Liquid discharge head and liquid discharge device

Abstract

To provide a liquid discharge head that can suppress reliability on a piezoelectric element from lowering and a liquid discharge device.SOLUTION: In a liquid discharge head, a pressure chamber substrate provided with a plurality of pressure chambers, a vibration plate, a first common electrode to which a reference voltage is applied, a first thin film piezoelectric body, an individual electrode, a second thin film piezoelectric body and a second common electrode to which a reference voltage is applied from a lower side toward an upper side in this order. When an area in an arranging direction in which the second thin film piezoelectric body overlaps with all of the individual electrode, the first common electrode and the second common electrode when viewed from a laminating direction is defined as an overlapping area and when an area in the arranging direction in which the second thin film piezoelectric body overlaps with the first common electrode and the second common electrode when viewed from the laminating direction and does not overlap with the individual electrode is defined as a non-overlapping area, a position of an upper surface of the second thin film piezoelectric body in the overlapping area is a first position and a position of the upper surface of the second thin film piezoelectric body in the non-overlapping area is a second position lower than the first position.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a liquid ejection head and a liquid ejection apparatus. [Background technology]

[0002] Liquid ejection devices equipped with a liquid ejection head that ejects liquid such as ink onto a medium such as printing paper have been proposed. Piezo inkjet printers are known as such liquid ejection devices. The piezoelectric method uses a piezoelectric element that vibrates a diaphragm that forms part of the wall of a pressure chamber. The vibration of the diaphragm caused by the piezoelectric element causes the liquid filled in the pressure chamber to be ejected from the nozzle.

[0003] The piezoelectric element of the liquid ejection head described in Patent Document 1 has a first common electrode, a thin-film lower piezoelectric layer, individual electrodes, a thin-film upper piezoelectric layer, and a second common electrode stacked in this order. In other words, the piezoelectric element has a configuration in which two thin-film piezoelectrics are stacked. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-256137 Summary of the Invention [Problem to be solved by the invention]

[0005] When thin-film piezoelectric elements are stacked as in Patent Document 1, the amount of displacement per unit voltage can be nearly doubled compared to when the thin-film piezoelectric element is a single layer. This makes it possible to improve ejection characteristics at the same voltage as a single layer, and to reduce costs by replacing components with lower rated voltages. However, with the piezoelectric element configuration described in Patent Document 1, it was difficult to ensure adhesion of the upper piezoelectric layer to the lower layer while also preventing damage to the upper piezoelectric layer. [Means for solving the problem]

[0006] A liquid ejection head according to a preferred aspect of the present invention comprises a pressure chamber substrate on which a plurality of pressure chambers are arranged in an arrangement direction, a vibration plate, a first common electrode provided in common to the plurality of pressure chambers and to which a reference voltage that does not change with time is applied, a first thin film piezoelectric element, individual electrodes provided individually for the plurality of pressure chambers so as to extend in an extension direction intersecting the arrangement direction, and to which a drive voltage that changes with time is applied, a second thin film piezoelectric element, and a second common electrode provided in common to the plurality of pressure chambers and to which the reference voltage is applied, all of which are arranged from bottom to top along a lamination direction intersecting the arrangement direction and the extension direction. In a liquid ejection head stacked in this order, when a region in the arrangement direction in which the second thin-film piezoelectric body overlaps with all of the individual electrodes, the first common electrode, and the second common electrode when viewed from the stacking direction is defined as an overlapping region, and a region in the arrangement direction in which the second thin-film piezoelectric body overlaps with the first common electrode and the second common electrode when viewed from the stacking direction but does not overlap with the individual electrodes is defined as a non-overlapping region, the position of the top surface of the second thin-film piezoelectric body in the overlapping region is a first position, and the position of the top surface of the second thin-film piezoelectric body in the non-overlapping region is a second position that is lower than the first position.

[0007] A liquid ejection apparatus according to a preferred aspect of the present invention includes a liquid ejection head and a voltage application circuit for applying the reference voltage and the drive voltage. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic view illustrating the configuration of a liquid ejection device according to a first embodiment. [Figure 2] FIG. 2 is an exploded perspective view of the liquid ejection head shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view of a portion of the liquid ejection head shown in FIG. [Figure 4] FIG. 4 is an enlarged cross-sectional view of a portion of the liquid ejection head shown in FIG. [Figure 5] FIG. 4 is an enlarged cross-sectional view of a portion of the liquid ejection head shown in FIG. [Figure 6] FIG. 5 is a diagram showing a planar arrangement of the individual electrodes in FIG. 4. [Figure 7] 6 is a plan view showing two conductors and a plurality of lead-out wirings shown in FIG. 5. FIG. [Figure 8] FIG. 3 is a diagram for explaining a driving voltage and a reference voltage. [Figure 9] 10 is a diagram illustrating an example of voltages applied to a first thin-film piezoelectric element and a second thin-film piezoelectric element. [Figure 10] 3 is a plan view showing through holes provided in the first thin-film piezoelectric element and the second thin-film piezoelectric element. FIG. [Figure 11] 5 is a plan view showing overlapping regions and non-overlapping regions of the piezoelectric elements shown in FIG. 4. FIG. [Figure 12] FIG. 3 is a cross-sectional view of a piezoelectric element of a first comparative example. [Figure 13] FIG. 10 is a cross-sectional view of a piezoelectric element of a second comparative example. [Figure 14] 10A and 10B are diagrams illustrating a modified piezoelectric element. [Figure 15] 10 is a flow chart showing a method for manufacturing a piezoelectric element, which is part of a method for manufacturing a liquid ejection head. [Figure 16] 10 is a flow chart showing a method for manufacturing a piezoelectric element, which is part of a method for manufacturing a liquid ejection head. [Figure 17] 10 is a flow chart showing a method for manufacturing a piezoelectric element, which is part of a method for manufacturing a liquid ejection head. [Figure 18] FIG. 10 is a cross-sectional view showing a modified piezoelectric element. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. The dimensions and scale of each part in the drawings may differ from the actual dimensions, and some parts are shown schematically to facilitate understanding. The scope of the present invention is not limited to these embodiments unless otherwise specified in the following description to limit the present invention. The term "equal" includes not only cases where the dimensions are strictly equal, but also cases where there is a difference within the measurement error range. Furthermore, the term "element α and element β are stacked" means that the elements α and β are aligned vertically, and does not necessarily mean that the elements α and β are in direct contact with each other.

[0010] The following description will use the mutually intersecting X-axis, Y-axis, and Z-axis as appropriate. One direction along the X-axis is referred to as the X1 direction, and the opposite direction to the X1 direction is referred to as the X2 direction. Opposite directions along the Y-axis are referred to as the Y1 direction and the Y2 direction. Opposite directions along the Z-axis are referred to as the Z1 direction and the Z2 direction. Viewing in the direction along the Z-axis is referred to as a "planar view." The Z-axis is typically a vertical axis. The Z1 direction is the upper side, and the Z2 direction is the lower side. However, the Z-axis does not have to be a vertical axis. Furthermore, the X-axis, Y-axis, and Z-axis are typically perpendicular to each other, but this is not limited thereto. For example, they may intersect at an angle between 80° and 100°. Furthermore, hereinafter, the "arrangement direction" refers to the direction along the Y-axis, specifically the Y1 direction or the Y2 direction. The "extension direction" refers to the direction along the X-axis, specifically the X1 direction or the X2 direction. The "stacking direction" is a direction that intersects with the "arrangement direction" and the "extension direction," and specifically is the Z1 direction.

[0011] 1. First embodiment 1-1. Overall configuration of the liquid ejection device 100 FIG. 1 is a schematic diagram illustrating a configuration of a liquid ejection device 100 according to a first embodiment. The liquid ejection device 100 is an inkjet printing device that ejects ink, an example of a liquid, as droplets onto a medium M. The medium M is typically printing paper. However, the medium M is not limited to printing paper, and may be a printing target made of any material, such as a resin film or fabric.

[0012] 1, a liquid container 90 for storing ink is attached to the liquid ejection device 100. Specific examples of the liquid container 90 include a cartridge that is detachable from the liquid ejection device 100, a bag-shaped ink pack made of flexible film, and an ink tank that can be refilled with ink. The type of ink stored in the liquid container 90 is arbitrary.

[0013] The liquid ejection device 100 has a control unit 91, a transport mechanism 92, a movement mechanism 93, and a liquid ejection head 1. The control unit 91 includes a processing circuit such as a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array) and a storage circuit such as a semiconductor memory, and controls the operation of each element of the liquid ejection device 100. The control unit 91 includes a voltage application circuit 910 that controls the driving of a piezoelectric element 7 included in the liquid ejection head 1 (described later), thereby causing ink to be ejected from the nozzles. The voltage application circuit 910 applies a reference voltage VBS and a drive voltage Com to the piezoelectric element 7 included in the liquid ejection device 100 (described later).

[0014] The transport mechanism 92 transports the medium M in the Y2 direction under the control of the control unit 91. The movement mechanism 93 reciprocates the liquid ejection head 1 in the X1 and X2 directions under the control of the control unit 91. In the example shown in FIG. 1, the movement mechanism 93 has a substantially box-shaped transport body 931 called a carriage that houses the liquid ejection head 1, and a transport belt 932 to which the transport body 931 is fixed. Note that the number of liquid ejection heads 1 mounted on the transport body 931 is not limited to one, and may be multiple. In addition to the liquid ejection head 1, a liquid container 90 may also be mounted on the transport body 931.

[0015] The liquid ejection head 1 ejects ink supplied from a liquid container 90 from each of a plurality of nozzles in the Z2 direction onto the medium M under the control of a control unit 91. This ejection is performed in parallel with the transport of the medium M by a transport mechanism 92 and the reciprocating movement of the liquid ejection head 1 by a movement mechanism 93, thereby forming an ink image on the surface of the medium M.

[0016] The liquid ejection device 100 includes a liquid ejection head 1, which will be described later, and a control unit 91. The control unit 91 includes a voltage application circuit 910 that causes ink to be ejected from the nozzles N. The liquid ejection device 100 includes a liquid ejection head 1 having the characteristics, which will be described later, and therefore is able to suppress a decrease in reliability.

[0017] 1-2. Overall configuration of liquid ejection head 1 FIG. 2 is an exploded perspective view of the liquid ejection head 1 shown in FIG. 1. FIG. 3 is a cross-sectional view of a portion of the liquid ejection head 1 shown in FIG. 2, taken along line III-III in FIG. 2. As shown in FIG. 2, the liquid ejection head 1 has a plurality of nozzles N arranged in a direction along the Y axis. In the example shown in FIG. 2, the plurality of nozzles N are divided into a first row L1 and a second row L2 arranged at intervals along the X axis. Each of the first row L1 and the second row L2 is a collection of a plurality of nozzles N linearly arranged in a direction along the Y axis. In the liquid ejection head 1, elements associated with each nozzle N in the first row L1 and elements associated with each nozzle N in the second row L2 are substantially symmetrical to each other in a direction along the X axis. In the following description, the elements associated with the first row L1 will be mainly described, and descriptions of elements associated with the second row L2 will be omitted as appropriate.

[0018] The positions of the nozzles N in the first row L1 and the nozzles N in the second row L2 along the Y axis may be the same or different. Also, elements related to each nozzle N in one of the first row L1 and the second row L2 may be omitted.

[0019] 2 and 3, the liquid ejection head 1 has a nozzle plate 11, a vibration absorber 12, a flow path substrate 13, a pressure chamber substrate 14, a diaphragm 15, a wiring substrate 16, a housing unit 17, and a drive circuit 20. The nozzle plate 11, the vibration absorber 12, the flow path substrate 13, the pressure chamber substrate 14, the diaphragm 15, the wiring substrate 16, and the housing unit 17 are each a plate-like member that is elongated in the direction along the Y axis. The nozzle plate 11, the flow path substrate 13, the pressure chamber substrate 14, the diaphragm 15, and the wiring substrate 16 are arranged in this order in the Z1 direction.

[0020] The nozzle plate 11 is a plate-like member in which a plurality of nozzles N are formed. Each of the plurality of nozzles N is a circular through-hole that allows ink to pass through. The nozzles N eject ink by vibration of the vibration plate 15. The nozzle plate 11 is bonded to the flow path substrate 13 with, for example, an adhesive.

[0021] The flow path substrate 13 is formed with flow paths for supplying ink to the multiple nozzles N. Specifically, the flow path substrate 13 is formed with a space Ra, multiple supply flow paths 131, multiple communication flow paths 132, and a supply liquid chamber 133. The space Ra is an elongated opening extending in the direction along the Y axis in a plan view seen in the direction along the Z axis. Each of the supply flow paths 131 and the communication flow paths 132 is a through-hole formed for each nozzle N. The supply liquid chamber 133 is an elongated space extending in the direction along the Y axis across the multiple nozzles N, and connects the space Ra and the multiple supply flow paths 131 to each other. Each of the multiple communication flow paths 132 overlaps with one nozzle N corresponding to that communication flow path 132 in a plan view. A pressure chamber substrate 14 is bonded to the flow path substrate 13 with, for example, an adhesive.

[0022] A plurality of pressure chambers C0 are provided in the pressure chamber substrate 14. The plurality of pressure chambers C0 are arranged in a direction along the Y axis, which is the "arrangement direction." Each pressure chamber C0 is formed for each nozzle N, and is an elongated space extending in a direction along the X axis in a plan view. The pressure chamber C0 is a space located between the flow path substrate 13 and the vibration plate 15. The pressure chamber C0 communicates with the nozzle N via a communication flow path 132, and also communicates with the space Ra via a supply flow path 131 and a supply liquid chamber 133.

[0023] The nozzle plate 11, the flow path substrate 13, and the pressure chamber substrate 14 are each manufactured by processing a silicon single crystal substrate using, for example, dry etching, wet etching, etc. However, other known methods may also be used as appropriate to manufacture the nozzle plate 11, the flow path substrate 13, and the pressure chamber substrate 14.

[0024] A diaphragm 15 is disposed on the surface facing the Z1 direction of the pressure chamber substrate 14. The diaphragm 15 is a plate-like member that can vibrate elastically.

[0025] A plurality of piezoelectric elements 7 corresponding to the nozzles N are arranged on the surface of the vibration plate 15 facing the Z1 direction. Each piezoelectric element 7 has an elongated shape extending in the direction along the X axis in a plan view. The plurality of piezoelectric elements 7 correspond to a plurality of pressure chambers C0 and are arranged in the direction along the Y axis. The piezoelectric elements 7 deform when a voltage is applied. When the vibration plate 15 vibrates in conjunction with the deformation, the pressure in the pressure chambers C0 fluctuates, causing ink to be ejected from the nozzles N.

[0026] The housing 17 is a case for storing ink to be supplied to the multiple pressure chambers C0. As shown in FIG. 3, a space Rb is formed in the housing 17. The space Rb in the housing 17 and the space Ra in the flow path substrate 13 are connected to each other. The space formed by the spaces Ra and Rb functions as a liquid storage chamber R, which is a reservoir that stores ink to be supplied to the multiple pressure chambers C0. Ink is supplied to the liquid storage chamber R via an inlet 171 formed in the housing 17. The ink in the liquid storage chamber R is supplied to the pressure chambers C0 via the supply liquid chamber 133 and each supply flow path 131.

[0027] The vibration absorber 12 is a flexible film that forms the wall surface of the liquid storage chamber R. The vibration absorber 12 is a compliant substrate that absorbs pressure fluctuations of the ink inside the liquid storage chamber R.

[0028] The wiring board 16 is a plate-like member on which wiring is formed for electrically connecting the drive circuit 20 and the plurality of piezoelectric elements 7. The surface of the wiring board 16 facing the Z2 direction is joined to the diaphragm 15 via a plurality of conductive bumps 16B. On the other hand, the drive circuit 20 is mounted on the surface of the wiring board 16 facing the Z1 direction. The drive circuit 20 is an IC (Integrated Circuit) chip that outputs a drive voltage Com and a reference voltage VBS for driving each piezoelectric element 7.

[0029] 2, ends of external wiring 21 are joined to the surface of wiring board 16 facing the Z1 direction. External wiring 21 is formed of a connecting component such as an FPC (Flexible Printed Circuit) or an FFC (Flexible Flat Cable). Wiring board 16 is formed with a plurality of wirings 22 that electrically connects external wiring 21 to drive circuit 20, and a plurality of wirings 23 to which drive voltage Com output from drive circuit 20 and reference voltage VBS are supplied.

[0030] The wiring board 16 is not limited to a rigid board, and may be, for example, an FPC (Flexible Printed Circuits) or an FFC (Flexible Flat Cable). In this case, the wiring board 16 may also serve as the external wiring 21.

[0031] 1-3.Vibration plate 15 Figures 4 and 5 are enlarged cross-sectional views of a portion of the liquid ejection head 1 shown in Figure 3. The diaphragm 15 shown in Figures 4 and 5 vibrates in response to the vibration of the piezoelectric element 7. The diaphragm 15 has, for example, a first layer 151 and a second layer 152. The first layer 151 and the second layer 152 are stacked in this order from bottom to top, i.e., in the Z1 direction.

[0032] The first layer 151 is, for example, an elastic film made of silicon oxide (SiO2). The elastic film is formed, for example, by thermally oxidizing one surface of a silicon single crystal substrate. The second layer 152 is, for example, an insulating film made of zirconium oxide (ZrO2). The insulating film is formed, for example, by forming a zirconium layer by sputtering and then thermally oxidizing the layer. Zirconium oxide has excellent electrical insulation properties, mechanical strength, and toughness. Therefore, by including the second layer 152 containing zirconium oxide in the diaphragm 15, the characteristics of the diaphragm 15 can be improved.

[0033] Note that another layer such as a metal oxide may be interposed between the first layer 151 and the second layer 152. Also, part or all of the diaphragm 15 may be configured integrally with the pressure chamber substrate 14. Also, the diaphragm 15 may be configured as a layer of a single material. Also, the neutral axis A1 of the diaphragm 15 is shown in FIG.

[0034] 1-4. Piezoelectric element 7 As shown in FIGS. 4 and 5 , the piezoelectric element 7 is disposed on the vibration plate 15. The piezoelectric element 7 overlaps the pressure chamber C0 in a plan view. The piezoelectric element 7 includes a first common electrode 71, a first orientation control layer 76, a first thin-film piezoelectric element 72, an individual electrode 73, a second orientation control layer 77, a second thin-film piezoelectric element 74, and a second common electrode 75. Of these, the first common electrode 71 and the second common electrode 75 are generally common to multiple piezoelectric elements 7. The first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 are separated by through-holes H0 (described later) between the multiple piezoelectric elements 7 in a range that overlaps with the pressure chamber C0 in a plan view seen along the Z axis. However, they are connected to each other in a range that does not overlap with the pressure chamber C0, forming a continuous member. However, the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 do not have to be continuous members. The individual electrodes 73 are provided for the respective piezoelectric elements 7 .

[0035] The pressure chamber substrate 14, diaphragm 15, first common electrode 71, first thin-film piezoelectric element 72, individual electrode 73, second thin-film piezoelectric element 74, and second common electrode 75 are stacked in this order from bottom to top along the Z1 direction, which is the "stacking direction." A first orientation control layer 76 is provided between the first thin-film piezoelectric element 72 and the first common electrode 71. A second orientation control layer 77 is provided between the second thin-film piezoelectric element 74 and the individual electrode 73. Other layers, such as layers for improving adhesion, may be interposed as appropriate between the multiple layers of the piezoelectric element 7 or between the piezoelectric element 7 and diaphragm 15. The first orientation control layer 76 and the second orientation control layer 77 may be omitted as appropriate.

[0036] 1-4a. First common electrode 71 The first common electrode 71 is provided in common to the multiple pressure chambers C0. The first common electrode 71 is strip-shaped and extends in the direction along the Y axis so as to be continuous with the multiple pressure chambers C0. A reference voltage VBS that does not change with time is applied to the first common electrode 71.

[0037] Examples of materials for the first common electrode 71 include metal materials or alloys such as platinum (Pt), iridium (Ir), aluminum (Al), nickel (Ni), gold (Au), and copper (Cu). The first common electrode 71 may be a single layer or multiple layers. For example, the first common electrode 71 has a layered structure in which a layer made of platinum is stacked on a layer made of iridium.

[0038] 1-4b. Individual electrode 73 The individual electrodes 73 extend in a direction along the Y axis, which is an “extension direction intersecting the arrangement direction.” A driving voltage Com that changes with time is applied to the individual electrodes 73.

[0039] Examples of materials for the individual electrodes 73 include metal materials such as platinum, iridium, aluminum, nickel, gold, and copper, or alloys thereof. The individual electrodes 73 may be single-layered or multi-layered.

[0040] FIG. 6 is a diagram showing the planar arrangement of the individual electrodes 73 in FIG. 4. As shown in FIG. 6, each individual electrode 73 is elongated and extends in the direction along the Y axis. The multiple individual electrodes 73 are spaced apart from one another and lined up along the Y axis. The individual electrodes 73 are individually provided for the multiple pressure chambers C0. Each individual electrode 73 overlaps with a pressure chamber C0 when viewed in the Z1 direction.

[0041] 1-4c.Second common electrode 75 The second common electrode 75 shown in Figures 4 and 5 is provided in common to the multiple pressure chambers C0 described above. The second common electrode 75 is strip-shaped and extends in the direction along the Y axis so as to be continuous with the multiple pressure chambers C0. A reference voltage VBS that does not change with time is applied to the second common electrode 75. Therefore, a common potential is applied to the first common electrode 71 and the second common electrode 75.

[0042] Examples of materials for the second common electrode 75 include metal materials such as platinum, iridium, aluminum, nickel, gold, and copper, or alloys thereof. The second common electrode 75 may be a single layer or multiple layers.

[0043] As shown in FIG. 6 , the second common electrode 75 overlaps the multiple individual electrodes 73 in a planar view. The aforementioned first common electrode 71 also overlaps the multiple individual electrodes 73 in a planar view. As described above, the second common electrode 75 has a strip shape extending in the direction along the Y axis. Although not shown in detail, the second common electrode 75 is connected to wiring for electrical connection to the drive circuit 20 mounted on the wiring substrate 16 via the aforementioned multiple conductive bumps 16B. Thus, the second common electrode 75 is electrically connected to the drive circuit 20. Furthermore, the aforementioned first common electrode 71 contacts the second common electrode 75 in a region that does not overlap with the pressure chamber C0 in a planar view along the Z axis, as shown at the Y1-direction end and Y2-direction end in FIG. 4 and the X1-direction end in FIG. 5 . Due to this contact, the first common electrode 71 and the second common electrode 75 have the same potential. In other words, the first common electrode 71 is electrically connected to the drive circuit 20 via the second common electrode 75. In this embodiment, the first common electrode 71 and the second common electrode 75 are in physical contact with each other, but other members may be interposed between them as long as they are electrically connected.

[0044] As shown in FIG. 5 , two conductors 781 and 782 are disposed on the second common electrode 75. Each of the conductors 781 and 782 is a strip-shaped conductive film extending in the direction along the Y-axis along the edge of the second common electrode 75 in the X1 or X2 direction. The conductors 781 and 782 are made of a conductive material with low electrical resistance, such as gold. The conductors 781 and 782 suppress a voltage drop in the reference voltage VBS at the second common electrode 75. The conductors 781 and 782 also function as weights that define the vibration region of the diaphragm 15. Note that the conductors 781 and 782 may be omitted.

[0045] Fig. 7 is a plan view showing two conductors 781 and 782 and a plurality of lead-out wirings 731 shown in Fig. 5. Note that in Fig. 7, the two conductors 781 and 782 and the plurality of lead-out wirings 731 are marked with dots to facilitate understanding.

[0046] 5 and 7, one end of each individual electrode 73 in the longitudinal direction along the X axis is connected to an outgoing wiring 731 via a connection wiring 730. The outgoing wiring 731 is connected to wiring 70 extending along the Y axis. The wiring 70 is electrically connected to the drive circuit 20 mounted on the wiring substrate 16 via the aforementioned plurality of conductive bumps 16B. Although not shown in detail, the first common electrode 71, like the second common electrode 75, is electrically connected to the drive circuit 20 mounted on the wiring substrate 16 via the aforementioned plurality of conductive bumps 16B.

[0047] 8 is a diagram for explaining the drive voltage Com and the reference voltage VBS, in which the horizontal axis represents time and the vertical axis represents voltage [V].

[0048] A voltage is applied to the piezoelectric element 7 by the aforementioned voltage application circuit 910. Specifically, the voltage application circuit 910 applies a voltage to the first thin-film piezoelectric element 72 via the first common electrode 71 and the individual electrode 73, and the first thin-film piezoelectric element 72 deforms in response to the voltage applied between the first common electrode 71 and the individual electrode 73. Similarly, the voltage application circuit 910 applies a voltage to the second thin-film piezoelectric element 74 via the second common electrode 75 and the individual electrode 73, and the second thin-film piezoelectric element 74 deforms in response to the voltage applied between the second common electrode 75 and the individual electrode 73.

[0049] A driving voltage Com according to the amount of ink ejection is applied to the individual electrode 73. The driving voltage Com changes over time. The driving voltage Com includes a driving waveform WCom. The driving waveform WCom is repeated in a unit period Tu. The driving waveform WCom includes an intermediate voltage Ek, a maximum voltage En, and a minimum voltage Em. The maximum voltage En is the maximum value of the driving voltage Com. The minimum voltage Em is the minimum value of the driving voltage Com. The driving waveform WCom drops from the intermediate voltage Ek to the minimum voltage Em, maintains the minimum voltage Em, then rises from the minimum voltage Em to the maximum voltage En, maintains the maximum voltage En, and then drops to the intermediate voltage Ek. Note that the driving waveform WCom shown in FIG. 8 is an example, and the driving voltage Com may have other waveforms.

[0050] A constant reference voltage VBS is applied to each of the first common electrode 71 and the second common electrode 75, regardless of the amount of ink ejected. The reference voltage VBS is constant and does not change over time. In the illustrated example, the reference voltage VBS is a voltage value higher than the minimum voltage Em of the drive voltage Com, but is not limited to this. The reference voltage VBS may also be the GND potential, i.e., 0 V.

[0051] 9 shows an example of the applied voltage Ea applied to the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74. The applied voltage Ea shown in FIG. 9 is obtained by subtracting the reference voltage VBS from the drive voltage Com shown in FIG. 8 at each time.

[0052] By applying the drive voltage Com and the reference voltage VBS, a voltage corresponding to the difference between the drive voltage Com and the reference voltage VBS is applied to the first thin-film piezoelectric element 72 between the first common electrode 71 and the individual electrode 73, deforming the first thin-film piezoelectric element 72. Similarly, by applying the drive voltage Com and the reference voltage VBS, a voltage corresponding to the difference between the drive voltage Com and the reference voltage VBS is applied to the second thin-film piezoelectric element 74 between the second common electrode 75 and the individual electrode 73, deforming the second thin-film piezoelectric element 74.

[0053] The horizontal axis in Figure 9 represents time, and the vertical axis represents voltage [V]. The applied voltage Ea includes a waveform WEa. The waveform WEa includes an intermediate voltage EK, a maximum voltage EN, and a minimum voltage EM. The maximum voltage EN is the difference between the maximum voltage En of the drive voltage Com and the reference voltage VBS. The minimum voltage EM is the difference between the minimum voltage Em of the drive voltage Com and the reference voltage VBS. Note that the waveform WEa shown in Figure 9 is an example and varies depending on the drive voltage Com and the reference voltage VBS.

[0054] Since the reference voltage VBS is constant, the voltage range RE of the applied voltage Ea and the voltage range RE of the drive voltage Com are equal.

[0055] 1-4d. First thin film piezoelectric element 72 and second thin film piezoelectric element 74 4 and 5 is disposed between a first common electrode 71 and an individual electrode 73, and deforms in response to the potential difference between the first common electrode 71 and the individual electrode 73. The first thin-film piezoelectric 72 is made of a composite oxide. A first orientation control layer 76 is disposed below the first thin-film piezoelectric 72. The orientation of the first thin-film piezoelectric 72 is controlled by the first orientation control layer 76.

[0056] As shown in FIG. 4, the top surface of first thin-film piezoelectric element 72 includes a portion that is parallel to the XY plane and contacts individual electrode 73, and a portion that is inclined relative to the XY plane and contacts second thin-film piezoelectric element 74.

[0057] The second thin-film piezoelectric element 74 is disposed between the second common electrode 75 and the individual electrode 73, and deforms in response to the potential difference between the second common electrode 75 and the individual electrode 73. The second thin-film piezoelectric element 74 is made of a composite oxide. A second orientation control layer 77 is disposed below the second thin-film piezoelectric element 74. The orientation of the second thin-film piezoelectric element 74 is controlled by the second orientation control layer 77 below it.

[0058] As shown in FIG. 4, the second thin-film piezoelectric element 74 has an upper surface 740. The upper surface 740 is in contact with the second common electrode 75. The upper surface 740 has a first upper surface portion 7401, a second upper surface portion 7402, a first inclined surface 7403, and a second inclined surface 7404. The first upper surface portion 7401 and the second upper surface portion 7402 are each parallel to the XY plane and perpendicular to the Z1 direction. The first inclined surface 7403 connects the first upper surface portion 7401 and the second upper surface portion 7402 and is inclined relative to them. The second inclined surface 7404 is connected to the second upper surface portion 7402 and is inclined relative to it.

[0059] Furthermore, first upper surface portion 7401 is located further in the Z1 direction than second upper surface portion 7402. The position of first upper surface portion 7401 in the Z1 direction is referred to as first position P1, and the position of second upper surface portion 7402 in the Z1 direction is referred to as second position P2. Therefore, first position P1 is located further in the Z1 direction than second position P2. Furthermore, first inclined surface 7403 is located lower than first position P1. Second inclined surface 7404 is located lower than second position P2.

[0060] Fig. 10 is a plan view showing through holes H0 provided in the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74. As shown in Fig. 10, the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 have through holes H0 provided in regions corresponding to the gaps between adjacent pressure chambers C0 when viewed from the Z1 direction. The through holes H0 separate the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 into individual pressure chambers C0.

[0061] As described above, each of the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 is made of a composite oxide. Specifically, each of the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 is made of a piezoelectric material having a perovskite crystal structure.

[0062] Examples of the piezoelectric material include lead titanate (PbTiO), lead zirconate titanate (PZT: Pb(Zr,Ti)O), lead zirconate (PbZrO), lead lanthanum titanate ((Pb,La),TiO), lead lanthanum zirconate titanate ((Pb,La)(Zr,Ti)O), lead zirconium niobate titanate (Pb(Zr,Ti,Nb)O), and lead magnesium zirconium niobate titanate (Pb(Zr,Ti)(Mg,Nb)O). Among these, lead zirconate titanate (PZT) is preferably used as the material for the thin-film piezoelectric element. The thin-film piezoelectric element may contain small amounts of other elements, such as impurities. Each of the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 may be a single layer or multiple layers.

[0063] The first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 may be made of the same material, but are preferably made of different materials. The desired physical properties of the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 may differ depending on the type of piezoelectric element 7. For this reason, if the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 were made of the same material, the degree of freedom in design would be reduced, making it difficult to optimize the physical properties of the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74. By using different materials for the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74, it is possible to design the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 to have optimal physical properties. This makes it possible to find the desired piezoelectric element 7.

[0064] From another perspective, it is preferable that the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 are made of the same material. If the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 are made of the same material, manufacturing is easy, and it is easy to design desired physical properties by simply controlling the film thickness, for example.

[0065] Each of the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 is a thin film. Specifically, in this embodiment, a thin film has a thickness of at least 5 μm or less, and more preferably 2 μm or less. The thicknesses of the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 may be the same or different.

[0066] During an expansion period T2 in which the voltage is reduced from the intermediate voltage EK to the minimum voltage EM in FIG. 9 to expand the pressure chamber C0, the piezoelectric element 7, including the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74, deforms so that the piezoelectric element 7 and the diaphragm 15 bend in the Z1 direction. That is, the piezoelectric element 7 deforms upward to expand the pressure chamber C0. As a result, ink is taken into the pressure chamber C0. Next, during a contraction period T1 in which the voltage is increased from the minimum voltage EM to the maximum voltage EN to contract the pressure chamber C0, the piezoelectric element 7 and the diaphragm 15 deform so that they bend in the Z2 direction. That is, the piezoelectric element 7 deforms downward to contract the pressure chamber C0. As a result, the ink in the pressure chamber C0 is ejected from the nozzle.

[0067] 1-4e. First alignment control layer 76 and second alignment control layer 77 4 and 5, the first orientation control layer 76 is provided between the first thin-film piezoelectric element 72 and the first common electrode 71. The second orientation control layer 77 is provided between the second thin-film piezoelectric element 74 and the individual electrode 73. The first orientation control layer 76 controls the orientation of the first thin-film piezoelectric element 72, and the second orientation control layer 77 controls the orientation of the second thin-film piezoelectric element 74.

[0068] By providing the first orientation control layer 76 and the second orientation control layer 77, it is possible to control the orientation of each of the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74. That is, the first orientation control layer 76 can preferentially orient the crystals of the first thin-film piezoelectric element 72 in a predetermined plane orientation and adjust the degree of orientation of the predetermined plane orientation. Similarly, the second orientation control layer 77 can preferentially orient the crystals of the second thin-film piezoelectric element 74 in a predetermined plane orientation and adjust the degree of orientation of the predetermined plane orientation.

[0069] For example, when the first orientation control layer 76 preferentially orients the crystals of the first thin-film piezoelectric element 72 in the (100) plane, the piezoelectric characteristics of the piezoelectric element 7 can be improved compared to when the crystals are preferentially oriented in the (110) plane. Similarly, when the second orientation control layer 77 preferentially orients the crystals of the second thin-film piezoelectric element 74 in the (100) plane, the piezoelectric characteristics of the piezoelectric element 7 can be improved compared to when the crystals are preferentially oriented in the (110) plane. Therefore, the displacement efficiency of the piezoelectric element 7 can be increased.

[0070] The crystal orientation of the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 can be determined by analyzing the X-ray diffraction intensity curves using X-ray diffraction (XRD). Preferential orientation in the (100) plane means that the peak intensity corresponding to the (100) plane is higher than the peak intensity corresponding to other directions, specifically the (110) plane. In particular, by orienting 50% or more, or even 80% or more, of the crystals of the thin-film piezoelectric element in the (100) plane, the displacement efficiency of the piezoelectric element 7 can be improved.

[0071] Furthermore, for example, the first orientation control layer 76 can adjust the degree of orientation of the crystals of the first thin-film piezoelectric 72 to the (100) plane. Similarly, the first orientation control layer 76 can adjust the degree of orientation of the crystals of the first thin-film piezoelectric 72 to the (100) plane. Therefore, by providing the first orientation control layer 76 that controls the orientation of the first thin-film piezoelectric 72 and the second orientation control layer 77 that controls the orientation of the second thin-film piezoelectric 74, it is possible to set the first thin-film piezoelectric 72 and the second thin-film piezoelectric 74 to their desired degrees of orientation. Therefore, it is possible to set optimal physical property values ​​for each of the first thin-film piezoelectric 72 and the second thin-film piezoelectric 74.

[0072] Each of the first orientation control layer 76 and the second orientation control layer 77 contains, for example, titanium (Ti) or a complex oxide having a perovskite structure. The complex oxide having a perovskite structure contains, for example, any of Ni (nickel), lanthanum (La), Bi (bismuth), lead (Pb), titanium (Ti), and iron (Fe) as a constituent element.

[0073] Specifically, for example, as the complex oxide having a perovskite structure, lead titanate (PbTiO3), lanthanum nickelate (LaNiO3), Pb x Bi (a-x) Fe y Ti (b-y) O z , and Pb x Fe y Ti (1-y) O z may be mentioned. Each of the first orientation control layer 76 and the second orientation control layer 77 may be a single layer or a plurality of layers. Therefore, each material of the first orientation control layer 76 and the second orientation control layer 77 may be one type or a plurality of types.

[0074] Also, in the aforementioned Pb x Bi (a-x) Fe y Ti (b-y) O z , a > x and b > y. Also, it is preferable that x / (a - x) satisfies 0.04 < x / (a - x) < 1.40. Further, in order to orient it to the (100) plane, it is more preferable that x / (a - x) < 0.72. Also, it is preferable that b = 1, and it is preferable that 0.8 < (a / b) < 1.4. Also, it is preferable that z satisfies 2.8 < z < 3.2.

[0075] Examples satisfying these preferable ranges include, for example, a = 1.2, b = 1.0, x = 0.1, y = 0.5.

[0076] Also, in Pb x Fe y Ti (1-y) O z , x satisfies the relationship of 1.00 ≦ x < 2.00. In order to orient it to the (100) plane, it is preferable that x satisfies the relationship of 1.00 ≦ x < 1.50. Also, y satisfies the relationship of 0.10 ≦ y ≦ 0.90. In order to orient it to the (100) plane, it is preferable that satisfies the relationship of 0.20 ≦ y ≦ 0.80. Also, typically, z satisfies the relationship of z = 3.00. However, z does not have to satisfy this relationship.

[0077] In the following, Pb x Bi (a-x) Fe y Ti (b-y) O z is simply referred to as "PbBiFeTiO". x Fe y Ti (1-y) O z is simply referred to as "PbFeTiO".

[0078] In particular, it is preferable that the first orientation control layer 76 and the second orientation control layer 77 each contain Bi, Fe, Ti, or Pb. Specifically, for example, it is preferable that the first orientation control layer 76 and the second orientation control layer 77 each be PbBiFeTiO. PbBiFeTiO has superior performance in controlling the orientation of thin-film piezoelectrics compared to PbFeTiO, lanthanum nickelate, and titanium. Therefore, for example, the degree of orientation of the second thin-film piezoelectric 74 to the (100) plane can be increased. This can therefore increase the piezoelectric efficiency of the second thin-film piezoelectric 74.

[0079] Furthermore, the second orientation control layer 77 containing PbBiFeTiO has a self-orientation property, which is a property of self-orienting in a predetermined plane orientation. Therefore, when the second orientation control layer 77 is made of PbBiFeTiO, the second orientation control layer 77 is less susceptible to the plane orientation of the substrate underneath. Therefore, regardless of the plane orientation of the substrate, the second orientation control layer 77 self-orients in a predetermined plane orientation without being affected by the substrate. Therefore, under the influence of the plane orientation of the second orientation control layer 77, the second thin-film piezoelectric element 74 can be oriented in the same plane orientation as the second orientation control layer 77. Specifically, the second orientation control layer 77 is oriented in the (100) plane. The second orientation control layer 77 controls the orientation of the second thin-film piezoelectric element 74 to the (100) plane. Note that a layer without self-orientation would be oriented in a plane orientation other than the predetermined plane orientation under the influence of the plane orientation of the substrate.

[0080] From the viewpoint of the self-orientation, the first orientation control layer 76 and the second orientation control layer 77 may be PbFeTiO. PbFeTiO has self-orientation similar to PbBiFeTiO. Note that a layer made of Ti and a layer made of PbTiOx are considered not to have self-orientation.

[0081] Furthermore, the thickness of the first orientation control layer 76 is thinner than the thickness of the first thin-film piezoelectric 72, and the thickness of the second orientation control layer 77 is thinner than the thickness of the second thin-film piezoelectric 74. Each thickness is an average length along the Z axis. The thicknesses of the first orientation control layer 76 and the second orientation control layer 77 are not particularly limited, but are, for example, in the range of 20 nm to 200 nm. The thicknesses of the first orientation control layer 76 and the second orientation control layer 77 may be the same as or different from each other.

[0082] 1-4f. Overlapping region S1 and non-overlapping region S2 Fig. 11 is a plan view showing the overlapping region S1 and the non-overlapping region S2 of the piezoelectric element 7 shown in Fig. 4. In Fig. 11, the overlapping region S1 and the non-overlapping region S2 are dotted for ease of understanding.

[0083] 4 and 11, the piezoelectric element 7 includes an overlapping region S1 and a non-overlapping region S2. The overlapping region S1 is a region in the Y1 direction, which is the "arrangement direction," in which the second thin-film piezoelectric element 74 overlaps with all of the individual electrode 73, the first common electrode 71, and the second common electrode 75, when viewed from the Z1 direction, which is the "stacking direction." The non-overlapping region S2 is a region in the Y1 direction in which the second thin-film piezoelectric element 74 overlaps with the first common electrode 71 and the second common electrode 75, but does not overlap with the individual electrode 73, when viewed from the Z1 direction. The overlapping region S1 and the non-overlapping region S2 are located at the same position in the X direction and adjacent to each other in the Y1 direction.

[0084] In this embodiment, the overlapping region S1 and the non-overlapping region S2 are provided in the region between the conductors 781 and 782. As described above, the two conductors 781 and 782 also function as weights that define the vibration region of the diaphragm 15. The overlapping region S1 is an active region where the piezoelectric element 7 vibrates. In contrast, the non-overlapping region S2 is a non-active region.

[0085] As shown in FIG. 11 , the overlapping region S1 and the non-overlapping region S2 each extend along the X-axis. A plurality of overlapping regions S1 are provided. The overlapping regions S1 are spaced apart from one another when viewed in the Z1 direction, and are arranged in the Y1 direction, similar to the individual electrodes 73. A plurality of non-overlapping regions S2 are provided. Two non-overlapping regions S2 are provided so as to sandwich one overlapping region S1 when viewed in the Z1 direction. Therefore, in one piezoelectric element 7, one overlapping region S1 is located between two non-overlapping regions S2 when viewed in the Z1 direction. The two non-overlapping regions S2 may be connected in the Y1 direction, which is the arrangement direction.

[0086] Fig. 12 is a cross-sectional view of a piezoelectric element 7x of a first comparative example. As shown in Fig. 12, in the piezoelectric element 7x of the first comparative example, an upper surface 740x of a second thin-film piezoelectric 74x is flat and does not have any steps. Note that Fig. 12 illustrates an active portion S1x and a non-active portion S2x of the piezoelectric element 7x.

[0087] In the piezoelectric element 7x of FIG. 12, the length along the Y-axis of the inactive portion S2x is uniformly reduced to the same extent as the length along the Y-axis of the inactive portion S2 of the piezoelectric element 7 of FIG. 4 on the Z1 side (upper surface side). If the length along the Y-axis of the second thin-film piezoelectric element 74x in the inactive portion S2x is reduced in this manner, the bond between the second thin-film piezoelectric element 74x and the first common electrode 71x may become unstable, resulting in peeling. In the first place, when the piezoelectric element is a single layer, peeling of the piezoelectric element 74x from the electrode disposed below it hardly occurs. This is because a single-layer piezoelectric element is bonded to the electrode disposed below it over a wide area. However, when the piezoelectric element is a multilayer, the contact area between the first thin-film piezoelectric element 72x and the first common electrode 71x is wide, while the contact area between the second thin-film piezoelectric element 74x and the first common electrode 71x is small. Therefore, the solid bonding strength of the first thin-film piezoelectric element 72x to the first common electrode 71x is sufficient, but the solid bonding strength of the second thin-film piezoelectric element 74x to the first common electrode 71x is not sufficient. Therefore, it is thought that the first thin-film piezoelectric element 72x is unlikely to peel off from the first common electrode 71x, but the second thin-film piezoelectric element 74x may peel off from the first common electrode 71x.

[0088] Although the second thin-film piezoelectric element 74x is in contact with the individual electrode 73x over a wide area, the individual electrode 73x is not integrally bonded to the vibration plate 15 and is therefore affected from both sides by the film stress from the first thin-film piezoelectric element 72x and the second thin-film piezoelectric element 74x. This makes the structure unstable and is thought not to contribute significantly to solid bonding.

[0089] FIG. 13 is a cross-sectional view of a piezoelectric element 7y of a second comparative example. FIG. 13 illustrates the active portion S1y and the inactive portion S2y of the piezoelectric element 7y. To solve the problem of the first comparative example, the length of the second thin-film piezoelectric element 74y along the Y axis in the inactive portion S2y can be increased, as in the piezoelectric element 7y of the second comparative example shown in FIG. 13. This ensures a certain degree of contact area between the second thin-film piezoelectric element 74y and the first common electrode 71y. In the piezoelectric element 7y of FIG. 13, the length along the Y axis of the inactive portion S2y is uniformly increased to the same extent as the length along the Y axis of the inactive portion S2 of the piezoelectric element 7 of FIG. 4 on the Z2 side (lower surface side).

[0090] However, it was found that doing so would cause damage to the upper portion of the second thin-film piezoelectric element 74y in the non-active portion S2y. The following two reasons are thought to be the cause of the damage to the upper portion.

[0091] First, it is believed that the damage is caused by distortion occurring at the boundary between the active portion S1y and the inactive portion S2y. At the boundary between the active portion S1y and the inactive portion S2y, distortion can occur because one portion displaces while the other does not. By stacking the piezoelectric bodies, the overall film thickness of the piezoelectric element 7y in the Z direction becomes thicker than when the piezoelectric body is a single layer. Furthermore, the second thin-film piezoelectric body 74y, which is located above the first thin-film piezoelectric body 72y, is farther from the neutral axis A1 of the vibration plate 15. Therefore, it is believed that the distortion is more likely to occur at the boundary between the active portion S1y and the inactive portion S2y in the second thin-film piezoelectric body 74y.

[0092] Second, the damage is thought to be caused by a potential difference applied to the second thin-film piezoelectric element 74y in the inactive portion S2y. The lower portion of the second thin-film piezoelectric element 74y in the inactive portion S2y is close to and surrounded by the first common electrode 71y and the second common electrode 75y, which have the same potential. Therefore, the potential difference in the lower portion of the second thin-film piezoelectric element 74y is almost zero. In contrast, the upper portion of the second thin-film piezoelectric element 74y is close to the second common electrode 75y but far from the first common electrode 71y. Therefore, the influence of the first common electrode 71y on the upper portion of the second thin-film piezoelectric element 74y is small. Furthermore, the upper portion of the second thin-film piezoelectric element 74y is closer to the individual electrode 73y than the first common electrode 71y. The individual electrode 73y and the second common electrode 75y are at different potentials. As a result, the upper portion of the second thin-film piezoelectric element 74y is affected by the potential difference between the individual electrode 73y and the second common electrode 75y. Therefore, even in the inactive portion S2y, the second thin-film piezoelectric element 74y is subjected to this potential difference. This phenomenon occurs particularly conspicuously when, as shown in FIG. 13, the upper portion of the second thin-film piezoelectric element 74y is provided in a slanted manner so that it gradually rises toward the inside in the Y-axis direction (the side where the first thin-film piezoelectric element 73y is located) in most of the inactive portion S2y.

[0093] In contrast to the second comparative example, in the piezoelectric element 7 of this embodiment, the second position P2 on the upper surface 740 of the second thin-film piezoelectric element 74 in the non-overlapping region S2 is lower than the first position P1 on the upper surface 740 of the second thin-film piezoelectric element 74 in the overlapping region S1. A step is provided on the upper surface 740. Furthermore, since the second position P2 is located lower than the first position P1, the thickness of the non-active portion of the second thin-film piezoelectric element 74, i.e., the non-overlapping region S2, is smaller in the piezoelectric element 7 of this embodiment than in the second comparative example. This thickness is the length along the Z1 direction. Therefore, in the piezoelectric element 7 of this embodiment, the upper portion of the second thin-film piezoelectric element 74y of the second comparative example does not exist, or the volume of the upper portion of the second thin-film piezoelectric element 74 can be made very small. This makes it possible to suppress the damage that could occur to the second thin-film piezoelectric element 74y as described above.

[0094] Furthermore, by ensuring a certain degree of length along the Y axis of the second thin-film piezoelectric 74x in the non-active portion, i.e., the non-overlapping region S2, in the lower portion of the second thin-film piezoelectric 74, it is possible to prevent the second thin-film piezoelectric 74 from peeling off from the first common electrode 71. Therefore, with the piezoelectric element 7 of this embodiment, it is possible to ensure adhesion to the first common electrode 71 located below the second thin-film piezoelectric 74 and to prevent damage to the second thin-film piezoelectric 74. This makes it possible to improve the reliability of the piezoelectric element 7, and therefore the reliability of the liquid ejection head 1.

[0095] 4, the overlapping region S1 has a first upper surface portion 7401, which is a portion where the position of the upper surface 740 of the second thin-film piezoelectric element 74 is constant at a first position P1. The non-overlapping region S2 has a second upper surface portion 7402, which is a portion where the position of the upper surface 740 of the second thin-film piezoelectric element 74 is constant at a second position P2. By processing, it is possible to manufacture a piezoelectric element 7 in which the second upper surface portion 7402 as well as the first upper surface portion 7401 are flat surfaces, and the upper surface 740 has a step.

[0096] Furthermore, a first inclined surface 7403 located at the boundary between the overlapping region S1 and the non-overlapping region S2 is inclined with respect to the Z1 direction. A first upper surface portion 7401 of the upper surface 740 is located inside the two second upper surface portions 7402 when viewed in the Z1 direction. From another perspective, at the boundary between the overlapping region S1 and the non-overlapping region S2, the position of the upper surface 740 of the second thin-film piezoelectric element 74 gradually descends from the second position P2 to the first position P1. Therefore, the corner formed by the first upper surface portion 7401 of the upper surface 740 of the second thin-film piezoelectric element 74 and the first inclined surface 7403 is an obtuse angle. Because the corner is an obtuse angle, the risk of cracks occurring due to stress concentration at the corner can be reduced compared to when the angle is less than 90°.

[0097] Furthermore, each of the two second inclined surfaces 7404 is inclined with respect to the Z1 direction, and the two second inclined surfaces 7404 are inclined so as to widen from the second upper surface portion 7402 toward the first common electrode 71. From another perspective, in a portion of the non-overlapping region S2 that is farther from the individual electrode 73 in the X1 direction (the "arrangement direction") than a portion where the upper surface 740 of the second thin-film piezoelectric element 74 is positioned at the second position P2, the position of the upper surface 740 of the second thin-film piezoelectric element 74 gradually descends from the second position P2. Therefore, the corner formed by the second upper surface portion 7402 of the upper surface 740 of the second thin-film piezoelectric element 74 and the second inclined surface 7404 is an obtuse angle. The obtuse angle of this corner can reduce the risk of cracks occurring due to stress concentration at the corner, compared to when the angle is less than 90°.

[0098] Fig. 14 is a diagram showing a piezoelectric element 7A of a modified example. In the piezoelectric element 7A shown in Fig. 14, the corner formed by the first upper surface portion 7401 of the upper surface 740 of the second thin-film piezoelectric element 74 and the first inclined surface 7403 is at an angle of 90°. In addition, the corner formed by the second upper surface portion 7402 of the upper surface 740 of the second thin-film piezoelectric element 74 and the second inclined surface 7404 is also at an angle of 90°. Compared to the piezoelectric element 7A of the modified example, the piezoelectric element 7 of this embodiment shown in Fig. 4 can reduce the risk of cracks occurring due to stress concentration at the corners, as described above.

[0099] Furthermore, even with the piezoelectric element 7 of Figure 14, it is possible to ensure adhesion to the first common electrode 71 located below the second thin-film piezoelectric element 74 while also suppressing damage to the second thin-film piezoelectric element 74.

[0100] Furthermore, in the non-overlapping region S2, the second thin-film piezoelectric 74 has a portion laminated on the first common electrode 71. In this embodiment, the second thin-film piezoelectric 74 is in direct contact with the first common electrode 71. By laminating the second thin-film piezoelectric 74 on the first common electrode 71, the effect of suppressing peeling of the second thin-film piezoelectric 74 from the first common electrode 71 can be significantly achieved in a configuration in which the upper portion of the second thin-film piezoelectric 74y described above is not present. In particular, when the second thin-film piezoelectric 74 is in direct contact with the first common electrode 71, the effect of suppressing peeling is effectively achieved. Note that even if a member having a thickness about 1 / 10 that of the first common electrode 71 is present between the second thin-film piezoelectric 74 and the first common electrode 71, the effect of suppressing peeling can be significantly achieved.

[0101] The width of the non-overlapping region S2 is 25% to 43% of the width of the overlapping region S1. Note that the width is the length along the X1 direction, which is the extension direction. In this embodiment, one piezoelectric element 7 has one overlapping region S1 and two non-overlapping regions S2 sandwiching it. Therefore, the width of the non-overlapping region S2 and the combined width of the two non-overlapping regions S2 are shown.

[0102] The non-overlapping region S2 is a non-active portion of the piezoelectric element 7. Therefore, by setting the width of the non-overlapping region S2 to be 25% or more and 43% or less of the width of the overlapping region S1, it is possible to remarkably achieve both ensuring adhesion to the first common electrode 71 located below the second thin-film piezoelectric element 74 and suppressing damage to the second thin-film piezoelectric element 74, compared to a case where this range is not satisfied.

[0103] 4, the third position P3, which is the position of the portion of the upper surface 720 of the first thin-film piezoelectric element 72 that overlaps with the individual electrode 73 when viewed in the Z1 direction, is lower than the first position P1. The third position P3 is a portion of the upper surface 720 of the first thin-film piezoelectric element 72 in the overlapping region S1 that is parallel to the XY plane. Furthermore, in this embodiment, the third position P3 is lower than the second position P2. By having the third position P3 lower than the first position P1, the risk of the aforementioned damage occurring to the second thin-film piezoelectric element 74 can be particularly effectively reduced. Furthermore, in this embodiment, the third position P3 is lower than the second position P2. Therefore, the risk of the aforementioned damage occurring to the second thin-film piezoelectric element 74 can be even more effectively reduced.

[0104] The third position P3 may be the same as the second position P2 or may be higher than the second position P2.

[0105] 1-5. Manufacturing method of piezoelectric element 7 15, 16, and 17 are diagrams illustrating a method for manufacturing the piezoelectric element 7 shown in Fig. 4. As shown in Fig. 15(a), first, a first common electrode 71 is formed on the diaphragm 15. The first common electrode 71 is formed by a known film formation technique such as vapor deposition or sputtering, or a known processing technique using photolithography, etching, or the like.

[0106] 15(b), a first orientation control layer 76 is formed on the first common electrode 71. The first orientation control layer 76 is formed by a known film formation technique such as evaporation or sputtering.

[0107] 15(c), the first thin-film piezoelectric element 72 is formed on the first orientation control layer 76. The first thin-film piezoelectric element 72 is formed, for example, by forming a precursor layer of the first thin-film piezoelectric element 72 by a sol-gel method, and then firing and crystallizing the precursor layer. The first thin-film piezoelectric element 72 may also be formed by a sputtering method. However, by using the sol-gel method, it is possible to suitably form the first thin-film piezoelectric element 72 having a thickness of 2 μm or less, or even 1 μm or less.

[0108] Next, as shown in Fig. 15(d), an individual electrode 73 is formed on the first thin-film piezoelectric element 72. As shown in Fig. 12(d), the individual electrode 73 is formed by patterning a film formed by a known film formation technique such as vapor deposition or sputtering, for example, by etching.

[0109] 15(e), a second orientation control layer 77 is formed on the individual electrodes 73. The second orientation control layer 77 is formed by a known film formation technique such as vapor deposition or sputtering.

[0110] 16(a), a resist mask M1 is formed by, for example, photolithography on the second orientation control layer 77. Next, as shown in Fig. 16(b), the second orientation control layer 77, the individual electrodes 73, the first thin-film piezoelectric element 72, and the first orientation control layer 76 are patterned by etching using the resist mask M1. Thereafter, the resist mask M1 is removed.

[0111] 16(c), a second thin-film piezoelectric element 74 is formed on the second orientation control layer 77 and the first common electrode 71. The second thin-film piezoelectric element 74 is formed, for example, by forming a precursor layer of the second thin-film piezoelectric element 74 by a sol-gel method, and then firing and crystallizing the precursor layer. The second thin-film piezoelectric element 74 may also be formed by a sputtering method. However, by using the sol-gel method, a second thin-film piezoelectric element 74 having a thickness of 2 μm or less, or even 1 μm or less, can be suitably formed.

[0112] 16(d), a resist mask M2 is formed by, for example, photolithography on the second thin-film piezoelectric element 74. Next, as shown in FIG. 17(a), the second thin-film piezoelectric element 74 is patterned by etching using the resist mask M2.

[0113] Next, as shown in FIG. 17(b), the resist mask M2 is peeled off, and a new resist mask M3 having a smaller plane area than the resist mask M2 is formed. Note that the resist mask M2 may be processed to form a resist mask M3 having a smaller plane area than the resist mask M2. Next, as shown in FIG. 17(c), a portion of the second thin-film piezoelectric element 74 is patterned. This forms the second thin-film piezoelectric element 74 having a first portion and a second portion. Thereafter, the resist mask M3 is removed, and then the second common electrode 75 is formed.

[0114] The piezoelectric element 7 of the liquid ejection head 1 is manufactured by the above method. This method allows the piezoelectric element 7 to be manufactured simply and with high precision. This method also allows the piezoelectric element 7 to be easily and reliably formed, having an overlapping region S1 where the second thin-film piezoelectric element 74 overlaps with the individual electrode 73 as viewed in the Z1 direction, and a non-overlapping region S2 where the second thin-film piezoelectric element 74 does not overlap with the individual electrode 73 as viewed in the Z1 direction. This method also allows the manufacture of a piezoelectric element 7 having an upper surface 740 that has a first upper surface portion 7401 at the above-mentioned first position P1 and a second upper surface portion 7402 at a second position P2 located below the first upper surface portion 7401.

[0115] It should be noted that the method for manufacturing piezoelectric element 7 is not limited to the above method. For example, the lower portion of second thin-film piezoelectric element 74 may be manufactured first, and then the remaining portion of second thin-film piezoelectric element 74 may be manufactured.

[0116] 2. Variations The above-described exemplary embodiment may be modified in various ways. Specific modifications that may be applied to the above-described exemplary embodiment are exemplified below.

[0117] 2-1. Variations 18 is a cross-sectional view of a modified piezoelectric element 7B. In the example shown in Fig. 18, the upper surface of the second thin-film piezoelectric element 74 has a step. Therefore, the upper surface of the second common electrode 75 also has a step that follows the upper surface of the second thin-film piezoelectric element 74. A second position P2 of a second upper surface portion 7402 of the second thin-film piezoelectric element 74 in the non-overlapping region S2 is located lower than a first position P1 of a first upper surface portion 7401 of the second thin-film piezoelectric element 74 in the overlapping region S1.

[0118] This type of modified piezoelectric element 7B also makes it possible to ensure adhesion to the first common electrode 71 located below the second thin-film piezoelectric element 74, while also suppressing damage to the second thin-film piezoelectric element 74. This makes it possible to increase the reliability of the piezoelectric element 7, and therefore the reliability of the liquid ejection head 1.

[0119] In the non-overlapping region S2, the first thin-film piezoelectric element 72 is laminated on the first common electrode 71. In this embodiment, the first thin-film piezoelectric element 72 is in direct contact with the first common electrode 71. In the non-overlapping region S2, the second thin-film piezoelectric element 74 is laminated on the first thin-film piezoelectric element 72. In this embodiment, the second thin-film piezoelectric element 74 is not in direct contact with the first common electrode 71. This makes it possible to prevent the second thin-film piezoelectric element 74 from peeling off from the first common electrode 71.

[0120] In this embodiment, second orientation control layer 77 exists between first thin-film piezoelectric element 72 and second thin-film piezoelectric element 74, but second orientation control layer 77 does not necessarily have to be interposed.

[0121] 2-2.Other variations The "liquid ejection head" may be a circulation type head having a so-called circulation flow path.

[0122] A "liquid ejection device" can be employed in various devices such as facsimile machines and copiers, as well as devices dedicated to printing. The uses of a liquid ejection device are not limited to printing. For example, a liquid ejection device that ejects a solution of a color material is used as a manufacturing device for forming color filters for display devices such as liquid crystal display panels. A liquid ejection device that ejects a solution of a conductive material is used as a manufacturing device for forming wiring and electrodes on a wiring board. A liquid ejection device that ejects a solution of an organic substance related to a living organism is used as a manufacturing device for manufacturing biochips, for example.

[0123] Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the above-described embodiments. Furthermore, the configuration of each part of the present invention can be replaced with any configuration that exhibits the same function as the above-described embodiments, and any configuration can be added. [Explanation of symbols]

[0124] 1...liquid ejection head, 7...piezoelectric element, 15...vibration plate, 20...driving circuit, 71...first common electrode, 72...first thin-film piezoelectric, 73...individual electrode, 74...second thin-film piezoelectric, 75...second common electrode, 76...first orientation control layer, 77...second orientation control layer, 100...liquid ejection device, 910...voltage application circuit, A1...neutral axis, C...pressure chamber, Com...driving voltage, P1...first position, P2...second position, P3...third position, N...nozzle, VBS...reference voltage.

Claims

1. a pressure chamber substrate on which a plurality of pressure chambers are arranged in an arrangement direction; A diaphragm and a first common electrode provided in common to the plurality of pressure chambers and to which a reference voltage that does not change over time is applied; a first thin film piezoelectric body; individual electrodes provided individually for the plurality of pressure chambers so as to extend in an extension direction intersecting the arrangement direction, and to which a driving voltage that changes with time is applied; a second thin film piezoelectric body; a second common electrode provided in common to the plurality of pressure chambers and to which the reference voltage is applied, and a second common electrode provided in common to the plurality of pressure chambers and to which the reference voltage is applied, are stacked in this order from bottom to top along a stacking direction intersecting the arrangement direction and the extension direction, an overlapping region is a region in the arrangement direction where the second thin-film piezoelectric body overlaps with any of the individual electrodes, the first common electrode, and the second common electrode when viewed from the stacking direction; When a region in the arrangement direction in which the second thin-film piezoelectric material overlaps the first common electrode and the second common electrode and does not overlap the individual electrodes when viewed from the stacking direction is defined as a non-overlapping region, a position of an upper surface of the second thin-film piezoelectric element in the overlapping region is a first position, The liquid ejection head is characterized in that the position of the upper surface of the second thin film piezoelectric element in the non-overlapping region is a second position that is lower than the first position.

2. 2. The liquid ejection head according to claim 1, wherein the position of the upper surface of the second thin-film piezoelectric element gradually decreases from the second position to the first position at the boundary between the overlapping region and the non-overlapping region.

3. A liquid ejection head as described in claim 1 or 2, characterized in that in the non-overlapping region, in a portion farther from the individual electrode in the arrangement direction than the portion where the position of the upper surface of the second thin-film piezoelectric is at the second position, the position of the upper surface of the second thin-film piezoelectric gradually decreases from the second position.

4. 2. The liquid ejection head according to claim 1, wherein the second thin film piezoelectric element is laminated on the first common electrode in the non-overlapping region.

5. In the non-overlapping region, the first thin-film piezoelectric element is laminated on the first common electrode, 2. The liquid ejection head according to claim 1, wherein the second thin film piezoelectric element is laminated on the first thin film piezoelectric element in the non-overlapping region.

6. 3. The liquid ejection head according to claim 1, wherein the position of the upper surface of the first thin film piezoelectric element in the overlapping region is a third position that is lower than the first position.

7. 2. The liquid ejection head according to claim 1, wherein the width of the non-overlapping region is 25% to 43% of the width of the overlapping region.

8. the overlapping region has a portion where the position of the top surface of the second thin-film piezoelectric element is constant at the first position, 2. The liquid ejection head according to claim 1, wherein the non-overlapping region has a portion where the position of the upper surface of the second thin film piezoelectric element is constant at the second position.

9. The liquid ejection head according to claim 1 , wherein the overlapping region and the non-overlapping region are located at the same position in the extending direction and adjacent to each other in the arrangement direction.

10. The liquid ejection head according to claim 1; a voltage application circuit for applying the reference voltage and the drive voltage;

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