Piezoelectric thin film and piezoelectric thin film element

Abstract

To provide a piezoelectric thin film having excellent piezoelectric characteristics.SOLUTION: A piezoelectric thin film includes a plurality of crystal grains 3g containing aluminum nitride. The aluminum nitride contains an additional element. The additive element includes at least a divalent element Ed and a tetravalent element Et. The concentration of the divalent element Ed in a grain boundary 3b between a pair of adjacent crystal grains 3g is expressed as [Ed]b atomic %. The concentration of the divalent element Ed in one crystal grain 3g adjacent to the grain boundary 3b is expressed as [Ed]g atomic %. The [Ed]b / [Ed]g is 0.7 or more and 1.6 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Aluminum nitride (AlN) is a type of piezoelectric material. Patent Documents 1 and 2 listed below disclose that the piezoelectric properties of AlN can be improved by doping AlN with one or more additive elements having a valence of 2 to 5. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-015148 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-219743 Summary of the Invention [Problem to be solved by the invention]

[0004] Typically, a piezoelectric thin film containing AlN consists of multiple columnar AlN crystals extending parallel to the thickness direction of the piezoelectric thin film, and the grain boundaries formed between the multiple columnar crystals also extend parallel to the thickness direction. The higher the concentration of the additive element in the AlN, the more likely it is that some of the additive element will segregate to the grain boundaries. The additive element segregated to the grain boundaries becomes a path for leakage current, so the additive element segregated to the grain boundaries reduces the resistivity of the piezoelectric thin film in the direction in which the grain boundaries extend (thickness direction of the piezoelectric thin film). As a result, the piezoelectric properties of the piezoelectric thin film deteriorate. In other words, the higher the concentration of the additive element in the AlN, the more likely it is that the piezoelectric properties of the piezoelectric thin film will deteriorate.

[0005] An object of one aspect of the present disclosure is to provide a piezoelectric thin film having excellent piezoelectric properties, and a piezoelectric thin film element including the piezoelectric thin film. [Means for solving the problem]

[0006] For example, the present disclosure relates to a piezoelectric thin film according to any one of the following items [1] to

[11] , and a piezoelectric thin film element according to any one of the following items

[12] to

[15] .

[0007] [1] A material comprising a plurality of crystal grains containing aluminum nitride, The aluminum nitride contains an additive element, The additional element includes at least a divalent element and a tetravalent element, The concentration of the divalent element in the grain boundary between a pair of adjacent crystal grains is expressed as [Ed]b atomic %; The concentration of the divalent element in one of the crystal grains adjacent to the grain boundary is expressed as [Ed]g atomic %, [Ed]b / [Ed]g is 0.7 or more and 1.6 or less, Piezoelectric thin film.

[0008] [2] The piezoelectric thin film has a first main surface and a second main surface located on the back side of the first main surface, the grain boundary extends from the first main surface to the second main surface, a cross section of the piezoelectric thin film is perpendicular to the first principal surface and the second principal surface; The length of the grain boundary in the cross section is represented as L; The distance between the first major surface and the second major surface is represented as d; (Ld) / d is 1% or more and 20% or less, [1] The piezoelectric thin film according to [1].

[0009] [3] The piezoelectric thin film has a first main surface and a second main surface located on a back side of the first main surface, The peak intensity of the diffracted X-rays from the (10-10) plane of the aluminum nitride is I (10-10) is expressed as The peak intensity of the diffracted X-rays from the (10-11) plane of the aluminum nitride is I (10-11) is expressed as I (10-10) and the above I (10-11) is measured in an in-plane direction of the first principal surface or the second principal surface, I (10-11) / I (10-10) is between 1% and 10%. [1] The piezoelectric thin film according to [1].

[0010] [4] The piezoelectric thin film has a first main surface and a second main surface located on the back side of the first main surface, the grain boundary extends from the first main surface to the second main surface, a cross section of the piezoelectric thin film is perpendicular to the first principal surface and the second principal surface; The length of the grain boundary in the cross section is represented as L; The distance between the first major surface and the second major surface is represented as d; (Ld) / d is 1% or more and 20% or less, The peak intensity of the diffracted X-rays from the (10-10) plane of the aluminum nitride is I (10-10) is expressed as The peak intensity of the diffracted X-rays from the (10-11) plane of the aluminum nitride is I (10-11) is expressed as I (10-10) and the above I (10-11) is measured in an in-plane direction of the first principal surface or the second principal surface, I (10-11) / I (10-10) is between 1% and 10%. [1] The piezoelectric thin film according to [1].

[0011] [5] A piezoelectric thin film including a plurality of crystal grains containing aluminum nitride, The aluminum nitride contains an additive element, The additional element includes at least a divalent element and a tetravalent element, the piezoelectric thin film has a first main surface and a second main surface located on a back side of the first main surface, grain boundaries between the plurality of crystal grains extend from the first main surface to the second main surface; a cross section of the piezoelectric thin film is perpendicular to the first principal surface and the second principal surface; The length of the grain boundary in the cross section is represented as L; The distance between the first major surface and the second major surface is represented as d; (Ld) / d is 1% or more and 20% or less, Piezoelectric thin film.

[0012] [6] The peak intensity of the diffracted X-rays from the (10-10) plane of the aluminum nitride is I (10-10) is expressed as The peak intensity of the diffracted X-rays from the (10-11) plane of the aluminum nitride is I (10-11) is expressed as I (10-10) and the above I (10-11) is measured in an in-plane direction of the first principal surface or the second principal surface, I (10-11) / I (10-10) is between 1% and 10%. [5] The piezoelectric thin film according to [5].

[0013] [7] A piezoelectric thin film including a plurality of crystal grains containing aluminum nitride, The aluminum nitride contains an additive element, The additional element includes at least a divalent element and a tetravalent element, the piezoelectric thin film has a first main surface and a second main surface located on a back side of the first main surface, The peak intensity of the diffracted X-rays from the (10-10) plane of the aluminum nitride is I (10-10) is expressed as The peak intensity of the diffracted X-rays from the (10-11) plane of the aluminum nitride is I (10-11) is expressed as I (10-10) and the above I (10-11) is measured in an in-plane direction of the first principal surface or the second principal surface, I (10-11) / I (10-10) is 1% or more and 10% or less.

[0014] [8] At least a portion of the divalent element is magnesium; At least a portion of the tetravalent element is at least one of zirconium and hafnium. The piezoelectric thin film according to any one of [1] to [7].

[0015] [9] The concentration of the additive element in the piezoelectric thin film is 3 atomic % or more and 70 atomic % or less. The piezoelectric thin film according to any one of [1] to [8].

[0016]

[10] The concentration of the additive element in the piezoelectric thin film is 36 atomic % or more and 70 atomic % or less. The piezoelectric thin film according to any one of [1] to [8].

[0017]

[11] The concentration of the divalent element in the piezoelectric thin film is expressed as [Ed] atomic %; the concentration of the tetravalent element in the piezoelectric thin film is expressed as [Et] atomic %, [Ed] / ([Ed]+[Et]) is 0.3 or more and 0.6 or less, The piezoelectric thin film according to any one of [1] to

[10] .

[0018]

[12] The piezoelectric thin film according to any one of [1] to

[11] , an electrode layer; Including, The piezoelectric thin film directly or indirectly overlaps the surface of the electrode layer. Piezoelectric thin film element.

[0019]

[13] The electrode layer includes a plurality of metal particles; the aspect ratio of the plurality of metal grains on the surface of the electrode layer is 1.3 or more and 2.0 or less;

[12] The piezoelectric thin film element according to

[12] .

[0020]

[14] The composition of the electrode layer is represented by any one of the following chemical formulas e1, e2, e3, and e4:

[12] The piezoelectric thin film element according to

[12] . W 1-x V x (e1) [In the above chemical formula e1, 0.00 <x≦0.10] Mo 1-x Wx (e2) [In the above chemical formula e2, 0.65≦x<1.00] Mo 1-x Nb x (e3) [In the above chemical formula e3, 0.18≦x<0.30] W 1-x Cr x (e4) [In the above chemical formula e4, 0.00 <x<0.05]

[0021]

[15] The composition of the electrode layer is represented by any one of the following chemical formulas e1, e2, e3, and e4:

[13] The piezoelectric thin film element according to

[13] . W 1-x V x (e1) [In the above chemical formula e1, 0.00 <x≦0.10] Mo 1-x W x (e2) [In the above chemical formula e2, 0.65≦x<1.00] Mo 1-x Nb x (e3) [In the above chemical formula e3, 0.18≦x<0.30] W 1-x Cr x (e4) [In the above chemical formula e4, 0.00 <x<0.05] [Effects of the Invention]

[0022] According to one aspect of the present disclosure, there are provided a piezoelectric thin film having excellent piezoelectric properties, and a piezoelectric thin film element including the piezoelectric thin film. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic exploded perspective view of a piezoelectric thin film element according to one embodiment of the present invention. [Figure 2]FIG. 2 shows a specific example of a schematic cross section of the piezoelectric thin film element shown in FIG. 1, and the cross section shown in FIG. 2 is approximately or completely perpendicular to the first and second main surfaces of the piezoelectric thin film, and is approximately or completely parallel to the thickness direction of the piezoelectric thin film. [Figure 3] (a) in Figure 3 shows a specific example of a schematic cross section of the piezoelectric thin film element shown in Figure 1, and the cross section shown in (a) in Figure 3 is approximately or completely perpendicular to the first and second main surfaces of the piezoelectric thin film and approximately or completely parallel to the thickness direction of the piezoelectric thin film, and (b) in Figure 3 is a schematic diagram of grain boundaries in the cross section shown in (a) in Figure 3. [Figure 4] Figure 4 shows a specific example of a schematic cross section of the piezoelectric thin film element shown in Figure 1, and the cross section shown in Figure 4 is approximately or completely perpendicular to the first and second main surfaces of the piezoelectric thin film and approximately or completely parallel to the thickness direction of the piezoelectric thin film. [Figure 5] FIG. 5 is a perspective view of a unit cell of the crystalline structure (wurtzite structure) of aluminum nitride contained in the piezoelectric thin film. [Figure 6] (a) in Figure 6 is a perspective view of a unit cell showing the (0001) plane of aluminum nitride, (b) in Figure 6 is a perspective view of a unit cell showing the (10-11) plane of aluminum nitride, and (c) in Figure 6 is a perspective view of a unit cell showing the (10-10) plane of aluminum nitride. [Figure 7] (a) in Figure 7 is an image of the surface of the first electrode layer made of W0.9V0.1, where the surface shown in (a) in Figure 7 is parallel to the first main surface of the piezoelectric thin film in the piezoelectric thin film element, and (b) in Figure 7 is an enlarged view of a portion of the surface shown in (a) in Figure 7. [Figure 8] (a) in Figure 8 is an image of the surface of the first electrode layer consisting of W alone, and the surface shown in (a) in Figure 8 is parallel to the first main surface of the piezoelectric thin film in the piezoelectric thin film element.(b) in Figure 8 is an image of the surface of the first electrode layer consisting of V alone, and the surface shown in (b) in Figure 8 is parallel to the first main surface of the piezoelectric thin film in the piezoelectric thin film element. [Figure 9]FIG. 9 is an image of a piezoelectric thin film according to one embodiment of the present invention, and the cross section shown in FIG. 9 is perpendicular to the first main surface of the piezoelectric thin film and parallel to the thickness direction of the piezoelectric thin film. DETAILED DESCRIPTION OF THE INVENTION

[0024] Preferred embodiments of the present invention will be described below with reference to the drawings. In the drawings, equivalent components are designated by equivalent reference numerals. The present invention is not limited to the following embodiments. X, Y, and Z shown in Figures 1 to 4 and 7 to 9 represent three mutually orthogonal coordinate axes. The directions of the X-axis, Y-axis, and Z-axis are common to Figures 1 to 4 and 7 to 9.

[0025] As shown in FIG. 1, the piezoelectric thin film element 10 according to this embodiment includes at least a first electrode layer 1 (e.g., a lower electrode layer) and a piezoelectric thin film 3. The piezoelectric thin film element 10 may further include a second electrode layer 2 (e.g., an upper electrode layer). The piezoelectric thin film 3 has a first main surface s31 and a second main surface s32 located on the back side of the first main surface s31. The "main surface" refers to the surface with the largest area among multiple surfaces of a polyhedron (e.g., the piezoelectric thin film 3, which is a thin rectangular parallelepiped). The area of ​​the first main surface s31 may be approximately or completely equal to the area of ​​the second main surface s32. The shape of the first main surface s31 may be approximately or completely equal to the shape of the second main surface s32. The first main surface s31 of the piezoelectric thin film 3 may directly or indirectly overlap the surface s1 of the first electrode layer 1. The surface s2 of the second electrode layer 2 may directly or indirectly overlap the second main surface s32 of the piezoelectric thin film 3. 1 are substantially or completely parallel to the first main surface s31 of the piezoelectric thin film 3 and the surface s1 of the first electrode layer 1. The Z axis in FIG. 1 is substantially or completely perpendicular to the first main surface s31 of the piezoelectric thin film 3 and the surface s1 of the first electrode layer 1.

[0026] The piezoelectric thin film 3 according to this embodiment contains crystalline aluminum nitride. For example, the aluminum nitride contained in the piezoelectric thin film 3 may be polycrystalline or imperfectly crystalline. The crystal structure of the aluminum nitride is a wurtzite structure. The aluminum nitride contains an additive element. The additive element includes at least a divalent element Ed and a tetravalent element Et. The divalent element Ed may be rephrased as at least one of a Group 2 element and a Group 12 element. The tetravalent element Et may be rephrased as a Group 4 element. Doping the aluminum nitride with the divalent element Ed and the tetravalent element Et distorts the wurtzite structure of the aluminum nitride and changes the strength of the chemical bonds between atoms in the wurtzite structure. As a result, the wurtzite structure of the aluminum nitride is easily deformed when a voltage or external force is applied to the piezoelectric thin film 3, and the piezoelectric properties of the piezoelectric thin film 3 are easily improved. The piezoelectric thin film 3 may be composed solely of AlN containing the divalent element Ed and the tetravalent element Et. That is, the piezoelectric thin film 3 may be composed only of Al, N, the divalent element Ed, and the tetravalent element Et. As will be described later, the piezoelectric thin film 3 may further contain other elements in addition to Al, N, the divalent element Ed, and the tetravalent element Et.

[0027] The cross section of the piezoelectric thin film 3 shown in each of FIGS. 2 to 4 is approximately or completely perpendicular to the first main surface s31 and the second main surface s32 of the piezoelectric thin film 3. In other words, the cross section of the piezoelectric thin film 3 shown in each of FIGS. 2 to 4 is approximately or completely parallel to the thickness direction (Z-axis direction) of the piezoelectric thin film 3. As shown in FIGS. 2 and 3, the piezoelectric thin film 3 may include a plurality of crystal grains 3g containing aluminum nitride. Each of the plurality of crystal grains 3g may be composed only of aluminum nitride containing an additive element. Each of the plurality of crystal grains 3g may be single crystal, polycrystal, or imperfect crystal. Each of the plurality of crystal grains 3g may be a columnar crystal extending from the first main surface s31 to the second main surface s32. Some or all of the plurality of crystal grains 3g may extend from the first main surface s31 to the second main surface s32. The grain boundaries 3b between the plurality of crystal grains 3g extending from the first main surface s31 to the second main surface s32 may also extend from the first main surface s31 to the second main surface s32.

[0028] The concentration of the divalent element Ed in the grain boundary 3b between a pair of adjacent crystal grains 3g is expressed as [Ed]b atomic %. For example, as shown in Figure 2, [Ed]b may be the average value of the concentrations of the divalent element Ed measured at five measurement points p1 aligned on one grain boundary 3b extending from the first main surface s31 to the second main surface s32. The cross section on which [Ed]b is measured is approximately or completely perpendicular to the first main surface s31 and the second main surface s32. The concentration of the divalent element Ed in one crystal grain 3g adjacent to one of the grain boundaries 3b is expressed as [Ed]g atomic %. For example, as shown in Figure 2, [Ed]g may be the average value of the concentrations of the divalent element Ed measured at five measurement points p2 in one of a pair of crystal grains 3g adjacent to one grain boundary 3b where [Ed]b was measured. Naturally, the cross section where [Ed]g is measured is the same as the cross section where [Ed]b is measured. [Ed]b / [Ed]g may be 0.70 or more and 1.60 or less. For example, the average value of [Ed]b / [Ed]g measured in 50 measurement regions (50 pairs of grain boundaries 3b and crystal grains 3g) may be 0.70 or more and 1.60 or less. Since the piezoelectric thin film 3 contains an additive element to the extent that [Ed]b / [Ed]g is 0.70 or more, the piezoelectric characteristics of the piezoelectric thin film 3 are likely to be improved. By suppressing the segregation of the divalent element Ed at the grain boundaries 3b to the extent that [Ed]b / [Ed]g is 1.60 or less, the conductivity of each grain boundary 3b is suppressed, and the decrease in the resistivity ρ (unit: Ωcm) of the piezoelectric thin film 3 in the direction in which the grain boundaries 3b extend (thickness direction of the piezoelectric thin film 3) is suppressed. As a result, the deterioration of the piezoelectric characteristics of the piezoelectric thin film 3 is suppressed. Furthermore, when [Ed]b / [Ed]g is 0.70 or more and 1.60 or less, the durability of the piezoelectric thin film 3 is likely to be improved. For example, the durability of the piezoelectric thin film 3 means the property that cracks caused by continuous application of an AC voltage to the piezoelectric thin film 3 are less likely to form in the piezoelectric thin film 3. [Ed]b / [Ed]g may be 0.73 or more and 1.58 or less, because this makes it easy to suppress a decrease in resistivity ρ and to improve piezoelectric characteristics and durability. In this disclosure, any element is represented as "X." The ratio of element X to all elements in 3 g of crystal grains (unit: atomic %) is <x>g. In other words, the proportions of Al, N, the divalent element Ed, and the tetravalent element Et in all elements in the crystal grain 3g are as follows: <al> g、 <n> g、 <ed>g, and <et>g. [Ed] g is 100 × <ed> g / ( <al> g+ <ed> g+ <et>It may be equal to g). The ratio of element X to all elements in grain boundary 3b (unit: atomic %) is <x>b. In other words, the proportions of Al, N, the divalent element Ed, and the tetravalent element Et in all elements in the grain boundary 3b are as follows: <al> b、 <n> b、 <ed>b, and <et>It is expressed as b. [Ed]b is 100 × <ed> b / ( <al> b+ <ed> b+ <et>It may be equal to b). The ratio of element X to all elements in piezoelectric thin film 3 (unit: atomic %) is <x>That is, the proportions of Al, N, the divalent element Ed, and the tetravalent element Et in all elements in the piezoelectric thin film 3 are expressed as follows: <al> 、 <n> 、 <ed>, and <et>[Ed] is expressed as 100× <ed> / ( <al> + <ed> + <et>) can be equal to [Et]. <et> / ( <al> + <ed> + <et>) can be equal to

[0029] As shown in (a) of FIG. 3, the distance between the first principal surface s31 and the second principal surface s32 is represented as d. d may be the average value of the distance between the first principal surface s31 and the second principal surface s32. For example, d may be the average value of measurements taken at 50 locations. The distance between the first principal surface s31 and the second principal surface s32 may be referred to as the thickness of the piezoelectric thin film 3 (the width of the piezoelectric thin film 3 in the Z-axis direction). The distance d between the first principal surface s31 and the second principal surface s32 may be substantially or completely uniform. In other words, the first principal surface s31 may be substantially or completely parallel to the second principal surface s32. For example, d may be 100 nm or more and 30,000 nm or less.

[0030] As shown in (a) of FIG. 3, when the cross section of the piezoelectric thin film 3 is approximately or completely perpendicular to the first principal surface s31 and the second principal surface s32 of the piezoelectric thin film 3, each grain boundary 3b is observed as a line extending from the first principal surface s31 to the second principal surface s32 in the cross section of the piezoelectric thin film 3. The length of one grain boundary 3b extending from the first principal surface s31 to the second principal surface s32 in the cross section of the piezoelectric thin film 3 is represented by L. L may be the average value of the lengths of multiple grain boundaries 3b included in the cross section of the piezoelectric thin film 3. For example, L may be the average value of measurements taken at 10 locations. L may also be the average value of the lengths of multiple grain boundaries 3b observed as broken lines among the multiple grain boundaries 3b included in the cross section of the piezoelectric thin film 3. 3(b), when one grain boundary 3b (broken line) observed in the cross section of the piezoelectric thin film 3 is composed of three straight lines, and the lengths of the lines are expressed as L1, L2, and L3, the length L of one grain boundary 3b (broken line) is expressed as L1+L2+L3. However, the shape of the grain boundary 3b observed in the cross section of the piezoelectric thin film 3 is not limited to a broken line. For example, the shape of each of the multiple grain boundaries 3b observed in the cross section of the piezoelectric thin film 3 may be a broken line, a curve, or a straight line extending obliquely from the first main surface s31 toward the second main surface s32.

[0031] d and L may be measured using a scanning transmission electron microscope (STEM) in a cross section (a cross section substantially or completely perpendicular to the first principal surface s31 and the second principal surface s32) of the piezoelectric thin film 3. An image of the cross section of the piezoelectric thin film 3 may be taken by the STEM, and d and L may be measured by analyzing the image of the cross section using commercially available image analysis software.

[0032] (Ld) / d may be 1.0% or more and 20.0% or less. That is, {(Ld) / d}×100 may be 1.0 or more and 20.0 or less. For example, the units of L and d may be nm. When the additive element segregates at the grain boundary 3b, the grain boundary 3b extending from the first principal surface s31 to the second principal surface s32 can become a path for leakage current in a direction substantially or completely perpendicular to the first principal surface s31 and the second principal surface s32. As the length L of the grain boundary 3b decreases, the insulation resistance (unit: Ω) of the grain boundary 3b decreases. Therefore, when the length L of the grain boundary 3b extending from the first principal surface s31 to the second principal surface s32 is the shortest (i.e., when the length L of the grain boundary 3b matches the distance d between the first principal surface s31 and the second principal surface s32), the insulation resistance of the grain boundary 3b tends to be the smallest, and the leakage current tends to be the largest. However, if each grain boundary 3b extending from the first principal surface s31 to the second principal surface s32 is bent or inclined relative to the first principal surface s31 or the second principal surface s32, the length L of the grain boundary 3b becomes longer than the distance d between the first principal surface s31 and the second principal surface s32, and (Ld) / d becomes greater than zero. Furthermore, if (Ld) / d is 1.0% or greater, each grain boundary 3b extending from the first principal surface s31 to the second principal surface s32 is sufficiently long, and each grain boundary 3b is likely to have a sufficiently high insulation resistance. As a result, the resistivity ρ of the piezoelectric thin film 3 in a direction substantially or completely perpendicular to the first principal surface s31 and the second principal surface s32 is likely to increase, and the piezoelectric characteristics of the piezoelectric thin film 3 are likely to improve. Furthermore, if (Ld) / d is 1.0% or greater, the durability of the piezoelectric thin film 3 tends to improve. When (Ld) / d is 20.0% or less, the crystal structure (wurtzite structure) of aluminum nitride is unlikely to be excessively damaged, and the orientation of the lattice plane (e.g., the (0001) plane) of the wurtzite structure is unlikely to be excessively damaged, making it easier to maintain sufficient piezoelectric properties of the piezoelectric thin film 3. Because the resistivity ρ is likely to increase and the piezoelectric properties and durability are likely to improve, (Ld) / d may be 1.1% or more and 19.2% or less, or 10.0% or more and 19.2% or less.

[0033] The peak intensity of the diffracted X-rays from the (10-10) plane of aluminum nitride contained in the piezoelectric thin film 3 is I (10-10) The peak intensity of the diffracted X-rays from the (10-11) plane of aluminum nitride contained in the piezoelectric thin film 3 is expressed as follows: (10-11) For example, I (10-10) and I (10-11) Each unit may be an arbitrary unit. (10-10) and I (10-11) Each unit may be cps (counts per second). (10-10) and I (10-11) is measured in the in-plane direction of the first principal surface s31 or the second principal surface s32. That is, by irradiating the piezoelectric thin film 3 with incident X-rays in a direction substantially or completely parallel to the first principal surface s31 or the second principal surface s32, an X-ray diffraction (XRD) pattern including the peaks of the diffracted X-rays from the (10-10) plane and the (10-11) plane is measured. For example, I (10-10) and I (10-11) The incident X-rays used for the measurement may be CuKα rays. (10-11) / I (10-10) may be 1.0% or more and 10.0% or less. That is, (I (10-11) / I (10-10) ) × 100 may be 1.0 or greater and 10.0 or less. Below, we will explain the details of the crystal structure of aluminum nitride and the I (10-11) / I (10-10) The technical significance of this is explained.

[0034] 5 shows the crystal structure (hexagonal wurtzite structure) of aluminum nitride contained in the piezoelectric thin film 3. The unit cell uc of aluminum nitride (wurtzite structure) is a hexagonal column. Some of the aluminum (Al) in the unit cell uc may be substituted with a divalent element Ed or a tetravalent element Et.

[0035] The unit cell uc shown in Figures 6(a), 6(b), and 6(c) is identical to the unit cell uc shown in Figure 5. One of aluminum, a divalent element Ed, and a tetravalent element Et may be positioned at each of the 12 vertices of the unit cell uc (hexagonal prism) shown in Figures 6(a), 6(b), and 6(c). However, in order to show the primitive translational vectors and lattice planes of the unit cell uc, each element is omitted in Figures 6(a), 6(b), and 6(c). In the unit cell uc, a1, a2, a3, and c are primitive translational vectors (crystal axes) that constitute the unit cell uc. The orientation of a1 is [2-1-10]. The orientation of a2 is [-12-10]. The orientation of a3 is [-1-120]. The orientation of c is

[0001] . The lengths of a1, a2, and a3 may be approximately or exactly equal to each other. All of a1, a2, and a3 may be approximately or exactly perpendicular to c. The angle formed by a1, a2, and a3 with each other may be approximately or exactly 120°. Figure 6(a) shows the (0001) plane of aluminum nitride. Figure 6(b) shows the (10-11) plane of aluminum nitride. Figure 6(c) shows the (10-10) plane of aluminum nitride.

[0036] Aluminum nitride is polarized in a crystal orientation perpendicular to the (0001) plane (i.e.,

[0001] ). Therefore, by orienting at least a portion of the (0001) plane of aluminum nitride in the piezoelectric thin film 3 approximately or completely parallel to the first main surface s31 (surface s1 of the first electrode layer 1) of the piezoelectric thin film 3, the piezoelectric characteristics of the piezoelectric thin film 3 are likely to be improved. During the manufacturing process of the piezoelectric thin film 3, the (0001) plane of aluminum nitride is likely to be oriented parallel to the first main surface s31 (surface s1 of the first electrode layer 1) of the piezoelectric thin film 3. Because the (10-10) plane is perpendicular to the (0001) plane, the (10-10) plane is likely to be oriented perpendicular to the first principal surface s31 and the second principal surface s32 of the piezoelectric thin film 3. Therefore, incident X-rays irradiated onto the piezoelectric thin film 3 in the in-plane direction of the first principal surface s31 or the second principal surface s32 are likely to be diffracted by the (10-10) plane. In other words, diffracted X-rays from the (10-10) plane are likely to be detected in the in-plane direction. On the other hand, because the (10-11) plane is inclined with respect to the (10-10) plane, the (10-11) plane is also inclined with respect to the first principal surface s31 and the second principal surface s32 of the piezoelectric thin film 3. Therefore, when all the (10-10) planes in the piezoelectric thin film 3 are perpendicular to the first principal surface s31 and the second principal surface s32 (in other words, when all the (0001) planes in the piezoelectric thin film 3 are parallel to the first principal surface s31 and the second principal surface s32), the diffracted X-rays from the (10-11) plane are difficult to detect in the in-plane direction of the first principal surface s31 or the second principal surface s32. Positive I (10-11) / I (10-10) means that some of the crystal grains 3g are tilted relative to the other crystal grains 3g, and the (10-11) plane in the tilted crystal grains 3g is approximately or completely perpendicular to the first principal surface s31 or the second principal surface s32. In other words, a positive value I (10-11) / I (10-10) means that some (0001) planes in the piezoelectric thin film 3 are inclined with respect to the first principal surface s31 and the second principal surface s32, as shown in FIG. 4. As the number of inclined crystal grains 3g increases, I (10-11) / I (10-10) The tilted crystal grains 3g function as a barrier that suppresses leakage current between the first main surface s31 and the second main surface s32. In other words, the tilted crystal grains 3g function as a barrier that suppresses leakage current at the grain boundary 3b where the additive element is segregated. I (10-11) / I (10-10) When I is 1.0% or more, the resistivity ρ of the piezoelectric thin film 3 is likely to increase due to the above-mentioned function of the tilted crystal grains 3g, and the piezoelectric properties of the piezoelectric thin film 3 are likely to improve. (10-11) / I (10-10) When the value of I is 1.0% or more, the durability of the piezoelectric thin film 3 tends to be improved. (10-11) / I (10-10) When the ratio is 10.0% or less, the crystal structure (wurtzite structure) of aluminum nitride is unlikely to be excessively damaged, the orientation of the lattice plane (e.g., the (0001) plane) of the wurtzite structure is unlikely to be excessively damaged, and sufficient piezoelectric properties of the piezoelectric thin film 3 are likely to be maintained. The resistivity ρ is easily increased, and the piezoelectric properties and durability are easily improved. (10-11) / I (10-10) may be 1.0% or more and 9.2% or less, or 1.0% or more and 7.0% or less.

[0037] The divalent element Ed contained in the aluminum nitride may be at least one element selected from the group consisting of magnesium (Mg), calcium (Ca), zinc (Zn), strontium (Sr), and barium (Ba). The tetravalent element Et contained in the aluminum nitride may be at least one element selected from the group consisting of zirconium (Zr), germanium (Ge), titanium (Ti), and hafnium (Hf). At least a portion of the divalent element Ed may be magnesium, and at least a portion of the tetravalent element Et may be at least one of zirconium and hafnium, because this tends to increase the resistivity ρ and improve the piezoelectric properties and durability.

[0038] The concentration (total concentration) of all divalent elements Ed in the piezoelectric thin film 3 is expressed as [Ed] atomic %. For example, [Ed] may be 1.4 atomic % or more and 34 atomic % or less. The concentration (total concentration) of all tetravalent elements Et in the piezoelectric thin film 3 is expressed as [Et] atomic %. For example, [Et] may be 1.4 atomic % or more and 35 atomic % or less. The concentration of the additional element may be rephrased as the doping amount of the additional element. The concentration (total concentration) of the additive elements in the piezoelectric thin film 3 may be 3.0 atomic % to 70.0 atomic %, 36.0 atomic % to 70.0 atomic %, or 2.8 atomic % to 69.0 atomic % because the resistivity ρ is likely to increase and the piezoelectric characteristics and durability are likely to improve. In other words, [Ed] + [Et] may be 3.0 atomic % to 70.0 atomic %, 36.0 atomic % to 70.0 atomic %, or 2.8 atomic % to 69.0 atomic %. [Ed] / ([Ed]+[Et]) may be 0.3 or more and 0.6 or less, because the resistivity ρ is likely to increase and the piezoelectric properties and durability are likely to improve.

[0039] The aluminum nitride contained in the piezoelectric thin film 3 may further contain at least one element selected from the group consisting of a monovalent element, a trivalent element, and a pentavalent element. The monovalent element may be at least one element selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). The trivalent element may be at least one element selected from the group consisting of scandium (Sc), yttrium (Y), lanthanides, and indium (In). The pentavalent element may be at least one element selected from the group consisting of chromium (Cr), vanadium (V), niobium (Nb), and tantalum (Ta). The aluminum nitride contained in the piezoelectric thin film 3 may further contain other elements such as oxygen (O) and argon (Ar).

[0040] 7(a) is an image of the surface s1 of the first electrode layer 1. The surface s1 shown in FIG. 7(a) is parallel to the first main surface s31 of the piezoelectric thin film 3 in the piezoelectric thin film element 10. FIG. 7(b) is an enlarged view of a portion of the surface s1 shown in FIG. 7(a). As shown in FIGS. 7(a) and 7(b), the first electrode layer 1 may include a plurality of metal grains 1g. As shown in (b) of Figure 7, the major axis of one metal grain 1g in a direction parallel to the surface s1 of the first electrode layer 1 is represented as LD. The minor axis of one metal grain 1g in a direction parallel to the surface s1 of the first electrode layer 1 is represented as SD. The aspect ratio of one metal grain 1g is represented as LD / SD. LD may be rephrased as the length of the major axis of the metal grain 1g. LD may be rephrased as the maximum distance between two points located on the outline of the metal grain 1g. SD may be rephrased as the length of the minor axis of the metal grain 1g. SD may be rephrased as the distance between a pair of lines that are perpendicular to the major axis of the metal grain 1g and tangent to the metal grain 1g. For example, the metal particle 1g may have a major diameter LD of 15 nm or more and a minor diameter SD of 10 nm or more and a minor diameter SD of 150 nm or less. The aspect ratio LD / SD of the plurality of metal grains 1g on the surface s1 of the first electrode layer 1 may be 1.30 or more and 2.00 or less. For example, the average aspect ratio LD / SD of the plurality of metal grains 1g on the surface s1 of the first electrode layer 1 may be 1.30 or more and 2.00 or less. For example, the average aspect ratio LD / SD of 50 metal grains 1g may be 1.30 or more and 2.00 or less. When the aspect ratio LD / SD is 1.30 or more and 2.00 or less, stress distribution in the piezoelectric thin film 3 is likely to occur when the piezoelectric thin film 3 is directly grown on the surface s1 of the first electrode layer 1 by sputtering and then rapidly cooled. In other words, when the aspect ratio LD / SD is 1.30 or more and 2.00 or less, stress generated in the piezoelectric thin film 3, which is rapidly cooled immediately after growth, is likely to be non-uniform. Due to non-uniform stress, the grain boundaries 3b extending from the surface s1 of the first electrode layer 1 (the first main surface s31 of the piezoelectric thin film 3) to the second main surface s32 of the piezoelectric thin film 3 tend to be inclined in a complex manner with respect to the surface s1 of the first electrode layer 1 (the first main surface s31 of the piezoelectric thin film 3). As a result, the total area (or volume) of the grain boundaries 3b formed in the piezoelectric thin film 3 tends to increase. As the total area (or volume) of the grain boundaries 3b increases, the concentration [Ed]b of the divalent element Ed in the grain boundaries 3b decreases appropriately, and [Ed]b / [Ed]g is easily controlled to be 0.7 or more and 1.6 or less. For the same reason, the shape of each of the multiple metal grains 1g observed on the surface s1 of the first electrode layer 1 may be elliptical. For the same reason, the aspect ratio LD / SD of the multiple metal grains 1g on the surface s1 of the first electrode layer 1 may be 1.31 or more and 1.62 or less. As the aspect ratio LD / SD increases, [Ed]b / [Ed]g tends to decrease. I (10-11) / I (10-10) Since the aspect ratio of the plurality of metal grains 1g on the surface s1 of the first electrode layer 1 can be easily controlled to be 1.0% or more and 10.0% or less, the aspect ratio of the plurality of metal grains 1g on the surface s1 of the first electrode layer 1 may be 1.55 or more and 1.62 or less.

[0041] The images shown in (a) and (b) of Figure 7 may be taken with an atomic force microscope (AFM). The aspect ratio LD / SD may be measured using an atomic force microscope (AFM). The aspect ratio LD / SD may be measured by analyzing an image of the surface s1 of the first electrode layer 1 with commercially available image analysis software (for example, Mac-View manufactured by Mountech Co., Ltd.).

[0042] The composition of the first electrode layer 1 may be represented by any one of the following chemical formulas: e1, e2, e3, and e4. That is, the first electrode layer 1 may contain an alloy represented by any one of the following chemical formulas: e1, e2, e3, and e4. The unit of x in each chemical formula is a molar ratio. When the composition of the first electrode layer 1 is represented by any one of the following chemical formulas: e1, e2, e3, and e4, the aspect ratio LD / SD is easily controlled to be 1.30 or more and 2.00 or less. W 1-x V x (e1) [In the above chemical formula e1, 0.00 <x≦0.10] Mo 1-x W x (e2) [In the above chemical formula e2, 0.65≦x<1.00] Mo 1-x Nb x (e3) [In the above chemical formula e3, 0.18≦x<0.30] W 1-x Cr x (e4) [In the above chemical formula e4, 0.00 <x<0.05]

[0043] The composition of the first electrode layer 1 is not limited to the above-described chemical formula. For example, the first electrode layer 1 may contain at least one element selected from the group consisting of platinum (Pt), iridium (Ir), gold (Au), rhodium (Rh), palladium (Pd), silver (Ag), nickel (Ni), copper (Cu), aluminum (Al), molybdenum (Mo), tungsten (W), vanadium (V), chromium (Cr), niobium (Nb), tantalum (Ta), ruthenium (Ru), zirconium (Zr), hafnium (Hf), titanium (Ti), yttrium (Y), scandium (Sc), and magnesium (Mg). The first electrode layer 1 may be a metal or an alloy.

[0044] The second electrode layer 2 may contain at least one element selected from the group consisting of Pt, Ir, Au, Rh, Pd, Ag, Ni, Cu, Al, Mo, W, V, Cr, Nb, Ta, Ru, Zr, Hf, Ti, Y, Sc, and Mg. The second electrode layer 2 may be a metal element or an alloy. The composition of the second electrode layer 2 may be the same as the composition of the first electrode layer 1. The composition of the second electrode layer 2 may be different from the composition of the first electrode layer 1.

[0045] The piezoelectric thin film element 10 may further include a substrate. The first electrode layer 1 may directly or indirectly overlap the substrate. The piezoelectric thin film element 10 may further include an adhesion layer. The adhesion layer may be interposed between the substrate and the first electrode layer 1. In other words, the first electrode layer 1 may indirectly overlap the substrate via the adhesion layer.

[0046] For example, the substrate may be a semiconductor substrate (such as a silicon substrate or a gallium arsenide substrate), an optical crystal substrate (such as a sapphire substrate), an insulator substrate (such as a glass substrate or a ceramic substrate), a metal substrate (such as a stainless steel plate), or an SOI (Silicon-on-Insulator) substrate. The substrate may be crystalline. For example, the substrate may be single crystal or polycrystalline.

[0047] For example, the adhesion layer may contain at least one element selected from the group consisting of aluminum (Al), silicon (Si), titanium (Ti), zinc (Zn), yttrium (Y), zirconium (Zr), chromium (Cr), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), platinum (Pt), and ruthenium (Ru). The adhesion layer may be a metal element, an alloy, or a compound (such as an oxide or nitride). The adhesion layer may be another piezoelectric thin film (e.g., aluminum nitride), a polymer, or a ceramic. The adhesion layer has the function of suppressing peeling of the first electrode layer due to mechanical impact, etc. The adhesion layer may also be referred to as an interface layer, a support layer, a buffer layer, or an intermediate layer.

[0048] For example, the thickness of the substrate may be 50 μm or more and 10,000 μm or less. For example, the thickness of the adhesion layer may be 0.003 μm or more and 2 μm or less. For example, the thickness of the first electrode layer 1 may be 0.01 μm or more and 1 μm or less. For example, the thickness of the piezoelectric thin film 3 may be 100 nm or more and 30,000 nm or less. For example, the thickness of the second electrode layer 2 may be 0.01 μm or more and 1 μm or less. The thickness of the first electrode layer 1 (the width of the first electrode layer 1 in the Z-axis direction) may be approximately or completely uniform. The thickness of the second electrode layer 2 (the width of the second electrode layer 2 in the Z-axis direction) may also be approximately or completely uniform. The thicknesses of the substrate and the adhesion layer may also be approximately or completely uniform.

[0049] The crystal structures of the substrate, adhesion layer, first electrode layer, piezoelectric thin film, and second electrode layer may be determined by X-ray diffraction or electron diffraction. The compositions of the substrate, adhesion layer, first electrode layer, piezoelectric thin film, and second electrode layer may be determined by at least one analytical method including X-ray fluorescence spectroscopy (XRF), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and electron probe microanalyzer (EPMA). The thicknesses of the substrate, adhesion layer, first electrode layer, piezoelectric thin film, and second electrode layer may be measured in a cross section of the piezoelectric thin film element 10 parallel to the stacking direction (Z-axis direction) using a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), or a scanning electron microscope (SEM).

[0050] The adhesion layer, first electrode layer, piezoelectric thin film, and second electrode layer may be sequentially deposited on the surface of the substrate by a vapor deposition method such as sputtering. In particular, the piezoelectric thin film may be formed by RF (Radio Frequency) magnetron sputtering. The adhesion layer, first electrode layer, piezoelectric thin film, and second electrode layer may be formed by sputtering using at least one target. The adhesion layer, first electrode layer, piezoelectric thin film, and second electrode layer may be formed by sputtering using multiple targets with different compositions. The target may contain at least one element from among the elements constituting each layer or piezoelectric thin film. The composition of the adhesion layer, first electrode layer, piezoelectric thin film, and second electrode layer can be controlled to the desired composition by selecting and combining targets with predetermined compositions. For example, the target may be an elemental metal, an alloy, or an oxide. For example, the piezoelectric thin film may be formed using a target made of aluminum, a target made of a divalent element, and a target made of a tetravalent element. The target may be one or more alloys made of two or more elements selected from the group consisting of aluminum, divalent elements, and tetravalent elements. For example, if the first electrode layer contains an alloy, it may be formed from multiple targets containing each of the elements constituting the alloy. If the first electrode layer contains an alloy, it may be formed from a single target made of the same alloy as the alloy contained in the first electrode layer. The composition of the sputtering atmosphere may be a controlling factor for the composition of each of the adhesion layer, first electrode layer, piezoelectric thin film, and second electrode layer. For example, nitrogen gas is a raw material for the piezoelectric thin film (aluminum nitride). The input power (power density) applied to the cathode on which each target is placed may be a controlling factor for the composition and thickness of each of the adhesion layer, first electrode layer, piezoelectric thin film, and second electrode layer. The total pressure of the sputtering atmosphere, the partial pressure or concentration of the raw material gas in the atmosphere, the duration of sputtering of each target, the temperature of the substrate surface, and the substrate bias may also be controlling factors for the composition and thickness of each of the adhesion layer, first electrode layer, piezoelectric thin film, and second electrode layer. A piezoelectric thin film having a desired shape or pattern may be formed by etching (e.g., plasma etching).

[0051] The piezoelectric thin film and piezoelectric thin film element are fabricated using a vacuum apparatus. The vacuum apparatus includes at least a deposition chamber, a transfer chamber, and a buffer chamber. The deposition chamber and buffer chamber are connected to the transfer chamber. The adhesion layer, first electrode layer, piezoelectric thin film, and second electrode layer are each formed in the deposition chamber. The piezoelectric thin film is grown on the surface of the first electrode layer deposited on the substrate by RF magnetron sputtering in the deposition chamber. During RF magnetron sputtering, the substrate placed on a heating unit (heater) in the deposition chamber is continuously heated to a predetermined temperature (e.g., 300°C) by the heating unit. Immediately after the growth of the piezoelectric thin film is completed (immediately after the RF magnetron sputtering is completed), the substrate on which the piezoelectric thin film is deposited is removed from the heating unit and quickly transferred from the deposition chamber to the buffer chamber via the transfer chamber. Nitrogen gas (N2) is supplied to the buffer chamber containing the substrate, and the piezoelectric thin film deposited on the substrate is rapidly cooled in the buffer chamber. For example, the cooling rate of the piezoelectric thin film from the time when the substrate on which the piezoelectric thin film is laminated is removed from the heating unit to the time when the temperature of the piezoelectric thin film in the buffer chamber reaches 30°C may be 50°C / min or more and 150°C / min or less. For example, the cooling rate of the piezoelectric thin film may be controlled based on the flow rate and temperature of nitrogen gas supplied into the buffer chamber. As the flow rate of the nitrogen gas increases, the cooling rate of the piezoelectric thin film increases. As the temperature of the nitrogen gas decreases, the cooling rate of the piezoelectric thin film increases. Rapid cooling of the piezoelectric thin film at the above cooling rate adequately suppresses segregation of the additive elements at the grain boundaries in the piezoelectric thin film. Furthermore, rapid cooling of the piezoelectric thin film is likely to cause stress distribution in the piezoelectric thin film. In other words, the stress generated in the piezoelectric thin film, which is rapidly cooled immediately after growth, is likely to be non-uniform. Due to the non-uniform stress, the grain boundaries extending from the surface of the first electrode layer (first main surface of the piezoelectric thin film) to the second main surface of the piezoelectric thin film are likely to be inclined in a complex manner relative to the surface of the first electrode layer (first main surface of the piezoelectric thin film). In other words, rapid cooling of the piezoelectric thin film at the above cooling rate makes it easy for some of the multiple crystal grains extending from the first main surface to the second main surface in the piezoelectric thin film to be inclined relative to the surface (first main surface) of the first electrode layer. As a result, (Ld) / d is easily controlled to be 1.0% or more and 20.0% or less, and I (10-11) / I (10-10) is easily controlled to 1.0% or more and 10.0% or less. Furthermore, the grain boundaries extending from the surface of the first electrode layer (the first principal surface of the piezoelectric thin film) to the second principal surface of the piezoelectric thin film are inclined in a complex manner relative to the surface of the first electrode layer (the first principal surface of the piezoelectric thin film), which tends to increase the total area (or volume) of the grain boundaries formed in the piezoelectric thin film. As the total area (or volume) of the grain boundaries increases, the concentration [Ed]b of the divalent element Ed in the grain boundaries decreases appropriately, and [Ed]b / [Ed]g is easily controlled to be 0.7 or more and 1.6 or less. As the cooling rate of the piezoelectric film increases, [Ed]b / [Ed]g tends to decrease. In particular, I (10-11) / I (10-10) Since the temperature dependence of the piezoelectric thin film on the surface of the first electrode layer is easily controlled to be 1.0% or more and 10.0% or less, the piezoelectric thin film may be formed directly on the surface of the first electrode layer containing the alloy represented by the above chemical formula, and the cooling rate of the piezoelectric thin film may be 100°C / min or more and 150°C / min or less.

[0052] The piezoelectric thin film element according to this embodiment has a wide range of applications. For example, the piezoelectric thin film element may be a piezoelectric microphone, a harvester, an oscillator, a resonator, an acoustic multilayer, or a filter. For example, the piezoelectric thin film element may be a piezoelectric actuator. The piezoelectric actuator may be used in haptics. That is, the piezoelectric actuator may be used in various devices requiring cutaneous (tactile) feedback. For example, devices requiring cutaneous feedback may be wearable devices, touchpads, displays, or game controllers. For example, the piezoelectric actuator may be used in a head assembly, a head stack assembly, or a hard disk drive. For example, the piezoelectric actuator may be used in a printer head or an inkjet printer device. The piezoelectric actuator may be used in a piezoelectric switch. For example, the piezoelectric thin film element may be a piezoelectric sensor or a piezoelectric transducer. For example, the piezoelectric sensor or the piezoelectric transducer may be used in a gyro sensor, a pressure sensor, a pulse wave sensor, an ultrasonic sensor, an ultrasonic transducer, or a shock sensor. The ultrasonic transducer may be a piezoelectric micromachined ultrasonic transducer (PMUT). Products applying the piezoelectric micromachined ultrasonic transducer may be biometric sensors such as fingerprint sensors and ultrasonic blood vessel authentication sensors, medical or healthcare sensors, or ToF (Time of Flight) sensors. For example, the filter may be a Bulk Acoustic Wave (BAW) filter or a Surface Acoustic Wave (SAW) filter. Each of the above-mentioned piezoelectric thin film elements may be a part or the whole of a Micro Electro Mechanical System (MEMS).

[0053] The present invention is not necessarily limited to the above-described embodiments. Various modifications of the present invention are possible without departing from the spirit of the present invention, and these modifications are also included in the present invention. [Example]

[0054] The present invention will be described in detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples.

[0055] Example 1 A wafer made of single crystal silicon (Si) was used as the substrate. The (100) plane of the silicon was parallel to the main surface of the substrate. The diameter of the substrate was 8 inches, and the thickness of the substrate was 725 μm. The thickness of the substrate was uniform.

[0056] An adhesion layer was formed directly on the entire main surface of the substrate by RF magnetron sputtering in a deposition chamber. The adhesion layer was made of aluminum nitride containing no additive elements. Al was used as the sputtering target. The atmosphere in the deposition chamber was a mixed gas of Ar and N2. The input power per unit area of ​​the sputtering target was 0.74 W / cm2. 2 The temperature of the substrate during the formation of the adhesion layer was maintained at 300°C. The substrate bias was 30 W. The thickness of the adhesion layer was uniform. The thickness of the adhesion layer was adjusted to 30 nm.

[0057] A first electrode layer made of W was formed on the entire surface of the adhesive layer by RF magnetron sputtering in the deposition chamber. W alone was used as the sputtering target. The atmosphere in the deposition chamber was Ar gas. The input power per unit area of ​​the sputtering target was 0.93 W / cm. 2 The temperatures of the substrate and adhesive layer during the formation of the first electrode layer were maintained at 300°C. The thickness of the first electrode layer was uniform. The thickness of the first electrode layer was adjusted to 0.2 µm.

[0058] A piezoelectric thin film was formed directly on the entire surface of the first electrode layer by RF magnetron sputtering in a deposition chamber and a rapid cooling process following the RF magnetron sputtering. An alloy consisting of Al and Mg and an alloy consisting of Al and Hf were used as sputtering targets. Specifically, the divalent element Ed used as the raw material for the piezoelectric thin film was Mg, and the tetravalent element Et used as the raw material for the piezoelectric thin film was Hf. The atmosphere in the deposition chamber was a mixed gas of Ar and N2. The thickness of the piezoelectric thin film was approximately uniform. The thickness of the piezoelectric thin film was 1 μm (1000 nm). During the RF magnetron sputtering, the temperatures of the substrate, adhesion layer, and first electrode layer were maintained at 300°C. The cooling rate CR of the piezoelectric thin film during the rapid cooling process was 150°C / min. The details of the rapid cooling process were as described in the above embodiment.

[0059] A second electrode layer made of W was formed on the entire second main surface of the piezoelectric thin film in the same manner as the first electrode layer, i.e., the composition of the second electrode layer was the same as the composition of the first electrode layer.

[0060] The laminated structure formed on the substrate was patterned by photolithography, and after patterning, the entire laminate was cut by dicing to obtain rectangular piezoelectric thin film elements.

[0061] The piezoelectric thin film element of Example 1 was composed of a substrate, an adhesive layer laminated directly on the surface of the substrate, a first electrode layer laminated directly on the surface of the adhesive layer, a piezoelectric thin film laminated directly on the surface of the first electrode layer, and a second electrode layer laminated directly on the surface (second main surface) of the piezoelectric thin film.

[0062] The following analyses and measurements were carried out during or after the fabrication of the piezoelectric thin film elements: A plurality of identical piezoelectric thin film elements were fabricated as samples for the following analyses and measurements.

[0063] <Aspect ratio measurement> Before forming the piezoelectric thin film, the surface of the first electrode layer was analyzed by atomic force microscopy (AFM), using a Park XE-HDD manufactured by Park Systems Corporation. An image of the surface of the first electrode layer taken by AFM is shown in (a) of FIG. 8. The dimensions of the measurement area shown in (a) of FIG. 8 were 1000 nm long x 1000 nm wide. As shown in (a) of FIG. 8, a plurality of metal particles were exposed on the surface of the first electrode layer. The average value of the aspect ratio LD / SD of 1 g of 50 metal particles exposed on the surface of the first electrode layer was measured using AFM. The average value of the aspect ratio LD / SD of Example 1 is shown in Table 1 below. Details of the method for measuring the aspect ratio LD / SD were the same as those in the above embodiment.

[0064] <Analysis of composition> The compositions of the first electrode layer and the piezoelectric thin film were analyzed by X-ray fluorescence analysis (XRF). A wavelength dispersive X-ray fluorescence spectrometer (AZX-400) manufactured by Rigaku Corporation was used for the XRF analysis. The composition of the piezoelectric thin film was calculated by the fundamental parameter method (FP method) based on the analytical values ​​of the composition of the entire stack consisting of only the substrate, adhesive layer, and first electrode layer, and the fluorescent X-ray spectrum.

[0065] The piezoelectric thin film of Example 1 was made of aluminum nitride containing Mg as Ed and Hf as Et. The concentration [Ed] of the divalent element Ed in the piezoelectric thin film and the concentration [Et] of the tetravalent element Et in the piezoelectric thin film are shown in Table 1 below. [Ed] / ([Ed]+[Et]) is shown in Table 2 below.

[0066] <Cross-section analysis of piezoelectric thin film> The cross section of the piezoelectric thin film was analyzed by scanning transmission electron microscope (STEM). A Titan G2 manufactured by Thermo Fisher Scientific Inc. (formerly FEI company) was used as the STEM. The cross section analyzed by STEM was perpendicular to the first main surface (the surface of the first electrode layer) of the piezoelectric thin film. The cross section of the piezoelectric thin film contained a plurality of crystal grains. Each crystal grain was a columnar crystal extending from the first main surface (the surface of the first electrode layer) of the piezoelectric thin film to the second main surface. The cross section of the piezoelectric thin film also contained a plurality of grain boundaries extending from the first main surface to the second main surface. The distance d between the first and second principal surfaces (thickness of the piezoelectric thin film) was measured at 50 points in the cross section. The average value of the distance d measured at the 50 points is shown in Table 1 below. The length L of one grain boundary extending from the first main surface to the second main surface was measured at 10 points in the cross section. The average value of the length L of the grain boundary measured at 10 points is shown in Table 1 below. The details of the method for measuring the average values ​​of the distance d and the length L are the same as those in the above embodiment. (Ld) / d calculated from the average values ​​of the distance d and the length L is shown in Table 2 below.

[0067] The average value of [Ed]b / [Ed]g was measured for the cross section analyzed by STEM. The average values ​​of [Ed]b / [Ed]g were measured using energy dispersive spectroscopy (EDS) attached to the STEM. The definitions of [Ed]b and [Ed]g are as in the above embodiment. The details of the method for measuring the average value of [Ed]b / [Ed]g were as in the above embodiment. The average values ​​of [Ed]b / [Ed]g for Example 1 are shown in Table 2 below.

[0068] <Crystal structure analysis> The crystal structures of the first electrode layer and the piezoelectric thin film were analyzed by the following X-ray diffraction (XRD) method, using a multipurpose X-ray diffractometer (SmartLab) manufactured by Rigaku Corporation.

[0069] 2θ-θ scans and 2θχ-φ scans were performed on the surface of the piezoelectric thin film. The 2θ-θ scans were performed in the out-of-plane direction of the second major surface of the piezoelectric thin film. The 2θχ-φ scans were performed in the in-plane direction of the second major surface of the piezoelectric thin film.

[0070] XRD analysis revealed that the piezoelectric thin film had a wurtzite structure. The X-ray diffraction pattern measured by 2θ-θ scanning included a peak derived from the (0001) plane of the wurtzite structure. This means that at least a portion of the (0001) plane of the aluminum nitride contained in the piezoelectric thin film was parallel to the first and second principal surfaces of the piezoelectric thin film. XRD analysis revealed that the first electrode layer had a body-centered cubic structure, with the (110) plane parallel to the surface of the first electrode layer (the first main surface of the piezoelectric thin film).

[0071] From the X-ray diffraction pattern measured by 2θχ-φ scan, I (10-11) / I (10-10) was calculated. I (10-11) and I (10-10) The definitions of each are as in the above embodiment. (10-11) / I (10-10) are shown in Table 2 below.

[0072] <piezoelectric constant d 33 Measurement of Piezoelectric constant d of the piezoelectric thin film 33 (unit: pC / N) was measured. 33 The details of the measurement are as follows: The piezoelectric constant d was measured at three points. 33 The average values ​​of d are shown in Table 2 below. 33 means excellent piezoelectric properties. Measurement equipment: Piezotest 33 Meter (PM200) Frequency: 110Hz Clamping pressure: 0.25N

[0073] <Measurement of resistivity ρ> The resistivity ρ (unit: Ωcm) of the piezoelectric thin film was measured in the thickness direction (direction perpendicular to the first and second principal surfaces) of the piezoelectric thin film. A measuring device (R8340A) manufactured by ADVANTEST Co., Ltd. was used to measure the resistivity ρ. During the measurement of the resistivity ρ, an electric field of 1 V / μm was applied to the piezoelectric thin film. The area of ​​the part of the first electrode layer and the second electrode layer to which the electric field was applied was 600 × 600 (μm). 2 The resistivity ρ of Example 1 is shown in Table 2 below. It is preferable that the resistivity ρ is high. In Table 2 or Table 4, "E+0n" (n is any positive integer) means "×10 n "In Table 2 or Table 4, "E+m" (m is any positive integer) means "×10 m " means.

[0074] <Measurement of durability rate DR> Thirty rectangular cantilevers (piezoelectric thin film elements) were fabricated as samples for fatigue testing. The dimensions of the cantilevers in the direction parallel to the first main surface (surface of the first electrode layer) of the piezoelectric thin film were 2 mm wide x 20 mm long. Except for the dimensions, the layer structure and composition of the cantilevers were the same as those of the piezoelectric thin film elements described above. In the fatigue test, an AC voltage (Vpp = 30 V, frequency = 500 Hz) was applied to each sample for 24 hours. After the AC voltage was applied, the number n of samples in which cracks had formed in the piezoelectric thin film was counted using an optical microscope. The durability factor DR (unit: %) is defined as (n / 30) x 100. The durability factors DR of Example 1 are shown in Table 2 below. A high durability factor DR is preferable.

[0075] (Examples 2 to 25 and Comparative Examples 1 to 5) The composition of the first electrode layer in each of Examples 2 to 25 and Comparative Examples 1 to 5 was adjusted to the composition shown in Tables 1 and 3 below. The divalent element Ed used in the raw materials of the piezoelectric thin films of Examples 2 to 25 and Comparative Examples 1 to 4 is shown in Tables 1 and 3 below. The concentration [Ed] of the divalent element in the piezoelectric thin films of Examples 2 to 25 and Comparative Examples 1 to 4 was adjusted to the values ​​shown in Tables 1 and 3 below. The tetravalent element Et used as the raw material for each of the piezoelectric thin films of Examples 2 to 25 and Comparative Examples 1 to 4 is shown in Tables 1 and 3 below. The concentration [Et] of the tetravalent element in each of the piezoelectric thin films of Examples 2 to 25 and Comparative Examples 1 to 4 was adjusted to the value shown in Tables 1 and 3 below. As the raw material for the piezoelectric thin film of Comparative Example 5, neither divalent nor tetravalent elements were used. The cooling rate CR of the piezoelectric thin film in the rapid cooling process in each of Examples 2 to 25 and Comparative Examples 1 to 5 was adjusted to the values ​​shown in Tables 1 and 3 below.

[0076] Except for the above-mentioned points, the piezoelectric thin film elements of Examples 2 to 25 and Comparative Examples 1 to 5 were fabricated in the same manner as in Example 1. Analysis and measurement were carried out on the piezoelectric thin film elements of Examples 2 to 25 and Comparative Examples 1 to 5 in the same manner as in Example 1. The results of the analysis and measurement of Examples 2 to 25 and Comparative Examples 1 to 5 are shown in Tables 1 to 4 below. Except for the differences shown in Tables 1 to 4 below, the piezoelectric thin film elements of Examples 2 to 25 and Comparative Examples 1 to 5 had the same characteristics as Example 1.

[0077] W 0.90 V 0.10 Images of the surface of the first electrode layer made of (a) and (b) in Figure 7 are shown in (a) and (b) in Figure 7. The first electrode layer shown in (a) and (b) in Figure 7 is the first electrode layer of Example 19. An image of the surface of the first electrode layer made only of V is shown in (b) of Figure 8. The first electrode layer shown in (b) of Figure 8 is the first electrode layer of Comparative Example 4. An image of the cross section of the piezoelectric thin film of Example 13 is shown in Figure 9. The image shown in Figure 9 was taken by a scanning electron microscope (SEM).

[0078] [Table 1]

[0079] [Table 2]

[0080] [Table 3]

[0081] [Table 4] [Industrial Applicability]

[0082] For example, a piezoelectric thin film according to one aspect of the present disclosure may be used in a microphone, a sensor, a transducer, a filter, a harvester, or an actuator. [Explanation of symbols]

[0083] 1...first electrode layer, 1g...metal grain, 2...second electrode layer, 3...piezoelectric thin film, 3b...grain boundary, 3g...crystal grain, 10...piezoelectric thin film element, s1...surface of first electrode layer, s2...surface of second electrode layer, s31...first main surface of piezoelectric thin film, s32...second main surface of piezoelectric thin film, uc...unit cell of aluminum nitride (wurtzite structure), Ed...divalent element, Et...tetravalent element, L...length of grain boundary, d...distance between the first main surface and the second main surface.< / et> < / ed> < / al> < / et> < / et> < / ed> < / al> < / ed> < / et> < / ed> < / n> < / al> < / x> < / et> < / ed> < / al> < / ed> < / et> < / ed> < / n> < / al> < / x> < / et> < / ed> < / al> < / ed> < / et> < / ed> < / n> < / al> < / x>

Claims

1. a plurality of grains including aluminum nitride; The aluminum nitride contains an additive element, the additional element includes at least a divalent element and a tetravalent element, The concentration of the divalent element in the grain boundary between a pair of adjacent crystal grains is expressed as [Ed]b atomic %, The concentration of the divalent element in one of the crystal grains adjacent to the grain boundary is expressed as [Ed]g atomic %, [Ed]b / [Ed]g is 0.7 or more and 1.6 or less; Piezoelectric thin film.

2. the piezoelectric thin film has a first main surface and a second main surface located on a back side of the first main surface, the grain boundary extends from the first main surface to the second main surface, a cross section of the piezoelectric thin film is perpendicular to the first principal surface and the second principal surface; The length of the grain boundary in the cross section is represented as L; The distance between the first major surface and the second major surface is represented as d; (L-d) / d is 1% or more and 20% or less, The piezoelectric thin film according to claim 1 .

3. the piezoelectric thin film has a first main surface and a second main surface located on a back side of the first main surface, The peak intensity of the diffracted X-rays from the (10-10) plane of the aluminum nitride is I （１０－１０） is expressed as The peak intensity of the diffracted X-rays from the (10-11) plane of the aluminum nitride is I （１０－１１） is expressed as I （１０－１０） and the above I （１０－１１） is measured in an in-plane direction of the first principal surface or the second principal surface, I （１０－１１） / I （１０－１０） is 1% or more and 10% or less, The piezoelectric thin film according to claim 1 .

4. the piezoelectric thin film has a first main surface and a second main surface located on a back side of the first main surface, the grain boundary extends from the first main surface to the second main surface, a cross section of the piezoelectric thin film is perpendicular to the first principal surface and the second principal surface; The length of the grain boundary in the cross section is represented as L; The distance between the first major surface and the second major surface is represented as d; (L−d) / d is 1% or more and 20% or less, The peak intensity of the diffracted X-rays from the (10-10) plane of the aluminum nitride is I （１０－１０） is expressed as The peak intensity of the diffracted X-rays from the (10-11) plane of the aluminum nitride is I （１０－１１） is expressed as I （１０－１０） and the above I （１０－１１） is measured in an in-plane direction of the first principal surface or the second principal surface, I （１０－１１） / I （１０－１０） is 1% or more and 10% or less, The piezoelectric thin film according to claim 1 .

5. A piezoelectric thin film comprising a plurality of crystal grains containing aluminum nitride, The aluminum nitride contains an additive element, the additional element includes at least a divalent element and a tetravalent element, the piezoelectric thin film has a first main surface and a second main surface located on a back side of the first main surface, grain boundaries between the plurality of crystal grains extend from the first main surface to the second main surface; a cross section of the piezoelectric thin film is perpendicular to the first principal surface and the second principal surface; The length of the grain boundary in the cross section is represented as L; The distance between the first major surface and the second major surface is represented as d; (L-d) / d is 1% or more and 20% or less, Piezoelectric thin film.

6. The peak intensity of the diffracted X-rays from the (10-10) plane of the aluminum nitride is I （１０－１０） is expressed as The peak intensity of the diffracted X-rays from the (10-11) plane of the aluminum nitride is I （１０－１１） is expressed as I （１０－１０） and the above I （１０－１１） is measured in an in-plane direction of the first principal surface or the second principal surface, I （１０－１１） / I （１０－１０） is 1% or more and 10% or less, The piezoelectric thin film according to claim 5 .

7. A piezoelectric thin film comprising a plurality of crystal grains containing aluminum nitride, The aluminum nitride contains an additive element, the additional element includes at least a divalent element and a tetravalent element, the piezoelectric thin film has a first main surface and a second main surface located on a back side of the first main surface, The peak intensity of the diffracted X-rays from the (10-10) plane of the aluminum nitride is I （１０－１０） is expressed as The peak intensity of the diffracted X-rays from the (10-11) plane of the aluminum nitride is I （１０－１１） is expressed as I （１０－１０） and the above I （１０－１１） is measured in an in-plane direction of the first principal surface or the second principal surface, I （１０－１１） / I （１０－１０） is 1% or more and 10% or less, Piezoelectric thin film.

8. At least a portion of the divalent element is magnesium, At least a portion of the tetravalent element is at least one of zirconium and hafnium. The piezoelectric thin film according to any one of claims 1 to 7.

9. the concentration of the additive element in the piezoelectric thin film is 3 atomic % or more and 70 atomic % or less; The piezoelectric thin film according to any one of claims 1 to 7.

10. the concentration of the additive element in the piezoelectric thin film is 36 atomic % or more and 70 atomic % or less; The piezoelectric thin film according to any one of claims 1 to 7.

11. The concentration of the divalent element in the piezoelectric thin film is expressed as [Ed] atomic %, the concentration of the tetravalent element in the piezoelectric thin film is expressed as [Et] atomic %, [Ed] / ([Ed]+[Et]) is 0.3 or more and 0.6 or less; The piezoelectric thin film according to any one of claims 1 to 7.

12. The piezoelectric thin film according to any one of claims 1 to 7, an electrode layer; Equipped with The piezoelectric thin film directly or indirectly overlaps the surface of the electrode layer. Piezoelectric thin film element.

13. the electrode layer includes a plurality of metal particles; the aspect ratio of the plurality of metal grains on the surface of the electrode layer is 1.3 or more and 2.0 or less; 13. The piezoelectric thin film element according to claim 12.

14. The composition of the electrode layer is represented by any one of the following chemical formulas e1, e2, e3, and e4:

13. The piezoelectric thin film element according to claim 12. W １－ｘ V ｘ (e1) [In the above chemical formula e1, 0.00<x≦0.10] Mỏ １－ｘ W ｘ (er) [0.65≦x<1.00 in the above chemical formula e2] *] １－ｘ b ｘ ()) [In the above chemical formula e3, 0.18≦x<0.30] W １－ｘ Cr ｘ (e4) [In the above chemical formula e4, 0.00<x<0.05]

15. The composition of the electrode layer is represented by any one of the following chemical formulas e1, e2, e3, and e4:

14. The piezoelectric thin film element according to claim 13. W １－ｘ V ｘ (e1) [In the above chemical formula e1, 0.00<x≦0.10] Mỏ １－ｘ W ｘ (er) [0.65≦x<1.00 in the above chemical formula e2] *] １－ｘ b ｘ ()) [In the above chemical formula e3, 0.18≦x<0.30] W １－ｘ Cr ｘ (e4) [In the above chemical formula e4, 0.00<x<0.05]

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