Thin film piezoelectric device

Abstract

A thin-film piezoelectric device with excellent piezoelectric characteristics and a large displacement amount is provided. This thin-film piezoelectric device includes a substrate and a movable part supported by the substrate. The movable part at least includes a buffer film containing zirconium oxide (ZrO2) provided on the substrate, 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. The piezoelectric film is a (001) or (100) oriented film 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 the in-plane direction in relation to the d 31 mode and thereby the movable part is displaced, and 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 is within ±11.5°.

Description

Technical Field

[0001] The present invention relates to thin-film piezoelectric devices.

Background Art

[0002] With the recent progress of the highly informationized society, attention has been focused on thin-film piezoelectric devices. In particular, the fifth-generation mobile communication system (5G), which started being used in 2020, has become a strong driving force for the development of thin-film piezoelectric devices. That is, 5G has features such as high speed and large capacity, a large number of simultaneous connections, and ultra-low latency, enabling the realization of an IoT society in which various things are connected to the Internet. In the IoT society, various sensors and actuators are frequently used as information input / output devices, and thus miniaturization and high performance of the thin-film piezoelectric devices used therefor are desired.

[0003] A thin-film piezoelectric device is one in which a piezoelectric element is integrated on a semiconductor substrate using MEMS (Micro Electro Mechanical Systems) technology, enabling miniaturization and high integration of the element. A piezoelectric element is an element that utilizes the piezoelectric effect of a piezoelectric material, that is, a phenomenon of directly converting an electrical signal and a mechanical signal. The piezoelectric effect includes a direct piezoelectric effect of converting a mechanical signal into an electrical signal and an inverse piezoelectric effect of converting an electrical signal into a mechanical signal. By utilizing the direct piezoelectric effect, a thin-film piezoelectric device can be used as a sensor. Also, by utilizing the inverse piezoelectric effect, a thin-film piezoelectric device can be used as an actuator.

[0004] As piezoelectric materials, various materials are known, among which perovskite-type compounds typified by lead zirconate titanate (Pb(Zr,Ti)O3; PZT) are frequently used. A perovskite-type compound has a composition represented by the general formula: ABO3, and the cations, A-site ions and B-site ions, are displaced, thereby generating a dielectric polarization. By applying a mechanical pressure, the magnitude and direction of the dielectric polarization change, and thereby the piezoelectric effect is exhibited.

[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, a PZT thin film on this metal thin film, and an atomic ratio Ti / (Ti+Zr) in the PZT thin film in the range of 0.65 to 0.90 (Claim 1 of Patent Document 1). Further, Patent Document 1 describes that regarding the thin-film piezoelectric element, it can be used in a thin-film oscillator, thin-film VCO, thin-film filter, liquid injector, etc. used in a mobile communication device, etc., and high-performance piezoelectric devices such as a broadband FBAR that is far superior can be realized (

[0001] and

[0068] of Patent Document 1).

[0006] Patent Document 2 discloses a method for manufacturing a single-crystal wafer, which includes a step of preparing a polygonal substrate of a single-crystal material, a step of forming a multi-polygonal columnar laminated block by laminating and bonding a plurality of polygonal substrates, a step of forming a first orifice by processing the multi-polygonal columnar laminated block into an arc-shaped cylinder, and a step of forming a second orifice on the arc-shaped surface of the laminated block (Claim 1 of Patent Document 2). Further, Patent Document 2 describes that the single-crystal wafer is a piezoelectric substrate, etc. (

[0018] of Patent Document 2).

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

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Non-Patent Literature

[0009]

Non-Patent Literature 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] Thus, although thin-film piezoelectric devices have been conventionally proposed, there has been room for improvement in conventional thin-film piezoelectric devices. That is, piezoelectric devices are required to have a large displacement amount when a voltage is applied. However, in general thin-film piezoelectric devices, the piezoelectric material is polycrystalline and does not grow along the crystal orientation of the substrate. Therefore, the displacement amount does not change according to the crystal orientation of the piezoelectric material, and there is a limit in improving the displacement amount. Since the displacement amount of general thin-film piezoelectric devices does not change according to the crystal orientation, the elements have been manufactured to be arranged parallel or perpendicular along the orifice or notch of the substrate.

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

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

[0012] The inventors of the present invention have conducted intensive studies to solve such conventional problems. As a result, in a thin-film piezoelectric device, it has been found that in a single-crystallized piezoelectric film, the in-plane orientation dependence of piezoelectric properties is large, and the piezoelectric properties can be improved by precisely controlling the in-plane orientation of the piezoelectric film. Specifically, it has been found that the displacement amount increases by controlling 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.

[0013] The present invention has been completed based on such findings, and an object thereof is to provide a thin-film piezoelectric device having excellent piezoelectric properties and a large displacement amount.

Means for Solving the Problems

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

[0015] (1) A thin-film piezoelectric device including a substrate and a movable part supported by the substrate, The movable part includes at least a buffer film containing zirconium oxide (ZrO2) provided on the substrate, 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. The piezoelectric film is a (001) or (100) oriented film 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 the in-plane direction in relation to the d 31 mode based on the piezoelectric effect, whereby the movable part is displaced. A thin-film piezoelectric device in which 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°.

[0016] (2) The movable part has an outer shape with two opposite parallel sides in a top view, and the direction perpendicular to the two sides coincides with the in-plane direction in which the displacement of the movable part is maximum, for the thin-film piezoelectric device of (1) above.

[0017] (3) The outer shape of the movable part is rectangular, substantially rectangular, or trapezoidal, for the thin-film piezoelectric device of (2) above.

[0018] (4) 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), for the thin-film piezoelectric device of any one of (1) to (3) above.

[0019] (5) The thin-film piezoelectric device of any one of (1) to (4) above further includes a first metal oxide film made of strontium ruthenate (SrRuO3; SRO) between the first electrode layer and the piezoelectric film.

[0020] (6) The thin-film piezoelectric device of any one of (1) to (5) above further includes a second metal oxide film made of strontium ruthenate (SrRuO3; SRO) between the piezoelectric film and the second electrode layer.

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

[0022] (8) The piezoelectric film is composed of a single crystal of lead zirconate titanate (Pb(Zr,Ti)O3; PZT), for the thin-film piezoelectric device of any one of (1) to (7) above.

[0023] (9) The buffer film and the first electrode layer are composed of single crystals, for the thin-film piezoelectric device of any one of (1) to (8) above.

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

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

[0026] (12) The thin-film piezoelectric device according to any one of (1) to (11) above, which is used for the application of a sensor or an actuator.

Advantages of the Invention

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

Brief Description of the Drawings

[0028]

Figure 1

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Figure 11A

Figure 11B

Embodiments for Carrying Out the Invention

[0029] Specific embodiments of the present invention (hereinafter referred to as "the present embodiments") will be described. Note that the present invention is not limited to the following embodiments, and various modifications are possible without changing the gist of the present invention.

[0030] <<1. Thin Film Piezoelectric Device>> The thin film piezoelectric device of the present embodiment (hereinafter may be simply referred to as "device") includes a substrate and a movable part supported by this substrate. The movable part includes at least a buffer film containing zirconium oxide (ZrO2) provided on the substrate, 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. The piezoelectric film is a (001) or (100) oriented film 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 the in-plane direction in relation to the d 31 mode, whereby the movable part is displaced. The angle θ between the in-plane direction in which the displacement of the movable part is maximized and the <100> azimuth 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 FIGS. 1 and 2. FIG. 1 shows an example of a cross-sectional schematic view of a device including an Si substrate. The thin-film piezoelectric device (100) includes an Si substrate (2) and a movable part (4) supported by the Si substrate (2). At least a part of the Si substrate (2) is removed to form a hollow part (22). The movable part (4) is provided above 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 a lead-out electrode (18) provided to be electrically connected to the second electrode layer (16). Each of the first electrode layer (8) and the second electrode layer (16) is made of a Pt film. Each of the first metal oxide film (10) and the second metal oxide film (14) is made of an SRO film. The piezoelectric film (12) is made of a PZT film. The lead-out electrode (18) is composed of a laminate of a Ti layer (18-1) and an Au layer (18-2). Further, 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] FIG. 2 shows an example of a cross-sectional schematic view of a device including an SOI substrate. In this case, an SOI substrate (2) is used instead of the Si substrate. The SOI substrate (2) is composed of an Si substrate part (2-1), a surface Si layer (2-3), and an insulating film (2-2) such as an SiO2 film provided therebetween. Otherwise, it is the same as the case where an Si substrate is used, and the thin-film piezoelectric device (100) includes an SOI substrate (2) and a movable part (4) supported by the SOI substrate (2). At least a part of the SOI substrate is removed to form a hollow part (22). The movable part (4) is provided above 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), a lead-out electrode (18), and a protective film (20).

[0033] <Substrate> The substrate functions as a base of the thin-film piezoelectric device and also serves to support the movable part. The material of the substrate is not particularly limited. Known substrates used for thin-film piezoelectric devices can be used. For example, a silicon (Si) substrate, a silicon-on-insulator (SOI) substrate, a substrate made of a semiconductor crystal other than Si, a substrate made of various oxide single crystals such as sapphire and garnet, a glass substrate with a polysilicon film formed on its surface, etc. can be used. The SOI substrate is a substrate having a structure in which an insulating film (such as an SiO2 film) is interposed between the Si substrate portion and the surface Si layer. 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.

[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, the (100) substrate means a substrate in which the (100) plane based on the crystal lattice faces the main surface. 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 while sufficiently achieving lattice matching thereon, and as a result, a single-crystalline buffer film, first electrode layer, and piezoelectric film can be obtained. However, it is also possible to separate the substrate after forming the single-crystalline piezoelectric film and bond another substrate. Therefore, the substrate of the thin-film piezoelectric device of the present embodiment is not limited to a Si(100) substrate or an SOI(100) substrate. Other substrates such as a (110) substrate and 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 including a Si substrate, the buffer film (6) constitutes the lowermost layer of the movable part (4). That is, the movable part (4) does not include the Si substrate (2). On the other hand, in the device of FIG. 2 including an SOI substrate, the surface Si layer (2-3) of the SOI substrate (2) constitutes the lowermost 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 includes a buffer layer containing zirconium oxide (ZrO2). The buffer layer is provided on a substrate. Also, the buffer layer constitutes a movable part. By using the buffer layer containing ZrO2, the single crystallization of the piezoelectric layer provided thereon can be promoted. That is, ZrO2 has a crystal structure of monoclinic, tetragonal, or cubic. When a ZrO2 buffer layer having such a crystal structure grows on the substrate, a nanopyramid structure is formed on its surface. When the first electrode layer and the piezoelectric layer are formed on the ZrO2 buffer layer having the nanopyramid structure, the nanopyramid structure itself is deformed to correct the crystal lattice misalignment between the substrate and the film. Therefore, it becomes possible to obtain a single crystal film with less residual stress.

[0037] The buffer layer may contain only ZrO2, or may contain rare earth elements or alkaline earth elements. Also, ZrO2 may contain oxygen defects. Further, for property improvement, it 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 layer is preferably 10 nm or more and 1500 nm or less, more preferably 20 nm or more and 1200 nm or less, and even more preferably 30 nm or more and 1000 nm or less. Also, the buffer layer is preferably an epitaxial film formed on the substrate, and more preferably a (100)-oriented epitaxial film.

[0039] <The first electrode layer> The first electrode layer constitutes a pair of electrodes that sandwich the piezoelectric layer together with the second electrode layer. The potential difference based on the surface charge of the piezoelectric layer generated by the direct piezoelectric effect can be detected through the electrode layer. Alternatively, a potential difference can be applied to the piezoelectric layer through the electrode layer to generate strain due to the inverse piezoelectric effect. As long as the first electrode layer has conductivity, its material is not limited. For example, it contains at least one 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 or more and 500 nm or less, more preferably 30 nm or more and 300 nm or less, and still more preferably 50 nm or more and 200 nm or less. Further, the first electrode layer is preferably an epitaxial film formed on the buffer film, and more preferably an epitaxial film oriented in the (100) direction.

[0041] <First metal oxide film> The thin-film piezoelectric device of the present embodiment may include a first metal oxide film between the first electrode layer and the piezoelectric film. The first metal oxide film preferably consists of strontium ruthenate (SrRuO3; SRO). SRO has conductivity. Therefore, the SRO film (first metal oxide film) can be used as part of the electrode layer (first electrode layer). Further, SRO has the same perovskite crystal structure as PZT, BT, or KNN that constitutes the piezoelectric film, and the lattice constants are approximately the same. Therefore, by providing an SRO film between the first electrode layer and the piezoelectric film, it becomes possible to further improve the crystallinity of the piezoelectric film formed thereon. In particular, a piezoelectric film with a film thickness as small as the submicron size is likely to have crystal defects. By providing the first metal oxide film, even if the film thickness is of the submicron size, a piezoelectric film with few crystal defects can be formed. However, the first metal oxide film is not an essential component. When the thickness of the piezoelectric film is sufficiently large, a piezoelectric film with few crystal defects can be obtained even without the first metal oxide film.

[0042] The thickness of the first metal oxide film (SRO film) is preferably 1 nm or more and 100 nm or less, more preferably 3 nm or more and 80 nm or less, and still more preferably 5 nm or more and 60 nm or less. Further, the first metal oxide film is preferably an epitaxial film formed on the first electrode layer, and more preferably an epitaxial film oriented in the (100) direction.

[0043] <Piezoelectric film> The piezoelectric film is a component that serves as the main body for exhibiting the piezoelectric effect and has the function of converting electrical energy and mechanical energy. That is, when pressure (force) is applied to the piezoelectric film, surface charges are generated above and below the piezoelectric film due to the direct piezoelectric effect, thereby generating a potential difference (voltage). Therefore, the piezoelectric film can be used as a sensor. Also, when a potential difference (voltage) is applied above and below the piezoelectric film, the piezoelectric film is displaced due to the inverse piezoelectric effect. Therefore, the piezoelectric film can be used as an actuator.

[0044] The piezoelectric film of this embodiment is characterized in that it is composed of a single crystal. That is, the crystal is continuous both in the cross section and on the upper surface of the piezoelectric film, and it has a crystal structure in which dice are stacked without rotation, that is, a Cube on Cube structure. Therefore, the microstructure is different from that of conventional piezoelectric films. That is, conventional piezoelectric films are polycrystalline films composed of a plurality of randomly oriented crystallites in the thickness direction and the plane direction, or piezoelectric films in which the crystal is continuous in the thickness direction but randomly oriented in the plane direction. Although epitaxial films oriented in the thickness direction and the plane direction have also been proposed, the crystals are not continuous and they are composed of polycrystals.

[0045] The piezoelectric film of this embodiment composed of a single crystal can completely align the polarization direction throughout the film. Therefore, it is possible to improve the electrical and mechanical properties. Specifically, it is possible to improve the piezoelectric constant. Also, since the dielectric constant can be suppressed compared to polycrystalline films, there is an effect of reducing power consumption and it has the advantage that high-precision output is possible when used as a sensor. Moreover, by making it single crystal, the bonding force between atoms is improved, so the temperature characteristics and reliability of the piezoelectric film are improved.

[0046] Whether the piezoelectric film is a single crystal or not can be confirmed by performing in-plane φ scan measurement by the X-ray diffraction method. 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 a single crystal.

[0047] The piezoelectric film of this embodiment is composed of lead zirconate titanate (Pb(Zr,Ti)O3; PZT), barium titanate (BaTiO3; BT), or potassium sodium niobate ((K,Na)NbO3; KNN). PZT, BT, and KNN are all perovskite-type compounds represented by the general formula: ABO3. The perovskite-type compound has a crystal structure such as a body-centered cubic structure, and many of them are dielectric and piezoelectric materials exhibiting dielectric and piezoelectric properties. In particular, PZT exhibits excellent piezoelectric properties and is widely used as a sensor and actuator material. Therefore, preferably, the piezoelectric film is composed of a single crystal of lead zirconate titanate (Pb(Zr,Ti)O3; PZT).

[0048] PZT has a rhombohedral crystal structure when it has a Zr-rich composition and a tetragonal crystal structure when it has a Ti-rich composition. Also, in the intermediate composition region, it becomes a morphotropic phase boundary (MPB) composition in which the rhombohedral and tetragonal crystal structures coexist, and at that time, the piezoelectric properties become significantly higher. When the composition of PZT is Pb(Zr 1-x Ti x )O3 (where 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. A piezoelectric film having a body-centered cubic crystal structure is likely to be (001) or (100) oriented by epitaxial growth. For example, a PZT film having a tetragonal crystal structure is likely to be (001) oriented when epitaxially grown. And when a PZT film having a tetragonal crystal structure is (001) oriented, the polarization direction parallel to the

[0001] direction and the electric field direction parallel to the thickness direction of the piezoelectric film are parallel to each other, so the piezoelectric properties are improved. That is, in a PZT film having a tetragonal crystal structure, a large piezoelectric constant can be obtained when an electric field is applied along the

[0001] direction.

[0050] In this embodiment, whether the piezoelectric film is a (001) or (100) oriented film can be examined by subjecting the piezoelectric film to θ-2θ scan using X-ray diffraction method. That is, when the piezoelectric film is subjected to θ-2θ scan, when the ratio of the diffraction peak intensity from other planes (peak intensity ratio) to the diffraction peak intensity from the target planes ((001) plane and (100) plane) is 10% or less, it can be determined as a (001) or (100) oriented film. It is preferable that the peak intensity ratio is smaller, and more preferably 5% or less.

[0051] The thickness of the piezoelectric film is preferably 0.1 μm or more and 10 μm or less. If the piezoelectric film is excessively thin, the effect of the piezoelectric film cannot be fully utilized, and the resulting displacement amount may be small. On the other hand, if the piezoelectric film is excessively 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 is composed of strontium ruthenate (SrRuO3; SRO). SrO has conductivity. Therefore, the SRO film (second metal oxide film) can be used as part of the electrode layer (second electrode layer).

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

[0054] <Second electrode layer> The second electrode layer forms a pair of electrodes that sandwich the piezoelectric film together with the first electrode layer. As long as the second electrode layer has conductivity, its material is not limited. For example, it contains at least one 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 or more and 200 nm or less, more preferably 3 nm or more and 150 nm or less, and even more preferably 10 nm or more and 120 nm or less. Also, 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. As the extraction electrode, a known conductive material can be used. For example, a laminate of a gold (Au) layer and a titanium (Ti) layer can be mentioned. The Au layer mainly functions as a conductive layer, and the Ti layer mainly functions as an adhesion layer.

[0057] <Protective film> A protective film may be provided on the second electrode layer or the second metal oxide film (SRO film). As the material of the protective film, although not limited, tetraethyl orthosilicate (TEOS) etc. can be used.

[0058] <Movable part> The movable part is supported by a substrate and includes at least a buffer film, a first electrode layer, a piezoelectric film, and a second electrode layer. Also, a metal oxide film (first metal oxide film, second metal oxide film) may be further provided between the first electrode layer and the piezoelectric film and / or on the second electrode layer.

[0059] In the thin-film piezoelectric device of the present embodiment, the piezoelectric film in the movable part expands and contracts in the in-plane direction in relation to the d 31 mode, whereby the movable part is displaced. In the piezoelectric effect, the piezoelectric longitudinal effect (d 33mode), the piezoelectric transverse effect (d) where the electrical input / output direction is orthogonal to the mechanical input / output direction 31 mode), the piezoelectric sliding effect (d) due to shear deformation 15 mode). In a thin-film piezoelectric device, an element configuration using the d 31 mode is advantageous in the element formation process and can increase the displacement amount.

[0060] In the thin-film piezoelectric device of this embodiment, electrodes (first electrode layer and second electrode layer) are provided above and below 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 directed in the vertical direction of the piezoelectric film is generated, and due to the inverse piezoelectric effect in the d 31 mode, displacement occurs in a direction perpendicular to this electric field, that is, in a direction parallel to the film surface. Alternatively, when a stress parallel to the film surface is applied to the movable part, surface charges are generated in the electrode layer due to the direct piezoelectric effect. By using the d 31 mode, displacement in the film surface direction of the piezoelectric film and displacement of the movable part due to this displacement can be utilized. The movable part is composed of a laminate of a piezoelectric film and other components (such as a buffer film). Even if the piezoelectric film expands and contracts in-plane (displaces), the other components do not expand and contract. Therefore, warping occurs in the movable part according to the displacement of the piezoelectric film. And the larger the displacement amount of the piezoelectric film, the larger 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 expansion and contraction amount (warping amount) is maximum in the plane parallel to the film surface of the piezoelectric film. Also, the <100> orientation includes all orientations equivalent to the

[0100] 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 in-plane orientation dependence of the piezoelectric displacement amount is large. As a result of investigations by the present inventors, it has been found that the smaller the angle θ, that is, the more the <100> orientation of the piezoelectric film and the in-plane direction in which the displacement of the movable part is maximized are aligned, the larger the displacement amount of the piezoelectric film becomes. For example, when a single crystal PZT film is used as the piezoelectric film, d 31 The piezoelectric constant can be increased to about 100 pm / V or more. On the other hand, conventional piezoelectric films are not single crystals. Therefore, they do not show in-plane orientation dependence of piezoelectric properties, and the piezoelectric displacement amount is small. For example, Non-Patent Document 1 shows that the radial piezoelectric constant (d 31 ) of a PZT thin film is 25 to 60 pC / N (25 to 60 pm / V) (page 136, Fig. 4 of Non-Patent Document 1). Moreover, since no in-plane orientation dependence is shown, the relationship between the in-plane orientation and piezoelectric properties has not been focused on conventionally. In this embodiment, since the piezoelectric film is a single crystal, it has a large in-plane orientation dependence, and there is a feature that the piezoelectric properties are remarkably improved by controlling the in-plane orientation.

[0063] Preferably, as shown in FIGS. 1 and 2, a hollow portion (22) is provided directly below the movable portion (4). That is, at least a part of the substrate (2) in the movable portion (4) is removed, and the movable portion (4) has a diaphragm structure. In this case, since the restraint of the movable portion from the substrate is small, the amount of warping of the movable portion becomes large.

[0064] In the thin-film piezoelectric device of this embodiment, the movable part preferably has an outer shape having two opposite 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 part is maximized. Further, the outer shape of the movable part is preferably rectangular, substantially rectangular, or trapezoidal. By thus providing the movable part with an outer shape having two opposite parallel sides, it becomes possible to set the direction perpendicular to these two sides as the maximum expansion and contraction direction. When the outer shape of the movable part is rectangular, the dimension in the width (short side) direction is preferably 30 μm or more and 500 μm or less, more preferably 50 μm or more and 300 μm or less. The dimension in the length (long side) direction is preferably 100 μm or more and 1000 μm or less, more preferably 250 μm or more and 600 μm or less. Further, the direction perpendicular to the width direction preferably coincides with the in-plane direction in which the displacement of the movable part is maximized.

[0065] In the thin-film piezoelectric device of this embodiment, the buffer film and the first electrode layer are preferably composed of single crystals. Further, it is preferable that the crystal orientations of the buffer film, the first electrode layer, and the piezoelectric film are aligned. By forming the buffer film and the first electrode layer of single crystals and aligning their crystal orientations, it becomes possible to make the crystallinity of the piezoelectric film formed on the first electrode layer better.

[0066] The thin-film piezoelectric device of this embodiment has a double-clamped beam structure or a single-clamped beam structure, and it is preferable that a movable part is provided in the beam part of the double-clamped beam structure or the single-clamped beam structure. In a device having a single-clamped beam structure, only one end of the movable part is fixed, and the other end is a free end. Therefore, according to the warp of the movable part, the free end of the movable part is displaced in the vertical direction. The single-clamped beam structure is also called a cantilever structure. On the other hand, in a device having a double-clamped beam structure, both ends of the movable part are fixed. Therefore, the movable part bends according to the warp, and the central part thereof is displaced vertically. The double-clamped beam structure can also be called a diaphragm structure.

[0067] The thin-film piezoelectric device of this embodiment is preferably used for applications such as sensors or actuators. The thin-film piezoelectric device of this embodiment is characterized by a large displacement amount of the movable part. Therefore, sensors and actuators with good characteristics can be fabricated. 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, mirrors, optical switches, and / or micropumps. In addition, the thin-film piezoelectric device of this embodiment can also be applied to applications of high-frequency circuit components such as RF filters and piezoelectric thin-film resonators (FBAR).

[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 the above-described requirements are satisfied. However, a preferred manufacturing method includes a step of preparing a substrate (substrate preparation step), a step of forming a buffer film containing zirconium oxide (ZrO2) on the substrate (buffer film formation step), a step of forming a first electrode layer on the buffer film (first electrode layer formation step), a step of forming a piezoelectric film on the first electrode layer (piezoelectric film formation step), and a step of forming a second electrode layer on the piezoelectric film (second electrode layer formation step). Further, a step of forming a first metal oxide film between the first electrode layer and the piezoelectric film (first metal oxide film formation 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 formation step) may be provided. A step of forming an extraction electrode on the second electrode layer and the second metal oxide film (extraction electrode formation 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 formation step) may be provided. Furthermore, a step of removing at least a part of the substrate in the movable part and forming a hollow part directly below the movable part (hollow part formation step) may be provided. Details of each step will be described below.

[0069] <Substrate Preparation Step> In the substrate preparation process, a substrate is prepared. The details of the substrate are as described above. That is, as the substrate, a silicon (Si) substrate, a silicon-on-insulator (SOI) substrate, a substrate made of a semiconductor crystal other than Si, a substrate made of various oxide single crystals such as sapphire and garnet, a glass substrate with a polysilicon film formed on the surface, etc. can be used. Also, 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 not limited either. For example, a Si(100) substrate, a Si(110) substrate, or a Si(111) substrate can be used.

[0070] <Buffer film deposition process> In the buffer film deposition process, a buffer film containing zirconium oxide (ZrO2) is deposited on the substrate. The deposition can be performed by methods such as electron beam evaporation or sputtering. When depositing by electron beam evaporation, for example, the substrate is placed in the vacuum chamber of the evaporation apparatus. Then, while flowing oxygen (O2) gas in a high vacuum atmosphere with the pressure in the vacuum chamber kept constant, a zirconium oxide (ZrO2) film is deposited while heating the substrate. By depositing under such conditions, a buffer film composed of an epitaxial film with (100) orientation can be surely obtained. Also, patterning processing for partially removing the buffer film after deposition may be performed using photolithography technology.

[0071] <First electrode layer deposition process> In the first electrode layer deposition process, a first electrode layer is deposited on the buffer film. The first electrode layer contains, for example, at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu). The deposition of the first electrode layer can be performed by methods such as sputtering. When depositing by sputtering, for example, while heating the substrate, an epitaxially grown first electrode layer is formed on the buffer film as part of the lower electrode by sputtering. Also, patterning processing for partially removing the first electrode layer after deposition may be performed using photolithography technology.

[0072] <First Metal Oxide Film Deposition Process> 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 forming the film by sputtering, for example, while heating the substrate, an epitaxially grown first metal oxide film may be formed on the first electrode layer as a part of the lower electrode by sputtering. Further, patterning processing may be performed to partially remove the first metal oxide film after film formation using photolithography technology.

[0073] <Piezoelectric Film Deposition Process> In the piezoelectric film deposition process, a piezoelectric film is formed on the first electrode layer. The piezoelectric film is a (001) or (100) oriented film composed of a single crystal of PZT, BT, or KNN. The piezoelectric film is formed by a method such as sputtering or sol-gel method. For example, a piezoelectric film containing lead zirconate titanate (Pb(Zr 1-x Ti x )O3 (0 < x < 1): PZT) grown epitaxially may be formed on the first electrode layer by a known sputtering method. Alternatively, a piezoelectric film containing lead zirconate titanate (Pb(Zr 1-x Ti x )O3 (0 < x < 1): PZT) grown epitaxially may be formed on the first electrode layer by a known sol-gel method. As long as a (001) or (100) oriented single crystal film can be obtained, the film formation method is not limited. Further, patterning processing may be performed to partially remove the piezoelectric film after film formation using photolithography technology.

[0074] <Second Metal Oxide Film Deposition 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 forming the film by sputtering, for example, an epitaxially grown second metal oxide film may be formed on the piezoelectric film as part of the lower electrode by sputtering. Further, patterning processing for partially removing the second metal oxide film after film formation may be performed using photolithography technology.

[0075] <Second Electrode Layer Film Formation Step> In the second electrode layer film formation step, a second electrode layer is formed on the piezoelectric film or the second metal oxide film. The second electrode layer contains, 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 as part of the lower electrode by sputtering. Further, patterning processing for partially removing the second electrode layer after film formation may be performed using photolithography technology.

[0076] <Extraction Electrode Film Formation Step> An extraction electrode may be formed on the second electrode layer. The extraction electrode may be formed by a method such as sputtering. Further, patterning processing for partially removing the extraction electrode layer after film formation may be performed using photolithography technology.

[0077] <Protective Film Formation Step> A protective film may be formed on the second electrode layer or the extraction electrode. As the protective film, but not limited to, tetraethyl orthosilicate (TEOS) etc. can be used. The protective film may be formed by a method such as sputtering. Further, patterning processing for partially removing the protective film after film formation may be performed using photolithography technology.

[0078] <Hollow Portion Formation Step> When manufacturing a thin-film piezoelectric device, a step of removing at least a part of the substrate in the movable part and forming a hollow part directly below the movable part may be provided. Thereby, a movable part having a cantilever structure or a diaphragm structure and having a large displacement amount can be formed. The formation of the hollow part is preferably performed after forming a buffer film, a first electrode layer, a piezoelectric layer, and a second electrode layer on the substrate.

[0079] The formation of the hollow part can be performed by combining photolithography technology and etching technology. Specifically, a mask having an opening is provided in close contact with the back surface of the substrate. Next, the substrate is etched and removed from the mask opening using an alkaline etching solution. For example, an Si substrate or an SOI substrate is anisotropically etched by an alkaline etching solution to form a hollow part in a frustum of a square pyramid shape. When an Si substrate is used, the buffer film (ZrO2 film) on the Si substrate functions as an etching stop layer. Therefore, a thin-film piezoelectric device having no substrate directly below the movable part can be manufactured. In the case of an SOI substrate, the insulating film (SiO2 film) contained therein functions as an etching stop layer. Further, the insulating film can be removed using an etching solution such as hydrofluoric acid. Therefore, a thin-film piezoelectric device having a surface Si layer, or a surface Si layer and an insulating film (SiO2 film) directly below the movable part can be manufactured.

Example

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

[0081] (1) Fabrication of thin-film piezoelectric device [Example 1] In Example 1, a buffer film (ZrO2 film), a 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 a lead-out electrode (Ti layer, Au layer) were formed on an SOI substrate in this order, and then the back surface of the SOI substrate was etched and removed to form a cavity part (hollow part). Thereby, a thin-film piezoelectric device having a movable part as shown in FIG. 2 was manufactured.

[0082] First, a wafer of a 6-inch diameter SOI substrate was prepared. This SOI substrate had a three-layer structure of an Si substrate portion, an insulating film (SiO2 film), and a surface Si layer. Also, the upper surface, which was the main surface, was a (100) plane. That is, the surface Si layer was (100)-oriented.

[0083] Next, a zirconium oxide (ZrO2) film was formed as a buffer film on the surface Si layer of the prepared SOI substrate by electron beam evaporation. The formed buffer film had a cubic crystal structure with (100) orientation, and its film thickness was 60 nm. The film formation was carried out under the following conditions.

[0084] - Apparatus: Electron beam evaporation apparatus - Pressure: 7.00×10 -3 Pa - Evaporation source: ZrO2 - Acceleration voltage / Emission current: 7.5 kV / 1.80 mA - Thickness: 60 nm - Film formation rate: 0.005 nm / second - Oxygen flow rate: 10 sccm - Substrate temperature: 500 - 600 °C

[0085] Next, a Pt film as the first electrode layer was formed by sputtering on the buffer film (ZrO2 film). The formed Pt film (first electrode layer) had a cubic crystal structure with (100) orientation, and its film thickness was 150 nm. The film formation was carried out under the following conditions.

[0086] - Apparatus: DC sputtering apparatus - Pressure: 3.20×10 -2 Pa - Evaporation source: Pt - Power: 100 W - Thickness: 150 nm - Film formation rate: 0.14 nm / second - Ar flow rate: 16 sccm - Substrate temperature: 400 °C

[0087] Next, an SRO film was formed as the first metal oxide film on the first electrode layer (Pt film) by sputtering. The formed first metal oxide film had a cubic crystal structure with (100) orientation, and its film thickness was 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 / second - Thickness: 40 nm

[0089] A PZT film as a piezoelectric film was formed 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 blended so that the composition ratio (mol ratio) was Pb:Zr:Ti = 100 + δ:52:48. Also, the raw material solution was adjusted so that the concentration as Pb(Zr 0.52 Ti 0.48 )O3 was 0.35 mol / l. Here, δ is the excess Pb amount considering the volatilization of Pb oxide in the subsequent heat treatment process, and δ = 20 in this example. 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 raw material solution was dropped onto the first metal oxide film (SRO film) of the substrate, and then the substrate was rotated at 3000 rpm for 10 seconds to coat the raw material solution on the substrate. Thereby, a film containing the precursor was formed. Then, the substrate on which the film containing the precursor was formed was placed on a hot plate at a temperature of 200 °C for 30 seconds, and further placed on a hot plate at a temperature of 450 °C for 30 seconds to dry the film. Thereafter, heat treatment was performed on the film at 600 to 700 °C for 60 seconds in an oxygen (O2) atmosphere of 0.2 MPa to oxidize and crystallize the precursor. Then, the steps from the application of the raw material solution to crystallization were repeated any number of times until the desired film thickness was obtained to form a piezoelectric film (PZT film).

[0091] The formed piezoelectric film (PZT film) was (001)-oriented, and its film thickness was 2 μm. Also, the composition of the piezoelectric film was Pb(Zr 0.52 Ti 0.48 )O3.

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

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

[0094] Furthermore, in order to ensure conduction to the second electrode layer (Pt film) and the second metal oxide film (SRO film) that act as the upper electrode, a 10-nm-thick Ti layer and a 300-nm-thick Au layer were formed by DC sputtering method, and then partially etched and removed using photolithography technology to form extraction electrodes.

[0095] Finally, anisotropic etching was performed from the back surface of the substrate (SOI substrate) to form a cavity portion (hollow portion). Specifically, a part of the Si substrate portion and the insulating film (SiO2 film) was removed from the back surface side of the substrate to form an opening on the back surface side of the substrate. Thereby, a movable portion having a rectangular cavity portion (hollow portion) was fabricated. The planar dimensions of the movable portion were 70 μm in width and 275 μm in length.

[0096] When fabricating the thin-film piezoelectric device of Example 1, the device was designed such that the angle θ between the width direction (short side direction) of the movable portion and the <100> orientation of the piezoelectric film became a predetermined angle. Specifically, the movable portion was designed such 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 respectively.

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

[0098] [Example 2] A piezoelectric film (PZT film) was formed by sputtering. Samples were fabricated in the same manner as in Example 1 except for this. The formation of the piezoelectric film was performed under the following conditions.

[0099] -Apparatus: RF magnetron sputtering apparatus -Power: 2000 W -Gas: Ar + O2 -Pressure: 1.8 Pa -Substrate temperature: 600 °C -Film formation rate: 0.3 nm / second -Thickness: 2 μm

[0100] [Example 3] An Si(100) substrate was used instead of the SOI substrate. Also, the film thickness of the buffer film (ZrO2 film) was set to 1.0 μm. Samples were fabricated in the same manner as in Example 1 except for this. As a result, a thin-film piezoelectric device having a movable part as shown in FIG. 1 was fabricated.

[0101] [Example 4] The film thickness of the buffer film (ZrO2 film) was changed to 0.8 μm. Samples were fabricated in the same manner as in Example 3 except for this.

[0102] [Example 5] The film thickness of the buffer film (ZrO2 film) was changed to 1.2 μm. Samples were fabricated in the same manner as in Example 3 except for this.

[0103] [Example 6] When forming the cavity part, the planar dimensions of the movable part were changed to 200 μm × 500 μm. Also, the movable part was designed such 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 except for this.

[0104] [Example 7] The piezoelectric film (PZT film) was formed by sputtering. Specifically, the piezoelectric film was formed under the same conditions as in Example 2. Samples were fabricated in the same manner as in Example 6 except for this.

[0105] [Example 8] An Si(100) substrate was used instead of the SOI substrate. Also, the film thickness of the buffer film (ZrO2 film) was set to 1.0 μm. Samples were fabricated in the same manner as in Example 6 except for this.

[0106] [Example 9] The film thickness of the buffer film (ZrO2 film) was changed to 0.8 μm. Samples were fabricated in the same manner as in Example 8 except for this.

[0107] [Example 10] The film thickness of the buffer film (ZrO₂ film) was changed to 1.2 μm. Samples were prepared in the same manner as in Example 8 except for this.

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

[0109]

Table 1

[0110] (2) Evaluation of the thin-film piezoelectric device Regarding the thin-film piezoelectric devices fabricated in Examples 1 to 10, evaluations of various characteristics were conducted 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 taken out, and the piezoelectric film was evaluated using a fully automatic multi-purpose horizontal X-ray diffractometer (Rigaku Corporation, Smart Lab). Specifically, for the 2θ-θ crystal peak of PZT(004), a 360° scan measurement in the φ direction was carried out.

[0112] <Resonance frequency> The resonance frequency of the thin-film piezoelectric device was measured using a spectrum impedance analyzer (Agilent Technologies, 4395A). Specifically, a probe connected to the spectrum impedance analyzer was brought into contact with the upper electrode (second electrode layer) and the lower electrode (first electrode layer) of the thin-film piezoelectric device so that conduction could be obtained. Then, a voltage of 15 V was applied, and the frequency at which the impedance (Z) and the phase difference (θ) changed was measured.

[0113] <Displacement amount> The displacement amount in the movable part of the thin-film piezoelectric device was evaluated. Specifically, a probe connected to an oscilloscope (Tektronix, TDS3014C) was 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 conduction. Next, a measurement signal was applied to the upper electrode and the lower electrode using a multifunction generator (NF Circuit Design Block Co., Ltd., WF1973). At this time, the measurement signal was applied under the conditions of a Sin wave (sine wave), 1 kHz, Vpp 20 V, and Offset 10 V. Then, the displacement amount of the movable part of the thin-film piezoelectric device was measured using a laser Doppler vibrometer (Polytec, VFX-Compact), and the obtained output value was captured by the oscilloscope.

[0114] (3) Evaluation results <Crystallinity of piezoelectric film> As a result of performing a θ-2θ scan by X-ray diffraction method, the diffraction peak intensity of the surface other than the (100) plane with respect to the peak intensity of the (100) plane of the piezoelectric films (PZT films) of the thin-film piezoelectric devices of Examples 1 to 10 was 0.09%. Therefore, it was found that these piezoelectric films were (100)-oriented.

[0115] In addition, a four-fold symmetric peak could be confirmed by in-plane φ scan. Therefore, it was confirmed that it was a single crystal film with three-axis orientation. The X-ray diffraction pattern (φ scan) of the piezoelectric film (PZT film) of Example 1 is shown in FIGS. 11A and B. Here, FIG. 11A shows the X-ray diffraction intensity plotted on a linear scale on the vertical axis, and FIG. 11B shows the logarithmic scale.

[0116] The displacement amounts of the movable parts of the thin-film piezoelectric devices of Examples 1 to 10 are shown in Tables 2 and 3 and FIGS. 5 and 6. 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 orifla direction

[0110] . 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> orientation of the piezoelectric film. In this embodiment, the piezoelectric film is (100)-oriented. Also, the crystal orientation of the piezoelectric film is aligned with the crystal orientation of the substrate. Therefore, θ and α have a relationship of θ = α - 45°.

[0117] As shown in Tables 2 and 3 and FIGS. 5 and 6, in the region where α is from 0 to 45°, the displacement amount increases as the angle α increases, and in the region where α is from 45 to 90°, the displacement amount decreases as the angle α increases. That is, the displacement amount was maximized near α = 45° (angle θ = 0°).

[0118] The resonance frequency Fa of the piezoelectric film is shown in Tables 4 and 5 and FIGS. 7 and 8. Also, the displacement / resonance frequency Fa is shown in Tables 6 and 7 and FIGS. 9 and 10. The resonance frequency Fa showed a tendency opposite to that of the displacement amount. That is, in the region where α is from 0 to 45°, Fa decreases as the angle α increases, and in the region where α is from 45 to 90°, Fa increases as the angle α increases. That is, Fa was minimized near α = 45° (angle θ = 0°).

[0119] From the above results, it is understood that by limiting 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 within a predetermined range, a thin-film piezoelectric device with excellent piezoelectric characteristics and a large displacement amount can be obtained.

[0120]

Table 2

[0121]

Table 3

[0122]

Table 4

[0123]

Table 5

[0124]

Table 6

[0125]

Table 7

Explanation of Symbols

[0126] 2 substrates 2-1 Si substrate part 2-2 Insulating film 2-3 Surface Si layer 4 Movable part 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 part

Claims

1. A thin-film piezoelectric device comprising a substrate and a movable part supported by the substrate, The movable part is provided on the substrate with a buffer film containing zirconium oxide (ZrO ２ ), 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, and at least includes The piezoelectric film is a lead zirconate titanate (Pb(Zr,Ti)O ３ ; PZT), barium titanate (BaTiO ３ ; BT), or potassium sodium niobate ((K,Na)NbO ３ ; KNN) single crystal (001) or (100) oriented film, The piezoelectric film in the movable part expands and contracts in the in-plane direction in relation to the d ３１ mode based on the piezoelectric effect, whereby the movable part is displaced. ３１ ​ wherein 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°.

2. The movable part has an outer shape having two opposite parallel sides in a top view, and the direction perpendicular to the two sides coincides with the in-plane direction in which the displacement of the movable part is maximum. The thin-film piezoelectric device according to Claim 1.

3. The outer shape of the movable part is rectangular, substantially rectangular, or trapezoidal. The thin-film piezoelectric device according to Claim 2.

4. 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). The thin-film piezoelectric device according to Claim 1 or 2.

5. A thin-film piezoelectric device according to claim 1 or 2, further comprising a first metal oxide film made of strontium ruthenium oxide (SrRuO ３ ; SRO) between the first electrode layer and the piezoelectric film.

6. Between the piezoelectric film and the second electrode layer, a second metal oxide film made of strontium ruthenate (SrRuO ３ ; SRO) is further provided. The thin-film piezoelectric device according to claim 1 or 2.

7. The substrate is a Si substrate or an SOI substrate. The thin-film piezoelectric device according to Claim 1 or 2.

8. The piezoelectric film is composed of a single crystal of lead zirconate titanate (Pb(Zr,Ti)O ３ ; PZT), and the thin-film piezoelectric device according to claim 1 or 2.

9. The buffer film and the first electrode layer are composed of single crystals. The thin-film piezoelectric device according to Claim 1 or 2.

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

11. The thin-film piezoelectric device has a double-clamped beam structure or a single-clamped beam structure, and the movable part is provided on the beam part of the double-clamped beam structure or the single-clamped beam structure. The thin-film piezoelectric device according to Claim 1 or 2.

12. It is used for the application of a sensor or an actuator. The thin-film piezoelectric device according to Claim 1 or 2.

Images