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

Abstract

The purpose of the present invention is to eliminate the influence of the crystal structure or lattice matching of a piezoelectric thin film layer and an electrode layer to thereby improve crystal alignment properties of the piezoelectric thin film layer. A laminate according to the present invention has a substrate and a laminated film provided on at least one surface of the substrate. The laminated film has a first underlayer, an electrode layer, and a piezoelectric thin film layer in the stated order from the substrate side. The first underlayer is in contact with the substrate and the electrode layer, and the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of groups III to VI elements.

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 layer) 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] To improve the piezoelectric performance of a piezoelectric thin film, it is important that the piezoelectric thin film layer has high orientation. Much research has been conducted to obtain a highly oriented piezoelectric thin film layer. For example, Patent Documents 1 and 2 disclose that the c-axis orientation can be improved by providing an underlayer of tungsten, platinum, or the like between a silicon substrate or glass substrate and aluminum nitride. Patent Document 3 discloses that good crystallinity can be obtained by using an underlayer of aluminum nitride that has the same hexagonal wurtzite structure crystals.

[0005] Japanese Patent Publication No. 2004-6535 Japanese Patent Publication No. 2004-265899 Japanese Patent Publication No. 2019-145677

[0006] However, in order to improve the crystal orientation using conventional methods, the electrode layer in contact with the piezoelectric thin film layer must have the same crystal structure or lattice matching, which limits the choice of electrode material that can be used to form the electrode layer.

[0007] The present invention has been made in view of the above problems, and has as its object to improve the crystal orientation of a piezoelectric thin film layer.

[0008] The present inventors have found 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 elements of groups III to VI between a substrate and an electrode layer, and have thus completed the present invention.

[0009] 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 has, from the substrate side, a first underlayer, an electrode layer, and a piezoelectric thin film layer in this order, the first underlayer being in contact with the electrode layer, and the first underlayer containing a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements. 2. The piezoelectric laminate according to 1 above, wherein the piezoelectric thin film layer contains aluminum nitride, and the aluminum nitride has a hexagonal wurtzite structure oriented in the c-axis direction. 3. The piezoelectric laminate according to 2 above, wherein the half-width of the peak of the (002) plane of the aluminum nitride measured by X-ray diffraction is 0.34 or less. 4. The piezoelectric laminate according to 1 above, wherein the first underlayer has a sodium chloride structure, a fluorite structure, or a perovskite structure. 5. 5. The piezoelectric stack according to 1 above, wherein the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of elements of groups III to V. 6. The piezoelectric stack according to 1 above, wherein the first underlayer is a nitrogen compound containing at least one element selected from Zr, Hf, Y, W, and Nb. 7. The piezoelectric stack according to 1 above, wherein the first underlayer is a compound represented by the chemical formula QN Ｘwherein Q in the chemical formula is at least one element selected from the group consisting of Group III to VI elements, and the degree of nitridation represented by x in the chemical formula satisfies 1 < x < 2. 8. The piezoelectric stack according to 7 above, wherein the degree of nitridation represented by x in the chemical formula satisfies 1.1 < x < 1.65. 9. The piezoelectric stack according to 1 above, wherein the thickness of the first underlayer is 0.2 nm or more and 100 nm or less. 10. The piezoelectric stack according to 9 above, wherein the thickness of the first underlayer is 0.4 nm or more and 80 nm or less. 11. The piezoelectric stack according to 1 above, wherein the arithmetic mean roughness (Ra) of the piezoelectric thin film layer is 3.0 nm or less. 12. The piezoelectric stack according to 1 above, further comprising a second underlayer, wherein the second underlayer is in contact with the electrode layer and the piezoelectric thin film layer, and wherein the second underlayer contains a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements. 13. 13. The piezoelectric stack according to 12, wherein the second underlayer has a thickness of 0.2 nm or more and 40 nm or less. 14. The piezoelectric stack according to 1, wherein the piezoelectric thin film layer has a film thickness of 100 nm or more and 10 μm or less. 15. A piezoelectric element having the piezoelectric stack according to any one of 1 to 14. 16. A method for manufacturing a piezoelectric stack having a substrate and a laminate film provided on at least one surface of the substrate, the method comprising: preparing the substrate; and depositing a first underlayer, an electrode layer, and a piezoelectric thin film layer in this order on at least one surface of the substrate, wherein the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements, and depositing the electrode layer so as to be in contact with the first underlayer.17. 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 a first underlayer, an electrode layer, a second underlayer, and a piezoelectric thin film layer in this order on at least one surface of the substrate, wherein the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements, and the second underlayer contains a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements, and the electrode layer is deposited so as to be in contact with the first underlayer. 18. The method for manufacturing a piezoelectric laminate according to paragraphs 16 or 17, wherein the piezoelectric thin film layer contains aluminum nitride, and the aluminum nitride has a hexagonal wurtzite structure oriented in the c-axis direction.

[0010] According to the present invention, the crystal orientation of the piezoelectric thin film layer can be improved.

[0011] 1 and 2 are schematic cross-sectional views of a piezoelectric laminate according to an embodiment of the present invention.

[0012] Hereinafter, the contents of the embodiments of the present invention will be described with reference to the embodiments. However, the present invention includes many different aspects and should not be construed as being limited to the contents of the embodiments exemplified below.

[0013] 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 having, in this order from the substrate side, a first underlayer, an electrode layer, and a piezoelectric thin film layer, the first underlayer being in contact with the electrode layer, and the first underlayer containing a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements. A second underlayer may be provided between the electrode layer and the piezoelectric thin film layer.

[0014] A second 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 a substrate; and depositing a first underlayer, an electrode layer, and a piezoelectric thin film layer in this order on at least one surface of the substrate, wherein the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements, and the electrode layer is deposited so as to be in contact with the first underlayer.

[0015] 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 a substrate; and depositing a first underlayer, an electrode layer, a second underlayer, and a piezoelectric thin film layer in this order on at least one surface of the substrate, wherein the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of Group III to Group VI elements, the second underlayer contains a nitrogen compound containing at least one element selected from the group consisting of Group III to Group VI elements, and the electrode layer is deposited so as to be in contact with the first underlayer.

[0016] The embodiments of the present invention (hereinafter also referred to as the present embodiments) include Embodiments 1 to 3. The method for manufacturing a piezoelectric laminate according to the second embodiment corresponds to the example of the piezoelectric laminate of the first embodiment that does not have a second underlayer, and the method for manufacturing a piezoelectric laminate according to the third embodiment corresponds to the example of the piezoelectric laminate of the first embodiment that has a second underlayer.

[0017] <Piezoelectric Laminate> The structure and manufacturing method of a piezoelectric laminate 100 according to this embodiment will be described with reference to FIG.

[0018] [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 106 provided on at least one surface of the substrate 101. The laminate film 106 includes, in order from the substrate 101 side, a first underlayer 102, an electrode layer 103, and a piezoelectric thin film layer 105. Here, the first underlayer 102 and the electrode layer 103 are in contact with each other.

[0019] (Substrate) The thickness, material, etc. of the substrate 101 are not particularly limited, and any conventionally known substrate can be used as long as it is capable of forming the laminated film 106 on its surface. 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 thereof, 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).

[0020] (First Underlayer) The first underlayer 102 is a layer formed on at least one surface of the substrate 101 directly or via another layer, and improves the crystal orientation of the piezoelectric thin film layer 105 .

[0021] The underlayer (e.g., substrate 101, first underlayer 102) of piezoelectric thin-film layer 105 affects the crystalline orientation of piezoelectric thin-film layer 105. Even after a cleaning process, the underlayer is susceptible to surface contamination by natural oxide films and carbon-based contaminants, which tends to result in non-uniform crystalline orientation of the material constituting piezoelectric thin-film layer 105. In response to this, the inventors have discovered that by providing first underlayer 102 containing a nitrogen compound including at least one element selected from the group consisting of III to VI group elements under electrode layer 103, the polarity of piezoelectric thin-film layer 105 can be controlled and the crystalline orientation of piezoelectric thin-film layer 105 can be improved.

[0022] In this way, it is possible to effectively improve the piezoelectric performance by improving the crystal orientation of the piezoelectric thin film layer 105. In particular, by forming the first underlayer 102 in a 100% nitrogen atmosphere, it is easy to form a crystal structure that incorporates nitrogen in excess of the stoichiometric ratio, and this effect can be further enhanced.

[0023] The first underlayer 102 contains a nitrogen compound containing at least one element selected from the group consisting of elements from groups III to VI. The nitrogen compound containing at least one element selected from the group consisting of elements from groups III to VI is represented by the chemical formula QN ＸIn the chemical formula, Q represents at least one element selected from the group consisting of Group III to VI elements, and x represents the degree of nitridation. The degree of nitridation x is greater than 0, preferably greater than 1, more preferably greater than 1.1, and even more preferably greater than 1.2. The degree of nitridation x is preferably less than 2, more preferably less than 1.65, and even more preferably less than 1.5. By setting the degree of nitridation x within the above range, the c-axis orientation of the piezoelectric thin film layer is further improved. This effect is particularly noticeable when the piezoelectric thin film layer contains aluminum nitride.

[0024] 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.

[0025] In this embodiment, the nitrogen compound contained in the first underlayer 102 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 first underlayer 102 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 layer 105, making it easier to align the polarity of the material constituting the piezoelectric thin film layer 105 and improve the crystal orientation.

[0026] In this embodiment, examples of the III to VI group elements contained in the nitrogen compound constituting the first underlayer 102 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 aforementioned Cubic and (111) plane main orientation and the possibility of taking an over-nitrided state (metastable state). In this embodiment, examples of the nitrogen compound constituting the first underlayer 102 include ZrN, Zr ３ N ４ , HfN, YN, Y ５ N １４ , WN,W ７ N １２ , NbN and Nb ２ N ３ are preferred, ZrN, Zr ３ More preferred is N. These nitrogen compounds may be used alone or in combination of two or more.

[0027] In this embodiment, the first underlayer 102 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 layer 105, thereby further improving the crystal orientation of the piezoelectric thin film layer 105.

[0028] In this embodiment, the first underlayer 102 preferably has a sodium chloride structure, a fluorite structure, or a perovskite structure, which facilitates preferential orientation in the (111) plane direction, thereby further improving the crystal orientation in the outermost layer of the piezoelectric thin film layer 105.

[0029] The thickness of the first underlayer is not particularly limited, but is preferably 0.2 nm or more, more preferably 0.4 nm or more, from the viewpoint of stably forming a continuous film and further enhancing the c-axis orientation of the piezoelectric thin film layer, and is preferably 100 nm or less, more preferably 80 nm or less, and even more preferably 60 nm or less, from the viewpoint of industrially improving film formation efficiency and preventing the loss of the continuous film due to the occurrence of cracks, etc.

[0030] (Electrode Layer) The material of the electrode layer 103 is not particularly limited, and any material commonly used for the piezoelectric laminate 100 can be used. The electrode layer 103 is in direct contact with the first underlayer 102. Examples of electrode materials constituting the electrode layer 103 include metal materials such as aluminum (Al), transition metals such as molybdenum (Mo), titanium (Ti), chromium (Cr), tantalum (Ta), iridium (Ir), and nickel (Ni), noble 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 103 may also be made of a combination of the above materials.

[0031] The thickness of the electrode layer 103 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.

[0032] The arithmetic mean roughness (Ra) of the electrode layer 103 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.

[0033] From the viewpoint of ensuring good conductivity, the specific resistance of the electrode layer 103 is preferably 1×10 Ω·cm or less, and more preferably 1×10 －２ The lower limit of the resistivity is not particularly limited, but is usually 1×10 －６ The resistivity of the electrode layer 103 is Ω·cm or more. The resistivity of the electrode layer 103 can be measured by using a Hall effect measuring device for the substrate on which the electrode layer 103 is formed.

[0034] (Second Underlayer) In this embodiment, the second underlayer 104 is not essential, but may be provided between the electrode layer 103 and the piezoelectric thin film layer 105. The second underlayer improves the crystalline orientation of the piezoelectric thin film layer. FIG. 2 shows an example of the configuration of the piezoelectric stack 100 in which the second underlayer 104 is provided between the electrode layer 103 and the piezoelectric thin film layer 105.

[0035] By forming the second underlayer 104 in an atmosphere of 100% nitrogen, it becomes easier to form a crystal structure that incorporates nitrogen in excess of the stoichiometric ratio, and this effect can be further enhanced.

[0036] The second underlayer 104 contains a nitrogen compound containing at least one element selected from the group consisting of elements from groups III to VI. The nitrogen compound containing at least one element selected from the group consisting of elements from groups III to VI is represented by the chemical formula QN Ｘ In the chemical formula, Q represents at least one element selected from the group consisting of Group III to VI elements, and x represents the degree of nitridation. The degree of nitridation x is greater than 0, preferably greater than 1, more preferably greater than 1.1, and even more preferably greater than 1.2. The degree of nitridation x is preferably less than 2, more preferably less than 1.65, and even more preferably less than 1.5. By setting the degree of nitridation x within the above range, the c-axis orientation of the piezoelectric thin film layer is further improved. This effect is particularly noticeable when the piezoelectric thin film layer contains aluminum nitride.

[0037] In this embodiment, the nitrogen compound contained in the second underlayer 104 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 second underlayer 104 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 layer 105, making it easier to align the polarity of the material constituting the piezoelectric thin film layer 105 and improve the crystal orientation.

[0038] In this embodiment, examples of the III to VI group elements contained in the nitrogen compound constituting the second underlayer 104 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 this embodiment, examples of the nitrogen compound constituting the second underlayer 104 include ZrN, Zr ３ N ４ , HfN, YN, Y ５ N １４ , W.N., W. ７ N １２ , NbN and Nb ２ N ３ are preferred, ZrN, Zr ３ More preferred is N. These nitrogen compounds may be used alone or in combination of two or more.

[0039] In this embodiment, the second underlayer 104 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 layer 105, thereby further improving the crystal orientation of the piezoelectric thin film layer 105.

[0040] In this embodiment, the second underlayer 104 preferably has a sodium chloride structure, a fluorite structure, or a perovskite structure, which facilitates preferential orientation in the (111) plane direction, thereby further improving the crystal orientation in the outermost layer of the piezoelectric thin film layer 105.

[0041] The thickness of the second underlayer is not particularly limited, but is preferably 0.2 nm or more, more preferably 0.4 nm or more, and even more preferably 1 nm or more from the viewpoint of further enhancing the c-axis orientation of the piezoelectric thin film layer, and is preferably 100 nm or less, more preferably 80 nm or less, and even more preferably 60 nm or less from the viewpoint of enhancing the film formation efficiency and preventing the loss of the continuous film due to the occurrence of cracks, etc.

[0042] (Piezoelectric Thin Film Layer) The piezoelectric thin film layer 105 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 to the (002) plane in the XRD diffraction pattern measured by the out-of-plane method is less than 0.3.

[0043] 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 layer 105 having a hexagonal wurtzite structure are exhibited is the

[002] direction of the hexagonal wurtzite structure. In other words, the orientation of the (002) plane of the hexagonal wurtzite structure (c-axis orientation) allows the piezoelectric thin film layer 105 to achieve excellent piezoelectric properties. The orientation of the (002) plane can be evaluated, for example, by XRD measurement. When a 2θ / θ scan is performed in the 2θ range of 30° to 60°, it is preferable that the half-width of the peak of the (002) plane of the AlN crystal appearing at 2θ = 35° to 37° is 0.34 or less. In order to obtain higher piezoelectric properties, the half width is more preferably 0.32 or less, even more preferably 0.30 or less, particularly preferably 0.26 or less, and most preferably 0.25 or less.

[0044] For example, a thin film of aluminum nitride (AlN), ZnO, GaN, etc. is preferably used as the piezoelectric thin film layer 105. 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 layer 105 contains AlN, and it is more preferable that the AlN has a hexagonal wurtzite structure oriented in the c-axis direction.

[0045] The thickness of the piezoelectric thin film layer 105 is not particularly limited, but from the viewpoint of ensuring good 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 1 μm or more. On the other hand, from the viewpoint of crystal growth without generating cracks, the thickness is preferably 10 μm or less, more preferably 7.5 μm or less, and even more preferably 5 μm or less.

[0046] The piezoelectric thin film layer 105 preferably has high smoothness and a small arithmetic mean roughness (Ra). The arithmetic mean roughness (Ra) of the surface of the piezoelectric thin film layer 105 refers to the arithmetic mean roughness of the surface that is not in contact with the electrode layer 103 or the second underlayer 104. The arithmetic mean roughness (Ra) is measured using an atomic force microscope (AFM). The arithmetic mean roughness (Ra) of the surface of the piezoelectric thin film layer is preferably 3.0 nm or less, more preferably 2.5 nm or less, even more preferably 2.0 nm or less, and particularly preferably 1.7 nm or less. There is no particular restriction on the lower limit of the arithmetic mean roughness (Ra), but from the viewpoint of adhesion during the formation of the 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.

[0047] The piezoelectric laminate according to this embodiment may include layers other than the substrate, electrode layer, underlayer, and piezoelectric thin film layer, as long as the effects of the present invention are not impaired. For example, an adhesive layer that adheres the substrate and the first underlayer may be provided between the substrate and the first 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 layer opposite the electrode layer. Any of the above layers may be conventionally known.

[0048] 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.

[0049] [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 a first underlayer, an electrode layer, and a piezoelectric thin film layer 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.

[0050] The first underlayer contains a nitrogen compound of a group III to group VI element, and the electrode layer is formed so as to be in contact with the first underlayer. After forming the electrode layer, a second underlayer may be formed, and then a piezoelectric thin film layer may be formed.

[0051] In this embodiment, the substrate, first underlayer, electrode layer, second underlayer, and piezoelectric thin film layer can all be the substrate 101, first underlayer 102, electrode layer 103, second underlayer 104, and piezoelectric thin film layer 105 described in the above [Structure of piezoelectric laminate], respectively.

[0052] The piezoelectric laminate obtained by this manufacturing method is preferably the piezoelectric laminate 100 described in the above [Structure of Piezoelectric Laminate].

[0053] That is, in the piezoelectric laminate obtained by the manufacturing method of this embodiment, the first underlayer and the electrode layer are in contact with each other, and the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of group III to VI elements.

[0054] (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.

[0055] (Laminated Film Formation) The laminated film 106 is formed on at least one surface of the substrate 101 prepared as described above. The laminated film 106 is formed in the order of the first underlayer 102, the electrode layer 103, and the piezoelectric thin film layer 105, and each of these can be formed by, for example, physical vapor deposition or chemical vapor deposition (CVD). 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 preferred. If the laminated film 106 includes a second underlayer, the second underlayer 104 can be formed after the electrode layer 103 is formed and before the piezoelectric thin film layer 105 is formed. The above-mentioned method or the like can be used for its formation.

[0056] The substrate temperature during the formation of the laminated film 106 is preferably from room temperature to 600° C. or less, and more preferably 250° C. or less.

[0057] To fully utilize the effects of the underlayer, it is preferable to continuously form the layers without breaking the vacuum not only during the formation of the first underlayer 102, but also during the formation of the electrode layer 103, the second underlayer 104, and the piezoelectric thin-film layer 105. In particular, if the vacuum is broken during the formation of the first underlayer 102, the second underlayer 104, and the piezoelectric thin-film layer 105, oxygen may be mixed in as an impurity, making it impossible to utilize the characteristics of the underlayer. In this case, good interfacial characteristics cannot be obtained, so it is preferable to continuously form the layers while maintaining the vacuum.

[0058] ((Formation of First Underlayer)) The first underlayer 102 may be formed directly on the substrate 101 or may be formed via an adhesive layer. The first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of elements of groups III to VI. When the first underlayer is formed by a sputtering method, the nitrogen compound QN can be easily formed by controlling the film formation conditions. Ｘ The composition, for example, the value of the degree of nitriding x, can be adjusted. Here, Q represents an element from Groups III to VI. The film formation conditions include, for example, the substrate temperature during film formation, the film formation pressure, the composition of the introduced gas, the target composition, and the post-heat treatment temperature.

[0059] The nitrogen compound constituting the first underlayer 102 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 from groups III to VI constituting the first underlayer 102 include Hf, Ti, Sc, V, Nb, Ta, Cr, Mo, W, O, C, etc.

[0060] A doping element may be included when the first underlayer 102 is formed. For example, when the piezoelectric thin film layer 105 contains aluminum nitride, it is preferable to include the doping element to the extent that the piezoelectric thin film layer 105 can maintain a hexagonal wurtzite structure. By including elements such as Sc, Y, Mg, Ca, Sr, Zr, Hf, V, and Nb as the doping element, strain is applied to the piezoelectric thin film layer 105, improving the piezoelectric performance. The Sc element is particularly preferable for improving the piezoelectric performance, and in this case, the doping can be up to about 43 at %.

[0061] The degree of nitridation x of the nitrogen compound in the first underlayer 102 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.

[0062] 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.

[0063] ((Formation of Electrode Layer)) The electrode layer 103 is formed directly on the first underlayer 102. The electrode layer 103 may be a single layer or may be made up of two or more layers.

[0064] ((Formation of Second Underlayer)) The formation of the second underlayer 104 is not essential, but the second underlayer 104 may be formed after the electrode layer 103. When the second underlayer 104 is formed, the second underlayer 104 contains a nitrogen compound containing at least one element selected from the group consisting of elements of groups III to VI. When the second underlayer 104 is formed by a sputtering method, the film formation conditions can be controlled to produce a nitrogen compound QN of elements of groups III to VI. Ｘ The composition, i.e., the value of the degree of nitriding x, can be adjusted. Here, Q represents an element of groups III to VI. The film formation conditions include, for example, the substrate temperature during film formation, the film formation pressure, the composition of the introduced gas, the target composition, and the post-heat treatment temperature.

[0065] The nitride compound constituting the second underlayer 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 impurity content in the target is about 10 at %. That is, impurities contained in a target containing a III to VI element that serves as the nitride compound target constituting the first underlayer 102 and a material target for the piezoelectric thin film layer, for example, Al in the case of aluminum nitride AlN, include Hf, Ti, Sc, V, Nb, Ta, Cr, Mo, W, O, C, etc.

[0066] A doping element may be included when forming the second underlayer 104. For example, when the piezoelectric thin film layer 105 contains aluminum nitride, the doping element may include elements such as Sc, Y, Mg, Ca, Sr, Zr, Hf, V, and Nb, which impart strain to the aluminum nitride and improve its piezoelectric performance. Sc is particularly preferable for improving piezoelectric performance, and in this case, the doping can be up to about 43 at %.

[0067] The degree of nitridation x of the nitrogen compound in the second underlayer 104 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.

[0068] 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.

[0069] ((Formation of Piezoelectric Thin Film Layer)) The piezoelectric thin film layer 105 may be formed directly on the electrode layer 103, or may be formed directly on the second underlayer 104. Alternatively, the piezoelectric thin film layer 105 may be formed on the electrode layer 103 or the second underlayer 104 via an adhesive layer.

[0070] The piezoelectric thin film layer 105 can be formed by a conventional method using a conventional 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.

[0071] The nitrogen compound constituting the piezoelectric thin film layer 105 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 layer 105 (e.g., Al when the material is AlN) include Hf, Ti, Sc, V, Nb, Ta, Cr, Mo, W, O, C, etc.

[0072] As explained above, this 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 has, from the substrate side, a first underlayer, an electrode layer, and a piezoelectric thin film layer in this order, the first underlayer being in contact with the electrode layer, and the first underlayer containing a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements. 2. The piezoelectric laminate according to item 1, wherein the piezoelectric thin film layer contains aluminum nitride, and the aluminum nitride has a hexagonal wurtzite structure oriented in the c-axis direction. 3. The piezoelectric laminate according to item 1 or 2, wherein the half-width of the peak of the (002) plane of the aluminum nitride measured by X-ray diffraction is 0.34 or less. 4. The piezoelectric laminate according to any one of items 1 to 3, wherein the first underlayer has a sodium chloride structure, a fluorite structure, or a perovskite structure. 5. 5. The piezoelectric laminate according to any one of 1 to 4 above, wherein the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of elements of groups III to V. 6. The piezoelectric laminate according to any one of 1 to 5 above, wherein the first underlayer is a nitrogen compound containing at least one element selected from Zr, Hf, Y, W, and Nb. 7. The piezoelectric laminate according to any one of 1 to 5 above, wherein the first underlayer is a nitrogen compound represented by the chemical formula QN Ｘwherein Q in the chemical formula is at least one element selected from the group consisting of group III to VI elements, and the degree of nitridation represented by x in the chemical formula satisfies 1<x<2. 8. The piezoelectric stack according to any one of items 1 to 6 above, wherein the degree of nitridation represented by x in the chemical formula satisfies 1.1<x<1.65. 9. The piezoelectric stack according to any one of items 1 to 8 above, wherein the first underlayer has a thickness of 0.2 nm or more and 100 nm or less. 10. The piezoelectric stack according to item 9 above, wherein the first underlayer has a thickness of 0.4 nm or more and 80 nm or less. 11. The piezoelectric stack according to any one of items 1 to 10 above, wherein the piezoelectric thin film layer has an arithmetic average roughness (Ra) of 3.0 nm or less. 12. 13. The piezoelectric stack according to any one of 1 to 11 above, further comprising a second underlayer, the second underlayer being in contact with the electrode layer and the piezoelectric thin film layer, and the second underlayer containing a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements. 13. The piezoelectric stack according to 12 above, wherein the second underlayer has a thickness of 0.2 nm to 40 nm. 14. The piezoelectric stack according to any one of 1 to 13 above, wherein the piezoelectric thin film layer has a film thickness of 100 nm to 10 μm. 15. A piezoelectric element comprising the piezoelectric stack according to any one of 1 to 14 above. 16. 1. 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 a first underlayer, an electrode layer, and a piezoelectric thin film layer in this order on at least one surface of the substrate, wherein the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of III to VI group elements, and the electrode layer is deposited so as to be in contact with the first underlayer.17. 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 a first underlayer, an electrode layer, a second underlayer, and a piezoelectric thin film layer in this order on at least one surface of the substrate, wherein the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements, and the second underlayer contains a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements, and the electrode layer is deposited so as to be in contact with the first underlayer. 18. The method for manufacturing a piezoelectric laminate according to paragraphs 16 or 17, wherein the piezoelectric thin film layer contains aluminum nitride, and the aluminum nitride has a hexagonal wurtzite structure oriented in the c-axis direction.

[0073] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Examples 1, 2, 5 to 10, 13, 14, 17, 18, 21, and 22 are working examples, and Examples 3, 4, 11, 12, 15, 16, 19, 20, 23, and 24 are comparative examples.

[0074] <Preparation of Piezoelectric Stack> (Example 1) A piezoelectric stack 100 was prepared by forming an electrode layer 103 and a piezoelectric thin film layer 105 in this order on a substrate 101 and a first underlayer 102, according to the procedures (1) to (4) below. (1) Preparation of Substrate 101 A conductive silicon substrate (abbreviated as "Conductive Si" in the table) measuring 25 mm x 25 mm x 0.625 mm was used as the substrate 101. (2) Preparation of First Underlayer 102 A first underlayer 102 was prepared on one surface of the substrate 101 by sputtering under the following conditions according to the following procedure. The first underlayer 102 was prepared by placing the substrate in a vacuum chamber of a sputtering device, evacuating the vacuum chamber, and reducing the pressure to 10 －３The pressure was reduced to 10 Pa or less. Film formation apparatus: 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 Film thickness: 10 nm Substrate heating temperature: room temperature (3) Formation of electrode layer 103 The electrode layer 103 was formed on the first underlayer 102 by sputtering according to the following procedure. The electrode layer 103 was formed by placing the sample on which the first underlayer 102 obtained above was formed in the vacuum chamber of the sputtering apparatus without breaking the vacuum from the formation of the first underlayer 102, and then evacuating the vacuum chamber and reducing the pressure to 10 －３ After the pressure was reduced to below 10 Pa, the film was formed under the following conditions: Film forming apparatus: vertical in-line sputtering apparatus (manufactured by ULVAC) Sputtering target material: Ti metal (manufactured by Kojundo Chemical Co., Ltd., purity 3N) Introduced gas: Ar gas (purity = 99.9% or more) 80 sccm Film forming pressure: 0.4 Pa Film thickness: 100 nm Substrate heating temperature: room temperature (4) Formation of piezoelectric thin film layer 105 Piezoelectric thin film layer 105 was formed on the above electrode layer 103 by sputtering according to the following procedure. The piezoelectric thin film layer was formed by placing the sample on which the electrode layer 103 obtained above was formed in the vacuum chamber of the sputtering apparatus without breaking the vacuum from the time of forming the electrode layer 103, and then evacuating the vacuum chamber and reducing the pressure to 10 －３ After the pressure was reduced to 0.2 Pa or less, the deposition was carried out under the following conditions: deposition apparatus: vertical in-line sputtering apparatus (manufactured by ULVAC) sputtering target material: Al metal (3N) manufactured by Kojundo Chemical Co., Ltd. Introduced gas: nitrogen gas (purity = 99.9% or more) 40 sccm deposition pressure: 0.2 Pa power density: 7.1 W / cm ２ Substrate heating temperature: room temperature Film thickness: 1000 nm

[0075] In this way, a ZrN film was formed on the substrate 101 as the first underlayer 102. Ｘ A piezoelectric laminate 100 was obtained in which a film, a Ti film as the electrode layer 103, and an aluminum nitride (AlN) film as the piezoelectric thin film layer 105 were formed in this order.

[0076] In Example 2, after the electrode layer 103 was formed, the second underlayer 104 was formed by the following procedure, and then the piezoelectric thin film layer 105 was formed. Except for the formation of the second underlayer 104, the piezoelectric stack 100 was fabricated using the same procedure as in Example 1.

[0077] The second underlayer 104 was formed on the surface of the electrode layer 103 by sputtering under the following conditions. The second underlayer 104 was formed by placing the sample on which the electrode layer 103 was formed in the vacuum chamber of the sputtering device without breaking the vacuum after the formation of the electrode layer 103. The vacuum chamber was then evacuated and the pressure was increased 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: 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 Film thickness: 10 nm Substrate heating temperature: room temperature The piezoelectric thin film layer 105 was formed by reducing the pressure to 10 －３ The test was carried out after the pressure was reduced to below 1 Pa.

[0078] Examples 3 and 4 In Examples 3 and 4, the piezoelectric laminates 100 were fabricated by the same film formation procedures as in Examples 1 and 2, respectively, except that the first underlayer 102 was not fabricated.

[0079] (Examples 5 to 10) In Examples 5 to 6 and 8 to 10, the piezoelectric laminate 100 was fabricated by film formation using the same procedure as in Example 1, except that alkali-free glass was used for the substrate 101 and the film thickness of the first underlayer 102 was changed to the conditions shown in Table 1. In Example 7, the piezoelectric laminate 100 was fabricated by film formation using the same procedure as in Example 2, except that alkali-free glass was used for the substrate 101.

[0080] (Examples 11 and 12) In Examples 11 and 12, the piezoelectric laminate 100 was fabricated by the same procedures as in Examples 1 and 2, respectively, except that alkali-free glass was used for the substrate 101 and the first underlayer 102 was not formed.

[0081] (Examples 13 to 14) In Examples 13 and 14, the piezoelectric laminate 100 was fabricated by the same procedures as in Examples 1 and 2, respectively, except that alkali-free glass was used for the substrate 101 and the electrode layer 103 was changed to an ITO film. The ITO film of the electrode layer 103 was formed under the following conditions. Film formation apparatus: vertical in-line sputtering apparatus (manufactured by ULVAC) Sputtering target material: ITO (In, manufactured by Mitsui Mining & Smelting Co., Ltd.) ２ O ３ : SnO ２ = 90:10 wt%) 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 Film thickness: 120 nm Substrate heating temperature: room temperature

[0082] Examples 15 and 16 In Examples 15 and 16, the piezoelectric laminate 100 was fabricated by the same procedures as in Examples 13 and 14, respectively, except that the first underlayer 102 was not formed.

[0083] Examples 17 and 18 In Examples 17 and 18, except that quartz was used for the substrate 101, films were formed in the same manner as in Examples 1 and 2, respectively, to produce the piezoelectric laminate 100.

[0084] Examples 19 and 20 In Examples 19 and 20, the piezoelectric stack 100 was fabricated by the same procedures as in Examples 1 and 2, respectively, except that quartz was used for the substrate 101 and the first underlayer 102 was not formed.

[0085] Examples 21 and 22 In Examples 21 and 22, except that quartz was used for the substrate 101, the piezoelectric laminate 100 was fabricated by the same procedures as in Examples 13 and 14, respectively.

[0086] Examples 23 and 24 In Examples 23 and 24, the piezoelectric stack 100 was fabricated by the same procedures as in Examples 13 and 14, respectively, except that quartz was used for the substrate 101 and the first underlayer 102 was not formed.

[0087] <Evaluation> The following measurements and evaluations were performed on each of the obtained piezoelectric laminates 100. (Crystal Orientation of Piezoelectric Thin Film Layer) For XRD measurement, an X-ray diffractometer (MiniFlex II, manufactured by Rigaku Corporation) was used. The sample was set to evaluate diffraction perpendicular to the substrate, and a divergence slit of 1.25°, a scattering slit of 1.25°, and a receiving slit of 0.3 mm were used to perform a 2θ / θ scan in the 2θ range of 30° to 60°. After background correction, the diffraction intensity ratio of the (002) plane of the AlN crystal, which appears at 2θ = 35° to 37°, was calculated, taking the value without the first and second underlayers as 1, and used as a normalized value. The normalized values ​​and the half-widths for the diffraction intensity of the (002) plane are shown in Tables 1 to 3.

[0088] (Arithmetic mean roughness of the piezoelectric thin film layer surface) The arithmetic mean roughness (Ra) of the piezoelectric thin film layer was measured using an atomic force microscope (AFM). The definition of arithmetic mean roughness (Ra) is in accordance with JIS B 0601:2001. An arithmetic mean roughness (Ra) of 3.0 nm or less can be judged to have good flatness, and an arithmetic mean roughness of 1.7 nm or less can be judged to have even better flatness. The results are shown in Tables 1 to 3 under "Arithmetic mean roughness Ra (nm) of piezoelectric thin film layer (aluminum nitride)". Apparatus: SII Nanotechnology Co., Ltd., model number: S-Image

[0089] (Degree of nitriding x) The "degree of nitriding x" of the first underlayer was calculated from the "refractive index n" by the following method. This is explained below. First, to serve as a reference, a first underlayer 1 and a first underlayer 2 of 20 nm were formed under the following "deposition conditions 1" and "deposition conditions 2." First underlayer 1: Deposition condition 1 Power used: 700 W Introduced gas: Ar: 40 sccm, N ２ : 10 sccm Film formation pressure: 0.37 Pa First underlayer 2: Film formation condition 2 Power used: 700 W Introduced gas: Ar: 0 sccm, N ２ : 40 sccm Film formation pressure: 0.35 Pa

[0090] For the first underlayer 1 and the first underlayer 2, the element ratio of Zr to N in the zirconium nitride constituting the crystallinity improving layer, i.e., ZrN Ｘ The degree of nitriding x of the first underlayer 1 in Example 1 was found to be 1.6.

[0091]

[0092]

[0093]

[0094] (Effect of the First Underlayer) Comparing Example 1 with Example 3, and Example 2 with Example 4 in Table 1, it can be seen that the provision of the first underlayer increases the crystal orientation. Furthermore, it can be seen that the arithmetic mean roughness Ra, which represents the surface flatness, decreases when the first underlayer is provided. In Table 2, a similar trend can be seen when Examples 5 to 10 are compared with Examples 11 and 12. Furthermore, a similar trend can be seen when Examples 13 and 14 are compared with Examples 15 and 16. In Table 3, a similar trend can be seen when Examples 17 and 18 are compared with Examples 19 and 20. Furthermore, a similar trend can be seen when Examples 21 and 22 are compared with Examples 23 and 24.

[0095] Examples 5 to 10 in Table 2 show that the first underlayer is ZrN Ｘ The graph shows the results of the crystal orientation and arithmetic mean roughness Ra measured by XRD measurement of a piezoelectric thin film layer made of AlN with a film thickness of 1000 nm when the film thickness was changed between 5 nm and 80 nm.

[0096] The results in Tables 1 to 3 show that when the film thickness of the first underlayer is 5 nm or more and 80 nm or less, the arithmetic mean roughness Ra is 1.7 nm or less, and the half-width of the peak of the (002) plane of the AlN crystal is 0.34 or less, and a piezoelectric laminate with a good surface shape and excellent orientation is obtained.

[0097] The results in Tables 1 to 3 confirm that the orientation and surface shape of the piezoelectric thin film layer are improved by providing the first underlayer, regardless of the type of substrate and electrode layer.

[0098] This application is based on Japanese Patent Application No. 2023-187764 filed on November 1, 2023, the contents of which are incorporated herein by reference.

[0099] 100: Piezoelectric laminate 101: Substrate 102: First underlayer 103: Electrode layer 104: Second underlayer 105: Piezoelectric thin film layer 106: 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 having, from the substrate side, a first underlayer, an electrode layer and a piezoelectric thin film layer, in that order, the first underlayer is in contact with the electrode layer, and the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements.

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

3. The piezoelectric laminate according to claim 2, wherein the half-value width of the peak of the (002) plane of said aluminum nitride measured by X-ray diffraction is 0.34 or less.

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

5. The piezoelectric stack according to claim 1, wherein said first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of Group III to V elements.

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

7. The first underlayer is represented by the chemical formula QN Ｘ wherein Q in the chemical formula is at least one element selected from the group consisting of group III to VI elements, and a degree of nitridation represented by x in the chemical formula satisfies 1<x<2.

8. The piezoelectric laminate according to claim 7, wherein the degree of nitridation represented by x in the chemical formula satisfies 1.1<x<1.

65.

9. The piezoelectric stack according to claim 1, wherein the first underlayer has a thickness of 0.2 nm or more and 100 nm or less.

10. The piezoelectric stack according to claim 9, wherein the first underlayer has a thickness of 0.4 nm or more and 80 nm or less.

11. The piezoelectric stack according to claim 1, wherein the arithmetic mean roughness (Ra) of the piezoelectric thin film layer is 3.0 nm or less.

12. The piezoelectric stack according to claim 1, further comprising a second underlayer, said second underlayer being in contact with said electrode layer and said piezoelectric thin film layer, and said second underlayer containing a nitrogen compound containing at least one element selected from the group consisting of Group III to VI elements.

13. The piezoelectric stack according to claim 12, wherein the second underlayer has a thickness of 0.2 nm or more and 40 nm or less.

14. The piezoelectric stack according to claim 1, wherein the thickness of the piezoelectric thin film layer is 100 nm or more and 10 μm or less.

15. A piezoelectric element comprising the piezoelectric laminate according to any one of claims 1 to 14.

16. 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 a first underlayer, an electrode layer and a piezoelectric thin film layer in this order on at least one surface of the substrate, wherein the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of elements of groups III to VI, and the electrode layer is deposited so as to be in contact with the first underlayer.

17. 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 a first underlayer, an electrode layer, a second underlayer and a piezoelectric thin film layer in this order on at least one surface of the substrate, wherein the first underlayer contains a nitrogen compound containing at least one element selected from the group consisting of III to VI elements, the second underlayer contains a nitrogen compound containing at least one element selected from the group consisting of III to VI elements, and the electrode layer is deposited so as to be in contact with the first underlayer.

18. The method for producing a piezoelectric laminate according to claim 16 or 17, wherein the piezoelectric thin film layer contains aluminum nitride, and the aluminum nitride has a hexagonal wurtzite structure oriented in the c-axis direction.

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