JP2011167875A - Piezoelectric actuator and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric actuator suppressing apparent decline in piezoelectric characteristics and a method of manufacturing the piezoelectric actuator. <P>SOLUTION: The piezoelectric actuator 32 includes: an upper piezoelectric layer 40 and a lower piezoelectric layer 41 laminated on each other; a plurality of individual electrodes 43 arranged on the upper face of the upper piezoelectric layer 40; a first common electrode 44 and a second common electrode 45 arranged between the upper piezoelectric layer 40 and the lower piezoelectric layer 41; and a metal film 46 bonded to the lower piezoelectric layer 41 via an adhesive 42. A recess 41a is formed in a portion of the lower piezoelectric layer 41 overlapped with the first common electrode 44. Either of a predetermined drive potential or ground potential is selectively applied to the individual electrode 43. The first common electrode 44 is held at a drive potential, and the second common electrode 45 is held at a ground potential. The adhesive 42 has permittivity lower than that of the lower piezoelectric layer 41 and bonds the lower piezoelectric layer 41 and the metal film 46 to each other. The recess 41a of the lower piezoelectric layer 41 is also filled with the adhesive 42. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a piezoelectric actuator and a manufacturing method thereof.

  2. Description of the Related Art Conventionally, in various technical fields, piezoelectric actuators that drive an object using deformation (piezoelectric distortion) of a piezoelectric layer when an electric field acts on the piezoelectric layer have been used. Such a piezoelectric actuator generally includes a plurality of stacked piezoelectric layers and a plurality of electrodes arranged on the surfaces of the plurality of piezoelectric layers and the piezoelectric layer, and a piezoelectric layer sandwiched between two electrodes. Although an active portion is formed, some of them have an internal electrode held at a constant potential different from the ground potential between two piezoelectric layers.

  For example, the piezoelectric actuator for an ink jet head described in FIG. 16 of Patent Document 1 has two piezoelectric layers laminated, and a ground potential and a predetermined positive potential are formed on the upper piezoelectric layer of the two piezoelectric layers. An individual electrode to which any one of the potentials is selectively applied is disposed, and the internal electrode held at the positive potential and the internal electrode held at the ground potential so as not to overlap each other between the two piezoelectric layers Is arranged. The individual electrodes and the respective internal electrodes are opposed to each other, and the piezoelectric layer portions sandwiched between these electrodes are subjected to polarization treatment to become active portions that are deformed by the action of an electric field. On the other hand, Patent Document 2 describes a piezoelectric actuator provided with a metal diaphragm.

JP 2009-96173 A (FIG. 16) JP 2009-208223 A

  Here, when the metal diaphragm of Patent Document 2 is disposed with respect to the piezoelectric actuator described in Patent Document 1, the first electrode disposed between the two piezoelectric layers is held at a positive potential. Thus, a voltage is applied to the piezoelectric layer between the first electrode and the diaphragm, and the piezoelectric layer portion contracts. As a result, a compressive force also acts on the active portion located above it, so that deformation of the active portion is suppressed, and the apparent piezoelectric characteristics of the active portion are degraded.

  Accordingly, an object of the present invention is to suppress the deformation of the piezoelectric layer disposed between the internal electrode to which a positive potential is applied and the metal film on the surface of the piezoelectric layer, and to suppress the apparent decrease in piezoelectric characteristics. It is to provide a method for manufacturing an actuator and a piezoelectric actuator.

  The piezoelectric actuator of the present invention is arranged between any one of a plurality of piezoelectric layers stacked in the thickness direction and two piezoelectric layers among the plurality of piezoelectric layers, and is provided with a first potential different from a ground potential. An electrode, a second electrode disposed on one side of the first electrode in the stacking direction of the plurality of piezoelectric layers, to which a second potential different from the first potential is applied, the first electrode, and the second An active part formed in the piezoelectric layer sandwiched between electrodes and polarized; a metal film disposed on the surface on the other side of the first electrode in the stacking direction of the plurality of piezoelectric layers; The piezoelectric layer on the opposite side of the active portion with respect to the first electrode and in contact with the metal film has the metal film disposed in a portion overlapping the first electrode in the stacking direction. A recessed part that is recessed from the surface side to be formed Ri, wherein the said recess interposed between the first electrode and the metal film, a low filler dielectric constant than the piezoelectric layer is filled.

  According to the piezoelectric actuator of the present invention, a voltage is applied between the first electrode to which the first potential different from the ground potential is applied and the metal film, but a recess is formed between the first electrode and the metal film. In addition to the piezoelectric layer, since a filler having a dielectric constant lower than that of the piezoelectric layer filled in the concave portion is disposed, the voltage applied to the piezoelectric layer is lowered, and the shrinkage generated in the piezoelectric layer is reduced, By reducing the compressive force generated in the active portion of the piezoelectric layer sandwiched between the first electrode and the second electrode, it is possible to suppress a decrease in the apparent piezoelectric characteristics of the active portion.

  The filler is preferably an adhesive that adheres the piezoelectric layer and the metal film. According to this, it is possible to fill the concave portion with a material having a low dielectric constant while adhering the piezoelectric layer and the metal film.

  Further, the second potential is a ground potential, and the first electrode is opposed to a part of the second electrode in the stacking direction and is held at the first potential, and the first electrode in a plan view. In a region that does not overlap with the second electrode in the stacking direction of the plurality of piezoelectric layers, and is opposed to a part of the second electrode in the stacking direction and is held at a ground potential. It is preferable that an electrode is further provided, and the second electrode is selectively supplied with either a ground potential or the first potential. According to this, since the third electrode is at the ground potential, a voltage is applied to the piezoelectric layer between the third electrode and the metal film, and no contraction occurs. On the other hand, since a voltage is applied between the first electrode having the first potential and the metal film, the piezoelectric layer filled with the recesses is not limited to the piezoelectric layer in which the recesses are formed between the first electrode and the metal film. In addition, since a filler having a low dielectric constant is disposed, the voltage applied to the piezoelectric layer is lowered, and the shrinkage generated in the piezoelectric layer is reduced.

  At this time, it is preferable that the third electrode is thicker than the first electrode. According to this, by increasing the thickness of the third electrode, it is possible to reduce the area of the third electrode in plan view without increasing the electric resistance of the third electrode held at the ground potential.

  The piezoelectric actuator manufacturing method of the present invention includes two piezoelectric layers stacked in the thickness direction, a first electrode disposed between the two piezoelectric layers and held at a first potential different from a ground potential, A second electrode disposed on the surface of one of the two piezoelectric layers and selectively applied with either the first potential or the ground potential, and disposed between the two piezoelectric layers. And a third electrode that is opposed to a part of the second electrode and is held at a ground potential across the one piezoelectric layer in a region that does not overlap the first electrode. The two piezoelectric layers are laminated with the first electrode and the third electrode thicker than the first electrode interposed therebetween, and fired while pressing, so that the two In the thickness direction of the other piezoelectric layer of the piezoelectric layers Then, a laminating step for forming a recess recessed from the surface side in a portion overlapping the first electrode, and an adhesive having a dielectric constant lower than that of the piezoelectric layer over the entire surface where the recess of the other piezoelectric layer is formed. And an adhesion step of applying and adhering to the metal film.

  According to the method for manufacturing a piezoelectric actuator of the present invention, a recess is formed in the piezoelectric layer between the first electrode to which the first potential different from the ground potential is applied and the metal film in the laminating step, This recess is filled with an adhesive having a dielectric constant lower than that of the piezoelectric layer. As a result, the voltage applied to the piezoelectric layer between the first electrode having the first potential and the metal film can be lowered, and the contraction that occurs in the piezoelectric layer is alleviated and sandwiched between the first electrode and the second electrode. By reducing the compressive force generated in the active portion of the piezoelectric layer, it is possible to suppress a decrease in the apparent piezoelectric characteristics of the active portion.

  By placing a filler having a dielectric constant lower than that of the piezoelectric layer in the recess formed in the piezoelectric layer between the first electrode to which the first potential is applied and the metal film, the first electrode and the metal film are The voltage applied to the piezoelectric layer in the meantime can be lowered to alleviate the shrinkage that occurs in this piezoelectric layer, and the compressive force that occurs in the active part of the piezoelectric layer sandwiched between the first electrode and the second electrode can be relaxed. It is possible to suppress a decrease in the apparent piezoelectric characteristics of the active portion.

1 is a schematic configuration diagram of a printer according to an embodiment. It is a top view of an inkjet head. It is the elements on larger scale of each piezoelectric layer surface of an inkjet head, (a) is the elements on larger scale of the surface of an upper piezoelectric layer, (b) is the elements on larger scale of the surface of a lower piezoelectric layer. It is each sectional drawing of an inkjet head, (a) is the sectional view on the AA line of Fig.3 (a), (b) is the sectional view on the BB line of Fig.3 (a). It is process drawing which shows the manufacturing process of a piezoelectric actuator, (a) is a lamination process, (b) is an adhesion process. FIG. 10 is a cross-sectional view of an ink jet head in Modification 1. It is sectional drawing of the inkjet head in the modification 2 and the modification 3. FIG. 10 is a cross-sectional view of an inkjet head in Modification 4 and Modification 5. FIG. FIG. 10 is a cross-sectional view of an ink jet head in Modification 6.

  Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 is a schematic configuration diagram of a printer according to the present embodiment. As shown in FIG. 1, the printer 1 includes a carriage 2, an inkjet head 3, a transport roller 4, and the like.

  The carriage 2 reciprocates in the scanning direction (left and right direction in FIG. 1). The inkjet head 3 is attached to the lower surface of the carriage 2 and ejects ink from nozzles 15 (see FIG. 4A) formed on the lower surface. The transport roller 4 transports the recording paper P in the paper feed direction (front side in FIG. 1). In the printer 1, ink is ejected from the nozzles 15 of the inkjet head 3 that reciprocates in the scanning direction together with the carriage 2 onto the recording paper P that is transported in the paper feeding direction by the transport roller 4. Printing is performed. Further, the recording paper P for which printing has been completed is discharged in the paper feeding direction by the transport roller 4.

  Next, the inkjet head 3 will be described in detail. FIG. 2 is a plan view of the inkjet head. FIG. 3 is a partially enlarged view of the surface of each piezoelectric layer of the inkjet head, (a) is a partially enlarged view of the surface of the upper piezoelectric layer, and (b) is a partially enlarged view of the surface of the lower piezoelectric layer. In FIGS. 3A and 3B, hatched areas indicate areas where electrodes are formed. 4A and 4B are cross-sectional views of the inkjet head. FIG. 4A is a cross-sectional view taken along line AA in FIG. 3A, and FIG. 4B is a cross-sectional view taken along line BB in FIG. .

  As shown in FIGS. 2 to 4, the inkjet head 3 includes a flow path unit 31 in which an ink flow path including the nozzle 15 and the pressure chamber 10 is formed, and a piezoelectric actuator 32 disposed on the upper surface of the flow path unit 31. And have.

  First, the flow path unit 31 will be described. As shown in FIG. 2, four ink supply ports 9 for supplying four colors of ink (black, yellow, cyan, magenta) used in the inkjet head 3 are provided on the upper surface of the flow path unit 31. ing. An ink flow path connected to the ink supply port 9 is formed in the flow path unit 31.

  As shown in FIGS. 4A and 4B, the flow path unit 31 is composed of four plates 11 to 14 stacked on each other. The flow path unit 31 has an ink supply port. 9, a plurality of pressure chambers 10 communicating with the manifold 16, and a plurality of nozzles 15 respectively communicating with the plurality of pressure chambers 10 are formed.

  The manifold 16 extends from the ink supply port 9 in the paper feeding direction (perpendicular to the paper surface in FIG. 4A). As shown in FIG. 3A, each of the plurality of pressure chambers 10 has a substantially elliptical planar shape whose longitudinal direction is the scanning direction. Further, as shown in FIG. 2, a plurality of pressure chambers 10 are arranged along a manifold 16 extending in the paper feeding direction, so that one pressure chamber row 8 is configured. Furthermore, one pressure chamber group 7 is constituted by two pressure chamber rows 8 adjacent in the scanning direction, and the flow path unit 31 is provided with a total of five pressure chamber groups 7 arranged in the scanning direction. Of the five pressure chamber groups 7, the two pressure chamber groups 7 located on the right side in FIG. 2 are black pressure chamber groups 7 to which black ink is supplied from the ink supply port 9. Also, the three pressure chamber groups 7 located on the left side in FIG. 2 are color pressure chamber groups 7 to which three color inks (yellow, magenta, cyan) are respectively supplied from three ink supply ports 9. is there.

  The plurality of nozzles 15 respectively communicating with the plurality of pressure chambers 10 are opened on the lower surface of the flow path unit 31 (the lower surface of the plate 14 positioned at the lowest layer). Although not shown, the plurality of nozzles 15 are also arranged in the same manner as the plurality of pressure chambers 10, and black ink corresponding to the two pressure chamber groups 7 is ejected on the right side in FIG. 2. 2 nozzle groups are arranged, and on the left side in FIG. 2, three nozzle groups for ejecting three color inks corresponding to the three pressure chamber groups 7 are arranged.

  Then, as shown in FIG. 4A, a plurality of individual ink flow branches from the manifold 16 connected to the ink supply port 9 into the flow path unit 31 and reaches the nozzle 15 through the pressure chamber 10. A path 17 is formed.

  Next, the piezoelectric actuator 32 will be described. As shown in FIGS. 4A and 4B, the piezoelectric actuator 32 includes an upper piezoelectric layer 40, a lower piezoelectric layer 41, a plurality of individual electrodes 43, a first common electrode 44, and a second common electrode 45. And an adhesive 42 and a metal film 46.

  The upper piezoelectric layer 40 and the lower piezoelectric layer 41 are each formed of a ferroelectric piezoelectric material whose main component is lead zirconate titanate, which is a mixed crystal of lead titanate and lead zirconate, and is laminated with each other. In this state, the flow path unit 31 is disposed on the upper surface so as to cover the plurality of pressure chambers 10. Each of the upper piezoelectric layer 40 and the lower piezoelectric layer 41 has a thickness of about 20 μm. Further, in the portions of the lower piezoelectric layer 41 facing the central portion of the plurality of pressure chambers 10 in the short direction (left-right direction in FIG. 4B), about 1 μm from the surface side opposite to the upper piezoelectric layer 40. A recessed portion 41a is formed.

  The plurality of individual electrodes 43 are provided in regions on the upper surface of the upper piezoelectric layer 40 facing the plurality of pressure chambers 10, respectively, and are arranged in a plane on the upper surface of the upper piezoelectric layer 40. As shown in FIG. 3A, each individual electrode 43 has substantially the same planar shape as that of the pressure chamber 10, and is provided in the entire area facing the one pressure chamber 10 on the upper surface of the upper piezoelectric layer 40. Yes. Further, from each individual electrode 43, a contact portion 43a for connecting the individual electrode 43 to a flexible wiring board (FPC) on which a driver IC (not shown) is mounted is drawn out to a region that does not face the pressure chamber 10. The individual electrode 43 is selectively given a predetermined drive potential (for example, 20 V) or a ground potential from the driver IC.

  The first common electrode 44 is disposed between the upper piezoelectric layer 40 and the lower piezoelectric layer 41. The first common electrode 44 includes a plurality of electrode portions 44a respectively opposed to the central portion in the short direction of the plurality of pressure chambers 10 (left and right direction in FIG. 4B). The electrode portion 44a faces the individual electrode 43 with the upper piezoelectric layer 40 interposed therebetween. Further, as shown in FIG. 3B, the plurality of electrode portions 44a are electrically connected to each other. The first common electrode 44 is connected to the driver IC and is always held at the driving potential.

  The second common electrode 45 is disposed between the upper piezoelectric layer 40 and the lower piezoelectric layer 41 without overlapping the first common electrode 44 in plan view. The second common electrode 45 includes a plurality of electrode portions 45a that respectively oppose the lateral ends of the plurality of pressure chambers 10. The electrode portion 45 a faces the individual electrode 43 with the upper piezoelectric layer 40 and the lower piezoelectric layer 41 interposed therebetween. Furthermore, as shown in FIG. 3B, the plurality of electrode portions 45a are electrically connected to each other. The second common electrode 45 is connected to the driver IC and is always held at the ground potential.

  Further, the piezoelectric layer portion sandwiched between the individual electrode 43 and the electrode portion 44a of the first common electrode 44 of the upper piezoelectric layer 40 (the portion facing the central portion of the pressure chamber 10 in FIG. 4B: first active) The portion 35) is polarized in advance in the thickness direction. Also, the piezoelectric layer portion of the upper piezoelectric layer 40 sandwiched between the individual electrode 43 and the electrode portion 45a of the second common electrode 45 (the portion facing the left and right ends of the pressure chamber 10 in FIG. 4B: second). The active portion 36) is also polarized in the thickness direction in advance. As described above, the first active part 35 and the second active part 36 are respectively formed in the upper piezoelectric layer 40 and arranged on the same plane. No active portion is formed in the lower piezoelectric layer 41 and functions as a diaphragm. The concave portion 41a of the lower piezoelectric layer 41 overlaps at least the electrode portion 44a of the first common electrode 44 in plan view. The individual electrode 43 and the first common electrode 44 have the same thickness, and the second common electrode 45 has a thickness twice that of the electrodes 43 and 44.

  The metal film 46 is made of a metal material such as stainless steel, has a thickness of about 10 μm, and is disposed on the upper surface of the flow path unit 31 so as to cover the plurality of pressure chambers 10. The metal film 46 functions as a vibration plate of the piezoelectric actuator 32 and comes into contact with the ink in the pressure chamber 10, but is made of a metal material, so that the ink hardly penetrates, and the ink in the pressure chamber 10 is not penetrated into the lower piezoelectric layer 41. It also functions as an isolating film that prevents contact. The metal film 46 is held at the ground potential.

  The adhesive 42 is an adhesive having a lower dielectric constant than that of the lower piezoelectric layer 41, for example, an epoxy thermosetting adhesive, and adheres the lower piezoelectric layer 41 and the metal film 46. In addition, the concave portion 41 a of the lower piezoelectric layer 41 is filled with the adhesive 42.

  The operation of the piezoelectric actuator 32 described above during ink ejection will be described. In a standby state where ink is not ejected, a ground potential is applied to each of the plurality of individual electrodes 43. The first common electrode 44 is always held at the drive potential, and the second common electrode 45 is always held at the ground potential. Therefore, in the standby state, a voltage is applied between the individual electrode 43 and the first common electrode 44, and the first active portion 35 of the upper piezoelectric layer 40 sandwiched between the electrodes 43 and 44 has a thickness direction. An electric field acts. Since the direction of the electric field is parallel to the polarization direction of the first active portion 35, the first active portion 35 contracts in a plane direction perpendicular to the thickness direction. Thereby, the part facing the pressure chamber 10 of the piezoelectric layers 40 and 41 is in a state of being deformed so as to protrude toward the pressure chamber 10 side (the lower side in FIG. 4B). At this time, the volume of the pressure chamber 10 is smaller than that in the state where the piezoelectric layer 40 is not deformed.

  From this state, when the potential of a certain individual electrode 43 is switched from the ground potential to the drive potential, no voltage is applied between the individual electrode 43 and the first common electrode 44, and the deformed first active portion 35 is Return to the original. At the same time, since a voltage is applied between the individual electrode 43 and the second common electrode 45, an electric field in the thickness direction is applied to the second active portion 36 of the upper piezoelectric layer 40 sandwiched between the electrodes 43 and 45. Act. Since the direction of the electric field is parallel to the polarization direction of the second active portion 36, the second active portion 36 contracts in a plane direction perpendicular to the thickness direction. As a result, the portion of the piezoelectric layers 40 and 41 facing the substantially central portion of the pressure chamber 10 is pulled upward, and the portion of the piezoelectric layers 40 and 41 facing the pressure chamber 10 is entirely opposite to the pressure chamber 10. By deforming so as to be convex (upper side in FIG. 4B), the volume of the pressure chamber 10 is increased.

  Thereafter, when the potential of the individual electrode 43 is returned to the ground potential again, no voltage is applied between the individual electrode 43 and the second common electrode 45, and the deformation of the second active portion 36 is restored. At the same time, the first active portion 35 contracts again in the surface direction, and the portions of the piezoelectric layers 40 and 41 that face the pressure chamber 10 are convex toward the pressure chamber 10 as a whole. At this time, since the volume of the pressure chamber 10 is greatly reduced, the pressure of the ink in the pressure chamber 10 is increased, and ink is ejected from the nozzle 15 communicating with the pressure chamber 10.

  Further, when the piezoelectric actuator 32 is driven as described above, when the potential of the individual electrode 43 is switched from the ground potential to the driving potential, the first active portion 35 expands from the contracted state to the state before contracting, Since the second active part 36 contracts, the extension of the first active part 35 is partially absorbed by the contraction of the second active part 36. On the other hand, when the potential of the individual electrode 43 is returned from the drive potential to the ground potential, the first active portion 35 contracts and the second active portion 36 expands to the state before contraction. Is partially absorbed by the extension of the second active portion 36.

  From the above, the driving timings of the first active portion 35 and the second active portion 36 are alternated, and the deformation of the portion of the piezoelectric layers 40 and 41 facing the pressure chamber 10 faces the other pressure chamber 10. It is possible to suppress so-called crosstalk in which the ejection characteristics of ink from the nozzle 15 that is transmitted to the portion and communicates with the other pressure chambers 10 fluctuate.

  If the lower piezoelectric layer 41 is bonded to the plate 11 in which the pressure chamber 10 of the flow path unit 31 is formed without sandwiching the metal film 46, the first common electrode 44 is always held at the drive potential. Therefore, the electric field leaking from the first common electrode 44 flows out to the ink in the pressure chamber 10 via the lower piezoelectric layer 41, and the ink is charged. When the ink is charged, the straightness of the ink ejected from the nozzle 15 is impaired. Therefore, by sandwiching the metal film 46 held at the ground potential between the lower piezoelectric layer 41 and the plate 11, the electric field due to the voltage applied to the first common electrode 44 is blocked by the metal film 46, and the pressure chamber 10 Ink can be prevented from being charged.

  On the other hand, when the metal film 46 is disposed between the plate 11 of the flow path unit 31 and the lower piezoelectric layer 41, a voltage is applied between the first common electrode 44 and the metal film 46, An electric field acts on the portion of the lower piezoelectric layer 41 sandwiched therebetween. Then, a high voltage is applied to the unnecessary portion sandwiched between the first common electrode 44 and the metal film 46 of the lower piezoelectric layer 41 where the active portion is not formed, and contracts. Since the contracted portion of the lower piezoelectric layer 41 is a portion overlapping the first active portion 35 in plan view, a contraction force acts on the first active portion 35, and the deformation of the first active portion 35 is performed. And the apparent piezoelectric characteristics of the first active portion 35 are deteriorated.

  Therefore, in the present embodiment, the lower piezoelectric layer 41 faces the central portion in the short direction (left and right direction in FIG. 4B) of the plurality of pressure chambers 10 including the portion facing the first common electrode 44. A concave portion 41 a is formed in the portion, and the concave portion 41 a is filled with an adhesive 42. Therefore, the portion to which the voltage is applied between the first common electrode 44 and the metal film 46 becomes the portion where the concave portion 41a of the lower piezoelectric layer 41 is formed and the adhesive 42 filled in the concave portion 41a.

  The dielectric constant ε of the lower piezoelectric layer 41 is very high (relative dielectric constant is about 2000), whereas the dielectric constant ε of the adhesive 42 which is an epoxy thermosetting adhesive is low (relative dielectric constant). About 10). Therefore, from the relationship between the thickness of the lower piezoelectric layer 41 in which the recess 41 a is formed and the thickness of the adhesive 42 filled in the recess 41 a and the dielectric constant of the lower piezoelectric layer 41 and the adhesive 42, for example, Therefore, about 1V is applied to 20V between the drive potential and the ground potential, and the remaining 19V is applied to the adhesive 42. Thus, by reducing the voltage applied to the portion of the lower piezoelectric layer 41 that overlaps the first active portion 35 in plan view, the contraction of the lower piezoelectric layer 41 can be reduced, and the compressive force generated in the first active portion 35 is reduced. And it can suppress that the apparent piezoelectric characteristic of the 1st active part 35 falls.

  If only the voltage applied to the portion of the lower piezoelectric layer 41 sandwiched between the first common electrode 44 and the metal film 46 is lowered, the lower piezoelectric layer 41 and the metal are not formed in the lower piezoelectric layer 41 without forming the recess 41a. This can also be realized simply by increasing the thickness of the entire adhesive 42 between the films 46. However, in this case, since the thickness of the adhesive 42 is large, the deformation of the first active part 35 and the second active part 36 when the piezoelectric actuator 32 is driven is also inhibited.

  Therefore, the first common electrode 44 is overlapped in plan view, and the concave portion 41a is formed only in the portion of the lower piezoelectric layer 41 to which the voltage is applied to increase the thickness of the adhesive 42, and other lower portions to which no voltage is applied. For the piezoelectric layer 41, the first active portion 35 and the first active portion 35 during driving of the piezoelectric actuator 32 are compared with the one where the thickness of the adhesive 42 is increased by reducing the thickness of the adhesive 42. The deformation inhibition of the second active part 36 can be suppressed.

  In the present embodiment, the first common electrode 44 corresponds to the first electrode in the present invention, the individual electrode 43 corresponds to the second electrode in the present invention, and the second common electrode 45 corresponds to the third electrode in the present invention. It corresponds to.

  Next, a method for manufacturing the piezoelectric actuator 32 will be described with reference to FIG. FIG. 5 is a process diagram showing the manufacturing process of the piezoelectric actuator, where (a) is a lamination process and (b) is an adhesion process.

  As shown in FIG. 5A, first, the individual electrode 43 is formed on the surface of one of the two green sheets made of piezoelectric ceramics, and the first common electrode 44 and the surface of the other green sheet are formed. A second common electrode 45 is formed. The individual electrode 43 and the first common electrode 44 are formed only once by screen printing. The second common electrode 45 is applied twice by screen printing so as to be twice as thick as the individual electrode 43 and the first common electrode 44. Then, the individual electrode 43 formed on the surface of one green sheet is exposed, and the first common electrode 44 and the second common electrode 45 formed on the surface of the other green sheet are sandwiched between the two green sheets. And firing at a predetermined temperature while pressing from both sides (lamination step).

  Then, since the thickness of the second common electrode 45 is thicker than that of the first common electrode 44, the portion facing the second common electrode 45 when the stacked green sheets are pressed is the first common electrode 44. It will be pressed more strongly than the part facing. The portion of the green sheet facing the second common electrode 45 has a higher density than the portion facing the first common electrode 44. When a green sheet having a portion having a different density is baked in this way, the portion of the green sheet facing the first common electrode 44 has a lower density than the portion facing the second common electrode 45, so the green sheet The amount of shrinkage increases when the binder contained therein vaporizes to form a crystal structure. Therefore, in the lower piezoelectric layer 41 formed by firing the green sheet, the side where the electrodes 44 and 45 are not formed on the portion not facing the second common electrode 45 (at least the portion facing the first common electrode 44). A recessed portion 41a is formed.

  Then, as shown in FIG. 5B, an epoxy thermosetting agent is applied to the surface of the lower piezoelectric layer 41, and the metal film 46 is pressed and bonded (bonding process) to manufacture the piezoelectric actuator 32. Then, the lower piezoelectric layer 41 and the metal film 46 are joined, and the adhesive 42 is filled in the recess 41 a of the lower piezoelectric layer 41.

  In the piezoelectric actuator 32 manufactured in this way, as described above, a driving potential is applied to the first common electrode 44 and a ground potential is applied to the metal film 46, and the lower piezoelectric layer sandwiched between the first common electrode 44 and the metal film 46. Even if an unnecessary voltage is applied to the portion 41, a large part of the voltage is applied to the adhesive 42 having a low dielectric constant of the recess 41a and applied to the portion of the lower piezoelectric layer 41 that overlaps the first active portion 35 in plan view. By lowering the applied voltage, the contraction of the lower piezoelectric layer 41 can be relaxed, the compressive force generated in the first active portion 35 is relaxed, and the apparent piezoelectric characteristics of the first active portion 35 are prevented from deteriorating. be able to.

  The first common electrode 44 has a relatively large total area because a plurality of electrode portions 44a may be electrically connected to each other. At this time, if a high voltage of 20 V is applied to the portion of the lower piezoelectric layer 41 sandwiched between the first common electrode 44 and the metal film 46, migration tends to occur in the lower piezoelectric layer 41. On the other hand, in this embodiment, since the concave portion 41a is filled with the adhesive 42, the voltage applied to the portion of the lower piezoelectric layer 41 sandwiched between the first common electrode 44 and the metal film 46 is about 1V. It becomes a small value, and migration can be made difficult to occur.

  Further, the second common electrode 45 is made thicker than the first common electrode 44 in order to form the recess 41 a in the portion of the lower piezoelectric layer 41 facing the first common electrode 44. Since the second common electrode 45 is a common electrode in which a plurality of electrode portions 45a are conducted, it is desired to make the electric resistance as small as possible. Therefore, by increasing the thickness and reducing the electrical resistance, the area of the second common electrode 45 in plan view can be reduced. Further, by reducing the area of the second common electrode 45, it becomes easy to route patterns of other electrodes (for example, the first common electrode 44), and the piezoelectric actuator 32 itself can be downsized. .

  Further, as described above, if only the voltage applied to the portion of the lower piezoelectric layer 41 sandwiched between the first common electrode 44 and the metal film 46 is lowered, the lower piezoelectric layer 41 is not formed with the recess 41a, This can also be realized simply by increasing the thickness of the entire adhesive 42 between the piezoelectric layer 41 and the metal film 46. However, in this case, when the lower piezoelectric layer 41 and the metal film 46 are bonded in the bonding step, the thickness variation of the adhesive 42 in the surface direction becomes large, and the deformation amount varies for each active portion. Therefore, the second common electrode 45 is made thicker than the first common electrode 44, and the two green sheets sandwiching the electrodes 44 and 45 are pressed and baked, whereby the first piezoelectric layer 41 of the lower piezoelectric layer 41 is pressed. Since the concave portion 41a is formed only in the portion facing the one common electrode 44, the thickness of the adhesive 42 in the concave portion 41a can be easily increased. Can be made thin, and variation in the amount of displacement for each active portion can be suppressed.

  Next, modified examples in which various changes are made to the present embodiment will be described. However, the same reference numerals are given to those having the same configuration as in the above embodiment, and the description thereof is omitted as appropriate.

  The present invention is also applicable to a piezoelectric actuator having the following configuration. An internal electrode to which a potential different from the ground potential is applied is disposed between the two piezoelectric layers, and this internal electrode is connected to the metal film via the piezoelectric layer without sandwiching the electrode to which the ground potential is applied. When facing each other, the inner electrode overlaps with the metal film, and a concave portion is formed in the portion of the piezoelectric layer adjacent to the metal film, so that an adhesive having a dielectric constant lower than that of the piezoelectric layer is filled. Play. Hereinafter, an example will be described with reference to FIGS.

  1) As shown in FIG. 6, the arrangement of the individual electrode 43, the first common electrode 44, and the second common electrode 45 is opposite to that of the present embodiment, and between the upper piezoelectric layer 40 and the lower piezoelectric layer 41. A plurality of individual electrodes 43 may be arranged, and a first common electrode 44 and a second common electrode 45 may be arranged on the upper surface of the upper piezoelectric layer 40 (Modification 1). In this case, the piezoelectric layer portion of the upper piezoelectric layer 40 sandwiched between the individual electrode 43 and the first common electrode 44 is the first active portion 35, and the piezoelectric layer sandwiched between the individual electrode 43 and the second common electrode 45. The layer portion is the second active portion 36. The plurality of individual electrodes 43 of the lower piezoelectric layer 41 serve as internal electrodes, and concave portions 41 a are formed in portions overlapping the plurality of individual electrodes 43, and are filled with the adhesive 42. At this time, as in the above-described embodiment, it is difficult to form the concave portion 41a using the difference in thickness between the two electrodes 44 and 45. Therefore, the surface of the lower piezoelectric layer 41 is mixed with compressed air by sandblasting. The lower piezoelectric layer 41 is scraped off and removed by spraying an abrasive, thereby forming a recess 41a. In this modification, the individual electrode 43 corresponds to the first electrode in the present invention, the first common electrode 44 corresponds to the second electrode in the present invention, and the second common electrode 45 corresponds to the third electrode in the present invention. It corresponds to.

  2) As shown in FIG. 7A, three piezoelectric layers 140 to 142 are laminated, a plurality of individual electrodes 43 are arranged on the upper surface of the upper piezoelectric layer 140, and an intermediate piezoelectric layer with the upper piezoelectric layer 140 is provided. The first common electrode 44 may be disposed between the layers 141, and the second common electrode 45 may be disposed between the intermediate piezoelectric layer 141 and the lower piezoelectric layer 142 (Modification 2). In this case, the piezoelectric layer portion sandwiched between the individual electrode 43 and the first common electrode 44 of the upper piezoelectric layer 140 is the first active portion 35, and the upper piezoelectric layer 140 and the intermediate piezoelectric layer 141 are individually separated. The piezoelectric layer portion sandwiched between the electrode 43 and the second common electrode 45 is the second active portion 36. 7B, the arrangement of the first common electrode 44 and the second common electrode 45 may be reversed from the piezoelectric actuator shown in FIG. 7A (Modification 3). . In this case, the piezoelectric layer portion sandwiched between the individual electrode 43 and the first common electrode 44 of the upper piezoelectric layer 140 and the intermediate piezoelectric layer 141 is the first active portion 35, and the individual piezoelectric layer 140 of the upper piezoelectric layer 140 is individually The piezoelectric layer portion sandwiched between the electrode 43 and the second common electrode 45 is the second active portion 36. In these modified examples, the first common electrode 44 and the second common electrode 45 arranged in the same plane in the present embodiment are arranged at different positions in the stacking direction on the metal film 46 side than the plurality of individual electrodes 43. It is what. As in the present embodiment, the first common electrode 44 serves as an internal electrode, and a concave portion 142 a is formed in a portion overlapping the first common electrode 44 of the lower piezoelectric layer 142 and is filled with the adhesive 42. In these modifications, the first common electrode 44 corresponds to the first electrode in the present invention, the individual electrode 43 corresponds to the second electrode in the present invention, and the second common electrode 45 corresponds to the third electrode in the present invention. It corresponds to an electrode.

  3) As shown in FIG. 8A, three piezoelectric layers 140 to 142 are laminated, the first common electrode 44 is disposed on the upper surface of the upper piezoelectric layer 140, and an intermediate piezoelectric layer is formed between the upper piezoelectric layer 140 and the intermediate piezoelectric layer 140. A plurality of individual electrodes 43 may be disposed between the layers 141, and the second common electrode 45 may be disposed between the intermediate piezoelectric layer 141 and the lower piezoelectric layer 142 (Modification 4). In this case, the piezoelectric layer portion sandwiched between the individual electrode 43 and the first common electrode 44 of the upper piezoelectric layer 140 is the first active portion 35, and the individual electrode 43 and the second common electrode of the intermediate piezoelectric layer 141 are the same. The piezoelectric layer portion sandwiched between the electrodes 45 is the second active portion 36. Further, as shown in FIG. 8B, the arrangement of the plurality of individual electrodes 43 and the second common electrode 45 may be reversed from the piezoelectric actuator shown in FIG. 8A (Modification 5). . In this case, the piezoelectric layer portion sandwiched between the individual electrode 43 and the first common electrode 44 of the upper piezoelectric layer 140 and the intermediate piezoelectric layer 141 is the first active portion 35, and the individual piezoelectric layers 141 of the intermediate piezoelectric layer 141 are individually The piezoelectric layer portion sandwiched between the electrode 43 and the second common electrode 45 is the second active portion 36. In these modifications, the plurality of individual electrodes 43 serve as internal electrodes, and a concave portion 142a is formed in a portion overlapping the first common electrode 44 without sandwiching other electrodes of the lower piezoelectric layer 142. 42 is filled. In these modifications, the individual electrode 43 corresponds to the first electrode in the present invention, the first common electrode 44 corresponds to the second electrode in the present invention, and the second common electrode 45 corresponds to the third electrode in the present invention. It corresponds to an electrode.

  4) As shown in FIG. 9, a common electrode 144 to which a ground potential is applied is arranged on the upper surface of the upper piezoelectric layer 40, and is individually arranged so as to face the common electrode 144 between the upper piezoelectric layer 40 and the lower piezoelectric layer 41. The electrode 143 may be disposed (Modification 6). In this case, the piezoelectric layer portion sandwiched between the upper piezoelectric layer 40, the individual electrode 143 and the common electrode 144 is the active portion 135. Unlike the present embodiment, this modification includes only a common electrode to which a ground potential is applied, and there is no common electrode to which a drive potential is applied. The individual electrode 143 serves as an internal electrode, and a concave portion 41 a is formed in a portion overlapping the individual electrode 143 of the lower piezoelectric layer 41 and is filled with the adhesive 42. In this modification, the individual electrode 143 corresponds to the first electrode in the present invention, and the common electrode 144 corresponds to the second electrode in the present invention.

  In this embodiment, the ground potential is applied to the metal film 46, but the metal film 46 may be in a floating state without being applied with a potential. Also in this case, the metal film 46 is connected to a drive target such as the flow path unit 31, and such a drive target is generally grounded. Therefore, the metal film 46 connected to the grounded driving object is also grounded and becomes a very low potential of the same potential as the ground potential.

  Furthermore, in this embodiment, the adhesive used for bonding the lower piezoelectric layer 41 and the metal film 46 is filled in the recess 41a as a filler having a dielectric constant lower than that of the lower piezoelectric layer 41. Apart from the adhesive, the recess 41a may be filled with a material having a lower dielectric constant than that of the lower piezoelectric layer 41. As this material, for example, powder alumina (relative dielectric constant ε = about 10) may be mixed with a binder and fired to fill the recess 41a.

  The present invention is not limited to the piezoelectric actuator that applies pressure to the liquid in the pressure chamber and the manufacturing method thereof, and the present invention can also be applied to a piezoelectric actuator that drives a predetermined moving portion and a manufacturing method thereof.

DESCRIPTION OF SYMBOLS 1 Printer 3 Inkjet head 32 Piezoelectric actuator 35 1st active part 36 2nd active part 40 Upper piezoelectric layer 41 Lower piezoelectric layer 41a Recessed part 42 Adhesive 43 Individual electrode 44 1st common electrode 45 2nd common electrode 46 Metal film

Claims (5)

A plurality of piezoelectric layers stacked in the thickness direction;
A first electrode disposed between any two piezoelectric layers of the plurality of piezoelectric layers and provided with a first potential different from a ground potential;
A second electrode disposed on one side of the first electrode in the stacking direction of the plurality of piezoelectric layers and applied with a second potential different from the first potential;
An active part formed on the piezoelectric layer sandwiched between the first electrode and the second electrode and polarized;
A metal film disposed on the surface on the other side of the first electrode in the stacking direction of the plurality of piezoelectric layers,
The piezoelectric layer that is on the opposite side of the active portion with respect to the first electrode and is in contact with the metal film from the surface side where the metal film is disposed in a portion overlapping the first electrode in the stacking direction. A concave recess is formed,
The piezoelectric actuator, wherein the concave portion sandwiched between the first electrode and the metal film is filled with a filler having a dielectric constant lower than that of the piezoelectric layer.   The piezoelectric actuator according to claim 1, wherein the filler is an adhesive that bonds the piezoelectric layer and the metal film. The second potential is a ground potential;
The first electrode is opposed to a part of the second electrode in the stacking direction and is held at the first potential,
In a region that does not overlap the first electrode in plan view, the plurality of piezoelectric layers are arranged at positions different from the second electrode in the stacking direction, and face a part of the second electrode in the stacking direction, A third electrode held at a potential;
3. The piezoelectric actuator according to claim 1, wherein the second electrode is selectively given a ground potential or a potential of the first potential. 4.   The piezoelectric actuator according to claim 3, wherein the third electrode is thicker than the first electrode. Two piezoelectric layers stacked in the thickness direction, a first electrode disposed between the two piezoelectric layers and held at a first potential different from a ground potential, and one of the two piezoelectric layers A second electrode disposed on the surface of the layer and selectively applied with one of the first potential and the ground potential; and a region disposed between the two piezoelectric layers and not overlapping the first electrode. A piezoelectric actuator having a third electrode opposed to a part of the second electrode and held at a ground potential across the one piezoelectric layer,
The two piezoelectric layers are laminated by sandwiching the first electrode and the third electrode thicker than the first electrode between them, and firing them while pressing them. A stacking step of forming a recess recessed from the surface side in a portion overlapping the first electrode in the thickness direction of the other piezoelectric layer,
And a bonding step of applying an adhesive having a dielectric constant lower than that of the piezoelectric layer to adhere to the metal film over the entire surface of the other piezoelectric layer where the concave portion is formed. Manufacturing method.

Images