JP3087381B2 - Piezoelectric laminate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric laminate used as a piezoelectric actuator utilizing a piezoelectric effect.

[0002]

2. Description of the Related Art In recent years, instead of an actuator using electromagnetic force, for example, Japanese Patent Application Laid-Open No. 62-291187,
As disclosed in Japanese Utility Model Application Laid-Open No. 64-30865 and the like, piezoelectric actuators utilizing the piezoelectric effect are frequently used. Since this piezoelectric actuator generates little heat, and is small in size and can be driven at high speed, it is very promising as various mechanical drive elements. However, since the mechanical displacement due to the piezoelectric effect is extremely small in nature, it is provided as a piezoelectric laminate having a structure in which piezoelectric plates and electrode plates are alternately multiplexed in layers and covered with an insulating protective layer in order to obtain a large displacement. ing.

When the piezoelectric plates and the electrode plates are alternately stacked, it is desirable to join the piezoelectric plates and the electrode plates in order to prevent displacement. It is also desired to ensure conduction between the piezoelectric plate and the electrode plate. Therefore, Japanese Patent Laid-Open No. 60-121
Japanese Patent Publication No. 784 and the like disclose a piezoelectric laminate in which a conductive silver paste or the like is interposed between a piezoelectric plate and an electrode plate, and joined using the bonding force of the paste. That is, for example, by attaching a silver paste to both surfaces of the piezoelectric plate by screen printing or the like, and by heating and pressing after alternately laminating the electrode plate, the glass component in the silver paste melts and functions as an adhesive, The piezoelectric plate and the electrode plate are integrally joined.

[0004]

However, in the above-described conventional piezoelectric laminate, cracks occur in the piezoelectric body during driving, and
In some cases, the cracks proceed to cause element cracks in the piezoelectric body. When the element cracks as described above, a short circuit phenomenon may occur when an electric field is applied, and in such a case, the element no longer serves as an actuator.

[0005] The following three are considered as causes of the crack. (1) After forming the piezoelectric body into a predetermined disk shape, the outer peripheral portion is machined to have a predetermined diameter. For this reason, fine irregularities and processing flaws are present on the outer peripheral end face, which serve as a crack generation source, and the crack proceeds from the outer peripheral end face toward the inside. (2) Although heat is generated at the time of driving, the piezoelectric plate has a temperature distribution in which the temperature is higher in the interior and lower in the outer periphery, so that the elongation increases toward the interior and cracks occur from the inner periphery to the outer peripheral end surface. (3) In order to prevent a short circuit on the outer peripheral end surface, the conductive paste layer is generally formed leaving a predetermined width from the outer peripheral end surface of the piezoelectric plate. Therefore, when a voltage is applied, the piezoelectric effect is not obtained in the outer peripheral portion without the conductive paste layer, the amount of deformation is different between the inner peripheral portion and the outer peripheral portion, and cracks occur at the interface with or without the conductive paste layer.

An object of the present invention is to prevent, from the above three causes, the progress of cracks from the outer peripheral end face of (1).

[0007]

According to the present invention, there is provided a piezoelectric laminate in which a plurality of piezoelectric plates and electrode plates are alternately laminated via a conductive paste layer having a diameter smaller than the diameter of the piezoelectric plate. In the piezoelectric laminate, the piezoelectric plate has an annular groove having a V-shaped cross section at the outer peripheral portion on the front and back surfaces on the outer peripheral side of the conductive paste layer.

[0008] The piezoelectric plate is formed of a piezoelectric material that generates distortion or stress when a voltage is applied. For example, it is formed in a disc shape from piezoelectric ceramics such as PbTiO ₃ -PbZrO ₃ (PZT) having a perovskite crystal structure.
The same as the conventional one is used. The electrode plate is used for extracting an external electrode, and is formed of a conductive metal such as copper. A tongue piece for taking out an electrode or the like is usually provided so as to protrude from a central hole provided at an outer peripheral portion or a center. The thickness of the electrode plate is suitably 0.1 to 0.15 mm.
If the thickness is less than 1 mm, the strength cannot be ensured, and if the thickness is more than 0.15 mm, electric resistance increases, causing problems such as heat generation and an increase in size.

The piezoelectric plate and the electrode plate are integrally joined via a conductive paste layer mainly composed of a conductive metal. This conductive paste layer has a diameter smaller than the diameter of the piezoelectric plate in order to prevent a short circuit on the outer peripheral end surface, and is formed on both front and back surfaces of the piezoelectric plate. The greatest feature of the present invention is that the piezoelectric plate has an annular groove having a V-shaped cross section at the outer peripheral portion on the front and back surfaces on the outer peripheral side of the conductive paste layer. This annular groove prevents cracks generated on the outer peripheral end face from advancing to the inner peripheral side, and prevents short circuit due to element cracking. Although the cross-sectional shape of this annular groove is V-shaped, it is preferable that the angle of the tip is small. In the case of a U-shaped cross section or a U-shaped cross section in which the angle of the tip is large, the possibility that the crack progresses toward the center is large, which is not preferable. The effect of preventing the crack from progressing toward the center is greater as the depth of the annular groove is larger.

[0010]

The effect of the present invention is that cracks generated on the outer peripheral end face of the piezoelectric plate due to fine irregularities and processing scratches progress radially toward the center. However, in the piezoelectric laminated body of the present invention, an annular groove having a V-shaped cross section is provided in the outer peripheral portion of the front and back surfaces on the outer peripheral side of the conductive paste layer of the piezoelectric plate. Therefore, the crack that has progressed is guided to the tip of the annular groove, and the course is changed in the thickness direction of the piezoelectric plate and in the circumferential direction in which the annular groove extends. Therefore, the progress of the crack to the center is prevented, and the element cracking in the portion where the conductive paste layer where the piezoelectric displacement can be obtained is prevented.

That is, according to the piezoelectric laminate of the present invention, short-circuiting due to element cracking is prevented, and durability and reliability are improved.

[0012]

The present invention will be specifically described below with reference to examples. FIG.
1 shows a piezoelectric laminate according to one embodiment of the present invention. This piezoelectric laminate includes a piezoelectric plate 1, an electrode plate 2, a silver paste layer 3, a pair of external electrode plates 4, and an insulating coating 5. Hereinafter, by describing the manufacturing method, the detailed description of the configuration is replaced.

The piezoelectric plate 1 is made of a PZT ceramic and has a diameter of 17 mm and a thickness of 0.1 mm as shown in FIGS.
It has a disk shape of 5 mm. An annular groove 10 is formed on the outer peripheral portions of both surfaces along the peripheral edge. The annular groove 10 has a V-shaped cross section as shown in an enlarged view in FIG. 3, has a depth t of 0.15 mm, and a bottom tip angle α of 30 °.

As shown in FIG. 4, the electrode plate 2 is formed from copper in a disk shape having a diameter of 17 mm and a thickness of about 30 μm, and has one tongue piece 20 projecting in the normal direction. First, a silver paste is applied to both surfaces of the piezoelectric plate 1 having the annular groove 10 by screen printing. At this time, the silver paste is applied inside the annular groove 10. Then, the tongue pieces 20 are alternately stacked with the electrode plate 2 so that the directions of the tongue pieces 20 are alternately 180 degrees. After laminating 60 piezoelectric plates, pressurizing with a force of 100 kgf / cm ^{2 in} the axial direction,
Heat at 700 ° C. for 5-30 minutes. Thereby, the silver paste is melted, and the piezoelectric plate 1 and the electrode plate 2 are integrally joined to form the silver paste layer 3.

Then, the tongue pieces 20 on the same side are connected to each other by the external electrode plate 4, the lead wire 40 is soldered, and the outer peripheral portion is covered with an insulating coating 5 made of silicon resin. A body is formed. The piezoelectric laminate was immersed in silicon oil at 100 ° C. and subjected to a polarization treatment by applying a high voltage of 1 kv to the lead wire 30 for 30 minutes. Then, 500 kgf is added as an initial load, and 0 to 8
An energization endurance test in which pulse driving was performed at a voltage of 00 V (100 Hz) was performed. Then, the number of piezoelectric bodies 1 in which cracks had progressed from the outer peripheral end surface to the portion where the silver paste layer 3 was formed was counted, and the ratio to the whole was calculated. FIG. 6 shows the results.

As a comparative example, a piezoelectric laminated body was formed in the same manner from the same piezoelectric plate 1 except that the shape of the annular groove 10 was U-shaped in cross section, and an energization durability test was similarly performed. The results are shown in FIG. As shown in FIG. 6, the piezoelectric laminate of the comparative example in which the annular groove 10 has a U-shaped cross section has a higher rate of crack propagation to the inside than the piezoelectric laminate of the present embodiment,
As the number of driving increases, the ratio increases rapidly.
That is, it is clear that it is more effective to make the annular groove 10 have a V-shaped cross section than a U-shaped in order to prevent the crack from progressing inward in the radial direction.

Next, the effect of the bottom tip angle α of the annular groove 10 was investigated. That is, when the angle α is 10 °, 30 °,
Piezoelectric laminates were formed in the same manner from the piezoelectric bodies 1 having the annular grooves 10 at 50 °, respectively, and subjected to an electric conduction durability test in the same manner as described above. Here, the depth t of the annular groove 10 is constant at 0.15 mm. Then, similarly, the number of piezoelectric bodies 1 in which cracks progressed from the outer peripheral end surface to the portion where the silver paste layer 3 was formed was counted, and the ratio to the whole was calculated. FIG. 7 shows the results.

FIG. 7 shows that the smaller the angle α of the annular groove 10 is, the more the progress of the crack can be prevented. Further, the influence of the depth t of the annular groove 10 was investigated. That is, a piezoelectric laminate was formed in the same manner from the piezoelectric body 1 having the annular grooves 10 having the depths t of 0.1 mm, 0.15 mm, and 0.2 mm, respectively, and an electric current durability test was performed in the same manner as described above. Here, the angle α of the annular groove 10 is constant at 30 °. Then, similarly, the number of piezoelectric bodies 1 in which cracks progressed from the outer peripheral end surface to the portion where the silver paste layer 3 was formed was counted, and the ratio to the whole was calculated. FIG. 8 shows the results.

FIG. 8 shows that the deeper the depth t of the annular groove 10 is, the more the progress of cracks can be prevented. That is, as is apparent from the above-described embodiment, in the piezoelectric laminate of the present invention, the annular groove having a V-shaped cross section is formed in the piezoelectric plate, so that the progress of cracks during energization driving is prevented and the durability is improved.

[Brief description of the drawings]

FIG. 1 is a plan view of a piezoelectric plate used in an example.

FIG. 2 is a sectional view of a piezoelectric plate used in an example.

FIG. 3 is an enlarged view of a main part of FIG. 2;

FIG. 4 is a plan view of an electrode plate used in an example.

FIG. 5 is a sectional view of a piezoelectric laminate according to one embodiment of the present invention.

FIG. 6 is a graph showing a relationship between the number of times of a current durability test and a ratio of a cracked piezoelectric body to the whole.

FIG. 7 is a graph showing a relationship between the number of times of an electric current endurance test and a ratio of a cracked piezoelectric body to the whole.

FIG. 8 is a graph showing a relationship between the number of times of an electric current endurance test and a ratio of a cracked piezoelectric body to the whole.

[Explanation of symbols]

1: piezoelectric plate 2: electrode plate 3: silver paste layer
4: External electrode plate 5: Insulating coating 10: Annular groove
20: Tongue piece 40: Lead wire

Claims (1)

(57) [Claims] 1. A piezoelectric laminate in which a plurality of piezoelectric plates and electrode plates are alternately laminated via a conductive paste layer having a diameter smaller than the diameter of the piezoelectric plate, wherein the piezoelectric plate is located on the outer peripheral side of the conductive paste layer. 3. A piezoelectric laminate having an annular groove having a V-shaped cross section on the outer periphery of the front and back surfaces of the piezoelectric laminate.