JP2006269851A - Multilayer piezoelectric element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer piezolectric element having a structure where the stress due to displacement of a multilayer body can be reduced without causing degradation in characteristics or difficulties in production. <P>SOLUTION: A multilayer body is constituted of a plurality of piezoelectric layers 1 and a plurality of internal electrodes 2. On the side face parallel with the layer direction of the multilayer body, a first external electrode 3 connected with a first internal electrode 2 and a second external electrode 3 connected with a second internal electrode 2 are provided. Edge of the first internal electrode (second internal electrode) 2 on the side of the second external electrode (first external electrode) is located on the inner side from the side face of the multilayer body for providing the second external electrode (first external electrode) 3. A glass layer 5 is provided between the edge of the first internal electrode (second internal electrode) 2 on the side of the second external electrode (first external electrode) 3 and the second external electrode (first external electrode) 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multilayer piezoelectric element.

  As a conventional piezoelectric element, there is a stacked piezoelectric element in which a plurality of piezoelectric layers and internal electrodes are alternately stacked. In such a piezoelectric element, the piezoelectric layer is displaced according to the applied voltage in the overlapping part (active part) of the internal electrodes, but the other part (inactive part) is not displaced. Since the inactive portion extends in the stacking direction of the stacked body, it inhibits displacement (stretching operation) of the stacked body in the stacking direction. For this reason, if a polarization process is performed at the time of manufacturing the piezoelectric element, or if the piezoelectric element is used for a long period of time, a crack that reaches the inside of the laminate occurs. And an external electrode may be cut | disconnected in the generation | occurrence | production position of the crack, and there exists a possibility that the disconnection from which a connection with an internal electrode and an external electrode is disconnected may arise.

  In order to prevent such disconnection, Patent Document 1 proposes a technique in which a stress generated by displacement is dispersed by forming grooves with a predetermined interval on a side surface parallel to the stacking direction of the stacked body. .

  In addition, when the inactive portion is provided in the laminate as described above, stress is generated in the portion, and therefore, the inactive portion is not provided in the laminate, and all peripheral portions of all internal electrodes are arranged in the stacking direction of the laminate. Japanese Patent Application Laid-Open No. H10-228688 discloses an insulating film that is exposed on parallel side surfaces and that is provided with external electrodes and that covers the internal electrodes with every other glass film to insulate the external electrodes.

JP-A-4-337682 JP-A-7-106656

  However, in the multilayer piezoelectric element having the groove described in Patent Document 1, if the groove is formed by cutting after firing, there is a problem that it takes time to form the groove because the element is hard. Further, as described in Patent Document 1, when a method of forming a groove by applying a paste containing carbon powder to a green sheet and flying the carbon at the time of firing, the reduction action of the material by carbon However, there are problems that the characteristics are deteriorated and the grooves are closed during the firing process.

  On the other hand, according to the method described in Patent Document 2, since one layer is a thin layer of, for example, about 30 μm, it is difficult to insulate the thin layer by applying glass after sintering by printing or the like. In addition, the exposed portion of the internal electrode may not be covered due to misalignment, or the exposed portion of the other internal electrode that should not be covered may be covered, and the number of steps of individual chips after firing increases, and There is a problem that miniaturization is difficult due to the thickness of the side glass layer.

  In view of the above problems, an object of the present invention is to provide a multilayer piezoelectric element having a structure in which the displacement of the multilayer body is large and the stress is small without causing deterioration of characteristics or difficulty in manufacturing.

In the multilayer piezoelectric element of the present invention, a multilayer body is constituted by a plurality of piezoelectric layers and a plurality of internal electrodes, and a first internal electrode is connected to a side surface parallel to the stacking direction of the multilayer body. A laminated piezoelectric element provided with a second external electrode to which the external electrode and the second internal electrode are connected,
The edge of the first internal electrode on the second external electrode side is located on the internal side from the side surface of the laminate on which the second external electrode is provided,
There is a glass layer between the second external electrode side edge of the first internal electrode and the second external electrode,
The edge of the second internal electrode on the first external electrode side is located on the internal side from the side surface of the laminate on which the first external electrode is provided,
A glass layer is provided between the edge of the second internal electrode on the first external electrode side and the first external electrode.

  In the multilayer piezoelectric element of the present invention, the peripheral portion of the internal electrode that should not be connected to the external electrode is located inside the side surface on which the external electrode is formed, and the internal electrode and the external electrode Since the insulating layer is insulated by a glass layer, the active portion can be formed on almost the entire surface that is substantially perpendicular to the stacking direction of the stacked body. For this reason, generation | occurrence | production of stress can be prevented and generation | occurrence | production of a crack can be prevented. Further, since the region where the displacement occurs is wide, the displacement of the entire laminated piezoelectric element can be increased.

  In addition, since the multilayer piezoelectric element of the present invention can be manufactured with a material that does not contain carbon or the like, the characteristics are not deteriorated without firing and reducing the piezoelectric layer and internal electrodes.

  In addition, the glass layer can be formed by printing a glass-containing conductor paste on a green sheet and firing, so that it does not increase the post-installation process as in the case of forming after firing, and more accurately by screen printing. It can be formed easily.

  In addition, when the glass is baked on the side surface of the laminate after sintering as in the conventional case, the portion protrudes, resulting in unevenness and difficulty in baking the external electrode, but in the present invention, the glass layer protrudes on the side surface. Therefore, the mounting surface of the external electrode becomes a flat surface, which facilitates the mounting and facilitates the miniaturization.

  In addition, the multilayer piezoelectric element of the present invention can secure most of the active layer other than the glass layer as an active part, and the area of the active part is enlarged, and electrical insulation between the external electrode to be insulated is achieved. Secured.

  The multilayer piezoelectric element according to the present invention can be manufactured by a method of printing a glass-containing conductor paste on the periphery of the internal electrode formation region and firing after the lamination. During the firing step in this method, the glass component is excluded from the internal electrode formation region and moves to the surface side of the laminate. For this reason, since the glass layer is formed between the internal electrode and the side surface formed over almost the entire surface of the laminated body (the surface perpendicular to the laminating direction of the laminated body), the laminated body is substantially substantially laminated. An active portion can be formed on the entire surface. Therefore, it is possible to provide a multilayer piezoelectric element that can prevent the generation of stress, prevent the generation of cracks, and has a large displacement. Further, the glass layer does not deteriorate the characteristics without reducing the piezoelectric layer and the internal electrode, which are ceramic layers, by firing.

  In addition, the glass layer can be formed by printing and baking a glass-containing conductor paste on a part of the green sheet, so that the screen printing can be performed without increasing the retrofitting process as in the case of forming after baking. Therefore, it can be easily formed with high accuracy.

  In addition, when glass is baked on the side surface of the laminate after sintering as in the conventional case, the portion protrudes, resulting in unevenness, increasing the outer dimensions, unsuitable for downsizing, and forming external electrodes. Although it becomes difficult, according to the said manufacturing method, since the laminated body from which a glass layer does not protrude to a side surface can be obtained, the attachment surface of an external electrode becomes a plane and the attachment becomes easy.

  FIG. 1 is a cross-sectional view showing an embodiment of the multilayer piezoelectric element of the present invention. This piezoelectric element has a piezoelectric layer 1 that exhibits piezoelectric characteristics such as lead zirconate titanate (PZT), and internal electrodes 2 that are arranged alternately with the piezoelectric layers 1 in the stacking direction, and are connected to the internal electrodes 2 to face each other. A pair of external electrodes 3, 3 provided on the side surfaces and protective layers (displacement transmission surfaces) 4, 4 provided on both ends in the stacking direction, that is, on the upper and lower surfaces in the drawing, are provided. In the present invention, in order to electrically insulate the external electrode 3 and the internal electrode 2 every other layer, a glass layer 5 is provided in the same layer as the internal electrode 2 to constitute a laminate.

  In FIG. 1, an internal electrode 2 formed on the left side (right side) is a first internal electrode (second internal electrode), and an external electrode 3 connected to the first internal electrode (second internal electrode) 2 is When the first external electrode (second external electrode) is used, the edge of the first internal electrode (second internal electrode) 2 on the second external electrode (first external electrode) side is the second external electrode. The electrode (first external electrode) 3 is located on the inner side from the side surface of the laminate. Further, between the edge of the first internal electrode (second internal electrode) 2 on the second external electrode (first external electrode) 3 side and the second external electrode (first external electrode) 3. There is a glass layer 5.

The glass layer 5 is formed by sintering and shrinking of the conductor in the glass-containing conductor paste, and the glass component moves in the surface (side surface) direction, and has a resistance value of 10 ⁷ Ω · cm or more. As the glass used for the glass layer 5, lead borosilicate glass, zinc borosilicate glass, aluminoborosilicate glass, or the like can be used.

  FIG. 2 is a view showing a green sheet 6 used for manufacturing the piezoelectric element shown in FIG. This example shows an example of taking a large number of pieces. The green sheet 6 forms the internal electrode 2, and the internal electrode 2 and the glass-containing internal electrode 10 are formed vertically and horizontally by printing a glass-containing conductor paste.

  FIG. 3 is an enlarged view of one internal electrode formation region (including the glass-containing internal electrode 10) on the green sheet shown in FIG. As shown in FIGS. 3A to 3D, the internal electrode 2 is formed in the internal electrode formation region leaving a part of the peripheral portion (one side). Further, the glass-containing internal electrode 10 is formed in the remaining part of the internal electrode formation region. The ratio a / b of the width a of the glass-containing internal electrode 10 to the green sheet width b is set to about 0.03 to 0.2. FIG. 3E shows a green sheet for forming a protective layer in which the internal electrode 2 is not formed.

The multilayer piezoelectric element of the present invention is manufactured by the following process. First, a green sheet 6 containing ceramic powder having a piezoelectric property, for example, a powder density of about 3000 kg / m ³ is prepared. The green sheet 6 is prepared by preparing a ceramic paste in which an organic binder, an organic solvent, and the like are mixed with a powder for obtaining piezoelectric characteristics, that is, a powder mainly composed of, for example, lead zirconate titanate (PZT). Thus, the PET film is formed into a sheet as a carrier film.

  On the internal electrode forming area of the green sheet 6, the conductor paste to be the internal electrode 2 is printed leaving a part of the peripheral area and dried. Before or after printing the conductor paste, the glass-containing internal electrode paste is printed in the remaining area and dried. Here, it is preferable that what is used as a conductor paste is silver-palladium, and in order to reduce the price of an electrode, it is preferable that the content rate of palladium is low. Specifically, the palladium content is preferably 30% or less.

  The conductor paste forming the internal electrode 2 preferably does not contain glass as an inorganic substance, but may contain some glass. In that case, the glass-containing conductor paste forming the glass-containing internal electrode 10 is set to have a higher glass content than the conductor paste forming the internal electrode 2.

  As described above, a plurality of green sheets printed with the conductor paste and the glass-containing conductor paste are laminated in the opposite direction so that the glass-containing internal electrodes 10 are on the opposite side every other sheet. . This lamination is performed by pressurizing at 55 to 65 ° C. with a pressure of about 90 to 110 MPa.

  Next, the laminated body thus laminated is fired. In this firing step, first, the binder removal treatment is performed at around 400 ° C., and then the firing is carried out in the range of 950 to 1050 ° C., preferably for 0.5 to 4 hours, in a sealed container. The thickness of the internal electrode 2 after firing is 1 to 5 μm, preferably 1.5 to 3 μm. Moreover, the thickness of the piezoelectric layer 1 is 20-100 micrometers, Preferably it is 50-80 micrometers.

  As shown in FIG. 4, during the firing, in the glass-containing internal electrode 10, the conductive powder therein is sintered and contracted to form the conductive portion 2 a. At the same time, the glass is removed on the side surface portion (surface portion) to form a glass layer 5 that does not contain conductive powder, and a non-conductive portion is formed. Therefore, between the internal electrode 2 and the external electrode 3 to be electrically cut off, Can be well insulated. In addition, since the containing glass is excluded, the conduction | electrical_connection part 2a has a function as an electrode substantially the same as the internal electrode 2. FIG.

  On the two laminated side surfaces where the glass layer 5 is exposed in an aligned manner with respect to the fired laminate, the exposed portions on the side surfaces of the aligned glass layer 5 and the internal electrodes 2 of other layers exposed in the row are arranged. The external electrodes 3 and 3 are provided so as to be fixed to the exposed portions on the side surfaces. The external electrode 3 is formed by printing and baking a conductor paste containing silver as a conductor powder. In addition to silver, an alloy of silver and another metal, gold, copper, or the like can be used as the conductor powder of the external electrode 3. In addition, sputtering, electroless plating, or the like can be used to form the external electrode 3.

  After the external electrode 3 is formed, a polarization treatment is performed by applying a high voltage (eg, 3 kV / mm) between the external electrodes 3 and 3 in a heated state (eg, 120 ° C.). The obtained piezoelectric element is, for example, a piezoelectric element in which the thickness of the piezoelectric layer 1 is 30 μm, the thickness of the internal electrode 2 is 3 μm, the number of layers of the piezoelectric layer 1 is 100, and the length × width × height is 10 mm × 10 mm × 30 mm It is. In addition, this multilayer piezoelectric element can also be realized with a hexagonal, octagonal, or circular planar shape. Further, the number of layers and the size can be appropriately changed depending on the purpose of use. In addition, the connection portion between one external electrode 3 and a plurality of internal electrodes 2 is not provided every other layer as a whole, but the internal electrode 2 is partially connected to the external electrode 3 on the same side in two consecutive layers. It may be configured to be connected.

  As described above, in the multilayer piezoelectric element of the present invention, the peripheral portion of the internal electrode 2 that should not be connected to the external electrode 3 is located inside the side surface on which the external electrode 3 is formed. Since the glass layer 5 and the external electrode 3 are insulated from each other, the active portion can be formed on almost the entire surface perpendicular to the stacking direction of the stacked body. For this reason, generation | occurrence | production of stress can be prevented and generation | occurrence | production of a crack can be prevented. Also, a large amount of displacement can be obtained.

  Further, since the glass layer 5 is obtained by printing a glass-containing conductor paste on the green sheet 6 and firing, the glass layer 5 can be easily and accurately performed by screen printing without increasing the number of retrofitting steps as in the case of forming after firing. Can be formed.

  In addition, when the glass is baked on the side surface of the laminate after sintering as in the conventional case, since the portion protrudes, unevenness is generated, the shape becomes large, unsuitable for downsizing, and the formation of the external electrode is difficult, In the present invention, since the glass layer 5 hardly protrudes on the side surface of the laminate, the external electrode 3 can be easily formed, and the size can be reduced.

It is sectional drawing which shows one Embodiment of the lamination type piezoelectric element of this invention. It is a top view which shows the printing pattern on the green sheet for obtaining the lamination type piezoelectric element of FIG. (A), (C) is a top view which shows the printing pattern of the internal electrode on one internal electrode printing area | region, and a glass containing internal electrode, (B), (D) is a side view of (A), (C), respectively. (D) is a top view which shows the green sheet used as a protective layer. It is an expanded sectional view of the glass layer part of the piezoelectric element of the embodiment of the present invention.

Explanation of symbols

1: piezoelectric layer, 2: internal electrode, 2a: conducting portion, 3: external electrode, 4: protective layer, 5: glass layer, 6: green sheet, 7, 8: cutting line, 10: glass-containing internal electrode

Claims (1)

A laminated body is constituted by a plurality of piezoelectric layers and a plurality of internal electrodes, and a first external electrode and a second internal electrode having a first internal electrode connected to a side surface parallel to the lamination direction of the laminated body A laminated piezoelectric element provided with a second external electrode to which is connected,
The edge of the first internal electrode on the second external electrode side is located on the internal side from the side surface of the laminate on which the second external electrode is provided,
There is a glass layer between the second external electrode side edge of the first internal electrode and the second external electrode,
The edge of the second internal electrode on the first external electrode side is located on the internal side from the side surface of the laminate on which the first external electrode is provided,
A laminated piezoelectric element, wherein a glass layer is provided between an edge of the second internal electrode on the first external electrode side and the first external electrode.

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