Liquid discharge head and liquid discharge device

Abstract

To provide a liquid discharge head which is excellent in discharge performance while suppressing occurrence of adverse effects, and a liquid discharge device.SOLUTION: A liquid discharge head has: a first electrode; a second electrode; a piezoelectric element driven by a voltage difference between a reference voltage and a drive voltage; a diaphragm which vibrates in response to drive of the piezoelectric element; and a nozzle from which liquid is discharged by vibration of the diaphragm. When a displacement magnitude of the diaphragm when a first reference voltage is applied to the first electrode and a first drive voltage is applied to the second electrode is represented by a first displacement magnitude and a displacement magnitude of the diaphragm when a second reference voltage is applied to the first electrode and a second drive voltage is applied to the second electrode is represented by a second displacement magnitude, a difference between a maximum value and a minimum value of the first drive voltage is equal to a difference between a maximum value and a minimum value of the second drive voltage, a difference between the minimum value of the first drive voltage and the first reference voltage corresponds to a coercive electric field of the piezoelectric element, a difference between the minimum value of the second drive voltage and the second reference voltage is closer to 0 than the difference between the minimum value of the first drive voltage and the first reference voltage, and the second displacement magnitude is greater than 90% of the first displacement magnitude.SELECTED DRAWING: Figure 12

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 driving voltage that changes with time is applied to the other electrode. By setting the difference between the minimum value of the driving voltage and the reference voltage (the minimum value of the voltage applied to the piezoelectric body) and the difference between the maximum value of the driving voltage and the reference voltage (the maximum value of the voltage applied to the piezoelectric body) to be large, the amount of displacement of the vibration plate vibrated by the piezoelectric element can be increased. This allows the ejection amount to be increased, making it easier to obtain the desired ejection amount.

[0006] Conventionally, in order to increase the difference between the voltage difference between the minimum value of the driving voltage and the reference voltage and the voltage difference between the maximum value of the driving voltage and the reference voltage, the voltage difference between the minimum value of the driving voltage and the reference voltage has been set to the voltage in the coercive electric field. However, it has been found that simply increasing this difference causes other problems.

[0007] For example, if the voltage difference between the minimum value of the driving voltage and the reference voltage is set to the voltage in the coercive electric field, a specific voltage must be applied to the reference voltage. Therefore, a circuit and wiring are required to apply the voltage, which leads to increased costs and size. For this reason, it is difficult to provide a piezoelectric element with excellent ejection performance with a simple configuration.

[0008] Furthermore, for example, when a voltage is applied to a piezoelectric body for a long time, an imprint phenomenon occurs in which the hysteresis shape of the piezoelectric body shifts. As a result, the coercive electric field may shift. Therefore, even if the reference voltage and the driving voltage are set based on the initial hysteresis shape of the piezoelectric body, it is difficult to suppress the rate of decrease in the ejection amount with the number of driving times. Therefore, it is difficult to obtain stable ejection performance over a long period of time.

[0009] In this way, if the difference between the voltage difference between the minimum value of the drive voltage and the reference voltage and the voltage difference between the maximum value of the drive voltage and the reference voltage is simply increased, there is a concern that other problems may occur. [Means for solving the problem]

[0010] A liquid ejection head according to a preferred embodiment of the present invention has a first electrode to which a reference voltage that does not change with time is applied, a second electrode to which a drive voltage that changes with time is applied, a piezoelectric body provided between the first electrode and the second electrode and driven by a voltage difference between the reference voltage and the drive voltage, a diaphragm that vibrates in response to the drive of the piezoelectric body, and a nozzle from which liquid is ejected by vibration of the diaphragm, wherein the amount of displacement of the diaphragm when a first reference voltage is applied to the first electrode and a first drive voltage is applied to the second electrode is determined by calculating a displacement amount of the diaphragm when a first reference voltage is applied to the first electrode and a first drive voltage is applied to the second electrode. When a first displacement amount is defined as a displacement amount of the vibration plate when a second reference voltage is applied to the first electrode and a second drive voltage is applied to the second electrode, the difference between the maximum and minimum values ​​of the first drive voltage is equal to the difference between the maximum and minimum values ​​of the second drive voltage, the difference between the minimum value of the first drive voltage and the first reference voltage corresponds to the coercive electric field of the piezoelectric body, the difference between the minimum value of the second drive voltage and the second reference voltage is closer to 0 than the difference between the minimum value of the first drive voltage and the first reference voltage, and the second displacement amount is greater than 90% of the first displacement amount. [Brief description of the drawings]

[0011] [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] FIG. 4 is a diagram for explaining a driving voltage and a reference voltage. [Figure 6] 1 is an example of a voltage applied to a piezoelectric body. [Figure 7] 10 is an example of a hysteresis curve showing the relationship between the voltage and polarization of a piezoelectric body of a piezoelectric element of a comparative example. [Figure 8] 4 is an example of a hysteresis curve showing the relationship between the voltage and polarization of a piezoelectric body of the piezoelectric element of the first embodiment. [Figure 9]FIG. 4 is a diagram showing a first driving voltage and a first reference voltage. [Figure 10] FIG. 4 is a diagram showing a second driving voltage and a second reference voltage. [Figure 11] 13 is a butterfly curve for a piezoelectric body of a comparative example. [Figure 12] 4 is a butterfly curve in the piezoelectric body of the first embodiment. [Figure 13] 1 is an example of a butterfly curve for explaining the imprint phenomenon. [Figure 14] FIG. 11 is a diagram showing a second driving voltage and a second reference voltage in the second embodiment. [Figure 15] 13 is an example of a hysteresis curve showing the relationship between voltage and polarization of a piezoelectric body according to a second embodiment. [Figure 16] 13 is a butterfly curve in the piezoelectric body of the second embodiment. [Figure 17] FIG. 13 is a diagram showing a second drive voltage and a second reference voltage in a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 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.

[0013] 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.

[0014] 1. First 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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 while ensuring a desired ejection amount.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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 then baking and crystallizing the precursor layer. The piezoelectric body 443 may be a single layer or multiple layers.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] In the above piezoelectric element 44, the piezoelectric body 443 deforms in response to a voltage applied between the first electrode 441 and the second electrode 442. A driving voltage Com according to the amount of ink ejected is applied to the second electrode 442. A constant reference voltage E0 is applied to the first electrode 441 regardless of the amount of ink ejected. When a voltage difference occurs between the first electrode 441 and the second electrode 442 due to the application of the driving voltage Com and the reference voltage E0, the piezoelectric body 443 deforms.

[0049] 1-4. Drive voltage Com, reference voltage E0 and applied voltage Ea 5 is a diagram for explaining the drive voltage Com and the reference voltage E0, in which the horizontal axis represents time and the vertical axis represents voltage [V].

[0050] 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 potential Ek, a maximum potential En, and a minimum potential Em. The maximum potential En is the maximum value of the driving voltage Com. The minimum potential Em is the minimum value of the driving voltage Com. The driving waveform WCom drops from the intermediate potential Ek to the minimum potential Em, maintains the minimum potential Em, then rises from the minimum potential Em to the maximum potential En, maintains the maximum potential En, and then drops to the intermediate potential Ek. Note that the driving waveform WCom shown in FIG. 5 is an example, and the driving voltage Com may have other waveforms.

[0051] The reference voltage E0 does not change over time and is constant. In the illustrated example, the reference voltage E0 is a voltage value higher than the minimum potential Em of the drive voltage Com, but is not limited to this.

[0052] As described above, the piezoelectric body 443 is provided between the first electrode 441 and the second electrode 442. The piezoelectric body 443 is driven by the voltage difference between the reference voltage E0 applied to the first electrode 441 and the drive voltage Com applied to the second electrode 442. An applied voltage Ea, which is the difference between the reference voltage E0 and the drive voltage Com, is applied to the piezoelectric body 443.

[0053] 6 is an example of the applied voltage Ea actually applied to the piezoelectric body 443 when the drive voltage Com and reference voltage E0 shown in FIG. 5 are applied to the first electrode 441 and the second electrode 442, respectively. In other words, the applied voltage Ea shown in FIG. 6 is obtained by subtracting the reference voltage E0 from the drive voltage Com shown in FIG. 5 at each time. The horizontal axis in FIG. 6 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 potential EN, and a minimum potential EM. The maximum potential EN is the difference between the maximum potential En of the driving voltage Com and the reference voltage E0. The minimum potential EM is the difference between the minimum potential Em of the drive voltage Com and the reference voltage E0. Note that the waveform WEa shown in Fig. 6 is an example and varies depending on the drive voltage Com and the reference voltage E0.

[0054] For example, consider the case where the reference voltage E0 in FIG. 5 is 6V, the minimum potential Em of the driving voltage Com is 2.5V, and the maximum potential En of the driving voltage Com is 27.5V. In this case, the minimum potential EM of the applied voltage Ea shown in FIG. 6 is −3.5V, and the maximum potential EN is 21.5V. Also, when the driving voltage Com in FIG. 5 includes a potential difference of 25V, that is, when the voltage range RE of the driving voltage Com is 25V, the voltage range RE of the applied voltage Ea is 25V. Since the reference voltage E0 is constant, the voltage range RE of the applied voltage Ea and the voltage range RE of the driving voltage Com are equal. In the following, the case where the driving voltage Com is a positive voltage will be mainly assumed and described.

[0055] 5, when the minimum potential Em of the driving voltage Com is lower than the reference voltage E0, the minimum potential EM of the applied voltage Ea is a negative value. When the reference voltage E0 is 0, that is, when no voltage is applied to the second electrode 442, the minimum potential EM of the applied voltage Ea is equal to the minimum potential Em of the driving voltage Com. In addition, when the minimum potential Em of the driving voltage Com is also set to 0, the minimum potential EM of the applied voltage Ea is also 0.

[0056] 1-5. Electrical characteristics of the comparative piezoelectric body 443z 7 is an example of a hysteresis curve showing the relationship between the voltage and polarization of the piezoelectric body 443z of the piezoelectric element 44z of the comparative example. In FIG. 7, the horizontal axis is voltage [V], and the vertical axis is polarization [μC / cm 2 ].

[0057] As shown in Fig. 7, the hysteresis curve of the piezoelectric body 443z includes a positive remnant polarization Prz and a negative coercive field -Ecz. The remnant polarization Prz is the polarization when the voltage is 0 V. The coercive field -Ecz is the polarization when the polarization is 0 μC / cm 2 is the magnitude of the electric field.

[0058] Fig. 11 is a butterfly curve showing the relationship between the voltage of piezoelectric body 443z of the comparative example and the displacement amount (distortion amount of the piezoelectric body) of vibration plate 36. The horizontal axis of Fig. 11 is voltage [V], and the vertical axis is the displacement amount [nm] of vibration plate 36. Note that the displacement amount of vibration plate 36 is shown by taking the position closest to Z1 side (opposite side to pressure chamber C) as 0, and shows how far it has displaced from that position toward Z2 side (pressure chamber C side), that is, the relative position when the position closest to Z1 side is used as a reference.

[0059] First, in the piezoelectric body 443z of the comparative example, a case will be considered in which the first driving voltage Com1 and the first reference voltage E01 are applied to the first electrode 441 and the second electrode 442 such that the first reference voltage E01=6V, the minimum potential Em1 of the first driving voltage Com1=2.5V, and the maximum potential En of the first driving voltage Com1=27.5V. The driving voltage Com1 and the first reference voltage E01 are shown in FIG. 9. In this case, the first applied voltage Ea1 applied to the piezoelectric body 443z has a minimum potential EM1 of -3.5V, a maximum potential EN1=21.5V, and a voltage range RE=25V. This minimum potential EM1=-3.5V corresponds to the coercive electric field -Ecz of the piezoelectric body 443z, and generally, a driving voltage Com and a reference voltage E0 having this relationship are used. As shown in FIG. 11, when the coercive electric field is -Ecz, the relative position of the vibration plate 36 is closest to the Z1 side, and when the vibration plate 36 is vibrated toward the Z2 side during subsequent driving, the volume change of the pressure chamber C becomes large, resulting in good ejection efficiency.

[0060] During the period in which the first applied voltage Ea1 changes from the intermediate voltage EK1 to the minimum potential EM1=-3.5V, the polarization changes to the negative side so as to trace the coercive electric field -Ecz along the path Rcv1 of the hysteresis curve shown in Fig. 7 until the polarization becomes 0. At this time, in the butterfly curve shown in Fig. 11, the displacement also changes to the negative side (Z1 side) along the path Rsv1, and the displacement of the diaphragm 36 becomes the most negative side (displacement amount 0 nm) when the coercive electric field becomes -Ecz=-3.5 as described above.

[0061] After that, during the period when the first applied voltage Ea1 changes from the minimum potential EM1=-3.5V to the maximum potential EN1=21.5V, the hysteresis curve shown in FIG. 7 shifts from the path Rcv1 to the path Rcv2, and the polarization also changes to the positive side by the voltage range RE=25V. At this time, the butterfly curve shown in FIG. 11 also shifts from the path Rsv1 to the path Rsv2, and the displacement of the vibration plate 36 also changes to the positive side, and becomes the displacement corresponding to the maximum potential EN1=21.5V. The displacement of the vibration plate 36 at this time is 790 nm. During this period, ink is ejected with the displacement of the vibration plate 36 to the Z2 side. In other words, the displacement difference SXz=790nm-0nm=790nm from the minimum potential EM1=-3.5V to the maximum potential EN1=21.5V corresponds to the ejection characteristics in this case. For ease of understanding, in terms of the ejection amount due to the change in volume of the pressure chamber C accompanying the displacement of the diaphragm 36, a relatively large displacement of 790 nm is performed, and therefore the ejection amount is also relatively large.

[0062] 11, the displacement amount SXz is a relatively large value. Therefore, the ejection efficiency is good. However, since it is necessary to apply the first reference voltage E01=6V to the first electrode 441, circuits and wiring are required, which may result in an increase in cost and size.

[0063] Next, consider the case where the second reference voltage E02 is 0V, that is, the second reference voltage E02 is the GND potential. In this case, the second drive voltage Com2 has a minimum potential Em2=0V and a maximum potential En2 of the second drive voltage Com2=25V. The drive voltage Com2 and the second reference voltage E02 are shown in FIG. 10. Since the second reference voltage E02=0V, the second applied voltage Ea2 applied to the piezoelectric body 443z also has a minimum potential EM2 of 0V, a maximum potential EN2=25V, and a voltage range RE=25V. The reason why the minimum potential Em2 of the second drive voltage Com2 is set to 0V is that, as described above, the ejection efficiency is improved when the minimum potential EM2 is closer to the coercive electric field -Ecz, and on the other hand, if the minimum potential EM2 is set to a negative value, the second drive voltage Com2 changes between positive and negative, which causes problems in the electrical circuit. Although the second reference voltage E02 is set to 0V as the optimum value that satisfies the above condition, the phenomenon described below also occurs when the second reference voltage is close to 0V, for example, when the second reference voltage is 0.1V.

[0064] During the period in which the second applied voltage Ea2 changes from the intermediate voltage EK2 to the minimum potential EM2=0V, the polarization changes to the negative side so as to trace the path Rcv1 of the hysteresis curve shown in Fig. 7 until the second applied voltage Ea2=0, that is, the positive remanent polarization Prz. At this time, in the butterfly curve shown in Fig. 11, the displacement amount also changes to the negative side (Z1 side) on the path Rsv1, but the displacement amount of the diaphragm 36 when the second applied voltage Ea2=0 does not reach the negative side very far, and is 200 nm.

[0065] Thereafter, during the period in which the second applied voltage Ea2 changes from the minimum potential EM2=0V to the maximum potential EN2=25V, the hysteresis curve shown in Fig. 7 shifts from path Rcv1 to path Rcv2, and the polarization also shifts to the positive side by the voltage range RE=25V. At this time, the butterfly curve shown in Fig. 11 also shifts from path Rsv1 to path Rsv2, and the displacement of the diaphragm 36 also shifts to the positive side, and the displacement of the diaphragm 36 at the maximum potential EN2=25V is 820nm. Therefore, the displacement difference SYz=820nm-200nm=620nm from the minimum potential EM2=0V to the maximum potential EN2=25V corresponds to the ejection characteristics in this case.

[0066] Here, in Fig. 11, the displacement difference SYz = 620 nm is much smaller than the displacement difference SXz = 790 nm, and the ratio is only SYz / SXz = 78%. This means that the former is far more preferable in terms of ejection efficiency than the latter in the case where the first reference voltage E01 = 6V, the minimum potential Em1 of the first driving voltage Com1 = 2.5V, and the maximum potential En1 of the first driving voltage Com1 = 27.5V, and the latter in the case where the second reference voltage E02 = 0V, the minimum potential Em2 of the second driving voltage Com2 = 0V, and the maximum potential En2 of the second driving voltage Com2 = 25V, even though the voltage range RE is the same at 25V. In other words, when using the piezoelectric body 443z of the comparative example, if the second reference voltage E02 = 0V, sufficient ejection efficiency cannot be obtained.

[0067] 1-6. Electrical characteristics of the piezoelectric body 443 of the first embodiment 8 is a hysteresis curve showing the relationship between the voltage and polarization of the piezoelectric body 443 of the piezoelectric element 44 of the first embodiment. In FIG. 8, the horizontal axis is voltage [V], and the vertical axis is polarization [μC / cm 2 ].

[0068] 8, the hysteresis curve of the piezoelectric body 443 of this embodiment includes a positive remnant polarization Pr and a negative coercive field -Ec. The remnant polarization Pr is the polarization when the voltage is 0 V. The coercive field -Ec is the polarization when the polarization is 0 μC / cm 2 is the magnitude of the electric field.

[0069] Fig. 12 is a butterfly curve showing the relationship between the voltage of the piezoelectric body 443 and the displacement amount (the distortion amount of the piezoelectric body) of the diaphragm 36 in the first embodiment. The horizontal axis of Fig. 12 is voltage [V], and the vertical axis is the displacement amount [nm] of the diaphragm 36. Note that the displacement amount of the diaphragm 36 indicates how far it has displaced toward the Z2 side (the pressure chamber C side) from the position closest to the Z1 side (the opposite side to the pressure chamber C), that is, indicates the relative position when the position closest to the Z1 side is used as a reference.

[0070] First, in the same manner as in the comparative example piezoelectric body 443z, consider the case in which the first driving voltage Com1 (minimum potential Em1=2.5 V, maximum potential En1=27.5 V) and the first reference voltage E01=6 V shown in FIG. 9 are applied to the first electrode 441 and the second electrode 442 in the piezoelectric body 443 of the first embodiment.

[0071] During the period in which the second applied voltage Ea2 changes from the intermediate voltage EK2 to the minimum potential EM2=-3.5V, the polarization changes to the negative side so as to trace the coercive electric field -Ec on the path Rcv3 of the hysteresis curve shown in Fig. 8 until the polarization becomes 0. At this time, in the butterfly curve shown in Fig. 12, the displacement also changes to the negative side (Z1 side) on the path Rsv3, and the displacement of the diaphragm 36 becomes the most negative side (displacement amount 0 nm) when the coercive electric field becomes -Ec=-3.5 as described above.

[0072] Thereafter, during the period when the second applied voltage Ea2 changes from the minimum potential EM2=-3.5V to the maximum potential EN2=21.5V, the hysteresis curve shown in FIG. 8 shifts from the path Rcv3 to the path Rcv4, and the polarization also changes to the positive side by the voltage range RE=25V. At this time, the butterfly curve shown in FIG. 12 also shifts from the path Rsv3 to the path Rsv4, and the displacement of the vibration plate 36 also changes to the positive side, and becomes the displacement corresponding to the maximum potential EN2=21.5V. The displacement of the vibration plate 36 at this time is 720 nm. Therefore, the displacement difference SX=720 nm-0 nm=720 nm from the minimum potential EM1=-3.5V to the maximum potential EN1=21.5V corresponds to the ejection characteristics in this case. In the following description, this displacement difference SX is also referred to as the first displacement.

[0073] Next, in the same manner as the comparative piezoelectric body 443z, consider the case in which the second driving voltage Com2 (minimum potential Em2=0V, maximum potential En2=25V) and the second reference voltage E02=0V shown in FIG. 10 are applied to the first electrode 441 and the second electrode 442 in the piezoelectric body 443 of the first embodiment.

[0074] During the period in which the second applied voltage Ea2 changes from the intermediate voltage EK2 to the minimum potential EM2=0V, the polarization changes to the negative side so as to trace the path Rcv3 of the hysteresis curve shown in Fig. 8 until the second applied voltage Ea2=0, that is, the positive remanent polarization Pr. At this time, in the butterfly curve shown in Fig. 12, the displacement amount also changes to the negative side (Z1 side) on the path Rsv3. At this time, unlike the piezoelectric body 443z of the comparative example, in the piezoelectric body 443 of the first embodiment, the displacement amount of the diaphragm 36 when the second applied voltage Ea2=0 reaches a relatively negative side, reaching 30 nm.

[0075] Thereafter, during the period when the second applied voltage Ea2 changes from the minimum potential EM2=0V to the maximum potential EN2=25V, the hysteresis curve shown in FIG. 8 shifts from the path Rcv3 to the path Rcv4, and the polarization also shifts to the positive side by the voltage range RE=25V. At this time, the butterfly curve shown in FIG. 12 also shifts from the path Rsv3 to the path Rsv4, and the displacement of the vibration plate 36 also shifts to the positive side, and the displacement of the vibration plate 36 at the maximum potential EN2=25V is 780nm. Therefore, the displacement difference SY=780nm-30nm=750nm from the minimum potential EM2=0V to the maximum potential EN2=25V corresponds to the ejection characteristics in this case. In the following description, this displacement difference SY is also referred to as the second displacement.

[0076] Here, in Fig. 12, the displacement difference SY = 750 nm is almost the same as the displacement difference SX = 720 nm, and the ratio SY / SX = 104%. This means that the voltage range RE is the same as 25V when the first reference voltage E01 = 6V, the minimum potential Em1 of the first driving voltage Com1 = 2.5V, and the maximum potential En1 of the first driving voltage Com1 = 27.5V, and when the second reference voltage E02 = 0V, the minimum potential Em2 of the second driving voltage Com2 = 0V, and the maximum potential En2 of the second driving voltage Com2 = 25V, and further the ejection efficiency of both is about the same. In other words, when using the piezoelectric body 443 of the first embodiment, even if the second reference voltage E02 = 0V, the ejection efficiency does not change much.

[0077] 1-7. Comparison of electrical properties of piezoelectric material 443 and piezoelectric material 443z 11 and 12, when the first drive voltage Com1 and the first reference voltage E01 shown in Fig. 9 are used, the displacement difference SX=720 nm of the piezoelectric body 443 in the first embodiment is slightly smaller than the displacement difference SXz=790 nm of the piezoelectric body 443z in the comparative example. In other words, when the first drive voltage Com1 and the first reference voltage E01 in Fig. 9 are used, the ejection characteristics of the piezoelectric body 443 in the first embodiment are slightly inferior.

[0078] However, when the second drive voltage Com2 and second reference voltage E02 shown in Fig. 10 are used, the displacement difference SY=750 nm of the piezoelectric body 443 in the first embodiment is significantly larger than the displacement difference SYz=620 nm of the piezoelectric body 443z in the comparative example. In other words, when the second drive voltage Com2 and second reference voltage E02 in Fig. 10 are used, the piezoelectric body 443 in the first embodiment has significantly better ejection characteristics.

[0079] Furthermore, in the piezoelectric body 443z of the comparative example, the displacement difference SYz=620 nm when the second driving voltage Com2 and the second reference voltage E02 shown in Fig. 10 are used is much smaller than the displacement difference SXz=790 nm when the first driving voltage Com1 and the first reference voltage E01 shown in Fig. 9 are used, and the ratio SYz / SXz is 78%. In other words, the piezoelectric body 443z of the comparative example has excellent ejection efficiency when the first driving voltage Com1 and the first reference voltage E01 shown in Fig. 9 are used, but the ejection efficiency is not so excellent when the second driving voltage Com2 and the second reference voltage E02 shown in Fig. 10 are used.

[0080] On the other hand, in the piezoelectric body 443 of the first embodiment, the displacement difference SY=750 nm when the second driving voltage Com2 and the second reference voltage E02 shown in Fig. 10 are used is similar to the displacement difference SX=720 nm when the first driving voltage Com1 and the first reference voltage E01 shown in Fig. 9 are used, and the ratio SY / SX is 104%. In other words, the piezoelectric body 443 of the first embodiment has excellent ejection efficiency to the same extent when the first driving voltage Com1 and the first reference voltage E01 shown in Fig. 9 are used and when the second driving voltage Com2 and the second reference voltage E02 shown in Fig. 10 are used.

[0081] Thus, according to the piezoelectric body 443 of this embodiment, sufficient ejection characteristics can be obtained even when the first drive voltage Com1 and the first reference voltage E01 as shown in Fig. 9 are used, and even when the circuit and wiring are reduced by using the second drive voltage Com2 and the second reference voltage E02 as shown in Fig. 10 and not applying two systems of positive and negative voltages, a large difference in the amount of displacement of the piezoelectric body 443 is unlikely to occur, and sufficient ejection characteristics can be obtained. This is because the piezoelectric body 443 is designed so that the change in the amount of displacement of the vibration plate 36 from the coercive electric field -Ec=-3.5 to 0V and the change in the amount of displacement of the vibration plate 36 from the coercive electric field -Ec+voltage range RE to the 0V+voltage range RE are as close as possible.

[0082] Here, in the first embodiment, the second displacement amount SY was 104% of the first displacement amount SX. In order to obtain the ejection characteristics even when using the second driving voltage Com2 and the second reference voltage E02 as shown in FIG. 10, the second displacement amount SY needs to be larger than 90% of the first displacement amount SX. Also, using the second driving voltage Com2 and the second reference voltage E02 as shown in FIG. 10 is preferable to using the first driving voltage Com1 and the first reference voltage E01 as shown in FIG. 9 because it has an effect of reducing the circuit and wiring, so the former has better ejection characteristics than the latter, that is, it is preferable that the second displacement amount SY is as large as possible. Specifically, it is preferable that the second displacement amount SY is larger than 95% of the first displacement amount SX. However, since there are cases where the first driving voltage Com1 and the first reference voltage E01 as shown in FIG. 9 are used, it is better to avoid a large drop in the ejection characteristics in that case, and from that point of view, it is preferable that the second displacement amount SY is smaller than 110% of the first displacement amount SX.

[0083] Here, in the first embodiment, the difference (27.5 V - 2.5 V = 25 V) between the maximum potential En1 (27.5 V) and the minimum potential Em1 (2.5 V) of the first driving voltage Com1 is equal to the difference between the maximum potential En2 (25 V) and the minimum potential Em2 (0 V) of the second driving voltage Com2 (25 V - 0 V = 25 V). Also, the difference (2.5 V - 6 V = -3.5 V) between the minimum potential Em1 (2.5 V) of the first driving voltage Com1 and the first reference voltage E01 (6 V) corresponds to the coercive electric field -Ec (-3.5 V) of the piezoelectric body 443. Further, the difference (0 V - 0 V = 0 V) between the minimum potential Em2 (0 V) of the second driving voltage Com2 and the second reference voltage E02 (0 V) is closer to 0 than the difference (2.5 V - 6 V = -3.5 V) between the minimum potential Em1 (2.5 V) of the first driving voltage Com1 and the first reference voltage E01 (6 V).

[0084] 1 - 8. Manufacturing Example of Piezoelectric Body 443 The piezoelectric body 443 of this 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 between the first electrode 441 and the piezoelectric body 443 is non-uniform is created. It is considered that due to this non-uniform state of the interface, the voltage at which polarization reversal occurs becomes more dispersed than in the past. As a result, the piezoelectric body 443 of the embodiment having the hysteresis curve shown in FIG. 8 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 this embodiment can be obtained.

[0085] Also, for example, when the piezoelectric body 443 is PZT, by satisfying the relationship of 0.55 < Zr / (Zr + Ti) for the zirconia (Zr) ratio of PZT, the piezoelectric body 443 of this embodiment can be obtained.

[0086] 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.

[0087] It should be noted that the piezoelectric body 443 of this embodiment only needs to have the electrical characteristics described above, and the method of manufacturing the piezoelectric body 443 is not limited to this method.

[0088] 2. Second embodiment A second embodiment will be described. In the following exemplary embodiment, for elements whose actions and functions are the same as those of the first embodiment, the reference symbols used in the description of the first embodiment will be used and detailed descriptions of each will be omitted as appropriate. In the second embodiment, the piezoelectric body 443 itself is the same as that in the first embodiment. In the second embodiment, the second drive voltage Com2, the second reference voltage E02, and the second applied voltage Ea2 are different from those in the first embodiment.

[0089] When the applied voltage Ea is applied to a piezoelectric body for a long period of time, i.e., when the number of shots of ink ejection from a liquid ejection head increases, an imprint phenomenon occurs in which the hysteresis shape of the piezoelectric body shifts. FIG. 13 is a diagram for explaining the imprint phenomenon, showing butterfly curves of a piezoelectric body before and after a long-term voltage application. The solid line in FIG. 13 is the butterfly curve of the initial piezoelectric body before the application of the applied voltage Ea for a long period of time. The dashed line in FIG. 13 is the butterfly curve of the piezoelectric body after the application of the applied voltage Ea for a long period of time. The horizontal axis in FIG. 13 is voltage [V], and the vertical axis is the amount of displacement.

[0090] This causes the butterfly curve of the piezoelectric body to shift. For example, the butterfly curve may shift from the solid line in Fig. 13 to the dashed line in Fig. 13. As a result, the voltage response of the piezoelectric body in the vicinity of the coercive field -Ec' changes significantly with respect to the voltage response in the high voltage region.

[0091] This imprint phenomenon occurs when the applied voltage Ea is applied to the piezoelectric body for a long time, that is, when the number of shots increases. The shift amount increases with each increase in the number of shots. Note that this imprint phenomenon occurs in both the piezoelectric body 443 of the first embodiment and the piezoelectric body 443z of the comparative example. In fact, it is known that the piezoelectric body shifts to the negative side by about 1.5 V between the initial state and 50 billion shots. As a result, when the imprint phenomenon occurs, a difference appears in the displacement amount. For example, when an applied voltage Ea from the coercive electric field -Ec' to the voltage V1 is used in the initial state of the piezoelectric body, the displacement amount C1 shown in FIG. 13 is obtained. However, after the imprint phenomenon occurs and the butterfly curve shifts to the dashed line shown in FIG. 13, when an applied voltage Ea from the coercive electric field -Ec' to the voltage V1 is used, the displacement amount C2 shown in FIG. 13 is obtained. As can be seen from FIG. 13, the displacement amount C2 is smaller than the displacement amount C1.

[0092] This displacement C2 can be estimated from the butterfly curve in the initial state if we consider applying a voltage that is shifted by the voltage shift caused by the imprint phenomenon from the applied voltage Ea. If we shift the applied voltage to the negative side by 1.5V as described above, we can obtain the displacement C2 by shifting the applied voltage Ea to the positive side by 1.5V, that is, by using a voltage from the coercive field -Ec´+1.5V to the voltage V1+1.5V.

[0093] In the second embodiment, in addition to the first drive voltage Com1 and the first reference voltage E01 shown in Fig. 9, the second drive voltage Com2 and the second reference voltage E02 shown in Fig. 14 are used for the study. Regarding the second drive voltage Com2 and the second reference voltage E02, differences from the first embodiment will be mainly described. In the example of Fig. 14, the second drive voltage Com2 is set in consideration of the amount of voltage shift due to the imprint phenomenon.

[0094] 9, the first applied voltage Ea1 has a minimum potential EM1 of -3.5V, a maximum potential EN1 of 21.5V, and a voltage range RE of 25V. This minimum potential EM1 of -3.5V is set to correspond to the coercive electric field -Ec of the piezoelectric body 443. The minimum potential EM of the applied voltage Ea is -3.5V, and the maximum potential EN is 21.5V.

[0095] Next, the second drive voltage Com2 and the second reference voltage E02 of the second embodiment will be described with reference to FIG. 14. The second drive voltage Com2 has a minimum potential Em2 of 4V and a maximum potential En2 of 29V. This is because the second drive voltage Com2 is set to a value that is 1.5V different from the first drive voltage Com1 on the positive side, taking into account the effect of the imprint phenomenon of 1.5V on the negative side. Specifically, the minimum potential Em2 (4V) = the minimum potential Em1 (2.5V) + 1.5V, and the maximum potential En2 (29V) = the maximum potential En1 (27.5V) + 1.5V. The voltage range RE, which is the difference between the minimum potential Em2 and the maximum potential En2, is 25V, which is equal to the voltage range RE of the first drive voltage Com1 shown in FIG. 9.

[0096] The second reference voltage E02 indicated by a solid line in Fig. 14 is equal to the first reference voltage E01 shown in Fig. 9. In the example of Fig. 14, the second reference voltage E02 is 6V.

[0097] Therefore, the second applied voltage Ea2 applied to the piezoelectric body 443 when the second driving voltage Com2 and the second reference voltage E02 are applied is as shown by the dashed line in FIG. 14. That is, the second applied voltage Ea2 has a minimum potential EM2=Em2-E02=4V-6V=-2V and a maximum potential EN2=En1-E02=29V-6V=23V. Therefore, the voltage range RE, which is the difference between the minimum potential EM2 and the maximum potential EN2, is 25V, which is equal to the voltage range RE of the first applied voltage Ea1 shown in FIG. 9 described above. The second applied voltage Ea2 is the first applied voltage Ea1 shifted to the positive side by 1.5V, which is the change due to the imprint phenomenon. Therefore, by using the second applied voltage Ea2, the displacement amount of the piezoelectric body after the imprint phenomenon can be evaluated.

[0098] In the second embodiment, the difference (27.5V-2.5V=25V) between the maximum potential En1 (27.5V) and the minimum potential Em1 (2.5V) of the first drive voltage Com1 is equal to the difference (29V-4V=25V) between the maximum potential En2 (29V) and the minimum potential Em2 (4V) of the second drive voltage Com2. The difference (2.5V-6V=-3.5V) between the minimum potential Em1 (2.5V) of the first drive voltage Com1 and the first reference voltage E01 (6V) corresponds to the coercive electric field -Ec (-3.5V) of the piezoelectric body 443. In addition, the difference (4V-6V=-2V) between the minimum potential Em2 (4V) of the second driving voltage Com2 and the second reference voltage E02 (6V) is closer to 0 than the difference (2.5V-6V=-3.5V) between the minimum potential Em1 (2.5V) of the first driving voltage Com1 and the first reference voltage E01 (6V).

[0099] 15 is an example of a hysteresis curve showing the relationship between the voltage and polarization of the piezoelectric body 443 of the second embodiment. The hysteresis curve in FIG. 15 is the same as the hysteresis curve in FIG.

[0100] 16 is a butterfly curve showing the relationship between the voltage of the piezoelectric body 443 and the amount of displacement (amount of distortion of the piezoelectric body) of the diaphragm 36 in the second embodiment. The butterfly curve in FIG. 16 is the same as the butterfly curve in FIG.

[0101] First, evaluate the displacement difference SX of the piezoelectric body 443 in the initial state. When the first applied voltage Ea1 is applied to the piezoelectric body 443, the first applied voltage Ea1, the hysteresis curve in Fig. 15, and the butterfly curve in Fig. 16 are all the same in the first and second embodiments, so the result is the same and the displacement difference SX (first displacement) is also the same, 720 nm.

[0102] Next, the displacement difference SY after the imprint phenomenon is evaluated. When the second applied voltage Ea2 is applied to the piezoelectric body 443 (initial state), as described above, the minimum potential EM2 is -2V and the maximum potential EN2 is 23V. At the minimum potential EM2, the polarization is P3 and the displacement of the diaphragm 36 is 10nm. At the maximum potential EN2, the polarization is P4 and the displacement of the diaphragm 36 is 750nm. Therefore, the displacement difference SY (second displacement) is 750nm-10nm=740nm.

[0103] Thus, in the second embodiment, the displacement difference SY=740 nm is almost the same as the displacement difference SX=720 nm, and the ratio SY / SX is 103%. In other words, the displacement difference, that is, the ejection characteristics, does not deteriorate significantly between the initial state and after the imprint phenomenon occurs. In order to sufficiently suppress the deterioration due to the imprint phenomenon, the second displacement amount SY needs to be larger than 90% of the first displacement amount SX. Also, after about 50 billion shots from the initial state, the imprint phenomenon does not occur much any more. Therefore, in the life of the liquid ejection head, the usage period after the imprint phenomenon of 1.5V occurs is likely to be longer than before. Therefore, if anything, it is better to place importance on the period after the imprint phenomenon occurs, that is, it is preferable that the second displacement amount SY is as large as possible. Specifically, it is preferable that the second displacement amount SY is larger than 95% of the first displacement amount SX. However, since it is of course necessary to avoid a deterioration in the ejection characteristics while the imprint phenomenon is occurring, it is better to ensure a certain degree of the first displacement amount SX, and specifically, it is preferable that the second displacement amount SY is smaller than 110% of the first displacement amount SX.

[0104] As described above, in this embodiment, the first reference voltage E01 is positive. The second reference voltage E02 is equal to the first reference voltage E01. Moreover, the minimum potential Em1, which is the minimum value of the first driving voltage Com1, is positive and smaller than the first reference voltage E01. Moreover, the minimum potential Em2, which is the minimum value of the second driving voltage Com2, is positive and larger than the minimum potential Em1 of the first driving voltage Com1. Therefore, in this embodiment, it is possible to evaluate the piezoelectric body taking into account the amount of voltage shift due to the imprint phenomenon.

[0105] In the second embodiment, in driving for actual liquid ejection, the first reference voltage E01 and the first driving voltage Com1 are basically used continuously from the initial state even after the occurrence of the imprint phenomenon. In other words, the second reference voltage E02 and the second driving voltage Com2 are used only for evaluation of the piezoelectric body 443, and are not used for actual liquid ejection.

[0106] However, for example, the first reference voltage E01 and the first driving voltage Com1 may be used in the initial stage, and the second reference voltage E02 and the second driving voltage Com2 may be used when the number of driving shots exceeds a predetermined number. In this case, when the number of driving times of the liquid ejection head 26 is the first driving number, the voltage application unit 29 shown in FIG. 1 applies the first reference voltage E01 to the first electrode 441 and applies the first driving voltage Com1 to the second electrode 442, thereby ejecting liquid from the nozzle N. When the number of driving times of the liquid ejection head 26 is the second driving number, which is greater than the first driving number, the voltage application unit 29 applies the second reference voltage E02 to the first electrode 441 and applies the second driving voltage Com2 to the second electrode 442, thereby ejecting ink from the nozzle N.

[0107] For example, the first driving count is equal to or greater than 1 and less than the second driving count. The second driving count is, for example, several hundred million times to several tens of billion times. By changing the driving voltage Com according to the driving count, it is possible to suppress the rate of decrease in the ejection amount due to the driving count over a long period of time. Note that the driving voltage Com may be changed in three or more stages instead of two stages.

[0108] In addition, in the second embodiment, the second driving voltage Com2 is shifted taking into account the imprint phenomenon and the second reference voltage E02 is not changed, but it is also possible to shift the second reference voltage E02 without changing the second driving voltage Com2.

[0109] Fig. 17 is a diagram showing the second drive voltage Com2 and the second reference voltage E02 of the modified example. Regarding the second drive voltage Com2 and the second reference voltage E02 in Fig. 17, differences from the example shown in Fig. 15 will be mainly described. In the example of Fig. 17, the second reference voltage E02 is set in consideration of the amount of voltage shift due to the imprint phenomenon.

[0110] The second drive voltage Com2 in Fig. 17 is equal to the first drive voltage Com1 shown in Fig. 9. For example, the minimum potential Em2 is 2.5 V, and the maximum potential En2 is 27.5 V. The voltage range RE, which is the difference between the minimum potential Em2 and the maximum potential En2, is 25 V.

[0111] The second reference voltage E02 shown by a solid line in Fig. 17 is different from the first reference voltage E01 shown in Fig. 9. In order to cancel the effect of the imprint phenomenon of 1.5V on the negative side, the second reference voltage E02 is set to a value that is different from the first reference voltage E01 by 1.5V on the negative side. Specifically, the second reference voltage E02 = (4.5V) = the first reference voltage E01 (6V) - 1.5V.

[0112] Therefore, in the modified example, the second applied voltage Ea2 applied to the piezoelectric body 443 when the second driving voltage Com2 and the second reference voltage E02 are applied is as shown by the dashed line in FIG. 17. That is, the second applied voltage Ea2 is a minimum potential EM2=Em2-E02=2.5V-4.5V=-2V, and a maximum potential EN2=En2-E02=27.5V-4.5V=23V. Therefore, the voltage range RE, which is the difference between the minimum potential EM2 and the maximum potential EN2, is 25V, which is equal to the voltage range RE of the first applied voltage Ea1 shown in FIG. 9 described above. The applied voltages in this modified example are equal to the applied voltages in the second embodiment in each value. Therefore, the same results are obtained.

[0113] In this modification, the difference (27.5V-2.5V=25V) between the maximum potential En1 (27.5V) and the minimum potential Em1 (2.5V) of the first drive voltage Com1 is equal to the difference (27.5V-2.5V=25V) between the maximum potential En2 (27.5V) and the minimum potential Em2 (2.5V) of the second drive voltage Com2. The difference (2.5V-6V=-3.5V) between the minimum potential Em1 (2.5V) of the first drive voltage Com1 and the first reference voltage E01 (6V) corresponds to the coercive electric field -Ec (-3.5V) of the piezoelectric body 443. In addition, the difference (2.5V-4V=-2V) between the minimum potential Em2 (2.5V) of the second driving voltage Com2 and the second reference voltage E02 (4.5V) is closer to 0 than the difference (2.5V-6V=-3.5V) between the minimum potential Em1 (2.5V) of the first driving voltage Com1 and the first reference voltage E01 (6V).

[0114] As described above, in this modified example, the first reference voltage E01 is positive. The second reference voltage E02 is positive and smaller than the first reference voltage E01. Moreover, the minimum potential Em1, which is the minimum value of the first driving voltage Com1, is positive and smaller than the first reference voltage E01. Moreover, the minimum potential Em2, which is the minimum value of the second driving voltage Com2, is equal to the minimum potential Em1 of the first driving voltage Com1. Therefore, in this embodiment, the piezoelectric body can be evaluated taking into account the amount of voltage shift due to the imprint phenomenon.

[0115] The shift in the amount of displacement of the piezoelectric body 443 is presumably 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 (morphotropic 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.

[0116] 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.

[0117] 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.

[0118] It is believed that such factors cause the imprint phenomenon, which shifts the hysteresis shape of the piezoelectric body 443. As described above, by setting the minimum potential EM2 to a voltage in the range from the coercive electric field -Ec to the remanent polarization Pr, it is possible to suppress the decrease in the discharge amount due to the shift caused by the imprint phenomenon.

[0119] 3. Other Modifications 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.

[0120] In each embodiment, the driving voltage Com is a positive voltage, but it may be a negative voltage. Even in this case, the applied voltage Ea is set based on the same technical idea as in each embodiment.

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

[0122] 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.

[0123] Although the present invention has been described based on the preferred embodiment, the present invention is not limited to the above-mentioned 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-mentioned embodiment, and any configuration can be added. [Explanation of symbols]

[0124] 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...transport belt, 322...supply flow path, 324 ...communicating 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...inlet, B...bump, C...pressure chamber, C1...initial displacement amount, C2...displacement amount, CX...first displacement amount, CXz...polarization displacement amount, CY...second displacement amount, CYz...polarization displacement amount, Com...driving voltage, Com1...first driving voltage, Com2 ...second drive voltage, E0...reference voltage, E01...first reference voltage, E02...second reference voltage, E2...minimum potential, EK...intermediate voltage, EM...minimum potential, EM1...minimum potential, EM2...minimum potential, EN...maximum potential, EN1...maximum potential, EN2...maximum potential, ER...voltage range, Ea...applied voltage, Ea1...first applied voltage, Ea2...second applied voltage, Ek...intermediate potential, Em...minimum potential, Em1...minimum potential, Em2...minimum potential, En...maximum potential, En 1...maximum potential, En2...maximum potential, L1...first row, L2...second row, N...nozzle, P1...polarization, P1z...polarization, P2...polarization, P2z...polarization, Pr...residual polarization, Prz...residual polarization, P3...polarization, P4...polarization, R...liquid reservoir, RE...voltage range, Ra...space, Rb...space, Tu...unit period, V1...voltage, WCom...driving waveform, WCom1...driving waveform, WEa...waveform, WEa1...waveform, WEa2...waveform, WEom2...driving waveform.

Claims

1. a first electrode to which a reference voltage that does not vary with time is applied; a second electrode to which a time-varying drive voltage is applied; a piezoelectric body provided between the first electrode and the second electrode and driven by a voltage difference between the reference voltage and the drive voltage; a vibration plate that vibrates in response to driving of the piezoelectric body; a nozzle from which liquid is ejected by vibration of the vibration plate, a first reference voltage is applied to the first electrode and a first driving voltage is applied to the second electrode, the first reference voltage being a displacement amount of the diaphragm; When a second reference voltage is applied to the first electrode and a second driving voltage is applied to the second electrode, the displacement amount of the diaphragm is defined as a second displacement amount. a difference between a maximum value and a minimum value of the first driving voltage is equal to a difference between a maximum value and a minimum value of the second driving voltage, a difference between the minimum value of the first driving voltage and the first reference voltage corresponds to a coercive electric field of the piezoelectric body; a difference between the minimum value of the second driving voltage and the second reference voltage is closer to 0 than a difference between the minimum value of the first driving voltage and the first reference voltage; The liquid ejection head according to claim 1, wherein the second displacement amount is greater than 90% of the first displacement amount.

2. 2. The liquid ejection head according to claim 1, wherein the second displacement amount is greater than 95% of the first displacement amount.

3. 2. The liquid ejection head according to claim 1, wherein the second displacement amount is smaller than 110% of the first displacement amount.

4. a difference between the first reference voltage and the first driving voltage is a voltage that causes liquid to be ejected from the nozzle when applied to the first electrode and the second electrode, 2. The liquid ejection head according to claim 1, wherein a difference between the second reference voltage and the second driving voltage is a voltage that causes liquid to be ejected from the nozzle when applied to the first electrode and the second electrode.

5. the first reference voltage is positive; the second reference voltage is equal to the first reference voltage; the minimum value of the first drive voltage is positive and less than the first reference voltage; 2. The liquid ejection head according to claim 1, wherein the minimum value of the second driving voltage is positive and is greater than the minimum value of the first driving voltage.

6. the first reference voltage is positive; the second reference voltage is positive and less than the first reference voltage; the minimum value of the first drive voltage is positive and less than the first reference voltage; 2. The liquid ejection head according to claim 1, wherein the minimum value of the second driving voltage is equal to the minimum value of the first driving voltage.

7. A liquid ejection head according to claim 5 or 6, a voltage application unit that applies the first reference voltage to the first electrode and the first drive voltage to the second electrode, thereby causing liquid to be ejected from the nozzle.

8. A liquid ejection head according to claim 5 or 6, a voltage application unit that, when the number of times the liquid ejection head is driven is a first driving number, applies the first reference voltage to the first electrode and applies the first driving voltage to the second electrode, thereby ejecting liquid from the nozzle, and, when the number of times the liquid ejection head is driven is a second driving number that is greater than the first driving number, applies the second reference voltage to the first electrode and applies the second driving voltage to the second electrode, thereby ejecting liquid from the nozzle.

9. the first reference voltage is positive; the second reference voltage is 0; The minimum value of the first driving voltage is positive and smaller than the first reference voltage.

2. The liquid ejection head according to claim 1, wherein the minimum value of the second driving voltage is zero.

10. A liquid ejection head according to claim 9 , a voltage application unit that applies the second reference voltage to the first electrode and the second driving voltage to the second electrode, thereby causing liquid to be ejected from the nozzle.

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