Piezoelectric film, method for manufacturing piezoelectric film, piezoelectric assembly, and piezoelectric device

Abstract

A piezoelectric film according to the present application contains a piezoelectric material having a wurtzite-type crystal structure as a main component, and contains an additive element of Kr. The piezoelectric material contains one component selected from the group consisting of Zn, Al, Ga, Cd, and Si as a positive element. The content of the Kr element in the piezoelectric material is 0.01 atm% to 0.05 atm% relative to the content of the contained elements.

Description

Technical Field

[0001] This invention relates to piezoelectric films, methods for manufacturing piezoelectric films, piezoelectric components, and piezoelectric devices. Background Technology

[0002] Piezoelectric films have high piezoelectric properties, so piezoelectric components with piezoelectric films are widely used in sensors such as pressure sensors and acceleration sensors, high-frequency filters, piezoelectric actuators and other piezoelectric devices.

[0003] When a piezoelectric film is formed by crystallizing and growing it on a substrate, the piezoelectric film possesses high-voltage properties by aligning the crystals along the c-axis. However, due to increased film stress, the piezoelectric film is prone to bending. Therefore, when the substrate on which the piezoelectric film is placed is a low-rigidity substrate such as PET, the laminate with the piezoelectric film on the substrate warps, and in cases of excessive warping, it deforms into a cylindrical shape. On the other hand, when the substrate is a high-rigidity substrate such as a Si substrate or a glass substrate, cracks appear in the piezoelectric film, making it easier for the substrate and the piezoelectric layer to peel off. Therefore, when the laminate is used in a piezoelectric device, it adversely affects the piezoelectric properties of the device.

[0004] Therefore, various studies have been conducted on methods to suppress the film stress of piezoelectric films while achieving high orientation of the piezoelectric film, and piezoelectric components with a stress control layer disposed between the substrate and the piezoelectric film have been proposed.

[0005] As such a piezoelectric component, for example, a piezoelectric component having a lower electrode layer, an orientation control layer, a piezoelectric body layer and an upper electrode layer stacked sequentially on a substrate has been disclosed (for example, see Patent Document 1).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2008-42069 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] However, conventional piezoelectric devices have an orientation control layer between the lower electrode layer and the piezoelectric layer. This leads to a problem where the lattice matching between the lower electrode layer and the piezoelectric layer is prone to collapse due to the influence of the orientation control layer. If the lattice matching collapses, the crystal orientation of the piezoelectric layer becomes disordered, making high orientation of the piezoelectric layer difficult and reducing its piezoelectric properties. Piezoelectric devices operate based on the vibration of the piezoelectric layer along its thickness (thickness vibration). Therefore, to exert high piezoelectric properties, the piezoelectric layer must have a high crystal orientation with its crystal orientation aligned in the same direction.

[0011] Furthermore, the alignment control layer itself has film stress. Therefore, the film stress brought by the alignment control layer acts on the lower electrode layer located below the alignment control layer, resulting in problems such as peeling between the lower electrode layer and the alignment control layer, cracking of the lower electrode layer, and warping of the substrate, which reduce the device characteristics of the piezoelectric component.

[0012] One aspect of the present invention aims to provide a piezoelectric film that can exhibit excellent piezoelectric properties and reduce film stress.

[0013] Methods for solving problems

[0014] The piezoelectric film of the present invention comprises a piezoelectric material having a fibrous wurtzite-type crystal structure as the main component, the piezoelectric film having an additive element containing Kr, the piezoelectric material comprising a component selected from the group consisting of Zn, Al, Ga, Cd and Si as a positive element, and the content of Kr in the piezoelectric material relative to the content of the contained element is 0.01 atm% to 0.05 atm.

[0015] One aspect of the piezoelectric film manufacturing method of the present invention is as follows: in a mixed gas atmosphere containing Kr and oxygen, the piezoelectric material is sputtered onto a substrate containing Kr by using a sputtering method with a target containing Zn, thereby forming the piezoelectric film.

[0016] One aspect of the piezoelectric component involved in this invention is that it has an electrode and a piezoelectric layer on a substrate, wherein the piezoelectric layer is the piezoelectric film.

[0017] The effects of the invention

[0018] The piezoelectric film of the present invention can exhibit excellent piezoelectric properties and reduce film stress. Attached Figure Description

[0019] Figure 1 This is a schematic cross-sectional view illustrating the structure of the piezoelectric film according to an embodiment of the present invention.

[0020] Figure 2 A schematic cross-sectional view showing an example of another configuration of a piezoelectric film.

[0021] Figure 3 This is a diagram illustrating an example of the relationship between crystal orientation degree and electromechanical coupling coefficient.

[0022] Figure 4 This is a schematic cross-sectional view showing the configuration of a piezoelectric assembly having the piezoelectric film according to an embodiment of the present invention.

[0023] Figure 5 A schematic cross-sectional view showing an example of another component of a piezoelectric assembly.

[0024] Figure 6 A schematic cross-sectional view showing an example of another component of a piezoelectric assembly.

[0025] Figure 7 A schematic cross-sectional view showing an example of another component of a piezoelectric assembly.

[0026] Figure 8 A schematic cross-sectional view showing an example of another component of a piezoelectric assembly.

[0027] Figure 9 A graph showing the measurement results of the axial ratio c / a of the piezoelectric components of Example 1 and Comparative Example 1. Detailed Implementation

[0028] Hereinafter, embodiments of the present invention will be described in detail. Furthermore, to facilitate understanding, the same reference numerals are used for the same constituent elements in each drawing, and repeated descriptions are omitted. Additionally, the scale of each component in the drawings may sometimes differ from the actual scale. Unless otherwise specified, the "~" indicating a numerical range in this specification refers to the lower and upper limits including the values ​​described before and after it.

[0029] <Piezoelectric film>

[0030] The piezoelectric film according to embodiments of the present invention will be described. Figure 1 This is a schematic cross-sectional view showing the structure of the piezoelectric film according to this embodiment. Figure 1 As shown, the piezoelectric film 10 of this embodiment comprises a piezoelectric material having a wurtzite-type crystal structure (wurtzite-type crystalline material) as the main component, and an additive element selected from the group consisting of Ar, Kr, Xe, and Rn. The piezoelectric film 10, for example, can be used in a piezoelectric assembly by being disposed on a substrate 11.

[0031] In addition, in this specification, the thickness direction (vertical direction) of the piezoelectric film 10 is defined as the Z-axis, and the transverse direction (horizontal direction) orthogonal to the thickness direction is defined as the X-axis. The direction opposite to the Z-axis on the substrate 11 side is defined as the +Z-axis, and the substrate 11 side is defined as the -Z-axis. In the following description, for ease of explanation, the +Z-axis will be referred to as "upper" or "above," and the -Z-axis will be referred to as "lower" or "below," but this does not represent a universal upper / lower relationship.

[0032] The main component refers to the piezoelectric material content of 95 atm% or more, preferably 98 atm% or more, and more preferably 99 atm% or more.

[0033] The substrate 11 is a substrate on which the piezoelectric film 10 is disposed. As the substrate 11, any material can be used, such as a plastic substrate, a silicon (Si) substrate, or a glass substrate.

[0034] When using a plastic substrate, it is preferable to use a material that has flexibility that can impart bending properties to the piezoelectric component having the piezoelectric film 10.

[0035] Materials used to form the plastic substrate include, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), acrylic resins, cyclic olefin polymers, and polyimide (PI). Among these materials, PET, PEN, PC, acrylic resins, and cyclic olefin polymers are colorless and transparent, suitable for situations where the electrodes used in piezoelectric components equipped with the piezoelectric film 10 are transparent electrodes. Furthermore, in applications such as pulse monitors, heart rate monitors, and automotive pressure monitoring devices, where light transmittance is not required for the piezoelectric components equipped with the piezoelectric film 10, the aforementioned materials, translucent or opaque plastic materials can be used to form the plastic substrate.

[0036] The thickness of the substrate 11 is not particularly limited, and can be formed to an appropriate or arbitrary thickness depending on the application of the piezoelectric film 10 and the material of the substrate 11. For example, when the substrate 11 is a plastic substrate, the thickness of the substrate 11 can be 1 μm to 250 μm. In addition, the method for measuring the thickness of the substrate 11 is not particularly limited, and any measurement method can be used.

[0037] As described above, the piezoelectric film 10 contains a fibrous wurtzite-type crystalline material as its main component.

[0038] The wurtzite-type crystal structure of piezoelectric materials is represented by the general formula AB (where A is the positive element and B is the negative element). Wurtzite-type crystalline materials possess a hexagonal unit lattice and have a polarization vector in the direction parallel to the c-axis.

[0039] Wurtzite-type crystalline materials exhibit piezoelectric properties of a certain value or higher, and materials that can be crystallized using a low-temperature process below 200°C are preferred. In wurtzite-type crystalline materials, the positive element A, represented by the general formula AB, includes one component selected from the group consisting of Zn, Al, Ga, Cd, and Si. Examples of wurtzite-type crystalline materials that can be used include, for example, zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), aluminum nitride (AlN), gallium nitride (GaN), cadmium selenide (CdSe), cadmium telluride (CdTe), and silicon carbide (SiC). Among these, ZnO is preferred as a wurtzite-type crystalline material. One type can be used alone, or two or more can be used in combination. When two or more wurtzite-type crystalline materials are used in combination, one or more of these components can be included as the main component, while other components can be included as arbitrary components.

[0040] The fibrous wurtzite-type crystalline material contains ZnO, preferably substantially formed from ZnO, and more preferably formed solely from ZnO. "Substantially" means that, in addition to ZnO, it may contain unavoidable impurities that may inevitably be introduced during the manufacturing process.

[0041] When using two or more fibrous wurtzite-type crystalline materials, individual piezoelectric films can be stacked. For example, Figure 2 As shown, piezoelectric films 10A and 10B can be sequentially laminated on substrate 11.

[0042] In wurtzite-type crystalline materials, in addition to ZnO, ZnS, ZnSe, and ZnTe mentioned above, alkaline earth metals such as Mg, Ca, and Sr, or metals such as vanadium (V), titanium (Ti), zirconium (Zr), silicon dioxide (Si), and lithium (Li) can be included in specified proportions. These components can be included in the form of elements or oxides. For example, in wurtzite-type crystalline materials, in addition to ZnO, Mg can be included as MgO. These components, by entering the Zn sites of ZnO, can cause strain in the crystal lattice of ZnO, thereby improving the piezoelectric properties.

[0043] As described above, the piezoelectric film 10 includes additive elements. Ar, Kr, Xe, Rn, etc., can be used as additive elements. One of them can be used alone, or two or more can be included.

[0044] The ratio of Kr content to the content of other elements in the piezoelectric material (Kr content ratio (Kr element / other elements)) is 0.01 atm% to 0.05 atm%, preferably 0.01 atm% to 0.04 atm%, and more preferably 0.01 atm% to 0.03 atm%. If the Kr content is 0.01 atm% or higher, the effects of adding the element can be achieved, thus improving the c-axis orientation of the piezoelectric material and suppressing the increase in film stress. Furthermore, if the Kr content is 0.05 atm% or lower, the increase in the offset component of sputtered particles reaching the substrate 11 during sputtering is suppressed, thereby suppressing the decrease in the crystal orientation of the piezoelectric material.

[0045] In addition, the elements contained include all the elements contained in piezoelectric materials.

[0046] The "Kr element content ratio (Kr element / contained elements)" refers to the total amount of contained elements. For example, if the contained element is only ZnO, it refers to the content of ZnO alone; if the contained elements include Al2O3 in addition to ZnO, it refers to the total content of ZnO, Al2O3, etc.

[0047] The content of added elements such as Kr and contained elements in the piezoelectric film 10 can be determined, for example, by Rutherford backscattering analysis (RBS) using Pelletron 3SDH and 5SDH-2 (manufactured by NEC Corporation) as the measuring device.

[0048] The thickness of the piezoelectric film 10 is preferably 100 nm to 3000 nm, more preferably 200 nm to 2000 nm, and even more preferably 300 nm to 1000 nm. If the thickness of the piezoelectric film 10 is 100 nm or more, when the piezoelectric film 10 is applied to a piezoelectric component, even if an alignment control layer is provided below the piezoelectric film 10, the piezoelectric film 10 can still have sufficient piezoelectric characteristics, that is, polarization characteristics proportional to pressure. If the thickness of the piezoelectric film 10 is 3000 nm or less, even if the piezoelectric film 10 contains the above-mentioned additive elements, it can reduce the occurrence of cracks in the piezoelectric film 10 and suppress leakage paths between electrodes, thereby enabling the piezoelectric film 10 to stably exert its piezoelectric characteristics.

[0049] Furthermore, as described above, when the piezoelectric film 10 contains a wurtzite-type crystalline material as the main component and the wurtzite-type crystalline material is added as an additive element containing Kr among Ar, Kr, Xe, and Rn, it is preferable that the degree of crystal orientation is 5° or less and the film density is 5.1 g / cm³. 3 The following is a further explanation. Additionally, fibrous wurtzite-type crystalline materials can be substantially composed of ZnO, or they can be composed solely of ZnO.

[0050] If the piezoelectric film 10 has a fibrous wurtzite-type crystalline material containing ZnO as the main component, and the degree of crystal orientation and the film density are below the above-mentioned upper limits, then the c-axis orientation of the piezoelectric material is improved, and the increase in film stress is suppressed.

[0051] The crystal orientation degree is preferably 5° or less, more preferably 2.8° or less, and even more preferably 2.5° or less. If the crystal orientation degree is 5° or less, the c-axis orientation of the piezoelectric material contained in the piezoelectric film 10 is good, improving the energy conversion efficiency and thus enhancing the piezoelectric properties of the piezoelectric film 10. In particular, ZnO has a fibrous wurtzite-type crystal structure, and compared with piezoelectric materials having other crystal structures, the correlation between crystal orientation degree and piezoelectric properties is high. Therefore, if the crystal orientation degree of ZnO is 5° or less, the energy conversion efficiency can be further improved. Therefore, when the piezoelectric film 10 is used in a piezoelectric component, the piezoelectric properties of the piezoelectric component can be improved.

[0052] The degree of crystal orientation is expressed as the Full Width at Half Maximum (FWHM) obtained when the surface of the piezoelectric film 10 is measured using the X-ray Rocking Curve (XRC) method. That is, the degree of crystal orientation is expressed as the FWHM of the peak waveform of the rocking curve obtained by measuring the reflection from the (0002) surface of the ZnO crystals, which are the main components contained in the piezoelectric film 10, using the XRC method. The ZnO contained in the piezoelectric film 10 has a wurtzite-type crystal structure; therefore, the FWHM represents the degree of parallelism of the c-axis alignment of the crystals constituting the piezoelectric material. Therefore, the FWHM of the peak waveform of the rocking curve obtained by the XRC method becomes an indicator of the c-axis orientation of the piezoelectric film 10. Thus, the smaller the FWHM of the rocking curve, the better the c-axis crystal orientation of the piezoelectric film 10 can be evaluated.

[0053] Figure 3 This is an example illustrating the relationship between crystal orientation degree and the electromechanical coupling coefficient K. Additionally, Figure 3 This relates the crystal orientation degree of AlN to the electromechanical coupling coefficient K. Figure 3 In the diagram, the horizontal axis represents the degree of crystal orientation, and the vertical axis represents the square of the electromechanical coupling constant K (K). 2 (Value). Furthermore, Figure 3 In the figure, the relationship between the degree of crystal orientation and the electromechanical coupling coefficient is shown in the case of AlN. The degree of crystal orientation and the electromechanical coupling coefficient of ZnO, ZnO-MgO, etc. show the same relationship as in the case of AlN.

[0054] K on the vertical axis 2The value represents the energy conversion efficiency of electrical energy relative to the piezoelectric film 10. The higher the energy conversion efficiency of electrical energy, the better the operating efficiency of the piezoelectric component with the piezoelectric film 10, and the better the piezoelectric component has piezoelectric characteristics.

[0055] Figure 3 As shown, in terms of crystal orientation degree and K 2 When FWHM is below 5°, the energy conversion efficiency is improved while K... 2 When the value becomes constant, a region of piezoelectric saturation is formed. Figure 3 The relationship between the degree of crystal orientation and the electromechanical coupling coefficient is shown for AlN. Similarly, the degree of crystal orientation and the electromechanical coupling coefficient also show the same relationship for ZnO, ZnO-MgO, and other crystals with a fibrous wurtzite-type crystal structure. Therefore, in this embodiment, the piezoelectricity begins to saturate while the degree of crystal orientation improves the energy conversion efficiency; good crystal orientation is achieved when it is below 5°.

[0056] The preferred membrane density is 5.1 g / cm³. 3 The preferred value is 4.96 g / cm³. 3 The following is a further preferred value: 4.94 g / cm³ 3 Below. Additionally, the lower limit for membrane density is appropriately determined. For example, if the membrane density is 5.1 g / cm³... 3 The following process inhibits the densification of the elements constituting the piezoelectric film 10, resulting in a so-called sparse state. This, in turn, improves the c-axis orientation of the crystal and suppresses the generation of stress within the piezoelectric film 10, thus preventing an increase in the film stress of the piezoelectric film 10. Therefore, when the piezoelectric film 10 is applied to a piezoelectric component, the reduction of the piezoelectric properties of the piezoelectric component can be prevented.

[0057] Furthermore, there are no particular limitations on the method for measuring film density; for example, X-ray reflectance measurement (XRR) can be used.

[0058] The degree of crystal orientation of the piezoelectric film 10 can be determined by measuring the peak intensity and FWHM of the rocking curve obtained from the reflection of the (0002) plane of the ZnO crystal contained in the piezoelectric film 10 as a piezoelectric material using the X-ray rocking curve method. The value obtained by dividing the integral value of the peak intensity by FWHM can be used as an evaluation value of the degree of crystal orientation. The stronger the peak intensity of the rocking curve and the smaller the FWHM, the better the c-axis orientation of ZnO. Therefore, it means that the larger the evaluation value obtained by dividing the integral value of the peak intensity by FWHM, the better the crystal orientation (i.e., the lower the degree of crystal orientation).

[0059] Furthermore, as described above, when the piezoelectric film 10 contains a wurtzite-type crystalline material as the main component and the wurtzite-type crystalline material is added as an additive element containing Kr among Ar, Kr, Xe, and Rn, the axial ratio c / a of the crystal structure contained in the piezoelectric material is preferably 1.59 or less, more preferably 1.585 or less, and even more preferably 1.582 or less. The wurtzite-type crystalline material, such as ZnO, has a hexagonal crystal system and is randomly oriented along the a-axis in the in-plane direction of the unit lattice of the wurtzite-type crystalline material. Since the wurtzite-type crystalline material, such as ZnO, extends along the a-axis in the in-plane direction, it is possible to homogenize the stress on the crystal plane parallel to the substrate 11. If the axial ratio c / a is within the above-mentioned preferred range, the piezoelectric material can homogenize the stress distribution within the crystal plane, thus maintaining the c-axis orientation while suppressing the increase in film stress. On the other hand, the lower limit of the axial ratio c / a is not particularly limited, but is preferably 1.560 or more.

[0060] The axial ratio c / a of the crystal structure of a piezoelectric material is the ratio of the c-axis length (lattice constant along the c-axis) to the a-axis length (lattice constant along the a-axis) in the unit cell lattice (c-axis / a-axis ratio). Generally, the axial ratio c / a can be controlled by adjusting the doping amount of other elements in ZnO, lattice integration with the substrate material, and the temperature and pressure during piezoelectric material formation. The axial ratio c / a of the crystal structure of a piezoelectric material can be evaluated at room temperature using in-plane X-ray diffraction.

[0061] The method for evaluating the film stress of the piezoelectric film 10 is not particularly limited if it is a method capable of evaluating the film stress of the piezoelectric film 10, and various measurement methods can be used for evaluation. For example, the film stress of the piezoelectric film 10 can be evaluated by the amount of warpage.

[0062] The warpage of the piezoelectric film 10 can be determined by setting the piezoelectric film 10 on the substrate 11 with the setting surface of the piezoelectric film 10 facing downwards, and calculating the average height of the surface of the piezoelectric film 10 in contact with the substrate 11 and the vertical direction of each corner of the piezoelectric film 10. For example, if the piezoelectric film 10 is formed into a quadrilateral shape in top view, the average height of the surface of the piezoelectric film 10 in contact with the substrate 11 and the vertical direction of the four corners of the piezoelectric film 10 is taken as the warpage of the piezoelectric film 10. When the warpage is less than a specified value (e.g., 10 mm), the warpage of the piezoelectric film 10 can be evaluated as good.

[0063] Next, an example of a method for manufacturing the piezoelectric film 10 will be described. The piezoelectric film 10 is formed in a mixed gas atmosphere containing Kr and oxygen by sputtering a Zn-containing target such as ZnO onto a substrate 11 while simultaneously sputtering a Zn-containing piezoelectric material containing Kr. As will be described later, the mixed gas atmosphere containing oxygen may sometimes use Ar in addition to Kr. When the mixed gas atmosphere contains Ar, Ar atoms enter the crystal lattice of the wurtzite-type crystalline material such as ZnO, causing the piezoelectric film to exhibit compressive stress, which is one reason for the increase in film stress. When the mixed gas atmosphere contains Kr, Kr atoms enter the crystal lattice of the piezoelectric material, but compared to Ar atoms, they are less likely to enter the crystal lattice of the wurtzite-type crystalline material, thus suppressing the compressive stress exhibited by the piezoelectric film 10. Therefore, by sputtering the piezoelectric film 10 in a mixed gas atmosphere containing Kr and oxygen, the piezoelectric film 10 can be formed while suppressing the increase in its film stress.

[0064] In a mixed gas atmosphere containing Kr and oxygen, the oxygen flow rate ratio relative to the total flow rate of Kr and oxygen is preferably 5% to 15%, more preferably 7% to 12%. If the oxygen flow rate ratio relative to the total flow rate of Kr and oxygen is within the above-mentioned preferred range, when a piezoelectric film 10 is formed by sputtering using a target containing Zn, the amount of Kr atoms entering the crystal lattice of fibrous wurtzite-type crystalline materials such as ZnO can be suppressed. Therefore, it is possible to maintain a high c-axis orientation of the piezoelectric material while suppressing the increase of film stress in the piezoelectric film 10.

[0065] The pressure within the mixed gas atmosphere during sputtering is preferably 0.1 Pa to 2.0 Pa, more preferably 0.5 Pa to 1.5 Pa. If the pressure is within the above-preferred range, when a piezoelectric film 10 is formed by sputtering using a target containing Zn, the amount of Kr atoms entering the crystal lattice of fibrous wurtzite-type crystalline materials such as ZnO can be suppressed. Therefore, while maintaining a high c-axis orientation of the piezoelectric material, the increase in film stress of the piezoelectric film 10 can be suppressed.

[0066] When the fibrous wurtzite-type crystalline material is ZnO, and Kr is included as an additive element, a ZnO sintered target can be used. A ZnO sintered target is placed in a sputtering apparatus, and a mixed gas containing Kr and oxygen is supplied to the sputtering apparatus. Sputtering is performed using the ZnO sintered target in a mixed gas atmosphere containing Kr and oxygen, thereby obtaining a piezoelectric film 10 on the substrate 11 while suppressing the amount of Kr that enters during ZnO film formation.

[0067] When the fibrous wurtzite-type crystalline material is a Mg-added ZnO thin film containing ZnO and MgO in a specified mass ratio, a multi-element sputtering method using a target formed from a ZnO sintered body and a target formed from a MgO sintered body, or a single-element sputtering method using an alloy target containing ZnO and MgO, such as a target containing a ZnO sintered body with MgO added in a predetermined ratio, can be used.

[0068] In the case of using a multi-element sputtering method, a multi-element sputtering apparatus is used, and a mixed gas containing Kr and oxygen is supplied into the apparatus. Under the mixed gas atmosphere containing Kr and oxygen, sputtering is performed simultaneously and independently on the substrate 11 using a target of ZnO sintered body and a target of MgO sintered body. This suppresses the amount of Kr entering the substrate 11 during the formation of the Mg-added ZnO film, allowing the Kr content to be suppressed to a desired range while forming a Mg-added ZnO film. Thus, a piezoelectric film 10 composed of a Mg-added ZnO film with a Kr content of 0.01 atm% or more is obtained.

[0069] When using a single-element sputtering method, sputtering is performed in a mixed gas atmosphere containing Kr and oxygen, for example, using a target containing a ZnO sintered body with MgO added in a predetermined ratio. This allows for the formation of a film on the substrate 11 in which Kr is contained in a desired proportion as in a Mg-added ZnO thin film. Thus, a piezoelectric film 10 containing a desired amount of Kr in the Mg-added ZnO thin film is obtained.

[0070] Thus, the piezoelectric film 10 according to this embodiment has a piezoelectric material with a fibrous wurtzite-type crystal structure as the main component, and Kr as an additive element. Furthermore, in the piezoelectric film 10, the piezoelectric material includes one element selected from the group consisting of Zn, Al, Ga, Cd, and Si as a positive element, and the content of Kr is 0.01 atm% to 0.05 atm%. By keeping the content of Kr in the piezoelectric material within the above range, the piezoelectric film 10 can improve its c-axis orientation and has high crystallinity orientation. The higher the crystallinity orientation of the piezoelectric material, the higher the energy conversion efficiency from electrical energy to mechanical energy, thereby enabling the piezoelectric film 10 to achieve a large displacement in the thickness direction. In addition, by suppressing the Kr content in the piezoelectric material to the above-mentioned content, the increase in film stress can be suppressed. Therefore, the piezoelectric film 10 can have a large displacement in the thickness direction and suppress the increase in film stress, thereby exhibiting excellent piezoelectric properties and reducing film stress. Therefore, by using the piezoelectric film 10 in the piezoelectric component, the piezoelectric characteristics of the piezoelectric component can be improved.

[0071] For example, Kr atoms are rare gases with larger atomic weights and radii compared to Ar atoms. Therefore, they are less likely to penetrate the interior of the piezoelectric film 10 compared to Ar, and the content of Kr entering the wurtzite-type crystalline material can be significantly reduced compared to Ar. Thus, even if the piezoelectric film 10 contains Kr atoms, its content is significantly lower than that of Ar, thereby reducing the film stress of the piezoelectric film 10. Furthermore, the low bounce component of Kr atoms reduces the deviation component of sputtered particles reaching the substrate 11 compared to Ar atoms, resulting in better crystal orientation. Therefore, if the piezoelectric film 10 is used to manufacture a piezoelectric component, even without an intermediate layer for stress mitigation between the orientation control layer, the lower electrode, and the piezoelectric layer, the piezoelectric component can still exhibit excellent piezoelectric properties and low film stress, thus ensuring long-term reliable performance of its superior piezoelectric characteristics.

[0072] The piezoelectric film 10 can be a piezoelectric material containing ZnO, with a crystal orientation degree of less than 5° and a film density of 5.1 g / cm³. 3 Therefore, the piezoelectric film 10 can improve the c-axis orientation of the piezoelectric material, has high crystallinity orientation, and can suppress the increase of film stress. Thus, the piezoelectric film 10 can have a large displacement in the thickness direction and can suppress the increase of film stress, thereby exhibiting excellent piezoelectric properties and reducing film stress.

[0073] The piezoelectric film 10 can contain a piezoelectric material including ZnO, and the axial ratio c / a of the crystal structure contained in the piezoelectric material is 1.59 or less. By including additive elements such as Kr, the a-axis length of the unit cell lattice can be elongated. By making the axial ratio c / a of the crystal structure contained in the piezoelectric film 10 1.59 or less, the stress distribution within the crystal plane of the piezoelectric material such as ZnO can be homogenized, thereby reducing compressive stress. As a result, the piezoelectric film 10 can further reduce film stress.

[0074] The piezoelectric film 10 can have a thickness of 100 nm to 3000 nm. Thus, the piezoelectric film 10 can achieve thin-film properties while exhibiting excellent piezoelectric characteristics and reducing film stress.

[0075] The piezoelectric film 10 has the properties described above, and is therefore suitable for use as a piezoelectric layer in a piezoelectric component.

[0076] <Piezoelectric Components>

[0077] A piezoelectric assembly incorporating the piezoelectric element described in this embodiment will be described. The piezoelectric assembly of this embodiment has electrodes and a piezoelectric element layer on a substrate, the piezoelectric element layer using… Figure 1 The piezoelectric film 10 shown in this embodiment is an example of piezoelectric film 10.

[0078] Figure 4 A schematic cross-sectional view showing the structure of a piezoelectric component. Figure 4 As shown, the piezoelectric component 20A comprises an alignment control layer 22, a first electrode 23, a piezoelectric layer 24, and a second electrode 25, which are sequentially stacked on the substrate 21. The piezoelectric layer 24 is composed of... Figure 1 The piezoelectric film 10 shown in this embodiment is configured as follows. Additionally, the piezoelectric assembly 20A may, depending on the application, not include at least one of the orientation control layer 22 and the second electrode 25.

[0079] Substrate 21 can be used with settings Figure 1 The substrate 11 of the piezoelectric film 10 shown in this embodiment is omitted, therefore details of the substrate 21 are omitted.

[0080] In addition, in this embodiment, the placement of the substrate 21 is not particularly limited, and it can be placed in an appropriate position according to the structure and manufacturing process of the piezoelectric component 20A. For example, the substrate 21 can be placed between the orientation control layer 22 and the first electrode 23.

[0081] An orientation control layer 22 can be disposed between the substrate 21 and the first electrode 23. The orientation control layer 22 has the function of adjusting the integration of crystal growth between adjacent substrates 21 and piezoelectric layers 24 in the stacking direction, and the piezoelectric layers 24 have the function of being formed by crystal growth that is close to epitaxial growth. Therefore, the piezoelectric layer 24 formed above the first electrode 23 can have good c-axis orientation even if its thickness is, for example, several hundred nm.

[0082] Furthermore, the orientation control layer 22 exhibits excellent surface smoothness, enhancing the c-axis orientation of the piezoelectric layer 24 located above it. When the piezoelectric layer 24 contains ZnO, the c-axis of the piezoelectric layer 24 can be oriented in the vertical direction (stack direction). Additionally, the orientation control layer 22 offers high gas barrier properties, reducing the impact of gases generated from the plastic substrate during film formation when the substrate 21 is used. For example, when the orientation control layer 22 is formed using a thermosetting resin, it is amorphous and exhibits high smoothness. When the orientation control layer 22 is formed using melamine resin, it has a three-dimensional cross-linked structure, further increasing the density within the layer and thereby improving barrier properties.

[0083] The orientation control layer 22 preferably comprises an amorphous material. The orientation control layer 22 does not necessarily need to be 100% amorphous; it can have non-amorphous regions within a range that improves the c-axis orientation of the piezoelectric layer 24. Preferably, the proportion of regions formed by amorphous components in the orientation control layer 22 is 90% or more, more preferably 95% or more, to achieve sufficient control over the c-axis orientation.

[0084] The orientation control layer 22 can be formed from inorganic materials, organic materials, or mixtures of inorganic and organic materials. There are no particular limitations on the materials used, whether inorganic, organic, or mixtures, as long as they improve the wettability of the substrate 21 and the first electrode 23 and enhance the crystal orientation of the first electrode 23.

[0085] As inorganic materials, silicon oxide (SiOx), silicon nitride (SiN), aluminum nitride (AlN), aluminum oxide (Al2O3), gallium nitride (GaN), gallium oxide (Ga2O3) can be used; ZnO with added Al2O3 and SiOx (aluminum or silicon with added zinc oxide (hereinafter referred to as "SAZO")); GaN, AlN, and ZnO with added at least one of Al2O3, Ga2O3, SiOx, and SiN; ITO (indium tin oxide), IZO (indium zinc oxide), IZTO (indium zinc tin oxide), IGZO (indium gallium zinc oxide), etc.

[0086] Examples of organic materials include acrylic resins, urethane resins, melamine resins, alkyd resins, and siloxane polymers. In particular, thermosetting resins formed from mixtures of melamine resins, alkyd resins, and organosilane condensates are preferred. Amorphous films can be formed using these materials through methods such as vacuum evaporation, sputtering, ion plating, and coating.

[0087] The orientation control layer 22 can be a single layer or a stack of two or more layers. When the orientation control layer 22 is constructed by stacking two or more layers, inorganic films and organic films can be stacked together.

[0088] The thickness of the orientation control layer 22 can be appropriately designed, for example, preferably 3 nm to 100 nm, more preferably 10 nm to 50 nm. If the thickness of the orientation control layer 22 is within the above-mentioned preferred range, it can perform the function of orientation control and can achieve the thin-film processing of the piezoelectric component. Therefore, the crystal orientation of the upper piezoelectric layer 24 can be made sufficiently good, and the crystallinity of the piezoelectric layer 24 can be improved.

[0089] The first electrode 23 is disposed on the alignment control layer 22. The first electrode 23 can be made of any conductive material. When light transmittance is required, transparent oxide conductive films such as ITO, IZO, IZTO, and IGZO can be used as the material. When transparency is not required, good conductors such as metals such as Au, Pt, Ag, Ti, Al, Mo, Ru, Cu, and W can be used.

[0090] From the viewpoint of suppressing the unevenness and grain boundaries at the interface between the first electrode 23 and the piezoelectric layer 24, the oxide conductor film can be made an amorphous film. By making it an amorphous film, the formation of grain boundaries, which are the cause of unevenness and leakage paths on the surface of the first electrode 23, can be suppressed. Furthermore, the upper piezoelectric layer 24 is not affected by the crystal orientation of the first electrode 23 and can grow with good crystal orientation.

[0091] The first electrode 23 can be formed as a thin film on a portion or the entire surface of the orientation control layer 22, or multiple electrodes can be arranged in parallel stripes.

[0092] The second electrode 25 can be disposed on the piezoelectric layer 24. The second electrode 25 can be formed of any conductive material. When light transmittance is required for the piezoelectric component 20A, transparent oxide conductive films such as ITO, IZO, IZTO, and IGZO can be fabricated. When light transmittance is not required, metal electrodes with good conductors such as Au, Pt, Ag, Ti, Al, Mo, Ru, Cu, and W can be fabricated.

[0093] The second electrode 25 can be formed as a thin film on a portion or the entire surface of the piezoelectric layer 24, or multiple electrodes can be arranged in parallel stripes.

[0094] An example of the manufacturing method for piezoelectric component 20A will be explained.

[0095] An alignment control layer 22 is formed on the surface of the substrate 21. An IZO film or similar material can be used as the alignment control layer 22. For example, a sputtering method at room temperature can be used as the method for forming the alignment control layer 22. The film formation temperature of the alignment control layer 22 does not need to be room temperature, as long as the amorphous structure can be maintained; for example, film formation can be performed at a substrate temperature below 150°C.

[0096] Next, a first electrode 23 is formed above the alignment control layer 22. The first electrode 23 can be, for example, an ITO film, a Ti film, etc., formed by a magnetron sputtering method using DC (direct current) or RF (high frequency).

[0097] According to the piezoelectric component 20A, the first electrode 23 can be used as a solid electrode, or the first electrode 23 can be processed into a predetermined shape and pattern through etching or other processes. When the piezoelectric component 20A is used as a pressure sensor such as a touch panel, multiple first electrodes 23 can be arranged in a stripe pattern.

[0098] Next, a piezoelectric layer 24 is formed on the first electrode 23. For example, a target containing Zn and Mg is used, and the film is formed by RF magnetron sputtering in a mixed gas atmosphere containing Kr and a trace amount of oxygen. At this time, the ratio of oxygen flow rate to the total flow rate of Kr and oxygen is preferably 5% to 15%, and the pressure in the mixed gas atmosphere during sputtering is preferably 0.1 Pa to 2.0 Pa. As a result, a piezoelectric layer 24 containing ZnO and MgO can be formed while suppressing the amount of Kr entering the crystal structure of ZnO and MgO, with a Kr content of 0.01 atm% to 0.05 atm%. Furthermore, as a method for forming the piezoelectric layer 24, sputtering can be performed in a mixed gas atmosphere containing Kr and a trace amount of oxygen using a MgZnO target containing a predetermined proportion of Mg in Zn. Furthermore, as another method for forming the piezoelectric layer 24, a multi-element sputtering apparatus can be used to simultaneously and independently sputter ZnO and MgO targets in a mixed gas atmosphere containing Kr and trace amounts of oxygen.

[0099] The piezoelectric layer 24 can be formed by stacking multiple layers.

[0100] The film-forming temperature of the piezoelectric layer 24 does not need to be room temperature, as long as the amorphous structure of the orientation control layer 22 located below the piezoelectric layer 24 is maintained. For example, the piezoelectric layer 24 can be formed at a substrate temperature below 150°C.

[0101] By using sputtering to form the alignment control layer 22, the first electrode 23, and the piezoelectric layer 24, a uniform film with strong adhesion can be formed while substantially maintaining the target composition ratio of the compound. Furthermore, the alignment control layer 22, the first electrode 23, and the piezoelectric layer 24 can be formed with good precision and only require time control.

[0102] Next, a second electrode 25 with a predetermined shape is formed on the piezoelectric layer 24. The second electrode 25 is formed, for example, by DC or RF magnetron sputtering, at room temperature as an ITO film with a thickness of 20 nm to 100 nm. The second electrode 25 can be formed on the entire surface of the piezoelectric layer 24, or it can be formed in any suitable shape. For example, if the first electrode 23 is patterned with stripes, the second electrode 25 can be formed such that, when viewed from above, multiple stripes extend in a direction orthogonal to the direction in which the stripes of the first electrode 23 extend.

[0103] Thus, the piezoelectric component 20A was obtained.

[0104] Furthermore, after the formation of the second electrode 25, the entire piezoelectric component 20A can be heat-treated at a temperature lower than the melting point or glass transition point of the substrate 21 (e.g., 130°C). This heat treatment allows the first electrode 23 and the second electrode 25 to crystallize, thereby reducing their resistance. The heat treatment is not mandatory; it may not be performed after the formation of the piezoelectric component 20A, for example, if the substrate 21 is made of a material without heat resistance.

[0105] Thus, the piezoelectric component 20A has a piezoelectric layer 24 between the first electrode 23 and the second electrode 25. The piezoelectric layer 24 can exhibit excellent piezoelectric characteristics and reduce film stress. Therefore, the piezoelectric component 20A can exhibit high piezoelectric efficiency in the thickness direction of the piezoelectric layer 24 and can reliably exhibit excellent piezoelectric characteristics.

[0106] The piezoelectric properties of the 20A piezoelectric component can utilize d 33 The value is evaluated. d 33 The value represents the expansion / contraction mode in the thickness direction of the piezoelectric layer 24, and is the amount of polarization charge [C / N] per unit pressure applied along the thickness direction of the piezoelectric layer 24. Additionally, d 33 The value is also called the piezoelectric constant. d 33 The higher the value, the better the polarization of the piezoelectric layer 24 in the thickness direction (c-axis) of the piezoelectric component 20A.

[0107] d 33 The value can be directly measured using a piezoelectric constant measuring device (LPF-02, manufactured by Lead Techno Co., Ltd.). The electrodes of the piezoelectric constant measuring device are clamped between the top and bottom surfaces of the piezoelectric layer 24. An indenter is placed against the surface of the piezoelectric layer 24, and a low-frequency load is applied to the piezoelectric layer 24. The amount of charge generated is measured using the coulomb counter of the piezoelectric constant measuring device. The value obtained by dividing the measured charge by the load is taken as d. 33 Output the value. d 33 The larger the absolute value, the better the piezoelectric properties of the piezoelectric layer 24 in the film thickness direction.

[0108] The piezoelectric component 20A possesses excellent piezoelectric characteristics, making it suitable for use in piezoelectric devices. Examples of piezoelectric devices include, for instance, force sensors, pressure sensors, accelerometers, acoustic emission (AE) sensors, and other devices utilizing the piezoelectric effect; as well as speakers, sensors, high-frequency filters, piezoelectric actuators, and optical scanners utilizing the inverse piezoelectric effect.

[0109] (Other methods)

[0110] Furthermore, in this embodiment, the piezoelectric component 20A is not limited to the above-described configuration. As long as the substrate 21 has a first electrode 23 and a piezoelectric layer 24, and the piezoelectric layer 24 can exhibit excellent piezoelectric properties in the thickness direction, it can be configured in other ways. An example of another configuration of the piezoelectric component 20A is shown below.

[0111] Figure 5 As shown, the piezoelectric component 20B may not have a second electrode 25.

[0112] Figure 6 As shown, the piezoelectric component 20C may not have an orientation control layer 22.

[0113] Figure 7 As shown, the piezoelectric component 20D may have an orientation control layer 22 between the first electrode 23 and the piezoelectric layer 24.

[0114] Figure 8 As shown, the piezoelectric component 20E may have an adhesive layer 26 between the piezoelectric layer 24 and the second electrode 25, and a substrate 27 on the second electrode 25.

[0115] The adhesive layer 26 suppresses leakage paths caused by cracks or pinholes in the piezoelectric layer 24. If metal grain boundaries or protrusions exist at the interface between the first electrode 23 and the piezoelectric layer 24 or the interface between the piezoelectric layer 24 and the second electrode 25, a leakage path will form between the first electrode 23 and the second electrode 25 due to cracks or other defects in any of the three electrodes, resulting in the loss of polarization. By providing the adhesive layer 26 between the piezoelectric layer 24 and the second electrode 25, the piezoelectric component 20E suppresses the formation of leakage paths and maintains good piezoelectric characteristics of the piezoelectric layer 24.

[0116] Substrate 27 can use the same material as substrate 21.

[0117] An example of a manufacturing method for the piezoelectric component 20E will be described. For example, a first laminate, in which an orientation control layer 22, a first electrode 23, and a piezoelectric layer 24 are sequentially stacked on a substrate 21. On the other hand, a second laminate, in which a second electrode 25 is formed on a substrate 27. Then, the piezoelectric layer 24 of the first laminate and the second electrode 25 of the second laminate are bonded together by an adhesive layer 26, with the piezoelectric layer 24 of the first laminate facing the second electrode 25 of the second laminate. Thus, the piezoelectric component 20E is manufactured.

[0118] The piezoelectric component 20E has a large electromechanical coupling coefficient in the thickness vibration mode and can suppress leakage paths between electrodes, thus exhibiting superior piezoelectric characteristics.

[0119] Example

[0120] The following describes the implementation in more detail with reference to examples and comparative examples, but the implementation is not limited to these examples and comparative examples.

[0121] <Fabrication of Piezoelectric Components>

[0122] [Example 1]

[0123] (Creation of the orientation control layer)

[0124] On a substrate (PET, thickness: 50 μm), an amorphous IZO film with a thickness of 50 nm was formed using DC sputtering in a mixed atmosphere of Ar and O2. On top of this, using a sputtering target with a ZnO and MgO mass ratio adjusted to 88 wt%:12 wt%, a Mg-added ZnO thin film with a hexagonal wurtzite structure was formed with a thickness of 30 nm using DC sputtering. Thus, a Mg-added ZnO thin film was formed on the IZO film. The overall thickness of the orientation control layer was 80 nm.

[0125] (Fabrication of the first electrode)

[0126] On the orientation control layer, a 30 nm thick Ti film, which serves as a hexagonal metal layer, is formed as the first electrode in a mixed gas atmosphere of Ar and O2 using DC magnetron sputtering.

[0127] (Fabrication of the piezoelectric layer)

[0128] At the first electrode, the gas pressure in a mixed atmosphere of Kr and O2 was adjusted to 0.7 Pa. Using DC sputtering, a Mg-doped ZnO film with a hexagonal wurtzite structure and a ZnO to MgO ratio of 88 wt%:12 wt% was deposited as a piezoelectric layer. The thickness of the piezoelectric layer was 500 nm.

[0129] Thus, a piezoelectric assembly having an orientation control layer, a first electrode, and a piezoelectric layer stacked sequentially on a substrate is produced.

[0130] In addition, a sample identical to the piezoelectric layer produced during the fabrication of the piezoelectric component was prepared. The types of added elements contained in the piezoelectric layer sample were determined, as well as the Kr content relative to the total content of other elements in the piezoelectric material (Kr / elements), and the piezoelectric layer's crystal orientation, film density, axial ratio c / a, and warpage. These results are shown in Table 1. (Kr content in the piezoelectric layer)

[0131] The Kr content (Kr element / containing elements) in the prepared sample was evaluated using Rutherford backscattering analysis (RBS) with Pelletron 3SDH and 5SDH-2 (NEC) under the following measurement conditions and evaluation criteria. The containing elements refer to ZnO and MgO. The detection limit for Kr content in the piezoelectric layer of the sample is 0.01 atm%.

[0132] ((Measurement conditions))

[0133] Incident ion: 4He ++

[0134] Incident energy: 2300keV

[0135] • Angle of incidence: 0°

[0136] • Scattering angle: 140°

[0137] • Sample current: 10nA

[0138] • Beam diameter: 2mmφ

[0139] • In-plane rotation: None

[0140] • Irradiation dose: 80μC

[0141] (Degree of crystallization orientation)

[0142] The surface of the prepared sample was subjected to X-ray diffraction using an X-ray diffraction apparatus (SmartLab, Rigaku Corporation). The XRC method was used to determine the half-width (FWHM) of the peak waveform of the rocking curve obtained when the reflection of the (0002) plane of the crystal of the main component contained in the sample was measured under the following conditions. This half-width was used as the crystal orientation degree of the piezoelectric layer.

[0143] ((Measurement conditions))

[0144] Measurement mode: ω scan

[0145] • Scanning range: 0°~34.2°

[0146] • Step width: 0.1°

[0147] • Speed / counting time: 4° / min

[0148] • Entrance slit: 1.0mm

[0149] • Parallel slits for incident and received light: 5°

[0150] • Length-limiting slit: 10mm

[0151] • Light-receiving optical element: PSA Open

[0152] (membrane density)

[0153] The film density of the prepared sample was determined using an X-ray diffraction apparatus (SmartLab, Rigaku) ​​under the following measurement conditions via X-ray reflectance measurement.

[0154] ((Measurement conditions))

[0155] • Measurement range: 0.2°~8.0°

[0156] • Measurement interval: 0.01°

[0157] • Speed / counting time: 0.5° / min

[0158] • Diverging slit: 0.05mm

[0159] (shaft ratio c / a)

[0160] The prepared samples were analyzed using an X-ray diffraction apparatus (SmartLab, Rigaku) ​​under the following measurement and analysis conditions. The a-axis and c-axis lengths of the crystal lattice were determined by in-plane X-ray diffraction with 2θχ / φ scanning, thus calculating the axial ratio c / a. An axial ratio c / a below 1.590 was rated as "good," while an axial ratio c / a above 1.590 was rated as "poor." The results of the axial ratio c / a determination are displayed on... Figure 9 .

[0161] ((Measurement conditions))

[0162] • Scan axis: 2θχ / φ scan

[0163] • Angle of incidence: 0.3°

[0164] • Scanning range: 5°~110°

[0165] Steps: 0.1°

[0166] • Scanning speed: 2.0° / min

[0167] (Analysis Method)

[0168] The diffraction peaks obtained using SmartLab Studio II software with an X-ray diffraction apparatus were fitted, and the a-axis length and c-axis length were calculated using the crystal structure database COD and ZnO (database number 1011258).

[0169] (Warpage Amount)

[0170] Cut the prepared sample into four 3cm corners, with the surface containing the piezoelectric layer facing down. Place the sample on a reference surface and calculate the average height of the reference surface perpendicular to each of the four corners. This will give you the warpage of the piezoelectric layer. A warpage of less than 10mm is considered good.

[0171] <Evaluation of Piezoelectric Components>

[0172] Evaluate the piezoelectric properties of the fabricated piezoelectric components.

[0173] (Piezoelectric properties)

[0174] A piezoelectric component is mounted on a platform, and the first electrode is pulled out onto the platform. A pressure head located on top of the piezoelectric component is applied with a set pressure to induce lattice strain within the piezoelectric layer. The generated charge caused by polarization in the film thickness direction due to this lattice strain is evaluated. The pressure difference from the initial pressure is varied from 1N to 9N, and the value obtained by dividing the generated charge by the applied pressure is calculated and evaluated as the piezoelectric characteristics.

[0175] piezoelectric properties with d 33 The value was evaluated. The d-value of the piezoelectric layer was directly measured using a PM300 piezoelectric tester (manufactured by a piezoelectric testing company). 33 Value. d 33 The value represents the expansion / contraction mode of the piezoelectric component in the thickness direction, and is the amount of polarization charge [C / N] per unit pressure applied in the thickness direction. d 33 A higher value indicates better polarization of the piezoelectric layer in the thickness direction (c-axis), suggesting that the piezoelectric component possesses high piezoelectric characteristics. The d-value is used as a piezoelectric characteristic of the piezoelectric component. 33 The results of the value determination are shown in Table 1.

[0176] Based on the measurements of the prepared samples, the obtained piezoelectric layer, even with a thickness of 500 nm, exhibits a crystal orientation degree of 2.5°, thus improving the energy conversion efficiency of the piezoelectric component to below 5°. Therefore, it can be said that the crystal orientation is excellent. Furthermore, the film density is 4.94 g / cm³. 3 The film stress of the piezoelectric layer increases to 5.1 g / cm. 3 Therefore, it can be said that the film density is good. Furthermore, the axial ratio c / a is 1.582 or less, below 1.590. In the lattice constants of the crystals constituting the main components of the piezoelectric layer, the length of the a-axis is longer than the length of the c-axis. The stress on the crystal planes in the direction parallel to the substrate is easily homogenized, thus the axial ratio c / a can be considered good. The piezoelectric properties d show the piezoelectricity of the piezoelectric material. 33The value is 12.7 pC / N. Furthermore, the warpage of the piezoelectric layer is 4.5 mm, indicating that the warpage of the piezoelectric layer is well suppressed. This confirms that the piezoelectric layer exhibits both suppression of film stress and good crystal orientation.

[0177] [Example 2]

[0178] In Example 1, the thickness of the piezoelectric layer was changed to 1000 nm. Otherwise, the piezoelectric component was fabricated using the same procedure as in Example 1. The proportion of Kr element in the piezoelectric layer, the thickness of the piezoelectric layer, the degree of crystal orientation, the film density, the axial ratio c / a, the warpage, and the piezoelectric properties (d) of the piezoelectric component were compared. 33 The results of the determination of the values ​​are shown in Table 1.

[0179] As shown in Table 1, even with a piezoelectric layer thickness of 1000 nm and an FWHM of 2.4°, the energy conversion efficiency of the resulting piezoelectric component is improved to below 5°, indicating good crystal orientation. The piezoelectric properties d show the piezoelectricity of the material. 33 The value is 11.2 pC / N. Furthermore, the warpage of the piezoelectric layer is 6.1 mm, indicating that the warpage of the piezoelectric layer is well suppressed. This confirms that even a piezoelectric component with a 1000 nm piezoelectric layer exhibits both suppression of film stress and good crystal orientation.

[0180] [Example 3]

[0181] In Example 1, the film-forming gas pressure of the piezoelectric layer was changed from 0.7 Pa to 1.6 Pa. Otherwise, the piezoelectric component was fabricated in the same manner as in Example 1. The proportion of Kr element in the piezoelectric layer, the thickness of the piezoelectric layer, the degree of crystal orientation, the film density, the axial ratio c / a, the warpage, and the piezoelectric properties (d) of the piezoelectric component were also analyzed. 33 The results of the determination of the values ​​are shown in Table 1.

[0182] As shown in Table 1, even with a film-forming gas pressure of 1.6 Pa and an FWHM of 3.6°, the resulting piezoelectric layer exhibits improved energy conversion efficiency as a piezoelectric component, below 5°, indicating good crystal orientation. The piezoelectric properties d show the piezoelectricity of the piezoelectric material. 33 The value is 9.2 pC / N. Furthermore, the warpage of the piezoelectric layer is 3.8 mm, indicating that the warpage of the piezoelectric layer is well suppressed. This confirms that even a piezoelectric layer formed at a film-forming gas pressure of 1.6 Pa exhibits both suppressed film stress and good crystal orientation.

[0183] [Comparative Example 1]

[0184] In Example 1, the fabrication of the piezoelectric layer is modified as follows, except that the piezoelectric component is fabricated in the same manner as in Example 1.

[0185] (Fabrication of the piezoelectric layer)

[0186] On the first electrode, in a mixed gas atmosphere of Ar and O2, the gas pressure is adjusted to 0.2 Pa, and a Mg-added ZnO thin film with a hexagonal crystal system and a fibrous wurtzite structure is formed into a piezoelectric layer by DC sputtering, with ZnO and MgO adjusted to a mass ratio of 88wt%:12wt%.

[0187] The proportion of Kr element in the piezoelectric layer, the thickness of the piezoelectric layer, the degree of crystal orientation, the film density, the axial ratio c / a and the warpage, and the piezoelectric properties of the piezoelectric component (d) were analyzed. 33 The measurement results of the axial ratio (c / a) are shown in Table 1. In addition, the measurement results of the axial ratio c / a are shown in... Figure 9 As shown in Table 1, even with a thickness of 500 nm and an FWHM of 2.5°, the energy conversion efficiency of the obtained piezoelectric layer as a piezoelectric component is improved to below 5°, thus confirming that the obtained piezoelectric layer has good crystal orientation. Furthermore, the axial ratio c / a is 1.601, exceeding 1.590. Therefore, in the lattice constant of the crystals constituting the main components of the piezoelectric layer, the length of the a-axis is shorter than the length of the c-axis, making it difficult to homogenize the stress on the crystal plane in the direction parallel to the substrate. Therefore, the axial ratio c / a is considered poor. The piezoelectric properties d show the piezoelectricity of the piezoelectric material. 33 The value is 11.8 pC / N. Furthermore, regarding the warpage of the piezoelectric layer, with the surface containing the piezoelectric layer facing down and placed on the reference surface, the sample became cylindrical, resulting in extremely high film stress that could not be measured.

[0188] [Comparative Example 2]

[0189] In Comparative Example 1, the gas pressure was changed from 0.2 Pa to 0.7 Pa during the fabrication of the piezoelectric layer. Otherwise, the piezoelectric component was fabricated in the same manner as in Comparative Example 1.

[0190] The proportion of Kr element in the piezoelectric layer, the thickness of the piezoelectric layer, the degree of crystal orientation, the film density, the axial ratio c / a and the warpage, and the piezoelectric properties of the piezoelectric component (d) were analyzed. 33The measurement results of the piezoelectric layer (value) are shown in Table 1. As shown in Table 1, in Comparative Example 2, even with a thickness of 500 nm and an FWHM of 2.4°, the energy conversion efficiency of the obtained piezoelectric layer as a piezoelectric component was improved to 5° or less, thus confirming that the obtained piezoelectric layer has good crystal orientation. Furthermore, the axial ratio c / a is 1.601, exceeding 1.590, therefore, in the lattice constant of the crystals constituting the main components of the piezoelectric layer, the length of the a-axis is shorter than the length of the c-axis, making it difficult to homogenize the stress on the crystal plane in the direction parallel to the substrate, thus confirming that the axial ratio c / a is poor. The piezoelectric properties d show the piezoelectricity of the piezoelectric material. 33 The value is 10.5 pC / N. Furthermore, regarding the warpage of the piezoelectric layer, with the surface containing the piezoelectric layer facing down and placed on a reference surface, the sample becomes cylindrical, resulting in extremely high film stress that cannot be measured.

[0191] [Comparative Example 3]

[0192] In Comparative Example 1, the gas pressure was changed from 0.2 Pa to 3.0 Pa during the fabrication of the piezoelectric layer. Otherwise, the piezoelectric component was fabricated in the same manner as in Comparative Example 1.

[0193] The proportion of Kr element in the piezoelectric layer, the thickness of the piezoelectric layer, the degree of crystal orientation, the film density, the axial ratio c / a and the warpage, and the piezoelectric properties of the piezoelectric component (d) were analyzed. 33 The measurement results of the values ​​are shown in Table 1. As shown in Table 1, the piezoelectric layer obtained in Comparative Example 3 has an FWHM of 5.4° when the thickness is 500 nm, which exceeds 5°, thus confirming that the crystal orientation of the obtained piezoelectric layer is poor. In addition, the axial ratio c / a is 1.603, which exceeds 1.590, thus in the lattice constant of the crystals constituting the main components of the piezoelectric layer, the length of the a-axis is shorter than the length of the c-axis, and the stress on the crystal plane in the direction parallel to the substrate is difficult to be homogenized, thus confirming that the axial ratio c / a is poor. Piezoelectric properties d showing the piezoelectricity of piezoelectric materials 33 The value was 6.5 pC / N. Furthermore, the warpage of the piezoelectric layer was 22.4 mm, exceeding 10 mm, thus confirming a significant defect in film stress.

[0194] [Comparative Example 4]

[0195] In Example 1, the gas pressure was changed from 0.7 Pa to 0.2 Pa during the fabrication of the piezoelectric layer. Otherwise, the piezoelectric component was fabricated in the same manner as in Example 1.

[0196] The proportion of Kr element in the piezoelectric layer, the thickness of the piezoelectric layer, the degree of crystal orientation, the film density, the axial ratio c / a and the warpage, and the piezoelectric properties of the piezoelectric component (d) were analyzed. 33The measurement results of the Kr content (value) are shown in Table 1. As shown in Table 1, in Comparative Example 4, the Kr content in the piezoelectric layer was less than the detection limit (0.01 atm%), thus confirming that the Kr content was less than 0.01 atm%. Even with a thickness of 500 nm and an FWHM of 2.4°, the piezoelectric layer obtained in Comparative Example 4 exhibited improved energy conversion efficiency of 5° or less as a piezoelectric component, thus confirming that the obtained piezoelectric layer had good crystal orientation. The piezoelectric properties d show the piezoelectricity of the piezoelectric material. 33 The value is 12.1 pC / N. However, the Kr content within the piezoelectric layer is less than 0.01 atm%, which is the detection limit. Therefore, the warpage of the piezoelectric layer is not suppressed and is large. The reasoning is as follows: Generally, under low gas pressure, the amount of Ar atoms present is low. Therefore, the intake of Ar atoms in the piezoelectric layer is low, the film density is high, and thus there is a tendency for the compressive stress to increase. Similarly, in Kr gas, there is a tendency for the intake of sputtered gas atoms to decrease and the film density to increase in regions with low gas pressure. Therefore, the film stress of the piezoelectric layer is considered to be very high.

[0197] [Table 1]

[0198]

[0199] As described above, the embodiments are illustrated, but these embodiments are provided as examples and the present invention is not limited to them. The embodiments described above can be implemented in various other forms, and various combinations, omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included within the scope and spirit of the invention, and are included within the scope equivalent to the invention described in the claims.

[0200] This application claims priority based on Japanese Patent Application No. 2021-056823 filed with the Japan Patent Office on March 30, 2021, Japanese Patent Application No. 2021-158022 filed with the Japan Patent Office on September 28, 2021, and Japanese Patent Application No. 2022-46696 filed with the Japan Patent Office on March 23, 2022, and incorporates the entire contents of Japanese Patent Application No. 2021-056823, Japanese Patent Application No. 2021-158022, and Japanese Patent Application No. 2022-46696 into this application.

[0201] Explanation of symbols

[0202] 10 Piezoelectric film

[0203] 11, 21, 27 Substrate

[0204] 20A, 20B, 20C, 20D, 20E piezoelectric components

[0205] 22 Orientation Control Layer

[0206] 23 First Electrode

[0207] 24 Piezoelectric layer

[0208] 25 Second electrode

[0209] 26 Adhesive layer

Claims

1. A piezoelectric film comprising a piezoelectric material having a fibrous wurtzite-type crystal structure as its main component. The piezoelectric film has an additive element containing Kr. The piezoelectric material contains one element selected from the group consisting of Zn, Al, Ga, Cd, and Si as a positive element. The content of Kr element in the piezoelectric material is 0.01 atm% to 0.05 atm relative to the content of other elements.

2. The piezoelectric film according to claim 1, The piezoelectric material comprises ZnO. The crystal orientation degree is less than 5°, and the film density is 5.1 g / cm³. 3 the following.

3. The piezoelectric film according to claim 1 or 2, The piezoelectric material comprises ZnO. The axial ratio c / a of the crystal structure contained in the piezoelectric material is 1.59 or less.

4. The piezoelectric film according to claim 1 or 2, The thickness of the piezoelectric film is 100nm to 3000nm.

5. A method for manufacturing a piezoelectric film, wherein the method for manufacturing a piezoelectric film is as described in any one of claims 1 to 4. In a mixed gas atmosphere containing Kr and oxygen, the piezoelectric material is sputtered onto a substrate while containing Kr by using a sputtering method with a target containing Zn, thereby forming the piezoelectric film.

6. The method for manufacturing a piezoelectric film according to claim 5, The sputtering method is either a multi-element sputtering method using targets formed of ZnO and MgO, or a single-element sputtering method using targets formed of an alloy of ZnO and MgO.

7. A piezoelectric component having electrodes and a piezoelectric layer on a substrate, The piezoelectric layer is the piezoelectric film according to any one of claims 1 to 4.

8. A piezoelectric device comprising the piezoelectric component of claim 7.

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