JPH0722557U - External electrodes for laminated piezoelectric components - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] Good conductivity with internal electrodes, can be formed at low cost, has low resistivity, and sufficiently prevents migration. Provided is an external electrode of a laminated piezoelectric component which can be manufactured and has excellent durability. A laminated piezoelectric actuator 10 in which piezoelectric ceramic substrates 12 and internal electrodes 13 are alternately laminated to form a laminated piezoelectric body 11, and external electrodes 15 are formed on both side surfaces of the laminated piezoelectric body 11 In the electrode 15, a multilayer piezoelectric component in which a base layer 16 in contact with the multilayer piezoelectric body 11 is composed of three vapor deposition films 16 and an outer layer is composed of a coating film 17 of a metal paste containing Au, Ni or platinum. 1
0 external electrodes 15.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an external electrode of a laminated piezoelectric component, and more particularly to an external electrode of a laminated piezoelectric component used as an actuator or the like.

[0002]

[Prior art]

 Conventionally, a piezoelectric material having a so-called piezoelectric effect, in which a stress causes an electric field proportional to the stress, and conversely, when an electric field is applied and polarized, a strain proportional to the electric field occurs, or a mechanical stress occurs. Is used for various applications such as vibrators, filters, and actuators by utilizing its characteristics. Among them, the laminated piezoelectric actuator, which is a type of actuator that utilizes mechanical strain in proportion to the applied electric field, has a large displacement amount, and the displacement amount can be freely selected by the number of laminated piezoelectric bodies. Since it has excellent characteristics such as excellent load bearing characteristics, it has been widely used as a precision positioning mechanism in precision machine tools, precision magnetic disks, recording / reproducing heads, linear step motors, and the like.

Such a laminated piezoelectric actuator has a structure in which piezoelectric ceramic substrates and internal electrodes are alternately laminated, and further external electrodes are formed, and has high performance and is widely used. .

FIG. 5 is a perspective view schematically showing a part of a conventional laminated piezoelectric actuator, and FIG. 6 is a schematic cross-sectional view showing an enlarged external electrode portion. In the figure, reference numeral 12 indicates a piezoelectric ceramic substrate. The laminated surface of the piezoelectric ceramic substrate 12 subjected to polarization is formed with an internal electrode 13 composed of a metal plating layer, and the polarization direction is different for each layer. They are bonded and laminated so as to face each other, and the piezoelectric ceramic substrate 12 and the internal electrodes 13 form a laminated piezoelectric body 11. The ends of the internal electrodes 13 are alternately insulated by two semi-cylindrical insulating coatings 14 on two opposite surfaces of the laminated piezoelectric body 11, and a conductive paste is applied on the insulating coatings 14 to form external electrodes. 25 are formed, and the external electrodes 25 are connected to the internal electrodes 13 every other layer.

In order to form the external electrode 25 of the laminated piezoelectric actuator having the above-described structure, it is necessary to form the outer surface of the inner electrode 13 on both side surfaces of the laminated piezoelectric body 11 on which the insulating coating 14 is formed and to expose the insulation. A conductive paste is applied to the coating film 14 by screen printing so as to have a predetermined thickness and a predetermined width, and then heat treatment is performed to remove the resin and solvent contained in the conductive paste.

By the way, Ag is a metal having the lowest volume resistivity among all metals and having good wettability with the ceramic surface. Therefore, by using Ag for the external electrode 25, good conductivity in the external electrode 25 is obtained, and the external electrode 25 is formed with good adhesion to the piezoelectric ceramic substrate 12 and the internal electrode 13, and the internal electrode 13 and the external electrode 25 are formed. Good conductivity with the pole 25 is obtained. Therefore, the conventional external electrode 25 is often formed by using a paste containing Ag.

However, in the external electrode 25 formed by using Ag as described above, the surface of the external electrode 25 is exposed, and Ag has a property that migration easily occurs under high humidity. Due to the fact that the external electrodes 25 have the above-mentioned characteristics, migration is likely to occur in the external electrode 25 when the pulse voltage is continuously applied for a long time in a high humidity atmosphere. When the migration occurs, there is a problem that a defective insulation portion is formed, the electrostatic capacity is reduced, or a failure occurs. Therefore, it is not preferable to use Ag for the external electrode 25 in order to prevent the occurrence of migration.

Conventionally, in order to deal with such a problem, an external electrode made of Ag-palladium alloy has been used. Further, there is proposed an external electrode in which the exposed surface of the external electrode formed of Ag is covered with a plating film made of a metal having higher migration resistance than Ag (JP-A-62-62571). Gazette).

However, in the external electrode formed using the Ag-palladium alloy, although migration is suppressed to some extent as compared with the case where only Ag is used, the Ag-palladium alloy contains Ag. However, there was a problem that the occurrence of migration could not be sufficiently prevented. Therefore, in order to sufficiently prevent the occurrence of migration, it is necessary to hermetically seal the entire laminated piezoelectric material, which causes a problem of labor and cost.

Further, in the external electrode described in JP-A-62-62571, since the external electrode is formed by using Ag, not only is moisture contained in the atmosphere, but also the element Since it also exists on the surface, it is difficult to block out moisture, and there is a problem that migration cannot be sufficiently prevented.

In any case, it is difficult to suppress such a problem as long as Ag is used as a constituent element.

Therefore, in order to solve such a problem, an external electrode formed of a metal such as Au, Ni, platinum, or Pd is used.

[0013]

[Problems to be solved by the device]

 In the external electrodes formed by using the above-mentioned conventional metals such as Au, Ni, platinum, Pd, etc., since these metals are more excellent in migration resistance than Ag, the laminated piezoelectric body after the external electrodes are formed. It is not necessary to hermetically seal the whole or to further form a metal film for migration resistance on the surface of the external electrode. However, these metals have a higher volume resistivity than Ag, and when the paste in a normal state is used, the amount of metal contained in the paste is small, so that the resistivity of the external electrode is high and good conductivity is obtained. There was a problem that the state could not be realized.

Therefore, in order to reduce the resistivity of the external electrodes, a method of roughening the noble metal flakes contained in the paste has been proposed. However, if the flakes of the paste are roughened, it will be difficult to reliably connect the internal electrode with the width of the exposed portion being several μm, the contact resistance with the internal electrode will increase, and the conductivity with the internal electrode will deteriorate. There was a problem.

In order to solve such a problem, formation of external electrodes by a vapor deposition method, a sputtering method, or the like, which can make particles finer, has been considered.

However, when the vapor deposition method or the sputtering method is used, the internal electrode can be surely connected, but in order to form the low resistance external electrode, the thickness must be close to the micron order. However, there is a problem that the manufacturing cost is high. In addition, a thin vapor-deposited film or sputtered film (FIG. 7) has a high resistivity in the external electrode 35 and cannot alleviate stress due to sudden strain such as pulse response. There is a problem that it becomes easy to break and the capacitance is significantly reduced.

The present invention has been devised in view of the above problems, and has good conductivity with internal electrodes, can be formed at low cost, and has low resistivity and migration. It is an object of the present invention to provide an external electrode of a laminated piezoelectric component which can be sufficiently prevented from occurring and has excellent durability.

[0018]

[Means for Solving the Problems]

 In order to achieve the above object, the external electrodes of the laminated piezoelectric component according to the present invention are formed by alternately laminating piezoelectric ceramic substrates and internal electrodes to form a laminated piezoelectric body, and both side surfaces of the laminated piezoelectric body are formed. In the external electrode of the laminated piezoelectric component in which the external electrode is formed, the underlying layer that contacts the multilayer piezoelectric body is composed of a vapor deposition film, and the external layer is a coating film of a metal paste containing Au, Ni or white gold. It is characterized by being configured.

[0019]

[Action]

 According to the external electrode of the laminated piezoelectric component having the above-described structure, since the underlayer contacting the laminated piezoelectric body is formed of the vapor deposition film, the particles of the underlayer become fine, so Good adhesion with the porcelain substrate can be obtained. In addition, good adhesion with the internal electrode having a narrow exposed width can be obtained, connection with the internal electrode can be performed well, and good conductivity with the internal electrode can be obtained. Further, the vapor deposition film is inexpensively formed.

Further, since the outer layer is composed of a coating film of a metal paste containing Au, Ni or platinum, the outer layer having a large thickness can be formed at a low cost by forming the outer layer using a screen printing method. It becomes possible to do. This reduces manufacturing costs. Further, an external electrode having a low resistance and hard to be cut is formed, and good conductivity can be obtained in the external electrode.

Further, since Ag is not used for the external electrodes, migration is sufficiently prevented and the durability of the multilayer piezoelectric component is greatly improved.

As a metal used for forming the underlayer, Cr is suitable for obtaining good adhesion to ceramics, but is superior in migration resistance to Ag such as Ni, Au and platinum. It may be a metal.

[0023]

[Examples and Comparative Examples]

 Hereinafter, examples and comparative examples of the external electrodes of the multilayer piezoelectric component according to the present invention will be described with reference to the drawings. It should be noted that components having the same functions as those of the conventional example are designated by the same reference numerals. In the embodiments, the laminated piezoelectric actuator 10 will be described as an example of the laminated piezoelectric component. The structure of the laminated piezoelectric actuator 10 is the same as the conventional structure shown in FIG. 5 except for the external electrode 15, and therefore only the structure of the external electrode 15 will be described here.

FIG. 2 is a perspective view schematically showing the laminated actuator 10 according to the embodiment, and FIG. 3 is a schematic cross-sectional view showing an enlarged external electrode portion according to the embodiment. In the figure, 10 indicates a laminated piezoelectric actuator, and 11 indicates a laminated piezoelectric body. The width is about 1 mm on both sides of the laminated piezoelectric body 11 on the insulating coating 14 and the end face of the internal electrode 13. A Cr vapor deposition film 16a having a thickness of about 1000Å is formed, a Ni vapor deposition film 16b having a thickness of about 4000Å is formed on the Cr vapor deposition film 16a, and an Au film having a thickness of about 1000Å is formed on the Ni vapor deposition film 16b. The vapor deposition film 16c is formed, and the Cr vapor deposition film 16a, the Ni vapor deposition film 16b, and the Au vapor deposition film 16c form the underlayer 16. Further, a coating film 17 of a metal paste containing Au having a thickness of about 500 μm is formed on the underlayer 16 as an outer layer, and the underlayer 16 and the coating film 17 constitute an external electrode 15. Are connected to the internal electrode 13 every other layer.

In order to form the external electrodes 15 of the laminated piezoelectric actuator 10 having the above-described structure, first, the piezoelectric ceramic substrate 12 is formed to have a length of 4.2 mm, a width of 5.5 mm, and a thickness of 0.11 mm. Sumitomo Metal Industries, Ltd.'s SPEM-5D (dielectric constant 4300, piezoelectric constant (d ₃₃ ) 640 × 10 ^-12 c / N, Curie point 210 ° C.) is used for 150 sheets, and this piezoelectric ceramic substrate 12 is laminated. The inner electrode 13 is formed by plating the surface with Ni having a thickness of about 2 μm. Next, the piezoelectric ceramic substrate 12 is laminated and adhered using an epoxy resin adhesive to form the laminated piezoelectric body 11. After that, a semi-cylindrical insulation coating 14 is formed on the opposite two surfaces of the laminated piezoelectric body 11 using an epoxy resin for every other layer including the end surface of the internal electrode 13.

Next, a Cr vapor deposition film 16 having a width of about 1 mm and a thickness of about 1000 Å is formed on both sides of the laminated piezoelectric body 11 on the insulating coating 14 and the end surface of the internal electrode 13 by using a vacuum vapor deposition method. a, a Ni vapor deposition film 16b having a thickness of about 4000Å and an Au vapor deposition film 16c having a thickness of about 1000Å are sequentially formed. Next, a conductive Au paste mixed with a solvent using a thermosetting resin as a binder is applied on the Au vapor-deposited film 16c using a screen printing method, and then heat treatment is performed to remove the resin and the solvent, and the thickness A coating film 17 of a metal paste containing Au 2 having a thickness of about 500 μm is formed, and an external electrode 15 is formed.

In the external electrode 15 formed as described above, a probe of a tester was brought into contact with both ends of the external electrode 15 in the longitudinal direction, and the conduction resistance value was measured. As a result, a low value of 0.5Ω was obtained. Was given.

This value was as low as a conduction resistance value in the conventional external electrode 25 (FIG. 5) using Ag paste. It is considered that this is because the underlayer 16 and the coating film 17 are connected in parallel by innumerable contact points as shown in FIG.

FIG. 4 shows a laminated piezoelectric actuator 10 according to an embodiment and a conventional laminated piezoelectric actuator whose external electrode is composed of only a coating film of a normal Au paste as a comparative example, without changing the temperature. 2 is a graph showing the results of examining the change with time of the electrostatic capacity by allowing the sample to stand in a room at 26 ° C. and a relative humidity (RH) of 60% for 1,000 hours.

As is clear from FIG. 4, in the laminated piezoelectric actuator according to the comparative example, the electrostatic capacitance was considerably reduced to about 907 nF before the start of the experiment, about 890 nF after 10 hours, and about 830 nF after 100 hours. However, after a lapse of 1000 hours, it is significantly reduced to about 740 nF. On the other hand, the capacitance of the laminated piezoelectric actuator 10 according to the example is about 908 nF before the start of the experiment, about 902 nF after 10 hours, about 901 nF after 100 hours, and about 1000 hours after 1000 hours. 901 nF, which is almost no decrease. In this way, the underlayer 16 connected to the internal electrode 13 is composed of vapor deposition films 16a, 16b, 16c that do not contain Ag, and the underlayer 16 is covered with the coating film 17 to prevent migration, It has been confirmed that it is possible to prevent the decrease in the capacitance of the laminated piezoelectric actuator 10 with the passage of time.

[0031]

[Table 1]

Table 1 shows the frequency difference between the laminated piezoelectric actuator 10 according to the example and a conventional laminated piezoelectric actuator in which the external electrode is composed only of a coating film of Au paste having a thickness of about 500 μm as a comparative example. This is a result of examining a change in capacitance and a deterioration state of parts by performing a pulse aging test at 20 Hz, a pulse voltage of 150 V (DC), and a pulse width of 100 μsec 100 million times.

As is clear from Table 1, in the laminated piezoelectric actuator according to the comparative example, the electrostatic capacity was about 911 nF before the test, but was about 788 nF after about 40 million times. A significant reduction of 123 nF was seen. Also, at the time of about 40 million times, many defective products were generated. On the other hand, in the laminated piezoelectric actuator 10 according to the example, the capacitance was about 902 nF before the test, but it was about 895 nF even after about 100 million times, and almost no decrease was observed. In addition, no defective products occurred at all about 100 million times, and all were normal. Since the external electrode 15 is thus composed of the underlayer 16 composed of the vapor deposition films 16a, 16b, 16c and the coating film 17 of the metal paste containing Au, the external electrode 15 can be thickened. It is possible to confirm that it is possible to prevent the deterioration of the parts, maintain the good conductivity of the external electrode 15 and prevent the decrease of the electrostatic capacitance in the laminated piezoelectric actuator 10. did it.

[0034]

[Table 2]

Table 2 shows a laminated piezoelectric actuator 10 according to the embodiment, and a conventional laminated piezoelectric actuator in which the external electrode 25 is composed only of a coating film of Ag paste having a thickness of about 300 μm as a comparative example (FIG. 5). In and, the temperature was 40 ° C, the relative humidity (RH) was 90%, and the rated voltage of 150V was continuously applied to 10 parts each, and the result of the investigation of the damage status of the parts after 100 hours elapsed was shown. It is shown.

As is clear from Table 2, in the laminated piezoelectric actuator according to the comparative example, 7 out of 10 pieces were destroyed after 100 hours passed, whereas the laminated layer type piezoelectric actuator 10 according to the example was broken. Then, after 100 hours, everything was normal. Thus, the underlayer 16 is composed of the Cr vapor deposition film 16a, the Ni vapor deposition film 16b, and the Au vapor deposition film 16c, and the coating film 17 of the metal paste containing Au is formed. Since it is not used, migration can be prevented, damage to parts of the laminated piezoelectric actuator 10 with the passage of electricity time can be prevented, and durability of the laminated piezoelectric actuator 10 can be prevented. We were able to confirm that can be greatly improved.

As described above, in the external electrode 15 of the laminated piezoelectric actuator 10 according to the example, the underlayer 16 that contacts the laminated piezoelectric body 11 includes the Cr vapor deposition film 16a, the Ni vapor deposition film 16b, and the Ni vapor deposition film 16b. Since it is composed of the Au vapor deposition film 16c, the underlayer 16 can be formed at a low cost by using the vacuum evaporation method, and the particles of the underlayer 16 can be made fine, so that the piezoelectric ceramic substrate 12 Good adhesion with can be obtained. Also, good adhesion with the internal electrode 13 having a narrow exposed width can be ensured, connection with the internal electrode 13 can be performed well, and good conductivity with the internal electrode 13 can be ensured. Therefore, it is possible to prevent the decrease of the electrostatic capacity and the deterioration of the laminated piezoelectric actuator 10 with the passage of time.

Further, since the outer layer is composed of the coating film 17 of the metal paste containing Au, the coating film 17 is formed by the screen printing method to form the thick coating film 17 at a low cost. can do. Therefore, it is possible to reduce the manufacturing cost. Further, the external electrode 15 having low resistance and hard to break can be formed, good conductivity can be secured, deterioration of the laminated piezoelectric actuator 10 is prevented, and durability of the laminated piezoelectric actuator 10 is improved. Can be made.

Further, since Ag is not used for the external electrode 15, migration can be sufficiently prevented, and the capacitance of the multilayer piezoelectric actuator 10 due to passage of energization time and repetition of pulse response and the like. Can be prevented, and the durability of the laminated piezoelectric actuator 10 can be greatly improved.

In the above-described embodiment, the case where the coating film 17 is a metal paste containing Au has been described as an example, but in another embodiment, the coating film 17 has high migration resistance. It may be a metal paste containing Ni or platinum.

Although the thickness of the coating film 17 is about 500 μm in the above-mentioned embodiment, the thickness of the coating film 17 may be about 100 μm to 500 μm in another embodiment.

Further, in the above-described embodiment, the case where Cr, Ni and Au are used as the material of the vapor deposition film has been described as an example, but in another embodiment, the material of the vapor deposition film is more resistant than Ag such as platinum or the like. You may use the metal excellent in migration property.

Although the thickness of the underlayer 16 is about 6000Å in the above-mentioned embodiment, the thickness of the underlayer 16 may be about 1000 to 6000Å in another embodiment.

[0044]

[Effect of device]

 As described above in detail, in the external electrode of the laminated piezoelectric component according to the present invention, the piezoelectric ceramic substrate and the internal electrode are alternately laminated to form a laminated piezoelectric body. In an external electrode of a laminated piezoelectric component having external electrodes formed on both side surfaces, the underlying layer that comes into contact with the laminated piezoelectric body is composed of a vapor deposition film. Since it can be formed and the particles of the underlayer can be made fine, good adhesion with the piezoelectric ceramic substrate can be secured. Further, it is possible to secure good adhesion to the internal electrode having a narrow exposed width, to perform good connection with the internal electrode, and to secure good electrical continuity with the internal electrode. Therefore, it is possible to prevent the capacitance from decreasing with the passage of time and the deterioration of the multilayer piezoelectric component.

Further, since the outer layer is composed of the coating film of the metal paste containing Au, Ni or platinum, the coating film having a large thickness can be formed at a low cost by forming the coating film by the screen printing method. Can be formed. Therefore, it is possible to reduce the manufacturing cost. Further, it is possible to form the external electrode having a low resistance and is hard to break, it is possible to ensure good electrical conductivity in the external electrode, deterioration of the multilayer piezoelectric component is prevented, and durability of the multilayer piezoelectric component is prevented. It is possible to improve the sex.

Further, since Ag is not used for the external electrodes, the occurrence of migration can be sufficiently prevented, and the capacitance of the multilayer piezoelectric component due to repetition of energization time and pulse response can be reduced. The decrease can be prevented, and the durability of the laminated piezoelectric component can be greatly improved.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram showing external electrodes of a laminated piezoelectric component according to the present invention.

FIG. 2 is a perspective view schematically showing an embodiment of an external electrode of the laminated piezoelectric component according to the present invention.

FIG. 3 is a schematic cross-sectional view showing an enlarged external electrode portion according to an example.

FIG. 4 shows a laminated piezoelectric actuator according to an embodiment of the present invention and a conventional laminated piezoelectric actuator whose external electrodes are composed only of a coating film of a normal Ag paste as a comparative example at a temperature of 26 ° C. without being energized. It is the graph which showed the result of having left 1000 hours of relative humidity (RH) indoors for 1000 hours, and investigating the time-dependent change of electrostatic capacitance.

FIG. 5 is a perspective view schematically showing a part of a conventional laminated piezoelectric actuator.

FIG. 6 is a schematic cross-sectional view showing an enlarged external electrode portion of a conventional laminated piezoelectric actuator.

FIG. 7 is a schematic cross-sectional view showing an external electrode formed by using a conventional sputtering method.

[Explanation of symbols]

 10 Multilayer Piezoelectric Actuator (Multilayer Piezoelectric Component) 11 Multilayer Piezoelectric Body 12 Piezoelectric Ceramic Substrate 13 Internal Electrode 15 External Electrode 16 Underlayer 16a Cr Vapor Deposition Film (Vaporization Film) 16b Ni Vapor Deposition Film (Vaporization Film) 16c Au Vapor Deposition Film ( Deposition film) 17 Coating film (outer layer)

Claims (1)

[Scope of utility model registration request] 1. An external electrode of a laminated piezoelectric component, wherein a piezoelectric ceramic substrate and internal electrodes are alternately laminated to form a laminated piezoelectric body, and external electrodes are formed on both side surfaces of the laminated piezoelectric body. An outer electrode of a laminated piezoelectric component, wherein a base layer in contact with the laminated piezoelectric body is composed of a vapor deposition film, and an outer layer is composed of a coating film of a metal paste containing Au, Ni or platinum.