Liquid discharge head and liquid discharge device

Abstract

To provide a liquid discharge head that is excellent in discharging performance, and a liquid discharge device.SOLUTION: The liquid discharge head satisfies a relational expression of I_peak / I_edge<15, where a hysteresis loop showing change of currents generated in a first application process for applying a first waveform and in a third application process for applying a third waveform, with respect to voltages, is set as a first hysteresis loop, a hysteresis loop showing change of currents generated in a second application process for applying a second waveform and in a fourth application process for applying a fourth waveform, with respect to voltages, is set as a second hysteresis loop, a current value of the first hysteresis loop in voltages corresponding to a coercive electric field of a piezoelectric body is set as I_peak, and a current value of the first hysteresis loop at voltages at which a differential between the current value of the first hysteresis loop and a current value of the second hysteresis loop starts to change from zero is set as I_edge.SELECTED DRAWING: Figure 8

Description

[Technical field]

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

[0002] Liquid ejection devices equipped with a liquid ejection head that ejects liquid such as ink onto a medium such as printing paper have been proposed. A known example of such a liquid ejection device is an inkjet printer that uses a piezoelectric method. In the piezoelectric method, a piezoelectric element is used to vibrate a vibration plate that constitutes part of the wall of a pressure chamber. By vibrating the vibration plate with the piezoelectric element, the liquid filled in the pressure chamber is ejected from a nozzle.

[0003] The piezoelectric element of the liquid ejection head described in Patent Document 1 has two electrodes and a piezoelectric body sandwiched between the two electrodes. The piezoelectric body has a saturation polarization, a remanent polarization, and a coercive electric field that satisfy predetermined conditions in the polarization-electric field hysteresis characteristics. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-135748 A Summary of the Invention [Problem to be solved by the invention]

[0005] In general, in a piezoelectric element that is included in a liquid ejection head, a constant reference voltage is applied to one of the two electrodes, regardless of time, and a drive voltage that changes with time is applied to the other electrode. The difference between the reference voltage and the drive voltage is then applied to the piezoelectric body, causing the piezoelectric element to deform. As a result, the deformation of the piezoelectric element causes the vibration plate to vibrate, and ink is ejected.

[0006] When the number of times the piezoelectric element is driven increases, an imprint phenomenon occurs in which the hysteresis shape of the piezoelectric body shifts. As a result, when the number of times the piezoelectric element is driven increases, the ejection amount may decrease. Therefore, it is difficult to obtain stable ejection performance over a long period of time. [Means for solving the problem]

[0007] A liquid ejection head according to a preferred embodiment of the present invention is a liquid ejection head having a first electrode to which a reference voltage is applied, a second electrode to which a drive voltage is applied, and a piezoelectric body provided between the first electrode and the second electrode, the liquid ejection head comprising: a first application process for applying to the piezoelectric body a first waveform that gradually increases from 0 to a first positive voltage and then gradually decreases to 0; a second application process for applying to the piezoelectric body a second waveform that gradually increases from 0 to the first positive voltage and then gradually decreases to 0; a third application process for applying to the piezoelectric body a third waveform that gradually decreases from 0 to a first negative voltage and then gradually increases to 0; and a fourth application process for applying to the piezoelectric body a fourth waveform that gradually decreases from 0 to the first negative voltage and then gradually increases to 0; Among the changes in current generated in the piezoelectric body when the first application process, the second application process, the third application process, and the fourth application process are performed in this order, a hysteresis loop showing the change in current generated in the first application process and the third application process versus voltage is defined as a first hysteresis loop, and a hysteresis loop showing the change in current generated in the second application process and the fourth application process versus voltage is defined as a second hysteresis loop, and the current value of the first hysteresis loop at a voltage corresponding to the coercive electric field of the piezoelectric body is defined as I_peak, and the current value of the first hysteresis loop at a voltage at which the difference between the current value of the first hysteresis loop and the current value of the second hysteresis loop begins to change from 0 is defined as I_edge, where I_peak / I_edge<15 is satisfied. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating a configuration of a liquid ejection device according to a first embodiment. [Diagram 2] FIG. 2 is an exploded perspective view of the liquid ejection head shown in FIG. [Diagram 3] 3 is a cross-sectional view of a portion of the liquid ejection head shown in FIG. 2. [Figure 4] 4 is an enlarged cross-sectional view of a portion of the liquid ejection head shown in FIG. [Diagram 5] 13 is an example of a hysteresis loop showing the relationship between the voltage and charge of a piezoelectric body of a piezoelectric element of a comparative example. [Figure 6] 4 is a hysteresis loop showing the relationship between the voltage and polarization of a piezoelectric body of the piezoelectric element of the present embodiment. [Figure 7] 11A and 11B are diagrams showing butterfly curves before and after long-term voltage application to the piezoelectric body of the present embodiment. [Figure 8] FIG. 13 is a graph showing the rate of change with respect to endurance time. [Figure 9] 13 is a butterfly curve for a piezoelectric body of a comparative example. [Figure 10] 4 shows a butterfly curve in the piezoelectric body of the present embodiment. [Figure 11] 13 is an example of a hysteresis loop showing the relationship between voltage and current of a piezoelectric body of a comparative example. [Figure 12] 4 is an example of a hysteresis loop showing the relationship between the voltage and current of the piezoelectric body of the present embodiment. [Figure 13] FIG. 13 is a diagram showing the relationship between I_ratio and a reduction rate. [Figure 14] FIG. 13 is a diagram showing an evaluation of ejection characteristics in relation to I_ratio. [Figure 15] FIG. 13 is a diagram showing waveforms used in measuring hysteresis characteristics. [Figure 16] FIG. 1 is a diagram showing a first hysteresis loop. [Figure 17] FIG. 11 is a diagram showing a second hysteresis loop. [Figure 18] FIG. 11 is a diagram showing the difference between the current value in the first hysteresis loop and the current value in the second hysteresis loop. [Figure 19] FIG. 19 is a partially enlarged view of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Note that the dimensions or scale of each part in the drawings may differ from the actual dimensions, and some parts are shown diagrammatically to facilitate understanding. The scope of the present invention is not limited to these forms unless otherwise specified in the following description to the effect that the present invention is limited. Note that "equal" includes cases where there is a difference within the measurement error range, in addition to cases where they are strictly equal.

[0010] The following description will be given using the mutually intersecting X-axis, Y-axis, and Z-axis as appropriate. One direction along the X-axis is called the X1 direction, and the opposite direction to the X1 direction is called the X2 direction. Opposite directions along the Y-axis are called the Y1 direction and the Y2 direction. Opposite directions along the Z-axis are called the Z1 direction and the Z2 direction. Viewing in a direction along the Z-axis is called "planar view." The Z-axis is typically a vertical axis. However, the Z-axis does not have to be a vertical axis. In addition, the X-axis, Y-axis, and Z-axis are typically perpendicular to each other, but are not limited to this, and may intersect at an angle within a range of 80° to 100°, for example.

[0011] 1. Embodiment 1-1. Overall configuration of the liquid ejection device 100 1 is a schematic diagram showing a configuration of a liquid ejection device 100 according to a first embodiment. The liquid ejection device 100 is an inkjet printing device that ejects ink, which is an example of a liquid, as droplets onto a medium 12. The medium 12 is typically printing paper. Note that the medium 12 is not limited to printing paper, and may be a printing target made of any material, such as a resin film or fabric.

[0012] 1, a liquid container 14 that stores ink is attached to the liquid ejection device 100. Specific examples of the liquid container 14 include a cartridge that is detachable from the liquid ejection device 100, a bag-shaped ink pack made of a flexible film, and an ink tank that can be refilled with ink. The type of ink stored in the liquid container 14 is arbitrary.

[0013] The liquid ejection device 100 has a control unit 20, a transport mechanism 22, a movement mechanism 24, and a liquid ejection head 26. The control unit 20 includes a processing circuit such as a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array) and a storage circuit such as a semiconductor memory, and controls the operation of each element of the liquid ejection device 100. The control unit 20 includes a voltage application section 29 that controls the driving of a piezoelectric element 44 (described later) to eject ink from the nozzle.

[0014] The transport mechanism 22 transports the medium 12 in the Y2 direction under the control of the control unit 20. The movement mechanism 24 reciprocates the liquid ejection head 26 in the X1 direction and the X2 direction under the control of the control unit 20. In the example shown in FIG. 1, the movement mechanism 24 has a substantially box-shaped transport body 242 called a carriage that houses the liquid ejection head 26, and a transport belt 244 to which the transport body 242 is fixed. The number of liquid ejection heads 26 mounted on the transport body 242 is not limited to one, and may be multiple. In addition to the liquid ejection head 26, a liquid container 14 may be mounted on the transport body 242.

[0015] The liquid ejection head 26 ejects ink supplied from the liquid container 14 from each of a plurality of nozzles onto the medium 12 in the Z2 direction under the control of the control unit 20. This ejection is performed in parallel with the transport of the medium 12 by the transport mechanism 22 and the reciprocating movement of the liquid ejection head 26 by the movement mechanism 24, thereby forming an ink image on the surface of the medium 12.

[0016] The liquid ejection device 100 includes a liquid ejection head 26, which will be described later, and a control unit 20. The control unit 20 includes a voltage application section 29 that ejects ink from the nozzles N. Since the liquid ejection device 100 includes the liquid ejection head 26 having the characteristics described later, it is possible to improve the ejection performance.

[0017] 1-2. Overall configuration of liquid ejection head FIG. 2 is an exploded perspective view of the liquid ejection head 26 shown in FIG. 1. FIG. 3 is a cross-sectional view of a part of the liquid ejection head shown in FIG. 2, taken along line III-III in FIG. 2. As shown in FIG. 2, the liquid ejection head 26 has a plurality of nozzles N arranged in a direction along the Y axis. In the example shown in FIG. 2, the plurality of nozzles N are divided into a first row L1 and a second row L2 arranged at intervals in a direction along the X axis. Each of the first row L1 and the second row L2 is a collection of a plurality of nozzles N linearly arranged in a direction along the Y axis. Here, the elements related to each nozzle N in the first row L1 in the liquid ejection head 26 and the elements related to each nozzle N in the second row L2 are approximately symmetrical to each other in a direction along the X axis. In the following description, the elements corresponding to the first row L1 will be mainly described, and the description of the elements corresponding to the second row L2 will be omitted as appropriate.

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

[0019] 2 and 3, the liquid ejection head 26 has a nozzle plate 62, a vibration absorber 64, a flow path substrate 32, a pressure chamber substrate 34, a vibration plate 36, a wiring substrate 46, a housing unit 48, and a drive circuit 50. The nozzle plate 62, the vibration absorber 64, the flow path substrate 32, the pressure chamber substrate 34, the vibration plate 36, the wiring substrate 46, and the housing unit 48 are each a plate-like member that is elongated in the direction along the Y axis. The nozzle plate 62, the flow path substrate 32, the pressure chamber substrate 34, the vibration plate 36, and the wiring substrate 46 are arranged in this order in the Z1 direction.

[0020] The nozzle plate 62 is a plate-like member in which a plurality of nozzles N are formed. Each of the plurality of nozzles N is a circular through-hole that allows ink to pass through. The nozzles N eject ink by vibration of the vibration plate 36. The nozzle plate 62 is bonded to the flow path substrate 32 by, for example, an adhesive.

[0021] In the flow path substrate 32, a flow path for supplying ink to the multiple nozzles N is formed. Specifically, in the flow path substrate 32, a space Ra, multiple supply flow paths 322, multiple communication flow paths 324, and a supply liquid chamber 326 are formed. The space Ra is an elongated opening extending in a direction along the Y axis in a plan view seen in a direction along the Z axis. Each of the supply flow paths 322 and the communication flow paths 324 is a through hole formed for each nozzle N. The supply liquid chamber 326 is an elongated space extending in a direction along the Y axis across the multiple nozzles N, and connects the space Ra and the multiple supply flow paths 322 to each other. Each of the multiple communication flow paths 324 overlaps with one nozzle N corresponding to the communication flow path 324 in a plan view. A pressure chamber substrate 34 is bonded to the flow path substrate 32 by, for example, an adhesive.

[0022] A plurality of pressure chambers C are formed in the pressure chamber substrate 34. The plurality of pressure chambers C are arranged in a direction along the Y axis. Each pressure chamber C is formed for each nozzle N, and is an elongated space extending in a direction along the X axis in a plan view. The pressure chamber C is a space located between the flow path substrate 32 and the vibration plate 36. The pressure chamber C communicates with the nozzle N via a communication flow path 324, and also communicates with the space Ra via a supply flow path 322 and a supply liquid chamber 326.

[0023] The nozzle plate 62, the flow path substrate 32, and the pressure chamber substrate 34 are each manufactured by processing a silicon single crystal substrate using, for example, dry etching, wet etching, etc. However, other known methods may be appropriately used to manufacture the nozzle plate 62, the flow path substrate 32, and the pressure chamber substrate 34.

[0024] A diaphragm 36 is disposed on the surface facing the Z2 direction of the pressure chamber substrate 34. The diaphragm 36 is a plate-like member that is capable of elastically vibrating.

[0025] A plurality of piezoelectric elements 44 corresponding to the nozzles N are arranged on the surface of the vibration plate 36 facing the Z1 direction. Each piezoelectric element 44 has an elongated shape extending in the direction along the X-axis in a plan view. The plurality of piezoelectric elements 44 correspond to a plurality of pressure chambers C and are arranged in the direction along the Y-axis. The piezoelectric elements 44 deform when a voltage is applied. When the vibration plate 36 vibrates in conjunction with the deformation, the pressure in the pressure chamber C fluctuates, and ink is ejected from the nozzle N.

[0026] The housing 48 is a case for storing ink to be supplied to the multiple pressure chambers C. As shown in FIG. 3, a space Rb is formed in the housing 48. The space Rb in the housing 48 and the space Ra in the flow path substrate 32 are connected to each other. The space formed by the space Ra and the space Rb functions as a liquid storage chamber R, which is a reservoir that stores ink to be supplied to the multiple pressure chambers C. Ink is supplied to the liquid storage chamber R via an inlet 482 formed in the housing 48. The ink in the liquid storage chamber R is supplied to the pressure chambers C via the supply liquid chamber 326 and each supply flow path 322.

[0027] The vibration absorber 64 is a flexible film that constitutes the wall surface of the liquid storage chamber R. The vibration absorber 64 is a compliant substrate that absorbs pressure fluctuations of the ink in the liquid storage chamber R.

[0028] The wiring board 46 is a plate-like member on which wiring is formed for electrically connecting the drive circuit 50 and the plurality of piezoelectric elements 44. The surface of the wiring board 46 facing the Z2 direction is joined to the vibration plate 36 via a plurality of conductive bumps B. On the other hand, the drive circuit 50 is mounted on the surface of the wiring board 46 facing the Z1 direction. The drive circuit 50 is an IC (Integrated Circuit) chip that outputs a drive voltage Com and a reference voltage E0 for driving each piezoelectric element 44. The wiring board 46 is not limited to a rigid board, and may be, for example, an FPC (Flexible Printed Circuits) or an FFC (Flexible Flat Cable). In this case, the drive circuit 50 may be mounted on the wiring board 46, or the wiring board 46 may also serve as the external wiring 52.

[0029] An end of the external wiring 52 is joined to a surface of the wiring board 46 facing the Z1 direction. The external wiring 52 is formed of a connection component such as an FPC (Flexible Printed Circuits) or an FFC (Flexible Flat Cable). As shown in FIG. 2, the wiring board 46 is provided with a plurality of wirings 461 that electrically connect the external wiring 52 and the drive circuit 50, and a plurality of wirings 462 to which the drive voltage Com and the reference voltage E0 output from the drive circuit 50 are supplied.

[0030] 1-3. Vibration plate 36 and piezoelectric element 44 Fig. 4 is an enlarged cross-sectional view of a portion of the liquid ejection head 26 shown in Fig. 3. The vibration plate 36 shown in Fig. 4 vibrates in response to driving of a piezoelectric body 443 of a piezoelectric element 44 described below. The vibration plate 36 has a first layer 361 and a second layer 362. The first layer 361 and the second layer 362 are laminated in this order in the Z1 direction.

[0031] The first layer 361 is, for example, an elastic film made of silicon oxide (SiO2). The elastic film is formed, for example, by thermally oxidizing one surface of a silicon single crystal substrate. The second layer 362 is, for example, an insulating film made of zirconium oxide (ZrO2). The insulating film is formed, for example, by forming a layer of zirconium by a sputtering method and thermally oxidizing the layer. Zirconium oxide has excellent electrical insulation properties, mechanical strength, and toughness. Therefore, by including the second layer 362 containing zirconium oxide in the diaphragm 36, the characteristics of the diaphragm 36 can be improved.

[0032] Note that another layer such as a metal oxide may be interposed between the first layer 361 and the second layer 362. Also, a part or the whole of the diaphragm 36 may be integrally formed with the pressure chamber substrate 34. Also, the diaphragm 36 may be formed of a layer of a single material.

[0033] The pressure chambers C of the pressure chamber substrate 34 are formed, for example, by anisotropically etching a silicon single crystal substrate. An etchant for the anisotropic etching is, for example, an aqueous potassium hydroxide solution (KOH). In the anisotropic etching, the first layer 361 is used as an etching stop layer. Although not shown, the shape of the pressure chambers C in a plan view is rectangular. However, the shape of the pressure chambers C in a plan view is not limited to this and may be any shape. For example, the shape of the pressure chambers C in a plan view when formed by anisotropically etching a silicon single crystal substrate with a surface orientation (110) is a parallelogram.

[0034] The piezoelectric element 44 overlaps the pressure chamber C in a plan view. The piezoelectric element 44 has a second electrode 442, a seed layer 444, a piezoelectric body 443, and a first electrode 441, which are laminated in this order in the Z1 direction. Note that other layers, such as a layer for improving adhesion, may be appropriately interposed between the layers of the piezoelectric element 44 or between the piezoelectric element 44 and the vibration plate 36.

[0035] The second electrodes 442 are individual electrodes spaced apart from each other for each piezoelectric element 44. Specifically, a plurality of second electrodes 442 extending in the direction along the X-axis are arranged in the direction along the Y-axis at intervals from each other. A driving voltage Com for ejecting ink from the nozzle N is applied to the second electrode 442 of each piezoelectric element 44 via the driving circuit 50.

[0036] Examples of materials for the second electrode 442 include metal materials or alloys such as aluminum (Al), nickel (Ni), gold (Au), and copper (Cu). The second electrode 442 may be a single layer or multiple layers. For example, the second electrode 442 has a first layer made of titanium (Ti), a second layer made of platinum (Pt), and a third layer made of iridium (Ir), which are stacked in this order in the Z1 direction. The second electrode 442 is formed by a known film formation technique such as sputtering, and a known processing technique using photolithography, etching, and the like.

[0037] The first electrode 441 is a band-shaped common electrode extending in the direction along the Y-axis so as to be continuous across the plurality of piezoelectric elements 44. A reference voltage E0 is applied to the first electrode 441.

[0038] Examples of materials for the first electrode 441 include metal materials such as aluminum (Al), nickel (Ni), gold (Au), and copper (Cu), or alloys. The first electrode 441 may be a single layer or multiple layers. For example, the first electrode 441 has a layer made of iridium, a layer made of iridium oxide (IrOx), a layer made of titanium oxide (TiOx), and a layer made of iridium, which are stacked in this order from the piezoelectric body 443. The first electrode 441 is formed by a known film formation technique such as sputtering, and a known processing technique using photolithography, etching, and the like.

[0039] The piezoelectric body 443 is disposed between the first electrode 441 and the second electrode 442. The piezoelectric body 443 is, for example, in the form of a strip extending along the Y axis, and is separated for each piezoelectric element 44 by forming a plurality of notches. Note that the piezoelectric body 443 may be provided for each of the plurality of piezoelectric elements 44.

[0040] The piezoelectric body 443 is composed of a piezoelectric material having a perovskite crystal structure represented by a general composition formula ABO3. 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 zirconium niobate titanate (Pb(Zr,Ti,Nb)O3), and lead magnesium zirconium niobate titanate (Pb(Zr,Ti)(Mg,Nb)O3). Among them, lead zirconate titanate (PZT) is preferably used as the material for the piezoelectric body 443. The piezoelectric body 443 may contain small amounts of other elements such as impurities.

[0041] The piezoelectric body 443 is formed by, for example, forming a precursor layer of the piezoelectric body 443 by a sol-gel method or a metal organic decomposition (MOD) method, and baking and crystallizing the precursor layer. The piezoelectric body 443 may be a single layer or multiple layers.

[0042] Seed layer 444 is disposed between second electrode 442 and piezoelectric body 443. Seed layer 444 is provided in the same region and with the same shape as second electrode 442 in a plan view. Note that seed layer 444 only needs to be disposed between second electrode 442 and piezoelectric body 443. Seed layer 444 may be provided, for example, in the same region and with the same shape as piezoelectric body 443 in a plan view.

[0043] The seed layer 444 has a function of improving the orientation of the piezoelectric body 443 when the piezoelectric body 443 is formed. Specifically, the seed layer 444 is made of, for example, titanium (Ti). When the seed layer 444 is made of titanium, islands of Ti become crystal nuclei when the piezoelectric body 443 is formed, improving the orientation of the piezoelectric body 443. The seed layer 444 containing titanium is formed by, for example, a known film formation technique such as a sputtering method, and a known processing technique using photolithography, etching, etc. Note that the seed layer 444 may be regarded as a part of the second electrode 442.

[0044] Moreover, the seed layer 444 is not limited to being made of titanium, and may be made of, for example, a complex oxide having a perovskite structure containing lead, iron, and titanium as constituent elements. In this case, when forming the piezoelectric body 443, the piezoelectric body 443 is influenced by the crystal structure of the seed layer 444, and the orientation of the piezoelectric body 443 is improved. The complex oxide is, for example, a solid solution of PbFeO3 and PbTiO3, and is expressed as Pb(Fe,Ti)O3. When made of such a complex oxide, the seed layer 444 is formed by, for example, forming a precursor layer of the complex oxide by the sol-gel method or the MOD method, and baking and crystallizing the precursor layer.

[0045] A voltage is applied to the above piezoelectric element 44 by the voltage application unit 29. Specifically, the voltage application unit 29 applies a voltage to the piezoelectric body 443 via the first electrode 441 and the second electrode 442, and the piezoelectric body 443 deforms in response to the voltage applied between the first electrode 441 and the second electrode 442. A driving voltage Com according to the ink ejection amount is applied to the second electrode 442. A constant reference voltage E0 is applied to the first electrode 441 regardless of the ink ejection amount. By applying the driving voltage Com and the reference voltage E0, a voltage that is the difference between the driving voltage Com and the reference voltage E0 is applied between the first electrode 441 and the second electrode 442 to the piezoelectric body 443, and the piezoelectric body 443 deforms.

[0046] 1-4. Electrical characteristics of piezoelectric material 443 Fig. 5 is an example of a hysteresis loop showing the relationship between the voltage and charge of the piezoelectric body 443z of the piezoelectric element 44z of the comparative example. Fig. 6 is a hysteresis loop showing the relationship between the voltage and polarization of the piezoelectric body 443 of the piezoelectric element 44 of this embodiment. The horizontal axis of Fig. 5 and Fig. 6 is voltage [V], and the vertical axis is polarization [μC / cm 2 ].

[0047] Each hysteresis loop shown in FIG. 5 and FIG. 6 includes a positive remnant polarization Pr, a negative remnant polarization -Pr, a positive coercive field Ec, a negative coercive field -Ec, a positive saturation polarization Pm, and a negative saturation polarization -Pm. The remnant polarization Pr is the polarization on the positive side at 0 V. The remnant polarization -Pr is the polarization on the negative side at 0 V. The coercive field Ec is the magnitude of the electric field when the polarization is reversed from negative to positive, and is the magnitude of the electric field when the polarization is 0 μC / cm 2 The coercive field -Ec is the magnitude of the electric field when the polarization is reversed from positive to negative, and when the polarization is 0 μC / cm 2The saturated polarization Pm is the magnitude of the negative electric field at which the charge generated in the piezoelectric body 443 is saturated. The saturated polarization -Pm is the negative polarization at which the charge generated in the piezoelectric body 443 is saturated. The positive voltage applied between the first electrode 441 and the second electrode 442 at the saturated polarization Pm is the saturated positive voltage Vp. The negative voltage applied between the first electrode 441 and the second electrode 442 at the saturated polarization -Pm is the saturated negative voltage Vn.

[0048] The positive remnant polarization Pr in the present embodiment in Fig. 6 is closer to zero than the positive remnant polarization Pr in the comparative example in Fig. 5. The negative remnant polarization -Pr in the present embodiment in Fig. 6 is closer to zero than the negative remnant polarization -Pr in the comparative example in Fig. 5.

[0049] Fig. 7 is a diagram showing butterfly curves of piezoelectric body 443 of this embodiment before and after long-term voltage application. The solid line in Fig. 7 is the butterfly curve of piezoelectric body 443 in the initial stage before voltage is applied for a long period of time. The dashed line in Fig. 7 is the butterfly curve of piezoelectric body 443 after voltage is applied for a long period of time. The horizontal axis in Fig. 7 is voltage [V], and the vertical axis is the displacement amount of diaphragm 36.

[0050] When the number of times the piezoelectric element 44 is driven increases and a voltage is applied to the piezoelectric body 443 for a long time, that is, when the number of shots of ink ejection from the liquid ejection head 26 increases, an imprint phenomenon occurs in which the hysteresis shape of the piezoelectric body 443 shifts. This causes the butterfly curve of the piezoelectric body 443 to shift as well. For example, the butterfly curve may shift from the butterfly curve shown by the solid line in Fig. 7 to the butterfly curve shown by the dashed line in Fig. 7. As a result, for example, the voltage response of the piezoelectric body 443 in the vicinity of the coercive electric field -Ec changes significantly with respect to the voltage response in the high voltage region.

[0051] When the butterfly curve shifts due to the imprint phenomenon, the displacement C2 after long-term voltage application becomes smaller than the initial displacement C1. The displacements C1 and C2 are the displacements of the vibration plate 36 in the range from the voltage at the negative coercive field -Ec to the saturated positive voltage Vp at the saturated polarization Pm. Therefore, if the reference voltage and the driving voltage are set based on the initial hysteresis shape of the piezoelectric body 443, the ejection amount decreases as the number of driving times increases. Therefore, it is difficult to obtain stable ejection performance over a long period of time.

[0052] The shift in the amount of displacement of the diaphragm 36 is presumed to be due to the following factors. The first factor is a change in the crystal structure of the piezoelectric body 443. For example, if the piezoelectric body 443 is a PZT thin film formed by a sol-gel method and the PZT thin film has a tetracomposition of Zr / Ti=30 / 70, the MPB (thetamorphotropic phase boundary) shifts to the Ti side. In addition, the crystal system of the PZT thin film formed by the sol-gel method is a monoclinic system, which is different from the crystal system of a bulk film formed by, for example, a sputtering method.

[0053] The PZT thin film formed by the sol-gel method is easily affected by the second electrode 442 that serves as the base. This is believed to cause a shift in the MPB and a crystal system different from that of the bulk film. This is believed to be due to the difference in thermal expansion coefficient between the second electrode 442 and the piezoelectric body 443. In the initial state after the formation of the piezoelectric body 443, the crystals of the piezoelectric body 443 are pulled in a direction parallel to the XY plane. In contrast, when the piezoelectric element 44 is driven and the piezoelectric body 443 is released from the stress of the second electrode 442, it tries to shift to its original stable crystal structure.

[0054] The second factor is thought to be the movement of charged particles. Electrons are trapped in oxygen defects, which fix the polarization axis that becomes a fixed charge, resulting in a distortion that makes it impossible to respond to an electric field. This distorted crystal state tends to be stable. As a result, the optimal operating range changes due to a shift in the coercive electric field.

[0055] It is believed that such factors cause the imprint phenomenon in which the hysteresis shape of the piezoelectric body 443 shifts.

[0056] 8 is a diagram showing the rate of change versus endurance time. The horizontal axis in FIG. 8 is endurance time [h], and the vertical axis is rate of change [%]. The endurance time indicates the time during which the piezoelectric element 44 is continuously driven. The rate of change on the vertical axis is the rate of change in the amount of displacement of the diaphragm 36.

[0057] The dashed line in Fig. 8 indicates the piezoelectric body 443z of the comparative example, and the solid line in Fig. 8 indicates the piezoelectric body 443 of the example. As shown in Fig. 8, in the piezoelectric body 443z of the comparative example, the absolute value of the rate of change increases as the endurance time increases. In contrast, in the piezoelectric body 443 of the example, the absolute value of the rate of change remains within a small range of 2% even when the endurance time increases. As can be seen from Fig. 8, by using the piezoelectric body 443 of the example, it is possible to suppress the increase in the rate of change due to the imprint phenomenon.

[0058] Fig. 9 shows a butterfly curve for piezoelectric body 443z of a comparative example. Fig. 10 shows a butterfly curve for piezoelectric body 443 of this embodiment. The horizontal axis in Fig. 9 and Fig. 10 is voltage [V], and the vertical axis is the amount of displacement of vibration plate 36. Note that the amount of displacement of vibration plate 36 is expressed by taking the position closest to the Z1 side (opposite side from pressure chamber C) as 0, and showing how far it has been displaced from that position toward the Z2 side (pressure chamber C side), that is, the relative position when the position closest to the Z1 side is used as a reference.

[0059] 9 and 10 show butterfly curves when the range of the voltage applied between the first electrode 441 and the second electrode 442 is fixed and the minimum potential of the voltage is changed. In the comparative example of FIG. 9, when the minimum potential of the voltage is changed, the displacement amount of the diaphragm 36 is likely to vary in the range of -5V to +5V. That is, the displacement amount of the diaphragm 36 is likely to vary in the vicinity of the voltages at the coercive electric fields Ec and -Ec. In contrast, in the present embodiment of FIG. 10, even if the minimum value is changed, the variation in the displacement amount of the diaphragm 36 can be made smaller than that of the comparative example in the range of -5V to +5V. That is, the variation in the displacement amount of the diaphragm 36 can be made smaller than that of the comparative example in the vicinity of the voltages at the coercive electric fields Ec and -Ec.

[0060] As can be seen from FIG. 10, the piezoelectric body 443 of this embodiment has a more gradual change in the amount of displacement near the coercive electric field Ec and -Ec than the comparative example. According to the piezoelectric body 443 of this embodiment, when imprint occurs due to an increase in the number of times the piezoelectric element 44 is driven, the characteristic variation due to the imprint can be suppressed. That is, it is possible to suppress an increase in the rate of change in the amount of displacement of the vibration plate 36 due to the imprint. On the other hand, as can be seen from FIG. 9, it is found that residual strain remains in the piezoelectric body 443z of the comparative example up to the coercive electric field Ec and -Ec. For this reason, it is difficult to suppress the characteristic variation due to the imprint.

[0061] 11 is an example of a hysteresis loop showing the relationship between the voltage and current of the piezoelectric body 443z of the comparative example. Consider a case where the voltage applied between the first electrode 441 and the second electrode 442 is gradually changed from a saturated negative voltage Vn to a saturated positive voltage Vp. In this case, the current based on the charge generated in the piezoelectric body 443z changes through a path R1z and a path R2z in this order. In the path R1z, the current increases as the voltage increases. In the path R2z, the current decreases as the voltage increases.

[0062] Also, consider a case where the voltage applied between the first electrode 441 and the second electrode 442 is gradually changed from a saturated positive voltage Vp to a saturated negative voltage Vn. In this case, the current based on the charge generated in the piezoelectric body 443z changes through the path R3z and the path R4z in this order. In the path R3z, the current decreases as the voltage decreases. In the path R4z, the current increases as the voltage decreases.

[0063] In the hysteresis loop of the piezoelectric body 443z in FIG. 11, there is one maximum current value P1z. The maximum current value P1z corresponds to the switching portion from path R1z to path R2z. The maximum current value P1z corresponds to a positive coercive electric field Ec. In addition, in the hysteresis loop of the piezoelectric body 443z in FIG. 8, there is one minimum current value P2z. The minimum current value P2z corresponds to the switching portion from path R3z to path R4z. The minimum current value P2z corresponds to a negative coercive electric field -Ec.

[0064] FIG. 12 is an example of a hysteresis loop showing the relationship between the voltage and the current of the piezoelectric body 443 of this embodiment. Consider a case where the voltage applied between the first electrode 441 and the second electrode 442 is gradually changed from a saturated negative voltage Vn to a saturated positive voltage Vp. In this case, the current based on the charge generated in the piezoelectric body 443 changes through the first path R1, the second path R2, the third path R3, and the fourth path R4 in this order. In the first path R1, the current increases as the voltage increases. In the second path R2, the current decreases as the voltage increases. In the third path R3, the current increases as the voltage increases. In the fourth path R4, the current decreases as the voltage increases. The hysteresis loop shown in FIG. 12 corresponds to a first hysteresis loop H1 described later.

[0065] Also, consider a case where the voltage applied between the first electrode 441 and the second electrode 442 is gradually changed from a saturated positive voltage Vp to a saturated negative voltage Vn. In this case, the current based on the charge generated in the piezoelectric body 443 changes through the fifth path R5, the sixth path R6, the seventh path R7, and the eighth path R8 in this order. In the fifth path R5, the current decreases as the voltage decreases. In the sixth path R6, the current increases as the voltage decreases. In the seventh path R7, the current decreases as the voltage decreases. In the eighth path R8, the current increases as the voltage decreases.

[0066] In the hysteresis loop of the piezoelectric body 443 in FIG. 12, it appears as if there are two maximum current values. The first maximum current value P1, which is the largest current value, corresponds to the switching portion from the first path R1 to the second path R2. The second maximum current value P2, which is the second largest current value, corresponds to the switching portion from the third path R3 to the fourth path R4. The first maximum current value P1 corresponds to the positive residual polarization Pr. The second maximum current value P2 corresponds to the positive coercive field Ec. In addition, in the hysteresis loop of the piezoelectric body 443 in FIG. 9, it appears as if there are two minimum current values. The first minimum current value P3, which is the smallest current value, corresponds to the switching portion from the fifth path R5 to the sixth path R6. The second minimum current value P4, which is the second smallest current value, corresponds to the switching portion from the seventh path R7 to the eighth path R8. The first minimum current value P3 corresponds to the negative residual polarization -Pr. The second minimum value P4 corresponds to the negative coercive field −Ec.

[0067] In the hysteresis loop of the piezoelectric body 443 in Fig. 12, the current value at the voltage corresponding to the negative coercive electric field -Ec is defined as I_peak. Also, the current value at the voltage at which the polarization inversion stops is defined as I_edge. In this case, the following formula [1] is satisfied. (I_peak / I_edge)=I_ratio<15 …[1]

[0068] By satisfying formula [1], the rate of decrease in characteristic fluctuations due to the imprint phenomenon can be reduced compared to when formula [1] is not satisfied. Therefore, even if the reference voltage and driving voltage are set based on the initial hysteresis shape of the piezoelectric body 443, the deterioration of the discharge amount can be suppressed. This is believed to be because the piezoelectric body 443 of this embodiment can cause polarization inversion in a dispersed manner.

[0069] Fig. 13 is a diagram showing the relationship between I_ratio and the rate of decrease. The horizontal axis of Fig. 13 is I_ratio=(I_peak / I_edge), and the vertical axis is the rate of decrease [%] of the displacement amount of the diaphragm 36.

[0070] As can be seen from Fig. 13, by satisfying I_ratio<15, the rate of decrease can be reduced compared to when this is not the case. Furthermore, as can be seen from Fig. 13, by satisfying I_ratio<12, the rate of decrease can be suppressed to a very small range of -3% or less.

[0071] Fig. 14 is a diagram showing an evaluation of the ejection characteristics in relation to the I_ratio. The desired ejection volume is A, and the maximum ejection volume when the piezoelectric element 44 is actually driven to eject is B. In this case, B / A exceeding 100% is indicated by "○". B / A between 95% and 100 is indicated by "△". Less than 95% is indicated by "X".

[0072] As shown in Fig. 14, by satisfying I_ratio>7, it is possible to suppress the deterioration of the ejection characteristics. If I_ratio is too small, specifically, if I_ratio>7 is not satisfied, the displacement of the piezoelectric body 443 may be too small, which may result in insufficient ink ejection. Furthermore, by satisfying I_ratio>9, it is possible to more effectively suppress the deterioration of the ejection characteristics. Therefore, by satisfying I_ratio>9, it is easy to ensure the desired amount of ink ejection.

[0073] Fig. 15 is a diagram showing a waveform W used in measuring the hysteresis characteristic of the piezoelectric body 443 in this embodiment. Specifically, for example, the hysteresis curve and the voltage at I_edge shown in Fig. 12 are obtained. The horizontal axis of Fig. 12 is time, and the vertical axis is voltage.

[0074] The waveform W includes a pre-measurement period T0 and a measurement period Tm. The waveform W includes one negative pulse in the pre-measurement period T0. The pre-measurement period T0 is performed before the measurement period Tm and is used for polarization processing of the piezoelectric body 443. The waveform W includes two positive pulses and two negative pulses in the pre-measurement period T0, and two pulses are applied to each of the positive side and the negative side. In the illustrated example, the waveform W includes a triangular wave, but may be, for example, a square wave.

[0075] The measurement period Tm includes a first application process T1, a second application process T2, a third application process T3, and a fourth application process T4. These processes proceed in this order.

[0076] The first application process T1 is a period during which a first waveform W1 is applied to the piezoelectric body 443, the first waveform W1 gradually increasing from 0 (zero) to a first positive voltage Va and then gradually decreasing to 0. The first positive voltage Va is a positive voltage at which the charge generated in the piezoelectric body 443 becomes saturated. The first positive voltage Va corresponds to the above-mentioned saturated positive voltage Vp. The first positive voltage Va is, for example, in the range of +30 [V] or more and +40 [V] or less. The first waveform W1 is an inversion pulse that is inverted from negative to positive. From the measurement result of the first application process T1, the result of the positive side current value including the polarity inversion is obtained.

[0077] The second application process T2 is a period during which the second waveform W2, which gradually increases from 0 to the first positive voltage Va and then gradually decreases to 0, is applied to the piezoelectric body 443. The second waveform W2 is a non-inverted pulse. From the measurement results of the second application process T2, the results of the positive current value that does not include polarity inversion are obtained.

[0078] The third application process T3 is a period during which a third waveform W3 is applied to the piezoelectric body 443, the third waveform W3 gradually decreasing from 0 to a first negative voltage Vb and then gradually increasing to 0. The first negative voltage Vb is a negative voltage at which the charge generated in the piezoelectric body 443 is saturated. The first negative voltage Vb corresponds to the above-mentioned saturated negative voltage Vm. The first negative voltage Vb is, for example, in the range of -40 [V] or more and -30 [V] or less. The third waveform W3 is an inversion pulse inverted from positive to negative. The measurement result of the third application process T3 provides a current value including the inversion to negative.

[0079] The fourth application process T4 is a period during which a fourth waveform W4 is applied to the piezoelectric body 443, the fourth waveform W4 gradually decreasing from 0 to the first negative voltage Vb and then gradually increasing to 0. The fourth waveform W4 is a non-inverted pulse. From the measurement result of the fourth application process T4, a result of a negative current value that does not include polarity inversion is obtained.

[0080] Fig. 16 is a diagram showing a first hysteresis loop H1, and Fig. 17 is a diagram showing a second hysteresis loop H2.

[0081] A change in current generated in the piezoelectric body 443 is measured when the above-mentioned first application process T1, second application process T2, third application process T3, and fourth application process T4 are performed on the piezoelectric body 443 in this order. Of the changes in current, a hysteresis loop showing the change in the current generated in the first application process T1 and the third application process T3 with respect to the voltage is the first hysteresis loop H1 shown in Fig. 16. Moreover, of the changes in current, a hysteresis loop showing the change in the current generated in the second application process T2 and the fourth application process T4 with respect to the voltage is the second hysteresis loop H2 shown in Fig. 17.

[0082] The first hysteresis loop H1 is a measurement result in the first application process T1 and the third application process T3, and therefore shows a change in current including the influence of polarity reversal. This first hysteresis loop H1 corresponds to the hysteresis loop shown in Fig. 12 described above. In contrast, the second hysteresis loop H2 is a measurement result in the second application process T2 and the fourth application process T4, and therefore shows a change in current not including the influence of polarity reversal.

[0083] Fig. 18 is a diagram showing the difference between the current value in the first hysteresis loop H1 and the current value in the second hysteresis loop H2. Fig. 18 shows the reversal current, which is the change in current that flows when the current is reversed from positive to negative, because it is the difference. In Fig. 18, the voltage value at which the current value goes from positive to 0 (zero) is the voltage at which polarization reversal is completed. In other words, the voltage value at which the current value goes from positive to 0 is the voltage at which polarization reversal ceases, and is the voltage value at I_edge.

[0084] Fig. 19 is a partial enlarged view of Fig. 18. Referring to Fig. 19, in piezoelectric body 443 of this embodiment, the voltage at which polarization inversion ceases is about 25 V. Therefore, in piezoelectric body 443 of this embodiment, for example, 25 V is the voltage value at I_edge.

[0085] 12 corresponds to the first hysteresis loop H1. Therefore, the current value of the first hysteresis loop at a voltage corresponding to the coercive electric field -Ec of the piezoelectric body 443 is defined as I_peak. The current value of the first hysteresis loop H1 at a voltage at which the difference between the current value of the first hysteresis loop H1 and the current value of the second hysteresis loop H2 starts to change from 0 is defined as I_edge. In this case, as described above, the piezoelectric body 443 satisfies the relationship (I_peak / I_edge)=I_ratio<15.

[0086] Also, it is preferable that I_peak satisfies the relationship of 0.01 < I_peak < 0.06, and I_edge satisfies the relationship of 0.001 < I_edge < 0.006. By I_peak and I_edge satisfying the above respective relationships, it is possible to suppress a decrease in ejection performance due to an imprint phenomenon while ensuring the ejection amount, as compared with the case where they do not satisfy the relationships. Note that I_peak and I_edge do not necessarily have to satisfy the above respective relationships. In the hysteresis loop shown in FIG. 12, I_peak = -0.0372 and I_edge = -0.0037.

[0087] 1-5. Production Example of Piezoelectric Body 443 The piezoelectric body 443 of the present embodiment is formed, for example, as follows. For example, when the first electrode 441 contains iridium, the state is such that the iridium is not completely oxidized. By shortening the annealing time for forming the first electrode 441 or increasing the film thickness of the first electrode 441, the degree of oxidation of iridium can be made insufficient. As a result, an amorphous state in which the interface with the first electrode 441 of the piezoelectric body 443 is not uniform is created. Due to this non-uniform state of the interface, it is considered that the voltage at which polarization reversal occurs becomes more dispersed than in the conventional case. As a result, the piezoelectric body 443 of the embodiment having the hysteresis curve shown in FIG. 12 is obtained. Note that even if the first electrode 441 is not an electrode made of iridium but an oxide electrode such as strontium ruthenate (SrRuO3) and lanthanum nickelate (LaNiO3), it is considered that the piezoelectric body 443 of the present embodiment can be obtained.

[0088] Also, for example, when the piezoelectric body 443 is PZT, by the Zr ratio of PZT satisfying the relationship of 0.55 < Zr / (Zr + Ti), the piezoelectric body 443 of the present embodiment can be obtained.

[0089] Furthermore, for example, when the piezoelectric body 443 is mainly composed of PZT, the piezoelectric body 443 of this embodiment can be obtained by including any one of additives Mg, Al, Fe, or Na in the piezoelectric body 443. For example, in the case of B-site substitution, additives include Mg, Al, Fe, etc. In the case of A-site substitution, additives include Na, etc. In a hard material whose valence is smaller than that of the substituting element, as the oxygen defects increase, the oxygen defects hinder or inhibit the movement of the domain wall. It is believed that this is why the piezoelectric body 443 of this embodiment can be obtained.

[0090] 2. Variations The above-described embodiment may be modified in various ways. Specific modified aspects that may be applied to the above-described embodiment are illustrated below. Two or more aspects selected from the following examples may be combined as appropriate to the extent that they are not mutually contradictory.

[0091] The "liquid ejection head" may be a circulation type head having a so-called circulation flow path.

[0092] The "liquid ejection device" can be used in various devices such as facsimile machines and copy machines, as well as devices dedicated to printing. The uses of the liquid ejection device are not limited to printing. For example, a liquid ejection device that ejects a solution of a color material is used as a manufacturing device for forming a color filter of a display device such as a liquid crystal display panel. A liquid ejection device that ejects a solution of a conductive material is used as a manufacturing device for forming wiring and electrodes of a wiring board. A liquid ejection device that ejects a solution of an organic substance related to a living body is used as a manufacturing device for manufacturing a biochip, for example.

[0093] Although the present invention has been described based on the preferred embodiment, the present invention is not limited to the above embodiment. Furthermore, the configuration of each part of the present invention can be replaced with any configuration that exhibits the same function as the above embodiment, and any configuration can be added. [Explanation of symbols]

[0094] 12...medium, 14...liquid container, 20...control unit, 22...transport mechanism, 24...movement mechanism, 26...liquid ejection head, 29...voltage application section, 32...flow path substrate, 34...pressure chamber substrate, 36...vibration plate, 44...piezoelectric element, 44z...piezoelectric element, 46...wiring substrate, 48...casing, 50...drive circuit, 52...external wiring, 62...nozzle plate, 64...vibration absorber, 100...liquid ejection device, 242...transport body, 244 . . . conveyor belt, 322... supply flow path, 324... communication flow path, 326... supply liquid chamber, 361... first layer, 362... second layer, 441... first electrode, 442... second electrode, 443... piezoelectric body, 443z... piezoelectric body, 444... seed layer, 461... wiring, 462... wiring, 482... introduction port, B... bump, C... pressure chamber, C1... displacement amount, C2... displacement amount, Ec... coercive electric field, H1... first hysteresis loop, H2... second hysteresis loop Steresis loop, L1...first row, L2...second row, N...nozzle, P1z...maximum, P2z...minimum, P1...first maximum, P2...second maximum, P3...first minimum, P4...second minimum, Pm...saturation polarization, Pr...residual polarization, R...liquid storage chamber, R1...first path, R1z...path, R2...second path, R2z...path, R3...third path, R3z...path, R4...fourth path, R4z...path, R5...third 5 path, R6...sixth path, R7...seventh path, R8...eighth path, Ra...space, Rb...space, T0...pre-measurement period, T1...first application process, T2...second application process, T3...third application process, T4...fourth application process, Tm...measurement period, Va...first positive voltage, Vb...first negative voltage, Vn...saturated negative voltage, Vp...saturated positive voltage, W...waveform, W1...first waveform, W2...second waveform, W3...third waveform, W4...fourth waveform.

Claims

1. a first electrode to which a reference voltage is applied; a second electrode to which a driving voltage is applied; a piezoelectric body provided between the first electrode and the second electrode, a first application process for applying a first waveform to the piezoelectric body, the first waveform gradually increasing from 0 to a first positive voltage and then gradually decreasing to 0; a second application step of applying to the piezoelectric body a second waveform that gradually increases from 0 to the first positive voltage and then gradually decreases to 0; a third applying step of applying to the piezoelectric body a third waveform that gradually decreases from 0 to a first negative voltage and then gradually increases to 0; a fourth application step of applying a fourth waveform to the piezoelectric body, the fourth waveform gradually decreasing from 0 to the first negative voltage and then gradually increasing to 0; Among changes in current generated in the piezoelectric body when the first application process, the second application process, the third application process, and the fourth application process are performed on the piezoelectric body in this order, a hysteresis loop showing the change in current generated in the first application process and the third application process relative to voltage is defined as a first hysteresis loop, and a hysteresis loop showing the change in current generated in the second application process and the fourth application process relative to voltage is defined as a second hysteresis loop, A current value of the first hysteresis loop at a voltage corresponding to the coercive electric field of the piezoelectric body is defined as I_peak, When the current value of the first hysteresis loop at a voltage at which the difference between the current value of the first hysteresis loop and the current value of the second hysteresis loop starts to change from 0 is I_edge, A liquid ejection head satisfying I_peak / I_edge<15.

2. 2. The liquid ejection head according to claim 1, wherein I_peak / I_edge<12 is satisfied.

3. 2. The liquid ejection head according to claim 1, wherein I_peak / I_edge>7 is satisfied.

4. 4. The liquid ejection head according to claim 3, wherein I_peak / I_edge>9 is satisfied.

5. the first positive voltage is a positive voltage at which charges generated in the piezoelectric body are saturated, 2. The liquid ejection head according to claim 1, wherein the first negative voltage is a negative voltage at which the charge generated in the piezoelectric body becomes saturated.

6. The first positive voltage is in the range of 30 V to 40 V, The first negative voltage is in the range of −40 [V] or more and −30 [V] or less, 2. The liquid ejection head according to claim 1, wherein 0.01<I_peak<0.06 and 0.001<I_edge<0.006 are satisfied.

7. A liquid ejection head according to any one of claims 1 to 6, a voltage application section that applies a voltage to the piezoelectric body via the first electrode and the second electrode.

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