JP2011134933A - Method of manufacturing piezoelectric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a piezoelectric actuator putting in order the directions of forces acting on an active part to reduce a variation in piezoelectric characteristics. <P>SOLUTION: Two green sheets 48 of almost the same thickness are laminated with a common electrode 43 interposed therebetween (the laminating step). The two green sheets 48 and the common electrode 43 are integrally sintered at a predetermined sintering temperature (the sintering step). Then, warping directions of two piezoelectric sheets 50 are confirmed to determine that the active part R1 is formed on one of the piezoelectric sheets 50 on the depressed side of a laminate of the two piezoelectric sheets 50 (the active part position-determining step). Then, a plurality of individual electrodes 42 are formed on a part of a surface of a piezoelectric layer 41 on which the active part R1 is to be formed and a voltage is applied between the individual electrodes 42 and the common electrode 43 to polarize a part of the piezoelectric layer 41 between these electrodes in a direction parallel to its thickness direction to form the active part R1 (the active part-forming step). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a piezoelectric actuator.

  Conventionally, two piezoelectric layers are laminated, electrodes are disposed on the surfaces of the two piezoelectric layers and one of the piezoelectric layers, respectively, and a voltage applied to the two electrodes on the piezoelectric layer sandwiched between the two electrodes. A piezoelectric actuator having an active part to which an electric field is applied is known. For example, in the piezoelectric actuator for an ink jet head described in Patent Document 1, two piezoelectric layers made of piezoelectric ceramics are laminated, and one piezoelectric layer is a piezoelectric layer having an active part subjected to polarization treatment. The other piezoelectric layer is an inactive piezoelectric layer that functions as a diaphragm. These two piezoelectric layers have the same thickness. An internal electrode is disposed between the two piezoelectric layers, and a surface electrode is disposed on the surface of the piezoelectric layer having the active portion. This piezoelectric actuator is manufactured by laminating two green sheets of the same thickness with an internal electrode sandwiched between them and firing them together, and then forming a surface electrode on the surface of one of the piezoelectric layers. And the piezoelectric actuator manufactured in this way is joined to the flow path member of an inkjet head.

Japanese Patent Laying-Open No. 2007-97280 (FIG. 1)

  Here, in the piezoelectric actuator described in Patent Document 1, the two piezoelectric layers are designed to have the same thickness. However, in actuality, for example, there is a thickness variation in the green sheet before firing. There is a slight thickness variation. Then, in the state before forming the surface electrode, the electrode sandwiched between the two piezoelectric layers having variations in thickness deviates from the neutral plane in the thickness direction of the two piezoelectric layers. Thus, when two piezoelectric layers in a state where the internal electrodes are displaced from the neutral plane are integrally fired together with the internal electrodes, the electrodes and the piezoelectric layers have different linear expansion coefficients due to differences in materials. The two piezoelectric layers warp due to temperature changes when they are naturally cooled to room temperature after firing at a high temperature. Then, when the two warped piezoelectric layers are bonded to a substrate such as a flow path member, the warpage of the two piezoelectric layers is corrected, whereby the piezoelectric on the concave side in the laminate of the two piezoelectric layers is corrected. A tensile force acts on the layer, and a compressive force acts on the convex piezoelectric layer.

  In this way, if the thickness of the two piezoelectric layers with the electrode sandwiched between them varies, the warping direction differs for each piezoelectric actuator, and the warping direction generated in the piezoelectric layer forming the active portion differs. End up. If the two piezoelectric layers are pressed against the substrate and joined while the warp directions occurring in the piezoelectric layer forming the active portion are different, the direction of the force acting on the active portion is different, and a plurality of When a piezoelectric actuator is created, the piezoelectric characteristics vary among a plurality of piezoelectric actuators.

  Accordingly, an object of the present invention is to provide a method of manufacturing a piezoelectric actuator that aligns the direction of the force acting on the active portion and reduces variations in piezoelectric characteristics.

  The method for manufacturing a piezoelectric actuator of the present invention includes two piezoelectric layers stacked in a thickness direction, a first electrode disposed between the two piezoelectric layers, and one of the two piezoelectric layers. A second electrode disposed on a surface of the layer opposite to the first electrode, and an active portion to which an electric field is applied by a voltage applied to the first electrode and the second electrode, A method of manufacturing a piezoelectric actuator to be joined, wherein the two piezoelectric layers having substantially the same thickness are stacked with the first electrode interposed therebetween, the two piezoelectric layers stacked, A firing step of firing the first electrode integrally and a warping direction of the two piezoelectric layers fired integrally are confirmed, and any one of the two piezoelectric layers is selected according to the warping direction. An active part position determining step for determining whether to form the active part in An active portion forming step of forming the active portion in the piezoelectric layer was determined in the active section position determining step, and a.

  According to the method for manufacturing a piezoelectric actuator of the present invention, in the active portion position determining step, the piezoelectric layer that forms the active portion is determined according to the warping direction of the two piezoelectric layers, and the active portion is formed on the piezoelectric layer. Yes. As a result, the direction of the force acting on the active portion is always the same by correcting the warp of the two piezoelectric layers during bonding to the substrate. Therefore, the direction of the force acting on the active portion can be aligned, and variations in piezoelectric characteristics can be reduced.

  In the active portion position determining step, it is preferable that the active portion is determined to be formed in the piezoelectric layer on the side of the two piezoelectric layers that is concave in the thickness direction. According to this, when an active part is formed in a piezoelectric layer that is concave in the thickness direction of the two piezoelectric layers, a tensile force acts on the active part when the two piezoelectric layers are bonded to the substrate. Therefore, by reducing the compressive force that acts on the piezoelectric layer during cooling after firing, it is possible to suppress the deterioration of the piezoelectric characteristics.

  Furthermore, in the active part forming step, the second electrode is formed on the surface of the piezoelectric layer that is determined to form the active part on the side opposite to the first electrode, and the first electrode and the second electrode are polarized. Preferably, a voltage is applied to polarize the portion of the piezoelectric layer between both electrodes to form the active portion. According to this, when the position of the active part is determined by determining the position where the second electrode is formed, the active part is formed according to the warping directions of the two piezoelectric layers confirmed in the active part position determining step. The piezoelectric layer can be determined.

  In addition, the method further includes a conductive layer forming step of forming a conductive layer on a surface opposite to the first electrode of the two piezoelectric layers before the firing step, and in the active portion forming step, 2 Of the two conductive layers, the conductive layer on the side opposite to the first electrode of the piezoelectric layer determined to form the active portion is used as the second electrode, and a polarization voltage is applied to the first electrode and the second electrode. Then, the portion of the piezoelectric layer between both electrodes may be polarized to form the active portion. According to this, when the position of the active portion is determined by forming the conductive layer on both surfaces before the firing step and determining which conductive layer is used as the second electrode to apply the polarization voltage, The piezoelectric layer that forms the active portion can be determined according to the warping directions of the two piezoelectric layers confirmed in the position determining step.

  Since the active portion is formed in any one of the piezoelectric layers corresponding to the warping directions of the two piezoelectric layers, the direction of the force acting on the active portion at the time of bonding with the substrate is always the same direction. Therefore, when the direction of the force acting on the active portion is aligned and a plurality of piezoelectric actuators are created, variations in piezoelectric characteristics among the plurality of piezoelectric actuators can be reduced.

1 is a schematic plan view of an ink jet printer according to a first embodiment. It is a top view of the inkjet head of FIG. FIG. 3 is a partially enlarged view of FIG. 2. FIG. 4 is a sectional view taken along line IV-IV in FIG. 3. It is a figure which illustrates schematically the manufacturing process of the inkjet head of FIG. FIG. 5 is a view corresponding to FIG. 4 according to a second embodiment. FIG. 6 is a diagram corresponding to FIG. 5 according to a second embodiment. It is a longitudinal cross-sectional view of the piezoelectric actuator in a modification.

<First Embodiment>
Next, a first embodiment of the present invention will be described. This embodiment is an example in which the present invention is applied to an inkjet printer having an inkjet head that ejects ink onto a recording sheet.

  First, a schematic configuration of the inkjet printer 1 of the present embodiment will be described. FIG. 1 is a schematic plan view of the ink jet printer according to the first embodiment. As shown in FIG. 1, a printer 1 includes a carriage 2 configured to be reciprocally movable along a predetermined scanning direction (left-right direction in FIG. 1), an inkjet head 3 mounted on the carriage 2, and a recording sheet. A transport mechanism 4 for transporting P in a transport direction orthogonal to the scanning direction is provided.

  The carriage 2 is configured to be able to reciprocate along two guide shafts 17 extending in parallel with the scanning direction (left-right direction in FIG. 1). An endless belt 18 is connected to the carriage 2. When the endless belt 18 is driven to travel by the carriage drive motor 19, the carriage 2 moves in the scanning direction as the endless belt 18 travels. It has become. The printer 1 is provided with a linear encoder 10 having a large number of light transmitting portions (slits) arranged at intervals in the scanning direction. On the other hand, the carriage 2 is provided with a transmissive photosensor 11 having a light emitting element and a light receiving element. The printer 1 can recognize the current position in the scanning direction of the carriage 2 from the count value (number of detections) of the light transmitting portion of the linear encoder 10 detected by the photosensor 11 while the carriage 2 is moving. .

  An ink jet head 3 is mounted on the carriage 2. The inkjet head 3 includes a plurality of nozzles 30 (see FIG. 2) on the lower surface (the surface on the opposite side of the paper in FIG. 1). The ink jet head 3 is configured to eject ink supplied from an ink cartridge (not shown) from a plurality of nozzles 30 onto a recording paper P that is transported downward (conveying direction) in FIG. ing.

  The transport mechanism 4 includes a paper feed roller 12 disposed on the upstream side in the transport direction with respect to the ink jet head 3 and a paper discharge roller 13 disposed on the downstream side in the transport direction with respect to the ink jet head 3. The paper feed roller 12 and the paper discharge roller 13 are rotationally driven by a paper feed motor 14 and a paper discharge motor 15, respectively. The transport mechanism 4 transports the recording paper P from above in FIG. 1 to the ink jet head 3 by the paper feed roller 12, and records the images and characters recorded by the ink jet head 3 by the paper discharge roller 13. The paper P is discharged downward in FIG.

  Next, the inkjet head 3 will be described. FIG. 2 is a plan view of the inkjet head. FIG. 3 is a partially enlarged view of FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. As shown in FIGS. 2 to 4, the inkjet head 3 includes a flow path unit 6 in which an ink flow path including a nozzle 30 and a pressure chamber 24 is formed, and a piezoelectric actuator 7 that applies pressure to the ink in the pressure chamber 24. And have.

  First, the flow path unit 6 will be described. As shown in FIG. 4, the flow path unit 6 includes a cavity plate 20, a base plate 21, a manifold plate 22, and a nozzle plate 23, and these four plates 20 to 23 are joined in a stacked state. Among these, the cavity plate 20, the base plate 21, and the manifold plate 22 are each substantially rectangular plates in plan view made of a metal material such as stainless steel. Therefore, ink flow paths such as a manifold 27 and a pressure chamber 24 described later can be easily formed on these three plates 20 to 22 by etching. The nozzle plate 23 is made of, for example, a polymer synthetic resin material such as polyimide, and is bonded to the lower surface of the manifold plate 22 with an adhesive.

  As shown in FIGS. 2 to 4, among the four plates 20 to 23, the uppermost cavity plate 20 has holes in which a plurality of pressure chambers 24 arranged along a plane penetrate the plate 20. It is formed by. The plurality of pressure chambers 24 are arranged in two rows in a staggered manner in the transport direction (the vertical direction in FIG. 2). Further, as shown in FIG. 4, the plurality of pressure chambers 24 are respectively covered with a diaphragm 40 and a base plate 21 described later from above and below. Furthermore, each pressure chamber 24 is formed in a substantially elliptical shape that is long in the scanning direction (left-right direction in FIG. 2) in plan view.

  As shown in FIGS. 3 and 4, the base plate 21, at positions overlapping the longitudinal ends of the pressure chambers 24 in a plan view, communicating holes 25 and 26 are formed. The manifold plate 22 is formed with two manifolds 27 extending in the transport direction so as to overlap with the communication hole 25 side portions of the pressure chambers 24 arranged in two rows in a plan view. These two manifolds 27 communicate with an ink supply port 28 (see FIG. 2) formed in a vibration plate 40 described later, and ink is supplied from an ink tank (not shown) to the manifold 27 via the ink supply port 28. The Further, a plurality of communication holes 29 that are continuous with the plurality of communication holes 26 are formed at positions where the manifold plate 22 overlaps the ends of the plurality of pressure chambers 24 opposite to the manifolds 27 in plan view.

  Further, a plurality of nozzles 30 are formed at positions where the nozzle plate 23 overlaps the plurality of communication holes 29 in plan view. As shown in FIG. 2, the plurality of nozzles 30 are disposed so as to overlap with the end portions of the plurality of pressure chambers 24 arranged in two rows along the transport direction on the side opposite to the manifold 27.

  As shown in FIG. 4, the manifold 27 communicates with the pressure chamber 24 through the communication hole 25, and the pressure chamber 24 communicates with the nozzle 30 through the communication holes 26 and 29. As described above, a plurality of individual ink flow paths 31 from the manifold 27 to the nozzles 30 through the pressure chambers 24 are formed in the flow path unit 6.

  Next, the piezoelectric actuator 7 will be described. As shown in FIGS. 2 to 4, the piezoelectric actuator 7 includes a vibration plate 40 disposed on the upper surface of the flow path unit 6 (cavity plate 20) so as to cover the plurality of pressure chambers 24, and an upper surface of the vibration plate 40. In addition, the piezoelectric layer 41 disposed to face the plurality of pressure chambers 24, the common electrode 43 disposed between the diaphragm 40 and the piezoelectric layer 41, and the plurality of individual disposed on the upper surface of the piezoelectric layer 41. Electrode 42.

  The vibration plate 40 and the piezoelectric layer 41 are both made of a piezoelectric material mainly composed of lead zirconate titanate (PZT), which is a solid solution of lead titanate and lead zirconate and is a ferroelectric material. It has a sheet shape having a shape and substantially the same thickness. The diaphragm 40 and the piezoelectric layer 41 are stacked on each other and are continuously disposed across the plurality of pressure chambers 24 so as to cover the plurality of pressure chambers 24 on the upper surface of the cavity plate 20. , Bonded to the cavity plate 20. The piezoelectric layer 41 is polarized in the thickness direction at least in a region facing the pressure chamber 24.

  The common electrode 43 is continuously disposed across the plurality of pressure chambers 24 in almost the entire region between the diaphragm 40 and the piezoelectric layer 41. The common electrode 43 is connected to the ground wiring of a head driver (not shown) that drives the piezoelectric actuator 7 and is always held at the ground potential.

  The plurality of individual electrodes 42 are respectively disposed in regions facing the plurality of pressure chambers 24 on the upper surface of the piezoelectric layer 41. Each individual electrode 42 has a substantially oval planar shape that is slightly smaller than the pressure chamber 24, and faces the central portion of the pressure chamber 24. Further, a plurality of contact portions 45 are drawn from the end portions of the plurality of individual electrodes 42 along the longitudinal direction of the individual electrodes 42. The plurality of contact portions 45 are electrically connected to a head driver (not shown) through a flexible printed circuit (FPC) (not shown). As a result, the head driver can selectively apply one of the two types of potentials of the predetermined drive potential and the ground potential to the plurality of individual electrodes 42.

  Of these two electrodes, the common electrode 43 is made of an alloy of silver and palladium (Ag—Pd) that is difficult to melt at a high temperature in the firing step of the manufacturing process of the piezoelectric actuator 7 described later. Further, the individual electrode 42 is made of gold (Au), which is a metal material having a high rust prevention property because it is exposed on the surface of the piezoelectric actuator 7 and is in contact with the outside air, and in addition, a metal material that is difficult to migrate.

  Then, at least a portion of the piezoelectric layer 41 sandwiched between the individual electrode 42 and the common electrode 43 that faces the pressure chamber 24 is polarized in the thickness direction to become an active portion R1.

  Next, the operation of the piezoelectric actuator 7 during ink ejection will be described. When a predetermined drive potential is applied to a certain individual electrode 42 from the head driver, a potential difference is generated in the active portion R1 between the individual electrode 42 to which this drive potential is applied and the common electrode 43 held at the ground potential. And an electric field in the thickness direction acts on the active portion R1. Since the direction of the electric field is parallel to the polarization direction of the active part R1, the active part R1 contracts in a plane direction perpendicular to the thickness direction. Here, since the lower vibration plate 40 of the piezoelectric layer 41 is fixed to the cavity plate 20, the active portion R1 of the piezoelectric layer 41 located on the upper surface of the vibration plate 40 contracts in the plane direction. The portion of the diaphragm 40 that covers the pressure chamber 24 is deformed so as to protrude toward the pressure chamber 24 (unimorph deformation). At this time, since the volume in the pressure chamber 24 decreases, the ink pressure in the pressure chamber 24 rises, and ink is ejected from the nozzle 30 communicating with the pressure chamber 24.

  Next, the manufacturing process of the inkjet head 3 described above will be described. FIG. 5 is a diagram schematically illustrating a manufacturing process of the inkjet head 3, (a) is a stacking process, (b) is a firing process, (c) is an active part position determining process, (D) is an active part formation process, (e) is a bonding process, and (f) is when the inkjet head is completed. In the present embodiment, first, the flow path unit 6 and the piezoelectric actuator 7 are individually manufactured in separate steps, and then the piezoelectric actuator 7 is joined to the upper surface of the flow path unit 6 to manufacture the inkjet head 3. Therefore, in the present embodiment, the manufacturing process of the flow path unit 6 will be briefly described, and the manufacturing process of the piezoelectric actuator 7 and the bonding process of the flow path unit 6 and the piezoelectric actuator 7 will be described in detail.

(Channel unit manufacturing process)
First, among the four plates 20 to 23 constituting the flow path unit 6, ink such as the pressure chamber 24 and the manifold 27 is applied to the three plates of the metal cavity plate 20, the base plate 21, and the manifold plate 22. The holes constituting the flow path are formed by etching. A plurality of nozzles 30 are formed on the nozzle plate 23 made of synthetic resin by laser processing. Then, the four plates 20 to 23 are bonded together with an adhesive in a state where the plates 20 to 23 are stacked on each other, thereby completing the flow path unit 6.

  Alternatively, in a state where the three metal plates 20 to 22 are stacked, the three plates 20 to 23 are metal diffusion bonded by pressing in the plate stacking direction while heating to a high temperature (for example, about 900 ° C.). May be joined together. In this case, the nozzle plate 23 made of synthetic resin is bonded to the laminated body of the three plates 20 to 22 obtained by metal diffusion bonding with an adhesive.

(Piezoelectric actuator manufacturing process)
First, as shown in FIG. 5 (a), a common electrode 43 made of an alloy of silver and palladium is formed on the surface of one green sheet 48 made of a piezoelectric material mainly composed of PZT by printing, and then on the surface. Green sheets 48 having substantially the same thickness are stacked with the common electrode 43 interposed therebetween (stacking step). At this time, the thickness of the two green sheets 48 varies slightly due to manufacturing variations. Therefore, the common electrode 43 sandwiched between the two green sheets 48 is shifted from the neutral plane in the thickness direction to the thin green sheet 48 side.

  Then, as shown in FIG. 5B, the two green sheets 48 and the common electrode 43 are integrally fired at a predetermined firing temperature (firing step). Then, the two green sheets 48 are fired to become two piezoelectric sheets 50. At this time, the silver and palladium alloy that is the common electrode 43 has a larger linear expansion coefficient than the piezoelectric material that is mainly composed of PZT that is the piezoelectric sheet 50. Accordingly, when the common electrode 43 deviates from the neutral plane, the two piezoelectric sheets 50 that are fired are stacked of the two piezoelectric sheets 50 due to a temperature change when naturally firing to room temperature after firing at a high temperature. The side where the common electrode 43 is located is warped so as to be concave. This warping direction depends on the thickness relationship between the two piezoelectric sheets 50. Although the two piezoelectric sheets 50 have the same thickness in design, the thickness is randomly varied due to, for example, thickness variations in the green sheet 48 before firing.

  Therefore, as shown in FIG. 5C, the warping direction of the two piezoelectric sheets 50 is confirmed visually or with a laser displacement meter or the like, and the concave side of the laminate in which the two piezoelectric sheets 50 are laminated. The piezoelectric sheet 50 is the piezoelectric layer 41, the other piezoelectric sheet 50 is the diaphragm 40, and the active portion R1 is located on the piezoelectric layer 41 located on the concave side of the laminate in which the diaphragm 40 and the piezoelectric layer 41 are laminated. Is determined (active part position determining step). Then, as shown in FIG. 5D, a plurality of individual electrodes 42 made of gold (Au) are formed by screen printing on the surface of the portion where the active portion R1 of the piezoelectric layer 41 is to be formed. Thereafter, a voltage is applied between the individual electrode 42 and the common electrode 43 to polarize the portion of the piezoelectric layer 41 between these electrodes in a direction parallel to the thickness direction, thereby forming the active portion R1 (active portion forming step). And the piezoelectric actuator 7 is completed. Thus, since the individual electrode 42 is formed after the firing step, there is no risk of melting due to the firing temperature in the firing step, and gold (Au) having a low melting point suitable for rust prevention and migration prevention is used. Can be used.

  Then, as shown in FIG. 5E, the cavity plate 20 of the flow path unit 6 and the vibration plate 40 of the piezoelectric actuator 7 are opposed to each other with an adhesive interposed therebetween, and are pressed from the piezoelectric layer 41 side to be bonded (bonded). Step), and as shown in FIG. 5F, the inkjet head 3 is completed. At this time, since the active portion R1 is formed on the side of the piezoelectric layer 41 that is a concave portion of the laminate in which the vibration plate 40 and the piezoelectric layer 41 are laminated, a tensile force acts when the warp is corrected and bonded. To do. A compressive force acts on the piezoelectric layer 41 due to the influence of the common electrode 43 having a linear expansion coefficient larger than that of the piezoelectric material during cooling after firing. When a compressive force is applied to the piezoelectric layer 41, deformation when an electric field is applied is restricted, and apparent piezoelectric characteristics are deteriorated. However, when the warp is corrected, the compressive force acting on the active portion R1 can be reduced by applying a tensile force, thereby suppressing the deterioration of the piezoelectric characteristics of the piezoelectric actuator 7. be able to.

  According to the manufacturing method of the piezoelectric actuator 7 in the first embodiment, in the active part position determining step, the piezoelectric layer 41 that forms the active part R1 is determined according to the warp directions of the two piezoelectric sheets 50. As a result, the direction of the force acting on the active portion R1 is always the same by correcting the warp of the vibration plate 40 and the piezoelectric layer 41 at the time of joining to the flow path unit 6. Therefore, the direction of the force acting on the active portion R1 can be aligned, and variations in piezoelectric characteristics can be reduced. In addition, variations in piezoelectric characteristics among the plurality of piezoelectric actuators 7 can be reduced.

Second Embodiment
Next, a preferred second embodiment of the present invention will be described. The second embodiment is the same as the first embodiment except for the configuration of the piezoelectric actuator 7 in the first embodiment. Components similar to those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 6, the piezoelectric actuator 107 includes a vibration plate 140 disposed on the upper surface of the flow path unit 6 (cavity plate 20) so as to cover the plurality of pressure chambers 24, and almost the entire upper surface of the vibration plate 140. Two piezoelectric layers 141 and 144 formed so as to face the plurality of pressure chambers 24, a plurality of conductive layers 146 disposed between the diaphragm 140 and the piezoelectric layer 144, and two sheets A common electrode 143 disposed between the piezoelectric layers 141 and 144 and a plurality of individual electrodes 142 disposed on the upper surface of the piezoelectric layer 141 are provided.

  The diaphragm 140 has the same outer shape as the four plates 20 to 23 constituting the flow path unit 6, and is substantially rectangular in a plan view made of a metal material such as stainless steel, like the three plates 20 to 22. It is a board. The piezoelectric layers 141 and 144 are both made of a piezoelectric material mainly composed of lead zirconate titanate (PZT), which is a solid solution of lead titanate and lead zirconate, and has a rectangular planar shape. It has a sheet shape with substantially the same thickness. The piezoelectric layers 41 and 143 are continuously disposed across the plurality of pressure chambers 24. The piezoelectric layer 141 is polarized in the thickness direction at least in a region facing the pressure chamber 24.

  The common electrode 143 and the plurality of individual electrodes 142 have the same shape and arrangement as the common electrode 43 and the plurality of individual electrodes 42 in the first embodiment, respectively. The plurality of conductive layers 146 have the same thickness and shape as the plurality of individual electrodes 142, and are disposed between the diaphragm 140 and the piezoelectric layer 144 so as to face the plurality of individual electrodes 142, respectively. For these three electrodes, an alloy of silver and palladium (Ag—Pd) that is not easily affected by the shape change due to high heat in the firing step of the manufacturing process of the piezoelectric actuator 107 described later is used. In addition, at least a portion of the piezoelectric layer 141 sandwiched between the individual electrode 142 and the common electrode 143 that faces the pressure chamber 24 is polarized in the thickness direction to become an active portion R101.

  Next, the manufacturing process of the ink jet head having the above-described piezoelectric actuator 107 will be described. 7A and 7B are diagrams schematically illustrating a manufacturing process of the inkjet head 3, wherein FIG. 7A is a stacking process and a conductive layer forming process, FIG. 7B is a firing process, and FIG. 7C is an active portion position. (D) is a joining step, and (e) is when the inkjet head is completed. In this embodiment, first, the flow path unit 6 is manufactured as a single unit, and then the piezoelectric actuator 7 is joined to the upper surface of the flow path unit 6 to manufacture the ink jet head 3. Since the manufacturing process of the flow path unit 6 is the same as that of the first embodiment, the manufacturing process of the piezoelectric actuator 7 and the bonding process of the flow path unit 6 and the piezoelectric actuator 7 will be described in detail. In the first embodiment, the position of the active portion R1 is determined by determining the position where the individual electrode 42 is formed, but in this embodiment, the conductive layer 146 is formed on both surfaces before the firing step. The position of the active portion R101 is determined by determining which conductive layer 146 is used as the individual electrode 142 to apply the polarization voltage.

(Piezoelectric actuator manufacturing process)
First, as shown in FIG. 7A, a common electrode 143 made of an alloy of silver and palladium and a plurality of conductive layers 146 are printed on both surfaces of a single green sheet 148 made of a piezoelectric material mainly composed of PZT. Then, a plurality of conductive layers 146 are formed on the surface of another green sheet 148 having substantially the same thickness by printing. Then, two green sheets 148 are stacked so that the plurality of conductive layers 146 face outward with the common electrode 143 interposed therebetween (stacking step and conductive layer forming step). At this time, as in the first embodiment, the thickness of the two green sheets 148 varies slightly due to manufacturing variations. Therefore, the common electrode 143 sandwiched between the two green sheets 148 is shifted from the neutral plane in the thickness direction to the thin green sheet 148 side.

  Then, as shown in FIG. 7B, a laminate of the two green sheets 148, the common electrode 143, and the plurality of conductive layers 146 is integrally fired at a predetermined firing temperature (firing step). Then, the two green sheets 148 are fired to form two piezoelectric sheets 150. At this time, the two baked piezoelectric sheets 150 are concave on the side where the common electrode 143 is located, on both sides with respect to the neutral plane, due to a temperature change when the piezo-electric sheet 150 is baked at a high temperature and naturally cooled to room temperature. Will be warped.

  Therefore, as shown in FIG. 7C, the warping direction of the two piezoelectric sheets 150 is confirmed visually or with a laser displacement meter, and the concave side of the laminate in which the two piezoelectric sheets 150 are laminated. One of the piezoelectric sheets 150 is the piezoelectric layer 141 and the other piezoelectric sheet 150 is the piezoelectric layer 144, and it is determined that the active portion R1 is formed in the piezoelectric layer 141 (active portion position determining step). The conductive layer 146 formed on the piezoelectric layer 141 is used as the individual electrode 142, and a voltage is applied between the individual electrode 142 and the common electrode 143 so that the portion of the piezoelectric layer 141 between these electrodes is parallel to the thickness direction. The active portion R101 is formed by polarization in the direction (active portion forming step).

  Then, as shown in FIG. 7D, an adhesive is interposed between the piezoelectric layer 144 and the vibration plate 140 so as to oppose each other, and the piezoelectric layer 141 is pressed and bonded and bonded (bonding process). 107 is completed. At this time, since the active portion R101 is formed on the side of the piezoelectric layer 141 that is a concave portion of the laminated body in which the piezoelectric layers 141 and 144 are laminated, a tensile force acts when the warp is corrected and bonded. As a result, the compressive force acting on the piezoelectric layer due to cooling after firing can be relaxed, and the piezoelectric characteristics of the piezoelectric actuator 107 can be prevented from deteriorating.

  In addition, when the piezoelectric layer 144 is pressed toward the vibration plate 140 and bonded and bonded, the conductive layer 146 in a position overlapping the active portion R101 in the thickness direction before the piezoelectric layer 144 contacts the vibration plate 140 is the vibration plate. 140 is contacted. For this reason, the region where the conductive layer 146 and the vibration plate 140 are bonded has a larger pressing force than the region where the piezoelectric layer 144 and the vibration plate 140 are bonded, and the excess adhesive overlaps the active portion R101 in the thickness direction. It can suppress that the adhesive of the area | region which extrudes from an area | region and overlaps with the active part R101 becomes thick.

  Thereafter, the cavity plate 20 of the flow path unit 6 and the vibration plate 140 of the piezoelectric actuator 7 are bonded to face each other, and the inkjet head 3 is completed.

  According to the manufacturing method of the piezoelectric actuator 107 in the second embodiment, the piezoelectric layer 141 that forms the active portion R101 is determined in accordance with the warping direction of the two piezoelectric sheets 150 in the active portion position determining step. As a result, the direction of the force acting on the active portion R101 becomes the same as the warp of the piezoelectric layer 141 is corrected at the time of joining to the vibration plate 140. Therefore, the direction of the force acting on the active portion R101 can be aligned, and variations in piezoelectric characteristics among the plurality of piezoelectric actuators 107 can be reduced.

  In addition, the conductive layer 146 formed on the piezoelectric sheet 150 that satisfies the condition among the plurality of conductive layers 146 on both sides can be used as the individual electrode 142 in accordance with the warping direction of the two piezoelectric sheets 150.

  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.

  In the embodiment described above, the two green sheets laminated with the electrodes sandwiched in the firing step are fired to form two piezoelectric layers. However, the two piezoelectric layers are included on both sides of the two piezoelectric layers. The same number of green sheets having substantially the same thickness may be laminated and fired to form four or more even number of piezoelectric layers. For example, as shown in FIG. 8A, four piezoelectric layers 201 to 204 having the same thickness are laminated, and between the two piezoelectric layers 201 and 202 and between the two piezoelectric layers 203 and 204. The electrodes 211 and 213 having the same shape are disposed on the piezoelectric layer 202, the common electrode 212 is disposed between the two piezoelectric layers 202 and 203, and the portion of the piezoelectric layer 202 sandwiched between the electrodes 211 and 212 is the active portion R201. The actuator 200 may be used. Further, as shown in FIG. 8B, four piezoelectric layers 301 to 304 having the same thickness are laminated, and between the two piezoelectric layers 301 and 302 and between the two piezoelectric layers 303 and 304. Common electrodes 312 and 314 are disposed respectively, and the individual electrode 313 is disposed between the two piezoelectric layers 302 and 303, and the individual electrode 311 having the same shape as the individual electrode 313 is disposed on the surface of the piezoelectric layer 301. The piezoelectric actuator 300 in which the portion of the sandwiched piezoelectric layers 301 to 303 becomes the active portion R301 may be used.

  In the above-described embodiment, the active portion is formed on the concave side of the laminate of the two piezoelectric layers. However, the active portion may be formed on the convex side, depending on the warping direction. What is necessary is just to determine the piezoelectric layer which forms an active part.

  Furthermore, in the above-described embodiment, the individual electrode is arranged at a position overlapping with the common electrode of the piezoelectric layer in the thickness direction, and the active portion is formed in the portion of the piezoelectric layer sandwiched between the individual electrode and the common electrode. However, the individual electrode may be arranged at a position that does not overlap the common electrode in the thickness direction. At this time, the active portion is formed at a portion connecting the individual electrode and the common electrode.

  As described above, in the embodiment described above and the modifications thereof, the present invention is applied to a method for manufacturing a piezoelectric actuator for an inkjet head that records an image or the like by ejecting ink onto a recording sheet. The present invention is not limited to such a piezoelectric actuator for an ink jet head, and can be applied to a method for manufacturing a piezoelectric actuator used for various purposes.

DESCRIPTION OF SYMBOLS 1 Inkjet printer 3 Inkjet head 6 Flow path unit 7 Piezoelectric actuator 40, 140 Vibrating plate 41, 141, 144 Piezoelectric layer 42, 142 Individual electrode 43, 143 Common electrode R1, R101 Active part

Claims (4)

Two piezoelectric layers stacked in the thickness direction, a first electrode disposed between the two piezoelectric layers, and one of the two piezoelectric layers opposite to the first electrode of the piezoelectric layer. A method of manufacturing a piezoelectric actuator having a second electrode disposed on a surface, an active portion to which an electric field is applied by a voltage applied to the first electrode and the second electrode, and bonded to a substrate. And
A laminating step of laminating the two piezoelectric layers having substantially the same thickness with the first electrode interposed therebetween,
A firing step of integrally firing the two piezoelectric layers laminated and the first electrode;
The activity of confirming the warping direction of the two piezoelectric layers fired integrally and determining which of the two piezoelectric layers the active portion is to be formed according to the warping direction A part positioning process;
An active portion forming step of forming the active portion in the piezoelectric layer determined in the active portion position determining step.   2. The active part position determining step, wherein the active part is determined to be formed in the piezoelectric layer on the concave side in the thickness direction of the two piezoelectric layers. A method for manufacturing a piezoelectric actuator.   In the active portion forming step, the second electrode is formed on the surface of the piezoelectric layer that is determined to form the active portion on the side opposite to the first electrode, and a polarization voltage is applied to the first electrode and the second electrode. 3. The method of manufacturing a piezoelectric actuator according to claim 1, wherein the active portion is formed by applying and polarizing a portion of the piezoelectric layer between both electrodes. Before the firing step, further comprising a conductive layer forming step of forming a conductive layer on the surface of the two piezoelectric layers opposite to the first electrode,
In the active part forming step, the conductive layer on the side opposite to the first electrode of the piezoelectric layer determined to form the active part of the two conductive layers is defined as the second electrode, and the first electrode and the 3. The method of manufacturing a piezoelectric actuator according to claim 1, wherein the active portion is formed by applying a polarization voltage to the second electrode to polarize the portion of the piezoelectric layer between the two electrodes.

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