JPH0587974U - Multilayer piezoelectric element - Google Patents

Abstract

(57) [Summary] [Structure] An electrode absent portion (8) is formed on the peripheral edge of each surface of the laminated polymer piezoelectric film (1), and a lead electrode (6a) is formed on the surface facing the absent portion. ) Is provided. [Effect] Leakage current and edge discharge are prevented from occurring, and lead wires are easily taken out.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a laminated piezoelectric element in which a plurality of polymer piezoelectric films or sheets and electrodes are alternately laminated in a plane, and particularly to an electrode structure of such laminated piezoelectric element.

[0002]

[Prior Art]

Polymer piezoelectric materials including polarized vinylidene fluoride resin (hereinafter typically referred to as PVDF) are (1) more flexible, thinner, and thinner than ceramic piezoelectric materials. Areas and lengths can be easily made, and arbitrary shapes and forms can be produced; (2) Hydrostatic pressure piezoelectric strain constant d _h is the same or less, but the dielectric constant ε is small, so d _h / epsilon hydrostatic voltage output coefficient determined in (g _h constant) becomes very Umate large, therefore the sensitivity characteristics are excellent; (3) low density, due to low elasticity, acoustic impedance (sound velocity × density) It has characteristics that it is close to the values of water and living organisms, therefore there is little reflection between water and living organisms and elements, and efficient energy transmission is possible. Taking advantage of these characteristics, polymer piezoelectric materials are generally used for electro-mechanical (acoustic) conversion elements such as speakers, microphones, ultrasonic probes, hydrophones, seismographs, strain gauges, blood pressure monitors, and bimorph fans. As a result, application to a wide range of applications has been proposed or put into practical use.

When forming a film-shaped or sheet-shaped polymer piezoelectric material (hereinafter, generically referred to as “polymer piezoelectric film”) as an element, electrodes are usually provided on both surfaces thereof. Then, this electrode and the electric circuit in the subsequent stage are connected by a lead wire or the like.

On the other hand, in this polymer piezoelectric body made into an element, a single-layer piezoelectric element in which electrodes are formed on both surfaces of one polymer piezoelectric film and a plurality of polymer piezoelectric films are used, and the electrodes are alternately arranged. And a laminated piezoelectric element, wherein the latter is an ultrasonic transducer or a transducer or bimorph oscillator such as the element described in Japanese Patent Application No. 3-356667 of the applicant's earlier application. Is widely used as.

The conventional piezoelectric element as described above is usually manufactured by cutting a large area piezoelectric film having electrodes formed on the surface in advance into desired dimensions, and the entire surface of the polymer film The electrode is formed on the surface.

[0006]

[Issues to be solved by the device]

However, in the polymer piezoelectric body, which has a larger _gh constant than the ceramic piezoelectric body and is usually used with a thickness of several tens of μm to 1000 μm, the electrodes are relatively thin and a high voltage is generated between them. Since it is applied, leakage current and edge discharge that occur along the side surface of the piezoelectric film cause a decrease in device sensitivity and efficiency, and at the same time cause noise, which is a problem that cannot be ignored. In particular, in a piezoelectric element cut out from a large-area piezoelectric element as described above, due to electrode burr when cutting out, this leakage current and edge discharge frequently occur, which lowers the yield of element manufacturing. It is one of the causes.

In addition to the above-mentioned problems, lead wire connection to an intermediate electrode sandwiched between piezoelectric bodies also becomes a problem in the laminated piezoelectric element. That is, in a laminated piezoelectric element, it is usually necessary to connect every other electrode in the laminating direction with lead wires so that all the piezoelectric elements are electrically parallel circuits. It is not easy to realize the parallel circuit without short-circuiting the electrodes and suppressing leakage current and edge discharge.

The main object of the present invention is to provide a polymer-based laminated piezoelectric element having an electrode structure in which leakage current and edge discharge are less likely to occur and lead wires can be easily connected to electrodes.

[0009]

[Means for Solving the Problems]

 As a result of continuing the research for the above-mentioned purpose, the present inventors have provided an electrode absent portion (margin) on the peripheral portion of the surface of the polymer piezoelectric film, and further, continuously and integrally from the piezoelectric electrodes constituting each piezoelectric element. The present inventors have found that the electrode structure in which the lead electrode is provided at a position corresponding to the margin on the opposing film surface is useful, and arrived at the present invention.

That is, the laminated piezoelectric element of the present invention is a laminated piezoelectric element in which at least two or more piezoelectric elements formed of a polymer piezoelectric film or sheet and piezoelectric electrodes arranged on both surfaces thereof are laminated in a plane. In the element, an absent portion of an electrode is formed on the peripheral edge of each surface of the polymer piezoelectric film or sheet, and the piezoelectric electrode is connected to the piezoelectric electrode at a predetermined position on the opposite surface facing the absent electrode portion. It is characterized in that the lead electrode is integrally formed.

In the present invention, the “piezoelectric element” of the laminated piezoelectric element is a combination of one polymer piezoelectric film and the electrodes on both surfaces, which produces a piezoelectric effect. It refers to the overlapped part of electrodes (this is called "piezoelectric electrode") and the piezoelectric film part sandwiched between them. The term "electrode" simply means a polymer piezoelectric formed on the surface of the piezoelectric element or continuously from the surface, including not only the above-mentioned piezoelectric electrode but also a lead electrode continuously and integrally formed from the piezoelectric electrode. A conductive member that inputs and outputs electrical energy to and from the body film.

[0012]

[Action]

 The electrodes are removed from the peripheral edge of the polymer piezoelectric film as much as possible, and the lead electrode is provided at a position corresponding to the electrode absent portion (margin) of the facing surface. The distance between the double-sided electrodes, which is surrounded by the double-sided electrode, becomes longer, and the short-circuiting or approaching of the double-sided electrodes due to the above-mentioned barriers or the occurrence of leakage current or edge discharge through the end faces of the piezoelectric body due to the high generated voltage is effective. To be prevented. Further, it becomes easy to take out the lead wire while effectively preventing a short circuit with an adjacent electrode at the time of stacking.

[0013]

[Specific explanation of the device]

 Hereinafter, preferred embodiments of the laminated piezoelectric element of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals used to describe different modes indicate similar parts.

FIG. 1 is a front view showing a laminated structure of a first embodiment of a laminated piezoelectric element of the present invention together with a connected state, and FIG. 2 is a plan view thereof. Referring to FIGS. 1 and 2, the laminated piezoelectric element 10a includes a polymer piezoelectric film 1 and a piezoelectric electrode 2 (2a, 2b) made of a metal foil integrated with a lead electrode 6 (6a, 6b). Has a laminated structure of 10 layers of piezoelectric elements in which the lead electrodes 6a and 6b are laminated via the adhesive layer 3 in such a manner that the directions thereof alternate. Lead electrodes 6a, 6b extend continuously and integrally from the piezoelectric electrodes 2a, 2b to reach the outside of the element, where they are connected to the short-circuit wires 4a, 4b and shown via terminals 5a, 5b. Not led to the subsequent electrical circuit. Thus all piezoelectric elements are wired to form a parallel circuit. Moreover, lead electrodes 6a and 6b each having a width narrower than the width of the piezoelectric electrodes 2a and 2b are formed (attached) on the opposing surfaces of the respective piezoelectric films 1 and in the vicinity of the diagonals of the opposing sides. An electrode absent portion (margin) 8 is formed on the entire peripheral edge portion except the lead electrode forming portion. As a result, the lead electrode 6 (6a, 6b) is formed in a predetermined position on the opposing surface facing the electrode absent portion 8. That is, in this embodiment, no electrodes are provided on the end surface 9 of the piezoelectric body 1 except for the lead electrodes 6a and 6b. Therefore, the insulation distance around the end face 9 between the adjacent piezoelectric electrodes 2a and 2b is long, and the leakage current and the edge discharge can be effectively suppressed.

Next, the details of the configuration of each unit will be described. As the polymer piezoelectric material forming the polymer piezoelectric film 1, vinylidene cyanide-vinyl acetate copolymer having a relatively high heat resistance is preferably used, and a vinylidene fluoride resin piezoelectric material having excellent piezoelectric characteristics is used. The preferred form is β-type crystallization under ordinary crystallization conditions, compared with vinylidene fluoride (VDF) homopolymer, which requires uniaxial stretching for β-type crystallization suitable for piezoelectricity. A VDF-based copolymer (for example, a copolymer of a predominant amount of VDF and a subordinate amount of vinyl fluoride (VF), trifluoroethylene (TrFE) or tetrafluoroethylene (TFE)) is preferable, and a predominant amount (particularly 70). A copolymer of VDF (about 80 to 80 mol%) and a subordinate amount (particularly 30 to 20 mol%) of TrFE is most preferably used.

After being formed into a film by melt extrusion or the like, these polymer piezoelectric materials are subjected to polarization treatment by uniaxial elongation or heat treatment at a softening temperature or lower, and application of an electric field at a softening temperature or lower, if necessary. The polymer piezoelectric film 1 preferably has a thickness of about 10 to 2000 μm, particularly 20 to 1000 μm. If the thickness of the film is less than 10 μm, sufficient wave transmission / reception sensitivity may not be obtained depending on the application. On the other hand, when the thickness exceeds 2,000 μm, a high voltage is required for polarization, which causes edge discharge and makes polarization processing extremely difficult.

As the piezoelectric electrode 2 and the lead electrode 6, foil electrodes are used in this example, and as a result, as shown in FIGS. 1 and 2, the lead electrode is continuously and integrally projected to the outside of the element laminated portion. End can be provided to facilitate the lead wire connection.

As the foil electrode, for example, a foil of a conductive metal such as copper, aluminum, tin, zinc, gold, silver and platinum having a thickness of 6 to 2000 μm, particularly 20 to 1000 μm is preferable. The thickness of the foil electrode is appropriately determined depending on the thickness and flexibility of the entire piezoelectric element, the flexibility required for the protruding lead electrode portion, and the like. A structure in which a foil electrode is attached to the surface of the polymer piezoelectric film via an adhesive is particularly preferably adopted.

The adhesive layer 3 can be formed of a conductive adhesive in which conductive particles are dispersed, but an epoxy resin, a urethane resin, a polyester resin, a butadiene resin having a higher adhesive strength can be used. It is preferable to form a layer having a thickness of about 5 to 40 μm with an adhesive such as a propylene resin or an acrylic resin.

The electrode absent portion (margin) 8 is provided in the peripheral portion of each surface of the polymer piezoelectric film 1 with a width of, for example, 0.3 to 20 mm, preferably 2 to 10 mm. If this width is shorter than 0.3 mm, there is little effect of suppressing leakage current and edge discharge, and if it is longer than 20 mm, the utilization efficiency of the polymer piezoelectric film is extremely reduced especially in small-sized elements. In particular, in the case of an element with a foil electrode bonded to a polymer piezoelectric film with an adhesive as in this example, even if the margin is short, it is filled with the adhesive, so leakage current and discharge Great deterrent effect. Also, if a wide margin is provided, leakage current will not increase even if a conductive adhesive is used.

It is particularly preferable that the direction in which the margin 8 is provided on each surface of the polymer piezoelectric film 1 is the entire circumferential direction (four directions) excluding the lead electrode portions 6 (6a, 6b) as in this example. However, the present invention is not limited to this. The margins may be provided in at least two directions such that the front and back surfaces of the film are aligned with the entire circumference. Further, for example, by combining an upper surface electrode having a longer length direction and a shorter width direction with respect to the polymer piezoelectric film 1 and a lower surface electrode opposite thereto, an element having a margin 8 provided in two directions is obtained.

The lead electrode 6 (6a, 6b) is formed continuously from the piezoelectric electrode 2 (2a, 2b) and integrally with the piezoelectric electrode 2 (2a, 2b), and electrically connects the subsequent electric circuit and the piezoelectric electrode. At least at the peripheral portion of the end surface 9 of the polymer piezoelectric film, the electrodes on the adjacent surfaces, that is, the piezoelectric electrode and the lead electrode may not overlap (do not form the piezoelectric element). It is necessary from the viewpoint of preventing discharge. The lead electrodes are preferably made of the same material as the piezoelectric electrodes, but need not have the same width.

In the laminated piezoelectric element including an even number of piezoelectric elements as in this example, both surface electrodes 2a and 6a of the element as a whole have the same polarity, and if they are grounded to the housing, they are electrically insulated on the high voltage side. Is preferred, which is preferable.

In this example, the adjacent polymer piezoelectric films 1 perform mechanical (acoustic) -electrical conversion due to contraction / expansion deformation in the thickness direction with polarization directions (arrows) opposite to each other. Although it has a suitable configuration, an electro-mechanical conversion element such as a bimorph oscillator has an unbalanced combination in which the polarization directions are laminated in one direction at the same direction. It does not have to be oriented.

FIG. 3 ((a) is a front view, (b) is a right side view) and FIG. 4 (a plan view) show a second embodiment of the laminated piezoelectric element of the present invention. In the laminated piezoelectric element 10b of this example, a plurality of polymer piezoelectric films 1 each having a sprayed piezoelectric electrode 12 (12a or 12b) provided on the upper surface thereof are connected to the respective piezoelectric electrodes 12a and 12b and lead electrodes 16a. 16b are laminated via the adhesive layer 3 so that they are alternately arranged on the left and right, and the lead electrode 16a, which is an extension of the sprayed electrode 12a extended to the right end face, is fully connected by the short wire 7a, The lead electrode 16b, which is an extension of the sprayed electrode 12b extending to the left end face, is fully connected by a short-circuit wire 7b. The margins 8 are provided in three directions along the three sides of the upper and lower surfaces of the polymer piezoelectric film 1. The short-circuit wire 7 (7a, 7b) can be formed as a sprayed electrode as well, and can be a foil electrode attached via a conductive adhesive or a coated electrode of a conductive paste. The short-circuit line 7 can be formed on the entire right and left side surfaces of the laminated element, but as shown in the drawing, the short-circuit line 7 is partially and gradually laterally arranged so as not to prevent deformation of the laminated piezoelectric element 10b in the thickness direction. It is preferable to form them in a staggered manner. Further, a vapor deposition electrode may be used instead of the sprayed electrode 12 (including the lead electrode 16 portion).

Further, examples of the material of the sprayed electrodes 12, 16 include copper, aluminum, zinc, etc. Among them, an electrode that can be sprayed at a relatively low temperature and has excellent solderability of lead wires Zinc or an alloy of zinc and copper or the like which gives a film is preferably used. The thickness of the sprayed electrode is, for example, in the range of 10 to 200 μm. The details of the thermal spraying electrode which can be used in the present invention are disclosed in the specification of Japanese Patent Application No. 3-356667.

The vapor deposition electrode used in the present invention has a thickness of, for example, 0.01 to 0.2 μm, in particular, 0. It is preferably formed in the range of 02 to 0.1 μm. Further, instead of the vapor deposition electrode, an electrode formed by plating, particularly electroless plating to a thickness of about 10 to 100 μm can be used.

In the case of the second embodiment, the number of the adhesive layers 3 can be reduced to almost half of that of the first embodiment.

FIG. 5 is a sectional view of a laminated piezoelectric element according to a third embodiment of the present invention when laminated and assembled, and FIG. 6 is a developed plan view of the same. FIG. 5 corresponds to a sectional view taken along line VV of the device shown in FIG.

This laminated piezoelectric element 10c is a piezoelectric electrode 2a composed of rectangular foil electrodes separated from each other on the surface of a polymer film 1 having a horizontally elongated strip-like developed shape, and is continuously integrated with the piezoelectric electrode 2a. A lead electrode 6a to be connected to each other is provided, a margin 8a is formed on the other portion, and a piezoelectric electrode 2b made of the same rectangular foil electrode is formed on the back surface at a position facing the piezoelectric electrode 2a on the front surface. A lead-shaped piezoelectric element having a lead electrode 6b continuously connected to and connected to it and a margin 8b formed in the other portion, and the lead electrodes 6 (6a, 6b) between the respective piezoelectric electrodes 2 (2a, 2b) are provided. The parts D are alternately folded in opposite directions. The lead electrodes 6a and 6b in this example also have the function of the short-circuit wire 4 (4a, 4b) in the first embodiment or the short-circuit wire 7 (7a, 7b) in the second embodiment, and accordingly, the multi-layered electrodes are formed. Wiring in the laminated piezoelectric element is facilitated. At this time, the polarization direction in the polymer piezoelectric film 1 automatically becomes opposite between the adjacent polymer piezoelectric layers as in FIG. Further, in this embodiment, the intermediate piezoelectric element has no end face in the length direction of the polymer piezoelectric film 1, which is advantageous for leakage current and discharge. In this embodiment, the lead electrodes 6a and 6b do not overlap each other, that is, the piezoelectric effect is not exhibited, but this is effective in improving the directionality of the wave transmission / reception sensitivity.

[0031]

[Production example]

 The laminated piezoelectric element having the structure of FIG. 1 was manufactured as follows. However, the width of the lead electrode 6 is the same as the width of the piezoelectric electrode 2.

A vinylidene fluoride (VDF) / trifluoroethylene (TrFE) copolymer having a molar ratio of 75/25 was sheet extruded at a die temperature of 265 ° C., heat-treated at 125 ° C. for 13 hours, and then subjected to an electric field of 75 MV / m. A polarization treatment was carried out at a temperature of 100 ° C. for 5 minutes and for a total of 1 hour including the ascending / descending time to obtain a polymer piezoelectric film 1 having a thickness of 500 μm, and both surfaces thereof were roughened.

On a copper foil 6 having a thickness of 70 μm with both surfaces roughened, a polyester adhesive (Toron Co., Ltd. <Byron 30SS> and Nippon Urethane Co., Ltd. <Coronate L> 99: 1 (weight: Ratio) The mixture was coated on both sides with a flow coater to a thickness of 10 μm, and the film obtained above was also coated with the adhesive mixture on both sides.

The piezoelectric film and copper foil were vacuum dried at 70 ° C. for 2 hours or more to remove the solvent and accelerate the urethane reaction.

Next, the adhesive-coated piezoelectric film 1 obtained above was cut into a size of 8 × 8 cm, and the adhesive-coated copper foil was cut into a size of 7 × 8 cm. These were cut alternately and the polarization directions of adjacent piezoelectric films were cut. So that the margins 8 are reversed so that the margin 8 has a width of 5 mm in the three directions of the piezoelectric film 1, and 10 layers are adhered as a piezoelectric body, and are removed under the conditions of 90 ° C. and 40 kg / cm ^2. It was made to be a laminate. In this laminated body, lead electrodes 6a and 6b having a width of 5 mm are provided so as to project. The dimensions of the piezoelectric electrodes 2a and 2b are 70 × 70 mm.

The insulation between the lead electrodes 6a and 6b of the thus obtained laminated piezoelectric element was examined at a direct current of 1 KV, but there was no phenomenon leading to leakage current or edge discharge. Moreover, hydrostatic piezoelectric constant of each layer (d _h constant) is in the range of 13.4~14.2pC / N, laminate piezoelectric element is obtained having a substantially uniform piezoelectric characteristics. The d _h constant was determined as follows.

A sample element is immersed in silicon oil placed in a pressure resistant container, and a charge amount Q (Coulomb (C)) of the sample is applied while applying a pressure P (Newton (N) / m ² ) from a nitrogen gas source to the container. To measure. Then give increment dQ of electric load for the pressure increase dp in the vicinity gauge pressure 2 kg / cm ^2, was calculated by the following _{equation: d h = (dQ / dP} ) / A unit is C / N. Here, A is the electrode area (m ² ).

[0038]

【effect】

 As described above, according to the present invention, the electrode is removed from the peripheral edge of the polymer piezoelectric film as much as possible, and the lead electrode is provided at a position corresponding to the electrode absent portion (margin) of the facing surface. Even with a comparatively thin polymer piezoelectric body, the distance between the electrodes on both sides of the end face becomes longer, and the leakage current through the end face of the piezoelectric body due to short-circuiting or approaching of the double-sided electrodes due to the burr etc. or high generated voltage, The occurrence of edge discharge is effectively prevented. In addition, it becomes easy to take out the lead wire while effectively preventing a short circuit with an adjacent electrode during stacking.

[Brief description of drawings]

FIG. 1 is a front view showing a laminated structure of a piezoelectric element according to a first embodiment of the present invention.

FIG. 2 is a corresponding plan view of the piezoelectric element of FIG.

3A is a front view showing a laminated structure of a piezoelectric element according to a second embodiment of the present invention, and FIG. 3B is a corresponding right side view.

FIG. 4 is a plan view of the piezoelectric element shown in FIG.

FIG. 5 is a sectional view showing a laminated structure of a piezoelectric element according to a third embodiment of the present invention.

FIG. 6 is a developed plan view of the piezoelectric element shown in FIG.

[Explanation of symbols]

 1: Polymer piezoelectric film 2 (2a, 2b): Foil piezoelectric electrode 3: Adhesive layer 4 (4a, 4b): Short-circuit wire 5 (5a, 5b): Terminal (wire) 6 (6a, 6b): Foil lead Electrode 7 (7a, 7b): Short-circuit line 8, 8a, 8b: Electrode absent part (margin) 9: Polymer piezoelectric film end face 10a, 10b, 10c: Multilayer piezoelectric element 12 (12a, 12b): Thermal spray piezoelectric electrode 16 (16a, 16b): Thermally sprayed lead electrode

Claims (3)

[Scope of utility model registration request] 1. A laminated piezoelectric element in which at least two or more piezoelectric elements formed of a polymer piezoelectric film or sheet and piezoelectric electrodes arranged on both surfaces thereof are laminated in a plane, and the polymer piezoelectric material is used. An electrode absent portion is formed on the peripheral portion of each surface of the film or sheet, and a lead electrode is formed integrally with the piezoelectric electrode at a predetermined position facing the electrode absent portion on the opposing surface. Piezoelectric element. 2. The laminated piezoelectric element according to claim 1, wherein the electrode absent portion is provided on the entire peripheral edge portion of the surface of the polymer piezoelectric film or sheet except the lead electrode portion. 3. The laminate according to claim 1, wherein the piezoelectric electrode and the lead electrode integrated with the piezoelectric electrode are made of metal foil, and the lead electrode is continuously provided so as to protrude to the outside of the piezoelectric element. Piezoelectric element.