JP5958665B2 - Piezoelectric element and piezoelectric sensor - Google Patents

Description

  The present invention relates to a piezoelectric element and a piezoelectric sensor.

  As a structure of a general piezoelectric element used for a sensor, an actuator, or the like, a structure in which a piezoelectric layer is sandwiched between two electrode layers is known. In a piezoelectric element, a physical signal such as stress applied to the piezoelectric element is converted into an electrical signal (positive piezoelectric effect) and output from an electrode, or an electrical signal input to the piezoelectric element is physically Is converted into a target signal (inverse piezoelectric effect).

  In recent years, with the miniaturization of electronic devices, piezoelectric elements such as sensors are also required to be smaller and lighter. In response to this demand, development of a piezoelectric element using a piezoelectric body (piezoelectric film) thinned on a film-like base material is in progress. In particular, a piezoelectric element used for a piezoelectric sensor or the like used for a human body needs to follow the body movement, and therefore needs to be thin and flexible.

  In such a piezoelectric element, as the piezoelectric material is made thinner, the insulation between the electrode layers is lowered, and the possibility of a short circuit is increased. In order to prevent the occurrence of such a short circuit, proposals have been made to interpose an insulating short circuit prevention film between the piezoelectric body and the electrode layer.

  Furthermore, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2006-66901), instead of a conventional piezoelectric element in which an insulating substrate as a support, an electrode layer, a piezoelectric layer, and an electrode layer are laminated in this order. The electrode layer, the insulating substrate, the piezoelectric layer, and the electrode layer are laminated in this order, and the laminated body is folded back and stacked along the width direction, thereby generating a short circuit without forming a separate short-circuit prevention film. A configuration of a piezoelectric element that can prevent the above is disclosed.

JP 2006-66901 A

  However, when the signal obtained with the piezoelectric film is sent to the detection device, noise may be mixed into the signal at the connection part between the transmission cable and the cable and the sensor, but noise is mixed into the signal inside the sensor. There is also. Noise mixed inside the sensor is directly transmitted to the detection device, which is an obstacle to transmitting an accurate signal. In the piezoelectric element of Patent Document 1, the inner electrode layer is covered with the outer electrode layer, and the outer electrode layer acts as a shield against noise, but the inner electrode layer is exposed at the end in the width direction of the piezoelectric body. Therefore, there is a possibility that noise is mixed into the signal from this end portion and the accuracy of the signal is lowered.

  Therefore, the present invention is a piezoelectric element that can reduce the number of parts and the number of assembly steps while meeting the demands for thinning and flexibility, and can suppress the mixing of noise into the output signal and output a highly accurate signal. An object of the present invention is to provide a piezoelectric element that can be used, and a piezoelectric sensor using the same.

The present invention includes a piezoelectric layer formed by laminating a piezoelectric film and an insulating film;
An internal electrode layer provided on one main surface of the piezoelectric layer;
A laminate including an external electrode layer provided on the other main surface of the piezoelectric layer;
The laminate is folded along at least one fold line so that the internal electrode layer is on the inside,
The piezoelectric element further includes a conductive member provided so as to cover at least a part of a portion of the internal electrode layer that is not covered with the external electrode layer, and electrically connected to the external electrode layer.

The laminate folded along the fold line has a rectangular shape when viewed in plan,
One side of the rectangle corresponds to the fold line,
It is preferable that the conductive member is provided on a side surface of the laminate corresponding to at least the other three sides of the rectangle.

  The insulating film preferably has a thickness of an end portion that does not overlap at least one of the piezoelectric film, the internal electrode layer, and the external electrode layer, which is thicker than a portion other than the end portion.

It is preferable that the thickness of the end portion of the internal electrode layer is thicker than the portion other than the end portion.
The thickness of the end portion of the external electrode layer is preferably thicker than the portion other than the end portion.

  It is preferable that the internal electrode layer has a slit, and the laminated body is bent along the bending line corresponding to the slit.

  The present invention also relates to a piezoelectric sensor including the above-described piezoelectric element.

  According to the present invention, a piezoelectric element capable of reducing the number of parts and the number of assembling steps while meeting demands for thinning and flexibility, and can suppress the mixing of noise into an output signal and output a highly accurate signal. The piezoelectric element which can be manufactured, and a piezoelectric sensor using the same can be provided.

FIG. 3 is a schematic perspective view for explaining the configuration of the piezoelectric element according to the first embodiment. It is a schematic sectional drawing in the A-A 'cross section of FIG. It is a schematic sectional drawing in the B-B 'cross section of FIG. It is a schematic sectional drawing for demonstrating the laminated body which comprises the piezoelectric element shown in FIG. 6 is a schematic cross-sectional view for explaining a configuration of a piezoelectric element according to Embodiment 2. FIG. 6 is a schematic cross-sectional view for explaining a configuration of a piezoelectric element according to Embodiment 3. FIG. 6 is a schematic cross-sectional view for explaining a configuration of a piezoelectric element according to Embodiment 4. FIG.

  The piezoelectric element of the present invention includes a piezoelectric layer formed by laminating a piezoelectric film and an insulating film, an internal electrode layer provided on one main surface of the piezoelectric layer, and the other main surface of the piezoelectric layer. A laminate including the provided external electrode layer is provided. This laminated body is bent along at least one fold line so that the internal electrode layer is on the inner side. The piezoelectric layer may be laminated on either the insulating film side or the piezoelectric film side, and the external electrode layer is laminated on the opposite side of the piezoelectric layer from the internal electrode layer. When bent, the inner electrode layer is on the inner side, and the outer electrode layer is on the outer side.

  The piezoelectric element of the present invention further includes a conductive member electrically connected to the external electrode layer, and the conductive member covers at least a part of the portion of the internal electrode layer that is not covered by the external electrode layer. It is provided in.

  With this feature, in the piezoelectric element that can reduce the number of parts and assembly man-hours while meeting the demands for thinning and flexibility, noise can be suppressed from being output to the output signal of the piezoelectric element, and a highly accurate signal can be output. It becomes possible.

  The insulating film is an insulating film, and is usually a flexible film. Furthermore, it is preferably a film mainly composed of a polymer having characteristics such as light weight and easy handling. The polymer used as the main component of the insulating film is not particularly limited, but is, for example, a polyolefin resin, a polyimide resin, a polyamide resin, or a polyester resin, and is a polyolefin resin as a general-purpose material. Polyethylene terephthalate (PET) can be preferably used. In addition, a polyimide resin is preferable in terms of excellent heat resistance, dielectric breakdown strength, and mechanical strength.

  The piezoelectric element is preferably a thin (film-like) piezoelectric element. The piezoelectric element is used for sensors and actuators, for example. Examples of the sensor include a sensor for measuring a physical signal such as a displacement signal and an audio signal.

The constituent material of the piezoelectric layer is not particularly limited as long as it is a substance having piezoelectricity. For example, a compound having a wurtzite structure or a composite oxide having a perovskite structure (ABO ₃ ) (perovskite composite) A material whose main component is an oxide) can be used.

  Examples of the compound having a wurtzite structure include aluminum nitride (AlN), gallium nitride, indium nitride, beryllium oxide, zinc oxide, cadmium sulfide, zinc sulfide, or silver iodide.

As the A site of the perovskite structure (ABO ₃ ) of the perovskite-based composite oxide, for example, at least one element selected from Pb, Ba, Ca, Sr, La, Li, and Bi can be adopted. . As the B site of the perovskite structure (ABO ₃ ), for example, at least one element selected from Ti, Zr, Zn, Ni, Mg, Co, W, Nb, Sb, Ta and Fe is adopted. .

Specific examples of such perovskite complex oxides include lead zirconate titanate [Pb (Zr, Ti) O ₃ ] (also referred to as PZT) and potassium tantalate niobate [K (Ta, Nb) O ₃ ]. And barium titanate (BaTiO ₃ ), (Pb, La) (Zr, Ti) O ₃ [lead titanate (PbTiO ₃ ) and the like] and the like.

  As a method for forming the piezoelectric layer, for example, a sputtering method, a vacuum deposition method, a laser ablation method, an ion plating method, a coating method, a chemical vapor deposition method such as a CVD method, an MOCVD method, and the like are known. Preferred ones can be selected as appropriate.

  The film thickness of the piezoelectric layer is preferably 0.1 to 100 μm, more preferably 0.5 to 30 μm. That is, when the thickness is less than 0.1 μm, it is difficult to obtain a sufficient output when used for, for example, a sensor or an actuator. On the other hand, when the thickness exceeds 100 μm, the flexibility is poor and cracking or peeling may occur.

  As a material of the internal electrode layer and the external electrode layer, for example, a conductive material composed of a metal such as Al, Ni, Pt, Au, Ag, Ti, Cu or Sn, or an alloy thereof, or a metal oxide or metal A conductive material containing nitride can be used. In particular, the material of the external electrode is Ti because it has good adhesion to the insulator layer and the piezoelectric layer, good biocompatibility (low risk of developing allergies), and high corrosion resistance. Is preferred.

  The formation method of the internal electrode layer and the external electrode layer is not particularly limited. For example, a physical vapor deposition method such as a coating process, a plating method, a sputtering method, or a vacuum vapor deposition method can be used.

  As a material for the conductive member, the same conductive material as that for the internal electrode layer and the external electrode layer described above can be used, but a material having a low electrical resistivity is preferable. As a material having a low electrical resistivity, it is particularly preferable to use Cu.

  The shape of the conductive member is not particularly limited, but is preferably a film shape. The thickness of the film-like conductive member is preferably 20 to 100 μm.

  Hereinafter, embodiments of a piezoelectric element of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and depth are changed as appropriate for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

(Embodiment 1)
FIG. 1 is a schematic perspective view for explaining the configuration of the piezoelectric element according to the first embodiment. 2 is a schematic cross-sectional view taken along the line AA ′ of FIG. 1, and FIG. 3 is a schematic cross-sectional view taken along the line BB ′ of FIG. FIG. 4 is a schematic cross-sectional view for explaining a laminated body (state before bending) constituting the piezoelectric element shown in FIG.

  In the piezoelectric element shown in FIG. 1, conductive members 5, 5 a and 5 b are provided so as to cover the side surface of the laminated body 100. As described above, at least part of the portion of the internal electrode layer that is not covered with the external electrode layer (for example, the side surface of the laminate) is covered with the conductive member 5, so that noise is mixed into the output signal in the internal electrode layer. Is suppressed, and a highly accurate signal can be output.

  In addition, with reference to FIG. 1, the cable 62 for external electrode layers is connected to the upper part of the electroconductive member 5a. In addition, the conductive member 5a, the external electrode layer 32, the piezoelectric film 2 and the insulating film 1 are partially cut off, and the internal electrode layer 31 is exposed. 61 is connected. The cables 61 and 62 can be electrically connected to the conductive member 5a and the internal electrode layer 31, respectively, using solder, a conductive adhesive, or the like.

  Referring to FIG. 4, laminated body 100 includes insulating film 1 and piezoelectric layer 10 including piezoelectric film 2 provided on one main surface of insulating film 1 and piezoelectric film 2 (piezoelectric layer). 10) an internal electrode layer 31 provided on the surface opposite to the insulating film 1, and an external electrode layer 32 provided on the other main surface of the insulating film 1 (main surface opposite to the piezoelectric film 2). It consists of.

  A slit 31b is formed in the width direction in the internal electrode layer 31 (FIG. 4), and the laminate 100 is bent so that the internal electrode layer 31 is on the inner side with the slit 31b as a fold line. Accordingly, the bending process can be easily performed, and damage to the internal electrode layer and other layers (piezoelectric layer, external electrode layer) in the bent portion are also suppressed.

  By providing the conductive member 5 on the laminated body 100 bent in this manner, the piezoelectric element of Embodiment 1 having a layer structure as shown in FIGS. 2 and 3 can be obtained. Here, the conductive member 5 is electrically connected to the external electrode layer 32 using a conductive adhesive or the like. Further, the portion where the internal electrode layers 31 are in contact with each other is bonded by the conductive adhesive 4.

  Further, as in the present embodiment, in the laminated body 100 after being bent, the external electrode layer 32 has a structure that covers the piezoelectric layer 10 (piezoelectric film 2) and the internal electrode layer 31. Has an electromagnetic shielding effect. In addition to this, since the conductive member 5 reduces the portion of the piezoelectric element that is not shielded, such as the side surface of the piezoelectric element, the shielding performance is further enhanced, and the effect of blocking external noise (noise) becomes more prominent. Electrical characteristics can be further improved.

  Either the internal electrode layer or the external electrode layer is the output side electrode (the electrode on the signal output side that is connected to an amplifier or the like for amplifying the voltage generated in the piezoelectric layer. Usually, the anode) or the ground electrode (the ground potential) In order to further improve the shielding performance of the output side electrode, it is preferable to connect the internal electrode layer 31 to the output side electrode and connect the external electrode layer 32 to the ground potential. .

  Further, by folding and stacking the laminated body along the width direction, it is possible to manufacture a piezoelectric element capable of preventing the occurrence of a short circuit without separately forming a short circuit prevention film, which is advantageous in terms of cost.

  Further, since the thickness of the outer peripheral portion of the piezoelectric element is increased, the rigidity of the outer peripheral portion that is likely to be broken due to torsion due to an external force is improved, so that the risk of breakage of the piezoelectric element is reduced.

  Further, since the conductive member 5 is electrically connected to the external electrode layer 32, there is an effect of lowering the resistance value of the front and back electrodes, so that it is difficult to be affected by noise from a commercial power source or the like. A sensor with a large ratio can be obtained.

  In addition, since the rigidity of the outer peripheral portion of the piezoelectric element is increased, each layer in the central portion can be thinned, and flexibility is improved. Thereby, for example, when used for a piezoelectric sensor that is used by being attached to a human body or the like, the adhesion between the piezoelectric element and the human body or the like is improved, so that the sensitivity of the sensor can be improved.

  In the present embodiment, the conductive member 5b is also provided on the side surface (the right side in FIG. 2) where the internal electrode layer 31 is covered with the external electrode layer 32. This conductive member 5b is a piezoelectric element. This is for improving the rigidity and the like of the outer peripheral portion and not for shielding the internal electrode layer 31, and thus is not necessarily provided. That is, in the rectangular laminated body bent along the folding line, the conductive members 5 and 5a are provided on the side surfaces of the laminated body corresponding to three sides other than the one side corresponding to the folding line. Preferably it is.

(Embodiment 2)
FIG. 5 is a schematic cross-sectional view for explaining the configuration of the piezoelectric element of the second embodiment. (A) is a schematic sectional drawing which shows the layer structure of the laminated body 100 before bending, (b) is a schematic sectional drawing which shows the structure of a piezoelectric element.

  In this embodiment, the insulating film 1 has an end portion that does not overlap at least one of the piezoelectric film, the internal electrode layer 31 and the external electrode layer 32 with a thickness greater than that of the end portion (that is, the insulating property). It differs from the first embodiment in that it protrudes in one or both of the directions perpendicular to the main surface of the film 1, but the other points are the same as in the first embodiment.

  In the present embodiment, since the rigidity of the outer peripheral portion of the piezoelectric element is further increased than in the first embodiment, each layer in the central portion can be made thinner, and the flexibility is further improved.

  Moreover, the effect of improving the insulation between the internal electrode layer 31 and the conductive member 5 connected to the external electrode layer 32 is also obtained.

(Embodiment 3)
FIG. 6 is a schematic cross-sectional view for explaining the configuration of the piezoelectric element of the third embodiment. (A) is a schematic sectional drawing which shows the layer structure of the laminated body 100 before bending, (b) is a schematic sectional drawing which shows the structure of a piezoelectric element.

  This embodiment is different from the first embodiment in that the thickness of the end portion 32a of the external electrode layer 32 is thicker than the portion other than the end portion 32a, but the other points are the same as in the first embodiment.

  In this embodiment, since the thickness of the outer peripheral portion of the piezoelectric element is further increased, the rigidity of the outer peripheral portion is further improved, and the risk of breakage of the piezoelectric element is reduced.

(Embodiment 4)
FIG. 7 is a schematic cross-sectional view for explaining the configuration of the piezoelectric element according to the fourth embodiment. (A) is a schematic sectional drawing which shows the layer structure of the laminated body 100 before bending, (b) is a schematic sectional drawing which shows the structure of a piezoelectric element.

  This embodiment is different from the first embodiment in that the thickness of the end portion 31a of the internal electrode layer 31 is thicker than the portion other than the end portion 31a, but the other points are the same as in the first embodiment.

  In addition to the same effects as in the first and third embodiments, the contact between the external electrode layer 32 and the conductive member 5 is reliably performed at the end portion 32a in the width direction of the external electrode layer 32, and the effect of suppressing poor contact and the like. Can also be obtained.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Insulating film, 1a edge part, 2 Piezoelectric film, 10 Piezoelectric layer, 31 Internal electrode layer, 31a Edge part, 31b Slit, 32 External electrode layer, 32a edge part, 4 Conductive adhesive, 5, 5a, 5b Conductive member, 61, 62 cable, 100 laminate.

Claims (6)

A piezoelectric layer formed by laminating a piezoelectric film and an insulating film;
An internal electrode layer provided on one main surface of the piezoelectric layer;
A laminate including an external electrode layer provided on the other main surface of the piezoelectric layer;
The laminate is folded along at least one fold line so that the internal electrode layer is on the inside,
A conductive member provided so as to cover at least part of the portion of the internal electrode layer not covered with the external electrode layer, and electrically connected to the external electrode layer ;
The insulating film is a piezoelectric element in which an end portion that does not overlap at least one of the piezoelectric film, the internal electrode layer, and the external electrode layer is thicker than a portion other than the end portion . The laminate folded along the fold line has a rectangular shape when viewed in plan,
One side of the rectangle corresponds to the fold line,
The piezoelectric element according to claim 1, wherein the conductive member is provided on a side surface of the multilayer body corresponding to at least the other three sides of the rectangle. When the thickness of the end portion of the internal electrode layer is thicker than the portion other than the end portion, the piezoelectric element according to claim 1 or 2. When the thickness of the end portion of the outer electrode layer is thicker than the portion other than the end portion, the piezoelectric element according to any one of claims 1-3. The internal electrode layer has a slit, the laminate along the folding line corresponding to the slit is bent, the piezoelectric element according to any one of claims 1-4. A piezoelectric sensor provided with the piezoelectric element of any one of Claims 1-5 .

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