JP7416376B2 - Piezoelectric elements and piezoelectric devices - Google Patents

Description

The present invention relates to a piezoelectric element, and more particularly, to a piezoelectric element having a generally elongated linear shape, which may be referred to as a cable shape, a wire shape, or the like. The present invention also relates to a piezoelectric device including such a piezoelectric element.

A piezoelectric element is an element that uses a piezoelectric material. For example, it can be used as a sensor by utilizing the positive piezoelectric effect of the piezoelectric material (converting external force applied to the piezoelectric material into voltage), or as a sensor that uses the piezoelectric material's inverse piezoelectric effect. By utilizing the effect (converting the voltage applied to the piezoelectric body into force), it is used as an actuator in piezoelectric devices for various purposes.

Piezoelectric materials can be broadly classified into inorganic piezoelectric materials represented by piezoelectric ceramics and organic piezoelectric materials represented by piezoelectric polymers. In general, inorganic piezoelectric materials are harder than organic piezoelectric materials, and organic piezoelectric materials can be flexible. A piezoelectric element using an inorganic piezoelectric body made of piezoelectric ceramics is usually configured in a planar form (for example, as a planar sensor) (see Patent Document 1). On the other hand, in piezoelectric elements having a generally elongated linear form, which may be referred to as cable-like or wire-like, flexible organic piezoelectric materials may be used so that they are flexible (bendable). (See Patent Document 2).

Japanese Patent Application Publication No. 2004-265899 Japanese Patent Application Publication No. 2017-183570

In general, inorganic piezoelectric materials can be stable even when exposed to high temperatures, and have a higher heat resistance temperature than organic piezoelectric materials. The present inventors have focused on applying an inorganic piezoelectric material to a piezoelectric element in order to realize a novel piezoelectric element that has an elongated linear shape as a whole, has flexibility, and has high heat resistance. investigated. However, a flexible piezoelectric element is formed from a core wire (inner electrode) with a conductive surface, an inorganic piezoelectric layer covering the core wire, and a conductive layer (outer electrode) covering the inorganic piezoelectric layer. As a result, piezoelectric responsiveness may not be exhibited, and as a sensor, the piezoelectric output cannot be measured in response to changes in external force over time, and as an actuator, there is a problem in that it cannot produce deformation in response to changes in voltage over time. There was found.

The present invention aims to provide a novel piezoelectric element which has an elongated linear shape as a whole, has flexibility, and has high heat resistance, and which exhibits sufficient piezoelectric responsiveness. purpose. Another object of the present invention is to provide a piezoelectric device including such a piezoelectric element.

According to one gist of the present invention, a core wire having a conductive surface, an inorganic piezoelectric layer covering the core wire, an organic protective layer covering the inorganic piezoelectric layer, and a covering the organic protective layer are provided. a conductor layer, the organic protective layer has a thickness of 0.1 to 100 μm, and the core wire and the conductor layer have the inorganic piezoelectric layer and the organic protective layer interposed therebetween. Piezoelectric elements are provided, each functioning as an interposed electrode.

According to another aspect of the present invention, there is provided a piezoelectric device including the piezoelectric element of the present invention.

The piezoelectric element of the present invention includes a core wire (inner electrode) having a conductive surface, an inorganic piezoelectric layer covering the core wire, an organic protective layer covering the inorganic piezoelectric layer, and a conductor covering the organic protective layer. layer (outer electrode), thereby providing a novel piezoelectric element having an elongated linear shape as a whole and having flexibility. According to the piezoelectric element of the present invention, the inorganic piezoelectric layer is protected by being coated with an organic protective layer having a thickness of 0.1 to 100 μm, thereby making it possible to exhibit sufficient piezoelectric responsiveness. Furthermore, according to the piezoelectric element of the present invention, an inorganic piezoelectric layer is used, and the organic protective layer can be freely selected from organic materials having electrical insulation properties. It can be realized. Furthermore, a piezoelectric device including the piezoelectric element of the present invention is also provided.

1 is a schematic diagram showing a piezoelectric element in one embodiment of the present invention, in which (a) shows a partially cutaway side view of the piezoelectric element, and (b) shows a cross-sectional view taken along line AA in (a). show. 1 is a graph of voltage signal changes over time showing the output from the piezoelectric element in Example 1 of the present invention (one scale on the vertical axis corresponds to 50 mV, and one scale on the horizontal axis corresponds to 1 second). 2 is a graph of voltage signal changes over time showing the output from the piezoelectric element in Comparative Example 1 (one scale on the vertical axis corresponds to 50 mV, and one scale on the horizontal axis corresponds to 1 second).

Embodiments of the present invention will be described in detail below with reference to the drawings. In addition, in the attached drawings, electrode terminals are schematically indicated by black circles.

Referring to FIG. 1, a piezoelectric element 10 of the present embodiment includes a core wire 1 having a conductive surface, an inorganic piezoelectric layer 3 covering the core wire 1, and an organic protective layer 5 covering the inorganic piezoelectric layer 3. and a conductor layer 7 covering the organic protective layer 5. The organic protective layer 5 has a thickness of 0.1 to 100 μm. The core wire 1 and the conductor layer 7 function as electrodes (inner electrode and outer electrode) with the inorganic piezoelectric layer 3 and the organic protective layer 5 interposed therebetween (see FIG. 1(b)). Although not essential to this embodiment, the piezoelectric element 10 may further include an insulator layer (sheath) 9 covering the conductor layer 7. The piezoelectric element 10 has an elongated linear shape as a whole, which may be called a cable shape or a wire shape, and is configured to have flexibility (bendability) as a whole. As used herein, "flexible" means flexible in other words.

The core wire 1 only needs to be conductive at least on its surface so that it can function as an electrode (inner electrode). The core wire 1 is, for example, a metal wire, a wire made of any conductive material (metal, a composite of metal and ceramics, etc.), or a wire made of any wire base material (heat-resistant resin wire, etc.) whose surface is coated with a conductive material layer. It may be a wire coated with (metal, conductive heat-resistant resin, conductive heat-resistant rubber, etc.). Further, the core wire 1 may have substantially any cross-sectional shape such as a circle, an ellipse, a rectangle, or a polygon, and may be hollow or solid, and may be a single wire, a stranded wire, a braided wire, or the like. You can. Moreover, two or more types of these wire rods may be used in combination.

It is preferable that the entire surface of the core wire 1 is conductive, but a portion of the surface of the core wire 1 (for example, 20% or less of the total surface area, preferably 10% or less, more preferably 5% or less) is not conductive. You can. For example, when the core wire 1 is constructed by wrapping a tape made of a conductive material around the surface of a non-conductive linear base material, a gap exists between the edges of the wound tape, and a non-conductive material is formed in the gap. The linear base material may be exposed.

The external cross-sectional dimensions of the core wire 1 (the maximum dimension of the cross section perpendicular to the wire direction, the wire diameter if it has a circular cross section, the same shall apply hereinafter) are not particularly limited, but the core wire 1 itself may be flexible. selected.

The inorganic piezoelectric layer 3 covering the core wire 1 is made of piezoelectric ceramics and does not contain resin. The piezoelectric ceramic may be one type of piezoelectric ceramic, or may be a mixture of two or more types of piezoelectric ceramic. In this specification, "consisting of...(material)" means that it is substantially composed of the material, and that there may be substances that may unavoidably be mixed in and/or remain. means. For example, the solvent, stabilizer, etc. used in the raw material for forming the inorganic piezoelectric layer (for example, the first solution described later) may remain in the inorganic piezoelectric layer 3. Piezoelectric ceramics have high heat resistance because they are inorganic materials.

It is particularly preferable that the inorganic piezoelectric layer 3 is made of piezoelectric ceramic having a wurtzite crystal structure. It is known that a substance (compound) having a wurtzite crystal structure exhibits piezoelectricity by aligning its crystal orientation in the c-axis direction and further controlling the degree of dipole orientation (see Patent Document 1) . Therefore, the piezoelectric element 10 can be manufactured without requiring a polarization process that is required in the manufacture of piezoelectric polymers (eg, polyvinylidene fluoride).

The piezoelectric ceramic having a wurtzite crystal structure contains at least one selected from the group consisting of ZnO, ZnS, ZnSe, ZnTe, MgO, CdO, CdS, CdSe, CdTe, AlN, GaN, InN, and InP as a main component. Among them, it is preferable that at least one of zinc oxide (ZnO) and aluminum nitride (AlN) is included, and it is more preferable that zinc oxide (ZnO) is included. Piezoelectric ceramics having such a wurtzite crystal structure are relatively inexpensive and safe for the environment and the human body in that they do not contain lead. In this specification, the "main component" of a material means that the proportion of the component in the material (or the total proportion of the compounds listed above if two or more are present) exceeds 50% by mass. , for example, 60% by weight or more, preferably 70% by weight or more.

A piezoelectric ceramic having a wurtzite crystal structure may contain other elements (dopants) other than the elements constituting the wurtzite crystal structure. This improves the control characteristics of the polarity distribution ratio in the inorganic piezoelectric layer 3, and realizes a piezoelectric element with high piezoelectric responsiveness. The other element is not particularly limited, but may be at least one selected from the group consisting of alkali metal elements, alkaline earth metal elements, and Group 13 elements. Examples of the alkali metal elements as other elements include lithium (Li), sodium (Na), and potassium (K). Examples of alkaline earth metal elements as other elements include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Examples of Group 13 elements as other elements include aluminum (Al), gallium (Ga), and indium (In). The concentration of other elements can be appropriately set depending on desired electrical characteristics. For example, when the substance (compound) having a wurtzite crystal structure is ZnO and the other element is Li, the atomic concentration of Li is 2 to 7.5 atoms relative to the sum of the atomic concentrations of Zn and Li. It is preferably within the range of %.

However, the inorganic piezoelectric layer 3 is not limited to being made of piezoelectric ceramics having a wurtzite crystal structure, but may be made of other piezoelectric ceramics. For example, other piezoelectric ceramics may include at least one selected from the group consisting of lead titanate, lead zirconate titanate, lanthanum lead zirconate titanate, titanium oxide, and barium titanate, among which titanate Preferably, it includes lead zirconate (PZT).

The thickness of the inorganic piezoelectric layer 3 can be appropriately set depending on the desired flexibility and electrical properties, but is, for example, 0.01 μm or more, preferably 0.05 μm or more, and, for example, 3.00 μm or less, preferably 1 It can be less than .00 μm.

The organic protective layer 5 covering the inorganic piezoelectric layer 3 is preferably made of an organic material having electrical insulation properties. For the organic protective layer 5, a material having a high heat resistance can be selected from various organic materials having electrical insulation properties. The organic protective layer 5 may be made of, for example, a material having a heat resistance temperature of 200° C. or higher. As used herein, "heat-resistant temperature" means a temperature at which the physical properties of the material are not substantially impaired even if the material is exposed to the temperature, and is a continuous use temperature (long-term heat-resistant temperature) or a short-term heat-resistant temperature. obtain. The short-term heat resistance temperature may be the melting point in the case of a crystalline organic material, and may be the glass transition temperature in the case of an amorphous organic material.

The material constituting the organic protective layer 5 includes at least one selected from the group consisting of fluororesin, imide resin, aromatic polymer, liquid crystal polymer (LCP), polycarbonate (PC), silicone resin, and epoxy resin. obtain. These may be used alone or as a mixture of two or more. Examples of fluororesins include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and ethylene-tetrafluoroethylene copolymer. Examples include polymer (ETFE) and polychlorotrifluoroethylene (PCTFE). Examples of imide resins include polyimide (PI), polyamideimide (PAI), and polyetherimide (PEI). Examples of aromatic polymers include polyphenylene sulfide resin (PPS) and polyetheretherketone resin (PEEK).

The organic protective layer 5 preferably covers the entire outer surface of the inorganic piezoelectric layer 3 so as to protect the inorganic piezoelectric layer 3 (do not bring the inorganic piezoelectric layer 3 into direct contact with the conductive layer 7).

The thickness of the organic protective layer 5 is set within the range of 0.1 to 100 μm. Thereby, it is possible to sufficiently exhibit piezoelectric responsiveness (as a sensor, it is possible to measure piezoelectric output according to the change in external force over time, and as an actuator, it can bring about deformation according to the change in voltage over time). In particular, since the organic protective layer 5 has a thickness of 0.1 μm or more, even when the inorganic piezoelectric layer 3 is formed by the coating method described later, the core wire (inner electrode) 1 and the conductor layer (outer electrode) It is possible to effectively prevent the occurrence of a short circuit with the electrode) 7. In addition, the thickness of the organic protective layer 5 is 100 μm or less to ensure its function as a piezoelectric element (more specifically, it can be used as a sensor to measure piezoelectric output, and as an actuator to bring about desired deformation). ) can be done. The thickness of the organic protective layer 5 is preferably set within the range of 1 to 30 μm.

The conductive layer 7 covering the organic protective layer 5 may be made of a conductive material so as to function as an electrode (outer electrode). The conductor layer 7 may be made of, for example, metal, a composite of metal and ceramics, conductive heat-resistant resin, conductive heat-resistant rubber, or the like.

The conductor layer 7 preferably covers the entire outer surface of the organic protective layer 5, but covers a portion of the outer surface of the organic protective layer 5 (eg, 60% or less, preferably 70% or less, more preferably 70% or less of the total surface area). 90% or less) may not be covered with the conductor layer 7.

The thickness of the conductor layer 7 can be appropriately set depending on the desired flexibility and electrical properties, and is, for example, 0.01 μm or more, preferably 0.05 μm or more, and, for example, 3000 μm or less, preferably 1000 μm or less. obtain.

The external cross-sectional dimension of the conductor layer 7 may be, for example, 10.0 mm or less, and preferably 0.1 mm or more and 5.0 mm or less. When the conductor layer 7 is the outermost layer of the piezoelectric element 10, this provides a so-called "linear" piezoelectric element 10 having a small external cross-sectional dimension (typically wire diameter) and flexibility. be able to. Such a piezoelectric element 10 has a high degree of freedom in attachment to a piezoelectric device, and can be used for a wide range of applications.

If present, the insulator layer (sheath) 9 consists of any suitable insulating material. The insulator layer 9 may be made of a material known as a flexible sheath for wires or cables, such as flexible heat-resistant resin or heat-resistant rubber. The specific material, form, thickness, etc. of the insulator layer 9 may be selected as appropriate depending on the use of the piezoelectric element 10.

The piezoelectric element 10 of this embodiment can be manufactured by any suitable method. An example of a method for manufacturing the piezoelectric element 10 of this embodiment will be shown below, but the method is not limited thereto.

The method for manufacturing the piezoelectric element 10 of this embodiment is as follows:
preparing a core wire 1 having a conductive surface;
forming an inorganic piezoelectric layer 3 covering the core wire 1;
forming an organic protective layer 5 covering the inorganic piezoelectric layer 3;
covering the organic protective layer 5 with a conductor layer 7 and, if necessary,
It may include covering the conductor layer 7 with an insulator layer 9 . More details are as follows.

First, the core wire 1 as described above in this embodiment is prepared. Such a core wire 1 is commercially available or can be easily produced.

Next, an inorganic piezoelectric layer 3 covering the core wire 1 is formed. The inorganic piezoelectric layer 3 can be formed to cover the core wire 1 by any suitable method such as a coating method (also referred to as a chemical solution deposition method or a sol-gel method), a sputtering method, a hydrothermal method, etc. , preferably by a coating method. When the inorganic piezoelectric layer 3 is formed by a coating method, continuous production is possible without using a vacuum device or the like, and the piezoelectric element 10 can be manufactured more easily and at lower cost.

When forming the inorganic piezoelectric layer 3 by a coating method, more specifically,
Applying a first solution (raw material) containing elemental species constituting piezoelectric ceramics (preferably piezoelectric ceramics having a wurtzite crystal structure) to the surface of the core wire 1 to form a coating film;
The inorganic piezoelectric layer 3 is formed by drying the formed coating film and firing the dried coating film.

The first solution contains a solvent in addition to the elemental species (including other elements (dopants) if present) constituting the piezoelectric ceramic (preferably a piezoelectric ceramic having a wurtzite crystal structure), and if It may contain any suitable additives such as stabilizers. Examples of solvents include 2-methoxyethanol, 2-propanol, ethanol, 1-butanol, trioctylphosphine, water, and the like.

The first solution can be applied using, for example, a dip coating method or a spray coating method. Preferably, by dip coating, the first solution can be applied to the surface of the core wire 1 to a substantially uniform thickness by dipping the core wire 1 in the first solution and pulling it up at a predetermined speed.

Drying is carried out by drying the coating film at a temperature below the heat resistant temperature of the core wire 1. The drying temperature is, for example, lower than 400°C, preferably 300°C or lower, and the drying time is set appropriately. The drying atmosphere is not particularly limited, and may be, for example, air, an inert gas atmosphere, or a mixed atmosphere of oxygen and inert gas. Drying allows the solvent and any additives that may be present to be removed, and the elemental species that make up the piezoelectric ceramic to precipitate and aggregate as crystals into particles. The coating film may be an aggregate in which such particles (preferably particles of a substance (compound) having a wurtzite crystal structure) are filled and deposited.

Thereby, a dried coating film is obtained. If the desired coating film thickness cannot be obtained by one coating and one drying, repeat multiple sets of coating and drying as one set until the desired coating film thickness is obtained. It's okay.

The firing is carried out by firing the coating film at a temperature lower than the allowable temperature limit of the core wire 1. The firing temperature is, for example, less than 600°C, preferably 450°C or less, and the firing time is appropriately set. The firing atmosphere is not particularly limited, and may be, for example, air, an inert gas atmosphere, or a mixed atmosphere of oxygen and inert gas. By firing, a bonding layer, which is a porous body formed by bonding the particles together, can be formed. This bonding layer may be an aggregate of (randomly) filled and deposited crystal particles forming the piezoelectric ceramic, and may be sintered with the shape of the particles remaining.

As a result, an inorganic piezoelectric layer 3 made of piezoelectric ceramic (preferably piezoelectric ceramic having a wurtzite crystal structure) is formed. If the desired inorganic piezoelectric layer thickness cannot be obtained by one or more sets of coating and drying and one firing, "one or more sets of coating and drying and one firing" may be repeated in multiple sets until the desired inorganic piezoelectric layer thickness is obtained.

Next, an organic protective layer 5 covering the inorganic piezoelectric layer 3 is formed. The organic protective layer 5 can be formed to cover the inorganic piezoelectric layer 3 by any appropriate method depending on the raw material of the organic insulator used, but preferably by a coating method.

When forming the organic protective layer 5 by a coating method, more specifically,
applying a second solution (raw material) constituting the organic protective layer 5 to the surface of the inorganic piezoelectric layer 3 to form a coating film;
Drying the formed coating film, and optionally,
The organic protective layer 5 is formed by subjecting the dried coating film to heat treatment.

In addition to the materials constituting the organic protective layer (which may be precursors before completion of the reaction), the second solution contains a solvent and may optionally contain any suitable additives such as stabilizers.

The second solution can be applied using, for example, a dip coating method or a spray coating method, and preferably a dip coating method is used. According to the dip coating method in which the core wire 1 coated with the inorganic piezoelectric layer 3 is dipped in the second solution, the second solution can be applied to the surface of the inorganic piezoelectric layer 3 to a substantially uniform thickness. can.

Drying conditions can be appropriately selected depending on the material constituting the organic protective layer.

Thereby, a dried coating film is obtained. If the desired coating film thickness cannot be obtained by one coating and one drying, repeat multiple sets of coating and drying as one set until the desired coating film thickness is obtained. It's okay.

Optionally, the dried coating film may be subjected to heat treatment. Such a heat treatment may be performed, for example, to allow a reaction to proceed in the material constituting the organic protective layer. The heat treatment conditions can be appropriately selected depending on the material constituting the organic protective layer.

As a result, an organic protective layer 5 is formed. If the desired organic protective layer thickness cannot be obtained by one or more sets of coating and drying and one heat treatment, "one or more sets of coating and drying and one heat treatment" One set may be repeated in multiple sets until the desired organic protective layer thickness is obtained.

Next, the organic protective layer 5 is covered with a conductor layer 7. The conductor layer 7 can be formed by any suitable method so as to cover the organic protective layer 5. For example, it can be formed by vapor deposition, winding, etc. If necessary, the conductor layer 7 may be covered with an insulator layer (sheath) 9. The insulator layer 9 can be formed by any suitable method so as to cover the conductor layer 7.

The piezoelectric element 10 of this embodiment can be obtained as described above. When the inorganic piezoelectric layer 3 and the organic protective layer 5 are sequentially formed, the organic protective layer 5 is not exposed to the relatively high firing temperature required for forming the inorganic piezoelectric layer 3, so the organic protective layer 5 is not exposed to heat. It is possible to avoid deterioration and/or decomposition due to Furthermore, when the inorganic piezoelectric layer 3 and the organic protective layer 5 are sequentially formed by a coating method, it can be performed in a continuous process, so that a long piezoelectric element 10 can be efficiently manufactured.

In the piezoelectric element 10 of this embodiment, the electrodes can be drawn out by appropriately exposing the core wire 1 (more specifically, the conductive portion) and the conductor layer 7 (in the figure, the electrode terminals are schematically indicated by black circles). ). The conductor layer 9 may be a ground, in which case it may also function as a shield.

The piezoelectric element 10 of this embodiment can be used as various sensors and/or actuators in piezoelectric devices for various uses.

The piezoelectric element 10 of this embodiment can be used as a sensor by utilizing the positive piezoelectric effect of the piezoelectric body. The piezoelectric element 10 can be used, for example, as a pressure-sensitive sensor that can be attached to and/or embedded in an object to be detected and detect when an external force is applied to the piezoelectric element 10, or as a sensor to be detected. It can be used as a sensor to detect internal fatigue of an object. Furthermore, a knitted fabric or a woven fabric can be constructed using a plurality of piezoelectric elements 10 and used as a fibrous piezoelectric sensor or a vibration-type power generation element. In addition, for example, crime prevention sensors, nursing care/monitoring sensors, shock sensors, wearable sensors, biosignal sensors (breathing/pulse), vehicle entrapment prevention sensors, vehicle bumper collision sensors, vehicle air flow sensors, weather detection sensors ( It can be used in piezoelectric devices for various applications such as rain/snow), fire detection sensors, underwater acoustic sensors, tactile sensors for robots, tactile sensors for medical equipment, fiber sheet pressure distribution sensors, and power generation wires for environmental vibrations. .

In place of/in addition to the above, the piezoelectric element 10 of this embodiment can be used as an actuator by utilizing the inverse piezoelectric effect of the piezoelectric body. The piezoelectric element 10 can be used, for example, as an actuator that excites vibrations when a driving voltage is applied to the piezoelectric element 10, and can also be used as an actuator drive sensor that uses the vibrations as a sensor. In addition, it can be used in piezoelectric devices for various uses, such as robot joint drive actuators, artificial muscle actuators, medical device operating wire drive actuators, fiberscope drive actuators, ultrasonic motors, piezoelectric motors, etc.

Among these, the piezoelectric element 10 of this embodiment can be preferably used in applications requiring high response characteristics.

Although the piezoelectric element and the piezoelectric device including the piezoelectric element according to one embodiment of the present invention have been described in detail above, this embodiment can be modified in various ways.

(Example 1)
The piezoelectric element of the above embodiment described in detail with reference to FIG. 1 was manufactured as follows.

Preparation of First Solution 2-methoxyethanol (48.20 g) as a solvent and 2-aminoethanol (1.83 g) as a stabilizer were placed in a glass container and stirred for 5 minutes at room temperature under an atmospheric atmosphere. Next, zinc acetate dihydrate (6.39 g) was added to the resulting mixed solution, and the mixture was stirred at room temperature under an air atmosphere until dissolved. Next, lithium acetate dihydrate (0.095 g) was added to the resulting mixed solution, and the mixture was stirred for 1 hour at room temperature under an air atmosphere. In this way, a first solution was prepared.

Preparation of second solution Pure water (30 g) was added to polyamide-imide varnish (manufactured by Hitachi Chemical Co., Ltd., HPC-1000) (22.5 g), and the mixture was stirred for 30 minutes to mix uniformly. In this way, a second solution was prepared.

Preparation of Core Wire 1 As the core wire 1, a SUS wire (SUS304, diameter 0.28 mm) was prepared.

Formation of Inorganic Piezoelectric Layer The core wire 1 prepared above was dipped in and coated with the first solution prepared above to form a coating film of the first solution on the surface of the core wire 1. Thereafter, it was dried at 250° C. for 1 minute, and one set of one application and one drying was repeated under the same conditions for a total of 3 sets. Next, the resulting dry coating film was baked at 400° C. for 1 minute. A total of 3 sets of ``3 sets of 1 application, 1 drying, and 1 firing'' were repeated under the same conditions. As a result, a layer made of zinc oxide (ZnO) having a wurtzite crystal structure was formed as the inorganic piezoelectric layer 3 covering the core wire 1. The thickness of the inorganic piezoelectric layer 3 was 0.1 μm.

Formation of Organic Protective Layer The core wire 1 on which the inorganic piezoelectric layer 3 was formed is dipped in the second solution prepared above to form a coating film of the second solution on the surface of the inorganic piezoelectric layer 3. Formed. Thereafter, it was dried at 200°C for 1 minute, and the resulting dried coating film was subjected to heat treatment at 350°C for 3 minutes. A total of 5 sets of "coating once, drying once, and firing once" were repeated under the same conditions. As a result, a layer made of polyamideimide was formed as the organic protective layer 5 covering the inorganic piezoelectric layer 3. The thickness of the organic protective layer 5 was 5 μm.

Formation of Conductive Layer Aluminum was deposited on the surface of the organic protective layer 5 formed above to form a layer made of aluminum as the conductive layer 7. The thickness of the conductor layer 7 was 0.2 μm.

The piezoelectric element 10 of Example 1 was produced as described above.

(Example 2)
A piezoelectric element was produced in the same manner as in Example 1, except that only one set of "coating once, drying once, and firing once" was performed (not repeated) in forming the organic protective layer. did. The thickness of the organic protective layer in the piezoelectric element of Example 2 was 1 μm.

(Example 3)
A piezoelectric element was formed in the same manner as in Example 1, except that in forming the organic protective layer, one set consisted of "one coating, one drying, and one firing", and a total of 30 sets were repeated under the same conditions. was created. The thickness of the organic protective layer in the piezoelectric element of Example 3 was 30 μm.

(Comparative example 1)
A piezoelectric element was produced in the same manner as in Example 1, except that an organic protective layer was not formed and a conductive layer was formed on the surface of the inorganic piezoelectric layer.

(evaluation)
The piezoelectric elements produced in Examples 1 to 3 and Comparative Example 1 were evaluated as follows.

Of the piezoelectric element for evaluation (length: 80 mm), lead wires were connected to a region near one end of the exposed core wire 1 and a region near the other end of the conductor layer 7, respectively. Then, pull out the core wire 1 (inner electrode) and conductor layer 7 (outer electrode), connect it to an oscilloscope (manufactured by Hagiwara Solutions Co., Ltd., UDS-1G02S-10K) via an analog amplifier circuit (2000 times amplification), The structure was such that the voltage signal generated between these electrodes could be output over time.

The piezoelectric element for evaluation with the lead wires connected as described above is set in an electromagnetic force micro-testing machine (Micro Servo MMT-101NV-10, manufactured by Shimadzu Corporation), and the line direction of the piezoelectric element for evaluation is Stress was repeatedly applied by applying vibration (frequency: 1 Hz, stress: 1 N to 3 N). While conducting such a test, a voltage signal generated between the core wire 1 (inner electrode) and the conductor layer 7 (outer electrode) was measured over time as a piezoelectric output. Representatively, the measurement results of the piezoelectric elements of Example 1 and Comparative Example 1 are shown in FIGS. 2 and 3, respectively.

In the piezoelectric element of Example 1, as shown in FIG. 2, the peak-to-peak value (difference between the maximum value and the minimum value) of the piezoelectric output was 95.00 mVp-p. Further, as understood from FIG. 2, a periodic waveform was observed in the piezoelectric output, and one period was approximately 1 second, that is, the frequency was 1 Hz. Since the frequency of this piezoelectric output matched the frequency of excitation, frequency tracking was confirmed. Therefore, the piezoelectric element of Example 1 exhibited excellent piezoelectric response.

In the piezoelectric element of Example 2, the peak-to-peak value of the piezoelectric output was 65.80 mVpp, and frequency tracking was confirmed. In the piezoelectric element of Example 3, the peak-to-peak value of the piezoelectric output was 65.83 mVp-p, and frequency tracking was confirmed. Therefore, the piezoelectric elements of Examples 2 and 3 exhibited excellent piezoelectric response.

On the other hand, in the piezoelectric element of Comparative Example 1, as shown in FIG. 3, the peak-to-peak value of the piezoelectric output was 44.15 mVpp. However, as understood from FIG. 3, no periodic waveform was observed in the piezoelectric output, confirming that there was no frequency tracking. Therefore, the piezoelectric element of Comparative Example 1 did not exhibit piezoelectric response.

The piezoelectric element of the present invention can be used as various sensors and/or actuators. Although not limiting the present invention, the piezoelectric element of the present invention has excellent flexibility and can be realized with a small external cross-sectional dimension (typically wire diameter), and for example, when an external force is applied to the piezoelectric element, It can be used as a pressure sensitive sensor etc. that can detect this.

1 Core wire (inner electrode)
3 Inorganic piezoelectric layer 5 Organic protective layer 7 Conductor layer (outer electrode)
9 Insulator layer (sheath)
10 Piezoelectric element

Claims (8)

a core wire having a conductive surface;
an inorganic piezoelectric layer covering the core wire;
an organic protective layer covering the inorganic piezoelectric layer;
a conductive layer covering the organic protective layer, the organic protective layer having a thickness of 0.1 to 100 μm, and the core wire and the conductive layer having the inorganic piezoelectric layer therebetween. and a piezoelectric element each functioning as an electrode with the organic protective layer interposed therein. The piezoelectric element according to claim 1, wherein the organic protective layer is made of a material having a heat resistance temperature of 200°C or higher. The piezoelectric material according to claim 1 or 2, wherein the organic protective layer contains at least one selected from the group consisting of a fluororesin, an imide resin, an aromatic polymer, a liquid crystal polymer, a polycarbonate, a silicone resin, and an epoxy resin. element. The piezoelectric element according to claim 1, wherein the inorganic piezoelectric layer is made of piezoelectric ceramic having a wurtzite crystal structure. The piezoelectric element according to claim 4, wherein the piezoelectric ceramic having a wurtzite crystal structure contains at least one of zinc oxide and aluminum nitride. The piezoelectric element according to any one of claims 1 to 5, wherein the inorganic piezoelectric layer has a thickness of 0.01 to 3.00 μm. The piezoelectric element according to any one of claims 1 to 6, further comprising an insulator layer covering the conductor layer. A piezoelectric device comprising the piezoelectric element according to any one of claims 1 to 7.

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