Liquid ejection head and liquid ejection apparatus

Abstract

The invention provides a liquid ejection head and a liquid ejection apparatus having excellent ejection characteristics. The liquid ejection head includes, stacked in order from bottom to top: a pressure chamber substrate provided with a plurality of pressure chambers; a vibration plate; a first common electrode that is provided in common to the plurality of pressure chambers and to which a reference voltage that does not change depending on time is applied; a first thin film piezoelectric body; independent electrodes which are provided independently for the plurality of pressure chambers and to which a driving voltage that varies according to time is applied; a second thin film piezoelectric body; and a second common electrode which is provided in common to the plurality of pressure chambers, to which the reference voltage is applied, and in which the amount of displacement of the first thin-film piezoelectric body is smaller than the amount of displacement of the second thin-film piezoelectric body during a contraction period, the contraction period is a period during which the reference voltage and the driving voltage are applied when the pressure chamber is contracted in order to discharge the liquid.

Description

Technical Field

[0001] The present invention relates to a liquid ejecting head and a liquid ejecting device. Background Art

[0002] Previously, a liquid ejection device has been proposed, comprising a liquid ejection head for ejecting a liquid such as ink onto a medium such as printing paper. A piezoelectric inkjet printer is known as such a liquid ejection device. In a piezoelectric system, a piezoelectric element is used to vibrate a vibration plate that forms part of the wall surface of a pressure chamber. The vibration of the vibration plate by the piezoelectric element causes the liquid filled in the pressure chamber to be ejected from a nozzle.

[0003] The piezoelectric element included in the liquid ejection head described in Patent Document 1 comprises a first common electrode, a thin film lower piezoelectric layer, an independent electrode, a thin film upper piezoelectric layer, and a second common electrode stacked in this order. In other words, the piezoelectric element is a stack of two thin film piezoelectric layers.

[0004] When thin-film piezoelectric layers are stacked, as in Patent Document 1, the displacement per unit voltage can be nearly doubled compared to a single-layer thin-film piezoelectric layer. This allows for improved ejection characteristics at the same voltage as a single layer, or for cost reduction by replacing components with lower-rated voltages. However, further research by the inventors has revealed that even more effective results can be achieved by setting the physical properties of the lower and upper piezoelectric layers to appropriate values.

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-256137 Summary of the Invention

[0006] The liquid ejection head involved in a preferred embodiment of the present invention is a liquid ejection head as follows, wherein the liquid ejection head is stacked with the following components in sequence from the bottom side to the top side, namely: a pressure chamber substrate, which is provided with a plurality of pressure chambers; a vibration plate; a first common electrode, which is commonly provided for the plurality of pressure chambers and is applied with a reference voltage that does not vary with time; a first thin film piezoelectric body; an independent electrode, which is independently provided for the plurality of pressure chambers and is applied with a driving voltage that varies with time; a second thin film piezoelectric body; a second common electrode, which is commonly provided for the plurality of pressure chambers and is applied with the reference voltage, and during a contraction period, the displacement of the first thin film piezoelectric body is smaller than the displacement of the second thin film piezoelectric body, wherein the contraction period is a period during which the reference voltage and the driving voltage are applied when the pressure chamber is contracted in order to eject liquid.

[0007] A liquid ejection device according to a preferred embodiment of the present invention includes: a liquid ejection head; and a voltage application circuit for applying the reference voltage and the drive voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a schematic diagram illustrating the structure of the liquid ejecting device according to the first embodiment.

[0009] Figure 2 for Figure 1 An exploded perspective view of the liquid ejection head is shown.

[0010] Figure 3 for Figure 2 A cross-sectional view of a portion of a liquid ejection head is shown.

[0011] Figure 4 For the general Figure 3 An enlarged cross-sectional view of a portion of a liquid ejection head is shown.

[0012] Figure 5 For the general Figure 3 An enlarged cross-sectional view of a portion of a liquid ejection head is shown.

[0013] Figure 6 To express Figure 4 FIG. 4 is a diagram showing a planar configuration of independent electrodes and a second common electrode.

[0014] Figure 7 A diagram for explaining driving voltage and reference voltage.

[0015] Figure 8 : .sub.(V) is an example of the voltage applied to the first thin film piezoelectric substance and the second thin film piezoelectric substance.

[0016] Figure 9 A diagram for explaining the displacement of the neutral axis of the diaphragm.

[0017] Figure 10 A diagram for explaining the displacement of the neutral axis of the diaphragm.

[0018] Figure 11 This is a graph showing the relationship between the displacement of the piezoelectric element and the ejection amount of ink.

[0019] Figure 12 FIG. 4 is a graph showing the butterfly curve of the first thin film piezoelectric material.

[0020] Figure 13 FIG2 is a graph showing the butterfly curve of the second thin film piezoelectric material.

[0021] Figure 14 For the Figure 8FIG. 1 is a diagram illustrating a path of a butterfly curve when a voltage is applied to a first thin film piezoelectric layer.

[0022] Figure 15 For the Figure 8 FIG. 1 is a diagram illustrating a path of a butterfly curve when a voltage is applied to the second thin-film piezoelectric layer.

[0023] Figure 16 This is a flowchart of a method for manufacturing a piezoelectric element, which is a part of a method for manufacturing a liquid ejecting head.

[0024] Figure 17 For use in Figure 16 A diagram illustrating a method for manufacturing a piezoelectric element shown in FIG.

[0025] Figure 18 For use in Figure 16 A diagram illustrating a method for manufacturing a piezoelectric element shown in FIG. DETAILED DESCRIPTION

[0026] Hereinafter, the preferred embodiment of the present invention will be described with reference to the accompanying drawings. In addition, in the accompanying drawings, the size or scale of each part is appropriately different from the actual situation, and there are also parts that are schematically shown for ease of understanding. In addition, as long as there is no record in the following description that specifically limits the meaning of the present invention, the scope of the present invention is not limited to these modes. In addition, "equal" includes not only the case of strict equality, but also the case of differences in the degree of measurement error. In addition, "element α and element β are stacked together" means that as long as element α and element β are arranged in the up and down direction, there is no limitation on the case where element α is in direct contact with element β.

[0027] The following description is appropriately made using mutually intersecting X-axis, Y-axis and Z-axis. A 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. Directions opposite to each other along the Y-axis are referred to as the Y1 direction and the Y2 direction. Directions opposite to each other along the Z-axis are referred to as the Z1 direction and the Z2 direction. The situation of observing in the direction along the Z-axis is referred to as "looking down". 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 may not be a vertical axis. In addition, although the X-axis, Y-axis and Z-axis are typically orthogonal to each other, they are not limited to this. For example, they can intersect at an angle within a range of 80° or more and 100° or less.

[0028] 1. Implementation Method

[0029] 1-1. Overall Structure of Liquid Dispensing Device 100

[0030] Figure 1 This is a schematic diagram illustrating the structure of a liquid ejection device 100 according to the 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 any other material, such as a resin film or fabric.

[0031] like Figure 1 As shown, a liquid container 90 for storing ink is mounted on 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 formed of a flexible film, and an ink tank capable of refilling the ink. The type of ink stored in the liquid container 90 is arbitrary.

[0032] The liquid ejection device 100 includes a control unit 91, a conveying mechanism 92, a moving mechanism 93, and a liquid ejection head 1. The control unit 91 includes, for example, a processing circuit such as a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array) and a storage circuit such as a semiconductor memory, and controls the operation of each element of the liquid ejection device 100. The control unit 91 includes a voltage application circuit 910, which controls the drive of the piezoelectric element 7 described later, thereby causing the ink to be ejected from the nozzle. The voltage application circuit 910 applies a reference voltage VBS and a drive voltage Com described later to the piezoelectric element 7. In addition, in this embodiment, when the voltage difference is not specifically stated, the voltage at the bottom of the piezoelectric body - the voltage at the top of the piezoelectric body is recorded as "voltage difference".

[0033] The transport mechanism 92 transports the medium M in the Y2 direction under the control of the control unit 91. The moving mechanism 93 moves the liquid ejecting head 1 back and forth in the X1 direction and the X2 direction under the control of the control unit 91. Figure 1 In the illustrated example, the moving mechanism 93 includes a generally box-shaped transport body 931, called a carriage, which houses the liquid ejecting head 1, and a conveyor belt 932 to which the transport body 931 is fixed. The number of liquid ejecting heads 1 carried on the transport body 931 is not limited to one, but may be multiple. Furthermore, in addition to the liquid ejecting head 1, the transport body 931 may also carry a liquid container 90.

[0034] Under the control of the control unit 91, the liquid ejection head 1 ejects ink supplied from the liquid container 90 from each of the plurality of nozzles in the Z2 direction toward the medium M. This ejection is performed in parallel with the transport of the medium M by the transport mechanism 92 and the reciprocating movement of the liquid ejection head 1 by the moving mechanism 93, thereby forming an image formed by the ink on the surface of the medium M.

[0035] The liquid ejection device 100 includes a liquid ejection head 1 described below and a control unit 91. The control unit 91 includes a voltage application circuit 910 for ejecting ink from the nozzles N. Since the liquid ejection device 100 includes the liquid ejection head 1 having the features described below, it is possible to achieve improved ejection performance.

[0036] 1-2. Overall structure of the liquid ejection head

[0037] Figure 2 To express Figure 1 An exploded perspective view of the liquid ejection head 1 is shown. Figure 3 for Figure 2 The cross-sectional view of a portion of the liquid ejection head 1 is shown. Figure 2 The III-III line cross-sectional view in FIG. Figure 2 As shown in FIG, the liquid ejection head 1 has a plurality of nozzles N arranged in a row along the Y-axis. Figure 2 In the illustrated example, 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 comprises a plurality of nozzles N arranged in a straight line along the Y-axis. The elements associated with the nozzles N in the first row L1 and the elements associated with the nozzles N in the second row L2 in the liquid ejection head 1 are generally symmetrical with each other along the X-axis. In the following description, the focus is on the elements corresponding to the first row L1, and the description of the elements corresponding to the second row L2 is omitted as appropriate.

[0038] 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 identical or different. Furthermore, elements associated with the nozzles N in either the first row L1 or the second row L2 may be omitted.

[0039] like Figure 2 as well as Figure 3As shown, the liquid ejection head 1 includes a nozzle plate 11, a vibration absorber 12, a flow path substrate 13, a pressure chamber substrate 14, a vibration plate 15, a wiring substrate 16, a frame 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 vibration plate 15, the wiring substrate 16, and the frame 17 are each plate-shaped members that are long and narrow along the Y-axis. The nozzle plate 11, the flow path substrate 13, the pressure chamber substrate 14, the vibration plate 15, and the wiring substrate 16 are arranged in this order along the Z1 direction.

[0040] The nozzle plate 11 is a plate-shaped member provided with a plurality of nozzles N. Each of the nozzles N is a circular through-hole through which ink passes. The nozzles N eject ink by the vibration of the vibration plate 15. The nozzle plate 11 is bonded to the flow path substrate 13, for example, with an adhesive.

[0041] A flow channel for supplying liquid to the plurality of nozzles N is formed on the flow channel substrate 13. Specifically, a space Ra, a plurality of supply flow channels 131, a plurality of connecting flow channels 132, and a supply liquid chamber 133 are formed on the flow channel substrate 13. The space Ra is an elongated opening extending in the direction of the Y axis when viewed from above as viewed in the direction of the Z axis. The supply flow channel 131 and the connecting flow channel 132 are through-holes formed for each nozzle N, respectively. The supply liquid chamber 133 is an elongated space extending in the direction of the Y axis across the plurality of nozzles N, and connects the space Ra and the plurality of supply flow channels 131 to each other. Each of the plurality of connecting flow channels 132 overlaps with a nozzle N corresponding to the connecting flow channel 132 when viewed from above. The pressure chamber substrate 14 is bonded to the flow channel substrate 13, for example, by an adhesive.

[0042] The pressure chamber substrate 14 is provided with multiple pressure chambers C. These chambers C are arranged in a row along the Y-axis. Each pressure chamber C is formed for each nozzle N and is a long, strip-shaped space extending along the X-axis when viewed from above. The pressure chamber C is located between the flow path substrate 13 and the vibration plate 15. The pressure chamber C communicates with the nozzles N via the communication channel 132 and with the space Ra via the supply channel 131 and the supply liquid chamber 133.

[0043] The nozzle plate 11, the flow path substrate 13, and the pressure chamber substrate 14 are each manufactured by processing a single crystal silicon substrate using, for example, dry etching or wet etching. However, other known methods may be used as appropriate for manufacturing the nozzle plate 11, the flow path substrate 13, and the pressure chamber substrate 14.

[0044] A vibration plate 15 is disposed on the surface facing the Z1 direction of the pressure chamber substrate 14. The vibration plate 15 is a plate-shaped member that can vibrate elastically.

[0045] Multiple 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 is in the shape of an elongated strip extending along the X-axis when viewed from above. The multiple piezoelectric elements 7 are arranged along the Y-axis, corresponding to the multiple pressure chambers C. The piezoelectric elements 7 deform when a voltage is applied. When the vibration plate 15 vibrates in conjunction with this deformation, the pressure in the pressure chambers C fluctuates, causing ink to be ejected from the nozzles N.

[0046] The frame portion 17 is a housing for storing ink supplied to the plurality of pressure chambers C. Figure 3 As shown, a space Rb is formed in the frame portion 17. Space Rb in the frame portion 17 communicates with space Ra in the flow path substrate 13. The space formed by spaces Ra and Rb functions as a liquid reservoir, or liquid storage chamber R, which stores ink supplied to the multiple pressure chambers C. Ink is supplied to the liquid storage chamber R via an inlet 171 formed in the frame portion 17. The ink in the liquid storage chamber R is supplied to the pressure chambers C via the liquid supply chamber 133 and the supply flow paths 131.

[0047] The vibration absorbing body 12 is a flexible thin film constituting the wall surface of the liquid storage chamber R. The vibration absorbing body 12 is a plastic substrate that absorbs the pressure fluctuation of the ink in the liquid storage chamber R.

[0048] The wiring substrate 16 is a plate-shaped component on which wiring is formed for electrically connecting the drive circuit 20 to the plurality of piezoelectric elements 7. The surface of the wiring substrate 16 facing the Z2 direction is bonded to the vibration plate 15 via a plurality of conductive bumps 16B. Meanwhile, the drive circuit 20 is mounted on the surface of the wiring substrate 16 facing the Z1 direction. The drive circuit 20 is an IC (Integrated Circuit) chip that outputs the drive voltage Com and reference voltage VBS for driving each piezoelectric element 7.

[0049] like Figure 2 As shown, the end of the external wiring 21 is bonded to the surface of the wiring substrate 16 facing the Z1 direction. The external wiring 21 is formed of a connecting component such as an FPC (Flexible Printed Circuit) or an FFC (Flexible Flat Cable). The wiring substrate 16 is provided with a plurality of wirings 22 for electrically connecting the external wiring 21 to the drive circuit 20, and a plurality of wirings 23 for supplying the drive voltage Com and the reference voltage VBS output from the drive circuit 20.

[0050] The wiring substrate 16 is not limited to a rigid substrate, and may be, for example, an FPC (Flexible Printed Circuit) or an FFC (Flexible Flat Cable). In this case, the wiring substrate 16 also serves as the external wiring 21 .

[0051] 1-3. Vibration plate 15

[0052] Figure 4 as well as Figure 5 Respectively Figure 3 An enlarged cross-sectional view of a portion of the liquid ejection head 1 is shown. Figure 4 as well as Figure 5 The vibration plate 15 shown vibrates according to the vibration of the piezoelectric element 7. The vibration plate 15 includes, 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 the bottom to the top, that is, along the Z1 direction.

[0053] The first layer 151 is, for example, an elastic film composed of silicon oxide (SiO2). The elastic film is formed, for example, by thermally oxidizing one surface of a single-crystal silicon substrate. The second layer 152 is, for example, an insulating film composed of zirconium oxide (ZrO2). The insulating film is formed, for example, by forming a zirconium layer by sputtering and thermally oxidizing the layer. Zirconium oxide has excellent electrical insulation, mechanical strength, and toughness. Therefore, by making the vibration plate 15 include the second layer 152 containing zirconium oxide, the characteristics of the vibration plate 15 can be improved.

[0054] In addition, another layer such as a metal oxide may exist between the first layer 151 and the second layer 152. In addition, a part or all of the vibration plate 15 may be integrally formed with the pressure chamber substrate 14. In addition, the vibration plate 15 may also be formed of a layer of a single material. Figure 4 , the neutral axis A1 of the vibration plate 15 is shown.

[0055] 1-4. Piezoelectric element 7

[0056] like Figure 3 As shown, the piezoelectric element 7 overlaps with the aforementioned pressure chamber C when viewed from above. Figure 4 as well as Figure 5As shown, the piezoelectric element 7 is arranged 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 body 72, an independent electrode 73, a second orientation control layer 77, a second thin-film piezoelectric body 74, and a second common electrode 75. Of these components, the first common electrode 71 and the second common electrode 75 are generally shared by multiple piezoelectric elements 7. Although the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 are separated from the multiple piezoelectric elements 7 by the through hole H0 described later in the range overlapping with the pressure chamber C when viewed from above along the Z axis, these components are connected together in the range not overlapping with the pressure chamber C, forming a series of components. However, the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 do not need to form a series of components. The independent electrode 73 is provided independently for each piezoelectric element 7. The pressure chamber substrate 14, vibration plate 15, first common electrode 71, first thin-film piezoelectric layer 72, individual electrode 73, second thin-film piezoelectric layer 74, and second common electrode 75 are stacked in order from bottom to top. Furthermore, a first orientation control layer 76 is provided between the first thin-film piezoelectric layer 72 and the first common electrode 71. A second orientation control layer 77 is provided between the second thin-film piezoelectric layer 74 and the individual electrode 73. Furthermore, other layers, such as layers for improving adhesion, may be appropriately provided between the layers of the piezoelectric element 7 or between the piezoelectric element 7 and the vibration plate 15.

[0057] 1-4a. First common electrode 71

[0058] The first common electrode 71 is provided commonly for the plurality of pressure chambers C. The first common electrode 71 is strip-shaped and extends in the Y-axis direction so as to be continuous with the plurality of pressure chambers C. A reference voltage VBS that does not change with time is applied to the first common electrode 71 .

[0059] 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 may have a laminated structure in which a layer composed of platinum is laminated on a layer composed of iridium.

[0060] 1-4b. Independent electrode 73

[0061] The individual electrodes 73 are independently provided for the plurality of pressure chambers C. A driving voltage Com that changes with time is applied to the individual electrodes 73 .

[0062] Examples of the material of the independent electrode 73 include metal materials such as platinum, iridium, aluminum, nickel, gold, and copper, or alloys thereof. The independent electrode 73 may be a single layer or a multilayer.

[0063] 1-4c. Second common electrode 75

[0064] The second common electrode 75 is provided commonly for the aforementioned multiple pressure chambers C. The second common electrode 75 is strip-shaped and extends along the Y-axis, continuously with the multiple pressure chambers C. A reference voltage VBS, which does not change over 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.

[0065] Examples of the material of 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 a multilayer.

[0066] In addition, if Figure 5 As shown, two conductors 781 and 782 are arranged on the second common electrode 75. Conductors 781 and 782 are strip-shaped conductive films extending along the Y-axis along the edges of the second common electrode 75 in the X1 direction or the X2 direction, respectively. Conductors 781 and 782 are made of a low-resistance conductive material such as gold. Conductors 781 and 782 suppress the voltage drop of the reference voltage VBS in the second common electrode 75. In addition, conductors 781 and 782 also function as weights to define the vibration range of the vibration plate 15. In addition, conductors 781 and 782 can also be omitted.

[0067] Figure 6 To express Figure 4 FIG. 7 is a diagram showing the planar configuration of the independent electrode 73 and the second common electrode 75. Figure 6 As shown in FIG, each independent electrode 73 is in the shape of a strip extending along the X axis. The multiple independent electrodes 73 are separated from each other and arranged along the Y axis. Figure 5 as well as Figure 6 As shown, one end of each individual electrode 73 in the longitudinal direction along the X-axis is connected to a lead-out wiring 731 via a connecting wiring 730. The lead-out wiring 731 is connected to the 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 plurality of conductive bumps 16B described above. Although not shown in detail, the first common electrode 71 and the second common electrode 75 are also electrically connected to the drive circuit 20 mounted on the wiring substrate 16 via the plurality of conductive bumps 16B described above.

[0068] In addition, the second common electrode 75 overlaps with the plurality of independent electrodes 73 when viewed from above. In addition, although not shown in detail, the first common electrode 71 overlaps with the plurality of independent electrodes 73 when viewed from above. As described above, the second common electrode 75 is in the shape of a strip extending in the direction along the Y-axis, and is, for example, in the shape of a rectangle. Lead-out wiring 750 is connected to the corner of the second common electrode 75. The lead-out wiring 750 is electrically connected to the drive circuit 20 mounted on the wiring substrate 16 via the aforementioned plurality of conductive bumps 16B. Therefore, the second common electrode 75 is electrically connected to the drive circuit 20. On the other hand, as Figure 4 The Y1 direction end and the Y2 direction end, Figure 5 As shown in FIG. 1 , the first common electrode 71 is in contact with the second common electrode 75 in a region that does not overlap with the pressure chamber C when viewed from above along the Z-axis, as shown in FIG. This contact provides the first common electrode 71 with 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 physically in contact, but other components may be present between the first common electrode 71 and the second common electrode 75 as long as they are electrically connected.

[0069] Figure 7 3 is a diagram for explaining the driving voltage Com and the reference voltage VBS. Figure 7 The horizontal axis shown is time, and the vertical axis is voltage [V].

[0070] A voltage is applied to the piezoelectric element 7 by the aforementioned voltage application circuit 910. Specifically, the voltage applied to the first thin-film piezoelectric body 72 via the first common electrode 71 and the individual electrode 73 by the voltage application circuit 910 is applied between the first common electrode 71 and the individual electrode 73, causing the first thin-film piezoelectric body 72 to deform. Similarly, the voltage applied to the second thin-film piezoelectric body 74 via the second common electrode 75 and the individual electrode 73 by the voltage application circuit 910 is applied between the second common electrode 75 and the individual electrode 73, causing the second thin-film piezoelectric body 74 to deform.

[0071] A driving voltage Com corresponding to the ejection amount of ink is applied to the independent electrode 73. The driving voltage Com changes with 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, and after maintaining the minimum voltage Em, it rises from the minimum voltage Em to the maximum voltage En, and after maintaining the maximum voltage En, it drops to the intermediate voltage Ek. In addition, Figure 7 The driving waveform WCom shown is an example, and the driving voltage Com may also have other waveforms.

[0072] 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 does not change over time but remains constant. While the illustrated example shows the reference voltage VBS at a higher value than the minimum voltage Em of the drive voltage Com, this is not limiting. Alternatively, the reference voltage VBS may be ground potential, i.e., 0V.

[0073] Figure 8 ⊂ is an example of the applied voltage Ea applied to the first thin film piezoelectric substance 72 and the second thin film piezoelectric substance 74 . Figure 8 The applied voltage Ea shown is the voltage at each time from Figure 7 The voltage shown is obtained by subtracting the reference voltage VBS from the driving voltage Com.

[0074] By applying the driving voltage Com and the reference voltage VBS, a voltage equal to the difference between the driving voltage Com and the reference voltage VBS is applied to the first thin film piezoelectric layer 72 between the first common electrode 71 and the individual electrode 73, thereby deforming the first thin film piezoelectric layer 72. Similarly, by applying the driving voltage Com and the reference voltage VBS, a voltage equal to the difference between the driving voltage Com and the reference voltage VBS is applied to the second thin film piezoelectric layer 74 between the second common electrode 75 and the individual electrode 73, thereby deforming the second thin film piezoelectric layer 74.

[0075] Figure 8 The horizontal axis 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. In addition, Figure 8 The waveform Wea shown is an example, and changes according to the drive voltage Com and the reference voltage VBS.

[0076] Furthermore, since the reference voltage VBS is constant, the voltage range RE of the applied voltage Ea is equal to the voltage range RE of the drive voltage Com.

[0077] 1-4d. First thin film piezoelectric body 72 and second thin film piezoelectric body 74

[0078] Figure 4 as well as Figure 5 The first thin film piezoelectric layer 72 shown is made of a complex oxide. A first orientation control layer 76 is provided below the first thin film piezoelectric layer 72. The first thin film piezoelectric layer 72 has its orientation controlled by the first orientation control layer 76.

[0079] The first thin film piezoelectric layer 72 includes an active portion and a passive portion. The portion of the first thin film piezoelectric layer 72 located between the first common electrode 71 and the individual electrodes 73 is the active portion, while the portion not located between the first common electrode 71 and the individual electrodes 73 is the passive portion.

[0080] As described above, the second thin film piezoelectric layer 74 is disposed between the second common electrode 75 and the individual electrodes 73 , and deforms according to the potential difference between the second common electrode 75 and the individual electrodes 73 .

[0081] The second thin film piezoelectric body 74 is made of a composite oxide. A second orientation control layer 77 is provided below the second thin film piezoelectric body 74. The second thin film piezoelectric body 74 is oriented by the second orientation control layer 77 below it.

[0082] like Figure 6 As shown, the second thin film piezoelectric body 74 is strip-shaped and extends along the Y axis. A through-hole H0 is provided in the second thin film piezoelectric body 74 in an area corresponding to the gap between adjacent pressure chambers C when viewed from above. The through-hole H0 partitions the second thin film piezoelectric body 74 into sections for each pressure chamber C. Although not shown in detail, the first thin film piezoelectric body 72 also has a through-hole similar to the through-hole H0 in the second thin film piezoelectric body 74, partitioning the second thin film piezoelectric body 74 into sections for each pressure chamber C.

[0083] In addition, if Figure 5As shown, the second thin film piezoelectric layer 74 includes an active portion 741 and a passive portion 742. The active portion 741 is located between the individual electrodes 73 and the second common electrode 75. The active portion 741 is located directly above the first thin film piezoelectric layer 72 and overlaps with the first thin film piezoelectric layer 72 when viewed from above. Furthermore, the passive portion 742 is located outside the individual electrodes 73 and the second common electrode 75. The passive portion 742 extends outward from the first thin film piezoelectric layer 72.

[0084] As described above, each of the first thin film piezoelectric layer 72 and the second thin film piezoelectric layer 74 is made of a composite oxide. Specifically, each of the first thin film piezoelectric layer 72 and the second thin film piezoelectric layer 74 is made of a piezoelectric material having a perovskite crystal structure.

[0085] Examples of the piezoelectric material include lead titanate (PbTiO3), lead zirconate titanate (PZT: Pb(Zr, Ti)O3), lead zirconate (PbZrO3), lead lanthanum titanate ((Pb, La), TiO3), lead lanthanum zirconate titanate ((Pb, La)(Zr, Ti)O3), lead zirconate titanate niobium (Pb(Zr, Ti, Nb)O3), and lead magnesium zirconate titanate niobium (Pb(Zr, Ti)(Mg, Nb)O3). Among them, lead zirconate titanate (PZT) is preferably used as the constituent material of the thin film piezoelectric body. In addition, the thin film piezoelectric body may also contain a small amount of other elements such as impurities. In addition, each of the first thin film piezoelectric body 72 and the second thin film piezoelectric body 74 may be either a single layer or a multilayer.

[0086] Although the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 may be made of the same material, they are preferably formed of different materials. Depending on the type of piezoelectric element 7 used, the desired physical properties of the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 may be different. Therefore, if the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 are made of the same material, the degree of freedom in design is reduced, making it difficult to optimize the physical property values ​​of the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74. By making the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 of different materials, it is possible to design the optimal physical property values ​​for each of the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74. Therefore, the desired piezoelectric element 7 can be found.

[0087] From another perspective, the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 are preferably made of the same material. By making the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 of the same material, manufacturing is facilitated, and desired physical properties can be easily designed simply by controlling the film thickness, for example.

[0088] The first thin-film piezoelectric layer 72 and the second thin-film piezoelectric layer 74 are each thin films. Specifically, the thickness of each of the first thin-film piezoelectric layer 72 and the second thin-film piezoelectric layer 74 is preferably 5 μm or less, and more preferably 2 μm or less. Furthermore, the thicknesses of the first thin-film piezoelectric layer 72 and the second thin-film piezoelectric layer 74 may be the same or different.

[0089] The first thin-film piezoelectric layer 72 and the second thin-film piezoelectric layer 74 are each thin films. Specifically, in this embodiment, the thin films have a thickness of at least 5 μm or less, and more preferably 2 μm or less. Furthermore, the thicknesses of the first thin-film piezoelectric layer 72 and the second thin-film piezoelectric layer 74 may be the same or different.

[0090] The piezoelectric element 7 including the first thin film piezoelectric body 72 and the second thin film piezoelectric body 74 is configured to change the voltage from Figure 8 During the expansion period T2, in which the intermediate voltage EK drops to the minimum voltage EM and the pressure chamber C expands, the piezoelectric element 7 and the vibration plate 15 are deformed in the Z1 direction. That is, the piezoelectric element 7 is deformed upward in such a way as to expand the pressure chamber C. As a result, ink is sucked into the pressure chamber C. Next, during the contraction period T1, in which the voltage is increased from the minimum voltage EM to the maximum voltage EN and the pressure chamber C contracts, the piezoelectric element 7 and the vibration plate 15 are deformed in the Z2 direction. That is, the piezoelectric element 7 is deformed downward in such a way as to contract the pressure chamber C. As a result, the ink in the pressure chamber C is ejected from the nozzle.

[0091] Here, the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 are thin films, each relatively thin. Therefore, the amount of displacement relative to their thickness is large. Consequently, when the pressure chamber C for liquid ejection contracts, if the piezoelectric element 7 and the vibration plate 15 displace downwardly, the neutral axis A1 of the vibration plate 15 may shift upward.

[0092] Figure 9 as well as Figure 10 1 and 2 are diagrams for explaining the displacement of the neutral axis A1 of the vibration plate 15. Figure 9 As shown, when the piezoelectric element 7 and the vibration plate 15 are not displaced, the distance from the piezoelectric element 7 to the neutral axis A1 is a. In addition, the neutral axis A1 is not compressed or contracted, and the stress of the vibration plate 15 in the axial direction along the XY plane is 0 (zero).

[0093] like Figure 10As shown, if the piezoelectric element 7 and the vibration plate 15 are displaced to protrude downward, the neutral axis A1 is displaced upward. Therefore, the distance b from the piezoelectric element 7 to the neutral axis A1 is shorter than the aforementioned distance a.

[0094] Figure 11 Graph showing the relationship between the displacement of the piezoelectric element 7 and the ejection amount of ink. Figure 11 Line segment L11 represents the ideal ejection amount (ideal displacement amount), line segment L12 represents the ejection amount of the upper piezoelectric body in the two stacked thin film piezoelectric bodies (the actual displacement amount of the upper piezoelectric body), and line segment L13 represents the ejection amount of the lower piezoelectric body (the actual displacement amount of the lower piezoelectric body).

[0095] The displacement of the neutral axis A1 depends on the displacement of the piezoelectric element 7 and the vibration plate 15. Figure 11 As shown, during the contraction of the pressure chamber C, when the displacement is small, the displacement of the neutral axis A1 has little effect. Therefore, when the displacement is small, the discharge rates of the upper and lower piezoelectric elements do not deviate from the ideal discharge rates. However, when the displacement is large, the effect of the displacement of the neutral axis A1 becomes significant. When the displacement is large, the discharge rates of the upper and lower piezoelectric elements deviate from the ideal discharge rates.

[0096] In particular, the first thin film piezoelectric body 72 is located closer to the neutral axis A1 than the second thin film piezoelectric body 74. Therefore, it is easily affected by the reduction in ejection volume caused by the displacement of the neutral axis A1. Figure 11 As shown, the greater the displacement, the more the ink ejection volume achieved by the lower piezoelectric element, i.e., the first thin-film piezoelectric element 72, deviates from the generally assumed ideal ejection volume. In other words, the wider the operating voltage range, the more the ink ejection volume achieved by the first thin-film piezoelectric element 72 deviates from the generally assumed ideal ejection volume. Therefore, the greater the displacement, the more difficult it becomes to control the desired ejection characteristics.

[0097] On the other hand, the second thin-film piezoelectric body 74 is separated from the neutral axis A1 by a considerable amount compared to the first thin-film piezoelectric body 72. Therefore, even if the neutral axis A1 shifts slightly, the effect is minimal. Therefore, even with a small amount of displacement, the reduction in discharge volume caused by the second thin-film piezoelectric body 74 compared to the first thin-film piezoelectric body 72 is not particularly detrimental.

[0098] A voltage is applied to the first thin-film piezoelectric element 72 via the independent electrode 73 and the first common electrode 71, and a voltage is applied to the second thin-film piezoelectric element 74 via the independent electrode 73 and the second common electrode 75. Furthermore, the first common electrode 71 and the second common electrode 75 are electrically connected. Therefore, while the voltage range applied to the first thin-film piezoelectric element 72 and the voltage range applied to the second thin-film piezoelectric element 74 differ in sign, their absolute values ​​are the same. In this context, if the displacement of the first and second thin-film piezoelectric elements 72, 74 in response to voltage changes is the same, the following problem arises. If the voltage range is increased to maximize ejection characteristics, while the second thin-film piezoelectric element 74 will not experience significant problems, the ejection characteristics of the first thin-film piezoelectric element 72 (the actual ejection amount of the lower piezoelectric element) will deteriorate, particularly in the high displacement range, making it difficult to maintain linear ejection characteristics. On the other hand, if the voltage range is reduced, while linearity is maintained, neither the first nor the second thin-film piezoelectric element 72, 74 will initially be able to utilize the high displacement range, potentially failing to achieve adequate ejection characteristics. In this way, when the first thin film piezoelectric material 72 and the second thin film piezoelectric material 74 have the same physical properties, since their voltage ranges are the same, a conflict problem may arise.

[0099] Therefore, in this embodiment, the structures of the first thin film piezoelectric layer 72 and the second thin film piezoelectric layer 74 are set so that the displacement amounts when voltage is applied are different between the first thin film piezoelectric layer 72 and the second thin film piezoelectric layer 74 .

[0100] Specifically, during the contraction period T1, which is the period during which the reference voltage E0 and the drive voltage Com are applied when the pressure chamber C contracts to eject ink, the displacement Sx of the first thin film piezoelectric layer 72 is smaller than the displacement Sy of the second thin film piezoelectric layer 74. That is, during the contraction period T1, when the voltage within the same voltage range RE is applied to the first thin film piezoelectric layer 72 and the second thin film piezoelectric layer 74, the displacement Sx of the first thin film piezoelectric layer 72 is smaller than the displacement Sy of the second thin film piezoelectric layer 74.

[0101] In this embodiment, the displacement amount Sx of the first thin-film piezoelectric body 72 is the displacement amount evaluated using the first thin-film piezoelectric body 72 in a state not incorporated into the piezoelectric element 7. In other words, the displacement amount Sx is not the displacement amount in a state incorporated into the piezoelectric element 7, but rather the displacement amount evaluated independently of the first thin-film piezoelectric body 72 formed using the same conditions (manufacturing method, materials, properties, etc.) as the first thin-film piezoelectric body 72 in a state incorporated into the piezoelectric element 7. Similarly, the displacement amount Sy of the second thin-film piezoelectric body 74 is the displacement amount evaluated independently of the second thin-film piezoelectric body 74 in a state not incorporated into the piezoelectric element 7.

[0102] In the second thin film piezoelectric body 74, increasing the displacement Sy can maximize the ejection characteristics. On the other hand, in the first thin film piezoelectric body 72, decreasing the displacement reduces the adverse effects of displacement even if the neutral axis A1 is displaced.

[0103] In order to set such a difference in displacement, for example, each thin film piezoelectric body is configured to have a different hysteresis. Specifically, the first thin film piezoelectric body 72 has Figure 12 The butterfly curve of the second thin film piezoelectric body 74 has Figure 13 Butterfly curve.

[0104] in addition, Figure 12 as well as Figure 13 However, as long as the displacement Sx of the first thin-film piezoelectric layer 72 is smaller than the displacement Sy of the second thin-film piezoelectric layer 74 during the contraction period T1, the butterfly curves of the first thin-film piezoelectric layer 72 and the second thin-film piezoelectric layer 74 may be identical.

[0105] Figure 12 Graph showing the butterfly curve C1 of the first thin film piezoelectric substance 72 . Figure 13 is a diagram showing the butterfly curve C2 of the second thin film piezoelectric layer 74. Figure 12 as well as Figure 13 In the graph, the horizontal axis represents voltage [V], and the vertical axis represents displacement of the thin film piezoelectric body [nm]. The vertical axis can also be understood as the expansion and contraction of the thin film piezoelectric body.

[0106] In addition, the displacement amount is the amount of expansion and contraction of each thin film piezoelectric body before it is assembled as a piezoelectric element 7 into the liquid ejection head 1. Even before being assembled into the liquid ejection head 1, each thin film piezoelectric body is arranged along the XY plane, with the Z axis being the thickness direction. In addition, even before being assembled into the liquid ejection head 1, each thin film piezoelectric body is displaced to the lower side, which is the Z1 direction, and to the upper side, which is the Z2 direction. In this case, the displacement amount of the thin film piezoelectric body indicates the extent to which the thin film piezoelectric body is displaced downward from the position where the thin film piezoelectric body is displaced to the uppermost side, under the condition that the position where the thin film piezoelectric body is displaced to the uppermost side is set to 0. In other words, the displacement amount of the thin film piezoelectric body indicates the relative position when the position where the thin film piezoelectric body is displaced to the uppermost side is used as a reference.

[0107] Figure 12 The butterfly curve C1 of the first thin-film piezoelectric layer 72 shown 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 where the displacement decreases from the first saturation negative voltage -E1 to the first coercive electric field voltage, which is a positive value, that is, the first coercive voltage +Ec1. The first saturation negative voltage -E1 is the voltage at which the displacement reaches the maximum on the negative side of the butterfly curve C1. The coercive electric field is polarized to 0 μC / cm. 2 The magnitude of the electric field when .

[0108] The second path Rsv2 is a path where the displacement increases from the first coercive voltage +Ec1, which is the voltage of the first coercive electric field, to the first saturated positive voltage +E1. The first saturated positive voltage +E1 is the voltage at which the displacement reaches its maximum on the positive side of the butterfly curve C1. The third path Rsv3 is a path where the displacement decreases from the first saturated positive voltage +E1 to the second coercive voltage -Ec1, which is the voltage of the second coercive electric field, which is a negative value. The fourth path Rsv4 is a path where the displacement increases from the second coercive voltage -Ec1, which is the voltage of the second coercive electric field, to the first saturated negative voltage -E1.

[0109] The displacement of the first thin-film piezoelectric substance 72 when the voltage is changed from the first saturated negative voltage -E1 to the first saturated positive voltage +E1 changes along the first path Rsv1 and the second path Rsv2, respectively. The displacement of the first thin-film piezoelectric substance 72 when the voltage is changed from the first saturated positive voltage +E1 to the first saturated negative voltage -E1 changes along the third path Rsv3 and the fourth path Rsv4, respectively.

[0110] Figure 13The butterfly curve C2 of the second thin-film piezoelectric layer 74 shown 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 where the displacement decreases from the second saturation negative voltage -E2 to the third coercive electric field voltage, which is a positive value, i.e., the third coercive voltage +Ec2. The second saturation negative voltage -E2 is the voltage at which the displacement reaches its maximum on the negative side of the butterfly curve C1.

[0111] The sixth path Rsv6 is a path where the displacement increases from the third coercive voltage +Ec2, which is the voltage of the third coercive electric field, to the second saturated positive voltage +E2. The second saturated positive voltage +E2 is the voltage at which the displacement reaches its maximum on the positive side of the butterfly curve C1. The third path Rsv3 is a path where the displacement decreases from the second saturated positive voltage +E2 to the fourth coercive voltage -Ec2, which is the voltage of the negative fourth coercive electric field. The fourth path Rsv4 is a path where the displacement increases from the fourth coercive voltage -Ec2, which is the voltage of the second coercive electric field, to the second saturated negative voltage -E2.

[0112] The displacement of the second thin-film piezoelectric substance 74 when the voltage is changed from the second saturated negative voltage -E2 to the second saturated positive voltage +E2 changes along the fifth path Rsv5 and the sixth path Rsv6, respectively. Furthermore, the displacement of the second thin-film piezoelectric substance 74 when the voltage is changed from the second saturated positive voltage +E2 to the second saturated negative voltage -E2 changes along the seventh path Rsv7 and the eighth path Rsv8, respectively.

[0113] Figure 14 For the Figure 8 The figure illustrates the path Lx of the butterfly curve C1 when the applied voltage Ea is applied to the first thin film piezoelectric layer 72. Furthermore, since the upper side of the first thin film piezoelectric layer 72 is the driving voltage Com and the lower side is the reference voltage VBS, the applied voltage Ea, that is, the actual "voltage difference" applied to the first thin film piezoelectric layer 72, is almost negative (it becomes positive only when the reference voltage VBS is higher than the driving voltage Com). Figure 15 For the Figure 8 1 is a diagram illustrating the path Ly of the butterfly curve C2 when the applied voltage Ea is applied to the second thin-film piezoelectric layer 74. Furthermore, since the upper side of the second thin-film piezoelectric layer 74 is VBS and the lower side is Com, the applied voltage Ea, that is, the actual "voltage difference" applied to the second thin-film piezoelectric layer 74, is almost always a positive value (it becomes a negative value only when the reference voltage VBS is higher than the drive voltage Com).

[0114] like Figure 14As shown in FIG. 1 , when the voltage Ea is applied to the first thin film piezoelectric body 72, the first thin film piezoelectric body 72 is displaced along the path Lx indicated by the solid line. Figure 15 As shown in FIG. 1 , when the applied voltage Ea is applied to the second thin film piezoelectric substance 74 , the second thin film piezoelectric substance 74 is displaced along a path Ly indicated by a solid line.

[0115] First, the transition of the voltage and displacement of the first thin film piezoelectric body 72 will be described. Figure 8 During the expansion period T2 when the intermediate voltage EK changes toward the minimum voltage EM, the voltage applied to the first thin film piezoelectric body 72 shifts from negative to positive. Figure 14 As shown, the displacement of the first thin film piezoelectric layer 72 during the expansion period T2 follows the first path Rsv1. When the first coercive voltage +Ec1 is reached, the first thin film piezoelectric layer 72 is displaced to the bottom, and the displacement amount becomes zero.

[0116] In from Figure 8 During the contraction period T1 during which the minimum voltage EM changes to the maximum voltage EN, the voltage applied to the first thin film piezoelectric body 72 changes from positive to negative. Figure 14 As shown, the displacement of the first thin film piezoelectric layer 72 during the contraction period T1 changes along the fourth path Rsv4 , and the first thin film piezoelectric layer 72 is displaced until it reaches the vicinity of the first saturation negative voltage −E1 .

[0117] However, this is because the minimum voltage EM is set near the first coercive voltage +Ec1 and the maximum voltage EN is set 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 first path Rsv1 may shift to the fourth path Rsv4 in the middle of the first path Rsv1. In addition, if the maximum voltage EN is set to a value larger than the first saturation negative voltage -E1, the first path Rsv1 may shift to the first path Rsv1 in the middle of 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 of the first thin film piezoelectric body 72 during the contraction period T1 is the displacement Sx = 680nm when the maximum voltage EN = -21.5V is applied.

[0118] Next, the transition of the voltage and displacement of the second thin film piezoelectric body 74 will be described. Figure 8 During the expansion period T2 when the intermediate voltage EK changes toward the minimum voltage EM, the voltage applied to the second thin film piezoelectric body 74 shifts from positive to negative. Figure 15 As shown, the second thin film piezoelectric layer 74 is displaced during the expansion period T2 along the seventh path Rsv7. When the fourth coercive voltage -Ec2 is reached, the second thin film piezoelectric layer 74 is displaced to the bottom, and the amount of displacement becomes zero.

[0119] In from Figure 8 During the contraction period T1 during which the minimum voltage EM changes to the maximum voltage EN, the voltage applied to the second thin film piezoelectric body 74 changes from negative to positive. Figure 15 As shown, the displacement of the second thin film piezoelectric layer 74 during the contraction period T1 changes along the sixth path Rsv6 , and the second thin film piezoelectric layer 74 is displaced until it reaches the vicinity of the second saturation positive voltage +E2 .

[0120] 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 positive saturation 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 lower than the second negative saturation voltage +E2 = +25V. Therefore, the displacement of the second thin film piezoelectric layer 74 during the contraction period T1 is the displacement Sy = 790nm when the maximum voltage EN = +21.5V is applied.

[0121] Furthermore, as described above, a voltage having a minimum voltage EM = +2.5 V and a maximum voltage EN = -21.5 V is applied to the first thin-film piezoelectric layer 72, and a voltage having a minimum voltage EM = -2.5 V and a maximum voltage EN = +21.5 V is applied to the second thin-film piezoelectric layer 74. This is because, as described above, voltages having the same absolute value but opposite signs are applied to the first and second thin-film piezoelectric layers 72 and 74.

[0122] like Figure 14 as well as Figure 15 As shown, the displacement S10 of the first thin film piezoelectric layer 72 at the first saturation negative voltage -E1 is smaller than the displacement S20 of the second thin film piezoelectric layer 74 at the second saturation positive voltage +E2. Therefore, during the contraction period T1, the displacement Sx of the first thin film piezoelectric layer 72 tends to be smaller than the displacement Sy of the second thin film piezoelectric layer 74.

[0123] By making the displacement Sx of the first thin-film piezoelectric body 72 smaller than the displacement Sy of the second thin-film piezoelectric body 74 during the contraction period T1, even if the neutral axis A1 shifts, the adverse effects on the first thin-film piezoelectric body 72 caused by this shift can be reduced. On the other hand, the displacement Sy of the second thin-film piezoelectric body 74 is larger than the displacement Sx of the first thin-film piezoelectric body 72. Therefore, as described above, the second thin-film piezoelectric body 74 can improve the discharge characteristics. The piezoelectric element 7 having such a first thin-film piezoelectric body 72 and a second thin-film piezoelectric body 74 can significantly improve the discharge characteristics compared to a case where the thin-film piezoelectric body is formed as a single layer, or can be replaced with a component with a lower rated voltage, significantly reducing costs.

[0124] Furthermore, the displacement amount S10 of the first thin film piezoelectric body 72 at the first saturation negative voltage -E1 is preferably not less than 80% and not more than 95% of the displacement amount S20 of the second thin film piezoelectric body 74 at the second saturation positive voltage +E2. Figure 14 as well as Figure 15 In the example shown, the displacement amount S10 is 710 nm, and the displacement amount S20 is 820 nm. Therefore, the displacement amount Sx is 87% of the displacement amount Sy.

[0125] Furthermore, the displacement Sx of the first thin film piezoelectric layer 72 during the contraction period T1 is preferably not less than 80% and not more than 95% of the displacement Sy of the second thin film piezoelectric layer 74. Figure 14 as well as Figure 15 In the example shown, the displacement amount Sx is 680 [nm] and the displacement amount Sy is 790 [nm]. Therefore, the displacement amount Sx is 86% of the displacement amount Sy.

[0126] If the displacement Sx is less than the lower limit, the effect of the shift of the neutral axis A1 may become more significant than if it is above the lower limit. For example, if the second thin-film piezoelectric layer 74 is too thick, the displacement Sx may become less than the lower limit. Furthermore, if the displacement Sx exceeds the upper limit, ensuring adequate ejection characteristics may become more difficult than if it is below the upper limit. For example, if the first thin-film piezoelectric layer 72 is too thin, the displacement Sx may exceed the upper limit.

[0127] Furthermore, as described above, during the contraction period T1, the voltage of the first thin film piezoelectric body 72 shifts from positive to negative. On the other hand, during the contraction period T1, the voltage of the second thin film piezoelectric body 74 shifts from negative to positive. Thus, during the contraction period T1, even if opposite voltages are applied to the first thin film piezoelectric body 72 and the second thin film piezoelectric body 74, the first thin film piezoelectric body 72 and the second thin film piezoelectric body 74 can be displaced in the same direction. Specifically, during the contraction period T1, the first thin film piezoelectric body 72 and the second thin film piezoelectric body 74 can be displaced downward. Therefore, compared to the case where the thin film piezoelectric body is a single layer, it is possible to significantly improve the ejection characteristics or replace it with a component with a lower rated voltage to significantly reduce costs.

[0128] Furthermore, as described above, the displacement of the first thin-film piezoelectric layer 72 during the contraction period T1 changes so as to follow the fourth path Rsv4. Furthermore, the displacement of the first thin-film piezoelectric layer 72 during the contraction period T1 changes so as not to follow the first path Rsv1, the second path Rsv2, and the third path Rsv3. Therefore, during the contraction period T1, the first thin-film piezoelectric layer 72 does not follow the third path Rsv3, but instead rapidly displaces along the fourth path Rsv4 starting from the first coercive voltage +Ec1 of 0 V. Consequently, the displacement during the contraction period T1 can be increased in a relatively short period of time.

[0129] Furthermore, the displacement of the second thin-film piezoelectric layer 74 during the contraction period T1 changes so as to follow the sixth path Rsv6. Furthermore, the displacement of the second thin-film piezoelectric layer 74 during the contraction period T1 changes so as not to follow the fifth path Rsv5, the seventh path Rsv7, and the eighth path Rsv8. Therefore, during the contraction period T1, the second thin-film piezoelectric layer 74 does not follow the fifth path Rsv5, but instead rapidly displaces along the sixth path Rsv6 starting from the fourth coercive voltage -Ec2 of 0 V. Consequently, the amount of displacement during the contraction period T1 can be increased in a relatively short period of time.

[0130] Furthermore, the displacement S10 of the first thin-film piezoelectric layer 72 at the first saturation negative voltage -E1 is smaller than the displacement Sx0 at the first saturation positive voltage +E1 of the first thin-film piezoelectric layer 72. In this embodiment, the negative side of the butterfly curve C1 of the first thin-film piezoelectric layer 72 is used. In this case, by making the displacement S10 smaller than the displacement Sx0, it is easier to make the displacement Sx of the first thin-film piezoelectric layer 72 smaller than the displacement Sy of the second thin-film piezoelectric layer 74 during the contraction period T1.

[0131] Furthermore, the displacement amount Sy0 of the second thin-film piezoelectric layer 74 at the second saturation negative voltage -E2 is smaller than the displacement amount S20 at the first saturation positive voltage +E2 of the second thin-film piezoelectric layer 74. In this embodiment, the positive side of the butterfly curve C2 of the second thin-film piezoelectric layer 74 is used. In this case, by making the displacement amount S20 larger than the displacement amount Sy0, it is easier to make the displacement amount Sy of the second thin-film piezoelectric layer 74 larger than the displacement amount Sx of the first thin-film piezoelectric layer 72 during the contraction period T1.

[0132] 1-4e. First alignment control layer 76 and second alignment control layer 77

[0133] like Figure 4 as well as Figure 5 As shown, the first orientation control layer 76 is provided between the first thin film piezoelectric layer 72 and the first common electrode 71. The second orientation control layer 77 is provided between the second thin film piezoelectric layer 74 and the independent electrode 73. The first orientation control layer 76 controls the orientation of the first thin film piezoelectric layer 72, and the second orientation control layer 77 controls the orientation of the second thin film piezoelectric layer 74.

[0134] The provision of the first orientation control layer 76 and the second orientation control layer 77 enables control of the orientation of the first thin-film piezoelectric layer 72 and the second thin-film piezoelectric layer 74. Specifically, the first orientation control layer 76 enables the crystals of the first thin-film piezoelectric layer 72 to be preferentially oriented toward a predetermined plane orientation, or the degree of orientation in a predetermined plane orientation to be adjusted. Similarly, the second orientation control layer 77 enables the crystals of the second thin-film piezoelectric layer 74 to be preferentially oriented toward a predetermined plane orientation, or the degree of orientation in a predetermined plane orientation to be adjusted.

[0135] For example, by preferentially orienting the crystals of the first thin-film piezoelectric layer 72 toward the (100) plane using the first orientation control layer 76, the piezoelectric characteristics of the piezoelectric element 7 can be improved compared to a case where the crystals are preferentially orientated toward the (110) plane. Similarly, by preferentially orienting the crystals of the second thin-film piezoelectric layer 74 toward the (100) plane using the second orientation control layer 77, the piezoelectric characteristics of the piezoelectric element 7 can be improved compared to a case where the crystals are preferentially orientated toward the (110) plane. Consequently, the displacement efficiency of the piezoelectric element 7 can be improved.

[0136] Furthermore, the crystal orientations of the first thin-film piezoelectric layer 72 and the second thin-film piezoelectric layer 74 can be analyzed using X-ray diffraction (XRD) intensity curves. Furthermore, preferential orientation toward the (100) plane means that the peak intensity corresponding to the (100) plane is higher than the peak intensity corresponding to other orientations, specifically, the (110) plane. In particular, by aligning at least 50%, or even at least 80%, of the thin-film piezoelectric crystals toward the (100) plane, the displacement efficiency of the piezoelectric element 7 can be improved.

[0137] Furthermore, for example, the first orientation control layer 76 can adjust the degree of orientation of the crystals of the first thin-film piezoelectric body 72 toward 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 body 72 toward the (100) plane. Therefore, by providing the first orientation control layer 76 for controlling the orientation of the first thin-film piezoelectric body 72 and the second orientation control layer 77 for controlling the orientation of the second thin-film piezoelectric body 74, the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 can each be oriented to a desired degree. Therefore, it is possible to set optimal physical property values ​​for each of the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74.

[0138] Each of the first orientation control layer 76 and the second orientation control layer 77 includes, for example, titanium (Ti) or a composite oxide having a perovskite structure. The composite oxide having a perovskite structure includes, for example, any of Ni (nickel), lanthanum (La), Bi (bismuth), lead (Pb), titanium (Ti), and iron (Fe) as constituent elements.

[0139] Specifically, as composite oxides having a perovskite structure, for example, 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 In addition, each of the first alignment control layer 76 and the second alignment control layer 77 may be a single layer or a multilayer layer. Therefore, the first alignment control layer 76 and the second alignment control layer 77 may be made of one material or a plurality of materials.

[0140] In addition, in the aforementioned Pb X Bi (a-x) FE y Ti (b-y) O ZIn the formula (a), a>x and b>y. In addition, X / (aX) preferably satisfies 0.04<X / (aX)<1.40. Moreover, in order to orient toward the (100) plane, X / (aX)<0.72 is more preferable. In addition, b=1 is preferred, and a / b is preferably 0.8<(a / b)<1.4. In addition, z preferably satisfies 2.8<z<3.2.

[0141] Examples of conditions satisfying these preferred ranges include a=1.2, b=1.0, x=0.1, and y=0.5.

[0142] In addition, in Pb X Fe y Ti (1-y) O Z In the equation, x satisfies the relationship of 1.00≤x<2.00. In order to orient toward the (100) plane, x preferably satisfies the relationship of 1.00≤x<1.50. In addition, y satisfies the relationship of 0.10≤Y≤0.90. In order to orient toward the (100) plane, it preferably satisfies the relationship of 0.20≤y≤0.80. In addition, z typically satisfies the relationship of z=3.00. However, z does not have to satisfy this relationship.

[0143] In addition, in the following text, Pb X Bi (a-x) FE y Ti (b-y) O Z It is only recorded as "PbBiFeTiO". X Fe y Ti (1-y) O Z It is only recorded as "PbFeTiO".

[0144] In particular, each of the first and second orientation control layers 76 and 77 preferably contains Bi, Fe, Ti, and Pb. Specifically, for example, each of the first and second orientation control layers 76 and 77 is preferably PbBiFeTiO. PbBiFeTiO exhibits superior thin-film piezoelectric orientation control performance compared to PbFeTiO, lanthanum nickelate, and titanium. Therefore, for example, the degree of orientation of the second thin-film piezoelectric layer 74 toward the (100) plane can be increased. Consequently, the piezoelectric efficiency of the second thin-film piezoelectric layer 74 can be improved.

[0145] In addition, the second orientation control layer 77 containing PbBiFeTiO has self-orientation, which is the property of self-orientation to a predetermined plane orientation. Therefore, if the second orientation control layer 77 is PbBiFeTiO, it is difficult to be affected by the plane orientation of the substrate of the second orientation control layer 77. Therefore, no matter what the plane orientation of the substrate is, the second orientation control layer 77 will not be affected by the substrate, but will self-orient to a predetermined plane orientation. Therefore, under the influence of the plane orientation of the second orientation control layer 77, the second thin film piezoelectric body 74 can be oriented to the same plane orientation as the second orientation control layer 77. Specifically, the second orientation control layer 77 is oriented to the (100) plane. Then, the second thin film piezoelectric body 74 is oriented to the (100) plane by the second orientation control layer 77. In addition, if it is a layer that does not have self-orientation, it will be affected by the plane orientation of the substrate and oriented to a plane orientation other than the predetermined plane orientation.

[0146] From the perspective of self-orientation, the first orientation control layer 76 and the second orientation control layer 77 may also be PbFeTiO. PbFeTiO has self-orientation similarly to PbBiFeTiO. In addition, it is considered that the layer composed of Ti and the layer composed of PbTiO X However, the formed layer does not have self-orientation.

[0147] In addition, if Figure 4 As shown, the second orientation control layer 77 includes a first portion 771 and a second portion 772. The first portion 771 is located directly above and in contact with the independent electrode 73. The active portion 741 of the second thin film piezoelectric layer 74 is provided on the first portion 771. Furthermore, the second portion 772 is located above and in contact with the first common electrode 71. The second portion 772 does not overlap with the independent electrode 73 when viewed from above.

[0148] Thus, the substrate of the second orientation control layer 77 comprises different portions, rather than identical portions. In other words, the second orientation control layer 77 contacts two or more different layers. Thus, even in the case of different substrates, the second orientation control layer 77 possesses self-orientation properties, allowing it to orient itself in a predetermined plane orientation without being affected by the substrate. Consequently, the second thin-film piezoelectric layer 74 can be preferentially oriented in a predetermined plane orientation without being affected by a complex substrate.

[0149] Furthermore, the thickness D76 of the first orientation control layer 76 is thinner than the thickness D72 of the first thin-film piezoelectric layer 72, and the thickness D77 of the second orientation control layer 77 is thinner than the thickness D74 of the second thin-film piezoelectric layer 74. Each thickness is an average length along the Z-axis. While not particularly limited to these values, thicknesses D76 and D77 are, for example, within a range of 20 nm to 200 nm.

[0150] The thickness D77 of the second orientation control layer 77 may be thicker than the thickness D76 of the first orientation control layer 76. Advantages of this structure are as follows. Figure 17 As shown in (e), when etching the first thin film piezoelectric body 72, the first orientation control layer 76 is also patterned. At this time, due to errors in the etching time, it is possible that the etching is carried out to the extent of penetrating the first orientation control layer 76, and then cutting the first common electrode 71. However, since the first thin film piezoelectric body 72 is relatively thin, the etching time is not short, making it unlikely that such a situation will occur. On the other hand, as Figure 18 As shown in (c), when etching the second thin-film piezoelectric layer 74, the second orientation control layer 77 is patterned. Similarly, errors in etching time can occur, potentially causing etching to penetrate the second orientation control layer 77 and, in turn, to cut into the first common electrode 71. Here, the second thin-film piezoelectric layer 74 is thicker than the first thin-film piezoelectric layer 72. Therefore, etching the second thin-film piezoelectric layer 74 takes longer than etching the first thin-film piezoelectric layer 72, increasing the likelihood of etching errors. Therefore, the likelihood of excessive etching penetrating the second orientation control layer 77 and thus cutting off the first common electrode 71 is higher than that of the first orientation control layer 76. In contrast, by thickening the second orientation control layer 77, the risk of cutting off the first common electrode 71 is reduced. Furthermore, since the orientation control layer serves to lower the dielectric constant between the electrodes and the thin-film piezoelectric layers during use, it is preferable to make the orientation control layer as thin as possible. Therefore, the first alignment control layer 76 , which inherently has a lower risk of being scraped off, is made thinner than the second alignment control layer 77 .

[0151] In addition, from another point of view, the thickness D77 of the second orientation control layer 77 can also be thinner than the thickness D76 of the first orientation control layer 76. The advantages brought by this structure are as follows. Each of the first orientation control layer 76 and the second orientation control layer 77 will be affected by the unevenness of each substrate. In particular, the first orientation control layer 76 is closer to the vibration plate 15 than the second orientation control layer 77, and is therefore more easily affected by the unevenness of the vibration plate 15 or the mixing of elements (such as Zr) contained in the vibration plate 15. In the case of wanting to suppress this influence, the thickness D76 of the first orientation control layer 76 is preferably thicker. On the other hand, since the second orientation control layer 77 is farther away from the vibration plate 15 than the first orientation control layer 76, this influence can also be not considered so much. In addition, as described above, since making the orientation control layer thicker unnecessarily will cause a decrease in the dielectric constant, the second orientation control layer 77, which is less affected by unevenness or element mixing, is preferably thinner than the first orientation control layer 76.

[0152] In addition, the thicknesses of the first alignment control layer 76 and the second alignment control layer 77 may be the same as each other.

[0153] 1-5. Method for Manufacturing Piezoelectric Element 7

[0154] Figure 16 FIG. 1 is a flow chart showing a method for manufacturing the piezoelectric element 7, which is a part of the method for manufacturing the liquid ejecting head 1. Figure 16 As shown, the method for manufacturing the piezoelectric element 7, which is part of the method for manufacturing the liquid ejecting 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 the order described above.

[0155] Figure 17 as well as Figure 18 Respectively for Figure 16 A diagram illustrating a method for manufacturing the piezoelectric element 7 shown. Figure 17 (a) is a diagram for explaining the first step S1. In the first step S1, the first common electrode 71 is formed on the vibration plate 15. The first common electrode 71 is formed using a known film forming technique such as vapor deposition or sputtering, and a known processing technique such as photolithography and etching.

[0156] Figure 17 (b) is a diagram for explaining the second step S2. In the second step S2, a first alignment control layer 76 is formed on the first common electrode 71. The first alignment control layer 76 is formed by a known film forming technique such as vapor deposition or sputtering.

[0157] Figure 17 (c) is a diagram for explaining the third step S3. In the third step S3, a first thin film piezoelectric layer 72 is formed on the first orientation control layer 76. The first thin film piezoelectric layer 72 is formed, for example, by forming a precursor layer of the first thin film piezoelectric layer 72 using a sol-gel method and sintering the precursor layer to crystallize it. Alternatively, the first thin film piezoelectric layer 72 can be formed by sputtering. However, by using a sol-gel method, the first thin film piezoelectric layer 72 can be appropriately formed to a thickness of less than 2 μm, and further less than 1 μm.

[0158] Figure 17 (d) is a diagram for explaining the fourth step S4. In the fourth step S4, the independent electrode 73 is formed on the first thin film piezoelectric layer 72. The first common electrode 71 is formed by a known film forming technique such as vapor deposition or sputtering.

[0159] Figure 17 (e) is a diagram for explaining the fifth step S5. In the fifth step S5, the independent electrodes 73, the first thin film piezoelectric layer 72, and the first orientation control layer 76 are patterned. These patterning processes are performed using a known processing technique such as etching.

[0160] Figure 18 (a) is a diagram for explaining the sixth step S6. In the sixth step S6, a second alignment control layer 77 is formed on the independent electrode 73. The second alignment control layer 77 is formed by a known film forming technique such as vapor deposition or sputtering.

[0161] Figure 18 (b) is a diagram for explaining the seventh step S7. In the seventh step S7, a second thin film piezoelectric layer 74 is formed on the second orientation control layer 77. The second thin film piezoelectric layer 74 is formed, for example, by forming a precursor layer of the second thin film piezoelectric layer 74 using a sol-gel method and sintering the precursor layer to crystallize it. Alternatively, the second thin film piezoelectric layer 74 can be formed by sputtering. However, by using a sol-gel method, the second thin film piezoelectric layer 74 can be appropriately formed to a thickness of less than 2 μm, and further less than 1 μm.

[0162] Figure 18(c) is a diagram illustrating the eighth step S8. In the eighth step S8, the second thin-film piezoelectric layer 74 and the second orientation control layer 77 are patterned. This patterning is performed using known processing techniques such as etching. During this etching, the active portion 741 and the passive portion 742 are etched to different depths. Furthermore, this etching process forms the first portion 771 and the second portion 772 of the second orientation control layer 77.

[0163] Figure 18 (d) is a diagram for explaining 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 layer 74. For example, the second common electrode 75 is formed using a known film forming technique such as vapor deposition or sputtering, or a known processing technique such as photolithography and etching.

[0164] The piezoelectric element 7 of the liquid ejecting head 1 is manufactured by the above method. According to the above method, the piezoelectric element 7 can be manufactured simply and with high precision. Furthermore, according to the above method, the first thin-film piezoelectric body 72 is formed on the first orientation control layer 76, thereby enabling alignment control by the first orientation control layer 76. Furthermore, the second thin-film piezoelectric body 74 is formed on the second orientation control layer 77, thereby enabling alignment control by the second orientation control layer 77. Therefore, since the physical properties of the first thin-film piezoelectric body 72 and the second thin-film piezoelectric body 74 can be adjusted to desired values, a piezoelectric element 7 having desired piezoelectric characteristics can be obtained.

[0165] Furthermore, in the aforementioned sixth step S6, 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 misorientation within the second thin-film piezoelectric layer 74. Specifically, it reduces the misorientation between the active and passive portions. Consequently, stress failure of the second thin-film piezoelectric layer 74 is minimized, making cracks less likely to form in the second thin-film piezoelectric layer 74, thereby improving the reliability of the piezoelectric element 7.

[0166] In addition, it can also be constructed in the following manner. The second thin film piezoelectric body 74 is farther from the neutral axis A1 than the first thin film piezoelectric body 72. Therefore, the strain of the second thin film piezoelectric body 74 itself will become larger, which may cause greater damage to the second thin film piezoelectric body 74. On the other hand, the spacing distance between the first thin film piezoelectric body 72 and the neutral axis A1 is not greater than that of the second thin film piezoelectric body 74. Therefore, it is difficult for the first thin film piezoelectric body 72 to be strained as much as the second thin film piezoelectric body 74. Therefore, by making the second thin film piezoelectric body 74 relatively thin to suppress damage, and making the first thin film piezoelectric body 72, which is less affected by damage, relatively thicker, the ejection characteristics can be improved as much as possible. In this way, the thickness of the first thin film piezoelectric body 72 can also be made thicker than the thickness of the second thin film piezoelectric body 74.

[0167] In addition, it can also be constructed in the following manner. The larger the Young's modulus of the thin film piezoelectric body, the greater the force generated by each thin film piezoelectric body. Therefore, in a structure in which multiple thin film piezoelectric bodies are stacked as in the present embodiment, in order to increase the displacement of the piezoelectric element 7 to improve the ejection characteristics as much as possible, it is preferred to increase the Young's modulus of each of the first thin film piezoelectric body 72 and the second thin film piezoelectric body 74. However, for the second thin film piezoelectric body 74, increasing the Young's modulus may also have disadvantages. In the manufacture of the piezoelectric element 7, when each layer is formed in sequence from bottom to top, after the second thin film piezoelectric body 74 is formed, a second common electrode 75 and various wirings are formed thereon. In this formation, for example, processing such as etching is performed. The influence of the processing such as etching when forming the second common electrode 75 and various wirings may involve the second thin film piezoelectric body 74 and cause film damage to the second thin film piezoelectric body 74. The larger the Young's modulus, that is, the stronger the film, the more significant the damage during film formation becomes. In view of this, although the larger the Young's modulus of the second thin-film piezoelectric body 74, the better from the perspective of ejection characteristics, it is difficult to increase the Young's modulus of the second thin-film piezoelectric body 74 to the above-mentioned extent when considering film formation damage. On the other hand, the influence of film formation damage on the first thin-film piezoelectric body 72 is relatively small. Therefore, in this embodiment, by increasing the Young's modulus of the first thin-film piezoelectric body 72 in accordance with the situation where the Young's modulus of the second thin-film piezoelectric body 74 cannot be increased, the ejection characteristics of the piezoelectric element 7 as a whole can be ensured. In this way, the Young's modulus of the first thin-film piezoelectric body 72 can also be made larger than the Young's modulus of the second thin-film piezoelectric body 74.

[0168] In addition, from another perspective, it can also be constructed as follows. Limited to the case where the possibility of the above-mentioned film damage is not considered, the Young's modulus of the first thin film piezoelectric body 72 can also be smaller than the Young's modulus of the second thin film piezoelectric body 74. Even if the first thin film piezoelectric body 72 and the second thin film piezoelectric body 74 each generate the same force, the moment will increase if they are away from the neutral axis A1, and therefore the contribution to the ejection characteristics will also increase. Therefore, from the perspective of improving the ejection characteristics as much as possible, it is preferable to increase the Young's modulus of the second thin film piezoelectric body 74. On the other hand, although the contribution of the first thin film piezoelectric body 72 is relatively small, it is preferable to increase the Young's modulus in order to maximize the ejection efficiency. However, if the Young's modulus of the first thin film piezoelectric body 72 is increased in the same way as the second thin film piezoelectric body 74, there is a possibility that the ejection characteristics will be disadvantageous, especially in high-frequency driving. During continuous ink ejection, if residual vibrations within the pressure chamber C from the previous ejection remain during the next ejection, this residual vibration can cause characteristic deviations in the next ejection. When the Young's modulus of the first thin-film piezoelectric layer 72 is low, its flexibility allows for smooth pressure absorption of the residual vibrations. Therefore, characteristic deviations caused by continuous ejection are less likely to occur. However, if the Young's modulus of the first thin-film piezoelectric layer 72 is high, the pressure absorption of the residual vibrations from the previous ejection cannot be fully achieved, potentially leading to characteristic deviations. Naturally, the closer the residual vibrations are to the pressure chamber C, the more effective the pressure absorption of these residual vibrations. Therefore, reducing the Young's modulus of the first thin-film piezoelectric layer 72, located near the pressure chamber C, is crucial for properly suppressing residual vibrations. From this perspective, reducing the Young's modulus of the first thin-film piezoelectric layer 72 relative to that of the second thin-film piezoelectric layer 74 is also effective.

[0169] 2. Modification

[0170] The embodiments described above can be modified in various ways. Specific modifications that can be applied to the embodiments described above are exemplified below.

[0171] The “liquid ejection head” may be a circulation type head having a so-called circulation flow path.

[0172] In addition to being used for dedicated printing, a "liquid ejecting device" can also be used in various devices such as fax machines and copiers. The use of liquid ejecting devices is not limited to printing. For example, a liquid ejecting device that ejects a solution of a color material can be used as a manufacturing device for forming a color filter for a display device such as a liquid crystal display panel. In addition, a liquid ejecting device that ejects a solution of a conductive material can be used as a manufacturing device for forming wiring or electrodes of a wiring substrate. In addition, a liquid ejecting device that ejects a solution of an organic substance related to a living organism can be used as a manufacturing device for manufacturing, for example, a biochip.

[0173] Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the aforementioned embodiments. In addition, the structure of each part of the present invention can be replaced with any structure that performs the same function as the aforementioned embodiment, and any structure can be added.

[0174] Explanation of symbols

[0175] 1…liquid ejection head; 7…piezoelectric element; 15…vibration plate; 20…driving circuit; 71…first common electrode; 72…first thin film piezoelectric body; 73…independent electrode; 74…second thin film piezoelectric body; 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; S20…displacement; Sx…displacement; Sy…displacement; T1…contraction period

Claims

1. A liquid ejection head, characterized in that: The following components are stacked in order from the bottom to the top: A pressure chamber, which is provided with a plurality of pressure chambers; Vibration plate; a first common electrode provided in common with respect 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; Independent electrodes are independently provided for the plurality of pressure chambers and are applied with a driving voltage that changes with time; a second thin film piezoelectric body; a second common electrode provided in common with respect to the plurality of pressure chambers and to which the reference voltage is applied, During a contraction period, in which the reference voltage and the drive voltage are applied when the pressure chamber contracts to eject liquid, a displacement of the first thin film piezoelectric body is smaller than a displacement of the second thin film piezoelectric body.

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

3. The liquid ejection head according to claim 1, wherein The displacement of the first thin film piezoelectric body when the voltage is changed from a first saturation negative voltage to a first saturation positive voltage changes in a manner following a first path and a second path, respectively, wherein the first path is a path in which the displacement decreases from the first saturation negative voltage to a first coercive electric field having a positive value, and the second path is a path in which the displacement increases from the first coercive electric field to the first saturation positive voltage. The displacement of the first thin film piezoelectric body when the voltage is changed from the first saturation positive voltage to the first saturation negative voltage changes in a manner following a third path and a fourth path, respectively, wherein the third path is a path in which the displacement decreases from the first saturation positive voltage to a second coercive electric field having a negative value, and the fourth path is a path in which the displacement increases from the second coercive electric field to the first saturation negative voltage. The displacement of the first thin film piezoelectric body during the contraction period changes so as to follow the fourth path.

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

5. The liquid ejection head according to claim 3, wherein The displacement amount of the first thin film piezoelectric body at the first saturation negative voltage is smaller than the displacement amount of the first thin film piezoelectric body at the first saturation positive voltage.

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

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

8. The liquid ejection head according to claim 6, wherein The displacement amount of the second thin film piezoelectric body at the second saturation negative voltage is smaller than the displacement amount of the second thin film piezoelectric body at the second saturation positive voltage.

9. The liquid ejection head according to claim 8, wherein The displacement amount of the first thin film piezoelectric body at the first saturation negative voltage is smaller than the displacement amount of the second thin film piezoelectric body at the first saturation positive voltage.

10. The liquid ejection head according to claim 1 or 2, wherein: The displacement of the first thin film piezoelectric layer during the contraction period is equal to or greater than 80% and equal to or less than 95% of the displacement of the second thin film piezoelectric layer.

11. A liquid ejection device, characterized in that: have: The liquid ejection head according to any one of claims 1 to 9; A voltage applying circuit is used to apply the reference voltage and the driving voltage.

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