JP2011054592A - Piezoelectric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To equalize density of electrodes for a plane direction of a piezoelectric layer in a structure in which a common electrode is led out up to the upper surface of the piezoelectric layer. <P>SOLUTION: A plurality of relay electrodes 48 opposite to a second common electrode 45 are arranged between a first piezoelectric layer 40 and a second piezoelectric layer 41, and the second common electrode 45 and the plurality of relay electrodes 48 are electrically continuous, by using a conductive material in a plurality of through-holes 39. Furthermore, a plurality of lead-out electrodes 47, corresponding to the plurality of relay electrodes 48 respectively, are arranged on the upper surface of the first piezoelectric layer 40, and the relay electrodes 48 and the lead-out electrodes 47, each of which is continuous by using the conductive material in a plurality of through-holes 38. Still further, the plurality of relay electrodes 48 are each disposed deviated from the lead-out electrodes 47 so that a relay electrode 48 can be positioned between adjacent two lead-out electrodes 47. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a piezoelectric actuator.

  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. For example, Patent Literature 1 discloses a piezoelectric actuator used in an inkjet head that ejects ink droplets from nozzles.

  The piezoelectric actuator disclosed in Patent Document 1 includes a plurality of laminated ceramic sheets (piezoelectric layers) and a large number of electrodes formed on the plurality of ceramic sheets. Among the plurality of ceramic sheets, the first ceramic sheet is formed with a plurality of individual electrodes respectively corresponding to the plurality of pressure chambers of the inkjet head. A common electrode (common electrode) facing the plurality of individual electrodes is formed on the second ceramic sheet. And these 1st ceramic sheets and several 2nd ceramic sheets are laminated | stacked alternately. Furthermore, two sheets of a dummy ceramic sheet and a top ceramic sheet are laminated on the upper part of the first and second ceramic sheets laminated alternately. The laminated ceramic sheets are fired at a high temperature and integrated.

  Also, on the top surface of the top ceramic sheet, a plurality of lead electrodes for connecting internal electrodes (a plurality of individual electrodes and a common electrode) located inside the laminated structure and a wiring member (flexible flat cable) (Surface electrode) is formed. Furthermore, an internal electrode (individual electrode or common electrode) and a relay electrode (conducting electrode) for conducting the lead electrode are formed at a position directly below the lead electrode of the sheet below the top ceramic sheet, The internal electrode and the relay electrode, and the relay electrode and the lead electrode on the upper surface are electrically connected to each other by the conductive material in the through hole formed in the ceramic sheet.

  By the way, as the number of individual electrodes increases, a larger current flows through the common electrode facing the individual electrodes in common. Therefore, it is necessary to reduce the electric resistance of the common electrode as much as possible. The extraction electrode and the relay electrode have a large electrode area. However, since the electrode material and the piezoelectric material (piezoelectric ceramics) have different thermal shrinkage rates, an electrode with a large area is formed when the ceramic sheet is fired if a portion with a large electrode area exists on the sheet. A large heat shrinkage difference occurs between the portion and the portion that does not, and as a result, a problem occurs that the piezoelectric actuator is warped. Therefore, in Patent Document 1, in order to absorb the above-described thermal shrinkage difference, a slit is formed in the extraction electrode for the common electrode on the top ceramic sheet, and the extraction electrode is divided into a plurality. Further, the relay electrode for the common electrode formed on the dummy ceramic sheet below it is also divided into a plurality.

JP 2007-324491 A (FIGS. 7, 8, and 10C)

  However, in Patent Document 1, a relay electrode connected to the lead electrode by a through hole is disposed directly below the common electrode lead electrode, and the plurality of lead electrodes and the plurality of relay electrodes are completely in plan view. It overlaps with. Therefore, a high electrode density region where both electrodes overlap and a low electrode density region where no electrode is formed are adjacent in the plane direction. Due to such variations in the electrode density in the surface direction, a difference in thermal shrinkage occurs when the ceramic sheet is fired. Therefore, the piezoelectric actuator is warped only by dividing the lead electrode and the relay electrode as in Patent Document 1. May occur, and the desired flatness may not be achieved.

  In addition, the portion where the lead electrode and the relay electrode overlap and where the electrode density is high has a larger electrode thickness than the portion where the electrode density is low, so when multiple green sheets (ceramic sheets before firing) are stacked and pressed In addition, the higher the electrode density, the stronger the green sheet is compressed and the higher the density. The variation in the density of the green sheet caused by the variation in the electrode density is also a factor in increasing the heat shrinkage difference during firing.

  An object of the present invention is to make the electrode density uniform in the plane direction of the piezoelectric layer in a structure in which the common electrode is drawn to the upper surface of the piezoelectric layer.

A piezoelectric actuator according to a first aspect of the present invention is planarly disposed between an upper piezoelectric layer and a lower piezoelectric layer stacked in a thickness direction, and an upper surface of the upper piezoelectric layer or between the upper piezoelectric layer and the lower piezoelectric layer. A plurality of individual electrodes, and a common electrode disposed on the lower surface of the lower piezoelectric layer and facing the plurality of individual electrodes with at least the lower piezoelectric layer interposed therebetween,
Between the upper piezoelectric layer and the lower piezoelectric layer, a plurality of relay electrodes facing the common electrode across the lower piezoelectric layer are arranged along a predetermined direction parallel to the surface direction of the piezoelectric layer. And the common electrode and the plurality of relay electrodes are electrically connected by a conductive material in a plurality of lower through holes formed in the lower piezoelectric layer,
On the upper surface of the upper piezoelectric layer, a plurality of lead electrodes respectively opposed to the plurality of relay electrodes across the upper piezoelectric layer are arranged along the predetermined one direction, similar to the plurality of relay electrodes, The plurality of relay electrodes and the plurality of lead electrodes are respectively conducted by a conductive material in a plurality of upper through holes formed in the upper piezoelectric layer,
Each of the plurality of relay electrodes is disposed so as to be shifted in the predetermined direction with respect to the lead electrode connected via the upper through hole, and the relay electrode is disposed between two adjacent lead electrodes. It is characterized by being located.

  The common electrode is disposed on the lower surface of the lower piezoelectric layer and faces a plurality of individual electrodes disposed above the common electrode. The common electrode is connected to the upper piezoelectric layer through a lower through hole formed in the lower piezoelectric layer, a relay electrode disposed between the upper piezoelectric layer and the lower piezoelectric layer, and an upper through hole formed in the upper piezoelectric layer. It is connected to an extraction electrode formed on the upper surface of the layer.

  Here, in order to reduce the electrical resistance from the common electrode to the extraction electrode, it is preferable to increase the electrode area of each of the relay electrode and the extraction electrode. However, in order to reduce the thermal contraction difference when the piezoelectric layer is fired, The electrode and the extraction electrode are not composed of one electrode having a large area, but are divided into a plurality of electrodes. The common electrode and one relay electrode are connected by a lower through hole formed in the lower piezoelectric layer, and one relay electrode and one lead electrode are connected by an upper through hole formed in the upper piezoelectric layer. ing.

  Further, each of the plurality of relay electrodes is arranged so as to be shifted in the arrangement direction with respect to the extraction electrode connected through the through hole, and the relay electrode is arranged between two adjacent extraction electrodes. It has a configuration. As a result, the area where the relay electrode below the upper piezoelectric layer and the extraction electrode above the upper piezoelectric layer overlap (area where the electrode density is high) is reduced, while the area where neither the relay electrode nor the extraction electrode is formed (electrode) The region having a low density is also reduced, and the electrode density is made uniform in the plane direction of the piezoelectric layer.

  The piezoelectric actuator according to a second aspect is the piezoelectric actuator according to the first aspect, wherein the upper through hole that connects one relay electrode and one lead electrode is the lower portion that connects the one relay electrode and the common electrode. It is characterized by being disposed with respect to the through hole with respect to the predetermined one direction.

  If the upper through hole and the lower through hole filled with the conductive material are also arranged to overlap each other, the electrode density is increased at that portion, and the variation in the electrode density in the plane direction of the piezoelectric layer is increased. According to the present invention, since the positions of the upper through hole and the lower through hole are shifted, the electrode density is further made uniform in the plane direction.

  The piezoelectric actuator according to a third aspect is the piezoelectric actuator according to the second aspect, wherein the upper through-holes and the lower through-holes are alternately arranged with respect to the predetermined direction, and the upper through-holes and the lower through-holes are further arranged. All the separation distances in the predetermined direction are the same.

  According to this configuration, since the upper through holes and the lower through holes are alternately arranged at equal intervals, the electrode density is further uniform in the plane direction.

  The piezoelectric actuator according to a fourth aspect of the present invention is the piezoelectric actuator according to any one of the first to third aspects, wherein each of the plurality of upper through-holes and the plurality of lower through-holes is locally concentrated in the piezoelectric layer. It consists of a bundle of a plurality of through-holes.

  As the through hole, a hole made of one large through hole may be adopted, but a hole made of a bundle of a plurality of small through holes can also be adopted. In the present invention, it is possible to suppress the local increase in the electrode density of the portion where the through hole is formed by employing the latter through hole formed of a bundle of a plurality of through holes.

  According to the present invention, each of the plurality of relay electrodes is displaced with respect to the extraction electrode connected through the through hole, and the relay electrode is disposed between two adjacent extraction electrodes. The electrode density is made uniform with respect to the plane direction of the layer.

It is a perspective view of the inkjet head of this embodiment. It is a top view of an inkjet head. It is the elements on larger scale of an inkjet head, (a) is a partially expanded plan view of FIG. 2, (b) is the BB sectional drawing of (a), (c) is CC sectional view of (a). FIG. FIG. 3 is a partially enlarged view of the left end portion of the piezoelectric actuator of FIG. 2, (a) is a view as seen from the upper surface of the first piezoelectric layer (uppermost layer), and (b) is from the upper surface of the second piezoelectric layer (intermediate layer). FIG. 3C is a view as seen from the upper surface of the third piezoelectric layer (lowermost layer). It is the VV sectional view taken on the line of Fig.4 (a). FIG. 6 is an enlarged view of the through hole in FIG. 5. It is sectional drawing equivalent to FIG.3 (c) of the inkjet head of a change form. It is sectional drawing equivalent to FIG.3 (c) of the inkjet head of another modification.

  Next, an embodiment of the present invention will be described. This embodiment is an example in which the present invention is applied to a piezoelectric actuator of an ink jet head that records an image or the like by ejecting ink onto a recording sheet.

  FIG. 1 is a perspective view of the ink jet head of the present embodiment, and FIG. 2 is a plan view of the ink jet head. In the following description, the front side in FIG. 1 and FIG. 2 is defined as the upper side, and the other side in FIG. 1 and FIG. 2 is defined as the lower side. The ink-jet head 3 reciprocates in the scanning direction in the figure, and a plurality of nozzles 15 (shown in the figure) opened on the lower surface with respect to recording paper (not shown) conveyed in the paper feeding direction orthogonal to the scanning direction. 3)), which is a so-called serial type ink jet head that ejects ink droplets. As shown in FIGS. 1 and 2, the inkjet head 3 includes a flow path unit 31 in which an ink flow path including a nozzle 15 and a pressure chamber 10 is formed, and a piezoelectric actuator 32 disposed on the upper surface of the flow path unit 31. And. As shown in FIG. 1, a flexible wiring board (FPC) 50 on which a driver IC 51 is mounted is bonded to the upper surface of the piezoelectric actuator 32.

  First, the flow path unit 31 will be described. As shown in FIGS. 1 and 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. Is provided. An ink channel connected to the ink supply port 9 is formed in the channel unit 31.

  3A and 3B are partially enlarged views of the inkjet head 3. FIG. 3A is a partially enlarged plan view of FIG. 2, FIG. 3B is a sectional view taken along the line BB in FIG. FIG. As shown in FIG. 3, the flow path unit 31 is composed of four plates 11 to 14 stacked on each other. The flow path unit 31 includes a manifold 16 connected to the ink supply port 9, and 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 shown in FIG. 3B extends from the ink supply port 9 in the paper feeding direction (perpendicular to the paper surface in FIG. 3B). 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. As shown in FIG. 2, the plurality of pressure chambers 10 are arranged along a manifold 16 extending in the paper feeding direction, thereby forming one pressure chamber row 8. Further, 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. 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.

  As shown in FIG. 3 (b), 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. The piezoelectric actuator 32 includes three piezoelectric layers (first piezoelectric layer 40, second piezoelectric layer 41, and third piezoelectric layer 42), a plurality of individual electrodes 43, a first common electrode 44, and a second common electrode 45. Have. FIG. 4 is a partially enlarged view of the left end portion of the piezoelectric actuator 32 of FIG. 2, (a) is a view seen from the upper surface of the first piezoelectric layer 40 (uppermost layer), and (b) is the second piezoelectric layer 41. FIG. 5C is a view as seen from the upper surface of the (intermediate layer), and FIG. 4A to 4C, hatched portions indicate regions where electrodes are formed.

  The three piezoelectric layers 40 to 42 are each formed of a ferroelectric piezoelectric material mainly composed of lead zirconate titanate, which is a mixed crystal of lead titanate and lead zirconate, and are laminated to 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. Moreover, the laminated body of the three piezoelectric layers 40 to 42 is obtained by forming the electrodes described later on three green sheets that have not been fired, and then laminating them and firing them at a high temperature.

  The plurality of individual electrodes 43 are provided in regions on the upper surface of the uppermost first piezoelectric layer 40 facing the plurality of pressure chambers 10, respectively, and are arranged in a plane on the upper surface of the first piezoelectric layer 40. As shown in FIGS. 3A to 3C, each individual electrode 43 has substantially the same planar shape as the pressure chamber 10, and faces one pressure chamber 10 on the upper surface of the uppermost piezoelectric layer 40. It is provided for the entire area. Further, from each individual electrode 43, a contact portion 43a for connecting the individual electrode 43 to the FPC 50 (see FIG. 1) is drawn out to a region that does not face the pressure chamber 10.

  The first common electrode 44 is disposed between the first piezoelectric layer 40 and the intermediate second piezoelectric layer 41. The first common electrode 44 includes a plurality of electrode portions 44a that respectively oppose the central portion of the plurality of pressure chambers 10 in the short direction (left-right direction in FIG. 3C). The electrode portion 44 a faces the individual electrode 43 with the first piezoelectric layer 40 interposed therebetween. Furthermore, as shown in FIG. 4B, the plurality of electrode portions 44a are electrically connected to each other. FIG. 4B shows a form in which the first common electrode 44 is disposed on the upper surface of the second piezoelectric layer 41, but the first piezoelectric layer 41 is superposed on the upper surface of the second piezoelectric layer 41. The first common electrode 44 may be disposed on the lower surface of the piezoelectric layer 40, and both forms are substantially the same.

  The second common electrode 45 is disposed between the second piezoelectric layer 41 and the lowermost third piezoelectric layer 42. 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 45a faces the individual electrode 43 with the first piezoelectric layer 40 and the second piezoelectric layer 41 interposed therebetween. Furthermore, as shown in FIG. 4C, the plurality of electrode portions 45a are electrically connected to each other. FIG. 4C shows a form in which the second common electrode 45 is disposed on the upper surface of the third piezoelectric layer 42, but the second common electrode 45 is superimposed on the upper surface of the third piezoelectric layer 42. A second common electrode 45 may be disposed on the lower surface of the piezoelectric layer 41, and both forms are substantially the same.

  The uppermost first piezoelectric layer 40 corresponds to the “upper piezoelectric layer” in the present invention, and the intermediate second piezoelectric layer 41 corresponds to the “lower piezoelectric layer” in the present invention. The second common electrode 45 located below the second piezoelectric layer 41 corresponds to the “common electrode” of the present invention.

  Also, the piezoelectric layer portion of the first piezoelectric layer 40 sandwiched between the individual electrode 43 and the electrode portion 44a of the first common electrode 44 (the portion facing the central portion of the pressure chamber 10 in FIG. 3C: first) The active portion 35) is previously polarized in the thickness direction. In addition, the piezoelectric layer portion of the first piezoelectric layer 40 and the second piezoelectric layer 41 sandwiched between the individual electrode 43 and the electrode portion 45a of the second common electrode 45 (the left and right end portions of the pressure chamber 10 in FIG. 3C). The portion opposite to the second active portion 36 is also polarized in the thickness direction in advance.

  As shown in FIG. 1, the FPC 50 is disposed on the upper surface of the piezoelectric actuator 32 (the upper surface of the first piezoelectric layer 40). The plurality of individual electrodes 43 positioned on the upper surface of the first piezoelectric layer 40 are connected to the FPC 50 via contact portions 43a drawn from each. Further, the first common electrode 44 positioned between the first piezoelectric layer 40 and the second piezoelectric layer 41 is connected to the FPC 50 via the lead electrode 46 formed on the upper surface of the first piezoelectric layer 40. Further, the second common electrode 45 located between the second piezoelectric layer 41 and the third piezoelectric layer 42 is also connected to the FPC 50 via the lead electrode 47 formed on the upper surface of the first piezoelectric layer 40. The structure of connecting the first common electrode 44 and the second common electrode 45 located inside the three piezoelectric layers 40 to 42 to the extraction electrodes 46 and 47 on the upper surface of the first piezoelectric layer 40 will be described later.

  As a result, the plurality of individual electrodes 43, the first common electrode 44, and the second common electrode 45 are each connected to the driver IC 51 mounted on the FPC 50. The potential of the individual electrode 43 is switched between a predetermined drive potential and a ground potential by the driver IC 51. The first common electrode 44 is always held at the driving potential, while the second common electrode 45 is always held at the ground potential.

The operation of the piezoelectric actuator 32 described above during ink ejection will be described.
In a standby state where ink is not ejected, the driver IC 51 applies a ground potential to each of the plurality of individual electrodes 43. Further, the driver IC 51 keeps the first common electrode 44 at a constant driving potential and the second common electrode 45 at a constant ground potential. Therefore, in the standby state, a voltage is applied between the individual electrode 43 and the first common electrode 44, and an electric field in the thickness direction acts on the first active portion 35 sandwiched between the electrodes 43 and 44. 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 to 42 is in a state of being deformed so as to protrude toward the pressure chamber 10 side (the lower side in FIG. 3C). 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 predetermined drive potential by the driver IC 51, no voltage is applied between the individual electrode 43 and the first common electrode 44, and the driver IC 51 is deformed. The first active part 35 is restored. 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 acts on the second active portion 36 sandwiched between the electrodes 43 and 45. 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 to 42 facing the substantially central portion of the pressure chamber 10 is pulled upward, and the portion of the piezoelectric layers 40 to 42 facing the pressure chamber 10 is entirely opposite to the pressure chamber 10. By deforming so as to be convex (upper side in FIG. 3C), 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 by the driver IC 51, 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 portion of the piezoelectric layers 40 to 42 facing the pressure chamber 10 is 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.

  Next, a structure in which the first common electrode 44 and the second common electrode 45 are connected to the lead electrodes 46 and 47 on the upper surface of the first piezoelectric layer 40 will be described. FIG. 5 is a cross-sectional view taken along the line V-V in FIG.

(Lead structure of first common electrode 44)
As shown in FIG. 4B, the upper surface of the upper left portion of the second piezoelectric layer 41 is electrically connected to the plurality of electrode portions 44a of the first common electrode 44, and has a large electrode area spread in a plane. A conductive electrode portion 44b is formed. Further, as shown in FIG. 4A, on the upper surface of the first piezoelectric layer 40, a plurality (six in this case) of lead electrodes 46 facing the conduction electrode portion 44b with the first piezoelectric layer 40 interposed therebetween. The plurality of lead electrodes 46 are connected to the FPC 50. The plurality of extraction electrodes 46 are arranged at equal intervals in a direction parallel to the edge of the first piezoelectric layer 40 (the vertical direction in FIG. 4). Further, as shown in FIG. 5, a plurality of through holes 37 are formed in the portion where the plurality of lead electrodes 46 of the first piezoelectric layer 40 are disposed, and each of the plurality of through holes 37 has a paste-like conductive property. The material is filled. As described above, the conductive electrode portion 44 b of the first common electrode 44 and the plurality of lead electrodes 46 are connected by the conductive material in the plurality of through holes 37.

(Extraction structure of the second common electrode 45)
As shown in FIG. 4C, the upper surface of the lower left portion of the third piezoelectric layer 42 is electrically connected to the plurality of electrode portions 45a of the second common electrode 45, and has a large electrode area spread in a plane. A conductive electrode portion 45b is formed. 4B, on the upper surface of the second piezoelectric layer 41, a plurality (six in this case) of relay electrodes 48 facing the conduction electrode portion 45b with the second piezoelectric layer 41 interposed therebetween. Is formed. The plurality of relay electrodes 48 are arranged at equal intervals in a direction parallel to the edge of the second piezoelectric layer 41 (up and down direction in FIG. 4). Furthermore, a plurality (six in this case) of extraction electrodes 47 are formed on the upper surface of the first piezoelectric layer 40 so as to face the plurality of relay electrodes 48, respectively. These plurality of extraction electrodes 47 are connected to the FPC 50. The The plurality of lead electrodes 47 are also arranged at equal intervals in the direction parallel to the edge of the second piezoelectric layer 41 (up and down direction in FIG. 4), similarly to the plurality of relay electrodes 48.

  Further, as shown in FIG. 5, a plurality of through holes 39 (lower through holes) are formed in a portion of the second piezoelectric layer 41 where the plurality of relay electrodes 48 are disposed. A plurality of through holes 38 (upper through holes) are also formed in the portion of the first piezoelectric layer 40 where the plurality of extraction electrodes 47 are disposed. These through holes 38 and 39 are filled with a paste-like conductive material. As described above, the conductive electrode portion 45b of the second common electrode 45 and the plurality of relay electrodes 48 are connected by the conductive material in the plurality of through holes 39, and further, the plurality of relay electrodes 48 and the plurality of lead electrodes 47 are connected. The conductive materials in the plurality of through holes 38 are connected.

  Here, when ink is ejected simultaneously from a large number of nozzles 15, the electrode portions 44 a, 44 a of the common electrodes 44, 45 are arranged from the driver IC 51 so that a large current easily flows through the first common electrode 44 and the second common electrode 45. The electrical resistance up to 45a is preferably as small as possible. Therefore, the conductive electrode portions 44b and 45b are formed as so-called solid electrodes having a large area. For the same reason, it is preferable to increase the electrode areas of the extraction electrodes 46 and 47 and the relay electrode 48. However, in order to suppress the thermal contraction difference when the piezoelectric layer is fired, the relay electrode 48 and the extraction electrodes 46 and 47 are respectively It is not composed of one electrode having a large area, but is divided into a plurality of electrodes.

  Further, in the present embodiment, as shown in FIGS. 4 and 5, each of the plurality of relay electrodes 48 is arranged with respect to the extraction electrode 47 connected via the through hole 38. They are displaced in the direction (vertical direction in FIG. 4 and horizontal direction in FIG. 5). As shown in FIG. 5, one relay electrode 48 is located between an extraction electrode 47 connected to the relay electrode 48 through the through hole 38 and another adjacent extraction electrode 47. Thereby, the area | region where the relay electrode 48 and the extraction electrode 47 overlap and the electrode density is high becomes small. In addition, there is almost no low electrode density region in which neither the relay electrode 48 nor the extraction electrode 47 is formed around the high electrode density region. In FIG. 5, with respect to the region where the relay electrode 48 and the lead electrode 47 overlap (the portion where the through hole 38 is formed), the left and right regions are regions where either one of the electrodes is formed. Yes. Therefore, the electrode density is made uniform with respect to the surface direction of the piezoelectric layer.

  In addition, when the through hole 38 (upper through hole) and the through hole 39 (lower through hole) filled with the conductive material are arranged so as to overlap each other, the electrode density is increased at that portion, and the electrode density is reduced. Variation will increase. In the present embodiment, as shown in FIG. 5, the upper through-hole 38 is formed in a portion where the end of the relay electrode 48 and the end of the extraction electrode 47 overlap, and the lower through-hole 39 is The relay electrode 48 is formed so as to be connected to the end opposite to the end connected to the through hole 38. Thereby, the through hole 38 that connects one relay electrode 48 and one lead electrode 47 is connected to the through hole 39 that connects the one relay electrode 48 and the second common electrode 45 (conduction electrode portion 45b). The electrodes 47 and 48 are arranged so as to be shifted with respect to the arrangement direction. With this configuration, the electrode density is further made uniform with respect to the surface direction of the piezoelectric layer. Further, as shown in FIG. 5, when the through holes 38 and 39 are alternately arranged in the arrangement direction of the electrodes 47 and 48, the separation distance L between the through holes 38 and 39 in the arrangement direction is all. Preferably equal.

  Further, each of the through holes 37, 38, and 39 is preferably formed of a bundle of a plurality of through holes formed locally densely in the first piezoelectric layer 40 and the second piezoelectric layer 41. FIG. 6 is an enlarged view of the through holes 38 and 39 of FIG. As the through hole, a through hole made of one large through hole may be adopted, but by adopting a through hole made of a bundle of a plurality of through holes 38a and 39a as shown in FIG. , 39 can be suppressed as much as possible from locally increasing the electrode density.

  When a through hole made up of a bundle of a plurality of through holes and a through hole made up of one large through hole are compared, if the size (diameter and length) of the entire through hole is the same, one large through hole A through hole made of a hole has a larger filling amount of the conductive material and has higher conduction reliability. However, when one first common electrode 44 or second common electrode 45 is connected to the extraction electrodes 46, 47 using a plurality of through holes 37, 38, 39 as in the present embodiment, The conduction reliability of the through holes 37, 38, and 39 may not be so high. Therefore, it is preferable to adopt a through hole as shown in FIG. 6 in order to prioritize uniform electrode density.

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

1] In the above embodiment, the positions of the relay electrode 48 and the extraction electrode 47 are shifted and the positions of the two through holes 38 and 39 positioned above and below the relay electrode 48 are also shifted. The positions of the through holes 38 and 39 may overlap.

  As described above, the electrode thickness is increased at the portion where the relay electrode 48 and the extraction electrode 47 overlap, and when the unfired green sheet is laminated, the portion is particularly strongly compressed and the density of the green sheet is increased. . Also, due to the variation in density of the green sheets, a difference in thermal contraction occurs in the piezoelectric layer during firing, and the flatness is lowered. When the influence of the thermal shrinkage difference due to the density variation of the green sheet is very large, the flatness can be sufficiently improved by merely shifting the positions of the relay electrode 48 and the extraction electrode 47.

  Alternatively, the filling amount of the conductive material in the through holes 38 and 39 is smaller than that of the relay electrode 48 and the extraction electrode 47, and the relay electrode 48 and the extraction electrode 47 are not disposed even if the through holes 38 and 39 are overlapped. If the variation in the electrode density in the surface direction does not increase as much as when they are completely overlapped, there will be no problem even if the positions of the upper and lower through holes 38 and 39 are overlapped.

2] The structure of the piezoelectric actuator 32 to which the present invention is applicable is not limited to the above embodiment. That is, if there are two or more piezoelectric layers on the common electrode, and the common electrode is drawn out to the lead electrode on the upper surface via a relay electrode arranged between the two piezoelectric layers, the structure is There is no particular limitation.

  For example, as shown in FIG. 7A, a diaphragm 60 made of an insulating material such as a synthetic resin, a piezoelectric ceramic such as PZT, or a ceramic material such as alumina or zirconia, and two sheets laminated on the diaphragm 60 Piezoelectric layers (upper piezoelectric layer 61, lower piezoelectric layer 62), individual electrodes 63 disposed on the upper surface of the upper piezoelectric layer 61, and common electrodes disposed on the lower surface of the lower piezoelectric layer 62 (the upper surface of the diaphragm 60). A unimorph type piezoelectric actuator 32A having 65 may be used. Further, the individual electrode 63 does not need to be disposed on the upper surface of the upper piezoelectric layer 61, and the individual electrode is disposed between the upper piezoelectric layer 61 and the lower piezoelectric layer 62 as shown in FIG. 7B. May be.

  Further, as shown in FIG. 8, four or more piezoelectric layers 70 to 73 are laminated, and individual electrodes 74 and common electrodes 75 are alternately arranged between the piezoelectric layers 70 to 73, so-called lamination. It may be a type of piezoelectric actuator 32B. In the form of FIG. 8, the present invention can be applied to a structure in which the common electrode 75 located at the bottom is drawn to the upper surface of the uppermost piezoelectric layer 70.

  The number of piezoelectric layers positioned above the common electrode is not limited to two, and three or more piezoelectric layers may be stacked on the common electrode (FIG. 8 is an example thereof). That is, one or both of the upper piezoelectric layer and the lower piezoelectric layer of the present invention may actually be composed of a plurality of piezoelectric layers.

  In the embodiment described above, the present invention is applied to a piezoelectric actuator for an inkjet head that records an image or the like by ejecting ink onto a recording sheet. The application target of the present invention is such an inkjet head. It is not limited to the piezoelectric actuator for use. Further, the present invention is not limited to a piezoelectric actuator used in a device that handles liquid such as ink.

32, 32A, 32B Piezoelectric actuator 38 Through hole 38a Through hole 39 Through hole 39a Through hole 40 First piezoelectric layer 41 Second piezoelectric layer 43 Individual electrode 45 Second common electrode 47 Lead electrode 48 Relay electrode 61 Upper piezoelectric layer 62 Lower piezoelectric Layer 63 Individual electrode 65 Common electrode 70 to 73 Piezoelectric layer 74 Individual electrode 75 Common electrode

Claims (4)

An upper piezoelectric layer and a lower piezoelectric layer laminated in the thickness direction;
A plurality of individual electrodes arranged in a plane between the upper surface of the upper piezoelectric layer or between the upper piezoelectric layer and the lower piezoelectric layer;
A common electrode disposed on the lower surface of the lower piezoelectric layer and facing at least the individual electrodes across the lower piezoelectric layer;
Between the upper piezoelectric layer and the lower piezoelectric layer, a plurality of relay electrodes facing the common electrode across the lower piezoelectric layer are arranged along a predetermined direction parallel to the surface direction of the piezoelectric layer. And the common electrode and the plurality of relay electrodes are electrically connected by a conductive material in a plurality of lower through holes formed in the lower piezoelectric layer,
On the upper surface of the upper piezoelectric layer, a plurality of lead electrodes respectively opposed to the plurality of relay electrodes across the upper piezoelectric layer are arranged along the predetermined one direction, similar to the plurality of relay electrodes, The plurality of relay electrodes and the plurality of lead electrodes are respectively conducted by a conductive material in a plurality of upper through holes formed in the upper piezoelectric layer,
Each of the plurality of relay electrodes is disposed so as to be shifted in the predetermined direction with respect to the lead electrode connected via the upper through hole, and the relay electrode is disposed between two adjacent lead electrodes. A piezoelectric actuator characterized by being positioned.   The upper through hole that connects one relay electrode and one lead electrode is arranged with a deviation from the lower through hole that connects the one relay electrode and the common electrode with respect to the predetermined direction. The piezoelectric actuator according to claim 1, wherein: The upper through hole and the lower through hole are alternately arranged with respect to the predetermined one direction,
3. The piezoelectric actuator according to claim 2, wherein the separation distances in the predetermined one direction between the upper through hole and the lower through hole are all equal. The plurality of upper through-holes and the plurality of lower through-holes each include a bundle of a plurality of through-holes formed to be locally densely formed in the piezoelectric layer. A piezoelectric actuator according to claim 1.

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