Thin film piezoelectric device

Abstract

The present invention provides a thin film piezoelectric device which has excellent piezoelectric characteristics and a large displacement amount. This thin film piezoelectric device is provided with a substrate and a movable part that is supported by the substrate. The movable part includes at least a buffer film that is provided on the substrate and contains zirconium oxide (ZrO2), a first electrode layer that is provided on the buffer film, a piezoelectric film that is provided on the first electrode layer, and a second electrode layer that is provided on the piezoelectric film. The piezoelectric film is a (001) or (100) oriented film which is composed of a single crystal of lead zirconate titanate (Pb(Zr,Ti)O3, PZT), barium titanate (BaTiO3, BT), or potassium sodium niobate ((K,Na)NbO3, KNN). The piezoelectric film in the movable part expands and contracts in an in-plane direction in relation to a d31 mode based on a piezoelectric or inverse piezoelectric effect, thereby displacing the movable part, and the angle θ between the in-plane direction in which the displacement of the movable part becomes maximum and the <100> orientation of the piezoelectric film is within ±11.5°.

Description

Thin-film piezoelectric devices

[0001] The present invention relates to a thin film piezoelectric device.

[0002] With the recent advancement of an advanced information society, thin-film piezoelectric devices have been attracting attention. In particular, the fifth-generation mobile communication system (5G), which began operation in 2020, has been a strong driving force behind the development of thin-film piezoelectric devices. 5G offers high speed, large capacity, multiple simultaneous connections, and ultra-low latency, making it possible to realize an IoT society in which a variety of things are connected to the Internet. In an IoT society, various sensors and actuators will be widely used as information input / output devices, and there is a demand for miniaturization and high performance of the thin-film piezoelectric devices used in them.

[0003] Thin-film piezoelectric devices are devices in which piezoelectric elements are integrated on a semiconductor substrate using MEMS (Micro Electro Mechanical Systems) technology, enabling miniaturization and high integration of elements. Piezoelectric elements utilize the piezoelectric effect of piezoelectric materials, that is, the phenomenon of direct conversion between electrical and mechanical signals. The piezoelectric effect includes the positive piezoelectric effect, which converts mechanical signals into electrical signals, and the inverse piezoelectric effect, which converts electrical signals into mechanical signals. By utilizing the positive piezoelectric effect, thin-film piezoelectric devices can be used as sensors. Furthermore, by utilizing the inverse piezoelectric effect, thin-film piezoelectric devices can be used as actuators.

[0004] Various materials are known as piezoelectric materials, among which lead zirconate titanate (Pb(Zr,Ti)O ３ Perovskite compounds, such as PZT (PbTiO 3 ), are widely used. Perovskite compounds have the general formula: ABO ３ The material has a composition expressed by the formula: where the A-site ions and B-site ions, which are cations, are displaced, resulting in dielectric polarization. The magnitude and direction of the dielectric polarization change when mechanical pressure is applied, resulting in the piezoelectric effect.

[0005] Regarding thin-film piezoelectric devices, Patent Document 1 discloses a thin-film piezoelectric element having a metal thin film, which is an epitaxial film, on a Si substrate, and a PZT thin film on the metal thin film, in which the atomic ratio Ti / (Ti+Zr) in the PZT thin film is in the range of 0.65 to 0.90 (claim 1 of Patent Document 1). Patent Document 1 also describes that the thin-film piezoelectric element can be used in thin-film vibrators, thin-film VCOs, thin-film filters, liquid ejectors, etc., used in mobile communication devices, and that high-performance piezoelectric devices such as FBARs with extremely wide bandwidths can be realized (paragraphs

[0001] and

[0068] of Patent Document 1).

[0006] Patent Document 2 discloses a method for producing a single crystal wafer, comprising the steps of preparing a polygonal substrate made of a single crystal material, stacking and bonding a plurality of polygonal substrates to form a polygonal columnar laminated block, forming a first orientation flat by processing the polygonal columnar laminated block into an arcuate cylindrical shape, and forming a second orientation flat on the arcuate surface of the laminated block (claim 1 of Patent Document 2). Patent Document 2 also describes that the single crystal wafer is a piezoelectric substrate (paragraph

[0018] of Patent Document 2).

[0007] Non-Patent Document 1 describes the synthesis of a lead zirconate titanate (PZT) thin film on a silicon substrate using a sol-gel method, and the transverse piezoelectric constant (d ３１ ) by the wafer bending method, and the measured piezoelectric constant (d ３１ ) is 25 to 60 pC / N (Non-Patent Document 1, page 133, Abstract, page 136, 6. Preliminary results, and Fig. 4).

[0008] JP 2000-332569 A JP 2013-115534 A

[0009] JFShepard Jr. et al., The wafer flexure technique for the determination of the transverse piezoelectric coefficient (d31) of PZT thin films, Sensors and Actuators A71 (1998) 133-138

[0010] Although thin-film piezoelectric devices have been proposed for some time, there is still room for improvement in these devices. Specifically, piezoelectric devices are required to have a large amount of displacement when a voltage is applied. However, in typical thin-film piezoelectric devices, the piezoelectric material is polycrystalline and does not grow along the crystal orientation of the substrate. As a result, the amount of displacement does not change depending on the crystal orientation of the piezoelectric material, limiting the amount of displacement that can be improved. Because the amount of displacement does not change depending on the crystal orientation, typical thin-film piezoelectric devices have been manufactured with elements aligned parallel or perpendicular to the orientation flat or notch of the substrate.

[0011] Although Patent Document 2 discloses a piezoelectric substrate made of a single crystal wafer, the material actually disclosed is quartz (paragraph

[0021] of Patent Document 2). Although quartz has excellent long-term stability, it is inferior to perovskite compounds in terms of charge output. Furthermore, Patent Document 2 does not involve the integration of piezoelectric materials on a semiconductor substrate, and this document is not intended for thin-film piezoelectric devices.

[0012] The inventors of the present invention have conducted extensive research to solve these conventional problems. As a result, they have discovered that in thin-film piezoelectric devices, the piezoelectric properties of single-crystallized piezoelectric films are highly dependent on the plane orientation, and that the piezoelectric properties can be improved by strictly controlling the plane orientation of the piezoelectric film. Specifically, they have discovered that the amount of displacement can be increased by controlling the angle θ between the in-plane direction in which the displacement of the movable part is maximized and the <100> orientation of the piezoelectric film.

[0013] The present invention was completed based on these findings, and an object of the present invention is to provide a thin film piezoelectric device that has excellent piezoelectric characteristics and a large amount of displacement.

[0014] The present invention includes the following aspects (1) to (12). In this specification, the expression "to" includes both ends of the expression. In other words, "X to Y" is synonymous with "X or more and Y or less."

[0015] (1) A thin film piezoelectric device comprising a substrate and a movable part supported by the substrate, wherein the movable part is made of zirconium oxide (ZrO ２ The piezoelectric film includes at least a buffer film containing lead zirconate titanate (Pb(Zr,Ti)O), a first electrode layer provided on the buffer film, a piezoelectric film provided on the first electrode layer, and a second electrode layer provided on the piezoelectric film, ３ ; PZT), barium titanate (BaTiO ３ ;BT), or potassium sodium niobate ((K,Na)NbO ３ The piezoelectric film in the movable portion is a (001) or (100) oriented film made of a single crystal of KNN, ３１ A thin-film piezoelectric device that expands and contracts in an in-plane direction in association with a mode, thereby displacing a movable part, and an angle θ between the in-plane direction in which the displacement of the movable part is maximum and the <100> orientation of the piezoelectric film is within ±11.5°.

[0016] (2) The thin-film piezoelectric device of (1) above, wherein the movable portion has an outer shape with two opposing parallel sides when viewed from above, and the direction perpendicular to the two sides coincides with the in-plane direction in which the displacement of the movable portion is maximum.

[0017] (3) The thin film piezoelectric device according to (2) above, wherein the outer shape of the movable part is rectangular, approximately rectangular, or trapezoidal.

[0018] (4) The thin-film piezoelectric device according to any one of (1) to (3), wherein one or both of the first electrode layer and the second electrode layer contains at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu).

[0019] (5) Between the first electrode layer and the piezoelectric film, strontium ruthenate (SrRuO ３The thin film piezoelectric device according to any one of (1) to (4) above, further comprising a first metal oxide film made of SRO.

[0020] (6) Between the piezoelectric film and the second electrode layer, strontium ruthenate (SrRuO ３ The thin film piezoelectric device according to any one of (1) to (5) above, further comprising a second metal oxide film made of SRO.

[0021] (7) The thin film piezoelectric device according to any one of (1) to (6) above, wherein the substrate is a Si substrate or an SOI substrate.

[0022] (8) The piezoelectric film is made of lead zirconate titanate (Pb(Zr,Ti)O ３ 10. The thin film piezoelectric device according to any one of (1) to (7) above, which is made of a single crystal of PZT.

[0023] (9) The thin film piezoelectric device according to any one of (1) to (8) above, wherein the buffer film and the first electrode layer are made of single crystal.

[0024] (10) The thin film piezoelectric device according to (9) above, wherein the crystal orientations of the buffer film, the first electrode layer and the piezoelectric film are aligned.

[0025] (11) The thin film piezoelectric device according to any one of (1) to (10) above, wherein the thin film piezoelectric device has a doubly supported beam structure or a cantilever beam structure, and the movable part is provided on a beam part of the doubly supported beam structure or the cantilever beam structure.

[0026] (12) A thin film piezoelectric device according to any one of (1) to (11) above, which is used as a sensor or actuator.

[0027] According to the present invention, a thin film piezoelectric device having excellent piezoelectric characteristics and a large displacement amount is provided.

[0028] 1 shows an example of a schematic cross-sectional view of a thin-film piezoelectric device. 2 shows another example of a schematic cross-sectional view of a thin-film piezoelectric device. 3 shows a top view of a thin-film piezoelectric device. 4 shows a top view of a thin-film piezoelectric device. 5 shows the relationship between angle α and displacement (cavity width 70 μm). 6 shows the relationship between angle α and displacement (cavity width 200 μm). 7 shows the relationship between angle α and resonance frequency Fa (cavity width 70 μm). 8 shows the relationship between angle α and resonance frequency Fa (cavity width 200 μm). 9 shows the relationship between angle α and displacement / resonance frequency Fa (cavity width 70 μm). 10 shows the relationship between angle α and displacement / resonance frequency Fa (cavity width 200 μm). 11 shows an X-ray diffraction pattern (φ scan) of a piezoelectric film (PZT) film. 12 shows an X-ray diffraction pattern (φ scan) of a piezoelectric film (PZT) film.

[0029] A specific embodiment of the present invention (hereinafter referred to as the "present embodiment") will be described. Note that the present invention is not limited to the following embodiment, and various modifications are possible within the scope of the present invention.

[0030] <<1. Thin-Film Piezoelectric Device>> The thin-film piezoelectric device (hereinafter, sometimes simply referred to as "device") of this embodiment includes a substrate and a movable part supported by the substrate. The movable part is made of zirconium oxide (ZrO ２ The piezoelectric film includes at least a buffer film containing lead zirconate titanate (Pb(Zr,Ti)O), a first electrode layer provided on the buffer film, a piezoelectric film provided on the first electrode layer, and a second electrode layer provided on the piezoelectric film. ３ ; PZT), barium titanate (BaTiO ３ ;BT), or potassium sodium niobate ((K,Na)NbO ３ The piezoelectric film in the moving part is a (001) or (100) oriented film made of a single crystal of KNN. ３１ The angle θ between the in-plane direction at which the displacement of the movable part is maximum and the <100> direction of the single-crystal piezoelectric film is within ±11.5°.

[0031] The thin-film piezoelectric device of this embodiment will be described with reference to Figures 1 and 2. Figure 1 shows an example of a cross-sectional schematic diagram of a device including a Si substrate. The thin-film piezoelectric device (100) includes a Si substrate (2) and a movable part (4) supported by the Si substrate (2). At least a portion of the Si substrate (2) has been removed to form a hollow part (22). The movable part (4) is provided on the hollow part (22), and includes a buffer film (6) provided on the Si substrate (2), a first electrode layer (8) provided on the buffer film (6), a first metal oxide film (10) provided on the first electrode layer (8), a piezoelectric film (12) provided on the first metal oxide film (10), a second metal oxide film (14) provided on the piezoelectric film (12), a second electrode layer (16) provided on the second metal oxide film (14), and an extraction electrode (18) provided to be electrically connected to the second electrode layer (16). The first electrode layer (8) and the second electrode layer (16) are each made of a Pt film. The first metal oxide film (10) and the second metal oxide film (14) are each made of an SRO film. The piezoelectric film (12) is made of a PZT film. The extraction electrode (18) is made of a laminate of a Ti layer (18-1) and an Au layer (18-2). In addition, a protective film (20) is provided so as to cover the first electrode layer (8), the first metal oxide film (10), the piezoelectric film (12), the second metal oxide film (14), and the second electrode layer (16).

[0032] Figure 2 shows an example of a cross-sectional view of a device equipped with an SOI substrate. In this case, an SOI substrate (2) is used instead of a Si substrate. The SOI substrate (2) consists of a Si substrate portion (2-1), a surface Si layer (2-3), and a SiO ２ The thin-film piezoelectric device (100) is otherwise similar to the device using a Si substrate, and includes an SOI substrate (2) and a movable part (4) supported by the SOI substrate (2). At least a portion of the SOI substrate is removed to form a hollow part (22). The movable part (4) is provided on the hollow part (22), and includes a buffer film (6), a first electrode layer (8), a first metal oxide film (10), a piezoelectric film (12), a second metal oxide film (14), a second electrode layer (16), an extraction electrode (18), and a protective film (20).

[0033] <Substrate> The substrate functions as the base of the thin-film piezoelectric device and also functions to support the movable part. There are no particular limitations on the material of the substrate. Any known substrate used in thin-film piezoelectric devices can be used. For example, a silicon (Si) substrate, an SOI (Silicon on Insulator) substrate, a substrate made of a semiconductor crystal other than Si, a substrate made of various oxide single crystals such as sapphire or garnet, or a glass substrate with a polysilicon film formed on the surface can be used. An SOI substrate has an insulating film (SiO ２ The size of the substrate is not limited, and a 4-inch substrate, a 6-inch substrate, an 8-inch substrate, or the like can be used.

[0034] The substrate is preferably a Si substrate or an SOI substrate, and particularly preferably a Si(100) substrate or an SOI(100) substrate. Here, a (100) substrate refers to a substrate whose main surface faces the (100) plane based on the crystal lattice. By using a Si(100) substrate or an SOI(100) substrate, a buffer film, a first electrode layer, and a piezoelectric film can be epitaxially grown on the substrate while ensuring sufficient lattice matching, resulting in a single-crystal buffer film, a first electrode layer, and a piezoelectric film. However, it is also possible to separate the substrate after depositing the single-crystal piezoelectric film and bond another substrate to it. Therefore, the substrate for the thin-film piezoelectric device of this embodiment is not limited to a Si(100) substrate or an SOI(100) substrate. Other substrates, such as a (110) substrate or a (111) substrate, may also be used.

[0035] The substrate may or may not be included in the movable part. In the device of FIG. 1 that includes a Si substrate, the buffer film (6) constitutes the bottom layer of the movable part (4). That is, the movable part (4) does not include the Si substrate (2). In contrast, in the device of FIG. 2 that includes an SOI substrate, the surface Si layer (2-3) of the SOI substrate (2) constitutes the bottom layer of the movable part (4). That is, the movable part (4) includes a part of the SOI substrate (2).

[0036] <Buffer film> The device of this embodiment is made of zirconium oxide (ZrO ２The buffer film is provided on a substrate. The buffer film also constitutes a movable portion. ２ By using a buffer film containing ZrO, it is possible to promote single crystallization of the piezoelectric film formed thereon. ２ has a monoclinic, tetragonal, or cubic crystal structure. ZrO with such a crystal structure ２ The buffer film is grown on the substrate, forming nanopyramid structures on the surface. ２ When the first electrode layer and piezoelectric film are deposited on the buffer film, the nanopyramid structure itself deforms, correcting the crystal lattice misalignment between the substrate and the film, resulting in a single-crystal film with minimal residual stress.

[0037] The buffer film is ZrO ２ Alternatively, rare earth elements and alkaline earth elements may be included. ２ may contain oxygen vacancies. Furthermore, to improve characteristics, the alloy may contain transition metal elements such as aluminum (Al), scandium (Sc), manganese (Mn), iron (Fe), cobalt (Co), and / or nickel (Ni).

[0038] The thickness of the buffer film is preferably 10 nm to 1500 nm, more preferably 20 nm to 1200 nm, and even more preferably 30 nm to 1000 nm. The buffer film is preferably an epitaxial film formed on a substrate, and more preferably an epitaxial film with a (100) orientation.

[0039] <First Electrode Layer> The first electrode layer and the second electrode layer constitute a pair of electrodes sandwiching the piezoelectric film. A potential difference based on the surface charge of the piezoelectric film generated by the positive piezoelectric effect can be detected through the electrode layer. Alternatively, a potential difference can be applied to the piezoelectric film through the electrode layer, thereby generating strain due to the inverse piezoelectric effect. The material of the first electrode layer is not limited as long as it is conductive. For example, it may include at least one material selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu).

[0040] The thickness of the first electrode layer is preferably 10 nm to 500 nm, more preferably 30 nm to 300 nm, and even more preferably 50 nm to 200 nm. The first electrode layer is preferably an epitaxial film formed on a buffer film, and more preferably a (100)-oriented epitaxial film.

[0041] <First Metal Oxide Film> The thin film piezoelectric device of this embodiment may include a first metal oxide film between the first electrode layer and the piezoelectric film. The first metal oxide film is preferably made of strontium ruthenate (SrRuO ３ The piezoelectric film is made of SRO (SrO, S ...

[0042] The thickness of the first metal oxide film (SRO film) is preferably 1 nm to 100 nm, more preferably 3 nm to 80 nm, and even more preferably 5 nm to 60 nm. The first metal oxide film is preferably an epitaxial film formed on the first electrode layer, and more preferably an epitaxial film with a (100) orientation.

[0043] <Piezoelectric film> Piezoelectric films are the main component that produces the piezoelectric effect, and they convert electrical energy into mechanical energy. That is, when pressure (force) is applied to a piezoelectric film, a surface charge is generated above and below the film due to the positive piezoelectric effect, which creates a potential difference (voltage). For this reason, piezoelectric films can be used as sensors. Furthermore, when a potential difference (voltage) is applied above and below the piezoelectric film, the film is displaced due to the inverse piezoelectric effect. For this reason, piezoelectric films can be used as actuators.

[0044] The piezoelectric film of this embodiment is characterized by being composed of a single crystal. That is, the piezoelectric film has continuous crystals on both the cross section and the top surface, and has a crystalline structure in which dice overlap without rotating, i.e., a cube-on-cube structure. Therefore, its microstructure differs from that of conventional piezoelectric films. Conventional piezoelectric films are polycrystalline films consisting of multiple crystal grains randomly oriented in the thickness and plane directions, or piezoelectric films in which the crystals are continuous in the thickness direction but randomly oriented in the plane direction. While epitaxial films oriented in the thickness and plane directions have also been proposed, they are composed of polycrystalline crystals with discontinuous crystals.

[0045] The piezoelectric film of this embodiment, which is made of a single crystal, allows for the polarization direction to be completely aligned throughout the film. This allows for improved electrical and mechanical properties. Specifically, the piezoelectric constant can be improved. Furthermore, since the dielectric constant is lower than that of a polycrystalline film, it has the advantage of reducing power consumption and enabling highly accurate output when used as a sensor. Furthermore, by making it single crystal, the bonding strength between atoms is improved, thereby improving the temperature characteristics and reliability of the piezoelectric film.

[0046] Whether a piezoelectric film is single crystal or not can be confirmed by performing in-plane φ scan measurement using X-ray diffraction. That is, if a four-fold symmetric peak is confirmed in the in-plane φ scan, it can be determined that the piezoelectric film is single crystal.

[0047] The piezoelectric film of this embodiment is made of lead zirconate titanate (Pb(Zr,Ti)O ３ ; PZT), barium titanate (BaTiO ３;BT), or potassium sodium niobate ((K,Na)NbO ３ PZT, BT, and KNN are all composed of a compound represented by the general formula: ABO ３ The perovskite-type compound has a crystal structure such as body-centered cubic, and many of them are dielectric and piezoelectric materials that exhibit dielectric and piezoelectric properties. In particular, PZT exhibits excellent piezoelectric properties and is widely used as a sensor and actuator material. Therefore, the piezoelectric film is preferably made of lead zirconate titanate (Pb(Zr,Ti)O ３ It is composed of a single crystal of PZT.

[0048] PZT has a rhombohedral crystal structure when it is Zr-rich, and a tetragonal crystal structure when it is Ti-rich. In the intermediate composition region, it reaches a morphotropic phase boundary (MPB) composition where rhombohedral and tetragonal crystal structures coexist, and at this point, the piezoelectric properties are significantly improved. １－ｘ Ti ｘ ) O ３ (However, if 0<x<1), from the viewpoint of obtaining excellent piezoelectric properties, x is preferably 0.2 or more and 0.8 or less, more preferably 0.3 or more and 0.7 or less, and even more preferably 0.4 or more and 0.6 or less.

[0049] The piezoelectric film of this embodiment is a (001) or (100) oriented film. Piezoelectric films with a body-centered cubic crystal structure tend to be (001) or (100) oriented when epitaxially grown. For example, PZT films with a tetragonal crystal structure tend to be (001) oriented when epitaxially grown. Furthermore, when a PZT film with a tetragonal crystal structure is (001) oriented, the polarization direction parallel to the

[001] direction and the electric field direction parallel to the thickness direction of the piezoelectric film are parallel to each other, thereby improving the piezoelectric characteristics. That is, a PZT film with a tetragonal crystal structure can achieve a large piezoelectric constant when an electric field is applied along the

[001] direction.

[0050] In this embodiment, whether a piezoelectric film is a (001) or (100) oriented film can be determined by θ-2θ scanning of the piezoelectric film using X-ray diffraction. That is, when the piezoelectric film is scanned using θ-2θ, if the ratio (peak intensity ratio) of the diffraction peak intensity from the target plane (the (001) plane and the (100) plane) to the diffraction peak intensity from other planes is 10% or less, the film can be determined to be a (001) or (100) oriented film. A smaller peak intensity ratio is preferable, and 5% or less is more preferable.

[0051] The thickness of the piezoelectric film is preferably 0.1 μm or more and 10 μm or less. If the piezoelectric film is too thin, the effect of the piezoelectric film cannot be fully utilized, and the amount of displacement obtained may be small. On the other hand, if the piezoelectric film is too thick, it may be difficult to obtain a sufficiently single-crystallized piezoelectric film. The thickness is more preferably 0.3 μm or more and 6 μm or less, and even more preferably 0.5 μm or more and 4 μm or less.

[0052] <Second Metal Oxide Film> The thin film piezoelectric device of this embodiment may include a second metal oxide film between the piezoelectric film and the second electrode layer. The second metal oxide film may be made of strontium ruthenate (SrRuO ３ The SRO film (second metal oxide film) is made of SrO. SrO is conductive. Therefore, the SRO film (second metal oxide film) can be used as a part of the electrode layer (second electrode layer).

[0053] The thickness of the second metal oxide film (SRO film) is preferably 1 nm to 60 nm, more preferably 3 nm to 30 nm, and even more preferably 5 nm to 20 nm. The second metal oxide film is preferably an epitaxial film formed on the piezoelectric film, and more preferably an epitaxial film with a (100) orientation.

[0054] <Second Electrode Layer> The second electrode layer and the first electrode layer constitute a pair of electrodes sandwiching the piezoelectric film. The material of the second electrode layer is not limited as long as it is conductive. For example, the second electrode layer may contain at least one material selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu).

[0055] The thickness of the second electrode layer is preferably 1 nm to 200 nm, more preferably 3 nm to 150 nm, and even more preferably 10 nm to 120 nm. The second electrode layer is preferably an epitaxial film formed on the piezoelectric film, and more preferably a (100)-oriented epitaxial film.

[0056] <Extraction electrode> An extraction electrode may be provided on the second electrode layer. Known conductive materials can be used as the extraction electrode. For example, a laminate of a gold (Au) layer and a titanium (Ti) layer can be used. The Au layer mainly functions as a conductive layer, and the Ti layer mainly functions as an adhesive layer.

[0057] <Protective Film> A protective film may be provided on the second electrode layer or the second metal oxide film (SRO film). The material of the protective film is not limited, but may be tetraethyl orthosilicate (TEOS) or the like.

[0058] The movable portion is supported by a substrate and includes at least a buffer film, a first electrode layer, a piezoelectric film, and a second electrode layer. The movable portion may further include a metal oxide film (first metal oxide film, second metal oxide film) between the first electrode layer and the piezoelectric film and / or on the second electrode layer.

[0059] In the thin film piezoelectric device of this embodiment, the piezoelectric film in the movable part has a d ３１ The piezoelectric effect includes the longitudinal piezoelectric effect (d ３３ mode), the piezoelectric transverse effect in which the electrical input / output direction and the mechanical input / output direction are perpendicular (d ３１ mode), piezoelectric slip effect due to shear deformation (d １５ In thin film piezoelectric devices, there are two modes: ３１ The device configuration utilizing the mode is advantageous in the device fabrication process and allows for a larger displacement.

[0060] In the thin film piezoelectric device of this embodiment, electrodes (first electrode layer and second electrode layer) are provided on the top and bottom of the piezoelectric film so as to sandwich the piezoelectric film. When a potential difference is applied to the electrode layers (first electrode layer and second electrode layer), an electric field is generated in the vertical direction of the piezoelectric film, and d ３１ The inverse piezoelectric effect of the mode causes displacement in a direction perpendicular to the electric field, i.e., parallel to the film surface. Alternatively, when stress parallel to the film surface is applied to the moving part, a surface charge is generated on the electrode layer due to the positive piezoelectric effect. ３１ By utilizing this mode, it is possible to utilize the displacement of the piezoelectric film in the film surface direction and the resulting displacement of the movable part. The movable part is composed of a laminate of the piezoelectric film and other components (such as a buffer film). Even if the piezoelectric film expands and contracts (displaces) in-plane, the other components do not expand and contract. Therefore, warping occurs in the movable part in response to the displacement of the piezoelectric film. The greater the displacement of the piezoelectric film, the greater the warping of the movable part.

[0061] In the thin-film piezoelectric device of this embodiment, the angle θ between the in-plane direction in which the displacement of the movable part is maximum and the <100> orientation of the piezoelectric film is within ±11.5°. Here, the in-plane direction in which the displacement of the movable part is maximum is the direction in which the amount of expansion and contraction (amount of warpage) is maximum in a plane parallel to the film surface of the piezoelectric film. Furthermore, the <100> orientation includes all orientations equivalent to the

[100] direction. The angle θ is preferably within ±11.0°, and more preferably within ±10.5°.

[0062] The piezoelectric film of this embodiment has a single crystal structure. Therefore, the amount of piezoelectric displacement is highly dependent on the plane orientation. The inventors' investigations have revealed that the smaller the angle θ, that is, the more the <100> orientation of the piezoelectric film is aligned with the in-plane direction in which the displacement of the movable part is maximized, the greater the amount of displacement of the piezoelectric film. For example, when a single crystal PZT film is used as the piezoelectric film, d ３１ It is possible to increase the piezoelectric constant to approximately 100 pm / V or more. In contrast, conventional piezoelectric films are not single crystals. Therefore, they do not show plane orientation dependency of the piezoelectric properties, and the amount of piezoelectric displacement is small. For example, Non-Patent Document 1 describes the radial piezoelectric constant (d ３１) is 25 to 60 pC / N (25 to 60 pm / V) (Fig. 4, page 136 of Non-Patent Document 1). Furthermore, because the plane orientation dependency is not shown, the relationship between plane orientation and piezoelectric properties has not been focused on in the past. In this embodiment, because the piezoelectric film is single crystal, the plane orientation dependency is large, and the piezoelectric properties are characterized by the fact that controlling the plane orientation significantly improves the piezoelectric properties.

[0063] Preferably, as shown in Figures 1 and 2, a hollow portion 22 is provided directly below the movable portion 4. That is, at least a portion of the substrate 2 in the movable portion 4 is removed, and the movable portion 4 has a diaphragm structure. In this case, the movable portion is less constrained by the substrate, and therefore the amount of warping of the movable portion increases.

[0064] In the thin-film piezoelectric device of this embodiment, the movable portion preferably has an outer shape with two opposing parallel sides in a top view, and the direction perpendicular to these two sides preferably coincides with the in-plane direction in which the displacement of the movable portion is maximum. Furthermore, the outer shape of the movable portion is preferably rectangular, approximately rectangular, or trapezoidal. By providing the movable portion with an outer shape with two opposing parallel sides in this manner, the direction perpendicular to these two sides can be set as the maximum expansion / contraction direction. When the outer shape of the movable portion is rectangular, the width (short side) dimension is preferably 30 μm to 500 μm, more preferably 50 μm to 300 μm. The length (long side) dimension is preferably 100 μm to 1000 μm, more preferably 250 μm to 600 μm. Furthermore, the direction perpendicular to the width direction preferably coincides with the in-plane direction in which the displacement of the movable portion is maximum.

[0065] In the thin-film piezoelectric device of this embodiment, the buffer film and the first electrode layer are preferably made of single crystal. Furthermore, it is preferable that the crystal orientations of the buffer film, the first electrode layer, and the piezoelectric film are aligned. By making the buffer film and the first electrode layer single crystal and aligning their crystal orientations, it is possible to improve the crystallinity of the piezoelectric film formed on the first electrode layer.

[0066] The thin-film piezoelectric device of this embodiment preferably has a doubly-supported beam structure or a cantilever beam structure, and a movable portion is provided on the beam portion of the doubly-supported beam structure or cantilever beam structure. In a device having a cantilever beam structure, only one end of the movable portion is fixed, and the other end is a free end. Therefore, the free end of the movable portion displaces up and down in response to warping of the movable portion. A cantilever beam structure is also called a cantilever structure. In contrast, in a device having a doubly-supported beam structure, both ends of the movable portion are fixed. Therefore, the movable portion bends in response to warping, and its central portion displaces up and down. A doubly-supported beam structure can also be called a diaphragm structure.

[0067] The thin-film piezoelectric device of this embodiment is preferably used as a sensor or actuator. The thin-film piezoelectric device of this embodiment is characterized by a large displacement of the movable part. Therefore, sensors and actuators with excellent characteristics can be manufactured. Examples of sensors include acceleration sensors, gyro sensors, pressure sensors, ultrasonic sensors, flow sensors, vibration power generation elements, odor sensors, and / or microphones. Examples of actuators include speakers, inkjet printer heads, autofocus sensors, mirrors, optical switches, and / or micropumps. In addition, the thin-film piezoelectric device of this embodiment can also be used as high-frequency circuit components such as RF filters and film bulk acoustic resonators (FBARs).

[0068] <<2. Manufacturing Method of Thin Film Piezoelectric Device>> The manufacturing method of the thin film piezoelectric device of this embodiment is not limited as long as it satisfies the above-mentioned requirements. However, a preferred manufacturing method includes a step of preparing a substrate (substrate preparation step), a step of depositing zirconium oxide (ZrO ２The method includes a step of forming a buffer film containing the piezoelectric film (buffer film forming step), a step of forming a first electrode layer on the buffer film (first electrode layer forming step), a step of forming a piezoelectric film on the first electrode layer (piezoelectric film forming step), and a step of forming a second electrode layer on the piezoelectric film (second electrode layer forming step). A step of forming a first metal oxide film between the first electrode layer and the piezoelectric film (first metal oxide film forming step) may be provided. A step of forming a second metal oxide film between the piezoelectric film and the second electrode layer (second metal oxide film forming step) may be provided. A step of forming an extraction electrode on the second electrode layer and the second metal oxide film (extraction electrode forming step) may be provided. A step of forming a protective film on the second electrode layer, the second metal oxide film, and / or the extraction electrode (protective film forming step) may be provided. Furthermore, a step of removing at least a portion of the substrate in the movable section to form a hollow section directly below the movable section (hollow section forming step) may be provided. Details of each step are described below.

[0069] <Substrate Preparation Step> In the substrate preparation step, a substrate is prepared. The details of the substrate are as described above. That is, as the substrate, a silicon (Si) substrate, an SOI (Silicon on Insulator) substrate, a substrate made of a semiconductor crystal other than Si, a substrate made of various oxide single crystals such as sapphire or garnet, a glass substrate with a polysilicon film formed on its surface, etc. can be used. In addition, the size of the substrate is not limited, and a 4-inch substrate, a 6-inch substrate, an 8-inch substrate, etc. can be used. The orientation of the substrate is also not limited. For example, a Si(100) substrate, a Si(110) substrate, or a Si(111) substrate can be used.

[0070] <Buffer Film Forming Step> In the buffer film forming step, zirconium oxide (ZrO ２ The film formation may be performed by a method such as electron beam evaporation or sputtering. When the film is formed by electron beam evaporation, for example, the substrate is placed in a vacuum chamber of an evaporation device. Then, oxygen (O ２ The substrate was heated with zirconium oxide (ZrO ２By forming the film under these conditions, it is possible to reliably obtain a buffer film consisting of a (100)-oriented epitaxial film. Furthermore, photolithography may be used to perform patterning to partially remove the buffer film after film formation.

[0071] <First Electrode Layer Formation Process> In the first electrode layer formation process, a first electrode layer is formed on the buffer film. The first electrode layer includes, for example, at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu). The first electrode layer may be formed by a method such as sputtering. When performing sputtering, for example, the epitaxially grown first electrode layer may be formed on the buffer film as part of the lower electrode by sputtering while heating the substrate. Furthermore, photolithography may be used to perform patterning to partially remove the first electrode layer after film formation.

[0072] <First Metal Oxide Film Formation Step> A first metal oxide film (SRO film) may be formed between the first electrode layer and the piezoelectric film. The first metal oxide film may be formed by a method such as sputtering. When performing sputtering, for example, while heating the substrate, the first metal oxide film may be epitaxially grown by sputtering and formed on the first electrode layer as part of the lower electrode. Furthermore, photolithography may be used to perform patterning to partially remove the first metal oxide film after film formation.

[0073] <Piezoelectric Film Forming Step> In the piezoelectric film forming step, a piezoelectric film is formed on the first electrode layer. The piezoelectric film is a (001) or (100) oriented film made of a single crystal of PZT, BT, or KNN. The piezoelectric film is formed by a method such as sputtering or a sol-gel method. For example, epitaxially grown lead zirconate titanate (Pb(Zr) １－ｘ Ti ｘ ) O ３A piezoelectric film containing lead zirconate titanate (Pb(Zr) (0<x<1): PZT) may be formed on the first electrode layer. Alternatively, a piezoelectric film containing lead zirconate titanate (Pb(Zr)) may be formed on the first electrode layer by a known sol-gel method. １－ｘ Ti ｘ ) O ３ A piezoelectric film containing (0<x<1): PZT) may be formed on the first electrode layer. The film formation method is not limited as long as a single-crystal film with a (001) or (100) orientation can be obtained. Furthermore, photolithography may be used to perform patterning, which partially removes the piezoelectric film after film formation.

[0074] <Second Metal Oxide Film Formation Process> A second metal oxide film (SRO film) may be formed between the piezoelectric film and the second electrode layer. The second metal oxide film may be formed by a method such as sputtering. When sputtering is used, for example, an epitaxially grown second metal oxide film may be formed on the piezoelectric film by sputtering as part of the lower electrode. Furthermore, photolithography may be used to perform patterning to partially remove the formed second metal oxide film.

[0075] <Second Electrode Layer Formation Process> In the second electrode layer formation process, a second electrode layer is formed on the piezoelectric film or the second metal oxide film. The second electrode layer includes, for example, at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu). The second electrode layer may be formed by a method such as sputtering. For example, a second electrode layer containing epitaxially grown Pt may be formed on the piezoelectric film or the second metal oxide film by sputtering as part of the lower electrode. Furthermore, photolithography may be used to perform patterning to partially remove the second electrode layer after deposition.

[0076] <Extraction Electrode Forming Step> An extraction electrode may be formed on the second electrode layer. The extraction electrode may be formed by a method such as sputtering. Alternatively, photolithography may be used to perform patterning to partially remove the extraction electrode layer after formation.

[0077] <Protective Film Forming Step> A protective film may be formed on the second electrode layer or the lead-out electrode. The protective film may be formed by, but is not limited to, tetraethyl orthosilicate (TEOS) or the like. The protective film may be formed by a method such as sputtering. Alternatively, photolithography may be used to perform patterning to partially remove the protective film after formation.

[0078] <Hollow Portion Forming Process> When manufacturing a thin-film piezoelectric device, a process may be performed in which at least a portion of the substrate in the movable portion is removed to form a hollow portion directly below the movable portion. This allows the formation of a movable portion having a cantilever structure or a diaphragm structure and a large amount of displacement. The hollow portion is preferably formed after the buffer film, the first electrode layer, the piezoelectric layer, and the second electrode layer are formed on the substrate.

[0079] The hollow portion can be formed by a combination of photolithography and etching techniques. Specifically, a mask having an opening is placed in close contact with the rear surface of the substrate. Then, the substrate is etched away through the opening in the mask using an alkaline etching solution. For example, a Si substrate or an SOI substrate is anisotropically etched with an alkaline etching solution to form a hollow portion in the shape of a quadrangular pyramid. When a Si substrate is used, a buffer film (ZrO ２ The insulating film (SiO ２ The insulating film functions as an etching stop layer. The insulating film can be removed using an etching solution such as hydrofluoric acid. Therefore, the surface Si layer, or the surface Si layer and the insulating film (SiO ２ It is possible to fabricate thin film piezoelectric devices having a piezoelectric film.

[0080] The present invention will be described in more detail using the following examples, but the present invention is not limited to the following examples.

[0081] (1) Fabrication of a Thin-Film Piezoelectric Device [Example 1] In Example 1, a buffer film (ZrO ２A first electrode layer (Pt film), a first metal oxide film (SRO film), a piezoelectric film (PZT film), a second metal oxide film (SRO film), a second electrode layer (Pt film), and an extraction electrode (Ti layer, Au layer) were formed in this order, and then the back surface of the SOI substrate was etched away to form a cavity (hollow portion). This resulted in the fabrication of a thin-film piezoelectric device with a movable portion as shown in Figure 2.

[0082] First, a wafer of an SOI substrate with a diameter of 6 inches was prepared. This SOI substrate consisted of a Si substrate part and an insulating film (SiO ２ The silicon dioxide film had a three-layer structure consisting of a silicon dioxide film and a surface silicon layer. The upper surface, which was the main surface, was a (100) plane. That is, the surface silicon layer was (100) oriented.

[0083] Next, a zirconium oxide (ZrO ２ The buffer film was formed by electron beam evaporation. The formed buffer film had a (100)-oriented cubic crystal structure and a thickness of 60 nm. The film was formed under the following conditions:

[0084] - Apparatus: electron beam evaporation apparatus - Pressure: 7.00 x 10 －３ Pa-evaporation source: ZrO ２ Acceleration voltage / emission current: 7.5 kV / 1.80 mA Thickness: 60 nm Film formation rate: 0.005 nm / sec Oxygen flow rate: 10 sccm Substrate temperature: 500 to 600°C

[0085] Next, the Pt film as the first electrode layer was covered with a buffer film (ZrO ２ The deposited Pt film (first electrode layer) had a (100)-oriented cubic crystal structure and a thickness of 150 nm. The film was deposited under the following conditions:

[0086] - Apparatus: DC sputtering apparatus - Pressure: 3.20 x 10 －２ Pa - Vapor deposition source: Pt - Power: 100 W - Thickness: 150 nm - Deposition rate: 0.14 nm / sec - Ar flow rate: 16 sccm - Substrate temperature: 400°C

[0087] Next, a SRO film was formed as a first metal oxide film on the first electrode layer (Pt film) by sputtering. The formed first metal oxide film had a (100)-oriented cubic crystal structure and a thickness of 40 nm. The film formation was carried out under the following conditions.

[0088] - Apparatus: RF magnetron sputtering apparatus - Power: 300 W - Gas: Ar - Pressure: 1.8 Pa - Substrate temperature: 600°C - Film formation rate: 0.11 nm / sec - Thickness: 40 nm

[0089] A PZT film was formed as a piezoelectric film on the formed first metal oxide film. The film formation was carried out by the Sol-Gel method. Specifically, first, organometallic compounds of Pb, Zr, and Ti were dissolved in a mixed solvent of ethanol and 2-n-butoxyethanol to prepare a raw material solution. At this time, the organometallic compounds of Pb, Zr, and Ti were mixed so as to have a composition ratio (molar ratio) of Pb:Zr:Ti=100+δ:52:48. In addition, Pb(Zr ０．５２ Ti ０．４８ ) O ３ The raw material solution was adjusted so that the concentration of Pb as a whole was 0.35 mol / L. Here, δ is the amount of excess Pb, taking into account the volatilization of Pb oxide in the subsequent heat treatment process, and in this example, δ was set to 20. Then, 20 g of polypyrrolidone with a K value of 27 to 33 was dissolved in the raw material solution.

[0090] Next, 3 ml of the prepared source solution was dropped onto the first metal oxide film (SRO film) of the substrate, and the substrate was then rotated at 3000 rpm for 10 seconds to coat the source solution onto the substrate. This resulted in the formation of a film containing the precursor. The substrate on which the precursor-containing film had been formed was then placed on a hot plate at 200°C for 30 seconds, and then placed on a hot plate at 450°C for 30 seconds to dry the film. Thereafter, the substrate was heated under oxygen (O ２ The film was then heat-treated in a SiO 2 atmosphere at 600-700°C for 60 seconds to oxidize and crystallize the precursor. The process from applying the raw material solution to crystallization was then repeated any number of times until the desired film thickness was reached, forming a piezoelectric (PZT) film.

[0091] The formed piezoelectric film (PZT film) was (001) oriented and had a film thickness of 2 μm. The composition of the piezoelectric film was Pb(Zr ０．５２ Ti ０．４８ ) O ３ It was.

[0092] An SRO film was formed on the piezoelectric film as a second metal oxide film, and a Pt film was further formed on the SRO film as a second electrode layer. The SRO film and Pt film were formed by sputtering. The SRO film (second metal oxide film) had a thickness of 10 nm, and the Pt film (second electrode layer) had a thickness of 100 nm.

[0093] Next, the second electrode layer (Pt film), the second metal oxide film (SRO film), and the piezoelectric film (PZT film) were partially etched away using photolithography. Furthermore, a tetraethoxysilane (TEOS) film was formed as a protective film by plasma CVD, and the TEOS film was partially etched away using photolithography.

[0094] Furthermore, in order to ensure electrical continuity to the second electrode layer (Pt film) and the second metal oxide film (SRO film) that function as the upper electrode, a 10 nm thick Ti layer and a 300 nm thick Au layer were formed by DC sputtering, and then partially etched away using photolithography to form an extraction electrode.

[0095] Finally, anisotropic etching was performed from the rear surface of the substrate (SOI substrate) to form a cavity (hollow portion). Specifically, the Si substrate portion and the insulating film (SiO ２ A portion of the film was removed to form an opening on the rear side of the substrate. This produced a movable part with a rectangular cavity (hollow part). The planar dimensions of the movable part were 70 μm wide x 275 μm long.

[0096] When fabricating the thin-film piezoelectric device of Example 1, the device was designed so that the angle θ between the width direction (short side direction) of the movable part and the <100> orientation of the piezoelectric film was a predetermined angle. Specifically, the movable part was designed so that the angle θ was 0°, 22.5°, 45.0°, 67.5°, 90.0°, 112.5°, 135.0°, 157.5°, or 180.0°, and devices corresponding to each angle θ were fabricated.

[0097] Top views (photographs) of the obtained thin-film piezoelectric devices are shown in Figures 3 and 4. Figure 3 shows all devices fabricated according to the angle θ, and Figure 4 shows one device. The movable part can be seen in the center of Figure 4, and the line segment A-A' that crosses the movable part is the width direction (short side direction) of the movable part.

[0098] [Example 2] A piezoelectric film (PZT film) was formed by sputtering. Except for this, a sample was fabricated in the same manner as in Example 1. The piezoelectric film was formed under the following conditions.

[0099] - Apparatus: RF magnetron sputtering apparatus - Power: 2000 W - Gas: Ar + O ２ Pressure: 1.8 Pa Substrate temperature: 600°C Film formation rate: 0.3 nm / sec Thickness: 2 μm

[0100] [Example 3] Instead of an SOI substrate, a Si(100) substrate was used. ２ The thickness of the film was set to 1.0 μm. Except for this, a sample was prepared in the same manner as in Example 1. As a result, a thin-film piezoelectric device having a movable part as shown in FIG. 1 was prepared.

[0101] [Example 4] Buffer film (ZrO ２ The thickness of the film was changed to 0.8 μm. Otherwise, the sample was prepared in the same manner as in Example 3.

[0102] [Example 5] Buffer film (ZrO ２ The thickness of the film was changed to 1.2 μm. Otherwise, the sample was prepared in the same manner as in Example 3.

[0103] [Example 6] When forming the cavity, the planar dimensions of the movable part were changed to 200 μm × 500 μm. The movable part was also designed so that the angle θ between the width direction of the movable part and the <100> orientation of the piezoelectric film was 0°, 11.25°, 22.5°, 33.75°, 45°, 56.25°, 67.5°, 78.75°, or 90°. Devices corresponding to each angle θ were fabricated in the same manner as in Example 1.

[0104] [Example 7] A piezoelectric film (PZT film) was formed by sputtering. Specifically, the piezoelectric film was formed under the same conditions as in Example 2. Otherwise, a sample was fabricated in the same manner as in Example 6.

[0105] [Example 8] A Si(100) substrate was used instead of an SOI substrate. ２ The thickness of the film was 1.0 μm. Other than that, the sample was prepared in the same manner as in Example 6.

[0106] [Example 9] Buffer film (ZrO ２ The thickness of the film was changed to 0.8 μm. Otherwise, a sample was prepared in the same manner as in Example 8.

[0107] [Example 10] Buffer film (ZrO ２ The thickness of the film was changed to 1.2 μm. Otherwise, a sample was prepared in the same manner as in Example 8.

[0108] The structures of the thin film piezoelectric devices of Examples 1 to 10 are summarized in Table 1 below.

[0109]

[0110] (2) Evaluation of Thin Film Piezoelectric Devices The thin film piezoelectric devices fabricated in Examples 1 to 10 were evaluated for various properties as follows.

[0111] <Crystallinity> The crystallinity of the piezoelectric film (PZT film) was evaluated. That is, before forming the second metal oxide film, the device was removed, and the piezoelectric film was evaluated using a fully automated multipurpose horizontal X-ray diffractometer (Rigaku Corporation, Smart Lab). Specifically, a 360° scan measurement was performed in the φ direction for the 2θ-θ crystal peak of PZT (004).

[0112] <Resonance Frequency> The resonance frequency of the thin-film piezoelectric device was measured using a spectrum impedance analyzer (Agilent Technologies, 4395A). Specifically, probes connected to the spectrum impedance analyzer were brought into contact with the upper electrode (second electrode layer) and the lower electrode (first electrode layer) of the thin-film piezoelectric device so as to obtain electrical continuity. Next, a voltage of 15 V was applied, and the frequency at which the impedance (Z) and the out-of-phase (θ) changed was measured.

[0113] <Displacement> The displacement of the movable portion of the thin-film piezoelectric device was evaluated. Specifically, probes connected to an oscilloscope (TDS3014C, Tktronix) were brought into contact with the upper electrode (second electrode layer) and lower electrode (first electrode layer) of the thin-film piezoelectric device to ensure electrical continuity. Next, a measurement signal was applied to the upper and lower electrodes using a multifunction generator (WF1973, NF Corporation, Circuit Design Block). The measurement signal was applied under the following conditions: sine wave, 1 kHz, Vpp 20 V, and Offset 10 V. The displacement of the movable portion of the thin-film piezoelectric device was then measured using a laser Doppler vibrometer (VFX-Compact, Polytec), and the obtained output value was captured on the oscilloscope.

[0114] (3) Evaluation Results <Crystallinity of Piezoelectric Film> As a result of θ-2θ scanning by X-ray diffraction, the diffraction peak intensity of planes other than the (100) plane was 0.09% of the peak intensity of the (100) plane for the piezoelectric films (PZT films) of the thin-film piezoelectric devices of Examples 1 to 10. Therefore, it was found that these piezoelectric films were (100) oriented.

[0115] Furthermore, a four-fold symmetric peak was confirmed in the in-plane φ scan. Therefore, it was confirmed that the film was a triaxially oriented single crystal. The X-ray diffraction patterns (φ scan) of the piezoelectric film (PZT film) of Example 1 are shown in Figures 11A and 11B. Here, Figure 11A shows the X-ray diffraction intensity on the vertical axis in antilogarithmic scale, while Figure 11B shows it in logarithmic scale.

[0116] The displacement of the movable parts of the thin-film piezoelectric devices of Examples 1 to 10 is shown in Tables 2 and 3 and Figures 5 and 6. Note that the angle α shown in the tables and figures is the angle (unit: °) between the long side direction of the device movable part and the substrate orientation flat direction

[110] . On the other hand, θ is the angle between the in-plane direction in which the displacement of the movable part is maximum and the <100> direction of the piezoelectric film. In this example, the piezoelectric film is (100) oriented. Furthermore, the crystal orientation of the piezoelectric film is aligned with the crystal orientation of the substrate. Therefore, θ and α have the relationship θ = α - 45°.

[0117] As shown in Tables 2 and 3 and Figures 5 and 6, in the region where α was 0 to 45°, the amount of displacement increased as the angle α increased, and in the region where α was 45 to 90°, the amount of displacement decreased as the angle α increased. In other words, the amount of displacement was maximum when the angle α was near 45° (angle θ was 0°).

[0118] The resonant frequency Fa of the piezoelectric film is shown in Tables 4 and 5 and Figures 7 and 8. The displacement / resonant frequency Fa is also shown in Tables 6 and 7 and Figures 9 and 10. The resonant frequency Fa showed a trend opposite to the amount of displacement. That is, in the region where α was 0 to 45°, the larger the angle α, the smaller Fa became, and in the region where α was 45 to 90°, the larger the angle α, the larger Fa became. In other words, Fa was minimum when the angle α was near 45° (angle θ was 0°).

[0119] From the above results, it can be seen that by limiting the angle θ between the in-plane direction in which the displacement of the movable part is maximum and the <100> orientation of the piezoelectric film within a predetermined range, a thin-film piezoelectric device with excellent piezoelectric characteristics and a large displacement amount can be obtained.

[0120]

[0121]

[0122]

[0123]

[0124]

[0125]

[0126] 2 Substrate 2-1 Si substrate portion 2-2 Insulating film 2-3 Surface Si layer 4 Movable portion 6 Buffer film 8 First electrode layer 10 First metal oxide film 12 Piezoelectric film 14 Second metal oxide film 16 Second electrode layer 18 Extraction electrode 18-1 Ti layer 18-2 Au layer 20 Protective film 22 Hollow portion

Claims

1. A thin-film piezoelectric device comprising a substrate and a movable part supported by the substrate, the movable part being made of zirconium oxide (ZrO ２ The piezoelectric film includes at least a buffer film containing lead zirconate titanate (Pb(Zr,Ti)O), a first electrode layer provided on the buffer film, a piezoelectric film provided on the first electrode layer, and a second electrode layer provided on the piezoelectric film, ３ ; PZT), barium titanate (BaTiO ３ ;BT), or potassium sodium niobate ((K,Na)NbO ３ The piezoelectric film in the movable portion is a (001) or (100) oriented film made of a single crystal of .KNN, ３１ a piezoelectric film having a thickness of 100 nm and a thickness of 150 nm, the thickness of the piezoelectric film being 100 nm and the thickness of the piezoelectric film being 150 nm.

2. The thin-film piezoelectric device according to claim 1, wherein the movable portion has an outer shape with two opposing parallel sides when viewed from above, and the direction perpendicular to the two sides coincides with the in-plane direction in which the displacement of the movable portion is maximum.

3. The thin film piezoelectric device according to claim 2, wherein the outer shape of the movable portion is rectangular, approximately rectangular, or trapezoidal.

4. The thin-film piezoelectric device according to claim 1 or 2, wherein one or both of the first electrode layer and the second electrode layer contain at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al) and copper (Cu).

5. Between the first electrode layer and the piezoelectric film, strontium ruthenate (SrRuO ３ 3. The thin-film piezoelectric device according to claim 1, further comprising a first metal oxide film made of SRO.

6. Between the piezoelectric film and the second electrode layer, strontium ruthenate (SrRuO ３ 3. The thin-film piezoelectric device according to claim 1, further comprising a second metal oxide film made of SRO.

7. The thin-film piezoelectric device according to claim 1 or 2, wherein the substrate is a Si substrate or an SOI substrate.

8. The piezoelectric film is made of lead zirconate titanate (Pb(Zr,Ti)O ３ 3. The thin-film piezoelectric device according to claim 1, which is made of a single crystal of PZT.

9. The thin film piezoelectric device according to claim 1 or 2, wherein said buffer film and said first electrode layer are made of single crystal.

10. The thin film piezoelectric device according to claim 9, wherein the crystal orientations of said buffer film, said first electrode layer and said piezoelectric film are aligned.

11. The thin film piezoelectric device according to claim 1 or 2, wherein the thin film piezoelectric device has a double-supported beam structure or a cantilever beam structure, and the movable portion is provided on a beam portion of the double-supported beam structure or the cantilever beam structure.

12. The thin-film piezoelectric device according to claim 1 or 2, which is used as a sensor or actuator.

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