Liquid discharge head and liquid discharge device

Abstract

To provide a liquid discharge head excellent in discharge characteristics, and a liquid discharge device.SOLUTION: In a liquid discharge head, a pressure chamber substrate in which a plurality of pressure chambers are provided, a vibration plate, a first common electrode which is provided commonly for 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 which are provided individually for the plurality of pressure chambers and to which a drive voltage that changes over time is applied, a second thin film piezoelectric body, and a second common electrode which is provided commonly for the plurality of pressure chambers and to which the reference voltage is applied are stacked in this order from a lower side to an upper side. In a contraction period during which the reference voltage and the drive voltage in contracting the pressure chamber for discharging liquid are applied, a displacement amount of the first thin film piezoelectric body is larger than a displacement amount of the second thin film piezoelectric body.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 those that have a lower rated voltage. However, as a result of further investigation by the inventors, it was found that more desirable effects can be obtained by setting the physical properties of the lower piezoelectric layer and the upper piezoelectric layer to appropriate values. [Means for solving the problem]

[0006] A preferred aspect of the present invention is a liquid ejection head comprising: a pressure chamber substrate having a plurality of pressure chambers; a vibration plate; a first common electrode provided in common to the plurality of pressure chambers and to which a time-invariant reference voltage is applied; a first thin-film piezoelectric; individual electrodes provided individually for the plurality of pressure chambers and to which a time-variant drive voltage is applied; a second thin-film piezoelectric; and a second common electrode provided in common to the plurality of pressure chambers and to which the reference voltage is applied, stacked in this order from bottom to top; and during a contraction period during which the reference voltage and the drive voltage are applied when the pressure chambers are contracted to eject liquid, the displacement amount of the first thin-film piezoelectric is greater than the displacement amount of the second thin-film piezoelectric.

[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] 5 is a diagram showing a planar arrangement of the individual electrodes and the second common electrode in FIG. 4. FIG. [Figure 7] FIG. 3 is a diagram for explaining a driving voltage and a reference voltage. [Figure 8] 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 9] 10A and 10B are diagrams for explaining a shift of the neutral axis of the diaphragm. [Figure 10] 10A and 10B are diagrams for explaining a shift of the neutral axis of the diaphragm. [Figure 11] 5 is a diagram showing the relationship between the displacement amount of a piezoelectric element and the amount of ink ejected. FIG. [Figure 12] FIG. 4 is a diagram showing a butterfly curve of the first thin-film piezoelectric element. [Figure 13] FIG. 10 is a diagram showing a butterfly curve of the second thin-film piezoelectric element. [Figure 14] 9 is a diagram for explaining a path in a butterfly curve when the voltage shown in FIG. 8 is applied to the first thin-film piezoelectric element. [Figure 15] 9 is a diagram for explaining a path in a butterfly curve when the voltage shown in FIG. 8 is applied to the second thin-film piezoelectric element. [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] 17A to 17C are diagrams for explaining a method for manufacturing the piezoelectric element shown in FIG. 16. [Figure 18] 17A to 17C are diagrams for explaining a method for manufacturing the piezoelectric element shown in FIG. 16. 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 direction opposite 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 a 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 are not limited to this and may intersect at an angle between 80° and 100°, for example.

[0011] 1. 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 also includes a voltage application circuit 910 that controls the driving of the piezoelectric elements 7 (described below) to eject ink from the nozzles. The voltage application circuit 910 applies a reference voltage VBS and a drive voltage Com (described below) to the piezoelectric elements 7. In this embodiment, unless otherwise specified, when specifying a voltage difference, the voltage below the piezoelectric element minus the voltage above the piezoelectric element is referred to as the "voltage difference."

[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 can achieve improved ejection performance.

[0017] 1-2. Overall configuration of liquid ejection head 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 C are provided in the pressure chamber substrate 14. The plurality of pressure chambers C are arranged in a direction along the Y axis. Each pressure chamber C 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 C is a space located between the flow path substrate 13 and the vibration plate 15. The pressure chamber C 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 C 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 C 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 C. 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 C. 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 C 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 FIG. 3, the piezoelectric element 7 overlaps the pressure chamber C in a plan view. As shown in FIGS. 4 and 5, the piezoelectric element 7 is disposed on the vibration plate 15. 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 C in a plan view seen along the Z axis. However, they are connected in a range that does not overlap with the pressure chamber C, 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 a continuous member. An individual electrode 73 is provided for each piezoelectric element 7. 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 laminated in this order from bottom to top. 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 appropriately interposed between the layers of the piezoelectric elements 7 or between the piezoelectric element 7 and the diaphragm 15.

[0035] 1-4a. First common electrode 71 The first common electrode 71 is provided in common to the multiple pressure chambers C. 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 C. A reference voltage VBS that does not change with time is applied to the first common electrode 71.

[0036] 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.

[0037] 1-4b.Individual electrode 73 The individual electrodes 73 are provided individually for the plurality of pressure chambers C. A driving voltage Com that changes with time is applied to the individual electrodes 73.

[0038] 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.

[0039] 1-4c.Second common electrode 75 The second common electrode 75 is provided in common to the multiple pressure chambers C. 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 C. 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.

[0040] 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.

[0041] 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.

[0042] FIG. 6 is a diagram showing the planar arrangement of the individual electrodes 73 and the second common electrode 75 of FIG. 4. As shown in FIG. 6, each individual electrode 73 is elongated and extends along the X-axis. The multiple individual electrodes 73 are spaced apart and aligned along the Y-axis. As shown in FIGS. 5 and 6, 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 multiple 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 multiple conductive bumps 16B.

[0043] The second common electrode 75 overlaps the individual electrodes 73 in a planar view. Although not shown in detail, the first common electrode 71 overlaps the individual electrodes 73 in a planar view. As described above, the second common electrode 75 is strip-shaped, e.g., rectangular, extending along the Y-axis. Lead wiring 750 is connected to the corners of the second common electrode 75. The lead wiring 750 is electrically connected to the drive circuit 20 mounted on the wiring substrate 16 via the conductive bumps 16B described above. Thus, the second common electrode 75 is electrically connected to the drive circuit 20. Meanwhile, the first common electrode 71 contacts the second common electrode 75 in a region that does not overlap with the pressure chambers C 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. This contact causes the first common electrode 71 to have the same potential as the second common electrode 75. 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] 7 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].

[0045] 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.

[0046] A driving voltage Com according to the amount of ink ejected 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. 7 is an example, and the driving voltage Com may have other waveforms.

[0047] 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.

[0048] 8 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. 8 is obtained by subtracting the reference voltage VBS from the drive voltage Com shown in FIG. 7 at each time.

[0049] 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.

[0050] The horizontal axis in Figure 8 is time, and the vertical axis is 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 8 is an example and varies depending on the drive voltage Com and the reference voltage VBS.

[0051] 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.

[0052] 1-4d. First thin film piezoelectric element 72 and second thin film piezoelectric element 74 As described above, first thin-film piezoelectric element 72 is disposed between first common electrode 71 and individual electrode 73 , and deforms in response to the potential difference between first common electrode 71 and individual electrode 73 .

[0053] 4 and 5 is made of a composite oxide. A first orientation control layer 76 is disposed below the first thin-film piezoelectric element 72. The orientation of the first thin-film piezoelectric element 72 is controlled by the first orientation control layer 76.

[0054] The first thin-film piezoelectric element 72 includes an active portion and a non-active portion. The portion of the first thin-film piezoelectric element 72 that is located between the first common electrode 71 and the individual electrode 73 is the active portion, and the portion that is not located between the first common electrode 71 and the individual electrode 73 is the non-active portion.

[0055] As described above, the second thin-film piezoelectric element 74 is disposed between the second common electrode 75 and the individual electrode 73 , and is deformed in response to the potential difference between the second common electrode 75 and the individual electrode 73 .

[0056] Second thin-film piezoelectric element 74 is made of a composite oxide. Second orientation control layer 77 is disposed below second thin-film piezoelectric element 74. The orientation of second thin-film piezoelectric element 74 is controlled by second orientation control layer 77 below it.

[0057] 6, the second thin-film piezoelectric element 74 has a strip shape extending along the Y-axis. The second thin-film piezoelectric element 74 has through-holes H0 formed in regions corresponding in plan view to the gaps between adjacent pressure chambers C. The through-holes H0 separate the second thin-film piezoelectric element 74 into individual pressure chambers C. Although not shown in detail, the first thin-film piezoelectric element 72 also has through-holes similar to the through-holes H0 of the second thin-film piezoelectric element 74, and is separated into individual pressure chambers C.

[0058] 5, the second thin-film piezoelectric element 74 includes an active portion 741 and a non-active portion 742. The active portion 741 is a portion located between the individual electrode 73 and the second common electrode 75. The active portion 741 is located directly above the first thin-film piezoelectric element 72 and overlaps with the first thin-film piezoelectric element 72 in a planar view. The non-active portion 742 is a portion not located between the individual electrode 73 and the second common electrode 75. The non-active portion 742 extends outside the first thin-film piezoelectric element 72.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] The first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 are each a thin film. Specifically, the thickness of each of the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 is preferably 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.

[0064] 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.

[0065] During an expansion period T2 in which the voltage is reduced from the intermediate voltage EK to the minimum voltage EM in FIG. 8 to expand the pressure chamber C, the piezoelectric element 7 including the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 undergoes deformation such 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 C. As a result, ink is taken into the pressure chamber C. 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 C, the piezoelectric element 7 and the diaphragm 15 deform so as to bend in the Z2 direction. That is, the piezoelectric element 7 deforms downward to contract the pressure chamber C. As a result, the ink in the pressure chamber C is ejected from the nozzle.

[0066] Here, the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 are thin films, each of which is thin. Therefore, the amount of displacement relative to the thickness is large. Therefore, when the pressure chamber C for liquid ejection contracts, if the piezoelectric element 7 and the diaphragm 15 are displaced so as to protrude downward, a phenomenon occurs in which the neutral axis A1 of the diaphragm 15 shifts upward.

[0067] 9 and 10 are diagrams illustrating the shift of the neutral axis A1 of the diaphragm 15. As shown in Fig. 9, when the piezoelectric element 7 and the diaphragm 15 are not displaced, the distance to the neutral axis A1 of the piezoelectric element 7 is a. Note that the neutral axis A1 is not compressed or contracted, and the stress in the axial direction of the diaphragm 15 along the XY plane is 0 (zero).

[0068] Fig. 11 is a diagram showing the relationship between the displacement amount of the piezoelectric element 7 and the ink ejection amount. Line segment L11 in Fig. 11 indicates the ideal ejection amount (ideal displacement amount), line segment L12 indicates the ejection amount of the upper piezoelectric element of the two laminated thin film piezoelectric elements (actual displacement amount of the upper piezoelectric element), and line segment L13 indicates the ejection amount of the lower piezoelectric element (actual displacement amount of the lower piezoelectric element).

[0069] The amount of shift of the neutral axis A1 described above depends on the amount of displacement of the piezoelectric element 7 and the diaphragm 15. For this reason, as shown in FIG. 11, when the amount of displacement is small during the contraction of the pressure chamber C, the shift of the neutral axis A1 has almost no effect. For this reason, when the amount of displacement is small, the ejection amounts of the upper and lower piezoelectric elements do not deviate from the ideal ejection amount. However, when the amount of displacement is large, the effect of the shift of the neutral axis A1 becomes significant. When the amount of displacement is large, the ejection amounts of the upper and lower piezoelectric elements deviate from the ideal ejection amount.

[0070] In particular, the first thin-film piezoelectric element 72 is located closer to the neutral axis A1 than the second thin-film piezoelectric element 74. Therefore, it is susceptible to the effect of a decrease in the ejection amount due to a shift in the neutral axis A1. Therefore, as shown in Figure 11, the greater the amount of displacement, the more the ink ejection amount by the lower piezoelectric element, i.e., the first thin-film piezoelectric element 72, deviates from the normally assumed ideal ejection amount.

[0071] On the other hand, the second thin film piezoelectric element 74 is spaced farther from the neutral axis A1 than the first thin film piezoelectric element 72. Therefore, even if the neutral axis A1 shifts slightly, the effect is small.

[0072] A voltage is applied to the first thin-film piezoelectric element 72 via the individual electrode 73 and the first common electrode 71, and a voltage is applied to the second thin-film piezoelectric element 74 via the individual electrode 73 and the second common electrode 75. The first common electrode 71 and the second common electrode 75 are electrically connected. Therefore, although the range of voltage applied to the first thin-film piezoelectric element 72 and the range of voltage applied to the second thin-film piezoelectric element 74 differ in positive and negative sign, their absolute values ​​are the same. In this context, if the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 have the same amount of displacement in response to a change in voltage, the following problem arises.

[0073] As shown in Figure 11, a shift in the neutral axis A1 causes saturation of the ejection volume in the high displacement region. It is known that even when applying an applied voltage Ea as shown in Figure 8, a voltage exceeding the maximum voltage EN may suddenly be applied during the contraction period T1, resulting in a so-called voltage overshoot. By utilizing this saturation, it is possible to suppress a sudden increase in the ejection volume, even when a voltage overshoot occurs and a voltage that results in a higher-than-expected displacement is applied.

[0074] As mentioned above, the first thin-film piezoelectric element 72 is located closer to the neutral axis A1 than the second thin-film piezoelectric element 74. Therefore, it is more susceptible to the shift of the neutral axis A1. Therefore, the above-mentioned effect of saturation is more pronounced in the first thin-film piezoelectric element 72 than in the second thin-film piezoelectric element 74. The displacement of the diaphragm 15 is the sum of the displacements of the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74. However, the more dominant the displacement of the first thin-film piezoelectric element 72, the more the ejection error can be reduced by the sudden ejection. In other words, to obtain the effect of suppressing overshoot due to saturation, it is preferable to maximize the amount of displacement of the first thin-film piezoelectric element 72 when a voltage is applied.

[0075] 1, the second thin-film piezoelectric element 74 can also suppress sudden ejection due to saturation to some extent. In particular, if the displacement of the second thin-film piezoelectric element 74 is increased, this effect is exerted, although the effect of the shift of the neutral axis A1 is small. Therefore, by utilizing saturation, it is possible to reduce the effect of ejection errors due to sudden ejection.

[0076] However, to achieve this effect, the amount of displacement of the second thin-film piezoelectric element 74 must be considerably large. This raises the risk of damage to the second thin-film piezoelectric element 74 due to its own deformation. Thin-film piezoelectric elements have internal strain due to their own deformation, and the magnitude of this strain depends on the distance from the neutral axis A1. This strain damages the thin-film piezoelectric element. Furthermore, since the second thin-film piezoelectric element 74 is farther from the neutral axis A1 than the first thin-film piezoelectric element 72, the strain is more likely to be large. Therefore, if the amount of displacement of the second thin-film piezoelectric element 74 becomes too large, there is a risk of significant damage to the second thin-film piezoelectric element 74.

[0077] In consideration of the above, in this embodiment, the first thin-film piezoelectric element 72 is set to have a larger displacement amount with a voltage change than the second thin-film piezoelectric element 74. In other words, the displacement amount Sx of the first thin-film piezoelectric element 72 is larger than the displacement amount Sy of the second thin-film piezoelectric element. By making the displacement amount Sx larger than the displacement amount Sy, it is possible to simultaneously prevent damage to each thin-film piezoelectric element as much as possible and reduce damage by utilizing saturation of sudden ejection, as described above.

[0078] It should be noted that the displacement Sx of the first thin-film piezoelectric element 72 in this embodiment is evaluated for the first thin-film piezoelectric element 72 when not incorporated into the piezoelectric element 7. In other words, the displacement Sx is not the displacement when incorporated into the piezoelectric element 7, but is the displacement evaluated independently for the first thin-film piezoelectric element 72 formed under the same conditions (manufacturing method, materials, properties, etc.) as the first thin-film piezoelectric element 72 when incorporated into the piezoelectric element 7. The same is true for the displacement Sy of the second thin-film piezoelectric element 74, and is the displacement evaluated independently for the second thin-film piezoelectric element 74 when not incorporated into the piezoelectric element 7.

[0079] Fig. 12 is a diagram showing a butterfly curve C1 of the first thin-film piezoelectric element 72. Fig. 13 is a diagram showing a butterfly curve C2 of the second thin-film piezoelectric element 74. In Fig. 12 and Fig. 13, the horizontal axis represents voltage [V], and the vertical axis represents the amount of displacement [nm] of the thin-film piezoelectric element. The vertical axis can also be interpreted as the amount of expansion and contraction of the thin-film piezoelectric element.

[0080] Note that this displacement amount is the amount of expansion and contraction of each thin-film piezoelectric element alone before it is incorporated into the liquid ejection head 1 as a piezoelectric element 7. Even before it is incorporated into the liquid ejection head 1, each thin-film piezoelectric element is arranged along the XY plane, with the Z axis as its thickness direction. Furthermore, even before it is incorporated into the liquid ejection head 1, each thin-film piezoelectric element displaces downward in the Z1 direction and upward in the Z2 direction. The displacement amount of the thin-film piezoelectric element indicates how far it has displaced downward from the position at which it is displaced most upward, which is set to 0. In other words, the displacement amount of the thin-film piezoelectric element indicates the relative position when the position at which it is displaced most upward is used as the reference position.

[0081] The butterfly curve C1 of the first thin-film piezoelectric element 72 shown in Figure 12 includes a first path Rsv1, a second path Rsv2, a third path Rsv3, and a fourth path Rsv4. The first path Rsv1 is a path in which the displacement decreases from the first saturation negative voltage -E1 to the first coercive voltage +Ec1, which is the voltage of the first coercive field that is a positive value. The first saturation negative voltage -E1 is the voltage at which the displacement is greatest on the other side of the butterfly curve C1. The coercive field is a voltage at which the polarization is 0 μC / cm 2 is the magnitude of the electric field when

[0082] The second path Rsv2 is a path in which the displacement increases from the first coercive voltage +Ec1, which is the voltage of the first coercive field, to the first saturated positive voltage +E1. The first saturated positive voltage +E1 is the voltage with the largest displacement on the positive side of the butterfly curve C1. The third path Rsv3 is a path in which the displacement decreases from the first saturated positive voltage +E1 to the second coercive voltage -Ec1, which is the voltage of the second coercive field, which is a negative value. The fourth path Rsv4 is a path in which the displacement increases from the second coercive voltage -Ec1, which is the voltage of the second coercive field, to the first saturated negative voltage -E1.

[0083] The displacement of the first thin-film piezoelectric element 72 when the voltage is changed from the first saturation negative voltage −E1 to the first saturation positive voltage +E1 changes along the first path Rsv1 and the second path Rsv2. The displacement of the first thin-film piezoelectric element 72 when the voltage is changed from the first saturation positive voltage +E1 to the first saturation negative voltage −E1 changes along the third path Rsv3 and the fourth path Rsv4.

[0084] 13 includes a fifth path Rsv5, a sixth path Rsv6, a seventh path Rsv7, and an eighth path Rsv8. The fifth path Rsv5 is a path in which the displacement decreases from the second saturation negative voltage −E2 to the third coercive voltage +Ec2, which is the voltage of the third coercive field, which is a positive value. The second saturation negative voltage −E2 is the voltage at which the displacement is greatest on the other side of the butterfly curve C1.

[0085] The sixth path Rsv6 is a path in which the displacement increases from the third coercive voltage +Ec2, which is the voltage of the third coercive field, to the second saturation positive voltage +E2. The second saturation positive voltage +E2 is the voltage with the largest displacement on the positive side of the butterfly curve C1. The third path Rsv3 is a path in which the displacement decreases from the second saturation positive voltage +E2 to the fourth coercive voltage -Ec2, which is the voltage of the fourth coercive field, which is a negative value. The fourth path Rsv4 is a path in which the displacement increases from the fourth coercive voltage -Ec2, which is the voltage of the second coercive field, to the second saturation negative voltage -E2.

[0086] The displacement when the voltage of the second thin-film piezoelectric element 74 is changed from the second saturation negative voltage −E2 to the second saturation positive voltage +E2 changes along the fifth path Rsv5 and the sixth path Rsv6. Also, the displacement when the voltage of the second thin-film piezoelectric element 74 is changed from the second saturation positive voltage +E2 to the second saturation negative voltage −E2 changes along the seventh path Rsv7 and the eighth path Rsv8.

[0087] 14 is a diagram for explaining the path Lx when the applied voltage Ea shown in FIG. 8 is applied to the first thin-film piezoelectric element 72. Note that the upper side of the first thin-film piezoelectric element 72 is at the driving voltage Com and the lower side is at the reference voltage VBS, so the applied voltage Ea, i.e., the actual "voltage difference" applied to the first thin-film piezoelectric element 72, is approximately a negative value (a positive value only when the reference voltage VBS exceeds the driving voltage Com). FIG. 15 is a diagram for explaining the path Ly when the applied voltage Ea shown in FIG. 8 is applied to the second thin-film piezoelectric element 74. Note that the upper side of the second thin-film piezoelectric element 74 is at VBS and the lower side is at Com, so the applied voltage Ea, i.e., the actual "voltage difference" applied to the second thin-film piezoelectric element 74, is approximately a positive value (a negative value only when the reference voltage VBS exceeds the driving voltage Com).

[0088] 14, when an applied voltage Ea is supplied to the first thin-film piezoelectric element 72, the first thin-film piezoelectric element 72 is displaced along a path Lx indicated by a solid line. Also, as shown in Fig. 15, when an applied voltage Ea is supplied to the second thin-film piezoelectric element 74, the second thin-film piezoelectric element 74 is displaced along a path Ly indicated by a solid line.

[0089] First, we will explain the transitions in voltage and displacement of the first thin-film piezoelectric element 72. During the expansion period T2 in which the voltage changes from the intermediate voltage EK to the minimum voltage EM in FIG. 8, the voltage applied to the first thin-film piezoelectric element 72 shifts from negative to positive. At this time, as shown in FIG. 14, the displacement of the first thin-film piezoelectric element 72 during the expansion period T2 follows a first path Rsv1. Then, when the first thin-film piezoelectric element 72 reaches the first coercive voltage +Ec1, it is displaced to the lowest side, and the displacement amount becomes zero.

[0090] During the contraction period T1 in which the voltage changes from the minimum voltage EM to the maximum voltage EN in Fig. 8, the voltage applied to the first thin-film piezoelectric element 72 changes from positive to negative. At this time, as shown in Fig. 14, the displacement of the first thin-film piezoelectric element 72 during the contraction period T1 changes so as to follow a fourth path Rsv4. The first thin-film piezoelectric element 72 then displaces to near the first saturation negative voltage -E1.

[0091] However, this is because the minimum voltage EM is set to a value near the first coercive voltage +Ec1 and the maximum voltage EN is set to a value near the first saturation negative voltage −E1. If the minimum voltage EM is set to a value smaller than the first coercive voltage +Ec1, the path may shift to the fourth path Rsv4 midway through the first path Rsv1. Also, if the maximum voltage EN is set to a value greater than the first saturation negative voltage −E1, the path may shift to the first path Rsv1 midway through the fourth path Rsv4. In this embodiment, the minimum voltage EM is set to the first coercive voltage +Ec1=+2.5V and the maximum voltage EN is set to −21.5V, which is slightly larger than the first saturation negative voltage −E1=−25V. Therefore, the displacement amount of the first thin-film piezoelectric element 72 during the contraction period T1 is the displacement amount Sx=790 nm when the maximum voltage EN=−21.5V is applied.

[0092] Next, the transitions in voltage and displacement of the second thin-film piezoelectric element 74 will be described. During the expansion period T2 in which the voltage changes from the intermediate voltage EK to the minimum voltage EM in FIG. 8, the voltage of the second thin-film piezoelectric element 74 shifts from positive to negative. At this time, as shown in FIG. 15, the displacement of the second thin-film piezoelectric element 74 during the expansion period T2 follows the seventh path Rsv7. Then, when the second thin-film piezoelectric element 74 reaches the fourth coercive voltage -Ec2, it is displaced to the lowest side, and the displacement amount becomes zero.

[0093] During the contraction period T1 in which the voltage changes from the minimum voltage EM to the maximum voltage EN in Fig. 8, the voltage applied to the second thin-film piezoelectric element 74 changes from negative to positive. At this time, as shown in Fig. 15, the displacement of the second thin-film piezoelectric element 74 during the contraction period T1 changes so as to follow a sixth path Rsv6. Then, the second thin-film piezoelectric element 74 is displaced to near the second saturation positive voltage +E2.

[0094] However, this is because the minimum voltage EM is set near the second coercive voltage -Ec2 and the maximum voltage EN is set near the second saturation positive voltage +E2. In this embodiment, the minimum voltage EM is set to the second coercive voltage -Ec2=-2.5V and the maximum voltage EN is set to +21.5V, which is slightly smaller than the second saturation positive voltage +E2=+25V. Therefore, the displacement amount of the second thin-film piezoelectric element 74 during the contraction period T1 is the displacement amount Sy=680nm when the maximum voltage EN=+21.5V is applied.

[0095] As described above, the first thin-film piezoelectric element 72 is applied with a minimum voltage EM of +2.5 V and a maximum voltage EN of -21.5 V, and the second thin-film piezoelectric element 74 is applied with a minimum voltage EM of -2.5 V and a maximum voltage EN of +21.5 V. This is because, as described above, the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 are configured such that voltages of the same absolute value but opposite polarities are applied.

[0096] 14 and 15, the displacement S10 of the first thin-film piezoelectric element 72 at the first saturation negative voltage −E1 is larger than the displacement S20 of the second thin-film piezoelectric element 74 at the second saturation positive voltage +E2. Therefore, it is easier to make the displacement Sx of the first thin-film piezoelectric element 72 larger than the displacement Sy of the second thin-film piezoelectric element 74 during the contraction period T1.

[0097] As described above, even if a shift of the neutral axis A1 occurs, the first thin-film piezoelectric element 72 can reduce the adverse effects of the shift. On the other hand, the displacement Sy of the second thin-film piezoelectric element 74 is larger than the displacement Sx of the first thin-film piezoelectric element 72. Therefore, as described above, the second thin-film piezoelectric element 74 can improve the ejection characteristics. A piezoelectric element 7 having such a plurality of thin-film piezoelectric elements can significantly improve the ejection characteristics and significantly reduce costs by replacing the thin-film piezoelectric element 7 with a component having a lower rated voltage, compared to a single layer of thin-film piezoelectric element.

[0098] Furthermore, the displacement S10 of the first thin-film piezoelectric element 72 at the first saturation negative voltage -E1 is preferably 105% to 120% of the displacement S20 of the second thin-film piezoelectric element 74 at the second saturation positive voltage +E2. In the example shown in Figures 14 and 15, the displacement S10 is 820 [nm] and the displacement S20 is 710 [nm]. Therefore, the displacement Sx is 115% of the displacement Sy.

[0099] The displacement Sx of the first thin-film piezoelectric element 72 during the contraction period T1 is preferably 105% or more and 120% or less of the displacement Sy of the second thin-film piezoelectric element 74. In the example shown in Figures 14 and 15, the displacement Sx is 790 [nm] and the displacement Sy is 680 [nm]. Therefore, the displacement Sx is 116% of the displacement Sy.

[0100] If the displacement Sx is less than the lower limit, the effect of the saturation may not be as sufficient as when the displacement Sx is equal to or greater than the lower limit. Also, if the displacement Sx exceeds the upper limit, the effect of reducing damage to the second thin-film piezoelectric element 74 may be reduced as compared to when the displacement Sx is equal to or less than the upper limit.

[0101] As described above, during the contraction period T1, the voltage of the first thin-film piezoelectric element 72 shifts from positive to negative. Meanwhile, during the contraction period T1, the voltage of the second thin-film piezoelectric element 74 shifts from negative to positive. Thus, even if opposite voltages are applied to the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 during the contraction period T1, the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 can be displaced in the same direction. Specifically, during the contraction period T1, the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 can be displaced downward. Therefore, compared to applying the same voltage as when the thin-film piezoelectric element is a single layer, it is possible to significantly improve the ejection characteristics and significantly reduce costs by replacing the thin-film piezoelectric element with a component having a lower rated voltage.

[0102] Furthermore, the displacement of the first thin-film piezoelectric element 72 during the contraction period T1 changes so as to follow the fourth path Rsv4. Furthermore, the displacement of the first thin-film piezoelectric element 72 during the contraction period T1 changes so as not to follow the first path Rsv1, the second path Rsv2, or the third path Rsv3. During the contraction period T1, the first thin-film piezoelectric element 72 rapidly displaces from the first coercive voltage +Ec1, which is 0 V, along the fourth path Rsv4 without following the third path Rsv3. This allows the amount of displacement during the contraction period T1 to be increased in a short period of time.

[0103] Furthermore, the displacement of the second thin-film piezoelectric element 74 during the contraction period T1 changes so as to follow the sixth path Rsv6. Furthermore, the displacement of the second thin-film piezoelectric element 74 during the contraction period T1 changes so as not to follow the fifth path Rsv5, the seventh path Rsv7, or the eighth path Rsv8. During the contraction period T1, the second thin-film piezoelectric element 74 is suddenly displaced from the fourth coercive voltage −Ec2 of 0 V along the sixth path Rsv6 without following the fifth path Rsv5. Therefore, the amount of displacement during the contraction period T1 can be increased in a short time.

[0104] Furthermore, the displacement S10 of the first thin-film piezoelectric element 72 at the first saturation negative voltage −E1 is larger than the displacement Sx0 of the first thin-film piezoelectric element 72 at the first saturation positive voltage +E1. In this embodiment, the negative side of the butterfly curve C1 of the first thin-film piezoelectric element 72 is used. In this case, since the displacement S10 is larger than the displacement Sx0, it is easier to make the displacement Sx of the first thin-film piezoelectric element 72 larger than the displacement Sy of the second thin-film piezoelectric element 74 during the contraction period T1.

[0105] Furthermore, the displacement Sy0 of the second thin-film piezoelectric element 74 at the second saturation negative voltage −E2 is larger than the displacement S20 of the second thin-film piezoelectric element 74 at the second saturation positive voltage +E2. In this embodiment, the positive side of the butterfly curve C2 of the second thin-film piezoelectric element 74 is used. In this case, since the displacement S20 is smaller than the displacement Sy0, it is easier to make the displacement Sx of the first thin-film piezoelectric element 72 larger than the displacement Sy of the second thin-film piezoelectric element 74 during the contraction period T1.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] Specifically, for example, composite oxides having a perovskite structure include 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 Each of the first orientation control layer 76 and the second orientation control layer 77 may be a single layer or multiple layers. Therefore, the first orientation control layer 76 and the second orientation control layer 77 may each be made of one type of material or multiple types of materials.

[0113] In addition, the aforementioned Pb x Bi (a-x) Fe y Ti (b-y) O zIn this case, a > x and b > y. Also, x / (a - x) preferably 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, z preferably satisfies 2.8 < z < 3.2.

[0114] Examples satisfying these preferable ranges include, for example, a = 1.2, b = 1.0, x = 0.1, and y = 0.5.

[0115] Also, Pb x Fe y Ti (1-y) O z In this case, x satisfies the relationship 1.00 ≦ x < 2.00. In order to orient it to the (100) plane, it is preferable that x satisfies the relationship 1.00 ≦ x < 1.50. Also, y satisfies the relationship 0.10 ≦ y ≦ 0.90. In order to orient it to the (100) plane, it is preferable that 0.20 ≦ y ≦ 0.80. Also, z typically satisfies the relationship z = 3.00. However, z does not necessarily have to satisfy this relationship.

[0116] Incidentally, hereinafter, Pb x Bi (a-x) Fe y Ti (b-y) O z will be simply described as "PbBiFeTiO". Pb x Fe y Ti (1-y) O z will be simply described as "PbFeTiO".

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 4, the second orientation control layer 77 includes a first portion 771 and a second portion 772. The first portion 771 is disposed directly above the individual electrode 73 and is in contact with the individual electrode 73. An active portion 741 of the second thin-film piezoelectric element 74 is provided on the first portion 771. The second portion 772 is disposed on the first common electrode 71 and is in contact with the first common electrode 71. The second portion 772 does not overlap with the individual electrode 73 in a plan view.

[0121] As described above, the base of the second orientation control layer 77 is not uniform but includes different portions. In other words, the second orientation control layer 77 is in contact with two or more different layers. Even if the base is not uniform, the second orientation control layer 77 has self-orientation properties, and thus the second orientation control layer 77 self-orients itself in a predetermined plane orientation without being affected by the base. Therefore, the second thin-film piezoelectric element 74 can be preferentially oriented in a predetermined plane orientation without being affected by a complex base.

[0122] Furthermore, the thickness D76 of the first orientation control layer 76 is thinner than the thickness D72 of the first thin-film piezoelectric 72, and the thickness D77 of the second orientation control layer 77 is thinner than the thickness D74 of the second thin-film piezoelectric 74. Each thickness is an average length along the Z axis. There are no particular limitations on either the thickness D76 or the thickness D77, but they are within the range of 20 nm to 200 nm, for example.

[0123] The thickness D77 of the second orientation control layer 77 may be thicker than the thickness D76 of the first orientation control layer 76, for example. This configuration has the following advantages. In the manufacturing process of the piezoelectric element 7, as described below, the first orientation control layer 76 is also patterned when the first thin-film piezoelectric element 72 is etched, as shown in FIG. 17( e). At this time, due to an error in the etching time or the like, the etching may penetrate the first orientation control layer 76, potentially removing the first common electrode 71. However, since the first thin-film piezoelectric element 72 is relatively thin, the etching time is not short, and this is unlikely to occur. On the other hand, as shown in FIG. 18( c), the second orientation control layer 77 is patterned when the second thin-film piezoelectric element 74 is etched. Similarly, due to an error in the etching time or the like, the etching may penetrate the second orientation control layer 77, potentially removing the first common electrode 71. Here, the second thin-film piezoelectric element 74 is thicker than the first thin-film piezoelectric element 72. Therefore, it takes longer to etch the second thin-film piezoelectric element 74 than the first thin-film piezoelectric element 72, and therefore the possibility of etching errors increases. Therefore, the possibility of over-etching the second orientation control layer 77 and etching away the first common electrode 71 is higher than that of the first orientation control layer 76. By contrast, by making the second orientation control layer 77 thicker, the risk of such etching away the first common electrode 71 is reduced. During use, the orientation control layer functions to reduce the dielectric constant between each electrode and each thin-film piezoelectric element, so it is preferable that the orientation control layer be thinner if possible. Therefore, the first orientation control layer 76, which is inherently less likely to etch away the first common electrode 71, is made thinner than the second orientation control layer 77.

[0124] From another perspective, the thickness D77 of the second orientation control layer 77 may be thinner than the thickness D76 of the first orientation control layer 76. This configuration has the following advantages. Each of the first orientation control layer 76 and the second orientation control layer 77 is affected, at least in part, by the unevenness of the respective substrates. In particular, the first orientation control layer 76 is closer to the diaphragm 15 than the second orientation control layer 77 and is therefore more susceptible to the unevenness of the diaphragm 15 and the influence of elements (such as Zr) contained in the diaphragm 15. To suppress this influence, it is preferable that the thickness D76 of the first orientation control layer 76 be thicker. On the other hand, the second orientation control layer 77 is farther from the diaphragm 15 than the first orientation control layer 76, so this influence does not need to be taken into consideration as much. In addition, as described above, an unnecessarily thick orientation control layer causes a decrease in the dielectric constant. Therefore, it is preferable that the second orientation control layer 77, which is less affected by the unevenness and the influence of elements (such as Zr), be thinner than the first orientation control layer 76.

[0125] The thicknesses of the first orientation control layer 76 and the second orientation control layer 77 may be the same.

[0126] 1-5. Manufacturing method of piezoelectric element 7 Fig. 16 is a flow chart showing a method for manufacturing the piezoelectric element 7, which is part of the method for manufacturing the liquid ejection head 1. As shown in Fig. 16, the method for manufacturing the piezoelectric element 7, which is part of the method for manufacturing the liquid ejection head 1, includes a first step S1, a second step S2, a third step S3, a fourth step S4, a fifth step S5, a sixth step S6, a seventh step S7, an eighth step S8, and a ninth step S9. These steps are performed in this order.

[0127] 17 and 18 are diagrams illustrating a method for manufacturing the piezoelectric element 7 shown in FIG. 16. FIG. 10(a) is a diagram illustrating the first step S1. In the first step S1, a first common electrode 71 is formed on the vibration plate 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.

[0128] 17(b) is a diagram for explaining the second step S2. In the second step S2, 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.

[0129] 17(c) is a diagram illustrating the third step S3. In the third step S3, the first thin-film piezoelectric 72 is formed on the first orientation control layer 76. The first thin-film piezoelectric 72 is formed, for example, by forming a precursor layer of the first thin-film piezoelectric 72 by a sol-gel method, and then firing and crystallizing the precursor layer. The first thin-film piezoelectric 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 72 having a thickness of 2 μm or less, or even 1 μm or less.

[0130] 17(d) is a diagram illustrating the fourth step S4. In the fourth step S4, the individual electrodes 73 are formed on the first thin-film piezoelectric elements 72. The first common electrode 71 is formed by a known film formation technique such as vapor deposition or sputtering.

[0131] 17(e) is a diagram for explaining the fifth step S5. In the fifth step S5, the individual electrodes 73, the first thin-film piezoelectric element 72, and the first orientation control layer 76 are patterned. These patterning processes are performed by a known processing technique using etching or the like.

[0132] 18(a) is a diagram for explaining the sixth step S6. In the sixth step S6, 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 evaporation or sputtering.

[0133] 18(b) is a diagram illustrating the seventh step S7. In the seventh step S7, the second thin-film piezoelectric 74 is formed on the second orientation control layer 77. The second thin-film piezoelectric 74 is formed, for example, by forming a precursor layer of the second thin-film piezoelectric 74 by a sol-gel method, and then firing and crystallizing the precursor layer. The second thin-film piezoelectric 74 may also be formed by a sputtering method. However, by using the sol-gel method, the second thin-film piezoelectric 74 can be suitably formed to a thickness of 2 μm or less, or even 1 μm or less.

[0134] FIG. 18(c) is a diagram illustrating the eighth step S8. In the eighth step S8, the second thin-film piezoelectric element 74 and the second orientation control layer 77 are patterned. This patterning is performed by a known processing technique using etching or the like. In this etching, the active portion 741 and the non-active portion 742 are etched to different depths. Furthermore, in this etching, a first portion 771 and a second portion 772 of the second orientation control layer 77 are formed.

[0135] 18(d) is a diagram illustrating the ninth step S9. In the ninth step S9, the second common electrode 75 is formed so as to cover the second thin-film piezoelectric element 74. For example, the second common electrode 75 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.

[0136] 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. Furthermore, this method allows the first thin-film piezoelectric element 72 to be formed on the first orientation control layer 76, and thereby the orientation of the first thin-film piezoelectric element 72 is controlled by the first orientation control layer 76, and the second thin-film piezoelectric element 74 to be formed on the second orientation control layer 77, and thereby the orientation of the second thin-film piezoelectric element 74 is controlled by the second orientation control layer 77. Therefore, the physical properties of the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 can be adjusted to desired values, and a piezoelectric element 7 having desired piezoelectric characteristics can be obtained.

[0137] Furthermore, in the sixth step S6 described above, the second orientation control layer 77 is formed not only on the individual electrodes 73 but also on the first common electrode 71. This reduces the orientation difference within the second thin-film piezoelectric element 74. Specifically, this reduces the orientation difference between the active section and the non-active section. This makes it less likely for stress fracture to occur in the second thin-film piezoelectric element 74, making it less likely for cracks to occur in the second thin-film piezoelectric element 74 and improving the reliability of the piezoelectric element 7.

[0138] The following configuration may also be used. The second thin-film piezoelectric element 74 is farther from the neutral axis A1 than the first thin-film piezoelectric element 72. This increases the strain on the second thin-film piezoelectric element 74, potentially causing significant damage to the second thin-film piezoelectric element 74. On the other hand, the distance from the neutral axis A1 of the first thin-film piezoelectric element 72 is not greater than that of the second thin-film piezoelectric element 74. This reduces the strain on the first thin-film piezoelectric element 72 compared to the second thin-film piezoelectric element 74. Therefore, the second thin-film piezoelectric element 74 can be made relatively thin to minimize damage, while the first thin-film piezoelectric element 72, which is less susceptible to damage, can be made relatively thick, thereby improving the ejection characteristics as much as possible. In this way, the thickness of the first thin-film piezoelectric element 72 may be greater than that of the second thin-film piezoelectric element 74.

[0139] The following configuration may also be used. The greater the Young's modulus of each thin-film piezoelectric element, the greater the generated force. Therefore, even in a structure in which multiple thin-film piezoelectric elements are stacked, as in this embodiment, it is preferable to increase the Young's modulus of each of the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 in order to increase the displacement of the piezoelectric element 7 and improve the ejection characteristics as much as possible. However, increasing the Young's modulus of the second thin-film piezoelectric element 74 may have adverse effects. In manufacturing the piezoelectric element 7, each layer is formed from bottom to top. After the second thin-film piezoelectric element 74 is formed, the second common electrode 75 and various wiring lines are formed on top of it. This formation involves processing such as etching. The etching process used to form the second common electrode 75 and various wiring lines may affect the second thin-film piezoelectric element 74, potentially causing damage during film formation. This damage during film formation is more pronounced as the Young's modulus increases, i.e., the film becomes harder. In view of this, from the viewpoint of ejection characteristics, it is better for the second thin-film piezoelectric element 74 to have a larger Young's modulus; however, when film formation damage is taken into consideration, it is difficult to make the Young's modulus of the second thin-film piezoelectric element 74 that large. On the other hand, the first thin-film piezoelectric element 72 is less affected by film formation damage. Therefore, in this embodiment, since the Young's modulus of the second thin-film piezoelectric element 74 cannot be made large, the Young's modulus of the first thin-film piezoelectric element 72 is made large to compensate for this, thereby ensuring the ejection characteristics of the piezoelectric element 7 as a whole. In this way, the Young's modulus of the first thin-film piezoelectric element 72 may be made larger than the Young's modulus of the second thin-film piezoelectric element 74.

[0140] From another perspective, the following configuration may also be used. Provided that the possibility of the above-described film damage is not a consideration, the Young's modulus of the first thin-film piezoelectric element 72 may be smaller than that of the second thin-film piezoelectric element 74. Even if the generated forces of the first thin-film piezoelectric element 72 and the second thin-film piezoelectric element 74 are the same, the moment increases with distance from the neutral axis A1, thereby contributing significantly to the ejection characteristics. Therefore, from the perspective of maximizing the ejection characteristics, it is preferable to increase the Young's modulus of the second thin-film piezoelectric element 74. On the other hand, although the contribution of the first thin-film piezoelectric element 72 is small, it is also preferable to increase the Young's modulus of the first thin-film piezoelectric element 72 to maximize the ejection efficiency. However, increasing the Young's modulus of the first thin-film piezoelectric element 72, like the second thin-film piezoelectric element 74, may adversely affect the ejection characteristics, especially during high-frequency driving. When ejecting ink continuously, if the next ejection is performed while residual vibrations remain inside the pressure chamber C from the previous ejection, the residual vibrations may cause deviations in the characteristics of the next ejection. If the first thin-film piezoelectric element 72 has a small Young's modulus, its flexibility allows it to smoothly absorb the pressure of residual vibrations. This makes it less likely that deviations in characteristics will occur due to successive ejections. However, if the first thin-film piezoelectric element 72 has a large Young's modulus, it will not be able to sufficiently absorb the pressure of residual vibrations from the previous ejection. This could result in deviations in characteristics. Naturally, this pressure absorption of residual vibrations is more effective in areas where residual vibrations are occurring, i.e., areas closer to pressure chamber C. Therefore, reducing the Young's modulus of the first thin-film piezoelectric element 72 located closer to pressure chamber C leads to effective suppression of residual vibrations. From this perspective, it is also effective to make the Young's modulus of the first thin-film piezoelectric element 72 smaller than that of the second thin-film piezoelectric element 74.

[0141] 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.

[0142] The "liquid ejection head" may be a circulation type head having a so-called circulation flow path.

[0143] 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.

[0144] 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]

[0145] 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, D76...thickness, D77...thickness, N...nozzle, VBS...reference voltage, Rsv1...first path, Rsv2...second path, Rsv3...third path, Rsv4...fourth path, Rsv5...fifth path, Rsv6...sixth path, Rsv7...seventh path, Rsv8...eighth path, S10...displacement amount, S20...displacement amount, Sx...displacement amount, Sy...displacement amount, T1...contraction period.

Claims

1. a pressure chamber substrate provided with a plurality of pressure chambers; 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 with time is applied; a first thin film piezoelectric body; individual electrodes provided individually for the plurality of pressure chambers, to which a driving voltage that varies 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 liquid ejection head characterized in that during a contraction period, which is a period during which the reference voltage and the drive voltage are applied when contracting a pressure chamber to eject liquid, the displacement amount of the first thin-film piezoelectric element is greater than the displacement amount of the second thin-film piezoelectric element.

2. During the contraction period, the voltage of the first thin-film piezoelectric element shifts from positive to negative, 2. The liquid ejection head according to claim 1, wherein the voltage of the second thin film piezoelectric element shifts from negative to positive during the contraction period.

3. a displacement of the first thin-film piezoelectric element when the voltage is changed from a first saturated negative voltage to a first saturated positive voltage follows a first path in which the displacement decreases from the first saturated negative voltage to a first coercive field which is a positive value, and follows a second path in which the displacement increases from the first coercive field to the first saturated positive voltage, a displacement of the first thin-film piezoelectric element when the voltage is changed from the first saturated positive voltage to the first saturated negative voltage follows a third path in which the displacement decreases from the first saturated positive voltage to a second coercive field which is a negative value, and a fourth path in which the displacement increases from the second coercive field to the first saturated negative voltage, 2. The liquid ejection head according to claim 1, wherein the displacement of the first thin film piezoelectric element during the contraction period changes so as to follow the fourth path.

4. 4. The liquid ejection head according to claim 3, wherein the displacement of the first thin film piezoelectric element during the contraction period changes so as not to follow the first path, the second path, or the third path.

5. 4. The liquid ejection head according to claim 3, wherein the displacement of the first thin film piezoelectric element at the first saturated negative voltage is greater than the displacement of the first thin film piezoelectric element at the first saturated positive voltage.

6. the displacement of the second thin-film piezoelectric element when the voltage is changed from the second saturated negative voltage to the second saturated positive voltage follows a fifth path in which the displacement decreases from the second saturated negative voltage to a third coercive field which is a positive value, and follows a sixth path in which the displacement increases from the third coercive field to the second saturated positive voltage, the displacement of the second thin-film piezoelectric element when the voltage is changed from the second saturated positive voltage to the second saturated negative voltage follows a seventh path in which the displacement decreases from the second saturated positive voltage to a fourth coercive field which is a negative value, and follows an eighth path in which the displacement increases from the fourth coercive field to the second saturated negative voltage, 4. The liquid ejection head according to claim 3, wherein the displacement of the second thin film piezoelectric element during the contraction period changes so as to follow the sixth path.

7. 7. The liquid ejection head according to claim 6, wherein the displacement of the second thin film piezoelectric element during the contraction period changes so as not to follow the fifth path, the seventh path, or the eighth path.

8. 7. The liquid ejection head according to claim 6, wherein the displacement of the second thin film piezoelectric element at the second saturated negative voltage is greater than the displacement of the second thin film piezoelectric element at the second saturated positive voltage.

9. 9. The liquid ejection head according to claim 8, wherein the displacement of the first thin-film piezoelectric element at the first saturated negative voltage is greater than the displacement of the second thin-film piezoelectric element at the second saturated positive voltage.

10. 3. The liquid ejection head according to claim 1, wherein the amount of displacement of the first thin film piezoelectric element during the contraction period is 105% to 120% of the amount of displacement of the second thin film piezoelectric element.

11. A liquid ejection head according to any one of claims 1 to 8; a voltage application circuit for applying the reference voltage and the drive voltage;

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