JP6348287B2 - Piezoelectric element - Google Patents

Description

  The present invention relates to a piezoelectric element that bends when a voltage is applied.

  There is known a piezoelectric vibrator in which electrodes are formed by baking Ag printing on the front and back of a single plate of a piezoelectric body and bonded to a metal plate (shim) after polarization treatment (for example, see Patent Document 1). FIG. 9 is a perspective view showing such a conventional piezoelectric vibrator 800. Lead wires 850 are connected to the surface of the metal plate 810 by solder 855, and lead wires 860 are also connected to the surface of the electrode 825 by solder 865.

  In the piezoelectric vibrator 800, a piezoelectric element 820 is bonded onto a metal plate 810, and an electrode 825 is provided on the end face of the piezoelectric element 820. When an AC voltage is applied between the metal plate 810 and the electrode 825, the piezoelectric element 820 expands and contracts in the radial direction. On the other hand, since the metal plate 810 does not expand and contract, the piezoelectric vibrator 800 vibrates with warpage.

  The piezoelectric vibrator 800 is used for a sounder, for example. FIG. 10 is a cross-sectional view showing a sounder 900 using a conventional piezoelectric vibrator 800. The sounder 900 includes a case 910, a lid 920, and a piezoelectric vibrator 800. The piezoelectric vibrator 800 is bonded to the edge of the deep hole of the case 910 provided with countersink holes, and the lid 920 is fitted into the case 910. It is worn. The case 910 is provided with terminals 917 and 918, and lead wires 850 and 860 are connected to the terminals 917 and 918, respectively. The sound generated by the piezoelectric vibrator 800 is radiated to the outside through the sound emission hole 915.

  In the piezoelectric vibrator 800, conduction between the metal plate 810 and the electrode of the piezoelectric element 820 is obtained by close adhesion using an adhesive. Moreover, the lead wire is connected to the electrode portion exposed to the outside by soldering.

JP 2007-300426 A

  However, when producing the piezoelectric vibrator as described above, the piezoelectric element must be bonded to a metal having a different thermal expansion coefficient, and the necessity of a heat-resistant adhesive and the thermal expansion coefficient are adjusted. Necessary. In particular, when a piezoelectric vibrator is used as an imposition sounder, the heat resistance of the product depends on the heat resistance of the adhesive that bonds the metal plate and the piezoelectric body.

  In addition, due to the use of Pb-free solder used for reflow, the reflow temperature is on the rise, and there is an urgent need to improve the heat resistance of components used. Epoxy adhesives are generally used for reflow heat resistance applications, but not only heat resistance, but also water absorption, it is desired to improve the heat resistance reliability of the adhesive during reflow.

  Further, the electrical connection with the outside of the piezoelectric element is performed by soldering a lead wire to the Ag or Ag-Pd electrode that has been printed and baked. At that time, the Ag or Ag—Pd conductor used for the laminated inner conductor causes Ag to diffuse into the piezoelectric body when the piezoelectric body is fired, and the Ag erosion due to the solder is large, which causes soldering to be impossible. Moreover, printing and baking the electrode paste after firing the laminate for electrical connection with the outside results in an increase in the number of production steps.

  The present invention has been made in view of such circumstances, and it is possible to eliminate the need for a design for adjusting the heat resistance and thermal expansion coefficient of the adhesive, and to facilitate the manufacture and to prevent the deterioration of the characteristics of the piezoelectric body. An object is to provide an element.

  (1) In order to achieve the above object, a piezoelectric element of the present invention is a piezoelectric element that bends when a voltage is applied, and a piezoelectric element between a plurality of electrode layers to which a voltage is applied and the plurality of electrode layers. A stretchable layer formed of a material that expands and contracts when a voltage is applied, and a shim layer that is formed of the same piezoelectric material as the stretchable layer and does not expand and contract when a voltage is applied. It is integrally formed in a plate shape and is bent by the expansion / contraction of the expansion / contraction layer with respect to the shim layer.

  In this way, the piezoelectric element is formed as an integral structure incorporating a shim structure without using an adhesive, so that it is not necessary to design the heat resistance and thermal expansion coefficient of the adhesive, and manufacturing is facilitated. . In addition, since the piezoelectric element is formed in an integral structure without using a metal plate, the overall thermal expansion coefficient becomes equal, and the deterioration of the characteristics of the piezoelectric body due to thermal strain stress such as in a reflow furnace can be prevented.

  (2) Further, the piezoelectric element of the present invention is characterized in that the stretchable layer and the shim layer form a unimorph type laminated structure. In this way, the stress concentration can be reduced by using the unimorph type.

  (3) Moreover, the piezoelectric element of the present invention is characterized in that the stretchable layer and the shim layer form a bimorph type laminated structure. By using the bimorph type in this way, a large force can be output even at a low voltage.

  (4) Moreover, the piezoelectric element of this invention is characterized by the electrode layer provided in the end surface among said several electrode layers containing Pt. As a result, it is possible to prevent electrode biting when soldering to the electrode layer on the end face.

  (5) Further, the piezoelectric element of the present invention is characterized in that among the plurality of electrode layers, electrode layers to which the same voltage is applied are connected to each other by via-hole electrodes. Thereby, the connection by an external electrode can be eliminated and the electrode erosion at the time of soldering can be prevented. In addition, it is possible to eliminate the need for printing and baking the electrode paste after the baking process, thereby reducing the number of production steps.

  According to the present invention, it is possible to make the manufacturing easy by eliminating the need for designing the heat resistance and thermal expansion coefficient of the adhesive, and to prevent the deterioration of the characteristics of the piezoelectric body.

(A), (b) is the perspective view and sectional drawing which respectively show the piezoelectric element of 1st Embodiment. It is a perspective view which shows the manufacturing method of the piezoelectric element of 1st Embodiment. It is a perspective view which shows the sounder using the piezoelectric element of 1st Embodiment. It is sectional drawing which shows the sounder using the piezoelectric element of 1st Embodiment. (A), (b) is the perspective view and sectional drawing which respectively show the piezoelectric element of 2nd Embodiment. It is a perspective view which shows the manufacturing method of the piezoelectric element of 2nd Embodiment. (A), (b) is the perspective view and sectional drawing which respectively show the piezoelectric element of 3rd Embodiment. It is a perspective view which shows the manufacturing method of the piezoelectric element of 3rd Embodiment. It is a perspective view which shows the conventional piezoelectric vibrator. It is sectional drawing which shows the sounder using the conventional piezoelectric vibrator.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, in order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted.

[First Embodiment]
(Configuration of piezoelectric element)
1A and 1B are a perspective view and a cross-sectional view showing the piezoelectric element 100, respectively. FIG. 1B shows a cross-sectional view taken along the cross-section 1b in FIG. The piezoelectric element 100 includes a plurality of electrode layers 111 and 112, a stretchable layer 120, and a shim layer 130. The piezoelectric element 100 bends when a voltage is applied to the electrode layers 111 and 112, and vibrates when an AC voltage is applied.

  The electrode layers 111 and 112 are made of a conductor such as Ag or Ag—Pd, for example. The electrode layer 111 is formed on the end face of the piezoelectric element 100, and the lead wire 150 is connected by solder 155. The electrode layer 112 is embedded in the piezoelectric element 100. The electrode layer 112 is connected to an electrode layer 112a formed on the end face of the piezoelectric element 100 by a via hole electrode 112b, and a lead wire 160 is connected to the electrode layer 112a by solder 165.

  As described above, in the piezoelectric element 100, among the plurality of electrode layers 111 and 112, the electrode layers to which the same voltage is applied are connected to each other by via-hole electrodes. Thereby, the connection by an external electrode can be eliminated and the electrode erosion at the time of soldering can be prevented. In addition, it is possible to eliminate the need for printing and baking the electrode paste after the baking process, thereby reducing the number of production steps.

  In the via hole electrode connection method, a piezoelectric green in which a hole having a diameter of about 0.1 to 0.2 is formed in a piezoelectric layer, and Ag or Ag-Pd in which the firing shrinkage rate is adjusted with a common material or the like is printed and filled therein. Press and press the sheet. Then, a via-hole electrode is formed by integral firing at a maximum temperature of about 1000 ° C. to 1260 ° C.

  In the piezoelectric element using the via hole electrode connection, the via hole electrode portion is pressure-bonded to the flexible substrate on which the external connection electrode is formed, and the connection is taken out to the outside. Alternatively, Ag and Ag-Pd paste may be printed and fired on the via hole electrode, and the lead wire may be soldered.

  Moreover, it is preferable that the electrode layer 111 provided in the end surface contains Pt. Thereby, when the reflow process is performed to connect the lead wires 150 and 160 to the electrode layer 111 on the end surface with the solder 155 and 165, the biting of the electrode can be prevented. Pt is preferably contained in Ag or Ag—Pd in an amount of 1 wt% or more to constitute an electrode layer, and may be an electrode layer of 100% Pt. Further, in the above example, the connection of the via hole electrode is used, but the connection may be made with an external electrode containing Pt.

  The stretchable layer 120 is formed of a piezoelectric material between the plurality of electrode layers 111 and 112, is polarized in advance, and stretches when a voltage is applied to the electrode layers 111 and 112. An example of the piezoelectric material is PZT.

  The shim layer 130 is formed of the same piezoelectric material as the stretchable layer 120, is not polarized, and does not stretch or contract even when a voltage is applied to the electrode layers 111 and 112. The piezoelectric element 100 is bent by the expansion / contraction of the expansion / contraction layer 120 without expansion / contraction of the shim layer 130.

  In this way, the piezoelectric element 100 is formed by laminating each layer in the thickness direction so as to be integrally formed in a plate shape, and bends when a voltage is applied. Since it is formed as a one-piece structure incorporating a shim structure without using an adhesive, it is not necessary to design an adjustment of the heat resistance and thermal expansion coefficient of the adhesive, which facilitates manufacture. In addition, since it is formed in an integral structure without using a metal plate, the overall thermal expansion coefficient becomes equal, and the deterioration of the characteristics of the piezoelectric body due to thermal strain stress such as in a reflow furnace can be prevented.

  In the example shown in FIGS. 1A and 1B, in the piezoelectric element 100, the stretchable layer 120 and the shim layer 130 form a unimorph type laminated structure. In this way, the stress concentration can be reduced by using the unimorph type.

(Method for manufacturing piezoelectric element)
A method for manufacturing the piezoelectric element 100 configured as described above will be described. FIG. 2 is a perspective view showing a method for manufacturing the piezoelectric element 100. First, piezoelectric green sheets 121, 131, and 132 are prepared by an extrusion molding method, a doctor blade molding method, or the like, and Ag or Ag-Pd paste is applied in a pattern of electrode layers 111, 112, and 112a thereon. It is preferable to print an Ag—Pt or Ag—Pd—Pt paste on the externally exposed electrode.

  These are press-press formed. The green sheet 121 is perforated and filled with a common material in which Ag or Ag—Pd and a piezoelectric material are mixed to form a via hole electrode 112b. After the laminated green sheet compact is cut into a required size, it is fired and sintered at a maximum temperature of 1000 to 1260 ° C. And the piezoelectric element 100 is producible by applying a DC voltage of 1-3 kV / mm with respect to the distance between electrodes to a sintered compact, and performing a polarization process.

  In the piezoelectric element 100, the green sheet 121 portion becomes the stretchable layer 120, and the green sheets 131 and 132 become the shim layer 130. The lead wires 150 and 160 for connection to the outside are soldered to the main body of the polarized piezoelectric element. In the above example, three layers of green sheets are stacked, but the present invention is not limited to three layers and may have a two-layer structure. Moreover, you may shape | mold by the printing lamination method, without using a green sheet.

(Sounder using piezoelectric element)
3 and 4 are a perspective view and a sectional view showing a sounder 200 using the piezoelectric element 100, respectively. The sounder 200 includes a case 210, a lid 220, and the piezoelectric element 100. The case 210 has a countersink hole, and the piezoelectric element 100 is bonded to the edge 211 of the deep hole. The piezoelectric element 100 is bonded in a state where the central portion is floated in a hollow state, the lid 220 is closed, and the piezoelectric element 100 is held inside the case 210.

  The case 210 has terminals 217 and 218 at the edge of the countersink hole, and the lead wires 150 and 160 are connected to the terminals 217 and 218, respectively. By applying alternating current from the terminals 217 and 218 to the electrode layers 111 and 112 of the piezoelectric element 100, the piezoelectric element 100 vibrates. Sound generated by the vibration is radiated to the outside from a sound emitting hole 215 provided at the bottom of the countersink hole.

[Second Embodiment]
(Configuration of piezoelectric element)
In the above-described embodiment, a single layer structure in which bending is generated by a single stretchable layer is possible, but a laminated structure in which a plurality of stretchable layers are provided may be used. FIGS. 5A and 5B are a perspective view and a sectional view showing a piezoelectric element 300 having a laminated structure, respectively. FIG. 5B shows a cross-sectional view taken along the cross-section 5b in FIG.

  The piezoelectric element 300 includes a plurality of electrode layers 311 to 314, a stretchable layer 320, and a shim layer 330. The piezoelectric element 300 bends when a voltage is applied to the electrode layers 311 to 314, and vibrates when an AC voltage is applied. The electrode layer 311 is formed on the end face of the piezoelectric element 300, and the lead wire 150 is connected by solder 155. The electrode layer 311 is connected to the electrode layer 313 by a via hole electrode 312b.

  The electrode layer 312 is embedded in the piezoelectric element 300. The electrode layer 312 is connected to the electrode layer 312a and the electrode layer 314 formed on the end face of the piezoelectric element 300 by the via hole electrode 312b, and a lead wire 160 is connected to the electrode layer 312a by solder 165.

  The stretchable layer 320 is formed of a piezoelectric material between the plurality of electrode layers 311 to 314, is polarized in advance, and stretches and contracts when a voltage is applied to the electrode layers 311 to 314. The shim layer 330 is formed of the same piezoelectric material as the stretchable layer 320, is not polarized, and does not stretch or contract even when a voltage is applied to the electrode layers 311 to 314. The piezoelectric element 100 is bent by the expansion / contraction of the expansion / contraction layer 320 without the expansion / contraction of the shim layer 330.

(Method for manufacturing piezoelectric element)
A method for manufacturing the piezoelectric element 300 configured as described above will be described. FIG. 6 is a perspective view showing a method for manufacturing the piezoelectric element 300. First, piezoelectric green sheets 321-323, 331, 332 are prepared, and Ag or Ag-Pd is formed on the green sheets 321-323, 331 in a pattern of electrode layers 311, 312a, 312, 313, 314, respectively. Apply paste.

  In addition, a hole is formed at the position of the electrode layer 312a of the green sheets 321 to 323 to fill the common material, thereby forming a via hole electrode 312b. 311b is formed. The piezoelectric element 300 can be manufactured by subjecting these to press-press forming and firing, and subjecting the obtained fired body to polarization treatment. In the piezoelectric element 300, the green sheets 321 to 323 become the stretchable layer 320, and the green sheets 331 and 332 become the shim layer 330.

[Third Embodiment]
(Configuration of piezoelectric element)
In each of the above embodiments, the piezoelectric element has a unimorph structure, but may have a bimorph structure. By using the bimorph type in this way, a large force can be output even at a low voltage. FIGS. 7A and 7B are a perspective view and a sectional view showing a piezoelectric element 400 having a bimorph structure, respectively. FIG. 7B shows a cross-sectional view taken along a cross section 7b in FIG.

  The piezoelectric element 400 includes a plurality of electrode layers 411 to 414, a stretchable layer 420, and a shim layer 430. The piezoelectric element 400 bends when a voltage is applied to the electrode layers 411 to 414, and vibrates when an AC voltage is applied. The electrode layer 411 is formed on one end face of the piezoelectric element 400, and lead wires 451 are connected by solder 455. The electrode layer 414 is formed on the other end face of the piezoelectric element 400, and the lead wire 462 is connected by solder.

  The electrode layers 412 and 413 are embedded in the piezoelectric element 400. The electrode layer 412 is connected to an electrode layer 412a formed on one end face of the piezoelectric element 400 by a via hole electrode 412b. A lead wire 461 is connected to the electrode layer 412a by solder 465. The electrode layer 413 is connected to an electrode layer 413a formed on the other end surface of the piezoelectric element 400 by a via hole electrode 413b, and a lead wire 452 is connected to the electrode layer 413a by solder. The same voltage is applied to the lead wires 451 and 452, and the same voltage is applied to the lead wires 461 and 462.

  The stretchable layer 420 is formed of a piezoelectric material between the electrode layers 411 and 412 and between the electrode layers 413 and 414, is polarized in advance, and stretches when a voltage is applied to the electrode layers 411 to 414. The shim layer 430 is formed between the central electrode layers 412 and 413 by the same piezoelectric material as the stretchable layer 420, is not polarized, and does not stretch even when a voltage is applied to the electrode layers 412 and 413. The shim layer 430 does not expand and contract, and the respective elastic layers 420 expand and contract with different expansion and contraction, whereby the piezoelectric element 400 bends.

(Method for manufacturing piezoelectric element)
A method for manufacturing the piezoelectric element 400 configured as described above will be described. FIG. 8 is a perspective view showing a method for manufacturing the piezoelectric element 400. First, piezoelectric green sheets 421, 431, 432, and 422 are prepared, and Ag or Ag-Pd paste is applied thereon in a pattern of electrode layers 411, 412a, 412, 413, 414, and 413a.

  Further, the green sheets 421 and 422 are perforated and filled with a common material to form via hole electrodes 412b and 413b. The piezoelectric element 400 can be manufactured by subjecting these to press-molding, firing, and subjecting the obtained fired body to polarization treatment. In the piezoelectric element 400, the green sheets 421 and 422 become the stretchable layer 420, and the green sheets 431 and 432 become the shim layer 430.

(Use)
The piezoelectric element as described above can be used as an actuator, but is preferably used as a sounding element that requires heat resistance. For example, it is also effective to use it as an imposition type piezoelectric material producing component that requires a soldering method to a circuit board by a reflow furnace. Durability is possible even if there is a step of soldering directly on the surface electrode.

100 Piezoelectric elements 111, 112, 112a Electrode layer 112b Via hole electrode 120 Stretch layer 130 Shim layers 121, 131, 132 Green sheet 150, 160 Lead wires 155, 165 Solder 200 Sounder 210 Case 211 Edge 215 Sound emission hole 217, 218 Terminal 220 Lid 300 Piezoelectric elements 311, 312, 312 a, 313, 314 Electrode layer 312 b Via hole electrode 320 Stretch layer 330 Shim layers 321-323, 331, 332 Green sheet 400 Piezoelectric elements 411, 412 a, 413, 413 a, 414 Electrode layer 412b, 413b Via hole electrode 420 Stretch layer 430 Shim layers 421, 422, 431, 432 Green sheets 451, 452, 461, 462 Lead wires 455, 465 Solder

Claims (3)

A sounder using a piezoelectric element that emits sound waves by applying a voltage,
A case in which a countersink hole with a sound emitting hole provided at the bottom is formed;
The piezoelectric element that is bonded to the case and is held inside the case in a state where the center part is floated in a hollow state,
A lid fitted into the case;
A terminal provided on the case and connected to an electrode of the piezoelectric element;
The piezoelectric element is
A plurality of electrode layers to which a voltage is applied;
A stretchable layer formed of a piezoelectric material between the plurality of electrode layers, and stretchable by application of the voltage;
A shim layer formed of the same piezoelectric material as the stretchable layer and not stretched by application of the voltage,
On the end face of the stretchable layer, one of the plurality of electrode layers and the extraction electrode to which a voltage different from the electrode layer is applied are both exposed and directly formed,
The shim layer does not have an electrode layer inside,
Each of the layers is laminated in the thickness direction and integrally formed in a plate shape,
The stretchable layer and the shim layer form a bimorph type laminated structure,
One end face of the stretchable layer is directly bonded to the case without any other member,
A sounder, wherein the elastic layer bends by expanding and contracting with respect to the shim layer and emits sound waves.   The sounder according to claim 1, wherein an electrode layer provided on the end face among the plurality of electrode layers contains Pt. Wherein among the plurality of electrode layers, the electrode layer which is applied the same voltage, according to claim 1 or claim 2, wherein the sounder, characterized in that it is connected with the via hole electrode from each other.

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