JP7293898B2 - Piezoelectric element - Google Patents

Description

The present disclosure relates to piezoelectric elements.

Patent Document 1 describes a piezoelectric element having electrodes made of conductive paste. In such an electrode, conduction is achieved by the contact of the conductive particles contained in the conductive paste.

Patent Document 2 describes a piezoelectric element having electrodes formed by baking a conductive paste. Since such an electrode has a porous structure in which conductive particles are connected to each other, the electrical resistance can be reduced as compared with a conductive paste.

JP 2016-100760 A Japanese Utility Model Laid-Open No. 6-62700

Electrodes having porous structures such as those described above are fragile and fragile. Therefore, peeling of the electrode and particles from the electrode are likely to occur.

One aspect of the present disclosure provides a piezoelectric element capable of suppressing electrode peeling and generation of particles from the electrode while reducing the electrical resistance of the electrode.

A piezoelectric element according to one aspect of the present disclosure includes a piezoelectric body having a first main surface and a second main surface facing each other, and an electrode provided on the first main surface, the electrode having a porous structure. and a resin portion impregnated in the metal portion, and the first main surface has a first region in contact with the metal portion and a second region in contact with the resin portion.

In this piezoelectric element, the electrode includes a metal portion having a porous structure, so the electrical resistance of the electrode can be reduced. The electrode includes a resin portion impregnated with a metal portion. Since the pores or voids of the metal portion are filled with the resin portion, the metal portion is hard to break. Therefore, peeling of the electrode and generation of particles from the electrode can be suppressed. The first principal surface has a second region in contact with the resin portion. By bonding the resin portion to the second region, the adhesion between the first main surface and the electrode can be improved.

The resin portion may join the first main surface and an external member arranged to face the first main surface. In this case, the resin portion can also function as a joining member that joins the first main surface and the external member.

The metal portion may be in contact with an electrically conductive outer member disposed opposite the first major surface. In this case, electrical resistance between the electrodes and the external member can be reduced.

A slit may be provided in the first main surface. In this case, since the first main surface is more easily deformed than the surface on which the slits are not provided, the effect of suppressing the peeling of the electrode and the generation of particles from the electrode is exhibited more effectively.

According to one aspect of the present disclosure, it is possible to provide a piezoelectric element capable of suppressing separation of the electrode and generation of particles from the electrode while improving adhesion between the electrode and the piezoelectric body.

1 is a cross-sectional view showing a piezoelectric device including a piezoelectric element according to one embodiment; FIG. FIG. 2 is a perspective view showing the piezoelectric element of FIG. 1; It is a photograph figure which shows the cross-section of a 1st electrode.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or corresponding elements are denoted by the same reference numerals, and overlapping descriptions are omitted.

FIG. 1 is a cross-sectional view showing a piezoelectric device including a piezoelectric element according to one embodiment. As shown in FIG. 1, the piezoelectric device 100 includes a piezoelectric element 1 and a vibrating member 20 provided with the piezoelectric element 1. As shown in FIG. The piezoelectric device 100 is used, for example, as an in-vehicle sensor that transmits and receives ultrasonic waves to detect an inter-vehicle distance, or a sensor such as a powder level sensor that detects the amount of toner in a copying machine. The piezoelectric device 100 is also used as an actuator.

The vibration member 20 has electrical conductivity. The vibrating member 20 is, for example, a metal plate such as SUS (stainless steel). The vibrating member 20 has a pair of main surfaces 20a and 20b facing each other. The vibrating member 20 is arranged to face a main surface 2a of the piezoelectric element 1, which will be described later. The vibrating member 20 may be, for example, part of a case that covers the piezoelectric element 1 .

2 is a perspective view showing the piezoelectric element of FIG. 1. FIG. As shown in FIGS. 1 and 2, the piezoelectric element 1 is adhered to the main surface 20a of the vibrating member 20, for example. A piezoelectric element 1 includes a piezoelectric body 2 , a first electrode 3 and a second electrode 4 .

The piezoelectric body 2 has, for example, a rectangular parallelepiped shape. The rectangular parallelepiped shape includes a rectangular parallelepiped shape with chamfered corners and edges, and a rectangular parallelepiped shape with rounded corners and edges. The piezoelectric body 2 has, as its outer surface, a main surface 2a and a main surface 2b facing each other, a pair of side surfaces 2c facing each other, and a pair of side surfaces 2d facing each other.

A direction D1 in which the main surface 2a and the main surface 2b face each other, a direction D2 in which the pair of side faces 2c face each other, and a direction D3 in which the pair of side faces 2d face each other intersect (for example, orthogonally). . The length of the piezoelectric body 2 in the direction D1 is, for example, 3 mm, the length of the piezoelectric body 2 in the direction D2 is, for example, 8 mm, and the length of the piezoelectric body 2 in the direction D3 is, for example, 8 mm.

The main surface 2a and the main surface 2b extend in the direction D2 so as to connect between the pair of side surfaces 2c. The main surface 2a and the main surface 2b also extend in the direction D3 so as to connect between the pair of side surfaces 2d. The pair of side surfaces 2c extends in the direction D1 so as to connect between the principal surfaces 2a and 2b. The pair of side surfaces 2c also extend in the direction D3 so as to connect the pair of side surfaces 2d. The pair of side surfaces 2d extends in the direction D1 so as to connect between the principal surfaces 2a and 2b. The pair of side surfaces 2d also extend in the direction D2 so as to connect the pair of side surfaces 2c.

The main surface 2a is a surface facing an external member with the first electrode 3 interposed therebetween. In this embodiment, the external member is the vibrating member 20 . A plurality of (here, three) slits 5 are provided on the main surface 2a. The multiple slits 5 are arranged at regular intervals in the direction D3. The slit 5 extends in the direction D2 and extends from one side surface 2c to the other side surface 2c. The slit 5 is provided, for example, to adjust the resonance frequency and impedance waveform for sensing when the piezoelectric element 1 is used as a sensor.

The bottom surface of the slit 5 faces the main surface 2b in the direction D1. The bottom surface of the slit 5 is provided parallel to the main surfaces 2a and 2b, for example. The distances between the bottom surfaces of the plurality of slits 5 and the main surface 2b are equal to each other. That is, the lengths of the plurality of slits 5 in the direction D1 are equal to each other.

The length of the slit 5 in the direction D1 (the depth of the slit 5) is, for example, 2.6 mm. The length of the slit 5 in the direction D2 matches the length of the piezoelectric body 2 in the direction D2, and is, for example, 8 mm. The length of the slit 5 in the direction D3 (the width of the slit 5) is, for example, 0.3 mm. The distance between the slit 5 and the main surface 2b in the direction D1 is, for example, 0.4 mm.

The main surface 2a has a plurality of (here, four) main surface portions 2a1 divided by a plurality of slits 5. As shown in FIG. A pair of main surface portions 2a1 adjacent in the direction D3 are separated from each other with a slit 5 interposed therebetween. The plurality of main surface portions 2a1 are arranged at regular intervals in the direction D3. The plurality of main surface portions 2a1 have the same shape.

The piezoelectric body 2 is made of a piezoelectric material. In this embodiment, the piezoelectric body 2 is made of a piezoelectric ceramic material. Piezoelectric ceramic materials include, for example, those containing lead zirconate titanate (PZT) as a main component to which an element such as Nb, Zn, Ni or Sr is added.

The first electrode 3 and the second electrode 4 are provided on the outer surface of the piezoelectric body 2 . Specifically, the first electrode 3 is provided on the main surface 2a. The first electrode 3 is provided on substantially the entire main surface 2a except for the slits 5 . The second electrode 4 is provided on the main surface 2b. The second electrode 4 is provided on substantially the entire main surface 2b. The thicknesses (lengths in the direction D1) of the first electrode 3 and the second electrode 4 are, for example, the same. The thickness of the first electrode 3 and the second electrode 4 is, for example, 5 μm.

The first electrode 3 has a plurality of (here, four) electrode portions 31 divided by a plurality of slits 5 . A pair of electrode portions 31 adjacent in the direction D3 are separated from each other via the slit 5 . The plurality of electrode portions 31 are provided on each of the plurality of main surface portions 2a1. The plurality of electrode portions 31 are provided on substantially the entire surfaces of the plurality of main surface portions 2a1.

FIG. 3 is a photograph showing the cross-sectional structure of the first electrode. FIG. 3 is a cross-sectional photograph taken along a plane parallel to the direction D1. As shown in FIG. 3, the first electrode 3 (specifically, each electrode portion 31 shown in FIG. 1) includes a metal portion 3m and a resin portion 3r. The metal portion 3m has a porous structure containing a plurality of holes or voids. This porous structure is three-dimensionally formed over the entire first electrode 3 . It can also be said that the metal portion 3m has a three-dimensional mesh structure formed over the entire first electrode 3 .

The metal portion 3m is made of a conductive material such as Ag, for example. Pd, Ag—Pd alloy, Au, Pt, Ni, or the like may be used as the conductive material. The metal portion 3m is formed by connecting conductive particles to each other by, for example, applying a conductive paste containing a conductive material to the main surface 2a and baking the paste. In this case, the metal portion 3m is sintered metal. The baking temperature can be, for example, 600° C. or higher and 800° C. or lower. The porous structure of the metal portion 3m may be formed by methods other than baking. Therefore, the metal portion 3m does not necessarily have to be sintered metal.

The resin portion 3r is impregnated into the metal portion 3m. The resin portion 3r permeates the porous structure and fills the pores or voids thereof. The resin portion 3r is made of resin such as epoxy, for example. The resin portion 3r is formed, for example, by applying a resin adjusted to a predetermined viscosity onto the metal portion 3m to impregnate the resin and then curing the resin. The resin may be impregnated into the metal portion 3m by applying a predetermined pressure.

As described above, the porous structure of the metal portion 3m extends over the entire first electrode 3, and the resin portion 3r impregnates the entire porous structure, so that the main surface 2a of the piezoelectric body 2 is , a first region R1 in contact with the metal portion 3m and a second region R2 in contact with the resin portion 3r. Further, the main surface 20a of the vibration member 20 has a third region R3 in contact with the metal portion 3m and a fourth region R4 in contact with the resin portion 3r. The resin portion 3r joins the main surface 2a and the main surface 20a and functions as an adhesive.

The proportion of the metal portion 3m in the first electrode 3 is, for example, 30% or more and 95% or less. The ratio of the resin portion 3r in the first electrode 3 is, for example, 5% or more and 70% or less. The proportion of the pores or voids in the metal portion 3m occupied by the resin portion 3r is, for example, 30% or more. Such a ratio is obtained, for example, as an area ratio in a cross-sectional photograph of a plane parallel to the direction D1.

The ratio of the metal portion 3m and the resin portion 3r does not change greatly depending on the position in the thickness direction (direction D1) of the first electrode 3, respectively.

Although illustration is omitted, the second electrode 4 includes, for example, a metal portion with a porous structure similar to that of the first electrode 3 . The metal portion of the second electrode 4 is made of, for example, the same conductive material as that of the first electrode 3, and is formed by applying a conductive paste containing the conductive material to the main surface 2b and baking it. Although the second electrode 4 does not contain a resin portion in this embodiment, the second electrode 4 may contain a resin portion.

An example of a method for manufacturing the piezoelectric element 1 and the piezoelectric device 100 will be described. First, a polyvinyl-based binder, water, and the like are added to a piezoelectric ceramic material powder to form a piezoelectric ceramic paste. Next, a die of a predetermined size is filled with a piezoelectric ceramic paste, and press-molded at a pressure of, for example, 40 MPa. Ceramic green is thus obtained. Subsequently, the ceramic green is subjected to binder removal treatment. The binder removal treatment is performed at 400° C. for 12 hours, for example. Subsequently, the ceramic green is fired. Firing is performed, for example, at 1250° C. for 4 hours. A piezoelectric body is thus obtained.

Next, the piezoelectric body is lap-polished and shaped into a plate having a thickness of 3.2 mm, for example. Subsequently, a conductive paste is applied to both main surfaces of the piezoelectric body. The conductive paste is formed, for example, by adding a binder, a plasticizer, an organic solvent, and the like to powder of a conductive material such as Ag. The conductive paste also contains a glass component (eg, primarily Si). The conductive paste is applied in a thickness of 20 μm, for example by screen printing. Subsequently, the outer periphery of the piezoelectric body is ground and slit processing is performed. After that, the conductive paste is baked. The baking process is performed at 500° C. for 10 minutes, for example.

Next, the piezoelectric element is subjected to polarization treatment. The polarization treatment is performed, for example, by applying a voltage having an electric field strength of 3.5 kV/mm at 150° C. to the electrodes of the piezoelectric element for 5 minutes. Thereby, metal portions of the first electrode and the second electrode are formed. Subsequently, a resin is applied onto the metal portion of the first electrode and then impregnated. The resin is applied, for example, by screen printing to a thickness of about 1000 μm. The viscosity of the resin is, for example, 10 Pa·s, and the metal portion is impregnated with the resin at 40° C. for 15 minutes.

Next, after the vibrating member is attached onto the first electrode, the resin is cured. Thereby, a first electrode including a metal portion and a resin portion is formed, and a piezoelectric element and a piezoelectric device are obtained.

As described above, in the piezoelectric element 1, the first electrode 3 includes the metal portion 3m having a porous structure. Therefore, according to the 1st electrode 3, compared with the electrode which consists of a conductive paste, an electrical resistance can be reduced. The first electrode 3 includes a resin portion 3r impregnated with a metal portion 3m. Since the holes or voids of the metal portion 3m are filled with the resin portion 3r, the metal portion 3m is reinforced by the resin portion 3r. As a result, the metal portion 3m is hard to break. Therefore, peeling of the first electrode 3 and generation of particles from the first electrode 3 caused by breakage of the metal portion 3m can be suppressed. Since the piezoelectric element is displaced, it is particularly important to suppress the peeling of the electrode and the generation of particles from the electrode compared to other electronic components that are not displaced.

The principal surface 2a has a second region R2 in contact with the resin portion 3r. When the main surface 2a does not have the second region R2, that is, when the main surface 2a is not in contact with the resin portion 3r, for example, the resin portion 3r is not impregnated with the metal portion 3m in the vicinity of the main surface 2a. case is conceivable. Compared to such a case, in the present embodiment, the adhesion between the main surface 2a and the first electrode 3 can be improved by joining the resin portion 3r to the second region R2.

Main surface 2a has first region R1 in contact with metal portion 3m. By baking the conductive paste, the piezoelectric body 2 reacts with the metal component of the conductive paste at the interface between the first region R1 and the metal portion 3m. Further, the glass component (mainly Si, for example) of the conductive paste melts and enters the grain boundary on the main surface 2a of the piezoelectric body 2, thereby improving the adhesion between the piezoelectric body 2 and the first electrode 3. As a result, the adhesion between the main surface 2a and the first electrode 3 is improved compared to an electrode made of a conductive paste and not baked. In addition to Si, Zn and Al may be detected as glass components that have entered grain boundaries.

The resin portion 3r joins the main surface 2a and a vibrating member 20 as an external member arranged to face the main surface 2a. Therefore, the resin portion 3r can function not only as a reinforcing member for the metal portion 3m, but also as a joining member that joins the main surface 2a and the vibration member 20 together.

The metal portion 3m is in contact with a vibrating member 20 as an electrically conductive external member arranged to face the main surface 2a. Thereby, the electrical resistance between the first electrode 3 and the vibrating member 20 can be reduced.

A slit 5 is provided in the main surface 2a. The main surface 2a deforms more easily than the main surface 2b on which the slits 5 are not provided. The first electrode 3 is provided on the main surface 2a that is easily deformed in this way. For this reason, compared with the case where the first electrode 3 is provided on the main surface 2b on which no slits are formed, the effect of suppressing the separation of the first electrode 3 and the generation of particles from the first electrode 3 is more effective. is demonstrated in

Although the embodiments have been described above, the present invention is not necessarily limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

For example, the second electrode 4 may have a resin portion impregnated in the metal portion in addition to the porous metal portion. In this case, peeling of the second electrode 4 and generation of particles from the second electrode 4 can be suppressed.

The slit 5 may not be provided on the main surface 2a. The vibrating member 20 may not be attached to the first electrode 3 .

Reference Signs List 1 Piezoelectric element 2 Piezoelectric body 2a Principal surface 3 First electrode 5 Slit 3m Metal portion 3r Resin portion 20 Vibration member (external member) R1 First region R2 . . . second area.

Claims (4)

a piezoelectric body having a first main surface and a second main surface facing each other;
and an electrode provided on the first main surface,
The electrode includes a metal portion having a porous structure that is a three-dimensionally formed network structure, and a resin portion impregnated in the metal portion,
The first main surface has a first region in contact with the metal portion and a second region in contact with the resin portion,
The metal part is a sintered metal baked on the first main surface ,
The piezoelectric element , wherein the resin portion is hardened . 2. The piezoelectric element according to claim 1, wherein said resin portion joins said first main surface and an external member arranged to face said first main surface. 3. The piezoelectric element according to claim 1, wherein said metal portion is in contact with a conductive external member arranged opposite said first main surface. The piezoelectric element according to any one of claims 1 to 3, wherein the first main surface is provided with slits.

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