JP6726508B2 - Piezoelectric actuator - Google Patents

Description

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

Conventionally, a bending type piezoelectric actuator based on a bimorph or a unimorph is known (see Patent Document 1). When such a piezoelectric actuator is composed of a thin piezoelectric ceramic body provided with an external electrode of silver and is continuously driven by using, for example, a needle selection device of a sock knitting machine, migration occurs in which silver ions move between the electrodes, Dielectric breakdown may occur. This can be countered by adopting a material that does not easily cause migration as the electrode.

JP, 2005-133415, A

However, if expensive gold or platinum is adopted as the electrode material instead of silver, for example, the material cost will increase. Therefore, in order to reduce the cost, it is necessary to design the shape of the electrode so that the electrode is as thin as possible. When the lead wire is joined to the thin electrode by soldering as described above, the electrode material is eroded by the solder, the joint is weakened, and as a result, the lead wire may come off from the electrode.

Further, although it is possible to use a carbon electrode as a material in which migration does not easily occur, lead wires cannot be soldered to the carbon electrode.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a piezoelectric actuator that can suppress the dielectric breakdown due to migration and can sufficiently maintain the connection between the lead member and the electrode.

(1) In order to achieve the above object, a piezoelectric actuator of the present invention is a piezoelectric actuator that bends when a voltage is applied, the shim plate having elasticity, and a piezoelectric element provided on the main surface of the shim plate. The piezoelectric element is formed in a plate shape, an external electrode formed on a surface of the piezoelectric ceramic body that is less likely to cause migration than silver, and provided on the external electrode. It is characterized in that it comprises a bonding auxiliary layer and a bonding portion for bonding the bonding auxiliary layer and the lead member with solder.

As a result, it is possible to prevent the occurrence of dielectric breakdown due to migration even when continuously driven in an environment of high temperature and high humidity. Further, it is possible to reliably bond the electrode material, which hardly causes migration, to the lead member.

(2) Further, the piezoelectric actuator of the present invention is characterized in that the bonding auxiliary layer is formed to have a thickness of 5 to 30 μm. Thereby, the bonding is strengthened, and the connection between the lead member and the electrode can be firmly maintained.

(3) Further, the piezoelectric actuator of the present invention is characterized in that the external electrode is formed of a noble metal having a thickness of 1 μm or less. As a result, migration can be prevented at low cost.

(4) Further, the piezoelectric actuator of the present invention is characterized in that the external electrode is made of gold and the bonding auxiliary layer is made of a thermosetting resin containing copper. As a result, the connection between the lead member and the electrode can be firmly maintained at low cost while preventing migration.

(5) Further, the piezoelectric actuator of the present invention is characterized in that the external electrode is formed of carbon. This makes it possible to firmly maintain the connection between the lead member and the electrode while preventing migration.

According to the present invention, it is possible to suppress the dielectric breakdown due to migration and sufficiently maintain the connection between the lead member and the electrode.

(A), (b) It is the front view and sectional drawing of the piezoelectric actuator of this invention.

Next, embodiments of the present invention will be described with reference to the drawings. A bimorph-type single-layer piezoelectric actuator will be described below as an example, but the present invention can be used for both a unimorph-type piezoelectric actuator and a bimorph-type piezoelectric actuator. Further, the present invention can be applied to the connection of the laminated piezoelectric element to the external electrode, and can be applied not only to the piezoelectric actuator but also to a piezoelectric element such as a piezoelectric transformer.

(Structure of piezoelectric actuator)
1A and 1B are a front view and a cross-sectional view of a bimorph type piezoelectric actuator 100, respectively. The piezoelectric actuator 100 includes a piezoelectric element 102 and a shim plate 107, and bends when a voltage is applied. The piezoelectric element 102 includes a piezoelectric ceramic body 103 and an external electrode 105, and the external electrode 105 is provided on the surface of the piezoelectric ceramic body 103.

The piezoelectric ceramic body 103 is made of, for example, a piezoelectric material containing PZT, barium titanate or the like as a main component, and formed into a plate shape. The piezoelectric ceramic body 103 is polarized in the thickness direction (for example, an arrow in the figure) and expands and contracts when a voltage is applied in the thickness direction. When the piezoelectric ceramic body 103 expands and contracts with respect to the shim plate 107, the piezoelectric actuator 100 bends.

The external electrode 105 is formed on the surface of the piezoelectric ceramic body 103 by baking gold (Au), for example. The external electrode 105 is preferably formed of a material that is less likely to cause migration than silver (Ag). Examples of materials that are less susceptible to migration than silver include nickel (Ni), copper (Cu), silver-palladium alloy (Ag/Pd), and platinum (Pt). This makes it possible to suppress dielectric breakdown due to migration even when continuously driven in an environment of high temperature and high humidity.

When the external electrode 105 is made of a noble metal, it preferably has a thickness of 1 μm or less. More preferably, the thickness is 0.1 μm or less. As a result, the amount of expensive material used is reduced, and migration can be prevented at low cost. Further, since the thickness is 1 μm or less, there is a high possibility that the material of the external electrode 105 will be eaten by the solder and the bonding with sufficient strength cannot be achieved. When the melting temperature of the solder used is high, the bonding auxiliary layer 106 is effective even if the external electrode 105 has a thickness of 1 μm or more. The external electrode 105 may be made of carbon. Thereby, the migration resistance of the piezoelectric actuator 100 can be improved. In addition, "to be eaten by solder" refers to a phenomenon in which particles of an electrode material melt into the solder.

Two piezoelectric ceramic bodies 103 are provided on the main surface of the shim plate 107. The shim plate 107 is formed of a metal such as SUS and also functions as one electrode of the piezoelectric ceramic body 103. The shim plate 107 and the piezoelectric ceramic body 103 are adhered by an epoxy or acrylic adhesive.

The bonding auxiliary layer 106 is preferably formed on the external electrode 105 with a thermosetting resin containing copper (cured copper conductive paste), for example. Bonding portions 115 and 116 are provided on the bonding auxiliary layer 106 and the shim plate 107 respectively for electrical connection, and the lead members 111 and 112 are bonded by soldering. By applying a drive voltage from the outside to the lead members 111 and 112, a voltage is applied between the external electrode 105 and the shim plate 107. Thus, the example shown in FIGS. 1A and 1B is a two-terminal type, but may be a three-terminal type.

With the above configuration, even when the external electrode 105 is made of an electrode material that does not easily cause migration, the electrical connection from the lead member 111 can be reliably established. The two external electrodes 105 are electrically connected by the lead member 121 joined to the joint portion 115 by soldering.

The bonding auxiliary layer 106 may be formed only of a metal such as copper or nickel. Copper or nickel is preferable because migration is unlikely to occur and cost can be suppressed even if a thick layer is formed. In addition, even if an expensive metal is used, the size of the bonding auxiliary layer 106 is limited, and thus the bonding auxiliary layer 106 may be formed of a silver-palladium alloy or platinum.

The bonding auxiliary layer 106 is preferably formed with a thickness of 5 to 30 μm and a size of 1 to 10 mm. Size refers to length, width or diameter. When the external electrode 105 is thin, the solder takes in the electrode material and weakens the bonding, but when the thickness of the bonding auxiliary layer 106 is 5 to 30 μm, the bonding is strengthened and the lead member 111 and the external electrode 105 are connected. Can be firmly maintained. Further, if the size is 1 to 10 mm, the joint 115 can be locally strengthened, the operator can easily handle it, and the manufacturing cost can be reduced.

As in the present embodiment, it is preferable that the external electrode 105 is made of gold and the bonding auxiliary layer 106 is made of copper, but the combination is not limited thereto. Not only a combination of different metals, but also a gold bonding auxiliary layer 106 may be provided on the gold external electrode 105, for example. Even in such a case, the lead member 111 and the bonding auxiliary layer 106 can be firmly bonded while preventing migration. Further, when the external electrode 105 and the bonding auxiliary layer 106 are made of different metals, a combination in which electrolytic corrosion does not easily occur even if the piezoelectric actuator 100 is used is preferable.

The piezoelectric actuator 100 as described above can effectively prevent the occurrence of migration when it is applied to an environment where migration is likely to occur such that high output is required at high temperature and high humidity. Further, it is also effective when cost reduction is required. For example, the piezoelectric actuator 100 is suitable for application to a needle selection device of a sock knitting machine.

(Piezoelectric actuator manufacturing method)
A method of manufacturing the piezoelectric actuator 100 configured as above will be described. First, a molded body formed of a piezoelectric material having a predetermined composition is fired to prepare the piezoelectric ceramic body 103. Then, the external electrode 105 is formed on the main surface of the piezoelectric ceramic body 103. For example, the external electrode 105 made of gold can be formed with a thickness of 0.1 μm or less by printing with a resinate.

The bonding auxiliary layer 106 is formed on the external electrode 105. The bonding auxiliary layer 106 can be formed by the following method using, for example, copper paste. That is, the piezoelectric ceramic body 103 on which a 2 mm□ copper paste (for example, S-5000 manufactured by Nippon Paint Anticorrosion Coatings Co., Ltd.) is printed on the external electrode 105 is dried at room temperature to 150° C. and the atmosphere at 140 to 200° C. It can be formed by heating in an atmosphere.

The piezoelectric element on which the bonding auxiliary layer 106 is formed by the above method is bonded to both main surfaces of the shim plate 107 with an adhesive, and polarization processing is performed. Then, the joining portion 115 by soldering is provided on the joining auxiliary layer 106, the lead member 121 is connected to the external electrode 105, and the piezoelectric actuator 100 can be manufactured. In addition, in the above example, the bonding auxiliary layer 106 is formed in a square having a side of 2 mm, but may be formed in a square having a side of 1 to 10 mm or a circle having a diameter of 1 to 10 mm. Good.

100 Piezoelectric actuator 102 Piezoelectric element 103 Piezoelectric ceramic body 105 External electrode 106 Bonding auxiliary layer 107 Shim plates 111, 112, 121 Lead members 115, 116 Bonding part

Claims (2)

A piezoelectric actuator that bends when a voltage is applied,
A shim plate having elasticity,
A piezoelectric element provided on the main surface of the shim plate,
The piezoelectric element is a plate-shaped piezoelectric ceramic body, an external electrode provided on the surface of the piezoelectric ceramic body and made of gold with a thickness of 1 μm or less, and thermosetting including copper provided on the external electrode. A piezoelectric actuator comprising: a joining auxiliary layer formed of a conductive resin; and a joining portion joining the joining auxiliary layer and a lead member with solder. The piezoelectric actuator according to claim 1, wherein the bonding auxiliary layer is formed to have a thickness of 5 to 30 µm.

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