Piezoelectric thin film, and piezoelectric thin film INT

Abstract

To provide piezoelectric thin films with excellent fatigue properties. [Solution] The piezoelectric thin film contains a metal oxide. The piezoelectric thin film is ferroelectric. The metal oxide contains hafnium, cerium, and pentavalent elements. The metal oxide contains a crystalline phase having a fluorite-type structure. The crystalline phase contains at least one crystal, either orthorhombic or tetragonal.

Description

[Technical Field]

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

[0002] As described in Patent Document 1 below, hafnium oxide (HfO2) is widely known as a dielectric. Furthermore, as described in Patent Document 2 below, it is also known that thin films containing a solid solution of HfO2 have ferroelectric properties. Patent Document 3 below also discloses a ferroelectric thin film containing HfO2. Ferroelectricity is a property in which electric dipoles are aligned within a dielectric material when there is no electric field outside the dielectric material, and the direction of the electric dipoles (polarization direction) changes reversibly along the electric field applied to the dielectric material. A ferroelectric material is a type of piezoelectric material and naturally possesses piezoelectric properties. It is believed that ferroelectric HfO2 has an orthorhombic crystal structure. However, the orthorhombic phase of HfO2 is an unstable phase at normal pressure. Therefore, it is not easy to form a ferroelectric thin film (piezoelectric thin film) containing the orthorhombic phase of HfO2. For example, the orthorhombic structure in a ferroelectric thin film is stabilized by the crystalline structure of the crystalline substrate on which the ferroelectric thin film is superimposed, thereby constraining the crystalline structure of the ferroelectric thin film. However, the thicker the ferroelectric thin film, the less its crystalline structure is constrained by the crystalline structure of the crystalline substrate. As a result, the thicker the ferroelectric thin film, the more likely it is to contain monoclinic layers rather than orthorhombic layers. Thin films containing monoclinic HfO2 exhibit inferior ferroelectric and piezoelectric properties. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-306036 [Patent Document 2] International Publication No. 2016 / 031986 Pamphlet [Patent Document 3] Patent No. 7061752 [Overview of the project] [Problems that the invention aims to solve]

[0004] Adding cerium (Ce) to a piezoelectric thin film easily stabilizes the crystalline phase (e.g., orthorhombic) of HfO2 in the piezoelectric thin film. However, the addition of Ce to the piezoelectric thin film easily introduces oxygen vacancies into the piezoelectric thin film. As a result, the residual polarization value (Pr) of the piezoelectric thin film tends to decrease with repeated polarization and polarization reversal. Furthermore, repeated polarization and polarization reversal of the piezoelectric thin film tends to increase the leakage current, ultimately leading to dielectric breakdown of the piezoelectric thin film. In this disclosure, "fatigue characteristic" refers to the property that the residual polarization value (Pr) of a piezoelectric thin film (ferroelectric thin film) does not easily decrease with repeated polarization and polarization reversal, and that the piezoelectric thin film (ferroelectric thin film) is less likely to undergo dielectric breakdown. For the practical application of piezoelectric thin films containing Hf oxides, improvement of fatigue characteristics is required. In other words, there is a need for piezoelectric thin films with excellent fatigue properties, such as those in which the residual polarization value (Pr) does not decrease easily with repeated polarization and polarization reversal, and which are resistant to dielectric breakdown.

[0005] One aspect of this disclosure is to provide a piezoelectric thin film with excellent fatigue characteristics, and a piezoelectric thin film element including said piezoelectric thin film. [Means for solving the problem]

[0006] For example, one aspect of the present disclosure relates to a piezoelectric thin film described in any one of [1] to [8] below, and a piezoelectric thin film element described in any one of [9] to

[11] below.

[0007] [1] A piezoelectric thin film containing a metal oxide, The piezoelectric thin film has ferroelectric properties, The metal oxide contains hafnium, cerium, and a pentavalent element, The metal oxide contains a crystal phase having a fluorite-type structure, The crystal phase contains at least one crystal of a cubic crystal and a tetragonal crystal, A piezoelectric thin film.

[0008] [2] The metal oxide further contains an amorphous phase, The piezoelectric thin film according to [1].

[0009] [3] The pentavalent element is one or more elements selected from the group consisting of vanadium, niobium, and tantalum, The piezoelectric thin film according to [1] or [2].

[0010] [4] The content of hafnium in the metal oxide is expressed as [Hf] atomic %, The content of cerium in the metal oxide is expressed as [Ce] atomic %, <000009]1>The content of the pentavalent element in the metal oxide is expressed as [Ev] atomic %, [Ce] / ([Hf]+[Ce]+[Ev]) is 0.01 or more and 0.40 or less, The piezoelectric thin film according to any one of [1] to [3].

[0011] [5] The content of hafnium in the metal oxide is expressed as [Hf] atomic %, The content of cerium in the metal oxide is expressed as [Ce] atomic %, The content of the pentavalent element in the metal oxide is expressed as [Ev] atomic %, [Ev] / ([Hf]+[Ce]+[Ev]) is 0.01 or more and 0.30 or less, The piezoelectric thin film according to any one of [1] to [4].

[0012] [6] The (111) plane of some or all of the crystal phases is oriented in the normal direction of the main surface of the piezoelectric thin film, The piezoelectric thin film according to any one of [1] to [5].

[0013] [7] Some or all of the (100) planes of the crystalline phase are oriented in the direction normal to the principal plane of the piezoelectric thin film. A piezoelectric thin film described in any one of [1] to [5].

[0014] [8] Some of the (111) planes of the crystalline phase are oriented in the direction normal to the main surface of the piezoelectric thin film, Other (100) planes of the crystalline phase are oriented in the direction normal to the principal surface of the piezoelectric thin film. A piezoelectric thin film described in any one of [1] to [5].

[0015] [9] The piezoelectric thin film described in any one of [1] to [8], Piezoelectric thin-film element.

[0016]

[10] First electrode layer and The second electrode layer, Includes, At least a portion of the piezoelectric thin film is disposed between the first electrode layer and the second electrode layer, [9] The piezoelectric thin film element described below.

[0017]

[11] At least one of the first electrode layer and the second electrode layer contains platinum or indium tin oxide.

[10] The piezoelectric thin film element described above. [Effects of the Invention]

[0018] According to one aspect of this disclosure, a piezoelectric thin film with excellent fatigue characteristics and a piezoelectric thin film element including the piezoelectric thin film are provided. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1(a) is a schematic cross-sectional view of a specific example of a piezoelectric thin-film device, and Figure 1(b) is an exploded perspective view of the piezoelectric thin-film device shown in Figure 1(a), where the substrate 1 and the second electrode layer 4 are omitted in Figure 1(b). [Figure 2]Figure 2(a) is a perspective view of an orthorhombic unit cell of fluorite-type structure (hafnium oxide), and Figure 2(b) is a perspective view of a tetragonal unit cell of fluorite-type structure (hafnium oxide). [Figure 3] Figure 3(a) is a schematic perspective view of the unit cell of the fluorite-type crystalline phase (orthorhombic), showing the (111) plane of the crystalline phase (orthorhombic), and Figure 3(b) is a schematic perspective view of the unit cell of the fluorite-type crystalline phase (orthorhombic), showing the (100) plane of the crystalline phase (orthorhombic). [Figure 4] Figure 4(a) is a schematic perspective view of the unit cell of the tetragonal crystalline phase with a fluorite-type structure, showing the (111) plane of the tetragonal crystalline phase, and Figure 4(b) is a schematic perspective view of the unit cell of the tetragonal crystalline phase with a fluorite-type structure, showing the (100) plane of the tetragonal crystalline phase. [Modes for carrying out the invention]

[0020] Preferred embodiments of the present disclosure will be described below with reference to the drawings. In the drawings, equivalent components are denoted by equivalent reference numerals. The present disclosure is not limited to the embodiments described below. X, Y, and Z shown in Figure 1(a) and Figure 1(b) respectively represent three mutually orthogonal coordinate axes. The directions of the X, Y, and Z axes are common to Figure 1(a) and Figure 1(b).

[0021] The piezoelectric thin-film element according to this embodiment includes a piezoelectric thin film. For example, the piezoelectric thin-film element may include a piezoelectric thin film, a first electrode layer, and a second electrode layer, and part or all of the piezoelectric thin film may be arranged between the first electrode layer and the second electrode layer. For example, as shown in Figure 1(a), the piezoelectric thin-film element 10 may include a substrate 1, a first electrode layer 2 directly or indirectly overlapping the substrate 1, a piezoelectric thin film 3 directly or indirectly overlapping the first electrode layer 2, and a second electrode layer 4 directly or indirectly overlapping the piezoelectric thin film 3. The first electrode layer 2 may be a lower electrode layer. The second electrode layer 4 may be an upper electrode layer. Modifications of the piezoelectric thin-film element 10 do not require the inclusion of the second electrode layer 4. For example, a piezoelectric thin-film element without the second electrode layer may be supplied as a product to an electronic equipment manufacturer, and then the second electrode layer may be added to the piezoelectric thin-film element during the assembly and manufacturing process of the electronic equipment.

[0022] As shown in Figures 1(a) and 1(b), the piezoelectric thin film 3 has a main surface s. The cross-section of the piezoelectric thin film element 10 shown in Figure 1(a) is parallel to the normal direction dn of the main surface s of the piezoelectric thin film 3. The "main surface" is the surface with the largest area among the multiple surfaces of a polyhedron. For example, the main surface may be a surface among the multiple surfaces of the piezoelectric thin film 3 that is substantially or completely perpendicular to the thickness direction (Z-axis direction) of the piezoelectric thin film 3. In other words, the thickness direction of the piezoelectric thin film 3 may be substantially or completely perpendicular to the main surface s of the piezoelectric thin film 3. The piezoelectric thin film 3 may have a pair of main surfaces that are parallel to each other and one or more end surfaces that are perpendicular to each main surface. The normal direction dn of the main surface s of the piezoelectric thin film 3 is the normal direction D of the main surface of the first electrode layer 2. N The main surface s of the piezoelectric thin film 3 may be approximately or perfectly parallel to the main surface of the first electrode layer 2. The shape of the piezoelectric thin film 3 (shape of the main surface s) is not limited. For example, the shape of the piezoelectric thin film 3 may be a polygon such as a square. For example, the piezoelectric thin film 3 may have a curved surface. For example, the piezoelectric thin film 3 may be a disc.

[0023] The piezoelectric thin film 3 according to this embodiment contains a metal oxide. Part or all of the piezoelectric thin film 3 may be a metal oxide. The piezoelectric thin film 3 has ferroelectric properties. In other words, the piezoelectric thin film 3 is a ferroelectric thin film. The piezoelectric thin film 3 may be an epitaxial thin film.

[0024] The metal oxide contains hafnium (Hf), cerium (Ce), and the pentavalent element Ev. The metal oxide includes a crystalline phase having a fluorite structure. In other words, the crystalline structure of the metal oxide is a fluorite structure. The crystalline phase having a fluorite structure includes at least one type of crystal from orthorhombic crystal and tetragonal crystal. In other words, part or all of the metal oxide is at least one type of crystal from orthorhombic and tetragonal. The piezoelectric properties and ferroelectric properties of the piezoelectric thin film 3 are due to one or both of the orthorhombic and tetragonal crystals. The crystalline phase may be a perfect crystal or an imperfect crystal. The crystalline phase may be a single crystal or a polycrystalline crystal. For example, the crystalline phase may contain a plurality of columnar crystals. A columnar crystal is a crystal that extends along the direction normal to the main surface s of the piezoelectric thin film 3.

[0025] The presence of Ce in a metal oxide containing Hf further stabilizes either orthorhombic or tetragonal crystal structures, or both. In other words, the crystalline phase is stabilized by Ce. However, if the metal oxide containing Hf and Ce does not contain the pentavalent element Ev, multiple oxygen vacancies due to Ce are likely to form in the crystalline phase. These multiple oxygen vacancies in the crystalline phase degrade the fatigue properties of the piezoelectric thin film 3. In contrast, if the metal oxide containing Hf and Ce further contains the pentavalent element Ev, the pentavalent element Ev suppresses the formation of multiple oxygen vacancies in the crystalline phase, improving the fatigue properties of the piezoelectric thin film 3. This is because the valence of the pentavalent element Ev (+5) is greater than the valences of Hf and Ce respectively (+4). In other words, the excess oxygen due to the pentavalent element Ev cancels out the multiple oxygen vacancies due to Ce, thus suppressing the formation of multiple oxygen vacancies in the crystalline phase. If an element with a valence greater than that of a pentavalent element Ev is included in the metal oxide, the formation of multiple oxygen vacancies caused by Ce is suppressed, but the crystalline phase tends to become monoclinic, and the piezoelectric properties and ferroelectric properties of the piezoelectric thin film 3 tend to deteriorate.

[0026] The crystalline phase may consist only of orthorhombic crystals. The crystalline phase may consist only of tetragonal crystals. The crystalline phase may contain both orthorhombic and tetragonal crystals. The crystalline phase may consist only of both orthorhombic and tetragonal crystals. In this disclosure, orthorhombic crystal may imply rhombic crystal. In contrast to orthorhombic and tetragonal crystals, neither monoclinic nor cubic crystals have piezoelectric properties. However, the metal oxide may further contain trace amounts of monoclinic crystals, provided that the piezoelectric properties of the piezoelectric thin film 3 are not impaired. The metal oxide may further contain trace amounts of cubic crystals, provided that the piezoelectric properties of the piezoelectric thin film 3 are not impaired.

[0027] For example, the unit cells (uco) constituting the orthorhombic crystal in the crystalline phase are shown in Figure 2(a), Figure 3(a), and Figure 3(b). The unit cells (uco) in each figure have a fluorite-type structure. Some of the Hf in the unit cell (uco) shown in Figure 2(a) may be substituted with Ce or the pentavalent element Ev. The ratio of the lengths of the fundamental translation vectors a, b, and c constituting the unit cell (uco) is not limited to the ratios shown in each figure. The fundamental translation vectors a, b, and c of the orthorhombic unit cell (uco) are orthogonal to each other. The lengths of the fundamental translation vectors a, b, and c of the orthorhombic unit cell (uco) are different from each other. For example, in the case of orthorhombic hafnium oxide, the length of fundamental translation vector a (lattice constant a) may be about 5.30 Å, the length of fundamental translation vector b (lattice constant b) may be about 5.11 Å, and the length of fundamental translation vector c (lattice constant c) may be about 5.10 Å.

[0028] For example, the unit cell uct constituting the tetragonal crystal in the crystalline phase is shown in Figure 2(b), Figure 4(a), and Figure 4(b). The unit cell uct in each figure has a fluorite-type structure. Some of the Hf in the unit cell uco shown in Figure 2(b) may be substituted with Ce or the pentavalent element Ev. The ratio of the lengths of the fundamental translation vectors a, b, and c constituting the unit cell uct is not limited to the ratio shown in each figure. The fundamental translation vectors a, b, and c of the tetragonal unit cell uct are orthogonal to each other, the length of fundamental translation vector a is equal to the length of fundamental translation vector b, and the length of fundamental translation vector a is different from the length of fundamental translation vector c. For example, in the case of tetragonal hafnium oxide, the length of fundamental translation vector a (lattice constant a) may be about 5.14 Å, the length of fundamental translation vector b (lattice constant b) may be about 5.14 Å, and the length of fundamental translation vector c (lattice constant c) may be about 5.25 Å.

[0029] Figure 3(a) shows the (111) plane of the orthorhombic crystal. The

[0111] indicated in Figure 3(a) is the orientation of the (111) plane of the orthorhombic crystal. Figure 3(b) shows the (100) plane of the orthorhombic crystal. The

[0100] indicated in Figure 3(b) is the orientation of the (100) plane of the orthorhombic crystal. Figure 4(a) shows the (111) plane of the tetragonal crystal. The

[0111] indicated in Figure 4(a) is the orientation of the (111) plane of the tetragonal crystal. Figure 4(b) shows the (100) plane of a tetragonal crystal. The

[0100] indicated in Figure 4(b) is the orientation of the (100) plane of the tetragonal crystal.

[0030] For the reason that the piezoelectric properties and ferroelectric properties of the piezoelectric thin film 3 are easily improved, at least one lattice plane selected from the group consisting of the (111) plane and the (100) plane of the crystalline phase may be oriented in the direction dn normal to the main surface s of the piezoelectric thin film 3. For example, at least one lattice plane selected from the group consisting of the (111) plane and the (100) plane of the crystalline phase may be substantially or perfectly parallel to the main surface s of the piezoelectric thin film 3. For example, some or all of the (111) planes of the crystalline phase may be oriented in the direction dn normal to the main surface s of the piezoelectric thin film 3. For example, some or all of the (100) planes of the crystalline phase may be oriented in the direction dn normal to the main surface s of the piezoelectric thin film 3. For example, the (111) planes of some crystalline phases may be oriented in the direction dn normal to the main surface s of the piezoelectric thin film 3, and the (100) planes of other crystalline phases may be oriented in the direction dn normal to the main surface s of the piezoelectric thin film 3. For example, some or all of the (111) planes of the orthorhombic crystals contained in the crystalline phase may be oriented in the direction dn normal to the main surface s of the piezoelectric thin film 3. For example, some or all of the (111) planes of the tetragonal crystals in the crystalline phase may be oriented in the direction dn normal to the main surface s of the piezoelectric thin film 3. For example, some or all of the (100) planes of the orthorhombic crystals contained in the crystalline phase may be oriented in the direction dn normal to the main surface s of the piezoelectric thin film 3. For example, some or all of the (100) planes of the tetragonal crystals in the crystalline phase may be oriented in the direction dn normal to the main surface s of the piezoelectric thin film 3.

[0031] The metal oxide may consist only of a crystalline phase. In addition to the crystalline phase, the metal oxide may further contain an amorphous phase. That is, the piezoelectric thin film 3 may contain both the crystalline phase and the amorphous phase of the metal oxide. For example, the amorphous phase in the piezoelectric thin film 3 may be located near the interface between the piezoelectric thin film 3 and the first electrode layer 2. In other words, the portion of the piezoelectric thin film 3 in contact with the first electrode layer 2 may contain not only the crystalline phase but also the amorphous phase. The piezoelectric thin film 3 according to this disclosure tends to contain both the crystalline and amorphous phases. In other words, a piezoelectric thin film 3 containing both the crystalline and amorphous phases tends to have excellent fatigue properties. However, the causal relationship between the amorphous phase and fatigue properties has not yet been clarified.

[0032] Because the crystalline phase of the metal oxide tends to contain at least one type of crystal from orthorhombic and tetragonal crystals, and the fatigue properties, piezoelectric properties, and ferroelectric properties of the piezoelectric thin film 3 tend to improve, the pentavalent element Ev may be one or more elements selected from the group consisting of vanadium (V), niobium (Nb), and tantalum (Ta). The metal oxide may contain multiple types of pentavalent elements Ev.

[0033] The hafnium content in a metal oxide may be expressed as [Hf] atoms in percent. The cerium content in a metal oxide may be expressed as [Ce] atoms in percent. The content of pentavalent elements in a metal oxide may be expressed as [Ev] atoms in percent. For the reason that the crystalline phase of the metal oxide tends to contain at least one type of crystal from orthorhombic and tetragonal, and that the fatigue characteristics, piezoelectric properties, and ferroelectric properties of the piezoelectric thin film 3 tend to improve, [Hf] / ([Hf]+[Ce]+[Ev]) may be 0.30 or more and 0.98 or less, or 0.59 or more and 0.88 or less. For the reason that the crystalline phase of the metal oxide tends to contain at least one type of crystal from orthorhombic and tetragonal, and that the fatigue characteristics, piezoelectric properties, and ferroelectric properties of the piezoelectric thin film 3 tend to improve, [Ce] / ([Hf]+[Ce]+[Ev]) may be between 0.01 and 0.40. For the reason that the crystalline phase of the metal oxide tends to contain at least one type of crystal from orthorhombic and tetragonal, and that the fatigue characteristics, piezoelectric properties, and ferroelectric properties of the piezoelectric thin film 3 tend to improve, [Ev] / ([Hf]+[Ce]+[Ev]) may be between 0.01 and 0.30.

[0034] The metal oxide may be represented by the following chemical formula 1 or 2 because its crystalline phase tends to include at least one type of crystal from orthorhombic and tetragonal structures, and because this easily improves the fatigue properties, piezoelectric properties, and ferroelectric properties of the piezoelectric thin film 3. (1-xy)HfO2+xCeO2+yEvO 2.5 (1) Hf (1-x-y) Ce x Ev y O 2+0.5y (2) Chemical formula 1 above is substantially the same as chemical formula 2 above. Ev in chemical formulas 1 and 2 above represents a pentavalent element. The units of (1-xy), x, and y in chemical formulas 1 and 2 above are molar ratios. x in chemical formulas 1 and 2 above may be between 0.01 and 0.40. y in chemical formulas 1 and 2 above may be between 0.01 and 0.30. In chemical formulas 1 and 2 above, (1-xy) may be equal to [Hf] / ([Hf]+[Ce]+[Ev]). In chemical formulas 1 and 2 above, x may be equal to [Ce] / ([Hf]+[Ce]+[Ev]). In the above chemical formulas 1 and 2, y may be equal to [Ev] / ([Hf]+[Ce]+[Ev]).

[0035] As long as the fatigue properties, piezoelectric properties, and ferroelectric properties of the piezoelectric thin film 3 are not impaired, the metal oxide contained in the piezoelectric thin film 3 may further include one or more additive elements in addition to Hf, Ce, the pentavalent element Ev, and oxygen (O). For example, the additive elements may be one or more elements selected from the group consisting of aluminum (Al), silicon (Si), bismuth (Bi), zirconium (Zr), yttrium (Y), and lanthanides (excluding Ce). In other words, the additive elements may be one or more elements selected from the group consisting of aluminum (Al), silicon (Si), bismuth (Bi), zirconium (Zr), yttrium (Y), zirconium (Zr), yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0036] The thickness of the piezoelectric thin film 3 may be uniform. The thickness of the piezoelectric thin film 3 is not particularly limited. For example, the thickness of the piezoelectric thin film 3 may be 5 nm or more and 3000 nm or less, or 5 nm or more and 1000 nm or less.

[0037] For example, the composition of the piezoelectric thin film 3 may be analyzed by X-ray fluorescence (XRF) or inductively coupled plasma (ICP) emission spectroscopy. For example, the crystalline structure of the piezoelectric thin film 3 (crystalline phase) may be determined by X-ray diffraction (XRD). For example, the thickness of the piezoelectric thin film 3 may be measured in cross-section using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). For example, the amorphous phase of a metal oxide (a phase in which Hf, Ce, Ev, and O are not regularly arranged) can be observed in cross-section of the piezoelectric thin film 3 by TEM. The cross-section in which the amorphous phase is observed may be perpendicular to the main surface s of the piezoelectric thin film 3.

[0038] <Method for manufacturing piezoelectric thin films> A method for manufacturing the piezoelectric thin film 3 may include the steps of forming a precursor film containing a monoclinic metal oxide with hafnium, cerium, and a pentavalent element Ev, and forming the piezoelectric thin film 3 from the precursor film by heating (annealing) the precursor film.

[0039] The precursor film is prepared from a raw material (target) consisting of a metal oxide containing hafnium, cerium, and the pentavalent element Ev. The composition of the raw material may be the same as that of the piezoelectric thin film 3. The raw material for the precursor film may be prepared by calcining a mixture (powder) consisting of oxides of hafnium, cerium, and the pentavalent element Ev. For example, the raw material for the precursor film may be hafnium oxide (HfO2), cerium oxide (CeO2), and an oxide of a pentavalent element (e.g., EvO2). 2.5 It may be produced by calcining a mixture (powder) consisting of , or Ev2O5. Hafnium oxide, cerium oxide, and oxides of pentavalent elements may be mixed in predetermined ratios so that the composition of the raw materials substantially or completely matches the composition of the metal oxide described above (chemical formula 1 or 2 above).

[0040] By vapor deposition, the elements constituting the raw materials are evaporated. The evaporated elements adhere to and deposit on the surface of the first electrode layer 2 or the surface of the substrate 1. As a result, the precursor film grows epitaxially on the surface of the first electrode layer 2 or the surface of the substrate 1. For example, the vapor deposition method may be sputtering, electron beam deposition, chemical vapor deposition (CVD), or pulsed-laser deposition (PLD). The excitation source differs depending on the type of vapor deposition method. For example, the excitation source for sputtering is Ar plasma. The excitation source for electron beam deposition is an electron beam. The excitation source for PLD is laser light (e.g., an excimer laser). When these excitation sources are irradiated onto the raw materials, the elements constituting the raw materials evaporate. The atmosphere for vapor deposition may be a vacuum or an inert gas. For example, the inert gas may be nitrogen gas or a noble gas. For example, the atmospheric pressure in the vapor phase growth method may be 1 Torr or less, or 10 mTorr or less.

[0041] Forming the precursor film by the PLD method is preferable because the precursor film readily contains monoclinic crystals, and annealing of the precursor film easily transforms it into a crystalline phase containing at least one of orthorhombic and tetragonal crystals. In the PLD method, the pulsed laser can instantly and uniformly plasmaize each element constituting the raw material (target). Therefore, a piezoelectric thin film 3 having the same composition as the raw material is easily formed. With the PLD method, the thickness, growth rate, and crystallinity of the piezoelectric thin film 3 can be easily controlled by adjusting various parameters such as the oscillation frequency of the laser pulse, the number of shots, the pulse energy, and the distance between the first electrode layer 2 or substrate 1 and the target. In the PLD method, the oscillation frequency of the pulsed light (e.g., KrF laser light) irradiated onto the target is preferably 3 Hz or less because the precursor film readily contains monoclinic crystals and the formation of an amorphous phase in the precursor film is suppressed. As the oscillation frequency of the pulsed light decreases, the growth rate of the precursor film decreases. As the growth rate of the precursor film decreases, time is ensured for the plasma-generated raw material to migrate on the surface of the first electrode layer 2 or the surface of the substrate 1. In other words, sufficient time is ensured for crystal growth in the precursor film. As a result, the precursor film tends to become monoclinic rather than amorphous. As the pulse energy decreases, the growth rate of the precursor film tends to decrease, and the precursor film tends to become monoclinic. The amorphous phase of the metal oxide contained in the precursor film may remain in the piezoelectric thin film 3. In other words, the amorphous phase of the metal oxide contained in the piezoelectric thin film 3 may originate from the precursor film.

[0042] In vapor deposition, the surface temperature of the first electrode layer 2 or the substrate 1 may be room temperature or ambient temperature (20°C ± 15°C). In other words, it is not necessary to heat the first electrode layer 2 or the substrate 1 during the formation of the precursor film, and the precursor film may be formed at room temperature or ambient temperature. Most precursor films formed at room temperature or ambient temperature are monoclinic. The lengths of the fundamental translation vectors a, b, and c that constitute the monoclinic unit cell are different from each other. The fundamental translation vectors a and b that constitute the monoclinic unit cell are perpendicular to each other, the fundamental translation vectors b and c that constitute the monoclinic unit cell are also perpendicular to each other, and the fundamental translation vectors c and a that constitute the monoclinic unit cell are not perpendicular to each other. For example, the precursor film may consist only of monoclinic material. However, a part of the precursor film may be one or both of orthorhombic and tetragonal. If the entire precursor film is amorphous, it is difficult to form a crystalline phase (metal oxide) containing at least one of orthorhombic or tetragonal crystals by annealing the precursor film.

[0043] The monoclinic crystals contained in the precursor film may have a fluorite-type structure. The lattice planes (for example, at least one of the (111) plane or (100) plane) of the monoclinic crystals (fluorite-type structure) in the precursor film may be substantially or perfectly parallel to the surface of the first electrode layer 2 or the surface of the substrate 1.

[0044] After the precursor film is formed at room temperature or ambient temperature, the precursor film may be heated (annealed). Annealing causes some or all of the monoclinic crystals in the precursor film to change into a crystalline phase containing one or both of orthorhombic and tetragonal crystals. The heating rate of the precursor film may be between 30°C / second and 50°C / second. Rapidly increasing the temperature of the precursor film during annealing facilitates the formation of a crystalline phase containing one or both of orthorhombic and tetragonal crystals. If the heating rate of the precursor film is below the lower limit, it is difficult to form a crystalline phase containing at least one of orthorhombic and tetragonal crystals. Orthorhombic crystals are unstable under atmospheric pressure. Therefore, during the annealing process of the precursor film, orthorhombic crystals tend to revert to monoclinic crystals, and orthorhombic crystals are less likely to be maintained than tetragonal crystals. However, the cooling process following annealing, described later, makes it easier to stabilize the orthorhombic crystals in the piezoelectric thin film 3 under atmospheric pressure.

[0045] For example, the temperature of the precursor film during annealing (annealing temperature) may be between 500°C and 1200°C, between 500°C and 1000°C, or between 800°C and 1000°C. By keeping the precursor film temperature within the above range, some or all of the monoclinic crystals in the precursor film are more likely to change to one or both orthorhombic and tetragonal crystals. For example, the time during which the annealing temperature is maintained (annealing time) may be between 5 seconds and 1200 seconds. The annealing of the precursor film may be carried out in an inert gas or an oxidizing gas. For example, the inert gas may be nitrogen gas or a noble gas. For example, the oxidizing gas may be air or oxygen.

[0046] Following annealing, the precursor film may be cooled at a predetermined cooling rate. The piezoelectric thin film 3 is completed by the cooling of the precursor film following annealing. During the cooling process of the precursor film following annealing, the orthorhombic crystals in the piezoelectric thin film 3 are easily stabilized under normal pressure. For example, the cooling rate may be between 45°C / min and 200°C / min. If the cooling rate is too low, the orthorhombic crystals in the precursor film are likely to change to monoclinic crystals. If the cooling rate is too high, stress caused by the rapid contraction of the precursor film is likely to act on the precursor film, and cracks are likely to form in the piezoelectric thin film 3 obtained after cooling. The precursor film may be cooled in an inert gas or an oxidizing gas. For example, the inert gas may be nitrogen gas or a noble gas. For example, the oxidizing gas may be air or oxygen.

[0047] The mechanism for the formation of the crystalline phase in the manufacturing process of piezoelectric thin films is not limited to the mechanism described above.

[0048] <Substrate, first electrode layer, and second electrode layer> The substrate 1 may be crystalline or amorphous. A crystalline substrate 1 may be single-crystal or polycrystalline. For example, a crystalline substrate 1 may have one crystal structure selected from the group consisting of fluorite-type structure, bixbite-type structure, pyrochlore-type structure, diamond-type structure, zincblende-type structure, face-centered cubic structure, hexagonal structure, perovskite-type structure, NaCl-type structure, rutile-type structure, spinel-type structure, and corundum-type structure. For example, an amorphous substrate 1 may be polyethylene terephthalate (PET) film or glass.

[0049] For example, the substrate 1 having a fluorite-type structure may be yttria-stabilized zirconia (YSZ), cerium oxide, or calcium fluoride.

[0050] For example, the substrate 1 having a bixbite structure may be indium oxide, indium tin oxide, scandium oxide, yttrium oxide, erbium oxide, thulium oxide, ytterbium oxide, or lutetium oxide.

[0051] For example, the substrate 1 having a pyrochlore structure may be bismuth ruthenium oxide (Bi2Ru2O7), rare earth ruthenium oxide (R2Ru2O7, where R is a rare earth element), bismuth iridium oxide (Bi2Ir2O7), or rare earth iridium oxide (R2Ir2O7, where R is a rare earth element).

[0052] For example, the substrate 1 having a diamond structure may be a semiconductor such as silicon or germanium. When the substrate 1 is silicon or germanium, an adhesion layer made of titanium or chromium or the like may be formed on the surface of the substrate 1 to improve the adhesion of the first electrode layer 2.

[0053] For example, the substrate 1 having a sphalerite structure may be a compound semiconductor such as gallium arsenide, aluminum arsenide, gallium phosphide, aluminum phosphide, beta zinc sulfide, or zinc selenide.

[0054] For example, the substrate 1 having a face-centered cubic structure may be platinum, iridium, or gold.

[0055] For example, the substrate 1 having a hexagonal crystal structure may be titanium, zirconium, hafnium, zinc, zinc oxide, or boron nitride.

[0056] For example, the substrate 1 having a perovskite structure may be strontium ruthenium oxide (SrRuO7), calcium ruthenium oxide (CaRuO3), strontium iridium oxide (SrIrO3), lanthanum nickel oxide (LaNiO3), lanthanum alkaline earth manganese oxide (La 1-x Ae x MnO3), or lanthanum alkaline earth cobalt oxide (La 1-x Ae x CoO3). Ae is at least one element selected from the group consisting of Ca, Sr, and Ba.

[0057] For example, the substrate 1 having an NaCl structure may be magnesium oxide or titanium nitride.

[0058] For example, the substrate 1 having a rutile structure may be titanium oxide, iridium oxide, or ruthenium oxide.

[0059] For example, the substrate 1 having a spinel structure may be magnesium aluminum spinel oxide (Mg2AlO4) or triiron tetroxide.

[0060] For example, the substrate 1 having a corundum structure may be aluminum oxide or ferric oxide.

[0061] The thickness of the substrate 1 may be uniform. For example, the thickness of the substrate 1 may be between 10 μm and 1000 μm. If the substrate 1 is conductive, the substrate 1 functions as an electrode, so the first electrode layer 2 may be omitted. In other words, if the substrate 1 is conductive, the piezoelectric thin film 3 may be directly superimposed on the substrate 1.

[0062] For example, the crystalline substrate 1 may be a uniaxially oriented substrate. For example, among the multiple lattice planes included in the crystalline substrate 1, the lattice plane parallel to the surface (principal plane) of the crystalline substrate 1 may be one lattice plane selected from the group consisting of (111) plane, (100) plane, (001) plane, (110) plane, and (101).

[0063] One or both of the (111) planes and (100) planes of the crystalline phase in the piezoelectric thin film 3 may be substantially or perfectly parallel to the surface (main surface) of the crystalline substrate 1, and the (111) plane in the crystalline substrate 1 may be substantially or perfectly parallel to the surface (main surface) of the crystalline substrate 1.

[0064] For example, the first electrode layer 2 may consist of at least one metal selected from the group consisting of Pt (platinum), Pd (palladium), Rh (rhodium), Au (gold), Ru (ruthenium), Ir (iridium), Mo (molybdenum), Ti (titanium), Ta (tantalum), and Ni (nickel). The first electrode layer 2 may also include a conductive composition from among the above compositions listed as specific examples of the substrate 1.

[0065] Because one or both of the (111) planes and (100) planes of the crystalline phase in the piezoelectric thin film 3 are easily oriented in the direction dn normal to the main surface s of the piezoelectric thin film 3, the main surface s of the piezoelectric thin film 3 may directly overlap the first electrode layer 2, and the first electrode layer 2 may contain platinum or indium tin oxide (ITO). The first electrode layer 2 may consist only of platinum or indium tin oxide.

[0066] The first electrode layer 2 may be crystalline. The first electrode layer 2 may be a single crystal or a polycrystalline material. For example, among the multiple lattice planes included in the first electrode layer 2, the lattice plane parallel to the principal plane of the first electrode layer 2 may be one lattice plane selected from the group consisting of (111) plane, (100) plane, (001) plane, (110) plane, and (101).

[0067] The thickness of the first electrode layer 2 may be uniform. For example, the thickness of the first electrode layer 2 may be between 1 nm and 1.0 μm.

[0068] For example, the second electrode layer 4 may be made of at least one metal selected from the group consisting of Pt, Pd, Rh, Au, Ru, Ir, Mo, Ti, Ta, and Ni. The second electrode layer 4 may also contain a conductive composition from among the above compositions listed as specific examples of the substrate 1. The first electrode layer 2 may contain platinum or indium tin oxide. The second electrode layer 4 may be crystalline. The second electrode layer 4 may be single crystal or polycrystalline. The thickness of the second electrode layer 4 may be uniform. For example, the thickness of the second electrode layer 4 may be 1 nm or more and 1.0 μm or less.

[0069] The piezoelectric thin-film element 10 may further include at least one intermediate layer (buffer layer). For example, a substrate-side intermediate layer may be interposed between the substrate 1 and the first electrode layer 2. For example, a first intermediate layer may be interposed between the first electrode layer 2 and the piezoelectric thin film 3. For example, a second intermediate layer may be interposed between the piezoelectric thin film 3 and the second electrode layer 4. For example, each intermediate layer may contain at least one composition from the compositions listed above as specific examples of the substrate 1. Each intermediate layer may be crystalline. Each intermediate layer may be single crystal or polycrystalline.

[0070] The formation methods for the first electrode layer 2, the second electrode layer 4, and each intermediate layer may be PLD, sputtering, vacuum deposition, printing, spin coating, or sol-gel methods. Annealing of each layer may be performed to enhance the crystallinity of each layer.

[0071] At least a portion or all of the surface of the piezoelectric thin-film element 10 may be covered with a protective film. Covering with a protective film improves the durability (e.g., moisture resistance) of the piezoelectric thin-film element 10.

[0072] <Specific examples of piezoelectric thin-film devices> The piezoelectric thin-film element according to this embodiment has a wide range of applications. For example, the piezoelectric thin-film element may be part of or all of a device selected from the group consisting of piezoelectric actuators, piezoelectric sensors, piezoelectric transducers, piezoelectric microphones, harvesters, oscillators, resonators, acoustic multilayer films, pyroelectric elements, and filters. For example, a piezoelectric actuator may be used in haptics. That is, a piezoelectric actuator may be used in various devices that require tactile feedback. For example, devices that require tactile feedback may be wearable devices, touchpads, displays, or game controllers. For example, a piezoelectric actuator may be used in a head assembly, a head stack assembly, or a hard disk drive. For example, a piezoelectric actuator may be used in a printer head or an inkjet printer. For example, a piezoelectric actuator may be used in a piezoelectric switch. For example, a piezoelectric sensor or piezoelectric transducer may be used in a gyro sensor, pressure sensor, pulse wave sensor, ultrasonic sensor, ultrasonic transducer, infrared sensor, or shock sensor. The ultrasonic transducer may be a piezoelectric micromachined ultrasonic transducer (PMUT). Products utilizing the piezoelectric micromachined ultrasonic transducer may be biometric sensors such as fingerprint sensors and ultrasonic vascular authentication sensors, medical or healthcare sensors, or ToF (Time of Flight) sensors. For example, the filter may be a BAW (Bulk Acoustic Wave) filter or a SAW (Surface Acoustic Wave) filter. Each of the piezoelectric thin-film elements described above may be part of or all of a micro electro-mechanical system (MEMS). Each of the piezoelectric thin-film elements described above may be a wearable device or a portable device.

[0073] This disclosure is not necessarily limited to the embodiments described above. Various modifications to this disclosure are possible and are included in this disclosure, without departing from the spirit of this disclosure. [Examples]

[0074] The present disclosure will be illustrated in detail by the following examples and comparative examples. The present disclosure is not limited to the following examples.

[0075] (Example 1) A single crystal of yttria-stabilized zirconia (YSZ) was used as the crystalline substrate. The (111) plane of the single crystal was parallel to the surface (principal plane) of the substrate. The substrate was rectangular, with dimensions of 5 mm x 5 mm. The substrate thickness was 500 μm. The substrate thickness was uniform.

[0076] A first electrode layer (lower electrode layer) made of indium tin oxide (ITO) was directly formed across the entire surface of the substrate by magnetron sputtering in a vacuum chamber. ITO itself was used as the raw material (target) for the first electrode layer. The input power to the target was 40W. The atmosphere in the vacuum chamber was a mixed gas of Ar and O2. The ratio of the volumes of Ar and O2 (in sccm) was Ar:O2 = 20:1. The substrate temperature was maintained at 700°C during the formation of the first electrode layer. The thickness of the first electrode layer was uniform. The thickness of the first electrode layer was adjusted to 0.05 μm.

[0077] Hafnium oxide (HfO2), cerium oxide (CeO2), and oxides of pentavalent elements (EvO2) 2.5 The raw material (target) for the precursor film was prepared by calcining a mixture (powder) consisting of the following. In Example 1, the pentavalent element Ev was vanadium (V). In other words, in Example 1, the oxide of the pentavalent element was VO 2.5 It was used. In the following, [Hf] / ([Hf]+[Ce]+[Ev]) <hf>It is written as follows. The definition of [Hf] / ([Hf]+[Ce]+[Ev]) is as shown in the embodiment above. In the following, [Ce] / ([Hf]+[Ce]+[Ev]) <ce>It is written as follows. The definition of [Ce] / ([Hf]+[Ce]+[Ev]) is as shown in the embodiment above. In the following, [Ev] / ([Hf]+[Ce]+[Ev]) <ev>It is written as follows. The definition of [Ev] / ([Hf]+[Ce]+[Ev]) is as shown in the embodiment above. <hf> 、 <ce>, and <ev>The content of Hf, Ce, and the pentavalent element Ev in the precursor film raw materials was adjusted so that each of them matched the values ​​shown in Table 1 below.

[0078] A precursor film was directly formed across the entire main surface of the first electrode layer using PLD in a vacuum chamber. The crystal structure of the precursor film was analyzed using an X-ray diffractometer, as described later. The precursor film was monoclinic with a fluorite-type structure. The input power to the target was 200 mJ. In the PLD method, pulses of KrF laser light were irradiated onto the target. The pulse oscillation frequency was 3 Hz. The atmosphere in the vacuum chamber was O2 gas. The pressure in the vacuum chamber was 10 mTorr. The substrate and lower electrode layer were not heated during the precursor film formation process. In other words, the precursor film was formed at room temperature. The thickness of the precursor film was adjusted to 500 nm. The thickness of the precursor film substantially matches the thickness of the piezoelectric thin film formed from the precursor film. The film formation time was 40 hours.

[0079] The precursor film was annealed in nitrogen gas. The heating rate during annealing was 30°C / second. The temperature of the precursor film during annealing (annealing temperature) was 1000°C. The annealing time was 10 seconds.

[0080] A piezoelectric thin film was formed by cooling the precursor film in nitrogen gas immediately following annealing. Cooling was carried out for 30 minutes. Cooling reduced the temperature of the precursor film from 1000°C to 25°C. The cooling rate was adjusted to 32.5°C / min. The thickness of the piezoelectric thin film was equal to the thickness of the precursor film.

[0081] A second electrode layer (upper electrode layer) made of Pt was formed across the entire main surface of the piezoelectric thin film by electron beam deposition in a vacuum chamber. Pure Pt was used as the raw material for the second electrode layer. The substrate was not heated during the formation process of the second electrode layer. The thickness of the second electrode layer was uniform. The thickness of the second electrode layer was adjusted to 0.17 μm.

[0082] The laminate fabricated using the above procedure consisted of a substrate, a first electrode layer directly laminated onto the main surface of the substrate, a piezoelectric thin film directly laminated onto the main surface of the first electrode layer, and a second electrode layer directly laminated onto the main surface of the piezoelectric thin film.

[0083] The laminated structure on the substrate was patterned using photolithography. Dicing of the entire laminate after patterning yielded multiple piezoelectric thin-film elements of Example 1. The piezoelectric thin-film elements had the same laminated structure as the above-mentioned laminate. The shape of the piezoelectric thin-film elements was rectangular. The following analyses and measurements were performed during or after the fabrication of the piezoelectric thin-film elements.

[0084] <Composition of the entire piezoelectric thin film> The overall composition of the piezoelectric thin film was analyzed by X-ray fluorescence analysis (XRF). A wavelength-dispersive X-ray fluorescence spectrometer (RIGAKU AZX-400) manufactured by Rigaku Corporation was used for the XRF analysis. The piezoelectric thin film of Example 1 was a metal oxide consisting of Hf, Ce, the pentavalent element Ev, and O. The composition of the piezoelectric thin film of Example 1 matched the composition of the raw materials for the precursor film. In other words, it was determined by the XRF method. <hf> 、 <ce>, and <ev>Each matched the values ​​shown in Table 1 below.

[0085] <Crystal structure> The X-ray diffraction (XRD) pattern of the piezoelectric thin film was measured using 2θ-ψ measurements. The measurement was performed using a Bruker Corporation D8 DISCOVER X-ray diffractometer. TM A piezoelectric thin film was used. The piezoelectric thin film consisted of a crystalline phase having a fluorite-type structure. The crystalline phase was orthorhombic. The (111) plane of the crystalline phase was oriented in the direction normal to the principal plane of the piezoelectric thin film. In other words, the (111) plane of the crystalline phase was substantially parallel to the principal plane of the piezoelectric thin film. The "orientation plane" described in Table 1 below refers to the lattice plane (lattice plane of the crystalline phase) that is oriented in the direction normal to the principal plane of the piezoelectric thin film.

[0086] Cross-sectional images of the piezoelectric thin-film element were taken using a transmission electron microscope (TEM). The TEM used was a Titan G2 manufactured by Thermo Fisher Scientific Inc. (formerly FEI company). TM The following was used. The photographed cross-section of the piezoelectric thin film element was perpendicular to the main surface of the piezoelectric thin film. The image of the piezoelectric thin film cross-section showed that the portion of the piezoelectric thin film in contact with the first electrode layer contained not only a crystalline phase but also an amorphous phase.

[0087] <Fatigue Characteristics> The fatigue characteristics of piezoelectric thin films were measured using piezoelectric thin film elements. The measurement of fatigue characteristics consisted of repeating two processes (process A and process B). Step A is the measurement of the hysteresis curve of the piezoelectric element. The horizontal axis of the hysteresis curve shows the intensity of the electric field E applied to the piezoelectric thin film (unit: V / mm). The vertical axis of the hysteresis curve shows the polarization value P of the piezoelectric thin film at any electric field E intensity (unit: C / cm). 2 The hysteresis curve shows the dependence of the polarization value P on the intensity of the electric field E. The hysteresis curve is a closed curve that loops through one polarization of the piezoelectric thin film with increasing electric field E intensity and one polarization reversal of the piezoelectric thin film with reversal of electric field E. The residual polarization value Pr of the piezoelectric thin film was determined from one hysteresis curve for each step A. A system combining an atomic microscope (AFM) and a ferroelectric evaluation system was used to measure the hysteresis curves. The atomic microscope used was a Seiko Instruments SPA-400. TM The ferroelectric evaluation system was manufactured by Toyo Technica Co., Ltd. TM The direction of the electric field E (AC voltage) applied to the piezoelectric thin film was parallel to the normal direction of the main surface of the piezoelectric thin film. The frequency of the AC voltage during the measurement of the hysteresis curve was 10 kHz. The maximum value of the AC voltage was 8 V. The temperature of the piezoelectric thin film element was maintained at room temperature (approximately 25°C) during the measurement of the hysteresis curve. Process B is the process of applying an electrical load to the piezoelectric thin film. In process B, a square wave of AC voltage (maximum value: 8V) with a frequency of 50kHz was applied to the piezoelectric thin film. In process B, the series of events from when the voltage went from zero to +8V, then to -8V, and then back to zero was defined as one cycle. In measuring the fatigue characteristics of the piezoelectric thin-film element, the first step A (measurement of the hysteresis curve) was performed. This was followed by the first step B (step B consisting of two cycles). After the first step B, the second step A was performed. If the piezoelectric thin-film element did not undergo dielectric breakdown in the second step A, the second step B (step B consisting of three cycles) was performed. In other words, a total of five cycles had been performed by the time the second step B was completed. After the second step B, the third step A was performed. If the piezoelectric thin-film element did not undergo dielectric breakdown in the third step A, the third step B (step B consisting of five cycles) was performed following the third step A. If the piezoelectric thin-film element did not undergo dielectric breakdown in the nth step A, the nth step B was performed following the nth step A. n is an arbitrary natural number. This repetition of steps A and B was repeated until the piezoelectric thin-film element underwent dielectric breakdown. The total number of cycles N repeated from the first step B to the completion of the nth step B is expressed by the following equations 1 to 3. n is a m The integer a can be expressed by the general formula = 3m - 2 (where m is any natural number). m If this is the case, N can be expressed by the following formula 1.

number

number

number

number

number

number

number

[0088] (Examples 2-6 and Comparative Example 1) <hf> 、 <ce>, and <ev>The Hf, Ce, and pentavalent element Ev content in the raw materials of the precursor films for Examples 2-6 and Comparative Example 1 were adjusted to match the values ​​shown in Table 1 below. The pentavalent element Ev used in the preparation of the raw materials for the precursor films of Examples 2-6 are shown in Table 1 below. The raw materials for the precursor film of Comparative Example 1 did not contain pentavalent element Ev.

[0089] Except for the matters mentioned above, piezoelectric thin films and piezoelectric thin film elements for Examples 2-6 and Comparative Example 1 were fabricated in the same manner as in Example 1. Analysis and measurements of the piezoelectric thin films and piezoelectric thin film elements for Examples 2-6 and Comparative Example 1 were performed in the same manner as in Example 1.

[0090] In all of Examples 2-6 and Comparative Example 1, the XRF method was used to identify the <hf> 、 <ce>, and <ev>Each of these values ​​matched the values ​​shown in Table 1 below. In other words, in all cases of Examples 2-6 and Comparative Example 1, the composition of the piezoelectric thin film matched the composition of the raw materials for the precursor film.

[0091] In all of Examples 2-6 and Comparative Example 1, the piezoelectric thin film consisted of a crystalline phase having a fluorite-type structure. In Examples 2-4 and Comparative Example 1, the crystalline phase was orthorhombic. In Examples 5 and 6, the crystalline phase was tetragonal. In all of Examples 2-6 and Comparative Example 1, the lattice planes of the crystalline phase were oriented in the direction normal to the main surface of the piezoelectric thin film. The orientation planes for Examples 2-6 and Comparative Example 1 are shown in Table 1 below. In all of Examples 2-6 and Comparative Example 1, the portion of the piezoelectric thin film in contact with the first electrode layer contained not only a crystalline phase but also an amorphous phase. The fatigue characteristics of the piezoelectric thin films in Examples 2-6 and Comparative Example 1 are shown in Table 1 below. In Table 1 below, "10^6" means "10 6 This means "10^7" in Table 1 below. 7 It means "...".

[0092] [Table 1] [Industrial applicability]

[0093] For example, the piezoelectric thin film relating to this disclosure may be used in piezoelectric thin film elements, pyroelectric thin film elements, or MEMS. [Explanation of Symbols]

[0094] 1...substrate, 2...first electrode layer, 3...piezoelectric thin film, 4...second electrode layer, 10...piezoelectric thin film element, s...main surface of the piezoelectric thin film, dn...normal direction to the main surface of the piezoelectric thin film, uco...orthorhombic unit cell, uct...tetragonal unit cell.< / ev> < / ce> < / hf> < / ev> < / ce> < / hf> < / ev> < / ce> < / hf> < / ev> < / ce> < / hf> < / ev> < / ce> < / hf>

Claims

1. A piezoelectric thin film containing a metal oxide, The piezoelectric thin film has ferroelectric properties, The aforementioned metal oxide includes hafnium, cerium, and a pentavalent element. The aforementioned metal oxide includes a crystalline phase having a fluorite-type structure. The crystalline phase includes at least one crystal from among orthorhombic and tetragonal. Piezoelectric thin film.

2. The metal oxide further comprises an amorphous phase. The piezoelectric thin film according to claim 1.

3. The aforementioned pentavalent element is one or more elements selected from the group consisting of vanadium, niobium, and tantalum. The piezoelectric thin film according to claim 1.

4. The hafnium content in the metal oxide is expressed as [Hf] atomic percent, The cerium content in the metal oxide is expressed as [Ce] atomic percent, The content of the pentavalent element in the metal oxide is expressed as [Ev] atomic percent, [Ce] / ([Hf]+[Ce]+[Ev]) is between 0.01 and 0.

40. The piezoelectric thin film according to claim 1.

5. The hafnium content in the metal oxide is expressed as [Hf] atomic percent, The cerium content in the metal oxide is expressed as [Ce] atomic percent, The content of the pentavalent element in the metal oxide is expressed as [Ev] atomic percent, [Ev] / ([Hf]+[Ce]+[Ev]) is between 0.01 and 0.

30. The piezoelectric thin film according to claim 1.

6. Some or all of the (111) planes of the crystalline phase are oriented in the direction normal to the main surface of the piezoelectric thin film. The piezoelectric thin film according to claim 1.

7. Some or all of the (100) planes of the crystalline phase are oriented in the direction normal to the main surface of the piezoelectric thin film. The piezoelectric thin film according to claim 1.

8. Some of the (111) planes of the crystalline phase are oriented in the direction normal to the main surface of the piezoelectric thin film. Other (100) planes of the crystalline phase are oriented in the direction normal to the principal surface of the piezoelectric thin film. The piezoelectric thin film according to claim 1.

9. The piezoelectric thin film according to any one of claims 1 to 8, Piezoelectric thin-film element.

10. The first electrode layer, The second electrode layer, Equipped with, At least a portion of the piezoelectric thin film is disposed between the first electrode layer and the second electrode layer, The piezoelectric thin-film element according to claim 9.

11. At least one of the first electrode layer and the second electrode layer contains platinum or indium tin oxide. The piezoelectric thin-film element according to claim 10.

Images