Patent Grant
7225514
This application claims priority to application Ser. No. 2003-157116, filed 02 Jun. 2003. The entire contents of this application is incorporated herein by reference.
The present invention relates to a method for producing a stacked piezoelectric element by alternately stacking a piezoelectric layer and an inner electrode layer.
Recently, in view of improving the fuel consumption and cleaning the exhaust gas of automobiles, development of injectors capable of more precisely controlling the fuel injection is demanded. As for such a highly precise injector, use of a stacked piezoelectric element as the actuator has been proposed. However, a stacked piezoelectric element having excellent durability and applicable to the actuator of those injectors has not yet been put into practice at present.
The stacked piezoelectric element can be produced, for example, by printing and forming an inner electrode layer of 5 μm on a green sheet having a thickness of about 100 μm, stacking, for example, hundreds of such green sheets, subjecting the stacked green sheets to press-molding, drying, firing, machining and the like to form a stacked body, and joining a side electrode to a side face of the stacked body.
For improving the durability of the stacked piezoelectric element, the inner electrode layer exposed to the side face of the stacked body must be insulated, without fail, so as to prevent the generation of migration or the like.
Japanese Unexamined Patent Publication (Kokai) No. 5-160458 discloses a method of applying an insulating resin coat to the inner electrode exposed to the side face of a stacked body and thereby preventing the migration of silver. However, this method has a problem in that if the resin coat is stripped off, water or the like intrudes to cause migration of silver and insulation failures.
As for the method of insulating the inner electrode layer exposed to the outer peripheral side face of a stacked body, Japanese Unexamined Patent Publication (Kokai) No. 2001-244514 has proposed a method of machining grooves and filling a resin in each groove to achieve insulation by resin. However, it is not practicable, in mass production, to machine grooves having a depth of 500 μm and a height (width) of 50 μm by a cutting saw as disclosed in this patent document.
For example, as described in Patent Publication No. 2001-244514, when grooves are provided on the side face of a stacked body, the insulating resin filled in the groove is stably maintained by an anchor effect and the durability can be improved.
However, machining of grooves by a cutting saw is industrially difficult in view of the working efficiency and, also, the stacked body may be damaged during the machining to cause a problem in quality.
The present invention has been made for solving these problems in conventional techniques and an object of the present invention is to provide a method for producing a stacked piezoelectric element, where grooves can be easily formed on the side face of a stacked body without causing damage.
The present invention is a method for producing a stacked piezoelectric element by alternately a stacking piezoelectric layer comprising a piezoelectric material and an inner electrode layer comprising an electrically conducting material, the method comprising:
a green sheet production step of producing a green sheet for a base, which constitutes a part of the piezoelectric layer,
a unit body formation step of forming a unit body by disposing a narrow stacked part on the green sheet for a base, wherein the narrow stacked part is comprised of a narrow piezoelectric material layer which constitutes a part of the piezoelectric layer and has an area smaller than the green sheet for a base and an electrode material layer, which constitutes the inner electrode layer, having an area smaller than the green sheet for a base,
a stacked body formation step of forming a stacked body having groove parts by stacking a plurality of the unit bodies, wherein the groove part having the bottom being defined by the side face of the narrow stacked part, and
a firing step of firing the stacked body.
In the present invention, at least the above-described unit body formation step is performed after the green sheet production step. In this unit body formation step, a unit body is formed by disposing the narrow stacked part on the green sheet for a base. The narrow stacked part is constituted, as described above, by stacking a narrow piezoelectric material layer and an electrode material layer each having an area smaller than the green sheet for a base and therefore, the narrow stacked part disposed on the green sheet for a base is in such a state that at least a part of the side face thereof is receding inward from the outer peripheral end face of the green sheet for a base.
As a result, the stacked body obtained by stacking a plurality of unit bodies in the stacked body formation step has a structure where many groove parts receding inward from the outer peripheral end part of the green sheet for a base are present on the side face of the stacked body and the bottom of each groove part is defined by a side face of the narrow stacked part.
The structure of the stacked body having many groove parts is maintained as it is even after the subsequent firing step. At the same time, the green sheet for a base and the narrow piezoelectric material layer are integrated with each other to compose the piezoelectric layer, and the electrode material layer interposed between these piezoelectric layers works out to the inner electrode layer. Accordingly, the stacked piezoelectric element obtained after firing has a structure where the portion having the inner electrode layer is constituted by the narrow stacked part and a groove part is present in the outer periphery thereof.
By virtue of such a structure, in the case of applying coating or the like of an insulating resin material so as to ensure insulation of the inner electrode layer of the stacked piezoelectric element, the insulating resin material intruded into the groove part exerts a so-called anchor effect and the coating state can be more stable than in conventional techniques, whereby the stacked piezoelectric element obtained can be enhanced in durability.
Furthermore, in providing many groove parts on the side face of the stacked piezoelectric element, this can be attained, as described above, by only forming a unit body having a specific structure and stacking the unit bodies, and a specific machining operation conventionally required for forming groove parts, such as cutting work by a cutting saw, is not necessary, so that the groove part can be very easily formed and at the same time, the stacked piezoelectric element (stacked body) can be free from damaging at the formation of groove parts.
In this way, according to the present invention, a method for producing a stacked piezoelectric element, where groove parts can be easily formed on the side face of a stacked body without causing damages, can be provided.
In the unit body formation step, the narrow stacked part may take a constitution where an electrode material layer is disposed directly on the green sheet for a base and one or more narrow piezoelectric layers are stacked thereon, a constitution where one or more narrow piezoelectric material layers are stacked directly on the green sheet for a base and an electrode material layer is disposed thereon, or a constitution where an electrode material layer is disposed between a plurality of narrow piezoelectric material layers.
In the unit body formation step, the unit body can also be formed by interposing the narrow stacked part between two green sheets for base.
In the unit body, the narrow stacked part is preferably provided to recede inward from the outer peripheral edge of the green sheet for a base around the entire circumference thereof. In this case, the groove part can be annularly formed around the entire circumference of the stacked piezoelectric element. The narrow stacked part may be of course provided such that a part of the outer peripheral edge thereof is flush with a part of the outer peripheral edge of the green sheet for a base. In this case, the groove part is not formed in the flush portion.
As for the piezoelectric layer of the stacked piezoelectric element, a piezoelectric material such as lead zirconate titanate (PZT) can be used.
As for the inner electrode layer, an Ag—Pd material is preferred in view of durability, and Cu or an alloy material thereof is preferred in view of cost.
In the present invention, a side electrode disposition step of disposing side electrodes on two side faces of the stacked piezoelectric element, namely, on a first side face part and a second side face part, is preferably performed after the firing step. The side electrode can be disposed by various methods. For example, in the groove parts on each of these first side face and second side face, an insulating material and an electrically conducting material are alternately filled along the stacking direction. On each of these first and second side faces, an electrically conducting material is further applied and through this electrically conducting material, respective side electrodes are disposed. In this case, although the groove parts are provided, an alternate electrical conduction structure between the side electrode and the inner electrode layer can be easily formed by alternately filling the insulting material and the electrically conducting material in the groove parts.
Also, a resin coating step of coating the entire side face of the stacked piezoelectric element, including a part of each side electrode, with an insulating resin is preferably performed. By this resin coating, even when the inner electrode layer is exposed to a side face where the side electrode is not provided, this can be covered with the insulating resin and therefore, excellent insulation can be obtained. In the present invention, particularly, by virtue of the presence of groove parts, the insulating resin material intruded into this groove part exerts a so-called anchor effect and the coating state can be more stabilized than in conventional techniques, whereby the durability of the stacked piezoelectric element can be enhanced.
Also, in the unit body formation step, it is preferred to dispose a plurality of narrow stacked parts on one green sheet for a base while leaving a gap between respective narrow stacked parts and cut and separate the green sheet for a base along the gaps to form unit bodies. In this case, a large number of unit bodies can be efficiently produced. Furthermore, for example, a method comprising providing many narrow stacked parts on a wide sheet- or belt-like green sheet for a base, sequentially cutting and separating these by stamping to form unit bodies, and at the same time, stacking the unit bodies, may also be employed. In this case, the unit body formation step and the stacked body formation step can be made to proceed in parallel and the production process can be streamlined.
Each narrow piezoelectric material layer and each electrode material layer are preferably formed by using a slurry- or paste-like raw material and printing it. In this case, the area of each of the narrow piezoelectric material layer and the electrode material layer can be controlled with good precision and at the same time, the thickness of each layer can be easily controlled by the number of printing operations.
It is preferred that, at the formation of the narrow stacked part, at least an uppermost layer is formed by printing and kept in the tacky state without drying and at the subsequent stacking of the unit body, the uppermost layer is used as an adhesive layer. In this case, by only stacking the unit body on the uppermost layer, a plurality of unit bodies can be integrated due to tackiness of the uppermost layer of the narrow stacked part and the stacked body can be easily formed.
This is also very effective in the case of using the above-described method of providing many narrow stacked parts on a wide sheet- or belt-like green sheet for a base, sequentially punching out these to form unit bodies and at the same time, stacking the unit bodies, because the unit bodies are sequentially bonded.
Furthermore, it is preferred that in the unit body formation step, the narrow stacked part is formed such that the electrode material layer comes into direct contact with the green sheet for a base, wherein a takeout electrode part is formed in the electrode material layer by extending a part of the outer periphery of the electrode material layer to the position nearly flush with the outer peripheral end face of the green sheet for a base constituting the unit body.
In this case, by virtue of the presence of a takeout electrode part, electrical connection between the side electrode disposed on the side face of the stacked body and the inner electrode layer can be relatively easily attained.
The method for producing a stacked piezoelectric element of the present invention is described below by referring to
As shown in
In producing this stacked piezoelectric element 1, as shown in
The green sheet production step is a step of producing a green sheet 110 for base (
The unit body formation step is, as shown in
The stacked body formation step is, as shown in
The firing step is a step of firing the stacked body 100 to produce a stacked piezoelectric element 1.
These steps are described in more detail below.
In this Example, the step for producing a green sheet for a base is performed as follows so as to employ PZT as the piezoelectric layer 11.
Lead oxide, zirconium oxide, titanium oxide, niobium oxide, strontium carbonate and the like each in the powder form, which are main raw materials of the piezoelectric material, are weighed into a desired composition. By taking account of the evaporation of lead, the lead oxide was formulated to be richer by 1 to 2% than the stoichiometric ratio of the above-described mixing ratio. These components are mixed in a dry system by a mixer and then calcined at 800 to 950° C.
Thereafter, pure water and a dispersant are added to the calcined powder and the obtained slurry is wet-ground in a pearl mill. The ground product is dried, powder degreased and after adding thereto a solvent, a binder, a plasticizer, a dispersant and the like, mixed in a ball mill. The resulting slurry is subjected to vacuum defoaming and adjustment of viscosity while stirring with a stirrer in a vacuum device.
This slurry is then shaped into a green sheet of a certain thickness by using a doctor blade device.
The green sheet obtained is stamped by a press or cut by a cutter and thereby shaped into a rectangular form and this is used as a green sheet 110 for base. The green sheet for a base can also be shaped, for example, in the circular, elliptic or barrel form according to the shape of the stacked piezoelectric element to be obtained. Also, as described later, a belt-like or wide sheet-like green sheet for a base can be prepared and afterward cut and separated into a desired shape.
On the surface of the resulting rectangular green sheet 110 for base, in this Example, as shown in
The material used for the narrow piezoelectric material layer 115 is the same slurry as the material of the green sheet 110 for base. The material used for the electrode material layer 20 is a paste comprising silver and palladium (hereinafter referred to as an Ag/Pd paste) at a ratio of silver/palladium=7/3. The material for the electrode material layer 20 may be changed to a material mainly comprising Cu.
In this Example, as shown in
Thus, as shown in
Thereafter, a stacked body formation step of, as shown in
Then, a firing step of degreasing and then firing the stacked body 100 is performed. The degreasing is performed by holding the stacked body 100 in an electric furnace at a temperature of 400 to 700° C. for a predetermined time. The firing is performed by holding the stacked body 100 at a temperature of 900 to 1,200° C. for a predetermined time. In this way, a stacked piezoelectric element 1 of this Example where, as shown in
Subsequently, in this Example, as shown in
In this Example, as shown in the Figures, an insulating material 61 and an electrically conducting material 62 are alternately filled in the groove parts 4 on each of the first side face 101 and the second side face 102 along the stacking direction. On each of the first side face 101 and the second side face 102, an electrically conducting material 62 is further applied and through this electrically conducting material, respective side electrodes 51 and 52 are disposed. In this Example, an electrically conducting adhesive comprising silver-palladium (Ag—Pd) is used as the electrically conducting material 62 and a silicon resin is used as the insulating material 61.
Furthermore, in this Example, a resin coating step of, as shown in
Furthermore, in this Example, in providing many groove parts 4 on the side face of the stacked piezoelectric element 1, this can be attained by only forming a unit body 3 having the above-described structure and stacking the unit bodies, and a specific machining operation conventionally required for forming groove parts, such as cutting work by a cutting saw, is not necessary, so that the groove part 4 can be very easily formed and at the same time, the stacked piezoelectric element 1 can be free from damage at the formation of groove parts 4.
In this Example, as shown in
More specifically, in the unit body formation step of this Example, as shown in
In the stacked body formation step, a stacked body 100 is obtained, as shown in
Thereafter, the firing step is performed in the same manner as in Example 1, whereby a stacked piezoelectric element 1 where, as shown in
Also, in this Example, a side electrode disposition step is performed in the same manner as in Example 1.
By this disposition, as shown in
In addition, the same operational effects as in Example 1 can be obtained.
In the unit body formation step of this Example, as shown in
More specifically, as shown in the Figure, a narrow piezoelectric material layer 115 and an electrode material 20 are disposed on one wide sheet-like green sheet 110 for base by printing in the same manner as in Example 1 to form a plurality of narrow stacked parts 30.
Thereafter, the green sheet 110 for base is cut and separated along the cutting line (broken line C), whereby a plurality of unit bodies 3 (
In this case, the production of unit body 3 can be more efficiently performed. In addition, the same operational effects as in Example 1 can be obtained.
In this Example, a method of, as shown in
More specifically, a belt-like green sheet 110 for base is produced in the same manner as in Example 1, many narrow stacked parts 30 are formed by printing on the top face of the green sheet and then, as shown in
The stamping device 8 comprises, as shown in the
The punch 82 of the stamping device 8 is thrust up every at advance of the green sheet 110 for base, whereby unit bodies 3 can be stamped and stacked.
In this Example, the unit body formation step and the stacking step can be made to simultaneously proceed by continuous stamping with the use of the stamping device 8 and therefore, the production efficiency can be more enhanced.
In addition, the same operational effects as in Example 1 can be obtained.
In this Example, as shown in
More specifically, in the unit body formation step of this Example, as shown in
Thereafter, as shown in
Subsequently, the firing step is performed in the same manner as in Example 1 and then side electrodes 51 and 52 are disposed and, as a result, a stacked piezoelectric body 1 as shown in
In this case, an inner electrode layer 2 having a step part 23 is obtained and a side electrode 51 or 52 is connected thereto through an electrically conducting material 62, so that the contact area can be more increased than in Example 1 and the electrical connection structure can be more stabilized.
In addition, the same operational effects as in Example 1 can be obtained.
In this Example, as shown in
This example is the same as those in Example 1 except for the above. Also in this case, the same operational effects as in Example 1 can be obtained.
In this Example, as shown in
More specifically, as shown in
In this Example, a method of forming a plurality of barrel-shaped narrow stacked parts on a belt- or wide sheet-like green sheet for a base and then obtaining unit bodies 3 by stamping can also be employed.
Also in this Example, the same operational effects as in Example 1 can be obtained.
In this Example, as shown in
More specifically, as shown in
In the subsequent stacked body formation step, the unit bodies 3 are stacked such that the takeout electrode parts 22 are on opposite sides of the unit bodies. As a result, a stacked body 100 as shown in
In addition, the same operational effects as in Example 1 can be obtained.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-157116 | Jun 2003 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4752712 | Tomita et al. | Jun 1988 | A |
| 5245734 | Issartel | Sep 1993 | A |
| 5440794 | Kaeriyama et al. | Aug 1995 | A |
| 6414417 | Tsuyoshi et al. | Jul 2002 | B1 |
| 6700306 | Nakamura et al. | Mar 2004 | B2 |
| 6757947 | Seipler et al. | Jul 2004 | B2 |
| 20020175591 | Schreiner et al. | Nov 2002 | A1 |
| Number | Date | Country |
|---|---|---|
| 05-160458 | Jun 1993 | JP |
| 07-7193 | Jan 1995 | JP |
| 10-290031 | Oct 1998 | JP |
| 2001-244514 | Sep 2001 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20040255443 A1 | Dec 2004 | US |
