JP2021158206A - Piezoelectric thin film, piezoelectric thin film element, and piezoelectric transducer - Google Patents

Abstract

To provide a piezoelectric thin film having a large piezoelectric performance index.SOLUTION: A piezoelectric thin film 3 contains an oxide having a perovskite structure. The piezoelectric thin film 3 contains a tetragon 1 of the oxide and a tetragon 2 of the oxide. A (001) face of the tetragon 1 is directed to a normal direction dn of a front face of the piezoelectric thin film 3. The (001) face of the tetragon 2 is directed in the normal direction dn of the front face of the piezoelectric thin film 3. An interval of the (001) face of the tetragon 1 is c1, and the interval of a (100) face of the tetragon 1 is a1. The interval of the (001) face of the tetragon 2 is c2, and the interval of the (100) face of the tetragon 2 is a2. The c2/a2 is larger than the c1/a1, a peak intensity of a diffraction X-ray of the (001) face of the tetragon 1 is I1. The peak intensity of the diffraction X-ray of the (001) face of the tetragon 2 is I2. The I2/(I1+I2) is 0.50 or more and 0.90 or less.SELECTED DRAWING: Figure 3

Description

The present invention relates to piezoelectric thin films, piezoelectric thin film devices and piezoelectric transducers.

Piezoelectric bodies are processed into various piezoelectric elements for various purposes. For example, a piezoelectric actuator converts a voltage into a force by an inverse piezoelectric effect that applies a voltage to the piezoelectric body to deform the piezoelectric body. In addition, the piezoelectric sensor converts force into voltage by the piezoelectric effect of applying pressure to the piezoelectric body to deform the piezoelectric body. These piezoelectric elements are mounted on various electronic devices.

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

Conventionally, lead zirconate titanate (so-called PZT), which is a perovskite-type ferroelectric substance, has been widely used as a piezoelectric material. However, since PZT contains lead that is harmful to the human body and the environment, the development of lead-free (Lead-free) piezoelectric material is expected as an alternative to PZT. For example, Non-Patent Document 1 describes _{BiFeO 3} as an example of a lead-free piezoelectric material. BiFeO ₃ has relatively excellent piezoelectricity among lead-free piezoelectric materials, and is particularly expected to be applied to piezoelectric thin film devices.

K. Ujimoto et al, Direct piezoelectric properties of (100) and (111) BiFeO3 applied thin films, APPLIED PHYSICS LETTERS. 100, 102901 (2012)

( _{−E 31, f} ) ² / ε ₀ ε _r is a piezoelectric figure of merit indicating the piezoelectricity of the piezoelectric thin film. -E _{31, f} is a kind of piezoelectric constant, and _{the unit of -e 31, f} is C / m ² . ε ₀ is the permittivity of vacuum, and _{the unit of ε 0} is F / m. ε _r is the relative permittivity of the piezoelectric thin film, and there is no unit of _{ε r.} The unit of (-e _{31, f} ) ² / ε ₀ ε _r is Pa. A piezoelectric thin film having a large piezoelectric figure of merit is suitable for a piezoelectric thin film element such as a piezoelectric transducer.

An object of the present invention is to provide a piezoelectric thin film having a large piezoelectric figure of merit, a piezoelectric thin film element including the piezoelectric thin film, and a piezoelectric transducer.

The piezoelectric thin film according to one aspect of the present invention is a piezoelectric thin film containing an oxide having a perobskite structure, and the piezoelectric thin film contains a tetragonal crystal 1 of the above oxide and a tetragonal crystal 2 of the above oxide, and is a tetragonal crystal 1. The (001) plane of the tetragonal crystal 2 is oriented in the normal direction of the surface of the piezoelectric thin film, and the (001) plane of the tetragonal crystal 2 is oriented in the normal direction of the surface of the tetragonal crystal 1. The distance between the (001) planes is c1, the distance between the (100) planes of the tetragonal crystal 1 is a1, the distance between the (001) planes of the tetragonal crystal 2 is c2, and the distance between the (001) planes of the tetragonal crystal 2 is c2. spacing surfaces are a2, c2 / a2 is greater than c1 / a1, the peak intensity of the diffracted X-ray tetragonal 1 (001) plane is _{I 1,} tetragonal 2 (001) The peak intensity of the diffracted X-rays on the surface is I ₂ , and I ₂ / (I ₁ + I ₂ ) is 0.50 or more and 0.90 or less.

c2-c1 may be greater than 0.100 Å and less than 0.490 Å.

c1 / a1 may be 1.030 or more and 1.145 or less, and c2 / a2 may be 1.085 or more and 1.195 or less.

The oxide may be represented by the following Chemical Formula 1, the E ^A in Formula 1 below, Na, it may be at least one element selected from the group consisting of K and Ag, E ^B in Formula 1 May be at least one element selected from the group consisting of Mg, Al, Ti, Ni and Zn, and x in the following chemical formula 1 may be 0.30 or more and 0.80 or less, and the following chemical formula 1 Α in the inside may be 0.00 or more and less than 1.00.
_{(1-x) Bi 1-} α E A α E B O 3 -xBiFeO 3 (1)

The piezoelectric thin film according to one aspect of the present invention may be an epitaxial film.

The piezoelectric thin film device according to one aspect of the present invention includes the above-mentioned piezoelectric thin film.

The piezoelectric thin film element according to one aspect of the present invention may include a single crystal substrate and the piezoelectric thin film that overlaps the single crystal substrate.

The piezoelectric thin film element according to one aspect of the present invention may include a single crystal substrate, an electrode layer overlapping the single crystal substrate, and the piezoelectric thin film overlapping the electrode layer.

The piezoelectric thin film element according to one aspect of the present invention may include an electrode layer and the piezoelectric thin film that overlaps the electrode layer.

The piezoelectric thin film device according to one aspect of the present invention may further include a first intermediate layer, and the first intermediate layer may be arranged between the single crystal substrate and the electrode layer.

The first intermediate layer may contain _{ZrO 2} and Y ₂ O _3.

The piezoelectric thin film device according to one aspect of the present invention may further include a second intermediate layer, and the second intermediate layer may be arranged between the electrode layer and the piezoelectric thin film.

The second intermediate layer may contain at least one of _{SrRuO 3} and LaNiO _3.

The electrode layer may contain a platinum crystal, the (002) plane of the platinum crystal may be oriented in the normal direction of the surface of the electrode layer, and the (200) plane of the platinum crystal may be the electrode layer. It may be oriented in the in-plane direction of the surface.

The piezoelectric transducer according to one aspect of the present invention includes the above-mentioned piezoelectric thin film.

The piezoelectric transducer according to one aspect of the present invention includes the above-mentioned piezoelectric thin film element.

According to the present invention, a piezoelectric thin film having a large piezoelectric figure of merit, a piezoelectric thin film element including the piezoelectric thin film, and a piezoelectric transducer are provided.

FIG. 1A is a schematic cross-sectional view of a piezoelectric thin film element according to an embodiment of the present invention, and FIG. 1B is a piezoelectric thin film element shown in FIG. 1A. It is a perspective exploded view of. FIG. 2 is a perspective view of a unit cell having a perovskite structure. FIG. 3 is a schematic perspective view of the unit cells of tetragonal crystal 1 and tetragonal crystal 2. FIG. 4 is a schematic cross-sectional view of a piezoelectric thin film element (ultrasonic transducer) according to another embodiment of the present invention.

Hereinafter, the details of one preferred embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments. In the drawings, the same or equivalent elements are labeled with the same reference numerals. (A) in FIG. 1, (b) in FIG. 1, and the X-axis, Y-axis, and Z-axis shown in FIG. 4 are three coordinate axes orthogonal to each other. The directions of the three coordinate axes are common to (a) in FIG. 1, (b) in FIG. 1, and FIG.

(Piezoelectric thin film and piezoelectric thin film element)
The piezoelectric thin film device according to the present embodiment includes a piezoelectric thin film. FIG. 1A shows a cross section of the piezoelectric thin film element 10 according to the present embodiment. 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 includes a single crystal substrate 1, a first electrode layer 2 (lower electrode layer) that overlaps the single crystal substrate 1, a piezoelectric thin film 3 that overlaps the first electrode layer 2, and a second electrode that overlaps the piezoelectric thin film 3. A layer 4 (upper electrode layer) may be provided. 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 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 shown in (b) in FIG. 1, the normal direction dn of the surface of the piezoelectric thin film 3 may be substantially parallel to the normal direction D _N of the single-crystal substrate 1 of the surface. In FIG. 1B, the first electrode layer, the first intermediate layer, the second intermediate layer, and the second electrode layer are omitted.

The modified example of the piezoelectric thin film element 10 does not have to include the single crystal substrate 1. For example, the single crystal substrate 1 may be removed after the formation of the first electrode layer 2 and the piezoelectric thin film 3. The modified example of the piezoelectric thin film element 10 does not have to include the second electrode layer 4. For example, after the piezoelectric thin film element without the second electrode layer is supplied as a product to the manufacturer of the electronic device, the second electrode layer may be added to the piezoelectric thin film element in the manufacturing process of the electronic device. When the single crystal substrate 1 functions as an electrode, the modified example of the piezoelectric thin film element 10 does not have to include the first electrode layer 2. That is, a modification of the piezoelectric thin film element 10 may include a single crystal substrate 1 and a piezoelectric thin film 3 that overlaps the single crystal substrate 1. In the absence of the first electrode layer 2, the piezoelectric thin film 3 may directly overlap the single crystal substrate 1. In the absence of the first electrode layer 2, the piezoelectric thin film 3 may overlap the single crystal substrate 1 via at least one intermediate layer of the first intermediate layer 5 and the second intermediate layer 6.

The piezoelectric thin film 3 contains an oxide having a perovskite structure. That is, at least a part of the oxide contained in the piezoelectric thin film 3 is a crystal having a perovskite structure. All oxides contained in the piezoelectric thin film 3 may be crystals having a perovskite structure. In some cases, oxides having a perovskite structure are referred to as "perovskite-type oxides". The perovskite-type oxide is the main component of the piezoelectric thin film 3. The ratio of the perovskite-type oxide to the entire piezoelectric thin film 3 may be 99% mol or more and 100 mol% or less. The piezoelectric thin film 3 may be composed of only a perovskite type oxide.

FIG. 2 shows a unit cell uc of a perovskite-type oxide. Element positioned at the A site of the unit cell uc may be a Bi or ^{E A.} Element positioned at unit cell uc B site can be a Fe or ^{E B.} Specific examples of each of the element E ^A and the element E ^{B will be described later.} Each of a, b and c in FIG. 2 is a basic vector of the perovskite structure. a, b and c are perpendicular to each other. The orientation of the vector a is [100]. The orientation of the vector b is [010]. The orientation of the vector c is [001]. The length a of the vector a is the spacing between the (100) planes of the perovskite oxide. In other words, the length a of the vector a is the lattice constant of the perovskite-type oxide in the [100] direction. The length b of the vector b is the spacing between the (010) planes of the perovskite oxide. In other words, the length b of the vector b is the lattice constant of the perovskite oxide in the [010] direction. The length c of the vector c is the spacing between the (001) planes of the perovskite oxide. In other words, the length c of the vector c is the lattice constant of the perovskite-type oxide in the [001] direction.

The piezoelectric thin film 3 contains a tetragonal crystal 1 of a perovskite-type oxide and a tetragonal crystal 2 of a perovskite-type oxide. FIG. 3 shows the unit cell uc1 of tetragonal crystal 1 and the unit cell uc2 of tetragonal crystal 2. For convenience in illustration, E ^B and O in the unit cell uc1 and unit cell uc2 (oxygen) is omitted, the unit cell uc1 and unit cell uc2其s, the same perovskite structure and unit cell uc in Fig have.

Each of a1, b1 and c1 in FIG. 3 is a basic vector of tetragonal crystal 1. The vector a1 in FIG. 3 corresponds to the vector a in FIG. The vector b1 in FIG. 3 corresponds to the vector b in FIG. The vector c1 in FIG. 3 corresponds to the vector c in FIG. a1, b1 and c1 are perpendicular to each other. The orientation of the vector a1 is [100]. The orientation of the vector b1 is [010]. The orientation of the vector c1 is [001]. The length a1 of the vector a1 is the distance between the (100) planes of the tetragonal crystal 1. In other words, the length a1 of the vector a1 is the lattice constant of the tetragonal crystal 1 in the [100] direction. The length b1 of the vector b1 is the distance between the (010) planes of the tetragonal crystal 1. In other words, the length b1 of the vector b1 is the lattice constant of the tetragonal crystal 1 in the [010] direction. The length c1 of the vector c1 is the distance between the (001) planes of the tetragonal crystal 1. In other words, the length c1 of the vector c1 is the lattice constant of the tetragonal crystal 1 in the [001] direction. a1 is equal to b1. c1 is larger than a1.

Each of a2, b2 and c2 in FIG. 3 is a basic vector of tetragonal crystal 2. The vector a2 in FIG. 3 corresponds to the vector a in FIG. The vector b2 in FIG. 3 corresponds to the vector b in FIG. The vector c2 in FIG. 3 corresponds to the vector c in FIG. a2, b2 and c2 are perpendicular to each other. The orientation of the vector a2 is [100]. The orientation of the vector b2 is [010]. The orientation of the vector c2 is [001]. The length a2 of the vector a2 is the distance between the (100) planes of the tetragonal crystal 2. In other words, the length a2 of the vector a2 is the lattice constant of the tetragonal crystal 2 in the [100] direction. The length b2 of the vector b2 is the distance between the (010) planes of the tetragonal crystal 2. In other words, the length b2 of the vector b2 is the lattice constant of the tetragonal crystal 2 in the [010] direction. The length c2 of the vector c2 is the distance between the (001) planes of the tetragonal crystal 2. In other words, the length c2 of the vector c2 is the lattice constant of the tetragonal crystal 2 in the [001] direction. a2 is equal to b2. c2 is larger than a2.

As shown in (b) and FIG. 3 in FIG. 1, the (001) plane of the tetragonal crystal 1 (uc1) is oriented in the normal direction dn of the surface of the piezoelectric thin film 3. The (001) plane of the tetragonal crystal 2 (uc2) is also oriented in the normal direction dn of the surface of the piezoelectric thin film 3. For example, the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2 may be substantially parallel to the surface of the piezoelectric thin film 3, and the directions of the tetragonal crystal 1 and the tetragonal crystal 2 [001] are respectively. , The surface of the piezoelectric thin film 3 may be substantially parallel to the normal direction dn. Direction normal to the surface of the piezoelectric thin film 3 dn may be the normal direction D _N substantially parallel single-crystal substrate 1 of the surface. Therefore, tetragonal 1 (001) plane may be oriented in the normal direction D _N of the single-crystal substrate 1 of the surface. Also tetragonal 2 (001) plane, may be oriented in the normal direction D _N of the single-crystal substrate 1 of the surface. In other words, the (001) plane of tetragonal crystal 1 and the (001) plane of tetragonal crystal 2 may be substantially parallel to the surface of the single crystal substrate 1, and tetragonal crystal 1 and tetragonal crystal 2 respectively [001]. ] direction may be substantially parallel to the normal direction D _N of the single-crystal substrate 1 of the surface.

Perovskite-type oxides are easily polarized in the [001] direction. That is, [001] is an orientation in which the perovskite-type oxide is more easily polarized than other crystal orientations. Therefore, the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2 are oriented in the normal direction dn of the surface of the piezoelectric thin film 3, so that the piezoelectric thin film 3 has excellent piezoelectricity. Can be done. For the same reason, the piezoelectric thin film 3 may be a ferroelectric material. The crystal orientation described below means that the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2 are respectively oriented in the normal direction dn of the surface of the piezoelectric thin film 3. ..

Since the piezoelectric thin film 3 has the above-mentioned crystal orientation, the piezoelectric thin film 3 can have a large (-e _{31, f} ) ² / ε ₀ ε _r (piezoelectric performance index). The above crystal orientation is a characteristic unique to thin films. The thin film is a crystalline film formed by a vapor phase growth method or a solution method. On the other hand, it is difficult for the bulk of the piezoelectric body having the same composition as the piezoelectric thin film 3 to have the above-mentioned crystal orientation. This is because the bulk of the piezoelectric body is a powder sintered body (ceramics) containing the essential elements of the piezoelectric body, and it is difficult to control the structure and orientation of a large number of crystals constituting the sintered body. Due to the fact that the bulk of the piezoelectric body contains Fe, the specific resistivity of the bulk of the piezoelectric body is lower than that of the piezoelectric thin film 3. As a result, leakage current is likely to occur in the bulk of the piezoelectric material. Therefore, it is difficult to polarize the bulk of the piezoelectric body by applying a high electric field, and it is difficult for the bulk of the piezoelectric body to have a large piezoelectric figure of merit.

c2 / a2 is larger than c1 / a1. That is, the anisotropy of tetragonal crystal 2 is higher than the anisotropy of tetragonal crystal 1.

Since c2 / a2 is larger than c1 / a1, the tetragonal crystal 2 is superior to the tetragonal crystal 1 in ferroelectricity. However, since c2 / a2 is larger than c1 / a1, the crystal structure of tetragonal crystal 2 is stronger than the crystal structure of tetragonal crystal 1. That is, the atoms in the tetragonal crystal 2 are harder to move than the atoms in the tetragonal crystal 1. Therefore, the polarization reversal of the tetragonal crystal 2 is less likely to occur than the polarization reversal of the tetragonal crystal 1. On the other hand, since c1 / a1 is smaller than c2 / a2, the tetragonal crystal 1 is inferior in ferroelectricity to the tetragonal crystal 2. However, since c1 / a1 is smaller than c2 / a2, the crystal structure of tetragonal crystal 1 is softer than that of tetragonal crystal 2. That is, the atoms in the tetragonal crystal 1 are easier to move than the atoms in the tetragonal crystal 2. Therefore, the polarization reversal of the tetragonal crystal 1 is more likely to occur than the polarization reversal of the tetragonal crystal 2. As described above, when the square crystal 2 having excellent ferroelectricity and the square crystal 1 whose polarization is easily reversed coexist in the piezoelectric thin film 3, −e _{31, f} of the piezoelectric thin film 3 increases, and the piezoelectric thin film 3 increases. The (-e _{31, f} ) ² / ε ₀ ε _r (piezoelectric performance index) of the thin film 3 increases.

In contrast to the piezoelectric thin film 3, the bulk of the piezoelectric material is less likely to cause distortion of the crystal structure due to stress. Therefore, the majority of perovskite-type oxides constituting the bulk of the piezoelectric material are cubic crystals, and it is difficult for the bulk of the piezoelectric body to have piezoelectricity due to the tetragonal crystals of the perovskite-type oxide.

c2-c1 may be larger than 0.100 Å and 0.490 Å or less, preferably 0.101 Å or more and 0.419 Å or less. When c2-c1 is within the above range, the piezoelectric figure of merit of the piezoelectric thin film 3 tends to increase due to the coexistence of tetragonal crystals 1 and tetragonal crystals 2. When c2-c1 is 0.100 Å or less, it is not easy to distinguish between tetragonal crystal 1 and tetragonal crystal 2 due to the resolution of the X-ray diffraction measuring device.

c1 / a1 may be 1.010 or more and 1.145 or less. c2 / a2 may be 1.085 or more and 1.200 or less. When c1 / a1 is within the above range and c2 / a2 is within the above range, the tetragonal crystal 2 tends to have better ferroelectricity than the tetragonal crystal 1, and the polarization reversal of the tetragonal crystal 1 is It is more likely to occur than the polarization reversal of tetragonal crystal 2. In other words, when c1 / a1 is within the above range and c2 / a2 is within the above range, the piezoelectric figure of merit of the piezoelectric thin film 3 increases due to the coexistence of tetragonal crystals 1 and tetragonal crystals 2. Easy to do. For the same reason, c1 / a1 may be 1.030 or more and 1.145 or less, and c2 / a2 may be 1.085 or more and 1.195 or less. For the same reason, c1 / a1 may be 1.034 or more and 1.143 or less, and c2 / a2 may be 1.085 or more and 1.194 or less.

As long as c2-c1 is larger than 0.100 Å and c2 / a2 is larger than c1 / a1, the values of a1, c1, a2 and c2 are not limited. a1 may be, for example, 3.800 Å or more and 3.950 Å or less. c1 may be, for example, 4.052 Å or more and 4.342 Å or less. a2 may be, for example, 3.760 Å or more and 3.930 Å or less. c2 may be, for example, 4.177 Å or more and 4.490 Å or less.

I ₂ / (I ₁ + I ₂ ) is 0.50 or more and 0.90 or less. I ₁ is the peak intensity of the diffracted X-rays on the (001) plane of the tetragonal crystal 1. That is, it is the maximum value of the diffracted X-rays on the (001) plane of the tetragonal crystal 1. I ₂ is the peak intensity of the diffracted X-rays on the (001) plane of the tetragonal crystal 2. That is, I ₂ is the maximum value of the diffracted X-rays on the (001) plane of the tetragonal crystal 2. The units of I ₁ and I ₂ may be, for example, cps (cоunts per secоnd). As I ₁ and I ₂其people increases of at least 3 orders of magnitude or more relative to the background intensity, I ₁ and I ₂其set of conditions may be set. That is, bag round correction may be performed in each of the measurements of _{I 1} and I _2.

I ₁ may be proportional to the total area of the (001) plane of the tetragonal crystal 1 oriented in _{the normal direction dn of the surface of the piezoelectric thin film 3, and I 2} is the normal direction dn of the surface of the piezoelectric thin film 3. It may be proportional to the total area of the (001) plane of the tetragonal crystal 2 oriented in. In other words, I ₁ may be proportional to the amount of tetragonal crystals 1 contained in the piezoelectric thin film 3, and I ₂ may be proportional to the amount of tetragonal crystals 2 contained in the piezoelectric thin 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 the tetragonal crystal 2 to the total amount of the tetragonal crystal 1 and the tetragonal crystal 2 may be 50% or more and 90% or less.

The above effect (large piezoelectric figure of merit) due to the coexistence of tetragonal crystal 1 and tetragonal crystal 2 _{is obtained within the range where I 2} / (I ₁ + I ₂ ) is 0.50 or more and 0.90 or less. When I ₂ / (I ₁ + I ₂ ) is less than 0.50, the (-e _{31, f} ) ² / ε ₀ ε _{r of} the piezoelectric thin film is remarkably small. Even when I ₂ / (I ₁ + I ₂ ) is larger than 0.90, the (-e _{31, f} ) ² / ε ₀ ε _{r of} the piezoelectric thin film is remarkably small. Since the piezoelectric thin film 3 tends to have a large piezoelectric figure of merit, I ₂ / (I ₁ + I ₂ ) may be 0.50 or more and 0.85 or less.

Tetragonal 1 and tetragonal 2 are identified by reciprocal space mapping. That is, the tetragonal crystal 1 and the tetragonal crystal 2 are detected in the reciprocal lattice space map of the diffracted X-rays of the perovskite type oxide (piezoelectric thin film 3) and are distinguished from each other. The reciprocal lattice space map of the diffracted X-rays of the perovskite-type oxide can be rephrased as a distribution map of the intensity of the diffracted X-rays of the perobskite-type oxide in the reciprocal lattice space. For example, a reciprocal lattice space map shows the intensity of diffracted X-rays of a perovskite oxide along two or more scanning axes selected from the group consisting of ω, φ, χ, 2θ, and 2θχ axes. It may be obtained by measuring. For example, the reciprocal lattice space map may be a two-dimensional map in a coordinate system composed of orthogonal horizontal axes and vertical axes. The horizontal axis of the two-dimensional reciprocal lattice space map may indicate the reciprocal of the lattice constant of the perovskite-type oxide in the in-plane direction of the surface of the piezoelectric thin film 3. In other words, the horizontal axis of the reciprocal lattice space map may indicate the reciprocal (that is, 1 / a) of the interval a of the (100) planes of the perovskite oxide. The vertical axis of the two-dimensional reciprocal lattice space map may indicate the inverse of the lattice constant of the perovskite-type oxide in the normal direction dn (or the Out-оf-Plane direction) of the surface of the piezoelectric thin film 3. In other words, the vertical axis of the reciprocal lattice space map may indicate the reciprocal (that is, 1 / c) of the spacing c of the (001) planes of the perovskite oxide. When the piezoelectric thin film 3 contains a tetragonal crystal 1 and a tetragonal crystal 2, at least two spots are present in the reciprocal lattice space map. One of the two spots may correspond to the diffracted X-rays of the crystal plane of tetragonal crystal 1, and the other spot of the two spots may correspond to the diffracted X-rays of the crystal plane of tetragonal crystal 2. good. For example, one of the two spots may correspond to the diffraction X-rays of the (204) plane of tetragonal crystal 1, and the other spot of the two spots may correspond to the diffraction of the (204) plane of tetragonal crystal 2. It may correspond to X-ray. The distance a1 between the (100) planes of the tetragonal crystal 1 and the distance c1 between the (001) planes of the tetragonal crystal 1 can be specified from the coordinates of one spot corresponding to the diffracted X-rays of the crystal plane of the tetragonal crystal 1. .. The distance a2 between the (100) planes of the tetragonal crystal 2 and the distance c2 between the (001) planes of the tetragonal crystal 1 can be specified from the coordinates of one spot corresponding to the diffracted X-rays of the crystal planes of the tetragonal crystal 2. .. The reciprocal lattice space map may include yet another spot in addition to the two spots derived from tetragonal crystal 1 and tetragonal crystal 2. For example, spots derived from metal crystals constituting the first electrode layer 2 (base electrode layer) may exist in the reciprocal lattice space map.

The degree of orientation of the (001) plane of tetragonal crystal 1 and the (001) plane of tetragonal crystal 2 may be quantified by the degree of orientation. The larger the degree of orientation of the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2, the larger the piezoelectric figure of merit 3 tends to have. The degree of orientation of each crystal plane may be calculated based on the peak of diffracted X-rays derived from each crystal plane. The peak of the diffracted X-rays derived from each crystal plane may be measured by the Out-оf-Plane measurement on the surface of the piezoelectric thin film 3. The degree of orientation of the (001) plane of the tetragonal crystal 1 in the normal direction dn of the surface of the piezoelectric thin film 3 may be expressed as _{100 × I 1} / ΣI _{1 (hkl).} ΣI _{1 (hkl)} is the sum of the peak intensities of the diffracted X-rays of each crystal plane of the tetragonal crystal 1 measured in the Out-оf-Plane direction of the surface of the piezoelectric thin film 3. ΣI _{1 (hkl)} may be, for example, I _{1 (001)} + I _{1 (110)} + I _{1 (111)} . I _{1 (001)} is the above-mentioned I ₁ . That is, I _{1 (001)} is the peak intensity (maximum value) of the diffracted X-rays on the (001) plane of the tetragonal crystal 1 measured in the Out-оf-Plane direction of the surface of the piezoelectric thin film 3. I _{1 (110)} is the peak intensity (maximum value) of the diffracted X-rays of the (110) plane of the tetragonal crystal 1 measured in the Out-оf-Plane direction of the surface of the piezoelectric thin film 3. I _{1 (111)} is the peak intensity (maximum value) of the diffracted X-rays of the (111) plane of the tetragonal crystal 1 measured in the Out-оf-Plane direction of the surface of the piezoelectric thin film 3. The degree of orientation of the (001) plane of tetragonal crystal 2 may be expressed as _{100 × I 2} / ΣI _{2 (hkl).} ΣI _{2 (hkl)} is the sum of the peak intensity of the diffracted X-rays of each crystal plane of the tetragonal crystal 2 measured in the Out-оf-Plane direction of the surface of the piezoelectric thin film 3. ΣI _{2 (hkl)} may be, for example, I _{2 (001)} + I _{2 (110)} + I _{2 (111)} . I _{2 (001)} is the above-mentioned I ₂ . That is, I _{2 (001)} is the peak intensity (maximum value) of the diffracted X-rays on the (001) plane of the tetragonal crystal 2 measured in the Out-оf-Plane direction of the surface of the piezoelectric thin film 3. I _{2 (110)} is the peak intensity (maximum value) of the diffracted X-rays on the (110) plane of the tetragonal crystal 2 measured in the Out-оf-Plane direction of the surface of the piezoelectric thin film 3. I _{2 (111)} is the peak intensity (maximum value) of the diffracted X-rays on the (111) plane of the tetragonal crystal 2 measured in the Out-оf-Plane direction of the surface of the piezoelectric thin film 3. The degree of orientation of the (001) plane of the tetragonal crystal 1 and the (001) plane of the tetragonal crystal 2 may be quantified by the degree of orientation F based on the Rotgering method. Regardless of which of the above methods is used to calculate the degree of orientation, the degree of orientation of each of the (001) plane of tetragonal crystal 1 and the (001) plane of tetragonal crystal 2 is preferably 70% or more and 100% or less. May be 80% or more and 100% or less, more preferably 90% or more and 100% or less. In other words, the (001) plane of the tetragonal crystal 1 may be oriented in the normal direction dn of the surface of the piezoelectric thin film 3 in preference to the other crystal planes of the tetragonal crystal 1. The (001) plane of the tetragonal crystal 2 may also be oriented in the normal direction dn of the surface of the piezoelectric thin film 3 in preference to the other crystal planes of the tetragonal crystal 2.

The piezoelectric thin film 3 may consist of only tetragonal crystals 1 and tetragonal crystals 2. As long as the piezoelectric thin film 3 has a large piezoelectric performance index, the piezoelectric thin film 3 is selected from at least a group consisting of cubic crystals and rhombohedral crystals in addition to tetragonal crystals 1 and tetragonal crystals 2. It may further contain crystals of a type of perovskite-type oxide.

Perovskite oxide contained in the piezoelectric thin film 3, at least bismuth (Bi), elements ^{E B,} may include iron (Fe)及酸element (O). E ^B is magnesium (Mg), aluminum (Al), titanium (Ti), there may be at least one element selected from the group consisting of nickel (Ni) and zinc (Zn). Perovskite oxide contained in the piezoelectric thin film 3 may further contain an element E ^A in addition to the above elements. E ^A is sodium (Na), it may be at least one element selected from the group consisting of potassium (K) and silver (Ag). When the perovskite-type oxide is composed of the above elements, the tetragonal crystal 1 and the tetragonal crystal 2 are likely to coexist in the piezoelectric thin film 3, and the tetragonal crystal 1 and the tetragonal crystal 2 are likely to have the above crystal orientation, and c2. -C1, c1 / a1 and c2 / a2 are likely to fall within the above range. As long as they include the piezoelectric figure of merit greater piezoelectric thin film 3, the piezoelectric thin film 3, Bi, E A, E ^B, in addition to ^Fe and O, it may further comprise other elements. The piezoelectric thin film 3 does not have to contain Pb. The piezoelectric thin film 3 may contain Pb.

The perovskite-type oxide contained in the piezoelectric thin film 3 may be represented by the following chemical formula 1. The following chemical formula 1 is substantially the same as the following chemical formula 1a.
_{(1-x) Bi 1-} α E A α E B O 3 -xBiFeO 3 (1)
_{(Bi (1-x) (} 1-α) + x E A (1-x) α) (E B 1-x Fe x) O 3 ± δ (1a)

E ^A in Formula 1 and 1a are, Na, may be at least one element selected from the group consisting of K and Ag. ^{E B} in Formula 1 and 1a are, Mg, Al, Ti, may be at least one element selected from the group consisting of Ni and Zn.

X in the above chemical formulas 1 and 1a may be 0.30 or more and 0.80 or less. When x is 0.30 or more and 0.80 or less, I ₂ / (I ₁ + I ₂ ) is likely to fall within the range of 0.50 or more and 0.90 or less, and the piezoelectric thin film 3 has a large piezoelectric figure of merit. Easy to hold. For the same reason, x may be 0.40 or more and 0.80 or less, or 0.50 or more and 0.80 or less. When x is 0.30 or more, I ₂ / (I ₁ + I ₂ ) tends to be 0.50 or more. When x is 0.80 or less, I ₂ / (I ₁ + I ₂ ) tends to be 0.90 or less. Α in the chemical formulas 1 and 1a may be 0.00 or more and less than 1.00. Since I ₂ / (I ₁ + I ₂ ) tends to fall within the range of 0.50 or more and 0.90 or less, and the piezoelectric thin film 3 tends to have a large piezoelectric figure of merit, α is 0.50. good.

Δ in the above chemical formula 1a may be 0 or more. As long as the crystal structure of the perovskite-type oxide (perovskite structure) is maintained, δ may be a value other than 0. For example, δ may be greater than 0 and less than or equal to 1.0. δ may be calculated from, for example, the valence of each ion located at each of the A site and the B site in the perovskite structure. The valence of each ion may be measured by X-ray photoelectron spectroscopy (XPS).

Number of moles of the sum of Bi and E ^A included in the perovskite oxide may be represented as [A], the number of moles of the sum of Fe and E ^B contained in the perovskite type oxide, [B] It may be expressed as, and [A] / [B] may be 1.0. As long as the crystal structure (perovskite structure) of the perovskite-type oxide is maintained, [A] / [B] may be a value other than 1.0. That is, [A] / [B] may be less than 1.0, and [A] / [B] may be larger than 1.0.

The composition of the tetragonal crystal 1 and the tetragonal crystal 2 may be within the range of the composition represented by the above chemical formula 1 or 1a. The composition of tetragonal crystal 1 may differ from the composition of tetragonal crystal 2 as long as the compositions of tetragonal crystal 1 and tetragonal crystal 2 are within the range of the composition represented by the above chemical formula 1 or 1a. The composition of the tetragonal crystal 1 may be the same as the composition of the tetragonal crystal 2. The composition of tetragonal crystal 1 may differ from that of tetragonal crystal 2 as long as the overall composition of the perovskite-type oxide constituting the piezoelectric thin film 3 falls within the range of the composition represented by the above chemical formula 1 or 1a. .. As long as the overall composition of the perovskite-type oxide constituting the piezoelectric thin film 3 falls within the range of the composition represented by the above chemical formula 1 or 1a, the composition of at least one of the tetragonal crystal 1 and the tetragonal crystal 2 is the above. It may be out of the range of the composition represented by the chemical formula 1 or 1a.

The thickness of the piezoelectric thin film 3 may be, for example, 10 nm or more and 10 μm or less. The area of the piezoelectric thin film 3 may be, for example, 1 μm ² or more and 500 mm ² or less. The area of each of the 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 be the same as the area of the piezoelectric thin film 3.

The composition of the piezoelectric thin film may be analyzed, for example, by fluorescent X-ray analysis (XRF method) or inductively coupled plasma (ICP) emission spectroscopy. The crystal structure and crystal orientation of the piezoelectric thin film may be specified by the X-ray diffraction (XRD) method. The crystal structure and crystal orientation of the piezoelectric thin film described above may be the crystal structure and crystal orientation of the piezoelectric thin film at room temperature.

The piezoelectric thin film 3 may be formed by, for example, the following method.

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

As starting materials, for example, ^Bi, E A, may oxides of s ^{E B} and Fe其are used. As a starting material, a substance that becomes an oxide by calcination, such as carbonate or oxalate, may be used instead of the oxide. After these starting materials were fully dried at 100 ° C. or higher, Bi, E ^A, is the number of moles of E ^B and Fe, so that within the range defined in Formula 1, each of the starting materials are weighed .. In the vapor phase growth method described later, Bi in the target is more likely to volatilize than other elements. Therefore, the molar ratio of Bi in the target may be adjusted to a value higher than the molar ratio of Bi in the piezoelectric thin film 3. If the raw material is used containing K as E ^A, K in the target is likely to volatilize when compared to other elements. Therefore, the molar ratio of K in the target may be adjusted to a value higher than the molar ratio of K in the piezoelectric thin film 3.

The weighed starting material is well mixed in an organic solvent or water. The mixing time may be 5 hours or more and 20 hours or less. The mixing means may be, for example, a ball mill. After the starting material after mixing is sufficiently dried, the starting material is formed by a press. A calcined product is obtained by calcine the molded starting material. The temperature of the calcining may be 750 ° C. or higher and 900 ° C. or lower. The baking time may be 1 hour or more and 3 hours or less. The calcined product is ground in an organic solvent or water. The crushing time may be 5 hours or more and 30 hours or less. The crushing means may be a ball mill. After the crushed calcined product is dried, the calcined product powder to which the binder solution is added is granulated to obtain the powder of the calcined product. By press molding the powder of the calcined product, a block-shaped molded product is obtained.

By heating the block-shaped molded product, the binder in the molded product is volatilized. The heating temperature may be 400 ° C. or higher and 800 ° C. or lower. The heating time may be 2 hours or more and 4 hours or less.

After volatilization of the binder, the molded product is sintered. The firing temperature may be 800 ° C. or higher and 1100 ° C. or lower. The firing time may be 2 hours or more and 4 hours or less. The temperature raising rate and the temperature lowering rate of the molded product in the firing process may be, for example, 50 ° C./hour or more and 300 ° C./hour or less.

The target is obtained by the above steps. The average particle size of the crystal grains of the oxide (perovskite type oxide) contained in the target may be, for example, 1 μm or more and 20 μm or less.

The piezoelectric thin film 3 may be formed by the vapor phase growth method using the above target. In the vapor phase growth method, the elements constituting the target are evaporated in a vacuum atmosphere. The piezoelectric thin film 3 grows by adhering and depositing the evaporated element on the surface of any one of the second intermediate layer 6, the first electrode layer 2, or the single crystal substrate 1. The vapor phase growth method may be, for example, a sputtering method, an electron beam deposition method, a chemical vapor deposition method, or a pulsed-laser deposition method. In the following, the pulsed laser deposition method will be referred to as the PLD method. The excitation source differs depending on the type of vapor deposition method. The excitation source of the sputtering method is Ar plasma. The excitation source of the electron beam deposition method is an electron beam. The excitation source for the PLD method is laser light (eg, excimer laser). When these excitation sources are applied to the target, the elements constituting the target evaporate. By using the above vapor phase growth method, the piezoelectric thin film 3 easily grows epitaxially. By using the above vapor phase growth method, it is possible to form the piezoelectric thin film 3 which is dense at the atomic level, and segregation of elements in the piezoelectric thin film 3 is suppressed.

Among the above-mentioned vapor deposition methods, the PLD method is relatively excellent in the following points. In the PLD method, each element constituting the target can be instantly turned into plasma without spots by using a pulse laser. Therefore, the piezoelectric thin film 3 having substantially the same composition as the target is likely to be formed. Further, in the PLD method, it is easy to control the thickness of the piezoelectric thin film 3 by changing the number of laser pulses (repetition frequency).

The piezoelectric thin film 3 may be an epitaxial film. That is, the piezoelectric thin film 3 may be formed by epitaxial growth. Due to the epitaxial growth, c1 / a1 of tetragonal crystal 1 and c2 / a2 of tetragonal crystal 2 are likely to fall within the range of the above period, and a piezoelectric thin film 3 having excellent anisotropy and crystal orientation is likely to be formed. When the piezoelectric thin film 3 is formed by the PLD method, the piezoelectric thin film 3 is likely to be formed by epitaxial growth.

In the PLD method, the piezoelectric thin film 3 may be formed while heating the single crystal substrate 1 and the first electrode layer 2 in the vacuum chamber. The temperature (deposition temperature) of the single crystal substrate 1 and the first electrode layer 2 may be, for example, 300 ° C. or higher and 800 ° C. or lower, 500 ° C. or higher and 700 ° C. or lower, or 500 ° C. or higher and 600 ° C. or lower. The higher the film formation temperature, the better the cleanliness of the surface of the single crystal substrate 1 or the first electrode layer 2, the crystallinity of the piezoelectric thin film 3, and the degree of orientation of the crystal planes of the tetragonal crystals 1 and the tetragonal crystals 2. Is easy to increase. If the film formation temperature is too high, Bi or K is likely to be separated from the piezoelectric thin film 3, and the composition of the piezoelectric thin film 3 is difficult to control.

In the PLD method, the oxygen partial pressure in the vacuum chamber may be, for example, greater than 10 mTorr and less than 400 mTorr, 15 mTorr or more and 300 mTorr or less, or 20 mTorr or more and 200 mTorr or less. In other words, the partial pressure of oxygen in the vacuum chamber may be, for example, greater than 1 Pa and less than 53 Pa, 2 Pa or more and 40 Pa or less, or 3 Pa or more and 30 Pa or less. By the oxygen partial pressure is maintained within the range, Bi deposited on a single crystal substrate 1, E ^A, easily E ^B and Fe are sufficiently oxidized. When the oxygen partial pressure is too low, the degree of orientation of the crystal plane of the piezoelectric thin film 3 tends to decrease, and the tetragonal crystals 1 and the tetragonal crystals 2 are unlikely to coexist in the piezoelectric thin film 3. If the oxygen partial pressure is too high, the growth rate of the piezoelectric thin film 3 tends to decrease, and the degree of orientation of the crystal plane of the piezoelectric thin film 3 tends to decrease.

Other parameters controlled by the PLD method are, for example, the laser oscillation frequency and the distance between the substrate and the target. By controlling these parameters, the crystal structure and crystal orientation of the piezoelectric thin film 3 can be easily controlled. For example, when the laser oscillation frequency is 10 Hz or less, the degree of orientation of the crystal plane of the piezoelectric thin film 3 tends to increase.

In the growth process of the piezoelectric thin film 3, a heat cycle may be carried out in which the temperature of the single crystal substrate 1 (the temperature in the vacuum chamber) rises and falls. The heat cycle may be repeated. The temperature range of the heat cycle may be within the above-mentioned film formation temperature range. In the growing piezoelectric thin film 3, tensile stress parallel to the surface of the single crystal substrate 1 is likely to occur. Alternatively, in the growing piezoelectric thin film 3, a compressive stress parallel to the surface of the single crystal substrate 1 is likely to occur. The tensile stress or compressive stress is caused, for example, by the lattice mismatch between the single crystal substrate 1 and the piezoelectric thin film 3, or the difference in the thermal expansion coefficient between the single crystal substrate 1 and the piezoelectric thin film 3. When the tensile stress or the compressive stress is too large, the tetragonal crystal 1 and the tetragonal crystal 2 are difficult to be formed, and a single tetragonal crystal (anisotropy uniform tetragonal crystal) is likely to be formed. By appropriately relaxing the tensile stress or compressive stress generated in the piezoelectric thin film 3 by a heat cycle, the piezoelectric thin film 3 in which the tetragonal crystals 1 and the tetragonal crystals 2 coexist can easily grow.

After the piezoelectric thin film 3 has grown, the piezoelectric thin film 3 may be annealed (heated). The temperature (annealing temperature) of the piezoelectric thin film 3 in the annealing treatment may be, for example, 300 ° C. or higher and 1000 ° C. or lower, 600 ° C. or higher and 1000 ° C. or lower, or 850 ° C. or higher and 1000 ° C. or lower. By the annealing treatment of the piezoelectric thin film 3, the piezoelectricity of the piezoelectric thin film 3 tends to be further improved. In particular, the piezoelectricity of the piezoelectric thin film 3 is likely to be improved by the annealing treatment at 850 ° C. or higher and 1000 ° C. or lower. However, annealing treatment is not essential.

The single crystal substrate 1 may be, for example, a substrate made of a single crystal of Si or a substrate made of a single crystal of a compound semiconductor such as GaAs. The single crystal substrate 1 may be a substrate made of a single crystal of an oxide. The single crystal of the oxide may be, for example, MgO or a perovskite-type oxide (for example, SrTiO ₃ ). The thickness of the single crystal substrate 1 may be, for example, 10 μm or more and 1000 μm or less. When the single crystal substrate 1 has conductivity, the single crystal substrate 1 functions as an electrode, so that the first electrode layer 2 may not be provided. That is, the conductive single crystal substrate 1 may be, for example, a single crystal of _{SrTiO 3 doped with niobium (Nb).}

Crystal orientation of the single crystal substrate 1 may be equal to the normal direction D _N of the single-crystal substrate 1 of the surface. That is, the 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 (for example, Si) may be parallel to the surface of the single crystal substrate 1. That is, [100] direction of the single crystal substrate 1 (e.g., Si), it may be parallel to the normal direction _{D N} of the single-crystal substrate 1 of the surface.

When the (100) plane of the single crystal substrate 1 (for example, Si) is parallel to the surface of the single crystal substrate 1, the (001) plane of the perovskite type crystal in the piezoelectric thin film 3 is in the normal direction of the surface of the piezoelectric thin film 3. It is easy to orient at dn.

As described above, the first intermediate layer 5 may be arranged between the single crystal substrate 1 and the first electrode layer 2. The first intermediate layer 5 contains, for example, at least one selected from the group consisting of titanium (Ti), chromium (Cr), titanium oxide (TiO ₂ ), silicon oxide (SiO ₂ ), and zirconium oxide (ZrO _2). It's fine. By passing through the first intermediate layer 5, the first electrode layer 2 easily adheres to the single crystal substrate 1. The first intermediate layer 5 may be crystalline. Crystal plane of the first intermediate layer 5 may have oriented in the normal direction D _N of the single-crystal substrate 1 of the surface. Both crystal plane crystal surface of the first intermediate layer 5 of the single crystal substrate 1 may be oriented in the normal direction D _N of the single-crystal substrate 1 of the surface. The method for forming the first intermediate layer 5 may be a sputtering method, a vacuum vapor deposition method, a printing method, a spin coating method, or a sol-gel method.

The first intermediate layer 5 _{may contain oxides of ZrO 2} and rare earth elements. Since the first intermediate layer 5 _{contains ZrO 2} and an oxide of a rare earth element, the first electrode layer 2 made of platinum crystals is easily formed on the surface of the first intermediate layer 5, and the platinum crystals (002). The surface is likely to be oriented in the normal direction of the surface of the first electrode layer 2, and the (200) surface of the platinum crystal is likely to be oriented in the in-plane direction of the surface of the first electrode layer 2. Rare earth elements are scandium (Sc), ittrium (Y), lantern (La), cerium (Ce), placeodium (Pr), neodym (Nd), promethium (Pm), samarium (Sm), uropyum (Eu), gadolinium. At least one selected from the group consisting of (Gd), terbium (Tb), dysprosium (Dy), formium (Ho), elbium (Er), thulium (Tm), terbium (Yb), and lutetium (Lu). good.

The first intermediate layer 5 may contain _{ZrO 2} and Y ₂ O _3. For example, the first intermediate layer 5 may consist of yttria-stabilized zirconia ( _{ZrO 2 to which Y 2} O ₃ has been added). The first intermediate layer 5 may have a first layer made of ZrO _{2 and a second} layer made of Y 2 O ₃ . The first layer made of ZrO ₂ may be directly laminated on the surface of the single crystal substrate 1. The second layer composed of Y ₂ O ₃ may be laminated directly on the surface of the first layer. The first electrode layer 2 may be directly laminated on the surface of the second layer made of _{Y 2} O _3. When the first intermediate layer 5 _{contains ZrO 2} and Y ₂ O ₃ , the piezoelectric thin film 3 is likely to grow epitaxially, and the tetragonal crystal 1 and the tetragonal crystal 2 are likely to coexist in the piezoelectric thin film 3, and the tetragonal crystal 1 and the tetragonal crystal 1 and the tetragonal crystal 2 are likely to coexist. The (001) plane of each of the crystals 2 tends to be preferentially oriented in the normal direction dn of the surface of the piezoelectric thin film 3. When the first intermediate layer 5 _{contains ZrO 2} and Y ₂ O ₃ , the first electrode layer 2 made of platinum crystals is likely to be formed on the surface of the first intermediate layer 5, and the (002) plane of the platinum crystals is easily formed. , The surface of the first electrode layer 2 is easily oriented in the normal direction, and the (200) plane of the platinum crystal is easily oriented in the in-plane direction of the surface of the first electrode layer 2.

The first electrode layer 2 includes, for example, platinum (Pt), palladium (Pd), rhodium (Rh), gold (Au), ruthenium (Ru), iridium (Ir), molybdenum (Mo), titanium (Ti), and tantalum. It may consist of at least one metal selected from the group consisting of (Ta) and nickel (Ni). The first electrode layer 2 is made of a conductive metal oxide such as _{strontium ruthenate (SrRuO 3} ), lanthanum nickelate (LaNiO ₃ ), or lanthanum lanthanum cobaltate ((La, Sr) CoO _3). May be good. The first electrode layer 2 may be crystalline. Crystal plane of the first electrode layer 2 may have oriented in the normal direction D _N of the single crystal substrate 1. The crystal plane of the first electrode layer 2 may be substantially parallel to the surface of the single crystal substrate 1. Both crystal plane crystal surface of the first electrode layer 2 of the single crystal substrate 1 may have oriented in the normal direction D _N of the single crystal substrate 1. Crystal plane of the first electrode layer 2 to be oriented in the normal direction D _N of the single crystal substrate 1 is tetragonal in the piezoelectric thin film 3 1 and tetragonal 2其's (001) plane may be substantially parallel. The thickness of the first electrode layer 2 may be, for example, 1 nm or more and 1.0 μm or less. The method for forming the first electrode layer 2 may be a sputtering method, a vacuum vapor deposition method, a printing method, a spin coating method, or a sol-gel method. In the case of the printing method, the spin coating method, or the sol-gel method, the first electrode layer 2 may be heat-treated (annealed) in order to enhance the crystallinity of the first electrode layer 2.

The first electrode layer 2 may contain platinum crystals. The first electrode layer 2 may be composed of only platinum crystals. Platinum crystals are cubic crystals having a face-centered cubic lattice structure (fcc structure). The (002) plane of the platinum crystal may be oriented in the normal direction of the surface of the first electrode layer 2, and the (200) plane of the platinum crystal may be oriented in the in-plane direction of the surface of the first electrode layer 2. It may be oriented. In other words, the (002) plane of the platinum crystal may be substantially parallel to the surface of the first electrode layer 2, and the (200) plane of the platinum crystal may be substantially perpendicular to the surface of the first electrode layer 2. It may be there. When the (002) plane and the (200) plane of the platinum crystals constituting the first electrode layer 2 have the above orientations, the piezoelectric thin film 3 easily grows epitaxially on the surface of the first electrode layer 2 and is tetragonal. The crystals 1 and the tetragonal crystals 2 are likely to coexist in the piezoelectric thin film 3, and the (001) planes of the tetragonal crystals 1 and the tetragonal crystals 2 are likely to be preferentially oriented in the normal direction dn of the surface of the piezoelectric thin film 3. The surface of the first electrode layer 2 may be substantially parallel to the surface of the piezoelectric thin 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 thin film 3.

As described above, the second intermediate layer 6 may be arranged between the first electrode layer 2 and the piezoelectric thin film 3. The second intermediate layer 6 may include, for example, at least one selected from the group consisting of _{SrRuO 3} , LaNiO ₃ and (La, Sr) CoO _3. The (La, Sr) CoO ₃ may be, 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 is at least two buffers selected from the group consisting _{of, for example, a layer containing crystals of SrRuO 3} , a layer containing crystals of LaNiO ₃ , and a layer containing crystals of (La, Sr) CoO _3. It may be a laminated body composed of layers. All of SrRuO ₃ , LaNiO ₃ and (La, Sr) CoO ₃ have a perovskite structure. Therefore, when the second intermediate layer 6 _{contains at least one selected from the group consisting of SrRuO 3} , LaNiO ₃ and (La, Sr) CoO ₃ , the piezoelectric thin film 3 tends to grow epitaxially, and tetragonal crystal 1 and tetragonal crystal 1 and square. The crystals 2 are likely to coexist in the piezoelectric thin film 3, and the (001) planes of the tetragonal crystal 1 and the tetragonal crystal 2 are likely to be preferentially oriented in the normal direction dn of the surface of the piezoelectric thin film 3. Further, the piezoelectric thin film 3 easily adheres to the first electrode layer 2 through the second intermediate layer 6. Crystal plane of the second intermediate layer 6 may have oriented in the normal direction D _N of the single-crystal substrate 1 of the surface. Both crystal plane crystal surface of the second intermediate layer 6 of the single crystal substrate 1 may be oriented in the normal direction D _N of the single-crystal substrate 1 of the surface. The method for forming the second intermediate layer 6 may be a sputtering method, a vacuum vapor deposition method, a printing method, a spin coating method, or a sol-gel method.

The second electrode layer 4 may consist of, for example, at least one metal selected from the group consisting of, for example, Pt, Pd, Rh, Au, Ru, Ir, Mo, Ti, Ta, and Ni. The second electrode layer 4 may consist of, for example, at least one conductive metal oxide selected from the group consisting of _{LaNiO 3} , SrRuO ₃ and (La, Sr) CoO _3. The second electrode layer 4 may be crystalline. Crystal plane of the second electrode layer 4 may have oriented in the normal direction D _N of the single crystal substrate 1. The crystal plane of the second electrode layer 4 may be substantially parallel to the surface of the single crystal substrate 1. The crystal plane of the second electrode layer 4 may be substantially parallel to the crystal planes of the tetragonal crystals 1 and the tetragonal crystals 2 in the piezoelectric thin film 3. The thickness of the second electrode layer 4 may be, for example, 1 nm or more and 1.0 μm or less. The method for forming the second electrode layer 4 may be a sputtering method, a vacuum vapor deposition method, a printing method, a spin coating method, or a sol-gel method. In the case of the printing method, the spin coating method, or the sol-gel method, the second electrode layer 4 may be heat-treated (annealed) in order to enhance the crystallinity of the second electrode layer 4.

The third intermediate layer may be arranged between the piezoelectric thin film 3 and the second electrode layer 4. The second electrode layer 4 easily adheres to the piezoelectric thin film 3 through the third intermediate layer. The composition, crystal structure, and forming method of the third intermediate layer may be the same as those of the second intermediate layer.

At least a part or the whole of the surface of the piezoelectric thin film element 10 may be covered with a protective film. By covering with a protective film, for example, the moisture resistance of the piezoelectric thin film element 10 is improved.

The applications of the piezoelectric thin film device according to this embodiment are various. For example, piezoelectric thin film devices may be used in piezoelectric transducers. That is, the piezoelectric transducer according to the present embodiment may include the above-mentioned piezoelectric thin film element. The piezoelectric transducer may be, for example, an ultrasonic transducer such as an ultrasonic sensor. The piezoelectric thin film element may be, for example, a harvester (vibration power generation element). The piezoelectric thin film element according to the present embodiment is suitable for an ultrasonic transducer or a harvester because it includes a piezoelectric thin film having _{a large (-e 31f} ) ² / ε ₀ ε _r. The piezoelectric thin film element may be a piezoelectric actuator. Piezoelectric actuators may be used in head assemblies, head stack assemblies, or hard disk drives. The piezoelectric actuator may be used in a printer head or an inkjet printer device. The piezoelectric actuator may be a piezoelectric switch. Piezoelectric actuators may be used for haptics. That is, the piezoelectric actuator may be used in various devices that require feedback by skin sensation (tactile sensation). The device for which skin-sensing feedback is required may be, for example, a wearable device, a touchpad, a display, or a game controller. The piezoelectric thin film element may be a piezoelectric sensor. For example, the piezoelectric sensor may be a piezoelectric microphone, a gyro sensor, a pressure sensor, a pulse wave sensor, or a shock sensor. The piezoelectric thin film element may be an oscillator or an acoustic multilayer film. Piezoelectric thin film elements may be part or all of a Micro Electro Mechanical Systems (MEMS), for example, Piezoelectric Micromachined Ultrasonic Transducers; PMUTs. Specific examples of products to which the piezoelectric micromechanical ultrasonic transducer is applied include a biometric sensor or a medical / healthcare sensor (fingerprint sensor, blood vessel sensor, etc.), and a ToF (Time of Flight) sensor.

FIG. 4 shows a schematic cross section of the ultrasonic transducer 10a including the piezoelectric thin film 3. The cross section of the ultrasonic transducer 10a is perpendicular to the surface of the piezoelectric thin film 3. The ultrasonic transducer 10a includes the substrates 1a and 1b, the first electrode layer 2 installed on the substrates 1a and 1b, the piezoelectric thin film 3 overlapping the first electrode layer 2, and the second electrode layer overlapping the piezoelectric thin film 3. 4 and may be provided. An acoustic cavity 1c may be provided below the piezoelectric thin film 3. An ultrasonic signal is transmitted or received due to bending or vibration of the piezoelectric thin 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 thin film 3.

The present invention will be described in detail with reference to the following examples and comparative examples. The present invention is not limited to the following examples.

(Example 1)
A single crystal substrate made of Si was used for producing the piezoelectric thin film device of Example 1. The (100) plane of Si was parallel to the surface of the single crystal substrate. The single crystal substrate was a 20 mm × 20 mm square. The thickness of the single crystal substrate was 500 μm.

In the vacuum chamber _{, a crystalline first intermediate layer consisting of ZrO 2} and Y ₂ O ₃ was formed over the entire surface of the single crystal substrate. The first intermediate layer was formed by a sputtering method. The thickness of the first intermediate layer was 30 nm.

In the vacuum chamber, a first electrode layer composed of Pt crystals was formed over the entire surface of the first intermediate layer. The first electrode layer was formed by a sputtering method. The thickness of the first electrode layer was 200 nm. The temperature of the single crystal substrate in the process of forming the first electrode layer was maintained at 500 ° C.

The XRD pattern of the first electrode layer was measured by the Out оf Plane measurement on the surface of the first electrode layer. The XRD pattern of the first electrode layer was measured by the In Plane measurement on the surface of the first electrode layer. An X-ray diffractometer (SmartLab) manufactured by Rigaku Co., Ltd. was used for measuring these XRD patterns. The measurement conditions were set so that each peak intensity in the XRD pattern was at least three orders of magnitude higher than the background intensity. The peak of the diffracted X-ray on the (002) plane of the Pt crystal was detected by the Out оf Plane measurement. That is, the (002) plane of the Pt crystal was oriented in the normal direction of the surface of the first electrode layer. The peak of the diffracted X-ray on the (200) plane of the Pt crystal was detected by the In Plane measurement. That is, the (200) plane of the Pt crystal was oriented in the in-plane direction of the surface of the first electrode layer.

In the vacuum chamber, a piezoelectric thin film was formed over the entire surface of the first electrode layer. The piezoelectric thin film was formed by the PLD method. The thickness of the piezoelectric thin film was 2000 nm. The temperature of the single crystal substrate (deposition temperature) in the process of forming the piezoelectric thin film was maintained at 500 ° C. The partial pressure of oxygen in the vacuum chamber during the process of forming the piezoelectric thin film was maintained at 10 Pa. A target (sintered body of raw material powder) was used as a raw material for the piezoelectric thin film. Bismuth oxide, potassium carbonate, titanium oxide, and iron oxide were used as raw material powders for the target. The blending ratio of the raw material powder was adjusted according to the composition of the target piezoelectric thin film. The composition of the target piezoelectric thin film was represented by the following chemical formula 1A. That is, in the case of Example 1, the E ^A in Formula 1 is K, E ^B in Formula 1 is Ti, the α in Formula 1 was 0.5. In the case of Example 1, the values of x in the following chemical formulas 1 and 1A were the values shown in Table 1 below.
(1-x) Bi _0.5 K _0.5 TiO _3- xBiFeO ₃ (1A)
_{(1-x) Bi 1-} α E A α E B O 3 -xBiFeO 3 (1)

The composition of the piezoelectric thin film was analyzed by the XRF method. An apparatus PW2404 manufactured by Philips Japan Ltd. was used for the analysis. As a result of the analysis, the composition of the piezoelectric thin film of Example 1 was almost the same as the composition of the target represented by the above chemical formula 1A.

The reciprocal lattice space mapping of the piezoelectric thin film was performed using the above-mentioned X-ray diffractometer. In addition, the XRD pattern of the piezoelectric thin film was measured by the Out оf Plane measurement on the surface of the piezoelectric thin film. Further, the XRD pattern of the piezoelectric thin film was measured by In Plane measurement on the surface of the piezoelectric thin film. The measurement conditions were set so that each peak intensity in the XRD pattern was at least three orders of magnitude higher than the background intensity. The XRD pattern measuring device and measuring conditions were the same as described above.

The analysis result of the piezoelectric thin film based on the above XRD method showed that the piezoelectric thin film had the following characteristics.

The piezoelectric thin film consisted of a perovskite-type oxide.
The piezoelectric thin film contained a perovskite-type oxide tetragonal crystal 1 and a perovskite-type oxide tetragonal crystal 2.
The (001) plane of tetragonal crystal 1 was preferentially oriented in the normal direction of the surface of the piezoelectric thin film. That is, the degree of orientation of the (001) plane of the tetragonal crystal 1 in the normal direction of the surface of the piezoelectric thin film was 90% or more. The degree of orientation of the (001) plane of tetragonal crystal 1 is expressed as 100 × I _{1 (001)} / (I _{1 (001)} + I _{1 (110)} + I _{1 (111)} ).
The (001) plane of tetragonal crystal 2 was preferentially oriented in the normal direction of the surface of the piezoelectric thin film. That is, the degree of orientation of the (001) plane of the tetragonal crystal 2 in the normal direction of the surface of the piezoelectric thin film was 90% or more. The degree of orientation 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)} ).
The interval c1 of the (001) plane of the tetragonal crystal 1 was the value shown in Table 1 below.
The distance c2 between the (001) planes of the tetragonal crystal 2 was the value shown in Table 1 below.
c1 / a1 was the value shown in Table 1 below.
c2 / a2 was the value shown in Table 1 below.
I ₂ / (I ₁ + I ₂ ) was the value shown in Table 1 below.
c2-c1 was the value shown in Table 1 below.

By the above method, a laminate comprising a single crystal substrate, a first intermediate layer overlapping the single crystal substrate, a first electrode layer overlapping the first intermediate layer, and a piezoelectric thin film overlapping the first electrode layer is produced. rice field. The following steps were further carried out using this laminate.

In the vacuum chamber, a second electrode layer made of Pt was formed over the entire surface of the piezoelectric thin film. The second electrode layer was formed by a sputtering method. The temperature of the single crystal substrate in the process of forming the second electrode layer was maintained at 500 ° C. The thickness of the second electrode layer was 200 nm.

Through the above steps, the single crystal substrate, the first intermediate layer overlapping the single crystal substrate, the first electrode layer overlapping the first intermediate layer, the piezoelectric thin film overlapping the first electrode layer, and the second electrode overlapping the piezoelectric thin film. A laminate comprising the layers was made. Subsequent photolithography was used to pattern the laminated structure on the single crystal substrate. After patterning, the laminate was cut by dicing.

Through the above steps, a strip-shaped piezoelectric thin film device of Example 1 was obtained. The piezoelectric thin film element includes a single crystal substrate, a first intermediate layer overlapping the single crystal substrate, a first electrode layer overlapping the first intermediate layer, a piezoelectric thin film overlapping the first electrode layer, and a second electrode overlapping the piezoelectric thin film. It had layers and. The area of the movable part of the piezoelectric thin film was 20 mm × 1.0 mm.

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

[Measurement of residual polarization]
The hysteresis of the polarization of the piezoelectric thin 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 Inc. The ferroelectric evaluation system was FCE manufactured by Toyo Corporation. The frequency of the AC voltage in the measurement of hysteresis was 5 Hz. In the measurement, the maximum value of the voltage applied to the piezoelectric thin film was 20V. The remanent polarization Pr of the piezoelectric thin film is shown in Table 1 below. The unit of remanent polarization Pr is μC / cm ² .

[Calculation of relative permittivity]
The capacitance C of the piezoelectric thin film element was measured. The details of the measurement of the capacity C were as follows.
Measuring device: Impedance Gain-Phase Analyzer 4194A manufactured by Hewlett-Packard Co., Ltd.
Frequency: 10kHz
Electric field: 0.1V / μm

_{The relative permittivity ε r} was calculated from the measured value of the capacitance C based on the following mathematical formula A. The ε _r of Example 1 is shown in Table 1 below.
C = ε ₀ × ε _r × (S / d) (A)
_{Ε 0} in the equation A is the permittivity of the vacuum (8.854 × ^10-12 Fm ^-1 ). S in the formula A is the area of the surface of the piezoelectric thin film. S can be rephrased as the area of the first electrode layer that overlaps the piezoelectric thin film. In the formula A, d is the thickness of the piezoelectric thin film.

[Measurement of piezoelectric constants −e _{31, f]}
In order to measure the piezoelectric constants −e _{31 and f} of the piezoelectric thin film, a rectangular sample (cantilever) was prepared as the piezoelectric thin film element. The dimensions of the sample were 3 mm wide x 15 mm long. Except for the dimensions, the sample was the same as the piezoelectric thin film device of Example 1 above. A self-made evaluation system was used for the measurement. One end of the sample was fixed and the other end of the sample was a free end. The displacement of the free end of the sample was measured with a laser while applying a voltage to the piezoelectric thin film in the sample. Then, the piezoelectric constants −e _{31, f} were calculated from the following mathematical formula B. Incidentally, E _s in formula B is a Young's modulus of the single crystal substrate. h _s is the thickness of the single crystal substrate. L is the length of the sample (cantilever). ν _s is the Poisson's ratio of the single crystal substrate. δ _out is the output displacement based on the measured displacement amount. V _in is the voltage applied to the piezoelectric thin film. The frequency of the AC electric field (AC voltage) in the measurement of the piezoelectric constants −e _{31 and f was 100 Hz.} The maximum value of the voltage applied to the piezoelectric thin film was 50V. The unit of −e _{31 and f} is C / m ² . _{-E 31, f} of Example 1 are shown in Table 1 below. The (-e _{31, f} ) ² / ε ₀ ε _r (piezoelectric figure of merit) of Example 1 is shown in Table 1 below.

(Examples 2 to 6 and Comparative Examples 1 to 3)
The composition of the target used for forming the piezoelectric thin films of Examples 2 to 6 and Comparative Examples 1 to 3 was different from that of the target of Example 1.

The composition of the target of Example 2 was represented by the following chemical formula 1B. That is, in the case of Example 2, the E ^A in Formula 1 is K, E ^B in Formula 1 is Zn and Ti, the α in Formula 1 was 0.5. In the case of Example 2, the values of x in the following chemical formulas 1 and 1B were the values shown in Table 1 below.
(1-x) Bi _0.5 K _0.5 Zn _0.5 Ti _0.5 O _3- xBiFeO ₃ (1B)
_{(1-x) Bi 1-} α E A α E B O 3 -xBiFeO 3 (1)

The composition of the target of Example 3 was represented by the following chemical formula 1C. That is, in the case of Example 3, the E ^A in Formula 1 is K, E ^B in Formula 1 is Mg and Ti, is α in Formula 1 was 0.5. In the case of Example 3, the values of x in the following chemical formulas 1 and 1C were the values shown in Table 1 below.
(1-x) Bi _0.5 K _0.5 Mg _0.5 Ti _0.5 O _3- xBiFeO ₃ (1C)
_{(1-x) Bi 1-} α E A α E B O 3 -xBiFeO 3 (1)

The composition of the target of Example 4 was represented by the following chemical formula 1D. That is, in the case of Example 4, the ^{E A} in Formula 1 is Na, ^{E B} in Formula 1 is Zn and Ti, the α in Formula 1 was 0.5. In the case of Example 4, the values of x in the following chemical formulas 1 and 1D were the values shown in Table 1 below.
(1-x) Bi _0.5 Na _0.5 Zn _0.5 Ti _0.5 O _3- xBiFeO ₃ (1D)
_{(1-x) Bi 1-} α E A α E B O 3 -xBiFeO 3 (1)

The composition of the target of Example 5 was represented by the following chemical formula 1E. That is, in the case of Example 5, the E ^A in Formula 1 is Ag, E ^B in Formula 1 is Ti, the α in Formula 1 was 0.5. In the case of Example 5, the values of x in the following chemical formulas 1 and 1E were the values shown in Table 1 below.
(1-x) Bi _0.5 Ag _0.5 TiO _3- xBiFeO ₃ (1E)
_{(1-x) Bi 1-} α E A α E B O 3 -xBiFeO 3 (1)

The composition of the target of Example 6 was represented by the following chemical formula 1F. That is, in the case of Example 6, the ^{E A} in Formula 1 is Ag, ^{E B} in Formula 1 is Zn and Ti, the α in Formula 1 was 0.5. In the case of Example 6, the values of x in the following chemical formulas 1 and 1F were the values shown in Table 1 below.
(1-x) Bi _0.5 Ag _0.5 Zn _0.5 Ti _0.5 O _3- xBiFeO ₃ (1F)
_{(1-x) Bi 1-} α E A α E B O 3 -xBiFeO 3 (1)

The composition of the target of Comparative Example 1 was represented by the following chemical formula 1G. That is, in the case of Comparative Example 1, the E ^A in Formula 1 is K, E ^B in Formula 1 is Zn and Ti, the α in Formula 1 was 0.5. In the case of Comparative Example 1, the values of x in the following chemical formulas 1 and 1G were the values shown in Table 1 below.
(1-x) Bi _0.5 K _0.5 Zn _0.5 Ti _0.5 O _3- xBiFeO ₃ (1G)
_{(1-x) Bi 1-} α E A α E B O 3 -xBiFeO 3 (1)

The composition of the target of Comparative Example 2 was represented by the following chemical formula 1H. That is, in the case of Comparative Example 2, the E ^A in Formula 1 is Na, E ^B in Formula 1 is Ti, the α in Formula 1 was 0.5. In the case of Comparative Example 2, the values of x in the following chemical formulas 1 and 1H were the values shown in Table 1 below.
(1-x) Bi _0.5 Na _0.5 TiO _3- xBiFeO ₃ (1H)
_{(1-x) Bi 1-} α E A α E B O 3 -xBiFeO 3 (1)

The target composition of Comparative Example 3 was _{BiFeO 3.} That is, in the case of Comparative Example 3, x in the following chemical formula 1 was 1.0.
_{(1-x) Bi 1-} α E A α E B O 3 -xBiFeO 3 (1)

Piezoelectric thin film devices of Examples 2 to 6 and Comparative Examples 1 to 3 were produced in the same manner as in Example 1 except that the composition of the target used for forming the piezoelectric thin film was different.

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 both Examples 2 to 6 and Comparative Examples 1 to 3, the (002) plane of the Pt crystal constituting the first electrode layer is oriented in the normal direction of the surface of the first electrode layer. The (200) plane of the Pt crystal was oriented in the in-plane direction of the surface of the first electrode layer.

The compositions of the piezoelectric thin films of Examples 2 to 6 and Comparative Examples 1 to 3 were analyzed by the same method as in Example 1. In both Examples 2 to 6 and Comparative Examples 1 to 3, the composition of the piezoelectric thin film was substantially the same as the composition of the target.

The piezoelectric thin films of Examples 2 to 6 and Comparative Examples 1 and 2 based on the XRD method were analyzed by the same method as in Example 1. In both Examples 2 to 6 and Comparative Examples 1 and 2, the piezoelectric thin film had the following characteristics.

The piezoelectric thin film consisted of a perovskite-type oxide.
The piezoelectric thin film contained a perovskite-type oxide tetragonal crystal 1 and a perovskite-type oxide tetragonal crystal 2.
The (001) plane of tetragonal crystal 1 was preferentially oriented in the normal direction of the surface of the piezoelectric thin film. The degree of orientation of the (001) plane of tetragonal crystal 1 in the normal direction of the surface of the piezoelectric thin film was 90% or more.
The (001) plane of tetragonal crystal 2 was preferentially oriented in the normal direction of the surface of the piezoelectric thin film. The degree of orientation of the (001) plane of the tetragonal crystal 2 in the normal direction of the surface of the piezoelectric thin film was 90% or more.
C1 of Examples 2 to 6 and Comparative Examples 1 and 2 were the values shown in Table 1 below.
C2 of Examples 2 to 6 and Comparative Examples 1 and 2 were the values shown in Table 1 below.
C1 / a1 of Examples 2 to 6 and Comparative Examples 1 and 2 were the values shown in Table 1 below.
C2 / a2 of Examples 2 to 6 and Comparative Examples 1 and 2 were the values shown in Table 1 below.
_{I 2} / (I ₁ + I ₂ ) of Examples 2 to 6 and Comparative Examples 1 and 2 were the values shown in Table 1 below.
The values of Examples 2 to 6 and c2-c1 of Comparative Examples 1 and 2 were the values shown in Table 1 below.

The piezoelectricity of each of the piezoelectric thin films of Examples 2 to 6 and Comparative Examples 1 to 3 was evaluated by the same method as in Example 1.
Prs of Examples 2 to 6 and Comparative Examples 1 to 3 are shown in Table 1 below.
_{The ε r} of Examples 2 to 6 and Comparative Examples 1 to 3 are shown in Table 1 below.
_{-E 31, f} of Examples 2 to 6 and Comparative Examples 1 to 3 are shown in Table 1 below.
_{(-E 31, f} ) ² / ε ₀ ε _r of Examples 2 to 6 and Comparative Examples 1 to 3 are shown in Table 1 below.

(Comparative Example 4)
The oxygen partial pressure in the vacuum chamber in the process of forming the piezoelectric thin film of Comparative Example 4 was maintained at 0.1 Pa.

The piezoelectric thin film device of Comparative Example 4 was produced in the same manner as in Example 2 except that the oxygen partial pressure in the process of forming the piezoelectric thin film was removed.

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 is oriented in the normal direction of the surface of the first electrode layer, and the (200) plane of the Pt crystal is the second. It was oriented in the in-plane direction on the surface of the one electrode layer.

The composition of the piezoelectric thin 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 thin film was almost the same as the composition of the target.

The piezoelectric thin film of Comparative Example 4 based on the XRD method was analyzed by the same method as in Example 1. The piezoelectric thin film of Comparative Example 4 had the following characteristics.

The piezoelectric thin film consisted of a perovskite-type oxide.
In the case of Comparative Example 4, a single tetragonal crystal was detected as a tetragonal crystal of the perovskite type oxide. That is, the piezoelectric thin film of Comparative Example 4 did not contain two types of tetragonal crystals having different anisotropy (c / a). The single tetragonal crystal contained in the piezoelectric thin film of Comparative Example 4 is regarded as tetragonal crystal 1.
In the case of Comparative Example 4, the degree of orientation of the (001) plane of the tetragonal crystal 1 in the normal direction of the surface of the piezoelectric thin film was less than 50%. In the case of Comparative Example 4, none of the crystal planes of the tetragonal crystal 1 was preferentially oriented in the normal direction of the surface of the piezoelectric thin film.
C1 of Comparative Example 4 was a value shown in Table 2 below.
The values of c1 / a1 of Comparative Example 4 were the values shown in Table 2 below.
_{I 2} / (I ₁ + I ₂ ) of Comparative Example 4 was a value shown in Table 2 below.

The piezoelectricity of the piezoelectric thin film of Comparative Example 4 was evaluated by the same method as in Example 1.
Pr of Comparative Example 4 is shown in Table 2 below.
_{The ε r of} Comparative Example 4 is shown in Table 2 below.
_{-E 31, f} of Comparative Example 4 are shown in Table 2 below.
_{(-E 31, f} ) ² / ε ₀ ε _r of Comparative Example 4 is shown in Table 2 below.

(Examples 7 and 8)
In the case of Examples 7 and 8, the second intermediate layer was formed on the entire surface of the first electrode layer, and the piezoelectric thin film was formed on the entire surface of the second intermediate layer. The second intermediate layer of Example 7 consisted of crystalline SrRuO ₃ . The thickness of the second intermediate layer of Example 7 was 50 nm. The second intermediate layer of Example 8 consisted of crystalline LaNiO ₃ . The thickness of the second intermediate layer of Example 8 was 50 nm. “SRO” in Table 3 below means _{SrRuO 3.} “LNO” in Table 3 below means _{LaNiO 3.}

Piezoelectric thin film devices of Examples 7 and 8 were produced in the same manner as in Example 2 except that the second intermediate layer was formed.

The XRD pattern of the first electrode layer of each of Examples 7 and 8 was measured by the same method as in Example 1. In each of Examples 7 and 8, the (002) plane of the Pt crystal constituting the first electrode layer is oriented in the normal direction of the surface of the first electrode layer, and the (200) of the Pt crystal is oriented. ) Surface was oriented in the in-plane direction of the surface of the first electrode layer.

The compositions of the piezoelectric thin films of Examples 7 and 8 were analyzed by the same method as in Example 1. In each of Examples 7 and 8, the composition of the piezoelectric thin film was substantially the same as the composition of the target.

The piezoelectric thin films of Examples 7 and 8 based on the XRD method were analyzed by the same method as in Example 1. In each of Examples 7 and 8, the piezoelectric thin film had the following characteristics.

The piezoelectric thin film consisted of a perovskite-type oxide.
The piezoelectric thin film contained a perovskite-type oxide tetragonal crystal 1 and a perovskite-type oxide tetragonal crystal 2.
The (001) plane of tetragonal crystal 1 was preferentially oriented in the normal direction of the surface of the piezoelectric thin film. The degree of orientation of the (001) plane of tetragonal crystal 1 in the normal direction of the surface of the piezoelectric thin film was 90% or more.
The (001) plane of tetragonal crystal 2 was preferentially oriented in the normal direction of the surface of the piezoelectric thin film. The degree of orientation of the (001) plane of the tetragonal crystal 2 in the normal direction of the surface of the piezoelectric thin film was 90% or more.
C1 of each of Examples 7 and 8 was the value shown in Table 3 below.
C2 of each of Examples 7 and 8 was the value shown in Table 3 below.
C1 / a1 of Examples 7 and 8 were the values shown in Table 3 below.
The values of c2 / a2 in each of Examples 7 and 8 were the values shown in Table 3 below.
_{The I 2} / (I ₁ + I ₂ ) of Examples 7 and 8 were the values shown in Table 3 below.
The values of c2-c1 in each of Examples 7 and 8 were the values shown in Table 3 below.

The piezoelectricity of the piezoelectric thin films of Examples 7 and 8 was evaluated in the same manner as in Example 1.
The Prs of Examples 7 and 8 are shown in Table 3 below.
_{Ε r} of each of Examples 7 and 8 is shown in Table 3 below.
_{-E 31, f} of Examples 7 and 8 respectively are shown in Table 3 below.
_{(-E 31, f} ) ² / ε ₀ ε _r of Examples 7 and 8 respectively are shown in Table 3 below.

(Example 9)
In the process of manufacturing the piezoelectric thin film device of Example 9, the first intermediate layer was not formed. The production process of the piezoelectric thin-film element of Example 9, the first electrode layer made of SrRuO ₃ crystalline is formed directly on the entire surface of the single crystal substrate. The thickness of the first electrode layer of Example 9 was 200 nm. The piezoelectric thin film device of Example 9 was produced in the same manner as in Example 2 except for these matters.

The XRD pattern of the first electrode layer of Example 9 was measured by the same method 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 in the first electrode layer.

The composition of the piezoelectric thin film of Example 9 was analyzed by the same method as in Example 1. In the case of Example 9, the composition of the piezoelectric thin film was substantially the same as the composition of the target.

The piezoelectric thin film of Example 9 was analyzed based on the XRD method by the same method as in Example 1. The piezoelectric thin film of Example 9 had the following characteristics.

The piezoelectric thin film consisted of a perovskite-type oxide.
The piezoelectric thin film contained a perovskite-type oxide tetragonal crystal 1 and a perovskite-type oxide tetragonal crystal 2.
The (001) plane of tetragonal crystal 1 was preferentially oriented in the normal direction of the surface of the piezoelectric thin film. The degree of orientation of the (001) plane of tetragonal crystal 1 in the normal direction of the surface of the piezoelectric thin film was 90% or more.
The (001) plane of tetragonal crystal 2 was preferentially oriented in the normal direction of the surface of the piezoelectric thin film. The degree of orientation of the (001) plane of the tetragonal crystal 2 in the normal direction of the surface of the piezoelectric thin film was 90% or more.
C1 of Example 9 was the value shown in Table 4 below.
C2 of Example 9 was the value shown in Table 4 below.
C1 / a1 of Example 9 was the value shown in Table 4 below.
The values of c2 / a2 in Example 9 were the values shown in Table 4 below.
_{I 2} / (I ₁ + I ₂ ) of Example 9 was the value shown in Table 4 below.
The values of c2-c1 of Example 9 were the values shown in Table 4 below.

The piezoelectricity of the piezoelectric thin film of Example 9 was evaluated by the same method as in Example 1.
Pr of Example 9 is shown in Table 4 below.
The ε _r of Example 9 is shown in Table 4 below.
_{-E 31, f} of Example 9 are shown in Table 4 below.
_{(-E 31, f} ) ² / ε ₀ ε _r of Example 9 is shown in Table 4 below.

The piezoelectric thin film according to the present invention is applied to, for example, a piezoelectric transducer, a piezoelectric actuator, and a piezoelectric sensor.

10 ... Piezoelectric thin film element, 10a ... Ultrasonic transducer, 1 ... Single crystal substrate, 2 ... First electrode layer, 3 ... Piezoelectric thin film, 4 ... Second electrode layer, 5 ... First intermediate layer, 6 ... Second intermediate layer , _DN ... Normal direction of the surface of the single crystal substrate, dn ... Normal direction of the surface of the piezoelectric thin film, uc ... Unit cell of perovskite structure, uc1 ... Unit cell of tetragonal crystal 1, uc2 ... Unit cell of tetragonal crystal 2 ..

Claims (16)

A piezoelectric thin film containing an oxide having a perovskite structure.
The piezoelectric thin film contains a tetragonal crystal 1 of the oxide and a tetragonal crystal 2 of the oxide.
The (001) plane of the tetragonal crystal 1 is oriented in the normal direction of the surface of the piezoelectric thin film.
The (001) plane of the tetragonal crystal 2 is oriented in the normal direction of the surface of the piezoelectric thin film.
The distance between the (001) planes of the tetragonal crystal 1 is c1.
The distance between the (100) planes of the tetragonal crystal 1 is a1.
The distance between the (001) planes of the tetragonal crystal 2 is c2.
The distance between the (100) planes of the tetragonal crystal 2 is a2.
c2 / a2 is larger than c1 / a1
The peak intensity of the diffracted X-rays on the (001) plane of the tetragonal crystal 1 is I ₁ .
The peak intensity of the diffracted X-rays on the (001) plane of the tetragonal crystal 2 is I ₂ .
I ₂ / (I ₁ + I ₂ ) is 0.50 or more and 0.90 or less.
Piezoelectric thin film. c2-c1 is greater than 0.100 Å and less than 0.490 Å.
The piezoelectric thin film according to claim 1. c1 / a1 is 1.030 or more and 1.145 or less.
c2 / a2 is 1.085 or more and 1.195 or less.
The piezoelectric thin film according to claim 1 or 2. The oxide is represented by the following chemical formula 1.
E ^A in Formula 1 is, Na, at least one element selected from the group consisting of K and Ag,
^{E B} in Formula 1 is, Mg, Al, Ti, and at least one element selected from the group consisting of Ni and Zn,
X in the following chemical formula 1 is 0.30 or more and 0.80 or less.
Α in the following chemical formula 1 is 0.00 or more and less than 1.00.
The piezoelectric thin film according to any one of claims 1 to 3.
_{(1-x) Bi 1-} α E A α E B O 3 -xBiFeO 3 (1) It is an epitaxial film,
The piezoelectric thin film according to any one of claims 1 to 4. The piezoelectric thin film according to any one of claims 1 to 5 is provided.
Piezoelectric thin film element. Single crystal substrate and
The piezoelectric thin film that overlaps the single crystal substrate,
To prepare
The piezoelectric thin film device according to claim 6. Single crystal substrate and
The electrode layer that overlaps the single crystal substrate and
The piezoelectric thin film that overlaps the electrode layer and
To prepare
The piezoelectric thin film device according to claim 6. With the electrode layer
The piezoelectric thin film that overlaps the electrode layer and
To prepare
The piezoelectric thin film device according to claim 6. With a further first middle layer
The first intermediate layer is arranged between the single crystal substrate and the electrode layer.
The piezoelectric thin film device according to claim 8. The first intermediate layer contains ZrO ₂ and Y ₂ O ₃ .
The piezoelectric thin film device according to claim 10. With a second middle layer
The second intermediate layer is arranged between the electrode layer and the piezoelectric thin film.
The piezoelectric thin film device according to any one of claims 8 to 11. The second intermediate layer contains at least one of _{SrRuO 3} and LaNiO _3.
The piezoelectric thin film device according to claim 12. The electrode layer contains platinum crystals and contains.
The (002) plane of the platinum crystal is oriented in the normal direction of the surface of the electrode layer.
The (200) plane of the platinum crystal is oriented in the in-plane direction of the surface of the electrode layer.
The piezoelectric thin film device according to any one of claims 8 to 13. The piezoelectric thin film according to any one of claims 1 to 5 is provided.
Piezoelectric transducer. The piezoelectric thin film device according to any one of claims 6 to 14 is included.
Piezoelectric transducer.

Images