Liquid ejection head and liquid ejection apparatus

Abstract

The invention provides a liquid ejecting head and a liquid ejecting apparatus. The liquid ejection head includes a first electrode, a second electrode, a piezoelectric body driven by a voltage difference between a reference voltage and a driving voltage, a vibration plate that vibrates in response to the driving of the piezoelectric body, and a nozzle that ejects a liquid by the vibration of the vibration plate. A displacement amount of the diaphragm when a first reference voltage is applied to the first electrode and a first driving voltage is applied to the second electrode is set as a first displacement amount, and a displacement amount of the diaphragm when a second reference voltage is applied to the first electrode and a second driving voltage is set 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, and a difference between the minimum value of the first driving voltage and the first reference voltage corresponds to a coercive field of the piezoelectric body. The difference between the minimum value of the second driving voltage and the second reference voltage is close to 0 than the difference between the minimum value of the first driving voltage and the first reference voltage, and the second displacement amount is greater than 90% of the first displacement amount.

Description

Technical Field

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

[0002] A liquid ejection device having a liquid ejection head for ejecting a liquid such as ink onto a medium such as printing paper has been proposed. As such a liquid ejection device, a piezoelectric inkjet printer is known. In the piezoelectric type, a piezoelectric element is used to vibrate a vibration plate that is a part of the wall surface of a pressure chamber. By vibrating the vibration plate using the piezoelectric element, the liquid filled in the pressure chamber is ejected from the nozzle.

[0003] The piezoelectric element included in the liquid ejection head described in Patent Document 1 includes two electrodes and a piezoelectric body sandwiched by the two electrodes. The saturation polarization, residual polarization, and coercive electric field of the piezoelectric body in the polarization-electric field hysteresis characteristics satisfy predetermined conditions.

[0004] Generally, in the piezoelectric element of the liquid ejection head, a fixed reference voltage that does not change with time is applied to one of the two electrodes, and a driving voltage that changes with time is applied to the other electrode. Furthermore, by setting the voltage difference between the minimum driving voltage and the reference voltage (the minimum value of the applied voltage applied to the piezoelectric body) and the voltage difference between the maximum driving voltage and the reference voltage (the maximum value of the applied voltage applied to the piezoelectric body) to be larger, the displacement of the vibration plate vibrated by the piezoelectric element can be increased. Therefore, the ejection amount can be increased, making it easy to obtain the target ejection amount.

[0005] In order to increase the voltage difference between the minimum driving voltage and the reference voltage and the voltage difference between the maximum driving voltage and the reference voltage, the voltage difference between the minimum driving voltage and the reference voltage is set as the voltage in the coercive electric field. However, simply increasing this difference may cause other problems.

[0006] For example, when the voltage difference between the minimum value of the driving voltage and the reference voltage is set as the voltage in the coercive electric field, a specific voltage needs to be applied to the reference voltage. Therefore, a circuit and wiring for applying the voltage are required, which becomes a factor of increasing cost and increasing size. Therefore, it is difficult to provide a piezoelectric element with excellent ejection performance with a simple structure.

[0007] In addition, for example, when a voltage is applied to a piezoelectric body for a long time, an imprint phenomenon of the hysteresis shape of the piezoelectric body may occur. As a result, the coercive electric field may be offset. Therefore, even if the reference voltage and the drive voltage are set based on the initial hysteresis shape of the piezoelectric body, it is difficult to suppress the reduction rate of the ejection amount accompanying the number of driving times. Therefore, it is difficult to obtain stable ejection performance for a long time.

[0008] In this way, if 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 is simply increased, other problems may occur.

[0009] Patent Document 1: Japanese Patent Application Publication No. 2010-135748 Summary of the invention

[0010] A preferred embodiment of the present invention involves a liquid ejection head, comprising: a first electrode, to which a reference voltage that does not change with time is applied; a second electrode, to which a driving voltage that changes with time is applied; a piezoelectric body, which is arranged between the first electrode and the second electrode and is driven by the voltage difference between the reference voltage and the driving voltage; a vibration plate, which vibrates in response to the driving of the piezoelectric body; and a nozzle, which ejects liquid through the vibration of the vibration plate, wherein in the liquid ejection head, the displacement of the vibration plate when the first reference voltage is applied to the first electrode and the first driving voltage is applied to the second electrode is set to a first position When the displacement of the vibration plate when the second reference voltage is applied to the first electrode and the second driving voltage is applied to the second electrode is set to the second displacement, the difference between the maximum value and the minimum value of the first driving voltage is equal to the difference between the maximum value and the minimum value of the second driving voltage, the difference between the minimum value of the first driving 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 driving voltage and the second reference voltage is closer to zero than the difference between the minimum value of the first driving voltage and the first reference voltage, and the second displacement is greater than 90% of the first displacement. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic diagram illustrating the structure of the liquid ejecting device according to the first embodiment.

[0012] Figure 2 for Figure 1 An exploded perspective view of a liquid ejection head is shown.

[0013] Figure 3 for Figure 2 A partial cross-sectional view of a liquid ejection head is shown.

[0014] Figure 4 For Figure 3 A partially enlarged cross-sectional view of the liquid ejection head is shown.

[0015] Figure 5 A diagram for explaining a driving voltage and a reference voltage.

[0016] Figure 6 is an example of the applied voltage applied to the piezoelectric body.

[0017] Figure 7 1 is an example of a hysteresis curve showing the relationship between the voltage and the polarization of the piezoelectric body included in the piezoelectric element of the comparative example.

[0018] Figure 8 1 is an example of a hysteresis curve showing the relationship between the voltage and the polarization of the piezoelectric body included in the piezoelectric element according to the first embodiment.

[0019] Fig. 9 is a diagram showing the first driving voltage and the first reference voltage.

[0020] Fig.10 is a diagram showing the second driving voltage and the second reference voltage.

[0021] Fig.11 It is a butterfly curve in the piezoelectric body of the comparative example.

[0022] Fig.12 This is a butterfly curve in the piezoelectric body of the first embodiment.

[0023] Fig.13 An example of a butterfly curve used to illustrate the imprinting phenomenon.

[0024] Fig.14 : is a diagram showing the second driving voltage and the second reference voltage in the second embodiment.

[0025] Fig.15 2 is an example of a hysteresis curve showing the relationship between the voltage and the polarization of the piezoelectric body according to the second embodiment.

[0026] Fig.16 This is a butterfly curve in the piezoelectric body of the second embodiment.

[0027] Fig.17 : is a diagram showing the second driving voltage and the second reference voltage of a modified example. DETAILED DESCRIPTION

[0028] Below, the preferred embodiments of the present invention are described with reference to the accompanying drawings. In addition, the size or scale of each part in the accompanying drawings is appropriately different from the actual one, and there are also parts schematically shown for easy understanding. In addition, as long as there is no record of the meaning of particularly limiting the present invention in the following description, the scope of the present invention is not limited to these modes. In addition, "equal" includes the case of a difference with a degree of measurement error in addition to the case of strict equality.

[0029] The following description is appropriately carried out using mutually intersecting X-axis, Y-axis and Z-axis. A direction along the X-axis is called the X1 direction, and the direction opposite to the X1 direction is called the X2 direction. The directions opposite to each other along the Y-axis are called the Y1 direction and the Y2 direction. The directions opposite to each other along the Z-axis are called the Z1 direction and the Z2 direction. The situation of observing in the direction along the Z-axis is called "planar observation". The Z-axis is typically a vertical axis. However, the Z-axis may not be a vertical axis. In addition, although the X-axis, Y-axis and Z-axis are typically orthogonal to each other, they are not limited to this, for example, as long as they intersect at an angle within the range of 80° or more and 100° or less.

[0030] 1. First Implementation

[0031] 1-1. Overall Structure of Liquid Dispensing Device 100

[0032] Figure 1 1 is a schematic structural diagram of a liquid ejection device 100 according to the first embodiment. The liquid ejection device 100 is an inkjet printing device that ejects ink, which is an example of a liquid, in the form of droplets onto a medium 12. The medium 12 is typically a printing paper. In addition, the medium 12 is not limited to the printing paper, and may be a printing object of any material such as a resin film or cloth.

[0033] like Figure 1 As shown in FIG. 1 , a liquid container 14 for storing ink is mounted on the liquid ejecting device 100. Specific examples of the liquid container 14 include a cartridge that can be attached to and detached from the liquid ejecting device 100, a bag-shaped ink bag formed of a flexible film, and an ink tank that can replenish ink. The type of ink stored in the liquid container 14 is arbitrary.

[0034] The liquid ejection device 100 includes a control unit 20, a conveying mechanism 22, a moving 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 unit 29, which controls the drive of a piezoelectric element 44 described later to eject ink from the nozzle.

[0035] The conveying mechanism 22 conveys the medium 12 along the Y2 direction under the control of the control unit 20. The moving mechanism 24 reciprocates the liquid ejecting head 26 along the X1 direction and the X2 direction under the control of the control unit 20. Figure 1 In the example shown, the moving mechanism 24 includes a substantially box-shaped conveying body 242 called a carriage that accommodates the liquid ejecting head 26, and a conveying belt 244 that fixes the conveying body 242. In addition, the number of liquid ejecting heads 26 carried on the conveying body 242 is not limited to one, and may be multiple. In addition, on the conveying body 242, in addition to the liquid ejecting head 26, the liquid container 14 may also be carried.

[0036] The liquid ejection head 26 ejects the ink supplied from the liquid container 14 from a plurality of nozzles toward the Z2 direction toward the medium 12 under the control of the control unit 20. This ejection is performed in parallel with the conveyance of the medium 12 by the conveyance mechanism 22 and the reciprocating movement of the liquid ejection head 26 by the moving mechanism 24, thereby forming an image composed of ink on the surface of the medium 12.

[0037] The liquid ejection device 100 includes a liquid ejection head 26 and a control unit 20, which will be described later. The control unit 20 includes a voltage application unit 29 for ejecting ink from the nozzle N. Since the liquid ejection device 100 includes the liquid ejection head 26 having the features described later, the target ejection amount can be ensured and the ejection performance can be improved.

[0038] 1-2. Overall structure of the liquid ejection head

[0039] Figure 2 for Figure 1 An exploded perspective view of the liquid ejection head 26 is shown. Figure 3 for Figure 2 A partial cross-sectional view of the liquid ejection head shown in FIG. Figure 2 The III-III line cross-sectional view in FIG. Figure 2 As shown in FIG. 1 , the liquid ejection head 26 has a plurality of nozzles N arranged in a direction along the Y axis. Figure 2 In the example shown, the plurality of nozzles N are divided into a first column L1 and a second column L2 arranged at intervals in the direction along the X-axis. The first column L1 and the second column L2 are respectively a set of a plurality of nozzles N arranged in a straight line in the direction along the Y-axis. Here, the elements associated with each nozzle N of the first column L1 and the elements associated with each nozzle N of the second column L2 in the liquid ejection head 26 are substantially symmetrical to each other in the direction along the X-axis. In the following description, the elements corresponding to the first column L1 are described in detail, and the description of the elements corresponding to the second column L2 is appropriately omitted.

[0040] The positions of the plurality of nozzles N in the first row L1 and the plurality of nozzles N in the second row L2 along the Y axis may be identical or different. Furthermore, elements associated with the nozzles N in either the first row L1 or the second row L2 may be omitted.

[0041] like Figure 2 as well as Figure 3 As shown, the liquid ejection head 26 includes 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 frame 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 frame 48 are respectively plate-shaped members that are 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.

[0042] The nozzle plate 62 is a plate-shaped member having a plurality of nozzles N formed thereon. The plurality of nozzles N are circular through holes through which ink passes. The nozzles N eject ink by the vibration of the vibration plate 36. The nozzle plate 62 is bonded to the flow path substrate 32 by, for example, an adhesive.

[0043] A flow channel for supplying ink to a plurality of nozzles N is formed on the flow channel substrate 32. Specifically, a space Ra, a plurality of supply flow channels 322, a plurality of connecting flow channels 324, and a supply liquid chamber 326 are formed on the flow channel substrate 32. The space Ra is an elongated opening extending in the direction of the Y axis when viewed in a plane along the direction of the Z axis. The supply flow channel 322 and the connecting flow channel 324 are through holes formed for each nozzle N, respectively. The supply liquid chamber 326 is an elongated space extending in the direction of the Y axis across a plurality of nozzles N, and interconnects the space Ra and the plurality of supply flow channels 322. When viewed in a plane, the plurality of connecting flow channels 324 overlap with a nozzle N corresponding to the connecting flow channel 324, respectively. On the flow channel substrate 32, the pressure chamber substrate 34 is bonded, for example, by an adhesive.

[0044] A plurality of pressure chambers C are formed on the pressure chamber substrate 34. The plurality of pressure chambers C are arranged in the direction along the Y axis. Each pressure chamber C is formed for each nozzle N and is a strip-shaped space extending in the direction along the X axis when viewed 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 is connected to the nozzle N via the communication flow path 324, and is connected to the space Ra via the supply flow path 322 and the supply liquid chamber 326.

[0045] The nozzle plate 62, the flow path substrate 32, and the pressure chamber substrate 34 are each manufactured by processing a single crystal silicon substrate by dry etching or wet etching, etc. However, other known methods may be used appropriately in the manufacture of each of the nozzle plate 62, the flow path substrate 32, and the pressure chamber substrate 34.

[0046] A vibration plate 36 is disposed on the surface of the pressure chamber substrate 34 that faces the Z2 direction. The vibration plate 36 is a plate-shaped member that can vibrate elastically.

[0047] 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 is in a strip shape extending in the direction along the X axis when viewed in a plan view. The plurality of piezoelectric elements 44 correspond to the plurality of pressure chambers C and are arranged in the direction along the Y axis. The piezoelectric element 44 is deformed by the application of voltage. When the vibration plate 36 vibrates in conjunction with the deformation, the pressure in the pressure chamber C changes, thereby ejecting ink from the nozzles N.

[0048] The frame portion 48 is a housing for storing ink supplied to the plurality of pressure chambers C. Figure 3 As shown in FIG. 4 , a space Rb is formed in the frame portion 48. The space Rb of the frame portion 48 and the space Ra of the flow path substrate 32 are communicated with each other. The space formed by the space Ra and the space Rb functions as a liquid reservoir R, which is a liquid reservoir for storing ink supplied to the plurality of pressure chambers C. The ink is supplied to the liquid reservoir R through the introduction port 482 formed in the frame portion 48. The ink in the liquid reservoir R is supplied to the pressure chamber C through the supply liquid chamber 326 and each supply flow path 322.

[0049] The vibration absorbing body 64 is a flexible film constituting the wall surface of the liquid storage chamber R. The vibration absorbing body 64 is a plastic substrate that absorbs the pressure fluctuation of the ink in the liquid storage chamber R.

[0050] The wiring substrate 46 is a plate-shaped component formed with wiring for electrically connecting the drive circuit 50 and the plurality of piezoelectric elements 44. The surface of the wiring substrate 46 facing the Z2 direction is joined to the vibration plate 36 via a plurality of conductive bumps B. On the other hand, a drive circuit 50 is mounted on the surface of the wiring substrate 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. In addition, the wiring substrate 46 is not limited to a rigid substrate, 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 substrate 46, or the wiring substrate 46 may also serve as an external wiring 52.

[0051] The end of the external wiring 52 is bonded to the surface of the wiring substrate 46 facing the Z1 direction. The external wiring 52 is composed of a connection member such as FPC (Flexible Printed Circuits) or FFC (Flexible Flat Cable). Figure 2 As shown, a plurality of wirings 461 for electrically connecting the external wiring 52 and the drive circuit 50 , and a plurality of wirings 462 for supplying the drive voltage Com and the reference voltage E0 output from the drive circuit 50 are formed on the wiring substrate 46 .

[0052] 1-3. Vibration Plate 36 and Piezoelectric Element 44

[0053] Figure 4 For Figure 3 A partially enlarged cross-sectional view of the liquid ejection head 26 is shown. Figure 4 The vibration plate 36 shown vibrates in response to the driving of a piezoelectric body 443 included in a piezoelectric element 44 described later. The vibration plate 36 includes a first layer 361 and a second layer 362. The first layer 361 and the second layer 362 are stacked in this order in the Z1 direction.

[0054] The first layer 361 is, for example, an elastic film composed of silicon oxide (SiO2). The elastic film is formed, for example, by thermally oxidizing one surface of a single crystal silicon substrate. The second layer 362 is, for example, an insulating film composed of zirconium oxide (ZrO2). The insulating film is formed, for example, by forming a zirconium layer by sputtering and thermally oxidizing the layer. Zirconium oxide has excellent electrical insulation, mechanical strength, and toughness. Therefore, by making the vibration plate 36 contain the second layer 362 containing zirconium oxide, the characteristics of the vibration plate 36 can be improved.

[0055] In addition, another layer such as a metal oxide may be interposed between the first layer 361 and the second layer 362. In addition, part or all of the vibration plate 36 may be integrally formed with the pressure chamber substrate 34. In addition, the vibration plate 36 may be formed of a layer of a single material.

[0056] The pressure chamber C of the pressure chamber substrate 34 is formed, for example, by anisotropically etching a single crystal silicon substrate. The etching solution for the anisotropic etching can be, for example, an aqueous potassium hydroxide solution (KOH). In addition, in the anisotropic etching, the first layer 361 is used as an etching stop layer. In addition, although not shown in the figure, the planar shape of the pressure chamber C is a rectangle. However, the planar shape of the pressure chamber C is not limited to this and is arbitrary. For example, the planar shape of the pressure chamber C formed by anisotropic etching on a single crystal silicon substrate with a plane orientation of (110) is a parallelogram.

[0057] The piezoelectric element 44 overlaps the pressure chamber C when viewed in a plan view. The piezoelectric element 44 includes a second electrode 442, a seed layer 444, a piezoelectric body 443, and a first electrode 441, and these components are stacked in this order along the Z1 direction. In addition, 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.

[0058] The second electrode 442 is an independent electrode disposed in a mutually separated manner for each piezoelectric element 44. Specifically, a plurality of second electrodes 442 extending in the direction along the X-axis are spaced apart from each other and arranged in the direction along the Y-axis. 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.

[0059] As the material of the second electrode 442, for example, metal materials or alloys such as aluminum (Al), nickel (Ni), gold (Au), and copper (Cu) can be listed. The second electrode 442 can be either a single layer or a multilayer. For example, the second electrode 442 has a first layer composed of titanium (Ti), a second layer composed of platinum (Pt), and a third layer composed of iridium (Ir), and these layers are stacked in this order along the Z1 direction. In addition, the second electrode 442 is formed by, for example, a well-known film forming technology such as sputtering, and a well-known processing technology such as photolithography and etching.

[0060] The first electrode 441 is a strip-shaped common electrode extending in the direction along the Y axis so as to continuously extend across the plurality of piezoelectric elements 44. A reference voltage E0 is applied to the first electrode 441.

[0061] As the material of the first electrode 441, for example, metal materials or alloys such as aluminum (Al), nickel (Ni), gold (Au), and copper (Cu) can be listed. The first electrode 441 can be either a single layer or a multilayer. For example, the first electrode 441 has, for example, a layer composed of iridium, a layer composed of iridium oxide (IrOx), a layer composed of titanium oxide (TiOx), and a layer composed of iridium, and these layers are stacked in this order from the piezoelectric body 443. The first electrode 441 is formed by, for example, a known film forming technique such as sputtering, and a known processing technique such as photolithography and etching.

[0062] 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 shape of a strip extending along the Y axis and is separated by forming a plurality of cuts corresponding to each piezoelectric element 44. Alternatively, the piezoelectric body 443 may be provided independently for each of the plurality of piezoelectric elements 44.

[0063] The piezoelectric body 443 is composed of a piezoelectric material having a perovskite crystal structure represented by the general 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 zirconate titanate niobate (Pb(Zr,Ti,Nb)O3), and lead zirconate titanate magnesium niobate (Pb(Zr,Ti)(Mg,Nb)O3). Among them, lead zirconate titanate (PZT) is preferably used as the constituent material of the piezoelectric body 443. In addition, the piezoelectric body 443 may also contain a small amount of other elements such as impurities.

[0064] The piezoelectric body 443 is formed by forming a precursor layer of the piezoelectric body 443 by, for example, a sol-gel method or a MOD (metal organic decomposition) method, and firing and crystallizing the precursor layer. The piezoelectric body 443 may be a single layer or a multi-layer.

[0065] The seed layer 444 is arranged between the second electrode 442 and the piezoelectric body 443. The seed layer 444 is arranged in the same region as the second electrode 442 in the same shape when viewed in a planar manner. In addition, the seed layer 444 only needs to be arranged between the second electrode 442 and the piezoelectric body 443. The seed layer 444 may also be arranged in the same region as the piezoelectric body 443 in the same shape when viewed in a planar manner, for example.

[0066] The seed layer 444 has the function of improving the orientation of the piezoelectric body 443 when the piezoelectric body 443 is formed. Specifically, the seed layer 444 is composed of titanium (Ti), for example. When the seed layer 444 is composed of titanium, when the piezoelectric body 443 is formed, the island-shaped Ti becomes a crystal nucleus, thereby improving the orientation of the piezoelectric body 443. The seed layer 444 containing titanium is formed by, for example, a well-known film forming technology such as sputtering, and a well-known processing technology such as photolithography and etching. In addition, it can also be understood that the seed layer 444 is a part of the second electrode 442.

[0067] In addition, the seed layer 444 is not limited to a structure composed of titanium, and may be composed of, for example, a composite oxide having a perovskite structure containing lead, iron, and titanium as constituent elements. In this case, when the piezoelectric body 443 is formed, the orientation of the piezoelectric body 443 is improved by subjecting the piezoelectric body 443 to the influence of the crystal structure of the seed layer 444. The composite oxide is, for example, a solid solution of PbFeO3 and PbTiO3, represented by Pb(Fe,Ti)O3. The seed layer 444 composed of the composite oxide as described above is formed, for example, by a sol-gel method or a MOD method to form a precursor layer of the composite oxide, and is formed by sintering and crystallizing the precursor layer.

[0068] In the above piezoelectric element 44, the piezoelectric body 443 is deformed in accordance with the voltage applied between the first electrode 441 and the second electrode 442. A driving voltage Com corresponding to the ejection amount of ink is applied to the second electrode 442. A reference voltage E0 that is fixed regardless of the ejection amount of ink is applied to the first electrode 441. When a voltage difference is generated between the first electrode 441 and the second electrode 442 by applying the driving voltage Com and the reference voltage E0, the piezoelectric body 443 is deformed.

[0069] 1-4. Driving Voltage Com, Reference Voltage E0, and Applied Voltage Ea

[0070] Figure 5 It is a diagram for explaining the driving voltage Com and the reference voltage E0. Figure 5 The horizontal axis is time, and the vertical axis is voltage [V].

[0071] The driving voltage Com changes over time. The driving voltage Com includes a driving waveform WCom. The driving waveform WCom is repeated every 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, and after maintaining the minimum potential Em, it rises from the minimum potential Em to the maximum potential En, and after maintaining the maximum potential En, it drops to the intermediate potential Ek. In addition, Figure 5 The driving waveform WCom shown is an example, and the driving voltage Com may also have other waveforms.

[0072] The reference voltage E0 does not change with time and is fixed. In the illustrated example, the reference voltage E0 is a voltage value higher than the minimum potential Em of the drive voltage Com, but the present invention is not limited to this.

[0073] 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 driving voltage Com applied to the second electrode 442. The applied voltage Ea which is the difference between the reference voltage E0 and the driving voltage Com is applied to the piezoelectric body 443.

[0074] Figure 6 For, in Figure 5 The example of the applied voltage Ea actually applied to the piezoelectric body 443 when the driving voltage Com and the reference voltage E0 are applied to the first electrode 441 and the second electrode 442, respectively. Figure 6 The applied voltage Ea shown is, at each time from Figure 5 The voltage shown is obtained by subtracting the reference voltage E0 from the driving voltage Com. Figure 6 The horizontal axis is time, and the vertical axis is voltage [V]. The applied voltage Ea includes a waveform WEA. The waveform WEA includes an intermediate voltage EK, a maximum potential EN, and a minimum potential EM.

[0075] The maximum potential EN is a difference between the maximum potential En of the driving voltage Com and the reference voltage E0.

[0076] The minimum potential EM is the difference between the minimum potential Em of the drive voltage Com and the reference voltage E0. Figure 6 The waveform WEa shown is an example, which varies according to the drive voltage Com and the reference voltage E0.

[0077] Consider, for example Figure 5The reference voltage E0 is 6V, the minimum potential Em of the drive voltage Com is 2.5V, and the maximum potential En of the drive voltage Com is 27.5V. In this case, Figure 6 The minimum potential EM of the applied voltage Ea shown is -3.5 V, and the maximum potential EN is 21.5 V. Figure 5 In the case where the driving voltage Com includes a potential difference of 25 V, that is, when the voltage range RE of the driving voltage Com is 25 V, the voltage range RE of the applied voltage Ea is 25 V. Since the reference voltage E0 is fixed, the voltage range RE of the applied voltage Ea is equal to the voltage range RE of the driving voltage Com. In the following, the description is mainly based on the assumption that the driving voltage Com is a positive voltage.

[0078] exist Figure 5 When the minimum potential Em of the driving voltage Com shown is lower than the reference voltage E0, the minimum potential EM of the applied voltage Ea becomes a negative value. When the reference voltage E0 is zero, that is, when no voltage is applied to the second electrode 442, the minimum potential EM of the applied voltage Ea becomes 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 zero, the minimum potential EM of the applied voltage Ea also becomes zero.

[0079] 1-5. Electrical Characteristics of Piezoelectric Body 443z of Comparative Example

[0080] Figure 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. Figure 7 In the figure, the horizontal axis is voltage [V] and the vertical axis is polarization [μC / cm 2 ].

[0081] like Figure 7 As shown, the hysteresis curve of the piezoelectric body 443z includes a positive remanent polarization Prz and a negative coercive electric field -Ecz. The remanent polarization Prz is the polarization when 0V. The coercive electric field -Ecz is the polarization when 0μC / cm 2 The size of the electric field.

[0082] Fig.11 It is a butterfly curve which shows the relationship between the voltage of the piezoelectric body 443z and the displacement amount of the vibration plate 36 (deformation amount of the piezoelectric body) of the comparative example. Fig.11 The horizontal axis represents voltage [V], and the vertical axis represents displacement [nm] of the vibration plate 36. The displacement of the vibration plate 36 represents how much the vibration plate 36 is displaced from the position closest to the Z1 side (the side opposite to the pressure chamber C) to the Z2 side (pressure chamber C side) when the position closest to the Z1 side is set to 0, that is, the relative position when the position closest to the Z1 side is set as the reference.

[0083] First, consider the following case, that is, in the piezoelectric body 443z of the comparative example, the first reference voltage E01=6V, the minimum potential Em1 of the first driving voltage Com1=2.5V, the first driving voltage Com1 maximum potential En=27.5V and the first driving voltage E01 are applied to the first electrode 441 and the second electrode 442. Fig. 9 The driving voltage Com1 and the first reference voltage E01 are shown in FIG. 1. In this case, the first applied voltage Ea1 applied to the piezoelectric body 443z is such that the minimum potential EM1 is -3.5V, the maximum potential EN1 is 21.5V, and the voltage range RE is 25V. The minimum potential EM1 = -3.5V corresponds to the coercive electric field -Ecz of the piezoelectric body 443z. In general, the driving voltage Com and the reference voltage E0 that have such a relationship are used. This is because, Fig.11 As shown, when the coercive electric field -Ecz is reached, the relative position of the vibration plate 36 is closest to the Z1 side. When the vibration plate 36 is vibrated toward the Z2 side in the subsequent driving, the volume change of the pressure chamber C becomes large, and the discharge efficiency is improved.

[0084] During the period when the first applied voltage Ea1 changes from the intermediate voltage EK1 to the minimum potential EM1 = -3.5 V, the coercive electric field becomes -Ecz, that is, before the polarization becomes zero. Figure 7 The polarization changes to the negative side along the path Rcv1 in the hysteresis curve shown. Fig.11 In the butterfly curve shown, the displacement also changes toward the negative side (Z1 side) on the path Rsv1. As described above, when the coercive electric field -Ecz=-3.5, the displacement of the vibration plate 36 becomes the most negative side (displacement is 0 nm).

[0085] Thereafter, during the period in which the first applied voltage Ea1 changes from the minimum potential EM1 = -3.5 V to the maximum potential EN1 = 21.5 V, Figure 7 In the hysteresis curve shown, the path Rcv1 is transferred to the path Rcv2, and the polarization also changes to the positive side by the voltage range RE = 25V. Fig.11In the butterfly curve shown, the path Rsv1 is also transferred to the path Rsv2, and the displacement of the vibration plate 36 also changes to the positive side, becoming a displacement corresponding to the maximum potential EN1 = 21.5V. The displacement of the vibration plate 36 at this time is 790nm. During this period, the ink is ejected as the vibration plate 36 is displaced to the Z2 side. That is, 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 easy understanding, if the ejection amount is achieved by the volume change of the pressure chamber C accompanying the displacement of the vibration plate 36, the ejection amount is relatively large due to the relatively large displacement of 790nm.

[0086] Depend on Fig.11 It can be seen that the displacement amount SXz becomes a somewhat large value. Therefore, the ejection efficiency is good. However, since the first reference voltage E01 = 6V needs to be applied to the first electrode 441, circuits and wiring will be required, which may lead to increased costs and increased size.

[0087] Next, consider the following case, that is, the second reference voltage E02 is set to 0V, that is, the second reference voltage E02 is set to the GND potential. At this time, the second drive voltage Com2 is set to a minimum potential Em2 = 0V and a maximum potential En2 = 25V. Fig.10 The driving voltage Com2 and the second reference voltage E02 are shown in FIG. Since the second reference voltage E02 = 0V, the second applied voltage Ea2 applied to the piezoelectric body 443z also becomes a minimum potential EM2 of 0V, a maximum potential EN2 = 25V, and a voltage range RE = 25V. The reason for setting the minimum potential Em2 of the second driving voltage Com2 to = 0V is that, as described above, the ejection efficiency becomes better when the minimum potential EM2 is close to the coercive electric field -Ecz. On the other hand, if the minimum potential EM2 is set to a negative value, the second driving voltage Com2 will change across positive and negative, thereby causing problems in the circuit. In addition, although the second reference voltage E02 is set to 0V as the optimal value that satisfies the above conditions, even if it is near 0V, for example, when the second reference voltage E02 = 0.1V, the phenomenon described later will also occur.

[0088] During the period when the second applied voltage Ea2 changes from the intermediate voltage EK2 to the minimum potential EM2 = 0 V, the second applied voltage Ea2 becomes 0, that is, before the positive residual polarization Prz is reached. Figure 7 The polarization gradually changes to the negative side along the path Rcv1 in the hysteresis curve shown. Fig.11In the butterfly curve shown, the displacement amount also changes toward the negative side (Z1 side) on the path Rsv1, but the displacement amount of the vibration plate 36 when the second applied voltage Ea2=0 does not reach that negative side and becomes 200 nm.

[0089] Thereafter, during the period in which the second applied voltage Ea2 changes from the minimum potential EM2 = 0 V to the maximum potential EN2 = 25 V, Figure 7 In the hysteresis curve shown, the path Rcv1 is transferred to the path Rcv2, and the polarization also changes to the positive side by the voltage range RE = 25V. Fig.11 In the butterfly curve shown, the path Rsv1 is also transferred to the path Rsv2, and the displacement of the vibration plate 36 also changes to the positive side. When the maximum potential EN2 = 25 V, the displacement of the vibration plate 36 becomes 820 nm. Therefore, the displacement difference SYz = 820 nm - 200 nm = 620 nm from the minimum potential EM2 = 0 V to the maximum potential EN2 = 25 V corresponds to the ejection characteristics in this case.

[0090] Here, in Fig.11 , the displacement difference SYz = 620nm is quite small compared with the displacement difference SXz = 790nm, and the ratio is only SYz / SXz = 78%. This means that in the case where the first reference voltage E01 is set to 6V, the minimum potential Em1 of the first drive voltage Com1 is set to 2.5V, and the maximum potential En1 of the first drive voltage Com1 is set to 27.5V, and in the case where the second reference voltage E02 is set to 0V, the minimum potential Em2 of the second drive voltage Com2 is set to 0V, and the maximum potential En2 of the second drive voltage Com2 is set to 25V, although the voltage range RE is the same as 25V, the former is much more preferred than the latter in terms of ejection efficiency. In other words, when the piezoelectric body 443z of the comparative example is used, if the second reference voltage E02 is set to 0V, sufficient ejection efficiency cannot be obtained anyway.

[0091] 1-6. Electrical Characteristics of the Piezoelectric Body 443 of the First Embodiment

[0092] Figure 8 : is a hysteresis curve showing the relationship between the voltage and polarization of the piezoelectric body 443 included in the piezoelectric element 44 of the first embodiment. Figure 8 In the figure, the horizontal axis is voltage [V] and the vertical axis is polarization [μC / cm 2 ].

[0093] like Figure 8 As shown, the hysteresis curve of the piezoelectric body 443 of this embodiment includes a positive remanent polarization Pr and a negative coercive electric field -Ec. The remanent polarization Pr is the polarization when 0V. The coercive electric field -Ec is the polarization when 0μC / cm 2 The size of the electric field.

[0094] Fig.12 It is a butterfly curve which shows the relationship between the voltage of the piezoelectric body 443 and the displacement amount of the vibration plate 36 (deformation amount of the piezoelectric body) in the first embodiment. Fig.12 The horizontal axis represents voltage [V], and the vertical axis represents displacement [nm] of the vibration plate 36. The displacement of the vibration plate 36 represents how much the vibration plate 36 is displaced from the position closest to the Z1 side (the side opposite to the pressure chamber C) as 0 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.

[0095] First, similarly to the piezoelectric body 443z of the comparative example, consider the following case, that is, in the piezoelectric body 443 of the first embodiment, the above-mentioned Fig. 9 The first driving voltage Com1 (minimum potential Em1 = ​​2.5V, maximum potential En1 = 27.5V) and the first reference voltage E01 = 6V are shown.

[0096] During the period when the second applied voltage Ea2 changes from the intermediate voltage EK2 to the minimum potential EM2 = -3.5 V, the coercive electric field becomes -Ec, that is, before the polarization becomes zero. Figure 8 The polarization gradually changes to the negative side along the path Rcv3 in the hysteresis curve shown. Fig.12 In the butterfly curve shown, the displacement gradually changes toward the negative side (Z1 side) on the path Rsv3, and when the coercive electric field -Ec=-3.5 as described above, the displacement of the vibration plate 36 becomes the most negative side (displacement is 0 nm).

[0097] Thereafter, during the period in which the second applied voltage Ea2 changes from the minimum potential EM2 = -3.5 V to the maximum potential EN2 = 21.5 V, Figure 8 In the hysteresis curve shown, the path Rcv3 is transferred to the path Rcv4, and the polarization also changes to the positive side by the voltage range RE = 25V. Fig.12 In the butterfly curve shown, the path Rsv3 is also transferred to the path Rsv4, and the displacement of the vibration plate 36 also changes to the positive side, thereby becoming a displacement corresponding to the maximum potential EN2 = 21.5V. The displacement of the vibration plate 36 at this time is 720nm. Therefore, the displacement difference SX = 720nm-0nm = 720nm 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.

[0098] Next, similarly to the piezoelectric body 443z of the comparative example, consider the case where the above-mentioned voltage is applied to the first electrode 441 and the second electrode 442 in the piezoelectric body 443 of the first embodiment. Fig.10 The second driving voltage Com2 (minimum potential Em2 = 0 V, maximum potential En2 = 25 V) and the second reference voltage E02 = 0 V are shown.

[0099] During the period when the second applied voltage Ea2 changes from the intermediate voltage EK2 to the minimum potential EM2 = 0 V, the second applied voltage Ea2 becomes 0, that is, before the positive residual polarization Pr is reached. Figure 8 The polarization gradually changes to the negative side along the path Rcv3 in the hysteresis curve shown. Fig.12 In the butterfly curve shown, the displacement also gradually changes toward 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 of the vibration plate 36 when the second applied voltage Ea2 = 0 reaches the relatively negative side and becomes 30nm.

[0100] Thereafter, during the period in which the second applied voltage Ea2 changes from the minimum potential EM2 = 0 V to the maximum potential EN2 = 25 V, Figure 8 In the hysteresis curve shown, the path Rcv3 is transferred to the path Rcv4, and the polarization also changes to the positive side by the voltage range RE = 25V. Fig.12 In the butterfly curve shown, the path Rsv3 is also transferred to the path Rsv4, and the displacement of the vibration plate 36 also changes to the positive side. When the maximum potential EN2 = 25 V, the displacement of the vibration plate 36 becomes 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 at this time. In the following description, this displacement difference SY is also referred to as the second displacement.

[0101] Here, in Fig.12, the displacement difference SY = 750nm and the displacement difference SX = 720nm are substantially the same, and the ratio SY / SX = 104%. This means that when the first reference voltage E01 = 6V, the minimum potential Em1 of the first drive voltage Com1 = 2.5V, and the maximum potential En1 of the first drive voltage Com1 = 27.5V, and when the second reference voltage E02 = 0V, the minimum potential Em2 of the second drive voltage Com2 = 0V, and the maximum potential En2 of the second drive voltage Com2 = 25V, the voltage range RE is the same as 25V, and the ejection efficiency of both is the same. In other words, when the piezoelectric body 443 of the first embodiment is used, the ejection efficiency does not change much even if the second reference voltage E02 = 0V.

[0102] 1-7. Comparison of electrical properties of piezoelectric body 443 and piezoelectric body 443z

[0103] Here, if Fig.11 and Fig.12 By comparison, it can be seen that when using Fig. 9 In the case of the first driving voltage Com1 and the first reference voltage E01 shown in FIG. 1 , the displacement difference SX of the piezoelectric body 443 in the first embodiment is 720 nm, which is slightly smaller than the displacement difference SXz of the piezoelectric body 443z in the comparative example is 790 nm. Fig. 9 In the case of the first driving voltage Com1 and the first reference voltage E01, the discharge characteristics of the piezoelectric body 443 of the first embodiment are slightly inferior.

[0104] However, when using Fig.10 In the case of the second driving voltage Com2 and the second reference voltage E02 shown in FIG. 1 , the displacement difference SY=750nm of the piezoelectric body 443 in the first embodiment is significantly larger than the displacement difference SYz=620nm of the piezoelectric body 443z in the comparative example. Fig.10 When the second driving voltage Com2 and the second reference voltage E02 are equal, the ejection characteristics of the piezoelectric body 443 of the first embodiment are quite excellent.

[0105] Furthermore, in the piezoelectric body 443z of the comparative example, Fig.10 The displacement difference SYz=620nm in the case of the second driving voltage Com2 and the second reference voltage E02 is shown. Fig. 9 The displacement difference SXz = 790 nm when the first driving voltage Com1 and the first reference voltage E01 are shown is quite small, and the ratio SYz / SXz is 78%. Fig. 9The first driving voltage Com1 and the first reference voltage E01 have excellent ejection efficiency, but when using Fig.10 In the case of the second driving voltage Com2 and the second reference voltage E02 shown, the ejection efficiency is not so excellent.

[0106] On the other hand, in the piezoelectric body 443 of the first embodiment, the Fig.10 The displacement difference SY=750nm in the case of the second driving voltage Com2 and the second reference voltage E02 is shown. Fig. 9 The displacement difference SX=720 nm in the case of the first driving voltage Com1 and the first reference voltage E01 is about the same, and the ratio SY / SX is 104%. Fig. 9 In the case of the first driving voltage Com1 and the first reference voltage E01 shown in FIG. Fig.10 In the case of the second driving voltage Com2 and the second reference voltage E02 shown, the ejection efficiency is equally excellent.

[0107] Thus, according to the piezoelectric body 443 of this embodiment, even if Fig. 9 Such a first driving voltage Com1 and a first reference voltage E01 can also obtain sufficient ejection characteristics, and even if Fig.10 Such second drive voltage Com2 and second reference voltage E02 reduce circuits and wiring because they do not apply positive and negative voltages, and the displacement of the piezoelectric body 443 is unlikely to have a large difference, so that sufficient ejection characteristics can be obtained. In addition, this is because the change in the displacement of the piezoelectric body 443 from the coercive electric field -Ec = -3.5 to the vibration plate 36 of 0V and the change in the displacement of the vibration plate 36 from the coercive electric field -Ec + voltage range RE to 0V + voltage range RE are set to be as close as possible.

[0108] Here, in the first embodiment, the second displacement amount SY is 104% of the first displacement amount SX. Fig.10 Such a second driving voltage Com2 and a second reference voltage E02 also obtain the ejection characteristics, and the second displacement SY needs to be greater than 90% of the first displacement SX. Fig.10 Such a second driving voltage Com2 and a second reference voltage E02 are used Fig. 9 Compared with the case of the first reference voltage E01, the first driving voltage Com1 is preferred because it has the effect of reducing circuits and wiring. Therefore, the former is preferred to have better ejection characteristics than the latter, that is, the second displacement SY is preferably as large as possible. Specifically, the second displacement SY is preferably greater than 95% of the first displacement SX. Fig. 9 In the case of the first driving voltage Com1 and the first reference voltage E01, it is desirable to avoid a situation in which the discharge characteristics are significantly degraded. From this viewpoint, the second displacement amount SY is preferably smaller than 110% of the first displacement amount SX.

[0109] Here, in the first embodiment, the difference between the maximum potential En1 (27.5V) and the minimum potential Em1 (2.5V) of the first driving voltage Com1 (27.5V-2.5V=25V) is equal to the difference between the maximum potential En2 (25V) and the minimum potential Em2 (0V) of the second driving voltage Com2 (25V-0V=25V). In addition, the difference between the minimum potential Em1 (2.5V) of the first driving voltage Com1 and the first reference voltage E01 (6V) (2.5V-6V=-3.5V) corresponds to the coercive electric field -Ec (-3.5V) of the piezoelectric body 443. In addition, the difference between the minimum potential Em2 (0V) of the second driving voltage Com2 and the second reference voltage E02 (0V) (0V-0V=0V) is closer to zero than the difference between the minimum potential Em1 (2.5V) of the first driving voltage Com1 and the first reference voltage E01 (6V) (2.5V-6V=-3.5V).

[0110] 1-8. Manufacturing Example of Piezoelectric Body 443

[0111] The piezoelectric body 443 of this embodiment is formed, for example, in the following manner. For example, when the first electrode 441 contains iridium, the iridium is set to a state where it is not completely oxidized. By shortening the annealing time required for forming the first electrode 441 or making the first electrode 441 thicker, the degree of oxidation of the iridium can be set to an insufficient state. As a result, an interface between the piezoelectric body 443 and the first electrode 441 is formed in an uneven and unformed state. Considering that the voltage causing the polarization reversal is more dispersed than before due to the uneven state of the interface. As a result, a device having Figure 8 The piezoelectric body 443 of the embodiment has a hysteresis curve shown in FIG. In addition, it is considered that the piezoelectric body 443 of the embodiment can be obtained even if the first electrode 441 is not an electrode composed of iridium, for example, an oxide electrode such as strontium ruthenate (SrRuO3) and lanthanum nickelate (LaNiO3).

[0112] Furthermore, for example, when the piezoelectric body 443 is PZT, the piezoelectric body 443 of the present embodiment can be obtained by making the zirconium oxide (Zr) ratio of PZT satisfy the relationship of 0.55<Zr / (Zr+Ti).

[0113] In addition, for example, when the piezoelectric body 443 has PZT as the main component, the piezoelectric body 443 of the present embodiment can be obtained by making the piezoelectric body 443 contain any additive of Mg, Al, Fe or Na. For example, if it is B site substitution, Mg, Al or Fe can be listed as the additive. If it is A site substitution, Na can be listed as the additive. In a hard material with a smaller valence than the substitution element, as the oxygen vacancies increase, the oxygen vacancies will hinder or inhibit the movement of the domain wall. Therefore, it can be considered that the piezoelectric body 443 of the present embodiment can be obtained.

[0114] It should be noted that the piezoelectric body 443 of this embodiment only needs to have the electrical characteristics as described above, and the manufacturing method thereof is not limited to this method.

[0115] 2. Second Implementation

[0116] The second embodiment is described. For the elements having the same effects and functions as those in the first embodiment described above in the following exemplary manner, the symbols used in the description of the first embodiment described above are used, and the respective detailed descriptions are appropriately omitted. In the second embodiment, the piezoelectric body 443 itself used is also the same as that in the first embodiment. In the second embodiment, the second driving voltage Com2, the second reference voltage E02 and the second applied voltage Ea2 are different from those in the first embodiment.

[0117] When the applied voltage Ea is applied to the piezoelectric body for a long time, that is, when the number of ejections of ink by the liquid ejection head increases, a marking phenomenon occurs in which the hysteresis shape of the piezoelectric body shifts. Fig.13 It is a diagram for explaining the imprint phenomenon and is a diagram showing a butterfly curve before and after long-term voltage application to a piezoelectric body. Fig.13 The solid line is a butterfly curve of the initial piezoelectric body before the voltage Ea is applied for a long time. Fig.13 The dotted line is a butterfly curve of the piezoelectric body after the applied voltage Ea is applied for a long time. Fig.13 The horizontal axis is voltage [V] and the vertical axis is displacement.

[0118] Therefore, the butterfly curve of the piezoelectric body is also displaced. For example, it is possible to change from Fig.13 The butterfly curve shown by the solid line Fig.13 As a result, the voltage response of the piezoelectric body near the coercive electric field -Ec' changes significantly compared to the voltage response in the high voltage region.

[0119] This imprinting phenomenon occurs when the applied voltage Ea is applied to the piezoelectric body for a long time, that is, when the number of injections increases. Each time the number of injections increases, the displacement increases. In addition, this imprinting phenomenon occurs in both the piezoelectric body 443 of the first embodiment and the piezoelectric body 443z of the comparative example. In fact, it can be seen that from the initial state of the piezoelectric body to after 50 billion injections, it shifts to the negative side by about 1.5V. As a result, when the imprinting phenomenon occurs, the displacement will be different. For example, when the applied voltage Ea of the coercive electric field -Ec' to the voltage V1 is used in the initial state of the piezoelectric body, it can be obtained. Fig.13 However, the imprint phenomenon occurs and the butterfly curve shifts to Fig.13 After the dotted line shown, if the applied voltage Ea is increased from the coercive electric field -Ec' to the voltage V1, then Fig.13 The displacement C2 is shown. Fig.13 It can be seen that the displacement C2 is smaller than the displacement C1.

[0120] If it is considered that the applied voltage Ea is shifted by the voltage offset caused by the imprint phenomenon, the displacement C2 can be estimated from the butterfly curve in the initial state. As described above, if it is considered that the applied voltage Ea is shifted to the positive side by 1.5V if it is shifted to the negative side, that is, the coercive electric field -Ec'+1.5V is used to obtain the voltage V1+1.5V, the displacement C2 can be obtained.

[0121] In the second embodiment, in addition to Fig. 9 In addition to the first driving voltage Com1 and the first reference voltage E01 shown in FIG. Fig.14 The second driving voltage Com2 and the second reference voltage E02 shown in the figure are studied. Regarding the second driving voltage Com2 and the second reference voltage E02, the differences from the first embodiment are mainly described. Fig.14 In the example of , the second driving voltage Com2 is set in consideration of the voltage offset caused by the marking phenomenon.

[0122] As mentioned above, in Fig. 9 In the first driving voltage Com1 and the first reference voltage E01, the first applied voltage Ea1 becomes the minimum potential EM1 = -3.5 V, the maximum potential EN1 = 21.5 V, and the voltage range RE = 25 V. The minimum potential EM1 = -3.5 V is set to correspond to the coercive electric field -Ec of the piezoelectric body 443. The minimum potential EM of the applied voltage Ea becomes -3.5 V, and the maximum potential EN becomes 21.5.

[0123] Next, use Fig.14The second driving voltage Com2 and the second reference voltage E02 of the second embodiment are described below. The minimum potential Em2 of the second driving voltage Com2 is 4V, and the maximum potential En2 is 29V. This is because the second driving voltage Com2 is set to a value that is 1.5V different from the first driving voltage Com1 toward the positive side in consideration of the influence of the 1.5V imprinting phenomenon toward 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 as the difference between the minimum potential Em2 and the maximum potential En2 is 25V, which is the same as Fig. 9 The voltage range RE of the first driving voltage Com1 shown is equal.

[0124] Fig.14 The second reference voltage E02 represented by the solid line in Fig. 9 The first reference voltage E01 shown is equal. Fig.14 In the example, the second reference voltage E02 is 6V.

[0125] Therefore, when the second driving voltage Com2 and the second reference voltage E02 are applied, the second applied voltage Ea2 applied to the piezoelectric body 443 is as follows: Fig.14 That is, in the second applied voltage Ea2, the minimum potential EM2 = Em2-E02 = 4V-6V = -2V, and the maximum potential EN2 = En1-E02 = 29V-6V = 23V. Therefore, the voltage range RE as the difference between the minimum potential EM2 and the maximum potential EN2 is 25V, which is consistent with the above Fig. 9 The voltage range RE of the first applied voltage Ea1 shown is equal. The second applied voltage Ea2 is a value obtained by shifting the first applied voltage Ea1 to the positive side by the change amount due to the imprinting phenomenon, that is, 1.5 V. Therefore, when the second applied voltage Ea2 is used, the displacement of the piezoelectric body after the imprinting phenomenon can be evaluated.

[0126] Here, in the second embodiment, the difference between the maximum potential En1 (27.5V) and the minimum potential Em1 (2.5V) of the first driving voltage Com1 (27.5V-2.5V=25V) is equal to the difference between the maximum potential En2 (29V) and the minimum potential Em2 (4V) of the second driving voltage Com2 (29V-4V=25V). In addition, the difference between the minimum potential Em1 (2.5V) of the first driving voltage Com1 and the first reference voltage E01 (6V) (2.5V-6V=-3.5V) corresponds to the coercive electric field -Ec (-3.5V) of the piezoelectric body 443. In addition, the difference between the minimum potential Em2 (4V) of the second driving voltage Com2 and the second reference voltage E02 (6V) (4V-6V=-2V) is closer to zero than the difference between the minimum potential Em1 (2.5V) of the first driving voltage Com1 and the first reference voltage E01 (6V) (2.5V-6V=-3.5V).

[0127] Fig.15 This is an illustration of a hysteresis curve showing the relationship between the voltage and polarization of the piezoelectric body 443 according to the second embodiment. Fig.15 The hysteresis curve of Figure 8 The hysteresis curves are the same.

[0128] Fig.16 It is a butterfly curve which shows the relationship between the voltage of the piezoelectric body 443 and the displacement amount of the vibration plate 36 (deformation amount of the piezoelectric body) in the second embodiment. Fig.16 The butterfly curve and Fig.12 The butterfly curve is the same.

[0129] First, the displacement difference SX of the piezoelectric body 443 in the initial state is evaluated. When the first applied voltage Ea1 is applied to the piezoelectric body 443, in the first embodiment and the second embodiment, the first applied voltage Ea1, Fig.15 The hysteresis curve of Fig.16 The butterfly curves are the same, so the results are also the same, and the displacement difference SX (first displacement) is also 720nm.

[0130] 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), the minimum potential EM2 becomes -2V and the maximum potential EN2 becomes 23V as described above. At the minimum potential EM2, the polarization becomes P3 and the displacement of the vibration plate 36 becomes 10nm. In addition, at the maximum potential EN2, the polarization becomes P4 and the displacement of the vibration plate 36 becomes 750nm. Therefore, the displacement difference SY (second displacement) becomes 750nm-10nm=740nm.

[0131] Thus, in the second embodiment, the displacement difference SY=740nm is substantially the same as the displacement difference SX=720nm, and the ratio SY / SX=103%. That is, the displacement difference, that is, the ejection characteristics, will not deteriorate significantly in the initial state and after the imprint phenomenon occurs. In order to fully suppress the degradation caused by the imprint phenomenon, the second displacement SY needs to be greater than 90% of the first displacement SX. In addition, when about 50 billion injections are completed from the initial state, a larger imprint phenomenon is unlikely to occur. Therefore, in the life of the liquid ejection head, the use period after the 1.5V imprint phenomenon occurs tends to be longer than before. Therefore, if you want to say which one, it is best to pay attention to the side after the imprint phenomenon occurs, that is, it is preferred that the second displacement SY is as large as possible. Specifically, it is preferred that the second displacement SY is greater than 95% of the first displacement SX. Even so, of course, the situation where the ejection characteristics decrease during the period of the imprint phenomenon should be avoided, so it is best to ensure the first displacement SX to a certain extent, specifically, it is preferred that the second displacement SY is less than 110% of the first displacement SX.

[0132] As described above, in the present embodiment, the first reference voltage E01 is positive. The second reference voltage E02 is equal to the first reference voltage E01. In addition, the minimum potential Em1, which is the minimum value of the first drive voltage Com1, is positive and is smaller than the first reference voltage E01. In addition, the minimum potential Em2, which is the minimum value of the second drive voltage Com2, is positive and is larger than the minimum potential Em1 of the first drive voltage Com1. Therefore, in the present embodiment, the evaluation of the piezoelectric body can be performed taking into account the voltage offset caused by the imprint phenomenon.

[0133] In the second embodiment, when driving for actual liquid ejection, the first reference voltage E01 and the first drive voltage Com1 are basically used from the initial state even after the mark phenomenon occurs. That is, the second reference voltage E02 and the second drive voltage Com2 are only voltages for evaluating the piezoelectric body 443 and are not used for actual liquid ejection.

[0134] However, for example, the first reference voltage E01 and the first drive voltage Com1 may be used in the initial stage, and the second reference voltage E02 and the second drive voltage Com2 may be used from the stage when the number of driven ejections exceeds a predetermined number of times. Figure 1The voltage applying unit 29 shown in the figure applies the first reference voltage E01 to the first electrode 441 and the first driving voltage Com1 to the second electrode 442 when the number of driving times of the liquid ejection head 26 is the first driving number, thereby ejecting the liquid from the nozzle N. Furthermore, when the number of driving times of the liquid ejection head 26 is the second driving number greater than the first driving number, the voltage applying unit 29 applies the second reference voltage E02 to the first electrode 441 and the second driving voltage Com2 to the second electrode 442, thereby ejecting the ink from the nozzle N.

[0135] For example, the first driving number is greater than 1 and less than the second driving number. The second driving number is, for example, several hundred million to several tens of billions of times. By changing the driving voltage Com according to the driving number, the rate of decrease in the ejection amount accompanying the driving number can be suppressed for a long time. In addition, the driving voltage Com is not changed in two stages, but can also be changed in three stages or more.

[0136] In the second embodiment, the second driving voltage Com2 is shifted in consideration of the marking phenomenon and the second reference voltage E02 is not changed. However, the second reference voltage E02 may be shifted without changing the second driving voltage Com2.

[0137] Fig.17 : is a diagram showing the second driving voltage Com2 and the second reference voltage E02 of the modified example. Fig.17 The second driving voltage Com2 and the second reference voltage E02 are mainly used for Fig.15 The examples shown are different from those shown here. Fig.17 In the example of , the second reference voltage E02 is set in consideration of the voltage offset caused by the marking phenomenon.

[0138] Fig.17 The second driving voltage Com2 in Fig. 9 The first driving voltages Com1 shown are equal. For example, the minimum potential Em2 is 2.5V, and the maximum potential En2 is 27.5V. The difference between the minimum potential Em2 and the maximum potential En2, that is, the voltage range RE, is 25V.

[0139] Fig.17 The second reference voltage E02 represented by the solid line in Fig. 9 The first reference voltage E01 shown is different. In order to eliminate the influence of the 1.5V mark phenomenon on the negative side, it is set to a value that is 1.5V different from the first reference voltage E01 on the negative side. Specifically, the second reference voltage E02 = (4.5V) = first reference voltage E01 (6V) - 1.5V.

[0140] Therefore, in the modified example, when the second driving voltage Com2 and the second reference voltage E02 are applied, the second applied voltage Ea2 applied to the piezoelectric body 443 becomes Fig.17 That is, in the second applied voltage Ea2, the minimum potential EM2 = Em2-E02 = 2.5V-4.5V = -2V, and the maximum potential EN2 = En2-E02 = 27.5V-4.5V = 23V. Therefore, the difference between the minimum potential EM2 and the maximum potential EN2, that is, the voltage range RE, is 25V, which is consistent with the above Fig. 9 The voltage range RE of the first applied voltage Ea1 shown is equal. The values ​​of the applied voltage in this modification are equal to those of the applied voltage in the second embodiment. Therefore, the obtained results are also the same.

[0141] Here, in the modified example, the difference between the maximum potential En1 (27.5V) and the minimum potential Em1 (2.5V) of the first driving voltage Com1 (27.5V-2.5V=25V) is equal to the difference between the maximum potential En2 (27.5V) and the minimum potential Em2 (2.5V) of the second driving voltage Com2 (27.5V-2.5V=25V). In addition, the difference between the minimum potential Em1 (2.5V) of the first driving voltage Com1 and the first reference voltage E01 (6V) (2.5V-6V=-3.5V) corresponds to the coercive electric field -Ec (-3.5V) of the piezoelectric body 443. In addition, the difference between the minimum potential Em2 (2.5V) of the second driving voltage Com2 and the second reference voltage E02 (4.5V) (2.5V-4V=-2V) is closer to zero than the difference between the minimum potential Em1 (2.5V) of the first driving voltage Com1 and the first reference voltage E01 (6V) (2.5V-6V=-3.5V).

[0142] As described above, in this modification, the first reference voltage E01 is positive. The second reference voltage E02 is positive and less than the first reference voltage E01. In addition, the minimum potential Em1, which is the minimum value of the first drive voltage Com1, is positive and less than the first reference voltage E01. In addition, the minimum potential Em2, which is the minimum value of the second drive voltage Com2, is equal to the minimum potential Em1 of the first drive voltage Com1. Therefore, in this embodiment, it is possible to evaluate the piezoelectric body taking into account the voltage offset caused by the imprint phenomenon.

[0143] In addition, it is inferred that the main reason for the displacement of the above-mentioned piezoelectric body 443 is as follows. As the first main reason, the change of the crystal structure of the piezoelectric body 443 can be considered. For example, when the piezoelectric body 443 is a PZT thin film formed by a sol-gel method, and the PZT thin film is a tetragonal system with Zr / Ti=30 / 70, the MPB (monomorphous phase boundary) is displaced 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 the bulk film formed by, for example, a sputtering method.

[0144] The PZT thin film formed by the sol-gel method is easily affected by the second electrode 442 as a substrate. Therefore, it is considered that there is a shift in the MPB and a crystal system different from the bulk film. This is believed to be caused by the difference in thermal expansion coefficient between the second electrode 442 and the piezoelectric body 443. In the initial state after the piezoelectric body 443 is formed, the crystals of the piezoelectric body 443 are stretched 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 will shift to the originally stable crystal structure.

[0145] As the second main reason, the movement of charged particles is considered. Electrons are captured by oxygen defects, and the polarization axis of the fixed charge is fixed, which becomes distorted and cannot respond to electric fields. It is easy to stabilize in this deformed crystalline state. As a result, the optimal driving range caused by the shift of the coercive electric field will change.

[0146] This may be the reason for the imprinting phenomenon in which the hysteresis shape of the piezoelectric body 443 is shifted. As described above, by setting the minimum potential EM2 to a voltage ranging from the coercive field -Ec to the residual polarization Pr, the reduction rate of the ejection amount due to the shift caused by the imprinting phenomenon can be suppressed.

[0147] 3. Other variations

[0148] The above-described embodiments can be modified in many ways. Specific modified forms that can be applied to the above-described embodiments are exemplified below. Two or more forms arbitrarily selected from the following examples can be appropriately combined within a range that does not contradict each other.

[0149] Although the driving voltage Com is described as a positive voltage in each embodiment, it may be a negative voltage. Even in this case, the applied voltage Ea is set based on the same technical concept as in each embodiment.

[0150] The “liquid ejection head” may be a circulation type head having a so-called circulation flow path.

[0151] In addition to equipment dedicated to printing, "liquid ejection devices" can also be used in various equipment such as fax machines and copiers. The use of liquid ejection devices is 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. In addition, 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 substrate. In addition, a liquid ejection device that ejects a solution of an organic substance related to a living body is used, for example, as a manufacturing device for manufacturing a biochip.

[0152] Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the above embodiments. In addition, the configuration of each part of the present invention can be replaced with an arbitrary configuration that performs the same function as the above embodiments, and an arbitrary configuration can be added.

[0153] Explanation of symbols

[0154] 12…medium; 14…liquid container; 20…control unit; 22…transport mechanism; 24…moving mechanism; 26…liquid ejection head; 29…voltage application unit; 32…flow path substrate; 34…pressure chamber substrate; 36…vibration plate; 44…piezoelectric element; 44z…piezoelectric element; 46…wiring substrate; 48…frame; 50…driving circuit; 52…external wiring; 62…nozzle plate; 64…vibration absorber; 100…liquid ejection device; 242…transport body; 244…transport belt; 322…supply channel; 324…connection channel; 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…initial displacement; C2…displacement; CX…first displacement; CXz…polarization displacement; CY…second displacement; C Yz…polarization displacement; Com…driving voltage; Com1…first driving voltage; Com2…second driving 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; En1…maximum potential; En2…maximum potential; L1…first column; L2…second column; N…nozzle; P1…polarization; P1z…polarization; P2…polarization; P2z…polarization; Pr…residual polarization; Prz…residual polarization; P3…polarization; P4…polarization; R…liquid storage chamber; RE…voltage range; Ra…space;

[0155] Rb…space; Tu…unit period; V1…voltage; WCom…drive waveform; WCom1…drive waveform;

[0156] WEa…waveform; WEa1…waveform; WEa2…waveform; WEom2…driving waveform.

Claims

1. A liquid ejection head, characterized in that: have: a first electrode to which a reference voltage which does not change with time is applied; a second electrode to which a time-varying driving voltage is applied; a piezoelectric body disposed between the first electrode and the second electrode and driven by a voltage difference between the reference voltage and the driving voltage; a vibration plate that vibrates in response to the driving of the piezoelectric body; a nozzle that ejects liquid by the vibration of the vibration plate, In the liquid ejection head, The displacement amount of the vibration plate when a first reference voltage is applied to the first electrode and a first driving voltage is applied to the second electrode is set as a first displacement amount, and When the displacement amount of the vibration plate when the second reference voltage is applied to the first electrode and the second drive voltage is applied to the second electrode is defined as the second displacement amount, The difference between the maximum value and the minimum value of the first driving voltage is equal to the difference between the maximum value and the minimum value of the second driving voltage. The difference between the minimum value of the first driving 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 driving voltage and the second reference voltage is closer to zero than the difference between the minimum value of the first driving voltage and the first reference voltage. The second displacement is greater than 90% of the first displacement.

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

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

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

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

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

7. The liquid ejection head according to claim 5 or 6, characterized in that: A voltage applying unit is provided for applying the first reference voltage to the first electrode and the first driving voltage to the second electrode, thereby causing the liquid to be ejected from the nozzle.

8. The liquid ejection head according to claim 1, wherein: The first reference voltage is positive, The second reference voltage is zero, The minimum value of the first driving voltage is positive and smaller than the first reference voltage. The minimum value of the second driving voltage is zero.

9. A liquid ejection device, characterized in that: have: The liquid ejection head according to claim 5 or 6; A voltage applying unit, which causes liquid to be ejected from the nozzle by applying the first reference voltage to the first electrode and applying the first driving voltage to the second electrode when the liquid ejection head is driven a first driving number of times, and causes liquid to be ejected from the nozzle by applying the second reference voltage to the first electrode and applying the second driving voltage to the second electrode when the liquid ejection head is driven a second driving number of times greater than the first driving number of times.

10. A liquid ejection device, characterized in that: have: The liquid ejection head according to claim 8; A voltage applying unit applies the second reference voltage to the first electrode and applies the second driving voltage to the second electrode, thereby ejecting the liquid from the nozzle.

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