WO2025204536A1 - Piezoelectric laminate, piezoelectric element, and production method for piezoelectric laminate - Google Patents

Abstract

Provided is a piezoelectric laminate that comprises a lower electrode, a first piezoelectric film, an intermediate electrode, and a second piezoelectric film that are provided in the given order on a substrate. The intermediate electrode comprises a first layer that is provided on the first piezoelectric film side and a second layer that is provided on the second piezoelectric film side of the first layer. The first layer includes a metal phase and a metal oxide phase that comprises an oxide of a metal that constitutes the metal phase. The second layer is a metal layer. Also provided are a piezoelectric element and a production method for the piezoelectric laminate.

Description

Piezoelectric laminate, piezoelectric element, and method for manufacturing piezoelectric laminate

This disclosure relates to a piezoelectric laminate, a piezoelectric element, and a method for manufacturing a piezoelectric laminate.

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 developed into 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-powered harvesting devices.

In order to achieve higher response, laminated piezoelectric elements have been proposed, in which multiple piezoelectric films are stacked with electrodes interposed between them (see, for example, JP 2013-080886 and JP 2013-080887).

In stacked piezoelectric elements obtained by sputtering piezoelectric films and electrodes, peeling can occur at or near the interface between the stacked piezoelectric film and intermediate electrode during the stacking process on the wafer and over long-term use. JP 2013-080886 A states that peeling occurs when the intermediate electrode is 250 nm or thicker, and that a thickness of 200 nm or less is preferable.

The inventors are considering making the intermediate electrode thicker than conventional ones to accommodate variations in the etching performed in the piezoelectric element manufacturing process. To achieve this, a highly adhesive layered structure that can provide a greater effect in preventing peeling than conventional structures is required.

The present disclosure has been made in light of the above circumstances, and aims to provide a highly adhesive piezoelectric laminate, piezoelectric element, and method for manufacturing a piezoelectric laminate that achieves a greater peeling prevention effect than conventional methods.

The piezoelectric laminate of the present disclosure includes a substrate and a lower electrode, a first piezoelectric film, an intermediate electrode, and a second piezoelectric film in this order.
the intermediate electrode includes a first layer disposed on the first piezoelectric film side and a second layer disposed on the second piezoelectric film side of the first layer;
the first layer includes a metal phase and a metal oxide phase including an oxide of a metal constituting the metal phase;
The second layer is a metal layer.

In the piezoelectric laminate of the present disclosure, it is preferable that the elemental ratio between the metal and oxygen, which are constituent elements of the first layer, is greater than the elemental ratio between the metal and oxygen in the stoichiometric composition of the metal oxide.

In the piezoelectric laminate of the present disclosure, it is preferable that the metal in the first layer and the metal constituting the second layer are the same element.

If the metal in the first layer and the metal constituting the second layer are the same element, it is preferable that the same element be a platinum group element.

If the metal in the first layer and the metal constituting the second layer are the same element, it is preferable that that same element be iridium.

It is preferable that the thickness of the intermediate electrode be greater than 200 nm.

It is preferable that the thickness of the intermediate electrode be 250 nm or more.

The first piezoelectric film and the second piezoelectric film preferably contain lead-containing perovskite oxide as their main component.

The piezoelectric element of the present disclosure comprises the piezoelectric laminate of the present disclosure and
and an upper electrode laminated on the second piezoelectric film of the piezoelectric laminate.

The method for manufacturing a piezoelectric laminate according to the present disclosure includes the steps of:
The method includes a step of depositing a lower electrode, a first piezoelectric film, an intermediate electrode, and a second piezoelectric film on a substrate by sputtering,
In the film formation process of the intermediate electrode, the first layer is formed under conditions such that, in an X-ray diffraction profile obtained for a sample in which the first layer is formed on a silicon oxide film, the ratio of the intensity of the peak due to the metal contained in the first layer to the intensity of the peak due to the oxide of the metal contained in the first layer is 0.1 to 10.

The technology disclosed herein provides a highly adhesive piezoelectric laminate, piezoelectric element, and method for manufacturing a piezoelectric laminate that provides a greater peeling prevention effect than conventional methods.

FIG. 2 is a cross-sectional view of a piezoelectric element. 1 is a cross-sectional STEM image of Sample 3. 10 is a cross-sectional STEM image of Sample 9. 1 is a cross-sectional STEM image of Sample 8. 1 is a cross-sectional STEM image of Sample 10.

Embodiments of the present invention will now be described with reference to the drawings. Note that in the drawings, the thicknesses of each layer and their ratios have been appropriately modified for ease of visualization and do not necessarily reflect the actual thicknesses and ratios. In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as its upper and lower limits. In the numerical ranges described in this disclosure in stages, the upper or lower limit stated in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit stated in a certain numerical range may be replaced with a value shown in the examples.

FIG. 1 is a cross-sectional schematic diagram showing the layer structure of a piezoelectric laminate 5 and piezoelectric element 1 according to one embodiment. As shown in FIG. 1, the piezoelectric element 1 comprises a piezoelectric laminate 5 and an upper electrode 20. The piezoelectric laminate 5 comprises a substrate 10 and, stacked in this order on the substrate 10, a lower electrode 12, a first piezoelectric film 14, an intermediate electrode 16, and a second piezoelectric film 18. The terms "lower" and "upper" in the lower electrode 12 and upper electrode 20 do not refer to the top and bottom in the vertical direction; rather, the electrode located on the substrate 10 side, sandwiching the first piezoelectric film 14, intermediate electrode 16, and second piezoelectric film 18, is simply referred to as the lower electrode 12, and the electrode located on the opposite side of the substrate 10 as the upper electrode 20.

The substrate 10 is not particularly limited, and examples include substrates of silicon, glass, stainless steel, yttrium-stabilized zirconia, alumina, sapphire, and silicon carbide. A laminated substrate in which a thermally oxidized silicon film is formed on the surface of a silicon substrate may also be used as the substrate 10.

The lower electrode 12 and intermediate electrode 16 form a pair to apply a voltage to the first piezoelectric film 14. The intermediate electrode 16 and upper electrode 20 form a pair to apply a voltage to the second piezoelectric film 18.

The materials constituting the lower electrode 12 and the upper electrode 20 are not particularly limited, but examples of the main components include metals or metal oxides such as Au (gold), Pt (platinum), Ir (iridium), Ru (ruthenium), Ti (titanium), Mo (molybdenum), Ta (tantalum), and Al (aluminum), as well as combinations thereof. ITO (indium tin oxide) and the like may also be used. ITO (indium tin oxide), LaNiO ₃ , and SrRuO ₃ may also be used. The lower electrode 12 and the upper electrode 20 may be a single layer or a multi-layer structure. When the lower electrode 12 has a multi-layer structure, it is also preferable to configure the substrate 10 side with an adhesive layer such as Ti, TiW, or ZrO ₂ in addition to the conductive layer made of the above materials.

There are no particular restrictions on the thickness of the lower electrode 12 and upper electrode 20, but it is preferably approximately 50 nm to 300 nm, and more preferably 100 nm to 300 nm.

The intermediate electrode 16 comprises a first layer 16a arranged on the first piezoelectric film 14 side and a second layer 16b arranged on the second piezoelectric film 18 side of the first layer 16a. The first layer 16a contains a metal phase MP and a metal oxide phase OP consisting of an oxide of the metal α that constitutes the metal phase MP. The second layer 16b is a metal layer.

As shown in FIG. 1, the first layer 16a contains multiple metal phases MP and metal oxide phases OP, with the metal phases MP and metal oxide phases OP arranged in a jumble throughout the entire first layer 16a. More specifically, the metal oxide phase OP is formed throughout the entire first layer 16a, and multiple granular metal phases MP are precipitated throughout the metal oxide phase OP. The particle size of the granular metal phases MP is, for example, several nanometers to several tens of nanometers.

The first layer 16a is a layer containing metal α and oxygen O. The elemental ratio α/O of the metal α and oxygen O, which are constituent elements of the first layer 16a, is preferably larger than the elemental ratio of the metal α to oxygen O in the stoichiometric composition of the oxide of the metal α. For example, when the metal is Ir (iridium), the ratio Ir/O of iridium Ir to oxygen O in the stoichiometric composition _IrO2 of iridium oxide is 0.5. In this case, it is preferable that the ratio of Ir to O in the first layer 16a is larger than 0.5, i.e., Ir/O>0.5.
The ratio of metal α to oxygen O in the first layer 16a is more preferably α/O≧2, and even more preferably α/O≧5.

The elemental ratio in the first layer 16a can be measured, for example, by X-ray photoelectron spectroscopy (XPS). In this specification, XPS measurement is performed while etching is performed in the depth direction (film thickness direction) using Ar sputtering, and the concentration (Atomic %) profiles of metal α and oxygen O in the depth direction are measured, and the elemental ratio α/O of metal α to oxygen O in the portion corresponding to the first layer 16a is determined.

The metal α of the first layer 16a and the metal constituting the second layer 16b may be different metal elements, but it is more preferable that they are the same metal element.

The metal α of the first layer 16a and the metal of the second layer 16b may each be gold (Au), platinum (Pt), iridium (Ir), ruthenium (Ru), titanium (Ti), molybdenum (Mo), tantalum (Ta), aluminum (Al), copper (Cu), silver (Ag), etc. It is more preferable that the metal α of the first layer 16a and the metal of the second layer 16b are the same and are a platinum group metal, and Ir is particularly preferable.

The thickness of the intermediate electrode 16 is preferably greater than 200 nm, and more preferably 250 nm or greater. The upper limit of the thickness of the intermediate electrode 16 is approximately 400 nm. When the intermediate electrode 16 has a laminated structure of multiple layers, the thickness of the intermediate electrode 16 refers to the total thickness of all layers. When the intermediate electrode 16 consists of two layers, a first layer 16a and a second layer 16b, as in this embodiment, the thickness of the intermediate electrode 16 is the sum of the thickness of the first layer 16a and the thickness of the second layer 16b. In the intermediate electrode 16, it is preferable that the thickness of the second layer 16b is thicker than the first layer 16a, and it is preferable that the ratio of the thickness of the first layer 16a to the thickness of the second layer 16b is approximately 1:2 to 1:7.

In this specification, the thickness of the intermediate electrode 16 is measured as follows.
The sample surface is coated with carbon (C) and platinum (Pt), and the cross section is processed using a focused ion beam (FIB). The cross section is then observed using a scanning electron microscope (SEM). The thickness of the intermediate electrode is measured at three locations within the field of view, and the average value is taken as the thickness of the intermediate electrode.

Although the first piezoelectric film 14 and the second piezoelectric film 18 are not particularly limited, they are preferably each composed primarily of a perovskite-type oxide represented by the general formula _ABO3 . In this specification, "main component" refers to a component that accounts for 80 mol% or more. It is preferable that the first piezoelectric film 14 and the second piezoelectric film 18 each be composed of a perovskite-type oxide that accounts for 90 mol% or more. It is more preferable that the first piezoelectric film 14 and the second piezoelectric film 18 are each composed of a perovskite-type oxide (however, containing 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 may be composed of the same constituent elements. However, from the perspective of cost reduction, it is preferable that the perovskite-type oxides of the first piezoelectric film 14 and the second piezoelectric film 18 be composed of the same constituent elements. The phrase "having the same constituent elements" means that the elements contained are the same, but the composition ratios may be different.

The perovskite oxide is preferably a lead zirconate titanate (PZT) oxide containing Pb (lead), Zr (zirconium), Ti (titanium) and O (oxygen).

In particular, a compound represented by the following general formula (1) containing an additive M at the B site of PZT is preferred.
Pb _a {(Zr _x Ti _1-x ) _1-y M _y }O ₃ (1)
Here, M is preferably one or more elements selected from V (vanadium), Nb (niobium), Ta (tantalum), Sb (antimony), Mo (molybdenum), and W (tungsten). Here, it is preferable that 0<x<1, 0<y<1, and 0.9≦a≦1.2, and more preferably 0.08≦y≦0.30. In general formula (1), the ratio of Pb:{( _{ZrxTi1 -x} ) _{1- yMy} }:O is 1:1:3 as a standard, but may deviate within a range in which a perovskite structure can be formed.

M may be a single element, such as V alone or Nb alone, or it 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 M is one of these elements, it can be combined with the A-site element Pb to achieve an extremely high piezoelectric constant.

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 the Zr:Ti (molar ratio) is near 52:48, and in the above general formula, the MPB composition or its vicinity is preferable. "At or near the MPB" refers to the region where a phase transition occurs when an electric field is applied to the piezoelectric film. Specifically, the Zr:Ti (molar ratio) is preferably in the range of 45:55 to 55:45, i.e., x = 0.45 to 0.55 in the above general formula (1).

The film thickness of the first piezoelectric film 14 and the second piezoelectric film 18 is preferably 0.1 μm or more and 5 μm or less, and more preferably 1 μm or more and less than 5 μm. The film thicknesses of the first piezoelectric film 14 and the second piezoelectric film 18 may be the same or different. It is preferable that the film thickness of the first piezoelectric film 14 and the second piezoelectric film 18 each be 2 μm or less.

As described above, the piezoelectric laminate 5 and piezoelectric element 1 of this embodiment comprise a lower electrode 12, a first piezoelectric film 14, an intermediate electrode 16, and a second piezoelectric film 18, arranged in this order on a substrate 10. The intermediate electrode 16 comprises a first layer 16a containing a metal phase MP and a metal oxide phase OP, and a second layer 16b which is a metal layer. The piezoelectric laminate 5 and piezoelectric element 1 of this configuration provide high adhesion to the intermediate electrode 16, resulting in a high delamination prevention effect. The metal phase MP of the first layer 16a and the second layer 16b, which is a metal layer, are both metal-to-metal, resulting in high adhesion. Furthermore, the mixture of the metal phase MP and the metal oxide phase OP in the first layer 16a significantly increases the interface area between the metal and the metal oxide, resulting in higher adhesion compared to a laminate structure of a metal layer and a metal oxide layer. This makes it less likely for delamination to occur even when the intermediate electrode is thick. Furthermore, contact between the first piezoelectric film 14 and the metal oxide phase OP in the first layer 16a suppresses oxygen migration from the first piezoelectric film 14 to the intermediate electrode 16, effectively preventing deterioration of the characteristics of the first piezoelectric film 14.

As described above, the piezoelectric stack 5 and piezoelectric element 1 of this embodiment have high adhesion and are less likely to peel, allowing the intermediate electrode 16 to be thicker than conventional ones. By making the intermediate electrode 16 thicker than 200 nm, and preferably 250 nm or thicker, the effects of variations in etching performed in the piezoelectric element manufacturing process can be reduced, and the reduction in yield that occurs due to variations in etching can be suppressed.

In the first layer 16a, if the elemental ratio α/O between the metal α and oxygen O, which are constituent elements of the first layer 16a, is greater than the elemental ratio between the metal α and oxygen O in the stoichiometric composition of the oxide of the metal α, then the metal phase MP will precipitate reliably, and phase separation between the metal phase MP and the metal oxide phase OP will be easily achieved.

If the metal α of the first layer 16a and the metal that makes up the second layer 16b are the same element, it is possible to simplify the manufacturing process and reduce manufacturing costs by simplifying the materials.

The intermediate electrode 16 of the piezoelectric stack 5 and the piezoelectric element 1 may have a third layer similar to the first layer 16a on the second piezoelectric film 18 side of the second layer 16b. Alternatively, a natural oxide film of the metal constituting the second layer 16b may be formed at the interface with the second piezoelectric film 18. If a layer containing oxygen is provided between the second piezoelectric film 18 and the second layer 16b, which is a metal layer, it is possible to prevent oxygen in the second piezoelectric film 18 from migrating to the intermediate electrode 16.

In this embodiment, the piezoelectric stack 5 and piezoelectric element 1 have been described as having a configuration in which two layers of piezoelectric films are stacked, but three or more layers of piezoelectric films may also be stacked by alternately stacking piezoelectric films and intermediate electrodes. When three or more layers of piezoelectric films are provided, it is preferable that all of the intermediate electrodes provided between the piezoelectric films be the intermediate electrodes 16 described in the above embodiment.

"Method of manufacturing a piezoelectric laminate"
A manufacturing method of one embodiment of the piezoelectric stack 5 includes the steps of forming the bottom electrode 12, the first piezoelectric film 14, the intermediate electrode 16, and the second piezoelectric film 18 on the substrate 10 by sputtering. In the step of forming the intermediate electrode 16, the first layer 16a is formed under conditions that cause phase separation between a metal phase MP and a metal oxide phase OP. Specifically, when an X-ray diffraction (XRD) profile is obtained for a sample in which the first layer 16a is formed on a silicon oxide film, the first layer 16a is formed under conditions that cause a ratio I _M /I _O of the intensity of the peak due to the metal contained in the first layer 16a to the intensity of the peak _{I O} due to the oxide of the metal contained in the first layer 16a (hereinafter referred to as the "peak intensity ratio I _M /I _O ") of 0.1 to 10. The second piezoelectric film 18 is formed at a temperature higher than the temperature at which the first layer 16 a and the second layer 16 b of the intermediate electrode 16 are formed.

The first layer 16a containing the metal α and oxygen can be deposited by using a metal target made of the metal α contained in the first layer 16a and supplying oxygen into the deposition atmosphere. The ratio of the metal α to oxygen in the first layer 16a can be adjusted by adjusting the deposition power and oxygen flow rate during deposition. According to the inventors' studies, when deposition is performed under deposition conditions such that the peak intensity ratio I _M /I _O is 0.1 to 10 as described above, the first layer 16a can be obtained in which a granular metal phase MP is precipitated in a metal oxide phase OP (see Examples below).

Specifically, the film formation conditions are determined as follows: Using the above-mentioned metal target, a plurality of samples are fabricated by varying the film formation power and oxygen flow rate (oxygen concentration) during sputtering on a thermal oxide film (silicon oxide film) of a silicon substrate with a thermal oxide film. An XRD profile is obtained for each sample, and the peak intensity ratio I _M /I _O is calculated. The film formation conditions for the sample among the plurality of samples that has a peak intensity ratio I _M /I _O of 0.1 to 10 are determined as the film formation conditions for the first layer 16a.

The XRD profile is obtained by the θ-2θ method, and the peak intensity ratio is calculated from the intensities of peaks observed in the diffraction angle 2θ range of 20° to 50°. The intensity I _M of the peak due to the metal contained in the first layer 16a is the sum of the intensities of the multiple peaks if there are multiple peaks due to the metal. Similarly, the intensity I _O of the peak due to the metal oxide is the sum of the intensities of the multiple peaks if there are multiple peaks due to the metal oxide. In calculating the peak intensity ratio I _M /I _O in this specification, if a peak that should appear in the XRD profile when a metal or metal oxide is present is not observed, the intensity of that peak is considered to be "1."

The method for manufacturing the piezoelectric element 1 includes the same method for manufacturing the piezoelectric stack 5 as above, but after depositing the second piezoelectric film 18, further includes a step of depositing the upper electrode 20 by sputtering.

As described above, in the method for manufacturing the piezoelectric laminate and piezoelectric element of this embodiment, the first layer 16a of the intermediate electrode 16 is formed under conditions such that, when an X-ray diffraction (XRD) profile is obtained for a sample in which the first layer 16a is formed on a silicon oxide film, the ratio I _M /I _O of the peak intensity I M due to the metal contained in the first layer 16a to _the peak intensity I _O due to the oxide of the metal contained in the first layer 16a is 0.1 to 10.

The film formation conditions under which the peak intensity ratio I _M /I _O is 0.1 to 10 are conditions under which the proportion of metal is higher than when a metal oxide film of stoichiometric composition is formed. In this embodiment, the first layer 16 a is formed under film formation conditions under which the proportion of metal is higher than the stoichiometric ratio of the metal oxide, so that the first layer 16 a including the metal phase MP and the metal oxide phase OP can be reliably obtained.

Specific examples and comparative examples of the piezoelectric laminate of the present disclosure are described below. Samples of the piezoelectric laminates of the examples and comparative examples were prepared and evaluated for adhesion. The configuration and manufacturing method of the piezoelectric laminates of the following samples will be described with reference to the reference numerals of the layers of the piezoelectric element 1 shown in Figure 1.

Samples 1 to 10 of piezoelectric stacks were fabricated, each having a lower electrode 12, a first piezoelectric film 14, an intermediate electrode 16 consisting of a first layer 16a and a second layer 16b, and a second piezoelectric film 18, arranged in that order on a substrate 10. A sputtering device was used to deposit each layer. For Samples 1 to 10, the deposition conditions for the first layer 16a of each intermediate electrode 16 were changed to vary the ratio of metal to oxygen in the first layer 16a. Samples 1 to 10 were fabricated using the same materials and under the same conditions, except for the first layer 16a.

"How to prepare a sample"
The method for preparing the sample will be described.

(Substrate with bottom electrode)
An electrode-equipped substrate was prepared, which had a lower electrode formed by sequentially laminating a 20 nm thick TiW film and a 230 nm thick Ir film on a substrate 10 made of a silicon wafer with a thermal oxide film.

(First piezoelectric film)
An Nb-doped PZT film with 12 at% Nb doping in the B site was formed on the lower electrode 12 as the first piezoelectric film 14. The thickness of the Nb-doped PZT film was 2 μm. The Nb-doped PZT was used as a target for sputtering. The Nb-doped PZT target had a Pb composition ratio a = 1.3 and a Zr/Ti molar ratio of MPB composition (Zr/Ti = 52/48).

The first piezoelectric film 14 was formed under the conditions of a degree of vacuum of 0.5 Pa, an atmosphere of a mixture of Ar and O ₂ (O ₂ volume fraction 2.5%), a substrate set temperature of 600° C., and a substrate bias voltage of +40V.

(Intermediate electrode)
The first and second layers 16a and 16b of the intermediate electrode 16 were sequentially formed by sputtering on the first piezoelectric film 14. The first layer 16a was a layer containing Ir and oxygen, i.e., an IrOx layer, and the second layer 16b was a metal layer composed of Ir, i.e., an Ir layer. The first and second layers 16a and 16b were sputtered using an Ir target. Oxygen was introduced into the deposition atmosphere during deposition of the first layer 16a. The vacuum level was set to 0.3 Pa. The first layer 16a was deposited in an Ar and _O2 mixed atmosphere, and the second layer 16b was deposited in an Ar atmosphere. The substrate temperature was set to room temperature. The thickness of the first layer 16a was 50 nm, and the thickness of the second layer 16b was 200 nm, resulting in an overall thickness of the intermediate electrode 16 of 250 nm.
The deposition power and oxygen concentration in the deposition atmosphere during deposition of the first layer 16a were varied for each sample. Table 1 shows the deposition power and oxygen concentration for each sample. The deposition power for sample 10 was used as the reference value, with samples 1 to 8 using deposition power five times the reference value, and sample 9 using deposition power three times the reference value. The Ar flow rate in the deposition atmosphere was set to 23 sccm, and the _O2 flow rate was varied between 15 and 46 ccm for each sample, thereby varying the oxygen concentration _O2 /(Ar+ _O2 ) in the deposition atmosphere for each sample. For example, for sample 1, the oxygen flow rate was 15 ccm, and the oxygen concentration was 39%.

Table 1 shows the results of XRD measurements of layers containing Ir and oxygen formed on silicon wafers with thermal oxide films under various deposition conditions for the first layer 16a for each of Samples No. 1 to 10, and the peak intensity ratios _I / _I calculated from the XRD profiles. In this example and comparative example, the peak intensity ratio _I / _I is the ratio of the peak intensity of Ir to the peak intensity of _IrO2 , and is hereinafter referred to as Ir/ _IrO2 . Table 1 also shows the measured values of the peak intensities of the (111) and (200) planes of Ir and the peak intensities of the (110), (101), and (200) planes of _IrO2 . Note that when no peak appears in the XRD profile, the peak intensity due to each plane is set to "1" for the convenience of calculating the intensity ratio.

As shown in Table 1, Samples No. 1 and 2 had only Ir peaks, and _no IrO2 peaks were observed. Samples Nos. 3 to 5 and 9 had both Ir and _IrO2 peaks, with the peak intensity ratio Ir/ _IrO2 ranging from 0.1 to 10. Samples Nos. 6 to 8 and 10 had only _IrO2 peaks, and no Ir peaks were observed.

(Second piezoelectric film)
A second piezoelectric film 18 was formed on the second layer 16b of the intermediate electrode 16. As the second piezoelectric film 18, an Nb-doped PZT film was formed, in which the amount of Nb doped in the B site was 12 at %, similar to the first piezoelectric film 14. The target and sputtering conditions were the same as those for the first piezoelectric film 14.

<Adhesion evaluation>
Each of Samples 1 to 10 was evaluated for adhesion (peeling prevention effect) of the piezoelectric laminate.
The adhesion evaluation was carried out in accordance with the procedures and evaluation methods described in ASTM (American Society for Testing and Materials) standard D3359-17, "Standard Test Method for Grading Adhesion by Tape Test." Adhesion is rated on a scale of 0B to 5B. Adhesion of 3B or higher is considered to be sufficient for practical use. The evaluation results are shown in Table 1.

<Observation of the first layer cross section>
The cross sections of the piezoelectric laminates of Samples 3 to 10 were observed using a scanning transmission electron microscope (STEM). Figure 2 shows cross-sectional STEM images of Sample 3, Figure 3 shows cross-sectional STEM images of Sample 9, Figure 4 shows cross-sectional STEM images of Sample 8, and Figure 5 shows cross-sectional STEM images of Sample 10. Samples 3 and 9 correspond to examples, while Samples 8 and 10 correspond to comparative examples. The cross-sectional STEM images show an intermediate electrode consisting of a first layer (IrOx layer in Figures 2 to 5) and a second layer (Ir layer in Figures 2 to 5) sandwiched between a first piezoelectric film (first PZT in Figures 2 to 5) and a second piezoelectric film (second PZT in Figures 2 to 5). In the cross-sectional STEM images, the IrOx layer of the intermediate electrode is gray, lighter than the PZT film overall, and the Ir layer is white. White granular portions are observed in the IrOx layer of Sample 3 (see Figure 2) and Sample 9 (see Figure 3). The white granular portions are the Ir phase (metal phase), and the light gray portions in the first layer are the IrO2 _phase (metal oxide phase).

Table 1 shows the film formation conditions for the first layer 16a of the intermediate electrode 16 and the evaluation results of the piezoelectric laminate.

As shown in Table 1, samples 3 to 5 and 9 are examples, and samples 1, 2, 6 to 8 and 10 are comparative examples.

All of the example samples with Ir/ _IrO2 peak intensity ratios in the range of 0.1 to 10 achieved adhesion of 3B or higher. Furthermore, as observed in the cross-sectional STEM images of Samples 3 and 9, a granular Ir phase, which is a metal layer MP, was precipitated in the _IrO2 phase, which is a metal oxide layer OP, in the first layer 16a. That is, the first layer 16a was phase-separated into a metal phase MP and a metal oxide phase OP. While STEM images have not been confirmed for Samples 1 and 2, only Ir peaks were observed, suggesting that the first layer 16a is composed almost entirely of Ir, and that an intermediate electrode 16 with an unclear interface between the first layer 16a and the second layer 16b was formed. On the other hand, in Samples 6-8 and 10, only _IrO2 peaks were observed, and as shown in the cross-sectional views of Samples 8 and 10, the first layer 16a is composed almost entirely of _IrO2 . In the cross-sectional views of Samples 8 and 10, white granular portions that appear to be Ir granules (Ir phase) are observed in some areas, but they are not formed over the entire area of the first layer 16a.

When the deposition power during deposition of the first layer 16a is the same as in Samples 1 to 8, the higher the oxygen concentration, the greater the amount of oxygen in the first layer 16a, making it easier to form _IrO2 , a metal oxide with a stoichiometric composition. Samples 3, 9, and 10 had the same oxygen concentration during deposition of the first layer 16a but different deposition powers. These evaluation results clearly show that changing the deposition power changes the ratio of Ir to oxygen.

The disclosure of Japanese Patent Application No. 2024-049356, filed on March 26, 2024, is incorporated herein by reference in its entirety.
All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

The following additional notes are further disclosed regarding the above embodiment.
<Appendix 1>
a lower electrode, a first piezoelectric film, an intermediate electrode, and a second piezoelectric film are provided on a substrate in this order;
the intermediate electrode includes a first layer disposed on the first piezoelectric film side and a second layer disposed on the second piezoelectric film side of the first layer;
the first layer includes a metal phase and a metal oxide phase including an oxide of a metal constituting the metal phase;
The second layer is a metal layer, a piezoelectric stack.
<Appendix 2>
2. The piezoelectric stack according to claim 1, wherein the element ratio of the metal and oxygen constituting the first layer is greater than the element ratio of the metal and oxygen in the stoichiometric composition of the metal oxide.
<Appendix 3>
3. The piezoelectric stack according to claim 1, wherein the metal in the first layer and the metal constituting the second layer are the same element.
<Appendix 4>
4. The piezoelectric stack of claim 3, wherein the element is a platinum group element.
<Appendix 5>
4. The piezoelectric stack of claim 3, wherein the element is iridium.
<Appendix 6>
6. The piezoelectric stack of claim 1, wherein the thickness of the intermediate electrode is greater than 200 nm.
<Appendix 7>
6. The piezoelectric stack according to claim 1, wherein the thickness of the intermediate electrode is 250 nm or more.
<Appendix 8>
8. The piezoelectric stack according to claim 1, wherein the first piezoelectric film and the second piezoelectric film are primarily composed of a lead-containing perovskite oxide.
<Appendix 9>
A piezoelectric laminate according to any one of Supplementary Note 1 to Supplementary Note 8;
and an upper electrode laminated on the second piezoelectric film of the piezoelectric laminate.
<Appendix 10>
A method for manufacturing a piezoelectric laminate according to any one of Supplementary Note 1 to Supplementary Note 8, comprising:
The method includes a step of depositing a lower electrode, a first piezoelectric film, an intermediate electrode, and a second piezoelectric film on a substrate by sputtering,
A method for manufacturing a piezoelectric laminate, wherein in a film formation step of an intermediate electrode, the first layer is formed under conditions such that in an X-ray diffraction profile obtained for a sample in which the first layer is formed on a silicon oxide film, the ratio of the intensity of a peak due to a metal contained in the first layer to the intensity of a peak due to an oxide of the metal contained in the first layer is 0.1 to 10.

Claims (10)

a lower electrode, a first piezoelectric film, an intermediate electrode, and a second piezoelectric film are provided on a substrate in this order;
the intermediate electrode includes a first layer disposed on the first piezoelectric film side and a second layer disposed on the second piezoelectric film side of the first layer,
the first layer includes a metal phase and a metal oxide phase including an oxide of a metal constituting the metal phase,
the second layer is a metal layer;
Piezoelectric stack. The piezoelectric stack of claim 1, wherein the elemental ratio of the metal and oxygen constituting the first layer is greater than the elemental ratio of the metal and oxygen in the stoichiometric composition of the metal oxide. The piezoelectric stack described in claim 1, wherein the metal in the first layer and the metal constituting the second layer are the same element. The piezoelectric stack of claim 3, wherein the same element is a platinum group element. The piezoelectric stack of claim 3, wherein the same element is iridium. The piezoelectric stack described in any one of claims 1 to 5, wherein the thickness of the intermediate electrode is greater than 200 nm. The piezoelectric stack described in any one of claims 1 to 5, wherein the thickness of the intermediate electrode is 250 nm or more. The piezoelectric stack described in any one of claims 1 to 5, wherein the first piezoelectric film and the second piezoelectric film are primarily composed of lead-containing perovskite oxide. The piezoelectric laminate according to any one of claims 1 to 5;
an upper electrode laminated on the second piezoelectric film of the piezoelectric laminate. 2. A method for manufacturing a piezoelectric laminate according to claim 1, comprising the steps of:
forming the lower electrode, the first piezoelectric film, the intermediate electrode, and the second piezoelectric film on the substrate by sputtering,
a method for manufacturing a piezoelectric laminate, wherein in the step of forming the intermediate electrode, the first layer is formed under conditions in which, in an X-ray diffraction profile obtained for a sample in which the first layer is formed on a silicon oxide film, the ratio of the intensity of a peak due to a metal contained in the first layer to the intensity of a peak due to an oxide of the metal contained in the first layer is 0.1 to 10.