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

Abstract

The present invention addresses the problem of providing: a piezoelectric laminate including a piezoelectric thin film having improved piezoelectric performance; a piezoelectric element; and a method for manufacturing the piezoelectric laminate. The piezoelectric laminate includes: a substrate; and a laminated film provided on at least one surface of the substrate, wherein the laminated film includes, in order from the substrate side, an electrode layer, an underlayer, and a piezoelectric thin film. The underlayer and the piezoelectric thin film are in contact with each other, the underlayer contains a nitrogen compound including at least one element selected from the group consisting of group III to VI elements, and the absolute value |e31 f| of the piezoelectric constant of the piezoelectric thin film is 0.5 C / m2 or more.

Description

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

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

[0002] In recent years, microelectromechanical systems (MEMS) have been attracting attention. MEMS are devices in which mechanical components and electronic circuits are integrated on a single substrate using microfabrication technology. MEMS, which have functions such as sensors, filters, harvesters, and actuators, utilize piezoelectric laminates or piezoelectric elements having such piezoelectric laminates.

[0003] A piezoelectric laminate is formed by providing a thin film (hereinafter also referred to as a piezoelectric thin film) made of an oriented substance (e.g., aluminum nitride) on a substrate such as silicon (Si), sapphire, glass, etc. The oriented piezoelectric thin film has piezoelectric and pyroelectric properties, and is used as a component of piezoelectric thin film resonators, MEMS, sensors, etc.

[0004] In order to improve the piezoelectric performance of a piezoelectric thin film, it is important to have a highly oriented piezoelectric film and to align the polarity of the outermost layer. However, the polarity of the piezoelectric thin film is affected by its base (e.g., substrate or electrode layer) and film formation conditions (Non-Patent Documents 1 to 3).

[0005] Regarding the control of the polarity of a piezoelectric thin film, Patent Document 1 describes that good piezoelectricity can be maintained if the piezoelectric thin film is formed so that the dipole orientation, which is the proportion of crystal pillars forming electric dipoles in the thin film surface that have positive or negative polarities in the same direction, is 75% or more. Patent Document 1 also describes that the dipole orientation of the piezoelectric thin film layer can be increased by providing an underlayer on the substrate that has the function of aligning the dipole orientation of the crystals in the piezoelectric layer, and then setting the substrate temperature, substrate-target distance, and gas pressure to optimal values ​​during the formation of the piezoelectric thin film layer.

[0006] Patent Document 2 describes that in order to obtain effective piezoelectric properties in a compound with a wurtzite structure, it is necessary to align not only the crystal orientation but also the direction of spontaneous polarization of each crystal grain in a certain direction. Patent Document 2 also describes that in the case of a compound with a wurtzite structure, control of the polarization direction must be performed simultaneously with the production thereof, and that the film formation conditions must be optimized.

[0007] Patent Document 3 describes a piezoelectric thin film resonator that includes a substrate, a pair of electrodes arranged along the substrate, and a piezoelectric thin film sandwiched between the pair of electrodes, one of the electrodes including a first conductive layer and a polarity control layer arranged between the first conductive layer and the piezoelectric thin film and made of a metal having a lower standard unipolar potential than the first conductive layer, the polarity control layer having an oxide film on the piezoelectric thin film side. Patent Document 3 also describes that the polarity control layer can align the polarity direction of the piezoelectric thin film to improve piezoelectricity, and that the piezoelectric thin film is preferably an AlN film.

[0008] Japanese Patent Publication No. 2004-184274 Japanese Patent Publication No. 2004-346335 Japanese Patent Publication No. 2006-174148

[0009] Journal of Applied Physics, 2013, 113 (8) Applied Physics Letters, 2008, 93, 021903Applied Physics Letters, 2007, 90(15), 151910

[0010] As described above, Patent Documents 1 and 2 state that the conditions for forming the piezoelectric thin film must be optimized to control the polarity of the piezoelectric thin film. However, it is believed that the optimal conditions for forming the piezoelectric thin film differ depending on the apparatus used, and it is expected that the piezoelectric performance will be unstable due to deviations in the apparatus or conditions during continuous film formation.

[0011] Furthermore, as described in Patent Document 3, if an oxide film is placed on the AlN film side, which is a piezoelectric thin film, as a polarity control layer, there is a concern that the polarity of the AlN will change due to contact between the AlN, which is a nitride, and the oxide, resulting in a deterioration in piezoelectric performance.

[0012] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a piezoelectric laminate including a piezoelectric thin film with improved piezoelectric performance, a piezoelectric element, and a method for manufacturing the piezoelectric laminate.

[0013] The inventors have discovered that the above-mentioned problems can be solved by providing an underlayer containing a nitrogen compound including at least one element selected from the group consisting of Group III to VI elements between the piezoelectric thin film and the substrate, and have thus completed the present invention.

[0014] That is, one embodiment of the present invention relates to the following: 1. A piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, wherein the laminate film includes, in order from the substrate side, an electrode layer, an underlayer, and a piezoelectric thin film, the underlayer and the piezoelectric thin film are in contact with each other, the underlayer contains a nitrogen compound containing at least one element selected from the group consisting of III to VI elements, and the absolute value of the piezoelectric constant |e ３１ ｆ | is 0.5 C / m ２A piezoelectric laminate as described above. 2. A piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, wherein the laminate film includes, in order from the substrate side, an electrode layer, an underlayer, and a piezoelectric thin film, wherein the underlayer and the piezoelectric thin film are in contact, and the underlayer contains a nitrogen compound, wherein the nitrogen compound contains at least one element selected from the group consisting of Group III to VI elements, excluding zirconium nitride. 3. The piezoelectric laminate as described above in 1 or 2, wherein the piezoelectric thin film contains aluminum nitride, and the aluminum nitride has a hexagonal wurtzite structure oriented in the c-axis direction. 4. The piezoelectric laminate as described above in 1 or 2, wherein the underlayer has a sodium chloride structure, a fluorite structure, or a perovskite structure. 5. The piezoelectric laminate as described above in 1 or 2, wherein the underlayer has a (111) plane preferred orientation structure that is preferentially oriented in the (111) plane direction. 6. 3. The piezoelectric stack according to 1 or 2 above, wherein the underlayer is a nitrogen compound containing at least one selected from Zr, Hf, Y, W, and Nb. 7. The piezoelectric stack according to 1 or 2 above, wherein the underlayer has a thickness of 0.2 nm or more and 100 nm or less. 8. The piezoelectric stack according to 7 above, wherein the underlayer has a thickness of 5 nm or more and 70 nm or less. 9. The piezoelectric stack according to 1 or 2 above, wherein the piezoelectric thin film has a thickness of 100 nm or more and 10 μm or less. 10. A piezoelectric element having the piezoelectric stack according to 1 or 2 above. 11. A method for manufacturing a piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, the method comprising: preparing the substrate; and depositing an electrode layer, an underlayer, and a piezoelectric thin film in this order on at least one surface of the substrate, wherein the underlayer contains a nitrogen compound containing at least one element selected from the group consisting of III to VI groups, the piezoelectric thin film is deposited so as to be in contact with the underlayer, and an absolute value of the piezoelectric constant |e of the piezoelectric thin film is ３１ ｆ | is 0.5 C / m ２12. A method for manufacturing a piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, comprising: preparing the substrate; and depositing an electrode layer, an underlayer, and a piezoelectric thin film in this order on at least one surface of the substrate, wherein the underlayer contains a nitrogen compound, the nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements, excluding zirconium nitride, and the piezoelectric thin film is deposited so as to be in contact with the underlayer. 13. The method for manufacturing a piezoelectric laminate according to 11 or 12 above, wherein the deposition is performed by sputtering.

[0015] According to the piezoelectric laminate of the present invention, the piezoelectric performance can be improved by providing an underlayer containing a nitrogen compound including at least one element selected from the group consisting of Group III to VI elements between the piezoelectric thin film and the substrate.

[0016] 1 and 2 are schematic cross-sectional views of a piezoelectric laminate according to an embodiment of the present invention.

[0017] The present invention will be described below with reference to embodiments. However, the present invention includes many different aspects and should not be construed as being limited to the embodiments exemplified below.

[0018] A first embodiment of the present invention is a piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, the laminate film including, in order from the substrate side, an electrode layer, an underlayer, and a piezoelectric thin film, the underlayer and the piezoelectric thin film are in contact with each other, the underlayer contains a nitrogen compound containing at least one element selected from the group consisting of III to VI elements, and the absolute value of the piezoelectric constant |e ３１ ｆ | is 0.5 C / m ２ This completes the piezoelectric laminate.

[0019] A second embodiment of the present invention is a piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, the laminate film including, in order from the substrate side, an electrode layer, an underlayer, and a piezoelectric thin film, the underlayer and the piezoelectric thin film being in contact with each other, the underlayer containing a nitrogen compound, the nitrogen compound containing at least one element selected from the group consisting of group III to VI elements, excluding zirconium nitride.

[0020] A third embodiment of the present invention is a method for manufacturing a piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, the method including preparing the substrate, and depositing an electrode layer, an underlayer, and a piezoelectric thin film in this order on at least one surface of the substrate, wherein the underlayer contains a nitrogen compound containing at least one element selected from the group consisting of III to VI groups, the piezoelectric thin film is deposited so as to be in contact with the underlayer, and the absolute value of the piezoelectric constant |e ３１ ｆ | is 0.5 C / m ２ This completes the method for manufacturing the piezoelectric laminate.

[0021] A fourth embodiment of the present invention is a method for manufacturing a piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, the method including: preparing the substrate; and depositing an electrode layer, an underlayer, and a piezoelectric thin film in this order on at least one surface of the substrate, wherein the underlayer contains a nitrogen compound, the nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements, excluding zirconium nitride, and the piezoelectric thin film is deposited so as to be in contact with the underlayer.

[0022] The embodiments of the present invention (hereinafter also abbreviated as the present embodiments) include first to fourth embodiments.

[0023] <Piezoelectric Laminate> The structure and manufacturing method of the piezoelectric laminate 100 according to this embodiment will be described with reference to the drawings.

[0024] [Structure of Piezoelectric Laminate] Fig. 1 is a schematic cross-sectional view illustrating the structure of a piezoelectric laminate 100 according to this embodiment. As shown in Fig. 1, the piezoelectric laminate 100 has a substrate 101 and a laminate film 105 provided on at least one surface of the substrate 101. The laminate film 105 includes, in order from the substrate side, an electrode layer 102, an underlayer 103, and a piezoelectric thin film 104. Here, the underlayer 103 and the piezoelectric thin film 104 are in contact with each other.

[0025] In one aspect of this embodiment, the underlayer 103 may also be disposed between the substrate and the electrode 102. That is, as shown in Fig. 2, the stacked film 105 may include, in order from the substrate side, the underlayer 103', the electrode layer 102, the underlayer 103, and the piezoelectric thin film 104.

[0026] (Substrate) The thickness or material of the substrate 101 is not particularly limited as long as the laminated film 105 can be formed on its surface, and conventionally known substrates can be used. Examples of the substrate 101 include substrates such as silicon (Si) single crystal with a silicon, diamond, or other polycrystalline film formed on the surface, metal substrates such as stainless steel (SUS), amorphous substrates such as glass, and films such as polyethylene terephthalate (PET), polycarbonate (PC), cycloolefin polymer, polyimide, and polyethylene naphthalate (PEN). The substrate 101 may have functions and properties that allow it to be used as an electrode, such as conductivity, and the substrate 101 may be used as the electrode layer 102.

[0027] (Electrode Layer) The electrode layer 102 is not particularly limited, and may be any electrode material that is commonly used for the piezoelectric laminate 100. Examples of electrode materials that form the electrode layer 102 include metal materials such as aluminum (Al), transition metals such as molybdenum (Mo), titanium (Ti), chromium (Cr), tantalum (Ta), iridium (Ir), and nickel (Ni), precious metals such as ruthenium (Ru), palladium (Pd), platinum (Pt), gold (Au), silver (Ag), and copper (Cu), and ruthenium oxide (RuO). ２ A film containing a conductive metal oxide such as CrN (chromium nitride) or a conductive metal nitride such as chromium nitride (CrN) is used. The electrode layer 102 may be made of a combination of the above materials.

[0028] The thickness of the electrode layer 102 is not particularly limited, but is preferably 5 nm or more from the viewpoint of forming a continuous film, and is preferably 1000 nm or less from the viewpoint of preventing the continuous film from being lost due to cracks or the like.

[0029] The arithmetic mean roughness (Ra) of the electrode layer 102 is not particularly limited, but is preferably 0.1 nm or more from the viewpoint of obtaining good conductivity due to the presence of crystal grains, and is preferably 10 nm or less from the viewpoint of preventing a decrease in conductivity due to grain boundary scattering.

[0030] From the viewpoint of ensuring good conductivity, the specific resistance of the electrode layer 102 is preferably 10 Ω·cm or less, more preferably 1 Ω·cm or less, and more preferably 1×10 －１ More preferably, it is 1×10 Ω cm or less. －２ The specific resistance of the electrode layer 102 can be measured by using a Hall effect measuring device on the substrate on which the electrode layer 102 is formed.

[0031] (Underlayer) The underlayer 103 is a layer formed on the electrode layer 102 directly or via another layer, and improves the crystal orientation of the piezoelectric thin film 104 provided on the underlayer 103. The underlayer 103 is in direct contact with the piezoelectric thin film 104.

[0032] The underlayer of the piezoelectric thin film 104 (e.g., the substrate 101, the electrode layer 102) and the conditions for forming the piezoelectric thin film 104 may affect the polarity, resulting in changes in piezoelectric performance. Even after a cleaning process, the underlayer is susceptible to surface contamination by natural oxide films and carbon-based contaminants, which can easily cause the polarity of the material constituting the piezoelectric thin film 104 to become non-uniform. In response to this, the inventors discovered that by providing an underlayer 103 containing a nitrogen compound containing at least one element selected from the group consisting of III- to VI-group elements on the electrode layer 102, the polarity of the piezoelectric thin film 104 can be controlled and the polarity of the outermost layer can be made uniform.

[0033] In this way, the piezoelectric performance can be effectively improved by controlling the polarity of the piezoelectric thin film 104 and aligning the polarity of the outermost layer. In particular, by forming the underlayer 103 in a 100% nitrogen atmosphere, it becomes easier to form a crystal structure that incorporates nitrogen in excess of the stoichiometric ratio, and this effect can be further enhanced.

[0034] In the first embodiment, the underlayer 103 contains a nitrogen compound containing at least one element selected from the group consisting of Group III to Group VI elements. In the second embodiment, the underlayer 103 contains a nitrogen compound, and the nitrogen compound contains at least one element selected from the group consisting of Group III to Group VI elements, excluding zirconium nitride.

[0035] In this embodiment, the nitrogen compound constituting the underlayer 103 is represented by the chemical formula QN Ｘ In the chemical formula, x represents the degree of nitriding, and the degree of nitriding x is greater than 0, preferably greater than 1, and more preferably greater than 1.1. The degree of nitriding x is preferably less than 2, and more preferably less than 1.65.

[0036] The degree of nitriding x can be determined by Rutherford backscattering spectroscopy (RBS). When there are multiple samples, the degrees of nitriding x of two or more samples may be measured by the RBS method and ellipsometry, respectively, and a correlation coefficient may be derived therebetween. Then, for the remaining samples, the degrees of nitriding x of the remaining samples may be calculated from the results of the ellipsometry measurement.

[0037] In this embodiment, the nitrogen compound contained in the underlayer 103 is a nitride, but it does not necessarily have to be in a stoichiometric ratio and may be in a per-nitrided (metastable) state. In this embodiment, the nitrogen compound constituting the underlayer 103 is preferably one that has a Cubic and (111) plane main orientation and can be in a per-nitrided state (metastable state). By using such a nitrogen compound, nitrogen is supplemented in the piezoelectric thin film 104, making it easier to align the polarity of the material constituting the piezoelectric thin film 104.

[0038] In the first embodiment, examples of the III to VI group elements contained in the nitrogen compound constituting the underlayer 103 include scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), rutherfordium (Rf), vanadium (V), niobium (Nb), tantalum (Ta), dubium (Db), chromium (Cr), molybdenum (Mo), tungsten (W), and seaborgium (Sg). Among the nitrogen compounds containing these, Zr, Hf, Y, W, and Nb are preferred from the viewpoint of the above-mentioned Cubic and (111) plane main orientation and the possibility of taking an over-nitrided state (metastable state). In the first embodiment, examples of the nitrogen compound constituting the underlayer 103 include ZrN, Zr ３ N ４ , HfN, YN, Y ５ N １４ , WN,W ７ N １２ , NbN and Nb ２ N ３ These nitrogen compounds may be used alone or in combination of two or more.

[0039] In the second embodiment, examples of the III to VI group elements contained in the nitrogen compound constituting the underlayer 103 include scandium (Sc), yttrium (Y), titanium (Ti), hafnium (Hf), rutherfordium (Rf), vanadium (V), niobium (Nb), tantalum (Ta), dubium (Db), chromium (Cr), molybdenum (Mo), tungsten (W), and seaborgium (Sg). Among these, Hf, Y, W, and Nb are preferred from the viewpoint of the aforementioned Cubic and (111) plane main orientation and the possibility of taking an over-nitrided state (metastable state). In the second embodiment, examples of the nitrogen compound constituting the underlayer 103 include HfN, YN, and Y. ５ N １４ , WN,W ７ N １２ , NbN and Nb ２ N ３ These nitrogen compounds may be used alone or in combination of two or more.

[0040] In this embodiment, the underlayer 103 preferably has a (111) plane preferential orientation structure that is preferentially oriented in the (111) plane, but does not necessarily have to have a (111) plane preferential orientation. Having a (111) plane preferential orientation structure improves lattice matching with the piezoelectric thin film 104, making it possible to more uniform the polarity of the outermost layer of the piezoelectric thin film 104 and further improve piezoelectric performance.

[0041] In this embodiment, the underlayer 103 preferably has a sodium chloride structure, a fluorite structure, or a perovskite structure, which facilitates preferential orientation in the (111) plane, thereby aligning the polarity of the outermost layer of the piezoelectric thin film 104 and further improving the piezoelectric performance.

[0042] In this embodiment, the thickness of the underlayer 103 is preferably 0.2 nm or more and 120 nm or less. From the viewpoint of further increasing the orientation of the piezoelectric thin film 104 and further aligning the polarity of the outermost layer, the thickness of the underlayer 103 is preferably 0.2 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. Furthermore, from the viewpoint of improving production efficiency and reducing costs, the thickness of the underlayer 103 is preferably 120 nm or less, more preferably 100 nm or less, and even more preferably 70 nm or less.

[0043] (Piezoelectric Thin Film) The piezoelectric thin film 104 is a layer having at least one of piezoelectric and pyroelectric properties, and is preferably a crystalline thin film having a hexagonal wurtzite structure oriented in the c-axis direction. In this specification, "oriented in the c-axis direction" and "c-axis oriented" refer to a state in which the peak intensity ratio of the (101) plane / (002) plane in the X-ray diffraction pattern measured by the out-of-plane method of the piezoelectric thin film is less than 0.3.

[0044] The presence of a hexagonal wurtzite structure can be confirmed by, for example, X-ray diffraction (XRD), X-ray absorption spectroscopy (XAFS, EXAFS), etc. The crystal orientation in which the piezoelectric properties of the piezoelectric thin film 104 having a hexagonal wurtzite structure are exhibited is the

[002] direction of the hexagonal wurtzite structure. In other words, by orienting the (002) plane of the hexagonal wurtzite structure (c-axis orientation), the piezoelectric thin film 104 can achieve superior piezoelectric performance.

[0045] For example, a thin film of aluminum nitride (AlN), ZnO, GaN, etc. is preferably used as the piezoelectric thin film 104. Among these, from the viewpoint of manufacturability and from the viewpoint of improving the crystallinity of the underlayer described below, it is particularly preferable that the piezoelectric thin film contains AlN, and it is more preferable that the AlN has a hexagonal wurtzite structure oriented in the c-axis direction.

[0046] The thickness of the piezoelectric thin film 104 is not particularly limited, but from the viewpoint of ensuring better crystal orientation and sufficient piezoelectric properties, it is preferably 100 nm or more, more preferably 250 nm or more, even more preferably 500 nm or more, and most preferably 1000 nm or more. On the other hand, from the viewpoint of crystal growth without generating cracks, the thickness of the piezoelectric thin film 104 is preferably 10 μm or less, more preferably 7.5 μm or less, and even more preferably 5 μm or less.

[0047] The piezoelectric thin film 104 preferably has high smoothness and a small arithmetic mean roughness (Ra). The arithmetic mean roughness (Ra) of the surface of the piezoelectric thin film 104 is preferably 8.0 nm or less, more preferably 6.0 nm or less, even more preferably 4.0 nm or less, and particularly preferably 3.5 nm or less. The lower limit of the arithmetic mean roughness (Ra) is not particularly limited, but from the viewpoint of adhesion during the formation of a laminated film, it is preferably 0.1 nm or more, more preferably 0.2 nm or more, and most preferably 0.3 nm or more. The arithmetic mean roughness (Ra) of the surface of the piezoelectric thin film is the arithmetic mean roughness of the surface not in contact with the underlayer 103. The arithmetic mean roughness (Ra) is measured using an atomic force microscope (AFM).

[0048] In the X-ray diffraction pattern of the piezoelectric thin film 104 measured by an out-of-plane method, the peak intensity ratio between the (101) plane and the (002) plane {(101) plane / (002) plane} is preferably 0.25 or less, more preferably 0.1 or less, even more preferably 0.05 or less, and most preferably 0.01 or less, from the viewpoint of further ensuring a hexagonal wurtzite structure oriented in the c-axis direction and ensuring sufficient piezoelectric properties. The lower limit of the peak intensity ratio is not particularly limited, and may be 0.

[0049] In the first embodiment, the absolute value of the piezoelectric constant |e ３１ ｆ | is 0.5 C / m ２ The absolute value of the piezoelectric constant |e ３１ ｆ | is 0.5 C / m ２ By satisfying the above, excellent piezoelectric performance can be obtained. ３１ ｆ | is 0.5 C / m ２ or more, preferably 0.8 C / m ２ More preferably, 1.1 C / m ２ More preferably, 1.3 C / m ２ The absolute value of the piezoelectric constant |e ３１ ｆ There is no particular upper limit to the absolute value of the piezoelectric constant |e ３１ ｆ can be calculated based on the following formula in accordance with IEC 62047-30:2017. ３１ ｆ has polarity and can take positive or negative values, and is therefore expressed as an absolute value in this specification.

[0050]

[0051] e ３１ ｆ : Piezoelectric constant (unit: C / m ２ ) Es: Young's modulus of the substrate (unit: GPa) t ｓ : Substrate thickness (unit: m) δ: Tip displacement (unit: m) V: Applied voltage (unit: V) L: Cantilever effective length (unit: m) ν ｓ : Poisson's ratio of the substrate

[0052] The piezoelectric laminate according to this embodiment may include layers other than the substrate, electrode layer, underlayer, and piezoelectric thin film, as long as the effects of the present invention are not impaired. For example, an adhesive layer that adheres the substrate to the metal may be provided between the substrate and the electrode layer, or an adhesive layer that adheres the electrode to the underlayer may be provided between the electrode layer and the underlayer. A thermal oxide film may be provided on at least one surface of the substrate. Furthermore, an upper electrode layer or a protective layer may be provided on the surface of the piezoelectric thin film opposite the underlayer and electrode layer. Any of the above layers may be conventionally known.

[0053] The piezoelectric laminate according to this embodiment can be suitably used in piezoelectric elements, such as gyro sensors, shock sensors, and microphones that utilize the piezoelectric effect, as well as actuators, inkjet heads, speakers, buzzers, and resonators that utilize the inverse piezoelectric effect.

[0054] [Method for Manufacturing Piezoelectric Laminate] The method for manufacturing a piezoelectric laminate according to this embodiment (hereinafter also referred to as the present manufacturing method) includes preparing a substrate, and depositing an electrode layer, an underlayer, and a piezoelectric thin film in this order on at least one surface of the substrate. The piezoelectric thin film preferably contains aluminum nitride, and the aluminum nitride has a hexagonal wurtzite structure oriented in the c-axis direction.

[0055] The substrate, electrode layer, and piezoelectric thin film in this embodiment can each be the substrate 101, electrode layer 102, and piezoelectric thin film 104 of this embodiment described in the above [Structure of Piezoelectric Laminate]. The base layer in the third embodiment can be the base layer 103 of the first embodiment described in the above [Structure of Piezoelectric Laminate]. The base layer in the fourth embodiment can be the base layer 103 of the second embodiment described in the above [Structure of Piezoelectric Laminate].

[0056] The piezoelectric laminate obtained by this manufacturing method is preferably the piezoelectric laminate 100 described in the above [Structure of Piezoelectric Laminate].

[0057] That is, in the piezoelectric laminate obtained by the manufacturing method of the third embodiment, the underlayer and the piezoelectric thin film are in contact with each other, the underlayer contains a nitrogen compound containing at least one element selected from the group consisting of elements of groups III to VI, and the absolute value of the piezoelectric constant |e ３１ ｆ | is 0.5 C / m ２ The absolute value of the piezoelectric constant |e ３１ ｆ | is 0.5 C / m ２ or more, preferably 0.8 C / m ２ More preferably, 1.1 C / m ２ More preferably, 1.3 C / m ２ The absolute value of the piezoelectric constant |e ３１ ｆ There is no particular upper limit for |.

[0058] Furthermore, in the piezoelectric laminate obtained by the manufacturing method of the fourth embodiment, the underlayer and the piezoelectric thin film are in contact with each other, and the underlayer contains a nitrogen compound, and the nitrogen compound includes at least one element selected from the group consisting of group III to VI elements, excluding zirconium nitride.

[0059] (Preparation of Substrate) The substrate may be, for example, the substrate 101 described above, and may be a commercially available product or a pre-fabricated product.

[0060] (Laminated Film Formation) The laminated film 105 is formed on at least one surface of the substrate 101 prepared as described above. The laminated film 105 is formed in the order of the electrode layer 102, the underlayer 103, and the piezoelectric thin film 104, and for each of these, for example, a physical vapor deposition method or a chemical vapor deposition method (CVD method) can be used. Examples of physical vapor deposition methods include physical vapor deposition, PVD, and sputtering. Among these, sputtering is particularly preferred from the viewpoint of being able to control the doping amount over a wide range, and magnetron sputtering and digital sputtering are particularly more preferred.

[0061] The electrode layer 102 may be provided directly on at least one surface of the substrate 101, or may be provided via an adhesive layer or the like. The electrode layer may be a single layer or may consist of two or more layers.

[0062] The underlayer 103 may be provided directly on the electrode layer 102 or may be provided via an adhesive layer or the like. The underlayer 103 contains a nitrogen compound containing at least one element selected from the group consisting of group III to VI elements. When the underlayer 103 is formed by a sputtering method, the composition of the nitrogen compound (e.g., the degree of nitridation) can be adjusted by controlling the film formation conditions. Examples of the film formation conditions include the temperature of the substrate 101 during film formation, the film formation pressure, the composition of the introduced gas, the target composition, and the post-heat treatment temperature.

[0063] The nitrogen compound constituting the underlayer 103 may contain impurities such as carbon and oxygen, which are inevitably introduced during film formation, at a maximum of about 10 at %. When a sputtering method is used, the maximum amount of impurities contained in the target is allowed to be about 10 at %. Examples of impurities contained in the target containing elements of groups III to VI constituting the underlayer 103 (e.g., Zr, Hf) include Hf, Ti, Sc, V, Nb, Ta, Cr, Mo, W, O, C, etc.

[0064] When forming the underlayer 103, the underlayer 103 may contain a doping element. The doping element is preferably contained in a range that allows the piezoelectric thin film 104 to maintain a hexagonal wurtzite structure. For example, when the piezoelectric thin film 104 contains AlN, the doping element may include elements such as Sc, Y, Mg, Ca, Sr, Zr, Hf, V, and Nb, which impart strain to the AlN and improve its piezoelectric performance. The Sc element is particularly preferable for improving piezoelectric performance, and in this case, the doping may be up to about 43 at %.

[0065] The degree of nitridation x of the nitrogen compound containing at least one element selected from the group consisting of III to VI group elements in the underlayer 103 can be adjusted by the flow rate of nitrogen gas during film formation. For example, when the degree of nitridation x is adjusted to the range of 0<x<2, the flow rate of nitrogen gas is adjusted to {N ２ / (Ar+N ２ )} ratio is preferably 20% or more, and particularly preferably 40% or more. Furthermore, even when the ratio is 100%, the nitrogen amount can be adjusted to a larger amount by increasing the nitrogen flow rate and raising the film formation pressure, and the degree of nitridation x can be set to a value close to 2.

[0066] From the viewpoint of crystal density and orientation, the film formation pressure is preferably 0.05 Pa or more, and more preferably 0.1 Pa or more. The film formation pressure is preferably 10 Pa or less, and more preferably 1 Pa or less.

[0067] The substrate temperature during deposition of the underlayer 103 is preferably from room temperature to 600° C. or less, more preferably 250° C. or less.

[0068] In order to fully utilize the effects of the underlayer 103, it is preferable to continuously form the layers without breaking the vacuum not only during the formation of the underlayer 103, but also until all of the electrode layer 102, underlayer 103, and piezoelectric thin film 104 are formed. In particular, if the vacuum is broken during the formation of the underlayer 103 and the piezoelectric thin film 104, oxygen may be mixed into the underlayer 103 as an impurity, making it impossible to utilize the characteristics of the underlayer 103. In this case, good interfacial characteristics cannot be obtained, so it is preferable to continuously form the layers while maintaining the vacuum.

[0069] The piezoelectric thin film 104 is formed directly on the underlayer 103. The piezoelectric thin film 103 can be formed by a conventionally known method using a conventionally known material. For example, when forming a thin film of aluminum nitride having a hexagonal wurtzite structure oriented in the c-axis direction by sputtering, the film formation conditions can be, for example, a pressure of 0.05 to 10 Pa, a nitrogen gas partial pressure ratio of 20 to 100%, and a substrate temperature of 25 to 200°C.

[0070] The nitrogen compound constituting the piezoelectric thin film 104 may contain impurities such as carbon and oxygen, which are inevitably introduced during film formation, at a maximum of about 10 at %. When using a sputtering method, the maximum amount of impurities contained in the target is allowed to be about 10 at %. Examples of impurities contained in a target containing elements constituting the piezoelectric thin film 104 (e.g., Al when the material is AlN) include Hf, Ti, Sc, V, Nb, Ta, Cr, Mo, W, O, C, etc.

[0071] As explained above, the present specification discloses the following: 1. A piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, wherein the laminate film includes, in order from the substrate side, an electrode layer, an underlayer, and a piezoelectric thin film, the underlayer and the piezoelectric thin film are in contact with each other, the underlayer contains a nitrogen compound containing at least one element selected from the group consisting of III to VI elements, and the absolute value of the piezoelectric constant |e ３１ ｆ | is 0.5 C / m ２A piezoelectric laminate as described above. 2. A piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, wherein the laminate film includes, in order from the substrate side, an electrode layer, an underlayer, and a piezoelectric thin film, the underlayer and the piezoelectric thin film are in contact with each other, and the underlayer contains a nitrogen compound, the nitrogen compound containing at least one element selected from the group consisting of group III to VI elements, excluding zirconium nitride. 3. The piezoelectric laminate as described above in 1 or 2, wherein the piezoelectric thin film contains aluminum nitride, and the aluminum nitride has a hexagonal wurtzite structure oriented in the c-axis direction. 4. The piezoelectric laminate as described above in 1 or 2, wherein the underlayer has a sodium chloride structure, a fluorite structure, or a perovskite structure. 5. The piezoelectric laminate as described above in any one of 1 to 4, wherein the underlayer has a (111) plane preferred orientation structure that is preferentially oriented in the (111) plane direction. 6. The piezoelectric stack according to any one of 1 to 5 above, wherein the underlayer is a nitrogen compound containing at least one selected from Zr, Hf, Y, W, and Nb. 7. The piezoelectric stack according to any one of 1 to 6 above, wherein the underlayer has a thickness of 0.2 nm to 100 nm. 8. The piezoelectric stack according to 7 above, wherein the underlayer has a thickness of 5 nm to 70 nm. 9. The piezoelectric stack according to any one of 1 to 8 above, wherein the piezoelectric thin film has a thickness of 100 nm to 10 μm. 10. A piezoelectric element having the piezoelectric stack according to any one of 1 to 9 above. 11. A method for manufacturing a piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, the method comprising: preparing the substrate; and depositing an electrode layer, an underlayer, and a piezoelectric thin film in this order on at least one surface of the substrate, wherein the underlayer contains a nitrogen compound containing at least one element selected from the group consisting of III to VI groups, the piezoelectric thin film is deposited so as to be in contact with the underlayer, and an absolute value of the piezoelectric constant |e of the piezoelectric thin film is ３１ ｆ | is 0.5 C / m ２12. A method for manufacturing a piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, comprising: preparing the substrate; and depositing an electrode layer, an underlayer, and a piezoelectric thin film in this order on at least one surface of the substrate, wherein the underlayer contains a nitrogen compound, the nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements, excluding zirconium nitride, and the piezoelectric thin film is deposited so as to be in contact with the underlayer. 13. The method for manufacturing a piezoelectric laminate according to 11 or 12 above, wherein the deposition is performed by sputtering.

[0072] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Examples 1 to 6, 8, 9, 11, and 13 to 32 are working examples, and Examples 7, 10, and 12 are comparative examples.

[0073] [Example 1] A piezoelectric stack 100 was fabricated by forming an underlayer 103 and a piezoelectric thin film 104, in this order, on a substrate 101 and an electrode layer 102, according to the following steps (1) to (3). (1) Preparation of Substrate 101 and Electrode Layer 102: A 25 mm x 25 mm x 0.625 mm conductive silicon substrate (abbreviated as "Conductive Si" in the table) was used as the substrate 101 and the electrode layer 102. The substrate 101 in Example 1 was made of conductive Si and also functioned as the electrode layer 102. Therefore, although the "Electrode Layer" item for Example 1 in Table 1 is shaded, the piezoelectric stack 100 of Example 1 includes the electrode layer 102. (2) Fabrication of Underlayer 103: The underlayer 103 was fabricated on one surface of the substrate 101 and the electrode layer 102 by sputtering under the following conditions according to the following procedure. The deposition of the underlayer 103 was carried out by placing the substrate 101 and the electrode layer 102 in the vacuum chamber of the sputtering device without breaking the vacuum, and then evacuating the vacuum chamber and reducing the pressure to 10. －３After the pressure was reduced to 10 Pa or less, the film formation was carried out under the following conditions: Film formation apparatus A: vertical in-line sputtering apparatus (manufactured by ULVAC) Sputtering target material: Zr metal (Tanaka Precious Metals, purity 2N2 (value including Hf)) Introduced gas: nitrogen gas (purity = 99.9% or more) 80 sccm Film formation pressure: 0.4 Pa Thickness: 10 nm Substrate heating temperature: room temperature (3) Fabrication of piezoelectric thin film 104 Aluminum nitride (AlN) was fabricated as the piezoelectric thin film 104 on the underlayer 103 by the following procedure. The piezoelectric thin film 104 was formed by reducing the pressure to 10 Pa or less without breaking the vacuum from the time of the formation of the underlayer 103. －３ The piezoelectric thin film 104 was formed using the same apparatus as that used to form the underlayer 103. Sputtering target material: Al metal (manufactured by Kojundo Chemical Co., Ltd., purity 3N) Introduced gas: mixed gas of nitrogen gas (purity = 99.9% or more) 16 sccm and Ar gas (purity = 99.9% or more) 24 sccm Film formation pressure: 0.2 Pa Substrate heating temperature: room temperature Thickness: 1000 nm

[0074] Examples 2 to 9 In Examples 2 to 9, the piezoelectric stack 100 was fabricated by the same procedure as in Example 1, except that the fabrication conditions for the underlayer 103 and the piezoelectric thin film 104 were changed as shown in Tables 1 and 2.

[0075] [Examples 10 and 11] The piezoelectric stack 100 was fabricated by the same procedure as in Example 1, except that the deposition apparatus used in fabricating the underlayer 103 and the piezoelectric thin film 104 was the following apparatus B, and the fabrication conditions for the underlayer 103 and the piezoelectric thin film 104 were changed as shown in Table 2. Deposition apparatus B: Deposition-down type in-line sputtering apparatus

[0076] For Example 11, a sample of the piezoelectric laminate 100 was processed with a focused ion beam (FIB, Helios 1200 manufactured by FEI) to form a thin slice, which was then observed with a transmission electron microscope (TEM, NEOARM manufactured by JEOL Ltd.), and the crystals and their orientations from the high-resolution TEM images were identified by FFT analysis (Fast Fourier Transform analysis). As a result, the ZrN film of the underlayer 103 was oriented in the (111) plane in the stacking direction.

[0077] [Example 12] The piezoelectric stack 100 was fabricated by the same procedure as in Example 1, except that the deposition apparatus for fabricating the underlayer 103 and the piezoelectric thin film 104 was changed to the following apparatus C, and the fabrication conditions for the underlayer 103 and the piezoelectric thin film 104 were changed as shown in Table 2. Deposition apparatus C: Post-nitridation sputtering apparatus

[0078] [Example 13] A piezoelectric laminate 100 was fabricated by the same procedure as in Example 12, except that the fabrication conditions for the underlayer 103 were changed as shown in Table 2, and the material of the underlayer 103 was HfN, and the film was formed under the following conditions: Film-forming apparatus C: post-nitriding sputtering apparatus Sputtering target material: Hf metal (manufactured by Kojundo Chemical Laboratory Co., Ltd.) Introduced gas: nitrogen gas (purity = 99.9% or more) 30 sccm Film-forming pressure: 0.35 Pa Thickness: 10 nm Substrate heating temperature: room temperature

[0079] [Example 14] A piezoelectric laminate 100 was fabricated by forming an electrode layer 102, a base layer 103, and a piezoelectric thin film 104 in this order on a substrate 101 according to the procedures (1) to (4) below. (1) Preparation of Substrate 101 A silicon substrate (abbreviated as "SiSiO" in the table) measuring 25 mm x 25 mm x 0.625 mm and having 1 μm of thermal oxidation on both surfaces was used as the substrate 101. (2) Fabrication of Electrode Layer 102 An electrode layer 102 was provided on one surface of the substrate 101 according to the following procedure. The electrode layer 102 consisted of only one layer of Pt. To form the electrode layer, the substrate was placed in the vacuum chamber of a sputtering device, and then the vacuum chamber was evacuated and the pressure was reduced to 10 －３ The deposition was carried out after the pressure was reduced to 10 Pa or less. Film deposition apparatus A: vertical in-line sputtering apparatus (manufactured by ULVAC) Sputtering target material: Pt metal Introduced gas: Ar gas (purity = 99.9% or more) 23 sccm Film deposition pressure: 0.4 Pa Thickness: 150 nm Substrate heating temperature: room temperature (3) Formation of underlayer 103 Underlayer 103 was formed on the surface of electrode layer 102 by sputtering under the following conditions according to the following procedure. The deposition of underlayer 103 was carried out by placing substrate 101 in a vacuum chamber of a sputtering apparatus without breaking the vacuum, evacuating the vacuum chamber, and reducing the pressure to 10 －３After the pressure was reduced to 10 Pa or less, the film formation was carried out under the following conditions: Film formation apparatus A: vertical in-line sputtering apparatus (manufactured by ULVAC) Sputtering target material: Zr metal (Tanaka Precious Metals, purity 2N2 (value including Hf)) Introduced gas: nitrogen gas (purity = 99.9% or more) 80 sccm Film formation pressure: 0.4 Pa Thickness: 5 nm Substrate heating temperature: room temperature (4) Fabrication of piezoelectric thin film 104 Aluminum nitride (AlN) was fabricated as the piezoelectric thin film 104 on the underlayer 103 by the following procedure. The piezoelectric thin film 104 was formed by reducing the pressure to 10 Pa or less without breaking the vacuum from the time of the formation of the underlayer 103. －３ The piezoelectric thin film 104 was formed using the same apparatus as that used to form the underlayer 103. Sputtering target material: Al metal (manufactured by Kojundo Chemical Co., Ltd., purity 3N) Introduced gas: mixed gas of nitrogen gas (purity = 99.9% or more) 20 sccm and Ar (purity = 99.9% or more) 20 sccm Film formation pressure: 0.2 Pa Substrate heating temperature: room temperature Thickness: 1000 nm

[0080] Examples 15 to 19 In Examples 15 to 19, the piezoelectric stack 100 was fabricated by the same procedure as in Example 14, except that the fabrication conditions for the underlayer 103 and the piezoelectric thin film 104 were changed as shown in Table 3.

[0081] Examples 20 to 24 A piezoelectric laminate 100 was fabricated by the same procedure as in Example 14, except that a 25 mm × 25 mm × 0.7 mm alkali-free glass substrate (abbreviated as "alkali-free" in the table) was used as the substrate 101 and the fabrication conditions for the underlayer 103 and the piezoelectric thin film 104 were changed as shown in Table 4.

[0082] [Example 25] A piezoelectric laminate 100 was fabricated by forming an electrode layer 102, a base layer 103, and a piezoelectric thin film 104 in this order on a substrate 101 according to the procedures (1) to (4) below. (1) Preparation of substrate 101: A 25 mm x 25 mm x 0.7 mm alkali-free glass (abbreviated as "alkali-free" in the table) was used as the substrate 101. (2) Fabrication of electrode layer 102: An electrode layer 102 was provided on one surface of the substrate 101 according to the following procedure. The electrode layer 102 consisted of only one layer of ITO. To form the electrode layer, the substrate was placed in a vacuum chamber of a sputtering device, and then the vacuum chamber was evacuated and the pressure was reduced to 10－３ Film forming apparatus A: vertical in-line sputtering apparatus (manufactured by ULVAC) Sputtering target material: In ２ O ３ : SnO ２ = 90:10 wt% (ITO manufactured by Mitsui Mining & Smelting Co., Ltd.) Introduced gas: Ar gas (purity = 99.9% or more) 80 sccm, O ２ Gas (purity = 99.9% or more) 0.8 sccm Film formation pressure: 0.5 Pa Thickness: 120 nm Substrate heating temperature: room temperature (3) Formation of Underlayer 103 Underlayer 103 was formed on the surface of the electrode layer 102 by sputtering under the following conditions: The underlayer 103 was formed by placing the substrate 101 in a vacuum chamber of a sputtering device without breaking the vacuum, and then evacuating the vacuum chamber and reducing the pressure to 10 －３ After the pressure was reduced to 10 Pa or less, the film formation was carried out under the following conditions: Film formation apparatus A: vertical in-line sputtering apparatus (manufactured by ULVAC) Sputtering target material: Zr metal (Tanaka Precious Metals, purity 2N2 (value including Hf)) Introduced gas: nitrogen gas (purity = 99.9% or more) 80 sccm Film formation pressure: 0.4 Pa Thickness: 10 nm Substrate heating temperature: room temperature (4) Fabrication of piezoelectric thin film 104 Aluminum nitride (AlN) was fabricated as the piezoelectric thin film 104 on the underlayer 103 by the following procedure. The piezoelectric thin film 104 was formed by reducing the pressure to 10 Pa or less without breaking the vacuum from the time of the formation of the underlayer 103. －３ The piezoelectric thin film 104 was formed using the same apparatus as that used to form the underlayer 103. Sputtering target material: Al metal (manufactured by Kojundo Chemical Co., Ltd., purity 3N) Introduced gas: mixed gas of nitrogen gas (purity = 99.9% or more) 20 sccm and Ar gas (purity = 99.9% or more) 20 sccm Film formation pressure: 0.2 Pa Substrate heating temperature: room temperature Thickness: 1000 nm

[0083] [Example 26] A 25 mm x 25 mm x 0.7 mm quartz glass substrate (abbreviated as "quartz" in the table) was used as the substrate 101, and the conditions for producing the underlayer 103 and the piezoelectric thin film 104 were changed as shown in Table 4. Except for this, film formation was performed in the same manner as in Example 25, and a piezoelectric stack 100 was produced.

[0084] [Example 28] A piezoelectric laminate 100 was fabricated by forming an underlayer 103', an electrode layer 102, an underlayer 103, and a piezoelectric thin film 104 in this order on a substrate 101 according to the procedures (1) to (4) below. (1) Preparation of Substrate 101 A silicon substrate (abbreviated as "SiSiO" in the table) measuring 25 mm x 25 mm x 0.7 mm and having 1 μm of thermal oxidation on both surfaces was used as the substrate 101. (2) Fabrication of Underlayer 103' An underlayer 103' was fabricated on one surface of the substrate 101 by sputtering under the following conditions according to the following procedure. The underlayer 103' was formed by placing the substrate 101 in a vacuum chamber of a sputtering device without breaking the vacuum, and then evacuating the vacuum chamber and reducing the pressure to 10 －３ After the pressure was reduced to below 100 Pa, the deposition was carried out under the following conditions: Deposition apparatus A: vertical in-line sputtering apparatus (manufactured by ULVAC) Sputtering target material: Zr metal [Tanaka Precious Metals, purity 2N2 (value including Hf)] Introduced gas: nitrogen gas (purity = 99.9% or more) 80 sccm Deposition pressure: 0.4 Pa Thickness: 10 nm Substrate heating temperature: room temperature (3) Preparation of electrode layer 102 An electrode layer 102 was provided on one surface of the underlayer 103' by the following procedure. The electrode layer 102 was formed by forming only one layer of Ti. The deposition of the electrode layer was carried out by placing a substrate in the vacuum chamber of the sputtering apparatus, evacuating the vacuum chamber, and reducing the pressure to 10 －３ The deposition was carried out after the pressure was reduced to 10 Pa or less. Deposition apparatus A: vertical in-line sputtering apparatus (manufactured by ULVAC) Sputtering target material: Ti metal (manufactured by Kojundo Chemical Co., Ltd.) Introduced gas: Ar gas (purity = 99.9% or more) 80 sccm Deposition pressure: 0.45 Pa Thickness: 100 nm Substrate heating temperature: room temperature (4) Preparation of underlayer 103 Underlayer 103 was prepared on electrode layer 102 by sputtering under the same conditions as for preparation of underlayer 103'. (5) Preparation of piezoelectric thin film 104 Aluminum nitride (AlN) was prepared as piezoelectric thin film 104 on underlayer 103 by the following procedure. The deposition of piezoelectric thin film 104 was carried out by reducing the pressure to 10 Pa or less without breaking the vacuum from the deposition of underlayer 103. －３The piezoelectric thin film 104 was formed using the same apparatus as that used to form the underlayer 103. Sputtering target material: Al metal (3N, manufactured by Kojundo Chemical Co., Ltd.) Introduced gas: Nitrogen gas (purity = 99.9% or more) 40 sccm Film formation pressure: 0.2 Pa Substrate heating temperature: Room temperature Thickness: 1000 nm

[0085] Example 27 A piezoelectric laminate 100 was fabricated by the same procedure as in Example 28, except that the underlayer 103' was not fabricated.

[0086] Example 29 Except for changing the conditions for producing the piezoelectric thin film 104 as shown in Table 5, the same procedure as in Example 27 was used to form the piezoelectric laminate 100.

[0087] [Example 30] A 100 mm x 100 mm x 2 mm alkali-free glass (abbreviated as "alkali-free" in the table) was used as the substrate 101, and a piezoelectric laminate 100 was produced by depositing films in the same manner as in Example 28, except that the underlayer 103' was not produced.

[0088] Example 31 A piezoelectric laminate 100 was fabricated by performing film formation in the same manner as in Example 28, except that a non-alkali glass substrate 101 measuring 100 mm×100 mm×2 mm was used.

[0089] Example 32 A piezoelectric laminate 100 was fabricated by performing film formation in the same manner as in Example 31, except that a quartz glass substrate 101 measuring 100 mm×100 mm×2 mm (abbreviated as “quartz” in the table) was used.

[0090] <Evaluation> The piezoelectric response of each of the obtained piezoelectric laminates was determined based on the following formula in accordance with IEC 62047-30:2017.

[0091]

[0092] e ３１ ｆ : Piezoelectric constant (unit: C / m ２ ) Es: Young's modulus of the substrate (unit: GPa) t ｓ : Substrate thickness (unit: m) δ: Tip displacement (unit: m) V: Applied voltage (unit: V) L: Cantilever effective length (unit: m) ν ｓ : Poisson's ratio of the substrate

[0093] To measure the piezoelectric response, a function generator (WF1974 manufactured by ENE-F Circuit Design Block Co., Ltd.) was used as an AC power source, and the voltage obtained by the laser Doppler was converted into a displacement using a laser Doppler (LV1800 manufactured by Ono Sokki Co., Ltd.) and an oscilloscope (TBS1072C manufactured by Tektronix Corporation), and the displacement was expressed as voltage amplitude / 2nf (frequency). The results are shown in Tables 1 to 5.

[0094]

[0095]

[0096]

[0097]

[0098]

[0099] Examples 1 to 6 in Table 1 and Examples 7 to 13 in Table 2 show the results of measuring the piezoelectric response of piezoelectric stack 100 in which base layer 103 and piezoelectric thin film 104 are formed in this order on substrate 101, when substrate 101 is made of conductive Si, by changing the film thickness of base layer 103 and the conditions for producing piezoelectric thin film 104.

[0100] Examples 14 to 19 in Table 3 show the results of measuring the piezoelectric response of the piezoelectric stack 100 fabricated when the substrate 101 is SiSiO, and Examples 20 to 24 in Table 4 show the results of measuring the piezoelectric response of the piezoelectric stack 100 fabricated by using Pt for the electrode layer 102 and varying the film thickness of the base layer 103 and the fabrication conditions for the piezoelectric thin film 104 when the substrate 101 is alkali-free glass.

[0101] Example 25 in Table 4 shows the results of measuring the piezoelectric response of piezoelectric laminate 100 fabricated using ITO for electrode layer 102 and varying the film thickness of base layer 103 when substrate 101 is alkali-free glass, and Example 26 in Table 4 shows the results of measuring the piezoelectric response of piezoelectric laminate 100 fabricated using ITO for electrode layer 102 and varying the film thickness of base layer 103 when substrate 101 is quartz glass.

[0102] Examples 27 to 29 in Table 5 show the results of measuring the piezoelectric response of piezoelectric stacks 100 fabricated using Ti as electrode layer 102 on substrate 101 and varying the film thickness of underlayer 103, when the substrate 101 is SiSiO, when Examples 30 and 31 show the results of fabricating the substrate 101 using alkali-free glass, and when the substrate 101 is quartz glass. Examples 28, 31, and 32 are examples in which underlayer 103' is included between substrate 103 and electrode layer 102.

[0103] These results show that by including the base layer 103 between the electrode layer 102 and the piezoelectric thin film 104, a piezoelectric stack 100 is obtained that exhibits superior piezoelectric performance, eliminating the influence of the base (substrate or electrode layer) and film formation conditions, compared to a configuration that does not include the base layer 103.

[0104] This application is based on Japanese Patent Application No. 2023-187762 filed on November 1, 2023, the contents of which are incorporated herein by reference.

[0105] 100: Piezoelectric laminate 101: Substrate 102: Electrode layer 103, 103': Underlayer 104: Piezoelectric thin film 105: Laminated film

Claims

1. A piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, the laminate film including, in order from the substrate side, an electrode layer, an underlayer, and a piezoelectric thin film, the underlayer and the piezoelectric thin film are in contact with each other, the underlayer contains a nitrogen compound containing at least one element selected from the group consisting of III to VI elements, and the absolute value of the piezoelectric constant |e ３１ ｆ | is 0.5 C / m ２ This is the piezoelectric laminate.

2. A piezoelectric laminate having a substrate and a laminate film provided on at least one surface of the substrate, the laminate film including, in that order from the substrate side, an electrode layer, an underlayer, and a piezoelectric thin film, the underlayer and the piezoelectric thin film are in contact with each other, the underlayer contains a nitrogen compound, the nitrogen compound includes at least one element selected from the group consisting of elements of groups III to VI, excluding zirconium nitride.

3. The piezoelectric laminate according to claim 1 or 2, wherein the piezoelectric thin film contains aluminum nitride, and the aluminum nitride has a hexagonal wurtzite structure oriented in the c-axis direction.

4. The piezoelectric laminate according to claim 1 or 2, wherein the underlayer has a sodium chloride structure, a fluorite structure or a perovskite structure.

5. The piezoelectric laminate according to claim 1 or 2, wherein the underlayer has a (111) plane preferential orientation structure in which the orientation is preferentially oriented in the (111) plane direction.

6. The piezoelectric laminate according to claim 1 or 2, wherein the underlayer is a nitrogen compound containing at least one element selected from the group consisting of Zr, Hf, Y, W and Nb.

7. The piezoelectric laminate according to claim 1 or 2, wherein the thickness of the underlayer is 0.2 nm or more and 100 nm or less.

8. The piezoelectric stack according to claim 7, wherein the thickness of the underlayer is 5 nm or more and 70 nm or less.

9. The piezoelectric laminate according to claim 1 or 2, wherein the thickness of the piezoelectric thin film is 100 nm or more and 10 μm or less.

10. A piezoelectric element comprising the piezoelectric laminate according to claim 1 or 2.

11. A method for manufacturing a piezoelectric laminate having a substrate and a laminated film provided on at least one surface of the substrate, comprising: preparing the substrate; and depositing an electrode layer, an underlayer, and a piezoelectric thin film in this order on at least one surface of the substrate, wherein the underlayer contains a nitrogen compound containing at least one element selected from the group consisting of III to VI groups, the piezoelectric thin film is deposited so as to be in contact with the underlayer, and the absolute value of the piezoelectric constant |e of the piezoelectric thin film is ３１ ｆ | is 0.5 C / m ２ This is the method for producing the piezoelectric laminate.

12. A method for manufacturing a piezoelectric laminate having a substrate and a laminated film provided on at least one surface of the substrate, comprising: preparing the substrate; and depositing an electrode layer, an underlayer, and a piezoelectric thin film in this order on at least one surface of the substrate, wherein the underlayer contains a nitrogen compound, the nitrogen compound containing at least one element selected from the group consisting of elements from groups III to VI, excluding zirconium nitride, and the piezoelectric thin film is deposited so as to be in contact with the underlayer.

13. The method for producing a piezoelectric laminate according to claim 11 or 12, wherein the film is formed by a sputtering method.

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