Piezoelectric element manufacturing method and piezoelectric device manufacturing method

Abstract

This method for manufacturing a piezoelectric element includes: an angle adjustment layer formation step for forming an angle adjustment layer containing an amorphous oxide on one main surface side of a flexible base material by sputtering an amorphous material containing Zn in a mixed-gas atmosphere that contains an inert gas and oxygen; and, a piezoelectric layer formation step for forming a piezoelectric layer on the angle adjustment layer using a roll-to-roll method. The angle adjustment layer formation step is such that the ratio of the flow rate of the oxygen to the total flow rate of the inert gas and the oxygen exceeds 1%.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a piezoelectric element and a method for manufacturing a piezoelectric device. [Background technology]

[0002] Piezoelectric elements including a piezoelectric layer have high piezoelectric properties and are therefore widely used in piezoelectric devices such as pressure sensors, acceleration sensors, high frequency filter devices, and piezoelectric actuators.

[0003] Piezoelectric elements are generally constructed by laminating a piezoelectric layer on a substrate. When the piezoelectric layer is formed by crystal growth on a conductive film on the substrate, the crystals of the piezoelectric layer are oriented in the c-axis direction, and the piezoelectric layer has high crystal orientation, resulting in high piezoelectric properties. A piezoelectric element including a piezoelectric layer with such high piezoelectric properties can have good piezoelectric properties. Various methods have been proposed for manufacturing piezoelectric elements by highly orienting the piezoelectric layer.

[0004] As a method for manufacturing a piezoelectric element, for example, a method for manufacturing a piezoelectric device has been disclosed in which a piezoelectric layer having a wurtzite crystal structure is formed on a first electrode consisting of a layer of amorphous oxide conductor formed on a substrate, and a second electrode is formed on the piezoelectric layer (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-57781 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the method for manufacturing a piezoelectric device disclosed in Patent Document 1, when a piezoelectric layer is formed by sputtering on a first electrode while the first electrode is transported by a drum roll using a roll-to-roll (R to R) method, the surface of the drum roll on which the piezoelectric layer is sputtered is curved, which causes a problem in that the crystal axis of the piezoelectric material contained in the piezoelectric layer is distorted.

[0007] If the crystal axis is distorted, the crystal orientation of the piezoelectric layer is disturbed, making it difficult to achieve high orientation of the piezoelectric layer, thereby reducing the piezoelectric properties of the piezoelectric element that includes the piezoelectric layer.Since the operating principle of piezoelectric elements that include a piezoelectric layer is vibration in the thickness direction of the piezoelectric layer (thickness vibration), in order for the piezoelectric layer to exhibit high piezoelectric properties, it is important that the piezoelectric layer has high crystal orientation, with the crystal orientation facing in the same direction.

[0008] An object of one aspect of the present invention is to provide a method for manufacturing a piezoelectric element that can manufacture a piezoelectric layer with high crystal orientation even when using a roll-to-roll method. [Means for solving the problem]

[0009] One aspect of the method for manufacturing a piezoelectric element according to the present invention includes an angle adjustment layer formation process in which an amorphous material containing Zn is sputtered on one main surface of a flexible substrate in a mixed gas atmosphere containing an inert gas and oxygen to form an angle adjustment layer containing an amorphous oxide, and a piezoelectric layer formation process in which a piezoelectric layer is formed on the angle adjustment layer by a roll-to-roll method, wherein the ratio of the flow rate of the oxygen to the total flow rate of the inert gas and the oxygen in the angle adjustment layer formation process exceeds 1%. [Effects of the Invention]

[0010] According to one aspect of the method for manufacturing a piezoelectric element of the present invention, even when the RtoR method is used, a piezoelectric thin film with high crystal orientation can be manufactured. [Brief explanation of the drawings]

[0011] [Figure 1]1 is a schematic cross-sectional view showing the configuration of a piezoelectric element obtained by a method for manufacturing a piezoelectric element according to an embodiment of the present invention. [Figure 2] 3 is a flowchart showing a method for manufacturing a piezoelectric element according to an embodiment of the present invention. [Figure 3] 1A and 1B are diagrams illustrating crystal distortions contained in a piezoelectric layer. [Figure 4] 10 is a diagram showing the relationship between the oxygen flow rate ratio during the formation of the angle adjustment layer and the peak waveform of the rocking curve obtained when measuring the diffraction from the (0002) plane of the crystal of the piezoelectric material contained in the piezoelectric layer. [Figure 5] FIG. 2 is a diagram showing the direction in which X-rays are incident on a piezoelectric layer. [Figure 6] FIG. 10 is a diagram showing X-ray diffraction intensity in the MD direction of a piezoelectric layer. [Figure 7] FIG. 2 is a diagram showing the direction in which X-rays are incident on a piezoelectric layer. [Figure 8] FIG. 10 is a diagram showing the X-ray diffraction intensity in the TD direction of a piezoelectric layer. [Figure 9] FIG. 10 is a schematic cross-sectional view showing an example of another configuration of a piezoelectric element. [Figure 10] FIG. 10 is a schematic cross-sectional view showing an example of another configuration of a piezoelectric element. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail. To facilitate understanding of the description, the same components in each drawing will be assigned the same reference numerals, and duplicate explanations will be omitted. The scale of each member in the drawings may differ from the actual scale. In this specification, unless otherwise specified, "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0013] A method for manufacturing a piezoelectric element according to this embodiment will be described. Before describing a method for manufacturing a piezoelectric element according to this embodiment, a piezoelectric element obtained by the method for manufacturing a piezoelectric element according to this embodiment will be described.

[0014] [Piezoelectric element] FIG. 1 is a schematic cross-sectional view showing the configuration of a piezoelectric element obtained by the piezoelectric element manufacturing method according to this embodiment. As shown in FIG. 1, the piezoelectric element 1A includes a flexible substrate 11, a first electrode 12, an angle adjustment layer 13, a piezoelectric layer 14, and a second electrode 15, which are laminated in this order from the flexible substrate 11 side. The piezoelectric element 1A is formed using a roll-to-roll (R to R) method by the piezoelectric element manufacturing method according to this embodiment, and a piezoelectric layer with high crystal orientation can be manufactured. Details of the crystal orientation will be described later. The piezoelectric element 1A may not include the second electrode 15 depending on the application, etc.

[0015] In this specification, the thickness direction (vertical direction) of the piezoelectric element 1A is defined as the Z-axis direction, and the lateral direction (horizontal direction) perpendicular to the thickness direction is defined as the X-axis direction. The second electrode 15 side of the Z-axis direction is defined as the +Z-axis direction, and the flexible substrate 11 side is defined as the -Z-axis direction. In the following description, for convenience of explanation, the +Z-axis direction will be referred to as up or upward, and the -Z-axis direction will be referred to as down or downward, but this does not represent a universal up-down relationship.

[0016] The flexible substrate 11 is a substrate on which the first electrode 12 is disposed. Any material can be used for the flexible substrate 11, and examples of the material that can be used include a plastic substrate, a silicon (Si) substrate, a metal plate, and a glass substrate.

[0017] When a plastic substrate is used, it is preferable to use a flexible material that can impart flexibility to the piezoelectric element including the piezoelectric layer 14 .

[0018] Examples of materials that can be used to form the plastic substrate include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), acrylic resin, cycloolefin polymer, and polyimide (PI). Among these materials, PET, PEN, PC, acrylic resin, and cycloolefin polymer are transparent materials and are suitable for use in piezoelectric elements having piezoelectric layer 14 when the electrodes used are transparent. Furthermore, when optical transparency is not required for piezoelectric elements having piezoelectric layer 14, such as in healthcare products such as pulse monitors and heart rate monitors, or in-vehicle pressure detection sheets, the plastic substrate may be formed from the above-mentioned materials or a translucent or opaque plastic material.

[0019] The thickness of flexible substrate 11 is not particularly limited, and can be any thickness appropriate depending on the application of piezoelectric element 1A, the material of flexible substrate 11, etc. For example, when flexible substrate 11 is a plastic substrate, the thickness of flexible substrate 11 may be 1 μm to 250 μm. The method for measuring the thickness of flexible substrate 11 is not particularly limited, and any measuring method can be used.

[0020] In this specification, the thickness of the flexible substrate 11 refers to the length in a direction perpendicular to the main surface of the flexible substrate 11. The thickness of the flexible substrate 11 may be, for example, the thickness measured at an arbitrary location on the cross section of the flexible substrate 11, or may be the average value of measurements measured at several arbitrary locations. Hereinafter, the definition of thickness is the same for other members.

[0021] The first electrode 12 is provided on the upper main surface (top surface) of the flexible substrate 11. When the flexible substrate 11 is a conductive material such as a metal plate, the flexible substrate 11 can also function as an electrode, and therefore the first electrode 12 does not need to be provided.

[0022] Any conductive material can be used for the first electrode 12. When optical transparency is required, the material can be an oxide conductive film such as ITO (indium tin oxide), IZO (indium zinc oxide), IZTO (indium zinc tin oxide), or IGZO (indium gallium zinc oxide). When optical transparency is not essential, metals such as Au, Pt, Ag, Ti, Al, Mo, Ru, and Cu can also be used.

[0023] From the viewpoint of suppressing unevenness and grain boundaries at the interface between the first electrode 12 and the piezoelectric layer 14, the first electrode 12 may be an amorphous film. By using an amorphous film, it is possible to suppress unevenness on the surface of the first electrode 12 and the generation of grain boundaries that cause leak paths. In addition, the upper piezoelectric layer 14 can grow with good crystal orientation without being affected by the crystal orientation of the first electrode 12.

[0024] The first electrode 12 may be formed as a thin film on a part of or the entire surface of the flexible substrate 11, or may be provided in a plurality of parallel stripes.

[0025] The thickness of the first electrode 12 can be appropriately designed and is preferably, for example, 3 nm to 100 nm, and more preferably 10 nm to 50 nm. If the thickness of the first electrode 12 is within the above-mentioned preferred range, it can function as an electrode and the piezoelectric element 1A can be made thinner.

[0026] The angle adjustment layer 13 is provided on the principal surface (top surface) above the first electrode 12. If the first electrode 12 is not provided, the angle adjustment layer 13 may be provided on the flexible substrate 11. The angle adjustment layer 13 has the function of adjusting the alignment of crystal growth between the piezoelectric layer 14 and the flexible substrate 11 or first electrode 12 adjacent in the stacking direction, and causing the piezoelectric layer 14 to undergo crystal growth close to epitaxial growth. Therefore, the piezoelectric layer 14 formed above the first electrode 12 can have good c-axis orientation even if its thickness is, for example, several hundred nm.

[0027] Furthermore, the angle adjustment layer 13 has excellent surface smoothness and functions to improve the c-axis orientation of the piezoelectric layer 14 located above it. Because the piezoelectric layer 14 contains an amorphous oxide containing Zn, such as ZnO, the c-axis of the piezoelectric layer 14 can be oriented in the vertical direction (stacking direction).

[0028] The angle adjustment layer 13 contains an amorphous material to enhance the smoothness of its surface. The angle adjustment layer 13 does not necessarily have to be 100% amorphous, and may have a non-amorphous region as long as it can enhance the c-axis orientation of the piezoelectric layer 14. If the ratio of the region of the angle adjustment layer 13 made of amorphous components is preferably 90% or more, and more preferably 95% or more, a sufficient effect of controlling the c-axis orientation can be obtained.

[0029] The angle adjusting layer 13 has an amorphous oxide containing Zn, such as ZnSiAlOx or ZnSnOx, as an amorphous material. In this embodiment, the amorphous oxide contains Zn, and is therefore also referred to as a ZnO-based amorphous oxide. The amorphous oxide is not particularly limited as long as it improves the wettability between the flexible substrate 11 or the first electrode 12 and the piezoelectric layer 14 and improves the crystal orientation of the piezoelectric layer 14. Examples of amorphous oxides that can be used include silicon oxide (SiOx), silicon nitride (SiN), aluminum nitride (AlN), aluminum oxide (Al2O3), gallium nitride (GaN), and gallium oxide (Ga2O3); ZnO doped with Al2O3 and SiOx (aluminum-silicon doped zinc oxide (hereinafter referred to as "SAZO")); ZnO doped with at least one of Al2O3, Ga2O3, SiOx, and SiN; IZO (indium zinc oxide), IZTO (indium zinc tin oxide), and IGZO (indium gallium zinc oxide).

[0030] The angle adjusting layer 13 can be formed using the above materials by a sputtering method, a vacuum deposition method, an ion plating method, a coating method, or the like.

[0031] The angle adjusting layer 13 may be a single layer or a laminate of two or more layers.

[0032] The thickness of the angle adjustment layer 13 can be designed as appropriate, and is preferably 3 nm to 100 nm, more preferably 10 nm to 50 nm, and even more preferably 15 nm to 30 nm. If the thickness of the angle adjustment layer 13 is within the above-mentioned preferred range, it can exhibit the function of improving the c-axis orientation of the piezoelectric layer 14 and can also facilitate the thinning of the piezoelectric element 1A. Therefore, it is possible to sufficiently improve the crystal orientation of the piezoelectric layer 14 located above, and to improve the crystallinity of the piezoelectric layer 14.

[0033] The piezoelectric layer 14 is provided on the upper principal surface (top surface) of the angle adjusting layer 13. The piezoelectric layer 14 contains, as a main component, a piezoelectric material having a wurtzite crystal structure (wurtzite crystal material).

[0034] The term "main component" means that the content of the wurtzite crystal material is 95 atm % or more, preferably 98 atm % or more, and more preferably 99 atm % or more.

[0035] The wurtzite crystal structure of the piezoelectric layer 14 is represented by the general formula AB (A is an electropositive element and B is an electronegative element). The wurtzite crystal material has a hexagonal unit cell and a polarization vector parallel to the c-axis.

[0036] As the wurtzite crystal material, it is preferable to use a material that exhibits piezoelectric properties above a certain value and can be crystallized in a low-temperature process at 200°C or less. The wurtzite crystal material is represented by the general formula AB and contains at least Zn as the electropositive element A, selected from Zn, Al, Ga, Cd, and Si. Examples of wurtzite crystal materials that can be used include zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), and zinc telluride (ZnTe). Among these, ZnO is preferred as the wurtzite crystal material because it is relatively easy to achieve good c-axis orientation even in a low-temperature process. These materials may be used alone or in combination of two or more. When two or more wurtzite crystal materials are used in combination, one or more of these components may be contained as the main component, and other components may be contained as optional components.

[0037] The positive element A may include at least one of Al, Ga, Cd, and Si in addition to Zn. Examples of wurtzite crystal materials that can be used include aluminum nitride (AlN), gallium nitride (GaN), cadmium selenide (CdSe), cadmium telluride (CdTe), and silicon carbide (SiC).

[0038] The wurtzite crystal material preferably contains ZnO, and more preferably consists essentially of ZnO. "Substantially" means that the wurtzite crystal material may contain, in addition to ZnO, inevitable impurities that may be inevitably contained during the manufacturing process.

[0039] When two or more wurtzite crystal materials are used in combination, the respective piezoelectric layers may be laminated.

[0040] In addition to the above-mentioned ZnO, ZnS, ZnSe, and ZnTe, the wurtzite crystal material may contain alkaline earth metals such as Mg, Ca, and Sr, or metals such as vanadium (V), titanium (Ti), zirconium (Zr), silica (Si), and lithium (Li) in a predetermined range of proportion. These components may be contained in the elemental state or in the oxide state. For example, if the wurtzite crystal material contains Mg in addition to ZnO, the Mg can be contained as MgO. These components can distort the crystal lattice of ZnO by entering the Zn site of ZnO, thereby improving the piezoelectric properties.

[0041] The thickness of the piezoelectric layer 14 is not particularly limited, and may be any thickness that provides sufficient piezoelectric properties, i.e., polarization properties proportional to pressure, reduces the occurrence of cracks in the piezoelectric layer 14, suppresses leak paths between electrodes, and ensures stable piezoelectric properties. The thickness of the piezoelectric layer 14 may be, for example, 5 μm or less.

[0042] The film density of the piezoelectric layer 14 is not particularly limited and can be designed as appropriate, as long as it is within a range that can enhance the crystal orientation of the piezoelectric layer 14 and suppress an increase in film stress. The method for measuring the film density is not particularly limited, and for example, X-ray reflectivity measurement (XRR) or the like can be used.

[0043] The crystalline orientation of the piezoelectric layer 14 is indicated by the full width at half maximum (FWHM) obtained when the surface of the piezoelectric layer 14 is measured by the X-ray rocking curve (XRC) method. That is, the crystalline orientation of the piezoelectric layer 14 is represented by the FWHM of the peak waveform of the rocking curve obtained when the diffraction from the (0002) plane of the crystal of the piezoelectric material contained as the main component of the piezoelectric layer 14 is measured by the XRC method. Because the piezoelectric material contained in the piezoelectric layer 14 has a wurtzite crystal structure such as ZnO, the FWHM indicates the degree of parallelism of the crystals constituting the piezoelectric material in the c-axis direction. Therefore, the FWHM of the peak waveform of the rocking curve obtained by the XRC method can be used as an indicator of the c-axis orientation of the piezoelectric layer 14. Therefore, the smaller the FWHM of the rocking curve, the better the crystalline orientation of the piezoelectric layer 14 in the c-axis direction can be evaluated.

[0044] The crystal orientation of the piezoelectric layer 14 can be evaluated by XRC, measuring the diffraction from the (0002) plane of the ZnO crystals contained as a piezoelectric material in the piezoelectric layer 14, and also by measuring the peak intensity in addition to the FWHM of the rocking curve. That is, the crystal orientation of the piezoelectric layer 14 can also be evaluated by using the value obtained by dividing the integrated value of the peak intensity by the FWHM as an evaluation value. In this case, the stronger the peak intensity of the rocking curve and the smaller the FWHM, the better the c-axis orientation of the ZnO can be evaluated. Therefore, the greater the evaluation value obtained by dividing the integrated value of the peak intensity by the FWHM, the better the crystal orientation of the piezoelectric layer 14 can be evaluated.

[0045] The second electrode 15 can be provided on the upper main surface (top surface) of the piezoelectric layer 14. The second electrode 15 can be made of any conductive material, and the same material as the first electrode 12 can be used.

[0046] Similar to the first electrode 12, the second electrode 15 may be formed as a thin film on a part or the entire surface of the second electrode 15, or a plurality of second electrodes 15 may be provided in parallel in stripes.

[0047] [Manufacturing method of piezoelectric element] A method for manufacturing a piezoelectric element according to this embodiment will now be described. Fig. 2 is a flowchart showing the method for manufacturing a piezoelectric element according to this embodiment. As shown in Fig. 2, the method for manufacturing a piezoelectric element according to this embodiment includes a first electrode forming step (step S11), an angle adjustment layer forming step (step S12), a piezoelectric layer forming step (step S13), and a second electrode forming step (step S14). In the method for manufacturing a piezoelectric element according to this embodiment, at least in the piezoelectric layer forming step (step S13) among these steps, a RtoR sputtering apparatus is used to form a piezoelectric layer 14 by a RtoR method, thereby manufacturing a piezoelectric element 1A.

[0048] When forming a piezoelectric layer 14 by the RtoR method using a RtoR sputtering apparatus, the deposition roll (drum roll) 21 of the RtoR sputtering apparatus is generally rounded, as shown in FIG. 3 . Therefore, the surface of a flexible substrate 110 wound around the drum roll 21 has a region where sputtered particles 221 emitted from a target 22 containing a piezoelectric material are incident obliquely on the surface of the flexible substrate 110 to form a piezoelectric layer 120. The present inventors have noted that when the sputtered particles 221 are incident obliquely on the surface of the flexible substrate 110 wound around the drum roll 21, the crystals of the piezoelectric material contained in the piezoelectric layer grow obliquely, resulting in crystal distortion in the piezoelectric layer 120. Therefore, when manufacturing a piezoelectric element 1A shown in FIG. 1 by the RtoR method using a RtoR sputtering apparatus, the present inventors have investigated a method for orienting the c-axis of the piezoelectric material contained in the piezoelectric layer 14 in the vertical direction (stacking direction). The inventors of the present application have discovered that by adjusting the amount of oxygen during the formation of the layer (angle adjustment layer 13) formed below the piezoelectric layer 14, the orientation of the crystals of the piezoelectric material contained in the piezoelectric layer 14 can be made vertical, thereby improving the orientation.

[0049] In the method for manufacturing a piezoelectric element according to this embodiment, if a RtoR sputtering apparatus is used for any of the above steps, the steps are performed in the respective deposition chambers within the RtoR sputtering apparatus. If an RtoR sputtering apparatus is used for only the piezoelectric layer formation step (step S13) among the above steps, the steps are performed in one deposition chamber within the RtoR sputtering apparatus. If an RtoR sputtering apparatus is used for any one or more steps other than the piezoelectric layer formation step (step S13), multiple deposition chambers are provided within the RtoR sputtering apparatus, and each step is performed individually in its respective deposition chamber.

[0050] Each step will be described below.

[0051] First, the first electrode 12 is formed on the upper surface of the flexible substrate 11 (first electrode forming step: step S11).

[0052] The method for forming the first electrode 12 is not particularly limited, and may be either a dry process or a wet process. If a dry process is used as the method for forming the first electrode 12, a thin first electrode 12 can be easily formed. Examples of dry processes include sputtering and vapor deposition, and examples of wet processes include plating. Examples of sputtering that can be used include DC (direct current) or RF (radio frequency) magnetron sputtering. By using sputtering as the method for forming the first electrode 12, a thin first electrode 12 with high density can be easily formed. Therefore, sputtering is preferred as the method for forming the first electrode 12. Examples of the first electrode 12 that can be used include an ITO film, a Ti film, or the like formed by DC (direct current) or RF (radio frequency) magnetron sputtering.

[0053] The first electrode 12 may be formed on the entire upper surface of the flexible substrate 11. Alternatively, the first electrode 12 may be formed into an arbitrary shape by processing the first electrode 12 into a pattern having a predetermined shape by etching or the like. For example, the first electrode 12 may be patterned into stripes and a plurality of first electrodes 12 may be arranged in the form of stripes.

[0054] Next, an amorphous material containing Zn is sputtered onto the upper surface of the first electrode 12 to form the angle adjustment layer 13 containing an amorphous oxide (angle adjustment layer forming step: step S12).

[0055] The amorphous material is not particularly limited as long as it is a material that can form an amorphous oxide containing Zn, such as ZnSiAlOx or ZnSnOx, by sputtering.

[0056] For example, a sputtering method can be used as a method for forming the angle adjustment layer 13. The film formation temperature for the angle adjustment layer 13 is not particularly limited as long as the amorphous structure can be maintained, and the film may be formed at a substrate temperature of, for example, 150°C or less.

[0057] In the mixed gas atmosphere containing Ar gas and oxygen, the ratio of the oxygen flow rate to the total flow rate of Ar gas and oxygen exceeds 1%, more preferably 1.5% to 4.0%, and even more preferably 2.0% to 2.5%. If the ratio of the oxygen flow rate to the total flow rate of Ar gas and oxygen exceeds 1%, the wettability of the surface of the angle adjustment layer 13 can be improved. Therefore, when the piezoelectric layer 14 is formed on the upper surface of the angle adjustment layer 13 by sputtering using a target containing Zn, as described below, the wettability between the angle adjustment layer 13 and the piezoelectric material constituting the piezoelectric layer 14 is improved, making it easier to tilt the growth direction of the crystals contained in the piezoelectric material so that they are oriented in the stacking direction, thereby improving the orientation so that the c-axis of the piezoelectric material is vertical.

[0058] The crystal orientation of the piezoelectric material can be determined from the peak waveform of the rocking curve obtained when measuring diffraction from the (0002) plane of the piezoelectric material crystal. Figure 4 shows the relationship between the oxygen flow rate ratio during the formation of the angle adjustment layer 13 and the peak waveform of the rocking curve obtained when measuring diffraction from the (0002) plane of the piezoelectric material crystal contained in the piezoelectric layer 14. Note that Figure 4 shows the case where IZO is used as the angle adjustment layer 13. As shown in Figure 4, when the oxygen flow rate ratio is 2.5%, the peak waveform intensity is highest and the half-width is small. However, as the difference from 2.5% of the oxygen flow rate ratio increases, the peak position of the peak waveform tends to shift and the half-width tends to increase. Therefore, it can be confirmed that if the oxygen flow rate ratio during the formation of the angle adjustment layer 13 is in the range exceeding 1%, the c-axis of the piezoelectric layer 14 is easily oriented in the stacking direction, resulting in high crystal orientation.

[0059] Next, above the angle adjusting layer 13, a wurtzite crystal material is sputtered by an R to R method using an R to R sputtering device in an atmosphere of a mixed gas containing inert gas Ar gas and oxygen, using a target containing the wurtzite crystal material, to form a piezoelectric layer 14 (piezoelectric layer forming process: step S13).

[0060] By using a R to R sputtering system to form the piezoelectric layer 14, it is possible to form a uniform film with strong adhesion while maintaining the composition ratio of the piezoelectric material target. Furthermore, by simply controlling the time, it is possible to precisely form the piezoelectric layer 14 to the desired thickness.

[0061] The laminate of the flexible substrate 11, the first electrode 12, and the angle adjusting layer 13 is wound around a film-forming roll (drum roll) that serves as an anode and is provided in the film-forming chamber of a R to R sputtering device. The laminate is wound so that the flexible substrate 11 is in contact with the drum roll. With the drum roll placed in the film-forming chamber, the piezoelectric layer 14 can be continuously formed on the amorphous film 2 while the laminate is transported by the R to R method.

[0062] A target containing a wurtzite crystalline material is used as the cathode.

[0063] The target containing the wurtzite crystal material may be a single or multiple targets containing the wurtzite crystal material contained as a main component in the piezoelectric layer 14. The single or multiple targets are arranged at an interval from the drum roll.

[0064] For example, the target may be an alloy target in which the atomic ratios of the materials contained in the piezoelectric layer 14 are adjusted. The alloy target may be a metal oxide target containing a wurtzite crystal material and oxygen.

[0065] Ar gas and oxygen gas are supplied as sputtering gases into a film formation chamber of a sputtering apparatus, and a gas atmosphere containing Ar gas and oxygen gas is created in the film formation chamber. A mixed gas containing Ar gas and oxygen gas may be supplied into the film formation chamber, or Ar gas and oxygen gas may be supplied separately.

[0066] The degree of vacuum in the deposition chamber was 1.0×10 -4 Pa or less is sufficient, 1.0 × 10 -6 Pa~1.0×10 -4 It is preferable to adjust the pressure to 1.0 x 10 Pa. -5 Pa ~ 6.0 × 10 -5 More preferably, Pa. If the degree of vacuum in the film formation chamber is within the above-mentioned preferred range, the piezoelectric layer 14 is easily formed containing a wurtzite crystal material.

[0067] The pressure of the mixed gas atmosphere in the film formation chamber during sputtering is not particularly limited as long as it is within a range in which the piezoelectric layer 14 can be formed, and may be, for example, 2.0 Pa or less.

[0068] The ratio of the flow rate of oxygen to the total flow rate of Ar gas and oxygen in the deposition chamber can be selected appropriately depending on the type of gas, the oxygen content in the piezoelectric layer 14, etc., and is preferably 0.1% to 20.0%, and more preferably 1.0% to 10.0%. If the oxygen flow rate ratio is within the above-mentioned preferred range, the piezoelectric layer 14 can easily form a wurtzite-type crystal material containing Zn.

[0069] The deposition temperature of the piezoelectric layer 14 does not have to be room temperature as long as the amorphous structure of the angle adjustment layer 13 located below the piezoelectric layer 14 is maintained. For example, the piezoelectric layer 14 may be deposited at a substrate temperature of 150° C. or lower.

[0070] The piezoelectric layer 14 may be configured by laminating a plurality of layers.

[0071] Next, a second electrode 15 having a predetermined shape is formed on the upper surface of the piezoelectric layer 14 (second electrode forming step: step S14).

[0072] The second electrode 15 can be formed using the same method as that for the first electrode 12 .

[0073] The thickness of the second electrode 15 can be appropriately designed and is, for example, preferably 20 nm to 100 nm, more preferably 10 nm to 50 nm. If the thickness of the second electrode 15 is within the above-mentioned preferred range, the function as an electrode can be exhibited and the piezoelectric element 1A can be made thinner.

[0074] The second electrode 15 may be formed on the entire surface of the piezoelectric layer 14, or may be formed in any suitable shape. For example, when the first electrode 12 is patterned in stripes, the second electrode 15 may be formed so that multiple stripes extend in a direction perpendicular to the direction in which the stripes of the first electrode 12 extend in a plan view.

[0075] As a result, the piezoelectric element 1A is obtained.

[0076] After the second electrode 15 is formed, the entire piezoelectric element 1A may be heat-treated at a temperature (for example, 130°C) lower than the melting point or glass transition point of the flexible substrate 11. This heat treatment crystallizes the first electrode 12 and the second electrode 15, reducing their resistance. The heat treatment is not essential, and may not be performed after the formation of the piezoelectric element 1A in cases where the flexible substrate 11 is made of a material that is not heat-resistant.

[0077] As described above, the method for manufacturing a piezoelectric element according to this embodiment includes an angle adjustment layer formation step (step S12) and a piezoelectric layer formation step (step S13). In the angle adjustment layer formation step (step S12) of the method for manufacturing a piezoelectric element according to this embodiment, an amorphous material containing Zn is sputtered in a mixed gas atmosphere containing Ar gas and oxygen, with the ratio of the oxygen flow rate to the total flow rate of Ar gas and oxygen exceeding 1%, to form angle adjustment layer 13 containing an amorphous oxide. The surface of the resulting angle adjustment layer 13 has high wettability. Therefore, even if the amorphous material is incident obliquely on the upper surface of angle adjustment layer 13 in the initial stage of forming piezoelectric layer 14 on the upper surface of angle adjustment layer 13, and the crystals contained in the piezoelectric material begin to grow at an angle with respect to the stacking direction of piezoelectric layer 14 (the perpendicular direction to the upper surface of angle adjustment layer 13), the c-axis of the crystals contained in the piezoelectric material is easily tilted to be aligned with the stacking direction of piezoelectric layer 14 as the crystals grow. This prevents the crystal growth of the piezoelectric material from being tilted, thereby improving the orientation of the c-axis of the piezoelectric material. Therefore, by using the manufacturing method of the piezoelectric element according to this embodiment, when using the RtoR method, even if a piezoelectric material is formed on the curved surface of the angle adjustment layer 13 wound around a drum roll or the like, the crystal orientation can be enhanced, and the piezoelectric layer 14 can be formed to have high crystal orientation. Therefore, the manufacturing method of the piezoelectric element according to this embodiment can manufacture a piezoelectric layer 14 with high crystal orientation even when using the RtoR method.

[0078] Generally, if the crystal growth direction of the piezoelectric material contained in the piezoelectric layer is tilted during the initial growth stage, which is important for crystal growth, it tends to be difficult to achieve high orientation in the piezoelectric layer. A misaligned crystal axis makes the crystal more susceptible to damage due to vertical pressure and reduces the amount of charge generated in response to vertical pressure. Furthermore, when a piezoelectric layer is deposited using a RtoR sputtering system, the crystal orientation of the piezoelectric material contained in the piezoelectric layer tends to tilt toward the MD direction, which is the flow direction (longitudinal direction) of the first electrode, but not toward the TD direction, which is the transverse direction (perpendicular to the flow direction). For example, when X-rays are incident on the surface of the piezoelectric layer along the MD direction of a flexible substrate in a RtoR sputtering system (as shown in Figure 5), the peak position of the crystal orientation of the piezoelectric material contained in the piezoelectric layer shifts toward the MD direction of the flexible substrate, as shown in Figure 6. On the other hand, when X-rays are incident on the surface of the piezoelectric layer along the TD direction of a flexible substrate or the like in a RtoR sputtering device as shown in FIG. 7, the peak position hardly fluctuates with temperature as shown in FIG.

[0079] In contrast, the method for manufacturing a piezoelectric element according to this embodiment increases the wettability of the surface of angle adjustment layer 13 formed in the angle adjustment layer formation step (step S12), so that when piezoelectric layer 14 is formed thereon using the RtoR method, even if the crystals are tilted in the initial stage of piezoelectric layer 14, the crystals can be oriented so that their direction becomes vertical as they grow. This makes it possible to improve the crystal orientation of the resulting piezoelectric layer 14.

[0080] The piezoelectric layer 14 obtained by the method for manufacturing a piezoelectric element according to this embodiment can have high crystal orientation, and therefore can exhibit high piezoelectric efficiency in its thickness direction, allowing the piezoelectric element 1A to exhibit excellent piezoelectric properties for a long period of time.

[0081] The piezoelectric characteristic of the piezoelectric element 1A is the piezoelectric constant d 33 It can be evaluated by the value. 33The value d represents the expansion / contraction mode of the piezoelectric layer 14 in the thickness direction, and is the polarization charge amount [C / N] per unit pressure applied in the thickness direction of the piezoelectric layer 14. 33 The higher the value, the better the polarization in the thickness direction (c-axis direction) of the piezoelectric layer 14 of the piezoelectric element 1A.

[0082] d 33 The value can be directly measured using a piezoelectric constant measurement device (LPF-02, manufactured by Lead Techno Corporation) or the like. The upper and lower surfaces of the piezoelectric layer 14 are sandwiched between the electrodes of the piezoelectric constant measurement device, an indenter is pressed against the surface of the piezoelectric layer 14, a load is applied to the piezoelectric layer 14, and the amount of generated charge is measured with a coulomb meter of the piezoelectric constant measurement device. The value obtained by dividing the measured amount of charge by the load is d 33 It is output as a value. 33 The larger the absolute value of the value, the better the piezoelectric characteristics of the piezoelectric layer 14 in the film thickness direction.

[0083] The piezoelectric layer 14 obtained by the method for manufacturing a piezoelectric element according to this embodiment has high crystal orientation, and therefore can exhibit high piezoelectric efficiency in its thickness direction, and can exhibit excellent piezoelectric properties for a long period of time.

[0084] In the method for manufacturing a piezoelectric element according to this embodiment, the ratio of the oxygen flow rate to the total flow rate of Ag gas and oxygen can be set to 1.5% to 4.0% in the angle adjustment layer formation step (step S12). This maximizes the intensity of the peak waveform of the rocking curve obtained when measuring diffraction from the (0002) plane of the piezoelectric material crystal, and also minimizes its FWHM. Therefore, by using the method for manufacturing a piezoelectric element according to this embodiment, a piezoelectric layer 14 with higher crystal orientation can be reliably formed even when using the RtoR method.

[0085] In the method for manufacturing a piezoelectric element according to this embodiment, in the angle adjustment layer formation step (step S12), sputtering can be performed using a target containing an amorphous material. This makes it possible to easily change the type of amorphous material contained in the piezoelectric layer 14 depending on the type of target used. Therefore, according to the method for manufacturing a piezoelectric element according to this embodiment, when forming the piezoelectric layer 14, the type of amorphous material contained in the piezoelectric layer 14 can be easily changed depending on the application.

[0086] In the method for manufacturing a piezoelectric element according to this embodiment, in the first electrode formation step (step S11), the first electrode 12 can be formed on one main surface 11a of the flexible substrate 11. As a result, in the method for manufacturing a piezoelectric element according to this embodiment, even if the flexible substrate 11 does not have conductivity, by forming the first electrode 12 on the flexible substrate 11, it is possible to reliably manufacture a piezoelectric layer 14 with high crystal orientation.

[0087] The piezoelectric element 1A thus obtained has excellent piezoelectric properties and is therefore suitable for use in piezoelectric devices, such as devices that utilize the piezoelectric effect, such as force sensors for touch panels, pressure sensors, acceleration sensors, and acoustic emission (AE) sensors, as well as speakers, transducers, high-frequency filter devices, piezoelectric actuators, and optical scanners that utilize the inverse piezoelectric effect.

[0088] (Other aspects) In this embodiment, the piezoelectric element 1A is not limited to the above configuration, and may have other configurations as long as it has a first electrode 12 and a piezoelectric layer 14 on a flexible substrate 11, and the piezoelectric layer 14 can exhibit excellent piezoelectric properties in the thickness direction. An example of another configuration of the piezoelectric element 1A is shown below.

[0089] As shown in FIG. 9, the piezoelectric element 1B does not necessarily have to include the second electrode 15.

[0090] As shown in FIG. 10, a piezoelectric element 1C may include an adhesive layer 16 between a piezoelectric layer 14 and a second electrode 15, and a substrate 17 on the upper surface of the second electrode 15.

[0091] The adhesive layer 16 suppresses leak paths caused by cracks or pinholes that occur in the piezoelectric layer 14. If metal grain boundaries or protrusions are present at the interface between the first electrode 12 and the piezoelectric layer 14 or the interface between the piezoelectric layer 14 and the second electrode 15, when a crack or the like occurs in any of the first electrode 12, the piezoelectric layer 14, or the second electrode 15, the crack or the like will form a leak path between the first electrode 12 and the second electrode 15, causing a loss of polarization. By providing the adhesive layer 16 between the piezoelectric layer 14 and the second electrode 15, the piezoelectric element 1C suppresses the formation of leak paths and maintains good piezoelectric properties of the piezoelectric layer 14.

[0092] The substrate 17 can be made of the same material as the flexible substrate 11 .

[0093] An example of a method for manufacturing the piezoelectric element 1C will be described. For example, a first laminate is formed by laminating a first electrode 12 and a piezoelectric layer 14 in this order on a flexible substrate 11. Meanwhile, a second laminate is formed by forming a second electrode 15 on a substrate 17. Thereafter, the piezoelectric layer 14 and the second electrode 15 are bonded together via an adhesive layer 16 so that the piezoelectric layer 14 of the first laminate faces the second electrode 15 of the second laminate. In this way, the piezoelectric element 1C is manufactured.

[0094] The piezoelectric element 1C has a piezoelectric strain constant d 33 Since the value is large and the leak path between the electrodes can be suppressed, it is possible to have better piezoelectric properties. [Example]

[0095] Hereinafter, the embodiment will be described in more detail with reference to examples and comparative examples, but the embodiment is not limited to these examples and comparative examples.

[0096] <Fabrication of piezoelectric elements> [Example 1] A 50 μm thick PET film roll substrate was attached to the unwinding section of the RtoR sputtering device, and two targets consisting of In, Zn, and O, and one target consisting of Mg, Zn, and O were attached to each of the three deposition chambers of the RtoR sputtering device along the winding direction of the PET film roll substrate.

[0097] While the PET film roll substrate was running from the unwinding section to the winding section, an 85 nm thick IZO film was deposited as the first electrode on the surface of the PET film roll substrate in the first deposition chamber using one of the targets consisting of In, Zn, and O. Ar gas was used as the inert gas and O2 gas was used as the reactive gas. Ar gas and O2 gas were introduced into the first deposition chamber at a ratio of O2 gas flow rate to the sum of Ar gas flow rate and O2 gas flow rate of 0.75%.

[0098] Then, in the second deposition chamber, a 15 nm thick IZO film was deposited as an angle adjustment layer on the surface of the IZO film of the PET film roll substrate using the other target consisting of In, Zn, and O. Ar gas and O2 gas were introduced into the second deposition chamber, with the ratio of O2 gas flow rate to the sum of Ar gas flow rate and O2 gas flow rate set to 1.5%.

[0099] Then, in the third film-forming chamber, a target consisting of Mg, Zn, and O was used to form a Mg-doped ZnO layer with a hexagonal wurtzite structure as a piezoelectric layer to a thickness of 200 nm on the surface of the IZO film of the PET film roll substrate on which two IZO films were laminated, and the film was then wound up on a winding section.

[0100] In this way, a piezoelectric element was produced, which included a first electrode, an angle adjusting layer, and a piezoelectric layer laminated in this order on a PET film roll substrate.

[0101] [Examples 2 and 3] Piezoelectric elements were manufactured in the same manner as in Example 1, except that the O 2 gas flow rate ratio during the formation of the angle adjusting layer was changed to the values ​​shown in Table 1.

[0102] [Examples 4 to 6] In Example 1, a piezoelectric element was manufactured in the same manner as in Example 1, except that the first electrode was not formed, the O2 gas flow rate ratio during the formation of the angle adjustment layer was changed to the value shown in Table 1, and the thickness of the angle adjustment layer was changed to 85 nm.

[0103] [Comparative Example 1] A piezoelectric element was manufactured in the same manner as in Example 1, except that the O2 gas flow rate ratio of the angle adjusting layer was changed to 1.0%.

[0104] Comparative Example 2 A piezoelectric film was manufactured in the same manner as in Example 1, except that the O2 gas flow rate ratio for the first electrode was set to 0.5% and no angle adjusting layer was formed.

[0105] Comparative Example 3 In Example 1, a piezoelectric element was manufactured in the same manner as in Example 1, except that the first electrode was not formed, the O2 gas flow rate ratio of the angle adjustment layer was changed to 5.0%, and the thickness of the angle adjustment layer was changed to 85 nm.

[0106] (Measurement of surface resistance of angle adjustment layer) In each example and comparative example, during the process of producing the piezoelectric element, the surface resistance (Ω / □) of the angle adjustment layer or the laminate in which the first electrode and the angle adjustment layer were laminated was measured by the four-terminal method in accordance with JIS K7194 (1994). The measurement results are shown in Table 1.

[0107] (Evaluation of crystal axis distortion and half-width of piezoelectric layer) The crystal axis strain and half-width of the piezoelectric layer of the obtained piezoelectric element were measured and evaluated. The crystal axis strain and half-width of the piezoelectric layer were measured by X-ray rocking curve measurement using an X-ray diffractometer (Rigaku Corporation, SmartLab Studio II) under the following measurement conditions. The angle and full width at half maximum (FWHM) at which the X-ray diffraction intensity was highest were then determined as the axial strain and half-width. The measurement results are shown in Table 1. ((Measurement conditions)) ·Light source: CuKα ray (1.5418Å) Measurement mode: θ scan Sample: A sample was prepared by attaching a piezoelectric element to a 30mm x 30mm glass substrate with adhesive. The sample was set up so that the MD direction of the sample was parallel to the incident direction of the X-rays. In addition, the direction of travel of the substrate during the deposition of the piezoelectric layer was unified with the incident direction of the X-rays. · 2θ position: The 2θ angle at which the ZnO (002) plane peak appears was determined for each sample by X-ray diffraction measurement. Measurement range: ω=0°~2θ Measurement interval: 0.1°

[0108] [Evaluation of piezoelectric properties] The piezoelectric characteristics of the obtained piezoelectric elements of each example and comparative example were d 33 The values ​​were measured.

[0109] (d 33 value) d 33 The value was evaluated using the following procedure. A piezoelectric element was placed on a stage, and the stage was electrically connected to the angle adjustment layer or a laminate in which the first electrode and the angle adjustment layer were laminated. An indenter was placed on the top surface of the sample, and a predetermined pressure was applied from the top surface of the sample with the indenter to generate lattice distortion in the piezoelectric layer, and the charge generated by polarization in the c-axis (film thickness) direction resulting from this lattice distortion was measured. The amount of charge generated when the applied load was changed from 1 N to 5 N was divided by the load difference of 4 N, and this value was used as d 33 The value was d 33 The value represents the expansion / contraction mode of the piezoelectric element in the thickness direction, and is the polarization charge amount [C / N] per unit pressure applied in the thickness direction. 33 The higher the value, the better the polarization in the thickness direction (c-axis direction) of the piezoelectric layer, and the piezoelectric element can be evaluated as having high piezoelectric properties. 33 The measurement results are shown in Table 1.

[0110] [Table 1]

[0111] From Table 1, Examples 1 to 3 are d 33 The values ​​of Examples 5 to 7 were larger than those of Comparative Example 2. 33 The value was confirmed to be large.

[0112] Therefore, in Examples 1 to 7, unlike Comparative Examples 1 to 3, the axial strain and half-width of the piezoelectric layer are reduced by forming the film by setting the oxygen flow rate ratio during film formation of the first electrode or the angle adjusting tank to exceed 1.0%, and the d 33 Therefore, it can be said that a piezoelectric element that can exhibit excellent piezoelectric properties can be obtained.

[0113] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the inventions and their equivalents as set forth in the claims.

[0114] This application claims priority based on Patent Application No. 2021-056825 filed with the Japan Patent Office on March 30, 2021, and the entire contents of Patent Application No. 2021-056825 are incorporated herein by reference. [Explanation of symbols]

[0115] 1A, 1B, 1C Piezoelectric elements 11 Flexible substrate 12 First electrode 13 Angle adjustment layer 14 Piezoelectric layer 15 Second electrode 16 Adhesive layer

Claims

1. an angle adjustment layer forming step of sputtering an amorphous material containing Zn in a mixed gas atmosphere containing an inert gas and oxygen on one main surface side of the flexible substrate to form an angle adjustment layer containing an amorphous oxide; a piezoelectric layer forming step of forming a piezoelectric layer on the angle adjusting layer by a roll-to-roll method; Including, In the angle adjustment layer forming step, the ratio of the flow rate of the oxygen to the total flow rate of the inert gas and the oxygen exceeds 1%.

2. 2. The method for manufacturing a piezoelectric element according to claim 1, wherein the ratio of the oxygen to the total flow rate of the inert gas and the oxygen in the angle adjusting layer forming step is 1.5% to 4.0%.

3. The method for manufacturing a piezoelectric element according to claim 1 or 2, wherein the angle adjusting layer forming step comprises sputtering using a target containing the amorphous material.

4. 4. The method for manufacturing a piezoelectric element according to claim 1, further comprising the step of forming an electrode on one main surface of the flexible substrate.

5. A method for manufacturing a piezoelectric device, comprising the method for manufacturing a piezoelectric element according to claim 4.

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