WO2022210438A1

WO2022210438A1 - Method for manufacturing piezoelectric element and method for manufacturing piezoelectric device

Info

Publication number: WO2022210438A1
Application number: PCT/JP2022/014719
Authority: WO
Inventors: 聖彦渡邊; 岳圓岡; 岳人石川; 大輔中村; 広宣待永
Original assignee: 日東電工株式会社
Priority date: 2021-03-30
Filing date: 2022-03-25
Publication date: 2022-10-06
Also published as: JPWO2022210438A1

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

Piezoelectric element manufacturing method and piezoelectric device manufacturing method

The present invention relates to a method for manufacturing a piezoelectric element and a method for manufacturing a piezoelectric device.

A piezoelectric element having a piezoelectric layer has high piezoelectricity, so it is widely used in piezoelectric devices such as sensors such as pressure sensors and acceleration sensors, high-frequency filter devices, and piezoelectric actuators.

A piezoelectric element is generally constructed by laminating a piezoelectric layer on a base material. When the piezoelectric layer is formed by growing crystals on the conductive film on the substrate, the piezoelectric layer has high piezoelectric characteristics by orienting the crystals of the piezoelectric layer in the c-axis direction and having high crystal orientation. . A piezoelectric element having a piezoelectric layer having such high piezoelectric properties can have good piezoelectric properties. Various methods have been proposed for manufacturing a piezoelectric element by highly aligning a piezoelectric layer.

As a method of manufacturing a piezoelectric element, for example, a piezoelectric layer having a wurtzite crystal structure is formed on a first electrode made of an amorphous oxide conductor layer formed on a substrate. , a method of manufacturing a piezoelectric device in which a second electrode is formed on a piezoelectric layer is disclosed (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2020-57781

However, in the method for manufacturing a piezoelectric device of Patent Document 1, the piezoelectric layer is sputtered on the first electrode while the first electrode is conveyed by drum rolls in a roll-to-roll (R to R) method. However, since the surface of the drum roll on which the piezoelectric layer is sputtered is curved, there is a problem that the crystal axis of the piezoelectric material contained in the piezoelectric layer is distorted.

When the crystal axis is distorted, the crystal orientation of the piezoelectric layer is disturbed, making it difficult to increase the orientation of the piezoelectric layer. A piezoelectric element having a piezoelectric layer operates on the principle of vibration in the thickness direction of the piezoelectric layer (thickness vibration). It is important that they have a high degree of crystallographic orientation in the same direction.

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 the RtoR method is used.

In one aspect of the method for manufacturing a piezoelectric element according to the present invention, an amorphous material containing Zn is sputtered in a mixed gas atmosphere containing an inert gas and oxygen on one main surface of a flexible base material. an angle adjusting layer forming step of forming an angle adjusting 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; and 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%.

One aspect of the method for manufacturing a piezoelectric element according to the present invention is that a piezoelectric thin film with high crystal orientation can be manufactured even when the RtoR method is used.

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 invention; FIG. 4 is a flow chart showing a method of manufacturing a piezoelectric element according to an embodiment of the present invention; FIG. 4 is a diagram for explaining crystal strain contained in a piezoelectric layer; FIG. 10 is a diagram showing the relationship between the flow rate ratio of oxygen during formation of the angle adjustment layer and the peak waveform of the rocking curve obtained when diffraction from the (0002) plane of the crystal of the piezoelectric material contained in the piezoelectric layer is measured. is. FIG. 4 is a diagram showing the direction of incidence of X-rays on the piezoelectric layer; It is a figure which shows the X-ray-diffraction intensity|strength in MD direction of a piezoelectric material layer. FIG. 4 is a diagram showing the direction of incidence of X-rays on the piezoelectric layer; It is a figure which shows the X-ray-diffraction intensity|strength in TD direction of a piezoelectric material layer. FIG. 4 is a schematic cross-sectional view showing an example of another configuration of the piezoelectric element; FIG. 4 is a schematic cross-sectional view showing an example of another configuration of the piezoelectric element;

Hereinafter, embodiments of the present invention will be described in detail. In addition, in order to facilitate understanding of the description, the same components are denoted by the same reference numerals in each drawing, and overlapping descriptions are omitted. Also, the scale of each member in the drawings may differ from the actual scale. Unless otherwise specified, "-" indicating a numerical range in this specification means that the numerical values before and after it are included as lower and upper limits.

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

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

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) orthogonal to the thickness direction is defined as the X-axis direction. The second electrode 15 side in the Z-axis direction is the +Z-axis direction, and the flexible substrate 11 side is the -Z-axis direction. In the following description, for convenience of explanation, the +Z-axis direction is referred to as upward or upward, and the −Z-axis direction is referred to as downward or downward, but this does not represent a universal vertical relationship.

The flexible base material 11 is a substrate on which the first electrode 12 is installed. Any material can be used as the flexible base material 11, and a plastic base material, a silicon (Si) substrate, a metal plate, a glass base material, or the like can be used.

When a plastic base material is used, it is preferable to use a flexible material that can give flexibility to the piezoelectric element including the piezoelectric layer 14 .

As materials for forming the plastic base material, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), acrylic resin, cycloolefin polymer, polyimide (PI), etc. can be used. Among these materials, PET, PEN, PC, acrylic resins, and cycloolefin polymers are transparent materials, and are suitable when the electrodes used in the piezoelectric element having the piezoelectric layer 14 are transparent electrodes. In the case where the piezoelectric element having the piezoelectric layer 14 is not required to have optical transparency, such as health care products such as a pulse meter and a heart rate monitor, and an in-vehicle pressure detection sheet, the material forming the plastic base material is the above-mentioned material. Alternatively, a translucent or opaque plastic material may be used.

The thickness of the flexible base material 11 is not particularly limited, and can be set to any desired thickness depending on the application of the piezoelectric element 1A, the material of the flexible base material 11, and the like. For example, when the flexible base material 11 is a plastic base material, the thickness of the flexible base material 11 may be 1 μm to 250 μm. A method for measuring the thickness of the flexible base material 11 is not particularly limited, and any measuring method can be used.

In this specification, the thickness of the flexible base material 11 refers to the length of the flexible base material 11 in the direction perpendicular to the main surface thereof. The thickness of the flexible base material 11 may be, for example, the thickness measured at an arbitrary location in the cross section of the flexible base material 11, or may be measured at several locations at arbitrary locations. may be the average value of Hereinafter, the definition of thickness is similarly defined for other members.

The first electrode 12 is provided on the upper main surface (upper surface) of the flexible base material 11 . If the flexible base material 11 is conductive such as a metal plate, the flexible base material 11 can also function as an electrode, so the first electrode 12 need not be provided.

Any conductive material can be used for the first electrode 12 . When light transmittance is required, the materials include conductive oxide films such as ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), IZTO (Indium Zinc Tin Oxide), and IGZO (Indium Gallium Zinc Oxide). etc. can be used. If light transmittance is not essential, metals such as Au, Pt, Ag, Ti, Al, Mo, Ru and Cu may be used.

The first electrode 12 may be an amorphous film from the viewpoint of suppressing unevenness and crystal grain boundaries at the interface between the first electrode 12 and the piezoelectric layer 14 . By using an amorphous film, it is possible to suppress unevenness on the surface of the first electrode 12 and generation of crystal grain boundaries that cause leakage paths. Also, the upper piezoelectric layer 14 can be grown with good crystal orientation without being affected by the crystal orientation of the first electrode 12 .

The first electrode 12 may be formed as a thin film on a part or the entire surface of the flexible base material 11, or may be provided in parallel in a stripe shape.

The thickness of the first electrode 12 can be appropriately designed, and is preferably 3 nm to 100 nm, more preferably 10 nm to 50 nm, for example. If the thickness of the first electrode 12 is within the above preferable range, the function as an electrode can be exhibited and the thickness of the piezoelectric element 1A can be reduced.

The angle adjustment layer 13 is provided on the main surface (upper surface) above the first electrode 12 . In addition, when the first electrode 12 is not provided, the angle adjustment layer 13 may be provided on the flexible base material 11 . The angle adjustment layer 13 adjusts the consistency of crystal growth between the piezoelectric layer 14 and the flexible base material 11 or the first electrode 12 adjacent in the stacking direction, so that the piezoelectric layer 14 is nearly epitaxially grown. It has the function of causing crystal 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.

In addition, the angle adjusting layer 13 has excellent surface smoothness and has a function of improving the c-axis orientation of the piezoelectric layer 14 located above. Since 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).

The angle adjusting layer 13 contains an amorphous material in order to improve 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 the c-axis orientation of the piezoelectric layer 14 can be enhanced. If the proportion of the region formed of the amorphous component in the region of the angle adjusting layer 13 is preferably 90% or more, more preferably 95% or more, a sufficient c-axis orientation control effect can be obtained. .

The angle adjustment layer 13 has an amorphous oxide containing Zn, such as ZnSiAlOx and ZnSnOx, as an amorphous material. In the present embodiment, the amorphous oxide contains Zn, so it is also called a ZnO-based amorphous oxide. The amorphous oxide is not particularly limited as long as it improves the wettability between the flexible base material 11 or the first electrode 12 and the piezoelectric layer 14 and improves the crystal orientation of the piezoelectric layer 14 . Amorphous oxides include silicon oxide (SiOx), silicon nitride (SiN), aluminum nitride (AlN), aluminum oxide ( _Al2O3 ) _, gallium nitride (GaN), gallium oxide ₍ _Ga2O3 ); ZnO added with _Al2O3 and SiOx (aluminum _- silicon-added zinc oxide (hereinafter referred to as "SAZO")); at least one of _Al2O3 _, _Ga2O3 _, SiOx, and SiN added ZnO; IZO (Indium Zinc Oxide), IZTO (Indium Zinc Tin Oxide), IGZO (Indium Gallium Zinc Oxide) and the like can be used.

The angle adjustment layer 13 can be formed using the above materials by a sputtering method (sputtering method), a vacuum deposition method, an ion plating method, a coating method, or the like.

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

The thickness of the angle adjustment layer 13 can be appropriately designed, and is preferably 3 nm to 100 nm, more preferably 10 nm to 50 nm, and even more preferably 15 nm to 30 nm, for example. If the thickness of the angle adjustment layer 13 is within the above preferred range, the function of increasing the c-axis orientation of the piezoelectric layer 14 can be exhibited, and the thickness of the piezoelectric element 1A can be reduced. Therefore, the crystal orientation of the piezoelectric layer 14 positioned above can be sufficiently improved, and the crystallinity of the piezoelectric layer 14 can be improved.

The piezoelectric layer 14 is provided on the main surface (upper surface) above the angle adjustment layer 13 . The piezoelectric layer 14 contains, as a main component, a piezoelectric material having a wurtzite crystal structure (wurtzite crystal material).

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.

The wurtzite crystal structure of the piezoelectric layer 14 is represented by the general formula AB (A is a positive element and B is a negative element). A wurtzite crystal material has a hexagonal unit cell and a polarization vector in a direction parallel to the c-axis.

As the wurtzite crystal material, it is preferable to use a material that exhibits piezoelectric properties of a certain value or more and can be crystallized by a low-temperature process of 200°C or less. The wurtzite crystal material contains at least Zn among Zn, Al, Ga, Cd and Si as the positive element A represented by the general formula AB. As the wurtzite crystal material, for example, zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), and the like can be used. Among these, ZnO is preferable as the wurtzite crystal material because it is relatively easy to achieve c-axis orientation even in a low-temperature process. These may be used individually by 1 type, and may be used together 2 or more types. When two or more wurtzite crystal materials are used in combination, one or more of these components may be included as the main component, and other components may be included as optional components.

The positive element A may contain 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).

The wurtzite crystal material contains ZnO, preferably consists essentially of ZnO, and more preferably consists of ZnO only. “Substantially” means that, in addition to ZnO, unavoidable impurities that may be unavoidably included during the manufacturing process may be included.

When two or more types of wurtzite crystal materials are used in combination, each piezoelectric layer may be laminated.

As the wurtzite crystal material, in addition to the above ZnO, ZnS, ZnSe and ZnTe, alkaline earth metals such as Mg, Ca and Sr, vanadium (V), titanium (Ti), zirconium (Zr), silica Metals such as (Si) and lithium (Li) may be included in a predetermined range of proportions. These components may be contained in the form of elements or may be contained in the form of oxides. For example, if the wurtzite crystal material contains Mg in addition to ZnO or the like, the Mg can be contained as MgO. These components can distort the crystal lattice of ZnO by entering the Zn sites of ZnO and the like, so that the piezoelectric properties can be improved.

The thickness of the piezoelectric layer 14 is not particularly limited, and it has sufficient piezoelectric characteristics, that is, polarization characteristics proportional to pressure, and reduces the occurrence of cracks or the like in the piezoelectric layer 14 to form a leak path between electrodes. Any thickness may be used as long as the thickness is such that the piezoelectric properties can be stably exhibited while suppressing the The thickness of the piezoelectric layer 14 may be, for example, 5 μm or less.

The film density of the piezoelectric layer 14 is not particularly limited, and can be appropriately designed, as long as it is within a range in which the crystal orientation of the piezoelectric layer 14 can be enhanced and an increase in film stress can be suppressed. The method for measuring the film density is not particularly limited, and for example, X-ray reflectometry (XRR) or the like can be used.

The crystal 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 an X-ray rocking curve (XRC) method. be That is, the crystal orientation of the piezoelectric layer 14 is obtained by measuring the diffraction from the (0002) plane of the crystal of the piezoelectric material contained as the main component in the piezoelectric layer 14 by the XRC method. It is represented by the FWHM of the waveform. Since the piezoelectric material contained in the piezoelectric layer 14 has a wurtzite crystal structure such as ZnO, FWHM indicates the degree of parallelism in the c-axis direction arrangement of the crystals forming the piezoelectric material. Therefore, the FWHM of the peak waveform of the rocking curve obtained by the XRC method can be used as an index of the c-axis orientation of the piezoelectric layer 14 . Therefore, it can be evaluated that the smaller the FWHM of the rocking curve, the better the crystal orientation of the piezoelectric layer 14 in the c-axis direction.

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

The second electrode 15 can be provided on the main surface (upper surface) above 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.

As with the first electrode 12, the second electrode 15 may be formed in a thin film on part or the entire surface of the second electrode 15, or may be provided in parallel in a stripe shape.

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

When the piezoelectric layer 14 is formed by the RtoR method using an RtoR sputtering apparatus, as shown in FIG. 3, the film-forming roll (drum roll) 21 of the RtoR sputtering apparatus is generally rounded. Therefore, on the surface of the flexible base material 110 wound around the drum roll 21, the sputtered particles 221 emitted from the target 22 containing the piezoelectric material are obliquely incident on the surface of the flexible base material 110 to form the piezoelectric layer. There is an area forming 120 . The inventor of the present application believes that when the sputtered particles 221 obliquely impinge on the surface of the flexible base material 110 wound around the drum roll 21, the crystals of the piezoelectric material contained in the piezoelectric layer grow obliquely, resulting in the formation of the piezoelectric layer. We focused on the fact that 120 has crystal strain. Therefore, the inventors of the present application, when manufacturing the piezoelectric element 1A shown in FIG. We considered the method. The inventors of the present application have found that the crystal orientation of the piezoelectric material contained in the piezoelectric layer 14 is adjusted by adjusting the amount of oxygen during the formation of the layer (angle adjustment layer 13 ) formed below the piezoelectric layer 14 . It was found that the orientation can be improved by making the direction of the vertical direction.

In the method for manufacturing a piezoelectric element according to the present embodiment, when any one of the above steps uses an RtoR sputtering apparatus, it is performed in each film formation chamber in the RtoR sputtering apparatus. Among the above steps, only the piezoelectric layer forming step (step S13) is performed in one film formation chamber in the RtoR sputtering apparatus when the RtoR sputtering apparatus is used. When any one or more steps other than the piezoelectric layer forming step (step S13) also use the RtoR sputtering apparatus, a plurality of film forming chambers are provided in the RtoR sputtering apparatus, and each step is performed in its own film forming chamber. performed individually in the room.

Each step will be explained below.

First, the first electrode 12 is formed on the upper surface of the flexible base material 11 (step of forming the first electrode: step S11).

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

The first electrode 12 may be formed on the entire upper surface of the flexible base material 11 . Also, the first electrode 12 may be processed into a pattern having a predetermined shape by etching or the like, and may be appropriately formed into an arbitrary shape. For example, the first electrodes 12 may be patterned in stripes and arranged in plurality in stripes.

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

The amorphous material is not particularly limited as long as it is a material capable of forming an amorphous oxide containing Zn by sputtering, such as ZnSiAlOx and ZnSnOx.

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

In a mixed gas atmosphere containing Ar gas and oxygen, the ratio of the flow rate of oxygen to the total flow rate of Ar gas and oxygen is more than 1%, more preferably 1.5% to 4.0%, and 2.0% to 2.0%. 0.5% is more preferred. If the ratio of the flow rate of oxygen to the total flow rate of Ar gas and oxygen exceeds 1%, wettability of the surface of the angle adjusting layer 13 can be enhanced. Therefore, when the piezoelectric layer 14 is formed on the upper surface of the angle adjustment layer 13 by a sputtering method using a target containing Zn, as will be described later, the angle adjustment layer 13 and the piezoelectric material forming the piezoelectric layer 14 The wettability with the piezoelectric material is improved, and the growth direction of the crystals contained in the piezoelectric material can be easily tilted so that the crystals are oriented in the stacking direction.

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

Next, above the angle adjustment layer 13, a target containing a wurtzite crystal material is placed in a mixed gas atmosphere containing inert gas Ar gas and oxygen by the R to R method using an R to R sputtering apparatus. to form the piezoelectric layer 14 (piezoelectric layer forming step: step S13).

By sputtering the piezoelectric layer 14 using an R-to-R sputtering apparatus in the R-to-R method, a uniform film with strong adhesion can be formed while maintaining the composition ratio of the target of the piezoelectric material. Further, the piezoelectric layer 14 having a desired thickness can be formed with high accuracy only by controlling the time.

A laminate of the flexible base material 11, the first electrode 12, and the angle adjusting layer 13 is wound around a film forming roll (drum roll) serving as an anode, which is provided in the film forming chamber of the R to R sputtering apparatus. The laminate is wound so that the flexible substrate 11 is in contact with the drum roll. The piezoelectric layer 14 can be continuously formed on the amorphous film 2 while a drum roll is placed in the film formation chamber and the laminate is transported by the R to R method.

A target containing a wurtzite crystal material is used as a cathode.

As the target containing the wurtzite crystal material, a plurality of targets or a single target containing the wurtzite crystal material contained in the piezoelectric layer 14 as a main component can be used. A target or targets are spaced apart from the drum roll.

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

Ar gas and oxygen gas are supplied as sputtering gases into the film forming chamber of the sputtering apparatus, and the inside of the film forming chamber is made into a gas atmosphere containing Ar gas and oxygen gas. A mixed gas containing Ar gas and oxygen gas may be supplied into the deposition chamber, or Ar gas and oxygen gas may be supplied separately.

The degree of vacuum in the film formation chamber may be 1.0×10 ⁻⁴ Pa or less, preferably adjusted to 1.0×10 ⁻⁶ Pa to 1.0×10 ⁻⁴ Pa, and 1.0×10 −4 Pa or less. 10 ^-5 Pa to 6.0×10 ^-5 Pa is more preferable. If the degree of vacuum in the deposition chamber is within the preferred range described above, the piezoelectric layer 14 can easily be formed including the wurtzite crystal material.

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 where the piezoelectric layer 14 can be formed, and may be, for example, 2.0 Pa or less.

The ratio of the flow rate of oxygen to the total flow rate of Ar gas and oxygen in the deposition chamber can be appropriately selected according to the type of gas, the content of oxygen contained in the piezoelectric layer 14, etc., and is, for example, 0.1. % to 20.0%, more preferably 1.0% to 10.0%. If the flow rate ratio of oxygen is within the above preferred range, the piezoelectric layer 14 is likely to form a wurtzite crystal material containing Zn.

The film forming temperature of the piezoelectric layer 14 does not have to be room temperature as long as the amorphous structure of the angle adjusting 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 less.

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

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

The second electrode 15 can be formed using the same forming method as the first electrode 12.

The thickness of the second electrode 15 can be appropriately designed, and is preferably 20 nm to 100 nm, more preferably 10 nm to 50 nm, for example. If the thickness of the second electrode 15 is within the above preferable range, the function as an electrode can be exhibited and the thickness of the piezoelectric element 1A can be reduced.

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 a stripe shape, the second electrode 15 has a plurality of stripes extending in a direction perpendicular to the direction in which the stripes of the first electrode 12 extend in plan view. may be formed so as to extend.

Thus, the piezoelectric element 1A is obtained.

After forming the second electrode 15, the entire piezoelectric element 1A may be heat-treated at a temperature lower than the melting point or glass transition point of the flexible base material 11 (for example, 130°C). By this heat treatment, the first electrode 12 and the second electrode 15 can be crystallized and have low resistance. The heat treatment is not essential, and in the case where the flexible base material 11 is made of a non-heat-resistant material, the heat treatment may not be performed after the piezoelectric element 1A is formed.

Thus, the method for manufacturing a piezoelectric element according to this embodiment includes the angle adjusting layer forming step (step S12) and the piezoelectric layer forming step (step S13). In the method for manufacturing a piezoelectric element according to the present embodiment, in the angle adjustment layer forming step (step S12), in a mixed gas atmosphere containing Ar gas and oxygen, the ratio of the flow rate of oxygen to the total flow rate of Ar gas and oxygen is 1. %, an amorphous material containing Zn is sputtered to form the angle adjusting layer 13 containing an amorphous oxide. Since the surface of the obtained angle adjustment layer 13 has high wettability, the amorphous material is obliquely incident on the upper surface of the angle adjustment layer 13 in the initial stage of forming the piezoelectric layer 14 on the upper surface of the angle adjustment layer 13. As a result, even if the crystals contained in the piezoelectric material begin to grow tilted with respect to the stacking direction of the piezoelectric layer 14 (the direction perpendicular to the upper surface of the angle adjustment layer 13), the crystals contained in the piezoelectric material will not grow. Accordingly, it becomes easier to tilt so that the c-axis is oriented in the stacking direction of the piezoelectric layers 14 . Since it is possible to prevent the c-axis from deviating from the stacking direction due to tilted crystal growth of the piezoelectric material, the orientation of the c-axis of the piezoelectric material can be enhanced. Therefore, if the method for manufacturing a piezoelectric element according to the present embodiment is used, even if the piezoelectric material is formed on the curved surface of the surface of the angle adjustment layer 13 wound around a drum roll or the like when using the RtoR method, the crystal Since the orientation can be enhanced, the piezoelectric layer 14 can be formed to have a high crystal orientation. Therefore, the piezoelectric element manufacturing method according to the present embodiment can manufacture the piezoelectric layer 14 with high crystal orientation even when the RtoR method is used.

In general, if the growth direction of the crystals of the piezoelectric material contained in the piezoelectric layer is tilted at the initial growth stage, which is important for crystal growth, during the manufacture of the piezoelectric layer, it tends to be difficult to highly orient the piezoelectric layer. If the crystal axis is distorted, the crystal is likely to be destroyed by pressure from the vertical direction, and the amount of charge generated with respect to the pressure from the vertical direction is reduced. Further, when the piezoelectric layer is formed using an RtoR sputtering apparatus, the crystal orientation of the piezoelectric material contained in the piezoelectric layer is the flow direction (longitudinal direction) of the first electrode, etc. in the RtoR sputtering apparatus. Although there is a tendency to incline toward the advancing direction in the MD direction, there is no tendency to incline in the TD direction, which is the direction perpendicular to the flow direction (transverse direction). For example, as shown in FIG. 5, when X-rays are incident on the surface of the piezoelectric layer along the MD direction of a flexible base material or the like in the RtoR sputtering apparatus, crystals of the piezoelectric material contained in the piezoelectric layer are formed. As for the orientation, as shown in FIG. 6, the peak position moves toward the traveling direction side of the MD direction of the flexible substrate or the like. On the other hand, as shown in FIG. 7, when X-rays are incident on the surface of the piezoelectric layer along the TD direction of a flexible base material or the like in the RtoR sputtering apparatus, as shown in FIG. No change in temperature.

On the other hand, in the method for manufacturing a piezoelectric element according to the present embodiment, by increasing the wettability of the surface of the angle adjusting layer 13 formed in the angle adjusting layer forming step (step S12), the RtoR method is used thereon. When the piezoelectric layer 14 is formed, even if the crystals are tilted in the initial stage of the piezoelectric layer 14, the crystals can be oriented so that the orientation becomes vertical as the crystals grow. Thereby, the crystal orientation of the obtained piezoelectric layer 14 can be enhanced.

The piezoelectric layer 14 obtained by the method of manufacturing the piezoelectric element according to the present embodiment can have high crystal orientation, and therefore can exhibit high piezoelectric efficiency in the thickness direction. Therefore, the piezoelectric element 1A can exhibit excellent piezoelectric characteristics over a long period of time.

The piezoelectric characteristics of the piezoelectric element 1A can be evaluated by the _d33 value, which is the piezoelectric constant. The _d33 value is a value representing 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 to the piezoelectric layer 14 in the thickness direction. The higher the _d33 value, the better the polarization in the thickness direction (c-axis direction) of the piezoelectric layer 14 included in the piezoelectric element 1A.

The d ₃₃ value can be directly measured using a piezoelectric constant measuring device (LPF-02, manufactured by Lead Techno Co., Ltd.) or the like. The upper and lower surfaces of the piezoelectric layer 14 are sandwiched between electrodes of a piezoelectric constant measuring 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 charge generated is measured by the piezoelectric constant measuring device. measured with a coulomb meter. A value obtained by dividing the measured amount of charge by the weight is output as the _d33 value. The larger the absolute value of the _d33 value, the better the piezoelectric properties of the piezoelectric layer 14 in the film thickness direction.

Since the piezoelectric layer 14 obtained by the method of manufacturing the piezoelectric element according to the present embodiment has high crystal orientation, it can exhibit high piezoelectric efficiency in the thickness direction and exhibits excellent piezoelectric properties over a long period of time. can be done.

In the method for manufacturing a piezoelectric element according to the present embodiment, the ratio of the flow rate of oxygen to the total flow rate of Ag gas and oxygen can be set to 1.5% to 4.0% in the angle adjusting layer forming step (step S12). As a result, the intensity of the peak waveform of the rocking curve obtained when diffraction from the (0002) plane of the crystal of the piezoelectric material is measured is the highest, and the FWHM can be reduced. Therefore, by using the method for manufacturing a piezoelectric element according to the present embodiment, it is possible to reliably form the piezoelectric layer 14 with higher crystal orientation even when using the RtoR method.

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

In the method for manufacturing a piezoelectric element according to this embodiment, the first electrode 12 can be formed on one main surface 11a of the flexible base material 11 in the step of forming the first electrode (step S11). As a result, the method for manufacturing a piezoelectric element according to the present embodiment can provide a A piezoelectric layer 14 with high crystal orientation can be reliably manufactured.

The piezoelectric element 1A obtained in this manner has excellent piezoelectric characteristics and can be suitably used for piezoelectric devices. Piezoelectric devices include, for example, force sensors for touch panels, pressure sensors, acceleration sensors, acoustic emission (AE) sensors, and other devices using the piezoelectric effect; speakers, transducers, high-frequency filter devices, and piezoelectric actuators using the inverse piezoelectric effect. , an optical scanner, and the like.

(Other aspects)
In addition, in the present embodiment, the piezoelectric element 1A is not limited to the above configuration, and has the first electrode 12 and the piezoelectric layer 14 on the flexible base material 11, and the piezoelectric layer 14 is Other configurations may be used as long as excellent piezoelectric characteristics can be exhibited in the thickness direction. An example of another configuration of the piezoelectric element 1A is shown below.

As shown in FIG. 9, the piezoelectric element 1B may not have the second electrode 15.

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

The adhesive layer 16 suppresses leak paths caused by cracks and pinholes that occur in the piezoelectric layer 14 . If metal grain boundaries or projections exist at the interface between the first electrode 12 and the piezoelectric layer 14 or at the interface between the piezoelectric layer 14 and the second electrode 15, the first electrode 12, the piezoelectric layer 14 and the second When a crack or the like occurs in one of the electrodes 15, a leak path is formed between the first electrode 12 and the second electrode 15 due to the crack or the like, and the polarization disappears. The piezoelectric element 1</b>C includes the adhesive layer 16 between the piezoelectric layer 14 and the second electrode 15 , thereby suppressing the formation of leak paths and maintaining good piezoelectric characteristics of the piezoelectric layer 14 .

A material similar to that of the flexible base material 11 can be used for the base material 17 .

An example of a method for manufacturing the piezoelectric element 1C will be described. For example, a first laminate is formed by laminating the first electrode 12 and the piezoelectric layer 14 in this order on the flexible base material 11 . On the other hand, a second laminate is formed by forming the second electrode 15 on the substrate 17 . After that, the piezoelectric layer 14 and the second electrode 15 of the second laminate are pasted together via the adhesive layer 16 so that the piezoelectric layer 14 of the first laminate and the second electrode 15 of the second laminate face each other. . Thus, the piezoelectric element 1C is manufactured.

The piezoelectric element 1C has a large d ₃₃ value, which is a piezoelectric strain constant in the thickness vibration mode, and can suppress leakage paths between electrodes, so that the piezoelectric element 1C can have better piezoelectric characteristics.

Hereinafter, the embodiments will be described more specifically by showing examples and comparative examples, but the embodiments are not limited by these examples and comparative examples.

<Production of piezoelectric element>
[Example 1]
A PET film roll substrate with a thickness of 50 μm is attached to the feeding part of the RtoR sputtering device, and two targets made of In, Zn, and O, and a target made of Mg, Zn, and O are placed in the three film formation chambers of the RtoR sputtering device. were respectively installed in the film formation chamber along the winding direction of the PET film roll substrate.

While the PET film roll base material is run from the unwinding part to the winding part, in the first film forming chamber, using one target made of In, Zn and O, the first film is formed on the surface of the PET film roll base material. An IZO film with a thickness of 85 nm was formed as an electrode of the . Ar gas was used as an inert gas, and O ₂ gas was used as a reactive gas. Ar gas and O ₂ gas were introduced into the first deposition chamber with the ratio of the O ₂ gas flow rate to the sum of the Ar gas flow rate and the O ₂ gas flow rate being 0.75%.

After that, in the second film forming chamber, using the other target composed of In, Zn and O, a 15 nm-thick angle adjustment layer was formed on the surface of the IZO film of the PET film roll substrate on which the IZO film was laminated. An IZO film was formed. Ar gas and O ₂ gas were introduced into the second deposition chamber with the ratio of the O ₂ gas flow rate to the sum of the Ar gas flow rate and the O ₂ gas flow rate being 1.5%.

After that, in a third film forming chamber, a target composed of Mg, Zn, and O was used to form a piezoelectric layer having a thickness of 200 nm on the surface of the IZO film of the PET film roll substrate on which the two IZO films were laminated. A Mg-added ZnO layer having a hexagonal wurtzite structure was formed so as to form a film and was wound up on a winding part.

As a result, a piezoelectric element having the first electrode, the angle adjustment layer and the piezoelectric layer laminated in this order on the PET film roll base material was manufactured.

[Examples 2 and 3]
A piezoelectric element was manufactured in the same manner as in Example 1, except that the ratio of the O ₂ gas flow rates during the formation of the angle adjusting layer was changed to the values shown in Table 1.

[Examples 4-6]
In Example 1, the first electrode was not formed, the ratio of the O ₂ gas flow rate 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. A piezoelectric element was manufactured in the same manner as in Example 1 except for the above.

[Comparative Example 1]
A piezoelectric element was manufactured in the same manner as in Example 1, except that the ratio of the O ₂ gas flow rate in the angle adjusting layer was changed to 1.0%.

[Comparative Example 2]
A piezoelectric film was manufactured in the same manner as in Example 1, except that the ratio of the O ₂ gas flow rate was set to 0.5% for the first electrode and the angle adjustment layer was not formed.

[Comparative Example 3]
In Example 1, the first electrode was not formed, the ratio of the O ₂ gas flow rate of the angle adjustment layer was changed to 5.0%, and the thickness of the angle adjustment layer was changed to 85 nm. A piezoelectric element was manufactured in the same manner as in Example 1.

(Measurement of surface resistance of angle adjustment layer)
In each example and comparative example, in the process of manufacturing the piezoelectric element, the surface resistance (Ω/□) of the laminate obtained by laminating the angle adjustment layer or the first electrode and the angle adjustment layer was measured according to JIS K7194 (1994 Measured by the four-probe method according to Table 1 shows the measurement results.

(Evaluation of crystal axis strain 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-value width of the piezoelectric layer were measured by X-ray rocking curve measurement under the following measurement conditions using an X-ray diffractometer (SmartLab Studio II manufactured by Rigaku Corporation). After that, the angle and full width at half maximum (FWHM) at which the X-ray diffraction intensity was the highest were determined as the axial strain and the half width. Table 1 shows the measurement results.
((Measurement condition))
・Light source: CuKα ray (1.5418 Å)
・Measurement mode: θ scan ・Sample: A sample was prepared by attaching a piezoelectric element to a glass substrate of 30 mm×30 mm via an adhesive. The sample was installed so that the MD direction and the incident direction of X-rays were parallel. Also, at that time, the traveling direction of the substrate during film formation of the piezoelectric layer and the incident direction of X-rays were unified so as to coincide with each other.
• 2θ position: The 2θ angle at which the ZnO (002) plane peak appears was set for each sample by X-ray diffraction measurement.
・Measuring range: ω = 0° to 2θ
・Measurement interval: 0.1°

[Evaluation of piezoelectric characteristics]
The _d33 value was measured as a piezoelectric characteristic of the obtained piezoelectric element of each example and comparative example.

( _d33 value)
The _d33 value was evaluated by the following procedure. A piezoelectric element was placed on the stage, and the stage was electrically connected to the angle adjustment layer or the laminate in which the first electrode and the angle adjustment layer were laminated. An indenter is placed on the upper surface of the sample, and a predetermined pressure is applied from the upper surface of the sample with the indenter to cause lattice strain in the piezoelectric layer. Charge was measured. The _d33 value was obtained by dividing the amount of charge generated when the applied load was changed from 1N to 5N by the load difference of 4N. The _d33 value is a value representing 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. The higher the _d33 value, the better the polarization in the thickness direction (c-axis direction) of the piezoelectric layer, and the higher the piezoelectric characteristics of the piezoelectric element. Table 1 shows the measurement results of the d ₃₃ value of the piezoelectric element in each example and comparative example.

From Table 1, it was confirmed that Examples 1 to 3 had larger d ₃₃ values than Comparative Example 1, and Examples 5 to 7 had larger d ₃₃ values than Comparative Example 2.

Therefore, in Examples 1 to 7, unlike Comparative Examples 1 to 3, the film was formed so that the ratio of the flow rate of oxygen during the film formation of the first electrode or the angle adjustment tank exceeded 1.0%. Since the axial strain and half width of the piezoelectric layer can be reduced and the _d33 value of the obtained piezoelectric element can be increased, it can be said that the piezoelectric element can exhibit excellent piezoelectric characteristics.

Although the embodiment has been described as above, the above embodiment is presented as an example, and the present invention is not limited by the above embodiment. The above embodiments can be implemented in various other forms, and various combinations, omissions, replacements, changes, etc. can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

This application claims priority based on Japanese Patent Application No. 2021-056825 filed with the Japan Patent Office on March 30, 2021, and the entire contents of Japanese Patent Application No. 2021-056825 are incorporated into this application. .

1A, 1B, 1C piezoelectric element 11 flexible base material 12 first electrode 13 angle adjusting layer 14 piezoelectric layer 15 second electrode 16 adhesive layer

Claims

Sputtering an amorphous material containing Zn in a mixed gas atmosphere containing an inert gas and oxygen on one main surface side of a flexible base material to form an angle adjustment layer containing an amorphous oxide. an angle adjusting layer forming step;
a piezoelectric layer forming step of forming a piezoelectric layer on the angle adjustment layer by a roll-to-roll method;
including
In the angle adjustment layer forming step, the method of manufacturing a piezoelectric element in which the ratio of the flow rate of the oxygen to the total flow rate of the inert gas and the oxygen exceeds 1%.
The method of 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%.
The method for manufacturing a piezoelectric element according to claim 1 or 2, wherein the angle adjusting layer forming step is performed by sputtering using a target containing the amorphous material.
The method for manufacturing the piezoelectric element according to any one of claims 1 to 3, comprising an electrode forming step of forming an electrode on one main surface of the flexible base material.
A method for manufacturing a piezoelectric device, including the method for manufacturing a piezoelectric element according to claim 4.