Thin film piezoelectric device

Abstract

Provided is a thin-film piezoelectric device having excellent piezoelectric characteristics and a large amount of displacement. The thin film piezoelectric device includes a substrate and a movable portion supported by the substrate. The movable part is provided with 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 formed by lead zirconate titanate (Pb (Zr, Ti) O3; pZT), barium titanate (BaTiO3; bT) or potassium sodium niobate ((K, Na) NbO3; the (001) or (100) alignment film is composed of a single crystal of (001) or (KNN). The piezoelectric film in the movable part expands and contracts in an in-plane direction in association with a d31 mode based on a piezoelectric or inverse piezoelectric effect, whereby the movable part moves, and an angle [theta] between the in-plane direction in which the displacement of the movable part is maximized and a < 100 > orientation of the piezoelectric film is within + / -11.5 DEG.

Description

Technical Field

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

[0002] With the recent advancement of a highly information-based society, thin-film piezoelectric devices have garnered increasing attention. In particular, the fifth-generation mobile communication system (5G), which began operating in 2020, has become a powerful driving force behind the development of thin-film piezoelectric devices. 5G's high speed, high capacity, multiple simultaneous connections, and ultra-low latency make it possible to realize an IoT society where various objects are connected to the internet. In the IoT society, various sensors and actuators are widely used as information input and output devices, leading to a demand for smaller and more powerful thin-film piezoelectric devices used in these devices.

[0003] Thin film piezoelectric devices are obtained by integrating piezoelectric elements on a semiconductor substrate using MEMS (Micro Electro Mechanical Systems) technology, which can achieve miniaturization and high integration of elements. Piezoelectric elements are elements that utilize the piezoelectric effect of piezoelectric materials, that is, the phenomenon of direct conversion of electrical signals and mechanical signals. In the piezoelectric effect, there is a positive piezoelectric effect that converts mechanical signals into electrical signals and an inverse piezoelectric effect that converts electrical signals into mechanical signals. By utilizing the positive piezoelectric effect, thin film piezoelectric devices can be used as sensors. In addition, by utilizing the inverse piezoelectric effect, thin film piezoelectric devices can be used as actuators.

[0004] Various materials are known as piezoelectric materials, with perovskite compounds, typified by lead zirconate titanate (Pb(Zr,Ti)O3; PZT), being the most commonly used. Perovskite compounds have a composition represented by the general formula: ABO3. The displacement of the A-site ions and B-site ions, which serve as cations, produces dielectric polarization. The magnitude and direction of this 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 comprising a metal thin film as an epitaxial film on a Si substrate, and a PZT thin film on the metal thin film, wherein 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 states that this thin-film piezoelectric element can be used in thin-film oscillators, thin-film VCOs, thin-film filters, and liquid ejectors used in mobile communication devices, and can realize high-performance piezoelectric devices such as FBARs with extremely wide bandwidths (patent document 1, paragraphs

[0001] and

[0068] ).

[0006] Patent Document 2 discloses a method for manufacturing a single crystal wafer, characterized by comprising the following steps: preparing a polygonal substrate of a single crystal material; forming a polygonal columnar stack by laminating and bonding multiple polygonal substrates; forming a first orientation flat surface by processing the polygonal columnar stack into an arcuate cylindrical shape; and forming a second orientation flat surface on the arcuate surface of the stack (Claim 1 of Patent Document 2). Patent Document 2 also states that the single crystal wafer is a piezoelectric substrate, for example (Patent Document 2,

[0018] ).

[0007] Non-patent document 1 discloses the following: a lead zirconate titanate (PZT) thin film is synthesized on a silicon substrate using a sol-gel method, and the transverse piezoelectric constant (d 31 ), the measured piezoelectric constant (d 31 ) is 25 to 60 pC / N (Abstract on page 133, 6. Preliminary results on page 136 and Fig. 4 of non-patent document 1).

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-332569

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2013-115534

[0012] Non-patent literature

[0013] Non-patent document 1: JF Shepard Jr. et al., The wafer flexure technique for the determination of the transverse piezoelectric coefficient (d 31 ) of PZT thinfilms, Sensors and Actuators A71 (1998) 133-138. Summary of the Invention

[0014] Problems to be solved by the invention

[0015] As described above, although thin film piezoelectric devices have been proposed in the past, such devices still have room for improvement. Specifically, piezoelectric devices are required to have a large displacement when a voltage is applied. However, in conventional thin film piezoelectric devices, the piezoelectric material is polycrystalline and does not undergo crystal growth along the crystal orientation of the substrate. Therefore, the displacement does not vary according to the crystal orientation of the piezoelectric material, and there is a limit to how much the displacement can be increased. Conventional thin film piezoelectric devices are manufactured so that the components are arranged parallel or perpendicular to the orientation plane or notch of the substrate because the displacement does not vary according to the crystal orientation.

[0016] Although Patent Document 2 discloses a piezoelectric substrate composed of a single crystal wafer, the material actually disclosed is quartz (Patent Document 2,

[0021] ). Although quartz has excellent long-term stability, it is inferior to perovskite compounds in terms of charge output. In addition, Patent Document 2 does not integrate the piezoelectric material onto the semiconductor substrate, and the document does not aim at thin-film piezoelectric devices.

[0017] The present inventors conducted intensive research to address these conventional issues. As a result, they discovered that in thin-film piezoelectric devices, the piezoelectric properties have a greater dependence on plane orientation than in single-crystal piezoelectric films. This finding suggests that strict control of the plane orientation of the piezoelectric film can improve the piezoelectric properties. Specifically, they discovered that controlling the angle θ between the in-plane direction, where the displacement of the movable portion is maximized, and the <100> orientation of the piezoelectric film increases the displacement.

[0018] The present invention has been made based on such findings, and an object of the present invention is to provide a thin film piezoelectric device having excellent piezoelectric characteristics and a large displacement.

[0019] Solutions to Problems

[0020] The present invention includes the following aspects (1) to (12). It should be noted that in this specification, expressions such as "to" include both values. That is, "X to Y" is synonymous with "X or more and Y or less."

[0021] (1) A thin film piezoelectric device comprising a substrate and a movable portion supported by the substrate, wherein:

[0022] The movable portion includes at least a buffer film including 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.

[0023] The piezoelectric film is a (001) or (100) oriented film composed of single crystals of lead zirconate titanate (Pb(Zr, Ti)O3; PZT), barium titanate (BaTiO3; BT) or potassium sodium niobate ((K, Na)NbO3; KNN).

[0024] The piezoelectric film in the movable part and the d 31 The movable part is displaced by expanding and contracting in the in-plane direction in a mode-dependent manner.

[0025] An angle θ between an in-plane direction in which displacement of the movable portion is maximum and the <100> orientation of the piezoelectric film is within ±11.5°.

[0026] (2) In the thin film piezoelectric device of (1) above, the movable portion has an outer shape including two opposing and mutually parallel sides in a plan view, and a direction perpendicular to the two sides coincides with an in-plane direction in which displacement of the movable portion becomes maximum.

[0027] (3) In the thin film piezoelectric device of (2) above, the outer shape of the movable portion is rectangular, substantially rectangular, or trapezoidal.

[0028] (4) In the thin film piezoelectric device of any one of (1) to (3) above, one or both of the first electrode layer and the second electrode layer includes at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al) and copper (Cu).

[0029] (5) In the thin film piezoelectric device according to any one of (1) to (4) above, a first metal oxide film composed of strontium ruthenate (SrRuO 3 ; SRO) is further provided between the first electrode layer and the piezoelectric film.

[0030] (6) In the thin film piezoelectric device according to any one of (1) to (5) above, a second metal oxide film composed of strontium ruthenate (SrRuO 3 ; SRO) is further provided between the piezoelectric film and the second electrode layer.

[0031] (7) In the thin film piezoelectric device according to any one of (1) to (6) above, the substrate is a Si substrate or an SOI substrate.

[0032] (8) In the thin film piezoelectric device according to any one of (1) to (7) above, the piezoelectric film is composed of a single crystal of lead zirconate titanate (Pb(Zr, Ti)O3; PZT).

[0033] (9) In the thin film piezoelectric device according to any one of (1) to (8) above, the buffer film and the first electrode layer are formed of a single crystal.

[0034] (10) In the thin film piezoelectric device of (9) above, the buffer film, the first electrode layer, and the piezoelectric film have the same crystal orientation.

[0035] (11) In the thin film piezoelectric device of any one of (1) to (10) above, the thin film piezoelectric device has a double-support beam structure or a single-support beam structure, and the movable portion is provided on the beam portion of the double-support beam structure or the single-support beam structure.

[0036] (12) In the thin film piezoelectric device according to any one of (1) to (11) above, the thin film piezoelectric device is used for a sensor or an actuator.

[0037] Effects of the Invention

[0038] According to the present invention, a thin film piezoelectric device having excellent piezoelectric characteristics and a large displacement is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 An example of a schematic cross-sectional view of a thin film piezoelectric device is shown.

[0040] Figure 2 Another example of a schematic cross-sectional view of a thin film piezoelectric device is shown.

[0041] Figure 3 A top view of a thin film piezoelectric device is shown.

[0042] Figure 4 A top view of a thin film piezoelectric device is shown.

[0043] Figure 5 The relationship between the angle α and the displacement amount is shown (the width of the cavity is 70 μm).

[0044] Figure 6 The relationship between the angle α and the displacement amount is shown (the width of the cavity is 200 μm).

[0045] Figure 7 The relationship between the angle α and the resonance frequency Fa is shown (the width of the cavity is 70 μm).

[0046] Figure 8 The relationship between the angle α and the resonance frequency Fa is shown (the width of the cavity is 200 μm).

[0047] Figure 9 The relationship between the angle α and the displacement / resonance frequency Fa is shown (the width of the cavity is 70 μm).

[0048] Figure 10 The relationship between the angle α and the displacement / resonance frequency Fa is shown (the width of the cavity is 200 μm).

[0049] Figure 11AThe X-ray diffraction pattern of the piezoelectric film (PZT) is shown ( scanning).

[0050] Figure 11B The X-ray diffraction pattern of the piezoelectric film (PZT) is shown ( scanning). DETAILED DESCRIPTION

[0051] A specific embodiment of the present invention (hereinafter referred to as "this embodiment") will be described. However, the present invention is not limited to the following embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0052] <<1. Thin Film Piezoelectric Devices>>

[0053] The thin film piezoelectric device of this embodiment (hereinafter sometimes simply referred to as "device") comprises a substrate and a movable portion supported on the substrate. The movable portion comprises at least a buffer film comprising 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 portion and the d based on the piezoelectric effect 31 The movable portion is displaced by mode-dependent expansion and contraction in the in-plane direction. The angle θ between the in-plane direction where the movable portion is displaced to a maximum and the <100> orientation of the single crystal piezoelectric film is within ±11.5°.

[0054] use Figure 1 and Figure 2 The thin film piezoelectric device of this embodiment will be described. Figure 1An example of a cross-sectional schematic diagram of a device having a Si substrate is shown. The thin film piezoelectric device (100) comprises a Si substrate (2) and a movable portion (4) supported on the Si substrate (2). At least a portion of the Si substrate (2) is removed to form a hollow portion (22). The movable portion (4) is arranged on the hollow portion (22) and comprises a buffer film (6) arranged on the Si substrate (2), a first electrode layer (8) arranged on the buffer film (6), a first metal oxide film (10) arranged on the first electrode layer (8), a piezoelectric film (12) arranged on the first metal oxide film (10), a second metal oxide film (14) arranged on the piezoelectric film (12), a second electrode layer (16) arranged on the second metal oxide film (14), and an extraction electrode (18) arranged to be conductive with the second electrode layer (16). The first electrode layer (8) and the second electrode layer (16) are respectively composed of Pt films. The first metal oxide film (10) and the second metal oxide film (14) are respectively composed of SRO films. The piezoelectric film (12) is composed of a PZT film. The extraction electrode (18) is composed of a stack of a Ti layer (18-1) and an Au layer (18-2). In addition, a protective film (20) is provided 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).

[0055] Figure 2 An example of a cross-sectional schematic diagram of a device having an SOI substrate is shown. In this case, an SOI substrate (2) is used instead of a Si substrate. The SOI substrate (2) is composed of a Si substrate portion (2-1) and a surface Si layer (2-3), and an insulating film (2-2) such as a SiO2 film arranged therebetween. Otherwise, the thin film piezoelectric device (100) is the same as the case where a Si substrate is used. The device comprises an SOI substrate (2) and a movable portion (4) supported on the SOI substrate (2). At least a portion of the SOI substrate is removed to form a hollow portion (22). The movable portion (4) is arranged on the hollow portion (22) and comprises 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).

[0056] <Substrate>

[0057] The substrate functions as the base of the thin film piezoelectric device and has the effect of supporting the movable part. The material of the substrate is not particularly limited. Known substrates used in thin film piezoelectric devices can be used. For example, a silicon (Si) substrate, an SOI (Silicon on Insulator) substrate, a substrate composed of semiconductor crystals other than Si, a substrate composed 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. The SOI substrate is a substrate with a structure in which an insulating film (SiO2 film, etc.) is inserted in the gap 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 or an 8-inch substrate can be used.

[0058] The substrate is preferably a Si substrate or an SOI substrate, and is particularly preferably a Si(100) substrate or an SOI(100) substrate. Here, the (100) substrate refers to a substrate with the (100) plane of the lattice facing the main surface. By using a Si(100) substrate or an SOI(100) substrate, the buffer film, the first electrode layer and the piezoelectric film are epitaxially grown on it while fully achieving lattice matching, as a result, a single-crystallized buffer film, the first electrode layer and the piezoelectric film can be obtained. However, it is also possible to separate the substrate after forming the single-crystal piezoelectric film and to join other substrates. Therefore, the substrate of the thin film piezoelectric device of this embodiment is not limited to a Si(100) substrate or an SOI(100) substrate. It can also be other substrates such as a (110) substrate and a (111) substrate.

[0059] The substrate may be included in the movable part or may not be included in the movable part. Figure 1 In the device, 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 having an SOI substrate Figure 2 In the device, 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).

[0060] <Buffer film>

[0061] The device of this embodiment has a buffer film containing zirconium oxide (ZrO2). The buffer film is arranged on a substrate. In addition, the buffer film constitutes a movable part. By using a buffer film containing ZrO2, the single crystallization of the piezoelectric film arranged thereon can be promoted. That is, ZrO2 has a monoclinic, tetragonal or cubic crystal structure. The ZrO2 buffer film with such a crystal structure is crystal-grown on the substrate, thereby forming a nano-pyramid structure on its surface. When the first electrode layer and the piezoelectric film are formed on the ZrO2 buffer film with the nano-pyramid structure, the nano-pyramid structure itself is deformed to correct the lattice dislocation between the substrate and the film. Therefore, a single crystal film with less residual stress can be obtained.

[0062] The buffer film may consist solely of ZrO2, or may also contain rare earth elements or alkaline earth elements. Furthermore, ZrO2 may contain oxygen vacancies. Furthermore, to improve properties, transition metal elements such as aluminum (Al), scandium (Sc), manganese (Mn), iron (Fe), cobalt (Co), and / or nickel (Ni) may also be included.

[0063] 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 the substrate, and even more preferably a (100)-oriented epitaxial film.

[0064] <First electrode layer>

[0065] The first electrode layer and the second electrode layer together form a pair of electrodes that sandwich the piezoelectric film. The electrode layers can detect a potential difference based on the surface charge of the piezoelectric film generated by the direct piezoelectric effect. Alternatively, a potential difference can be applied to the piezoelectric film through the electrode layers, thereby generating deformation caused by the inverse piezoelectric effect. The material of the first electrode layer is not limited as long as it is conductive. For example, it includes at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu).

[0066] 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. Furthermore, the first electrode layer is preferably an epitaxial film formed on the buffer film, and even more preferably a (100)-oriented epitaxial film.

[0067] <First Metal Oxide Film>

[0068] The thin-film piezoelectric device of this embodiment may also have a first metal oxide film between the first electrode layer and the piezoelectric film. The first metal oxide film is preferably composed of strontium ruthenate (SrRuO3; SRO). SRO has conductivity. Therefore, the SRO film (first metal oxide film) can be used as a part of the electrode layer (first electrode layer). In addition, SRO has the same perovskite crystal structure as PZT, BT or KNN that constitutes the piezoelectric film, and the lattice constant is similar. Therefore, by providing an SRO film between the first electrode layer and the piezoelectric film, the crystallinity of the piezoelectric film formed thereon can be further improved. In particular, piezoelectric films with a film thickness as small as submicron size are prone to crystal defects. By providing the first metal oxide film, a piezoelectric film with few crystal defects can be formed even if the film thickness is submicron size. However, the first metal oxide film is not an essential component. When the thickness of the piezoelectric film is large enough, a piezoelectric film with few crystal defects can be obtained even without the first metal oxide film.

[0069] The thickness of the first metal oxide film (SRO film) is preferably from 1 nm to 100 nm, more preferably from 3 nm to 80 nm, and even more preferably from 5 nm to 60 nm. Furthermore, the first metal oxide film is preferably an epitaxial film formed on the first electrode layer, and even more preferably an epitaxial film having a (100) orientation.

[0070] Piezoelectric film

[0071] The piezoelectric film is the main component that manifests the piezoelectric effect and has the function of converting electrical energy into mechanical energy. Specifically, 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. In addition, 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.

[0072] The piezoelectric film of this embodiment is characterized in that it is composed of a single crystal. That is, the piezoelectric film is crystal-continuous in both the cross-section and the upper surface, and has a crystal structure in which hexahedrons overlap without rotating, 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 multiple grains randomly oriented in the thickness direction and the surface direction, or piezoelectric films that are crystal-continuous in the thickness direction but randomly oriented in the surface direction. Although epitaxial films oriented in the thickness direction and the surface direction have also been proposed, the crystals are discontinuous and are composed of polycrystals.

[0073] The piezoelectric film of this embodiment, constructed from a single crystal, enables completely consistent polarization across the entire film. This improves both electrical and mechanical properties. Specifically, it improves the piezoelectric constant. Furthermore, compared to polycrystalline films, the dielectric constant is suppressed, resulting in reduced power consumption. Furthermore, when used as a sensor, it offers the advantage of achieving high-precision output. Furthermore, single crystallization enhances the bonding strength between atoms, improving the temperature characteristics and reliability of the piezoelectric film.

[0074] Whether the piezoelectric film is single crystal can be determined by X-ray diffraction. Scanning measurement to confirm. That is, if the If a quadratically symmetrical peak is confirmed during scanning, it can be determined that the piezoelectric film is a single crystal.

[0075] 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 compounds represented by the general formula: ABO3. Perovskite compounds have a crystal structure such as body-centered cubic, and most of them are dielectric / piezoelectric materials that show dielectric / piezoelectric properties. In particular, PZT shows excellent piezoelectric properties and is mostly used as a sensor and actuator material. Therefore, it is preferred that the piezoelectric film is composed of a single crystal of lead zirconate titanate (Pb(Zr, Ti)O3; PZT).

[0076] PZT has a rhombohedral crystal structure when it is rich in Zr, and a tetragonal crystal structure when it is rich in Ti. In addition, in the intermediate composition region, it becomes a morphotropic phase boundary (MPB) composition where rhombohedral and tetragonal crystal structures coexist. At this time, the piezoelectric properties are significantly improved. 1-x Ti x )O3 (wherein 0<x<1), from the viewpoint of obtaining excellent piezoelectric properties, x is preferably greater than or equal to 0.2 and less than or equal to 0.8, more preferably greater than or equal to 0.3 and less than or equal to 0.7, and further preferably greater than or equal to 0.4 and less than or equal to 0.6.

[0077] The piezoelectric film of this embodiment is a (001) or (100) oriented film. A piezoelectric film having a body-centered cubic crystal structure is easily (001) or (100) oriented by epitaxial growth. For example, a PZT film having a tetragonal crystal structure is easily (001) oriented during epitaxial growth. Moreover, when a PZT film having 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, and therefore, the piezoelectric characteristics are improved. That is, in a PZT film having a tetragonal crystal structure, when an electric field along the

[001] direction is applied, a larger piezoelectric constant is obtained.

[0078] In this embodiment, whether the piezoelectric film is a (001) or (100) oriented film can be determined by performing a θ-2θ scan on the piezoelectric film using an X-ray diffraction method. Specifically, when the θ-2θ scan is performed on the piezoelectric film, if the ratio of the diffraction peak intensity from a surface other than the target surface (the (001) surface and the (100) surface) to the diffraction peak intensity from the target surface (the (001) surface and the (100) surface) (peak intensity ratio) is 10% or less, the film can be determined to be a (001) or (100) oriented film. A smaller peak intensity ratio is preferred, and more preferably 5% or less.

[0079] The thickness of the piezoelectric film is preferably 0.1 μm to 10 μm. If the piezoelectric film is too thin, the piezoelectric effect may not be fully exerted, and the resulting displacement may be reduced. On the other hand, if the piezoelectric film is too thick, it may be difficult to obtain a fully single-crystalline piezoelectric film. The thickness is more preferably 0.3 μm to 6 μm, and even more preferably 0.5 μm to 4 μm.

[0080] <Second Metal Oxide Film>

[0081] The thin-film piezoelectric device of this embodiment may also 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 is conductive. Therefore, the SRO film (second metal oxide film) can be used as part of the electrode layer (second electrode layer).

[0082] The thickness of the second metal oxide film (SRO film) is preferably from 1 nm to 60 nm, more preferably from 3 nm to 30 nm, and even more preferably from 5 nm to 20 nm. Furthermore, 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.

[0083] <Second electrode layer>

[0084] The second electrode layer, together with the first electrode layer, forms 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, it may include at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu).

[0085] 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. Furthermore, the second electrode layer is preferably an epitaxial film formed on the piezoelectric film, and even more preferably a (100)-oriented epitaxial film.

[0086] <Removing the Electrode>

[0087] An extraction electrode may also be provided on the second electrode layer. A known conductive material may be used as the extraction electrode. For example, a stack of a gold (Au) layer and a titanium (Ti) layer is provided. The Au layer primarily functions as a conductive layer, while the Ti layer primarily functions as an adhesion layer.

[0088] <Protective film>

[0089] 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 tetraethyl orthosilicate (TEOS) or the like can be used.

[0090] <Movable Part>

[0091] The movable portion is supported by a substrate and comprises at least a buffer film, a first electrode layer, a piezoelectric film, and a second electrode layer. Furthermore, a metal oxide film (a first metal oxide film and a second metal oxide film) may be further provided between the first electrode layer and the piezoelectric film and / or on the second electrode layer.

[0092] In the thin film piezoelectric device of this embodiment, the piezoelectric film in the movable part and the d 31 The mode is linked to the expansion and contraction in the in-plane direction, thereby displacing the movable part. 33 mode), piezoelectric transverse effect (d 31 mode), piezoelectric slip effect caused by shear deformation (d 15 mode). In thin film piezoelectric devices, the use of d 31 When the device structure of the mode is used, it is advantageous in the device process and can increase the displacement.

[0093] In the thin film piezoelectric device of this embodiment, electrodes (first electrode layer and second electrode layer) are provided above and below 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 toward the piezoelectric film. 31 The reverse piezoelectric effect of the mode generates displacement in the direction perpendicular to the electric field, that is, in the direction parallel to the membrane surface. Alternatively, when stress parallel to the membrane surface is applied to the movable part, surface charge is generated on the electrode layer due to the direct piezoelectric effect. 31 The mode can utilize the displacement of the piezoelectric film in the direction of the film surface and the displacement of the movable part caused by this displacement. The movable part is composed of a stack of piezoelectric film and other components (such as buffer film). Even if the piezoelectric film expands and contracts (displaces) in the plane, the other components do not expand and contract. Therefore, warping occurs in the movable part according to the displacement of the piezoelectric film. Moreover, the greater the displacement of the piezoelectric film, the greater the warping of the movable part.

[0094] In the thin film piezoelectric device of this embodiment, the angle θ between the in-plane direction in which the displacement of the movable portion is maximized and the <100> orientation of the piezoelectric film is within ±11.5°. Here, the in-plane direction in which the displacement of the movable portion is maximized refers to the direction in which the amount of expansion (warping) is maximized within a plane parallel to the film surface of the piezoelectric film. Furthermore, the <100> orientation includes all orientations equivalent to the

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

[0095] The piezoelectric film of this embodiment has a single crystal structure. Therefore, the piezoelectric displacement is highly dependent on the plane orientation. The inventors have found that the smaller the angle θ is, that is, the more consistent the <100> orientation of the piezoelectric film is with the in-plane direction where the displacement of the movable part is the largest, the greater the displacement of the piezoelectric film. For example, when a single crystal PZT film is used as the piezoelectric film, the d 31 The piezoelectric constant increases to about 100 pm / V or more. In contrast, the previous piezoelectric film is not a single crystal. Therefore, the surface orientation dependence of the piezoelectric characteristics is not shown, and the piezoelectric displacement is small. For example, 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 dependence is not shown, the relationship between plane orientation and piezoelectric properties has not been previously considered. In this embodiment, since the piezoelectric film is a single crystal, the plane orientation dependence is large, and the piezoelectric properties are significantly improved by controlling the plane orientation.

[0096] Preferably, if Figure 1 and 2As shown, 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 constraint of the movable portion from the substrate is small, and therefore the warping amount of the movable portion increases.

[0097] In the thin film piezoelectric device of the present embodiment, it is preferred that the movable portion has an outer shape including two sides that are opposite and parallel to each other when viewed from above, and the direction perpendicular to the two sides is consistent with the in-plane direction in which the displacement of the movable portion becomes the largest. In addition, the outer shape of the movable portion is preferably rectangular, roughly rectangular or trapezoidal. In this way, by giving the movable portion an outer shape including two sides that are opposite and parallel, the direction perpendicular to the two sides can be made into the maximum expansion and contraction direction. In the case where the outer shape of the movable portion is rectangular, the dimension in the width (short side) direction is preferably greater than 30 μm and less than 500 μm, more preferably greater than 50 μm and less than 300 μm. The dimension in the length (long side) direction is preferably greater than 100 μm and less than 1000 μm, more preferably greater than 250 μm and less than 600 μm. In addition, it is preferred that the direction perpendicular to the width direction is consistent with the in-plane direction in which the displacement of the movable portion becomes the largest.

[0098] In the thin-film piezoelectric device of this embodiment, the buffer film and the first electrode layer are preferably composed of single crystal. Furthermore, the crystal orientations of the buffer film, the first electrode layer, and the piezoelectric film are preferably aligned. By making the buffer film and the first electrode layer of single crystal and aligning their crystal orientations, the piezoelectric film formed on the first electrode layer can achieve improved crystallinity.

[0099] The thin film piezoelectric device of this embodiment preferably has a double-support beam structure or a single-support beam structure, and a movable part is provided on the beam portion of the double-support beam structure or the single-support beam structure. In a device having a single-support beam structure, only one end of the movable part is fixed, and the other end becomes a free end. Therefore, the free end of the movable part is displaced in the up-down direction in accordance with the warping of the movable part. The single-support beam structure is also called a cantilever structure. In contrast, in a device having a double-support beam structure, both ends of the movable part are fixed. Therefore, the movable part bends in accordance with the warping, and its central portion is displaced in the up-down direction. The double-support beam structure can also be called a diaphragm structure.

[0100] The thin film piezoelectric device of this embodiment is preferably used for the purpose of a sensor or an actuator. The thin film piezoelectric device of this embodiment has the characteristic that the displacement of the movable part is large. Therefore, a sensor or actuator with good characteristics can be produced. As sensors, acceleration sensors, gyroscope sensors, pressure sensors, ultrasonic sensors, flow sensors, vibration power generation elements, odor sensors, and / or microphones are cited. As actuators, speakers, inkjet printer heads, autofocus devices, mirrors, optical switches, and / or micro pumps are cited. In addition, the thin film piezoelectric device of this embodiment can also be applied to high-frequency circuit components such as RF filters and piezoelectric thin film resonators (FBARs).

[0101] <<2. Method for Manufacturing Thin Film Piezoelectric Device>>

[0102] The thin film piezoelectric device of this embodiment is not limited in its manufacturing method as long as it meets the above requirements. However, the preferred manufacturing method has the following steps: preparing a substrate (substrate preparation step); forming a buffer film containing zirconium oxide (ZrO2) on the substrate (buffer film forming step); forming a first electrode layer on the buffer film (first electrode layer forming step); forming a piezoelectric film on the first electrode layer (piezoelectric film forming step); and forming a second electrode layer on the piezoelectric film (second electrode layer forming step). In addition, a step of forming a first metal oxide film between the first electrode layer and the piezoelectric film (first metal oxide film forming step) can also 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) can also be provided. A step of forming a take-out electrode on the second electrode layer and the second metal oxide film can also be provided (take-out electrode forming step). A step of forming a protective film on the second electrode layer, the second metal oxide film and / or the take-out electrode can also be provided (protective film forming step). Furthermore, a step of removing at least a portion of the substrate in the movable portion to form a hollow portion immediately below the movable portion (hollow portion forming step) may be provided.

[0103] <Substrate preparation process>

[0104] In the substrate preparation step, a substrate is prepared. The details of the substrate are as described above. That is, as a substrate, a silicon (Si) substrate, an SOI (Silicon on Insulator) substrate, a substrate composed of a semiconductor crystal other than Si, a substrate composed of various oxide single crystals such as sapphire or garnet, a glass substrate with a polysilicon film formed on the surface, etc. can be used. In addition, the size of the substrate is not limited, and a 4-inch substrate, a 6-inch substrate, or an 8-inch substrate 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.

[0105] <Buffer film forming process>

[0106] In the buffer film forming process, a buffer film containing zirconium oxide (ZrO2) is formed on a substrate. The film formation can be performed by methods such as electron beam evaporation and sputtering. In the case of performing film formation by electron beam evaporation, a substrate is set in a vacuum chamber of an evaporation device, for example. Then, under a high vacuum atmosphere in which the pressure in the vacuum chamber is set to a constant, the zirconium oxide (ZrO2) film is formed while heating the substrate while flowing oxygen (O2) gas. By performing film formation under such conditions, a buffer film composed of a (100) oriented epitaxial film can be reliably obtained. In addition, photolithography technology can also be used to perform patterning processing to partially remove the buffer film after film formation.

[0107] <First Electrode Layer Film Formation Step>

[0108] In the first electrode layer film forming process, the first electrode layer is formed on the buffer film. The first electrode layer, for example, includes at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al) and copper (Cu). The first electrode layer can be formed by a method such as sputtering. In the case of sputtering film formation, for example, while heating the substrate, the epitaxially grown first electrode layer can be formed on the buffer film as part of the lower electrode by sputtering. In addition, photolithography technology can also be used to perform patterning processing to partially remove the first electrode layer after film formation.

[0109] <First Metal Oxide Film Forming Step>

[0110] Alternatively, 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. In the case of sputtering, for example, while heating the substrate, the epitaxially grown first metal oxide film may be formed on the first electrode layer as part of the lower electrode by sputtering. Alternatively, photolithography may be used to perform patterning to partially remove the formed first metal oxide film.

[0111] <Piezoelectric film formation process>

[0112] In the piezoelectric film forming process, the 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 a sol-gel method. For example, by a known sputtering method, a layer containing epitaxially grown lead zirconate titanate (Pb(Zr) 1-x Ti x)O3(0<x<1):PZT) piezoelectric film can be formed on the first electrode layer. Alternatively, a piezoelectric film containing epitaxially grown lead zirconate titanate (Pb(Zr 1-x Ti x A piezoelectric film of )O3(0<x<1):PZT can be formed on the first electrode layer. The film formation method is not limited as long as a (001) or (100) oriented single crystal film can be obtained. Alternatively, patterning can be performed using photolithography to partially remove the formed piezoelectric film.

[0113] <Second Metal Oxide Film Formation Step>

[0114] Alternatively, 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. In the case of 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. Alternatively, patterning may be performed using photolithography to partially remove the formed second metal oxide film.

[0115] <Second Electrode Layer Film Formation Step>

[0116] In the second electrode layer formation step, the second electrode layer is formed on the piezoelectric film or the second metal oxide film. The second electrode layer, for example, includes at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu). The second electrode layer can be formed by a method such as sputtering. For example, a second electrode layer comprising epitaxially grown Pt can be formed on the piezoelectric film or the second metal oxide film as part of the lower electrode by sputtering. Alternatively, photolithography technology can be used to perform patterning to partially remove the formed second electrode layer.

[0117] <Removal of electrode film forming process>

[0118] Alternatively, the extraction electrode may be formed on the second electrode layer. The extraction electrode may be formed by sputtering or other methods. Alternatively, photolithography may be used to perform patterning to partially remove the formed extraction electrode layer.

[0119] <Protective film formation process>

[0120] A protective film may also be formed on the second electrode layer or the extraction electrode. The protective film is not limited, but tetraethyl orthosilicate (TEOS) and the like can be used. The protective film can be formed by a method such as sputtering. Alternatively, photolithography techniques can be used to perform patterning to partially remove the formed protective film.

[0121] <Hollow portion forming process>

[0122] When manufacturing a thin-film piezoelectric device, a step may be included 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 for the formation of a movable portion having a cantilever or diaphragm structure and a large displacement. The hollow portion is preferably formed after the buffer film, first electrode layer, piezoelectric layer, and second electrode layer are formed on the substrate.

[0123] The hollow portion can be formed by combining photolithography technology and etching technology. Specifically, a mask having an opening is placed in close contact with the back of the substrate. Then, an alkaline etching solution is used to etch and remove the substrate from the mask opening. For example, a Si substrate or an SOI substrate is anisotropically etched by an alkaline etching solution to form a square pyramid-shaped hollow portion. When a 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 can be produced that does not have a substrate directly below the movable portion. For an SOI substrate, the insulating film (SiO2 film) contained therein functions as an etching stop layer. In addition, the insulating film can be removed using an etching solution such as hydrofluoric acid. Therefore, a thin film piezoelectric device can be produced that has a surface Si layer or a surface Si layer and an insulating film (SiO2 film) directly below the movable portion.

[0124] [Example]

[0125] The present invention will be described in more detail using the following examples, but the present invention is not limited to the following examples.

[0126] (1) Fabrication of thin film piezoelectric devices

[0127] [Example 1]

[0128] 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 an extraction electrode (Ti layer, Au layer) are sequentially formed on an SOI substrate, and then the back side of the SOI substrate is etched away to form a cavity (hollow portion). Thus, a silicon substrate is produced. Figure 2 The thin film piezoelectric device with a movable portion is shown.

[0129] First, a 6-inch diameter SOI substrate wafer was prepared. This SOI substrate has a three-layer structure consisting of a Si substrate portion, an insulating film (SiO2 film), and a surface Si layer. The top surface, serving as the primary surface, is a (100) plane. That is, the surface Si layer is (100) oriented.

[0130] Next, a zirconium oxide (ZrO2) film was deposited as a buffer film on the surface Si layer of the prepared SOI substrate using electron beam evaporation. The resulting buffer film had a (100)-oriented cubic crystal structure and a thickness of 60 nm. The film formation was performed under the following conditions.

[0131] -Equipment: Electron beam evaporation device

[0132] -Pressure: 7.00×10 -3 Pa

[0133] -Evaporation source: ZrO2

[0134] -Accelerating voltage / emission current: 7.5kV / 1.80mA

[0135] -Thickness: 60nm

[0136] -Film forming speed: 0.005nm / s

[0137] -Oxygen flow rate: 10 sccm

[0138] -Substrate temperature: 500~600℃

[0139] Next, a Pt film, serving as the first electrode layer, was sputtered onto the buffer film (ZrO2 film). The resulting Pt film (first electrode layer) had a (100)-oriented cubic crystal structure and a thickness of 150 nm. The film formation was performed under the following conditions.

[0140] -Device: DC sputtering device

[0141] -Pressure: 3.20×10 -2 Pa

[0142] -Evaporation source: Pt

[0143] -Power: 100W

[0144] -Thickness: 150nm

[0145] -Film forming speed: 0.14nm / s

[0146] -Ar flow rate: 16 sccm

[0147] -Substrate temperature: 400°C

[0148] Next, an SRO film was sputtered onto the first electrode layer (Pt film) as a first metal oxide film. The formed first metal oxide film had a (100)-oriented cubic crystal structure and a thickness of 40 nm. The film formation was performed under the following conditions.

[0149] -Device: RF magnetron sputtering device

[0150] -Power: 300W

[0151] -Gas: Ar

[0152] -Pressure: 1.8Pa

[0153] -Substrate temperature: 600°C

[0154] -Film forming speed: 0.11nm / s

[0155] -Thickness: 40nm

[0156] A PZT film as a piezoelectric film is formed on the formed first metal oxide film. The film is formed by the Sol-Gel method. Specifically, first, the organic metal compound of Pb, Zr and Ti is dissolved in a mixed solvent of ethanol and 2-n-butoxyethanol to adjust the raw material solution. At this time, the organic metal compound of Pb, Zr and Ti is mixed in such a way that the composition ratio (mol ratio) becomes Pb:Zr:Ti=100+δ:52:48. In addition, as Pb(Zr 0.52 Ti 0.48 The raw material solution was adjusted to a concentration of 0.35 mol / l of )O3. Here, δ represents the excess Pb content, set to account for the volatilization of Pb oxide during the subsequent heat treatment process. In this embodiment, δ = 20. Furthermore, 20 g of polypyrrolidone with a K value of 27 to 33 was dissolved in the raw material solution.

[0157] Next, after dripping 3 ml of the modulated raw material solution onto the first metal oxide film (SRO film) of the substrate, the substrate was rotated at 3000 rpm for 10 seconds, and the raw material solution was applied to the substrate. Thus, 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 then placed on a hot plate at a temperature of 450°C for 30 seconds to dry the film. Afterwards, the film was heat-treated 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 process from applying the raw material solution to crystallization was repeated any number of times until the desired film thickness was achieved, thereby forming a piezoelectric film (PZT).

[0158] The piezoelectric film (PZT film) after film formation has a (001) orientation and a film thickness of 2 μm. In addition, the composition of the piezoelectric film is Pb(Zr 0.52 Ti 0.48 )O3.

[0159] An SRO film, serving as the second metal oxide film, was deposited on the formed piezoelectric film. Furthermore, a Pt film, serving as the second electrode layer, was deposited on top of this film. The SRO and Pt films were deposited 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.

[0160] 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 using plasma CVD, and the TEOS film was partially etched away using photolithography.

[0161] Furthermore, in order to ensure conductivity to the second electrode layer (Pt film) and the second metal oxide film (SRO film) serving as the upper electrode, a Ti layer with a thickness of 10 nm and an Au layer with a thickness of 300 nm were formed by DC sputtering, and then partially etched away using photolithography technology to form a take-out electrode.

[0162] Finally, anisotropic etching was performed on the backside of the substrate (SOI substrate) to create a cavity (hollow portion). Specifically, the Si substrate and a portion of the insulating film (SiO2 film) were removed from the backside of the substrate, creating an opening on the backside of the substrate. This produced a movable portion with a rectangular cavity (hollow portion). The planar dimensions of the movable portion were 70 μm wide by 275 μm long.

[0163] In 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 portion and the <100> orientation of the piezoelectric film was a predetermined angle. Specifically, the movable portion 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.

[0164] Figure 3 and Figure 4 A top view (photograph) of the obtained thin film piezoelectric device is shown. Figure 3 Shows all devices made according to angle θ, Figure 4 A device is shown. Figure 4 The movable part can be seen in the center, and the line segment AA' that crosses the movable part is the width direction (short side direction) of the movable part.

[0165] [Example 2]

[0166] A piezoelectric film (PZT film) was formed by sputtering. A sample was prepared in the same manner as in Example 1 except for this. The piezoelectric film was formed under the following conditions.

[0167] -Device: RF magnetron sputtering device

[0168] -Power: 2000W

[0169] -Gas: Ar+O2

[0170] -Pressure: 1.8Pa

[0171] -Substrate temperature: 600°C

[0172] -Film forming speed: 0.3nm / s

[0173] -Thickness: 2μm

[0174] [Example 3]

[0175] Instead of SOI substrate, Si(100) substrate was used. And the thickness of buffer film (ZrO2 film) was set to 1.0μm. Except for this, the sample was prepared in the same manner as in Example 1. Figure 1 The thin film piezoelectric device with a movable portion is shown.

[0176] [Example 4]

[0177] A sample was prepared in the same manner as in Example 3 except that the thickness of the buffer film (ZrO2 film) was changed to 0.8 μm.

[0178] [Example 5]

[0179] A sample was prepared in the same manner as in Example 3 except that the thickness of the buffer film (ZrO2 film) was changed to 1.2 μm.

[0180] [Example 6]

[0181] When forming the cavity, the planar dimensions of the movable portion were changed to 200 μm × 500 μm. Furthermore, the movable portion was designed so that the angle θ between the width of the movable portion 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 various angles θ were fabricated in the same manner as in Example 1.

[0182] [Example 7]

[0183] The piezoelectric film (PZT film) was formed by sputtering. Specifically, the piezoelectric film was formed under the same conditions as in Example 2. A sample was prepared in the same manner as in Example 6 except for these conditions.

[0184] [Example 8]

[0185] A Si(100) substrate was used instead of the SOI substrate. The thickness of the buffer film (ZrO2 film) was set to 1.0 μm. A sample was prepared in the same manner as in Example 6 except for these steps.

[0186] [Example 9]

[0187] A sample was prepared in the same manner as in Example 8 except that the thickness of the buffer film (ZrO2 film) was changed to 0.8 μm.

[0188] [Example 10]

[0189] A sample was prepared in the same manner as in Example 8 except that the thickness of the buffer film (ZrO2 film) was changed to 1.2 μm.

[0190] The structures of the thin film piezoelectric devices of Examples 1 to 10 are summarized in Table 1 below.

[0191] [Table 1]

[0192] Table 1 Structure of thin film piezoelectric devices

[0193]

[0194] (2) Evaluation of thin film piezoelectric devices

[0195] Various characteristics of the thin film piezoelectric devices produced in Examples 1 to 10 were evaluated in the following manner.

[0196] <Crystallinity>

[0197] The crystallinity of the piezoelectric film (PZT film) was evaluated. That is, the device was taken out before the second metal oxide film was formed, and the piezoelectric film was evaluated using a fully automatic multi-purpose horizontal X-ray diffraction device (Smart Lab, Rigaku Corporation). Specifically, the 2θ-θ crystallization peak of PZT (004) was analyzed. 360° scanning measurement of direction.

[0198] Resonance frequency

[0199] The resonant 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 lower electrode (first electrode layer) of the thin-film piezoelectric device to establish electrical continuity. A voltage of 15 V was then applied, and the frequency at which the impedance (Z) and the phase shift (θ) changed was measured.

[0200] <Displacement>

[0201] The displacement of 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 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 Sin wave (sine wave), 1kHz, Vpp20V and Offset10V. Then, a laser Doppler vibrometer (Polytech, VFX-Compact) was used to measure the displacement of the movable part of the thin film piezoelectric device, and the obtained output value was taken into the oscilloscope.

[0202] (3) Evaluation results

[0203] <Crystallinity of Piezoelectric Film>

[0204] X-ray diffraction analysis using θ-2θ scanning revealed that the diffraction peak intensity for planes other than the (100) plane in the piezoelectric films (PZT films) of Examples 1 to 10 relative to the peak intensity for the (100) plane was 0.09%. Therefore, these piezoelectric films were found to be (100) oriented.

[0205] In addition, through the in-plane The scan confirmed four symmetrical peaks. Therefore, it was confirmed that it was a triaxially oriented single crystal film. Figure 11A and Figure 11B The X-ray diffraction pattern of the piezoelectric film (PZT film) of Example 1 is shown ( Scan). Here, Figure 11A is a graph showing the X-ray diffraction intensity in real numbers on the vertical axis. Figure 11B The graph is displayed in logarithmic form.

[0206] Tables 2 and 3 and Figure 5 and Figure 6 The displacement of the movable part of the thin film piezoelectric device of Examples 1 to 10 is shown. It should be noted that the angle α shown in the table and the figure is the angle between the long side direction of the movable part of the device and the direction of the substrate orientation plane

[110] (unit: °). On the other hand, θ is the angle between the in-plane direction in which the displacement of the movable part becomes the largest and the <100> orientation of the piezoelectric film. In this embodiment, the piezoelectric film is (100) oriented. In addition, the crystal orientation of the piezoelectric film is consistent with the crystal orientation of the substrate. Therefore, θ and α have a relationship of θ = α-45°.

[0207] As shown in Tables 2 and 3, Figure 5 and Figure 6As shown in FIG. 1 , in the region where α is 0 to 45°, the larger the angle α, the greater the displacement. In the region where α is 45 to 90°, the larger the angle α, the smaller the displacement. In other words, the displacement is maximum near angle α of 45° (angle θ of 0°).

[0208] Tables 4 and 5 and Figure 7 and Figure 8 The resonant frequency Fa of the piezoelectric film is shown in Table 6 and Table 7. Figure 9 and Figure 10 The displacement / resonance frequency Fa is shown. The resonant frequency Fa shows an inverse trend to the displacement. Specifically, in the range of α from 0 to 45°, Fa decreases as the angle α increases. In the range of α from 45 to 90°, Fa increases as the angle α increases. Specifically, Fa reaches its minimum near angle α of 45° (angle θ of 0°).

[0209] From the above results, it is understood that by limiting the angle θ between the in-plane direction where the displacement of the movable portion is maximum and the <100> orientation of the piezoelectric film to a predetermined range, a thin film piezoelectric device having excellent piezoelectric characteristics and a large displacement can be obtained.

[0210] [Table 2]

[0211] Table 2 Displacement of thin film piezoelectric devices

[0212]

[0213] [Table 3]

[0214] Table 3 Displacement of thin film piezoelectric devices

[0215]

[0216] [Table 4]

[0217] Table 4 Resonant frequency Fa of thin film piezoelectric devices

[0218]

[0219] [Table 5]

[0220] Table 5 Resonant frequency Fa of thin film piezoelectric devices

[0221]

[0222] [Table 6]

[0223] Table 6 Displacement / resonance frequency Fa of thin film piezoelectric devices

[0224]

[0225] [Table 7]

[0226] Table 7 Displacement / resonance frequency Fa of thin film piezoelectric devices

[0227]

[0228] Description of Reference Numerals

[0229] 2 substrates

[0230] 2-1Si substrate part

[0231] 2-2 Insulation film

[0232] 2-3 Surface Si layer

[0233] 4 movable parts

[0234] 6 buffer film

[0235] 8First electrode layer

[0236] 10First metal oxide film

[0237] 12 piezoelectric film

[0238] 14 Second metal oxide film

[0239] 16 second electrode layer

[0240] 18. Remove the electrodes

[0241] 18-1Ti layer

[0242] 18-2Au layer

[0243] 20 protective film

[0244] 22 Hollow part

Claims

1. A thin film piezoelectric device comprising a substrate and a movable portion supported by the substrate, wherein: The movable portion 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 single crystals 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 and the d 31 The movable part is displaced by expanding and contracting in the in-plane direction in a mode-dependent manner. An angle θ between an in-plane direction in which displacement of the movable portion is maximum and the <100> orientation of the piezoelectric film is within ±11.5°.

2. The thin film piezoelectric device according to claim 1, wherein The movable portion has an outer shape including two sides that are opposed to each other and parallel to each other in a plan view, and a direction perpendicular to the two sides coincides with an in-plane direction in which 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, substantially 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 includes at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu).

5. The thin film piezoelectric device according to claim 1 or 2, wherein: A first metal oxide film made of strontium ruthenate (SrRuO 3 ; SRO) is further provided between the first electrode layer and the piezoelectric film.

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

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 thin film piezoelectric device according to claim 1 or 2, wherein: The piezoelectric film is composed of a single crystal of lead zirconate titanate (Pb(Zr, Ti)O3; PZT).

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

10. The thin film piezoelectric device according to claim 9, wherein The buffer film, the first electrode layer, and the piezoelectric film have consistent crystal orientations.

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

12. The thin film piezoelectric device according to claim 1 or 2, wherein: The thin film piezoelectric device is used for a sensor or an actuator.

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