Piezoelectric element and actuator

Abstract

To provide a piezoelectric element and a piezoelectric actuator at low cost, which are capable of obtaining large driving force, have good responsiveness, and have long-term reliability.SOLUTION: In a piezoelectric element and an actuator, the piezoelectric element includes a first electrode, a first piezoelectric film, a second electrode, a second piezoelectric film, and a third electrode in this order on a substrate, the first piezoelectric film and the second piezoelectric film each have a perovskite-type oxide as a main component, one of the first piezoelectric film and the second piezoelectric film is an epitaxial film and the other is a uniaxially oriented film.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to piezoelectric elements and actuators. [Background technology]

[0002] Perovskite oxides such as lead zirconate titanate (Pb(Zr,Ti)O3, hereafter referred to as PZT) are known as materials with excellent piezoelectric and ferroelectric properties. Piezoelectrics made of perovskite oxides are used as piezoelectric films in piezoelectric elements that have a lower electrode, a piezoelectric film, and an upper electrode on a substrate. These piezoelectric elements are being deployed in a variety of devices, including memories, inkjet heads (actuators), micromirror devices, angular velocity sensors, gyro sensors, ultrasonic elements (PMUT: Piezoelectric Micromachined Ultrasonic Transducers), and vibration power generation devices.

[0003] As a piezoelectric element, a laminated type piezoelectric element in which a plurality of piezoelectric films are laminated via electrodes has been proposed in order to obtain high piezoelectric characteristics (Patent Documents 1, 2, etc.).

[0004] Patent Document 1 discloses a piezoelectric element in which multiple layers of uniaxially oriented PZT films are laminated via electrodes. a La b )(Zr c Ti d Nb e )O 3-δ In each case, the electrodes are connected to a positive terminal and a negative terminal of the multiple electrodes, and the direction of the electric field applied to the multiple laminated piezoelectric films is alternately inverted. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-233844 [Patent Document 2] International Publication No. 2017 / 018222 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the piezoelectric element having a piezoelectric film of multiple layers as disclosed in Patent Documents 1 and 2, it is possible to obtain a larger driving force than a piezoelectric element having a piezoelectric film of a single layer.

[0007] However, the piezoelectric elements described in Patent Documents 1 and 2 have the following problems. In a laminated piezoelectric element in which multiple uniaxially oriented PZT films are laminated, an electric field in the opposite direction to self-poling is applied to at least some of the multiple piezoelectric films, which generates a nonlinear response component, resulting in low linearity and making it impossible to achieve the displacement behavior expected of the device. A laminated piezoelectric element in which piezoelectric films made of epitaxial films are laminated may have low long-term reliability.

[0008] In view of the above circumstances, an object of the present disclosure is to provide a piezoelectric element and a piezoelectric actuator that are capable of obtaining a large driving force, have good responsiveness, and have long-term reliability at low cost. [Means for solving the problem]

[0009] The piezoelectric element of the present disclosure includes a first electrode, a first piezoelectric film, a second electrode, a second piezoelectric film, and a third electrode, in this order, on a substrate; the first piezoelectric film and the second piezoelectric film each contain a perovskite-type oxide as a main component; One of the first piezoelectric film and the second piezoelectric film is an epitaxial film, and the other is a uniaxially oriented film.

[0010] It is preferable that the first piezoelectric film is an epitaxial film and the second piezoelectric film is a uniaxially oriented film.

[0011] It is preferable that the surface of the first electrode that contacts the first piezoelectric film is an epitaxial film.

[0012] The perovskite oxide that is the main component of the first piezoelectric film and the perovskite oxide that is the main component of the second piezoelectric film are preferably made of the same constituent elements.

[0013] The perovskite oxide is lead zirconate titanate or lead zirconate titanate doped with a metal element M, and the metal element M is preferably at least one of vanadium, niobium, tantalum, antimony, molybdenum, and tungsten.

[0014] It is preferable that the metal element M in the perovskite oxide is niobium, and that the first piezoelectric film and the second piezoelectric film have the same amount of at least the metal element M in the composition ratio of the perovskite oxide contained therein.

[0015] The first electrode, the second electrode and the third electrode each preferably contain at least one of iridium, platinum, strontium ruthenate, barium ruthenate, zirconium oxide, hafnium oxide, ruthenium, ruthenium oxide, iridium oxide, platinum oxide and rhenium oxide.

[0016] The first electrode and the third electrode may be maintained at ground potential, and the second electrode may be a drive electrode for applying a positive drive voltage to the first piezoelectric film and the second piezoelectric film.

[0017] The second electrode may be maintained at a ground potential, and the first electrode and the third electrode may be drive electrodes for applying a negative drive voltage to the first piezoelectric film and the second piezoelectric film.

[0018] The actuator of the present disclosure is an actuator including the piezoelectric element of the present disclosure and a drive circuit that applies a drive voltage to the piezoelectric element, The driving circuit applies an electric field to the piezoelectric film, which is a uniaxially oriented film, in the same direction as the self-poling direction, which is the spontaneous polarization that the piezoelectric film has immediately after deposition, and applies an electric field to the piezoelectric film, which is an epitaxial film, in the opposite direction to the electric field applied to the piezoelectric film, which is a uniaxially oriented film. Effect of the Invention

[0019] The technique disclosed herein aims to provide a piezoelectric element and a piezoelectric actuator that are capable of obtaining a large driving force, have good responsiveness, and have long-term reliability at low cost. [Brief description of the drawings]

[0020] [Figure 1] FIG. 2 is a cross-sectional view of a piezoelectric element according to an embodiment. [Diagram 2] FIG. 1 is a diagram showing a schematic configuration of an actuator; [Diagram 3] FIG. 2 is a diagram showing a schematic configuration of an actuator. [Figure 4] This is measurement data of a PZT epitaxial film by XRD-φ scan. [Diagram 5] 4 is a diagram showing a drive signal and a velocity waveform for the piezoelectric element of Example 1. FIG. [Figure 6] 6 is a diagram showing a drive signal and a velocity waveform for the piezoelectric element of Comparative Example 1. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the thicknesses and ratios of each layer are appropriately changed for ease of viewing, and do not necessarily reflect the actual thicknesses and ratios.

[0022] Fig. 1 is a cross-sectional schematic diagram showing the layer structure of a piezoelectric element 1 according to one embodiment. As shown in Fig. 1, the piezoelectric element 1 includes a first electrode 12, a first piezoelectric film 14, a second electrode 16, a second piezoelectric film 18, and a third electrode 20 on a substrate 10, in this order.

[0023] There are no particular limitations on the substrate 10, and examples of the substrate include silicon, glass, stainless steel, yttrium-stabilized zirconia, alumina, sapphire, silicon carbide, etc. As the substrate 10, a substrate made of single crystal silicon is particularly preferable.

[0024] The first electrode 12 and the second electrode 16 are paired to apply a voltage to the first piezoelectric film 14. The second electrode 16 and the third electrode 20 are paired to apply a voltage to the second piezoelectric film 18.

[0025] The main components of the first electrode 12, the second electrode 16, and the third electrode 20 are not particularly limited, but may be iridium (Ir), platinum (Pt), strontium ruthenate (SrRuO3), barium ruthenate (BaRuO3), zirconium oxide (ZrO2), hafnium oxide (HfO2), ruthenium (Ru), ruthenium oxide (RuO x ), iridium oxide (IrO x ), platinum oxide (PtO x ), and rhenium oxide (ReO x Each of the first electrode 12, the second electrode 16 and the third electrode 20 may be a single layer, or may have a multi-layer structure.

[0026] There are no particular limitations on the thickness of the first electrode 12, the second electrode 16, and the third electrode 20, but the thickness is preferably about 50 nm to 300 nm, and more preferably 100 nm to 300 nm.

[0027] The first piezoelectric film 14 and the second piezoelectric film 18 are each mainly composed of a perovskite-type oxide represented by the general formula ABO3. In this specification, the main component refers to a component that occupies 80 mol% or more. It is preferable that the first piezoelectric film 14 and the second piezoelectric film 18 each have a perovskite-type oxide occupying 90 mol% or more, and it is more preferable that the first piezoelectric film 14 and the second piezoelectric film 18 are composed of a perovskite-type oxide (including inevitable impurities). The perovskite-type oxide that is the main component of the first piezoelectric film 14 and the perovskite-type oxide that is the main component of the second piezoelectric film 18 may be composed of different constituent elements, or their constituent elements may be the same. However, from the viewpoint of cost reduction, it is preferable that the perovskite-type oxides of the first piezoelectric film 14 and the second piezoelectric film 18 have the same constituent elements. Note that "the constituent elements are the same" means that the contained elements are the same, but the composition ratios may be different.

[0028] The first piezoelectric film 14 and the second piezoelectric film 18 are preferably so-called PZT-based perovskite-type oxides containing Pb (lead) at the A site, Zr (zirconium), and Ti (titanium) at the B site. In particular, it is preferably M-added PZT in which a metal element M is added to the B site. Here, the metal element M is at least one of vanadium (V), niobium (Nb), tantalum (Ta), antimony (Sb), molybdenum (Mo), and tungsten (W). M-added PZT is represented by the following general formula. Pb a {(Zr x Ti 1-x ) 1-y M y}O3 Here, 0 < x < 1, 0 < y < 1, and 0.9 ≤ a ≤ 1.2. The molar ratio a of Pb is based on 1, but as long as it is in the range of 0.9 ≤ a ≤ 1.2, it can take a perovskite-type structure.

[0029] The metal element M may be a single element such as only V or only Nb, or may be a combination of two or more elements such as a mixture of V and Nb, or a mixture of V, Nb and Ta. When the metal element M is any of these elements, a very high piezoelectric constant can be achieved in combination with the A-site element Pb.

[0030] In particular, Pb where the metal element M is Nb a {(Zr x Ti 1-x ) 1-y Nb y}O3 is optimal. At this time, a higher piezoelectric constant can be obtained when 0.1≦y≦0.3.

[0031] It is preferable that both the first piezoelectric film 14 and the second piezoelectric film 18 are mainly composed of Nb-added PZT. In this case, it is preferable that the Nb composition ratios of the Nb-added PZT, which is the main component of the first piezoelectric film 14, and the Nb-added PZT, which is the main component of the second piezoelectric film 18, are the same. That is, when the Pb composition ratio in the first piezoelectric film 14 is a1, the Zr composition ratio is x1, and the M composition ratio is y1, and the Pb composition ratio in the perovskite oxide in the second piezoelectric film 18 is a2, the Zr composition ratio is x2, and the M composition ratio is y2, it is preferable that y1=y2. Furthermore, it is more preferable that y1=y2 and x1 and x2 are the same. Here, the composition ratio being the same means that they are equal within the range of measurement error. There are several analysis methods such as ICP (Inductively Coupled Plasma) emission spectroscopy and XRF (X-ray Fluorescence) as a method for measuring the composition. For example, when composition analysis is performed using XRF, the measurement error is about 0.005.

[0032] It is said that PZT-based perovskite oxides exhibit high piezoelectric properties at or near the morphotropic phase boundary (MPB). The MPB composition is when Zr:Ti (molar ratio) is close to 52:48, and in the above general formula, the MPB composition or its vicinity is preferable. "At or near the MPB" refers to a region where a phase transition occurs when an electric field is applied to the piezoelectric film. Specifically, the Zr:Ti (molar ratio) is preferably within the range of 45:55 to 55:45, that is, within the range of x = 0.45 to 0.55.

[0033] The thickness t1 of the first piezoelectric film 14 and the thickness t2 of the second piezoelectric film 18 are preferably 0.1 μm or more and 5 μm or less, and more preferably 1 μm or more and less than 5 μm. The thicknesses of the first piezoelectric film 14 and the second piezoelectric film 18 may be the same or different. The thickness of the first piezoelectric film 14 and the second piezoelectric film 18 is preferably 2 μm or less.

[0034] One of the first piezoelectric film 14 and the second piezoelectric film 18 is an epitaxial film, and the other is a uniaxially oriented film. In particular, it is preferable that the first piezoelectric film 14 disposed on the substrate 10 side is an epitaxial film, and the second piezoelectric film 18 is a uniaxially oriented film. In the following, a case where the first piezoelectric film 14 is an epitaxial film, and the second piezoelectric film 18 is a uniaxially oriented film will be described.

[0035] In order to epitaxially grow the first piezoelectric film 14, it is particularly preferable to use a single crystal silicon substrate as the substrate 10, and to provide the first electrode 12 with a laminated structure of a first film 12A made of a ZrO2 or HfO2 film, a second film 12B made of a Pt film or Ir film, and a third film 12C made of SrRuO3 or BaRuO3 on the single crystal silicon substrate. In order to epitaxially grow the first piezoelectric film 14, it is preferable that the surface of the first electrode 12 that contacts the first piezoelectric film 14 is an epitaxial film. That is, when the first electrode 12 has the above-mentioned three-layer structure, it is preferable that the third film 12C that is closest to the first piezoelectric film 14 is an epitaxial film.

[0036] The second piezoelectric film 18, which is a uniaxially oriented film, has spontaneous polarization aligned upward in the film thickness direction when no external electric field is applied. Arrow P2 in FIG. 1 indicates the direction of polarization. Hereinafter, this will be referred to as the polarization direction P2. Whether or not the spontaneous polarization in the piezoelectric film is aligned and the direction in which the spontaneous polarization is aligned can be confirmed by measuring the PV hysteresis curve (or PE hysteresis curve), which indicates the polarization-voltage characteristics (or polarization-electric field characteristics) of the piezoelectric film.

[0037] The second piezoelectric film 18 being a uniaxially oriented film means that the perovskite oxide, which is the main component of the second piezoelectric film 18, is uniaxially oriented. The uniaxially oriented perovskite oxide is spontaneously polarized immediately after deposition without poling, that is, the direction of spontaneous polarization is uniform, and the film is polarized in the film thickness direction. The reason why the spontaneous polarization is uniform in the piezoelectric film without poling when no external electric field is applied is considered to be because an electric field (hereinafter referred to as spontaneous internal electric field) caused by distortion or defects of the crystal structure is generated in the piezoelectric film. The second piezoelectric film 18 has spontaneous polarization that is uniform in the film thickness direction due to such spontaneous internal electric field. The second piezoelectric film 18 is a piezoelectric film that is polarized in the film thickness direction when no external electric field is applied because the spontaneous polarization is uniform in the film thickness direction. The piezoelectric film is composed of a large number of spontaneously polarized domains. In this specification, "spontaneous polarization aligned in a specific direction" means a state in which the spontaneous polarization component in a specific direction is relatively greater than the spontaneous polarization components in other directions. If the spontaneous polarization component in a specific direction in a piezoelectric film is relatively greater than the spontaneous polarization components in other directions, the film can be regarded as polarized in that specific direction.

[0038] In contrast, the first piezoelectric film 14 is an epitaxial film, and in the unpoled state, the spontaneous polarization is isotropic, so that the film is polarized in the direction in which the electric field is applied, and a stable polarization state is obtained.

[0039] 2 shows a schematic configuration of an actuator 5 including a piezoelectric element 1. The actuator 5 includes the piezoelectric element 1 and a drive circuit 30.

[0040] The driving circuit 30 is a means for supplying a driving voltage to the first piezoelectric film 14 and the second piezoelectric film 18 sandwiched between the electrodes in order to drive the piezoelectric element 1. In this example, the second electrode 16 is connected to the ground terminal (GND) of the driving circuit 30, and the first electrode 12 and the third electrode 20 are connected to the driving voltage output terminal (-V) of the driving circuit 30. As a result, the driving circuit 30 applies electric fields in opposite directions to each other to the first piezoelectric film 14 and the second piezoelectric film 18. In this example, the driving circuit 30 applies an electric field Ef in the same direction as the direction (polarization direction) P2 in which the spontaneous polarization is aligned to the second piezoelectric film 18, which is one of the piezoelectric films, and applies an electric field Er in the opposite direction to the electric field Ef applied to the second piezoelectric film 18 to the first piezoelectric film 14, which is the other piezoelectric film. The driving circuit 30 is a negative driving circuit that gives a negative potential to the driving electrode (here, the second electrode 16).

[0041] 2, the second electrode 16 of the piezoelectric element 1 is set to a ground potential, and the first electrode 12 and the third electrode 20 are used as drive electrodes. In this example, when the piezoelectric element 1 is driven, a negative potential (-V) is applied to the drive electrodes (here, the first electrode 12 and the third electrode 20). As a result, an electric field Ef in the same direction as the aligned direction (polarization direction) P2 of the spontaneous polarization is applied to the second piezoelectric film 18, which is one of the piezoelectric films, and an electric field Er in the opposite direction to the electric field Ef applied to the second piezoelectric film 18 is applied to the first piezoelectric film 14, which is the other piezoelectric film.

[0042] It is preferable that the first electrode 12 and the third electrode 20 of the piezoelectric element 1 are connected. If the first electrode 12 and the third electrode 20 are connected, drive control is easy.

[0043] In contrast, as in the actuator 6 of the modified example shown in Fig. 3, the driving circuit 32 may include a positive driving circuit that applies a positive potential to the driving electrode. In the example shown in Fig. 3, the first electrode 12 and the third electrode 20 are connected to the ground terminal of the driving circuit 32, and the second electrode 16 is connected to the driving voltage output terminal of the driving circuit 32. That is, the first electrode 12 and the third electrode 20 are at ground potential, and the second electrode 16 functions as a driving electrode. In this case, too, the driving circuit 32 can apply to the second piezoelectric film 18 an electric field Ef in the same direction as the direction (polarization direction) P2 in which the spontaneous polarizations are aligned, and apply to the first piezoelectric film 14 an electric field Er in the opposite direction to the electric field Ef applied to the second piezoelectric film 18.

[0044] In the actuators 5 and 6 (see FIGS. 2 and 3), an electric field is applied to the first piezoelectric film 14 in the opposite direction to the electric field applied to the second piezoelectric film 18. Therefore, as shown in FIGS. 2 and 3, the first piezoelectric film 14 is polarized in a direction P1 opposite to the polarization direction P2 of the second piezoelectric film 18.

[0045] The actuators 5 and 6 each include a drive circuit of only one polarity as the drive circuits 30 and 32, and can be realized at low cost.

[0046] The inventors have found that a configuration like the present piezoelectric element 1, which comprises a first electrode 12, a first piezoelectric film 14, a second electrode 16, a second piezoelectric film 18, and a third electrode 20 in this order on a substrate 10, with the first piezoelectric film 14 and the second piezoelectric film 18 each having a perovskite-type oxide as a main component, one of the first piezoelectric film 14 and the second piezoelectric film 18 being an epitaxial film and the other being a uniaxially oriented film, provides good responsiveness during operation and high long-term reliability (see examples below).

[0047] Since this piezoelectric element has multiple layers of piezoelectric film, it can obtain a larger driving force than a piezoelectric element having a single layer of piezoelectric film. Also, as shown in Figure 2 or Figure 3, by setting the first electrode 12 and the third electrode 20 to the same potential and applying a voltage to generate an electric field between them and the second electrode 16, it is possible to configure a single driving circuit, which allows for cost reduction when applied to an actuator, and realizes an actuator with a large driving force at low cost. EXAMPLES

[0048] Specific examples and comparative examples of the piezoelectric element of the present disclosure will be described below. First, the configuration and manufacturing method of the piezoelectric element of each example will be described.

[0049] As examples and comparative examples, piezoelectric elements (see FIG. 1) were fabricated having a first electrode, a first piezoelectric film, a second electrode, a second piezoelectric film, and a third electrode in this order on a substrate. The layer configurations of the examples and comparative examples are summarized in Table 1 below.

[0050] "Example 1" A method for producing the piezoelectric element of Example 1 will be described.

[0051] (Substrate with first electrode) An electrode-attached substrate (SiZrO2 / Pt / SrRuO3) was prepared, which had a first electrode layer in which a 40 nm-thick ZrO2 film, a 150 nm-thick Pt film, and a 60 nm-thick SrRuO3 film were sequentially laminated on a silicon wafer substrate.

[0052] (First piezoelectric film) On the first electrode, a Nb-added PZT film with an Nb content of 12 at% in the B site was formed as the first piezoelectric film. The thickness of the Nb-added PZT film was 2 μm. Nb-added PZT was used as the target, and the sputtering conditions were as follows. The Nb-added PZT target had a Pb composition ratio a=1.3, and the Zr / Ti molar ratio was MPB composition (Zr / Ti=52 / 48), that is, x=0.52, and Nb composition ratio y=0.12. In Table 1, the case where the Nb composition ratio y=0.12, that is, the Nb content in the B site is 12%, is the default and is described as Nb-PZT.

[0053] -Sputtering conditions for the first piezoelectric film- Target-substrate distance: 100mm Target input power: 3kW Degree of vacuum: 0.5 Pa, Ar and O2 mixed atmosphere (O2 volume fraction 2.5%) Substrate temperature setting: 600℃ Substrate bias voltage: +40V

[0054] (2nd electrode) On the first piezoelectric film, a 50 nm thick IrO was applied as the second electrode. x (x≦2) and 200 nm of Ir were laminated in this order. The sputtering conditions were as follows:

[0055] -IrO x , Ir sputtering conditions - Target-substrate distance: 100mm Target input power: 200W Degree of vacuum: 0.3 Pa, Ar atmosphere during Ir deposition, IrO x During deposition, the atmosphere was a mixture of Ar and O2 (O2 volume fraction 5%). Board temperature setting: Room temperature After the IrO2 and Ir films were formed, they were annealed at 350° C. for 15 minutes.

[0056] (Second piezoelectric film) On the second electrode, a Nb-doped PZT film was formed as a second piezoelectric film, in which the amount of Nb doped in the B site was 12 at %, similar to the first piezoelectric film. The target and sputtering conditions were the same as those for the first piezoelectric film.

[0057] (3rd electrode) On the second piezoelectric film, a 50 nm thick IrO was applied as the third electrode. x A 100 nm thick layer of Ir was then laminated in this order under the same sputtering conditions as for the second electrode.

[0058] (Formation of electrode pattern for evaluation) In order to form electrode pads for applying voltage to the first electrode, the second electrode, and the third electrode, patterning was performed in this order on the third electrode, the second piezoelectric film, the second electrode, and the first piezoelectric film by photolithography and dry etching.

[0059] The piezoelectric laminate of Example 1 was produced by the above steps.

[0060] "Examples 2 to 8, Comparative Examples 1 and 2" For Examples 2 to 8 and Comparative Examples 1 and 2, substrates with electrodes were prepared that had a different configuration of the first electrode from that of the substrate with electrodes in Example 1. The configuration of each first electrode was as shown in Table 1. For example, in Example 2, a substrate with a first electrode (Si / ZrO2 / Pt / BaRuO3) was prepared in which the third film constituting the outermost surface of the first electrode in Example 1 was changed from SrRuO3 to BaRuO3, and in Example 3, a substrate with a first electrode (Si / HfO2 / Pt / SrRuO3) was prepared in which the first film closest to the substrate in the first electrode in Example 1 was changed from ZrO2 to HfO2.

[0061] For Comparative Example 1, an electrode-attached substrate (Si / SiO2 / ZrO2 / Pt / SrRuO3) was prepared, which had a first electrode layer in which a 40 nm-thick ZrO2 film, a 150 nm-thick Pt film, and a 60 nm-thick SrRuO3 film were sequentially laminated on a substrate made of a silicon wafer with an oxide film (SiO2 film), similar to that in Example 1. For Comparative Example 2, an electrode-attached substrate (Si / SiO2 / TiW / Ir) was prepared, which had a first electrode layer in which a 20 nm-thick TiW film and a 150 nm-thick Ir film were sequentially laminated on a substrate made of a silicon wafer with an oxide film (SiO2 film).

[0062] The configurations other than the first electrode substrate were the same as in Example 1, and piezoelectric laminates of Examples 2 to 8 and Comparative Examples 1 and 2 were obtained.

[0063] In Examples 1 to 8, the first piezoelectric film was an epitaxial film (indicated as "epi" in the column for orientation state in Tables 1 and 2), and the second piezoelectric film was a uniaxially oriented film (indicated as "uniaxially oriented" in the column for orientation state in Tables 1 and 2). In Examples 1 to 8 in Table 1, the orientation state of the first electrode-attached substrate means the orientation state of the outermost surface of the first electrode. For example, in Example 1, SrRuO3, which is the outermost surface of the first electrode, was an epitaxial film. In Comparative Examples 1 and 2, both the first piezoelectric film and the second piezoelectric film were uniaxially oriented films. In addition, the SrRuO3 on the outermost surface of the first electrode in Comparative Example 1 and the Ir on the outermost surface of the first electrode in Comparative Example 2 were uniaxially oriented films.

[0064] "Examples 11 to 15, Comparative Example 3" Examples 11 to 15 and Comparative Example 3 have different compositions of the second electrode from Example 1. For example, the second electrode of Example 11 had a laminated structure (PtOx / Pt) in which PtOx and Pt were laminated in this order. Example 14 had a laminated structure (TaOx / Ta / Pt) in which TaOx, Ta, and Pt were laminated in this order on the first piezoelectric film.

[0065] In Examples 11 to 15, the first piezoelectric film is an epitaxial film, and the second piezoelectric film is a uniaxially oriented film. In Comparative Example 3, both the first piezoelectric film and the second piezoelectric film are epitaxial films.

[0066] "Examples 21 to 26" As shown in Table 2, Examples 21 to 26 differ from Example 1 in the composition combination of the first and second piezoelectric films. In Example 21, both the first and second piezoelectric films are PZT films not doped with metal element M. The first piezoelectric film in Example 21 is a PZT film doped with Nb12% like Example 1, but the second piezoelectric film is a PZT film doped with Nb10%. The first and second piezoelectric films in Examples 24 to 26 were as shown in Table 1.

[0067] In Examples 21 to 26, the first piezoelectric film was an epitaxial film, and the second piezoelectric film was a uniaxially oriented film. However, the epitaxial film of the first piezoelectric film in Example 26 had lower crystallinity than the other Examples. Also, the uniaxial orientation of the second piezoelectric film in Examples 25 and 26 had lower crystallinity than the uniaxial orientation of the other Examples.

[0068] "Examples 31 to 35" In Examples 31 to 35, the compositions of the first and second piezoelectric films are different from Example 1. The first and second piezoelectric films in Example 31 were PZT films with 1% vanadium added. Similarly, in Examples 32 to 35, PZT films with 1% Ta, Sb, Mo, and W added were used, respectively.

[0069] In Examples 31 to 35, the first piezoelectric film was an epitaxial film, and the second piezoelectric film was a uniaxially oriented film.

[0070] <Crystalline> The crystallinity of the first and second piezoelectric films was measured by observing the (111) peak of each piezoelectric film by φ scanning of XRD (X-Ray Diffraction). The measurement was performed using a Rigaku RINT3000 measuring device under the following conditions. Source: CuKα Optical system used: Parallel optical system X-ray incident angle: Set to an angle where the (111) peak of PZT-based perovskite oxide can be observed (θ=approximately 38 deg, χ=approximately 55 deg) φScan conditions: -180deg~180deg range at 0.1deg / step, 100deg / min

[0071] In the case of an epitaxial film, a peak with four-fold symmetry was confirmed as shown in Figure 4. In the case of a uniaxially oriented film, data on a nearly straight line of a specific intensity was obtained.

[0072] The characteristics of each of the examples and comparative examples were evaluated.

[0073] (Preparation of evaluation samples) -Evaluation sample- A rectangular piece measuring 2 mm×25 mm was cut out from the laminate to prepare a cantilever as evaluation sample 1.

[0074] <Measurement of piezoelectric properties> The piezoelectric properties of each example and comparative example were evaluated using the piezoelectric constant d 31 was measured. Piezoelectric constant d 31 The measurement of the piezoelectric constant d was performed using an evaluation sample according to the method described in I. Kanno et al. Sensor and Actuator A 107 (2003) 68. 31 Specifically, the second electrode 16 was grounded, the first electrode 12 and the third electrode 20 were used as driving electrodes, and a sine wave voltage of +10 V±10 V was applied, i.e., a bias voltage of 10 V and a sine wave voltage with an amplitude of 10 V were applied to measure the piezoelectric constant d 31 The measurement results are shown in Tables 1 and 2. Tables 1 and 2 also show the evaluation results based on the following criteria. a:360pm / V or more c: less than 360pm / V

[0075] <Measurement of displacement waveform> The displacement waveform is obtained by measuring the velocity waveform using the evaluation sample and integrating the velocity waveform. The second electrode was set to ground potential, and the first and third electrodes were set to driving electrodes, and a 200 Hz driving signal (positive potential) was applied. The driving signal was a sine wave with an amplitude of 15 V. In this case, the velocity waveform of the evaluation sample was measured using an Ono Sokki LV-1720A. Fig. 5 shows the drive signal (dashed line) and velocity waveform (solid line) for Example 1. Fig. 6 shows the drive signal (dashed line) and velocity waveform (solid line) for Comparative Example 1. In Fig. 5 and Fig. 6, the drive signal is shown in voltage, and the velocity waveform is shown in arbitrary units (au). Since the displacement waveform is found by integrating the velocity waveform, the presence of a nonlinear component in the velocity waveform means that the displacement waveform also has a nonlinear component. The evaluation results based on the following criteria are shown in Tables 1 and 2. a: Nonlinear components included c: No nonlinear components

[0076] <Measurement of sheet resistance of second electrode> A general high-precision flexible resistivity measurement system was used for the sheet resistance measurement. Specifically, a VR250 manufactured by Kokusai Electric Semiconductor Services was used. The sheet resistance was measured at 5 or 9 points on the surface of the second electrode, and the average value was calculated. The probe used was a JS-TC-200-EP-200HK 4-terminal probe, with a needle diameter of 200μmR, needle spacing of 1mm, needle pressure of 200g per probe, and needle material of tungsten carbide. For each example, the sheet resistance of the second electrode was evaluated as a, b, or c based on the following criteria. a: 1Ω or less b: More than 1Ω, less than 10Ω, c: More than 10Ω

[0077] The layer structures and evaluation results for each of the Examples and Comparative Examples are shown in Tables 1 and 2. As an overall evaluation, the piezoelectric characteristics, the displacement waveform, and the sheet resistance of the second electrode were evaluated as follows: a: 2 points, b: 1 point, and c: 0 point. The overall evaluation score was calculated based on the three evaluations, and the overall evaluation score is shown in Tables 1 and 2.

[0078] [Table 1] [Table 2]

[0079] In the examples in which the first piezoelectric film is an epitaxial film and the second piezoelectric film is a uniaxially oriented film, the overall evaluation was 5 points or more. If the overall evaluation was 5 points or more, the piezoelectric characteristics were high (i.e., a large driving force was obtained), the response was good, and long-term reliability was obtained. If the overall evaluation was 6 points or more, it is considered that better long-term reliability was obtained. In Comparative Examples 1 and 2 in which both the first and second piezoelectric films were uniaxially oriented films, there was a nonlinear component in the displacement waveform and the response was low. In Comparative Examples 1 and 2, both the first and second piezoelectric films were uniaxially oriented films. In this case, the spontaneous polarization of the two piezoelectric films is in the same direction. When an electric field in the opposite direction is applied to the first and second piezoelectric films as in this embodiment, in the cases of Comparative Examples 1 and 2, an electric field in the opposite direction to the spontaneous polarization is applied to at least one of the piezoelectric films. Since it is necessary to reverse the direction of the spontaneous polarization, a delay occurs in the response, and it is considered that a nonlinear component occurs in the displacement waveform shown by the solid line with respect to the shape of the drive waveform shown by the dashed line, as shown in Fig. 6. When at least one layer is an epitaxial film as in the embodiment, the spontaneous polarization of the epitaxial film is isotropic, so that by applying an electric field in the opposite direction to the uniaxially oriented film, it can be easily polarized in that direction, and a stable polarization state can be obtained. Therefore, it is considered that no nonlinear component occurs in the displacement waveform when electric fields in opposite directions are applied to the first piezoelectric film and the second piezoelectric film.

[0080] In Comparative Example 3, in which both the first and second piezoelectric films are epitaxial films, there was no problem with the responsiveness, but the sheet resistance of the second electrode was large. If the sheet resistance is large, heat is generated by driving, and the power consumption increases due to the heat. In addition, if the sheet resistance is large, Pb is precipitated in the piezoelectric film at the interface with the piezoelectric film due to the temperature rise caused by heat during long-term driving, leading to a decrease in withstand voltage and durability, and low long-term reliability. In addition, when both the first and second piezoelectric films are epitaxial films as in Comparative Example 3, it is presumed that the stress is larger than when at least one of the first and second piezoelectric films is a uniaxially oriented film. When driven for a long time, the larger the stress, the more likely defects such as cracking and peeling are to occur. Therefore, it is considered that by making one of the two piezoelectric films an epitaxial film and the other a uniaxially oriented film, the long-term reliability can be improved compared to when both the two piezoelectric films are epitaxial films.

[0081] All publications, patent applications, and standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or standard was specifically and individually indicated to be incorporated by reference.

[0082] The following supplementary notes are further disclosed regarding the above embodiment. <Appendix 1> a first electrode, a first piezoelectric film, a second electrode, a second piezoelectric film, and a third electrode are provided on a substrate in this order; the first piezoelectric film and the second piezoelectric film each contain a perovskite-type oxide as a main component; A piezoelectric element, wherein one of the first piezoelectric film and the second piezoelectric film is an epitaxial film, and the other is a uniaxially oriented film. <Appendix 2> 2. The piezoelectric element of claim 1, wherein the first piezoelectric film is an epitaxial film and the second piezoelectric film is a uniaxially oriented film. <Appendix 3> 3. The piezoelectric element according to claim 2, wherein a surface of the first electrode in contact with the first piezoelectric film is an epitaxial film. <Appendix 4> 4. The piezoelectric element according to claim 1, wherein the perovskite oxide that is a main component of the first piezoelectric film and the perovskite oxide that is a main component of the second piezoelectric film are composed of the same constituent elements. <Appendix 5> The perovskite oxide is lead zirconate titanate or lead zirconate titanate doped with a metal element M, 5. The piezoelectric element according to claim 1, wherein the metal element M is at least one of vanadium, niobium, tantalum, antimony, molybdenum, and tungsten. <Appendix 6> The metal element M in the perovskite oxide is niobium; 6. The piezoelectric element according to claim 5, wherein the first piezoelectric film and the second piezoelectric film have the same amount of at least the metal element M in the composition ratio of the perovskite oxide contained therein. <Appendix 7> 7. The piezoelectric element of any one of Appendix 1 to Appendix 6, wherein the first electrode, the second electrode, and the third electrode each contain at least one of iridium, platinum, strontium ruthenate, barium ruthenate, zirconium oxide, hafnium oxide, ruthenium, ruthenium oxide, iridium oxide, platinum oxide, and rhenium oxide. <Appendix 8> 8. The piezoelectric element of claim 1, wherein the first electrode and the third electrode are maintained at ground potential, and the second electrode is a drive electrode for applying a positive drive voltage to the first piezoelectric film and the second piezoelectric film. <Appendix 9> 8. The piezoelectric element of claim 1, wherein the second electrode is maintained at ground potential, and the first electrode and the third electrode are driving electrodes for applying a negative driving voltage to the first piezoelectric film and the second piezoelectric film. <Appendix 10> An actuator comprising: a piezoelectric element according to any one of claims 1 to 9; and a drive circuit that applies a drive voltage to the piezoelectric element, The drive circuit applies an electric field to the other piezoelectric film, which is a uniaxially oriented film, in the same direction as the self-poling direction of the other piezoelectric film, which is the spontaneous polarization that the other piezoelectric film has immediately after deposition, and applies an electric field to one piezoelectric film, which is an epitaxial film, in the opposite direction to the electric field applied to the other piezoelectric film. [Explanation of symbols]

[0083] 1 Piezoelectric element 5, 6 Actuator 10 Substrate 12 1st electrode 12a 1st membrane 12b Second membrane 12c 3rd membrane 14 First piezoelectric film 16 2nd electrode 18 Second piezoelectric film 20 3rd electrode 30, 32 Drive circuit

Claims

1. a first electrode, a first piezoelectric film, a second electrode, a second piezoelectric film, and a third electrode are provided on a substrate in this order; the first piezoelectric film and the second piezoelectric film each contain a perovskite oxide as a main component; A piezoelectric element, wherein one of the first piezoelectric film and the second piezoelectric film is an epitaxial film, and the other is a uniaxially oriented film.

2. The piezoelectric element according to claim 1 , wherein the first piezoelectric film is the epitaxial film, and the second piezoelectric film is the uniaxially oriented film.

3. The piezoelectric element according to claim 2 , wherein a surface of the first electrode that contacts the first piezoelectric film is an epitaxial film.

4. 3. The piezoelectric element according to claim 1, wherein the perovskite oxide which is a main component of the first piezoelectric film and the perovskite oxide which is a main component of the second piezoelectric film are composed of the same constituent elements.

5. the perovskite oxide is lead zirconate titanate or lead zirconate titanate doped with a metal element M; 4. The piezoelectric element according to claim 3, wherein the metal element M is at least one of vanadium, niobium, tantalum, antimony, molybdenum, and tungsten.

6. the metal element M in the perovskite oxide is niobium; 6. The piezoelectric element according to claim 5, wherein the first piezoelectric film and the second piezoelectric film have the same amount of at least the metal element M in the composition ratio of the perovskite oxide contained therein.

7. 3. The piezoelectric element according to claim 1, wherein the first electrode, the second electrode and the third electrode each contain at least one of iridium, platinum, strontium ruthenate, barium ruthenate, zirconium oxide, hafnium oxide, ruthenium, ruthenium oxide, iridium oxide, platinum oxide, and rhenium oxide.

8. 2. The piezoelectric element according to claim 1, wherein the first electrode and the third electrode are maintained at a ground potential, and the second electrode is a drive electrode for applying a positive drive voltage to the first piezoelectric film and the second piezoelectric film.

9. 2. The piezoelectric element according to claim 1, wherein the second electrode is maintained at a ground potential, and the first electrode and the third electrode are drive electrodes for applying a negative drive voltage to the first piezoelectric film and the second piezoelectric film.

10. 2. An actuator comprising: the piezoelectric element according to claim 1; and a drive circuit that applies a drive voltage to the piezoelectric element, The actuator includes a driving circuit that applies an electric field to the other piezoelectric film, which is the uniaxially oriented film, in the same direction as the self-poling direction, which is the spontaneous polarization of the other piezoelectric film immediately after deposition, and applies to the one piezoelectric film, which is the epitaxial film, an electric field in the opposite direction to the electric field applied to the other piezoelectric film.

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