Liquid ejecting head and liquid ejecting apparatus

Abstract

To enhance ejection efficiency of a liquid ejecting head.SOLUTION: A liquid ejecting head includes: a piezoelectric element including a first electrode, a piezoelectric layer and a second electrode; a pressure compartment substrate in which a pressure compartment communicating with a nozzle is provided; and a diaphragm that applies pressure to liquid in the pressure compartment by vibrating by being driven by the piezoelectric element. The pressure compartment substrate, the diaphragm, and the piezoelectric element are stacked in this order in a stacking direction. A neutral plane of a stacked body made up of the piezoelectric element and the diaphragm is located inside the piezoelectric layer. When, of two regions obtained by dividing the piezoelectric layer with respect to the neutral plane, a region located closer to the diaphragm is defined as a lower region, and a region located farther from the diaphragm is defined as an upper region, a piezoelectric constant of the lower region is less than a piezoelectric constant of the upper region.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] A liquid ejection head used in a liquid ejection device, such as a piezoelectric inkjet printer, has a diaphragm that forms part of the wall of a pressure chamber that communicates with a nozzle that ejects liquid such as ink, and a piezoelectric element that vibrates this diaphragm, as disclosed in Patent Document 1, for example.

[0003] In Patent Document 1, the vibration plate has a thick portion in a first region corresponding to the end of the pressure chamber and a thin portion thinner than the thick portion in a second region corresponding to the center of the pressure chamber, so that the neutral axis is set at an appropriate position in each of the first and second regions of the vibration plate, thereby increasing the amount of displacement of the vibration plate caused by driving the piezoelectric element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-116604 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the past, even if the technology described in Patent Document 1 was applied, the neutral plane would be located within the piezoelectric layer if the thickness of the diaphragm was reduced. Here, in the past, the piezoelectric constant of the piezoelectric layer of the piezoelectric element was uniform in the thickness direction, so if the neutral plane was located within the piezoelectric layer, the displacement efficiency of the diaphragm due to driving of the piezoelectric element may decrease. [Means for solving the problem]

[0006] In order to solve the above problems, one embodiment of a liquid ejection head according to the present disclosure comprises a piezoelectric element having a first electrode, a piezoelectric layer, and a second electrode, a pressure chamber substrate having a pressure chamber connected to a nozzle, and a vibration plate that applies pressure to the liquid in the pressure chamber by vibrating when driven by the piezoelectric element, wherein the pressure chamber substrate, the vibration plate, and the piezoelectric element are stacked in this order in a stacking direction, and the neutral plane of the laminate formed of the piezoelectric element and the vibration plate is located within the piezoelectric layer, and when the region closer to the vibration plate is defined as a lower region and the region farther from the vibration plate is defined as an upper region of the two regions obtained by dividing the piezoelectric layer by the neutral plane, the piezoelectric constant of the lower region is smaller than the piezoelectric constant of the upper region.

[0007] Another aspect of the liquid ejection head according to the present disclosure includes a piezoelectric element having a first electrode, a piezoelectric layer, and a second electrode, a pressure chamber substrate having a pressure chamber communicating with a nozzle, and a vibration plate that applies pressure to the liquid in the pressure chamber by vibrating when driven by the piezoelectric element, wherein the pressure chamber substrate, the vibration plate, and the piezoelectric element are stacked in this order in a stacking direction, a neutral plane of a laminate formed of the piezoelectric element and the vibration plate is located within the piezoelectric layer, and the piezoelectric layer includes a first piezoelectric layer formed of crystals preferentially oriented in a plane other than the (100) plane, and a second piezoelectric layer formed of crystals preferentially oriented in the (100) plane, the first piezoelectric layer is located between the vibration plate and the neutral plane, and the neutral plane is located between the first piezoelectric layer and the second piezoelectric layer.

[0008] One aspect of a liquid ejection apparatus according to the present disclosure includes the liquid ejection head of the above aspect, and a control unit that controls driving of the liquid ejection head. [Brief description of the drawings]

[0009] [Figure 1] 1 is a configuration diagram that illustrates a liquid ejection device according to an embodiment. [Diagram 2] FIG. 2 is an exploded perspective view of the liquid ejection head according to the embodiment. [Diagram 3] 3 is a cross-sectional view taken along line AA in FIG. 2. [Figure 4] FIG. 2 is a plan view showing a part of a liquid ejection head according to an embodiment. [Diagram 5] 5 is a cross-sectional view taken along line BB in FIG. 4. [Figure 6] 4 is a partially enlarged cross-sectional view of a laminate including a piezoelectric element and a diaphragm. FIG. [Figure 7] FIG. 13 is a diagram showing the relationship between the conditions of Samples Nos. 1 to 18 in which the piezoelectric constant of the lower portion of the piezoelectric layer is changed and the deformation efficiency ratio of the laminate. [Figure 8] 13 is a graph showing the relationship between the piezoelectric constant ratio of a lower portion of a piezoelectric layer and the deformation efficiency ratio of a laminate. [Figure 9] FIG. 13 is a diagram showing the relationship between the conditions of Samples Nos. 19 to 34 in which the film thickness of the lower part of the piezoelectric layer is changed and the deformation efficiency ratio of the laminate. [Figure 10] 13 is a graph showing the relationship between the film thickness ratio of a lower portion of a piezoelectric layer and the deformation efficiency ratio of a laminate. [Figure 11] FIG. 11 is a cross-sectional view of a liquid ejection head according to a first modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, preferred embodiments of the present disclosure will be described with reference to the accompanying drawings. Note that the dimensions and scale of each part in the drawings may differ from the actual dimensions, and some parts are shown diagrammatically to facilitate understanding. In addition, the scope of the present disclosure is not limited to these forms unless otherwise specified in the following description to the effect that the present disclosure is limited.

[0011] In the following description, the mutually intersecting X-axis, Y-axis, and Z-axis are used as appropriate. In the following description, one direction along the X-axis is the X1 direction, and the direction opposite the X1 direction is the X2 direction. Similarly, the opposite directions along the Y-axis are the Y1 direction and the Y2 direction. In addition, the opposite directions along the Z-axis are the Z1 direction and the Z2 direction. The Z1 direction is an example of a "stacking direction." In addition, viewing in a direction along the Z-axis is sometimes called a "planar view."

[0012] Typically, the Z axis is the vertical axis, and the Z2 direction corresponds to the vertical downward direction. However, the Z axis does not have to be the vertical axis. Also, the X axis, the Y axis, and the 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°.

[0013] 1. Embodiment 1-1. Overall configuration of the liquid ejection device 1 is a schematic diagram showing a configuration of a liquid ejection device 100 according to an 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 M. The medium M is typically printing paper. Note that the medium M is not limited to printing paper, and may be a printing target made of any material, such as a resin film or fabric.

[0014] As shown in FIG. 1, the liquid ejection device 100 includes a liquid container 10, a control unit 20 which is an example of a “control unit”, a transport mechanism 30, a moving mechanism 40, and a liquid ejection head 50.

[0015] The liquid container 10 is a container that stores ink. Specific examples of the liquid container 10 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 10 is not particularly limited and may be any type.

[0016] 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. Here, the control unit 20 controls the driving of the liquid ejection head 50. Therefore, as described later, the liquid ejection head 50 has excellent ejection characteristics, and therefore it is possible to provide a liquid ejection device 100 with excellent ejection characteristics.

[0017] The transport mechanism 30 transports the medium M in the Y2 direction under the control of the control unit 20. The movement mechanism 40 reciprocates the liquid ejection head 50 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 40 has a substantially box-shaped carriage 41 that houses the liquid ejection head 50, and a transport belt 42 to which the carriage 41 is fixed. Note that the number of liquid ejection heads 50 mounted on the carriage 41 is not limited to one, and may be multiple. In addition to the liquid ejection head 50, the above-mentioned liquid container 10 may be mounted on the carriage 41.

[0018] Under the control of the control unit 20, the liquid ejection head 50 ejects ink supplied from the liquid container 10 from each of a plurality of nozzles onto the medium M in the Z2 direction. This ejection is performed in parallel with the transport of the medium M by the transport mechanism 30 and the reciprocating movement of the liquid ejection head 50 by the movement mechanism 40, thereby forming an ink image on the surface of the medium M. The configuration and manufacturing method of the liquid ejection head 50 will be described in detail later.

[0019] 1-2. Overall configuration of liquid ejection head Fig. 2 is an exploded perspective view of a liquid ejection head 50 according to an embodiment. Fig. 3 is a cross-sectional view taken along line AA in Fig. 2. As shown in Fig. 2 and Fig. 3, the liquid ejection head 50 has a flow path substrate 51, a pressure chamber substrate 52, a nozzle substrate 53, a vibration absorber 54, a vibration plate 55, a plurality of piezoelectric elements 56, a sealing plate 57, a case 58, and a wiring substrate 59.

[0020] Here, a pressure chamber substrate 52, a vibration plate 55, a plurality of piezoelectric elements 56, a case 58, and a sealing plate 57 are disposed in an area located in the Z1 direction from the flow path substrate 51. On the other hand, a nozzle substrate 53 and a vibration absorber 54 are disposed in an area located in the Z2 direction from the flow path substrate 51. Each element of the liquid ejection head 50 is roughly a plate-like member that is elongated in the direction along the Y axis, and is joined to one another by, for example, an adhesive.

[0021] 2, the nozzle substrate 53 is a plate-like member provided with a plurality of nozzles N arranged in a direction along the Y axis. Each nozzle N is a through hole that allows ink to pass through. The nozzle substrate 53 is manufactured by processing a silicon single crystal substrate by a semiconductor manufacturing technique that uses a processing technique such as dry etching or wet etching. However, other known methods and materials may be used as appropriate to manufacture the nozzle substrate 53.

[0022] The flow path substrate 51 is a plate-like member for forming a flow path of ink. As shown in FIG. 2 and FIG. 3, the flow path substrate 51 is provided with an opening R1, a plurality of supply flow paths Ra, and a plurality of communication flow paths Na. The opening R1 is an elongated through hole extending in a direction along the Y axis in a plan view seen in a direction along the Z axis so as to be continuous across a plurality of nozzles N. On the other hand, each of the supply flow paths Ra and the communication flow paths Na is a through hole provided individually for each nozzle N. Each of the plurality of supply flow paths Ra communicates with the opening R1. The flow path substrate 51 is manufactured by processing a silicon single crystal substrate by, for example, a semiconductor manufacturing technique, in the same manner as the nozzle substrate 53 described above. However, other known methods and materials may be appropriately used for manufacturing the flow path substrate 51.

[0023] The pressure chamber substrate 52 is a plate-like member in which a plurality of pressure chambers C corresponding to a plurality of nozzles N are formed. The pressure chambers C are located between the flow path substrate 51 and the vibration plate 55, and are spaces called cavities for applying pressure to the ink filled in the pressure chambers C. The pressure chambers C are arranged in a direction along the Y axis. Each pressure chamber C is formed of a hole 52a that opens on both sides of the pressure chamber substrate 52, and is elongated in a direction along the X axis. The end of each pressure chamber C in the X2 direction communicates with the corresponding supply flow path Ra. On the other hand, the end of each pressure chamber C in the X1 direction communicates with the corresponding communication flow path Na. The pressure chamber substrate 52 is manufactured by processing a silicon single crystal substrate by, for example, a semiconductor manufacturing technique, in the same manner as the nozzle substrate 53 described above. However, other known methods and materials may be appropriately used for manufacturing each of the pressure chamber substrates 52.

[0024] A diaphragm 55 is disposed on the surface facing the Z1 direction of the pressure chamber substrate 52. The diaphragm 55 is an elastically deformable plate-like member. Details of the diaphragm 55 will be described later with reference to FIG.

[0025] A plurality of piezoelectric elements 56 corresponding to different nozzles N or pressure chambers C are arranged on the surface of the vibration plate 55 facing the Z1 direction. Each piezoelectric element 56 is a passive element that deforms when a drive signal is supplied, and has an elongated shape extending in the direction along the X axis. The plurality of piezoelectric elements 56 are arranged in the direction along the Y axis so as to correspond to the plurality of pressure chambers C. When the vibration plate 55 vibrates in conjunction with the deformation of the piezoelectric elements 56, the pressure in the pressure chambers C fluctuates, and ink is ejected from the nozzles N. Details of the piezoelectric elements 56 will be described later with reference to FIGS. 4 and 5.

[0026] The case 58 is a case for storing ink to be supplied to the multiple pressure chambers C, and is bonded to the surface of the flow path substrate 51 facing the Z1 direction with an adhesive or the like. The case 58 is made of, for example, a resin material, and is manufactured by injection molding. The case 58 is provided with a storage section R2 and an inlet IH. The storage section R2 is a recessed portion whose outer shape corresponds to the opening R1 of the flow path substrate 51. The inlet IH is a through hole that communicates with the storage section R2. The space formed by the opening R1 and the storage section R2 functions as a liquid storage chamber R, which is a reservoir that stores ink. Ink is supplied to the liquid storage chamber R from the liquid container 10 via the inlet IH.

[0027] The vibration absorber 54 is an element for absorbing pressure fluctuations in the liquid storage chamber R. The vibration absorber 54 is, for example, a compliance substrate that is a flexible sheet member that can be elastically deformed. Here, the vibration absorber 54 is disposed on a surface of the flow path substrate 51 facing the Z2 direction so as to close the opening R1 and the multiple supply flow paths Ra of the flow path substrate 51 and form the bottom surface of the liquid storage chamber R.

[0028] The sealing plate 57 is a structure that protects the multiple piezoelectric elements 56 and reinforces the mechanical strength of the pressure chamber substrate 52 and the vibration plate 55. The sealing plate 57 is bonded to the surface of the vibration plate 55 by, for example, an adhesive. The sealing plate 57 has recesses that accommodate the multiple piezoelectric elements 56.

[0029] A wiring board 59 is bonded to the surface of the pressure chamber substrate 52 or the vibration plate 55 facing the Z1 direction. The wiring board 59 is a mounting component on which a plurality of wires for electrically connecting the control unit 20 and the liquid ejection head 50 are formed. The wiring board 59 is a flexible wiring board such as an FPC (Flexible Printed Circuit) or an FFC (Flexible Flat Cable). A drive circuit 60 for driving the piezoelectric elements 56 is mounted on the wiring board 59. The drive circuit 60 selectively supplies a drive signal for driving each piezoelectric element 56 to each piezoelectric element 56 via the wiring board 59.

[0030] As described above, the liquid ejection head 50 has the piezoelectric element 56, the pressure chamber substrate 52 in which the pressure chamber C communicating with the nozzle N is provided, and the vibration plate 55 which applies pressure to the liquid in the pressure chamber C by vibrating when the piezoelectric element 56 is driven. Here, as described above, the pressure chamber substrate 52, the vibration plate 55 and the piezoelectric element 56 are layered in this order in the Z1 direction.

[0031] 1-3. Details of the diaphragm and piezoelectric element Fig. 4 is a plan view showing a part of a liquid ejection head 50 according to an embodiment. Fig. 5 is a cross-sectional view taken along line BB in Fig. 4. Below, the pressure chamber substrate 52, the piezoelectric element 56, and the vibration plate 55 will be described in this order with reference to Figs. 4 and 5.

[0032] As shown in Figs. 4 and 5, the pressure chamber substrate 52 is provided with holes 52a that form pressure chambers C. Accordingly, in the pressure chamber substrate 52, a wall-like partition 52b extending in the direction along the X-axis is provided between two adjacent holes 52a. The pressure chamber substrate 52 is manufactured, for example, by processing a silicon single crystal substrate using semiconductor manufacturing technology. In Fig. 4, the planar shape of the hole 52a when formed by anisotropic etching on a silicon single crystal substrate with a surface orientation (110) is shown by a dashed line. Note that the planar shape of the hole 52a is not limited to the example shown in Fig. 4 and may be any shape.

[0033] Here, the pressure chambers C are formed after the piezoelectric elements 56 are formed. The pressure chambers C are formed, for example, by anisotropically etching one of the two surfaces of the silicon single crystal substrate after the piezoelectric elements 56 are formed, which is different from the surface on which the piezoelectric elements 56 are formed. At this time, for example, an aqueous potassium hydroxide solution (KOH) is used as an etchant for the anisotropic etching. Furthermore, at this time, if the elastic film 55a is made of silicon oxide, the elastic film 55a functions as a stopping layer that stops the anisotropic etching. After the pressure chambers C are formed as described above, the flow path substrate 51 and the like are bonded to the pressure chamber substrate 52 with an adhesive.

[0034] 4, in plan view, the piezoelectric element 56 overlaps the pressure chamber C. As shown in Fig. 5, the piezoelectric element 56 has a first electrode 56a, a piezoelectric layer 56b, and a second electrode 56c, which are laminated in this order in the Z1 direction.

[0035] The first electrodes 56a are individual electrodes spaced apart from one another for each piezoelectric element 56. Specifically, a plurality of first electrodes 56a extending in the direction along the X-axis are arranged in the direction along the Y-axis at intervals from one another. A drive signal including a predetermined voltage pulse is supplied from the control unit 20 to the first electrodes 56a of each piezoelectric element 56.

[0036] The first electrode 56a has, for example, a layer made of iridium (Ir) and a layer made of titanium (Ti), which are laminated in this order in the Z1 direction. Here, iridium is an electrode material with excellent conductivity. Therefore, by using iridium as a constituent material of the first electrode 56a, it is possible to reduce the resistance of the first electrode 56a. In addition, when forming the piezoelectric layer 56b, the layer made of titanium controls the orientation of the piezoelectric layer 56b by using island-shaped Ti as crystal nuclei, thereby enhancing the crystallinity or orientation of the piezoelectric layer 56b.

[0037] Instead of or in addition to the layer made of iridium, a layer made of another metal material may be provided. Examples of the other metal material include platinum (Pt), aluminum (Al), nickel (Ni), gold (Au), copper (Cu), and the like, and one of these may be used alone or two or more may be used in combination. The material constituting the first electrode 56a is not limited to a metal material, and may be, for example, a conductive metal oxide such as ITO (indium tin oxide) and IZO (indium zinc oxide).

[0038] In the examples shown in Figs. 4 and 5, the piezoelectric layer 56b is in the form of a strip extending in the direction along the Y-axis so as to be continuous across the piezoelectric elements 56. In the example shown in Fig. 4, the piezoelectric layer 56b is provided with through-holes 56b1 extending in the direction along the X-axis in regions corresponding to the gaps between the adjacent pressure chambers C in a plan view. As a result, the piezoelectric layer 56b is provided individually for each piezoelectric element 56, as viewed in the cross section shown in Fig. 5. In the example shown in Fig. 4, in the portion where the through-holes 56b1 are not provided, the piezoelectric layer 56b is provided continuously to the pressure chambers C, but the present invention is not limited to this configuration, and the continuous portion may be removed and the piezoelectric layer 56b may be provided individually to the piezoelectric elements 56.

[0039] The piezoelectric layer 56b has the general composition formula ABO 3 The piezoelectric material is made of a piezoelectric material having a perovskite crystal structure represented by the formula:3 ), lead zirconate titanate (Pb(Zr,Ti)O 3 ), lead zirconate (PbZrO 3 ), lead lanthanum titanate ((Pb,La),TiO 3 ), lead lanthanum zirconate titanate ((Pb,La)(Zr,Ti)O 3 ), lead zirconium titanate niobate (Pb(Zr,Ti,Nb)O 3 ), lead magnesium zirconium titanate (Pb(Zr,Ti)(Mg,Nb)O 3 Among these, lead zirconate titanate, potassium sodium niobate, and barium titanate are preferably used as the constituent material of the piezoelectric layer 56b from the viewpoint of easily improving the piezoelectric performance.

[0040] The piezoelectric layer 56b may be composed of a single layer, or may be composed of a laminate of multiple layers as described later with reference to Fig. 6. However, when the piezoelectric layer 56b is composed of a laminate of multiple layers, there is an advantage in that the piezoelectric constant of the piezoelectric layer 56b can be easily made different in the thickness direction, as described later.

[0041] The second electrode 56c is a band-shaped common electrode that extends in the direction along the Y-axis so as to be continuous across the plurality of piezoelectric elements 56. A predetermined constant potential is supplied to the second electrode 56c.

[0042] The second electrode 56c is made of, for example, iridium (Ir). However, the material of the second electrode 56c is not limited to iridium, and may be, for example, a metal material such as platinum (Pt), aluminum (Al), nickel (Ni), gold (Au), or copper (Cu). The second electrode 56c may be made of one of these metal materials alone, or may be made of two or more of these materials in a combination such as a laminate.

[0043] The first electrode 56a, the piezoelectric layer 56b, and the second electrode 56c are obtained by forming films on the vibration plate 55 in this order. The first electrode 56a and the second electrode 56c are each formed by a known film forming technique such as a sputtering method, and a known processing technique using photolithography, etching, and the like. The piezoelectric layer 56b is formed, for example, by forming a precursor layer of a piezoelectric material by a sol-gel method, and baking and crystallizing the precursor layer. In addition, the piezoelectric layer 56b is subjected to a polarization process by applying a voltage between the first electrode 56a and the second electrode 56c.

[0044] In the above-described piezoelectric element 56, when a voltage is applied between the first electrode 56a and the second electrode 56c, the piezoelectric layer 56b is deformed due to the inverse piezoelectric effect. In response to this deformation, the diaphragm 55 vibrates.

[0045] 5, the vibration plate 55 has an elastic film 55a and an insulating film 55b, which are laminated in this order in the Z1 direction. Here, the elastic film 55a is provided on the pressure chamber substrate 52. The insulating film 55b is provided between the elastic film 55a and the piezoelectric element 56.

[0046] 5, for convenience of explanation, the interface between the layers constituting the diaphragm 55 is clearly shown, but the interface does not have to be clear, and for example, the constituent materials of two adjacent layers may be mixed near the interface between the layers. Also, the diaphragm 55 is not limited to a configuration having the elastic film 55a and the insulating film 55b, and may be configured without the insulating film 55b, or a TiO 2 layer for increasing adhesion between the elastic film 55a and the insulating film 55b may be used. X , AlO X , CrO X Alternatively, a film made of TiN may be provided.

[0047] The elastic film 55a is made of, for example, silicon oxide (SiO 2Here, in addition to silicon oxide and its constituent elements, the elastic film 55a may contain small amounts of elements such as zirconium (Zr), titanium (Ti), iron (Fe), chromium (Cr) or hafnium (Hf) as impurities. Such impurities include silicon oxide (SiO 2 The impurities may be elements that are inevitably mixed in when the elastic film 55a is formed, or may be elements that are intentionally mixed in the elastic film 55a. In addition, silicon may be present in the elastic film 55a in the form of an oxide, or silicon may be present in the form of a simple substance, a nitride, an oxynitride, or the like.

[0048] The thickness td1 of the elastic film 55a is determined according to the thickness td and width of the vibration plate 55, and is not particularly limited, but is preferably in the range of 100 nm to 2000 nm, and more preferably in the range of 500 nm to 1500 nm.

[0049] The insulating film 55b is made of, for example, zirconium oxide (ZrO 2 In addition to zirconium oxide and its constituent elements, the insulating film 55b may contain small amounts of titanium (Ti), iron (Fe), chromium (Cr), hafnium (Hf), or other elements as impurities. Such impurities include zirconium oxide (ZrO 2 ) has an effect of softening the insulating film 55b. The impurity may be an element that is inevitably mixed in when the insulating film 55b is formed, or an element that is intentionally mixed in the insulating film 55b. In addition to zirconium being present in the insulating film 55b in the form of an oxide, zirconium may be present in the form of a simple substance, a nitride, an oxynitride, or the like.

[0050] The insulating film 55b is made of ZrO 2 For example, but not limited to, PbTiO X , T.I.O. X , ((Pb,Bi)(Fe,Ti)O X ) The insulating film 55b may be configured as a single layer, or may be configured as a laminate of multiple layers.

[0051] The thickness td2 of the insulating film 55b is determined according to the thickness td and width of the vibration plate 55, and is not particularly limited, but is preferably within the range of 100 nm or more and 2000 nm or less, and more preferably within the range of 500 nm or more and 1500 nm or less.

[0052] The elastic film 55a and insulating film 55b are obtained by being formed in this order on a silicon single crystal substrate for forming the pressure chamber substrate 52. For example, when the elastic film 55a is made of silicon oxide, the elastic film 55a is formed by thermally oxidizing one surface of the silicon single crystal substrate. For example, when the insulating film 55b is made of zirconium oxide, the insulating film 55b is formed by forming a zirconium layer on the elastic film 55a by a sputtering method, and then thermally oxidizing the layer.

[0053] The method of forming each of the films constituting the diaphragm 55 is not limited to the above-mentioned example, and may be any method. For example, at least a part of the elastic film 55a may be formed by a CVD method or the like. Furthermore, the method of forming the insulating film 55b is not limited to a method using thermal oxidation, and may be formed by a CVD method, an atomic layer deposition (ALD) method, or the like.

[0054] The above-described diaphragm 55 has a vibration area PV that vibrates when driven by the piezoelectric element 56. The vibration area PV is a portion of the diaphragm 55 that overlaps with the pressure chamber C in a plan view. Here, the above-described elastic film 55a and insulating film 55b are each provided across the entire vibration area PV when viewed in the direction along the Z axis.

[0055] The vibration region PV is divided into an active region RE1 and a non-active region RE2. The active region RE1 is a portion of the vibration plate 55 that overlaps with the pressure chamber C, the first electrode 56a, the piezoelectric layer 56b, and the second electrode 56c when viewed in the direction along the Z axis. The non-active region RE2 is a portion of the vibration plate 55 that overlaps with the pressure chamber C when viewed in the direction along the Z axis and is different from the active region RE1.

[0056] 5, the inactive area RE2 has an arm portion RE2a. The arm portion RE2a is a portion of the vibration plate 55 that overlaps the pressure chamber C without overlapping the piezoelectric layer 56b between the active area RE1 and the end of the pressure chamber C in the width direction when viewed in the direction along the Z axis.

[0057] Therefore, the short-side end of the pressure chamber C does not overlap the piezoelectric layer 56b when viewed in the direction along the Z axis. By providing the arm portion RE2a in this manner, it is possible to make the end of the vibration plate 55 in the width direction more easily deformable. This makes it possible to improve the efficiency with which the vibration plate 55 is deformed by driving the piezoelectric element 56.

[0058] In order to efficiently deform the laminate LA composed of the above-mentioned piezoelectric element 56 and vibration plate 55 by driving the piezoelectric element 56, it has conventionally been preferable to position the neutral plane of the laminate LA between the vibration plate 55 and the piezoelectric element 56, since the piezoelectric constant of the piezoelectric layer 56b is uniform.

[0059] On the other hand, as the pitch of the nozzles N has become narrower in recent years, the width of the vibration plate 55 has become smaller. Therefore, in order to improve the efficiency of deformation of the vibration plate 55 by driving the piezoelectric element 56, it is necessary to reduce the thickness td of the vibration plate 55.

[0060] When the thickness td of the vibration plate 55 is thin, the neutral plane AN of the laminate LA is located within the piezoelectric layer 56b, as shown in FIG. 5. Here, the "neutral plane AN" of the laminate LA is a plane parallel to both the X-axis and the Y-axis in which no compressive strain or tensile strain occurs when a bending moment occurs in the laminate LA. The neutral axis of the laminate LA corresponds to an axial portion of any plane parallel to both the X-axis and the Z-axis that intersects with the neutral plane. In this embodiment, the piezoelectric element 56 is deflected and deformed along the Z-direction, and the pressure chamber C is formed longitudinally along the X-axis, so that the deformation of the laminate LA becomes noticeable when viewed along the X-axis, and the neutral axis is an axis along the X-direction.

[0061] Here, when the surface of the first layer of a laminate consisting of n layers is taken as the reference, the position y of the neutral plane of the laminate is 0is defined by the following equation (1).

number

[0062] When the laminate is applied to the laminate LA, k is 5, the first layer is the elastic film 55a, the second layer is the insulating film 55b, the third layer is the first electrode 56a, the fourth layer is the piezoelectric layer 56b, and the fifth layer is the second electrode 56c. 0 is the position of the neutral plane AN based on the surface of the laminate LA facing the Z2 direction, and the position y 0 where Young's modulus E 1 is the Young's modulus [GPa] of the elastic membrane 55a, and the Young's modulus E 2 is the Young's modulus [GPa] of the insulating film 55b, and the Young's modulus E 3 is the Young's modulus [GPa] of the first electrode 56a, and the Young's modulus E 4 is the Young's modulus [GPa] of the piezoelectric layer 56b, and the Young's modulus E 5 is the Young's modulus [GPa] of the second electrode 56c. 1 is the thickness td1 [nm] of the elastic film 55a, and the film thickness h 2 is the thickness td2 [nm] of the insulating film 55b, and the film thickness h 3 is the thickness [nm] of the first electrode 56a, and the film thickness h 4 is the thickness tp [nm] of the piezoelectric layer 56b, and the film thickness h 5 is the thickness [nm] of the second electrode 56c. The cross-sectional area Ak is the cross-sectional area of ​​the laminate LA, and corresponds to the thickness T of the laminate LA times the width a. The width a is the width W of the active region RE1.

[0063] Of the two regions obtained by dividing the piezoelectric layer 56b by the neutral plane AN, the region closer to the vibration plate 55 is the lower region RB, and the region farther from the vibration plate 55 is the upper region RT. That is, the lower region RB is the region of the piezoelectric layer 56b located in the Z2 direction from the neutral plane AN, and the upper region RT is the region of the piezoelectric layer 56b located in the Z1 direction from the neutral plane AN. In this way, the piezoelectric layer 56b has the lower region RB and the upper region RT.

[0064] Here, a portion of the second electrode 56c of the piezoelectric element 56 is disposed on each of the side surfaces of the lower region RB and the upper region RT. Since the second electrode 56c has a portion disposed on each of the side surfaces of the lower region RB and the upper region RT in this manner, the first electrode 56a can be an individual electrode and the second electrode 56c can be a common electrode, as described above.

[0065] In this way, when the neutral plane AN is located within the piezoelectric layer 56b, the efficiency of deformation of the vibration plate 55 by driving the piezoelectric element 56 may decrease by making the piezoelectric constant of the piezoelectric layer 56b approximately uniform in the Z-axis direction. The reason for this will be explained. When a voltage is applied to the piezoelectric element 56 by two electrodes, the piezoelectric element deforms to contract approximately along the Y-axis due to the inverse piezoelectric effect, and a bending moment is generated so that the laminate LA becomes convex toward the pressure chamber side. Here, when the neutral plane AN is located within the piezoelectric layer 56b, the displacement of the piezoelectric layer 56b in the upper region RT contributes to the bending moment, whereas the deformation of the piezoelectric layer 56b in the lower region RB inhibits the bending moment. This is because the laminate LA becomes convex toward the pressure chamber side, and a tensile strain is generated, that is, a force in the direction of contraction is applied to the piezoelectric layer 56b due to the inverse piezoelectric effect in the lower region RB where a force in the direction of extension is applied. For the reasons described above, if the piezoelectric layer 56b has a piezoelectric constant that is approximately uniform in the Z-axis direction, the deformation efficiency decreases.

[0066] Therefore, in order to improve the deformation efficiency of the vibration plate 55 by driving the piezoelectric element 56, in the liquid ejection head 50, the piezoelectric constant of the lower region RB is smaller than that of the upper region RT. Therefore, when a voltage is applied to the piezoelectric element 56, the lower region RB is less likely to deform due to the inverse piezoelectric effect than the upper region RT. Therefore, since the lower region RB essentially functions as the vibration plate 55, the deformation due to the inverse piezoelectric effect of the lower region RB is less likely to hinder the bending moment of the laminate LA caused by the deformation due to the inverse piezoelectric effect of the upper region RT. As a result, even if the neutral plane AN of the laminate LA is located within the piezoelectric layer 56b, the deformation efficiency of the vibration plate 55 by driving the piezoelectric element 56 can be improved. Moreover, when the piezoelectric constant of the lower region RB is low enough that the lower region RB can be regarded as the vibration plate 55, a configuration equivalent to the thickness of the end of the vibration plate 55 in the width direction is pseudo-obtained, so that the deformation efficiency can be further improved. Below, the lower region RB and the upper region RT will be described in detail based on FIG. 6 to FIG. 10.

[0067] Fig. 6 is a partially enlarged cross-sectional view of a laminate LA composed of a piezoelectric element 56 and a vibration plate 55. For convenience of explanation, Fig. 6 illustrates an example in which the piezoelectric layer 56b is composed of a laminate of five layers. The number of layers constituting the piezoelectric layer 56b is not limited to five layers, but may be any number, such as four layers or less or six layers or more. The thicknesses of the layers constituting the piezoelectric layer 56b may be equal to or different from each other.

[0068] As shown in FIG. 6, the piezoelectric layer 56b has a plurality of layers LA1, LA2, LA3, LA4, and LA5. The layers LA1, LA2, LA3, LA4, and LA5 are laminated in this order in the Z1 direction. Here, the layer LA1 is an example of a "first piezoelectric layer" and is located between the vibration plate 55 and the neutral plane AN. Among the plurality of layers LA1 to LA5, the layer LA1 is included in the lower region RB and is the layer closest to the vibration plate 55. Furthermore, the layer LA5 is an example of a "second piezoelectric layer" and is included in the upper region RT and is the layer farthest from the vibration plate 55 among the plurality of layers LA1 to LA5. The neutral plane AN is located between the layers LA1 and LA5.

[0069] Here, in order to make the piezoelectric constant of the lower region RB smaller than that of the upper region RT, the average value of the piezoelectric constants of the layers belonging to the lower region RB among the layers LA1 to LA5 may be smaller than the average value of the piezoelectric constants of the layers belonging to the upper region RT. However, from the viewpoint of preferably obtaining the effect of reducing the piezoelectric constant of the lower region RB, it is preferable that the piezoelectric constant of the layer LA1, which is closest to the diaphragm 55, among the layers belonging to the lower region RB, is the smallest. Also, from the viewpoint of preferably obtaining the effect of increasing the piezoelectric constant of the upper region RT, it is preferable that the piezoelectric constant of the layer LA5, which is the farthest from the diaphragm 55, among the layers belonging to the upper region RT, is the largest.

[0070] The thickness and piezoelectric constant of the layer in the piezoelectric layer 56b that reduces the piezoelectric constant will be described in detail below.

[0071] 7 is a diagram showing the relationship between the conditions of Samples Nos. 1 to 18 in which the piezoelectric constant d1 of the lower part of the piezoelectric layer 56b is changed and the deformation efficiency ratio of the laminate LA. The lower part of the piezoelectric layer 56b is the part closer to the vibration plate 55 of the two parts obtained by dividing the piezoelectric layer 56b in the thickness direction. In the following, the part farther from the vibration plate 55 of the two parts obtained by dividing the piezoelectric layer 56b in the thickness direction is referred to as the upper part of the piezoelectric layer 56b.

[0072] The "position of the neutral plane" in FIG. 7 is the position of the neutral plane AN. Here, in the "member" section, "piezoelectric layer" indicates that the neutral plane AN is located within the piezoelectric layer 56b, and "diaphragm" indicates that the neutral plane AN is located within the diaphragm 55. Also, the "distance from the first electrode" is the distance [nm] between the first electrode 56a and the neutral plane AN. However, the distance is a positive value when the neutral plane AN is located in the Z1 direction from the first electrode 56a, and is a negative value when the neutral plane AN is located in the Z2 direction from the first electrode 56a.

[0073] In Samples Nos. 1 to 9, the neutral plane AN is located within the piezoelectric layer 56b. In the example shown in FIG. 7, the distance between the first electrode 56a and the neutral plane AN is 115 nm in Samples Nos. 1 to 9. In contrast, in Samples Nos. 10 to 18, the neutral plane AN is located within the diaphragm 55. In the example shown in FIG. 7, the distance between the first electrode 56a and the neutral plane AN is −275 nm in Samples Nos. 10 to 18. Note that in Samples Nos. 10 to 18, the thickness td of the diaphragm 55 is greater than that of Samples Nos. 1 to 9, and therefore the position of the neutral plane AN is located within the diaphragm 55.

[0074] "Thickness of piezoelectric layer" in Fig. 7 is the thickness tp [nm] of the piezoelectric layer 56b. Also, "Thickness of lower part of piezoelectric layer" in Fig. 7 is the thickness tpb [nm] of the lower part of the piezoelectric layer 56b. Furthermore, "tpb / tp" in Fig. 7 is the ratio tpb / tp of thickness tpb to thickness tp.

[0075] The thicknesses tp, tpb and the ratio tpb / tp are equal to each other in Samples No. 1 to 18. In the example shown in Fig. 7, the thickness tp is 1200 nm, the thickness tpb is 100 nm, and the ratio tpb / tp is 8%. More specifically, the piezoelectric layer 56b is 1200 nm thick, formed by stacking 12 layers, each of which has a thickness of 100 nm.

[0076] The "piezoelectric constant of the lower part of the piezoelectric layer" in Fig. 7 is the piezoelectric constant d1 of the lower part of the piezoelectric layer 56b. Moreover, the "piezoelectric constant of the upper part of the piezoelectric layer" in Fig. 7 is the piezoelectric constant d2 of the upper part of the piezoelectric layer 56b. Furthermore, "d1 / d2" in Fig. 7 is the ratio d1 / d2 of the piezoelectric constant d1 to the piezoelectric constant d2.

[0077] The piezoelectric constants d2 of samples Nos. 1 to 18 are equal to each other. In the example shown in Fig. 7, the piezoelectric constants d2 of samples Nos. 1 to 18 are 200 [pm / V]. On the other hand, the piezoelectric constants d1 of samples Nos. 1 to 9 are different from each other. Similarly, the piezoelectric constants d1 of samples Nos. 10 to 18 are different from each other. In the example shown in Figure 7, the piezoelectric constant d1 in samples No. 1 and 10 is 10 [pm / V], the piezoelectric constant d1 in samples No. 2 and 11 is 25 [pm / V], the piezoelectric constant d1 in samples No. 3 and 12 is 50 [pm / V], the piezoelectric constant d1 in samples No. 4 and 13 is 75 [pm / V], the piezoelectric constant d1 in samples No. 5 and 14 is 100 [pm / V], the piezoelectric constant d1 in samples No. 6 and 15 is 125 [pm / V], the piezoelectric constant d1 in samples No. 7 and 16 is 150 [pm / V], the piezoelectric constant d1 in samples No. 8 and 17 is 175 [pm / V], and the piezoelectric constant d1 in samples No. 9 and 18 is 200 [pm / V].

[0078] 7 is the ratio of the deformation efficiency when the piezoelectric constants d1 and d2 are equal to each other, which is taken as the standard deformation efficiency of 1. The deformation efficiency is, for example, the ratio of the amount of displacement of the vibration plate 55 to the voltage applied to the piezoelectric element 56. The deformation efficiency ratio shown in FIG. 7 is the result obtained by simulation.

[0079] Fig. 8 is a graph showing the relationship between the piezoelectric constant ratio d1 / d2 of the lower part of the piezoelectric layer 56b and the deformation efficiency ratio of the laminate LA. Fig. 8 shows the relationship between the piezoelectric constant ratio d1 / d2 shown in Fig. 7 and the deformation efficiency ratio of the laminate LA. In Fig. 8, the vertical axis shows the deformation efficiency ratio of the laminate LA, and the horizontal axis shows the piezoelectric constant ratio d1 / d2.

[0080] 8, when the neutral plane AN is located within the piezoelectric layer 56b, the smaller the piezoelectric constant ratio d1 / d2, the higher the deformation efficiency ratio of the laminate LA. This is because the effect of the lower region RB not impeding the action of the upper region RT is enhanced.

[0081] Here, from the viewpoint of suitably increasing the deformation efficiency ratio of the laminate LA, the piezoelectric constant ratio d1 / d2 is preferably 25% or less, and more preferably 12.5% ​​or less.

[0082] On the other hand, when the neutral plane AN is located within the diaphragm 55, the smaller the piezoelectric constant ratio d1 / d2, the lower the deformation efficiency ratio of the laminate LA. This is because the piezoelectric constant of the layers that should contribute to the bending deformation of the diaphragm 55 among the layers constituting the piezoelectric layer 56b is simply lowered. Also, when the neutral plane AN is located within the diaphragm 55, the deformation efficiency ratio of the laminate LA is lower over the entire range between 0% and 100% of the piezoelectric constant ratio d1 / d2 than when the neutral plane AN is located within the piezoelectric layer 56b. This is because when the neutral plane AN is located within the diaphragm 55, the thickness td of the diaphragm 55 is thicker than when the neutral plane AN is located within the piezoelectric layer 56b.

[0083] As can be seen from the results shown in Fig. 8, the piezoelectric constant of the lower region RB may be smaller than that of the upper region RT, but is preferably less than half the piezoelectric constant of the upper region RT. In this case, the deformation efficiency of the vibration plate 55 caused by driving the piezoelectric element 56 can be improved compared to an embodiment in which the piezoelectric constant of the lower region RB is greater than half the piezoelectric constant of the upper region RT. As described above, the piezoelectric constant ratio d1 / d2 is preferably 25% or less, and more preferably 12.5% ​​or less, so that the piezoelectric constant of the lower region RB is more preferably 25% or less, and even more preferably 12.5% ​​or less, of the piezoelectric constant of the upper region RT.

[0084] To make the piezoelectric constant of the lower region RB smaller than that of the upper region RT, for example, among the layers LA1-56b5, the layers belonging to the lower region RB may be made of crystals preferentially oriented in a plane other than the (100) plane, and the layers belonging to the upper region RT may be made of crystals preferentially oriented in the (100) plane. In this case, the layer LA5 is made of crystals preferentially oriented in the (100) plane, and the layer LA1 is made of crystals preferentially oriented in a plane other than the (100) plane. With this configuration, the piezoelectric constant of the lower region RB can be made smaller than that of the upper region RT.

[0085] The lower region RB and the upper region RT may be made of piezoelectric materials with different compositions. For example, the lower region RB and the upper region RT are made of piezoelectric materials with different lead contents. In this case, even if the lower region RB and the upper region RT are made of crystals preferentially oriented in the (100) plane, the piezoelectric constant of the lower region RB can be made smaller than that of the upper region RT. In addition, when the second piezoelectric layer is made of crystals preferentially oriented in the (100) plane and the first piezoelectric layer is made of crystals preferentially oriented in a plane other than the (100) plane, the lower region and the upper region are made of piezoelectric materials with different compositions, so that the piezoelectric constant of the lower region can be effectively made smaller than that of the upper region.

[0086] The layers LA1 to LA5 constituting the piezoelectric layer 56b may have different crystal states. For example, the layers in the lower region RB may be in an amorphous state, and the layers in the upper region RT may be in a polycrystalline or single crystalline state.

[0087] In addition, the dielectric constant of the lower region RB is preferably higher than that of the upper region RT. In this case, even if the lower region RB is interposed between the first electrode 56a and the upper region RT, the voltage between the first electrode 56a and the second electrode 56c can be applied to the upper region RT more efficiently than in a case where the dielectric constant of the lower region RB is equal to or lower than that of the upper region RT.

[0088] FIG. 9 is a diagram showing the relationship between the conditions of Samples Nos. 19 to 34 in which the film thickness of the lower part of the piezoelectric layer 56b is changed and the deformation efficiency ratio of the laminate LA.

[0089] In samples Nos. 19 to 26, the neutral plane AN is located within the piezoelectric layer 56b, similar to the above-mentioned samples Nos. 1 to 9. In the example shown in Fig. 9, the distance between the first electrode 56a and the neutral plane AN is 115 nm in samples Nos. 19 to 26. In contrast, in samples Nos. 27 to 34, the neutral plane AN is located within the diaphragm 55, similar to the above-mentioned samples Nos. 10 to 18. In the example shown in Fig. 9, the distance between the first electrode 56a and the neutral plane AN is -275 nm in samples Nos. 27 to 34.

[0090] Similarly to the above-mentioned samples No. 1 to 18, the thicknesses tp in samples No. 19 to 34 are equal to each other. However, the thicknesses tpb in samples No. 19 to 26 are different from each other. Similarly, the thicknesses tpb in samples No. 27 to 34 are different from each other. In the example shown in FIG. 9, the thicknesses tpb in samples No. 19 and 27 are 0 nm, the thicknesses tpb in samples No. 20 and 28 are 200 nm, the thicknesses tpb in samples No. 21 and 29 are 300 nm, the thicknesses tpb in samples No. 22 and 30 are 400 nm, the thicknesses tpb in samples No. 23 and 31 are 600 nm, the thicknesses tpb in samples No. 24 and 32 are 800 nm, the thicknesses tpb in samples No. 25 and 33 are 1000 nm, and the thicknesses tpb in samples No. 26 and 34 are 1200 nm.

[0091] The piezoelectric constants d1 and d2 and the ratio d1 / d2 are equal to each other in Samples Nos. 19 to 34. In the example shown in Fig. 9, the piezoelectric constant d1 is 10 [pm / V], the piezoelectric constant d2 is 200 [pm / V], and the ratio d1 / d2 is 5.0%.

[0092] Fig. 10 is a graph showing the relationship between the ratio tpb / tp, which is the film thickness ratio of the lower part of the piezoelectric layer 56b, and the deformation efficiency ratio of the laminate LA. Fig. 10 shows the relationship between the ratio tpb / tp shown in Fig. 9 and the deformation efficiency ratio of the laminate LA. In Fig. 9, the vertical axis shows the deformation efficiency ratio of the laminate LA, and the horizontal axis shows the ratio tpb / tp.

[0093] 10, when the neutral plane AN is located within the piezoelectric layer 56b, the improvement of the displacement efficiency ratio of the laminate LA by reducing the piezoelectric constant d1 of the layer LA1 is recognized in the range where the ratio tpb / tp is 40% or less. Here, when the ratio tpb / tp is 40%, the thickness tpb is greater than the distance between the first electrode 56a and the neutral plane AN. Therefore, even when the thickness tpb is greater than the distance between the first electrode 56a and the neutral plane AN, the improvement of the displacement efficiency ratio of the laminate LA by reducing the piezoelectric constant d1 of the layer LA1 is recognized.

[0094] On the other hand, when the neutral plane AN is located within the diaphragm 55, the larger the ratio tpb / tp is, the lower the deformation efficiency ratio of the laminate LA becomes in the entire range of the ratio tpb / tp from 0% to 100%. This is because the piezoelectric constant of the piezoelectric layer 56b that should contribute to the bending deformation of the diaphragm 55 simply decreases. Also, when the neutral plane AN is located within the diaphragm 55, the deformation efficiency ratio of the laminate LA is lower than when the neutral plane AN is located within the piezoelectric layer 56b in the entire range of the ratio tpb / tp from 0% to 100%. This is because when the neutral plane AN is located within the diaphragm 55, the thickness td of the diaphragm 55 is thicker and deformation is more likely to be hindered than when the neutral plane AN is located within the piezoelectric layer 56b.

[0095] As can be seen from the results shown in Fig. 10, it is preferable that the thickness tp1 of the lower region RB is thinner than the thickness tp2 of the upper region RT. In this case, the effect of the inverse piezoelectric effect of the lower region RB is reduced, and the deformation efficiency of the vibration plate 55 caused by driving the piezoelectric element 56 can be improved, compared to the embodiment in which the thickness tp1 of the lower region RB is equal to or greater than the thickness tp2 of the upper region RT. In addition, from the relationship between the above-mentioned ratio tpb / tp and the deformation efficiency ratio, it is more preferable that the thickness tp1 of the lower region RB is 40% or less of the thickness tp2 of the upper region RT.

[0096] As described above, in the liquid ejection head 50, by making the piezoelectric constant of the lower region RB smaller than the piezoelectric constant of the upper region RT, the deformation efficiency of the vibration plate 55 caused by driving the piezoelectric elements 56 can be improved.

[0097] 2. Variations The above-mentioned exemplary embodiments can be modified in various ways. Specific modified embodiments that can be applied to the above-mentioned embodiments are illustrated below. Two or more embodiments selected from the following examples can be appropriately combined as long as they are not contradictory to each other.

[0098] 2-1. Variation 1 11 is a cross-sectional view of a liquid ejection head 50A according to Modification 1. The liquid ejection head 50A is configured similarly to the liquid ejection head 50 described above, except that it has a piezoelectric element 56A instead of the piezoelectric element 56. The piezoelectric element 56A is configured similarly to the piezoelectric element 56 described above, except that the first electrode 56a is a common electrode and the second electrode 56c is an individual electrode. That is, in Modification 1, the first electrode 56a is a band-shaped common electrode extending in the direction along the Y axis so as to be continuous across the multiple piezoelectric elements 56A, while the second electrodes 56c are individual electrodes arranged spaced apart from each other for each piezoelectric element 56A.

[0099] In the above-described first modification, the piezoelectric constant of the lower region RB is set smaller than the piezoelectric constant of the upper region RT, thereby improving the efficiency of deformation of the diaphragm 55 caused by driving the piezoelectric element 56A.

[0100] It is noted that both the first electrode 56a and the second electrode 56c may be individual electrodes.

[0101] 2-2. Variation 2 In the above-described embodiment, a serial type liquid ejection device 100 in which a carriage 41 carrying a liquid ejection head 50 is moved back and forth is exemplified, but the present disclosure can also be applied to a line type liquid ejection device in which multiple nozzles N are distributed across the entire width of the medium M.

[0102] 2-3. Variation 3 The liquid ejection device 100 exemplified in the above embodiment can be adopted in various devices such as facsimile machines and copy machines, in addition to devices dedicated to printing. However, the use of the liquid ejection device of the present disclosure 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 that forms a color filter of a liquid crystal display device. Also, a liquid ejection device that ejects a solution of a conductive material is used as a manufacturing device that forms wiring and electrodes of a wiring board.

[0103] 3. Summary of this disclosure The following is a summary of this disclosure.

[0104] (Additional Note 1) A liquid ejection head of a first aspect which is a preferred example of the present disclosure comprises a piezoelectric element having a first electrode, a piezoelectric layer, and a second electrode, a pressure chamber substrate provided with a pressure chamber communicating with a nozzle, and a vibration plate which applies pressure to the liquid in the pressure chamber by vibrating when driven by the piezoelectric element, wherein the pressure chamber substrate, the vibration plate, and the piezoelectric element are stacked in this order in a stacking direction, the neutral plane of the laminate formed of the piezoelectric element and the vibration plate is located within the piezoelectric layer, and when the region closer to the vibration plate is defined as a lower region and the region farther from the vibration plate is defined as an upper region of the two regions divided by the neutral plane, the piezoelectric constant of the lower region is smaller than the piezoelectric constant of the upper region.

[0105] In the first embodiment described above, since the piezoelectric constant of the lower region is smaller than that of the upper region, the lower region is less likely to deform due to the voltage applied to the piezoelectric element. Therefore, the lower region essentially functions as a vibration plate, and the deformation due to the inverse piezoelectric effect of the lower region is less likely to interfere with the deformation due to the inverse piezoelectric effect of the upper region. As a result, even if the neutral plane of the laminate consisting of the piezoelectric element and the vibration plate is located within the piezoelectric layer, the deformation efficiency of the vibration plate due to the driving of the piezoelectric element can be improved. Moreover, by reducing the thickness of the end portion in the width direction of the vibration plate, the deformation efficiency can be further improved.

[0106] (Note 2) In the second aspect, which is a preferred example of the first aspect, the pressure chamber has a longitudinal shape when viewed in the stacking direction, and the end of the pressure chamber in the short direction does not overlap the piezoelectric layer when viewed in the stacking direction. In the second aspect described above, the end of the vibration plate in the width direction can be easily deformed. This makes it possible to improve the efficiency of deformation of the vibration plate when the piezoelectric element is driven.

[0107] (Note 3) In a third aspect, which is a preferred example of the first or second aspect, the piezoelectric constant of the lower region is half or less of the piezoelectric constant of the upper region. In the third aspect, the efficiency of deformation of the diaphragm caused by driving the piezoelectric element can be improved compared to an aspect in which the piezoelectric constant of the lower region is greater than half of the piezoelectric constant of the upper region.

[0108] (Note 4) In a fourth embodiment, which is a preferred example of any of the first to third embodiments, the piezoelectric layer has a plurality of layers, and when a layer included in the lower region and closest to the vibration plate is a first piezoelectric layer, and a layer included in the upper region and farthest from the vibration plate is a second piezoelectric layer, the second piezoelectric layer is made of crystals preferentially oriented in the (100) plane, and the first piezoelectric layer is made of crystals preferentially oriented in a plane other than the (100) plane. In the above fourth embodiment, the piezoelectric constant of the lower region can be made smaller than the piezoelectric constant of the upper region.

[0109] (Note 5) In a fifth aspect, which is a preferred example of any one of the first to fourth aspects, the thickness of the lower region is thinner than the thickness of the upper region. In the fifth aspect, the efficiency of deformation of the diaphragm caused by driving the piezoelectric element can be improved compared to the aspect in which the thickness of the lower region is equal to or greater than the thickness of the upper region.

[0110] (Note 6) In a sixth embodiment, which is a preferred example of any of the first to fifth embodiments, the lower region and the upper region are made of piezoelectric materials having different compositions. In the sixth embodiment, even if the lower region and the upper region are each made of crystals preferentially oriented in the (100) plane, the piezoelectric constant of the lower region can be made smaller than that of the upper region. In addition, when the second piezoelectric layer is made of crystals preferentially oriented in the (100) plane and the first piezoelectric layer is made of crystals preferentially oriented in a plane other than the (100) plane, the lower region and the upper region are made of piezoelectric materials having different compositions, so that the piezoelectric constant of the lower region can be effectively made smaller than that of the upper region.

[0111] (Note 7) In a seventh aspect, which is a preferred example of any of the first to sixth aspects, the dielectric constant of the lower region is higher than that of the upper region. In the seventh aspect, even if the lower region is interposed between the first electrode and the upper region, the voltage between the first and second electrodes can be applied to the upper region more efficiently than in an aspect in which the dielectric constant of the lower region is equal to or lower than that of the upper region.

[0112] (Note 8) In an eighth aspect which is a preferred example of any one of the first to seventh aspects, the pressure chamber has a longitudinal shape when viewed in the stacking direction, the first electrode, the piezoelectric layer and the second electrode are stacked in this order in the stacking direction, and the second electrode has a portion disposed on each of the side surfaces of the lower region and the upper region. In the above eighth aspect, the first electrode can be an individual electrode and the second electrode can be a common electrode.

[0113] (Appendix 9) A liquid ejection head according to a ninth aspect, which is a preferred example of the present disclosure, comprises a piezoelectric element having a first electrode, a piezoelectric layer, and a second electrode, a pressure chamber substrate provided with a pressure chamber communicating with a nozzle, and a vibration plate that applies pressure to the liquid in the pressure chamber by vibrating when driven by the piezoelectric element, wherein the pressure chamber substrate, the vibration plate, and the piezoelectric element are stacked in this order in a stacking direction, a neutral plane of a laminate formed of the piezoelectric element and the vibration plate is located within the piezoelectric layer, and the piezoelectric layer includes a first piezoelectric layer formed of crystals preferentially oriented in a plane other than the (100) plane, and a second piezoelectric layer formed of crystals preferentially oriented in the (100) plane, the first piezoelectric layer is located between the vibration plate and the neutral plane, and the neutral plane is located between the first piezoelectric layer and the second piezoelectric layer.

[0114] In the ninth aspect, when the piezoelectric layer is divided into two regions by the neutral plane, the region closer to the vibration plate is the lower region, and the region farther from the vibration plate is the upper region, the piezoelectric constant of the lower region can be made smaller than that of the upper region. Therefore, since the lower region is less likely to deform due to the voltage applied to the piezoelectric element, the lower region essentially functions as a vibration plate, and the deformation due to the inverse piezoelectric effect of the lower region is less likely to interfere with the deformation due to the inverse piezoelectric effect of the upper region. As a result, even if the neutral plane of the laminate composed of the piezoelectric element and the vibration plate is located within the piezoelectric layer, the deformation efficiency of the vibration plate due to the driving of the piezoelectric element can be improved. Moreover, by reducing the thickness of the end portion in the width direction of the vibration plate, the deformation efficiency can be further improved.

[0115] (Supplementary Note 10) A liquid ejection device according to a tenth aspect, which is a suitable example of the present disclosure, includes the liquid ejection head according to any one of the first to ninth aspects, and a control unit that controls the driving of the liquid ejection head. In the tenth aspect, the liquid ejection head has excellent ejection efficiency, and therefore it is possible to provide a liquid ejection device with excellent ejection characteristics. [Explanation of symbols]

[0116] 10...liquid container, 20...control unit (control part), 30...transport mechanism, 40...movement mechanism, 41...carriage, 42...transport belt, 50...liquid ejection head, 50A...liquid ejection head, 51...flow path substrate, 52...pressure chamber substrate, 52a...hole, 52b...partition wall, 53...nozzle substrate, 54...vibration absorber, 55...diaphragm, 55a...elastic membrane, 55b...insulating film, 56...piezoelectric element, 56A...piezoelectric element, 56a...first electrode, 56b...piezoelectric layer, 56b1...through hole, 56c...second electrode, 57...sealing plate, 58...case, 59...wiring substrate, 60...drive circuit, 100...liquid liquid ejection device, AN...neutral surface, Ak...cross-sectional area, C...pressure chamber, IH...inlet, LA...laminated body, LA1...layer, LA2...layer, LA3...layer, LA4...layer, LA5...layer, M...medium, N...nozzle, Na...communicating flow path, PV...vibration region, R...liquid storage chamber, R1...opening, R2...container, RB...lower region, RE1...active region, RE2...inactive region, RE2a...arm portion, RT...upper region, Ra...supply flow path, W...width, d1...piezoelectric constant, d2...piezoelectric constant, td...thickness, td1...thickness, td2...thickness, tp...thickness, tp1...thickness, tp2...thickness, tpb...thickness.

Claims

1. a piezoelectric element having a first electrode, a piezoelectric layer, and a second electrode; a pressure chamber substrate provided with pressure chambers communicating with the nozzles; a vibration plate that applies pressure to the liquid in the pressure chamber by vibrating when the piezoelectric element is driven, the pressure chamber substrate, the vibration plate, and the piezoelectric element are stacked in this order in a stacking direction, a neutral plane of a laminate formed of the piezoelectric element and the vibration plate is located within the piezoelectric layer; In the two regions obtained by dividing the piezoelectric layer by the neutral plane, a region closer to the diaphragm as a lower region; When the region farther from the diaphragm is defined as the upper region, the piezoelectric constant of the lower region is smaller than the piezoelectric constant of the upper region; A liquid ejection head characterized by:

2. The pressure chamber has a longitudinal shape when viewed in the stacking direction, an end of the pressure chamber in the short side direction does not overlap the piezoelectric layer when viewed in the stacking direction; 2. The liquid ejection head according to claim 1.

3. the piezoelectric constant of the lower region is less than half the piezoelectric constant of the upper region; 3. The liquid ejection head according to claim 1, wherein the ink is a liquid having a thickness of 100 nm or less.

4. the piezoelectric layer has a plurality of layers, Among the plurality of layers, a layer included in the lower region and closest to the vibration plate is a first piezoelectric layer; When the layer included in the upper region and farthest from the vibration plate is defined as a second piezoelectric layer, the second piezoelectric layer is composed of crystals preferentially oriented in the (100) plane, The first piezoelectric layer is composed of crystals preferentially oriented in a plane other than the (100) plane.

3. The liquid ejection head according to claim 1, wherein the ink is a liquid having a thickness of 100 nm or less.

5. The thickness of the lower region is less than the thickness of the upper region.

3. The liquid ejection head according to claim 1, wherein the ink is a liquid having a thickness of 100 nm or less.

6. The lower region and the upper region are made of piezoelectric materials having different compositions.

3. The liquid ejection head according to claim 1, wherein the ink is a liquid having a thickness of 100 nm or less.

7. the dielectric constant of the lower region is higher than the dielectric constant of the upper region; 3. The liquid ejection head according to claim 1, wherein the ink is a liquid having a thickness of 100 nm or less.

8. the pressure chamber has a longitudinal shape when viewed in the stacking direction, the first electrode, the piezoelectric layer, and the second electrode are stacked in this order in the stacking direction; the second electrode has portions disposed on respective sides of the lower region and the upper region; 3. The liquid ejection head according to claim 1, wherein the ink is a liquid having a thickness of 100 nm or less.

9. a piezoelectric element having a first electrode, a piezoelectric layer, and a second electrode; a pressure chamber substrate provided with pressure chambers communicating with the nozzles; a vibration plate that applies pressure to the liquid in the pressure chamber by vibrating when the piezoelectric element is driven, the pressure chamber substrate, the vibration plate, and the piezoelectric element are stacked in this order in a stacking direction, a neutral plane of a laminate formed of the piezoelectric element and the vibration plate is located within the piezoelectric layer; The piezoelectric layer is a first piezoelectric layer composed of crystals preferentially oriented in a plane other than the (100) plane; a second piezoelectric layer composed of crystals preferentially oriented in the (100) plane, the first piezoelectric layer is located between the vibration plate and the neutral plane, the neutral surface is located between the first piezoelectric layer and the second piezoelectric layer. A liquid ejection head characterized by:

10. The liquid ejection head according to claim 1 or 9, a control unit that controls the driving of the liquid ejection head, A liquid ejection device characterized by:

11. A diaphragm; a piezoelectric element laminated on the vibration plate, the piezoelectric element having a first electrode, a piezoelectric layer, and a second electrode; the neutral plane of the laminate is located within the piezoelectric layer; In the two regions obtained by dividing the piezoelectric layer by the neutral plane, a region closer to the diaphragm as a lower region; When the region farther from the diaphragm is defined as the upper region, the piezoelectric constant of the lower region is smaller than the piezoelectric constant of the upper region; A laminate characterized by:

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