process may be 20 Hz. By adjusting f1 to 20 Hz, it is easy to control c1 / a1 of the tetragonal crystal 1 in the first piezoelectric layer 3A to be greater than 1.015 and less than 1.050. For example, the repetition frequency f2 of the pulsed laser in the second film-forming process may be 10 Hz. By adjusting f2 to 10 Hz, it is easy to control c2 / a2 of the tetragonal crystal 2 in the second piezoelectric layer 3B to be greater than c1 / a1.

[0102] The first target and the second target can be produced separately by the following method.

[0103] As the starting materials of each target material, for example, Bi, E A 、E B , Fe and Ti oxides. As the starting material, instead of oxides, carbonates or oxalates that can be converted into oxides by sintering can be used. After these starting materials are fully dried at 100°C or above, Bi, E A 、E B The starting materials are weighed in such a way that the molar ratios of Fe, Ti and the elements in each piezoelectric layer are consistent. In the first film forming step and the second film forming step, 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 value higher than the molar ratio of Bi in each piezoelectric layer. A In the case of, in the first film forming step and the second film forming step, K in the target material is easy to volatilize to other elements. Therefore, the molar ratio of K in each target material can be adjusted to a value higher than the molar ratio of K in each piezoelectric layer.

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

[0105] By heating the block-shaped compact, the binder in the compact is volatilized. The heating temperature may be 400° C. or higher and 800° C. or lower. The heating time may be 2 hours or higher and 4 hours or lower.

[0106] After the binder is volatilized, the molded body is sintered. The sintering temperature may be 800°C or higher and 1100°C or lower. The sintering time may be 2 hours or higher and 4 hours or lower. The heating rate and cooling rate of the molded body during the sintering process may be, for example, 50°C / hour or higher and 300°C / hour or lower.

[0107] Through the above steps, the first target and the second target are separately manufactured. The average particle size of the crystal grains of the oxide (perovskite oxide) contained in each target can be, for example, 1 μm or more and 20 μm or less. Each target contains Fe 3+ , but each target material may not contain Fe 2+ In the first film forming step, the Fe 3+ part of the Fe 2+ In the second film forming step, the Fe 3+ part of the Fe 2+ The second piezoelectric layer 3B.

[0108] In the first film forming step, the elements constituting the first target are evaporated in a vacuum atmosphere, and the evaporated elements are attached and deposited on any surface of the second intermediate layer 6, the first electrode layer 2, or the single crystal substrate 1, thereby forming the first piezoelectric layer 3A.

[0109] In the second film forming step following the first film forming step, the elements constituting the second target material are evaporated in a vacuum atmosphere, and the evaporated elements are attached and deposited on the surface of the first piezoelectric layer 3A, thereby forming the second piezoelectric layer 3B.

[0110] In the first film forming step, the first piezoelectric layer 3A can be formed while heating the single crystal substrate 1 and the first electrode layer 2 in the vacuum chamber. The temperature (film forming temperature) of the single crystal substrate 1 and the first electrode layer 2 can be, for example, 450° C. or higher and 600° C. or lower. When the film forming temperature is 450° C. or higher, the Fe from the first target material can be easily reduced. 3+ part, which easily forms 2+ When the film forming temperature is lower than 450°C, it is difficult to reduce Fe from the target. 3+ , it is difficult to obtain Fe 2+ The first piezoelectric layer 3A. The higher the film forming temperature, the more the cleanliness of the surface of the single crystal substrate 1 or the first electrode layer 2 is improved, the crystallinity of the first piezoelectric layer 3A becomes higher, and the orientation degree of the crystal plane of the tetragonal crystal 1 tends to become higher. When the film forming temperature is too high, the elements constituting the first piezoelectric layer 3A are excessively reduced, and it is difficult to obtain the first piezoelectric layer 3A with the desired composition. In addition, when the film forming temperature is too high, Bi or K is easily separated from the first piezoelectric layer 3A, and it is difficult to control the composition of the first piezoelectric layer 3A.

[0111] The oxygen partial pressure in the vacuum chamber may be, for example, 0.1 Pa to 3.0 Pa, preferably 0.1 Pa to 1.0 Pa, and more preferably 0.1 Pa to 0.5 Pa. By maintaining the oxygen partial pressure within the above range, the Fe 3+ part, which easily forms 2+ When the oxygen partial pressure is too low, it is difficult for the elements from the target to be fully oxidized, and it is difficult to form a perovskite-type oxide, and the orientation degree of the crystal plane of the tetragonal crystal 1 is easily reduced. When the oxygen partial pressure is too high, it is difficult to reduce the Fe from the target. 3+ , it is difficult to obtain Fe 2+ In addition, when the oxygen partial pressure is too high, the growth rate of the first piezoelectric layer 3A is likely to decrease, and the orientation degree of the crystal plane of the tetragonal crystal 1 is likely to decrease.

[0112] In the first film forming step, in addition to controlling the repetition frequency f1 of the pulsed laser, parameters such as the number of times the pulsed laser is irradiated to the first target (film forming time) and the distance between the single crystal substrate 1 and the first target can be controlled. As the number of times the pulsed laser is irradiated to the first target (film forming time) increases, the thickness of the first piezoelectric layer 3A tends to increase. As the distance between the single crystal substrate 1 and the first target decreases, the thickness and growth rate of the first piezoelectric layer 3A tend to increase.

[0113] The second film forming step can be performed by substantially the same method as the first film forming step described above, except for the composition of the target material and the repetition frequency of the pulsed laser.

[0114] After the piezoelectric film 3 is formed by the first film forming step and the second film forming step, the piezoelectric film 3 may be subjected to an annealing treatment (heat treatment). The temperature of the piezoelectric film 3 during the annealing treatment (annealing temperature) may be, for example, 300°C to 1000°C, 600°C to 1000°C, or 850°C to 1000°C. By annealing the piezoelectric film 3, the piezoelectricity of the piezoelectric film 3 tends to be further improved. In particular, by annealing at 850°C to 1000°C, the piezoelectricity of the piezoelectric film 3 is easily improved. However, the annealing treatment is not necessary. The annealing treatment may be performed in nitrogen (N 2 ) or the like. By annealing in a reducing atmosphere, the Fe 2+ Oxidation (Fe 3+ The generation of Fe in the piezoelectric film 3 is easy to maintain 2+ .

[0115] In the temperature drop process subsequent to the formation process of the piezoelectric thin film 3 described above, compressive stress is generated in the piezoelectric thin film 3. Due to the compressive stress, the piezoelectric thin film 3 is compressed in the direction (the a-axis direction and the b-axis direction) substantially parallel to the surface of the piezoelectric thin film 3. As a result, the tetragonal crystals 1 and the tetragonal crystals 2 are easily formed. The compressive stress is caused by, for example, lattice mismatch between the single crystal substrate 1 and the piezoelectric thin film 3 (first piezoelectric layer 3A), or a difference in thermal expansion coefficient between the single crystal substrate 1 and the piezoelectric thin film 3 (first piezoelectric layer 3A).

[0116] The single crystal substrate 1 may be, for example, a substrate composed of a single crystal of Si, or a substrate composed of a single crystal of a compound semiconductor such as GaAs. The single crystal substrate 1 may be a substrate composed of a single crystal of an oxide. The single crystal of the oxide may be, for example, MgO or a perovskite-type oxide (e.g., SrTiO 3 ). The thickness of the single crystal substrate 1 can be, for example, not less than 10 μm and not more than 1000 μm. When the single crystal substrate 1 is conductive, the single crystal substrate 1 functions as an electrode, and therefore, the first electrode layer 2 may not be present. For example, the conductive single crystal substrate 1 can be SrTiO doped with niobium (Nb). 3 of single crystal.

[0117] The crystal orientation of the single crystal substrate 1 may be in the direction D of the normal to the surface of the single crystal substrate 1. NThe surface of the single crystal substrate 1 may be parallel to the crystal plane of the single crystal substrate 1. The single crystal substrate 1 may be a uniaxially oriented substrate. For example, the (100) plane of the single crystal substrate 1 of Si or the like may be parallel to the surface of the single crystal substrate 1. That is, the

[100] direction of the single crystal substrate 1 of Si or the like may be parallel to the normal direction D of the surface of the single crystal substrate 1. N parallel.

[0118] When the (100) plane of single crystal substrate 1 such as Si is parallel to the surface of single crystal substrate 1 , the (001) planes of tetragonal crystals 1 and 2 are easily oriented in the normal direction dn of the surface of piezoelectric thin film 3 .

[0119] As described above, the first intermediate layer 5 may be disposed between the single crystal substrate 1 and the first electrode layer 2. The first intermediate layer 5 may contain, for example, titanium (Ti), chromium (Cr), titanium oxide (TiO 2 ), silicon oxide (SiO 2 ), and zirconium oxide (ZrO 2 ). The first electrode layer 2 is easily adhered to the single crystal substrate 1 through the first intermediate layer 5. The first intermediate layer 5 may be crystalline. The crystal plane of the first intermediate layer 5 may be in the normal direction D of the surface of the single crystal substrate 1. N The crystal plane of the single crystal substrate 1 and the crystal plane of the first intermediate layer 5 can be oriented in the normal direction D of the surface of the single crystal substrate 1. N The first intermediate layer 5 may be formed by sputtering, vacuum evaporation, printing, spin coating, or sol-gel method.

[0120] The first intermediate layer 5 may contain ZrO 2 and oxides of rare earth elements. The first intermediate layer 5 contains ZrO 2 and oxides of rare earth elements, the first electrode layer 2 composed of platinum crystals is easily formed on the surface of the first intermediate layer 5, the (002) plane of the platinum crystals is easily oriented in the normal direction of the surface of the first electrode layer 2, and the (200) plane of the platinum crystals is easily oriented in the in-plane direction of the surface of the first electrode layer 2. The rare earth element may 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), holoium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0121] The first intermediate layer 5 may contain ZrO 2 and Y 2 O 3 For example, the first intermediate layer 5 may be made of yttria-stabilized zirconia (with Y 2 O 3ZrO 2 ) is composed. The first intermediate layer 5 may have a ZrO 2 The first layer consists of Y 2 O 3 The second layer is composed of ZrO 2 The first layer composed of Y can be directly laminated on the surface of the single crystal substrate 1. 2 O 3 The second layer composed of Y can be directly laminated on the surface of the first layer. 2 O 3 The first intermediate layer 5 contains ZrO 2 and Y 2 O 3 In the case of , the first piezoelectric layer 3A and the second piezoelectric layer 3B are easily epitaxially grown, and the (001) planes of the tetragonal crystals 1 and 2 are easily preferentially oriented in the normal direction dn of the surface of the piezoelectric film 3. 2 and Y 2 O 3 In this case, it is easy to form the first electrode layer 2 composed of platinum crystals on the surface of the first intermediate layer 5, the (002) plane of the platinum crystals is easy to be oriented in the normal direction of the surface of the first electrode layer 2, and the (200) plane of the platinum crystals is easy to be oriented in the in-plane direction of the surface of the first electrode layer 2.

[0122] The first electrode layer 2 may be composed of at least one metal selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), gold (Au), ruthenium (Ru), iridium (Ir), molybdenum (Mo), titanium (Ti), tantalum (Ta), and nickel (Ni). The first electrode layer 2 may be composed of, for example, strontium ruthenate (SrRuO 3 ), lanthanum nickel oxide (LaNiO 3 ), or lanthanum strontium cobaltate ((La,Sr)CoO 3 ) or other conductive metal oxides. The first electrode layer 2 may be crystalline. The crystal plane of the first electrode layer 2 may be in the normal direction D of the single crystal substrate 1. N The crystal plane of the first electrode layer 2 may be substantially parallel to the surface of the single crystal substrate 1. The crystal plane of the single crystal substrate 1 and the crystal plane of the first electrode layer 2 may be substantially parallel to the surface of the single crystal substrate 1. N In the normal direction D of the single crystal substrate 1 NThe crystal plane of the top-oriented first electrode layer 2 may be substantially parallel to the (001) planes of the tetragonal crystal 1 and the tetragonal crystal 2. The thickness of the first electrode layer 2 may be, for example, greater than 1 nm and less than 1.0 μm. The first electrode layer 2 may be formed by sputtering, vacuum evaporation, printing, spin coating, or sol-gel. In the case of printing, spin coating, or sol-gel, in order to improve the crystallinity of the first electrode layer 2, the first electrode layer 2 may be subjected to a heat treatment (annealing).

[0123] The first electrode layer 2 may include platinum crystals. The first electrode layer 2 may also be composed only of platinum crystals. The platinum crystals are cubic crystals having a face-centered cubic lattice structure (fcc structure). The (002) plane of the platinum crystals may be oriented in the normal direction of the surface of the first electrode layer 2, and the (200) plane of the platinum crystals may be oriented in the in-plane direction of the surface of the first electrode layer 2. In other words, the (002) plane of the platinum crystals may be approximately parallel to the surface of the first electrode layer 2, and the (200) plane of the platinum crystals may be approximately perpendicular to the surface of the first electrode layer 2. When the (002) plane and the (200) plane of the platinum crystals constituting the first electrode layer 2 have the above-mentioned orientation, the first piezoelectric layer 3A and the second piezoelectric layer 3B are easy to epitaxially grow on the surface of the first electrode layer 2, and the (001) planes of the tetragonal crystals 1 and 2 are easy to be preferentially oriented in the normal direction dn of the surface of the piezoelectric film 3. The surface of the first electrode layer 2 may be approximately parallel to the surface of the piezoelectric film 3. That is, the normal direction of the surface of the first electrode layer 2 may be substantially parallel to the normal direction dn of the surface of the piezoelectric film 3 .

[0124] As described above, the second intermediate layer 6 may be disposed between the first electrode layer 2 and the piezoelectric film 3. The second intermediate layer 6 may contain, for example, a material selected from SrRuO 3 、LaNiO 3 and (La,Sr)CoO 3 At least one of (La,Sr)CoO 3 For example, La 0.5 Sr 0.5 CoO 3 The second intermediate layer 6 may be crystalline. For example, the second intermediate layer 6 may be selected from a material including SrRuO 3 The crystalline layer contains LaNiO 3 The crystalline layer and (La, Sr)CoO 3 A stacked body consisting of at least two buffer layers in the crystalline layer. SrRuO 3 、LaNiO 3 and (La,Sr)CoO 3 Therefore, the second intermediate layer 6 contains a SrRuO 3 、LaNiO3 and (La,Sr)CoO 3 In the case of at least one of the above, the first piezoelectric layer 3A and the second piezoelectric layer 3B are easily epitaxially grown, and the (001) planes of the tetragonal crystals 1 and 2 are easily preferentially oriented in the normal direction dn of the surface of the piezoelectric film 3. In addition, the piezoelectric film 3 (the first piezoelectric layer 3A) is easily adhered to the first electrode layer 2 by passing through the second intermediate layer 6. The crystal plane of the second intermediate layer 6 can be in the normal direction Dn of the surface of the single crystal substrate 1. N Both the crystal plane of the single crystal substrate 1 and the crystal plane of the second intermediate layer 6 can be oriented in the normal direction D of the surface of the single crystal substrate 1. N The second intermediate layer 6 may be formed by sputtering, vacuum evaporation, printing, spin coating, or sol-gel method.

[0125] The second electrode layer 4 may be composed of at least one metal selected from the group consisting of Pt, Pd, Rh, Au, Ru, Ir, Mo, Ti, Ta, and Ni. The second electrode layer 4 may be composed of at least one metal selected from the group consisting of LaNiO 3 、SrRuO 3 and (La,Sr)CoO 3 The second electrode layer 4 may be crystalline. The crystal plane of the second electrode layer 4 may be in the normal direction D of the single crystal substrate 1. N The crystal plane of the second electrode layer 4 may be substantially parallel to the surface of the single crystal substrate 1. In the normal direction D of the single crystal substrate 1 N The crystal plane of the second electrode layer 4 oriented upward may be substantially parallel to the (001) planes of the tetragonal crystal 1 and the tetragonal crystal 2. The thickness of the second electrode layer 4 may be, for example, greater than 1 nm and less than 1.0 μm. The second electrode layer 4 may be formed by sputtering, vacuum evaporation, printing, spin coating, or sol-gel. In the case of printing, spin coating, or sol-gel, the second electrode layer 4 may be subjected to a heat treatment (annealing) to improve the crystallinity of the second electrode layer 4.

[0126] The third intermediate layer may be disposed between the piezoelectric thin film 3 and the second electrode layer 4. The second electrode layer 4 is easily adhered to the piezoelectric thin film 3 (the second piezoelectric layer 3B) via the third intermediate layer.

[0127] The composition, crystal structure and formation method of the third intermediate layer may be the same as those of the second intermediate layer.

[0128] The protective film may cover at least a part or the entire surface of the piezoelectric thin-film element 10. The protective film covers the piezoelectric thin-film element 10 to improve durability (moisture resistance, etc.).

[0129] The piezoelectric thin film element of this embodiment has various uses. For example, the piezoelectric thin film element can be used in a piezoelectric transducer. That is, the piezoelectric transducer of this embodiment can include the above-mentioned piezoelectric thin film element. The piezoelectric transducer can be, for example, an ultrasonic transducer such as an ultrasonic sensor. The piezoelectric thin film element can also be, for example, a collector (vibration power generation element). The piezoelectric thin film element of this embodiment includes a large (-e 31,f ) 2 / ε 0 ε r The piezoelectric film is therefore suitable for ultrasonic transducers or collectors. The piezoelectric film element can also be a piezoelectric actuator. The piezoelectric actuator can also be used in a head assembly, a head cantilever assembly, or a hard disk drive. The piezoelectric actuator can also be used in a printer head or an inkjet printer device. The piezoelectric actuator can also be a piezoelectric switch. The piezoelectric actuator can also be used in haptics. That is, the piezoelectric actuator can be used in various devices that require feedback of skin sensation (tactile sensation). Devices that require feedback of skin sensation can be, for example, wearable devices, touch panels, displays, or game controllers. The piezoelectric film element can also be a piezoelectric sensor. For example, the piezoelectric sensor can be a piezoelectric microphone, a gyroscope sensor, a pressure sensor, a pulse wave sensor, or an impact sensor. The piezoelectric film element can also be a filter (SAW filter or BAW filter), an oscillator, or an acoustic multilayer film. The piezoelectric film element can also be part or all of a microelectromechanical system (MEMS). For example, the piezoelectric thin film element can be a piezoelectric micromachined ultrasonic transducer (PMUT). For example, a product using a piezoelectric micromachined ultrasonic transducer can be a biometric authentication sensor or a medical / healthcare sensor (fingerprint sensor or ultrasonic blood vessel authentication sensor, etc.), or a ToF (Time of Flight) sensor.

[0130] Figure 4The schematic cross section of the ultrasonic transducer 10a including the above-mentioned piezoelectric film 3 is shown. The cross section of the ultrasonic transducer 10a is perpendicular to the surface of the piezoelectric film 3. The ultrasonic transducer 10a may include substrates 1a and 1b, a first electrode layer 2 provided on the substrates 1a and 1b, a piezoelectric film 3 overlapping the first electrode layer 2, and a second electrode layer 4 overlapping the piezoelectric film 3. The piezoelectric film 3 includes a first piezoelectric layer 3A overlapping the first electrode layer 2, and a second piezoelectric layer 3B overlapping the first piezoelectric layer 3A. A cavity 1c for sound may be provided below the piezoelectric film 3. Ultrasonic signals are transmitted or received by the deflection or vibration of the piezoelectric film 3. The first intermediate layer may be interposed between the substrates 1a and 1b and the first electrode layer 2. The second intermediate layer may be interposed between the first electrode layer 2 and the piezoelectric film 3.

[0131] The present invention is not limited to the above-described embodiment. For example, the piezoelectric film 3 may include a second piezoelectric layer 3B overlapping the first electrode layer 2 and a first piezoelectric layer 3A directly overlapping the second piezoelectric layer 3B.

[0132] [Example]

[0133] The present invention will be described in detail by the following examples and comparative examples. The present invention is not limited to the following examples.

[0134] (Example 1)

[0135] A single crystal substrate made of Si was used in the production of the piezoelectric thin film element of Example 1. The (100) plane of Si was parallel to the surface of the single crystal substrate. The single crystal substrate was a square of 20 mm×20 mm. The thickness of the single crystal substrate was 500 μm.

[0136] In the vacuum chamber, ZrO 2 and Y 2 O 3 The crystalline first intermediate layer is formed on the entire surface of the single crystal substrate. The first intermediate layer is formed by sputtering. The thickness of the first intermediate layer is 30 nm.

[0137] In a vacuum chamber, a first electrode layer composed of Pt crystals is formed on the entire surface of the first intermediate layer. The first electrode layer is formed by sputtering. The thickness of the first electrode layer is 200 nm. The temperature of the single crystal substrate is maintained at 500° C. during the formation of the first electrode layer.

[0138] The XRD pattern of the first electrode layer was measured by Out-of-Plane measurement on the surface of the first electrode layer. The XRD pattern of the first electrode layer was measured by In-Plane measurement on the surface of the first electrode layer. An X-ray diffraction device (Smart Lab) manufactured by Rigaku Co., Ltd. was used in the measurement of these XRD patterns. The measurement conditions were set in such a way that the intensity of each peak in each XRD pattern was at least 3 digits higher than the background intensity. By Out-of-Plane measurement, the peak of diffracted X-rays of the (002) plane of the Pt crystal was detected. That is, the (002) plane of the Pt crystal was oriented in the normal direction of the surface of the first electrode layer. By In-Plane measurement, the peak of diffracted X-rays of the (200) plane of the Pt crystal was detected. That is, the (200) plane of the Pt crystal was oriented in the in-plane direction of the surface of the first electrode layer.

[0139] The first piezoelectric layer was formed on the entire surface of the first electrode layer by performing the above-mentioned first film forming process (PLD method) in a vacuum chamber. The repetition frequency f1 of the pulsed laser in the first film forming process was adjusted to 20 Hz. The thickness Ta of the first piezoelectric layer was adjusted to the value shown in Table 2 below.

[0140] The composition of the first target material used in the first film forming step is represented by the following chemical formula 1A. When the composition of the first target material is represented by the chemical formula 1', E in the following chemical formula 1' is A is K, and E in the following chemical formula 1' B1 is Ti, without E in the following chemical formula 1' B2 , α in the following chemical formula 1' is 0.5, and β in the following chemical formula 1' is 0. In the case of Example 1, x1, y1, and z1 in the following chemical formula 1A are the values ​​shown in Table 1 below.

[0141] x1(Bi 0.5 K 0.5 )TiO 3 -y1BiFeO 3 -z1Bi(Fe 0.5 Ti 0.5 ) 3 (1A)

[0142] x1(Bi 1-α E A α )(E B1 1-β E B2 β ) 3 -y1BiFeO 3 -z1Bi(Fe 0.5 Ti0.5 ) 3 (1')

[0143] After the first film forming step, the second film forming step (PLD method) is performed in a vacuum chamber, thereby forming the second piezoelectric layer on the entire surface of the first piezoelectric layer. The repetition frequency f2 of the pulsed laser in the second film forming step is adjusted to 10 Hz. The thickness Tb of the second piezoelectric layer is adjusted to the value shown in Table 2 below.

[0144] The composition of the second target material used in the second film forming step is represented by the following chemical formula 2A. When the composition of the second target material is represented by the chemical formula 2', E in the following chemical formula 2' is A is K, and E in the following chemical formula 2' B1 is Ti, without E in the following chemical formula 2' B2 , α in the following chemical formula 2' is 0.5, and β in the following chemical formula 2' is 0. In the case of Example 1, x2, y2, and z2 in the following chemical formula 2A are the values ​​shown in Table 1 below.

[0145] x2(Bi 0.5 K 0.5 )TiO 3 -y2BiFeO 3 -z2Bi(Fe 0.5 Ti 0.5 ) 3 (2A)

[0146] x2(Bi 1-α E A α )(E B1 1-β E B2 β ) 3 -y2BiFeO 3 -z2Bi(Fe 0.5 Ti 0.5 ) 3 (2')

[0147] The piezoelectric film composed of the first piezoelectric layer and the second piezoelectric layer is formed by the above-mentioned first film forming step and the second film forming step. The thickness Tp of the piezoelectric film is the value shown in the following Table 2. The temperature (film forming temperature) of the single crystal substrate in the first film forming step and the second film forming step is maintained at 500° C. The oxygen partial pressure in the vacuum chamber in the first film forming step and the second film forming step is maintained at 1 Pa.

[0148] The thickness Tp of the piezoelectric film 3 is uniformly reduced by sputtering the surface of the piezoelectric film 3, and the composition of the surface of the piezoelectric film 3 is continuously analyzed along the thickness direction of the piezoelectric film 3 by the XPS method. The analysis results show that the composition of the first piezoelectric layer is consistent with the composition of the first target material, and the composition of the second piezoelectric layer is consistent with the composition of the second target material.

[0149] The XRD pattern of the piezoelectric film is measured by out-of-plane measurement on the surface of the piezoelectric film using the above-mentioned X-ray diffraction device. In addition, another XRD pattern of the piezoelectric film is measured by in-plane measurement on the surface of the piezoelectric film. The measurement conditions are set in such a way that the intensity of each peak in each XRD pattern is at least 3 digits higher than the background intensity. The measuring device and measurement conditions of each XRD pattern are the same as the above-mentioned conditions. A scanning transmission electron microscope (STEM) is used to observe the cross section of the piezoelectric film parallel to the thickness direction of the piezoelectric film with atomic energy resolution.

[0150] The results of the above analysis using an X-ray diffraction apparatus and STEM have shown that the piezoelectric film has the following characteristics.

[0151] The first piezoelectric layer is composed of tetragonal crystals 1 of a perovskite-type oxide.

[0152] The (001) plane of the tetragonal crystal 1 is preferentially oriented in the normal direction of the surface of the piezoelectric film. That is, the orientation degree of the (001) plane of the tetragonal crystal 1 in the normal direction of the surface of the piezoelectric film is 90% or more. As described above, the orientation degree of the (001) plane of the tetragonal crystal 1 is expressed as 100×I 1(001) / (I 1(001) +I 1(110) +I 1(111) ).

[0153] The c1 / a1 of the tetragonal crystal 1 is the value shown in Table 2 below.

[0154] The second piezoelectric layer is composed of tetragonal crystals 2 of a perovskite-type oxide.

[0155] The (001) plane of the tetragonal crystal 2 is preferentially oriented in the normal direction of the surface of the piezoelectric film. That is, the orientation degree of the (001) plane of the tetragonal crystal 2 in the normal direction of the surface of the piezoelectric film is 90% or more. As described above, the orientation degree of the (001) plane of the tetragonal crystal 2 is expressed as 100×I 2(001) / (I 2(001) +I 2(110) +I 2(111) ).

[0156] c2 / a2 of the tetragonal crystal 2 is a value shown in Table 2 below.

[0157] I 2 / (I 1 +I 2 ) are the values ​​shown in the following Table 2. 2 / (I 1 +I 2 ) is as defined above.

[0158] By the above method, a stacked body consisting of a single crystal substrate, a first intermediate layer stacked on the single crystal substrate, a first electrode layer stacked on the first intermediate layer, and a piezoelectric thin film stacked on the first electrode layer is prepared. The following steps are further performed using the stacked body.

[0159] In a vacuum chamber, a second electrode layer made of Pt was formed on the entire surface of the piezoelectric thin film. The second electrode layer was formed by sputtering. The temperature of the single crystal substrate during the formation of the second electrode layer was maintained at 500° C. The thickness of the second electrode layer was 200 nm.

[0160] Through the above steps, a stacked body consisting of a single crystal substrate, a first intermediate layer overlapped on the single crystal substrate, a first electrode layer overlapped on the first intermediate layer, a piezoelectric film overlapped on the first electrode layer, and a second electrode layer overlapped on the piezoelectric film is manufactured. Next, the stacked structure on the single crystal substrate is patterned by photolithography. After patterning, the stacked body is cut by dicing.

[0161] Through the above steps, a rectangular piezoelectric thin film element of Example 1 is obtained. The piezoelectric thin film element is composed of a single crystal substrate, a first intermediate layer overlapped with the single crystal substrate, a first electrode layer overlapped with the first intermediate layer, a piezoelectric thin film overlapped with the first electrode layer, and a second electrode layer overlapped with the piezoelectric thin film. The area of ​​the movable part of the piezoelectric thin film is 20 mm×1.0 mm.

[0162] <Evaluation of piezoelectricity>

[0163] The piezoelectric property of the piezoelectric film was evaluated by the following method.

[0164] [Measurement of remanent polarization]

[0165] The hysteresis of the polarization of the piezoelectric film was measured. A device combining an atomic force microscope (AFM) and a ferroelectric evaluation system was used for the measurement. The atomic force microscope was SPA-400 manufactured by Seiko Instruments Co., Ltd. The ferroelectric evaluation system was FCE manufactured by Toyo Technica Co., Ltd. The frequency of the AC voltage in the hysteresis measurement was 5 Hz. The maximum value of the voltage applied to the piezoelectric film during the measurement was 20 V. The residual polarization Pr of the piezoelectric film is shown in Table 2 below. The unit of the residual polarization Pr is μC / cm 2 .

[0166] [Calculation of relative dielectric constant]

[0167] The electrostatic capacitance C of the piezoelectric thin film element was measured. Details of the measurement of the electrostatic capacitance C are as follows.

[0168] Measurement device: Impedance Gain-Phase Analyzer 4194A manufactured by Hewlett Packard Corporation

[0169] Frequency: 10kHz

[0170] Electric field: 0.1V / μm

[0171] The relative dielectric constant ε is calculated from the measured value of the electrostatic capacitance C based on the following formula A: r .

[0172] ε of Example 1 r This is shown in Table 2 below.

[0173] C=ε 0 ×ε r ×(S / d) (A)

[0174] ε in equation A 0 is the dielectric constant of vacuum (8.854×10 -12 Fm -1 ). S in formula A is the surface area of ​​the piezoelectric film. S is also called the area of ​​the first electrode layer overlapping the piezoelectric film. d in formula A is the thickness of the piezoelectric film.

[0175] [Piezoelectric constant-e 31,f Determination of

[0176] In order to determine the piezoelectric constant of the piezoelectric film -e 31,f As a piezoelectric film element, a rectangular sample (cantilever) was produced. The size of the sample is 3 mm in width × 15 mm in length. Except for the size, the sample is the same as the piezoelectric film element of Example 1 mentioned above. The produced evaluation system was used in the measurement. One end of the sample is fixed, and the other end of the sample is a free end. While applying voltage to the piezoelectric film in the sample, the displacement of the free end of the sample is measured by laser. In addition, the piezoelectric constant -e is calculated according to the following formula B: 31,f In addition, E in formula B s is the Young's modulus of the single crystal substrate. s is the thickness of the single crystal substrate. L is the length of the sample (cantilever). ν s is the Poisson's ratio of the single crystal substrate. out is the output displacement based on the measured displacement. V in is the voltage applied to the piezoelectric film. Piezoelectric constant - e 31,fThe frequency of the alternating electric field (AC voltage) in the measurement is 100 Hz. The maximum value of the voltage applied to the piezoelectric film is 50 V. 31,f The unit is C / m 2 Example 1-e 31,f The following Table 2 shows the (-e) of Example 1. 31,f ) 2 / ε 0 ε r (Piezoelectric Performance Index) is shown in Table 2 below.

[0177] [Mathematical formula 1]

[0178]

[0179] (Examples 2 to 6 and Comparative Examples 1 to 3)

[0180] The composition of the first target material of each of Examples 2 to 6 and Comparative Examples 1 to 3 is different from that of the first target material of Example 1. The composition of the first target material of each of Examples 2 to 6 and Comparative Examples 1 to 3 is represented by the following chemical formula 1'. A 、E B1 and E B2 The results are shown in Table 1 below. α, β, x1, y1, and z1 in Chemical Formula 1′ of Examples 2 to 6 and Comparative Examples 1 to 3 are shown in Table 1 below.

[0181] x1(Bi 1-α E A α )(E B1 1-β E B2 β ) 3 -y1BiFeO 3 -z1Bi(Fe 0.5 Ti 0.5 ) 3 (1')

[0182] The composition of the second target material of each of Examples 2 to 6 and Comparative Examples 1 to 3 is different from that of the second target material of Example 1. The composition of the second target material of each of Examples 2 to 6 and Comparative Examples 1 to 3 is represented by the following chemical formula 2'. A , E B1 and E B2 The values ​​of α, β, x2, y2, and z2 in the chemical formula 2′ of Examples 2 to 6 and Comparative Examples 1 to 3 are shown in Table 1 below. In any of Examples 2 to 6 and Comparative Examples 1 to 3, E A 、EB1 、E B2 , α and β are common in the above chemical formula 1' (first target) and the following chemical formula 2' (second target).

[0183] x2(Bi 1-α E A α )(E B1 1-β E B2 β ) 3 -y2BiFeO 3 -z2Bi(Fe 0.5 Ti 0.5 ) 3 (2')

[0184] In the case of Comparative Example 1, the repetition frequency f1 of the pulse laser in the first film forming step was adjusted to 10 Hz. The composition of the second target material of Comparative Example 1 was the same as that of the first target material of Comparative Example 1, and the composition of the piezoelectric thin film of Comparative Example 1 was uniform.

[0185] The thickness Ta of the first piezoelectric layer of each of Examples 2 to 6 and Comparative Examples 2 and 3 was adjusted to the value shown in Table 2 below. The thickness Tb of the second piezoelectric layer of each of Examples 2 to 6 and Comparative Examples 2 and 3 was adjusted to the value shown in Table 2 below. The thickness Tp of the piezoelectric film of each of Examples 2 to 6 and Comparative Examples 1 to 3 is the value shown in Table 2 below.

[0186] Piezoelectric thin-film elements of Examples 2 to 6 and Comparative Examples 1 to 3 were prepared in the same manner as in Example 1 except for the above-mentioned matters.

[0187] The XRD patterns of the first electrode layers of Examples 2 to 6 and Comparative Examples 1 to 3 were measured by the same method as in Example 1. In any of Examples 2 to 6 and Comparative Examples 1 to 3, the (002) plane of the Pt crystal constituting the first electrode layer is also oriented in the normal direction of the surface of the first electrode layer, and the (200) plane of the Pt crystal is oriented in the in-plane direction of the surface of the first electrode layer.

[0188] The composition of each piezoelectric film of Examples 2 to 6 and Comparative Examples 1 to 3 was analyzed by the same method as Example 1. In any of Examples 2 to 6 and Comparative Examples 2 and 3, the composition of the first piezoelectric layer was consistent with the composition of the first target material, and the composition of the second piezoelectric layer was consistent with the composition of the second target material. In Comparative Example 1, the uniform composition of the piezoelectric film was consistent with the composition of the first target material and the second target material.

[0189] The piezoelectric thin films of Examples 2 to 6 and Comparative Examples 1 to 3 were analyzed using an X-ray diffraction apparatus and STEM in the same manner as in Example 1. The piezoelectric thin films of Examples 2 to 6 and Comparative Examples 1 to 3 had the following characteristics.

[0190] In any of Examples 2 to 6 and Comparative Example 2, the first piezoelectric layer is also composed of tetragonal crystals 1 of the perovskite-type oxide.

[0191] In any of Examples 2 to 6 and Comparative Example 2, the second piezoelectric layer is also composed of tetragonal crystals 2 of the perovskite-type oxide.

[0192] In the case of Comparative Example 1, tetragonal crystals 1 of the perovskite type oxide and tetragonal crystals 2 of the perovskite type oxide coexist in the piezoelectric thin film having a uniform composition.

[0193] In any of Examples 2 to 6 and Comparative Examples 1 and 2, the (001) planes of the tetragonal crystals 1 were also preferentially oriented in the normal direction of the surface of the piezoelectric thin film.

[0194] In any of Examples 2 to 6 and Comparative Examples 1 and 2, the (001) planes of the tetragonal crystals 2 are also preferentially oriented in the normal direction of the surface of the piezoelectric thin film.

[0195] The c1 / a1 of the tetragonal crystal 1 of each of Examples 2 to 6 and Comparative Examples 1 and 2 is the value shown in Table 2 below.

[0196] c2 / a2 of the tetragonal crystal 2 of each of Examples 2 to 6 and Comparative Examples 1 and 2 is the value shown in Table 2 below.

[0197] I of each of Examples 2 to 6 and Comparative Examples 1 and 2 2 / (I 1 +I 2 ) are the values ​​shown in Table 2 below.

[0198] In the analysis of the piezoelectric film of Comparative Example 3, two types of tetragonal crystals with different anisotropy (c / a) were not detected, and only one type of tetragonal crystal composed of a perovskite-type oxide was identified. That is, in the case of Comparative Example 3, it is difficult to distinguish the diffraction X-rays from the crystalline structure of the first piezoelectric layer and the diffraction X-rays from the crystalline structure of the second piezoelectric layer, and it is difficult to identify the difference in the crystalline structure of the first piezoelectric layer and the second piezoelectric layer. The (001) plane of the tetragonal crystal of Comparative Example 3 is preferentially oriented in the normal direction of the surface of the piezoelectric film. As the c / a of the tetragonal crystal of Comparative Example 3, only one value (1.037) is identified. The analysis results of Comparative Example 3 suggest that the c1 / a1 of the tetragonal crystal 1 constituting the first piezoelectric layer is equal to the c2 / a2 of the tetragonal crystal 2 constituting the second piezoelectric layer.

[0199] By the same method as in Example 1, the piezoelectric properties of the piezoelectric films of Examples 2 to 6 and Comparative Examples 1 to 3 were evaluated.

[0200] The Pr of each of Examples 2 to 6 and Comparative Examples 1 to 3 is shown in Table 2 below.

[0201] ε of Examples 2 to 6 and Comparative Examples 1 to 3 r This is shown in Table 2 below.

[0202] -e of each of Examples 2 to 6 and Comparative Examples 1 to 3 31,f This is shown in Table 2 below.

[0203] Examples 2 to 6 and Comparative Examples 1 to 3 (-e 31,f ) 2 / ε 0 ε r This is shown in Table 2 below.

[0204] [Table 1]

[0205] Table 1 f1 <![CDATA[E A ]]> <![CDATA[E B1 ]]> <![CDATA[E B2 ]]> α β x1 y1 z1 f2 x2 y2 z2 Orientation plane unit Hz - - - - - - - - Hz - - - - Example 1 20 K Ti none 0.5 0 0.15 0.80 0.05 10 0.10 0.85 0.05 (001) Example 2 20 Ag Mg Ti 0.5 0.5 0.15 0.05 0.80 10 0.10 0.10 0.80 (001) Example 3 20 K Zn Zr 0.5 0.5 0.85 0.10 0.05 10 0.80 0.15 0.05 (001) Example 4 20 none Al none 0 0 0.20 0.10 0.70 10 0.15 0.15 0.70 (001) Example 5 20 Na Ni Ti 0.5 0.5 0.25 0.15 0.60 10 0.20 0.20 0.60 (001) Example 6 20 none Mg Ti 0 0.5 0.15 0.35 0.50 10 0.10 0.40 0.50 (001) Comparative Example 1 10 K Zn Ti 0.5 0.5 0.10 0.90 0.00 10 0.10 0.90 0.00 (001) Comparative Example 2 20 K Ti none 0.5 0 0.10 0.00 0.90 10 0.10 0.05 0.85 (001) Comparative Example 3 20 K Ti none 0.5 0 1.00 0.00 0.00 10 0.95 0.05 0.00 (001)

[0206] [Table 2]

[0207] Table 2 Pr <![CDATA[ε r ]]> <![CDATA[-e 31,f ]]> <![CDATA[(-e 31,f ) 2 / e 0 e r ]]> <![CDATA[I 2 / (I 1 +I 2 )]]> c2 / a2 c1 / a1 Ta Tb Tp unit <![CDATA[μC / cm 2 ]]> - <![CDATA[C / m 2 ]]> GPa - - - nm nm nm Example 1 91 97 8.1 76.4 0.93 1.235 1.048 150 2850 3000 Example 2 96 88 7.5 72.2 0.92 1.193 1.032 220 2000 2220 Example 3 105 78 7.1 73.0 0.91 1.122 1.015 300 3500 3800 Example 4 85 99 7.9 71.2 0.97 1.062 1.031 120 4800 4920 Example 5 95 84 7.5 75.6 0.95 1.051 1.024 190 1500 1690 Example 6 90 87 7.5 73.0 0.99 1.058 1.019 80 500 580 Comparative Example 1 120 95 1.8 3.9 0.95 1.191 1.052 - - 2700 Comparative Example 2 20 300 1.9 1.4 0.89 1.059 1.055 90 2100 2190 Comparative Example 3 40 150 2.2 3.6 - 1.037 1.037 50 2000 2050

[0208] (Comparative Example 4)

[0209] As shown in Table 3 below, the composition of the first target material of Comparative Example 4 is the same as that of the first target material of Example 1, and the composition of the second target material of Comparative Example 4 is the same as that of the second target material of Example 1.

[0210] The oxygen partial pressure in the vacuum chamber in the first film forming step and the second film forming step of Comparative Example 4 was maintained at 0.01 Pa.

[0211] The thickness Ta of the first piezoelectric layer of Comparative Example 4 was adjusted to the value shown in Table 4 below. The thickness Tb of the second piezoelectric layer of Comparative Example 4 was adjusted to the value shown in Table 4 below. The thickness Tp of the piezoelectric film of Comparative Example 4 was the value shown in Table 4 below.

[0212] A piezoelectric thin-film element of Comparative Example 4 was produced by the same method as in Example 1 except for the above-mentioned matters.

[0213] The XRD pattern of the first electrode layer of Comparative Example 4 was measured by the same method as in Example 1. In the case of Comparative Example 4, the (002) plane of the Pt crystal constituting the first electrode layer was oriented in the normal direction of the surface of the first electrode layer, and the (200) plane of the Pt crystal was oriented in the in-plane direction of the surface of the first electrode layer.

[0214] The composition of the piezoelectric film of Comparative Example 4 was analyzed by the same method as in Example 1. In the case of Comparative Example 4, the composition of the piezoelectric film was different from the compositions of the first target and the second target in terms of the oxygen content.

[0215] The piezoelectric film of Comparative Example 4 was analyzed using an X-ray diffraction apparatus and STEM in the same manner as in Example 1. The piezoelectric film of Comparative Example 4 had no crystallinity or crystal orientation, and therefore, the c1 / a1, c2 / a2, and I of Comparative Example 3 could not be determined. 2 / (I 1 +I 2 ).

[0216] By the same method as in Example 1, the piezoelectric property of the piezoelectric film of Comparative Example 4 was evaluated.

[0217] The Pr of Comparative Example 4 is shown in Table 4 below.

[0218] ε of Comparative Example 4 r This is shown in Table 4 below.

[0219] -e of Comparative Example 4 31,f This is shown in Table 4 below.

[0220] Comparative Example 4 (-e 31,f ) 2 / ε 0 ε r This is shown in Table 4 below.

[0221] [Table 3]

[0222] Table 3 f1 <![CDATA[E A ]]> <![CDATA[E B1 ]]> <![CDATA[E B2 ]]> α β x1 y1 z1 f2 x2 y2 z2 Orientation plane unit Hz - - - - - - - - Hz - - - - Example 1 20 K Ti none 0.5 0 0.15 0.80 0.05 10 0.10 0.85 0.05 (001) Comparative Example 4 20 K Ti none 0.5 0 0.15 0.80 0.05 10 0.10 0.85 0.05 none

[0223] [Table 4]

[0224] Table 4 Pr <![CDATA[ε r ]]> <![CDATA[-e 31,f ]]> <![CDATA[(-e 31,f ) 2 / e 0 e r ]]> <![CDATA[I 2 / (I 1 +I 2 )]]> c2 / a2 c1 / a1 Ta Tb Tp unit <![CDATA[μC / cm 2 ]]> - <![CDATA[C / m 2 ]]> GPa - - - nm nm nm Example 1 91 97 8.1 76.4 0.93 1.235 1.048 150 2850 3000 Comparative Example 4 36 358 1.0 0.3 - - - 30 2500 2530

[0225] (Examples 7 and 8)

[0226] As shown in Table 5 below, the composition of the first target material of each of Examples 7 and 8 is the same as that of the first target material of Example 1, and the composition of the second target material of each of Examples 7 and 8 is the same as that of the second target material of Example 1.

[0227] In the case of Examples 7 and 8, the second intermediate layer is formed on the entire surface of the first electrode layer, and the first piezoelectric layer is formed on the entire surface of the second intermediate layer.

[0228] The second intermediate layer of Example 7 is composed of crystalline SrRuO 3 The thickness of the second intermediate layer in Example 7 is 50 nm. "SRO" in the following Table 5 refers to SrRuO 3 .

[0229] The second intermediate layer of Example 8 is made of crystalline LaNiO 3 The thickness of the second intermediate layer in Example 8 is 50 nm. "LNO" in the following Table 5 refers to LaNiO 3 .

[0230] The thickness Ta of the first piezoelectric layer of Examples 7 and 8 was adjusted to the values ​​shown in Table 6. The thickness Tb of the second piezoelectric layer of Examples 7 and 8 was adjusted to the values ​​shown in Table 6. The thickness Tp of the piezoelectric film of Examples 7 and 8 was the values ​​shown in Table 6.

[0231] Piezoelectric thin-film elements of Examples 7 and 8 were produced in the same manner as in Example 1 except for the above-mentioned matters.

[0232] The XRD patterns of the first electrode layers of Examples 7 and 8 were measured in the same manner as in Example 1. In any of Examples 7 and 8, the (002) plane of the Pt crystal constituting the first electrode layer was also oriented in the normal direction of the surface of the first electrode layer, and the (200) plane of the Pt crystal was oriented in the in-plane direction of the surface of the first electrode layer.

[0233] The composition of the piezoelectric thin films of Examples 7 and 8 was analyzed in the same manner as in Example 1. In either of Examples 7 and 8, the composition of the first piezoelectric layer was consistent with the composition of the first target, and the composition of the second piezoelectric layer was consistent with the composition of the second target.

[0234] The piezoelectric thin films of Examples 7 and 8 were analyzed using an X-ray diffraction apparatus and STEM in the same manner as in Example 1. The piezoelectric thin films of Examples 7 and 8 had the following characteristics.

[0235] The first piezoelectric layer is composed of tetragonal perovskite crystals 1 .

[0236] The second piezoelectric layer is composed of tetragonal perovskite crystals 2 .

[0237] The (001) plane of the tetragonal crystal 1 is preferentially oriented in the normal direction of the surface of the piezoelectric thin film.

[0238] The (001) planes of the tetragonal crystals 2 are preferentially oriented in the normal direction of the surface of the piezoelectric thin film.

[0239] The c1 / a1 of the tetragonal crystal 1 of each of Examples 7 and 8 is the value shown in Table 6 below.

[0240] The c2 / a2 of the tetragonal crystal 2 of each of Examples 7 and 8 is the value shown in Table 6 below.

[0241] I of each of Examples 7 and 82 / (I 1 +I 2 ) are the values ​​shown in Table 6 below.

[0242] By the same method as in Example 1, the piezoelectric properties of the piezoelectric films of Examples 7 and 8 were evaluated.

[0243] The Pr of each of Examples 7 and 8 is shown in Table 6 below.

[0244] ε of Examples 7 and 8 r This is shown in Table 6 below.

[0245] -e of each of Examples 7 and 8 31,f This is shown in Table 6 below.

[0246] Examples 7 and 8, respectively (-e 31,f ) 2 / ε 0 ε r This is shown in Table 6 below.

[0247] [Table 5]

[0248]

[0249] [Table 6]

[0250] Table 6 Pr <![CDATA[ε r ]]> <![CDATA[-e 31,f ]]> <![CDATA[(-e 31,f ) 2 / e 0 e r ]]> <![CDATA[I 2 / (I 1 +I 2 )]]> c2 / a2 c1 / a1 Ta Tb Tp unit <![CDATA[μC / cm 2 ]]> - <![CDATA[C / m 2 ]]> GPa - - - nm nm nm Example 1 91 97 8.1 76.4 0.93 1.235 1.048 150 2850 3000 Example 7 95 99 8.3 78.6 0.95 1.210 1.042 170 2830 3000 Example 8 110 95 7.8 72.3 0.95 1.249 1.050 120 2880 3000

[0251] (Example 9)

[0252] As shown in Table 7 below, the composition of the first target material of Example 9 is the same as that of the first target material of Example 1, and the composition of the second target material of Example 9 is the same as that of the second target material of Example 1.

[0253] In the process of manufacturing the piezoelectric thin film element of Example 9, the first intermediate layer is not formed. In the process of manufacturing the piezoelectric thin film element of Example 9, the crystalline SrRuO 3 The first electrode layer of Example 9 is directly formed on the entire surface of the single crystal substrate. The thickness of the first electrode layer of Example 9 is 200 nm.

[0254] The thickness Ta of the first piezoelectric layer of Example 9 was adjusted to the value shown in Table 8 below. The thickness Tb of the second piezoelectric layer of Example 9 was adjusted to the value shown in Table 8 below. The thickness Tp of the piezoelectric film of Example 9 was the value shown in Table 8 below.

[0255] A piezoelectric thin film element of Example 9 was produced by the same method as Example 1 except for the above matters.

[0256] The XRD pattern of the first electrode layer of Example 9 was measured by the same method as in Example 1. The in-plane orientation of the crystals of the first electrode layer of Example 9 was evaluated by the same In-Plane measurement as in Example 1. In the case of Example 9, the crystal plane of the first electrode layer was not oriented in the in-plane direction of the surface of the first electrode layer. That is, in the case of Example 9, there was no in-plane orientation of the crystals of the first electrode layer.

[0257] The composition of the piezoelectric film of Example 9 was analyzed by the same method as Example 1. In Example 9, the composition of the first piezoelectric layer was consistent with the composition of the first target material, and the composition of the second piezoelectric layer was consistent with the composition of the second target material.

[0258] The piezoelectric film of Example 9 was analyzed using an X-ray diffraction apparatus and STEM in the same manner as in Example 1. The piezoelectric film of Example 9 has the following characteristics.

[0259] The first piezoelectric layer is composed of tetragonal perovskite crystals 1 .

[0260] The second piezoelectric layer is composed of tetragonal perovskite crystals 2 .

[0261] The (001) plane of the tetragonal crystal 1 is preferentially oriented in the normal direction of the surface of the piezoelectric thin film.

[0262] The (001) planes of the tetragonal crystals 2 are preferentially oriented in the normal direction of the surface of the piezoelectric thin film.

[0263] The c1 / a1 of the tetragonal crystal 1 of Example 9 is the value shown in Table 8 below.

[0264] The c2 / a2 of the tetragonal crystal 2 of Example 9 is the value shown in Table 8 below.

[0265] Example 9 I 2 / (I 1 +I 2 ) are the values ​​shown in Table 8 below.

[0266] By the same method as in Example 1, the piezoelectric property of the piezoelectric film of Example 9 was evaluated.

[0267] The Pr of Example 9 is shown in Table 8 below.

[0268] Example 9 r This is shown in Table 8 below.

[0269] Example 9-e 31,f This is shown in Table 8 below.

[0270] Example 9 (-e 31,f ) 2 / ε0 ε r This is shown in Table 8 below.

[0271] [Table 7]

[0272]

[0273] [Table 8]

[0274] Table 8 Pr <![CDATA[ε r ]]> <![CDATA[-e 31,f ]]> <![CDATA[(-e 31,f ) 2 / e 0 e r ]]> <![CDATA[I 2 / (I 1 +I 2 )]]> c2 / a2 c1 / a1 Ta Tb Tp unit <![CDATA[μC / cm 2 ]]> - <![CDATA[C / m 2 ]]> GPa - - - nm nm nm Example 1 91 97 8.1 76.4 0.93 1.235 1.048 150 2850 3000 Example 9 85 117 7.5 54.3 0.95 1.155 1.023 110 2890 3000

[0275] Industrial Applicability

[0276] The piezoelectric film according to one aspect of the present invention is applied to, for example, a piezoelectric transducer, a piezoelectric actuator, and a piezoelectric sensor.

[0277] Explanation of symbols

[0278] 10 ... piezoelectric thin film element, 10a ... ultrasonic transducer, 1 ... single crystal substrate, 2 ... first electrode layer, 3 ... piezoelectric thin film, 3A ... first piezoelectric layer, 3B ... second piezoelectric layer, 4 ... second electrode layer, 5 ... first intermediate layer, 6 ... second intermediate layer, D N ...the normal direction of the surface of the single crystal substrate, dn ...the normal direction of the surface of the piezoelectric film, uc ...the unit cell of the perovskite structure, uc1 ...the unit cell of tetragonal crystal 1, uc2 ...the unit cell of tetragonal crystal 2.

Claims

1. A piezoelectric film, in, A piezoelectric film having a first piezoelectric layer and a second piezoelectric layer directly overlapping the first piezoelectric layer. The first piezoelectric layer comprises tetragonal crystals 1 of a perovskite-type oxide, The second piezoelectric layer comprises tetragonal crystals 2 of a perovskite-type oxide, The (001) plane of the tetragonal crystal 1 is oriented in the normal direction of the surface of the piezoelectric film. The (001) plane of the tetragonal crystal 2 is oriented in the normal direction of the surface of the piezoelectric film. The spacing of the (001) planes of the tetragonal crystal 1 is c1, The interval of the (100) planes of the tetragonal crystal 1 is a1, The spacing of the (001) planes of the tetragonal crystal 2 is c2, The interval between the (100) planes of the tetragonal crystal 2 is a2, c2 / a2 is greater than c1 / a1, c1 / a1 is 1.015 or more and 1.050 or less, The tetragonal crystal 1 is represented by the following chemical formula 1: In the following chemical formula 1, E A is at least one element selected from Na, K and Ag, In the following chemical formula 1, E B 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 more and 0.90 or less, In the following chemical formula 1, y1 is 0.05 or more and 0.85 or less, In the following chemical formula 1, z1 is 0.05 or more and 0.85 or less, x1+y1+z1 is 1.00, In the following chemical formula 1, α is greater than or equal to 0.00 and less than 1.00, The tetragonal crystal 2 is represented by the following chemical formula 2: In the following chemical formula 2, E A is at least one element selected from Na, K and Ag, In the following chemical formula 2, E B 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 or equal to 0.10 and less than or equal to 0.85, and in the following chemical formula 2, z2 is greater than or equal to 0.05 and less than or equal to 0.

80. x2+y2+z2 is 1.00, In the following chemical formula 2, α is greater than or equal to 0.00 and less than 1.00, x1(Bi 1-α E A α )E B O 3 -y1BiFeO 3 -z1Bi(Fe 0.5 Ti 0.5 ) 3 (1) x2(Bi 1-α E A α )E B O 3 -y2BiFeO 3 -z2Bi(Fe 0.5 Ti 0.5 ) 3 (2).

2. The piezoelectric film according to claim 1, in, c2 / a2 is greater than or equal to 1.051 and less than or equal to 1.

250.

3. The piezoelectric film according to claim 1 or 2, in, The peak intensity of the diffraction X-ray of the (001) plane of the tetragonal crystal 1 is I 1 The peak intensity of the diffraction X-ray of the (001) plane of the tetragonal crystal 2 is I 2 , I 2 / (I 1 +I 2 ) is greater than 0.90 and less than 1.

00.

4. The piezoelectric film according to claim 1 or 2, in, The thickness of the first piezoelectric layer is greater than or equal to 10 nm and less than or equal to 300 nm.

5. A piezoelectric thin film element, in, A piezoelectric film according to claim 1 or 2.

6. The piezoelectric thin film element according to claim 5, in, have: Single crystal substrate; an electrode layer overlapping the single crystal substrate; and The piezoelectric film overlaps the electrode layer, The first intermediate layer is arranged between the single crystal substrate and the electrode layer, The first intermediate layer comprises ZrO 2 and Y 2 O 3 .

7. The piezoelectric thin film element according to claim 5, in, have: an electrode layer; and The piezoelectric film overlaps the electrode layer, The second intermediate layer is arranged between the electrode layer and the piezoelectric film, The second intermediate layer comprises SrRuO 3 and LaNiO 3 At least one of .

8. The piezoelectric thin film element according to claim 5, in, have: an electrode layer; and The piezoelectric film overlaps the electrode layer, The electrode layer includes platinum crystals, The (002) plane of the platinum crystal is oriented in the normal direction of the surface of the electrode layer, and the (200) plane of the platinum crystal is oriented in the in-plane direction of the surface of the electrode layer.

9. A piezoelectric transducer, in, A piezoelectric thin film element according to claim 5 is provided.

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