Piezoelectric thin film and piezoelectric thin film element

Abstract

A piezoelectric thin film includes a plurality of crystal grains containing aluminum nitride. The aluminum nitride includes an additive element. The plurality of crystal grains includes a plurality of first crystal grains and a plurality of second crystal grains. A proportion of a number of the additive element in the first crystal grains with respect to a total of a number of aluminum and the additive element in the first crystal grains is represented as [Eadd]1 atomic %. A proportion of a number of the additive element in the second crystal grains with respect to a total of a number of aluminum and the additive element in the second crystal grains g2 is represented as [Eadd]2 atomic %. [Eadd]2 is higher than [Eadd]1.

Description

Technical Field

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

[0002] In recent years, MEMS (Micro Electro Mechanical Systems) has attracted much attention. MEMS are devices that integrate mechanical components, sensors, actuators, and electronic circuits onto a single substrate using microfabrication techniques. For example, piezoelectric thin films used in MEMS include aluminum nitride (AlN), zinc oxide (ZnO), lithium niobate (LiNbO3), and lead zirconate titanate (PZT).

[0003] For example, the performance indicators of piezoelectric thin films are the piezoelectric constant d (piezoelectric strain constant) and the piezoelectric constant g (voltage output constant). The piezoelectric constant d is an indicator of the strain per unit electric field (transmitting capability). The larger the piezoelectric constant d, the higher the performance of the piezoelectric element as an actuator (e.g., an inkjet recording head). On the other hand, the piezoelectric constant g is an indicator of the generated electric field strength per unit stress (receiving capability). The larger the piezoelectric constant g, the higher the performance of the piezoelectric element as a sensor. Among the piezoelectric thin films mentioned above, AlN has attracted much attention because it has a small piezoelectric constant d but a high piezoelectric constant g and is inexpensive. (See Patent Document 1 below.)

[0004] For example, Patent Document 1 below discloses an AlN containing Group 2 or Group 12 elements and Group 4 or Group 5 elements as additive elements.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 6535637 Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] It is known that the piezoelectric properties of AlN are improved by adding elements. However, with increasing content of added elements, it becomes difficult to maintain the crystal structure of AlN (wurtzite structure). As a result, the piezoelectric properties of AlN deteriorate. This tendency is significant when the nitrides of the added elements do not possess piezoelectric properties. Furthermore, due to the random segregation of added elements in AlN, heterogeneous phases without piezoelectric properties are randomly formed, and these phases tend to concentrate locally. This, in turn, deteriorates the piezoelectric properties of AlN.

[0010] One aspect of this disclosure is to provide a piezoelectric thin film with excellent piezoelectric properties, and a piezoelectric thin film element comprising the piezoelectric thin film.

[0011] Technical solutions for solving technical problems

[0012] This disclosure relates, for example, to the piezoelectric thin film described in any of [1] to

[10] below, and the piezoelectric thin film element described in

[11] below.

[0013] [1] A piezoelectric thin film, wherein,

[0014] It contains multiple crystal grains containing aluminum nitride.

[0015] The aluminum nitride contains additive elements.

[0016] The plurality of grains includes a plurality of first grains and a plurality of second grains.

[0017] The ratio of the amount of the added element in the first grain to the total amount of aluminum and the added element in the first grain is expressed as [Eadd]1 atom%.

[0018] The ratio of the amount of the added element in the second grain to the total amount of aluminum and the added element in the second grain is expressed as [Eadd]2 atomic%.

[0019] [Eadd]2 is higher than [Eadd]1.

[0020] [2] According to the piezoelectric thin film described in [1], wherein,

[0021] The added elements contain at least divalent and tetravalent elements.

[0022] [3] According to the piezoelectric thin film described in [2], wherein,

[0023] At least some of the divalent elements are magnesium.

[0024] At least a portion of the tetravalent elements are at least one of zirconium and hafnium.

[0025] [4] According to any one of [1] to [3], the piezoelectric thin film, wherein,

[0026] The added element contains at least a trivalent element.

[0027] [5] According to the piezoelectric thin film described in [4], wherein,

[0028] At least some of the trivalent elements are scandium.

[0029] [6] According to any one of [1] to [5], the piezoelectric thin film, wherein,

[0030] The added elements are either only divalent and tetravalent elements, or only trivalent elements, or a combination of the divalent, trivalent, and tetravalent elements.

[0031] The ratio of the amount of the divalent element in the first grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the first grain is expressed as [Ed] 1 atom%.

[0032] The ratio of the amount of the trivalent element in the first grain to the total amount of the aluminum, divalent element, trivalent element and tetravalent element in the first grain is expressed as [Etr]1 atom%.

[0033] The ratio of the amount of the divalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Ed]2 atoms%.

[0034] The ratio of the amount of the trivalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Etr]2 atomic%.

[0035] ([Ed]2 + [Etr]2) / ([Ed]1 + [Etr]1) is greater than 1.000 and less than 3.000.

[0036] [7] According to any one of [1] to [6], the piezoelectric thin film, wherein,

[0037] The total volume of the plurality of first grains in the piezoelectric film is expressed as A1 volume%.

[0038] The total volume of the plurality of second grains in the piezoelectric film is expressed as A2% (volume %).

[0039] A2 / (A1+A2) is above 0.1% and below 15.0%.

[0040] [8] According to any one of [1] to [7], the piezoelectric thin film, wherein,

[0041] The added elements contain at least two valent elements and two tetravalent elements.

[0042] The ratio of the amount of the divalent element in the first grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the first grain is expressed as [Ed] 1 atom%.

[0043] The ratio of the amount of the tetravalent element in the first grain to the total amount of the aluminum, divalent element, trivalent element and tetravalent element in the first grain is expressed as [Et]1 atom%.

[0044] The ratio of the amount of the divalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Ed]2 atoms%.

[0045] The ratio of the amount of the tetravalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Et]2 atoms%.

[0046] [Ed]1 / ([Ed]1+[Et]1) is greater than 0.40 and less than 0.58.

[0047] [Ed]2 / ([Ed]2+[Et]2) is greater than 0.40 and less than 0.58.

[0048] [9] According to any one of [1] to [8], the piezoelectric thin film, wherein,

[0049] The added elements are either only divalent and tetravalent elements, or only trivalent elements, or a combination of the divalent, trivalent, and tetravalent elements.

[0050] The ratio of the amount of the divalent element in the first grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the first grain is expressed as [Ed] 1 atom%.

[0051] The ratio of the amount of the trivalent element in the first grain to the total amount of the aluminum, divalent element, trivalent element and tetravalent element in the first grain is expressed as [Etr]1 atom%.

[0052] The ratio of the amount of the tetravalent element in the first grain to the total amount of the aluminum, divalent element, trivalent element and tetravalent element in the first grain is expressed as [Et]1 atom%.

[0053] The ratio of the amount of the divalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Ed]2 atoms%.

[0054] The ratio of the amount of the trivalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Etr]2 atomic%.

[0055] The ratio of the amount of the tetravalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Et]2 atoms%.

[0056] [Ed]1 + [Etr]1 + [Et]1 is 9.0 atomic% or more and less than 61.0 atomic%.

[0057] [Ed]2+[Etr]2+[Et]2 is greater than 9.0 atomic% and less than 61.0 atomic%.

[0058]

[10] According to any one of [1] to [9], the piezoelectric thin film, wherein,

[0059] The first grain extends along a direction perpendicular to the main surface of the piezoelectric film.

[0060] The second grain extends along a direction perpendicular to the main surface of the piezoelectric film.

[0061]

[11] A piezoelectric thin film element, wherein,

[0062] have:

[0063] The piezoelectric thin film described in any one of [1] to

[10] ; and

[0064] Electrode layer,

[0065] The piezoelectric film overlaps directly or indirectly with the surface of the electrode layer.

[0066] Invention Effects

[0067] According to one aspect of this disclosure, a piezoelectric thin film with excellent piezoelectric properties and a piezoelectric thin film element can be provided. Attached Figure Description

[0068] [ Figure 1 ] Figure 1 This is a schematic exploded perspective view of a piezoelectric thin film element, which is a specific example of the present invention.

[0069] [ Figure 2 ] Figure 2 express Figure 1 A specific example of a schematic cross-section of the piezoelectric thin film element shown. Figure 2The cross section shown is approximately perpendicular or completely perpendicular to the first principal surface of the piezoelectric film, and approximately parallel or completely parallel to the thickness direction of the piezoelectric film.

[0070] [ Figure 3 ] Figure 3 It is a three-dimensional diagram of the unit cell of the aluminum nitride crystal structure (wurtzite structure) contained in the piezoelectric thin film.

[0071] [ Figure 4 ] Figure 4 Image (a) is a cross-sectional image of a piezoelectric thin film according to a specific example of the present invention. Figure 4 The cross section shown in (a) is approximately perpendicular or completely perpendicular to the first principal surface of the piezoelectric film, and approximately parallel or completely parallel to the thickness direction of the piezoelectric film. Figure 4 (b) in the text indicates Figure 4 Image of the distribution of magnesium in the cross section shown in (a). Detailed Implementation

[0072] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numerals are used to denote the same constituent elements. The present invention is not limited to the embodiments described below. Figure 1 , Figure 2 and Figure 4 In (b) above, X, Y, and Z refer to three mutually orthogonal coordinate axes. The directions of the X-axis, Y-axis, and Z-axis are respectively in... Figure 1 , Figure 2 and Figure 4 The same as in (b) of the above.

[0073] like Figure 1 As shown, the piezoelectric thin film element 10 of 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 also 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. A "main surface" is the surface with the largest area among the multiple surfaces of a polyhedron (e.g., a thin cuboid piezoelectric thin film 3). The area of ​​the first main surface s31 may be approximately equal to or exactly equal to the area of ​​the second main surface s32. The shape of the first main surface s31 may be approximately equal to or exactly equal to the shape of the second main surface s32. The first main surface s31 of the piezoelectric thin film 3 may directly overlap or indirectly overlap with the surface s1 of the first electrode layer 1. The surface s2 of the second electrode layer 2 may directly overlap or indirectly overlap with the second main surface s32 of the piezoelectric thin film 3. Figure 1 The X-axis and Y-axis are approximately parallel 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. Figure 1The Z-axis is approximately perpendicular 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.

[0074] The piezoelectric thin film 3 of this embodiment comprises multiple grains containing aluminum nitride. The crystal structure of aluminum nitride is a wurtzite-type structure of the hexagonal crystal system. For example, the aluminum nitride contained in each of the multiple grains can be single crystal, polycrystalline, or incomplete crystal.

[0075] Aluminum nitride contains an additive element, Eadd, which differs from aluminum (Al) and nitrogen (N). For example, the additive element Eadd can contain at least divalent Ed and tetravalent Et. Alternatively, it can contain trivalent Etr. Furthermore, it can be solely divalent Ed and tetravalent Et, or solely trivalent Etr, or a combination of divalent Ed, trivalent Etr, and tetravalent Et. The doping of aluminum nitride with Eadd causes deformation of the wurtzite structure or changes in the strength of the interatomic bonds within the wurtzite structure. Consequently, the wurtzite structure of aluminum nitride is easily deformed when voltage or external force is applied to the piezoelectric film 3, thus enhancing its piezoelectric properties. The piezoelectric film 3 can consist solely of AlN containing the additive element Eadd. As described later, the piezoelectric film 3 may further contain other elements besides Al, N, and the additive element Eadd.

[0076] Figure 3 The diagram represents the wurtzite structure of aluminum nitride contained in the piezoelectric thin film 3. The unit cell uc of aluminum nitride (wurtzite structure) is a hexagonal prism. A portion of the aluminum in the unit cell uc can be replaced by the additive element Eadd. For example, a portion of the Al in the unit cell uc can be replaced by the divalent element Ed, the trivalent element Etr, or the tetravalent element Et. At least a portion or all of the (0001) facet of the aluminum nitride in the piezoelectric thin film 3 can be oriented substantially parallel or completely parallel to the first principal facet s31 (the surface s1 of the first electrode layer 1) of the piezoelectric thin film 3. The aluminum nitride is polarized in a crystal orientation perpendicular to the (0001) facet (i.e.,

[0001] ). Therefore, by oriented substantially parallel or completely parallel to the first principal facet s31 of the piezoelectric thin film 3, the piezoelectric properties of the piezoelectric thin film 3 are easily improved. During the manufacturing process of the piezoelectric film 3, the (0001) face of aluminum nitride is easily oriented parallel to the first main face s31 (surface s1 of the first electrode layer 1) of the piezoelectric film 3.

[0077] like Figure 2As shown, the piezoelectric film 3 comprises multiple first grains g1 and multiple second grains g2 as multiple grains containing aluminum nitride. The piezoelectric film 3 may also be composed solely of multiple first grains g1 and multiple second grains g2. One or more first grains g1 may be directly connected to one or more second grains g2. One or more first grains g1 may also be indirectly connected to one or more second grains g2 via grain boundary phases.

[0078] The ratio of the amount of added element Eadd in the first grain g1 to the total amount of aluminum and added element Eadd in the first grain g1 is expressed as [Eadd]1 atoms.

[0079] The ratio of the amount of added element Eadd in the second grain g2 to the total amount of aluminum and added element Eadd in the second grain g2 is expressed as [Eadd]2 atoms.

[0080] For existing piezoelectric thin films, as the content of the additive element Eadd increases, heterogeneous phases are easily incorporated. A "heterogeneous phase" refers to a phase (e.g., grain or grain boundary phase) that differs from aluminum nitride with a wurtzite-type structure, formed due to the segregation of Eadd. Heterogeneous phases are unlikely to possess piezoelectric properties.

[0081] On the other hand, in the piezoelectric thin film 3 of this embodiment, [Eadd]2 is higher than [Eadd]1. That is, the piezoelectric thin film 3 not only contains a first grain g1 with a lower proportion of added element Eadd, but also contains a plurality of second grains g2 with a higher proportion of added element Eadd. During the growth process of the piezoelectric thin film 3 of this embodiment, not only do the first grains g1 with a lower proportion of added element Eadd grow, but the second grains g2 with a higher proportion of added element Eadd also grow, thus suppressing random segregation of added element Eadd during the growth process of the piezoelectric thin film 3. As a result, it is difficult for heterogeneous phases to form randomly in the piezoelectric thin film 3, and heterogeneous phases are less likely to concentrate locally in the piezoelectric thin film 3.

[0082] For the reasons stated above, the piezoelectric film 3 is unlikely to contain heterogeneous phases lacking piezoelectric properties, and the wurtzite-type structure of aluminum nitride in the piezoelectric film 3 is difficult to be disrupted by added elements. As a result, the piezoelectric properties of the piezoelectric film 3 are easily improved, and the relative permittivity (ε) of the piezoelectric film 3 is... r The dielectric loss (tanδ) is easily reduced. For example, as a piezoelectric material with excellent piezoelectric properties, the piezoelectric film 3 can have a large e 31,f e 31,f It is the piezoelectric stress constant of the transverse vibration (in-plane vibration) of the piezoelectric thin film 3. 31,f The unit is [C / m] 2The transverse length vibration is the vibration (stretching) of the piezoelectric film 3 in a direction orthogonal to the polarization direction (e.g., the thickness direction of the piezoelectric film 3). In other words, the transverse length vibration can be the vibration (stretching) of the piezoelectric film 3 in a direction that is approximately parallel or completely parallel to the first main surface s31 or the second main surface s32 of the piezoelectric film 3, and the transverse length vibration can also be the vibration (stretching) of the piezoelectric film 3 in a direction that is approximately parallel or completely parallel to the surfaces of the first electrode layer 1 and the second electrode layer 2, respectively.

[0083] As long as the piezoelectric properties of the piezoelectric film 3 are not damaged, the piezoelectric film 3 can also contain a small amount of heterogeneous phase.

[0084] The divalent element Ed in aluminum nitride can be at least one element selected from magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and zinc (Zn). The trivalent element Etr in aluminum nitride can be at least one element selected from scandium (Sc), yttrium (Y), lanthanides, and indium (In). The tetravalent element Et in aluminum nitride can be at least one element selected from zirconium (Zr), germanium (Ge), titanium (Ti), and hafnium (Hf).

[0085] Based on the reason that the piezoelectric properties of the piezoelectric film 3 can be easily improved, at least a portion of the divalent element Ed can be magnesium, and at least a portion of the tetravalent element Et can be at least one of zirconium and hafnium. For the same reason, at least a portion of the trivalent element Etr can be scandium.

[0086] The aluminum nitride contained in the piezoelectric film 3 may also contain at least one element selected from monovalent and pentavalent elements. The monovalent element may be at least one element selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). The pentavalent element may be at least one element selected from chromium (Cr), vanadium (V), niobium (Nb), and tantalum (Ta). The aluminum nitride contained in the piezoelectric film 3 may also contain other elements such as oxygen (O) and argon (Ar).

[0087] In this disclosure, any element is denoted as "X", the concentration (in atomic %) of element X in the first grain g1 is denoted as <X>1, and the concentration (in atomic %) of element X in the second grain g2 is denoted as <X>2.

[0088] That is, the concentrations of Al, N, divalent element Ed, trivalent element Etr, and tetravalent element Et in the first grain g1 are represented as <Al>1, <N>1, <Ed>1, <Etr>1, and <Et>1, respectively.

[0089] The concentrations of Al, N, divalent element Ed, trivalent element Etr, and tetravalent element Et in the second grain g2 are represented as <Al>2, <N>2, <Ed>2, <Etr>2, and <Et>2, respectively.

[0090] The proportion of aluminum in the first grain g1 relative to the total amount of aluminum, divalent element Ed, trivalent element Etr, and tetravalent element Et in the first grain g1 is expressed as [Al]1 atomic%. [Al]1 can be equal to 100 × <Al>1 / (<Al>1 + <Ed>1 + <Etr>1 + <Et>1).

[0091] The proportion of the divalent element Ed in the first grain g1 relative to the total amount of aluminum, divalent element Ed, trivalent element Etr, and tetravalent element Et in the first grain g1 is expressed as [Ed]1 atomic%. [Ed]1 can be equal to 100 × <Ed>1 / (<Al>1 + <Ed>1 + <Etr>1 + <Et>1).

[0092] The proportion of the trivalent element Etr in the first grain g1 relative to the total amount of aluminum, divalent element Ed, trivalent element Etr, and tetravalent element Et in the first grain g1 is expressed as [Etr]1 atomic%. [Etr]1 can be equal to 100 × <Etr>1 / (<Al>1 + <Ed>1 + <Etr>1 + <Et>1).

[0093] The proportion of the tetravalent element Et in the first grain g1 relative to the total amount of aluminum, divalent element Ed, trivalent element Etr, and tetravalent element Et in the first grain g1 is expressed as [Et]1 atomic%. [Et]1 can be equal to 100 × <Et>1 / (<Al>1 + <Ed>1 + <Etr>1 + <Et>1).

[0094] The proportion of aluminum in the second grain g2 relative to the total amount of aluminum, divalent element Ed, trivalent element Etr, and tetravalent element Et in the second grain g2 is expressed as [Al]2 atomic%. [Al]2 can be equal to 100 × <Al>2 / (<Al>2 + <Ed>2 + <Etr>2 + <Et>2).

[0095] The proportion of the divalent element Ed in the second grain g2 relative to the total amount of aluminum, divalent element Ed, trivalent element Etr, and tetravalent element Et in the second grain g2 is expressed as [Ed]2 atomic%. [Ed]2 can be equal to 100 × <Ed>2 / (<Al>2 + <Ed>2 + <Etr>2 + <Et>2).

[0096] The proportion of the trivalent element Etr in the second grain g2 relative to the total amount of aluminum, divalent element Ed, trivalent element Etr, and tetravalent element Et in the second grain g2 is expressed as [Etr]2 atomic%. [Etr]2 can be equal to 100 × <Etr>2 / (<Al>2 + <Ed>2 + <Etr>2 + <Et>2).

[0097] The proportion of the tetravalent element Et in the second grain g2 relative to the total amount of aluminum, divalent element Ed, trivalent element Etr, and tetravalent element Et in the second grain g2 is expressed as [Et]2 atomic%. [Et]2 can be equal to 100 × <Et>2 / (<Al>2 + <Ed>2 + <Etr>2 + <Et>2).

[0098] The above [Eadd]1 can be equal to [Ed]1 + [Etr]1 + [Et]1.

[0099] The above [Eadd]2 can be equal to [Ed]2 + [Etr]2 + [Et]2.

[0100] Based on the reason that the piezoelectric properties of the piezoelectric film 3 can be easily improved and the dielectric loss of the piezoelectric film 3 can be easily reduced, ([Ed]2 + [Etr]2) / ([Ed]1 + [Etr]1) can be greater than 1.000 and less than 3.000. Based on the same reason, ([Ed]2 + [Etr]2) / ([Ed]1 + [Etr]1) can be greater than 1.005 and less than 2.262, or greater than 1.010 and less than 2.250.

[0101] The total volume ratio of the plurality of first grains g1 in the piezoelectric film 3 is expressed as A1 volume%. The total volume ratio of the plurality of second grains in the piezoelectric film 3 is expressed as A2 volume%. Based on the reason that the piezoelectric properties of the piezoelectric film 3 can be easily improved and the relative permittivity of the piezoelectric film 3 can be easily reduced, A2 / (A1+A2) can be more than 0.1% and less than 15.0%.

[0102] The volume ratio a1 of a first grain g1 in the piezoelectric thin film 3 tends to be similar to the area a1' of a first grain g1 in the cross section of the piezoelectric thin film 3 (unit: (nm)). 2 The proportions of the volumes of the second grain g2 in the piezoelectric thin film 3 and the area a2' of the second grain g2 in the cross section of the piezoelectric thin film 3 are equal. 2The proportions are equal. Therefore, an a2' / (a1'+a2') can be calculated based on the area of ​​each of the adjacent pairs of first grains g1 and second grains g2 in the cross section of the piezoelectric film 3. The average value of a2' / (a1'+a2') of multiple pairs of first grains g1 and second grains g2 can be regarded as A2 / (A1+A2).

[0103] The cross sections of a1' and a2', which are measured respectively, can be approximately perpendicular or completely perpendicular to the first main surface s31 or the second main surface s32 of the piezoelectric film 3.

[0104] In each of the first grain g1 and the second grain g2, based on the reasons that it is easy to achieve a balance between the average valence of aluminum, divalent element Ed, trivalent element Etr, and tetravalent element Et and the valence of nitrogen, easy to maintain the wurtzite structure of aluminum nitride, and easy to improve the piezoelectric properties of the piezoelectric film 3, [Ed]1 / ([Ed]1 + [Et]1) can be 0.40 or higher and 0.58 or lower, and [Ed]2 / ([Ed]2 + [Et]2) can be 0.40 or higher and 0.58 or lower. For the same reasons, [Ed]1 / ([Ed]1 + [Et]1) can be 0.35 or higher and 0.58 or lower, and [Ed]2 / ([Ed]2 + [Et]2) can be 0.29 or higher and 0.65 or lower.

[0105] Based on the premise that the piezoelectric properties of the piezoelectric thin film 3 can be easily improved, [Ed]1 + [Etr]1 + [Et]1 can be 9.0 atomic% or more and less than 61.0 atomic%, and [Ed]2 + [Etr]2 + [Et]2 can be greater than 9.0 atomic% and less than 61.0 atomic%. That is, [Eadd]1 can be 9.0 atomic% or more and less than 61.0 atomic%, and [Eadd]2 can be greater than 9.0 atomic% and less than 61.0 atomic%. For the same reasoning, [Ed]1 + [Etr]1 + [Et]1 can be 9.1 atomic% or more and less than 59.4 atomic%, and [Ed]2 + [Etr]2 + [Et]2 can be 9.5 atomic% or more and less than 60.5 atomic%. That is, [Eadd]1 can be 9.1 atomic% or more and less than 59.4 atomic%, and [Eadd]2 can be 9.5 atomic% or more and less than 60.5 atomic%.

[0106] Based on the reason that the piezoelectric properties of the piezoelectric film 3 can be easily improved, some or all of the plurality of first grains g1 can extend along a direction perpendicular to the first principal surface s31 or the second principal surface s32 of the piezoelectric film 3. For the same reason, at least some or all of the plurality of second grains g2 can extend along a direction perpendicular to the first principal surface s31 or the second principal surface s32 of the piezoelectric film 3. For the same reason, one or more first grains g1 extending along a direction perpendicular to the first principal surface s31 or the second principal surface s32 of the piezoelectric film 3, and one or more second grains g2 extending along a direction perpendicular to the first principal surface s31 or the second principal surface s32 of the piezoelectric film 3 can be alternately arranged in a direction parallel to the first principal surface s31 or the second principal surface s32. That is, in a direction parallel to the first principal surface s31 or the second principal surface s32, the concentration difference of the additive element Eadd between the first grains g1 and the second grains g2 can be repeated. As a result, compared with a piezoelectric film having a concentration difference of added element Eadd in the thickness direction of the piezoelectric film, the piezoelectric properties of the piezoelectric film 3 are easily improved, and the relative permittivity and dielectric loss of the piezoelectric film 3 are easily reduced.

[0107] R(Eadd) is defined by the following mathematical formula 1. Based on the reason that the piezoelectric properties of the piezoelectric film 3 are easily improved, and the relative permittivity and dielectric loss of the piezoelectric film 3 are easily reduced, R(Eadd) can be greater than 1.01 and less than 1.49. An R(Eadd) greater than 1.00 means that the proportion of added element Eadd in the plurality of second grains g2 is higher than the proportion of added element Eadd in the plurality of first grains g1.

[0108] Mathematical formula 1:

[0109]

[0110] R(Ed + Etr) is defined by the following mathematical formula 2. Based on the reason that the piezoelectric properties of the piezoelectric film 3 are easily improved, and the relative permittivity and dielectric loss of the piezoelectric film 3 are easily reduced, R(Ed + Etr) can be greater than 1.005 and less than 2.262. An R(Ed + Etr) greater than 1.000 means that the proportion of divalent element Ed and trivalent element Etr in the plurality of second grains g2 is higher than the proportion of divalent element Ed and trivalent element Etr in the plurality of first grains g1.

[0111] Mathematical formula 2:

[0112]

[0113] The first electrode layer 1 may contain at least one element selected from 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 metallic element or an alloy.

[0114] The second electrode layer 2 may contain at least one element selected from 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 metallic element or an alloy. The composition of the second electrode layer 2 may be the same as that of the first electrode layer 1. Alternatively, the composition of the second electrode layer 2 may differ from that of the first electrode layer 1.

[0115] The piezoelectric thin film element 10 may further include a substrate. The first electrode layer 1 may directly overlap or indirectly overlap with the substrate. The piezoelectric thin film element 10 may further include an adhesive layer. The adhesive layer may be disposed between the substrate and the first electrode layer 1. That is, the first electrode layer 1 may indirectly overlap with the substrate via the adhesive layer.

[0116] For example, the substrate can be a semiconductor substrate (silicon substrate, or gallium arsenide substrate, etc.), an optical crystal substrate (sapphire substrate, etc.), an insulator substrate (glass substrate, or ceramic substrate, etc.), a metal substrate (stainless steel plate, etc.), or an SOI (Silicon-on-Insulator) substrate. The substrate can be crystalline. For example, the substrate can be monocrystalline or polycrystalline. The substrate can also be amorphous.

[0117] For example, the adhesive layer may contain at least one element selected from 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 adhesive layer can be a metallic element, alloy, or compound (oxide, etc.). The adhesive layer can also be other piezoelectric films (e.g., aluminum nitride), polymers, or ceramics. The adhesive layer functions to suppress the peeling of the first electrode layer caused by mechanical impact, etc. The adhesive layer may also be referred to as an interface layer, support layer, buffer layer, or intermediate layer.

[0118] For example, the thickness of the substrate can be 50 μm or more and 10,000 μm or less. For example, the thickness of the adhesive layer can be 0.003 μm or more and 2 μm or less. For example, the thickness of the first electrode layer 1 can be 0.01 μm or more and 1 μm or less. For example, the thickness of the piezoelectric film 3 can be 100 nm or more and 30,000 nm or less. For example, the thickness of the second electrode layer 2 can be 0.01 μm or more and 1 μm or less. The thicknesses of the substrate, adhesive layer, first electrode layer 1, piezoelectric film 3, and second electrode layer 2 can be substantially uniform or completely uniform.

[0119] The crystal structures of the substrate, adhesive layer, first electrode layer, piezoelectric thin film, and second electrode layer can be determined by X-ray diffraction and electron beam diffraction. The compositions of the substrate, adhesive layer, first electrode layer, piezoelectric thin film, and second electrode layer can be determined by at least one of the following analytical methods: X-ray fluorescence (XRF), X-ray photoelectron spectrometry (XPS), energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma mass spectrometry (ICP-MS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and electron probe microanalysis (EPMA). The thicknesses of the substrate, adhesive layer, first electrode layer, piezoelectric thin film, and second electrode layer can be measured in cross-section of the piezoelectric thin film element using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), or scanning electron microscopy (SEM). The crystallinity and crystal structure of each grain can be analyzed and determined based on the electron beam diffraction patterns measured within the cross-section of the piezoelectric thin film (parallel to the stacking direction) of each exposed grain.

[0120] The bonding layer, the first electrode layer, the piezoelectric thin film, and the second electrode layer can be sequentially stacked on the surface of the substrate by vapor phase growth methods such as sputtering. In particular, the piezoelectric thin film is formed by RF (Radio Frequency) magnetron sputtering. The bonding layer, the first electrode layer, the piezoelectric thin film, and the second electrode layer can each be formed by sputtering using at least one target material. Alternatively, the bonding layer, the first electrode layer, the piezoelectric thin film, and the second electrode layer can be formed separately by sputtering using multiple targets with different compositions. The target material can contain at least one element selected from the elements constituting each layer or the piezoelectric thin film. By selecting and combining targets with a predetermined composition, the compositions of the bonding layer, the first electrode layer, the piezoelectric thin film, and the second electrode layer can be controlled to a target composition. For example, the target material can be a metallic element, an alloy, or an oxide. For example, when the piezoelectric thin film is aluminum nitride containing divalent and tetravalent elements, a target material made of aluminum, a target material made of a divalent element, and a target material made of a tetravalent element can be used. Alloys composed of two or more elements selected from aluminum, divalent elements, and tetravalent elements can also be used as the target material. For example, when the piezoelectric thin film is aluminum nitride containing a trivalent element, targets made of aluminum and targets made of a trivalent element can be used. The composition of the sputtering atmosphere can be a control factor of the composition of each of the sealing layer, the first electrode layer, the piezoelectric thin film, and the second electrode layer. For example, nitrogen is used as the raw material for the piezoelectric thin film (aluminum nitride). The input power (power density) applied to the cathode on which each target material is disposed can be a control factor of the composition and thickness of each of the sealing layer, the first electrode layer, the piezoelectric thin film, and the second electrode layer. The total pressure of the sputtering atmosphere, the partial pressure or concentration of the raw gas in the atmosphere, the sputtering duration of each target, the temperature of the substrate surface, and the substrate bias voltage can also be control factors for the composition and thickness of the bonding layer, the first electrode layer, the piezoelectric thin film, and the second electrode layer. Piezoelectric thin films with desired shapes or patterns can also be formed by etching (e.g., plasma etching).

[0121] In existing RF magnetron sputtering for forming piezoelectric thin films, the film formation chamber (vacuum chamber) is filled with a mixture of Ar and N2 gases before an electric current is supplied to the target. The Ar ions (Ar...) within the film formation chamber... ＋ The atoms collide with the surface of the target material supplied with electricity. Atoms that have gained kinetic energy from the Ar ions detach from the surface of the target material and reach the surface of the substrate (the surface of the first electrode layer stacked on the substrate). As a result, a piezoelectric thin film grows on the surface of the substrate (the surface of the first electrode layer stacked on the substrate).

[0122] In conventional RF magnetron sputtering, power is supplied to the target material while N2 is present in the film-forming chamber. Consequently, the inner wall of the film-forming chamber is covered with nitrides derived from atoms of the target material (at least one of Al and Eadd). That is, in conventional RF magnetron sputtering, piezoelectric thin films are grown while the inner wall of the film-forming chamber is covered with nitrides (insulators).

[0123] In contrast, in the RF magnetron sputtering used to form the piezoelectric thin film of this embodiment, the film-forming chamber is filled with a gas consisting only of Ar (a gas that does not actually contain N2) before N2 is supplied into it. Electricity is supplied to the target while the film-forming chamber is filled only with Ar. That is, electricity is supplied to the target when N2 is not actually present in the film-forming chamber. As a result, the inner wall of the film-forming chamber is covered with a conductor (metal) composed of atoms derived from the target, rather than with a nitride (insulator). After the inner wall of the film-forming chamber is covered with the conductor, the film-forming chamber is filled with a mixed gas of Ar and N2. By supplying electricity to the target while the film-forming chamber is filled with a mixed gas of Ar and N2, the piezoelectric thin film of this embodiment grows on the surface of the substrate (the surface of the first electrode layer stacked on the substrate). That is, in the RF magnetron sputtering of this embodiment, the piezoelectric thin film grows while the inner wall of the film-forming chamber is covered with a conductor.

[0124] The potential of the inner wall covered by the conductor is more stable than that of the inner wall covered by the nitride (insulator). Therefore, the distribution of plasma (Ar ions) in the film-forming chamber with the inner wall covered by the conductor differs from that in the film-forming chamber with the inner wall covered by the nitride. As a result, random segregation of the added element Eadd is suppressed in the film-forming chamber with the inner wall covered by the conductor. Multiple seed crystals of the first grain (crystallizations with lower concentrations of the added element) and multiple seed crystals of the second grain (crystallizations with higher concentrations of the added element) are easily and uniformly dispersed on the surface of the substrate (the surface of the first electrode layer stacked on the substrate). Consequently, heterogeneous phases with added element segregation are difficult to form in the piezoelectric thin film, and multiple first grains and multiple second grains easily grow on the surface of the substrate (the surface of the first electrode layer stacked on the substrate).

[0125] In contrast, the potential of the inner wall covered by nitrides is more unstable than that of the inner wall covered by a conductor. Therefore, within the film-forming chamber with nitride-covered inner walls, the distribution of Al and the additive element Eadd on the substrate surface (the surface of the first electrode layer stacked on the substrate) tends to be non-uniform and random. As a result, the additive elements tend to randomly segregate on the substrate surface (the surface of the first electrode layer stacked on the substrate), and easily form heterogeneous phases randomly within the piezoelectric thin film. That is, within the film-forming chamber with nitride-covered inner walls, it is difficult to form first and second grains with controlled additive element concentrations.

[0126] The piezoelectric thin-film element of this embodiment has applications in various aspects. For example, the piezoelectric thin-film element can be a piezoelectric microphone, a sensor, an oscillator, a resonator, an acoustic multilayer film, or a filter. For example, the piezoelectric thin-film element can also be a piezoelectric actuator. Piezoelectric actuators can be used for haptics. That is, piezoelectric actuators can be used in various devices that require feedback from skin sensation (tactile feedback). For example, devices requiring feedback from skin sensation can be wearable devices, touchpads, displays, or game controllers. For example, piezoelectric actuators can be used in magnetic head assemblies, magnetic head cantilever assemblies, or hard disk drives. For example, piezoelectric actuators can also be used in printheads or inkjet printer devices. Piezoelectric actuators can also be used in piezoelectric switches. For example, the piezoelectric thin-film element can also be a piezoelectric sensor or a piezoelectric transducer. For example, piezoelectric sensors or piezoelectric transducers can be used in gyroscope sensors, pressure sensors, pulse wave sensors, ultrasonic sensors, ultrasonic transducers, or impact sensors. The ultrasonic transducer can be a piezoelectric micromachined ultrasonic transducer (PMUT). Products using piezoelectric micromachined ultrasonic transducers can be biometric sensors such as fingerprint sensors and ultrasonic vascular authentication sensors, medical or healthcare sensors, or Time of Flight (ToF) sensors. For example, the filter can be a BAW (Bulk Acoustic Wave) filter or a SAW (Surface Acoustic Wave) filter. The aforementioned piezoelectric thin-film elements can be part of or integral into a Micro Electro Mechanical System (MEMS).

[0127] This invention is not necessarily limited to the embodiments described above. Various modifications can be made to this invention without departing from its spirit, and these modifications are also included in this invention.

[0128] Example

[0129] The present invention will be described in detail through the following embodiments and comparative examples. The present invention is not limited to the following embodiments.

[0130] (Example 1)

[0131] A wafer made of single-crystal silicon (Si) was used as the substrate. The substrate has a diameter of 8 inches and a thickness of 725 μm. The substrate has a uniform thickness. The main surface of the substrate is parallel to the (100) plane of the Si.

[0132] An adhesive layer was directly formed on the entire main surface of the substrate using RF magnetron sputtering within a vacuum chamber. The adhesive layer consisted of aluminum nitride without any additives. Elemental Al was used as the sputtering target. The atmosphere within the vacuum chamber was a mixture of Ar and N₂. The input power per unit area of ​​the sputtering target was 3.72 W / cm². 2 The substrate temperature was maintained at 300°C during the formation of the adhesive layer. The substrate bias voltage was 30W. The thickness of the adhesive layer was uniform. The thickness of the adhesive layer was adjusted to approximately 30nm.

[0133] A first electrode layer composed of Mo was formed integrally on the surface of the sealing layer using RF magnetron sputtering within a vacuum chamber. Elemental Mo was used as the sputtering target. The atmosphere within the vacuum chamber was Ar gas. The input power per unit area of ​​the sputtering target was 0.93 W / cm². 2 The temperature of the substrate and the bonding layer is maintained at 600°C during the formation of the first electrode layer. The thickness of the first electrode layer is uniform. The thickness of the first electrode layer is adjusted to 0.2 μm.

[0134] Before placing the substrate with the first electrode layer formed thereon into the film-forming chamber for the piezoelectric thin film, a gas consisting only of Ar (actually a gas without N2) is supplied into the film-forming chamber for the piezoelectric thin film. With the film-forming chamber filled only with Ar, electricity is supplied to multiple targets for the piezoelectric thin film. As multiple targets, targets made of Al (metal), targets made of the divalent element Ed (metal), and targets made of the tetravalent element Et (metal) were used. That is, by using RF magnetron sputtering in Ar gas with multiple metal targets, the inner wall of the film-forming chamber is covered with a metal film derived from the multiple targets. Ed of Example 1 is shown in Table 1 below. Et of Example 1 is shown in Table 1 below. The input power (cathode power) per unit area of ​​each sputtering target is 3.72 W / cm². 2 The gas pressure in the film deposition chamber was 0.2 Pa. No substrate bias was applied. The duration of RF magnetron sputtering in Ar gas was 10 minutes.

[0135] After the inner wall of the film-forming chamber is covered with a metal film, a piezoelectric thin film is directly formed on the surface of the first electrode layer by RF magnetron sputtering within the film-forming chamber using multiple targets described above. During the formation of the piezoelectric thin film, the atmosphere within the film-forming chamber is a mixture of Ar and N2 gases. The input power (cathode power) per unit area of ​​each sputtering target is 3.72 W / cm². 2 The film-forming pressure (air pressure inside the film-forming chamber) is 0.2 Pa. The substrate bias voltage is 20 W. The thickness of the piezoelectric film is adjusted to approximately 1000 nm.

[0136] A second electrode layer composed of Mo was formed on the entire second main surface of the piezoelectric thin film using the same method as the first electrode layer. That is, the composition of the second electrode layer is the same as that of the first electrode layer.

[0137] The laminated structure is patterned on the substrate using photolithography. After patterning, the laminate is cut as a whole to obtain a quadrilateral piezoelectric thin film element.

[0138] The piezoelectric thin film element of Example 1 is composed of a substrate, an adhesive layer directly stacked on the surface of the substrate, a first electrode layer directly stacked on the surface of the adhesive layer, a piezoelectric thin film directly stacked on the surface of the first electrode layer, and a second electrode layer directly stacked on the surface (second main surface) of the piezoelectric thin film.

[0139] The following analyses and measurements were performed during or after the fabrication of the piezoelectric thin film element. Multiple identical piezoelectric thin film elements were fabricated as samples for the following analyses and measurements.

[0140] <Composition of piezoelectric thin films>

[0141] The overall average composition of the piezoelectric thin film was analyzed using X-ray fluorescence (XRF). A wavelength dispersive X-ray fluorescence apparatus (RIGAKU AZX-400) manufactured by Rigaku Corporation, Japan, was used in the XRF method. The results showed that the piezoelectric thin film is composed of aluminum nitride containing added elements Eadd (i.e., Ed and Et).

[0142] <Analysis of the cross-section of piezoelectric thin films>

[0143] The cross-section of the piezoelectric thin film was observed using scanning transmission electron microscopy (STEM). The cross-section observed by STEM is perpendicular to the first principal surface of the piezoelectric thin film (the surface of the first electrode layer). The composition of the cross-section of the piezoelectric thin film was analyzed using an energy-dispersive X-ray spectrometer (EDS) attached to the STEM. A Titan G2 from Thermo Fisher Scientific Inc. (formerly FEI company) was used as the STEM.

[0144] Five observation regions were randomly selected from the same cross-section of the piezoelectric thin film. The distance from the center of the main surface (circle) of the substrate to each observation region was 10 mm. Concentration (atomic %) of each element in each measurement region was mapped. Each measurement region contained multiple grains with varying concentrations of the added element Edd. The composition of each grain was determined through region analysis within its cross-section. The regions analyzed were quadrilateral, with dimensions approximately 100 nm x 100 nm. The grain with the lowest Edd concentration (first grain) and the grain with the highest Edd concentration (second grain) within each observation region were identified. The average concentration of each element in the five first grains identified across the five observation regions was calculated. The average concentration of each element in the five second grains identified across the five observation regions was also calculated.

[0145] The results of the above analysis using STEM-EDS are as follows.

[0146] The piezoelectric thin film comprises multiple first grains and multiple second grains.

[0147] Each grain is a columnar crystal that extends approximately or completely perpendicular to the first main surface of the piezoelectric film (the surface of the first electrode layer).

[0148] Each grain is composed of aluminum nitride containing the additive element Eadd.

[0149] [Eadd]2 is higher than [Eadd]1.

[0150] Details of the results of the analysis using STEM-EDS are shown in Tables 1 and 2 below.

[0151] <Determination of grain area>

[0152] The five pairs of first and second grains exposed in the aforementioned cross-section of the piezoelectric thin film were determined using STEM-EDS. The first and second grains were determined based on the contrast of the cross-sectional image captured by STEM and the concentration difference of the added element Eadd between the grains. The concentration difference of the added element Eadd was determined according to the mapping of the added element Eadd in the aforementioned cross-section. The mapping of the added element Eadd was performed by STEM-EDS.

[0153] The area a1' of each first grain was determined using the images of the aforementioned cross-section (unit: (nm)). 2 ) and the area a2' of each second grain (unit: (nm) 2The area of ​​each grain was measured using image analysis software (not for sale) manufactured by TDK Corporation. Mac-View manufactured by Mounttech Corporation can also be used as the image analysis software. a2' / (a1'+a2') was calculated based on the area of ​​each pair of first and second grains. The average value of a2' / (a1'+a2') for the five pairs of first and second grains was taken as A2 / (A1+A2). A2 / (A1+A2) for Example 1 is shown in Table 2 below.

[0154] <Crystal Structure of Piezoelectric Thin Films>

[0155] The crystal structure of the piezoelectric thin film was analyzed by X-ray diffraction (XRD) as described below. A multi-object X-ray diffraction apparatus (SmartLab) manufactured by Rigaku Corporation, Japan, was used in the XRD method. 2θ-θ scans, ω scans, and 2θχ-φ scans were performed on the surface of the piezoelectric thin film using the aforementioned X-ray diffraction apparatus.

[0156] The XRD pattern obtained by the XRD method shows that the piezoelectric film (i.e., aluminum nitride containing the additive element Eadd) has a wurtzite structure. In addition, the XRD pattern shows that the (0002) plane (and (0001) plane) of the wurtzite structure is parallel to the surface of the first electrode layer (the first and second main planes of the piezoelectric film).

[0157] <piezoelectric constant e 31,f The determination >

[0158] The piezoelectric constant e of the piezoelectric thin film of Example 1 was determined. 31,f (Unit: C / m) 2 piezoelectric constant e 31,f The measurements used a combination of a laser Doppler vibrometer and an oscilloscope. The laser Doppler vibrometer used was the LV-1800 manufactured by Ono Gyokki Co., Ltd. of Japan. The oscilloscope used was the Wavepro960 manufactured by Teledyne Technologies Inc. (formerly Teledyne LeCroy Inc.). The measurements of e... 31,f The frequency of the AC voltage in the circuit is 500 Hz. The measurement of e... 31,f The voltage applied to the piezoelectric film is 20V / μm. Table 2 below shows the voltage of Example 1. 31,f (The average value of the three measurement points).

[0159] <relative permittivity ε r The determination >

[0160] The relative permittivity ε of the piezoelectric thin film of Example 1 was measured. r (Unit: None). ε rThe measurement was performed using a measuring device (E4980A) manufactured by Agilent Technologies, Inc. ε r In the measurement, an electric field of 1 V / μm was applied to the piezoelectric thin film. The area of ​​the portion of the first and second electrode layers to which the electric field was applied was 600 × 600 (μm). 2 The ε of Example 1 is shown in Table 2 below. r .

[0161] <Determination of Dielectric Loss Tangent>

[0162] The dielectric loss tangent (in %) of the piezoelectric thin film of Example 1 was measured. The E4980A described above was used in the measurement of the dielectric loss tangent (tanδ). An electric field of 1 V / μm was applied to the piezoelectric thin film during the tanδ measurement. The area of ​​the portion of the first and second electrode layers to which the electric field was applied was 600 × 600 (μm). 2 The tanδ of Example 1 is shown in Table 2 below.

[0163] (Examples 2-20, Comparative Examples 1 and 2)

[0164] As raw materials for the piezoelectric films of Examples 2, 3, 5-20 and Comparative Example 2, targets made of Al, divalent element Ed, and tetravalent element Et were used. The Ed and Et values ​​for Examples 2, 3, 5-20 and Comparative Example 2 are shown in Table 1 below.

[0165] As raw materials for the piezoelectric thin film of Example 3, a target material composed of Al and a target material composed of the trivalent element Etr were used. The Etr of Example 3 is shown in Table 1 below. As raw materials for the piezoelectric thin film of Example 3, a target material composed of the divalent element Ed and a target material composed of the tetravalent element Et were used.

[0166] As the raw material for the piezoelectric thin film of Comparative Example 1, a target containing the additive element Eadd was not used.

[0167] By changing the input power of each target, the composition of the piezoelectric films in Examples 5-10 and 13-16 was adjusted to be different from each other.

[0168] By changing the input power of each target, the composition of the piezoelectric films in Examples 11, 12, and 17-20 was adjusted to be different from each other.

[0169] Before the formation of the piezoelectric thin films in Comparative Examples 1 and 2, the inner wall of the film-forming chamber was not covered by a metal film.

[0170] In addition to the matters described above, piezoelectric thin film elements of Examples 2-20 and Comparative Examples 1 and 2 were prepared using the same method as in Example 1. Analysis and measurements related to the piezoelectric thin film elements of Examples 2-20 and Comparative Examples 1 and 2 were performed using the same method as in Example 1. The results of the analysis and measurements of Examples 2-20 and Comparative Examples 1 and 2 are shown in Tables 1 and 2 below.

[0171] Apart from the differences shown in Tables 1 and 2 below, the piezoelectric films of Examples 2 to 20 each have the same characteristics as those of Example 1.

[0172] As shown in Table 1 below, the composition of the first grain of Comparative Example 1 is the same as that of the second grain of Comparative Example 1. That is, the composition of the plurality of grains contained in the piezoelectric film of Comparative Example 1 is uniform.

[0173] As described in Table 1 below, the second grain of Comparative Example 2 contains an excessive amount of the additive element Eadd, does not have a wurtzite-type structure, and is not aluminum nitride. That is, in the second grain of Comparative Example 2, the excessive additive element segregated. In Comparative Example 2, the composition of the multiple first grains composed of aluminum containing the additive element Eadd is homogeneous.

[0174] An image of the cross-section of the piezoelectric thin film in Example 15 is shown in... Figure 4 As shown in (a) of the document. Figure 4 The image shown in (a) was taken by STEM. Figure 4 The distribution of magnesium in the cross section shown in (a) is as follows: Figure 4 As shown in (b) of the document. Figure 4 (b) in the example is obtained by using the mapping of STEM-EDS. Figure 4 The white part in (b) is where magnesium is present.

[0175] In Table 1 below, r(Ed)1 refers to [Ed]1 / ([Ed]1+[Et]1).

[0176] In Table 1 below, r(Ed)2 refers to [Ed]2 / ([Ed]2+[Et]2).

[0177] In the above implementation, R(Eadd) and R(Ed+Etr) are defined in Table 2 below.

[0178] [Table 1]

[0179]

[0180] [Table 2]

[0181]

[0182] Industrial availability

[0183] For example, the piezoelectric film of one aspect of this disclosure can be used in microphones, sensors, transducers, filters, acquisition devices, or actuators.

[0184] Explanation of reference numerals in the attached figures

[0185] 1: First electrode layer, 2: Second electrode layer, 3: Piezoelectric thin film, 10: Piezoelectric thin film element, s1: Surface of the first electrode layer, s2: Surface of the second electrode layer, s31: First principal surface of the piezoelectric thin film, s32: Second principal surface of the piezoelectric thin film, uc: Unit cell of aluminum nitride (wurtzite structure), Ed: Divalent element, Etr: Trivalent element, Et: Tetravalent element, g1: First grain, g2: Second grain.

Claims

1. A piezoelectric thin film, wherein, It contains multiple grains of aluminum nitride. The aluminum nitride contains additive elements. The plurality of grains includes a plurality of first grains and a plurality of second grains. The ratio of the amount of the added element in the first grain to the total amount of aluminum and the added element in the first grain is expressed as [Eadd]1 atom%. The ratio of the amount of the added element in the second grain to the total amount of aluminum and the added element in the second grain is expressed as [Eadd]2 atomic%. [Eadd]2 is higher than [Eadd]1.

2. The piezoelectric thin film according to claim 1, wherein, The added elements contain at least divalent and tetravalent elements.

3. The piezoelectric thin film according to claim 2, wherein, At least some of the divalent elements are magnesium. At least a portion of the tetravalent elements are at least one of zirconium and hafnium.

4. The piezoelectric thin film according to claim 1, wherein, The added element contains at least a trivalent element.

5. The piezoelectric thin film according to claim 4, wherein, At least some of the trivalent elements are scandium.

6. The piezoelectric thin film according to claim 1, wherein, The added elements are either only divalent and tetravalent elements, or only trivalent elements, or a combination of the divalent, trivalent, and tetravalent elements. The ratio of the amount of the divalent element in the first grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the first grain is expressed as [Ed] 1 atom%. The ratio of the amount of the trivalent element in the first grain to the total amount of the aluminum, divalent element, trivalent element and tetravalent element in the first grain is expressed as [Etr]1 atom%. The ratio of the amount of the divalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Ed]2 atoms%. The ratio of the amount of the trivalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Etr]2 atomic%. ([Ed]2 + [Etr]2) / ([Ed]1 + [Etr]1) is greater than 1.000 and less than 3.

000.

7. The piezoelectric thin film according to claim 1, wherein, The total volume of the plurality of first grains in the piezoelectric film is expressed as A1 volume%. The total volume of the plurality of second grains in the piezoelectric film is expressed as A2% (volume %). A2 / (A1+A2) is above 0.1% and below 15.0%.

8. The piezoelectric thin film according to claim 1, wherein, The added elements contain at least two valent elements and two tetravalent elements. The ratio of the amount of the divalent element in the first grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the first grain is expressed as [Ed] 1 atom%. The ratio of the amount of the tetravalent element in the first grain to the total amount of the aluminum, divalent element, trivalent element and tetravalent element in the first grain is expressed as [Et]1 atom%. The ratio of the amount of the divalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Ed]2 atoms%. The ratio of the amount of the tetravalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Et]2 atoms%. [Ed]1 / ([Ed]1+[Et]1) is greater than 0.40 and less than 0.

58. [Ed]2 / ([Ed]2+[Et]2) is greater than 0.40 and less than 0.

58.

9. The piezoelectric thin film according to claim 1, wherein, The added elements are either only divalent and tetravalent elements, or only trivalent elements, or a combination of the divalent, trivalent, and tetravalent elements. The ratio of the amount of the divalent element in the first grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the first grain is expressed as [Ed] 1 atom%. The ratio of the amount of the trivalent element in the first grain to the total amount of the aluminum, divalent element, trivalent element and tetravalent element in the first grain is expressed as [Etr]1 atom%. The ratio of the amount of the tetravalent element in the first grain to the total amount of the aluminum, divalent element, trivalent element and tetravalent element in the first grain is expressed as [Et]1 atom%. The ratio of the amount of the divalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Ed]2 atoms%. The ratio of the amount of the trivalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Etr]2 atomic%. The ratio of the amount of the tetravalent element in the second grain to the total amount of aluminum, the divalent element, the trivalent element, and the tetravalent element in the second grain is expressed as [Et]2 atoms%. [Ed]1 + [Etr]1 + [Et]1 is 9.0 atomic% or more and less than 61.0 atomic%. [Ed]2+[Etr]2+[Et]2 is greater than 9.0 atomic% and less than 61.0 atomic%.

10. The piezoelectric thin film according to claim 1, wherein, The first grain extends along a direction perpendicular to the main surface of the piezoelectric film. The second grain extends along a direction perpendicular to the main surface of the piezoelectric film.

11. A piezoelectric thin film element, wherein, have: The piezoelectric thin film as described in any one of claims 1 to 10; and Electrode layer, The piezoelectric film overlaps directly or indirectly with the surface of the electrode layer.

Images