Piezoelectric actuator and manufacturing method thereof

Abstract

To suppress a difference in electrostatic capacitance between actuators.SOLUTION: A piezoelectric actuator 22 comprises first to third piezoelectric layers and first to third electrode layers. A low-potential electrode 53 constituting the third electrode layer 73 is formed on a surface of the third piezoelectric layer 43 positioned at a lowermost layer of the first to third electrode layers. A branch part 533 positioned at one end in a Y-direction (a left end shown by a figure 9) of a plurality of branch parts 533 of the low-potential electrode 53 is smaller in width than the branch parts 533 at positions other than the end part in the Y-direction (a center other than left and right ends shown by the figure 9).SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric actuator that is composed of a plurality of piezoelectric layers and a plurality of electrode layers, and to a method for manufacturing the same. [Background technology]

[0002] Patent Document 1 discloses a piezoelectric actuator in which individual electrodes (drive electrodes) are arranged on the surface of an upper piezoelectric layer (first piezoelectric layer), an intermediate common electrode (first potential electrode) is arranged on the surface of an intermediate piezoelectric layer (second piezoelectric layer), and a lower common electrode (second potential electrode) is arranged on the surface of a lower piezoelectric layer (third piezoelectric layer). Each of the intermediate common electrode (first potential electrode) and the lower common electrode (second potential electrode) includes a plurality of protruding portions (individual portions) having portions overlapping with each of the plurality of individual electrodes in the stacking direction (first direction), a plurality of extending portions (branch portions) extending in the transport direction (second direction) and connecting the plurality of protruding portions, and an extending portion (trunk portion) extending in the scanning direction (third direction) and connecting the plurality of extending portions (branch portions). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-171681 A (Figs. 5, 7, and 8) Summary of the Invention [Problem to be solved by the invention]

[0004] When forming each electrode by screen printing, bleeding is likely to occur downstream in the printing direction of each electrode. Here, the branch portion is an element that constitutes the actuator unit together with the drive electrode, and if bleeding occurs in the branch portion, the capacitance of the actuator unit becomes larger than the desired capacitance (capacitance without bleeding).

[0005] Furthermore, the ends of the piezoelectric actuator are prone to warping, and localized force is applied when the piezoelectric actuator is bonded to a flow path member, etc. At this time, a large tensile stress acts on the branch portion located at the end in the third direction, increasing the electrostatic capacitance of the actuator portion formed by the branch portion.

[0006] In the actuator units located at the ends in the third direction, an increase in capacitance due to the above-mentioned bleeding and an increase in capacitance due to the tensile stress during bonding occur, whereas in the actuator units located other than the ends in the third direction, an increase in capacitance due to bleeding occurs but an increase in capacitance due to the tensile stress during bonding does not occur. As a result, a difference in capacitance (and therefore deformation performance) occurs between the actuator units located at the ends in the third direction and the actuator units located other than the ends in the third direction.

[0007] An object of the present invention is to provide a piezoelectric actuator capable of suppressing the difference in capacitance between actuator elements, and a method for manufacturing the same. [Means for solving the problem]

[0008] According to a first aspect of the present invention, there is provided a piezoelectric actuator including: a first piezoelectric layer; a second piezoelectric layer stacked on the first piezoelectric layer in a first direction along a thickness direction of the first piezoelectric layer; a third piezoelectric layer stacked on the first piezoelectric layer and the second piezoelectric layer in the first direction, sandwiching the second piezoelectric layer between the first piezoelectric layer and the second piezoelectric layer; a first electrode layer arranged on a surface of the first piezoelectric layer opposite to the second piezoelectric layer in the first direction; a second electrode layer arranged between the first piezoelectric layer and the second piezoelectric layer in the first direction; and a third electrode layer arranged between the second piezoelectric layer and the third piezoelectric layer in the first direction, wherein the first electrode layers are each selectively set to one of a first potential and a second potential different from the first potential. the second electrode layer includes a first potential electrode held at the first potential, and the third electrode layer includes a second potential electrode held at the second potential, at least one of the first potential electrode and the second potential electrode includes a plurality of individual parts having portions overlapping with each of the plurality of driving electrodes in the first direction, a plurality of branch parts extending in a second direction perpendicular to the first direction and connecting the plurality of individual parts, and a trunk extending in a third direction perpendicular to the first direction and the second direction and connecting the plurality of branch parts, wherein among the plurality of branch parts, a branch part located at one end in the third direction has a smaller width than branch parts located other than the ends in the third direction.

[0009] According to a second aspect of the present invention, there is provided a method for manufacturing a piezoelectric actuator including: a first piezoelectric layer; a second piezoelectric layer stacked on the first piezoelectric layer in a first direction along a thickness direction of the first piezoelectric layer; and a third piezoelectric layer stacked on the first and second piezoelectric layers in the first direction, sandwiching the second piezoelectric layer between the first piezoelectric layer and the third piezoelectric layer, the method comprising: forming a first electrode layer on a surface of the first piezoelectric layer, the first electrode layer including a plurality of drive electrodes to which either a first potential or a second potential different from the first potential is selectively applied; and forming a first electrode layer on a surface of the second piezoelectric layer, the first electrode layer including a plurality of drive electrodes to which either a first potential or a second potential different from the first potential is selectively applied, the second piezoelectric layer having a first potential and a second potential held at the first potential. a second electrode layer including a first potential electrode held at the second potential is formed on a surface of the third piezoelectric layer, a third electrode layer including a second potential electrode held at the second potential is formed on a surface of the third piezoelectric layer, the first electrode layer is disposed on a surface of the first piezoelectric layer opposite to the second piezoelectric layer in the first direction, the second electrode layer is disposed between the first piezoelectric layer and the second piezoelectric layer in the first direction, and the third electrode layer is disposed between the second piezoelectric layer and the third piezoelectric layer in the first direction; a first piezoelectric layer, a second piezoelectric layer, and a third piezoelectric layer stacked in the first direction such that the individual parts have portions that overlap with the driving electrodes in the first direction; and a second electrode layer, when forming the first piezoelectric layer, a second piezoelectric layer, and a third piezoelectric layer, stacked in the first direction such that the individual parts have portions that overlap with the driving electrodes in the first direction. Furthermore, when forming the second electrode layer or the third electrode layer, at least one of the first potential electrode and the second potential electrode is formed by screen printing along the third direction such that, of the branch parts, a branch part located at one end in the third direction has a smaller width than a branch part located at any other end in the third direction. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating the overall configuration of a printer 1 including a piezoelectric actuator according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the head 3 shown in FIG. [Figure 3] FIG. 3 is an enlarged view of region III in FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 4 is a cross-sectional view taken along line VV in FIG. [Figure 6] 6A and 6B are diagrams showing the operation of the actuator section 90 in the cross section of FIG. 5. [Figure 7] 1 is a plan view showing the top surface of the uppermost piezoelectric layer 41 of the three piezoelectric layers 41 to 43 that constitute the piezoelectric actuator 22. FIG. [Figure 8] 1 is a plan view showing the top surface of the middle piezoelectric layer 42 of the three piezoelectric layers 41 to 43 that make up the piezoelectric actuator 22. FIG. [Figure 9] 1 is a plan view showing the top surface of the lowermost piezoelectric layer 43 of the three piezoelectric layers 41 to 43 that constitute the piezoelectric actuator 22. FIG. [Figure 10] 4 is a flowchart showing a method for manufacturing the piezoelectric actuator 22. FIG. [Figure 11] 10A and 10B are diagrams showing a process of forming an electrode layer 73 on the upper surface of a piezoelectric layer 43 by screen printing. [Figure 12] 10 is a view corresponding to FIG. 9 and showing a piezoelectric actuator 222 according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the following description, the Z direction is the vertical direction, and the X and Y directions are horizontal directions. Both the X and Y directions are perpendicular to the Z direction. The X direction is perpendicular to the Y direction.

[0012] <Overall printer configuration> First, with reference to FIG. 1, the overall configuration of a printer 1 including a piezoelectric actuator according to a first embodiment of the present invention will be described.

[0013] The printer 1 includes a head 3, a carriage 2, and two pairs of conveying rollers 4.

[0014] The carriage 2 is supported by two guide rails 5 extending in the Y direction, and is movable along the guide rails 5 in the Y direction.

[0015] The head 3 is of a serial type, is mounted on the carriage 2, and is movable in the Y direction together with the carriage 2. A plurality of nozzles 15 are formed on the bottom surface of the head 3.

[0016] The two conveying roller pairs 4 are arranged in the X direction, sandwiching the carriage 2. When the conveying roller pairs 4 rotate with the paper P sandwiched between them, the paper P is conveyed in a conveying direction along the X direction.

[0017] A control unit (not shown) of the printer 1 alternately performs an ejection operation in which ink is ejected from the nozzles 15 while moving the head 3 in the Y direction together with the carriage 2, and a transport operation in which the transport roller pair 4 transports the paper P a predetermined distance in the transport direction. In this way, an image is recorded on the paper P.

[0018] <Head configuration> 2, the head 3 includes a flow path unit 21 and a piezoelectric actuator 22 according to the first embodiment of the present invention. Both the flow path unit 21 and the piezoelectric actuator 22 have a rectangular shape in which the length in the X direction is longer than the length in the Y direction in a plane perpendicular to the Z direction.

[0019] <Configuration of the flow path unit> As shown in FIG. 4, the flow path unit 21 is made up of four metal plates 31 to 34 stacked in the Z direction.

[0020] A plurality of pressure chambers 10 are formed in the plate 31. A plurality of communication passages 12, 13 are formed in the plate 32 for each pressure chamber 10. The communication passages 12, 13 overlap one end and the other end of the corresponding pressure chamber 10 in the Y direction, respectively, in the Z direction. A communication passage 14 is formed in the plate 33 for each communication passage 13. The communication passage 14 overlaps the corresponding communication passage 13 in the Z direction. The plate 33 is further formed with eleven manifold channels 11. The manifold channels 11 are provided for each row 10R of the pressure chambers 10 arranged in the X direction (see FIG. 2). Each manifold channel 11 extends in the X direction and communicates with the plurality of pressure chambers 10 belonging to the corresponding row 10R via the communication passages 12. A plurality of nozzles 15 are formed in the plate 34. Each nozzle 15 overlaps with the communication passage 14 in the Z direction.

[0021] Four ink supply ports 8 are formed on the upper surface of the plate 31 in an area where the piezoelectric actuators 22 are not disposed (see FIG. 2). Each ink supply port 8 communicates with an ink cartridge (not shown) and also communicates with three manifold channels 11. Ink supplied from the ink cartridge to each ink supply port 8 is supplied to the three manifold channels 11. Ink is supplied from each manifold channel 11 to a plurality of pressure chambers 10 belonging to each row 10R via communication channels 12. Then, as will be described later, when the piezoelectric actuators 22 are driven, pressure is applied to the ink in the pressure chambers 10, and the ink is ejected from the nozzles 15 through the communication channels 13 and 14.

[0022] <Configuration of Piezoelectric Actuator> 4, the piezoelectric actuator 22 is disposed on the upper surface of the flow path unit 21. The piezoelectric actuator 22 has three piezoelectric layers 41-43 and three electrode layers 71-73.

[0023] The three piezoelectric layers 41 to 43 are stacked in the Z direction, with the Z direction being the thickness direction of each. Piezoelectric layer 42 is stacked in the Z direction relative to piezoelectric layer 41. Piezoelectric layer 43 is stacked in the Z direction relative to piezoelectric layers 41 and 42, with piezoelectric layer 42 sandwiched between piezoelectric layer 41 and piezoelectric layer 43. The Z direction corresponds to the "first direction" of the present invention. Piezoelectric layer 41 corresponds to the "first piezoelectric layer" of the present invention, piezoelectric layer 42 corresponds to the "second piezoelectric layer" of the present invention, and piezoelectric layer 43 corresponds to the "third piezoelectric layer" of the present invention.

[0024] The piezoelectric layers 41 to 43 have the same thickness (approximately 10 to 15 μm), and the total thickness of the piezoelectric layers 41 to 43 is approximately 30 to 45 μm. Each of the piezoelectric layers 41 to 43 is made of a piezoelectric material whose main component is lead zirconate titanate or the like.

[0025] The piezoelectric layer 43 is disposed on the upper surface of the plate 31, and covers all of the pressure chambers 10 formed in the plate 31. The piezoelectric actuator 22 and the flow path unit 21 are bonded to each other by an adhesive (not shown) disposed between the piezoelectric layer 43 and the plate 31.

[0026] The electrode layer 71 is disposed on the upper surface of the piezoelectric layer 41 (the surface of the piezoelectric layer 41 opposite to the piezoelectric layer 42 in the Z direction). The electrode layer 72 is disposed on the upper surface of the piezoelectric layer 42 (between the piezoelectric layer 41 and the piezoelectric layer 42 in the Z direction). The electrode layer 73 is disposed on the upper surface of the piezoelectric layer 43 (between the piezoelectric layer 42 and the piezoelectric layer 43 in the Z direction). The electrode layer 71 corresponds to the "first electrode layer" of the present invention, the electrode layer 72 corresponds to the "second electrode layer" of the present invention, and the electrode layer 73 corresponds to the "third electrode layer" of the present invention.

[0027] The thickness of each of the electrode layers 71 to 73 in the Z direction is 0.5 to 1.5 μm. The electrode layers 71 and 72 have the same thickness. The thickness of the electrode layer 73 is greater than the thickness of each of the electrode layers 71 and 72 (see FIGS. 4 to 6).

[0028] As shown in FIG. 7, the electrode layer 71 includes a plurality of drive electrodes 51, a plurality of dummy electrodes 59, two high potential connection electrode portions 54, and two low potential connection electrode portions 55.

[0029] The multiple drive electrodes 51 are arranged corresponding to the respective pressure chambers 10. Each drive electrode 51 has a main portion 51a and a protruding portion 51b. The main portion 51a overlaps with substantially the entire area of ​​the corresponding pressure chamber 10 in the Z direction. The protruding portion 51b protrudes from the main portion 51a in the Y direction and does not overlap with the corresponding pressure chamber 10 in the Z direction. The protruding portion 51b is provided with a contact point that is electrically connected to a COF (Chip On Film) (not shown). A driver IC (not shown) mounted on the COF selectively applies either a high potential (VDD potential) or a low potential (GND potential) to each drive electrode 51 individually via the wiring of the COF under the control of a control unit.

[0030] The multiple drive electrodes 51 are arranged in the X direction in a central region (region excluding both ends of the piezoelectric layer 41 in the X direction and both ends of the piezoelectric layer 41 in the Y direction) on the upper surface of the piezoelectric layer 41, and form multiple drive electrode rows 51R corresponding to the rows 10R (see FIG. 2) of the pressure chambers 10. The multiple drive electrode rows 51R are lined up in the Y direction.

[0031] Dummy electrodes 59 are provided on each drive electrode row 51R on one side (upper side in FIG. 7) and the other side (lower side in FIG. 7) in the X direction. The dummy electrodes 59 have the same size and shape as the drive electrodes 51 belonging to the corresponding drive electrode row 51R in a plane perpendicular to the Z direction, and are arranged at equal intervals in the X direction together with the drive electrodes 51. The dummy electrodes 59 are not electrically connected to the COF, and no potential is applied to them. By providing the dummy electrodes 59, it is possible to reduce the difference in the amount of shrinkage due to electrode formation between the drive electrodes 51 located at the center in the X direction and the drive electrodes 51 located at the ends in the X direction in each drive electrode row 51R, and ultimately to reduce variations in the ejection amount from the multiple nozzles 15 corresponding to each drive electrode row 51R.

[0032] The two high-potential connecting electrode portions 54 are respectively arranged on one side in the X direction (upper side in FIG. 7) of the piezoelectric layer 41 at one end (left end in FIG. 7) and the other end (right end in FIG. 7) of the piezoelectric layer 41 in the Y direction. The two low-potential connecting electrode portions 55 are respectively arranged on the other side in the X direction (lower side in FIG. 7) of the piezoelectric layer 41 at one end (left end in FIG. 7) and the other end (right end in FIG. 7) of the piezoelectric layer 41 in the Y direction.

[0033] Each of the two high-potential connection electrode sections 54 is composed of eight connection electrodes 54a spaced apart from one another in the X direction. Each of the two low-potential connection electrode sections 55 is composed of eight connection electrodes 55a spaced apart from one another in the X direction. The connection electrodes 54a, 55a have substantially the same size and shape in a plane perpendicular to the Z direction. Under the control of the control unit, the driver IC applies a high potential (VDD potential) to the connection electrode 54a and a low potential (GND potential) to the connection electrode 55a via the COF wiring. The connection electrode 54a is held at a high potential, and the connection electrode 55a is held at a low potential.

[0034] As shown in FIG. 8, the electrode layer 72 includes a high potential electrode 52, two low potential connection electrode portions 56, two floating electrode portions 64, and a floating electrode portion 65.

[0035] The high potential electrode 52 includes a trunk 521, a plurality of branch portions 523 branching from the trunk 521, a plurality of individual portions 52a branching from each of the branch portions 523, and two high potential receiving portions 522.

[0036] The trunk portion 521 extends in the Y direction from one end in the X direction of the piezoelectric layer 42 (the upper end in FIG. 8). The multiple branch portions 523 are aligned in the Y direction, and each extend from the trunk portion 521 to the other side in the X direction (the lower side in FIG. 8). Each individual portion 52a overlaps in the Z direction with the center portion in the X direction of each pressure chamber 10, and has a portion that overlaps with each drive electrode 51 in the Z direction (see FIG. 5). Each branch portion 523 connects the multiple individual portions 52a. The trunk portion 521 connects the multiple branch portions 523.

[0037] The X direction corresponds to the "second direction" of the present invention, and the Y direction corresponds to the "third direction" of the present invention. Furthermore, the high potential corresponds to the "first potential" of the present invention, and the high potential electrode 52 corresponds to the "first potential electrode" of the present invention.

[0038] One of the two high potential receiving portions 522 is connected to one end in the Y direction (the left end in FIG. 8) of the trunk portion 521. The other of the two high potential receiving portions 522 is connected to the other end in the Y direction (the right end in FIG. 8) of the trunk portion 521. The two high potential receiving portions 522 extend in the X direction at one end (the left end in FIG. 8) and the other end (the right end in FIG. 8) of the piezoelectric layer 42 in the Y direction, respectively.

[0039] The two high potential receiving portions 522 each overlap in the Z direction with the four connection electrodes 54a (the four connection electrodes 54a arranged on one side in the X direction (upper side in FIG. 7)) of the high potential connection electrode portion 54. The two high potential receiving portions 522 are each electrically connected to the four connection electrodes 54a via through holes formed in the piezoelectric layer 41, and receive a high potential from the connection electrodes 54a.

[0040] The two low potential connection electrode portions 56 are respectively arranged on the other side in the X direction (lower side in FIG. 8) of the piezoelectric layer 42 at one end (left end in FIG. 8) and the other end (right end in FIG. 8) in the Y direction of the piezoelectric layer 42. Each of the two low potential connection electrode portions 56 is composed of two connection electrodes 56a and one connection electrode 56b arranged spaced apart from each other in the X direction.

[0041] The two floating electrode portions 64 are respectively arranged at one end (the left end in FIG. 8) and the other end (the right end in FIG. 8) in the Y direction of the piezoelectric layer 42, between the high potential receiving portion 522 and the low potential connecting electrode portion 56 in the X direction. Each of the two floating electrode portions 64 is composed of ten floating electrodes 64a arranged at a distance from each other in the X direction.

[0042] The floating electrode section 65 is disposed at the other end in the X direction of the piezoelectric layer 42 (the lower end in FIG. 8). The floating electrode section 65 is composed of a plurality of floating electrodes 65a disposed at a distance from one another in the Y direction. The floating electrodes 65a have substantially the same size and shape in a plane perpendicular to the Z direction, and are disposed at equal intervals in the Y direction.

[0043] The connection electrode 56a of the low potential connection electrode portion 56 and the floating electrode 64a of the floating electrode portion 64 have approximately the same size and shape in a plane perpendicular to the Z direction, and are arranged at equal intervals in the X direction at one end (the left end in FIG. 8) and the other end (the right end in FIG. 8) in the Y direction of the piezoelectric layer 42. On the other hand, the connection electrode 56b of the low potential connection electrode portion 56 is longer in the X direction than the connection electrode 56a.

[0044] The two connection electrodes 56a overlap in the Z direction with the two connection electrodes 55a (the two connection electrodes 55a arranged third and fourth from the other side in the X direction (the lower side in FIG. 7)) of the low potential connection electrode portion 55. The two connection electrodes 56a are electrically connected to the two connection electrodes 55a via through holes formed in the piezoelectric layer 41.

[0045] The connection electrode 56b overlaps in the Z direction with the two connection electrodes 55a (the two connection electrodes 55a arranged at the other end in the X direction (the lower end in FIG. 7)) of the low potential connection electrode portion 55. The connection electrode 56b is electrically connected to the two connection electrodes 55a via a through hole formed in the piezoelectric layer 41.

[0046] The floating electrodes 64a and 65a of the floating electrode sections 64 and 65 are not electrically connected to any of the electrodes, and no potential is applied thereto.

[0047] As shown in FIG. 9, the electrode layer 73 includes a low potential electrode 53, a high potential connecting electrode portion 57, and two floating electrode portions 66.

[0048] The low potential electrode 53 includes a trunk 531 , a plurality of branch portions 533 branching from the trunk 531 , a plurality of individual portions 53 a branching from each of the branch portions 533 , and two low potential receiving portions 532 .

[0049] The trunk portion 531 extends in the Y direction from the other end of the piezoelectric layer 43 in the X direction (the lower end in FIG. 9). The multiple branch portions 533 are aligned in the Y direction and each extend from the trunk portion 531 to one side in the X direction (the upper side in FIG. 9). Of the multiple individual portions 53a, except for the individual portions 53a located at one end and the other end in the X direction, each individual portion 53a spans two pressure chambers 10 adjacent to each other in the X direction and has a portion overlapping with the two pressure chambers 10 in the Z direction (see FIG. 5). The individual portions 53a located at one end and the other end in the X direction have a portion overlapping with one pressure chamber 10 in the Z direction. In addition, each individual portion 53a has a portion overlapping with each driving electrode 51 in the Z direction. Each branch portion 533 connects the multiple individual portions 53a. The trunk portion 531 connects the multiple branch portions 533.

[0050] The low potential corresponds to the "second potential" of the present invention, and the low potential electrode 53 corresponds to the "second potential electrode" of the present invention.

[0051] One of the two low potential receiving portions 532 is connected to one end in the Y direction (the left end in FIG. 9) of the trunk portion 531. The other of the two low potential receiving portions 532 is connected to the other end in the Y direction (the right end in FIG. 9) of the trunk portion 531. The two low potential receiving portions 532 extend in the X direction at one end (the left end in FIG. 9) and the other end (the right end in FIG. 9) of the piezoelectric layer 43 in the Y direction, respectively.

[0052] The two low potential receiving portions 532 each overlap in the Z direction with the four connection electrodes 55a of the low potential connecting electrode portion 55 (the four connection electrodes 55a arranged on the other side in the X direction (the lower side in FIG. 7)) and the three connection electrodes 56a, 56b of the low potential connecting electrode portion 56 (see FIG. 8). Each low potential receiving portion 532 is electrically connected to the three connection electrodes 56a, 56b of the low potential connecting electrode portion 56 via a through-hole formed in the piezoelectric layer 42. As described above, the three connection electrodes 56a, 56b are each electrically connected to the four connection electrodes 55a of the low potential connecting electrode portion 55. Therefore, each low potential receiving portion 532 is electrically connected to the low potential connecting electrode portion 55 (see FIG. 7) via the low potential connecting electrode portion 56 (see FIG. 8) and receives a low potential from the low potential connecting electrode portion 55.

[0053] The high-potential connecting electrode portion 57 has a portion 57a ​​extending in the Y direction and two portions 57b extending in the X direction. The portion 57a ​​extends in the Y direction at one end in the X direction of the piezoelectric layer 43 (the upper end in FIG. 9). One of the two portions 57b is connected to one end in the Y direction of the portion 57a ​​(the left end in FIG. 9). The other of the two portions 57b is connected to the other end in the Y direction of the portion 57a ​​(the right end in FIG. 9).

[0054] The two portions 57b each overlap in the Z direction with the four connection electrodes 54a of the high potential connection electrode portion 54 (the four connection electrodes 54a arranged on one side in the X direction (the upper side in FIG. 7)) and the high potential receiving portions 522 (see FIG. 8) of the high potential electrode 52. Each portion 57b is electrically connected to the corresponding high potential receiving portion 522 via a through-hole formed in the piezoelectric layer 42. As described above, each high potential receiving portion 522 is electrically connected to the four connection electrodes 54a of the high potential connection electrode portion 54. Therefore, the portion 57b is electrically connected to the high potential connection electrode portion 54 (see FIG. 7) via the high potential receiving portion 522 (see FIG. 8) and receives a high potential from the high potential connection electrode portion 54.

[0055] The two floating electrode sections 66 are respectively arranged at one end (the left end in FIG. 9) and the other end (the right end in FIG. 9) of the piezoelectric layer 43 in the Y direction, between the portion 57b and the low potential receiving section 532 in the X direction. Each of the two floating electrode sections 66 is composed of ten floating electrodes 66a arranged at a distance from each other in the X direction. The floating electrodes 66a have approximately the same size and shape in a plane perpendicular to the Z direction, and are arranged at equal intervals in the X direction.

[0056] Each floating electrode 66a of the floating electrode section 66 is not electrically connected to any electrode and no potential is applied thereto.

[0057] <Actuator section> 5, a portion of the piezoelectric layer 41 that is sandwiched in the Z direction between the drive electrode 51 and the individual portion 52a of the high-potential electrode 52 is referred to as a first active portion 91. A portion of the piezoelectric layers 42, 43 that is sandwiched in the Z direction between the drive electrode 51 and the individual portion 53a of the low-potential electrode 53 is referred to as a second active portion 92. The first active portion 91 is polarized mainly upward, and the second active portion 92 is polarized mainly downward. The piezoelectric actuator 22 has an actuator portion 90 for each pressure chamber 10, which is composed of one first active portion 91 and two second active portions 92 that sandwich the first active portion 91 in the X direction.

[0058] Here, with reference to FIG. 6, the operation of the actuator element 90 corresponding to a certain nozzle 15 when ink is ejected from that nozzle 15 will be described.

[0059] Before the printer 1 starts a recording operation, as shown in Fig. 6(a), a low potential (GND potential) is applied to each drive electrode 51. At this time, the potential difference between the drive electrode 51 and the high potential electrode 52 generates an upward electric field in the first active section 91 that is equal to the polarization direction of the first active section 91, causing the first active section 91 to contract in the planar direction (directions along the X and Y directions). As a result, the portion of the laminate made up of the piezoelectric layers 41 to 43 that overlaps with the pressure chamber 10 in the Z direction is bent so as to be convex (downward) toward the pressure chamber 10. At this time, the volume of the pressure chamber 10 is smaller than when the laminate is flat.

[0060] When the printer 1 starts a recording operation and ejects ink from a certain nozzle 15, first, as shown in FIG. 6(b), the potential of the drive electrode 51 corresponding to that nozzle 15 is switched from low potential (GND potential) to high potential (VDD potential). At this time, the potential difference between the drive electrode 51 and the high-potential electrode 52 disappears, and the contraction of the first active section 91 is eliminated. Meanwhile, the potential difference between the drive electrode 51 and the low-potential electrode 53 is generated, and a downward electric field equal to the polarization direction of the second active section 92 is generated in the second active section 92, causing the second active section 92 to contract in the planar direction. However, the second active section 92 has the function of suppressing crosstalk (a phenomenon in which pressure fluctuations caused by deformation of the actuator section 90 in a certain pressure chamber 10 are transmitted to another pressure chamber 10 adjacent to the pressure chamber 10 in the X direction), and therefore does not contribute much to the deformation of the actuator section 90. In other words, at this time, the portion of the laminate overlapping with the pressure chamber 10 in the Z direction does not bend convexly (upward) away from the pressure chamber 10, but remains flat. As a result, the volume of the pressure chamber 10 becomes larger than that in FIG. 6(a).

[0061] 6(a), the potential of the drive electrode 51 corresponding to the nozzle 15 is switched from a high potential (VDD potential) to a low potential (GND potential). At this time, the potential difference between the drive electrode 51 and the low potential electrode 53 disappears, and the contraction of the second active portion 92 is canceled. Meanwhile, a potential difference between the drive electrode 51 and the high potential electrode 52 is generated, and an upward electric field equal to the polarization direction of the first active portion 91 is generated in the first active portion 91, and the first active portion 91 contracts in the planar direction. As a result, the portion of the laminate that overlaps with the pressure chamber 10 in the Z direction bends so as to become convex (downward) toward the pressure chamber 10. At this time, the volume of the pressure chamber 10 decreases significantly, and a large pressure is applied to the ink in the pressure chamber 10, and ink is ejected from the nozzle 15.

[0062] <Description of the Invention> 9, of the multiple branch portions 533 of the low potential electrode 53, the branch portion 533 located at one end in the Y direction (the left end in FIG. 9) has a smaller width than the branch portions 533 located other than the ends in the Y direction (the center other than the left and right ends in FIG. 9). For example, the width W1 of the branch portion 533 located at one end in the Y direction is 1 / 2 to 2 / 3 of the width W2 of the branch portion 533 located other than the ends in the Y direction. The width W3 of the branch portion 533 located at the other end in the Y direction (the right end in FIG. 9) is larger than the widths W1 and W2.

[0063] The width of each branch portion 533 is constant in the second direction (that is, from the base end 533a connected to the trunk portion 531 of the branch portion 533 to the tip end 533b).

[0064] Of the multiple individual parts 53a protruding from the branch part 533 located at one end in the Y direction (left end in Figure 9), the length P1 of the individual part (first individual part) located at one end in the Y direction (left side in Figure 9) is longer than the length P2 of the individual part (second individual part) located at the other end in the Y direction (right side in Figure 9).

[0065] The minimum distance L1 in the Y direction between the portion where multiple individual parts 53a are connected in the branch portion 533 located at one end in the Y direction (the left end in Figure 9) and one end 22a in the Y direction of the piezoelectric actuator 22 is smaller than the minimum distance L2 in the Y direction between the portion where multiple individual parts 53a are connected in the branch portion 533 located at the other end in the Y direction (the right end in Figure 9) and the other end 22b in the Y direction of the piezoelectric actuator 22.

[0066] Comparing the widths of the branches 533 of the low potential electrode 53 (see FIG. 9) and the branches 523 of the high potential electrode 52 (see FIG. 8), the width of each branch 533 is greater than the width of each branch 523. The width W2 of the branch 533 located other than the ends in the Y direction (the center, other than the left and right ends in FIG. 9) is greater than the width W5 of the branch 523 located other than the ends in the Y direction (the center, other than the left and right ends in FIG. 8).

[0067] 8, among the multiple branch portions 523 of the high-potential electrode 52, the branch portion 523 located at one end in the Y direction (the left end in FIG. 8) has a smaller width than the branch portions 523 located other than the ends in the Y direction (the center other than the left and right ends in FIG. 8). For example, the width W4 of the branch portion 523 located at one end in the Y direction is 1 / 2 to 2 / 3 of the width W5 of the branch portion 523 located other than the ends in the Y direction.

[0068] <Manufacturing method of piezoelectric actuator> 10, the piezoelectric actuator 22 is manufactured by forming electrode layers 71-73 on the surfaces of the piezoelectric layers 41-43 (S1), and then stacking and bonding the piezoelectric layers 41-43 to each other (S2). In S2, the piezoelectric layers 41-43 are stacked in the Z direction so that each of the individual parts 52a, 53a has a portion that overlaps with each of the drive electrodes 51 in the Z direction.

[0069] In S1, as shown in Fig. 11, the electrode layers 71 to 73 are formed by screen printing using a squeegee 100. In this embodiment, the screen printing is performed from the other side of the Y direction (the right side in Figs. 7 to 9) to one side (the left side in Figs. 7 to 9).

[0070] For example, when forming the electrode layer 73, as shown in FIG. 11 , a mask 101 having holes 101x formed therein corresponding to the low-potential electrodes 53 and the like that constitute the electrode layer 73 is placed on the surface of the piezoelectric layer 43. Then, a squeegee 100 is moved from the other side (the right side in FIG. 11 ) to the other side (the left side in FIG. 11 ) in the Y direction to form the low-potential electrodes 53 and the like by screen printing. At this time, the squeegee 100 moves while holding electrode material (e.g., silver, nickel, gold, etc.) 110 downstream in the printing direction of the screen printing (the left side in FIG. 11 ). The material 110 fills the holes 101x, thereby forming the electrode layer 73 including the low-potential electrodes 53.

[0071] Furthermore, at this time, material 110 flows downstream in the printing direction (leftward in FIG. 11) relative to electrode layer 73, causing bleed A. Bleed A has a thickness of 0.1 μm or less and a length in the Y direction of 10 to 100 μm, for example.

[0072] In this embodiment, in consideration of the occurrence of bleeding A, the width W1 of the branch portion 533 located at one end in the Y direction (the left end in FIG. 9), where there is particular concern about an increase in capacitance due to tensile stress during bonding, is made smaller than the width W2 of the branch portion 533 located other than the end in the Y direction (the center other than the left and right ends in FIG. 9). Also, of the multiple individual portions 53a protruding from the branch portion 533 located at one end in the Y direction, the length P1 of the individual portion (first individual portion) located at one end in the Y direction (the left side in FIG. 9) is made longer than the length P2 of the individual portion (second individual portion) located at the other end in the Y direction (the right side in FIG. 9).

[0073] Furthermore, in this embodiment, not only in the low potential electrode 53 but also in the high potential electrode 52, the width W4 of the branch 523 located at one end in the Y direction (the left end in Figure 8) among the multiple branch portions 523 is made smaller than the width W5 of the branch 523 located other than the end in the Y direction (the center other than the left and right ends in Figure 8).

[0074] <Configuration and Effects of This Embodiment> As described above, according to this embodiment, in at least one of the high potential electrode 52 and the low potential electrode 53 (in this embodiment, both), the width of the branch portions 523, 533 located at one end in the Y direction (the left end in FIGS. 8 and 9) is smaller than the width of the branch portions 523, 533 located other than the end in the Y direction (the center other than the left and right ends in FIGS. 8 and 9). Also smallWhen the high-potential electrode 52 and the low-potential electrode 53 are formed by screen printing along the Y direction during manufacturing of the piezoelectric actuator 22, the width W1 of the branch 533 located at one end in the Y direction (the left end in FIG. 9 ) of the low-potential electrode 53 is made smaller than the width W2 of the branch 533 located other than the end in the Y direction (the center, other than the left and right ends in FIG. 9 ), and the width W4 of the branch 523 located at one end in the Y direction (the left end in FIG. 8 ) of the high-potential electrode 52 is made smaller than the width W5 of the branch 523 located other than the end in the Y direction (the center, other than the left and right ends in FIG. 8 ). This suppresses an increase in capacitance due to bleeding A (see FIG. 11 ) for the actuator element 90 located at one end in the Y direction (the left end in FIGS. 8 and 9 ). Therefore, the actuator element 90 located at one end in the Y direction experiences an increase in capacitance due to tensile stress during bonding (caused by warping of the end of the piezoelectric actuator 22), but is less likely to experience an increase in capacitance due to seepage A. The actuator elements 90 located other than the end in the Y direction experience an increase in capacitance due to seepage A, but are less likely to experience an increase in capacitance due to tensile stress during bonding. This makes it possible to suppress differences in capacitance between the actuator elements 90.

[0075] If a difference in capacitance occurs between the actuator elements 90, the ejection performance may vary between the nozzles 15 corresponding to the actuator elements 90, which may result in a deterioration in recording quality. In this embodiment, this problem can be suppressed.

[0076] The width W2 of the branch portion 533 located other than the ends in the Y direction (the center, other than the left and right ends in FIG. 9) is larger than the width W5 of the branch portion 523 located other than the ends in the Y direction (the center, other than the left and right ends in FIG. 8). The larger the width, the more likely bleeding is to occur and the more likely the capacitance is to increase. Therefore, by configuring at least the branch portion 533 of the widest low potential electrode 53 as described above, the effect of suppressing the influence of bleeding A and suppressing the difference in capacitance between the actuator elements 90 can be more reliably achieved.

[0077] The thickness of the branch portion 533 of the low potential electrode 53 is greater than the thickness of the branch portion 523 of the high potential electrode 52 (see FIG. 4). The greater the thickness, the more likely it is that bleeding will occur and the capacitance will increase. Therefore, by configuring at least the branch portion 533 of the low potential electrode 53 that is thicker as described above, the effect of suppressing the influence of bleeding A and suppressing the difference in capacitance between the actuator elements 90 can be more reliably achieved.

[0078] In both, not just one, but both of the high potential electrode 52 and the low potential electrode 53, the width of the branch portions 523, 533 located at one end in the Y direction (the left end in FIGS. 8 and 9) is smaller than the width of the branch portions 523, 533 located other than the ends in the Y direction (the center other than the left and right ends in FIGS. 8 and 9). This makes it possible to more reliably suppress the influence of bleeding A in both the branch portions 523 of the high potential electrode 52 and the branch portions 533 of the low potential electrode 53, and to achieve the effect of suppressing the difference in capacitance between the actuator elements 90.

[0079] The minimum distance L1 in the Y direction between the portion of the branch 533 located at one end in the Y direction (the left end in FIG. 9 ) where the multiple individual parts 53a are connected and the Y end 22a of the piezoelectric actuator 22 is smaller than the minimum distance L2 in the Y direction between the portion of the branch 533 located at the other end in the Y direction (the right end in FIG. 9 ) where the multiple individual parts 53a are connected and the Y end 22b of the piezoelectric actuator 22. The closer to the ends 22a and 22b of the piezoelectric actuator 22, the more likely warping occurs and the more likely localized force is applied during bonding. Therefore, the actuator element 90 located near the one end 22a of the piezoelectric actuator 22, where the minimum distance L1 is smaller, is more likely to experience an increase in capacitance due to tensile stress during bonding, and therefore it is particularly important to suppress the capacitance. Therefore, by reducing the width W1 of the branch 533 corresponding to the actuator element 90, the increase in capacitance due to bleeding A can be suppressed, and the effect of suppressing the difference in capacitance between the actuator elements 90 can be more effectively achieved.

[0080] The length P1 of the individual part (first individual part) located on one side in the Y direction (left side in FIG. 9) is different from the length P2 of the individual part (second individual part) located on the other side in the Y direction (right side in FIG. 9). When the low potential electrode 53 is formed by screen printing from the other side to the one side in the Y direction during the manufacture of the piezoelectric actuator 22, the length P1 is made longer than the length P2. This makes it possible to suppress an increase in the capacitance of the actuator element 90 even if bleeding A occurs in the branch part 533.

[0081] The width of the branch portion 533 located at one end in the Y direction (the left end in FIG. 9) is constant throughout the X direction, thereby suppressing the bleeding A and the increase in capacitance throughout the entire X direction.

[0082] The width W1 of the branch 533 located at one end in the Y direction (the left end in FIG. 9) is 1 / 2 to 2 / 3 of the width W2 of the branch 533 located at a position other than the end in the Y direction (the center other than the left and right ends in FIG. 9). This makes it possible to reliably suppress an increase in capacitance due to bleeding A even when the thickness of the branch 533 is large.

[0083] Second Embodiment Next, a piezoelectric actuator 222 according to a second embodiment of the present invention will be described with reference to FIG.

[0084] In the first embodiment, the width of each branch portion 533 is constant along the second direction, whereas in the second embodiment, the width of each branch portion 533 gradually decreases from the base end 533a to the tip 533b. In each branch portion 533, the width of the tip 533b is smaller than the width of the base end 533a. Specifically, in a branch portion 533 located at one end in the Y direction (the left end in FIG. 12), the width Wb of the tip 533b is smaller than the width Wa of the base end 533a. In a branch portion 533 located other than the ends in the Y direction (the center other than the left and right ends in FIG. 12), the width Wb' of the tip 533b is smaller than the width Wa' of the base end 533a. In a branch portion 533 located at the other end in the Y direction (the right end in FIG. 12), the width Wb" of the tip 533b is smaller than the width Wa" of the base end 533a.

[0085] This configuration takes advantage of the fact that the high-potential electrode 52 has a trunk (band) 521 (see FIG. 8 ) extending in the Y direction, which tends to cause warping near one end 222c of the piezoelectric actuator 222 in the X direction. The trunk 521 of the high-potential electrode 52 is disposed in the X direction between the tips 533b of the branches 533 of the low-potential electrode 53 and one end 222c of the piezoelectric actuator 22 in the X direction (the end 222c whose distance from the tip 533b of each branch 533 is shorter than the distance from the base end 533a of each branch 533). The tips 533b of the branches 533 are close to the one end 222c, where the influence of warping is significant (i.e., the capacitance is likely to increase due to tensile stress during bonding). Therefore, it is particularly important to suppress the capacitance. Therefore, by narrowing the width of the tips 533b, the increase in capacitance due to the bleed A can be suppressed, and the effect of suppressing the difference in capacitance between the actuator elements 90 can be more effectively achieved.

[0086] The second embodiment is similar to the first embodiment, except that the width of each branch 533 gradually decreases from the base end 533a toward the tip 533b. For example, the width of the branch 533 located at one end in the Y direction (the left end in FIG. 12) is smaller than the width of the branch 533 located other than the end in the Y direction (the center, other than the left and right ends in FIG. 12). When the low-potential electrode 53 is formed by screen printing along the Y direction during manufacturing of the piezoelectric actuator 222, the width of the branch 533 located at one end in the Y direction (the left end in FIG. 12) of the low-potential electrode 53 is made smaller than the width W2 of the branch 533 located other than the end in the Y direction (the center, other than the left and right ends in FIG. 12). The screen printing is performed from the other end in the Y direction (the right side in FIG. 12) to one end in the Y direction (the left side in FIG. 12).

[0087] <Modification> Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various design modifications are possible within the scope of the claims.

[0088] In the second embodiment (see FIG. 12), the width of each branch 533 gradually decreases from the base end 533a toward the tip 533b, but this is not limiting. For example, the portion near the tip 533b and the other portion may each have a constant width in the X direction, and the width of the portion near the tip 533b may be smaller than the width of the other portion.

[0089] In the above-described embodiment, in both the high-potential electrode 52 and the low-potential electrode 53, the width of the branch portions 523, 533 located at one end in the Y direction (the left end in FIGS. 8 and 9) is smaller than the width of the branch portions 523, 533 located other than the ends in the Y direction (the center other than the left and right ends in FIGS. 8 and 9), but this is not limited thereto, and only the branch portions 523 of the high-potential electrode 52 or only the branch portions 533 of the low-potential electrode 53 may have this configuration. For example, in a configuration in which the low-potential electrode 53 has the trunk 531, the branch portions 533, and the individual portions 53a, while the high-potential electrode 52 has the individual portions 52a but does not have the trunk 521 or the branch portions 523, only the branch portions 533 of the low-potential electrode 53 may have the above-described configuration.

[0090] In the above-described embodiment, for example, in the low potential electrode 53, only the width of the branch portion 533 located at one end in the Y direction (the left end in FIGS. 9 and 12) is made small, but the width of each of the branch portions 533 located at both ends in the Y direction (the left and right ends in FIGS. 9 and 12) may be made smaller than the width of the branch portion 533 located other than the ends in the Y direction (the center other than the left and right ends in FIGS. 9 and 12). The same applies to the high potential electrode 52 (see FIG. 8).

[0091] In the above-described embodiment, the screen printing direction is from the other side in the Y direction (the right side in Figures 8, 9, and 12) to one side (the left side in Figures 8, 9, and 12), but it may also be from one side in the Y direction (the left side in Figures 8, 9, and 12) to the other side (the right side in Figures 8, 9, and 12). In this case, the length P2 of the individual part (second individual part) located on the other side in the Y direction (the right side in Figure 9) is made longer than the length P1 of the individual part (first individual part) located on one side in the Y direction (the left side in Figure 9).

[0092] In the above-described embodiment, the thickness of the low potential electrode 53 is greater than the thickness of the high potential electrode 52, but this is not limited to this, and for example, the thickness of the low potential electrode 53 may be the same as the thickness of the high potential electrode 52.

[0093] The first potential is not limited to being a high potential and the second potential is a low potential, and the opposite may be true (i.e., the first potential is a low potential and the second potential is a high potential). In this case, the high potential electrode 52 may be located in the bottom layer, and the low potential electrode 53 may be located in the middle layer.

[0094] The number of piezoelectric layers constituting the piezoelectric actuator is three in the above-described embodiment, but may be four or more. For example, in the above-described embodiment (see FIG. 4, etc.), another piezoelectric layer may be disposed between the piezoelectric layer 43 of the piezoelectric actuator 22 and the plate 31 of the flow path unit 21.

[0095] The present invention is not limited to printers, but can also be applied to facsimiles, copiers, multifunction peripherals, etc. The present invention can also be applied to liquid ejection devices used for purposes other than image recording (for example, liquid ejection devices that eject conductive liquid onto a substrate to form a conductive pattern). Furthermore, the piezoelectric actuator according to the present invention can be applied to any device other than a liquid ejection device. [Explanation of symbols]

[0096] 22;222 Piezoelectric Actuator 41 Piezoelectric layer (first piezoelectric layer) 42 Piezoelectric layer (second piezoelectric layer) 43 Piezoelectric layer (third piezoelectric layer) 51 Drive electrode 52 High potential electrode (first potential electrode) 52a Individual section 521 Executive (Obi) 523 Branch 53 Low potential electrode (second potential electrode) 53a Individual section 531 Executive 533 Branch 533a proximal end 533b Tip 71 Electrode layer (first electrode layer) 72 Electrode layer (second electrode layer) 73 Electrode layer (3rd electrode layer) 90 Actuator section

Claims

1. a second piezoelectric layer stacked on the first piezoelectric layer in a first direction along a thickness direction of the first piezoelectric layer; a third piezoelectric layer stacked on the first piezoelectric layer and the second piezoelectric layer in the first direction, sandwiching the second piezoelectric layer between the first piezoelectric layer and the second piezoelectric layer; a first electrode layer disposed on a surface of the first piezoelectric layer opposite to the second piezoelectric layer in the first direction; a second electrode layer disposed between the first piezoelectric layer and the second piezoelectric layer in the first direction; and a third electrode layer disposed between the second piezoelectric layer and the third piezoelectric layer in the first direction, the first electrode layer includes a plurality of drive electrodes to each of which a first potential or a second potential different from the first potential is selectively applied; the second electrode layer includes a first potential electrode held at the first potential; the third electrode layer includes a second potential electrode held at the second potential; at least one of the first potential electrode and the second potential electrode includes a plurality of individual parts each having a portion overlapping with each of the plurality of drive electrodes in the first direction, a plurality of branch parts extending in a second direction perpendicular to the first direction and connecting the plurality of individual parts, and a trunk part extending in a third direction perpendicular to the first direction and the second direction and connecting the plurality of branch parts, a branch portion located at one end in the third direction among the plurality of branch portions has a width smaller than that of a branch portion located at a position other than the end in the third direction and that of a branch portion located at the other end in the third direction.

2. a second piezoelectric layer stacked on the first piezoelectric layer in a first direction along a thickness direction of the first piezoelectric layer; a third piezoelectric layer stacked on the first piezoelectric layer and the second piezoelectric layer in the first direction, sandwiching the second piezoelectric layer between the first piezoelectric layer and the second piezoelectric layer; a first electrode layer disposed on a surface of the first piezoelectric layer opposite to the second piezoelectric layer in the first direction; a second electrode layer disposed between the first piezoelectric layer and the second piezoelectric layer in the first direction; and a third electrode layer disposed between the second piezoelectric layer and the third piezoelectric layer in the first direction, the first electrode layer includes a plurality of drive electrodes to each of which a first potential or a second potential different from the first potential is selectively applied; the second electrode layer includes a first potential electrode held at the first potential; the third electrode layer includes a second potential electrode held at the second potential; at least one of the first potential electrode and the second potential electrode includes a plurality of individual parts each having a portion overlapping with each of the plurality of drive electrodes in the first direction, a plurality of branch parts extending in a second direction perpendicular to the first direction and connecting the plurality of individual parts, and a trunk part extending in a third direction perpendicular to the first direction and the second direction and connecting the plurality of branch parts, Among the plurality of branch portions, a branch portion located at one end in the third direction has a width smaller than that of branch portions located other than the end in the third direction, each of the first potential electrode and the second potential electrode includes the plurality of individual portions, the plurality of branch portions, and the trunk portion; the plurality of branch portions of one of the first potential electrode and the second potential electrode have a thickness greater than the plurality of branch portions of the other of the first potential electrode and the second potential electrode; a piezoelectric actuator, characterized in that, in at least one of the first potential electrode and the second potential electrode, among the plurality of branch portions, a branch portion located at one end in the third direction has a smaller width than branch portions located other than the end in the third direction.

3. a second piezoelectric layer stacked on the first piezoelectric layer in a first direction along a thickness direction of the first piezoelectric layer; a third piezoelectric layer stacked on the first piezoelectric layer and the second piezoelectric layer in the first direction, sandwiching the second piezoelectric layer between the first piezoelectric layer and the second piezoelectric layer; a first electrode layer disposed on a surface of the first piezoelectric layer opposite to the second piezoelectric layer in the first direction; a second electrode layer disposed between the first piezoelectric layer and the second piezoelectric layer in the first direction; and a third electrode layer disposed between the second piezoelectric layer and the third piezoelectric layer in the first direction, the first electrode layer includes a plurality of drive electrodes to each of which a first potential or a second potential different from the first potential is selectively applied; the second electrode layer includes a first potential electrode held at the first potential; the third electrode layer includes a second potential electrode held at the second potential; at least one of the first potential electrode and the second potential electrode includes a plurality of individual parts each having a portion overlapping with each of the plurality of drive electrodes in the first direction, a plurality of branch parts extending in a second direction perpendicular to the first direction and connecting the plurality of individual parts, and a trunk part extending in a third direction perpendicular to the first direction and the second direction and connecting the plurality of branch parts, Among the plurality of branch portions, a branch portion located at one end in the third direction has a width smaller than that of branch portions located other than the end in the third direction, each of the first potential electrode and the second potential electrode includes the plurality of individual portions, the plurality of branch portions, and the trunk portion; a branch portion located at one end in the third direction among the plurality of branch portions of each of the first potential electrode and the second potential electrode has a width smaller than that of the branch portions located at any other end in the third direction.

4. a second piezoelectric layer stacked on the first piezoelectric layer in a first direction along a thickness direction of the first piezoelectric layer; a third piezoelectric layer stacked on the first piezoelectric layer and the second piezoelectric layer in the first direction, sandwiching the second piezoelectric layer between the first piezoelectric layer and the second piezoelectric layer; a first electrode layer disposed on a surface of the first piezoelectric layer opposite to the second piezoelectric layer in the first direction; a second electrode layer disposed between the first piezoelectric layer and the second piezoelectric layer in the first direction; and a third electrode layer disposed between the second piezoelectric layer and the third piezoelectric layer in the first direction, the first electrode layer includes a plurality of drive electrodes to each of which a first potential or a second potential different from the first potential is selectively applied; the second electrode layer includes a first potential electrode held at the first potential; the third electrode layer includes a second potential electrode held at the second potential; at least one of the first potential electrode and the second potential electrode includes a plurality of individual parts each having a portion overlapping with each of the plurality of drive electrodes in the first direction, a plurality of branch parts extending in a second direction perpendicular to the first direction and connecting the plurality of individual parts, and a trunk part extending in a third direction perpendicular to the first direction and the second direction and connecting the plurality of branch parts, Among the plurality of branch portions, a branch portion located at one end in the third direction has a width smaller than that of branch portions located other than the end in the third direction, The plurality of individual parts connected to the branch part located at one end in the third direction are a first individual part located on one side in the third direction relative to the branch part; a second individual part located on the other side of the branch part in the third direction, A piezoelectric actuator, wherein the length of the first individual portion in the third direction and the length of the second individual portion in the third direction are different from each other.

5. a second piezoelectric layer stacked on the first piezoelectric layer in a first direction along a thickness direction of the first piezoelectric layer; a third piezoelectric layer stacked on the first piezoelectric layer and the second piezoelectric layer in the first direction, sandwiching the second piezoelectric layer between the first piezoelectric layer and the second piezoelectric layer; a first electrode layer disposed on a surface of the first piezoelectric layer opposite to the second piezoelectric layer in the first direction; a second electrode layer disposed between the first piezoelectric layer and the second piezoelectric layer in the first direction; and a third electrode layer disposed between the second piezoelectric layer and the third piezoelectric layer in the first direction, the first electrode layer includes a plurality of drive electrodes to each of which a first potential or a second potential different from the first potential is selectively applied; the second electrode layer includes a first potential electrode held at the first potential; the third electrode layer includes a second potential electrode held at the second potential; at least one of the first potential electrode and the second potential electrode includes a plurality of individual parts each having a portion overlapping with each of the plurality of drive electrodes in the first direction, a plurality of branch parts extending in a second direction perpendicular to the first direction and connecting the plurality of individual parts, and a trunk part extending in a third direction perpendicular to the first direction and the second direction and connecting the plurality of branch parts, Among the plurality of branch portions, a branch portion located at one end in the third direction has a width smaller than that of branch portions located other than the end in the third direction, the other of the first potential electrode and the second potential electrode includes a band portion extending in the third direction, the band portion being arranged in the second direction between tips of the plurality of branch portions of one of the first potential electrode and the second potential electrode and one end of the piezoelectric actuator in the second direction, the one end being a distance from the tips of the plurality of branch portions that is shorter than a distance from base ends of the plurality of branch portions; A piezoelectric actuator, wherein in one of the first potential electrode and the second potential electrode, the plurality of branch portions each have a width at the tip end that is smaller than the width at the base end.

6. each of the first potential electrode and the second potential electrode includes the plurality of individual portions, the plurality of branch portions, and the trunk portion; Among the plurality of branch portions of one of the first potential electrode and the second potential electrode, a branch portion located other than an end portion in the third direction has a larger width than among the plurality of branch portions of the other of the first potential electrode and the second potential electrode, a branch portion located other than an end portion in the third direction, 6. The piezoelectric actuator according to claim 1, wherein, in at least one of the first potential electrode and the second potential electrode, among the plurality of branch portions, a branch portion located at one end in the third direction has a smaller width than branch portions located other than the end in the third direction.

7. A piezoelectric actuator according to any one of claims 1 to 6, characterized in that the minimum distance in the third direction between a portion of the plurality of branch portions located at one end in the third direction, where the plurality of individual parts are connected, and one end of the piezoelectric actuator in the third direction, is smaller than the minimum distance in the third direction between a portion of the plurality of branch portions located at the other end in the third direction, where the plurality of individual parts are connected, and the other end of the piezoelectric actuator in the third direction.

8. 8. The piezoelectric actuator according to claim 1, wherein the width of the branch portion located at one end in the third direction is constant throughout the second direction.

9. 9. The piezoelectric actuator according to claim 1, wherein a width of the branch portion located at one end in the third direction is 1 / 2 to 2 / 3 of a width of the branch portion located at a position other than the end in the third direction.

10. A method for manufacturing a piezoelectric actuator including: a first piezoelectric layer; a second piezoelectric layer stacked on the first piezoelectric layer in a first direction along a thickness direction of the first piezoelectric layer; and a third piezoelectric layer stacked on the first piezoelectric layer and the second piezoelectric layer in the first direction, sandwiching the second piezoelectric layer between the first piezoelectric layer and the third piezoelectric layer, forming a first electrode layer on a surface of the first piezoelectric layer, the first electrode layer including a plurality of drive electrodes to each of which a first potential or a second potential different from the first potential is selectively applied; forming a second electrode layer on a surface of the second piezoelectric layer, the second electrode layer including a first potential electrode held at the first potential; forming a third electrode layer on a surface of the third piezoelectric layer, the third electrode layer including a second potential electrode held at the second potential; the first piezoelectric layer, the second piezoelectric layer, and the third piezoelectric layer are stacked in the first direction so that the first electrode layer is disposed on a surface of the first piezoelectric layer opposite to the second piezoelectric layer in the first direction, the second electrode layer is disposed between the first piezoelectric layer and the second piezoelectric layer in the first direction, and the third electrode layer is disposed between the second piezoelectric layer and the third piezoelectric layer in the first direction; at least one of the first potential electrode and the second potential electrode is formed to include a plurality of individual parts, a plurality of branch parts extending in a second direction perpendicular to the first direction and connecting the plurality of individual parts, and a trunk part extending in a third direction perpendicular to the first direction and the second direction and connecting the plurality of branch parts, when forming the second electrode layer or the third electrode layer; when the first piezoelectric layer, the second piezoelectric layer, and the third piezoelectric layer are stacked in the first direction, the first piezoelectric layer, the second piezoelectric layer, and the third piezoelectric layer are stacked in the first direction such that the plurality of individual portions have portions that overlap with the plurality of drive electrodes, respectively, in the first direction; Furthermore, when forming the second electrode layer or the third electrode layer, at least one of the first potential electrode and the second potential electrode is formed by screen printing along the third direction so that, of the plurality of branch portions, a branch portion located at one end in the third direction has a smaller width than branches located other than the ends in the third direction and the branch portion located at the other end in the third direction.

11. A method for manufacturing a piezoelectric actuator including: a first piezoelectric layer; a second piezoelectric layer stacked on the first piezoelectric layer in a first direction along a thickness direction of the first piezoelectric layer; and a third piezoelectric layer stacked on the first piezoelectric layer and the second piezoelectric layer in the first direction, sandwiching the second piezoelectric layer between the first piezoelectric layer and the third piezoelectric layer, forming a first electrode layer on a surface of the first piezoelectric layer, the first electrode layer including a plurality of drive electrodes to each of which a first potential or a second potential different from the first potential is selectively applied; forming a second electrode layer on a surface of the second piezoelectric layer, the second electrode layer including a first potential electrode held at the first potential; forming a third electrode layer on a surface of the third piezoelectric layer, the third electrode layer including a second potential electrode held at the second potential; the first piezoelectric layer, the second piezoelectric layer, and the third piezoelectric layer are stacked in the first direction so that the first electrode layer is disposed on a surface of the first piezoelectric layer opposite to the second piezoelectric layer in the first direction, the second electrode layer is disposed between the first piezoelectric layer and the second piezoelectric layer in the first direction, and the third electrode layer is disposed between the second piezoelectric layer and the third piezoelectric layer in the first direction; at least one of the first potential electrode and the second potential electrode is formed to include a plurality of individual parts, a plurality of branch parts extending in a second direction perpendicular to the first direction and connecting the plurality of individual parts, and a trunk part extending in a third direction perpendicular to the first direction and the second direction and connecting the plurality of branch parts, when forming the second electrode layer or the third electrode layer; when the first piezoelectric layer, the second piezoelectric layer, and the third piezoelectric layer are stacked in the first direction, the first piezoelectric layer, the second piezoelectric layer, and the third piezoelectric layer are stacked in the first direction such that the plurality of individual portions have portions that overlap with the plurality of drive electrodes, respectively, in the first direction; further, when forming the second electrode layer or when forming the third electrode layer, at least one of the first potential electrode and the second potential electrode is formed by screen printing along the third direction so that, among the plurality of branch portions, a branch portion located at one end in the third direction has a smaller width than a branch portion located other than the end in the third direction; When forming the second electrode layer or when forming the third electrode layer, screen printing is performed from the other side of the third direction to the one side of the third direction; A method for manufacturing a piezoelectric actuator, characterized in that the multiple individual parts connected to a branch part located at one end in the third direction include a first individual part located at one side in the third direction relative to the branch part, and a second individual part located at the other side in the third direction relative to the branch part, and at least one of the first potential electrode and the second potential electrode is formed so that the length in the third direction of the first individual part is longer than the length in the third direction of the second individual part.

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