WO2018123354A1 - Piezoelectric element - Google Patents

Piezoelectric element Download PDF

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Publication number
WO2018123354A1
WO2018123354A1 PCT/JP2017/041775 JP2017041775W WO2018123354A1 WO 2018123354 A1 WO2018123354 A1 WO 2018123354A1 JP 2017041775 W JP2017041775 W JP 2017041775W WO 2018123354 A1 WO2018123354 A1 WO 2018123354A1
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Prior art keywords
lead wire
external electrode
reaction layer
piezoelectric element
cross
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PCT/JP2017/041775
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French (fr)
Japanese (ja)
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康弘 浅倉
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京セラ株式会社
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Priority to JP2018558905A priority Critical patent/JP6923560B2/en
Publication of WO2018123354A1 publication Critical patent/WO2018123354A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/16—Measuring force or stress, in general using properties of piezoelectric devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/30—Piezoelectric or electrostrictive devices with mechanical input and electrical output, e.g. functioning as generators or sensors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/50—Piezoelectric or electrostrictive devices having a stacked or multilayer structure
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details
    • H10N30/87—Electrodes or interconnections, e.g. leads or terminals

Definitions

  • the present disclosure relates to a piezoelectric element used as a pressure sensor element.
  • a piezoelectric element can be used as the pressure sensor element.
  • the piezoelectric element includes, for example, a laminated body in which piezoelectric bodies and internal electrodes are alternately laminated, an external electrode that is provided on a side surface of the laminated body and is electrically connected to the internal electrode, and an electrical electrode electrically connected to the external electrode. Connected lead wires.
  • a reaction layer of an external electrode and a lead wire is provided at a joint portion between the external electrode and the lead wire is known (see, for example, Patent Documents 1 and 2).
  • the piezoelectric element of the present disclosure includes a laminated body in which piezoelectric bodies and internal electrodes are alternately laminated, an external electrode that is provided on a side surface of the laminated body and is electrically connected to the internal electrode, and an electrical electrode connected to the external electrode. Connected lead wires. Furthermore, it has a reaction layer of the external electrode and the lead wire at a joint portion between the external electrode and the lead wire, and the reaction layer is a cross section perpendicular to the axial direction of the lead wire, While having a width along the lead wire, the thickness of the central portion of the width is the largest.
  • FIG. 2 is an enlarged view of a main part of a cross section taken along line II-II shown in FIG.
  • FIG. 5 is an enlarged view of a main part of a cross section taken along line VV shown in FIG. 4.
  • An object of the present invention is to provide a piezoelectric element having excellent stability over a long period of time in an environment.
  • FIG. 1 is a schematic perspective view showing an example of an embodiment of a piezoelectric element
  • FIG. 2 is an enlarged view of a main part of a cross section taken along line II-II shown in FIG.
  • the piezoelectric element 1 shown in FIGS. 1 and 2 includes a laminated body 2 in which piezoelectric bodies 21 and internal electrodes 22 are alternately laminated, and an external body that is provided on a side surface of the laminated body 2 and is electrically connected to the internal electrodes 22.
  • An electrode 3 and a lead wire 4 electrically connected to the external electrode 3 are provided.
  • the reaction layer 5 of the external electrode 3 and the lead wire 4 is provided at the joint portion between the external electrode 3 and the lead wire 4, and the reaction layer 5 is viewed in a cross section perpendicular to the axial direction of the lead wire 4.
  • the thickness of the central portion of the width is the thickest.
  • the laminated body 2 has a portion where the piezoelectric bodies 21 and the internal electrodes 22 are alternately stacked, and a portion where only the piezoelectric bodies 21 provided at both ends in the stacking direction are stacked.
  • the laminated body 2 has a rectangular column shape (rectangular shape) having a length of 0.5 to 10 mm, a width of 0.5 to 10 mm, and a height of 1 to 100 mm, for example.
  • the laminated body 2 may have a hexagonal prism shape, an octagonal prism shape, a cylindrical shape, or the like.
  • the piezoelectric body 21 constituting the laminate 2 is made of ceramics having piezoelectric characteristics.
  • a ceramic for example, a perovskite oxide made of lead zirconate titanate (PbZrO 3 —PbTiO 3 ), lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), or the like can be used.
  • the thickness of the piezoelectric body 21 is 3 to 250 ⁇ m, for example.
  • the internal electrode 22 constituting the laminate 2 is fired at the same time as the ceramic that becomes the piezoelectric body 21.
  • a conductor mainly composed of a silver-palladium alloy or a conductor containing copper, platinum, or the like can be used.
  • the internal electrode 22 includes first internal electrodes 221 and second internal electrodes 222 that are alternately arranged.
  • the first internal electrode 221 and the second internal electrode 222 are each a laminated body. 2 are alternately drawn to a pair of opposing side surfaces, and are electrically connected to a pair of external electrodes 3 provided on the side surfaces of the laminate 2 described later.
  • the thickness of the first internal electrode 221 and the second internal electrode 222 is, for example, 0.1 to 5 ⁇ m.
  • the laminate 2 may include a metal layer that is a layer for relaxing stress and does not function as an internal electrode.
  • external electrodes 3 are respectively provided on the pair of side surfaces of the stacked body 2 that one of the end surfaces of the first internal electrode 221 and the second internal electrode 222 reaches, and the first internal electrode 221 or the second internal electrode 222 It is electrically connected to the internal electrode 222.
  • the external electrode 3 can be produced by baking a conductive paste containing a metal such as Ag or Cu.
  • the thickness of the external electrode 3 is set to 5 to 70 ⁇ m.
  • the lead wire 4 is joined to the external electrode 3 and is electrically connected.
  • the external electrode 3 is electrically connected to an external circuit via the lead wire 4.
  • the lead wire 4 for example, a metal wire made of copper or the like having a cross-sectional shape such as a polygon such as a quadrangle, a circle or an ellipse can be used.
  • a copper wire having a diameter of 50 to 500 ⁇ m and having a surface plated with Ni, or a copper wire having a surface enamel-coated can be used.
  • reaction layer 5 of the external electrode 3 and the lead wire 4 at a joint portion between the external electrode 3 and the lead wire 4. Further, the reaction layer 5 has a width along the lead wire 4 when viewed in a cross section perpendicular to the axial direction of the lead wire 4, and the thickness of the central portion of the width is the largest.
  • the stress caused by the difference in thermal expansion between the reaction layer 5 of the external electrode 3 and the lead wire 4 and the member (external electrode 3 or lead wire 4) adjacent thereto is applied to the central portion (lead of the width of the reaction layer 5).
  • the central portion where the reaction layer 5 is thick has a large amount of thermal expansion and is subjected to thermal stress, but the end portion where the reaction layer 5 is thin has a small amount of thermal expansion and can hardly be subjected to thermal stress.
  • the reaction layer 5 is a layer formed by melting at least one of the external electrode 3 and the lead wire 4 when they are joined.
  • the reaction layer 5 shown in the figure has a shape in which the thickness gradually increases from the end in the width direction toward the center when viewed in a cross section perpendicular to the axial direction of the lead wire 4. The shape may be such that the thickness is increased.
  • the reaction layer 5 is a layer formed by a reaction of a part of the external electrode 3 and a part of the lead wire 4, and it cannot be said that it is a part of the external electrode 3 or a part of the lead wire 4.
  • the reaction layer 5, the external electrode 3, and the lead wire 4 are different members.
  • the thickness of the thickest part of the reaction layer 5 is, for example, 5 to 50 ⁇ m.
  • the width of the reaction layer 5 is appropriately determined according to the shape and width of the lead wire 4.
  • Convex shape convex toward the electrode 3 for example, convex curve shape
  • convex shape where the boundary between the reaction layer 5 and the lead wire 4 is convex toward the lead wire 4 side convex shape that is convex at either side boundary, etc.
  • convex shape here is convex curve shape, for example.
  • the reaction layer 5 when viewed in a cross section perpendicular to the axial direction of the lead wire 4, the reaction layer 5 may have a convex curve shape on both the external electrode 3 side and the lead wire 4 side. That is, when viewed in a cross section perpendicular to the axial direction of the lead wire 4, the boundary between the reaction layer 5 and the external electrode 3 has a convex curve shape that protrudes toward the external electrode 3, and the reaction layer 5 and the lead wire 4.
  • the boundary may be a convex curve shape that protrudes toward the lead wire 4.
  • FIG. 5 which is an enlarged view of the main part of the cross section taken along the line VV shown in FIGS. 3, 4 and 4, the joint portion 41 with the external electrode 3 in the lead wire 4 You may swell in the width direction rather than the site
  • a joint portion 41 to be joined to the external electrode as the lead wire 4 is processed into a shape swelled in the width direction in advance.
  • the lead wire 4 when the lead wire 4 is joined to the external electrode 3 by pressing a heat source against the lead wire 4, the lead wire 4 is crushed and swells in the width direction simultaneously with this joining.
  • An elliptical joining portion 41 is provided.
  • a heat source made of a metal rod whose tip is heated to 700 to 1200 ° C. or a ceramic rod such as alumina is pressed onto the lead wire 4 made of enamel-coated copper wire, so that the copper constituting the lead wire 4 is made. While melting, the heat source is joined by applying more pressure.
  • the joining portion 41 of the lead wire 4 has a shape swelled in the width direction.
  • the lead wire 4 while the copper of the lead wire 4 reacts with the silver of the external electrode 3, the lead wire 4 has a width along the lead wire 4 and the reaction layer 5 having the thickest central portion of the width is formed. Is joined to the external electrode 3.
  • the width of the lead wire 4 when viewed from the front is, for example, 0.2 to 2 mm
  • the joint portion with the external electrode 3 is, for example, 1.5 to 2.5 times.
  • the outer peripheral shape when the reaction layer 5 is viewed from the front approaches a circular shape, and the central portion that is the thickest part of the reaction layer 5 where stress is concentrated is the entire outer periphery (end). Therefore, the stress on the edge of the interface can be further reduced.
  • the cross-sectional shape obtained by cutting at least a portion of the lead wire 4 excluding the joint portion 41 with the external electrode 3 with a cross section perpendicular to the axial direction may be circular. With such a shape, there is no edge on the outer periphery of the portion of the lead wire 4 excluding the joint portion with the external electrode 3, and there is no portion where the vibration is concentrated. Can contribute to attenuation. In addition, since noise easily propagates to the space outside the lead wire 4, vibration noise of the electric signal transmitted through the lead is reduced.
  • the external electrode 3 contains a lot of glass on the laminated body 2 side in the thickness direction.
  • the layer on the laminate 2 side can be a layer containing a large amount of glass
  • the layer on the outer surface side can be a layer having a small amount of glass.
  • the reaction layer 5 can be formed only at the portion where the lead wire 4 and the external electrode 3 are in contact with each other.
  • the reaction proceeds so that the reaction layer 5 can be provided also on the portion of the lead wire 4 that is not in contact with the external electrode 3.
  • a ceramic green sheet to be the piezoelectric body 21 is produced. Specifically, a calcined powder of piezoelectric ceramic, a binder made of an acrylic or butyral organic polymer, and a plasticizer are mixed to prepare a slurry. And a green sheet is produced using this slurry by using tape molding methods, such as a doctor blade method and a calender roll method.
  • the piezoelectric ceramic any material having piezoelectric characteristics may be used.
  • a perovskite oxide made of lead zirconate titanate (PbZrO 3 —PbTiO 3 ) can be used.
  • the plasticizer dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.
  • a conductive paste to be the internal electrode 22 is produced.
  • a conductive paste is prepared by adding and mixing a binder and a plasticizer to a metal powder of a silver-palladium alloy. This conductive paste is applied on the green sheet in the pattern of the internal electrodes 22 using a screen printing method. Further, a plurality of green sheets on which this conductive paste is printed are stacked, debindered at a predetermined temperature, fired at a temperature of 900 to 1200 ° C., and then a predetermined shape using a surface grinder or the like.
  • the laminated body 2 including the piezoelectric bodies 21 and the internal electrodes 22 that are alternately laminated is manufactured by performing a grinding process.
  • the laminate 2 is not limited to the one produced by the above manufacturing method, and any production method can be used as long as the laminate 2 formed by laminating a plurality of piezoelectric bodies 21 and internal electrodes 22 can be produced. It may be produced.
  • the external electrode 3 is formed on the side surface of the multilayer body 2 in order to perform electrical exchange between the internal electrode 22 and the outside.
  • the external electrode 3 can be formed by the method described below.
  • a conductive paste is produced by, for example, admixing silver powder, copper powder and a plasticizer.
  • a pattern of the external electrode 3 is formed by controlling the predetermined thickness and width of the conductive paste at a position where the internal electrode 22 on the side surface of the laminate 2 is exposed using a screen printing method or a dispensing method. For example, a thickness of 5 to 70 ⁇ m is applied and baked at a temperature of 500 to 800 ° C.
  • the conductive paste may contain glass powder, or may be applied in two stages with different amounts of glass powder.
  • a lead wire 4 is formed by pressing a heat source made of a metal rod whose tip is heated to 700 to 1200 ° C. or a ceramic rod such as alumina from the lead wire 4 made of enamel-coated copper wire.
  • the heat source is further pressure-bonded while melting copper.
  • the reaction layer 5 having a width along the lead wire 4 and the thickest central portion of the width can be formed. Can be produced.
  • the reaction layer 5 is unlikely to protrude toward the external electrode 3 and tends to protrude toward the lead wire 4.
  • the joint portion 41 of the lead wire 4 is not crushed, and only the central portion of the reaction layer 5 is thickened.
  • the lead wire 4 plated with Ni on the surface of the copper wire is used and only the joint portion 41 is stripped of the Ni plating to expose the copper, only that portion becomes easy to react and only the central portion of the reaction layer 5 is exposed. Can be made thicker.
  • the piezoelectric element of the example was manufactured as follows.
  • a ceramic slurry was prepared by mixing calcined powder of a piezoelectric ceramic mainly composed of lead zirconate titanate (PbZrO 3 —PbTiO 3 ) having an average particle size of 0.4 ⁇ m, a binder and a plasticizer. Using this ceramic slurry, a ceramic green sheet serving as a piezoelectric body having a thickness of 50 ⁇ m was prepared by a doctor blade method.
  • a piezoelectric ceramic mainly composed of lead zirconate titanate (PbZrO 3 —PbTiO 3 ) having an average particle size of 0.4 ⁇ m, a binder and a plasticizer.
  • a binder was added to the silver-palladium alloy to produce a conductive paste to be an internal electrode.
  • a conductive paste serving as an internal electrode was printed on one side of the ceramic green sheet by a screen printing method, and 50 layers of ceramic green sheets on which the conductive paste was printed were formed. A total of 10 ceramic green sheets not printed with the conductive paste serving as the internal electrode were laminated on the top and bottom of the 50 ceramic green sheets printed with the conductive paste serving as the internal electrode. Then, it was fired at 980 to 1100 ° C. and ground to a predetermined shape using a surface grinder to obtain a 3 mm square laminate.
  • an external electrode was formed by screen printing a conductive paste containing Ag on the side surface of the laminate.
  • a reaction layer shown in FIG. 2 was prepared as an example (sample 1).
  • the lead wire is an enamel-coated copper wire with a diameter of 150 ⁇ m
  • an alumina ceramic rod whose tip is heated to 800 to 900 ° C. is pressed against the lead wire, and copper and silver Bonding was performed while forming the reaction layer.
  • the lead wire starts to melt, it is pressed against the external electrode with a force of 5 to 10 N and reacted for 15 to 30 seconds while spreading the lead wire, so that it gradually increases from the end in the width direction toward the center.
  • a reaction layer having a large thickness was formed.
  • a reaction layer having an end in the width direction thicker than the central portion was prepared. Specifically, a laser welding method was used to melt from the outside of the reaction layer, thereby increasing the thickness of the end in the width direction.
  • the pressure sensor output was measured by applying an external force and extracting the charge.
  • an external force of about 1,000 N was applied, a charge of about 15 mC was obtained.
  • the piezoelectric element of Sample 1 as an example was free from cracks around the end of the reaction layer. Furthermore, when the output signal of this piezoelectric element was evaluated, a value equivalent to that before the durability test was obtained, and the characteristics were not deteriorated.
  • the piezoelectric element of Sample 2 as a comparative example has a crack at the end of the reaction layer as a result of SEM analysis, and when the cross section near the end is observed, the crack at the end is inside the reaction layer. It was progressing to. Furthermore, when the output signal of the sample 2 was measured, a value 30% lower than that before the reliability test was obtained, which was deteriorated.
  • the piezoelectric element of the present disclosure has reduced stress due to the difference in thermal expansion between the reaction layer of the external electrode and the lead wire and a member adjacent to the reaction layer, and cracks are suppressed. It turns out that it is excellent.

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  • General Physics & Mathematics (AREA)
  • General Electrical Machinery Utilizing Piezoelectricity, Electrostriction Or Magnetostriction (AREA)
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Abstract

A piezoelectric element 1 according to the present disclosure is provided with a laminate 2 in which a piezoelectric body 21 and an internal electrode 22 are alternatingly laminated, an external electrode 3 which is provided to a side face of the laminate 2 and is electrically connected to the internal electrode 22, and a lead wire 4 which is electrically connected to the external electrode 3. Furthermore, a reaction layer 5 of the external electrode 3 and the lead wire 4 is provided at the site where the external electrode 3 and the lead wire 4 join. The reaction layer 5 has a thickness which matches the lead wire 4 when viewed in a cross-section perpendicular to the axial direction of the lead wire 4, the thickness of the central section of the width being greatest. Stress caused by a difference in thermal expansion between the reaction layer 5 of the external electrode 3 and the lead wire 4 and neighboring members is thereby reduced, making it possible to suppress cracks.

Description

圧電素子Piezoelectric element
　本開示は、圧力センサ素子として用いられる圧電素子に関する。 The present disclosure relates to a piezoelectric element used as a pressure sensor element.
　圧力センサ素子として圧電素子を用いることができる。圧電素子は、例えば、圧電体および内部電極が交互に積層された積層体と、該積層体の側面に設けられて内部電極に電気的に接続された外部電極と、該外部電極に電気的に接続されたリード線とを備える。この圧電素子として、外部電極とリード線との接合部位に、外部電極とリード線との反応層を有している例が知られている（例えば、特許文献１，２を参照）。 A piezoelectric element can be used as the pressure sensor element. The piezoelectric element includes, for example, a laminated body in which piezoelectric bodies and internal electrodes are alternately laminated, an external electrode that is provided on a side surface of the laminated body and is electrically connected to the internal electrode, and an electrical electrode electrically connected to the external electrode. Connected lead wires. As this piezoelectric element, an example in which a reaction layer of an external electrode and a lead wire is provided at a joint portion between the external electrode and the lead wire is known (see, for example, Patent Documents 1 and 2).
特開２０１２－４９４２６号公報JP 2012-49426 A 特開２００８－６６５６０号公報JP 2008-66560 A
　本開示の圧電素子は、圧電体および内部電極が交互に積層された積層体と、該積層体の側面に設けられて前記内部電極に電気的に接続された外部電極と、該外部電極に電気的に接続されたリード線とを備える。さらに、前記外部電極と前記リード線との接合部位に前記外部電極および前記リード線の反応層を有し、該反応層は、前記リード線の軸方向に垂直な断面で見たときに、前記リード線に沿った幅を有するとともに、当該幅の中央部の厚みが最も厚くなっている。 The piezoelectric element of the present disclosure includes a laminated body in which piezoelectric bodies and internal electrodes are alternately laminated, an external electrode that is provided on a side surface of the laminated body and is electrically connected to the internal electrode, and an electrical electrode connected to the external electrode. Connected lead wires. Furthermore, it has a reaction layer of the external electrode and the lead wire at a joint portion between the external electrode and the lead wire, and the reaction layer is a cross section perpendicular to the axial direction of the lead wire, While having a width along the lead wire, the thickness of the central portion of the width is the largest.
圧電素子の実施形態の一例を示す概略斜視図である。It is a schematic perspective view which shows an example of embodiment of a piezoelectric element. 図１に示すII－II線で切断した断面の要部拡大図である。FIG. 2 is an enlarged view of a main part of a cross section taken along line II-II shown in FIG. 圧電素子の実施形態の他の例を示す概略斜視図である。It is a schematic perspective view which shows the other example of embodiment of a piezoelectric element. 圧電素子の実施形態の他の例を示す概略斜視図である。It is a schematic perspective view which shows the other example of embodiment of a piezoelectric element. 図４に示すＶ－Ｖ線で切断した断面の要部拡大図である。FIG. 5 is an enlarged view of a main part of a cross section taken along line VV shown in FIG. 4.
　圧力センサ素子への要求として、より強い応力・高温環境下で繰り返し長期間安定に使用できるものが求められている。 Demand for pressure sensor elements is required that can be used repeatedly and stably for a long time under stronger stress and high temperature environment.
　しかしながら、従来の圧電素子を圧力センサ素子として高温環境下で使用すると、熱膨張差に起因して、外部電極およびリード線の反応層と外部電極との界面または外部電極およびリード線の反応層とリード線との界面の端からクラックが入り、クラックが入った部分の抵抗が増加することで、センサとしての感度が下がるおそれがある。 However, when a conventional piezoelectric element is used as a pressure sensor element in a high temperature environment, due to the difference in thermal expansion, the interface between the external electrode and the lead wire reaction layer and the external electrode or the external electrode and the lead wire reaction layer A crack enters from the end of the interface with the lead wire, and the resistance of the cracked portion increases, which may reduce the sensitivity as a sensor.
　本開示は上記事情に鑑みてなされたもので、外部電極およびリード線の反応層とこれに隣接する部材との熱膨張差による応力を低減してクラックの発生を抑制し、より強い応力・高温環境下での繰り返し長期間安定に優れた圧電素子を提供することを目的とする。 The present disclosure has been made in view of the above circumstances, and suppresses the occurrence of cracks by reducing the stress due to the difference in thermal expansion between the reaction layer of the external electrode and the lead wire and the member adjacent thereto, and the stronger stress / high temperature An object of the present invention is to provide a piezoelectric element having excellent stability over a long period of time in an environment.
　以下、本実施形態の圧電素子について図面を参照して説明する。 Hereinafter, the piezoelectric element of the present embodiment will be described with reference to the drawings.
　図１は圧電素子の実施形態の一例を示す概略斜視図であり、図２は図１に示すII－II線で切断した断面の要部拡大図である。 FIG. 1 is a schematic perspective view showing an example of an embodiment of a piezoelectric element, and FIG. 2 is an enlarged view of a main part of a cross section taken along line II-II shown in FIG.
　図１および図２に示す圧電素子１は、圧電体２１および内部電極２２が交互に積層された積層体２と、積層体２の側面に設けられて内部電極２２に電気的に接続された外部電極３と、外部電極３に電気的に接続されたリード線４とを備える。さらに、外部電極３とリード線４との接合部位に、外部電極３およびリード線４の反応層５を有し、反応層５は、リード線４の軸方向に垂直な断面で見たときに、リード線４に沿った幅を有するとともに、当該幅の中央部の厚みが最も厚い。 The piezoelectric element 1 shown in FIGS. 1 and 2 includes a laminated body 2 in which piezoelectric bodies 21 and internal electrodes 22 are alternately laminated, and an external body that is provided on a side surface of the laminated body 2 and is electrically connected to the internal electrodes 22. An electrode 3 and a lead wire 4 electrically connected to the external electrode 3 are provided. Furthermore, the reaction layer 5 of the external electrode 3 and the lead wire 4 is provided at the joint portion between the external electrode 3 and the lead wire 4, and the reaction layer 5 is viewed in a cross section perpendicular to the axial direction of the lead wire 4. In addition to having a width along the lead wire 4, the thickness of the central portion of the width is the thickest.
　積層体２は、圧電体２１と内部電極２２とが交互に積層された部分と、積層方向両端部に設けられた圧電体２１のみが積層された部分とを有している。 The laminated body 2 has a portion where the piezoelectric bodies 21 and the internal electrodes 22 are alternately stacked, and a portion where only the piezoelectric bodies 21 provided at both ends in the stacking direction are stacked.
　この積層体２は、例えば縦０．５～１０ｍｍ、横０．５～１０ｍｍ、高さ１～１００ｍｍの四角柱状（直方体状）にされている。積層体２としては、六角柱形状や八角柱形状、円柱状などであってもよい。 The laminated body 2 has a rectangular column shape (rectangular shape) having a length of 0.5 to 10 mm, a width of 0.5 to 10 mm, and a height of 1 to 100 mm, for example. The laminated body 2 may have a hexagonal prism shape, an octagonal prism shape, a cylindrical shape, or the like.
　積層体２を構成する圧電体２１は、圧電特性を有するセラミックスからなるものである。このようなセラミックスとして、例えばチタン酸ジルコン酸鉛（ＰｂＺｒＯ3－ＰｂＴｉＯ3）からなるペロブスカイト型酸化物、ニオブ酸リチウム（ＬｉＮｂＯ3）、タンタル酸リチウム（ＬｉＴａＯ3）などを用いることができる。この圧電体２１の厚みは、例えば３～２５０μｍとされる。 The piezoelectric body 21 constituting the laminate 2 is made of ceramics having piezoelectric characteristics. As such a ceramic, for example, a perovskite oxide made of lead zirconate titanate (PbZrO 3 —PbTiO 3 ), lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), or the like can be used. The thickness of the piezoelectric body 21 is 3 to 250 μm, for example.
　積層体２を構成する内部電極２２は、圧電体２１となるセラミックスと同時焼成されたものである。内部電極２２の材料として、例えば銀－パラジウム合金を主成分とする導体、あるいは銅、白金などを含む導体を用いることができる。 The internal electrode 22 constituting the laminate 2 is fired at the same time as the ceramic that becomes the piezoelectric body 21. As a material for the internal electrode 22, for example, a conductor mainly composed of a silver-palladium alloy or a conductor containing copper, platinum, or the like can be used.
　内部電極２２は、互い違いに配置された第１の内部電極２２１と第２の内部電極２２２とからなり、図に示す例では、第１の内部電極２２１および第２の内部電極２２２がそれぞれ積層体２の対向する一対の側面に互い違いに引き出されて、後述する積層体２の側面に設けられた一対の外部電極３とそれぞれ電気的に接続されている。第１の内部電極２２１および第２の内部電極２２２の厚みは、例えば０．１～５μｍとされる。 The internal electrode 22 includes first internal electrodes 221 and second internal electrodes 222 that are alternately arranged. In the example shown in the figure, the first internal electrode 221 and the second internal electrode 222 are each a laminated body. 2 are alternately drawn to a pair of opposing side surfaces, and are electrically connected to a pair of external electrodes 3 provided on the side surfaces of the laminate 2 described later. The thickness of the first internal electrode 221 and the second internal electrode 222 is, for example, 0.1 to 5 μm.
　なお、積層体２には、応力を緩和するための層であって、内部電極として機能しない金属層等が含まれていてもよい。 Note that the laminate 2 may include a metal layer that is a layer for relaxing stress and does not function as an internal electrode.
　そして、第１の内部電極２２１および第２の内部電極２２２のいずれか一方の端面が達する積層体２の一対の側面にはそれぞれ外部電極３が設けられ、第１の内部電極２２１または第２の内部電極２２２と電気的に接続されている。この外部電極３は、例えばＡｇやＣｕなどの金属を含んだ導電性ペーストを焼き付けて作製することができる。ここで、外部電極３を積層体２の側面に垂直な横断面で見たときに、外部電極３の厚みは５～７０μｍとされる。 Then, external electrodes 3 are respectively provided on the pair of side surfaces of the stacked body 2 that one of the end surfaces of the first internal electrode 221 and the second internal electrode 222 reaches, and the first internal electrode 221 or the second internal electrode 222 It is electrically connected to the internal electrode 222. The external electrode 3 can be produced by baking a conductive paste containing a metal such as Ag or Cu. Here, when the external electrode 3 is viewed in a cross section perpendicular to the side surface of the multilayer body 2, the thickness of the external electrode 3 is set to 5 to 70 μm.
　外部電極３にはリード線４が接合され、電気的に接続されている。そして、外部電極３はリード線４を介して外部回路と電気的に接続される。 The lead wire 4 is joined to the external electrode 3 and is electrically connected. The external electrode 3 is electrically connected to an external circuit via the lead wire 4.
　また、リード線４としては、例えば四角形など多角形、円形、楕円形などの断面形状を有する銅などからなる金属線を使用することができる。そして、例えば、直径５０～５００μｍで、表面にＮｉメッキが施された銅線や、表面がエナメルコートされた銅線などを使用することもできる。 Further, as the lead wire 4, for example, a metal wire made of copper or the like having a cross-sectional shape such as a polygon such as a quadrangle, a circle or an ellipse can be used. For example, a copper wire having a diameter of 50 to 500 μm and having a surface plated with Ni, or a copper wire having a surface enamel-coated can be used.
　そして、外部電極３とリード線４との接合部位には、外部電極３およびリード線４の反応層５がある。さらに、反応層５は、リード線４の軸方向に垂直な断面で見たときに、リード線４に沿った幅を有するとともに、当該幅の中央部の厚みが最も厚くなっている。 And, there is a reaction layer 5 of the external electrode 3 and the lead wire 4 at a joint portion between the external electrode 3 and the lead wire 4. Further, the reaction layer 5 has a width along the lead wire 4 when viewed in a cross section perpendicular to the axial direction of the lead wire 4, and the thickness of the central portion of the width is the largest.
　これにより、外部電極３およびリード線４の反応層５とこれに隣接する部材（外部電極３あるいはリード線４）との熱膨張差に起因する応力を、反応層５の幅の中央部（リード線４の軸方向に垂直な断面で見たときの幅方向の中央部）に集めることができる。言い換えると、反応層５の厚みの厚い中央部は熱膨張量が大きく熱応力がかかるが、反応層５の厚みの薄い端部は熱膨張量が小さく熱応力がかかりにくくすることができる。その結果、反応層５と外部電極３との界面および反応層５とリード線４との界面の端にクラックが生じるのを抑制することができる。 As a result, the stress caused by the difference in thermal expansion between the reaction layer 5 of the external electrode 3 and the lead wire 4 and the member (external electrode 3 or lead wire 4) adjacent thereto is applied to the central portion (lead of the width of the reaction layer 5). The central portion in the width direction when viewed in a cross section perpendicular to the axial direction of the line 4. In other words, the central portion where the reaction layer 5 is thick has a large amount of thermal expansion and is subjected to thermal stress, but the end portion where the reaction layer 5 is thin has a small amount of thermal expansion and can hardly be subjected to thermal stress. As a result, it is possible to suppress the occurrence of cracks at the interface between the reaction layer 5 and the external electrode 3 and the interface between the reaction layer 5 and the lead wire 4.
　ここで、反応層５とは、外部電極３とリード線４とが接合される際にこれらの少なくとも一方が溶融するなどしてできた層のことである。図に示す反応層５は、リード線４の軸方向に垂直な断面で見たときに、幅方向の端から中央部に向けて漸次厚みが厚くなっている形状であるが、例えば段階的に厚みが厚くなっているような形状であってもよい。 Here, the reaction layer 5 is a layer formed by melting at least one of the external electrode 3 and the lead wire 4 when they are joined. The reaction layer 5 shown in the figure has a shape in which the thickness gradually increases from the end in the width direction toward the center when viewed in a cross section perpendicular to the axial direction of the lead wire 4. The shape may be such that the thickness is increased.
　なお、反応層５は、外部電極３の一部およびリード線４の一部が反応してできた層であって、外部電極３の一部またはリード線４の一部とも言えなくもないが、便宜上反応層５と外部電極３およびリード線４とは異なる部材であるものとする。 The reaction layer 5 is a layer formed by a reaction of a part of the external electrode 3 and a part of the lead wire 4, and it cannot be said that it is a part of the external electrode 3 or a part of the lead wire 4. For convenience, the reaction layer 5, the external electrode 3, and the lead wire 4 are different members.
　反応層５の最も厚い部分の厚みは、例えば５～５０μｍとされる。また、反応層５の幅はリード線４の形状や幅に合わせて適宜決定される。 The thickness of the thickest part of the reaction layer 5 is, for example, 5 to 50 μm. The width of the reaction layer 5 is appropriately determined according to the shape and width of the lead wire 4.
　リード線４の軸方向に垂直な断面で見たときに、幅方向の端から中央部に向けて漸次厚みが厚くなっている形態の例として、反応層５と外部電極３との境界が外部電極３側に凸となる凸状（例えば凸曲線状）、反応層５とリード線４との境界がリード線４側に凸となる凸状、どちら側の境界においても凸となる凸状などの形態が挙げられる。なお、ここでいう凸状とは、例えば凸曲線状である。 As an example of a form in which the thickness gradually increases from the end in the width direction toward the center when viewed in a cross section perpendicular to the axial direction of the lead wire 4, the boundary between the reaction layer 5 and the external electrode 3 is external. Convex shape convex toward the electrode 3 (for example, convex curve shape), convex shape where the boundary between the reaction layer 5 and the lead wire 4 is convex toward the lead wire 4 side, convex shape that is convex at either side boundary, etc. The form is mentioned. In addition, convex shape here is convex curve shape, for example.
　特に、リード線４の軸方向に垂直な断面で見たときに、反応層５が外部電極３側とリード線４側のどちらにも凸曲線状になっている形状であってよい。すなわち、リード線４の軸方向に垂直な断面で見たときに、反応層５と外部電極３との境界が外部電極３側に凸となる凸曲線状であり、反応層５とリード線４との境界がリード線４側に凸となる凸曲線状である形状であってよい。これにより、反応層５の中央部にかかる応力を外部電極３側とリード線４側との両側に分散でき、さらにこれらの界面の端にかかる応力を小さくできる。 Particularly, when viewed in a cross section perpendicular to the axial direction of the lead wire 4, the reaction layer 5 may have a convex curve shape on both the external electrode 3 side and the lead wire 4 side. That is, when viewed in a cross section perpendicular to the axial direction of the lead wire 4, the boundary between the reaction layer 5 and the external electrode 3 has a convex curve shape that protrudes toward the external electrode 3, and the reaction layer 5 and the lead wire 4. The boundary may be a convex curve shape that protrudes toward the lead wire 4. Thereby, the stress applied to the central portion of the reaction layer 5 can be dispersed on both sides of the external electrode 3 side and the lead wire 4 side, and the stress applied to the ends of these interfaces can be reduced.
　また、図３、図４および図４に示すＶ－Ｖ線で切断した断面の要部拡大図である図５に示すように、リード線４における外部電極３との接合部位４１は、他の部位よりも幅方向に膨らんでいてもよい。 Further, as shown in FIG. 5 which is an enlarged view of the main part of the cross section taken along the line VV shown in FIGS. 3, 4 and 4, the joint portion 41 with the external electrode 3 in the lead wire 4 You may swell in the width direction rather than the site | part.
　図３に示す形態は、リード線４として外部電極に接合される接合部位４１があらかじめ幅方向に膨らんだ形状に加工されたものである。 In the form shown in FIG. 3, a joint portion 41 to be joined to the external electrode as the lead wire 4 is processed into a shape swelled in the width direction in advance.
　一方、図４および図５に示す形態は、熱源をリード線４に押し当てるなどしてリード線４を外部電極３に接合する場合に、この接合と同時にリード線４がつぶれて幅方向に膨らんだ形状の接合部位４１が設けられたものである。例えば、先端を７００～１２００℃に加熱した金属棒もしくはアルミナなどのセラミック棒からなる熱源を、エナメルコートされた銅線からなるリード線４の上から押し当てて、リード線４を構成する銅を溶かしながら熱源をさらに圧力をかけて接合させる。このとき、リード線４の接合部位４１が幅方向に膨らんだ形状になる。なお、リード線４の銅が外部電極３の銀と反応して、リード線４に沿った幅を有するとともに、当該幅の中央部の厚みが最も厚い反応層５が形成されつつ、リード線４が外部電極３に接合される。 On the other hand, in the embodiment shown in FIGS. 4 and 5, when the lead wire 4 is joined to the external electrode 3 by pressing a heat source against the lead wire 4, the lead wire 4 is crushed and swells in the width direction simultaneously with this joining. An elliptical joining portion 41 is provided. For example, a heat source made of a metal rod whose tip is heated to 700 to 1200 ° C. or a ceramic rod such as alumina is pressed onto the lead wire 4 made of enamel-coated copper wire, so that the copper constituting the lead wire 4 is made. While melting, the heat source is joined by applying more pressure. At this time, the joining portion 41 of the lead wire 4 has a shape swelled in the width direction. In addition, while the copper of the lead wire 4 reacts with the silver of the external electrode 3, the lead wire 4 has a width along the lead wire 4 and the reaction layer 5 having the thickest central portion of the width is formed. Is joined to the external electrode 3.
　ここで、リード線４を正面に見たときのリード線４の幅（外部電極３との接合部位４１以外の部位の幅）が例えば０．２～２ｍｍのとき、外部電極３との接合部位４１（幅方向に膨らんだ部位）の幅は例えば１．５～２．５倍の幅とされる。 Here, when the width of the lead wire 4 when viewed from the front (the width of the portion other than the joint portion 41 with the external electrode 3) is, for example, 0.2 to 2 mm, the joint portion with the external electrode 3 For example, the width of 41 (the part swollen in the width direction) is, for example, 1.5 to 2.5 times.
　このような形状であることで、反応層５を正面に見たときの外周形状が円形に近づき、応力が集中する反応層５の最も厚みの厚い部分となる中央部が外周（端）の全ての位置からほぼ均等な距離に位置するようになるので、さらに界面の端への応力を小さくできる。 With such a shape, the outer peripheral shape when the reaction layer 5 is viewed from the front approaches a circular shape, and the central portion that is the thickest part of the reaction layer 5 where stress is concentrated is the entire outer periphery (end). Therefore, the stress on the edge of the interface can be further reduced.
　また、図４に示すように、リード線４における少なくとも外部電極３との接合部位４１を除く部位を、軸方向に垂直な断面で切断した断面形状が円形状であってもよい。このような形状であると、リード線４の外部電極３との接合部位を除く部位の外周にエッジが無く、振動が集中するような箇所が無いので、反応層５の界面付近で生じる応力の減衰に寄与することができる。また、ノイズがリード線４の外側の空間に伝搬しやすくなるので、リードを伝わる電気信号の振動ノイズが低減される。 Further, as shown in FIG. 4, the cross-sectional shape obtained by cutting at least a portion of the lead wire 4 excluding the joint portion 41 with the external electrode 3 with a cross section perpendicular to the axial direction may be circular. With such a shape, there is no edge on the outer periphery of the portion of the lead wire 4 excluding the joint portion with the external electrode 3, and there is no portion where the vibration is concentrated. Can contribute to attenuation. In addition, since noise easily propagates to the space outside the lead wire 4, vibration noise of the electric signal transmitted through the lead is reduced.
　また、外部電極３は厚み方向の積層体２側にガラスを多く含んでいるのがよい。例えば銀を主成分とする外部電極３が２層構造であったとき、積層体２側の層をガラスが多く含まれる層とし、外表面側の層をガラスが少ない層とすることができる。このような構成とすると、外部電極３と積層体２との接合強度を大きくするとともに、銀と銅との反応層５中にガラスを分散させた構造とすることができ、反応層５の界面が増えることで応力を緩和させることができる。 Further, it is preferable that the external electrode 3 contains a lot of glass on the laminated body 2 side in the thickness direction. For example, when the external electrode 3 mainly composed of silver has a two-layer structure, the layer on the laminate 2 side can be a layer containing a large amount of glass, and the layer on the outer surface side can be a layer having a small amount of glass. With such a configuration, the bonding strength between the external electrode 3 and the laminate 2 can be increased, and a structure in which glass is dispersed in the reaction layer 5 of silver and copper can be obtained. The stress can be relieved by increasing.
　なお、リード線４として、表面がＮｉメッキされた銅線の場合、リード線４と外部電極３とが接した部分だけに反応層５ができる。一方、リード線４として、表面にＮｉメッキが無い銅線の場合、反応が進行することで、リード線４の外部電極３に接していない部分にも反応層５を設けることができる。 In addition, when the surface of the lead wire 4 is a Ni-plated copper wire, the reaction layer 5 can be formed only at the portion where the lead wire 4 and the external electrode 3 are in contact with each other. On the other hand, when the lead wire 4 is a copper wire with no Ni plating on the surface, the reaction proceeds so that the reaction layer 5 can be provided also on the portion of the lead wire 4 that is not in contact with the external electrode 3.
　次に、本実施形態の圧電素子１の製造方法について説明する。 Next, a method for manufacturing the piezoelectric element 1 of this embodiment will be described.
　まず、圧電体２１となるセラミックグリーンシートを作製する。具体的には、圧電セラミックスの仮焼粉末と、アクリル系，ブチラール系等の有機高分子からなるバインダーと、可塑剤とを混合してスラリーを作製する。そして、ドクターブレード法、カレンダーロール法等のテープ成型法を用いることにより、このスラリーを用いてグリーンシートを作製する。圧電セラミックスとしては圧電特性を有するものであればよく、例えば、チタン酸ジルコン酸鉛（ＰｂＺｒＯ3－ＰｂＴｉＯ3）からなるペロブスカイト型酸化物等を用いることができる。また、可塑剤としては、フタル酸ジブチル（ＤＢＰ），フタル酸ジオクチル（ＤＯＰ）等を用いることができる。 First, a ceramic green sheet to be the piezoelectric body 21 is produced. Specifically, a calcined powder of piezoelectric ceramic, a binder made of an acrylic or butyral organic polymer, and a plasticizer are mixed to prepare a slurry. And a green sheet is produced using this slurry by using tape molding methods, such as a doctor blade method and a calender roll method. As the piezoelectric ceramic, any material having piezoelectric characteristics may be used. For example, a perovskite oxide made of lead zirconate titanate (PbZrO 3 —PbTiO 3 ) can be used. As the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.
　次に、内部電極２２となる導電性ペーストを作製する。具体的には、銀－パラジウム合金の金属粉末にバインダーおよび可塑剤を添加混合することによって導電性ペーストを作製する。この導電性ペーストを上記のグリーンシート上に、スクリーン印刷法を用いて内部電極２２のパターンで塗布する。さらに、この導電性ペーストが印刷されたグリーンシートを複数枚積層し、所定の温度で脱バインダー処理を行なった後、９００～１２００℃の温度で焼成し、平面研削盤等を用いて所定の形状になるよう研削処理を施すことによって、交互に積層された圧電体２１および内部電極２２を備えた積層体２を作製する。 Next, a conductive paste to be the internal electrode 22 is produced. Specifically, a conductive paste is prepared by adding and mixing a binder and a plasticizer to a metal powder of a silver-palladium alloy. This conductive paste is applied on the green sheet in the pattern of the internal electrodes 22 using a screen printing method. Further, a plurality of green sheets on which this conductive paste is printed are stacked, debindered at a predetermined temperature, fired at a temperature of 900 to 1200 ° C., and then a predetermined shape using a surface grinder or the like. The laminated body 2 including the piezoelectric bodies 21 and the internal electrodes 22 that are alternately laminated is manufactured by performing a grinding process.
　なお、積層体２は、上記の製造方法によって作製されるものに限定されるものではなく、圧電体２１と内部電極２２を複数積層してなる積層体２を作製できれば、どのような製造方法によって作製されてもよい。 The laminate 2 is not limited to the one produced by the above manufacturing method, and any production method can be used as long as the laminate 2 formed by laminating a plurality of piezoelectric bodies 21 and internal electrodes 22 can be produced. It may be produced.
　次に、内部電極２２と外部との電気的なやり取りをするために、積層体２の側面に外部電極３を形成する。外部電極３は、以下に述べる方法により形成することができる。最初に、例えば銀粉末や銅粉末および可塑剤を添付混合することで導電性ペーストを作製する。次に、この導電性ペーストを上記の積層体２の側面の内部電極２２が露出している箇所に、スクリーン印刷法やディスペンス方式を用いて所定の厚みや幅を制御して外部電極３のパターンで例えば５～７０μｍの厚さ塗布し、５００～８００℃の温度で焼き付ける。ここで、導電性ペーストにはガラス粉末を含有させてもよく、ガラス粉末の量を異ならせた導電性ペーストを２段階に塗布してもよい。 Next, the external electrode 3 is formed on the side surface of the multilayer body 2 in order to perform electrical exchange between the internal electrode 22 and the outside. The external electrode 3 can be formed by the method described below. First, a conductive paste is produced by, for example, admixing silver powder, copper powder and a plasticizer. Next, a pattern of the external electrode 3 is formed by controlling the predetermined thickness and width of the conductive paste at a position where the internal electrode 22 on the side surface of the laminate 2 is exposed using a screen printing method or a dispensing method. For example, a thickness of 5 to 70 μm is applied and baked at a temperature of 500 to 800 ° C. Here, the conductive paste may contain glass powder, or may be applied in two stages with different amounts of glass powder.
　次に、リード線４を外部電極３に接合する。このとき、例えば、先端を７００～１２００℃に加熱した金属棒もしくはアルミナなどのセラミック棒からなる熱源を、エナメルコートされた銅線からなるリード線４の上から押し当てて、リード線４を構成する銅を溶かしながら熱源をさらに圧力をかけて接合させる。この際、リード線４の溶融が始まってから熱源を押し当てることで、リード線４に沿った幅を有するとともに、当該幅の中央部の厚みが最も厚い反応層５を形成でき、圧電素子１を作製することができる。 Next, the lead wire 4 is joined to the external electrode 3. At this time, for example, a lead wire 4 is formed by pressing a heat source made of a metal rod whose tip is heated to 700 to 1200 ° C. or a ceramic rod such as alumina from the lead wire 4 made of enamel-coated copper wire. The heat source is further pressure-bonded while melting copper. At this time, by pressing the heat source after the melting of the lead wire 4 starts, the reaction layer 5 having a width along the lead wire 4 and the thickest central portion of the width can be formed. Can be produced.
　なお、外部電極３に含まれるガラスの量が多いと反応層５が外部電極３側に凸となりにくく、リード線４側に凸となりやすくなる。 If the amount of glass contained in the external electrode 3 is large, the reaction layer 5 is unlikely to protrude toward the external electrode 3 and tends to protrude toward the lead wire 4.
　また、断面形状が四角形状のリード線の場合において、熱源を押し当てる圧力をあまり加えずに接触させると、リード線４の接合部位４１がつぶれずに、反応層５の中央部だけが厚くなる。特に、銅線の表面にＮｉメッキしたリード線４を用いて、接合部位４１だけＮｉメッキを剥いで銅を露出させておくと、その部位だけ反応しやすくなって、反応層５の中央部のみをより厚くすることができる。 Further, in the case of a lead wire having a quadrangular cross-sectional shape, if contact is made without applying much pressure to press the heat source, the joint portion 41 of the lead wire 4 is not crushed, and only the central portion of the reaction layer 5 is thickened. . In particular, when the lead wire 4 plated with Ni on the surface of the copper wire is used and only the joint portion 41 is stripped of the Ni plating to expose the copper, only that portion becomes easy to react and only the central portion of the reaction layer 5 is exposed. Can be made thicker.
　本開示の圧電素子の実施例について説明する。 Examples of the piezoelectric element according to the present disclosure will be described.
　実施例の圧電素子を以下のようにして作製した。 The piezoelectric element of the example was manufactured as follows.
　まず、平均粒径が０．４μｍのチタン酸ジルコン酸鉛（ＰｂＺｒＯ3－ＰｂＴｉＯ3）を主成分とする圧電セラミックスの仮焼粉末、バインダーおよび可塑剤を混合したセラミックスラリーを作製した。このセラミックスラリーを用いてドクターブレード法により厚み５０μｍの圧電体となるセラミックグリーンシートを作製した。 First, a ceramic slurry was prepared by mixing calcined powder of a piezoelectric ceramic mainly composed of lead zirconate titanate (PbZrO 3 —PbTiO 3 ) having an average particle size of 0.4 μm, a binder and a plasticizer. Using this ceramic slurry, a ceramic green sheet serving as a piezoelectric body having a thickness of 50 μm was prepared by a doctor blade method.
　次に、銀－パラジウム合金にバインダーを加えて、内部電極となる導電性ペーストを作製した。 Next, a binder was added to the silver-palladium alloy to produce a conductive paste to be an internal electrode.
　次に、セラミックグリーンシートの片面に、内部電極となる導電性ペーストをスクリーン印刷法により印刷し、導電性ペーストが印刷されたセラミックグリーンシートを５０層した。また、内部電極となる導電性ペーストが印刷されたセラミックグリーンシート５０枚を中心にして、その上下に、内部電極となる導電性ペーストが印刷されていないセラミックグリーンシート合計１０枚を積層した。そして、９８０～１１００℃で焼成し、平面研削盤を用いて所定の形状に研削して、３ｍｍ角の積層体を得た。 Next, a conductive paste serving as an internal electrode was printed on one side of the ceramic green sheet by a screen printing method, and 50 layers of ceramic green sheets on which the conductive paste was printed were formed. A total of 10 ceramic green sheets not printed with the conductive paste serving as the internal electrode were laminated on the top and bottom of the 50 ceramic green sheets printed with the conductive paste serving as the internal electrode. Then, it was fired at 980 to 1100 ° C. and ground to a predetermined shape using a surface grinder to obtain a 3 mm square laminate.
　次に、外部との電気のやりとりをする為に、積層体の側面にＡｇを含む導電性ペーストをスクリーン印刷により外部電極を形成した。 Next, in order to exchange electricity with the outside, an external electrode was formed by screen printing a conductive paste containing Ag on the side surface of the laminate.
　ここで、実施例（試料１）として図２に示す反応層を作製した。具体的には、リード線は直径１５０μｍのエナメルコートされた銅線を使用し、先端が８００～９００℃に加熱されたアルミナのセラミック棒を使用し、これをリード線に押し当て、銅と銀の反応層を形成しつつ接合を行った。この際、リード線の溶融が始まってから、外部電極上に５～１０Ｎの力で押し当て、リード線を広げながら１５～３０秒間反応させることで、幅方向の端から中央部にいくにつれて徐々に厚みが厚くなる反応層を形成した。 Here, a reaction layer shown in FIG. 2 was prepared as an example (sample 1). Specifically, the lead wire is an enamel-coated copper wire with a diameter of 150 μm, an alumina ceramic rod whose tip is heated to 800 to 900 ° C. is pressed against the lead wire, and copper and silver Bonding was performed while forming the reaction layer. At this time, after the lead wire starts to melt, it is pressed against the external electrode with a force of 5 to 10 N and reacted for 15 to 30 seconds while spreading the lead wire, so that it gradually increases from the end in the width direction toward the center. A reaction layer having a large thickness was formed.
　一方、比較例（試料２）として、反応層が幅方向の端が中央部よりも厚くなるものを作製した。具体的には、レーザー溶接法を用い、反応層の外側から溶融させることで、幅方向の端の厚みが厚くなるものを作製した。 On the other hand, as a comparative example (sample 2), a reaction layer having an end in the width direction thicker than the central portion was prepared. Specifically, a laser welding method was used to melt from the outside of the reaction layer, thereby increasing the thickness of the end in the width direction.
　これらの圧電素子について、外力を加え電荷を取り出す方法にて圧力センサ出力を測定したところ、約１，０００Ｎの外力を加えた時、約１５ｍＣの電荷が得られた。 For these piezoelectric elements, the pressure sensor output was measured by applying an external force and extracting the charge. When an external force of about 1,000 N was applied, a charge of about 15 mC was obtained.
　また、これらの圧電素子について、１，０００Ｎの荷重を２００Ｈｚの振動で１．０×１０9回繰り返し加える耐久性試験を行った。 These piezoelectric elements were subjected to a durability test in which a load of 1,000 N was repeatedly applied 1.0 × 10 9 times at a vibration of 200 Hz.
　その後、実施例である試料１の圧電素子は、反応層付近をＳＥＭ（Ｓｃａｎｎｉｎｇ　Ｅｌｅｃｔｒｏｎ　Ｍｉｃｒｏｓｃｏｐｅ；走査型電子顕微鏡）で分析した結果、反応層の端部周辺にクラックの発生はなかった。さらに、この圧電素子の出力信号を評価すると、耐久性試験前と同等の値が得られ、特性劣化はしていなかった。 Then, as a result of analyzing the vicinity of the reaction layer by SEM (Scanning Electron Microscope), the piezoelectric element of Sample 1 as an example was free from cracks around the end of the reaction layer. Furthermore, when the output signal of this piezoelectric element was evaluated, a value equivalent to that before the durability test was obtained, and the characteristics were not deteriorated.
　これに対し、比較例である試料２の圧電素子は、ＳＥＭの分析の結果、反応層の端部にクラックが有り、端部付近の断面を観察すると、端部にあるクラックが反応層の内部にまで進展していた。さらに、試料２の出力信号を測定すると、信頼性試験前より３０％低い値が得られ、劣化していた。 On the other hand, the piezoelectric element of Sample 2 as a comparative example has a crack at the end of the reaction layer as a result of SEM analysis, and when the cross section near the end is observed, the crack at the end is inside the reaction layer. It was progressing to. Furthermore, when the output signal of the sample 2 was measured, a value 30% lower than that before the reliability test was obtained, which was deteriorated.
　以上の結果から、本開示の圧電素子は、外部電極およびリード線の反応層とこれに隣接する部材との熱膨張差による応力が低減され、クラックが抑制されていて、長期間の耐久性に優れていることがわかる。 From the above results, the piezoelectric element of the present disclosure has reduced stress due to the difference in thermal expansion between the reaction layer of the external electrode and the lead wire and a member adjacent to the reaction layer, and cracks are suppressed. It turns out that it is excellent.
１・・・圧電素子
２・・・積層体
２１・・圧電体
２２・・内部電極
３・・・外部電極
４・・・リード線
５・・・反応層 DESCRIPTION OF SYMBOLS 1 ... Piezoelectric element 2 ... Laminated body 21 .. Piezoelectric body 22 .. Internal electrode 3 ... External electrode 4 ... Lead wire 5 ... Reaction layer

Claims (6)

  1. 　圧電体および内部電極が交互に積層された積層体と、該積層体の側面に設けられて前記内部電極に電気的に接続された外部電極と、該外部電極に電気的に接続されたリード線とを備え、前記外部電極と前記リード線との接合部位に、前記外部電極および前記リード線の反応層を有し、該反応層は、前記リード線の軸方向に垂直な断面で見たときに、前記リード線に沿った幅を有するとともに、当該幅の中央部の厚みが最も厚いことを特徴とする圧電素子。 Laminated bodies in which piezoelectric bodies and internal electrodes are alternately laminated, an external electrode provided on a side surface of the laminated body and electrically connected to the internal electrodes, and a lead wire electrically connected to the external electrodes And a reaction layer of the external electrode and the lead wire at a joint portion between the external electrode and the lead wire, and the reaction layer is viewed in a cross section perpendicular to the axial direction of the lead wire. In addition, the piezoelectric element has a width along the lead wire, and the thickness of the central portion of the width is the largest.
  2. 　前記反応層は、前記リード線の軸方向に垂直な断面で見たときに、幅方向の端から中央部に向けて漸次厚みが厚くなっていることを特徴とする請求項１に記載の圧電素子。 The piezoelectric layer according to claim 1, wherein the reaction layer has a thickness that gradually increases from an end in the width direction toward a center portion when viewed in a cross section perpendicular to the axial direction of the lead wire. element.
  3. 　前記リード線の軸方向に垂直な断面で見たときに、前記反応層と前記外部電極との境界が前記外部電極側に凸となる凸曲線状であり、前記反応層と前記リード線との境界が前記リード線側に凸となる凸曲線状であることを特徴とする請求項１または請求項２に記載の圧電素子。 When viewed in a cross section perpendicular to the axial direction of the lead wire, the boundary between the reaction layer and the external electrode is a convex curve shape that protrudes toward the external electrode, and the reaction layer and the lead wire 3. The piezoelectric element according to claim 1, wherein the boundary has a convex curve shape that is convex toward the lead wire side. 4.
  4. 　前記リード線における前記外部電極との接合部位は、他の部位よりも幅方向に膨らんでいることを特徴とする請求項１乃至請求項３のうちのいずれかに記載の圧電素子。 4. The piezoelectric element according to claim 1, wherein a joint portion of the lead wire with the external electrode swells in a width direction as compared with other portions. 5.
  5. 　前記リード線における少なくとも前記外部電極との接合部位を除く部位を、軸方向に垂直な断面で切断した断面形状が円形状であることを特徴とする請求項１乃至請求項４のうちのいずれかに記載の圧電素子。 5. The cross-sectional shape obtained by cutting at least a portion of the lead wire excluding the joint portion with the external electrode by a cross section perpendicular to the axial direction is a circular shape. 6. The piezoelectric element described in 1.
  6. 　前記外部電極は厚み方向の積層体側にガラスを多く含んでいることを特徴とする請求項１乃至請求項５のうちのいずれかに記載の圧電素子。 The piezoelectric element according to any one of claims 1 to 5, wherein the external electrode includes a large amount of glass on a laminated body side in a thickness direction.
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