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

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

[0001] The present disclosure relates to a piezoelectric stack, a piezoelectric element, and a method for manufacturing a piezoelectric stack.

[0002] Lead zirconate titanate (Pb(Zr,Ti)O) is a material with excellent piezoelectric and ferroelectric properties. ３ Perovskite oxides such as PZT (Piezoelectric Crystalline Zinc Oxide, hereafter referred to as PZT) are known. Piezoelectric materials 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 have been applied to 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.

[0003] As a piezoelectric element, a laminated piezoelectric element in which a plurality of piezoelectric films are laminated with electrodes interposed therebetween has been proposed in order to obtain higher response (Japanese Patent Laid-Open Nos. 2013-080886 and 2013-080887, etc.).

[0004] In a laminated piezoelectric element obtained by forming a piezoelectric film and an electrode by sputtering, peeling may occur at or near the interface between the laminated piezoelectric film and the intermediate electrode during the process of stacking on a wafer and during long-term use. JP 2013-080886 A describes that peeling occurs when the thickness of the intermediate electrode is 250 nm or more, and that the thickness of the intermediate electrode is preferably 200 nm or less.

[0005] The inventors are considering increasing the thickness of the intermediate electrode to accommodate variations in etching during the manufacturing process of piezoelectric elements, which requires a highly adhesive laminate structure that can provide a greater effect in preventing peeling than conventional structures.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide a highly adhesive piezoelectric laminate, a piezoelectric element, and a method for manufacturing a piezoelectric laminate that can achieve a higher peel-suppression effect than conventional methods.

[0007] The piezoelectric laminate of the present disclosure comprises a lower electrode, a first piezoelectric film, an intermediate electrode, and a second piezoelectric film, in this order, on a substrate; the intermediate electrode comprises a first layer arranged on the first piezoelectric film side and a second layer arranged on the second piezoelectric film side of the first layer; the first layer includes a metal phase and a metal oxide phase consisting of an oxide of the metal that constitutes the metal phase; and the second layer is a metal layer.

[0008] In the piezoelectric laminate of the present disclosure, the element ratio between the metal and oxygen constituting the first layer is preferably greater than the element ratio between the metal and oxygen in the stoichiometric composition of the metal oxide.

[0009] In the piezoelectric laminate of the present disclosure, the metal in the first layer and the metal constituting the second layer are preferably the same element.

[0010] When the metal in the first layer and the metal constituting the second layer are the same element, the same element is preferably a platinum group element.

[0011] When the metal in the first layer and the metal constituting the second layer are the same element, that same element is preferably iridium.

[0012] The thickness of the intermediate electrode is preferably greater than 200 nm.

[0013] The thickness of the intermediate electrode is preferably 250 nm or more.

[0014] The first and second piezoelectric films preferably contain lead-containing perovskite oxide as a main component.

[0015] The piezoelectric element of the present disclosure includes the piezoelectric laminate of the present disclosure and an upper electrode laminated on the second piezoelectric film of the piezoelectric laminate.

[0016] The method for manufacturing a piezoelectric laminate according to the present disclosure includes the steps of depositing a lower electrode, a first piezoelectric film, an intermediate electrode, and a second piezoelectric film on a substrate by sputtering, and in the step of depositing the intermediate electrode, the first layer is deposited under conditions such that, in an X-ray diffraction profile obtained for a sample in which the first layer is deposited 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 an oxide of the metal contained in the first layer is 0.1 to 10.

[0017] According to the technology of the present disclosure, it is possible to obtain a piezoelectric laminate, a piezoelectric element, and a method for manufacturing a piezoelectric laminate, which have high adhesion and are capable of suppressing peeling to a greater extent than conventional methods.

[0018] 1 is a cross-sectional schematic diagram of a piezoelectric element; 2 is a cross-sectional STEM image of Sample 3; 3 is a cross-sectional STEM image of Sample 9; 4 is a cross-sectional STEM image of Sample 8; 5 is a cross-sectional STEM image of Sample 10;

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the thicknesses and ratios of each layer 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 the upper and lower limits. In the numerical ranges described in stages in this disclosure, 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.

[0020] Fig. 1 is a cross-sectional schematic diagram showing the layer configuration of a piezoelectric laminate 5 and a piezoelectric element 1 according to one embodiment. As shown in Fig. 1, the piezoelectric element 1 includes a piezoelectric laminate 5 and an upper electrode 20. The piezoelectric laminate 5 includes a substrate 10 and a lower electrode 12, a first piezoelectric film 14, an intermediate electrode 16, and a second piezoelectric film 18, which are laminated in this order on the substrate 10. 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, with the first piezoelectric film 14, intermediate electrode 16, and second piezoelectric film 18 sandwiched therebetween, is simply referred to as the lower electrode 12, and the electrode located on the opposite side from the substrate 10 is simply referred to as the upper electrode 20.

[0021] The substrate 10 is not particularly limited, and examples thereof include substrates of silicon, glass, stainless steel, yttrium-stabilized zirconia, alumina, sapphire, silicon carbide, etc. The substrate 10 may be a laminated substrate in which a thermally oxidized silicon film is formed on the surface of a silicon substrate.

[0022] The lower electrode 12 and the intermediate electrode 16 form a pair to apply a voltage to the first piezoelectric film 14. The intermediate electrode 16 and the upper electrode 20 form a pair to apply a voltage to the second piezoelectric film 18.

[0023] There are no particular limitations on the materials that make up the lower electrode 12 and the upper electrode 20, 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. Also, ITO (indium tin oxide) and the like may be used. Also, ITO (indium tin oxide), LaNiO ３ , and SrRuO ３ The lower electrode 12 and the upper electrode 20 may be a single layer or may have a multi-layer structure. When the lower electrode 12 has a multi-layer structure, in addition to the conductive layer made of the above materials, Ti, TiW or ZrO may be used on the substrate 10 side. ２ It is also preferable to have a structure including an adhesive layer such as the above.

[0024] There are no particular limitations on the thickness of the lower electrode 12 and the upper electrode 20, but it is preferably about 50 nm to 300 nm, and more preferably 100 nm to 300 nm.

[0025] The intermediate electrode 16 includes a first layer 16a disposed on the first piezoelectric film 14 side and a second layer 16b disposed on the second piezoelectric film 18 side of the first layer 16a. The first layer 16a includes a metal phase MP and a metal oxide phase OP made of an oxide of the metal α that constitutes the metal phase MP. The second layer 16b is a metal layer.

[0026] 1, the first layer 16a includes a plurality of metal phases MP and metal oxide phases OP, and the metal phases MP and the metal oxide phases OP are arranged in a jumble throughout the entire region of the first layer 16a. More specifically, the metal oxide phases OP are formed throughout the entire region of the first layer 16a, and a plurality of granular metal phases MP are precipitated throughout the entire region of the metal oxide phases OP. The particle diameter of the granular metal phases MP is, for example, several nanometers to several tens of nanometers.

[0027] The first layer 16a is a layer containing metal α and oxygen O. It is desirable that the element ratio α / O between the metal α and oxygen O, which are constituent elements of the first layer 16a, is larger than the element ratio between the metal α and oxygen O in the stoichiometric composition of the oxide of the metal α. For example, when the metal is Ir (iridium), the stoichiometric composition of iridium oxide is IrO. ２ In this case, the ratio Ir / O of iridium Ir to oxygen O is 0.5. In this case, it is desirable that the ratio of Ir to O in the first layer 16a is greater than 0.5, i.e., Ir / O>0.5. It is more preferable that the ratio of metal α to oxygen O in the first layer 16a is α / O≧2, and even more preferably α / O≧5. It is preferable that α / O≦10.

[0028] The element ratio in the first layer 16 a can be measured by, for example, X-ray photoelectron spectroscopy (XPS). In this specification, XPS measurement is performed while etching is performed in the depth direction (thickness direction) by Ar sputtering, thereby measuring the concentration (Atomic %) profile of metal α and oxygen O in the depth direction, and determining the element ratio α / O of metal α and oxygen O in the portion corresponding to the first layer 16 a.

[0029] 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.

[0030] Examples of the metal α of the first layer 16a and the metal of the second layer 16b include 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 it is particularly preferable that the metal α be Ir.

[0031] 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 multi-layer structure, the thickness of the intermediate electrode 16 refers to the total thickness of all layers. When the intermediate electrode 16 is composed 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 the ratio of the thickness of the first layer 16a to the thickness of the second layer 16b is preferably approximately 1:2 to 1:7.

[0032] In this specification, the thickness of the intermediate electrode 16 is measured as follows: A sample surface is coated with C (carbon) and Pt (platinum), and the cross section is processed with a focused ion beam (FIB), and then the cross section is observed with 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.

[0033] The first piezoelectric film 14 and the second piezoelectric film 18 are not particularly limited, but each may be formed of a material having the general formula ABO ３Preferably, the piezoelectric film 14 and the second piezoelectric film 18 are primarily composed of a perovskite oxide represented by the formula (1). In this specification, "primary component" refers to a component that accounts for 80 mol % or more. Preferably, the first piezoelectric film 14 and the second piezoelectric film 18 each comprise a perovskite oxide that accounts for 90 mol % or more, and more preferably, the first piezoelectric film 14 and the second piezoelectric film 18 are composed of a perovskite oxide (however, containing inevitable impurities). The perovskite oxide that is the primary component of the first piezoelectric film 14 and the perovskite oxide that is the primary component of the second piezoelectric film 18 may be composed of different constituent elements, or may comprise the same constituent elements. However, from the perspective of cost reduction, it is preferable that the perovskite oxides of the first piezoelectric film 14 and the second piezoelectric film 18 have the same constituent elements. Note that "having the same constituent elements" means that the elements contained are the same, but the composition ratios may be different.

[0034] The perovskite oxide is preferably a lead zirconate titanate (PZT) oxide containing Pb (lead), Zr (zirconium), Ti (titanium) and O (oxygen).

[0035] In particular, a compound represented by the following general formula (1) containing an additive M at the B site of PZT is preferred. 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 the general formula (1), Pb:{(Zr ｘ Ti 1-ｘ ) 1-ｙ M ｙ}:O is based on a ratio of 1:1:3, but may deviate within a range in which a perovskite structure can be formed.

[0036] 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 M is one of these elements, a very high piezoelectric constant can be achieved in combination with the A-site element Pb.

[0037] It is said that PZT-based perovskite oxides exhibit high piezoelectric properties at or near the morphotropic phase boundary (MPB). The MPB composition is near a Zr:Ti (molar ratio) of 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).

[0038] The 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 thicknesses of the first piezoelectric film 14 and the second piezoelectric film 18 may be the same or different. The thickness of each of the first piezoelectric film 14 and the second piezoelectric film 18 is preferably 2 μm or less.

[0039] As described above, the piezoelectric stack 5 and piezoelectric element 1 of this embodiment include a substrate 10 on which a lower electrode 12, a first piezoelectric film 14, an intermediate electrode 16, and a second piezoelectric film 18 are arranged in this order. The intermediate electrode 16 includes a first layer 16a containing a metal phase MP and a metal oxide phase OP, and a second layer 16b that is a metal layer. The piezoelectric stack 5 and piezoelectric element 1 of this configuration provide high adhesion of the intermediate electrode 16, resulting in a high delamination suppression effect. The metal phase MP of the first layer 16a and the second layer 16b, which is a metal layer, are both metal-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 interfacial area between the metal and the metal oxide, thereby achieving higher adhesion compared to a laminate structure consisting of a metal layer and a metal oxide layer. This reduces the likelihood of delamination 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 can suppress 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.

[0040] As described above, the piezoelectric stack 5 and piezoelectric element 1 of this embodiment have high adhesion and are prevented from peeling, so that the intermediate electrode 16 can be made thicker than conventional ones. By making the intermediate electrode 16 thicker than 200 nm, preferably 250 nm or thicker, the influence of variations in etching performed in the manufacturing process of the piezoelectric element can be suppressed, and the reduction in yield caused by variations in etching can be suppressed.

[0041] In the first layer 16a, if the element ratio α / O between the metal α, which is a constituent element of the first layer 16a, and oxygen O is larger than the element ratio between the metal α and oxygen O in the stoichiometric composition of the oxide of the metal α, the metal phase MP is reliably precipitated, and phase separation into the metal phase MP and the metal oxide phase OP is easily achieved.

[0042] If the metal α of the first layer 16a and the metal constituting the second layer 16b are the same element, the manufacturing process can be simplified and the manufacturing costs can be reduced by simplifying the materials.

[0043] 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 layer 16b facing the second piezoelectric film 18. 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.

[0044] In this embodiment, the piezoelectric laminate 5 and the piezoelectric element 1 are described as having two layers of piezoelectric films stacked together, but three or more layers of piezoelectric films may be stacked together 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.

[0045] "Method for Manufacturing Piezoelectric Stack" A method for manufacturing an 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 intensity I of the peak due to the metal contained in the first layer 16a is Ｍ and peak I due to the oxide of the metal contained in the first layer 16a. Ｏ The ratio of the intensity of I Ｍ / I Ｏ (Hereinafter, "peak intensity ratio I Ｍ / I Ｏ The second piezoelectric film 18 is formed under conditions that result in the first layer 16a having a value of 0.1 to 10. The film formation temperature during film formation is set to a higher temperature than the film formation temperatures for the first layer 16a and the second layer 16b of the intermediate electrode 16.

[0046] By using a metal target made of the metal α contained in the first layer 16a and supplying oxygen into the film formation atmosphere, the first layer 16a containing the metal α and oxygen can be formed. By adjusting the film formation power and oxygen flow rate during this film formation, the ratio of the metal α to oxygen in the first layer 16a can be adjusted. According to the study by the present inventors, as described above, the peak intensity ratio I Ｍ / I Ｏ When the film is formed under film formation conditions in which the ratio of the metal phase MP to the granular metal phase MP is 0.1 to 10, the first layer 16a can be obtained in which the granular metal phase MP is precipitated in the metal oxide phase OP (see Examples below).

[0047] Specifically, the film formation conditions are determined as follows: Using the above-mentioned metal target, a plurality of samples are prepared by forming a film on a thermal oxide film (silicon oxide film) of a silicon substrate with a thermal oxide film by changing the film formation power and oxygen flow rate (oxygen concentration) during sputtering. An XRD profile is obtained for each sample, and the peak intensity ratio I Ｍ / I Ｏ Calculate the peak intensity ratio I Ｍ / I Ｏ The film formation conditions for the samples where the value is 0.1 to 10 are defined as the film formation conditions for the first layer 16a.

[0048] 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°. Ｍ When there are multiple peaks due to the metal, the intensity I is the sum of the multiple peak intensities. Similarly, the intensity I of the peak due to the metal oxide is Ｏ When there are multiple peaks due to metal oxides, the peak intensity ratio I is the sum of the multiple peak intensities. Ｍ / I Ｏ In calculating the intensity of a peak, 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."

[0049] The method for manufacturing the piezoelectric element 1 includes the same method for manufacturing the piezoelectric laminate 5 as above, but further includes a step of forming the upper electrode 20 by sputtering after forming the second piezoelectric film 18 .

[0050] As described above, in the method for manufacturing the piezoelectric laminate and the piezoelectric element according to this embodiment, when an X-ray diffraction (XRD) profile is obtained for a sample in which the first layer 16 a of the intermediate electrode 16 is formed on a silicon oxide film, the intensity I of the peak due to the metal contained in the first layer 16 a is Ｍ and the intensity I of the peak due to the oxide of the metal contained in the first layer 16a. Ｏ Relative to I Ｍ / I Ｏ The film is formed under conditions that result in the first layer 16a having a value of 0.1 to 10.

[0051] The above-mentioned peak intensity ratio I Ｍ / I Ｏ The film formation conditions under which the ratio of metal 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 16a 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 16a including the metal phase MP and the metal oxide phase OP can be reliably obtained.

[0052] Specific examples and comparative examples of the piezoelectric laminate of the present disclosure will be described below. Samples of the piezoelectric laminates of the examples and comparative examples were prepared and evaluated for adhesion. The configurations and manufacturing methods 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 FIG.

[0053] Samples 1 to 10 of piezoelectric laminates 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 this 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 formed using the same materials and under the same conditions, except for the first layer 16a.

[0054] "Method of Preparing Samples" The method of preparing samples will be explained.

[0055] (Substrate with Lower Electrode) A substrate with an electrode was prepared, which was provided with 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.

[0056] (First Piezoelectric Film) An Nb-doped PZT film with 12 at% Nb doping to 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).

[0057] The first piezoelectric film 14 is formed in a vacuum of 0.5 Pa with Ar and O ２ Mixed atmosphere (O ２ The film was formed under the conditions of a volume fraction of 2.5%, a substrate set temperature of 600° C., and a substrate bias voltage of +40V.

[0058] (Intermediate Electrode) The first layer 16a and second layer 16b of the intermediate electrode 16 were successively formed on the first piezoelectric film 14 by sputtering. 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 made of Ir, i.e., an Ir layer. The first layer 16a and the second layer 16b were formed by sputtering using an Ir target. Oxygen was introduced into the film formation atmosphere when the first layer 16a was formed. The degree of vacuum was set to 0.3 Pa, and the first layer 16a was formed using Ar and O. ２ The deposition of the first layer 16a was performed in a mixed atmosphere, and the deposition of the second layer 16b was performed in an Ar atmosphere. The substrate temperature was set to room temperature. The thickness of the first layer 16a was 50 nm, the thickness of the second layer 16b was 200 nm, and the overall thickness of the intermediate electrode 16 was 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 set to a reference value, and the deposition power for samples 1 to 8 was set to five times the reference value, and for sample 9 it was set to three times the reference value. The Ar flow rate in the deposition atmosphere was set to 23 sccm, and the O ２The oxygen concentration O in the film formation atmosphere of each sample was adjusted by changing the flow rate between 15 and 46 ccm. ２ / (Ar + O ２ For example, in the case of Sample 1, the oxygen flow rate was set to 15 ccm and the oxygen concentration was set to 39%.

[0059] Table 1 shows the XRD measurement results of the layers containing Ir and oxygen formed on the silicon wafers with thermal oxide films under the respective film formation conditions of the first layer 16a for each of Samples No. 1 to 10, and the peak intensity ratios I Ｍ / I Ｏ In the present example and the comparative example, the peak intensity ratio I Ｍ / I Ｏ is the peak intensity of Ir and IrO ２ Hereinafter, Ir / IrO ２ Table 1 shows the peak intensities of the (111) and (200) planes of Ir and the ２ The measured values ​​of the peak intensities of the (110), (101), and (200) planes are shown. Regarding the peak intensity of each plane, if a peak does not appear in the XRD profile, the intensity was set to "1" for the convenience of calculating the intensity ratio.

[0060] As shown in Table 1, samples 1 and 2 only had peaks of Ir, and IrO ２ No peak was observed. Samples No. 3 to 5 and 9 were composed of Ir and IrO ２ Both peaks were observed, and the peak intensity ratio Ir / IrO ２ The range of the porosity was 0.1 to 10. Samples Nos. 6 to 8 and 10 were IrO ２ Only the peak of Ir was observed, and no peak of Ir was observed.

[0061] (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 into 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.

[0062] <Adhesion Evaluation> The adhesion (peeling prevention effect) of the piezoelectric laminate was evaluated for each of Samples 1 to 10. The adhesion evaluation was carried out in accordance with the procedures and evaluation method 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.

[0063] <Observation of the Cross Section of the First Layer> 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 overall, lighter than the PZT film, 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 parts are the Ir phase (metallic phase), and the light gray parts in the first layer are IrO ２ phase (metal oxide phase).

[0064] 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.

[0065] 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.

[0066] Ir / IrO ２In the samples of the example having a peak intensity ratio in the range of 0.1 to 10, adhesion of 3B or more was obtained. As observed in the cross-sectional STEM images of Samples 3 and 9, in these samples, the IrO ２ In the sample 1, the Ir phase, which is a granular metal layer MP, was precipitated in the IrO phase. That is, the first layer 16a was separated into a metal phase MP and a metal oxide phase OP. Although the STEM images of Samples 1 and 2 have not been confirmed, since only the Ir peak was observed, it is expected that the first layer 16a is composed almost entirely of Ir, and an intermediate electrode 16 is formed in which the interface between the first layer 16a and the second layer 16b is not clear. On the other hand, in Samples 6-8 and 10, the IrO ２ As shown in the cross-sectional views of Samples 8 and 10, the first layer 16a is composed of almost IrO. ２ 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.

[0067] When the film-forming power during film formation of the first layer 16a is the same as in samples 1 to 8, the amount of oxygen in the first layer 16a increases as the oxygen concentration increases, and the amount of IrO, a metal oxide with a stoichiometric composition, decreases. ２ The first layer 16a was formed using the same oxygen concentration but different deposition power in samples 3, 9, and 10. These evaluation results clearly show that the ratio of Ir to oxygen changes when the deposition power is changed.

[0068] The disclosure of Japanese Patent Application No. 2024-049356, filed on March 26, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

[0069] The following supplementary notes are further disclosed regarding the above embodiments. <Supplementary Note 1> A piezoelectric stack comprising a substrate, a lower electrode, a first piezoelectric film, an intermediate electrode, and a second piezoelectric film, in this order; the intermediate electrode comprising 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 including a metal phase and a metal oxide phase including an oxide of the metal constituting the metal phase; and the second layer being a metal layer. <Supplementary Note 2> The piezoelectric stack according to Supplementary Note 1, wherein the elemental ratio of metal constituting the first layer to oxygen is greater than the elemental ratio of metal to oxygen in the stoichiometric composition of the metal oxide. <Supplementary Note 3> The piezoelectric stack according to Supplementary Note 1 or Supplementary Note 2, wherein the metal in the first layer and the metal constituting the second layer are the same element. <Supplementary Note 4> The piezoelectric stack according to Supplementary Note 3, wherein the same element is a platinum group element. <Supplementary Note 5> The piezoelectric stack according to Supplementary Note 3, wherein the same element is iridium. <Appendix 6> The piezoelectric stack according to any one of Appendices 1 to 5, wherein the thickness of the intermediate electrode exceeds 200 nm. <Appendix 7> The piezoelectric stack according to any one of Appendices 1 to 5, wherein the thickness of the intermediate electrode is 250 nm or more. <Appendix 8> The piezoelectric stack according to any one of Appendices 1 to 7, wherein the first piezoelectric film and the second piezoelectric film are mainly composed of a lead-containing perovskite oxide. <Appendix 9> A piezoelectric element comprising the piezoelectric stack according to any one of Appendices 1 to 8, and an upper electrode laminated on the second piezoelectric film of the piezoelectric stack. <Supplementary Note 10> A method for manufacturing a piezoelectric stack according to any one of Supplementary Note 1 to Supplementary Note 8, comprising the steps of depositing a lower electrode, a first piezoelectric film, an intermediate electrode, and a second piezoelectric film on a substrate by sputtering, wherein in the step of depositing the intermediate electrode, the first layer is deposited under conditions such that, in an X-ray diffraction profile obtained for a sample in which the first layer is deposited 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

1. A piezoelectric laminate comprising a substrate and, in this order, a lower electrode, a first piezoelectric film, an intermediate electrode, and a second piezoelectric film, wherein the intermediate electrode comprises 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, wherein the first layer includes a metal phase and a metal oxide phase consisting of an oxide of the metal that constitutes the metal phase, and the second layer is a metal layer.

2. The piezoelectric stack according to claim 1, wherein the elemental ratio of the metal constituting the first layer to oxygen is greater than the elemental ratio of the metal to oxygen in the stoichiometric composition of the oxide of the metal.

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.

4. The piezoelectric stack of claim 3, wherein said same element is a platinum group element.

5. The piezoelectric stack of claim 3, wherein said same element is iridium.

6. The piezoelectric stack according to any one of claims 1 to 5, wherein the thickness of the intermediate electrode is greater than 200 nm.

7. The piezoelectric stack according to any one of claims 1 to 5, wherein the thickness of the intermediate electrode is 250 nm or more.

8. The piezoelectric stack according to 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.

9. A piezoelectric element comprising: a piezoelectric laminate according to any one of claims 1 to 5; and an upper electrode laminated on the second piezoelectric film of the piezoelectric laminate.

10. A method for manufacturing a piezoelectric laminate as recited in claim 1, comprising the steps of depositing the lower electrode, the first piezoelectric film, the intermediate electrode, and the second piezoelectric film on the substrate by sputtering, and in the step of depositing the intermediate electrode, depositing the first layer is carried out under conditions such that in an X-ray diffraction profile obtained for a sample in which the first layer is deposited 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.

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