阅读说明：本技术 压电器件、以及压电器件的制造方法 (Piezoelectric device and method for manufacturing piezoelectric device ) 是由 中村大辅 永冈直树 石川岳人 待永广宣 于 2020-03-10 设计创作，主要内容包括：本发明提供一种压电器件,其能够抑制包夹压电体层(13)的电极间的泄漏,从而能够降低压电特性的劣化。压电器件(10A)在基材(11)之上依次层叠第一电极(12)、压电体层、以及第二电极(14),上述第一电极和上述第二电极成为在层叠方向彼此不重合的配置。(The invention provides a piezoelectric device, which can inhibit leakage between electrodes of an interlayer piezoelectric layer (13) so as to reduce deterioration of piezoelectric characteristics. A piezoelectric device (10A) is formed by sequentially laminating a first electrode (12), a piezoelectric layer, and a second electrode (14) on a base material (11), wherein the first electrode and the second electrode are arranged so as not to overlap each other in the laminating direction.)

1. A piezoelectric device in which a first electrode, a piezoelectric layer, and a second electrode are stacked in this order on a substrate,

the first electrode and the second electrode are arranged so as not to overlap each other in the stacking direction.

2. The piezoelectric device according to claim 1,

the first electrode is formed by a pattern having two or more stripes,

the second electrode is formed in a region corresponding to a space between adjacent stripes of the first electrode.

3. The piezoelectric device according to claim 1,

one of the first electrode and the second electrode is formed of a patch pattern,

the other of the first electrode and the second electrode is formed by a planar pattern obtained by cutting the patch pattern.

4. The piezoelectric device according to claim 1,

the first electrode and the second electrode are a pair of comb-tooth electrodes or spiral electrodes arranged in different layers with a gap therebetween.

5. The piezoelectric device according to any one of claims 1 to 4,

the surface area of the first electrode is substantially equal to the surface area of the second electrode.

6. The piezoelectric device according to any one of claims 1 to 5,

further comprising an amorphous layer disposed between the substrate and the piezoelectric layer,

the first electrode is formed on the amorphous layer.

7. The piezoelectric device according to claim 6,

the amorphous layer is an organic amorphous layer.

8. The piezoelectric device according to any one of claims 1 to 7,

the base material is formed of plastic or resin.

9. The piezoelectric device according to any one of claims 1 to 8,

the piezoelectric layer is formed using, as a main component, a material selected from zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), aluminum nitride (AlN), gallium nitride (GaN), cadmium selenide (CdSe), cadmium telluride (CdTe), silicon carbide (SiC), and combinations thereof.

10. The piezoelectric device according to claim 9, wherein,

the piezoelectric layer contains, as a subcomponent, a material selected from magnesium (Mg), vanadium (V), titanium (Ti), zirconium (Zr), lithium (Li), silicon (Si), and a combination thereof among the main components.

11. The piezoelectric device according to any one of claims 1 to 10,

the thickness of the piezoelectric layer is 200nm to 5 μm.

12. A method of manufacturing a piezoelectric device, comprising the steps of:

forming a first electrode over a substrate;

forming a piezoelectric layer having a wurtzite-type crystal structure on the first electrode; and

a second electrode is formed on the piezoelectric layer so as not to overlap the first electrode in the film thickness or lamination direction.

13. The method of manufacturing a piezoelectric device according to claim 12,

the first electrode is formed on the plastic or resin substrate by a sputtering method at room temperature.

Technical Field

The present invention relates to a piezoelectric device and a method of manufacturing the same.

Background

Conventionally, a piezoelectric element using a piezoelectric effect of a substance has been used. The piezoelectric effect is a phenomenon in which polarization proportional to pressure is obtained by applying pressure to a substance. Various sensors such as a pressure sensor, an acceleration sensor, and an Acoustic Emission (AE) sensor for detecting elastic waves have been produced by utilizing the piezoelectric effect.

In recent years, touch screens have been used as input interfaces of information terminals such as smartphones, and the application of piezoelectric elements to touch screens has increased. A touch panel is integrally configured with a display device of an information terminal, and high transparency to visible light is required for improving visibility. On the other hand, in order to correctly detect the operation of the finger, the piezoelectric layer is desired to have high pressure responsiveness.

In a cantilever type displacement element in which a piezoelectric film and an electrode for displacing the piezoelectric film by a reverse piezoelectric effect are laminated, a configuration is known in which electrode ends of the respective layers do not overlap on the same line in a film thickness direction (for example, see patent document 1). In this configuration, the stress concentration due to the deformation during driving of the element is alleviated by setting the electrode at the lowermost layer to be the largest and the electrode size to be smaller toward the upper layer. < Prior Art document >

< patent document >

Patent document 1: japanese unexamined patent publication Hei 5-296713

Disclosure of Invention

< problems to be solved by the present invention >

Due to irregularities or foreign matter of the substrate, microcracks often occur in the piezoelectric film. Such microcracks may serve as leakage paths for electrically short-circuiting the upper and lower electrodes. This phenomenon is becoming more apparent with the thinning of the piezoelectric film.

The purpose of the present invention is to provide a structure that can suppress leakage between electrodes sandwiching a piezoelectric film and reduce deterioration of piezoelectric characteristics.

< means for solving the problems >

In a first aspect of the present invention, a piezoelectric device includes a first electrode, a piezoelectric layer, and a second electrode stacked in this order on a substrate,

the first electrode and the second electrode are arranged so as not to overlap each other in the stacking direction.

As an example, the first electrode is formed of a pattern having two or more stripes, and the second electrode is formed in a region corresponding to a space between adjacent stripes of the first electrode.

As another example, one of the first electrode and the second electrode is formed of a patch (patch) pattern, and the other of the first electrode and the second electrode is formed of a planar pattern from which the patch pattern is cut.

In a second aspect of the present invention, a method of manufacturing a piezoelectric device includes the steps of:

forming a first electrode over a substrate;

forming a piezoelectric layer having a wurtzite-type crystal structure on the first electrode; and

a second electrode is formed on the piezoelectric layer so as not to overlap the first electrode in the film thickness or lamination direction.

< effects of the invention >

According to the above configuration, leakage between the electrodes sandwiching the piezoelectric layer can be suppressed, and deterioration of piezoelectric characteristics can be reduced.

Drawings

Fig. 1 is a diagram for explaining microcracks generated in a piezoelectric layer.

Fig. 2 is a schematic diagram of a piezoelectric device of the first embodiment.

Fig. 3 is a schematic diagram of a piezoelectric device of a second embodiment.

Fig. 4 is a schematic diagram of a piezoelectric device of a third embodiment.

Fig. 5 is a schematic view of a piezoelectric device of a fourth embodiment.

Fig. 6 is a diagram showing a modification of the electrode pattern.

Detailed Description

FIG. 1 is a diagram illustrating in more detail the problem of microcracks discovered by the inventors. In general, from the viewpoint of stability of the manufacturing process and structure, a laminate in which the piezoelectric layer 103 is sandwiched between the electrode 102 and the electrode 104 is formed on the base material 101.

In an ideal state shown in fig. 1 (a), by applying pressure, a charge of a specific polarity (for example, a positive charge) appears at or near the interface between the piezoelectric layer 103 and the electrode 104, and a charge of an opposite polarity (for example, a negative charge) appears at or near the interface between the piezoelectric layer 103 and the electrode 102. When the piezoelectric layer 103 is stretched in the thickness direction, negative charges appear on the interface between the piezoelectric layer 103 and the electrode 104, and positive charges appear on the interface between the piezoelectric layer 103 and the electrode 102. The mechanical energy can be converted into electric energy by polarization of crystals of the piezoelectric layer 103.

As shown in fig. 1 (B), if foreign matter, projections, pinholes, or the like is present on the surface of the base material 101 or the surface of the electrode 102, fine cracks are generated in the piezoelectric layer 103 from this portion. When the crack extends in the film thickness direction of piezoelectric layer 103, a leakage path is formed between electrode 104 and electrode 102. In this case, the generated electric charges cancel and the piezoelectric effect disappears.

When the substrate 101 is formed of plastic, resin, or the like, irregularities are likely to be generated on the surface thereof. However, the crystal of the metal constituting the electrode 102 cannot absorb the irregularities on the surface of the substrate 101. Irregularities are also formed on the surface of the metal film of the electrode 102 in reflection of the surface state of the substrate 101. Cracks are likely to occur just above foreign substances, projections, pinholes, and the like present at the interface between the electrode 102 and the piezoelectric layer 103.

In the embodiment, in order to prevent a leak path from being formed between the electrodes sandwiching the piezoelectric layer, the electrodes of the piezoelectric device are configured so as not to overlap in the lamination direction. Even if the electrodes do not overlap in the stacking direction, it is possible to extract electric charges uniformly distributed on the surface (or interface) of the piezoelectric film. The electrodes do not overlap each other in the stacking direction, and thus stress is relaxed and bending of the stacked body is suppressed. In the present specification and claims, the term "do not overlap" in the stacking direction means that substantially all of the lower electrode and the upper electrode do not overlap when viewed in the stacking direction. The configuration in which the electrodes are slightly overlapped due to variations in edge positions and dimensions of the electrodes caused by manufacturing errors and the like, avoidance design, and the like is also included in the configuration in which the electrodes are "not overlapped".

< first embodiment >

Fig. 2 is a schematic diagram of a piezoelectric device 10A of the first embodiment. FIG. 2 shows a plan view (A) and a cross-sectional view (I-I') at (B). The piezoelectric device 10A has a first electrode 12 formed over a substrate 11, a piezoelectric layer 13 disposed over the first electrode 12, and a second electrode 14 disposed over the piezoelectric layer 13. Here, the case of "above" means an upper side when viewed in the stacking direction.

The first electrode 12 and the second electrode 14 are formed in a stripe pattern extending in the same direction, but are not arranged to overlap each other when viewed in a cross section in the thickness direction. The second electrode 14 is disposed in a region corresponding to a space between adjacent stripes of the first electrode 12.

In this configuration, when pressure is applied to the piezoelectric layer 13, surface charges appear in the piezoelectric layer 13, and a voltage is generated. By detecting the current at this time, polarization according to the pressure can be known. The unit crystal of the piezoelectric layer 13 does not have a point symmetry center, and the atoms at the center of the crystal structure are displaced from the point symmetry center of the crystal toward, for example, the upper side in the crystal growth direction. In this case, although the positive charges are biased toward the interface between the piezoelectric layer 13 and the upper electrode 14 and the negative charges are biased toward the interface between the piezoelectric layer 13 and the lower electrode 12, these charges are combined with floating charges in the air and charges on the metal surface and neutralized without applying a pressure, and no voltage is generated.

For example, when pressure is applied to the piezoelectric layer 13 from the upper electrode 14 side, atoms in the center of the crystal structure approach the center of point symmetry, polarization of the piezoelectric layer 13 decreases, and electric charges distributed in the vicinity of the interface decrease. As a result, the electric charges that have been combined into a pair remain, and a voltage is generated. Since the charges generated as surplus are uniformly distributed in the vicinity of the interface, even if the upper electrode 14 and the lower electrode 12 do not overlap each other in the film thickness direction or the lamination direction, a change in the polarization state due to the application of pressure can be detected.

With this configuration, even if a micro-crack is generated from a foreign substance, a projection, a pinhole, or the like on the surface of the substrate 11 or the electrode 12 and the crack extends in the film thickness direction, the formation of a leakage path electrically connecting the lower electrode 12 and the upper electrode 14 can be suppressed.

The piezoelectric device 10A can be formed by, for example, the following steps. First, the electrode 12 is formed over the substrate 11. The material of the substrate 11 is arbitrary, and may be a substrate made of an inorganic material such as a glass substrate, a sapphire substrate, or an MgO substrate, or may be a plastic substrate. In the case of using a substrate made of an inorganic material, since the surface is smooth and the irregularities causing cracks are small, the occurrence of cracks can be reduced. When the base material 11 made of plastic or resin is used, although unevenness is likely to occur on the surface, it has flexibility, and is easy to handle and widely applicable.

Since the piezoelectric device 10A is configured such that the electrodes 12 and 14 do not overlap each other in the film thickness direction or the stacking direction, the formation of a leakage path can be suppressed even when irregularities are present on the surface of the substrate 11. Examples of the plastic substrate 11 include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), Polycarbonate (PC), acrylic resins, cycloolefin polymers, and Polyimide (PT). Among these materials, in particular, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), Polycarbonate (PC), acrylic resin, and cycloolefin polymer are colorless and transparent materials, and the rear surface of the base material 11 is preferably set to be a light-transmitting side.

An electrode 12 is formed over the substrate 11. The electrode may be formed of a suitable good conductor, and for example, may be formed of a transparent amorphous oxide conductor. The oxide conductor may be "transparent" to visible light or to light in a specific wavelength band to be used, depending on the use mode of the piezoelectric device 10A.

As the transparent amorphous oxide conductor, ito (indium Tin oxide), izo (indium Zinc oxide), or the like can be used. By using these materials, an electrode film having a thickness of, for example, 10 to 200nm, more preferably 10 to 100nm is formed by magnetron sputtering with DC (direct current) or RF (high frequency), and the electrode 12 can be patterned by general photolithography and wet etching.

In the case of using ITO, the content ratio of tin (Sn) (Sn/(In + Sn)) may be, for example, 5 to 15 wt%. Within the range of the content, the film is transparent to visible light, and can be formed into an amorphous film by sputtering at room temperature.

In the case of IZO, the content ratio of zinc (Zn) (Zn/(In + Zn)) may be, for example, about 10 wt%. IZO is also transparent to visible light, and can be formed into an amorphous film by sputtering at room temperature.

Next, the piezoelectric layer 13 is formed by sputtering so as to cover the electrode 12 and the substrate 11. The piezoelectric layer 13 is formed of, for example, a piezoelectric material having a wurtzite-type crystal structure, and has a thickness of 200nm to 5 μm.

If the thickness of the piezoelectric layer 13 is less than 200nm, the first electrode 12 and the second electrode 14 approach each other, and even if they are arranged so as not to overlap each other in the thickness direction, the influence of the microcracks becomes large, and it becomes difficult to suppress leakage. The thickness of the piezoelectric layer 13 is preferably 500nm to 5 μm, more preferably 700nm to 5 μm.

By using the sputtering method for forming the electrode 12 and the piezoelectric layer 13, a uniform film having a strong adhesive force can be formed while substantially maintaining the target composition ratio of the compound. In addition, a film having a desired thickness can be formed with high accuracy only by controlling the time.

The wurtzite-type crystal structure is represented by the general formula AB. Here, A is a positive element (A)ⁿ⁺) B is a negative element (B)^n-). As the wurtzite-type piezoelectric material, it is desirable to use a material which exhibits a certain or higher degree of piezoelectric properties and can be crystallized by a low-temperature process of 200 ℃. As an example, zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), aluminum nitride (A) may be used]N), gallium nitride (GaN), cadmium selenide (CdSe), cadmium telluride (CdTe), silicon carbide (SiC), and a combination of these components or a combination of two or more thereof may be used.

When two or more components are combined, the components may be stacked, or film formation may be performed using targets for the components. Alternatively, the above-described components or a combination of two or more thereof may be used as a main component, and other components may be optionally included. The content of the component other than the main component is not particularly limited as long as the effect of the present invention can be exerted. When a component other than the main component is included, the content of the component other than the main component is preferably 0.1 at.% or more and 25 at.% or less.

As an example, a wurtzite-type material containing ZnO or AlN as a main component is used. A metal which does not exhibit conductivity when added, such as silicon (Si), magnesium (Mg), vanadium (V), titanium (Ti), zirconium (Zr), or lithium (Li), may be added as a dopant to ZnO, AlN, or the like. The dopant may be one, or two or more dopants may be added in combination. By adding these metals, the frequency of occurrence of cracks can be reduced. When a transparent wurtzite-type crystal material is used as the material of the piezoelectric layer 13, the material is suitably applied to a display.

Next, a pattern of the electrode 14 is formed on the piezoelectric layer 13. The electrode 14 is formed in a pattern not overlapping the electrode 12 in the film thickness or the lamination direction. In the case where the lower electrode 12 includes a pattern of stripes, or lines and spaces, the electrode 14 is formed in a region corresponding to the spaces between the stripes.

The electrode 14 may be formed of an amorphous transparent oxide conductor, or may be formed of a good conductor such as a metal or an alloy. When an amorphous transparent oxide conductor is used, an ITO film having a thickness of 20nm to 100nm is formed at room temperature by magnetron sputtering such as DC or RF, and a predetermined shape is formed by photolithography and etching. The material of the electrode 14 may be the same material as the electrode 12 or may be a different material.

By forming the electrode 12 from an amorphous oxide conductor, it is possible to suppress formation of projections and pores on the surface of the electrode 12, which cause generation of micro cracks.

< second embodiment >

Fig. 3 is a schematic diagram of a piezoelectric device 10B of the second embodiment. FIG. 3 (A) is a plan view and (B) is a sectional view taken along line I-I'. In the second embodiment, as in the first embodiment, a configuration is also set in which a pair of electrodes sandwiching a piezoelectric layer do not overlap in the film thickness direction or the lamination direction.

The piezoelectric device 10B has a first electrode 22 formed on the substrate 11, a piezoelectric layer 13 disposed on the first electrode 22, and a second electrode 24 disposed on the piezoelectric layer 13. Here, "above" means the upper side when viewed from the stacking direction.

The first electrode 12 and the second electrode 14 have complementary planar shapes. In the example of fig. 3, the second electrode 24 is a circular electrode, and the first electrode 22 is a circular electrode having a planar shape after being cut out. The shape of the electrode 24 is not limited to a circle, and may be an ellipse or a polygon. The polygon may be any shape such as a triangle, a quadrangle, a hexagon, and an octagon.

The other electrode 22 paired with the electrode 24 has a planar shape in which the shape of the electrode 24 is cut out. The patch-like electrode pattern such as a circle or a polygon is not necessarily the electrode 24 formed on the upper surface of the piezoelectric layer 13, and the lower electrode 22 may be a patch electrode. In this case, the upper electrode 24 is formed as an inverted pattern of the lower patch electrode. The stripe patterns of the first embodiment may also be referred to as auxiliary electrode patterns because they do not overlap with each other.

With this configuration, when pressure is applied to the piezoelectric layer 13, positive charges appear on one surface (for example, the upper electrode 24 side) of the piezoelectric layer 13, and negative charges appear on the other surface (for example, the lower electrode 22 side). By measuring the current flowing through the electrodes 22 and 24, the pressure applied to the piezoelectric layer 13 can be detected.

With this configuration, even if a micro-crack is generated from a foreign substance, a projection, a pinhole, or the like on the surface of the substrate 11 or the electrode 22 and the crack extends in the film thickness direction, the formation of a leakage path electrically connecting the lower electrode 22 and the upper electrode 24 can be suppressed.

The piezoelectric device 10B is manufactured in substantially the same manner as the piezoelectric device 10A except that the electrodes 22, 24 are formed in different shapes. The material of the substrate 11 is arbitrary, and may be a substrate made of an inorganic material such as a glass substrate, a sapphire substrate, or an MgO substrate, or a plastic substrate. In the case of using the base material 11 made of plastic or resin, the application range is expanded from the point of flexibility and easy handling.

The electrode 22 formed on the substrate 11 may be formed of an appropriate good conductor, but may be formed of a transparent conductive film "transparent" to visible light or a use wavelength depending on a use mode of the piezoelectric device 10B.

The piezoelectric layer 13 is formed of, for example, a piezoelectric material having a wurtzite-type crystal structure, as in the first embodiment. As the piezoelectric material, for example, zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), aluminum nitride (an) N, gallium nitride (GaN), cadmium selenide (CdSe), cadmium telluride (CdTe), silicon carbide (SiC) may be used, or a combination of two or more of these components may be used alone.

When two or more components are combined, the components may be stacked, or film formation may be performed using targets for the components. Alternatively, the above-described components or a combination of two or more thereof may be used as a main component, and other components may be optionally contained. The content of the component other than the main component is not particularly limited as long as the effect of the present invention can be exerted. When a component other than the main component is included, the content of the component other than the main component is preferably 0.1 at.% to 20 at.%, more preferably 0.1 at.% to 10 at.%, and still more preferably 0.2 at.% to 5 at.%.

For example, a wurtzite-type material containing ZnO or AlN as a main component may contain, as a sub-component, a metal that does not exhibit conductivity when added, such as silicon (Si), magnesium (Mg), vanadium (V), titanium (Ti), zirconium (Zr), or lithium (Li). The dopant may be one, or two or more dopants may be added in combination. By adding these metals, the frequency of occurrence of cracks can be reduced. When a transparent wurtzite-type crystal material is used as the material of the piezoelectric layer 13, the material is suitably applied to a display.

The upper electrode 24 may be formed of an amorphous transparent oxide conductor or a good conductor such as a metal or an alloy, as long as it is a pattern that does not overlap with the electrode 22 in the film thickness or the lamination direction. When an amorphous transparent oxide conductor is used, an ITO film having a thickness of 20 to 100nm is formed at room temperature by magnetron sputtering such as DC or RF, and a predetermined shape is formed by photolithography and etching. The material of the electrode 24 may be the same material as the electrode 22 or may be a different material.

With the configuration of the second embodiment, it is possible to extract generated charges while suppressing formation of a leakage path between the upper and lower electrodes. Further, since the upper and lower sides of the piezoelectric layer 13 are formed with the auxiliary electrode patterns, a stress relaxation effect can be expected.

< third embodiment >

Fig. 4 is a schematic diagram of a piezoelectric device 10C of the third embodiment. FIG. 4 (A) is a plan view and (B) is a sectional view of TII-III'. The piezoelectric device 10C has a stripe pattern similar to that of the first embodiment as an auxiliary electrode pattern which does not overlap with each other in the stacking direction.

In the third embodiment, an amorphous layer 15 is provided between the piezoelectric layer 13 and the substrate 11. The lower electrode 12 is formed on the amorphous layer 15. By disposing the amorphous layer 15 on the substrate 11, unevenness can be absorbed when the substrate 11 is a plastic substrate, and projections, pinholes, and the like that may occur on the surface of the electrode 12 can be reduced. The amorphous layer 15 has a smooth surface and is hard to initiate cracks.

As the substrate 11, in the case of using plastic or resin such as PET, PEN, PC, acrylic resin, or the like, the amorphous layer 15 may be an organic amorphous layer. Examples of the organic amorphous layer include acrylic resins, urethane resins, melamine resins, alkyd resins, siloxane-based polymers, and the like. In particular, as the organic substance, a thermosetting resin composed of a mixture of a melamine resin, an alkyd resin, and an organosilane condensate is preferably used. The organic amorphous layer is formed by a coating method, a spraying method, or the like.

In the case where the organic amorphous material used for the amorphous layer 15 has conductivity, the amorphous layer 15 may function as a part of the electrode 12. Since the amorphous layer 15 absorbs the irregularities on the surface of the substrate 11 and the surface is formed smoothly, there is a low possibility that cracks will occur from the region of the amorphous layer 15 facing the electrode 14.

According to this configuration, it is possible to suppress the formation of a leak path between the electrode 12 and the electrode 14 sandwiching the piezoelectric layer 13 in the lamination direction.

Other configurations, materials, manufacturing steps, and the like of the piezoelectric device 10C are the same as those of the first embodiment, and redundant description is omitted.

The configuration of the third embodiment can extract generated charges while more effectively suppressing the formation of a leakage path between the upper and lower electrodes. Further, since the upper and lower sides of the piezoelectric layer 13 are formed with the auxiliary electrode patterns, the stress relaxation effect can be expected.

< fourth embodiment >

Fig. 5 is a schematic diagram of a piezoelectric device 10D of the fourth embodiment. FIG. 5 (A) is a plan view and (B) is a sectional view of IV-TV'. As in the second embodiment, the piezoelectric device 10D is configured to combine a patch pattern and an inverted pattern obtained by cutting out a patch as electrode patterns that do not overlap each other in the lamination direction. The patch pattern is not limited to a circle, but may be an ellipse, a polygon, a rectangle, or the like.

In the fourth embodiment, as in the third embodiment, an amorphous layer 15 is interposed between a piezoelectric layer 13 and a substrate 11. The lower electrode 22 is formed on the amorphous layer 15. By disposing the amorphous layer 15 on the substrate 11, in the case where the substrate 11 is a plastic substrate, unevenness can be absorbed, and projections, pinholes, and the like that may be generated on the surface of the electrode 22 can be reduced. The amorphous layer 15 has a smooth surface, and is less likely to initiate cracks, and cracks are less likely to occur from the region facing the upper electrode 234.

As the substrate 11, in the case of using plastic or resin such as PET, PEN, PC, acrylic resin, or the like, the amorphous layer 15 may be an organic amorphous layer. Examples of the organic amorphous layer include acrylic resins, polyurethane resins, melamine resins, alkyd resins, siloxane-based polymers, and the like. In particular, as the organic substance, a thermosetting resin composed of a mixture of a melamine resin, an alkyd resin, and an organosilane condensate is preferably used. The organic amorphous layer is formed by a coating method, a spraying method, or the like.

Other configurations, materials, manufacturing steps, and the like of the piezoelectric device 10D are the same as those of the second embodiment, and redundant description is omitted.

The configuration of the fourth embodiment can also extract generated charges while effectively suppressing the formation of a leakage path between the upper and lower electrodes. Further, since the upper and lower sides of the piezoelectric layer 13 are formed with the auxiliary electrode patterns, a stress relaxation effect can be expected.

< modification example >

Fig. 6 is a diagram showing a modification of the electrode pattern. The pair of electrodes sandwiching the piezoelectric layer 13 in the stacking direction is not limited to the shape of the first to fourth embodiments. Any pattern may be set so as to sandwich the piezoelectric layer 13 and not to overlap each other in the lamination direction. From the viewpoint of extracting charges on the surface (or interface) of the piezoelectric layer 13, it is preferable that the charge extraction port is located at one position on the upper electrode and at one position on the lower electrode. In addition, the surface area of the upper electrode and the surface area of the lower electrode may be set to be substantially equal.

In the example of fig. 6 (a), the lower electrode 32 and the upper electrode 34 are comb-teeth-shaped or interdigital electrodes that intersect each other alternately in different layers with the piezoelectric layer 13 interposed therebetween. The surface area of electrode 32 and the surface area of electrode 34 are substantially equal. Even when a micro-crack is generated due to a projection, a pinhole, a foreign substance, or the like on the surface of the lower electrode 32 and the crack extends in the film thickness direction of the piezoelectric layer 13, the crack can be prevented from serving as a leakage path that electrically short-circuits the lower electrode 32 and the upper electrode 34.

In the example of fig. 6 (B), the lower electrode 42 and the upper electrode 44 are spiral electrodes that are wound so as to intersect each other in different layers with the piezoelectric layer 13 interposed therebetween. The shape of the electrode is not limited to the circular spiral shown in fig. 6 (B), and may be a spiral such as a rectangle or polygon as long as it does not overlap vertically.

Although not shown, the electrodes may be concentric circles in which the upper and lower electrodes do not overlap each other. The lower electrode may be set to one or two or more annular patterns, and the upper electrode may be set to one or two or more annular patterns formed in a region corresponding to the ring of the lower electrode and a space between the rings. The ring is not limited to a circular ring, and may be a rectangular ring, a polygonal ring, or the like.

In the electrode pattern of the modified example, as shown in the third and fourth embodiments, the amorphous layer 15 may be interposed between the substrate 11 and the lower electrode. This can more effectively suppress the leakage path.

When the lower electrode is formed of a transparent amorphous oxide conductor on the plastic substrate 11, a low-resistance amorphous film can be formed on the plastic substrate 11 by introducing water through a sputtering process.

The piezoelectric device having the electrode structure of the present invention can be applied to a touch panel or the like as a piezoelectric sensor. Even when the piezoelectric layer is made thinner by setting the thickness to 200 μm or less, the formation of a leakage path between electrodes can be suppressed, and the reliability of operation can be maintained.

The application claims priority of japanese patent application No. 2019-052876, applied on 3/20/2019, and includes the entire contents of the japanese patent application.

Description of the reference numerals

10A-10D piezoelectric device

11 base material

12. 22, 32, 42 first electrode

13 piezoelectric layer

14. 24, 34, 44 second electrode

15 amorphous layer